JP2001228548A - Fresnel lens sheet and method of manufacturing the same - Google Patents

Abstract

(57) [Summary] [Problem] To provide a Fresnel lens sheet and a method for manufacturing the same, which are used for a rear projection type screen in which an image is not obstructed even when observed from above and below the screen. SOLUTION: A diffusion layer 12 having an upper end portion and a lower end portion which are thicker than a central portion and which diffuses light containing a diffusing agent.
And a base material sheet 13 including a base material layer 11 containing no diffusing agent. A lens layer 14 having a Fresnel lens formed of a radiation curable resin is provided on the base sheet 13 to produce a Fresnel lens sheet 15, which is combined with a lenticular lens sheet 16 to form a rear projection screen 10.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a Fresnel lens sheet used for a rear projection type screen in combination with a light diffusing plate, and a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, as a rear projection screen used for a rear projection television or the like, a Fresnel lens sheet that refracts projection light from an image source to make it substantially parallel light, and scatters projection light to form an image. A lenticular lens sheet which is a light diffusion plate to be formed is known.

[0003]

In such a rear projection type screen, the image light transmitted through the Fresnel lens sheet reflects several percent of the light on the lens surface and becomes stray light. Due to this stray light, image disturbances such as color cones and rainbows have occurred. In particular, when viewed from above or below the screen, these image defects are more likely to appear than when viewed from the front of the screen. FIG. 4 is a diagram showing an image defect that occurs when the conventional rear projection screen is viewed from above. FIG. 4A is a side view illustrating an observation position, and FIG. 4B is a diagram illustrating an image obstacle seen on a screen. Rear projection TV 1
When observing the rear projection screen 110 provided at 00 from a position P above it, a color cone (C) is generated above the center of the Fresnel lens of the screen 110, and near the left and right corners below the screen 110. And a rainbow-colored image defect called Rainbow (R).

[0004] As a method of solving these image problems,
For example, Japanese Patent Application Laid-Open No. H01-210942 proposes a method of forming a minute lenticular lens for vertical diffusion on a light incident surface of a Fresnel lens sheet. But,
Since the lenticular lens for vertical diffusion diffuses light only in the vertical direction, especially in the case of a color cone where a vertically long image is obstructed, the function of weakening the intensity by merely exchanging stray light with each other is insufficient. Further, with respect to a rainbow in which an image obstruction occurs obliquely, there is a problem that although the intensity is weakened, the image obstruction remains.

Japanese Patent Application Laid-Open Nos. Hei 7-134338 and Hei 8-107536 propose that the diffusion angle of a minute lenticular lens for vertical diffusion is made larger at the upper and lower ends than at the center of the screen. Have been. The screens proposed in these publications have an improvement effect compared to a vertical lenticular lens having a single diffusion angle because the brightness of the image light in the peripheral portion increases.
However, since these screens use a lenticular lens for vertical diffusion, light is diffused only in the vertical direction, and the improvement effect is not sufficient, and there is a problem that an image obstacle remains.

An object of the present invention is to provide a Fresnel lens sheet used for a rear projection type screen which does not cause an image failure even when viewed from above and below the screen, and a method of manufacturing the same.

[0007]

The present invention solves the above-mentioned problems by the following means. In addition, in order to make it easy to understand, description is given with reference numerals corresponding to the embodiment of the present invention, but the present invention is not limited to this. That is, in the Fresnel lens sheet (15) used for the rear projection screen (10) in combination with the light diffusing plate (16), the upper end portion and / or the light diffusion angle of the central portion are more than the light diffusion angle. A diffusion layer (1) having a large light diffusion angle at the lower end.
It is a Fresnel lens sheet (15) characterized by having 2).

According to a second aspect of the present invention, in the Fresnel lens sheet according to the first aspect, the diffusion layer (12) contains a diffusing agent, and the upper end and / or the lower end has a greater thickness than the center. Fresnel lens sheet (1)
5).

[0009] The invention of claim 3 is claim 1 or claim 2.
In the Fresnel lens sheet described in 1, the diffusion layer (12), the base material layer (11) not containing the diffusing agent,
A Fresnel lens sheet (15) comprising two or more layers containing:

[0010] The invention of claim 4 is the first to third aspects of the present invention.
The Fresnel lens sheet according to any one of the above, wherein a base sheet (13) comprising the diffusion layer (12) and the base layer (11) and a Fresnel lens formed on the base sheet by a radiation-curable resin. A Fresnel lens sheet (15), comprising: a lens layer (14) having a lens shape.

