The development of polyurethane adhesive in China was in the 1960s. Since the 1980s, the country has been more active in exploring water-soluble polyurethane, but it is still in the design stage compared with the level of the general industry of water-soluble polyurethane adhesives abroad. In the 1990s, many production lines were introduced in various fields, and a number of foreign-funded enterprises were established in succession. Imported goods urgently needed to be industrialized. Relevant scientific research institutions and production enterprises have increased their development efforts, and new products are emerging in endlessly.
Polyurethane adhesive refers to the adhesive containing carbamate functional group or isocyanate group in the polymer chain. According to the reflected composition, it can be divided into polyisocyanate adhesive, polyurethane adhesive containing isocyanate group, methyl polyurethane adhesive and polyurethane epoxy resin adhesive. According to the use and characteristics, it can be divided into general adhesives, adhesives for food packaging materials, shoe adhesives, paper plastic composite adhesives, engineering adhesives, structural adhesives, low-temperature adhesives, foaming material adhesives, anaerobic adhesives, conductivity adhesives, hot melt adhesives, pressure sensitive adhesives Sealing adhesive, water-soluble adhesive and sealing adhesive, etc. However, no matter which kind of polyurethane adhesive is used, all the isocyanate groups in the field react with active hydrogen containing substances in the system or outside the management system to form polyurethane functional groups or aspartic polyurea, thus further improving the compressive strength of the management system to achieve the bonding effect.
Up to now, in addition to the original adhesive types, there are almost all kinds of additives free polyurethane weather resistant adhesive, reactive polyurethane hot-melt adhesive and other foreign adhesive types in China. At present, the domestic polyurethane industry has a considerable scale of production, but there is still a big gap compared with developed countries, usually the production volume is not large, and the technical strength is still relatively low. What are the characteristics of polyurethane adhesive? What areas is it also used in? Today, Shanghai Caoshi Chemical Plant Technology Co., Ltd. will give you a brief introduction!
1、 Characteristics of polyurethane adhesive
1. The adhesive force is strong, the initial viscosity is large, and the adaptability is strong. Because the - NCO in the polymer chain of polyurethane adhesive can react with a variety of groups containing active hydrogen, resulting in page ionic bond fusion, it has a strong adhesive property to a variety of materials. It can not only bond raw materials with porous structure, such as foam, porcelain, wood, textiles, etc., but also bond a wide range of metal materials, inorganic materials, plastics, rubber and leather products.
2. Remarkable low temperature resistance Under very low conditions, general polymer materials are converted to glass state and become brittle, while polyurethane adhesive can maintain high tensile strength even below - 250 ℃, and its shear strength increases significantly with the decrease of temperature.
2、 Defects of polyurethane adhesive and improvement plan
1. Free acrylate in polyurethane adhesive has great toxic and side effects. The epoxy polyurethane can be prepared by methyl terminated diversified epoxy compound and isocyanate terminated polyurethane oligomer, and then compounded with polyamine chemicals to form polyurethane adhesive. The adhesive takes into account the excellent performance of epoxy resin and polyurethane, and almost contains no free acrylate, with a high solid content. Polyurethane adhesive is developing towards green, energy-saving and environmental friendly adhesive with water solubility and no additives.
2. Polyurethane adhesives generally dry and solidify slowly at room temperature, and sometimes they dry and solidify completely for several days. If multi-component mixing is used, the curing time at room temperature can be significantly shortened, which is more convenient and usable.
3. The heat resistance of polyurethane adhesive is not as good as its low temperature resistance. If it is used in composite packaging materials for food packaging materials, it needs to have cooking resistance. Allowing human gold nanoparticles can significantly improve its temperature resistance, tensile strength, tensile strength and tensile strength, but the added nanocomposites should be appropriate. If too much is added, it may destroy the tight arrangement of hard segments in some biomacromolecules, thus reducing the structural mechanical properties.
