U.S. patent application number 09/879121 was filed with the patent office on 2001-12-13 for rear projection screen having reduced scintillation.
This patent application is currently assigned to DAI NIPPON PRINTING CO., LTD.. Invention is credited to Miyata, Hideki.
Application Number | 20010050811 09/879121 |
Document ID | / |
Family ID | 26507664 |
Filed Date | 2001-12-13 |
United States Patent
Application |
20010050811 |
Kind Code |
A1 |
Miyata, Hideki |
December 13, 2001 |
Rear projection screen having reduced scintillation
Abstract
A rear projection screen of the present invention comprises lens
sheets or optical sheets having an optical function of condensing
or diffusing light. The lens sheets or optical sheets have, as a
whole, two or more diffusing layers (diffusing parts) separately
provided in the light-transmitting direction. It is preferable that
one of the two or more diffusing layers be provided on the
light-entering-side surface of the outermost lens sheet or optical
sheet on the light source side and that another one of the
diffusing layers be provided on the light-emerging-side surface of
the outermost lens sheet or optical sheet on the observation side.
Any two of the two or more diffusing layers are such that the
light-source-side diffusing layer has a diffusing power lower than
that of the observation-side diffusing layer. Further, it is
preferable that the types (refractive indexes or average particle
diameters) of diffusers to be respectively incorporated into any
two of the two or more diffusing layers be different from each
other.
Inventors: |
Miyata, Hideki;
(Shinjuku-Ku, JP) |
Correspondence
Address: |
PARKHURST & WENDEL, L.L.P.
Suite 210
1421 Prince Street
Alexandria
VA
22314-2805
US
|
Assignee: |
DAI NIPPON PRINTING CO.,
LTD.
|
Family ID: |
26507664 |
Appl. No.: |
09/879121 |
Filed: |
June 13, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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09879121 |
Jun 13, 2001 |
|
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|
09029848 |
Mar 26, 1998 |
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6271965 |
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Current U.S.
Class: |
359/453 |
Current CPC
Class: |
G03B 21/625
20130101 |
Class at
Publication: |
359/453 |
International
Class: |
G03B 021/60 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 23, 1996 |
JP |
193039/1996 |
Claims
1. A rear projection screen comprising a lens sheet having an
optical function of condensing or diffusing light, wherein the lens
sheet has two or more diffusing parts separately provided in a
light-transmitting direction.
2. The rear projection screen according to claim 1, wherein one of
the two or more diffusing parts is provided on a
light-entering-side surface of the lens sheet, and another one of
the diffusing parts is provided on a light-emerging-side surface of
the lens sheet.
3. The rear projection screen according to claim 1, wherein the two
or more diffusing parts are provided on a surface of the lens sheet
and inside the same.
4. The rear projection screen according to claim 1, wherein any two
of the two or more diffusing parts are such that a
light-source-side diffusing part has a diffusing power lower than
that of an observation-side diffusing part.
5. The rear projection screen according to claim 1, wherein any two
of the two or more diffusing parts are such that a
light-source-side diffusing part is formed by incorporating first
diffusive fine particles into a first base material, that an
observation-side diffusing part is formed by incorporating second
diffusive fine particles into a second base material, and that a
difference between a refractive index of the first diffusive fine
particles and that of the first base material is smaller than a
difference between a refractive index of the second diffusive fine
particles and that of the second base material.
6. The rear projection screen according to claim 5, wherein the
second diffusive fine particles have an average particle diameter
not greater than 15 micrometers.
7. A rear projection screen comprising two or more lens sheets or
optical sheets having an optical function of condensing or
diffusing light, wherein at least one of the two or more lens
sheets or optical sheets has at least one diffusing part, and the
two or more lens sheets or optical sheets have, as a whole, two or
more diffusing parts.
8. The rear projection screen according to claim 7, wherein the
diffusing parts are provided on surfaces of the two or more lens
sheets or optical sheets, or inside the same.
9. The rear projection screen according to claim 7, wherein the
diffusing part of the outermost lens sheet or optical sheet on a
light source side is provided on a light-entering-side surface of
this lens sheet or optical sheet, and the diffusing part of the
outermost lens sheet or optical sheet on an observation side is
provided on a light-emerging-side surface of this lens sheet or
optical sheet.
10. The rear projection screen according to claim 7, wherein any
two of the two or more diffusing parts are such that a
light-source-side diffusing part has a diffusing power lower than
that of an observation-side diffusing part.
11. The rear projection screen according to claim 7, wherein any
two of the two or more diffusing parts are such that a
light-source-side diffusing part is formed by incorporating first
diffusive fine particles into a first base material, that an
observation-side diffusing part is formed by incorporating second
diffusive fine particles into a second base material, and that a
difference between a refractive index of the first diffusive fine
particles and that of the first base material is smaller than a
difference between a refractive index of the second diffusive fine
particles and that of the second base material.
12. The rear projection screen according to claim 11, wherein the
second diffusive fine particles have an average particle diameter
not greater than 15 micrometers.
Description
TECHNICAL FIELD
[0001] The present invention relates to rear projection screens
chiefly used for rear-projection-type projectors such as video
projectors and slide projectors.
BACKGROUND ART
[0002] As rear projection screens of this type, there have
conventionally been known those screens composed of a single
lenticular lens sheet comprising as a base material a synthetic
resin such as polymethyl methacrylate, and those screens composed
of such a lenticular lens sheet and other lens sheets. To form
images on these rear projection screens, imaging light is projected
on the screens by using light sources such as CRTs.
