Chapter 3 Plastics, Mold Materials and Management 3.1 Plastics 3.1.1 Condition for Injection and Molding The large molecular structure of polymer and the features of molecular thermodynamic movement have determined that polymer has such states of aggregation as the glassy state, highly-elastic state as well as viscous flow state etc. The transformation of aggregative state is nfluenced by chemical composition, molecular structure, the stress applied whereon and the environment temperature, and is mainly related with temperature when the composition of Membrane blow molding Calendering forming Extrusion forming Processing and molding temperature njection molding 加工与型方法的适应 Flexibility of processing (或Tm)7 and molding 熔纺 Vacuum and pressure molding Heat stretch of membrane and fiber Melting spinning 延成型 空吹塑成型 Deformation rate Cold stretch of the membrane and 空和压力成型 fiber 膜和纤维热拉伸 薄膜和纤维冷拉伸 Hollow molding Glassy state 玻璃态尚弹态黏 固体移皮状弹性体数娃 Hard solid Highly-elastic state Rubber-elastomer viscous liquid Viscous flow state Fig 3-1: relationship between polymer state and plastic molding As indicated in the Fig 3-1, when the temperature is below the vitrification temperature(T.), the polymer is under glassy state, which is hard solid, wherein energy from the molecular thermodynamic movement is low, the elastic modulus is large, and the deformation is reversible Under such aggregative state, it is not suitable for molding with large-scale deformation. When the temperature is above the vitrification temperature(T,), the plastics will become softer, and
Chapter 3 Plastics, Mold Materials and Management 3.1 Plastics 3.1.1 Condition for Injection and Molding The large molecular structure of polymer and the features of molecular thermodynamic movement have determined that polymer has such states of aggregation as the glassy state, highly-elastic state as well as viscous flow state etc. The transformation of aggregative state is influenced by chemical composition, molecular structure, the stress applied whereon and the environment temperature, and is mainly related with temperature when the composition of polymer is certain. Fig.3-1: relationship between polymer state and plastic molding As indicated in the Fig.3-1, when the temperature is below the vitrification temperature (Tg ), the polymer is under glassy state, which is hard solid, wherein energy from the molecular thermodynamic movement is low, the elastic modulus is large, and the deformation is reversible. Under such aggregative state, it is not suitable for molding with large-scale deformation. When the temperature is above the vitrification temperature (Tg ), the plastics will become softer, and Hollow molding Hard solid Highly-elastic state Rubber-elastomer Viscous liquid Viscous flow state Processing and molding temperature Deformation rate Heat stretch of membrane and fiber Vacuum and pressure molding Cold stretch of the membrane and fiber Extrusion forming Injection molding Membrane blow molding Calendering forming Glassy state Flexibility of processing and molding Melting spinning
therefore, the vitrification temperature(Tg)is the maximum temperature that can be used for plastics. The lower limit temperature applied to plastics is called the brittle temperature, below which the plastics will easily get cracked and damaged under stress When the temperature is between vitrification temperature and viscous flow temperature (T), the polymer shall be under highly-elastic state, wherein energy of the molecular thermodynamic movement increases and the elastic modulus greatly reduces. For amorphous polymer, certain materials can be molded through pressurization, bending, hollow molding or vacuum molding For crystalline polymer, stretch and drawing of the membrane and fiber can be made between vitrification temperature and melting point (T-Tm) When the temperature is above viscous flow temperature(or melting point ) viscous flow will happen to the polymer under external force; calendering molding, certain extrusion and blow molding are usually adopted when the temperature is within a range slightly higher than the viscous flow temperature. When at a temperature much higher than the viscous flow temperature flow deformation of the fusant will occur under small external force. The deformation herein is mainly nonreversible viscous deformation which can be permanently preserved upon cooling of the fusant. Hence, this range of temperature is usually used for injection molding. Excessively high temperature, however, will greatly reduce the viscosity of polymer, thereby bringing difficulty to molding and worsening the quality of products. Moreover, when the temperature is higher than the decomposition temperature (Td), decomposition and metamorphism of the polymer will occur. Moldability refers to the plastics'ability of deforming under the action of temperature and pressure as well as their molding ability in the mold cavity. Plastics with moldability can be made into plastic products of various shapes through such molding methods as injection, mold pressing and extrusion etc. The moldability mainly depends on such factors as the rheology, thermal property, physical mechanical property of materials, the chemical property of thermoset plastics, technical factors(such as temperature, pressure and molding period etc) as well as the structural dimension of molds. As indicated in the figure is the relationship between moldability temperature and pressure. Exceedingly high temperature will produce sound fluidity yet will also result in high shrinkage and even decomposition; excessively low temperature will lead to low fluidity and formability, and the performance of products may be reduced; excessively high pressure will cause overflow and increase the internal stress of products; excessively low pressure will instead lead to insufficient filling in the mold and subsequent material shortage. The area formed by the four curves in the figure is the optimal molding area
therefore, the vitrification temperature (Tg ) is the maximum temperature that can be used for plastics. The lower limit temperature applied to plastics is called the brittle temperature, below which the plastics will easily get cracked and damaged under stress. When the temperature is between vitrification temperature and viscous flow temperature ( Tf ), the polymer shall be under highly-elastic state, wherein energy of the molecular thermodynamic movement increases and the elastic modulus greatly reduces. For amorphous polymer, certain materials can be molded through pressurization, bending, hollow molding or vacuum molding. For crystalline polymer, stretch and drawing of the membrane and fiber can be made between vitrification temperature and melting point （Tf ~ Tm ）. When the temperature is above viscous flow temperature (or melting point), viscous flow will happen to the polymer under external force; calendering molding, certain extrusion and blow molding are usually adopted when the temperature is within a range slightly higher than the viscous flow temperature. When at a temperature