PMMA has the advantages of light weight, low price and easy molding. Its forming methods include casting, injection molding, machining, thermoforming and so on. Especially injection molding, which can be produced in large quantities, has simple process and low cost. Therefore, its application is increasingly extensive. At present, it is widely used in instrument parts, automobile lights, optical lenses, transparent pipes and so on. Evowe acrylic textured board
Ordinary plexiglass plate is cast with ordinary plexiglass cracking material and pigment, which has low surface hardness and is easy to fade, and the polishing effect is poor after polishing with fine sand. The composite board has only a thin layer of acrylic with ABS plastic in the middle, which is easy to be layered due to thermal expansion and cold contraction in use. True and false acrylic can be identified from the subtle color difference and polishing effect of the plate section.
Extrusion, thermoforming and other processes.
Casting molding
Casting is used to shape profiles, such as plexiglass plates and rods, that is, profiles are formed by bulk polymerization. After casting, the products need to be post-treated, and the post-treatment conditions are 60℃ for 2 hours and 120℃ for 2 hours.
Jet molding method
Pellets prepared by suspension polymerization are used for injection molding, and they are molded on ordinary plunger or screw injection molding machines. Table 1 is a typical process condition of PMMA injection molding.
Process parameters screw injection molding machine plunger injection molding machine
The temperature behind the barrel is 180-200℃
Intermediate 190-230
Qianmian180-210210-240
Nozzle temperature℃180-210210-240.
The mold temperature is 40-80℃
Injection pressure MPa 80- 120 80- 130
Holding pressure MPa 40-60 40-60
Screw speed rpm- 1 20-30
Injection molding products also need post-treatment to eliminate internal stress. The treatment is carried out in a hot air circulation drying box at 70-80℃. The processing time of acrylic rod depends on the thickness of the product, which usually takes about 4 hours.
Extrusion molding
Polymethyl methacrylate can also be extruded into plexiglass plates, rods, tubes, sheets, etc. Made of granular materials produced by suspension polymerization. However, the profile prepared in this way, especially the plate, is not as good as the profile formed by casting because of the low molecular weight of the polymer, and its advantage is high production efficiency, especially for the molds such as pipes used by casting. A contour that is difficult to manufacture. Extrusion molding can adopt single-stage or two-stage exhaust extruder, and the length-diameter ratio of screw is generally 20-25. Table 2 shows the typical process conditions of extrusion molding.
processing parameter
stalloy
Screw compression ratio 2 2
The temperature at the back of the barrel is150-180150-180.
Middle 170-200 170-200
Front 170-230 170-200
Extrusion pressure MPa 2.8- 12.4 0.7-3.4
The inlet temperature is 50-80℃ and 50-80℃.
Mold temperature℃180-200170-190.
Heating forming
Thermoforming is the process of making plexiglass plates or sheets into products of various sizes and shapes. Clamping the blank cut to the required size on the die frame, heating it to soften it, then pressing it into the same shape as the surface of the die, and cooling it to get the product. Pressing can be done by vacuum stretching or directly pressing the punch with the die surface. The hot forming temperature can refer to the recommended temperature range in Table 3. When using rapid vacuum low-drawing molding products, the temperature close to the lower limit should be used, and the temperature close to the upper limit should be used for deep-drawing products with complex shapes, generally at room temperature.
Carving and cutting
Mainly for the molding of acrylic or color acrylic materials for hollow carving. Ordinary laser engraving and cutting machine can meet the engraving and hollowing requirements of most acrylic products. [4] Acrylic handicrafts (3 pieces)
Product model JQ 1390
Laser power 100W (optional)
Laser CO2 sealed glass tube laser, water cooled, 10.6um.
The effective width is 1300mm×900mm.
Cold water cooling CW3000
The engraving scanning speed is 0-60000mm/min.
The maximum moving speed is 5 mm/s.
Cutting speed is 0- 1000 mm/min.
Laser energy control 1- 100% software setting
The minimum formed Chinese character is 2.0mm×2.0mm English1.0mm×1.0mm.
The maximum scanning accuracy is 2500DPI.
Supported graphics formats DST, PLT, BMP, DXF, artificial intelligence.
Support software CORELDRAW, PHOTOSHOP, AUTOCAD, all kinds of clothing CAD software.
Color separation and cutting are
Edit the characteristics of this paragraph
1. Hardness:
Hardness is one of the parameters that can best reflect the production process and technology of cast acrylic board, and it is an important link of quality control. The hard acrylic lampshade can reflect the purity of PMMA, the weather resistance and high temperature resistance of the plate. Hardness directly affects whether the plate will shrink and bend during processing and whether the surface will crack. Hardness is one of the hard indexes to judge the quality of acrylic board, and the average Dallow hardness is about 89 degrees.
