One. Selection of printing light source
In the light-sensitive screen-making process, printing is an extremely important process. If the light source is selected and used correctly, it is of great significance to improve the quality of the screen printing plate, effectively save energy, simplify operation, maintain the health of the operator, and reduce costs. Due to the different types of photosensitive resin photosensitive materials, it is necessary to choose to use a light source that meets the needs of various photosensitive materials.
At present, the color sensitivity of various screen photosensitive materials we use is mostly distributed between 250 and 510 μm. Therefore, in theory, any light source with a peak wavelength on the emission spectrum energy emission curve of 250-510 μm can be used for screen printing. In addition, when printing, we must fully study the size of the plate, the output power of the light source, the distance between the plate and the light source, and pay special attention to the role of the light reflector.
two. Considerations when choosing a light source
1. The emission spectrum of the light source should match the absorption characteristics and color sensitivity of the photosensitive material. The energy of light varies with the frequency of the wavelength. The shorter the wavelength, the higher the frequency and the greater the energy of the photon. When light is absorbed by a substance in the process of radiation, because the photon has a certain energy, the substance will undergo physical and chemical changes. The chemical reaction caused by the light energy is called a photochemical reaction. The so-called photochemical matching means that the spectral output distribution of the selected light source should match the spectral color sensitivity of the photosensitive material. That is, the wavelength range in which the photosensitive material absorbs light and undergoes a photochemical reaction is exactly the output range of the light emission spectrum of the light source, and the maximum absorption peak of the photosensitive material is exactly at the output peak of the light source. In this way, the light energy of the light source is absorbed by the photosensitive material to the maximum extent and a photochemical reaction occurs.
2. High luminous efficiency and high intensity. When other conditions remain unchanged, the greater the power and luminous efficiency of the light source, the greater the luminous intensity or brightness, the greater the illuminance of the exposed surface, and the shorter the time required for the photosensitive material to obtain the same exposure .
3. The heat radiation of the light source is small. Under the premise of ensuring that the light source has sufficient luminous intensity or bright light, the heat radiation of the light source should be as small as possible. When using a high-power and strong light source, measures such as forced cooling (air cooling, water cooling) and other measures must be taken on the lamp tube, and other measures should be adopted to make the exposure of the photosensitive material and the temperature be controlled below 32 ℃.
4. The luminous intensity is uniform. The luminous intensity of the illuminated surface of the light source should be as uniform as possible. The design of the exposure device should ensure that the difference in illumination of each point of the exposed surface of the photosensitive material does not exceed 15%. The light source environment has strong adaptability. The light source should have a strong ability to adapt to the environment, and it can work normally under various temperature, airflow and voltage changes. Of course, in actual production, it is unrealistic to choose a light source that can completely meet the above requirements. The purpose of the above selection principle is only to hope that the plate-making operator should consider the influence of the light source on the exposure quality of the photosensitive material when choosing to use the plate-making light source, so as to be targeted. [next]
pay attention:
(1) When exposing high mesh fine dots, the exposure time is reduced by 5% on the basis of the above table, and after exposure, do another exposure after exposure (without film) to ensure the durability of the printing plate, the time is the normal exposure time 2 to 3 times.
(2) If the photosensitive paste is a thick film photosensitive paste, the exposure time needs to be extended, for example, the 40-micron thick 120 mesh needs to be extended by 50%, and so on.
(3) If you want to do high-quality printing, please use the exposure measurement card (EXPOSNRECALCULATOR) to calculate the accurate exposure time.
5. development. Immerse the exposed printing plate in water for a minute or two. Shake the non-photosensitive parts such as the screen plate to absorb moisture and swell, then rinse with water to develop. The development should use a strong pressure spray gun, but in any case, it must be completely dissolved in the unsensitized part in a short time. When the pattern is fine, use a magnifying glass of 8 to 10 times to check whether the subtle part is completely transparent. It must be completely transparent. After developing, use a large clean white paper, sponge or blower to quickly remove moisture and dry. Control principle, under the premise of soaking, the shorter the time, the better. If the time is too long, the wet expansion of the film layer will severely punish the clarity of the image; if the time is too short, the development will not be complete, and there will be fogging, which will block the mesh and cause the waste version. Meng Yi is a very thin film of residual photoresist. It is easy to appear in the details of the image. It is highly transparent and difficult to distinguish from the water film. It is often mistaken for transparency.
6. dry. The developed screen should be placed in a dust-free dry box and dried with warm air. The drying temperature of the screen drying box can generally be controlled at around 40 degrees. When drying, the moisture on the surface of the screen should be blown off in advance to avoid the moisture from flowing down on the surface of the screen to produce residual glue and fogging, which affects the clarity of the edge of the line and the lack of fine dots.
7. Reinforcement and correction of plate film. In order to strengthen the plate film and improve water resistance and solvent resistance, methods such as applying a hardener can be adopted.
8. an examination. Screen inspection is the final process of the entire plate-making work, and it is also an extremely important process. Small defects exposed after development can be corrected by plate revision. If a major defect occurs, the plate must be remade. In the quality inspection of the screen version, at least the following issues must be paid attention to:
(1) Whether the exposure time is accurate. In addition to using the density ladder to check the degree of film hardening, you can also see how the fine part of the master plate is reproduced on the silk screen. You should observe whether the lines are complete, whether the edges are clear, whether the zigzag is serious, whether the small dots are transparent, etc. .
(2) Whether the mesh is completely transparent. Check the quality of the screen printing plate, including whether the graphics are all developed, whether the graphics dots and lines have burrs, defects, broken pens and mesh sealing, etc. If you find the above situation, you should take various methods to make up in time. Consider remaking the plate to ensure printing quality.
(3) Test the adaptability of various photosensitive materials. Check if there is air bubbles and trachoma in the omentum. Seal the four-sided wire mesh. Check whether the printing positioning marks meet the printing requirements.
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