Introduction to ACR
I. Introduction to ACR
ACR is an abbreviation of acrylic acids (Acrylics), and is also a general term for acrylate series modifiers, which are polymer copolymers of acrylates.
ACR resin is a thermoplastic graft polymer obtained by the polymerization of methyl methacrylate and acrylate monomer by emulsion, and a plastic additive with the dual functions of impact modification and process modification. Mainly used in hard, semi-hard polyvinyl chloride (PVC) products, especially chemical building materials, such as profiles, pipe fittings, plates, foam materials (pipes, plates), wood plastics and so on. It can not only improve the impact resistance of the product, but also can significantly improve the melt flow, thermal deformation, weather resistance and gloss of the product surface of the resin to show excellent comprehensive properties. It can be divided into two categories: processing modifiers and impact modifiers: the additives used to improve the impact performance of plastics are called impact modifiers, which have a core-shell structure; the process type ACR is mainly aimed at improving the processability of PVC.
Second, the application of ACR in PVC processing
(1) Promote the melting of PVC
PVC, which is generally used for the production of suspension polymerization and bulk polymerization, has a particle diameter of about 100 microns, and the size of the primary particles in the particles is about 1 micron. In order to process into a useful melting state, it is necessary to heat and increase the shear force to disperse the PVC particles into primary particles, and to form a melt through the mutual diffusion of the primary particle boundary between molecules, but the transfer of heat and shear force by the granular PVC is not good, so that the formed melt is uneven, and some parts have been completely melted, while the other part may also remain in the particle state. ACR processing additives promote PVC melting by increasing the transfer of heat and shear force, because the processing auxiliaries and PVC have mixing and high molecular weight, and their particles increase friction in the PVC system, accelerate the melting process, and make the melt more uniform, so that the molded products and other defects are reduced, the surface state and appearance are improved, and the physical and mechanical properties of PVC products are improved.
(2) Improve melt rheology
The PVC melting system is a viscoelastic fluid that is both viscous and blocks the flow of the melt, and is elastic, tending to return to the initial state after deformation. Both of these properties rely heavily on the tangled state of the POLYMER molecules of the PVC system ACR processing additive molecules inserted into the molecular chains, playing a tangling and crosslinking role. Thus the viscosity and elasticity of the PVC melt can be significantly increased.
(3) Improve lubrication performance
Many polymers, because of their own chemical properties, are easily bonded to hot metal surfaces during processing, and the addition of lubricants can reduce or avoid such problems. There are already many conventional lubricants that can be used. However, ACR can not only promote PVC processing modification, but also has the effect of promoting external lubrication, the use of lubricating ACR has no impact on the transparency of PVC, and will not produce migration after processing. In addition, the impact on pvc meltability does not exceed the impact of conventional lubricants.
(4) Impact resistance
ACR impact modifier is a kernel-shell structure copolymer formed by the multilayer copolymerization of methyl methyl ester (MMA) and some crosslinked monomers of low alkyl acrylate. Its core is a mildly crosslinked acrylate rubber component, which plays the role of stress concentration point in PVC products, and by inducing a large number of silver streaks to form, the shear belt absorbs the impact energy, thereby improving the impact strength; its shell is a plastic component with PMMA as the main body grafted on the rubber core, which has good compatibility with PVC resin, which can promote the uniform dispersion of the modifier in the base resin, and improve the adhesion of rubber particles to PVC resin. The outstanding feature of the core-shell structure is that the size of the rubber particles has been determined at the time of preparation, and is fixed in a certain position in the processing, and maintains its shape, the impact resistance effect is very prominent, compared with other types of impact modifiers, ACR impact modifiers have the following application characteristics:
1、Easy to disperse, strong processing adaptability;
2、High impact resistance efficiency, does not reduce the VICAT temperature of the product;
3、Does not contain saturated and double bond groups, excellent weather resistance, suitable for outdoor applications such as door and window profiles, pipes and other outdoor applications;
4、It also has a certain processing modification effect to improve the processing performance of products.