[0011] The invention of claim 5 is the invention of claims 1 to 4.
In the Fresnel lens sheet according to any one of the above, the half value diffusion angle at the upper end and / or the lower end is 1.2 to 2.0 times the half value diffusion angle at the center. Fresnel lens sheet (15).

[0012] The invention of claim 6 is the first to fifth aspects of the present invention.
In the Fresnel lens sheet according to any one of the above, the diffusion layer (12) has an upper end portion and / or a lower end portion having a thickness of 1.2 to 2.0 times the center thickness. A Fresnel lens sheet (15) characterized by the following.

[0013] The invention of claim 7 is the invention of claims 1 to 6.
The Fresnel lens sheet according to any one of the above, wherein the diffusion layer (12) has a layer thickness of a thinnest portion of 3 to 75% of a layer thickness of the base sheet. It is a Fresnel lens sheet (15).

The invention of claim 8 is the first to seventh aspects of the present invention.
In the Fresnel lens sheet according to any one of the above, the difference between the thickest part and the thinnest part of the diffusion layer (12) is 5 times the layer thickness of the base sheet (13).
The Fresnel lens sheet (15), which is not more than 0%.

According to a ninth aspect of the present invention, there are provided the first to eighth aspects.
The Fresnel lens sheet according to any one of the above, wherein the difference between the thickest part and the thinnest part of the diffusion layer (12) is 0.3 mm or less. (15).

According to a tenth aspect of the present invention, there is provided a base material layer (11) formed of the base resin by extruding two layers of a base resin containing no diffusing agent and a diffusing resin containing a diffusing agent. A base sheet forming step of forming a base sheet (13) having a diffusion layer (12) formed of a diffusion resin and having an upper end portion and / or a lower end portion having a thickness greater than that of a center portion; A lens layer forming step of forming a lens layer (14) having a Fresnel lens shape with a radiation-curable resin on the Fresnel lens sheet.

[0017]

Embodiments of the present invention will be described below in more detail with reference to the drawings. FIG.
It is the perspective view which made a rear projection type screen using an embodiment of the Fresnel lens by the present invention a partial section. The rear projection screen 10 is a lenticular lens sheet 1
6 and a Fresnel lens sheet 15 arranged on the light incident side of the lenticular lens sheet 16.

The lenticular lens sheet 16 has a lenticular lens 16a for horizontal diffusion on the light entrance side and a black stripe 16b on the light exit side, and is a light diffusion plate that scatters projection light to form an image. is there.

The Fresnel lens sheet 15 has a base sheet 13 and a lens layer 14, and the base sheet 13 further has a base layer 11 and a diffusion layer 12.

FIG. 2 is a cross-sectional view of the Fresnel lens sheet 15 in the present embodiment, which is cut vertically at the center of the lens. The diffusion layer 12 is a layer in which a diffusing agent that diffuses light is mixed, and the layer thickness is continuously changed so that the layer thickness te at the upper end and the lower end is larger than the thickness tc at the center. I have.
The diffusing agent plays a role in reducing image disturbance due to stray light of the Fresnel lens sheet. Diffusion by a diffusing agent
Since it is isotropic in all directions, unlike the vertical diffusion lenticular lens in the prior art, it works effectively even for a vertically long image obstacle. The image disturbance due to the stray light of the Fresnel lens sheet hardly occurs at the center of the Fresnel lens where the lens angle is small, and is remarkable at the periphery where the lens angle is large, especially outside the center in the height direction more than 1/2. appear. Therefore, by increasing the diffusion angle of the diffusion layer at the upper and lower ends, it is possible to effectively reduce image disturbance without unnecessarily lowering the intensity (gain) of image light.

In particular, in the corner portion of the screen where the rainbow can be easily seen, the intensity of the image light reaching the eyes of the observer itself is:
It is weaker and darker than the center of the screen, so the contrast of the rainbow is high and it is easy to see. Therefore, by increasing the amount of the diffusing agent in the peripheral portion of the screen from the central portion, the brightness of the image light reaching the viewer from the peripheral portion of the screen is increased without lowering the screen gain, and the stray light such as a rainbow is diffused. The strength of the rainbow can be reduced, making it difficult to visually recognize the rainbow.

