Epoxy Resin

1、 Introduction

Epoxy resin is usually used together with additives. Additives can be selected according to different uses. Common additives include Curing Agent, Modifier, Filler, Diluent, etc.

Curing agent is an indispensable additive. Whether the epoxy resin is used as adhesive, coating, castable, curing agent should be added, otherwise it can not be cured. Due to the different requirements of application and performance, there are different requirements for epoxy resin, curing agent, modifier, filler, diluent and other additives.

2、 Selection of Epoxy Resin

(1)    Choose according to the Aplication

①　When used as adhesive, it is better to choose the resin with medium epoxy value (0.25-0.45);

②　When used as castable, it is better to choose resin with high epoxy value (0.40);

③　When used as coating, the resin with low epoxy value (< 0.25) is generally selected.

(2)    Choose according to Mechanical Strength

The strength is related to the degree of crosslinking. The epoxy value is high, and the crosslinking degree is also high after curing. The epoxy value is low and the crosslinking degree is low after curing. Different epoxy value will also cause different strength.

①　The resin with high epoxy value has higher strength but is brittle;

②　The resin with medium epoxy value has good strength at high and low temperature;

③　The resin with low epoxy value has poor strength at high temperature.

(3)    Choose according to Operational Requirements

①　For those who don’t require high temperature resistance and strength, they can choose the resin with lower epoxy value which can dry quickly and is not easy to be lost.

②　For those who require good permeability and strength, they can choose the resin with higher epoxy value.

3、  Selection of Curing Agent

(1)    Type of Curing Agent:

Common curing agents for epoxy resin include aliphatic amine, alicyclic amine, aromatic amine, polyamide, anhydride, resin and tertiary amine. In addition, under the affect of photoinitiator, UV or light can also make epoxy resin curing. Amine curing agent is generally used for room temperature or low temperature curing, while anhydride and aromatic curing agent are commonly used for heating curing.

(2)    Dosage of Curing Agent

①　When amine is used as crosslinking agent, it is calculated as follows:

Amine dosage = MG / HN

M = molecular weight of amine;

HN = number of active hydrogen;

G = epoxy value (epoxy equivalent per 100 g of epoxy resin)

The change range is not more than 10-20%. If cured with excessive amine, the resin will become brittle. If the dosage is too small, the curing is not perfect.

②　When anhydride is used as crosslinking agent, it is calculated as follows:

Anhydride dosage = MG (0.6 ~ 1) / 100

M = molecular weight of anhydride;

G = epoxy value (0.6 ~ 1) is the experimental coefficient.

(3)    The Principle of Choosing Curing Agent

①　Performance Requirements.

Some require high temperature resistance, some require flexible, and others require good corrosion resistance. Appropriate curing agent is selected according to different requirements.

②　Curing Method.

Some products can not be heated, then the curing agent of heat curing cannot be selected.

③　Application Period.

The so-called application period refers to the period from the time when the epoxy resin is added with the curing agent to the time when it cannot be used. For long application, anhydrides or latent curing agents are generally used.

④　Safety.

Generally, the curing agent with less toxic is better and safe for production.

⑤　Cost.

4、 The Selection of Modifier

The effect of modifier is to improve the tanning, shearing resistance, bending resistance, impact resistance and insulation performance of epoxy resin.

(1)    Common Modifiers and Characteristics

①　Polysulfide rubber: improve the impact strength and peeling resistance;

②　Polyamide resin: improve brittleness and adhesion;

③　Polyvinyl alcohol TERT butyraldehyde: improve the impact tanning resistance;

④　NBR: improve impact tanning resistance;

⑤　Phenolic resin: improve the temperature resistance and corrosion resistance;

⑥　Polyester resin: improve the impact tanning resistance;

⑦　Urea formaldehyde melamine resin: increase chemical resistance and strength;

⑧　Furfural resin: improve the static bending performance, improve the acid resistance;

⑨　Vinyl resin: improve peeling resistance and impact strength;

⑩　Isocyanate: reduce moisture permeability and increase water resistance;

11　Silicone: improve heat resistance.

(2)    Dosage

①　Polysulfide rubber: 50-300% ( with curing agent);

②　Polyamide resin and phenolic resin: 50-100%;

③　Polyester resin: 20-30% (without curing agent, or a small amount of curing agent to accelerate the reaction.

Generally speaking, the more modifier is used, the greater the flexibility is, but the thermal deformation temperature of resin products decreases accordingly. In order to improve the flexibility of the resin, toughening agents such as dibutyl phthalate or dioctyl phthalate are often used.

5、 Selection of Fillers

The function of fillers is to improve some properties of products and the heat dissipation conditions of resin curing. It can also reduce the amount of epoxy resin and reduce the cost. Different fillers can be used for different purposes. It should be less than 100 mesh, and the dosage depends on its application. The common fillers are as follows:

(1)    Asbestos fiber and glass fiber: increase toughness and impact resistance;

(2)    Quartz powder, porcelain powder, iron powder, cement, emery: increase hardness;

(3)    Alumina and porcelain powder: increase adhesive force and mechanical strength;

(4)    Asbestos powder, silica gel powder and high temperature cement: improve heat resistance;

(5)    Asbestos powder, quartz powder and stone powder: reduce the shrinkage rate;

(6)    Aluminum powder, copper powder, iron powder and other metal powders: increase thermal conductivity and conductivity;

(7)    Graphite powder, talc powder and quartz powder: improve the anti-wear performance and lubrication performance;

(8)    Emery and other abrasives: improve the anti-wear performance;

(9)    Mica powder, porcelain powder and quartz powder: increase insulation performance;

(10) All kinds of pigments and graphite: with color;

In addition, according to the data, the appropriate amount (27-35%) of P, As, Sb, Bi, Ge, Sn and Pb oxides added in the resin can maintain the adhesion under high heat and pressure.

6、 Selection of Diluent

The function of diluent is to reduce the viscosity and improve the permeability of resin. It can be divided into inert and active two categories, and the amount is generally not more than 30%. Common diluents include diglycidyl ether, polyglycidyl ether, propylene oxide butyl ether, propylene oxide phenyl ether, dicyclopropane ethyl ether, triethoxypropane propyl ether, inert diluent, xylene, toluene, acetone, etc.

7、 Material Requirements

Before adding curing agent, all materials used, such as resin, curing agent, filler, modifier, diluent, etc., must be inspected, which shall meet the following requirements:

(1)    No water: materials containing water should be dried first, and solvents containing a small amount of water should be used as little as possible.

(2)    Purity: the content of impurities other than water should be less than 1%. Although it can also be used with 5%-25% impurities, other materials’ percentage in formula should be increased. It is better to use reagent grade in small amount.

(3)    Term of Validity: It is necessary to know whether the materials are invalid.