much higher than the viscous flow temperature, flow deformation of the fusant will occur under small external force. The deformation herein is mainly nonreversible viscous deformation which can be permanently preserved upon cooling of the fusant. Hence, this range of temperature is usually used for injection molding. Excessively high temperature, however, will greatly reduce the viscosity of polymer, thereby bringing difficulty to molding and worsening the quality of products. Moreover, when the temperature is higher than the decomposition temperature (Td ), decomposition and metamorphism of the polymer will occur. Moldability refers to the plastics’ ability of deforming under the action of temperature and pressure as well as their molding ability in the mold cavity. Plastics with moldability can be made into plastic products of various shapes through such molding methods as injection, mold pressing and extrusion etc. The moldability mainly depends on such factors as the rheology, thermal property, physical mechanical property of materials, the chemical property of thermoset plastics, technical factors (such as temperature, pressure and molding period etc) as well as the structural dimension of molds. As indicated in the figure is the relationship between moldability, temperature and pressure. Exceedingly high temperature will produce sound fluidity yet will also result in high shrinkage and even decomposition; excessively low temperature will lead to low fluidity and formability, and the performance of products may be reduced; excessively high pressure will cause overflow and increase the internal stress of products; excessively low pressure will instead lead to insufficient filling in the mold and subsequent material shortage. The area formed by the four curves in the figure is the optimal molding area
Viscoelastic limit Overflow and distortion 黏弹性极限 Decomposition line Pressure Material overflow line Material shortage line 缺料丝 Difficulty to mold 模不足 Temperature Insufficient filling in the mold Fig 3-2: relationship between plastic molding pressure and temperature A-molding area: abad line of surface: b-material overflow line c-Decomposition line: d--Material shortage line 3.1.2 Definition and Classification of Plastics According to the chemical property, plastics roughly fall into such two types lastics and thermoplastic plastics 1. Thermoplastic Plastics 1)Polyvinyl chloride(Pvc)resin 2) Polystyrene(PS)resin 3)ABS resin and As resin 4)Acrylic resins(PMMA) 5)Polyethylene(PE) 6) Polypropylene(PP) 7)Flurocarbon resins 8)Polyamide resins(nylon, PA) 9)Acetal resins(POM 10)Polycarbonate resin(PC) 1) Cellulose plastics 2. Thermoset plastics 1)Phenol resins(bakelite) 2)Urea resins. 3)Melamine resins 4)Unsaturated polyester resins(FRP) 5)Epoxy resins 6) Polyurethanes resin 3.1.3 Properties of Thermoplastic Plastics 1. Polyvinyl Chloride(Pvc) resin The PVC monomer arises from the reaction between ethyne and hydrochloric acid, and the monomer thereafter is aggregated into pvc through various methods. pvc is devoid of
Fig.3-2: relationship between plastic molding pressure and temperature A—molding area；a—bad line of surface；b—material overflow line； c—Decomposition line；d—Material shortage line 3.1.2 Definition and Classification of Plastics According to the chemical property, plastics roughly fall into such two types as thermoset plastics and thermoplastic plastics. 1. Thermoplastic Plastics 1) Polyvinyl chloride (PVC) resin. 2) Polystyrene (PS) resin. 3) ABS resin and AS resin . 4) Acrylic resins (PMMA). 5) Polyethylene (PE). 6) Polypropylene (PP). 7) Flurocarbon resins. 8) Polyamide resins (nylon, PA). 9) Acetal resins (POM). 10) Polycarbonate resin (PC). 11) Cellulose plastics. 2. Thermoset Plastics 1) Phenol resins (bakelite) 2) Urea resins. 3) Melamine resins. 4) Unsaturated polyester resins (FRP). 5) Epoxy resins. 6) Polyurethanes resin. 3.1.3 Properties of Thermoplastic Plastics 1. Polyvinyl Chloride (PVC) Resin • The PVC monomer arises from the reaction between ethyne and hydrochloric acid, and the monomer thereafter is aggregated into PVC through various methods. PVC is devoid of Temperature Difficulty to mold Pressure Viscoelastic limit Overflow and distortion Material overflow line Material shortage line Decomposition line Insufficient filling in the mold
stability against heat and light, and therefore, stabilizers shall be added therein to avoid discoloration or decomposition upon the materials' being processed into finished products. Various stabilizers are available, including metal soap and organic tin compounds and they fall into such types as transparent, opaque, soft and hard ones. The processing temperature of soft PVC is 70C-100 C. Hard PVC requires less time for processing, yet the temperature therewith must rise to approximately 150C. Due to its low fluidity during fusion, hard PVC tends to be more difficult to be injected and molded than polystyrene(PS). However, even without intensifier, hard PvC still boasts a pretty high mechanical intensity; it is also sound in electric insulation, acid resistance kali resistance as well as water resistance; moreover, it is transparent and can be colored freely and processed effectively. Soft PVC is endowed with sound plasticity and hence is inferior to hard PVC in the aforementioned properties, yet it can be made into soft membranes or thin plates. The softening temperature whereof is approximately 80C and the decomposition temperature is round273℃ PVC, with such shortcoming as weak heat resistance capacity, will soften promptly under the temperature of 65C-80C and can decompose easily under high temperature PVC can be used to make tablecloth, packing membranes, vehicle curtains, briefcases handbags and chemical shoes etc. Its glue film can absorb ultraviolet radiation and therefore embodies sound thermal insulation property. Hard PVC can be applied to such fields watercourse piping, chemical plant piping, building materials, signboards, telephones, electric parts as well as drug-proof apparatus etc 2. Polystyrene(PS)Resin The composite ethylene gas made from benzene(adopted from coal tar or petroleum) and ethylene gas, is dehydrogenated by metal oxide catalyzer heated to 600C into styrene monomer which is then catalyzed and aggregated into polystyrene resin through such catalyzer as inorganic or organic peroxide The polystyrene resin in the market is colorless and transparent, hard and slightly crispy, with an average molecular weight of 70 thousand -100 thousand. It is excellent in water resistance and electric insulation and can fight against erosion from strong acid or alkali, yet it is devoid of resistance against organic solvent and oil and is weak in heat resistance. Another important feature of polystyrene resin is that it is endowed with sound thermal stability and fluidity in fusing resin, and thereby can be molded very well. Though a bit crispy, the PS can be colored freely. High impact polystyrene(HIPS)resin is obtained by adding butadiene and styrene copolymerized rubber in styrene resin, wherein the two substances are in several hierarchies respectively; in addition, ultraviolet radiation absorbent or antioxidant can be added therein to improve lightfastness and also fiberglass is sometimes added into the basal material to increase PS caters to the transparency and color tone of modern visual beauty. It can be extensivel applied to the manufacturing of table articles like bread boxes and beef oil cans, commodity containers, toys, fruit dishes, toothbrushes, handles of brushes, soapboxes as well as flavoring containers etc 3. ABS Resin and As resin The aggregation of styrene monomer, acrylonitrile monomer and butadiene rubber can produce a polymer(ABS)constituted by acrylonitrile(A), butadiene rubber(B)and styrene(s)in
