JP2009169006A - Reflection screen - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a reflection screen for improving uniformity and contrast of brightness. <P>SOLUTION: The reflection screen 1 has a screen face 11 for reflecting projection light emitted from a projection light source. A screen face 11 includes a circular fresnel lens part 12 whose cross section is in the form of a saw blade. The center of a concentric circle of the circular fresnel lens part 12 is positioned on the outside of the screen face 11. In addition, the circular fresnel lens part 12 is composed as an assemblage of unit prisms having a first oblique face being a tilt face of the side of the center of the concentric circle and a second oblique face being a tilt face of the opposite side to the first oblique face. The first oblique face is light reflection face and the second oblique face is a non-reflection face. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a reflective screen.

Front projectors using liquid crystal and DMD (Digital Micro mirror Device) as video sources are widely used. In particular, a front projector that projects the image light L ₀ on the front surface of the screen is widely used because it has the advantage that the screen can be easily enlarged. Here, compared with a transmissive projector, the front projector has a drawback in that when viewed in a bright room, external light is reflected on the screen surface and the contrast of the image tends to decrease. To deal with such a problem, Patent Document 1 discloses a screen including a prism row composed of a reflective portion and a non-reflective portion. That is, Patent Document 1 describes a front projection screen having a Fresnel structure. In a Fresnel facet where a lot of projection light is incident, the projection light is reflected toward the viewer, and in a rising Fresnel facet where a lot of external light is incident, Suppresses reflection.
With such a configuration, high contrast is realized.

    Further, in Patent Document 2, from the incident surface side, a translucent plate having a minute protrusion having a light-shielding black layer on a vertical side surface of a triangular cross section, a transmissive light diffusing plate, and a reflective fresnel sheet, The screen provided is described. Thereby, reflection of external light is suppressed by the light-shielding black layer of the light transmitting plate on the front surface, and the black level is maintained. Furthermore, since the reflection direction of the light beam can be made a predetermined direction by the Fresnel sheet, vignetting by the light-shielding black layer of the translucent plate is reduced, and the light beam utilization efficiency is increased. As a result, the contrast can be increased.

However, in recent years, front projectors are used in various projection arrangements.
For example, the front projector 2 is arranged on a desk, and the screen 110 is arranged as shown in FIG. 15 in which the entire screen 110 is arranged above the height of the desk so as not to be a shadow of the desk when viewed from the observer. There are many cases. In such a case, the projection system optical axis K ₁ of the front projector 2 may be biased to the lower side of the screen 110, and the position of the projection system optical axis K ₁ may be outside the screen 110.
Further, a front projector 2 having a shorter projection distance than the conventional one is also used so that a large screen can be viewed even in a narrow room. If the screen described in Patent Document 1 or Patent Document 2 is used in such a projection arrangement, the image light is reflected outward at the four corners of the screen, particularly the upper left and upper right corners. There is a problem that the four corners become dark images.

JP-A-1-161228 Japanese Patent Laid-Open No. 11-338056

  An object of the present invention is to provide a reflective screen that improves brightness uniformity and contrast even if the projection optical axis is off the screen.

  A reflective screen according to the present invention is a reflective screen having a screen surface that reflects projection light emitted from a projection light source, and the screen surface includes a circular Fresnel lens portion having a sawtooth cross section. The concentric circle center of the circular Fresnel lens portion is located outside the screen surface, and the circular Fresnel lens portion is a first inclined surface that is an inclined surface on the concentric circle center side and an inclined surface opposite to the first inclined surface. It is preferable that the first inclined surface is a light reflecting surface and the second inclined surface is a non-reflecting surface.

According to such a configuration, even when the projection optical axis and the screen surface deviate due to the arrangement relationship between the projection light source and the reflective screen, the concentric center of the circular Fresnel lens portion is outside the screen surface. If the center of the concentric circle and the optical axis of the projection system are present, the image light is effectively reflected toward the viewer in front of the screen, and the mixing of external light can be suppressed. As a result, uniform and high contrast can be realized on the entire screen.
Further, according to this configuration, the image light diffused and projected from the center side of the concentric circle is reflected by the first slope, and the external light entering the second slope is not reflected. As a result, an image that is uniform and has high contrast on the entire screen can be realized.

In addition, it is preferable that the concentric center of the circular Fresnel lens part is out of the screen in the downward direction of the screen surface in a state where the reflective screen is installed.
According to such a configuration, the projection light source can be disposed at a position close to the screen below the screen in a narrow room, and space efficiency is improved. In particular, it is natural that the projection light source can be installed on the table under the screen, and the convenience of use is very high.

