Accurately Control Ink Quality in Letterpress Printing

In the letterpress printing process, the following factors are closely related to the quality of the printed ink. Correctly understanding and understanding the relationship between these factors and ink color is of great significance for accurately controlling the quality of printed ink.

Correctly adjust printing pressure
1. The technology of printing plate bottom pad: the bottom of wooden structure is the traditional bottom pad material of the embossing process, but its stability is poor, and the ink color variation during the printing process is large. If it is used to print large-size plate products, Easy to appear black ink, lightening phenomenon, it is only suitable for printing small format products. When printing a large-size map version including a field version, it is preferable to use a magnetic version of a cast iron plate (base pad) or other metal structure plate holder.

2. The technology of the good printing plate lining process: The packing material should be made of a material with low compression coefficient and good elasticity, so as to prevent the ink from being evenly and fully affected by the sagging after the embossing of the lining. Transfer. In general, when the surface of the substrate is relatively smooth, the printed text version and cable screen version should use a neutral and hard lining, and when the printing surface is rough, suitable soft and flexible lining should be adopted. In order to prevent poor contact between the rough paper surface and the layout, resulting in ink color, lightening, lightening and other ills. In addition, during the printing process, it should be noted whether the lining is overprinted due to too many stampings and there are depressions that affect the stability of the pressure. At this time, measures should be taken to supplement or replace the lining in order to ensure uniform ink color. However, for high-precision overprint products, the lining must not be changed during the printing process, and the blind lining thickness must not be blindly increased to eliminate the phenomenon of imprinting.

Correctly adjust the ink roller device
1. Reasonable selection of ink roller: The rubber ink roller has hard texture and strong toughness, so it is not easy to be plastically deformed. It is more suitable for acting as an ink transfer roller and an even ink roller for printing lines and text versions. If it is used for printing real maps, It is prone to print marks and ink unevenness. The plastic ink roller has the advantages of soft texture, good elasticity, etc. It can be used not only as an ink roller printing plate product, but also as a line or text version of a printed type printing plate.

2. Adjust the position of the contact between the rubber roller and the chain iron roller: The rotary plate printing machine with a round flattening structure generally has several sets of ink mixing devices. If the contact between the rubber roller and the iron chain roller is poor, it will inevitably cause the ink to be transferred insufficiently and unevenly so that the horizontal layout of the printed material will be uneven. In this regard, the bearings at both ends of the rubber roller should be adjusted so that the rubber roller and the iron roller are in uniform contact. After adjustment, a 0.05mm steel sheet can be inserted into the space between the rubber roller and the iron roller for inspection, and it is preferable to have obvious resistance when pulling the steel sheet.

3. Adjust the position of the contact between the ink roller and the plate: If the ink roller is adjusted too high, the platen will not be even and sufficient ink coating amount, it is easy to produce print marks due to the ink roller in the plate slipping. If the ink roller is adjusted too low, the ink on the plate will be scraped to the tip of the plate, causing the printed ink to fade in and out. The ink roller and the layout should be adjusted to be parallel and evenly in contact with each other. A 0.05mm steel plate can be used to insert the ink roller between the plate and the plate, so that there is a clear sense of resistance when drawing. If the machine is equipped with a height gauge attachment, it can be pulled into the platen to draw, so that the ink roller touches the plate with a sense of resistance.

Reasonable selection of media
Zinc plate should not be used to print large format plate products. The resin plate is an ideal plate for printing plate products, especially printed large format products. The use of offset printing paper products for offset printing, the use of resin plates for plate printing, can better prevent the ink color, lightening and other ills.

Correctly adjust the inking device
1. Intensively agitate the ink in the ink fountain, and pay attention to adding ink regularly: In the printing process, the ink in the ink fountain should be frequently used to prevent precipitation and suspension. In addition, due to the reduction of the amount of ink in the ink fountain, the gap between the ink fountain steel sheet and the transfer iron roller is easily reduced, resulting in a reduction in the amount of ink output and lightening of the printed ink. In order to avoid this situation, we must also pay attention to adding ink.

2. Scientifically and reasonably adjust the inking device
(1) The adjustment of the local ink color in the horizontal position of the printed material: If the position of the horizontal layout is mainly text, texture, and lines, the amount of ink suction is relatively small, and the corresponding ink adjustment screw of the ink fountain can be screwed inwards. , to appropriately reduce the amount of ink in this area. If the position of a certain section of the horizontal layout is mainly on the ground or on the plate, the amount of ink should be increased accordingly, so that the full-page ink color remains uniform.

(2) Adjustment of the full-page ink color: Different inks in the ink fountain are to increase or decrease the amount of transport in an all-round way. There are two adjustment methods: Firstly, the gap between the ink-carrying steel sheet and the ink-carrying (to-ink) iron roller is adjusted to realize the difference. The second is through adjusting the size of the rotating arc of the transfer roller. In the case of a thin ink, it is not appropriate to adjust the gap between the steel sheet and the iron roll so as to prevent ink leakage due to ink leakage. When adjusting the amount of ink, the rotational arc of the transfer roller should be controlled within 1/2 of its adjustment range, so that the amount of ink can be flexibly adjusted when the ink density changes during the printing process.

Correctly adjust and use ink
In general, when the temperature is lower, the ink is thicker and its fluidity is poor, which may cause poor transfer and unevenness. This should be based on the characteristics of the printed matter, and the auxiliary agent should be used to properly dilute the ink so as to maintain good Liquidity and transfer effect to keep the ink uniform. If the ink is adjusted too thin, the ink of the print will appear light. The adjustment of the ink flowability should fully consider the characteristics of the printing press speed and the structure of the ink feed. If the speed is fast, the length of the ink path, and the number of ink rollers are large, then due to the large coefficient of friction, the ink tends to become thin and light. Therefore, the above situation should be fully taken into account when adjusting the ink, and the printability of the ink can be reasonably adjusted. In addition, the deployment of color and complex color ink, it should try to avoid mixing with the proportion of ink, so as not to print due to the difference in the proportion of the ink on the ink fountain, resulting in "layered" (precipitation and suspension) phenomenon, resulting in color printing .

Turn off the good operation technology
First, it is necessary to pay attention to the reasonable maintenance of the machine, and usually to maintain the feeder and air pump to maintain, so that the mechanical parts to maintain a good use of the state, so that the air path unimpeded, the printing sheet to send smooth; second, according to the thickness of the sheet and Size, adjust feeders, air pumps, and parts related to paper feeding to ensure the normal transport of printed sheets; Thirdly, make necessary adjustments to the printability of paper, such as by processing the paper with shaking and knocking, The paper transport eliminates adsorption and adhesion, and maintains a certain degree of stiffness, so as to facilitate smooth paper feeding, and at the same time better avoid the occurrence of empty sheets, multiple sheets, and paper feed skew; Fourth, it is necessary to make a good pile of paper handling technology Off, if the pile of paper is not smooth, measures should be taken in time for flattening so that there is no significant difference in height. Through these measures, the control is checked to maintain the continuity of the paper feeding, so as to prevent printing color difference caused by parking.


Reprinted from: Yantai Printing Network