Epoxy resins are generally used together with additives to obtain application value. Additives can be selected according to different applications. Common additives include curing agents, modifiers, fillers, thinners, and others.
Among them, the curing agent is an indispensable additive, and it is necessary to add a curing agent for the adhesive, the paint, and the castable, otherwise the epoxy cannot be cured. Due to the different performance requirements of the application, there are also different requirements for additives such as epoxy resins and curing agents, modifiers, fillers, and thinners.
First, the choice of epoxy resin
1, choose from the use
The best choice for the adhesive medium epoxy value (0.25-0.45) of the resin, such as 6101,634; for the casting material is best to use high epoxy (0.40) resin, such as 618,6101; for coating The general choice of low epoxy value (
2, choose from mechanical strength
The resin with too high epoxy value has higher strength, but it is more brittle. When the epoxy value is medium, the strength at high and low temperatures is good. When the epoxy value is low, the strength at high temperature is poor. Because of the strength and degree of cross-linked degree, high cross-linking degree of the epoxy value after curing is also high, the epoxy value is low, the degree of cross-linking after curing is also low, it causes the difference in strength.
3, choose from operating requirements
No need for high temperature resistance, little strength requirements, I hope the epoxy resin can be quick-drying, not easy to lose, you can choose low epoxy resin; if you want permeability, strength is better, you can use a higher epoxy value Resin.
Second, the choice of curing agent
1, curing agent type:
Common epoxy resin curing agents include aliphatic amines, alicyclic amines, aromatic amines, polyamides, acid anhydrides, resins, and tertiary amines. In addition, ultraviolet light or light can also cure the epoxy resin under the action of a photoinitiator. Curing at room temperature or under low temperature is generally used for amine curing agent, and curing agent is commonly used for curing by heating and curing.
2, the amount of curing agent
(1) When amines are used as cross-linking agents, they are calculated as follows:
Amine dosage = mg/hn
In the formula:
m=amine molecular weight
Hn = number of active hydrogens
g = epoxy value (epoxy equivalent weight per 100 grams of epoxy resin)
The range of change is no more than 10-20%. If cured with excess amine, the resin will become brittle. If the amount is too small, the curing is not perfect.
(2) When using anhydrides, the following formula is used:
Anhydride dosage=mg(0.6~1)/100
In the formula:
m = anhydride molecular weight
g=epoxy value (0.6~1) is the experimental coefficient
3, choose the principle of curing agent
(1) Select from the performance requirements: some require high temperature resistance, some require good flexibility, and some require good corrosion resistance, then use appropriate curing agents according to different requirements.
(2) Select from the curing method: Some products can not be heated, you can not use heat curing curing agent.
(3) Select from the applicable period: The so-called pot life refers to the time from when the epoxy resin is added to the curing agent to when it cannot be used. For long-term applications, anhydrides or latent curing agents are generally used.
(4) Choose from safety: Generally, it is better to require less toxicity and to facilitate safe production.
(5) Choose from the cost.
Third, the choice of modifier
The role of modifiers is to improve the toughness, shear resistance, bending resistance, impact resistance, and insulation properties of epoxy resins. Commonly used modifiers and features to do a brief introduction.
(1) Polysulfide rubber: It can improve impact strength and stripping resistance;
(2) Polyamide resin: It can improve the brittleness and improve the bonding ability;
(3) Polyvinyl tert-butyl aldehyde: improve impact resistance;
(4) Nitrile rubber: improve impact resistance;
(5) Phenolic resins: can improve the temperature resistance and corrosion resistance;
(6) Polyester resin: improve impact resistance;
(7) Urine aldehyde melamine resin: increase chemical resistance and strength;
(8) Furfural resin: improving static bending performance and improving acid resistance;
(9) Vinyl resins: improve stripping and impact strength;
(10) Isocyanates: reduce moisture permeability and increase water resistance;
(11) Silicone: Improves heat resistance.
The amount of polysulfide rubber, etc. may be between 50-300%, and the curing agent must be added; the amount of polyamide resin and phenolic resin is generally 50-100%, the amount of polyester resin is generally 20-30%, and it can be no longer reinforced Chemicals can also be added in 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 heat distortion temperature of the resin product will decrease accordingly. In order to improve the flexibility of the resin, toughening agents such as dibutyl phthalate or dioctyl phthalate are also commonly used.
Fourth, the choice of filler
The function of the filler is to improve some of the properties of the product and improve the heat dissipation conditions when the resin is cured. The use of fillers can also reduce the amount of epoxy resin and reduce the cost. Different fillers can be used depending on the application. Its size is preferably less than 100 mesh, depending on the use. The commonly used fillers are as follows:
Asbestos fiber, glass fiber: increase toughness, impact resistance;
·Quartz powder, porcelain powder, iron powder, cement, corundum: increase 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 powders: increase heat conduction and conductivity;
· Graphite powder, talcum powder, quartz powder: improve anti-wear properties and lubricating properties;
· Emery and other abrasives: improve wear resistance;
· Mica powder, porcelain powder, quartz powder: increase insulation performance;
· A variety of pigments, graphite: with color;
In addition, according to the data, it has been shown that the appropriate amount (27-35%) of oxides of p, as, sb, bi, ge, sn, and pb can be added to the resin to maintain the adhesion under high heat and pressure.
Fifth, the choice of thinner
The role of the diluent is to reduce the viscosity and improve the permeability of the resin. Diluent can be divided into inert and active two major categories, the amount is generally not more than 30%. Commonly used diluents are: diglycidyl ether, polyglycidyl ether, propylene oxide butyl ether, propylene oxide phenyl ether, dipropylene oxide ethyl ether, tripropylene oxide propyl ether, inert diluents, two Toluene, toluene, acetone, etc.
Before adding the curing agent, all materials such as resins, curing agents, fillers, modifiers, and thinners must be inspected. The following requirements must be met:
(1) No moisture content: The water-containing material should be dried first, and the solvent containing a small amount of water should be used as little as possible.
(2) Purity: The content of impurities other than moisture is preferably less than 1%. If the impurity is available at 525%, the percentage of the formulation must be increased. When using a small amount of reagent grade is better.
(3) Learn if each material fails.
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