FTA (изд-во). Flexography: Principles And Practices. Vol.1-6

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86 FLEXOGRAPHY: PRINCIPLES AND PRACTICES

the film, plate- and press-mounting process.

Thick, elastomeric flexographic printing

plates do not punch easily – especially in the

uncured state; with liquid photopolymers, it

is practically impossible. As an alternative,

drilling plates has been found to be a suitable

method. In addition to drilling the plate mate-

rial, a procedure is required to use pin regis-

tration during the mounting operation with-

out extensive modification to the press cylin-

der. One solution is to mount a temporary

pin-registration bar on the printing cylinder.

System Components

A pin-registration system for sheet pho-

topolymer plates consists of two parts: a film

and plate drill, and a registration bar. The

film and plate drill (Figure

) is used to

place up to 11 registration holes in a line

across the film and plates. The drill can be

positioned to avoid drilling holes in image

areas, and individual drill bits can be

removed. The standard drill table accepts

plates up to 41" but can be modified to

accept wider plates.

The second part of the system is the regis-

tration bar. This is a portable bar that clamps

securely to the printing cylinder. Registration

pins on the bar are aligned with the holes

drilled in the plates. Plates mounted on these

pins are in precise alignment with the cylin-

der. Registration bars are available up to 112"

wide with either fixed or sliding pins.

Preparation for Pin Mounting

1. Select hole locations for drilling the

film, avoiding any image areas. A com-

posite proofing film that has been

exposed to show all printing plates on

one film helps in this step. Remove any

unwanted drill bits (Figure

2. Assemble plate-making films in position

over each other. Align plates by the reg-

istration marks made during the film

preparation step.

3. Drill pin-registration holes in the assem-

bled plate films simultaneously while

they are held in place by the reigstration

pins in the punched holes used during

the film preparation steps (Figure

During this step, a transition is made

from the punched film-register system

to the drilled plate-register system. This

is a critical step.

4. The printing plates are prepared for

drilling. Cut the individual plates to size

for each color, then back expose to pro-

duce smoother drilled holes. The imag-

ing face is not exposed.

5. Drill pin-register holes in each of the

prepared plates, one at a time.

6. Position the drilled plate and negative

together on the registration pins for

exposure.

The initial step in pin

mounting requires

determining the hole

locations and removing

the unwanted drill bits.

After the hole locations

are determined, the

plate-making films are

positioned over each

other and pin-registra-

tion holes are drilled.

7. Use the standard plate-making proce-

dures for sheet photopolymer plate-

making to process the plates.

8. Repeat steps 6 and 7 for all plates for

the job.

Procedure for Pin Mounting

Pin-registration bars can be used for

mounting to the plate cylinder either on the

mounting and proofing machine (if an inked

proof is required before going to press), or on

the cylinder rack (if no proofing is required).

The following procedure should be used:

1. Attach the registration bar to the plate

cylinder by clamping the bar end-plates

to the bearing surfaces of the plate

cylinder shaft (Figure

). This accu-

rately aligns the pins on the bar to the

plate cylinder.

2. Select the required drill-hole locations

and remove unused pins from the regis-

tration bar.

3. Apply stickyback to the plate cylinder

in the conventional way, then remove a

small portion of the backing paper.

4. Position the printing plate over the pins

on the bar.

5. The plate should then be held tightly

between the bar and the plate cylinder

while contact is made with the sticky-

back.

6. Smooth the first portion of the plate

down onto the sticky-back (Figure

Remove the plate from the pins, then

remove the pin registration bar from the

plate cylinder (Figure

7. Remove the rest of the backing sheet

from the sticky-back and smooth the

plate onto the plate cylinder.

Advantages of Pin Mounting

Pin mounting provides fast, easy, accurate

mounting. Complex, normally time-consum-

ing mounting jobs can be reduced to a few

minutes per cylinder. It is especially advan-

tageous in permitting accurate mounting of

one large plate per color carrying many

small repeats, resulting from step-and-repeat

imaging techniques. This process eliminates

MOUNTING AND PROOFING 87

Accurately aligning

the pins onto the regis-

tration bar of the plate

cylinder requires the bar

to be attached to the

plate cylinder by clamp-

ing the bar end-plates to

the bearing surface of

the plate cylinder shaft.

The next step requires

smoothing the plate

down onto the sticky-

back

In this final step, the

pin registration bar is

removed from the plate

cylinder.

88 FLEXOGRAPHY: PRINCIPLES AND PRACTICES

the time and registration difficulty of mount-

ing many small plates per cylinder.

Pin mounting minimizes differences in

labor-intensive conventional mounting meth-

ods and reduces press setup. Mounting times

are multiplied as jobs are rerun.

