JP2008250158A - Fresnel lens sheet, transmission screen and projection type image display apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a Fresnel lens sheet capable of suppressing noise light, a transmission screen using the Fresnel lens sheet and a projection type image display apparatus using the transmission screen. <P>SOLUTION: A Fresnel lens part 201B of a Fresnel lens sheet 201 for a transmission screen is configured by arraying many unit lenses 203 having triangular cross-sectional shapes at a fixed pitch and each unit lens 203 is formed as a shape whose cross-sectional shape indicates a frustum triangle by cutting off its vertical angle portion, so that a tip part 203c capable of reducing the vignetting quantity of light which is generated by shielding incident light L11 on a total reflection surface 203a out of incident light L11 obliquely projected to the Fresnel lens part 201B by the vertical angle portion of an adjacent unit lens 203 is formed on the vertical angle portion of each unit lens 203. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a Fresnel lens sheet used in a projection type video display device such as a rear projection television, for example, a transmission type screen using the same, and a projection type video display device.

2. Description of the Related Art Conventionally, for example, a rear projection television is known as a projection display device (projection image display device) provided with a transmissive screen.
This type of rear-projection television is positioned on the front side of the screen by causing the image light projected from the projector as a light source to be reflected by a reflecting mirror and incident on the back side of a transmission screen having a substantially rectangular flat plate shape. The observer who observes can observe the image light which permeate | transmits and radiate | emits a screen (for example, refer patent document 1).

The transmissive screen is, for example, a Fresnel lens sheet having a Fresnel lens portion that adjusts the direction of incident light to be emitted, and lenticular that diffuses the emitted light from the Fresnel lens sheet in the horizontal direction (horizontal direction) of the transmissive screen. A base material comprising a diffusion lens sheet (such as a lenticular lens sheet) having a minute lens portion such as a lens sheet, and a diffusion plate that diffuses light emitted from the diffusion lens sheet in the vertical direction (vertical direction) of the transmission screen It has.
Further, in order to reduce the thickness of the projection television, the optical axis of the Fresnel lens sheet (P1: see FIG. 1) and the center of the Fresnel lens sheet on the screen (P2: see FIG. 1) are removed, and the Fresnel lens sheet is inclined from the oblique direction. Attempts have been made to reduce the thickness of televisions by emitting the projected light substantially in parallel.

However, the light reflection loss due to reflection on the incident surface of the Fresnel lens sheet 20 cannot be completely eliminated. In addition, if it is attempted to reduce the reflection loss, the structure becomes complicated and causes an increase in cost.
JP 2006-018072 A JP-A 61-269135

On the other hand, recently, Fresnel lens sheets using total reflection with relatively little light loss are known as transmissive screens on which projected light is incident at a steep angle.
For example, Patent Document 2 discloses a transmissive screen having a structure using a total reflection type Fresnel lens sheet composed of a plurality of unit prisms having a triangular cross section arranged concentrically at a constant pitch. It is disclosed.
As shown in FIG. 5, in order to avoid problems such as chipping of a cutting tool for die cutting in die processing with a sharp apex angle like a unit prism of a total reflection type Fresnel lens sheet, In general, rounding is performed by dropping the cutting edge of a cutting tool for die cutting linearly.

  However, in contrast to the conventional refractive Fresnel lens with a Fresnel lens part on the exit surface, the total reflection Fresnel lens with the Fresnel lens part on the entrance surface causes refraction, reflection, scattering, etc. due to the rounded prism apex angle. There was a problem that noise light was strongly generated by light. In particular, by a projection optical system projected from an oblique direction, a clear double image or ghost image is generated in the direction of oblique projection (generally, there are many vertical directions). These not only lower the contrast of the image due to noise light, but also cause adverse effects such as fine character blurring and double outlines, and thereby significantly deteriorate the image quality. In addition, concentric unevenness, streaks and the like generated during cutting were a major cause of visual observation.

  The present invention has been made to solve the above-described conventional problems, so that it is possible to manufacture a Fresnel lens and a screen using the same, which can suppress the manufacturing cost and can be produced stably, and can emit noise light. It is an object of the present invention to provide a Fresnel lens sheet that can be pressed, a transmissive screen using the same, and a projection display device using the transmissive screen.

