Talk about color screen printing

Screen printing, if it is limited to printing simple lines and words, cannot meet people's increasingly demanding decoration requirements. Today, screen printing has begun to go into the color field. Needless to say, it is common for color printing on special substrates such as plastic bottles and metals. The main difference between color printing and general line text printing lies in the dot. This is no different from other printing techniques. The standard of evaluation is to see if the original manuscript can be restored.

1 sample analysis

Customers often provide samples for manufacturers to design solutions. He simply explains his intentions to you and most tasks are done by you. It is important to understand his intentions. The cause of many disputes is that you do not really understand his true ideas. You also need to figure out the type of sample materials and determine the printing process. Sometimes customers know the type of material, but most of the time they do not know it, you can identify it based on your own judgment. The type of material also determines the choice of printing parameters, such as the number of screens, the number of screens, prepress, and the hardness of the squeegee.

2 Select ink

Choosing ink is difficult and simple. You may be well-versed in the suitability of inks for printing materials, and knowing how well inks containing resins are compatible with the substrate. However, the division of labor in society doesn't care much about how much you understand. You can always choose according to the information provided by the ink manufacturer on hand. You only need to verify the authenticity of the data. In most cases, the ink may be suitable, but there are exceptions in some special circumstances, you may wish to prepare more ink for testing.

The choice of the ink is firstly understood theoretically as a simple matter, and the key is to test according to the existing ink type. Silk screen printing ink mainly has the following brands. COATES is a famous ink brand produced by Coats Brothers in the UK. It has established the authority status of solvent ink in long-term production practice. As an environmentally friendly product, you must be familiar with Dolby's Dolby UV ink. Although Dolby Company is not big, UV ink is the leader. From the initial screen printing ink and pad printing ink to UV credit card ink and offset printing ink, Dolby has a good performance. Apollo ink is known for its bright colors, and it has been widely praised for its current ink type and adaptability. If you want to print on metal products and glass products, the first choice of Apollo ink, the quality of the German ink has been the best in the world, the leading level of the printing process has created excellent system quality, which of course includes the ink resin and pigment At present, German ink still maintains the world record of fineness and adhesion. In the special printing field, you cannot but pay attention to the Marabu ink of Malay Bao. “Supreme” is a special ink developed by Henghui Industrial Co., Ltd. for the development of the mid-range market. We respect quality, but we value it more. The plastic prints printed with it even made you suspect that it was printed with European inks.

3 consider the curing process

The vast majority of inks used in plastic substrates are volatile dry. After the solvent contained in the solvent ink is volatilized, the ink is fixed on the substrate. However, some printing needs drying equipment drying, ink can be dried, especially involving metal, ceramic, glass printing, drying equipment generally required. It is important to configure the drying device. For printing with UV inks, curing equipment and equipment must be taken into account. UV inks do not contain solvents and can only be cured under UV light. Both drying and UV curing machines can dry quickly. The degree of curing is too low, the ink ink layer will show poor adhesion, and the gloss is also very poor; if cured excessively, the ink film layer will be brittle and easily cracked and deformed.

4 About the printing sequence

The color prints reproduce the rich color and layer information of the original by superimposing the four primary colors. In theory, the complete transparency of the ink can ensure the true reduction of the colors. However, the ink is composed of the resin binder and the pigment, and the resin cannot be completely transparent. The pigment itself also has a certain hiding power, and these factors ultimately affect the color.

The order of the stacking is related to the transparency of the ink. The transparency of the ink is not high hiding power, should be printed. The first yellow ink was the least transparent, and the yellow ink should be printed first. Now the situation has changed, and the yellow ink has little relation with India. Theoretically speaking, in addition to the differences in hue, the four primary inks should be the closer to better the other indicators. The fact is another situation. The saturation of cyan has a great influence on printing color, and the saturation of cyan is high. It tends to cool, so when cyan saturation is high, cyan can be placed in a slightly earlier color sequence. The role of black is to increase the outline of the print. If the graphic requirements for contrast are high, the black is printed last. The density of black is also influential on the printed matter. Excessive density will cover some layers, so the darker black ink can be printed on the first color sequence, and the darker black ink on the final print.

5 Determine the number of screens

The higher the number of screens, the more layers can be reproduced, but the excessive number of screens will make screen printing difficult. To determine the number of screens, we must first consider the visual environment, that is, from what distance to observe the image, the visual distance should be the most basic criteria for determining the number of lines. The closer the visual distance is, the higher the number of screen lines can be, which can improve the clarity. The farther the visual distance is, the lower the number of screen lines is, which can reduce the printing difficulty. Sometimes customers do not understand the characteristics of screen printing and blindly require unnecessary screen lines. You should persuade him to change his mind. The scope of screen printing is usually below 80 mesh, and printing with a high number of screens in the high light area will result in the loss of dots and the details cannot be reproduced. In addition, the high number of screens will make it difficult to select screens. According to the usual selection method, the number of screen meshes should be 4 times the screen number of the printing film. Excessively high number of screen lines will cause the ink layer to be too thin, and the contrast of the graphic and text will be reduced. This will also affect the expressiveness of the image.