2. Tolerance of acrylic thickness:
Acrylic tolerance exists in the thickness of acrylic plate, so the control of acrylic tolerance is an important embodiment of quality management and production technology. The production of acrylic has the international ISO7823 standard.
Tolerance requirements of pouring plate: tolerance = (0.4+0. 1 x thickness)
Tolerance requirements of extruded board: tolerance = 3 mm thickness: 5%
3. Transparency/whiteness:
Strict raw material selection, advanced formula follow-up and modern production technology ensure the excellent transparency and pure whiteness of the plate. After flame polishing, it is crystal clear.
Edit this paragraph operation method
The nature of acrylic is physical and mechanical, showing a strong dependence on temperature;
Effect of (1) temperature on the tensile strength and tensile elastic modulus of acrylic fiber: With the increase of temperature, the tensile strength and tensile elastic modulus decrease approximately linearly, because with the increase of temperature, the fluidity of polymer segments increases, and gradually changes from glassy state to high elastic state and viscous state, showing an increase in flexibility and a decrease in strength and elastic modulus. Acrylic products (20 sheets)
(2) Influence of temperature on the impact strength of acrylic with different thickness: Temperature has similar influence on the impact properties of acrylic. With the increase of temperature, the movement of plexiglass molecular segments is strengthened, which shows the increase of flexibility and impact strength.
(3) Effect of temperature on the elongation of acrylic: With the increase of temperature, the elongation at break of PMMA increases gradually when brittle fracture occurs, reaching 5.6% at 60℃. When the temperature exceeds a certain temperature, plexiglass begins to soften and yield failure occurs during the stretching process. Relationship between temperature and elongation at break and yield of PMMA.
(4) Influence of temperature and other factors on the hardness of acrylic: The hardness of plexiglass decreases with the increase of temperature. In addition, the greater the load value, the lower the measured hardness value. In a certain range, the greater the thickness of plexiglass, the higher the hardness value measured. However, when the thickness increases to a certain extent, the measured hardness value will not be significantly improved.
(5) Influence of temperature on Poisson's ratio of acrylic: Temperature also has a certain influence on Poisson's ratio of plexiglass. The higher the temperature, the greater the Poisson's ratio and the more products formed by hot bending. [5]
Edit the mechanical properties of this section.
Poly (methyl methacrylate) (PMMA) has good comprehensive mechanical properties and ranks among the best in general plastics. Its tensile, bending and compressive strength is higher than that of polyolefin, polystyrene and PVC, and its impact toughness is poor, but it is also slightly better than that of polystyrene. The mechanical properties such as tensile strength, bending strength and compressive strength of the cast bulk polymerized polymethylmethacrylate sheet (such as plexiglass for aviation) are high, which can reach the level of engineering plastics such as polyamide and polycarbonate.
Generally speaking, the tensile strength of PMMA 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 the mechanical properties are basically hard, brittle and plastic, and it has notch sensitivity and is easy to crack under stress, but the fracture surface is not as sharp and uneven as polystyrene and ordinary inorganic glass. 40℃ is the second-order transition temperature, which is equivalent to the temperature at which the side methyl group begins to move. When the temperature exceeds 40℃, the toughness and ductility of the material are improved. Polymethyl methacrylate has low surface hardness and is easy to scratch.
The strength of polymethyl methacrylate is related to the stress action time, and decreases with the increase of action time. After tensile orientation, the mechanical properties of PMMA (oriented PMMA) are obviously improved, and the notch sensitivity is also improved.
The heat resistance of polymethyl methacrylate is not high. Although its glass transition temperature reaches 104℃, the maximum continuous use temperature varies between 65℃ and 95℃ according to different working conditions. The thermal deformation temperature is about 96℃( 1. 18MPa), and the Vicat softening temperature is about 1 13℃. The heat resistance can be improved by copolymerization of monomer with propylene methacrylate or ethylene glycol acrylate. The cold resistance of PMMA is also poor, and the brittle temperature is about 9.2℃. The thermal stability of PMMA is moderate, better than PVC and POM, but not as good as polyolefin and polystyrene. Its thermal decomposition temperature is slightly higher than 270℃, and its flowing temperature is about 65438 060℃, so it still has a wide melting processing temperature range.
The thermal conductivity and specific heat capacity of polymethyl methacrylate are at a medium level in plastics, which are 0. 19W/CM respectively. K and 1464J/Kg. K respectively.
