JP7516463B2 - Louvers, head mounted displays, optical devices - Google Patents

Description

The present invention relates to louvers used in head mounted displays, optical devices such as head mounted displays, and methods for manufacturing the same.

In recent years, head-mounted displays have come to be used in a variety of fields, including virtual reality. Compared to direct-view flat panel displays and projection displays, head-mounted displays have advantages such as the ability to display images that can be viewed from any direction and the ability to superimpose images onto the external world as seen from the user's position.

As shown in FIG. 15, the head mounted display has a display panel 21 that displays an image, and an optical element 22 that focuses the display light IMG displayed on the display panel 21 near the position of the user's eye 24. Note that FIG. 15 is merely a conceptual schematic diagram, and an optical path changing element such as a mirror or PBS may be provided between the display panel 21 and the user's eye 24, and the display panel 21 and the optical element 22 may be laid out in different positions. In addition, the optical element 22 may be a transmissive optical element such as a convex lens, a reflective optical element such as a concave mirror, or a combination of multiple elements thereof.

For the convenience of the user's visibility, it has been proposed to provide louvers within the housing of the head mounted display.
Patent Document 1 proposes providing a louver having a light-blocking property to a combiner in a head mounted display having a combiner that combines external light from the front with display light of a display image.
Furthermore, Patent Document 2 discloses a technique for roughening both the front and back surfaces of the light-shielding portion of the louver in order to suppress ghosts, which are double images of light.

Japanese Patent Application Publication No. 11-95160 JP 2009-75266 A

To provide easy-to-view images on a head-mounted display, it is necessary to transmit the display light from the display panel to the user's eyes with as little loss or disturbance as possible, and to prevent external light and stray light within the head-mounted display from entering the user's eyes as much as possible.
However, with the louvers disclosed in Patent Documents 1 and 2, it is difficult to sufficiently achieve these.

A first aspect of the present invention is a louver arranged in an optical path of display light directed from an optical unit of a head-mounted display comprising a louver, a display panel, and an optical unit that directs display light output from the display panel toward a user's eye, the louver being characterized in that a shading unit made of a light-blocking material is provided inside a base made of a light-transmitting material, and when, of the surfaces of the shading unit that contact the light-transmitting material, the surface on the outer edge side of the base is defined as a second surface and the surface opposite the second surface is defined as a first surface, the surface roughness of the first surface is greater than the surface roughness of the second surface, and the first surface of the shading unit is a surface closer to the optical axis of the light path than the second surface .

The present invention provides a louver that can transmit display light to the user's eyes with reduced loss and disturbance, while preventing external light and stray light within the head-mounted display from entering the user's eyes.

FIG. 2 is a schematic diagram showing the configuration of an optical system of the head mounted display according to the first embodiment. FIG. 11 is a schematic diagram showing a configuration of an optical system of a head mounted display according to a modified example of the first embodiment. 1A is a schematic cross-sectional view showing a cross section of a plate-shaped louver 23 cut in a direction perpendicular to the main surface, FIG. 1B is a plan view of the main surface of the louver 23 viewed from the direction of the optical axis OX, and FIG. 1C is a plan view of the main surface of a modified louver 23 viewed from the direction of the optical axis OX. FIG. 1 is a plan view of a head mounted display according to a first embodiment as viewed from a user's side. 1A is a cross-sectional view of a louver for explaining the surface roughness of a light-shielding portion, and FIG. 1A is a schematic cross-sectional view for explaining the optical function of a light blocking portion in the first embodiment; 13A is a schematic cross-sectional view for explaining the optical action of a light-shielding portion in the second embodiment; FIG. 13B is a schematic cross-sectional view for explaining the optical action of a light-shielding portion in the third embodiment; 1A is a diagram for explaining a method for preparing a sample for measuring the surface roughness of a concentric light-shielding portion, and FIG. 1B is a diagram for explaining a method for measuring the surface roughness of the light-shielding portion. 1A is a diagram for explaining a method for preparing a sample for measuring the surface roughness of a striped light-shielding portion, and FIG. 1B is a diagram for explaining a method for measuring the surface roughness of the light-shielding portion. (a) is a diagram showing a stage in which a resin material is applied to a substrate in a first example of a method for manufacturing a louver according to the first embodiment, (b) is a diagram showing an intermediate stage in which the resin material on the substrate is molded using a mold, (c) is a diagram showing a stage in which the resin material is cured by irradiating it with ultraviolet light, and (d) is a diagram showing a stage in which the mold has been released. (a) is a diagram showing a step of applying a material for the light blocking portion using a dispenser in a first example of a method for manufacturing a louver according to the first embodiment, (b) is a diagram showing a step of applying a resin material for forming a first base portion and then curing the resin material by irradiating ultraviolet light through a template, and (c) is a diagram showing a step of releasing the template. (a) is a diagram showing a stage in which a resin material is applied to a substrate in a second example of a method for manufacturing a louver according to the first embodiment, (b) is a diagram showing an intermediate stage in which the resin material on the substrate is molded using a mold, (c) is a diagram showing a stage in which the resin material is hardened by irradiating it with ultraviolet light, and (d) is a diagram showing a stage in which the mold has been released. (a) is a diagram showing a step of applying a material for the light blocking portion using a dispenser in a second example of the method for manufacturing a louver according to the first embodiment, (b) is a diagram showing a step of applying a resin material for forming a first base portion and then curing the resin material by irradiating ultraviolet light through a template, and (c) is a diagram showing a step of releasing the template. 5 is a schematic cross-sectional view showing an embodiment in which the inclination of the main surface of the light-shielding portion 5 changes. FIG. FIG. 1 is a schematic diagram showing the configuration of a conventional head mounted display. 13A is a cross-sectional view of a louver for explaining the surface roughness of a light blocking portion in a second embodiment, and FIG. 2A is a schematic cross-sectional view for explaining the optical function of a light-shielding portion in embodiment 2A, and FIG. 2B is a schematic cross-sectional view for explaining the optical function of a light-shielding portion in embodiment 2B. 13A is a schematic cross-sectional view for explaining the optical action of a light-shielding portion in the fourth embodiment; FIG. 13B is a schematic cross-sectional view for explaining the optical action of a light-shielding portion in the fifth embodiment; 1A is a diagram for explaining a method for measuring the surface roughness of an end face of a concentric light-shielding portion on the eyepiece side, and FIG. 1B is a diagram for explaining a method for measuring the surface roughness of an end face of a concentric light-shielding portion on the display panel side. 1A is a diagram for explaining a method for measuring the surface roughness of an end face of a striped light-shielding portion on the eyepiece side, and FIG. 1B is a diagram for explaining a method for measuring the surface roughness of an end face of a striped light-shielding portion on the display panel side. 10A is a schematic cross-sectional view showing a cross section of a plate-shaped louver 23 according to a third embodiment, cut in a direction perpendicular to the main surface, (b) a plan view of the main surface of the louver 23 viewed from the direction of the optical axis OX, and (c) a plan view of the main surface of a modified louver 23 viewed from the direction of the optical axis OX. FIG. 13 is a schematic cross-sectional view for explaining an optical function of a second light-shielding portion in the third embodiment. 3A is a schematic cross-sectional view for explaining the optical function of a second light-shielding portion in embodiment 3A, and FIG. 3B is a schematic cross-sectional view for explaining the optical function of a second light-shielding portion in embodiment 3B. 13 is a diagram showing a stage in which material for the second light-shielding portion is applied using a dispenser in the method for manufacturing a louver according to the third embodiment. FIG.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A head mounted display, a louver for a head mounted display, and the like according to embodiments of the present invention will be described with reference to the drawings.
The embodiments described below are merely examples, and those skilled in the art can appropriately modify and implement the detailed configurations without departing from the spirit and scope of the present invention.
In the drawings referred to in the following description of the embodiments and examples, elements denoted by the same reference numbers have the same functions unless otherwise specified.

[First embodiment]
(Head-mounted display optical system)
Fig. 1 is a schematic diagram showing the configuration of the optical system of a head mounted display 100 according to an embodiment. Note that Fig. 1 is a schematic diagram for explaining the arrangement of the optical system, and therefore omits a wearing device and a housing for wearing on a user's head, a communication unit for communicating video information, a power supply unit, and the like.

21 indicates a display panel as a display unit, 22 an optical element as an optical unit, 23 a louver, and 24 the user's eyes. The head mounted display 100 is provided with one optical system unit each for the right eye and the left eye, and an image for the right eye is displayed on the display panel of the right eye unit, and an image for the left eye is displayed on the display panel of the left eye unit. Figure 1 shows one unit of the right eye optical system or the left eye optical system. The display panel 21 is specifically, for example, an organic EL panel or a liquid crystal panel.

The optical element 22 as an optical unit is an optical element that focuses the display light IMG emitted by the display panel 21 toward the user's eye near the position of the user's eye, and allows the user to recognize the image displayed on the display panel 21 as an enlarged image at the clear vision distance. The optical element 22 is disposed midway along the optical path of the display light IMG from the display panel 21 to the position of the user's eye 24, and is disposed so that its optical axis OX connects the center of the screen of the display panel 21 with the user's eye. The optical element 22 is typically a convex single lens, but may also be a lens system in which multiple lenses are combined to have a positive power overall. The optical elements 22 that constitute the lens system may include those that do not have the function of forming an image, and may include, for example, those that have the function of efficiently directing light from the entire display panel 21 into the user's eye.

The louver 23 (louver element) is a plate-like member arranged in the optical path space occupied by the optical path of the display light IMG heading from the optical element 22 to the user's eyes. In other words, the louver 23 is arranged in the optical path of the display light IMG heading to the user's eyes from the optical unit that directs the display light output from the display panel to the user's eyes.

The louver 23 has a plurality of light-shielding parts inside. As will be described later with reference to FIG. 3B, the plurality of light-shielding parts of the louver 23 are arranged along a plurality of concentric circles having different diameters when viewed from the direction of the optical axis OX of the optical element 22. The louver 23 is arranged so that the center of the concentric circle is located on the optical axis OX of the optical element 22. Here, the length of the louver 23 when viewed along the optical axis OX is L1. Also, when viewed along the optical axis OX, the distance from the position of the user's eye to the center of the louver 23 is L2, and the distance from the center of the louver 23 to the center of the optical element 22 is L3. The center of the louver 23 refers to the center of the light-shielding part 5 when viewed along the optical axis OX. It is preferable that L1 is set within a range of 0.3 mm or more and 3 mm or less, L2 is set within a range of 30 mm or less, and L3 is set within a range of 5 mm or more and 25 mm or less. Furthermore, if the vertical length of the louver 23 is L4, L4 is set to a length sufficient to cover the cross section of the optical path of the display light IMG traveling from the optical element 22 toward the user's eye.

The light-shielding portion 5 of the louver 23 is positioned and oriented so as to block external light 25 heading toward the optical element 22 while transmitting most of the display light IMG heading from the optical element 22 to the user's eye 24. External light 25 shown by the solid line in FIG. 1 reaches the light-shielding portion 5 of the louver 23, but is blocked there and does not pass through the optical path shown by the dotted line, and thus is significantly prevented from reaching the user's eye 24 as an external light ghost.

The head mounted display 100 may further include an optical element. For example, as shown in FIG. 2, a polarizing beam splitter PBS may be provided between the optical element 22 and the louver 23. Alternatively, a window material EW (transparent plate material) for protecting the inside of the device from dust and the like may be provided between the louver 23 and the position of the user's eye 24. Even in such a case, the louver 23 of the embodiment is disposed within the optical path space occupied by the optical path of the display light IMG that travels from the optical element 22 toward the user's eye.

Figure 4 is a plan view of the head mounted display 100 according to the embodiment as seen from the user's side. Note that since Figure 4 is a schematic diagram for explaining the arrangement of the optical system, the attachment for mounting the head mounted display 100 on the user's head, the communication unit for communicating video information, the power supply unit, etc. are omitted.

PF is a frame (frame portion) made of a light-shielding material, and functions as a housing that supports the display panel and optical components, and also as a cover that blocks external light from the front direction. The frame PF is provided with a nose pad NF for positioning on the user's face. As elements for the right eye, the window material EWR, louver 23R, optical system 22R, and display panel 21R are arranged in this order from the user's face side, and as elements for the left eye, the window material EWL, louver 23L, optical system 22L, and display panel 21L are arranged in this order from the user's face side. Note that, as in the example shown in FIG. 1, when the louver 23 also serves as a window material that protects the inside of the device from dust, etc., the window materials EWR and EWL do not need to be provided.

Display panels 21R and 21L are preferably, but not limited to, those with a screen aspect ratio of, for example, 4:3 or 16:9. The screen center of each display panel, the optical axis OX of each imaging optical system, and the center line C of each louver are arranged so as to overlap when viewed in a planar view from the user side. However, to achieve convergence, the screen center of each display panel, the optical axis OX of each imaging optical system, and the center line C of each louver may be slightly misaligned.

Also, as shown in Figure 4, by making the outer shape of the louver substantially the same as the outer shape of the imaging optical system (for example, the outer shape of a convex lens or concave mirror), it is possible to achieve a high level of balance between the efficiency of use of the display light and the blocking of external light.

(Louver)
Next, the louver 23 (louver element) will be described in detail with reference to the drawings. Fig. 3(a) is a schematic cross-sectional view showing a cross section of the plate-shaped louver 23 cut in a direction perpendicular to the main surface, and Fig. 3(b) is a plan view of the main surface of the plate-shaped louver 23 viewed from the direction of the optical axis OX in Fig. 1. The cross-sectional view in Fig. 3(a) shows a cross section cut along line A-A' in Fig. 3(b). In order to show the correspondence with the installation posture when the louver 23 is installed on the head mounted display, a coordinate system is shown in each figure in correspondence with the XYZ coordinate system shown in Fig. 1.

The line that passes through the center point of the louver 23 in a plan view and is perpendicular to the main surface is called the center line C, and is shown by a dashed line in FIG. 3(a). When the louver 23 is mounted on the head-mounted display, the louver 23 is positioned so that the center line C approximately coincides with the optical axis OX of the optical element 22.

Louver 23, which is a plate-shaped optical element viewed as a whole, is an optical element in which substrate 1 made of a light-transmitting material, first base 2 made of a light-transmitting resin material, second base 3 made of a light-transmitting resin material, and shading portion 5 made of a light-blocking material are integrated. In the following description, first base 2, second base 3, and shading portion 5 may be collectively referred to as the louver body. Also, first base 2 and second base 3 may be collectively referred to simply as the base.

3(a), the louver 23 includes a substrate 1, but if the louver body alone ensures sufficient mechanical strength, the substrate 1 may be omitted and the louver 23 may be formed only from the first base 2, the second base 3, and the light-shielding portion 5. Conversely, if it is desired to provide stronger protection for the louver body, a substrate 1 may be provided not only on the second base 3 side but also on the first base 2 side, so that the louver body is sandwiched between the two substrates 1.
Below, the substrate and the louver body will be described in order, and then the surface roughness of the light blocking portion, which is a feature of this embodiment, will be described in detail.

