Acrylic, also known as PMMA or plexiglass, is derived from the English word 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 and weather resistance, is easy to dye, easy to process, and has a beautiful appearance. It is widely used in the construction industry. Organic glass products can usually be divided into cast plates, extruded plates and molded materials.

Uses

Acrylic products include acrylic boards, acrylic plastic pellets, acrylic light boxes, signs, acrylic bathtubs, acrylic artificial marble, acrylic resin, acrylic (latex) paint, acrylic adhesives and many other products.

Acrylic products that people often see are made of acrylic particles, sheets or resins through various processing methods, and assembled with various parts of different materials and functions. As for acrylic fibers, acrylic cotton, acrylic yarn, acrylic nylon, etc., which are commonly heard, they refer to artificial fibers polymerized from acrylic acid and have nothing to do with acrylic products.

Among them, the acrylic sheet that people often talk about is the polymethyl methacrylate (PMMA ) sheet, which is made by polymerizing ” methyl methacrylate monomer Methyl Methacrylate (MMA)”. Or it is made by extruding acrylic pellets through an extruder. In the past, the sheet was commonly known as plexiglass. Acrylic comes from the English word acrylic, which means PMMA sheet made of organic compound MMA, which is as transparent and transparent as glass. It comes from the fact that all sheets made of transparent plastics such as PS, PC, etc. or made of inferior recycled MMA are collectively called plexiglass. In order to distinguish, the PMMA sheet made of high-quality pure MMA is named acrylic sheet to distinguish it from the general plexiglass sheet.

Performance characteristics

Characteristic

1. It has crystal -like transparency, with a light transmittance of over 92%, soft light and clear vision. 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 sheets have good processing properties and can be thermoformed or machined.

4. Transparent acrylic sheet has a transmittance comparable to that of glass, but its density is only half of 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 wear resistance of acrylic sheet is close to that of aluminum, it has good stability and is resistant to corrosion from a variety of chemicals.

6. Acrylic sheets have good printability and sprayability. Appropriate printing and spraying processes can give acrylic products ideal surface decorative effects.

7. Flame resistance : It does not spontaneously ignite but is flammable and does not have self-extinguishing properties.

Features

1. Hardness

Hardness is one of the parameters that best reflects the production process and technology of cast acrylic sheets, and is an important part of quality control. Hardness can reflect the purity of the raw material PMMA, the weather resistance of the sheet, and the high temperature resistance. Hardness directly affects whether the sheet will shrink, bend, or deform, and whether cracks will appear on the surface during processing. Hardness is one of the hardness indicators for judging the quality of acrylic sheets.

2. Thickness ( Acrylic Tolerance )

There is an acrylic tolerance in the thickness of acrylic sheets, so the control of acrylic tolerance is an important manifestation of quality management and production technology. The production of acrylic has an international standard ISO7823

Tolerance requirements for cast plates: Tolerance = ± (0.4 + 0.1 x thickness)

Tolerance requirements for extruded sheets: Tolerance = < 3 mm thickness: ± 10 % > 3 mm thickness: ± 5 %

3. Transparency/whiteness

Strict raw material selection, advanced formula follow-up and modern production process ensure the excellent transparency and pure whiteness of the board. It is crystal clear after flame polishing.

Property

Mechanical properties

Polymethyl methacrylate has good comprehensive mechanical properties, and is at the forefront of general-purpose plastics. Its tensile, bending, and compression strengths are higher than those of polyolefins, polystyrene, and polyvinyl chloride. Its impact toughness is poor, but slightly better than that of polystyrene. Cast bulk polymerized polymethyl methacrylate sheets (such as plexiglass sheets for aviation) have higher tensile, bending, and compression mechanical properties, which can reach the level of engineering plastics such as polyamide and polycarbonate.

Generally speaking, the tensile strength of polymethyl methacrylate can reach 50-77MPa, and the bending strength can reach 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%, so its mechanical properties are basically hard and brittle plastics, and it is notch sensitive and easy to crack under stress, but the fracture is not as sharp and uneven as polystyrene and ordinary inorganic glass. 40℃ is a secondary transition temperature, which is equivalent to the temperature at which the side methyl groups begin to move. Above 40℃, the toughness and ductility of the material are improved. The surface hardness of polymethyl methacrylate is low and it is easy to be scratched.

