K Mean Black

• Name: Printing Technology
• Branch: Printing Technology Diploma 5th Sem
• Published: May 21, 2025

Press work (Offset Process)

SHEET FED OFFSET

1400, Johannes Guttenberg made some alphabets called movable type.

Lithography: alloys Senefelder in 1796, lithography is a method for printing on a smooth surface. Lihtography is a printing process that uses chemical processes to create an image, for instance, the positive part of an image would be a hydrophobic chemical, while the negative image would be water. Thus, when the plate is introduced to a compatible ink and water mixture, the ink will adhere to the positive image and the water will clean negative image.

The allow for a relatively flat print which allows for much longer runs that the older physical methods of imaging (e.g. embossing or engraving high volume lithography is used today to produce posters, maps, books, newspaper and packaging just about any smooth, mass-produced item with print and graphics on it. Indeed all types of high-volume text, are now printing using offset lithography.

Basic principal of offset sheet-fed machine:

1. When used in combination with the lithographic process, which is based on the repulsion of oil and water.
2. The offset technique employs and flat (plano-graphic image carries on which the image to printed obtain ink from ink roller, while the non-printing area attract a film of water keeping the non-printing areas ink free.
3. Indirect process
4. Chemical separation
5. Ink and water roller are separate.
6. Dipteral process:- two transfer
7. Image area and non-image area lie in the same level.

 

Advantage of offset:

1. Suitable for a very wide range of work, from short-to long run.
2. Wide range of substrate able to be printed to a high standard.
3. Paper and plastic plate used for small-offset, short run job.
4. Negative positive work PS plate used for high quality.
5. High definition reproduction of type matter, line and tone illustrations.
6. Speed of machine depend upon printing of quantity.
7. Film or plate for possible reprints.

 

Disadvantage of offset:

1. Alterations to machine plates impracticable.
2. Care must be exercised in ensuring the printed quality is maintain by adjusting and controlling the ink and water balance.

 

Classification of offset machines: an offset lithographic press is a mechanical device that dampens and inks the printing plate and transfers the inked image to the blanket and then to the printing surfaces.

A sheet offset lithographic press is a printing press that feeds and prints on individual sheet of paper (or other substrate) using the offset lithographic printing method.

A web, or web-fed offset lithographic press is a press that prints on a continuous web, of paper fed from roll and threaded through the press.

The four unit common to all presses:-

1. Feeder unit: a unit in which we feed the paper in automatic machine. When the taken pile of feeding. The pile in the top-sheet of fans automatically and lifts a sheet with mechanical finger.

The common is to feed stock into the press rapidly and uniformly.

Two types of feeder:

1. Front separation feeder.
2. Back separation feeder.

 

2. Speed of the machine: different speed of different machine. There is a range, there is no fixed speed. This is depend upon machine. (5000-18000) sheet per hour. The maximum speed 5000 sph and medium is 13000 sph and high is 18000 sph.

 

3. Format of the machine: two type of format

1. Large is used for map and large printing production wallpaper are printed (A0 to 2A0 sizes).
2. Small format: A1 sizes and small jobs used.

 

4. Delivery: some machines have normal delivery system (half of the feeder height) to avoid the set-off condition. The height of delivery system is half of the feeder height. Because ink is still wet, it may cause the transfer of ink to next sheet in pile.

 

Method of avoid set-off:

1. The machine 3 sets of gripper are used, extended delivery is used.
2. The delivery is normal but there are two delivery piles method used in double delivery system.
3. Sheet insertion device (SID): paper directly goes into the cylinder front lay. This process is called tumbler gripper system.

A device put between impression cylinder and lays so that the sheet can’t delivery directly into the cylinder.

This is indirect system call swing arm gripper assembly.

Rotary gripper assembly: it is continuously rotating. It has grippers on shaft.

 

Configuration of machine: a sheet-fed press consists of a feeder, one or more printing units, transfer devices to move the paper through the press, a delivery and various auxiliary device ( such as a control console).

1. Plate cylinder
2. Blanket cylinder: fabric with synthetic rubber.
3. Impression cylinder
4. Dampening system: additives such as acid, gum Arabic, isopropyl alcohol and other wetting agent.
5. Inking system

 

Unit of sheet fed:

1. Feeding
2. Inking
3. Dampening
4. Printing
5. Delivery

 

Various offset printing machine configuration:

1. Single color: single color in which there is one set of printing cylinder arranged to print only one color on one side of each sheet as it passes through the press.

 

2. Multicolor sheet-fed press: in which more than one color is printed on one side of a sheet during a single pass through the press because there is more than one printing unit.

 

 

3. Perfecting press: in which sheet are printed on both sides during one pass through the press.

 

Single color sheet-fed- a press consisting of a single printing unit, its integral inking and dampening system, a feeder, a sheet transfer system and a delivery is called single color press.

Single color machine to print multicolor printing; normally, it can print only a single color in any color in any one pass through the press. On some presses, the inking system can be modified-split-with ink fountain ink roller dividers so that two or more color can be printed at one time. On these presses, the same printing plate is used, and the colors are widely separated.

A single color press can also be used for true multicolor printing. The printing of two or more colors. Often one over another. Multicolor printing on a single color press requires that the sheet be fed through the press as many times as there are colors to be printed. After each printing, the just used plate is removed and the inking system is thoroughly cleaned. A new plate is mounted on the plate cylinder, and the inking system is filled with the next color. The sheet of paper is run through the press again and printed with this new color. (Multicolor printing on a single-color-press is dependent upon dry trapping-the ability of a dry, printed ink film to accept a wet ink film over it. The wet ink dries by oxidation polymerization.

The printing unit of the single-color sheet fed press is sometimes described as an “open unit”. The plate cylinder blanket cylinder impression cylinder are usually arranged in a near right-angle, relationship. The arrangement is common for three reason.

1. To reduce the overall height of the press.
2. To make it easier to feed the paper into the impression cylinder grippers.
3. To make it possible, by movement of only the blanket cylinder, to throw all three cylinder out of contact with each other.

 

There are exceptions this nearly right angle arrangement of cylinder.

Multicolor sheet-fed press: a press consisting of several printing unit (each with its own inking and dampening system), a feeder, a sheet transfer and a delivery is called a multicolor, or multiunit press. A Multi-color press can have two, three, four, five, six, for more printing units. Multi-color presses are capable to wet trapping, the ability of a wet, printing ink film to accept another wet ink film printed over it.

In the larger press sizes, the printing units are almost identical and are arranged in tendem with some of the other two and four-color presses, one obtain better accessibility.

 

Multicolor sheet fed press: an odd number of transfer cylinders is needs between units so that the side of the sheet to be printed faces away from the impression cylinder.

In another multicolor sheet-fed press design, a single (common) important cylinder serves two pairs of plate and blanket cylinder.

Offset perfecting press: most sheet-fed presses can print on only one side of the sheet in a single pass. For the other side to be printed. The entire paper pile must be turned over and the paper run through the press a second time. There is however, a type sheet in a single pass. The printing of at least one color on both sides of a sheet in a single pass through a press is called perfecting. Any press that can do so is called perfecting press, or pefector.

The most common sheet-fed perfecting press is called convertible perfector. Special transfer cylinder tumble the paper and for end between printing unit so that the other side of the sheet is printed by the second unit. This type of press usually has the capability, through transfer cylinder adjustment to print either two color on one side of the sheet or one color on each side in a single pass through the press.

 

With another type of sheet-fed perfecting press, the blanket from two printing units are in contact, with the paper passing the two blanket. This type of press blanket to blanket press because the two blanket in contact No. of impression cylinder is needed.

Small offset press: generally, any press smaller than 11X17 inch (279X437mm) without bearer is called small offset press or more often, a duplicator. There are extremely simple, but they have developed into efficient offset presses that fill many printing needs. Many are being used for multicolor work.

Web offset presses: lithography is the printing process by which ink and water transfer image from a level surface plate (onto another surface image and non-image areas are chemically separated.

Common impression cylinder (satellite) each printing units of a common-impression cylinder (CIC) press has one very large impression cylinder with four or five printing couples radially arranged around it. Because of the arrangement of the couples and size of the impression cylinder. These presses are called satellite presses.

 

SHEET FEEDING SYSTEM

Feeders are used to feed the sheets.

It is important that the pile of press sheets be accurately cut to the same size, be of the same thickness (paper thickness) and not be wrinkled or stuck together. Begin by fanning the pile to remove any static electricity that might be holding individual sheet together. Place the pile in the feeder section of the press, in the center. When the sheet passes through the registration unit, it is generally jogged or pulled from 1/8 to 3/16 inch and is then centered on the registration board.

