JP7740348B2 - Reflective transparent member and image display system - Google Patents

Description

The present invention relates to a reflective transparent component and an image display system.

An example of a reflective screen that can visually display the image light projected from a projector and also allow the image on the back of the screen to be observed is the reflective transparent screen described in Patent Document 1.

The reflective transparent screen described in Patent Document 1 exhibits relatively high brightness over a wide area of the screen. As shown in Figure 14, the reflected light intensity distribution of the reflective transparent screen is Gaussian. In Figure 14, the horizontal axis x indicates a certain direction parallel to the plane of the screen. Hereinafter, relatively high brightness will be referred to as "moderate brightness." Furthermore, relatively high reflected light intensity will be referred to as "moderate reflected light intensity."

International Publication No. 2020/110961

When the reflective transparent screen described in Patent Document 1 is used, referring to Figure 14, it can be seen that the range of high reflected light intensity, i.e., the region near the peak value, is narrow. In other words, because the range of high brightness (see region P in Figure 14) is narrow, the brightness corresponding to the desired light-focusing range (e.g., the region where the observer is present) is high. However, even in regions outside the desired light-focusing range (e.g., the region where the observer is not present), the reflected light intensity is moderate (see region Q in Figure 14). Note that in Figure 14, B indicates the peak value. B/2 indicates half of the peak value. Furthermore, while Figure 14 shows the reflected light intensity distribution in the x direction, when the reflective transparent screen described in Patent Document 1 is used, a similar reflected light intensity distribution is exhibited in the y direction, which is perpendicular to the x direction, on the same plane.

When the reflective transparent screen described in Patent Document 1 is used, moderate brightness is exhibited over a wide area of the screen, but the area near the peak value of reflected light intensity is narrow. Furthermore, since the reflected light intensity is relatively high even in areas where no observer is present, it can be said that the utilization efficiency of reflected light is reduced.

The present invention aims to provide a reflective transparent component and an image display system that can expand the area of high brightness while preventing a decrease in the utilization efficiency of reflected light.

In the present invention, the reflective transparent member includes a reflective transparent screen, a reflective diffraction grating, a radio wave reflective transparent element, a HUD (head-up display), and the like.
The reflective transparent component according to the present invention comprises a first transparent layer having an uneven surface, a reflective layer on the uneven surface, and a second transparent layer formed on the uneven surface of the reflective layer so as to fill the unevenness, and is characterized in that the full width at half maximum of the luminance distribution in a first direction due to reflected light is 20% or more larger than the full width at half maximum of the luminance distribution in a second direction perpendicular to the first direction, and the luminance distribution in at least the first direction exhibits a top-hat shape.

The present invention makes it possible to obtain a reflective transparent component and an image display system that can expand the area of high brightness while preventing a decrease in the utilization efficiency of reflected light.

1 is an explanatory diagram conceptually showing the function of a reflective transparent member according to the present invention. FIG. 2 is a cross-sectional view showing a cross section of a main part of a reflective transparent member. FIG. 2 is a perspective view showing a unit lens that constitutes a part of the reflective transparent member of the first embodiment. 10A and 10B are three-view diagrams for explaining an example of a first reference direction and a second reference direction. FIG. 4 is an explanatory diagram for explaining an example of a first reference direction and a second reference direction. FIG. 2 is an explanatory diagram for explaining an example of the structure of a reflective transparent member according to the first embodiment. FIG. 1 is a cross-sectional view showing an example of the structure of an image projection structure. FIG. 2 is a cross-sectional view showing an example of the structure of a reflective transparent member. 10A and 10B are explanatory diagrams for explaining an example of the structure of a reflective transparent member according to a second embodiment. FIG. 2 is an explanatory diagram showing the reflected light intensity distribution when light is incident on a screen. FIG. 10 is an explanatory diagram for explaining a preferable distribution of reflected light intensity. FIG. 4 is an explanatory diagram showing an example of the distribution of the shapes of the unit lenses 110. FIG. 10 is an explanatory diagram showing parameter values and the like in Examples and Comparative Examples. FIG. 10 is an explanatory diagram showing the reflected light intensity distribution when the reflective transparent member described in Patent Document 1 is used.

Embodiments of the present invention will be described below with reference to the drawings. In this specification, the side of the observer relative to the reflective transparent member (hereinafter referred to as the transparent screen) will be referred to as the front, and the side opposite the observer relative to the transparent screen will be referred to as the rear.

Figure 1 is an explanatory diagram conceptually illustrating the function of a reflective transparent member according to the present invention. As shown in Figure 1, a projector 200, an example of a movie projector, is installed at a predetermined position in front of a transparent screen 100. A general projector can be used as the projector 200. The transparent screen 100 reflects the light (incident light) of the image from the projector 200. Light (reflected light) from most of the area (e.g., the entire area) of the transparent screen 100 is reflected toward the observer 300. Note that while Figure 1 shows the projector 200 and the observer 300 as being at the same height, in reality, the projector 200 is installed above, below, to the left, or to the right of the observer 300.