With the increase in the number of lines, the size of outlets continues to decrease until outlets cannot be printed. Screen printing does not duplicate 3% to 98% of outlets like offset printing. It strictly means that only 15% to 85% of outlets can be copied. If the number of outlets is higher than 15%, the number of outlets less than 85% will be changed. In fact, for very fine-grained manuscripts, scanning into the computer requires gradation correction and gradation compression to be restored. Compressed image highlights and shadow points are easily reproduced at a given number of lines. Of course, the tonal range transition compression can cause some loss of detail in the image.

6 determine the film output resolution

If the output resolution (dpi) is set too low, the film will appear jagged. If the resolution is too high (the number of lines does not change), the level of the printing film will be more abundant, but the number of gray levels will increase exponentially. The copying ability of web printing is limited, which makes even screen printing impossible. Practice has proved that screen printing is difficult to copy over 100 lines of printed matter. Of course, the development of technology has driven the progress of screen printing. This conclusion is not absolute either.

7 Select the screen

The screen should have a consistent number of lines and a uniform tension in the latitude and longitude direction, otherwise it will cause moire and overprinting. Wire mesh parameters should include wire diameter, screen mesh number, tension curve and screen thickness.
(1) Rough screen printing chooses low-mesh screens, fine graphics and hierarchical printing to select high-mesh screens;
(2) The number of screen meshes should be matched with the number of screen printing screens for soft printing, and the screen mesh number should be 4 times of the number of printing screens.
(3) For UV inks, the screen mesh number should not be too low considering the curing effect.
(4) Fine graphic printing and gradation printing preferentially select dyeing screens, and the resolution of dyed screens is much higher than that of white screens.
(5) Selecting the Mesh Calculator helps you to get data support and can determine the relationship between the number of static screen meshes and the number of dynamic screen meshes.

8 Setting the press stroke

First, install the substrate, and then use the hand to hold the scraper to move on the surface of the substrate. When the position is proper, the stop can be fixed. For curved screen printers, the stroke of the adjustment screen should exceed the circumference of the plastic bottle. Proper journey saves time, increases printing speed, reduces inconsistencies to ink, and can print good dots.

9 Select squeegee

Generally the length of the scraper is about 5~10mm longer than the image length. The choice of squeegee involves both hardness and shape. The harder squeegee enables very fine graphic and gradation printing; the softer squeegee is suitable for printing substrates with very rough surfaces and the printing ink layer is also thick. Curved printing often uses a sharp scraper. Plane printing often uses a scraper with a rectangular cross section.

10 Select a frame

Aluminium products are preferred for frame materials. They are lighter and have higher strength. They are suitable for printing hierarchical images. Especially for four-color printing, mesh frames with good rigidity must be selected. There are many non-standard frames used in the special printing industry. , This is because of the strange shape of the special printing substrate. It is very important that many specially-made screen frames can not be restricted by the screen printer when completing the screen printing task. One important aspect of selecting the screen frame is to maintain tension in the printed image area.
The manufacture of the frame is also an aspect to be considered. The frame should be as hard as possible, with good resistance to bending and distortion.
11 Determine the net distance

The net distance is the distance of the screen from the surface of the printing material. Setting the net pitch too large or too small will change the size and accuracy of the image.

No matter what the tension is, high mesh distance will cause the image to expand. Under greater tension, the separation of the screen from the substrate is faster than the speed of the blade, which will cause deformation of the blade. Excessive net distance is also very bad for screen damage. Bonded pulp is not impeccable. It may also fall off due to excessive tension.

Too low grid distance will cause the screen and the substrate to be difficult to separate. The separation speed of the screen and the substrate is slower than that of the squeegee. It will leave a net mark and cause dirt. The correct distance between the screen and the substrate should ensure rapid separation of the screen and the substrate. The selection of the mesh distance is related to the screen tension. The high tension screen can select a lower mesh distance, and the low tension screen should select a higher mesh distance. Generally, this data is between 2~3mm.

12 Printing

Color screen printing should first pay attention to the problem of overprinting. Only accurate printing can obtain good prints. To achieve accurate overprinting, first the screen plate tension should be basically the same, the error is less than 1N/cm. The tension of each plate was measured with a screen tension meter and should be kept at 18 N/cm. The unity of the positioning device is very important, each substrate must have the same position in the printing, otherwise it will cause overprinting is not allowed, four-color printing ink is four primary colors ink, choose to meet international standards