Curing agents, also known as hardeners, curing agents or setting agents, are substances or mixtures that promote or control curing reactions. Resin curing is through condensation, ring closure, addition or catalysis and other chemical reactions, so that the thermosetting resin undergoes an irreversible change process. Curing is accomplished by adding a curing (crosslinking) agent. The curing agent is an indispensable additive. Whether it is used as an adhesive, coating, or castable, a curing agent needs to be added, otherwise the epoxy resin cannot be cured. The type of curing agent has a great influence on the mechanical properties, heat resistance, water resistance and corrosion resistance of the cured product.
At 12:48 on October 1, the public security bureau of Yiwu City received a report from the public that an explosion occurred during the unloading of No. 3 Building 3 in Jiangdong Fan Village, and many people were injured at the scene. After receiving the report, our bureau immediately dispatched police to deal with it, and at the same time notified Jiangdong Subdistrict, Health and Family Planning Commission, Environmental Protection Bureau, Safety Supervision Bureau, Transportation Bureau, etc. to go to the scene for disposal.
After a preliminary investigation, the cause of the accident was an explosion in the plastic bucket of a truck on the scene. The main component of the article was methyl ethyl ketone peroxide, commonly known as white water, which is a curing agent for unsaturated resins. Excessive concentration may easily cause an explosion.
Methyl ethyl ketone peroxide (MEKPO) is the most commonly used curing agent in the FRP room temperature curing process, and its dosage is usually 1%-2% of the resin dosage. Although the amount is small, it plays a vital role in the quality of FRP products. According to statistics, at present more than 50% of the poor resin curing quality problems are caused by poor quality curing agents. Therefore, inferior curing agents have become the black sheep of the FRP industry.
At present, there are many factories producing methyl ethyl ketone peroxide in China, but most of them are small workshop-type enterprises, which have neither technical standards and specifications nor quality control methods, especially lack of sufficient safety facilities. In the past 20 years, almost all domestic methyl ethyl ketone peroxide factories have experienced safety accidents of various sizes, which can be described as heavy casualties. Not only that, but safety accidents during transportation, storage and use caused by poor quality methyl ethyl ketone are also common reports. Therefore, inferior methyl ethyl ketone peroxide not only seriously endangers the quality of FRP products, but also seriously endangers the life and property safety of production enterprises, transportation enterprises and users.
The main raw materials of methyl ethyl ketone peroxide are hydrogen peroxide and methyl ethyl ketone. The production process is divided into two stages. The first stage is the synthesis reaction stage, and the latter stage is the dehydration stage. Since hydrogen peroxide contains a large amount of water, strictly speaking, this part of the water must be separated in the production process, thereby improving the purity of methyl ethyl ketone peroxide. Therefore, the water content of methyl ethyl ketone peroxide has become an extremely critical indicator. Whether to carry out the dehydration process has become the key factor to distinguish between high quality and safety and poor quality and dangerous methyl ethyl ketone peroxide. The international standard for methyl ethyl ketone peroxide is generally less than 5% water content, while domestic products are generally more than 20%. Although methyl ethyl ketone peroxide with high water content is cheap, but due to the presence of a large amount of water, the resin curing will be abnormal, and the early gelation will be fast and the later will not cure, which will seriously affect the strength of the FRP product and produce water. Fog and air bubbles cause cloudy patches on transparent products and polyester paint films. Generally, there are two reasons why the methyl ethyl ketone peroxide plant does not perform dehydration. One is that the product with high water content is low in cost, and the other is that the dehydration process is very dangerous, and it is easy to explode in the absence of automatic control means. Therefore, the methyl ethyl ketone peroxide sold in the market basically does not indicate the water content index, in order to achieve the purpose of touching fish in muddy water.
The second indicator of methyl ethyl ketone peroxide is the flash point, which is a very important safety indicator. The flash point of high-quality methyl ethyl ketone peroxide can exceed 70 degrees, and can be used with confidence in any production environment, while the flash point of low-quality methyl ethyl ketone peroxide is often only more than 30 degrees, which is prone to safety accidents under the high temperature in summer. Nonetheless, such critical indicators are often overlooked by most FRP factories, resulting in many security tragedies that should not happen.
The third indicator of methyl ethyl ketone peroxide is active oxygen content, which is currently the basic basis for purchasing methyl ethyl ketone peroxide in China. In developed countries, in order to ensure the safety of transportation and use, the active oxygen content of methyl ethyl ketone peroxide is limited to less than 9%, while the active oxygen content of methyl ethyl ketone peroxide commonly used in China often exceeds 11%, or even reaches 13%. In order to reduce the amount of use, at the same time shorten the curing cycle and improve production efficiency. Excessive active oxygen content is also one of the main reasons for the low safety performance of domestic methyl ethyl ketone peroxide.