Figure 2 illustrates a cross section (longitudinal cross section) of a key portion of the transparent screen 100 of this embodiment. As shown in Figure 2, the transparent screen 100 has a first transparent layer 32 having an uneven surface formed thereon, a reflective layer 40 formed on the uneven surface of the first transparent layer 32, and a second transparent layer 52 formed on the reflective layer 40. The second transparent layer 52 is formed on the reflective layer 40 so as to fill the unevenness. The surface 51 of the second transparent layer 52 opposite the reflective layer 40 may be a flat plane or a curved surface. Furthermore, the back surface (reference surface) 31 of the first transparent layer 32 may be a flat plane or a curved surface.

When the manufactured transparent screen 100 is put to practical use, the second transparent layer 52 is located in the front, i.e., on the observer side. Furthermore, a system including the transparent screen 100 and the projector 200 is an image display system.

First embodiment.
3 is a perspective view showing a unit lens 110 constituting a part of the transparent screen 100 of the first embodiment. The surface shape of the first transparent layer 32 of the transparent screen 100 (corresponding to the shape of the reflective layer 40) is a shape in which the unit lenses 110 are arranged. Specifically, the surface shapes of the plurality of unit lenses 110 realize the unevenness of the first transparent layer 32. In other words, the surface shape of the reflective layer 40 is realized by the surface shapes of the plurality of unit lenses 110.

Hereinafter, the individual lenses constituting the unit lens 110 will also be referred to as small lenses 110 ₁ to 110 ₉ .

3 illustrates a unit lens 110 including 3×3 (=9) small lenses 110 ₁ to 110 _9. Also, while FIG. 3 illustrates small lenses 110 ₁ to 110 ₉ that have a rectangular shape when viewed from the front (shape in plan view), the shape of the small lenses is not limited to a rectangle and may be a polygon with three or more sides or a circle.
In FIG. 3, the x direction represents a first reference direction shown in FIG. 4, which will be described later, and the y direction represents a second reference direction shown in FIG.

Fig. 4 is a three-view diagram for explaining the "first reference direction" and "second reference direction" for the small lenses _110-1 to _110-9 used in this embodiment and embodiments described later. Fig. 4(A) is a front view, Fig. 4(B) is a side view, and Fig. 4(C) is a plan view. Note that Fig. 4 illustrates three small lenses _110-1 to _110-3 .

The "first reference direction" is, for example, one direction that forms the largest angle (tilt angle θ ₁ ) in a cross-sectional view with respect to the reference plane 41 (see FIG. 4A). As an example, the reference plane 41 is a plane that is perpendicular to the normal to the transparent screen 100. The "second reference direction" is, when the "first reference direction" is selected, the direction that forms the largest angle (tilt angle θ ₂ ) in a cross-sectional view in a direction perpendicular to the line obtained by projecting the line indicating the "first reference direction" onto the reference plane (see FIG. 4C).

The curvature in the first reference direction and the curvature in the second reference direction of each of the small lenses 110 ₁ to 110 ₉ may be the same or different. Here, the curvature in the first reference direction or the second reference direction may be 0, i.e., the surface may be flat.

For convenience, as shown in Figure 5, the height direction of the transparent screen 100 may be the second reference direction, and the longitudinal direction of the transparent screen 100 (the direction perpendicular to the second reference direction) may be the first reference direction. Even when the shape of the transparent screen 100 is curved and concave toward the back side (rear side) when viewed from the front, the height direction of the transparent screen 100 is the second reference direction. The first reference direction is, for example, parallel to a plane perpendicular to the normal at the center of the transparent screen 100 and perpendicular to the second reference direction.

As shown in Fig. 6, in this embodiment, the surface shape of the first transparent layer 32 of the transparent screen 100 is realized by arranging a large number of unit lenses 110 over the entire surface. The angle (tilt angle θ1) of each unit lens 110 in the first reference direction and the angle (tilt angle _θ2 ) in the second reference direction are set so that incident light is reflected toward a viewer 300 present in a specific area across the entire transparent screen _100. That is, the surface shape of the first transparent layer 32 (corresponding to the shape of the reflective layer 40) is realized by the shape of the unit lenses 110 whose angles in the first reference direction and the second reference direction are set as described above. The tilt angle _θ1 is defined as a positive value when the angle formed by the unit lenses 110 is counterclockwise when viewed from the second reference direction relative to the reference plane of the first reference direction, and as a negative value when the angle is clockwise. The tilt angle _θ2 is defined as a positive value when the angle formed by the unit lenses 110 is counterclockwise when viewed from the first reference direction side relative to the reference plane of the second reference direction, and as a negative value when the angle is clockwise.

