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Thermoplastic refers to polymer materials that can be repeatedly softened by heating and hardened by cooling within a certain temperature range. Thermoplastics usually have a higher molecular weight, no chemical bonds are formed between the molecular chains, and they can soften quickly when heated.
Unlike thermosetting materials, thermoplastics can soften or melt into any shape after heating, and the shape remains unchanged after cooling. This state can be repeated many times and always remains plastic. Most linear polymers are thermoplastic materials, which are easy to be formed by extrusion, injection or blow molding. Most of the plastics used in daily life belong to the category of thermoplastics. For example, polyethylene, polypropylene, polyvinyl chloride, polystyrene, polyoxymethylene, polycarbonate, polyamide, etc. are all thermoplastics.
Thermoplastics are the most widely used type of plastics, which are made of thermoplastic resin as the main component and various additives. Under certain temperature conditions, plastic can soften or melt into any shape, and the shape remains unchanged after cooling; this state can be repeated many times and always has plasticity, and this repetition is only a physical change. This plastic is called thermoplastic.
Polyethylene, polypropylene, polyvinyl chloride, polystyrene, polyoxymethylene, polycarbonate, polyamide, acrylic plastics, other polyolefins and their copolymers, polysulfone, polyphenylene ether, etc. are all thermoplastics.
Thermoplastics can be divided into general plastics, engineering plastics, special plastics, etc. according to performance characteristics, wide range of uses and universal molding technology.
The main characteristics of general plastics: wide range of uses, easy processing, and good comprehensive performance. For example, polyethylene (PE), polyvinyl chloride (PVC), polypropylene (PP), polystyrene (PS), and acrylonitrile-butadiene-styrene (ABS) are also commonly known as the "five major general plastics". The characteristics of engineering plastics and special plastics are: some structures and properties of polymers are particularly prominent, or the molding and processing technology is difficult, etc., and they are often used in professional engineering or special fields and occasions. The main engineering plastics are: nylon (Nylon), polycarbonate (PC), polyurethane (PU), polytetrafluoroethylene (Teflon, PTFE), polyethylene terephthalate (PET), etc., special plastics such as "synthetic heart valves" and "artificial joints" of the "medical polymer" category.
According to the aggregate structure and performance characteristics of copolymers, they can be divided into two categories: crystalline plastics and non-crystalline plastics. Non-crystalline plastics are also called amorphous plastics.
Different classification angles or methods can also be divided into different results.
The molecular weight of polymers in general thermoplastics can reach hundreds of thousands to millions, and the length of macromolecular chains can reach 10^-3mm. These macromolecules can be linear, such as LLDPE, HDPE; or branched, such as LDPE. The macromolecules are entangled with each other, arranged in disorder or relatively orderly, forming an "aggregate structure".
When the macromolecules are completely disordered, we call it amorphous thermoplastics. Such as PVC, PC, PMMA, etc. Its performance characteristics are: good transparency, low mechanical strength, good flexibility.
The structure with some macromolecules or macromolecules arranged evenly is called crystalline thermoplastics. Such as LLDPE, POM, nylon, etc., its performance characteristics are: poor transparency, high mechanical strength, low flexibility.
¡ª¡ªBecause the polymer molecular chain is very long, it is impossible to achieve complete crystallization by having the entire molecule enter the "crystallization zone" like low molecular substances. Therefore, "crystallization" is often used to describe the degree of crystallization (or the size of the crystallization area) of crystalline thermoplastics.
The characteristic temperature of amorphous thermoplastics is the glass transition temperature (Tg). When it is lower than Tg, the polymer exhibits "glass" characteristic properties, which is professionally called "glass state". At this time, the polymer has the function of use, but cannot be "plastic"; when it is higher than Tg, the polymer has high elasticity and certain plasticity characteristics, and loses the function of use, which is professionally called "high elastic state". After further heating, its elasticity is lost and it is completely plastic. Therefore, its maximum use temperature should be below Tg, and its minimum processing temperature should be above Tg.
The characteristic temperature of crystalline thermoplastics is the crystallization temperature (Tc). When it is lower than Tc, the polymer exhibits a hard texture, has the function of use, and cannot be "plastic" processed; when it is higher than Tc, the polymer is melted and plasticized, loses the function of use, and can be plastic processed.
