JPS59182430A - Back-projection screen - Google Patents

Abstract

PURPOSE:To expand a range of a field of view, also to raise a balance of a light emission, and to secure a brightness by constituting so that a light which is made incident from a projection side and reflected by a total reflecting surface transmits through a part of a curved surface part, and forming a thin connecting surface between each lens unit. CONSTITUTION:In a back projection screen having a lenticular lens on an observation side, the lenticular lens is provided with a total refleting surface (1), and also constituted of a lens unit (1) provided with plural curves surface parts (12) so as to be connected between both side inclinations, more concretely speaking, from the tip of the total reflecting surface (11), and the screen is constituted by providing a thin and flat connecting surface between each lens unit (1).

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a rear projection screen VC used, for example, in a video projector, and aims to provide a bright rear projection screen with a large viewing angle on the viewing side.

Rear projection screens are used as projection surfaces for video projectors, microfilm readers, computers, etc., but various studies have not been done on their light transmission characteristics, such as widening the viewing angle. . And is a minute cylindrical lens one of the means to achieve this purpose? A large number of consecutively formed lenticular lenses can be used alone or in combination with other lenses or a diffuser plate.As mentioned above, this lenticular lens is used to diffuse incident light. It has the function of forming many small cylindrical lenses in a row in the vertical direction to diffuse the light tube in the horizontal direction, and forming small cylindrical lenses in the horizontal direction to diffuse the light tube in the vertical direction. are doing. Also, when using this lenticular lens as a full screen, what about the lens surface? The maximum diffusion angle is limited when facing the incident light side, that is, the light source side, and when facing the exit side, that is, the observer side. It is known that it is possible to increase the diffusion angle compared to the case where the beam is oriented toward the object.

However, even when a lenticular lens is placed on the observation side, there is a limit to the viewing range if the lenticular lens has a simple circular unit. This is because the collimated light incident from the projection side has a large loss of light quantity at a large bending angle according to the critical angle condition and Fresnel's equation, so that the viewing range cannot be expanded.

In other words, if parallel light (L) is incident as shown in Figure 14, total reflection will occur when n-5inθ=sinψ=1, where n is the refractive index of the medium at that time. , f or more (θ)
The incident light will not be transmitted to the observation side. In addition, in Fresnel's equation, the reflectance r at the interface is defined as n, and this value becomes large near the critical angle O As is clear from the above, it forms a simple circle. The lenticular lens used as a unit [, as shown in Figure 15, has the disadvantage that the amount of light becomes almost zero when the angle from the center is about 500 degrees, and it cannot be seen in a viewing range exceeding this. .

Therefore, the present inventor proposed a rear projection frame 17 which expanded the field of view and improved the balance of light output (Patent Application No. 57-29178).

The present invention is a rear projection screen in which a lenticular lens is formed at least on the observation side, and a lens unit constituting the lenticular lens has a total reflection surface on both inclined surfaces, and a plurality of total reflection surfaces are provided between the inclined surfaces on both sides. A curved surface portion is formed, and the device is designed such that light incident from the projection side and reflected by the total reflection surface passes through a portion of the curved surface portion.

Although this greatly improves the performance of the screen, the valley between each lens unit becomes narrower and therefore this
Due to T-manufacturing, this part of the mold was too steep and lacked stability as a mold, and also had no effect on the reproducibility of the (2) product.

The present invention was made in view of this situation, and its gist is that a rear projection screen is provided with a lenticular lens formed at least on the observation side, and the lens units constituting the lenticular lens are arranged on both sides. A total reflection surface is provided on the slope, and a plurality of curved surfaces are formed between the slopes on both sides, and light that enters from the projection side and is reflected by the total reflection surface passes through a part of the curved surface. The rear projection screen is designed to provide a rear projection screen, and is further characterized in that a thin connecting surface is formed between these lens units.

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

1 to 3 are perspective views showing embodiments of the rear projection screen of the present invention. In these figures, (1) indicates a lens unit, and this lens unit (1) is equipped with total reflection surfaces αρ, r'r on both side inclined surfaces, and has more specific reflection surfaces between both inclined surfaces. A plurality of curved surface portions (2) and (6) are provided so as to be continuous from the tips of the total reflection surfaces α■ and α→. The present invention is characterized in that a thin flat connecting surface (2) is provided between each lens unit (1).

