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Flame-retardant PP materials have been favored by many manufacturers because of their light density, excellent weather resistance and low overall price. They have successfully replaced flame retardant PS and flame retardant ABS in many applications. Behind the rise of flame retardant PP materials, there may be a problem that may be encountered frequently, that is, the problem of the precipitation of flame retardant materials, especially in halogen-free flame retardant materials. The precipitation of flame retardant not only often causes mold scale, powdery agglomeration, and sticking mold to affect normal production during the injection molding process, but also often precipitates in the finished product, and the white misty substance affects the appearance of the product and causes the flame retardancy to decrease. Wait.
Before solving the problem of flame retardant precipitation, let us first discuss two important factors that affect the problem of precipitation:
First, the compatibility of flame retardant with PP substrate resin
The flame retardant generally has two states in the PP resin: the resin is filled in a similar filler form, and the other is uniformly dispersed in the resin in a molten state. Since PP is a non-polar material, there is a problem of interface compatibility between the polar flame retardant and PP. The worse the interface compatibility, the more prone to the problem of precipitation.
Second, the effect of temperature on the precipitation of flame retardants
PP is a semi-crystalline material with a low glass transition temperature. When the ambient temperature is higher than its glass transition temperature, the thermal motion of the amorphous segment will increase as the temperature increases, making it compatible with the PP resin. Poorly accommodating small molecule flame retardants can easily overcome the migration of resistance to the surface.
This is also the reason why the surface sometimes appears on the surface after the workpiece is stored for a period of time. The high temperature injection molding process is the most obvious process of precipitation, and the precipitation often reflects the mold scale on the mold. The higher the injection temperature, the more the precipitation is. The relationship between the migration rate of the flame retardant and the temperature can be roughly as shown in Fig. 4. In the decomposition temperature range of the flame retardant, the precipitation rate is obviously accelerated with the increase of the temperature. At a constant temperature, precipitation also has a certain relationship with time.
Solution:
After understanding the cause of the precipitation, the improvement of the flame retardant precipitation problem can be achieved with less effort. There are two main methods:
1. Introducing strong polar groups (such as amine groups, carboxyl groups, epoxy groups, etc.) to enhance the interface between the flame retardant and PP, which can effectively reduce the problem of flame retardant precipitation.
2. Improve the migration resistance between the flame retardant and the resin, and reduce the migration rate of the low molecular weight flame retardant: lowering the temperature to reduce the movement between the segments or increasing the polymerization degree of the flame retardant molecules and reducing the molecular weight distribution width Effective measures for the precipitation of agents.
It should be pointed out that the non-precipitating flame retardant PP is not completely precipitated, but it only greatly reduces the migration of the flame retardant. The current non-precipitating flame retardant PP is often built on excessive technical costs, so low-cost anti-precipitation is still a topic that needs to be perfected for current flame-retardant PP materials.