stability against heat and light, and therefore, stabilizers shall be added therein to avoid discoloration or decomposition upon the materials’ being processed into finished products. Various stabilizers are available, including metal soap and organic tin compounds and they fall into such types as transparent, opaque, soft and hard ones. The processing temperature of soft PVC is 70℃-100 ℃. Hard PVC requires less time for processing, yet the temperature therewith must rise to approximately 150℃. Due to its low fluidity during fusion, hard PVC tends to be more difficult to be injected and molded than polystyrene (PS). However, even without intensifier, hard PVC still boasts a pretty high mechanical intensity; it is also sound in electric insulation, acid resistance, alkali resistance as well as water resistance; moreover, it is transparent and can be colored freely and processed effectively. Soft PVC is endowed with sound plasticity and hence is inferior to hard PVC in the aforementioned properties, yet it can be made into soft membranes or thin plates. The softening temperature whereof is approximately 80 and ℃ the decomposition temperature is around 273 . ℃ PVC, with such shortcoming as weak heat resistance capacity, will soften promptly under the temperature of 65℃~80℃ and can decompose easily under high temperature. PVC can be used to make tablecloth, packing membranes, vehicle curtains, briefcases, handbags and chemical shoes etc. Its glue film can absorb ultraviolet radiation and therefore embodies sound thermal insulation property. Hard PVC can be applied to such fields as watercourse piping, chemical plant piping, building materials, signboards, telephones, electric parts as well as drug-proof apparatus etc. 2. Polystyrene (PS) Resin The composite ethylene gas made from benzene (adopted from coal tar or petroleum) and ethylene gas, is dehydrogenated by metal oxide catalyzer heated to 600℃ into styrene monomer, which is then catalyzed and aggregated into polystyrene resin through such catalyzer as inorganic or organic peroxide。The polystyrene resin in the market is colorless and transparent, hard and slightly crispy, with an average molecular weight of 70 thousand ~100 thousand. It is excellent in water resistance and electric insulation and can fight against erosion from strong acid or alkali, yet it is devoid of resistance against organic solvent and oil and is weak in heat resistance. Another important feature of polystyrene resin is that it is endowed with sound thermal stability and fluidity in fusing resin, and thereby can be molded very well. Though a bit crispy, the PS can be colored freely. High impact polystyrene (HIPS) resin is obtained by adding butadiene and styrene copolymerized rubber in styrene resin, wherein the two substances are in several hierarchies respectively; in addition, ultraviolet radiation absorbent or antioxidant can be added therein to improve lightfastness and also fiberglass is sometimes added into the basal material to increase intensity. PS caters to the transparency and color tone of modern visual beauty. It can be extensively applied to the manufacturing of table articles like bread boxes and beef oil cans, commodity containers, toys, fruit dishes, toothbrushes, handles of brushes, soapboxes as well as flavoring containers etc. 3. ABS Resin and AS Resin The aggregation of styrene monomer, acrylonitrile monomer and butadiene rubber can produce a polymer (ABS) constituted by acrylonitrile (A), butadiene rubber (B) and styrene (S) in
various proportions. The characteristic thereof, due to the ingenious combination by the three components, shows such features as high impact resistance, large tensile strength and high rigidity which will not alter even under low temperature. Above all, the polymer possesses strong heat al and oil resistance, which endows it with such outstanding quali devoid of in ps and hips as resin is a butadiene free resin in abs resin it retains the transparency of styrene resin and is greatly improved in such properties as heat resistance, chemical resistance, oil resistance as well as mechanical intensity etc ABs resin boasts such quali th and mechanical intensity, sound emical resistance and heat resistance, stable dimension and easy processing etc and is relatively cheaper industrial material. It is mainly applied to the manufacturing of shells for radios and televisions, air conditioning and warming machines, juice machines, hair driers and shavers basal body of electric fans, vehicle meters, front protective grillages as well as air conditioning carrla AS resin can be used in such fields which require high mechanical intensity, chemical resistance and transparency such as battery compartments, meter boxes, blades of electric fans and beef oil case et 4. Acrylic Resins(PMMA) Acetone works together with prussic acid to form cyaniding propyl alcohol which is dehydrated with oil of vitriol, the substance is further combined into methacrylates through reaction with alcohol ester, and finally through polymerization with catalyzer, PMMA is thereby PMMA, like polystyrene(PS) he optimal transparency among all plas more difficult to be cut than polystyrene resin. It can be tabular polymethyl methacrylate and can be heated and bent into curved surface, the relative density thereof is also light. PMMA can be tinged into gallant colors and is extensively applied in building materials and furniture PMMA can be used to manufacture vehicle parts. Provided with sound lightfastness and ceilings. In addition, it embodies sound mechanical processing and bonding properties and can be applied in the manufacturing of delicate transparent models, optic lens, false teeth, contact lenses 5. Polyethylene(Pe) The commonest plastic that can be found in daily life is polyethylene(PE)which lymerized from ethylene industrially fractionated from petroleum Polyethylene of low density added with a small quantity of oxygen is heated to 200C under high pressure of approximately 2000 air pressure, white wax like polyethylene can thereby be obtained, and the method is called high pressure ethylene polymerization. With special organic metal catalyzer, the ethylene can be polymerized under normal temperature into polyethylene of high density, and such method is called low pressure ethylene polymerization. Polyethylene is generally a milk white, translucent or opaque substance which is lighter than water and can fall drop by drop like olefin when being burnt. It has sound water resistance, electric insulation, acid and alkali resistance. The substance can dissolve in hot toluene yet is quite stable against most chemicals and therefore it can be easily molded. The melt index indicates the fusion viscosity of
