Detailed explanation of epoxy resin adhesive and its adhesive technology

Epoxy adhesive is made from epoxy resin as the main body. The end of the resin polymer has epoxy, there are hydroxyl and ether bonds between the chains, and during the curing process will continue to produce hydroxyl and ether bonds, the structure contains benzene ring and hex ring, these structures determine the epoxy adhesive has excellent performance. Epoxy adhesive is a long-standing and extremely versatile adhesive

. Epoxy adhesives are recognized by a wide range of users due to their strength, diversity and excellent adhesion to a wide variety of viscous surfaces. They have participated in and accelerated the technological revolution in certain industrial sectors. Epoxy resins can be used to bond metals, glass, ceramics, many plastics, wood, concrete and other surfaces. More than 10% of epoxy resins produced in the United States are used as adhesives. In the past, people's modified epoxy resin has been limited to rubber, such as end-oxybutyl-butyl rubber, end hydroxybutyl-butyl rubber, polysulfur rubber and so on. In recent years, the modified epoxy resin has been deepening, the modified method is changing with each other, such as interoperability network method, chemical copolymer method, especially liquid crystal toughening method and nanoparticle toughening method is the focus of research in recent years. With the establishment of the development mode of "scale, high purification, refinement, specialization, series and functionalization", the modified research of epoxy resin is changing rapidly, which has now formed the focus of the industry, which will promote the further and more widespread application of epoxy resin in economic construction and people's life.
I. Excellent performance of epoxy adhesive applications in a wide range of
glue (bonding, bonding, bonding, adhesive) refers to homogenous or heterogeneous surface adhesive connection technology, with stress adhesive cloth continuous, light weight, or sealing, most of the process temperature is low and so on. Glue is ideal for connections of different materials, thicknesses, ultra-thin sizes and complex components. Glue is close to the fastest-growing generation, the application industry is very wide, and high-speed scientific and technological progress and the improvement of people's daily life has a significant impact. Therefore, the research, development and production of various types of adhesives is very important.
Epoxy resin adhesive (referred to as epoxy adhesive or epoxy adhesive) refers to a molecular structure that contains two or more epoxy-based, and under the appropriate chemical reagents and appropriate conditions, can form a three-dimensional cross-curing compound.
epoxy adhesive consists of epoxy resin, curing agent, plasticizer, promoter, thinner, filler, coupled agent, flame retardant, stabilizer, etc. composed of liquid or solid adhesive. Among them, epoxy resin, curing agent, toughener is an indispensable part, the other as needed to decide whether to add no. The adhesive process of epoxy adhesive is a complex physical and chemical process, including immersion, adhesion, curing and other steps, resulting in a three-dimensional cross-linking structure of the curing material, the adhesive into a whole.
many types of epoxy gel, in all kinds of epoxy resin, bisphenol A epoxy resin is the largest yield, the most widely used one of the largest varieties. According to its molecular weight can be divided into low, medium, high, ultra-high molecular weight epoxy resin (polyphenol oxygen resin). Low-molecular weight resins can be cured at room temperature or at high temperatures, but high-molecular-weight epoxy resins must be cured at high temperatures, while ultra-high-molecular-weight polyphenol oxygen resins do not require curing agents to form tough membranes at high temperatures. With the successive development of various adhesive theories, as well as basic research work such as adhesive chemistry, adhesive fluidology and adhesive destruction, the properties, varieties and applications of adhesives have developed rapidly. Epoxy resin and its curing system also with its unique, excellent performance and new epoxy resin, new curing agents and additives continue to emerge, become excellent performance, a wide variety of adaptability of a wide range of important adhesives.
years, high-strength light fiber-reinforced composite materials have been gradually used in ultra-low temperature environment, and the research on the ultra-low temperature performance of epoxy resin has been strengthened day by day. Some progress has been made in china's research on substation materials as liquid hydrogen storage tanks for composite materials and substation materials used as adhesives, impregnated materials and fiber-reinforced composites in the field of superconductivity. Pure epoxy resin has a high cross-link density, even at room temperature there are brittle, low toughness, poor impact resistance and other shortcomings. As a composite resin substation, it is generally usually required to cure at very high temperatures. During the cooling process after curing, the internal stress caused by heat contraction resin substate will be more significant when the temperature is reduced from room temperature to ultra-low temperature (below -150 degrees C), and once the thermal stress exceeds the strength of the resin itself, it will lead to the destruction of the resin substation. Therefore, improved toughness is essential for the use of epoxy resins at ultra-low temperatures. At present, the method to improve the ultra-low temperature toughness of epoxy resin is mainly to use flexible adipose resin and liquid rubber, as well as flexible curing agent to strengthen epoxy resin. Due to the low glass transition temperature of such materials, there is a large free volume at room temperature, when the temperature drops to ultra-low temperature, the resin system will produce a large heat contraction, resulting in greater thermal stress, which limits its application at ultra-low temperature. The co-mixing of high-performance thermoplastics and epoxy resins at room temperature can make the mixing system have both superior properties, that is, while maintaining the high mould of thermostat resin, it also has the high toughness of thermoplastics.
