The development of POM (polyoxymethylene) engineering plastics

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The last edit to this post was made by chengkang on 2009-11-3 at 13:22. Development of POM (Polyoxymethylene) Engineering Plastics Table of Contents Abstract and Keywords... - 2 - 1 Overview of the global development of polyoxymethylene... - 3 - 1.1 Development abroad... - 3 - 1.2 Development in China... - 3 - 2. Overview of the DO/TOX units... - 3 - 2.1 Chemical reactions involving the DO unit... - 4 - 2.2 Process overview of the DO unit... - 4 - 2.3 Reactions involved in the TOX unit:... - 5 - 2.4 Process overview of the TOX unit... - 5 - 3. Overview of the POL/FIN units... - 7 - 3.1 Overview of the POL unit... - 8 - 3.2 The FIN unit... - 9 - 4. Applications of polyoxymethylene... - 11 - 4.1 Applications in pharmaceutical packaging machinery... - 11 - 4.2 Applications in the automotive industry... - 11 - 4.3 Applications in electronics and electrical equipment... - 12 - 4.4 Applications in agricultural machinery... - 12 - 4.5 Other applications... - 12 - 5. Analysis of China’s POM industry... - 12 - 5.1 The importance of polyoxymethylene technology for China’s economic development... - 12 - 5.2 Challenges faced by China’s POM industry... - 13 - 5.2.1 Insufficient POM production capacity to meet market demand... - 13 - 5.2.2 Imbalance between imports and exports... - 13 - 5.2.3 The technological gap cannot be ignored... - 13 - 6. References... - 14 - Abstract and Keywords Abstract: With the rapid development of the automotive and machinery manufacturing industries, there is an increasing demand for steel. However, the world’s steel production is limited, prompting the search for new materials to replace steel in various applications. Engineering plastics are excellent substitutes for steel; they possess good comprehensive properties and colorability, high elastic modulus, great stiffness and hardness, with specific strength and specific stiffness comparable to those of metals； It exhibits excellent tensile strength, bending strength, creep resistance, and fatigue resistance, as well as good resistance to repeated impacts and excellent recovery after unloading ； It has a low coefficient of friction, is wear-resistant, offers good dimensional stability, has a pleasant surface finish, exhibits high viscoelasticity, low water blowout, excellent electrical insulation properties, and is not affected by temperature ； It has excellent chemical resistance, except against strong acids; it also possesses vibration-damping and noise-reducing properties ； Low water absorption, good insulation resistance, and unaffected by humidity ； Excellent chemical resistance: Stable against other chemicals except strong acids, phenols, and organic halides; oil-resistant ； Its mechanical properties are little affected by temperature, and it has a high heat deformation temperature. As a result, there is an increasing demand for POM engineering plastic. This article introduces the production process of POM engineering plastic as well as some related information. Keywords: POM, copolymerized formaldehyde, homopolymerized formaldehyde, engineering plastic. 1 Overview of the development of polyformaldehyde 1.1 Development abroad Polyformaldehyde (POM) was developed by the American company DuPont in 1959; industrial production of homopolymerized formaldehyde was first achieved under this material’s trade name, Delrin ； In 1960, the American company Celanese developed a technology for producing copolymerized formaldehyde using paraformaldehyde and ethylene oxide, and industrial production began in 1962; its trade name is Ceicon. Subsequently, Hoechst-Celanese, a joint venture between German companies Hoechst and Celanese, began industrial production of copolymerized formaldehyde under the trade name “Hostaform” in 1963; the American company BASF started production under the trade name “Uhraform” in 1969; and Polyplastic, a joint venture between Hoechst-Celanese and Daicel, began production under the trade name “Duraeon” in 1968. Asahi Kasei Corporation began producing homopolymerous formaldehyde and copolymerous formaldehyde in 1972 and 1987 respectively, under the trade names “Tenac” and “Tenac—C”. Mitsubishi Gas Chemical Company began industrial production of copolymerized formaldehyde under the name “Jupital” in 1981. 