Epoxy Adhesives Overview - Formulation Design

Acid anhydrides with high heat resistance such as benzophenonetetracarboxylic dianhydride (BTDA), diphenyl ether tetracarboxylic dianhydride (DPEDA) and the like are all solid, and are often used in combination with cycloaliphatic epoxy resins. Curing temperature 175 °C, long-term use temperature -60 ~ 175 °C. The main disadvantage is that it is relatively brittle and the fineness and dispersion of the curing agent are not easily controlled. Toughened using temperature up to 175 ~ 200 °C, such as J-30 adhesive. Liquid heat-resistant anhydrides include 70 anhydrides (tetrahydrophthalic anhydride isomers THPA), methyl tetrahydrophthalic anhydride (MeTHPA), methylendimethyl tetrahydrophthalic anhydride (MNA) Methylhexahydrophthalic anhydride (MeHHPA).

Phenolic resins and silicone resins are both curing agents and heat-resistant modifiers. Usually, low-molecular-weight thermosetting phenolic resin (M=350-450) or thermoplastic phenolic resin (M=500-650) is compounded with high relative average molecular weight bisphenol A epoxy resin, and an acidic or alkaline accelerator is added, such as 3- Hydroxynaphthoic acid, phosphoric acid, resorcinol, hexamethylenetetramine, DMP-30, benzyldimethylamine, and the like. Curing temperature 175 °C, long-term use at -60 ~ 260 °C. The maximum use temperature can reach 260 ~ 316 °C. Heat resistance is second only to heterocyclic polymer adhesives. Epoxy-phenolic adhesive has the advantages of complete performance, high and low temperature resistance, heat aging resistance, atmospheric aging and hygrothermal aging, and high temperature creep resistance. The main disadvantage is that it is more brittle. The alkoxy groups of the silicone resin can react with hydroxyl groups in the epoxy resin. The modified material has the dual advantages of epoxy resin and silicone resin.

This is part 2 of the introduction of high temperature resistant epoxy adhesive components that are resistant to high curing agents, such as aromatic amines, aromatic rings or alicyclic anhydrides, phenolic resins, silicone resins, dicyandiamide, and the like. Experts from the China Epoxy Resin Industry Association also said that other parts of the high-temperature epoxy adhesive also have -

(3) toughening agent. Due to the rigidity of macromolecules and the high cross-linking density, high-temperature epoxy adhesives have high brittleness, which affects the bonding strength, especially the strength of the wire, and therefore require toughening. Commonly used toughening agents are carboxylated nitrile rubbers, polyphenols, polysulfone resins, and the like. Generally, as the toughness increases, the heat resistance decreases. In recent years, heat-resistant thermoplastic resins such as polyarylsulfone, polyether ketone, and polyether ether ketone have been used for toughening. As the toughness increases, the heat resistance does not substantially decrease, and even slightly increases.

(4) Filler. From the viewpoint of heat resistance, the filler is also an important component. Ultra-fine aluminum powder can significantly improve the bonding strength. Vapor-phase SiO2 and asbestos powders also control the flow and prevent the effect of turbulence. The commonly used fillers include silicon powder and lithopone.

(5) Anti-hot oxygen agent. The adherent metal ions such as copper and iron ions can catalyze the thermal oxidative degradation reaction of organic polymers at a high temperature, resulting in interfacial adhesion failure. In order to eliminate the catalytic degradation activity of metal ions and improve the high temperature resistance, metal ion chelating agents such as 8-hydroxyquinoline, propyl gallate (n-propyl ester), acetylacetone, catechol and the like are often added. They can trap these metal ions, thereby reducing the catalytic degradation of metal ions. Some arsenic, manganese, molybdenum oxide can also effectively reduce the activity of metal ions, such as AS2O5 can generate very stable iron arsenate with Fe ions.

Source: 21st Century Fine Chemicals Network