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

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98 FLEXOGRAPHY: PRINCIPLES & PRACTICES

As a digital printing application, xerogra-

phy works much the same way. The differ-

ence is that a laser is used to write onto the

selenium drum, instead of light reflected

through a lens. An office laser writer is an

example of digital xerography.

Numerous attempts have been made to use

xerography for color proofing. To date, suc-

cess has been limited. Xerography is avail-

able in a wide range of price and quality lev-

els. Low-cost technologies work well in black

and white and quick color applications, such

as color laser copiers, but are not suitable for

digital color proofing applications where

color judgments are made from the repro-

duction. Higher-end applications have been

demonstrated, but none have taken to market

– presumably because of the cost to bring the

technologies into final product form.

Xerography also suffers from that “it just

doesn’t look right” issue. This may be

because of the powdered toners and the fus-

ing process used to adhere the toner to the

paper. For whatever reason, many viewers

aren’t satisfied with the look of xerographic

output compared to ink on paper. Emerging

liquid toner technologies change this objec-

tion. Today, however, these technologies

have not been refined and are far too expen-

sive for digital proofing.

Wax Transfer. Wax transfer is a technology in

which colorant is transferred from precoat-

ed wax ribbons onto a substrate through the

use of heat (Figure

). The print head con-

sists of an array of tiny heat elements. The

image signal is used to instruct the print

head elements to heat. These elements melt

the wax on the ribbon, which then transfers

to the substrate. For process printing, four-

colored ribbons are used: cyan, magenta,

yellow and black (CMYK). Imaging is

processed one color at a time.

Wax transfer is fairly economical for quick

one-out color applications. Its low resolu-

tion and appearance make it unsuitable for

color proofing applications where color

judgment is required. Put simply, melted

wax on a special substrate doesn’t come

close to simulating ink on press

Dye Sublimation. Dye sublimation is similar

to wax transfer in concept (Figure

). The

difference is that the colorant is coated on

the ribbon. A more expensive compound,

which does not melt, is used. It sublimes

(evaporates) into the substrate. This can be

done at higher resolutions than wax, and

more closely simulates ink on paper.

Dye sublimation has been used increas-

ingly in graphics applications, particularly

at design stage of the process. Its main

advantage is fairly high quality at a reason-

able price. An emerging workflow beginning

to gain wide acceptance is to use dye subli-

mation up front for proofing design and

A wax transfer proofing

system uses heated ele-

ments to melt the wax

containing the colorant

onto the substrate in the

image area.

Dye sublimation works

by evaporation (subli-

mation) of the colorant

onto the substrate.

These proofs are capa-

ble of producing higher

resolutions than the

wax-transfer method.

Colorant

Signal

Substrate

Colorant

Signal

Substrate

composition-related attributes, and to use

continuous ink jet for proofing color-critical

attributes.

The resolution available with dye sublima-

tion can be increased by using a laser instead

of a mechanically heated print head. Laser

thermal dye-sublimation printers are the

high-end of this category. They use lasers to

burn dots onto a carrier sheet, which is cov-

ered by laser-sensitive color-donor material.

The donor sheets are C, M, Y and K, and are

burned individually and automatically regis-

tered. The registration of these devices is

very precise.

Many recent advances in dye sublimation

have made it a more attractive technology

than it was in the past. One manufacturer

has opened up its device to be driven by sev-

eral different RIP manufacturers. With the

systems currently on the market, it is now

possible to get the same halftone-dot shape

and screen angle that will appear on final

plate or film. This means one can see moirés,

rastering of logos, break-up or banding in

blends, etc. At this time, the machines do not

have the ability to produce custom colors,

but that capability is coming in the future.

They offer very high resolutions, up to 4,000

DPI and can produce proofs up to about 21"

x 30". The cost of the consumables for these

devices is about the same as conventional

proofing material. The cost of the devices is

in the hundreds of thousands of dollars.

Continuous Ink Jet. As with drop-on-demand

ink jet, continuous ink jet is based on the

principle of spraying ink through a nozzle

onto a substrate (Figure

). Hence, contin-

uous ink jet produces actual ink on paper. To

overcome the predictability and resolution

limitations associated with the stop-and-start

characteristic of drop-on-demand, an ink jet

sprays a continuous ink stream onto the sub-

strate. Great precision is taken in nozzle

design and pump pressure to ensure that the

finest and most uniform stream of drops are

continuously sprayed through the nozzle.

