JPH04281403A - High visible heat ray reflecting laminate - Google Patents

Abstract

PURPOSE:To offer the laminate with a high visible transmitted heat ray reflecting function which reflects near infrared rays with high efficiency without decreasing the transmissivity of visible light. CONSTITUTION:A transparent substrate 1 coated with a reflection increasing film 2 which reflects heat rays within a range where visible light is not reflected and a wavelength filter 4 which is made of cholesteric liquid crystal and reflects near infrared rays in a range where the short-wavelength side of a reflection area do not overlap with the visible range with sharp wavelength selectivity are laminated to obtain the heat-ray reflecting laminate which reflects the near infrared rays over a wide range and has high visible light transmissivity.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laminate having a so-called high visible heat ray reflection function that efficiently reflects infrared rays (heat rays) and efficiently transmits visible light.

0002

2. Description of the Related Art Heat-reflecting glass is a glass that transmits visible light and reflects near-infrared rays, and is used as window glass for architectural buildings and residences. By using this heat-reflecting glass, it is possible to block infrared rays, which account for about half of the radiation energy that reaches the earth's surface from the sun, and let in only visible light, thereby reducing the cooling load.

[0003] Heat-reflecting glasses are classified into reflection-enhancing film types and interference filter types. The reflection increasing film type is
It can be produced relatively easily by thermal decomposition methods (spray, CVD), vacuum methods (evaporation, sputtering), plating methods, etc., and has been put into practical use. Heat-reflecting glass produced by such a method has a high reflectance in a wide band, mainly in the near-infrared rays, and can largely block the heat rays of sunlight. On the other hand, since part of the reflected wavelength range extends to visible light, part of the visible light is also reflected, resulting in coloring and a decrease in the overall transmittance of visible light.

[0004] The interference filter type utilizes the optical interference of a multilayer thin film, and consists of several to several dozen layers of high refractive index layers and low refractive index layers. In this case, it is necessary to laminate each refractive index layer in multiple layers, and more accurate film thickness control is required for each layer, making industrialization quite difficult.

[0005]

[Problems to be Solved by the Invention] The conventional heat-reflecting glass described above cannot be used for applications that require high transmittance for visible light; increasing the transmittance for visible light reduces the transmittance for near-infrared light. There was a problem in that the heat ray reflection function decreased. An object of the present invention is to provide a laminate having a highly visible heat ray reflection function that efficiently reflects near infrared rays without lowering the transmittance of visible light.

[0006]

SUMMARY OF THE INVENTION The present invention achieves the above objects. That is, the present invention uses a transparent substrate coated with a reflection increasing film that reflects a wide range of heat rays without reflecting visible light, and a transparent substrate coated with a reflection increasing film that reflects heat rays in a wide range while not reflecting visible light. This is a laminate that reflects near-infrared rays over a wide range and has high visible light transmittance.

The present invention will be explained in detail below. In the text,
Visible light or visible range is about 400 nm to about 750 nm
The near-infrared or near-infrared region refers to the wavelength band of approximately 75
It means a wavelength band from 0 nm to about 2000 nm. Further, "high visible light" or "high visible light transmission" means that the transmittance in the visible range is about 70% or more.

[0008] The reflection increasing film is produced by conventional techniques such as thermal decomposition method, vacuum method, plating method, etc. so that it reflects in a wide band in the near-infrared region and has high transmittance in the visible region. One example of this method is the method disclosed in Japanese Patent Publication No. 57-24524, in which a tin-doped indium oxide layer is heat-treated in an atmosphere with a controlled oxygen partial pressure. As the wavelength filter, a filter is used that reflects near-infrared rays in a wavelength range in which the short wavelength side of the reflection range does not overlap with the visible range, with sharp wavelength selectivity. That is, a wavelength filter is used that can reflect near-infrared rays in a range that cannot be reflected sufficiently by the reflection increasing film. The present inventors have discovered that it is effective to use cholesteric liquid crystal as a wavelength filter having such optical characteristics. As an optical filter using cholesteric liquid crystal, JP-A-60
-191203, JP-A-62-136602, JP-A-2-186301, etc., and these optical filters can be used in the present invention.

