JPS6128979B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a rear projection screen used, for example, as a screen for a video projector.

Rear projection screens are used as projection surfaces for video projectors, microfilm readers, computer displays, etc., and various studies have been made on their light transmission characteristics, such as increasing their viewing angle. One of the means to achieve this purpose is to use a lenticular lens sheet in which a large number of minute cylindrical lenses are continuously formed, either alone or in combination with other lenses or a diffuser plate. ing.

As mentioned above, this lenticular lens sheet is effective in diffusing the incident light, and the one in which a large number of tiny cylindrical lenses are continuously formed in the vertical direction diffuses the light in the horizontal direction. The one formed with minute cylindrical lenses has the function of diffusing light in the vertical direction. Also, when using this lenticular lens sheet as a screen,
The maximum diffusion angle is limited when the lens surface faces the incident light side, that is, the light source side, and when it faces the exit side, that is, the observer side. It is known that the diffusion angle can be increased compared to the case where However, in general, the angle of light diffusion by this type of lenticular lens is narrow, for example, the first
As shown in Figure 6, the problem is that the brightness rapidly decreases at points beyond 30 degrees from the center.

Regarding such screens, the present inventors have already proposed inventions in Japanese Patent Application No. 56-51194 and Japanese Patent Application No. 56-91896. The former invention is a lenticular lens in which a total reflection surface is formed on both side surfaces of the lens unit, and the totally reflected light rays are emitted from the top, which makes it bright and has a large viewing angle. It turns out that a rear projection screen is obtained. In addition, the latter invention forms a concave surface on the top of the former invention, thereby making it possible to reduce the height of the lens and facilitate molding. However, further investigation into the latter of these inventions revealed that if the angle between the concave surface at the top and the total reflection surface becomes sharp, it is not only difficult to manufacture the mold, but also difficult to manufacture. In fact, it was found that this part was prone to chipping and, moreover, it was difficult to release the mold from the mold during molding. The present invention aims to improve these points and provide a rear projection screen that has superior performance and is easy to manufacture.

That is, the gist of the present invention is a rear projection screen in which a lenticular lens is formed at least on the viewing side of the medium, and the lenticular lens has a concave surface in the central portion and a junction adjacent to both sides of the concave surface. The lens unit is composed of a series of lens units each having a top portion and both side surfaces formed by a flat surface, and the concave surface of the top portion of this lens unit is formed so as to emit the light rays directly incident on this portion. At least a part of each side surface of each lens unit is formed with a total reflection surface that totally reflects the light rays incident on this part, and most of the light rays that are totally reflected on the total reflection surface are reflected on the concave total reflection surface. A first invention provides a rear projection screen characterized in that light is emitted from the near side, and the rear projection screen has a lenticular lens formed at least on the viewing side of the medium, the lenticular lens being a first lens unit having a top portion and both side surface portions formed by one concave surface in the central portion and bonded planes adjacent to both sides thereof; and a second lens unit located between the first lens unit; The concave surface at the top of the first lens unit is formed so as to emit the light rays directly incident on this part, and at least the concave surface on the top of the first lens unit In some parts, total reflection surfaces are formed that completely reflect the light rays incident on these parts, and most of the light rays totally reflected on the total reflection surfaces exit from the side of the concave surface that is closer to the total reflection surface. A second aspect of the present invention provides a rear projection screen, characterized in that the second lens unit is formed with a lens surface that emits light rays directly incident on the second lens unit.

The present invention will be described below with reference to drawings of embodiments.

FIG. 1 is a perspective view of a rear projection screen showing an embodiment of the first invention, and FIG. 4 is a perspective view of a rear projection screen showing an embodiment of the first invention.
FIG. 3 is a cross-sectional plan view cut along a line. First, to explain this embodiment, 1 is a lens unit constituting a lenticular lens, which includes one concave surface 10a at the center and bonding planes 10 adjacent to both sides of the concave surface 10a.
It is composed of a top portion 10 and both side portions 11 formed by b. In this example, the entire surface of both side surfaces 11 is a total reflection surface.
It may be partially formed. Also, both side parts 11
As will be described later, the total reflection surface totally reflects the light rays incident on this portion and emits the light from the concave surface 10a. Note that 3 in the figure is the entrance surface on the opposite side to the lenticular lens. This shape is the seventh
To explain in more detail based on the figure, this is an enlarged lens unit 1 of the lenticular lens of the present invention, and the central part of the top part 10 has a concave surface 10.
Total reflection surfaces are formed on the joint plane 10b adjacent to the joint plane 10a on both sides thereof, and on both side surfaces 11. For such a lenticular lens, the entrance surface 3
When parallel light is incident from , as shown in Figure 7, A ₁ of this ray hits the slope LM of the total reflection surface, is totally reflected here, and is reflected on the total reflection surface of the concave NO in the center of the top surface. It emits from the near side as A ₁ ′. Further, the light ray A ₂ directly incident on the concave surface 10a is diffused and emitted as A ₂ ', and the light ray A ₃ incident on the joining plane 10b continues straight and exits as A ₃ '. Although FIG. 7 describes the state of refraction of light in the left half of the center, such refraction of light also occurs in the symmetrical right half.