Each drop is given a charge upon exiting the

nozzle. The image signal instructs which

drops are to hit the paper by charging deflec-

tion plates through which the drops travel.

Unwanted drops are deflected to a recycling

or waste container. Continuous ink jet is the

best print-engine technology for color proof-

ing of color-critical applications. In compari-

son with drop-on-demand ink jet and other

quick-color technologies, its disadvantage is

price. However, in comparison to conven-

tional proofing technologies, it is actually

less expensive. Materials and labor costs for

a continuous ink-jet proof are significantly

less than those for a conventional proof. An

additional advantage is the faster turnaround

times associated with digital proofing.

As more and more of these devices are

used, the technology will undoubtedly

mature and become more reliable and trou-

ble-free. Another disadvantage of the tech-

nology is that the final proof does not have

the same halftone dots as an analog proof or

the printed sheet. While the color can be very

accurately matched using color management

software, many people still object to the lack

of the familiar dot structure in the proof.

PREPRESS 99

A continuous ink-jet

system utilizes a steady

stream of charged ink

drops that come in con-

tact with the substrate in

image areas. Unwanted

dots of ink are diverted

to the recycling or waste

container.

Colorant Signal

–

Substrate

100 FLEXOGRAPHY: PRINCIPLES & PRACTICES

he quality control check is tradi-

tionally where “the rubber meets

the road.” Digital technology, has

made prepress more of a science

and less of a craft. Almost every

step of the process can be mea-

sured, recorded and repeated and verifying

accuracy is as simple as utilizing a checklist

showing all of the in- or out-of-tolerance spec-

ifications. The quality-control check should

be done on all films, proofs or plates pro-

duced by the prepress facility.

Densitometers and spectrophotometers,

are used to inspect proofs and printed sheets

while a transmission densitometer is best

suited to inspect film specifications. Addi-

tional tools for inspection may also include:

• machinist’s hundred scale;

• metal t-square;

• metal triangle;

• 7-mil film-positive grid;

• 10x magnifying glass (loupe);

• transparent yellow overlay; and

• light table.

It is also essential to examine films and

proofs, using both a magnifier and the naked

eye. Color comparisons and evaluations

should be done in the proper environment. It

is highly recommended that color proofs be

examined in a viewing booth equipped with a

neutral gray surround – Munsell N8 or equiv-

alent – and a standard 5,000° K light with a

color rendering index (CRI) of 90 or higher.

CHECKING PROOFS

Once the proof is produced, the following

should be checked:

• dot gain;

• solid-ink density;

• ink hue/spectral data; and

• substrate.

Dot Gain

Proofs should be proofed to manufactur-

er’s requirements for dot gain. Most analog

proofs are set up to reproduce a 50% dot as a

72% for a 22% gain. This is only to assure con-

sistency of the proof. Matching a proof to a

press by manipulating dot gain changes the

size of the dot sent to the proofing engine.

The inherent dot gain of the proofing system

is not changed. The key to quality control is

to assure a consistent proof.

Solid-ink Density

The solid-ink density of the contract proof

should be the same as the density that will be

reproduced on press. Proofs done at densities

that are not achievable on press will result in

a poor press match. Unfortunately, the printer

is usually blamed for not matching the proof.

In reality, the proofs should be made to match

Back-End Quality Control

CMYK

■ WIDE WEB

Paper Products 1.25 1.25 1.0 1.5

Film Products 1.25 1.20 1.0 1.4

■ NARROW WEB

Paper Products 1.35 1.25 1.0 1.5

Film Products 1.25 1.20 1.0 1.4

SOLID-INK DENSITY

Table 14

the press. Table 14 lists recommended solid-

ink densities for process inks.

Ink Hue/Spectral Data

In addition to making the proof with the

proper solid-ink density, it should also be

made with colors that are as close as possi-

ble to those that are used on press. While a

perfect match is not always possible, both

separator and printer need to be aware of the

discrepancies between the two. This will aim

toward achieving a better match on press.

The colorants used by the off-press proof

and the press can be measured for compari-

son using a spectrophotometer. Combined

with color management software and other

techniques, the hue difference between the

press inks and proofing inks can be compen-

sated for in the proof. Using only densitomet-

ric or dot-gain methods to achieve the match

will have a larger affect on the hue difference.