Compared with crystalline thermoplastics, amorphous thermoplastics have three physical states, while the latter have no "high elastic state" and only two physical states. This is reflected in the processing technology as the former often uses a "gradual screw" and the latter uses a "mutated screw".
For crystalline thermoplastics, the area containing regularly arranged molecular chains is usually called the crystallization area. The crystallinity of many crystalline thermoplastics can be adjusted by controlling the cooling rate of the molding temperature. When the cooling rate is fast, the crystallization process is inhibited, and finally a product with better transparency is obtained, such as PET bottles, transparent PET sheets and transparent polypropylene sheets.
Thermoplastic vulcanizate, referred to as TPV, the Chinese abbreviation of thermoplastic vulcanizate is thermoplastic rubber, referred to as TPR, but this name is easily confused with other types of thermoplastic elastomers, because thermoplastic elastomers are usually also called thermoplastic rubber, especially styrene elastomers, at least in China it seems that "TPR" has become its proprietary name, when mentioning TPR, it refers to thermoplastic elastomers based on SBS, SEBS and other styrene elastomers, which is inseparable from the large consumption of styrene elastomers in the fields of civil and terminal consumer products.
If the name of thermoplastic vulcanizate is described in more detail, it should be thermoplastic dynamic vulcanizate. The word "dynamic" is added to more specifically explain the process of producing this thermoplastic vulcanizate - dynamic vulcanization. This process refers to vulcanizing rubber during the melt blending of rubber and thermoplastics. Of course, while the rubber is being vulcanized, it is also continuously mixed with thermoplastics. Therefore, the vulcanized rubber is distributed as a dispersed phase in the continuous phase of thermoplastics. Corresponding to it, thermoplastic static vulcanizate means that the rubber is first vulcanized by the traditional method, and then the vulcanized rubber is ground into powder by a grinding equipment, and finally blended with molten thermoplastics. In theory, this method can also produce TPV with excellent performance, but it is only in the laboratory stage.
TPV is mainly composed of two parts, one is plastic, as a continuous phase, and the other is rubber as a dispersed phase. Usually rubber needs to be matched with softening oil or plasticizer. Vulcanizers and some auxiliary additives are also indispensable. In addition, in order to reduce costs or improve certain performance, some inorganic fillers will be added.
Many plastics and rubbers can form TPV, but only a few blends have practical value after dynamic vulcanization. The commercial ones are PP/PE/EPDM, PP/NBR, PP/ACM, and PS/SEBS. In the book "Thermoplastic Elastomers" published by Chemical Industry Press, 99 rubber/plastic blends prepared from 11 rubbers and 9 plastics were reviewed. The study found that in order to obtain the best performance of rubber/thermoplastic plastic dynamic vulcanization blends, the following conditions must be met:
(1) The surface energy of the two polymers of plastic and rubber matches;
(2) The length of the rubber entanglement molecular chain is low;
(3) The crystallinity of the plastic is greater than 15%. When the polarity or surface energy difference between (PA66) plastic and rubber is relatively large, adding a suitable compatibilizer and then performing dynamic vulcanization can also obtain a blend with excellent performance.
1. Good elasticity and compression deformation resistance, environmental resistance and aging resistance are equivalent to EPDM rubber, and its oil and solvent resistance are comparable to general-purpose chloroprene rubber.
2. Wide application temperature range (¨C60¡ª150¡æ), wide application range of soft and hardness (25A¡ª54D), and the advantage of easy dyeing greatly improves the freedom of product design.
3. Excellent processing performance: It can be processed by thermoplastic processing methods such as injection and extrusion, which is efficient, simple and easy, without adding equipment, high fluidity and small shrinkage.
4. Green and environmentally friendly, recyclable, and no significant performance reduction after repeated use for six times, in line with EU environmental protection requirements.
5. Light specific gravity (0.90¡ª0.97), uniform appearance quality, high surface grade and good feel.
Based on the above performance characteristics, TPV has certain substitution advantages in comprehensive performance and comprehensive cost compared with traditional rubber materials, other TPE elastomers (including TPR\SBS, SEBS, TPU, etc.) materials or plastic materials such as PVC in a wide range of applications, thus providing new choices for product companies in product innovation, increasing product added value and improving competitiveness.