various proportions. The characteristic thereof, due to the ingenious combination by the three components, shows such features as high impact resistance, large tensile strength and high rigidity, which will not alter even under low temperature. Above all, the polymer possesses strong heat resistance as well as chemical and oil resistance, which endows it with such outstanding qualities devoid of in PS and HIPS. AS resin is a butadiene-free resin in ABS resin. It retains the transparency of styrene resin and is greatly improved in such properties as heat resistance, chemical resistance, oil resistance as well as mechanical intensity etc. ABS resin boasts such qualities as high impact strength and mechanical intensity, sound chemical resistance and heat resistance, stable dimension and easy processing etc and is a relatively cheaper industrial material. It is mainly applied to the manufacturing of shells for radios and televisions, air conditioning and warming machines, juice machines, hair driers and shavers, basal body of electric fans, vehicle meters, front protective grillages as well as air conditioning machines in the carriage etc. AS resin can be used in such fields which require high mechanical intensity, chemical resistance and transparency such as battery compartments, meter boxes, blades of electric fans and beef oil case etc. 4. Acrylic Resins (PMMA) Acetone works together with prussic acid to form cyaniding propyl alcohol which is dehydrated with oil of vitriol, the substance is further combined into methacrylates through reaction with alcohol ester, and finally through polymerization with catalyzer, PMMA is thereby got. PMMA, like polystyrene (PS), possesses the optimal transparency among all plastics and is more difficult to be cut than polystyrene resin. It can be tabular polymethyl methacrylate and can be heated and bent into curved surface; the relative density thereof is also light. PMMA can be tinged into gallant colors and is extensively applied in building materials and furniture. PMMA can be used to manufacture vehicle parts. Provided with sound lightfastness and transmittance, it is most suitable for making signboards, transparent covers and transparent ceilings. In addition, it embodies sound mechanical processing and bonding properties and can be applied in the manufacturing of delicate transparent models, optic lens, false teeth, contact lenses as well as machine parts. 5. Polyethylene (PE) The commonest plastic that can be found in daily life is polyethylene (PE) which is polymerized from ethylene industrially fractionated from petroleum. Polyethylene of low density added with a small quantity of oxygen is heated to 200℃ under a high pressure of approximately 2000 air pressure, white wax like polyethylene can thereby be obtained, and the method is called high pressure ethylene polymerization. With special organic metal catalyzer, the ethylene can be polymerized under normal temperature into polyethylene of high density, and such method is called low pressure ethylene polymerization. Polyethylene is generally a milk white, translucent or opaque substance which is lighter than water and can fall drop by drop like olefin when being burnt. It has sound water resistance, electric insulation, acid and alkali resistance. The substance can dissolve in hot toluene yet is quite stable against most chemicals and therefore it can be easily molded. The melt index indicates the fusion viscosity of
olyethylene, the smaller the index is, the larger the molecular weight and the higher the mechanical strength, although the fluidity is lower The low heat resistance and the inactive chemical property of polyethylene result in bad nd bondin The substance can be used to manufacture all kinds of bottles, fishnet, ropes, cables, telephone wire stringing, chopping boards as well as dustbins etc 6. Polypropylene(PP) Polypropylene is closely connected with polyethylene with respect to raw materials, manufacturing technique as well as properties. The raw materials, i. e. propylene and ethylene, are both contained in a large amount in the decomposing gas of petroleum. Above all, polypropylene and polyethylene are manufactured with the same industrial method, namely, through polymerization with catalyzer under low pressure. Polypropylene is an equilibrious polymer, with regular molecular structure and orderly arrangement, and which is provided with high crystallinity and superior heat resistance and intensity. Its relative density is 0.90-0.92 and thus is the lightest plastic. It can burn like polyethylene after being ignited, with rather stinky smoke, which can be differentiated from polyethylene. The softening point of polypropylene, far higher than polyethylene of high density, can reach 170C. It is of sound transparency and high tensile resistance and surface hardness Polypropylene is of low impact resistance under low temperature Foodstuff containers made of such substance can crack easily if falling off during their being taken in or out of the refrigerator. moreover, it cannot resist against ultraviolet radiation Polypropylene can be used to make shells of electric appliances, water buckets, foodstuff containers, pipes and tubes, filter cloth, fishnet and ropes etc 7. Flurocarbon Resins Flurocarbon resin is a kind of engineering plastic with excellent performance. Its chemical sistance and electric insulation is the best among plastics and its property will not change whether under high temperature or low temperature. The price, however, is a bit too high Flurocarbon resin contains various types of polymers, though in industry only four types are available: quadri-fluorinated-resin, tri-fluorinated-resin, polyvinylidene fluoride and FEP resin. It is basically made through the polymerization of dichlorodifluoro-methane monomer. The advantage of Flurocarbon resin over other plastics is that it is against erosion from chemicals and is sound in such electric properties as heat resistance and high frequency resistance. Quadri-fluorinated-resin, tri-fluorinated-resin and polyvinylidene fluoride are stable respectively ithin the range of-200℃-250℃,-200℃~250℃and-60℃-150℃. Since it does not absorb moisture. the substance can serve as the ideal electric insulation or anti-erosion material. It can be improved in performance and can be miniaturized respect to the field of wireless communication equipment such as electric instruments, radars, televisions as well as microwave relay devices etc. Polyvinylidene fluoride can fight against ultraviolet radiation and its performance remains unchanged all the year round. Endowed with such attributes, it can be applied in building material 8. Polyamide Resins(Nylon, PA)