1.2 Overview of domestic development: At the end of the 1970s, China developed and built its first polyformaldehyde production facility; however, progress was slow over more than 20 years of efforts. Before 1998, there were only two manufacturing enterprises in China: the Shanghai Solvent Factory and the Shijinggou Joint Chemical Plant of Jihua Company. Their production capacities were 1,700 tons per year and 1,000 tons per year respectively. Due to low one-pass conversion rates of polyoxymethylene, inadequate technologies for the recovery and purification of formaldehyde, high consumption of raw materials and utility resources, and unstable product quality, the polyoxymethylene technology developed in China had many shortcomings from an engineering perspective, preventing the achievement of economies of scale and thus limiting the development of China’s polyoxymethylene industry. This meant that the industry could not meet domestic demand; in fact, these two enterprises ceased operations in 1998. In 2000, Yuntianhua Group Company introduced the 10kt/year polyoxymethylene production technology from the Polish company ZAT, and built a polyoxymethylene production facility with an annual capacity of 10,000 tons in 2001. In 2003, the total domestic production capacity for polyoxymethylene reached 12.7 kt/year. By 2005, the newly built and planned polyoxymethylene production facilities in China included: Daqing’s 20kt/year polyoxymethylene plant, and China Blue Star (Group) Corporation’s 20kt/year polyoxymethylene plant ； Japan’s Boride Plastics Co., Ltd., Mitsubishi Gas Chemical Company, and the U.S.-based Ticona Corporation joined forces to build and put into operation a polyoxymethylene production facility with an annual capacity of 60 kt in Nantong City, Jiangsu Province, in 2004 ； DuPont (China) Group Co., Ltd. and the Japanese company Asahi Kasei jointly established a joint venture in Zhangjiagang, Jiangsu, to produce polyoxymethylene resin; the initial production capacity was 20 kt/year, and it was increased to 60 kt/year by 2005. By the end of this year, domestic production capacity is expected to exceed 170,000 tons. 2. Overview of the DO/TOX unit: This article describes the process of the 60 kt/year copolymerized formaldehyde production plant at Nantong Baotailing Engineering Plastics Co., Ltd. The production process at Baotailing Company consists of the following units: FO (Formalin) unit, DO (Dioxolane) unit, TOX (Trioxane) unit, POL (Polymerization) unit, and FIN (Finishing) unit. 2.1 Chemical reaction in the DO unit In the DO unit, formaldehyde and glyoxal (EG) react at a temperature of 120°C in the presence of an acidic catalyst, methanesulfonic acid (MSA). HCHO + HOH2C-CH2OH → DO + H2O. In the DO reaction, two undesirable side reactions can occur: 2HCHO + HOH2C-CH2OH → C4H8O3 + H2O; HCHO + 2CH3OH → CH3O-CH2-OCH3 + H2O. 2.2 Process overview of the DO unit: The raw material EG is stored in a 50 M3 stainless steel tank, with nitrogen being used to remove oxygen and moisture from within the tank. EG and formaldehyde are converted into DO using a reactor and a reaction tower; methanesulfonic acid at a concentration of 1-2% (by weight) is used as a catalyst, and a thermosyphon reboiler is employed to supply heat to it. The reaction tower is equipped with packing at its top, which serves to prevent unreacted HCHO and EG from leaving the reactor. The reactor, reaction tower, and reboiler are made of Monel corrosion-resistant material. The liquid at the top of the reactor is supplied to the stripping tower, while the residual liquid is removed (usually once every 6 months to eliminate the accumulated heavy components). The stripping tower is used to separate water from the azeotrope of DO and water; heat is supplied by a thermal siphon reboiler, and the upper product stream is condensed by a standard shell-and-tube condenser. The residue is mainly water, which is sent to a wastewater treatment plant ； The top liquid (about 93% DO, 7% water) is sent to the absorption tower. The absorption tower utilizes EG to break the azeotrope between DO and water; EG enters the tower from its upper part, and as it moves downward through the tower it absorbs water. The azeotrope of DO and water from the stripping tower enters the tower from its bottom, and a forced-circulation reboiler is used to boil the DO. A small backflow (of pure DO from the distillation tower) prevents EG from leaving the top of the absorption tower; the material at the top of the absorption tower (containing most of the DO and some light substances) is not condensed, but enters the distillation tower in vapor form ； The absorbent tower residue (containing EG, water, and a small amount of DO) is sent back to the reactor. The product tower separates light materials and a small amount of water from the DO; the distillate at the top is sent to the formaldehyde unit, while the residue is the final product, which, after cooling, is pumped into storage tanks. Figure 2-1 Process flow of the DO unit. 2.3 Reactions involved in the TOX unit: Main reaction: 3HCHO → TOX. Side reactions: 2HCHO + H2O → HCOOH + CH3OH; 2HCHO + H2O → HCOOCH3 + H2O; HCHO + 2CH3OH → (CH3O)2CH2 + H2O; 3HCHO → -C-C-C-C-C-. 