Acrylic, also known as PMMA or plexiglass, is derived from the English acrylic (acrylic plastic), and its chemical name is polymethyl methacrylate .
It is an important plastic polymer material that was developed earlier. It has good transparency , chemical stability , weather resistance , easy dyeing, easy processing, and beautiful appearance . It has a wide range of applications in the construction industry . Plexiglass products can usually be divided into cast plates, extruded plates and molding compounds .
use
Acrylic products include acrylic sheets , acrylic plastic pellets, acrylic light boxes , signboards , acrylic bathtubs , acrylic artificial marble , acrylic resin, acrylic ( latex ) paint, acrylic adhesives, etc., with a wide variety of products.
Commonly seen acrylic products are acrylic products assembled from raw materials such as acrylic pellets, plates, or resins through various processing methods, combined with various parts of different materials and functions. As for the commonly heard acrylic fiber , acrylic cotton, acrylic yarn, acrylic nylon, etc., it refers to man-made fibers made by the polymerization of acrylic acid , and has nothing to do with acrylic products.
Wherein the acrylic plate is often said that polymethyl methacrylate Polymeric Methyl Methacrylate (PMMA) sheet, which is " a methyl methacrylate monomer Methyl Methacrylate (MMA)" polymerized together. Or it is extruded from acrylic pellets through an extruder. In the past, the board was commonly called plexiglass. Acrylic is derived from the English acrylic, which means PMMA board made of organic compound MMA. Its transparency and light transmittance are like glass. All boards made of transparent plastics such as PS, PC, etc. or poor-quality recycled MMA are collectively referred to as plexiglass. In order to distinguish, the PMMA board made of high-quality pure material MMA is named acrylic board in order to distinguish it from the general plexiglass board .
Performance characteristics
characteristic
1. It has crystal-like transparency , the light transmittance is above 92%, the light is soft, and the vision is clear. Acrylic colored with dyes has a good color development effect.
2. Acrylic sheet has excellent weather resistance, high surface hardness and surface gloss, and good high temperature performance.
3. Acrylic sheet has good processing performance, which can be processed by thermoforming or mechanical processing.
4. The transparent acrylic sheet has a light transmittance comparable to that of glass, but the density is only half that of glass. In addition, it is not as fragile as glass, and even if it is broken, it will not form sharp fragments like glass.
5. The abrasion resistance of acrylic sheet is close to that of aluminum, it has good stability and is resistant to corrosion by various chemicals.
6. Acrylic sheet has good printability and sprayability, and the use of appropriate printing and spraying processes can give acrylic products an ideal surface decoration effect.
7. Flammability: It is not spontaneously combustible but is flammable and does not have self-extinguishing property .
Features
1. Hardness
Hardness is one of the parameters that best reflects the production process and technology of cast acrylic sheet, and it is an important part of quality control. The hardness can reflect the purity of the raw material PMMA, the weather resistance of the sheet and the high temperature resistance. The hardness directly affects whether the sheet will shrink and bend, and whether the surface will crack during processing. Hardness is one of the rigid indicators for judging the quality of acrylic sheets.
2. Thickness ( Acrylic Tolerance )
Acrylic sheet thickness has acrylic tolerance, so the control of acrylic tolerance is an important manifestation of quality management and production technology. Acrylic production has an international standard ISO7823
Tolerance requirements for cast plates: Tolerance = ± (0.4 + 0.1 x thickness)
Tolerance requirements for extruded plates: Tolerance=< 3 mm Thickness: ± 10 %> 3 mm Thickness: ± 5%
3. Transparency/Whiteness
Strict raw material selection, advanced formula follow-up and modern production technology production ensure excellent transparency and pure whiteness of the board . Crystal clear after flame polishing.
Attributes
Mechanical properties
Polymethyl methacrylate has good comprehensive mechanical properties and ranks in the forefront of general-purpose plastics . Its tensile, bending, and compressive strengths are higher than polyolefins, and higher than polystyrene, polyvinyl chloride, etc., and its impact toughness is poor. But it is also slightly better than polystyrene . The cast bulk polymerized polymethyl methacrylate sheet (such as aerospace plexiglass sheet ) has higher tensile, bending, and compression mechanical properties, and can reach the level of engineering plastics such as polyamide and polycarbonate .
