JPH0360104B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improved transmission projection screen with no uneven screen brightness. In particular, the present invention relates to a transmission type projection screen suitable for color television projection and with less color tone defects.

As a transmission type projection screen that projects and magnifies images from the side opposite to the observation side, it is desirable that the projection light utilization efficiency is high and that there is little reduction in image contrast when used in a bright room.

For example, as shown in FIG. 1, a circular Fresnel lens sheet 1 and a lenticular lens sheet 2 can be arranged so that the lens surface of the lenticular lens sheet 2 is on the side of the circular Fresnel lens sheet 1, as shown in FIG. The projection light emitted from the projector P is first focused by the circular Fresnel lens 1, and then diffused at an appropriate angle α in the horizontal direction using the lenticular lens 2. A light absorption layer 3 is provided on the output side of the lenticular lens 2 at a location corresponding to the non-light condensing part of the lenticular lens to reduce the reflection of external light coming from the viewer side as much as possible and improve the contrast of the image. things are known.

The conventional transmissive projection screen mentioned above condenses the projection light using a circular Fresnel lens, so the utilization efficiency of the projection light is high, and by changing the focal length of the lenticular lens, the diffusion angle of the output light can be adjusted. This has the advantage that the emitted light can be uniformly distributed over a certain preferable range, and that the brightness of the image will not change much even if the viewing position changes somewhat.

However, in the above-mentioned conventional transmission type projection screen, the light absorption layer is provided just behind the boundary of each lenticular lens, so near the center of the lenticular lens sheet, the incident light is is the optical axis 4 of the lenticular lens
However, near the periphery of the lenticular lens sheet, as shown in Figure 3, the incident light enters at an angle to the optical axis 4 of the lens, so it tends to be refracted and emitted. The brightness of the image decreases because part or all of the light is blocked by the light absorption layer.Also, as in many color television projection devices, red, green, and blue projectors are arranged horizontally. If you use a projection device like this, the angle of incidence of each color of light that enters the same lenticular lens is different, so the way the light is blocked by the light absorption layer is different, resulting in disadvantages such as not being able to obtain the correct color tone. have.

It is easy to understand that the above disadvantages can be solved by shifting the position of the light absorption layer of the transmission projection screen to a position where it does not block the emitted light, but the formation position of each light absorption layer is determined by In order to do this, it is necessary to analyze in detail the refraction of each lenticular lens during use, and to examine the light emission range for each color light, especially in color television projectors. It is very complicated to reflect this in the formation of the light absorption layer.

Therefore, the present invention has an extremely small loss of projection light in the peripheral area, the light absorption layer is formed with the maximum area, so an image with good contrast can be obtained, and a three-tube projection type is used. It is an object of the present invention to provide a transmission type projection screen that provides a regular color tone and is free from color tone defects such as color unevenness when applied to a color television.

The present invention has a Fresnel lens sheet on the projection side and a lenticular lens sheet on the observation side, which are arranged one on top of the other, and the lenticular lens sheet has a lenticular lens on the Fresnel lens sheet side, and the Fresnel lens sheet In a transmission projection screen that has a light absorption layer in the non-condensing part of each lenticular lens on the opposite side, light incident on the central part of the lenticular lens from the Fresnel lens sheet is absorbed by the light absorption layer. By setting the position of the light absorption layer so that it passes through the center between the two, the loss of projection light at the periphery is extremely small.
A transmissive type that has a light absorption layer formed with the largest area to obtain images with good contrast, and when applied to a three-tube projection color television, a normal color tone can be obtained and there is no color unevenness or other color tone defects. This was done based on the discovery that it is possible to construct a projection screen.

That is, the transmission type projection screen of the present invention has the following characteristics:
A Fresnel lens sheet is placed on the projection side and a lenticular lens sheet is placed on the observation side, and the lenticular lens sheet has a lenticular lens on the Fresnel lens sheet side, and is opposite to the Fresnel lens sheet. on the side of
Each of the lenticular lenses has a light absorption layer in a non-condensing part, and the center of the light absorption layer is d expressed by the following relational expression from a position on the back surface corresponding to the boundary line of each lenticular lens. The lenticular lens sheet is provided offset toward the center line of the lenticular lens sheet.

d=t×tan sin ^-1 sin tan ^-1 (R/F)/n (however, d is offset, t is the thickness of the lenticular lens sheet, R is the boundary to which the light absorption layer whose center is offset by d corresponds) The distance between the center of the lenticular lens and the center of the lenticular lens sheet, which is located close to the outside when viewed from the center line, F is the focal length of the Fresnel lens sheet on the observation side, and n is the lenticular lens sheet. The present invention will be described below with reference to the drawings.