polyethylene; the smaller the index is, the larger the molecular weight and the higher the mechanical strength, although the fluidity is lower. The low heat resistance and the inactive chemical property of polyethylene result in bad printing and bonding. The substance can be used to manufacture all kinds of bottles, fishnet, ropes, cables, telephone wire stringing, chopping boards as well as dustbins etc. 6. Polypropylene (PP) Polypropylene is closely connected with polyethylene with respect to raw materials, manufacturing technique as well as properties. The raw materials, i.e. propylene and ethylene, are both contained in a large amount in the decomposing gas of petroleum. Above all, polypropylene and polyethylene are manufactured with the same industrial method, namely, through polymerization with catalyzer under low pressure. Polypropylene is an equilibrious polymer, with regular molecular structure and orderly arrangement, and which is provided with high crystallinity and superior heat resistance and intensity. Its relative density is 0.90~0.92 and thus is the lightest plastic. It can burn like polyethylene after being ignited, with rather stinky smoke, which can be differentiated from polyethylene. The softening point of polypropylene, far higher than polyethylene of high density, can reach 170 . It ℃ is of sound transparency and high tensile resistance and surface hardness. Polypropylene is of low impact resistance under low temperature. Foodstuff containers made of such substance can crack easily if falling off during their being taken in or out of the refrigerator. Moreover, it cannot resist against ultraviolet radiation. Polypropylene can be used to make shells of electric appliances, water buckets, foodstuff containers, pipes and tubes, filter cloth, fishnet and ropes etc. 7. Flurocarbon Resins Flurocarbon resin is a kind of engineering plastic with excellent performance. Its chemical resistance and electric insulation is the best among plastics and its property will not change whether under high temperature or low temperature. The price, however, is a bit too high. Flurocarbon resin contains various types of polymers, though in industry only four types are available: quadri-fluorinated-resin, tri-fluorinated-resin, polyvinylidene fluoride and FEP resin. It is basically made through the polymerization of dichlorodifluoro-methane monomer. The advantage of Flurocarbon resin over other plastics is that it is against erosion from chemicals and is sound in such electric properties as heat resistance and high frequency resistance. Quadri-fluorinated-resin, tri-fluorinated-resin and polyvinylidene fluoride are stable respectively within the range of -200℃~250 , ℃ -200℃~250 and ℃ -60℃~150℃. Since it does not absorb moisture, the substance can serve as the ideal electric insulation or anti-erosion material. It can be improved in performance and can be miniaturized with respect to the field of wireless communication equipment such as electric instruments, radars, televisions as well as microwave relay devices etc. Polyvinylidene fluoride can fight against ultraviolet radiation and its performance remains unchanged all the year round. Endowed with such attributes, it can be applied in building materials. 8. Polyamide Resins (Nylon, PA)
Nylons are generally tough and strong and boast high oil resistance and chemical resistance They can be in stable use whether under high temperature or low temperature and hence possess excellent qualification for being used as engineering plastics. The friction coefficient of nylons is small, which indicates that it is high in abrasion resistance. Their friction coefficient against steel is 0. 15, whereas that of polyamide against polyamide is 0. 1. Therefore, nylons or polyamide resins are specially used to manufacture mechanical parts and pulleys such as the small gears, cam and axletrees of recorders, duplicating machines as well as computers. Nylons can absorb moistures easily, whereby their dimension and strength will change with the absorption. Hence, special attention should be paid when it requires high precision and the materials must be fully dried during molding The substance can be used to make such products as gears, connector of electric appliances, lamp shells, engine fan blades, mirrors, crusts, electronic parts, axletrees, computers, TV modules, roller skates soles, ball cases, zippers, fishing threads, brush hair, combs, high pressure tubes and 9. Acetal Resins(POM) POM is a tough and strong material with sound heat resistance and solvent resistance. The property of POM is similar to nylon and PC, which is pretty strong and requires high thermal deformation temperature. In addition, the substance is superior in abrasion resistance and will not easily get deformed even under long-time loading. Moreover, its property hardly changes after repeated bending, and thus it is also called plastic spring. Its low friction coefficient against steel almost equals that of nylon and its dimension change attributed to moisture absorption is also far ower than that of nylon camera parts, internal parts of clocks and watches, zippers as well as computer parts ef os, cams, The substance can be used to make vehicle parts, gears, electronic parts, water ta 10. Polycarbonate Resin(PC) PC is a kind of colorless or primrose material, with high tensile strength, bending intensity, elasticity and impact resistance. These physical properties, almost equal to metallic materials, will not change dramatically with different temperature and the intensity can be retained under 140C Its brittle temperature is as low as-100C-140C and the impact resistance is pretty high mounting to the top among plastics. It can be made into rubber helmets and safety helmets. It is also provided with strong resistance against ultraviolet radiation; a weather resistance test wherein the substance is exposed outdoors for ten years proves that its mechanical property remains tota unchanged. In addition, it is sound in electric property. The chemical resistance is against acid rather than alkali. Only when temperature reaches 220 C-230C will PC begin to be softened and fused. Due to its high viscosity, the substance, during molding and processing, requires high temperature and pressure higher than that of polystyrene or propylene resins PC can be manufactured into safety helmets, various mechanical parts and shells as well as components of electric mechanic appliances which require high electric insulation, intensity, heat resistance, transparency, vibration endurance and stable dimension. 11. Cellulose plastics The cellulose plastic is provided with high transparency and pliability as well as sound
