JP2007011213A - Transmission-type screen - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent damages on the microlens surface, caused by the friction between the microlens array and a Fresnel lens and asperity losses on the Fresnel lens and reduce the outside front light reflected for image observation, and to reduce the scintillations (speckles) on a transmission-type screen. <P>SOLUTION: The surface of the microlenses 1 is overcoated with a material 8, having a refractive index higher than the material of the microlenses 1. Alternatively, either the surface of the microlenses 1 or the surface of the Fresnel lens 5 is at least overcoated with a material, having a wear-resistance higher than the material of the microlenses 1 and the Fresnel lens 5. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a transmissive screen that includes a microlens array and a Fresnel lens and is used in, for example, a rear projection display (rear pro display).

  Conventionally, as an image display device (display), there are a direct view type display that directly observes an image displayed in a cell and a projection type display that projects image light onto a screen and observes the screen.

  As a cell used for a direct-view display, a fluorescent film cell used for a CRT display, a liquid crystal cell used for an LCD, a light emitting cell used for a PDP, and the like have been proposed.

  As a projection display, a rear projection display (rear projection display) is proposed in which an image is projected from the rear side of the transmissive screen and the displayed image is observed from the front side of the transmissive screen. ing. Such a rear projection type display can increase the size of the display image at low cost as long as it has a screen capable of displaying a high-definition image.

  As such a transmissive screen for rear projection display, a microlens array formed by closely arranging a large number of minute unit lenses protruding in the shape of a convex lens on the main surface of a transparent substrate is used as a main component. What has been proposed is proposed. A microlens array has a large number of minute unit lenses formed on a transparent substrate by microfabrication technology, and is expected to be applied to optical coupling optical elements and image input / output devices in addition to transmissive screens. ing.

  A microlens array generally used as a transmissive screen for a rear projection display is a lenticular lens array sheet with a light shielding layer. As a method for producing this lenticular lens array sheet, extrusion molding, injection molding, press roll molding using a photocurable resin, or the like is known. The light shielding layer is formed by applying a light shielding material on a predetermined portion of the back surface of the microlens array, and is located in the vicinity of a plane including the focal point of each microlens. This light shielding layer has a light transmission portion (transparent portion) corresponding to the focal position of each microlens, and is configured to block light beams passing through other than this light transmission portion. That is, the light beam incident on the microlens array is collected for each microlens, passes through the light shielding layer, passes through the transparent plate on the front side, and is emitted to the front side of the transmissive screen.

  By the way, a one-dimensional concavo-convex lens array in which curved surfaces (kamaboko-shaped curved surfaces) indicated by trajectories obtained by translating arc-shaped curves are arranged in only one direction, such as lenticular lenses, can be microlensed with a fine lens pitch. Even with such an array sheet, the viewing angle expansion effect can be obtained only in one horizontal or vertical direction.

  For this reason, a microlens array has been developed in which a transparent sphere such as a glass bead sphere is used and a part thereof is buried and spread on a flat resin substrate. When such a microlens array is used, a viewing angle expansion effect can be obtained in the circumferential direction, that is, in both the horizontal and vertical directions.

  However, in this microlens array, each microlens has a spherical shape and a circular cross section, so that the occupation ratio of the area having a lens function with respect to the substrate area cannot be 100%. In other words, even when transparent microspheres having the same diameter are closely packed and arranged, the occupancy ratio of the area having the lens function is 90.7% at the maximum, and between the microlenses and the microlenses. This inevitably results in a flat area having no lens function. When a glass bead sphere is used as a microlens, the upper limit of the filling rate of the peas sphere is usually about 80%, and the remaining 20% does not have a lens function, and optical characteristics, particularly light transmittance. Loss.

  Therefore, as described in Patent Document 1 and Patent Document 2, the microlens has a hexagonal cross section, and the microlenses are arranged in a honeycomb shape, thereby occupying an area having a lens function. A transmissive screen using a microlens array in which is set to 100% of the substrate area has been proposed.

  In a transmissive screen having such a microlens array, a diffused light beam emitted from a light source and intensity-modulated in accordance with a display image has a Fresnel lens 101 having the function of a convex lens as a whole as shown in FIG. After that, a substantially parallel light beam is formed, and enters the microlens array 103 from the main surface side in parallel to the optical axis of each microlens 102, that is, perpendicular to the main surface of the microlens array 103. The Fresnel lens 101 and the microlens array 103 are arranged in contact (contact).

