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Yuanlei Small Classroom | Composition of UV Ink and Its Function Analysis

Release time:

2024-01-29 09:38

 

Yuanlei Small Classroom | Composition of UV Ink and Its Function Analysis

 

The main components of UV ink are polymerizable prepolymers, photosensitive monomers, photoinitiators, and auxiliary components are coloring pigments, fillers, additives (leveling agents, polymerization inhibitors), etc.

 

1. Polymerizable prepolymer

Polymerizable prepolymer is an important component that determines the performance of UV varnish coating, is the most basic component of UV ink, is a film-forming material, and its performance plays an important role in the curing process and the properties of the ink film after curing. Generally classified according to the skeleton structure. The skeleton structure affects coating hardness, abrasion resistance, adhesion, light resistance, chemical resistance, and water resistance.

From the structural point of view of the prepolymer, the oligomer is a low molecular resin containing "C = C" unsaturated double bond, such as acrylic acid group, methacrylic acid group, vinyl group, allyl group, etc. There are mainly epoxy acrylate resin, polyurethane acrylate resin, polyester acrylate resin, polyether acrylic resin, polypropyl acrylate, unsaturated polyester resin and other resin types. Under the same conditions, the photocuring speed of acryl is the fastest, so most of the oligomers are acrylic resins.

 

 

2. Photosensitive monomer (reactive diluent)

UV ink and UV varnish need to adapt to the viscosity of the coating machine when coating, generally by adding 20% to 80% of the monomer to reduce the viscosity of the prepolymer, while the monomer itself polymerizes to become a part of the cured film.

Reactive diluent is also called crosslinking monomer, is a functional monomer, its role in the ink is to adjust the viscosity of the ink, curing speed and curing film performance. Reactive diluents also contain "C = C" unsaturated double bonds in the structure, which can be acryloyl, methacryloyl, vinyl and allyl. In view of the fastest speed of acryloyl light fixation, the active diluents currently used are mostly acrylate monomers. Due to the different number of acryloyl groups, it can be divided into three categories: single functional group and double functional group. The release effect and curing speed of reactive diluents of various functional groups are different. Generally speaking, the more functionality, the faster the curing speed, but the worse the dilution effect.

Traditional reactive diluents, such as styrene, the first generation of acrylate monomers, are very toxic, and some acrylate monomers have a strong irritating effect on the skin. In order to reduce the irritation of active diluents to the skin, there are usually two methods: one is to use ethylene oxide, propylene oxide and ester ring-opening polymerization to increase the molecular weight of the monomer; the other is to change the structure of the monomer ester group; Another is to change the previous use of alcohol esterification method. In the use of alcohol addition to the acryloyl group, the multi-functional monomer skin irritation is greatly reduced, such as neopentyl glycol diacrylate using esterification synthesis, the PH value (skin irritation index) is 4.96, and the use of additive synthesis, the PH value is reduced to 0.3.

Recently, some monomers with good performance have been developed, such as: alkoxy acrylate, carbonic acid monoacrylate, imidazolyl monoacrylate, cyclic carbonate monoacrylate, epoxy silicone monomer, silicone acrylate and vinyl ether monomer. When selecting monomers, follow the following principles:

A, low viscosity, good dilution effect;

B, curing fast;

C, in the material has good adhesion;

D, the skin irritation, small toxicity;

E, in the coating does not leave odor.

 

 

3. Photoinitiator

Photoinitiators are substances that can absorb radiation energy and undergo chemical changes to produce active intermediates with initiator polymerization capabilities. They are also the main components required for any UV curing system. Photoinitiators can be divided into hydrogen abstraction type and cleavage type. Hydrogen abstraction type needs to be combined with a compound containing active hydrogen (generally called co-initiator) to form free radicals through hydrogen abstraction reaction, which is a bimolecular photoinitiator. Cracking type is a monomolecular photoinitiator after photoinitiator is excited and decomposed into free radicals within molecules.

(1) hydrogen abstraction type: taking xylene ketone (BP) as an example, when benzophenone is used alone, vinyl monomers cannot be photopolymerized, and the requirements for it to become a photoinitiator are different. The reaction mechanism is different alkyl and aryl, from the alcohol and ether extraction of hydrogen atoms, oxygen is easy to quench the excited state of benzophenone. When extracting hydrogen atoms from amines, the amine system is not easy to be quenched by oxygen due to the formation of an excited state complex with the amine immediately after the ketone forms an excited state, thus avoiding the energy transfer to the oxygen molecule. Compared with the alcohol ether system, the possible type of energy transfer to the monomer is also reduced. Therefore, in practical applications, amine systems are generally used. In addition to benzophenone, this type of photoinitiator and anthraquinone thioxanthone, such as commonly used in UV ink 2-isopropyl thioxanthone.

(2) Cracking type: Take benzoin ethers as an example, benzoin ether was the most widely used photoinitiator, which is characterized by the direct decomposition of excited state grams into two total free radicals. The resulting free radicals can all initiate polymerization of the monomer. The excited state life of benzoin ether is short, it is not easy to be quenched by oxygen, and it can not be quenched by styrene, so it can be used for the polymerization of styrene. However, benzoin ether has different degrees of thermal decomposition even if it is not light, and its storage stability is not good. Generally, stabilizers and polymerization inhibitors are added. At present, the commonly used one is dimethyl ether.

Principles to be followed in selecting photoinitiators:

A, the UV range of light absorption efficiency;

B. Good relative stability;

 

C, low cost.

 

 

4. Other auxiliaries

Additives are mainly used to improve the performance of the ink, UV ink commonly used additives are stabilizers, leveling agents, defoamers, dispersants, waxes and so on.

(1) Stabilizer: Stabilizer is used to reduce thermal polymerization during storage and improve the storage stability of ink. Commonly used hydroquinone, p-methoxyphenol, p-benzoquinone, 2,6-di-tert-butyl cresol, etc.

(2) Leveling agent: Leveling agent is used to improve the leveling of the ink layer, prevent the generation of shrinkage, make the surface of the ink film smooth, but also increase the gloss of the ink printing.

(3) Defoamer: Defoamer is used to improve the leveling of the ink layer, prevent the generation of shrinkage, make the surface of the ink film smooth, and also increase the gloss of the ink printing.

(4) dispersant: dispersant can make the pigment in the ink in the binder is very good low wetting, so that the pigment in the ink has a good dispersion, shorten the grinding time when the ink is made; Reduce the pigment oil absorption, in order to produce high concentration of ink; To prevent the ink pigment particles in the cohesion of precipitation. The dispersant is generally a surfactant.

 

(5) Wax: The main function of wax is to change the rheology of ink, improve water resistance and printing performance (such as adjusting viscosity), reduce dirt, paper hair and other ills, and can form a smooth wax film on the surface of the dried ink film to improve the abrasion resistance of printed matter. In the UV ink, wax also plays a barrier to air, reduce the oxygen blocking effect, is conducive to surface curing. However, adding excessive wax to the ink and selecting the wrong wax variety will reduce the gloss of the ink, destroy the ink transfer performance, and extend the drying time.

 

 

 

 

 

 

 

 

Action, ink, monomer, initiation, uv, polymerization, acrylate, curing, activity, resin

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