Generally speaking, the tensile strength of polymethyl methacrylate can reach the level of 50-77MPa, and the bending strength can reach the level of 90-130MPa. The upper limit of these performance data has reached or even exceeded some engineering plastics. Its elongation at break is only 2% -3%, the mechanical performance characteristics essentially hard and brittle plastic, and has a notch sensitivity, easy to crack under stress, but not breaking the fracture ordinary inorganic glass and polystyrene That's sharp and jagged. 40°C is a secondary transition temperature, which is equivalent to the temperature at which the pendant methyl group starts to move. If it exceeds 40°C, the toughness and ductility of the material will be improved. Polymethyl methacrylate has low surface hardness and is easy to scratch.
The strength of polymethyl methacrylate is related to the stress time, and the strength decreases as the time increases. After stretching and orientation, the mechanical properties of polymethyl methacrylate (oriented plexiglass ) have been significantly improved, and the notch sensitivity has also been improved.
The heat resistance of polymethyl methacrylate is not high. Although its glass transition temperature reaches 104°C, the maximum continuous use temperature varies between 65°C and 95°C depending on the working conditions, and the heat distortion temperature is about 96 ℃ (1.18MPa), Vicat softening point is about 113℃. The heat resistance can be improved by copolymerization of monomers with propylene methacrylate or ethylene glycol diester acrylate. The cold resistance of polymethyl methacrylate is also poor, with an embrittlement temperature of about 9.2°C. The thermal stability of polymethyl methacrylate is moderate, better than polyvinyl chloride and polyoxymethylene, but not as good as polyolefin and polystyrene. The thermal decomposition temperature is slightly higher than 270°C, and its flow temperature is about 160°C. There is a wide range of melt processing temperature.
The thermal conductivity and specific heat capacity of polymethyl methacrylate are in the middle level of plastics, which are 0.19W/MK and 1464J/Kg.K, respectively.
Electrical properties
Since polymethyl methacrylate contains polar methyl ester groups at the side of the main chain, its electrical properties are inferior to non-polar plastics such as polyolefin and polystyrene. The polarity of the methyl ester group is not too great, and polymethyl methacrylate still has good dielectric and electrical insulation properties. It is worth pointing out that polymethyl methacrylate and even the entire acrylic plastics have excellent arc resistance. Under the action of arc, the surface will not produce carbonized conductive paths and arc track phenomena. 20°C is a secondary transition temperature, which corresponds to the temperature at which the pendant methyl ester groups start to move. Below 20°C, the pendant methyl ester groups are in a frozen state, and the electrical properties of the material will be improved compared to those above 20°C.
Solvent resistance
Polymethyl methacrylate can withstand relatively dilute inorganic acids, but concentrated inorganic acids can make it corroded, and it can be resistant to alkalis, but warm sodium hydroxide and potassium hydroxide can make it corrode and can be salt-resistant And grease, resistant to aliphatic hydrocarbons, insoluble in water, methanol, glycerin, etc., but can absorb alcohol and swell and cause stress cracking. It is not resistant to ketones, chlorinated hydrocarbons and aromatic hydrocarbons. Its solubility parameter is about 18.8 (J/CM3) 1/2, and it can be dissolved in many chlorinated hydrocarbons and aromatic hydrocarbons, such as dichloroethane , trichloroethylene , chloroform, toluene, etc., vinyl acetate and acetone can also make it Dissolve.
Polymethyl methacrylate has good resistance to gases such as ozone and sulfur dioxide .
Weather resistance
Polymethyl methacrylate has excellent atmospheric aging resistance. After 4 years of natural aging test, the sample has a slight decrease in tensile strength and light transmittance , a slight yellowing in color, and a decrease in crazing resistance. Obviously, the impact strength has been slightly improved, and other physical properties have hardly changed.
Combustibility
Polymethyl methacrylate is easy to burn, and its limiting oxygen index is only 17.3.
Main classification
Types of plexiglass (acrylic) sheets
Common boards include: transparent board, dyed transparent board, milk white board, color board;
Special boards include: bathroom board, cloud board, mirror board, cloth sandwich board, hollow board, impact board, flame retardant board , super wear-resistant board, surface pattern board , frosted board , pearlescent board, metal effect board, etc.
Different performance, different colors and visual effects to meet the ever-changing requirements.
1. Acrylic boards are divided into cast boards and extruded boards according to the production process. According to the transmittance, they can be divided into transparent boards, semi-transparent boards (including dyed transparent boards), color boards (including black and white and color boards); according to performance Impact board, anti-ultraviolet board, ordinary board and special board such as high impact board, flame retardant board, frosted board, metal effect board, high wear-resistant board, light guide board, etc.