Push the pile forward so that it is squarely seated against the front plate of the feeder when held by the side and back guides. The top of the paper pile must be perfectly level and parallel to the registration board.

Feeder section where paper is removed from the top of a pile table, forward on a feed board to front stops, laterally positioned on the feed board, and fed into the first printing unit. Feeder section can be divided into two categories.

1. Single sheet feeder /front sheet: where only one sheet of paper (travelling at press speed) is on the feed board at any instant. When we lift it from form edge. The whole pile is engaged in forwarding the sheet. So, it caused slowness.

Advantages:

1. The structural design is simple.
2. To change the GSM of the paper.
3. Make ready is faster.
4. Changing the paper size.

 

2. Stream separation feeder:

1. A continuous stream of sheet is made on feed table.
2. Sheets are separated from back edge and lifting from back edge.
3. 1/3 of sheet is forward only.
4. The speed of machine can be increased.
5. Only one sheet at a tome should be lifting and forwarding.
6. 3 times more speed in feeder.

 

Stream sheet feeder parts:

1. Lifting sucker:
2. Forwarding sucker:
3. Pile height: usually 3/16 (5mm) below the forwarding flops.
4. Flip spring: it is a thin blade position in line wise. It is used to control more than one sheet. Low pressure is applied in flip spring.
5. Combers: it is a brush separator brushes or fingers prevent the suckers from picking up more than one sheet at a time.
6. Side guage: it is used for forwarding the paper in correct direction. It is not fit in closely paper set between even with 1mm difference.
7. Blowers: separate the paper in pressed air by combined paper.

 

Feeder assembly: Sequence of working of stream feeder:-

1. Air is forced into the back edge of the pile separating top sheets, the rear suckers descent to take hold of the top floating sheets.
2. The suckers raise the back of the sheet and the hold round foot descends to firmly hold to remaining sheets in the pile. This hold down foot acts as a pile height governor. A stream of high velocity air is now directed under the top sheet lifting from edge of the sheet to a level with the forwarding roller.
3. The sheet is now moved forward on its cushion of air to pass between the forwarding roller and drop wheels which closed on to the sheet and convey it forward. As the sheet is taken by forwarding roller. The back separation unit began its next cycle.

Drop wheel/forwarding wheel are same.

Sheet feeder: it was manual while during light activity every sheet forwarding in the same place and same time and in the accurately help during side lays and center lays. Feeder in three types.

Feeder is work: (separate, lifting, forwarding, alignment)

Machines in which feeder are used:- printing machine, folding machine, it may manual semi-automatic, automatic.

Work of feeder: to separate the sheet, lift the sheet and to forward the sheet and aligning in feeder unit.

Sensor are used to only one sheet at a time of lifted & forwarding. This sensor is used to detect of two or more sheet lift at a time and the given alert. When the two or more sheet lift so, machine is tripped of sheet after this sensor will be down and measure of thickness of paper and your alert. If was not lifted at all, may be due to vacuum, pressure or sticking of paper.

No sheet detector: it is only absence of sheet. The gap will be created. All the forward & feed table on not sheet forward and it will trip the machine again. It also detect the paper are going parallel or not.

The gap should be expanded when GSM needs to be change.

In this feeder is important factor in lift the 300GSM.

Spacing: spacing is helpful because the more space to not create wear and tear.

Feeder has many assemblies, some control sheets, some forwarding one sheet.

Tail guide assemblies: sheet is both edges to set and guides the tail of sheets.

Sheet controls- applied on sheet’s back edge on feed table.

1. Side weight: 4 conveyer tape
2. Flip assembly: 1. Small steel strips , 2. Keep intact the remaining sheet
3. Brushes: two brushes, 1.to hold the remaining sheets.
4. Air separator.
5. Hold down foot or pile height governor

1. A high velocity air is forced into the top sheet
2. It governs the height of the pile.
3. To hold the remaining sheet.

Forwarding roller: 1. Two drop wheel, 2. two or more sheet detector (it has thickness of 2 sheets, if there are 3 sheets it trips).

Feed table/ramp board: 2 outer tapes are aligned to front lays i.e. conveyor tap.

Why only 2 front lays are used at a time?

For perfecting alignment, only 2 front lays are used.

 

There are two types of lays: (1) front lays      (2) side lays (push or pull)

Pull type: finger to finger, roller to finger, roller to roller these are mostly used

Pull type side lays are very satisfactory to use.

Sheet insertion device: 1. direct system,   2. indirect system

1. Direct system: the paper goes into printing unit without any intermediate between lays and grippers. It is also known as tumbler gripper.

Sheet detector: running in wheels, brush roller, brush, ball control assembly.

These are used to control aligned sheet of paper during feeding.

Weight of ball should be in ratio to the other wheels and unit of paper.

There is no +ve control on the aligned sheet at the time of transfer of the sheet into the tumbler gripper.

 

2. Indirect system: there are two types of indirect system

1.  Swing arm assembly.
2. Rotary gripper assembly.

 Both are springs of metal in the gripper finger to control the force of the gripper finger onto the paper.

 

Technical knowledge of offset machine:

Control on the feeder table:

Printing material  - pulleys - suction drive roller - suction tape vacuum - suction tape vacuum

 

1. Air setting for pneumatic side lay.
2. Air setting for the driving rollers of the pneumatic pull lays.
3. Suction air setting for the front suction chamber.
4. Height adjustment of the separator rolls.

 

Side lay on and off:

Printing material grammage in GM2.

70 gsm = weak

135 gsm = off

240 gsm = medium

350 gsm = strong

Air setting of venture nozzles.

 

Double sheet detector:

Sheet length                                                   number of sheet

210 – 315 mm                                                 2 sheet, 3^rd get off

315 – 470 mm                                                 3 sheets, 4 get off

470 – 530 mm                                                             4 sheets, 5 get off

 

 

PRINTING CYLINDER

All the cylinders are same. Their diameter, weight

Bearer to bearer:

The printing unit of a sheet-fed offset lithographic press generally consists of three primary cylinders and system for dampening and inking the plate:

1. Plate cylinder: a cylinder that carries the printing plate, flexible image carrier with ink-receptive image areas and when moistened with a water based solution, ink-repellant iron image areas.

All the three cylinders are aligned at an angle an aluminum, or bimetal plate is mounted over this cylinder. The plate courses the image to be printed. Dampening and inking rollers are set in contact with the plate cylinder. The plate cylinder revolves along with the dampeners and inking rollers. Water layer is applied onto the non-printing areas of the plate by dampening form rollers. Similarly ink layer is applied onto the printing areas of the plate by inking form rollers.

The plate cylinder which is usefully the upper most cylinder of the three cylinder, carries the printing plate.

 

• To hold the lithographic printing plate tightly and in register.
• To carry the late into contact with the dampening roller that wet the non-image area.
• To bring the plate into contact with the inking roller that inks the image area.
• To transfer the inked image to be blanket carried by the blanket cylinder.

 

1. Bearer: it smoothness for working. It also show the reference height. Also functions the smooth rolling of the cylinder.

Bearer at each end of the plate cylinder bearer, a hardened metal ring attached to the cylinder body or journal. On many presses, the bearer of the plate cylinder run in contact with the bearers of the blanket in contact with the bearers of the blanket cylinder during printing. General width of bearer = 20mm, wide.

 

2. Under cut: it will accomdate plate packing + plate thickness.

Bearer height + cylinder body

Plate cylinder has less undercut than blanket cylinder,

Under cut, the body of the plate cylinder is smaller in diameter than the bearer. The difference between the radius of the body surface and that of the bearer is called the undercut, a plate clamp is a device designed to first grip to edge of the plate cylinder and then pull it tight against the cylinder body. Gutter, narrow gap between body of the plate cylinder and the bearer is called gutter.

 

3. Gears: cylinder drive gear is generally helical size. The gear whose teeth are cut at an angle. It is generally more used.

The plate cylinder is driven by this gear, which is in turn driven by a similar gear on the blanket cylinder. The cylinder gear may be spur or helical (on older presses). A spur gear has teeth cut straight across the gear. The helical gear has teeth cut at an angle. A spur gear as a plate cylinder gear nearly always has a backlash gear. A thin second gear bolted to bit to reduce play-free or unimpeded movement between gears.

 

Plate edge: two types:

1. Gripper edge: gripper edge is inserted first. Plate should be perfectly clamped. There should be no gap between plate and cylinder.

Identify: if plate is big and print area is very less than the gap between edge and print area is called gripper edge. Print edge and print area where there will be less gap, called gripper edge.

 

2. Back edge:

 

Part of plate cylinder:

1. Depression gap: a small segment which is cut. It is not flat. Printing area will be decreased. If we reduce the length of depression gap.