In reality, the uneven surface of the reflective layer 40 (corresponding to the uneven surface of the first transparent layer 32) is formed over the entire area of the transparent screen 100 in a single process.

Furthermore, assuming that the transparent screen 100 is incorporated into a vehicle windshield, the specific area is typically the driver's seat and passenger seat. The specific area may also be the rear seat. Furthermore, assuming that there are multiple observers 300, unit lenses of multiple shapes are used, and each unit lens is configured to reflect light to each of the observers. An example of a case in which there are multiple observers 300 is when there is an observer 300 in the driver's seat and passenger seat inside the vehicle. Another example is when there are multiple observers 300 in the rear seats inside the vehicle. Furthermore, even if there is actually only one observer 300, if that observer 300 moves around inside the vehicle, it can still be considered that there are essentially multiple observers 300.

Each unit lens 110 shown in FIG. 6 is composed of a surface with an inclination angle that reflects light incident on the projection area toward the viewer. In the first embodiment, the surface shape of the first transparent layer 32 of the transparent screen 100 is such that unit lenses 110 whose shapes are determined as described above are arranged across the entire area of the transparent screen 100. In other words, the transparent screen 100 has unit lenses 110 that focus reflected light to a focusing point, and has a structure in which unit lenses 110 of the same shape are arranged two-dimensionally when viewed from above (when observed from the surface side of the transparent screen 100).

The tilt angle of each unit lens 110 is set by randomly selecting a focal point of reflected light set at an arbitrary position. In other words, the tilt angle of each unit lens 110 is set so that incident light is reflected at a randomly selected focal point. Furthermore, the random ratio of focal points selected for each unit lens 110 (the probability that each focal point is selected) is set to an arbitrary ratio.

Fine irregularities may also be formed on the surface of the unit lenses. Details of the fine irregularities will be described later.

Figure 7 is a cross-sectional view showing an example of the structure of an image projection structure 120, which is the substrate of a transparent screen 100 according to the present invention. In the structure illustrated in Figure 7, the image projection structure 120 is formed on a transparent substrate 60.

The transparent substrate 60 is, for example, glass or transparent resin. When glass is used as the transparent substrate 60, it is preferable to use soda lime glass or alkali-free glass. The glass may be chemically strengthened or hard-coated to improve durability. When a transparent resin is used as the transparent substrate 60, it is preferable to use polycarbonate, PET, PEN, cycloolefin polymer, etc. It is preferable that the transparent substrate 60 does not have birefringence. It is also preferable to select a thickness for the transparent substrate 60 that will maintain its durability as a substrate.

The first transparent layer 32 is preferably a transparent resin layer. Examples of transparent resins constituting the transparent resin layer include acrylic resin, epoxy resin, polycarbonate resin, silicone resin, unsaturated polyester resin, and mixed resins of these. The resin is preferably a photocurable resin, a thermosetting resin, or a thermoplastic resin. The transmittance of the first transparent layer 32 is preferably 50% or more, more preferably 75% or more, and even more preferably 90% or more.

In addition, it is preferable that the first transparent layer 32 be formed from a resin with a refractive index of 1.4 or higher, since this reduces the angle of inclination at which the image light is refracted when it enters the first transparent layer 32 and reflected toward the viewer.

The first transparent layer 32 may be composed of multiple layers and may contain a filler. When composed of multiple layers, the difference in refractive index between the layers or between the filler and the resin layer serving as a binder is preferably 0.05 or less to suppress cloudiness, more preferably 0.02 or less to enhance transparency, and even more preferably 0.01 or less to suppress deterioration of rear visibility similar to halo-like blurring.
An example of the filler is silica filler.

The second transparent layer 52 is preferably a transparent resin layer. The difference between the refractive index of the first transparent layer 32 and the refractive index of the second transparent layer 52 is preferably small, more preferably 0.05 or less. The second transparent layer 52 and the first transparent layer 32 may be formed of the same material or different materials, but are preferably formed of the same material. When the second transparent layer 52 and the first transparent layer 32 are formed of the same transparent resin, the refractive indices of the two can be easily matched. Furthermore, as with the first transparent layer 32, the transmittance of the second transparent layer 52 is preferably 50% or more, more preferably 75% or more, and even more preferably 90% or more.

The second transparent layer 52 may also be composed of multiple layers. It may also contain a filler. When composed of multiple layers, the difference in refractive index between the layers and between the filler and the resin layer that serves as the binder is preferably 0.05 or less to suppress cloudiness, more preferably 0.02 or less to enhance transparency, and even more preferably 0.01 or less to suppress deterioration of rear visibility similar to halo-like blurring.