FIG. 2 shows another embodiment of the present invention, showing a plurality of curved portions (2) in a lens unit (1).

This is an example in which a convex lens (2) 5 is further formed between the lens units (2), and in the same figure, a thin connecting surface (
2) is formed.

The thin connecting surface (2) between (1) is formed as a concave lens surface, showing an n* example. Of course, this thin connecting surface (2
) may be a convex lens surface ◇In the present invention, at least on the observation side (s), a thin connecting surface (2) of a lenticular lens consisting of the above-mentioned lens position (1) is formed. However, it is more effective if the entire Fresnel lens (3) is formed on the projection side CP'). These embodiments are shown in FIGS. 4 and 5. FIG. 4 shows an example in which a Fresnel lens (3) is formed on the projection side CP of the rear projection screen in FIG. 1, and FIG. Fresnel lens (3) on the projection side (P') of the rear projection screen in Figure 2
This is an example of + formation. In this case, Fresnel v y s(
3) Ti f-cular Fresnel lenses are common, and their focal length depends on the purpose of the screen, but
For example, for rear projection screens for large video projectors, f=1.0 to 1.2 m is most common.

When the thin connecting surface (2) is completely formed as in the present invention,
The area of the valley formed by the two total reflection surfaces (b) and α (r) becomes larger, and conversely, the protruding portion of the mold for manufacturing this can be made larger. Without the connecting surface as in the present invention, the mold corresponding to the trough of this product would be steep, the strength would be lower than 9, and the life of the mold would inevitably be shortened. At the same time, the presence of the thin connecting surface (2) leads to improved mold releasability of the product and improves the productivity of products with the desired shape. Also,
Optically, the amount of light near the front increases by that area,
You can also increase the brightness of the front.

The width of the thin connecting surface (2) in the present invention depends on the width and shape of the lens unit (1), but
When the width of 1) is 1, it is best to set it to about 0.001 to 0.05. If it is too large, a see-through defect is likely to occur, so care must be taken.

Furthermore, since the valley portion of the product is wide, the area of the external light absorbing layer that can be formed in this portion can also be increased, which can be an effective means for improving contrast. FIG. 6 is an example in which an external light absorbing layer is formed in the valley portion. In the figure, (4) is a light reflecting layer that does not absorb any light incident on the total reflection surface α, and (5) is an external light absorbing layer provided on top of this layer. It shows.

FIG. 7 shows an example in which the light-absorbing filamentous material (6) is placed in the entire valley, and if there is a thin connecting surface (2), a filamentous material with a larger wire diameter can be used.

Figures 8 and 9 are examples in which the total reflection surface (11') in the lens unit (1) has an outwardly convex curved shape.
FIG. 8 is an example of a product corresponding to FIG. 1, and FIG. 9 is an example of a product corresponding to FIG. 2. The advantage of forming such a curved total reflection surface (1 line) is that it is easier to control the distribution of light reflected by the total reflection surface (11') and emitted to the observation side compared to a straight one. 0 When the total reflection surface is made into an αη curved surface like this, the valleys of the product become particularly deep and sharp, so forming a thin connecting surface (2) as in the present invention is an extremely effective means. .

Now, the rear projection screen of the present invention has total reflection surfaces (11) on both side inclined surfaces as described above. , which also has a lens unit (1) having a plurality of curved surface portions (2) between both inclined surfaces.The light transmission characteristics of this lens unit will be explained below based on FIG. 10. That is, FIG. 10 shows one lens unit (1), the α force is the total reflection surface, and (6) is the curved surface portion. This shape is determined by the length of the straight line part (4) of the overall pitch (''\i:) and the slope of the α force of the total reflection surface.
A, B It can be determined by

Here, it is desirable that ( is sufficiently larger than the angle at which parallel light is totally reflected, that is, the critical angle. That is, θ1nθ>1 where n is the refractive index. For example, if the refractive index is n = 1.49
In this case, it is desirable to set the angle to 65 to 80 degrees.
The above is preferable; conversely, if the angle is too close to 90°, it will be difficult to manufacture the mold.

