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Applied Sciences for Printing
UNIT-1
Color Fundamental: Color Image Processing
In 1666, Isaac Newton Discovered that when a beam of light of sunlight passes through a glass Prism, the emerging beam of light is split into a spectrum of colors ranging from violet at one end to red at the other.
Understanding Colors:
Color is most important element in the world. We see myriad color around us in the world. We have special ability to see color and distinguish between millions of colors in their various shades.
Three basic quantities are used to describe the quality of chromatic light source.
1. Radiance: radiance is the total amount of energy that flows from light source measured in watts (W).
2. Luminance: Luminance gives a measure of the amount of energy an observer perceives from a light source – measured in lumens (LM).
3. Brightness: Brightness is a subjective descriptor that is practically unmeasurable.
Hue: Hue and saturation taken together are called chromaticity.
A color may be characterized by its brightness and chromaticity.
The amount of red, green, and blue needed to form any color are called the tristimulus values and are denoted, X, Y, and Z.
A color is then specified by its trichromatic coefficients which means
X + Y +Z = 1
The use of color is important in image processing because:
1. Color is a powerful descriptor that simplifies object identification and extraction.
2. Humans can discern thousands of color shades and intensities, compared to about only two dozen shades of gray.
Color image processing is divided into two major areas:
1. Full-color processing: images are acquired with a full-color sensor, such as a color TV camera or color scanner.
2. Pseudocolor processing: The problem is one of assigning a color to a particular monochrome intensity or range of intensities.
Color Fundamentals
Colors are seen as variable combinations of the primary color s of light: red (R), green (G), and blue (B). The primary colors can be mixed to produce the secondary colors: magenta (red + blue), cyan (green + blue), and yellow (red + green). Mixing the three primaries, or a secondary with its opposite primary color, produces white light.
RGB colors are used for color TV, monitors, and video cameras.
However, the primary colors of pigments are cyan (C), magenta (M), and yellow (Y), and the secondary colors are red, green, and blue. A proper combination of the three pigment primaries, or a secondary with its opposite primary, produces black.
CMY colors are used for color printing.
Color characteristics
The characteristics used to distinguish one color from another are:
1. Brightness: means the amount of intensity (i.e. color level).
2. Hue: represents dominant color as perceived by an observer.
3. Saturation: refers to the amount of white light mixed with a hue.
1. LIGHT AND COLOR
To understand the process of color reproduction, it is first necessary to gain an appreciation of the phenomenon of color. To do this, we must examine the nature of light, without which color would not exist.
Light is radiant energy that is visible to the average human eye. For the purposes of this discussion it can be assumed that light travels in wave motion, with the color of light varying according to the length of the wave. The wavelengths can be measured and classified along with other forms of energy on the electromagnetic or energy spectrum. Light can either be a wave as was first proposed by Christian Huygens, or as a series of discrete particles as was first proposed by Sir Isaac Newton. Eventually it was decided that light could be both a wave and a series of particles.
The intensity (or luminosity) of a light source is measured in candles. The intensity of light reflected from a surface (or luminance) is measured in candles per square meter, or foot candles or foot lamberts.
Color is an optical phenomenon, a sensory impression conveyed by the eye and the brain. Light reflected or transmitted by an object is received by our eyes and transformed into nervous impulses, which trigger the colour sensation in our brain. Color is not a physical variable, accordingly it has no physical unit. An object is not colored, but the sensation of color is produced as a result of irradiation by light, Sunlight, which appears to be white, radiates on to an object and is partially reflected. Consequently an object that reflects the red area of the spectrum appears colored. An object that reflects completely in the entire visible spectrum usually appears to be white and a completely absorbent body appears to be black.
When perceiving and describing colors, physical and physiological effects are always involved. The physical components are measurable, where as the physiological components are not measurable.
The mixing of certain basic colors produces all of the colors we can perceive. There are three categories of colors: primary colors, secondary colors, and tertiary colors. Primary colors are those that are not formed by mixing of any other colors and can be said to be “pure” colors. Secondary colors are those formed by the mixing of two or more primary colors. Tertiary colors are those produced by mixing of two or more secondary colors. What constitutes a primary color differs depending on whether one is talking about light or pigments.
Interestingly, according to Hope and Watch in The Color Compendium, polls have consistently found that in Western Europe and North America over half of the adults surveyed name “blue” as their favorite color, while children under eight consistently name “red” as their favorite. (In Japan, however, over half of the people surveyed named either white or black as their favorite color).
Color preferences tend to vary by culture, not unexpectedly. This may seem like a trivial matter, but it is an important consideration in planning multinational advertising campaigns, designing products such as clothing for other markets, and other such endeavors. It also manifests itself in appropriate dress when visiting other cultures; white is not universally accepted as the bride’s dress color at a wedding, for example, nor is black universally appropriate for funerals or other mourning rites. In other words, color is a cultural specific concept; various colors are symbolic of different things, and these symbols are not universally consistent.
Here, the biological vision of human beings is contrasted with the process of physical measurement, as performed by a measuring system. Light falls on a sample. The sample absorbs part of the light, while the rest is reflected or re-emitted as diffused radiation.
We perceive this re-emitted light with our, eyes. In the process of seeing, cones in the retinas of our eyes are stimulated. Different cones are sensitive to blue, green, and red. The stimuli are transformed into excited states, in turn, causing signals to be sent along the optic nerve to the brain, which interprets them as colour.
This same process can be emulated in a measuring instrument. One such measuring instrument is the spectrophotometer. Of course, a measuring instrument cannot actually perceive anything, but it is able to perform calculations on predefined and measured values.
Thus, during the measuring process light also falls on the printed sample. The reflected light, also known as spectral reflectance, passes through a series of lenses to strike a detector. This then relays the values it registers to the computer. There, digital filters that simulate the visual sensitivity of our eyes are used to calculate values, referred to as standard stimuli, or tristimulus values.
The standard stimuli are equivalent to the excitation of cones in our eyes. These tristimulus values are then converted and mapped onto a colorimetric system. With the aid of the figures thus determined, a colour can be precisely described and compared with other colors. This, in very simplistic terms, is the measurement principle underlying a colorimetric instrument.
Colour is a very complex issue and there are many factors which need to be considered in order to understand how we perceive and reproduce it.
We can see the visible wavelengths between 380 and 760nm (one nanometre equals one millionth of a millimeter). If one particular wavelength dominates or, more specifically, the spectral power distribution is unequal we see a particular colour - if there is a balanced distribution of all wavelengths we see white or gray - i.e. - neutral. Light with a wavelength of 380nm appears as violet, 760nm ‘as red and 570nm as green. Colour, as we know it, can be in the form of a ‘physical’ solid, such as printing ink or colored toner; or in the form of an energy light source, such as with a TV or computer colour monitor.
The sensation of colour is the effect of light upon the eye interpreted by the brain. White light is composed of a mixture of all colours of the rainbow or spectrum, and most objects are visible by the light reflected or transmitted from them, depending upon whether the object is opaque or transparent. The colors of the visible spectrum include (in order of increasing wavelength) violet, indigo, blue, green, yellow, orange and red.
White light appears to have no color because all the wavelengths are present in equal amounts, effectively “cancelling” each other out. Objects appear colored because they reflect or transmit some parts of the spectrum and absorb the others. For example, a red object appears red as it reflects the red light and absorbs most of the violet, blue, green and yellow lights. White objects reflect or transmit almost all parts of the spectrum, while tones of gray absorb equal proportions of all its constituents and black absorbs almost the whole of it.
The perception or sensation of color, despite attempts to objectively quantity it, is a highly subjective phenomenon. We speak of, for example, a “red apple,” but the redness of the apple is more dependent on our own peculiar visual systems than any inherent “redness” in the apple. (To organisms with different types of photoreceptors, it could appear to possess a much different color.) Even among different humans, the redness perceived is not absolute, varying according to minute physiological differences in visual acuity or according to the illumination used.
1. THE PROPERTIES OF COLOUR
The colorimetric properties of color are those that describe its three dimensions:
hue, saturation, and lightness.
a. Hue
Hue is the name given to a specific colour, to differentiate it from any other.The hues blue, green and red; yellow, magenta and cyan form the familiar colour wheel- see Figure Color Wheel.
The hue identifies whether a color is red, blue, green, yellow, or some combination term as greenish yellow or bluish red. Such other terms as magenta or crimson are often used as hue names. Hue may have an infinite number of steps, or variations, within a color circle. A circle displays all the hues that exist; indeed, it can be said that any reproduction process is capable of matching any given hue.
b. Saturation
Saturation, similar to chroma, indicates the purity of a colour. It refers to the strength of a colour, - i.e. - how far it is from neutral gray.
A gray-green, for example, has low saturation, whereas an emerald green has higher saturation. A color gets purer or more saturated as it gets less gray. In practice this means that there are fewer contaminants of the opposite hue present in a given color. To illustrate this concept, imagine mixing some magenta pigment with a green pigment (the opposite hue). The green will become less and less saturated until eventually a neutral gray will be produced. A gray scale has zero saturation. The figure below shows the magenta-green saturation continum. Magenta becomes desaturated by the addition of green in the same way green becomes desaturated by the addition of magenta.
As a color becomes less saturated, it is said to be dirtier or duller, and as it becomes more saturated, it is described as cleaner or brighter. There is a limit to how desaturated a color can be (it will always reach neutral gray) and there are practical limits in reproduction processes to how saturated a color may appear. These practical limitations in printing are due to the characteristics of the chosen ink-substrate combination.
