Selection Of Adhesives For Polyurethane Artificial Leather Peel Test

　　 Introduction

Peel strength is polyurethane (PU leather) artificial. Leatherwear A very important physical performance index, it directly affects the quality and performance of artificial leather. If the peel property is not good, the separation between coating layer and base cloth will occur during the use of the product, resulting in the rupture of the surface, which will not only affect the appearance of the product, but also seriously affect the service life of the product.

GB/T 8949 - 2008 "polyurethane dry synthetic leather" points out that when testing the peel performance of polyurethane artificial leather, it is necessary to use the appropriate adhesive to glue the coating surface of the artificial leather to the same kind of leather coating layer. If the adhesive is not selected properly, not only the adhesion effect is not ideal, but also directly affect the peel property. If the adhesive strength of the adhesive is less than the connection strength between the coating and the base cloth, the coating surface can not be stripped. Starting from the processing technology of polyurethane artificial leather and the bonding principle of adhesives, suggestions are made for the selection of adhesives in the test of artificial leather peel.

　　 1. Introduction of polyurethane artificial leather

Polyurethane artificial leather is a synthetic material that forms polyurethane resin film or similar leather structure on the base cloth of woven fabric, non-woven fabric and other materials, and looks like natural leather material [1]. Polyurethane artificial leather was introduced into the Chinese market in the last century, and developed rapidly due to its excellent properties. In recent years, with the improvement of the performance of polyurethane artificial leather, the variety of its color is increasing day by day, and in some ways it has become a substitute for natural leather and widely used in leather products. clothing , shoes Cap, automobile decoration and other industries [2]. Polyurethane artificial leather is divided into two main categories, [3], wet process and dry process. The dry polyurethane artificial leather is made of polyurethane resin with a certain solid content. First, the surface layer is made on the release paper, then the adhesive paste is scraped on the epidermis, and then bonded with the base cloth, and then dried and ripened. The wet polyurethane artificial leather is coated with polyurethane paste on the lint cloth, solidified into the liquid tank, and then washed, dried and decorated to form a microporous artificial leather. The PU artificial leather produced by wet processing produces breathable microporous layer, which makes the products have breathability, moisture permeability, good softness and full elastic touch, and is similar to natural leather.

　　 2. Types of adhesives and bonding principle

Adhesive, also known as adhesive, is a non-metallic media material that makes the object tightly connected with another object. It can effectively bind materials together. Adhesives are usually made of base materials, curing agents, accelerators, fillers, toughening agents, diluents, coupling agents, stabilizers, antioxidants, tackifier, thickeners, etc. Adhesives belong to organic polymer compounds. They are classified into the following categories.

2.1 polyurethane adhesive

Polyurethane adhesive [4] refers to the binder containing carbamate (NHCOO -) and / or isocyanate (NCO -) in the base material. Polyurethane adhesives have high polarity and reactivity because of their carbamate and isocyanate groups. Its molecular formula is:

Polyurethane adhesives can form strong chemical bonds and physical bonds with all kinds of substrates with active hydrogen. Therefore, the adhesive has high adhesive strength and is a chemical reaction adhesive. It is especially suitable for bonding metal to rubber, rubber and fabric, metal and plastics, plastics and plastics.

Polyurethane artificial leather coating is mainly composed of polyurethane. It also contains highly polar and highly reactive isocyanate groups and urethane groups. It can form strong chemical bonding and physical bonding with polyurethane adhesives to achieve good adhesion effect and meet the needs of experiments. Polyurethane adhesives can be cured at room temperature or can be heated and solidified. Curing is a polymerization reaction without any by-products, and it is not easy to cause defects in the bonding layer. It is very convenient for daily testing.

2.2 chloroprene rubber adhesive (chloroprene rubber)

Neoprene [5] is a synthetic rubber compound produced by mass production. Chloroprene rubber has wide application scope, high initial adhesion and high bond strength. It is mainly used for decoration, Woodenware industry, shoe making industry and other industries in home and public facilities.

