Third, the screen printing of optical discs and the selection of screen printing equipment:
1. Screen
In the screen printing of a disc, it is very important that the parameters of the screen and the selection thereof play a role in reproducing the color picture of the disc and that little or no noise is generated. As we all know, screens used in four-color dot printing should have a high mesh number. A high-strength, low-extension, large-opening, plain-weave yellow polyester mesh is used to make the stencil because the screen stencil produced with this stencil ensures high tension and has good tension stability. When printing, The ink can be quickly leveled after it is transferred to the disc, which helps reduce the appearance of the texture and makes the color graphics more delicate. The purpose of using a yellow silk screen is to ensure that when the net stencil is produced, the photo-textured edge film does not deform due to halation, and the distortion of the dot is avoided.
The four-color screen printing of optical discs is also in accordance with the rules of color dot screen printing screen selection: the number of dot lines: the number of screen meshes 31:35, can reduce or avoid the "moiré" in printed graphics. The number of meshes usually used for CDs is 140~165 mesh/cm plain woven wire mesh to print color images with dot line number of 40L/Cm or more, in which the mesh size is 150 mesh/cm, and the mesh diameter should be selected as 31u and 34u, use this screen diameter, you can help ensure that the screen template tension in the 20N/cm ~ 26N/Cm high tension printing, resulting in high-quality printing graphics. The screens that can achieve this kind of tension of the screen template are: Swiss-made PET1000 and exemption-free PET1500 series screens, and NBC's EXSCREEN-series screens. However, it should be noted that because the wire diameter of the NBC mesh is larger than that of the SEFAR mesh wire in the same mesh series, the tension of the NBC stretch is relatively higher than that of the SEFAR mesh. This is because when the PET wire is used When the wire diameter is doubled, the tensile strength (tension) is increased by a factor of four. However, when the net is stretched, the diameter of the net wire cannot be increased simply by pursuing high tension. If the diameter of the net wire is increased in the same number of screens, the same hole is reduced, and the same hole is reduced and the impact is reduced. Ink volume and ink performance. Therefore, in the specific use, reasonable matching should be based on the requirements of the fineness of the optical disc graphic.
Here it is clearly stated that the technical parameters of the screen in screen printing:
a. The mesh number of the screen: it determines the fineness of the print graphic, determines the stable tension value of the stretch net, and also determines the amount of ink (volume) at the time of printing. It also determines whether the text may be generated in color dot printing. The size of the moire and its moiré. The unit is based on several filaments (or a number of cells) per inch of length or per inch of length, 1 inch 2.54 cm;
b. The diameter of the wire: it affects the tension of the stretch net and the width of the opening of the wire mesh, that is, in the same number of meshes and under the same weaving method, the filaments. The diameter of the wire is smaller than that of the thick wire, and the width of the opening is large, so the amount of ink is large. Therefore, the use of the same mesh and the use of different wire diameter of the same weaving method of the screen, you can change the depth of color printing graphics to achieve the purpose of printing graphics hue;
C. The theoretical ink volume of the screen: Determine the thickness (volume) of the ink on the substrate. In color dot printing, it affects the depth of the color and the degree of hue reduction and color shift, etc. Provide the calculation basis for the amount of ink required for each batch of prints;
d. Tension: The tension of a screen is determined by the mesh size of the screen, the diameter of the screen, and the weaving method. Whether the tension is reasonable or not determines the service life of the screen template and screen printing quality. When the size of the tension is not printed (static), the distance between the screen template and the substrate is determined, which is called the network distance, and the high tension must be adjusted to be low. Net distance printing, the resulting image and text location accuracy is high. Therefore, before the printing, the screen template should reach the optimal tension. During the whole process of printing, the tension of the screen template is stable, and the stable tension must also be ensured by the best network distance. Only in this way can the printing quality and service life of the screen template be guaranteed. The best tension here refers to the tension at the same time, so that the screen retains a certain amount of elasticity, this elastic allowance ensures that during the whole process of screen printing, the scraper (squeegee) scrapes the template at the moment. The net template can immediately shoot away from the substrate. Otherwise, not many pieces can be printed. The tension of the same template is reduced. The screen quickly changes from the elastic deformation to the plastic deformation and changes the original tension value. There will be bars in the disc printing. Traces, patches, and shades of color are inconsistent. At the same time, the same static mesh distance must be set under the optimal stretching tension. That is, during the entire printing process, the screen plate can always stabilize the rebound distance, so as to ensure the quality and long life of the network template. .
If the tension value of the stretch net is optimal, and the static mesh distance is set unreasonably, if the mesh pitch is low, the squeegee, the screen, and the substrate cannot be in contact with each other, and at this time, the stencil rebound during the printing process is not In time, it is prone to image smearing, ghosting, deformation, etc. If you set the static network distance higher than the optimal network distance? The best tension of the stencil is destroyed, especially when the printing is dynamic, the tension of the stencil under the scraping pressure of the squeegee will be very large, and the wire will be stretched beyond the limit. The initial stage has not found that the printing is not good. Phenomenon, just to increase the scraping pressure of the scraper can complete the transfer of the graphic, but as the printing continues, the net wire is stretched over the limit and fatigue, it will inevitably produce the tension on the screen gradually changes. ]. With the increase in the number of prints, there will be quality problems such as inaccurate positions and deviations. When the net distance is so large that the mesh can no longer be stretched. The end of the life of the screen, the screen collapsed.
Therefore, the four-color printing of optical discs requires the same version to be printed under high tension and low web distance. Therefore, the tension of the stretch net and the setting of the static mesh distance before printing are very important. Unreasonable mesh distance must not be arbitrarily pursued from the characteristics of the screen to high tension, even if the other fine screen printing is also the case, otherwise it is just the opposite. Seen from this truth. The screen brand chosen for CD-ROM screen printing must have high tensile strength, and the low-extension characteristics are particularly important.
e. The color of the screen: The screen printing of the optical disc, the majority of the screen template production use the direct method photoresist and the capillary photosensitive film whose spectral wave wavelength is 330~400um. Therefore, the screen template is made of yellow or lemon yellow PET. Screen, because the yellow wavelength of the spectrum is 550 ~ 600nm, so the screen plate with yellow screen in the printing process, due to the screen (anti-fold) shot on the photosensitive film layer does not need exposure, The wavelength of this light is far away from the photosensitive wavelength (365 nm peak) of the photosensitive film, and the haze phenomenon of the photochemical adhesive reaction rarely occurs on the photosensitive film layer that does not require exposure, and the photographic film is kept transparent during the printing. More than 99% of the sensitive light was irradiated on the photosensitive film on the non-image area, so that the image points on the film were uniformly reproduced with the photographic film. Therefore, the use of yellow light between the printing plate for lighting, in the printing process does not affect the photosensitive film, compared with the red light is not easy to fatigue people, at the same time when the printing plate to see clearly, and people Eyes feel comfortable.
f. CD-ROM screen printing should use monofilament, plain weave to produce a film version: because the mesh of the plain-weave woven wire mesh is woven one by one, compared with the two-two-under-two or one-two-under-twist woven wire mesh The node area between the plain weave mesh radial and the weft meat is twice or one times smaller than that of the twill, so the ink made by the plain weave mesh can be printed smoothly and the ink can be very quickly leveled on the optical disk. , so ink is not easy to produce net marks, while high-profile outlets are not easy to lose, which is good for optical disc fine graphic printing.