NL1013664C2 - Anti-reflective film and image display device. - Google Patents

Description

5 '*> 1.

ANTI-REFLECTIVE FILM EM IMAGE VIEWING DEVICE

Field of the Invention

The present invention relates to an anti-reflective film and an image display device, more particularly an anti-reflective film to prevent reflection of external light and an image display device in which the anti-reflective film is formed on the surface of a panel base for displaying an image.

BACKGROUND OF THE INVENTION

When a person views an object through a transparent material such as spectacle lenses, he perceives a phenomenon called a hint or fanning, which is a reflected image that appears clearly when the intensity of the reflected light becomes strong. On the other hand, an ordinary window glass or the glass of a shop window causes an image phenomenon in the glass, which occurs due to mirror reflection of ambient light, such as sunlight or incident light, from the window glass. Such an image phenomenon in the glass can deteriorate the light transmitting power of the window glass. To overcome this inconvenience, an attempt has been made to form an anti-reflective film on a base panel made of a material that differs in refractive index from the base panel material by means of a vacuum vapor deposition process or the like. In this case, as is well known, it is important to appropriately choose the thickness of the cover layer formed on the base panel to maximize the effect of preventing the reflection. For example, it is known that for a single layer cover, the minimum reflective power, that is, the maximum transmissive power, of the cover layer can be obtained from a cover material having a refractive index. lower than that of the material of the base panel to select an optical layer thickness at 1/4 (or an odd multiple thereof) of the wavelength of the intended light. It should be noted that the optical layer thickness of the coating material is given by the product of the refractive index of the coating material and the layer thickness of the coating material. The anti-reflective layer can be composed by stacking a plurality of layers on the base panel. With regard to such an anti-reflective layer with a multi-layer structure, various techniques have been proposed concerning the choice of thickness of each layer, for example in "Optical Technique Contact", Vol. 9. No. 8, page 17, 1971. The cover layer forming the above anti-reflective film is essentially made of an inorganic oxide or an inorganic halide and generally has a low reflectivity in combination with a high transmissivity in a range of 20 visible. light.

Even in an image display device such as a Braun tube or a liquid crystal display device. There may be the inconvenience of an image becoming obscure due to the reflection of external light or incident light in a screen, and in many cases an anti-reflective film is formed on the surface of a base panel for displaying such an image about such an image. prevent reflection of the front surface. On the other hand, depending on its structure or application, the image display device requires that the light transmitting power of the base panel be adjusted in a range of 20 to 92% in order to improve the contrast. For example, in the base panel, such as a glass tube for a Braun tube or a front plate 35 of a projector (rear-facing projector) of the acrylic type, the light-transmitting power is controlled by 101J664 3 the light-transmitting power of change the basic panel itself.

However, the basic panel for displaying an image plays the role of maintaining the mechanical strength of the image display device. That is | say that if the image display device is made larger, the base panel must be made thicker. In order to change the light transmittance of the base panel, thus thickened, it is required to prepare several base panels that are different in transmissivity, by changing the strength of a dye or the concentration of a pigment.

Furthermore, with a glass panel, such as the base panel for a Braun tube, the central portion is thin and the portion at the end thick to ensure sufficient mechanical strength. Consequently, in the case of adjusting the light transmitting power of the glass panel by changing the light transmitting power of the glass panel itself, the problem has arisen that the light transmitting power at the central portion is different from that at the end portion. In particular, for the Braun tube of recent times, in which a display screen for displaying an image is taken as a substantially flat plate, since the central portion becomes thin and the end portion becomes thick around the mechanical increase the intensity, the difference in light transmitting power between the central part and the part at the end larger.

One type of heat-radiation cut-off film components using optical thin films is composed so that an optical absorption layer is formed from a metal thin film for the purpose of adjusting light transmissivity. Specific examples of material for forming the optical absorption layers may include Au, Pt, Ni-Cr, Al, In 2 O 3-SnO 2, Cul and CuS. Such a heat radiation cut-off film has a visible light transmissivity, which is preferably in a range of 60 to 90%. Specific examples using such an optical absorption layer as an anti-reflective film may include a dark mirror, a selective absorption mirror, or a mirror with increased absorption. As an anti-reflective film in an area of visible light, a composition called a "dark mirror" can be used. A dark double layer mirror in which an optical absorption layer is combined with a dielectric layer is described, for example, in Optical Thin Film User Handbook *, page 160 (published by Nikkan Kogyou Shinbunsha). Japanese Patent Laid-open 9-156964 describes a technique in which a layer of metal nitrile made of TiN, ZrN or HfN is used as an optical absorption layer to thereby provide a low reflectivity in a wide range of visible light. to gain. U.S. Patent No. No. 5,091,244 describes an anti-reflective film with a structure of four to six layers, in which a layer of metal or metal nitride is used as an optical absorption layer to allow adjustments of light transmitting power while having a low reflecting power in an area visible light is preserved.