[0003] In recent years, projection tubes having small projection
apertures, such as liquid crystal projectors and light bulbs came
to be used as light sources in place of CRTs. However, the
conventional rear projection screens have such a problem that, when
images are formed on these screens by the use of projection tubes
having small projection apertures, scintillation or speckle is
caused on the images.
[0004] In order to solve this problem, there have conventionally
been proposed a method in which the screens are scanned by using
laser light sources (see Japanese Patent Laid-Open Publication No.
173094/1993); a method in which the screens are vibrated (see
Reference 1 (J. Opt. Soc. Am., Vol. 66, No. 11, Nov. 1976,
"Speckle-free rear-projection screen using two close screens in
slow relative motion")); and a method in which large amounts of
diffusers are incorporated into lens sheets.
DISCLOSURE OF THE INVENTION
[0005] However, in the aforementioned conventional methods, the
modification of the projectors themselves is needed, or additional
apparatus are required in order to prevent images from undergoing
scintillation or the like. Further, the incorporation of large
amounts of diffusers into lens sheets causes such troubles that the
gain is decreased and that the resolution is unfavorably
lowered.
[0006] The present invention was accomplished in view of the
above-described drawbacks. An object of the present invention is
therefore to provide a rear projection screen capable of forming
thereon an image free from scintillation or the like with the
decrease in gain and resolution minimized without using any
additional apparatus even when a projection tube having a small
projection aperture is used.
[0007] The first aspect of the present invention is a rear
projection screen comprising a lens sheet having an optical
function of condensing or diffusing light, wherein the lens sheet
has two or more diffusing parts separately provided in a
light-transmitting direction.
[0008] In the first aspect of the present invention, it is
preferable that one of the two or more diffusing parts be provided
on a light-entering-side surface of the lens sheet and that another
one of the diffusing parts be provided on a light-emerging-side
surface of the lens sheet. Further, it is preferable that the two
or more diffusing parts be provided on a surface of the lens sheet
and inside the same.
[0009] The second aspect of the present invention is a rear
projection screen comprising two or more lens sheets or optical
sheets having an optical function of condensing or diffusing light,
wherein at least one of the two or more lens sheets or optical
sheets has at least one diffusing part, and the two or more lens
sheets or optical sheets have, as a whole, two or more diffusing
parts.
[0010] In the second aspect of the present invention, it is
preferable that the diffusing parts be provided on surfaces of the
two or more lens sheets or optical sheets, or inside the same.
Further, it is preferable that the diffusing part of the outermost
lens sheet or optical sheet on a light source side be provided on
the light-entering-side surface of this lens sheet or optical sheet
and that the diffusing part of the outermost lens sheet or optical
sheet on an observation side be provided on a light-emerging-side
surface of this lens sheet or optical sheet.
[0011] In the above-described first and second aspects of the
present invention, any two of the two or more diffusing parts are
preferably such that a light-source-side diffusing part has a
diffusing power lower than that of an observation-side diffusing
part. Further, any two of the two or more diffusing parts are
preferably such that a light-source-side diffusing part is formed
by incorporating first diffusive fine particles into a first base
material, that an observation-side diffusing part is formed by
incorporating second diffusive fine particles into a second base
material and that a difference between a refractive index of the
first diffusive fine particles and that of the first base material
is smaller than a difference between a refractive index of the
second diffusive fine particles and that of the second base
material.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 is an illustration showing a first embodiment of a
rear projection screen according to the present invention.
[0013] FIG. 2 is an illustration showing a second embodiment of a
rear projection screen according to the present invention.
[0014] FIG. 3 is an illustration showing a rear projection screen
of Example 1 according to the present invention.
[0015] FIG. 4 is an illustration showing a rear projection screen
of Example 2 according to the present invention.
[0016] FIG. 5 is an illustration showing a rear projection screen
of Example 3 according to the present invention.
[0017] FIG. 6 is an illustration showing a rear projection screen
of Example 4 according to the present invention.
[0018] FIG. 7 is an illustration showing a rear projection screen
of Example 5 according to the present invention.
[0019] FIG. 8 is an illustration showing a rear projection screen
of Example 6 according to the present invention.
[0020] FIGS. 9A and 9B are illustrations showing rear projection
screens of Example 7 according to the present invention.
[0021] FIG. 10 is an illustration showing a comparative rear
projection screen.
BEST MODE FOR CARRYING OUT THE INVENTION
[0022] By referring now to the accompanying drawings, embodiments
of the present invention will be described below.
First Embodiment
[0023] FIG. 1 is an illustration showing a first embodiment of a
rear projection screen according to the present invention.
[0024] As shown in FIG. 1, a rear projection screen 1 is composed
of a single lens sheet having on one surface or both surfaces
thereof a Fresnel lens or lenticular lenses, wherein two or more
diffusing parts 1A, 1B are provided separately in the
light-transmitting direction (in the direction of the left and
right sides in the figure). In this first embodiment, the diffusing
parts 1A and 1B are provided on the light-entering-side surface
(light-entering surface) and light-emerging-side surface
(light-emerging surface) of the lens sheet, respectively.
[0025] The diffusing parts 1A, 1B are parts for diffusing light,
and can readily be formed by a conventional method, for example, by
using a resin layer containing a diffuser (diffusive fine
particles) such as microlenses, glass beads or organic beads, or by
embossing the surfaces of microlenses.
[0026] It is noted that the diffusing parts can be provided not
only on the surfaces of the lens sheet but also inside the lens
sheet like a diffusing part 1C.
[0027] The diffusing parts 1A, 1B diffuse light emitted from a
light source to destroy the coherence of the light, so that they
can solve the problem of scintillation or speckle. However, when
light from a light source is diffused, the resolution is lowered.
