What Is a Thermal Epoxy?

Epoxy resin is a general term for a class of polymers containing more than two epoxy groups in the molecule. It is the polycondensation product of epichlorohydrin and bisphenol A or polyol. Due to the chemical activity of epoxy groups, a variety of compounds containing active hydrogen can be used to open the ring, cure and crosslink to form a network structure, so it is a thermosetting resin. Bisphenol A epoxy resin not only has the largest output and the most complete varieties, but new modified varieties are still increasing and the quality is constantly improving. ^[1]

Epoxy resin

Epoxy resin is a general term for a class of polymers containing more than two epoxy groups in the molecule. It is the polycondensation product of epichlorohydrin and bisphenol A or polyol. Due to the chemical activity of epoxy groups, a variety of compounds containing active hydrogen can be used to open the ring, cure and crosslink to form a network structure, so it is a thermosetting resin. Bisphenol A epoxy resin not only has the largest output and the most complete varieties, but new modified varieties are still increasing and the quality is constantly improving. ^[1]

China has been conducting research on epoxy resin since 1958, and has put it into industrial production at a rapid rate. So far, it has flourished throughout the country.

Introduction

The excellent physical and mechanical and electrical insulation properties of epoxy resins, the adhesion properties to various materials, and the flexibility of their use processes are not available in other thermosetting plastics. Therefore, it can be made into coatings, composite materials, casting materials, adhesives, molding materials and injection molding materials, and has been widely used in various fields of the national economy.

Epoxy engineering plastics mainly include epoxy molding plastics and epoxy laminated plastics for high pressure molding, and epoxy foam plastics. Epoxy engineering plastics can also be regarded as a broad epoxy composite. The epoxy composite materials mainly include epoxy glass fiber reinforced plastics (general-purpose composite materials) and epoxy structural composite materials, such as pultrusion epoxy profiles, wind-molded hollow rotary products and high-performance composite materials. Epoxy composite is an important structural material and functional material in high-tech fields such as chemical industry, aviation, aerospace, and military industry.

Mainly used as anti-corrosion floor, epoxy mortar and concrete products, high-grade roads and airport runways, quick repair materials, grouting materials to strengthen the foundation, construction adhesives and coatings, etc.

Preference control

First of all, the advantages of epoxy resin, the epoxy resin mentioned here usually refers to bisphenol A epoxy resin.

1. The application value of the epoxy resin alone is very low, and it needs to be used in combination with the curing agent to have practical value.

2. High bonding strength: The bonding strength of epoxy resin adhesives ranks first in synthetic adhesives.

3 The curing shrinkage is small, and the shrinkage of epoxy resin is the smallest in the adhesive. This is one of the reasons for the high curing adhesion of epoxy resin.

4 Chemical resistance: The ether group, benzene ring and fatty hydroxyl group in the curing system are not easy to be attacked by acid and alkali. It can be used for two years in seawater, petroleum, kerosene, 10% H2SO4, 10% HCl, 10% HAc, 10% NH3, 10% H3PO4 and 30% Na2CO3; while immersed in 50% H2SO4 and 10% HNO3 for half a year at room temperature; % NaOH (100 ) immersed for one month, the performance remains unchanged.

5. Excellent electrical insulation: the breakdown voltage of epoxy resin can be greater than 35kv / mm

6. Good process performance, stable product size, good resistance and low water absorption.

Second, the advantages of bisphenol A epoxy resin are good, but they also have their disadvantages:

First, the operating viscosity is large, which is a bit inconvenient in construction.

Second, the properties of the cured product are brittle and the elongation is small.

Third, the peel strength is low.

Fourth, poor resistance to mechanical and thermal shock.

Application characteristics of epoxy softener

1. Various forms. A variety of resins, curing agents, and modifier systems can be adapted to almost any application's requirements on form, and can range from extremely low viscosity to high melting solids.

2. Easy curing. By using various curing agents, the epoxy resin system can be cured in a temperature range of 0 to 180 ° C.

3. Strong adhesion. The presence of polar hydroxyl groups and ether bonds in the molecular chain of epoxy resin makes it highly adhesive to various substances. Epoxy resin has low shrinkage when cured and generates low internal stress, which also helps to improve adhesion strength.

4. Low shrinkage. The reaction between the epoxy resin and the curing agent used is carried out by a direct addition reaction or a ring-opening polymerization reaction of epoxy groups in the resin molecule, and no water or other volatile by-products are emitted. Compared with unsaturated polyester resins and phenolic resins, they show very low shrinkage (less than 2%) during curing.

5. Mechanical properties. The cured epoxy resin system has excellent mechanical properties.

6. Electrical performance. The cured epoxy resin system is an excellent insulating material with high dielectric properties, resistance to surface leakage, and arc resistance.

7. Chemical stability. Generally, the cured epoxy resin system has excellent alkali resistance, acid resistance, and solvent resistance. Like other properties of the cured epoxy system, chemical stability also depends on the resin and curing agent chosen. Appropriate selection of epoxy resin and curing agent can make it have special chemical stability performance.

