Application Of UV Curable Coatings In Leather Finishing

UV curing (Uv curing) is a kind of radiation curing technology and a new green technology.

UV curing coatings (UvCC) is an energy saving and environment-friendly coating developed in 1960s.

After UV irradiation, it will undergo photochemical reactions. Liquid oligomers (including monomers) will form solid coatings in a pient manner after cross-linking polymerization.

UVCC can be widely applied and developed because it has the unique advantages of energy saving, environmental protection, excellent coating performance and high production efficiency.

The main components of 1.UVCC consist of UVCC polymerized prepolymer (photo active oligomer), active diluent (photo active monomer), photoinitiator, auxiliaries (leveling agent, defoamer, matting agent, surface slip agent).

Their respective properties and research progress are as follows.

1.1 oligomer oligomer is one of the most proportions of light cured products. It is the base resin of light curing formula, which determines the basic properties of cured products (including hardness, flexibility, adhesion, optical properties, aging resistance, etc.).

It mainly includes unsaturated polyester resin, epoxy acrylate, polyurethane acrylate, polyester and acrylonitrile polyacrylate.

In the late 1930s, unsaturated polyester resins were first developed as photocurable oligomers.

Epoxy acrylate is made from commercial epoxy resin and acrylic acid or methacrylate. It is the most widely used photocurable oligomer in the domestic light curing industry.

Its chemical resistance, strong adhesion and good wettability of pigment make it widely used in paper coatings, wood coatings and metal primers.

In order to highlight the performance advantages of the oligomer, there are many researches on its modification at home and abroad. For example, amine modified epoxy acrylate and quaternary amine groups are introduced. Its main characteristics are high curing speed, increased adhesion strength and toughness of the cured film. Therefore, it has important application value in screen printing, flat printing and flexographic printing ink.

There are also phosphate modification, polyanhydride modification, siloxane modification, long chain fatty acid modified epoxy acrylate and so on.

The application of polyurethane acrylate is second only to epoxy acrylate, and plays an important role in the light curing of soft substrates such as paper, leather and fabrics.

However, because of its slow curing and relatively high price, it is seldom used as the main oligomer in the light curing formula, but as an auxiliary functional resin.

In the late 1980s, oligomers, such as vinyl ether series and epoxy series, were formed by cationic mechanism, such as acrylates oligomers. The curing of these oligomers was not affected by the inhibition of oxygen in the air, and the curing speed was fast and developed rapidly.

A hybrid oligomer of vinyl group with oxygen free radical curing mechanism and oxygen ionic curing mechanism has been synthesized.

With the continuous development of UVCC and the increasing awareness of environmental protection, various kinds of waterborne oligomers are emerging.

Research papers have reported unsaturated polyester used for UV curable waterborne coatings.

Phifips and others reported polyester acrylate with different polyols and polybasic acids. It is considered that at least 6% to 7% hydrophilic groups must be obtained to obtain good water solubility, and its relative molecular weight is 6403000. The cured product has good solvent resistance and water resistance.

1.2 the traditional solvent based coatings for photo active monomers usually need to add organic solvents to play a role in regulating viscosity. These organic solvents generally do not participate in the formation of membrane reaction. When the film is formed, volatilization into the air will cause environmental pollution.

In the light curing system, photo active monomer (active diluent) not only plays a role in regulating the viscosity of the system, but also usually takes part in the curing film forming reaction, and rarely volatiles into the air, which gives the system environmental protection characteristics.

According to the reactive group contained in the molecule, the active diluent is divided into single functional and multifunctional reactive diluent.

Young studied the effect of functionality on the polymerization rate. The results showed that the greater the functionality, the faster the curing rate and the higher the crosslinking degree.

At present, the most widely used active diluent is (methyl) acrylate, which has developed into the third generation of active diluent, and has the advantages of high reactivity and low shrinkage.

1.3 photoinitiator photoinitiator is a key component of UVCC, and its action is to produce active groups that initiate curing reaction.

Generally, it is divided into free radical polymerization photoinitiator and cationic polymerization photoinitiator.

There are few studies on anionic photoinitiators, and no commercial application has yet been reported.

Free radical photoinitiators are divided into two categories: splitting type and hydrogen abstraction type.

Most of the free radical photoinitiators are aryl alkyl ketones, such as benzoin derivatives, benzoyl ketal derivatives, two alkoxy acetophenones, a hydroxyalkylbenzophenones, a amine alkyl benzophenones, etc. benzoin is an early photoinitiator, and is rarely used because of its yellowing.

A hydroxy alkyl benzene ketone is the most successful photoinitiator in application development. The most widely used in China is I~OCUY1173 and Irgacure184 of Ciba company.

The initiator / photosensitizer complex initiator system using the tertiary amine photosensitizer can inhibit the inhibition of oxygen and improve the curing speed.

The cationic initiator represented by cylinder salt can rapidly induce oligomers and monomers to form film, and is not affected by the inhibition of O in air.

Several kinds of Weng salts have been synthesized, and the initiating behavior of Weng salt has been studied in depth. Their photoinitiating efficiency has been compared. It is found that not all salts have cation initiating function.

Effective Weng salts are: sulfur salts, iodine salts, nitrogen salts, aromatic ferric salts, etc. their negative ions are [B (PhF5) 4] 1, PF6 1, SbF6 1, AsF6 1, etc. the curing rate depends on the activity of these negative ions. The study shows that the activity size is SbF6 equal to AsF6 greater than PF6 PF6 or BF4 one [B (PF6) 1.