JP 2001-305315 A JP 2002-357869 A

  By the way, in the transmissive screen as described above, the microlens array and the Fresnel lens rub against each other during transportation or use, so that the surface of the microlens is scratched or irregularities in the Fresnel lens are lost. There is a problem that “tooth spilling” occurs and optical characteristics deteriorate.

  In addition, such a transmissive screen has a problem that the contrast of the display image is deteriorated, especially in a place where the ambient light is bright, since there is a lot of reflected light of the external light from the front side where the image is observed.

  Further, in such a transmissive screen, there is a problem that a part of a display image called scintillation or speckle is glaring.

  Therefore, the present invention has been proposed in view of the above-described circumstances, and the damage of the surface of the microlens and the unevenness of the Fresnel lens due to the abrasion between the microlens array and the Fresnel lens are prevented. An object of the present invention is to provide a transmission screen in which reflected light of external light from the front side for observing an image is reduced and scintillation (speckle) is reduced.

  In order to solve the above-described problems and achieve the above object, a transmission screen according to the present invention has any one of the following configurations.

[Configuration 1]
A microlens array formed by closely arranging a number of microlenses that protrude in the shape of a convex lens on the main surface of a transparent substrate, and the microlens array on the side where the microlenses are formed is incident from a light source. And a Fresnel lens that makes the parallel light beam substantially parallel to the main surface of the microlens array, and the surface portion of the microlens is higher than the material forming the microlens. It is characterized by being overcoated with a material having a refractive index.

[Configuration 2]
A microlens array formed by closely arranging a number of microlenses that protrude in the shape of a convex lens on the main surface of a transparent substrate, and the microlens array on the side where the microlenses are formed is incident from a light source. And a Fresnel lens that makes the parallel light beam substantially parallel to the main surface of the microlens array, and on the surface of the microlens and on the side facing the microlens array of the Fresnel lens. At least one of the surface portions is overcoated with a material having higher wear resistance than a material forming the microlens and a material forming the Fresnel lens.

  In the transmissive screen according to the present invention, the surface portion of the microlens is overcoated with a material having a higher refractive index than that of the material forming the microlens. Of this, the amount of light transmitted through the microlens array is reduced, the amount of light that this external light is emitted to the front side again as reflected light is reduced, and the optical path length difference of the transmitted light is reduced between the center and the periphery of the microlens. Increases and reduces scintillation (speckle).

  In the transmissive screen according to the present invention, at least one of the surface portion of the microlens and the surface portion of the Fresnel lens facing the microlens array forms the material for forming the microlens and the Fresnel lens. Since it is overcoated with a material having higher wear resistance than the material, scratches on the surface of the microlens due to abrasion of the microlens array and the Fresnel lens, and irregularities in the Fresnel lens are prevented.

  That is, the present invention prevents damage to the surface of the microlens due to abrasion between the microlens array and the Fresnel lens, and loss of unevenness in the Fresnel lens, and also reflects reflected light from the front side from which the image is observed. And a transmission screen with reduced scintillation (speckle) can be provided.

  Hereinafter, the configuration of the transmission screen according to the present invention will be described in detail.

[Configuration of transmissive screen]
This transmissive screen is used in a rear projection display (rear projection display) or the like, and is configured such that an image is projected from the rear side and the image displayed from the front side is observed. .

  FIG. 1 is a sectional view showing a configuration of a transmission screen according to the present invention.

  As shown in FIG. 1, the transmissive screen includes a microlens array 2 formed by closely arranging a number of microlenses (micro-unit lenses) 1 protruding in a convex lens shape on the main surface portion of a transparent substrate. Have. Each microlens 1 is formed of a transparent material, for example, an ultraviolet curable resin. These microlenses 1 have a hexagonal cross section perpendicular to the optical axis and are arranged in a honeycomb shape. Therefore, in the microlens array 2, the occupation ratio of the area having the lens function is approximately 100% with respect to the area of the main surface portion of the transparent substrate. The microlens array 2 is attached to the back surface of a transparent plate 3 (a resin plate made of acrylic or the like containing a diffusing material) that is a front panel of a transmissive screen with the microlenses 1 facing rearward. Yes.