The strength of polymethyl methacrylate is related to the stress action time. As the action time increases, the strength decreases. The mechanical properties of polymethyl methacrylate (oriented organic glass ) after stretching and orientation are significantly improved, and the notch sensitivity is also improved.

The heat resistance of polymethyl methacrylate is not high. Although its glass transition temperature reaches 104℃, its maximum continuous use temperature varies between 65℃-95℃ depending on the working conditions. Its heat deformation temperature is about 96℃ (1.18MPa) and its Vicat softening point is about 113℃. The heat resistance can be improved by copolymerizing the monomer with propylene methacrylate -based ethylene glycol acrylate. The cold resistance of polymethyl methacrylate is also poor, and its brittle temperature is about 9.2℃. The thermal stability of polymethyl methacrylate is medium, better than polyvinyl chloride and polyoxymethylene, but not as good as polyolefins and polystyrene. Its thermal decomposition temperature is slightly higher than 270℃, and its flow temperature is about 160℃, so it still has a wide melt processing temperature range.

The thermal conductivity and specific heat capacity of polymethyl methacrylate are both at a medium level among plastics, which are 0.19W/MK and 1464J/Kg.K respectively.

Electrical properties

Since polymethyl methacrylate contains polar methyl groups on the side of the main chain, its electrical properties are inferior to those of non-polar plastics such as polyolefins and polystyrene. The polarity of the methyl group is not too large, so 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 an arc, no carbonized conductive path or arc track will be generated on the surface. 20°C is a secondary transition temperature, corresponding to the temperature at which the side methyl groups begin to move. Below 20°C, the side methyl groups are in a frozen state, and the electrical properties of the material will be improved compared to above 20°C.

Solvent resistance

Polymethyl methacrylate is resistant to dilute inorganic acids, but it can be corroded by concentrated inorganic acids. It is resistant to alkalis, but it can be corroded by warm sodium hydroxide and potassium hydroxide. It is resistant to salts, oils and fats, and aliphatic hydrocarbons. It is insoluble in water, methanol, glycerol, etc., but it can absorb alcohols to swell and produce stress cracking. It is not resistant to ketones, chlorinated hydrocarbons and aromatic hydrocarbons. Its solubility parameter is about 18.8 (J/CM3)1/2. It can be dissolved in many chlorinated hydrocarbons and aromatic hydrocarbons, such as dichloroethane, trichloroethylene, chloroform, toluene, etc., and vinyl acetate and acetone can also make it soluble.

Polymethyl methacrylate has good resistance to gases such as ozone and sulfur dioxide.

Weather resistance

Polymethyl methacrylate has excellent resistance to atmospheric aging. After 4 years of natural aging test, the weight of the sample changed, the tensile strength and light transmittance decreased slightly, the color turned slightly yellow, the resistance to silver streak decreased significantly, the impact strength increased slightly, and other physical properties remained almost unchanged.

Combustibility

Polymethyl methacrylate is very flammable, with a limiting oxygen index of only 17.3.

Main categories

There are many types of acrylic sheets.

Common boards include: transparent boards, dyed transparent boards, milky white boards, and colored boards;

Special boards include: bathroom boards, cloud boards, mirror boards, plywood boards, hollow boards, impact-resistant boards, flame-retardant boards, super wear-resistant boards, surface patterned boards, frosted boards, pearlescent boards, metal effect boards, etc.

Different performances, different colors and visual effects to meet ever-changing requirements.

1.Acrylic sheets are divided into cast sheets and extruded sheets according to the production process, and can be divided into transparent sheets, translucent sheets (including dyed sheets and transparent sheets), and color sheets (including black and white and color sheets) according to light transmittance; according to performance, they can be divided into impact-resistant sheets, UV-resistant sheets, ordinary sheets and special sheets such as high-impact sheets, flame-retardant sheets, frosted sheets, metal effect sheets, high-wear-resistant sheets, light guide sheets, etc.

Casting plate: high molecular weight, excellent stiffness, strength and excellent chemical resistance. Therefore, it is more suitable for processing large-sized signboards, and the softening time is slightly longer. This type of plate is characterized by small batch processing, unparalleled flexibility in color system and surface texture effect, and a full range of product specifications, which is practical for various special purposes.