(substrate)
As the substrate 1, any of glass materials and optical resin materials can be used as long as they satisfy the desired optical characteristics such as transparency. When emphasis is placed on the viewpoint of less variation in characteristics (reliability, durability), glass materials are suitable. For example, various glasses such as general optical glass represented by silicate glass, borosilicate glass, and phosphate glass, quartz glass, and glass ceramics can be used. On the other hand, when emphasis is placed on the viewpoint of cost and weight reduction, it is preferable to use a resin, for example, a thermoplastic resin, a thermosetting resin, an ultraviolet curing resin, a two-component curing resin, and the like. Examples of the thermoplastic resin include polymethyl methacrylate (PMMA), polycarbonate, polystyrene, MS resin, AS resin, polyolefin such as polyethylene and polypropylene, polyester such as polyethylene terephthalate and polybutylene terephthalate, polyvinyl chloride, cellulose acylate, thermoplastic elastomer, and cycloolefin polymer. Examples of the thermosetting resin include phenolic resin. These resins may be used alone or in combination of two or more. The substrate 1 can be manufactured by, for example, a thermal imprinting method, a photoimprinting method, extrusion molding, injection molding, etc. The shape of the main surface of the substrate 1 when viewed in cross section is not necessarily limited to a flat surface as shown in Fig. 3(a) and can be selected from, for example, a concave spherical surface, a convex spherical surface, an axisymmetric aspherical surface, etc. Furthermore, the outer shape of the substrate 1 when viewed in plan from a direction perpendicular to the main surface (a direction along the center line C) can be of various shapes, and can be selected from, for example, a circle, a rectangle, etc.

(Louver body)
The louver body comprises a first base 2 , a second base 3 , and a light blocking portion 5 .
3A, the first base 2 has a flat main surface that is the emission side (the side of the user's eye) of the display light IMG when assembled to the head mounted display. The main surface (the surface facing the second base 3) that is the incidence side of the display light IMG has an uneven portion. The second base 3 has a flat main surface (the side of the optical element 22) that is the incidence side of the display light IMG when assembled to the head mounted display, and the main surface (the surface facing the first base 2) that is the emission side of the display light IMG has an uneven portion.
In addition, when a substrate whose main surface shape is not flat when viewed in cross section is used as the substrate 1, the flat surfaces of the above-mentioned first base 2 and second base 3 are shaped (non-flat surfaces) according to the main surface shape of the substrate 1.

The uneven portion of the first base 2 and the uneven portion of the second base 3 are fitted or abutted against each other, and the first base 2 and the second base 3 are integrated. The first base 2 and the second base 3 are made of materials having substantially the same refractive index, and are preferably formed of the same type of resin material. There are no particular limitations on the resin material that forms them, as long as it satisfies optical characteristics such as transmittance and reliability, but photosensitive resin materials are preferably used because they are easy to manufacture. Specifically, acrylate resins, polycarbonate resins, and the like are preferably used. In order to achieve predetermined optical characteristics, it is also possible to add inorganic fine particles to this optical resin material. The inorganic fine particles to be added are selected depending on the required optical characteristics. Specifically, zirconia oxide, titanium oxide, zinc oxide, indium oxide, tin oxide, antimony oxide, indium tin oxide (ITO), antimony-doped tin oxide (ATO), zinc-doped indium oxide (IZO), and the like can be mentioned.

The uneven portions of the first base 2 and the second base 3 may have any shape that can fit or abut against each other and can form the light-shielding portion 5 at a predetermined position and in a predetermined direction, as described below. As shown in FIG. 3(a), the cross-sectional shape of the uneven portions is preferably a sawtooth shape with triangles arranged in a row, but other shapes are also acceptable. Examples include cross-sectional shapes in which triangles such as isosceles and right-angled triangles, squares, trapezoids, and semicircles are arranged continuously. In addition, when viewed in a plan view from the direction of the optical axis OX in FIG. 1, the uneven portions are formed along multiple concentric circles with different diameters.

When the portion where the first base 2 and the second base 3 are fitted or abutted is viewed along the Z direction, it can be seen that the portion where the first base 2 and the second base 3 are abutted and the portion 4 where the first base 2 and the second base 3 sandwich the light-shielding portion 5 are arranged alternately. In other words, when viewed along the Z direction, the bases and light-shielding portions made of a transparent resin material are arranged alternately. The Z direction here can also be viewed as the direction parallel to the main surface, the direction perpendicular to the center line C, or the vertical direction.

FIG. 5B is an enlarged cross-sectional view of a portion of FIG.
The interface where surface 2a of the first base 2 and surface 3a of the second base 3 abut is an interface where the same materials abut, and therefore does not have any optical effect, and this portion serves as a window that transmits the display light IMG.

Meanwhile, the light shielding portion 5 is sandwiched between the surface 2b of the first base portion 2 and the surface 3b of the second base portion 3. When viewed in a plan view from the direction of the optical axis OX in FIG. 1, the light shielding portion 5 is formed in the shape of multiple concentric circles with different diameters, as shown in FIG. 3(b). Here, FIG. 3(a) corresponds to a cross section taken along the line A-A' in FIG. 3(b). As shown in FIG. 1, the light shielding portion 5 is provided at a position and direction that effectively blocks the external light 25 heading toward the optical element 22, but does not easily block the display light IMG heading from the optical element 22 toward the user's eye 24.

In this embodiment, the shape of the light-shielding portion 5 in a plan view is not limited to the multiple concentric circles shown in FIG. 3(b), but may be, for example, a stripe shape as shown in FIG. 3(c). In this case, FIG. 3(a) corresponds to a cross section taken along line B-B' in FIG. 3(c).

As shown in FIG. 3(a), the louver 23 of this embodiment has a plurality of light-shielding portions 5 repeatedly arranged along a vertical direction (Z direction) perpendicular to the optical axis OX of the optical element 22. When viewed along a vertical direction (Z direction) perpendicular to the direction connecting the user's left and right eyes (Y direction), the louver 23 of this embodiment has a structure that is symmetrical above and below with respect to the center line C, as shown in FIG. 3(a).

When mounting the louver 23 on the head mounted display, the center line C is positioned so as to substantially coincide with the optical axis of the optical section, i.e., the optical axis OX of the optical element 22 shown in FIG. 1. In other words, the centers of the multiple concentric circles or the centers of the multiple stripes that make up the light blocking section 5 are positioned on the line connecting the screen center of the display panel 21 and the position of the user's eye 24. When using a concentric light blocking section, there is an advantage that the brightness uniformity of the displayed image is excellent. In addition, when creating the louver using mold molding or a dispenser, there is an advantage that, for example, the stress acts isotropically, so distortion is small, and the light blocking material can be easily applied by rotating the substrate, making it easy to manufacture.

As shown in FIG. 5(b), when the distance between the light-shielding portions (the difference in radius between adjacent concentric circles, or the distance between stripes) is P and the thickness of the light-shielding portion (the width of the light-shielding portion when viewed in a plan view from the direction of the optical axis OX) is t, it is preferable to set t/P to 9% or less (t/P≦9%). In this case, it is preferable to set P within the range of 500 μm or more and 2000 μm or less, and t within the range of 0.1 μm or more and 45 μm or less. Furthermore, when the length of the light-shielding portion 5 in the optical axis direction is L1, it is preferable to set L1 within the range of 1 mm or more and 3 mm or less.

To ensure sufficient light-shielding performance against external light, it is desirable to set t to 0.1 μm or more, P to 2000 μm or less, and L1 to 1 mm or more. However, if t is set to 45 μm or more, or P to 500 μm or less, or L1 to 3 mm or more, the proportion of the display light IMG blocked by the light-shielding portion 5 increases, and the displayed image becomes dark. Therefore, it is desirable to set t, P, and L1 within the above-mentioned ranges, and in particular, by setting t/P≦9%, it is possible to achieve a good balance between preventing ghosting caused by external light and ensuring the brightness and uniformity of the displayed image.

The light-shielding portion 5 only needs to be able to block the visible light component of the external light 25 from traveling toward the optical element 22, and can be formed using a light-absorbing material that absorbs visible light or a light-reflective material that reflects visible light, and in some cases, a multi-layer structure in which these materials are layered may be used. When using a material that reflects visible light, the position and shape of the light-shielding portion 5 are set so that the reflected external light does not become stray light.

Materials that absorb visible light can be appropriately selected and used, for example paints containing pigments and dyes. However, when it is particularly desired to increase light absorption capacity, it is preferable to select black paint, and from the viewpoint of durability, it is preferable to use a pigment-containing material. Examples of pigments include ivory black, peach black, lamp black, bitumen, carbon black, black aniline, etc. Among these, it is particularly preferable to use carbon black and black aniline. It is also possible to use color materials appropriately for various purposes, such as obtaining different effects depending on the wavelength of incident external light.

When a reflective layer is formed in the light-shielding portion, it can be of a specular reflection type or a diffuse reflection type. When the specular type is used, it is possible to suppress external light ghosts by reflecting external light in a direction that does not affect the observation of the display light IMG. For the specular reflection type light-reflective layer, it is preferable to use a metallic pigment-containing material such as aluminum, silver, nickel, stainless steel, copper, zinc, iron, etc. When fine powders of aluminum, silver, nickel, stainless steel, etc. are used alone or in combination, a silver specular reflection type light-reflective layer is obtained. When fine powders of copper, zinc, iron, etc. are used alone or in combination, a gold or red copper specular reflection type light-reflective layer is obtained. When the diffuse reflection type is used, it is easy to average the light amount distribution, suppress external light ghosts, and suppress uneven brightness. For the diffuse reflection type light-reflective layer, it is preferable to use a pigment-containing material such as silver white, titanium white, zinc white, aluminum powder, etc. Note that the difference between the refractive index of the light-shielding portion and the refractive index of the translucent base is preferably 0.01 or more and 0.2 or less.

In addition, there is no particular restriction on the method of forming the light-shielding portion, and an appropriate manufacturing method can be adopted. For example, a coating method in which paint containing a coloring material is applied to a predetermined surface of the uneven shape of the first base 2 and/or the second base 3, or a method in which a metal material such as aluminum is vacuum-deposited can be used. When forming the light-shielding portion 5 by a coating method, there are contact and non-contact methods. For example, a contact method is a method in which a brush or sponge, which is also used for inking lenses, is used for coating. For example, a non-contact method is a method in which a spray or dispenser is used for coating. As described later, when coating with a dispenser, a ring-shaped light-shielding portion can be formed by applying paint from an oblique direction toward a predetermined surface of the uneven portion of the first base 2 and/or the second base 3.

(Surface roughness of the light-shielding part)
With reference to Fig. 5(a), the surface roughness of the light-shielding portion 5, which is one of the features of this embodiment, will be described. Fig. 5(a) is a diagram showing the cross-sectional view of Fig. 3(a) in more detail. A plurality of light-shielding portions 5 are arranged in the louver 23 of this embodiment, and in each light-shielding portion 5, the main surface close to the center line C is designated as 5A, and the main surface opposite the center line C is designated as 5B. In other words, among the surfaces of the light-shielding portion 5 that contact the base made of a light-transmitting material, the surface on the center side of the base can be called 5A (first surface), and the surface on the outer edge side of the base can be called 5B (second surface).

The louver 23 according to this embodiment has a feature in that, in the light-shielding portion 5, when comparing the main surface 5A closer to the center line C with the main surface 5B opposite the center line C, the surface roughness Ra of 5A is greater than the surface roughness Ra of 5B (5A>5B).

With reference to Figures 6(a) to 7(b), the reason why the surface roughness Ra of the light-shielding portion 5 is set to 5A>5B in this embodiment will be described in detail. For convenience of explanation and illustration, the enlarged cross-sectional views of Figures 6(a) to 7(b) show only a part of the louver body. Figure 6(a) shows the present embodiment, i.e., the case where the surface roughness Ra of the light-shielding portion 5 is set to 5A>5B. Figure 6(b) shows the reference embodiment 1, which shows the case where the surface roughness Ra of 5A and 5B is roughly equal and the flatness is high (the surface roughness Ra is small).
FIG. 7( a ) shows, as Reference Form 2, a case in which the surface roughness Ra of 5A and 5B are roughly equal and roughened (surface roughness Ra is increased). FIG. 7( b ) shows, as Reference Form 3, a case in which the surface roughness Ra of 5B is made larger than the surface roughness Ra of 5A (5A<5B), which is the opposite of this embodiment.

As shown in FIG. 5(b), the light shielding portion 5 has a length of L1 when viewed along the optical axis OX. Therefore, some of the light rays of the display light IMG that are focused by the optical element 22 in the head mounted display and directed toward the user's eyes can be irradiated onto the main surface 5A or 5B.

Although not shown in Figures 6(a) to 7(b), the amount of display light irradiated to 5B, which is the main surface farther from center line C, is less than the amount of display light irradiated to 5A, and even if it is reflected by 5B, the light path is changed in a direction that does not reach the user's eye, so the effect on image quality is small.

On the other hand, the amount of display light IMG2 irradiated to 5A, which is the main surface closer to center line C, is greater than the amount of display light irradiated to 5B. For this reason, as shown in FIG. 6(b) or FIG. 7(b), if 5A is highly flat (surface roughness Ra is small), the display light IMG2R, which is reflected by 5A and has its optical path changed, reaches the user's eye via an optical path different from the original optical path of optical element 22. Such light leads to a decrease in image quality for the user, such as a decrease in contrast and resolution.

In this embodiment, the louver 23 has a large surface roughness on the main surface 5A that is closer to the center line C of the light-shielding portion, so that, as shown in FIG. 6(a), the display light IMG2 irradiated to 5A is scattered, and only a small portion of the scattered light reaches the user's eyes. This makes it possible to suppress factors that degrade image quality, such as reduced contrast and reduced resolution.

In addition, external light that enters the housing of the head mounted display and stray light that is generated when the external light that entered is reflected inside the housing are likely to irradiate 5B, which is the main surface farther from the center line C, as shown as OL in Figures 6(a) to 7(b). If 5B is roughened (surface roughness Ra is large) as in the form shown in Figure 7(a) or 7(b), OLD, which is a part of the external light or stray light scattered by 5B, reaches the user's eyes. Generally, external light or stray light OL has a higher brightness than display light, so even a scattered part of OL can cause a decrease in image quality for the user, such as the occurrence of ghosts.

In this embodiment, the louver 23 has a small surface roughness on the main surface 5B, which is the side farther from the center line C of the light-shielding portion, so that, as shown in FIG. 6(a), OL, which is external light or stray light irradiated onto 5B, is reflected as reflected light OLR in a direction that does not reach the user's eyes. This makes it possible to suppress factors that degrade image quality, such as the occurrence of ghosts.

In this way, this embodiment can achieve both of the following: preventing the display light from being reflected by the louvers, which would result in a decrease in contrast and resolution, and preventing external light and stray light from being scattered by the louvers, which would result in ghosting. On the other hand, the reference forms shown in Figures 6(b), 7(a), and 7(b) are unable to achieve both of these effects, as in this embodiment.

Here, regarding the preferred aspect of 5A, which is the main surface closer to the center line C, it is preferable that the surface roughness Ra of 5A is 20 nm or more and 2000 nm or less. To achieve the scattering ability to scatter the display light, it is preferable that the surface roughness Ra is 20 nm or more, but if it exceeds 2000 nm, it becomes difficult to manufacture. Furthermore, regarding the preferred aspect of 5B, which is the main surface farther from the center line C, it is preferable that the surface roughness Ra of 5B is 20 nm or less. This is to reflect external light or stray light in a direction that does not reach the user's eyes without scattering it.