TPV is the abbreviation of Thermoplastic Vulcanizate, and its Chinese name is thermoplastic EPDM dynamic vulcanized elastomer or thermoplastic EPDM dynamic vulcanized rubber. It is a polymer elastomer material composed of highly vulcanized EPDM rubber EPDM particles dispersed in a continuous polypropylene PP phase. The physical properties and functions of TPV at room temperature are similar to those of thermosetting rubber, and at high temperatures, it exhibits the characteristics of thermoplastic plastics, and can be processed and formed quickly, economically and conveniently. TPV thermoplastic EPDM dynamically vulcanized elastomer/rubber disperses the vulcanized rubber material through dynamic vulcanization so that the EPDM is dispersed in the polypropylene PP plastic matrix in the form of particles less than 2 microns in size, combining the properties of rubber and plastic well to obtain a high-performance elastomer material with excellent comprehensive performance.
The main properties of TPV thermoplastic EPDM dynamic vulcanized elastomer/rubber:
1. TPV can be used in the temperature range of -60¡æ to 135¡æ, with a wide range of application temperature;
2. The hardness range of TPV is between 25A and 65D, which can meet a wide range of hardness requirements;
3. TPV has good weather resistance and excellent anti-aging, ozone resistance and UV resistance;
4. TPV does not require vulcanization when used, and can be directly processed and formed by injection, extrusion, calendering, blow molding, etc., which can shorten the processing process and reduce processing costs;
5. TPV's environmental resistance is similar to that of EPDM, and its oil and solvent resistance is similar to that of chloroprene rubber;
6. TPV is easy to weld, reusable, environmentally friendly and non-toxic.
The main features of TPV thermoplastic EPDM dynamic vulcanized elastomer/rubber:
1. Excellent anti-aging performance and good weather resistance and heat resistance;
2. Excellent resistance to permanent deformation;
3. Excellent tensile strength, high toughness and high resilience;
4. Excellent environmental protection performance and reusability;
5. Excellent electrical insulation performance;
6. Wide hardness range;
7. Wide operating temperature range;
8. Diversified colors, including fully transparent, translucent and light-colored series, easy to color and easy to process;
9. Can be co-injected or extruded with PP, PA, PC, ABS, PS, PBT, PET and other materials.
Application fields of TPV thermoplastic EPDM dynamic vulcanized elastomer/rubber:
Automotive industry
1. Automobile sealing strips and sealing series;
2. Automobile dust cover, fender, ventilation pipe, buffer, bellows, intake pipe, etc.;
3. Automobile high-voltage ignition wire. It can withstand 30-40KV voltage and meet UL94V0 flame retardant requirements.
Consumer goods
1. Parts of gardening equipment such as hand tools, power tools, and lawn mowers;
2. Gaskets and parts used in household appliances;
3. Handles of scissors, toothbrushes, fishing rods, sports equipment, kitchen supplies and other products;
4. Various packaging for cosmetics, beverages, food, bathroom supplies, medical appliances and other products;
5. Soft parts of various wheels, buzzers, pipes, belts and other joints.
6. Needle plugs, bottle plugs, straws, sleeves and other soft rubber parts;
7. Flashlight shells, children's toys, toy tires, golf bags, various grips, etc.
Electronic appliances
1. Various headphone cable sheaths, headphone cable connectors;
2. Mining cables, CNC coaxial cables, ordinary and high-end wire and cable insulation layers and sheaths;
3. Power sockets, plugs and sheaths, etc.;
4. Batteries, wireless phone shells and electronic transformer shells and sheaths;
5. Insulation layers and sheaths of power cables for ships, mines, drilling platforms, nuclear power plants and other facilities.