2.4 Overview of the TOX unit process: An aqueous solution containing about 55% formaldehyde and 1% methanol, coming from the formaldehyde unit, is fed into the TOX unit. The aqueous solution was concentrated under vacuum to obtain an aqueous solution containing 75% HCHO. Under the catalysis of 0,6%–0,8% H2SO4, 75% of this concentrated formaldehyde was converted into TOX. TOX was separated from the mixture through distillation and extraction, thereby producing polymeric TOX. This polymeric TOX had the HFO removed through alkaline treatment, and its light and heavy components were removed via distillation. The unreacted HCHO is separated and returned to the reactor to continue participating in the reaction. TOX, CO-H, and SL-D are recovered and concentrated in the TOX recovery equipment, while the recovered TOX, HCHO, and CH3OH are returned to the devices related to other processes involving TOX. Formaldehyde recovery tower, pressure tower, formaldehyde storage tank, concentrator, formaldehyde recovery evaporator, defoamer. CO-H from the top of the reactor; approximately 50% of CO-H, approximately 75% of CO-H goes back to the reactor. Figure 2-2: Process flow of the CONCENTRATION system in the TOX unit. Extraction tower, reactor, reaction tower, liquid/vapor phase, H2SO4. CO-H from the concentrator, from the bottom of the TOX distillation tower, sent to the pressure tower; approximately 65% of CO-H. Figure 2-3: Process flow of the REACTION system in the TOX unit. TOX distillation tower, TOX product, TOX/benzene buffer tank, dehydrator, soda, light product tower. From the reactor, extraction tower, OH receiving tower, benzene buffer tank. From the TOX recovery tower, benzene, benzene circulation, aqueous layer. TOX recovery tower, aqueous layer, reaction tower, methanol recovery tower, TOX recovery tower. Figure 2-4: Process flow of the DISTILLATION system in the TOX unit. To the methylformaldehyde unit, TOX recovery tower evaporator, reactor reboiler, CCS generator, pressure tower, formaldehyde recovery tank, extraction tower, recovery evaporator top, OH receiving tower, aqueous layer, to the recovery evaporator, methanol recovery tower, feed tank, methanol recovery tower, TOX recovery tower, circulating formaldehyde buffer tank. From the DO unit, returned to the bottom of the reactor, to WWT. Bottom of the extraction tower, bottom of the TOX distillation tower, bottom of the reaction tower, defoamer, top of the concentrator. Figure 2-5: Process flow of the RECOVERY system in the TOX unit. 3. Overview of the POL/FIN unit. Principles of polymerization reaction: (1) Chain initiation: BF3-H2O initiation system forms a trivalent oxygen cation; a carbon cationic active center is formed. (2) Chain growth: Long-chain carbon cations are formed. (3) Chain termination: Butyl acetal termination occurs; chain transfer controls the molecular weight, and thermally stable butoxy groups are formed to terminate the chains. ～O-CH2-O-CH2 (BF3OH) + C4H9-O-CH2-O-C4H9 → ～O-CH2-O-CH2-O-C4H9 + C4H9-O-CH2 (BF3OH) 3.1 Overview of the POL unit: Using TOX and DO as main raw materials, phosphotungstic acid (IO-PT) as an initiator, methyl formate (OR-MF) and dimethoxymethane (OR-B) as chain transfer agents, along with stabilizers, fluorescent agents, etc. TOX and DO undergo copolymerization in the presence of the initiator IO-PT; this polymerization reaction involves the ring-opening of TOX and the insertion of DO, with OR-B being used as a chain transfer agent to terminate the polymerization. Since unstable terminal HO groups are present at the ends of the polymer molecules after the reaction, it is necessary to control the feeding ratio of IO-PT in order to form stable polymers. During the polymerization process, TOX and DO produced and purified from the TOX and DO production units undergo copolymerization in the presence of the initiator IO-PT to produce copolymerized formaldehyde, with OR-B being used as a chain transfer agent to terminate the polymerization reaction. The polymer coming out of the reactor is continuously ground into powder in a polymer grinder, and then conveyed to a polymer powder tank. The initiator IO-PT remains active in the powder tank; it will lose its activity in the final product extruder. The TOX from the TOX unit first enters the TOX cooling tower, where it is used to cool the TOX that has absorbed during the polymerization reaction. By serving as the feed for the polymerization reactor, this TOX cooling system enables the POL unit to achieve a higher conversion rate. TOX and HCHO that have not been cooled in the TOX cooling tower are absorbed in the POL exhaust gas scrubber, and the absorbed TOX and HCHO are returned to the TOX recovery tower of the TOX unit. In the polymer powder, the deactivator and nucleator (U10) are added to the extruder in the FIN zone using their respective weight feeders. The polymer powder is transported from the