It is to be noted that the light diffusion characteristics are such that the diffusion half-value angles at the upper end and the lower end are 1.2 to 0.5 compared with the diffusion half-value angle at the center.
Preferably it is 2.0 times. If the ratio of the diffusion half-value angles of the central portion, the upper end portion, and the lower end portion is smaller than 1.2 times, there is almost no difference from the case where the diffusion angle is fixed, and if the ratio is larger than 2.0 times, the gain of the end portion is reduced. Because it is too low, the surroundings are too dark. For the same reason, the layer thickness te at the upper end and the lower end is 1.
It is preferable to make it 2 to 2.0 times.

The base layer 11 is a layer containing no diffusing agent, and its layer thickness changes in accordance with the layer thickness of the diffusion layer 12, so that the layer thickness tb of the base sheet 13 is uniform. It has become. The lens layer 14 is disposed on the light exit side of the base sheet 13 and is a layer on which a circular Fresnel lens is formed.

The relationship between the thickness of the diffusion layer and the thickness of the substrate layer in the substrate sheet can be arbitrarily selected, and the thickness of the substrate layer or the thickness of the diffusion layer can be increased. However, as for the range of the layer thickness, it is necessary that the layer thickness tc at the central portion where the layer thickness of the diffusion layer is the smallest is 3 to 75% with respect to the layer thickness tb of the base material sheet. If the ratio is out of this range, one is too thick compared to the other, so that molding is difficult to be stabilized.

In the case where the Fresnel lens substrate sheet is manufactured by the extrusion molding method, the difference between the layer thickness te of the thickest part of the diffusion layer and the layer thickness tc of the thinnest part is as follows.
It is preferably 50% or less, more preferably 20% or less, with respect to the layer thickness tb of the base sheet. If the difference in the thickness of the diffusion layer is further increased, the amount of the resin containing the diffusing agent and the amount of the resin not containing the diffusing agent in the molding machine are greatly different between the central portion and the peripheral portion of the die. As a result, an unnatural flow of the resin occurs, and as a result, internal strain accumulates in the base sheet, resulting in undulation and warpage. For the same reason, the layer thickness te of the portion where the layer thickness including the diffusing agent is the thickest
And the thickness of the thinnest portion tc is preferably 0.5 mm or less, more preferably 0.3 mm or less.

Based on the above-described embodiment, three types of rear projection screens according to the present invention were produced, and six types of comparative examples were compared and examined. (Embodiment 1-1) A Fresnel lens sheet 13 having the form shown in FIG. 2 was manufactured as Embodiment 1-1. In the diffusion layer 12, a light diffusing agent (styrene, refractive index 1.59) is mixed into an acrylic resin to form a base layer 1 made of an acrylic resin.
The base sheet 13 was produced by a base sheet forming step of extruding and forming the base sheet together with the base sheet 1 through a two-layer extruder. The diffusion layer 12 is formed so as to be thin at the center and thick at both sides. The base layer has a thickness tc of 0.1 mm, a top layer and a bottom layer te of 0.18 mm, and a base material. Sheet 13
Was set to a layer thickness tb = 1.8 mm. Next, an ultraviolet curable resin is applied on a mold having an inverted shape of the Fresnel lens, and a base sheet 13 is placed on the resin with the base layer 11 side inside. A Fresnel lens sheet is formed by irradiating this with ultraviolet light to cure the ultraviolet curable resin, releasing the mold from the mold, and forming a lens layer 14 having a layer thickness tl of about 0.2 mm. 15 was manufactured and combined with the lenticular lens sheet 16 to produce a rear projection screen.

The lenticular lens sheet 16 is formed by melting and extruding an acrylic base material mixed with a diffusing agent from an extruder, and then guiding it between calender rolls cut into the opposite shape of the lenticular lens and cooling it to a thickness of about 1 mm. Was used. In addition, the light diffusion characteristics of the lenticular lens sheet 16 alone are as follows.
8.5, vertical diffusion half-value angle αV (angle in the vertical direction at half the maximum luminance) = 3.9 °, βV (angle in the vertical direction at one-third the maximum luminance) = 5.8
°, αH (the angle in the horizontal direction at which the luminance is の of the maximum luminance) = 39 °, and βH (the angle in the horizontal direction at which the luminance is ３ of the maximum luminance) = 44 °.

(Embodiment 1-2) A Fresnel lens sheet having the same form as that of Embodiment 1-1 but having different specifications was manufactured as Embodiment 1-2. The thickness of the diffusion layer 12 is
Embodiment 1-except that the center layer thickness tc = 0.4 mm, the upper and lower end layer thicknesses te = 0.6 mm, and the light diffusing agent to be mixed is glass (refractive index 1.56). A Fresnel lens sheet was formed in the same manner as in Example 1, and was combined with the lenticular lens sheet 16 to produce a rear projection screen.

