ASA resin, also known as AAS resin, is a ternary graft polymer composed of acrylonitrile (A), styrene (S) and acrylate (A). Compared with ABS, Due to the introduction of acrylate rubber without double bonds to replace butadiene rubber, the weather resistance has been substantially improved, about 10 times higher than ABS. Other mechanical properties, processing properties, electrical insulation, chemical resistance and ABS is similar. In addition, ASA has good colorability. Since the resin itself has excellent weather resistance, it can be dyed into various bright colors without fading easily. Products processed with ASA resin do not require surface protection such as spray painting or electroplating. They can be used directly outdoors. After being exposed to sunlight for 9 to 15 months, there will be almost no decrease in impact strength and elongation, and there will be almost no change in color.
Physical and chemical properties
Terpolymer ASA can be produced using a patented reaction process or grafting process. In the reaction method, ASA is produced by attaching an acrylic elastomer to the polymerization process of styrene and acrylonitrile (SAN). The elastomer fine powder is evenly dispersed into and attached to the SAN molecular chain. .
ASA’s outstanding weather resistance comes from acrylic elastomers. For many plastics, embrittlement and yellowing will occur under the combined action of solar radiation, especially radiation at the ultraviolet end of the spectrum, and oxygen in the atmosphere. It takes much longer for ASA parts to undergo this change than for other plastics.
ASA parts have high smoothness even at low temperatures, good chemical stability and heat resistance, and high impact strength. Under the pressure of 1.82MPa, the standard heat distortion temperature of ASA is 180-220°F; the tensile strength is 27.6-48.3MPa; the elongation at break is 25-40%; the flexural modulus is 1516-1723MPa; with Notched Izod impact strength is 9.0 to 11.0 ft. lbs/in.
ASA can withstand the effects of the following substances: saturated hydrocarbons, low aromatic hydrocarbon gasoline and lubricating oils, vegetable oils and animal oils, water, aqueous salt solutions, dilute acids and dilute alkali. However, it is susceptible to concentrated inorganic acids, aromatic hydrocarbons, chlorinated hydrocarbons, and esters. Attack by ethers, ketones and certain alcohols. ASA has better environmental stress fracture resistance than ABS. The flame retardant grade of ASA material is UL94-HB.
1. The influence of the glass transition temperature (Tg) of the rubber phase on the impact strength of ASA. According to the different types of polymerized rubber phases, the homologues of ASA include ABS, AES (ethylene-propylene*** polyrubber as the rubber backbone). Research shows that rubber with low Tg has better impact effect than SAN. The Tg of several rubber phases are as follows: Therefore, under the same rubber content, the order of normal temperature impact strength is ABS>AES>ASA. In terms of low temperature impact resistance , ABS is also the best, AES is second, and ASA is worse.
2. Effect of rubber grafting rate on ASA properties. The toughening mechanism of ASA resin is mainly to absorb impact energy by inducing silver streaks. The key factor affecting the occurrence of silver streaks is the interface between SAN and rubber phases. If the interface bonding force is weak, there will be less silver cracks and only low impact strength can be obtained. This is why ABS made by blending nitrile rubber and SAN is much higher than ABS made by blending styrene-butadiene rubber grafted with SAN and SAN. The impact strength of ABS blended with SAN is much higher. The reason why ABS is produced by direct blending. Because after grafting, the bonding force at the interface between SAN resin and rubber increases, but when the grafting rate exceeds a certain level, the impact strength no longer increases, but has a downward trend. This is because as the grafting rate of the rubber backbone increases, the rubber elasticity may decrease, thereby reducing the effect of rubber caused by entropy change. In addition, as the grafting rate increases, the fluidity of the resin decreases. Therefore, considering the balance between the mechanical properties and processing performance of the ASA resin, the appropriate grafting rate should be controlled. The impact of the type and molecular weight of SAN on the performance of ASA. If the molecular weight of the blended SAN is increased, the impact strength of the ASA resin will be increased and the fluidity will be reduced. If SAN with a high acrylonitrile content is selected for blending, the tensile strength, impact strength, and melt of the resin will decrease. Strength is improved, flowability is reduced, and chemical resistance is improved. Therefore, by changing the type and brand of SAN blended with grafted ASA powder, products with different physical properties can be produced and the brands can be diversified.
