JP2007058030A - Fresnel lens sheet, transmissive screen and rear projection display - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a Fresnel lens sheet used in a projection optical system that is incident obliquely with respect to a light incident surface, having good light utilization efficiency and easy to manufacture.
A projection optical system in which a minimum incident angle θ1 of light incident on a light incident surface S1 is in a range of 25 ° to 45 ° and a maximum incident angle θ2 is in a range of 65 ° to 85 °. The Fresnel lens sheet 11 used is a unit prism having a light incident surface S1 having a refractive surface 15 that refracts incident light 3 and a total reflection surface 16 that totally reflects light refracted by the refractive surface 15. 14 is formed, the angle θa between the refracting surface 15 and the total reflection surface 16 is in the range of 34 ° to 41 °, and the angle between the virtual plane forming the light incident surface S1 and the refracting surface 15 is 90 ° or less. The above-mentioned problem was solved by the Fresnel lens sheet.
[Selection] Figure 2

Description

The present invention relates to a Fresnel lens sheet, a transmissive screen, and a rear projection display device. More specifically, the Fresnel lens sheet used in a projection optical system that enters obliquely with respect to a light incident surface has good light utilization efficiency. And a transmissive screen having the Fresnel lens sheet and a rear projection display device.

  A projection television, which is a rear projection display device, includes a transmissive screen that projects image light emitted from a light source. This transmissive screen generally has a Fresnel lens sheet for deflecting image light enlarged and projected from a light source into parallel light or substantially parallel light (hereinafter referred to as substantially parallel light) toward the viewer, and the substantially parallel light. And a light diffusion sheet (hereinafter also referred to as a lenticular lens sheet) for widening the viewing angle of the image. The Fresnel lens sheet is manufactured using a high-precision shaping mold and an ultraviolet curable resin in order to deflect incident video light with high accuracy. Specifically, it is manufactured by applying an ultraviolet curable resin to a flat mold for forming a Fresnel lens sheet, curing it by irradiating with ultraviolet rays, and then releasing the Fresnel lens sheet from the mold. Has been.

  On the other hand, in recent years, it has been required to reduce the thickness of a rear projection type display device, and as a means for that purpose, it is a part of a circular Fresnel lens that does not have a Fresnel center (a concentric center) in the sheet. There has been proposed an integral transmission screen in which a total reflection Fresnel lens is formed on the light incident surface side (see, for example, Patent Documents 1 and 2). The total reflection Fresnel lens sheet is a Fresnel lens sheet used in a rear projection display device that projects image light from an oblique direction with respect to a screen. A triangular prism group is provided on a light incident surface. This is a Fresnel lens sheet that refracts incident light with a refracting surface that is a second surface, and then totally reflects the light with a total reflection surface that is a second surface and then emits the light to the viewer. Therefore, it is necessary to deflect incident light in a desired direction with high accuracy, and it is required to manufacture with higher accuracy than the conventional circular Fresnel lens sheet.

  For example, the transmissive screen described in Patent Document 1 is mounted on a rear projection display device in which the incident angle of light incident on the light incident surface is approximately 40 ° to 75 °, and is used as the apex angle of the unit prism. A 50 ° one is disclosed.

On the other hand, in the transmissive screen described in Patent Document 2, the apex angle of the unit prisms constituting the prism group changes according to the position of each unit prism on the light incident surface of the Fresnel lens sheet. And in this patent document 2, it is changing continuously so that the side far from the side close | similar to the Fresnel center may become large in the range whose apex angle of each unit prism is 30 degrees or more and 45 degrees or less. Is described. Thereby, it is said that a decrease in surface luminance and a decrease in contrast can be suppressed and a high-quality image can be displayed.
Japanese Patent Laid-Open No. 61-208041 JP 2004-86187 A

  In recent years, however, the rear projection display device has become particularly large and thin, and the minimum incident angle of light incident on the light incident surface is in the range of 25 ° to 45 °, and the maximum incident angle is 65 ° to 85 °. When a projection optical system within a range of less than or equal to ° is used, a Fresnel lens sheet having a unit lens designed at an angle described in Patent Documents 1 and 2 is emitted from a light source. There is a demand for improved light utilization efficiency. On the other hand, it is also required to improve the productivity by easily releasing the Fresnel lens sheet from the mold.

  The present invention has been made to solve the above-mentioned problems, and its purpose is to produce a Fresnel lens sheet used in a projection optical system that is incident obliquely with respect to a light incident surface with good light utilization efficiency. It is to provide an easy Fresnel lens sheet. Another object of the present invention is to provide a transmission screen and a rear projection display device having such a Fresnel lens sheet.

  The Fresnel lens sheet of the present invention for solving the above problems has a minimum incident angle of light incident on the light incident surface in the range of 25 ° to 45 °, and a maximum incident angle of 65 ° to 85 °. A Fresnel lens sheet used in a projection optical system within a range, wherein the light incident surface includes a refracting surface that refracts incident light and a total reflection surface that totally reflects light refracted by the refracting surface. A plurality of unit prisms are formed, an angle between the refracting surface and the total reflection surface is in a range of 34 ° to 41 °, and an angle between a virtual plane forming the light incident surface and the refracting surface is 90 °. It is characterized by the following.

  According to this invention, the minimum incident angle of light incident on the light incident surface is in the range of 25 ° to 45 ° and the maximum incident angle is in the range of 65 ° to 85 °. In the reflection type Fresnel lens sheet, the use efficiency of light emitted from the light source can be improved by setting the angle between the refracting surface and the total reflection surface within the range of 34 ° to 41 °. Further, according to the present invention, in such a total reflection type Fresnel lens sheet, the angle between the imaginary plane forming the light incident surface and the refracting surface is set to 90 ° or less, thereby releasing the Fresnel lens sheet from the mold. Productivity can be improved and productivity can be improved.

  In the Fresnel lens sheet of the present invention, the unit prism preferably has a refractive index in the range of 1.49 to 1.60.

  In the Fresnel lens sheet of the present invention, it is preferable that the Fresnel lens portion having the unit prism is formed on a sheet-like substrate.

