U.S. patent application number 15/532979 was filed with the patent office on 2017-11-09 for diffusion sheet, laminated prism sheet, and laminated optical sheet.
The applicant listed for this patent is SUNTECHOPT CO., LTD.. Invention is credited to Kiyoshi SAKAI, Yukio SHIMAMURA.
Application Number | 20170322348 15/532979 |
Document ID | / |
Family ID | 56091347 |
Filed Date | 2017-11-09 |
United States Patent
Application |
20170322348 |
Kind Code |
A1 |
SHIMAMURA; Yukio ; et
al. |
November 9, 2017 |
DIFFUSION SHEET, LAMINATED PRISM SHEET, AND LAMINATED OPTICAL
SHEET
Abstract
Provided is a diffusion sheet having a function for preventing
warping, and having excellent optical and diffusion
characteristics. A diffusion sheet 1 has a minute roughness pattern
formed on the surface thereof, the pattern configured such that
first protrusions 3a having a first height and second protrusions
3b having a second height lower than the first height are disposed
in parallel. A portion of the first protrusions 3a is bonded to a
bonding layer on the rear surface of an upper-layer sheet laminated
on the surface of a diffusion sheet 2, and the second protrusions
3b are not bonded to said bonding layer. The following
relationships are satisfied: h.sub.1:h.sub.2=1: 0.5-0.1, and
w.sub.1:w.sub.2=1:1.0-0.1, where h.sub.1 is the height of the first
protrusions 3a, w.sub.1 is the width of the first protrusions 3a,
h.sub.2 is the height of the second protrusions 3b, and w.sub.2 is
the width of the second protrusions 3b.
Inventors: |
SHIMAMURA; Yukio; (Osaka,
JP) ; SAKAI; Kiyoshi; (Osaka, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SUNTECHOPT CO., LTD. |
Chuo-ku, Osaka-shi, Osaka |
|
JP |
|
|
Family ID: |
56091347 |
Appl. No.: |
15/532979 |
Filed: |
December 7, 2015 |
PCT Filed: |
December 7, 2015 |
PCT NO: |
PCT/JP2015/006073 |
371 Date: |
June 2, 2017 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G02B 5/0231 20130101;
G02B 5/0268 20130101; G02B 5/0278 20130101; G02B 27/283 20130101;
G02B 6/0053 20130101; G02B 5/0215 20130101; G02B 6/0051 20130101;
G02B 6/0056 20130101 |
International
Class: |
G02B 5/02 20060101
G02B005/02; F21V 8/00 20060101 F21V008/00; F21V 8/00 20060101
F21V008/00; G02B 5/02 20060101 G02B005/02; G02B 5/02 20060101
G02B005/02; G02B 27/28 20060101 G02B027/28; G02B 5/02 20060101
G02B005/02 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 5, 2014 |
JP |
2014-247435 |
Claims
1-8. (canceled)
9. A laminated prism sheet, comprising: at least 2 layer prism
sheet having a prism column of a plural number of unit prism of
quasi triangle pole being disposed in parallel; a prism column of a
lower layer prism sheet to be laminated to an upper layer prism
with a plural number of first prism column having a first height
and a plural number of a second prism column having a second height
higher than the first height being disposed periodically; said
upper layer prism sheet being furnished by a diffusion layer having
a minute convex-concave shape at the back surface thereof; a vertex
portion of said first prism column of said lower layer prism sheet
being adhered to an adherence layer laminated on the diffusion
layer on the back surface of said upper layer prism sheet, and a
vertex portion of said second prism column being not adhered.
10. A laminated prism sheet as set forth in claim 9, further
comprising: at least one second prism column being disposed in an
interim of adjacent first prism columns.
11. A laminated prism sheet as set forth in claim 9, further
comprising: at least one second prism column being disposed in an
interim of first prism column group wherein only a plural number of
first prism columns adjacent to each other.
12. A laminated prism sheet as set forth in claim 9, wherein: a
refractive index of said adhesion layer n.sub.b and a refractive
index of said diffusion layer n.sub.m satisfying
|n.sub.b-n.sub.m|>0.1.
