Demand for photosensitive resist inks in LCD graphic manufacturing (2)

5, exposure and special exposure equipment:

5.1 Selection of light sources:

1) The light energy emitted by the UV light is used by the photoinitiator, and the emitted spectrum should match the spectrum of the initiator. Mostly halogen lamps are used. The principle of the light emission is a high-pressure mercury lamp. The mercury in the vacuum lamp and the filling material are evaporated at high pressure to form a luminous body. The emitted spectrum can excite the initiator and photoreceptor in the ink, thereby forming cross-linking of the ink layer. Commonly used high-pressure mercury lamps are more common.

2) The efficiency of conversion of electrical energy to ultraviolet light is high and the amount of heat generated is small.

3) Light energy uses higher intensity. If the intensity is too low, free radicals are generated too slowly and oxygen is severely blocked, which affects the image quality.

5.2 Spectral Peak Matching and Selection:

1) Light source: In the ink supplier's technical data, the spectral value of exposure of the photosensitive resist ink is not provided, but the spectral range of all the halogen lamps and high-pressure mercury lamps is suitable for the exposure of this ink, but the difference in intensity.

2) High-quality polyester film is used for the exposure table. The thickness is 0.175mm. There should be no scratches and scratches. The transmittance of UV is excellent. When the spectrum is 365-400nm, the transmittance is more than 85%.
In the early 1970s, the polyester used in the bench of the exposure machine produced in the United States was replaced with a convex-concave surface. Its advantages are strong ultraviolet light transmission, good air conductivity, fast vacuum suction, and no dead space in vacuum, so it is not necessary to use it. The squeegee and self-made tools are used to catch air, and the film does not move. It is particularly prominent in the manufacture of LCD thin lines. It is reported that China has this material available. It should be reminded that the convex-concave polyester film is processed with a special mold in the drawing process, and the surface and bottom surface of the protrusion are very high in finish. Therefore, in the purchase and use, the polyester film must not be pockmarked or roughened. Confused.

3) Reflector and parallel light: Strictly speaking, the light sources we use are point light sources. How to obtain parallel light or the difference in energy of each effective part of the light source on the table is the main indicator for measuring the level and performance of the exposure machine. This indicator mainly depends on the design and manufacturing level of reflectors. The reflectors are oval in shape, and the drawings of many manufacturers' reflectors are confidential. This is because it is difficult to obtain parallel light, and in particular, the edge of the mesa gets the same energy as the center. The key is to see who can minimize this energy difference. Therefore, after determining the geometrical size of the mask, how to make the light absorbed by the surface of the reflector reflect to the surface maximum. Generally, the surface is treated with a concave-convex surface, and finally the surface is subjected to electropolishing or chemical polishing so that the surface is at or near the mirror level. Reflectors are made of aluminum-magnesium alloys because aluminum is the only reflective material that reflects 200-450 nm of UV light. The surface has a protective layer, excellent reflectors have 75% of the UV light reflected to the surface, the remaining 25% of the energy has been directly radiated to the surface, the intensity of the center and edge of the light does not exceed 15% error.

4) Control of light energy and exposure time: The ideal exposure machine should have energy display, and the time control accuracy display should be 0.5-0.25S, which is particularly important in the graphic manufacturing of LCD ITO layer. The accuracy of light energy and exposure time can prevent overexposure and deficiency, which is an important part of overall quality control.

5.3 Measurement of light energy:

1) Application of UV photometer: In order to ensure accurate exposure energy, UV photometer and gradient rule are mostly used as measuring tools in exposure, and exposure intensity is measured by UV photometer.

Measurement method: Place the probe of the UV photometer on the underside of the drying plate film with the probe facing upward. Put the probe in different positions to measure the different data of the light. Generally at least 5 points, that is, the middle point, each point of the four corners, to see whether the light intensity of each part is consistent, in order to pay attention to adjust the operation, UV photometer is a measuring tool, after a period of time will produce errors, in order to maintain its accuracy Regularly sent to the national measurement department for identification.

Exposure intensity measurement and energy calculation: First adjust the UV photometer to 0, then put the probe into the drying frame and push it into the exposure area. Observe after 5 seconds. The reading data is the intensity of the light. Unit of measurement: mw/cm2.

2) Light energy: E=IT
I = light intensity mw/cm2, E = light energy mj/cm2, T = time (seconds)
Some automatic UV photometers do not need to be calculated, and the exposure energy can be automatically displayed as the exposure time increases or decreases.

3) Gradient ruler application: The gradient ruler is also a tool for measuring exposure data. It is developed by exposing the sample, and finally reads the number of retained cells. (Note: The concentration, temperature, and transfer rate of each developer during the measurement. Must be consistent to be accurate). Gradient scale has 17 grades, 21 grades and 25 grades. At present, most of the 21 levels are used. The light transmittance of the adjacent two grids of the 21-level optical gradient ruler is 2 = 1.414. That is, each additional grid needs to increase 1.414 times the exposure. Many factories use the 21 grid ruler always according to the usual experience, and add or subtract time according to the first exposure grid number until the required number of grids is reached. . This not only takes a lot of man hours, but sometimes it is not very accurate. For this reason, a coefficient table is made based on the multiple relationship of the light transmittance between two adjacent cells.

21 light ladder scale base coefficient comparison


21 light step scale 21 light step scale coefficient 21 light step scale 21 light step scale coefficient
1 1.414 9 22.590
2 1.999 10 31.942
3 2.827 11 45.167
4 3.997 12 63.866
5 5.651 13 90.306
6 7.990 14 127.693
7 11.298 15 180.557
8 15.976


The exposure time required to obtain a predetermined number of stages (optimal number of stages) can be calculated as follows (in the case of a fixed light source).

4) Calculation of exposure time:

a. Increase the number of stages: increase the number of stages required by the selected exposure coefficient multiplied by the original measurement series exposure time is the exposure time of your desired series.
For example: Exposure 16s is measured as 6 levels of normal development (temperature, concentration, time), and 8 is recommended, and 2 levels need to be added. The 2-stage coefficient was found to be 1.999, so the exposure time to obtain 8 levels is 16s×1.999=31 which is 31s.

b. Decrease the number of stages: Also select the number of steps required to reduce, and then divide the exposure time of the original measured series, which is the exposure time you need.
For example: Exposure 40s is measured as 13, and recommended as 8, according to the required number of stages to be reduced by 5, to find the coefficient of 5.61 to 5.651, so to obtain 8 levels of exposure time should be 40s ÷ 5.651 = 7s .

Source: China Polymer Network

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