Photosensitive adhesive and photosensitive film for screen printing (1)

Screen-printing photosensitive materials for use in printing plate, according to its existing form of photosensitive adhesive and photosensitive film (also known as film film, film paper); according to the composition of the material properties are divided dichromate, diazonium salt, iron Salt system, etc.; according to their use, there are screen sensitive adhesive, screen sensitive film, sealing net adhesive, hardener, stripper, and developer.

First, the basic requirements of screen printing on photosensitive materials

1. Screen printing plate requirements for photosensitive materials. Silk screen printing plate requirements for photosensitive materials are: good plate making, such as easy coating; have a suitable range of photosensitive spectrum, generally suitable in 340 ~ 440mm, photosensitive wavelength is too long, plate making operation and plate storage need to be in strict darkroom conditions, If the wavelength is too short, the choice of light source and the protection of personnel will become more difficult; the sensitivity is high, and the purpose of energy saving and rapid plate making can be achieved; the development performance is good, the resolution is high; the stability is good, the storage is convenient, the waste is reduced; Health, non-toxic, pollution-free.

2. Screen printing requirements for photosensitive materials. The requirements for screen printing on photosensitive materials are: the film formed by the photosensitive material should be adapted to the performance requirements of different types of ink; it has considerable resistance to printing and can withstand considerable scraping pressure of the squeegee; the ability to bond with the screen Good, no filming failure occurs during printing; easy to peel, which is conducive to the regeneration of screen plate material.

Second, the development of screen printing photosensitive materials

Sensitive glue (also called photosensitive emulsion) and light source (also known as film film) are commonly used in the silk screen industry at home and abroad.

Sensitive adhesives or films are generally based on gelatin, polyvinyl alcohol (PVA), nylon, etc., and dichromates and diazonium salts are used as photosensitizers. Since dichromate contains hexavalent chromium ions, it is toxic to humans and can easily cause public hazards. It also has the disadvantage of fast dark reaction and can only be used with (usually within two days). Now it has begun to be new type of diazo. Salt sensitizer (film) instead. The diazonium salt photosensitive material has high resolving power and clear plate-making image. The photosensitizer can be used in long-term use in the emulsion (23 months at room temperature). It has high resistance to printing and is non-toxic and non-polluting. Therefore, it has good promotion and use value. .

Photosensitive adhesives are generally divided into single liquid type and double liquid type. One-shot sensitizers are formulated with sensitizers mixed into emulsions and two-liquids during production. One-shot type photosensitive adhesive in the production of the photosensitive agent is mixed into the latex, the use of no need to be formulated to be coated; double liquid photosensitive adhesive before use first need to be photosensitizer soluble in water, and then mixed with latex in the fully stirred , Place it for 1 to 2 hours until the bubbles disappear.

The early sensitized adhesive was based on gelatin (colloid bone) and had no photosensitizing effect. After the addition of dichromate, it had sensitization, and when light cured, the colloids were cross-linked. However, after the colloidal cross-linked curing, it will slowly swell in contact with water, long-term soaking can still dissolve, long-term storage will be dry and brittle, so it has been gradually replaced by PVA (polyvinyl alcohol) emulsion.

The main body of PVQ is polyvinyl alcohol, and most of the sensitizers use dichromate. The plate-making quality has been improved compared with that of gelatin, and the operation is simple. However, the accuracy is still not high enough and the pollution problem remains unresolved.

In recent years, the development of photosensitive adhesives in China has progressed rapidly and diazonium salt + PVA has been widely promoted. Diazide silk-screen sensitive adhesive is a new type of photosensitive adhesive, with excellent resolution and printability, and there is no environmental pollution and toxic to the human body.

Third, the main components of screen printing photosensitive adhesive

The main components of silkscreen printing are film formers, sensitizers, and auxiliaries.

1. Film former. The film former acts as a film and is the main component of the film. It determines the net fastness and resistance of the film (such as water resistance, solvent resistance, print resistance, aging resistance, etc.). Screen-printing sensitizers commonly used film-forming agents are: water-soluble polymers such as gelatin, protein and PVA (polyvinyl alcohol). Early photoemulsions were formulated using such single film formers, but the plates produced were poorly resistant. Later, PVA was used to modify the colloids, which can be divided into three categories:

1PVA physical modification of colloids. PVA + emulsion of water-insoluble high-molecular substances. The latter are PVAC (polyvinyl acetate) emulsions, acrylic emulsions, PVAC and acrylic copolymer emulsions. With their addition, the resistance of the plate is improved.

2PVA chemically modified gum. That is to say, the PVA bonds are chemically connected to vinyl acetate, acrylonitrile, acrylic acid, and other groups to improve the resistance.

3PVA (or gelatin) + crosslinker. The characteristics of this system are: water-soluble polymers do not necessarily participate in photochemical reactions, and light-bonded polymers are mainly formed by cross-linking agents and sensitizers. The cross-linking agent uses vinyl monomers, polyvinyl monomers or oligomers, which are water-soluble or have good dispersibility in water-soluble polymer solutions. Once cured, it is insoluble in water. This system level accommodates more sensitizer types and thus can achieve certain special properties of plate making, such as indirect dry film.

2. Photosensitizer. Photosensitizers are compounds that can photochemically react under blue-violet light and can cause film formers to polymerize or crosslink. Sensitizers determine the sensitivity, resolution, and clarity of the photoresist.

3. Additives. Film formers and sensitizers are the main ingredients of formulas, but sometimes they are needed to adjust the performance of the main components. Some auxiliary agents such as dispersants, colorants, sensitizers, plasticizers, stabilizers, etc. are needed.