(Embodiment 2) A Fresnel lens sheet in which positions of diffusion layers are different from Embodiments 1-1 and 1-2 is manufactured as Embodiment 2. FIG. 3 is a cross-sectional view of the Fresnel lens sheet 35 according to the second embodiment shown in FIG. In the Fresnel lens sheet 35 of the second embodiment, the arrangement of the base layer 31 and the diffusion layer 32 is different from those of the first and second embodiments.
Unlike Example 2, the diffusion layer 32 is disposed on the lens layer 14 side. The diffusion layer 32 has a central part thickness tc = 0.15 m.
m, the layer thickness te at the upper and lower ends is te = 0.2 mm,
The light diffusing agent to be mixed was an MS type (methacrylate-styrene copolymer resin, refractive index 1.53). Otherwise, a Fresnel lens sheet was formed in the same manner as in Embodiment 1-1, and a rear projection screen was manufactured in combination with the lenticular lens sheet 16. As described above, when the Fresnel lens is formed using the ultraviolet curable resin, the diffusion layer may be on the light incident side or on the Fresnel lens side. On the Fresnel lens side, blurring of an image can be weakened, and on the light incident side, scintillation can be weakened.

Embodiment 1 produced as described above
Table 1 shows the light diffusion characteristics of a single Fresnel lens sheet of No. 1, 1-2, and 2 and a combination with the lenticular lens 16.
Shown in

[0031]

[Table 1]

In order to confirm the effect of this embodiment, a rear projection type screen according to the prior art (Comparative Examples 1 to 4) was used.
Rear projection screens (Comparative Examples 5 and 6) having specifications outside the numerical range specified in the present embodiment were produced and compared with the present embodiment. (Comparative Example 1) A Fresnel lens sheet is formed in the same manner as in Embodiment 1-1, except that the base sheet is a single layer containing no diffusing agent, and rear projection is performed in combination with the lenticular lens sheet 16. A mold screen was manufactured.

Comparative Example 2 A Fresnel lens sheet was formed in the same manner as in Embodiment 1-1, except that a vertical diffusion lenticular lens was formed on the light incident surface of the Fresnel lens sheet instead of providing a diffusion layer. The light diffusion characteristics of this Fresnel lens sheet are αV = 3.1 ° and βV = 3.3.
°. This was combined with a lenticular lens sheet 16 to produce a rear projection screen.

(Comparative Example 3) Instead of providing a diffusion layer, a vertical diffusion lenticular lens is formed on the light incident surface of a Fresnel lens sheet, and this vertical diffusion lenticular lens is vertically aligned at the upper and lower ends with respect to the center. A Fresnel lens sheet was formed in the same manner as in Embodiment 1-1 except that the diffusion angle was increased. The light diffusion characteristics of this Fresnel lens sheet are such that αV = 2.8 ° and βV = 3.0 at the center.
°, αV = 3.3 ° and βV = 3.5 ° at the upper and lower ends. This was combined with a lenticular lens sheet 16 to produce a rear projection screen.

(Comparative Example 4) A Fresnel lens sheet was formed in the same manner as in Embodiment 1-1, using a substrate sheet in which a diffusing agent was uniformly mixed as a whole. The light diffusion characteristics of this Fresnel lens sheet are αV = 2.4 °, βV
= 3.0 °. This was combined with a lenticular lens sheet 16 to produce a rear projection screen.

(Comparative Example 5) The thickness of the diffusion layer was set such that the thickness tc of the central portion was 0.1 mm, the thickness te of the upper end portion and the lower end portion was te =
A Fresnel lens sheet was formed in the same manner as in Embodiment 1-1, except that the thickness was 0.25 mm. This was combined with a lenticular lens sheet 16 to produce a rear projection screen.

(Comparative Example 6) The thickness of the diffusion layer was set such that the thickness tc at the center was 0.5 mm, the thickness te at the upper end and the lower end was te =
A Fresnel lens sheet was formed in the same manner as in Embodiment 1-1, except that 1.5 mm was set. However, the formed base sheet had a strong local undulation, and its diffusion characteristics varied greatly from sheet to sheet.

(Evaluation) The Fresnel lens sheet of each embodiment and each comparative example was set on a 60-inch rear projection television as shown in FIG. 4 and evaluated. Table 2 below summarizes the specifications of these rear projection screens and the evaluation results.

