K Mean Black

• Name: B.Tech 3rd Year
• Branch: B.Tech Printing Technology 6th Sem
• Published: Sept. 30, 2025

Paper Technology

PAPER: Paper word derived from Greek ‘papyrous’ which is the name of a tree. It Is invented to TS’ai lun of china in the year 105A.D.

Paper consists of a compact web, of felting of vegetable fibres, usually in the form a thin flexible sheet.

Nature of paper

• thin or thick
• smooth and rough
• hard and soft
• strong and weak
• white and coloured
• transparent and opaque

Raw material used: Two material used while paper make:

1. Fibers material

2. Non-Fibrous material

 

Fibrous: cellulose fiber can be regarded as the common building brick of the tree. In a few material like cotton and linen, the cellulose exists in a purer form.

Fibers have the form of long usually hollow tubes. This range in length from 1 to 7.50mm and width from 0.01 to 0.05mm according to the plant in which they occur. Cellulose made of carbon, hydrogen and oxygen.

1. Cotton fibers: it is second hair of the cotton plant of natural cellulose. It is used in high grade writing, currency and legal paper.

2. Linen: it is obtained from the ring of last tissues of the stem of the flax plant but as with cotton. It is used in thin strong paper like bank notes and air mill paper.

3. Wood: wood pulp is spruce, pine, deciduous, aspen, eucalytus, birch are some of the material are mix and clean and make white bulky opaque and uniform sheet for printing paper.

A pure form of wood cutting and subjecting it to chemical treatment and remove the natural gums and resin leaving a soft pure pulp.

It is made of mechanical pulp in found dust and doing grinding process by left impurities and make a less strength and poor color paper.

4. Sparto grass: it is found North-Africa and Spain. It is made good writing paper.

5. Straw: it is stem of the wheat, it is made writing paper like bank and bond paper and high bursting strength.

6. Manila: it is found from Phillipine Island and used in wrapping tissue Cigrette paper and bank note.

7. Jute: it is tissues of annual Indian plant and shorter than linen and hamp used in the thin wrapping.

8. Ramie and china-grass: it is used in Bible paper.

9. Bagasse: it obtains from sugarcane and used in corrugated paper and board.

 

Non-fibrous material: like chemicals

1. Filler and loader: it is used for strength and optical agent.

a. Strength:- (tensile strength, bursting strength, tearing strength)

b. Optical agent: (brightness, opacity, reflectance).

2. Sizing agent

 

Manufacturing of paper: there below many methods following as:

1. Mechanical pulping:

a. The tree cut into logs and grinding in big revolving stone and steam.

b. This process during water mix fibers convert into pulp form.

In this process by made paper is good absorbency, bulking and opacity but it become yellow and brittle caused by obtained resins, gums and lignin content

 

2. Mechanical/chemical pulping:

a. Initial preparation: wood cut into small pieces.

b. Refiner mechanical: a series of disc presence of water called breaking.

c. Thermo-mechanical: digesting, it is cooking material under pressure in 135 degree celcious and it process commonly used in new paper.

d. Chemical-thermo-mechanical pulp: washing, bleaching, and screening.

1. The pulp is washed in clean water and leaker are removed.

2. Bleaching solution chloride is remove coloring impurities.

3. Screening is remove fiber lump and knots.

 

e. Bio-chi-thermo-Mechanical pulp: it also called beating and it is decrease opacity, bulk and strength and increase transparency or baste and tensile strength.

Give more strength and fibers hold together for mix acetate 7%.

 

3. Chemical pulping: it obtains wood and other vegetable raw material. It is aim reduce the lignins because the separate more cleanly from each other.

a. Initial preparation: same as above

b. Breaking: in this process sheet and pulp mix with water and some ingredients will be added.

c. Sizing agent: it is used for resistance to wetting and penetration and it is sticky substance and bind fibers together.Sizing material are:

• •  
• Resin size: aluminum Sulphate add with paper
• Paraffin wax
• Wax derivatives
• Asphalt emulsion
• Synthetic sizing agent.

