Electromagnetic wave reflecting member

Abstract

Disclosed is a selectively reflective member which can uniformly reflect only a desired wavelength with high efficiency even in a large area and, at the same time, is highly cost effective. Specifically, there is provided an electromagnetic wave reflecting member that reflects electromagnetic waves with a specific wavelength, the electromagnetic wave reflecting member comprising a first selectively reflective layer that reflects only a clockwise or counterclockwise circularly polarized light component with wavelength λ in incident electromagnetic waves, a phase difference layer, and a second selectively reflective layer that reflects only a clockwise or counterclockwise circularly polarized light component with wavelength λ, provided in that order, the phase difference layer having a retardation satisfying the following equation:Re={(2n+1) / 2±0.2}×λwherein Re represents average retardation; λ represents wavelength; and n is an integer of 1 or more.

Description

BACKGROUND OF THE INVENTION[0001]1. Field of the Invention[0002]The present invention relates to an electromagnetic wave reflecting member and more specifically to an electromagnetic wave reflecting member that can efficiently and uniformly reflect electromagnetic waves with a specific wavelength falling within a visible to far-infrared light wavelength range.[0003]2. Background Art[0004]Selectively reflective members using cholesteric liquid crystals are known as a member that can selectively reflect a light component with a desired wavelength in a visible light to heat radiation wavelength range. These selectively reflective members can selectively reflect only light (electromagnetic waves) with a desired wavelength and thus are expected to be used, for example, as heat radiation reflecting films or light transparent and heat insulating films that are transparent to visible light and reflect only a heat radiation. In the cholesteric liquid crystal which can realize selective refle...

AI Technical Summary

Benefits of technology

[0010]The present inventors have now found that, in a selectively reflective member having a structure comprising a pair of cholesteric liquid crystal films stacked on top of each other through a phase difference film, even when a general-purpose stretched film such as a polyethylene terephthalate film is used as the phase difference film, the selectively reflective member can uniformly reflect only a light component with a desired wavelength with high efficiency even in a large area and, at the same time, is highly cost effective if the phase difference film satisfies specific conditions. The present invention has been made based on such finding.

[0011]Accordingly, an object of the present invention is to provide an electromagnetic wave reflecting member, which can uniformly reflect only a light component with a desired wavelength with high efficiency even in a large area, using a very inexpensive material.

[0024]According to the present invention, the phase difference layer held between the first and second selectively reflective layers that reflect only a clockwise or counterclockwise polarized light component with wavelength λ in electromagnetic waves has an average retardation satisfying the following relationship: Re={(2n+1) / 2±0.2}×λ. Accordingly, for example, when a selectively reflective layer that selectively reflects near-infrared light with a wavelength of 1200 nm is used, the average retardation Re of the phase difference layer is 1800 nm at n=1, 3000 nm at n=2, 4200 nm at n=3, and 5400 nm at n=4. Therefore, even when a commercially available phase difference film having an in-plane retardation distribution of about 4200±50 nm as such is used, the deviation from the retardation value necessary for converting clockwise or counterclockwise circularly polarized light to counterclockwise or clockwise circularly polarized light is about 8% at the maximum. Therefore, the deviation hardly affects the reflection efficiency. Consequently, an electromagnetic wave reflecting member can be realized that can uniformly reflect only a desired wavelength with high efficiency even in a large area and, at the same time, is highly cost effective.

Problems solved by technology

Cholesteric liquid crystals having a counterclockwise spiral pitch, however, hardly exist in nature, and thus should be chemically synthesized and thus are highly expensive.

Accordingly, this leads to an increase in cost of selectively reflective members comprising a cholesteric liquid crystal film, which reflects a counterclockwise circularly polarized light component, and a cholesteric liquid crystal film, which reflects a clockwise circularly polarized light component, stacked on top of each other.

For this reason, the production of the above laminates on a commercial scale at low cost is difficult.

The casting method, that is, the method which comprises coating a solution of a cellulose ester dissolved in an organic solvent onto a support to form a coating, removing the solvent from the coating to dry the coating, and separating the dried coating from the support, however, requires large equipment and special techniques.

Accordingly, as compared with general-purpose stretched films formed by melt extrusion, films formed by casting is still expensive.

On the other hand, for the stretched films formed by melt extrusion, difficulties are experienced in regulating in-plane birefringence and film thickness that determine retardation values.

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