Excessive development; strong acids, strong bases, organic solvents, decontamination fluids, etc. are attached to the printing plate; too many times of wiping with plate cleaning agent, etc., these are the reasons that will affect the printing plate durability. In printing, if the printing pressure is too large or the paper powder is too much, and the strong printing plate cleaning agent and roller cleaning (development trend in the industrial cleaning field) agent are used in UV printing, it will inevitably cause print resistance decline.
In particular, it should be pointed out that in order to prevent running out of light, for the ordinary PS version, yellow safety lights should be used to fully block harmful light. There is a bottom blue on the printed plate in production. One plate is printed out, whether it is because of the problem of pre-production of the plate material, or the matching conditions of exposure and development time of the printed version are not suitable. Bottom blue. The "secret" of the bottom blue is that when the plate is made, the sand is too coarse and the current of the electrolytic oxidation does not match; the exposure is insufficient during printing, the concentration of the developer is not enough, or the two conditions are not matched properly. The bottom blue phenomenon is a headache for many operators. If this problem occurs, more development will not work, and less development will not work. If you develop more, the dots to be retained will be reduced or lost; if you develop less, it will affect the entire layout. Under the conditions of moderate exposure and development, the bottom blue will be repaired after the film is displayed, but once it is repaired, there will be a watermark on the layout. After the watermark is removed, the machine will be printed on the machine, and the watermark will be around. If you want to get dirty, if you use the cleaning fluid to repair this circle of dirt, you will get another circle of dirt. If it is stuck in pictures, text or online, the printing plate will not be used at all. To solve this problem, it is necessary to apply a thin layer of glue before decontamination, and high-quality prints can not use this version.
1 General principles for evaluating the printing quality of newspapers To judge and evaluate the quality of newspaper printing, the evaluation is mainly from the following aspects.
1) Appearance â‘ The layout is clean and unblemished. There should be no quality problems such as print through due to high transparency of the paper or rubbing due to poor stacking on the printed matter. There should also be no obvious stains and wrinkles; â‘¡ Even ink color, clear text, no ghosting, no obvious pen missing , Broken paintings, paste characters and bad characters.
2) Picture â‘ The picture requires rich levels, moderate tones, and moderate contrast. There is no large-scale blackout on the edge of the picture and no blackout that affects the level; â‘¡ The visual effect of the color picture is bright and colorful, not dull and low, basically in line with natural tones, not partial Color; â‘¢Overprint is accurate. The four corners, the edges of the picture, and the layers in the picture must be overprinted very accurately, without ghosting or dark marks.
3) Ink color â‘ A newspaper is divided into two sides, the ink color is required to be uniform.
The dark and light tone ink colors should be uniform, and the density should be consistent. There are no bars and no different shades of writing.
â‘¡Newspapers with multiple layouts require each pair of opening ink colors to be basically the same.
2 Testing and inspection of the printing quality of newspapers is an essential means to evaluate the quality of printing, and also an indispensable important step in evaluating whether the quality of semi-finished products reaches the standard in the production process.
Testing Standards, Methods and Evaluation of Newspaper Printing Quality In GB / T 1793.4-2003, an important content is the requirement for quantitative testing of newspaper printing quality.
1) The quality standards of the mesh color separation film must be strictly inspected for the film output by the laser imagesetter, which lays the foundation for the smooth progress of the subsequent process and guarantees the printing quality of the newspaper. There are the following aspects to determine the quality of the mesh tone color separation film: ①The solid density of the color separation film (including the base density) ≥3.50, the film base fog density ≤0.15, the transparent part of the dot area should be transparent.
â‘¡ Mesh line number Monochrome and color printing of newspaper, the mesh line number should be: 34 ～ 48 lines / cm, 85 ～ 120 ï¼ cm.
③ The screen angle for monochrome printing, the screen angle should be 45 °; for color printing, the screen dots without spindle (such as square, round screen dots), the difference between the screen angles of the cyan, magenta and black plates should be 30 °, yellow The screen angle of the plate and other color plates should be 45 °; the screen dots with a main axis (such as oval screen dots) are used. The difference between the standard screen angles of the cyan, magenta and black plates should be 60 °, and the angle of the yellow screen is 0 ° . The screen angle of the main color version should be 45 ° or 135 °.
2) Registration error The diagonal length error of a set of dichroic film should be ≤0.02%.
3) Sum of tone values ​​The sum of tone values ​​refers to the sum of the tone values ​​of the four dichroic patches. For most dichroic patches, the sum of the largest tone values ​​is in the darkest part of the image. The sum of tone values ​​must not exceed 260%. When the sum of tone values ​​reaches this limit, the black tone value should not exceed 85%.
4) Gray balance If a printed product produced under the specified printing conditions is gray under the specified observation conditions, the tone values ​​(dot area) of cyan, magenta, and yellow on the dichroic film are in a gray balance state.
The gray balance internationally recommends the combination of the following tone values, expressed as a percentage of the dot area on the color separation sheet.
Cyan magenta yellow 1/4 tone 25% 18% intermediate tone 50% 40% 3/4 tone 70% 64% Under different paper, ink and printing conditions, gray balance data is different.
5) The inspection rules formulated by the China Press Association Newspaper Committee Appraisal Group In the "Color and Black and White Newspaper Printing Quality Inspection Rules" prepared by the China Press Association Newspaper Committee Appraisal Group, the following four aspects are proposed according to the national standard Check the rules.
â‘ The appearance is clean and tidy, without obvious stains and wrinkles; the ink color is uniform, the text is clear, there is no ghosting, and there is no obvious lack of pens, broken strokes, pasted characters and bad characters.
â‘¡Pictures and pictures require rich levels, moderate tones, and moderate contrast. There are no large-scale screens at the edges of the image and screens that affect the level; color images are bright and intuitive, not dull and low, basically in line with natural tones, no color cast; accurate overprinting , The minimum error is not greater than 0.3 mm.
â‘¢ The headline of the inscription, the headline above the first line and the headline with net decoration, the field density is between 0.95 and 1.20.
â‘£ A newspaper with ink color is divided into two sides, the ink color is required to be uniform and the text density is subject to 0.18. Multi-page newspapers require that the ink color of each version is basically the same.
The detailed rules quantify the above four parts, and use a percentage system to check and evaluate.
92-93 points are qualified, 93-94 points are excellent, 94-95 points are excellent, and 95 points or more are excellent newspapers.
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