13. A laminated prism sheet as set forth in claim 9, wherein: a
second height of said second prism column being 0.6.about.0.9
assuming that a first height of said first prism column being
1.
14. A laminated prism sheet as set forth in claim 9, wherein
assuming a height of said first prism column to be m.sub.1 and
width to be k.sub.1 and further a height of said second column to
be m.sub.2 and width to be k.sub.2, a relationships
m.sub.1:m.sub.2=1:x (x being 0.6.about.0.9) and k.sub.1:k.sub.2=1:1
being satisfied.
15. A laminated prism sheet as set forth in claim 9, wherein: a
shape of a said first prism column forming a shape similar to a
shape of said second prism column.
16-17. (canceled)
18. A laminated prism sheet as set forth in claim 9, further
comprising: a shape of a vertex portion of unit prism of a prism
column at said lower layer prism sheet being a curved surface, said
vertex portion of a prism column of said lower layer prism sheet
being in contact with a surface of said adhesion layer at a back
surface of a prism sheet, preventing penetration.
19. A prism sheet as set forth in claim 9, being laminated on a
diffusion sheet and forming at least a portion of a laminated
optical sheet.
20. (canceled)
21. A laminated optical sheet as set forth in claim 19, wherein:
said prism sheet being a prism sheet for transmitting a P wave and
reflecting S wave.
22. A laminated prism sheet as set forth in claim 9, wherein: a
thickness of said adhesion layer being 0.5.about.5 .mu.m.
23. A diffusion sheet in the laminated optical sheet as set forth
in claim 19, comprising: a first convex portion having a first
height being disposed in parallel; a second convex portion having a
random height lower than the height of the first height being
disposed periodically or randomly; having a minute concave and
convex configuration at a surface thereof.
24. A diffusion sheet as set forth in claim 23, further comprising;
a part of a first convex portion being adhered to an adherence
layer at a back surface of said upper layer sheet to be laminated
to a surface of said diffusion sheet; a second convex portion being
not adhered.
25. A diffusion sheet as set forth in claim 23, wherein: a height
difference between a height of a first convex portion and a height
of a second convex portion being larger than a thickness of said
adherence layer.
26. A diffusion sheet as set forth in claim 23, wherein:
considering a height being h.sub.1 and a width being w.sub.1 for a
first convex portion, and a height being h.sub.2 and a width being
w.sub.2 for a second convex portion, h.sub.1:h.sub.2=1:X (x being
0.5.about.0.1) and w.sub.1:w.sub.2=1:y (y being 1.0.about.0.1)
being satisfied.
27. A diffusion sheet as set forth in claim 23, wherein: at least
one second convex portion being disposed between neighboring first
convex portions.
28. A diffusion sheet as set forth in claim 23, further comprising:
at least one second convex portion being disposed among a first
convex portion group consisting of only a first convex portion
being neighboring in a plural number.
29. A diffusion sheet as set forth in claim 23, wherein: said first
convex portion being linear.
30. A diffusion sheet as set forth in claim 23, wherein: light
diffusive particles being not included in said diffusion sheet.
31. A diffusion sheet as set forth in claim 23, further comprising:
an interval of neighboring first convex portion being 0.1.about.0.6
mm; an air layer having thickness of 1.about.100 .mu.m being
disposed between said adhesion layer and a second convex portion at
a back surface of said upper layer sheet laminated to a surface of
said diffusion sheet.
Description
Technical Field
[0001] The present invention relates to a light diffusion sheet, a
laminated prism sheet and a laminated optical sheet having a
non-warping function for preventing waviness (warping) caused by
thinning of an optical film.
BACKGROUND ART
[0002] Abacklight unit employed in a liquid crystal panel is known
to be comprised of a structure wherein a diffusion sheet, a prism
sheet and a light guide plate are physically stacked. (Refer to the
patent literature 1, for example.) Namely, as shown in FIG. 9, a
backlight unit is configured with a light-guiding plate 30 for
guiding light from a light source 32 and a reflective sheet 34 with
a lower diffusion sheet 2, a lower prism sheet 11 and an upper
prism sheet with a diffusion function thereon. Above an upper prism
sheet 21 a liquid crystal panel is placed. A liquid crystal panel
40 has a configuration wherein the front surface side and the back
surface side of a liquid crystal cell 42 are sandwiched with
polarizing plates (41, 43).
