How to print printed matter?

Sunshine exposure, printed matter printing is the work of copying pictures and texts on high transparency carriers such as film and sulfuric acid paper to screen, PS and resin plates coated with photosensitive materials through exposure. Coating a photosensitive film on the surfaces of screen, PS and resin plates, drying, covering the film with an image, irradiating the film with strong light, exposing the image on the film, and copying to the photosensitive film on the plate. This exposure photocopying process is usually called printing.

The device that completes the printing work is called a printer.

Printers can be divided into screen printers, PS printers and resin printers according to photosensitive materials.

Printers can be divided into: 1KW printers, 3KW printers, 5KW printers, etc.

According to the types of light sources, printers can be divided into bright (instantaneous lighting) printers and thermal insulation (continuous lighting) printers.

Printers can be divided into: upper light source printer, lower light source printer, double-sided printer, double drawer printer, etc.

In order to improve the photocopying quality and reduce the shadow caused by light projection, printers are generally equipped with a vacuum pumping system, so that the stacked graphic films and exposure plates are in a negative pressure environment, as close as possible to seamless, and the image exposure photocopying is accurate. Printing is a bridge process between plate making and printing. On the basis of color separation and plate making, it is required to transfer the text of the original picture without deformation. For the next printing, it is required that the ink affinity of the graphic part and the hydrophilicity of the blank part should be clear, and at the same time, it should be able to withstand tens of thousands of imprint frictions without changing its ink adhesion and hydrophilicity.

However, since it is an intermediate transfer process, it will inevitably change. In order to keep it stable, it is necessary to control the photosensitive performance, printing operation process, image transfer data and printing adaptability of the plate in the overall standard data of plate-making printing process to ensure smooth and good reproduction.

Printing has to go through two times in the whole copying process, once proofing and once printing. Therefore, printing is very important in the whole reproduction process, and its quality directly affects the quality and printing efficiency of printed matter. However, there are many problems in the current printing process, such as proofing and printing mostly use different plates, and the dot change between them is very different; The dot gain of proofing and printing is inconsistent, which needs to be adjusted reasonably through printing; The print quality itself is unstable, resulting in a lot of rework. Therefore, it is an urgent and important task to strengthen the standardization of printing process and data quality management and stabilize and optimize printing quality.

Second, the manuscript and printing preparation

1. Preparation and inspection of the original version

According to the production instruction and process design sheet, the manuscript to be printed shall be comprehensively inspected to see whether the pictures, graphics, characters, shading and other contents in the layout are complete, whether the number of color plates is complete, whether the vacancy of each color plate is accurate, whether the picture direction is correct and whether the paste is firm. The distance between the tape and the graphics should be above 7mm, otherwise it will affect the firmness of the printing plate dot.

The subsidiary contents of the layout, such as cross-gauge lines, corner lines, center lines and cutting lines, and whether the color codes and control bars are pasted completely and accurately. The cover mask, table paper mask and its positioning of this set of pictures and printed matter, layout of repeated continuous printed matter, etc., which need to be exposed several times, should be checked for correctness.

Then check whether the original graphics are clean, and whether the blackness and solidity of the dot and graphics meet the printing requirements. For inferior manuscripts that have to be used, according to the actual situation and density of their dots, data adjustment and remedy are carried out during printing.

2. Preparation for printing

Make clear the production instructions and process design arrangements, and decide to adopt printing methods such as single sheet printing, imposition printing, set printing or continuous printing. According to the process design requirements of printing, cutting and binding, determine the typesetting mode, order and quantity.

When printing a single picture, an imposition or printer should prepare a cover mask (also called falling plate) that is positioned with the picture, so as to make a second exposure after (or before) printing the picture and expose unnecessary stains outside the picture.

When you need to manually copy (or multiply) the original image, you need to make a shading paper with exposed crosshairs according to the layout, so that the crosshairs are exposed before printing, and a single picture is printed one by one. And prepare shading materials to protect the temporarily unexposed parts.

When making a copy of a group of pictures, the processing method is basically the same as making a copy of a group of pictures. According to the typesetting of that set of pictures, the organizer usually makes a set of table paper that is positioned with the pictures and with the plates, and also makes a mask that exposes the stains outside the pictures.