Brightness, similar to lightness, luminance or value, describes how light or dark a colour is, indicating whether a colour is closer to white or to black: brightness does not affect the hue or saturation of a colour. Grey is a neutral ‘colour’ between white and black - to lighten a colour the brightness or lightness element is changed.
In fact, the terms lightness and darkness are synonymous. Lightness or darkness of a solid color may be changed by mixing either white or black ink with the color. In process- color printing this is achieved by printing a color at various halftone percentages from 0 to
100 (mixing with white), then overprinting the 100% solids with increasing percentages of black (mixing with black). The figure below shows the lightness aspect of color.
In practice both lightness and darkness have limits. In printing, the lightness of a color is limited by the properties of the substrate. It is generally possible, for example, to achieve lighter colors on a good coated paper than on newsprint or uncoated recycled paper. The darkness of a printed color is limited by the gloss of the substrate and the ink, and the amount of ink (and pigment) that can be physically
transferred to the substrate. Drying, trapping, dot spread, and economic factors restrict the thickness and number of ink films that can be sequentially printed.
Neutral colours do not possess the properties of hue or saturation but are described according to their lightness - white, black and gray are neutral ‘colours’.
A simplified illustration of how hue, saturation and lightness operates is shown opposite:
1. four different hues or colours - yellow, red, green and blue
2. four different saturations of one colour -cyan as 100%,50%,25% and 0%
3. four different levels of lightness - black,50% gray, 25% gray and pure white
Neutral subtractive ‘colour’ - when yellow, magenta and cyan printing inks or toners are present in equal amounts, the coloured result appears gray or black Neutral additive ‘colour’ - when blue, green and red lights are present in equal amounts, the colored result appears gray or white.
Opposite colour pairs - colours which appear opposite to each other when combined together, form a ‘neutral’ colour - e.g:’ red + cyan, green + magenta, yellow + blue (blue/violet).
Reproduced below is a colour wheel, showing the additive primary colours of blue, green and red as well as the subtractive primary colours of yellow, magenta and cyan - note blue, green and red; yellow, magenta and cyan appear opposite to each other on the colour wheel.
2. THE ELECTROMAGNETIC SPECTRUM
Of the overall spectrum of electromagnetic waves, the human eye is only able to perceive a narrow band between 380 and 780 nanometers (nm). This visible spectrum is situated between, ultraviolet and infrared light. If the light of this visible range is passed through a prism, then the individual spectral colors can be seen.
However, light is not absolute. For example, if a printed image is compared with a proof under artificial light, the two may seem identical, but regarded in daylight, differences may suddenly appear.
The Visible Spectrum
Wave length (in Nanometers)
Light is a small portion of the much larger electromagnetic spectrum, a broad range of different types of generated energy, ranging from radio waves and electrical oscillations, through microwaves, infrared, the visible spectrum, ultraviolet radiation, gamma rays, and high-energy cosmic rays. All of these sources of electromagnetic radiation exist as waves, and it is the variations in wavelength and frequency that determine the precise nature of the energy. These wavelengths range in size from many meters (such as radio waves) to many billionths of a meter (gamma and cosmic rays). Visible light is technically defined as electromagnetic radiation having a wavelength between approximately 400 and 780 nanometers (one nanometer is equal to one billionth of a meter).
The electromagnetic spectrum ranges from the extremely short waves of gamma rays emitted by certain radioactive materials to the radio waves, the longest of which can be miles in length. Light, the visible spectrum, ranges from about 400 to 700 nm (nanometers, or billionths of a meter) in length. Some sources suggest that the visible spectrum could range from about 380 to 770 nm, but the exact limits will depend on the visual system of a given observer. Below 400 nm are the ultraviolet rays, which are important when dealing with fluorescent materials. Above 700 nm are the infrared rays, which have significance in certain kinds of photography or image capture.
The visible spectrum occurs in nature as a rainbow. It can be duplicated in a laboratory by passing a narrow beam of white light through a glass prism. The spectrum appears to be divided into three broad bands of color-blue, green, and red-but in fact is made up of a large number of colors with infinitesimal variations between 400 and 700 nm. The colors in the spectrum are physically the purest colors possible. The splitting of white light into the visible spectrum, and the recombining of the spectrum to form white light, was first demonstrated and reported by the English scientist Sir Isaac Newton in 1704.
The reason that a spectrum can be formed by passing white light through a prism has to do with the refraction of light as it passes from one medium (air) to another(glass).The prism bends light of the shorter wavelengths more than light of the longer wavwlengths, thus speading the light out into the visible spectrum. In nature, drops of rain act in a manner similar to that of a prism: when a beam of sunlight breaks through the clouds it is refracted by by moisture in the air and a rainbow is formed.
Color wheel:
Cool Color: Blue to Green
Warm Color: Yellow to Red
Additives color: Additive colour mixing is creating a new colour by a process that adds one set of wavelengths to another set of wavelengths. The additive colours are red, green and blue, or RGB. Additive colour starts with black and adds red, green and blue light to produce the visible spectrum of colours.
Subtractive colour: Subtractive colour mixing is creating a new colour by the removal of wavelengths from a light with a broad spectrum of wavelengths.
Primary colour: primary colour of printers is Red, Blue, & Yellow and primary colour of light is Red, Blue, & Green.
Secondary colour: These are colour combinations created by the equal mixture of two primary colours. On the colour wheel, secondary colours are located between primary colours. According to the traditional colour wheel, red and yellow make orange, red and blue make purple, and blue and yellow make green.
Colour is the sensation created in the human eye and brain when light interacts with objects.
To see colour, three things are needed:
1. Light source (sunlight, bulb, lamp).
2. Object (reflects, absorbs, or transmits light).
3. Observer (human eye or an instrument).
The visible spectrum ranges from 380 nm (violet) to 780 nm (red).
Light is a form of electromagnetic radiation.
Colour of an object depends on how it interacts with light:
1. Reflection: Light bounces back (e.g., wall paint).
2. Transmission: Light passes through (e.g., coloured glass).
3. Absorption: Certain wavelengths are absorbed; the rest create the visible colour.
Example: A red rose absorbs most wavelengths but reflects red.
1. Additive Primaries (Light): Red, Green, Blue (RGB).
2. Subtractive Primaries (Pigments/Inks): Cyan, Magenta, Yellow (CMY).
These are called primary because they cannot be created by mixing other colours.
1. Based on mixing coloured light.
2. Primaries: RGB.
3. Equal mixing of all three = White light.
4. Used in digital displays, projectors, theatre lighting.
1. Based on mixing pigments, inks, or paints.
2. Primaries: CMY.
3. Mixing all ideally = Black (in practice, dark grey → so printing adds black = CMYK).
4. Used in printing, packaging, painting, textiles.
1. A graph showing how much light of each wavelength passes through or is reflected by a material.
2. Each material has its own curve.
Example: A red filter transmits mainly red light (600–700 nm) and absorbs others.
Surface Chemistry:
Surface tension: surface tension may be defined as a force in dynes actin gat right angle to the surface of liquid. Surface tension are expressed in dynes cm. water 72.8 nitrobenzene 41.8, benzene 28.9, tolene 2834, acetic acid 27.8 carbon tetra chloride 26.8, methyle alcohol 22.6.
It is interesting that surface tension of water is much higher that of ethyl or any other organic liquid.
Tolene: it is mixture of petrol and kerosene.
Contact angle: the relative wetability of metals in lithographic process has been investigated by the measurement of contact angle. The contact angle is a measured by introducing a small drop of oil from a pipette under the metal plate immersed in water and projecting the image of this oil drop as to a surface so that its contact angle can be measured.
Contact angle
Zinc = 30 degree
Aluminium = 50 degree
Cupper = 60 degree.
Capillary Action: Capillary action (or capillarity) is the movement of a liquid inside very narrow spaces, such as small tubes or porous materials, without the help of external forces (like gravity). It happens because of a balance between:
1. Cohesive forces (between liquid molecules).
2. Adhesive forces (between liquid and solid surface).
How Is Works
If adhesion > cohesion → liquid rises in the capillary (e.g., water in glass tube).
If cohesion > adhesion → liquid level is depressed (e.g., mercury in glass tube).
In Printing Context
1. Paper fibres are porous; they draw ink into the structure by capillary action.
2. This affects:
a. Ink absorption → how deep ink penetrates into paper.
b. Drying rate → faster on absorbent paper.
c. Print sharpness → excessive penetration causes dot gain, reduced clarity.
Coating and sizing of paper are used to control capillary action for better print quality.
Interfacial Tension:
1. Interfacial tension is the force acting at the boundary between two immiscible liquids (liquids that do not mix, like oil and water).
2. It is similar to surface tension, but instead of liquid–air, it refers to liquid–liquid interfaces.
Cause:
1. At the interface, molecules of each liquid experience stronger attraction to their own kind than to the other liquid.
2. This imbalance creates a “tension” at the boundary, trying to minimize the contact area.
Example:
1. Water (polar) and ink/oil (non-polar) do not mix easily because of high interfacial tension.
2. Surfactants (like soap, wetting agents) reduce interfacial tension, making liquids mix or spread better.
In Printing Context: 1. Offset printing: Ink (oil-based) and fountain solution (water-based) must coexist.
A controlled interfacial tension keeps them separate but allows emulsification (tiny water droplets in ink).
a. Coating/lamination: Adhesion between layers depends on controlling interfacial tension.
b. Wetting of substrates: Lower interfacial tension between ink and paper/film → better spreading and adhesion.
Hydrophobic & Hydrophilic
a. Meaning: “Water-fearing.”
b. Surfaces/materials that repel water (do not allow water to spread).
c. Water forms beads/droplets with a high contact angle (> 90°).
