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- The difference between oil-sensitive adhesive and water-oil sensitive adhesive
- TIME： 2020-04-14 HITS：2173
- The difference between oil-sensitive adhesive and water-oil sensitive adhesiveThe so-called oil and water sensitive adhesive is actually refers to the solvent resistance and water resistance, oil is the so-called solvent sexy light adhesive, produced by the screen can resist solvent erosion, suitable for solvent-based ink printing.Water is the so-called water resistant photographic adhesive, the production of the screen can be resistant to water-based paste erosion, suitable for water-based paste and water-based ink printing.Water and oil dual use is actually a relative concept, water and oil dual use refers to strong solvent resistance and water resistance or strong water resistance and solvent resistance.Basic requirements for photosensitive materials in screen printing1. Requirements for photosensitive materials for screen printing. Screen printing plate making requirements for photosensitive materials are: plate making, such as easy to coating; Have appropriate photosensitive spectral range, generally should be in 340~440mm, photosensitive wavelength is too long, plate making operation and plate storage need to be in strict darkroom conditions, wavelength is too short, the choice of light source, personnel protection will become more difficult; High sensitivity, can achieve the purpose of energy saving, fast plate making; Good developing performance, high resolution; Good stability, easy storage, reduce waste; Economic, hygienic, non-toxic and pollution-free.2. Screen printing requirements for photosensitive materials. Screen printing on the requirements of photosensitive materials: photosensitive materials formed plate should adapt to the performance of different types of ink requirements; It has considerable printing resistance and can withstand the scraping pressure of a considerable number of ink scraping plates. The combination ability with the screen is good, the printing does not produce the film failure; Easy to peel, conducive to the screen plate regeneration use.Second, the development of screen printing sensitive materialsPhotosensitive adhesive (also known as photosensitive latex) and photosensitive source (also known as film film) are the most widely used photosensitive materials in the field of screen printing at home and abroad.Photosensitive adhesive or film generally with gelatin, polyvinyl alcohol (PVA), nylon as the matrix, using dichromate and diazonium salt as photosensitizer. Because dichromate contains 6 chromium ions, toxic to the human body, easy to cause public hazards, but also has a dark reaction fast, can only be used with the shortcomings (generally within two days), has now begun to be a new diazonium salt photosensitive adhesive (film) instead. Diazo salt photosensitive materials have high image resolution power, clear plate image, photosensitizer mixed with latex can be used for a long time (23 months at room temperature), high printing resistance, and non-toxic, pollution-free, so it has a good promotion and use value.Photosensitive adhesive is generally divided into single liquid type and double liquid type two. Single liquid type photosensitive adhesive in the production of photosensitive agent mixed with emulsion type and double liquid type two. Single liquid type photosensitive adhesive in the production of photosensitive agent mixed with latex, use without the need to prepare can be coated; Before using the double liquid type photosensitive adhesive, it is necessary to first dissolve the photosensitive agent in water according to the formula, and then mix and dissolve in the latex, stir it fully, place it for 1 ~ 2 hours, and use it after the bubble disappears.The early photosensitive glue is based on gelatin (bone glue) and has no photosensitive effect. After adding dichromate, it has photosensitive property. When cured by light, the colloid is cross-linked. However, this kind of colloid cross-linked curing, water will be slow expansion, long-term immersion can still dissolve, long-term storage and dry crack brittle, so it has been gradually replaced by PVA(polyvinyl alcohol) photosensitive glue.PVQ photosensitive body is polyvinyl alcohol, photosensitive agent mostly used dichromate. The plate-making quality is better than gelatin, and the operation is simple, but the accuracy is still not high enough, and the pollution problem is still not solved.In recent years, the development of photosensitive adhesives in China has made rapid progress, and diazonium salt +PVA has been widely used. Diazo screen photosensitive adhesive is a new type of photosensitive adhesive, has excellent resolution and printing resistance, and does not exist environmental pollution and toxic to human body.Three, the main components of screen printing sensitizerThe main components of screen printing sensitizer are film forming agent, photosensitizer and additive.1. Film-forming agent. Film forming agent plays a role in film forming, is the main component of the plate film. It determines the version of the film adhesion fastness and resistance (such as water resistance, solvent resistance, printing resistance, aging resistance, etc.). Film-forming agents commonly used in screen printing are water-soluble polymer materials such as gelatin, protein and PVA(polyvinyl alcohol), etc. Early photosensitive glue with this kind of single film forming agent to formula, but the production of the version of the film, its resistance is poor. PVA modified colloids were later used, which can be divided into three categories:① Physical modification of PVA colloid. Emulsion of PVA+ insoluble polymer material. The latter such as PVAC(polyvinyl acetate) emulsion, acrylic emulsion, PVAC and acrylic copolymer emulsion. Their addition improved the resistance of the plate film.② The chemical modified colloidal properties of PVA. That is, on the PVA bond by chemical means, selectively connected with vinyl acetate, acrylonitrile, acrylic acid and other groups, so that the improvement of resistance more comprehensive.