Range (1/4 to 1/2) circumference of simultaneous cutting of cylinder is called depression gap. If we increase the depression gap, then printing length will decrease vice-versa.

1/16 = web offset machine.

2. Cam: It is used in letterpress, it is steel body but coated with nickel. To avoid rust, because it is anti-corrosive.
3. Cam clamp: it is of any shape or size. It is used in machine where depression gap is less.
4. Cam follower: to reduce the waste in web offset machine, depression is kept less.

Cam follower is also called, “small bearing”.

5. Gripper: metal spring loaded finger.

 

Plate clamping assembly: plate is fixed by plate clamping assembly. Machine in which plate clamping assembly can be removed. Detachable clamping assembly.

Plate can be moved to register clamping by plate cylinder, circumferencial or laterally.

Laterally movement in single color is not possible.

Paper is avoided as packing because they became wet due to different chemicals used.

Plate clamping assembly could be done through hexa and allen bolts.

Bolting calmp: secured

Under cut of plate cylinder = 0.50mm.

Thickness of metal sheet = 0.3mm, 0.28mm.

 

 

2. Blanket cylinder: this is called second cylinder. The both of the gear on both side of the plate cylinder and blanket cylinder mesh and cause both cylinder to rotate together. The ink applied on the image on the plate, gets transferred to the blanket (rubber) cylinder because the ink has the ability to get printed on rubber (blanket) surface. The image printed on blanket cylinder becomes opposite (indirect) to the plate cylinder.

Two primary functions:

• To carry the offset rubber blanket into contact.
• Under cut is different but depression gap is same in every cylinder.
• To transfer, or offset the ink film image to the paper (or other substrate) carried by the impression cylinder.

 

It is very similar to the plate cylinder because it has a gap, gutter, bearers, a gears and bearing. However, it does not have clamps like a plate cylinder it has one or two reels for holding and stretching the blanket tighter. The blanket ends are attached to bars, which in turn, are mounted to reels.

 

The distance between blanket cylinder and impression cylinder must also be adjusted to accomdance difference thickness of substrate and blanket packing. This distance is adjusted by another pair of eccentric bushings.

If any machine has 2 blanket cylinder, one will be called top and other will be called under.

Undercut will be more enough to put two blanket cylinder.

Top = 2.90mm

Under = 2.4mm

Width of bearer = 20mm

 

3. Impression cylinder: impression cylinder carries the paper into the printing unit, and contact pressure from blanket cylinder transfer the print to the paper, impression cylinder too has a gear and gap. The gap accomdates the gripper shaft on which are mounted the gripper finger that hold the sheet during printing. The grippers hold the unprinted paper in register as the cylinder turns the resses it against the ink image on the blanket cylinder.

The body of the impression cylinder is not undercut but is approximately. The diameter of the bearers of the other two cylinders. The impression cylinder bearers are, in fact, undercut are used only as paralleling devices when setting up the press.

 

Cylinder packing:

 

Calculation:-

Plate thickness                                               +0.27mm

Plate cylinder undercut                                 -0.15mm

Plate above undercut                        +0.12mm

 

 

 

 

Blanket thickness                               +1.95mm

Under lays                                          +0.35mm

Blanket cylinder undercut                 -2.30mm

Blanket on bearer height                  0.00mm

 

 

Plate above bearer                            +0.12mm

Blanket on bearer                                0.00mm

Pressure plate blanket                                     0.12mm

 

Blanket on bearer height                  0.00mm

Printing material                                +0.10mm

Pressure                                              0.10mm

 

 

 

There are two basic mechanical designs for varying the clearance between the blanket and impression cylinder to accommodate different thickness of stock.

 

• In the first design, the impression cylinder is mounted on a set of eccentrics. A shaft of the eccentrics by an impression lever moves the impression cylinder towards or away from the blanket cylinder.
• The second method uses two sets of eccentrics, but these are on the blanket cylinder. The inner set adjusts the blanket to plate pressure and actuates automatic on-and-off printing contact. The outer set moves the blanket cylinder only in relation to the impression cylinder.

In this cylinder has no bearer, because no packing or rolling of material is done. In one case, bearer are used in letterpress.

 

Alignment of sheets: is done when the feeder unit starts.

 The sheet will be aligned perfectly if there is more gap.

A1 size machine = (10-12 grippers_

A2 will have less grippers.

 

Grippers are opened or closed with the help of cam. All the gripper will put equal force & equal time, they will grip the sheets.

 

To deliver the sheets

Direct system of sheet insertion: Tumbler gripper: they have to tumble at 180 impression cylinder is made of stainless steel is chromium plate instead of nickel plating.

 

Undercut: the difference between bearer and cylinder surface.

Machine run bearer to bearer contact. Such machines are called bearer to bearer contact machine.

 

Work of bearer:

1. It acts as a reference for printing height.
2. It also ensures the smooth running of the cylinder without any vibration and jerks.

Overpack: the plate should be kept 0.1mm above the bearer height so that it can transfer minutes detail with the blanket cylinder.

Bearer cause smooth running & prevent wear % tear.

Eccentric bearing: out of center bearing.

Vertical line = lateral movement

Horizontal line = circumferencial movement.

Plate cocking: a manual method of adjusting the plate if the difference is higher side lays & should be adjusted machine should be set in zero condition.

 

Guage ring: diameter of guage rings is less than bearers. In the ring is bearer and bearer is found in cylinder and it is found in plate cylinder and blanket cylinder and it is safe of cylinder edge and it is small of bearer and it is made in both side cylinder.

 

Feeler guage: a gap which is used in adjusting the gap between blanket and impression cylinder. It is an instrument and it is measure the between two surfaces and light is the set of ink duct. It is name based on feeling.

Thin metal strips are used to fill the gap between cylinders.

Blanket cylinder has higher undercut than plate cylinder.

Cam: it is a desire function achieved and cam is always follow of follower and it is small roller. Cam is the role in machine. It is help the bed and platen moved and it is help of open and close is bed and platen and it is help to open and close grippers. This is working the help of follower.

 

Plate mounting:

1. Inch the machine so, that the plate clamping assembly in the plate cylinder is in front of you.
2. Loosen the clamping assembly bolt at back edges of remove the plate back edge from the clamp.
3. Backward inch the machine so that the front edge of the clamp is accersible to you.
4. Loosen the bolts in the front edge, gripper edge of the clamp, by doing so the front edge/ gripper edge of the rate is free in the clamp of remove the plate & packing also.
5. Clean the surface of the plate cylinder and give a wipe of wipe of oil cloth to the body of the cylinder ensure that the clamping assembly is in the central.
6. Identify the gripper edge of the plate and insert the gripper edge of the plate into the gripper edge clamp in the center of the plate cylinder.
7. Centre the plate mark to coincide with the center mark present it the cylinder.
8. Insert the packing sheet of required thickness between the cylinder body and plate.
9. Press the lock button present in the clamp so that it holds the plate, and tighten the side belts.
10. Forward inch the machine and till the back edge of the clamp is excessible to you ensuring that pressure is on.
11. Insert the back edge of the plate in the plate clamp and tightened all the bolts in the clamp.
12. Give the required tension to the plate from back edge so that plate is in perfect contact with cylinder body and is not loose.
13. Make the impression off and turn the machine forward for few revolution.
14. Ensure that the plate is perfectly tension on the cylinder by tapping at the back edge and front edge, if not give the proper tension.

 

Some machine use double blanket:

Rubber blanket: offset press blanket are made of supporting fabric and a rubber composition. Various rubber material are used for the transfer of the image from the plate to the blanket. Blanket come in compressible to hard finishes along with smooth to rough surfaces. The majority of printers today use compressible type blankets. These blankets give good compression which eliminates many smashed blanket. Slightly rough blankets are also preffered as they have less contact with the paper surfaces thus reducing blanket contamination.

One side is synthetic rubber is other side is hybrid fabric so that it stops the absorption.

High grade cotton ply are taken and synthetic layer is spread on the blanket. Adhesive is used for pasting microcellular layer which has bubbles is inserted between cotton ply and synthetic layer.

 

Blanket mounting procedure:

1. Measure the thickness of the blanket for giving correct thickness of packing sheet.
2. Insert the leading edges and trailing edge of the blanket with the clamp bars and tighten the holds in the clamp bars.
3. Mount the leading edge of the blanket with clamp bar and tight it in the leading edge of the blanket cylinder, with required amount of packing sheet under the blanket.
4. Inch the press forward to reach the opposite edge of the cylinder and tighten the other end of the blanket with clamp bar with blanket cylinder.
5. Adjust the blanket tension by tightening the blanket clamps using the torque wrench to make correct tension of blanket over blanket cylinder.