Examples: Oil, wax, Teflon, plastic films.
a. Meaning: “Water-loving.”
b. Surfaces/materials that attract water (allow water to spread and wet easily).
c. Water shows a low contact angle (< 90°).
Examples: Paper fibres, glass, cotton, metals.
1. Printing plates (especially in offset lithography) use this principle:
a. Image area → Oleophilic (ink-loving, hydrophobic).
b. Non-image area → Hydrophilic (water-loving, repels ink).
2. This difference ensures ink stays only on the image parts.
3. In packaging & coatings:
a. Hydrophilic substrates absorb water/ink easily (e.g., uncoated paper).
b. Hydrophobic substrates (e.g., plastics) need surface treatment (corona, plasma, flame) to improve wettability.
Water and Ink Interaction
a. Ink (usually oil-based) and water are immiscible (do not mix easily).
b. Their interaction is crucial in printing processes, especially offset lithography.
c. The right balance of water and ink ensures clean printing, sharp images, and proper colour strength.
1. Fountain solution (water) keeps the non-image areas of the plate clean (hydrophilic).
a. Ink (oil-based) adheres only to the image areas (oleophilic).
b. Controlled water-ink interaction maintains separation but allows slight emulsification (tiny water droplets in ink).
1. Excess water:
a. Ink becomes too thin.
b. Colour strength decreases (print looks faded).
c. Paper distortion (wavy paper).
2. Too little water:
a. Ink spreads to non-image areas → scumming.
b. Poor print clarity and background toning.
a. Ensures clean background (no ink in non-image areas).
b. Maintains sharp dots and lines for high-quality printing.
c. Controls ink transfer, density, and gloss.
d. Prevents defects like scumming, toning, and smearing.
Emulsification of Ink
a. Emulsification is the process where tiny droplets of one liquid (water) are dispersed into another immiscible liquid (ink – oil-based).
b. In printing, especially offset lithography, emulsification means controlled mixing of fountain solution (water) into ink.
a. On the press, ink rollers and dampening rollers work together.
b. A small amount of water from the fountain solution gets mixed into the ink.
c. This creates a water-in-ink emulsion (not ink-in-water).
a. Necessary for smooth printing – a controlled amount of emulsification is good.
1. Ink Transfer: Correct viscosity ensures smooth transfer of ink from rollers to the substrate (paper, board, film, etc.).
2. Print Quality: Balanced viscosity gives proper ink spreading → sharp images, uniform color, and clear text.
3. Press Performance: If viscosity is too high → ink won’t flow properly, causing uneven printing, scumming, or roller streaks. If too low → ink spreads excessively, leading to smudging, dot gain, and loss of detail.
4. Drying Time: Proper viscosity helps maintain correct drying speed; too thin ink may dry slowly, too thick may clog.
5. Consistency: Maintains uniform color density throughout the run → very important for long print jobs.
6. Compatibility with Substrate: Different materials (paper, plastic, metal, etc.) need inks of specific viscosity to ensure good adhesion and finish.
a. The force that makes a liquid surface behave like a stretched elastic sheet.
b. Caused by cohesive forces between liquid molecules.
c. Important in printing because it controls ink spreading and wetting on paper or substrate.
a. The angle between the liquid drop and solid surface.
b. Low angle (< 90°): Good wetting (ink spreads well).
c. High angle (> 90°): Poor wetting (ink beads up).
Determines print quality and adhesion of ink.
a. Movement of liquid in narrow spaces (tubes or pores) without external force.
b. In printing:
1. Paper fibres absorb ink by capillary action.
2. Affects ink penetration, drying, and sharpness of print.
a. Tension at the boundary between two immiscible liquids (e.g., water and oil-based ink).
b. Lower interfacial tension = easier mixing or emulsification.
a. Hydrophobic: Water-repelling (oil, wax, non-polar surfaces).
b. Hydrophilic: Water-attracting (paper fibres, polar surfaces).
c. Printing plates use this principle:
1. Image area (oleophilic, ink-loving).
2. Non-image area (hydrophilic, water-loving).
a. Critical in offset printing.
b. Ink (oil-based) and fountain solution (water) must balance.
c. Too much water → ink thinning, colour fading.
d. Too little water → scumming, poor print quality.
a. Formation of tiny water droplets dispersed in ink.
b. Necessary in offset printing to maintain balance between ink and dampening solution.
Role in Printing:
a. Correct emulsification improves ink transfer, print consistency, and colour strength.
b. Over-emulsification causes ink instability, smearing, or loss of gloss.
a. Resistance of a fluid to flow.
b. High viscosity = thick, resists flow.
c. Low viscosity = thin, flows easily.
Importance in Printing:
a. Determines ink transfer from roller to plate to substrate.
b. Controls dot sharpness, print density, and drying.
c. Too viscous → poor flow, uneven print.
d. Too thin → spreading, feathering, poor edge definition.
Effect of light in Printing and Packaging
a. Offset / Flexo Plates: Coatings are sensitive to UV and visible light.
b. Effect:
1. Overexposure → premature hardening, loss of image area detail.
2. Underexposure → weak image, poor ink receptivity.
Result: Reduced plate life, poor reproduction quality.
Protection: Plates must be handled under yellow safe-light or stored in dark conditions.
a. Polyester (PET): Good resistance, but long UV exposure reduces clarity.
b. Polypropylene (PP/BOPP): May become brittle, shrink, or warp.
c. Polyethylene (PE): Discolors (yellowing) and loses flexibility.
d. PVC Films: Yellowing and loss of transparency under sunlight.
e. Effect on Coatings: Protective coatings on films can crack, dull, or lose adhesion under UV light.
a. Photodegradation: Light causes chemical breakdown of coating molecules.
b. Surface Changes: Loss of gloss, color shift, brittleness, micro-cracks.
c. Barrier Properties: Reduction in moisture and oxygen resistance of coated films.
1. Printing plates and coatings (photo-sensitive layers) are sensitive to UV and visible light.
2. Excess exposure can cause premature hardening, degradation, or loss of sensitivity, affecting image transfer quality.
3. Films used in packaging (like PET, BOPP, PVC) may experience yellowing, brittleness, or reduced transparency when exposed to strong light over time.
a. Adhesives: Prolonged light (especially UV) may weaken adhesive bonds → resulting in delamination in laminates.
b. Ink Films: Ink layers exposed to sunlight can fade, chalk, or discolor due to photochemical reactions.
Some pigments break down faster under light → leading to uneven colors or loss of brand identity on packaging.
a. Definition: The ability of a printed ink or color to resist fading or discoloration when exposed to light.
b. Poor light fastness → fading of colors in outdoor or shelf-exposed packaging.
c. Inks with inorganic pigments (like carbon black, titanium dioxide) have higher light fastness than organic pigments.
d. Important in outdoor advertising, labels, and long-shelf-life packaging.
a. Gloss: Light may dull the surface over time.
b. Color Stability: Continuous exposure causes shade variations and loss of vibrancy.
c. Surface Damage: UV can make coatings brittle, reducing scratch resistance.
a. Polyethylene (PE): Susceptible to yellowing and cracking under UV.
b. Polypropylene (PP / BOPP): May degrade, become brittle, and lose mechanical strength.
c. Polyester (PET): More resistant, but prolonged UV can reduce clarity.
d. PVC Films: Tend to yellow and lose flexibility under sunlight.
e. Paper Substrates: Can become brittle, yellowed, and lose brightness.
UNIT-2
Power of Hydrogen
pH - pH is the measure of acidity or alkalinity of a solution.
The most fundamental acid-base reaction is the dissociation of water:
H2O H+ + OHIn
this reaction, water breaks apart to form a hydrogen ion (H+) and a hydroxyl ion
(OH-).
1. [H+] is the molar concentration of hydrogen
2. [OH- is the molar concentration of hydroxide
Water actually behaves both like an acid and a base. The acidity or basicity of a
substance is defined most typically by the pH value, defined as below:
pH = -log[H+]
3. Also, pH is measured in the fountain solutions that are used when printing the paper on the press.
4. Measured on a scale of 0 to 14, pH7 being neutral, pH above that is alkaline and below that is acidic.
5. The measure of the acidity or alkalinity of a material or solution.
6. Maintenance of fountain solution at optimum pH is vital to high-grade, trouble free offset printing.
7. 7 is neutral, below 7 is acid, above 7 is alkaline.
8. Acid allows the highest quality printing - 4.8 to 5.3 (}2) pH is typically a good range for sheetfed printing.
9. The acid side of the table allows gum to adhere to the plate better.
Principle of pH Meter
1. pH meter basically works on the fact that interface of two liquids produces a electric potential which can be measured.
2. In other words when a liquid inside an enclosure made of glass is placed inside a solution other than that liquid, there exists an electrochemical potential between the two liquids.
pH meter Components:
It is basically an electrode consisting of 4 components:
1. A measuring electrode: It generates the voltage used to measure pH of the unknown solution.
2. A Reference Electrode: It is used to provide a stable zero voltage connection to the complete the whole circuit.
3. Preamplifier: It is a signal conditioning device and converts the high impedance pH electrode signal to a low impedance signal.
4. Transmitter or Analyzer: It is used to display the sensor’s electrical signal and consists of a temperature sensor to compensate for the change in temperature.
Working of pH meter:
1. When you dip the two electrodes into the blue test solution, some of the hydrogen ions move toward the outer surface of the glass electrode and replace some of the metal ions inside it, while some of the metal ions move from the glass electrode into the blue solution.