3. Effect of rubber content on ASA performance. Generally speaking, when the blended SAN variety is fixed, as the rubber content increases, the tensile strength, flexural strength, heat distortion temperature, and MI decrease, while the impact strength, The tensile elongation at break is increased. Therefore, by adjusting the rubber content, general-purpose and high-impact ASA resins can be prepared.
4. The aging resistance of ASA resin can cause the aging of SAN resin in ASA. The wavelength of light is 250-290nm. This band has less content in sunlight. By adding appropriate ultraviolet absorbers and light stabilization UV-screening agents such as UV-screening agents and carbon black can provide good protection for SAN. For the rubber phase, sunlight with a wavelength less than 700nm has enough energy to photooxidize butadiene, but only light waves with a wavelength less than 300nm can photooxidize acrylate. Ultraviolet absorbers are selective in the absorption of light waves, and generally can effectively absorb light waves of 270 to 400nm. Therefore, for ABS, only the addition of barrier agents such as carbon black and titanium dioxide can significantly protect the resin. The protective effect of ultraviolet absorbers is limited. For ASA, adding an appropriate amount of light stabilizer, ultraviolet absorber, and pigment can play a very good protective role. Mixed modification of ASA resin ASA resin has excellent weather resistance, good processing performance, chemical resistance, and balanced mechanical properties. However, general ASA resin also has shortcomings such as low heat distortion temperature and poor cold resistance, which limits the 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 The heat distortion temperature of general-purpose ASA resin is similar to that of general-purpose ABS, about 80 to 85°C (1.82MPa, 6.4mm, not annealed). Generally speaking, HDT can be improved by blending SAN with high acrylonitrile content and high molecular weight and reducing the amount of acrylic rubber, but the improvement is not significant. Heat-resistant ASA resin can be prepared by introducing monomers with large steric hindrance and high rigidity. The industrialized methods mainly include the following: 1) Substituting all or part of the styrene monomer with α-methylstyrene*** Polymerization can prepare heat-resistant ASA resin. However, the HDT improvement of ASA resin prepared by this method is limited. Since the Tg of α-SMAN is 140-150°C, the maximum heat distortion temperature can be increased to 110-115°C, but the fluidity decreases, the color turns yellow, the gloss becomes worse, and the product becomes brittle. 2) Using SMA as a heat-resistant component mixed with ASA, heat-resistant ASA can be prepared, but the increase in heat-resistant temperature is limited. 3) The introduction of N-phenylmaleimide (NPMI) monomer polymerization not only maintains the planar five-membered ring structure, but also increases the polarity and steric hindrance of the side chain, which can give the ASA resin higher Thermal distortion temperature and thermal stability. For example, if NPMI is polymerized with PS, the Tg of the polymer can be as high as 195°C. Then blending the polymer with ASA can give ASA a higher HDT. According to different blending ratios of polymers, ASA resins of different heat resistance levels can be prepared, and even extremely heat-resistant ASA resins with HDTs as high as 120°C can be developed. This method is currently the best way to improve the heat resistance of ASA resins. One of the good ways. Currently, Kumho Rili has developed a series of commercialized heat-resistant ASA grades using the NPMI method. 4) Mix PC and ASA to prepare ASA/PC alloy. Heat-resistant ASA can also be prepared. ASA/AES*** mixed gold Since the rubber phase Tg of ASA is -45°C, the low-temperature impact strength of ASA resin is not high. Mixing ASA and AES** not only maintains the weather resistance of the resin, but also improves the resin's durability. Cold resistance, suitable for low temperature applications. ASA/PC alloy ASA resin has certain compatibility with PC. Mixing ASA with PC can greatly improve the impact strength and heat distortion temperature of ASA. At the same time, it maintains the excellent weather resistance and glossiness of the resin. Application Used in automobiles, commercial machinery and equipment, and consumer electronics. Adding a compatibilizer to improve the interface between ASA resin and PC resin is beneficial to improving alloy performance. The performance characteristics of ASA/PC alloy are mainly reflected in the following aspects: 1) Mechanical properties: bending strength, bending strength of ASA/PC alloy The modulus and tensile strength are equivalent to PC, and the thin-wall impact strength is higher than ASA and equivalent to PC.