 

RUBBER BLANKET

1. Compressible blanket: these blankets are now-days used in offset printing machines. These blankets consists of compressible layer along with the fabrics layer in its underside. Due to this while printing when the compressible blanket is squeeze in a nip. These blanket bulges very low, which does not, affects the printing solid work, fine halftone work.

(Microcellular layer is inserted between cotton ply and synthetic layer).

 

2. Non-compressible blankets or conventional blankets: these blankets are used in olden days. These blanket do not have compressible nature because these blanket only have fabrics at its underside. The conventional blanket is squeezed in a nip. It bulges either in one (or) both side of the nope. Due to this formation of bulge the problem like, slurring may be caused. These blankets are used for printing ink works, solid tints etc. the disadvantage of these blankets is that these are not use for fine halftone works.

Solid blankets & these blankets does not compress when pressure is applied. This cause deformity (bulge) in it, becomes loose. It would cause the cylinder to loose.

 

3ply blanket and 4- ply blanket both are same. Only one fabric layer have extra addition.

 

 

Type of grades: depend upon hardness

Hardness =76 – 82 degree                 hard blanket

                = 74 – 76 degree                 medium

                = 70-74 degree                   soft

 

1. Hard blanket are used when solids are print. When we are experiencing a difficult in finding stocks.
2. When speed of machine is high and when metal sheet is print.
3. 74 – 76 used for general work.
4. 70 – 74 used for proofing.

Machine which have slow speed. It is used when fast make ready is required.

MEK = methyl ethyleketon.

C6H6 = Benezene

CCL4 = carbon tetrachloride.

 

The above three can be used with cotton for temporary purpose on blanket when sensor don’t work.

Dotted line = under blanket

Straight line = top blanket

When we give tension to the top cylinder, it automatically settles down, so that, no water, fountain solution, chemicals etc. can creep so that top cylinder cover the side.

Blanket care:

1. Blanket versatile: problem solving, supreme rejuvenator, de-glazer, and instant conditioner for offset rubber blankets.
2. Blanket refresh: end-of-the day conditioner wash for offset rubber blankets.
3. Blanket reviver: premium low hazardous conditioning and reviving solution for offset rubber blanket.
4. Revivarol de-glazer: powerful liquid de-glazer cum conditioner for roller & blanker.
5. Swell: rapid action repairing get for blanket low spots and punctures.

 

Storage of blanket: whenever a blanket is not used immediately ensure that it is stored in a proper way. That means, if we talk about rolls of printing blankets, these should be kept standing upright to avoid that the full weight of the roll cause damages like shown below:

Cut to size sheets have to be stored flat laying rubber to rubber and fabric to avoid a fabric impressions on the rubber surfaces.

If these guidelines are followed, the blankets are stored in dry (60% humidity), dark (no sun or UV-light) and at an ambient temperature of 18-22 degree, they can be kept for approximately 2 years.

 

INKING SYSTEM

Inks: inking system a series of rollers that apply material film of ink to a printing plate. In addition to one or more printing units, a press also includes the following.

Ink has to apply fresh and adequate quality of ink onto the printing surface.

Requirements of ink system: milling/grinding, storage capacity, good penetration into the paper, good viscocity, good color/ brightness etc.

Characteristic of good roller system: it must be so arranged that the ink is milled to the required consistency without the need to thin the ink with varnish. The storage capacity of the system must be adequate to effect good recovery of the plate roller ink film during each cylinder revolution.

The ink should be evenly and equality distributed over the rollers. The roller layout should minimize any tendency for the plate. Dampening solution to mix with the ink on the rollers.

Theory of ink flow: when a roller which is covered with an even film of ink is brought into contact with another un-inked roller of the same diameter, ink film splits and approximately 50% of the ink passes on to the roller in one revolution. If there is a train of rollers in contact the ink flow path can be traced as the ink splits from one roller to another.

50% of the ink from the ink roller is transferred to the other rollers in the same in 1 revolution

Ink film depth = 1 um

Front part of the inking system is havier.

 

 

Percentage of ink transferred by ink rollers.

A1 & A2 = smooth roller (smooth down).

A3 & A4 = main rollers.

 

Machine has two inking system:

1. Multicolor inking system: all the rollers have approximately the same diameter and may vary be small amounts. Tracing the flow path, the primary path of fresh ink flows to the first two plate inkers. Designers use this type of system on the premise that the fresh ink on the front rollers counters the main front of moisture on the plate with these rollers resisting the emulsification with fresh ink, the remaining plate inking function by equalizing the ink film on the image.

(A1 & A2) are primary ink flow. It countract the moisture on the plate.

(A3 & A4) equalize the ink density on the image.

 

2. Drum inking system: a large diameter drum is included in the roller pyramid. The ink flow path can be traced to feed the last two plate inkers with fresh ink. The first two plate inkers take the secondary supply of ink. The function of large drum is to increase the storage capacity during each revolution. By directing the fresh ink to the last two plate inkers the designers purpose to apply fresh ink to the image as it leaves the rollers, thus giving added tone and density to the print. To first two plate inkers are so arranged to remove excess moisture from the plate to a point in the roller train where it can be evaporated and effectively controlled. Both these system are in current use and give satisfactory results.

(First two front rollers secondary ink supplier).

(Primary back rollers added tone & density).

(Emulsification of water & ink is evaporated from the system).

1. Ink fountain: a pan that contains the ink supply.
2. Doctor or doctor roller: a transfer roller that alternately contact the ink fountain roller and the first roller of the train often an oscillating drum.

 

Element of inking system:

1. Ink duct: gap between plate & duct is important. It should be set carefully.

We filling guage 0.75mm for setting it.

Movement of duct roller can be adjustable at zero, it stops at 20, it is minimum.

Some machine have roller which are continuously moving or majorized movement. It is of metals.

 

It is a reservoir in which ink is metered to the roller pyramid. It incorporates a large steel roller which rotates at a controlled speed in a tough of ink. As the steel roller turns a film of ink is carried on its surface, and the thickness of the film can be controlled by adjusting the spring steel blade which is fitted close to the roller surface. The finger screws are turned to either open or close the gap between blade and the steel roller.

 

2. In-feed roller or vibrator or doctor:

1.  It feed the ink supply from original supply. It is rubber roller.
2. It contact the duct roller, then it moves with it moves with it for some stroke, then it makes contact with another roller.

The duration feed roller is duct roller is called Dwel time. During the cycle in which the duct roller turns, the feed roller moves into contact with it and takes a strip of ink from the duct roller. The feed roller then moves into contact with the roller pyramid and transfers the ink to the roller train. The length of the time during which the feed remains in contact with the rotating

 

3. Drive roller: the ink pyramid derives its drive from a number of fixed metal or plastic covered roller which are rotates by gear or chain connected to the main drive of the press.

Two or three rollers which drive the whole system, they are gear roller.

 

4. Oscillator: driven rollers that not only rotates but oscillate from side to side distribution and smoothing out the ink film and using image patterns from the form rollers.

The roller in which lateral movement happens other than the movement. It is of metal.

 

5. Ink form roller: they have apply ink by coming into direct contact with plate surface. Ink changing, Ink transfer are same.

A1 size offset machine have four ink foam rollers. They are of neoprene rubber.

Copper is good conductor of ink acceptance.

A series of three to five roller that contact the printing plate and transfer ink to the cylinder.

 

Fall of point: consider an inked roller brought in contract with a large diameter cylinder. On completion of one cylinder revolution the ink film transferred to the cylinder will vary in thickness with distinct fall off point which correspond directly with the diameter of the small ink roller with an increase in the number of ink rollers the same fall off point will be in evidence. When this occurs on the press the fall of points may be quite noticeable on solids and tints, in the form of streaks running parallel to the gripper edge of the sheet. The overcome this tendency the plate inking rollers are made in varying diameters which results in the fall off occurring in non-coincidental point on the plate, thus eliminating the streaks.

All rollers are of different diameters. But these roller will be of minute difference.

1. Fall off point visible & noticeable in printing.
2. Different come visible in solid printing & this is a defect. These are objectional things.

Scavengers: small diameter rollers clean the system small diameter roller added to the pyramid to act as scavengers because of their small diameter the rollers rotate at high speed causing them run earm, thus evaporating the moisture entrained in the ink.

Conditions for setting the rollers:

1.  The undercut must be completely filled with packing.
2. Ink rollers must be on.
3. These foam rollers should be driven by oscillator.
4. Machine has an ink washing device called knife.

 

The rollers which face the dampening roller roller called from roller and the roller which face the back of the dempening roller is called back roller.

