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Status And Development Of Unsaturated Polyester Resin Products

Jun 03, 2020

The development of unsaturated polyester resin products has a history of more than 70 years. In such a short period of time, unsaturated polyester resin products have developed rapidly in terms of output and technical level. At present, unsaturated polyester resin products have developed into one of the largest varieties in the thermosetting resin industry.

In the development process of unsaturated polyester resins, technical information from product patents, business magazines, technical books, etc. emerged endlessly. There are hundreds of invention patents every year about unsaturated polyester resins. It can be seen that the manufacturing and application technologies of unsaturated polyester resins are becoming more and more mature with the development of production, and gradually formed their own unique and complete technical system of production and application theory.

In the past development process, unsaturated polyester resin has a special meaning for general use. In the future, we will develop into some special-purpose fields, and at the same time, we must reduce the cost of general-purpose resins. The following introduces several types of unsaturated polyester resins that are meaningful and promising.

1) Low shrinkage resin. This type of resin may be just an old topic. Unsaturated polyester resins are accompanied by large shrinkage during curing, and the general volume shrinkage rate is 6-10%. This shrinkage can severely deform or even break the material, especially in the compression molding process (SMC, BMC). To overcome this shortcoming, thermoplastic resins are usually used as low-shrinkage additives. The first patent in this field was DuPont in 1934 with the patent number U.S. 1,945,307. The patent describes the copolymerization of dicarboxylic acids and vinyl compounds. Obviously, at the time, this patent pioneered the low-shrinkage technology of polyester resin. Since then, many people have devoted themselves to the study of copolymer systems, which were considered plastic alloys. In 1966, Marco's low-shrinkage resin was first used in molding and industrial production. Later, the Plastics Industry Association referred to this product as "SMC", meaning sheet molding compound, and its low-shrink premix compound "BMC" meaning bulk molding compound. For SMC sheet, the resin molded parts are generally required to have good fit tolerance, flexibility and A-level gloss. To avoid micro-cracks on the surface, this requires the compounded resin to have a low shrinkage rate.

Of course, there have been many patents that have improved and improved this technology. The understanding of the mechanism of low shrinkage has gradually matured, and various varieties of low shrinkage agents or low profile additives have emerged. Commonly used low shrinkage additives are polystyrene, polymethyl methacrylate, etc.

2) Flame retardant resin. Sometimes flame retardant materials have the same importance as drug rescue. Flame retardant materials can avoid or reduce the occurrence of disasters. Due to the use of flame retardants in Europe in the last ten years, the number of fire fatalities has decreased by about 20%. The safety of the flame retardant material itself is also very important. In the industry, it is a slow and difficult process to regulate the type of material used. At present, the European Community has been and is harming many halogen and halogen-phosphorus flame retardants. Evaluation, many of which will be completed between 2004 and 2006.

At present, my country generally uses chlorine-containing or bromine-containing diols or dibasic acid halogen substitutes as raw materials to prepare reactive flame retardant resins. Halogen flame retardants will produce a lot of smoke when burning, accompanied by the formation of highly irritating hydrogen halide. This dense smoke and poisonous mist produced in the combustion process causes great harm to people. According to statistics, more than 80% of deaths in fire accidents are caused by this. Another disadvantage of using bromine or chlorine as a flame retardant is that it will also produce corrosive and environmentally polluting gases when it burns, which will cause damage to the original electrical appliances. Using inorganic flame retardants such as hydrated alumina, magnesium, boron, molybdenum compounds and other flame retardant additives, although it has obvious smoke elimination effect, it can produce low smoke and low toxicity flame retardant resin, but if the amount of inorganic flame retardant filler is too large, Not only the viscosity of the resin increases, but it is not conducive to construction. At the same time, when a large amount of added flame retardant is added to the resin, it will affect the mechanical strength and electrical properties of the resin after curing and molding.

At present, many foreign patents report the use of phosphorus-based flame retardants to produce low-toxic, low-smoke flame retardant resin technology. The flame retardant effect of the phosphorus flame retardant is quite large. The metaphosphoric acid generated during combustion can be polymerized into a stable polymeric state, forming a protective layer, covering the surface of the burnt, isolating oxygen, promoting dehydration and carbonization of the resin surface, and forming a carbonized protective film Thereby preventing burning. At the same time, phosphorus flame retardants can also be used in conjunction with halogen flame retardants, which has a very obvious synergistic effect.

Of course, the future research direction of flame retardant resins is low smoke, low toxicity and low cost. The ideal resin is a flame-retardant resin that is smoke-free, low-toxic, low-cost, does not affect the inherent physical properties of the resin, does not need to add additional materials, and can be directly produced in the resin production plant.