Further, when a large amount of a diffuser is incorporated into one
diffusing part as in the conventional method, the gain is
decreased, and the image thus becomes very dark.
[0028] According to the first embodiment of the present invention,
since the two diffusing parts 1A and 1B are separately provided on
the lens sheet, it is possible to make the intensity of
scintillation or the like low by using a diffuser in an amount
smaller than that of a diffuser which is required for a lens sheet
having only one diffusing part to attain the equally low intensity
of scintillation or the like. Moreover, since the amount of the
diffuser used is small, the lowering of the gain is prevented, and
the brightness of the image can thus be prevented from being
unfavorably decreased.
[0029] Further, since the two diffusing parts 1A and 1B are
separately provided on the lens sheet, it is enough to incorporate
a decreased amount of a diffuser into one diffusing part.
Therefore, the amount of stray light to be produced inside the
diffusing parts 1A, 1B can be decreased, and the unfavorable
lowering of resolution to be caused by flare, ghost or the like can
thus be prevented.
[0030] Furthermore, by this light-diffusing effect, moires to be
formed by the interference between Fresnel lenses, lenticular
lenses, or pixels of a light source can be decreased.
[0031] It is preferable that the diffusing parts 1A and 1B be
provided on the light-entering-side surface and light-emerging-side
surface of the lens sheet, respectively. The reason for this is as
follows. When the diffusing parts 1A and 1B are provided at the
above-described positions, the distance between the two diffusing
parts becomes long, so that light emitted from a light source
cannot show coherence. Therefore, the intensity of scintillation or
the like can be decreased, and the lowering of the brightness of
the image can be minimized while controlling the light-diffusing
effect at the diffusing parts 1A and 1B to extremely low.
[0032] Further, it is preferable that the diffusing power of the
diffusing part 1A on the light source side be made lower than that
of the diffusing part 1B on the observation side. By doing so, the
degree of the diffusion of light which is caused on the
light-entering side by diffusing elements becomes low. The
intensity of scintillation or the like can thus be decreased while
preventing the resolution from being unfavorably lowered.
[0033] Scintillation or the like can be evaluated not only by the
above-described intensity of scintillation or the like, but also by
the magnitude (roughness) of scintillation or the like which is
caused when a dynamic picture image is projected. In order to
decrease the intensity of scintillation or the like, it is
preferable to use such a diffuser that the difference between the
refractive index of the diffuser and that of a base material in
which the diffuser is dispersed is small. On the other hand, in
order to decrease the magnitude (roughness) of scintillation or the
like, it is preferable to use a diffuser whose average particle
diameter is small.
[0034] For this reason, when only scintillation or the like is
taken into consideration, it seems to be effective to incorporate,
into both the diffusing part 1A on the light source side and the
diffusing part 1B on the observation side, a diffuser whose average
particle diameter is small and whose refractive index is such that
the difference between the refractive index of the diffuser and
that of a base material in which the diffuser is dispersed is
small. However, a diffuser whose refractive index is such that the
difference between the refractive index of the diffuser and that of
a base material in which the diffuser is dispersed is small, or a
diffuser whose average particle diameter is small makes the angle
of visibility narrow. Therefore, in order to solve the problem of
scintillation or the like and that of the angle of visibility at
the same time, it is preferable that the type of a diffuser to be
incorporated into the diffusing part 1A be made different from that
of a diffuser to be incorporated into the diffusing part 1B.
[0035] Specifically, as will be described later in Example 7, it is
preferable that the difference between the refractive index of a
diffuser to be incorporated into the diffusing part 1A on the light
source side and that of a base material in which the diffuser is
dispersed be made smaller than the difference between the
refractive index of a diffuser to be incorporated into the
diffusing part 1B on the observation side and that of a base
material in which the diffuser is dispersed, and that a diffuser
having an average particle diameter not greater than a
predetermined size (e.g., 15 micrometers) be incorporated into the
diffusing part 1B on the observation side.
[0036] A variety of methods have been known as the method for
controlling the degree of the diffusion of light. Specifically,
when a diffusing part is formed by means of embossing,
irregularities to be produced by embossing are changed; and when a
diffuser is employed, the particle diameter, refractive index, or
amount of the diffuser to be used is changed. The relationship
between the particle diameter, refractive index or the like of a
diffuser and the light-diffusing effect is described in, for
example, Reference 2 (J. Opt. Soc. Am. A, Vol. 2, No. 12, Dec.
1985, "Diffraction analysis of bulk diffusers for projection-screen
applications").
Second Embodiment
[0037] FIG. 2 is an illustration showing a second embodiment of a
rear projection screen according to the present invention.
[0038] As shown in FIG. 2, a rear projection screen 2 is composed
of two or more lens sheets or optical sheets 2-1, 2-2, 2-3, . . . ,
and diffusing parts 2A, 2B, 2C, . . . are provided on the lens
sheets or optical sheets 2-1, 2-2, 2-3, . . . , respectively.
[0039] In this figure, the diffusing part 2A is provided on the
light-entering-side surface (light-entering surface) of the
outermost lens sheet or optical sheet 2-1 on the light source side;
the diffusing part 2B is provided on the light-emerging-side
surface (light-emerging surface) of the outermost lens sheet or
optical sheet 2-2 on the observation side; and the diffusing part
2C is provided on the light-entering-side surface (light-entering
surface) of the lens sheet or optical sheet 2-3.
[0040] As the lens sheet for use in this embodiment, it is possible
to employ a linear or circular Fresnel lens sheet, a lenticular
lens sheet having on one surface or both surfaces thereof
lenticular lenses, a lens sheet having on each surface thereof a
combination of Fresnel lenses or lenticular lenses, or the
like.