When a continuous printer is used for continuous printing, it is necessary to calculate the number, formal position and spacing of design graphics, as well as the vertical and horizontal moving order and moving size of pictures according to the printing layout. Based on the layout, make a shading frame or stick a shading red tape outside the original picture, and paste the original picture on the printer frame according to the exact position. And make a sunshade to cover the whole layout.

According to the production instruction, determine the printing plate, plate size and mouth size. Do a good job of positioning and punching (it is best to use a unified positioning system for imposition, printing and printing), arrange the manuscripts in a designed way according to the requirements of the manuscripts and printing layout, review the materials that need shading, prepare the light-back materials, and start the printing operation after everything is ready.

Third, the content of standardized quality management

The printing process of positive PS plate mainly includes printing, developing, cleaning, drying and applying developing ink. There are two main ways to do a good job in standardized quality management of printing process: one is to find out the main factors affecting the quality of each link in the printing process; The second is to do everything possible to stabilize these factors.

The determination of printing quality standard data should ensure two points: first, the correct reproduction of the original graphic tone; The second is to make the printing plate print well, that is, the layout has a stable printing foundation, the graphic part has good oleophilic and oleophobic properties, and the blank part has good hydrophilic and oleophobic properties.

The printing process should completely transfer the image levels and dots on the manuscript to the printing plate. Theoretically, the more faithful the transferred image level and dot, the better. According to the principle of geometric position equality, the plates corresponding to 1% and 99% are qualified. When 1% ~ 2% bright spots are not exposed, it means that the printing time is too long, while 98% ~ 99% dark spots are stuck, which means that the printing time is not enough. Only the black and white dots of 1% and 99% or 2% and 98% can be exposed correctly, which is the ideal printing quality. However, in actual production, due to the influence of various conditions, it is very difficult to completely and faithfully correspond to printing, and there will always be some changes, and standardized quality management is to make this change as small as possible, so as to achieve the purpose of stabilizing and optimizing the quality of printed matter. Four, the main factors affecting the printing quality

1. Influence of original dot quality

(1) The dot density is higher. In order to achieve effective exposure, the positive film should not let light pass through the part covered by dots. Therefore, the dot density must be sufficient, the density of a single dot should reach above 3.0, and the field density should reach above 4.5. The common problems in actual production are: first, the dot density is insufficient, especially 1% ~ 2% small black dots are gray; Secondly, improper corrosion of the revised edition leads to gray and yellow dots, which affects the printing plate quality.

(2) the dot should be smooth, no virtual halo. The center density of each dot is required to be consistent with the edge density, so as to expand the tolerance of exposure time and realize faithful transfer.

Problems often occur in daily production: First, some original ideas, with high center density, low surrounding density and virtual edges, will cause small changes in the exposure of printing plates and great changes in the dots on printing plates. Second, the quality of the text is poor, the middle density of the text is high, and the density of fine strokes such as the pen tip is low, which causes the font of the printing plate to shrink, and the lack of pens and broken diameters affect the quality of the text. Therefore, before printing, we should check the dot and text quality of the original, and solve the problems in time when found.

2. The influence of plate quality

Processing of (1) plate base. The PS base should be clean, the sand mesh should be evenly distributed, and the thickness and depth should be moderate. At present, PS plate produced by China Institute of Printing Science and Technology adopts continuous coarsening, which has the advantages of uniform sand and moderate thickness. RZ (average sand net depth) = 5 ~ 7.5 microns, and Ra (average roughness) = about 0.6 microns.

② Coating of photosensitive adhesive layer. The photosensitive coating should be uniform and of moderate thickness. It should completely cover the rough peak to prevent the blank part from getting dirty, and it should not be too thick to affect the resolution of the printing plate. The coating thickness of PS plate of Sino-Indian Institute is 1.8g/m2, which is ideal.

In daily production, the quality problem of plate has the greatest influence. First, there are different kinds of PS versions produced in China, and the quality is unstable. If some boards have coarse sand grains, many boards are not clean, and there are many disadvantages such as dirty spots and "horseshoe" marks. Second, at present, the plates used for proofing are all recycled plates, and the quality problem is serious, which intensifies the contradiction between proofing and printing. Therefore, attention should be paid to the selection of plates.

3. The influence of exposure

Proper exposure is an important condition for the correct transmission of large and small points in the whole tone.

