In selectingcoupling agentPreviously, the moisture content of the filler used should be determined first, and the specific variety should be determined based on the moisture state and the characteristics of the various types of titanium esters mentioned above. Dry fillers should use monoalkoxy type, while wet fillers can choose chelating type or monoalkoxy pyrophosphate type. When selecting coupling agents, the melting point, crystallinity, molecular weight, polarity, aromaticity, lipophilicity, copolymer structure, etc. of the polymer should also be considered. For thermosetting polymers, their curing temperature and curing mechanism should also be taken into account.
The shape, specific surface area, moisture content, acidity, chemical composition, etc. of the filler can all affect the coupling effect. The coupling effect of general coarse particle fillers is not as good as that of fine particles, but the opposite phenomenon occurs for ultrafine (such as CaCO₃ ≥ 2000 mesh) fillers. The dosage of coupling agent is generally 0.5-3% of the weight of the treated material, and the recommended dosage is 0.8-1.5%. The dosage and effect are not directly proportional. If the dosage is too large, the excess coupling agent will actually lead to a decrease in performance (such as a decrease in tensile and impact resistance indicators in plastics, and a significant decrease in adhesion in coatings). If the dosage is too small, the effect will not be significant due to incomplete encapsulation. So in application, it is necessary to experiment with the optimal dosage to achieve both economy and effectiveness. Due to the low dosage of titanium ester coupling agent, in order to achieve the desired effect, it must be uniformly dispersed in the filler (or pigment, etc.), otherwise the coupling effect cannot be achieved.
usage method:
1. Mixing method: It is to directly mix polymers, fillers or pigments, other additives and coupling agents. This method is relatively simple and does not require additional equipment or changes to the original processing technology. The disadvantage is that the dispersion is not ideal, as other additives and coupling agents have competitive reactions.
2. Pre treatment method: First, the filler or pigment is pre treated with a coupling agent, and then processed and mixed with polymers and other additives. This method has many advantages, especially suitable for certain engineering plastics with complex polymer components or high processing temperatures. It can prevent unnecessary side reactions from occurring, and the decomposition point of coupling agents and fillers is greatly improved after pretreatment.
This law can be further divided into:
① Dry mixing method: In order to evenly coat a small amount of titanium acid ester on the surface of the pigment and filler, a small amount of diluent is generally added, and the amount of coupling agent is in a ratio of 1:1 to evenly distribute the small amount of titanium acid ester on the surface of the filler. Without diluent, the filler cannot be evenly coated. This diluent can use the solvents and lubricants in the original process formula. In the plastic industry, white oil (liquid paraffin) can be used, in the rubber industry, machine oil can be used, and in the coating industry, 200 # solvent oil or isopropanol can be used. The processing equipment generally uses a high-speed kneading machine, which sprays the diluted coupling agent into the filler in a mist under high-speed stirring, and then continues stirring for 5-15 minutes (depending on the effectiveness of the stirrer), and then follows the original process or discharges for later use (pay attention to cooling, otherwise it may cause local overheating, discoloration of the filler, and decrease in filling performance).
② Wet mixing method: Monoalkoxyl and coordinating coupling agents can be diluted with solvents such as solvent oil, petroleum ether, and benzyl alcohol to immerse the pigment, and then the solvent can be removed by heating or reducing pressure. For chelating agents that are soluble in water, they can be diluted and soaked with water, and then the water content can be removed. This method of coupling is relatively complete, but it consumes too much in industrial production and is not cost-effective economically.
