JPH0980210A - Lenticular lens sheet - Google Patents

Abstract

(57) [Summary] (Correction) [Problem] To provide a lenticular lens sheet having high characteristics in the horizontal direction and having a constitution easy to manufacture by an extrusion molding method. An angle formed by a straight line parallel to the optical axis of the entrance surface lens and a light beam refracted at the entrance surface and traveling inside the lenticular lens sheet is represented by θ ₁ , and with respect to the optical axis of the exit surface lens. When the angle between the parallel straight line and the ray that is refracted and emitted at the exit surface is represented by θ ₂ , the absolute value of the angle (θ ₁ ) at which the ray is refracted at the incident surface is represented by Δθ ₁ and When the absolute value of the angle (θ ₂ −θ ₁ ) at which the light beam is refracted on the surface is represented by Δθ ₂ , the center is on the optical axis of the incident surface lens and the width is 80% or less of the pitch of the incident surface lens. Δθ ₁ within the range
When △ ratio of _{θ 2 (△ θ 2 / △} θ 1) is 1 or more.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lenticular lens sheet used for a transmissive screen such as a rear projection television. In particular, the present invention relates to a lenticular lens sheet suitable for use in a rear projection television using a liquid crystal panel.

[0002]

2. Description of the Related Art In a projection device such as a rear projection television using a liquid crystal panel, moire occurs because the pixels of the liquid crystal panel and the lenticular lens of the transmissive screen both have a periodic structure in the horizontal direction. I have something to do. In order to avoid the occurrence of the moire, the ratio of the pitch of the lenticular lens to the pitch of the image of the pixel of the liquid crystal panel projected on the transmissive screen is 1 / (N + 1 /
2) (N is an integer greater than or equal to 1) is known (see Japanese Patent Laid-Open No. 2-97991). If N is set to 1, moire may remain, so N
Is generally 2 or more. However, when N is 2 or more, if the pitch of the image of the pixels projected on the screen is 1.0 mm, the pitch of the lenticular lens that satisfies the above formula is 0.4 mm (N = 2), and 0. Two
Since the values are as small as 86 mm (N = 3) and 0.222 mm (N = 4), it is necessary to make the lenticular lens fine pitch.

On the other hand, in the three-tube type projector, the lens pitch p ₁ on the incident surface side and the distance d between the lens on the incident surface side and the lens on the exit surface side in the double-sided lenticular lens sheet constituting the transmissive screen. Ratio (d /
When p ₁ ) exceeds 1.3, the characteristics of the screen in the horizontal direction deteriorate, so that the above ratio is generally 1.1 to
1.25. Therefore, the pitch of the lenticular lens is small, for example, the lens pitch p ₁ on the incident surface side.
Is 0.4 mm, the distance d is 0.44 to 0.
The value is as small as 5 mm.

[0004]

Usually, the lenticular lens sheet is manufactured by an extrusion molding method using a thermoplastic resin. According to the extrusion molding method, the thickness of the lenticular lens sheet is the above distance d (0.44 to 0.5 m).
m), and there is a problem that a double-sided lenticular lens with a fine pitch cannot be manufactured.

Therefore, in order to produce a thin lenticular lens sheet, a technique of extruding a molten resin into a thread shape to form a lens on the incident surface side and a lens on the exit surface side (Japanese Patent Laid-Open Nos. 3-200948 and 2). -1465
No. 36), etc. have been developed.

In order to reduce the lens pitch while maintaining the rigidity of the lenticular lens sheet, a single-sided lenticular lens having a flat incident surface side has been developed. However, the single-sided lenticular lens has a problem that the contrast is low because there is no black stripe on the exit surface side.

The present invention has been made in order to solve the above problems, and an object thereof is to provide a lenticular lens sheet having a high characteristic in the horizontal direction and having a constitution which can be easily manufactured by an extrusion molding method. Especially.

[0008]

In the lenticular lens sheet of the present invention for solving the above problems, an entrance surface lens is formed on one main surface and an exit surface lens corresponding to the above entrance surface lens is formed on the other main surface. A double-sided lenticular lens sheet in which a light beam that is formed parallel to the optical axis of the entrance surface lens travels inside the lenticular lens sheet and is emitted from the exit surface lens, and The parallel angle between the straight line and the ray that is refracted at the entrance surface and travels inside the lenticular lens sheet is represented by θ ₁ , and the ray that is refracted at the straight line parallel to the optical axis of the exit surface lens and exits when it expressed that ray and an angle formed by the theta _2, the absolute value of the light at the incident surface is refracted angle (θ ₁₎ △ θ _1, light at the exit surface is refracted The absolute value of the degrees (θ ₂ -θ ₁₎ △
When expressed in theta _2, the center within the width is in the optical axis of the incident plane lens is 80% or less of the size of the pitch of the incident surface lens, △ ratio of theta ₁ and △ θ ₂ (△ θ ₂ / △
θ ₁ ) is 1 or more.

