Talking about the technology of printing on the disc network

Optical disc screen printing is the process of transferring ink to the substrate (disc surface) by means of a squeegee press and squeegee printing plate to form a graphic ink trace. Since the screen is a support, the screen production is of utmost importance.

1 Reasonably choose the tension of the stretch net

The important parameters for screen printing are the number of screen meshes, the diameter of the screen, the screen thickness, the size of the openings, and the amount of ink under the screen. The screen diameter, number of screens, and the weaving method of the screen and the selected materials directly affect the stretch net. The tension is measured according to these parameters on the tension of the screen during stretching. When measuring tension, the measured tension point should be 10 cm away from the inner frame of the frame, otherwise the measured tension is inaccurate. Tension can be divided into the warp and weft tension. The tension in the warp direction is the tension in the winding direction of the entire roll. The tension in the weft direction of the screen is the tension in the direction of the screen width. The size of the tension has a direct impact on the quality of the screen. Higher tension screens use a lower screen pitch. Less pressure can be used in the printing process. The screen wear is reduced, and the service life is prolonged. At the same time, a small pressure helps to prevent the ink and deformation around the screen points and improve the network. The sharpness of the edges guarantees the printing effect. When the net distance increases by a factor of 1, it will increase the distortion of printed graphics by 3 times. When the screen plate tension is low, the ink is uneven and the dots are distorted, affecting the hue. Uneven tension in the screen will cause the ink layer thickness to be uneven, the pattern text will be distorted, the local image will be blurred, and the dots will be deformed or misaligned when the dots are printed, resulting in color shift. However, various specifications of the wire can withstand the maximum value of different pull, if the value exceeds the maximum set value, the screen will lose elasticity, called plastic deformation or broken net, should pay attention in the stretch net.

2 The correct use of the frame

The material, cross-section size, shape of the frame, and the flatness and strength after processing directly affect the tension of the screen and the stability of the tension. The mesh frame must be deburred on the adhesive mesh surface and its periphery before use. The reusable frame should be cleaned with solvents such as acetone to remove any residual ink, glue, or mesh debris from the surface of the frame. Before the stretching of the net, pre-apply a layer of sticky net glue (see Fig. 1) on the net surface of the frame. When sticking the net, apply a layer of glue on the screen. Note that the glue must penetrate the side of the surface of the screen. Within the mesh, the screen is completely bonded to the frame. When necessary, when the glue is not completely dry, use a squeegee to scrape and press the fitting surface to help the wire mesh completely adhere to the frame.

3 Stretching method

(1) Standard stretch net

Tear off the unsmooth end of the wire mesh, insert the same amount into the chuck, lay the wire mesh, clamp the other end of the wire mesh, and finally clamp the weft edge into the mesh clamp. tension.

Pull the warp net to 1/2 of the required tension value, and then stretch the weft to make the tension close to the required tension value. At the same time, adjust the weft and warp tensions so that they all reach the required tension value, and remain still for 10 min. So that it fully releases the stress (Figure 3). Ten minutes later, the tension in the warp and weft directions is adjusted to reach the required tension, and it is left to stand for about 10 minutes. This operation is repeated twice. Then the photosensitive adhesive is brushed and the screen is glued on the frame to complete the whole stretching process. This method is a widely used standard stretching method.

(2) 30 minutes stretching method

Firstly, make the tension in the warp and weft directions reach half of the required, stabilize it for about 1 to 2 minutes, then pull the net, increase the tension to 80% to 90% of the required value, stop for 5 minutes, and then pull the net to reach the required tension. After the tension is stabilized for about 10 to 15 minutes, it is stretched again to the required tension value, and the mesh is then added after one more repetition to complete the stretching.

The following points should be noted during the stretching process:

● The maximum allowable gap between the chucks on the four sides of the stretching net is within 3 mm, so that all the nets are under tension and ensure that the nets are under the same force;

● One-to-one correspondence between the clamps on the side of the stretch net to ensure that the net mesh is close to a square when it is stretched, and the tension is uniform everywhere;

● The four corners have a proper stretch margin according to the size of the frame to minimize the possibility of screen tearing;

● The screen printing plate can be made only after stretching for 24 h because the tension of the high tension screen will decrease by 10% to 20% after 24 hours, and most of the tension loss occurs within the first 4 hours, and then it gradually stabilizes. ;

● Stretch net can be divided into straight stretch net and oblique stretch net according to angle. In order to make the edges of the printed lines straight and smooth, no jaggies are generated, and at the same time, moiré (grid lines and dot lines) are avoided during the plate making process. When the nets are stretched, the latitude and longitude lines of the screen and the corresponding edges of the frame are required. At a certain angle, this method is called diagonal stretching. There are various angles of the stretch net, and the general angle is 15°, 22.5°, 45°, 7.5°, 30°, and the like. Among these kinds of stretch angles, the edges of the resulting 22.5mm lines have better flatness and smoothness. The 90° stretch net is a straight stretch net, resulting in the worst quality of the edge of the line.