[0041] As the optical sheet, a panel made from polymethyl
methacrylate or the like, whose both surfaces are flat, or the like
can be used.
[0042] The properties of the diffusing parts 2A, 2B, 2C, . . . ,
and the properties related to the configuration of the diffusing
parts 2A, 2B. 2C, . . . , are the same as those of the diffusing
parts 1A, 1B, 1C in the above-described first embodiment.
Therefore, detailed explanations for these properties are herein
omitted.
EXAMPLES
[0043] Specific examples of the rear projection screens as shown in
FIGS. 1 and 2 will be given below.
[0044] Example 1
[0045] FIG. 3 is an illustration showing a rear projection screen
of Example 1 according to the present invention. Example 1
corresponds to the first embodiment shown in FIG. 1, and, in this
rear projection screen of Example 1, two diffusing layers
(diffusing parts) are separately provided on both surfaces of a
single lens sheet.
[0046] Namely, in this Example, a rear projection screen 10 was
produced, as shown in FIG. 3, by respectively providing diffusing
layers 10A and 10B on the light-entering surface 11a and
light-emerging surface 11b of a lens sheet 11 made from polymethyl
methacrylate, having a thickness of 5 mm. The diffusing layer 10A
was formed on the light-entering surface 11a by embossing a Fresnel
lens part on the light-entering surface 11a. On the light-emerging
surface 11b of the lens sheet 11 was formed the diffusing layer 10B
having a thickness of 500 micrometers, in which 15 parts by weight
of glass beads having an average particle diameter of 11
micrometers and a refractive index of 1.535 were dispersed. It is
noted that, in this Example and also in the following Examples 2 to
7 and Comparative Example, the amount (parts by weight) of the
diffuser such as glass beads is a value based on 100 parts by
weight of the base material into which the diffuser is
incorporated.
[0047] As the base material of the lens sheet 11, an
impact-resistant methacrylic resin (refractive index 1.51)
manufactured by Sumitomo Chemical Co., Ltd., Japan was used. As the
glass beads having an average particle diameter of 11 micrometers
and a refractive index of 1.535, "EMB20" manufactured by
Toshiba-Ballotini Co., Ltd., Japan was used.
[0048] An image was projected on the thus-produced rear projection
screen 10 by using an LCD projector, and observed for evaluation.
As a result, it was confirmed that the intensity of scintillation
caused on the image was low and that the resolution of the image
was excellent.
Example 2
[0049] FIG. 4 is an illustration showing a rear projection screen
of Example 2 according to the present invention. Example 2
corresponds to the second embodiment shown in FIG. 2, and, in this
rear projection screen of Example 2, two diffusing layers
(diffusing parts) are separately provided on two lens sheets, one
diffusing part on one lens sheet. One of the two diffusing layers
is provided on the surface of the lens sheet (the
light-entering-surface of a Fresnel lens sheet).
[0050] Namely, in this Example, a rear projection screen 20 was
produced, as shown in FIG. 4, by the combination use of a Fresnel
lens sheet 21 having a thickness of 2 mm, made from polymethyl
methacrylate, and a lenticular lens sheet 22 having a thickness of
1 mm, made from polymethyl methacrylate. On the light-entering
surface 21a of the Fresnel lens sheet 21 was formed a diffusing
layer 20A having a thickness of 150 micrometers, in which 7.0 parts
by weight of organic beads (cross-linked polymer beads) having an
average particle diameter of 12 micrometers and a refractive index
of 1.59 were dispersed. Further, into the lenticular lens sheet 22
(diffusing layer 20B) were homogeneously incorporated 0.75 parts by
weight of organic beads having an average particle diameter of 12
micrometers and a refractive index of 1.59.
[0051] As the base material of the Fresnel lens sheet 21 and that
of the lenticular lens sheet 22, an impact-resistant methacrylic
resin (refractive index 1.51) manufactured by Sumitomo Chemical
Co., Ltd., Japan was used. As the organic beads having an average
particle diameter of 12 micrometers and a refractive index of 1.59,
"PB3011" (styrene beads) manufactured by Sumitomo Chemical Co.,
Ltd., Japan was used.
[0052] An image was projected on the thus-produced rear projection
screen 20 by using an LCD projector, and observed for evaluation.
As a result, it was confirmed that the intensity of scintillation
caused on the image was low and that the resolution of the image
was excellent.
Example 3
[0053] FIG. 5 is an illustration showing a rear projection screen
of Example 3 according to the present invention. Example 3
corresponds to the second embodiment shown in FIG. 2, and, in this
rear projection screen of Example 3, two diffusing layers
(diffusing parts) are separately provided on three lens/optical
sheets. One of the two diffusing layers is provided on the surface
of the outermost lens sheet on the light source side (the
light-entering-surface of a Fresnel lens sheet), and the other
diffusing layer is provided on the surface of the outermost optical
sheet on the observation side (the light-entering-surface of a flat
face panel).
[0054] Namely, in this Example, a rear projection screen 30 was
produced, as shown in FIG. 5, by the combination use of a Fresnel
lens sheet 31 having a thickness of 2 mm, made from polymethyl
methacrylate, a flat face panel 32 having a thickness of 2 mm, made
from polymethyl methacrylate, and a lenticular lens sheet 33 having
a thickness of 1 mm, made from polymethyl methacrylate, containing
no diffuser, provided between the Fresnel lens sheet 31 and the
flat face panel 32. On the light-entering surface 31a of the
Fresnel lens sheet 31 was formed a diffusing layer 30A having a
thickness of 150 micrometers, in which 45 parts by weight of glass
beads having an average particle diameter of 11 micrometers and a
refractive index of 1.535 were dispersed. On the light-entering
surface 32a of the flat face panel 32 was formed a diffusing layer
30B having a thickness of 150 micrometers, in which 45 parts by
weight of glass beads having an average particle diameter of 11
micrometers and a refractive index of 1.535 were dispersed.