[0003] When the upper and lower prism sheets (11, 21) and the lower
diffusion sheet are made to be thinner in the aim to make this
backlight unit thinner, corrugation occurs at each sheet member due
to the heat radiated from the LED, making mounting of the member
difficult. For that reason, there is consequently a limit in
thinness of prism sheets and diffusion sheets. Therefore, it
becomes necessary to make the prism sheet and the diffusive sheet
free of waviness in pursuing slimming and miniaturization of prism
sheets and diffusion sheets.
[0004] FIG. 6 represents a cross sectional view of a backlight unit
having a conventional structure configured with a prism sheet and a
diffusive sheet physically stacked (an adhesive material not
illustrated). It is necessary for the upper and lower prism sheets
(11, 21) and the lower diffusive sheet 2 to have a waviness-free
function in order to evade waviness generation with a good handling
capability during mounting of the member. The display size of the
current mobile information terminals is usually 4 to 5 inches and
each thickness of D1, D2 and D3 in FIG. 6 needs to be thicker than
150 .mu.m. As a result, the thickness of the backlight unit becomes
thicker than 450 .mu.m. In cases wherein each thickness of D1, D2
and D3 is smaller than 150 .mu.m, problems such as appearance
defects occur due to generation of waviness at each sheet under an
influence of radiation heat by an LED light source of a backlight
unit.
[0005] As a method to solve such a problem, a method to integrate
the upper prism sheet 21, the lower prism sheet 11 and the lower
diffusion sheet 2 by pasting all three together is studied.
However, in a case wherein the lower prism sheet 11 and the upper
prism sheet 21 are unified, an adhesion layer 23 is conventionally
disposed at the back surface of the upper prism sheet 21 as shown
in FIG. 7 (an enlarged view of the A portion in FIG. 6) and the
adhesion layer 23 and the lower prism sheet 11 are pasted to
achieve integration, which results in filling up of vertex portions
of all the prism columns at the surface, which results in
deterioration of optical perfoimance in comparison with a case of
not unifying sheets. Namely, in a case wherein the lower prism
sheet 11 and the upper prism sheet 21 are integrated, there are
such problems as not being able to obtain enough condensation
perfoimance.
[0006] Also, conventionally, in a case wherein the lower prism
sheet 11 and the lower diffusion sheet 2 are integrated, an
adhesion layer 13 is disposed at the back surface of the prism
sheet 11 as shown in FIG. 8 (an enlarged view of the B portion in
FIG. 6) and the adhesion layerl3 and the diffusion layer 3 of the
lower diffusion layer are pasted together to be integrated, which
causes complete filling of the diffusion layer 3 at the surface of
the lower diffusion sheet 2 with an adhesion layer 3, resulting in
a remarkable loss of the diffusion performance of the lower
diffusion sheet 2, which is a problem.
[0007] As mentioned above, the deterioration of an optical
performance and a diffusion performance resulting from integration
of the upper prism sheet, the lower prism sheet and the lower
diffusion sheet by the pasting of all the sheets.
PRIOR ART
Patent Literature
[0008] [Patent literature 1] JP 2000-352607 A
OUTLINE OF THE INVENTION
Problems to be Solved by the Invention
[0009] In view of such a circumstance, the present invention aims
to present a diffusion sheet, a laminated prism sheet and a
laminated optical sheet using aforementioned sheets, having a
no-waviness function that prevents waviness (warping) generation
with an excellent optical performance and a diffusion
performance.
Means to Solve the Objects
[0010] Namely, the diffusion sheet according to the present
invention is configured to have minute irregularities at its
surface, with the first convex portion having the first height
disposed in a parallel configuration and the second convex portion
having a random height lower than the first height, disposed
periodically or randomly.
[0011] And when an upper layer sheet is laminated to a diffusion
sheet, a portion of the first convex portion is adhered to the
adhesion layer at the back surface of the upper layer sheet
laminated to the surface of the diffusion sheet and the second
convex portion is not adhered.