The reflective layer 40 may be a single-layer or multi-layer metal or dielectric film, or a combination thereof. Examples of the reflective layer 40 include a film formed of a metal selected from Au, Ag, Pt, Cu, Ru, Ir, Rh, Os, Bi, Nd, Al, Ni, Ti, Pd, Co, Si, Ta, W, Mo, and Ge, an alloy containing two or more of these metals, or a material primarily composed of an oxide such as NbO or _SiO2 . A portion of the light incident on the reflective layer 40 is transmitted, and the other portion is reflected. The reflective layer 40 is preferably formed of Ag or Al, or an alloy of Ag and at least one metal selected from the group consisting of Pd, Au, Pt, Cu, Ru, Ir, Rh, Os, Bi, Nd, and Ge, as this facilitates achieving both brightness of the projected image and transmittance of the image projection structure 120.

Below, a manufacturing example of the image projection structure 120 in the first embodiment will be described with reference to Figure 7. However, the manufacturing examples shown below are illustrative of the present invention, and the present invention is not limited to these.

A PET film (0.075 mm thick) was prepared as the support member (transparent substrate 60). A mold with the desired shape (as illustrated in Figures 3 and 4) on its surface was prepared as the molding tool. The mold had a shape corresponding to the shape of the unit lenses described below (hereinafter also referred to as the unit shape).

The molding molds used can be processed not only by bit machining, but also by laser machining or photolithography. When processed by laser machining or photolithography, the peaks and valleys of the processed shape are rounded, which reduces the haze value. In addition, because the reproducibility of the peaks and valleys of the processed shape is lower than with bit machining, the periodicity of the shape is eliminated, making it possible to suppress diffraction.

Next, a first resin was applied onto the PET film using a die coating method to form a first transparent layer 32. The first resin used was a bifunctional UV-curable acrylic resin (acrylic equivalent: 152).

Next, a molding die was placed on top of the first resin so that the side with the irregularities was in contact with the first resin. In this state, 1000 mJ of UV light was irradiated from the opposite side of the molding die to harden the first resin and form a first transparent layer 32.

After that, the mold was removed, and a first transparent layer 32 (approximately 35 μm thick) with an uneven surface was formed on the PET film. The unevenness of the lens, described below, had been transferred to this uneven surface.

Next, an Ag-Au alloy layer was deposited by sputtering on the uneven surface of the first transparent layer 32 to form the reflective layer 40. The thickness of the reflective layer 40 was 15 nm.

Next, an adhesion layer resin (not shown in Figure 7) was applied on top of the reflective layer 40 using a die coating method. The adhesion layer resin was a linear polymer resin with a Tg of 47°C, primarily composed of a polyester resin made from dicarboxylic acid and diol, and was diluted with toluene as a diluent.

Then, the product was heated at 110°C for 5 minutes to dry and remove the dilution solvent, forming an adhesive layer. The molding shrinkage of the adhesive layer was less than 3%. The thickness of the adhesive layer was 1.5 μm.

Next, a second resin was applied onto the adhesive layer using a die coating method. The second resin was an acrylic resin similar to the first resin.

In this state, 1000 mJ of UV light was irradiated from the second resin side to harden the second resin and form a second transparent layer 52 (approximately 35 μm thick). The shrinkage rate of the second transparent layer 52 was approximately 10%.

The image projection structure 120 is manufactured using the above method. Note that the above-mentioned adhesion layer is an optional layer, and a second transparent layer may be formed directly on the reflective layer 40.

Next, a manufacturing example of the transparent screen 100 in the first embodiment will be described with reference to Figure 8. However, the manufacturing examples shown below are illustrative of the present invention, and the present invention is not limited to these.

First, soda lime glass with a thickness of 2 mm was prepared as the first transparent substrate 10 and the second transparent substrate 11. PVB films with a thickness of 0.38 mm were also prepared as the first adhesive layer and the second adhesive layer (not shown in Figure 8).

Next, the first transparent substrate 10, the first adhesive layer, the image projection structure 120, the second adhesive layer, and the second transparent substrate 11 were laminated in that order to form a laminate. The laminate was then vacuum-packed and heated at 120°C for 1 hour to obtain the transparent screen 100.

In Figure 8, the transparent substrate 60 and the first transparent substrate 10 are shown as separate entities for convenience, but the transparent substrate 60 can be considered as one aspect of the first transparent substrate 10. Therefore, the transparent substrate 60 can be made of the same material as described for the first transparent substrate 10. Furthermore, the transparent substrate 60 and the first transparent substrate 10 may be combined into a single transparent layer.

Second embodiment.
In the first embodiment, the transparent screen 100 has a structure in which unit lenses 110 of the same shape (note: the inclination angle is not the same) are arranged over the entire surface (see FIG. 6). However, if unit lenses 110 of the same shape (planar shape) are arranged periodically, diffraction may occur, which may cause uneven brightness.