The principal method of sizing:

1. Engine sizing: rosin add for normal size.

2. Surface sizing: starch used when paper made in machine and other used PVA, gelatin and it is water resist and prevent ink from ‘feathering’. When the paper is printed. It is used for Reduce fluffing.

3. Tub sizing: it is used in reel for pass in two rollers easily.

 

2. Fillers and loading: loading and fillers and coloring material.

a. It is main purpose is to fill-up gap to it the fibers and improve opacity and form a smooth and uniform surface.

b. Printing paper: 15%-25% used.

c. Bond and ledger paper: 2%-6% used.

 

Paper manufacture machine: Paper machine dividing into four part

1. Feed section

2. Wire section

3. Press part

4. Drying

After drying paper made special category for used some part in machine.

5. Size press

6. Drying

7. Calender

8. Jumbo reel

Wet end: at this stage the stock is 99% water, 10% fiber and filler.

 

1. In-feed section:

a. A stirrer in take keep the pulp suspension uniform viscosity.

b. Head box: keep the dispered and prevent them from flocculating.

c. Splice: outlet (it is even amount of fiber and weight per area, fibers direction (long and short) controlled.

 

2. Wire section: the moving belt, fibers distributed. The gauge is make up of phosphores, bronze.

Two suction roller remove water called founder.

Dandy roller remove water and give smoothness and strength. It is special use for water mark.

 

3. Press section: paper jump wire mesh to cotton felt. It is reduce moisture 60-70%. In this unit all rolls called couch rolls.

 

4. Drying: it is steam-heated drying cylinder. When the cylinder too hot this can cause such problems as picking, cockling and moisture content down is 2-8%.

After dying include some additives:

1. Include filler

2. Surface sizing: it improves absorbency of ink.

3. Machine Calendaring: it is polished steel roller for give smooth finish (8 to 12) rollers.

4. Machine glazing: one side give smoothness.

Coating:

A. Pigment: china clay (for increase opacity and accept ink uniform), calcium carbonate (for dull coating), titanium di-oxide (opacity and whiteness).

B. Dispersant: polyphosphate.

C. Anti-foaming.

D. Adhesive: starch.

Paper finished: Paper at this point is uncoated, coated paper has a thin layer of material chine clay for create high resolution halftone screens.

 

Varieties of paper:

1. Newspaper print-absorbing ability, quick drying, 75% mechanical wood pulp only coarse-screen halftone, good bulk and opacity lacks strength, yellow and brittle color.

2. Mechanical printing paper: chemical wood pulp writing, paper, one side smooth and thinner.

3. Machine finished: high calendering.

4. Super calendered: suitable for 100 lines upto screen rulling, extra polish and smooth.

5. Wood-free-chemical wood pulp, good color for magazine, leaflets, Booklets, reports 135 GSM.

6. Bible paper: thin white opaque paper, it is made cotton or linen with sulphite, Tio2, china clay.

7. Antique paper: esparto sulphite & soda with up to 15% china clay, rough surface short fibre. It is available 70 to 90 GSM. It is not suitable for writing purpose.

8. Catridge paper: the surface is uneven but strong use for drawing and painting and screen printing. It is not use for halftone and multicolor.

9. Offset cartridge paper: non-fluffy paper, esparto, sulphite or soda with china clay, Tio2.

10. Art paper: fine halftone, art books, technical journal, pamphlets.

11. Chromo paper: one side coated, printing of labels, stickers, posters, book jackets.

12. Cast coated: paper have mirror like glossy, it is only used in USA.

13. Imitation art: not coated, writing paper.

14. Bond paper: matt surface, more opaque, not penetrate ink easily used for letter heading.

15. Ledger paper: strong and durable writing paper made rage and cellulose additives used in banks, it is light blue, light green, yellow, off-white

 

UNIT-2

Finishing Operations in Paper Industry

Finishing operations are processes applied after paper formation to improve surface smoothness, gloss, printability, and mechanical properties.

a) Calendaring

• Purpose: Improve surface smoothness, gloss, thickness uniformity, and density.
• Process: Paper passes between rollers under pressure, sometimes with heat.

