Characteristics and uses of unsaturated polyester resins

The unsaturated polyester is a linear polyester obtained by reacting di-alcohol with a dibasic acid, and the unsaturated polyester containing a double bond is soluble in the styrene monomer in the presence of an initiator and a promoter. , cross-linking into a good insoluble, non-melting coating. Styrene is both a solvent for unsaturated polyesters and a film-forming material. The most commonly used peroxides are initiators such as cyclohexanone peroxide and methyl ethyl ketone peroxide. The accelerator is generally cobalt naphthenate, which is added depending on the content of the resin and the temperature at the time of use. If the amount is too much, the coating will cure quickly, but it will be too late to be applied. The amount of peroxide applied is about 2% of the resin. The cobalt naphthenate is 1% or less. The reaction between the initiator and the accelerator is fierce, and must be used with great care. It cannot be directly mixed, stored, and transported. In the case of compounding, the peroxide is often thoroughly mixed with the resin, and then the accelerator is added, and the mixed resin is cured at room temperature for about 30 minutes, so that it is ready for use.

In order for the unsaturated polyester and styrene to polymerize well under the action of the initiator, the resin must be isolated from the air when it cures. There are two ways to isolate from air: one is to add a trace amount of wax to the resin to precipitate on the surface of the coating to form a cover layer when the resin is cured, and to separate the coating from the air. Another method is to cover the coating with a cellophane or polyester film and squeeze the air bubbles in the middle. The film is placed against the coating and isolated from the air until the film is cured and dried before the film is removed. The two unsaturated polyesters are referred to as a floating wax type and a non-float wax type unsaturated polyester resin, respectively.

The utility model has the advantages that: no volatile matter, the paint film is full and thick, almost no shrinkage, the paint film has high hardness, good wear resistance, water resistance, heat resistance, good chemical resistance, and the paint film has high gloss and transparency. The disadvantages are: the coating film is brittle and not resistant to impact, and the initiator and the accelerator are added during the preparation of the coating, and the compounding process is complicated. After the floating wax type coating is cured, it must be polished and polished to produce gloss. When the non-floating wax type coating is cured, the film is coated on the coating, which is troublesome to operate.

This unsaturated polyester resin is currently widely used in the decorative coating of wood products and wood-based panels.

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