[0012] By such a configuration, the diffusion sheet is securely
fixed by a portion of the first convex portion being adhered to the
adhesion layer at the back surface of the upper sheet, restraining
the waviness (warping) of the diffusion sheet. Namely, the
diffusion sheet is equipped with a non-waviness function
(warping-less function). Also, the diffusion sheet becomes superb
in its optical characteristics and diffusion characteristics as a
whole because the second convex portion is not adhered to the
adhesion layer of the diffusion sheet, evading or minimizing the
decline of the diffusion performance of the second convex
portion.
[0013] Here, in the diffusion sheet described above, it is
preferable that the height difference between the height of the
first convex portion and the height of the second convex portion is
larger than the thickness of the adhesion layer. It is because the
deterioration of the diffusion performance at the second convex
portion of the diffusion sheet is prevented due to the fact that
the vertex portion of the second convex portion is not adhered to
the adhesion layer even when the first convex portion is securely
adhered to the adhesion layer.
[0014] Also, for the diffusion sheet described above, it is
preferable that a condition h.sub.1:h.sub.2=1:x (x being
0.5.about.0.1) and w.sub.1:w.sub.2=1:y (y being 1.0.about.0.1) is
satisfied when the height and width of the first convex portion is
expressed by h.sub.1 and w.sub.1, and also the height and width of
the second convex portion is expressed by h.sub.2 and w.sub.2 ,
respectively.
[0015] The deterioration of the diffusion performance at the second
convex portion can be avoided by providing a no-waviness function
(warping-less function) to the diffusion sheet by making the height
of the second convex portion (h.sub.1) less than half the height of
the first convex portion (h.sub.2), making the vertex portion of
the second convex portion not adhered to the adhesion region even
when the first convex portion is firmly adhered to the adhesion
layer of the upper sheet.
[0016] Also, the width of the second convex portion (w.sub.2) is
made to be the same to or shorter than the width of the first
convex portion (w.sub.1). This is a condition for adjusting the
shape and the apex angle of the second convex portion. For example,
when the height of the second convex portion (h.sub.2) is half the
height of the first convex portion (h.sub.1), the width of the
second convex portion (w.sub.2) is made to be half the width of the
first convex portion in order to make the shape of the first convex
portion and the shape of the second convex portion equal. Supposing
that the height of the second convex portion (h.sub.2) is half the
height of the first convex portion (h.sub.1), the second convex
portion has a convex shape with a gentler and wider foot than that
of the first convex portion, if the width of the second convex
(w.sub.2) and the width of the first convex (w.sub.1) are the
same.
[0017] The diffusion sheet according to the present invention, the
first convex portion is preferably linear. Making the first convex
portion linear makes the molding easy, which improves the quality
of the product. Also, the production cost can be reduced as a
result that molding becomes easy. Although the arrangement under
linearly placed convex portion is preferably a periodical parallel
arrangement, a parallel arrangement with random intervals is also
acceptable.
[0018] The diffusion sheet according to the present invention may
have at least one second convex portion placed between the two
neighboring first convex portions.
[0019] Because the vertex portion of the second convex portion
lower than the height of the first convex portion is not adhered to
the adhesion layer, the optical performance does not deteriorate
and the high diffusion performance intrinsically aimed can be
preserved. Therefore, the total diffusion performance of the
diffusion sheet can be enhanced by placing a plural number of the
second convex portion between the first convex portions. Note that
the first convex portion and the second convex portion are
alternatively arranged when one second convex portion is arranged
between two adjacent first convex portions.
[0020] Also, in the diffusion sheet according to this invention, at
least one second convex portion may be placed among a group of the
first convex portions where only a plural number of first convex
portions are adjacent to each other. Because the vertex portion of
the first convex portion is adhered to the adhesion layer, the
adhesion strength with the upper layer sheet can be further
heightened by disposing a group of the first convex portion only
the first convex portion is adjacent to.
[0021] The diffusion sheet according to the present invention does
not preferably contain light scattering particles. In order to
prevent generation of unevenness and faults caused by flocculation
of the light scattering particles, a diffusion sheet is
manufactured without using light scattering particles by forming
unevenness at the mold surface and transferring the unevenness at
the mold surface by using a UV curing resin or a thermoplastic
resin.
