Basic Properties And Molding of ABS Resins

ABS resins are ternary copolymers consisting of acrylonitrile (A), butadiene (B), styrene (S), and modified resins, and are called ABS plastics. The plastic made from ABS resin is called ABS plastic, ABS has the rigidity, drug resistance and heat resistance of polyacrylonitrile, the molding performance and appearance of Polystyrene, and the impact resistance and cold resistance of polybutadiene.ABS is a light-yellow granular or powder opaque resin, non-toxic, odorless, lightweight, with a density of 1.04-1.07g/cm3, excellent impact resistance, good low temperature performance and chemical resistance, dimensional stability, good low temperature performance and chemical resistance, good dimensional stability. It has excellent impact resistance, good low temperature performance and chemical resistance, good dimensional stability, good surface gloss, easy to paint and coloring. Disadvantages are combustible, low heat distortion temperature, poor weather resistance.

1. ABS resin classification and typical performance

ABS composition and structure can be designed according to the performance requirements in a wide range of its classification is shown in Table 1-1, Table 1-2 lists the typical performance of different grades of ABS resin.

Classification of ABS resin

Typical Properties of ABS Resins

2. Mechanical properties

Different levels of ABS tensile strength varies greatly, generally 33 ~ 52MPa. ABS resin has excellent impact strength, high impact ABS resin at room temperature cantilever beam impact strength of up to 400J / m or so, even at -40 ℃ low temperature, the value is greater than 120J / m. ABS resin is a non-homogeneous system, two-phase structure, resin is a continuous phase, rubber is a dispersed phase. The resin is a continuous phase and the rubber is a dispersed phase. Rubber particles dispersed in the resin, rubber particles to absorb the external impact energy and inhibit the cracking of the product, so that ABS has excellent impact properties.ABS resin impact properties and the rubber content in the resin, grafting rate and particle size and other factors. With the increase of rubber content, the impact strength of ABS resin increases rapidly, but the rubber content can not be too large, otherwise other mechanical properties, such as tensile strength, modulus of elasticity, etc. is significantly reduced. Usually ABS resin in the rubber mass fraction of 25% to 40% is appropriate.

ABS has excellent creep resistance, ABS pipe specimens at room temperature creep test results show that, when subjected to 7.2MPa load, even after up to two and a half years, there is no significant change in size.

ABS resin wear resistance is good, although can not be used as self-lubricating materials, but because of good dimensional stability, it can be used as a medium load bearing.

3. Electrical properties

ABS resin has good electrical insulation properties in a wide frequency range, and is rarely affected by temperature or humidity.The electrical properties of ABS resin are shown in Table 1-3.

Electrical properties of ABS resin

4. Thermal properties

The heat distortion temperature of ABS resin is about 93°C at a load of 1.82MPa, which can be increased by 6-10°C with annealing treatment during processing. Due to the amorphous structure characteristics of ABS resin, it has a smooth stress-temperature effect, so when the load is reduced from 1.82MPa to 0.45MPa, its heat distortion temperature increases only 4 ~ 8 ℃. Heat-resistant ABS resin heat distortion temperature up to 115 ° C. ABS resin embrittlement temperature of -7 ° C, usually in -40 ° C still have considerable strength. ABS resin grades of linear expansion coefficient from 6.4 × 10-5 / ℃ to 11.0 × 10-5 / ℃, in the thermoplastics is a smaller coefficient of linear expansion. the thermal stability of ABS resin in engineering plastics is low, at 260 ℃ that is, the decomposition of toxic volatile substances. the ABS resin is flammable, no self-extinguishing.

5. Chemical properties

ABS resin has good chemical resistance, due to the existence of nitrile group in its molecular structure, it is almost unaffected by dilute acids, alkalis and salts, but it can dissolve in ketones, aldehydes, esters and chlorinated hydrocarbons; it is insoluble in most of the alcohols, such as ethanol, but in methanol, it is softened after a few hours; it is insoluble in hydrocarbon solvents but it will dissolve in prolonged contact with the hydrocarbon solvents. Like most plastics, ABS resin under stress, its surface by acetic acid, vegetable oil and other chemical reagents will produce stress cracking. Table 1-4 shows the quality and appearance changes of ABS resin in some chemicals after long-term impregnation.

Modified ABS resin

Although ABS resin has many excellent properties, but as an engineering plastic, there are shortcomings, such as strength and heat distortion temperature is not high enough, weather resistance is poor, does not have self-extinguishing, opaque and so on. Therefore, there are many modified varieties, such as reinforced ABS, flame retardant ABS, transparent ABS, ASA resin, ACS resin, MBS resin and so on.

1. Enhanced ABS

ABS can be 20% to 40% (mass fraction) of glass fiber reinforced, Table 2-1 lists the properties of glass fiber reinforced ABS. Reinforced ABS tensile strength, flexural strength, flexural modulus has increased substantially, the heat distortion temperature increased significantly, the coefficient of linear expansion is reduced, the dimensional stability and precision has been greatly improved, but the impact strength with the increase in the content of glass fibers and reduce.

2. Flame retardant ABS

ABS is a flammable material, low molecular organic flame retardant and flame retardant synergist can be added to ordinary ABS to produce flame retardant ABS, flame retardant ABS is mainly used in the manufacture of electronic appliances requiring flame retardant and good mechanical strength, such as TV housings, radomes etc.

3. Transparent ABS

ABS resin is an opaque resin, if acrylonitrile, butadiene, styrene three components and then add methyl methacrylate, through the graft copolymerization reaction can be produced transparent ABS resin. Transparent ABS has high transparency, good solvent resistance and high impact strength.