It has been well known that cholesteric liquid crystals exhibit selective light reflection properties, and this specific reflection wavelength (λ0) and the helical pitch (P) of cholesteric liquid crystals
The relationship between the average refractive index (n) and the incident angle (θ) of light with respect to the helical axis of the cholesteric liquid crystal is expressed by the following equation. λ0=P・n・cosθ Therefore, by selecting the helical pitch (P) and average refractive index (n) of the cholesteric liquid crystal, near-infrared light, especially about 75
A wavelength filter having a specific reflection wavelength (λ0) of 0 nm to about 1000 nm can be obtained. In addition, since there is a distribution in the degree of orientation of the helical axis and the helical pitch, it is important to note that the specific wavelength (λ
0) has a spectroscopic distribution.

[0010] The helical pitch of this cholesteric liquid crystal is
Although it changes depending on external factors such as temperature, light, electric field, and magnetic field, cholesteric liquid crystal polymer composites in which cholesteric liquid crystal is fixed to a polymer are known (e.g., Japanese Patent Application Laid-open No. 139506/1983), and the reflection wavelength can be set to a specified value. It is now possible to fix the wavelength. Note that a single cholesteric film can reflect only the right or left circularly polarized light component of a specific reflection wavelength, but it is possible to stack two cholesteric films with different directions of the helical axis, or to stack two cholesteric films with the same direction of the helical axis. By inserting a λ/2 plate between the films, it becomes a total reflection filter.

The helical pitch (P) and the right-handed or left-handed direction of the helical axis can be adjusted by adjusting the liquid crystal material, the temperature, concentration, etc. when preparing the liquid crystal or its solution. In the present invention, a polymer film or a laminated film thereof is used in which a cholesteric liquid crystal whose helical axis is right-handed or left-handed and whose specific reflection wavelength is near infrared rays is fixed. The cholesteric liquid crystal that can be used in the present invention may be either a lyotropic liquid crystal or a thermotropic liquid crystal.

[0012] As a method for producing a polymer film using a predetermined cholesteric liquid crystal, for example, a cholesterol derivative monomer having an addition polymerizable group is added to a photoinitiator and, if necessary, a photoreactive polyfunctional monomer. etc. are added,
By photopolymerizing at a predetermined temperature, a film that selectively reflects desired near-infrared rays can be obtained. Specifically, JP-A-59-
109505, the specific reflection wavelength (λ
0) is 950 nm, the half width is 50 nm, and the reflectance is approximately 50%.
A near-infrared reflective film is obtained. In the case of thermotropic cholesteric liquid crystals such as glutamic acid ester copolymers, a desired polymer film with a fixed cholesteric structure can be obtained by rapidly cooling the liquid crystal from a predetermined heated molten state. A specific example is JP-A-62-
As described in No. 136602, a specific reflection wavelength (λ0) of 756 is obtained by heating and melting a D-form and/or L-form glutamic acid ester copolymer at 154°C and then rapidly cooling it.
A left-handed circularly polarized light reflective film and/or a right-handed circularly polarized light reflective film having a half width of 30 nm is obtained. Furthermore, a polymer liquid crystal that becomes a lyotropic cholesteric liquid crystal, for example a polymer liquid crystal having polypeptide bonds, is dissolved in a monomer solvent having a photopolymerizable unsaturated group at a predetermined concentration and temperature, and then photopolymerized at a predetermined temperature. A film that selectively reflects near-infrared rays is obtained. The cholesteric liquid crystal polymer film obtained in this way, whose specific reflection wavelength is fixed in the near-infrared region, has sharp wavelength selectivity as shown in Figure 1, so it transmits visible light and has the shortest reflection wavelength in the near-infrared region. It is possible to reflect a portion of the wavelength. When the reflection wavelength band of this cholesteric liquid crystal polymer film is narrow, cholesteric liquid crystal films that reflect two or more different wavelength bands may be laminated.