Fresh rollers countract the dampening system and back roller neutralizes the dampening roller.

50% of the ink from ink roller is transferred in 1 revolution.

Cause of streaks:

1. Streaks or rollers streaks is a defect which can came if two rollers have same diameter.
2. Gear streaks.

 

DAMPENING SYSTEM

It applies a fine layer of moisture on the printing surface which is clamped on the plate cylinder.

This is a system with a series of rollers that dampening the printing plate with a water based dampening solution that contains additives such as acid, gum-Arabic, and isopropyl alcohol or other wetting agent. Dampening system used for sheet-fed offset lithography are classified into two categories the

1. Intermittent flow (doctor or conventional)
2. Continuous flow.

Types of dampening system:

1. Print on substrate
2. Emulsified : mixed with ink
3. Evaporates.

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) DH (degree of German hardness).

 

Types of dampening system:

1. Conventional dampening system: the intermittent flow dampening system, usually referred to as conventional dampening system, consist of the following.

 

 

1. Water pan or fountain which hold the dampening solution to be fed to the plate.
2. Fountain pan roller which rotates in the fountain and carries dampening solution on its metal surface.
3. Doctor roller which intermittently contact the fountain roller and an oscillator roller, transferring the dampening solution.
4. Oscillator roller which oscillates from side to side to even out dampening across the press.
5. Form roller which transfer dampening solution from the oscillator roller to the printing plate.

 

Conventional dampening system is contacting system i.e. the film of fountain solution applied by a roller in direct contact.

PH. (4.5 – 5.5).

Universal indicator is used to measure PH.

Demerit:

1. High maintenance.
2. High paper waste rate because the required ink/ dampening solution balance is reached very slowly.
3. Frequently malfunction due to covering becoming fluffy.
4. Often uneven distribution of dampening solution.
5. High risk of excessive supply of solution.

 

2. Continuous dampening system: the continuous dampener is actually a roll type coater. There are two type of continuous dampener. One type feed fountain solution directly to the plate and the other feeds it directly into the ink system. The continuous dampener uses a four roller system.

 

1. Fountain pan roller
2. Slip roller: the slip roller controls the amount of fountain solution supplied to the plate. Speed the roller up and you feed more fountain solution slow it down and you supply less. The use of alcohol on these type of dampener was standard for year.
3. Transfer roller (oscillator)
4. Water form roller.

 

Muller dampening system

Brush dampening system

Air mist dampening system

Continuous via inking roller

Continuous dampening system

Flapper bar dampening system.

All roller are in permanent contact.

 

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%.

 

Making of dampening solution:

1. Water: it is mixed maximum ratio. It is should be pure with minimum impurities.
2. Fountain solution:-

1. Acid or base: this present in fount solution and it is maintain the PH value while the dampening solution is mixed during printing.
2. Gum Arabic: desensitize the non-image
3. Corrosion inhibitor: it is avoid the reaction of ingredients over the plate from corrosion.
4. Buffer: magnesium nitrate is used for neutralize the acidity or alkanlity of the solution.
5. Wetting agent: ISO propyl alcohol is used as the wetting agent.
6. Drying stimulator: during the contact of ink and water over the plate surface the drying capability of the ink becomes low. Hence the drying stimulator helps to speed up the drying of ink.
7. Fungicide: it is avoid the formation of fungus while using the dampening solution.
8. Anti-foaming agent: avoid the formation of foams.

 

3. IPA: it is reduce the ST and increase the CA.

 

Conductivity: the term to determine the amount of ion present in the dampening solution PH is the level of hydrogen ion concentration, hence ion must be present in the dampening solution in a minimum value. If pure water have not free electron. Without ion not charge dampening. So, impurities mixed for maintain conductivity. Fountain solution for proper hydrogen ion combination. So the PH of the dampening solution is directly proportional to the conductivity of dampening solution.

Correct calculation: desired quantity-

Additives        4%

Alcohol                       10%

Water              86%

Actual quantity          100%

 

The ideal dampening solution should have:

1. Plain water hardness of 8 to 12 degree DH.
2. Conductivity of plain water can be up to 400 micro siemens.
3. PH value of dampening solution 4.8 to 5.5 for metallic inks and 4.8 to 5.2 for normal ink.
4. Temperature that is about 10-15 C below the ambient temperature.
5. Alcohol percentage 8 to 10%.
6. If the solution conductivity increased by 1000 micro siemens from freshly mixed solution conductivity value then, it is time to replace the dampening solution.

 

Water hardness test procedure:

1. Water hardness is determined mainly by the content of calcium and magnesium.
2. Hold the strip briefly (15 sec) into the water, shake off the surplus water wait 2 minimum then read off the result.

Less than 3 degree     =          very soft          categories 1

4-7 degree                  =          soft                  categories 2

8-14 degree                =          medium          categories 3

16-21 degree              =          hard                categories 4

More than 23 degree =          very hard        categories 5

 

Evaluation:-

Categories 1: 3 degree = very soft

Categories 2: 4-7 degree = soft, suitable for offset printing.

Categories 3: 8-14 degree = medium, suitable for offset printing.

Categories 4: 16-21 degree = hard, problematic for offset printing.

Categories 5: more than 23 degree = very hard – problematic for offset printing.

 

DELIVERY SYSTEM

The delivery section begins as the sheet leaves the final impression cylinder, delivery grippers take the printed sheet from impression cylinder grippers and transport it to the delivery pile (or) table. The grippers typically travel on gripper bars.

 

Delivery section is the section where printed sheets are jogged and stacked one on top of another. The first portion of the sheet control system that the press operator is concerned with is the feeder section.

It is usually consists of pair of endless chains which carry the transfer gripper assemblies. These grippers grip the sheet while it is passed through the impression nip. There are skeleton wheel, joggers, delivery may be of extended deep pile type or double delivery type.

 

Element for delivery system:    

1. Skelton wheel: skeleton wheel are movable wheels that are positioned in non-printing areas of the press sheet. Properly positioned skeleton wheels evenly support and help to peel the sheet from the last impression cylinder. There is a cut-out disk which are adjusted to the shaft.

 

2. Joggers: it is movable device and jog the sheet into a pile, out the neatness of the pile depends on the proper positioning of the devices. (Metal sheet guides which helps in side jogging & front jogging).

 

3. Delivery gripper bar: there are 3 grippers bar. There are metal spring loaded finger in it. They grip the sheet while it is passed through impression cylinder.

 

4. Cams

 

5. Endless chain: they causes the transfer of gripper assemblies.

 

6. Sheet deculer: often located between the last press unit and the delivery is a sheet decular, a device that is designed to take troublesome curl out of press sheet.

 

7. Suction slow down rollers: suction rollers slow down and steady the sheet as it enter the delivery. They are usually positioned just behind the rear sheet guide and beneath the chain delivery.

 

8. Front guide

 

9. Wedge: wooden or plastic wedges are used at starting to produce a neat pile. By holding up the rear edge of the sheet, wedge help to counter tail end hock edge can cause marking.

 

10. Blow-down: near the top of the delivery are the blow down, a series of air holes that assist in dropping the sheet on to the delivery table. Air is blown on the top side of the sheet, forcing it downward.

 

 

Types of normal delivery system:

1. Normal delivery system: there are 3 gripper bars in it. Three gripper bars are fixed at endless chain at equal distance.

1. Extended deep pile delivery system: endless chain length is increased i.e. the delivery path is double.

6 gripper bars are used pile height is increased. The wet ink will dry in the route. The pile height

The increase in machine speed and continuous feeding facilities. It has double advantage in that it can take a deeper pile before changing the pile stand becomes necessary, and because it is set father away from the printing unit the ink film has additional time to again on initial set.

 

2. The double delivery system: the double delivery system is a further existion of deep pile delivery, this system utilizes two delivery piles, the sheets bring delivery to alternate piles during the run, this gives the ink more time to set and enables one pile to be changed while the other is being used.

There are 2 delivery piles on it & the printed sheets are delivered to the alternate piles.

Odd no. of sheets on one pulls even no. of another pile. Feeder pile is raised with the help of pile height governor. Delivery pile is raised down.

1. Chute delivery system: it is type of delivery system fount is small machine.

Sheet is printed & comes out between two rollers it is also called synochronisation.

 

 

 

MAKE READY

Sequence of operation of pre-make ready:

1. Cutting the paper to size.
2. Clamping the plate.
3. Packing for plate & blanket.

Blanket for 1.95 mm.

Plate cylinder packing for 0.30mm.