4. ASA resin

ASA resin is a terpolymer produced by grafting acrylonitrile and styrene onto acrylic acetate rubber, also known as AAS resin.ASA resin has superior weather resistance, excellent impact resistance, thermal stability and chemical resistance. Table 2-2 lists the properties of BASF ASA resins, which are used in the manufacture of automobile bodywork, ignitions, fuel tanks, radiator grills, mirror covers, switchboards, and taillight covers.

5. ACS Resin

ACS resins are terpolymers produced by the graft polymerization of acrylonitrile and styrene on hydrogenated Polyethylene.ACS resins have excellent weathering resistance and are flame retardant.

6. MBS Resin

MBS resin is a graft copolymer of methyl methacrylate, butadiene and styrene. As the monomer acrylonitrile is replaced by methyl methacrylate, transparent material is obtained, and the light transmittance is up to 90%; at the same time, it has good impact strength and cold resistance; it still has good toughness at the low temperature of -40℃; it has good resistance to inorganic acids, alkalis, salt solutions and oils and fats, but it is not resistant to ketones, aromatic hydrocarbons, aliphatic hydrocarbons and chlorinated hydrocarbons.

The molding process of ABS plastic

1. Processing characteristics

(1) Flow characteristics

ABS melt flow rate (MFR) is generally 0.02 ~ 1g / min (200 ℃, 5kg), individual MFR exceeds this range. the larger the MFR, the better the fluidity. Generally, ABS with MFR less than 0.1g/min is suitable for extrusion molding, and ABS with MFR more than 0.1g/min is suitable for injection molding.

ABS melt is a pseudoplastic fluid, showing the rheological property of "shear thinning", and the melt viscosity can be changed by adjusting the shear rate. However, for the process, if the viscosity of the plastic melt is available in a wide range of shear rate, it should be selected in the viscosity of the shear rate is less sensitive to the shear rate of the shear rate of the operation, because at this time the fluctuation of the shear rate will not cause significant differences in the quality of the products, so that product quality and uniformity of the product is guaranteed.

ABS resin melt viscosity is moderate, its fluidity is slightly worse than polyamide, better than polycarbonate, melt cooling curing speed is faster.

(2) Thermophysical properties

ABS resin is an amorphous polymer, no obvious melting point, glass transition temperature Tg is generally around 115 ℃, so the molding temperature should be greater than 115 ℃. ABS thermal stability is poor, heat to 260 ℃ or more began to decompose, producing toxic volatile substances, usually ABS molding temperature control at 250 ℃ or less. For injection molding, the processing temperature is generally 160 to 230 ℃; for extrusion molding, the processing temperature is generally 160 to 195 ℃; for blow molding, the processing temperature is generally 200 to 240 ℃; for vacuum molding, the processing temperature is generally 140 to 180 ℃. The size of the range between the viscous fluid temperature and the decomposition temperature of plastics is very important for molding, which determines the difficulty of molding and the range of molding temperatures that can be selected. The smaller the temperature range and the higher the temperature, the more difficult the molding is. ABS has a lower melt temperature, generally 160 to 190°C, and a wider range of temperatures, making it easier to process. Thermal stability is not only related to the processing temperature, but also to the residence time at the processing temperature. The higher the processing temperature, the shorter the residence time should be in order to keep the plastic from reacting chemically. In order to improve the thermal stability of plastics, heat stabilizers are often added to plastics so as to make the processing temperature range wider and prolong the permissible residence time. the thermal stability of ABS is poor, so the residence time should be minimized, and the barrel should be cleaned after processing.

(3) Drying characteristics

Since ABS resin contains strong polar groups such as cyano groups, it has a high water absorption. Its water absorption is greater than that of polystyrene and second only to polyamide, and the moisture absorption of ABS is less than 1%, generally 0.3% to 0.8%. Regardless of the molding method, ABS resin should be pre-dried before processing. According to the amount of water content, in the molding should be dried at about 80 ℃ for 2 ~ 4h, so that its water content to 0.1% or less. The commonly used drying method is circulating air drying, temperature control at 70 ~ 80 ℃, time for more than 4h; can also be used ordinary oven drying, temperature control at 80 ~ 100 ℃, time for 2h, the thickness of the particle layer is less than 50mm.

2. Injection molding

ABS resin injection molding usually adopts screw injection machine. The type of screw should be single-ended, isometric, gradual, fully threaded, with a check ring, screw L/D ratio of 20, compression ratio of 2.0 to 2.5. The nozzle can be open or extended to avoid the use of self-locking nozzles, so as not to reduce the injection process or cause material discoloration.

ABS resin injection temperature in addition to heat-resistant grade, plating grade and other grades require a little higher, in order to improve its melt molding or plating performance, for general-purpose grade, high impact resistance level should be lower, in order to prevent decomposition or mechanical properties to bring about adverse effects.

ABS resin injection pressure for thin-walled, long flow, small gate products or heat-resistant, flame retardant grade, require higher; for thick-walled, large gate products can be lower. In addition, in order to obtain the products with less internal stress, the holding pressure should not be too high.

ABS injection molding temperature for: general-purpose 200 ~ 260 ℃, heat-resistant 220 ~ 270 ℃, flame retardant 190 ~ 240 ℃. Mold temperature is generally 50 ℃, in order to improve the appearance of products, to avoid the mold line and pit and other undesirable phenomena, reduce product deformation, the mold temperature can be increased to 70 ℃.

3. Extrusion molding

ABS resin can be extruded by a general-purpose single-screw extruder with an L/D ratio of 18-20 and a compression ratio of 2.5-3.0, either with a gradual-change compression screw or with a sudden-change compression screw. Compression gradient screw or compression mutation screw are suitable. ABS resin melt viscosity is moderate, easy to flow, so the screw does not need to be cooled. Extrusion molding can be used to produce profiles such as ABS tubes, rods, and sheets.