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What's Gel Coat Resin ?

Feb 14, 2019

Definition: Gel coat English name gel coat, which is a pigmented thixotropic product developed by adding FRP and countertop paints, which are dispersed in unsaturated polyester (UP), such as pigments and thixotropic agents. It is mainly used for the surface of resin products, which is a continuous covering thin layer, and its thickness is generally about 0.4 mm (the thickness of the mold gel coat is generally 0.7-0.8 mm).


I. Introduction


Gel coat resin is a special resin in unsaturated polyester resin. It is developed to improve the appearance quality of glass fiber, reinforced unsaturated polyester resin-based FRP products, and protect the material of structural layer from external environmental media. Developed, the main role of gel coat resin is to protect the surface of FRP products and the protection of structural layers. The development of new weather-resistant flame-retardant gel coat resins has received increasing attention and played an increasingly important role.


Gel coat resin is a special grease for making a gel coat layer of FRP products. Styrene is still the most suitable monomer for the current UP resin. However, styrene has a high vapor pressure at room temperature and is easily volatilized, especially in the process of making a gel coat layer and a backing reinforcement layer of a FRP product by a hand lay-up or a spray molding process. When the vapor concentration exceeds a certain amount (greater than 50Pg/g), it may cause symptoms such as dizziness and nausea. Therefore, it is very necessary and practical to develop low-styrene sporalen gel coat resin. Many new gel coat resins have been developed abroad, and the domestic market is currently catching up. With the maturity of FRP basic research technology and the continuous introduction of advanced foreign equipment and technology, the domestic FRP industry has developed rapidly, and the variety of gel coat resin has been expanding.


2, The type


According to its composition, gel coat resins can be roughly classified into the following categories: phthalic acid type gel coat resin, isophthalic acid type gel coat resin, bisphenol A type gel coat resin and vinyl ester type gel coat resin:


Isophthalic acid type


The isophthalic acid type gel coat resin is a gel coat resin mainly composed of an isophthalic acid type polyester, and the cured product has good mechanical properties, toughness, heat resistance and corrosion resistance. It is more pure than phthalic acid type gel coat resin. The ester bond on the molecular chain is affected by the steric hindrance effect of isophthalic acid, and has the characteristics of good resistance to water and other corrosive media. (m-phenylene is superior to ortho-benzene)


Bisphenol A


Bisphenol A (also known as diphenolic propane) gel coat resin is a gel coat resin based on bisphenol A type polyester resin. It is synthesized by replacing the dihydric alcohol with an adduct of diphenolylpropane and propylene oxide (also known as D-33 monomer) and then undergoing polycondensation reaction with a dibasic acid.


These resins have excellent corrosion resistance and heat resistance after curing, and have been used as temperature-resistant and corrosion-resistant gel coats.


Vinyl ester type


The vinyl ester type gel coat resin is a gel coat resin mainly composed of a vinyl ester resin. The vinyl ester resin is a thermosetting resin having an unsaturated double bond at a terminal group obtained by addition polymerization of an unsaturated acid with an epoxy compound. Such resins are typically prepared by reacting acrylic or methacrylic acid with different types of epoxy resins.


An outstanding advantage of this type of resin is its excellent corrosion resistance, its acid resistance over amine-cured epoxy resins, and its alkali resistance over acid-cured epoxy resins and unsaturated polyester resins. It also has good toughness and wettability to glass fibers. (Because vinyl gel coats have better hardness and weather resistance than polyester gel coats, more and more manufacturers now choose them as mold gel coats, which is also a trend in the future)


3, Function and Application


Function and use can be divided into product gel coat, mold gel coat, flame retardant gel coat, marine gel coat, high elastic gel coat, food grade gel coat and so on. The variety and performance of gel coat resin have been continuously improved, and the application field of gel coat resin has been expanding.


Mold gel coat


The base resin of the mold gel coat is a special polyester. The structure of the resin imparts good mechanical properties, high gloss, chemical resistance and flexibility to the FRP mold.


Air dry gel coat


Air-drying gel coat is a wax-free air-drying gel coat with strong adhesion and peel strength. Its molecular special structure makes it have higher corrosion resistance and excellent high temperature resistance, high specific strength and crack resistance than ordinary polyester. The maximum characteristics of air-drying gel coat, 20-30min after spraying, finger dry, 2h up to the ordinary gel coat strength, reaching the highest intensity value after one week. After molding, the surface of the product is smooth, bright, non-hanging, and has excellent leveling performance and is not sticky. Hand lay and spray type are available upon request.


Transparent gel coat


The transparent gel coat is a colorless transparent gel coat. Its base resin is an isophthalic unsaturated polyester resin with medium viscosity and reactivity. It is widely used in non-reinforced castings, polyester concrete and artificial marble. Artificial agate, ornate stone.


4, The method of application


1) Select the appropriate gel coat model before use.


2) Prepare the mold completely and thoroughly, and the surface of the mold determines the surface of the product.


3) Stir the gel coat thoroughly before use, but at a slower speed to avoid mixing bubbles.


4) Before starting work, the temperature of the gel coat and the mold should be kept at 16 ° C -30 ° C. The ideal mold temperature should be 2 ° C - 3 ° C higher than the gel coat temperature. Thus, a more lustrous gel coat surface is obtained after curing.


5) The relative humidity in the workshop is less than 80%, and the humidity assembly leads to an increase in the required curing temperature. Also prevent water from collecting on the surface of the mold.


6) The surface of the mold should be fully waxed. Do not use silicone-containing release wax. The water-soluble release wax must be coated with a gel coat after the water has evaporated.


7) Do not dilute with solvents such as acetone. If a lower viscosity is required during use, a small amount of styrene (<2%) may be added.


8) The amount of curing agent (MEKP) is generally between 1 and 2%. If the amount of the curing agent is too high or too low, the water resistance and weather resistance of the article are lowered.


9) If adding color paste, ensure the uniformity and stability of the color. According to the recommended amount, accurately weigh and stir with low shear equipment. Color gel coats can also be used.


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