[0055] As the base materials of the Fresnel lens sheet 31, of the
flat face panel 32 and of the lenticular lens sheet 33, an
impact-resistant methacrylic resin (refractive index 1.51)
manufactured by Sumitomo Chemical Co., Ltd., Japan was used. As the
glass beads having an average particle diameter of 11 micrometers
and a refractive index of 1.535, "EMB20" manufactured by
Toshiba-Ballotini Co., Ltd., Japan was used.
[0056] An image was projected on the thus-produced rear projection
screen 30 by using an LCD projector, and observed for evaluation.
As a result, it was confirmed that the intensity of scintillation
caused on the image was low and that the resolution of the image
was excellent.
Example 4
[0057] FIG. 6 is an illustration showing a rear projection screen
of Example 4 according to the present invention. Example 4
corresponds to the second embodiment shown in FIG. 2, and, in this
rear projection screen of Example 4, two diffusing layers
(diffusing parts) are separately provided on two lens sheets. One
of the two diffusing layers is provided on the surface of the
outermost lens sheet on the light source side (the
light-entering-surface of a Fresnel lens sheet), and the other
diffusing layer is provided inside the outermost lens sheet on the
observation side (inside a lenticular lens sheet). Further, the
diffusing layer provided on the light source side has a diffusing
power lower than that of the diffusing layer provided on the
observation side.
[0058] Namely, in this Example, a rear projection screen 40 was
produced, as shown in FIG. 6, by the combination use of a Fresnel
lens sheet 41 having a thickness of 2 mm, made from polymethyl
methacrylate, and a lenticular lens sheet 42 obtained by forming
transparent lenses 42b on both surfaces of a film 42a having a
thickness of 200 micrometers, made from polymethyl methacrylate. On
the light-entering surface 41a of the Fresnel lens sheet 41 was
formed a diffusing layer 40A having a thickness of 100 micrometers,
in which 35 parts by weight of glass beads having an average
particle diameter of 11 micrometers and a refractive index of 1.535
were dispersed. Further, into the film 42a (diffusing layer 40B) of
the lenticular lens sheet 42 were homogeneously incorporated 10.0
parts by weight of organic beads having an average particle
diameter of 12 micrometers and a refractive index of 1.59.
[0059] As the base material of the Fresnel lens sheet 41, an
impact-resistant methacrylic resin (refractive index 1.51)
manufactured by Sumitomo Chemical Co., Ltd., Japan was used. As the
glass beads having an average particle diameter of 11 micrometers
and a refractive index of 1.535, "EMB20" manufactured by
Toshiba-Ballotini Co., Ltd., Japan was used. Further, as the
organic beads having an average particle diameter of 12 micrometers
and a refractive index of 1.59, "PB3011" (styrene beads)
manufactured by Sumitomo Chemical Co., Ltd., Japan was used. The
lenticular lens sheet 42 was obtained by covering, with the film
42a, a UV- (ultraviolet-) or EB- (electron beam-) curable resin
poured into a mold in a shape reverse to the shape of the
transparent lenses 42b, and applying ultraviolet rays or electron
beams to the UV- or EB-curable resin.
[0060] An image was projected on the thus-produced rear projection
screen 40 by using an LCD projector, and observed for evaluation.
As a result, it was confirmed that the intensity of scintillation
caused on the image was low and that the resolution of the image
was excellent.
Example 5
[0061] FIG. 7 is an illustration showing a rear projection screen
of Example 5 according to the present invention. Example 5
corresponds to the second embodiment shown in FIG. 2, and, in this
rear projection screen of Example 5, two diffusing layers
(diffusing parts) are separately provided on two lens sheets. One
of the two diffusing layers is provided on the surface of the
outermost lens sheet on the light source side (the
light-entering-surface of a Fresnel lens sheet), and the other
diffusing layer is provided on the surface of the outermost lens
sheet on the observation side (the light-emerging surface of a
lenticular lens sheet). Further, the diffusing layer provided on
the light source side has a diffusing power lower than that of the
diffusing layer provided on the observation side.
[0062] Namely, in this Example, a rear projection screen 50 was
produced, as shown in FIG. 7, by the combination use of a Fresnel
lens sheet 51 having a thickness of 2 mm, made from polymethyl
methacrylate, and a lenticular lens sheet 52 having a thickness of
1 mm, made from polymethyl methacrylate. On the light-entering
surface 51a of the Fresnel lens sheet 51 was formed a diffusing
layer 50A having a thickness of 100 micrometers, in which 35 parts
by weight of glass beads having an average particle diameter of 11
micrometers and a refractive index of 1.535 were dispersed. On the
light-emerging surface 52b of the lenticular lens sheet 52 was
formed a diffusing layer 50B having a thickness of 100 micrometers,
in which 12.0 parts by weight of organic beads having an average
particle diameter of 12 micrometers and a refractive index of 1.59
were dispersed.