2. This ion-swapping process is called ion exchange, and it's the key to how a glass electrode works.
3. Ion-swapping also takes place on the inside surface of the glass electrode from the orange solution.
4. The two solutions on either side of the glass have different acidity, so a different amount of ion-swapping takes place on the two sides of the glass.
5. This creates a different degree of hydrogen-ion activity on the two surfaces of the glass, which means a different amount of electrical charge builds up on them.
6. This charge difference means a tiny voltage (sometimes called a potential difference, typically a few tens or hundreds of millivolts) appears between the two sides of the glass, which produces a difference in voltage between the silver electrode (5) and the reference electrode (8) that shows up as a measurement on the meter.
Dampening solution that is too acidic has the following effects:
1. The printing layer of the plate is fretted resulting in sharp pointed halftone dots.
2. The useful life of the plate is impaired.
Ink drying is delayed. In extreme cases, ink does not dry at all.
The effects of alkaline solutions are:
1. High dot increase
2. Tendency towards scumming and emulgating
3. Inks with metallic pigments will oxydate resulting in blunt quality in printing
2) Conductivity of a Dampening Solution:
a. Conductivity unit = μS/cm
b. Conductivity describes how electricity is conducted through a liquid; impurities in the dampening solution allow conductivity to increase.
c. In water or any solution the degree of conductivity is determined by the amount of minerals and other ions present.
d. Conductivity is measured on a linear scale, which is represented by the inverse of resistance. The units of measure are micromhos.
e. When considering fountain solutions, most conductivities fall in the 1000 to 3000 micromhos range.
f. There are several variables that influence conductivity. Organic solvents such as isopropyl alcohol will reduce the actual conductivity reading.
g. A 25 to 30 percent isopropyl alcohol solution can cut the conductivity in half.
h. Temperature also influences conductivity. As the temperature goes up, the conductivity goes up, as temperature decreases, so does the conductivity.
i. A good rule of thumb, is for every 10° F change in temperature, conductivity will change by 100 micromhos.
j. Conductivity should be determined using a “freshly prepared dampening solution”, so that this measure can then serve as a “benchmark” when the dampening solution is later exchanged.
k. When the conductivity in the dampening solution has climbed by approx. 1000 μs/cm, this should be taken as a signal that it is time to change the dampening solution.
l. In order to guard against printing problems, it is recommended that the dampening solution be renewed every 14 days.
HOW A CONDUCTIVITY METER WORKS
1. To measure conductivity we use a machine called a conductivity meter.
2. The actual amount of electricity that a given water solution will conduct changes with how far apart the electrodes are and what temperature the water is.
3. The meter has a probe with two electrodes, usually 1 centimeter apart.
4. The meter is equipped with a probe, usually handheld, for field or on-site measurements.
5. After the probe is placed in the liquid to be measured, the meter applies voltage between two electrodes inside the probe.
6. Electrical resistance from the solution causes a drop in voltage, which is read by the meter.
7. The meter converts this reading to milli- or micromhos or milli- or microSiemens per centimeter.
8. This value indicates the total dissolved solids. Total dissolved solids is the amount of solids that can pass through a glass-fiber filter.
Requirement of dampening/ fountain solution.
1. It separates image from non-Image area.
2. It keep the plate clean (desensitize).
3. It protect the plate.
4. Ph value should be stabilize (4.5-5.5).
5. Temperature control.
6. Conductivity: good conductor of electricity.
7. Preservatives are added to maintain the equality for long time.
8. Drying simulator: helps in ink drying.
9. Anti-microbe substance are added to prevent algae, bacteria, fungi etc.
10. Anti-foaming agent: prevent foam fountain solution should be minimum and even.
11. We have to apply a heavy film of water, if we use running water because surface tension of water is very high 72.8.
12. Water hardness: 8-12dh (German hardness) (degree of German hardness).
a. Humidity = amount of water vapor present in the air.
b. It directly affects printing materials (paper, films, inks, adhesives) since they are sensitive to moisture.
a. Ratio of actual water vapor in air to the maximum it can hold at a given temperature (expressed as %).
b. Example: 50% RH means air holds half the water vapor it could at that temperature.
a. Measured with a Hygrometer or Psychrometer.
b. Digital Humidity Sensors → modern automatic monitoring in press rooms.
a. A hygrometer is an instrument used to measure the moisture content (humidity) of air.
b. Essential in printing & packaging industries to control humidity for consistent print quality and substrate stability.
a. Uses human or animal hair that changes length with humidity.
b. Movement is transferred to a needle on a dial.
c. Simple, traditional, but less accurate.
2. Psychrometer (Wet & Dry Bulb Hygrometer)
a. Has two thermometers:
3. Electrical / Electronic Hygrometer
a. Dew Point Hygrometer
a. All hygrometers work on the principle that materials or sensors respond to moisture in the air by changing shape, temperature, resistance, or condensation point.
b. This change is measured and converted into %RH.
a. Maintains stable Relative Humidity (RH) (usually 45–55%) in press rooms.
b. Prevents paper curling, misregister, static charge, ink drying issues, and adhesive failure.
c. Ensures consistent print quality and substrate performance.
a. Printing/packaging units use HVAC systems to maintain stable humidity (usually 45–55% RH).
b. Dehumidifiers reduce moisture, while humidifiers add moisture.
a. Printing & packaging materials (paper, board, films, adhesives, inks) are sensitive to moisture changes.
b. Stable Relative Humidity (RH 45–55%) is essential for quality printing and packaging operations.
1. Humidification (Adding Moisture)
2. Dehumidification (Removing Moisture)
3. Temperature Control
1. Ensures dimensional stability of paper/board → avoids misregister.
2. Maintains ink drying balance → not too fast (skin-drying), not too slow (smudging).
3. Prevents adhesive failure in laminates and cartons.
4. Improves operator comfort → consistent production quality.
1. Eco-Friendly Inks
a. Soy-based, vegetable-based, or water-based inks instead of petroleum inks.
b. Reduce emission of VOC (Volatile Organic Compounds).
c. Easier to de-ink in recycling.
2. Sustainable Substrates
a. Use of recycled paper, FSC-certified paper, biodegradable films.
b. Promotes renewable resources and reduces deforestation.
3. Reduced VOC & Chemicals
a. Less use of solvent-based inks, varnishes, and cleaning agents.
b. Shift towards UV-curable inks and aqueous coatings.
4. Energy Efficiency
a. Use of energy-efficient presses, LED-UV curing, and digital workflows to save electricity.
b. Reduced use of water and chemicals in plate-making (CTP – Computer to Plate).
5. Waste Reduction & Recycling
a. Recycling of paper, plates, solvents, and chemicals.
b. Use of closed-loop systems for water and chemical recovery.
a. Environmental → Less air & water pollution, reduced landfill waste.
b.Economic → Saves energy, reduces material costs, improves efficiency.
c. Social/Health → Safer workplace, fewer toxic emissions, healthier community.
d. Brand Value → Meets sustainability expectations of customers, boosts brand i
a. Definition: Organic chemicals that easily evaporate into the air during printing (from solvents, inks, cleaning agents).
b. Sources: Offset inks, flexo inks, gravure inks, varnishes, adhesives.
c. Impacts:
a. Volatile Organic Compounds (VOCs) are organic chemicals that easily evaporate at room temperature and enter the atmosphere.
b. Common in solvent-based inks, coatings, adhesives, and cleaning agents used in printing and packaging.
1. Solvent-based inks (offset, flexo, gravure).
2. Varnishes & coatings (gloss/matte finishes).
3. Cleaning agents & thinners.
4. Adhesives & laminating solutions.
a. Inks
b. Varnishes & Coatings
c. Cleaning Agents & Solvents
d. Plate-making Chemicals
e. Adhesives & Laminating Agents
UNIT-3
Posted July 22, 2021 by X-Rite Color
Electro magnetic radiation in the wavelength range from 380 nm to 730 nm is seen as light by our eyes. Low wavelengths show as blue light, then the spectrum continues from green to yellow, orange, and red. UV radiation is located in the range below 380 nm; the range above 730 nm is called infrared radiation. The visual impression of a colored body changes by the composition of the incoming light.
Each color has its typical spectral curve. The color pigments absorb specific wavelengths of the incoming light while other wavelengths are reflected. Perfect white reflects the entire incoming light (i.e.: no absorption) while perfect black absorbs all wavelengths at 100%. If you add saturated dyestuffs to a white base, specific sections of the spectral curve are lowered more and more. The spectral curve can never be raised by dyestuffs.
The CIELAB color space is the most common used color space in the industry. The vertical L* axis reflects the lightness of a color. Here L*=0 represents absolute black and L*=100 represents perfect white. The positive a* axis represents the red parts of a color and the negative a* axis represents the green shares. The positive b* axis is for the color yellow and negative b* values mean blue. Thus, in this three-dimensional structure you can "address" all real existing colors at one light type, measurement geometry, and standard observer.
Another way to display the a* and b*-axes is the representation in polar coordinates. C* is named chroma and shows the difference from the neutral gray axis to the sample. H is called the Hue angle. It is always measured counterclockwise starting from the positive a* axis. This set of definitions is mainly used for saturated colors, since values in numbers are easier to understand. For instance, the color orange is more saturated than the sample, not more red and more yellow. The difference from a sample to the standard is stated in delta values (Δ or d):
- ΔL* = 0.5 sample is 0.5 units brighter - Δa* = -1.5 sample is -1.5 units greener - Δb* = -3.6 sample is -3.6 units bluer - ΔC* = -3.9 sample is -3.9 units less colored - ΔH = 0.7 sample is 0.7 depending on the location of the color shades
Similar to the axes of the CIELAB system, several directions must also be observed for the tolerances. The difference from standard value to tolerance limits need not always be the same. Especially in saturated colors, a tolerable color difference along the chroma axis (=ΔC) can be much higher than a color difference in the hue (=ΔH) or in the lightness (=ΔL).