  In the microlens array 2, a light shielding layer 4 is formed on the surface on the front side between the transparent plate 3. The light shielding layer 4 is located in the vicinity of a plane including the focal point of each microlens 1 and is formed of a light shielding material. The light shielding layer 4 has a light transmission portion (transparent portion) corresponding to the focal position of each microlens 1 and is configured to block a light beam passing through other than the light transmission portion.

  In this transmissive screen, the Fresnel lens 5 is arranged on the rear side of the microlens array 2, that is, on the side where the microlens 1 is formed. The Fresnel lens 5 has a function of making diffused light incident from a light source (not shown) into a substantially parallel light beam and causing the parallel light beam to enter the main surface of the microlens array 2 substantially perpendicularly. The Fresnel lens 5 is made of a transparent material, and has an unevenness (Fresnel lens) that causes a lens function on the main surface portion facing the microlens array 2. The Fresnel lens 5 is arranged in contact (contact) with the microlens array 2.

In this transmissive screen, the surface portion of the microlens 1 is formed by a thin film made of a material having a refractive index higher than the refractive index of the material forming the microlens 1 (1.51 in the case of an ultraviolet curable resin). It is overcoated. Examples of the material having a higher refractive index than the material forming the microlens 1 include DLC (diamond-like carbon). Further, as other materials, as inorganic materials, diamond (refractive index 2.42), SiO ₂ (refractive index 1.55), BeO (refractive index 1.73), Al ₂ O ₃ (refractive index 1.76). ), ZrO ₂ (refractive index 2.20), PbO (refractive index 2.61), TiO ₂ (refractive index 2.71), Al ₂ O ₃ .SiO ₂ (refractive index 1.65), ZrSiO ₄ (refractive index). 1.95), (Pb, La) (Zr, Ti) O ₃ (refractive index 2.5), LiNbO ₃ (refractive index 2.31), BaTiO ₃ (refractive index 2.40), CaF ₂ (refractive) 4.0) and CbS (refractive index 2.62). Furthermore, as a polymer material, polystyrene (refractive index 1.59), styrene acrylonitrile copolymer (refractive index 1.56), polyvinyl chloride (refractive index 1.55), polyethylene (refractive index 1.54), Examples thereof include polycarbonate (refractive index 1.58), polyamide (refractive index 1.53), polychlorostyrene (refractive index 1.61), and polyvinylidene chloride (refractive index 1.63).

  Alternatively, in this transmissive screen, at least one of the surface portion of the microlens 1 and the surface portion of the Fresnel lens 5 on the side facing the microlens array 2 is made of the material for forming the microlens 1 and the Fresnel lens 5. It is preferable to overcoat with a thin film made of a material having higher wear resistance than the material to be formed. Examples of the material having higher wear resistance than the material forming the microlens 1 and the material forming the Fresnel lens 5 include DLC.

  That is, if the surface portion of the microlens 1 is overcoated with a thin film made of DLC, the material has a higher refractive index than the material forming the microlens 1 and higher wear resistance than the material forming the microlens 1. Is most preferable. Note that a material having high wear resistance is a material having high hardness and good solid lubricity.

  However, it is not preferable to overcoat the surface portion of the microlens 1 and the surface portion of the Fresnel lens 5 on the side facing the microlens array 2 with the same material. In this case, there is a possibility that the both surface portions may be damaged by scratching.

  As a material having higher wear resistance than the material forming the microlens 1 and the material forming the Fresnel lens 5, in addition to the diamond material such as DLC, the inorganic material may be a carbon-based graphite material, Examples thereof include a crystalline material, a composite material of carbon fiber and carbon and graphite, and fine ceramic type silicon carbide, silicon nitride, aluminum oxide, zirconium oxide, titanium carbide, titanium oxide, chromium oxide, and the like. Also, solid lubricant-based boron nitride, graphite, molybdenum disulfide, tungsten disulfide, polymer materials containing these, metals, ceramic composites, and the like can be given. As the metal, a hexagonal lattice crystal structure material is preferable to a cubic lattice crystal structure material. Examples of the polymer material include general-purpose phenol resin, nylon 6, nylon 66, and high density polyethylene.

  Furthermore, as a material having a higher refractive index than the material forming the microlens 1 and higher wear resistance than the material forming the microlens 1, in addition to DLC, as an inorganic material, diamond, oxidation, Aluminum, zirconium oxide, titanium oxide and the like can be mentioned, and examples of the polymer material include high-density polyethylene and synthetic polyamide (nylon).

