Epoxy adhesives

Epoxy resin is a general term for compounds that contain two or more epoxy groups in a molecule and form a three-way cross-linked structure in the presence of a suitable chemical aid such as a curing agent. It is a thermosetting resin with good bonding performance, corrosion resistance, and high electrical insulation and mechanical strength. It has many excellent properties. It has good bonding effect on metal and non-metal, so epoxy resin is called "all-purpose adhesive".

Two major discoveries in the late 19th and early 20th century unveiled the curtain of epoxy resin. In 1891, Lindmann in Germany reacted with hydroquinone and epichlorohydrin to form a resinous product. In 1909, Russian chemist Prileschajew discovered that the reaction of anisole and olefin can produce epoxy compounds. These two chemical reactions are still the main route in epoxy resin synthesis. In 1934 Schlack polymerized a compound containing more than one epoxy group with an amine compound to obtain a high molecular polymer, which was published as a German patent. After 1938, a number of patents issued by P. Castan of Switzerland and SO Greenlee of the United States all revealed the synthesis of epoxy resin by polycondensation reaction of bisphenol A and epichlorohydrin. Both organic polyamines and phthalic anhydride can be used. The resin is cured and has excellent adhesion properties. Soon, CIBA in Switzerland (Ciba), Shell in the United States, and Dow Chemical all started the industrial production and application development of epoxy resins.

In 1947, the adhesive of Araldite, the brand of Swiss Ciba, began to attract attention. Since then, epoxy has been known as the “ubiquitous adhesive”. In addition, Shell's EPON epoxy resin was introduced to the market as a coating. In 1956, U.S. Joint Carbon Compounds began selling cycloaliphatic epoxy resins. Dow Chemical Company produced phenolic epoxy resin in 1959. The development has been widely used in various fields so far.

Epoxy adhesive properties

(1) Adhesive strength, high mechanical strength

Reasons: Strong polar groups such as hydroxyls and ether bonds produce strong adhesion between the epoxy resin and the adjacent interface; epoxy groups react with the metal surface containing active hydrogen to form strong chemical bonds.

(2) Low shrinkage during curing: Epoxy resin has the lowest shrinkage in the adhesive (phenol resin: 8%~10%, silicone resin: 6%~8%, polyester resin: 4%~8 %, epoxy resin: 1%~3%).

(3) Good chemical resistance: The ether bonds, benzene rings, and aliphatic hydroxyls in the curing system are not susceptible to acid-base attack.

(4) Excellent electrical insulation: The breakdown voltage of epoxy resin is greater than 35KV/mm

(5) can be room temperature curing, but also high temperature curing;

(6) Large operating temperature range. -60~150 °C.

Epoxy adhesive composition

It is mainly composed of epoxy resin and curing agent. To improve certain properties, diluents, accelerators, coupling agents, fillers, etc. are also added.

Epoxy type

1, a wide variety of epoxy resins, according to its chemical structure and epoxy-based combination of ways into the following categories:

(1) Glycidyl ethers

(2) Glycidyl esters

(3) Glycidylamines

(4) Aliphatic Epoxy Compounds

(5) Alicyclic epoxy compounds

(6) Hybrid epoxy resin

2, according to the state of the resin at room temperature is divided into:

(1) Liquid epoxy resin: It can be used as castables, solvent-free adhesives, and coatings.

(2) Solid epoxy resin: A simple epoxy resin with a relatively high molecular mass, a thermoplastic solid oligomer. Can be used as solvent-based coatings, powder coatings, and solid-state molding materials.