Register Systems

Register alignment and setup operations require great

care to keep assembly errors to a bare minimum. This

makes such work very time-consuming and demanding.

The time taken to achieve this or even greater accuracy

may be reduced by the use of a mechanical registration

system. This is particularly true if register systems

are used throughout the entire processes of:

• page assembly,

• sheet assembly,

• platemaking, and

• mounting the plate in the press.

The principle of registration systems lies in the production of a one-to-one positive position fixing of the information carriers when relative movement to one another is still possible, which means before securing with adhesive tape in the case of page and sheet assembly, before pneumatic pressing in the case of vacuum frames, before clamping of the printing plates in the case of mounting the plates in the press, before

beveling the plates for web-fed presses, and so on.

For example, register pins with a tight tolerance for

their external diameter are used, on which the information carriers are placed having punched holes with equally tight tolerances in defined places. The register pins are applied to a flat base rail, which is fastened with adhesive tape to the light table in the exact position. The information carrier (e.g., the assembling sheet) is precisely fixed at certain points (x- and y-direction) by means of one register pin and the related hole. The remaining degree of freedom, the possibility of rotating the assembling sheet on the supporting surface around the register pin, is clearly fixed by a second register pin on which the assembling sheet with its punched elongated hole is placed.The axis of the elongated hole must lie in the direction of the center of the round register hole. This produces a definite one-to-one positioning. This principle is used for: • positioning assembling sheets on the light table with attached millimeter grid, layout sheet, and ruler shifting device, • positioning assembling sheets one below the other in multicolor assembly,

• positioning the assembling sheet to the printing

plate in the vacuum frame before pneumatic tension,

• positioning the plate in the plate cylinder before attaching

the clamping bars,

• positioning the plate in the beveling device for web

offset machines.

Although one round and one elongated hole, each carrying a register pin, give an exact one-to-one positioning in the plane of the film/plate, for large-format work more elongated holes are punched out to ensure that position is maintained over a greater width without the edges of the elongated hole being exposed to excessive strain. Although this means that the system is overconstrained, this method of working has become accepted practice.

To mount the printing plates on the plate cylinders

they are pushed into the open clamping bars. Threading

them into punched holes would require too much effort;

the plate is therefore provided with U-shaped, punched

holes on the leading edge, that is to say half-round and

half-elongated holes.When the plate is lying evenly on

all the register pins of the clamping bar or plate cylinder,

it is in the correct position. Register scope pins allow an additional visual check of the correct position of the plate. Figure 3.1-41 shows a system for punching register holes. (Fig. 1.2-27 shows the positioning of the carrier sheet in the vacuum frame for the platemaking process.)

3.1.6 Proofs/Test Print

The result of prepress – in particular error-free typesetting and its correct location on the page, the quality of the images, the registration, the quality of color reproduction on the paper, the reproduction of details and their correct location on the sheet in all color separations/ colors in accordance with the original – should be checked for accuracy at the earliest possible stages in the process. In doing so, the necessary corrections can be recognized in good time and printing errors avoided at the outset. Section 3.2.11 describes the proofing processes in detail, in particular for the digital proof. The following proofs are typical of what is used in conventional prepress:

• galley proof,

• position proof/blueprint,

• color proof,

• press proof.

Depending on its position in the total process the function

of the proof is:

• quality control,

• quality monitoring,

• agreement document between customer and print

producer,

• reference standard for printing the job,

• documentation for the job as the basis of possible

repeat jobs.

The different proofs listed above are used in the following manner during prepress, up to the point of

printing and during the job.

Galley Proof

Galley proofs are produced for corrections to typesetting products such as continuous text, headings and titles, headers and footers for individual pages, picture captions, footnotes, indexes, and tables of contents, as well as to control the completeness and correct location of marks and control strips. They are produced as a paper printout of typesetting files, or as a paper print or blueprint of typeset columns preset in film form or film assemblies. After checking and marking necessary corrections the originals are altered and released for the next processing steps.

Position Proof/Blueprint

Position proofs are required to check the completeness

and correct location of text and image. Blueprints from

the film assemblies or full-page films fulfil this purpose

very well and are also cost-effective (see sec. 3.2.11.3,

“ Blueprint ”).

Color Proof

Color proofs are necessary for judging the quality of

multicolor products. The color proofmay be produced

for individual images, but it is preferable to produce

them for the whole page, although this is less often feasible

for the whole sheet – mainly due to reasons of format.

For the printing side the color proof may be used

to control the correct position of the individual color

separations on the page, accurately registered assembly, the approximate overall color effect of the page or the representative color reproduction of the printed product to be produced, but with certain limitations, since the proofing process and materials used are generally not the same as the technology and materials used to produce the job; color management assists in optimizing this (see sec. 3.2.10). Analog proofing, that is processes that are based on film, use colored diazo layers on thin films, which are individually exposed with the color separation halftone film of each respective component color, developed using the wet process, and transferred to a carrier material.

Examples of these are the products “Matchprint”

and “Color-Key” from Imation (formerly 3M) or “Color Art System” from Fuji. The analog proofing systems “Cromalin Tonerproof” and “Cromalin StudioSprint” (or “EuroSprint”) from DuPont use layers of colored powder toners that are applied dry or partially removed from evenly covered carrier films. The individual processes mentioned before work as follows:

The “ Matchprint ” proofing process offers a wide

variety of color sets and the possibility of simulating

various printing processes. A film is laminated onto a

dimensionally stable white carrier, the film having a

light-sensitive coating of the color to be proofed. The

color separation for the job to be proofed is placed on

this film in register and exposed in the vacuum frame.