  In the transmissive screen configured in this way, a diffused light beam emitted from a light source (not shown) and intensity-modulated according to a display image is projected from the back side of the transmissive screen, and as shown in FIG. Is converted into a substantially parallel light flux through a Fresnel lens 5 having the function of a convex lens, and parallel to the optical axis of each microlens 1, that is, perpendicular to the main surface of the microlens array 2, from the main surface side. 2 is incident.

  The light beam incident on the microlens array 2 is collected for each microlens 1, passes through the light transmission part (transparent part) of the light shielding layer 4, and forms a transparent base material and a transparent part that forms the front part of the transmission type screen. The light passes through the plate 3 and is emitted to the front side. In this way, in this transmissive screen, a viewing angle expansion effect can be obtained in the circumferential direction, that is, in both the horizontal and vertical directions.

[One Example of Manufacturing Method of Microlens Array]
Hereinafter, an embodiment of a method for producing the microlens array 2 used in the transmission screen according to the present invention will be described.

  FIG. 2 is a cross-sectional view showing each step in the method of manufacturing the microlens array.

  A microlens array 2 manufactured by this manufacturing method has a large number of microlenses 1 on the main surface portion of a base film 6 that is a transparent substrate, as shown in FIG. A light shielding layer 4 having a plurality of light transmission portions 7 having a complementary function corresponding to each microlens 1 is formed on the surface opposite to the surface on which 1 is formed. As described above, the light shielding layer 4 absorbs light other than the light transmitted through the light transmission portion 7. Each microlens 1 is overcoated with a DLC film 8, which is a material having a higher refractive index than the material forming the microlens 1 and higher wear resistance than the material forming the microlens 1. .

(Step 1) Formation of Microlens In (Step 1) shown in FIG. 2A, the microlens 1 is formed on the main surface portion of the base film 6. In order to form the microlens 1, a plate-shaped glass mold (not shown) is used, and this glass mold is filled with an ultraviolet curable resin having a viscosity of 180 mPa · s and a good light transmittance (“TB3087B” manufactured by ThreeBond). did. This glass mold is, for example, arranged in a honeycomb shape so that concave substantially hemispheres (radius of about 25 μm) with a diameter of 50 μm at a pitch of 50 μm are closely packed. This glass mold is prepared in advance by a microplast method and a wet etching method.

  Next, the base film 6 is overlaid on the surface of the ultraviolet curable resin filled in the glass mold, and the ultraviolet curable resin is cured by irradiating with ultraviolet rays. As the base film 6, a PC (polycarbonate) film having a thickness of 30 μm was used. When the ultraviolet curable resin and the base film 6 are bonded and then separated from the glass mold, a large number of substantially hemispherical microlenses 1 are formed on the base film 6 as shown in FIG. An array is formed. The refractive index n ″ after curing of the ultraviolet curable resin used in this example is 1.51.

  In addition, as a method of arranging the microlenses 1 in the closest packing, as described above, there is a method of arranging the substantially hemispherical microlenses having a substantially regular hexagonal bottom surface in a honeycomb shape without gaps. Any arrangement method may be used as long as the microlenses 1 are arranged without gaps.

  The microlens 1 may have any shape as long as it functions as an array of minute unit lenses. The minute unit lens here is a minute unit part having a lens function such as a convex lens, and the area of the microlens array as an array is sufficiently larger than the size of the unit part (unit lens). means. For example, a well-known lenticular lens, a spherical surface including a spheroid, or an aspherical cluster-like microlens (a compound lens in which a lens smaller than the diameter is formed in each microlens) or the like is used. As long as a large number of arrays are formed on the material 6, microlenses having any shape may be used.

  The substance forming the microlens 1 is not particularly limited as long as it is transparent to at least visible light. That is, well-known thermosetting resin, photocurable resin, thermoplastic resin, glass, etc. with high light transmittance are mentioned. A photocurable resin is preferably used. In particular, use of an ultraviolet curable resin is most suitable from the viewpoints of production efficiency, shape accuracy, curability, and ease of equipment.