Electrical property
The electrical properties of polymethyl methacrylate (PMMA) are lower than those of nonpolar plastics such as polyolefin and polystyrene, because it contains polar methyl groups on one side of the main chain. The polarity of 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 whole acrylic plastic have excellent arc resistance, and under the action of arc, there will be no carbonized conductive path and arc trajectory on the surface. 20℃ is the second-order transition temperature, which corresponds to the temperature at which the pendant methyl ester groups begin to move. Below 20℃, the side methyl ester group is frozen, and above 20℃, the electrical properties of the material will be improved.
solvent resistance
Polymethyl methacrylate can resist dilute inorganic acid, but concentrated inorganic acid can corrode it, it can resist alkali, but warm sodium hydroxide and potassium hydroxide can corrode it, it can resist salt and grease, aliphatic hydrocarbon, insoluble in water, methanol, glycerol and so on. However, it can absorb stress cracking caused by alcohol expansion and is intolerant 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 and so on. , can also be dissolved with vinyl acetate and acetone.
Polymethyl methacrylate has good resistance to gases such as ozone and sulfur dioxide.
weather ability
Polymethyl methacrylate (PMMA) has excellent atmospheric aging resistance. After four years of natural aging test, its weight change, tensile strength and light transmittance decreased slightly, its color turned yellow slightly, its crack resistance decreased obviously, its impact strength increased slightly, and other physical properties remained almost unchanged.
combustibility
Polymethyl methacrylate is easy to burn, and its limiting oxygen index is only 17.3. [6]
Edit the bonding method of this paragraph.
Adhesion of acrylic products is a key process in acrylic processing. How to show the clear and transparent characteristics of plexiglass, reflect the sense of value of acrylic alcohol and tobacco packaging handicrafts, and maximize the grade and taste of acrylic handicrafts, bonding technology plays a decisive role.
The adhesion of plexiglass is mainly affected by two aspects: one is the applicability of the adhesive itself; The second is the skill of bonding.
At present, there are many adhesives on the market at home and abroad, mainly two kinds, one is two-component, such as all-purpose adhesive and epoxy resin; There are also single components, such as CCl3 (chloroform). Generally speaking, two-component adhesives are bonded by curing reaction, and one-component adhesives are bonded by final evaporation of solvent.
The two-component adhesive has the characteristics of good bonding effect, no bubbles, no whitening and high strength after bonding. The disadvantages are complicated operation, great difficulty, long curing time and slow speed, which are difficult to meet the requirements of mass production. The general one-component adhesive is characterized by high speed, which can meet the technological requirements of mass production. However, the disadvantage is that the bonded products are easy to foam, whiten and have poor weather resistance, which directly affects the external beauty and product quality of plexiglass products. Therefore, in the processing of plexiglass products, how to choose the appropriate adhesive and 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 important. Here is a brief analysis of their practical experience in several common bonding processes.
1. Butt-in: Put two plexiglass plates to be butted horizontally on the operating platform, close them, and stick adhesive tape on the bottom, leaving a gap no more than 0.3 mm wide for adhesive application. Inject the adhesive evenly and slowly into the gap from one side with a syringe until it is completely filled, and remove the adhesive tape after it is completely cured. [7]
2. Facade bonding: Facade bonding is the most widely used bonding technology, which is widely used to make various plexiglass IT electronic digital display shelf products. First, the surface to be bonded should be wiped clean. It is best to use the template to achieve bonding, so that the bonded object will not shake, which is conducive to improving the bonding quality. Adhesive thickness of 3mm plexiglass plate, can insert thin metal wire, through capillary action to complete the bonding, can pull out the metal wire before the adhesive curing, also can use adhesive tape and then apply adhesive. [7]
3. Bevel bonding: 90-degree angle profile model must be used for bonding bevel to prevent the displacement of bonding surface. The adhesive should be applied evenly and slowly. After it is completely cured, the replica mold can be removed. [7]
4. Surface bonding: Plane bonding is a special bonding method. First, clean the adhered surface, place it horizontally, and inject an appropriate amount of adhesive on it. One side of another plexiglass plate is inclined to contact the plexiglass plate coated with adhesive, and then it is evenly and slowly put down to drive out bubbles from one side to complete bonding. The adhesive of plexiglass will corrode the surface of plexiglass and leave indelible marks. Therefore, adhesive tape can be used to protect the parts that do not need to be bonded. Grease, dust or air holes will hinder the uniform application of adhesive and leave bubbles. Excessive use of adhesive will bring in air when the adhesive shrinks. Direct blowing will make the edge of the bonding surface white because of the volatilization of glue. Indoor humidity and temperature have a direct impact on the adhesion of plexiglass. [7]