3) Toughened resin. Compared with the original unsaturated polyester resin varieties, the toughness of the current resin has been greatly improved. However, with the development of the downstream industries of unsaturated polyester resins, more new requirements have been put on the performance of unsaturated resins, especially in terms of toughness. The brittleness of unsaturated resins after curing has almost become an important issue limiting the development of unsaturated resins. Regardless of whether it is a cast or molded product or a molded or wound product, the elongation at break has become an important indicator for evaluating the quality of resin products.

At present, some foreign manufacturers use the method of adding saturated resin to improve toughness. Such as adding saturated polyester, styrene-butadiene rubber and carboxyl-terminated styrene-butadiene rubber, etc., this method belongs to the physical toughening method. It is also possible to introduce block polymers into the main chain of unsaturated polyester, such as the interpenetrating network structure formed by unsaturated polyester resin and epoxy resin and polyurethane resin, which greatly improves the tensile strength and impact strength of the resin This toughening method belongs to the chemical toughening method. It is also possible to use a combination of physical toughening and chemical toughening, such as mixing unsaturated polyesters with higher activity with materials with lower activity to achieve the required flexibility. At present, SMC sheet has been widely used in the automotive industry due to its light weight, high strength, corrosion resistance, and design flexibility. For important parts such as automotive panels, rear doors, and outer panels, good toughness is required, such as automotive exterior. The guard plate can be bent back to a limited extent after being slightly touched and restored to its original state.

Increasing the toughness of the resin will often lose other properties of the resin, such as hardness, bending strength, heat resistance, and curing speed during construction. Improving the toughness of the resin without losing other inherent properties of the resin has become an important issue in the research and development of unsaturated polyester resins.

4) Low styrene volatile resin. In the process of processing unsaturated polyester resins, volatile toxic styrene will cause great harm to the health of construction workers. At the same time, the emission of styrene into the air can also cause serious air pollution. Therefore, the functional authorities of many countries limit the allowable concentration of styrene in the air of production workshops. For example, in the United States, its allowable PEL value (permissible exposure level) is 50 ppm, while in Switzerland, its PEL value is 25 ppm. Such low content is not easy to achieve. Relying on strong ventilation is also very limited. At the same time, strong ventilation will also lead to the loss of styrene from the surface of the product and the volatilization of a large amount of styrene into the air. Therefore, looking for ways to reduce styrene volatilization, from the root, it is still necessary to complete this work in the resin production plant. This requires the development of low-styrene volatile (LSE) resins that do not pollute or pollute the air or unsaturated polyester resins that do not contain styrene monomer.

Reducing the content of volatile monomers has been the subject of development in the unsaturated polyester resin industry abroad in recent years. There are many methods currently used: 1) The method of adding low volatile inhibitors. 2) The formulation of unsaturated polyester resin without styrene monomer uses divinyl, vinyl methylbenzene and α-methylstyrene to replace the vinyl monomer containing styrene monomer 3) Low styrene monomer The unsaturated polyester resin formulation of the body is to use the above monomers and styrene monomers together, such as the use of high boiling point vinyl monomers such as diallyl phthalate, acrylic copolymers and styrene monomers. 4) Another One method to reduce the volatility of styrene is to introduce other units such as dicyclopentadiene and its derivatives into the skeleton of the unsaturated polyester resin to achieve low viscosity and ultimately reduce the styrene monomer content.

In seeking to solve the problem of styrene volatilization, it is necessary to comprehensively consider the applicability of the resin to the existing molding methods such as surface spraying, lamination process, SMC molding process, the raw material cost of industrial production, and the compatibility with the resin system , Reactivity of resin, viscosity, mechanical properties of resin after molding, etc. In China, there is no clear legislation on restricting styrene volatilization, but with the improvement of people’s living standards, people’s awareness of their own health and environmental protection, for the unsaturated consumer countries like us, the relevant legislation is only a matter of time. .

5) Corrosion-resistant resin. One of the larger uses of unsaturated polyester resins is their corrosion resistance to chemicals such as organic solvents, acids, alkalis, and salts. At present, corrosion-resistant resins are divided into the following categories: 1) o-benzene type, 2) m-benzene type, 3) p-benzene type, 4) bisphenol A type, 5) vinyl ester type, and other such as xylene type, containing The halogen compound type, etc., after decades of continuous exploration by several generations of scientists, the corrosion of the resin and the corrosion resistance mechanism have been thoroughly studied.

