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Gel coat guide Water whitening analysis and improvement

Mar 06, 2019

Gel coat guide  Water whitening analysis and improvement

Gel Coat is a coating for the surface of sanitary ware, boats, etc. by adding pigments, fillers, thixotropic agents, etc. to unsaturated polyester resin (UPR). Some brightly colored gel coats, in the water or water vapor environment, the surface of the gel coat will be whitened.

Analysis of the cause of whitening
Since the water resistance of the gel coat is not good, water molecules pass through the gel coat layer, and a water molecular film is formed thereafter. Because the gel coat layer is relatively thick, water molecules do not easily diffuse back into the air. When the sunlight is irradiated onto the water molecular film and then reflected, the human eye receives the reflected light and feels that the gel coat is white. The refractive index of each color is different, so the phenomenon of water whitening does not occur in each gel coat color. Under the same conditions, blue, green, purple, red, yellow and medium gray are more likely to occur.

Influencing factors of water whitening

Gel coat base resin water resistance: Three types of gray gel coats were immersed in a constant temperature water bath at 65 ° C for 1 hour. The experiment can be obtained: the gel coat matrix resin type is different, and the water absorption is also different. Among the three gel coat matrix resins, benzene neopentyl glycol has the best water resistance, followed by m-benzene, and the water resistance of o-benzene is the worst. If there is a FRP product that is required to prevent rainwater whitening, it is preferable to use a meta-benzene/neopentyl glycol gel coat.

 Effect of filler water absorption: There is a certain amount of filler in the gel coat formula, which not only reduces the cost but also provides strength; some also helps the pigment to disperse in the gel coat system and reduce the occurrence of sedimentation. However, the filler also brings some hidden dangers, such as the filler may absorb water, which makes the gel coat easy to absorb whitening.

Selecting the meta-phenyl neopentyl glycol type resin as the matrix resin, and selecting two kinds of fillers with different water absorption ratios to configure two kinds of gel coat base materials, which can be configured into four kinds of glass steel plates, and the same warm water bath condition is taken out and dried after 1 hour. Then, the color difference meter is used to observe the change of the L value of the gel coat. In the water environment, the choice of the gel coat formula filler is also very important.

The effect of the gelatinization degree of the gel coat: The phenomenon of water whitening is mainly related to water resistance. In addition to relying on the material itself, the water resistance depends on whether the degree of solidification of the gel coat is already in a watery environment.

All in all, it can be summarized as follows:

1. The water resistance of the gel coat itself must meet the requirements of the product.

2. Pay attention to the curing degree of the gel coat during the operation, and enter the oven if necessary.

3. Select the spraying process, the compressed air must be dewatered and degreased, and the pipeline is smooth.

3. After the FRP paste is prepared, it should be placed for a period of time, and then put into use after a certain degree of curing.

4. Products should not be stacked in the open air, as far as possible in a covered place.

5. Do not rush the plastic film, pay attention to the breathability of the film.

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QuanZhou Neweco High Polymer Material Co.,Ltd.

Neweco is one of the leading unsaturated polyester resin manufacturers and     suppliers,widely used in automobiles, ships, rail transit, wind power    generation, pipe cans, heat and corrosion protection, building     materials, stone repair, sanitary ware, artificial stone and other     industries. Suitable for hand lay-up, spray, pultrusion, winding,     molding, vacuum introduction / RTM, casting and other molding    processes. Neweco Resin is committed to excellence and focuses on the    application  of composite materials to provide customers with    comprehensive  solutions.

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