① light source. The light source for printing is very important. Choosing it correctly and reasonably can not only shorten the exposure time, but also improve the resolution of the plate and reduce the dot change. The most ideal is metal halogen lamp, which has a strong ultraviolet spectrum between 350 ~ 360 um, and has the advantages of cleanliness, safety, stability and high light efficiency utilization rate, which matches the spectral sensitivity of PS version. However, it should be noted that the long-term aging of the lamp tube will change the spectral radiation and affect the uniformity of lighting. It is best to measure the working time of the lamp (it is best to use an automatic timing switch) and replace it in time before the specified maximum working time expires.

② Exposure time. The exposure time of printing plate is related to the depth of printing plate. There is no printing time for positive PS version, the printing plate is deep and the layout is easy to get dirty. On the contrary, the more exposure time, the smaller the printing plate dot, the shallower the printing plate, and the different depth changes of high, medium and dark tones. Therefore, when the printing conditions have been selected and fixed, it is necessary to find out the appropriate exposure. The method is to expose black and white spots step by step with test paper. After development, according to the geometric position correspondence principle, 1% and 99% or 2% and 98% can be exposed correspondingly, which is a suitable exposure.

In daily production, due to the different types of PS plates, the exposure time required is also different. Therefore, every batch of PS plates should be exposed to test to get the best exposure time.

4. The influence of the contact state between the manuscript and the photosensitive layer of PS plate in the printing process.

When printing, the contact between the manuscript and the photosensitive layer of PS plate is an important factor affecting the printing quality. Different contact states have different rules of dot change, and good contact is the premise of controlled transfer of dot adjustment. The operation should be airtight, the vacuum degree should be high, and the original should be in close contact with the plate, even and consistent. In daily production, there are many problems in this regard, as follows.

① The vacuum contact of the printer itself is poor, the glass and rubber of the printer frame are uneven, and some new printers are uneven, so a piece of woolen cloth must be put in the middle to smooth the clothes.

② The pumping capacity of vacuum pump is too low.

③ Some original films overlap 1 ~ 3 small pieces, and the edge of the picture is covered with adhesive tape, which leads to some weak areas on the edge of the picture.

(4) There is dirt on some original films and plates, which causes local air suction not tight and weak dot. Check carefully before printing.

⑤ Poor temperature and humidity conditions and low relative humidity in the printing workshop will aggravate the generation of dust and static electricity, resulting in poor contact between the film and the photosensitive layer of PS plate. The fluctuation of humidity will affect the activity of developer. The indoor temperature is 20℃ 2℃ and the relative humidity is (55 5)%.

5. Impact of development conditions

Correct exposure should be accompanied by correct development, and the development conditions include the chemical composition of the developer, temperature, development time, mechanical stirring and so on. Before developing with automatic developer, the developer should be stirred circularly to keep the liquid uniform and constant temperature. The temperature of developer is generally 20 ~ 25℃. If the temperature is not suitable, the developer will not drop or appear incomplete.

① Precise control of developer concentration. Different developers should be selected according to different types of plates. At present, cheap alkali such as sodium hydroxide is used as the main agent, which has a large dosage ratio and strong medicinal properties. The general formula is 10000mL water with 50 g. Although this developer is fast, it has the disadvantage of etching and dissolving the oxide layer and photosensitive layer on the surface of the plate base, and it also has a certain destructive effect on the hydrophilic performance of the plate base surface. At present, there are many weak alkaline agents used at home and abroad, such as sodium silicate. Although the price is high, the development speed is fast and the service life is long, which can increase the hydrophilicity of the layout and the printing resistance of the printing plate.

To accurately control the developer concentration, test paper should be used for detection, and exposure and development should be carried out at normal time. After development, the hollow spots are clear and the corresponding small black spots are firm, which proves that the developer concentration is standard. If too many small black dots are lost, the concentration is too high; if hollow dots are stuck, the concentration is too low. Based on this, the main agent content of the developer should be increased or decreased.

If the vision recognizes the correct development effect, it should be that the green color of the graphic part of the layout has not changed, while the green color of the blank part has completely disappeared, and the plate base is light gray. If the blank is still blue-green after development, it means that the developer is weak or ineffective and the exposure is insufficient.

The problem in daily production is that because the photosensitive layer of PS plate is not properly matched with exposure time and developer concentration, when the blank part is still yellow-green after development, secondary development is carried out, resulting in excessive dot loss.