Chloroprene rubber is divided into two types: anionic and nonionic. The non-ionic type is a copolymer of chloroprene and methacrylic acid with good stability and carboxyl functional groups. Chloroprene rubber is produced by emulsion polymerization. The production process is mostly single pot batch polymerization. The polymerization temperature was mostly controlled at 40 ~ 60 C, and the conversion rate was about 90%.

Neoprene adhesive has high cohesive strength, heat resistance, oil resistance and aging resistance. It has good adhesive effect on polyurethane artificial leather.

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2.3 epoxy resin adhesive

Epoxy resin adhesive [6] is a kind of engineering adhesive made of epoxy resin, curing agent, diluent, accelerant and filler. It is an important variety of structural adhesives.

Epoxy resin refers to organic polymers containing two or more than two epoxy groups. The molecular structure of epoxy resin is characterized by its active epoxy group in the molecular chain. The epoxy group can be located at the end, middle or ring structure of the molecular chain. Because of the active epoxy group in the molecular structure, they can crosslink with various kinds of curing agents to form insoluble or non melting polymer with three direction network structure.

Epoxy resin has good adhesive properties for various metal materials such as aluminum, steel, iron and copper, non-metallic materials such as glass, wood, concrete, and thermosetting plastics such as phenolic aldehyde, amino and unsaturated polyester in addition to the poor bonding property of polyolefin and other non-polar plastics. Polyurethane artificial leather coating contains active carbamate group, which can form strong adhesive force with epoxy resin adhesive. The epoxy resin has high cohesive strength and high adhesion strength, and it can meet the requirements of polyurethane artificial leather peeling performance test.

2.4 silicone adhesive

Silicone adhesive [7] is a kind of adhesive with silicone resin or silicone elastomer as the basic film forming material. Generally, it is divided into two categories: silicone resin based adhesives and silicone rubber based adhesives. Silicone has special properties and strong adaptability. It is known as "all-purpose".

Organosilicon has the characteristics of no reaction with chemicals, poor mechanical properties, poor wear resistance and low adhesion strength. It can not form good bonding layer with polyurethane artificial leather coating, and its adhesive strength is low.

2.5 cyanoacrylate adhesive (CA)

The main component of alpha cyanoacrylate adhesive [8] is alpha cyanoacrylate, which contains a small amount of thickeners and stabilizers. Because of its quick curing, it is commonly used as instant dry glue. It is one of the most important engineering adhesives and an important household adhesive.

The curing mechanism is that when the substrate is solidified, there must be a certain humidity on the surface of the substrate. After moisture and acid stabilizer, the monomer can react anionic polymerization on the surface of the substrate under the action of water vapor. From the curing mechanism, it can be seen that raising temperature does not accelerate the curing of instant dry glue. Because of high temperature and low humidity, it is impossible to destroy acid stabilizer quickly and completely.

Because of the strong polar cyanide and ester bonds, the polar cyanide acrylate adhesive has strong adhesion to the polar stickies, and is easy to wet and permeate. When testing the peeling performance, it will permeate into the polyurethane artificial leather cloth, which leads to the test that it is not the peeling performance of the coating layer, and it is a low viscosity glue, and can not be used for the porous materials such as adhesive polyurethane artificial leather. The adhesive layer is brittle and the peel strength is low, so it can not meet the requirements of the peeling performance test.

　　 3. Conclusion

Through the analysis of the bonding principle of the above adhesive, the adhesion strength of polyurethane glue, chloroprene rubber and epoxy resin adhesive is higher, and the adhesion strength of organic silica gel and cyanoacrylate glue is lower. Polyurethane and other adhesive can produce chemical action with the coating layer of polyurethane artificial leather. The coating surface of the two samples can be firmly bonded together to make the coating completely separated from the base cloth, so that it can meet the test requirements satisfactorily. When silicone rubber and cyanoacrylate are used to test the peeling performance, they can not separate the coating from the base cloth because of the low adhesion strength. To sum up, it is recommended that polyurethane adhesives be selected for testing the peel properties of artificial leather, followed by epoxy resin and neoprene.