FIG. 4 is a schematic cross-sectional view showing an example of the structure of the transmission type projection screen A of the present invention, in which a circular Fresnel lens sheet 5 and a lenticular lens sheet 6 are arranged so that their respective lens surfaces face each other. The light absorbing layer 7 is arranged on the non-lens surface of the lenticular lens sheet 6, that is, the lower surface in FIG. As it approaches both the left and right ends of the cyular lens sheet, it is provided closer to the center line 8 of the lens sheet than the position directly below.

In the above, when the light absorption layer 7 is provided, the deviation d when the light absorption layer is provided at a position shifted from the position of the light absorption layer in a conventional transmission type projection screen will be explained using FIG. 5. After being refracted by the lenticular lens sheet 6, the light enters the center (the most convex part) of the lenticular lens at a distance R from the center line 8 at an angle θ with respect to the optical axis of the lens. is refracted according to the following formula (a).

sinθ=n sinφ …(a) (where n is the refractive index of the material of the lenticular lens sheet) Therefore, the position where the light is supposed to be emitted is closer to the center of the lenticular lens sheet by d from the optical axis of the lens. Assuming that the thickness of the portion of the lenticular lens sheet 6 without the light absorption layer is t,
d is represented by the following formula (b).

d=t×tanφ …(B) From the formula (A), φ=sin ^-1 sinθ/n …(C), and substituting (C) into (B), d=t×tan sin ^-1 sinθ /n...(d), and θ is the distance R between the above-mentioned incident position of the lenticular lens and the center of the lens sheet containing that lens, and the distance F of the observation side conjugate point of the Fresnel lens sheet. θ=tan ^{- 1} R/F... (E) Since it is expressed as (E), by substituting (E) into (D), it becomes d=t×tan sin ^-1 sin tan ^-1 (R/F)/n.

To explain the function of the lenticular lens sheet 6 in the above embodiment, as shown in FIG. Since the line b is the center, the light incident almost parallel to the optical axis is refracted and then exits from the center between the light absorption layers, as shown in Figure 8, and the light is not reflected at the periphery of the lens sheet. Since the absorption layer is separated from the position on the opposite side of the boundary of the lenticular lens by the distance d as described above from the position of the line b, it can also be seen from the center between the adjacent light absorption layers without being blocked by the light absorption layer. Emission is possible.

Also, from formula (f), the thickness t of the lenticular lens sheet, the focal length F on the observation side of the Fresnel lens sheet, and the refractive index n of the material of the lenticular sheet
Once determined, the deviation d of the light absorption layer is calculated between the central part of the lenticular lens on the back surface corresponding to the light emitting part that is in contact with the outside of the light absorption layer provided on the lenticular lens sheet and the lenticular lens sheet. Since it is a function only of the distance R from the center of the projection screen, there is no need to perform complicated light ray analysis, and the design and manufacture of the transmission projection screen can be performed extremely easily.

As mentioned above, the light enters at an angle θ through the most convex part (center part) of the lenticular lens, is refracted at a refraction angle φ, and passes through the center of the light-transmitting part between the light-absorbing layers. If the deviation d of the light absorption layer is set according to the above formula (f), then if this light is made to correspond to the light from the central green light projector of a three-tube projection color television, then the central green light will be The light from the red light projector and the blue light projector, which are located on both sides of the light projector in the horizontal direction (in the direction of the paper in Figure 4), is transmitted across the center of the light transmitting part between the light absorbing layers. , the color images projected from these three projectors can reproduce the regular color tone, and the color images can be reproduced in the normal color tone. Does not cause color tone defects such as unevenness.

Furthermore, in formula (f), if the distance R is sufficiently smaller than the distance F of the observation side conjugate point of the Fresnel lens sheet and is within the range of the condition 0<(R/F)<1...(g), then the formula (F) It can be considered as

In a normal transmission type projection screen, the formula (T)
Since the relationship holds true, the deviation d of the light absorption layer can be calculated using the formula
It can be approximated by a function that changes linearly with respect to the distance R, expressed as (H).

Therefore, according to the present invention, the pitch of the light absorption layer may be made smaller by the shift d of the light absorption layer than the pitch of the lenticular lens.

Regarding the specifications of the circular Fresnel lens sheet and the lenticular lens sheet in the above explanation, firstly, the distance F of the observation side conjugate point of the circular Fresnel lens is 2 to 20 m;
More preferably, it is 5 to 10 m. Here, the distance F of the conjugate point of the circular Fresnel lens is not obtained by measuring using parallel light, but is the actual conjugate point on the observer's side when the projector is actually placed and projection is performed. means the distance. In other words, the position of the projector is usually a little farther from the original focal point on the incident side of the circular Fresnel lens, and furthermore, it is placed at a position that prevents the projected light from becoming parallel light. The projection light enters the circular Fresnel lens while being diffused, and after being refracted, it is focused at a position farther from the original focal point on the output side.

