Application technology of ACR and MSB impact modifier

PVC is one of the general-purpose plastics with a wide range of applications and large output. Rigid PVC products have the advantages of high hardness, rigidity and strength, excellent chemical corrosion resistance and aging resistance, wear resistance and flame retardant, etc., can be widely used as building materials to replace traditional steel and wood, and it is easy to process and low price. With the continuous development of the use of rigid PVC products and the continuous increase of the proportion, the consumption of rigid PVC products in developed countries in the world has greatly exceeded the soft products. From the end of the 20th century to the present, the proportion of rigid PVC products in the total amount of PVC has been an important sign to measure the development level of a country's plastic processing technology. In recent years, energy saving and consumption reduction has become the main development trend of hard PVC products, so the development and application of hard PVC products such energy-saving materials not only has good economic benefits, but also in the case of energy shortage and wood shortage in China, vigorously develop hard PVC products has important social benefits. Since the 1970s, hard PVC products have been used to manufacture pipes, plastic doors and Windows, building materials, decorative materials, etc., widely used in construction, chemical industry, machinery, electronics, light industry, agriculture and other fields.

However, ordinary rigid PVC products are brittle materials, and their impact resistance is poor, and the notched impact strength of the simple supported beam is only 2.5kJ/m at 23℃. Therefore, it is often necessary to add impact modifiers in processing applications to improve impact resistance without significantly reducing PVC tensile, thermal deformation and other properties. Impact modifiers for PVC mainly include ethylene-propylene rubber (EPDM), nitrile butadiene rubber (NBR), ethylene-vinyl acetate copolymer (EVA), chlorinated polyethylene (CPE), acrylate copolymer (ACR), methyl methacrylate - butadiene - styrene copolymer (MBS) and ABS. At present, the commonly used impact modifiers are CPE, EVA, ACR and MBS.

Among the above 4 kinds of PVC impact modifiers, ACR is the best impact modifier with good overall performance, good processing performance of modified PVC, high tensile strength, modulus, thermal deformation temperature, and excellent weather resistance. In addition to poor weather resistance, MBS is also a PVC impact modifier with good overall performance, especially MBS has a refractive index similar to PVC, and is the only impact modifier used for the processing of transparent impact modified PVC products.

ACR and MBS impact modifiers are generally core-shell structural composite polymers with cross-linked rubber as the core and polymer with high glass transition temperature (Tg) and good compatibility with PVC as the shell. The core layer rubber is the part that really plays the impact modification. The shell layer polymer is grafted with the core layer polymer to provide coating effect on the nuclear layer. Improve the dispersion of impact modifier in PVC and its compatibility with PVC. ACR impact modifiers generally take cross-linked acrylate rubber as the core and polymethyl methacrylate, etc. The higher polymer is the shell. MBS generally takes styrene-butadiene rubber as the core and methyl methacrylate - styrene copolymer as the shell layer.

The United States Rohm-Hass company has been developing ACR impact modifiers since the 1950s, and launched the first commercial products. Subsequently, France's Alto company, Germany's BASF and Huls Company, Japan's Jabuchi and Kwuha Chemical Company have also joined the research and development of ACR impact modifiers, thus promoting the rapid development of ACR impact modifiers.

MBS impact modifier research began in the late 1950s, the United States Borg-Warner and Rohm-Hass company first began the development of MBS resin, and in 1960 obtained the preparation of PVC impact modifier MBS patent. At present, Japan's MBS production technology is in a leading position in the world, among which the two companies with the largest output and the most advanced technology are Jongyuan and Kurea.

The development and application of ACR impact modifier in China began in the early 1980s, and the synthesis and application research have been carried out by Beijing Research Institute of Chemical Industry, Shanxi Research Institute of Chemical Industry, Hebei University of Technology, Qilu Research Institute of Chemical Industry, Zhejiang University and other units. However, compared with foreign ACR impact modifier products, there is still a certain gap in the toughening modification effect, and the production of ACR impact modifier is also limited to a few plastic varieties such as PVC.

Foreign technology developed countries in the processing of PVC hard products and a small number of other plastic types are more widely used
ACR and MBS are impact resistant modifiers. Japan mainly consumes MBS resin in PVC processing, and the consumption proportion of the resin accounts for 40% to 50% of the impact modifier. Europe mainly uses ACR impact modifiers, products mainly include profiles, pipes and profiles, and the amount of MBS impact modifiers is also large, especially in Western Europe's packaging industry, PVC sheet and film products, the demand for MBS is strong. The United States is a major producer of ACR and MBS in the world, as well as a major consumer of applications, occupying an important position. From the perspective of the global development trend of PVC impact modifiers, due to the increasing volume of PVC processing, the consumption of anti-impact modifiers also tends to increase. At present, China takes CPE as the main impact modifier, but this is a temporary situation, according to the international development situation analysis, the consumption of varieties with poor quality and relatively low efficiency will gradually decrease, while the amount of high-efficiency ACR and MBS will gradually increase, and the domestic impact modifier will appear CPE, ACR and MBS in the future. It is expected that by 2005 and 2010, the amount of domestic PVC hard products will reach 4 million tons and 6 million tons respectively, and the corresponding impact modifier demand is 80,000 to 110,000 tons and 130,000 to 150,000 tons, so actively develop high-performance ACR, MBS impact modifier is promising.

The preparation of ACR and MBS impact modifiers mainly involves the synthesis of rubber nuclear particles and shell polymers, which are mainly synthesized by emulsion polymerization. The rubber nuclear particles are mainly synthesized by intermittent, semi-continuous or seed emulsion polymerization, and the latter is synthesized by core-shell emulsion polymerization using kernel latex particles as seeds. For MBS, in order to obtain rubber particles with larger particle size, some companies also use the method of condensation of small particle size rubber particles to form large particle size particles, and then polymerization to cover the shell polymer. ACR and MBS latex particles obtained by emulsion polymerization were condensed, dried, or sprayed directly to get ACR and MBS impact modifier powder.