Types of Calendaring

1. Hard Calendaring

• Uses hard steel rollers.
• Produces highly glossy, dense paper.
• Suitable for coated papers and high-quality printing.

2. Soft Nip Calendaring

• Uses a soft rubber roller + hard steel roller.
• Balances smoothness and bulk retention.
• Prevents excessive compression of paper.

3. Super Calendaring

• Series of alternating hard and soft rollers.
• Achieves very high gloss and finish.
• Used for magazines, art papers, and coated papers.

 

b) Machine Glazing

• Purpose: Imparts a shiny surface without coating.
• Process: Paper passes over heated rollers at high speed.
• Produces glossy papers for photography, writing, and fine art papers.

 

c) Paper Coatings

• Purpose: Improve surface smoothness, printability, brightness, and barrier properties.
• Process: Apply coating slurry containing pigments (clay, calcium carbonate), binders, and additives.
• Application: Coated papers for printing, packaging, and high-quality publications.

 

2. Recycling Process of Paper

• Purpose: Reduce waste, conserve resources, and produce reusable paper pulp.
• Process Steps:

a. Collection and Sorting: Separate paper types (office paper, newspaper, cartons).

b. Pulping: Shredded paper mixed with water to form slurry.

c. Deinking: Remove inks, adhesives, and coatings using chemicals or flotation.

d. Cleaning & Screening: Remove contaminants like staples, plastics, or sand.

e. Refining & Bleaching: Improve fiber quality, brightness, and smoothness.

f. Sheet Formation: Pulled into sheets on paper machine.

g. Drying & Finishing: Calendaring, coating, or glazing as required.

 

3. Summary Table

Operation	Purpose	Key Features / Notes
Hard Calendaring	Smooth, glossy surface	Hard rollers, high density
Soft Nip Calendaring	Smoothness with bulk retention	Soft + hard roller combination
Super Calendaring	Very high gloss	Alternating series of hard & soft rollers
Machine Glazing	Glossy surface without coating	Heated rollers, high speed
Paper Coatings	Improve printability & barrier	Pigments + binders applied
Recycling	Reuse waste paper	Pulping, deinking, cleaning, finishing

 

1. Paper Recycling Process

Recycling paper involves converting waste paper into reusable pulp, which can be processed into new paper products.

Steps in the Recycling Process

1. Collection and Sorting

• Waste papers collected from homes, offices, industries.
• Sorted by type (newsprint, office paper, cardboard) to ensure uniform pulp quality.

2. Fibre Preparation

• Pulping: Shredded paper mixed with water in continuous drum pulpers to form slurry.
• Pre-screening and Cleaning: Large contaminants (staples, plastics, sand) removed using screens and centrifugal cleaners.
• Primary Flotation: Air bubbles remove inks, adhesives, and light contaminants.
• Fine Screening: Further separation of small impurities.
• Washing: Removes fillers, dirt, and ink residues.
• Thickening: Concentrates pulp to desired consistency.
• Dispersing: Ensures even fiber distribution for smooth sheet formation.
• Brightness Control: Bleaching or optical brightening to improve whiteness.
• Storage: Cleaned and treated pulp stored for further paper production.

3. Deinking Plant Function

• Removes inks and toners from printed paper.
• Process includes pulping, flotation, washing, screening, and thickening.
• Ensures high-quality recycled pulp suitable for printing-grade paper.