  The Fresnel lens sheet of the present invention is, for example, (i) after applying an ultraviolet curable resin to a flat mold for forming a Fresnel lens sheet, and then curing by irradiating with ultraviolet rays, and then the mold It may have a single-layer structure manufactured by releasing the Fresnel lens sheet from, or, as another example, (ii) a flat mold for forming the Fresnel lens sheet is irradiated with ultraviolet rays. After the curable resin is applied, the sheet-like substrate is placed on the sheet-like substrate, and then the ultraviolet ray curable resin is cured by irradiating the sheet-like substrate with ultraviolet rays, and then the Fresnel lens sheet is separated from the mold. It may have a two-layer structure manufactured by molding, but the latter two-layer structure in which a Fresnel lens portion having a unit prism is formed on a sheet-like substrate is more productive. Excellent This is advantageous.

  In the Fresnel lens sheet of the present invention, (1) containing a diffusing agent that diffuses light, (2) colored to absorb light, and (3) a light absorbing layer that absorbs light. It is preferable to have one or two or more of (4) the coating layer which reduces a reflectance being formed in the one or both of the light-incidence surface and the light emission surface.

  The Fresnel lens sheet of the present invention can have any one or more of the configurations (1) to (4) as necessary in order to prevent the generation of stray light or attenuate the generated stray light. For example, (1) is an effective means for diffusing and attenuating stray light, (2) is an effective means for absorbing and attenuating stray light, and (3) is an effective means for absorbing stray light. This is an effective means for eliminating the absorption, and (4) is an effective means for reducing the generation of stray light.

  In order to solve the above problems, a transmission screen according to the present invention includes the Fresnel lens sheet according to the present invention described above and a light diffusion sheet.

  According to the present invention, since the Fresnel lens sheet that has good light utilization efficiency and is easy to manufacture and the light diffusion sheet that expands the viewing angle, it is possible to provide a transmission screen that is excellent in optical characteristics and high in mass productivity. .

  In the transmissive screen of the present invention, it is preferable that a coating layer for reducing the reflectance is formed on the surface of the transmissive screen on the viewer side.

  According to the present invention, since the coating layer for reducing the reflectance is formed on the surface of the transmissive screen on the viewer side, it is possible to provide a transmissive screen that can suppress the decrease in contrast.

  The rear projection type display device of the present invention for solving the above-described problems has a Fresnel lens sheet according to the present invention described above or a transmission type screen according to the present invention described above, and a minimum incident angle of light incident on the light incident surface. And a light source arranged so that the maximum incident angle is within a range of 65 ° or more and less than 85 ° within a range of 25 ° or more and less than 45 °.

  As described above, according to the Fresnel lens sheet of the present invention, the minimum incident angle of light incident on the light incident surface is in the range of 25 ° to 45 °, and the maximum incident angle is in the range of 65 ° to 85 °. In the total reflection type Fresnel lens sheet used in the projection optical system, the utilization efficiency of the light emitted from the light source can be improved and the releasability of the Fresnel lens sheet from the mold is facilitated. Productivity. Further, according to the Fresnel lens sheet of the present invention, it is possible to reduce the stray light and improve the utilization efficiency of the image light.

  According to the transmission type screen of the present invention, the optical properties are excellent and the mass productivity is good. In addition, by forming a coating layer that reduces the reflectance on the surface on the viewer side, it is possible to provide a transmission screen that can suppress a decrease in contrast.

  According to the rear projection type display device of the present invention, it is possible to provide a rear projection type display device that has high use efficiency of image light and can suppress a decrease in contrast.

  Hereinafter, the Fresnel lens sheet, transmissive screen, and rear projection display device of the present invention will be described with reference to the drawings.

(Fresnel lens sheet)
FIG. 1 is a schematic perspective view showing an example of the Fresnel lens sheet of the present invention, and FIG. 2 is a schematic longitudinal sectional view of the Fresnel lens sheet of FIG.

  As shown in FIGS. 1 and 2, the Fresnel lens sheet 11 of the present invention has a minimum incident angle θ1 of the light 3 incident on the light incident surface S1 in the range of 25 ° to 45 °, and a maximum incident angle θ2. Is a Fresnel lens sheet used in a projection optical system in the range of 65 ° or more and 85 ° or less. The light incident surface S1 includes a refracting surface 15 that refracts incident light 3 and the refracting surface 15 thereof. A plurality of unit prisms 14 each having a total reflection surface 16 that totally reflects refracted light are formed, the angle θa between the refraction surface 15 and the total reflection surface 16 is in the range of 34 ° to 41 °, and the light incident surface The feature is that the angle θb between the imaginary plane forming S1 and the refracting surface 16 is 90 ° or less. The symbol Q indicates a perpendicular extending from the Fresnel center O.

  As shown in FIG. 2, such a Fresnel lens sheet totally reflects part or all of the light 3 incident from the light incident surface S <b> 1 and deflects the light so as to be substantially parallel light 4 on the viewer side.

  As the form of the Fresnel lens sheet, as shown in FIGS. 1 and 2, a Fresnel lens part 13 having a unit prism 13 formed on a sheet-like base material 12 and a two-layer structure are shown in FIG. Thus, the thing of the single layer structure formed integrally, without distinguishing the base material 12 and the Fresnel lens part 13 may be sufficient. The former two-layer structure is excellent in accuracy, and the latter single-layer structure is excellent in productivity.

  As a resin material for forming the Fresnel lens portion 13, a resin such as a styrene resin, an acrylic-styrene copolymer resin, or a polycarbonate resin having a refractive index after molding in the range of 1.49 to 1.60. The material is arbitrarily used depending on the production method of the Fresnel lens sheet, but an acrylic-styrene copolymer resin which is an ultraviolet curable resin is particularly preferably used from the viewpoint of accuracy. The Fresnel lens sheet is manufactured by using a mold having the opposite shape of the unit prism 13 and molding the resin by press molding, injection molding, casting molding, or the like.

  The Fresnel lens sheet having a single layer structure can be manufactured by a casting method, a pressing method, a UV curing method, or the like. When manufacturing by the UV curing method, for example, an ultraviolet curable resin is applied to a flat mold for forming a Fresnel lens sheet, and then cured by irradiating with ultraviolet rays, and then the Fresnel lens sheet is removed from the mold. It can be manufactured by releasing the mold. On the other hand, the Fresnel lens sheet having a two-layer structure is obtained by, for example, applying a UV curable resin to a flat mold for forming a Fresnel lens sheet, and then placing the sheet-like substrate 12 thereon, and then the sheet-like substrate. It can be manufactured by irradiating ultraviolet rays from above the material 12 to cure the ultraviolet curable resin, and then releasing the Fresnel lens sheet from the mold.