On the other hand, in the second embodiment, in order to prevent diffraction, the transparent screen 100 has a structure in which unit lenses 110 of multiple shapes are arranged.

Figure 9 is an explanatory diagram illustrating an example of the structure of a reflective transparent member of the second embodiment. In the second embodiment, the shape of the first transparent layer 32 in the transparent screen 100 may be a shape in which unit lenses 110 of multiple shapes are two-dimensionally arranged, or may be a shape in which unit lenses 110 of multiple shapes are randomly arranged, as shown in Figure 9. Note that in Figure 9, each rectangle corresponds to a unit lens 110.

The example shown in Figure 9 is an example of a random arrangement, and in the example shown in Figure 9, the center point is first randomly arranged with respect to each of the first reference direction and the second reference direction.

The shape of each unit lens 110 is then determined so that each of the arranged center points becomes the center point of each unit lens 110. The tilt angles of the first reference direction and the second reference direction for each unit lens 110 on the transparent screen 100 are determined using the same concept as those in the first embodiment.

In this case, the shape of the unit lens 110 is determined by simulation so that light is reflected toward the location of the observer 300. Specifically, assuming that there are multiple observers 300, unit lenses 110 of multiple shapes are used, and each unit lens 110 is configured to reflect light toward a randomly selected observer.

In the second embodiment, diffraction is prevented from occurring by eliminating the periodicity of the arrangement of the unit lenses 110.

Fine irregularities may also be imparted to the surface of the unit lenses. By imparting a fine irregularity, it becomes possible to scatter light within a specified angle. Methods for imparting a fine irregularity include physical cutting of the surface of the material forming the mold (e.g., dry etching, wet etching, sandblasting, laser ablation), surface molding by extrusion molding, use of the surface structure that arises when molding mixed components such as fine particles, or application of a self-organizing material.

When a micro-irregularity is imparted to the surface of the unit lenses, the reflective layer 40 is formed to conform to the micro-irregularity. In this case, because the reflective layer 40 is thinner than the micro-irregularity, the surface of the reflective layer 40 has a shape that reflects the micro-irregularity. Here, from the perspective of scattering light within a specified angle, it is preferable that the surface roughness of the reflective layer 40 (i.e., the surface roughness of the unit lenses 110) be in the range of 0.005 μm to 5 μm in arithmetic surface average roughness Ra (JIS B0601-2001). The surface roughness Ra of the reflective surface of the reflective layer 40 can be selected appropriately depending on the desired optical performance, etc.

Figure 10 is an explanatory diagram showing the reflected light intensity distribution when light is incident on the screen. The scattering angle will be explained with reference to Figure 10. Figure 10 (A) shows how light from the projector 200 is incident on the transparent screen 100. Figure 10 (B) shows the reflected light intensity distribution in the direction of the largest FWHM of the transparent screen 100 according to the present invention. Assuming a situation in which an observer 300 is present inside a vehicle, as shown in Figure 10 (D), it is preferable that the direction of the largest FWHM (defined as the x direction) be the direction connecting the driver's seat 410 and the passenger seat 420. The direction perpendicular to the x direction is defined as the y direction. The y direction is the height direction. The z direction is the direction of travel of the vehicle.

FIG. 10C shows the reflected light intensity distribution in the y direction of the transparent screen 100 according to the present invention, which is similar to the reflected light intensity distribution shown in FIG.
In Figure 10 (B), FWHM1 indicates the full width at half maximum (hereinafter also referred to as FWHM) of the reflected light intensity distribution in the x direction in front of the transparent screen 100, and in Figure 10 (C), FWHM2 indicates the full width at half maximum of the reflected light intensity distribution in the y direction in front of the transparent screen 100.

As will be described in the following examples, in the present invention, the FWHM1 of the reflected light intensity distribution in the x direction is 20% or more larger than the FWHM2 of the reflected light intensity distribution in the y direction. That is, the present invention satisfies the following formula (1).
FWHM1 ≧ FWHM2 × 120% (1)
In the following examples, it is assumed that anisotropy exists when formula (1) is satisfied.

Furthermore, in the above-described embodiment and the following examples, a transparent screen 100 is fabricated that maximizes the FWHM in the x direction. In other words, the x direction corresponds to the first direction that maximizes the FWHM. The y direction corresponds to the second direction that is perpendicular to the first direction.

Figure 11 is an explanatory diagram illustrating a preferred reflected light intensity distribution. The reflected light intensity distribution shown in Figure 11 exhibits a top-hat pattern. Since brightness can be defined as the light intensity (luminous intensity) per unit area, hereafter the term brightness will be used instead of reflected light intensity.

