Abstract: Polyurethane adhesive refers to an adhesive containing a urethane group (-NHCOO-) or an isocyanate group (-NCO) in the molecular chain. Because polyurethane adhesives contain highly polar and highly reactive isocyanate groups and urethane groups, they have good chemical adhesion to materials containing active hydrogen. Therefore, they are widely used in various fields of the national economy such as construction, industry, and automobiles. application. So what are the polyurethane adhesive formulas? What is the principle of polyurethane adhesive? Polyurethane adhesive What are the polyurethane adhesive formulas and the principles of polyurethane adhesive
Polyurethane is the abbreviation of polyurethane. A general term for polymer compounds formed by the interaction of binary or polyvalent isocyanates and binary or polyvalent hydroxyl compounds. Depending on the raw materials used, products with different properties and uses can be produced. Polyurethane adhesive is one of them, which can be cured at room temperature, has high initial viscosity, good impact resistance, shear strength and peel strength, cold water resistance, oil resistance, and dilute acid resistance. It has a wide range of uses and can bond non-metals to non-metals, non-metals to metals, and metals to metals. The bonding force is very strong.
Principle of polyurethane adhesive
No matter what kind of polyurethane adhesive, the isocyanate group in the system reacts with substances containing active hydrogen inside or outside the system to form polyurethane groups. Polyurethane or polyurea, thereby greatly improving the strength of the system and achieving the purpose of bonding.
Classification and application of polyurethane adhesives
Polyurethane adhesives are an important component of polyurethane resins that are currently undergoing rapid development. They have excellent properties and have been used in many aspects. It is widely used and is one of the important varieties among the eight major synthetic adhesives.
Polyurethane adhesives have excellent shear strength and impact resistance, are suitable for various structural bonding fields, and have excellent flexibility properties.
Polyurethane adhesive has excellent rubber properties and can adapt to the bonding of substrates with different thermal expansion coefficients. It forms a soft-hard transition layer between substrates, which not only has strong adhesion, but also It also has excellent buffering and shock-absorbing functions. The low and ultra-low temperature performance of polyurethane adhesives exceeds that of all other adhesive types.
Water-based polyurethane adhesives have the characteristics of low VOC content, low or no environmental pollution, and non-flammability. They are the key development direction of polyurethane adhesives.
The diversity of polyurethane adhesives provides solutions to many bonding problems, and is especially suitable for places where other types of adhesives cannot bond or are difficult to bond.
In addition, polyurethane adhesives also have the characteristics of adjustable toughness, simple bonding process, excellent low temperature resistance and excellent stability. It is precisely because of the excellent bonding performance and adaptability of polyurethane adhesives to a variety of substrates that its application fields continue to expand, and it has become the fastest-growing adhesive at home and abroad in recent years.
1. Polyurethane adhesives for automobiles
The introduction of a large number of lightweight metals, composite materials and plastics into new automobile structures has resulted in the continued growth of automobile adhesives and sealants. The most widely used polyurethane adhesives in automobiles mainly include one-component moisture-curing polyurethane sealant for assembling windshields; structural adhesives for bonding glass fiber reinforced plastics and sheet molding composite materials; and two-component polyurethane adhesives for interior parts. And water-based polyurethane glue, etc. Automotive interior parts are also an area where adhesive usage is growing. For a long time in the past, my country's automobile manufacturing industry has been importing polyurethane windshield glue from abroad. It was not until the "Eighth Five-Year Plan" period that the development of this glue was included in the national key scientific and technological projects. Water-based polyurethane adhesives widely used in automobiles refer to adhesives formed by polyurethane dissolved or dispersed in water. Most water-based polyurethane is linear thermoplastic polyurethane. Since its coating film is not cross-linked and has a low molecular weight, its water resistance, solvent resistance, film strength and other properties are still poor. It must be modified to improve its performance. . The hybrid dispersion of polyester and acrylic acid is combined with uretdione and isocyanurate to prepare an automobile repair varnish that does not require high-speed stirring equipment, is easy to mix together, and has good adhesion properties.
2. Polyurethane adhesives for wood
With the rapid reduction of forest resources worldwide and the implementation of my country's natural forest resource protection projects, the joining of small timber to large boards requires adhesives with bonding strength and Its durability and weather resistance are better than those of wood itself.