However, in the case of using the material 25 suitable for forming the above optical absorption layer as part of the anti-reflective film, a problem arises. In the art described in Japanese Patent Laid-open No. For example, the reflective power of light from the front surface of the base panel is sufficiently low, but the reflective power of light from the inner surface of the base panel is 5 to 10%. In the image display device, the reflection of light from the inner surface of the base panel may cause a double image (or a cast) of a letter or an image or obscure the outline of a letter or an image, resulting in a considerably deteriorated display quality. In the anti-reflective film described in U.S. Pat. Patent No. 5,091,244, the patent teaches the method of decreasing the reflection of light from the front surface while controlling the light transmittance; however, it does not study the reduction of the reflection of light from the inner surface of the base panel, which is the matter of interest of the image display device as described above, with the result that the reflectivity of light from the inner surface of the base panel is 8 to 20%.

If the light transmissivity of the base panel for a Braun tube has a low value of 35 to 60%, the reflection of light from the inner surface of the base panel does not cause so much a problem because the reflective light from the inner surface is weakened by passing the reflected light through the base panel three times. On the other hand, if the light transmittance of the base panel for a Braun tube is 60% or more, for example, in the case of using the base panel, the class "Clear" (transmittance: 75% or more) or the class "Gray" (transmissivity: 60-75%) exhibits as specified under EIAJ EC-2138, the reflection of light from the inner surface of the base panel causes a non-negligible problem.

An object of the present invention is to provide an anti-reflective film that allows the control of light transmitting power in a wide area 30 and to provide an image display device that has a desired display quality.

SUMMARY OF THE INVENTION

To solve the above problem, according to the present invention, an anti-reflective film is provided which has a multi-layer structure in which a plurality of thin films are stacked on a base panel, characterized in that the thin films include: 1 3 664 6 a first optical absorption layer composed of at least one type selected from a group consisting of a film of metal, a film of metal nitride and a film of metal oxide; a second optical absorption layer composed of at least one type selected from a group consisting of a film of metal, a film of metal nitride and a film of metal oxide; and a dielectric film with a refractive index ranging from about 1.4 to about 1.9, wherein the dielectric film; 10 is placed between the first optical absorption layer and the second optical absorption layer.

According to the present invention, there is also provided an image display device in which an anti-reflective film is formed on a surface of a base panel for displaying an image, characterized in that the anti-reflective film comprises: a first optical absorption layer composed of at least one type selected from a group consisting of a film of metal, a film of metal nitride and a film of metal oxide; a second optical absorption layer composed of at least one type selected from a group consisting of a film of metal, a film of metal nitride and a film of metal oxide; and a dielectric film with a refractive index ranging from about 1.4 to about 1.9, wherein the dielectric film is disposed between the first optical absorption layer and the second optical absorption layer. In this image display device, the base panel preferably has a light transmitting power in a range of 60% or more.

Other objects and advantages of the invention will become apparent upon reading the following detailed description and appended claims and with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a drawing showing the changes in the reflection of light from the front surface and the reflection of light from the inner surface depending on a change in the refractive index of i 10 1 3 664 if, * 7 a dielectric film formed between two optical absorption layers of an anti-reflective film according to the present invention.

It is to be understood that the drawings are not necessarily to scale and that the embodiments are sometimes represented by graphic symbols, imaginary lines, sketch-like representations and partial views. In certain cases, details that are not necessary for understanding the present invention or that make other details difficult to distinguish may be omitted. Of course, it is to be understood that the invention is not necessarily limited to the specific embodiments shown herein.

15 DETAILED DESCRIPTION OF THE PRESENT EMBODIMENTS

The base panel for an image display device is made of a glass material or a material of synthetic resin. The specific examples of glass material can include sodium glass, lead glass, hard glass, quartz glass and liquid crystal glass. For a Braun tube, silicate glass is preferably used which contains strontium or barium; and for a liquid crystal display device, low-alkali glass is preferably used.