When forming a UV curing method using an ultraviolet curable resin, for example, Young's modulus at 40 ° C. of the resin after curing is the use of the 20000 kg / cm ² or less of the ultraviolet curing resin, the unit prisms upon release from the mold Since the mold can be released while being elastically deformed, it is easy to release the mold.

(Unit prism)
FIG. 4 is a schematic side view showing an example of a projection optical system in which the Fresnel lens sheet of the present invention is used, and FIG. 5 is a schematic longitudinal view showing the shape of a unit prism included in the Fresnel lens sheet of the present invention. FIG.

  As shown in FIG. 4, the projection optical system using the Fresnel lens sheet of the present invention intersects at a point O where the optical axis deviates from the surface of the Fresnel lens sheet 11 (this point is the Fresnel center). It is configured. In such a projection optical system, the Fresnel lens sheet 11 of the present invention has a minimum incident angle θ1 of the light 3 incident on the light incident surface S1 in the range of 25 ° to 45 °, and a maximum incident angle θ2 of 65 ° or more. It arrange | positions so that it may become in the range of 85 degrees or less.

  The unit prism 14 included in the Fresnel lens sheet 11 is a lens element that is formed on the light incident surface S1 side and deflects the light 3 emitted from the light source 2 into the substantially parallel light 4 directed toward the observer side. An arc-shaped prism extending concentrically with O as a reference. As shown in FIG. 5, the unit prism 14 includes a refracting surface 15 that refracts incident light and a total reflection surface 16 that totally reflects light refracted by the refracting surface 15. The angle θa formed with the total reflection surface 16 is in the range of 34 ° to 41 °.

  In addition, although the pitch P1 and height h of each unit prism 14 are not specifically limited, Usually, the pitch P1 is 100-200 micrometers and the height h is 150-300 micrometers.

  In the unit prism 14, since the incident angle θ of the incident light 3 varies depending on the distance from the Fresnel center O, the shape of the unit prism 14 changes according to the incident angle θ.

  For example, the apex angle θa can be continuously changed within a range of 34 ° or more and 41 ° or less so that the side farther than the side closer to the Fresnel center O becomes larger. Further, the apex angle θa may be constant within a range of 34 ° to 41 °, and the angle θb between the refracting surface 15 and the virtual plane 17 and the angle θc between the total reflection surface 16 and the virtual plane 17 may be changed. . Further, the apex angle θa is changed within the range of 34 ° to 41 °, and the angle θb between the refractive surface 15 and the virtual plane 17 and the angle θc between the total reflection surface 16 and the virtual plane 17 are simultaneously changed. Also good.

  In the following, the apex angle θa (refractive surface and total reflection) of a unit prism of a Fresnel lens sheet used in a projection optical system having a minimum incident angle θ1 of 25 ° to 45 ° and a maximum incident angle θ2 of 65 ° to 85 °. The reason why the angle with respect to the surface is set to 34 ° to 41 ° will be described.

(Incident angle of projection optical system and apex angle of unit prism)
First, the maximum incident angle θ2 of the projection optical system will be described.

  For example, in a conventional refractive type Fresnel lens sheet having a refractive index of 1.55, when the incident angle θ is 65 °, the transmittance is reduced to 65.76%, which is a limit transmittance that can be used as a Fresnel lens sheet. On the other hand, since the Fresnel lens sheet of the present invention is a total reflection type Fresnel lens sheet, it can exhibit high transmittance even when the incident angle θ is 65 ° or more, and can be used. The upper limit of the incident angle θ in the total reflection type Fresnel lens sheet is not particularly limited, but the upper limit of the incident angle θ as a practical value is 85 °. Therefore, the Fresnel lens sheet of the present invention is preferably used in a projection optical system having a maximum incident angle θ2 of 65 ° to 85 °.

  Next, the apex angle θa of the unit prism will be described.

  In the Fresnel lens sheet of the present invention, when determining the apex angle θa of the unit prism 14, two matters are the light transmittance in the vicinity of the minimum incident angle θ 1 and the angle θb of the refracting surface in the vicinity of the maximum incident angle θ 2. Is considered.

  First, the light transmittance near the minimum incident angle θ1 will be discussed. FIG. 6 is a schematic diagram showing a light path when the incident angle θ of the light 3 entering the Fresnel lens sheet is 28 °. When the incident angle θ of the light 3 is as small as 28 °, a part of the light 3 refracted by the refracting surface 15 is not totally reflected by the total reflection surface 16 and is not deflected into substantially parallel light toward the viewer side. It becomes. As a result, the substantially parallel light deflected toward the viewer side may be relatively reduced to reduce the transmittance. To reduce the transmittance, the apex angle θa of the unit prism 14 is reduced to relatively increase the amount of light that is totally reflected by the total reflection surface 16 and deflected to the viewer side. The rate can be increased.

  Second, the angle of the refracting surface near the maximum incident angle θ2 will be examined. Since the unit prism 14 plays a role of totally reflecting the light 3 to make it substantially parallel light, the apex angle θa of the unit prism 14 must be reduced when the incident angle θ is large. However, if the apex angle θa is too small, the angle θb between the virtual plane 17 of the light incident surface S1 and the refractive surface 15 (sometimes simply referred to as the angle θb of the refractive surface 15) exceeds 90 °. If the angle θb exceeds 90 °, there is a problem in that the top of the unit lens 14 is bitten into the mold during molding, making it difficult to release the mold. Accordingly, it is desirable that the angle θb of the refracting surface 15 be 90 ° or less in the vicinity of the maximum incident angle θ2.

  On the other hand, when the apex angle θa of the unit prism 14 is increased, light that is not totally reflected by the total reflection surface 16 is likely to be generated, and the transmittance may be reduced. Therefore, it is preferable to make the apex angle θa of the unit prism 14 as small as possible near the maximum incident angle θ2 under the condition that the angle θb of the refractive surface 15 is 90 ° or less.

  In this regard, first, a case where the maximum incident angle θ2 is 65 ° will be considered. When the maximum incident angle θ2 is 65 °, the apex angle θa of the unit prism 14 is preferably as small as possible. Therefore, if the apex angle θa is 34 ° and the angle θb of the refracting surface 15 is 90 °, all the light refracted by the refracting surface 15 is totally reflected by the total reflection surface 16, and the substantially parallel light totally reflected is 10 ° downward. Light is emitted toward the viewer at an angle of. At this time, if the apex angle θa is less than 34 °, the totally reflected light is emitted downward, and the difference in luminance between the image light emitted substantially perpendicularly to the viewer side at the center of the screen. Is not preferable because it becomes too large. In consideration of the difference in brightness, the angle of downward deflection is considered to be 10 °, so when the maximum incident angle θ2 is 65 °, the apex angle θa is preferably 34 ° or more.

