Lithography process flow

The lithography process includes: preparation before printing, mounting plates, trial printing, formal printing, post-press processing, etc., which can be represented by the following block diagrams.
(a) Preparation before printing The lithographic process is complicated and adequate preparations must be made before printing.
Before the paper is put into print, especially the paper used for the multicolor offset press needs to be humidified. The purpose is to reduce the paper's sensitivity to moisture and improve the stability of the paper size. There are generally two methods for conditioning the humidity.
One is to hung the paper in the printing shop so that the moisture content of the paper is balanced with the temperature and humidity of the printing shop.
The second is to put the paper first in a high-temperature, high-humidity environment and humidify it, and then put it into the printing workshop or printing plant where the temperature and humidity are the same so that the moisture content of the paper is even.
The ink produced by the ink factory is generally the primary color ink (Y, M, C three colors). When the printing factory is in use, it is required to determine the hue and viscosity of the ink according to the type of the printed matter, the type of the printing machine, and the color sequence of the printing. , tackiness, and dryness are adjusted.
When printing from the depository shop to the printing plate of the machine, the color of the printing plate must be rechecked so as to avoid printing failures in which the color of the printing plate does not match the hue of the printing unit ink.
The shades of the lithographic shades are represented by the percentage of dots, the percentage of dots is too large and the printing plate is dark, otherwise, the printing plate is shallow. Deep, shallow plates need to be corrected or reprinted.
In addition, check the plate's gauge, cut line, plate size, and more.
Lithography must be used for lithography. In water, chemical components such as phosphate, phosphoric acid, citric acid, ethanol, gum arabic, and surfactants are generally added to make the wettability slightly different according to the different requirements of the printing machine, printing plate, and printing materials. liquid. During printing, the wetting fluid forms a uniform water film on the blank part of the printing plate to prevent it from becoming dirty. When the hydrophilic portion of the blank portion is worn out, a new hydrophilic layer can be formed to maintain the hydrophilicity of the blank portion, at the same time, the temperature of the printing plate can be reduced, and the dot gain value can be reduced. The wetting fluid used in the PS version is weakly acidic, with a pH of about 5-6. Newspaper printing can use slightly alkaline wetting fluids due to the use of slightly acidic paper.
The surface of a blanket cylinder of a lithographic printing press is covered with a blanket consisting of a blanket and a backing material. Comparing the hardness of the bag is divided into hard, neutral, soft and other three. Hard liners are generally used for multi-color, high-speed offset presses; software liners are often used in low-precision offset presses. The performance of neutral liners is between hard and soft, and the range of applications is wider.
Printing color sequence is a very complicated issue, generally the printing of ink with poor transparency is the first printing; the color of the dots with low dot coverage is lost; the ink with low luminance is printed first; the figure with warm colors as the main character, and the magenta and yellow are printed. Landscape images, mainly in cool tones, are printed in blue and yellow; ink is used in spot inks with a large amount of ink; printed in newspapers and printed in black ink. Sheet-fed four-color printing presses mostly use black, cyan, magenta, and yellow color sequences; the color sequence of monochrome machines and two-color machines is more flexible.
(b) Mounting Plates Place the plates together with the underlay material under the plates, and install and fix them on the plate cylinders in accordance with the positioning requirements of the plates.
(C) After the trial printing plate is installed, trial printing can be carried out. The main operations are: checking the situation of the offset printing machine for feeding, transferring, and collecting paper, and make appropriate adjustments to ensure smooth paper conveyance and accurate positioning. With the standard line on the printing plate as the standard, the position of the printing plate is adjusted to meet the requirements for overprinting accuracy. Calibrate the pressure and adjust the supply of ink and dampening fluid so that the ink conforms to proofs. Printed proofs are printed, and they can be officially printed after they pass the examination.
(4) Formal printing In the printing process, the quality of printed product should be regularly checked, including: whether the overprint is accurate, whether the darkness of the ink conforms to the proofs, whether the clarity of the graphic arts can meet the requirements, whether the outlets are empty, whether the blanks are clean, etc. At the same time, it is necessary to pay attention to whether the machine is in operation and whether there is any abnormality and the fault is eliminated immediately.
(5) The main contents of the post-press processing include: the cleaning of the ink roller and the ink tank, the surface coating of the printing plate or the removal of ink on the plate surface, the finishing of the printed sheets, the maintenance of the printing machine, and the cleaning of the operating environment.