In the present invention,
It is preferable that a substrate of the circular Fresnel lens portion is made of a light absorbing material, and a light reflecting layer is provided on the first slope.

    In the present invention, the base material of the circular Fresnel lens part is made of a translucent material, a light reflection layer is provided on the first slope, and a light absorption layer is provided on the back side of the circular Fresnel lens part. preferable.

    According to such a configuration, only the first slope may be subjected to reflection processing, and the second slope may be a base material. Therefore, the manufacturing process can be simplified and the manufacturing cost can be reduced.

    According to the present invention, it is possible to provide a screen that improves brightness uniformity and contrast even when the projection optical axis is off the screen. In particular, when a front projector with a short projection distance is used and the projection system optical axis is shifted from the center of the screen, the reflective screen of the present invention is very suitable.

The best mode for carrying out the present invention will be described below with reference to the drawings.
Note that the present invention is not limited to the following embodiments.

FIG. 1 is a schematic diagram showing an example of a usage pattern of a reflective screen 1 (hereinafter referred to as a screen 1) according to the present invention.
A front projection display device (front projector) 2 having a projection light source (not shown) is installed further downward from the lower end of the screen 1 as shown in FIG.
That is, a projection system optical axis K _{1 of} a projection lens (not shown) that emits image light (projection light) L ₀ of the front projection display device 2 is below the screen 1. Then, the image light L ₀ projected from the front projection display device 2 spreads radially around the projection optical axis K ₁ of the front projection display device 2 and reaches the screen 1. In other words, the screen 1 is located higher than the projection system optical axis K ₁ of the front projection display device 2, therefore, the image light L ₀ enters from below the screen 1.

The screen surface 11 of the reflective screen 1 includes a circular Fresnel lens portion 12 having a sawtooth cross section.
FIG. 2 is a perspective view of the reflective screen 1 showing auxiliary lines representing concentric circles C of the circular Fresnel lens portion 12.
FIG. 3 is a cross-sectional view of the reflective screen 1 taken along line III-III in FIG.
The circular Fresnel lens portion 12 has a concentric center C located outside the screen 1 as shown in FIG.
The pitch of the circular Fresnel is preferably set to 0.3 mm or less, so that moire generated by interference with the pixel pitch of the projected image can be prevented.

FIG. 4 is an enlarged schematic view of a part of the cross section of the circular Fresnel lens portion 12 extracted.
As shown in FIG. 4, the circular Fresnel lens portion 12 has a light reflecting surface (121) and a non-reflecting surface (122) on its slope. The circular Fresnel lens unit 12 is an aggregate of unit prisms 120, and a first inclined surface (Fresnel surface) 121 that is an inclined surface on the concentric circle center C side in each unit prism 120 is used as a light reflecting surface. In other words, the observation surface side inclined surface of the sawtooth unit prism 120 of the circular Fresnel lens portion 12 serves as a light reflecting surface as the first inclined surface 121. Further, in each unit prism 120 of the circular Fresnel lens unit 12, the second inclined surface (rise surface) 122 which is the inclined surface opposite to the concentric circle center C is a non-reflecting surface.

    Here, the first inclined surface (light reflecting surface) 121 may be a substantially mirror-like reflecting layer, or may be a diffuse reflecting layer in which fine irregularities are formed. The first slope (light reflecting surface) 121 can also be formed to have a concave curved surface shape or a convex curved surface shape. Further, the light absorption layer may be formed on the second inclined surface (non-reflecting surface) 122 by sputtering, spin coating, lift-off using a photoresist, or the like.

FIG. 5 is a diagram showing paths of the external light L ₁ from the illumination 9 and the video light L ₀ from the front projection display device (front projector) 2.
As shown in FIG. 5, the image light L ₀ from the front projection display device (front projector) 2 is reflected toward the observer M by the first inclined surface 121, while the external light L ₁ is directly or _first reflected. It reaches the second slope 122 via the slope 121. Then, the image light L ₀ from the front projection display device 2 enters the observer M, and the external light L ₁ does not enter. As a result, a high contrast image is observed by the observer M.

The production of such a reflective screen 1 will be briefly described.
The base material of the circular Fresnel lens portion 12 can be manufactured using, for example, a mold and an ultraviolet curable resin. The reflective layer of the first slope 121 can be formed by vapor deposition, sputtering, spin coating, lift-off processing using a photoresist, or the like.