  When the apex angle θa is 34 ° and the Fresnel lens sheet is arranged so that the minimum incident angle θ1 is 25 °, the light is emitted downward 10 °, and the transmittance at that time is 63.5%. Since transmission below this is not preferred, it is not appropriate to use a minimum incident angle θ1 of less than 25 °. Therefore, when the apex angle θa is 34 °, it is preferable to use a projection optical system having an incident angle θ of 25 ° (minimum incident angle θ1) to 65 ° (maximum incident angle θ2).

  Next, a case where the maximum incident angle θ2 is 85 ° will be considered. Even when the maximum incident angle θ2 is 85 °, the apex angle θa of the unit prism 14 is preferably as small as possible within a range where the angle θb of the refractive surface 15 does not exceed 90 °. Therefore, if the apex angle θa is 41 ° and the angle θb of the refracting surface 15 is 90 °, all the light refracted by the refracting surface 15 is totally reflected by the total reflection surface 16, and the substantially parallel light totally reflected is 10 ° downward. Light is emitted toward the viewer at an angle of.

  When the apex angle θa is 41 ° and the Fresnel lens sheet is arranged so that the minimum incident angle θ1 is 30 °, the light is emitted downward 10 °, and the transmittance at that time is 63.1%. Since transmission below this is not preferred, it is not appropriate to use a minimum incident angle θ1 of less than 30 °. Therefore, when the apex angle θa is 34 °, it is preferable to use a projection optical system having an incident angle θ of 30 ° (minimum incident angle θ1) to 85 ° (maximum incident angle θ2).

  The above examination was performed under the condition that the apex angle θa of the unit prism 14 was constant, but the apex angle θa can be changed according to the distance from the Fresnel center O. For example, the transmittance can be increased by setting the apex angle θa of the unit prism 14 near the minimum incident angle θ1 to a smaller angle.

  However, even if the apex angle θa is less than 34 °, this improvement effect may hardly occur. For example, even when the incident angle is 25 ° and the apex angle θa of the unit prism 14 is 32 °, the transmittance when the image light is emitted 10 ° downward from the normal line of the light exit surface is 63.9%, and the apex angle θa is Compared to the transmittance in the case of 34 °, only 0.4% is improved. Therefore, it can be considered that it is not so meaningful to make the apex angle θa of the unit prism 14 less than 34 °.

  For this reason, even when the apex angle θa of the unit prism 14 is changed according to the distance from the Fresnel center O, the apex angle θa of the unit prism 14 should be set within a range of 34 ° to 41 °. Is preferred.

  As described above, in the Fresnel lens sheet of the present invention, the apex angle θa of the unit prism 14 is in the range of 34 ° or more and 41 ° or less, so that the normal to the light exit surface S2 of the Fresnel lens sheet is obtained. Light can be emitted efficiently in the range of 0 ° to 10 ° downward (at least 60% or more of incident light), and a Fresnel lens sheet with good optical performance can be obtained. Further, by setting the angle θb between the imaginary plane forming the light incident surface and the refracting surface 15 to be 90 ° or less, it is easy to release during molding, and a Fresnel lens sheet with good mass productivity can be provided.

(Stray light suppression means)
Various means for suppressing stray light can be applied to the Fresnel lens sheet of the present invention.

  Here, stray light will be described. As shown in FIG. 7, the stray light 5 is light that does not enter the total reflection surface 16 among the light 3 that enters from the light incident surface S <b> 1 side. The stray light 5 is likely to be generated when the incident angle θ of the image light 5 with respect to the Fresnel lens sheet 31 is small, and is likely to be generated near the lower end of the Fresnel lens sheet. The stray light 5 generated in the Fresnel lens sheet 31 is reflected by the light exit surface S2, enters the prism element again, repeats refraction, and then exits again. The light 6 that is emitted at this time is different from the normal image light 4 that is reflected by the total reflection surface 16 and emitted. Such a difference in light output position causes a double image.

  In the Fresnel lens sheet of the present invention, it is preferable to suppress the occurrence of double images due to stray light by the following means.

  The first is a means for containing a diffusing agent in the Fresnel lens sheet. FIG. 8 is a cross-sectional view showing an example in which the Fresnel lens sheet of the present invention contains a diffusing agent 7 that diffuses light. The diffusing agent 7 may be contained in the entire Fresnel lens sheet 41 as shown in FIG. 8A, or a sheet constituting the Fresnel lens sheet 51 as shown in FIG. 8B. It may be contained only in the substrate 12. The diffusing agent 7 is selected in consideration of the difference in refractive index depending on the type of resin constituting the Fresnel lens sheet. For example, styrene resin fine particles, silicone resin fine particles, acrylic resin fine particles, MS resin fine particles, etc. Organic fine particles, barium sulfate fine particles, glass fine particles, aluminum hydroxide fine particles, calcium carbonate fine particles, silica (silicon dioxide) fine particles, titanium oxide fine particles, and other inorganic fine particles can be mentioned, and one or more of these are included. It is blended in the resin. Various particle shapes such as a true spherical shape, a substantially spherical shape, and an indefinite shape can be used. In this Fresnel lens sheet, stray light 5 having a long optical path length is repeatedly refracted in the Fresnel lens sheet, but is diffused by the diffusing agent 7 contained in the sheet, so that the double image becomes inconspicuous.

  Secondly, there is a means for coloring the Fresnel lens sheet to absorb light. Examples of the colorant include black dyes, pigments, carbon black, and the like. Examples of the coloring method include a method of casting by mixing these colorants and a resin, and a method of extrusion molding. In this Fresnel lens sheet, stray light having a long optical path length is greatly absorbed in the colored Fresnel lens sheet as compared with video light having a short optical path length that is emitted as designed, so that the double image becomes inconspicuous.

