Industry Science | Detailed explanation of screen printing technology

1. What is the online version?

Screen plate (also known as screen printing plate) is
the core tool of screen printing technology. It consists of a screen, a screen frame and a photosensitive adhesive layer, and pattern transfer is achieved by controlling the ink transparency of the graphics and text areas. Its core principle is to use the exposure and development characteristics of the photosensitive adhesive to form a comparative structure between transparent (printed area) and closed (non-printed area) on the surface of the screen. Screen versions are widely used in electronic circuits, glass printing, textile printing and other fields, and have the advantages of high adaptability, low cost and large-scale production.
2. Analysis of the entire process of screen production
(I) Preparation before screen production
1. Select
the number of screen mesh mesh mesh according to the printing needs: Select the number of mesh mesh (such as 80-400 mesh) according to the printing needs. The high mesh number is suitable for fine patterns, and the low mesh number is suitable for thick ink layer printing.
Wire mesh material: Commonly used mesh yarns include stainless steel yarn, polyester yarn and nylon yarn. When printing normally, it is recommended to choose yellow polyester yarn, because the white wire mesh surface is smooth and light in color, and scattering occurs when ultraviolet rays are irradiated (light diffuses in multiple directions). The scattered light may accidentally expose the area that should be blocked by the film negative, causing the pattern edges to 'difference' or the lines to become thicker. The yellow dye can absorb the ultraviolet band (300-420nm), reducing light scattering during exposure and preventing light from being reflected through the side wall of the mesh to the non-patterned area of ​​the photosensitive adhesive. Makes pattern edges clearer and reduces jagged or imaginary edge problems.
Mesh frame: Commonly made of aluminum alloy, it must have high flatness and resistance to deformation.
Photosensitive adhesive: divided into water resistance and solvent resistance, and must match the ink characteristics.
Environmental requirements: Operation must be carried out in a dust-free, constant temperature (20-25℃) environment to avoid dust affecting the uniformity of the glue layer.
(II) Screen production process
The process of screen production is: clear frame-open net-adhesive web-mounted frame-cut excess wire mesh-washed plate-photosensitive adhesive coating-drying plate-development-checking plate-checking plate-checking plate-checking plate-checking plate-checking plate-checking plate-checking plate-checking plate and repair.
1. Clear the frame: Use a blade or a special shovel to thoroughly scrape away the old mesh, photosensitive glue, ink, etc. remaining on the frame. The cleaned mesh frame needs to be completely dry (can be dried naturally or dried with a hairdryer in a cold air) to avoid moisture affecting subsequent glue or sticking to the mesh.
2. Spread the mesh and sticky mesh frame
to open the mesh: Use a web stretcher to stretch the mesh to the target tension (usually 18-25N/cm²) to ensure uniform tension.
Adhesive: Apply epoxy resin glue to the edge of the mesh frame, attach the wire mesh to the mesh frame, and let it stand for 24 hours to cure.
Key points: After the net is stretched, the tension meter needs to be used to detect the four angles and center tension, and the error must be controlled within ±1N/cm².
3. Cut excess wire mesh.
Use a hot cutter or sharp utility knife to cut off excess wire mesh along the outer edge of the mesh frame to avoid tension changes caused by pulling.
4.
Clean the screen with a neutral degreasing agent (such as 5% sodium carbonate solution) to remove grease and dust, and enhance the adhesion of the photosensitive adhesive.
Note: After rinsing, use non-woven fabric to dry, and it is not allowed to directly contact the mesh with your hands.
5.
Use a scraper groove to evenly apply the photosensitive adhesive on both sides of the wire mesh. The thickness of the glue layer is controlled by the scraper pressure and speed (usually 5-8μm).
Tips: First apply the printing surface (contact the side of the printing substrate), then apply the ink surface. Repeat 2-3 times to obtain a uniform coating.
6.
Place the film negative (patterned surface fitting wire mesh) in the plate dryer and expose it with an ultraviolet light source (such as a metal halide lamp).
Parameter adjustment: The exposure time is determined based on the light source intensity and the type of photosensitive adhesive (usually 30-120 seconds), and the optimal duration needs to be determined through exposure tests.
7. Development: Spray the screen with water (pressure 0.2-0.4MPa), the unexposed part of the photosensitive glue dissolves, revealing the transparent pattern.
Fine treatment: Complex patterns can be used to lightly brush the brush to assist in development, avoiding high-pressure water column from destroying details.
8. Inspection and repair
quality inspection items:
pattern edge clarity (no sawtooth or broken wire).
There are no pinholes or bubbles on the mesh.
Retest of tension stability.
Repair: Use sealing glue to fill in defects, and reexpose them after local glue.
3. Frequently asked questions and solutions . Causes of
blurred patterns after development
: insufficient exposure or the negatives are not fit tightly.
Countermeasures: Extend exposure time and use a vacuum adsorption exposure machine. Causes of
photosensitive adhesive layer falling off
: Incomplete degreasing or drying temperature is too high.
Countermeasures: Strengthen the cleaning process and strictly control the drying conditions. Reasons for
printing ink leakage
: insufficient thickness of the glue layer or excessive development.
Countermeasures: Increase the number of glue applied and shorten the development time.
Screen production is a technology that combines scientific and empirical technology, and the accuracy control of each step is crucial. With the development of digital technology, some links (such as tension control and exposure parameters) can be precisely regulated through automated equipment, but the operator's experience accumulation is still the core of ensuring quality. In the future, high-resolution photosensitive materials and environmentally friendly plate making processes will become the key direction for industry upgrading.