Sekisui Chemical Co Ltd developed an interlayer film for laminated glass of head-up displays. The film, "SSF-W," features enhanced visibility as well as sound and heat insulation properties.
The SSF-W belongs to the company's "S-LEC" series and was exhibited at Automotive Engineering Exposition 2009, which opened May 20, 2009, at Pacifico Yokohama in Yokohama City, Japan.
The product is used as an interlayer film of an automotive windshield equipped with a head-up display, which is usually offered as an option. This is the world's first interlayer film that realizes sound and heat insulation and visibility of head-up displays at the same time. The film was adopted by the Honda "Insight," the Toyota "Prius" and the MBW "7-Series" of Germany.
The new interlayer film consists of three layers, with a sound insulation layer between two heat insulation layers. The ratio of thickness of the layers is 3:2:3. This interlayer film is sandwiched by glass layers to make an automotive windshield, and, therefore, the completed windshield is composed of five layers.
Sekisui Chemical adjusted the thickness of the glass so as to enhance the visibility of head-up display. The vertical cross section of the front glass is shaped like a "wedge" that is thinnest at the bottom and becomes thicker as it progresses to the top. The thickness of the interlayer film is 0.8mm at the bottom and more than 1mm at the top.
Characters and arrows from the fluorescent display tubes that light up from the area below the windshield are seen by the driver's eyes as lights from two different channels.
They are the light that is reflected by the glass on the cabin side (inner glass) and the light that transmits through the inner glass and the intermediate layers and is reflected by the glass on the exterior side (outer glass).
The lights meet just in front of the driver because of the wedge-shaped windshield, allowing the driver to see the numbers showing the vehicle speed and the arrows indicating the direction of travel clearly without blurring.
The sound and heat insulation layers are both made of PVB (polyvinyl butyral). The sound insulation layer was softened by adding an additive to PVB and enhancing the processing method so that it absorbs the vibration of the exterior glass to reduce the vibration transmitted to the inner glass and lower the noise.
The sound insulation layer is especially effective for shielding mid-frequency sounds ranging from 1,000 to 4,000Hz, which are most audible to human ears.
The heat insulation layer has ultrafine nm-order indium particles nearly homogeneously dispersed in the PVB material. The indium particles absorb infrared light at the wavelength of about 800 to 1,800nm and store the heat. And they release the heat when the vehicle is driven and the outer glass cools down. The layer is most effective for shielding the heat from 1,400nm light, softening scorching sunlight that stimulates the skin.