Also known as AAS resin, it is a ternary graft copolymer composed of acrylonitrile (A), styrene (S) and acrylate (A). Compared with ABS, due to introduction of double bond-free acrylate rubber instead of butadiene rubber, weather resistance has been substantially improved, which is about 10 times higher than ABS. Other mechanical properties, processing properties, electrical insulation, and chemical resistance are similar to those of ABS.
In addition, ASA has good colorability, because resin itself is excellent in weather resistance, it can be dyed into various bright colors and is not easy to fade. Products processed with ASA resin do not require surface protection such as spray painting, electroplating, etc., can be used directly outdoors. When exposed to sunlight for 9 to 15 months, impact strength and elongation are almost unchanged, color is almost unchanged.
What are factors that affect performance of ASA?

Depending on type of rubber phase copolymerized, homologues of ASA include ABS and AES (ethylene-propylene copolymer rubber as rubber backbone). Studies have shown that low-Tg rubber has a better impact effect than SAN. Tg of several rubber phases is as follows: Under same rubber content, order of impact strength at room temperature is ABS>AES>ASA, in terms of low-temperature impact resistance , ABS is best, AES is second, and ASA is worse.

Toughening mechanism of ASA resin is mainly to absorb impact energy by inducing crazing. Key factor affecting generation of crazing is interface bonding force between SAN and rubber. Interface bonding force is weak, there will be less crazing and only low impact strength can be obtained. Compared with ABS made by blending nitrile rubber with SAN and ABS made by blending SAN grafted styrene butadiene rubber with SAN, impact strength of ABS grafted with SAN is much higher than that of ABS prepared by direct blending. This is reason.
After grafting, adhesion between SAN resin and rubber increases, but grafting rate exceeds a certain level, impact strength does not increase anymore. Instead, there is a downward trend. This is because as grafting rate of rubber trunk increases, rubber elasticity may decrease, and effect of entropy change of rubber is reduced. In addition, grafting rate increases and resin fluidity decreases. Therefore, considering balance between mechanical properties and processing properties of ASA resin, appropriate grafting rate should be controlled.
Influence of type and molecular weight of SAN on performance of ASA
Increase molecular weight of blended SAN, impact strength of ASA resin will increase, fluidity will decrease; choice of SAN blending with high acrylonitrile content will increase tensile strength, impact strength, melt strength of resin, decrease fluidity, and improve chemical resistance. Therefore, changing type and brand of SAN blended with grafted ASA powder can produce products with different physical properties and diversify brand.

Generally speaking, when blended SAN varieties are fixed, rubber content is increased, tensile strength, bending strength, heat distortion temperature, and MI decrease, while impact strength and tensile elongation at break increase. Therefore, by adjusting rubber content, general-purpose and high-impact ASA resins can be prepared.

Wavelength of light that can make SAN resin phase aging in ASA is 250-290nm, which is less in sunlight. By adding suitable ultraviolet absorbers, light stabilizers, carbon black and other ultraviolet shielding agents, it can play a role in SAN. Very good protection. For rubber phase, light waves with a wavelength of less than 700nm in sunlight have sufficient energy to photo-oxidize butadiene, but only light waves less than 300nm have a photo-oxidation effect on acrylate. Ultraviolet absorbers are selective in absorption of light waves, and generally can effectively absorb light waves from 270 to 400 nm.
Therefore, for ABS, only addition of carbon black, titanium dioxide and other shielding agents can play an obvious protective effect on resin, protective effect of UV absorbers is limited. For ASA, adding an appropriate amount of light stabilizers, ultraviolet absorbers, and pigments can play a good protective role.
Blending modification of ASA resin
ASA resin has excellent weather resistance, good processing properties, chemical resistance, and balanced mechanical properties. However, general-purpose ASA resins also have shortcomings such as low heat distortion temperature and poor cold resistance, which limit application of ASA in certain fields. Therefore, it is necessary to blend and modify ASA to expand its application fields.