Optical brightening agents (OBAs) absorb invisible UV radiation and emit in the visible range. This can create reflectance values of more than 100%, i.e.: at specific wavelengths more light is reflected by the sample than had come in at these wavelengths. This effect is utilized in white papers or textiles, where blue light is excited. The CIE whiteness correlates better to the visual assessment than ISO whiteness, since the entire visual range is taken into consideration.
LENSES AND CAMERAS
Graphic arts cameras are now only retained to handle the odd price of flat artwork in conjunction with existing analogue film. When an original is exposed to light in front of a graphic art camera, the light is absorb in the black area of the original and reflected back by the white areas, through the lens onto the photosensitive material (photographic film) held in the camera. After development of the film material, a negative is obtained on which the white or clear area of the original appear dense and black area transparent.
Two sides of film:-
The negative is produce line negative. The negative used for litho plate and the wrong side up and emulsion to emulsion contact in film and plate for exposing.
PROCESS CAMERA: Produce high contrast film image from other 2- dimensional images such as line art, text. Black and white photograph and full colour.
Two types of process camera: (1) horizontal camera, (2) vertical camera.
A. Horizontal camera: the lens of a horizontal camera faces parallel with the floor and component are built in a horizontal line.
1. Galley camera: it are made in different sizes for larger size film.
It called light room camera.
2. Darkroom camera: two room camera. It installed through a wall between a darkroom and adjacent room with normal lighting.
Darkroom: Dark room that hold the film for exposing.
Normal light room: major portion like (artwork and copy, lens adjustment and exposure setting).
After exposing process doing in darkroom.
B. Vertical camera: it small room occupying less floor space. All elements (lens, copy-board, bellows) are arranged vertically with the copy-board being close to the floor. The component are built in vertical line and lens faces the floor. It installed in darkroom and daylight models that have special film holders that allow the camera to be used outside of the darkroom.
It have not allow for enlargement or reduction.
Operational steps:
1. Inspecting the scaling copy:
(a) The quality of the copy received,
(b) The reproduction size or scale required for the copy.
(c) Quality of copy: check colour, background and line quality. Ortho film not produce all colour and use of certain filers and background for use special filter.
(d) Setting copy: enlargement and reduction.
FORMULA= REPRODUCTION = IMAGE SIZE/ ORIGIANL SIZE * 100
2. Placing copy on copy-board: exact position for give marking are follows:-
a. Rectangles
b. Diagonals
c. Centrelines
Copy board hold the copy while it is being photographed. The copy-board usually consists of flat cushioned board while the hinged glass cover. Copy that is placed between the board and cover is held in position by pressure when the glass is closed.
Copy-board illumination lamp:
The light serves to illuminate the copy during exposure.
1. Incandescent lamp: light produced by in candescent light sources. It depends upon the temperature attained when the light sources are operating.
2. Tungsten halogen: regular light bulbs. The light emitted is high in red wavelengths and low in the blue-violet end of the spectrum.
3. Quartz-halogen: a quartz-iodine lamp used a tungsten filament surrounded by iodine and insert gases enclosed in a quartz bulb.
4. Pulsed Xenon: it electronic flash used in photography. The light output is close to that of daylight.
5. Mercury vapour: an electrical current passes through gaseous mercury with the lamp in order to emit light. The light is high—U.V radiation and useful when longer periods of exposure are required.
6. Metal Helide: it good source of blue-violet wavelength, metal helide lamps are mercury lamps with a metal helide.
45 degree angle require.
3. Setting the camera: the lens aperture, use of filters, lighting and camera setting for proper reproduction size.
a. Lens board: it is made up of several carefully sharped polished pieces of optical glass that are all held together in a barrel. The barrel is attached to the lens board.
b. Lens: it controls the amount of light reaching the film and the overall quantity of the photographed image.
1. Converging or positive lens: it is thicker in the centre than at the periphery.
2. Diverging or negative lens: diverging or negative lens which are thicker at the periphery than in the centrer.
When the lens is rotated, the metal blades of the iris inside the barrel of the lens, open or close creating a larger or smaller opening through which light can pass.
As the diameter of the aperature increase f-number decrease. So bigger the f. no. smaller the opening. Smaller the f. no. bigger the opening.
For line work, the most common lens opening (f-stops) used at same size are f-16 and f/22 as process lenses have their definition and resolution at these aperaturs. The aperature is varied according to the enlargement or reduction while the exposure time remains constant. In modern types of process cameras, the lens is equipped with a diaphragm chart mounted on the lens board.
c. Lens stop: it is an auxiliary device that will give a smaller or different shaped aperture than that produced by the diaphragm.
d. Shutter: it used to control the exposure time in process photography. It positioned behind the lens.
e. Ground glass: mounted on a hinged frame on the back of camera case, the ground glass is swung into place in order to check the positioning and focus of the copy.
f. Bellow: the bellows is an according like structure that extends from the lens assembly to the camera back because it is flexible.
g. Screen holder and filter holder: the screen required a screen positioning mechanism. The contact screen is made on a flexible film base, designed to be in contact with the film during exposure. The contact screen is held by vacuum camera back. The vacuum cause the contact screen to stay in place.
h. Filter: filter is necessary for holding the filter. Filter used for black and white reproduction serve two purpose: to increase the contrast of the original and to reproduce certain colour monochromatic. Contrast filter used for poor copy, pencil drawing and copy with a grayed or yellowed background. A filter is essentially a transparent foil of film or sheet of glass which transmits certain rays of the white light, while absorbing others.
i. Light angle: the lighting angle of 45 degree at a distance of 3 foot from copy-board is considered normal for process camera.
j. Setting for reproduction percentage: they require the use of a percentage scale for obtain the reproduction size and reference to the camera scale for proper setting number.
We might consider another step in the camera setting, namely the focusing of the image on the ground glass. Here the check sharpness of the image and adjust the positioning.
k. Colour temperature: a body which reflects no light falling on it and which on the other hand completely absorb all the radiation falling on it, is called a black body.
4. Loading film: after inspecting the setting the camera, the next step is the actual insertion of film in the camera.
5. Exposing film: during exposure, the photographic film receives the light reflected from the copy; the result of exposure is the formation of a latent image on the film.
6. Removing exposed film form camera: after exposing, the film is removed from the camera for further processing and store the film for developing.
7. Processing exposed film: during processing the latent image is converted into a visible image through the process of reduction in a solution called a developer. The developing agent reduce the exposed silver helide to black metallic silver, and fixer those unexposed and under developed area of the film.
a. Powder-type developers and fixer: these powders, which are packaged in a box, must be diluted to working strength using water. The temperature is between 90 and 100 degree F.
b. Liquid concentrate developer and fixers: it quite popular. It is so easy to mix them. Those developers supplied in powder form. It stored at temperature above 40 degree F.
Introduction to Densitometer and Spectro-Densitometer
1. A densitometer is an optical instrument that measures the optical density (OD) of printed inks on paper or other substrates.
2. Optical density = how much light is absorbed or blocked by the ink layer.
1. Transmission Densitometer – measures density of transparent materials (films).
2. Reflection Densitometer – measures density of opaque surfaces (paper with ink).
1. Checks ink film thickness and uniformity.
2. Monitors gray balance in multi-color printing.
3. Helps in maintaining consistent color and print quality.
1. A spectro-densitometer combines a densitometer with a spectrophotometer.
2. Measures ink density and color across multiple wavelengths of visible light.
1. Provides precise color measurement (L*, a*, b* values).
2. Detects subtle color differences that normal densitometer cannot.
3. Useful for color matching, quality control, and Delta E calculation.
1. Ensures accurate reproduction of brand colors.
2. Monitors process control in CMYK printing.
3. Evaluates color differences in coated/uncoated papers or different substrates.
SUMMARY
a. Definition: Bouncing back of light from a surface.
b. Relevance in printing: Determines gloss, sheen, and visibility of print.
c. Specular Reflection → mirror-like (shiny surface)
d. Diffuse Reflection → scattered light (matte surface)
a. Definition: Passage of light through a transparent or semi-transparent material.
b. Relevance: Important for films, laminates, and packaging materials.
c. Determines opacity and clarity of substrates.
a. Viewing angle affects perception of color, gloss, and details.
b. Same print can appear different at 0° vs 45° due to reflection and scattering.
c. Standard viewing angles: 45°/0° for consistent color assessment.
a. Human perception can misinterpret colors due to surrounding colors, light source, and texture.
b. Important for color matching in printing.
a. Definition: Ability of a material to prevent light from passing through.
b. High opacity → no show-through of underlying layers (important in labels, packaging).
a. Optical density (OD) = measure of darkness or light absorption of ink on paper.
b. Measured with a densitometer.
c. Determines ink thickness, print uniformity, and color control.
a. Angle subtended by an object at the observer’s eye.
b. Affects perceived size and detail of printed images.
a. Definition: Ratio of visual angle with magnifying instrument to that without.
b. Used to examine small print details.
a. Convex lens that enlarges image for easier viewing.
b. Used to inspect dots, registration, and print defects.
a. Provide high magnification for detailed study of halftone dots, ink laydown, substrate fibers.
b. Essential for quality control in high-end packaging.
a. Low-intensity yellow or red light used in darkrooms or plate-making.
b. Prevents unwanted exposure of photosensitive materials.
a. Cameras → capture images for printing.
b. Contact Printer → used to transfer film images onto plates in traditional processes.
a. Densitometer → measures optical density of inks on substrates.
b. Spectro-densitometer → measures color density across multiple wavelengths → precise color control & matching.
a. Uses instruments like spectrophotometers and densitometers.
b. Parameters measured: L*, a*, b* values, optical density, hue, chroma.
a. ISO 12647 → standard for process control in printing.
b. Ensures consistent color reproduction globally.
a. Definition: Numerical value representing difference between two colors.