  In order to achieve the above object, the invention described in claim 1 includes a transparent base material, and a plurality of unit lenses having a triangular cross-sectional shape on one surface of the base material arranged in a concentric manner at a constant pitch. A Fresnel lens sheet comprising a Fresnel lens portion that adjusts the direction of incident light to be emitted light, wherein one opposing surface forming the apex angle of the triangle of the unit lens is a light incident surface, and the other Is a total reflection surface that totally reflects light incident from the light incident surface, and the apex angle portion of each unit lens is cut off, and the incident light is projected from an oblique direction to the Fresnel lens portion. The tip portion is provided at the apex portion for reducing the amount of light vignetting that is blocked by the apex portion of the adjacent unit lens.

According to a second aspect of the present invention, in the Fresnel lens sheet according to the first aspect, the tip portion is formed in a rounded shape so as to reduce the directivity of the incident light beam to the tip portion. Features.
According to a third aspect of the present invention, in the Fresnel lens sheet according to the first or second aspect, the tip portion of each unit lens has a certain width along a direction in which the unit lenses are arranged, and the width is , 0.01 μm to 2 μm.

According to a fourth aspect of the present invention, in the Fresnel lens sheet according to the first or second aspect, the base member has a light emitting surface on a surface opposite to the one surface, and the tip portion is parallel to the light emitting surface. It is comprised including a top surface, The said top surface is 50% or less of the area of the surface which comprises the said front-end | tip part, It is characterized by the above-mentioned.
According to a fifth aspect of the present invention, in the Fresnel lens sheet according to the first or second aspect, the base member has a light emitting surface on a surface opposite to the one surface, and the tip portion is parallel to the light emitting surface. The top surface width T is in the range of P × 0.005 ≦ T ≦ P × 0.04, where T is the width of the top surface and P is the pitch of the unit lenses. It is characterized by being.

A sixth aspect of the present invention is the Fresnel lens sheet according to the first aspect, wherein the troughs located between the unit lenses adjacent to each other are formed in an arc shape or a polygonal shape.
According to a seventh aspect of the present invention, in the Fresnel lens sheet according to the first or sixth aspect, the base member has a light emitting surface on a surface opposite to the one surface, and the tip portion is parallel to the light emitting surface. It is configured to include a top surface, and when T is the width of the top surface and B is the width of the valley formed in the arc shape or polygonal shape, T <B is satisfied.
The invention according to claim 8 is the Fresnel lens sheet according to any one of claims 4, 5 or 7, wherein the top surface is a straight surface perpendicular to the light incident surface.

The invention according to claim 9 is the Fresnel lens sheet according to claim 1, wherein the incident angle of the light beam projected from an oblique direction to the Fresnel lens portion is θ, and the light beam is incident at the incident angle θ. When the height of the unit lens at the portion is H and the pitch of the unit lens is P, the relationship of P ÷ tan (θ) <H is satisfied.
The invention according to claim 10 is the Fresnel lens sheet according to claim 1, wherein the Fresnel lens portion has a haze value of 10% or more.
The invention according to claim 11 is the Fresnel lens sheet according to claim 1, wherein the total thickness including the Fresnel lens portion and the base material is 2 mm to 20 mm.

The invention of claim 12 is a transmissive screen, comprising the Fresnel lens sheet according to any one of claims 1 to 11 and a diffusion lens sheet that diffuses light emitted from the Fresnel lens sheet. Features.
A transmissive screen according to a thirteenth aspect of the present invention is the transmission screen according to the twelfth aspect, wherein the diffusing lens sheet includes a transparent base material and a microlens or a microprism formed on a surface of the base material facing the Fresnel lens sheet. It is characterized by having.

The invention of claim 14 is a projection-type image display device, which is disposed on a unit lens side of the transmissive screen according to claim 12 or 13 and the Fresnel lens sheet constituting the transmissive screen, and the Fresnel And a projection optical system that projects image light obliquely downward or obliquely upward with respect to the lens sheet.
According to a fifteenth aspect of the present invention, in the projection display apparatus according to the fourteenth aspect, the projection optical system is a projector.