It is better than PC in terms of stress cracking, low-temperature impact, and notch sensitivity of thick products. It shows a good synergistic effect in terms of impact strength and is especially suitable for making structural products. The high mechanical strength is also conducive to the thin-wall design of the product and makes the product lightweight. 2) Temperature resistance: The heat deformation temperature of ASA/PC alloy is between ASA and PC, showing a certain linear relationship. 3) Rheological properties and processing properties: ASA/PC alloy has a higher melt index than PC and can form large thin-walled parts. Increasing temperature and pressure can increase the MI of ASA/PC. Increasing temperature is more effective than increasing pressure. 4) Weather resistance: The weather resistance of ASA/PC is better than that of ABS/PC. It can be directly applied to outdoor products without painting. It can also be used for indoor products. Good weather resistance means long-term use and can keep colored products as bright as ever. color. By selecting appropriate flame retardants, flame retardant and weather-resistant ASA/PC resin can be produced. ASA/PBT alloy ASA is incompatible with PBT. Appropriate compatibilizers must be added to prepare ASA/PBT alloys with good properties. Generally, ASA homologues with certain compatibility with PBT are selected as compatibilizers, such as PMMA. , MBS, SMA, etc. Mixing ASA with PBT can greatly improve the processing fluidity of ASA, further improve the chemical resistance and scratch resistance of ASA resin, and at the same time improve the dimensional stability of PBT, excellent weather resistance, and high impact strength, which is particularly suitable for Produces large-scale thin-walled products, such as car bumpers, anti-scratch strips, commercial machine casings, laptop computer casings, etc.
Injection molding process
ASA injection molding reference process
Project unit ASA801 ASA7045
Drying temperature ℃ 75~85 85~95
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Drying time h 3~4 3~4
Injection molding temperature nozzle ℃ 200~220 220~240
One period ℃ 200~230 220~250
Second stage ℃ 200~230 220~250
Third stage ℃ 180~210 200~230
Mold temperature ℃ 40~80 60~90
Injection molding pressure, first-level pressure MPa 80~120 80~120
Second-level pressure MPa 60~90 60~90
Third-level pressure MPa 40~60 40~60
Back pressure MPa 1~4 1~5
Secondary processing
ASA resin can be processed by most traditional methods. These methods include profile and sheet extrusion and plastic extrusion, injection molding, structural foam molding and extrusion blow molding. Extruded sheet can be thermoformed.
Blow molding should be carried out in a grooved extruder with a cooling and thermally insulated charging section. The screw should have slightly deeper threads to reduce frictional heat. Using an extruder with an accumulator works best.
The ASA resin slices must be pre-dried. Before processing, pre-dry the slices in a circulating air oven at 185°F for 4 to 6 hours. ASA components can be welded using thermal spin welding techniques; in some cases, ultrasonic welding is also possible. ASA parts can also be solvent welded with 2-butanone, diethylene chloride or cyclohexane. Parts readily accept and remain printed and painted without surface preparation. It is also possible to perform vacuum metal plating using traditional methods.
Applications
ASA’s outstanding weather resistance makes it very useful in the following areas: construction, sinks, drain pipes and fittings, signs, mailboxes, lightweight household protection Wall panels, flower pots, shutter frame decoration.
Leisure and entertainment: outdoor furniture, weather deflectors, swimming pool pump and filter housings, spas, pool steps and boats.
Automotive and Transportation: Outside mirror housings, brackets. Bumper cover and decoration.
Frequently Asked Questions
Flash, bubbles, sink marks, weld marks, burnt and black lines, silver threads and markings, surface scratches, surface fog and patterns, Burnt discoloration and impurities, burnt black, poor gloss, cracks and whitening, uneven color, brittleness, delamination, warping, poor demoulding, severe mold corrosion.