Calcium carbonate is widely used to fill polyvinyl chloride (PVC), polyethylene (PE) and other resins. Appropriate addition of calcium carbonate helps to improve the performance and processing performance of PVC products, such as improving the dimensional stability of products and improving product quality. Rigidity and hardness, improve the heat resistance of products, improve the printability of products, etc.
Because the price of calcium carbonate itself is relatively low, only by understanding the properties of different calcium carbonate types and the processing technology during use can the cost performance of the products be better improved.
1. Selection of calcium carbonate types
Heavy calcium is widely used in the foamed layer of PVC calendered synthetic leather. Light calcium is widely used in calendered leather surface layer, calendered hard sheet and calendered film. The light calcium used in calendering molding has a fine particle size and is easy to agglomerate, which is easy to cause white spots on the product, so the surface needs to be activated. The surface organic coating of calcium carbonate can make it hydrophobic, reduce agglomeration, increase the compatibility with PVC polymer, and improve its mechanical properties. The particle size of nano-calcium carbonate is 1~100nm, which shows better performance than active calcium, and has a certain reinforcing effect.
2. The effect of calcium carbonate addition on the properties of calendered products
Calcium carbonate mainly plays the role of increasing capacity and reducing cost in PVC calendered products. With the increase of calcium carbonate filling ratio, the mechanical properties of calendered products gradually decrease. Among them, nano-calcium carbonate has little effect on the strength of PVC products. In the case of requirements on the mechanical properties of products, nano-calcium carbonate can be preferred.
3. The effect of calcium carbonate surface treatment on product performance
Calcium carbonate, especially light calcium carbonate and nano-calcium carbonate, have small particle size, large surface area, strong hydrophilicity, and easy secondary agglomeration, so their surface needs to be treated to obtain hydrophobic calcium carbonate. Heavy calcium carbonate mainly has a filling and compatibilizing effect on PVC. It has poor compatibility with PVC and has a great impact on mechanical properties. It is recommended to be used in the foam layer of PVC calendered synthetic leather or in application scenarios where mechanical properties are not required. middle. For application scenarios that require high mechanical properties, it is better to use light calcium carbonate and nano-calcium carbonate. Light calcium carbonate or nano calcium carbonate.
4. The influence of the feeding sequence on the product
The feeding sequence of calcium carbonate is very important in the PVC processing process. Add PVC powder, calcium carbonate and stabilizer in sequence to the high-speed mixer, stir evenly at low speed, then turn to high-speed stirring until the temperature rises to 40~60°C, and add plasticizer and other liquids while stirring at high speed. Continue to stir to 100~120°C, the mixture is preferably in the form of flowable sand, and then put into an internal mixer for kneading and calendering to form a film. In the above feeding process, if the plasticizer is added first and then calcium carbonate is added, the calcium carbonate is prone to agglomeration under the infiltration of a large amount of plasticizer, and it is difficult to completely mix with other materials in the formula combination.
5. Abnormal problems and improvement of calcium carbonate in the application of PVC calendering
The abnormal problems of calcium carbonate in the application of PVC calendering are mainly clutter, white spots, drag lines, white folds, and decreased mechanical properties. Miscellaneous spots appear in calendered products, the reason is that calcium carbonate is mixed with impurities during production or transportation. You can observe the sieve residue during incoming inspection to see if there are variegated particles, and replace the qualified batch of calcium carbonate. The main cause of white spots and drag lines is the secondary agglomeration of calcium carbonate. The solution is to replace it with surface-treated calcium carbonate. The outer packaging of calcium carbonate should be protected from moisture to reduce the secondary agglomeration of calcium carbonate caused by moisture.