Extruded sheet: Compared with cast sheet, extruded sheet has lower molecular weight, slightly weaker mechanical properties and higher flexibility. However, this feature is conducive to bending and thermoforming processing, and the softening time is short. When processing large-sized sheets, it is conducive to various rapid vacuum forming. At the same time, the thickness tolerance of extruded sheet is smaller than that of cast sheet. Since extruded sheet is mass -produced automatically, the color and specifications are not convenient to adjust, so the diversity of product specifications is subject to certain restrictions.

2. There is another type of acrylic called recycled board, which is made of recycled acrylic scraps, which are thermally degraded to obtain recycled MMA (methyl methacrylate) monomers, and then obtained through chemical polymerization. After a strict process flow, pure MMA monomers can be obtained again, which are no different in quality from newly synthesized monomers. However, the produced degraded monomers are not of high purity, and after the board is formed, its quality and performance are very poor.

Summary: Extruded board uses granular raw materials, which are extruded after being dissolved at high temperature, while cast board is directly cast with MMA monomer (liquid). Although the extruded board is relatively flat and smooth in appearance, it is processed into board because the granular raw materials have been polymerized during the molding process. Its structure and performance are weak, and it is not suitable as a material for outdoor sign products, but only suitable for indoor products such as crystal characters or product brackets.

In addition, since most extruded sheets do not have UV protection, their outdoor service life is not the same as that of cast sheets. The color will fade and it will easily become brittle until it breaks. Cast sheets are polymerized during the sheet processing process, during which UV absorbers are added. They have extremely high strength and UV resistance. Their outdoor service life can last for more than 5 years or even 10 years, and their color remains bright and new during use.

Process characteristics

1. Polymethyl methacrylate contains polar side methyl groups and has obvious hygroscopicity. The water absorption rate is generally 0.3%-0.4%. It must be dried before molding. The drying conditions are 80℃-85℃ for 4-5h.

2. Polymethyl methacrylate has obvious non-Newtonian fluid properties within the temperature range of molding. The melt viscosity will decrease significantly with the increase of shear rate, and the melt viscosity is also very sensitive to temperature changes. Therefore, for the molding 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, and it has a wide processing temperature range.

4. The melt viscosity of polymethyl methacrylate is high and the cooling rate is fast, so the product is prone to internal stress. Therefore, strict control of process conditions is required during molding, and post-processing is also required after the product is molded.

5. Polymethyl methacrylate is an amorphous polymer with a small shrinkage rate and a small range of variation, generally about 0.5%-0.8%, which is conducive to molding plastic parts with higher dimensional accuracy.

6. Polymethyl methacrylate has excellent cutting performance, and its profiles can be easily machined into various required sizes.

Processing Technology

Polymethyl methacrylate can be processed by casting, injection molding, extrusion, thermoforming and other processes.

Casting

Casting is used to form organic glass plates, rods and other profiles, that is, the profiles are formed by bulk polymerization. The products after casting need to be post-processed, and the post-processing conditions are 60℃ for 2h and 120℃ for 2h.

Injection molding

Injection molding uses pellets made by suspension polymerization and is performed on a common plunger or screw injection molding machine. Table 1 shows the typical process conditions for injection molding of polymethyl methacrylate.

Injection molded products also need post-processing to eliminate internal stress. The processing is carried out in a hot air circulation drying oven at 70-80℃. The processing time depends on the thickness of the product and generally takes about 4 hours.

Extrusion

Polymethyl methacrylate can also be extruded to prepare plexiglass plates, rods, pipes, sheets, etc. using pellets produced by suspension polymerization. However, the profiles prepared in this way, especially the plates, are inferior to the profiles formed by casting due to the small molecular weight of the polymer, and the mechanical properties, heat resistance, and solvent resistance are not as good as those of the profiles formed by casting. Its advantage is high production efficiency, especially for pipes and other profiles that are difficult to manufacture by molds using the casting method. Extrusion molding can use a single-stage or double-stage exhaust extruder, and the screw aspect ratio is generally 20-25. Table 2 is the typical process conditions for extrusion molding.