[0022] Next, the laminated prism sheet according to the present
invention is explained.
[0023] The laminated prism sheet according to the present invention
is a prism sheet made of at least two layers with a surface having
a prism column consisting of unit prisms in the shape of quasi
triangular pole disposed in parallel with plurality, and the prism
column of the lower layer prism sheet whereon the upper layer prism
sheet is laminated consists of the plural number of the first prism
columns having the first height and the plural number of the second
prism columns having the second height lower than the first height,
which are periodically placed. And the vertex portion of the first
prism column is adhered to the adhesive layer at the back surface
of the upper prism sheet, faulting a structure wherein the vertex
portion of the second prism column is not adhered.
[0024] By furnishing a characteristics that the vertex portion of
the first prism column of the lower prism sheet is adhered to the
back surface of the upper prism sheet but the vertex portion of the
second prism columns is not adhered, the problems that the optical
performance deteriorates and enough condensation performance is not
acquired resulting from filling of the vertex portion of all the
prism columns at the surface of the lower layer prism when compared
with the case wherein integration is not established, are
avoided.
[0025] Also, foimation of stain that occurs when prism sheets are
stacked, which is caused by the fact that the prism height is not
uniform and is called "wet out", can be suppressed.
[0026] In the laminated prism sheet according to the present
invention, at least one second prism column can be disposed between
two neighboring first prism columns. Because the vertex portion of
the second prism column with a height lower than the height of the
first prism column is not adhered to the adhesion layer, the
optical performance is not deteriorated and the original light
condensation performance can be maintained. Therefore, light
condensation performance of the whole prism sheet can be heightened
by arranging a plural number of the second prism columns between
the first prism columns. Further, when one second prism column is
placed between two neighboring first prism columns, the first prism
column and the second prism column are disposed alternatingly.
[0027] Also, at least one second prism column may be disposed among
the first prism column group wherein only a plural number of the
first prism columns are neighboring. Because the vertex portion of
the first prism column is adhered to the adherence layer, the
adherence intensity can be heightened by disposing a neighboring
first prism column group wherein only the first prism columns
adjoin.
[0028] Here, it is preferable that the upper layer prism sheet
according to the present invention is furnished with a diffusion
layer having minute projecting-recessed shape at its back surface,
adhesion layer is stacked to the diffusion layer and the refractive
index of the adhesion layer n.sub.b and the refractive index of the
diffusion layer n.sub.m satisfy the relationship
[n.sub.b-n.sub.m]>0.1.
[0029] In this case, the upper layer prism sheet becomes an upper
layer prism sheet furnished with a diffusion function.
[0030] The reason for setting up a predetermined refractive index
difference to the refractive index n.sub.b of the adhesion layer
and the refractive index n.sub.m of the diffusion layer is that the
diffusion function of the diffusion layer can be exerted even when
an adhesion layer is stacked over the diffusion layer.
[0031] The second height of the second prism column at the
laminated prism sheet being 0.6.about.0.9 under an assumption that
the height of the first prism column being 1, is a preferable mode
according to this invention. If the height difference between the
first height of the first prism column and the second height of the
second prism column is too small, there is a shortcoming that the
degree of coupling with the adhesion layer becomes week when the
vertex portion of the first prism column at the lower layer prism
sheet is adhered while the vertex portion of the second prism
column is not adhered. On the other hand, if the height difference
between the first height of the first prism column and the second
height of the second prism column is too large, there is a
shortcoming that the optical performance deteriorates when the
vertex portion of the second prism column is not adhered while the
vertex portion of the first prism column of the lower layer prism
sheet is adhered, resultantly the engagement degree with the
adhesion layer is strengthened while the portion adhered to the
adhesion layer becomes larger. For that reason, it is preferable
that the height difference between the first height of the first
prism column and the second height of the second prism column is
kept at the predetermined value.