It is shown that [B (PhF5) 4] has a stronger activity than SbF6, which uses 0.4% [B (PhF5) 4] iodide salt to initiate functionalized siloxane polymer, and its curing speed can reach 457m / rain.

Because SbF has a certain toxicity, [B (PhF5) 4] salt has the tendency to replace sb salt.

In addition, polymer photoinitiators and polymerizable photoinitiators were also studied to overcome the degradation effect of small molecules or fragments retained in the cured films after the decomposition of small photoinitiators.

1.4 in other practical applications, the UV curing system often needs to add various auxiliaries to meet other requirements.

For example, in the coloured system (paint, ink, etc.), pigments need to be added. In order to achieve good flow smoothness, it is necessary to add levelling agent. In order to suppress the formation of bubbles in the system, defoamers are often added, and the addition of matting agents is to reduce the gloss of the curing film and obtain low gloss or matt coatings.

Because of the advantages of fast curing speed and friendly environment, the application range of 2UVCC has been developed rapidly in various industries. The base material adapted to the UVCC has been extended from the earliest wood to paper, plastic, metal, stone, cement, fabric, leather and so on.

2.1 paper glazing paint glazing is a varnish, commonly known as light cured varnish, suitable for book covers, advertising posters, merchandise packaging cartons, decorative paper bags and other coating decoration, giving products high gloss, wear resistance, water resistance, enhance the beauty of products.

2.2 wood coatings UVCC was originally used for woodwork painting. Now wood UVCC is a large output of light cured products.

According to the use occasions and quality requirements, wood UVCC can be divided into wood flooring coatings and decorative board coatings, and can also be divided into varnish and colored paint.

For construction purposes, it includes UV putty, UV primer and UV topcoat.

UVCC for wood furniture requires high gloss, abrasion resistance, scratch resistance, high hardness and multi color. UVCC for wooden floor requires matte, abrasion resistance, scratch resistance, impact resistance and corrosion resistance.

2.3 plastic coatings generally include ordinary plastic coatings and engineering plastic coatings.

It can give ordinary plastics such as polystyrene products, plexiglass, polyester film products and other frictional and scratch resistant properties. It gives high performance, high gloss, beautiful appearance and other engineering plastics such as phenolic products and ABS products. For plastic flooring, UVCC can give it no scratch, wear resistance, low gloss, beautiful appearance and so on.

2.4 metal coatings are widely used in metal label decoration, cans processing, metal decorations, aluminum alloy doors and windows protection and temporary coating protection of steel pipes.

It plays a protective role for the products, and makes it more elegant and beautiful.

2.5 the research of optical fiber coatings for optical fiber UV coatings has begun in foreign countries in 1970s, and Hubei Institute of chemistry and Xi'an Jiaotong University have made special researches in this field.

The main function of optical fiber UV coating is to protect the strength of quartz glass and to prevent environmental pollution.

2.6 other coatings, according to the different materials, UVCC can also be used for glass, leather, ceramics, silicate stones, compact discs and so on.

The application scope of UVCC is very wide. People are still researching and developing new application fields.

3 leather UVCC UVCC was originally used for wood coating. With the continuous development and improvement of technology, its application scope is more and more extensive.

The study of UVCC applied to leather finishing began in 1970s, but in China, research in this field is still rare.

Compared with the traditional leather finishing agents, the advantages of UVCC applied to leather finishing are: (1) the curing speed is greatly increased, the drying time is even less than 1min, and the wet film adheres to the dust to reduce the possibility of gloss reduction. (2) the amount of solvent volatilization is greatly reduced; (3) the curing temperature is low; (4) the gloss and aesthetics of the film are excellent; (5) the use of crosslinking agent such as formaldehyde in leather finishing agent is avoided, which is environmentally friendly and accords with the development direction of ecological leather; (6) it can be used for leather finishing, and also can be used for the finishing of synthetic leather and synthetic leather, and the equipment is simple.

The leather making process with Uv coating mainly includes the following steps: leather (synthetic leather), ironing, one UVCC bottom coating, one radiation curing, one I a, top coating and one radiation curing.

With the continuous development of society, people's awareness of environmental protection is also growing. More attention should be paid to developing environmentally friendly technologies and chemicals that are environmentally friendly and harmless to human body.

UV curing technology is a new environment-friendly technology. It is believed that its application in leather finishing will become a major trend. Uv leather finishing agent will also become one of the research hotspots in leather finishing agents.

4 the current situation and development trend of UVCC at home and abroad, as early as the early 1970s, China began to study UV curing coatings.

Several furniture production lines were established in Shanghai and Beijing, but they were dismounted due to lack of raw materials, light source and curing equipment.

The real development should start in 1990s. In the past more than 10 years, the research and product varieties in this field have made considerable progress and have formed the industrial scale.

In 1993, the radiation curing branch (RadtechChina) was set up in China. It is the only country in Asia that owns the association after Japan. Now there are 200 member units.

According to incomplete statistics, our country has more than 200 UV curing wood flooring production lines and more than 400 printing lines.

At present, a batch of Uv curing coatings factories have sprung up in China. Their quality has been continuously improved, their varieties have been increasing, their output has increased rapidly, and their development prospects are good.

Peking University, Tsinghua University, Beijing Normal University, Beijing University of Chemical Technology, Beijing University of Chemical Technology,