Thermoforming

Thermoforming is the process of making organic glass plates or sheets into products of various sizes and shapes. The blanks cut into the required size are clamped on the mold frame, heated to soften them, and then pressurized to make them close to the mold surface to obtain the same shape as the surface. After cooling and shaping, the edges are trimmed to obtain the product. Pressurization can be done by vacuum drawing or by directly pressurizing the punch with the surface. Thermoforming temperature can refer to the recommended temperature range in Table 3. When using fast vacuum low-drawing to form products, it is advisable to use a temperature close to the lower limit. When forming deep-drawing products with complex shapes, it is advisable to use a temperature close to the upper limit. Normal temperature is generally used.

Engraving and cutting

It is mainly used for hollowing out and engraving of already formed acrylic or colored acrylic materials. Ordinary laser engraving and cutting machines can meet the engraving and hollowing needs of most acrylic products.

Main Applications

PMMA is a polymer obtained by the polymerization of acrylic acid resins, and the corresponding plastics are collectively known as polyacrylic plastics, among which polymethyl methacrylate is the most widely used. The abbreviation code of polymethyl methacrylate is PMMA, commonly known as organic glass, which is the best quality synthetic transparent material so far.

PMMA has the advantages of light weight, low price and easy molding. Its molding methods include casting, injection molding, machining, thermoforming, etc. Injection molding, in particular, can be mass-produced, with simple process and low cost. Therefore, its application is becoming more and more extensive, and it is widely used in instrument parts, automobile lights, optical lenses, transparent pipes, etc.

advantage

Acrylic is the best new material for making sanitary ware after ceramics. Compared with traditional ceramic materials, acrylic has the following advantages in addition to its incomparable high brightness: good toughness, not easy to break; strong repairability, as long as you use soft foam and toothpaste to wipe the sanitary ware clean; soft texture, no freezing cold feeling in winter; bright colors, can meet the individual pursuit of different tastes. Using acrylic to make basins, bathtubs, and toilets is not only exquisite in style and durable, but also environmentally friendly. Its radiation is almost the same as the radiation of human bones. Acrylic sanitary ware first appeared in the United States and has occupied more than 70% of the entire international market.

shortcoming

Since acrylic is difficult to produce and expensive, there are many low-quality and low-priced substitutes on the market. These substitutes are also called “acrylic”, but they are actually ordinary organic boards or composite boards (also called sandwich boards ). Ordinary organic boards are cast with ordinary organic glass cracking materials and pigments. They have low surface hardness, are easy to fade, and have poor polishing effect after grinding with fine sand. Composite boards only have a very thin layer of acrylic on the surface, and ABS plastic in the middle. They are easy to delaminate due to thermal expansion and contraction during use. True and false acrylic can be identified by the slight color difference and polishing effect of the cross section of the board.

Acrylic is widely used and can be used for test racks and patch trays.

Application Areas

1. Architectural applications: display windows, soundproof doors and windows, skylights, telephone booths, etc.

2. Advertising applications: light boxes, signs, signboards, display racks, etc.

3. Transportation applications: doors and windows of trains, cars and other vehicles, etc.

4. Medical applications: infant incubators, various surgical medical instruments; Civilian products : bathroom facilities, handicrafts, cosmetics, stents, aquariums, etc.

5. Industrial applications : instrument panels and protective covers, etc.

6. Lighting applications: fluorescent lamps, chandeliers, street lamp covers, etc.

Application areas: hotels, shopping malls, office buildings, clubs, villas, museums, medical treatment, education, catering, exhibitions, etc.

Application areas: suspended ceiling, integrated suspended ceiling, partitions, screens, sliding doors, transparent walls, hotel furniture, office furniture, bar counters, lighting, 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, bonding technology plays a vital role.

The bonding of plexiglass plates is mainly affected by two aspects: one is the applicability of the adhesive itself; the other is the bonding technique.

There are many adhesives on the markets, mainly of two types, one is two-component, such as all-purpose glue, epoxy resin; the other is one-component, such as CHCl3 ( chloroform ). Generally speaking, two-component adhesives achieve bonding through curing reaction, while one-component adhesives achieve bonding through the final volatilization of a solvent.