The transparent substrate with the reflection increasing film and the wavelength filter are laminated, and the transparent substrate may be made of so-called inorganic glass or organic glass such as commonly used soda-lime glass or low-expansion heat-resistant glass. Plastic films such as acrylic plates, bisphenol type polycarbonate plates, diethylene glycol bisallyl carbonate polymers, or polyester films can be used, and the structure of the laminate includes, for example, a reflection increasing film. Examples include soda-lime glass/wavelength filter/soda-lime glass, acrylic plate with reflection-enhancing film/wavelength filter/polyethylene terephthalate film, soda-lime glass with reflection-increasing film/wavelength filter, etc. An interlayer film may be used if necessary. An interlayer film such as plasticized polyvinyl butyral, polyurethane or ethylene-vinyl acetate copolymer is suitably used, for example, to increase adhesive strength or to add an ultraviolet absorber to block ultraviolet rays.

[0014]

[Effects of the Invention] According to the present invention, it has become possible to produce a highly visible heat-ray reflective glass having a high visible light transmittance without impairing its near-infrared reflecting function.

[0015]

EXAMPLES The present invention will be explained in more detail by examples below, but the present invention is not limited to these examples. Example 1 A laminate of three types of cholesteric liquid crystal polymer films that reflect different wavelength bands as shown in Figure 1 and a glass coated with a reflection increasing film having the spectral reflectance shown in Figure 2 were made of polyvinyl butyral film. A laminate shown in FIG. 3 was obtained. As a result, a highly visible heat ray reflective laminate having the spectral reflectance shown in FIG. 4 was obtained.

[Brief explanation of the drawing]

FIG. 1 shows the spectral reflectance of a cholesteric liquid crystal polymer film used in one example of the present invention.

FIG. 2 shows the spectral reflectance of the reflection increasing film used in one example of the present invention.

FIG. 3 is a cross-sectional view showing the structure of a laminate according to an example of the present invention.

FIG. 4 shows the spectral reflectance of a laminate according to an example of the present invention.

[Explanation of symbols] 1. ．． glass 2. ．． reflection increasing film 3. ．． polyvinyl butyral

Claims (9)

[Claims] Claim 1: It has high infrared reflectance and high visible light transmittance, consisting of a transparent substrate coated with a thin film that reflects near infrared light in a wide band and a cholesteric liquid crystal wavelength filter that has sharp wavelength-selective reflection in the near infrared region. laminate. 2. The laminate according to claim 1, wherein the transparent substrate is one selected from inorganic glass, organic glass, and plastic film. 3. The laminate according to claim 2, wherein the organic glass is a film or sheet made of acrylic, polyester, or polycarbonate. 4. The laminate according to claim 1, wherein the cholesteric liquid crystal is a cholesterol derivative monomer having an addition polymerizable group. 5. The laminate according to claim 1, wherein the cholesteric liquid crystal is a polymeric cholesteric liquid crystal. 6. The laminate according to claim 1, wherein the wavelength filter is a polymer film in which the helical pitch of cholesteric liquid crystal is fixed. 7. The laminate according to claim 1, wherein the wavelength filter is a polymer film in which a cholesterol derivative monomer having an addition polymerizable group is fixed by photopolymerization. 8. The laminate according to claim 1, wherein the wavelength filter is a filter made by laminating polymer films on which cholesteric liquid crystals having right-handed and left-handed helical axes are respectively fixed. 9. The laminate according to claim 1, wherein said filter is a filter in which a λ/2 plate is inserted and laminated between two films on which cholesteric liquid crystal having a right-handed or left-handed helical axis is fixed.