Acrylic plastics Acrylic plastics include a wide variety of polymers and copolymers, and there are two main monomer components: acrylates and methacrylates. They can be used alone or in combination, and sometimes in combination with other monomers to achieve a range of products ranging from soft elastomers to rigid thermoplastic and thermoset plastics. Within such a wide range of properties, acrylic plastics can be produced in a variety of forms, such as plate, rod, tube, film, granule, bead, solution, latex and active paste.
Acrylic plastic is widely used in many fields because of its crystal clear transparency, excellent surface hardness, excellent weather resistance, chemical resistance, environmental adaptability and good stable mechanical properties. By utilizing their optical properties and compatibility with pigments and dyes, a variety of transparent and translucent products can be produced, which can also be used to control the transmittance of light in the ultraviolet, visible and near-infrared spectral ranges.
The combination of product form and performance makes acrylic plastic widely used in magnifying glass and post-illumination signs for automotive taillight glass, architectural decoration and lighting. Medical equipment and color electronic display filters.
Most of the chemical acrylics are derived from methyl methacrylate (MMa), which is usually synthesized in a two-step process. That is, acetone and hydrogen cyanide react with acetone cyanohydrin, and then react with methanol or other alcohol to produce methacrylic acid ester. MMa can also be converted to other esters by transesterification.
The acrylic resin is obtained by radical polymerization or redox polymerization using a peroxide or an azo catalyst as an initiator. There are four polymerization methods for acrylic resins. Bulk polymerization, suspension polymerization, emulsion polymerization, and solution polymerization. These methods can achieve continuous production, especially bulk polymerization and solution polymerization.
The polymer is modified by copolymerization of methacrylate with other monomers such as methyl and ethyl acrylate; enoate, acryl and styrene; and vinyl, butadiene and other acrylic rubber; It can be blended with a polyester resin to improve its physical properties and processability.
Production Formulations It is possible to use additives or modifiers when producing different forms of acrylic plastic sheets and molding compounds, which are produced in different formulations to give them special properties.
The plate product is obtained by several casting methods, melt calendering or extrusion methods. Grooved form casting is a batch process. During this process, the catalyzed monomer or slurry is heated between two polished glass plates that are held by a spring clamp to accommodate shrinkage of the acrylic material during curing. The plate product can also be produced by continuous casting on a polished stainless steel moving belt. Both methods have their own advantages and their product quality is excellent. The continuous casting plate has uniform thickness and small thickness variation, and the grooved template casting product has better optical properties and a smoother surface.
The pellets used for extrusion or melt calendering are formed by bulk polymerization or solution polymerization to re-extrude the pellets or continuously polymerize in an extruder. Granular panels are less maneuverable than casts of the same quality, but the finished panels have lower molecular weights and some less physical properties such as thermal deformation, design stress limits and chemical resistance. Recently, panels extruded from impact-modified pellets have been applied to applications where better damage resistance or higher toughness is required to resist destructive impact during processing, such as outdoor signage or use. Used as a surface material for coextrusion and increased hardness.
Extruded panels typically have a thickness of 0.060 to 0.250 inches, slotted form casting panels have a thickness in the range of 0.030 to 4.500 inches, continuous processing panels range from 0.125 to 0.375 inches, and continuous web lengths of 600 feet.
The wear plate is made by coating a polysilicate. The abrasion resistance of the coated sheet was 75 times that of the uncoated sheet, and the solvent resistance was also improved.
Other special products include mirror panels, UV shielding panels and double-layer poles that are as hot as the glass.
Resin product molding pellets vary widely in molecular weight and main properties, especially activity rate, heat resistance and toughness. The activity of medium molecular weight materials (aSTM 5.6 and 8) and heat resistance are quite different, but the difference in toughness is not significant. High molecular weight pellets have a lower activity rate (aSTMS grade) and heat resistance than medium molecular pellets, but are tougher and are therefore used to extrude parts to make parts more resistant during processing. Damaged. They also exhibit higher thermal strength during processing and improved fracture resistance during injection molding. Highly active pellets are suitable for molding complex parts with “difficult to fill moldsâ€. Some special pellets give the extrudate a matte surface or absorb or transmit UV light. In addition to colorless pellets, there are also transparent, translucent and opaque pellets.
Impact-Resistant Modification As early as the early 1970s, a high-impact acrylic pellet was developed for injection molding, molding or extrusion. It consists of a polyacrylate solid phase and a soft phase of its modifier. The refractive index of the two phases needs to be matched so that the molded or extruded article made of this material has a high transparency at room temperature, and the polyacrylate mixture has excellent weather resistance. Recently, varieties with various impact resistance and improved processing properties have been developed. Products for the medical field that are specifically designed for anti-Y-ray radiation have also been reported.
The performance polyacrylate can transmit 92% of white light, typically 1% to 3% turbidity. Transparency is close to optical glass.
Weather resistance. Polyacrylate has been subjected to long-term outdoor wind and rain, and there is no significant change in color and physical properties. Special UV-resistant products are mainly used where parts are exposed to more intense UV rays than sunlight or fluorescent lamps.
Chemical resistance. Polyacrylate products are not affected by most household detergents, detergents, mineral acids, bases and aliphatic hydrocarbons, but cannot be used with halogenated hydrocarbons, aromatic hydrocarbons, esters and ketones.
toughness. Articles made from general grade polyacrylates have a notch sensitivity (0.2-0.5 ft. lb/in, notched cantilever), and articles made with medium and high impact polyacrylate are significantly better. The wall thickness of the part is designed to minimize stress concentration and will allow the part to have sufficient strength in most applications.