4. Shades matching and ink mixing.
5. Proofing of the plate and necessary correction to be feed.

 

Following sequence of operation is carried out:

1. Gum the plate.
2. Removing the dampeners and cleaning them.
3. Cleaning the ink duct and inking system. (Wash up of inking system).
4. Cleaning and checking of blanket.
5. Cleaning the impression cylinder

 

Feeder:

1. Jogging and placing the sheet on sheet table.
2. Setting the feeders.
3. Setting the ram board according to side lays and front lays.
4. Setting the delivery.

 

Printing unit:

1. Feeling the ink duct with ink.
2. Setting relies keys according to requirement.
3. Charging the inking system/rollers.
4. Set the dampening rollers in position.
5. Clean the plate switch on the dampeners and charge the plate.
6. Inspect the plate and check it that engrave fully charge (inkling) now run 10 to 15 sheets and check the registration.
7. Ink every think is ok and start and run (printing).

 

Delivery:

1. Set the joggers to collect the sheets of same way.

 

Step for make ready:

1. Check paper for the job.
2. Prepare make ready book on the feeder pile.
3. Set the feeder for sheet size.
4. Inch the sheet through the press and set sheet controls.
5. Sheet controls, lays and joggers.
6. Run a few sheet through the press at speed. To check sheet path examine and prepare plate for job.
7. Fit the plate with packing.
8. Check the fountain solution and set dampener controls (how much regulate the dampening rollers).
9. Prepare the ink and set the ink duct and run up ink in the roller pyramid.
10. Wash the gum off the plate and set the dampeners and run the press.
11. Set the ink onn the plate and ink up the image.
12. Commence the printing by working through time make ready book.
13. Adjust impression pressure, position skeleton wheels.
14. Obtain ok press.
15. Recheck make ready settings and commence the run.
16. Maintain quality during printing.

 

Mae ready on multicolor presses:

1. The first printing unit has front and side lays, additional printing units obtains, register by the facilities of plate cylinder movement which can be moved laterally and circumferentially to a limited degree.
2. The lays must be set squarely, the side by must move the sheet to the center, the plate fixed squarely.
3. The circumferential movement of the first unit set at zero, if possible.
4. It is common practice to make ready on the first printing unit with all the following units disengaged or out of impression. Make ready on the following units is done progressively bringing each unit into line with the first.

 

Make ready book:

100 sheets of waste--- initial run to machine the dampening and inking system.

5 sheet of stock---- 1 copy to reading department, 1 copy to the layout and 2 copies to the finishing department.

6 sheets of waste

2sheets of stock

6 sheet of waste

2 sheets of stock

6 sheets of waste

2 sheets of stock---------- register, adjustment.

 

50 sheets of waste

2 sheets of stock

50 sheets of waste

2 sheets of stock---- adjustment of color and uniformity of ink.

 

100 sheets of waste

3 sheets of stock------- print quality assessment and pass sheet.

 

 

Color sequence and printing sequence:

The order in which color are printed in a multicolor work is department on a large number of factories.

The following factors may find applications in the use of four color process ink on while paper or board.

1. The proofs book may indicate the order in which color are to be printed.
2. Although process colors are relatively transparent, when two or more film of ink are printed on top of each other. The top most film of ink will impart its own sheen to the final color. In practice, this means that a green produced with the yellow ink printed last will have a brighter appearance than a green in which cyan ink falls last with this is mind, the job must be evaluated and color arranged to give the best result.
3. The traditional method of printing yellow first, has the draw back that evaluation of its color weight is difficult because it is a pale color and is often difficult to see on some papers, variation in the weight of ink printed during the run may only becomes apperant. When printing the subsequent colors. It is common practice to print dark or colors such a cyan first, because a variation in the printing of yellow ink is more easily seen when superimposed.

 

 

Process color guides and color matching swatch: for scanned image and art work, it is difficult to specify the exact CMYK values for each individual color. These are usually determined images are converted to the CMYK color mode. If you want to add a headline, rule, color illustration, or background color, you can specify the percentage of the CMYK inks used to create the color, most people do not know the exact percentage of CMYK that needs to be used. To remedy this problem, you can purchase a commercial process-color guide or color matching swatches from a company such a pantone, true match or focol-tone. You can at art store. These guides gives you the CMYK values used to create each color, and show you a sample of what they will look like on coated or uncoated stock. Many software programmes also have pantone or other color libraries available for you to choose from on your computer.

 

PMS is a widely accepted method for specifying and mixing colors from a numbering system listed in a swatch book using this technique, artists and customer can select any of usually divided into two sections, one showing them on uncoated stock. It is important to see both because the papers finish will have a definite effect on how the color will look when printed. If the paper is uncoated the color will appear soft or flat. Although there are other color matching system, pantone offers the designer the widest range of worldwide services.

The printers canmix be desired color by using the swatch number and referring to a formula guide. The guide gives the formula for making the color. It identifies the basic color involved and indicates how much of each to mix together. The ten basic color in PMS are rhodamine red, purple, reflex blue, yellow, warm red, process blue, green, black and transparent white. (8 base color and two black and transparent white).

All the 10 colors mixed in varying amount to produce a total of 500 different colors and all are numbered and arranged in a swatch book available at art supply stores in a designers edition as well as in a printers edition that includes ink mixing instructions. To specify a color, the designer looks through the swatch book, chooses the color he want and indicates its number on mechanical, it is also a good idea to attach a sample of the color atleast ½ inch X ½ inch to avoid any possibility of error.

 

RUNNING DEFECTS

Learning for formula: B³ C³ D⁴ F² G H L M² P² S⁹

1. Baking, blanket glazing, blanket smash.
2. Catch up, color variation, chalking and powdering.
3. Doubling, dampener marks, dot gain, dot loose.
4. Flocculation, (flugging, linting and dusting).
5. Ghosting
6. Hickies
7. Low spot
8. Molting, Mis-registration.
9. Picking and plucking, pilling.
10. Set-off, scumming, show through, strike through, sticking blocking, scuffing, streaks, slurr, static electricity.

 

Running defect explain:

1. Backing: new ink fails to replace ink removed by fountain roller, resulting in progressively lighter color.

Cause: (1) insufficient ink in fountain, ink too thixotropic. (2) Ink too short & buttery

Remedy: (1) add virgin ink to fountain; stire ink in fountain with knife to keep fluid.(2) consult ink manufacturer to reformulate ink for better flow.

 

2. Blanket glazing: a glazed blanket will lose its ability to transfer enough in to produce an acceptable ink density on the press sheet.

In this the pores of the blanket fill up with ink, ink solvent and gum and dry. Blanket become very smooth, hard glossy.

Cause: due improper cleaning at a proper time.

Remedy: (1) clean the blanket from blanket wash. (2) Use of de-glazing compound.

 

3. Blanket smash: if enough pressure is applied the smashed areas will be pushed in too far to receive the ink from the plate cylinder and unable to transfer an image to the press sheets.

Cause: (1) blanket become smashed when more material is passed between the important and blanket cylinder than the gap will permit. (2) Each time press sheets is wrinkled or folded as it travels through the printing unit, the blanket becomes smashed.

Remedy: (1) if the smash is small, a commercial blanket fix is available when this is pointed over the smash area, it cause the surface swell. (2) Use of blanket rewilver.

 

4. Catch up: plate takes ink at the N.I A of the plate. Catch is also called dry-up. Catch up is defect which is occurs when the plate has ink at the N.I.A of the plate.

Cause: due to low supply of water or dampening solution.

Remedy: (1) properly, wetting the plate. (2) Cleaning the plate.

 

5. Color variation: inconsistent color reproduction between proof and print

Cause: substrate variation.

Remedy: consult ink manufacturer to adjust hue or hold out of ink consult substrate manager to change the substrate.

Cause: special spot color do not match.

Remedy: consult your ink manufacturer.

 

6. Chalking and powdering: (1) ink pigment do not bind to substrate. (2) Defect in printing by improperly-dried ink being easily rubbed off the paper. Although ink set-off rarely occurs.

Cause: fountain solution pH too low.

Remedy: adjust fountain solution to proper PH.

Cause: ink is more acidity.

Remedy: consult your ink manufacturer.

 

 

7. Doubling: found in all multi-color machines. The first down ink image is transferred rom sheet on the non-image area of the blanket of the second unit. The second down ink image transfer to the blanket of 3^rd unit and so on. These images print back on to the following sheets. Unless this print back is in exact register with the original print, a double is produced.

Cause: sheets slipping in grippers.

Remedy: adjust impression and transfer cylinder grippers making sure that tension is sufficient and uniform.

 

Cause: if a sheet slips slightly in the grippers. The print back from the following blanket is out of register causing a double and increasing the color value. Such slippage varies from sheet to sheet.

Remedy: the pressure between blanket and impression cylinder.

Cause: causing           variation in color values.