  Third, there is a means for forming a light absorption layer on the Fresnel lens sheet. FIG. 9 is a cross-sectional view showing an example in which the Fresnel lens sheet 61 of the present invention has the light absorption layer 8. The light absorbing layer 8 has a groove shape formed from the surface on the light exit surface S2 side of the Fresnel lens sheet 61 toward the inside, and has a thickness of, for example, about 5 μm when viewed from the light exit surface S2 side. Thin grooves having a depth of about 50 μm are arranged in parallel to the light traveling direction at equal intervals, and are formed by embedding black ink in the thin grooves by a wiping method. In the Fresnel lens sheet 61, the stray light 5 having a long optical path length is absorbed by the light absorption layer 8, so that the double image becomes inconspicuous.

  In the Fresnel lens sheet of the present invention, the influence of stray light generated can be suppressed as much as possible by applying each of these means.

  Moreover, you may form the coating layer which reduces a reflectance in the any one surface of the Fresnel lens sheet of this invention, ie, any one or both of the light-incidence surface S1 and the light emission surface S2. The coating layer is preferably formed of a material having a low refractive index. For example, a fluorine resin or a silicone resin is preferably used. Examples of the coating method include a dipping method and a flow coating method. The coating layer is preferably provided on the light exit surface side of the Fresnel lens sheet, but it is more effective when provided on both surfaces. In this Fresnel lens sheet, since the coating layer exhibits an antireflection effect, a decrease in image contrast due to reflected light on the surface is suppressed.

  A coating layer similar to the above is also formed on a Fresnel lens sheet having a lenticular lens element, which will be described later, and a composite transmission screen having a two-sheet structure in which a Fresnel lens sheet and a lenticular lens sheet are combined. can do.

(Transparent screen)
As long as the transmission type screen of the present invention has the Fresnel lens sheet of the present invention described above, various modes can be exemplified. For example, as shown in FIGS. 10 to 15, a transmission screen (FIGS. 10 to 13) in which a light diffusion sheet (lenticular lens sheet) and the Fresnel lens sheet according to the present invention are integrated with an adhesive, or The thing which both arranged oppositely (FIG. 14, FIG. 15) can be mentioned. These will be briefly described below.

  FIG. 10 shows an example in which a lenticular lens sheet 102 in which cylindrical lenses 104 extending in the vertical direction are juxtaposed in the horizontal direction is bonded to the light exit surface of the Fresnel lens sheet 11 with an adhesive 103. Since this lenticular lens sheet 102 diffuses light in the horizontal direction by the action of the cylindrical lens 104, stray light is also diffused and the double image becomes inconspicuous.

  FIG. 11 shows an example in which a lenticular lens sheet 112 in which trapezoidal lens portions extending in the vertical direction are juxtaposed in the horizontal direction is bonded to the light output surface of the Fresnel lens sheet 11 via an adhesive 113. Since the lenticular lens sheet 112 totally reflects the stray light on the slopes 115 and 115 of the trapezoid 114, the stray light can be made inconspicuous. Reference numeral 116 denotes a V-shaped groove that exists between adjacent trapezoids 114, 114.

  FIG. 12 is a schematic perspective view showing another example of the transmissive screen. In the lenticular lens sheet 122 used here, the V-shaped groove 116 included in the lenticular lens sheet 112 of FIG. 11 is filled with the low-refractive-index light absorbing material 125, and a rigid support plate 124 is pasted thereon. It is a combination. A transmissive screen 121 in FIG. 12 is an example in which the Fresnel lens sheet 11 of the present invention and a lenticular lens sheet 112 are bonded together with an adhesive 123.

  FIG. 13 is a schematic perspective view showing another example of the transmission screen. The lenticular lens sheet 132 used here is provided with a resin layer 134 instead of the support plate 124 included in the lenticular lens sheet 122 of FIG. A transmission screen 131 in FIG. 13 is an example in which the Fresnel lens sheet 11 of the present invention and a lenticular lens sheet 132 are bonded together with an adhesive 133.

  14 and 15 are perspective views showing other forms of the transmission screen of the present invention. These are forms in which the Fresnel lens sheet 11 of the present invention and a lenticular lens sheet are arranged to face each other.

  The lenticular lens sheet 142 constituting the transmission screen of FIG. 14 includes a lenticular lens portion 143 in which cylindrical lenses 144 extending in the vertical direction are arranged side by side and a rigid support plate 145 via an adhesive 148. Further, a photosensitive resin layer 146 and a black stripe layer 147 formed on the photosensitive resin layer 146 are formed on the bonding surface. 14 is an example in which a lenticular lens sheet 142 is opposed to the Fresnel lens sheet 11 so that the cylindrical lens 144 faces the Fresnel lens sheet 11 side.

  The lenticular lens sheet 152 constituting the transmission screen of FIG. 15 is a lenticular lens sheet 152 in which cylindrical lenses 154 extending in the vertical direction are arranged side by side, and a colored layer 153 is formed on the cylindrical lens 154. It is a thing. The transmission screen 151 in FIG. 15 is an example in which a lenticular lens sheet 152 is opposed to the Fresnel lens sheet 11 so that a cylindrical lens 154 faces the Fresnel lens sheet 11 side.

  As in the case of the Fresnel lens sheet, a coating layer that reduces the reflectance can be provided on the surface of these transmissive screens, whereby the reduction in contrast can be suppressed.

(Rear projection display)
FIG. 16 is a schematic diagram illustrating an example of the rear projection display device of the present invention, and FIG. 17 is a schematic diagram illustrating another example of the rear projection display device of the present invention.

  The rear projection display devices 70 and 80 of the present invention use a transmissive screen 71 in which the surface on the Fresnel lens sheet side according to the present invention is arranged in the light source direction. The above-described transmission type screen according to the present invention can be applied to the transmission type screen 71.

  In the rear projection display devices 70 and 80, the image light source 73 is disposed at the bottom of the relatively thin casings 72 and 82, and the transmissive screen 71 is attached to the front window portion of the casings 72 and 82. ing. A rear projection display device 70 shown in FIG. 16 is a device in which a video light source 73 is disposed below a transmissive screen 71 and is projected obliquely from the video light source 73 toward the transmissive screen 71. On the other hand, the rear projection display device 80 shown in FIG. 17 is also a device in which the image light source 73 is disposed below the transmissive screen 71 and is projected obliquely from the image light source 73 toward the transmissive screen 71. In the rear projection display device 80, the image light 3 is reflected by a mirror 83 that is disposed close to the inner surface of the rear wall of the housing 82.

