In recent years, uv (ultraviolet) glazing technology is gaining popularity in the printing field. So what is uv? What is the use of uv for printing? What are the benefits of using uv technology for printing? and many more. Below we take these problems to get closer to uv.
Uv is the abbreviation of Ultraviolet Ultraviolet in English. Ultraviolet light is a band in the electromagnetic spectrum. Waves with a wavelength of 100 nm to 400 nm are called ultraviolet rays. The uv that we generally say in printing is actually the abbreviation of ultraviolet curing, that is, the process that the printed matter is dried under ultraviolet irradiation after the printing is finished.
First, the advantages and disadvantages of uv polishing:
1 There is no solvent in the formula, so there is no problem caused by solvent evaporation;
2 can quickly cure at room temperature;
3 Reduce energy consumption. Curing speed, so that the required energy per unit area decreases;
4 can be coated with a thermosensitive substrate;
5 coating process is simple and easy;
6 save space, much shorter than infrared heat drying box;
7 finished products can be stacked immediately;
8 coating performance.
1 If you do not use harmful monomers, it is often difficult to prepare coatings with very low viscosity;
3 has skin irritation;
4uv light source produces ozone;
5 coating has low adhesion and shrinkage.
Second, the chemical composition of uv coating oil.
The chemical composition of uv coating mainly includes radiation prepolymer, thinner and photoinitiator:
1. Radiation prepolymer. Prepolymers are chemical systems with residual unsaturation molecules. This molecule is capable of cross-linking with other unsaturated molecules when in certain conditions, from a liquid to a solid coating. It is required that these unsaturated molecules must be stable and not react with each other before crosslinking.
1) Epoxy acrylate;
2) Acrylated oil;
3) Acrylic urethane;
4) unsaturated polyester;
5) Polyester acrylate;
6) Polyether acrylate and the like.
2. Thinner. Diluents are also chemical systems containing unsaturated molecules. Use it to adjust the viscosity, while it is a film-forming substance. Some situations can replace prepolymers. To make the viscosity reach the desired range, it is often necessary to add a small amount of volatile organic solvent to the mixture of prepolymer and diluent, but up to no more than 5%-10%.
Diluents are divided into active and inactive two. Inactive diluents include solvents and plasticizers. Solvents are mainly volatiles. Plasticizers impart certain flexibility to the cured coating, which not only reduces viscosity but also facilitates coating and leveling. The addition of a reactive diluent to the prepolymer can change the viscosity, tackiness, flexibility and hardness. Reactive diluents can be divided into monofunctional and polyfunctional groups.
Monofunctional reactive diluents, such as 2-ethylethyl acrylate, are flammable, volatile, and irritating to the skin. The polyfunctional reactive diluents have low volatility, high flash point, and low skin irritation.
The role of reactive diluents is as follows:
1Adjust the viscosity and leveling;
2 and photoinitiator system determine the curing speed;
3 with high molecular weight prepolymer molecules linked together to accelerate curing;
4 to improve and improve the performance of the cured coating.
3. Photoinitiator. Photoinitiators are defined as molecules that absorb radiant energy and undergo chemical changes to produce reactive intermediates that have the ability to initiate polymerization.
The photoinitiator does not participate in the curing, so the photoinitiator concentration is low, and the amount thereof requires that the initiator itself or its photochemical product must not adversely affect the chemical and physical properties of the polymer after curing. Benzophenones are usually used.
Photoinitiators In the process of initiating polymerization, two more substances are indispensable. Photosensitive type refers to a chemical reaction that transfers energy to a photoinitiator molecule to initiate polymerization after absorbing light energy, and the photosensitizer recovers to its initial inactive state. The other is called photoactive agent or photo-enhancer (usually amines). It mainly enhances the activation rate of photoinitiator. It does not absorb radiation by itself and does not initiate polymerization, but it can increase the curing rate.
Third, uv coating the chemical process.
The basic composition of photo-curing materials are prepolymers, diluents, photoinitiators, auxiliaries, and pigments. The curing chemical process of light is excited by the absorption of photon energy by photoinitiators to form free radicals, which initiate polymerization of the prepolymer and the diluent (initiate molecular chain growth).
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