  In the Fresnel lens sheet of the present invention, a transmissive screen using the same, and a projection-type image display device, a Fresnel lens portion that adjusts the direction of incident light to be emitted light is provided on the incident surface side of the light beam, and at least the light beam In the case of a total reflection type Fresnel lens sheet having an incident light incident surface and a total reflection surface that totally reflects the light incident on the light incident surface, the incident light is only near the tip corresponding to the apex angle of the unit lens. In many cases, it is not incident, and even if the tip of the unit lens has the same rounded shape, the effect of rounding the tip is more than that of the conventional Fresnel lens sheet that has a Fresnel lens that uses refraction on the exit surface side. It will come out greatly. For this reason, in the present invention, the apex angle portion of each unit lens is excised, and the apex angle portion of the unit lens adjacent to the total reflection surface among the incident light rays projected from the oblique direction to the Fresnel lens portion. The apex portion that reduces the amount of light vignetting blocked at the apex angle portion is provided, and the end portion of each unit lens has a certain width along the direction in which the unit lenses are arranged, and this width is reduced to 0. By setting the thickness to 0.01 μm or more to 2 μm or less, it is possible to reduce the noise light component and reduce the double image and the ghost image by appropriately diverging the noise light. It has been confirmed by actual experiments that if the width of the tip of the unit lens is smaller than 0.01 μm, chipping of the cutting tool frequently occurs during cutting, and the tip of the unit lens cracks during transportation to deteriorate the quality. It was. It was also confirmed that the amount of noise light increased when the width of the unit lens tip exceeded 2 μm.

In the present invention, the tip of the unit lens is configured to include a top surface parallel to the light exit surface of the substrate, and the top surface has an area of the surface constituting the tip of the unit lens. By being 50% or less, the amount of noise light coming out from the exit surface can be reduced. This is because if the light exit surface of the substrate and the incident surface of the top surface are parallel, the multiple reflection component tends to be emphasized there, but the area of the surface where the top surface constitutes the tip of the unit lens. It was found that the influence of the multiple reflection component is reduced when the ratio is 50% or less. Furthermore, it has been found that if it is 30% or less, the effect of noise can be reduced to a level where it is hardly recognized when used as a screen.
In the present invention, the width of the top surface of the front end portion of the unit lens per unit area varies depending on the unit lens pitch of the Fresnel lens portion. If the unit lens pitch is large, the width of the top surface of the unit lens tip per unit area of the entrance surface will be reduced, and noise generation can be suppressed even if the rounding amount of the unit lens tip is increased. . Conversely, when the unit lens pitch is made fine for the purpose of reducing moire or the like, it is desirable that the rounding amount of the unit lens tip is small.

As a result of various experiments, when the relationship between the unit lens pitch and the width of the top surface of the unit lens tip is determined, and the width of the top surface of the unit lens tip is T and the unit lens pitch is P, P × 0. By setting 005 ≦ T ≦ P × 0.04, the amount of noise light per unit area can be reduced to a level that does not cause a problem in practice.
If T ≦ P × 0.02, the influence of noise light hardly occurs.

  In the present invention, rounding the tip of the unit lens into an arc shape or a polygonal shape with two or more sides is highly effective in reducing noise, but cutting with a cutting tool becomes difficult. Therefore, even when the tip of the unit lens is rounded simply and linearly, the area of the top surface where the incident light hits can be reduced by making the straight line substantially perpendicular to the light incident surface of the unit lens. Therefore, it is possible to reduce noise light components. Here, as a simple method, the top surface of the tip of the unit lens is linearly rounded substantially perpendicularly to the incident surface, but if the unit lens top surface is rounded linearly substantially parallel to the incident light, High effect. These effects are preferably within ± 3 degrees, and the effects are further enhanced within ± 1 degrees.