  In the rear projection display device of the present invention, the Fresnel lens sheet according to the present invention is arranged so as to be a projection optical system having a minimum incident angle of 25 ° to 45 ° and a maximum incident angle of 65 ° to 85 °. Is done.

  The present invention will be described more specifically with reference to the following examples.

Example 1
As a rear projection display device in which image light is projected obliquely from the rear, the screen size is 50 inches (aspect ratio 4: 3, length 762 mm × width 1062 mm), the horizontal distance from the transmissive screen to the projector (light source) is 460 mm, and the bottom of the screen The projection optical system was configured such that the vertical distance from the projector to the horizontal plane including the projector was 386 mm, the minimum incident angle θ1 of the image light was 40 °, and the maximum incident angle θ2 of the image light was 70 °.

  Preparation of Fresnel lens sheet: First, a shaping mold having a prism (pitch: 0.11 mm, apex angle θa: constant 38 °, angle of refraction surface θb: 90 ° or less) formed is prepared, and its shaping is performed. A Fresnel lens sheet according to the present invention having an apex angle θa of 38 °, a thickness of 3 mm, and a refractive index of 1.49 was prepared by a casting method in which an acrylic resin monomer was applied to the mold and then polymerized and cured.

  Characteristics in the vicinity of the minimum incident angle θ1; the unit prism of this Fresnel lens sheet is designed so that the angle θb of the refracting surface at the portion where the minimum incident angle θ1 (40 °) of the image light is 77.5 ° Yes. At this minimum incident angle θ1, the angle of light emitted to the viewer side is 5 ° downward, and 87% of the image light incident on the refracting surface of the unit prism is totally reflected on the total reflection surface of the unit prism. Reflected and emitted to the viewer side.

  Characteristics near maximum incident angle θ2: The unit prism of this Fresnel lens sheet is designed so that the angle θb of the refracting surface at the portion where the maximum incident angle θ2 (70 °) of the image light is 90 °. At the portion of the maximum incident angle θ2, the angle of the light emitted to the observer side is 8 ° downward, and 100% of the image light incident on the refracting surface of the unit prism is totally reflected on the total reflection surface of the unit prism. Reflected and emitted to the viewer side.

  Characteristics at minimum incident angle θ1 to maximum incident angle θ2; the unit prism of this Fresnel lens sheet has a refractive surface angle θb gradually ranging from 77.5 ° to 90 ° between minimum incident angle θ1 and maximum incident angle θ2. It is designed to be large. Between the minimum incident angle θ1 and the maximum incident angle θ2, the angle of light emitted to the observer side gradually decreases from 5 ° downward to 0 °, and further gradually decreases from 0 ° downward to 8 °. Within this range, 87% or more of the image light incident on the refracting surface of the unit prism was totally reflected by the total reflection surface of the unit prism and emitted to the viewer side.

  Production of light diffusion sheet (lenticular lens sheet); Extrusion having a cylindrical lens shaping mold on the peripheral surface using a resin material containing 3% by mass of a diffusing agent composed of MS resin fine particles in acrylic styrene copolymer resin It formed using the forming roll. The obtained lenticular lens sheet had a thickness of 1 mm and a cylindrical lens pitch of 0.14 mm.

  An acrylic resin adhesive is applied to the surface of the light diffusion sheet thus obtained, and a Fresnel lens sheet is bonded to the adhesive surface to produce an integrated transmission screen of Example 1 having the form shown in FIG. did.

  Optical characteristics: The optical characteristics of the transmission screen were measured. This transmissive screen had a peak gain of 4, αH25 °, and αV8 °. Here, the gain is measured by measuring the angular distribution of the luminance of light incident from the rear of the screen and coming out of the screen, and gain G = π × luminance (cd / m2) / illuminance (lx). The peak gain is the maximum gain value in the screen. In the present application, the peak gain is the maximum value when the center of the screen is observed from the front of the screen. ΑH is the half-value angle of the peak gain in the horizontal direction, and αV represents the half-value angle of the peak gain in the vertical direction.

  The transmissive screen of Example 1 manufactured in this way can improve the utilization efficiency of the light emitted from the light source, and can easily improve the productivity by easily releasing the Fresnel lens sheet from the mold. Can do. Moreover, stray light was reduced and a good image was obtained.

(Example 2)
As a rear projection display device in which image light is projected obliquely from the rear, the screen size is 60 inches (aspect ratio 4: 3, length 914 mm × width 1219 mm), the horizontal distance from the transmissive screen to the projector (light source) is 225 mm, the bottom of the screen The projection optical system was configured so that the vertical distance from the projector to the horizontal plane including the projector was 210 mm, the minimum incident angle θ1 of the image light was 43 °, and the maximum incident angle θ2 of the image light was 80 °.

  Preparation of Fresnel lens sheet: First, a shaping mold having a prism (pitch: 0.11 mm, apex angle θa: constant 40 °, angle of refraction surface θb: 90 ° or less) formed is prepared, and its shaping is performed. After the molten polycarbonate resin flows down from the top of the mold, the flat plate is pressed from above, and after cooling, the mold is released from the shaping mold, and the apex angle θa is 40 °, the thickness is 3 mm, and the refractive index is 1.59. A Fresnel lens sheet according to the invention was produced.

  Characteristics near the minimum incident angle θ1; the unit prism of this Fresnel lens sheet is designed so that the angle θb of the refracting surface at the portion where the minimum incident angle θ1 (43 °) of the image light is 76.1 °. Yes. At the portion of the minimum incident angle θ1, the angle of the light emitted to the observer side is 5 ° downward, and 90% of the image light incident on the refractive surface of the unit prism is totally reflected on the total reflection surface of the unit prism. Reflected and emitted to the viewer side.

  Characteristics in the vicinity of the maximum incident angle θ2: The unit prism of this Fresnel lens sheet is designed so that the angle θb of the refracting surface at the portion where the maximum incident angle θ2 (80 °) of the image light is 90 °. At the portion of the maximum incident angle θ2, the angle of light emitted to the observer side is 5 ° downward, and 100% of the image light incident on the refractive surface of the unit prism is totally reflected on the total reflection surface of the unit prism. Reflected and emitted to the viewer side.

  Characteristics at minimum incident angle θ1 to maximum incident angle θ2; the unit prism of this Fresnel lens sheet has a refractive surface angle θb gradually ranging from 76.1 ° to 90 ° between minimum incident angle θ1 and maximum incident angle θ2. It is designed to be large. Between the minimum incident angle θ1 and the maximum incident angle θ2, the angle of light emitted to the observer side gradually decreases from 5 ° downward to 0 °, and further gradually decreases from 0 ° downward to 5 °. In this range, 90% or more of the image light incident on the refracting surface of the unit prism was totally reflected by the total reflection surface of the unit prism and emitted to the viewer side.

