Several issues that are easily overlooked in the PS printing

The purpose of printing is to reproduce high quality prints. Color registration and accuracy of printed images are important parameters for evaluating image quality. For a long time, people have paid enough attention to the quality of outlets before printing, and paid attention to the transfer of outlets during the printing process. The outlets on the film were transferred to the PS version. The emphasis is not enough, and even some very important issues are often overlooked. According to the experience of internships with students, the author has ignored many of the seemingly simple but important issues of the printing version as follows:

First, the correct operation of the graphic point transferred from the film to the PS version

Commonly used in China is a positive-type PS plate. This type of plate is prepared by coating a prepared photosensitive liquid onto a surface-treated aluminum plate, which is heated and dried to form a photosensitive layer. The pre-coated plate is used for storage and use. During the printing, the sensitized plate and the positive plate coated with a photosensitive layer are closely exposed to light, and the photosensitizer in the light part is decomposed to release nitrogen, causing cracking of the ring, rearrangement of the molecular structure, formation of an anthrone compound, and formation of tannic acid in water. The compound is subjected to a development treatment to remove the photo-decomposed photosensitive layer, and a non-photosensitive region, that is, a graphic portion of the plate, is stored to make a printing plate.

We know that the contact between the film and the photosensitive layer of the PS plate is an important factor influencing the quality of the plate. The contact state is different, and the dot change rule is also different. Good contact is a prerequisite for adjusting the controlled transfer of the dot. Operation should be strictly relative to the surface of the drug film, suction tightly, to ensure good transfer of graphic network points. However, the production of drug film surface is still the case back, due to the thickness of the film base will cause light scattering, uneven transfer of dots, the change can not be controlled, should be strictly avoided. In daily production, there are many problems in this area, as described below.

1 The platen itself has poor vacuum contact, and the glass and rubber of the platen are not even. A good blanket pad should be raised in the middle, or suction offset; if not flat, the middle pad to be a cloth, in order to pump flat service.

2 The pumping volume of the vacuum pump is too low. A good squeegee can take a piecewise evacuation, which is sufficient to ensure that it is closely packed and vacuumed for good contact.

3 Overlaid films l ~ 3 pieces of small pieces and stickers on the sides of the map, resulting in pumping is not true, the local figure edge hair. The inconsistent cutting of the negative film, the distance from the base of the film is different, resulting in different deformation of the spelling graphic.

4 There are dirt on the original film and plate, resulting in incomprehensive local pumping.

In response to these problems, the author proposes several suggestions:

1. Ensure that the printing equipment is in a good working condition to ensure that the pumping can be vacuumed and the film is in good contact.

2. Before the printing, you should check the film carefully to minimize the overlap of the imposition pictures and the excessive sticking of the tape.

3. Check the printing plate glass, PS plate and film, no dirt.

4. Add a diffuser or diffuser and use a split or double exposure to reduce film and dirt.

Second, the printing body version of the registration problem

For a set of film, we will pay attention to their registration. When the image is transferred to the printing plate, the registration is given to the next process: printing. In fact, some operations in production often result in imprints that cannot be registered:

1. Film transfer occurs during printing.

2. The temperature in the baking plate is unstable or non-uniform, resulting in different degrees of deformation of the plate.

Because the printing plate is not allowed to be dried, corrections such as pull plates are required during printing, which inevitably results in graphic distortion.