In the present invention, the trough of the Fresnel lens part is rounded into a substantially arc shape or a substantially polygonal shape to increase the stability of cutting of the mold for molding the Fresnel lens part, and at the time of cutting By reducing the burrs, the generation of noise light can be prevented, and by reducing the burrs, the product can be smoothly peeled off from the mold during mass production and the mass productivity can be improved.
Furthermore, in the Fresnel lens sheet using total reflection, incident light is concentrated and incident on the tip of the unit lens, so that the influence of rounding is stronger at the tip than at the valley of the unit lens. Therefore, when the width of the top surface of the unit lens tip is T and the width of the valley of the unit lens is B, it is possible to achieve both production stability and reduction of noise light by satisfying T <B. It becomes possible.
Also, assuming that the incident angle incident on the Fresnel lens portion is θ, the height of the unit lens in the portion where the light beam is incident at this incident angle is H, and the unit lens pitch is P, P ÷ tan (θ) <H. By satisfying the relationship, it becomes possible to prevent light from entering the rounded portion of the valley, and it is possible to prevent generation of noise light due to the rounding of the valley.

Further, in the present invention, when the haze value of the Fresnel lens portion is 10% or more, it is possible to diverge noise light and further prevent the generation of a double image or a ghost image.
In addition, by setting the thickness Df of the Fresnel lens sheet to 2 mm to 20 mm, it is possible to further prevent the generation of a double image or a ghost image by further reducing the direction of noise light.
In the present invention, a high-contrast screen with less noise can be realized by a transmissive screen including a Fresnel lens sheet and a diffusing lens sheet that diffuses light emitted from the Fresnel lens sheet.
Further, the lens structure of the diffusing lens sheet allows the noise reduction effect of the Fresnel lens sheet to be effectively utilized by arranging the minute lens or the minute prism horizontally with respect to the observer.

Further, in the present invention, a thin and high-quality projection type image display device can be realized by using the projection type video display device equipped with the above-described transmission type screen.
Furthermore, in projection television, the projection optical system of the projection television is an off-axis projection system that projects from diagonally downward or diagonally upward, so that the noise reduction effect of the Fresnel lens sheet can be used effectively, making it thinner and higher. A projection type image display device with high image quality can be realized.

In the Fresnel lens sheet of the present invention, productivity can be maintained while suppressing as much as possible noise light generated at the apex and valley portions of the unit lens. When this Fresnel lens sheet is applied to a screen for a projection display, the optical axis of the Fresnel lens part is arranged so as to deviate from the center of the lens body. Further, it is possible to make the projection type image display apparatus thinner by making the inclination of the reflecting mirror disposed opposite to the back of the screen gentle.
Here, by using the Fresnel lens sheet that decenters the optical axis and utilizes total reflection as described above, the image light is scattered at the apex and valley portions of the unit lens of the Fresnel lens portion and is emitted. Many scattering components that are not substantially parallel light are included.

  However, in the Fresnel lens sheet of the present invention, the width of the top surface of the unit lens tip is set within the above-mentioned value range, so that the noise light caused by this Fresnel lens sheet can be reduced to an unnecessary angle. Ejecting stray light can be eliminated. In addition, when used in a projection display screen, double images and ghost images due to stray light can be reduced. Further, even when used in an FPD illumination device or the like, light is emitted only in a necessary direction, so that light can be used efficiently without unevenness. Moreover, also when it uses for the light condensing uses, such as a solar cell, the utilization efficiency of light can be improved more. Furthermore, it is effective for improving the uniformity and efficiency of light of the lighting device.

(First embodiment)
FIG. 1 is a schematic side view showing a configuration of a projection-type image display apparatus using a transmission screen according to the present invention, FIG. 2 is an enlarged cross-sectional view of the main part of the transmission screen in the embodiment of the present invention, and FIG. FIG. 4 is an explanatory view of incident light rays of the total reflection type Fresnel lens sheet in the embodiment of the present invention, and FIG. 5 is a refractive type Fresnel lens. It is explanatory drawing of the incident light ray of a sheet | seat.

  In FIG. 1, a projection display apparatus 10 includes a housing 11, a transmission screen 20 attached to the front part of the housing 11, and a projector 12 as a light source attached to the rear part of the housing 11. The image light projected from the projector 12 is reflected by the reflecting mirrors 13 and 14 disposed in the housing 11 and is incident on the back surface of the transmissive screen 20. It is configured so that an observer located at can observe video light transmitted through the transmissive screen 20 and emitted.