Substrate

Proofing substrates should have the same

“cast” as the actual printing substrate, espe-

cially when using colored substrates. Color

management techniques can simulate the

substrate, while densitometric or dot-gain

methods cannot.

CHECKING FILMS

Films should be checked for the following

attributes to be accurate:

• D-min/D-max;

• dot shape and accuracy;

• screen rulings and angles;

• trap;

• distortion;

• color breaks; and

• completed job.

Table 15 summarizes what to look for in

film separations.

D-min/D-max

All plate-ready film comes with a manufac-

turer’s specification for the minimum (D-

min) and maximum density (D-max). D-min

represents the value obtained when reading

the clear area of the film with a transmission

densitometer, specified as a maximum value,

typically 0.04 density units. D-max is mea-

sured in the exposed or “black” areas of the

film, specified at a minimum value, typically

4.00 density units.

Dot Shape and Accuracy

Inspect the film’s dot shape and accuracy

to ensure it conforms to customer or printer

specifications. Dot shape can be checked

visually using a high-power magnification

device. In flexo, the usual shape is a round

dot. Dot accuracy is checked with a trans-

mission densitometer. Dot values in the file

should be checked to ensure there are no

variations in the film output. It is good prac-

PREPRESS 101

■ OVERALL QUALITY OF THE FILM SEPARA-

TIONS, look for streaking, scratches or other

damage to the film, also make sure that

areas that should be clear are not foggy.

■ MAXIMUM DENSITY, the D-max of the

black areas on the film are measured by a

densitometer.

■ DOT VALUE of the tints and halftones.

■ SCREEN ANGLE and ruling for each

separation.

■ TINTS AND HALFTONES (including scanned

images) look consistent and smooth.

■ DIMENSIONS of the layout are correct.

■ OBJECTS are printed on the correct separa-

tions.

■ FONTS are printed correctly.

■ BLEED OBJECTS extend beyond the crop

marks.

■ TRAPS are trapping

■ SEPARATIONS are printed as specified and

INSPECTION CHECKLIST FOR

FILM SEPARATIONS

Table 15

102 FLEXOGRAPHY: PRINCIPLES & PRACTICES

tice to daily output a step scale on the image-

setter and measure the values on a transmis-

sion densitometer. Figure

illustrates a

step scale for negative film; clear is 100%

dot, solid black is 0% dot. With a linear cali-

bration on the imagesetter, the values should

read the same as those in the digital file.

Typically, the steps go from 0 to 100 in incre-

ments of 10. The scale can also be used to

check the film’s D-min and D-max.

Screen Rulings and Angles

Check for line screen and screen angles to

be consistent with the printer’s specifica-

tions. A standard screen detector is a quick

and easy way to verify correct screen ruling

and angle. Screen rulings can also be direct-

ly measured with a high-power magnifier.

Trap

Check the film to make sure that all trap-

ping is done correctly and sufficiently meets

the printer’s specifications. The best way to

do this is to lay each film on top of the other

and look for the “spillover” – the area where

two colors meet. The technique is illustrated

in Figure

and

. Figure

shows an

image with and without trap. The top image

is trapped poorly, evident by the gap between

the blue apple and red background. The bot-

tom image is trapped properly. Viewing the

negatives, one by one, is a difficult way to

gauge trap. A simple, accurate method is by

placing a piece of transparent, yellow overlay

between the films (Figure

Distortion and Compensation

Check the film to verify that the proper dis-

tortions and compensations have been

applied. Distortions are checked easily with a

machinist’s hundred scale (ruler), a calculator

and the job instructions. What is not so easy

is knowing an object’s dimension prior to dis-

tortion. Some prepress shops actually place a

0.5 point rule of a specific length on the job

(outside the live area) and use that as a guide

to check distortion. For example, suppose a

13” repeat job requires a 0.97 distortion fac-

tor. A 10" long, 0.5 point rule is placed. If the

correct distortion is applied, this 10" rule

should measure 9.70" on the films. Com-

pensations are checked by measuring areas

on the platemaking film and comparing them

to precompensated film. In cases where the

prepress shop works without compensating

the film for dot gain on the back end and

instead does all of the scanning and stripping

with the compensations built in, then the film

must be checked to ensure the minimum and

maximum dot values are adhered to.

