In this article, we will explain about epoxy resin. By introducing its applications, characteristics, types, and a wide range of information, this article covers everything you need to know about epoxy resin.
What is Epoxy Resin?
Epoxy resin is a type of engineering plastic—a plastic that excels in applications that require strength and heat resistance—that undergoes a chemical reaction when heated, resulting in solidification.
History of Epoxy Resin
The first bisphenol-type epoxy resin was developed in 1930. Since 1948 where it began to be used for industrial purposes, it is now widely utilized as an adhesive and coating for materials; this is especially true in the electronics industry, as well as in the automotive and construction sectors. (Reference: The Japan Society of Epoxy Resin Technology(Q1))
Applications of Epoxy Resin
Epoxy resin is widely used in various applications due to its numerous features and benefits. Here, we will introduce some of its representative uses.
Electronic Components
Encapsulation materials for electronic components require excellent thermal properties, electrical insulation, and mechanical properties.
Since there are various types of electronic components, such as passive components, LEDs, sensors, and automotive electronic components, the encapsulation material must also offer flexibility in molding to the desired shape.
Epoxy resin as an encapsulation material meets all these requirements.
Semiconductors
In semiconductor products, semiconductor chips are bonded to substrates or lead frames using bonding wires. During this process, resin encapsulation is performed to prevent damage to the semiconductor chips and bonding wires as well as to enhance the reliability of the device.
The resin used for encapsulation must possess various properties, including mechanical strength, insulation, heat resistance, thermal expansion coefficient, and good adhesion to both the semiconductor chips and substrates; thus, epoxy resin encapsulants are widely used for semiconductors.
Coating Materials
Epoxy resin is widely used as a coating material due to its excellent adhesion, water resistance, and insulation properties.
There are two types of epoxy coatings: liquid coatings and powder coatings, with various coating methods available depending on the intended use.
Adhesives
Epoxy resin has very strong adhesive and bonding properties. As a result, it is widely used as an adhesive in a wide range of applications, from industrial projects to everyday use.
The strength of the bond depends not only on the properties of the epoxy resin itself, but also on the type of curing agent and the materials being bonded. Therefore, it is important to choose the optimal combination to ensure the best adhesion.
Characteristics of Epoxy Resin: Advantages
The advantages of epoxy resin are as follows:
- Versatility: By adjusting the molecular weight, there can be broader molecular weight distribution which leads to varying viscosity.
- Corrosion Resistance: It can prevent corrosion by blocking water and oxygen.
- Adhesiveness: It can bond various materials such as wood, metal, concrete, and glass.
- Electrical Insulation: It has excellent electrical insulation properties, making it electrically non-conductive.
- Water Resistance: It is impermeable to water.
- Chemical Resistance: It shows strong resistance to chemicals; it does not absorb dangerous metals ions like chromium, lead, and the like.
- Heat Resistance: It is suitable for use in high-temperature environments.
- Weather Resistance: It has properties that make it resistant to material degradation or alteration due to weather conditions such as wind, rain, temperature changes, and sunlight.
Characteristics of Epoxy Resin: Disadvantages
The disadvantages of epoxy resin are as follows:
- Toughness: It has low viscosity, making it susceptible to damage from external pressure. As a countermeasure, adding materials such as polyurethane can improve its toughness.
- UV Sensitivity: It is weak against ultraviolet light; material may deteriorate, become brittle, and turn white with prolonged exposure.
- Slow Curing at Low Temperatures: It tends to cure more slowly at low temperatures.
Types of Epoxy Resin
Epoxy resin can change its properties widely from liquid to solid by adjusting its molecular weight.
This characteristic allows it to be used in a wide range of applications. Typically, it is formulated by mixing prepolymers and curing agents to produce products, with the way they are combined creating variance on its physical properties such as binders, molded products, adhesives, and coatings.
Here, we will introduce nine types of epoxy resins.
