1,000 Offset Printing (357-367)

357. What is the difference between mechanical proofing and printing?
A: Mechanical proofing (round press proofer) requirements for ink performance: high viscosity, low fluidity, slow drying speed; requirements for process parameters: low pressure, thick ink layer, wet-press dry overprint, slow speed , fewer dot gains, less amount of fountain solution, low ink emulsification, and color sequence from shallow to deep.
Printing (round press circular rotary printing press) requirements for ink performance: low viscosity, high fluidity, fast drying speed; requirements on process parameters: high pressure, thin ink layer, wet wet or wet dry press, Faster, more dot gain, more fountain solution, higher ink emulsification, light-to-dark sequence (monochrome) and deep to light (four-color).

358. How to compensate or eliminate the difference between proofing and printing?
Answer: In order to compensate for or eliminate the difference between proofing and printing in order to achieve the best effect of graphic and textual copying, the following methods are often used.
(1) Shaiban compensation method: By adjusting the exposure amount of the printing plate, the dot characteristics of the proof printing plate and the printing plate are changed, so that the proofing and printing have similar or similar dot reproduction effects.
(2) Inkability compensation method: Proofing and printing use different inks with different viscosity and fluidity according to the respective work requirements, and the dot reproduction effect is consistent.
(3) Pressure compensation method: The same dot reproduction effect is achieved by using unequal pressure during proofing and printing.

359. What are the basic ways of proofing?
Answer: The proofing is divided into normal proofing (print proofing) and pre proofing (non-printing proofing). Among them, conventional proofing is divided into proofer proofing and proofing. Pre-proofing is divided into hard proofing (physical proofing) and soft proofing (screen proofing or electronic proofing). Hard proofing is divided into photochemical proofing (including toner proofing and color film proofing) and digital proofing (including inkjet proofing, electrostatic proofing, Laser proofing and heat-sensitive proofing, etc.)

360. What is mechanical proofing?
A: Mechanical proofing refers to the use of mechanical proofing machine, under the same conditions with the printing conditions, the graphic printing ink on the printing plate transferred to the substrate, the preparation of small batch proofs. This method completely simulates the printing method. It is based on the principle of pressure action to realize graphic ink transfer and can accurately reflect

Near and good quality. However, the disadvantages are complicated process, poor operating performance, and low quality stability.

361. What is photochemical proofing?
A: Photochemical proofing is a method of making sample sheets using the principle of exposure imaging through a film master before printing. This method utilizes the change of adhesiveness or solubility of certain photosensitive materials under light conditions, leaving a dot image of the color of the corresponding color separation film on the film base. Photochemical proofing has the characteristics of fast proofing, stable quality and easy operation.

362. What is electronic proofing?
A: Electronic proofing refers to a proofing method that uses photoelectric conversion and screen display of color reproduction effects. It is an instantaneous monitoring sample commonly used in digital image processing and typesetting in computer prepress processing systems, but it only sees proof images on the display screen. Because this kind of proofing method can't get proofs, it doesn't have the function of signature and guide printing, so it is also called soft proofing. In an ideal situation, it should have the "what you see is what you get" feature.

363. What is the basic principle of mechanical proofing?
A: Mechanical proofing is the process of synthesizing and reproducing images using analog printing on the basis of plate making. The basic principle is to select the ink absorption principle, ink balance principle, and the reproduction principle of dot reproduction and the principle of overprinting and coloring of printing plates for ink transfer. .

364. What are the basic types of mechanical proofer?
Answer: (1) According to the form of imprinting, it can be divided into two categories: round-press flat reciprocating proofer (abbreviated as platform-type proofer) and round-press circular rotary proofer.
(2) According to the size of the proofing format, it can be divided into three specifications: four-opening, splitting, and full-sheet proofing machine.
(3) According to the sample color number, it can be divided into monochrome, two-color and four-color proofer. Monochrome proofer is wet and dry-printing. The proofing quality is relatively stable, and the ink is full and thick. The two-color and four-color proofer is wet and wet overprinting, which can reflect the printing effect of two-color and four-color printing presses.
(4) According to the automation program, it can be divided into manual, semi-automatic and automatic proofing machines. The main difference is in the way of water delivery, ink delivery and paper feeding.

365. What is the basic structure of the mechanical proofer?
Answer: The basic composition of the mechanical proofing machine is similar to that of an offset printing press. It is mainly composed of a frame, a proofing platform, a rubber transfer drum, an inking device, a water delivery device, a refrigeration device, and a transmission operating system.
Figure 1 shows the basic structure of a monochrome proofer.
366. What is the working principle of the mechanical proofer?
A: As shown in Figure 2, the working principle of the mechanical proofing machine includes two working processes and auxiliary travel.
The auxiliary stroke refers to the right-to-left movement of the roller frame. The front roller bracket is located at the right end of the frame, and the water roller keeps enough moisture to run to the left after the ink supply roller replenish ink to the ink roller. After the platen stage, the water roller and the ink roller sequentially transfer water and ink to the printing plate on the platen, and finally reach the left end point. The water supply roller supplements the fountain roller with the fountain solution, and the blanket cylinder is always lifted during this stroke. It will only fall when it reaches the left endpoint. The working stroke refers to the movement of the roller frame from left to right. First, the ink roller conveys ink to the plate, and the rubber roller then rolls over the plate, transferring the graphic ink on the plate to the blanket; then, the water roller then prevents the plate surface from being dirty, and when the roller frame continues When the paper runs right through the paper table, the graphic ink on the blanket is transferred to the paper. A working cycle is completed when the roller carriage returns to the right end point, during which the water roller and the ink roller are always lifted when passing through the paper table.

367. What is the composition and role of the proofing platform?
A: The proofing platform is divided into a printing platform and a paper platform. The printing platform is used for installing printing plates, and the paper platform is used for placing substrates such as paper. The proofing platform is equivalent to the plate cylinder and the impression cylinder of the printing press, and it constitutes the printing transfer device of the proofer together with the rubber transfer drum.
The printing plate platform is provided with a circulating pipe of a folder mechanism and a refrigerating device. The plate clamp is used for the proofing plate on the fixed platen. The role of the cooling circulation pipe in the platen cavity is to use the cooling water circulation to cool the printing plate on the platen and the platen, to automatically condense the water in the platelet, and reduce the plate water content. The purpose of volatilization. The paper platform has grippers and positioning components (positioning gauges). The function of the positioning gauge is to control the paper during the proofing process so as to achieve the purpose of accurate overprinting. Therefore, it is also referred to as a register device, and the positioning gauge has two types, the front gauge and the side gauge.

- From "Printing Technology"