Since the lens unit 1 of the present invention has the above-mentioned characteristics, light incident from the back surface is diffused as shown in FIG. 8. That is, the light Y incident on the concave surface 10a exits as refracted Y', but
The light X incident on the total reflection surface is to be totally reflected and diffused at an angle distant from the center as indicated by X'. On the other hand, the light Z incident on the joint surface 10b travels straight and exits as Z'. When measuring the amount of transmitted light through the lenticular lens in this example, there is a peak of Y' near the center as shown in Figure 17.
The light of X' is transmitted up to 30 to 50 degrees Celsius, and the light of Z' is concentrated and emitted only in the center, making it possible to secure a viewing angle over a considerably wide range.

Here, the total reflection surfaces on both side surfaces 11 of the lens unit 1 allow the light rays incident on the medium to be totally reflected on these surfaces and exit from the concave surface 10a.
It is necessary to prevent the light reaching the concave surface 10a from being totally reflected again on the concave surface 10a, and the angle θ that this total reflection surface makes with the surface connecting the concave surface 10a of the lenticular lens, in other words, with the optical axis.
is determined by the refractive index n of the medium, and can be calculated using the following formula.

Now, as shown in Figure 7, the rays parallel to the vertical axis
A ₁ is incident at angle θ, and it is totally reflected to concave surface 1
Suppose that the light ray is emitted from 0a, it intersects the vertical axis S, which is the optical axis, at an angle 2θ, and the concave surface 10a
Emits from. And this ray A ₁ is concave surface 1
The condition for all light to be emitted to the outside at 0a is that total reflection must not occur on this surface, so this angle 2θ must be less than or equal to the total reflection angle. When this relationship is determined from the formula for total reflection, n sin 2θ≦1, so sin 2θ≦1/n, 2θ≦sin ^-1 1/n, and further θ≦1/2 sin ^-1 1/n. From this, the angle α between the total reflection surface and the horizontal plane is α≧90°−1/2 sin ⁻¹ 1/n.

The angle α formed by the total reflection surface can be found from the above formula. For example, if the medium is acrylic resin and its refractive index n is 1.492, then α≧90°−1/2sin ^-1 1/1.492 α≧ 90°-1/2×42.09° α≧68.96°, and the angle must be approximately 69° or more. Note that the angle 2θ of the light ray passing through the concave surface 10a is the critical angle.
If the angle is too close to 42.09°, the rate of internal reflection at the concave surface 10a will increase, so that the smaller the angle, ie, the angle α, is, the closer it is to 90°. However, if the angle .alpha. of the total reflection surface becomes too large, manufacturing difficulties will arise, so when acrylic resin is used as the medium, it is particularly preferable that the angle .alpha. be 70 to 80 degrees.

On the other hand, the shape of the concave surface 10a is preferably a concave lens-like concave surface as shown in the figure, but it is preferable that the light that reaches this concave surface 10a is not totally reflected by this surface. That is, considering the conditions under which total reflection does not occur on this top surface, as shown in Fig. 9, the pitch of the concave surface 10a is _P1 , the curvature of the concave surface 10a is _r1 , and the end of this concave surface 10a is the point (R). Then, the angle β between r ₁ , which is the normal to point (R), and the center line N is, Since this angle consists of the incident angle of the ray V passing through the point (R), it is preferable to set it so that r ₁ =P ₁ n/2.

In this embodiment, since each lens unit 1 is continuous in a narrow valley, narrow joining planes may be provided at the bottoms of both side surfaces 11. Examples of this case are shown in Figures 2 and 5, where 12
is the joining plane. FIG. 10 shows the state of transmission of light rays in this example, and the number of light rays traveling straight is slightly increased compared to the above embodiment.

