Manufacturing and application of polybutene pipes
1. Overview of polybutene (PB) pipelines: In recent years, the amount of cold and hot water plastic pipelines used in buildings in China has soared. By 2007, the total amount had reached 400,000 tons. Among them, poly pipes, including PP-R and PP-B, are about 220,000 tons; polyethylene pipes, including PEX, PE-RT, HDPE, aluminum-plastic composite pipes, and various steel (copper)-plastic composite pipes, are about 120,000 tons; Vinyl chloride pipelines, including PVC-U, PVC-C, and PVC-M, are about 50,000 tons; other pipelines such as polybutene (PB) and ABS are about 10,000 tons. According to a survey conducted by the Ministry of Construction, except for a few regions such as Guangdong and Guangxi, most of China has a climate with four distinct seasons, which are cold in winter and hot in summer. 90% of the population needs heating in winter and air conditioning in summer. Radiant floor heating is rapidly spreading, which has greatly promoted the development of new plastic pipes. Looking to the future, due to the established national energy-saving policy, the hot and cold water pipelines used in buildings in China will maintain a strong momentum of sustained and rapid development. Among them, the polybutene (PB) pipeline, which has developed abnormally in recent years, is particularly eye-catching. The high price of its raw materials, strictly controlled raw material supply channels, and the hype of “plastic gold” add to its mystery. This article is to introduce the production and use technology of this product, in order to get rid of the mysterious veil shrouded in the polybutene pipe.
Polybutene (PB) resin is a polymer made of butene. It is an isotactic semi-crystalline polyolefin thermoplastic with linear molecular structure, and its crystallinity is generally 50-55%. ISO 8986-1: 1993 stipulates that polybutene (PB) resin can be a homopolymer of butene or a copolymer with a butene content of more than 50%.
Commercial products of polybutene are based on isotactic (98-99.5%), high molecular weight (average molecular weight of 230,000-750,000) polymers. There are five known crystalline variations of polybutene: Form I; Form II; Form III; Form I’; Form II’. The glass transition temperature ranges from approximately -20°C for homopolymers to -34°C for high ethylene content copolymers. The crystallization reaction of the melt first produces the metastable form II of the tetragonal crystal form; at ambient temperature and atmospheric pressure, the homopolymer will irreversibly transform from form II to the stable state of twin hexagonal crystal form after 5-7 days I. For copolymers, this process takes 1 to 3 days. Therefore, after the production of PB pipes is off the line, it needs to be placed for 5-7 days before they can be delivered to the user; while in the production of coils, they should be laid flat for 5-7 days before rewinding into coils; otherwise, it will be difficult for the coils to reach the user. Uncoiling and straightening will affect the user’s construction and laying.
For various homopolymers, the melting point of Form I ranges from 107 to 130°C, for copolymers with low ethylene content, the melting point ranges from 114 to 118°C, and for copolymers with high ethylene content, the melting point ranges from 90～95℃. After switching to form I, the homopolymer has a crystallinity of 48-55%, while the copolymer has a crystallinity of 35-45% depending on the ethylene content.
PB resin is generally resistant to acids, alkalis, solvents, paraffin oil and naphthenic oil, detergents and various chemicals, but its resistance at high temperatures will be reduced. The resin also has good water blocking properties and electrical insulation properties. The material shows a wide range of flexural properties, with a homopolymer having a tensile modulus of 286 MPa and a high ethylene content copolymer of 52 MPa. PB’s creep resistance, environmental open stress resistance and abrasion resistance are very good. All grades are supplied in pellets. PB resin with a melt index (MI) of 0.4g/10min (ASTM D-1238, condition E) can be used to process hot and cold water pipes. There are many other grades of PB resin, which can be used to produce films, or as an impact modifier and processability modifier for other polyolefin resins.
2. The characteristics of polybutene (PB) pipe ) Hot and cold water pipes, pipe fittings can be produced by standard injection molding machines.