COLLOIDS
Photo emulsion is colloids compound.
A colloid as a kind of solution in which the size of solute particle is intermediate between those in true solution and suspension.
Ex- starch solution, milk, blood etc.
Where 1A degree = 10-8 m.
Properties:
a. Heterogeneous is nature.
b. Do not settle down.
c. Filterability (colloid particle will note be separated by filter paper).
d. Mechanical properties:-
1. Brownian movement.
2. Diffusion (high concentration – low concentration).
e. Sedimentation (do not settle down).
f. Colour of the solution (will depend on size and shape).
g. Electrical properties.
h. Absorption (due to high molecular weight on the surface of colloid partial the other particles which are suspended in the solution will be accumulated).
i. Optical properties.
Types of solution: basis of size of particle dispersed size.
1. True solution: it is “homogeneous” solution containing dispersed particles of molecular size. The particles of solute are invisible.
2. Suspension: it is a “heterogeneous” mixture containing suspended insoluble particles of size greater than 1000A or 100nm. It particles are cannot pass through an ordinary filter paper.
3. Colloidal solution: it is a “heterogeneous” two phase system in which a substance is distribution in colloidal state in an insoluble medium. The particles of the dispersed substance in internal or discontinuous phase, are called dispersed phase, while insoluble medium or external phase, in which they are dispersed, is called dispersion medium.
Types of colloidal solution: based on their solvent affinity.
1. Lyophilic: solutions are those in which the dispersion medium possesses great affinity for the dispered phase.
Ex: starch, gelatine, glue, agar solutions in water.
2. Lyophobic: solutions are those in which there is no apparent affinity/ interaction between the dispersion medium add the dispersed phase.
Ex: gold, silver solution, and arsenic sulphite solution in water.
Multi molecular, macromolecular and associates colloids:
1. Multi molecular: it consist of aggregates of atoms or molecular having diameter less than 1mm.
Ex: gold solution in water consists of dispersed particles of various made up of “several atoms of gold”.
2. Macromolecular: it particles are very large molecular of high molecular mass.
Ex: starch, cellulose, proteins, natural rubber, synthetic polymer (polythene, nylon, synthetic rubber, polystyrene etc.), egg albumin.
3. Associated colloids: it particles behave as normal strong electrolyles at low concentration but at higher concentration.
Ex: soaps and synthetic detergents.
Characteristics of colloids solution:
1. Heterogeneous nature: it consisting of two distinct phases (the dispersed phase and the dispersion medium).
2. Filterability: colloidal particles can readily pass through ordinary filer paper.
3. Colour: the size and shape of dispersed particles, affect the colour of the solution.
Ex: spherical gold particles impart a red colour to gold solution; while flat particles a blue colour.
4. Adsorption: the colloidal particles, due to the presence of unbalanced forces on their surface, attach a variety of suspended particles of their surfaces.
5. Mechanical properties:
a. Brownian movement: this motion is rapid in case of particles of smaller sizes and in less viscous dispersion medium.
b. Diffusion: the diffusion process has been used to separate colloidal particles of different sizes and to determine their sizes.
c. Sedimentation.
6. Optical properties or tyndall effect: if a powerful beam of light is passed through a colloid solution (contained in a glass cell) placed in a dark room the path of the beam become visible when viewing through a microscope placed at right angle to the path of light. Due to scattering of light by the colloid particles the tyndall effect is happened. The molecule of true solution do not scatter light as their size comparatively very small.
7. Electrical properties: colloidal particles are electrically charged either positive or negative. When a high potential gradient is applied between U tube filled particle with a colloid solution and rest with distilled water the colloid particles move towards oppositely charge electrode. On reaching the electrode they lose their movement of colloid particles under the influence of an electric field known as electrophoresis.
Application of colloids:
1. In everyday life: the food (milk, butter, cheese, fruit etc.) the clothes and shoes that we wear are based on colloids.
2. In analytical chemistry: silica and alumina gels are used as absorbent for gases and as drying agents in laboratory.
3. In medicine: argyrols and protargrol are colloidal solutions of Ag and used as eye-lotions.
4. In industry: smoke precipitation, purification of water, leather tanning, in laundry.
5. In nature: the blue of sky, tails of comets etc. are due to scattering of upon by the colloidal particles of dust or smoke in air.
Light sensitive coating used for plate making are of colloidal in nature important are dichromated colloids, each containing of dichromatic salt combined with natural or synthetic polymer e.g. potassium dichromate and gelation, ammonium dichromate and PVA.
Colloids used in printing:
Negative working colloids and form hand coating.
1. Egg albumin
2. Casein
3. Soya protein
Positive working colloids forms partially hard coating.
1. Gum Arabic
2. Polyvinyl alcohol
3. Fish glue
Ammonium dichromate solution and colloids are coated on plate, exposed and become insoluble in water to a degree. This happened appeals due to oxidation.
Colloids in combination of chromo salt and this material used in plate making depending nature of the electronegative or electropositive. It is used for different type of plate making like surface plate, other paper based plate deep etch paper etc.
1. Egg albumin: based on protein material on ammonium dichromate is mixed with optical sensitization. It used in letter press block and surface making, preservatives are added for stability.
2. Casein:
3. Soya protein:
4. Gum Arabic: gum Arabic which obtained from acacia tree and supplied in form of yellow brown lump. It is dissolved in water to for gumming dispersion. It is used with ammonium dichromate in deep etch plate making.
5. PVA:
6. Fish glue: it is obtained from fish lain, bond. It is in mixed with ammonium dichromate for preparing coating solution. Earlier it was used in halftone block for letter press printing.
7. Gelatine: it is a protein based material and mixed with potassium dichromate from plate making and gravure cylinder making.
Preparation of fountain solution: to maintain consistent ink quality and a trouble free run, the fountain solution must be formulated according to the following requirement.
Plate dampening must be uniform are moisture kept to a minimum. To obtain this ordinary water may be used but because water has high surface tension. If does not wet the plate surface effectively unless a heavy film of water is applied to the plate. This leads to problem of ink/water emulsification. Substances may be added to the fountain solution to reduce the surface tension and thereby, permit good dampening with less moisture on the plate.
Gum Arabic = 14 degree be solution added in the proportion of 2% is used to reduce surface tension. Proportion higher than this may give emulsification problem. IPA when mixed in the proportion 20-30% with water be one half. This reduce tendency to emulsification because alcohol evaporates from the ink at a greater rate than does water.
The dampening solution should maintain the de-sensitization of the plate during the run. It is maintained during the run if phosphate salt is mixes with gum Arabic as a fountain solution additive is phosphoric acid be added in the proportion of 2% the acid value of fountain solution will depend on the PH of water. Aim at a normal of 5-5.6. To prevent the accumulation of fungus and bacteria, organic substances such of gum Arabic quickly, becomes the breeding ground for micro-organism, sunlight + accumulation of fluffy and dirt in the fountain tray acceleration this. The use of IPA will reduce this as the alcohol has damaging effect on the bacteria. A suitable additive recommended to prevent the souring of solution which contains gum Arabic is hydroxyquindin added in the proportion of 0.001%.
UNIT-4
Chemistry of Photography & Light Sensitive Materials
Coating solution:
All photosensitive lithographic metal plates have a photo emulsion surface consisting of some form of light sensitive material combined with a collation coated on a grained metal surface. A colloidian is an organic compound that forms a strong continuous layer. When mixed with the light sensitive solution and then exposed to the light the colloid becomes in-soluable and forms a strong continuous coating on the printing plate.
Ammomium bichromate combined with the egg albumin was previously used as the photo emulsion in the lithography process. Albumin has gradually been replaced by other solution until it is now very nearly obsolete. Popular coating are polyvinyl alcohol (PVA) diazo and photo polymers.
1. Egg albumin: the proteins are complex colloidal substances found in the cell of all animals and plants. Proteins contain the elements carbon hydrogen oxygen and nitrogen and certain proteins such as albumin, contain sulphur.
In its preparation the egg are broken by hand and the whites are separated from yolks and transferred to castes, a small amount of ammonia which acts as preservative.
2. Ammonium dichromate: it is manufacturer by adding ammonium hydroxide to chronic acid solution in controlled quantities. The pure product having the composition (NH4)2 CrO7 mixture of albumin glue, gum Arabic, gelatine and the like with a dichromate. When dried and exposed to liquid became in-soluable in water.
3. Water: it is used for only vehicle of solution.
4. Ammonia: ammonium hydroxide or aqua ammonia is the essential constituent of the coating solution. It is a gas (NH3) which combine to form ammonium hydroxide.
DIAZO COMPOUNDS: It form a family of man-made chemicals of which contain two linked nitrogen atom (N2). They are prepared from compounds called amines, containing (NH2) group when these amines are treated with nitrous acid (HNO3) and (HCL) acid, a diazonation reaction takes place and diazo compound is produced.
RHN2 + HNO2 + HCL ------------------------------------------ RN2Cl + 2H2O.
Plate chemistry: Many metals and alloys are technologically well known but only a few of them fulfil the quantity parameters for an offset plate.