polymer powder tank in the POL unit to the finished product unit, where it is mixed with stabilizers and additives in the finished product extruder. The molten polymer in the extruder is pelletized, and after exiting the extruder, the pellets are dried in a dryer using hot air in order to reduce the residual levels of formaldehyde and moisture in the product. At the final stage of the finished product unit, the product must first have the powder and metal removed from it before it can be packaged. Introduction to the main equipment and processes of the polymerization unit: polymerization reactor, polymer grinder, TOX cooler, extruder, dryer. In the polymer reactor, TOX and DO polymerize in the presence of the initiator IO-PT to produce copolymerized formaldehyde. The materials fed into the reactor are purified TOX and DO, as well as the chain transfer agent OR-B and the initiator IO-PT. Thanks to the TOX cooling system, the conversion rate of TOX in the reactor is generally 75%-95%. The main properties of copolymerized formaldehyde resin, such as melt index and thermal stability, are determined by the polymerization process. Therefore, it is very important to properly monitor and control the reaction conditions. Polymers with HO levels of 0, 2%-0, 4% should be obtained as continuously as possible. Productivity, conversion rate, and the properties of the polymer are greatly influenced by the quality of TOX. Therefore, when the TOX quality changes, the aforementioned standard feeding ratio must be adjusted to meet the requirements for yield and product quality. The ratio of DO to TOX: A ratio below 2 WT% results in a relatively high level of unstable end groups, leading to thermal instability of the polymer; a ratio above 5 WT% causes a decrease in the softening point and mechanical properties of the polymer. Addition of IO-PT: The optimal feeding ratio of the initiator IO-PT is 50–100PPM, and the actual feeding ratio is, to some extent, a function of the TOX feeding amount. The concentration of IO-PT in the reactor must be maintained at at least 2.5 PPM to initiate and sustain the reaction. An inlet flow rate of IO-PT exceeding 3.5 WTPPM will cause the reaction temperature to rise above 127 °C (referred to as the limit temperature). Beyond the limit temperature, the polymerization reaction stops while the degradation reaction begins. This leads to an increase in the amount of unstable end groups, thereby deteriorating the product quality. Excessive addition can also lead to reactor overload and shutdown. To properly control the addition of IO-PT, it is very important to monitor the reactor’s conversion rate and the HO index of the polymer. Addition of OR-B: OR-B is used to control the melt index of the product. The polymer exiting the polymerization reactor is sent to a grinder, while the unreacted TOX enters the TOX cooling tower via a cyclone separator. The cyclone separator can remove the powder from the unreacted TOX gas, preventing it from affecting the feed of TOX from the cooling tower to the reactor. The polymer exiting the reactor is ground in a polymer grinder into powder with particle sizes of 0, 3–0,4 mm; this step is taken to make the solid material easier to handle downstream. If the particle size is below the target value, the capacity of the extruder will decrease due to the low bulk density. The polymer powder container should be protected with nitrogen to remove air; otherwise, since the polymer powder has not yet lost its reactivity, it will absorb moisture from the air, forming unstable OH end groups. This increase in the amount of unstable end groups leads to a decline in the quality of the polymer. The polymer grinder receives the polymer coming from the reactor; there, the polymer is ground into powder with an average particle size of 0.3–0.4, and then it is transferred to the polymer powder tank. The powder size is determined by the gap between the fixed and rotating blades of the grinder, as well as the mesh size of the sieve. Both the unreacted TOX in the polymerization reactor and the TOX produced by the TOX units go into the TOX cooling tower. The unreacted TOX is cooled in the TOX cooling tower and then fed back into the polymerization reactor. The application of the TOX cycle system enables the system conversion rate of the polymerization unit to reach around 90%. The design of the TOX cooling tower also reduces the steam consumption of the TOX unit, and it is capable of cooling unreacted DO as well, thereby minimizing DO loss. The reason why TOX from the TOX unit is fed into the TOX cooler is to maintain a low concentration of HCHO in the TOX cooling tower and prevent blockage accidents. The flow rate of TOX from the TOX unit into the TOX cooling tower is determined by the liquid level at the bottom of the TOX tower, while all unreacted