Flame-retardant PP materials are favored by more and more manufacturers due to their light density, excellent weather resistance and low overall price. In many applications, they have successfully replaced flame-retardant PS, flame-retardant ABS, etc. Behind the rise of flame-retardant PP materials. , There is a problem that may be encountered often, that is, the problem of the precipitation of flame-retardant materials, in the halogen-free flame retardant material is even more apparent.
Precipitation of flame retardant not only often generates mold deposits during the injection molding process, powdery agglomerates, sticking molds, etc. affect the normal production, but also often precipitates in finished products, resulting in white spray-like substances that affect the appearance of the product and result in decreased flame retardancy. Wait.
Before solving the problem of flame retardant precipitation, we first discuss two important factors that affect the precipitation problem:
First, the compatibility of flame retardant and PP base material resin
Flame retardants generally have two states in PP resin: they are filled with resin in the form of similar fillers, and the other types are uniformly dispersed in the resin in a molten state. Because PP is a non-polar material, polar flame retardants and PP are There will be interface compatibility problems. The poorer the interface compatibility, the easier it is to produce precipitation problems.
Second, the impact of temperature on the flame retardant precipitation
PP is a semi-crystalline material with a low glass transition temperature. When the ambient temperature is higher than its glass transition temperature, as the temperature rises, the thermal movement of the amorphous segment will accelerate, making the reaction with PP resin. Poorly contained small molecular flame retardants can easily overcome the resistance to migrate to the surface.
This is also the reason why the surface of the part is stored for a period of time. The high-temperature injection process is the most obvious process of precipitation, and the precipitation is often reflected in the mold to produce mold deposits. The higher the injection temperature, the higher the precipitation. The relationship between the migration rate of the fuel and the temperature can be roughly shown in Fig. 4. Within the range of the decomposition temperature of the flame retardant, the precipitation rate significantly increases with the increase of temperature. At a constant temperature, the precipitation also has a certain correlation with time. Plastic Knowledge Communication WeChat Group Plus Xiaobian WeChat: NB58250988
Solution
After understanding the causes of precipitation, the improvement of the fire-retardant precipitation problem can be done with half the effort. There are two main methods:
1. The introduction of strong polar groups (such as amine groups, carboxyl groups, epoxy groups, etc.) enhances the interface between flame retardant and PP, which can effectively reduce the problem of precipitation of flame retardants.
2. Improve the migration resistance between flame retardant and resin, and reduce the migration rate of low molecular weight flame retardant: Reduce the temperature to reduce the movement between segments or increase the degree of polymerization of flame retardant molecules and reduce the width of the molecular weight distribution to reduce the flame retardancy Precipitation effective measures.
It should be pointed out that: Non-precipitating flame-retardant PP is not completely without precipitation. It only reduces the migration of flame retardant to a great extent. Currently, non-precipitated flame-retardant PP is often built on high technical cost, so it is low. The cost anti-precipitation is still a subject that needs to be improved in the current flame-retardant PP material.