1. Liquid bisphenol A
There are roughly two general methods for synthesizing epoxy resins: one-step and two-step methods.
The one-step method can be further divided into a single alkali addition method and a secondary alkali addition method. The two-step method can be divided into a batch method and a continuous method. The one-step process is the polycondensation of bisphenol A and epichlorohydrin under the action of NaOH, that is, the ring opening and ring closure reactions are carried out under the same reaction conditions. At present, the largest E-44 epoxy resin produced in China is synthesized by a one-step process.
The two-step process is the reaction of bisphenol A and epichlorohydrin under the action of a catalyst (such as a quaternary ammonium salt), the first step by an addition reaction to form a diphenolic propane chlorohydrin ether intermediate, and the second step is carried out in the presence of NaOH. A closed loop reaction produces an epoxy resin. The advantages of the two-step method are: short reaction time; stable operation, small temperature fluctuation, easy to control; short alkali addition time, can avoid large-scale hydrolysis of epichlorohydrin; product quality is good and stable, and the yield is high. The domestic E-51 and E-54 epoxy resins are synthesized by a two-step process.


2, solid bisphenol A
The synthesis of epoxy resins can be roughly divided into two types: one-step method and two-step method. The one-step method can be further divided into a water washing method, a solvent extraction method, and a solvent method. The two-step method can be further divided into a bulk polymerization method and a catalytic polymerization method.
The one-step process (known locally as the Taffy method) is a polycondensation reaction of bisphenol A with epichlorohydrin under the action of NaOH for the manufacture of solid epoxy resins of medium relative molecular mass. Such as domestic production of E-20, E-14, E-12.
The two-step method (known as the advancment method in foreign countries) is a method of heating and dissolving a low molecular weight liquid E-type epoxy resin and bisphenol A, and then performing an addition reaction under high temperature or a catalyst, continuously expanding the chain, and finally forming a high molecular weight. Quality solid epoxy resins, such as E-10, E-06, E-03, etc., are synthesized by this method.


3. Advantages and disadvantages of one-step method and two-step method
In the one-step synthesis, the reaction is carried out in an emulsion in water. Post-treatment is more difficult when preparing high molecular weight resins. The obtained resin has a relatively wide molecular mass distribution and a high organic chlorine content. It is not easy to obtain products with high epoxy value and high softening point to meet the requirements of powder coatings.
When the two-step method is synthesized, the reaction proceeds in a homogeneous phase, and the chain growth reaction is relatively stable. Therefore, the obtained resin has a relatively narrow molecular weight distribution, a low organic chlorine content, and an epoxy value and a softening point can pass the ratio and the reaction temperature. To control and adjust. The utility model has the advantages of simple process, convenient operation, less equipment, short working hours, no three wastes, one reaction, easy product quality control and regulation, and the like, and thus has received increasing attention.


Three characteristics of epoxy resin application
1, with great flexibility and diversity of formula design. The best formula can be designed according to different performance and process performance requirements. This is a major feature and advantage in epoxy applications. However, each of the best formulations has a certain range of conditions (conditions), and should not be used under any process conditions and any conditions of use. In other words, there is no optimal formula for “universal”. Different optimal formulations must be designed according to different conditions.
Since the curing principle of the epoxy resin curing system of different formulations is not completely the same, the curing history of the epoxy resin, that is, the curing process conditions have a great influence on the structure and performance of the epoxy cured product. The performance of the resulting product under the different curing conditions of the same formulation can vary greatly. Therefore, the correct material formulation design and process design are the key to epoxy resin application technology, and it is also the technical secret.
It is necessary to deeply understand and master the structure and properties of epoxy resin and its curing agent, modifier, etc., the reaction mechanism between them and the influence on the structure and properties of epoxy cured products. In this way, in the material formulation design and process design, it is easy to use, to achieve the best solution, to produce and develop the best performance and lowest cost epoxy materials and products.


2, different epoxy resin curing system can be cured at low temperature, room temperature, medium temperature or high temperature, can be cured on wet surface or even in water, can be cured quickly and slowly, so its adaptability to construction and manufacturing process requirements Very strong. Epoxy resin can be formed by low pressure molding or contact compression molding, thereby reducing the requirements on molding equipment and molds, reducing investment and reducing costs.


3. Among the three general-purpose thermosetting resins, the price of epoxy resin is high, which is affected by the application. However, due to its excellent performance, it is mainly used in applications where high performance requirements are required, especially in areas where comprehensive performance is required.