A: Casting plate: high molecular weight, excellent rigidity, strength and excellent chemical resistance. Therefore, it is more suitable for processing large-size identification plaques, and the time in the softening process is slightly longer. This kind of board is characterized by small batch processing, incomparable flexibility in color system and surface texture effect, and complete product specifications, which can be used for various special purposes.
B: Extruded plate: Compared with the cast plate, the extruded plate has a lower molecular weight, slightly weaker mechanical properties, and higher flexibility. However, this feature is conducive to bending and hot forming processing , and the softening time is shorter. When processing large-sized plates, it is beneficial to various rapid vacuum forming. At the same time, the thickness tolerance of the extruded plate is smaller than that of the cast plate. Because the extruded plate is mass-produced and automated, the colors and specifications are inconvenient to adjust, so the variety of product specifications is subject to certain restrictions.
2. Acrylic There is also a kind of recycled acrylic board that uses recycled acrylic scrap, which is thermally degraded to obtain recycled MMA (methyl methacrylate) monomer, which is then obtained after chemical polymerization. After a rigorous process, the pure MMA monomer can be re-obtained, and there is no difference in quality from the newly synthesized monomer. However, the purity of the produced degradable monomers is not high, and the quality and performance of the sheet after forming are very poor.
Summary: The extruded plate uses granular raw materials, which are extruded after being dissolved at high temperature, while the cast plate is directly casted with MMA monomer (liquid). Although the extruded plate is relatively flat and smooth in appearance, it is because it is formed when the granular raw material is formed. To complete the polymerization. When processed into plates, its structure and performance are weak, and it is not suitable as a material for outdoor marking products. It is only suitable for indoor products such as crystal letters or product brackets.
In addition, since most of the extruded panels do not have the function of UV protection, their outdoor use life is not the same as that of the cast panels. The color will gradually fade and it is easy to become brittle until it breaks. The casting plate is to complete the structural polymerization during the processing of the plate, during which the ultraviolet absorber is added, which has extremely high strength and UV function. The outdoor service life is more than 5 years or even 10 years, and the color is always bright as new during use.
Process characteristics
1. Polymethyl methacrylate contains polar pendant methyl groups and has obvious hygroscopicity. The water absorption rate is generally 0.3%-0.4%. It must be dried before molding. The drying condition is 80℃-85℃ for 4-5h. .
2. Polymethyl methacrylate has obvious effective non-Newtonian fluid characteristics in the temperature range of molding processing . The melt viscosity will obviously decrease with the increase of shear rate, and the melt viscosity is also very sensitive to temperature changes. Therefore, for the molding process of polymethyl methacrylate, increasing the molding pressure and temperature can significantly reduce the melt viscosity and achieve better fluidity.
3. The temperature at which polymethyl methacrylate starts to flow is about 160°C, and the temperature at which it starts to decompose is higher than 270°C, which has a wide processing temperature range.
4. Polymethyl methacrylate has higher melt viscosity and faster cooling rate, and the product is prone to internal stress. Therefore, the process conditions are strictly controlled during molding, and post-processing is also required after the product is molded.
5. Polymethyl methacrylate is an amorphous polymer, and the shrinkage rate and its variation range are small, generally about 0.5%-0.8%, which is conducive to forming plastic parts with high dimensional accuracy.
6. The cutting performance of polymethyl methacrylate is very good, and its profile can be easily machined to various required sizes.
Processing technology
Polymethyl methacrylate can be cast, injection, extrusion, thermoforming and other processes.
Casting
Casting is used to form plexiglass plates, bars and other profiles, that is, the profiles are formed by bulk polymerization . After casting, the product needs to be post-treated. The post-treatment conditions are heat preservation at 60°C for 2h and heat preservation at 120°C for 2h.
Injection molding
Injection molding uses pellets made by suspension polymerization and molding on a common plunger or screw injection molding machine . Table 1 shows the typical process conditions of polymethyl methacrylate injection molding.
Injection molding products also need post-processing to eliminate internal stress. The processing is performed in a 70-80°C hot air circulating drying oven . The processing time depends on the thickness of the product, and generally takes about 4 hours.
Extrusion molding
Polymethyl methacrylate can also be extruded, and plexiglass plates, rods, pipes , sheets, etc. can be prepared from particles produced by suspension polymerization . However, the profiles prepared in this way, especially plates, have a small molecular weight due to the low molecular weight of the polymer . The mechanical properties, heat resistance, and solvent resistance are not as good as cast-molded profiles. Its advantage is high production efficiency, especially for pipes and other profiles that are difficult to manufacture when using the casting method . Single-stage or double-stage vented extruder can be used for extrusion molding , and the ratio of screw length to diameter is generally 20-25. Table 2 is the typical process conditions of extrusion molding.
