Screen printing 1000 questions (58-62)

â–¼58. What issues should be noted before printing?

Apart from making preparations before screen printing, other related issues should also be noted. Precautions should be taken from the following aspects before printing.
1 Printing site cleaning Screen printing With the continuous improvement of printing accuracy requirements, especially high-precision printing of printed circuit boards, electrical components, and so on, the environment has also put forward higher requirements. General requirements The printing shop and Plate making shop must be clean and there is no dust in the air, otherwise it will affect the printing quality. For workshops with high requirements for printing accuracy, air purification equipment must also be installed if necessary to keep the printing and plate making workshops clean.
2 Temperature and Humidity In spring, summer, autumn and winter, the temperature and humidity in the four seasons change greatly, and the impact on printing accuracy is also relatively large. Especially for multi-color overprinting, the effect is more obvious. Therefore, indoor humidity and temperature must be relatively stable. And according to the seasonal changes in the indoor temperature and humidity properly adjusted to ensure the print size accuracy.
3 fully understand the nature of the substrate due to a wide range of screen printing applications, a wide range of printing materials, and the shape of the substrate is also different, according to the different requirements in the choice of appropriate ink and solvent and scraper.

â–¼59. What aspects of screen printing inks are usually tested?

Due to the wide range of screen printing applications, the requirements for screen printing inks are also stricter. Therefore, in order to meet the different requirements of printing products for inks, the following aspects of screen printing inks should be tested.
1 Adhesion Tested to determine the degree of ink adhesion on different materials.
2 Flexibility The fastness of adhesion of the ink to the substrate material is checked by the resistance test.
3) Resistance to rubbing and rubbing The rubbing resistance is mainly performed on the printed surface of materials such as cloth, paper and film to test the degree of adhesion and firmness of the ink to the printed material.
4 After the printing surface of the abrasion-resistant cotton cloth is exposed to sunlight, the cotton cloth is rubbed for a certain number of times to check the degree of contamination of the cotton cloth.
5 Weather resistance Weather resistance also contains light resistance. Weather resistance is usually placed outside the print, the wind and sun, rain and other tests to test the printed pigment discoloration, bleaching degree and decomposition of the printing ink film, discoloration and so on.
6 heat resistance, cold resistance Because some prints to use at different temperatures. Therefore, some prints are processed by high temperature after printing, and some prints are subjected to low temperature processing after printing. Through the heat resistance and cold resistance test to test the ink at different temperatures.
7 Hot water resistance The hot water resistance test is usually to add a certain amount of warm water to the printing surface per unit area for a certain period of time to test the degree of contamination of the water. In particular, the extent to which the pigment in the ink is soluble in water is observed to determine whether the ink is suitable for the printing of food utensils and toys.
8 Oil resistance Oil resistance refers to the suitability of oils and fats, mechanical oils, etc., which is different from solvent resistance.

â–¼60. What are the characteristics of color screen printing?

Compared with gravure printing and offset printing, color screen printing has the following features in addition to the characteristics of screen printing itself.
1 has a very strong expression, colorful, strong three-dimensional.
2 has a strong light resistance, drug resistance, durability, long-lasting use, without fading, especially in the screen printing on plastic sheet substrates this feature is particularly prominent.
3 The cost is relatively low.
In addition to the above advantages, color screen printing is also unsatisfactory. This is the reason for considering the factors such as matching of photographic screen lines and screen meshes, screen angles, etc. in color screen printing. A certain degree of difficulty.

â–¼61. Color screen printing color sequence is how to arrange?

Color screen printing color sequence arrangement is generally yellow, cyan, magenta, and black. Taking into account the process requirements, the order of the colors is also cyan, magenta, yellow and black. In foreign countries, black, yellow, magenta and cyan are also used for printing color sequences. Since the shapes of the substrates in screen printing are different (planes and curved surfaces) and the nature of substrates is different, the color sequence is also different. For example, When printing on transparent objects, the color sequence should be black, yellow, cyan, magenta. The arrangement of the color sequence has an important restriction relationship to reflect the original color. How to ensure that the color of the copy is not distorted, in addition to the correct use of the ink, it also requires long-term work practices and experience accumulation, to constantly explore and summarize. Determine the screen printing color sequence to consider two factors, one of which is the transparency of the ink on the substrate, which is the main factor in the two factors. Since in the screen printing, ink of a new color is produced by mixing or superimposing inks of various colors, if the transparency of the ink on the substrate is poor, the ink of the first color will be covered when the second color is printed. It cannot be combined with the second color to create a new color. The second factor is that people’s eyes have different abilities to experience various colors. In general, people's eyes are most sensitive to magenta, followed by cyan and least sensitive to yellow. Because people have different color sensitivities, it often results in the expansion or reduction of yellow dots, the loss and the change in the size of ink, which can affect the printing quality.
The correct screen printing procedure and requirements are that the first color should be printed with a cyan version, and after printing, a contrast check of the gradation reproduction shall be performed with a step scale and a color scale. The second color is printed with a yellow printing plate, so that the two colors are laminated to form a green color, and then the human eye's ability to recognize the green tone is used to check the print quality against the scale and the color mark. The third color is printed in red, and the black version is used last. The black version enhances contours and dark levels. After the four-color version is printed, the same color copy as the original is obtained.

â–¼62. Color screen printing should pay attention to what issues?

Color screen printing should pay attention to several issues, as described below.
1 Use a strong, non-deformable metal mesh frame for color screen printing. This is because if an unsturdy frame or a wood frame plate is used, skew or deformation is likely to occur during printing, the quality of the screen plate will be reduced, and accuracy will be difficult to guarantee. When the deformation is severe, the screen plate cannot be used. This will affect the print quality. So you must use a sturdy metal mesh frame. The frame size of a set of color screen printing plates should be the same. Mainly for printing with a unified positioning rules, and easy to color printing. The number of screen meshes of a set of color screen printing plates should be the same as that of the screen materials, and the tension of the stretch net and the thickness of the screen plate should be the same. It is mainly to ensure that the ink layers after printing of different colors are uniform and have the same effect, and the original colors and graphics are perfectly reproduced.
2 The use of scraper hardness is generally 70 degrees Shore hardness. Scraper edge accuracy is high. Due to its moderate hardness, it is conducive to meeting printing requirements, facilitating the improvement of printing accuracy and ensuring the printing quality.
3 The screen printing ink with high viscosity should be used as much as possible. The ink with higher viscosity will not cause the problem of thickening of the graphic lines due to the diffusion of oil, which will help to improve the fineness and sharpness of the lines.
4 Photo-screen plate screen number (line / inch), usually between 55 ~ 120 lines. This can reduce or avoid moire.
The general relationship between the number of screens and the number of screens is: screen (number of lines): 4.2X screen number.

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