JP2004233500A - Light reflection type optical medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light reflection type optical medium having a reflection layer reflecting specified visible light and possessing structure where the deterioration of image quality caused by scattering external light unrelated to an image by the defect part of the reflection layer is hardly caused, and applied to a reflection type screen or the like. <P>SOLUTION: The light reflection type optical medium is constituted by laminating a red light reflection layer 2, a green light reflection layer 3 and a blue light reflection layer 4 which are photonic crystal layers on a visible light absorbing layer 1. The reflection layers 2-4 selectively reflect three primary color light beams projected from a projector or the like and form a high-contrast full color image. Visible light absorbing substance is contained in at least one of the reflection layers 2-4 and/or at least one of boundary parts between the layers. Thus, even if the external light is made incident on a screen in a figure, it is partially absorbed by the visible light absorbing substance before it reaches the defect parts of the photonic crystal layers 2-4. Even if the external light is scattered, the scattered light is absorbed by the visible light absorbing substance, so that the scattered light reaching an observer's eye is reduced. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a light reflection type optical medium which can be applied to a reflection type screen suitable for projecting an image from, for example, a CRT (Cathode Ray Tube) projector or a liquid crystal projector.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, as a reflective screen that reflects light projected from a projector to display an image, a white screen that has no wavelength characteristics and reflects or scatters all light in the visible wavelength region has been used. On a white screen, when light unrelated to the image enters the screen, the light is reflected or scattered in the same manner as the image (hereinafter, in this specification, other than the image projected from a projector or the like, regardless of the image) The visible light incident on the screen is referred to as external light.) As a result, this external light overlaps the image and enters the eyes of the observer, deteriorating the contrast of the image.
[0003]
For this reason, when an image is projected from a projector onto a white screen, it is general that the image is projected in a dark room where external light is restricted. However, restricting image display to a dark room significantly impairs the usefulness of a display system using a screen and greatly restricts applications. Even when projected in a dark room, reflected light from the screen is scattered in the dark room and re-enters the screen, light leaks from the outside, and external light such as light remaining in the dark room such as an emergency light. Due to the reflection of light, the contrast of the image is reduced, and the dark part of the image cannot be displayed as a true dark part on the screen.
[0004]
On the other hand, CRT projectors and liquid crystal projectors include projectors that project three primary colors of red (R), green (G), and blue (B) onto a screen and mix the colors on the screen to display various colors. . In such a projector, since the spectral half width (FWHM) of each of the three primary colors used is as wide as 60 to 100 nm, the color reproduction range on the chromaticity diagram that can be expressed is narrowed, and accurate color tone can be reproduced. There is a problem that is difficult.
[0005]
[Procedure leading to the invention]
As a result of diligent studies on the above problems, the present applicant has previously proposed a method of forming a fine particle layer by a pull-up rotation method and a reflective screen using the fine particle layer as a light reflecting layer (Japanese Patent Application No. 2001-2001). 380670; hereinafter, the invention according to Japanese Patent Application No. 2001-380670 will be referred to as a prior application invention.)
[0006]
As a method of assembling particles in a self-organizing manner to form a particle aggregate in which the particles are regularly and regularly arranged two-dimensionally or three-dimensionally, a spontaneous sedimentation method and a lifting method are known. In either method, fine particles are once dispersed in a dispersion medium to prepare a fine particle dispersion, and then the fine particles are gradually deposited on the substrate by sedimentation due to its own weight or reduction of the dispersion medium due to evaporation.
[0007]
If the particle diameters are the same, the arrangement structure in which spherical particles such as silica fine particles are most densely packed is the closest packed structure. Therefore, by assembling the fine particles densely, a fine particle aggregate having a close-packed structure at least partially can be formed in a self-organizing manner.
[0008]
The pulling rotation method combines the advantages of the natural sedimentation method, in which a three-dimensional array can be formed in a single operation, with the advantages of the single particle film pulling method, which has less unevenness in thickness, and can significantly reduce the preparation time. This is a method of forming.
[0009]
More specifically, in the pull-up rotation method, as in the pull-up method, the substrate is immersed, pulled up, and the dispersion medium is evaporated in one cycle, and this cycle is repeated to form a fine particle aggregate. However, the substrate is pulled up at a high speed (for example, 0.6 m / min) using a fine particle dispersion having a high concentration (for example, 2 to 50% by mass). As the lifting speed increases, the amount of the fine particle dispersion liquid that wets the substrate increases. In this way, a plurality of fine particle layers are formed in one cycle, and the time required for the manufacturing process can be significantly reduced as compared with the conventional pulling method. If the concentration of the fine particle dispersion liquid is high and the pulling speed is high, a thin film having a thickness distribution that is thicker downward and thinner upward is formed in the vertical direction, and the thickness tends to be uneven. It is suppressed by rotating the direction.
[0010]
FIG. 22 shows a reflection spectrum (a) of a silica fine particle layer 53 formed on a substrate 51 from a dispersion in which silica fine particles 52 having a diameter of 280 nm are dispersed in water by a pulling rotation method, and an arrangement structure of fine particles (b). is there. Here, as for the reflection spectrum, as shown in FIG. 22B, white light is made incident on the surface of the fine particle layer 53 perpendicularly, and the spectrum of the reflected light reflected perpendicularly on the surface is measured.
[0011]
From FIG. 22 (a), it is found that the reflectance is maximum for light having a wavelength of 624.5 nm (red light), the reflectance is relatively high at 54%, and the half width of the peak is as narrow as about 30 nm. I understand.
[0012]
It is known that Bragg's law holds for X-ray interference caused by atoms and molecules forming a crystal. Further, it is known that light is generally liable to be reflected by a periodic arrangement structure of fine particles repeated at intervals (pitch) substantially equal to the wavelength. Therefore, assuming that a relationship similar to the condition of the Bragg reflection is established also in the reflection of visible light by the silica fine particle layer, the wavelength λ of the light that is most likely to be reflected.₀A relationship shown in the following (Formula 1) is established between the distance d and the interval (pitch) d between the fine particle layers.
kλ₀  = 2nd (Equation 1)
Here, n is the mode refractive index of the constituent material of the fine particles, and k is a positive integer.
[0013]
On the other hand, it is assumed that the arrangement structure of the fine particles is a close-packed structure. The close-packed structure has a cubic close-packed structure in which three fine particle layers having different arrangement positions of particles in a plane are sequentially stacked, and a two-fine particle layer having different arrangement positions of particles in a plane is sequentially stacked. Although there is a hexagonal close-packed structure, the interval (pitch) d between two adjacent fine particle layers is the same, and the relationship with the diameter D of the fine particles is represented by the following (formula 2).
d = (2 × 3)^1/2  D / 3 (Equation 2)
[0014]
Substituting 280 nm for the diameter of the silica fine particles as D and 1.36 for the mode refractive index of the silica fine particles as n in (Equation 1) and (Equation 2).₀= 622 nm. This is the measured value λ₀= 624.5 nm.
[0015]
From the above, in the silica fine particle layer 53 of FIG. 22B formed in a self-organizing manner by the pulling rotation method, a periodic particle arrangement having a close-packed structure is formed at least partially, and this is , 624.5 nm as the central wavelength.
[0016]
Furthermore, a model calculation that simplifies the close-packed structure shows that when silica fine particles having a refractive index of 1.36 and a particle size of 280 nm are used, a reflection layer having a sharp peak at around 625 nm and a half width of about 30 nm can be formed. This result is in good agreement with the experimental value. In this calculation, the incident light having a wavelength of 625 nm penetrates only from the surface to the 8th to 15th layers, and most of the light is reflected up to this vicinity to reverse the traveling direction. The boundary is also shown. From this result, it is understood that when the light reflecting layer is formed using the silica fine particles, about 11 layers are sufficient.