As an example, as shown in Fig. 11, the peak is defined as a range where the reduction value is equal to or greater than a first predetermined value relative to the maximum brightness (maximum brightness) of the flat portion where the brightness is maximum. That is, in the reflected light intensity distribution shown in Fig. 11, the lower limit of the peak is expressed by the following equation (2).
Top lower limit = maximum brightness × (100 - first predetermined value) % (2)

As shown in Figure 11, the range where the brightness relative to the maximum brightness is equal to or less than a second predetermined value is defined as the floor. In the reflected light intensity distribution, the range from the lower limit of the peak to the upper limit of the floor is defined as the transition section.

As will be described in the examples below, it is preferable that the first predetermined value is 30% and the second predetermined value is 20%, and it is also preferable that the width C of the apex (see FIG. 11) is 10° or more and the width (distance) D of the transition portion (see FIG. 11) is 20° or less.
That is, it is preferable that the brightness distribution in the first direction includes a peak having a width of 10° or more where the brightness is reduced by 30% or less from the maximum brightness, and the width of the transition portion between the lower limit of the peak and the upper limit of the floor where the brightness is 20% or less from the maximum brightness is 20° or less.
In this embodiment, it is assumed that a top hat shape appears in the reflected light intensity distribution when the width C of the apex is 10° or more and the width D of the transition portion is 20° or less.

FIG. 12 is an explanatory diagram showing an example of the distribution of the shapes of the unit lenses 110 (specifically, small lenses 110 ₁ to 110 ₉ , see FIG. 3 ) used in the above embodiment. As shown in FIG. 12A, the angles of the unit lenses 110 within a predetermined region on the transparent screen 100 are measured. As an example, the predetermined region is a square measuring 2 mm in height and 2 mm in width. The lens angles are measured using a laser microscope, and the angle in the direction with the largest FWHM is taken as the tilt angle of the small lenses. In the above embodiment, it is assumed that the spacing (average spacing) between a small lens and its adjacent small lens is 20 μm to 150 μm. Hereinafter, the spacing between the small lenses will be referred to as the spacing between the concave and convex portions.

Figure 12 (B) shows an example of the distribution of tilt angles of small lenses when the spacing between the concave and convex portions is 150 μm. In the example shown in Figure 12 (B), the tilt angles are organized into a histogram with 10 classes. The vertical axis shows the number of tilt angles (degrees) included in the range of tilt angles for each class.

Figure 12 (C) shows an example of the distribution of tilt angles of small lenses when the spacing between the concave and convex portions is 20 μm. In the example shown in Figure 12 (C), the tilt angles are organized into a histogram with 10 classes. The vertical axis shows the number of tilt angles (degrees) included in the range of tilt angles for each class.

As shown in Figures 12B and 12C, it is preferable that the minimum frequency is 50% or less of the maximum frequency. In other words, it is preferable that the following formula (3) is satisfied.
Minimum frequency ≦ Maximum frequency × 50% (3)

The following describes examples and comparative examples with reference to Figure 13. First, the parameters shown in Figure 13 are explained. "Anisotropy" means that the reflected light intensity distribution (brightness distribution) in the x direction is different from the reflected light intensity distribution in the y direction. In the examples and comparative examples, the differences are compared using FWHM. The parameters related to top hat are as described above. "Transmittance" is a value (%) measured using a method conforming to ISO 9050. Transmission haze (cloudiness) is a value measured using a method conforming to ISO 14782.

The "screen gain" is a value as follows: Light is irradiated from a light source (e.g., projector 200) perpendicularly onto the transparent screen 100, and the luminance value is measured with a luminance meter while changing the angle relative to the transparent screen 100 within the same plane (e.g., between -80° and +80° in 5° increments). The highest value among the ratios of each measured luminance value to the luminance value when the light is directed onto a perfect diffuser is taken as the screen gain.

"Image luminance" is expressed, for example, as follows:
Image luminance (cd/m ² )=light source (e.g., projector 200) brightness (lm)×screen gain/(projection area (m ² )×circularity constant)

In the following examples (Examples 1 to 6), a transparent screen 100 was fabricated in which anisotropy was observed, such that the FWHM of the luminance distribution in the x direction was 20% or more larger than the FWHM of the luminance distribution in the y direction, and the luminance distribution in the x direction was top-hat shaped. The average tilt angle of the small lenses constituting the transparent screen 100 was set to 6°, but the ratio (minimum frequency/maximum frequency) in the frequency distribution of the tilt angle was set to less than 50%.

[Example 1]
A transparent screen 100 was produced with an x-direction FWHM (see FIG. 10B) of 80°, a y-direction FWHM (see FIG. 10C) of 30°, a peak width C (see FIG. 11) of 70°, and a transition width D (see FIG. 11) of 10°. In Example 1, the average spacing between the concave and convex portions was 50 μm, and the average tilt angle of the concave and convex portions was 6°. The ratio (minimum frequency/maximum frequency) in the frequency distribution of the tilt angle was 30%.

