UV Curing Adhesives and Their Application (2)

3, radiation curing features:

Radiation curing advantages:

(1) One-component system without mixing, easy to use;

(2) Curing speed is fast, curing can be completed in a few seconds to several tens of seconds, which is beneficial to automated production lines and increase labor productivity;

(3) low curing temperature, energy saving, room temperature can be cured, can be used for materials that are not suitable for high temperature curing, the energy consumed by ultraviolet light curing can save energy consumption ~ 90% compared with thermal curing resin;

(4) No pollution, can use low volatile monomers and oligomers, no solvent, 100% curing, so basically no air pollution, there is no waste water pollution problems;

(5) Excellent performance, wear resistance, solvent resistance, high impact, and high strength.

The disadvantage of radiation curing:

(1) Large equipment investment, especially electron beam curing equipment, the price of radiation curing adhesive is higher than the price of conventional adhesive, which can be compensated by low energy consumption and high production efficiency;

(2) Due to the weak penetrating power of UV light, the curing depth is limited, and the geometry of the curable product is limited. The non-transparent part and the dead angle where the UV light cannot reach are not easily cured;

(3) UV light can produce ozone and require an exhaust system.

Second, the curing mechanism:

The UV light curing system is divided into a free radical system and a cation system, and both of them have different curing mechanism components. The free radical system is generated by photoinitiators excited by UV radiation to generate free radicals, which initiate polymerization and cross-linking of monomers and prepolymers. The cationic system is a cationic photoinitiator that is irradiated by radiation to produce strong protonic acid, and catalytic addition polymerization to cure the resin. Here is an example of a free radical system:

UV radical curing proceeds through the following steps:

(1) When the radical photoinitiator is exposed to UV radiation, it initiates decomposition and generates free radicals:

(2) Chain initiation: The radical generated by the initiator initiates the unsaturated double bonds of the resin and monomer molecules to generate new free radicals.

(3) Chain growth: Free radicals generated from resins and monomers can continue to initiate the generation of free radicals in the unsaturated double bonds in the resin and monomer molecules, and carry out radical chain reactions.

(4) Chain termination: In the chemical reaction, free radicals contain uncoupled electrons and are very active. They are very prone to radical radical coupling or acidification and terminate the chain reaction.

As a result of the above reaction, a macromolecular compound is produced, and the glue liquid is converted into a solid.

Third, the composition of UV curing adhesive

1, prepolymer

The prepolymer is the skeleton of the UV light-curing adhesive. It is a reactive low-molecular polymer. The main function of the prepolymer is to provide the key layers of the adhesive, such as: viscosity, tensile strength, shear strength, hardness, and Flexibility and so on. The prepolymers used in the photo-curing free radical systems are some unsaturated polymers containing double bonds, mainly polyacrylates, epoxy acrylates, urethane acrylates, unsaturated polyesters, polyolefins/thiols, etc. Among them, epoxy acrylates and urethane acrylates have high reactivity, rich raw materials, many varieties, and moderate prices, so the dosage is the most.

2, single

The monomer in the radiation curing component is also called reactive diluent. Its main function is to adjust the viscosity and participate in the polymerization reaction. Monomers can be divided into monofunctional monomers, difunctional monomers and polyfunctional monomers according to the number of functionalities. Monofunctional monomers cure to form linear polymers, which are beneficial to improve the flexibility and adhesion of the adhesive layer; difunctional And polyfunctional monomers not only act as reactive diluents, but also act as cross-linkers, which have a significant influence on the hardness, toughness and strength of the adhesive layer. Increasing the functionality of the monomers accelerates the curing process. To accommodate the production of good performance adhesives, monofunctional, difunctional, and polyfunctional mixtures are often used.

The monomers used in the free radical curing system mainly include (meth)acrylates, vinyls, and vinyl ethers, such as styrene, butyl acrylate, isooctyl acrylate, isobornyl acrylate, and biscondensed. Propylene glycol diacrylate, hexanediol diacrylate, trimethylolpropane triacrylate, and the like. In addition to considerations such as adhesive performance and cost, the application of these monomers requires consideration of irritation and toxicity. Some irritant and toxic species are gradually eliminated, and more irritating and less toxic species are developed and used. In industrial production.

The prepolymers and monomers used in the cationic cure system are similar to the epoxy adhesives.