[0017]
Further, the wavelength λ of the light reflected by the aggregate of fine particles₀  And the diameter D of the fine particles are considered to have a proportional relationship shown in (Equation 1) and (Equation 2). Wavelength λ₀Can be formed in a self-assembled manner. Such a fine particle layer of silica or the like is a material useful as an optical medium such as a reflector that reflects only light of a specific wavelength.
[0018]
Therefore, in this specification, a particle aggregate formed in a self-organizing manner and reflecting only light of a specific wavelength is called a photonic crystal, and reflection of light of a specific wavelength by the photonic crystal is called Bragg reflection. To In addition, a fine particle aggregate having good Bragg reflection characteristics in which fine particles are regularly arranged and have few defects such as particle loss and disorder in arrangement may be referred to as a “highly crystalline” fine particle aggregate.
[0019]
FIG. 23 illustrates the relationship between the diameter of silica fine particles and the Bragg reflection wavelength for silica fine particles having a refractive index of n = 1.36. That is, when silica fine particles having a particle diameter of 305 nm are used, a fine particle aggregate that reflects red light (wavelength: about 645 nm) can be formed. When silica fine particles having a particle diameter of 250 nm are used, green light (wavelength: about 535 nm) can be formed. A fine particle aggregate that reflects light can be formed, and if silica fine particles having a particle diameter of 220 nm are used, a fine particle aggregate that reflects blue light (wavelength: about 465 nm) can be formed. Here, the refractive index n and the wavelength λ₀Between λ₀There is a relation of ∝1 / n.
[0020]
FIG. 24 shows a basic structure of a reflective screen based on a preferred embodiment of the invention of the prior application. In this screen, photonic crystal layers (fine particle layers) 2 to 4 that selectively reflect only light in a narrow wavelength region near the three primary colors are provided as light reflecting surfaces, and the photonic crystal layers are provided below the photonic crystal layers in the thickness direction. A visible light absorbing layer 1 that absorbs visible light transmitted through the layers 2 to 4 is provided. Specifically, 11 layers of silica fine particles having a particle diameter of 290 nm are laminated as the red light reflecting layer 2, 11 layers of silica fine particles having a particle diameter of 240 nm are laminated as the green light reflecting layer 3, and blue light is further laminated thereon. As the reflection layer 4, silica fine particles having a particle diameter of 210 nm are laminated. The silica particles used this time have a refractive index of n = 1.36 to 1.43. This refractive index slightly varies depending on the conditions for producing the silica fine particles. As the visible light absorbing layer 1, for example, a black base material made of carbon is used.
[0021]
When an image is displayed on the above-mentioned screen, three primary colors of red (R), green (G), and blue (B) are projected onto the screen from a projector or the like, and various colors are mixed by the color mixture on the screen. To form an image. These three primary color lights are reflected by the photonic crystal layers 2 to 4 provided on the screen, reach the eyes of an observer, and are perceived as an image.
[0022]
As mentioned earlier, various external light irrelevant to the image enters the screen. On a white screen, the external light is reflected in the same manner as the image, deteriorating the contrast of the image. However, even when external light is incident on the screen, most of the light is not reflected by the photonic crystal layers 2 to 4 but is absorbed by the visible light absorbing layer 1. This is because, unlike the three primary color lights, the external light contains light of various wavelengths, and most of the light is out of the wavelength region near the three primary color lights that the photonic crystal layers 2 to 4 can reflect. Because it is. Therefore, external light hardly overlaps the image and enters the eyes of the observer. As a result, when the above-described screen is used, the deterioration of the contrast due to the external light becomes small, and the dark part of the image can be displayed on the screen as a true dark part. Also, screen display can be performed outside a dark room, such as in a room with lighting or outdoors.
[0023]
As described above, since the screen itself functions as a filter for selecting light according to the wavelength, the color reproducibility of an image is also improved for the following reasons (see FIG. 25). Since each of the three primary color lights emitted from a CRT projector or a liquid crystal projector has a large spectral half width, usually 60 to 100 nm, and poor color purity, when projected on a white screen, the color reproduction range is as shown in FIG. Is limited. On the other hand, when these lights are projected onto the screen, only the three primary color lights and light in a narrow wavelength region near the three primary colors are reflected, and the other light is absorbed. As a result, each of the three primary color lights reflected from the screen is improved to light of good color purity with a half-value width of about 30 nm. The color reproduction range of an image formed by mixing these three primary color lights is shown in FIG. To expand.
[0024]
[Problems to be solved by the invention]
As described above, the screen based on the invention of the prior application has excellent characteristics. However, if there is a defect 5 such as a defect of a fine particle or a disorder of arrangement in the fine particle layers 2 to 4, as shown in FIG. In the defective portion 5, scattering of external light occurs. When such external light is scattered, the external light is not sufficiently absorbed, the contrast of the image is reduced, and the dark portion of the image cannot be displayed as a true dark portion on the screen.
[0025]
One solution to this problem is to increase the crystallinity of the fine particle layers 2 to 4 and reduce the defects 5 that cause scattering. However, it is unlikely that the crystallinity of the fine particle layers 2 to 4 will dramatically increase unless there is a breakthrough in the method of forming the fine particle layers 2 to 4.
[0026]
An object of the present invention is to provide a structure having a reflective layer that reflects a specific visible light, and in which a defective portion of the reflective layer scatters external light and in which image quality is unlikely to be reduced, in view of the above-described circumstances. Another object of the present invention is to provide a light reflection type optical medium applicable to a reflection type screen or the like.
[0027]
[Means for Solving the Problems]
That is, the present invention provides a reflective layer that reflects light in a single visible light region or a plurality of visible light regions, and at least one of the inside of the reflective layer, the upper part in the thickness direction, and the lower part in the thickness direction. The present invention relates to a light reflection type optical medium containing a visible light absorbing substance.
[0028]
According to the present invention, the light reflective optical medium includes the reflective layer that reflects light in the single visible light region or a plurality of visible light regions. Has an effect as a filter for selecting only the visible light of the wavelength region. Therefore, for example, a reflection type screen is formed using the light reflection type optical medium, and the light of the single visible light region or a plurality of visible light regions reflected by the light reflection type optical medium is projected from a projector or the like. If a display system for forming an image is formed by using the above-described method, the image is correctly displayed, while most of the extraneous light irrelevant to the image, which is incident on the screen except from a projector or the like, is removed by the filtering. As a result, it is possible to construct a display system in which the contrast is not deteriorated by external light, and it is possible to display a dark part of an image as a true dark part on a screen. Also, screen display can be performed outside a dark room, such as in a room with lighting or outdoors.
[0029]
The light reflection type optical medium contains a visible light absorbing substance in at least one of the inside of the reflection layer, the upper part in the thickness direction, and the lower part in the thickness direction. Therefore, even if external light is incident on the light reflection type optical medium, a part of the light is absorbed by the visible light absorbing substance before reaching the defective portion of the reflection layer. Since the amount of light incident on the defect, which is the source of the scattered light, is reduced, the scattered light is reduced. Further, even when external light is scattered by the defective portion of the reflective layer, the scattered light is absorbed by the visible light absorbing substance, and thus the scattered light reaching the observer's eyes is reduced. As a result, in the light-reflective optical medium, even if the reflective layer has a defect, the defect rarely causes deterioration in image quality due to scattering of external light.
[0030]
BEST MODE FOR CARRYING OUT THE INVENTION
In the present invention, the reflection layer is preferably formed by a fine particle layer made of fine particles having a particle diameter, a material, or a shape corresponding to the wavelength of visible light to be reflected. The method for forming the fine particle layer is not particularly limited, but it is preferable that the fine particles are regularly arranged by self-organization or close packing to form the fine particle layer. In the fine particle layer, the fine particles are preferably stacked in multiple layers in the thickness direction. The material of the fine particles is not particularly limited, but silica fine particles or fine particles of a material having the same refractive index as silica are particularly preferable.
[0031]
A visible light absorbing layer that absorbs visible light is provided below the reflective layer in the thickness direction, and visible light transmitted through the reflective layer is absorbed by the visible light absorbing layer. Good. Accordingly, it is possible to absorb external light and prevent transmission of light that enters the screen from behind and exits forward.
