Processing aids

Although rigid PVC has a higher viscosity, its melt strength is lower, and melt fracture may occur at normal shear rates. After adding processing aids, it can be intertwined and adhered with PVC, which can effectively prevent melt rupture and significantly improve its tensile strength, flexural strength, elongation at break, impact strength and appearance quality. very important meaning.

ACR processing aids

The molecular structure of the processing aid determines the intrinsic properties. Depending on the molecular weight, processing aids act differently. Different molecular weights and viscosity numbers have different effects on the plasticizing properties, melt strength and appearance of PVC melts.

According to its melting point and molecular weight, it can be divided into lubricity, promoting plasticization, and improving strength. Low molecular weight processing aid, mainly acts as an internal lubricant and plasticizer. Although the plasticization speed is fast and the material dispersibility is good, it is beneficial to plasticization, but it is not good for the melt strength. Medium molecular weight processing aids mainly play a role in promoting plasticization. ACR with medium viscosity is mostly used in the production of profiles and pipes.

High molecular weight processing aids increase the melt strength through the entanglement of the molecular chains on the resin. In rigid low-foaming products, they are collectively referred to as foaming regulators. The difference from ACR processing aids is that the molecular weight of the former is above 300W, the molecular chain is longer, the viscosity is higher, the entanglement between the PVC molecular chains is relatively strong, the pressure is high, the melt strength can be improved, and the late plasticizing ability is strong.

The disadvantage is that the plasticizing speed is slow, the fluidity is poor, and the plasticizing temperature needs to be increased; the molecular weight of the former is generally about 20W-30W, the melting point is low, and it is first plasticized in the PVC melt, which has good compatibility with PVC and can adhere to PVC. Particles, increase friction, generate internal heat, improve melt heat and shear force transfer, promote PVC plasticization under the condition of less external heat supply, good melt flow and heat transfer performance, fast plasticization speed, and balanced plasticization degree, But the melt viscosity and strength are low.

The two are the same kind of material, and the molecular weight is very different. The molecular weight has a great relationship with the melt elongation ability, and the effect of promoting plasticization is weakened with the increase of molecular weight. Therefore, ACR cannot replace foaming regulators, nor can foaming regulators replace ACR.

Foam regulator

Processing aid ACR is a high molecular polymer with low melting point, high molecular weight and intrinsic viscosity, and high friction coefficient. At a lower temperature of about 160 degrees, PVC can be transformed into a wall-stick melt with shear flow, which increases the friction characteristics and wall-stick properties of the material. Eliminate the phenomenon of rigid PVC only adding stabilizers and lubricants sliding in the extruder. Without increasing the plasticizing temperature, it can effectively promote plasticization and reduce the melting process.

The presence of processing aids may alter the solubility of other additives in PVC, of ​​which the effect on lubricants is particularly important. Due to the change of melting degree, the migration of some internal lubricants may increase and become external lubrication, which will increase the sliding wall. When this happens, the amount of lubricant should be adjusted appropriately, or the lubricant should be changed. .

ACR processing aid is commonly used for extrusion of plastic door and window profiles. The domestic brands are ACR-401 and ACR-801 with similar performance, and 801 has better effect