Nylons are generally tough and strong and boast high oil resistance and chemical resistance. They can be in stable use whether under high temperature or low temperature and hence possess excellent qualification for being used as engineering plastics. The friction coefficient of nylons is small, which indicates that it is high in abrasion resistance. Their friction coefficient against steel is 0.15, whereas that of polyamide against polyamide is 0.1. Therefore, nylons or polyamide resins are specially used to manufacture mechanical parts and pulleys such as the small gears, cam and axletrees of recorders, duplicating machines as well as computers. Nylons can absorb moistures easily, whereby their dimension and strength will change with the absorption. Hence, special attention should be paid when it requires high precision and the materials must be fully dried during molding. The substance can be used to make such products as gears, connector of electric appliances, lamp shells, engine fan blades, mirrors, crusts, electronic parts, axletrees, computers, TV modules, roller skates soles, ball cases, zippers, fishing threads, brush hair, combs, high pressure tubes and gunstock etc. 9. Acetal Resins (POM) POM is a tough and strong material with sound heat resistance and solvent resistance. The property of POM is similar to nylon and PC, which is pretty strong and requires high thermal deformation temperature. In addition, the substance is superior in abrasion resistance and will not easily get deformed even under long-time loading. Moreover, its property hardly changes after repeated bending, and thus it is also called plastic spring. Its low friction coefficient against steel almost equals that of nylon and its dimension change attributed to moisture absorption is also far lower than that of nylon. The substance can be used to make vehicle parts, gears, electronic parts, water taps, cams, camera parts, internal parts of clocks and watches, zippers as well as computer parts etc. 10. Polycarbonate Resin (PC) PC is a kind of colorless or primrose material, with high tensile strength, bending intensity, elasticity and impact resistance. These physical properties, almost equal to metallic materials, will not change dramatically with different temperature and the intensity can be retained under 140 . ℃ Its brittle temperature is as low as -100℃~140℃ and the impact resistance is pretty high, amounting to the top among plastics. It can be made into rubber helmets and safety helmets. It is also provided with strong resistance against ultraviolet radiation; a weather resistance test wherein the substance is exposed outdoors for ten years proves that its mechanical property remains totally unchanged. In addition, it is sound in electric property. The chemical resistance is against acid rather than alkali. Only when temperature reaches 220℃~230℃ will PC begin to be softened and fused. Due to its high viscosity, the substance, during molding and processing, requires high temperature and pressure higher than that of polystyrene or propylene resins. PC can be manufactured into safety helmets, various mechanical parts and shells as well as components of electric mechanic appliances which require high electric insulation, intensity, heat resistance, transparency, vibration endurance and stable dimension. 11. Cellulose Plastics The cellulose plastic is provided with high transparency and pliability as well as sound
processability, fluidity and molding ability. The plastic has bright surface and sound dimension It can be manufactured into fire resistant spectacles frame, tools, electric parts and transparent packing cases 3. 1.4 Properties of Thermoset plastics 1. Phenol Resins( Bakelite Phenol resins are made from phenol and formaldehyde and mostly contain such fillers as wood meal, asbestos, craft paper and cloth. Molding will be a lot easier when being added with wood meal; the heat resistance can be improved with asbestos in it; with mica the electric insulation can be increased; with long fiber the mechanical intensity can be strengthened, and with synthetic fiber the electric insulation and intensity can be increased. The substance is provided with high mechanical intensity, sound electric insulation and heat resistance as well as resistance against such strong acid as vitriol; it is noncombustible and can be molded easily. Above all, it lso possesses high precision. Mechanical processing is simple and easy. Furthermore, it is cheap and durable The substance can be eroded by alkali solvent. The original color is snuff color which can discolor easily Phenol resins can be made into such products as electric insulation materials, electric and ns parts, wiring instruments, linkers, switches, sockets, kettles handles of electric iron and beaters 2. Urea resins Jrea resin can be produced through the reaction between urea(ammonia) and formalin, catalyzed by acid or base. It is formed through compression molding adopting hard chrome plating model, with a temperature controlled at approximately 130C-150C. Although its heat resistance is not as good as phenol resin, it can withstand continuous use below 100C. Above all,it possesses a strong resistance against organic solvent and oil. The resin intrinsically can be colored freely and it is of excellent glossiness and appearance. As for electric property, its arc resistance is superior to that of phenol resin. Its molding shrinkage, however, is larger than that of phenol resin and it is also inferior with respect to water resistance, age resistance and boiling endurance Therefore it is unsuitable for outdoor or industrial use The substance can be applied to such fields as the lids for cosmetic and medical use or fo various containers, foodstuff vessels such as chopsticks, basins, bowls, tea trays and fruit dish etc hich are of low heat resistance yet high water resistance, groceries and commodities such as buttons, ashtrays, toys and stationery; electric parts such as vehicle parts, motor parts, lighting appliances, shell of radios, switches and shell of ammeters etc 3. Melamine Resins The substance is colorless and transparent, and can be colored freely; it is very hard and is of sound chemical resistance. water resistance. solvent resistance. heat resistance and fire resistance. Its mechanical intensity, electric insulation and arc resistance are also good. Melamine resin can resist aging and its overall performance is superior to that of urea resin, although it is more