TOX in the polymerization reactor enters the middle section of the TOX cooler. The condensed TOX is circulated through the cooler and sprayed at the top of the TOX cooling tower to cool the unreacted TOX. The outlet temperature of the cooler is controlled at 80°C, and the heat from the unreacted TOX gas is absorbed by the cooling medium of the cooler, which is hot water at 65°C. The uncondensed gas enters the POL exhaust gas scrubber from the top of the tower, and the scrubbing water that has absorbed TOX and HCHO is returned to the TOX unit. 3.2 The powder in the FIN unit’s polymer powder tank is conveyed to the finished product extruder. In the extruder, the powder loses its activity and is mixed with various stabilizers to form stable polymer products. Stabilizers, especially those that enter the extruder hopper, not only have a stabilizing effect but also an inerting effect. The initiator in the polymer powder remains active upon entering the extruder. Therefore, during the melting of the polymer in the extruder, the initiator loses its activity due to the effect of the deactivator. The grade of the polymer depends on the type of stabilizer. The polymer powder and the stabilizer are fed into the extruder via separate metering feeders; the feeding rates of the polymer powder and the stabilizer are determined by the extrusion rate and the feeding ratio of the stabilizer relative to the polymer powder. Process water (pw) is injected into the molten material in the extruder at 4%-5% of the extrusion rate. The purpose of water injection is to reduce the chroma (B-value) of the particles and the formaldehyde concentration in the product. The polymer mixed with a stabilizer enters an water ring pelletizer from the extruder, where it is pelletized into particles with a diameter of approximately 3.0 MM. Since the granulation stage determines the shape of the final product, special attention must be paid to maintaining acceptable particle size and shape during this stage. If the size and shape of the particles change suddenly, it is easy to encounter problems such as mold bridging during processing by the customer. In the stabilizer mixing tank, the stabilizer and a portion of the polymer powder are polymerized. The relative proportion of polymer powder mixed with the stabilizer varies depending on the product grade. The typical ratio is 1/3 part of powder per part of stabilizer. The purposes of mixing polymer powder with stabilizers are as follows: to improve the fluidity of the stabilizer, to reduce bridging in the stabilizer mixing tank, weighing feeder, and other downstream equipment, and to enhance the dispersion of the stabilizer within the extruder. The polymer powder and stabilizers are metered using their respective feeders before being fed into the extruder. Additionally, recycled particles can also be fed into the extruder through a recycling tank; product particles are recovered into this recycling tank under certain conditions. When laboratory analysis shows failures, or when there are obvious quality issues such as black spots or discoloration, or when changes in the filter elements of the extruder or fluctuations in the motor load of the extruder can cause the particles to have black spots or discoloration, the volatile components in the molten polymer are removed from the extruder’s vent section under a vacuum of 600 mmHG. The volatile components extracted from the extruder include those present in the raw materials, process water, as well as TOX and formaldehyde in the polymer. Formaldehyde and other volatile components are very important to be removed from polymers under vacuum conditions, as a high residual formaldehyde content in the polymers can cause sedimentation during injection molding by customers. Since the final product is formed in the extruder, a polymer filter is installed at the end of the extruder to remove solid contaminants from the polymer, such as metal fragments, black spots, and unmelted stabilizers. By comparing the readings of the pressure difference indicators installed upstream and downstream of the filter, it is possible to determine whether the filter element is dirty (the pressure difference for a clean filter element is generally 30–50 kg/c㎡); when the pressure difference reaches 50 kg/c㎡, the filter element must be replaced as it is dirty. The molten polymer in the extruder passes through a water ring pelletizing system. To prevent the molten material from solidifying in the die, the die must be heated with medium-pressure steam. The particles formed in the pelletizer are generally spherical, with a diameter of about 3.0 mm. Since the pelletizer determines the size and shape of the particles in the final product, its proper operation and maintenance are very important. After coming out of the pelletizer, the particles are