Printing ink for sheet metal printing and troubles

Printing ink for printing tinplate and troubleshooting (Part 1)

tinplate printing also uses the physical property of water and ink repelling each other to transfer the printing plate graphics and text to the tinplate through the blanket with the help of printing pressure, which belongs to the principle of offset lithography. Due to the special physicochemical properties of tinplate and the reprocessing performance of printed matter, its printing process is quite different from that of ordinary offset printing

tinplate printing has special requirements for ink:

(1) the ink is required to have good adhesion and mechanical properties

because the tinplate printing materials are finally made into cans of food, toys, metal photo frames and barrels and cans of chemical products, they need to be cut, bent and stretched, so the printing ink is required to have good adhesion and corresponding mechanical properties to the tinplate. In order to improve the ink adhesion, white backing should be applied to the sheet before printing. White is the basic color of all pictures, with high lightness. After adding other high-energy hues, the brightness of each hue can be improved to form a color scale

(2) requirements for white ink

the surface of the sheet is silver white (or yellow) and has metallic luster. Before printing color pictures and texts, the total demand for plastic pipes will continue to grow. The surface will be painted or printed white. Due to the limitation of ink coverage, monochrome machines often need to be printed twice, and the whiteness can reach 75%. Whiteness, as an important indicator of the quality of tinplate printing products, requires that the white ink has a good adhesion with the primer, and does not turn yellow after repeated high-temperature baking and high-temperature steaming. Priming the sheet can increase the adhesion to the sheet and have a good adhesion to white ink. The commonly used primer is epoxy amine based, which has the characteristics of light color, no yellowing and aging after repeated baking, and good flexibility and impact resistance

(3) requirements for color inks

color inks printed on tinplate should have special requirements in addition to a certain degree of water resistance. As the surface of the sheet is impervious to moisture and solvent, it needs to be baked and dried, so the ink should be heat cured. The requirements for coloring power and durability of pigments are high. In addition to the basic properties of general offset printing ink, iron printing ink should also have the characteristics of heat resistance, strong ink film adhesion, impact resistance, good hardness, cooking resistance and light resistance according to the characteristics of iron printing

(4) ink drying process

in the production of sheet printing, ink drying is a complex physical and chemical reaction process. Only by reasonably controlling the drying speed of ink and mastering the physical and chemical mechanism of ink drying can we effectively carry out rapid printing and ensure product quality. Drying the ink too fast will reduce the normal transmission performance of the ink and affect the normal production; It causes the blotting to be weak, the ink color to be weak, and the ink on the surface of the printing plate and the ink roller to be dry, which hinders the inking in the transmission; Make the dry layer of printing plate expand outward; The excessive amount of desiccant causes the increase of ink adsorption, and the blank part becomes dirty. And the ink drying too slowly can cause overprint difficulties, adhesion, adhesion, etc., its mechanical strength is not high, and its firmness is reduced; It is easy to cause scratches during transmission. Therefore, the drying speed of ink should be appropriate, too fast and too slow are unfavorable

(5) special structure of printing equipment

due to the different substrates, the auxiliary mechanism of the sheet press is also different from the paper offset press. Tinplate is insoluble in water and does not adsorb solvent, so printing ink needs to be baked at high temperature to make solvent volatilize and film solidify. Therefore, the printing process device generally needs to be equipped with a drying room. The whole automatic tinplate printing line is generally called as a long-distance line, with a load of more than 50 meters, which has the characteristics of precision and bulkiness. In addition, the sheet metal printing machine is controlled by magnets for separating sheets and double sheets. The high hardness of the sheet metal material also determines that the advanced continuous iron conveying structure cannot be used in the printing process. The structure of the pushing section, alignment and stacking section is different from that of the offset printing machine

the following problems may occur in sheet printing:

1. Inaccurate overprinting

the accuracy of printed products is of great importance to product quality. With the application of multi-color iron printing machine, higher requirements are put forward for the accuracy of overprint. Even if the local overprint is not accurate, the quality of the printed parts will be affected. Overprint error of the printing plate itself, stretching deformation of the printing plate, unreasonable cylinder liner, poor quality, poor elasticity and easy deformation of the blanket; Improper adjustment of the iron printing machine and poor precision of the parts may cause inaccurate overprint

according to the requirements of printing iron, the first printing plate must have a positioning crosshair, and the crosshair of later printing plates shall coincide with this crosshair. During adjustment, the following principles shall be mastered:

(1) the positioning shall be extended and lowered to facilitate adjustment

(2) the adjustment direction, position and quantity of printing plate shall be consistent

(3) the method of more looseness and less tension shall be adopted to calibrate the plate, so as to prevent the plate from being separated from the plate clamp or deformed due to excessive force during plate adjustment

(4) the adjustment range of the printing plate should be in advance, so as to leave margin for the attachment of the printing plate and the cylinder

(5) two points should be mastered in the adjustment of side rules: first, the spring force should be properly adjusted according to the thickness of the sheet; Second, the distance between the rules and the sheet is generally 4-5 mm

2. When printing the full version of the product, the sheet and the rubber drum stick.

solution:

(1) reduce the viscosity of the ink and appropriately increase some ink blending oil

(2) check whether the horse mouth iron and printing pressure are reasonable

(3) adjust the appropriate running speed of the iron printing machine

(4) control the ink amount

3. The color of the imprint is not correct, resulting in the phenomenon of shallowness

solution:

(1) check whether the blanket and liner are reasonable or have changes and displacement

(2) control the water consumption of the layout

(3) properly adjust the ink delivery

(4) check the absorption of printing plate to ink and the formation of residual ink layer