As shown in FIG. 1, the projector 12 is disposed on the optical axis P1 of the Fresnel lens portion, and this optical axis P1 is parallel to the center P2 of the transmissive screen 20 and is transmissive. It is below the transmission screen 20 outside the area of the screen 20. Therefore, when the projector 12 is disposed on the optical axis P1 in the housing 11, the optical path of the image light projected from the projector 12 is deflected by the two reflecting mirrors 13 and 14, and the image light is transmitted through the transmission screen. The rear surface of 20 is projected obliquely upward from the lower rear portion. Further, θ _max shown in FIG. 1 represents the maximum incident angle of the image light incident on the transmissive screen 20.

  As shown in FIG. 2, the transmissive screen 20 has a total reflection type Fresnel lens sheet 201 that converts incident light into parallel light and emits it as parallel light, and is opposed to the light emission side of the Fresnel lens sheet 201. And a diffusing lens sheet (lenticular lens sheet) 202 that diffuses and emits parallel light to a predetermined aspect ratio.

As shown in FIG. 2, the Fresnel lens sheet 201 includes a transparent base material 201A and a large number of unit lenses 203 arranged concentrically at a constant pitch on the surface of the base material 201A facing the light incident side. The unit lens 203 is formed integrally with the base material 201A so that the cross section of the unit lens 203 has a triangular shape, and the apex portion of the triangle protrudes to the light incident side from the projector 12.
As shown in FIGS. 2 to 4, the unit lens 203 has a light incident surface 203 a as one opposite surface forming the apex angle of the triangle, and a light ray L11 incident from the light incident surface 203 a as the other surface. The total reflection surface 203b is configured to be totally reflected and emitted as an outgoing light beam L12.

  As shown in FIGS. 2 to 4, each unit lens 203 is formed into a cross-sectional shape having a truncated triangle shape by cutting away the apex portion. In the corner portion, the amount of vignetting of light that is blocked by the apex angle portion of the unit lens 203 adjacent to the total reflection surface 203a of the incident light L11 projected from the oblique direction to the Fresnel lens portion 201B. A tip portion 203c to be reduced is provided. The distal end portion 203c includes a top surface 203d having a constant width T parallel to the light emitting surface 201a on the surface opposite to the unit lens 203 of the base material 201A.

Further, as shown in FIG. 2, the diffusing lens sheet 202 includes a light diffusing layer 202A and a minute lens part 202C laminated on the light incident side surface of the light diffusing layer 202A via a light mask 202B. ing.
The micro lens unit 202C is configured by, for example, arranging a large number of cylindrical lenses having a semi-cylindrical cross section in parallel at a constant pitch in a direction orthogonal to the observer's vertical direction indicated by an arrow in FIG. The The optical mask 202B is provided on the exit surface side of the micro lens unit 202C, and a well-known light shielding unit (not shown) that shields the stripe-shaped non-condensing part by the cylindrical lens, and the micro lens unit 202C exits. It is composed of a well-known light transmitting portion (not shown) that is provided on the surface side and transmits the image light collected by the cylindrical lens, and the image light transmitted through the light transmitting portion of the light mask 202B is a light diffusion layer. After being diffused in the vertical direction or the horizontal direction by 202A, the light is emitted toward the front surface of the transmissive screen 20.

As shown in FIG. 5, the refractive type Fresnel lens sheet 41 refracts the light L1 incident on the Fresnel lens sheet 41 using the exit surface Wf1 of the Fresnel lens 41a, thereby making the projection light substantially parallel. The light beam L2 is emitted.
On the other hand, in the total reflection type Fresnel lens sheet 201, as shown in FIG. 4, when the angle of the light ray L11 incident on the Fresnel lens portion is steep, the incident light ray L11 becomes the tip of the adjacent unit lens 203. Since the total reflection surface 203b of the unit lens 203 has a width corresponding to Wf2, the portion where light is actually incident is only the width of Wi2 that is half or less of Wf2.

