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Before selecting the coupling agent, the moisture content of the filler used shall be determined first, and the specific type shall be determined according to the moisture content state and the characteristics of the aforementioned aluminate coupling agents. The dry filler should be monoalkoxy type, and the wet filler can be chelating type or monoalkoxy pyrophosphate type. When selecting aluminate coupling agent, the melting point, crystallinity, molecular weight, polarity, aromaticity, fatty foot, copolymer structure, etc. of the polymer should also be considered. For thermosetting polymers, the curing temperature and curing mechanism should also be considered.
The shape, specific surface area, moisture content, acid-base property and chemical composition of filler can affect the coupling effect. Generally, the coupling effect of coarse particle fillers is not as good as that of fine particles, but the effect of superfine fillers (such as CaCO3 ≥ 2000 mesh) is opposite.
The amount of coupling agent is generally 0.5-3% of the weight of the treated material, and the recommended amount is 0.8-1.5%. The amount of coupling agent is not directly proportional to the effect. If the amount is too much, the excess coupling agent will reduce the performance. If the amount is too little, the effect will not be significant because of incomplete encapsulation. Therefore, the best dosage should be tested in application, which is both economical and effective.
Due to the small amount of aluminate coupling agent, it must be evenly dispersed in the filler (or pigment and other treatment materials) in order to play its due role, otherwise, the coupling effect will not be achieved.
1. Mixing method: it is to directly mix polymer, filler or pigment and other additives with aluminate coupling agent. This method is simple and convenient. Do not add equipment and change the original processing technology. The disadvantage is that the dispersion is not ideal, because other additives have competitive reaction with coupling agent.
2. Pretreatment method: the filler or pigment is pretreated with coupling agent, and then processed and mixed with polymer and other additives. This method has many advantages, especially suitable for some engineering plastics with complex polymer components or high processing temperature. It can prevent unnecessary side reactions, and the decomposition point of coupling agent and filler will be greatly improved after pretreatment.
This method can be divided into:
① Dry mixing method: In order to evenly coat a small amount of titanate on the surface of the pigment and filler, a small amount of diluent is generally added. When the dosage ratio of the diluent to the coupling agent is 1 to 1, a small amount of titanate can be evenly distributed on the surface of the filler. The filler can not be uniformly coated without diluent. This diluent can use the solvent and lubricant in the original process formula. For example, white oil (liquid paraffin) can be used in the plastic industry, engine oil can be used in the rubber industry, 200 # solvent oil or isopropanol can be used in the paint industry, and the processing equipment is generally a high-speed kneader, that is, the filler is mixed at a high speed, and the diluted coupling agent is sprayed in mist form, and then mixed for 5 to 15 minutes (depending on the effect of the mixer), Then carry out according to the original process or discharge for standby (pay attention to cooling, otherwise local overheating may easily cause discoloration of the filler and decrease the filling performance).
② Wet mixing method: coupling agents such as monoalkoxy type and coordination type can be diluted with solvent oil, petroleum ether, benzene alcohol and other solvents to soak the pigment, and then the solvent can be removed by heating or decompression, and the water soluble chelating type can be diluted and soaked with water, and then the water can be removed. This method is relatively complete, but it costs too much in industrial production and is not economical.
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