Any type of material of an organic high polymer can be used as the synthetic resin material for forming the base panel. From the point of view of optical characteristics such as transmissivity, refractive index and dispersion, as well as other characteristics such as impact resistance, heat resistance and durability, however, it is preferable to use: a resin based on (with) acrylate such as polymethylmetacrylate, or a copolymer of methyl methacrylate and a vinyl monomer such as alkyl (met) acrylate or styrene; a polycarbonate resin such as polycarbonate or diethylene glycol bisallyl carbonate (CR-39); a thermosetting resin based on (with) acrylate such as a single 1 664. i, ΐ 8-fold polymer or a copolymer of (brominated) bisferiol A-type di (met) acrylate or a single polymer or a copolymer of urethane-modified (brominated) bisphenol A-mono (met) acrylate; polyester, in particular polyethylene terephthalate, polyethylene naphthalate or unsaturated polyester; acrylonitrile-styrene copolymer; polyvinyl chloride; polyurethane; or epoxy resin. Furthermore, an aramid-based resin can be used from the point of view of heat resistance. A film-like base can be produced by flowing out the above-described synthetic resin material or by diluting the above-described synthetic resin material with a solvent, applying the diluted material in a film-like form and drying it. The thickness of the film-like base is generally in a range of 25 to 500 microns.

If the base panel for the display device is made of a synthetic resin material, the surface of the base panel can be covered with a covering material such as a hard coat, described in Japanese Patent Publication Nos. Sho 50-28092, Sho 50-28446, Sho 51-24368, Japanese Patent Publication No. Sho 52-112698 and Japanese Patent Publication No. Sho 57-2735.

Also, for the base panel made of a synthetic resin material, various characteristics thereof, such as adhesion, hardness, chemical resistance, durability, and dye affinity can be improved by providing an inorganic covering material 30 as a lower layer of an anti-reflective film. The thickness of the hard cover layer is generally in a range of about 3 to 20 microns. Furthermore, the base panel for the image display device can be colored with a pigment such as black carbon or a colorant. In this case, as described in Japanese

Patent Publication No. 7-36044, the base panel, thus colored, serve as a selective absorption filter 101 3 664/9 which selectively absorbs light with a specific wavelength.

The anti-reflective film containing an optical absorption layer can be formed with a PVD (physical vapor deposition) process, represented by a vacuum vapor deposition process, a process of electrolytic coating or a process of sputtering. The specific examples of materials suitable for forming an optical absorption layer by the PVD process 10 can include metals such as Au, Pt, Pd, Fe, Fe-Ni, Ni-Cr, Ni-V, Al, Ag, Cr , Fe-Cr, Cu, Ti, Zr and Hf, and nitrides and oxides thereof. Furthermore, specific examples of dielectric film forming materials may include inorganic oxides or inorganic nitrides such as SiO 2, SiO, Si 3 N 4, Al 2 O 3, ZrO 2, TiO 2, Ta 2 O 5, TaHf 2, TiO, Ti 2 O 3, HfO 2, ZnO, ln 2 O 3, In 2 O 3 / SnO 2, Y 2 O 3, Yb 2 O 3, Sb 2 O 3, MgO and CeO 2.

An oxidation barrier layer, to prevent oxidation of an optical absorption layer, can be inserted into the anti-reflective film, as described in Japanese Patent Laid-open Nos. Sho 59-165001 and Hei 9-156964. Specific examples of materials for forming the above oxidation barrier layer may include various metals and metal nitrides, such as Si.N, or AlN.

The oxidation barrier layer is unnecessary from an optical point of view, and therefore the thickness of the oxidation barrier layer is preferably in a range of 20 micrometers or less in order to prevent the deterioration of the reflection prevention property. Furthermore, if the base panel is made of a synthetic resin material as described in U.S. Pat. Patent No. 2,628,927 and Japanese Patent Publication No. 3-81121, a film of a metal oxide, such as SiO 2, or a metal sulfide in an extremely thin way are formed as a first layer (adhesive layer) of the anti-reflective film to promote adhesion between the base panel and the anti-reflective film .

According to the means described above, it is possible to provide an anti-reflective film with a desired reflective property with a minimal number of layers. In an image display apparatus in which such an anti-reflective film is formed on the surface of a base panel for displaying an image, it is possible to control the light transmissivity in a wide area without the necessity, as usual, of preparing various base panels that vary in light transmitting power. It is also possible in this image display device, since a homogeneous light transmitting power can be obtained over the entire surface of the base panel for displaying an image irrespective of the mechanical strength of the image display device, to ensure a good display quality without the occurrence of tinge or fanning due to reflection of light from the inner surface of the base panel.

