General grade polystyrene is a thermoplastic resin, which is a shiny, transparent bead or granular solid. The density is 1.04 to 1.09, the transparency is 88% to 92%, and the refractive index is 1.59 to 1.60. Under the action of stress, birefringence occurs, which is the so-called stress-optical effect. The melting temperature of the product is 150 ～ 180 ℃, thermal decomposition temperature is 300 ℃, thermal deformation temperature is 70 ～ 100 ℃, and long-term use temperature is 60 ～ 80 ℃. At a temperature lower than the thermal deformation temperature by 5 to 6 ° C, after annealing treatment, the stress can be eliminated and the thermal deformation temperature can be increased. If a little α-methylstyrene is added in the production process, the heat resistance level of general polystyrene can be improved.
It is soluble in aromatic hydrocarbons, chlorinated hydrocarbons, aliphatic ketones and esters, but can only swell in acetone. Resistant to the action of certain mineral oils, organic acids, alkalis, salts, lower alcohols and their aqueous solutions. Low water absorption, can still maintain its mechanical properties and dimensional stability in humid environments. Optical performance is second only to acrylic resin. It has excellent electrical properties, high volume resistivity and surface resistivity, and is not affected by changes in temperature and humidity, or by corona discharge. Radiation resistance is also good. Its main disadvantages are brittleness and fragility, low impact strength, poor heat resistance, resistance to boiling water, and use at lower temperatures and loads. Poor sunlight resistance and flammable. It emits black smoke when burning and has a special odor.
General-purpose polystyrene is prepared by radical polymerization or ionic polymerization using styrene as a monomer. Production methods include bulk polymerization, solution polymerization, suspension polymerization, and emulsion polymerization. The main methods used in industrial production today are suspension polymerization and bulk polymerization.
1. The bulk polymerization method sends the styrene monomer into the prepolymerization kettle, and then adds a small amount of additives and initiators, and heats and stirs at 95 to 115 ° C for prepolymerization. After the conversion rate reaches 20% to 35%, it is sent to the Continuous polymerization was carried out in a tower reactor with a stirrer. The polymerization temperature was increased to about 170 ℃ step by step to achieve complete conversion. A small amount of unreacted styrene is discharged from the top of the tower and can be recovered and reused. The polymer is continuously discharged from the bottom of the tower and extruded and granulated to obtain the finished product. The process is as follows.
2.The suspension polymerization method uses styrene as the monomer and water as the medium, and uses gelatin or starch, polyvinyl alcohol, hydroxyethyl cellulose and other protective gels or insoluble inorganic salts such as magnesium carbonate, magnesium silicate, and calcium phosphate as the dispersion. Agent, maleic anhydride-styrene copolymer sodium salt as co-dispersant, benzoyl peroxide as initiator, polymerization was initiated at about 85 ℃. It is also possible to carry out high-temperature polymerization in an autoclave at a high temperature above 100 ° C without using an initiator. The polymer was washed, separated, and dried to obtain colorless and transparent fine-beaded resin.
Polystyrene has good fluidity, good processability, easy coloring, and good dimensional stability. It can be processed into various parts by injection molding, extrusion, blow molding, foaming, thermoforming, bonding, coating, welding, machining, printing and other methods, and is especially suitable for injection molding.
Materials for injection molding can generally be used without drying. However, in order to improve the product quality, it can be pre-dried in a blast oven at 55 ～ 70 ℃ for 1 ～ 2h. The specific processing conditions are roughly: barrel temperature of about 200 ° C, mold temperature of 60-80 ° C, injection temperature of 170-220 ° C, 60-150MPa, and compression ratio of 1.6-4.0. In order to eliminate the internal stress of the molded product, it can be thermostatically treated in an infrared lamp or a blast oven at 70 ° C for 2 to 4 hours.
During extrusion molding, the L / D ratio of the screw generally used is 17-24, which is cooled by air, and the extrusion temperature is 150-200 ° C.
When blow molding, the parisons obtained by injection molding and extrusion can be used for blow molding to obtain the required products. The blow molding pressure is generally 0.1 to 0.3 MPa.
