Application Of Polyurethane Adhesive For Shoes Making

Waterborne polyurethane adhesive has no solvent odour, no poison, no pollution, convenient operation, easy to clean residual glue, high solid content, safe and convenient storage and transportation. In recent years, with the attention of environmental protection and the increasingly stringent restrictions on volatile organic compounds and toxic substances in various countries, water based polyurethane adhesives with high environmental protection and low consumption are becoming more and more important. Their application fields are also expanding, and will gradually replace solvent based polyurethane adhesives in the market leading position.

1. Waterborne polyurethane and waterborne polyurethane adhesive

Waterborne polyurethane refers to polyurethane, which is soluble in water or dispersed in water. It can be divided into 3 categories according to its appearance and particle size, namely polyurethane emulsion, polyurethane dispersion and polyurethane aqueous solution.

Polyurethane emulsion: polyurethane dispersion system containing emulsifiers in water dispersions. It can be obtained by external emulsification. Its particle size is >0.1 m and its appearance is white and turbid.

Polyurethane dispersions: usually polyurethane dispersions without emulsifiers are called waterborne polyurethane dispersions or polyurethane dispersions. The particle size is 0.001-0.1 m and the appearance is translucent. It can be obtained by internal emulsification or self emulsification. According to the different hydrophilic groups introduced in polyurethane molecules, it can be divided into anionic, cationic and non-ionic types.

Polyurethane aqueous solution refers to the solution of polyurethane molecules dissolved in water. Its particle size is <0.001 m and its appearance is transparent. However, due to its poor water resistance and complex technology and high cost, its application is limited.

In practical applications, waterborne polyurethane adhesives are mainly composed of waterborne polyurethane dispersions or emulsions with thickeners, defoamer, wetting agents, curing agents and so on. Aqueous solutions are seldom applied to adhesives.

Two, the present situation and application of waterborne polyurethane adhesives

Foreign Studies on waterborne polyurethane adhesives began in 1950s, and did not break through in 80s until 90s. China's research started in the early 1970s, but it is still in the stage of development and development compared with foreign level. With the rapid development of the economy and the increasing demand for environmental protection, many domestic companies are actively investing in the development of waterborne polyurethane. At present, there are hundreds of research and production units for waterborne polyurethane adhesives in China. Waterborne polyurethane adhesive has the advantages of low temperature resistance, flexibility, good adhesion, wide physical properties and wide adjustable range. It has been used in flocking, laminating, bonding, woodworking, pressure sensitive adhesives, etc. Shoemaking It has been widely applied in other fields.

When waterborne polyurethane is used for adhesives, it must be adjusted to suit construction conditions and substrate. Based on waterborne polyurethane, crosslinking agents, thickeners, fillers, plasticizers, pigments, other additives, other types of waterborne resins and water can be added. In order to obtain high water resistance, heat resistance and bonding strength, many waterborne polyurethane systems have been used as crosslinker to form a two component system, which is similar to the one component solvent type (volatile) polyurethane adhesive system. The sizing methods of waterborne polyurethane adhesives are basically the same as those of solvent based adhesives, such as hand brushing, mechanical roll coating and spraying. When spraying, it should be noted that the particle size and viscosity of the emulsion should not be too large.

Three. Application of waterborne polyurethane adhesives in shoemaking industry

1. Adhesive for shoes development history

modern Shoemaking industry Most of the soles and shoe upper parts of the key parts are connected by adhesives, so that the products are beautiful, light, comfortable, durable and reliable in quality, and the manufacturing process is simple and convenient, and the automation and continuous operation can be carried out.

The adhesive used for shoemaking was used in the 30~40 's in the twentieth Century, but because of its low cohesive force, it can only bind the leather backing. The era of real shoe adhesives began in 50s, and the advent of rapid crystallization neoprene made the adhesive process in shoemaking industry develop rapidly.

Common chloroprene adhesive is the first generation product. In 1957, after the introduction of the quick crystallization chloroprene rubber in Germany Bayer company, because of the high polar chlorine atoms contained in the molecular structure, it gave the polar materials good adhesive properties, and its rapid crystallization increased the initial viscosity, which made the neoprene adhesive widely used and gradually became the leading adhesive in the shoe making industry.

Graft modified chloroprene rubber and solvent polyurethane adhesive are the second generation products. In 1970s, grafted chloroprene rubber was developed, that is, grafting methyl methacrylate onto the main chain of chloroprene rubber can ease the migration of plasticizers in PVC and other shoe materials, thereby enhancing the adhesive properties and fastness of shoes. After introducing other acrylic monomers and polymers, the graft copolymerization of polychloroprene rubber can be more suitable for shoe making.

The "three benzene" common chloroprene rubber, graft modified chloroprene rubber and polyurethane adhesive modified by methacrylic acid are the third generation products. Polyurethane adhesive not only has the wide applicability of neoprene adhesive, excellent elasticity, flexibility and flexural properties, but also has better water resistance, grease resistance, plasticizers and heat-resistant properties than the latter. The developed countries in Europe and the United States gradually converted their shoe adhesive from polychloroprene rubber to polyurethane in the 80~90 's in the twentieth Century.

Waterborne polyurethane adhesive is the fourth generation product and is the most advanced product at present. With the improvement of global environmental awareness and the intensification of the oil crisis, the number of shoe factories began to control in various countries. The traditional oil-based adhesives gradually changed to water-based adhesives, prompting the fourth generation of environment-friendly solvent-free and water-based adhesives for shoes to emerge and gradually occupy the market.