The present invention is applicable to an anti-reflective film with a multi-layer structure in which a plurality of thin films are formed on a base; and 20 on an image display device in which the above-mentioned anti-reflective film is formed on the surface of a base panel for displaying an image. In the following, an example will be described that uses an anti-reflective film formed on the surface of a base panel represented by a glass panel ("Clear" glass, specified under EIAJ H-8601) for a Braun tube. Moreover, the thickness of the central part of an image display surface of the glass panel is 12 millimeters. It should be noted that the present invention is of course not limited thereto.

Inventive Example 1

In this example, the following four films were sequentially formed on the glass panel of a Braun tube 35: a first optical absorption layer of TiN with a thickness of 10 nanometers, a dielectric film of A1203 (refractive index: about 1.7) with a thickness of 82 nanometers; a second optical absorption layer of TiN with a thickness of 12 nanometers; and a dielectric film of SiO 2 with a thickness of 90 nanometers, so as to obtain a four-layer anti-reflective film. Comparative Example 1 In this comparative example, the following two films were formed on the glass panel for a Braun tube: a first optical absorption layer of TiN with a thickness of 10 nanometers; and a dielectric film of SiO 2 (refractive index: about 1.4) with a thickness of 87 nano-10 meters, so as to obtain a two-layer anti-reflective film. In this comparative example, the second optical absorption layer is not formed. Comparative Example 2

In this comparative example, the following four films were sequentially stacked on the glass panel for a Braun tube: a first optical absorption layer of TiN with a thickness of 19.9 nanometers; a dielectric film of TiO 2 (refractive index: about 2.6) with a thickness of 30 nanometers; a second optical absorption layer of TiN with a thickness of 6.7 nanometers; and a dielectric film of SiO 2 with a thickness of 82.2 nanometers, so as to obtain an anti-reflective film. In this comparative example, the refractive index of the dielectric film formed between the first and second optical absorption layers is more than 1.9.

The results of simulating the anti-reflective films in Inventive Example 1 and Comparative Examples 1 and 2, using a computer, are shown in Table 1. As complex refractive indices of the film materials used for the simulation, values obtained at on the basis of a relationship for the complex refractive index = (n - 1) and shown in Table 2. It should be noted that for a dielectric substance k becomes zero.

10 1 3 664 ·· »12 'Table 1 5 -: -: -: -: ---

Reflective power of Reflective power Dooriateod light from front of light from inner power surface (Visible surface (Visible (Wavelength: reflective power) reflective power) 546 nm) ..

Inventive 0.1% 0.8% S3%

Example 1____

Comparative 0.1% 6.6% 7S% 10 Example 1 ____ ·

Comparative 0.1% 16.8% 48% I Example 2____

Table 2 15 Film material Complex Wavelength refractive index ___ 4S0 nm SS0 nm 6S0 nm ΠΝ Refractive index (s) 2.00 1.75 1.70

TiN _Bsthaction coefficientl (k) 0.95_ 1.20__1.67_

AbQ »~ Refractive index (s) 1.67 1.67_1.67_20 | BwhlHaMndeK (n) 11.46 | 1.46 | 1.44 |

As is clear from Table 1, for the anti-reflective film obtained in Inventive Example 1, the visible reflective power of light reflected from the front surface is 0.1%; the visible reflective power of light reflected from the inner surface is 0.8%; and the transmissivity of light with a wavelength of 546 nanometers is 53%. These results meet the requirements of the image display device. In contrast, for the anti-reflective films obtained in Comparative Examples 1 and 2, the visible reflectivity of light reflected from the front surface is of a low value, namely, 0.1%; however, the visible reflectivity of light reflected from the inner surface is of a high value, namely 6.6% for Comparative Example 1 and 16.8% for Comparative Example 2. These results do not meet the requirements of the image display device.

Figure 1 is a drawing showing a relationship between the light-reflecting power and the refractive index of a dielectric substance that forms a dielectric film of an anti-reflective film. To be more precise, the following four layers were sequentially formed on a transparent glass as a base panel: an optical absorption layer of TiN with a thickness of 10 nanometers, a dielectric film (quarter-wavelength film); an optical absorption layer of TiN with a thickness of 12 µm; and a dielectric film of SiO 2 with a thickness of 90 nanometers, to form an anti-reflective film. For such an anti-reflective film, the visible reflective power of light reflected from both the front surface and the inner surface was calculated taking the refractive index of the dielectric substance of the dielectric film 20 as a parameter.