3、 Use of polyurethane adhesive
1. Polyurethane adhesive for automobile The introduction of a large number of light metal materials, composite materials and plastics into the multi-functional automobile structure has led to a steady increase in the demand for adhesives and sealants for automobiles. The polyurethane adhesives most widely used in automobiles mainly include two-component wet and dry curing polyurethane sealants for installing automobile windshields, structural adhesives for bonding fiber reinforced plastics and block rubber plastic composite materials, component polyurethane adhesives for interior window parts and water-soluble polyurethane adhesives. Auto parts are an area where the use of adhesives is increasing rapidly. For a long time in the past, China's machinery manufacturing industry has been importing polyurethane automobile windshield adhesive from abroad. Until the eighth five-year plan period, research and development of such adhesive was listed as a national key scientific and technological project.
The water-soluble polyurethane adhesive widely used in vehicles refers to the adhesive formed by polyurethane which is easily soluble in water or dispersed in water. Most of the water-soluble polyurethane is linear thermosetting plastic polyurethane. Because its coating is not chemically cross-linked and its molecular weight is relatively low, its water resistance, solvent resistance, adhesive strength and other properties are weak, so it needs to be modified to improve its performance
2. With the sharp decline of global natural resources and the implementation of ecological forest protection project in China, polyurethane adhesive for wood needs adhesive strength, durability, weather resistance and other properties better than wood itself when combining small wood with large board. The amount of adhesive used has become a symbol of the development level of wood manufacturing technology and economy. In the past, most of the commonly used wood adhesives were urea formaldehyde resin, urea formaldehyde resin and melamine formaldehyde resin with indoor formaldehyde as raw material. However, due to the existence of free indoor formaldehyde, formaldehyde gas will slowly release to the surrounding during the use of commodities, causing environmental pollution. Wood processing industry has begun to pay attention to the new environment-friendly adhesive polyurethane adhesive in order to reduce the impact on the environment.
The two-component moisture cured polyurethane adhesive used in the carpentry field is liquid and applied at room temperature. Generally, it has high bonding strength, good flexibility and water resistance, and can be bonded with many non wood plates (such as textile fibers, metal materials, plastics, rubber, etc.). The dry and wet strength of two-component polyurethane adhesive is better than that of phenolic resin adhesive.
3. China is a strong country in shoe industry. After three generations of high-speed development of shoe adhesives, with the improvement of international environmental awareness and the aggravation of economic crisis, the fourth generation of green and environmentally friendly solvent-free and water-based shoe adhesives were born. In recent years, the preparation methods of water-soluble polyurethane have become increasingly perfect. For the bonding of some low positive and negative shoe materials such as SBS with different materials, the tensile strength of polyurethane adhesive does not meet the requirements. The polyurethane shoe adhesive with high grain size, faster crystallization speed, high cohesive strength and ideal tensile strength can be developed by adding tackifying resin and other modified materials.
4. Packaging bag polyurethane adhesive plastic flexible packaging, also known as soft can, has exceeded hard packaging such as plastic, glass bottles and cans because of its distinctive comprehensive properties such as light and convenient weight, long freshness, environmental sanitation, easy storage and transportation, easy disassembly, waste reduction, and good storage shelf effectiveness. Due to its excellent performance, polyurethane adhesive can bond different film materials together to obtain composite packaging materials for flexible packaging materials with various properties such as low temperature resistance, acid and alkali resistance, drug resistance, full transparency, abrasion resistance, etc. Now in the international market, polyurethane adhesive has become the key adhesive for processing and manufacturing composite packaging materials for plastic flexible packaging. In the adhesive market in China, the polyurethane adhesive used in the packaging bag composite packaging material manufacturing industry ranks second only to the machinery manufacturing industry.
There are many kinds of polyurethane adhesives used for packaging, such as waterborne polyurethane adhesive, hot melt polyurethane adhesive, solution polyurethane adhesive and solvent-free polyurethane adhesive. The common polyurethane thermosols can be divided into two categories, one is thermosetting plastic polyurethane elastomer material thermosol, and the other is reflective thermosol. The biggest disadvantage of thermosetting plastic thermosol is its high viscosity, so it has a great impact on the apparent quality of sizing. Reflective polyurethane hot melt adhesive is a new kind of adhesive developed on the basis of traditional thermosol. It not only has the characteristics of good initial adhesion and excellent post curing performance of traditional thermosol adhesive, but also has the advantages of polyurethane composition and structure changing and a wide range of performance adjustment, and has good bonding performance for various plates.