  In addition, as a method of manufacturing the microlens array, there is also a method of manufacturing by a roll-to-roll method using a cylindrical glass mold instead of a plate shape as a glass mold. Furthermore, not only glass molds but also molds, rubber molds, plastic molds, and the like can be used as long as the cured ultraviolet curable resin can be peeled off from the mold. The manufacturing method of the substantially hemispherical concave shape in the mold is not limited to the microplast method and the wet etching method, and other known methods can be used.

(Step 2) Formation of light transmission part (self-alignment method)
In (Step 2) shown in FIGS. 2B and 2C, complementary functions corresponding to the individual microlenses 1 are provided on the opposite surface side of the microlenses 1 with the transparent substrate 6 interposed therebetween. The light transmission part 7 is formed by a self-alignment method. That is, as shown in FIG. 2B, an ultraviolet curable resin having a viscosity of 160 mPa · s and a good light transmittance is applied to the back side of the transparent substrate 6 on which the microlenses 1 are formed on the main surface portion. To a thickness of about 20 μm. The ultraviolet curable resin in the region along the optical path of the emitted light from the microlens 1 was cured by irradiating substantially parallel ultraviolet rays from the microlens 1 side.

  And the light-transmitting part 7 was formed as shown to (C) in FIG. 2 by removing the uncured part of the ultraviolet curable resin by solvent cleaning.

  In addition, as a substance which forms such a light transmission part 7, if it is transparent at least with respect to visible light, it will not specifically limit. Examples of the substance that forms the light transmitting portion 7 include known thermosetting resins, photocurable resins, thermoplastic resins, and glass having a high light transmittance. A photocurable resin is preferably used. In particular, use of an ultraviolet curable resin is most suitable from the viewpoints of production efficiency, shape accuracy, curability, and ease of equipment.

(Step 3) Formation of light absorbing portion of light shielding layer In (Step 3) shown in (D) in FIG. 2, a light absorbing portion having light absorption is formed in a portion other than the light transmitting portion 7. The light shielding layer 4 is used. That is, a light-absorbing black material is applied by a roll extrusion method to a concave portion (around the light transmitting portion 7) formed by removing the uncured ultraviolet curable resin in (Step 2). And cured to form a light absorbing portion. And the front-end | tip part of the light transmission part 7 used as the emission part of the emitted light from the microlens 1 is grind | polished with the surface of a light absorption part, and the front-end | tip part of these light transmission parts 7 is the light absorption part in the surface of the light shielding layer 4. I tried to face the outside in a flush state.

  The material for forming the light absorbing portion of the light shielding layer 4 is not particularly limited as long as it is a material having light absorptivity and light shielding properties for at least visible light. As a material for forming the light absorption part, for example, a pigment such as carbon black having a light absorption property, titanium black or the like, or a black dye or the like may be dispersed or dissolved in the resin composition.

(Step 4) Overcoat Formation of DLC Film In (Step 4) shown in FIG. 2E, a DLC (diamond-like carbon) film is overcoated on the surface of the microlens 1. That is, as shown in FIG. 2E, a thickness of about 6 nm or more is formed on the surface of the microlens 1 by a well-known CVD method (chemical vapor deposition) using ethylene gas. A 12 nm DLC film 8 was overcoated. The microlens array 2 thus completed is used as a main part of a transmission screen by being attached to a transparent plate 3 as shown in FIG.

  FIG. 3 is a graph showing the relationship between the thickness of the DLC film and the refractive index at that time with respect to the ethylene gas pressure in the CVD method.

  Note that the data shown in FIG. 3 is measured by forming the DLC film 8 on a wafer substrate. The film thickness was calculated by measuring with a “DEKTAK step meter” and the refractive index with an ellipsometer.

  Since the refractive index n ″ of the ultraviolet curable resin (“TB3087B” manufactured by ThreeBond Co., Ltd.) constituting the microlens 1 in the above-described embodiment is 1.51, the formed DLC film 8 is shown in FIG. It can be seen that the refractive index is higher than that of the material forming the microlens 1 under all the conditions. Further, it is well known that the DLC film 8 has extremely high wear resistance (hardness and solid lubrication characteristics) than the ultraviolet curable resin material.

[Contrast of Example of Transmission Type Screen According to the Present Invention and Comparative Example]
As an example of the present invention, various ethylene gas pressures in the CVD method for forming the DLC film 8 on the surface of the microlens were changed, and as shown in [Table 1] below, seven types (in Table 1) Sample No. 1 to Sample No. 7) microlens arrays were prepared. Further, a microlens array not overcoated with the DLC film 8 was produced as a comparative example (sample No. 8 in Table 1).