The resin is modified by various methods, such as introducing a molecular skeleton that is difficult to resist corrosion into the unsaturated polyester resin or using an unsaturated polyester to form an interpenetrating network structure with vinyl ester and isocyanate, which improves the corrosion resistance of the resin It is very effective, and the resin made by mixing with acid resin can also achieve better corrosion resistance. Compared with epoxy resin, the low cost and easy processing of unsaturated polyester resin have become a great advantage, but the corrosion resistance of unsaturated polyester resin, especially alkali resistance, is far inferior to epoxy resin for a long period of time. Later, especially in the occasions with severe corrosion, unsaturated polyester resins cannot replace epoxy resins. The rise of the anti-corrosion floor is currently forming opportunities and challenges for unsaturated polyester resins. Therefore, the development of special corrosion-resistant resins has broad prospects.

6) Gel coat resin. Gel coat plays an important role in composite materials. It not only plays a role in decorating the surface of FRP products, but also plays a role in wear resistance, aging resistance and chemical corrosion resistance. The development direction of gel coat resins is to develop gel coat resins with low styrene volatility, good air drying properties and strong corrosion resistance. The heat-resistant water gel coat in gel coat resin has a great market. If the glass fiber reinforced plastic material is immersed in hot water for a long time, blisters will appear on the surface. At the same time, the water blisters gradually expand because the water gradually penetrates into the composite material. The appearance of the gel coat, and will gradually reduce the strength properties of the product. Kansas Kitchen Appliances Co., Ltd. (CookComposites and Polymers Co.) uses epoxy resin and glycidyl ether-terminated method to make a gel coat resin with low viscosity and excellent water resistance and solvent resistance. In addition, the company also uses resin A (flexible resin) modified with polyether polyol and epoxy resin termination and resin B (rigid resin) modified with dicyclopentadiene (DCPD), both of which have The water-resistant resin is compounded, in addition to good water resistance, it also has good toughness and strength. It can be used as a gel coat resin or a barrier resin between the gel coat resin and the ordinary resin, which can effectively prevent water Or solvents or other low-molecular substances penetrate into the glass fiber reinforced plastic material system through the gel coat layer and become a water-resistant resin with excellent comprehensive performance.

7) Light-cured unsaturated polyester resin. The photo-curing characteristics of unsaturated polyester resins are long application period and fast curing speed. Unsaturated polyester resin can meet the requirement of styrene volatilization limit by light curing. Due to the advancement of photosensitizers and lighting devices, it has laid the foundation for the development of photocurable resins. Various UV-curable unsaturated polyester resins have been successfully developed and put into mass production. Improve the material performance, process performance and surface wear resistance, while using this process also improves production efficiency.

8) Low-cost resin with special properties. Such resins include foamed resins and water-containing resins-at present, the lack of wood energy has an upward trend worldwide. There is also a shortage of skilled operating workers engaged in the wood processing industry, and these workers are getting higher and higher salaries. Under these conditions, conditions have been created for engineering plastics to enter the wood market. Unsaturated foamed resin and water-containing resin as artificial wood will be developed in the furniture industry with its low cost and high strength. The application will be slow at the beginning, and with the continuous improvement of processing technology, this application will be developed rapidly.

Unsaturated polyester resin can be foamed into foamed resin, which can be used as wallboard, pre-formed bathroom partition, etc. Foam with unsaturated polyester resin as the matrix has better toughness and strength than foamed PS; processing is easier than foamed PVC; the cost is lower than that of foamed polyurethane plastic; adding flame retardants can also make it flame retardant and resistant to aging. Although the application technology of resin has been fully developed, the application of foamed unsaturated polyester resin in furniture has not been paid attention to. After investigation, some resin manufacturers have great interest in developing this new type of material. Some major problems (skin formation, honeycomb structure, gel-foaming time relationship, exothermic curve control) have not been completely solved before industrial production. Before getting the answer, this resin can only be used in the furniture industry because of its low cost. Once these problems are resolved, this resin will be widely used in foam flame retardant materials and other fields rather than just use its economy.

The water-containing unsaturated polyester resin can be divided into two types: water-soluble type and emulsion type. Foreign countries have had patents and literature reports in this area since the 1960s. The water-containing resin is a filler that uses water as the unsaturated polyester resin and is added to the resin before the resin gel. The water content can be up to 50%. Such a resin is called WEP resin. The resin has the characteristics of low cost, light weight after curing, good flame retardancy, low shrinkage and so on. The development and research of water-containing resin in my country began in the 1980s, and has been for a long time. In terms of application, it has been used as an anchoring agent. Water-containing unsaturated polyester resin is a new variety of UPR. The technology of the laboratory is becoming more mature, but there is less research on the application. The problems that need to be further solved are the stability of the emulsion and some problems in the curing process and the customer's approval. Generally, a 10,000-ton unsaturated polyester resin can produce about 600 tons of waste water per year. If the shrinking water produced in the production process of unsaturated polyester resin is used to produce water-containing resin, the resin cost is reduced and the environmental protection problem is solved.