Even when using a pin-mounting system,

however, proofing for accuracy and mak-

eready is still recommended.

PIN-REGISTER

MOUNTING SYSTEM II

This registration system combines the

accuracy of pin registration with the versatil-

ity of computer-controlled micro-video cam-

eras for locating imaged register marks. The

system provides for the alignment of the

plate cylinder, preplate positioning, punching

or drilling of negatives or photopolymer

plates for accurate register and mounting.

The technology for negative and printing-

plate alignment is adapted from the same

registration techniques used in the electron-

ics industry for aligning multilayer printed

circuit boards. The equipment includes a

planning grid sheet, target punch, optical

plate punch, plate mounter and pin-bar

mounter. The plate mounter is adjustable for

various sized cylinders.

System Components

A planning grid sheet, which consists of a

30" x 40" polyester sheet, is laser-plotted

with 37 intersecting lines spaced in 1" incre-

ments. The intersecting grid lines are identi-

fied by numbers and letters along the side

and bottom margins. Along the top edge is a

series of five punched slots, one vertical,

flanked by two pairs of horizontal slots.

The film is then punched using a target

punch, a precision, air-actuated film punch

(target punch) that creates target slots in the

negative at any selected grid line intersect-

ing point with an accuracy within 0.001"

(Figure

). The vacuum table holds the film

flat and immobilized during punching. Ori-

ginal art and negatives for new jobs, as well

as existing negatives in inventory, are target-

slotted for pin-register platemaking.

An optical plate punch punctures a series of

registration slots in the fully processed print-

ing plate, aligning with the target slots in the

negative (Figure

). The plate punch uses a

high-resolution micro-video camera, closed-

circuit, split-monitor screen at 20x magnifica-

tion to facilitate operator location and align-

ment of register punching targets. Punching

accuracy is within 0.001" punch to target, and

0.0005" repeatability plate-to-plate.

The plate punch uses a center-zeroing ver-

tical slot and a series of horizontal slots left

and right of center along one edge. It is

thought that this slotting configuration caus-

es less buckling or stretching of the plate

than is sometimes associated with other pin

shapes.

The plate mounter is a free-standing, plate-

cylinder holding device, under which is

located a plate-mounting pin bar that pivots

up and permits the retractable plate-holding

pins to contact the stickyback-covered cylin-

der (Figure

Procedure for Punching Negatives

When punching negatives, use the follow-

ing procedure:

In this pin-register

system, the film is held

flat and immobilized on

the vacuum table, while

holes are punched with-

in an accuracy 0.001"

by a precision, air-

actuated punch.

MOUNTING AND PROOFING 89

By using a high-resolu-

tion micro-video cam-

era, a closed-circuit,

and a 20x split-monitor

screen, this plate-punch

unit offers a punch-to-

target accuracy of

0.001" and a plate-to-

plate repeatability of

0.0005".

On the plate mounter, a

plate-mounting pin bar

pivots up from the print

cylinder to allow the

retractable plate-holding

pins to contact the

stickyback-covered

cylinder.

90 FLEXOGRAPHY: PRINCIPLES AND PRACTICES

1. Place a transparent, prepunched ace-

tate “carrier sheet” over the planning

grid sheet. This allows the grid pattern

to be seen clearly.

2. Place the first negative on top of the

carrier sheet and planning grid. The first

negative can be a composite, entire

repeat-stripped working negative or a

composite entire repeat-finished nega-

tive. The planning-grid sheet represents

the plate cylinder divided into set areas.

3. Select the best position for the printing

plates on the plate cylinder by moving

the negative or job layout composite of

negatives into that position on the grid.

Tape the negative to the acetate carrier

sheet in that position.

4. Select two target-punch positions, out

of the image areas, along the grid-sheet

– line “A” or “B” – corresponding to the

inner or outer slotted holes, and record

these grid-intersecting point numbers

and letters on a job-specification sheet.

5. Establish the plate-punch positions on

the “y” line along the top of the negative

and record these positions on the job

sheet.

6. Move the acetate carrier sheet, with its

negative taped into position, to the target

punch. Position the air-activated target

punches to coincide with the target loca-

tions chosen on the grid, and punch the

two holes at the targets locations in the

negative simultaneously (Figure

Procedure for Punching

Printing Plates

The following procedure should be used

when punching printing plates:

1.Lay out the same grid reference points

on the vacuum table’s optical-plate

punch as the negative target punch. This

allows the two closed-circuit video cam-

eras and plate-punch heads to move into

those same positions. The cameras pro-

ject electronic crosshairs and the plate-

punch targets on the split-screen moni-

tor, enlarged to 20x (Figure

2.Move the two cameras and the two

plate-punch heads into the recorded

grid-reference target points, selected in

the planning stage and taken from the

job specification sheet.