In the lenticular lens sheet of the present invention, the distance between the entrance surface lens and the exit surface lens is d.
When the main focal length of the entrance surface lens is represented by f, d and f are the following equations (1), d = k · f (where 0.7 ≦ k ≦ 0.9). It is preferable to satisfy (1). In the lenticular lens sheet of the present invention described above, the cross-sectional shape of the exit surface lens is represented by the following formula (2), where the pitch of the entrance surface lens is 1, and y = cx ² / [1+ {1- (k + 1) c ² x ² } ^1/2 ] When it is approximated by (2), it is preferable that the main shape factors c and k satisfy c ≧ 5.0 and k ≦ −1.5.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION According to the lenticular lens sheet of the present invention, the distance between the entrance surface lens and the exit surface lens is larger than that of the lenticular lens sheet manufactured according to the conventional design method (that is, the lenticular lens sheet is thick. ), The same horizontal viewing angle characteristic as that of the conventional lenticular lens sheet can be obtained. The reason will be described by comparing the conventional lenticular lens sheet designing method with the designing method according to the present invention.

In the present invention, attention is paid to the following three design elements. Absolute value △ theta ₁ and the ratio of the absolute value △ theta ₂ of the angle the ray is refracted at the exit surface (θ ₂ -θ ₁₎ of the light beam at the incident surface is refracted angle (theta _1). That is, the ratio of the refracting power of the entrance surface lens to the refracting power of the exit surface lens. The ratio of the distance between the entrance surface lens and the exit surface lens to the focal length of the entrance surface lens. Cross-sectional shape of the exit surface lens.

First, the above design elements will be described with reference to FIG. 3 showing a double-sided lenticular lens sheet having an entrance surface lens and an exit surface lens. In the conventional double-sided lenticular lens sheet design, as shown in FIG.
As shown in (a), the cross-sectional shape of each lens and the distance between both lenses are determined so that the main condensing point of the entrance surface lens and the surface of the exit surface lens coincide with each other.

In the lenticular lens sheet designed by such a conventional method, as shown in FIG.
An angle formed by a straight line parallel to the optical axis of the entrance surface lens 1 and a light beam refracted at the entrance surface and traveling inside the lenticular lens sheet is represented by θ ₁ , and is parallel to the optical axis of the exit surface lens 2. When the angle formed by the straight line and the light beam refracted and emitted at the emission surface is represented by θ ₂ , respectively,
Represents the absolute value of the optical at the incident surface is refracted angle (θ ₁₎ △ θ _1, when a ray represents the absolute value of the refracted angle (θ ₂ -θ ₁₎ △ θ ₂ at the exit plane , Within the range where the center is on the optical axis of the entrance surface lens and the width is 80% or less of the pitch of the entrance surface lens, Δθ ₁ > Δ
The condition of θ ₂ and Δθ ₂ / Δθ ₁ <1 is satisfied. That is, the refracting power is distributed so that it is large on the incident surface side and small on the emitting surface side. Here, when the distance between both lenses is represented by d, the ratio d / p ₁ between the distance d between both lenses and the pitch p ₁ of the entrance surface lens is generally in the range of 1.1 to 1.25 as described above. Is.

On the other hand, in the present invention, as shown in FIG. 3B, the entrance surface lens is made to have a long focus. That is, FIG.
As shown in FIG. 1, when the angles θ ₁ and θ ₂ are determined as in FIG. 1, within the range in which the center is on the optical axis of the entrance surface lens and the width is 80% or less of the pitch p ₁ of the entrance surface lens, the ratio Δθ ₂ / Δθ ₁ is 1 or more. With this configuration, even if the ratio d / p ₁ of the distance d between both lenses and the pitch p ₁ of the entrance surface lens is 1.6 to 1.9, it is at the same level as that of the conventional lenticular lens sheet. A horizontal viewing angle characteristic can be obtained. Therefore, according to the present invention, even if the pitch p ₁ of the entrance surface lenses is the same,
Since the thickness of the lenticular lens sheet can be made larger than that of the conventional lenticular lens sheet (the distance d between both lenses can be made larger), the production by the extrusion molding method becomes easy.

An example of the relationship between Δθ ₁ and Δθ ₂ in the lenticular lens sheet of the present invention is shown in FIG. 4 by the solid line (a).
Indicated by As shown in FIG. 4, from the center (x = 0) corresponding to the optical axis of the entrance surface lens to the pitch p ₁ of the entrance surface lens of 80.
Within the range of not more than%, Δθ ₂ / Δθ ₁ is 1 or more. FIG. 4 also shows an example of the relationship between Δθ ₁ and Δθ ₂ in the conventional lenticular lens sheet.
As shown by the broken line (b) in FIG. 4, in the conventional lenticular lens sheet, within the above range, Δθ ₂ / Δθ
₁ is less than ₁ .

