Discover the versatility of unsaturated polyester resin (UPR) in various industries. This article explores UPR’s composition, production process, and applications, from corrosion-resistant coatings to foam materials. Delve into the world of UPR and uncover its essential role in modern manufacturing.
Unsaturated polyester resin is a chemical raw material commonly used to thicken and solidify the surface of objects. It applies in layers like paint. Harmful gases such as styrene are released during the curing process.
Unsaturated polyester resin is the most used thermosetting resin. It is a linear polymer formed by the condensation polymerization of saturated diacid, unsaturated diacid, and diol. It is a resin solution with a certain viscosity formed by diluting cross-linking monomers or active solvents, referred to as UP.
Ingredient name: mass (%)
Propylene Glycol: 16.74
Phthalic anhydride: 9.86
Theoretical water production: 36.04
Polyester yield: 37.53
As can be seen from the table, the molar ratio of diol to diacid is 2.2:2.0. There is an excess of 10% diol, which is necessary to control the relative molecular weight of polyester.
Add diol, diacid, and hydroquinone to the reaction kettle according to a certain formula. Pour in nitrogen and heat until the material dissolves. Start stirring and keep refluxing for 1 hour. Heat to 190°C and esterify until the acid value is less than 40mg KOH/g. Cool to 60°C and add TDI evenly within 1 hour. Keep the reaction temperature around 75°C until the temperature no longer rises. The -NCO value was measured after 1 hour. When the -NCO value reaches the specified value, add styrene diluent. A polyester-modified unsaturated polyester resin with a solid content of 75% was obtained.
Unsaturated polyester resin is a linear polyester produced by the reaction of diol and diacid. This unsaturated polyester containing double bonds is soluble in styrene monomer. Cross-linking occurs in the presence of initiators and accelerators. Forms a good insoluble and infusible coating. Styrene is both a solvent for unsaturated polyester and a film-forming substance. The most commonly used initiators are peroxides such as ketone peroxide and acetone peroxide. The accelerator is generally cobalt naphthenate. The amount added depends on the resin content and the ambient temperature during use. If used in large quantities, the paint will cure quickly. If it’s too fast, it may not be applied in time. The amount of peroxide used is approximately 2% of the resin. Cobalt naphthenate is less than 1%. Initiators and accelerators react violently and must be handled with care. Cannot be mixed directly. Storage and transportation must be individually packaged. When mixing, the peroxide is usually thoroughly mixed with the resin before adding the accelerator. The mixed resin cures at room temperature for approximately 30 minutes. Therefore it should be used immediately after preparation.
The main downstream demand areas for unsaturated polyester resin include fiberglass materials, artificial stone, and coating industries. From demand composition, glass fiber composite materials account for the highest proportion. It accounts for more than half of the market demand, accounting for 55%. Followed by the field of artificial stone, it accounts for 30%. The coatings sector accounts for 15%.
It uses thermoplastic resin to reduce and alleviate the curing shrinkage of UPR. It has been widely used in SMC manufacturing. Commonly used low shrinkage agents include polystyrene, polymethyl methacrylate, and polydiallylene glycol ester polymers. At present, in addition to using polystyrene and its copolymers, foreign countries have also developed polyhexamethylene adipamide (LPS-60), modified polyurethane, cellulose acetate butyrate (CAB), etc.
LPAS is a new type of low-shrinkage additive for UP resin developed by Japan’s Advanced Polymer Science Research Institute. This additive contains elastic segments and segments compatible with UP resin. Used in the molding process of UP resin SMC/BMC. The surface of the product is shiny, the shrinkage rate is low, and the coloring performance is good.
Ohio State University in the United States studied the addition of modified thermoplastic LPAS additives to low-temperature curing UP/ST/LPAS systems. The co-accelerator DVB and the second monomer trimethylolpropane trimethacrylate (TMPT-MA) were introduced into the low-temperature curing system. It improves control of resin shrinkage during curing.
In Canada, thermoplastic PVAC is added to UP resin as a low-shrinkage additive LPAS. It also effectively solves the shrinkage problem.
Japanese companies such as Showa Denko Co., Ltd. add low-shrinkage solid agents. The bonding strength of the unsaturated polyester composition can be increased to 2.45MPa. The linear shrinkage coefficient is reduced to 0.32%.
Japan’s Mitsubishi Chemical Company uses polyvinyl acetate (DenkaASRM4) as a low-shrinkage additive. Developed a molding material with a shrinkage rate of only 0.096%.
Corrosion-resistant resins include bisphenol A-type unsaturated polyester, phthalic acid-type resin, rosin-modified unsaturated polyester, etc. According to reports, the 8250 vinyl ester resin developed by Japan’s Ube Kosan not only has good corrosion resistance but also has a shelf life of up to 14 months. Japan uses phthalic acid type, bisphenol A type, or vinyl ester type to make glass fiber composite materials. They are resistant to 25% NaCl aqueous solution.
