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Thousands of years ago, humans had used adhesives and bonding techniques, and many unearthed artifacts had traces of adhesives. At that time, natural adhesives were used, such as animal glues such as bone glue, blood glue, fish glue, and casein, and starches such as starch, rosin and rubber, and mineral glues such as clay, sulfur, and asphalt. In order to improve the adhesive strength, water resistance, and mildew resistance of natural adhesives, people began to chemically modify natural adhesives from the beginning of the 19th century. In the 1920s, with the rapid development of polymer chemistry and industry, a large number of synthetic polymer materials emerged, prompting the endless variety of synthetic adhesives. In 1912 the first synthesis of phenolic resin adhesives available, and Araldite epoxy adhesive product series is put on the market in 1946, after half a century of development, has been widely used in aerospace, DIY household, construction reinforcement, Bonding in the fields of sports equipment, natural gas carriers, sandwich plates and pipes. Since the Dutch first established animal glue factory in 1690, the industrial production of adhesives has been more than 300 years. No matter the type, performance and application of adhesives, or the progress, innovation and promotion of adhesive technology, it has been rapid. Amazing progress.
In the 1960s, through the addition of plasticizers and other methods to reduce brittleness, the first generation of room-temperature curing epoxy adhesives was developed, and the performance was unsatisfactory. Early 1970s, the use of elastomers, such as liquid-terminal carboxyl nitrile rubber (CTBN), amino-terminated liquid nitrile rubber (ATBN) and the urethane rubber and the like, modified epoxy resin, was prepared at room temperature curable epoxy 2nd generation Adhesives, due to the "island structure" produced by phase separation during the curing process, have improved toughness and improved the peel strength by about 4 times. The third-generation room-temperature curing epoxy adhesive is obtained from acrylate rubber or cross-linked CTBN toughened epoxy resin. Its characteristic is that the phase separation of rubber and epoxy resin is completed before the epoxy resin is cured. The shear strength can reach 30MPa or more, and the T-type peel strength is 5-7kN/m. In the early 1990s, in order to further improve the performance of room-temperature curing epoxy adhesives, aliphatic diamines or triamines with longer molecular chains and multiple ether bonds in the chain were used as curing agents to achieve "sea phase" or epoxy resin. Internal toughening of the continuous phase, the room temperature curing epoxy glue has higher strength, better toughness, better heat resistance. Ciba-Geigy Corporation successfully developed LMH263-29 type room temperature curing adhesive, shear strength at room temperature of -55 ℃ / 7d curing 42MPa, elongation at break of nearly 50%, the adhesion between the different coefficients of thermal expansion and very suitable flexible material Then. There is also LMH262-48 type glue at room temperature / 7d curing, room temperature shear strength of 31MPa, 80 °C shear strength of 18MPa, with good durability. The DP420/460 developed in Japan is toughened with an amino-terminated liquid nitrile rubber. The shear strength at room temperature is 30.8 MPa and the peel strength is 10 kN/m. MasterBond's EP33 ambient-cured epoxy adhesive is used at a temperature of -55 to 232°C. Hysol's EA9394 epoxy adhesive, after room temperature/7d curing, shear strength at room temperature 32MPa, 175°C, 10MPa, the adhesive has excellent adhesion, flexibility and temperature resistance, which can partially replace the high temperature curing epoxy adhesive Adhesives. Domestic use of double toughening system, with polyether diamine or other flexible chain polyamine as internal toughening curing agent, the shear strength of room-temperature curing epoxy adhesive exceeds 30MPa, and the 90° peel strength is higher than 3.5kN/ m. For example, J-135 room-temperature curing high toughness epoxy adhesive consists of epoxy resin, CTBN, polyetheramine, tertiary amine accelerator, etc. Room temperature / 4 ~ 7d after curing shear strength at room temperature ≥ 33.6MPa, floating roller Peel strength ≥ 4.5kN/m, has replaced EA9309.3N/A imported rubber for helicopter rotor production. There are WJ-17 super high strength epoxy adhesives, room temperature shear strength ≥ 45MPa.