This typical step scale is

used to check film from

an imagesetter for sta-

bility; the illustration

shows negative film

output where a 0% dot

is black and a 100% dot

is clear film.

010

20 30 40 50 60 70 80 90 100

PREPRESS 103

The printed image on

top is trapped poorly,

evident by the white line

or gap between the blue

gecko and the red back-

ground.

To check the trapping

on the film negatives

used to print the image

of Figure 26, a transpar-

ent, yellow overlay is

placed between the film

to dramatically show the

trap as the white outline

around the gecko.

Blue

Negative of Blue

Red

Negative of Red

Red

View with no trap

Blue

Red

Blue

Red

View with trap

COLOR BREAKS

For analog proofs, nothing helps more

than a Dylux of the plate negative and a laser

proof of the original copy. A Dylux of each

color will allow the inspector to see a posi-

tive image of what each negative will pro-

duce. If the Dylux is laid on top of a negative

of another color, the relationship between

the two colors can be easily checked for fit

(negative-to-negative comparison is the

most accurate way of doing this), relation-

ship of register marks to each color and

color break (Figure

). This method is also

used to verify the relationship of common

negatives to each variable copy.

Table 16, on the following page, summa-

rizes what one should look for in contract

proof.

104 FLEXOGRAPHY: PRINCIPLES & PRACTICES

THE LAST LOOK

Final inspection of the job requires a

check for accuracy. This means making sure

that all elements are present prior to the

pressrun. Special care should be taken to

check for missing marks such as “®”, “TM”;

incorrect UPC code, missing copy, kinks,

scratches or other miscellaneous film

defects. Even in this day of electronic step

and repeat, it pays to check the film for

squareness with a T-square and triangle.

Table 17 is a checklist of the review process

for press proofs.

Color breaks are

checked by overlaying a

positive proof of the

blue color onto the neg-

ative film of the red

color.

Blue Blue Blue Blue Blue Blue

Red Red Red

■ CHECK COLOR TINTS to make sure they are

accurate and do not look mottled.

■ CHECK COLORS to make sure they are even

and consistent throughout the proofs.

■ CHECK CUSTOM COLORS selected from

color-matching systems against printed

swatches.

■ EXAMINE COLOR BARS to determine if

detail has been lost in the film because of

overexposure.

■ CHECK TRIM MARKS to make sure that

bleeds and crossovers extend the required

amount beyond the marks.

■ CHECK TYPE to make sure it is not too

weak or breaking up due to overexposure.

CHECKING A CONTRACT PROOF

Table 16

■ IS THE TYPE SHARP? Use a loupe to look

for broken or double lines.

■ ARE THE DENSITIES CONSISTENT? Check

for consistency from one end of the sheet to

the other.

■ IS THE COLOR CORRECT? Compare the

press sheet to the contract proof.

■ IS THE SUBSTRATE CORRECT? Bring a

sample to compare the printed substrate to

the one specified.

■ ARE THE CROSSOVERS CORRECT? Fold

the press page and chek the alignment and

color match.

■ ARE HALFTONE DOTS SHARP? Use a loupe

to make sure the details and highlights

match the contract proof.

■ ARE SPOT COLORS CORRECT?

■ ARE THERE BLEMISHES OR MOTTLING OF

COLOR? Check the entire sheet for spots

caused by problems with the press.

■ ARE ALL GRAPHIC ELEMENTS PRESENT?

Compare the press sheet to the contract

proof.

■ ARE SEPARATIONS IN REGISTER? Check to

make sure all separations align on the regis-

ter marks. Under a loupe, four-color sub-

jects using conventional screening should

show a rosette pattern, with no more than a

single line of dots of single color visible at

the edge of the image

CHECKING A PRESS PROOF

Table 17

he responsibilities of the cus-

tomer service representative

(CSR) vary from company to

company. For our purposes

here, we will discuss the abili-

ties of the customer service rep-

resentative who handles all facets of pro-

duction prior to manufacturing. Even in a

converting or in-house workflow, the same

duties will apply.