Next, a method for measuring the surface roughness Ra of 5A and 5B will be described. First, a method for measuring the surface roughness Ra of the louver having the concentric light-shielding portion 5 shown in FIG. 3(b) will be described with reference to FIG. 8(a) and FIG. 8(b). Note that the measurement method described below is only one example, and the surface roughness Ra may be measured by other methods.

First, the louver 23 is cut along the lines D1 and D2 shown in FIG. 8(a) to create a sample piece for observation shown in FIG. 8(b). The sample piece for observation is cut so that the surface 5A, which is the main surface close to the center line C of the light-shielding part 5, can be observed directly through the resin from the observation direction DA, and the main surface 5B, which is the main surface far from the center line C, can be observed directly through the resin from the observation direction DB. The cutting can be performed, for example, using a microcutting machine BS-300CP manufactured by Meiwa Force Co., Ltd. at a band speed of 60 m/min. After cutting, the cut surface is polished. For example, a precision polishing machine Doctor Lap ML-180 is used for polishing, and the surface is polished with a diamond lap plate (#2000) and then finished with a polishing cloth.

Once the sample pieces for observation were created, the surface of 5A was observed directly through the resin from observation direction DA, and the surface of 5B was observed directly through the resin from observation direction DB. Specifically, a white light interferometer Newview8300 manufactured by ZYGO was used to measure the surface roughness Ra over an area of approximately 0.2 mm square with an objective lens magnification of 10x. For each of the objects 5A or 5B to be measured, the surface roughness Ra was measured at, for example, five locations, and the average value was taken as the surface roughness Ra of the sample.

In the case of a louver having striped light-shielding portions 5 as shown in FIG. 3(c), the louver 23 is cut along lines D1 and D2 as shown in FIG. 9(a) to create a sample piece for observation as shown in FIG. 9(b). The explanation of the subsequent observation procedure is omitted as it is the same as in the case of concentric light-shielding portions.

(Method of manufacturing louvers)
Next, a method for manufacturing the louver according to this embodiment will be described.
In the manufacturing method according to this embodiment, one method for controlling the surface roughness of the light-shielding portion of the louver is to control the surface roughness of the base, which serves as the base for the light-shielding portion, to a predetermined surface roughness when the base is formed using a resin material. The surface roughness of the base can be controlled by the molding conditions when the base is transfer-molded using a mold, i.e., the type of resin material, the temperature of the resin material at the time of injection, the pressure holding conditions, etc. The surface roughness of the molding surface of the mold used when transfer-molding the base is particularly useful as a parameter for controlling the surface roughness of the light-shielding portion of the louver.

In addition, in the manufacturing method according to the present embodiment, one method for controlling the surface roughness of the light-shielding portion of the louver is to control it by coating the base with a light-shielding material under predetermined conditions. The predetermined conditions include, for example, a coating method such as liquid-phase coating or vacuum deposition, and a coating device. In the case of liquid-phase coating, the predetermined conditions include, for example, the physical properties of the paint (viscosity, temperature, additives, etc.), the coating method (dispenser, inkjet, coater, etc.), and the drying method (natural, air blow, oven, etc.). The amount of solvent contained in the paint is particularly useful as a parameter for controlling the surface roughness of the light-shielding portion of the louver.
These methods for controlling the surface roughness of the light blocking portion of the louver can be implemented in any suitable combination or by changing the conditions as appropriate.

(First Example)
A first example of a method for manufacturing a louver according to this embodiment will be described with reference to FIGS. 10(a) to 10(d) and 11(a) to 11(c).
First, as shown in FIG. 10A, a suitable amount of ultraviolet-curable resin material 11 for forming the second base portion 3 is applied onto the substrate 1.

Next, as shown in FIG. 10(b), the resin material 11 is pressed with a mold 12 for transferring and molding the shape of the second base 3, and the resin material 11 is filled between the substrate 1 and the mold 12 so that no gaps are formed. The mold 12 has a pattern for forming a plurality of concentric circular irregularities with different diameters on the main surface of the second base 3. More specifically, the mold 12 has a transfer surface shape such that the surface roughness Ra of the 3b surface is 20 nm or more and 2000 nm or less in the mold. The transfer surface shape of the mold can be controlled by adjusting the cutting processing conditions and blast processing conditions when forming the transfer surface on the mold.

Once the filling of the resin material 11 is complete, as shown in FIG. 10(c), ultraviolet light is irradiated from an ultraviolet light source 13 to harden the ultraviolet-curable resin material 11. Once the irradiation of ultraviolet light is complete, as shown in FIG. 10(d), the second base 3 formed in close contact with the substrate 1 is released from the mold 12. Furthermore, to completely harden the resin material, it may be placed in an oven and subjected to a heat treatment. In this way, the surface 3b of the base 3 is formed to have a surface roughness Ra of 20 nm or more and 2000 nm or less.

Next, a light-shielding portion is formed on surface 3b of second base 3 described with reference to FIG. 5(b). Specifically, as shown in FIG. 11(a), substrate 1 is rotated around the center line C of multiple concentric circles of different diameters as the rotation axis, and the material of light-shielding portion 5 is applied along surface 3b of each concentric circle using dispenser 14. By applying with dispenser 14 at an appropriate tilt, it is possible to apply paint containing light-shielding material only to surface 3b without contaminating surface 3a. After application is complete, the paint is dried and hardened by heating and baking in an oven, forming light-shielding portion 5 on second base 3.

In this example, the light-shielding material covers surface 3b of base 3, which has a surface roughness Ra of 20 nm or more and 2000 nm or less, to form 5A, which is the main surface closer to center line C of light-shielding part 5. Therefore, the surface shape of 5A is a direct inversion of the surface shape of surface 3b of base 3, and the surface roughness of 5A is 20 nm or more and 2000 nm or less. On the other hand, the surface shape of the exposed front surface (the surface opposite base 3, which is the base) at the time the light-shielding material is applied can be controlled by the conditions when applying using dispenser 14.

For example, if the solvent content of the paint used to form the light-shielding portion is increased and the viscosity of the paint is reduced, a thin coating can be formed, and the surface shape of the front side will reflect the surface shape of the base relatively faithfully. On the other hand, if the solvent content of the paint is reduced and the viscosity of the paint is increased, the surface shape of the front side will tend to differ from that of the base. Alternatively, it is possible to control the surface shape of the front side by changing the drying conditions after applying the paint (for example, whether or not to use an air blower). In this example, the solvent content is adjusted and applied so that the surface roughness of the front side is smaller than that of the base, and the surface roughness of the main surface of the light-shielding portion formed as a result is controlled to be 5A > 5B.

Next, an appropriate amount of ultraviolet-curing resin material 16 for forming the first base 2 is applied onto the second base 3 on which the light-shielding portion 5 is formed. The resin material 16 is then pressed with a template 15 for transferring and molding the shape of the flat surface of the first base 2, and the resin material 16 is filled between the second base 3 on which the light-shielding portion 5 is formed and the template 15 so that no gaps are formed. The template 15 is made of a transparent material that transmits ultraviolet light, and the molding surface that comes into contact with the resin material 16 is a flat surface.

When the filling of the resin material 16 is complete, as shown in FIG. 11(b), ultraviolet light is irradiated from the ultraviolet light source 13 to harden the ultraviolet-curable resin material 16. When the irradiation of ultraviolet light is complete, the mold is released from the template 15 as shown in FIG. 11(c). Furthermore, to completely harden the resin material, it may be placed in an oven and subjected to a heat treatment.

The first example of the manufacturing method described above allows the manufacture of the two-layered, close-contact louver 23 according to the embodiment. In this example, a mold is used to transfer a surface shape with a surface roughness Ra of 20 nm or more and 2000 nm or less to the surface 3b of the second base 3, which serves as the base for the main surface 5A closer to the center line C. Then, a paint having an adjusted solvent content ratio so that the surface roughness of the front side is smaller than that of the base is applied from above the surface 3b, forming a light-shielding portion whose main surface has a surface roughness of 5A > 5B.

(Second Example)
Next, a second example of a method for manufacturing a louver according to this embodiment will be described with reference to Figures 12(a) to 12(d) and 13(a) to 13(c). The second example differs from the first example described above in that the substrate 1 is disposed on the base 2 side, and a mold is used to first form the surface 2b of the base 2 shown in Figure 5(b) on the substrate 1.
In the second example, first, as shown in FIG. 12( a ), a suitable amount of ultraviolet-curable resin material 11 for forming the first base portion 2 is applied onto the substrate 1 .

Next, as shown in FIG. 12(b), the resin material 11 is pressed with a mold 12 for transferring the shape of the first base 2, and the resin material 11 is filled between the substrate 1 and the mold 12 so that no gaps are formed. The mold 12 has a pattern for forming a plurality of concentric circular irregularities with different diameters on the main surface of the first base 2. More specifically, the mold 12 has a transfer surface shape such that the surface roughness Ra of the 2b surface is 20 nm or less on the surface of the base 2 shown in FIG. 5(b). The transfer surface shape of the mold can be controlled by adjusting the cutting processing conditions and blast processing conditions when forming the transfer surface on the mold.

Once the filling of the resin material 11 is complete, as shown in FIG. 12(c), ultraviolet light is irradiated from an ultraviolet light source 13 to harden the ultraviolet-curable resin material 11. Once the irradiation of ultraviolet light is complete, as shown in FIG. 12(d), the first base 2 formed in close contact with the substrate 1 is released from the mold 12. Furthermore, to completely harden the resin material, it may be placed in an oven and subjected to a heat treatment. In this way, the surface 2b of the base 2 is formed to have a surface roughness Ra of 20 nm or less.

Next, a light-shielding portion is formed on surface 2b of first base 2 described with reference to FIG. 5(b). Specifically, as shown in FIG. 13(a), substrate 1 is rotated around center line C of multiple concentric circles with different diameters as the rotation axis, and the material of light-shielding portion 5 is applied along surface 2b of each concentric circle using dispenser 14. By applying with dispenser 14 at an appropriate tilt, it is possible to apply paint containing light-shielding material only to surface 2b without contaminating surface 2a. After application is complete, the paint is dried and hardened by heating and baking in an oven, forming light-shielding portion 5 on first base 2.

In this example, the 2b surface of the first base 2, which has a surface roughness Ra of 20 nm or less, is covered with a light-shielding material to form 5B, which is the main surface far from the center line C of the light-shielding part 5. Therefore, the surface shape of 5B directly reflects the surface shape of the 2b surface of the first base 2, and the surface roughness of 5B is 20 nm or less. On the other hand, the surface shape of the front surface (the surface opposite the first base 2, which is the base) exposed at the time of applying the light-shielding material can be controlled by the conditions when applying the material using the dispenser 14. For example, if the solvent content in the paint is reduced to increase the viscosity of the paint, the surface shape of the front surface tends to be different from the surface shape of the base. Alternatively, the surface shape of the front side can be controlled by changing the drying conditions after applying the paint (for example, whether or not air blowing is performed). In this example, the solvent content is adjusted and applied so that the surface roughness of the front side is greater than the surface roughness of the base, and the surface roughness of the main surface of the light-shielding part formed as a result can be made 5A>5B.

Next, an appropriate amount of ultraviolet-curing resin material 16 for forming the second base 3 is applied onto the first base 2 on which the light-shielding portion 5 is formed. Furthermore, the resin material 16 is pressed with a template 15 for transferring and molding the flat surface shape of the second base 3, and the resin material 16 is filled between the first base 2 on which the light-shielding portion 5 is formed and the template 15 so that no gaps are formed. The template 15 is made of a transparent material that transmits ultraviolet light, and the molding surface that comes into contact with the resin material 16 is a flat surface.

When the filling of the resin material 16 is complete, as shown in FIG. 13(b), ultraviolet light is irradiated from the ultraviolet light source 13 to harden the ultraviolet-curable resin material 16. When the irradiation of ultraviolet light is complete, the mold is released from the template 15 as shown in FIG. 13(c). Furthermore, to completely harden the resin material, it may be placed in an oven and subjected to a heat treatment.

The second example of the manufacturing method described above allows the manufacture of a two-layered, close-fitting louver 23 according to the embodiment. In this example, a mold is used to transfer a surface shape with a surface roughness Ra of 20 nm or less to surface 2b of the first base 2, which serves as the base for 5B, the main surface farther from the center line C. Then, a paint with an adjusted solvent content is applied from above surface 2b so that the surface roughness of the front side is greater than that of the base, forming a light-shielding portion whose main surface has a surface roughness of 5A > 5B.

By implementing the louver according to the embodiment in a head mounted display, it is possible to transmit the display light to the user's eyes with reduced loss and disturbance, and it is also possible to prevent external light and stray light within the head mounted display from entering the user's eyes.

[Example]
Specific examples and comparative examples are given below.
Each sample in the examples was produced according to the first or second example of the manufacturing method described above. In addition, by applying the method for controlling surface roughness described in the embodiment, the surface roughness Ra of the main surface was set to 5A=5B in Comparative Example 1 and Comparative Example 2, and the surface roughness Ra of the main surface was set to 5A<5B in Comparative Example 3.

First, common points between the examples and the comparative examples will be described.
For the substrate 1, optical glass containing boron and silicon was used. Specifically, a circular plate material with a diameter of 45 mm was prepared using S-BSL7 manufactured by Ohara Corporation. For the mold 12 for forming the uneven portion on the base, a NiP layer plated on a metal base material was cut with a precision machine to form the inverted shape of the desired uneven portion. At this time, high-precision cutting was performed to adjust the surface roughness of the surface of the mold 12.

The first base 2 was formed using an ultraviolet-curable acrylic resin composition with a refractive index of 1.58 after curing. The light-shielding portion 5 was formed by applying the paint, which is the raw material of the light-shielding portion, from an oblique direction using a dispenser while rotating the substrate 1 around the center of the concentric circles of the first base 2. A dispenser was used because it can supply an appropriate amount of paint to form a film thickness of about 10 μm, and the number of concentric circles to be applied per substrate is small (about 20), making it compatible with previous and next processes. The paint was applied by diluting the original solution with an organic solvent. It was then heated and dried in an oven at 80°C for 4 hours. The refractive index of the paint after drying is 1.68.

The light shielding portion had a concentric shape in plan view, and the pitch P between the light shielding portions (the distance between adjacent light shielding portions, or the difference in radius between adjacent concentric circles) was 1 mm. The length L1 of the light shielding portion 5 in the optical axis direction was 1 mm. The thickness t of the light shielding portion (the width of the light shielding portion when viewed in plan from the direction of the optical axis OX) was 10 μm.
Next, the second base 3 was formed from the same ultraviolet-curable acrylic resin composition as the first base 2, to produce a close-contact two-layer louver element.

The evaluation of each sample was carried out as follows: A head mounted display equipped with a louver element to be evaluated was placed in a dark room that was not affected by external light, and a digital camera was placed at a position that would correspond to the eye of a user when wearing the head mounted display.
First, in order to evaluate the degradation of image quality caused by the reflection of the display light on the main surface of the light-shielding part, a chart in which 1 mm square white and black squares were arranged in a grid pattern was displayed on the head mounted display and photographed with a digital camera. The ratio of the white display part to the black display part in the data was 1:1. The average light intensity of the five white display parts photographed with the digital camera was taken as the white display part intensity, and the average light intensity of the five black display parts was taken as the black display part intensity.
The ratio of the intensity of the black display portion to the intensity of the white display portion of the display light was 0.01 or less, and the ratio was evaluated as A, i.e., excellent. The ratio of the intensity of the black display portion to the intensity of the white display portion of the display light was 0.01 or more, and the ratio was evaluated as B, i.e., poor.