 

2. Importance and Benefits of Recycling

• Environmental Benefits: Reduces deforestation, landfill waste, and energy consumption.
• Resource Conservation: Saves water, wood, and raw materials.
• Cost-effective: Lower production cost compared to virgin paper.
• Energy Saving: Less energy required to produce recycled pulp than virgin pulp.
• Sustainability: Supports circular economy and eco-friendly practices.

 

3. Problems in Recycling

• Fiber Shortening: Recycled fibers become shorter, reducing paper strength.
• Contamination: Plastics, adhesives, metals, or inks may remain.
• Degradation of Quality: Multiple recycling cycles reduce pulp quality.
• High Chemical Usage: Bleaching and deinking may require chemicals.
• Color Consistency: Maintaining consistent brightness and color can be challenging.

 

4. Fibre Preparation and Equipment

Step	Equipment / Function
Continuous Drum Pulper	Converts waste paper into slurry pulp
Pre-Screening & Cleaning	Removes large contaminants
Primary Flotation	Removes inks and light impurities via air bubbles
Cleaning & Fine Screening	Eliminates smaller particles and debris
Washing	Removes fillers, dirt, and residual inks
Thickening	Concentrates pulp for storage and further processing
Dispersing	Ensures uniform fiber distribution
Brightness Control	Bleaching or brightening to improve whiteness
Storage	Holds cleaned pulp for future paper production

 

5. Summary Flow of Recycling

1. Collection → Sorting → Pulping

2. Screening & Cleaning → Flotation → Washing

3. Thickening & Dispersing → Brightness Control → Storage

4. Recycled Pulp → New Paper Production

 

UNIT-3

1. Characteristics of Paper

Paper for printing must meet certain physical, mechanical, and optical properties to ensure good print quality and handling:

Characteristic	Significance
Basis Weight / Grammage	Determines thickness, bulk, and strength.
Smoothness / Surface Texture	Affects ink transfer, print clarity, and image sharpness.
Porosity / Absorbency	Controls ink penetration and drying.
Opacity	Prevents show-through from reverse side.
Brightness & Whiteness	Influences color reproduction and contrast.
Strength (Tensile, Folding)	Withstands printing process and handling.
Dimensional Stability	Prevents warping or curling during printing.
Gloss / Finish	Impacts aesthetic appeal, especially for coated papers.

 

2. Printing Process Requirements

Different printing processes demand specific paper properties:

Printing Process	Paper Requirement
Offset / Lithography	Smooth, medium to high opacity, consistent absorbency, flatness.
Gravure	Very smooth, strong surface, high brightness, coated papers preferred.
Flexography	Flexible, moderate smoothness, suitable absorbency for inks.
Screen Printing	Can be rough or textured; paper should withstand pressure and thick ink layers.
Inkjet Printing	Highly smooth, coated or specially treated to prevent ink bleeding.
Pad Printing	Paper should provide adhesion for inks during pad transfer.

 

3. Paper Varieties for Printing

1. Uncoated Papers

• Examples: Bond, Newsprint, Writing, and Ledger papers.
• Applications: Newspapers, books, office stationery.
• Properties: Moderate smoothness, absorbs ink well.

2. Coated Papers

• Examples: Art paper, Gloss paper, Matte coated paper.
• Applications: Magazines, brochures, packaging.
• Properties: Smooth, high brightness, good ink holdout, high-quality image reproduction.

3. Specialty Papers

• Examples: Thermal paper, Carbonless paper, Security paper.
• Applications: Tickets, receipts, certificates.
• Properties: Specific chemical or physical treatments for unique applications.

4. Board / Carton Papers

• Examples: Folding carton board, Box board, Greyboard.
• Applications: Packaging, displays.
• Properties: Thick, stiff, good printing surface.