  Further, generally, as shown in FIGS. 4 and 5, the tip 203c of the unit lens 203 prevents the cutting tool from being chipped at the time of cutting, scratches to the unit lens at the time of transportation, and the reduction of foreign matters due to the chipping of the unit lens. For the purpose, the unit lens 203 is often rounded so that the top surface 203d of the unit lens tip 203c is a flat surface so that the width T of the top surface 203d of the tip 203c is about 10 μm. Here, assuming that the width of the top surface 203d of the unit lens front end portion 203c is T, in the conventional Fresnel lens sheet, light is refracted using the entire surface of the exit surface Wf1 of the Fresnel lens. The ratio at which the influence of the rounding process of the lens is relatively small. On the other hand, in the total reflection type Fresnel lens sheet 201, the effective reflection surface of the total reflection surface 203b of the unit lens 203 actually used by the incident light is Wi2, and therefore the influence of the rounding processing of the unit lens tip 203c. And the generation of noise light due to the rounding of the unit lens tip 203c becomes a problem. Further, in the total reflection type Fresnel lens sheet 201, since the Fresnel lens portion 201B is formed on the light incident surface, the light that is not affected by light scattering by the base material 201A of the Fresnel lens sheet 201 is unit lens. Since the light is incident on the top surface 203d of the tip portion 203c, the directivity of noise light is increased.

Here, generation of noise light at the unit lens front end portion 203c in the total reflection type Fresnel lens sheet 201 will be described in more detail.
As shown in FIG. 6, the incident light L11 is refracted and reflected (reflection is not shown) on the unit lens top surface 203d rounded into a straight line. The refracted light L13 enters the unit lens with a strong directivity and causes stray light. If the width T of the unit lens top surface 203d is small, the generation of noise light is suppressed. However, since the apex angle of the unit lens 203 is sharp, problems such as chipping of a cutting tool, scratches, and foreign matters occur during cutting. It was.

Therefore, total reflection that achieves both noise light and production stability is achieved by making prototypes of Fresnel lens sheets of various sizes and experimenting so that the width T of the unit lens top surface 203d is 0.01 μm to 2 μm. It became possible to realize a type Fresnel lens sheet. Further, it was found that when the width T of the unit lens top surface 203d is 1 μm or less, the performance is improved to a level at which almost no noise light can be recognized when used as a screen.
In addition, if the pitch P of the unit lenses 203 is increased, it is possible to relatively reduce the influence of noise due to the tip 203c of the unit lens 203. Therefore, the relationship between the pitch P of the unit lenses 203 and the width T of the unit lens top surface 203d is obtained by experiments, and if P × 0.005 ≦ T ≦ P × 0.04 is satisfied, the stability of noise light and production is improved. It was found that a compatible total reflection type Fresnel lens sheet was realized.

Further, when the pitch P of the unit lenses 203 is increased, noise tends to be reduced, but there is a possibility of causing moire with the pixels. Therefore, by making the lens pitch of the diffusion lens sheet 202 and the unit lens pitch of the Fresnel lens sheet 201 substantially equal, it is possible to achieve both moire and noise. This is because the total reflection type Fresnel lens sheet 201 mainly has a frequency component in the vertical direction, and the diffusion lens sheet 202 mainly has a diffusion component in the horizontal direction. This is because the vertical and horizontal components often have almost the same frequency component.
For example, a projection television having a screen constituted by a total reflection type Fresnel lens sheet in which the lens pitch of the Fresnel lens sheet 201 and the diffusing lens sheet 202 is 98 μm and the width of the unit lens top surface 203 d of the Fresnel lens portion is 2 μm is good. Although an image was obtained, strong noise light was observed on a projection television in which the lens pitch of the diffusing lens sheet 202 was 98 μm, the unit lens pitch of the Fresnel lens portion was 60 μm, and the width of the top surface of the unit lens was 3 μm.

As image degradation due to noise light, there is a so-called double image or ghost image. This is because highly directional noise light creates a fake image, which significantly deteriorates the image quality.
As shown in FIG. 6, when the top surface 203d of the unit lens 203 is rounded into a straight line, noise light due to refraction or reflection has strong directivity. In particular, when the top surface 203d of the unit lens 203 is parallel to the light exit surface 201a of the Fresnel lens sheet 201, it has been found that repeated reflection tends to occur between the light exit surface 201a and cause a large double image. .
Therefore, as shown in FIG. 7, when the width of the top surface of the tip 203c of the unit lens 203 is T, and the width of the surface 203d 'parallel to the light exit surface 201a of the Fresnel lens sheet 201 is Tp, the width dimension. It was found that the directivity of noise light can be greatly reduced when the ratio (or the area ratio of the surface constituting the tip portion 203c and the area of the top surface) Tp is 50% or less of T.

