Epoxy resins and epoxy resin adhesives are not toxic by themselves, but due to the addition of solvents and other toxic substances during the preparation process, many epoxy resins are therefore "toxic." In recent years, the domestic epoxy resin industry is undergoing water-based modification and avoidance. Add other ways to maintain the "non-toxic" nature of epoxy resin. At present, the vast majority of epoxy resin coatings are solvent-based coatings containing a large amount of volatile organic compounds (VOC), which are toxic and flammable, thus causing damage to the environment and the human body.
Epoxy resins are generally used together with additives to obtain application value. Additives can be selected for different applications. Common additives include the following types: (1) Curing Agents; (2) Modifiers; (3) Fillers; (4) Diluents; (5) 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. Now introduce their selection methods to the following: (a) the choice of epoxy resin
1, choose from the use
The best choice for adhesives 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 paint Used generally 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. (b) Selection 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.
Epoxy value is the most important indicator to identify the quality of epoxy resin, epoxy resin model division is based on the difference in epoxy value to distinguish. The epoxy value refers to the number of gram equivalents of epoxy groups contained in 100 grams of resin.
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 hydrogen
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 Where:
M = anhydride molecular weight
G = epoxy value (0.6~1) is the experimental coefficient
3, choose the principle of curing agent: curing agent has a greater impact on the performance of epoxy resin, generally selected according to the following points.
(1) Select from performance requirements: some require high temperature resistance, some require good flexibility, and some require good corrosion resistance, and 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 to facilitate safe production.
(5) Choose from cost. (III) Selection of Modifiers
The role of modifiers is to improve the toughness, shear resistance, bending resistance, impact resistance, and insulation properties of epoxy resins. Commonly used modifiers are:
(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 alcohol tert-butyl aldehyde: Improves impact resistance.
(4) Nitrile rubber: Improve shock resistance.
(5), phenolic resins: can improve the temperature and corrosion resistance.
(6) Polyester resin: Improves impact resistance.
(7) Urine aldehyde melamine resin: Increase chemical resistance and strength.
(8) Furfural resin: It improves static bending performance and improves acid resistance.
(9) Vinyl Resin: Improves peel resistance and impact strength.
(10) Isocyanates: reduce moisture permeability and increase water resistance.
(11) Silicone: Improve heat resistance.
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