[0032]
Preferably, a light diffusion layer made of a light diffusion film or the like and diffusing visible light is provided on the surface side of the light reflection type optical medium. The light diffusion layer functions to diffuse the light reflected from the screen, reduce directivity, and provide uniform brightness to the entire screen. In addition, the light diffusion layer acts as a protective layer to prevent the reflective layer from being damaged by mechanical shock.
[0033]
As the material of the light diffusion layer, a material that is transparent in the visible light region and diffuses light, that is, a material having a refractive index distribution such that the refractive index changes at each location in the light diffusion layer, or a film It is preferable that the surface has irregularities. The light diffusion film may be replaced with a microlens film having a two-dimensional microlens array formed on the surface.
[0034]
The reflection type screen according to the present invention preferably constitutes an image display system integrated with a projector for projecting an image. Here, one of the points of the present invention is to make the wavelength of light projected from the projector and displaying an image coincide with the wavelength of light reflected by the screen by the reflective layer. At this time, as the half width of the spectrum of the projection light is narrower, the half width of the reflection spectrum of the reflection layer can be narrowed without reducing the light amount of the projection light, and the effect of the present invention can be exhibited more effectively.
[0035]
As the light source having a narrow spectral half width, a light emitting diode and, particularly, a semiconductor laser are preferable. As the semiconductor laser for red, for example, an AlGaInP-based laser is preferable, for the semiconductor laser for green, for example, an InGaN-based laser is preferable, and for the semiconductor laser for blue, for example, a GaN-based laser is preferable.
[0036]
It is preferable that the reflection layer comprises at least one of three primary color light reflection layers of a red light reflection layer, a green light reflection layer, and a blue light reflection layer. The reflection wavelength is not particularly limited, but for full-color display, it is preferable that the reflection layer reflects at least one of the three primary color lights. In this case, light having a shorter wavelength is more likely to be scattered. In order to reduce the scattered light, the blue light reflecting layer, the green light reflecting layer, and the It is preferable that the red light reflecting layers are laminated in this order.
[0037]
Particle diameter or periodic length of fine particles forming the red light reflecting layer, particle diameter or periodic length of fine particles forming the green light reflecting layer, and particle diameter or periodic length of fine particles forming the blue light reflecting layer It is preferable that the particle diameter or the periodic length is smaller in the order of the red light reflecting layer, the green light reflecting layer, and the blue light reflecting layer. Here, the term “periodic length” means a distance (pitch) between two fine particle layers that are vertically stacked adjacent to each other in the fine particle layer.
[0038]
The visible light absorbing substance may be contained in the gaps between the fine particles or in the fine particles, or a layer containing the visible light absorbing substance may be provided at a boundary between the fine particle layers.
[0039]
While taking care not to attenuate the three primary color lights forming an image as much as possible, the visible light absorption contained in each of the reflection layers is made so that the effect of reducing the scattered light by the visible light absorbing substance is maximized. When optimizing a substance, the following should be performed. That is, the reflection layer is formed by stacking the blue light reflection layer, the green light reflection layer, and the red light reflection layer in this order from the light incident side so that scattering is reduced. In addition, the blue light reflecting layer does not contain the visible light absorbing material, the green light reflecting layer transmits green light to red light, and has a shorter wavelength than green light. The visible light absorbing material that absorbs light is contained, and the red light reflecting layer contains the visible light absorbing material that transmits red light and absorbs blue light to yellow light having a shorter wavelength than red light.
[0040]
In such a case, the visible light absorbing substance is not particularly limited, but is preferably a metal fine particle or a pigment that absorbs light of a specific wavelength. For example, the green light reflecting layer preferably contains silver fine particles or a yellow pigment, and the red light reflecting layer preferably contains gold fine particles or a red pigment.
[0041]
On the other hand, in the case where the absorption of the three primary colors by the visible light absorbing material is somewhat tolerated, for example, the blue light reflecting layer may contain the visible light absorbing material that absorbs blue light. However, in order to prevent excessive absorption of the three primary colors, it is necessary to consider that the depth of penetration of the light by the visible light absorbing substance (described in detail later) is larger than the thickness up to the bottom surface of the reflective layer. Is good.
[0042]
In such a case, the visible light absorbing substance is not particularly limited, and other than metal fine particles and pigments, a substance having no property of absorbing only light in a specific wavelength region, such as carbon black, may be used. You can also.
[0043]
Here, when the blue light reflecting layer, the green light reflecting layer, and the red light reflecting layer are stacked in this order in the traveling direction of the incident light (lower in the thickness direction), the light has a short wavelength. It is preferable to use the above visible light absorbing substance having a high absorption coefficient and a low absorption coefficient for long wavelength light.
[0044]
Conversely, when the red light reflecting layer, the green light reflecting layer, and the blue light reflecting layer are sequentially stacked in the traveling direction (lower in the thickness direction) of the incident light, the light has a short wavelength. It is preferable to use the above visible light absorbing substance having a high absorption coefficient and a low absorption coefficient for long wavelength light.
[0045]
Next, a preferred embodiment of the present invention will be specifically described with reference to the drawings.
[0046]
FIG. 1 is an enlarged sectional view of a main part showing the principle of reducing scattered light in a reflection type screen formed of a light reflection type optical medium according to a preferred embodiment of the present invention. In this reflection type screen, a red light reflection layer 2, a green light reflection layer 3, and a blue light reflection layer 4, which are photonic crystal layers, are laminated on a substrate also serving as a visible light absorption layer 1. The reflective layers 2 to 4 reflect three primary color lights projected from a projector or the like to form a full-color image. Since light having a shorter wavelength is more susceptible to scattering, as shown in FIG. 1, in order to reduce the scattered light, the blue light reflecting layer 4, the green light reflecting layer 3, and the red light reflecting layer 2 are arranged in this order from the light incident side. It is desirable that the layers are stacked.
[0047]
Eleven layers of silica fine particles having a particle diameter of 290 nm are laminated as the red light reflecting layer 2, and eleven layers of silica fine particles having a particle diameter of 240 nm are laminated thereon as the green light reflecting layer 3. Silica fine particles having a particle diameter of 210 nm are laminated (the same applies hereinafter; see FIG. 23 for the Bragg reflection wavelength). As the visible light absorbing layer 1, for example, a black base material made of carbon is used.
[0048]
Although not shown, at least one of the photonic crystal layers 2 to 4 and / or at least one of the boundaries between the layers contains a visible light absorbing substance. When external light is incident on the photonic crystal layer, a part of the light is absorbed by the visible light absorbing substance before reaching the defect portion of the photonic crystal layer. Since the amount of light incident on the defect, which is the source of the scattered light, is reduced, the scattered light is reduced. Further, even when external light is scattered due to a defect in the photonic crystal layer, the scattered light is absorbed by the visible light absorbing material, so that scattered light reaching the eyes of the observer is reduced.
[0049]
The material of the visible light absorbing substance is not particularly limited, and any material that can absorb light, such as metal fine particles, pigments, and carbon fine particles, can be used. The following specifically describes which layer of the photonic crystal layers 2 to 4 should contain a visible light absorbing substance having what kind of visible light absorbing property.
[0050]
Embodiment 1
In the present embodiment, each photonic crystal layer is designed so that the three primary colors forming an image are not attenuated as much as possible, and the effect of reducing the scattered light of the visible light absorbing substance is maximized. This is an example in the case where the contained visible light absorbing substance is optimized.
[0051]
That is, since all three primary color lights for forming an image are incident on the blue light reflecting layer 4, it is preferable not to contain a visible light absorbing substance so that the three primary color lights are not absorbed. Of course, if there is a visible light absorbing material that can absorb light in the intermediate wavelength region without absorbing the three primary color lights in the wavelength region reflected by the photonic crystal layers 2 to 4, it is used as the blue light reflecting layer 4. May be contained.
