In hand lay-up molding and spray molding, the resin is layered on the opening mold. Especially in spray molding, the resin is sprayed, and part of it becomes a mist, which is deposited, so that before the resin is fully cured, Styrene continuously volatilizes from the resin and is emitted into the workshop air. On the one hand, some styrene is lost, and on the other hand, the environment is polluted. Especially when the workshop is not sufficiently ventilated, the styrene content in the air is high and operation Workers are in this atmosphere for a long time, which is harmful to health. Therefore, countries around the world have stipulated the threshold value of styrene (TLV), that is, the average styrene concentration in the air measured within a 40h working week on an 8h working day The highest value. For example, the threshold value of styrene in the United Kingdom and the United States is 100, that is, the highest value of the average content of styrene vapor in the air is 100g/m³. Sweden is specified as 50g/m³.
In order to ensure that the workshop air is below the threshold limit, the workshop must strengthen ventilation. However, ventilation alone will bring down the room temperature in winter and increase the cost of air conditioning, so the volatile amount of styrene in the polyester resin must be reduced.
Early rise low volatility resin contains a small amount of paraffin as a volatilization inhibitor. During curing, a wax film is formed on the surface to isolate the resin from the air. But after adding wax, it is easy to cause delamination of the laminated material.
In the future, it was improved to use a high melting point and low melting point paraffin and various polymers, such as polybutylene fumarate, polybutyl acrylate, etc.
There is also a volatile inhibitor (such as paraffin) and a compound called "adhesion promoter". This adhesion promoter can be described as acrylic acid with two hydrocarbon groups and each hydrocarbon group has at least one double bond hydrophobic ether or Ester; there are also unsaturated isoprene (meta) compounds and their ethers or esters, such as linseed oil, dipentene and trimethylolpropane diene diyl ether, etc. The amount of paraffin is 0.05%~0.5 % (Mass fraction), the amount of adhesion promoter is 0.1%~2% (mass fraction)
In addition, in order to reduce the volatilization of styrene, the amount of styrene can also be reduced, or some (or all) styrene can be replaced with low-volatile monomers. However, reducing the styrene content will cause the performance of the resin to decrease after curing, and other substitutes are often used. Can't compare with styrene (styrene has low price, many sources and good comprehensive performance)
In order to reduce the volatility of styrene, the process also promotes the transition of hand lay-up process and spray process to closed mold molding (such as resin injection molding process)