Disc four-color printing - screen printing (four)

5. screen printing:

The screen printing of optical discs is performed on a dedicated automatic multicolor disc screen printing machine. The ink is a UV (ultraviolet) curing ink. Therefore, there are several stations for the special screen printing machine for discs. For example, the six-color printing press has 32 stations and is closed. Each station has 80W/cm~120W. /cm UV (ultraviolet light) curing device (UV lamp and light reflector), when the ink is silk-screened on the disc, then the ink is dried by the UV lamp. Therefore, special printing optical disc screen printing machine, once the end of pre-press debugging can be fully automatic printing, printing 1000 ~ 3600 times per hour or more.

1) Projects that need to be debugged before screen printing for special optical discs include:

a. Adjust the distance between the four printing colors of the net template and the optical disc (called the static net distance) and achieve the same. The grid distance is controlled at a value of 1~2 disc thicknesses; not only that, the retina version must be fixed firmly and stably; otherwise, After silk screen printing, a mark consistent with the blade of the squeegee will be produced on a certain position of the optical disc;

b. Adjust the suitable squeegee pressure of the squeegee and the squeegee angle of the squeegee. At the same time, the contact state of the ink squeegee and the stencil should also be adjusted so as to ensure the uniformity of the ink on the stencil and the stability of the squeegee process.

C. According to the requirements of each printing color, the hardness of the squeegee can be changed from 80 to 90 degrees. For example, in VCD and CD discs, the printing of color blocks or bottoming white ink can be selected with about 80” right-angle squeegee, and the same template can be used with more than 140 mesh/cm~180 mesh/cmPW, PET screen, and the resolution is high. The dot printing is printed with a 90" hardness squeegee. No matter what, the squeegee blade must be strictly flat, straight, and smooth. Otherwise, uneven, curved, blunt, and hairy marks can reflect the ink being printed. Deviations from the text.

2) To prevent moiré, the angle between the screen angle and the dot line should be reasonably matched. The color of the four-color positive negative film is generally Y- 0°, C- 15°, M-75°, and K-45°. It should also be properly adjusted according to the characteristics of the printed graphics and texts: for example, mainly people, mainly Highlight the character's face, so Y-0°”, C—15°, M-45°, and K-75° arrange Y and M by 45°, which highlights the ruddyness of the face; When the theme is Y - 0 °, K - 15 °, C - 45 °, M - 75 °, the C is set to 45 ° to make outdoor scenery better, the picture is more realistic.

3) The color sequence of CD-ROM screen printing is commonly used C-M-Y-K.

4) Screen printing ink:

a. UV ink color density adjustment:

The better ink color purity is high, transparency is good, and has good thixotropic properties and moderate UV curing. In general, the ink can be used directly without adjustment. However, due to the four-color UV ink on the disc, due to the large number of brands on the market, the quality varies, and four-color overprintable special ink, the optical disc factory still needs to color, therefore, the need for the ink viscosity color density, concentration Even the special color is to be adjusted or the dots on the disc will be affected by the difference in the ink's color density and viscosity, and the printing effect will be biased. For example, Y and M in the three primary colors should be red (R) if they are superimposed in equal proportions, no matter who overprints them. However, due to the ink's own density, darkness, and brand differences, it sometimes appears as reddish or yellowish red. Therefore, we must adjust the color density of the inks appropriately. Methods are: You can change the printing color sequence test printing, or when the color sequence is fixed, when changing the order of the printing color, then you should change the color density of the overprint ink, so that the color density decreases, the transparency of the ink increases. The method of changing the color density of the ink is to add the gloss oil (colorless ink) of this series of inks to the source ink. The amount of varnish added is determined by the color density of the color ink. In summary, when adjusting, the varnish is added to the color ink while stirring, and the amount of varnish that has just been added to the color ink but has not changed the original color is added. Stop immediately and you can use it.

b. The ink particles should be fine and uniform, and the pigment particle size should be 1/3~1/4 of the mesh opening. Therefore, the ink used must be able to pass through the mesh mesh used well, when the color particles are fine If it is not even, or does not match with the screen, the color difference will be produced at the beginning of printing and after printing to a certain number of discs, which is common in optical stack printing plants.

C. Requirements for UV screen printing inks:

UV inks used in CD, VCD discs, in addition to the above requirements, the ink should also have good adhesion with PC (polycarbonate) materials, if used on DVD discs, when dealing with writing/reading, the laser deflects the beam The tilt angle (in the direction of the radiation can not be greater than ± 0.8 ° or along the tangential direction does not exceed 0.3 °), so the shrinkage of the ink and ink after drying is small; so as to ensure the flatness of the disc: At the same time, the ink layer printed on the DVD disc is required to be thin and uniform, so as to minimize the impact of the IR component in the UV on the flatness of the DVD when the UV is rapidly cured. To print a thin, even layer of ink on a disc, the ink must have a high color density and the thickness of the photosensitive layer on the stencil should be controlled.

d. Photo-curing basic conditions for UV inks for optical discs:

Fast UV curing under low power, especially for UV ink on DVD, usually about 1 second for 80W C power. If UV ink requires >80W/cm for UV irradiation on CD printer Prolonged time can not reach the bottom of the ink layer curing, while extending the curing duration even if cured, but the UV exposure of the disc at the same time, IR in the UV also radiates on the disc, which is subject to optical discs, especially DVD performance constraints;

Because UV inks are required to be cured at low power, the printing environment, especially over the stencil, should avoid the direct exposure of white “harmful” light, resulting in a chronic photocross-linking reaction of the ink on the reticular film, making the beginning of printing the graphic. , Hue deviation in the end, the final difficulty in ink;

The conditions of the printing environment: UV light-cured inks are subject to changes in temperature, and the ink's viscosity also changes. At high temperatures, the viscosity of the ink drops, and the printed ink layer is thinned and the hue is shifted. At low temperatures, the viscosity of the ink is increased and the printing ink is thick and dark. Therefore, when printing UV inks, the temperature of the printing environment should be controlled to be 18~25, and about 23aC is appropriate. The relative humidity is about 65%. When the humidity is high, the ink will become sticky and gel, so the printing environment is warm and humid. When stable, the viscosity of the UV ink is also stable, the viscosity is stable, the thixotropy of the ink is relatively stable, the printing adaptability of the ink is good, the ink layer is suitable, and the printing quality is easily ensured. Therefore, the fine graphic color UV ink Printing must provide constant temperature and humidity in the printing environment.

At present, UV screen printing inks used on optical discs include domestic Fuji ink, French Dolby ink, Selenium disc series ink and German RVCO (Digo), etc., which are printed on CD-R, CD, VCD and DVD respectively. Special silk/offset UV ink meets requirements.

Source: CD production network