conveyed in the form of a slurry to the centrifugal drier, which separates the particles from the cooling water. The dehydrated particles contain 0, 5–2.0 wt% moisture and are blown into a dryer or a recovery tank (as defective products). The granulation cooling water in the dehydrator flows back to the cooling water tank by gravity. After leaving the cooling water tank, it passes through a filter first to remove any particles or solids containing residual formaldehyde, then through a cooler to absorb excess heat, and is finally pumped back to the granulator. The pellet cooler uses cooling water to remove the molten heat absorbed by the pellets, and the temperature of the cooling water exiting the cooler is generally kept at 60°C. The temperature of the extruder barrel is divided into 12 separate zones for independent control. The temperature in these 12 zones is regulated using electric heaters for heating and cooling water for cooling. The particle dryer is a two-stage funnel-type dryer, in which the particles are dried. The function of the primary dryer is to raise the temperature of the particles ； The function of the secondary dryer is to remove the wet powder from the particles, reducing its content to less than 0.1%, and to lower the level of residual formaldehyde. The removal of residual formaldehyde is particularly important for customers, as residual formaldehyde can initiate chain reactions that result in deposits within the injection molding machine. The residual formaldehyde content in the particles coming out of the extruder is generally 300–500 ppm; however, after treatment in a dryer, this level can be reduced to below 100 ppm. The main variables affecting the dryer’s ability to reduce residual formaldehyde are the temperature of the polymer and the effective residence time. The temperature of the polymer is set at 120°C, while the residence time is set at 4–6 hours. The flow rate of hot air through the dryer has no significant effect on the reduction of residual formaldehyde. However, to ensure a steady distribution of the hot air flowing through the particle bed, the surface flow velocity must be maintained at at least 0.15 m/s. Another factor that needs to be taken into account during design and operation is preventing particles from remaining in the high-temperature dryer for too long. If the particles remain for too long, they will change color (the B-value will increase). To prevent this phenomenon, the temperature of the polymer in the dryer must be limited to a maximum of 120°C, and the total residence time must be kept at no more than 6 hours. The finished product storage tank is installed downstream of the dryer, with the finished product particles being blown directly from the dryer into the storage tank. Under normal operating conditions, the finished particles are directly blown into the dryer. The residence time of the particles in the dryer is indirectly controlled by the weight controller for drying. The weight controller can control the speed of the cyclone valve at the dryer outlet. To maintain a normal dryer residence time, the setpoint of the dryer weight controller must be determined based on the extruder’s extrusion rate. The normal residence time for residual formaldehyde particles in the dryer to be removed is 4-6 hours. The temperature of the particles in the dryer is controlled by the temperature of the hot air used to heat the dryer, and can be maintained at 115–120°C. The hot air for heating the dryer is supplied by a fan; the air exiting the fan is filtered before being heated by a heater that uses medium-pressure steam as the heating medium. The hot air is divided into three streams, which are supplied to the dryer respectively. The air intake at a lower position serves mainly to remove residual formaldehyde, while the air intake at a higher position functions to dry the air and remove residual formaldehyde. The waste gas from the dryer enters the flue gas scrubber through a dust collector. The particles at the dryer outlet are conveyed to the finished product tank via a vibrating screen, which serves to remove particles that are too large in size. 4. Applications of polyoxymethylene: Its regular molecular structure and crystallinity confer excellent physical and mechanical properties, earning it the nickname \"metal plastic\". POM is a milky, opaque, crystalline linear thermoplastic resin with excellent overall properties and coloring capabilities; it features a high elastic modulus, as well as high stiffness and hardness, while its specific strength and specific stiffness are comparable to those of metals ； It exhibits excellent tensile strength, bending strength, creep resistance, and fatigue resistance, as well as good resistance to repeated impacts and excellent recovery after unloading ； It has a low coefficient