[0063] As the base material of the Fresnel lens sheet 51, and that
of the lenticular lens sheet 52, an impact-resistant methacrylic
resin (refractive index 1.51) manufactured by Sumitomo Chemical
Co., Ltd., Japan was used. As the glass beads having an average
particle diameter of 11 micrometers and a refractive index of
1.535, "EMB20" manufactured by Toshiba- Ballotini Co., Ltd., Japan
was used. Further, as the organic beads having an average particle
diameter of 12 micrometers and a refractive index of 1.59, "PB3011"
(styrene beads) manufactured by Sumitomo Chemical Co., Ltd., Japan
was used.
[0064] An image was projected on the thus-produced rear projection
screen 50 by using an LCD projector, and observed for evaluation.
As a result, it was confirmed that the intensity of scintillation
caused on the image was low and that the resolution of the image
was excellent.
Example 6
[0065] FIG. 8 is an illustration showing a rear projection screen
of Example 6 according to the present invention. Example 6
corresponds to the second embodiment shown in FIG. 2, and, in this
rear projection screen of Example 6, three diffusing layers
(diffusing parts) are separately provided on three lens/optical
sheets, one diffusing layer on one lens or optical sheet. The three
diffusing layers are respectively provided on the surfaces (the
light-entering surfaces) of the three lens/optical sheets.
[0066] Namely, in this Example, a rear projection screen 60 was
produced, as shown in FIG. 8, by the combination use of a Fresnel
lens sheet 61 having a thickness of 2 mm, made from polymethyl
methacrylate, a flat face panel having a thickness of 2 mm, made
from polymethyl methacrylate, and a lenticular lens sheet 63 having
a thickness of 1 mm, made from polymethyl methacrylate, provided
between the Fresnel lens sheet 61 and the flat face panel 62. On
the light-entering surface 61a of the Fresnel lens sheet 61 was
formed a diffusing layer 60A having a thickness of 100 micrometers,
in which 3.5 parts by weight of glass beads having an average
particle diameter of 11 micrometers and a refractive index of 1.535
were dispersed. On the light-entering surface 62a of the flat face
panel 62 was formed a diffusing layer 60B having a thickness of 100
micrometers, in which 3.5 parts by weight of glass beads having an
average particle diameter of 11 micrometers and a refractive index
of 1.535 were dispersed. On the light-entering surface 63a of the
lenticular lens sheet 63 was formed a diffusing layer 60C having a
thickness of 300 micrometers, in which 5.0 parts by weight of
organic beads having an average particle diameter of 30 micrometers
and a refractive index of 1.49 were dispersed.
[0067] As the base materials of the Fresnel lens sheet 61, of the
flat face panel 62, and of the lenticular lens sheet 63, an
impact-resistant methacrylic resin (refractive index 1.51)
manufactured by Sumitomo Chemical Co., Ltd., Japan was used. As the
glass beads having an average particle diameter of 11 micrometers
and a refractive index of 1.535, "EMB20" manufactured by
Toshiba-Ballotini Co., Ltd., Japan was used. Further, as the
organic beads having an average particle diameter of 30 micrometers
and a refractive index of 1.49, "XC01" (acrylic beads) manufactured
by Sumitomo Chemical Co., Ltd., Japan was used.
[0068] An image was projected on the thus-produced rear projection
screen 60 by using an LCD projector, and observed for evaluation.
As a result, it was confirmed that the intensity of scintillation
caused on the image was low and that the resolution of the image
was excellent.
Example 7
[0069] FIGS. 9A and 9B are illustrations showing rear projection
screens of Example 7 according to the present invention. Example 7
corresponds to the second embodiment shown in FIG. 2, and, in these
rear projection screens of Example 7, two diffusing layers
(diffusing parts) are separately provided on two lens sheets.
Further, the type (refractive index and average particle diameter)
of the diffuser incorporated into the diffusing layer provided on
the light source side is different from that of the diffuser
incorporated into the diffusing layer provided on the observation
side.
[0070] Namely, in this Example, rear projection screens 70, 80 were
produced, as shown in FIGS. 9A and 9B, by the combination use of
Fresnel lens sheets 71, 81 made from polymethyl methacrylate, and
lenticular lens sheets 72, 82 having a thickness of 1 mm, made from
polymethyl methacrylate. As shown in FIGS. 9A and 9B, the shape and
structure of the rear projection screen 70 are identical with those
of the rear projection screen 80 except that the structure of the
Fresnel lens sheet 71 is different from that of the Fresnel lens
sheet 81.
[0071] As the base material of the Fresnel lens sheets 71, 81, an
impact-resistant methacrylic resin (refractive index 1.51)
manufactured by Sumitomo Chemical Co., Ltd., Japan was used. This
resin was subjected into extrusion molding, and a Fresnel lens part
was formed on one surface of the molded product by coating thereto
a UV-curable resin containing no diffuser, followed by curing the
UV-curable resin by the application of ultraviolet rays, thereby
obtaining the Fresnel lens sheets 71, 81. It is noted that the
boundary between the substrate and the Fresnel lens part formed
thereon by the use of the UV-curable resin is not shown in FIGS. 9A
and 9B.
[0072] The Fresnel lens sheet 71 shown in FIG. 9A is a lens sheet
obtained by forming a Fresnel lens part on one surface of a single
layer (diffusing layer 70A), serving as a substrate, into which a
diffuser having a predetermined average particle diameter and
refractive index is homogeneously incorporated. On the other hand,
the Fresnel lens sheet 81 shown in FIG. 9B is a lens sheet obtained
by forming a Fresnel lens part on one surface of a co-extruded
two-layered substrate having, on the light-entering surface 81a
thereof, a diffusing layer 80A in which a diffuser having a
predetermined average particle diameter and refractive index is
dispersed.