1. Ductility of the metals or alloys.
2. Good durability and hardness.
3. Fine grain structure.
4. Thermal stability.
5. Ability for etching.
6. Low cost.
These factors reduce the number of material to zinc, copper, aluminium, magnesium and other special alloys are often used in bi-metal and tri-metal plates. The metal behaviour and surface of an offset plate are critical for a good working product. The following properties are important for offset plates.
1. Good adhesion of photopolymer coating and the ink film to the image areas.
2. Strong bonding between plate surface and lacquer during plate development and subsequent fixing.
3. Good wettability of the whole non-image area by water.
Oleophilic and hydrophic behaviour: offset plate should have special qualities in their receptivity to water and ink besides general qualities like strength, fine grain structure, resistance to temperature and sensitivity to etching. Normally offset plates are coated with special lacquer for ink receptivity. The main property is the hydrophilic behaviour to the plate combines with the rejection of ink the wettability of metal for the offset process can be investigated by measuring the contact angle.
For measuring, a loventzen and wetness contact angle measuring device is used drops of size 0.04 ml + 10% of either Castrol oil or distilled water were applied from a pipette to the polished and degreased surface of the plate. Measurement were made after 10 second. Copper is most hydrophilic metal followed by zinc and magnesium.
Chromium, aluminium, and iron or steel are metals having similar contact angles against water than against oil. These metals are hydrophilic, chromium and aluminium also show good hydrophilic properties.
POLYMER
Monomer and polymer: A low-molecular-weight compound that can be reacted and united with other low-molecular-weight compounds to form a long, higher-molecular-weight chain-like polymer. The formation of polymers—a chemical process called polymerization—is the basis of the drying of many types of printing inks, commonly preceded by the chemical process of oxidation, and many printing ink resins are produced by the process of polymerization. A monomer is considered the basic structural unit of a polymer, and various smaller combinations of monomers are described as dimers, trimmers, or oligomers.
Homo-polymer and Copolymer: Homo-polymers consist of single species of repeating units whereas copolymers consist of two or more types of repeating units. Homo-polymers have a single type of monomer whereas Copolymers have two or more types of monomers. Homo-polymers usually have a simple structure whereas copolymers have a complex structure.
Copolymer: A large molecule created by the polymerization of two or more smaller molecules (called monomers)
Homo-polymer: A homo-polymer is a polymer made from many copies of a single repeating unit.
Types of Polymer: The polymers are divided into 3 types depending on their source of availability. They are natural, synthetic, and semisynthetic polymers. Natural polymers are present in plants and animals and exist naturally. Proteins, starch, cellulose, and rubber are a few examples. Biodegradable polymers are also called biopolymers. Semi-synthetic polymers are produced from naturally existing polymers and then chemically modified, for example cellulose nitrate and cellulose acetate. Synthetic polymers are man-made polymers. The most prevalent and commonly used synthetic polymer is plastic. It is utilized in a variety of industries and dairy products, for example nylon-6, polyethers.
Natural polymers: They are of two type’s organic and inorganic polymers. Organic polymers are important in living organisms because they provide basic structural components and participate in key life processes. Polymers, for example, make up the solid components of all plants. Among them are cellulose, lignin, and different resins. Cellulose is a polysaccharide, which is a polymer made up of sugar molecules. Lignin is made up of a complex three-dimensional network of polymers; wood resins are polymers of isoprene, a simple hydrocarbon. Rubber is another well-known isoprene polymer. Proteins, which are polymers of amino acids, and nucleic acids, which are polymers of nucleotides—complex molecules consisting of nitrogen containing bases, sugars, and phosphoric acid—are two other major natural polymers. In the cell, nucleic acids convey genetic information. Starches are natural polymers made of glucose that are essential sources of nutritional energy supplied by plants. Many inorganic polymers, such as diamond and graphite, can also be found in nature. Both are made of carbon. Carbon atoms in diamonds are bonded in a three-dimensional network, which gives the substance its strength. Carbon atoms join in planes that may glide across one another in graphite, which is employed as a lubricant and in pencil leads.
Synthetic polymers: Synthetic polymers are produced by a variety of processes. Many simple hydrocarbons, such as ethylene and propylene, may be converted into polymers by adding monomers to the developing chain one after the other. Polyethylene is an additive polymer comprised of repeated ethylene monomers. It might include up to 10,000 monomers linked together in long coiled strands. Polyethylene is crystalline, transparent, and thermoplastic, which means that when heated, it softens. It is used to make coatings, packaging, molded components, and bottles and containers. Polypropylene, like polyethylene, is crystalline and thermoplastic, but it is tougher. Its molecules can be made up of 50,000 to 200,000 monomers. This compound is utilized in the textile sector as well as in the manufacture of molded products.
Classification of polymer based on structure:
Polymerization
2.3.1 Linear, Branched, and Cross-linked Polymers
Polymeric materials could be linear, branched, or cross-linked subjected to the intermolecular linkages between the individual chains. The chain structures of linear, branched, and cross-linked polymer.
Schematic representation of linear, branched, and cross-linked polymers.
2.3.1.1 Linear Polymers
In linear polymers the repeating units are joined together end to end in a single flexible chain. The polymeric chains are kept together through physical attractions. These polymers have extensive Vander Waals attractions keeping the chains together. Typically linear polymers are made from monomers with single end group. Linear polymers containing side groups as part of monomer structure do not qualify as branched polymers. Some of the common examples of linear polymers are polyethylene, PVC, polystyrene, and polyamides. Linear polymers are generally more rigid.
2.3.1.2 Branched Polymers
Branched polymers have side chains or branches growing out from the main chain. The side chains or branches are made of the same repeating units as the main polymer chains. The branches result from side reactions during polymerization. Monomers with two or more end groups are likely to support branching. For a polymer to classify as branched polymer the side chains or branches should comprise of a minimum of one complete monomer unit. One of the most common example is low-density polyethylene (LDPE) and has applications ranging from plastic bags, containers, textiles, and electrical insulation, to coatings for packaging materials.
Branched polymers display lower density as consequence of reduced packing efficiency of the branched chains. The length of the side chains or branches differentiates between long- or short-branched polymers. Long branches could have comb-like, random, or star-shaped structures. While the branches may in turn be branched however, they do not connect to another polymer chain.
2.3.1.3 Cross-linked Polymers
Cross-linked polymers, as the name suggest, are polymers in which the adjacent polymer chains are connected in a three-dimensional network structure. The connections are also known as crosslinks. The crosslinks could be a consequence of covalent bonding between the chains or branches. The structure produced. Crosslinks tend to be permanent in nature. Once the crosslinks between the chains develop the polymer then becomes thermoset. Such polymers are characterized by their crosslink density or degree of crosslink which is the indication of number of junction points per unit volume. Common examples include epoxies, bulk molding compounds, rubber, and various adhesives.
Polymerization:
Polymerization is the process to create polymers. These polymers are then processed to make various kinds of plastic products. During polymerization, smaller molecules, called monomers or building blocks, are chemically combined to create larger molecules or a macromolecule.
Polymerization is the process in which the basic units of monomers combine together to form long-chain polymers. Monomers can be either the same or different molecules. Various types of polymers like PVC, Bakelite, and Teflon can be produced by different polymerization techniques.
Polymerization is a process through which a large number of monomer molecules react together to form a polymer. The macromolecules produced from a polymerization may have a linear or a branched structure. They can also assume the shape of a complex, three-dimensional network. There exist several categories of polymerization reactions; the most important ones are step-growth polymerization, chain-growth polymerization (both fall under the category of addition polymerization), and condensation polymerization.
A polymer is a substance that is made up of very large molecules that are, in turn, made up of many repeating units called monomers. Polymerization is the process through which these monomers come together to form the macromolecules that constitute polymers. An illustration detailing the polymerization of the monomer styrene into the polymer known as polystyrene is provided below.
Depending on the functional groups present in the reacting monomers, the complexity of the mechanism of the polymerization reaction may vary. The most simple polymerization reactions involve the formation of polymers from alkenes via free-radical reaction. Polyethylene, which is one of the most commercially important polymers, is prepared through such a polymerization process (the reactant monomer used here is ethylene).
It should be noted that polymerizations involving only one type of monomer are called photo-polymerization, whereas those involving more than one type of monomer are called copolymerization processes. In simple words, we can describe polymerization as a chemical process that results in the formation of polymers or the process of creating polymers. When polymerization occurs, the smaller molecules, which are known as monomers via chemical reaction, are combined to form larger molecules. A collection of these large molecules form a polymer. The term polymer, in general, means “large molecules” with higher molecular mass. They are also referred to as macromolecules.
1. Step Growth Polymerization
2. Condensation Polymerization
3. Chain Growth Polymerization
4. Preparation of Polymers
5. Classification of Polymerization
Polymers are formed by the addition of a network of structural units or monomers, as mentioned above. The interesting part is that these are reactive molecules and are usually linked to each other by covalent bonds. These monomers add together to form a long chain to form a product with specific properties. This whole process of the formation of polymers is called polymerization. Polythene and Nylon 66 are some examples of polymers.
Generally, polymerization consists of three steps which include initiation, propagation, and termination. As for the reaction mechanism, the process of polymerization mainly involves two different methods, the step-growth mechanism and the chain-growth mechanism.
In step-growth polymerization, the polymers are formed by the independent reaction between the functional groups of simple monomer units. In step-growth, each step may consist of a combination of two polymers having a different or the same length to form a longer-length molecule.
The reaction is a lengthy process, and the molecular mass is increased at a very slow rate. An example of step-growth polymerization is condensation polymerization, where a water molecule is evolved in the reaction when the chain is lengthened.