However, it is difficult and extremely expensive to cut a very hard cutting edge of a cutting tool into a polygon or to round it into an arc shape.
Therefore, as shown in FIG. 8, the rounding process of the top surface 203d of the unit lens front end portion 203c is formed at right angles to the light incident surface 203a of the unit lens 203. Then, the incident area of the top surface 203d with respect to the incident light L11 can be reduced, and the generation of noise light can be reduced. At this time, the formed top surface 203d is desirably a rough surface that is not a mirror surface.
Further, when the unit lens 203 is molded, if both the top surface 203d and the valley 203e of the unit lens 203 are sharp, the mold and the product are caught when the mold and the product are peeled off, and mass production is performed. There arises a problem that the efficiency of the system decreases. In the case of the total reflection type Fresnel lens sheet, the influence of noise light due to the rounding process is strongly generated on the top surface 203d of the unit lens 203 from the lens valley portion 203e. Therefore, as shown in FIG. When the rounding width of the lens trough 203e formed in T, arc shape or polygonal shape is B, it is possible to satisfy both mass production efficiency and noise reduction by setting T <B.

Also, as shown in FIG. 1, light incident on the Fresnel lens portion 201B at an angle θ is incident on the unit lens 203 by a depth of P ÷ tan (θ), where P is the pitch of the unit lenses 203. . Therefore, by making the depth H of the unit lens 203 larger than P ÷ tan (θ), light directly incident on the rounded portion of the lens valley portion 203e can be eliminated, and noise light caused by the lens valley portion 203e can be reduced. It becomes possible.
Further, it has been confirmed by experiments that noise light with high directivity is reduced by setting the haze value of the Fresnel lens portion to 10% or more, or the thickness of the unit lens 203 to 2 mm to 20 mm. It was.

In this embodiment, the unit lens 203 having a triangular cross-sectional shape is a total reflection type Fresnel lens sheet arranged concentrically at a constant pitch, but this is a linear Fresnel made up of a collection of parallel prisms. May be.
In addition, when the apex angle of the unit lens having a triangular cross-sectional shape is constant, the shape of the cutting edge of the cutting tool may be a rounded shape, and workability is further improved.
Further, the application of the Fresnel lens sheet of the present invention is a transmissive screen or a rear projection television using the same, but it may be used for a reflective screen or for an FPD backlight such as a liquid crystal display. It may be used as a directivity control member on the observation surface side. It can also be used to improve the efficiency of solar cells and the like. Furthermore, it is also effective for controlling sunlight and illumination light sources.
In addition, although a lenticular lens was used as a diffusion lens sheet, a reflection lens using a reflection by a prism, a micro lens, a scatter effect by a mat surface due to unevenness, etc. May be used.

Furthermore, in the Fresnel lens sheet of the present embodiment, the example in which the light incident surface 203a and the total reflection surface 203b of the unit lens 203 are configured with straight lines is shown, but the present invention is not limited thereto, and is configured with curves. May be.
In addition, by adhering one or both of the Fresnel lens portion of the Fresnel lens sheet and the exit surface in the present embodiment via an adhesive layer or an adhesive layer, other members such as a diffusion lens sheet or a light guide plate for backlight, Integrated with members that mainly transmit light, such as LCD display panels, polarizing plates, window glass, solar battery panels, protective panels, etc., improving strength, improving assembly work and maintenance, and light The utilization efficiency can be improved. In addition, by integrating by interposing between the spacers at the time of the above integration, it becomes possible to add an optical action by an interface with a medium having a different refractive index such as air.