In Example 1, the surface of the small lenses was subjected to a micro-irregularity treatment. The screen 100 had a transmittance of 75%, a transmission haze of 1.9%, and a screen gain of 0.3. The image brightness was 520 cd/ ^m2 .

[Example 2]
A transparent screen 100 was produced with an x-direction FWHM of 80°, a y-direction FWHM of 7°, a peak width C of 70°, and a transition width D of 10°. In Example 2, the average spacing between the concave and convex portions was 50 μm, and the average tilt angle of the concave and convex portions was 6°. The ratio (minimum frequency/maximum frequency) in the frequency distribution of the tilt angle was 30%.

In Example 2, the surface of the small lenses was subjected to a micro-irregularity treatment. The screen 100 had a transmittance of 75%, a transmission haze of 1.9%, and a screen gain of 0.8. The image brightness was 1400 cd/ ^m2 .

[Example 3]
A transparent screen 100 was produced with an x-direction FWHM of 23°, a y-direction FWHM of 7°, a peak width C of 20°, and a transition width D of 5°. In Example 3, the average spacing between the concave and convex portions was 50 μm, and the average tilt angle of the concave and convex portions was 6°. The ratio (minimum frequency/maximum frequency) in the frequency distribution of the tilt angle was 30%.

In Example 3, the surface of the small lenses was subjected to a micro-irregularity treatment. The screen 100 had a transmittance of 75%, a transmission haze of 1.9%, and a screen gain of 2.7. The image brightness was 4700 cd/ ^m2 .

[Example 4]
A transparent screen 100 was produced with an x-direction FWHM of 20°, a y-direction FWHM of 10°, a peak width C of 20°, and a transition width D of 2°. In Example 4, the average spacing between the concave and convex portions was 50 μm, and the average tilt angle of the concave and convex portions was 6°. The ratio (minimum frequency/maximum frequency) in the frequency distribution of the tilt angle was 30%.

In Example 4, the surface of the small lenses was not subjected to micro-irregularity treatment. The screen 100 had a transmittance of 75%, a transmission haze of 1.9%, and a screen gain of 9. The image brightness was 15,000 cd/ ^m2 .

[Example 5]
A transparent screen 100 was produced with an x-direction FWHM of 20°, a y-direction FWHM of 4°, a peak width C of 20°, and a transition width D of 2°. In Example 5, the average spacing between the concave and convex portions was 50 μm, and the average tilt angle of the concave and convex portions was 6°. The ratio (minimum frequency/maximum frequency) in the frequency distribution of the tilt angle was 30%.

In Example 5, the surface of the small lenses was not subjected to micro-irregularity treatment. The screen 100 had a transmittance of 75%, a transmission haze of 1.9%, and a screen gain of 18. The image brightness was 32,000 cd/ ^m2 .

[Example 6]
A transparent screen 100 was produced with an x-direction FWHM of 20°, a y-direction FWHM of 10°, a peak width C of 20°, and a transition width D of 10°. In Example 6, the average spacing between the concave and convex portions was 100 μm, and the average tilt angle of the concave and convex portions was 6°. The ratio (minimum frequency/maximum frequency) in the frequency distribution of the tilt angle was 30%.

In Example 6, the surface of the small lenses was not subjected to micro-irregularity treatment. The screen 100 had a transmittance of 75%, a transmission haze of 1.9%, and a screen gain of 9. The image brightness was 15,000 cd/ ^m2 .

When using the transparent screen 100 of the above examples (Examples 1 to 6), the area in which the intensity of the collected light is high is wider in the x direction, making it possible to widen the range in which a bright image can be viewed compared to, for example, the transparent screen described in Patent Document 1. Furthermore, by narrowing the width D (see Figure 11) of the transition portion in the luminance distribution, it is possible to prevent a decrease in the efficiency of reflected light utilization.

Therefore, for example, when the transparent screen 100 is installed inside a vehicle, such as on the vehicle's front window (windshield), both the observer 300 in the driver's seat and the observer 300 in the passenger seat can see a bright image. Furthermore, when the observer 300 in the front seat of the vehicle moves in the x direction, or when the observer 300 in the rear seat moves in the x direction, the observer 300 can see a bright image before, during, or after the movement. In the y direction, assuming that the range in which the bright image can be seen does not need to be wide, the luminance distribution can be the same as that of the transparent screen described in Patent Document 1, for example.

Comparative examples are described below. In the following comparative examples (Examples 7 to 11), transparent screens were produced that do not exhibit anisotropy or that do not result in a top-hat luminance distribution, or transparent screens that do not exhibit anisotropy and do not result in a top-hat luminance distribution.