Next, in order to evaluate the deterioration of image quality caused by the reflection of external light or stray light reflected from the main surface of the light-shielding portion, a white parallel light with a diameter of 5 mm was irradiated using an LED light, simulating external light or stray light reflected from external light. The irradiation direction of the white parallel light was in three levels inclined at 45°, 60°, and 75° with respect to the YZ plane of the louver element, and was irradiated at a total of six levels, two levels each corresponding to the upper rear and the lateral rear as seen from the user. In addition, the irradiation position of the white parallel light was irradiated at three locations: the center of the louver, the intermediate position between the center and the periphery from the center toward the upward direction Z, and the intermediate position between the center and the periphery from the center toward the lateral direction Y outward. The levels of the irradiation direction and irradiation position were 18 levels in total. The light intensity per unit area of the white parallel light was 100 times the light intensity of the display panel 21 when displaying white. The display panel 21 was photographed with a digital camera while displaying white and the LED light was turned on. The light intensity average value of the five white display areas photographed by the digital camera was taken as the white display area intensity. After that, the LED lighting was turned on while the display panel 21 was displayed in black, and the 18 levels of illumination were applied as described above. The light intensity average value of the entire area photographed by the digital camera was taken as the unwanted light intensity.
The ratio of the unnecessary light intensity to the white display portion intensity of the display light was evaluated as A, ie, excellent, when it was 0.01 or less, and as B, ie, poor, when it was more than 0.01.

Example 1
The surface roughness Ra of the molding surface of the mold 12 used to form the base was 8 nm. The surface roughness Ra of the 2b surface of the first base 2 transferred by the mold 12 was 8 nm. The paint, which is the raw material of the light-shielding portion 5, was applied to the 2b surface using the dispenser 14. The paint stock solution was diluted 4 times with an organic solvent and applied. The surface roughness Ra of the 5B of the main surfaces of the light-shielding portion was 8 nm, reflecting the shape of the 2b surface of the first base 2. The surface roughness Ra of the 5A of the main surfaces of the light-shielding portion was 100 nm. As described above, in Example 1, the surface roughness Ra of the main surface of the light-shielding portion 5 satisfies the relationship 5A>5B.

Example 2
Example 2 was manufactured by the same manufacturing method as Example 1, except for the paint used to form the light-shielding portion 5. In Example 2, a paint stock solution was diluted 1.5 times with an organic solvent and applied. Of the main surfaces of the light-shielding portion, 5B had a surface roughness Ra of 8 nm, reflecting the shape of surface 2b of the first base 2. Of the main surfaces of the light-shielding portion, 5A had a surface roughness Ra of 1800 nm.
As described above, in Example 2, the surface roughness Ra of the main surface of the light shielding portion 5 satisfies the relationship 5A>5B.

Example 3
Example 3 was manufactured using the same manufacturing method as Example 1, except for the paint used to form the light-shielding portion 5. In Example 3, the paint concentrate was diluted 10 times using an organic solvent and then applied. Of the main surfaces of the light-shielding portion, 5B had a surface roughness Ra of 8 nm, reflecting the shape of surface 2b of the first base 2. Of the main surfaces of the light-shielding portion, 5A had a surface roughness Ra of 25 nm. As described above, in Example 3, the surface roughness Ra of the main surfaces of the light-shielding portion 5 satisfies the relationship 5A>5B.

Example 4
Example 4 was manufactured by the same manufacturing method as Example 1, except that the surface roughness Ra of the molding surface of the mold 12 used to form the base was 20 nm. The surface roughness Ra of the 2b surface of the first base 2 replica molded by the mold 12 was 18 nm. Of the main surfaces of the light shielding portion, 5B had a surface roughness Ra of 18 nm, reflecting the shape of the 2b surface of the first base 2. Of the main surfaces of the light shielding portion, 5A had a surface roughness Ra of 100 nm. As described above, in Example 4, the surface roughness Ra of the main surface of the light shielding portion 5 satisfies the relationship 5A>5B.

(Comparative Example 1)
Comparative Example 1 is a specific example of Reference Form 1 described with reference to Fig. 6B, in which the surface roughness Ra of 5A and 5B is made approximately equal and the flatness is increased (the surface roughness Ra is reduced). The surface roughness Ra of 5A and 5B was set to 8 nm.

(Comparative Example 2)
Comparative Example 2 is a specific example of Reference Form 2 described with reference to Fig. 7(a), in which the surface roughness Ra of 5A and 5B is made roughly equal and roughened (the surface roughness Ra is increased). The surface roughness Ra of 5A and 5B was set to 1800 nm.

(Comparative Example 3)
Comparative Example 3 is a specific example of Reference Form 3 described with reference to Fig. 7B, in which the surface roughness Ra of 5B is made larger than the surface roughness Ra of 5A (5A < 5B). The surface roughness Ra of 5A was 8 nm, and the surface roughness Ra of 5B was 100 nm.

The evaluation results of the examples and comparative examples are summarized in Table 1 below.

When the louvers of Examples 1 to 4 were implemented in a head-mounted display, it was possible to display an image to the user with reduced loss and disturbance, and it was also possible to prevent external light and stray light from entering the user's eyes. In contrast, when the louvers of Comparative Examples 1 to 3 were implemented in a head-mounted display, none of them were able to simultaneously prevent both the degradation in image quality caused by the reflection of display light and the degradation in image quality caused by the scattering of external light and stray light.

[Second embodiment]
(Louver body)
The louver body comprises a first base 2 , a second base 3 , and a light blocking portion 5 .
3A, the first base 2 has a flat main surface that is the emission side (the side of the user's eye) of the display light IMG when assembled to the head mounted display. The main surface (the surface facing the second base 3) that is the incidence side of the display light IMG has an uneven portion. The second base 3 has a flat main surface (the side of the optical element 22) that is the incidence side of the display light IMG when assembled to the head mounted display, and the main surface (the surface facing the first base 2) that is the emission side of the display light IMG has an uneven portion.
In addition, when a substrate whose main surface shape is not flat when viewed in cross section is used as the substrate 1, the flat surfaces of the above-mentioned first base 2 and second base 3 are shaped (non-flat surfaces) according to the main surface shape of the substrate 1.

The uneven portion of the first base 2 and the uneven portion of the second base 3 are fitted or abutted against each other, and the first base 2 and the second base 3 are integrated. The first base 2 and the second base 3 are made of materials having substantially the same refractive index, and are preferably formed of the same type of resin material. There are no particular limitations on the resin material that forms them, as long as it satisfies optical characteristics such as transmittance and reliability, but photosensitive resin materials are preferably used because they are easy to manufacture. Specifically, acrylate resins, polycarbonate resins, and the like are preferably used. In order to achieve predetermined optical characteristics, it is also possible to add inorganic fine particles to this optical resin material. The inorganic fine particles to be added are selected depending on the required optical characteristics. Specifically, zirconia oxide, titanium oxide, zinc oxide, indium oxide, tin oxide, antimony oxide, indium tin oxide (ITO), antimony-doped tin oxide (ATO), zinc-doped indium oxide (IZO), and the like can be mentioned.

The uneven parts of the first base 2 and the second base 3 may have any shape as long as they can be fitted or abutted against each other and can form the light-shielding part 5 at a predetermined position and in a predetermined direction as described below. As shown in Fig. 3(a), a sawtooth shape with triangles arranged is preferably used as the cross-sectional shape of the uneven parts, but other shapes are also acceptable. For example, a cross-sectional shape in which triangles such as isosceles triangles and right-angled triangles, rectangles, trapezoids, semicircles, etc. are arranged continuously can be used.
In addition, when viewed in a plan view from the direction of the optical axis OX in FIG. 1, the concave and convex portions are formed along a plurality of concentric circles having different diameters.

When the portion where the first base 2 and the second base 3 are fitted or abutted is viewed along the Z direction, it can be seen that the portion where the first base 2 and the second base 3 are abutted and the portion 4 where the first base 2 and the second base 3 sandwich the light-shielding portion 5 are arranged alternately. In other words, when viewed along the Z direction, the bases and light-shielding portions made of a transparent resin material are arranged alternately. The Z direction here can also be viewed as the direction parallel to the main surface, the direction perpendicular to the center line C, or the vertical direction.

Figure 16(b) shows an enlarged cross-sectional view of a portion of Figure 3(a). The interface where surface 2a of the first base 2 and surface 3a of the second base 3 abut is an interface where the same materials abut, so it does not act optically, and this portion becomes a window that transmits the display light IMG.

Meanwhile, the light shielding portion 5 is sandwiched between the surface 2b of the first base portion 2 and the surface 3b of the second base portion 3. When viewed in a plan view from the direction of the optical axis OX in FIG. 1, the light shielding portion 5 is formed in the shape of multiple concentric circles with different diameters, as shown in FIG. 3(b). Here, FIG. 3(a) corresponds to a cross section taken along the line A-A' in FIG. 3(b). As shown in FIG. 1, the light shielding portion 5 is provided at a position and direction that effectively blocks the external light 25 heading toward the optical element 22, but does not easily block the display light IMG heading from the optical element 22 toward the user's eye 24.

In this embodiment, the shape of the light-shielding portion 5 in a plan view is not limited to the multiple concentric circles shown in FIG. 3(b), but may be, for example, a stripe shape as shown in FIG. 3(c). In this case, FIG. 3(a) corresponds to a cross section taken along line B-B' in FIG. 3(c).

As shown in FIG. 3(a), the louver 23 of this embodiment has a plurality of light-shielding portions 5 repeatedly arranged along a vertical direction (Z direction) perpendicular to the optical axis OX of the optical element 22. When viewed along a vertical direction (Z direction) perpendicular to the direction connecting the user's left and right eyes (Y direction), the louver 23 of this embodiment has a structure that is symmetrical above and below with respect to the center line C, as shown in FIG. 3(a).

When the louver 23 is mounted on the head mounted display, the center line C is arranged so as to substantially coincide with the optical axis of the optical unit, that is, the optical axis OX of the optical element 22 shown in FIG. 1. In other words, the centers of the concentric circles or stripes constituting the light shielding unit 5 are arranged on the line connecting the screen center of the display panel 21 and the position of the user's eye 24. When a concentric light shielding unit is used, there is an advantage that the brightness uniformity of the displayed image is excellent. Note that even if the centers of the concentric circles of the light shielding unit are offset from the center line C, the brightness uniformity of the displayed image is excellent if the centers of the concentric circles coincide with the optical axis OX. In addition, when the louver is created using mold molding or a dispenser, for example, the stress acts isotropically, so distortion is small, and the light shielding material can be easily applied by rotating the substrate, making it easy to manufacture.

As shown in FIG. 16(b), when the distance between the light-shielding portions (the difference in radius between adjacent concentric circles, or the distance between stripes) is P and the thickness of the light-shielding portion (the width of the light-shielding portion when viewed in a plan view from the direction of the optical axis OX) is t, it is preferable to set t/P to 9% or less (t/P≦9%). In this case, it is preferable to set P within the range of 500 μm or more and 2000 μm or less, and t within the range of 0.1 μm or more and 45 μm or less. Furthermore, when the length of the light-shielding portion 5 in the optical axis direction is L1, it is preferable to set L1 within the range of 1 mm or more and 3 mm or less.

To ensure sufficient light-shielding performance against external light, it is desirable to set t to 0.1 μm or more, P to 2000 μm or less, and L1 to 1 mm or more. However, if t is set to 45 μm or more, or P to 500 μm or less, or L1 to 3 mm or more, the proportion of the display light IMG blocked by the light-shielding portion 5 increases, and the displayed image becomes dark. Therefore, it is desirable to set t, P, and L1 within the above-mentioned ranges, and in particular, by setting t/P≦9%, it is possible to achieve a good balance between preventing ghosting caused by external light and ensuring the brightness and uniformity of the displayed image.

The thickness t of the light-shielding portion can also be referred to as the width of the eyepiece-side end face 5C, which will be described later, or the width of the display panel-side end face 5D. In order to form a surface structure that controls the reflection of external light at the eyepiece-side end face 5C, or the reflection of display light at the display panel-side end face 5D, it is more desirable to set t within the range of 5 μm or more and 45 μm or less.

The light-shielding portion 5 only needs to be able to block the visible light component of the external light 25 from traveling toward the optical element 22, and can be formed using a light-absorbing material that absorbs visible light or a light-reflective material that reflects visible light, and in some cases, a multi-layer structure in which these materials are layered may be used. When using a material that reflects visible light, the position and shape of the light-shielding portion 5 are set so that the reflected external light does not become stray light.

Materials that absorb visible light can be appropriately selected and used, for example paints containing pigments and dyes. However, when it is particularly desired to increase light absorption capacity, it is preferable to select black paint, and from the viewpoint of durability, it is preferable to use a pigment-containing material. Examples of pigments include ivory black, peach black, lamp black, bitumen, carbon black, black aniline, etc. Among these, it is particularly preferable to use carbon black and black aniline. It is also possible to use color materials appropriately for various purposes, such as obtaining different effects depending on the wavelength of incident external light.

When a reflective layer is formed in the light-shielding portion, it can be of a specular reflection type or a diffuse reflection type. When the specular type is used, it is possible to suppress external light ghosts by reflecting external light in a direction that does not affect the observation of the display light IMG. For the specular reflection type light-reflective layer, it is preferable to use a metallic pigment-containing material such as aluminum, silver, nickel, stainless steel, copper, zinc, iron, etc. When fine powders of aluminum, silver, nickel, stainless steel, etc. are used alone or in combination, a silver specular reflection type light-reflective layer is obtained. When fine powders of copper, zinc, iron, etc. are used alone or in combination, a gold or red copper specular reflection type light-reflective layer is obtained. When the diffuse reflection type is used, it is easy to average the light amount distribution, suppress external light ghosts, and suppress uneven brightness. For the diffuse reflection type light-reflective layer, it is preferable to use a pigment-containing material such as silver white, titanium white, zinc white, aluminum powder, etc. Note that the difference between the refractive index of the light-shielding portion and the refractive index of the translucent base is preferably 0.01 or more and 0.2 or less.

In addition, there is no particular restriction on the method of forming the light-shielding portion, and an appropriate manufacturing method can be adopted. For example, a coating method in which paint containing a coloring material is applied to a predetermined surface of the uneven shape of the first base 2 and/or the second base 3, or a method in which a metal material such as aluminum is vacuum-deposited can be used. When forming the light-shielding portion 5 by a coating method, there are contact and non-contact methods. For example, a contact method is a method in which a brush or sponge, which is also used for inking lenses, is used for coating. For example, a non-contact method is a method in which a spray or dispenser is used for coating. As described later, when coating with a dispenser, a ring-shaped light-shielding portion can be formed by applying paint from an oblique direction toward a predetermined surface of the uneven portion of the first base 2 and/or the second base 3.

