The lithographic printing outlets are missing

First, the original factor

In the lithographic printing, the original is a copying object, and the quality of the original will directly affect the quality of the printing plate. The following factors of the original plate will cause the dots on the plate to be lost and become imaginary.

1, the original mistaken for Zhengyang film

In lithography, since lithographic printing is indirect printing and one of the characteristics of lithographic printing is reverse image, it is determined that reverse printing is required when lithographic printing is used. However, there are quite a number of small output agencies. The level of business is not high, and the printing process is not well understood. The original used for lithography is often output as forward film. It is difficult to avoid the loss of dots and small dots when using this original printing. Therefore, improving the level of output personnel and strengthening their understanding of the printing process is something that output agencies should do.

2, the original density is low

In the process of film output, due to underexposure or overdevelopment of the film, the original density value will be lower than the density required by the printing version (general requirement of the original density value is about 3.0). If the original density value is slightly lower than the required value, the dot loss can be reduced by appropriately lowering the exposure time when printing, but if the original density value is too low, only the original plate is replaced.

3, film outlets in the middle of virtual

In one printing, the author found that the printing plate was not inked, and it was useless in many ways. Later, the original plate was observed with a high magnification magnifying glass and sent to the middle of the dot on the original plate. As a result, when the printing plate was printed, the printing plate became empty. Ink. This may be caused by the improperly focused recording head of the imagesetter during film output.

2. Loss of network points caused by overexposure in the printing process

The printing exposure time relates to the depth of the printing plate. The printing time of the positive printing version of the PS plate is short, the printing plate is dark, and the layout is easy to get dirty. On the contrary, the exposure time is long, because the printing plate outlet is lost, and the printing plate is missing because the printing plate is shallow. It is not easy to get inked when printing. Therefore, the proper exposure time for printing is extremely important.

If you change the lampshade and adjust the lamp distance, use different brands of photographic plates or photographic plates of the same brand but with different batches. Before the official printing, apply continuous adjustment ruler, dot ladder or other test strips. Want to use the PS version of the trial printing, find the right exposure time, to ensure the correct transfer of dots in the printing process.

In the actual printing, a considerable number of operators choose the exposure time based on experience, and in the printing process often uses a longer exposure time to avoid dirt on the layout, remove small spots on the layout, this method of text The influence of the edition is not obvious, but for the dot edition, it will cause the loss of outlets and the emergence of virtual phenomenon.

Third, there is a gap between the original and photosensitive version

1, lack of vacuum

Before the exposure, it is necessary to vacuum the printing machine's drying chamber so that the original plate and the photosensitive plate are closely attached together. If the vacuum is improperly set or if the vacuum pump malfunctions, the suction tube ages and breaks, and the weatherstrip sealant strip ages and cracks, vacuum insufficiency will occur. The original and sensitized plates will not cling together and cause dots to be lost and become imaginary.

2, there is dirt between the original and photosensitive version

Before the printing, the film should be cleaned. If the cleaning is not thorough, there will be small sand and other dirt on the film. After the printing plate is developed, dirt will appear, and the surrounding network of the dirty spots will also be lost. .

3, fight the original group

In many print editions for books and magazines, printers often output small format films for cost considerations, and then use hand-crafted imposition to make up large prints. When assembling large plates, the edges of small films may show “wavy edges” or “glitches” when they are cut. These phenomena will cause gaps between the original plate and the photosensitive plate to be used during the printing process. Loss of outlets and occurrence of virtual phenomenon.

In addition, due to the use of adhesive tape to fix the small film on the film base, if the tape is too close to the text or image area, it will also cause the loss of the network points, hair vomiting, or lack of writing.

4, even when the cover of the sun too close to the original

When printing, sometimes encounter the situation that requires the use of a four-open film or even an eight-open film to dry off the half-printing plate. In most small-scale printing factories, this kind of situation is often encountered by hand. The way to solve. In the case of using a four-shot film for printing, a two-part exposure is required. During each exposure, half of the sensitized plate needs to be covered. If the cover is too far from the original position, waste of paper will be caused during printing; however, if the cover is too close, it will cause the original plate to cling to the photosensitive plate in the process of pumping, so that the dots on the plate will appear. Lost and made false. Therefore, during the continuous drying, the size of the middle seam should be selected according to the size of the paper used for printing.

Fourth, other factors

1, the photosensitive or original crease

In the case of printing, both the original or the photographic plate do not cling closely to each other in a creased position. This can result in the loss of the dots and the appearance of ghosts during the printing process. Therefore, it is very important to carefully check the original and photographic plate before printing.

2, double exposure

The double exposure is a book edition, especially a method used to eliminate dirt from the layout, which is often used in the original printing of the group. This method of removing dirt is to use a scattering film to refract light so as to remove the dirty lines and dirt generated on the edges of the film. However, this method also causes the loss of small dots. Therefore, it is not appropriate to use the image printing plate for secondary printing. exposure.

3, over development

Excessive development will not only cause the loss of small outlets, but also reduce the printing rate of printing plates.

4, repair accidentally

At the time of revision, if the revision paste or the correction fluid were eroded to the graphic part, the loss of dots and hairlines would be inevitable. When revising, repair the paste or repair liquid medicine in time to avoid damage to the layout.

Source: Shandong Provincial Publishing Technology School