[0039]

[Table 2]

(Comparative Examples 1 to 4) In Embodiments 1-1, 1-2 and 2 according to the present invention, rainbow, color cone, ghost (double image), corner darkness (low brightness at four corners) Regarding the condition), all are improved. On the other hand, in Comparative Example 1 in which no countermeasure was taken,
Needless to say, the countermeasures according to the prior art shown in Comparative Examples 2 to 4 have improved image failure to some extent, but are insufficient. In comparison, the image was hard to see.

(Comparative Example 5) Regarding the light diffusion characteristics, the half diffusion angle at the upper end and the lower end is preferably 1.2 to 2.0 times the half diffusion angle at the center. ,
It is preferable that the thickness te of the upper end portion and the lower end portion be 1.2 to 2.0 times the thickness tc of the central portion of the diffusion layer.
In contrast, the embodiments 1-1, 1-2, and 2 have a layer thickness that satisfies all of these conditions.
Color cones, ghosts, and corner darkness have all been improved. However, in Comparative Example 5, the layer thickness te at the upper end and the lower end of the diffusion layer is different from the thickness t at the center.
There is 2.5 times c. As a result, the rainbow, the color cone, and the ghost are improved, but the corner darkness becomes conspicuous because the brightness at the upper and lower ends is too low.

(Comparative Example 6) The difference between the layer thickness te of the portion where the layer thickness of the diffusion layer is the thickest and the layer thickness tc of the portion where the diffusion layer is the thinnest is different from the layer thickness tb of the base material sheet for reasons of molding. It is preferably 50% or less, more preferably 20% or less. For the same reason, the difference between the layer thickness te of the portion having the thickest layer containing the diffusing agent and the layer thickness tc of the thinnest portion may be 0.5 mm or less, more preferably 0.3 mm or less. preferable. Embodiment 1-1, 1-2, 2
Has a layer thickness satisfying all of these conditions. However, in Comparative Example 6, neither value satisfies this condition, and the formed base sheet has strong local undulation,
Since the diffusion characteristics vary greatly from sheet to sheet,
Needless to say, it could not be used.

According to the present embodiment, the diffusion layer containing the diffusing agent is provided, and the thickness of the diffusion layer is made larger at the upper end and the lower end than at the center. , Color cones and ghosts can be eliminated. In addition, since the thickness of the diffusion layer is limited within a certain condition, the brightness at the upper and lower ends is not excessively reduced, so that corner darkness is not conspicuous, and an image obstacle can be eliminated. Furthermore, also in the screen of the configuration of the present embodiment,
As described in JP-A-7-134338 and JP-A-8-107536, similar to a screen in which the diffusion angle of a minute lenticular lens for vertical diffusion is larger at the upper and lower ends than at the center of the screen, the periphery of the screen is similar. Since the amount of light reaching the observer from the part increases, white uniformity can be improved. Furthermore, since the conditions for the layer thickness suitable for the two-layer extrusion molding are also specified, a high-precision Fresnel lens sheet can be easily and reliably manufactured.

(Modifications) Various modifications and changes are possible without being limited to the above-described embodiment, and these are also within the equivalent scope of the present invention. (1) In each embodiment, the light incident surface side of the Fresnel lens sheet has been described as an example in which the plane is flat. However, the present invention is not limited to this. For example, a lenticular lens for vertical diffusion or the like may be provided on the light incident surface side of the Fresnel lens sheet. A fine uneven shape may be formed to further enhance the diffusion effect.

(2) In each of the embodiments, the base sheet is formed to be a parallel plate, but is not limited thereto.
For example, a diffusion layer having a different layer thickness depending on the portion may be provided on the parallel-plate base layer, and the layer thickness of the base sheet may be different depending on the portion.

(3) In each embodiment, the example in which the layer thickness of the diffusion layer continuously changes along the curve has been described. However, the present invention is not limited to this. For example, the layer thickness may change linearly. Otherwise, it may change stepwise.

(4) In each embodiment, an example is shown in which the thickness of the diffusion layer is thick at both ends of the upper end and the lower end. However, the present invention is not limited to this. For example, only the upper end or the lower end is thick. It may be.

(5) In Embodiments 1-1 and 1-2,
Although the example in which the lens layer 14 is provided by an ultraviolet curable resin separately from the base material layer 11 and the diffusion layer 12 is shown, the invention is not limited to this. For example, as shown in FIG. After producing a sheet having the material layer 11-2 and the diffusion layer 12-2, a Fresnel lens sheet 15-2 may be produced by press-forming a Fresnel lens shape on this sheet.