4 Web processing

The use of special grinding paste and degreaser to roughen the stencil to increase the porous and non-smooth surface and remove the oil stain on the surface and increase the bonding area between the screen and the photosensitive material, thereby improving the attachment of the photosensitive material to the screen Efforts will be made to increase the number of screen prints and reduce the number of pinholes on the screen photosensitive layer during the production process.

5 coated sensitized adhesive, sensitized film

Photoresist has good thixotropy, proper viscosity, certain solid content and good bridging properties. The photosensitive adhesive should be set up 12 hours in advance before use, and should be fully stirred and used only after 12 hours of standing still to prevent the bubbles generated during the stirring process from affecting the quality of the glue. The photosensitive glue application program wet-presses and wets the printing surface of the screen (Fig. 4) and the squeegee (Fig. 5) 1 and 2 times, respectively, and then the screen printing surface is laid flat and dried. The drying temperature is controlled. At 35-40 °C, the degree of drying is 80%. Wet-pressing and drying the printing surface of the screen and the ink surface respectively 1 + 1 times to scrape the glue, and then lay the screen printing surface down flat, the drying temperature is controlled at 35 ~ 40 °C, the degree of drying is 80%.

Finally, scrape the glue once on the printing surface of the screen, then dry the screen with the printing surface facing down. The drying temperature is controlled at 35-40 °C, and it is completely dried.

When drying the screens, the screened screens and the preprocessed screens cannot be dried in the same oven. The moisture content of the pre-screen screens is very high, and a large amount of water will evaporate during the drying process, thus mixing the photosensitive adhesives. The screen dryness is reduced and the drying time is extended. After the screen printing is coated with sensitized adhesive, it must be thoroughly dried. If the sensitized adhesive layer contains moisture, the moisture will refract the light when exposed, which will affect the degree of crosslinking of the sensitized adhesive. In addition, the sensitized adhesive is not completely dried. It will hinder cross-linking, which will lead to defects such as pinholes, stripping, and decreased adhesion of the adhesive layer and the screen, and reduced resistance to printing.

The first step is to pay attention to coating speed, because the coating speed is too fast, it is easy to produce pinholes; too slow, the glue can easily penetrate to the ink surface, and can easily cause uneven coating, so it should be at a moderately uniform speed. Coated photoresist.

When sensitized films are coated on coarse mesh screens, pinholes, etc., often occur. To avoid the occurrence of these problems, the photosensitive resists must be thicker. When the first coat is applied, the printed surfaces must be scraped back and forth several times to make The screen is fully wetted, and then the ink surface is squeegeeed. After drying, the squeegee is continuously applied 2 to 3 times on the printing surface, and the speed is slightly faster. The capillary photosensitive film should have a wide exposure latitude, high resolution, good solvent resistance and strong sticky network, good stripping recovery, and excellent storage stability.

Before applying the sensitized film, the screen must be properly screen-treated (grinding, degreasing, etc.), the film should be affixed to the wet screen, and excessive moisture should be removed with a squeegee to dry the web with the sensitized film. When the plate is selected, the temperature below 30 °C is selected to prevent cross-linking during the drying process. After the screen is completely dried, the back-protection film base is torn off.

6 screen exposure

The dried emulsion layer is exposed to UV light, hardening the uncovered area (polymerization), no longer water soluble, and the unexposed area is still water soluble, then rinsed with cold or lukewarm water Drop it.

Pre-exposure methods are used to determine the correct exposure time by using the exposure time measurement sheet to perform a graded exposure. The exposure time is insufficient, the photosensitive layer is thinned, pin holes are likely to appear, the edges of the graphic or wire are prone to jaggies, the resistance of the screen is reduced, the screen plate is difficult to recover, and the shadow on the screen that has been removed from the film easily appears; Excessive, graphic and textual distortion, thin lines will be more detailed, low-key network expansion, high-light network, narrow, difficult to punch, missed part of the residual glue, so that the ink but the mesh, the film becomes brittle, intolerant of India.

7 Development flush

After exposure, the screen should be washed and developed with proper pressure water. In particular, the ink surface must be fully cleaned until the surface is not slippery (see Figure 7). Use a soft, clean paper, a clean cloth or a water-absorber. Remove excess moisture, put it in an oven and dry at a temperature of 30 to 40 °C to prevent over-temperature deformation of the screen.

8 Complement

Use special seal material to repair the non-inking area or leak point (as shown in Figure 8), double exposure after drying, increase the screen strength, reinforce the screen with Silver Dragon tape, and make the screen The relevant data is recorded.

Reprinted from: Screen Printing