An analog image of the color separation is produced

during the subsequent wet development process.A film

with the next color in sequence is now laminated onto

this partially present image. This film has a light-sensitive layer for the respective color. The film of the color separation is laid on and positioned in register with the first color. In order to aid positioning, the color having the greatest contrast should be used as the first color, that is, black or cyan. After registering, the film is exposed and developed. This simulates the printing of the second color. The remaining color separations are processed in a similar fashion, until the complete multicolor print has been simulated. The color films are available in process colors in accordance with the Europe scale and the American standard, as well as numerous special colors.They are available as positives or negatives to allow use for positive or negative films. In both cases the color densities and tone values are simulated according to the standard, for instance, a dot gain of 18–22% or 22–25% for a screen ruling of L = 60 cm–1. Various carrier films and gloss adjustment foils are available to aid simulation of the whiteness, color, and gloss of the intended substrate. The Color Art System (overlay type) from Fuji also uses colored transparent sheets that are produced for each separate color in an exposure, wet development, and drying process. The transparent sheets with the separated color images are transferred in the sequence black-cyan-magenta-yellow onto a receiver film in the Fuji Color-Art thermal-transfer printer/laminator. The four-color product can then be transferred onto a base paper with the thermal-transfer printer/laminator. To stabilize the transferred image a bump exposure is carried out. The product can finally be laminated with a matte film if required.

In the “Color-Key” color proofing process, films are

produced by copying and wet development in each

component color – positive films for color separations,

which are then mounted in register onto a carrier board.

This allows the final paper stock to be placed underneath so that the expected printed result can be easily judged.Color-Key films are also available in many hues. The Color-Art system (single sheet type) from Fuji uses a similar method. Figure 3.1-42 shows the superimposed films with the color separation images for black, magenta, cyan, and yellow. In the “ Cromalin Toner Proof ” a colorless transparent film with an adhesive acting layer on the surface (fig.

3.1-43) is laminated onto a white carrier and exposed in a vacuum frame with the color separation film (halftone positive) placed on top. The exposed areas of the film lose their adhesive nature due to polymerization.A finely grained powder toner (in the same shade of the color separation film used before) is then applied onto the film in the automatic proof press. The toner adheres only to the unexposed (tacky) areas. An image of the color separation is produced. A second film is then laminated, which is again exposed in the vacuum frame with the positive film of the next color separation exactly in register; this is then treated with powder in the corresponding color and so on up to the final color separa- tion. This produces a complete color proof. Dot gain in the standard range is also simulated in this process by the properties of the film and toner materials. With the Cromalin-StudioSprint (fig. 3.1-44) the coloring of the exposed Cromalin Proof sheets laminated onto the film is not performed with a dry toner, but each sheet has an even layer of color distributed over the entire sheet, which is then brought into contact with the proof.When the color sheet is removed from the proof sheet the color will only adhere to the tacky areas of the proof sheet. The image of the color separation has formed. After that the next proof sheet is laminated, exposed, and treated as described above. The work steps of laminating, exposure, color film application, and the color films in the proofing system are illustrated in figure 3.1-44.

These color proofs produce colored images similar to

prints without the need to prepare a printing plate, by

using the films used for producing the plates. In the

case of simulating offset printing, the limits of the

process are in simulating the substrate with respect to

its color, opacity, light scattering properties including

light entrapment (“light gathering”/optical dot gain)

and gloss, and also regarding the actual “mechanical”

dot gain occurring, ink acceptance, and the related effect of the color sequence in printing. These color

proofing processes are not effective for screen rulings

of greater than L= 100 cm–1.

Press Proof

This proofing process has the best achievable correlation with the subsequent printing of the job, especially if the printing press used is the same one that will be used to print the job. This requires a full set of printing plates. The printed proof is produced on the paper and with the ink used for the job. The effort for producing such a printed proof is considerable and only justified for very high quality requirements. To keep high speed production machines available during the time it takes to produce the printed proofs, special proofing machines are available. Figure 3.1-45 shows an offset proofing press in flat-bed design. This flat-bed press is equipped in succession with the printing plates of the color set. The plates are fixed on a flat table with a register system.The paper is placed and held in position on a second flat table. Dampening and inking rollers are arranged in a moveable inking system as is the blanket cylinder. After the plate has been dampened and inked, the dampening and inking rollers are moved away from the plate, and while the carriage reverses, the blanket cylinder is brought into contact with the plate and the image is transferred.Next the image is transferred from the blanket cylinder onto the substrate, which is located on the table behind the table with the plate. Each color separation is transferred in this way; in between the printing of individual color separations, the inking form rollers and the blanket must be cleaned. Figure 3.1-46 shows the diagrammatic view and a photograph of a multicolor offset proofing press in satellite configuration. These machines have not found widespread use for economic reasons.

Section 2.2.1 (fig. 2.2-9) describes proofing presses for

gravure printing.The printed results of the production

machine may be simulated in the proofing machine by

specially altering the consistency of the ink.

Section 3.2.11 explains digital proofing processes,

which are based on the use of the digital data for the print job and do not require the use of previously produced films. “Color management” plays a particularly important part in this process, to enable creation of a proof that is faithful to the job to be printed. In conventional prepress the proofing processes explained earlier for color printing and checking text, graphics, and images regarding content and position represent the basis for giving the “ok” to proceed with platemaking.

LECTURE 5

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