PS plastic (polystyrene)
English name: Polystyrene
Specific gravity: 1.05 g / cm3
Molding shrinkage: 0.6-0.8%
Molding temperature: 170-250 ° C
Drying conditions: ---
a, mechanical properties: high strength, fatigue resistance, dimensional stability, and small creep (very little change under high temperature conditions);
PS plastic sheet
PS plastic sheet
b. Heat aging resistance: The enhanced UL temperature index reaches 120 ~ 140 ℃ (long-term outdoor aging is also very good);
c. Solvent resistance: no stress cracking;
d. Stability to water: easy to decompose in water (caution should be used under high temperature and high humidity environment);
e. Electrical performance:
1. Insulation performance: excellent (humidity, high temperature can also maintain stable electrical performance, is an ideal material for manufacturing electronic and electrical parts)
2. Dielectric coefficient: 3.0-3.2;
3. Arc resistance: 120s
f. Molding processability: injection molding or extrusion of common equipment. Because of the fast crystallization speed and good fluidity, the mold temperature is lower than other engineering plastics. When processing thin-walled parts, it only takes a few seconds, and it only takes 40-60s for large parts.
a. Electronic appliances: connectors, switch parts, household appliances, accessories, small electric covers or (heat resistance, flame retardancy, electrical insulation, molding processability);
1. Exterior parts: There are corner geshan, engine radiation cover, etc.
2. Internal parts: mainly endoscope stays, wiper brackets and control system valves;
3. Automotive electrical parts: automotive ignition coil stranded tubes and various electrical connectors.
c. Mechanical equipment: belt drive shaft of video tape recorder, electronic computer cover, mercury lamp cover, iron cover, baking machine parts and a large number of gears, cams, buttons, electronic watch housings, camera parts (with heat Flame retardant requirements)
According to different needs, you can choose the following adhesives:
1.G-955: One-component curing soft elastic shock-proof adhesive at room temperature, resistant to high and low temperature, but the bonding speed is slow, the glue usually takes one or several days to cure.
2. KD-833 instant adhesive can quickly bond PS plastic in seconds or tens of seconds, but the adhesive layer is hard and brittle and not resistant to hot water immersion above 60 degrees.
3. QN-505, two-component adhesive, soft adhesive layer, suitable for PS large area bonding or compounding. But the high temperature resistance is poor.
4.QN-906: two-component adhesive, high temperature resistance.
5.G-988: One-component room temperature vulcanizate. After curing, the elastomer has excellent waterproof, shock-resistant adhesive, high and low temperature resistance. If the thickness is 1-2mm, it will basically cure in 5-6 hours and have certain strength. It takes at least 24 hours to fully cure. Single component, no need to mix, just apply and let stand after extrusion without heating.
6. KD-5600: UV curing adhesive, bonding transparent PS sheet and board, can achieve no trace effect, you need to use UV light to cure. The effect is beautiful after sticking. But the high temperature resistance is poor.
Material performance editing
Excellent electrical insulation (especially high frequency insulation), colorless and transparent, light transmittance second only to plexiglass, colorability, water resistance, good chemical stability, average strength, but brittle, easy to cause stress brittle cracking, not resistant Organic solvents such as benzene, gasoline, etc. Suitable for making insulating transparent parts, decorative parts and chemical instruments, optical instruments and other parts.
⒈Amorphous material, small moisture absorption, does not need to be fully dried, and is not easy to decompose, but has a large thermal expansion coefficient and easy to generate internal stress. It has good fluidity and can be formed by screw or plunger injection machine.
⒉It is better to use high material temperature, high mold temperature, low injection pressure, and prolong the injection time is beneficial to reduce internal stress and prevent shrinkage and deformation.
⒊Gate can be used in various forms. The gate is connected with the arc of the plastic part to avoid damaging the plastic part when the gate is removed. The demoulding slope is large and the ejection is uniform. There are inserts that should be preheated.
PS is widely used in the optical industry because of its good light transmission. It can be used to manufacture optical glass and optical instruments, as well as transparent or colorful, such as lampshades, lighting appliances, etc. PS can also produce many electrical components and instruments that work in high frequency environments. Because PS plastic is a difficult-to-inert surface material, it is necessary to use professional PS glue for bonding in the industry.
Using PS alone as a product has great brittleness, and adding a small amount of other substances in PS, such as butadiene, can significantly reduce brittleness and improve impact toughness. This plastic is called impact-resistant PS. Its mechanical properties are greatly improved. Plastic makes many excellent mechanical parts and components.