JP3002477B2 - Transmission screen - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a transmission screen used for a screen of a projection television or the like.

(Prior art) A transmission type screen used in projection televisions and the like is a Fresnel lens that prevents light from diverging and concentrates on the observer side, and a lenticular lens that widens the horizontal directional characteristics. Is commonly used.

In such a configuration, the arrangement of the Fresnel lens is the third.
As shown in the figure, the Fresnel lens surface 1
Two types have been proposed: a single-sheet type and a two-sheet type directed to the observer side as shown in FIG. When the lens surface is directed to the incident side, the light incident on the non-lens surface (rising portion) of each prism of the Fresnel lens becomes a loss light, and the farther away from the center, the larger the ratio becomes, the darker the surrounding image becomes. Become. On the other hand, in the case of a two-lens system in which the lens surface faces the observation side, the loss due to surface reflection increases, but the loss on the non-lens surface is eliminated, and uniformity of brightness can be obtained. Therefore,
It can be said that it is advantageous to use a screen having a configuration in which the lens surface is arranged on the observer side for an application such as a projection television that requires uniform brightness of the entire screen.

(Problems to be Solved by the Invention) However, in the case of a two-panel screen, points near the top, bottom, left, right, and four corners of the screen are set at an angle of about 30 ° or more in a direction closer to the center of the Fresnel lens from that point. Ghost (double image) inside regular image when observed
Is known to be observed.

In a normal projection television, the height of the center of the screen is designed to be much lower than the height of the human eye when standing upright, so when observing characters etc. that appear at the bottom of the screen from a short distance, ghosts The problem of being noticeable occurred.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems of the prior art and to provide a transmission screen in which ghosts are not noticeable.

(Means for Solving the Problems) That is, the present invention has been made to achieve the above-mentioned problems, and the gist of the present invention is to provide a lenticular lens sheet disposed on the observation side, and a light source for the lenticular lens sheet. A Fresnel lens sheet, and a light-transmitting sheet disposed on the light source side of the Fresnel lens sheet.
The transmissive screen has a size of 0.7 mm, and is arranged such that the lens surface of the sheet is on the observation side, and the Fresnel lens sheet is tightly attached by a lenticular lens sheet and a translucent sheet.

Hereinafter, the present invention will be described with reference to FIG.
The figure shows the transmission screen according to the present invention together with the optical path, the structure of which is as shown in FIG. 2, and the second light transmissive sheet (12) is shown in FIG. Not shown.

In the figure, (1) is a Fresnel lens sheet, (2)
Is the first lenticular lens as the substrate
(3) is a Fresnel lens incident surface,
(4) is the Fresnel lens surface, (5) is the non-lens surface,
(6) shows incident light. This light is shown as green light for the sake of simplicity, and shows a cross-section on a plane perpendicular to the Fresnel lens sheet (1) including transmissive light at the lower part of the screen. The light (6) transmitted through the second translucent sheet (12) (not shown) is refracted by the incident surface (3) of the Fresnel lens to become light (7). Most of the light (7), except for the light (9) reflected by the Fresnel lens surface (4), is refracted and travels in the direction of the light (8) to reach the observation side.

On the other hand, the light (9) reflected by the Fresnel lens surface (4) travels inside the Fresnel lens and enters the Fresnel lens incident surface (3).
If the incident angle at that time is larger than the critical angle as shown in FIG. 1, the light is totally reflected and travels in the direction of light (10). This light (10) was refracted by the non-lens surface (5) of the Fresnel lens, traveled in the direction of the light (11), and reached the observer.
Since the normal image by the light (8) and the image by the light (11) exist at a distance (P), they are observed as ghosts. Usually, the first translucent sheet (2) on which the lenticular lens is formed has a diffusive property, and thus has a luminance distribution centering on the direction of the principal ray. Since the intensity of the light (11) is much lower than that of the light (8), when the screen is observed from the direction in which the light (8) travels, the image due to the light (11) is not recognized and there is no problem. Is viewed from the angle of the light (11) (about 30 ° or more), the light (8) has a high intensity and is recognized as two images.

Let us calculate the distance (P) between two images in a normal case.

The material of the Fresnel lens sheet (1) is polymethyl methacrylate (refractive index 1.49), the screen size is 50 inches (width 1016 mm x length 762 mm), the focal length of the Fresnel lens sheet (1) is 1,000 mm, and the lens surface of the projection tube It is assumed that the distance between the Fresnel lens sheets (1) is 1,100 mm and the optical axis of the projection tube and the central axis of the Fresnel lens sheet (1) are coincident. From the center of the Fresnel lens sheet
At a position 340 mm away, the green light enters the Fresnel incident surface at an incident angle a = 17.2 degrees, and exits at an outgoing angle b = 11.4 degrees. The inclination angle (u) of the Fresnel lens is 34.6 degrees, and the Fresnel lens surface (4) reflects about 5%. The reflected light enters the Fresnel lens entrance surface (3) at an incident angle e = 57.8 degrees. Since the critical angle is 42.2 degrees, this light is totally reflected and enters the non-lens surface (5) of the Fresnel lens. Non-lens surface (5)
Is j from the plane perpendicular to the Fresnel lens entrance plane (3).
= If the angle is 2 degrees, the incident angle f to the non-lens surface is
It emits at 30.2 degrees and the emission angle g = 48.5 degrees. Accordingly, the distance (P) between the two images is obtained by P ≒ 2 × t × tane (A) where t is the thickness of the Fresnel lens sheet (1), so that e = 57.8 degrees and t = Assuming 3mm, P = 9.5
mm.