The light that has just entered the total reflection surface αη is (force → (G) → (m
→ (1), but unless (ψ) is particularly large, such light will have little light loss along the way and will reach a portion with a large viewing angle. As mentioned above, in order to effectively diffuse the light reflected by the total reflection surface a through the curved surface portion (2), the radius of curvature (r) of the curved surface portion α4 must be made small. It is desirable to increase the pitch/r'fr in the part (2).For example, the pitch of the curved part (A) is as follows: lens unit (1)
The pitch should be approximately 40% to 70% of the pitch, and the pitch/r should be 1.3 to 70%.
It is preferable to set the degree to 2.0. In this way, the light incident on the total reflection surface αυ spreads over the area with a large viewing angle, but the light incident on the straight curved surface part (2) spreads over the area with a small viewing angle, just like in the case of a general circular lenticular lens. It will spread. FIG. 11 shows the state in which these lights are combined. In other words, the light incident between (~-(B) and (car (G)) is totally reflected by the total reflection surface a, passes through the curved part, and is reflected at the large viewing angle (A')-(B
') and reaches the navel between (F') and (G'). Also, the light (c) − (D) and (
D) -(l is A according to Snell's law of refraction)
(0') - (D) and (S') - (E'). Therefore, the lenticular lens equipped with the lens unit (1) according to the present invention has a wide viewing angle. A uniform amount of light can be obtained over the viewing angle.

In the embodiment shown in FIG. 11, if the amount of light is insufficient in a small viewing range, that is, in a range close to the center of the screen, multiple curved portions (6), (6) as shown in FIG.
It is preferable to form a convex lens portion υ in between. The shape of this convex lens part (2) may be circular or non-circular, but if it is circular, the pitch of the convex lens part αj / r f 1.4 ~
If it is about 1.7, the light amount distribution can be made more uniform and wide.

Materials used for the rear projection screen of the present invention include:
Acrylic resin is most suitable, since acrylic resin is particularly superior in terms of optical properties and moldability. However, it is also possible to use vinyl chloride resin, polycarbonate resin, olefin resin, styrene resin, etc. instead of this, and when using these synthetic resin materials, it is possible to use extrusion molding, hot pressing, or injection molding. , the entire rear projection screen according to the present invention can be manufactured.

Further, in order to further improve the light diffusing properties of the rear projection screen according to the present invention, it is preferable to provide a light diffusing means. This light diffusion means is made of synthetic resin constituting the medium, such as acrylic resin, and Si02, . 0a(303, At2
03. T'103. BaSO4, ZnO.

A1(oH)3. One or more types of diffusive substances that do not melt or chemically change are uniformly mixed and distributed in a liquid synthetic resin medium such as fine glass powder or an organic diffusing agent, or It is preferable to form a layer containing a diffusing substance.

It is also effective to form a fine matte surface on the projection side (P) surface and/or the viewing side (S) surface. If such a means for imparting light diffusivity is taken, the diffusivity of the screen in the horizontal and vertical directions is compensated for and the n1 uniformity of the tube can be improved.

Specific examples will be described below.

Example 1 An acrylic resin plate with a thickness of 5 mm was prepared using an acrylic resin with a refractive index of 1.49 and mixed with 5102 as a light diffusing agent during production of the resin plate. A Fresnel lens surface with a focal length f = 1.1 m was formed on this acrylic resin plate.
The mold was sandwiched between the mold and the mold in which the lens unit as shown in Fig. 12 was constructed, and the temperature was 180°C and the pressure was 40 kg/cm.
A rear projection screen as shown in FIG. 5 was manufactured by hot pressing under cyrP conditions. In addition, in Fig. 12, the angle (reflection 70°, rlFin, 17w, r2 is
■, 1° is α2111 + 1% t3 is 0.15m, t4 is 0.5 constant, t5 is 1.22■, t6 is a02 bait, pitch of curved part / rI is 1.76, pitch of lens part / rz
was designed as 1.43. By this method, an excellent-looking screen as shown in Figure 5 was obtained, but it is certain that the mold releasability was greatly improved during manufacturing. Figure 13 (N~
A screen having an external light absorbing layer as shown in FIG. 6 was manufactured in the same manner as in (0).