In addition, considering the production of demulsifiers or the introduction of water absorbing cationic groups in the molecular structure, the waterproof property of the water-soluble polyurethane adhesive layer of the packaging bag has been reduced. In recent years, the exploration of improving the waterproof property has become a hot spot. And because of the large specific heat of water, how to improve its solid content and thus improve its drying speed is one of the problems to be solved at this stage.
5. In addition to the advantages of non-toxic, zero pollution and convenient application, polyurethane adhesive for engineering has the advantages that other adhesives do not have, namely, good low temperature resistance, water washing resistance, aging resistance, ozone resistance and bacteria resistance. It plays an important role in the application of engineering floor paving materials. It is widely used in elastic rubber floor mat, hard rubber floor tile and paved rubber runway sports ground.
The new component polyurethane adhesive breaks the difference between the shear strength and tensile strength of the traditional adhesive, allowing both to obtain relatively high strength at the same time. It highlights excellent performance in the bonding of steel plates for engineering purposes. The bonding is firm and easy to cause bending. At the same time, the indoor temperature can be adjusted to stabilize the speed, making these polyurethane adhesives easy to use and widely used. Polyurethane adhesive is widely used in engineering PVC raw material bonding, sandwich panel production and building waterproof coating.
6. The offset printing ink with polyurethane adhesive for printing ink is listed as the best choice for environmentally friendly packaging printing. The chemical crosslinked water-soluble polyurethane adhesive at room temperature can produce a two-component polyurethane offset printing ink suitable for gravure printing. The offset printing ink has good moisture resistance, strong adhesion, adjustable dryness, bright colors, clear layers, non-toxic, flame retardant, weather resistant, thick and easy to control. Compared with other offset printing inks, it has a wide range of adaptability to various printing plate raw materials.
As the bonding material of offset printing ink, polyurethane acrylate emulsion combines the properties of polyurethane adhesive and acrylate emulsion during the drying process of printing ink plastic film printing, so the moisturizing emulsion obtained from the modified material also has strong adhesion fastness to plastic film.
The wall fixing used in the field of color printing mainly includes polyester film, nylon film, polypropylene film, polyethylene film, etc. Experts from Tianjiang Chemical Plant pointed out that the key to selecting printing ink is to solve these problems with good adhesion.
7. In the past 20 years, the use of thermosol in book binding has made rapid development. The main reason is that the production and manufacturing of cheap paperback books have improved surprisingly. In addition, the wireless network printing and binding processing technology has been formed. Because EVA thermosol has very good adhesive flexibility, the vast majority of book binding thermosol used in the domestic market at this stage is EVA thermosol. However, EVA type thermosol is expensive, and EVA type thermosol has memory ability and other problems. The polyurethane hot-melt adhesive can fill in the above shortcomings. The adhesive is simple in production and manufacture, low in price, good in toughness and flexibility, strong in bonding strength, and can be repeatedly melted for application. The product occupies a small area, so it has a broader application prospect.
8. Other polyurethane adhesives, due to their excellent bonding characteristics, play an important role in the bonding of aerospace equipment, protection and restoration of cultural relics, military industry, office stationery, medical services, etc.
4、 Conclusion
Because of its excellent performance, polyurethane adhesive is widely used in all walks of life, and gradually becomes the key composite material in our life. With the gradual expansion of the use of polyurethane and the further enhancement of people's environmental awareness, at this stage, the global polyurethane adhesive industry is integrating into the development of ecological environment protection, health and safety, waste recycling and other aspects. The production of polyurethane adhesive industry in China has also shown a rapid growth trend, and scientific research and development have also made great progress.
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