About Offset Printing (Part 2)

Third, the official printing

The printing plate is installed on the plate cylinder of the offset printing machine. At the beginning of printing, the printing plate should be carefully inspected and calibrated to check the situation of the paper feeding, transfer and collection of the offset printing machine; correcting the pressure, adjusting the printing plate cylinder and the blanket cylinder , Print the relationship between the rollers, so that the pressure is even, and then check the machine for ink, water supply.

When printing, first wipe the film of the printing plate clean, then remove the solid ink with gasoline, start the printing press to test, check the rules, to ensure that the overlay is accurate. Printed samples can be printed in large quantities after passing the approval.

Always check the quality of the product during the printing process, including: the depth of the ink. Accuracy of overlay, clarity of images and texts, actuality of dots, and whether or not there are oil stains in blanks.

The key to ensuring the printing quality in the printing process is the water supply device to provide stable moisture with a minimum amount of dampening solution and control the ink supply of the ink fountain. Foreign use of electronic technology, data processing and computer technology and other advanced technology, manufacturing a variety of printing presses automatic control system. For example, the Heidelberg press in Germany adopts the CPC automatic control system, the CCI system of Roland printing presses, and the PQC system of Komori printing presses in Japan can control the ink transfer amount of ink fountains according to the density of printing plates on the graphic texts. And on the control panel through the button remote control graphic registration and infusion, so that workers get rid of conventional methods of operation, focus on the main tasks, in a more economical way to improve the quality of printing.

Fourth, common faults in lithography

In lithographic printing, various factors are improperly matched, causing problems and affecting the quality of printing. In the preparation of printing, problems caused by improper handling of paper, ink, dampening syrup, etc. have been described. Now only the failures caused by other factors are described.

1. Printing caused failure

The thickness of the platen is not suitable. Improper plate making operation will cause the printing part to become imaginary. If the plateau is too fine, the blank part will be easy to get dirty. The plate surface will be oxidized or attached with fatty substances, and the blank part will be dirty. Pumice sticks can be used to gently rub on the plate surface to remove dirt, and then gum arabic can be used to prevent dirt after drying.

2. Blanket-induced failure

The blanket is sticky because of the effects of gasoline and heat. Therefore, the rubber market must prevent oil immersion and high temperatures, and often rub some talcum powder.

The blanket was not stretched on the blanket cylinder. When printing, it produced ghost images and tightened the blanket to eliminate ghosting.

If there is a depression in the surface of the blanket, there will be missing marks on the printed matter on the printed matter. The underside of the repaired fabric can be repaired with a lining. A small part of the depression can be coated with turpentine oil or kerosene to make it swell and eliminate malfunctions.

3. Ink roller failure

Ink roller diameter is different, so that the layout of ink uneven, if there is a small part of the diameter is different, can be sandpaper, pumice stone friction.

Ink roller pressure is too high, easy to hurt the printing part of the layout, should reduce the ink roller pressure.

Dust or ink hardened on the roller, causing the roller to slide on the plate, causing the tone on the printed material to lose luster and eliminating the malfunction with the cleaning roller.

4. Water roller failure

Poor contact of water roller and water transfer roller will cause uneven water supply and change of ink color. The water roll velvet will become hard and the pressure of the water roller on the plate surface will be too great to damage the printing plate. It is necessary to find out the reason to eliminate it.

5. Malfunction caused by each cylinder

Excessive pressure on the blanket cylinder will cause wear on the surface of the plate. The graphics and text will be damaged and the pressure should be appropriate. The pressure can be adjusted according to the graphic text.

Excessive pressure on the impression cylinder will cause the paper to stretch, misprint, and wrinkle and fail to print.

The local abrasion of the paper teeth on the impression cylinder makes the biting paper teeth not hold the paper or bite little, and the book paper is more difficult to bite and should be replaced in time.

Source: PACK.CN