Color reproduction is the process of color decomposition, and color printing is a combination of color, the color combination of the process called overlay. A color printing quality requirements at least, is the overlay accuracy, namely each monochrome graphics are in the same position corresponding to the sequentially laminated, the printed volume become copy faithful to the original. But in the production process, due to various reasons, it is easy to cause the products exceed the standard overprint error, so that a large number of products and therefore become inferior or waste, so that enterprises suffer great losses. Therefore, the majority of printing workers to make unremitting efforts, summed up some valuable experience. In order to better exchange of learning, then make a discussion to the problem of printing precision.

First, factors affecting the overprint precision

Many factors affect the overprinter precision, the error caused by the factors except film plate, aiming at several main aspects in printing are as follows:

1, the printing plate to overprint precision

Lithographic printing plate, are mostly thin and light aluminum. In the printing process, because of its shape or volume change will affect the overprinter precision.

Plate deformation caused by two aspects, the first is stretching deformation, the second is baking deformation. The stretch distortion refers to the school edition in the process, due to the operator in the plate and pull version of improper force, causing the metal plate in the drum circumferential extension (elongated) and layout changes caused by misregister. Bake deformation, refers to in order to improve the drying of the PS version of the printing resistance and baking, due to improper baking caused by the printing plate linear size changes. As we all know, most of the metal has the characteristics of thermal expansion, plate heating in the oven to reach 250 degrees Celsius, the base will be baked soft, affecting the stability of the size of the layout. The oven temperature is not uniform or Overbaking especially, can cause serious waste.

2, the cylinder lining impact on overprinter precision can ensure the plate, rubber roller, embossing 3 line speed, the transfer can be effectively carried out under pressure. If the plate cylinder liners are too thick, the drum radius increases accordingly. In the same angular velocity, the radius of the drum surface line speed will accelerate. The resulting speed difference will not only cause the plate image of the wear and tear, but also caused layout size in front and rear compression". The cylinder lining is too thin, the radius is reduced accordingly, roller surface line speed is slow, the network will be stretched in the transfer process, which will cause the image area "amplification", caused by misregister. In two-color machine, this phenomenon is particularly apparent surface.

3, the paper overprint precision

In lithography, the larger is the paper of printing, especially offset paper. The result of the paper caused by misregister is difficult to control.

Paper constitutes mainly fiber. Fiber is characterized by water swelling, dehydration contraction. In the offset printing process, first printed on the end of the second set of color paper, due to the expansion of misregister is very obvious. Paper structural strength, smoothness, coating thickness, water absorption of little better, for some loose structure, sizing light, absorbent paper is particularly serious.

The deformation of the paper due to the paper itself by the surrounding environment temperature and humidity changes, in the printing process, also by the drum extrusion. Extrusion paper from its mouth parts was a more outward extension, on both sides of the drag and shoot, the greater the overprint error. This phenomenon is often called "throw angle".

4, mechanical aspects of printing

Printing paper must be controlled effectively throughout the machine, and the relative position must be stable during transmission and handover. The only way to meet the requirements of accuracy, or accuracy will be greatly affected. The biggest impact mainly in the following situations: one is the orientation of the paper, the problem of mechanical components caused by misregister rules; two is the paper in the transfer and transfer process, due to transfer of instability, caused by the relative position of the paper changes caused by misregister.

In addition, when the paper is stripped from the drum, the adhesive force and the stripping tension, if the gripper force can not overcome the peeling force, that will occur paper twitch, a small displacement. This is like in the single performance for the misregister, in multi-color machine performance for the ghost (ghost).

Two, the printing precision control method

According to the factors affecting overprinter precision, adopt corresponding control methods, to achieve the purpose of accurate registration.

1, the printing plate baking treatment, must do oven temperature......

School edition must be standardized operation, the clip clip center, the plate is positive, clamping screws fastening. Pull the plate, the top screws to loosen. As long as the force moderate, generally avoid plate version deformation.

2, roller center distance strictly according to the standard measurement, must do drum axis line mutual level, bag lining calculation precision. After good package lining, do stress test. Generally use the "screen", "map", "bar" and other measures to ensure that the "pressure level", in order to meet the requirements of printing precision.

3, to solve the influence of paper overprint precision is difficult, there are many related factors. In order to improve the printability of the paper and enhance its stability, the temperature and humidity of the printing environment should be kept relatively constant. At the same time, according to the "lag effect" of the paper, do prepress processing paper. The usual way is to hang dry, paper by hanging