 9) High-performance resin synthesized with new raw materials and new processes. Dicyclopentadiene modified unsaturated polyester resin is a resin variety that has developed rapidly in my country in recent years. According to the test data provided by Jiangsu Yabang Coatings Co., Ltd. and Tianjin Hemu Co., Ltd., the technical indicators of the performance of the cast body and glass fiber reinforced plastics of the DCPD modified resin are comparable to those of the ordinary o-benzene resin. At present, dicyclopentadiene resin is quickly accepted by the market with its low price and good performance. Various enterprises have developed such products one after another, and the product technology has gradually matured. Among them, the "Low Temperature Catalytic Synthesis of Dicyclopentadiene Unsaturated Polyester Resin" developed by Tianjin Hecheng Resin Co., Ltd. passed the scientific and technological achievements appraisal of Tianjin Science and Technology Commission in 2004 and won the second prize of Tianjin Excellent Project in 2005.

 The use of recycled waste polyethylene terephthalate (PEF) or recycled waste terephthalic acid (PTA) can produce unsaturated polyester resins, which not only solves environmental problems, but also reduces the cost of synthetic high-performance resins. Synthetic resins have excellent toughness, elasticity, and strength, some properties are even better than resins made with isophthalic acid, and the cost is comparable to phthalic resins. Since p-benzene resin is superior to o-benzene and m-benzene resins in corrosion resistance and heat resistance, it also greatly expands the application of this resin in the field of chemical corrosion protection. The 199A resin produced by Tianjin Synthetic Material Factory (Tianjin Composite Material Resin Co., Ltd.) using this technology won the Tianjin Science and Technology Progress Award. BMC resins for manhole covers in Jiangsu and Zhejiang areas and winding resins in Guangdong have partially used lower-leg p-type resins. There are large markets in Wenzhou, Fuyang, Wujin, Quanzhou, Panyu, etc. Xiamen Huida Chemical Company is expanding the production capacity of 100,000 tons of resin for the comprehensive utilization of PTA scraps from Xiamen Xianglu Petrochemical Company. As the country puts forward the development policy of "circular economy", the production of these two types of resins will accelerate.

 In recent years, some patents report that dicyclopentadiene is used in combination with waste PET as a raw material for the production of unsaturated polyester resins, which can produce complementary advantages. It not only solves the defect of poor compatibility between PET resin and styrene, but also solves the defect of poor toughness of dicyclopentadiene modified resin, and can further reduce resin cost.

2-Methyl 1,3-propanediol (MPD) is a common species on the market in recent years. It has a high boiling point and has two hydroxyl groups for rapid condensation reaction. The resulting resin has high reactivity and excellent The mechanical properties and corrosion resistance. It can be used in combination with terephthalic acid to complement each other's advantages. The manufactured resin can be used in highly corrosive environments such as glass fiber reinforced plastic tanks and tanks.

 Glycidyl methacrylate (GMA) is used as the raw material for synthetic resin. GMA contains an active epoxy group, which can react with the carboxyl group in the polyester chain to play a blocking effect. This resin produces a methacryloyl component at the end of the molecular chain, which can undergo polymerization reaction with styrene monomer. The middle of the molecular chain is a flexible link, which can make the cured resin have good toughness and resilience. .

 10) For the development of unsaturated polyester resin accessories. The auxiliary materials related to unsaturated polyester resin include: various catalysts, dispersants, defoamers, antioxidants, ultraviolet absorbers, accelerators, curing agents, color pastes, gel coats, mold release agents, additives and other materials. The development of various auxiliary materials in China has been relatively perfect, especially the development of composite accelerators, which provides good conditions for the rapid curing of resins. At present, the quality of domestic accelerators has been greatly improved, and it is superior to imported materials in terms of curing speed and the effect on the color of products after curing. However, the quality of the domestic curing agent (mainly methyl ethyl ketone peroxide) has declined. There are shortcomings such as too high low molecular weight and high water content in the curing agent, and there are explosions in the curing agent production plant, which is mainly due to The production technology of curing agent in China is not enough, and it needs to be further consolidated and improved. In terms of other auxiliary materials, high-end additives (such as dispersants, defoamers, antioxidants, etc.) are still mainly imported. There are few manufacturers specialized in researching and producing unsaturated polyester resin related additives in China. There is still a big gap in auxiliary materials technology.

In short, if a material has low cost, then it will find its use and value in industry; if a material has the performance to meet the market demand, it will definitely have vitality, and some of these materials in the manufacturing process Technical problems will eventually be overcome. It's very simple. For example, if we can manufacture a common flame retardant resin, we will see that all the resin materials on the market will be flame retardant.