[0052]
Since blue light of the three primary color lights is reflected by the blue light reflection layer 4, the three primary color lights entering the green light reflection layer 3 are green light and red light. As a visible light absorbing substance contained in the green light reflecting layer 3 so as not to absorb these, a substance that transmits green light to red light and absorbs blue light to blue green light having a shorter wavelength than green light is used. Good to use. Of course, if there is a visible light-absorbing substance capable of absorbing light in the intermediate wavelength region without absorbing green light and red light in the wavelength region reflected by the photonic crystal layers 2 and 3, the visible light absorbing material may be used as the green reflection layer 3. May be contained.
[0053]
The three primary color lights entering the red light reflection layer 2 are only red light. As a visible light absorbing substance contained in the red light reflecting layer 2, it is preferable to use a substance that transmits red light and absorbs blue light to yellow light having a shorter wavelength than red light so as not to absorb the light. . Of course, if there is a visible light absorbing substance capable of absorbing the light in the other red light region without absorbing the red light in the wavelength region reflected by the photonic crystal layer 2, the visible light absorbing material is contained in the red light reflecting layer 2. May be.
[0054]
In the present embodiment, fine metal particles are used as the visible light absorbing substance, and surface plasmon absorption of the fine metal particles is used. Since the surface area per unit volume is increased by making the particles fine, the efficiency with which the metal absorbs light increases. In order to increase the surface effect, nano-particles having a diameter on the order of nanometers, preferably 1 to 100 nm in diameter, and particularly preferably 1 to 10 nm in diameter are used as the metal fine particles.
[0055]
FIG. 2 shows an absorption spectrum of fine particles of gold, silver and copper as an example of surface plasmon absorption of fine metal particles. From FIG. 2, it can be seen that the absorbance characteristics differ depending on the surface properties of the fine particles.
[0056]
Note that the absorbance in FIG. 2 is defined as follows. Incident light intensity I₀And the logarithm of the ratio (light attenuation ratio) to the transmitted light intensity I (light attenuation ratio) is proportional to the thickness L of the absorbing medium.
I = I₀e^{−α L}                  ... (Equation 3)
When holds, this relationship is called Lambert's law. Here, α is called an absorption coefficient, and αL is called an absorbance or an optical density.
[0057]
FIG. 3 is an enlarged cross-sectional view of a main part of a reflection type screen in which metal fine particles are put in a gap between the fine particles of the photonic crystal layer. As described above, the blue light reflecting layer 4 does not contain a visible light absorbing substance, and the green light reflecting layer 3 contains the silver fine particles 11 that absorb blue light to blue green light (light having a wavelength of 400 to 500 nm). The red light reflecting layer 2 has a structure in which gold fine particles 12 that absorb blue light to orange light (light having a wavelength of 400 to 600 nm) are contained.
[0058]
By making the structure of the light reflection type optical medium as described above, a reflection type screen which is excellent in color reproducibility with little deterioration of contrast due to external light can be constituted as in the prior application. Moreover, the effect of reducing the scattered light by the visible light absorbing substance including the silver fine particles 11 and the gold fine particles 12 can be maximized without impairing the three primary color lights for forming an image as much as possible. As a result, even if there is a defect in the photonic crystal layers 2 to 4, it is possible to configure a reflective screen that is less likely to cause a deterioration in image quality due to scattering of external light.
[0059]
In this embodiment, the case where metal fine particles are contained in the gap between the fine particles constituting the photonic crystal layers 2 to 4 has been described. However, the same effect can be obtained even if the metal fine particles are contained in the fine particles themselves. can get. Also, the photonic crystal layers 2 to 4 do not necessarily need to contain metal fine particles, and a layer containing metal fine particles may be provided at the boundary between the photonic crystal layers. Good.
[0060]
Embodiment 2
In the present embodiment, as in the first embodiment, the three primary colors forming the image are considered so as not to be attenuated as much as possible, and the effect of reducing the scattered light of the visible light absorbing substance is maximized. This is an example of optimizing the visible light absorbing substance contained in each photonic crystal layer.
[0061]
The only difference from the first embodiment is that a pigment is used as a visible light absorbing substance. FIG. 4A is a transmission spectrum of the yellow pigment 13 which mainly absorbs blue light to blue green light and transmits green light to red light, and FIG. 4B shows absorption spectrum of blue light to yellow light. 3 is a transmission spectrum of a red pigment 14 transmitting red light.
[0062]
FIG. 5 is an enlarged cross-sectional view of a main part of a reflective screen in which a pigment is filled in the gap between the fine particles of the photonic crystal layer. As described above, the blue light reflecting layer 4 does not contain a visible light absorbing substance, and the green light reflecting layer 3 contains the yellow pigment 13 that absorbs blue light to blue green light (light having a wavelength of 400 to 500 nm). The red light reflective layer 2 has a structure in which a red pigment 14 that absorbs blue light to yellow light (light having a wavelength of 400 to 600 nm) or a pigment that absorbs only green light is included.
[0063]
By making the structure of the light reflection type optical medium as described above, a reflection type screen which is excellent in color reproducibility with little deterioration of contrast due to external light can be constituted as in the prior application. In addition, the effect of reducing the scattered light by the visible light absorbing substance including the yellow pigment 13 and the red pigment 14 can be maximized without impairing the three primary colors forming the image as much as possible. As a result, even if there is a defect in the photonic crystal layers 2 to 4, it is possible to configure a reflective screen that is less likely to cause a deterioration in image quality due to scattering of external light.
[0064]
In the present embodiment, the case where the pigment is contained in the gap between the fine particles constituting the photonic crystal layers 2 to 4 has been described, but the same effect can be obtained even if the pigment is contained in the fine particles themselves. . Further, the pigment does not necessarily have to be contained in the photonic crystal layers 2 to 4. As described later, a layer containing the pigment is provided at the boundary between the photonic crystal layers. It may be provided.
[0065]
Embodiment 3
The first and second embodiments have a structure in which the three primary colors forming an image are not attenuated as much as possible. For example, the blue light reflective layer has no visible light absorbing material that absorbs blue light, the green light reflective layer has no visible light absorbing material that absorbs green light, and the red light reflective layer has no visible light absorbing material. There is no visible light absorbing substance.
[0066]
However, in the case where the absorption of the three primary colors by the visible light absorbing substance is somewhat tolerated, for example, the blue light reflecting layer may contain a visible light absorbing substance that absorbs blue light. Hereinafter, such a case will be described.
[0067]
As described above, the intensity of the incident light is I₀  If the intensity of light passing through is I, the absorption coefficient of the light absorbing medium is α, and the thickness of the light absorbing medium is L, Lambert's law
I = I₀e^{−α L}                  ... (Equation 3)
Holds. In the present specification, the thickness of the light absorbing medium in which light attenuates to 1 / e is called the light penetration depth, and the symbol L_{1 / e}  Will be shown. In (Equation 3)
I / I₀  = 1 / e
In other words, the absorption coefficient α and the light penetration depth L_{1 / e}  Between
αL_{1 / e}  = 1 (Equation 4)
And L_{1 / e}  Is inversely proportional to α. α is larger as the light absorbing substance is more likely to absorb light of that wavelength, and is larger as the concentration of the light absorbing substance in the light absorbing medium is higher.
[0068]
Here, as a simplest example, consider a case where a visible light absorbing material that absorbs light of three primary colors is contained in the entire photonic crystal layer at a uniform concentration. Even in such a case, by appropriately selecting the visible light absorbing substance and its concentration, as shown in FIG. 6A or 6B, the penetration depth of each of the three primary color lights can be reduced by three times from the surface. If the primary color light can be made sufficiently large compared to the thickness of the bottom surface of the reflective layer, the visible light absorbing substance can effectively exert the action of reducing the scattered light without impairing the three primary color lights. it can. However, FIG. 6A shows a case where the photonic layer is laminated in the order of the blue light reflecting layer 4, the green light reflecting layer 3, and the red light reflecting layer 2 from the light incident side, and FIG. Conversely, this corresponds to the case where the red light reflecting layer 2, the green light reflecting layer 3, and the blue light reflecting layer 4 are stacked in this order from the light incident side.