In addition, since the thickness of the lenticular lens sheet (2) is usually 1 mm to 2 mm, when the light (11) enters at h = 39.5 degrees and proceeds through the lenticular lens sheet 2 at i = 25.3 degrees. Since the amount of increase in the value of P is about 0.5 mm to 1 mm,
May be approximated by equation (1).

The image with the strongest ghost is when observing the characters that appear at the bottom of the screen. On a 50-inch screen, the thickness of the characters is about 5 mm. It is recognized as a character.

As a result of various studies, the inventors have found that if the distance (P) between the two images is reduced, the ghost is substantially not bothersome. In order to reduce P, it is only necessary to reduce the angle e or t in equation (A), but the value of the angle e cannot be largely changed due to the restriction of the optical system of the projection television.

If the thickness of the Fresnel lens sheet is actually reduced to a certain extent, the ghost will not be a problem depending on the type of image to be projected. If it was less than half the line width (t ≦ 0.7), it was acceptable. Also, the limit of thinness is that the pitch of the Fresnel lens normally used for projection television is about 0.1 mm, and the maximum inclination angle of the Fresnel lens is about 50 to 60 degrees, so it is not more than 0.2 mm Have difficulty.

Thin Fresnel lens sheet used in the present invention (1)
Is vinyl chloride, polycarbonate, polymethacryl,
It is desirable to use a film having good translucency, such as polystyrene, polyethylene, or polyester, having a Fresnel lens shape by thermal transfer or the like. Alternatively, the shape of the Fresnel lens can be transferred by using these films as a base material and using an ultraviolet curable resin. This method is extremely effective because thermoforming becomes difficult when the thickness becomes thin.

According to the present invention, the ghost generated in the projection television can be improved. However, if the non-lens surface of the Fresnel lens is roughened or a light absorbing layer is formed on the non-lens surface, the effect is further enhanced. The effect is particularly great in applications where high resolution is required. The first light-transmitting sheet (2) serving as a base material is made of synthetic resin or glass. The first light-transmitting sheet (2) is made of a synthetic resin or glass. A simple sheet or a flat sheet formed with a layer containing a light diffusing agent can be used. Since the Fresnel lens sheet is thin, a sheet having rigidity to support the sheet is desirable.

FIG. 2 shows the configuration of a transmission screen of the present invention. The Fresnel lens sheet (1) is composed of a second translucent sheet (12) and the first translucent sheet (2). It is tightly attached and the periphery is fixed with adhesive tape (13). This is preferable because the flatness of the thin Fresnel lens sheet (1) can be maintained, and even if the second light transmissive sheet (12) is used to increase the apparent thickness, ghosting can be prevented. It is not affected. The second light-transmitting sheet (12) is formed of the first light-transmitting sheet (2).
The same material as described above may be used, and a flat sheet is generally used.

(Example) Hereinafter, a specific example will be described.

A Fresnel lens mold with a focal length of 1,000 mm was manufactured, and a transparent sheet of polymethyl methacrylate was hot-pressed to prepare the samples shown in Table 1. Combined with a 1 mm thick lenticular lens sheet, a 50-inch Attach it to the projection television, put out a character with a line width of 5 mm at the bottom of the screen 340 mm from the center of the Fresnel lens, observe that point from above 40 mm, and perform a visual evaluation to see if a ghost can be recognized, The results in Table 1 were obtained.

As is clear from these results, those in the range of the present invention were excellent without generation of ghost.

Note) Ghost recognition was performed with the naked eye.

(Effects of the Invention) Since the present invention has a configuration as described in detail above, there is an effect that generation of ghost can be suppressed while having a very simple configuration.

[Brief description of the drawings]

FIG. 1 is a partial sectional view showing one embodiment of the present invention, and FIG.
FIG. 1 is a partial cross-sectional view showing a configuration of a transmission screen according to an embodiment of the present invention, and FIGS. 3 and 4 are partially cutaway perspective views showing a general transmission screen. (1) Fresnel lens sheet (2) First translucent sheet (12) Second translucent sheet

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-2-22637 (JP, A) JP-A-3-29802 (JP, U) JP-A-1-117634 (JP, U) (58) Survey Field (Int.Cl. ⁷ , DB name) G03B 21/62

Claims (2)

(57) [Claims] 1. A lenticular lens sheet disposed on an observation side, a Fresnel lens sheet disposed on a light source side of the lenticular lens sheet, and a light transmitting sheet disposed on a light source side of the Fresnel lens sheet, The Fresnel lens sheet has a thickness of 0.2 to 0.7 mm, and the lens surface of the sheet is arranged so as to be on the observation side, and the Fresnel lens sheet is tightly attached by the lenticular lens sheet and the translucent sheet. Transmissive screen. 2. The transmission screen according to claim 1, wherein the lens portion of the Fresnel lens sheet is formed of an ultraviolet curable resin.