Polybutene (PB) pipe has excellent heat and creep resistance and high temperature resistance. It can be used for a long time at 82.2°C, and the temperature can be as high as 95°C for a short time. PB pipes are light, flexible, and have good impact resistance, so they are used in cold and hot water systems in buildings. In recent years, domestically produced PB pipelines are mainly made of polybutene (PB) produced by the Dutch company Basel (BASELL) as raw materials (grey 4237, white 4235). Basel (BASELL) has adopted and other European manufacturers to develop in China The open supply of special materials for PP-R and HDPE pipes has completely different raw material supply methods. All Chinese companies wishing to produce polybutene (PB) pipes should apply to Basel (BASELL) and be inspected by Basel (BASELL) It is believed that the production conditions are qualified before it can be included in the list of raw materials to be supplied; this has allowed the number of domestic enterprises producing polybutene (PB) pipelines to remain at seven for a considerable period of time. The pipeline industry calls the seven alliances: George -Fisher, Weixing, Akcome, Angu, Yuxin, Huayuan Asia Pacific, North Jingda (later added a “Chuan Road”), etc. Basel (BASELL) strictly controls the supply of raw materials so that the polybutene (PB) pipe products on the market can only come from these seven companies, effectively controlling the fraud problem that has been a headache for the domestic plastic pipe industry, and also keeping it The reputation of polybutene (PB) pipelines maintains the high prices and high profits of raw materials and products. Moreover, due to the timely formulation of the national standard GB/T 19473.1-2004, there are standards for the production and application of polybutene (PB) pipelines, and the development of China’s PB pipelines has been relatively healthy.
But the market rules are beyond anyone’s control. In recent years, after Japan’s “Mitsui” expanded its polybutene (PB) resin production capacity, it began to promote polybutene (PB) pipe special materials in the Chinese market. Weifang Paikang and Langfang Toyo Companies that use Mitsui’s raw materials to produce PB pipes have also risen rapidly. Therefore, BASELL’s monopoly on China’s polybutene (PB) resin has been broken. In the future, the domestic polybutene (PB) pipeline production and sales market will definitely face Reshuffle the cards.
PB pipeline has the following characteristics: 1. Light weight, good flexibility, and convenient construction: The weight of PB pipeline is about 1/5 of galvanized steel pipe, easy to handle, flexible, and the minimum bending radius is 6D (D: outer diameter of the pipe). Hot melt connection can also be mechanically connected, which is convenient for construction; 2. Good durability, non-toxic and harmless: Because of its high molecular weight and stable molecular structure, the service life is not less than 50 years without ultraviolet radiation. , And non-toxic and harmless; 3. Good frost resistance and heat resistance: at -20℃, it can also maintain good low-temperature impact resistance. After thawing, the pipe can be restored to its original shape; at 82℃ , The performance of all aspects is still maintained well; 4. The pipe wall is smooth and does not scale: Compared with galvanized pipe, the water flow can be increased by 30%; 5. The connection method is advanced: the connection method is an integrated hot melt connection, so When burying, it can avoid the movement of the pipe and the leakage of the joint caused by temperature changes and water hammer; PB pipe fittings are produced by injection molding, and only all plastic pipe fittings can be produced in China. In recent years, due to the continuous advancement of technology, Domestically, it has been able to produce pipe fittings with metal inserts, realizing the serialization of PB pipe fittings, and greatly promoting the application of PB pipe systems. 6. Easy to repair: When PB pipe is buried, it does not bond with concrete. When it is damaged, it can be repaired quickly by replacing the pipe. However, the best way to embed plastic pipes is to use a casing (i.e. pipe-in-pipe) method. First, put a PVC single-wall corrugated pipe on the outer jacket of the PB pipe, and then bury it, so that future maintenance can be guaranteed. . Third, the performance and application of polybutene (PB) pipeline 1, the characteristics of BASELL 4235 PB resin
2. Characteristics of Mitsui PB resin
3. The main application areas of polybutene (PB) pipelines 1) Cold and hot water pipes for domestic water, pipes for direct drinking water projects to ensure no secondary pollution of water quality; 2) Heating pipes, which can be used to connect radiators and other high-temperature radiant heating The system is also suitable for low-temperature heating systems such as floor and wall radiant heating and air-conditioning pipe systems; 3) Solar residential warm water pipes, used for warm water and heating piping of solar residential buildings; 4) Snow melting pipes, suitable for roads and parking lots As heating piping for deicing and snow removal; 5) Industrial pipes, due to their strong chemical resistance, non-toxic and odorless, can be used in chemical engineering, food processing, industrial water and other fields.
