Calcium carbonate has been used as an inorganic filler in plastic filling for many years. In the past, calcium carbonate was generally used as a filler for the main purpose of reducing costs, and received good results. In recent years, with the extensive use in production and a large number of research findings, filling a large amount of calcium carbonate can also not significantly reduce the performance of the product, and even greatly improve some aspects, such as mechanical properties, thermal properties, etc.
In the actual use process, calcium carbonate is generally not directly added to the plastic. In order to make the calcium carbonate evenly dispersed in the plastic and play a role in optimizing the performance, the surface activation treatment of the calcium carbonate must be carried out first.
According to the molding process and performance requirements of the final plastic product, calcium carbonate with a certain particle size is selected, first activated and treated with auxiliary agents such as coupling agent, dispersant, lubricant, etc., and then a certain amount of carrier resin is added to mix evenly. Screw extruder to extrude and granulate to obtain calcium carbonate film masterbatch. In general, the calcium carbonate content in the masterbatch is 80wt%, the total content of various additives is about 5wt%, and the carrier resin is 15wt%.
The addition of calcium carbonate can greatly reduce the cost of plastics
Calcium carbonate is extremely abundant and its preparation is very simple, so the price is relatively cheap. In terms of special materials for pipes, the price of polyethylene (with carbon black) at home and abroad is high, and the price is very different from calcium carbonate. The more calcium carbonate is added to the plastic, the lower the cost.
Of course, calcium carbonate cannot be added indefinitely. Considering the toughness of plastic products, the filling amount of calcium carbonate is generally controlled within 50wt% (data provided by calcium carbonate filler manufacturers). For the production of plastic and steel-plastic composite pipes, plastics are the main raw materials, and greatly reducing the cost of plastics will undoubtedly greatly reduce the production cost and be beneficial to the improvement of profits.
Modification of calcium carbonate
Heavy calcium carbonate can increase the volume of plastic products, reduce costs, improve hardness and stiffness, reduce the shrinkage rate of plastic products, and improve dimensional stability; improve the processing performance of plastics, improve its heat resistance, improve the astigmatism of plastics, anti- At the same time, it has obvious effects on the toughening effect of notched impact strength and the viscous flow during the mixing process.
Mechanical properties
Calcium carbonate has been used as an inorganic filler in plastic filling for many years. In the past, calcium carbonate was generally used as a filler for the main purpose of reducing costs, and received good results. In recent years, with the extensive use in production and a large number of researches, it is also possible to fill a large amount of calcium carbonate without significantly reducing the production
After filling with calcium carbonate, due to the high hardness of calcium carbonate, the hardness and stiffness of plastic products will be improved, and the mechanical properties will be enhanced. The tensile strength and flexural strength of the product have been improved, and the elastic modulus of the plastic product has been significantly improved. Compared with FRP, its tensile strength, flexural strength and flexural modulus are roughly the same as those of FRP, and the thermal deformation temperature is generally Higher than FRP, the only thing inferior to FRP is its lower notched impact strength, but this disadvantage can be overcome by adding a small amount of short glass fibers.
For pipes, filling calcium carbonate can improve several of its indicators, such as tensile strength, steel ball indentation strength, notched impact strength, viscous flow, heat resistance, etc.; but at the same time it will reduce several of its toughness indicators, Such as elongation at break, rapid cracking, impact strength of simply supported beams, etc.
Thermal performance
After adding fillers, due to the good thermal stability of calcium carbonate, the thermal expansion coefficient and shrinkage rate of the product can be reduced in the same way, unlike glass fiber reinforced thermoplastics, which have different shrinkage rates in different aspects. Afterwards, the warpage and curvature of the product can be reduced, which is the biggest feature compared with the fiber filler, and the thermal deformation temperature of the product increases with the increase of the filler.
radioactivity
The filler has a certain ability to absorb rays, and generally can absorb 30% to 80% of incident ultraviolet rays to prevent the aging of plastic products.
Special modification of ultrafine calcium carbonate
The particle size of calcium carbonate can also be made into various types, by calling the calcium carbonate with a particle size of 0.1~1μm fine, and calling the calcium carbonate in the range of 0.1~0.02μm ultrafine, and calling the particle size ≤ 0.02μm. Ultra fine. The superfine or finer calcium carbonate is filled in the plastic, which has a special effect in changing the performance of the product.
Rigidity and toughness are two important performance indicators of plastic products. How to ensure that plastic products have good rigidity and toughness at the same time is one of the important topics in material science research for a long time.
In order to improve the toughness of plastic products, the method of adding rubber or elastomer is generally used, which can achieve the purpose of toughening and modification, but it damages the valuable rigidity of the material, and the processing performance and heat resistance of the material will be reduced.
In the 1990s, people found through a large number of experiments that after filling a large amount of ultrafine calcium carbonate particles in the plastic, not only the rigidity of the plastic is not damaged, but the toughness is also greatly improved, and the maximum can be increased by 2 to 3 times. It has changed the situation that the filling of modified plastics must sacrifice certain mechanical properties in the past, and the mechanical properties of modified plastics will decrease with the increase of filler loading.
In the past, coupling agents such as aluminate, titanate, silane and acid phosphite were generally used for surface activation treatment of inorganic fillers. After mixing with carrier resin and lubricant, surface activation treatment was carried out in a molten state. In addition to the use of coupling agents, the new surface activation treatment process also selects a certain amount of plasticizers, compatibilizers and dispersants according to the molding process and performance requirements of the final plastic products. Cold-wrapped inside the machine.