[AEE] Toray's Resin Film Adds Metallic Sheen to Auto Parts

May 22, 2009
Motohiko Hamada, Nikkei Automotive Technology
A door handle. When it is operated in conjunction with a remote key, the user can make it glow simply by coming close to it.
A door handle. When it is operated in conjunction with a remote key, the user can make it glow simply by coming close to it.
[Click to enlarge image]
The front side of a switch board looks like an ordinary metal.
The front side of a switch board looks like an ordinary metal.
[Click to enlarge image]
The back side of a switch board is coated black with the pictograms left uncoated. They can be displayed when the board is illuminated from the back.
The back side of a switch board is coated black with the pictograms left uncoated. They can be displayed when the board is illuminated from the back.
[Click to enlarge image]

Toray Industries Inc developed a resin film that can add metallic sheen to automotive and other parts and exhibited it at Automotive Engineering Exposition 2009.

The film, "Picasus," does not contain any metal, which is used in plating or vapor deposition. So, it is free from rust or peeling. It can be easily recycled and causes no environmental problems peculiar to plating plants.

The Picasus can display characters and pictograms because it allows light to pass through when illuminated from the back side. And it can be used, for example, as door handles, switch plates and instrument panels that normally have a metallic shiny surface and displays characters only when necessary.

The product name was coined by combining a Japanese word "pica," which means "a flash of light," and "SUS" (stainless steel).

The film has a structure in which a total of approximately 1,000 layers of highly refractive polyethylene terephthalate (PET) and less refractive PET are alternately stacked. The total width is 200μm. If the total width is simply divided by the number of layers, each layer is 0.2μm thick.

However, the layer widths are not equal. They are thinner on one side and thicker on the other. In addition, the layer width varies in a continuous manner at substantially regular intervals.

If all the layers had an equal thickness, the film would be colored due to interference. But when the widths are distributed at regular intervals, the film has metallic sheen because light of all visible wavelengths is evenly reflected.

A nozzle with 500 branched outlets that look like comb teeth is used to extrude each of the materials. The two "combs" are combined so that the nozzles for the highly refractive PET and less refractive PET are alternately arranged.

With this setup, both resins are extruded in an alternatively stacked fashion to form a thick film. It can be called "thousand-color formation" like two-color formation. Finally, the film is stretched so that its thickness is reduced to 200μm.

The resultant film is insert-molded and formed into a final product. Because the film can still be stretched to some extent, it can be warped by preforming. But when the stretch rate exceeds 150%, the layers become so thin that the reflection wavelengths will change, making the film look slightly bluish.

Toray has already started operating mass-production facilities and shipping the Picasus for notebook computers. Also, the film will be supplied to mobile phone manufacturers shortly. For automotive applications, Toray plans to find users of the new product at the exhibition site of the Automotive Engineering Expo, which is taking place from May 20 to 22, 2009, in Yokohama City, Japan.