[0049]

As described above in detail, according to the present invention, the diffusion layer in which the light diffusion angle at the upper end and / or the lower end is larger than the light diffusion angle at the center of the Fresnel lens sheet. Because of the provision, it is possible to eliminate image troubles that easily occur at the upper and lower ends. In addition, since the diffusion layer diffuses light with a diffusing agent, it also diffuses light in the left-right direction, so that the effect is higher and the diffusion layer can be easily formed. Furthermore, since the thicknesses of the base material layer and the diffusion layer are specified, the diffusion effect is not too small and is not excessive, so that the optimum conditions can be obtained, and a layer configuration that does not hinder molding is adopted. be able to. Furthermore, since the method includes the step of forming a base sheet extruded by two-layer extrusion and the step of forming a lens layer using a radiation-curable resin, the production of the above-mentioned Fresnel lens sheet without image hindrance can be simplified.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an embodiment of the present invention.

FIG. 2 is a cross-sectional view illustrating Embodiments 1-1 and 1-2 of the present invention.

FIG. 3 is a sectional view showing a second embodiment.

FIG. 4 is a diagram for explaining a problem of the related art.

FIG. 5 is a diagram illustrating a modification.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Rear projection screen 11, 31 Base layer 12, 32 Diffusion layer 13, 33 Base sheet 14 Lens layer 15, 35 Fresnel lens sheet 16 Lenticular lens sheet

 ────────────────────────────────────────────────── ─── Continued on front page (72) Inventor Makoto Honda 1-1-1 Ichigaya-Kaga-cho, Shinjuku-ku, Tokyo F-term within Dai Nippon Printing Co., Ltd. 2H021 BA22 BA27 BA28 BA29 BA32 4F213 AA21 AA44 AH75 WA02 WA06 WA43 WA54 WA56 WA60 WA86 WA87 WB01 WB13 WB22 WC01 WE02 WE07 WE16 WF05 WF27 WK05 WW34

Claims (10)

[Claims] 1. A Fresnel lens sheet used for a rear projection screen in combination with a light diffusion plate, comprising a diffusion layer having a light diffusion angle at an upper end and / or a lower end larger than a light diffusion angle at a center. A Fresnel lens sheet, characterized in that: 2. The Fresnel lens sheet according to claim 1, wherein the diffusion layer contains a diffusing agent, and an upper end portion and / or a lower end portion has a greater thickness than a center portion. Sheet. 3. The Fresnel lens sheet according to claim 1, comprising two or more layers including the diffusion layer and a base layer not containing the diffusing agent. Fresnel lens sheet. 4. One of claims 1 to 3
In the Fresnel lens sheet according to the above, comprising: a base sheet comprising the diffusion layer and the base layer; and a lens layer having a Fresnel lens shape formed by a radiation-curable resin on the base sheet. Characteristic Fresnel lens sheet. 5. The method according to claim 1, wherein:
The Fresnel lens sheet according to any one of the preceding claims, wherein the half-value diffusion angle at the upper end and / or the lower end is 1.2 to 2.0 times the half-value diffusion angle at the center. Sheet. 6. Any one of claims 1 to 5
The Fresnel lens sheet according to claim 1, wherein the diffusion layer has an upper end portion and / or a lower end portion having a thickness of 1.2 to 2.0 times a thickness of a central portion. . 7. One of claims 1 to 6
The Fresnel lens sheet according to claim 1, wherein the diffusion layer has a thickness of a thinnest portion of 3 to 75% of a thickness of the base sheet. 8. One of claims 1 to 7
The Fresnel lens sheet according to claim 1, wherein the difference between the thickest part and the thinnest part of the diffusion layer is 50% or less of the layer thickness of the base sheet. . 9. Any one of claims 1 to 8
The Fresnel lens sheet according to claim 1, wherein a difference between a thickest part and a thinnest part of the diffusion layer is 0.3 mm or less. 10. A two-layer extrusion of a base resin containing no diffusing agent and a diffusing resin containing a diffusing agent to form a base layer formed of the base resin, an upper end formed of the diffusing resin, A base sheet forming step of forming a base sheet having a diffusion layer having a layer thickness at a lower end portion larger than that of a center portion; and a lens layer having a Fresnel lens shape on the base sheet by a radiation-curable resin. And f) forming a Fresnel lens sheet.