Ways to Make PET Shiny

It is not difficult to make polyethylene terephthalate (PET) plastic have a beautiful luster. Just grasp a few key links and do it step by step. Whether the surface of PET is bright enough depends mainly on whether the molecules are arranged neatly, whether the surface is flat, and whether it can reflect light well. Let's talk about how to do it.

1. Choose the right raw materials and prepare the right recipes

This is the first step. If there are impurities in the PET resin, such as catalysts that have not been cleaned up and small volatile molecules, there will be small flaws on the surface after molding, and the light will be scattered, and it will not look bright. So you have to choose high-purity PET chips, such as bottle-grade or film-grade PET chips, with an ash content of less than 0.01%. 

In addition, you can add something to change the formula: add 0.1% to 0.5% nano-silicon dioxide or talcum powder. These small particles can help the crystals grow evenly without making the surface rough; add some fluorine-based lubricants, such as polytetrafluoroethylene powder, to reduce the friction between the melt and the mold, so that the surface will not have lines like orange peel. ​

2. Adjust the molding process parameters well

This is also very critical. During injection molding, the mold temperature is very important. If the mold temperature is lower than the glass transition temperature of PET (about 70℃), the melted material cools too quickly, the molecular chains on the surface are frozen, and the arrangement is not neat, and the gloss is poor; adjust the mold temperature to 80-120℃, the melted material crystallizes in the mold for a long time, the surface molecules are arranged neatly, and the gloss can be increased by 15%-20%.

In addition, the injection pressure must be sufficient, maintained at 80-120MPa, so that the melted material can fill the mold and there will be no surface depressions or shrinkage marks due to insufficient pressure.​

If you use extrusion blow molding or casting, the temperature of the melted material must also be controlled. The processing temperature of PET is generally 270-290℃. If the temperature is too low, the material cannot flow and the surface is not flat; if the temperature is too high, the material may break down, produce things like acetaldehyde, and there will be bubbles on the surface.

The cooling speed must also match the crystallization speed. For example, when making a biaxially oriented film, the temperature is controlled at 100-120℃ before longitudinal stretching to allow it to crystallize, and the temperature is set at 200-230℃ during transverse stretching. In this way, the surface can form a dense structure and the glossiness can reach above 85GU. ​

3. The mold and equipment are precise enough

In this way, the surface can be flat. The surface roughness of the mold cavity must be below Ra0.02μm, and it is usually necessary to grind with diamond paste for mirror polishing, so that the melted material can perfectly replicate the mold surface. For products with complex shapes, mold exhaust is very important.

Make a 0.01-0.02mm wide exhaust groove at the place where the material is finally filled, so that no gas will be trapped inside to form burns or pinholes. In addition, the gap between the screw and the barrel of the equipment must be controlled within 0.3-0.5mm, otherwise the material backflow will cause unevenness and unstable discharge. ​

4. Do a good job of post-processing​

The gloss can be further improved. For injection molded products, a 50-100nm metal film, such as aluminum or nickel, is plated on the surface using ion sputtering technology, which not only makes the glossiness reach above 90GU, but also makes it more scratch-resistant.

For PET film, although corona treatment is mainly to increase surface tension, the energy is controlled at 38-42dyn/cm, the surface molecules can be moderately cross-linked, and the reflected light is more uniform; then apply a 5-10μm thick layer of polyurethane or acrylic varnish, which is transparent and smooth, and the gloss can be increased by more than 30%, and it is more durable.

5. Pay attention to balance and details

One point to note is that the gloss and the crystallinity of the material must be balanced. If the crystallinity is too high, small cracks may appear on the surface, especially for thick products, which are not bright. The cooling speed can be adjusted, such as using gradient cooling to make the surface crystallinity lower, about 10%-15%, and the crystallinity inside is high, so that the surface is smooth and the performance is good. In addition, during secondary processing, such as printing or lamination, do not use solvents that will corrode the surface of PET, otherwise the gloss will be gone.

In general, to make PET glossy, it is necessary to do a good job in raw material purity, process parameters, mold accuracy and post-processing technology. In actual production, it depends on what product is made. For example, beverage bottles, food packaging films, and cosmetic shells have different requirements for gloss. By adjusting the parameters through experiments, you can make PET products that are both beautiful and easy to use.

Our platform connects hundreds of verified Chinese chemical suppliers with buyers worldwide, promoting transparent transactions, better business opportunities, and high-value partnerships. Whether you are looking for bulk commodities, specialty chemicals, or customized procurement services, TDD-Global is trustworthy to be your fist choice.