Next, the size of the circular Fresnel lens sheet and lenticular lens sheet is the horizontal length, that is, the horizontal dimension from the observer's perspective is 500~
2000mm, more preferably 700 to 1200mm, and
The thickness of the part of the lenticular lens sheet where the light absorption layer is not provided is set so that the output range of the emitted light is the narrowest, in other words, the light absorption layer is provided so that it does not block the emitted light and has the maximum area. It is necessary to decide, and preferably it is about 0.8 to 2 mm. The cross-sectional shape of the lenticular lens of the lenticular lens sheet is circular, oval,
Common objects such as a portion of a parabola can be used.

The distance between the discontinuous surfaces of the convex lenses of the circular Fresnel lens sheet is usually 0.1 to 1.0 mm, and the pitch of the lenses of the lenticular lens sheet is usually 0.8 to 1.5 mm. If the former interval and the latter pitch are the same or similar, moiré patterns are likely to occur due to interference, so it is better to change the ratio to, for example, 2:3. Further, although the width of the light absorption layer provided on the lenticular lens sheet cannot be generalized, it is 40% to 70% of the pitch of the above-mentioned lenticular lens, and the width of the above-mentioned deviation is, for example, lateral.
Largest 950mm lenticular lens sheet
It is about 50μ.

The projection screen according to the embodiment of the present invention described above can be manufactured by any suitable method, but one typical method is to use a mold roll to form the screen during melt extrusion of thermoplastic resin. . That is, this is a method in which a thermoplastic synthetic resin with high transparency and a large refractive index, such as an acrylic resin, is melt-extruded to form a sheet, and the sheet is immediately shaped using a predetermined mold. For the production of circular Fresnel lens sheets, a mold roll with the inverse shape of the same lens can be used in conjunction with a roll with a smooth surface, and for the production of lenticular lens sheets, the same mold roll can be used. A mold roll having a reverse shape and a mold roll having a reverse shape of a convex portion for providing a light absorption layer may be used together. The light-absorbing layer can be formed by printing, transfer, coating, flocking, etc., but it can be formed by adding a light-shielding pigment, preferably a black pigment, and a matting agent if necessary to a suitable synthetic resin paint. It is easy to use printing, transfer, and coating methods using absorbent paints.

Although one embodiment of the present invention has been described above,
The present invention is not limited to the above description, and may take various forms as described below without departing from the gist of the present invention.

First, in the above explanation, the lens surface of the circular Fresnel lens sheet and the lens surface of the lenticular lens sheet are arranged to face each other, but the lens surface of the circular Fresnel lens is on the opposite side of the incident light side. It may be suitable for However, if the lens surfaces of both lens sheets face each other and are in close contact with each other, it is advantageous in terms of dust adhesion and contamination, and since total reflection of incident light is less likely to occur, circuit It is possible to shorten the focal length of the Yuler-Fresnel lens sheet, making it possible to downsize the device when combining a projector and a transmission projection screen to create a single projection device, and furthermore prevent loss of light amount at discontinuous portions of the lens.

Next, the light absorption layer may be provided on the convex portion as shown in FIG. 4, or may be provided on the flat portion as shown in FIGS. 8 and 9, or may be provided on the concave portion. Among these structures, the position of the light absorption layer in the convex portion is determined in advance when creating the lenticular sheet, so the light absorption layer is applied by printing, transfer, or roll coating after the sheet is created. When forming the light-absorbing composition, it is necessary to simply attach the light-absorbing composition only to the convex portions, which is advantageous in manufacturing. In the above explanation, the cross-sectional shape of the convex portion is a part of a quadrilateral, but it may also be circular, oval, trapezoidal, etc. This prevents the emitted light from hitting the convex portion. can. In the same sense, when the cross section is part of a quadrilateral or trapezoid, the corners may be rounded. When a light-absorbing layer is applied using paint to a convex part that is part of a rounded object, circle, or oval, the paint hangs down and the sides of the convex part also become light-absorbing. This allows for more reliable reflection of external light on the observation side. Note that if the top of the convex part is depressed, the light that enters the lenticular lens sheet from the viewing side and is totally reflected will often return to the center of the light absorption layer. By increasing the thickness of the light absorption layer in the recessed portion, it is possible to more reliably block light. Furthermore, if the light absorption layer is provided by the flocking method, the degree of matteness will be large;
Furthermore, compared to the case where the image is provided using paint, the contrast of the image can be improved because there is less of a scene effect that makes the image appear shiny when viewed from a different angle.