That is, for a screen containing lens units having the shape as shown in FIG. 12, first, a polyvinyl alcohol-based strippable paint (7) is applied on a plurality of curved surfaces and convex lenses as shown in FIG. 8(A). Formed by treatment.

Next, vacuum evaporation of aluminum is performed on this, approximately 50%
The aluminum reflective layer (4) of No. 001 was completely formed (FIG. 8(B)). -Subsequently, acrylic resin-based black paint was completely sprayed on top of this to form the external light absorbing layer (5) (
Figure 8(C)). If you reach this state, screen? Immerse it in water and remove the masking layer with strippable paint (7
)', and the reflective layer (4) and external light absorbing layer (5) in this area were completely peeled off.

By this method, a rear projection screen with good contrast can be obtained.

[Brief explanation of the drawing]

1 to 6 are partial perspective views showing an embodiment of the rear projection screen of the present invention, and FIG. 4 is a cross section showing an embodiment in which the Fresnel lens is entirely formed on the projection side of the rear projection screen in FIG. 1. Figure 5 is a cross-sectional view showing an embodiment in which a Fresnel lens is formed on the rear surface and the projection screen (7) in Figure 2, and Figure 6 is an embodiment in which an external light absorption layer is formed on the total reflection surface. A cross-sectional view showing a part of an example, FIG. 7 is a cross-sectional view showing a part of an example in which all the light-absorbing filaments are arranged on the total reflection surface, and FIGS. 8 and 9 show a total reflection surface as a curved surface. FIG. 10 is an explanatory diagram of the light transmission characteristics of each lens in the present invention, FIG. 11 is an explanatory diagram of the light transmission characteristics of the rear projection screen of the present invention,
FIG. 12 is an explanatory diagram of the shape of each lens unit in Example 1, FIGS. 16(A) to (C) are cross-sectional views for explaining the manufacturing method in Example 2, and FIG. 14 is a general lenticular lens. FIG. 15 is a graph of the light transmission characteristics. (1)... Lens unit αη... Total reflection surface (2)... Curved surface portion (2)... Convex lens portion (2)... Thin connecting surface (3)--1111 Fresnel lens (4)...Light-reflecting layer (5)...External light-absorbing layer (6)...Light-absorbing filament (S)... ... Observation side (P) ... Projection side No. 7 / Figure 3V Rod, Figure 2 Tail Figure 5 Figure 2 // Mouth Qin Figure 10 Bottom / 2UZJ

Claims (1)

[Claims] 1. A f'Lfc rear projection screen in which a lenticular lens is formed at least on the observation side, and the lens unit constituting the lenticular lens has total reflection surfaces on both inclined surfaces, and A plurality of curved surface portions are formed between the inclined surfaces, and the design is such that the light incident from the projection side and reflected by the total reflection surface is partially transmitted through the curved surface portions. A rear projection screen characterized in that a thin connecting surface is formed between the lens units. 2. The rear projection screen according to claim 1, wherein the connecting surface is a flat surface. (v) The rear projection screen according to claim 1, wherein the connecting surface is a concave lens surface. 4. The rear projection screen according to claim 1, wherein the connecting surface is a convex lens surface. 5. Claims 1, 2, 3, or 4 characterized in that a convex lens portion is formed between a plurality of curved surface portions located between both inclined surfaces. Rear projection screen. 6. Claims 1 and 2, characterized in that a Fresnel lens is formed on the projection side. Rear projection screen according to item 3, 4 or 5. 1. Claims 1, 2, and 3, characterized in that a light diffusing means is provided. Rear projection screen according to item 4, 5 or 6. Claim 1, characterized in that: a) at least one surface is subjected to a matting treatment; Rear projection screen according to item 2, 3, 4, 5, 6 or 7. 9. Claims 1 and 2, characterized in that an external light absorbing means is provided on the total reflection surface of the lenticular lens. Rear projection screen according to item 5, item 4, item 5, item 6, item 7 or item 8.