[0032] When the height and the width of the first prism column is
expressed by m.sub.1, and k.sub.1, respectively and the height of
the second prism column is expressed by m.sub.2 and k.sub.2,
respectively, for the laminated prism sheet according to the
present invention, the preferable mode here is that the conditions
m.sub.1:m.sub.2=x (Note that x is 0.6.about.0.9) and
k.sub.1:k.sub.2=1:1, are satisfied. These are conditions for
obtaining an efficient diffusion effect and an optical effect. Note
that the shape of the first prism column and the shape of the
second prism column can be in similar figures.
[0033] Regarding the diffusion sheet according to the present
invention, it is preferable that the mutual interval of the
neighboring first convex portion is preferably 0.1.about.0.6 mm. By
satisfying such a scope, it becomes possible to effectively
constrain warping while maintaining an optical performance. When
the mutual interval of the first convex portion is larger than 0.6
mm, filamentous pattern becomes recognizable by naked eyes, which
is not preferable. When the mutual interval of the first convex
portion is smaller than 0.1 mm, moire tends to easily appear
deteriorating the optical performance, which is not preferable.
[0034] In the diffusion sheet according to the present invention,
it is preferable that an air layer of 1.about.100 .mu.m thickness
is disposed between the adhesion layer laminated at the back
surface of the upper layer sheet to be laminated at the surface of
the diffusion sheet and the second convex portion. Disposition of
air layer prevents deterioration of the optical performance and
makes it possible to maintain the primary diffusion
performance.
[0035] It is also acceptable that the shape of the top of the unit
prism in the prism column at the lower layer prism sheet in the
laminated prism sheet according to the present invention is curved
and the top portion of the prism column in the lower prism sheet is
in contact with the adhesion layer at the back surface of the upper
layer prism sheet as a plane, without penetration. This arrangement
of no penetration by the top portion of the unit prism prevents the
deterioration of light condensing performance of the prism sheet,
preventing the luminance deterioration. Also, if the laminated
prism sheet with a conventional lower layer prism sheet having
vertex portion of an acute angle is tried to be adhered without
penetration of the vertex portion of the unit prism into the
adhesion layer, the adhesion area is narrow and the boundary
surface proximity between the adhesion point at the vertex portion
and the adhesion layer can scarcely be expected and the adhesion
strength was not enough unless the adhesion point penetrates into
the adhesion layer by a .mu.m order to heighten the strength of the
adhesion layer from the viewpoint of elasticity. However, according
to the laminated prism sheet of the present invention, the shape of
the vertex portion has a curved surface providing a large adhesion
area resulting in a large ratio of the boundary surface against the
adhesion layer, which strengthens the electrostatic interaction at
the boundary and further molecular bonding phenomenon at the
boundary resulting in large adhesion strength and heightens the
peeling strength.
[0036] Also, the shape of the vertex portion of the unit prism
being round improves the viewing angle luminance
characteristics.
[0037] With regard to the laminated prism sheet according to the
present invention, the shape of the vertex portion of the unit
prism of the prism column in the lower layer prism sheet is round
and the vertex portion of the prism column in the lower prism sheet
contacts the adhesion layer of the back surface of the upper prism
sheet by a surface, the thickness of the adhesion layer is
preferably 0.5.about.2 .mu.m, when penetration does not occur, and
more preferably 0.8.about.1.3 .mu.m. Because the vertex portion of
the unit prism does not penetrate the adhesion layer, it becomes
possible to set the thickness of the adhesion layer thin as is
described here.
[0038] The laminated optical sheet according to the present
invention consists of a laminated prism sheet according to the
present invention being laminated onto the diffusion sheet
according to the present invention. Also, the laminated optical
sheet according to the present invention may consist of an already
known prism sheet laminated on the diffusion sheet according to the
present invention. Furthermore, the laminated optical sheet
according to the present invention may have a prism sheet that
transmits P-wave and reflects S-wave laminated on the diffusion
sheet according to the present invention. Because the prism sheet
that transmits P-wave and reflects S-wave increases P-wave by
polarizing the reflected S-wave by reflection at the reflection
sheet, the brightness can be further improved.
EFFECTS OF THE INVENTION
[0039] The diffusion sheet, the laminated prism sheet and the
laminated optical sheet according to the present invention has no
waviness (non-warping) function and at the same time shows
excellency in optical characteristics and diffusion
characteristics, as their effects.