Adhesive bonding properties (strength, heat resistance, corrosion resistance, impermeability, etc.) not only depends on its structure and performance, as well as the structure and adhesive properties of the viscose surface, but also closely related to joint design, preparation of adhesive and bonding process, but also by the surrounding environment constraints. Therefore, the application of epoxy adhesive is a systematic engineering. The performance of epoxy adhesive must be adapted to the above factors affecting the bonding performance in order to obtain the best results. With the same formula of epoxy adhesive glue to different properties of objects, or the use of different glue conditions, or in different environments of use, its performance will be greatly different, the application should be given full attention.
epoxy adhesive is mainly composed of epoxy resin and curing agent two parts. To improve some properties, auxiliary materials such as tougheners, thinners, promoters, and coupled agents can also be added for different purposes. Due to the high bonding strength and versatility of epoxy adhesives, there have been "universal glue", "strong glue" called, in aviation, aerospace, automotive, machinery, construction, chemical, light industry, electronics, electrical appliances and daily life and other fields have been widely used.
china's current synthetic adhesive manufacturers about 2000, can produce more than 2500 varieties of brand products, production capacity of 3 million t/a. With the increasingly sound environmental protection regulations in China, as well as the improvement of people's own health awareness, good quality, non-polluting, in line with international standards of environmentally friendly epoxy adhesives are gradually becoming the mainstream products of synthetic adhesives.
II, epoxy adhesive molecular structure and variety classification
epoxy resin is a molecule containing two or more epoxy groups and relatively low molecular mass polymer compounds I, classification epoxy resin varieties, many brands, but bisphenol A shrinking glycelyceride epoxy resin is commonly referred to as bisphenol A epoxy resin is the most important category. It accounts for 90% of total epoxy resin production. Bisphenol Type A epoxy resin, also known as general purpose epoxy resin and standard epoxy resin, China is named E epoxy resin, by BPA or DPP and epoxy chloropropane (ECH) in sodium hydroxide concentration: depending on the ratio of raw materials, reaction conditions and methods used, can be produced with different polymerization of low relative molecular mass of viscous liquid and high relative molecular mass, high soft point. The average relative molecular mass is 300 to 7000. Appearance is almost colorless or pale yellow transparent viscous liquid or flaky brittle solids. Epoxy resin itself is a thermoplastic line polymer, when heated liquid resin viscosity is lower, solid resin softening or melting. Dissolved in acetone, methyl ethyl ketone, cyclosterone, ethyl acetate, benzene, toluene, xylene, waterless ethanol, glycol and other organic solvents. Hydrogenated Bisphenol A type A epoxy resin chemically named hydrogenated biphenol A ii shrink glycelin ether, is obtained by bisphenol A hydrogenation of hexahydrobiphenol A and epoxy chloropropane under the catalysis of sodium hydroxide. It is a epoxy resin with very low viscosity, long gel time and good weather resistance.
Bisphenol F epoxy resin chemical name is BPA F dissored glycelin ether, referred to as DGEBF or BPF, is produced by phenol and formaldehyde react under an acidic catalyst to produce BPAF, and then with epoxy chloropropane in sodium hydroxide catalytic polymerization process produced by the colorless or pale yellow transparent viscous liquid; The chemical name is BPAS S di-shrinking glyphosate ether, referred to as BPS or KGEBS, is made by BPAS and epoxy dump propane under the catalysis of sodium hydroxide, BPA S epoxy resin heat resistance is high, thermal deformation temperature is 60 to 700C higher than BPA epoxy resin stability, good solvent resistance. Bisphenol P epoxy resin is made from the synthesis of BPA with 3-chloropropylene and phenol as the main raw materials, and then with epoxy chloropropane in sodium hydroxide catalytic cogeneration. Bisphenol P-type epoxy resin molecular chain flexibility is large, good fluidity at low temperature, viscosity is lower than BPA epoxy resin, compression strength and impact strength is higher than BPA epoxy resin.
phenolic epoxy resin mainly has phenol-type phenol acetic epoxy resin and phthalates-type phenolic epoxy resin, as well as interphenol-type phenolic ethyloxy resin. In addition, tetraphenol-based ethane epoxy resin also belongs to phenolic epoxy resin; phenol-type phenolic epoxy resin (EPN) is a line-type phenolic resin obtained by phenol and formaldehyde in the acidic medium polymerizing reaction, and then with excessive ethylene chloropropane in the presence of sodium hydroxide in the production of a solid or semi-solid line brown, phthalol-type phenolic phenoxygen resin is Phthalol and formaldehyde shrinkage obtained by the line phthalates resin, and epoxy chloropropane in the presence of sodium hydroxide reaction, after multi-step treatment and the production of yellow to amber solids; Orange-yellow viscous liquid that shrinks with sodium hydroxide with ethylene chloropropane, and tetraphenolic ethane epoxy resin chemically named tetraphenolic ethane shrinkage glycelin ether (PGEE), which is produced by the reaction of phenol and ethyl dialdehyde in the presence of acid catalysts, and then oxychloropropane under sodium hydroxide catalysis The reaction was made; the epoxy resin (EEPN) is a-phenol and formaldehyde solution to shrink, synthesize the out-line caiphenol resin, and then react with epoxy chloropropane under the catalysis of sodium hydroxide, fluorinated epoxy resin due to the introduction of fluorine atoms, so that the molecular structure is dense, the carbon fluorine atoms are closely arranged around the main chain of resin. Therefore, the central table temperature, friction coefficient, refractive index is very low, has excellent corrosion resistance, wear resistance, heat resistance, pollution resistance, durability. But high prices are not quite the usual use.