Thermoforming
Thermoforming is the process of making plexiglass plates or sheets into products of various sizes and shapes. The blank cut to the required size is clamped on the mold frame, heated to soften it, and then pressurized to make it close to the mold surface , To obtain the same shape as the molding surface, and trim the edge after cooling and shaping to obtain the product. Pressurization can be done by vacuum drafting or by directly pressurizing a convex mold with a profile. The thermoforming temperature can refer to the recommended temperature range in Table 3. When adopting rapid vacuum low-draft molding products, the temperature should be close to the lower limit, and the deep drawing products with complex shapes should be close to the upper limit temperature. Normally, the normal temperature should be used.
Engraving and cutting
Mainly for hollowing out and engraving formed acrylic or colored acrylic materials. Ordinary laser engraving and cutting machines can meet the engraving and hollowing needs of most acrylic products.
The main purpose
PMMA is the polymer obtained by the polymerization of acrylic acid and its esters, collectively referred to as acrylic resins, and the corresponding plastics are collectively referred to as polyacrylic plastics. Among them, polymethyl methacrylate is the most widely used. The abbreviation code of polymethyl methacrylate is PMMA, commonly known as plexiglass, which is by far the most excellent synthetic transparent material .
PMMA has the advantages of light weight, low price, and easy molding. Its molding methods include casting, injection molding, machining, thermoforming and so on. Especially for injection molding, it can be produced in large quantities, with simple manufacturing process and low cost. Therefore, its application is becoming more and more extensive. It is widely used in instrument and meter parts, automobile lights, optical lenses, transparent pipes, etc.
advantage
Acrylic is the best new material for sanitary ware after ceramics . Compared with traditional ceramic materials, in addition to acrylic unmatched highlight brightness, there are the following advantages: good toughness, unbreakable; repair is strong, with a long dip soft foam the toothpaste can be sanitary wipe, a new; soft texture, Winter There is no icy feeling; the colors are bright, which can satisfy the individual pursuit of different tastes. Basins, bathtubs, and toilets made of acrylic are not only exquisite in style, durable, but also environmentally friendly. The radiation level is almost the same as that of the human body's own bones. Acrylic sanitary ware first appeared in the United States and has accounted for more than 70% of the entire international market.
shortcoming
Due to the difficulty and high cost of acrylic production, there are many low-quality and inexpensive substitutes on the market. These substitutes are also called "acrylic", in fact they are ordinary organic boards or composite boards (also known as sandwich boards). Ordinary organic board is cast with ordinary plexiglass cracking material and pigment, the surface hardness is low, it is easy to fade, and the polishing effect is poor after sanding with fine sand. The composite board has only a very thin layer of acrylic on the surface and ABS plastic in the middle. It is easy to delamination due to thermal expansion and contraction during use. True and false acrylic can be identified from the slight chromatic aberration and polishing effect of the sheet section
Acrylic is widely used and can be used in test racks and patch trays .
Application field
1. Architectural applications: shop windows, soundproof doors and windows , lighting shades, telephone booths, etc.
2. Advertising applications: light boxes, signs, signs, display racks, etc.
3. Transportation applications: doors and windows of trains, automobiles and other vehicles.
4. Medical applications: baby incubators, various surgical medical appliances and civilian products: sanitary facilities, handicrafts, cosmetics, brackets, aquariums, etc.
5. Industrial applications: instrument surface panels and protective covers, etc.
6. Lighting applications: fluorescent lamps, chandeliers , street lampshades, etc.
Application areas: hotels, shopping malls, office buildings, clubs, villas, museums, medical care, education, catering, exhibitions, etc.
Application areas: suspended ceilings, integrated ceilings , partitions, screens, sliding doors, transparent walls, hotel furniture , office furniture , bar counters, lighting, chandeliers, signs, signs, floors, landscapes, etc.
Bonding method
The bonding of acrylic products is a very critical process in acrylic processing. How to show the clear and transparent characteristics of plexiglass , reflect the value of acrylic tobacco and alcohol packaging crafts, and maximize the grade and taste of acrylic crafts. The bonding technology starts To the pivotal role.
The adhesion of plexiglass panels is mainly affected by two aspects, one is the applicability of the adhesive itself; the other is the bonding skills.
There are many adhesives on the domestic and foreign markets, mainly two types, one is two-component, such as universal glue, epoxy resin; the other is one-component, such as CHCl3 ( chloroform ). Generally speaking, two-component adhesives are bonded through curing reaction, and single-component adhesives are the final volatilization of a solvent to achieve bonding.
