The design and determination of a PVC paste resin formula generally go through the following steps
1. According to the properties of the products, the brand of PVC paste resin is determined;
2. Determine the amount of plasticizer added according to the hardness and softness of the product;
3. Determine the type and amount of stabilizer according to performance (such as transparency, toxicity, etc.) and economy;
4. Determine the composition and addition amount of the lubricating system according to the product performance, equipment condition, stability category and the addition amount of plasticizer;
5. According to the main composition of PVC paste resin formula and equipment, determine the addition amount of processing aids;
6. Determine the amount of filler (and adjust the proportion of lubricant) according to the cost and performance;
7. Determine whether to add other additives according to product performance.
Selection of paste PVC resin
First, select the appropriate Emulsion PVC resin type according to the mechanical properties of the products to be processed. PVC products with high degree of polymerization have high mechanical strength, high gel temperature and plasticization temperature, and high price. They are suitable for making wear-resistant layer, tensile resistance layer, hard surface layer and matting layer. PVC products with low polymerization degree have low gel temperature, low plasticization temperature, low price, but low mechanical strength.
Secondly, the appropriate brand of paste PVC resin should be selected according to the use, type and processing form of paste resin. Viscosity of paste resin products is an important selection index. For example, for high foaming products, paste resin products with relatively high viscosity and low gel temperature are selected to control good foaming performance and uniform cell distribution; Other products generally require that the paste viscosity should not be too high to facilitate processing. If the paste layer is thick, the resin with relatively high viscosity has little effect on the apparent properties of the product; If the pasted product layer is thin, if the selected pasted resin has a high viscosity, it will not only affect the uniformity and surface smoothness of the product, but also the coating is easy to fall off, and the amount of raw materials will be increased.
For paste products produced by impregnation, if the resin with high viscosity is selected, its appearance is easy to wrinkle, which will affect the product quality. At the same time, when considering the paste PVC resin, especially for the coating and scraping process, the manifold of the plasticized paste must be considered. The paste resin product that the plasticized paste can well maintain or approach the Newtonian fluid should be selected, which is conducive to the control of processing conditions. In addition, the stability and degassing performance of the plasticized paste should be considered. Only the plasticized paste with good stability can be processed into a good paste product under the optimized process conditions; For PVC paste resin that needs vacuum defoaming, it is required to have better degassing property, etc.
For most paste products, the general paste resin should be selected. It has the advantages of large production batch, wide application range, reliable and stable product quality, easy to master the performance of the resin, relatively low price, mature processing technology and simple process optimization and adjustment. However, when there are special requirements for products, the brand number of paste PVC resin for special purposes can be selected. Although the application scope of these resins is not wide and the price may be relatively high, when used for their designated purposes, the effect is generally better than the general effect, and the performance and quality characteristics of the products can better meet the special requirements. At present, the varieties of special paste resins in China mainly include bright type, foaming type, extinction type, etc.
Control of paste resin processing formula
The formula of paste PVC resin has an important influence on the use, quality, processing efficiency and production cost of products. It is very necessary to select the appropriate formula after the use of the product is defined and the appropriate paste resin is selected.
First of all, we should select the appropriate paste additives according to the requirements of the products. Three factors should be considered in the selection of additives: (1) to meet the performance requirements of products, for example, cold resistant plasticizers should be selected for cold resistant products; Lead salt composite stabilizer can be selected to obtain good stabilization effect. Calcium zinc, organic tin, rare earth stabilizer, etc. can be used to achieve environmental protection. (2) to meet the good processing requirements of paste PVC resin, if the viscosity of plasticized paste is high and does not meet the requirements, viscosity reducer can be added; If the strength of artificial leather products is not very good, about 0.2% vapor phase white carbon black can be added for reinforcement. (3) Reduce production costs while ensuring appropriate quality. For example, in the production of low-grade foaming products, the requirements for cell are not high, so the low-cost sodium bicarbonate foaming agent can be used to replace some AC foaming agents; Another example is artificial leather. When the filler of heavy calcium (particle size less than 400 mesh), light calcium and modified calcium carbonate can meet the product requirements, it is obvious that heavy calcium is the most suitable.
The preparation method of plasticized paste is also very important. First, the formulation design should meet the performance requirements of the product, and then consider meeting the good processing performance of plasticized paste. On this basis, consider increasing the dosage proportion of cheap additives as much as possible, so as to maximize the economic benefits and competitive advantages of the product. In the formulation, it is necessary to optimize the formulation according to the product requirements and processing requirements. The order and mode of adding raw materials, how to mix the additives, and the pretreatment of raw materials not only have a great impact on the processing conditions, but also determine the quality of the final product performance. The same formula and different preparation methods will produce different effects, and the quality of products will also change greatly, which needs to be paid great attention.
Control of processing conditions
After selecting the appropriate formula and processing method, the control of PVC paste resin products mainly depends on the gel process and the plasticization process. The quality of gel process control of paste resin has the greatest impact on the processing and performance of products, which is the most difficult to master. The gel process of the resin is related to the gel temperature and gel time of the resin. In the production process, if the gel temperature increases, the gelation speed will be accelerated, and the time required for gel can be shortened; On the contrary, gel can be completed at lower temperature and longer time, but the production efficiency is low.
The gel temperature is related to the polymerization degree, particle size distribution and viscosity of the resin. Generally, there is the following empirical rule: the gel of the resin under the same polymerization mode and the viscosity difference is small
The temperature is mainly affected by the degree of polymerization. The gel temperature increases by about 3 ℃ with the increase of the degree of polymerization by 100; The paste viscosity also has a great influence on the gel temperature. For resins with bimodal or wide unimodal distribution of primary particle size, the larger the primary particle size, the lower the paste viscosity, and the lower the paste viscosity, the higher the gel temperature of the resin. Therefore, the gel temperature of the resin is the result of the comprehensive influence of polymerization degree and viscosity. In the actual production of products, the gel process can often be controlled within a certain range by adjusting the heating temperature and time, but the equipment efficiency, equipment capacity and the stability of the production process should also be comprehensively considered. This adjustment is limited. Therefore, the paste resin product model should be properly selected in the formulation.
