1. Epoxy resin is an amorphous viscous liquid that is plastic when heated. There is no obvious melting point. It is softened by heat. It gradually melts and becomes sticky. It does not dissolve in water. It will not harden. Therefore, it has almost no single use value. The insoluble and infusible polymer of the network structure has application value. When a certain amount of curing agent is added, it gradually solidifies to form chemical substances with different properties. Therefore, it is necessary to add a curing agent to form a formula resin, and perform a curing reaction under certain conditions to produce a product with a three-dimensional network structure. Various excellent properties become epoxy materials with real use value. Commonly used amine curing agents in engineering: ethylene diamine, diethylene polyamine, polyethylene polyamine, etc.
2. The curing agent is an indispensable additive. Whether it is used as an adhesive, coating, or casting material, the curing agent needs to be added, otherwise the epoxy resin cannot be cured. Filler name function Asbestos fiber, glass fiber increase toughness, impact resistance quartz powder, porcelain powder, iron powder, cement, emery powder increase hardness alumina, porcelain powder increase adhesion, increase mechanical strength asbestos powder, silica gel powder, high temperature cement increase Heat-resistant asbestos powder, quartz powder, stone powder reduce shrinkage, aluminum powder, copper powder, iron powder and other metal powders increase thermal conductivity, conductivity graphite powder, talc powder, quartz powder improve anti-wear performance and lubricity. Emery and other abrasive materials increase resistance Grinding performance mica powder, porcelain powder, quartz powder to increase insulation performance, various pigments, graphite with color
3. Definition of epoxy resin curing agent
It reacts chemically with epoxy resin to form a net-shaped three-dimensional polymer, which encloses the composite material in the net-shaped body. It is an additive that turns the linear resin into a tough solid body.
4. Classification of epoxy resin curing agent
(1) Alkaline and acidic curing agents: alkaline curing agents include aliphatic diamines and polyamines, aromatic polyamines, other nitrogen-containing compounds and modified fatty amines. Acidic curing agents include organic acids, anhydrides, and boron trifluoride and their complexes.
(2) Add molding and catalytic curing agent:
Addition molding curing agent. This type of curing agent and epoxy group undergo an addition reaction to form a part of the cured product segment, and through the stepwise polymerization reaction, linear molecules are cross-linked to form structural molecules. This type of curing agent is also called melon-type curing agent. .
Catalytic curing agent This type of curing agent only initiates the epoxy resin. After the epoxy group is opened, the epoxy resin itself is catalyzed to polymerize into a network structure to form a homopolymer with an ether bond as the main structure.
(3) Explicit curing agent and latent curing agent.
(1) The obvious curing agent is a commonly used curing agent, and can be divided into addition polymerization type and catalytic type. The so-called addition polymerization type means that the ring of the epoxy group is opened for the addition polymerization reaction, and the curing agent itself participates in the three-dimensional network structure. If this kind of curing agent is added in too small amount, the cured product is connected to the unreacted epoxy group. Therefore, for this type of curing agent
(3) There is a suitable dosage. Catalytic curing agents cationic or anionic to ring-open addition polymerization of epoxy groups. Eventually, the curing agent does not participate in the network structure, so there is no suitable amount of equivalent reaction; however, increasing the amount will cause Make the curing speed faster. Latent curing agent refers to a relatively long-term stability at room temperature after mixing with epoxy resin
5. Epoxy resin
Generally, it requires more than 3 months to have greater practical value, and the most ideal requires half a year or more than 1 year), and only needs to be exposed to heat, light, moisture and other conditions to start the curing reaction. This type of curing agent basically uses physical and chemical methods to block the activity of the curing agent. Among the obvious curing agents, varieties such as dicyandiamide and adipic acid dihydrazide are insoluble in epoxy resins at room temperature, but start to cure after dissolving at high temperatures, so they also show a latent state. Therefore, in some books, these varieties are also classified as latent curing agents, which can actually be called functional latent curing agents. Because the latent curing agent can be mixed with epoxy resin to make a one-component complex, simplifying the application procedures of epoxy resin, its application range from single packaging adhesive to coating, impregnating paint, potting material, powder coating, etc. Development. Latent curing agents have attracted more and more attention abroad, and can be said to be a key topic in research and development. Various varieties of curing agents modified and new technologies are emerging endlessly and are very active