The two-component adhesive is characterized by good bonding effect, no bubbles, no whitening, and high strength after bonding. The disadvantages are complex operation, difficult, long curing time, slow speed, and it is difficult to adapt to the requirements of mass production. The general one-component adhesive is characterized by fast speed and can meet the technological requirements of mass production. The disadvantage is that the bonded products are easy to produce bubbles, easy to whiten, and have poor weather resistance, which directly affects the performance of plexiglass products . External beauty and product quality, therefore, in the processing of plexiglass products, how to choose a suitable adhesive to improve the grade and grade of plexiglass products is a big problem that must be solved first in the bonding process.
In addition, bonding skills are also very important. Here are a few common bonding processes, and a brief analysis of their practical experience.
1. Butt joint: Place two plexiglass plates that need to be jointed horizontally on the operating platform, close them, and stick a tape on the bottom, leaving a gap not greater than 0.3mm wide for the application of adhesive. Use a syringe to inject the adhesive uniformly and slowly from one side into the gap until it is completely filled. After it is completely cured, remove the tape.
2. Facade bonding: Facade bonding is the most widely used bonding technology, and it is widely used in the production of various plexiglass IT electronic digital display products. First, wipe clean the surface to be bonded. It is best to use a master mold to achieve bonding, so that the bonded object does not shake, which is beneficial to improve the quality of bonding. Plexiglass panels with a thickness of 3mm can be bonded with thin metal wires. The bonding can be completed by capillary action. The metal wires can be drawn out before the adhesive is cured, or adhesive tape and then adhesive can be used for bonding. .
3. Bevel bonding: The bonding bevel must use a 90-degree angle and other profiling to prevent the displacement of the bonded surface. The adhesive should be applied evenly and slowly. The master can be removed only after it is completely cured.
4. Plane bonding: Plane bonding is a special bonding method. First, wipe the sticky surface clean and place it horizontally, and pour an appropriate amount of adhesive on it. Place one side of another plexiglass board diagonally in contact with the plexiglass board coated with the adhesive, and then lower it evenly and slowly, and drive out the bubbles from one side to complete the bonding. Plexiglass adhesive can corrode the surface of the plexiglass board and leave traces that are difficult to eliminate. Therefore, you can use a self-adhesive tape to protect the parts that do not need to be bonded. Grease, dust or pores will prevent the uniform application of the adhesive and leave bubbles. Using an excessively small amount of adhesive will bring in air when the adhesive shrinks. Direct blowing will cause the edges of the bonding surface to turn white due to the volatilization of the adhesive. Indoor humidity, temperature, etc. all have a direct effect on the adhesion of plexiglass panels.
develop
Acrylic (ACRYLIC), the common name of special treatment plexiglass. The research and development of acrylic has a history of more than one hundred years.
The polymerizability of acrylic acid was discovered in 1872 ;
In 1880, the polymerizability of methacrylic acid was known;
In 1901, the research on the synthesis of propylene polypropionate was completed;
In 1927, the aforementioned synthesis method was used to try industrial manufacturing;
In 1937, the industrial manufacturing of methyl esters was successfully developed, and thus entered large-scale manufacturing.
During World War II, because of its excellent toughness and light transmittance, acrylic was firstly used in the windshield of aircraft and the field of vision mirror in the driver’s cab of a tank.
The birth of the world's first acrylic bathtub in 1948 marked a new milestone in the application of acrylic.
Latest application
Acrylic furniture
Acrylic furniture first appeared in Europe and developed in the 1990s. Acrylic furniture has only gained considerable development in the 21st century. Acrylic furniture can be seen in high-end hotels and villas in the field of home decoration.
Since the German Rohm & Haas ( Rohm & Haas ) company produced the first acrylic sheet in 1920, the application of acrylic has become more and more extensive. Acrylic furniture first appeared in Germany.
In 1941, a German crafts designer had a sudden thought when he was designing accessories. If acrylic can be used as a material for furniture, it would definitely be perfect. So he designed a design drawing of a coffee table using acrylic as the material. Tianhou made the coffee table. The appearance was perfect as he originally expected, but the structural design was lacking. So far, acrylic furniture was born.
Acrylic can also be used to make environmental buttons. Because of its high light transmittance, the buttons are shiny. At the same time, because of its strong hardness and not fragile, it can achieve the effect of long-term use.
Most of the furniture on the market is made of traditional materials such as wooden materials , metal materials, and glass materials. Furniture made of such materials has problems such as high cost, unenvironmental protection, and complicated craftsmanship.
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