The amount of adhesive used has become a symbol of the technological development level of the wood industry. In the past, most of the wood adhesives used were urea-formaldehyde resin, phenolic resin and melamine-formaldehyde resin with formaldehyde as the main raw material. However, due to the presence of free formaldehyde, the product will gradually emit formaldehyde gas to the surroundings during use, causing environmental pollution. The wood processing industry has begun to turn its attention to new environmentally friendly adhesives, polyurethane glue, in order to reduce environmental pollution. One-component moisture-curing polyurethane adhesives used in the woodworking industry are liquid and are used at room temperature. Generally, it has high bonding strength, good flexibility and water resistance, and can be bonded to many non-wood substrates (such as textile fibers, metals, plastics, rubber, etc.). The dry and wet strength of the one-component polyurethane adhesive in the test was better than that of the phenolic adhesive. Before bonding, coating hydroxymethylresorcin (HMR) coupling agent on the surface of the bonding substrate can improve the bonding strength. HMR can strengthen the bonding strength of all thermosetting wood adhesives. When the wood surface is precoated with HMR coupling agent, the strength and durability of the one-component polyurethane adhesive can meet the most stringent testing requirements.
3. Polyurethane adhesives for shoes
Our country is a big shoe-making country. After three generations of development, the development of shoe adhesives has increased with the increase in global environmental awareness and the oil crisis. Intensified, prompting the emergence of the fourth generation of environmentally friendly solvent-free and water-based shoe adhesives. In recent years, the preparation process of water-based polyurethane has become increasingly mature. For the bonding of some low-polarity shoe materials such as SBS, the peel strength of polyurethane adhesive does not meet the requirements. By adding tackifying resin and other modifications, a polyurethane shoe adhesive with high crystallinity, fast crystallization speed, high cohesive strength and ideal peel strength can be developed.
4. Polyurethane adhesive for packaging
Soft packaging, also known as soft cans, is lightweight and convenient, has a long shelf life, is hygienic, is easy to store and transport, is easy to disassemble, has less waste, and Unique comprehensive properties such as good shelf effect now exceed rigid packaging such as plastic, glass bottles and cans. Due to its excellent performance, polyurethane adhesive can bond film materials of different properties together to obtain composite films for flexible packaging with various properties such as cold resistance, oil resistance, chemical resistance, transparency, and wear resistance. At present, in domestic and foreign markets, polyurethane adhesives have become the main adhesives used in composite film processing for flexible packaging. In the domestic adhesive market, the consumption of polyurethane adhesives in the packaging composite film manufacturing industry ranks second after the shoemaking industry. There are many types of polyurethane adhesives used for packaging, such as water-based polyurethane adhesives, hot-melt polyurethane adhesives, solvent-based polyurethane adhesives, and solvent-free polyurethane adhesives.
The commonly used polyurethane hot melt adhesives can be divided into 2 categories:
1) Thermoplastic polyurethane elastomer hot melt adhesives:
2) Reactive thermal adhesives Melt glue.
The main disadvantage of thermoplastic hot melt adhesive is its high viscosity, which has a greater impact on the apparent quality of the coating. Reactive polyurethane hot-melt adhesive is a new type of adhesive developed on the basis of traditional hot-melt adhesive. It not only has the characteristics of good initial viscosity and excellent post-curing performance of traditional hot-melt adhesive, but also has polyurethane's versatile structure and performance. It has the advantage of large adjustment range and excellent bonding performance to a variety of substrates. In addition, in terms of packaging water-based polyurethane glue, the water resistance is reduced due to the use of emulsifiers or the introduction of hydrophilic ionic groups in the molecules. In recent years, research on improving its water resistance has become a hot topic. At the same time, due to the large heat capacity of water, how to increase its solid content and thereby increase its drying speed is also one of the problems that need to be solved urgently.
5. Polyurethane adhesives for construction
In addition to being non-toxic, non-polluting and easy to use, polyurethane adhesives also have advantages that other adhesives cannot match, namely excellent low temperature resistance, Solvent resistance, aging resistance, ozone resistance and bacteria resistance play an important role in the application of building paving materials [42]. It is widely used in elastic rubber floor mats, hard rubber floor tiles and plastic track sports fields. The new two-component polyurethane adhesive breaks through the contradiction between the shear strength and peel strength of traditional adhesives, allowing both to reach high strength at the same time. It shows excellent performance in bonding steel plates for construction, and the bond is strong and not prone to deformation. , and the curing speed can be adjusted at room temperature, making the polyurethane glue convenient and easy to use and widely used. Polyurethane adhesives are widely used in the bonding of PVC materials for construction, the production of sandwich panels, and building waterproof coatings.
