06.06.2022

Epoxy is the family of basic components or cured end products of epoxy resins. Epoxy resins, also known as polyepoxides, are a class of reactive prepolymers and polymers which contain epoxide groups. The epoxide functional group is also collectively called epoxy. The IUPAC name for an epoxide group is an oxirane. Epoxy resins may be reacted (cross-linked) either with themselves through catalytic homopolymerisation, or with a wide range of co-reactants including polyfunctional amines, acids (and acid anhydrides), phenols, alcohols and thiols (usually called mercaptans). These co-reactants are often referred to as hardeners or curatives, and the cross-linking reaction is commonly referred to as curing. Reaction of polyepoxides with themselves or with polyfunctional hardeners forms a thermosetting polymer, often with favorable mechanical properties and high thermal and chemical resistance. Epoxy has a wide range of applications, including metal coatings, composites, use in electronics, electrical components, LEDs, high-tension electrical insulators, paint brush manufacturing, fiber-reinforced plastic materials, and adhesives for structural and other purposes. The health risks associated with exposure to epoxy resin compounds include contact dermatitis and allergic reactions, as well as respiratory problems from breathing vapor and sanding dust, especially when not fully cured. Most of the commercially used epoxy monomers are produced by the reaction of a compound with acidic hydroxy groups and epichlorohydrin. First a hydroxy group reacts in a coupling reaction with epichlorohydrin, followed by dehydrohalogenation. Epoxy resins produced from such epoxy monomers are called glycidyl-based epoxy resins. The hydroxy group may be derived from aliphatic diols, polyols (polyether polyols), phenolic compounds or dicarboxylic acids. Phenols can be compounds such as bisphenol A and novolak. Polyols can be compounds such as 1,4-butanediol. Di- and polyols lead to diglycid polyethers. Dicarboxylic acids such as hexahydrophthalic acid are used for diglycide ester resins. Instead of a hydroxy group, also the nitrogen atom of an amine or amide can be reacted with epichlorohydrin.

Epoxy potting compound can be cured at room temperature or heated. After curing, it has excellent electrical properties, high surface gloss and simple and convenient operation. The SGS test has passed the EU ROHS standard. The cured product has high hardness, smooth surface, good gloss, and has the characteristics of fixation, insulation, waterproof, oil-proof, dust-proof, anti-theft, corrosion resistance, aging resistance, and thermal shock resistance. It is suitable for potting of small and medium-sized electronic components, such as automobile, motorcycle igniter, LED driving power supply, sensor, toroidal transformer, capacitor, trigger, LED waterproof lamp, and circuit board confidentiality, insulation and moisture-proof potting.

A silicone or polysiloxane is a polymer made up of siloxane (−R2Si−O−SiR2−, where R = organic group). They are typically colorless oils or rubber-like substances. Silicones are used in sealants, adhesives, lubricants, medicine, cooking utensils, thermal insulation, and electrical insulation. Some common forms include silicone oil, silicone grease, silicone rubber, silicone resin, and silicone caulk. More precisely called polymerized siloxanes or polysiloxanes, silicones consist of an inorganic silicon–oxygen backbone chain (⋯−Si−O−Si−O−Si−O−⋯) with two organic groups attached to each silicon center. Commonly, the organic groups are methyl. The materials can be cyclic or polymeric. By varying the −Si−O− chain lengths, side groups, and crosslinking, silicones can be synthesized with a wide variety of properties and compositions. They can vary in consistency from liquid to gel to rubber to hard plastic. The most common siloxane is linear polydimethylsiloxane (PDMS), a silicone oil. The second-largest group of silicone materials is based on silicone resins, which are formed by branched and cage-like oligosiloxanes.

One component silicone rubber is named after two component silicone rubber. Different from the two component silicone, the one-component silicone does not need to be mixed into the adhesive (curing agent) before use, and the one-component silicone has already added a latent curing agent to its production formula. This type of curing agent generally either starts to react and cures when it encounters a suitable high temperature or suitable water molecules. One component silicones have latent curing agents added to their production formulations, so there is no need to mix in the adhesive (curing agent) before use. This type of curing agent generally starts to react and cure when it encounters a suitable high temperature or suitable water molecules. One-component silicone rubber includes the following three categories: one-component room temperature vulcanized silicone rubber, one-component heating-curing silicone rubber and one-component mixing silicone rubber. Two component silicone is generally divided into two categories: condensation type and addition type. The condensation type will release low molecular substances during the curing process, and the addition type will not produce low molecular weight. Therefore, the condensation type has obvious shrinkage during curing, and the addition type has almost no shrinkage. Typical two-component condensed silica gel such as mold silica gel cured at room temperature, typical addition-type two-component silica gel wrapped silica gel, common liquid silica gel, etc. Two-component condensation type RTV silicone rubber is the most common type of RTV silicone rubber. Its raw rubber is usually hydroxyl-terminated polysiloxane, which is combined with other compounding agents and catalysts to form a rubber compound. The viscosity can range from 100 centistokes to one million centistokes.

Polyurethane resin adhesive glues are referred to as polyurethane adhesives, commonly known as urethane adhesives, with polyurethane as the main component. It has good adhesion and can be cured not only at room temperature, but also by heating. Polyurethane resin adhesive has high initial adhesion, soft adhesive layer, excellent peel strength, flexural strength, torsion resistance and impact resistance, as well as cold water resistance, oil resistance, dilute acid resistance and abrasion resistance. Thermal properties are not high enough and are often used as non-structural adhesives. It is widely used in the bonding of non-metallic and metal materials, and can also be used in cryogenic equipment such as liquid nitrogen, liquid oxygen and liquid hydrogen. Special Polyurethane resin adhesives distinguish themselves from other reaction resin adhesives in that they have a low tendency to yellow. Akemi has developed adhesives of this kind and marketed them since 2014. They are used for the durable bonding of particularly light-coloured natural and engineered stone. They are also suitable for grouting stone surfaces. These adhesives can be used indoors as well as outdoors.

Thermal paste (also called thermal compound, thermal grease, thermal interface material (TIM), thermal gel, heat paste, heat sink compound, heat sink paste or CPU grease) is a thermally conductive (but usually electrically insulating) chemical compound, which is commonly used as an interface between heat sinks and heat sources such as high-power semiconductor devices. The main role of thermal paste is to eliminate air gaps or spaces (which act as thermal insulation) from the interface area in order to maximize heat transfer and dissipation. Thermal paste is an example of a thermal interface material. As opposed to thermal adhesive, thermal paste does not add mechanical strength to the bond between heat source and heat sink. It has to be coupled with a mechanical fixation mechanism such as screws to hold the heat sink in place and to apply pressure, spreading the thermal paste. Thermal paste is used to improve the heat coupling between different components. A common application is to drain away waste heat generated by electrical resistance in semiconductor devices including power transistors, CPUs, GPUs, and LED COBs. Cooling these devices is essential because excess heat rapidly degrades their performance and can cause a runaway to catastrophic failure of the device due to the negative temperature coefficient property of semiconductors.

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