Epoxy resin is generally used with additives to obtain application value. Additives can be selected according to different uses, commonly used additives are curing agents, modifiers, fillers, diluents, other.
Among them, curing agent is an indispensable additive, whether it is used as adhesive, coating, castable need to add curing agent, otherwise epoxy resin can not be cured. Because of the different requirements of use and performance, there are different requirements for epoxy resin and additives such as curing agents, modifiers, fillers, diluents and so on.
I. selection of epoxy resin.
1. Select from the use.
When using as adhesive, it is best to choose resin with medium epoxy value (0.25-0.45), such as 6101 and 634, and resin with high epoxy value (0.40) as castable, such as 128,6101; Low epoxy value (< 0.25) resins are generally used as coatings, such as 901, 904, 907, 909 and so on.
2. Select from the mechanical strength.
The resin with high epoxy value has higher strength, but brittle; the resin with medium epoxy value has better strength at high temperature, and the resin with low epoxy value has worse strength at high temperature. Because the strength is related to the cross-linking degree, the cross-linking degree after curing with high epoxy value is also high, and the cross-linking degree after curing with low epoxy value is also low, which leads to the difference in strength.
3. Select from the operational requirements.
Do not need to withstand high temperature, do not require much strength, hope that epoxy resin can dry quickly, not easy to lose, you can choose the resin with lower epoxy value; if you want permeability, good strength, you can choose the resin with higher epoxy value.
II. Selection of curing agents.
1. Types of curing agents:
Commonly used epoxy resin curing agents are aliphatic amine, alicyclic amine, aromatic amine, polyamide, anhydride, resin, tertiary amine, in addition, UV or light can also cure epoxy resin under the action of photoinitiator. Amine curing agent is generally used for curing at room temperature or low temperature, and acid anhydride and aromatic curing agent are often used for curing at room temperature or low temperature.
2. The dosage of curing agent.
(1) when amines are used as cross-linking agents, they are calculated according to the following formula:
Amine dosage = mg/hn.
In the formula:
M = molecular weight of amine.
Number of active hydrogen in hn=.
G = epoxy value (epoxy equivalent per 100 grams of epoxy resin).
The range of change 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 using anhydride, it is calculated according to the following formula:
Anhydride dosage = mg (0.6% 1) / 100.
In the formula:
M = molecular weight of anhydride.
G = epoxy value (0.6) is the experimental coefficient.
3. The principle of selecting curing agent.
(1) choose from the performance requirements: some require high temperature resistance, some require good flexibility, and some require good corrosion resistance, choose appropriate curing agents according to different requirements.
(2) choose from the curing method: some products can not be heated, the heat curing agent can not be selected.
(3) Select from the applicable period: the so-called applicable period refers to the time from the time when the epoxy resin is added to the curing agent to the time when it cannot be used. To be applicable for a long period, generally choose anhydride or latent curing agent.
(4) Choice from safety: generally speaking, it is better to have low toxicity, which is convenient for safe production.
(5) choose from the cost.
III. Selection of modifiers.
The function of modifier is to improve the tanning property, shear resistance, bending resistance, impact resistance and insulation property of epoxy resin. The commonly used modifiers and their characteristics are briefly introduced.
(1) polysulfide rubber: it can improve impact strength and peeling resistance;
(2) Polyamide resin: it can improve brittleness and bonding ability;
(3) PVA tert-butyraldehyde: improving impact tanning resistance;
(4) nitrile butadiene rubber: improve impact tanning resistance;
(5) phenolic resin: it can improve temperature resistance and corrosion resistance;
(6) polyester resin: improve the resistance to impact tanning;
(7) urinary aldehyde melamine resin: increase chemical resistance and strength;
(8) Furfural resin: improve the static bending property and improve the acid resistance;
(9) Ethylene resin: improve peeling resistance and impact strength;
(10) isocyanate: reducing moisture permeability and increasing water resistance;
(11) silicone resin: improve heat resistance.
The dosage of polysulfide rubber can be between 50-300% and needs curing agent. Polyamide resin, phenolic resin dosage is generally 50-100%, polyester resin dosage is generally 20-30%, can no longer add additional curing agent, can also add a small amount of curing agent to promote the reaction faster.
Generally speaking, the more the amount of modifier, the greater the flexibility, 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 also commonly used.
IV. Selection of fillers.
The role of fillers is to improve some properties of products, and improve the heat dissipation conditions of resin curing, the use of fillers can also reduce the amount of epoxy resin and reduce the cost. Different fillers can be selected for different uses. Its size is best less than 100 mesh, depending on the use. A brief introduction to the common fillers is as follows:
Asbestos fiber, glass fiber: increase toughness, impact resistance;
Quartz powder, porcelain powder, iron powder, cement, Emery: improve hardness;
Alumina, porcelain powder: increase adhesion, increase mechanical strength;
Asbestos powder, silica gel powder, high temperature cement: improve heat resistance;
Asbestos powder, quartz powder, stone powder: reduce shrinkage;
Aluminum powder, copper powder, iron powder and other metal powder: increase thermal conductivity, electrical conductivity;
Graphite powder, talc powder, quartz powder: improve wear resistance and lubrication performance;
Emery and other abrasives: improve anti-wear properties;
Mica powder, porcelain powder, quartz powder: increase insulation performance;
All kinds of pigments, graphite: with color;
In addition, the data show that the addition of appropriate (27-35%) p, as, sb, bi, ge, sn, pb oxides in the resin can maintain adhesion under high heat and pressure.
V. selection of diluents.
The function of diluent is to reduce viscosity and improve the permeability of resin. Diluents can be divided into two categories: inertia and activity, and the dosage generally does not exceed 30%. Commonly used diluents are: Diglycidyl ether, polyglycidyl ether, epoxy propane butyl ether, epoxy propane phenyl ether, diepoxy propane ethyl ether, triepoxy propane propyl ether, inert diluent, xylene, acetone and so on.
Before adding a curing agent, all materials used, such as resins, curing agents, fillers, modifiers, diluents, etc., must be checked to meet the following requirements:
(1) No moisture: water-containing materials 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 except moisture should be less than 1%, and the reagent grade should be used in a small amount.
(3) to know whether each material is invalid or not.