(Surface roughness of the light-shielding part)
With reference to Fig. 16(a), the surface roughness of the light-shielding portion 5, which is one of the features of this embodiment, will be described. Fig. 16(b) is a diagram showing the cross-sectional view of Fig. 3(a) in more detail. In the following description, for example, when the X-plus direction is described, it refers to the same direction as the X-axis arrow in the coordinate system shown in the figure, and when the X-minus direction is described, it refers to the direction 180 degrees opposite to the X-axis arrow in the coordinate system shown in the figure. The same applies to directions other than X.

In this embodiment, the louver 23 has a plurality of light-shielding sections 5 arranged thereon, and in each light-shielding section 5, the main surface closer to the center line C is designated as 5A, and the main surface opposite the center line C is designated as 5B. In other words, of the surfaces of the light-shielding section 5 that contact the base made of a translucent material, the surface closest to the center of the base can be called 5A (first surface), and the surface closest to the outer edge of the base can be called 5B (second surface).

In addition, in each light-shielding portion 5, the end side surface on the negative X side is designated as 5C, and the end side surface on the positive X side is designated as 5D. In the light-shielding portion 5, 5C can also be called the eyepiece side end surface (third surface), and 5D can also be called the display panel side end surface (fourth surface).

The louver 23 according to this embodiment is characterized in that the surface roughness Ra of the eyepiece-side end surface 5C (the end side surface on the negative X-direction side) of the light-shielding portion 5 is less than 20 nm. With reference to Figures 17(a) to 18(b), the reason why the surface roughness Ra of the eyepiece-side end surface 5C of the light-shielding portion 5 in this embodiment is set to less than 20 nm will be explained in detail. For ease of explanation and illustration, only a portion of the louver body is shown diagrammatically in the enlarged cross-sectional views of Figures 17(a) to 18(b).

Figure 17(a) shows a structure as embodiment 2A in which the eyepiece-side end face 5C of the light shielding portion 5 is a highly flat surface with a surface roughness Ra of less than 20 nm, and the display panel-side end face 5D is a rough surface with a surface roughness Ra greater than that of the eyepiece-side end face 5C. Figure 17(b) shows a structure as embodiment 2B in which the eyepiece-side end face 5C and the display panel-side end face 5D of the light shielding portion 5 are both highly flat surfaces with a surface roughness Ra of less than 20 nm. Figure 18(a) shows a structure as reference form 4 in which the eyepiece-side end face 5C and the display panel-side end face 5D of the light shielding portion 5 are both rough surfaces with a surface roughness Ra of 20 nm or more and less flat. FIG. 18(b) shows a structure of reference form 5 in which the eyepiece-side end face 5C of the light shielding portion 5 is a rough surface with a low flatness, with a surface roughness Ra of 20 nm or more, and the display panel-side end face 5D is a flatter surface with a smaller surface roughness Ra than the eyepiece-side end face 5C. Note that in the embodiment and reference form, the surface roughness of the main surface 5A close to the center line C of the louver 23 and the main surface 5B opposite the center line C are the same in all forms, allowing comparison of only the effects of the eyepiece-side end face 5C and the display panel-side end face 5D.

As shown in FIG. 16(b), the light blocking portion 5 has a thickness of t when viewed along the optical axis C. Therefore, external light OL entering the housing of the head mounted display can be irradiated onto the eyepiece side end face 5C. Also, display light IMG2, which is a part of the display light, can be irradiated onto the display panel side end face 5D. The external light OL may have a higher light intensity than the display light IMG2, and may reach the user's eye with a single reflection at the eyepiece side end face 5C, so it has a large impact on image quality.

When the louver is used, components of external light with a low angle of incidence are blocked by the user's head, and therefore the external light OL that enters the housing has a component with a high angle of incidence with respect to the louver.
In the louvers 23 of the second embodiment and the second embodiment, the eyepiece-side end surface 5C is a highly flat surface with a surface roughness Ra of less than 20 nm. Therefore, as shown in FIG. 17(a) or 17(b), the external light OL irradiated to the eyepiece-side end surface 5C of the light-shielding portion 5 at a high angle of incidence is reflected as reflected light OLR in a direction that does not reach the user's eye. In other words, in the first and second embodiments, degradation of image quality, such as the occurrence of flare and ghost images due to reflection of the external light OL, can be suppressed.

Furthermore, the influence of the display light IMG2 irradiated to the display panel side end surface 5D will be considered for embodiment 2A and embodiment 2B. In embodiment 1, the display panel side end surface 5D is a rough surface with a surface roughness Ra of 20 nm or more, so that the display light IMG2 is reflected as scattered light as shown in FIG. 17(a). Since the light intensity reflected in each direction is weak in the scattered light, even if there is a light path in which the light is reflected again by the optical element 22 or the like and headed toward the user's eye, the light intensity is weak, and image quality degradation such as ghosting and contrast reduction is suppressed. In contrast, in embodiment 2B, the display panel side end surface 5D is a highly flat surface with a surface roughness Ra of less than 20 nm, so that the display light IMG2 can be specularly reflected as shown in FIG. 17(b). In any of the light shielding parts 5, if the specularly reflected light is reflected again by the optical element 22 or the like and headed toward the user's eye as IMG2R, there is a possibility that effects such as ghosting and contrast reduction will occur. Both embodiment 2A and embodiment 2B can suppress the occurrence of flare and ghosting caused by external light OL, but embodiment 2A is more effective at suppressing image quality degradation such as ghosting and reduced contrast caused by display light.

Next, the influence of external light OL irradiated to the eyepiece end surface 5C of the louvers 23 of Reference Form 4 and Reference Form 5 will be considered. In Reference Form 4 and Reference Form 5, the eyepiece end surface 5C is a rough surface with a low flatness, with a surface roughness of 20 nm or more. Therefore, as shown in FIG. 18(a) or FIG. 18(b), the external light OL irradiated to the eyepiece end surface 5C is reflected over a wide area as scattered light OLD. As described above, external light often has a high light intensity, so even if it is scattered light, if some of it reaches the user's eye, it will become a factor that reduces the display image quality as flare or ghost. Therefore, Reference Form 4 and Reference Form 5 have lower practical image quality for the user than Embodiment 2A and Embodiment 2B.

The effects of the display light IMG2 irradiated to the display panel side end surface 5D are similar to those described for embodiment 2A and embodiment 2B. Therefore, in both reference embodiment 4 and reference embodiment 5, flare and ghosting due to external light OL are greater than in embodiment 2A and embodiment 2B, and reference embodiment 5 is more susceptible to image quality degradation such as ghosting and contrast reduction due to display light.

As described above, according to the embodiment shown in Fig. 17(a) and Fig. 17(b), it is possible to prevent flare and the like from occurring due to external light being scattered by the eyepiece-side end face 5C. On the other hand, in the reference embodiment shown in Fig. 18(a) and Fig. 18(b), it is not possible to prevent flare and the like from occurring because external light is scattered by the eyepiece-side end face 5C. Furthermore, in the embodiment of Fig. 17(a), in addition to preventing flare and the like from occurring due to external light being scattered by the eyepiece-side end face 5C, it is also possible to prevent ghosting and contrast degradation from occurring due to display light being reflected by the display panel-side end face 5D.

In addition, regarding 5A (first surface), which is the main surface close to the center line C, and 5B (second surface), which is the main surface opposite to the center line C, it is desirable to make the surface roughness Ra of the first surface larger than the surface roughness Ra of the second surface. (5A>5B). External light entering the housing of the head mounted display and stray light generated by external light being reflected inside the housing are likely to irradiate 5B, which is the main surface far from the center line C. For this reason, if the surface roughness Ra of 5B (second surface) is large, scattered light is generated and it becomes easy for it to reach the user's eye. Therefore, in the embodiment, it is desirable not only to make the eyepiece side end surface 5C (third surface) a highly flat surface with a surface roughness Ra of less than 20 nm, but also to make the surface roughness Ra of 5A (first surface) larger than the surface roughness Ra of 5B (second surface). Specifically, it is preferable that the surface roughness Ra of 5A (first surface) is 20 nm or more and 2000 nm or less. Additionally, it is preferable that the surface roughness Ra of 5B (second surface) be 20 nm or less.

Here, regarding the preferred aspect of 5A, which is the main surface closer to the center line C, it is preferable that the surface roughness Ra of 5A is 20 nm or more and 2000 nm or less. To achieve the scattering ability to scatter the display light, it is preferable that the surface roughness Ra is 20 nm or more, but if it exceeds 2000 nm, it becomes difficult to manufacture. Furthermore, regarding the preferred aspect of 5B, which is the main surface farther from the center line C, it is preferable that the surface roughness Ra of 5B is 20 nm or less. This is to reflect external light or stray light in a direction that does not reach the user's eyes without scattering it.

Next, we will explain how to measure the surface roughness Ra of the eyepiece-side end surface 5C (third surface) and the display panel-side end surface 5D (fourth surface). Note that the measurement method described below is just one example, and other methods may be used to measure the surface roughness Ra.

In the case of a louver having a concentric light-shielding portion 5 as shown in FIG. 3(b), first, as shown in FIG. 19(a), the louver 23 is set in an orientation in which the eyepiece-side end surface 5C (third surface) can be observed directly, and the eyepiece-side end surface 5C is observed through the resin of the first base 2. Specifically, using a white light interferometer Newview8300 manufactured by ZYGO Corporation, the surface roughness Ra was measured over an area of approximately 0.2 mm square with an objective lens magnification of 10x. The surface roughness Ra was measured at, for example, five points on the eyepiece-side end surface 5C to be measured, and the average value was taken as the surface roughness Ra of the sample.

Similarly, as shown in FIG. 19(b), the louver 23 is set in a direction that allows the display panel side end surface 5D (fourth surface) to be observed from the front, and the display panel side end surface 5D is observed through the resin of the second base 3. The specific observation method is the same as that described in FIG. 19(a).

In the case of a louver having striped light-shielding portions 5 as shown in FIG. 3(c), first, as shown in FIG. 20(a), the louver 23 is set in an orientation in which the eyepiece-side end surface 5C (third surface) can be observed directly, and the eyepiece-side end surface 5C is observed through the resin of the first base 2. Specifically, using a white light interferometer Newview8300 manufactured by ZYGO, the surface roughness Ra was measured over an area of approximately 0.2 mm square at an objective lens magnification of 10x. The surface roughness Ra was measured at, for example, five points on the eyepiece-side end surface 5C to be measured, and the average value was taken as the surface roughness Ra of the sample.

Similarly, as shown in FIG. 20(b), the louver 23 is set in a direction that allows the display panel side end surface 5D (fourth surface) to be observed from the front, and the display panel side end surface 5D is observed through the resin of the second base 3. The specific observation method is the same as that described in FIG. 20(a).

(Method of manufacturing louvers)
Next, a method for manufacturing the louver according to this embodiment will be described.
In the manufacturing method according to this embodiment, one method for controlling the surface roughness of the light-shielding portion of the louver is to control the surface roughness of the base, which serves as the base for the light-shielding portion, to a predetermined surface roughness when the base is formed using a resin material. The surface roughness of the base can be controlled by the molding conditions when the base is transfer-molded using a mold, i.e., the type of resin material, the temperature of the resin material at the time of injection, the pressure holding conditions, etc. The surface roughness of the molding surface of the mold used when transfer-molding the base is particularly useful as a parameter for controlling the surface roughness of the light-shielding portion of the louver.

In addition, in the manufacturing method according to the present embodiment, one method for controlling the surface roughness of the light-shielding portion of the louver is to control it by coating the base with a light-shielding material under predetermined conditions. The predetermined conditions include, for example, a coating method such as liquid-phase coating or vacuum deposition, and a coating device. In the case of liquid-phase coating, the predetermined conditions include, for example, the physical properties of the paint (viscosity, temperature, additives, etc.), the coating method (dispenser, inkjet, coater, etc.), and the drying method (natural, air blow, oven, etc.). The amount of solvent contained in the paint is particularly useful as a parameter for controlling the surface roughness of the light-shielding portion of the louver.
These methods for controlling the surface roughness of the light blocking portion of the louver can be implemented in any suitable combination or by changing the conditions as appropriate.

(First Example)
A first example of a method for manufacturing a louver according to this embodiment will be described with reference to FIGS. 10(a) to 10(d) and 11(a) to 11(c).
First, as shown in FIG. 10A, a suitable amount of ultraviolet-curable resin material 11 for forming the second base portion 3 is applied onto the substrate 1.

Next, as shown in FIG. 10(b), the resin material 11 is pressed with a mold 12 for transferring and molding the shape of the second base 3, and the resin material 11 is filled between the substrate 1 and the mold 12 so that no gaps are formed. The mold 12 is formed with a pattern for forming a plurality of concentric uneven parts with different diameters on the main surface of the second base 3. The molding surface of the mold 12 is configured so that a base for forming the display panel side end surface 5D of the light shielding part 5 with a desired surface roughness is transferred to the second base 3. For example, in the case of embodiment 2A shown in FIG. 17(a), in order to set the surface roughness Ra of the display panel side end surface 5D of the light shielding part 5 to 20 nm or more, the mold molding surface is configured so that a surface with a surface roughness Ra of 20 nm or more is transferred to the second base 3, which is the base part. The shape of the molding surface of the mold can be controlled by adjusting the cutting processing conditions and blast processing conditions when forming the molding surface on the mold.

Once the filling of the resin material 11 is complete, as shown in FIG. 10(c), ultraviolet light is irradiated from an ultraviolet light source 13 to harden the ultraviolet-curable resin material 11. Once the irradiation of ultraviolet light is complete, as shown in FIG. 10(d), the second base 3 formed in close contact with the substrate 1 is released from the mold 12. Furthermore, to completely harden the resin material, it may be placed in an oven and subjected to a heat treatment. In this way, a base surface with a predetermined surface roughness is formed on the portion that will be the base of the display panel side end surface 5D of the light-shielding portion 5.

Next, a light-shielding portion is formed on surface 3b of second base 3 described with reference to FIG. 16(b). Specifically, as shown in FIG. 11(a), substrate 1 is rotated around center line C of multiple concentric circles of different diameters as the rotation axis, and the material of light-shielding portion 5 is applied along surface 3b of each concentric circle using dispenser 14. By applying with dispenser 14 at an appropriate tilt, it is possible to apply paint containing light-shielding material only to surface 3b without contaminating surface 3a. After application is complete, the paint is dried and hardened by heating and baking in an oven, forming light-shielding portion 5 on second base 3.

In this example, the light-shielding material covers the base surface having a predetermined surface roughness, and the light-shielding portion 5 has a display panel side end surface 5D having a predetermined surface roughness. On the other hand, the surface shape of the front surface (eyepiece side end surface 5C) exposed at the time when the light-shielding material is applied can be controlled by the conditions when applying the material using the dispenser 14.

For example, if the solvent content in the paint that forms the light-shielding portion is increased and the viscosity of the paint is reduced, a thin coating can be formed, and the surface shape of the front side will reflect the surface shape of the base relatively faithfully. On the other hand, if the solvent content in the paint is reduced and the viscosity of the paint is increased, the surface shape of the front side tends to differ from that of the base. Alternatively, it is possible to control the surface shape of the front side by changing the drying conditions after applying the paint (for example, whether or not to use an air blower). In this example, the solvent content is adjusted and applied so that the surface roughness of the front side is smaller than that of the base, thereby controlling the formation of an eyepiece-side end surface 5C with low surface roughness and high flatness.