of friction, is wear-resistant, offers good dimensional stability, has a pleasant surface finish, exhibits high viscoelasticity, low water blowout, excellent electrical insulation properties, and is not affected by temperature ； It has excellent chemical resistance, except against strong acids; it also possesses vibration-damping and noise-reducing properties ； Low water absorption, good insulation resistance, and unaffected by humidity ； Excellent chemical resistance: Stable against other chemicals except strong acids, phenols, and organic halides; oil-resistant ； Its mechanical properties are little affected by temperature, and it has a high heat distortion temperature. The disadvantages are poor flame retardancy, as it burns slowly when exposed to fire; its oxygen index is low, and even the addition of flame retardants does not yield satisfactory results. Additionally, its weather resistance is inadequate, requiring the use of stabilizers for outdoor applications. Due to its high hardness, wear resistance, fatigue resistance, high impact strength, good dimensional stability, and self-lubricating properties, polyoxymethylene is widely used in the manufacture of various structural components for mechanical equipment such as gears, rollers, bearings, conveyor belts, springs, cams, bolts, as well as pump bodies, housings, and impeller friction bearings. Machine tool guides made of highly lubricious polyoxymethylene modified with polytetrafluoroethylene emulsion possess excellent stiffness and fatigue resistance, overcoming the drawbacks of pure polytetrafluoroethylene such as susceptibility to wear and creep. Moreover, they have essentially the same static and dynamic friction coefficients when in contact with metals, demonstrating outstanding self-lubricating properties. 4.1 Applications of pharmaceutical packaging machinery: conveyor screws, star wheels, racks, sprockets, shims, etc. The image shows imported equipment parts manufactured by our company using polyoxymethylene. 4.2 Applications in the automotive industry: Polyoxymethylene is used in large quantities in the automotive industry. Parts made of polyoxymethylene offer advantages such as reduced number of lubrication points, wear resistance, ease of maintenance, simplified design, improved efficiency, lower costs, and savings in copper usage. Using alternatives to copper for components such as half-shafts and planetary gears in cars not only saves copper but also increases their service life. In engine fuel systems, POM can be used to manufacture components such as radiator water pipe valves, radiator caps, spare coolant tanks, water valve bodies, fuel tank caps, water impellers, carburetor housings, and throttle pedals. 4.3 Applications in electronics and electrical appliances Due to its low power consumption, high dielectric strength and insulation resistance, as well as arc resistance, polyoxymethylene is widely used in the field of electronics and electrical appliances. Polyoxymethylene can be used to manufacture the casings of electric wrenches, electric wool cutters, coal drills, and switch handles, as well as components for telephones, radios, recorders, video recorders, televisions, computers, and fax machines, timer parts, and recorder tape holders. 4.4 Applications of agricultural machinery: components of manual sprayers, connection and coupling parts of seeders, moving parts of milking machines, pump housings for irrigation and drainage, inlet and outlet valve seats, fittings, and sleeves, etc. It can also be used for aerosol packaging, delivery tubes, components immersed in oil, and standard resistor panels, among other things. 4.5 Other applications in construction: It can be used for tap handles, window frames, washbasins, water tanks, door curtain pulleys, meter casings, and pipe connectors, among other things. 5. Analysis of China’s POM industry 5.1 The importance of polyoxymethylene technology for China’s economic development As an engineering plastic with excellent properties, polyoxymethylene is a strategic product for China, and its development should be promoted actively. It is highly necessary and important for China to develop its own technology for producing tens of thousands of tons of polyoxymethylene as soon as possible. Firstly, China’s energy structure is dominated by coal, and methanol, the starting material for polyoxymethylene, is one of the coal-based chemical products that can be manufactured on a large scale in the country. Therefore, from the perspective of the energy structure, it holds strategic significance for China to develop polyoxymethylene vigorously. It is conducive to fostering a new coal chemical industry in our country in the 21st century. Secondly, as a pillar industry in our country, the automotive industry is developing rapidly at present. However, the