JPS6128978B2 - - 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. And as one of the means to achieve this purpose,
A lenticular lens sheet in which a large number of minute cylindrical lenses are successively formed is used alone or in combination with other lenses or a diffuser plate.

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 microscopic cylindrical lens 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 5, the problem is that the brightness drops sharply at points beyond 30 degrees from the center.

Regarding such screens, the present inventors immediately filed a patent application for a rear projection screen with a wider viewing angle.
It is proposed as an invention of No. 56-51194. This invention forms total reflection surfaces on both sides of each lens unit of a lenticular lens so that the totally reflected light rays are emitted from the top, thereby creating a bright rear projection screen with a large viewing angle. It turned out that it was possible to obtain However, as a result of further study on this invention, it was found that a taper that does not affect the bending of light was created, and the height of the peak was also increased, making it difficult to manufacture.In the present invention, these points have been improved. The present invention aims to provide a rear projection screen with excellent performance.

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 top portion formed of one concave surface and both side portions. A concave surface at the top of each lens unit is formed to emit a light beam directly incident on this portion, and at least a portion of each side surface of each lens unit has a concave surface. A total reflection surface is formed on which the light beam incident on this part is totally reflected, and most of the light beam totally reflected on the total reflection surface is emitted from the side of the concave surface near the total reflection surface. The first invention provides a rear projection screen having a lenticular lens formed at least on the observation side of the medium, the lenticular lens having a top portion formed by one concave surface and both side portions. and a second lens unit located between the first lens units are arranged alternately, and the concave surface of the top of the first lens unit is formed so as to emit light rays 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 incident on this part, and Most of the light rays that are totally reflected by the reflective surface are emitted from the side of the concave surface that is close to the total reflection surface, and the second lens unit has a lens surface that emits the light rays that are directly incident on this part. A second aspect of the present invention is a rear projection screen characterized in that a rear projection screen is formed.

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. 3 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 has one concave surface 10.
It is composed of a top portion 10 formed by a and both side portions 11. In this example, the entire surface of both side surfaces 11 is a total reflection surface, but it may be formed in a portion thereof. Further, the total reflection surfaces of both side portions 11 are designed to totally reflect the light beams incident on these portions and emit them from the concave surface 10a, as will be described later. Note that 3 in the figure is the entrance surface on the opposite side to the lenticular lens. To explain this shape in more detail based on FIG. 6, this is an enlarged lens unit 1 of the lenticular lens of the present invention, in which the top portion 10 is a concave surface 10a, and both side portions 11 are formed with total reflection surfaces. has been done. When parallel light enters such a lenticular lens from the entrance surface 3, as shown in FIG. It is refracted and emitted. At this time, the light rays incident on both side surfaces 11 at portions A or A' are totally reflected, and most of the light rays are emitted from the side of the concave surface 10a that is close to the total reflection surface.

Lens unit 1 of the lenticular lens of the present invention
is constructed as above, but the total reflection surface is
The light beam incident on the medium is totally reflected by this surface and exits from the concave surface 10a, and the total reflected light and the light directly reaching the concave surface 10a are prevented from being totally reflected again at the concave surface 10a. The angle θ that this total reflection surface makes with the surface connecting the concave surface 10a of the lenticular lens, in other words, the optical axis, is equal to the refractive index n of the medium.
This is determined by a mathematical formula.

Now, as shown in Figure 6, the rays parallel to the vertical axis
A ₁ is incident at angle θ, and it is totally reflected to concave surface 1
If the light ray is emitted from the concave surface 10a, it intersects the vertical axis N, which is the optical axis, at an angle 2θ.
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 equation for total reflection, n sin2θ≦1, therefore sin2θ≦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 α is too close to 42.09°, the rate of internal reflection on the concave surface 10a will increase, so the angle α smaller than this will increase.
The closer the angle is to 90°, the more preferable it is.
However, if the angle α of the total reflection surface becomes too large, it will cause manufacturing difficulties, so when using acrylic resin as the medium, the angle α should be 70 to 80.
It is particularly preferable that the temperature is .degree.

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 reaching this concave surface 10a is not totally reflected by this surface. In other words, considering the conditions that do not cause total reflection on this top surface, as shown in Fig. 7, the pitch of the concave surface 10a is _P1 , the curve 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 is 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.

Next, the second embodiment of the invention shown in FIGS. 2 and 4 will be described. In this case, a structure similar to the above lens unit is used as the first lens unit, and 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. 8, since the second lens unit 2 having the lens surface 20 is positioned between the first lens units 1,
Rays B and A incident on the first lens unit 1,
The portion A' is emitted in the same manner as in the first embodiment of the invention, but the light beam of the portion C is emitted directly 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, but it may also be a concave lens as shown in FIG.
It is desirable that the light emitted from this surface does not undergo total internal reflection, and a predetermined curvature may be set in the same way as the concept shown in FIG. 7 described above.

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 even if it is a curved surface with a convex outer surface, the point is that it can totally reflect the incident light beam. That's fine.

