Control of textured relief printing technology
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The letterpress screen printing is a kind of technology with strong production technology. The quality of this kind of products, in addition to the production hardware factors, depends mainly on the degree of correct control of the operation technology in the production process. Therefore, to print the relief and ensure the quality of the product printing, we must pay attention to the reasonable control of the production process technology.
1. The understanding of the textured version and its characteristics
At present, there are mainly three types of printed relief embossed plates, namely zinc plate, copper plate and resin plate. The plate made of zinc metal sheet is made of zinc plate, and its thickness specifications are various. The thickness of 1~1.5mm is suitable for making the screen version, and it is also suitable for making the letter plate with lines in the layout. Because the zinc plate material is brittle, the wear resistance and plasticity are poor, so it is often used to make coarse mesh relief plates below 100 lines, so that it is compatible with its material properties. The copper plate made of copper plate material has better wear resistance and higher fineness, and is more suitable for making an anilox plate. The material price of the copper plate is more expensive than that of the zinc plate, and it is suitable for the fine product with high printing quality requirements, in order to obtain the best effect. The photosensitive resin plate (solid type) is a new type of letterpress plate developed after the metal plate. It is also suitable for the flexographic printing process. The plate has the advantages of light material, fast plate making speed, soft texture, elasticity and printing pressure. Small, high printing durability, and other significant advantages, suitable for printing large-area reticulated plates, solid version of the structure of the product, printing pressure, printing ink color quality are better.
2. Put a good pre-press technology to ensure the quality of product printing
The color prints of the letterpress process are often overprinted in three or four color versions. However, in daily production, more is monochrome monochromatic printing, or a printed version of the text, real map version, and line version of the printed matter, the printing process is relatively simple. Among them, multi-color overprinting products are difficult to print, and if the pre-press process is improperly processed, it will directly affect the color effect. Under normal circumstances, ordinary color printing products with low quality requirements can adopt the three-color printing process. However, because the three-color version of the process is less than one color black version, the layout of the printed product is not natural and soft, so the products with high quality requirements are printed by the four-color version, and the printing effect is better. Of course, this can only be achieved if the number of screen lines and the angle of the various plates are accurate. The higher the number of network lines, the finer the network points, and the richer the graphics level. The process experiment shows that the higher the plate mesh line must be, the smoother the paper surface is, so as to ensure the printing quality of the product. Therefore, for fine products printed on coated paper or glass cards, it is advisable to make 150 to 200 lines of the textured version for printing. Paper with a smooth paper surface can be made into a textured version of 120 to 150 lines. For rough paper such as printing newsprint, low-grade offset paper, and stickers, you can make a 60-100 mesh reticulated version as appropriate. In addition, the reasonable choice of the angle of each color plate is also an important part of ensuring the quality of printing. Because, only the difference in the angle of the screen between the various color plates, after printing, can present a layered and comfortable color effect. Therefore, in general, the yellow plate is generally made 90°, the black plate is made 45°, and the green plate and the red plate are made to be 15° or 75° for printing. However, since the 45o cable angle is visually most comfortable, the 45o cable angle is relatively stable and not stiff, and it is the best cable angle. Therefore, for the printing of manuscript-based originals, since the picture is mainly magenta-colored, the magenta plate can be made 45°, the yellow plate is made 90°, and the green and black plates are made 75. Printing at ° or 15 ° is more suitable. For the printing of landscape originals with a blue-green tone, the blue version can be made 45°, the yellow plate can be made 90°, and the black and magenta plates can be made 15° or 75° for printing. .
3. Improve the printing operation technology and improve the printing quality of products.
3.1 Pay attention to save the plate to prevent the layout from being damaged. The mesh version of the dot is relatively small, can not withstand rubbing and heavy pressure. Therefore, the plate should be handled with care when moving and extracting. A few plates should be placed on top of each other with a smooth, soft paper that protects the layout from the top of each plate to prevent scratching the layout.
3.2 should pay attention to master the position of the plate. When loading the plate, try to install the plate in the centered part to ensure uniform printing pressure. Because the center of the plate and the roller is the largest part of the printing pressure, the entire plate can receive a relatively uniform printing pressure, thereby obtaining better printing quality.
3.3 to good quality of the paste. The circular press structure of the rotary machine should be used to accurately position the plate at one time, that is, the textured version of the roller should not be removed and re-attached, so as to avoid the deformation of the plate due to the fold. Affect the overprinting accuracy of the product and the cleanliness of the blank layout. Therefore, the plate should be carefully and carefully pasted according to the squares and marks on the drum. The screen printing plate is printed with a circular flattening machine, and the plate of the plate is preferably used with a metal plate, so that the four sides are relatively straight, the plate is relatively firm, and the plate is not easy to be bowed, and the pressure is relatively tight. Uniform, good blotting results.
3.4 to choose and adjust the ink roller. The color of the ink of the reticulated printing product depends mainly on the ink application effect of the inking roller. Therefore, the ink roller should be centered and flexible, and the surface of the gel should not have scratch marks on the printing plate. At the same time, it is required that the height adjustment of the inking roller should be accurate, and the contact pressure with the tandem roller should be suitable and maintain uniform contact conditions, so as to avoid the occurrence of ink transfer or poor ink application, and ensure the printing quality of the dot.