The characteristics of two-component adhesives are good bonding effect, no bubbles, no whitening, and high strength after bonding. The disadvantages are complex operation, high difficulty, long curing time, slow speed, and it is difficult to adapt to the requirements of mass production. The characteristics of general one-component adhesives are fast speed and can meet the process requirements of mass product production. The disadvantages are that the products after bonding are prone to bubbles, whitening, and poor weather resistance, which directly affects the appearance and product quality of organic glass products. Therefore, in the processing of organic glass products, how to choose a suitable adhesive to improve the taste and grade of organic glass products is a major problem that must be solved first in the bonding process.

The bonding technique is also very important. Here we briefly analyze the practical operation experience of several common bonding processes.

1. Docking: Place the two plexiglass plates to be docked horizontally on the operating platform, close them, and stick a piece of tape on the bottom, leaving a gap no wider than 0.3mm for applying adhesive. Use a syringe to evenly and slowly inject the adhesive into the gap from one side until it is completely filled. After it is completely cured, remove the tape.

2. Vertical bonding: Vertical bonding is the most widely used bonding technology and is widely used in the production of various organic glass IT electronic digital display products. First, the surface to be bonded should be wiped clean. It is best to use a template to achieve bonding so that the bonded object does not shake, which is conducive to improving the quality of bonding. For bonding of organic glass plates with a thickness of 3mm, thin metal wires can be padded and capillary action can be used to complete the bonding. The metal wires can be pulled out before the adhesive solidifies, or adhesive tape can be used and then the adhesive can be applied for bonding.

3. Bevel bonding: A 90-degree angle must be used for the bevel to prevent the bonded surface from shifting. The adhesive should be applied evenly and slowly. The template can only be removed after it is completely cured.

4. Plane bonding: Plane bonding is a special bonding method. First, clean the bonded surface, place it horizontally, and apply an appropriate amount of adhesive on it. Place one side of another plexiglass board diagonally on the plexiglass board to which the adhesive is applied, and then lower it evenly and slowly, and drive out the bubbles from one side to complete the bonding. The plexiglass adhesive can erode the surface of the plexiglass board and leave traces that are difficult to eliminate, so you can use a self-adhesive tape to protect the parts that do not need to be bonded. Grease, dust or pores will hinder the uniform application of the adhesive and leave bubbles. Using too little adhesive will bring in air when the adhesive shrinks. Direct blowing will make the edge of the bonding surface turn white due to the volatilization of the adhesive. Indoor humidity, temperature, etc. have a direct impact on the bonding of plexiglass boards.

Development

Acrylic, commonly known as specially treated organic glass, has a history of more than 100 years in the research and development of acrylic.

In 1872, the polymerizability of acrylic acid was discovered;

In 1880, the polymerizability of methacrylic acid was known;

In 1901, the synthesis of propylene polypropionate was completed;

In 1927, the aforementioned synthesis method was used to attempt industrial production;

In 1937, the industrial manufacturing of methyl esters was successfully developed, and large-scale production began.

During World War II, acrylic was first used in aircraft windshields and tank driver ‘s cab vision mirrors due to its excellent toughness and light transmittance.

The birth of the world’s first acrylic bathtub in 1948 marked a new milestone in the application of acrylic.

Latest Applications

Acrylic furniture

Acrylic furniture first appeared in Europe in the 1990s. It was not until the 21st century that acrylic furniture achieved rapid development. Acrylic furniture can be seen in high-end hotels and villas, interpreting the aesthetic classics in the field of home decoration.

Since the German company Rohm & Haas 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 handicraft designer had an idea when designing accessories. It would be perfect if acrylic could be used as the material for furniture. So he designed a coffee table using acrylic as the material and produced it three days later. Just as he had expected, the appearance was perfect, but the structural design was lacking. Thus, acrylic furniture was born.

Acrylic can also be used to make environmentally friendly buttons. Because of its high light transmittance, the buttons made are shiny. At the same time, because of its strong hardness and not easy to break, it can achieve the effect of long-term use.

Most of the furniture on the market is made of traditional materials such as wood, metal, glass, etc. Furniture made of these materials has problems such as high cost, environmental pollution, and complex process.