Remedy: try reducing ink’s tackiness on the unit ‘where slippage is a occurring. This unit is likely to be the one printing of the largest solid areas.

 

8. Dampening marks: when the print on the some marks and unwanted marks are print.

Cause: dampening roller are tightly.

Remedy: adjust the dampening roller.

 

9. Dot gain: printed halftone appear muddy, show higher value than proof.

Cause: improper pressure setting between plate, blanket and roller.

Remedy: adjust to proper pressure setting.

Cause: excessive ink in the roller train.

Remedy: reduce ink reduce fountain solution.

Cause: blanket and rollers too soft.

Remedy: recondition blankets or rollers, replace it if necessary.

 

10. Dot loose: random generally minutes, spots of unprinted areas showing through a printed area. Engraving dot that have not printed to the cylinder.

Cause: rough printed surface.

Remedy: use primer coat if possible.

Cause: ink drying too fast.

Remedy: use slower solvent.

Cause: ink has high velocity.

Remedy: reduce viscosity to the required level.

 

11. Fluffing, linting and dusting: due to fluffing spoil good print production.

These are common terms which are used to denote loose fibres (lint and fluffing) and loose loadings (dusting) which are carried onto the paper surface accumulated on the press blanket and spoil good paint reproduction (blurred).

Cause: paper which are surface sized (tub sizing).

Remedy: go to long way in overcoming this problem.

 

12. Ghosting: a large solid on the back-up side of a sheet shows excessive gloss oppsite the ink on the side printed first.

Cause: (a) poor job layout.

2. Ink film too thin.
3. Ink too transparent.

Remedy: (a) improve job layout.

2. Consult ink manufacturer to weaker ink for havier film.
3. Consult ink manufacturer to reformulate ink for greater opacity.

 

13. Hickies: unprinted spot on the image area.

Cause: due to dust or paper particles that have stuck to the blanket.

Remedy: the press operator has to wash the blanket too eliminate hickies.

 

14. Molting: solid areas not of uniform density resulting in uneven appearance.

Cause:  non-uniform stock surface.

Remedy: consult stock manufacturer to change stock.

Cause: improper printing pressure.

Remedy: adjust printing pressure.

 

15. Mis-registration: the mis-alignment of succeeding plate or poor relative to those already printed. Mis-registration can be lateral and circumferential as well.

Cause: fault workman ship.

Remedy: replace with right type of skilled worker.

Cause: fault in machine (feeder\ front lay or side lay).

Remedy: check the feeder form or side lays and adjust it according to the job.

Cause: fault material standard stock (unsquared, expanded stretched (ontrached).

Remedy: consult your stock manufacturer.

 

16. Picking and linting:-picking: lifting of the coaking from the coated stock on to plates, blanket and or ink trains rollers.

Linting: lot of fibres from uncoated stockers onto plates, blankets and or ink trains roller.

Cause: To much water reaching paper.

Remedy: adjust to proper ink/water balance.

Cause: pressure too high for ink/ stock.

Remedy: adjust improper pressure.

 

17. Piling: build-up of ink on printing plate

Cause: paper problem.

Remedy: see picking.

Cause: blanket too tacky.

Remedy: consult blanket manufacturer.

 

18. Set-off/ blocking: set-off: ink transfer to the backside.

Blocking: sheet in a bundle or load stick together.

Cause: ink dries too slowly.

Remedy: see drying.

Cause: Rough handling of loads.

Remedy: do not drop or jerks load.

 

19. Scumming: Scumming is the condition in which non-image area accept ink.

Scum on the plate can also be caused to improper plate making or improper wetting of plate.

Cause: low alcohol content in dampening system.

Cause: glazed blanket, ink rollers or dampening roller.

Cause: improper PH value or dampening solution low acidic.

Remedy: set PH value.

Remedy: change roller.

Remedy: clean plate.

Remedy: properly wet the plate.

 

20. Show through: it is referred to as opacity.

The thinner the paper than, the height opacity or show through.

The thicker the paper than, the less opacity or show through.

The visibility of printing on the reverse side of a sheet of paper under normal lighting conditions.

Cause: paper is too porus.

Cause: the gap between fibres.

Remedy: adjust the gap between the fibres in paper manufacturer process.

 

21. Strike though: it show through is resulting from increased ink absorption and penetration through the paper referred to as strike through.

Cause: ink too thin.

Remedy: consult your ink manufacturer.

 

22. Sticking blocking: sheet in a bundle or load stick together.

Cause: ink dries too slowly.

Remedy: see drying.

Cause: rough handling of load.

Remedy: do not drop or jerk load.

 

23. Scuffing: printing ink appears dry but exhibits poor resistance to rubbing or scuffing when a broaded.

Cause: excessive water on press, in paper.

Remedy: reduce dampener setting, change dampener.

Cause: ink not fully dry.

Remedy: see drying.

Cause: excessive ink.

Remedy: adjust press setting to carry less ink, consult ink manufacturer.

Remedy: improper packing or planned blanket cylinder, incorrect bearer pressure, too much backlash, worn cylinder bearer.

 

24. Streaks:

 

25. Slurr: dots appear elongated or smeared occurs on a single unit.

Cause: loose, uneven and soft blanket.

Remedy: tightened blanket clamps, adjust packing and replace blanket if necessary.

Cause: excessive ink on coated stock.

Remedy: adjust press to carry less ink, adjust water accordingly.

 

26. Static electricity:

 

27. Tapping: cannot achieve good coverage.

Cause: improve register.

Remedy: see register.

Cause: poor ink transfer from blanket.

Remedy: consult blanket manufacturer and consult ink manufacturer.

 

28. Tinting: emulsified ink transfer to printed sheet as background tint.

Cause: improper ink/water balance.

Cause: pressure between the plate and blanket cylinder too high.

Remedy: adjust.

 

29. Plate wear: loss of image areas of plate.

Cause: improperly processed plates.

Remedy: check for excess diazo on plates.

Cause: running plate beyond capacities.

Remedy: change to higher quality plates for longer life.

Cause: inks too much strong.

Remedy: reduce ink strength to improve lubrication.

Cause: form rollers too hard.

Remedy: replace form rollers.

 

Picking: used on coated paper.

Fluffing: when the fibre of paper starts to remove.

 

30. Misting: this is due to drying of water on the plkate due to oxidation.

 

 

31. Mottel: it is a defect which is due to ink, fountain solution and paper.

Cause: ink not properly adjusted to the paper.

Remedy: the viscosity of ink should be less.

Cause: non-ink receptive paper.

Remedy: double print the job.

Cause: uncoated paper with uneven surface.

Remedy: seasoning and conditioning.

 

SPECIAL EFFECT

Metallic inks, fluroscent inks, embossing in offset.

Base can be used in dampening solution for fugetice or magnetic ink.

 

1. Dry offset: thermo-plate neopron plate is used. It is also known as letterset, water less offset, indirect letterpress. It user features find in two other printing processes, the raised surface plate of letterpress and the rubber blanket of offset lithography. The image of the letter press plate is transferred to the paper via an intermediate carrier- a cylinder is covered with the blanket that is by indirect letterpress printing. Typically, upto six colors are transferred consecutively for raised plate on to a common impression blanket, then printed on the container in one pass. A decorating or protective varnish may be applied by a satellite roller coating unit dependent on the type of packaging bending produced. Ink is fed to the printing plate from an ink duct down a chain of distribution rollers, the chain is short, usually of seven or eight alternating metal and rubber which produce a thin, even ink film on the plate. After subsequent transfer to the blanket and then container of 2 to 4 mum film thickness is obtains. Dry offset printing is used to decorate a diverse range of plastic containers.

 

The main advantage:

Daily products cups and lids.

Emulsion paint cans, rigid tubes.

Cosmetic and toiletry tubes.

Polylaminate, metal and plastic laminate, tubes for toothpaste.

Detergent, bleach, motor oil plastic bottles.

 

Polyethylene and polypropylene are non-polar with an insert, low energy surface, it is necessary to alter their surface chemistry and create a thin, oxidized micro roughened surface layer if ink adhesion to be obtained. This is done by either electric corona discharge or gas flame treatment. Corona is usually used on thin walled food containers. Pretreatment improves ink adhesion as it leads to increased wetting of the substrate, the generally multicolored background in bank notes is printed by dry offset.

2. Map printing: special shades are used.

Pantone is a system which has 45 million colors used in photo-shop.

When black is added, shade is made.

When white is added, tint is made.

 

Fading: yellow and magenta becomes weak.

Black and blue remains strong.

 

Mileage of ink depends upon quality of pigment & continuous quantity.