processability, fluidity and molding ability. The plastic has bright surface and sound dimension precision. It can be manufactured into fire resistant spectacles frame, tools, electric parts and transparent packing cases. 3.1.4 Properties of Thermoset Plastics 1. Phenol Resins (Bakelite) Phenol resins are made from phenol and formaldehyde and mostly contain such fillers as wood meal, asbestos, craft paper and cloth. Molding will be a lot easier when being added with wood meal; the heat resistance can be improved with asbestos in it; with mica the electric insulation can be increased; with long fiber the mechanical intensity can be strengthened, and with synthetic fiber the electric insulation and intensity can be increased. The substance is provided with high mechanical intensity, sound electric insulation and heat resistance as well as resistance against such strong acid as vitriol; it is noncombustible and can be molded easily. Above all, it also possesses high precision. Mechanical processing is simple and easy. Furthermore, it is cheap and durable. The substance can be eroded by alkali solvent. The original color is snuff color which can discolor easily. Phenol resins can be made into such products as electric insulation materials, electric and mechanical parts, communications parts, wiring instruments, linkers, switches, sockets, kettles, handles of electric iron and beaters. 2. Urea Resins Urea resin can be produced through the reaction between urea (ammonia) and formalin, catalyzed by acid or base. It is formed through compression molding adopting hard chrome plating model, with a temperature controlled at approximately 130℃~150 . ℃ Although its heat resistance is not as good as phenol resin, it can withstand continuous use below 100 . Above all, it ℃ possesses a strong resistance against organic solvent and oil. The resin intrinsically can be colored freely and it is of excellent glossiness and appearance. As for electric property, its arc resistance is superior to that of phenol resin. Its molding shrinkage, however, is larger than that of phenol resin, and it is also inferior with respect to water resistance, age resistance and boiling endurance. Therefore, it is unsuitable for outdoor or industrial use. The substance can be applied to such fields as the lids for cosmetic and medical use or for various containers, foodstuff vessels such as chopsticks, basins, bowls, tea trays and fruit dish etc. which are of low heat resistance yet high water resistance; groceries and commodities such as buttons, ashtrays, toys and stationery; electric parts such as vehicle parts, motor parts, lighting appliances, shell of radios, switches and shell of ammeters etc. 3. Melamine Resins The substance is colorless and transparent, and can be colored freely; it is very hard and is of sound chemical resistance, water resistance, solvent resistance, heat resistance and fire resistance. Its mechanical intensity, electric insulation and arc resistance are also good. Melamine resin can resist aging and its overall performance is superior to that of urea resin, although it is more
expensIV It can be manufactured into tobacco pipes, kettles, decorative boards as well as parts with xcellent electric insulation 4. Unsaturated Polyester Resins (UP) P is the compound formed by the alkyd of unsaturated binary acid and ethylene monomer. The resin is a kind liquid of low viscosity, which will not produce gas when being solidified Hence the molding pressure thereof is rather low. Intensified by glass fiber, its mechanical intensity will be much higher The substance can be used to manufacture airplane parts, ship parts, gasket for helm bathtubs, sports cars, cooling towers, troughs as well as drug boxes 5. Epoxy Resins(EP) Major raw material for epoxy resin is reacted from propylene and benzene. The substance is adhesive to other substances, especially metals, and therefore, it can be mad esives Another important feature is that it will not produce volatile substance when being solidified, and hence is of small shrinkage Endowed with such advantages it can be manufactured into molding products with excellent precision of dimension which is very stable. It can be used as adhesives and coatings 6. Polyurethanes Resin Polyurethanes resin embodies the properties of foam, rubber, thermoplastic plastics as well as d as elastor tings etc and can also adopted as synthetic fiber of large shrinkage. The substance is of high elasticity, obdurability and tensile strength, and can fight against the erosion from oil or solvent and can resist aging and It will decompose in water and cannot resist against acid, alkali, boiled water and vapor. Application 1)As foam. Due to its properties such as high elasticity, tensile strength and fatigue resistance. the substance can be used as soft foam 2)As rubber elastomer. The substance is of sound elasticity, tensile strength, rupture strer brasion resistance as well as age resistance and can be used as tires for trucks. various rollers or conveying belts and quiet gears 3)As coating and adhesive. Coatings and adhesives made from polyurethanes resin can be well adhered to the adhesive interface and can be used to adhere such materials as wood. rubber. glass and metals. It will turn yellow under ultraviolet radiation 3.2 Mold Materials Plastic mold is of multiplex varieties and specifications. Due to its complicated shapes and low surface roughness, it is rather difficult to be manufactured. Therefore, it seems very important to comprehensively analyze its working condition and performance so as to improve the service life, ensure processing quality and reduce production cost
expensive. It can be manufactured into tobacco pipes, kettles, decorative boards as well as parts with excellent electric insulation. 4. Unsaturated Polyester Resins (UP) UP is the compound formed by the alkyd of unsaturated binary acid and ethylene monomer. The resin is a kind liquid of low viscosity, which will not produce gas when being solidified. Hence the molding pressure thereof is rather low. Intensified by glass fiber, its mechanical intensity will be much higher. The substance can be used to manufacture airplane parts, ship parts, gasket for helmets, bathtubs, sports cars, cooling towers, troughs as well as drug boxes. 5. Epoxy Resins (EP) Major raw material for epoxy resin is reacted from propylene and benzene. The substance is adhesive to other substances, especially metals, and therefore, it can be made into adhesives. Another important feature is that it will not produce volatile substance when being solidified, and hence is of small shrinkage. Endowed with such advantages, it can be manufactured into molding products with excellent precision of dimension which is very stable. It can be used as adhesives and coatings. 6. Polyurethanes Resin Polyurethanes resin embodies the properties of foam, rubber, thermoplastic plastics as well as thermoset plastics. It can be used as elastomers, adhesives and coatings etc and can also be adopted as synthetic fiber of large shrinkage. The substance is of high elasticity, obdurability and tensile strength, and can fight against the erosion from oil or solvent and can resist aging and abrasion. It will decompose in water and cannot resist against acid, alkali, boiled water and vapor. Application: 1) As foam. Due to its properties such as high elasticity, tensile strength and fatigue resistance, the substance can be used as soft foam. 2) As rubber elastomer. The substance is of sound elasticity, tensile strength, rupture strength, abrasion resistance as well as age resistance and can be used as tires for trucks, various rollers or conveying belts and quiet gears. 3) As coating and adhesive. Coatings and adhesives made from polyurethanes resin can be well adhered to the adhesive interface and can be used to adhere such materials as wood, rubber, glass and metals. It will turn yellow under ultraviolet radiation. 3.2 Mold Materials Plastic mold is of multiplex varieties and specifications. Due to its complicated shapes and low surface roughness, it is rather difficult to be manufactured. Therefore, it seems very important to comprehensively analyze its working condition and performance so as to improve the service life, ensure processing quality and reduce production cost