3.Refine the alignment of the camera

crosshairs and the punch targets with

the micrometer adjustments provided.

4.Place the fully processed printing plate

on the vacuum table and align with the

plate-target register marks, using the

microvideo monitor. Further refine tar-

get positions by moving the adjustable

vacuum table holding the plate.

5.Move the cameras and their transverse-

holding bar to the plate-punch position-

ing line, recorded on the job sheet.

6.Move the punches into the recorded

punch positions.

7.When camera crosshairs and plate tar-

get marks are precisely aligned on the

split-screen video monitor, activate the

punching button and punch the plate.

This entire procedure takes less than one

minute and should be repeated for each

printing plate.

Electronic crossharis

and plate-punch targets,

enlarged 20x, as seen

on the split monitor of

the computerized plate

punching unit.

Procedure for Plate Mounting

For this process, use the following proce-

dure:

1. Place the first plate cylinder on the

plate mounter.

2. Position the plate cylinder journals into

a set of preloaded bearings.

3. Apply stickyback to the plate cylinder

in the conventional way. This may be

done with the cylinder off the mounting

machine.

4. Find the pivoting pin-bar mounter,

which is located below the plate cylin-

der. Locate the pins in the pin bar at the

numbered positions given on the job

sheet.

5. Load the first plate onto the retractable,

spring-loaded pins that hold the plate to

the pivoting pin bar. (Figure

6. Remove the protective cover sheet

from the stickyback.

7. Pivot the pin bar until the leading edge

of the plate and retractable pins come

into contact with the stickyback. Push

the bar until the pins retract and the

plate sticks to the cylinder across the

entire leading edge, releasing itself from

the pivoting bar.

8. Lower the pin bar (Figure

) and

rotate the plate cylinder slowly as the

remainder of the plate is smoothed

down.

Repeat these steps with all plate cylinders

for the job. The actual mounting of each

plate takes less than one minute. In most

cases, cylinder handling and mounting for a

six-color job takes less than one hour.

Advantages of the System

The pin-mounting system provides accu-

racy and speed of registration and mount-

ing. It moves the responsibility for registra-

tion to the planning stage when plates are

prepared.

The system provides the ability to accu-

rately mount multiple plates around and

across the cylinder and to nest images.

Mounting multiple plates often eliminates

the need for step-and-repeating negatives

and mounting large, unmanageable plates.

PLATE MOUNTING TO PINS

IN THE PLATE CYLINDER

This system requires the printer to have

the inventory of plate cylinders drilled with

tiny holes to accept the 0.094" diameter shaft

of the pins used for mounting. The holes in

the cylinder must be precision bored, both in

diameter and position, in order to correlate

to the holes punched into the printing plate.

The system will work with any plate cylinder

width or circumference from 6" to 80".

MOUNTING AND PROOFING 91

The plate is loaded onto

the retractable, spring-

loaded pins to hold the

plate to the pivoting pin

bar.

The pin bar is lowered

and the plate cylinder is

slowly rotated until the

remainder of the plate is

smoothed.

Exposed

Stickyback

Retractable

Pins

Back of

Plate

92 FLEXOGRAPHY: PRINCIPLES AND PRACTICES

The pin registration system is as follows:

1. Produce mechanical artwork with pin

placements indicated at the center of the

repeat and at a set distance from each

edge of the web. Make a web layout

showing pin placement and dimensions.

2. Prepare and make one-up negatives

using the pin placements as shown on the

black-and-white mechanical artwork.

3. Blind punch (before imaging) the nega-

tives with the holes for the pins and the

images are step-and-repeated in multi-

ples to form a single plate image

(Figure

)

4. Make and lay a color key on pins corre-

sponding to the artwork. This is a posi-

tive register control. If the color key is in

perfect register, the plates will reflect

this. This step ensures that negatives are

correct for color separation, register,

size and that the pinhole locations are

accurate. Although this step is not essen-

tial, it is a way to verify film accuracy.

5. Punch a sheet of photopolymer plate

with the same hole placement as the

negatives and color key. Do this after

back exposure, but before imaging the

plate material.

6. Place the pins into the punched holes of

the photopolymer plate and place the

pin bar over the pins.

7. Expose the photopolymer plate to the

negative.

8. After exposing the negative, remove the

pins. Process, dry, cure and finish the

plate. It is ready to be mounted on the

cylinder.

9. Cover the plate cylinder with sticky-

back.

10. Uncover the pinholes in the cylinder by

removing only a small piece of the

stickyback.

