1.4 Nitrogen-containing Heterocyclic Adhesives
In high temperature organic adhesives, heterocyclic polymer compounds have the best heat resistance. The main varieties are polyimide, polybenzimidazole and polyphenylquinoxaline. Among them, polyimide (PI) is a commercially available polymer material with the highest heat-resistant grade so far and is widely used in high-tech fields such as aerospace, electrical engineering, and microelectronics. Polyimide is a ring chain polymer containing an imide ring structure in its molecular chain. It has excellent heat aging resistance and chemical stability, solvent resistance, small thermal expansion coefficient and excellent mechanical properties and electrical properties. .
Polyimide adhesives can be divided into thermoset and thermoplastic categories. In recent years, thermosetting resins have been valued and developed with their excellent heat resistance, and are classified into polycondensation type and addition molding according to a thermal curing mechanism. The polycondensation type polyimide adhesive was firstly produced by reacting an aromatic tetracarboxylic dianhydride with an aromatic diamine in a polar solution, and was then condensed with a heating glue, and was first applied to the aviation field; Imide adhesives are short-chain prepolymers with unsaturated reactive groups as the end groups. They form polymers with highly crosslinked networks through the reaction between the end groups. They have the advantages of good melt fluidity and no volatiles during curing. Good processing performance. However, the toughness of both cured products is poor. The modification method is mainly to introduce a flexible group in the main chain or to introduce a second structurally different linking group in the homopolymer.
An HR-600 acetylene-terminated polyimide reported by Hughes Aircraft Company in 1974, which can bond titanium, aluminum, copper, and composites, has an operating temperature of 316°C, and has mechanical properties after 288°C aging. Maintain a high level [6]. A bismaleimide adhesive developed by Zhang Bin et al. [7] has a curing temperature of less than 300°C and a shear strength of more than 2MPa at 400°C, which can meet the heat resistance requirements of the aerospace industry. Zeng et al. used aniline diphenyl ether and bismaleimide to copolymerize an anilide-diphenyl ether bismaleimide (ANDPOB-MI), which has good heat resistance and shear. The shear strength is high, the surface decomposition temperature is 390°C, the temperature index is greater than 220°C, and the glass transition temperature is 270°C.
Polybenzimidazole (PBI) is another important high-temperature adhesive that is obtained by polycondensation reaction of aromatic tetraamines with aromatic dicarboxylic acids or their derivatives. Good adhesion to many metal and non-metal materials, high initial bonding strength, good water resistance, oil resistance, high temperature resistance and instant ultra-high temperature performance, long-term use at -253 ~ 260 °C, Short-term use at 539°C. However, due to the presence of N-H bonds in the molecular structure of PBI, poor thermal aging resistance and high raw material costs have made PBI adhesives not widely used. Polyphenylquinoxaline (PB0) is a polycondensation of bis(ortho)phenylenediamine and terephthalic acid compounds. It is a kind of aromatic heterocyclic polymer with high temperature resistance. It does not decompose when heated at 500°C for 3 hours. It is easy to form a film and can be used as a large-area bonding. However, its high price and high processing temperature (370°C) limit its wide application.
2 inorganic high temperature adhesive
Inorganic adhesives consist of inorganic salts, inorganic acids, inorganic bases, and metal oxides, hydroxides, and the like. The inorganic adhesive is extremely excellent in high temperature resistance (usually resistant to 900 ~ 1000 °C, can be used in the range of -183 - 2900 °C), small shrinkage, good aging resistance, low raw materials, is a very promising type of adhesive. Disadvantages are poor acid and alkali resistance and water resistance, brittleness, and resistance to shock. Currently used high-temperature inorganic adhesives are mainly silicates and phosphates.
Silicate adhesives are generally formulated with alkali metal silicates, added with curing agents and fillers. Its heat-resistant temperature up to 1500-1700 °C. The aluminum silicate zirconia adhesive has excellent water resistance, oil resistance, heat resistance and electrical insulation properties. The use temperature range is -70 to 1200°C and can be used for metal fittings.
Phosphate adhesives are based on acid phosphates, metaphosphates, pyrophosphates or directly from acids and metal oxides, halides, hydroxides, basic salts, silicates, borates, etc. The reaction product is a binder. Compared with silicate adhesives, its water resistance is better, curing shrinkage is small, high-temperature strength, can be bonded metal, ceramics, glass and so on. The copper oxide monophosphate adhesive is resistant to high and low temperatures of -70 to 1300°C. If a high melting point compound (zirconia, alumina, etc.) is added, it can be increased to about 1500°C. Liu Xinjin [8] and others modified the copper oxide mono-phosphate adhesive to greatly increase the bonding strength, which can increase up to 2.4 times.
3 Conclusion
In recent years, the application of high-temperature adhesives has been expanding, and their technical requirements have become increasingly demanding. Although new products and new uses of high-temperature adhesives have been continuously reported, it has so far been limited to inherent breakthroughs in inorganic and organic adhesives, and their performance has been difficult to achieve a fundamental breakthrough, which has limited their application to a large extent. The overall development trend of high-temperature adhesives is reflected in the following aspects: The development of new organic high-temperature adhesives. Prepare adhesives with high temperature resistance, good mechanical properties and high durability.
Utilizes and develops new type of modification technology to modify the existing high-temperature resistant resin, improve its comprehensive performance, and expand its application range. The special properties of new materials such as nanomaterials and whisker materials are used to prepare high-performance and new-functional composite adhesives. Improve the performance of inorganic adhesives. Mainly to improve the adhesive strength of the substrate, reduce brittleness and improve water resistance. Using the advantages of both inorganic and organic adhesives, research and development of organic and inorganic composite adhesives.