    Further, a backing sheet may be laminated on the back side of the base material of the circular Fresnel lens portion 12. For example, a soft vinyl chloride resin sheet or a polyester film can be bonded with an adhesive or an adhesive.

    Alternatively, as shown in FIG. 6, the base material of the circular Fresnel lens portion 12 may be a light-absorbing material. Then, the process of providing the light absorption layer on the second inclined surface 122 can be omitted.

Alternatively, as shown in FIG. 7, the base material of the circular Fresnel lens portion 12 may be a light-transmitting material, and a light absorption layer 123 may be provided on the back side. Then, the external light L ₁ incident on the second slope 122 is absorbed by the back side of the light absorbing layer 123, it is possible to increase the contrast. For example, a base material is made of urethane-based ultraviolet curable resin, a reflective layer is formed on the first slope (Fresnel surface) 121 of the unit prism, and then black ink is applied to the back side or black using a transparent adhesive material. A resin sheet may be attached. According to such a configuration, the step of providing the light absorption layer on the second inclined surface 122 can be omitted.

Further, as shown in FIG. 8, a transparent protective layer 124 may be provided on the observation side (surface side) of the circular Fresnel lens portion 12. In this case, it is more preferable that the protective layer is thicker than the uneven height of the unit prism structure 120, and the surface (surface) on the observation side is flat. Thereby, even if dust etc. adhere, it can remove comparatively easily.
Furthermore, a light diffusing material may be mixed in the transparent protective layer, and the surface of the transparent protective layer 124 preferably has fine irregularities. This is because the reflection of external light can be prevented. In this case, the degree of unevenness is preferably about Ra = 0.1 to 3 μm.

Next, the angle of each unit prism 120 of the circular Fresnel lens unit 12 will be described.
The angle (Fresnel angle) α of the first slope (Fresnel surface) 121 is set to an angle that reflects the image light beam L ₀ projected from the front projection display device 2 obliquely below in the screen front direction. The angle (rise angle) β of the second slope (rise surface) 122 is set so that the image light beam L ₀ projected from the obliquely lower front projection display device 2 does not enter the second slope (rise surface) 122. Is set.

Referring to FIG. 9, in order to reflect the image light L ₀ from the front projection display device 2 toward the front of the screen 1, the angle α of the first inclined surface (Fresnel surface) 121 is as follows. . Note that the arc of the Fresnel is R, and the projection distance of the projector 2 is d (see FIG. 10).

    The angle (Fresnel angle) α of the first slope 121 with respect to θ satisfying the above equation (1) is obtained as follows.

With respect to the angle (rise angle) beta of the second inclined surface 122, in order to prevent the reflection loss of the image light L _0, it is necessary to set the angle at which the projection image light L ₀ does not enter the second slope (rise surface) 122.
That is, it is necessary to satisfy the following relational expression.

The angle (rise angle) β of the second inclined surface 122 is not particularly limited in terms of optical performance.
However, if it exceeds 90 degrees, it becomes difficult to produce and mold the mold, and therefore, it is preferably 90 degrees or less.

With reference to FIG. 11, the case where the surface is overcoated with a transparent protective layer 124 having a refractive index n so that the outermost surface is flat will be described.
In the case of such overcoat, when the refractive index of the transparent medium to be overcoated is n and the refraction angle by the transparent medium is θ ′, the following relationship is obtained with respect to the incident angle θ of the image light L ₀ .

  That is, the angle α of the first inclined surface 121 (Fresnel surface) is as follows.

    The angle (rise angle) β of the second inclined surface 122 is expressed by the following equation.

In the above description, regarding the angle α of the first inclined surface (Fresnel surface) 121, the angle design for reflecting the image light beam in the screen front direction on the entire screen surface is described, but the present invention is not limited to this.
For example, a design in which the light is deflected and reflected in either the upper, lower, left, or right directions, or a design in which the light is reflected inward so as to converge slightly toward the front of the screen may be employed.

  In consideration of the arrangement of the front projection display device 2 and the screen 1 and the versatility of the viewing position, the first inclined surface 121 that is the reflection surface is made a diffuse reflection layer with fine irregularities formed, or light in the transparent protective layer You may perform a viewing angle expansion process, such as mixing a diffusing material.