Next, the second embodiment of the invention shown in FIGS. 3 and 6 will be described. In this case, a structure similar to the above lens unit is used as the first lens unit, and the distance between the first lens units is A second lens unit having a lens surface is positioned at the second lens unit, and both are alternately arranged in series. That is, as shown in FIG. 6, since the second lens unit 2 having the lens surface 20 is positioned between the first lens units 1,
As shown in FIG. 11, the portion of the light beam incident on the first lens unit 1 will be emitted in the same manner as in the embodiment of the first invention, but the portion of the light beam incident on the second lens unit 2 will be emitted. is directly emitted from the lens surface 20. Therefore, in this example, the amount of light emitted from the lens surface 20 can be ensured even in a small viewing angle range. Note that this lens surface 20 may be a convex lens as shown in the figure, but it may also be a concave lens, and it is desirable that this lens surface 20 is such that the light emitted from this surface does not cause total internal reflection. It is preferable to set a predetermined curvature in the same way as the idea shown in FIG.

In the rear projection screen according to the present invention, the lenticular lens described above can be used alone as a screen, or it can be combined with other screens or lenses to form a screen. In this case, the total reflection surface of the lenticular lens according to the present invention does not necessarily have to be planar, but may be a curved surface with a convex outer surface, or a concave curved surface as shown in FIG. In short, any material that can totally reflect the incident light beam is sufficient.

Furthermore, in any of the inventions of the present invention, when the lenticular lens surface on the viewing side is irradiated with external light, this reduces the contrast of the pixels. In order to prevent this, as shown in the embodiment of FIG. 13, external light absorbing layers 4 are formed on the total reflection surfaces of both side surfaces 11 of the lens unit (or first lens unit) 1 to prevent transmission of light rays. By this, the contrast of the pixels facing each lenticular lens can be increased. However, there is a possibility that such external light absorbing layer 4 absorbs a small portion of the light rays reflected by the total reflection surface. In order to prevent absorption of such light, as shown in the embodiment shown in FIG. A slight absorption of the light beam can prevent this and allow the light beams from the pixels to be projected more effectively. As the reflective layer 5, in addition to reflective materials such as metal vapor deposition films and reflective paints,
It is also possible to coat the material with a refractive index lower than that of the medium. Examples of the substance with a low refractive index include fluorine-containing resins when the medium is an acrylic resin.

As described above, the rear projection screen according to the present invention can be used alone as a screen because it can obtain high diffusion characteristics due to the configuration of one lens surface. It is also possible to use a further combination of incident surfaces 3. From this point of view, the entrance plane 3
Instead of being a smooth surface, it may be a finely uneven surface, or may be an inclined surface or other lens surface. Effective use of the incident side surface in this way is advantageous because it becomes a single-lens structure, which prevents flare between the lenses and makes it possible to create an effective screen. In particular, in the present invention, if the entrance side of the lenticular lens is a Fresnel lens 6 as in the embodiment shown in FIG. 15, the light rays can be used effectively and an excellent screen can be obtained.

Note that the degree of the viewing angle of the present invention can be variously selected depending on the pitch of the lenticular lens, the height of the lens unit (or first lens unit) 1, the shape of the concave surface 10a, etc.; The height of the top portion 10 is preferably about 0.3 to 2 mm.

As the medium used in the rear projection screen of the present invention, acrylic resin has been described in the above embodiments because acrylic resin is particularly excellent in terms of optical properties and moldability. However, instead of this, vinyl chloride resin, polycarbonate resin, olefin resin,
Styrene-based resins and the like can also be used, and when these synthetic resin materials are used, the lenticular lens according to the present invention can be manufactured by extrusion molding, hot pressing, or injection molding.

In order to further improve the light diffusion properties of the rear projection screen according to the present invention, it is preferable to provide the medium with other light diffusion means. As this light diffusion means, synthetic resin that constitutes the medium, such as acrylic resin, is used.
One or more diffusing substances that do not melt or chemically change in the liquid synthetic resin medium, such as SiO ₂ , CaCO ₃ , Al ₂ O ₃ , TiO ₃ , BaSO ₄ , ZnO, fine glass powder, or organic diffusing agents. The additive may be uniformly mixed and dispersed in the medium, a layer containing these diffusing substances may be formed, or a finely uneven surface may be formed on the incident surface and/or the peak portion. By taking such a light diffusion means, for example, it becomes possible to diffuse a large amount of light between the ranges Y' and X' in FIG. 17, and also to diffuse light in the vertical direction in FIGS. It also contributes to diffusion.