[0073] Into the diffusing layers 70A, 80A was incorporated, as the
diffuser, one of (1) acrylic beads having an average particle
diameter of 30 micrometers and a refractive index of 1.49 ("XC01"
manufactured by Sumitomo Chemical Co., Ltd., Japan), (2) acrylic
beads having an average particle diameter of 11 micrometers and a
refractive index of 1.49 ("MBX" manufactured by Sekisui Chemical
Co., Ltd., Japan), (3) glass beads having an average particle
diameter of 17 micrometers and a refractive index of 1.535
("EGB210" manufactured by Toshiba-Ballotini Co., Ltd., Japan), and
(4) styrene beads having an average particle diameter of 12
micrometers and a refractive index of 1.59 ("PB3011" manufactured
by Sumitomo Chemical Co., Ltd., Japan).
[0074] These diffusers (1) to (4) were incorporated into the
diffusing layers 70A, 80A of the Fresnel lens sheets 71, 81 in a
manner as shown in the following Table 1.
1 TABLE 1 Concentration of Diffuser Thickness of on Light- on
Observation Diffusing Layer Entering Side Side (mm) XC01 2.5t 2.0P
-- XC01 1.8t 3.0P -- XC01 1.8t (2) 17P Clear 0.2 MBX 1.8t 1.15P --
MBX 1.8t (2) 9.0P Clear 0.2 EGB 1.8t (2) 6.8P Clear 0.2 EGB 2.5t
(2) 3.4P Clear 0.4 PB3011 1.8t 0.17P --
[0075] In the above Table 1, the numeral (e.g. "2.5 t") shown next
to the type of the diffuser (e.g., "XC01") indicates the thickness
(mm) of the substrate of the Fresnel lens sheet 71, 81. The
thickness of the Fresnel lens sheet 71, 81 is the sum total of the
thickness of the substrate and 0.2 mm, the thickness of the Fresnel
lens part formed by using a UV-curable resin. Further, the numeral
in parentheses, "(2)", shown next to the numeral (e.g., "1.8 t")
indicating the thickness (mm) of the substrate represents that the
substrate of the Fresnel lens sheet into which the diffuser is
incorporated has a two-layered structure (the structure as shown in
FIG. 9B). The unit (P) of the concentration of the diffuser is
parts by weight (number of grams) of the diffuser incorporated into
100 parts by weight (100 g) of polymethyl methacrylate, the base
material.
[0076] On the other hand, as the base material of the lenticular
lens sheets 72, 82, an impact-resistant methacrylic resin
(refractive index 1.51) manufactured by Sumitomo Chemical Co.,
Ltd., Japan was used as in the case of the above-described Fresnel
lens sheets 71, 81. The entire lenticular lens sheets 72, 82 were
obtained by subjecting the resin to extrusion molding. As shown in
FIGS. 9A and 9B, diffusing layers 70B, 80B having a thickness of
600 micrometers, in which a diffuser having a predetermined
particle diameter and refractive index was dispersed were
respectively formed on the light-emerging surfaces of the
lenticular lens sheets 72, 82.
[0077] Into the diffusing layers 70B, 80B was incorporated, as the
diffuser, one of (1) glass beads having an average particle
diameter of 11 micrometers and a refractive index of 1.535 ("EMB20"
manufactured by Toshiba-Ballotini Co., Ltd., Japan), (2) glass
beads having an average particle diameter of 17 micrometers and a
refractive index of 1.535 ("EGB210" manufactured by
Toshiba-Balliotini Co., Ltd., Japan), (3) a 6:1 mixture of acrylic
beads having an average particle diameter of 30 micrometers and a
refractive index of 1.49 ("XC01" manufactured by Sumitomo Chemical
Co., Ltd., Japan) and the above "EGB210" manufactured by
Toshiba-Ballotini Co., Ltd., Japan (XC01+EGB-1), and (4) a 2:3
mixture of the above "XC01" manufactured by Sumitomo Chemical Co.,
Ltd., Japan and the above "EGB210" manufactured by
Toshiba-Ballotini Co., Ltd., Japan (XC01+EGB-2).
[0078] These diffusers (1) and (4) were incorporated into the
diffusing layers 70B, 80B of the lenticular lens sheets 72, 82 in
the following manner. Namely, among the above-described diffusers
(1) and (4), the diffuser (3), which is a 6:1 mixture of "XC01"
manufactured by Sumitomo Chemical Co., Ltd., Japan and "EGB210"
manufactured by Toshiba-Ballotini Co., Ltd., Japan, "XC01+EGB-1",
was taken as a standard, and the concentration of the "EG210"
contained in the "XC01+EGB-1" was made 2.0 P. The concentrations of
the other diffusers (1), (2) and (4) were so adjusted that the gain
of a rear projection screen obtainable by the combination use of a
lenticular lens sheet containing the diffuser (1), (2) or (4), and
the Fresnel lens sheet having the diffusing layer indicated by
"XC01 2.5 t" in the above Table 1 would be almost equal
(within+0.2) to the gain of a rear projection screen obtainable by
the combination use of the lenticular lens sheet having the
diffusing layer containing the above-described diffuser
"XC01+EGB-1", and the above-described Fresnel lens sheet having the
diffusing layer indicated by "XC01 2.5 t".
[0079] Rear projection screens 70, 80 were respectively produced by
assembling, in a frame (not shown in the figure), the
above-described various Fresnel lens sheets 71, 81 and lenticular
lens sheets 72, 82. White images were projected on the
thus-produced various rear projection screens 70, 80 by using an
LCD projector, and evaluated in terms of the intensity and
magnitude (roughness) of scintillation or the like caused on the
images. The results obtained are as shown in the following Table 2.