It is a schematic side view which shows the structure of the rear projection type video display apparatus using the transmissive screen concerning this invention. It is an expanded sectional view in an important section of a transmission type screen in an embodiment of the invention. It is an enlarged view of the principal part of the total reflection type | mold Fresnel lens sheet in embodiment of this invention. It is explanatory drawing of the incident light ray of the total reflection type Fresnel lens sheet in embodiment of this invention. It is explanatory drawing of the incident light ray of a refraction type Fresnel lens sheet. It is explanatory drawing which shows the generation | occurrence | production concept of the noise light in the conventional total reflection Fresnel lens sheet. It is an expanded sectional view of the unit lens in the Fresnel lens sheet of the present invention. It is an expanded sectional view of the unit lens in the Fresnel lens sheet of the present invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Projection type image display apparatus, 11 ... Housing, 12 ... Projector, 13, 14 ... Reflector, 20 ... Transmission type screen, 201 ... Fresnel lens sheet, 201A ... Base material, 201B ... Fresnel lens portion, 202... Diffuse lens sheet, 202 A... Light diffusion layer, 202 B... Optical mask, 202 C .. Micro lens portion, 203 ... Unit lens, 203 a ... Light incident surface, 203 b. , 203c... Tip portion, 203d... Top surface, 203e.

Claims (15)

A Fresnel made of a transparent base material and a plurality of unit lenses having a triangular cross-sectional shape on one surface of the base material, arranged concentrically at a constant pitch, and adjusting the direction of incident light to be emitted light A Fresnel lens sheet comprising a lens part,
One opposing surface forming the apex angle of the triangle of the unit lens is a light incident surface, and the other surface is a total reflection surface that totally reflects light incident from the light incident surface,
The apex angle portion of each unit lens is cut off from the apex angle portion, and the incident light rays incident on the total reflection surface among the incident light rays projected from the oblique direction to the Fresnel lens portion are adjacent to each other. Provided at the apex portion to reduce the amount of light vignetting blocked by
This is a Fresnel lens sheet.   The Fresnel lens sheet according to claim 1, wherein the tip portion is formed in a rounded shape so that directivity of the incident light beam to the tip portion is reduced.   2. The tip of each unit lens has a certain width along a direction in which the unit lenses are arranged, and the width is 0.01 μm or more to 2 μm or less. 2. The Fresnel lens sheet according to 2.   The base material has a light emitting surface on a surface opposite to the one surface, the tip portion includes a top surface parallel to the light emitting surface, and the top surface constitutes the tip portion. The Fresnel lens sheet according to claim 1 or 2, wherein the surface area is 50% or less of the surface area.   The base member has a light exit surface on a surface opposite to the one surface, and the tip portion includes a top surface parallel to the light exit surface, the width of the top surface is T, and the unit lens 3. The Fresnel lens sheet according to claim 1, wherein a width T of the top surface is in a range of P × 0.005 ≦ T ≦ P × 0.04, where P is a pitch.   The Fresnel lens sheet according to claim 1, wherein a trough located between the unit lenses adjacent to each other is formed in an arc shape or a polygonal shape.     The base has a light exit surface on a surface opposite to the one surface, and the tip portion includes a top surface parallel to the light exit surface, and the top surface has a width T and the arc shape. Alternatively, the Fresnel lens sheet according to claim 1, wherein T <B is satisfied, where B is a width of a valley formed in a polygonal shape.   The Fresnel lens sheet according to claim 4, wherein the top surface is a straight surface perpendicular to the light incident surface.   The incident angle of the light beam projected from the oblique direction with respect to the Fresnel lens unit is θ, the height of the unit lens at the part of the Fresnel lens unit where the light beam is incident at the incident angle θ is H, 2. The Fresnel lens sheet according to claim 1, wherein when the pitch is P, a relationship of P ÷ tan (θ) <H is satisfied.   The Fresnel lens sheet according to claim 1, wherein a haze value of the Fresnel lens portion is 10% or more.   2. The Fresnel lens sheet according to claim 1, wherein the total thickness including the Fresnel lens portion and the base material is 2 mm to 20 mm. A Fresnel lens sheet according to any one of claims 1 to 11, and a diffusion lens sheet that diffuses light emitted from the Fresnel lens sheet.
A transmissive screen characterized by that.   13. The transmission screen according to claim 12, wherein the diffusion lens sheet includes a transparent base material and microlenses or microprisms formed on a surface of the base material facing the Fresnel lens sheet. The transmissive screen according to claim 12 or 13, and a unit lens side of the Fresnel lens sheet constituting the transmissive screen, and image light is obliquely downward or obliquely upward with respect to the Fresnel lens sheet. A projection optical system for projecting,
A projection-type image display device characterized by that.   15. The projection type image display apparatus according to claim 14, wherein the projection optical system is a projector.

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