BRIEF DESCRIPTION OF THE DRAWINGS
[0040] FIG. 1 illustrates a cross sectional configuration view of
the diffusion sheet of the present invention.
[0041] FIG. 2 illustrates a comparison view of the junction
cross-sectional configuration of the lower prism sheet and the
lower diffusion sheet.
[0042] FIG. 3 illustrates a cross sectional configuration view of
laminated prism sheet of the present invention.
[0043] FIG. 4 illustrates a comparison view of the junction
cross-sectional configuration of the upper prism sheet and the
lower prism sheet.
[0044] FIG. 5 illustrates a cross sectional configuration view of
the laminated optical sheet of the present invention.
[0045] FIG. 6 illustrates a cross sectional configuration view of a
backlight unit having a conventional structure.
[0046] FIG. 7 illustrates a cross sectional configuration view of a
conventional joining portion between an upper prism sheet and a
lower prism sheet.
[0047] FIG. 8 illustrates a cross sectional configuration view of a
joint portion of a conventional lower prism sheet and a lower
diffusion sheet.
[0048] FIG. 9 illustrates a structural view of a liquid crystal
panel.
[0049] FIG. 10 illustrates an enlarged cross sectional photographs
of prototypes.
[0050] FIG. 11 illustrates a measurement results of brightness
performance thereof.
[0051] FIG. 12 illustrates a cross sectional configuration view of
a joining portion of the lower prism sheet and the diffusion sheet
having convex portions.
[0052] FIG. 13 illustrates a cross sectional configuration of the
diffusion sheet according to embodiment 2.
[0053] FIG. 14 illustrates a cross sectional configuration of the
adherence portion between the upper prism sheet and the lower prism
sheet according to embodiment 3.
[0054] FIG. 15 illustrates an enlarged cross sectional view of the
first prism column according to embodiment 3.
BEST MODE FOR CARRYING OUT THE INVENTION
[0055] Embodiments of the present invention will be described in
detail below with reference to the drawings. The present invention
is not limited to the following embodiment and examples of shown in
the figure, and the present invention can be variously changed in
design.
[0056] FIG. 1 shows a cross sectional view of the diffusion sheet
of the present invention. The diffusion sheet 1 having a convex
portion with the surface of the diffusion sheet 2 whereon a
diffusion layer 3 having a minute concave-convex shape with the
first convex portion 3a having the first height and the second
convex portion 3b having the height lower than the first height
both arranged in parallel and the diffusion layer 4 having the
convex portion 4a with a uniform or random height are foamed.
[0057] And, to the adhesion layer (not illustrated) at the back
surface of the upper sheet (not illustrated) laminated to the
surface of the diffusion sheet 1, one portion of the first
protruding portion 3a of the diffusion layer 3 is adhered and the
second protruding portion of the diffusion layer 3 is not
adhered.
[0058] Note that the diffusion sheet 1 in FIG. 1 is illustrated
representing the height of the first convex portion 3a by h.sub.1
and width by w.sub.1, and the height of the second convex portion
3.sub.b by h.sub.2 and width w.sub.2, with the assumption that the
relationship above lies somewhere around h.sub.1:h.sub.2=1:0.5,
w.sub.1:w.sub.2=1:1. Also, the difference between the height
h.sub.1 of the first convex portion 3 and the height h.sub.2 of the
second convex portion 2 is set larger than the thickness of the
adhesion layer.
[0059] FIG. 2 shows a comparison between the conventional
configuration and the configuration of the diffusion sheet
according to the present invention regarding the configuration of
the adhesion cross section of the lower prism sheet and the
diffusion sheet. FIG. 2 (1) represents the conventional
configuration and the FIG. 2 (2) represents the diffusion sheet
configuration according to the present invention. In the case of
the conventional configuration shown in FIG. 2 (1), the height of
the convex portion foamed at the diffusion layer 3 at the surface
of the diffusion sheet (lower diffusion sheet) 2 is uniform and all
the convex portions are structurally buried into the adhesion layer
13 at the back surface of the upper layer sheet (lower prism sheet)
to be laminated to the surface. If the convex portion is buried,
the diffusion performance is lowered and especially if all the
convex portions are buried, diffusion performance is markedly
deteriorated.