proportion of polyoxymethylene used in China’s automotive sector is far below the world average. Therefore, it is necessary to increase the use of polyoxymethylene in this industry; this will not only promote the development of China’s polyoxymethylene industry but also contribute to the localization of automobile production. As the process of localizing China’s automotive industry accelerates, this sector will be one of the areas with the fastest growth in polyoxymethylene consumption in the future. **Relevant departments should organize experts to digest and absorb the introduced technologies, and then mobilize various resources to work on solving key challenges, in order to develop domestic production facilities capable of producing tens of thousands of tons per year as soon as possible, with a focus on advancing technology related to copolymerized formaldehyde. The top priority is to invest considerable funds to improve various supporting processes and ensure the proper operation of the 10,000-ton polyoxymethylene plant already introduced in the country by Yuntianhua. Even if it is difficult to make breakthroughs in domestic production technology for polyoxymethylene on a ten-thousand-ton scale in the short term, given the current market demand and future trends in demand growth, it is necessary to take various measures—such as setting up wholly-owned enterprises—to introduce more advanced foreign technologies for copolymerized polyoxymethylene and build several production facilities with a capacity of ten thousand tons each. The development of China’s polyoxymethylene industry is an urgent matter that cannot wait. 5.2 Problems Faced by China’s POM Industry 5.2.1 The growth in China’s POM production capacity is not sufficient to meet market demand. The domestic POM market is growing rapidly, yet China’s foundation for POM production is relatively weak ； Furthermore, POM is a capital- and technology-intensive chemical product in the materials sector. China’s large market has attracted the attention of foreign companies, which have been trying to gain a foothold in this market with their own products. They are reluctant to transfer technology, which has resulted in slow progress in improving the technical level of domestically produced POM, failing to meet the needs of users ； Furthermore, for a long time, China’s economic system and corporate management mechanisms have not conformed to the laws of a market economy; as a result, enterprises have been unable to obtain sufficient funding in a timely manner, which has hindered the development of POM production. 5.2.2 Imbalance between imports and exports: Although China’s POM production has increased, it still cannot meet the demands of the domestic market, resulting in the need to import large quantities of POM each year. The main countries and regions from which China imports POM are Japan, the United States, South Korea, and Taiwan Province of China. In 2002, China’s POM imports amounted to 135,570 tons, and the average annual growth rate of POM imports from 1995 to 2002 was 26.3%. Our country also engages in small-scale export trade of POM each year; in 2002, 9,000 tons of POM were exported. The development of high-tech industries and emerging sectors in our country has led to a significant increase in the demand for engineering plastics. As an engineering plastic suitable for various industries, POM has promising prospects for development. Given the situation of planned POM projects in our country, it will be the trend for the development of the POM industry there to introduce capital and advanced technical equipment to build POM production facilities on a scale that is economically viable, in locations that possess the necessary raw material and technical foundations. 5.2.3 The technological gap cannot be ignored. Although the market demand for POM in China is on the rise, due to the relatively late start of POM research and development in the country, the domestic production scale, output, as well as the variety and quality of POM products fail to meet market demands. Compared with the advanced levels abroad, China’s POM production still faces issues such as high raw material consumption, small plant scale, unstable quality, and a limited range of grades and types. For example, DuPont’s consumption of formaldehyde per ton of POM produced via its homopolymerization process is 2.56 tons; some reports indicate this figure to be 3.08 tons. In China, the formaldehyde consumption per ton of POM produced is between 5 and 6 tons. Although this figure has decreased as a result of improvements, the gap remains significant. 6. References: Handbook of Engineering Plastics, edited by Shi Anfu and Gong Yunbiao. -- Shanghai: Shanghai Science and Technology Press, 2003. 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