Note that when manufacturing lenticular lens sheets by melt extrusion of thermoplastic resin and embossing using metal rolls, the temperature of the resin extruded from the center of the die is lower than that from both ends of the die in order to smooth the melt extrusion of the sheet. If there is a difference in the temperature of the resin, which is lower than the temperature of the resin being extruded, the reproducibility of the mold roll will be worse in the part of the resin extruded from the center of the die, where the temperature is lower, than at both ends, and the lenticular The curvature of the cross-sectional shape of the mirror lens is small, and the focal length tends to be long at the center and shorten toward the ends. Therefore, as a result of having such a focal length distribution, if the entire thickness of the lenticular lens sheet is adjusted to the central light focusing position and a light absorption layer is provided in the non-light focusing area, the focused light will be absorbed at both ends. After it starts to diffuse, it hits the light absorption layer, so both ends become dark. Conversely, if the thickness of the entire lenticular lens sheet is adjusted to the light focusing position at both ends, and a light absorption layer is provided in the non-light focusing area, the light will disappear in the center. The disadvantage is that the light hits the light absorption layer before it is focused enough. To prevent such defects, the thickness of the lenticular lens sheet should be made thicker in the center and thinner as it approaches both ends, or the radius of curvature of the inverted shape of the lenticular lens in the mold roll should be made thicker in the center. It is best to increase the size closer to both ends of the lens sheet.

Furthermore, when the lenticular lens sheet is transparently colored, the light reflectance of the portion where the light absorption layer is not provided decreases both physically and visually, so that the contrast of the image can be improved. Transparent coloring can also be done by external operations such as coating, pasting, printing, and transfer, but it is best to knead coloring materials such as dyes and pigments into the material beforehand when forming the lenticular lens sheet. Alternatively, the light scattering material, such as silica powder, glass powder, glass beads, etc., which is usually added to diffuse the emitted light in the vertical direction of the lenticular lens sheet, may be colored in advance. You can also do it later. When using a light scattering material, if it is uniformly distributed within the lens sheet, the sharpness of the image will be slightly lost, so it is preferable to concentrate it near the exit side surface. In addition, matting the exit surface by sandblasting can also contribute to improving image contrast.

As described above, according to the transmission projection screen of the present invention, a Fresnel lens sheet is placed on the projection side and a lenticular lens sheet is placed on the observation side, and the lenticular lens sheet is placed on the Fresnel lens sheet side. In a transmission projection screen having a lenticular lens and having a light absorbing layer in a non-concentrating portion of each of the lenticular lenses on the side opposite to the Fresnel lens sheet, the lenticular lenses are separated from the Fresnel lens sheet. Since the position of the light absorption layer is set so that the light incident on the central part passes through the center of the light transmission part between the light absorption layers according to equation (f), there is no loss of projected light in the peripheral part. The light-absorbing layer is formed with the largest area to provide an image with good contrast, and when applied to a three-tube projection color television, the light from any projector is vignetted and blocked. Therefore, it is possible to construct a transmission type projection screen that provides a regular color tone and is free from color tone defects such as color unevenness.

Furthermore, the position at which the light absorption layer of the transmission type projection screen of the present invention should be provided is the center of the lenticular lens sheet once the thickness of the lenticular lens sheet, the refractive index of the material, and the focal length of the observation side of the Fresnel lens sheet are determined. Since it is determined as a function of the distance from the line to each lenticular lens, it is easy to design and manufacture, and there is no need to perform complicated analysis. Furthermore, in the transmission type projection screen of the present invention, the pitch of the light absorption layer may be made smaller than the pitch of the lenticular lenses of the lenticular lens sheet by the amount of the deviation d of the light absorption layer. It is extremely easy to manufacture.

[Brief explanation of drawings]

1 to 3 are cross-sectional views of a conventional transmission type projection screen, and FIGS. 4 to 7 are views relating to a transmission type projection screen according to an embodiment of the present invention.
7 and 7 are cross-sectional views, FIG. 5 is an explanatory diagram for explaining the position where the light absorption layer is provided, and FIGS. 8 and 9.
The figure is a sectional view of another embodiment of the invention.

Claims (1)

[Claims] 1. A Fresnel lens sheet is placed on the projection side and a lenticular lens sheet is placed on the observation side, and the lenticular lens sheet has a lenticular lens on the Fresnel lens sheet side, and , on the side opposite to the Fresnel lens sheet, each of the lenticular lenses has a light absorption layer in a non-condensing part, and the center of the light absorption layer is on the back surface corresponding to the boundary line of each lenticular lens. A transmission type projection screen characterized in that it is provided offset from the position of d toward the center line of the lenticular lens sheet by d expressed by the following relational expression. d=t×tan sin ^-1 sin tan ^-1 (R/F)/n (however, d is offset, t is the thickness of the lenticular lens sheet, R is the boundary to which the light absorption layer whose center is offset by d corresponds) The distance between the center of the lenticular lens and the center of the lenticular lens sheet, which is located close to the outside when viewed from the center line, F is the distance of the observation side conjugate point of the Fresnel lens sheet, n is the wrench. (This is the refractive index of the material of the cyular lens sheet.)