Photosensitive adhesives for screen printing plate-making include dichromate-based photosensitive adhesives, diazonium-based photosensitive adhesives and single-liquid type photosensitive adhesives. Diazo-based photosensitive adhesives are generally composed of diazo resin, vinyl acetate and polyvinyl alcohol in a certain proportion Formulated, also known as nitrogen photosensitive adhesive, is currently commonly used screen printing plate photosensitive material.
Photosensitive adhesives can be divided into two categories: solvent-resistant and water-resistant. This article will take the Starlight series of diazo photosensitive adhesives as an example to introduce the use of diazo photosensitive adhesives. Solvent-resistant photosensitive adhesive is suitable for solvent-based inks, mainly used for screen printing of advertising signs, ceramic decals, plastics, glass, metal products; water-resistant photosensitive adhesive is suitable for printing and dyeing, fabric printing, T-shirt color dot printing, etc. Screen printing of water-based ink and water-based paste.
The plate making process is as follows:
Stretching the net → cleaning → drying → coating photosensitive adhesive → drying → exposure → developing → drying → retouching → curing treatment → printing.
1. Stretching and cleaning
First, select the appropriate screen frame and silk screen according to the printing requirements, stretch the screen mechanically or manually, and then clean the screen frame. Generally, a special cleaning agent or a neutral or weak alkaline detergent is used for repeated wiping. Use a mesh paste to polish and rinse with water to set aside.
2. Preparation of photosensitive adhesive
The component ratio of diazo photosensitive adhesive: colloid 1000g + diazo photosensitizer 8 ~ 10g + water 50 ~ 100ml.
Preparation sequence:
â‘ Pour 8 ~ 10g of photosensitizer powder in 50 ~ 100ml water;
â‘¡ Stir to dissolve into liquid;
â‘¢ Pour the dissolved photosensitizer into 1000g colloid and mix well;
â‘£ Defoam for 30 to 60 minutes, and let it stand for 2 to 3 hours before use.
Preparation points:
â‘ The amount of water depends on the viscosity requirements of the coating colloid;
â‘¡ Be sure to dissolve the photosensitizer powder before pouring into the colloid;
â‘¢ Clockwise during stirring to avoid air bubbles;
â‘£The shelf life of the photoresist is 1 year before being prepared, and the best use period after preparation is about 15 days, and the low temperature storage can be up to 2 months or longer.
3. Coating photosensitive adhesive
Pour the defoamed photosensitive glue directly into the sizing device, the amount of pouring should account for more than half of the volume of the sizing device; fix the cleaned frame on the bracket at an angle of 80 ± 5 ° to the horizontal surface, the sizing device and the wire mesh The surface is at an angle of 75 °, and it is evenly scraped from bottom to top. The printing surface is coated first, and then the scraped surface is coated. Generally, the screen is required to be coated upside down for 4 times, and then placed in an oven to dry. The Internet version must be dry. In addition, the number of coatings should be appropriately increased according to printing requirements to control the thickness of the adhesive layer.
4. Dry
The drying temperature is most suitable at 40 ℃. If conditions permit, equipment such as an oven can be selected. Simple tools such as hair dryers and fans can be used under unconditional conditions, but they must work in a dust-free environment to avoid affecting the quality of the screen.
5. Exposure
The photosensitive wavelength of the diazo series photoresist is 330 ~ 430nm, and it can use iodine gallium lamp, ultra-high pressure mercury lamp and other similar light sources. For exposure, it is best to use a professional printing machine, and the film and photosensitive film should be compacted and compacted; unconditional sandbags can be used to prevent light refraction and affect the quality of the printing.
Commonly used parameters for printing are:
â‘ 1.3kW iodine gallium lamp, lamp distance 1m, exposure 250 ~ 300 pulses.
â‘¡ 1kW high-pressure mercury lamp, lamp distance 60cm, exposure for about 2 minutes.
â‘¢ 6 40W ultraviolet lamp tubes, the interval is 5 ~ 10cm, the lamp distance is 15cm, and the exposure is 3 ~ 5 minutes.
6. Development
After exposure, the screen should be immersed in water for about 2 minutes, and then rinsed with a spray gun or pressurized tap water until the pattern is clear, and then dried with 40 ° C hot air or naturally dried.
7. Revision
Repair the dried screen with sealing glue. The adhesive layer should not be too thick.
8. Curing
To improve the screen printing durability, the repaired screen can be exposed for a second time, and then an external curing agent can be applied for curing.
The method of using the external curing agent is to use a sponge to dip the external curing solution to paint the front and back sides of the film. After painting evenly, put it in a 40 ° C oven for 10 to 20 minutes to print on the machine. In addition, there is an external curing agent that does not need to be baked. Its use method is the same as before, but it can be printed without baking and drying.
9. Analysis and solutions of common faults in plate making
When printing, you must strictly follow the requirements to obtain the best results. When encountering common faults in plate making, the operator should analyze the cause of the fault as soon as possible and solve it with corresponding methods.
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