As a result of polyfunctional epoxy resins, liquid nitrile rubber, and the terminal carboxyl group polyetheramine (polyetherdiamine) a curing agent, so that the shear strength at room temperature curing epoxy adhesive bicomponent and T-peel strength is significantly improved, e.g. U.S. Dexter Corporation products EA9309.3N / a, shear strength at room temperature up to 33 ~ 35MPa, the peel strength of 4 ~ 5kN / m; Ciba-Geigy Redux 420 of the two-component epoxy adhesive, room temperature / 4d curing, the shear strength of 33 ~ 37MPa 3M company brand Scotch-Weld 2216B / A two-component epoxy adhesive, room temperature 1h gel, 7d after curing, the shear strength of 28 ~ 35MPa. U.S. Cotronics has developed Duralco 4538, a super-flexible epoxy adhesive that cures at room temperature and has high bonding strength. The maximum operating temperature is 232°C.
In recent years, the curing speed of room-temperature curing epoxy adhesive has been greatly accelerated. The gel has been cured for 1 to 6 minutes and cured for 3 to 8 hours. The shear strength has reached 28.1 MPa. The United States has developed the high-strength, fast-curing (5 min) epoxy adhesive Appli-Tec 5400. American Devcon has developed epoxy adhesives for bonding metals, glass, ceramics, concrete, etc., and it can form a bright, hard bond at room temperature in a matter of minutes. There are several 5min fast-setting epoxy adhesives that can produce multiple brands in China, such as SK-111, EX-501, TH-2000, J-156, and Hezhong 100.
In order to meet the needs of bonding of handicrafts and optical components, transparent epoxy adhesives have been produced in the country, but they are prone to yellowing, and there is still a big gap with foreign products.
Room-temperature curing epoxy adhesive has a temperature of 200 ~ 260 °C varieties, heat resistance up to 275 °C (Formulted Resin ER-2050 + ER-2048). In 2005, it was reported abroad that MasterBond developed a room temperature curing toughened and heat-resistant epoxy glue Supreme33 with 100% solid content without any diluent or solvent. High adhesion to metals, glass, ceramics, wood, most plastics and vulcanized rubber. After curing, it is resistant to shock, vibration, oil, water and chemicals. The maximum operating temperature is 218°C.
Multi-functional epoxy resin, rigid group-containing epoxy resin and bismaleimide or silicone-modified epoxy resin, heat-resistant curing agent, fumed silica, aluminum powder, antioxidant , metal ion passivation agents, etc., made of high temperature epoxy adhesive can be used above 200 °C. Silicone-modified epoxy adhesives can be used at 300°C for a long time and short-term resistance to 460°C. Epoxy adhesive with FB high-temperature flame-retardant phenolic resin as a curing agent, the adhesive steel test piece is not shed after being calcined at 800°C for 1 hour. The adhesive composed of epoxy resin/CTBN/SP curing agent and 70 # anhydride compound curing agent has a tensile strength of 12 MPa when heated and cured at 200-250°C.
The new high temperature resistant fluorinated epoxy resin can extend the operating temperature range of epoxy adhesives. The cured product of these resins has a Tg of 290°C.
One-component epoxy adhesives are mainly heat-curable, moisture-curable, microcapsule-coated, and cationic photocurable. The one-component moisture cured epoxy adhesive is formulated with a ketimine as a curing agent, and the curing speed is balanced with the storage stability, and can be rapidly cured at room temperature, low temperature and in a humid environment. Among them, a ketimine having a phenol-formaldehyde skeleton structure has excellent properties, such as a phenol-modified ketimine obtained by reacting phenolamine, formaldehyde, m-xylylenediamine, and methyl isobutyl ketone. Cationic light-cured epoxy adhesive is generally added to the bisphenol A epoxy resin in 1% to 3% of the photoinitiator, commonly used triaryl sulfate anchor hexafluorophosphate (Cyracure
UVI-6990). Merchandise ム° ã‚ツト light curing epoxy glue is green when not cured, transparent after curing, only UV irradiation (440nm/20min), without post-heating can be completely cured. For optical element bonding, liquid crystal encapsulation, etc., the shear strength of bonded aluminum plates is greater than 24 MPa. Germany uses light-curing epoxy adhesives to bond electronic components.