[0069]
For example, in FIG. 6A, the penetration depth of the blue light is sufficiently larger than the thickness of the blue light reflection layer 4. Therefore, the blue light is reflected by the blue light reflecting layer 4 before being attenuated by the absorption by the visible light absorbing substance, so that the loss of the blue light by the visible light absorbing substance is small. Similarly, the penetration depth of the green light is sufficiently larger than the thickness up to the bottom surface of the green light reflecting layer 3, so that the green light is absorbed by the visible light absorbing substance before being attenuated by the green light reflecting layer 3. , And is reflected, so that the loss of green light by the visible light absorbing substance is small. Similarly, since the penetration depth of the red light is sufficiently larger than the thickness up to the bottom surface of the red light reflecting layer 2, the red light is absorbed by the visible light absorbing substance before being attenuated by the red light reflecting layer 2. , And is reflected, so that the loss of red light by the visible light absorbing substance is small. The same applies to the case of FIG.
[0070]
In principle, the visible light absorbing substance may be any material that absorbs light, for example, carbon black, metal fine particles, pigments, or a mixture thereof. It is not necessary that the material be a visible light absorbing material that absorbs only light in a specific wavelength range.
[0071]
However, in the case of FIG. 6A, since the thickness from the surface to the bottom surface of the reflective layer becomes larger in the order of the blue light reflective layer 4, the green light reflective layer 3, and the red light reflective layer 2, light having a longer wavelength enters. It is desirable to increase the depth. That is, as shown in FIG. 7A, it is preferable to use the visible light absorbing material having a high absorption coefficient for short wavelength light and a low absorption coefficient for long wavelength light. desirable. Conversely, in the case of FIG. 6B, since the thickness from the surface to the bottom surface of the reflective layer increases in the order of the red light reflective layer 2, the green light reflective layer 3, and the blue light reflective layer 4, light with shorter wavelengths It is desirable to make the penetration depth large, and as shown in FIG. 7B, the absorption coefficient has a low absorption coefficient for short-wavelength light and a high absorption coefficient for long-wavelength light. It is desirable to use the visible light absorbing substance having the following.
[0072]
By making the structure of the light reflection type optical medium as described above, a reflection type screen which is excellent in color reproducibility with little deterioration of contrast due to external light can be constituted as in the prior application. Moreover, by reflecting each of the three primary colors forming an image in a region having a thickness smaller than the penetration depth, the effect of reducing the scattered light by the visible light absorbing material can be effectively reduced while minimizing attenuation of the three primary colors. Can be demonstrated. As a result, even if there is a defect in the photonic crystal layers 2 to 4, it is possible to configure a reflective screen that is less likely to cause a deterioration in image quality due to scattering of external light.
[0073]
As described above, as the simplest example, the case where the visible light absorbing material that absorbs the three primary colors is contained in the photonic crystal layer at a uniform concentration has been described. Alternatively, a visible light absorbing substance may be added only to a part of the photonic crystal layer. Further, the visible light absorbing substance may be put in the gap between the fine particles constituting the photonic crystal, or may be previously contained in the fine particles.
[0074]
Embodiment 4
In the first to third embodiments, the case where the visible light absorbing substance is contained in the photonic crystal layers 2 to 4 has been described, but it is not always necessary to contain the visible light absorbing substance in the photonic crystal. In this embodiment mode, a layer containing a visible light absorbing substance is provided at a boundary portion between the photonic crystal layers.
[0075]
FIG. 8 shows that a yellow pigment that absorbs blue light to blue-green light (light having a wavelength of 400 to 500 nm) is applied to a polymer film at the boundary between the blue light reflecting layer 4 and the green light reflecting layer 3 of the photonic crystal layer. The yellow filter layer 15 was attached, and a red pigment that absorbs blue light to yellow light (light having a wavelength of 400 to 600 nm) was attached to the boundary between the green light reflecting layer 3 and the red light reflecting layer 2. This is a structure provided with a red filter layer 16 attached to a polymer film.
[0076]
In this case, the blue light of the three primary color lights is reflected by the blue light reflecting layer 4 and is not affected by the filter layers 15 and 16. The green light passes through the yellow filter layer 15 before and after being reflected by the green light reflection layer 3, but the yellow filter layer 15 absorbs blue light to blue-green light. It is not absorbed by the filter layer 15. Similarly, the red light passes through the yellow filter layer 15 and the red filter layer 16 before and after being reflected by the red light reflection layer 2, but the yellow filter layer 15 and the red filter layer 16 absorb the red light. Since the light is blue light to yellow light, red light is not absorbed by the filter layers 15 and 16. On the other hand, external light and scattered light are effectively absorbed by the yellow filter layer 15 and the red filter layer 16.
[0077]
Of the above filter layers, the use of only the yellow filter layer 15 is effective, and the use of only the red filter layer 16 is effective. In the case where external light can be sufficiently absorbed by the yellow filter layer 15 and the red filter layer 16, the visible light absorbing layer 1 can be omitted. Therefore, as a modified example of the structure of FIG. 8, the same effect can be obtained by replacing the red light reflecting layer 2 with a reflecting material 19 having no special reflection wavelength characteristic, for example, a metal film such as aluminum. Obtainable.
[0078]
Accordingly, by making the structure of the light reflection type optical medium as shown in FIG. 8 or FIG. 9, a reflection type screen having a small deterioration of contrast due to external light and excellent color reproducibility is formed as in the prior application. it can. Moreover, the effect of reducing the scattered light by the visible light absorbing substance composed of the yellow pigment or the red pigment can be maximized without impairing the three primary color lights for forming an image as much as possible. As a result, even if there is a defect in the photonic crystal layers 2 to 4, it is possible to configure a reflective screen that is less likely to cause a deterioration in image quality due to scattering of external light.
[0079]
Here, a pigment was used as the visible light absorbing substance, but any metal fine particles or any other substance capable of absorbing visible light can be used. This structure has an advantage that a visible light absorbing substance which is difficult to be contained in the gap between the fine particles or in the fine particles, such as a vapor-deposited film, can be used.
[0080]
Next, a process of manufacturing the reflection type screen of FIG. 8 using the transfer of the photonic crystal layers 2 to 4 will be described below with reference to FIGS.
[0081]
First, as shown in FIG. 10A, silica fine particles are deposited on a substrate 41 by a pulling-up method from a dispersion liquid in which silica fine particles are dispersed in water, and a photonic crystal layer 2 for Bragg reflection of red light is formed. Form. The substrate 41 may be anything as long as the silica fine particle dispersion is wet. For example, a polyethylene terephthalate (PET) film subjected to sand matting may be used, or a glass substrate may be used. Similarly, a photonic crystal layer 3 that reflects green light and a photonic crystal layer 4 that reflects blue light are separately manufactured.
[0082]
Next, after the transparent pressure-sensitive adhesive sheet 17 having the pressure-sensitive adhesive on both sides thereof is pressed on the photonic crystal layer 2 (FIG. 10B), the pressure-sensitive adhesive sheet 17 is separated from the substrate 41 by separating the pressure-sensitive adhesive sheet 17 from the substrate 41. Is transferred to the photonic crystal layer 2 (FIG. 10C). At this time, since the other surface of the adhesive sheet 17 has the protective film 18 stuck thereon, the other surface of the adhesive sheet 17 does not adhere to anything else.
[0083]
Next, as shown in FIG. 10D, the protective film 18 is peeled off, and the red filter 16 is bonded to the adhesive surface of the adhesive sheet 17 thereon. Similarly, although not shown, the photonic crystal layer 3 that reflects green light is also transferred to the adhesive sheet, and then the yellow filter 15 is attached to the adhesive surface. After transferring the photonic crystal layer 4 that reflects blue light to the adhesive sheet, the light diffusion film 22 is attached to the adhesive surface.