2, the present situation of shoe adhesive in China

The wet starch adhesive used in the shoe making industry in China is the earliest and the most widely used. It is mainly used in the bottom shoe lining of cloth shoes. In the early 60s, chloroprene rubber and grafted chloroprene rubber were used in the early 60s. The shoe adhesives developed rapidly in the middle of 80s. At present, there are more than 200 manufacturers of shoe adhesive in the country, of which more than 100 are located in coastal areas, and are generally accompanied by factories in shoemaking bases.

Guangdong province is the largest footwear production base in China. The shoe adhesive plant is the largest in the country, with a total of more than 70, and more than 30 of the above scale level, most of which belong to foreign-funded enterprises. About half of these adhesive factories produce export products (equipped with export shoe factories). Fujian and Zhejiang each have about 40 enterprises producing adhesive for shoes. Jiangsu, Shandong and Tianjin have more than 10 enterprises producing adhesive for shoes.

Since the reform and opening up, China's footwear industry has been developing rapidly, with output of about 10000000000 pairs in 2007 and output of about 20000000000 pairs in 2013. There are about more than 20 thousand shoemaking enterprises in the country. Over 80% of the footwear produced is adhesive shoes (including leather shoes, travel shoes, sports shoes, casual shoes and cloth shoes). Adhesives are basically used. The adhesive quantity is about 600 thousand tons (non volatile mass fraction <20%).

At present, adhesives for sticking to the outer base are mainly solvent polyurethane and neoprene, both domestic and abroad. For less demanding shoemaking occasions, neoprene latex can be used. Waterborne polyurethane adhesive is an important class of waterborne adhesives. It has developed rapidly in recent years due to its excellent adhesiveness, outstanding oil resistance, impact resistance, wear resistance and low temperature resistance. Some of the three funded footwear factories in China have begun to use waterborne polyurethane adhesives. The main raw materials of adhesives are waterborne polyurethanes, which are basically imported products (such as Germany's Bayer OispercollU54, which is a high solid waterborne polyurethane emulsion prepared by acetone method). It is mainly used to produce 4 famous brand shoes (Nike, Adidas, etc.) exported to China from abroad, and some OEM foreign trade orders, etc., which consumes more than 20 thousand tons of waterborne polyurethane adhesive annually. The domestic manufacturers of adhesives have more influence on Nan Guang resin, Tai Dong resin and Nan Bao resin. These manufacturers mainly produce solvent based adhesives. Although they already have waterborne adhesives products and have been put on the market, they mainly satisfy the above market demand, and have not vigorously promoted their applications. A few years ago I Only a few manufacturers of domestic shoe brands, such as Kangnai, Hongxing Erke, double star and red dragonfly, began to use waterborne polyurethane adhesives before and after 2005.

Yantai Liancheng macromolecule material Co., Ltd. is a patent of waterborne polyurethane adhesives. Since its establishment in 2011, it has been specializing in the development of environmentally friendly, high-performance waterborne polyurethane adhesives. At present, a series of waterborne polyurethane adhesives have been developed. Only 5 kinds of waterborne polyurethane adhesives and curing agent products are available. At present, it has been applied in many OEM factories such as Lining, Binxing, ABC (Tong Xie), Decathlon and other famous brands such as Fujian, Quanzhou, Putian, Shandong Gaomi and Yinan. Its excellent hydrolysis resistance, heat resistance, no yellowing and good initial viscosity and high peel strength are superior to imported and domestic waterborne polyurethane adhesives, which are in the leading international level.

3. The application prospect of environmental protection, fire pressure and waterborne polyurethane adhesives in shoemaking industry

China has become the largest footwear producer, exporter and consumer in the world. In the year, 600 thousand tons of adhesives were used, and more than 90% were solvent based adhesives. These adhesives contained large amounts of toluene, xylene, butanone, acetone, ethyl acetate, alkane and other organic solvents, accounting for 80% or more of the total weight of the glue. These organic solvents have certain toxicity. Some of the inferior adhesives are even produced by benzene, and the toxicity is even greater. In addition to adhesives, cleaning agents, treatment agents and polishing agents are widely used in the footwear industry. Organic solvents are also widely used in these materials.

In addition to the occupational diseases caused by direct contact, the organic solvents in the atmosphere generate photochemical reactions under the action of ultraviolet radiation and produce two pollutants, such as ozone and aldehydes. In addition, volatile organic compounds (FLO) are inflammable and explosive, and require higher requirements for fire protection and explosion protection in the transportation, storage and use of related products. In recent years, there have been many poisoning and fire incidents in Guangdong, Fujian, Zhejiang and other shoe making areas, which fully reflects that the environmental protection and fire protection problems in shoemaking industry need to be fundamentally solved.

So many countries in the world have promulgated many laws and regulations concerning VOC (VOC is the general term of volatile organic compounds). In the shoemaking industry, according to the EU directive rule 1999/13/EG, by October 31, 2005, the VOC limit of each pair of shoes is 37.5g, and by October 31, 2007, VOC is 25g. For Nike, Adidas and other sports shoes brand, the demand for VOC is even higher. At present, the VOC of each pair of shoes is lower than 25g, but they are still adopting various processes and methods to lower the VOC of each pair of shoes, and zero VOC is the ultimate goal.