Polyurethane epoxy resin, also known as epoxy methylmate resin, is polyester (or ether) polyol and epoxy chloropropane under the action of BF3 and NaOH to produce polyol shrinkage glycelin ether and then added to diocyanate to shrink, silicone epoxy resin is a molecular structure containing silicone epoxy is composed of polymethyl silica and epoxy resin copolymer. Toluene is a solution, pale yellow uniform liquid, organic titanium epoxy resin is from bisphenol A epoxy resin hydroxyl and titanate positive butyl reaction. Due to the introduction of the metal element titanium in the resin, not only to solve the hydroxyl presence caused by increased water absorption, moisture resistance and electrical performance reduction, and because the resin has P electron oxygen atoms and titanium with D electron absence directly connected, resulting in the presence of P-D conjugate effect in the large molecular chain, and make heat-resistant aging performance significantly improved, dielectic performance is better. The appearance is yellow to amber high viscosity transparent liquid.
with the continuous development of high-tech and technology. In recent years, the modified epoxy resin has been deepening, inter-permeable network, chemical co-cohesion and nanoparticle toughening and other methods are widely used, and a variety of high-performance adhesive varieties made from epoxy resin are also increasing.
variety of epoxy adhesives, the classification methods and classification indicators have not been unified. It is usually classified according to the following methods. Classification by form of adhesive: such as solvent-free adhesive, (organic) solvent-based adhesive, water-based adhesive (which can be divided into water-milk type and water-soluble type two), paste-like adhesive, thin-film adhesive (epoxy film) and so on.
are classified according to curing conditions: cold curing glue (not heating curing glue). It is divided into low temperature curing glue, curing temperature <15 degrees C, room temperature curing glue, curing temperature 15 to 40 degrees C, and thermo-curing glue can be divided into: medium temperature curing glue, curing temperature of about 8 0 to 120 degrees C, high temperature curing glue, curing temperature >150 degrees C, other methods of curing glue, such as photo-curing glue, wet surface and water curing glue, latent curing glue.
by glue strength classification: structural glue anti-shearing and anti-pull strength, but also should have a high uneven tearing strength, so that the glue joint in a long time can withstand vibration, fatigue and shock and other planting load. At the same time should also have a high heat resistance and weather resistance, secondary force structure glue can withstand medium load, usually shear strength 17 to 25Mpa, uneven tearing strength 20 to 50kN/m; non-structural glue, that is, general-purpose adhesive. Its room temperature strength is still relatively high, but with the increase of temperature, the glue strength decreases faster. Can only be used in areas where the force is not significant.
by use classification: general purpose adhesives, specialty adhesives, such as high temperature adhesive (using temperature ≥150 degrees C), low temperature adhesive (can withstand -50 degrees C or lower temperature), strain adhesive (paste strain film), conductive adhesive, sealant (vacuum sealing, mechanical sealing), optical adhesive (colorless transparent, light aging, refraction rate and optical parts matching), corrosion resistance, structural adhesive, etc. Can also be classified according to the type of curing agent, such as amine curing epoxy, acid curing glue and so on. It can also be divided into two-part glue and single-part glue, pure epoxy glue and modified epoxy glue.
3. Performance characteristics of epoxy adhesives
General epoxy resin structure contains hydroxyl, ether bonds to make it high adhesion, because of these polar groups, so that the adjacent interface can produce electromagnetic force, less in the curing process, accompanied by the chemical curing agent The effect, but also can further generate meso-based and ether bonds, not only has a high cohesion force, but also produces a strong adhesion force, so epoxy adhesive on many materials such as metals, plastics, glass, wood, fiber, etc. have a strong bonding strength, commonly known as "all-powerful glue."
the molecules of the epoxy resin are arranged closely, the low molecules are not presumed in the curing process, and it can be made into solvent-free adhesives, so its shrinkage rate is generally relatively low. If the appropriate filler is selected, the shrinkage rate can be reduced to 0.1 to 0.2%.
ethylene tree refers to the existence of stable benzene rings, ether chains and dense structure after curing, which determines that epoxy adhesive has an atmosphere, moisture, chemical medium, bacteria.