Bisphenol A Epoxy Resin
One of the most representative types of epoxy resin is Bisphenol A type epoxy resin. Different forms can be obtained based on the ratio of Bisphenol A to epichlorohydrin molecular weights.
| Material | Bisphenol A, Epichlorohydrin |
| Characteristics | Good electrical insulation and chemical resistance |
| Applications | Molded products, glass fiber reinforced materials, adhesives, coatings, plasticizers for polyvinyl chloride (PVC) |
Bisphenol F Epoxy Resin
Bisphenol F type epoxy resin can also yield epoxy groups similar to Bisphenol A type epoxy resin.
| Bisphenol F Epoxy Resin Compared to Bisphenol A Epoxy Resin | |
| Epoxy Content | Higher ↑ |
| Viscosity | Lower ↓ |
| Curing Properties | Almost the same ≈ |
| Heat Resistance | Slightly lower ↓ |
| Chemical Resistance | Slightly improved ↑ |
Novolac Epoxy Resin
It is made using novolac (phenolic resin).
| Material | Novolac (Derived from phenolic resin, reacted with epichlorohydrin to produce it) |
| Characteristics | Good heat resistance, chemical resistance, and electrical properties |
| Applications | Semiconductor encapsulation material (most common), molding materials, coatings, and laminates |
Using cresol novolac as a substitute for phenol novolac results in cresol novolac type phenolic resin.
Aliphatic Epoxy Resin
Aliphatic epoxy resins are formed by glycidylation of aliphatic alcohols or polyols.
| Characteristics | Good electrical insulation, weather resistance, and heat resistance |
| Applications | Used to modify/reduce the viscosity of other epoxy resins, electrical insulation materials, glass fiber reinforcement |
Glycidyl Amine Epoxy Resin
It is known as high functionality epoxy resin.
| Property | High heat resistance, good mechanical properties |
| Applications | Critical material in composite applications used in the aerospace industry |
Polyfunctional Epoxy Resin
An epoxy resin with a high number of epoxy groups per molecule.
| Property | Good heat & chemical resistance |
Flexible Epoxy Resin
| Property | Good heat shock resistance, plasticity, and flexibility |
Polymeric Epoxy Resin
| Property | Good machinability of cured coating film |
Biphenyl Epoxy Resin
| Properties of the cured material | Good heat resistance, low stress |
Reaction Mechanism of Epoxy Resin
Epoxy resins do not react on their own and require curing agents or catalysts to initiate curing.
The reaction of epoxy resin proceeds through addition polymerization or ring-opening polymerization concurrent with the opening of the epoxide ring. This process does not produce any by-products after the reaction.
The resulting cured material forms a three-dimensional cross-linked network structure, which is insoluble, has a high melting point, and exhibits high heat resistance.
Commonly used curing agents include acid anhydrides, amine compounds, basic catalysts, and Lewis acid catalysts.
Now, let’s take a look at typical curing reaction systems of epoxy resin.
Addition Reaction of Epoxy Resin with Amines
The most commonly used method for curing epoxy resin involves room temperature curing, producing strong and adhesive cured materials.
Types include aliphatic polyamines, cycloaliphatic polyamines, modified polyamides, aromatic polyamine amides, etc. It is crucial to choose the appropriate type based on the intended use and curing conditions.
Co-condensation Reaction of Epoxy Resin with Anhydrides
To achieve this reaction, heat curing (above 100°C) is required, facilitated by the low viscosity of acid anhydrides and their long pot life after mixing, making them easy to handle.
The resulting cured material has a high glass transition temperature (Tg), excellent electrical insulation properties, mechanical characteristics, and thermal stability.
Additionally, they are safer compared to amine compounds, making them the most commonly used curing agents in the field of electrical and electronic insulation materials.
Self-polymerization of Epoxy Resin
For the self-polymerization of epoxy resins, methods involving basic or acidic catalysts are used, with anionic polymerization using basic catalysts such as imidazoles being commonly employed. Unlike other curing agents, a small amount of catalyst is sufficient to initiate the curing of epoxy resin.
Furthermore, at relatively low temperatures ranging from 120°C to 150°C, curing progresses rapidly, resulting in cured materials with high glass transition temperatures (Tg).
Conclusion
In this article, we have explained the characteristics, types, and reaction mechanisms of epoxy resins.
Epoxy resins, with their high-performance properties, can create highly functional products when combined with other materials. Epoxy resins play a crucial role behind the scenes, significantly contributing to the improvement of product performance as a versatile plastic material.
The “CrowdChem Data Platform” published by CrowdChem provides insights and knowledge in the field of chemistry, including catalog information categorizing products under epoxy resins and patent information associated with these products. Some resources are available for free, so please take advantage of them.