The magnitude (roughness) of scintillation or the like was
evaluated by the roughness of speckle perceived by an observer when
he/she moved his/her eyes. The intensity and magnitude (roughness)
of scintillation or the like were evaluated according to 6 ranks of
"5" (most excellent) to "0" (poorest).
2 TABLE 2 XC01 + EGB-1 XC01 + EGB-2 EGB EMB magnitude magnitude
magnitude magnitude intensity (roughness) intensity (roughness)
intensity (roughness) intensity (roughness) XC01 2.5t 5 4 5 4 5 4 5
5 XC01 1.8t 3 2 3 2 2 2 2 3 XC01 1.8(2) 4 4 4 4 3 4 5 5 MBX 1.8t 3
2 3 2 2 2 2 3 MBX 1.8t(2) 4 4 4 4 3 4 5 5 EGB 1.8t(2) 3 2 2 2 2 2 2
4 EGB 2.5t(2) 4 4 3 4 3 4 3 4 PB3011 1.8t 1 1 1 0 0 0 0 1 XC01:
acrylic beads (30 .mu.m, 1.49) EMB: glass beads: (11 .mu.m, 1.535)
MBX: acrylic beads (11 .mu.m, 1.49) XC01 + EGB-1: a 6:1 mixture of
"XC01" and "EGB" EGB: glass beads: (17 .mu.m, 1.535) XC01 + EGB-2:
a 2:3 mixture of "XC01" and "EGB" PB3011: styrene beads (12 .mu.m,
1.59)
[0080] The results shown in the above Table 2 demonstrate that
those screens produced by using acrylic beads having an average
particle diameter of 30 micrometers and a refractive index of 1.49
("XC01" manufactured by Sumitomo Chemical Co., Ltd., Japan) as the
diffuser to be incorporated into the Fresnel lens sheet (FL) on the
light source side, and glass beads having an average particle
diameter of 11 micrometers and a refractive index of 1.535 ("EMB20"
manufactured by Toshiba-Ballotini Co., Ltd., Japan) as the diffuser
to be incorporated into the lenticular lens sheet (LL) on the
observation side show good results in terms of both the intensity
and magnitude (roughness) of scintillation or the like.
[0081] Further, from the results shown in the above Table 2, the
following tendency is confirmed: the intensity of the scintillation
or the like becomes lower and the magnitude (roughness) of the same
becomes smaller as the difference between the refractive index of
the diffuser to be incorporated into the Fresnel lens sheet (FL) on
the light source side and that (1.51) of the base material in which
the diffuser is dispersed becomes smaller (for instance, compare
the "MBX 1.8 t" series results with the "PB3011 1.8 t" series
results, where the average particle diameter of "MBX" is almost
equal to that of "PB3011"). Furthermore, it is also confirmed that
the magnitude (roughness) of scintillation or the like becomes
smaller as the average particle diameter of the diffuser
incorporated into the lenticular lens sheet (LL) on the observation
side becomes smaller (for instance, compare the "EGB" series
results with the "EMB" series results, where the refractive index
of "EGB" is equal to that of "EMB"). With respect to the average
particle diameter of the diffuser to be incorporated into the
lenticular lens sheet (LL), a great improvement is found in the
magnitude (roughness) of scintillation between the average particle
diameter of 17 micrometers ("EGB210") and that of 11 micrometers
("EMB20"), especially in the vicinity of the average particle
diameter of 15 micrometers.
[0082] The following is also confirmed from the results shown in
the above Table 2: the intensity of scintillation becomes lower and
the magnitude (roughness) of the same becomes smaller as the
thickness of the Fresnel lens sheet (FL) becomes greater, and when
the Fresnel lens sheet is not composed of a single layer but
composed of two layers.
Comparative Example
[0083] FIG. 10 is an illustration showing a comparative rear
projection screen.
[0084] In this Comparative Example, a rear projection screen 70 was
produced, as shown in FIG. 10, by the combination use of a Fresnel
lens sheet 91 having a thickness of 2 mm, made from polymethyl
methacrylate. containing no diffuser, and a lenticular lens sheet
92 having a thickness of 1 mm, made from polymethyl methacrylate.
Into the lenticular lens sheet 72 (diffusing layer 90B), 5 parts by
weight of glass beads having an average particle diameter of 11
micrometers and a refractive index of 1.535 were homogeneously
incorporated.
[0085] As the base material of the Fresnel lens sheet 91, and that
of the lenticular lens sheet 92, an impact-resistant methacrylic
resin (refractive index 1.51) manufactured by Sumitomo Chemical
Co., Ltd., Japan was used. As the glass beads having an average
particle diameter of 11 micrometers and a refractive index of
1.535, "EMB20" manufactured by Toshiba-Ballotini Co., Ltd., Japan
was used.
[0086] An image was projected on the thus-produced rear projection
screen 90 by using an LCD projector, and observed for evaluation.
As a result, it was confirmed that the intensity of scintillation
caused on the image was high and that the quality of the image was
poor.
[0087] According to the present invention, since at least two
diffusing parts are separately provided on one lens sheet or
optical sheet, or on a plurality of lens sheets or optical sheets,
it is possible to make the intensity of scintillation low by using
a diffuser in an amount smaller than that of a diffuser which is
required for a lens sheet having only one diffusing part to attain
tile equally low intensity of scintillation. Further, by
respectively incorporating diffusers of different types into two
diffusing parts, not only the intensity of scintillation or the
like can be made low, but also the magnitude (roughness) of the
same can be made small. Scintillation or the like to be caused on
an image can thus be effectively decreased without lowering the
resolution and brightness of the image.
* * * * *