Before using coupling agent, you should measure the moisture content of the filler you use. Then you decide the specific varieties of coupling agent on the basis of the filler's moisture content and the mentioned-before coupling agent properties, e.g. monoalkoxy-coupling agent suitable for the dry filler and chelate type or mono-alkoxy pyrophophato coupling agent suitable for the wet filler.
During choosing coupling agent, you should consider polymer's melting point, crystallinity, molecular weight, polarity, aromatic character, fatsoluble property and copolymerization structure. Regarding the thermosetting polymer, you should consider the solidifying-temperature and solidifying-mechanism.
The filler's properties such as shape, specific surface, acidic/basic property, moisture content and chemical composition can affect coupling effect. By and large, the coupling effect for coarse-particle filler is not better than the fine-particle filler. But when filler is super-fine (e.g. CaCO32000 mesh), the coupling effect has the opposite case.
The dosage of coupling agent is commonly 0.3-0.5% of the weight of the material to be treated and the recommended dosage is 0.8-1.5%. But the coupling effect is not in direct proportion to the volume of coupling agent used. If the volume of coupling agent is too much, the excess coupling agent may cause the material's performance drop. (In plastic, the index of elongation and impact will drop; in coating, the adhesive force will drop by a large margin.) If the volume is too little, the coupling effect will not be good because the covering on material is not complete. So the best volume should be determined before using through experiments during the application of which is economy and effective.
Because the dosage of coupling agent is little, the coupling agent should be evenly dispersed into filler/pigment to get good coupling effect. Otherwise the coupling effect will not be good.
Usage
1. Direct mixing method
This method is to directly mix polymer, filler or pigment and other assistants with coupling agent. It is an easy method and no additional equipment is needed and the original process keeps unchanged.. The disadvantage of this method is that the dispersion of material is not ideal for there are competitive reactions among coupling agent and other assistants.
2. Method of preprocessing
This method is to pre-treating filler/pigment with coupling agent, then mix polymers and other assistants. This method has many virtues and it is especially fit for polymer of complicated composition or engineering plastics that need to be processed under relatively high temperature. This method can prevent from arising of unnecessary side-reactions. And the decomposition point of the coupling agent and filler (after treatment) will rise by a large margin.
This method can be divided into:
a. Dry mixing method:
In order to coat a small amount of titanic acid ester on the surface of pigment and filler evenly, a small amount of dilute (the ratio of dilute to coupling agent is 1:1) which can be the solvent or lubricant in the original process recipe should be added generally. If not adding, the filler can not be coated well. For example, white oil (liquid wax) can be chosen in the plastic industry, machine oil can be chosen in the rubber industry and 200# solvent oil or isopropyl alcohol in the coating industry. The processing equipment is high-speed kneading machine. In the case of high-speed stirring filler, spraying the diluted coupling agent and stirring continuously for 5-12 minutes (depend on the effect of the mixer). then, further treat the material according to the original process or discharge the material for spare use (please pay attention to cooling, if not, it is easy to cause overheat in some parts, color change of filler and the filling property decrease.
b. Wet mixing method:
For the monoalkaoxy type and co-ordination type coupling agent, you can use solvent oil, ligarine and phenol to dilute and immerse the pigment among them. Then, remove the solvent by heating or pressure degree. For the chelating type coupling agent which is water dissolvable, you can use water to dilute and immerse. Then, remove moisture. In this method, the material can couple completely. But the consumption is very large in the industrial production.