③PVA(or gelatin)+ crosslinking agent. The characteristics of this system are: water-soluble polymer does not necessarily participate in the photochemical reaction, photoadhesive mainly by crosslinking agent and photosensitizer action. The crosslinking agents are mainly vinyl monomers, polyvinyl monomers or oligomers, which are water-soluble or have good dispersion in water-soluble polymer solution. Once solidified, it is insoluble in water. This system level to adapt to more varieties of photosensitizer, so you can obtain some special properties of plate making, such as indirect dry film, etc.2. Photosensitive. Photosensitizer A compound that reacts photochemically in the presence of blue-violet light and that results in the polymerization or cross-linking of the film forming agent. Photosensitizer determines the photosensitive adhesive light sensitivity, resolution and clarity and other properties.3. The additives. Film forming agent and photosensitizer is the main component of the formula, but sometimes to adjust the performance of the main component is insufficient, still need to add some additional auxiliary agents, such as dispersant, colorant, sensitizer, plasticizer, stabilizer, etc.. `Four, the photosensitive principle of photosensitive adhesiveEarly plate making with photosensitive materials is the chromate as a photosensitive agent, and the egg folding, gelatin, chromium prion and other water-soluble natural polymer materials as a film material mix after use. But since the development of the water-soluble synthetic polymer polyvinyl alcohol, it has been used as a film material.1. Photosensitive principle of dichromate. It has long been known that the 6-valent chromium ions in dichromate, which absorb ultraviolet light, are reduced to 3-valent chromium ions. Water-soluble polymer substance polyvinyl alcohol in the plate with the music material has been widely used, in the screen plate in the long - term ammonia dichromate as a photosensitizer to add PVA, but at present due to the chromium pollution problems and has been stopped using.As for the photochemical reaction of dichromate, the current general theory is that when the 6-valent chromium ion is photoreduced to 3-valent chromium ion, if it coexists with PVA, part of its hydroxyl group will be oxidized, and the water-solubility of PVA will therefore decrease. At the same time, due to the non-shared electron of the generated 3 valence chromium ion, the hydroxyl group of polyvinyl alcohol is formed and coordinated. Through the cross-linking reaction, the insoluble water of PVA is further deepened, so that the colloid can produce light curing.2. Sensitive principle of diazo resin. As dichromate becomes more and more difficult to act as a photosensitizer due to environmental hazards, diazo resins are now being developed. Diazo resin as offset PS plate photosensitizer has been widely used; For screen making, due to the mixture of hydrophilic polyvinyl alcohol, photosensitive layer of diazo root with water decomposition, so the use of diazo resin manufacturing screen PS version is difficultOne aspect of the photohardening insolubility of polyvinyl alcohol emulsions of diazo resins, namely the cross-linking reaction of polyvinyl alcohol molecules, is well defined.Diazo resin molecules, the smallest n within 2 ~ 3, if n is 2, diazo dimer resin with polyvinyl alcohol light crosslinking of condensation, the lost of the polyvinyl alcohol hydroxyl is less, this to lose its hydrophilicity, although there is no obvious effect, but the molecular chain structure of poly (vinyl alcohol) caused by crosslinking becomes a three-dimensional reticular structure, It has a great influence on the water insolubility after light hardening.3. The photosensitive principle of allyl esters. Acrylic ester acrylonitrile group, as a photosensitive resin photosensitive base is very important, its high sensitivity, good preservation, can be used as screen PS plate photosensitive materials. Acrylate monomer or low polymer is a photosensitive resin formed by condensation with various polyacrylate. When used as a photosensitive material for screen plate, it needs to be combined with polyvinyl alcohol which can be developed by water.The pentaerythritol triallyl ester with high sensitivity has three photofunctional groups bonded by double bonds, showing excellent photohardening, which is insoluble in water after hardening. As a result, mixing with the water-soluble polyvinyl alcohol is difficult. The long saponification value of low soluble organic solvent polyethylene and acrylate together for mixing and dissolving, can be made into screen PS plate with photosensitive materials.Photosensitizer Acrylates The double bonds of acrylic resins that absorb ultraviolet light and initiate free radicals to form active molecules with an initiator that has a free radical. If the reactive molecule is polymerized with PVA, a three-dimensional network of quantitative domain molecules is formed, making the PVA water insoluble. If the hydroxyl group of the polyvinyl alcohol is insoluble due to the active molecule. Of course, the light hardening theory about this part is not very clear.As the screen plate with photosensitive materials, now the most used is emulsified vinyl acetate in polyvinyl alcohol solution, and then add diazo resin as a photosensitive agent, the photosensitive film formation mechanism is shown in Figure 261. Sensitive film due to exposure and hardening, become insoluble water version of the film. The role of polyvinyl acetate is to strengthen the adhesion of the screen fiber, the development of the unexposed image and the unhardened polyFive, the classification of photosensitive adhesiveScreen printing plate making with photosensitive materials, according to the existence of the form of photosensitive glue and film (also known as film film, film paper); According to the material properties of its composition to distinguish the dichromate system, diazonium salt system, ferric salt system, etc. According to its use, there are screen photosensitive glue, screen photosensitive film, screen sealing glue, hard film agent, stripping agent, developer, etc.Photosensitive adhesive can be generally divided into solvent - resistant and water - resistant two types. Solvent-resistant photosensitive adhesive, resistant to all kinds of organic solvents, suitable for printing oily ink; Water-resistant photosensitive adhesive, suitable for water-based ink (water-soluble printing coatings, such as textile printing paste) printing, the former screen can be removed from the film recovery; The latter generally can not be removed from the film recovery. Special water - resistant photosensitive adhesive nylon photosensitive adhesive and diazo photosensitive adhesive. The user must choose the appropriate photosensitive adhesive according to the printing object and with reference to the relevant instructions.Photosensitive adhesive is used for direct printing plate printing photosensitive materials, can also be divided into single liquid type and double liquid type. Single liquid type photosensitive adhesive in the production of photosensitive agent has been added to the latex, use without preparation can be coated; Double liquid type photosensitive glue before use to the photosensitive agent according to the formula to release, and then disperse mixed in latex, defoaming can be coated.
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