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How to choose epoxy resin

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The curing agent has a great influence on the performance of the epoxy resin and is generally selected according to the following points.

(1) Select from the performance requirements: some require high-temperature resistance, some require good flexibility, and some require good corrosion resistance, then select the appropriate curing agent according to different requirements.
(2) Choose from the curing method: some products can not be heated, you can not choose the heat curing agent.
(3) Choose from the application period: The so-called application period refers to the time from when the epoxy resin is added to the curing agent when it cannot be used. For long-term applications, acid anhydrides or latent curing agents are generally used.
(4) Choose from safety: Generally, it is better to require less toxicity, which is convenient for safe production.
(5) Choose from cost.

Modification options
The purpose of the modifier is to improve the tanning properties, shear resistance, bending resistance, impact resistance, and insulation performance of the epoxy resin. Common modifiers are:
(1) Polysulfide rubber: can improve impact strength and anti-stripping performance.
(2) Polyamide resin: It can improve brittleness and improve bonding ability.
(3) Polyvinyl alcohol test-butyraldehyde: Improve impact tanning resistance.
(4) Nitrile rubber: improve the impact of tanning resistance.
(5) Phenolic resins: can improve temperature resistance and corrosion resistance.
(6) Polyester resin: improve the impact of tanning resistance.
(7) Urea-formaldehyde melamine resin: increase chemical resistance and strength.
(8) Furfural resin: improve static bending performance and acid resistance.
(9) Vinyl resin: improve peel resistance and impact strength.
(10) Isocyanate: reduce moisture permeability and increase water resistance.
(11) Silicone resin: improve heat resistance.

The amount of polysulfide rubber can be between 50-300%, and a curing agent needs to be added; the amount of polyamide resin and phenolic resin is generally 50-100%, and the amount of polyester resin is generally 20-30%. Chemical agent, you can also add a small amount of curing agent to promote the faster reaction.
Generally speaking, the greater the amount of modifier, the greater the flexibility, but the heat distortion temperature of the resin product will decrease accordingly. To improve the flexibility of the resin, toughening agents such as dibutyl phthalate or dioctyl phthalate is also commonly used.

Filler selection
The role of the filler is to improve some properties of the product and improve the heat dissipation conditions when the resin is cured. The use of the filler can also reduce the amount of epoxy resin and reduce the cost. Different fillers can be used for different purposes. The size is preferably less than 100 mesh, the amount depends on the use. Commonly used fillers are introduced as follows:

Filler name Function
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 adhesion and increase mechanical strength
4. Asbestos powder, silica gel powder, high-temperature cement to improve heat resistance
5. Asbestos powder, quartz powder, stone powder reduce shrinkage
6. Aluminum powder, copper powder, iron powder, and other metal powders increase thermal conductivity and electrical conductivity
7. Graphite powder, talc powder, quartz powder to improve anti-wear performance and lubrication performance
8. Emery and other abrasives to improve anti-wear performance
9. Mica powder, porcelain powder, quartz powder increase insulation performance
10. Various pigments and graphite with colors
In addition, it is reported that appropriate amounts (27-35%) of oxides of P, As, Sb, Bi, Ge, Sn, and Pb can be added to the resin to maintain adhesion under high heat and pressure.

Dilution options
Its role is to reduce the viscosity and improve the permeability of the resin. The thinner can be divided into two categories: inert and active, and the dosage is generally not more than 30%. Commonly used thinners are as follows:

Active thinner
Name Grade Use Remarks
Diglycidyl ether 600 ~ 30%, need to add the more calculated amount of curing agent
Polyglycidyl ether 630 Ibid. Ibid.
Propylene oxide butyl ether 660 ~ 15% Same as above
Propylene oxide phenyl ether 690 Ibid. Ibid.
Propylene oxide ethyl ether 669 Ibid. Ibid.
Tripropylene oxide propyl ether 662 Ibid. Ibid.

Inert thinner
Name Dosage Remarks
Xylene ~ 15% without an additional curing agent
Toluene Ibid Ibid
Benz Ibid Ibid
Acetone Ibid Ibid
Before adding the curing agent, all materials such as the resin, curing agent, filler, modifier, diluent, etc. used must be checked and should meet the following requirements:

(1) Moisture-free: materials containing water should be dried first, and solvents containing a small amount of water should be used sparingly.
(2) Purity: The content of impurities other than moisture is preferably less than 1%. Although the impurities can be used when the impurities are 5-25%, the percentage of the formula must be increased (reagent grade is better when used in small amounts).
(3) Understand whether each material is invalid.
In factories lacking acceptance conditions, it is best to do a small sample test according to the formula before use.

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