Transportation equipment
1. Road and bridge expansion joints;
2. Road safety facilities, buffer and anti-collision components;
3. Container sealing strips.
Building materials
1. Power component sealing strips
2. Building expansion joints and sealing strips
3. Water supply and drainage pipe seals, water irrigation system control valves, etc.
Thermoplastic Elastomer (TPE), also known as Thermoplastic Rubber (TPR), is a material that has the characteristics of both rubber and thermoplastic plastics. Thermoplastic elastomers have a variety of possible structures. The most fundamental one is that there must be at least two mutually dispersed polymer phases. At normal use temperature, one phase is a fluid (making the temperature higher than its Tg-glass transition temperature), and the other phase is a solid (making the temperature lower than its Tg or equal to Tg), and there is interaction between the two phases. That is, a polymer material that shows rubber elasticity at room temperature and can be plasticized and formed at high temperature, has mechanical properties and use properties similar to rubber, and can be processed and recycled according to thermoplastic plastics. It builds a bridge between plastics and rubber. Therefore, thermoplastic elastomers can be processed into rubber products as quickly, effectively and economically as thermoplastic plastics. In terms of processing, it is a plastic; in terms of properties, it is a rubber. Thermoplastic elastomers have many advantages over thermosetting rubbers. There is no unified name for thermoplastic elastomers. It is customary to use the English abbreviations TPR to represent thermoplastic rubber and TPE to represent thermoplastic elastomer. Both are used in relevant materials and books. For the sake of uniformity, they are all called TPE or thermoplastic elastomer. In China, thermoplastic styrene-butadiene block copolymer is called SBS (styrene-butadiene-styrenblockcopolymer), thermoplastic isoprene-styrene block copolymer is called SIS (styrene-isopreneblockcopolymer), and saturated SBS is called SEBS, which is the abbreviation of Styrene-ethylene-butylene-styreneblockcopolymer, that is, styrene-ethylene-butylene-styrene block copolymer. Other types of thermoplastic elastomers are called by the manufacturer's trade name. China also uses the code SBS, which stands for thermoplastic styrene-butadiene-styrene block copolymer, commonly known as thermoplastic styrene-butadiene rubber. Elastomer is a man-made thermoplastic elastomer with unique properties and has a very wide range of uses. Its excellent product applicability comes from the adjustability and controllability of its special molecular structure, thus showing the following excellent properties:
Excellent physical properties: good appearance texture, mild touch, easy to color, uniform color tone, stable; adjustable physical properties, providing a wide range of product design; mechanical properties comparable to vulcanized rubber, but no vulcanization cross-linking is required; wide hardness range, adjustable from SHORE-A0 degree to SHORE-D70 degree; excellent tensile resistance, tensile strength up to more than ten MPa, elongation at break up to more than ten times; long-term temperature resistance can exceed 70¡æ, good low temperature environment performance, still maintain good flexibility at -60¡æ; good electrical insulation and voltage resistance characteristics. It has outstanding anti-slip performance, wear resistance and weather resistance.
Excellent chemical properties: resistant to general chemicals (water, acid, alkali, alcohol solvents); can be processed in solvents, can be immersed in solvents or oils for a short period of time; non-toxic; good resistance to ultraviolet radiation and oxidation, can be used in outdoor environments; good bonding performance, using appropriate adhesive technology can directly and firmly bond with the surface of genuine leather, synthetic leather or artificial leather.
Production and processing advantages: It has the characteristics of traditional vulcanized rubber without vulcanization, saving auxiliary raw materials such as vulcanizers and accelerators; it is suitable for various processes such as injection molding, die-casting, hot melt and dissolving coating; the edge materials, residual materials and waste materials can be completely recycled and reused without changing the performance, reducing waste; simplifying the processing technology, saving processing energy consumption and equipment resources, short processing cycle, reducing production costs and improving work efficiency; simple processing equipment and process, saving production space, reducing the rate of unqualified products; the product is non-toxic, has no irritating odor, and does not harm the environment, equipment and personnel; the material can be reused repeatedly, and the edge waste can be recycled. It can be said that there is no waste in production; there are fewer processing aids and compounding agents, which can save the cost of product quality control and testing; the product has high dimensional accuracy and easier quality control; the material specific gravity is low and adjustable; it can be directly mixed with PP, ABS and other plastics to make special plastic alloys.
The elastomer has excellent physical and chemical properties and is easy to process. At the same time, the product also has the environmental advantages of being non-toxic, pollution-free and recyclable for secondary processing. Therefore, it is widely used in many industrial fields, such as toys, sports equipment, shoes, stationery, hardware, power tools, communications, electronic products, food and beverage packaging, household appliances, kitchen supplies, medical equipment, automobiles, construction engineering, wires and cables, etc. What is more valuable is that it is a high-quality material that leads the design and market orientation of new products. Its soft texture, adjustable physical properties, hardness, suitability for a variety of processing techniques and environmental advantages provide a huge space for product designers to play. This undoubtedly provides great help for you to innovate products, increase value and lead market trends.