 

Common Printing Defects

a) Curling

• Description: Paper edges curl or bend.
• Cause: Uneven moisture content, improper drying, or paper storage.
• Effect on Printing: Misfeeds, poor alignment, uneven ink transfer.

b) Wavy and Tight Edges

• Wavy Edges: Paper edges are uneven and rippled.
  • Cause: High moisture content, uneven calendering, or improper storage.
• Tight Edges: Paper edges curl inward.
  • Cause: Drying shrinkage, tension during finishing.
• Effect: Feeding problems, misregistration during printing.

c) Picking

• Description: Surface fibers or coatings are lifted from the paper during printing.
• Cause: Low surface strength, high ink tack, improper drying.
• Effect: Spotty or missing print areas.

d) Blocking-in-the-Pile

• Description: Sheets stick together during storage or handling.
• Cause: Excessive moisture, heat, or pressure in stacked sheets.
• Effect: Sheet separation issues, uneven feeding, scratches.

e) Linting

• Description: Loose fibers come off the paper and adhere to rollers or printed surfaces.
• Cause: Low-quality fibers, insufficient beating, or rough surface.
• Effect: Printing defects, scratches, and ink smearing.

f) Dusting

• Description: Fine paper particles detach during printing.
• Cause: Poor fiber bonding or excessive dryness.
• Effect: Contamination of machinery and prints.

g) Powdering

• Description: Coating pigments or fillers detach as fine powder.
• Cause: Improper coating adhesion, rough handling.
• Effect: Printing defects, loss of print quality, and surface roughness.

 

2. Influence of Moisture and Relative Humidity (RH)

• Moisture Content: Paper absorbs or loses water depending on environmental RH.
• Effects on Paper:
  • High RH / Moist Paper: Waviness, swelling, sticking, curl, and blocking.
  • Low RH / Dry Paper: Brittleness, tight edges, cracking, poor ink absorption.
• Effect on Printing Quality:
  • Misregistration, uneven ink absorption, pickings, curling, and feeding problems.
• Control Measures:
  • Store paper in controlled environment (40–60% RH).
  • Condition paper before printing.
  • Maintain stable humidity in the pressroom.

 

3. Summary Table of Defects

Defect	Cause	Effect on Printing
Curling	Uneven moisture, drying	Misfeeds, uneven print
Wavy Edges	High moisture, poor finishing	Sheet feeding issues
Tight Edges	Drying shrinkage	Misalignment, jams
Picking	Low surface strength, high ink tack	Missing spots, fiber lifting
Blocking	Heat, moisture, pressure	Stuck sheets, scratches
Linting	Loose fibers	Ink smearing, scratches
Dusting	Poor fiber bonding	Contamination, defects
Powdering	Poor coating adhesion	Surface roughness, print quality loss

 

Paper Storage – Requirements

Proper paper storage ensures dimensional stability, printability, and minimal defects:

Requirements

• Dry Environment: Prevent moisture absorption which causes curling, waviness, and blocking.
• Temperature Control: Maintain moderate temperature to prevent brittleness or expansion.
• Flat Stacking: Avoid deformation; pallets or racks recommended.
• Protection from Light and Dust: Prevent yellowing, contamination, and surface defects.
• Rotation of Stock: Use older stock first to avoid long-term degradation.
• Air Circulation: Prevent mold growth in high humidity.

 

Variables Affecting Paper Storage

Variable	Effect on Paper
Relative Humidity (RH)	High RH → swelling, curl, blocking; Low RH → brittleness, tight edges
Temperature	High temperature → accelerated aging, curling; Low temperature → brittle paper
Storage Position	Stacked improperly → edge deformation, wavy sheets
Light Exposure	UV/light → yellowing, degradation
Air Circulation	Poor ventilation → mold, moisture retention
Time of Storage	Long storage → loss of strength, print quality deterioration

 

Print Quality Achievable on Different Types of Paper

Paper Type	Achievable Print Quality	Notes
Newsprint	Medium	Absorbs ink well, limited resolution
Bond / Writing Paper	High	Smooth, consistent ink absorption, good for text printing
Coated Paper	Very High	Smooth, glossy/matte finish, sharp images, high ink holdout
Board / Carton	Medium to High	Thick surface, may require pre-treatment or coating for high-quality prints
Specialty Paper	Depends on treatment	Thermal, security, or carbonless papers require compatible inks

