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- The difference between oily photoresist and water oily photoresist
- TIME£º 2020-4-14¡¡CLICKS£º2600¡¡
- The difference between oily photoresist and water oily photoresist
The so-called oily and water-based of photoresist actually refers to the solvent resistance and water resistance. Oily is the so-called solvent-resistant photosensitive adhesive. The screens produced are resistant to solvent attack and suitable for printing with solvent-based inks.
Water-based is the so-called water-resistant photosensitive adhesive. The screens produced can resist the erosion of water-based paste, and are suitable for the printing of water-based paste and water-based ink.
Water-oil dual-use is actually a relative concept. Water-oil dual-use refers to a strong solvent-resistant type with both water resistance or strong water-resistant and solvent resistance.
Screen printing basic requirements for photosensitive materials
1. The requirements of photosensitive materials for silk-screen printing. The requirements of the screen printing plate for photosensitive materials are: good plate-making performance, such as easy coating; with an appropriate photosensitive spectrum range, generally 340~440mm, the photosensitive wavelength is too long, the plate-making operation and plate storage must 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; high sensitivity can achieve the purpose of energy saving and rapid plate-making; good developing performance, high resolution; good stability, easy storage, reducing waste; economic, Hygienic, non-toxic and pollution-free.
2. Screen printing requirements for photosensitive materials. The requirements of the screen printing on the photosensitive material are: the plate film formed by the photosensitive material should adapt to the performance requirements of different types of ink; have a considerable printing resistance, can withstand a considerable number of scraping pressure of the ink scraping plate; and the ability to combine with the screen Well, there is no film release failure during printing; it is easy to peel off, which is conducive to the recycling of screen materials.
2. Development of screen printing photosensitive materials
Photosensitive adhesive (also known as photosensitive latex) and light source (also known as film) are currently commonly used photosensitive materials at home and abroad.
Photosensitive glue or film generally uses gelatin, polyvinyl alcohol (PVA), nylon, etc. as the matrix, and uses dichromate and diazonium salt as photosensitizers. Since dichromate contains hexavalent chromium ions, it is toxic to human body and easy to cause pollution. At the same time, it has the shortcomings of fast dark reaction and can only be used with it (usually within two days). Replaced by salt photoresist (film). The diazonium-based photosensitive material has high resolution and clear plate-making images. The photosensitizer can be used for a long time after being mixed into latex (23 months at room temperature). It has high printing resistance, and is non-toxic and non-polluting, so it has good promotion and use value. .
Photosensitive adhesives are generally divided into two types: single-liquid type and double-liquid type. The single-liquid type photoresist is mixed with emulsion type and two-liquid type during production. The single-liquid photosensitive adhesive is mixed with latex in the latex during production, and it can be coated without preparation during use; the two-liquid photosensitive adhesive needs to first dissolve the photosensitizer according to the formula before use, and then dissolve in the latex to fully stir , Leave for 1 to 2 hours, use after bubbles disappear.
Early photosensitizers used gelatin (bone gel) as the matrix and had no photosensitizing effect. After adding dichromate, it had photosensitizing properties. When it was cured by light, the colloids were cross-linked. However, after the cross-linking and curing of this colloid, it will slowly swell in water, it will still dissolve after long-term immersion in water, and it will crack and become brittle after long-term storage, so it has been gradually replaced by PVA (polyvinyl alcohol) photosensitive adhesive.
The main body of PVQ photosensitive adhesive is polyvinyl alcohol, and most of the sensitizers use dichromate. The quality of plate making is improved compared with gelatin, and the operation is simple, but the accuracy is still not high enough, and the pollution problem has not been solved.
In recent years, the development of domestic photosensitive adhesives has made rapid progress, and diazonium salts + PVA have been widely promoted and used. Diazo screen photosensitive adhesive is a new type of photosensitive adhesive, which has excellent resolution and printing resistance, and there is no environmental pollution and poisoning to human body.
3. The main components of screen printing photoresist
The main components of screen printing photoresist are film-forming agent, photosensitizer and auxiliary agent.
1. Film-forming agent. The film-forming agent plays a film-forming role and is the main component of the plate film. It determines the fastness and resistance (such as water resistance, solvent resistance, printing resistance, aging resistance, etc.) of the sticky mesh of the plate film. The commonly used film-forming agents for screen printing photoresist are: water-soluble polymer substances such as gelatin, protein and PVA (polyvinyl alcohol). Early photoresists were formulated with this type of single film-forming agent, but the fabricated film has poor resistance. Later, PVA modified colloids were used, which can be divided into three categories:
¢Ù Physically modified colloid of PVA. Emulsion of PVA+ water-insoluble polymer. The latter include PVAC (polyvinyl acetate) emulsion, acrylic emulsion, PVAC and acrylic copolymer emulsion, etc. The addition of them improves the resistance of the plate film.
¢Ú Chemical modification of PVA. That is, by chemical means on the PVA bond, selectively connect vinyl acetate vinegar, acrylonitrile, acrylic acid and other groups, so that the improvement of resistance is more comprehensive.
¢ÛPVA (or gelatin) + crosslinking agent. The characteristics of this system are: water-soluble polymers do not necessarily participate in photochemical reactions, and photo-glue is mainly formed by the action of crosslinking agent and sensitizer. Vinyl monomers, polyvinyl monomers or oligomers are commonly used as cross-linking agents. They have water solubility or good dispersibility in water-soluble polymer solutions. Once cured, it is insoluble in water. This system level is suitable for more varieties of sensitizers, so it can obtain some special characteristics of plate making, such as indirect dry film.
2. Sensitizer. The sensitizer can act as a photochemical reaction under the blue-violet light, and can cause the film-forming agent to polymerize or crosslink. The sensitizer determines the performance of the photoresist, such as its spectral sensitivity, resolution and clarity.