11. Remove the small strip of the protective

cover paper from the stickyback

between the pinholes and insert the

pins into the pinholes in the cylinder.

12. Place the plate onto the stickyback with

the punched holes fitting over the pins

(Figure

13. Remove the rest of the stickyback cover

paper and smooth the plate uniformly

around the cylinder.

14. Remove the pins from the cylinder. It is

now ready to be positioned in the press.

DIGITAL PIN REGISTRATION FOR

CORRUGATED POSTPRINT

Computerized pin registration harnesses

the digital prepress information to improve

mounting accuracy. The system significantly

reduces mounting time compared to conven-

tional corrugated plate mounting, where sev-

eral plates carrying image elements are

The negative is blind

punched with holes for

the pins and the images

stepped and repeated to

form a single plate

image.

The plate is affixed to

the stickyback with the

punched holes fitting

over the pins.

Exposed

Stickyback

Stickyback removed

from cylinder, pin

inserted in pinhole

MOUNTING AND PROOFING 93

Computer software

assigns “x” and “y”

coordinates on the plate,

which tells the computer-

controlled drill the loca-

tions for the drill holes.

Two video cameras,

positioned just above

the plate cylnder, assist

in the alignment of one

color plate to another.

Registration is achieved

through the use of two

micro dots placed on

the plates and imaged

by the video camera at

a 140x magnification.

assembled and positioned on a single carrier.

In conventional plate mounting, the individ-

ual plate elements are positioned by looking

through a semitransparent mirror using eye-

to-hand coordination. Both the viewing and

the manual placing of plates induces errors

which cannot be tolerated as increased print

quality demands tighter print registration.

To use this technology, registration marks

are added to the graphics and their positions

are recorded in the digital file during the pre-

press stage. These register marks are output

to the negatives and thus are captured on the

plates when they are made.

During the insertion of the register marks

to the graphic elements, the software

assigns “x” and “y” coordinates to these posi-

tions. The coordinates are then sent to a

computer-controlled drill (Figure

), which

drills the holes in the plate carrier sheet in

the precise positions for locating the print-

ing plates. The individual photopolymer

plates, with the register marks on them, are

drilled to accept register pins using the same

drilling machine.

Double-sided stickyback is applied to the

back of the printing plate ready for mounting

on the carrier sheet. Pins are then inserted

through the back of the carrier sheet and the

holes in the plates are aligned with the pins

to precisely position the plates in the proper

relationship. Accuracy of this technology is

quoted at 0.001" up to a 5" x 80" drilling area

for all colors. Productivity can be increased

even further by prepunching the carrier

sheets and drilling all the colors for a multi-

color job at the same time.

When this is done, a predrilled fastening

bar is used which contains holes that are

positioned exactly to the holes created when

the carrier sheet is punched. Special plastic

fastening pins are then used to attach the bar

to the carrier sheet. This assures the fasten-

ing bar is always square to the image, elimi-

nating the need to “cock”, or reposition the

lead-edge slot in the printing cylinder, thus

reducing press makeready time. Using this

technology, plates can be mounted “in the

round” or flat, depending on customer spec-

ification.

VIDEO-MOUNTING SYSTEMS

The latest approach to alignment of one

color plate to another in the mounting

process is through the use of video cameras

(Figure

). Registration is achieved

through the use of two micro dots placed on

the plate and imaged with the video camera

at a typical magnification of 140x. The micro

dots are 0.01" in diameter and are put in

exactly the same location on each color

plate. They are placed on the left and right

side of the copy and in the center of the

94 FLEXOGRAPHY: PRINCIPLES AND PRACTICES

copy’s web direction (Figure

). When the

job is in register, the dots will overprint each

other and appear to be an almost perfect dot.

Figure

shows an enlargement of four

micro dots of the process colors. Perfect

alignment would be a single black dot with

no other colors showing. Using micro dots,

plate-to-plate registration to within 0.001"

can be achieved.

The procedure for mounting using micro

dots is as follows:

1. Position the camera of the mounting

system directly above the cylinder.

2. Apply stickyback to the first print cylin-

der

3. Remove the protective cover sheet

from the stickyback.

4. Cut two strips of cover sheet and place

it back on the stickyback in such a way

as to leave a strip of exposed sticky-

back under the cameras.

5. Align the micro dot on one side of the

copy with the camera.

6. Move the camera on the other side

along the cylinder direction and move

the plate to align the micro dot.

7. Lock down the camera and “tack” the

plate to the exposed strip of stickyback.

8. Remove the rest of the cover sheet and

smooth the plate onto the rest of the

cylinder.