 

ASA resin heat-resistant modification
Heat distortion temperature of general ASA resin is similar to general ABS, about 80～85℃(1.82MPa, 6.4mm, unannealed). Generally speaking, use of SAN blending with high acrylonitrile content and high molecular weight, reducing acrylate rubber can increase HDT, but increase is not large. Heat-resistant ASA resin can be prepared by introducing monomers with large steric hindrance and high rigidity. Industrialized methods mainly include following:
1) Using α-methylstyrene to replace all or part of styrene monomer copolymerization, heat-resistant ASA resin can be prepared. However, HDT of ASA resin prepared by this method can be improved to a limited extent. Since Tg of α-SMAN is 140-150℃, maximum heat distortion temperature can be increased to 110-115℃, but fluidity decreases, color becomes yellow, gloss becomes poor, and product becomes brittle.
2) Using SMA as a heat-resistant component to blend with ASA, heat-resistant ASA can be prepared, but heat-resistant temperature increase is also limited.
3) Introduction of N-phenylmaleimide (NPMI) monomer copolymerization not only maintains planar five-membered ring structure, but also increases polarity and steric hindrance of side chain, which can give ASA resin a higher heat distortion temperature and thermal stability. If NPMI is copolymerized with PS, Tg of copolymer can be as high as 195℃, then blending copolymer with ASA can give ASA a higher HDT. According to different blending ratios of copolymers, ASA resins of different heat resistance grades can be prepared, even extremely super heat-resistant ASA resins with HDT up to 120℃ or higher can be developed. This method is currently one of the best ways to improve heat resistance of ASA resins. At present, Kumho Sunny has developed a series of commercial heat-resistant ASA grades using NPMI method.
4) Blend PC and ASA to prepare ASA/PC alloy, or heat-resistant ASA. As rubber phase Tg of ASA is -45℃, low temperature impact strength of ASA resin is not high. Blending ASA with AES not only maintains weather resistance of resin, but also improves cold resistance of resin, which can meet requirements of low temperature use.

ASA resin has a certain compatibility with PC. Blending ASA with PC can greatly improve impact strength and heat distortion temperature of ASA. At the same time, it maintains excellent weather resistance and gloss of resin. It is used in automobiles, business machines and equipment, and consumer electronics. Adding a compatibilizer can improve combination of ASA resin and PC resin interface, which is conducive to improving performance of alloy. Performance characteristics of ASA/PC alloy are mainly manifested in following aspects:
1) Mechanical properties: Flexural strength, flexural modulus, and tensile strength of ASA/PC alloy are equivalent to those of PC, thin-wall impact strength is higher than that of ASA and equivalent to PC. It is superior to PC in terms of stress cracking, low-temperature impact and notch sensitivity of thick products, and shows good synergistic effects in impact resistance, which is especially suitable for making structural products. High mechanical strength is also conducive to thin-walled design of product, which makes product lighter.
2) Temperature resistance: Heat distortion temperature of ASA/PC alloy is between ASA and PC, showing a certain linear relationship.
3) Rheological properties and processing properties: Melt index of ASA/PC alloy is higher than that of PC, and large thin-walled parts can be formed. Increasing temperature and pressure can increase MI of ASA/PC, heating up is more effective than increasing pressure.
4) Weather resistance: Weather resistance of ASA/PC is better than that of ABS/PC. It can be directly applied to outdoor products without coating. It can be used in indoor products. Good weather resistance means long-term use and can maintain vivid color of colored products as before. Choose suitable flame retardants to produce flame-retardant and weather-resistant ASA/PC resins.

ASA and PBT are incompatible, and suitable compatibilizers must be added to prepare ASA/PBT alloys with good properties. Generally, ASA homologues with certain compatibility with PBT are used as compatibilizers, such as PMMA, MBS, SMA, etc. Blending of ASA and PBT can greatly improve processing fluidity of ASA, further improve chemical resistance and scratch resistance of ASA resin, and at the same time improve dimensional stability of PBT, excellent weather resistance, high impact strength, especially suitable for production of large thin-walled products, such as car bumpers, anti-scratch strips, commercial machine casings, laptop casings, etc.