 

Measurement and Calculations – Paper Sizes

Standard Paper Sizes (ISO 216 – A Series)

• A0: 841 × 1189 mm (1 m² area)
• A1: 594 × 841 mm
• A2: 420 × 594 mm
• A3: 297 × 420 mm
• A4: 210 × 297 mm (common office size)
• A5: 148 × 210 mm
• A6: 105 × 148 mm

Principle

• Each size is half of the previous larger size along the longer edge.
• Aspect ratio is √2:1, maintaining consistency when folded.

Other Paper Size Systems

• B Series: Intermediate between A sizes, used for posters and books.
• C Series: Used mainly for envelopes to fit corresponding A series paper.

 

Introduction

Paper properties play a critical role in print quality, efficiency, and consistency. Understanding these properties helps in selecting the right paper for each printing process and minimizing printing problems.

• Printability: The ability of paper to accept ink, reproduce images/text accurately, and provide consistent quality.
• Runnability: The ability of paper to run smoothly through printing machines without causing jams, misfeeds, or defects.

 

Paper Properties Affecting Printability

1. Surface Smoothness / Texture

• Smooth surfaces improve ink transfer and sharpness of printed images.
• Rough surfaces may lead to poor ink coverage and grainy prints.

2. Porosity / Absorbency

• Controls ink penetration and drying.
• Too porous → excessive ink absorption → blurred prints.
• Too non-absorbent → ink smudging or slow drying.

3. Strength (Tensile, Folding, Bursting)

• Ensures paper withstands printing pressure and handling without tearing.

4. Opacity

• Prevents show-through from reverse side, essential for double-sided printing.

5. Brightness and Whiteness

• Influences contrast, color reproduction, and visual appeal.

6. Moisture Content & Dimensional Stability

• Affects curling, wrinkling, and alignment during printing.

7. Surface Chemistry

• Surface sizing and coatings influence ink adhesion, spreading, and drying rate.

 

Paper Properties Affecting Runnability

1. Smoothness and Thickness Uniformity

• Prevents jams and misfeeds in high-speed presses.

2. Moisture Content

• Balanced moisture prevents curl, sticking, and static electricity.

3. Fiber Strength and Elasticity

• Ensures paper withstands mechanical stress during printing.

4. Coating and Finish

• Coated papers may require slower printing speeds or special inks to maintain smooth operation.

5. Dusting and Linting Tendency

• Low-quality fibers can generate dust/lint → roller contamination, scratches.

 

Summary Table

Property	Influence on Printability	Influence on Runnability
Surface Smoothness	Sharpness, ink coverage	Smooth feed through press
Porosity	Ink absorption, drying	Ink smearing if excessive
Strength	Tear resistance	Prevents sheet breakage
Opacity	Prevents show-through	Not critical for feed
Brightness/Whiteness	Color reproduction	-
Moisture Content	Curling, dimensional stability	Prevents jams, sticking
Fiber Quality	Ink adherence, surface defects	Minimizes linting and dust

 

Introduction

Paper and board have surface and directional properties that affect printability, runnability, and end-use performance. These properties are influenced by fiber orientation, manufacturing processes, and finishing treatments.