High-temperature (200°C) fast-curing (<5min) one-component epoxy adhesive prepared with o-toluidine, dicyandiamide and hydrochloric acid, o-methylphenylbiguanide (4 parts) as curing agent, stored at room temperature During half a year, the gel time at 180°C is 1.8-1.9 min. Dexter's EA9414, Henkel's Matallon
E2760 and 2700 belong to this type and can be cured at 180-230°C/1～2min. The shear strength of bonding aluminum and steel is 12～18MPa, which is especially suitable for automated flow production line.
Low-temperature rapid-curing epoxy adhesive is very practical value. Bisphenol F epoxy resin is reacted with potassium thiocyanate (KSCN) to obtain bisphenol F episulfide resin, which is combined with diphenyl phosphite ester and DMP-30. Etc., can quickly cure at -5 °C, has been used in civil engineering. Replacing some epoxy resin with epoxy resin to form an epoxy resin-episulfide resin-curing agent system can not only accelerate the curing speed, but also reduce the internal stress and increase the service temperature.
In order to reduce the shrinkage rate and reduce the internal stress, the expansion monomers may be formed by blending an expansible monomer such as spiro orthocarbonate, spiro orthoester, and bicyclic orthoester with an appropriate ratio of an epoxy resin, a curing agent, and the like. The volumetric expansion during bulk polymerization just offsets the volume shrinkage produced when the epoxy resin is cured, and a zero-shrinkage epoxy adhesive is obtained, improving the bond strength and durability.
Utilizing the unique characteristics of nanomaterials, 3% to 5% of nano-SiO2, nano-CaCO3, and nano-TiO2 are added to the epoxy resin to prepare a nano-modified epoxy adhesive, and the impact strength and tensile strength are greatly improved. There are obvious effects such as toughening, strengthening, and hardening, and the heat resistance does not decrease but rises.
Whisker is a fiber material with a certain aspect ratio grown in the form of single crystal. Due to the highly ordered atomic structure, the strength is close to the theoretical value of intact crystal, and it has excellent properties such as high strength, high modulus, and high heat resistance. Zinc oxide whiskers, calcium sulfate whiskers, calcium carbonate whiskers, aluminum borate whiskers, etc. have been reinforced and toughened by epoxy adhesives. The effect is very obvious, and zinc oxide whiskers are particularly preferred.
With the increasingly stringent environmental protection requirements, the advantages of water-based adhesives have been highlighted, and water-based epoxy adhesives have followed the trend. Domestic water-based and water-soluble products have been on the market and their performance has been continuously improved. Germany's Reichhold GmbH has developed three types of water-based epoxy resin emulsions, as well as an emulsion curing agent Epotulf 37-147.
Membrane epoxy adhesives do not contain solvents, the thickness of the adhesive layer is uniform, and the adhesive strength is high. It is safe and environmentally friendly. It has long been used as an aerospace structural adhesive and generally requires 120 to 175° C. curing. The A-1402 film developed by Japan Nagase Corporation has a thickness of 50μm and the curing conditions are 0.01MPa at pressure and 60°C/3h.
India developed Powdered-AD947 powdery heat-resistant one-component epoxy glue. The powder was coated on the surface to be adhered. After curing at 150°C, the continuous use temperature was 180°C.
In order to solve the problem of the toxicity of solvent-based epoxy adhesives, Solectron Japan has developed EP-9100 series epoxy resin that is soluble in solvent oil.
Epoxy resins, carboxyl-terminated polybutadienes, imidazoline curing agents and the like can produce epoxy resin pressure-sensitive adhesives with superior peel strength.
Epoxy adhesives are an important class of engineering adhesives, with production and consumption increasing year by year. The consumption of epoxy rubber in the United States in 1996 was 43,000 tons; in 1999, it was 5 million tons; in 2004, it was 62,000 tons. The yield of epoxy adhesives in China is shown in Table 1-1.
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