Tough resins are increasingly valued. The main method currently adopted abroad is to improve toughness by adding saturated resin. For example, add saturated polyester, butadiene rubber, carboxyl-terminated nitrile rubber, etc. Amercoat Chemical Company of the United States uses a resin produced by the reaction of hydroxyl-terminated unsaturated polyester and diisocyanate. It can increase toughness by 2-3 times. Its brand name is Xycon. The SD resin developed by Japan’s Showa Polymer Company has good toughness. It can be widely used in the manufacture of artificial marble. Brazil grafted flexible polydimethylsiloxane segments (APTS) onto unsaturated polyester resins containing glycidyl methacrylate (GMA) for modification. Resins and glass fiber-reinforced resins with high-impact strength are obtained. The University of Poland found that as the TDI content increases, the viscosity of TDI-modified unsaturated polyester resin increases. When the TDI mass fraction reaches 3%, the resin has good thixotropy. When 4,4′-methylene diphenylamine (BM) was added to the resin for modification, the compressive strength of the modified resin increased to 159 MPa. The glass transition temperature is increased to 184°C. The decomposition temperature increases to 280°C. The curing speed is also increased accordingly.
Germany developed IR radiation-curable unsaturated polyester resin. It reduces the curing time of composites when cured by IR radiation. Thereby it reduces the water absorption rate of the product.
The product developed by Kao Corporation of Japan has a tensile strength of 44.1MPa, a light transmittance of 48%, and excellent heat resistance. This bisphenol A type transparent unsaturated polyester resin is used for artificial marble. Japan’s NOF Corporation has developed unsaturated polyester resin with low residual styrene content. It is a good anti-yellowing unsaturated polyester resin. It is suitable for FRP, SMC, and BMC resin. After curing at 130°C, the residual styrene mass fraction is only 0.03%.
PET-type unsaturated polyester resin has achieved many results. The United States and Egypt have used waste PET alcoholysis products to synthesize unsaturated polyester resins. By adjusting the reaction, a resin with a curing temperature of 74 to 90°C and a curing time of a few minutes to more than 20 minutes can be obtained. South Korea has synthesized a series of products using various alcoholysis products. And control the alcoholysis degree of PET-type resin through various alcohol compositions. It can be achieved by controlling the gel time and brittleness. It has been successfully used in SMC and BMC.
Foamed unsaturated polyester resin also appeared. As the matrix of foam plastics, unsaturated polyester resin has better toughness and strength than foamed PS. And it is easier to process than foamed PVC. Adding additives such as flame retardants can make it flame-retardant and aging-resistant. Lower cost than foamed polyurethane plastic. Chemical foaming agents are mainly used for foaming unsaturated polyester resin. There is little literature on the use of physical blowing agents. Physical blowing agents are mainly fluorocarbons. But it causes pollution to the environment. Chemical foaming agents mainly include isocyanate, azo, sulfonyl hydrazide, carbonate, etc.
There are many varieties of low-volatility resins and gel coat resins. Low-volatility resin is a topic currently being developed abroad. It is generally required that the styrene content in the air around the workshop is less than 50ug/g. Methods include adding surface film-forming agents to reduce styrene volatilization. Use a high boiling point crosslinker instead of styrene. Cyclopentadiene and its derivatives are combined with uPR to reduce the molecular weight. Thereby it reduces the amount of styrene used. BYK Chemical Co., Ltd. has developed a new additive LPX-5500. It can reduce styrene emissions by 70-90%.
Gelcoat resin is a special resin used to make the gel coat layer of fiberglass products. Styrene is still the most suitable monomer for UP resin. But, styrene has a high vapor pressure at room temperature and is prone to volatilization. Especially when hand lay-up or injection molding processes are used to produce gel coats and backing reinforcements for fiberglass products. When its vapor concentration exceeds a certain amount (>50ug/g), it can irritate the eyes and nasal mucosa. It causes symptoms such as dizziness and nausea. So, the development of low-styrene emission gel coat resins is necessary. It has great practical significance. Sartomer Technologies has developed low VOC (volatile organic compounds) compositions containing maleic anhydride monomer. They are applied to gel coats, adhesives, laminating resins, or molding resins. The United States and Germany have developed unsaturated polyester resins and compositions that do not contain (styrene) monomers. It can be used in open casting, gel coat, and electronic industries respectively.
Water-containing unsaturated polyester resin WCUP is on the rise. Water-containing unsaturated polyester resin WCUP is a new type of resin developed in the 1950s with water as a filler. In addition to its remarkable low-cost characteristics, it has many excellent properties. These include low heat release during curing, low volume shrinkage, flame retardancy, ease of processing, etc. It can be used in engineered wood, decorative materials, foam products, porous materials, construction materials, polyester concrete, impregnants, and coatings. In 1967, Horie et al. first reported the use of alkaline substances such as sodium hydroxide to prepare stable resin emulsions. This method is called the polyester salt formation method. In recent years, the research on dynamic phase/multicomponent polymer systems has attracted great international attention. The relationship between dynamic rheological behavior and morphological structure was studied by Nguven-Thue et al. Subsequently, this type of research became a hot topic in rheological research on many polymer systems. Ewa Kicko-walczak summarizes the latest developments in unsaturated polyester resins that comply with EU requirements.
