Deterioration due to UV Rays is the Fate of PP Parts | Difficult-to-Paint Materials, Apply a Silicone-Based Gloss Revival Agent

Compared to painted ABS resin, unpainted PP resin is more resistant to minor scratches and less costly to manufacture, making it a suitable material for scooter underbody, steps, and front and rear fenders. However, its biggest and unavoidable weakness is whitening, which occurs when the black luster fades and the material becomes crumbly as it deteriorates over time. To alleviate the tarnished look of PP, which becomes blurry as it is used outdoors, it is effective to use silicone-based chemicals to restore its luster.

PP = Polypropylene resin discolors and cures the same for both motorcycle parts and poly buckets

Some scooters that have been stored outdoors and left to ride have had the PP resin whiten to this degree, which is not an exaggeration. If a gloss revitalizer had been used properly before the deterioration progressed to this level, it would have maintained a more presentable appearance, but there is not a hint of love in the air. The black unpainted resin not only turns white but in the next stage, crumbly resin spills from the surface, a condition known as chalking.

Spraying a resin resurrection agent on the chalking condition will not improve the roughness, so add to improve adhesion while cleaning the surface of the parts with a non-woven cloth or steel wool. Rough steel wool is more suitable because sandpaper will change the texture of the surface and make it slippery.

Rubbing the chalking part with Bonstar brings back the blackness of the PP resin to some extent. Actually, it is finely scratched, but it does not bother me because there is a grain pattern on the surface of the part.

In contrast to old and out-of-print motorcycles, where most of the bodywork was made of metal except for tires and other rubber parts, resin parts are increasingly present on modern motorcycles. There are many models with cowls, screens, and even fuel tanks that have a plastic cover attached to a steel inner tank. Resin parts, which are lightweight, can be molded into complex designs, and costs can be kept down, are classified by material into ABS, PP, and acrylic, with PP (polypropylene) being the most user-friendly.

PP, like PE=polyethylene, is flexible and is used in an unpainted state without painting by adding a coloring agent called toner during the molding process, as in the case of poly buckets. Often used for motorcycle exteriors, fenders, mudguards, chain covers, and scooter step boards, PP is unpainted black and does not easily get scratched even when rubbed somewhat hard with shoes or worn when pushed around or stored in the garage. This compares favorably with ABS plastic used for cowls, side covers, etc., which is supposed to be painted and requires careful daily care.

However, PP has one major weakness: low weather resistance. PP deteriorates and discolors due to sunlight, ultraviolet rays, wind, rain, and temperature changes, causing the black luster to disappear and the material to turn white and crumbly. This phenomenon is called "bleaching," and it is a drawback that spoils the appearance of PP and PE materials.
This is not so much of a problem for motorcycle parts, which require a certain level of strength, because the material is thicker, but cracks in gardening buckets and clothespins are caused by age-related deterioration.

The best way to avoid deterioration is to keep them indoors to avoid exposure to UV light. However, this is not practical for motorcycles that are driven outdoors. Even if storage in a garage is not possible, you can at least slow down the progression of deterioration by covering the vehicle with a body cover. However, in addition to sunlight and ultraviolet rays, deterioration also progresses due to rainwater and oxidation caused by oxygen in the air.

ABS has similar weaknesses, but most ABS is protected by paint. Paint for metal and ABS has excellent outdoor durability due to the focus on development to improve weather resistance as well as good appearance. Although it has a weakness in that it is more easily scratched than PP when rubbed against something, it offers high protection against material deterioration.

It would be better if PP parts could also be painted, but since one of the reasons for choosing PP resin is to reduce cost, painting after molding is not an option. In addition, the high flexibility of PP and PE materials makes it difficult for paint to adhere to them. In order to paint PP parts, costly processes must be taken, such as using an adhesive to prevent the paint film from peeling off from the PP material and adding a softener to the paint film itself to prevent it from cracking due to bending.

For whitened PP parts, apply resin resurrection agent frequently to protect the surface.

The main ingredient of Super Plastic Gloss Reviver from Yamalube is silicone, which moisturizes whitened PP, PE, and other unpainted resins. The basic ingredients are the same as those of silicone sprays sold at home centers, but the adhesion and thickness of the silicone when sprayed are far better.

Daytona's resin luster revival agent restores the luster of the resin itself through a glass-like transparent film.
By spreading it evenly with the included sponge, it repels water and prevents dirt from adhering. The high heat resistance temperature of 300°C makes it suitable for use on muffler covers and other resin parts around the engine.

Daytona Resin Black can be painted directly on PP resin without priming. Compared to silicone-based luster enhancers, Daytona Resin Black is more durable and the black color lasts longer. Another advantage is that the paint film is so thin that it does not fill in the grain patterns characteristic of unpainted parts.

After adjusting the substrate with Bonster and removing oil with a mild detergent, spray the gloss revival spray while maintaining a certain distance from the surface. As with painting, thin layers are applied to achieve an even finish.

Immediately after application, the gloss is as natural as new, but the unpainted resin gloss revivifier, which is not painted, will turn white again as time goes by. However, the image is completely different between leaving the vehicle in a pure white state without maintenance because it will turn white anyway, and taking care of the vehicle with a gloss revival agent. The surface of the center tunnel caution label had also turned white, and the silicone coating made the letters clearly readable.

To restore the whitening of unpainted resin, as typified by PP, it is effective to form a coating film on the white, crusty surface, just as water splashed on a deteriorated area of clear paint temporarily restores its gloss when it is wet. Chemicals for this purpose are also available.

Spray-type silicone-based gloss revitalizers are easy to apply and produce results easily. When sprayed on degreased and cleaned parts, the transparent silicone film brings back the black gloss on the whitened PP surface. There are inexpensive sprays available at home improvement stores, but the gloss revivifier developed by Yamalube features a thick silicone film, resulting in a black glossy finish.

Apart from silicone sprays, Daytona also offers a canned spray that can be used to paint degreased resin parts directly.
Although this paint is an acrylic synthetic resin, it has an extremely thin film and does not fill in the fine irregularities (grains) that are common on the surface of PP parts.

Apart from the spray type, there are also chemicals that form a glass-like film on the PP surface, such as Daytona's resin gloss revivifier. These chemicals are applied with a sponge to create a clear film on the whitened areas, bringing out the blackness of the base material, and are attractive because they last longer than the spray type, lasting from six months to a year, depending on the extent of the material.

As for non-Daytona paint-type gloss revivals, silicone and glass-like coatings deteriorate under ultraviolet light, so continuous application is necessary to maintain the blackness. Also, preventative application before the deterioration progress can be expected to delay the whitening, rather than applying after the complete whitening.

Just as you protect painted surfaces with coatings and waxes, you should try to keep unpainted PP parts as beautiful as possible for as long as possible by properly caring for them.