  The same light diffusion sheet (lenticular lens sheet) as in Example 1 was used, an acrylic resin adhesive was applied to the surface of the light diffusion sheet, and the Fresnel lens sheet was bonded to the adhesive surface, as shown in FIG. An integral transmission screen of Example 2 having a shape was produced.

  Optical characteristics: The optical characteristics of the transmission screen were measured. This transmissive screen had a peak gain of 4, αH25 °, and αV8 °.

  The transmissive screen of Example 2 manufactured in this way can improve the utilization efficiency of light emitted from the light source, and easily improve the productivity by releasing the Fresnel lens sheet from the mold. be able to. Moreover, stray light was reduced and a good image was obtained.

(Example 3)
As a rear projection display device in which image light is projected obliquely from the rear, the screen size is 70 inches (aspect ratio 4: 3, length 1066 mm × width 1422 mm), horizontal distance from the transmissive screen to the projector (light source) is 345 mm, and the bottom edge of the screen The projection optical system was configured such that the vertical distance from the projector to the horizontal plane including the projector was 251 mm, the minimum incident angle θ1 of the image light was 36 °, and the maximum incident angle θ2 of the image light was 77 °.

  Preparation of Fresnel lens sheet; First, a shaping mold in which an inverted shape of a prism (pitch: 0.11 mm, apex angle θa: variable from 34 ° to 41 °, refractive surface angle θb: 90 ° or less) is prepared The urethane acrylate resin, which is an ultraviolet curable resin, was applied to the shaping mold. Thereafter, a sheet-like substrate (thickness 4 mm) made of a polycarbonate resin is placed on the ultraviolet ray curable resin, and then ultraviolet rays (wavelength range: 300 to 400 nm, irradiation intensity: 700 mJ / cm 2) from above the substrate. Was applied to cure the ultraviolet curable resin, and a Fresnel lens sheet according to the present invention having an apex angle θa of 34 ° to 41 ° variable, a thickness of 4.3 mm, and a refractive index of 1.55 was produced.

  Characteristics near the minimum incident angle θ1; the unit prism of this Fresnel lens sheet is designed so that the angle θb of the refracting surface at the portion where the minimum incident angle θ1 (36 °) of the image light is 79.3 ° Yes. At the portion of this minimum incident angle θ1, the angle of the light emitted to the observer side is 10 ° downward, and 87.5% of the image light incident on the refractive surface of the unit prism is the total reflection surface of the unit prism. And totally reflected on the viewer side.

  Characteristics near maximum incident angle θ2: The unit prism of this Fresnel lens sheet is designed so that the angle θb of the refracting surface at the portion where the maximum incident angle θ2 (77 °) of image light is 90 °. At the maximum incident angle θ2, the angle of the light emitted to the viewer side is 0 ° downward, and 100% of the image light incident on the refractive surface of the unit prism is totally reflected on the total reflection surface of the unit prism. Reflected and emitted to the viewer side.

  Characteristics at minimum incident angle θ1 to maximum incident angle θ2; the unit prism of this Fresnel lens sheet has a refractive surface angle θb of 90 ° or less between minimum incident angle θ1 and maximum incident angle θ2. The angle θa was gradually increased from 34 ° to 41 °. Between the minimum incident angle θ1 and the maximum incident angle θ2, the angle of light emitted to the viewer side gradually decreases from 10 ° downward to 0 °. In this range, 87.5% or more of the image light incident on the refracting surface of the unit prism was totally reflected by the total reflection surface of the unit prism and emitted to the viewer side.

  The same light diffusion sheet (lenticular lens sheet) as in Example 1 was used, an acrylic resin adhesive was applied to the surface of the light diffusion sheet, and the Fresnel lens sheet was bonded to the adhesive surface, as shown in FIG. An integral transmission screen of Example 3 having a shape was produced.

  Optical characteristics: The optical characteristics of the transmission screen were measured. This transmissive screen had a peak gain of 4, αH25 °, and αV8 °.

  The transmissive screen produced in Example 3 in this way can improve the utilization efficiency of the light emitted from the light source, and can easily improve the productivity by releasing the Fresnel lens sheet from the mold. Can do. Moreover, stray light was reduced and a good image was obtained.

Example 4
In Example 1, the transmissive screen of Example 4 was configured in the same manner as Example 1 except that the light diffusion sheet (lenticular lens sheet) was changed to the following.

  Production of light diffusing sheet (lenticular lens sheet); a shaping mold for forming a trapezoidal shape on the peripheral surface using a resin material containing 3% by mass of a diffusing agent composed of glass fine particles in an acrylic styrene copolymer resin It formed using the extrusion-molding roll which has. The obtained lenticular lens sheet has a shape in which a light guide (condensing part) having a plurality of trapezoidal cross sections extends in the vertical direction, the thickness is 1 mm, and the pitch of the trapezoidal lenses is 0.14 mm. . Further, a light-absorbing material having a lower refractive index than that of the acrylic styrene copolymer resin was filled in the V-shaped groove between the trapezoidal shapes.

  An acrylic resin-based adhesive was applied to the surface of the light diffusion sheet thus obtained, and a Fresnel lens sheet was bonded to the adhesive surface to produce an integrated transmission screen of Example 4 having the form shown in FIG. did.

  Optical characteristics: The optical characteristics of the transmission screen were measured. This transmissive screen had a peak gain of 2, αH 40 °, and αV 10 °.

  The transmissive screen of Example 4 manufactured in this way can improve the utilization efficiency of the light emitted from the light source, and can easily improve the productivity by easily releasing the Fresnel lens sheet from the mold. Can do. Moreover, stray light was reduced and a good image was obtained.

(Comparative Example 1)
Screen size 50 inches (aspect ratio 4: 3, length 762 mm x width 1062 mm), horizontal distance from the transmissive screen to the projector (light source) 300 mm, vertical distance from the bottom of the screen to the horizontal plane including the projector Minimum incident angle of image light The projection optical system was configured such that θ1 was 30 ° and the maximum incident angle θ2 of the image light was 77 °.