As described above, in the screen 1 according to the present embodiment, the concentric center C of the circular Fresnel lens portion 12 is located outside the screen 1.
As a result, even when a front projector with a short projection distance is used, a bright screen with improved contrast can be easily manufactured.
If concentric center C is in the screen surface, and the projection system optical axis K ₁ and the screen 1 is out of position disposed can not be effectively reflects light projected screen front to the viewer M, the screen four corners darkens Sometimes.
On the other hand, in this embodiment, the concentric center C of the circular Fresnel lens portion 12 is located outside the screen 1 and below the lower end of the screen 1.
Therefore, even when the projection distance of the front projection display device 2 is short and the front projection display device 2 is installed slightly below the lower end of the screen 1, the image light is effectively reflected to the observer in front of the screen. Can do. As a result, the entire screen 1 is bright and has excellent contrast.

FIG. 12 is a schematic view of the screen 1, the front projection display device 2, and the observer M viewed from the ceiling.
Since the screen surface 11 has a circular Fresnel lens portion not only in the vertical direction but also in the horizontal direction, image light incident on the four corners of the screen, particularly the upper left corner and the upper right corner, is effectively applied to the observer M in front of the screen. It can be seen that the image light can be reflected.

(Example)
In this example, a screen 1 was produced as follows.
First, using a lathe, a die having a shape opposite to that of the concentric Fresnel lens portion 12 was prepared.
The pitch of the concentric circles was 0.1 mm. The angle (Fresnel angle) α of the surface that becomes the first slope (Fresnel surface) 121 was about 0 degree near the concentric center and about 20 degrees near the outermost periphery. The angle (rise angle) β of the second slope (rise surface) 122 was about 90 degrees near the concentric circle center and about 60 degrees near the outermost periphery. Next, a urethane-based ultraviolet curable resin liquid is applied to the entire surface of the mold, a transparent polyester sheet having a thickness of 0.15 mm is laminated, and then the resin liquid is cured by irradiating ultraviolet light from the transparent polyester sheet side. A lens part base sheet was prepared. The thickness of the ultraviolet curable resin after curing was about 0.1 mm.

    Thereafter, the Fresnel lens part base sheet was subjected to metal vapor deposition, and a reflective layer was formed on the first slope 121 to produce a Fresnel lens part sheet. At this time, the vapor deposition source was arranged at a position about 1 m away from the sheet surface on the concentric center axis of Fresnel. As a result, no reflective layer was formed on the second slope (rise surface) 122.

Next, an ultraviolet curable hard coat resin solution containing a light diffusing agent was applied to the entire surface of the Fresnel lens part sheet, and the resin solution was cured by irradiating ultraviolet rays. The cured hard coat layer had a refractive index of 1.55 and a thickness of about 0.05 mm. Thereby, the surface on the observation side became almost flat.
As the diffusing agent, an acrylic light diffusing agent having a particle size of 8 μm was used, and the concentration was 4% by weight.

Then, black ink was apply | coated to the whole surface by the side of the transparent polyester sheet of the said Fresnel lens part sheet | seat, and the light absorption layer was formed.
Further, a back protective layer made of urethane resin was applied on the black ink.

    Thereafter, the Fresnel lens part sheet was cut, and a winding jig was attached to complete the screen. The effective size of the screen was a diagonal size of 80 inches with a height of 1.22 m and a width of 1.63 m. At this time, the center of the concentric circle of Fresnel was at a position 0.15 m below the lower end of the screen effective size on the extension line in the middle of the screen width direction. The angle α of the first slope (Fresnel surface) 121 was about 3 degrees at the lower end of the effective screen size in the middle of the screen width direction and about 16 degrees at the upper end of the effective screen size in the middle of the screen width direction. The angle β of the second slope (rise surface) 122 was about 85 degrees at the lower end of the effective screen size in the middle of the screen width direction and about 60 degrees near the outermost periphery.

(Evaluation of Examples)
Visual evaluation was performed on the screen 1 of this example.

FIG. 13 and FIG. 14 show an example of the screen arrangement state in the present embodiment.
As shown in FIGS. 13 and 14, an image was projected on the screen 1 of the example in a bright room, and the brightness and contrast were visually evaluated.
The front projection display device 2 (projection light source) used here is “LP-XL40” manufactured by Sanyo Electric Co., Ltd.
As the projection system optical axis K ₁ of the front projection display device 2 is located about 0.15m from the bottom of the screen, it was placed the front projection display device 2.
The illumination (external light source) is fluorescent lamp illumination. The illuminance at the center of the screen of the illumination was 360 lux when lit.