[0084]
Next, as shown in FIG. 11E, a transparent pressure-sensitive adhesive sheet 17 having a pressure-sensitive adhesive on both sides is also bonded to the surface on the opposite side of the photonic crystal layer 2. Similarly, although not shown, the double-sided pressure-sensitive adhesive sheet 17 is also bonded to the surface on the opposite side of the photonic crystal layers 3 and 4.
[0085]
Next, after removing the protective film 18 remaining on the photonic crystal layers 2 to 4, as shown in FIG. 11F, the visible light absorbing layer 1 also serving as a substrate such as a black PET film and the photonic crystal layer A member composed of the layer 2 and the red filter 16, a member composed of the photonic crystal layer 3 and the yellow filter 15, and a member composed of the photonic crystal layer 4 and the light diffusion film 22 are bonded and integrated. Then, the reflection type screen shown in FIG. 8 is completed.
[0086]
As described above, in the reflective screen according to the embodiment of the present invention, even when external light unrelated to the image enters the screen, the contrast of the image does not deteriorate, and the black Can provide a perfect image. Further, it is not always necessary to perform the projection in a dark room, and the contrast does not deteriorate under a normal fluorescent lamp or outdoors. In particular, by reducing the scattering of light due to defects in the photonic crystal, the effect of black sinking becomes greater.
[0087]
Further, when an image is formed by projecting light having a small half-value width and high color purity, such as a laser or an LED (Light Emitting Diode), only light of an image is efficiently and selectively reflected to emit light of another wavelength. By cutting, the black will sink well while maintaining high contrast. In addition, even when light such as a liquid crystal projector having a large spectral half width of each of the three primary colors is projected, the color reproducibility on the chromaticity diagram is improved, and pure colors can be expressed.
[0088]
【Example】
Next, preferred embodiments of the present invention will be specifically described with reference to the drawings.
[0089]
Example 1： When metal fine particles are used as a visible light absorbing substance
First, after verifying the effect of reducing the scattered light by the fine gold and silver particles, a reflective screen having the structure shown in Embodiment 1 (see FIG. 3) was manufactured.
[0090]
The gold fine particle dispersion was prepared by dispersing 7 mg of gold fine particles having a diameter of about 7 nm in 3.4 g of toluene. FIG. 12A is a transmission spectrum of the gold fine particle dispersion. The spectrum was measured using a spectrometry cell 30 in which a U-shaped spacer 32 was sandwiched between two glass plates 31 (see FIG. 12B). At this time, the measurement was carried out for two cases in which the thickness of the dispersion liquid was changed to 35 μm by changing the thickness of the spacer 32, and in the case where the thickness was increased to increase the absorbance. It can be seen that the transmittance is low on the short wavelength side of 630 nm or less due to plasmon absorption of the gold fine particles.
[0091]
From a dispersion in which silica fine particles having a diameter of 290 nm were dispersed in water, a photonic crystal layer of silica fine particles was formed on a PET substrate by a lifting method. The fine particle layer performs Bragg reflection of red light having a wavelength of 640 nm. The gold fine particle dispersion prepared above was applied to the fine particle layer three times by a pulling-up method to prepare a sample screen. FIG. 13 shows the results of measuring the reflection spectra of the sample screen at several points where the gold fine particle dispersion was applied and where it was not applied. In this case, in consideration of the bias in the thickness of the photonic crystal layer (thickness distribution in the plane), the portions where the dispersion liquid is applied and the portions where the dispersion liquid is not applied are measured at portions having substantially the same thickness as each other. did.
[0092]
Referring to FIG. 13 (a), the Bragg reflection intensity around the wavelength of 640 nm varies considerably at each measurement point, but is significant when the gold fine particle dispersion is applied (solid line) and not (dotted line). No difference is seen. This is presumably because the gold fine particles transmitted red light and did not affect light near the wavelength of 640 nm.
[0093]
On the other hand, in the wavelength region of 400 to 550 nm where scattered light is dominant, the scattered light intensity is small when the gold fine particle dispersion is applied. FIG. 13B is an enlarged view of the spectrum in the wavelength region. It can be seen that there is considerable variation between measurement points, but there is a significant difference between when the gold fine particle dispersion is applied (solid line) and when it is not applied (dotted line). For example, from the scattering intensity at a wavelength of 460 nm, it was found that the luminance level of black on the coated sample screen was suppressed to about 50% as compared with that without coating. This means that the scattered light was absorbed by the fine gold particles, and the black became deeper.
[0094]
Next, similarly to the red light reflecting layer, a green light reflecting layer was formed using silica fine particles having a diameter of 240 nm, and the fine particle layer contained silver fine particles having a diameter of about 5 nm. Also in this case, similarly, it was confirmed that the Bragg reflection of the green light was hardly affected, and the scattered light intensity was reduced.
[0095]
Based on the above results, a reflective screen shown in FIG. 14 was produced. However, as in the first embodiment shown in FIG. 3, the red light reflecting layer 2 contains gold fine particles 12, and the green light reflecting layer 3 contains silver fine particles 11. The fabrication method is as follows.
[0096]
First, a dispersion liquid in which fine silica particles having a diameter of 290 nm were dispersed in water was applied on a black PET film 21 subjected to sand mat processing by a pull-up coating method and dried. By repeating this operation, a photonic crystal layer 2 that reflects red light was deposited to a thickness of about 3 μm. Subsequently, a dispersion obtained by dispersing 7 mg of gold fine particles in 3.4 g of toluene was applied thereon by a pull-up coating method, and then dried. Gold fine particles 12 were placed in the gap between the silica fine particles of the red light reflecting layer 2 and the silica fine particles. Contained.
[0097]
Next, a dispersion obtained by dispersing silica fine particles having a diameter of 240 nm in water was applied on the red light reflection layer 2 by a pull-up coating method, and dried. This operation was repeated, and a photonic crystal layer 3 reflecting green light was deposited to a thickness of about 3 μm. Subsequently, a dispersion liquid in which silver fine particles were dispersed in toluene was applied thereon, followed by drying, and silver fine particles 11 were contained in the gap between the silica fine particles in the green light reflecting layer.
[0098]
Further, a silica fine particle dispersion having a diameter of 210 nm was applied in the same manner to form a blue light reflecting layer having a thickness of about 3 μm. Finally, the light diffusion film 22 was stuck on the uppermost surface.
[0099]
In the reflective screen manufactured in this way, black was sunk even in a bright place due to external light, and it was confirmed that the contrast was high.
[0100]
Example 2: When a pigment is used as a visible light absorbing substance
First, after verifying the effect of reducing the scattered light by the red pigment and the yellow pigment, a reflective screen having the structure shown in Embodiment 2 (see FIG. 5) was manufactured.
[0101]
In the same manner as in Example 1, a red pigment (Dainichi Seimitsu) was formed on a photonic crystal layer formed on a PET substrate by a pull-up coating method of silica fine particle dispersion liquid and formed of silica fine particles having a diameter of 290 nm and reflecting 640 nm wavelength red light. A dispersion obtained by dispersing 0.04 g of Chromofine Red 6150EC in 1.8 g of ethanol was applied three times by a pull-up coating method to prepare a sample screen. The diameter of the pigment fine particles is several tens to 100 nm. FIG. 15 shows the results of measuring the reflection spectra of the sample screen at several points where the dispersion of the red pigment was and was not applied.
[0102]
Referring to FIG. 15A, the intensity of Bragg reflection near the wavelength of 640 nm varies considerably at each measurement point, but is significant when the gold fine particle dispersion is applied (solid line) and not (dotted line). No difference is seen. This is presumably because the red pigment transmits red light and did not affect light near the wavelength of 640 nm.