Next, an appropriate amount of ultraviolet-curing resin material 16 for forming the first base 2 is applied onto the second base 3 on which the light-shielding portion 5 is formed. The resin material 16 is then pressed with a template 15 for transferring and molding the shape of the flat surface of the first base 2, and the resin material 16 is filled between the second base 3 on which the light-shielding portion 5 is formed and the template 15 so that no gaps are formed. The template 15 is made of a transparent material that transmits ultraviolet light, and the molding surface that comes into contact with the resin material 16 is a flat surface.

When the filling of the resin material 16 is complete, as shown in FIG. 11(b), ultraviolet light is irradiated from the ultraviolet light source 13 to harden the ultraviolet-curable resin material 16. When the irradiation of ultraviolet light is complete, the mold is released from the template 15 as shown in FIG. 11(c). Furthermore, to completely harden the resin material, it may be placed in an oven and subjected to a heat treatment.

The first example of the manufacturing method described above can be used to manufacture the two-layered, tightly-fitted louver 23 according to the embodiment.

(Second Example)
Next, a second example of a method for manufacturing a louver according to this embodiment will be described with reference to Figures 12(a) to 12(d) and 13(a) to 13(c). The second example differs from the first example described above in that the substrate 1 is disposed on the base 2 side, and a mold is used to first form the surface 2b of the base 2 shown in Figure 16(b) on the substrate 1.
In the second example, first, as shown in FIG. 12( a ), a suitable amount of ultraviolet-curable resin material 11 for forming the first base portion 2 is applied onto the substrate 1 .

Next, as shown in FIG. 12(b), the resin material 11 is pressed with a mold 12 for transferring the shape of the first base 2, and the resin material 11 is filled between the substrate 1 and the mold 12 so that no gaps are formed. The mold 12 is formed with a pattern for forming a plurality of concentric uneven parts with different diameters on the main surface of the first base 2. The molding surface of the mold 12 is configured so that a base for forming the eyepiece side end surface 5C of the light shielding part 5 with a desired surface roughness is transferred to the first base 2. For example, in the case of embodiment 2A shown in FIG. 17(a), in order to make the surface roughness Ra of the eyepiece side end surface 5C of the light shielding part 5 less than 20 nm, the mold molding surface is configured so that a surface with a surface roughness Ra of less than 20 nm is transferred to the first base 2, which is the base part. The shape of the mold molding surface can be controlled by adjusting the cutting processing conditions and blast processing conditions when forming the molding surface on the mold.

Once the filling of the resin material 11 is complete, as shown in FIG. 12(c), ultraviolet light is irradiated from an ultraviolet light source 13 to harden the ultraviolet-curable resin material 11. Once the irradiation of ultraviolet light is complete, as shown in FIG. 12(d), the first base 2 formed in close contact with the substrate 1 is released from the mold 12. Furthermore, to ensure complete hardening of the resin material, it may be placed in an oven and subjected to a heat treatment. In this way, the surface of the base 2 that serves as the base for the eyepiece side end surface 5C is formed to have a surface roughness Ra of less than 20 nm.

Next, a light-shielding portion is formed on surface 2b of first base 2 described with reference to FIG. 16(b). Specifically, as shown in FIG. 13(a), substrate 1 is rotated around the center line C of multiple concentric circles of different diameters as the rotation axis, and the material of light-shielding portion 5 is applied along surface 2b of each concentric circle using dispenser 14. By applying with dispenser 14 at an appropriate tilt, it is possible to apply paint containing light-shielding material only to surface 2b without contaminating surface 2a. After application is complete, the paint is dried and hardened by heating and baking in an oven, forming light-shielding portion 5 on first base 2.

In this example, the light-shielding material covers the base surface formed with a surface roughness Ra of less than 20 nm, so that the surface shape of the eyepiece-side end surface 5C reflects the surface shape of the base surface as it is, and the surface roughness of the eyepiece-side end surface 5C is less than 20 nm. On the other hand, the surface shape of the front surface (display panel-side end surface 5D) exposed at the time of applying the light-shielding material can be controlled by the conditions when applying the material using the dispenser 14. For example, if the solvent content in the paint is reduced to increase the viscosity of the paint, the surface shape of the front side tends to differ from the surface shape of the base. Alternatively, the surface shape of the front side can be controlled by changing the drying conditions after applying the paint (for example, whether or not to use an air blower). In this example, the solvent content is adjusted and applied so that the surface roughness of the front side is greater than the surface roughness of the base, and the surface roughness Ra of the display panel-side end surface 5D of the light-shielding part formed as a result can be made 20 nm or more.

Next, an appropriate amount of ultraviolet-curing resin material 16 for forming the second base 3 is applied onto the first base 2 on which the light-shielding portion 5 is formed. Furthermore, the resin material 16 is pressed with a template 15 for transferring and molding the flat surface shape of the second base 3, and the resin material 16 is filled between the first base 2 on which the light-shielding portion 5 is formed and the template 15 so that no gaps are formed. The template 15 is made of a transparent material that transmits ultraviolet light, and the molding surface that comes into contact with the resin material 16 is a flat surface.

When the filling of the resin material 16 is complete, as shown in FIG. 13(b), ultraviolet light is irradiated from the ultraviolet light source 13 to harden the ultraviolet-curable resin material 16. When the irradiation of ultraviolet light is complete, the mold is released from the template 15 as shown in FIG. 13(c). Furthermore, to completely harden the resin material, it may be placed in an oven and subjected to a heat treatment.

The second example of the manufacturing method described above allows the manufacture of a two-layered, close-fitting louver 23 according to the embodiment. In this example, a mold is used to transfer a surface shape with a surface roughness Ra of less than 20 nm to the first base 2, which serves as the base for the eyepiece-side end face 5C. Then, a light-shielding paint is applied onto the base to form a light-shielding portion 5 with a surface roughness Ra of less than 20 nm for the eyepiece-side end face 5C.

By implementing the louver according to the embodiment in a head mounted display, it is possible to transmit display light to the user's eyes with reduced loss and disturbance, and it is also possible to prevent external light and stray light within the head mounted display from entering the user's eyes.

[Example]
Specific examples and comparative examples are given below. Each sample in the examples was produced in accordance with the second example of the manufacturing method described above. First, common points between the examples and comparative examples are described.
For the substrate 1, optical glass containing boron and silicon was used. Specifically, a circular plate material with a diameter of 45 mm was prepared using S-BSL7 manufactured by Ohara Corporation. For the mold 12 for forming the uneven portion on the base, a NiP layer plated on a metal base material was cut with a precision machine to form the inverted shape of the desired uneven portion. At this time, high-precision cutting was performed to adjust the surface roughness of the surface of the mold 12.

The first base 2 was formed using an ultraviolet-curable acrylic resin composition with a refractive index of 1.58 after curing. When the light-shielding portion 5 was annular, the substrate 1 was rotated around the center of the concentric circle of the first base 2 as the center of rotation, and the paint that was the raw material for the light-shielding portion was applied from an oblique direction using a dispenser. When the light-shielding portion 5 was striped, the first base 2 and the dispenser were scanned relatively along a straight line, and the paint that was the raw material for the light-shielding portion was applied from an oblique direction. The dispenser was used because it can supply an appropriate amount of discharge to form a film thickness of about 10 μm, and the number of light-shielding portions 5 formed per substrate is small, about 20, and it is compatible with the previous and next processes. The paint was applied by diluting the original solution with an organic solvent. After that, it was heated and dried in an oven at 80°C for 4 hours.

The light shielding portions of Examples 5 to 8, 10 to 11 and Comparative Example 4 had a concentric shape in plan view, and the pitch P between the light shielding portions (the distance between adjacent light shielding portions, or the difference in radius between adjacent concentric circles) was 1 mm. The length L1 of the light shielding portion 5 in the optical axis direction was 1 mm. The thickness t of the light shielding portion (the width of the light shielding portion when viewed from the direction of the optical axis OX) was 10 μm. The shape of the light shielding portion of Example 9 in plan view was parallel stripes as shown in FIG. 3(a).
Next, the second base 3 was formed from the same ultraviolet-curable acrylic resin composition as the first base 2, to produce a close-contact two-layer louver element.

The evaluation of each sample was carried out as follows: A head mounted display equipped with a louver element to be evaluated was placed in a dark room that was not affected by external light, and a digital camera was placed at a position that would correspond to the eye of a user when wearing the head mounted display.
First, in order to evaluate the degradation of image quality caused by the reflection of the display light on the main surface of the light-shielding part and the display panel side end surface 5D, a chart in which 1 mm square white and black squares are arranged in a grid pattern was displayed on the head mounted display and photographed with a digital camera. The ratio of the white display part to the black display part in the data was 1:1. The average light intensity of the five white display parts photographed with the digital camera was taken as the white display part intensity, and the average light intensity of the five black display parts was taken as the black display part intensity.
The ratio of the intensity of the black display portion to the intensity of the white display portion of the display light was 0.01 or less, and the ratio was evaluated as A, i.e., excellent. The ratio of the intensity of the black display portion to the intensity of the white display portion of the display light was 0.01 or more, and the ratio was evaluated as B, i.e., poor.

Next, in order to evaluate the deterioration of image quality caused by the reflection of external light or stray light reflected from the end face of the light shielding part (particularly the eyepiece end face 5C), a white parallel light with a diameter of 5 mm was irradiated using an LED light, simulating external light or stray light reflected from external light. The irradiation direction of the white parallel light was three levels inclined at 45°, 60°, and 75° with respect to the YZ plane of the louver element, and two levels each corresponding to the upper rear and lateral rear as seen from the user, for a total of six levels. In addition, the irradiation position of the white parallel light was irradiated at three locations: the center of the louver, the intermediate position between the center and the periphery from the center toward the upward direction Z, and the intermediate position between the center and the periphery from the center toward the lateral direction Y outward. There were a total of 18 levels of irradiation direction and irradiation position. In addition, the light intensity per unit area of the white parallel light was 100 times the light intensity when the display panel 21 displayed white. The display panel 21 was photographed with a digital camera while the LED light was turned on and the white display was displayed. The light intensity average value of the five white display areas photographed by the digital camera was taken as the white display area intensity. After that, the LED lighting was turned on while the display panel 21 was displayed in black, and the 18 levels of illumination were applied as described above. The light intensity average value of the entire area photographed by the digital camera was taken as the unwanted light intensity.
The ratio of the unnecessary light intensity to the white display portion intensity of the display light was evaluated as A, ie, excellent, when it was 0.01 or less, and as B, ie, poor, when it was more than 0.01.

Example 5
The surface roughness Ra of the portion of the molding surface of the mold 12 used to form the base that serves as the base of the eyepiece-side end face 5C was 8 nm. The surface roughness Ra of the portion of the first base 2 that was transfer molded by the mold 12 that serves as the base of the eyepiece-side end face 5C was 8 nm. The paint, which is the raw material of the light-shielding portion 5, was applied using a dispenser 14. The paint stock solution was diluted four times using an organic solvent and then applied. The surface roughness Ra of the eyepiece-side end face 5C was 8 nm. The surface roughness Ra of the display panel-side end face 5D was 100 nm. The surface roughness Ra of the main surface 5A close to the center line C and the main surface 5B opposite the center line C were both 8 nm.

(Example 6)
Example 6 was manufactured by the same manufacturing method as Example 5, except for the paint used to form the light-shielding portion 5. In Example 6, the paint stock solution was diluted 1.5 times with an organic solvent and applied. As in Example 5, the surface roughness Ra of the eyepiece-side end face 5C was 8 nm. Furthermore, as a result of changing the dilution ratio of the paint, the surface roughness Ra of the display panel-side end face 5D was 9000 nm. The surface roughness Ra of the main surface 5A close to the center line C and the main surface 5B opposite the center line C were both 8 nm.

(Example 7)
Example 7 was manufactured by the same manufacturing method as Example 5, except for the paint used to form the light-shielding portion 5. In Example 7, the paint stock solution was diluted 10 times with an organic solvent and applied. As in Example 5, the surface roughness Ra of the eyepiece-side end face 5C was 8 nm. Furthermore, as a result of changing the dilution ratio of the paint, the surface roughness Ra of the display panel-side end face 5D was 25 nm. The surface roughness Ra of the main surface 5A close to the center line C and the main surface 5B opposite the center line C were both 8 nm.

(Example 8)
Example 8 was manufactured by the same manufacturing method as Example 5, except that the surface roughness Ra of the portion of the molding surface of the mold 12 used to form the base that serves as the base for the eyepiece-side end face 5C was 20 nm. The surface roughness Ra of the portion that serves as the base for the eyepiece-side end face 5C of the first base 2 transfer molded by the mold 12 was 18 nm. The surface roughness Ra of the eyepiece-side end face 5C formed by coating was 18 nm. The surface roughness Ra of the display panel-side end face 5D was 100 nm. The surface roughness Ra of the main surface 5A close to the center line C and the main surface 5B opposite the center line C were both 8 nm.

Example 9
Example 9 was manufactured by the same manufacturing method as Example 5, except that the uneven shape of the mold 12 used to form the base was a stripe shape. As in Example 5, the surface roughness Ra of the eyepiece side end face 5C was 8 nm. Also, the surface roughness Ra of the display panel side end face 5D was 100 nm. The surface roughness Ra of the main surface 5A close to the center line C and the main surface 5B opposite the center line C were both 8 nm.

(Example 10)
Example 10 was manufactured by the same manufacturing method as Example 5, except that, among the molding surfaces of the mold 12 used to form the base, the surface roughness Ra of the base portion of the main surface 5A closer to the center line C was 100 nm. As in Example 5, the surface roughness Ra of the eyepiece-side end surface 5C was 8 nm, the surface roughness Ra of the display panel-side end surface 5D was 100 nm, and the surface roughness Ra of the main surface 5B opposite the center line C was 8 nm, but the surface roughness Ra of the main surface 5A closer to the center line C was 100 nm.

Example 11
Example 11 was manufactured by the same manufacturing method as Example 7, except that the dilution ratio of the paint was made even larger than that of Example 7. As in Example 7, the surface roughness Ra of the eyepiece-side end face 5C was 8 nm. Furthermore, as a result of changing the dilution ratio of the paint, the surface roughness Ra of the display panel-side end face 5D was 8 nm. The surface roughness Ra of the main surface 5A close to the center line C and the main surface 5B opposite the center line C were both 8 nm.

(Comparative Example 4)
Comparative Example 4 is a specific example of Reference Form 4 described with reference to Figure 18(a), and was manufactured by the same manufacturing method as Example 5, except that the surface roughness Ra of the eyepiece-side end face 5C was roughened to 100 nm. That is, the surface roughness Ra of the portion of the molding surface of the mold 12 used to form the base that serves as the base for the eyepiece-side end face 5C was set to 100 nm, and the base was manufactured. The surface roughness Ra of the eyepiece-side end face 5C of Comparative Example 4 was 100 nm, which was larger than that of each of the Examples.

The evaluation results of the examples and comparative examples are summarized in Table 2 below.

