Color printing and printing
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Dirty prints are common faults in color printing. The occurrence of such failures will affect the quality of printing, and the large-scale scrapping of products will cause great losses to the enterprise. There are many reasons why the printed matter is sticky, such as thick printing ink layer, too smooth back surface of the paper, improper ink adjustment, and unsuitable printing pressure. Sticky dirt has both ink properties and environmental temperature and humidity. Only by carefully controlling the technology can we guarantee the printing quality of the products.
1. Correct understanding of the relationship between printing pressure and ink layer thickness
Appropriate printing pressure is an important condition for achieving uniform transfer of the printing ink layer. Insufficient or uneven plate pressure will affect the uniform transfer of the ink layer. When the pressure on the layout is insufficient or uneven during printing, the ink color of the printed product will be embossed, and the thickness of the entire layout is also inconsistent. Increasing the amount of ink can indeed make up for the defects caused by poor contact between the printing ink layer and the substrate caused by insufficient printing pressure, but it is also easy to cause the printed matter to be dirty. Therefore, the printing pressure should be adjusted first, and then the amount of ink in the layout should be adjusted, so that a good printing effect can be obtained.
2. Handle the relationship between paper printability and ink layer thickness
Paper with poor surface smoothness absorbs ink quickly and absorbs a large amount of ink. When printing such paper, if the printing pressure is insufficient or uneven, it will be easy to expose the bottom and make a flower after printing. If the ink volume is increased, the ink layer will be thicker. If the printing speed is slow, it will easily become sticky. For paper with poor surface smoothness, the printing pressure should be increased accordingly; for paper with better surface smoothness such as coated paper and glass paper, the ink layer should be as thin as possible to avoid sticking. From the point of view of anti-adhesive and dirty, printing large-area plates should adopt “deep ink thin printing”, that is, the color of the ink should be adjusted to a deeper level, and the ink layer should be correspondingly thinner, so that it can meet the requirements of printing hue and Avoid sticking.
3. Master the relationship between the characteristics of the plate and the thickness of the printed ink layer.
There is a certain relationship between the quality of the plate, the thickness of the printing ink layer and the printing pressure. The smoothness of the layout is poor, and the ink layer and pressure required for printing are large; otherwise, it is small. If zinc printing is used, due to poor ink affinity and poor surface gloss, only by increasing the printing pressure and the thickness of the ink layer, the effect of the printing ink layer is full, but it is easy to cause stickiness, so it is not suitable to use zinc plate. Printing color printing products above the open size. The photosensitive resin plate has good surface glossiness, soft texture, good flatness and ink affinity, and the printing ink layer is correspondingly thinned, and can still achieve better printing effect, and is also less prone to stickiness. Therefore, a photosensitive resin plate should be used when printing large-area images.
4. Avoid backside stains caused by improper thickness of the printed ink layer
It is determined whether the printing ink layer is moderate, mainly because the printing plate is evenly pressed, and the printing plate is evenly exposed to the bottom without being exposed, and the printing hue is consistent with the sample. If the printing pressure is not uniform or insufficient, the gloss of the printing paper is poor, the color of the printed original is deep, and the color of the ink is too light, which may easily lead to the determination of the thickness of the printing ink layer. If the amount of ink is blindly increased, The back of the print will be dirty due to the thick ink layer.
5. Avoid printing improperly caused by improper operation
(1) Incorrect adjustment of the ink roller, excessive or uneven ink volume
When the roller head and the shaft hole of the ink roller have a large gap or eccentricity due to wear; when the elasticity of the ink roller is deteriorated, the ink roller is unevenly contacted with the plate during the process of rolling the ink along the layout, and the partial layout is easy to be inked. Uneven, the ink layer is thin. In addition, if the ink roller is adjusted too high or too high, it is easy to make the coating ink layer insufficient or uneven. At this time, if the ink amount is blindly increased, the partial layout ink layer is thickened to cause stickiness. Therefore, when printing a large area of the plate product, the ink roller device is required to have high precision, the rubber roller has good roundness, the rubber roller colloid is soft and hard, the ink roller and the ink roller are in uniform contact, and the height adjustment should be accurate to reduce the offset of the printed product. Opportunity.
(2) improper delivery
When printing and receiving the paper, the angle and height of the paper should be accurately adjusted according to the degree of softness and hardness of the printed product. Otherwise, the edge of the printed paper can easily be rubbed to the mark of the previous printed sheet, so that the ink on the surface of the printed product is damaged. In addition, the printed sheets should be lightly handled to prevent the upper and lower sheets from moving and rubbing to cause sticking. According to the ink receiving condition of the printing plate, the number of paper towels should be grasped as appropriate to prevent heavy pressure and dirt.
(3) The plate bottom is not true, the pressure is uneven
The plywood material is not solid enough, and the compression deformation coefficient is large. If the material is used as the printing plate support, the printing pressure and the thickness of the ink layer must be increased, so that the printed matter is easily soiled. Therefore, it is better not to use a plywood bottom when printing the ground. A magnetic plate or other metal bottom should be used to make the printed ink layer thin without being used, which is good for preventing sticking.
(4) The paper is too acidic, the climate is humid, and the printed products are not easy to dry.
When printing on offset paper or some domestic coated paper, since the printing ink layer is thick and the paper is sour, the ink layer is not easy to be dried, and it is easy to be sticky. At this time, dry oil should be added to the ink to prevent the printed matter from getting dirty.
(5) knocking paper creases cause friction of printed products
When printing coated paper, the surface of the paper is smooth, and if the paper crease is prominent, it is easy to rub with the print to cause sticking. Therefore, knocking paper should be based on the layout structure and paper characteristics as appropriate. For thicker coated paper, try not to knock it. Use only the upper or lower jaw to make the paper straight and firm.
In summary, the reasons for causing the color prints to be dirty in printing are various. As long as we are technically good, we can not only receive better anti-sticking effect, but also improve the quality and productivity of the printed products.