The reflectivity of light reflected from both the front surface and the interior surface of a base panel made of a glass material or a synthetic resin material is in a range of about 4 to 6%. A measure of determining the reflection prevention requirement required for an image display device is specified under Europe Standard TUV. To meet this standard, visible reflectivity must be suppressed to a value of 2% or less (see Television Society's Technical Report, Vol. 19, No. 2, 1995). In particular in the simulation results described above, in order for both the reflective power of light from the front surface and the reflective power of light from the inner surface to be simultaneously in a range of 2% or less, the refractive index of the dielectric film must be in a range of 1.4 to 1.9; preferably in a range of 1.5 to 1.8.

101 3 664

The present invention can provide an anti-reflective film with a desired reflection-inhibiting effect with a minimum number of layers. The image display device in which the anti-reflective layer is formed on the surface of a base panel for displaying an image has the following effects: (1) The light transmitting power can be adjusted in a wide range without the necessity of it, as usual , preparing various types of base panel that differ in light transmittance.

(2) A desired display quality without the occurrence of hint or flare due to reflection of light from the inner surface of the base panel can be ensured.

(3) A homogeneous light transmitting power can be obtained over the entire surface of the base panel for displaying an image, regardless of the mechanical strength of the image display device.

While the preferred embodiments of the present invention have been described using specific terms, such description is for illustrative purposes only and it is to be understood that changes and variations can be made without departing from the spirit or scope of the following claims. .

101 3 6 6 4

Claims (11)

An anti-reflective film with a multilayer structure in which a plurality of thin films are stacked on a base, the anti-reflective film comprising: a first optical absorption layer selected from a group consisting of a metal, a metal nitride and a metal oxide; a second optical absorption layer selected from a group consisting of a metal, a metal nitride and a metal oxide; and a dielectric film with a refractive index ranging between about 1.4 and about 1.9, the dielectric film being placed between the first optical absorption layer and the second optical absorption layer. 2. The anti-reflective film of claim 1, wherein the metal of the first optical absorption layer comprises a metal, a metal nitride or a metal oxide selected from the group consisting of Au, Pt, Pd, Fe, Fe-Ni, Ni-Cr, Ni-V, Al, Ag, Cr, Fe-Cr, Cu, Ti, Zr and Hf, and nitrides and oxides thereof. 3. The anti-reflective film of claim 1, the metal of the second optical absorption layer comprises a metal, a metal nitride or a metal oxide selected from the group consisting of Au, Pt, Pd, Fe, Fe-Ni, Ni-Cr, Ni -V, Al, Ag, Cr, Fe-Cr, Cu, Ti, Zr and Hf, and nitrides and oxides thereof. 30 The anti-reflective film of claim 1, wherein the dielectric film comprises a material selected from the group consisting of SiO 2, SiO, Si 3 N 4, Al 2 O 3, ZrO 2, TiO 2, Ta 2 O 5, TaHf 2, TiO, Ti 2 O 3, HfO 2, ZnO, ln 2 O 3, In 2 O 3 / SnO 2, Y 2 O 3, 35 Yb 2 O 3, Sb 2 O 3, MgO and CeO 2. 5. An image display device in which an anti-reflective film is formed on the surface of an image display panel, the anti-reflective film comprising:. a first optical absorption layer selected from a group consisting of a metal, a metal nitride and a Metal oxide; a second optical absorption layer selected from a group consisting of a metal, a metal nitride, and a metal oxide; and a dielectric film with a refractive index ranging between about 1.4 and about 1.9, the dielectric film being placed between the first optical absorption layer and the second optical absorption layer. 6. An image display device as claimed in claim 2, wherein the base panel has a light transmitting power in a range of 60% or more. j 7. The anti-reflective film of claim 5, wherein the metal of the first optical absorption layer comprises a metal, a metal nitride or a metal oxide selected from the group consisting of Au, Pt, Pd, Fe, Fe-Ni, Ni-Cr , Ni-V, Al, Ag, Cr, Fe-Cr, Cu, Ti, Zr and Hf, and nitrides and oxides thereof. The anti-reflective film of claim 5, wherein the metal of the second optical absorption layer comprises a metal, a metal nitride or a metal oxide selected from the group consisting of Au, Pt, Pd, Fe, Fe-Ni, Ni-Cr, Ni -V, Al, Ag, Cr, Fe-Cr, Cu, Ti, Zr and Hf, and nitrides and oxides thereof. The anti-reflective film of claim 5, wherein the dielectric film comprises a material selected from the group consisting of SiO 2, SiO, Si 3 N 4, Al 2 O 3, ZrO 2, TiO 2, Ta 2 O 5, TaHf 2, TiO, Ti 2 O 3, HfO 2, ZnO, In 2 O 3, In 2 O 3 / SnO 2, Y 2 O 3, Yb 2 O 3, Sb 2 O 3, MgO and CeO 2. 10 1 3664