When the louvers of Examples 5 to 11 were mounted on a head-mounted display, it was possible to prevent external light reflected by the eyepiece-side end face 5C, which has a large effect on image quality, from entering the user's eyes. In addition, in Examples 5 to 10, the occurrence of contrast reduction and the like caused by display light reflected by the display panel-side end face 5D was prevented. In addition, in Example 10, by making the surface roughness of the main surface 5A closer to the center line C larger than the surface roughness Ra of the main surface 5B opposite the center line C, it was also possible to obtain the effect of suppressing the influence of external light and the like reflected by these main surfaces. In contrast, when the louvers of Comparative Example 4 were mounted on a head-mounted display, some of the external light reflected by the eyepiece-side end face 5C, which has a large effect on image quality, tended to easily enter the user's eyes, and a decrease in image quality was observed.

[Third embodiment]
(Louver body)
The third embodiment differs from the first and second embodiments in that the louver 23 has a second light-shielding portion 30 on the side surface 2D. The shape of the light-shielding portion 5, which is the first light-shielding portion in the third embodiment, may be different from that of the first and second embodiments. However, as in the first embodiment, it is preferable that the surface roughness Ra of the light-shielding portion 5, which is the main surface closer to the center line C, is greater than the surface roughness Ra of the main surface 5B opposite the center line C. Also, as in the second embodiment, it is preferable that the surface roughness Ra of the eyepiece-side end surface 5C of the light-shielding portion 5 is less than 20 nm.

21(a) is a schematic cross-sectional view showing a cross section of a plate-like louver 23 according to the third embodiment cut in a direction perpendicular to the main surface. A second light-shielding portion 30 is formed on a side surface 2D of the louver 23. It is preferable that the second light-shielding portion 30 is formed so as to cover the entire side surface 2D. It is also preferable that the second light-shielding portion 30 is formed so as to cover a portion of the surface 2C on the eyepiece side of the first base 2 of the louver.
It is desirable to set the thickness of the second light-shielding portion 30 within the range of 0.1 μm to 45 μm inclusive. A thickness of 0.1 μm or more is for ensuring sufficient light-shielding performance against external light, and a thickness of 45 μm or less is for maintaining good accuracy of the outer shape of the element.

In embodiment 3A, as shown in FIG. 23(a), a second light-shielding portion 30 is formed to cover the outer periphery of the eyepiece-side surface 2C of the louver 23. It is desirable that the width M by which the second light-shielding portion 30 covers the eyepiece-side surface 2C of the louver 23 is in the range of 0.01 mm or more and 1 mm or less. If it is less than 0.01 mm, it is difficult to sufficiently cover the outer periphery in manufacturing, and if it exceeds 1 mm, there is a risk that the optically effective area of the louver will be narrowed.

The second light shielding portion 30 is formed using a light absorbing material that absorbs visible light. The light absorbing material used for the second light shielding portion 30 may be the same as that for the light shielding portion 5 inside the element, or may be different.
As the material that absorbs visible light, for example, paint containing a pigment or dye can be appropriately selected and used, but when it is particularly desired to enhance light absorption ability, it is preferable to select a black paint, and from the viewpoint of durability, it is preferable to use a pigment-containing material. Examples of pigments include ivory black, peach black, lamp black, bitumen, carbon black, black aniline, etc. Among these, it is particularly preferable to use carbon black and black aniline. It is also possible to appropriately use color materials for various purposes, such as obtaining different effects depending on the wavelength of incident external light.

(Surface roughness of second light shielding portion 30)
A preferred surface roughness of the second light-shielding portion 30 will be described with reference to FIG.
The fifth surface 30A, which is the surface opposite to the center line C in the second light-shielding portion 30, preferably has a surface roughness Ra of less than 20 nm. In addition, the surface on the center line C side in the second light-shielding portion 30 (the sixth surface 30B, which is the interface with the side surface 2D of the light-transmitting portion 2 of the second light-shielding portion 30) is preferably a rough surface having a surface roughness Ra greater than that of the fifth surface 30A.

When the louver is used, components of external light with a low angle of incidence are blocked by the user's head, and therefore the external light OL that enters the housing has a component with a high angle of incidence with respect to the louver.
In the louver 23 of the third embodiment, the fifth surface 30A of the second light-shielding portion 30 has a high flatness with a surface roughness Ra of less than 20 nm. Therefore, as shown in FIG. 22, most of the external light OL irradiated to the fifth surface 30A of the second light-shielding portion 30 at a high incidence angle is absorbed by the second light-shielding portion 30, but a part of the external light OL is reflected as reflected light OLR in a direction that does not reach the user's eye. That is, in the third embodiment, it is possible to suppress deterioration in image quality such as the occurrence of flare and ghosting due to reflection of the external light OL. Regarding the third embodiment, the influence of the display light IMG irradiated to the interface between the second light-shielding portion and the light-transmitting portion will be considered. In the third embodiment, the interface between the second light-shielding portion 30 and the light-transmitting portion (i.e., the sixth surface 30B) is a rough surface with a surface roughness Ra of 20 nm or more, so that a part of the display light IMG is reflected as scattered light IMGD as shown in FIG. 22. Since the light intensity of scattered light reflected in each direction is weak, even if there is an optical path that leads toward the user's eye, the light intensity is weak, and image quality degradation such as ghosts and reduced contrast is suppressed.
Furthermore, in embodiment 3A, as shown in Fig. 23(a), a second light-shielding portion 30 is formed so as to cover the outer periphery of the eyepiece-side surface 2C of the louver 23. Therefore, as shown in Fig. 23(a), part of the external light OL irradiated to the second light-shielding portion is reflected as reflected light OLR in a direction that does not reach the user's eye.

In contrast, in embodiment 3B shown in FIG. 23(b), the outer periphery of surface 2C on the eyepiece side of louver 23 is exposed to light-transmitting portion 2. Therefore, as shown in FIG. 23(b), external light OL is scattered, and the light rays that travel toward the user's eye as scattered light OLD may cause effects such as ghosting and reduced contrast.

Both embodiment 3A and embodiment 3B can suppress the occurrence of flare and ghosting caused by external light OL and display light IMG, but embodiment 3A is more effective at suppressing image quality degradation such as ghosting and reduced contrast caused by external light.

(Method of manufacturing louvers)
Next, a method for manufacturing the louver according to this embodiment will be described. The process for providing the second light-shielding portion 30 will be mainly described. In the manufacturing method according to this embodiment, as one method for controlling the surface roughness of the interface between the second light-shielding portion 30 of the louver and the light-transmitting portion 2, i.e., the sixth surface 30B, when the base serving as the base of the second light-shielding portion 30 is formed using a resin material, the surface roughness of the base is controlled to a predetermined surface roughness. The surface roughness of the base can be controlled by the molding conditions when the base is transfer-molded using a mold, i.e., the type of resin material, the temperature of the resin material at the time of injection, the pressure holding conditions, etc. In addition, the surface roughness of the molding surface of the mold used in transfer-molding the base is particularly useful as a parameter for controlling the surface roughness of the louver side surface. In addition, the surface roughness of the side surface of the substrate 1 can be controlled by the material of the substrate 1, the polishing conditions, the blasting conditions, etc.

In addition, in the manufacturing method according to this embodiment, one method for controlling the surface roughness of the fifth surface 30A of the second light-shielding portion 30 of the louver is to control it by coating the base with a light-shielding material under predetermined conditions. The predetermined conditions include, for example, the selection of a coating method such as liquid-phase coating or vacuum deposition, and a coating device. In the case of liquid-phase coating, the predetermined conditions include, for example, the physical properties of the paint (viscosity, temperature, additives, etc.), the coating method (dispenser, inkjet, coater, etc.), and the drying method (natural, air blow, oven, etc.). The amount of solvent contained in the paint is particularly useful as a parameter for controlling the surface roughness of the light-shielding portion of the louver.

The louver body is manufactured in the same manner as in the first and second embodiments. Next, in this embodiment, a second light-shielding portion 30 is formed on the side surface 2D of the louver body. Specifically, as shown in FIG. 24, the louver body is rotated around the center line C as the rotation axis, and the material for the second light-shielding portion is applied along the side surface 2D of the louver using a dispenser 14. After application is complete, the material is dried and hardened by heating and baking in an oven, thereby forming the second light-shielding portion 30 on the side surface 2D of the louver body.

In this example, the side surface 2D of the louver body, which has a surface roughness Ra of 20 nm or more and 2000 nm or less, is covered with a light-shielding material, forming an interface between the second light-shielding portion 30 and the light-transmitting portion 2. As a result, the surface shape of the interface between the second light-shielding portion 30 and the light-transmitting portion 2, i.e., the sixth surface, is a shape that is a direct inversion of the surface shape of the side surface 2D of the louver body, and has a surface roughness of 20 nm or more and 2000 nm or less. On the other hand, the surface shape of the fifth surface 30A on the front side, which is exposed when the light-shielding material is applied, can be controlled by the conditions when applying it using a dispenser.

For example, if the content ratio of the solvent in the paint forming the light-shielding portion is increased and the viscosity of the paint is reduced, a thin coating film can be formed, and the surface shape of the front side will relatively faithfully reflect the surface shape of the base. On the other hand, if the content ratio of the solvent in the paint is reduced and the viscosity of the paint is increased, the surface shape of the front side tends to differ from the surface shape of the base. Alternatively, it is possible to control the surface shape of the front side by changing the drying conditions after applying the paint (for example, whether or not air is blown). In this example, the content ratio of the solvent is adjusted and applied so that the surface roughness of the front side is smaller than the surface roughness of the base, and the surface roughness of the fifth surface of the second light-shielding portion formed as a result is controlled to be smaller than the surface roughness of the sixth surface.
By implementing the louver of the third embodiment in a head-mounted display, it is possible to transmit display light to the user's eyes with reduced loss and disturbance, and it is also possible to prevent external light and stray light within the head-mounted display from entering the user's eyes.

[Example]
Specific examples of the third embodiment and comparative examples are given below. Each sample of the examples was produced according to the second example of the manufacturing method described above. First, matters common to the examples and comparative examples are described.

Optical glass containing boron and silicon was used for the substrate 1. Specifically, a circular plate material with a diameter of 45 mm was prepared using S-BSL7 manufactured by Ohara Corporation. The mold 12 for forming the unevenness on the base was made by cutting a NiP layer plated on a metal base material with a precision machining machine to form the inverse shape of the desired unevenness. At this time, high-precision cutting was performed to adjust the surface roughness of the mold 12 surface.

The first base 2 was formed using an ultraviolet-curable acrylic resin composition with a refractive index of 1.58 after curing. When the light-shielding portion 5 was annular, the substrate 1 was rotated around the center of the concentric circle of the first base 2 as the center of rotation, and the paint that was the raw material for the light-shielding portion was applied from an oblique direction using a dispenser. When the light-shielding portion 5 was striped, the first base 2 and the dispenser were scanned relatively along a straight line, and the paint that was the raw material for the light-shielding portion was applied from an oblique direction. The dispenser was used because it can supply an appropriate amount of discharge to form a film thickness of about 10 μm, and the number of light-shielding portions 5 formed per substrate is small, about 20, and it is compatible with the previous and next processes. The paint was applied by diluting the original solution with an organic solvent. After that, it was heated and dried in an oven at 80°C for 4 hours.

The shape of the first light-shielding portion in plan view in Examples 12 to 17 and Comparative Example 5 was concentric as shown in FIG. 21(b), and the pitch P between the light-shielding portions (the distance between adjacent light-shielding portions, or the difference in radius between adjacent concentric circles) was 1 mm. The length L1 of the light-shielding portion 5 in the optical axis direction was 1 mm. The thickness t of the light-shielding portion (the width of the light-shielding portion when viewed from the direction of the optical axis OX) was 10 μm. The shape of the first light-shielding portion in plan view in Example 15 was parallel stripes as shown in FIG. 21(c).
Next, the second base 3 was formed from the same ultraviolet-curable acrylic resin composition as the first base 2, and a louver body not having a second light-shielding portion was produced.

Then, while rotating the louver body around the center line C, a dispenser was used to apply the paint that will be the raw material for the second light-shielding portion 30. The paint was applied by diluting the original solution with an organic solvent. It was then heated and dried in an oven at 80°C for 4 hours. The refractive index of the paint after drying was 1.68.

Each sample was evaluated as follows: A head-mounted display equipped with the louver element to be evaluated was placed in a dark room that was not affected by external light, and a digital camera was placed at a position that would correspond to the user's eyes when wearing the head-mounted display.

First, in order to evaluate image quality degradation caused by reflection of display light at the interface between the second light-shielding portion 30 and the light-transmitting portion, a chart in which 1 mm square white and black squares are arranged in a grid pattern was displayed on a head-mounted display and photographed with a digital camera. The ratio of white display portions to black display portions in the data was 1:1. The average light intensity of the five white display portions photographed with the digital camera was taken as the white display portion intensity, and the average light intensity of the five black display portions was taken as the black display portion intensity.
The ratio of the intensity of the black display portion to the intensity of the white display portion of the display light was 0.01 or less, and the ratio was evaluated as A, i.e., excellent. The ratio of the intensity of the black display portion to the intensity of the white display portion of the display light was 0.01 or more, and the ratio was evaluated as B, i.e., poor.

Next, in order to evaluate the degradation of image quality caused by the scattering of external light on the fifth surface 30A of the second light-shielding portion 30, a white parallel light with a diameter of 5 mm simulating external light was irradiated using an LED light. The irradiation direction of the white parallel light was three levels inclined at 45°, 60°, and 75° with respect to the YZ plane of the louver element, and two levels each corresponding to the upper rear and lateral rear as seen from the user were irradiated at a total of six levels. The irradiation position of the white parallel light was irradiated at the side position of the louver. The light intensity per unit area of the white parallel light was 100 times the light intensity of the display panel 21 when displaying white. The display panel 21 was photographed with a digital camera while the LED light was turned on while displaying white. The light intensity average value of the five white display parts photographed with the digital camera was taken as the white display part intensity. After that, the LED light was turned on while displaying black, and the six levels were irradiated, and the light intensity average value of the entire surface photographed with the digital camera was taken as the unnecessary light intensity.

When the ratio of the unwanted light intensity to the white display portion intensity of the display light was 0.01 or less, it was rated as A, i.e., excellent, and when it was greater than 0.01 and less than 0.02, it was rated as A-, i.e., good. When the ratio of the unwanted light intensity to the white display portion intensity of the display light was greater than 0.02, it was rated as B, i.e., poor.

Example 12
The substrate 1 used had a surface roughness Ra of 100 nm on the side surface. The surface roughness Ra of the molded surface of the mold 12 forming the louver side surface was 100 nm. The surface roughness Ra of the louver side surface transferred by the mold 12 was 100 nm. A dispenser was used to apply paint, which is the raw material of the second light-shielding portion, to the side surface 2D of the louver. The paint was applied to a range of 0.3 mm from the side surface so as to cover the surface 2C on the eyepiece side from the side surface of the louver. The paint stock solution was diluted 4 times with an organic solvent and applied. The surface roughness Ra of the sixth surface 30B, which is the interface of the light-transmitting portion 2 of the second light-shielding portion 30, was 100 nm. The surface roughness Ra of the fifth surface 30A of the second light-shielding portion was 8 nm. As described above, in Example 12, the surface roughness Ra satisfies the relationship of the sixth surface 30B>the fifth surface 30A.