Once the first plate has been mounted,

leave the cameras in place and mount the

subsequent plates with their micro dots

aligned to the cameras. While video mount-

ing gives excellent alignment, it is still rec-

ommended to proof the job before going on

press. This will reveal that no other make-

ready is needed or point out areas where

makeready (including correcting high or low

spots) can help to make the job run more

smoothly on press.

SLEEVE-MOUNTING SYSTEMS

Fast… Effective… Economical – these

characteristics are causing sleeve mounting

systems to be widely embraced by the flexo-

graphic printing industry. Sleeves, (Figure

) carrying prepositioned printing plates,

can be quickly and easily mounted to, or

removed from, a press cylinder. These

devices prived considerable advantages to

the printer, all of which contribute to

reduced costs and increased efficiency. For

example:

1. With the addition of only one more plate

cylinder, a multicolored job can be pre-

mounted while another job is running.

This is especially useful when only a limit-

ed number of plate cylinders are available

for a particular print repeat size.

2.Repeat jobs can be stored on sleeves,

which saves mounting time and plate and

stickyback costs. The next time the job is

run, it is simple to remount the sleeves

and rerun the job. The plates are not dam-

aged because they are not manhandled in

any way since they were last in the press.

3.Jobs stored on sleeves can be easily

remounted and will print in register. This

can save time on difficult-to-register jobs.

4.Press downtime is reduced.

5. Continuous design printing plates may be

formed on sleeves by coating them with

either unexposed photopolymer or vulcan-

ized rubber, which can be subsequently

An enlargement of four

micro dots of the

process colors. Perfect

alignment would be a

single black dot with

no other colors show-

ing. Using micro dots,

plate-to-plate registra-

tion to within 0.001"

can be achieved.

engraved by light exposure or laser. By the

same process, covered sleeves are ideally

suited for solid flood coating and tint or

varnish applications, allowing the oppor-

tunity to use only one plate cylinder for

this purpose

6. Sleeve storage is easier and more conve-

nient than plate cylinder storage, particu-

larly on larger cylinders. Many convenient

forms of storage are available, depending

on the sleeve manufacturer. Sleeve stor-

age is simplier due to the ease of handling

a mounted sleeve which is much lighter

than a plate cylinder. Transportation costs

are also reduced dramatically and over-

night shipping becomes feasible and

affordable.

7. Flexibility is achieved by obtaining differ-

ent repeat ranges from the same diameter

plate cylinder. This is possible by mount-

ing sleeves of different thicknesses. By

careful calculations, the repeat size may

be increased by the precise amounts that

coincide with what will be needed to

match extra teeth on the gear. This is done

by using rubber-covered sleeves or thicker

composite sleeves.

8. Sleeves allow a printer with a large stock

of cylinders undercut for a certain plate

thickness and mounting tape to change to

a thinner plate. The decrease in the under-

cut for the thinner plate can be compen-

sated for by increasing the thickness of

the sleeve.

9. The majority of sleeve systems permit the

cutting and trimming of plates once they

are mounted on the sleeve. Obviously,

care has to be taken not to perforate the

sleeves.

The most important characteristic that the

sleeve must demonstrate is that it will not

slip. Unless this can be guaranteed, the

sleeve cannot be used for quality flexo print-

ing. A sleeve that slips is unacceptable due

to the serious deterioration of print quality

and the impossibility of maintaining register.

TYPES OF SLEEVES

There are basically two types of sleeve

systems: parallel (or cylindrical) and tapered

(or conical). Parallel sleeves have constant

and parallel inner and outer diameters and

are designed to be mounted on existing plate

cylinders. Tapered sleeves have a tapered

inner diameter and constant outer diameter

and are designed to mount on matched,

tapered mandrels or cylinders.

Sleeves are available in different materi-

als, depending on either the printer’s per-

sonal preference or the type of application.

The nickel sleeve is the thinnest sleeve

available and has a standard wall thickness

of 0.005". It permits the printer to become a

sleeve user with minimum modification to

existing equipment. The only modifications

required are:

• Appropriate air holes need to be drilled in

the plate cylinder.

• Thinner stickyback must be used for

mounting the plate on the sleeve to com-

pensate for the extra 0.005" thickness. The

same thickness plate can be used.

Nickel sleeves are produced by plating

nickel electrolytically onto a very precise

MOUNTING AND PROOFING 95

Plates are monted on

a sleeve, which is then

slid over the print

cylinder with the aid

of air pressure. After

the run, the sleeve is

slid off the cylilnder,

plates intact, and stored

for future pressruns,

which will be marked

by a drastic reducion in

setup time. Pictured is a

Strachen Henshaw

sleeve.