8. Dimensional stability. The combination of many properties mentioned above makes the epoxy resin system have outstanding dimensional stability and durability.

9, resistant to mold. The cured epoxy system is resistant to most molds and can be used in harsh tropical conditions.

Type classification

According to the molecular structure, epoxy resins can be roughly divided into five categories:

1.Glycidyl ether epoxy resin

2.Glycidyl epoxy resin

3.Glycidylamine epoxy resin

4. Linear aliphatic epoxy resin

5, cycloaliphatic epoxy resin

The most widely used type of epoxy resin in the composite material industry is the above-mentioned first type of glycidyl ether epoxy resin, and among them, diphenol-based propane epoxy resin (referred to as bisphenol A epoxy resin) is the main type. The second is glycidylamine-based epoxy resin.

1.Glycidyl ether epoxy resin

Glycidyl ether epoxy resin is formed by polycondensation of active hydrogen-containing phenols or alcohols with epichlorohydrin.

(1) Diphenol-based propane epoxy resin

Diphenol-based propane epoxy resin is made by polycondensing diphenol-based propane and epichlorohydrin.

The industrial control index of resin is as follows

:

epoxy value. Epoxy value is the most important indicator to identify the properties of epoxy resin. Industrial epoxy resin types are distinguished according to different epoxy values. The epoxy value refers to the number of epoxy-containing substances per 100 g of the resin. The inverse of the epoxy value multiplied by 100 is called the epoxy equivalent. The meaning of epoxy equivalent is: grams of epoxy resin containing 1 mol epoxy group.

Inorganic chlorine content. The chloride ion in the resin can interact with the amine curing agent to affect the curing of the resin, and also affect the electrical properties of the cured resin. Therefore, the chlorine content is also an important indicator of epoxy resin.

Organic chlorine content. The content of organic chlorine in the resin indicates the content of the chloroalcohol group in the molecule that has not undergone a ring-closing reaction. Its content should be reduced as much as possible, otherwise the resin's curing and the properties of the cured product will be affected.

Volatile matter.

viscosity or softening point.

(2) Phenolic polyepoxy resin Phenolic polyepoxy resin includes phenol formaldehyde type and o-cresol formaldehyde type poly epoxy resin. Compared with diphenol-based propane type epoxy resin, it contains more than two in-line molecules. Epoxy group, so the crosslinked density of the cured product is large, with excellent thermal stability, mechanical properties, electrical insulation, water resistance and corrosion resistance. They are made by condensation polymerization of novolac resin and epichlorohydrin.

(3) Other polyhydric phenolic glycidyl ether type epoxy resins have practical representatives: resorcinol epoxy resin, resorcinol-formaldehyde epoxy resin, tetraphenol ethyl ester Alkane type epoxy resin and trishydroxyphenylmethane type epoxy resin. These polyfunctional glycidyl ether resins have high heat distortion temperature and rigidity after curing, and can be blended alone or with general E type resin for high performance compounding. Materials (ACM), printed circuit boards and other base materials.

(4) aliphatic polyglycidyl ether epoxy resin aliphatic polyglycidyl ether contains two or more epoxy groups in the molecule, most of these resins have very low viscosity; most of them are long chain Linear molecules are therefore flexible.

2.Other types of epoxy resin

(1) Glycidyl-based epoxy resin Glycidyl-based epoxy resin and diphenol-based propane epoxidized resin have low viscosity, good processability, high reactivity, and better adhesion than general epoxy resins. High, good mechanical properties of the cured product; good electrical insulation; good weather resistance, and good ultra-low temperature resistance, under ultra-low temperature conditions, still has higher bonding strength than other types of epoxy resins. Has good surface gloss, good light transmission and weather resistance.

(2) Resins such as glycidylamine-based epoxy resins have the advantages of multifunctionality, high epoxy equivalent, large crosslinking density, and significantly improved heat resistance. Previously at home and abroad, the superior adhesion and heat resistance of glycidylamine epoxy resins have been used to manufacture carbon fiber reinforced composite materials (CFRP) for aircraft secondary structural materials.

(3) cycloaliphatic epoxy resins such epoxy resins are prepared by epoxidation of double bonds of cycloaliphatic olefins, their molecular structure and diphenol-based propane epoxy resins and other epoxy resins There is a big difference. The former epoxy groups are directly connected to the alicyclic ring, while the latter epoxy groups are all connected to the benzene core or the aliphatic hydrocarbon with epoxypropyl ether. The cured product of cycloaliphatic epoxy resin has the following characteristics: high compressive and tensile strength; can maintain good mechanical properties under long-term exposure to high temperature conditions; arc resistance, ultraviolet light aging resistance and Good weather resistance.

(4) Aliphatic epoxy resins not only have no benzene nucleus, but also no alicyclic structure in their molecular structure. There is only a fatty chain, and an epoxy group is connected to the fatty chain. The cured epoxy polybutadiene resin has good strength, toughness, adhesion, and positive and negative temperature resistance.