  In the transmission type screen using the microlens array of each example, the surface of the microlens 1 and the surface of the Fresnel lens 5 are rubbed together, and then the surface of the microlens 1 is damaged (scratched) and the Fresnel lens. The state of damage (tooth spilling) on the lens surface in No. 5 was evaluated using a laser microscope. As the Fresnel lens 5, the same lens was used.

  Moreover, the total light transmittance of the transmission type screen using the microlens array of each Example and Comparative Example was measured in the visible light region in consideration of specific luminous efficiency. The total light transmittance was measured using an integrating sphere photometer manufactured by Murakami Color Research Laboratory.

  Furthermore, in a place with an illuminance of 200 lx, which is about the brightness of a room where a normal fluorescent lamp is lit, the contrast and scintillation of the image projected from the back onto the transmissive screen using the microlens array of each example and comparative example ( The state of speckle was evaluated. Note that scintillation (speckle) is a phenomenon in which a display screen appears to flicker due to interference between light rays projected as an image. The image contrast and scintillation (speckle) state were visually evaluated by projecting an image on a rear projection television (“HD-ILA” produced by the present applicant).

  As shown in [Table 1], the transmissive screen using the microlens array of each of the examples (sample No. 1 to sample No. 7) of the present invention is a transmissive screen using the microlens array of the comparative example (sample No. 8). Compared with, the total light transmittance is slightly reduced, but unlike the comparative example (sample No. 8), no damage on the surface of the microlens 1 and no damage on the Fresnel lens 5 were observed.

  As described above, the surface of the microlens 1 and the Fresnel lens 5 are not damaged in the transmission screen according to the present invention because the DLC film 8 is a material for forming the microlens 1. This is because it has extremely higher wear resistance characteristics (hardness and solid lubrication characteristics).

  Moreover, as shown in [Table 1], the transmission type screen using the microlens array of each example (sample No. 1 to sample No. 7) of the present invention is a transmission using the microlens array of the comparative example (sample No. 8). It was found that a so-called black tightened image with a good contrast feeling was displayed in a place of normal brightness as compared with the mold screen.

  FIG. 4 is a cross-sectional view for explaining the effect of reducing external light reflection by the DLC film in the transmission screen according to the present invention.

  As described above, the reason why the image having a good contrast feeling is displayed on the transmissive screen according to the present invention is considered to be because the reflection of external light is reduced as shown in FIG. In the external light reflection, external light incident on the light transmission part 7 of the light shielding layer 4 from the outside (front of the transmission screen) is transmitted to the rear side of the transmission screen and reflected by a spatial light modulation element or the like on the light source side. Then, the light beam is emitted again to the front side of the transmission screen through the same optical path as the light beam from the light source. Therefore, if the external light transmitted to the rear side of the transmissive screen decreases, the external light reflection is reduced.

  In the transmissive screen according to the present invention, the DLC film 8 overcoated on the surface of the microlens array 1 has a significantly higher refractive index than the material forming the microlens 1, and the material forming the microlens 1. And a high refractive index difference with air. Therefore, the light beam incident on the microlens array 2 is largely refracted at the interface between the air and the DLC film 8 and the interface between the DLC film 8 and the microlens 1, and causes interface reflection and scattering. This is the reason why the total light transmittance of the transmissive screen according to the present invention is slightly lower than that of the comparative transmissive screen. Due to the interface reflection and scattering by the DLC film 8, the external light incident from the front) is less likely to be transmitted behind the transmissive screen than the conventional transmissive screen (comparative example).

That is, as shown in FIG. 4, the refractive index n of air is 1.0, the refractive index n ′ of the DLC film 8 is 2.0, the refractive index n ″ of the microlens 1 is 1.5, Assuming that the lens 1 has a hemispherical shape, an analysis based on Snell's law (n ₁ · sin θ ₁ = n ₂ · sin θ ₂ ) indicates a region less than 28.6 ° with respect to the optical axis of each microlens 1. The external light from the light passes through the microlens 1 and the DLC film 8 and is transmitted to the rear side of the transmission screen. However, the external light from the region of 28.6 ° or more with respect to the optical axis reaches the DLC film 8. When this occurs, the critical angle is formed with respect to the interface between the DLC film 8 and air, and the inner surface is reflected at this interface and does not transmit to the rear side of the transmissive screen. Thus, it is considered that the external light reflected on the inner surface at the interface between the DLC film 8 and air repeats the inner surface reflection and is absorbed by the light shielding layer 4.