Thermal performance. The heat distortion temperature is 165 to 216 F, and the typical use temperature is 200 F. Like most thermoplastics, polyacrylates have a higher coefficient of thermal expansion than metals and should be properly considered in the design. The acrylate-imine copolymer can withstand 313F temperature without deformation.
Electrical performance. Polyacrylate has low conductivity, good arc resistance and high dielectric strength.
Flammability. Polyacrylates are flammable and require wood-like fire protection. Strict adherence to building codes and the Underwriters Association's research standards, as well as established fire safety guidelines, allows fire control to be acceptable. There are provisions in the regulations to control the application of light-transmissive plastics.
When using polyacrylate as a large-area curtain wall, it is not necessary to comply with the restrictions, and it can be changed according to the analysis of life safety and fire prevention measures. When the polyacrylate is used as a lamp, the concentrating sheet and the scatter sheet are not fixedly mounted, and will fall off before the fire, preventing the flame from spreading to the ceiling, so it is not necessary to comply with the regulations on interior decoration in the building code.
Processed acrylate plastics can be made into useful parts by conventional injection molding, extrusion, thermoforming, blow molding, and machining processes. Powdered acrylate plastics have poor hot melt properties and cannot be rotationally molded.
Injection molding. Although injection molding can use a column type machine, the screw type injection machine is widely used due to uniform melting temperature, short residence time, and small hanging area. The pellets can be processed using a vented or non-vented molding machine. General ram machines are only used to produce products with marbled or wood grain. This effect can be achieved by adding a special colorant to the colorless pellets. The machine should be selected to the appropriate specifications so that the clamping pressure is 2.5 to 3 t/in*in (the projected area of ​​the molded part) and the injection volume is 40% to 75% of the barrel volume. If the cycle is short or the melting temperature is low, the injection volume should be as low as 20%. Generally, acrylate plastics do not require a specially designed screw, and the aspect ratio (L/D) is greater than or equal to a general screw of 16:1, and the compression ratio is preferably 2:1 and 3:1.
Polyacrylate absorbs moisture and needs to be dried before processing. In the low humidity month, the pellets in the closed cylinder or paper tube can be directly processed. If the pellets are exposed to the air in a general processing workshop for more than 4 hours, drying is required. It is usually placed in a desiccator with a desiccant for 2 to 4 hours.
Unmodified polyacrylate processing conditions can vary. The most active 5-grade product requires a cylinder temperature that is lower than the difficult-to-active level to achieve the desired flow rate. The 0.13-inch thick workpiece has a cycle time of typically 40-50 seconds.
All Y products of the previous grade can be processed within a wide range of process conditions. For example, the grade temperature of the cylinder is 16F. The easy-to-active material processing temperature range is wider. If the parts are difficult to mold and require a long length of activity, the simplified temperature should be the upper limit of the processing temperature range. The residual stress of the workpiece processed at the upper limit temperature is minimized, so that the use temperature of the workpiece produced by each active grade can be improved. All types of polyacrylate (modified and unmodified) shrinkage are in the range of 0.37% to 0.6%.
The molding temperature of the impact-modified active grade polyacrylate also varies depending on the activity. The most difficult to move high impact modified grade processing range is approximately 120F. Other easy-to-active grades have a processing range of 195F. These grades should be avoided at the melting temperature (above 510F) or degradation will occur. Spiral activity length data is a good basis for guessing whether a particular active product can meet a certain length of activity for a predetermined thickness.
Extrusion. The polyacrylate pellets can be extruded into sheets or profiles using conventional single, two or three stage (vented) screw extruders. A metering screw with a compression ratio of 3:1 can be used. Depending on the application, the embossing cylinder can be attached to the machine for special decoration, special style, or lens attachment.
In general, the extrusion conditions depend on the formulation of the extruded polyacrylate and the relevant conditions of the screw and mold used. Polyacrylate sheets or profiles have a high gloss surface when the material is extruded under suitable processing conditions. Some impact grades are extruded on the surface of aBS and PVC sheets or profiles by coextrusion to give good toughness on the surface. Gloss, weatherability and other characteristics required for special applications. These grades of material and matrix have excellent adhesion and rheological properties are basically matched to achieve a uniform surface layer.
Thermoforming. Due to its good thermoforming properties, polyacrylate sheets can be processed over a wide temperature range with the most convenient processes and equipment. All standard 2D and 3D forming techniques can be used. The plate extruded with pellets has an excellent elastic memory effect and can be repeatedly heated and formed without difficulty.
Thermoforming can be carried out over a wide temperature range using standard presses and equipment. The calendering depth and molding details vary depending on the formulation and generally work well. Thermoformed polyacrylate shell molds can be used to cast and cure polyester fibers with glass fibers to make highly rigid workpieces.
Blow molding. Unmodified polyacrylates are difficult to process by extrusion blow molding due to poor hot melt strength. If you want to blow a bulb, you first need to inject the preform and then heat blow it into the desired shape.
Impact grade polyacrylates can be injection blow molded or extruded blow molded, but there are only a few applications that are manufactured using this process. The acrylate acid imide copolymer is easily blow molded.
Processing and molding. The board can be cut with a chainsaw, which can be split along the scored lines. Ordinary metal processing machines generally meet the processing requirements. As the binder, a solvent-based binder may be used, but it is preferred to use a dosage form which is specially thickened or polymerizable in advance. The workpiece can be joined by hot blades, hot gas, ultrasonic or spin welding.
Application of polyacrylic acid
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