Method for controlling sticky back of color prints

Dirty prints are a common failure in color printing. The occurrence of such failures will inevitably affect the printing quality, and it will result in the mass scrapping of products, which will bring great losses to the company. There are many reasons that cause the prints to become dirty, such as a thicker layer of printing ink, a too smooth back of the paper, improper ink transfer, and unsatisfactory printing pressure. The reason for the dirty nature of both inks is related to the temperature and humidity of the environment. Only by carefully putting a good technology in order to ensure the quality of the product's printing.

1. Correctly understand the relationship between printing pressure and ink thickness

Appropriate printing pressure is an important condition for uniform transfer of the layout ink layer. Insufficient or uneven layout pressure will affect the uniform transfer of the ink layer. When the printing pressure is insufficient or uneven during printing, the printing ink will be colored, and the ink thickness of the entire layout is also inconsistent. Increasing the ink volume can indeed make up for the defects caused by the poor contact between the ink layer and the substrate caused by insufficient printing pressure, but it is also likely to cause the ink to be dirty. Therefore, it is necessary to adjust the printing pressure first, and then adjust the layout of the ink, so as to get a good printing effect.

2. Handle the relationship between printability and ink thickness

Paper with poor surface smoothness absorbs ink fast and absorbs large amounts of ink. When printing this kind of paper, if the printing pressure is insufficient or uneven, it is easy to expose the bottom of the paper after printing, and if the ink volume is increased, the ink layer becomes thicker, and if the printing speed is slow, the stickiness is likely to occur. For papers with poor surface smoothness, the printing pressure should be increased a bit; for papers with good surface smoothness, such as coated paper and glass cardboard, the ink layer should be as thin as possible to avoid sticking. From the perspective of stickiness prevention, printing large-area plates should adopt “deep ink thin printing”, that is, the hue of the ink should be adjusted darker, and the ink layer should be thinner accordingly. In this way, the requirements for printing hue can be satisfied. Avoid sticking.

3. Grasp the relationship between the characteristics of plate material and the thickness of printing ink layer

The quality of the plate, the thickness of the printing ink layer, and the printing pressure have a certain relationship. The smoothness of the layout is poor, and the ink layer and pressure needed for printing are large; otherwise, it is small. If the use of zinc printing, because of poor ink affinity, poor surface gloss, only to increase the printing pressure and ink layer thickness, in order to achieve full effect of printing ink layer, but this can easily lead to dirty, it is not appropriate to use zinc plate Printing products with more than eight open format printing products. The photosensitive resin plate has good surface glossiness, soft texture, good flatness and ink receptivity, and its printing ink layer is thinned accordingly, and good printing effect can still be achieved, and stickiness is not easy to occur. Therefore, a photosensitive resin plate should be used when printing large-area images.

4. To avoid the back of the printing ink layer due to improper thickness

Determine whether the printing ink layer is moderate, mainly press the printing plate surface evenly, the layout is uniform by the ink to reach the bottom, not falsified, the printing product hue is consistent with the sample draft as the main basis. If the printing pressure is uneven or insufficient, the gloss of the printed paper is poor, the hue of the original is dark, and the hue of the ink is too light, which can easily lead to inaccurate determination of the thickness of the printing ink layer. If the ink volume is blindly increased, Thickness of the ink layer will cause the back of the printed product to become dirty.

5. Avoid sticking caused by improper operation

(1) Improper adjustment of ink roller, excessive ink or uneven ink

When the ink roller shaft head, shaft hole due to wear there is a larger gap or eccentric; when the elasticity of the ink roller colloidal deterioration, the ink roller in the process of rolling along the layout of the ink and the printing plate inhomogeneous contact, easy to cause partial layout brush Uneven, there is a thin layer of ink. In addition, if the ink roller is adjusted to a high level or one end is too high, it is easy to make the ink layer of the printing plate insufficient or non-uniform. In this case, if the ink volume is blindly increased, the local ink layer will be thickened to cause a dirty film. Therefore, when printing a large-area plate product, it is required that the roller roller device has high precision, the rubber roller has a good roundness, the rubber roller is soft and hard, and the ink roller is in contact with the ink roller uniformly, and the height adjustment should be accurate so as to reduce the occurrence of stickiness of the printed product. Opportunity.

(2) improper delivery

When the paper is delivered, the angle and height of the paper should be accurately adjusted depending on the printing format and the degree of softness and hardness of the paper. Otherwise, the edge of the paper on the printed sheet can be easily bumped and scratched to the mark of the previous print sheet to make the ink on the surface of the print damaged. In addition, printed sheets should be gently lifted to prevent the upper and lower sheets from moving and rubbing to cause stickiness. The amount of paper should be determined as appropriate, depending on the situation of the ink on the printing plate, so as to prevent heavy pressure.

(3) Improper plate pressure and uneven pressure

The plywood material is not solid enough, and the compression deformation coefficient is large. If this material is used as a plate support, the printing pressure and the ink layer thickness must be increased, so that it is easy to make the printing material sticky. Therefore, it is best not to use plywood bottom trays in the printing field, and magnetic plates or other metal bottom trays should be used so that the printed ink layer is thin and does not take off, which is conducive to preventing stickiness.

(4) The paper is acidic, the climate is humid, and the prints are not easy to dry

When printing with offset paper or some domestic coated paper, the ink layer is thick and the acidity of the paper is large, and the ink layer is not easy to dry, and stickiness is also likely to occur. At this point, dry oil should be properly added to the ink to prevent the print from sticking.

(5) Knock paper creases to make prints rub

When printing coated paper, because the surface of the paper is relatively smooth, if the paper is creased, the paper will easily rub against the prints and become dirty. Therefore, knocking on paper should be dictated by the structure of the layout and the characteristics of the paper. For thicker coated paper, do not knock as much as possible, only use the method of rubbing or kneading, rub the paper straight and firm.

In summary, there are many reasons for causing the printed prints to become dirty, as long as we are technically good, we can not only get a better anti-sticking effect, but also improve the quality and productivity of printed products. .

Source: China Brewing Network