Source: Chemical Fine Network
In high temperature organic adhesives, heterocyclic polymer compounds have the best heat resistance. The main varieties are polyimide, polybenzimidazole and polyphenylquinoxaline. Among them, polyimide (PI) is a commercially available polymer material with the highest heat-resistant grade so far and is widely used in high-tech fields such as aerospace, electrical engineering, and microelectronics. Polyimide is a ring chain polymer containing an imide ring structure in its molecular chain. It has excellent heat aging resistance and chemical stability, solvent resistance, small thermal expansion coefficient and excellent mechanical properties and electrical properties. .
Polyimide adhesives can be divided into thermoset and thermoplastic categories. In recent years, thermosetting resins have been valued and developed with their excellent heat resistance, and are classified into polycondensation type and addition molding according to a thermal curing mechanism. The polycondensation type polyimide adhesive was firstly produced by reacting an aromatic tetracarboxylic dianhydride with an aromatic diamine in a polar solution, and was then condensed with a heating glue, and was first applied to the aviation field; Imide adhesives are short-chain prepolymers with unsaturated reactive groups as the end groups. They form polymers with highly crosslinked networks through the reaction between the end groups. They have the advantages of good melt fluidity and no volatiles during curing. Good processing performance. However, the toughness of both cured products is poor. The modification method is mainly to introduce a flexible group in the main chain or to introduce a second structurally different linking group in the homopolymer.
An HR-600 acetylene-terminated polyimide reported by Hughes Aircraft Company in 1974, which can bond titanium, aluminum, copper, and composites, has an operating temperature of 316°C, and has mechanical properties after 288°C aging. Maintain a high level [6]. A bismaleimide adhesive developed by Zhang Bin et al. [7] has a curing temperature of less than 300°C and a shear strength of more than 2MPa at 400°C, which can meet the heat resistance requirements of the aerospace industry. Zeng et al. used aniline diphenyl ether and bismaleimide to copolymerize an anilide-diphenyl ether bismaleimide (ANDPOB-MI), which has good heat resistance and shear. The shear strength is high, the surface decomposition temperature is 390°C, the temperature index is greater than 220°C, and the glass transition temperature is 270°C.
Polybenzimidazole (PBI) is another important high-temperature adhesive that is obtained by polycondensation reaction of aromatic tetraamines with aromatic dicarboxylic acids or their derivatives. Good adhesion to many metal and non-metal materials, high initial bonding strength, good water resistance, oil resistance, high temperature resistance and instant ultra-high temperature performance, long-term use at -253 ~ 260 °C, Short-term use at 539°C. However, due to the presence of N-H bonds in the molecular structure of PBI, poor thermal aging resistance and high raw material costs have made PBI adhesives not widely used. Polyphenylquinoxaline (PB0) is a polycondensation of bis(ortho)phenylenediamine and terephthalic acid compounds. It is a kind of aromatic heterocyclic polymer with high temperature resistance. It does not decompose when heated at 500°C for 3 hours. It is easy to form a film and can be used as a large-area bonding. However, its high price and high processing temperature (370°C) limit its wide application.
2 inorganic high temperature adhesive
Inorganic adhesives consist of inorganic salts, inorganic acids, inorganic bases, and metal oxides, hydroxides, and the like. The inorganic adhesive is extremely excellent in high temperature resistance (usually resistant to 900 ~ 1000 °C, can be used in the range of -183 - 2900 °C), small shrinkage, good aging resistance, low raw materials, is a very promising type of adhesive. Disadvantages are poor acid and alkali resistance and water resistance, brittleness, and resistance to shock. Currently used high-temperature inorganic adhesives are mainly silicates and phosphates.
Silicate adhesives are generally formulated with alkali metal silicates, added with curing agents and fillers. Its heat-resistant temperature up to 1500-1700 °C. The aluminum silicate zirconia adhesive has excellent water resistance, oil resistance, heat resistance and electrical insulation properties. The use temperature range is -70 to 1200°C and can be used for metal fittings.
Phosphate adhesives are based on acid phosphates, metaphosphates, pyrophosphates or directly from acids and metal oxides, halides, hydroxides, basic salts, silicates, borates, etc. The reaction product is a binder. Compared with silicate adhesives, its water resistance is better, curing shrinkage is small, high-temperature strength, can be bonded metal, ceramics, glass and so on. The copper oxide monophosphate adhesive is resistant to high and low temperatures of -70 to 1300°C. If a high melting point compound (zirconia, alumina, etc.) is added, it can be increased to about 1500°C. Liu Xinjin [8] and others modified the copper oxide mono-phosphate adhesive to greatly increase the bonding strength, which can increase up to 2.4 times.
3 Conclusion
In recent years, the application of high-temperature adhesives has been expanding, and their technical requirements have become increasingly demanding. Although new products and new uses of high-temperature adhesives have been continuously reported, it has so far been limited to inherent breakthroughs in inorganic and organic adhesives, and their performance has been difficult to achieve a fundamental breakthrough, which has limited their application to a large extent. The overall development trend of high-temperature adhesives is reflected in the following aspects: The development of new organic high-temperature adhesives. Prepare adhesives with high temperature resistance, good mechanical properties and high durability.
Utilizes and develops new type of modification technology to modify the existing high-temperature resistant resin, improve its comprehensive performance, and expand its application range. The special properties of new materials such as nanomaterials and whisker materials are used to prepare high-performance and new-functional composite adhesives. Improve the performance of inorganic adhesives. Mainly to improve the adhesive strength of the substrate, reduce brittleness and improve water resistance. Using the advantages of both inorganic and organic adhesives, research and development of organic and inorganic composite adhesives.
Source: Chemical Fine Network
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