Plastics can be divided into two categories: thermosetting and thermoplastic. The former cannot be reshaped and used, while the latter can be repeatedly produced.
Thermoplastic
It softens and flows when heated, and hardens when cooled. This process is reversible and can be repeated. Polyethylene, polypropylene, polyvinyl chloride, polystyrene, polyoxymethylene, polycarbonate, polyamide, acrylic plastics, other polyolefins and their copolymers, polysulfone, polyphenylene ether, chlorinated polyether, etc. are all thermoplastics. The resin molecular chains in thermoplastics are all linear or branched structures. There are no chemical bonds between the molecular chains. They soften and flow when heated. The process of cooling and hardening is a physical change.
Thermosetting plastics
It can soften and flow when heated for the first time. When heated to a certain temperature, a chemical reaction occurs, cross-linking and solidification occurs, and it hardens. This change is irreversible. After that, it can no longer soften and flow when heated again. It is precisely with the help of this characteristic that molding is carried out. The plasticization flow during the first heating is used to fill the mold cavity under pressure, and then solidify into a product of a certain shape and size. This material is called a thermosetting plastic.
The resin of thermosetting plastics is linear or branched before solidification. After solidification, chemical bonds are formed between the molecular chains to form a three-dimensional network structure. Not only can it no longer melt, but it can also not be dissolved in solvents. Phenolic, fluorine aldehyde, melamine formaldehyde, epoxy, unsaturated polyester, silicone and other plastics are all thermosetting plastics.
Mainly used for heat insulation, wear resistance, insulation, high voltage resistance and other harsh environments, most of the plastics are thermosetting plastics, the most commonly used should be frying pan handles and high and low voltage electrical appliances.
The factors that affect the shrinkage of thermoplastic molding are:
1. Plastic variety During the molding process of thermoplastics, due to the volume change caused by crystallization, strong internal stress, large residual stress frozen in the plastic parts, strong molecular orientation and other factors, the shrinkage rate is larger than that of thermosetting plastics, the shrinkage rate range is wide, and the directionality is obvious. In addition, the shrinkage after molding, annealing or humidity treatment is generally larger than that of thermosetting plastics.
2. Characteristics of plastic parts During molding, the molten material contacts the surface of the cavity and the outer layer is immediately cooled to form a low-density solid shell. Due to the poor thermal conductivity of plastics, the inner layer of the plastic part cools slowly and forms a high-density solid layer with large shrinkage. Therefore, the thicker the wall, the slower the cooling, and the thicker the high-density layer, the larger the shrinkage. In addition, the presence or absence of inserts and the layout and number of inserts directly affect the direction of material flow, density distribution, shrinkage resistance, etc., so the characteristics of the plastic part have a greater impact on the shrinkage size and directionality.
3. The form, size, and distribution of the feed port directly affect the direction of material flow, density distribution, pressure holding and shrinkage compensation, and molding time. Direct feed ports and feed ports with large cross-sections (especially thicker cross-sections) have small shrinkage but large directionality, and feed ports with short width and length have small directionality. Those close to the feed port or parallel to the material flow direction have large shrinkage.
4. Molding conditions The mold temperature is high, the molten material cools slowly, has high density, and shrinks greatly. Especially for crystallized materials, the shrinkage is greater due to the high degree of crystallinity and large volume changes. The mold temperature distribution is also related to the internal and external cooling and density uniformity of the plastic part, which directly affects the size and directionality of the shrinkage of the part. In addition, the holding pressure and time also have a great influence on the shrinkage. The higher the pressure and the longer the time, the smaller the shrinkage but the greater the directionality. The higher the injection pressure, the smaller the viscosity difference of the molten material, the smaller the interlayer shear stress, and the greater the elastic rebound after demolding, so the shrinkage can also be reduced appropriately. The higher the material temperature, the greater the shrinkage, but the less directionality. Therefore, adjusting the mold temperature, pressure, injection speed, cooling time and other factors during molding can also appropriately change the shrinkage of the plastic part.
When designing the mold, according to the shrinkage range of various plastics, the wall thickness and shape of the plastic part, the size and distribution of the feed port, the shrinkage rate of each part of the plastic part is determined based on experience, and then the cavity size is calculated.
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