(Example 13)
The light-shielding material was applied to the side of the louver on the eyepiece side so as to leave the corners exposed, but the louver samples were fabricated in the same manner as in Example 12.

(Example 14)
The substrate 1 used had a surface roughness Ra of 1800 nm on the side. The surface roughness Ra of the molding surface of the mold 12 forming the louver side was 1800 nm. The surface roughness Ra of the side 2D of the louver transfer molded by the mold 12 was 1800 nm. A paint stock solution diluted four times with an organic solvent was applied. The surface roughness Ra of the sixth surface 30B, which is the interface with the light transmitting portion of the second light shielding portion 30, was 1800 nm. The surface roughness Ra of the fifth surface 30A of the second light shielding portion was 18 nm.

(Example 15)
Except for the fact that the uneven shape of the mold 12 used to form the base was a stripe shape, this was manufactured by the same manufacturing method as in Example 12. The surface roughness Ra of the sixth surface 30B, which was the interface with the light-transmitting portion of the second light-shielding portion 30, was 100 nm. The surface roughness Ra of the fifth surface 30A of the second light-shielding portion was 8 nm.

(Example 16)
The paint stock solution was diluted 20 times with an organic solvent and applied. Except for this, a louver sample was prepared in the same manner as in Example 12. The surface roughness Ra of the sixth surface 30B, which is the interface between the second light-shielding portion 30 and the light-transmitting portion, was 20 nm. The surface roughness Ra of the fifth surface 30A of the second light-shielding portion was 20 nm.

(Example 17)
The side surface of the substrate 1 used had a surface roughness Ra of 18 nm. The molding surface of the mold 12 forming the louver side surface had a surface roughness Ra of 18 nm. The side surface 2D of the louver transfer molded by the mold 12 had a surface roughness Ra of 18 nm. The paint stock solution was diluted 20 times with an organic solvent and applied. A louver sample was otherwise produced in the same manner as in Example 12. The surface roughness Ra of the sixth surface 30B, which is the interface with the light transmitting portion of the second light shielding portion 30, was 18 nm. The surface roughness Ra of the fifth surface 30A of the second light shielding portion was 18 nm.

(Comparative Example 5)
No paint was applied to the side surfaces of the louver, and no second light-shielding portion was formed. Except for this, a louver sample was produced in the same manner as in Comparative Example 1. Although there was no second light-shielding portion, the surface roughness Ra of the louver side surfaces was 100 nm.

The evaluation results of the examples and comparative examples are summarized in Table 3 below.

When the louvers of Examples 12 to 17 were mounted on a head-mounted display, it was possible to prevent external light scattered by the sides of the louvers, which has a large impact on image quality, from entering the user's eyes. Furthermore, in Examples 12 to 17, a decrease in contrast and the like caused by display light reflected by the sides of the louvers entering the user's eyes was prevented. In particular, in Examples 12, 14, and 15, the second light-shielding portion 30 covered the outer periphery of the surface 2C on the eyepiece side, which also provided the effect of suppressing the effects of external light scattering. In contrast, when the louvers of Comparative Example 5 were mounted on a head-mounted display, a decrease in image quality was observed due to scattering of external light or reflection of display light.

[Other embodiments]
The present invention is not limited to the above-described embodiment and examples, and many modifications are possible within the technical concept of the present invention. Different embodiments and examples described above may be combined and implemented.
For example, in the above-mentioned example of the manufacturing method, the surface roughness of the base part that serves as the base of the light-shielding member is controlled by transfer molding using a mold, and the surface roughness of the side exposed at the time of applying the light-shielding material is controlled by the solvent content in the paint and the drying conditions. However, the method of controlling the surface roughness of the light-shielding member is not limited to the example, and for example, after covering the light-shielding member, the surface roughness of the light-shielding member may be controlled by processing the surface of the exposed side by carrying out a grinding process or a blasting process. Alternatively, when the light-shielding member is formed by vacuum film formation (e.g., vapor deposition), the surface roughness of the front side can be controlled by adjusting the film formation conditions.

The shape of the light-shielding portion 5 is not limited to the example shown in FIG. 1 etc., but can be changed as appropriate according to the angle of view determined by the display panel 21 and the optical element 22. For example, as shown in the cross section of FIG. 14, the inclination of the main surface of the light-shielding portion 5 may change as it moves away from the center line C of the louver 23.

The shape of the light-shielding portion 5 in a plan view is not limited to the multiple concentric circles shown in FIG. 3(b) or the stripe shape shown in FIG. 3(c). The shape in a plan view may be, for example, multiple concentric arcs with different diameters, an ellipse, or a polygon.

Furthermore, the method of evaluating the image quality is not limited to the method of the above-mentioned embodiment. For example, when evaluating the degradation of image quality caused by the reflection of the display light on the main surface of the light-shielding part, various charts such as checkered or lattice patterns may be displayed on the display panel, and the in-plane uniformity, contrast, sharpness, etc. of the image may be subjectively evaluated by an observer.
In addition, when evaluating the degradation in image quality caused by external light or stray light reflected from external light being reflected by the main surface of the light-shielding portion, the LEDs may be switched on and off while displaying black on the display panel, and a comparison may be made based on a subjective evaluation by an observer.

The louvers of the present invention may be provided in optical devices other than head-mounted displays, such as handheld displays, cameras that capture still or video images, microscopes, and endoscopes.

The disclosure of the above-described embodiment includes the following configurations.
[Configuration 1]
a light-shielding portion made of a light-shielding material is provided inside a base made of a light-transmitting material;
among the surfaces of the light-shielding portion in contact with the light-transmitting material, a surface on an outer edge side of the base is defined as a second surface, and a surface opposite to the second surface is defined as a first surface, the surface roughness of the first surface is larger than the surface roughness of the second surface;
A louver characterized by:
[Configuration 2]
The surface roughness Ra of the first surface is 20 nm or more and 2000 nm or less.
2. The louver of claim 1.
[Configuration 3]
The surface roughness Ra of the second surface is 20 nm or less.
3. The louver according to claim 1 or 2.
[Configuration 4]
a light-shielding portion made of a light-shielding material is provided inside a base made of a light-transmitting material;
a surface roughness Ra of a third surface of the light-shielding portion, the third surface being an eyepiece-side end surface of the light-shielding portion in contact with the light-transmitting material, is less than 20 nm;
A louver characterized by:
[Configuration 5]
a fourth surface, which is an end surface on a display panel side among surfaces of the light-shielding portion in contact with the light-transmitting material, has a surface roughness Ra greater than a surface roughness Ra of the third surface;
5. The louver according to claim 4,
[Configuration 6]
The surface roughness Ra of the fourth surface is 20 nm or more.
6. The louver according to claim 5,
[Configuration 7]
The width of the third surface is 5 μm or more and 45 μm or less.
7. The louver according to any one of claims 4 to 6.
[Configuration 8]
Among the surfaces of the light-shielding portion that are in contact with the light-transmitting material, when a surface on an outer edge side of the base is defined as a second surface and a surface opposite to the second surface is defined as a first surface,
The surface roughness of the first surface is greater than the surface roughness of the second surface.
8. The louver according to any one of claims 4 to 7.
[Configuration 9]
The surface roughness Ra of the first surface is 20 nm or more and 2000 nm or less.
9. The louver of claim 8.
[Configuration 10]
The surface roughness Ra of the second surface is 20 nm or less.
10. The louver according to claim 8 or 9.
[Configuration 11]
a first light-shielding portion made of a light-shielding material is provided inside a base made of a light-transmitting material;
A second light-shielding portion made of a light-shielding material is provided on at least a part of a side surface of the base portion.
A louver characterized by:
[Configuration 12]
a surface roughness Ra of a sixth surface of the second light-shielding portion in contact with a side surface of the base portion is greater than a surface roughness Ra of a fifth surface of the second light-shielding portion located on the opposite side to the sixth surface;
12. The louver of claim 11.
[Configuration 13]
The surface roughness Ra of the sixth surface is 20 nm or more and 2000 nm or less.
13. The louver of claim 12.
[Configuration 14]
The surface roughness Ra of the fifth surface is 20 nm or less.
14. The louver according to claim 12 or 13.
[Configuration 15]
the second light-shielding portion extends from a side surface of the base portion to a part of the eyepiece-side principal surface;
15. The louver according to any one of claims 11 to 14.
[Configuration 16]
A second light-shielding portion made of a light-shielding material is provided on at least a part of a side surface of the base of the louver according to any one of configurations 1 to 10.
16. The louver according to any one of claims 11 to 15.
[Configuration 17]
17. The louver according to any one of claims 1 to 16,
A display panel;
an optical unit that directs display light output from the display panel to a user's eye;
The louver is disposed in an optical path of the display light traveling from the optical unit to the user's eye.
A head mounted display characterized by:
[Configuration 18]
17. An optical device comprising the louver according to any one of configurations 1 to 16 and a housing supporting the louver.

The disclosure of the above-described embodiments includes the following methods.
[Method 1]
In a method for manufacturing a louver,
forming a base having a predetermined surface roughness from a resin material;
and forming a light-shielding portion by covering the base with a light-shielding material under predetermined conditions,
When the surface of the light-shielding portion on the center side of the louver is defined as a first surface and the surface on the outer edge side of the louver is defined as a second surface, the predetermined surface roughness of the base and the predetermined conditions for covering the light-shielding material are controlled so that the surface roughness of the first surface is greater than the surface roughness of the second surface.
A method for manufacturing a louver comprising the steps of:
[Method 2]
The predetermined surface roughness of the base is controlled by molding conditions when the base is transfer molded using a mold.
2. A method for producing the louver according to claim 1.
[Method 3]
The predetermined surface roughness of the base is controlled by the surface roughness of a molding surface of a mold used when transfer molding the base.
3. A method for producing the louver according to method 1 or 2.
[Method 4]
The predetermined conditions for coating the light-shielding material are controlled by an apparatus for coating the light-shielding material, and/or the physical properties of a paint containing the light-shielding material, and/or a drying method.
4. A method for manufacturing a louver according to any one of Methods 1 to 3.
[Method 5]
The predetermined condition for coating the light-shielding material is controlled by the amount of a solvent contained in a paint for coating the light-shielding material.
5. A method for manufacturing a louver according to any one of Methods 1 to 4.
[Method 6]
The surface roughness Ra of the first surface is controlled to be 20 nm or more and 2000 nm or less.
6. A method for manufacturing a louver according to any one of Methods 1 to 5.
[Method 7]
The surface roughness Ra of the second surface is controlled to 20 nm or less.
7. A method for manufacturing a louver according to any one of Methods 1 to 6.
[Method 8]
In a method for manufacturing a louver,
forming a base having a predetermined surface roughness from a resin material;
and forming a light-shielding portion by covering the base with a light-shielding material under predetermined conditions,
the predetermined surface roughness of the base and the predetermined conditions for coating the light-shielding material are controlled so that the surface roughness Ra of an eyepiece-side end face of the light-shielding portion is less than 20 nm.
A method for manufacturing a louver comprising the steps of:
[Method 9]
The predetermined surface roughness of the base is controlled by molding conditions when the base is transfer molded using a mold.
9. The method of claim 8, wherein the louver is
[Method 10]
The predetermined surface roughness of the base is controlled by the surface roughness of a molding surface of a mold used when transfer molding the base.
10. A method for producing a louver according to method 8 or 9.
[Method 11]
The predetermined conditions for coating the light-shielding material are controlled by an apparatus for coating the light-shielding material, and/or the physical properties of a paint containing the light-shielding material, and/or a drying method.
11. A method for producing a louver according to any one of methods 8 to 10.
[Method 12]
The predetermined condition for coating the light-shielding material is controlled by the amount of a solvent contained in a paint for coating the light-shielding material.
12. A method for producing a louver according to any one of methods 8 to 11.
[Method 13]
The surface roughness Ra of the display panel side end surface of the light-shielding portion is controlled to be 20 nm or more.
13. A method for producing a louver according to any one of methods 8 to 12.
[Method 14]
14. The method of claim 8, further comprising the steps of:
Furthermore, a second light-shielding portion made of a light-shielding material is formed on at least a part of a side surface of the base portion.
A method for manufacturing a louver comprising the steps of:

1: Substrate / 2: First base / 3: Second base / 4: Part that holds the light-shielding part 5 / 5: Light-shielding part / 5A: Main surface closer to the center line C / 5B: Main surface opposite the center line C / 11: Resin material / 12: Mold / 13: Ultraviolet light source / 14: Dispenser / 15: Template / 16: Resin material / 21, 21L, 21R: Display panel / 22: Optical element / 23: Louver / 24: Eye / 25: External light / 30: Second light-shielding part / 100: Head-mounted display / EW, EWL, EWR: Window material / IMG: Display light / NF: Nose pad / OX: Optical axis / PBS: Polarizing beam splitter / PF: Frame

Claims (12)

a head mounted display including a louver, a display panel, and an optical unit that directs display light output from the display panel to a user's eye; the louver being disposed in an optical path of the display light directed from the optical unit to the user's eye,
The louver is
a light-shielding portion made of a light-shielding material is provided inside a base made of a light-transmitting material;
When the surface of the light-shielding portion that is in contact with the light-transmitting material on the outer edge side of the base is defined as a second surface, and the surface opposite to the second surface is defined as a first surface,
the surface roughness of the first surface is greater than the surface roughness of the second surface;
The first surface of the light blocking portion is a surface closer to the optical axis of the optical path than the second surface.
A louver characterized by: The surface roughness Ra of the first surface is 20 nm or more and 2000 nm or less.
2. The louver of claim 1. The surface roughness Ra of the second surface is 20 nm or less.
3. A louver according to claim 1 or 2. a surface roughness Ra of a third surface of the light-shielding portion, the third surface being an eyepiece-side end surface of the light-shielding portion in contact with the light-transmitting material, is less than 20 nm;
2. The louver of claim 1 . When the surface of the light-shielding portion that is in contact with the light-transmitting material is the eyepiece-side end surface as a third surface and the surface that is the display panel-side end surface as a fourth surface,
The surface roughness Ra of the fourth surface is greater than the surface roughness Ra of the third surface.
2. The louver of claim 1 . a fourth surface of the light-shielding portion that is in contact with the light-transmitting material and is a display panel side end surface has a surface roughness Ra of 20 nm or more;
2. The louver of claim 1 . The width of the third surface is 5 μm or more and 45 μm or less.
5. The louver of claim 4 . A second light-shielding portion made of a light-shielding material is further provided on at least a part of a side surface of the base portion.
2. The louver of claim 1 . a surface roughness Ra of a sixth surface of the second light-shielding portion in contact with a side surface of the base portion is greater than a surface roughness Ra of a fifth surface of the second light-shielding portion located on the opposite side to the sixth surface;
9. The louver of claim 8 . The surface roughness Ra of the sixth surface is 20 nm or more and 2000 nm or less.
10. The louver of claim 9 . The surface roughness Ra of the fifth surface is 20 nm or less.
10. The louver of claim 9 . A louver according to any one of claims 1 to 11 ;
A display panel;
an optical unit that directs display light output from the display panel to a user's eye;
The louver is disposed in an optical path of the display light traveling from the optical unit to the user's eye.
A head mounted display characterized by:

Images