Through all reproduction processes may be used in printing maps. More are printing lithography, either by direct photo litho or transfer from copper engraved plates, the letter method is often used in the reproduction of old maps.

Lithographic reproduction are also made from originals drawn from transparent materials such as KODA trace and Astra foil. Line block too is favored for map printing. Place names may be drawn in the original from which plate is made, but more often they are type-set. Film setting is useful, here e.g. the name of river may be curved to follow the line of river.

 

Small, medium and large maps.

Single color and multicolor.

Paper must be Stron and durable.

Folding endurance must be good.

Exact color/ shades.

Exact scale (accuracy).

Offset printing process is used.

Single color maps in small books.

Alleast maps are more durable maximum (10-12 shades special) and special paper is used.

Wall map 200 GSM paper for displaying is printing is A0 large offset machine in A0 paper size exact registration something large size map making is made by positing of two A0 size paper.

 

3. Security printing: it does not refer to a separate printing technology but rather to an application or combination of conventional printing technologies such as offset, gravure and letterpress. Security printing encompasses the printing of bank notes, postage, stamps, document as stock, certificate, identify cards. A product of security printing is expected to withstand all external influences on if for a long time.

Security paper should be practically forgery-proof, this is achieved not only by the way in which the printing technologies and their combination are used.

Authorized specialist paper manufacturers deliver an exact number of sheet of paper to the bank notes print houses. It is normally rag paper with positive and negative water marks. They are produced on cylinder paper machine. Coated rag paper is often used. This is already gummed on the reverse side.

 

 

There are following three main concerns for security printing:

1. To secure the confidentiality of the document, through origination and production, from the preparation of artwork to proofing, platemaking and printing.
2. To ensure the authenticity of the document and make them readily identifiable by all concerned.
3. To make copying duplicating and forgery of the documents as difficult as possible.
4. Combination of conventional printing two or more process (letterpress + offset + gravure).

 

Identity of security:

1. Security thread (aluminum and some material mixed).
2. Water mark.
3. Special ink.
4. See through register: it is a register which can be seen by placing the printed product in front of a lamp where half portion of the register is visible on the front side and half remaining is seen from the other side.
5. Latent image.

 

 

 

4. Label printing: the labels of today are very diverse and the machine for producing them are equally varied, a label may describe the product, advertise the contents, and also carry out security function. In the simplest cases if may contain only price information or bar codes. Labels often replace printing of the packaging.

The printing of label is usually done on relatively small format flexo printing presses on web material with a working width of 180 to 560mm. the labels are often printed on “table top machine”. Where the printing and processing units are arranged on a machine table.

The printed labels are punched out in-line at another processing station. The die-cutter has to work so precisely that only the web with the gummed labels is cut through; the carrying web material must not be damage.

 

Special paper-   chromo art paper.

Printing is used for label printing in offset machine.

One side glossy.

Smooth side- printed matter.

Rough side – adhesive apply and pasting of paper.

Labels now-a-days printed on to a thin plastic and plasticize.

 

 

AUTOMATION

Hybrid machine: there are many method and practical examples demonstrating that it is not always just a single printing technology that is used for the production of a printed product, but that a combination of various printing technologies and can bring apart very interesting production options, with both a high degree of economy for the printing company and benefit to the customer, referred in.

Hybrid printing system can also be set up from a combination of various conventional system, that is technology using a master, or by combining various non-impact printing technology.

For computer ----- to ---- technology selected parts of the computer to press various of direct image and computer to press. (When machine involved two or more process in printing in single that is called hybrid machine. It is made by Heidelberg).

Speed master 74 (offset + flexo)

Combi-print geobel (offset + flexo + screen).

Speed master CD D40 102.

 

Press console: computerized point control – CIC press console and plate scanner are attach with the automatic machine plate scanner scan the quality strip and when any variation is there then it alerts the operation on set it automatically.

Plate scanner – read the density, duct roller movement and keys of ink-preset it.

 

Automation: automation using remote control and measurement & control technology in carrying out the make-ready in printing system and in monitoring the print run is of very high level. Nevertheless there is potential for further development aimed at further reducing make-ready times and wastes.

The production speeds of the multicolor presses available, which is typically approximately 1500 impression per hour for sheet fed offset and approximately 60000 impression an hour for web presses, is at a very high technology level. Increasing these time spent on preparing the press prior to printing production. In this machine shorter make-ready and reduce the waste. A typical four color job can now a day be set up in about 15 to 20 minutes as compared to a make ready time of 60 to 90 minutes.

The production process and to enable work to the performed in clean and environment friendly surrounding.

Non-stop feeder: separate attachment to racks. Rakes are fitted below the running pile then when pile is over then we remove the rake and it becomes the continuous pile. Sometime metal rakes are used then all of running pile of paper is over it.

Plate changing: removing the printing plates from the proceeding job and mounting the printing plates for the next job can take place at various stages on an automatic process. Plate removing and feeding operation any be performed successively fully automatically by means of cassette system with no operator intervention, once the change-over process has been initiated. The first design for an automatic plate changing system for sheet fed presses came from Japan in 1990. Where the printing plates for several jobs can be stored in one cassette in the correct sequence. This means that the plate for several successive job can be ejected and loaded automatically.

(Removing and mounting plate can take place at various stage by means of cassette system with no intervention of the operation) (Plate start automatically loaded simultaneously in different unit of the machine).

Automatic wash up: automatic wash up device is available for blanket wash up and impression cylinder wash-up. In some machine it is only available for blanket wash while in some machine it is available for both.

It separate unit consisting of a brush wheel and cleaning agent placed in a container tray and when we want to use it. It is placed in contact with cylinder and set on. (Two roller in it blanket wash cloth is used).

Application:

This cuts down start up waste and such automation should be in such a way that the first sheet printed is produced in a suitable quality.

Non-stop feeder.

Non-stop delivery.

 

Waste diverter: between the last printing unit and delivery image inspection units put then waste sheet divert separately from there.

Sheeter: sometimes some device or reel stand and cutting cylinder are put in feed board web unit is feed in sheet fed and then the printing done.

It is operational thing that sheeter or feeder machine we want.

Enough quality of paper can be stocked in a machine-advantage.

Numbering: imprinting many sheet-fed offset presses are equipped for the installation of special numbering boxes. The numbers are inked by a simple inking unit (letterpress process) and are then printed on the sheet at the final impression cylinder before the sheet is taken over by the chain of gripper system. The numbers are indexed with each revolution of the cylinder, mostly by mechanical means letterpress plates logos, for ex-depending on the application, a hard or soft packing (sheet metal, cork, plastic film etc.) must be mounted on the cylinder to protect the surface to the impression cylinder and to achieve the appropriate counter pressure.

 

Imprint: some small design or numbering is printed by it which can be attached in machine. If any job is printed, then if we have to add some information of our company in special, it is called imprinting, satellite units also do imprints.

Hydroxyquilonine: preservation of fountain solution.

Perforation: perforation, creasing and so forth can usually only be done in the sheet’s direction of travel and not at right angles to it. It must also be taken into account that the tools can only be fitted in the areas between grippers.

Perforated tapes are put on blanket cylinder. It is made of fibres.

Slitting, perforation: only lines and wheels are there like in challenge. It facilitates the tearing of the main stroke.

It is a finishing operation in which small, tiny holes are made in the stock/slits are cut into the stock, so that a portion of stock from the counter foil may be from easily.

Creasing: to facilitate a clear fold to the hard cover, case, etc.

Process of creasing paper grain with the help of a hardened steel strip to create a straight line for folding.

The creasing and cutting is a combining operation simultaneously done on the job. It is basically concerned with packaging industry manufacturing cartons for the packing of all kinds of products like tooth paste, medicines, electrical and electronic items.

It is done by three method- metal die, wooden black die, wooden one piece.

 

Embossing: it is a finishing operations that produces a recess image by pressing the paper/stock between special dies (female and male). It is a type of blind printing.

The method of raising the surface of a paper by pressing it between a make and a female die. The female die is generally made of smooth polished surfaces thick steel plate having an engraved mirror image of the design to be embossed on the paper. The female dies made of paper of soft board sheet. The monogram, logos, letterheads, visiting card, commercial papers.

Varnishing: to enhance the printing quality on the substrate the printing product is subjected to a solution called varnish for improving the quality of printing line gloss varnishing.

The use printing plate makes it easy to do spot varnish to highlight only the desired areas on printed sheet. The paper varnish dries by oxidation but the process of drying is very slow.

Hologram: it is a special printing technique which is mainly employed for safe grading the interest of the owner/creator for the purpose of security like bar code print or special print from itself. Like on one cane print it except owner, Like watermark, hologram, bar code, due to duplicating problem is not here hour.