Infrared-blocking transparent film

Details Infrared-blocking transparent film Infrared-blocking transparent film

1998-12-17

2001-07-17

Zirker, Daniel (Department: 1771)

Stock material or miscellaneous articles

Web or sheet containing structurally defined element or...

Adhesive outermost layer

C428S354000, C428S328000, C428S327000, C428S323000

Reexamination Certificate

active

06261684

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to an infrared ray blocking transparent film, for example, a film adhered to a windowpane of a building, an automobile, or the like, primarily in order to block infrared ray in sunlight.
Transparent films having infrared ray blocking properties, transparency (transmissivity) for visible light, and properties of reflection or absorbing of infrared light, have been used for controlling the thermal effects of solar radiation. For example, an infrared ray blocking film is adhered to a windowpane of a building or an automobile or the like so as to reduce heat caused by direct sunlight being transmitted therethrough. In the summer, air conditioning load is reduced by reducing the elevation of room temperature, and in the winter, the heat insulating efficiency at room temperature is improved. As an additional effect, if the windowpane is broken, the scattering of pieces of glass is prevented. In general, such an infrared ray blocking transparent film is formed in such a way that an infrared ray blocking layer is provided on one surface of a base film composed of a synthetic resin such as PET (polyethylene terephthalate) or the like, a hard coat layer as a surface protective layer is laminated on another surface of the base film, and a separate material composed of paper, film, or the like, is adhered via an adhesive layer on the surface of the infrared ray blocking layer. When the film is affixed, the separate material is taken off, whereby the adhesive layer may be adhered to a glass plate.
The infrared ray blocking layer has been formed on a base film by coating various kinds of infrared ray absorbers (for example, immonium, aluminum, and anthraquinone-type compounds) or an infrared ray reflecting material (for example, ZnO, SnO
2
, and phthalocyan-type pigments, or the like). However, when the conventional infrared ray absorber is used, the layer is a dark brown or a dark blue, whereby transparency of the layer is inferior since visible light transmissivity is lowered to 50% or less. Alternatively, the layer can absorb only infrared ray having long wavelengths ranging from 1000 to 1500 nm or more, or the layer can absorb only infrared ray having a very small range of wavelengths. Therefore, in order to overcome the above-mentioned defects of the infrared ray absorber and the infrared ray reflecting material, indium tin oxide powder (hereinafter referred to as ITO) which was developed as a conductive coating material, has come into use. In this case, the ITO powder is coated on a base film by a vacuum deposition method or a sputtering method to form a thin film.
The ITO powder may be formed on a base film by a vacuum deposition method or a sputtering method, thereby reflecting infrared ray having wavelengths ranging from 800 to 2500 nm, so that an infrared ray blocking film having high transparency can be provided. However, these methods require a high-vacuum performance apparatus and a high-precision atmosphere controlling system; the cost of production therefore increases and adversely affects mass-productivity. The properties of the method for forming a thin film results in a metallic luster on the reflection surface for visible ray, which is esthetically undesirable even if the film has high transparency. Furthermore, the film has a comparatively low resistance with respect to electromagnetic waves and therefore tends to absorb electromagnetic waves, so that a mobile telephone or a car navigation system occasionally cannot be used inside a vehicle.
Therefore, it is an object of the present invention to provide an infrared ray blocking transparent film which can be produced at low cost even though it employs an ITO powder, which can inhibit occurrence of metallic luster, and which can exhibit excellent electromagnetic wave transmissivity.
SUMMARY OF THE INVENTION
The inventors have discovered that the most suitable method to accomplish the object is to mix and disperse a conductive coating material in a conductive transparent ITO powder in a resin, which is then laminated on a base film by a coating method, thereby accomplishing the present invention. In particular, after conducting diligent research with regard to the compounding ratio of the ITO powder and the resin, in the case in which the compounding ratio of the ITO powder and the resin is 90/10 to 60/40 by weight, preferably 85/15 to 65/35, and more preferably 80/20 to 70/30, the infrared ray blocking film having high transparency with low haze (for example, having a HAZE value according to the Japanese Industrial Standard K 7105 of 1.0 or less) can be obtained. It should be noted that the numerical limitations are based on the following. In the case in which the compounding ratio of the ITO powder is 90% by weight or more, the film is colored by the ITO powder and the haze degree thereof increases, thereby increasing metallic luster and causing peeling or cohesive failure of the infrared ray blocking layer, so that the adhesion to a base film becomes inferior. In the case in which the compounding ratio of the ITO powder is 60% by weight or less, the object, i.e., infrared ray blocking ability is not obtained, thereby resulting in undesirably high HAZE values due to the difference between refractive indexes of the particles of the ITO powder and that of the resin. When the invention is used in practice, a hard coat layer is laminated by coating a hard coat material on a front surface of a base film or an infrared ray blocking layer. An adhesive layer is then laminated by coating an adhesive material on a rear surface of the base film, thereby constructing a completed film. Then, the adhesive layer of the film is adhered to a glass plate or the like. As a base film, a hard coat material, and an adhesive material, materials having high transparency must be used.
Therefore the infrared ray blocking transparent film according to the present invention is characterized by comprising a base film and an infrared ray blocking layer provided on at least a surface of the base film, and the infrared ray blocking layer includes the indium tin oxide powder and the resin in a weight ratio ranging from 90/10 to 60/40.
The infrared ray blocking transparent film having high transparency with low haze (low HAZE value) can be obtained by the composition described above. Conductive coating material mixed with the ITO powder into the resin is laminated on a base film by a coating method, so that the cost for forming a thin film decreases remarkably, as compared with a vacuum deposition method or a sputtering method, and metallic luster is inhibited. Furthermore, the ITO powder is dispersed into the resin, whereby the electromagnetic wave transmissivity is excellent; for example, a mobile telephone or a car navigation system can be used in an automobile without hindrance. As a method for coating a conductive coating material mixed with the ITO powder in the resin, a wire bar coating method, a doctor blade coating method, a gravure coat method, a dip coat method, or the like can be applied.
In the present invention, a pigment such as ZnO, SnO
2
, TiO
2
, or the like, can be added into the infrared ray blocking layer. In other words, an infrared ray blocking layer may be composed of the resin mixed with these pigments and the ITO powder. The pigments are employed as infrared ray blockers with the ITO powder and the wavelengths blocked by the infrared ray blocking pigments range from 1200 to 2500 nm. Therefore, the ITO powder is combined to shield against the range of infrared wavelengths from 800 to 2500 nm (the so-called “near infrared”). In addition, the pigments are mixed with the resin, thereby setting tip the compounding ratio of the ITO powder within the lower end of the above range, so that the amount used of the ITO powder, which is relatively expensive, is reduced, and the overall cost can be reduced. Furthermore, the average particle size of these pigments must be 100 nm or less in order to obtain metallic luster inhibition and excellent electromagnetic wave transmissivity.
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