The application of Guangxi calcium carbonate in PVC foam board. For PVC foam board, whether calcium carbonate filling affects the foaming performance is very complex, mainly depending on the size, addition amount, dispersibility and water content of calcium carbonate. If these factors of calcium carbonate are used properly, it can promote foaming; otherwise, it will seriously affect foaming.

Guangxi The application of calcium carbonate in PVC foam board materials is complex. For PVC foam board materials, whether calcium carbonate filling affects foaming performance depends mainly on the size, amount added, dispersibility, and water content of the calcium carbonate. If these factors are used properly, they can promote foaming; otherwise, they will seriously affect foaming.

　　 Guangxi There are two reasons why calcium carbonate can positively promote foaming: First, calcium carbonate can act as a nucleating agent, adsorbing foaming gas to form gas bubbles, controlling the number of pores, and making the PVC pores finer; second, calcium carbonate can improve the melt performance of PVC. The relatively rigid calcium carbonate itself can slow down the deformation and movement of the melt, thereby inhibiting the rapid expansion of pores and controlling the pore size to be finer. However, not all calcium carbonates can promote PVC foaming; calcium carbonate must meet the following appropriate conditions to promote foaming.

 

 

　　1 Guangxi Selection of Calcium Carbonate Characteristics

　　 Guangxi Particle Size of Calcium Carbonate

　　 Guangxi When the particle size of calcium carbonate matches the foaming agent, it can act as a nucleating agent and have a positive effect on foaming. The specific suitable size is less than 5μm and greater than 1.5μm without agglomeration. If the particle size of the inorganic powder is greater than 10μm, or too fine to cause self-agglomeration, it will not act as a nucleating agent and will have a negative impact on foaming. Xiangfa Powder, a Guangdong calcium carbonate manufacturer, recommends selecting 3000 mesh (4μm) calcium carbonate, which ensures the size is not greater than 5μm and prevents agglomeration.

　　 Guangxi Amount of Calcium Carbonate Added

　　A suitable amount of calcium carbonate can promote foaming quality. The optimal filling amount is generally recommended to be 10%-20%. If the amount of calcium carbonate added is too low, not enough nucleation points will be formed in the melt, resulting in a low foaming rate. If the amount of calcium carbonate added is too high, many nucleation points can be formed, but the melt strength is too low due to excessive filling, leading to excessive bubble breakage and a reduction in the foaming rate.

　　 Guangxi Dispersibility of Calcium Carbonate

　　If the inorganic powder is evenly dispersed in the resin, agglomeration can be avoided, ensuring that calcium carbonate with a size of 5μm can act as a nucleating agent without affecting foaming. Methods to ensure the dispersibility of calcium carbonate include surface treatment. If the surface treatment of the inorganic powder is thorough, completely changing its original hydrophilicity to lipophilicity, it will not affect foaming. Specific surface treatment methods can use a dual-affinity treatment, i.e., dual treatment with an aluminate coupling agent/polyol surfactant, or the selection of an aluminum titanate coupling agent. One way to ensure the dispersibility of calcium carbonate is to have the right size, and the other is surface coupling agent coating. If the surface coating of calcium carbonate is not thorough, uneven dispersion will occur, causing fine powders to agglomerate into larger particles. Because the thermal conductivity of calcium carbonate is far greater than that of the resin, it begins to absorb heat in the melt to form local hot spots, reducing the strength of the melt near the hot spots. The foaming agent decomposes prematurely, causing the product to foam prematurely before reaching the cooling area, resulting in an unformed or poorly formed surface.

　　2 Guangxi Selection of Calcium Carbonate Type

　　 Guangxi After selecting the characteristics of calcium carbonate, among the various types of calcium carbonate, PVC tends to choose light calcium carbonate, for the following reasons: Guangxi Light calcium carbonate has a high pH value of 9-10, while Guangdong heavy calcium carbonate has a pH value of 8-9. Therefore, light calcium carbonate is more alkaline and can absorb a large amount of HCL produced by PVC decomposition, assisting heat stabilizers in their heat stabilization function.

　　Particle size advantage: Light calcium carbonate has a relatively fine particle size, generally easily reaching 2500 mesh, which is exactly what PVC needs and can meet the performance requirements of PVC pipes and profiles. Heavy calcium carbonate has only been able to achieve this particle size in the last 10 years, as usage habits are gradually shifting towards heavy calcium carbonate.

　　Eliminating color cast: PVC products generally contain a yellow color cast, while light calcium carbonate contains a blue color cast, which can eliminate the yellow color cast when added.

　　Improving toughness: Light calcium carbonate is beneficial for modifying the impact strength of PVC products, while heavy calcium carbonate makes a significant contribution to tensile strength.

　　However, currently because Guangxi The particle size of heavy calcium carbonate can now reach the nanometer level. PVC can choose both Guangdong heavy calcium carbonate and Guangdong light calcium carbonate. Considering the different focuses of the modification contributions of the two calcium carbonates, it is often best to use a combination of the two. Generally, a ratio of 3:1 of large calcite heavy calcium carbonate/light calcium carbonate is chosen to balance the tensile strength and impact strength of PVC.

　　For Guangxi Heavy calcium carbonate and Guangdong light calcium carbonate, the formulation design is slightly different. For the selection of Guangxi PVC formulations using light calcium carbonate: Guangxi Light calcium carbonate can promote the thermal stability of PVC, so the amount of stabilizer in the formulation can be reduced accordingly. Guangxi Light calcium carbonate is beneficial for impact strength, so the amount of toughening agent can be reduced accordingly. Guangxi Light calcium carbonate has a relatively high oil absorption value, so the amount of small-molecule auxiliaries such as coupling agents, lubricants, and dispersants needs to be increased accordingly. For the selection of Guangxi Formulations using heavy calcium carbonate, the opposite is true.