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 embodiments of FIGS. 9 and 10, external light absorbing layers 4 are formed on the total reflection surfaces of both side portions 11 to prevent the transmission of light rays, so that each lenticular The contrast of the pixels facing the 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 such light absorption, as shown in the embodiments shown in FIGS. 11 and 12, the refractive index n
By covering the material layer 5 with a smaller refractive index and forming the external light absorbing layer 4 thereon, the slight absorption of the reflected light on the total reflection surface can be prevented, and the light rays from the pixels can be prevented. can be projected more effectively. This material with a low refractive index is
For example, when the medium is an acrylic resin, a fluorine-containing resin may be used.

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 entrance side surface in this way is effective because an effective screen can be formed with a single lens. 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 FIGS. 13 and 14, the light rays can be used effectively and an excellent screen can be obtained. .

Next, to explain the projected light rays, the first
In the invention, as shown in FIG. 6, the light B in the range corresponding to the concave surface 10a of the lens unit is
The light A and A' in the range corresponding to the total reflection surface are refracted and emitted as A and A', respectively. When the light is emitted widely and diffused in this way, the viewing angle becomes wide as shown in FIG. In other words, as shown in FIG. 16, although the brightness at the center of the diffusion is slightly reduced by the lenticular lens of the present invention, the diffusion of light corresponding to B is greater than the center.
By compensating for the significant drop in brightness around 30° with the light corresponding to A, a predetermined brightness can be maintained as a whole from the center to around 30°. In addition, the range shown by the dotted line in the figure shows the brightness when the sum of A and B described above and a light diffusing means to be described later are added. In the above description, the first embodiment was explained with reference to FIG. 6, but the second embodiment shown in FIG. Brightness is increased and a well-balanced screen with a large viewing angle can be provided. Note that the degree of viewing angle can be selected in various ways 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.;
Approximately 0.3 to 1.5 mm, height of top 10 is 0.3 to 2
It is best to set it to about 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. Additives may be uniformly mixed and dispersed in the medium, a layer containing these diffusing substances may be formed, or finely uneven surfaces may be formed on the incident surface and also on the peaks. By taking such a light diffusion means, for example, it becomes possible to diffuse a large amount of light between ranges A and B in Fig. 16 and eliminate an extreme distribution, and it is also possible to eliminate an extreme distribution of light between the ranges A and B in Fig. 16, and also to It also contributes to directional light diffusion.

[Brief explanation of the drawing]

Fig. 1 is a perspective view showing a first embodiment of the lenticular lens of the present invention as seen from the projection side, Fig. 2 is a similar perspective view showing the second embodiment, and Fig. 3 is a line taken from Fig. 1. 4 is a cross-sectional plan view taken along the line of FIG. 2, FIG. 5 is a cross-sectional plan view showing still another example, and FIGS. 6 and 7 are FIG. 8 is an explanatory diagram for explaining the light diffusion state in Example 1, FIG. 8 is an explanatory diagram for explaining the light diffusion state in Example 2, and FIGS. 9 and 10 are diagrams for the example in which a light absorption layer is formed. Cross-sectional plan view, 1st
1 and 12 are cross-sectional plan views of an embodiment in which an external light absorption layer and a material layer are formed, FIG. 13 and FIG. 14 are cross-sectional plan views of an embodiment in which a Fresnel lens is formed on the opposite surface, and FIG. 15. 16 is a graph showing the light diffusion of the conventional lenticular lens, and FIG. 16 is a graph showing the light diffusion of the lenticular lens of the present invention. 1...(first) lens unit, 10...Top part,
10a...Concave surface, 11...Both side parts, 2...Second
Lens unit of 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 portion and both side surfaces formed by one concave surface, and the concave surface of the top portion of this lens unit emits light rays directly incident on this portion. Furthermore, 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 A rear projection screen characterized in that light is emitted from a 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 an external light absorbing layer is formed at a position covering the total reflection surfaces of both side portions. 4. Claims 1 or 2, characterized in that a substance and an external light absorbing layer each having a refractive index smaller than the refractive index of the medium are formed at positions covering the total reflection surfaces of both side parts. Rear projection screen as described. 5. The rear projection screen according to claim 1, 2, 3, or 4, wherein the medium is provided with a light diffusing means. 6. A rear projection screen in which a lenticular lens is formed at least on the viewing side of the medium,
The lenticular lens includes a first lens unit having a top portion and both side surfaces formed by one concave surface, and a second lens unit located between the first lens units, which are arranged in series alternately. 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 a part of each side surface of the lens unit has this part. A total reflection surface is formed on which the incident light beam is totally reflected, and most of the light beam totally reflected on the total reflection surface is emitted from the side of the concave surface near the total reflection surface. A rear projection screen characterized in that the lens unit No. 2 is formed with a lens surface that emits light rays directly incident on this portion. 7 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 6, characterized in that: 8. The rear projection screen according to claim 6 or 7, 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. 9. Claim 6, characterized in that a substance with a refractive index smaller than the refractive index of the medium and an external light absorbing layer are respectively formed at positions covering the total reflection surfaces of both side surfaces of the first lens unit. 7. The rear projection screen according to item 7. 10. The rear projection screen according to claim 6, 7, 8 or 9, characterized in that the medium is provided with light diffusing means.