[Brief explanation of the drawing]

1 and 2 are perspective views showing an embodiment of the first invention of the lenticular lens of the present invention as seen from the projection side, FIG. 3 is a similar perspective view showing an embodiment of the second invention, and FIG. Figure 4 is a cross-sectional plan view taken along the line from Figure 1, Figure 5 is a cross-sectional view taken along the line from Figure 2, and Figure 6 is a cross-sectional view taken along the line from Figure 3. Plan view, Figures 7 to 1
FIG. 0 is an explanatory diagram for explaining the light diffusion state in the first embodiment, FIG. 11 is an explanatory diagram for the light diffusion state in the second embodiment, and FIG. 12 is a cross-sectional plan view showing still another example. , FIG. 13 is a cross-sectional plan view of an example in which an external light absorption layer is formed, and FIG. 14 is a cross-sectional plan view of an example in which an external light absorption layer and a reflective layer are formed.
Fig. 5 is a cross-sectional plan view of an example in which a Fresnel lens is formed on the incident surface, Fig. 16 is a graph showing the light diffusion of the conventional lenticular lens, and Fig. 17 is a graph showing the light diffusion of the lenticular lens of the present invention. It is a graph showing diffusion. 1...(first) lens unit, 10...Top part,
10a...concave surface, 10b...joining plane, 11...
Both side parts, 2... second lens unit, 20... lens surface.

Claims (1)

[Claims] 1. A rear projection screen in which a lenticular lens is formed at least on the observation side of the medium,
The lenticular lens is composed of a series of lens units each having a top and both side surfaces formed by one concave surface in the center and bonded planes adjacent to both sides of the concave surface, and the top of this lens unit The concave surface of is formed so as to output the light rays that are directly incident on this part, and at least a part of each side surface of the lens unit is formed with a total reflection surface that totally reflects the light rays that are incident on this part, and A rear projection screen characterized in that most of the light rays totally reflected by the total reflection surface are emitted from the concave side closer to the total reflection surface. 2. If the angle between the total reflection surface and the plane perpendicular to the optical axis is α, then α≧90°−1/2 sin ⁻¹ 1/n (where n is the refractive index of the medium). A rear projection screen according to claim 1. 3. The rear projection screen according to claim 1 or 2, wherein a light absorption layer is formed at a position covering the total reflection surfaces of both side portions. 4. The rear projection screen according to claim 1 or 2, wherein a reflective layer and an external light absorbing layer are respectively formed at positions covering the total reflection surfaces of both side portions. 5. The rear projection screen according to claim 1, 2, 3, or 4, wherein the medium is provided with a light diffusing means. 6 Claims 1 and 2 characterized in that a narrow joining plane is formed at the bottom of both side parts.
5. The rear projection screen according to item 3, item 4, or item 5. 7 A rear projection screen in which a lenticular lens is formed at least on the viewing side of the medium,
The lenticular lens is located between a first lens unit having a top portion and both side surface portions formed by one concave surface of the central portion and cemented planes adjacent to both sides thereof; and a first lens unit located between the first lens unit. The concave surface of the top of the first lens unit is formed so as to emit the light rays directly incident on this part, and the lens unit A total reflection surface is formed on at least a part of each side surface of the side surface, and most of the light rays totally reflected on the total reflection surface are formed on at least a part of each side surface of the concave surface near the total reflection surface. A rear projection screen characterized in that the second lens unit is formed with a lens surface that emits light that is directly incident on the second lens unit. 8 If the angle between the total reflection surfaces of both side surfaces of the first lens unit and the plane orthogonal to the optical axis is α, then α≧90°−1/2 sin ⁻¹ 1/n (where n is the refractive index of the medium The rear projection screen according to claim 7, characterized in that: 9. The rear projection screen according to claim 7 or 8, wherein an external light absorbing layer is formed at a position covering the total reflection surfaces of both side surfaces of the first lens unit. 10. The rear projection according to claim 7 or 8, wherein a reflective layer and a light absorption layer are respectively formed at positions covering the total reflection surfaces of both side surfaces of the first lens unit. screen. 11. The rear projection screen according to claim 7, 8, 9 or 10, characterized in that the medium is provided with light diffusing means.