Factors affecting the quality of screen printing of middle and high-grade wrinkle ink

At present, with the rapid growth of commodity economy and the diversified development of printing technology, packaging and decoration printing products have entered a new development realm in China. In the past 20 years, the share of packaging and decoration printing in total printing output has increased from about 20% to about 70%, which is the highest in China's printing industry. Although lithography, letterpress, and gravure printing are the main printing technologies for packaging, decorating, and printing products, due to the complexity of the technical process of packaging and decorating printing products and special quality specifications, special printing processes must be used. This process accounts for the output value of packaging and decoration printing. 5% to 10%, while the application of screen printing is to meet this trend, to fill the blank packaging and decoration printing.

From the market division, screen printing is not a major printing process in the field of packaging and trademark anti-counterfeit printing. However, according to the recent development of the domestic and international packaging market, it can be seen that screen printing has appeared in the field of anti-counterfeiting packaging printing. With steady growth, screen printing has occupied an extremely important position in the packaging and printing market with its own characteristics. Wrinkle ink is born in this trend. The ink is printed on substrates such as gold cardboard and silver cardboard. After being wrinkled and dried by UV, it will produce a special wrinkle effect on the surface due to UV wrinkle ink. With three-dimensional strong, luxurious and elegant, ink film full and good visual effects and other characteristics, its application has expanded to print high-grade tobacco packets, wine boxes, gift boxes, health products packaging boxes and other fields. However, in the actual printing process, due to the short time available for this ink, the widespread application and lack of research and discussion, UV-wrinkle ink printing quality will be affected by many factors, such as the number of screens, Stretching angle, printing pressure, squeegee angle, printing speed, drying speed, etc., if these factors are not well controlled, will inevitably affect the quality of the final product.

In addition, UV wrinkle inks are difficult to get the desired wrinkle effect after printing. This is the biggest problem encountered in UV wrinkle ink printing. Any change in the parameters during the printing process may cause printing failure. This requires a lot of experiments to determine the quality The printing conditions required for the prints.

1. experimental method

In the initial analysis of the factors affecting the printing quality of UV wrinkle ink (screen mesh number, stretch tension, stretch angle, emulsion thickness, printing pressure, printing speed, blade angle, mesh distance and drying speed), Crude experiments were carried out to determine the most important influences and determine the general scope. Then the optimal design was carried out to determine 16 sets of printing solutions. The final fine test was used to obtain prints and the conclusions were reached through analysis and evaluation of prints.

2. experiment procedure

2.1 Crude Experiments 2.1.1 Specific Experiments The main purpose of the crude experiments was to screen the main factors and determine the general scope of the main factors.
The mesh parameter is set to 150 mesh;
The maximum pressure of the air pump used in the experiment was 1 Mpa, and the empirical value range during use was 0.6-0.8 MPa, so the experiment was selected to be 0.7 MPa;
At present, the commonly used methods for coating photosensitive adhesives in screen printing enterprises are three-time printing on the printing surface and one-time coating on the backside. Therefore, the printing surface coating is set to 3 times.
Coarse experiment (1): Determining the range of wrinkling speed Fixed stretch net tension, blade angle, printing pressure, printing speed and web distance, and determine the wrinkling speed range through experiments.
Coarse experiment (2): Determine the net distance range of the fixed stretch net angle, the scraper angle, the printing pressure, the printing speed and the wrinkle speed, and determine the range of the net distance by experiment.
Coarse experiment (3): Testing the effect of printing pressure on the printing effect Fixing the stretch angle, blade angle, wrinkle speed, printing speed and mesh distance, and determining the effect of printing pressure on the printing effect through experiments.
Coarse experiment (4): Determining the effect of printing speed on the printing effect Fixing the stretch angle, blade angle, wrinkle speed, mesh distance and printing pressure, and determining the effect of printing speed on the printing effect through experiments.
Coarse experiment (5): Effect of the test blade angle on the printing effect Fixing the stretching angle, printing pressure, printing speed, creping speed and mesh distance, and determining the effect of the doctor blade angle on the printed product through experiments.
Coarse experiment (6): Testing the influence of the stretch angle on the printing effect Fixed printing pressure, printing speed, creping speed, mesh distance and squeegee angle, and the influence of the stretching angle on the print quality was determined through experiments.
Coarse experiment (7): further testing the influence of stretch angle on printing quality. From the rough experiment (6), it can be seen that when the stretch angle is 45°, the moire is the most severe; when the stretch angle is 60°, 75° The tortoiseshell pattern was also severe; when the stretch angle was 30°, no moire was observed. In order to determine the further extent of the stretch angle, the experiments listed in Table 7 were performed.

2.1.2 Rough experiment conclusion

(1) Screen mesh number

The higher the precision required of the print, the higher the number of screen meshes, and vice versa. In the selection of screen mesh number, manufacturers recommend the use of 100, 150, 200 mesh screens. If the precision of the printing equipment is high, meshes with a higher mesh number can be properly selected. At the same time, taking into account the limited experimental conditions, the mesh size selected for this experiment was 150 mesh.

(2) Tensile web angle experiments showed that the stretch angle was 0°, and the print did not produce moire; when the stretch angle was 30°, the moire was lighter; when the stretch angle reached 45°, the moire was most severe; When the angle is 60° or 75°, the print produces a lighter moiré pattern.
In a further experiment, it was confirmed that no moiré was produced when the stretch angle was 10°, 20°, and 25°.
Therefore, in the following fine experiment, the range of the stretch angle is set between 0 and 30°.

(3) When the net distance is within 5mm, the image can be fully displayed on the substrate; and when the net distance exceeds 5mm, the image displayed on the substrate will become less and less as the net distance increases.
And because the minimum value of the pitch adjustment in this experiment is about 1.5mm. Therefore, in the following fine test, the setting range of the mesh distance is 2 to 5 mm.

(4) The printing speed The change of the printing speed cannot bring about the change of the quality, only can change the size of the ink wrinkle pattern. The printing speed is fast, the pattern is small; the printing speed is slow, and the pattern is large.
Because the size of the pattern is not included in the scope of the quality evaluation, the factor of the printing speed is not considered in the precision test.

(5) The change of the angle of the blade angle of the blade can not change the quality of the printed material, only changing the size of the pattern. Scraper angle is small, pattern is small, on the contrary, the pattern is large.
Also because the pattern size is not included in the scope of the quality assessment, the scraper angle is not considered in the precision test.

(6) Ink wrinkle, drying speed Crease speed is too slow, and the print cannot wrinkle. Experimental measurements When the wrinkle speed is less than 14m/min, the ink cannot wrinkle. When the speed reaches 14m/min and 14m/min or more, the ink will wrinkle.
Therefore, the range set in the precision test is 14 to 20 m/min.