 

Key Surface and Directional Properties

Property	Definition / Description	Significance
Substance (GSM / Basis Weight)	Mass of paper per unit area (g/m²)	Determines strength, stiffness, opacity, and feel
Caliper (Thickness)	Measured thickness of paper or board	Affects bulk, stiffness, and mechanical behavior during printing
Bulk	Caliper divided by GSM (thickness per unit weight)	Indicates thickness relative to weight; high bulk = thicker, cushioned feel
Compressibility	Ability to deform under pressure	Affects smoothness under press, impression during printing, and cushioning in packaging
Surface Smoothness / Roughness	Evenness of paper surface	Smooth surfaces improve ink transfer and image clarity; rough surfaces may cause picking or uneven printing
Air Permeance	Rate of air passing through paper (ml/min)	Influences ink absorption, drying, and coating adhesion
Static Friction	Resistance to starting motion between paper and machine parts	Affects sheet feeding, stacking, and runnability
Dynamic Friction	Resistance to motion when paper is sliding	Determines smooth operation during high-speed printing and rolling processes

 

Directional Properties

• Machine Direction (MD): Direction in which paper fibers are aligned during manufacturing.
• Cross Direction (CD): Perpendicular to machine direction.
• Influence:
  • Strength: Higher along MD than CD.
  • Dimensional Stability: Expansion/contraction varies with direction.
  • Printability & Runnability: Curling, stretching, and sheet feeding are affected by MD/CD orientation.

 

Summary Table of Effects on Printing & Packaging

Property	Effect on Printing	Effect on Packaging / Use
Substance	Ink absorption, stiffness	Strength, durability
Caliper	Impression depth, image quality	Thickness control, cushioning
Bulk	Print impression	Stiffness, cushioning
Compressibility	Smooth print under pressure	Shock absorption in packaging
Surface Smoothness	Image sharpness, ink coverage	Aesthetics, barrier properties
Air Permeance	Drying rate, ink holdout	Coating adhesion, barrier properties
Static / Dynamic Friction	Sheet feed, misfeeds	Handling, stacking efficiency

 

Surface & Internal Bond Strength

Property	Description	Related Defect
Surface Strength	Resistance of the paper surface to being pulled off by printing ink or mechanical action	Low surface strength → Picking (fibers/coating lifted by ink tack)
Internal Bond Strength	Ability of fibers within the sheet to remain bonded under stress	Low bond strength → Splitting (layers separate)
Picking	Lifting of coating/fibers due to high ink tack or poor surface strength	Leads to missing dots/patches in print
Fluffing	Small fibers loosen and transfer to press blankets or rollers	Causes dirty print, roller deposits
Splitting	Paper delaminates internally under pressure	Weakens sheet, affects packaging & converting

 

Strength Properties of Paper

Strength Property	Definition	Importance
Stiffness	Resistance to bending under load	Essential for cartons, packaging, and smooth runnability
Folding Endurance	Number of times paper can be folded before breaking	Important for maps, books, currency, packaging
Bursting Strength	Pressure required to rupture paper (measured by Mullen tester)	Indicates sheet durability, packaging performance
Tear Resistance	Ability to resist tearing once initiated	High tear resistance needed for sacks, wrapping, and heavy-duty packaging

 

Optical Properties of Paper

Optical Property	Definition	Significance
Gloss	Surface reflection of light	Affects image sharpness, contrast, and luxury appeal
Brightness	% reflectance of blue light (457 nm)	Higher brightness = better contrast and readability
Whiteness	Balance of light reflectance across visible spectrum	Neutral whiteness ensures natural color reproduction
Yellowness & Tint Indices	Deviation of paper color toward yellow or other tints	Impacts print color accuracy; yellowing reduces appeal
Fluorescence	Optical brightening agents (OBA) absorb UV and re-emit blue light	Enhances brightness/whiteness but may cause color shifts
Opacity	Resistance to light transmission	Prevents show-through in duplex printing

 

Summary Table

Category	Property	Effect on Printing / Packaging
Surface & Internal Strength	Surface strength, internal bond	Prevents picking, fluffing, splitting
Mechanical Strength	Stiffness, folding endurance, bursting, tear	Ensures durability, smooth converting, packaging strength
Optical Properties	Gloss, brightness, whiteness, yellowness, fluorescence, opacity	Determines visual appeal, print sharpness, readability