  Preparation of Fresnel lens sheet: A shaping mold in which an inverted shape of a prism (pitch: 0.1 mm, apex angle θa: constant 42 °, angle of refraction surface θb: 90 ° or less) is formed, and the shaping mold Acrylic resin was applied to the surface. Thereafter, a Fresnel lens sheet having an apex angle θa of 42 °, a thickness of 3 mm, and a refractive index of 1.49 was produced by a casting method for polymerization and curing.

  The unit prism of this Fresnel lens sheet is designed so that the angle θb of the refracting surface at the portion where the minimum incident angle θ1 (30 °) of the image light is 66.81 °. In the region having the minimum incident angle θ1, the angle of light emitted to the viewer side is 10 ° downward. Of the image light incident on this unit prism, only 62.4% of the light is reflected by the total reflection surface and is emitted to the viewer side, which is less than 65% of the transmittance that can be used as a Fresnel lens sheet, and light diffusion. When this sheet was combined with a sheet (lenticular lens sheet) to form a transmissive screen, this portion looked dark, so a good image could not be obtained.

(Comparative Example 2)
Fabrication of Fresnel lens sheet: A shaping mold having a prism (pitch: 0.1 mm, apex angle θa: constant 33 °, refracting surface angle θb: 95.7 ° or less) is prepared, A urethane acrylate resin, which is an ultraviolet curable resin, was applied to the mold. Thereafter, a sheet-like base material (thickness 4 mm) made of a polycarbonate resin is placed on the ultraviolet curable resin, and then ultraviolet rays (wavelength range: 300 to 400 nm, irradiation intensity: 700 mJ / cm ² ) are applied from above the base material. Irradiation was attempted to release the base material and the cured UV curable resin from the shaping mold, but the UV curable resin did not peel from the shaping mold at a portion where θb exceeded 90 °, and a Fresnel lens sheet was obtained. I couldn't.

It is a typical perspective view which shows an example of the Fresnel lens sheet of this invention. It is a typical longitudinal cross-sectional view of the Fresnel lens sheet of FIG. It is a typical longitudinal section showing other examples of the Fresnel lens sheet of the present invention. It is a typical side view showing an example of a projection optical system in which the Fresnel lens sheet of the present invention is used. It is a typical longitudinal cross-sectional view which shows the shape of the unit prism which the Fresnel lens sheet of this invention has. It is a schematic diagram which shows a light beam path | route when the incident angle (theta) of the light which injects into a Fresnel lens sheet is 28 degrees. It is a ray tracing diagram explaining the stray light in a Fresnel lens sheet. It is a section lineblock diagram showing an example in which a Fresnel lens sheet contains a diffusing agent which diffuses light. It is sectional drawing which shows an example in which the Fresnel lens sheet has a light absorption layer. It is a typical perspective view which shows an example of the transmission type screen of this invention. It is a typical perspective view which shows another example of the transmission type screen of this invention. It is a typical perspective view which shows another example of the transmission type screen of this invention. It is a typical perspective view which shows another example of the transmission type screen of this invention. It is a typical perspective view which shows another example of the transmission type screen of this invention. It is a typical perspective view which shows another example of the transmission type screen of this invention. It is a typical side view which shows an example of the rear projection type display apparatus of this invention. It is a typical side view which shows another example of the rear projection type display apparatus of this invention.

Explanation of symbols

2, 73 Light source 3 Light (incident light)
4 substantially parallel light 4 'light not totally reflected 5 stray light 6 emitted light 7 diffusing agent 8 light absorbing layer 11, 21, 31, 41, 51, 61 Fresnel lens sheet 12 base material 13 Fresnel lens part 14 unit prism 15 refractive surface 16 Total reflection surface 17 Virtual plane of light incident surface 70, 80 Rear projection display device 72, 82 Case 83 Mirror 71, 101, 111, 121, 131, 141, 151 Transmission type screen 102, 112, 122, 132, 142, 152 Lenticular lens sheet 103, 113, 123, 133, 143, 153 Adhesive 104, 144, 154 Cylindrical lens 114 Trapezoid 115 Slope 116 V-shaped groove 124, 145 Support plate 125, 135 Light absorber 134 Resin layer 146 Photosensitive resin layer 147 Black stripe layer 14 Adhesive 153 Colored layer θ1 Minimum incident angle θ2 Maximum incident angle θa Angle between the refracting surface and the total reflection surface θc Angle between the imaginary plane forming the light incident surface and the refractive surface Q Vertical line extending from the Fresnel center O Fresnel center S1 Light incident surface S2 Light exit surface P Unit prism pitch h Unit prism height

Claims (10)

This is a Fresnel lens sheet used in a projection optical system in which the minimum incident angle of light incident on the light incident surface is in the range of 25 ° to 45 ° and the maximum incident angle is in the range of 65 ° to 85 °. And
A plurality of unit prisms having a refracting surface that refracts incident light and a total reflection surface that totally reflects light refracted by the refracting surface are formed on the light incident surface,
An angle between the refractive surface and the total reflection surface is in a range of 34 ° to 41 °,
The Fresnel lens sheet, wherein an angle between a virtual plane forming the light incident surface and the refracting surface is 90 ° or less.   The Fresnel lens sheet according to claim 1, wherein a refractive index of the unit prism is in a range of 1.49 to 1.60.   The Fresnel lens sheet according to claim 1, wherein the Fresnel lens portion having the unit prism is formed on a sheet-like base material.   The Fresnel lens sheet according to any one of claims 1 to 3, further comprising a diffusing agent that diffuses light.   The Fresnel lens sheet according to claim 1, wherein the Fresnel lens sheet is colored so as to absorb light.   The Fresnel lens sheet according to claim 1, further comprising a light absorption layer that absorbs light.   The Fresnel lens sheet according to any one of claims 1 to 3, wherein a coating layer for reducing the reflectance is formed on one or both of the light incident surface and the light outgoing surface.   A transmissive screen comprising the Fresnel lens sheet according to claim 1 and a light diffusing sheet.   9. The transmissive screen according to claim 8, wherein a coating layer for reducing the reflectance is formed on the surface of the transmissive screen on the viewer side. The Fresnel lens sheet according to any one of claims 1 to 7, or the transmission screen according to claim 8 or 9,
And a light source arranged so that the minimum incident angle of light incident on the light incident surface is within a range of 25 ° to less than 45 ° and a maximum incident angle is within a range of 65 ° to less than 85 °. A rear projection type display device.

Images