4. Oxygen barrier polybutene (PB) pipes. In the field of HVAC, PB pipes have superior characteristics that other plastics cannot match. However, the oxygen permeability of polybutene pipes is slightly higher. If the hot water pipe contains more oxygen, it will easily corrode the metal pipe fittings and other devices in the system, which is even more unfavorable for the high-temperature heating system connected to the metal radiator. In addition, although the inner wall of the pipe is smooth and does not scale; practice has proved that after 3 to 5 years of use, a thin layer of biological slime will adhere to the inner wall of the pipe. After this layer of slime completely covers the inner wall of the pipe, the pipe wall The diameter will be reduced quickly, the water flow resistance will increase, and the water flow will drop sharply; over time, it will also block the pipeline. The cleaning of the pipeline is very difficult, and it can only be cleaned by mechanical methods, and other methods such as chemical methods are difficult to achieve results. This is because the rich oxygen in the water leads to the reproduction of microorganisms, and the high oxygen permeability of the pipe means that the pipe will breathe, which promotes the proliferation of microorganisms. A large number of dead microorganisms accumulate to form biological slime. Therefore, oxygen barrier technology must be used to inhibit the reproduction of microorganisms, so as to effectively ensure the safe use of pipelines.
There are currently two types of oxygen barrier PB pipelines on the market, both of which use a very thin (only about 10 filaments) ethylene-vinyl alcohol copolymer (EVOH) resin layer as the oxygen barrier. One is a three-layer oxygen barrier PB pipe, that is, a layer of hot melt adhesive and EVOH resin layer is evenly coated on the outside of the PB pipe. The structure from the outside to the inside is: oxygen barrier layer/hot melt adhesive/PB resin, 20*2.0 The design size of pipe wall thickness is: 0.10/0.05/2.0mm. Because EVOH resin is easier to absorb moisture and the oxygen barrier capacity of EVOH resin after absorbing moisture will be greatly reduced, and the surface is easily scratched during construction, the oxygen barrier effect will be reduced; therefore, the three-layer oxygen barrier PB tube is not in a complete sense. The oxygen barrier tube. The other is a five-layer co-extruded oxygen barrier PB tube, in which the inner layer PB is thicker to bear pressure, and the outer layer PB is thinner to protect and weld. The structure is: PB resin / hot melt adhesive / oxygen barrier Layer/hot melt adhesive/PB resin, 20*2.0 pipe wall thickness design size is 0.60/0.05/.010/0.05/1.40; it is not difficult to see that this kind of pipe is ideal, but the processing is difficult and the equipment cost is high. According to the test results, the increase of the oxygen barrier layer can reduce the oxygen permeability of the PB monolayer tube by 99.6%. In layman’s terms, without an oxygen barrier layer, the oxygen penetration rate is 100% (equivalent to replacing the entire system with new water every 2 days). If you want to add an oxygen barrier layer to it, its oxygen penetration rate The input rate has been reduced by 99.6% (equivalent to a new water change for the entire system every 125 days), which can fully meet the requirements of the German standard DIN 4726 for the oxygen barrier properties of heating plastic pipes. The production of oxygen-barrier PB pipes is more complicated. The three-layer structure can be co-extrusion process or two-co-extrusion coating process. The latter method is relatively easy to control, and the design and manufacture of the mold are relatively simple. The main advantage is that the rejection rate is relatively low. Because the PB pipeline waste with oxygen barrier layer cannot be recycled and reused, and the price of raw materials is high, many companies choose the secondary co-extrusion coating process. Of course, it also has disadvantages. Compared with the one-time co-extrusion process, the coating layer of the secondary co-extrusion coating process pipe is thicker; because the price of EVOH is almost twice as high as that of PB, the thicker the coating layer, the thicker the pipe The production cost is also higher. For the production of five-layer PB pipes with oxygen barriers, only one co-extrusion process is currently being used.
At present, there are not many domestic manufacturers of oxygen barrier tubes, mainly George, Weixing, Angu, Huayuan, Broadway, Paikang, etc. Some of them use imported production lines, while enterprises like Broadway and Paikang are It is produced with domestic equipment.
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