6. Polyurethane adhesive for ink
Water-based ink is listed as the first choice for environmentally friendly printing. The normal temperature cross-linked water-based polyurethane adhesive can produce a one-component polyurethane water-based ink suitable for gravure printing. The water-based ink has high gloss and water resistance, strong adhesion, adjustable dryness, bright colors, clear layers, non-toxic and non-flammable, weather-resistant, and easy to control viscosity. , compared with other water-based inks, has wide adaptability to various substrate materials. As a connecting material for water-based ink, polyurethane-polyacrylate combines the properties of polyurethane adhesive and polyacrylate during the drying process of ink film prints. The modified emulsion also has good adhesion fastness to the film.
The base films used in the color printing industry mainly include polyester film, nylon film, polypropylene film, polyethylene film, etc. The key to choosing ink is that it has good adhesion to these base films. Focus. A new type of polyurethane adhesive can be produced by reacting vinyl chloride-hydroxyethyl acrylate polymer containing hydroxyl groups with macromolecular diols, small molecule chain extenders, and toluene diisocyanate. Improve the quality of color printing ink.
7. Polyurethane adhesives for book binding
In the past 20 years, the application of hot melt adhesives in book binding has developed rapidly. The main reason is that the production of low-priced paperback books has experienced an astonishing growth, and at the same time, wireless binding technology has been produced. Because EVA hot melt adhesive has good adhesion and elasticity, the book binding hot melt adhesive currently used in the domestic market Most of them are EVA hot melt adhesives. However, EVA hot melt adhesive is expensive, and EVA hot melt adhesive has shortcomings such as memory. Polyurethane hot melt adhesive can make up for the above shortcomings. The production process of the adhesive is simple, the cost is low, the adhesive has good elasticity and toughness, the bonding strength is high, the adhesive can be melted and used repeatedly, the product utilization rate is high, and it has broader application prospects.
8. Application in railway construction
The adhesive used for ballastless track laying (the development direction of high-speed rail engineering technology) will be mainly domestic polyurethane adhesive products, with one embedded every 5 meters in the single track For convex blocks, about 17.8kg of polyurethane adhesive needs to be poured on both sides of each block. The construction of double-track ballastless track per kilometer requires more than 7 tons of polyurethane potting adhesive. In addition to railway laying, the production of high-speed trains has also greatly increased the demand for the use of polyurethane adhesives. Polyurethane plays various essential roles in vehicles such as glass bonding, floor bonding, caulking, sealing and waterproofing. On the vehicle, based on EMU CRH3, the polyurethane glue used in a single carriage is about 84.07L, which is equivalent to about 109.3Kg. It is mainly used for bonding and sealing of window glass and sealing of partial filling parts.
9. Others
Due to its excellent bonding properties, polyurethane adhesives are used in the bonding of aerospace equipment, protection and restoration of cultural relics, military industry, stationery, medical and health care, etc. increasingly important role.
Polyurethane adhesives are widely used in various fields due to their excellent properties and are increasingly becoming important synthetic materials in human life. At present, the world's polyurethane adhesive industry is developing in the direction of environmental protection, safety and health, and resource recycling. my country's polyurethane adhesive industry has also shown rapid growth momentum, and technology development has also made great progress. With the gradual expansion of polyurethane uses and the increasing awareness of human environmental protection.
Polyurethane adhesive formula and its usage:
1. Two-component polyurethane adhesive
Formula 1:
A 100 parts of component toluene diisocyanate (TDI for short) modified resin (dissolved in ethyl acetate to form a solution)
10 to 50 parts of modified hydroxyl compound of component B curing agent TDI
p>This method is suitable for bonding between metals.
Formula 2:
100 parts of component A
10 parts of component B
This method is suitable for general materials bonding.
Formula 3:
100 parts of component A
5-10 parts of component B
This method is suitable for paper and leather , the bonding between wood.
Construction method: Before use, accurately weigh the two components (A) and (B) and mix them evenly. Then apply it to the surface of the object that needs to be bonded. After the first application, wait 5 minutes before applying the second time. The coating should not be too thick. After 10-20 minutes, the object will be glued. combine.
It is best to pressurize at a pressure of 0.3 to 0.5 kg/cm for 5 minutes to 10 hours.
Curing time: 5-10 days at room temperature
1.5-2 hours at 100℃
0.5 hours at 130℃
Two , one-component polyurethane adhesive
Formula:
38 parts of castor oil
11.75 parts of toluene diisocyanate
Styrene 49.75 parts
0.5 parts of dibenzoyl peroxide
The above is dissolved and mixed evenly at 20-80℃.
Construction and curing are roughly similar to two-component. This product is suitable for packaging of electrical materials.