3.5 to put a good pad technology. Clear dots originate from uniform printing pressure, while the letterpress process pad is an effective measure to achieve uniform printing pressure. In the case of uniform underlay, the upper pad is the key link to ensure the quality of the printed product. Therefore, a plate of about 35g is used to print a plate, and then the dark tone pattern of the printed plate is dug out and glued to the corresponding lining. The dark tone is printed on the mark to achieve uniform pressure on the light and dark layout and clear dot print.
3.6 should be good lining process technology. The lining is the medium for the transfer of the print, which greatly affects the printing quality of the product. If the texture of the lining is too soft, it will easily enlarge the deformation of the dot, and if it is too hard, it will easily wear the mesh. Therefore, with a neutral hard pad, the printed mesh version is more suitable. The reasonable grasp of the thickness of the lining is also very important. If the lining is too thin or too thick, the overprinting error is easy to occur. Therefore, the thickness of the lining must be determined according to the technical parameters of the equipment specification. In addition, the lining of the lining should be firm and firm, and there should be no bad conditions such as looseness and drumming, so as to avoid the occurrence of overprinting and ghost quality failure.
3.7 It is necessary to set the printing rules to ensure the accuracy of product overprinting. For overprinted webbed products, the position of the front gauge and side gauge should be fixed at one time, and the needle position (rules) should not be adjusted too much during overprinting. Because there may be unevenness after cutting the paper edge, if there is a wavy edge or a beveled edge that is invisible to the naked eye, if the position of the front gauge and the side gauge are moved, the overprint will not occur. Quasi-illness. Therefore, the needle position of the first color printing is determined, and it is preferable that the respective colors should be overprinted according to the original rule position.
3.8 To properly use and dispense the ink. The same batch of products should be printed with the same type of ink to ensure consistency before and after the hue of the print. Adjust the viscosity and consistency of the ink according to the difference in paper characteristics. Due to the different ink absorption of the paper, as well as the temperature and other reasons, the original ink with large concentration, poor fluidity and excessive viscosity needs to be diluted and adjusted to enhance the fluidity of the ink and reduce the viscosity, thus ensuring normal ink transfer and Ink effect. However, the ink can not be adjusted too thin, so as not to dilute the hue of the ink and cause the spread of dot defects to appear.
3.9 It is necessary to arrange the printing color sequence correctly and improve the process quality of the product. The scientific and reasonable arrangement of the printing color sequence by the printed lithographic plate plays an extremely important role in ensuring the printing quality. The printed two-color mesh version is usually printed with a light color and then printed with a dark color. If the printing of the two colors is not affected, the dark color can be printed first and then the light color can be printed, so that the printing color effect is better. If you print three-color, four-color textured version, you should try to consider the color version with poor transparency and the transparent version. If the printed surface is dominated by warm colors, it can be printed in cyan and black, followed by yellow and magenta. For printing on cool-toned layouts such as woods and sky, you should first print yellow and magenta, then print black and cyan, and the printing effect is better.
4. Several fault phenomena that are prone to occur in the process of screen printing
4.1 print page layout has expanded. When printing the mesh pattern, if the printing pressure is too heavy; the texture of the lining is too soft or the package is not tight, there is a phenomenon of looseness and bulging; the texture of the printing plate is too soft and the plate has a bowing phenomenon; the ink is too thin, If the amount of coating is too large or an excessive amount of anti-adhesive agent is added to the ink, it is easy to cause the dot of the printed product to expand. Therefore, when printing the textured version, it should be printed with the lightest pressure as possible; the printing plate can be printed with a solid resin plate or copper plate which is not easy to wear and compressive; the post-exposure time of the resin plate is sufficient, and the curing temperature and time should be appropriate. The liner should be made of a medium-hard material and attention should be paid to tightening the inner liner. Printing a screen pattern with a platform printing machine, using a metal plate material with a flat, solid, right-angled, straight edge on the four sides to prevent the bowing of the plate after fastening; adjust the appropriate ink concentration and coating The amount of cloth, and try not to add other auxiliary materials in the ink to ensure the printing quality of the dots.
4.2 print layout is not clear. When the surface of the lining is uneven, the height of the rubber roller is improperly adjusted; the ink roller is too hard; the coating amount of the printing ink is too large; the ink is too thin or too thick; when the pad is not uniform enough, it is easy to make the local The plate prints are faint or creaking, and corresponding measures should be taken to correct them.
4.3 printed ink color appears color difference. If there is a problem with the machine, such as the front gauge, side gauge, transfer paper, teething, etc., there are unstable and abnormal phenomena in the working process; the surface strength of the paper is poor, it is easy to produce powder falling and fluffing, and the paper edge exists due to the rules. Wavy, the position of the front gauge or the side gauge is adjusted when overprinting, and the presence of these conditions is likely to cause the chromatic aberration due to inaccurate overprinting. In addition, the use of three primary color inks of different brands and different batches, due to the difference in hue, is likely to cause the occurrence of printing chromatic aberration. Therefore, the process technology should be strictly controlled and controlled during the printing process to prevent and reduce the chance of printing chromatic aberration.
In summary, as long as the various aspects of the screen printing process are carefully taken into account, according to the characteristics of the product and printing conditions, scientific and reasonable formulation of the corresponding production process measures can not only ensure the printing quality of the product, but also effectively Improve production efficiency and improve the economic efficiency of enterprises.