Research and Application of One-Component Epoxy Adhesives

1. 2 microcapsule type

The microcapsule one-component epoxy adhesive is a component of the adhesive that is wrapped with a fine oil film to form a microcapsule. It is activated by heat and pressure and reacts with another component of the adhesive to cure. The thickness of the capsule film should be appropriate. When it is too thin, it is easy to damage during transportation. When it is too thick or too strong, it needs to exceed the pressure or temperature of the general conditions to make it damaged. It is inconvenient to use.

The microcapsule one-component epoxy adhesive is usually coated with a curing agent in a microcapsule, and the epoxy resin and the modifier are used as another component. For example, a microcapsule adhesive is prepared as follows: a microcapsule is prepared by a melt spray method using boron trifluoride-diethyl ether as a core and a mixture of solid materials having different melting points as a wall material. Take E-44 epoxy resin 10g, add acetone 6ml to dilute, stir well, add 0.8g boron trifluoride microcapsule, gently stir evenly, and inject into a closed container for use. According to different bonding materials and application requirements, it is also possible to add reinforcing agents, reinforcing agents and other additives. The boron trifluoride and the epoxy resin are stably coexisting through the blocking action of the capsule wall, and they rapidly mix at the melting temperature of the capsule wall material, thereby achieving the purpose of rapid solidification. The prepared microcapsule heat-curing epoxy resin adhesive can be stably stored at room temperature for more than 3 months. One-time preparation can be used continuously for 3 months and the shear strength reaches 16MPa. Some microcapsule epoxy adhesives are coated with epoxy components in microcapsules and then dispersed into polyamide curing agents. The resulting adhesives have good fluidity and storage stability, and the bonding strength and the two groups The score is quite.

1 .3 Latent curing agent type

One-component epoxy adhesives are formulated with an epoxy resin matrix (including plasticizers, tougheners, or fillers, etc.) and a curing agent. It does not cure at room temperature and cures immediately after heating. Therefore, latent curing agents, accelerators, or co-curing agents are needed to inhibit ring-opening curing of the epoxy resin at room temperature by chemical or physical modification— Once heated, releasing the reactive group causes the epoxy to cure. The latent curing agents used in the good one-component epoxy adhesives have significantly different stability constants under normal temperature conditions and under warming conditions.

Latent curing type is the most practical type of one-component epoxy adhesive. Most of the commercially available one-component epoxy adhesives belong to this category, their research is most active, and significant progress has been made. This type of adhesive is mainly a base epoxy resin, a dicyandiamide, an organic hydrazide, etc. as a latent curing agent for epoxy resins, and can be combined with components such as a curing accelerator, a toughening agent, a diluent, and a filler. The cured material has high strength and good overall performance and can be used as a structural adhesive. One-component epoxy adhesives are used as new high-strength structural adhesives. They are characterized by a long pot life, no curing for several months, no deterioration, and ready use. There is no need to temporarily weigh and mix rubber to reduce measurement errors and ensure that Quality, saving equipment such as mixing devices, easy to use, and no residual glue loss during use, has now been applied to many industrial sectors, such as car door folding edge bonding, car front and rear box structure bonding, Electronic components in the electronic industry potting, the production of mechanical and electrical products. In particular, the application of one-component epoxy adhesives in the assembly line of electrical components is promising. Looking at the recent development of latent curing one-component epoxy adhesives, the research content mainly focuses on the following aspects: toughening and modification of adhesives; lowering the curing temperature; and accelerating the curing speed.

1.3.1 Toughening of Epoxy Resin

One-component epoxy adhesives cure at high temperatures and are prone to brittleness. Resolving its brittleness at high temperatures is a key factor. The toughening technology using CTBN modified epoxy resin is a classic and effective method, and it has applications both at home and abroad. Structural adhesives used by the United States aviation industry dominated by CTBN as a toughening agent. This adhesive has been tested for more than 20 years of atmospheric aging tests. The one-component epoxy adhesive modified with carboxyl-terminated nitrile rubber CTBN can not only be used as structural bonding of the sheet, but also used for the bonding of honeycomb core material. A one-component epoxy glue SU-1 rubber, using nitrile rubber elastomer modified epoxy resin, with high tensile, shear and impact strength. Good adhesion properties to steel, copper, aluminum, carbide, and other metal materials. Can be widely used in aviation, automobiles, tractors, machine tools, instruments, instruments, mechanical and electrical products, electronic products, molds, measuring tools and tools such as bonding and repair, but also for casting and as magnetic powder, magnetic steel adhesives.

The automotive hemming adhesive is used for the bonding of the body sheet metal parts, such as doors, hoods, trunk lids, etc. The use of hemming glue can replace spot welding, simplify the production process, and effectively improve the anti-vibration, anti-corrosion and sealing performance of the hemming part, and also make the appearance more beautiful. Epoxy resin as the base material of the hemming adhesive, there is usually a problem that the fluidity of the rubber compound is greatly affected by the ambient temperature before curing, which is unfavorable to the on-site coating, the adhesive layer has small elongation after elongation, and the brittleness is large. Performance requirements must be modified. Through the use of carboxylated nitrile rubber (CTBN) and epoxy resin prepolymerization to achieve the purpose of toughening modification, and through the addition of other modifiers to obtain a balance of technical performance and process requirements, developed a good Thixotropic, low-temperature extrudability, ZG-2 folding glue that can be completely cured under the body electrophoretic primer drying conditions (170-180°C, 30min), thus satisfying Dongfeng EQ-1031 series light vehicle manufacturing process Need for glue.

Because CTBN is difficult to obtain in China and it is expensive, Chenguang Chemical Research Institute uses inexpensive carboxyl-terminated polyether (CTPE) to soften or toughen epoxy resin to prepare single-component epoxy resin folding edge glue. Get a satisfactory toughening effect. The method comprises adding an epoxy resin, a toughness resin CEF and a suitable auxiliary agent into a reaction kettle, heating and blending and dissolving to obtain a modified epoxy resin, and then modifying the epoxy resin with a diluent, a curing agent, an accelerating agent, and defoaming. Agents, fillers, colorants and other additives are metered into the kneader, mixed uniformly, the material is transferred to a three-roll mill, roller uniform pressure, discharge, metering and packaging to obtain single-component epoxy vehicle folding Edge plastic products. In addition to the use of liquid nitrile rubber toughening, there have also been reports of toughening using solid carboxylated rubber. Wang Chao used the addition of solid carboxyl rubber to improve the toughness. The obtained single-component epoxy glue satisfies the requirement for high-speed flight of spacecraft fairings. The use of styrene-ethylene-butadiene-styrene copolymer in combination with Epikote 828, dicyandiamide, and imidazole as one-component epoxy adhesives improves toughness and the product has high impact strength and shear strength. It has been reported that bisphenol F epoxy and polyurethane modified bisphenol A epoxy and rubber modified bisphenol A epoxy are used together to produce synergistic toughening effect. The product has low viscosity and does not foam during the curing process. Good adhesion. (to be continued)