  Thus, in the transmissive screen according to the present invention, under the above-described conditions, external light from a region of 28.6 ° or more with respect to the front direction (the optical axis direction of each microlens 1) is transmitted to the DLC film. 8 is totally reflected, so that there is little external light transmitted to the rear side of the transmissive screen, and external light reflection is reduced.

  FIG. 5 is a cross-sectional view for explaining external light reflection in a conventional transmission screen (comparative example).

On the other hand, in the conventional transmission type screen using the microlens array of the comparative example, the refractive index n of air is set to 1.0 and the refractive index n ″ of the microlens 102 is set to 1. 5 and the microlens 102 has a hemispherical shape, analysis based on Snell's law (n ₁ · sinθ ₁ = n ₂ · sinθ ₂ ) External light from an area within 59.4 ° with respect to the axis passes through the microlens 102 and passes through the rear side of the transmissive screen.

  Thus, it can be seen that in the transmissive screen according to the present invention, the reflection of external light is reduced by the DLC film.

  Furthermore, as shown in [Table 1], the microlens array of each of the examples of the present invention (sample No. 1 to sample No. 7) has a glare of a display screen called scintillation as compared with the comparative example (sample No. 8). It was found that a high-performance transmissive screen was constructed.

  The cause of the display screen glare called scintillation (speckle) is considered to be interference in an irregular phase relationship due to coherent light from the light source. In particular, when an ultra-high pressure mercury lamp (UHP lamp) is used as the light source, the coherency is higher than that of other lamp light sources and a lot of scintillation occurs. For this reason, in order to reduce scintillation, measures such as controlling coherence spatially or temporally or averaging spatially are considered necessary.

  In the transmissive screen according to the present invention, the DLC film overcoated on the surface of the microlens has a large difference in refractive index with air and a refractive index difference with the material forming the microlens. The speed of light passing through the light beam fluctuates depending on the wavelength and location, and the reflection and scattering of the interface causes the phase of these light beams to shift, and the coherency of the light incident on the microlens 1 is reduced. It is done. Therefore, it is considered that these rays are spatially averaged and scintillation is reduced.

  It should be noted that the present invention is not limited to the configuration and the microlens array manufacturing procedure in each of the embodiments described above, and it goes without saying that various modifications can be made without departing from the spirit of the present invention.

It is sectional drawing which shows the structure of the transmission type screen which concerns on this invention. It is sectional drawing which shows each process in the manufacturing method of the micro lens array which comprises the said transmissive screen. It is a graph which shows the film thickness of the DLC film with respect to the ethylene gas pressure in the CVD method in the manufacturing process of the said micro lens array, and the relationship of the refractive index at that time. It is sectional drawing for demonstrating the external light reflection reduction effect by the DLC film in the said transmissive screen. It is sectional drawing for demonstrating external light reflection in the conventional transmissive screen (comparative example). It is sectional drawing which shows the structure of the conventional transmissive screen.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Micro lens 2 Micro lens array 5 Fresnel lens 6 Transparent base material 8 DLC film

Claims (2)

A microlens array formed by closely arranging a number of microlenses protruding in a convex lens shape on the main surface of the transparent substrate;
The microlens array is disposed on the side where the microlens is formed, and diffused light incident from a light source is made into a substantially parallel light beam, and the parallel light beam is incident substantially perpendicular to the main surface of the microlens array. With a Fresnel lens,
A transmission type screen, wherein a surface portion of the microlens is overcoated with a material having a higher refractive index than a material forming the microlens. A microlens array formed by closely arranging a number of microlenses protruding in a convex lens shape on the main surface of the transparent substrate;
The microlens array is disposed on the side where the microlens is formed, and diffused light incident from a light source is made into a substantially parallel light beam, and the parallel light beam is incident substantially perpendicular to the main surface of the microlens array. With a Fresnel lens,
At least one of the surface portion of the microlens and the surface portion of the Fresnel lens facing the microlens array is more wear resistant than the material forming the microlens and the material forming the Fresnel lens. A transmission screen characterized by being overcoated with high materials.