Next, the above design elements will be described. As described above, in the design of the conventional double-sided lenticular lens sheet, the cross-sectional shape of each lens and the distance between both lenses are determined so that the main focusing point of the entrance surface lens and the surface of the exit surface lens coincide with each other. Has been. When the exit surface lens is arranged at the main condensing point of the entrance surface lens in this manner, it becomes necessary to increase the radius of curvature of the exit surface lens. However, if the radius of curvature of the exit surface lens is increased,
It is not preferable to increase the curvature of the exit surface lens because the horizontal viewing angle characteristics are likely to be deteriorated due to the deviation of the optical axes of the entrance surface lens and the exit surface lens.

On the other hand, according to the lenticular lens sheet of the present invention, the position of the exit surface lens is closer to the entrance surface side than the main condensing position, and the light refracted by one entrance surface lens is The light does not concentrate on one point of one exit surface lens corresponding to the above, but the light reaches a wide area within a range of 70 to 80% around the optical axis of the exit surface lens, for example, almost uniformly. That is, the refracting power on the exit surface lens is dispersed, and it is not necessary to increase the curvature of the exit surface lens. When the distance between the entrance surface lens and the exit surface lens is represented by d, and the main focal length of the entrance surface lens is represented by f, respectively, the preferred range in which the exit surface lens should be arranged is the distance between both lenses with respect to the focal length f. The ratio (d / f) of d is 0.7 or more and 0.9 or less.

Finally, design elements will be described. According to the conventional lenticular lens sheet design method, the cross-sectional shape of the exit surface lens is a circle, an ellipse, or a part of a parabola, but according to the lenticular lens sheet of the present invention, a part of a hyperbola is used and a horizontal viewing angle is used. The characteristics are secured.

In order to obtain such an exit surface lens,
Following formula sectional shape of the exit surface lens pitch of the entrance surface lens as 1, when approximated by ^{y = cx 2 / [1+ {} 1- (k + 1) c 2 x 2} 1/2], c is 5. It suffices to satisfy 0 or more and k of −1.5 or less. Here, in the above equation, x is the distance in the pitch direction, as shown in FIG.
Let y be the distance in the height direction. By setting the cross-sectional shape of the exit surface lens in this way, the rate of change of the inclination of the lens surface with respect to the distance in the pitch direction of the exit surface lens is large on the inside,
The outside becomes smaller. As a result, total reflection at the exit surface lens is reduced, and horizontal viewing angle characteristics can be secured.

[0020]

EXAMPLES Table 1 shows each parameter in an example of the lenticular lens sheet of the present invention produced by variously changing extrusion molding conditions.

[Table 1] With the lenticular lens sheet of each of the examples shown in Table 1, a screen having horizontal viewing angle characteristics at practical levels as shown in Table 2 was obtained.

[Table 2]

[0021]

According to the present invention, there is provided a transmissive screen having a horizontal viewing angle characteristic.

[Brief description of drawings]

FIG. 1 is a diagram showing a refraction angle in a conventional lenticular lens sheet.

FIG. 2 is a diagram showing a refraction angle in a lenticular lens sheet according to the present invention.

FIG. 3 is a diagram showing a path of light incident on an entrance surface lens.

FIG. 4 is a diagram showing an example of a relationship between Δθ ₁ and Δθ ₂ .

[Explanation of symbols]

 1 ... Incident surface lens 2 ... Exit surface lens

Claims (3)

[Claims] 1. An entrance surface lens is formed on one main surface,
An exit surface lens corresponding to the above-mentioned entrance surface lens is formed on the other main surface, and a light ray incident parallel to the optical axis of the entrance surface lens travels inside the lenticular lens sheet and is emitted from the exit surface lens. A double-sided lenticular lens sheet, the angle formed by a straight line parallel to the optical axis of the entrance surface lens and a light beam refracted on the entrance surface and traveling inside the lenticular lens sheet is represented by θ ₁ , and the light of the exit surface lens When the angle formed by a straight line parallel to the axis and the light ray refracted and emitted at the exit surface is represented by θ ₂ , the absolute value of the angle (θ ₁ ) at which the light ray is refracted at the entrance surface is Δθ ₁ When the absolute value of the angle (θ ₂ −θ ₁ ) at which the light beam is refracted on the exit surface is represented by Δθ ₂ , the center is on the optical axis of the entrance surface lens and the width is 80 pitches of the entrance surface lens. % Or less Δθ ₁ within a certain range
Lenticular lens sheet, wherein the ratio between the _{△ θ 2 (△ θ 2 /} △ θ 1) is 1 or more. 2. When the distance between the entrance surface lens and the exit surface lens is represented by d and the main focal length of the entrance surface lens is represented by f, d and f are expressed by the following formula (1), d = k.multidot. The lenticular lens sheet according to claim 1, wherein f (provided that 0.7 ≦ k ≦ 0.9) (1) is satisfied. 3. The cross-sectional shape of the exit surface lens, where the pitch of the entrance surface lens is 1, is given by the following formula (2): y = cx ² / [1+ {1- (k + 1) c ² x ² } ^1/2 ] ( The lenticular lens sheet according to claim 1 or 2, which satisfies c ≧ 5.0 and k ≦ −1.5 when approximated by 2).