(2) Measurement should be made to supplement and replace new liquid. The aging degree of the developer depends on the number of developing plates and the storage conditions of the developer. Generally, an automatic film processor displays 60 ~ 70 films on average every day. If the liquid is changed, the development speed can be slightly slower when the labor force is reduced in the afternoon. Manual development, the developer should be put in the tray, covered with a cover to avoid contact with air oxidation, and new liquid should be added and replaced by metering.

Five, print quality standards and control data

One of the printing quality standards is to correctly transmit the original graphic output port, and the other standard is to print the printed version. The control data are as follows.

(1) proofread version data

(1) Get proper sun exposure, and keep the small black spots as neat as possible. High-quality PS version should reach 2% small black dots, 2% fine dot loss is unqualified, 50% hollow white dots adjusted to 98% ~ 99% deep tones are faithfully restored, 98% small white dots are not stuck, and the resolution line pattern detection standard shows that 6 ~ 8 microns are incomplete.

② Centrifugally coated regenerated PS plate, 3% of dots are aligned, 97% of white holes are not pasted, and the resolution line 1 1μm is incomplete.

(2) The printing plate data should be properly exposed to improve printability, and 3% dot alignment should be controlled, 50% parts should be exposed to 3% ~ 5%, 97% white dots should not be pasted, and the resolution line mark display 1 1μm is incomplete.

(3) The plate quality meets the standard.

① The thickness of slab foundation is basically the same, and the sand net is evenly distributed with moderate thickness.

② The photosensitive liquid is evenly coated without bubbles and scars.

(4) The layout has a stable printing foundation.

(1) The graphic part has good lipophilicity and hydrophobicity, and the ink is discharged quickly, while the blank part has good lipophilicity and hydrophobicity, so it is easy to print.

(2) The layout is neat and the printing resistance is high.

Six, several work should be paid attention to.

1. Pay attention to taking ink.

The PS version after ink lifting treatment can improve the sensitivity of the photosensitive adhesive layer, protect the graphic part and make it ink quickly when printing and proofing. At the same time, the friction development ink can prevent the light reaction of the graphic part, prolong the service life of the printing plate, and improve the printing resistance by raising the ink. Therefore, in addition to the version that is eager to print on the computer, we must also adhere to the ink treatment, and pay attention to the uniform development of ink when operating, so that the layout will not be dirty.

2. Pay attention to the version.

Wash and dry the fixed PS plate, and then bake it on the machine, so that the adhesive layer developed by alkali liquor is stable after heating, and the residual alkali liquor volatilizes after heating. Therefore, the treated PS plate has good oleophilicity, rapid ink extraction and high printing resistance. Pay attention to the shift of baking process when operating. Before inking, the layout should be cooled and have some moisture. If necessary, we can coat it with two thin layers of glue, so as to avoid ink lifting.

3. Pay attention to the environment and machine maintenance.

(1) The environment of the printing workshop should be clean, especially the printing glass, which must be cleaned before work, and the developer should be cleaned and maintained regularly.

(2) The light source and lighting should be checked regularly. Voltage and power grid inspection, 380 V (360 ~ 400 V).

(3) PS version storage place should be set in cold air darkroom or low temperature dry place, especially to avoid the sink. When using PS version, be careful not to bend or scratch, and be careful not to touch the page with hands stained with oil or developer.

4. Pay attention to treating the plate with phosphoric acid solution.

Manually developed plates should be treated with 2% ~ 3% phosphoric acid. Because the photosensitive agent of the exposed part is removed by the developer after development, the graphic part that has not seen the light is not corroded by the developer and still remains on the layout, which is photosensitive. They need to be fixed with 2% ~ 3% dilute phosphoric acid solution to neutralize the surface of alkaline printing plate and thus stabilize the graphic part. When operating, be careful not to treat it with phosphoric acid as soon as it is taken out of the developing tray, but rinse it with clear water first and then with developing solution.

5. Pay attention to post-processing

When developing PS plate aging, wet Bobby Chen is generally used. Although this method is easy to remove, it will be dirty because of some shortcomings in the early development. The best way is to apply a thin layer of glue first, and then remove the dirt when it is dry, which is conducive to cleaning the page.

6. Pay attention to rubber printing

Pay attention to rub the glue very thin and evenly when operating, which can effectively protect the layout. However, in daily production, we often do not pay attention to this work, and the thickness of the glue is inconsistent, uneven or even incomplete, thus causing local damage to the printing plate.