1. Oligomer

Oligomer, also known as prepolymer, is the most basic component of UV varnish. It is a film-forming substance whose properties play an important role in the curing process and the properties of the cured film. From a structural point of view, oligomers are low molecular resins containing C=C unsaturated double bonds, mostly acrylic resins. At present, oligomers commonly used in UV varnishes include epoxy acrylic resin, polyaminase acrylic resin and polyester acrylic resin. Epoxy acrylic resin has the characteristics of fast curing speed and low price. The glazing oil produced is coated on paper or cardboard, which can make it have good chemical resistance and high mechanical strength. Polyurethane acrylic resin has the characteristics of good flexibility, strong elasticity and high gloss, but it is more expensive and is often mixed with epoxy acrylic resin. Polyester acrylic resin has low viscosity, good flexibility and is relatively cheap. Because of its good adhesion to non-absorbent substrates such as plastics and metals, it is often used as glazing oil for such materials. It is usually mixed with other resins and sometimes used as a diluent for glazing oil to adjust the environment. Viscosity of oxyacrylic and urethane acrylic resins.

2. Reactive diluent

Reactive diluent, also called cross-linking monomer, is a functional monomer. Its role in glazing oil is to adjust the viscosity, curing speed and cured film properties. Reactive diluents also contain C=C unsaturated double bonds in their structure, and most of them currently used are acrylic ester monomers. Due to the different number of acrylic groups, it can be divided into three categories: monofunctionality, difunctionality and multifunctionality. Reactive diluents with different functionalities have different dilution effects and curing speeds. Generally speaking, the more functionality, the faster the curing speed, but the poorer the dilution effect. Commonly used bifunctional glazing oil reactive diluents include: hexanediol diacrylate (HDDA), neopentyl glycol diacrylate (NPGDA), tripropylene glycol diacrylate (TPGDA), etc.; trifunctional There are: trimethylolpropane triacrylate (TMPTA), etc.

3. Photoinitiator

Photoinitiator is a substance that can absorb radiation energy and undergo chemical changes to produce active intermediates with the ability to initiate polymerization. It is the main component required for any UV curing system.

Photoinitiators can be divided into hydrogen abstraction type and cracking type. Hydrogen-abstraction photoinitiators need to be combined with a compound containing active hydrogen (generally called a co-initiator, usually an amine compound) to form free radicals through a hydrogen-abstraction reaction. It is a bimolecular photoinitiator, and benzophenone (BP) is commonly used in glazing oils. After being excited by light, the cleavage-type photoinitiator decomposes free radicals within the molecule and is a single-molecule photoinitiator. Commonly used in glazing oils are 1173 (α-hydroxyisopropylbenzophenone), 184 (α-hydroxycyclohexylbenzophenone), etc.

4. Additives

Additives are mainly used to improve the performance of ink. Commonly used additives in UV glazing oil include stabilizers, leveling agents, defoaming agents, etc.

(1) Stabilizer

Stabilizer is used to reduce thermal polymerization during storage and improve the storage stability of glazing oil. Commonly used stabilizers include hydroquinone, p-methoxyphenol, p-benzoquinone, tert-butylcresol, etc.

(2) Leveling agent

Leveling agent is used to improve the leveling of the glazing film surface, prevent the occurrence of shrinkage cavities, and also increase the strength of the glazing coating. Glossiness.

(3) Defoaming agent

Defoaming agent is used to prevent and eliminate bubbles generated during the manufacturing and use of glazing oil.

Although ordinary UV varnish does not contain solvents, because the oligomers used generally have high viscosity, low molecular reactive diluents must be added for coating needs, and they generally have certain Volatile or irritating, it is still harmful to the environment. Therefore, water-based UV glazing oil has been developed. It does not need to use reactive diluents to adjust the viscosity. Instead, water or thickeners are used to control the rheological properties of the glazing oil, which solves the problems of volatility and irritation. It is An ideal environmentally friendly product is the future development direction of glazing oil.

Post-press processing: some precautions when using UV varnish

UV varnish is a non-condensing material in the correct storage environment, just like cooking oil. There will be no dry film on the surface in the air.

UV varnish will solidify immediately after seeing ultraviolet light, such as sunlight, welding arc light, and printing light. However, general lighting sources such as fluorescent lamps and incandescent lamps will not cause UV varnish to solidify. The photoinitiators and diluents in UV varnish have a certain irritating effect on human skin.

Considering the above characteristics of UV varnish, you should pay attention to the following points when using UV varnish:

(1) The normal use temperature of UV varnish is 50-55℃ When used at low temperatures in winter, the UV varnish needs to be cyclically heated in constant-temperature waters to make its viscosity reach the designed viscosity, which is beneficial to the leveling and rapid curing of the UV varnish.

(2) When UV varnish passes through the UV lamp irradiation area, the optimal temperature should be 50-60°C, because at this temperature, UV varnish solidifies quickly and has strong adhesion after curing. In other words, the lower the temperature under the UV lamp, the better. This is the main reason why some manufacturers have poor adhesion and leveling when glazing their low-temperature workshops in winter.

(3) The glazing machine should be placed in a location where the sun cannot directly shine, otherwise the UV varnish will solidify on the coating roller under the action of ultraviolet light in the sun. If you cannot avoid direct sunlight, you should also use red and black curtains to block the sun's rays.

(4) The UV varnish that is scraped off during glazing will bring the ink that has been printed on the printing material to the UV varnish on the glazing machine, causing the varnish to be colored. However, after filtering and settling, these varnishes can still be used and do not need to be thrown away.

(5) With the development of science and technology, the irritation of UV varnish has been greatly reduced. However, if the skin comes into contact with UV varnish during the glazing operation, it should be washed off immediately with soapy water, otherwise the skin may become red, swollen and blistered.

(6) The viscosity of UV varnish varies depending on the type of glazing machine. Special varnishing oil should be selected according to the model of the glazing machine. If the viscosity of the UV varnish cannot reach the viscosity required by the glazing machine, you can use a diluent to remove the viscosity or use a thickener to add viscosity. However, after such adjustment, the curing speed, brightness and adhesion of UV varnish will be lost.

(7) UV varnish flows to the rotating part of the transmission shaft of the glazing machine and will stick to the transmission shaft at high temperatures, affecting the transmission. Therefore, care should be taken to clean the shaft head.

(8) Special printing materials such as gold cardboard and PFT must use special UV glazing oil according to their respective surface properties.