Condensation Polymerization
In condensation polymerization, the formation of the polymer occurs when there is a loss of some small molecules as byproducts through the reaction, where molecules are joined together. The byproducts formed may be water or hydrogen chloride. Polyamide and proteins are examples of condensation polymers.
Some of the different types of condensation polymerization are given below.
Polyamides
They are synthetic fibres and are called nylons. These polymers have an amide linkage between them. Condensation polymerization of di-amines with di-carboxylic acid and also of amino acids and their lactams will create a polyamide.
1. Nylon 66: This polymer is prepared under the condition of high pressure and temperature by the condensation polymerization of hexamethylenediamine with adipic acid.
2. Nylon 6: It is prepared by heating caprolactam with water under high temperatures. It is used for tyre cords, fabrics and ropes.
Polyesters
When dicarboxylic acids and diols undergo poly-condensation, polyesters are formed. They are prepared by heating a mixture of terephthalic acid and ethylene glycol at 460 k by using zinc acetate antimony trioxide as a catalyst. Dacron or terylene are the best-known examples of polyesters. And also they are used for glass reinforcing materials in safety helmets.
Phenol-Formaldehyde Polymer
These are the old synthetic polymers obtained by condensation polymerization of phenol with formaldehyde in the presence of either an acid or base as a catalyst.
Novolac, on heating with formaldehyde, undergoes crosslinking and forms an infusible sold mass named as Bakelite. They are used for combs, electric switches and phonograph records.
Melamine-Formaldehyde Polymer
It is formed by the condensation polymerization of melamine and formaldehyde in certain conditions. They are used for the manufacture of unbreakable crockery.
In chain-growth polymerization, the molecules of the monomers are added together to form a large chain. The monomers added may be the same type or different. Generally, alkenes, alkadienes and their derivatives are used. In this mode, the lengthening of chains occurs as a result of the formation of either free radicals or ionic species.
Many of the monomers, like alkenes or dienes and their derivatives, are polymerized in the presence of free radicals. The polymerization of ethene to polythene is by heating or exposing it to light by using a small amount of benzoyl peroxide initiator. The phenyl free radical formed by peroxide is added to the ethene double bond and hence forms a new larger free radical.
It is called a chain initiation step. This newly formed radical will react with another molecule of ethene to form another new free radical, and so on. This repeated formation of a new free radical is called chain propagation. Finally, at some stage, the polymerized product will be formed, and this step is called a chain termination step. The steps are detailed below.
The three steps followed by a free radical mechanism:
When we talk about polymerization chemical reactions, we basically refer to a polymerization reaction of organic monomers. These monomers are in a solution, which further consists of particles that will be coated with the formed polymer deposited on the particle surface. This leads to the formation of a coating layer. The reaction includes either monomer adsorption polymerization or emulsion polymerization.
There are two types of polyethylenes, and they are given below:
1. Low-Density Polyethene
This type of polymer is obtained by the polymerization of ethene under the condition of high pressure of 1000 to 2000 atmospheres at 350 to 520 k temperature in the presence of dioxygen or peroxide initiator as a catalyst in a very small amount.
It is formed through the free radical addition and H-atom abstraction, having a highly branched structure. It is chemically inert in nature and tough but flexible. It is a poor conductor of electricity. LDP is used for the manufacture of toys, squeeze bottles and flexible pipes.
2. High-Density Polyethene
It is prepared by the polymerization addition of ethene in the presence of a catalyst like triethyl aluminium and titanium tetrachloride. The process takes place in a hydrocarbon solvent, in a condition of low pressure of 3 to 4 atmospheres and 343 k temperature.
Like the LDP, it is chemically inert but comparatively tougher and harder. It is used for the manufacture of buckets, dustbins, pipes, etc.
It is also known as Teflon and is manufactured by heating tetrafluoroethylene with a free radical at high pressure. Teflon is chemically inert and less corrosive due to its resistive property against corrosive agents. It is used for gaskets and non-stick surface-coated utensils.
This polymer is formed by the addition polymerization of acrylonitrile in the presence of a peroxide catalyst. It is used as a substitute for wool in the making of commercial fibres such as Acrilan.
It is an addition polymerization that involves the polymerization of monomers that are initiated with anions. This polymerization will be initiated by the transfer of electrons from the ion to the monomer.
The initiators used may be weakly nucleophilic if the monomer is highly electrophilic. In the propagation, the complete consumption of monomer occurs, and this will be faster even at low temperatures. Generally, vinyl monomers are polymerized by this method. It is very sensitive to the solvent used in the reaction. This method is used for the production of synthetic polydiene rubbers, SBR and thermoplastic styrene elastomers.
Polymers are classified into different categories based on several factors such as source, structures, mode of polymerization, molecular forces and growth of polymers. Let’s discuss them in detail below.
Polymers are again divided into three subcategories:
1. Natural polymers: They are found naturally in plants and animals. Resins, starch and rubber are examples of this.
2. Semi-synthetic polymers: This is a modified version of natural rubber; rubbers are treated with chemicals to make them semi-synthetic. Cellulose acetate and cellulose nitrate are examples that come under this subcategory.
3. Synthetic polymers: Polymers which are completely man-made are called synthetic polymers. Polythene, Nylon 66, and synthetic rubber are the widely used synthetic polymers.
There are three different types polymers, based on their structure:
1. Linear polymers: They consist of a long and straight-chain of monomers. PVC is a linear polymer
2. Branched polymers: They are linear polymers containing some branches. Low-density polythene is an example.
3. Network or cross-linked polymer: Polymers having cross-linked bonds with each other is called cross-linked or network polymer. Generally, they are formed from bi-functional or tri-functional monomers. Bakelite and melamine are examples of this type of polymer.
Based on the mode of polymerization, they are divided into two subcategories:
1. Addition polymers: Polymers formed by the repeated addition of monomers by possessing double or triple bonds are called addition polymers. If the addition is of the same species, they are called homo-polymers, and if the addition is of different monomers, they are called copolymers. Examples are polythene and Buna-s, respectively.
2. Condensation polymers: These polymers are formed by repeated condensation of tri or bi functional monomeric units. In this reaction, the elimination of some small molecules, like water and hydrogen chloride etc., will take place. Terylene and Nylon 6.6 are examples.
They are again classified into four subgroups.
1. Elastomers: Polymers that are rubber-like solids and have elastic properties. Here, the polymer bonds are held together by weak intermolecular forces and that allows these polymers to stretch. The cross-links present in the polymer between the chains help to retrace the original position after the removal of the applied force. Examples are Buna-s and Buna-s.
2. Fibres: They are polymers having strong intermolecular forces like hydrogen bonding. Due to this strong force, molecules are kept closer, that is, they are closely packed. Because of this property, they are crystalline in nature. Polyamide and polyesters are examples.
3. Thermoplastic polymers: These are the liner or slightly changed to branched polymers that can be softened on continuous heating and hardened on cooling. Their intermolecular force lies in between the fibres and elastomers. Polyvinyls, polystyrene etc., are examples of thermoplastic polymers.
4. Thermosetting polymers: These polymers come under the category of heavily branched or cross-linked, which can mould on heating and can’t regain the original shape. So, these cannot be reused. Bakelite is an example.
Rubber: Rubber is a type of material called a polymer. It can be produced from natural sources (e.g. natural rubber) or can be synthesised on an industrial scale. Many things are made from rubber, like gloves, tires, plugs, and masks. Some things can be made only from rubber. Sometimes the word means only natural rubber (latex rubber). Natural rubber is made from the white sap of some trees such as the Hevea brasiliensis (Euphorbiaceae). Synthetic rubbers are made by chemical processes.
Synthetic Rubber: In the 20th century, synthetic (artificial) rubbers such as Neoprene began to be used. They were much used when World War II cut off supplies of natural rubber. They have continued to grow because natural rubber is becoming scarce and also because for some uses they are better than natural rubber.
Uses of Rubber: Rubber moulded products are widely used industrially (and in some household applications) in the form of rubber goods and appliances. Rubber is used in garden hoses and pipes for small scale gardening applications. Most of the tyres and tubes used in automobiles are made up of rubber. Rubber plays a very important role in the automobile industry and the transportation industry. Rubber products are also employed in matting and flooring applications.
Difference between Polymer and rubber: Rubber is a natural polymer of isoprene (polyisoprene), and an elastomer (a stretchy polymer). Polymers are simply chains of molecules that can be linked together. Rubber is one of the few naturally occurring polymers and prized for its high stretch ratio, resilience, and water-proof properties. Other examples of natural polymers include tortoise shell, amber, and animal horn.[38] When harvested, latex rubber takes the form of latex, an opaque, white, milky suspension of rubber particles in water. It is then transformed through industrial processes to the common solid form so commonly seen today.
Here, we will list some of the important uses of polymers in our everyday life.
Polypropene finds usage in a broad range of industries, such as textiles, packaging, stationery, plastics, aircraft, construction, rope, toys, etc.
1. Polystyrene is one of the most common plastic actively used in the packaging industry. Bottles, toys, containers, trays, disposable glasses and plates, TV cabinets and lids are some of the daily-used products made up of polystyrene. It is also used as an insulator.
2. The most important use of polyvinyl chloride is the manufacture of sewage pipes. It is also used as an insulator in electric cables.
3. Polyvinyl chloride is used in clothing and furniture and has recently become popular for the construction of doors and windows as well. It is also used in vinyl flooring.
4. Urea-formaldehyde resins are used for making adhesives, moulds, laminated sheets, unbreakable containers, etc.
5. Glyptal is used for making paints, coatings and lacquers.
6. Bakelite is used for making electrical switches, kitchen products, toys, jewellery, firearms, insulators, computer discs, etc.