[0103]
On the other hand, in the wavelength region of 400 to 550 nm where scattered light is dominant, the scattered light intensity is small when the red pigment dispersion is applied. FIG. 15B is an enlarged view of the spectrum in the wavelength region. It can be seen that there is considerable variation between the measurement points, but there is a significant difference between when the red pigment dispersion was applied (solid line) and when it was not applied (dotted line). For example, from the scattering intensity at a wavelength of 460 nm, it was found that the luminance level of black on the sample screen when coated was suppressed to about 56% as compared with that without coating. This means that the scattered light was absorbed by the red pigment and the black became deeper.
[0104]
FIG. 16 is an external appearance photograph taken from the oblique direction by irradiating the sample screen with light from the front (this is a condition under which Bragg reflection does not occur). In the lower part where the red pigment dispersion was applied, it can be seen that the scattered light was reduced and the black was deepened.
[0105]
Next, a green light reflecting layer is formed using silica fine particles having a diameter of 240 nm in the same manner as the red light reflecting layer, and a yellow pigment (Dainichi Seika Co., Ltd., ECY-297 (PY-138)) is formed on the fine particle layer. Was contained. The diameter of the pigment fine particles is several tens to 100 nm. Also in this case, similarly, it was confirmed that the Bragg reflection of the green light was hardly affected, and the scattered light intensity was reduced.
[0106]
Based on the above results, a reflective screen shown in FIG. 14 was produced. However, similar to the second embodiment shown in FIG. 5, the red light reflecting layer 2 contains a red pigment 14 and the green light reflecting layer 3 contains a yellow pigment 13. The fabrication method is as follows.
[0107]
First, a dispersion liquid in which silica fine particles having a diameter of 290 nm were dispersed in water was applied on a sand matted black PET film 21 by a pull-up coating method and dried. By repeating this operation, a photonic crystal layer 2 that reflects red light was deposited to a thickness of about 3 μm. A dispersion obtained by dispersing 0.04 g of a red pigment in 1.8 g of ethanol was applied thereon by a pull-up coating method, and then dried. The red pigment 14 was placed in a gap between the silica fine particles of the red light reflecting layer 2 and the silica fine particles. Was put.
[0108]
Next, a dispersion obtained by dispersing silica fine particles having a diameter of 240 nm in water was applied on the red light reflection layer 2 by a pull-up coating method, and dried. By repeating this operation, a photonic crystal layer 3 reflecting green light was deposited to a thickness of about 3 μm. Subsequently, a dispersion liquid in which a yellow pigment was dispersed in ethanol was applied thereon, followed by drying, and the yellow pigment 13 was put in a gap between the silica fine particles in the green light reflection layer.
[0109]
Further, a silica fine particle dispersion having a diameter of 210 nm was applied in the same manner to form a blue light reflecting layer having a thickness of about 3 μm. Finally, the light diffusion film 22 was stuck on the uppermost surface. In the reflective screen thus produced, it was confirmed that black sank even in a bright place due to external light, and that the contrast was high.
[0110]
Example 3: When carbon black is used as a visible light absorbing substance
First, after verifying the effect of reducing scattered light by carbon black, a reflective screen having the structure described in Embodiment 3 was manufactured.
[0111]
First, in order to estimate the absorption coefficient of carbon black, the transmission spectrum of a dispersion in which carbon black was dispersed in water at a concentration of 0.2% by mass was measured (see FIG. 17A). The diameter of the carbon black fine particles is about 20 nm. The spectrum was measured using a spectrometry cell 30 in which a U-shaped spacer 32 was sandwiched between two glass substrates 31 and the thickness of the dispersion (gap between the glass substrates) was 35 μm (see FIG. 17B). ). The dispersion was placed in the cell 30 using capillary action. For comparison with this sample sample, the transmission spectrum of an empty sample containing no carbon black was also measured. It can be seen that the transmittance differs depending on the presence or absence of carbon black, and this difference is considered to correspond to the absorption by carbon black.
[0112]
So Lambert's law
I = I₀e^{−α L}                  ... (Equation 3)
Is used to determine the wavelength dependence of the absorption coefficient α,
αL_{1 / e}  = 1 (Equation 4)
Was used to estimate the penetration depth when the visible light absorbing substance was carbon black. FIG. 18 shows the absorption coefficient α, and FIG. 19 shows the estimated penetration depth. Thus, the absorption coefficient α is large for short-wavelength light and small for long-wavelength light. Conversely, when the visible light absorbing substance is carbon black, the penetration depth is small for short-wavelength light. On the other hand, it can be seen that the length is shorter for light of a long wavelength.
[0113]
Utilizing these characteristics, it is desired that carbon black be uniformly contained in the red light reflecting layer, the green light reflecting layer, and the blue light reflecting layer, and that the scattered light from each of the layers be absorbed as efficiently as possible. However, it is necessary not to absorb the three primary colors so that the image is damaged. As described with reference to FIG. 6 in the third embodiment, a design may be made such that the penetration depth of absorption by carbon black is larger than the thickness from the surface to the bottom surface of the layer where Bragg reflection occurs. Based on the above, a sample having the basic structure of the reflective screen was manufactured.
[0114]
First, in the same manner as in Examples 1 and 2, a red light reflecting layer 2 composed of silica fine particles having a diameter of 290 nm and silica fine particles having a diameter of 240 nm were formed on a black PET film 21 subjected to sand matting by pulling-up application of a silica fine particle dispersion. A green light reflecting layer 3 made of and a blue light reflecting layer 4 made of silica fine particles having a diameter of 210 nm were laminated to form a sample substrate for producing a sample screen.
[0115]
A dispersion in which carbon black is dispersed in water at a concentration of 0.75% by mass and a dispersion in which carbon black is dispersed at a concentration of 5% by mass are prepared. Then, a sample substrate in which a photonic crystal layer was laminated in the order of the green light reflecting layer 3 and the blue light reflecting layer 4 was immersed for a day and a night without immersion, and their surfaces were observed with an optical microscope. The results are shown in FIG. It can be seen that the surface of the sample screen containing carbon black is sinking black. The goal is to reduce the luminance of black by half.
[0116]
By adding carbon black, the black sinks further, but it is meaningless if the three primary colors are absorbed and the Bragg reflection of the image itself is reduced. Then, the reflection spectrum of each sample screen was measured. The results are shown in FIG. It can be seen that the one immersed in the dispersion having a concentration of 5% by mass has reduced reflectance of the three primary colors. Further, it can be seen that the one immersed in the dispersion having a concentration of 0.75% by mass hardly reduces the reflection intensity of the three primary color lights as compared with the one not containing carbon black. Thus, it can be said that the treatment of dipping in a dispersion having a concentration of 5% by mass or less may be performed.
[0117]
The above-described embodiments and examples can be appropriately modified based on the technical idea of the present invention.
[0118]
Operation and Effect of the Invention
Since the light reflection type optical medium according to the present invention includes the reflection layer that reflects light in a single visible light region or a plurality of visible light regions, it functions as a filter that selects only visible light in a specific wavelength region. Is included in the light reflection type optical medium itself.
[0119]
Therefore, for example, a reflective screen is configured using a light reflective optical medium, and an image is projected by projecting light in a single visible light region or a plurality of visible light regions reflected by the light reflective optical medium from a projector or the like. If the display system to be formed is made, the image is displayed correctly, but most of the external light irrelevant to the image, which is incident on the screen other than from the projector or the like, is filtered out. As a result, it is possible to construct a display system in which the contrast is not deteriorated by external light, and it is possible to display a dark part of an image as a true dark part on a screen. Also, screen display can be performed outside a dark room, such as in a room with lighting or outdoors.
[0120]
In addition, since the light reflection type optical medium contains a visible light absorbing substance in at least one of the inside of the reflection layer, the upper part in the thickness direction, and the lower part in the thickness direction, external light is transmitted to the light reflection type optical medium. Even if the light enters, a part of the light is absorbed by the visible light absorbing material before reaching the defective portion of the reflective layer. Since the amount of light incident on the defect, which is the source of the scattered light, is reduced, the scattered light is reduced. Further, even when external light is scattered by the defective portion of the reflective layer, the scattered light is absorbed by the visible light absorbing substance, and thus the scattered light reaching the observer's eyes is reduced. As a result, in the light reflection type optical medium, even if the reflection layer has a defect, the defect rarely causes deterioration in image quality due to scattering of external light.
