Epoxy resin curing agent is a chemical reaction with epoxy resin to form a network of three-dimensional polymer, the composite material envelope in the network body. An additive that turns a linear resin into a tough solid.

1 Classification of curing agents

Curing agent by use can be divided into room temperature curing agent and heating curing agent. Epoxy resins generally have excellent performance when cured at high temperature, but the coatings and adhesives used in civil buildings need to be cured at room temperature due to heating difficulties. So most of the use of aliphatic amine, lipolyamide and polyamide, especially the winter use of coatings and adhesives have to be used with polyisocyanate, or the use of polyol with a foul smell.

The variety of curing agent has a great influence on the mechanical properties, heat resistance, water resistance, corrosion resistance, etc. For example, the heat resistance of epoxy resin cured by curing agent such as aromatic polyamine, imidazole and anhydride is higher than that of aliphatic polyamine and low molecular polyamide curing agent. The water resistance of aromatic anhydride curing epoxy resin is better than that of aromatic diamine and aliphatic polyamine curing agent. The alkali resistance of epoxy resin cured by anhydride curing agent is better than that of acid resistance. Appropriate curing agent should be selected according to different use and performance requirements.

The curing temperature of various curing agents is different, and the heat resistance of cured products is also very different. Generally speaking, the use of curing agent with high curing temperature can obtain excellent heat resistant curing materials. For addition polymer-based curing agents, curing temperature and heat resistance are increased in the following order:

Aliphatic polyamines < aliphatic polyamines < aromatic polyamines ≈ phenolics < anhydride

2. Selection of curing agent

Curing agent selection: Curing agent has a great influence on the performance of epoxy resin, generally according to the following points of selection:

(1) Select from the performance requirements: some require high temperature resistance, some require good flexibility, 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, can not choose the curing agent of heat curing;

(3) Choose from the applicable period: the so-called applicable period refers to the time when the curing agent is added to the epoxy resin and can not be used. To be suitable for a long period, generally choose anhydride or latent curing agent;

(4), from the safety of choice: general requirements of small toxicity is better, convenient for safe production;

(5) Choose from the cost.

The use of curing agent in epoxy floor paint

Because of the literal understanding of the "curing agent" of epoxy paint, many people will understand the curing agent as an auxiliary agent to help epoxy resin curing. As long as the curing agent is added, the epoxy resin will cure into the floor. As long as the curing agent is added enough, the curing speed will be faster.

This concept leads many users to ask businesses to distribute more curing agents when they buy epoxy floor paint, because they feel that as long as the curing agent is put more, the curing speed of epoxy floor can be accelerated, so as to shorten the construction time. In fact, this is an impractical practice, on the contrary, the curing agent added more, in fact, the curing speed is slower, and even there may be no curing situation.

The reaction process between epoxy resin and curing agent is a process of chemical reaction. After evenly mixed epoxy coating, the hydroxyl group in the resin will first open the ring from the closed state, and then recombine with the hydrogen and oxygen bond in the curing agent to form a new closed ring. This new closed loop cross interconnects to form a solid three-dimensional structure. The new structure is in a very stable state, which gives the epoxy floor paint strong mechanical properties and chemical resistance, and has good resistance to daily damage or chemical agents.

Since the curing process is a chemical reaction process, there must be a reaction component quality ratio problem, only when the epoxy resin and curing agent to achieve a balanced state, curing reaction can be both adequate and appropriate. When the curing agent is too much, the ring-opening epoxy resin has been linked with enough curing components, the extra curing agent can not find more ring-opening resin, so it can only be free in the original state of the epoxy film; And when the curing agent is too small, epoxy resin also can not find the curing components can be linked, so it can only be free in the film. This is usually seen can not cure the situation, too much or too little curing agent, will affect the quality of the film.

In addition, uneven stirring is also a serious problem affecting the curing reaction. Many users still cannot cure after construction according to the materials proported by the manufacturer, which is a typical case of uneven mixing. Good reaction between resin and curing agent requires two materials to be correctly mixed together, uneven mixing, two kinds of paint can not be very good fusion, not in contact with the material will not react, so can only maintain their original liquid state, the performance of paint can not dry, or long time to deal with the sticky state of the situation.

Application of curing agent in powder coating

In the thermoplastic powder coating does not need curing agent, but in the thermosetting powder coating, curing agent is an essential component in the composition of the powder coating, if there is no curing agent, thermosetting powder coating can not be cross-linked curing film to obtain a certain physical and mechanical properties and chemical resistance of the film. The property of curing agent is the main factor that determines the performance of powder coating and coating film.

The curing agent should have good chemical reaction activity with the resin, at room temperature and melt extrusion mixing temperature conditions do not react with the resin, and under the condition of baking curing, rapid crosslinking curing reaction with the resin, the appearance of good leveling, physical and mechanical properties and good chemical resistance of the film.

Considering the manufacturing process and storage stability of the powder coating, the curing agent is a solid, not a liquid, under normal or room temperature conditions, and it is best to be a solid powder or a solid granule or flake that is easy to be crushed.

From the consideration of energy saving, the crosslinking curing reaction temperature of curing agent and resin is low and the reaction time is short, which is conducive to the low temperature and short time curing film, which can save energy and improve production efficiency.