3. Additives. The film-forming agent and the photosensitizer are the main ingredients of the formulation, but sometimes in order to adjust the performance of the main ingredients, some auxiliary agents, such as dispersants, colorants, sensitizers, plasticizers, stabilizers, etc., need to be added. `
Fourth, the photosensitive principle of photosensitive resin
Early photosensitive materials for platemaking used chromates as photosensitizers, mixed with water-soluble natural polymer materials such as egg folds, gelatin, and chromium as film-forming materials. However, since the development of water-soluble synthetic polymer substance polyvinyl alcohol, it has been specifically used as a film-forming material.
1. Photochromic principle of dichromate. The hexavalent chromium ions in the dichromate are reduced to trivalent chromium ions after absorbing ultraviolet rays, which is well known from a long time ago. After the water-soluble polymer substance polyvinyl alcohol has been widely used in plate-making sensation materials, ammonia dichromate was used as a photosensitizer in PVA for a long time in screen-making, but it is currently discontinued due to chromium pollution problems. .
Regarding the photochemical reaction of dichromate, the current general theory is that when hexavalent chromium ions undergo photoreduction to trivalent chromium ions, if they coexist with PVA, part of their hydroxyl groups are oxidized, and the water solubility of their PVA is also It is therefore reduced. At the same time, due to the non-shared electrons of the generated trivalent chromium ions, the hydroxyl groups of polyvinyl alcohol are formed and coordinated and combined. Through the cross-linking reaction, the insoluble water of PVA is further deepened, and the colloid is photocured.
2. Photosensitive principle of diazo resin. The role of dichromate as a photosensitizer due to environmental hazards has become more and more difficult, and diazo resins have now been developed. Diazo resins have been widely used as sensitizers for offset PS plates; for screen-making, due to the mixing of hydrophilic polyvinyl alcohol, the diazonium radicals of the photosensitive layer are decomposed by water, so diazo resins are used to make screen PS plates More difficult
Regarding the photohardening of the polyvinyl alcohol emulsion of the diazo resin insoluble in water, the cross-linking reaction of the polyvinyl alcohol molecules is clear.
The molecular weight of the diazo resin is the smallest, n is in the range of 2 to 3, if n is 2, the diazo dimer resin loses less hydroxyl groups of polyvinyl alcohol due to condensation of the polyvinyl alcohol during photocrosslinking. Although it has no obvious effect, the polyvinyl alcohol molecules with chain structure caused by cross-linking will become a three-dimensional network structure, which has a great influence on the insoluble water after photohardening. .
3. Photosensitive principle of allyl alcohol esters. Acrylonitrile groups of acrylic esters are very important as photosensitive groups of photosensitive resins. They have high sensitivity and good storage properties, and can be used as a screen PS plate photosensitive material. Acrylate monomers or low polymers are photosensitive resins condensed with various polyacrylates. When used as a photosensitive material for a screen, they need to be combined with polyvinyl alcohol that can be developed in water.
Pentaerythritol triacrylate with high sensitivity has 3 photo-functional groups bonded by a double bond, showing excellent photo-hardenability, which is insoluble in water after hardening. Therefore, it becomes difficult to mix with water-soluble polyvinyl alcohol. By mixing and dissolving the soluble organic solvent polyethylene with low long saponification value and acrylate together, a photosensitive material for the screen PS plate can be made.
The double bond of the acrylic resin of the photosensitizer acrylic resin absorbs ultraviolet rays, and the free radical initiator is used to initiate free radicals to form active molecules. If such active molecules are polymerized with polyvinyl alcohol, quantitative domain molecules with a three-dimensional network structure will be formed, making polyvinyl alcohol water-insoluble. At this time, if the hydroxyl group of the polyvinyl alcohol has insoluble water due to the active molecule. Of course, there are still some unclear points about the light hardening theory in this part.
As the photosensitive material for screen-making, the most commonly used is to emulsify vinyl acetate in a polyvinyl alcohol solution, and then add a diazo resin as a photosensitizer. The formation mechanism of the photosensitive film is shown in Figure 2-61. The photosensitive film is hardened by exposure and becomes a water-insoluble plate film. The role of polyvinyl acetate is to strengthen the adhesion of the mesh fiber. The unexposed image parts and unhardened poly
V. Classification introduction of photosensitive adhesive
Photosensitive materials for screen printing plate-making are divided into photosensitive glue and photosensitive film (also known as film and film) according to their existing forms; they are divided into dichromate system, diazonium salt system and iron according to the material properties of their composition Salt series, etc.; according to their use, there are screen photosensitive adhesive, screen photosensitive film, sealing adhesive, film hardener, film stripping agent, developer, etc.
Photosensitive adhesives can be generally divided into two types: solvent-resistant and water-resistant. Solvent-resistant photoresist, which is resistant to various organic solvents, suitable for the printing of oil-based inks; water-resistant photoresist, suitable for the printing of water-based inks (water-soluble printing coatings, such as textile printing pastes), the former screen can be stripped Recycling; the latter generally cannot be stripped and recycled. Special water-resistant photosensitive adhesives include nylon photosensitive adhesives and diazo photosensitive adhesives. The user must choose the appropriate photoresist according to the printing object and refer to the relevant instructions.
Photosensitive glue is a photosensitive material used for screen printing in the direct process, and can also be divided into single-liquid type and double-liquid type. The single-liquid photosensitive adhesive has been added to the latex during production, and it can be coated without preparation when used; the two-liquid photosensitive adhesive should first dissolve the sensitizer according to the recipe before use, and then disperse and mix in In latex, apply after defoaming.a - PREVIOUS£ºDifficult problems and handlin
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