Several easily overlooked problems in the PS version of the sun
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The purpose of printing is to replicate high-quality prints. The color registration and accuracy of printed images are important indicators for evaluating image quality. All along, people pay enough attention to the quality of the pre-press outlets, pay attention to the transfer of the dots in the printing process, and the dots on the film are transferred to the PS version. It is not enough attention, and often ignores some very important issues. According to the experience of taking students to work in the factory, the author has neglected some seemingly simple but important print problems in many factories as follows:
First, the correct operation of the graphic network point transferred from the film to the PS version
The positive-working PS plate is commonly used in China. The printing plate is applied to a surface-treated aluminum plate by a prepared photosensitive liquid, and is dried by heating to form a photosensitive layer, which is prepared for use in a pre-coated plate. When the plate is printed, the photosensitive plate coated with the photosensitive layer is closely exposed to the positive film, and the sensitizer in the light portion is decomposed to release nitrogen gas, causing cracking of the ring, rearrangement of the molecular structure, formation of an anthrone compound, and formation of tannic acid upon contact with water. The compound is subjected to development treatment to remove the photosensitive layer which has been photodecomposed, and the non-photosensitive region, that is, the image portion of the layout, is preserved to form a printing plate.
We know that the contact between the film and the PS plate is an important factor affecting the quality of the printing plate. The contact state is different, and the change rules of the dot are also different. The good contact is a prerequisite for the controlled transfer of the dot adjustment. When operating, the film surface should be strictly opposite, and the air suction should be tight to ensure the good transfer of the graphic and text points. However, in the production process, the film surface is reversed. Because the thickness of the substrate causes scattering of light, the transfer of the dots is uneven, and the change is uncontrollable and should be strictly avoided. In daily production, there are many problems in this area, as described below.
1 The printing machine itself has poor vacuum contact, and the glass and rubber of the printing frame are not flat. A good printing machine rubber pad should be raised in the middle, otherwise the suction is offset; if it is not flat, a piece of cloth must be padded in the middle to pump the air.
2 The pumping capacity of the vacuum pump is too low. A good printing machine can take a segmental pumping, enough to ensure that it is tightly combined with a vacuum to make good contact.
3 splicing films overlap 1 to 3 small pieces and tape on the side of the picture, causing unsatisfactory pumping and partial imaginary edges. The cuts of the negatives are inconsistent, and the distance between the bases of the bases is different, resulting in different deformations of the spelled graphics.
4 Some of the original film and the plate have dirt, causing local exhaustion is not tight, and the outlet is faint.
In response to these questions, the author makes several suggestions:
1. Ensure the good working condition of the printing equipment to ensure that the pumping can be vacuumed and the film contact is good.
2. Before printing, you should carefully check the film to minimize the overlap of the imposition pictures and the excessive adhesion of the tape.
3. Check the plate glass, PS plate and film, and do not have dirt.
4. Add a diffusing film or diffuser, using a segmentation exposure or double exposure to reduce the film marks and dirty spots.
Second, the registration version of the registration problem
For a set of film, we will pay attention to their registration. When the graphic is transferred to the printing plate, the registration is handed over to the next process: printing. In fact, some operations in production often cause the printed version to fail to register:
1. Film transfer occurs when printing.
2. The temperature in the baking plate is unstable or uneven, causing the plate to be deformed to varying degrees.
Due to the inaccurate printing of the printing plate, the correction operation such as drawing is required in the printing, which inevitably causes deformation of the graphic. In this regard, the author believes that: in the imposition or film, even if you pay attention to the registration of the picture, you can not take it lightly when printing the printing plate, thinking that the printing plate must be accurate, only strict technical specifications can be dried. High quality qualified plates. A good printing opportunity has a plate punching and positioning device, which cooperates with the plate loading device of the printing machine to ensure the registration accuracy of the printing plate. For example, in Heidelberg, there is a professional plate positioning device, which cooperates with the automatic plate loading device of the printing machine to minimize the operation of the printing plate in printing, and it is almost unnecessary. When the long version must be baked, it is necessary to make the baking machine work under stable working conditions to ensure the uniform deformation of the PS plate.
As the intermediate of the transfer of graphic information, the quality of the printing plate directly determines the quality of the printed graphic, so it must be given full attention. It cannot be taken for granted, and the printing operation will be troublesome, and the graphic will not be well reproduced.