[Example 7]
In Example 7, the brightness distribution in the x direction is top-hat shaped. That is, the width C of the apex is 10° or more, and the width D of the transition is 20° or less. However, since the FWHM in the x direction is 28° and the FWHM in the y direction is 28°, there is no anisotropy. That is, the above formula (1) is not satisfied.

[Example 8]
In Example 8, the FWHM in the x direction is 14° and the FWHM in the y direction is 12°, so there is no anisotropy. Also, in the brightness distribution in the x direction, the width C of the top is 8.5°, which is less than 10°, and no top hat shape appears.

[Example 9]
In Example 9, the FWHM in the x direction is 6° and the FWHM in the y direction is 5°, so there is no anisotropy. Also, in the brightness distribution in the x direction, the width C of the apex is 3°, which is less than 10°, so no top hat shape appears.

[Example 10]
In Example 10, the FWHM in the x direction is 30° and the FWHM in the y direction is 10°, so there is anisotropy. However, the top width C is 20°, but the transition width D is 35°, which exceeds 20°, so the top hat shape does not appear.

[Example 11]
In Example 11, the brightness distribution in the x direction is top-hat shaped. That is, the width C of the apex is 10° or more, and the width D of the transition is 20° or less. However, since the FWHM in the x direction is 30° and the FWHM in the y direction is 30°, there is no anisotropy. That is, the above formula (1) is not satisfied.

The screens of the examples (Examples 1 to 6) are anisotropic and have a top-hat luminance distribution, so when these screens are installed on a vehicle windshield, multiple observers can view bright images. On the other hand, the screens of the comparative examples (Examples 7 to 11) are not anisotropic or do not have a top-hat luminance distribution, so when these comparative example screens are installed on a windshield, multiple observers will have difficulty viewing bright images.

REFERENCE SIGNS LIST 10 First transparent substrate 11 Second transparent substrate 32 First transparent layer 40 Reflective layer 52 Second transparent layer 60 Transparent substrate 100 Transparent screen 110 Unit lens 110 ₁ to 110 ₉ Small lenses 120 Image projection structure 200 Projector 300 Observer

The entire contents of the specification, claims, drawings and abstract of Japanese Patent Application No. 2021-156598, filed on September 27, 2021, are hereby incorporated by reference as the disclosure of the specification of the present invention.

Claims (12)

a first transparent layer having an uneven surface;
a reflective layer on the uneven surface;
a second transparent layer formed on the uneven surface of the reflective layer so as to fill the unevenness,
the full width at half maximum of the luminance distribution in a first direction due to the reflected light is 20% or more larger than the full width at half maximum of the luminance distribution in a second direction perpendicular to the first direction;
A reflective transparent member in which the luminance distribution in at least the first direction exhibits a top hat shape. The reflective transparent member according to claim 1 , wherein the full width at half maximum of the luminance distribution in the first direction is maximum. 3. The reflective transparent member according to claim 1, wherein the luminance distribution exhibiting a top-hat shape includes an apex having a width of 10° or more and where the luminance is reduced by 30% or less relative to the maximum luminance, and the width of the transition portion between the lower limit of the apex and the upper limit of the floor, where the luminance is reduced by 20% or less relative to the maximum luminance, is 20° or less. The reflective transparent member according to claim 1 or 2, wherein the frequency distribution of the inclination angles of the plurality of concave and convex portions included in the predetermined region includes a portion where the minimum frequency is 50% or less of the maximum frequency. the concave-convex surface is formed by a two-dimensional array of a plurality of unit lenses,
3. The reflective transparent member according to claim 1, wherein the unit lenses are each formed of small lenses arranged at an average interval of 20 μm to 150 μm. A reflective transparent member as described in claim 1 or 2, wherein the first transparent layer and the second transparent layer are transparent resin layers. A reflective transparent member as described in claim 6, wherein the transparent resin constituting the transparent resin layer is a photocurable resin, a thermosetting resin, or a thermoplastic resin. A reflective transparent member as described in claim 6 or 7, wherein the transparent resin constituting the transparent resin layer is an acrylic resin, an epoxy resin, a polycarbonate resin, a silicone resin, an unsaturated polyester resin, or a mixed resin thereof. A reflective transparent member as described in claim 1 or 2, wherein the reflective layer is a single layer or multilayer film of a metal film or a dielectric film. The reflective transparent member described in claim 9, wherein the reflective layer is a film formed of Ag or Al alone, or an alloy of Ag and at least one metal selected from the group consisting of Pd, Au, Pt, Cu, Ru, Ir, Rh, Os, Bi, Nd and Ge. A reflective transparent member according to claim 1 or 2, which is a reflective transparent screen. An image display system comprising: the reflective transparent member according to claim 1 or 2; and a projector that projects an image onto the reflective transparent member.