JOB ENGINEERING/PREFLIGHT

A CSR with preflighting and some job

engineering experience can be a valuable

asset to the company and the end-use cus-

tomer as well. When a CSR can detect pos-

sible print problems or out-of-specification

elements minutes or hours after receipt of

the order, it allows the customer to address

those elements early in the process and

make changes. These changes can generally

be done without the customer incurring any

additional cost.

ESTIMATING/QUOTING

The best CSR is able to estimate incoming

work and also has a process in place to sup-

ply quotes to customers within a few hours

after the job arrives at the plant in order to

begin manufacturing.

A distinction must be made between “esti-

mates” and “quotes”. Estimates denote that

the cost of the job is subject to change, even

if the customer has not authorized any actu-

al changes. Quotes, on the other hand, are

firm commitments to manufacture the job at

the stated price, regardless of any internal

changes that occur on the job.

When a customer demands changes be

made, the CSR should re-quote the job and

submit a new quote. Initial and revised

quotes should be faxed to and signed off by

the customer prior to manufacturing.

It also is helpful to the customer if the CSR

sends, as soon as possible, the final invoice

of the job, while it is still fresh in his/her

mind. An invoice received weeks after the

project is completed may seem “too high” to

the customer. Hhe/she may not remember

authorizing a certain cost for retouching. If

the signed-off quote arrives with the final

invoice, in most cases, there is no need for

the customer to review the invoice. If the

quote and the invoice match, it will facilitate

faster payment processing.

ORDER ENTRY

This involves entering job production

information. This information, when pre-

sented in a clear, concise and easy-to-under-

stand format, is a great benefit to the manu-

facturing process as a whole.

The CSR must be familiar with relevant

manufacturing terminology and be detail ori-

ented. The CSR should, whenever possible,

spell out all relevant instructions and never

assume that an operator knows what is

intended. A CSR has to prepare the instruc-

tions as though the operator has never

worked on that particular job before. The

more questions that can be answered in the

job instructions, before the operator has

them, the better.

PLATES 105

Customer Service

106 FLEXOGRAPHY: PRINCIPLES & PRACTICES

LIAISON BETWEEN

CUSTOMER AND PLANT

CSRs act as the “face” or “voice” of the

plant. While a customer knows that there are

many people actually producing the work,

the CSR is usually the recipient of the praise

as well as the blame. Customers expect the

CSR to look out for their projects and to be

in their corner. A good CSR does this and

balances it with the requirements of the

company at the same time. It is important

that a CSR’s motto be: “Never let ‘em see you

sweat.” A customer has to have confidence

in the person handling his/her project and no

matter what happens, that person will be

there for him/her.

“LAST LINE OF DEFENSE”

The CSR is usually the last person in a

shop to be able to review the materials

before they ship out of the plant. It is OK to

make a mistake, internally, but it’s not OK to

let the customer see it. The CSR must be

focused on every element of the job to make

sure that the materials going out to the cus-

tomers or printers are right and exact.

PLATES 107PREPRESS 107

Appendix A

1. LASER SUPPLIED AT CORRECT SIZE: ■■ YES ■■ NO

Comments

2. TRANSPARENCIES COLOR:

Colors Required

Colors Available

3. SOFTWARE USED (CHECK ALL THAT APPLY):

■■ ADOBE PAGEMAKER VERSION

■■ ADOBE ILLUSTRATOR VERSION

■■ ADOBE PHOTOSHOP VERSION

■■ MACROMEDIA FREEHAND VERSION

■■ QUARK XPRESS VERSION

4. INKS (COLORS REQUESTED):

5. PMS COLORS:

■■ SPOT ■■ SCREEN MIX ■■ MATCH ON 4/C PROCESS ■■ USE EXISTING SCREEN MIX

6. INK ROTATION: ■■ YES ■■ NO

7. RESIZED LOGOS: ■■ YES ■■ NO

8. TINT BUILDS: ■■ YES ■■ NO COLOR TYPE: ■■ 3/C ■■ 4/C

9. SCREENS:

ON LINE DECK ■■ YES ■■ NO LINE SCREEN FILM VALUE %

10. UPC WEB DIRECTION: ■■ YES ■■ NO LIST SIZE: ■■ BWA ■■ MAG

11. VIGNETTES: ■■ YES ■■ NO ■■ USE EXISTING ■■ RECREATE

12. TRAPPING: ■■ YES ■■ NO

FIRST SPECIFICATIONS IN PREFLIGHT