[Brief description of the drawings]
FIG. 1 is an enlarged cross-sectional view of a principal part showing a principle of reducing scattered light in a reflection type screen formed of a light reflection type optical medium according to a preferred embodiment of the present invention.
FIG. 2 is an absorption spectrum based on surface plasmon absorption of fine particles of gold, silver, and copper based on Embodiment 1 of the present invention.
FIG. 3 is an enlarged sectional view of a main part of the reflective screen.
FIG. 4 is a transmission spectrum of a pigment according to Embodiment 2 of the present invention.
FIG. 5 is an enlarged sectional view of a main part of the reflection screen.
FIG. 6 is a schematic cross-sectional view showing a relationship between a stacking order of three primary color light reflecting layers and a preferred penetration depth according to a third embodiment of the present invention.
FIG. 7 is a schematic cross-sectional view showing the relationship between the stacking order of the three primary color light reflecting layers and the preferable wavelength characteristic of the absorption coefficient of the visible light absorbing substance.
FIG. 8 is an enlarged sectional view of a main part of a reflective screen according to a fourth embodiment of the present invention.
FIG. 9 is an enlarged cross-sectional view of a main part of another reflective screen based on Embodiment 4 of the present invention.
FIG. 10 is an enlarged cross-sectional view of a main part showing a manufacturing step of the reflective screen.
FIG. 11 is an enlarged cross-sectional view of a main part showing a manufacturing process of the reflective screen.
FIG. 12 is a transmission spectrum of a gold fine particle dispersion according to Example 1 of the present invention.
FIG. 13 is a reflection spectrum of the same sample screen.
FIG. 14 is an enlarged sectional view of a main part of the practical reflective screen.
FIG. 15 is a reflection spectrum by the sample screen of Example 2 of the present invention.
FIG. 16 is an external photograph of a sample screen of Example 2 of the present invention.
FIG. 17 is a transmission spectrum of a carbon black dispersion according to Example 3 of the present invention.
FIG. 18 is a graph showing the wavelength dependence of the absorption coefficient of the carbon black dispersion.
FIG. 19 is a graph showing the wavelength dependence of the penetration depth of the carbon black dispersion.
FIG. 20 is an image observed by an optical microscope on the surface of a sample screen according to Example 3 of the present invention.
FIG. 21 is a reflection spectrum by the sample screen of Example 3 of the present invention.
FIG. 22 is a schematic sectional view (b) showing a reflection spectrum (a) and an arrangement structure of fine particles of an aggregate of silica fine particles formed by a pull-up rotation method according to a preferred embodiment of the prior application;
FIG. 23 is a graph showing the relationship between the wavelength of light Bragg reflected by the aggregated silica particles and the diameter of the silica particles.
FIG. 24 is an enlarged sectional view of a main part of the basic structure of a reflective screen that reflects only the three primary color lights.
FIG. 25 is a chromaticity diagram showing that the color reproduction range is improved by the reflective screen that reflects only the three primary color lights.
FIG. 26 is an enlarged cross-sectional view of a main part showing the cause of the generation of scattered light in the reflective screen that reflects only the three primary color lights.
[Explanation of symbols]
1. visible light absorbing layer (substrate), 2. fine particle layer that reflects red light,
3 ... a fine particle layer that reflects green light, 4 ... a fine particle layer that reflects blue light,
5 defects (part), 6 scattered light, 11 silver fine particles, 12 gold fine particles,
13: yellow pigment, 14: red pigment, 15: yellow filter layer,
16: red filter layer, 17: double-sided adhesive sheet, 18: protective film,
19 ... reflecting material such as aluminum,
21: black PET film subjected to sand mat processing, 22: light diffusion film,
Reference numeral 30: spectrometry cell, 31: glass plate, 32: spacer, 41: substrate,
51: substrate, 52: silica fine particles, 53: silica fine particle layer

Claims (24)

A reflection layer that reflects light in a single visible light region or a plurality of visible light regions is provided, and a visible light absorbing material is contained in at least one of the inside of the reflection layer, the upper part in the thickness direction, and the lower part in the thickness direction. Light-reflective optical media. The light reflection type optical medium according to claim 1, wherein the reflection layer is formed by a fine particle layer made of fine particles having a particle diameter, a material, or a shape corresponding to a wavelength of visible light to be reflected. 3. The light-reflective optical medium according to claim 2, wherein the fine particles are regularly arranged by self-organization or close-packing. The light reflection type optical medium according to claim 2, wherein the fine particles are stacked in multiple stages in the thickness direction in the fine particle layer. The optical medium according to claim 2, wherein the fine particles are silica fine particles or fine particles of a material having the same refractive index as silica. 3. The light-reflective optical medium according to claim 2, wherein the visible light-absorbing substance is placed in a gap between the fine particles. 3. The light-reflective optical medium according to claim 2, wherein the visible light absorbing substance is contained in the fine particles. The light reflection type optical medium according to claim 1, wherein a visible light absorbing layer that absorbs visible light is provided at a lowermost portion in a thickness direction of the reflection layer. The light reflection type optical medium according to claim 1, further comprising a layer that diffuses visible light. The light-reflective optical medium according to claim 1, which constitutes a reflective screen used in an image display system that displays an image projected from a projector. 3. The light reflection type optical medium according to claim 1, wherein the reflection layer comprises at least one of three primary color light reflection layers of a red light reflection layer, a green light reflection layer, and a blue light reflection layer. The light reflection type optical medium according to claim 11, wherein the blue light reflection layer, the green light reflection layer, and the red light reflection layer are sequentially stacked in a traveling direction (a lower part in a thickness direction) of the incident light. . Particle diameter or periodic length of fine particles forming the red light reflecting layer, particle diameter or periodic length of fine particles forming the green light reflecting layer, and particle diameter or periodic length of fine particles forming the blue light reflecting layer Are different from each other. 14. The light-reflective optical medium according to claim 13, wherein the particle diameter or the periodic length decreases in the order of the red light reflecting layer, the green light reflecting layer, and the blue light reflecting layer. 2. The light-reflective optical medium according to claim 1, wherein the visible light absorbing substance is metal fine particles. 13. The light-reflective optical medium lean according to claim 12, wherein the red light-reflective layer contains fine gold particles as the visible light absorbing substance. The light reflection type optical medium according to claim 12, wherein the green light reflection layer contains silver fine particles as the visible light absorbing substance. The light-reflective optical medium according to claim 1, wherein the visible light absorbing substance is a pigment. 13. The light reflection type optical medium according to claim 12, wherein the red light reflection layer contains a red pigment as the visible light absorbing substance. The light reflection type optical medium according to claim 12, wherein the green light reflection layer contains a yellow pigment as the visible light absorbing substance. The light reflection type optical medium according to claim 1, wherein a light penetration depth is larger than a thickness up to a bottom surface of the reflection layer. The blue light reflecting layer, the green light reflecting layer, and the red light reflecting layer are sequentially stacked in the traveling direction (lower in the thickness direction) of the incident light. 22. The light reflection type optical medium according to claim 21, wherein the visible light absorbing material having a low absorption coefficient with respect to light having a long wavelength is used. The red light reflecting layer, the green light reflecting layer, and the blue light reflecting layer are stacked in this order toward the traveling direction of the incident light (the lower part in the thickness direction), and have a high absorption coefficient for short wavelength light, 22. The light reflection type optical medium according to claim 21, wherein the visible light absorbing substance having a low absorption coefficient for long wavelength light is used. 22. The light reflective optical medium according to claim 21, wherein the visible light absorbing substance is carbon black.

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