According to different molding and solidification, plastic mold falls into such two types as thermoset plastic mold and thermoplastic plastic mold. The plastics, during the working of thermoset plastic molds, are solid powder materials or prefabricated blank materials, which are added into the cavity and molded through thermal pressing under certain temperature. The force pplied thereon is large, friction is also large due to the impact it is subject to; thermal mechanical load and abrasion is large. Plastics for thermoplastic plastic mold are injected or pressed into the cavity under viscous flow state, wherein the deformation resistance is relatively smaller and the heat, pressure and abrasion applied on the molds are usually not very serious. However, when solid fillers are added therein, the abrasion will increase enormous Basic requirements for the performance of plastic mold steel are as follows O High rigidity and sound abrasion resistance; surface hardness of cavity should be 30-60HRC and hardenability >55HRC, sufficient hardening dept is required and sufficient obdurability is demanded at the heart therein to avoid brittle fracture and deformation 2 Certain heat resistance and erosion resistance. Due to the generally complicated structure of plastic molds, it requires low surface roughness and high precision for the cavity and excellent technical performance should be ensured. The specific requirement is as follows O Slight deformation during heat treatment and sound hardenability 2 Sound performance for cutting processing and superior polishing property and abrasion 3 For plastic molds employing cold extrusion forming process, it requires sound cold extrusion molding ability, and to make it convenient for molding, the hardness after anneal should be low, the plasticity good, and deformation resistance small. The deformation resistance after quenching is hig Other processing properties, such as forging and jointing properties, should be fine Plastic mold parts fall into working parts and structural parts. Working parts refer to those determining the geometrical shape, dimension and precision of plastic products, and are also called molding parts or the molding section of parts, such as cavity, core, insert, molding pin and molding ring etc. Their working condition is rather complicated and the technical requirement is high, especially the surface quality of the working face of molding parts, which is the major factor influencing the appearance and quality of plastic products as well as the service life of molds Commonly-used plastic mold steel includes the following 1. Casehardened Plastic Mold Steel Casehardened steel can be provided with tough core and abrasion-resistant surface, wherein high surface hardness will be beneficial for polishing treatment. Carbon content in the casehardened steel is less than 0.25%. During heat treatment carbon element can strengthen the intensity of core. To get higher surface hardness, carbon content on the surface must be increased, whereby can be achieved through adding carbon accelerant during the course of heat treatment he ideal carbonization temperature depth is 0.6-lmm. After quenching and tempering, the surface hardness can reach HRC58-62. Since the carbonization temperature is rather high, the dimension change is bound to occur, which requires extra follow-up treatment 2. Through-hardened Plastic Mold Steel
According to different molding and solidification, plastic mold falls into such two types as thermoset plastic mold and thermoplastic plastic mold. The plastics, during the working of thermoset plastic molds, are solid powder materials or prefabricated blank materials, which are added into the cavity and molded through thermal pressing under certain temperature. The force applied thereon is large; friction is also large due to the impact it is subject to; thermal mechanical load and abrasion is large. Plastics for thermoplastic plastic mold are injected or pressed into the cavity under viscous flow state, wherein the deformation resistance is relatively smaller and the heat, pressure and abrasion applied on the molds are usually not very serious. However, when solid fillers are added therein, the abrasion will increase enormously. Basic requirements for the performance of plastic mold steel are as follows: ① High rigidity and sound abrasion resistance; surface hardness of cavity should be 30~60HRC and hardenability ＞55HRC; sufficient hardening dept is required and sufficient obdurability is demanded at the heart therein to avoid brittle fracture and deformation. ② Certain heat resistance and erosion resistance. Due to the generally complicated structure of plastic molds, it requires low surface roughness and high precision for the cavity and excellent technical performance should be ensured. The specific requirement is as follows: ① Slight deformation during heat treatment and sound hardenability. ② Sound performance for cutting processing and superior polishing property and abrasion resistance. ③ For plastic molds employing cold extrusion forming process, it requires sound cold extrusion molding ability, and to make it convenient for molding, the hardness after anneal should be low, the plasticity good, and deformation resistance small. The deformation resistance after quenching is high. ④ Other processing properties, such as forging and jointing properties, should be fine. Plastic mold parts fall into working parts and structural parts. Working parts refer to those determining the geometrical shape, dimension and precision of plastic products, and are also called molding parts or the molding section of parts, such as cavity, core, insert, molding pin and molding ring etc. Their working condition is rather complicated and the technical requirement is high, especially the surface quality of the working face of molding parts, which is the major factor influencing the appearance and quality of plastic products as well as the service life of molds. Commonly-used plastic mold steel includes the following: 1. Casehardened Plastic Mold Steel Casehardened steel can be provided with tough core and abrasion-resistant surface, wherein high surface hardness will be beneficial for polishing treatment. Carbon content in the casehardened steel is less than 0.25%. During heat treatment, carbon element can strengthen the intensity of core. To get higher surface hardness, carbon content on the surface must be increased, whereby can be achieved through adding carbon accelerant during the course of heat treatment. The ideal carbonization temperature depth is 0.6~1mm. After quenching and tempering, the surface hardness can reach HRC58~62. Since the carbonization temperature is rather high, the dimension change is bound to occur, which requires extra follow-up treatment. 2. Through-hardened Plastic Mold Steel