In the case of the arrangement and angle setting of the present embodiment, the external light that is incident on the second inclined surface (rise surface) 122 after being reflected directly or by the reflecting layer (first inclined surface 121) and absorbed by the black ink layer on the back side is , 30% at the upper end and 12% at the lower end. The remaining reflected light goes to the observation side once, but if the incident surface of the transparent overcoat layer is a mirror surface, it will totally reflect there and follow the path entering the second slope (rise surface) again. It enters the (rise surface) and is absorbed by the back black ink layer.
Here, since the incident surface of the transparent overcoat layer is a matte surface, it is not necessarily totally reflected. Assuming that the reflectance is 50%, the external light absorption efficiency is estimated to be 65% at the upper end and 55% at the lower end. The total external light absorption efficiency under this assumption is estimated to be about 50% over the entire surface.

<Visual visual evaluation>
In order to perform visual image evaluation, lighting was turned on, and a TV image was projected onto the screen 1 of the example and evaluated visually. As a result, the image was brightly displayed on the entire screen, and the contrast of the image was excellent. As described above, according to the present invention, it has been shown that a reflective screen with excellent brightness uniformity and contrast performance can be easily manufactured.

Of course, the reflective screen of the present invention may be used not only in the state of use in the above-described embodiment, but also in other modes of use.
For example, not only when the projection light source is installed below the screen and emits light upward, the projection light source may be installed above the screen and emits light downward. In this case, the concentric center of the circular Fresnel lens part is disposed on the optical axis side of the projection light source.
The sawtooth unit prism of the circular Fresnel lens part may have a chamfered top or a polygonal shape in addition to the triangular shape described above.

The schematic diagram which shows an example of the usage type of a reflection type screen in embodiment which concerns on this invention. In the said embodiment, the figure which showed the auxiliary line showing the concentric circle of the circular Fresnel lens part in the perspective view of a reflection type screen. In the said embodiment, sectional drawing of the reflection type screen in the III-III line | wire in FIG. The schematic diagram which extracted and expanded some cross sections of the circular Fresnel lens part in the said embodiment. The figure which shows the path | route about the external light from illumination and the image light from a front projection type display apparatus in the said embodiment. The figure which shows the case where the base material of the circular Fresnel lens part is comprised with the light absorptive material in the said embodiment. In the said embodiment, the figure which shows the case where the base material of the circular Fresnel lens part is used as the translucent material, and the light absorption layer is provided in the back side. The figure which shows the case where the transparent protective layer is provided in the observation side of the circular Fresnel lens part in the said embodiment. In the embodiment described above, it shows the angular relationship, including the angle of the first slope and the angle of the second inclined surface when the image light L ₀ from the front projection display device is reflected by the screen. The figure which shows the arc R of Fresnel and the projection distance d of a projector in the said embodiment. The figure which shows the angle relationship at the time of overcoating the surface layer with a transparent protective layer in the said embodiment. In the said embodiment, the schematic diagram which looked at the screen, the front projection type display apparatus, and the observer from the ceiling direction. The Example which shows the state which looked at an example of arrangement | positioning of a screen from the side in the Example which concerns on this invention. The figure which shows the state which looked at an example of arrangement | positioning of a screen from the upper direction in the Example which concerns on this invention. The figure which shows the arrangement | positioning relationship between a projection type display apparatus and a reflective screen in description of background art.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Reflective type screen, 2 ... Front projection type display apparatus, 11 ... Screen surface, 12 ... Circular Fresnel lens part, 110 ... Screen, 120 ... Unit prism, 121 ... 1st slope, 122 ... 2nd slope, 123 ... Light Absorbing layer, 124 ... Transparent protective layer.

Claims (3)

A reflection type screen having a screen surface for reflecting projection light emitted from a projection light source,
The screen surface includes a circular Fresnel lens portion having a sawtooth cross section,
The concentric center of the circular Fresnel lens part is located outside the screen surface,
The circular Fresnel lens part is
It is configured as an assembly of unit prisms having a first inclined surface that is an inclined surface on the concentric center side and a second inclined surface that is an inclined surface opposite to the first inclined surface,
The first slope is a light reflecting surface;
The reflective screen according to claim 1, wherein the second slope is a non-reflective surface. 2. The reflective screen according to claim 1, wherein a substrate of the circular Fresnel lens portion is made of a light-absorbing material, and a light reflecting layer is provided on the first slope. The base material of the circular Fresnel lens part is composed of a translucent material,
A light reflecting layer is provided on the first slope;
The reflective screen according to claim 1, further comprising a light absorption layer on a back side of the circular Fresnel lens unit.

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