Photosensitive adhesives for screen printing include dichromate-based emulsions, diazonium-based emulsions, and single-liquid emulsions. Diazo-based photoresists are generally composed of diazo-resin, vinyl acetate and polyvinyl alcohol. Prepared, also weighed nitrogen sensitive adhesive, is commonly used screen printing plate material.

Diazo photosensitive adhesives can be divided into solvent-resistant and water-resistant two major categories, this article will be Star Series diazo photosensitive adhesive as an example, describes the use of diazo photosensitive adhesive.

Solvent-resistant photosensitive adhesives are suitable for solvent-based inks. They are mainly used for screen printing of advertising signs, ceramic decals, plastics, glass, and metal products. Water-resistant photosensitive adhesives are suitable for printing and dyeing, fabric printing, and T-shirt color dot printing, etc. Water-based ink, screen printing of aqueous slurry. The process flow of plate making is as follows:

Stretching → cleaning → drying → coating photosensitive adhesive → drying → exposure → development → drying → correction → curing treatment → printing.

1. Stretching and cleaning

First of all, according to the printing requirements to select the appropriate frame and screen, through mechanical or manual stretching, and then to clean the frame, usually use a special cleaning agent or neutral, weak alkaline detergent repeatedly wipe, if necessary, can be Grind with a gauze paste and rinse with water before use.
2. Preparation of photosensitive adhesive

The proportion of the diazo photosensitive adhesive: colloidal 1000g + diazonium photosensitizer 8 ~ 10g + water 50 ~ 100ml.

Preparation sequence:

1 in 50 ~ 100ml water into the photosensitizer powder 8 ~ 10g;
2 stir to dissolve into liquid;
3 Pour the dissolved photosensitizer into 1000g of colloid and mix well;
4 Defoam 30 to 60 minutes, use it after standing for 2 to 3 hours.

Preparation points:

1 The amount of water to be used depends on the viscosity of the coating colloid;
2 must be dissolved in the photosensitizer powder and then poured into the colloid;
3 When stirring, turn clockwise to avoid air bubbles;
4 Photoresist is not equipped with a shelf life of 1 year before it is formulated. The best use period after preparation is 15 days, and cryogenic storage can be up to 2 months or longer.

3. Coating photosensitive adhesive

Dissolve the defoaming photosensitive adhesive directly into the sizing device, and pour it into more than half of the volume of the sizing device. Fix the cleaned frame on the bracket to an angle of 80±5° from the horizontal plane. The sizing device and the screen The surface is formed into an angle of 75°, and the coating is uniformly applied from the bottom to the top. The printing surface is applied first, and then the squeegee is coated. Generally, the screen is switched up and down 4 times, and then placed in an oven to dry. Remember that each coating is applied. The online version must be dry. In addition, the number of coating should be increased according to the printing requirements to control the thickness of the adhesive layer.

4. Drying

Drying temperature is the most suitable at 40°C. Conditional ovens and Other optional equipment can be used. Hair dryers, electric fans and other simple tools can be used unconditionally, but they must work in a dust-free environment to avoid affecting the quality of the screen.

5. Exposure

The photosensitizing wavelength of the diazo series is 330-430nm, and iodine lamps, ultra-high pressure mercury lamps and other similar light sources are available.

Exposure is best to use professional stencil machine, film and photographic film should be squeezed and squeezed; unconditional sandbags can be used to prevent light refraction, affecting the quality of printing.

The commonly used printing parameters are:

11.3kW iodine lamp, lamp distance 1m, exposure 250 to 300 pulses.
21kW high-pressure mercury lamp with 60cm lamp and exposure for 2 minutes.
340W UV lamp 6, spacing 5 ~ 10cm, lamp distance of 15cm, exposure 3 to 5 minutes.

6. Development

After exposure, the screen should be soaked in water for about 2 minutes, then rinsed with a spray gun or pressurized tap water until the pattern is clear, and then dried with hot air at 40°C or allowed to air dry.

7. Revision

The dried screen plate is repaired with a sealer, and the adhesive layer should not be too thick.

8. Curing

If you want to improve the screen printing resistance, you can double-exposure the screen after the repair, and then apply external curing agent for curing.

The method of using the external curing agent is to use a sponge to dip the outer curing liquid to paint the front and back surfaces of the adhesive film. After the brushing is uniform, the resist is baked in an oven at 40° C. for 10 to 20 minutes, and then the machine can be printed. In addition, there is an external curing agent that does not need to be baked. Its use method is the same as above, but it can be printed without baking and drying.

9. Plate-making common failure analysis and solution

When printing, strictly follow the requirements to obtain the best results. When encountering common failures in the platemaking process, the operator should analyze the cause of the failure as soon as possible and solve it with a corresponding method. Table 1 shows the common faults and solutions in screen plate making.


China Institute of Printing Science and Technology Sanhe Xingguang Printing Materials Co., Ltd. Back to Jinhua Source: Ke Yin Media - "Printing Technology - Equipment and Special Printing"