Paper printing prepress process

First, the main performance indicators of paper and newspaper printing features

Paper is the carrier of newspapers. The paper used in newspapers is mainly newsprint, which is the main subject of discussion in this article. We have always treated newsprint as medium and low-grade printing paper. However, with the development of newspaper printing in recent years, we have also put forward higher requirements for the quality of newsprint. Newspapers produced with high-quality paper are well-grounded, well-knit, plain, and accurate in color reproduction; while papers with poor quality have low density of ink layers, severe damage to outlets and high dot gain rates, resulting in reproduction of color gradations. difference. The difference in the quality of printed products produced by the quality of paper is quite obvious. The large volume of imported newsprint with good quality sent to the newspaper market, and the huge amount of it, is enough to show that the newspaper publishing industry has continuously improved the quality of paper. In particular, for the production of color newspapers, the number of overprints, the richness of levels, and the quality of reproduction of outlets are high. With poor newsprint, it is difficult to produce high quality newspapers.

The main performance indicators of newsprint are print smoothness, whiteness, dimensional stability, ink absorption, surface strength, breakage length, etc. This article only discusses printing-related paper-making index, which directly affects the quality of printed products. We often say in the production which kind of paper is easy to use, and it is actually an overall evaluation of the printability of the paper. The various paper properties affect the print quality in production. They also have a lot to do with the production environment of each factory. The equipment, process, and product variety are different, and the paper's performance requirements are also certain. The difference, such as the performance requirements for printing double-sided film on paper, will be very different from that for printing single-sided color printing; printing and black-and-white printing, with increasing machines and non-tower batches in terms of dimensional stability There will also be some differences in requirements.

The characteristics of newsprint and newspaper printing production mainly include the following aspects:

1, using high-speed newspaper press production, machine speed, printing paper belt running speed up to 9-13m / s.
2. The ink path design of the rotary press adopts a short ink path, and the ink roller is generally about 7-11. 3, generally use BB type imprinting method to complete two-sided printing.
4, newspaper printing is a continuous printing of paper tape, using high-speed automatic paper.
5, printing analysis page once completed, up to 10 times open page 80 pairs of open pages.
6. The four-color imprint in color newspaper printing is continuous wet-wet printing.
7. Newsprint should have good breaking strength to ensure printing tension.
8. The composition of newsprint is mainly filament fabrics with poor surface smoothness.
9, newsprint surface without coating, strong ink-absorbing ability, high dot gain value, strong water absorption.
10. The whiteness of newsprint is low, and the color difference between batches of different brands is larger.
11. The surface strength of newsprint is low, and there is a certain degree of hair loss in printing.

Second, the impact of paper smoothness on print quality

The so-called paper smoothness refers to the surface roughness of the paper. Paper flatness is a very important paper performance index. There is a certain degree of difference between the smoothness of the paper and the print smoothness. As the effect on the print quality is discussed, the paper only refers to the print smoothness of the paper. The smoothness of newsprint is low in all types of printed paper. Its composition is mainly long fibers. It is filled with short fibers and properly calendered. The surface smoothness is low. At present, the offset printing process has been widely used in the production of newspapers. Offset printing is produced by the principle of immiscible oil and water. Its printing pressure is lower than that of lead printing. In order to obtain good graphic quality, we must ensure that the paper has a good surface. Smoothness. Newspapers produced on paper with a smoother surface, due to better contact during printing to transfer the ink, can obtain a higher dot quality, allowing the graphic image to be reproduced clearly and plumply on the paper. With the development of the newspaper industry in recent years and the expansion of the production of color newspapers, the requirements for the surface smoothness of paper have also been continuously improved.

Dots are the basic elements of the printing tone reproduction. The 50% dots at 100 LPI are only about 0.2 mm in diameter. If the surface smoothness of the paper is poor, the dots will easily cause the phenomenon of incomplete deformation and cause the loss of small dots, which will affect the reproduction of the picture and the quality of the picture and picture, and will particularly affect the reproduction of subtle levels. In order to coordinate the complete reproduction of the picture level, it is necessary to ensure that the dots on the paper have a clear and accurate form. We have such experience that the better the surface thirst of the paper, the higher the reproduction quality of the dot and the clear and neat ideas. From a microscopic point of view, the coarse paper surface will not fully transfer the ink of the dots here due to insufficient pressure in the recesses, resulting in a certain degree of dot distortion or even incompleteness. The quality of the newspaper will be affected obviously; the smoothness of the paper High, the small outlets in the printing process are not easily lost, which can effectively ensure that the picture text is rich in layers and the color reproduction is good.

In addition, the higher the number of lines, the richer the picture layer, and the higher the number of screen lines, the smaller the diameter of the dots at the same coordination point. This also requires that the paper with good surface smoothness is not printed, therefore, The number of meshes and print paper smoothness are also of great relevance. However, the number of complaints in the newspaper is not fixed. Newspaper printing requires that the paper have a good surface smoothness to maximize the number of hanging copies and ensure that the copy quality of the picture text is more refined. The number of newspapers printed with the same amount of money is generally around 80100 LPI. In the case of ensuring the smoothness of the surface of the paper, properly increasing the number of pictures on the screen is also one of the means to improve the printing quality of newspapers. That is to say, newspapers with good surface smoothness should be used for newspaper production as much as possible, and the number of hanging nets can be appropriately increased to improve the printing quality of newspapers.

Compared with black and white newspapers, the quality of outlets has a greater impact on print quality. The color newspaper emphasizes a "color" word. To ensure the quality of important color elements such as pictures, titles, bottom nets, and maps, it is important to improve the reproduction quality of the outlets. The black-and-white newspaper outlets are mainly used for the reproduction of pictures, and the color newspaper outlets are very important for the reproduction of color, level, and coordination. In order to ensure the quality of the reproduction of pictures, color newspapers generally have a higher number of identities than black-and-white newspapers. Therefore, the requirements for the level of clarity of papers for color newspapers are also high.

The difference in surface thirst between the front and back of newsprint is also an important performance indicator. It is important to reduce the positive and negative surface thirst to be less than to reduce the gap between the printing quality of newspapers. The International 1910-89 standard also has a large improvement in the surface smoothness difference between the front and back of the paper, and the level A newsprint requirement is within 15%. In recent years, the surface smoothness of newsprint of major brands has been greatly improved, and the gap between the smoothness of the front and back surfaces of some papers has been far less than this value, providing good conditions for publishing double-sided newspapers.