[0060] On the other hand, in the case of the diffusion sheet
structure as shown in FIG. 2 (2), the height of the convex portion
fouled at the diffusion layer 3 at the diffusion sheet 2 (the lower
diffusion sheet) is not uniform and the first convex portion 3a and
the second convex portion 3b having a height lower than that of the
first convex portion 3a are arranged in parallel, and it is
arranged in such a way that only a part of the first convex portion
3a is adhered to the adhesion layer 13 at the back surface of the
upper layer sheet (the lower prism sheet) laminated to the surface.
Because the second convex portion 3b having a lower height is not
adhered to the adhesion layer 13 at the back surface of the lower
prism sheet 11, the diffusion performance of the second convex
portion 3b is maintained as it is. Accordingly, the diffusion sheet
structure of the present invention provides a more excellent
diffusion performance with only a small deterioration in diffusion
performance, compered in the case of the conventional
configuration.
[0061] FIG. 12 shows a cross sectional configuration drawing of the
lower prism sheet and the diffusion sheet according to the present
invention in a laminated state. As is shown in FIG. 12, the
diffusion sheet 1 having convex portions has the diffusion sheet 2
with a diffusion layer 3 formed at the surface of the diffusion
sheet 2, whereon the first convex portion 3a having the first
height and the second convex portion 3b having the second height
lower than the first height are arranged in parallel, and a
diffusion layer 4 having convex portions of a uniform or random
height 4a is formed at the back surface of the diffusion sheet
2.
[0062] And, to the adhesion layer 13 at the back surface of the
lower prism sheet 11 laminated to the surface of the diffusion
sheet 1, a portion of the first convex portion 3a at the diffusion
layer3 is adhered, and the second convex portion 3b at the
diffusion layer 3 is not adhered. Here, the interval P of the
neighboring first convex portion is 0.1.about.0.6 mm. Also, the
height difference .DELTA.d.sub.3 is 1.about.100 .mu.m.
[0063] FIG. 3 represents a cross sectional configuration of the
adhesion portion of the upper prism sheet 21 and the lower prism
sheet 11. At the lower prism sheet 11, a plural number of the first
prism columns 12a having the first height and a plural number of
the second prism columns 12b having the second height lower than
the first height are periodically disposed. And, the convex portion
of the first prism column 12a at the lower prism sheet 11 is
adhered to the adhesion layer 23 at the back surface of the upper
prism sheet 21, so that the convex portion of the second prism
column 12b is not adhered.
[0064] In the case of the upper prism sheet 21 shown in FIG. 3, a
plural number of prism columns 22a consisting of a unit prism in
the shape of quasi triangular pole are disposed in parallel and a
diffusion layer 24 at the convex portion with a height uniform or
random is fouled at the back surface and further an adhesion layer
23 is formed. Here, the thickness of the adhesion layer is
expressed by D.sub.b.
[0065] FIG. 3 illustrates the lower prism sheet 11 supposing the
first prism column 12a having the height m.sub.1 and the width
k.sub.1 and the second prism column 12b having the height m.sub.2
and the width k.sub.2, under an assumption that
m.sub.1:m.sub.2=1:0.5 and k.sub.1:k.sub.2=1:1. Also, the difference
.DELTA.d.sub.2 between he height m.sub.1 of the first prism column
and the height m.sub.2 of the second prism column 12b is set at a
larger value than the thickness D.sub.b of the adhesion layer.
[0066] FIG. 4 illustrates a comparison between the conventional
configuration and the laminated prism sheet configuration according
to the present invention regarding the adhesion cross sectional
configuration between the upper prism sheet and the lower prism
sheet. FIG. 4 (1) represents the conventional configuration and the
FIG. 4 (2) represents the laminated prism sheet structure. In the
conventional configuration as shown in FIG. 4 (1), the height of
the prism column 12 at the surface of the lower prism sheet 11 is
uniform and all the convex portion of the prism column 12 is
configured to be embedded in the adhesion layer 23 at the back
surface of the upper prism sheet 21 laminated to the surface of the
lower prism sheet. When the convex portion of the prism column is
embedded, the diffusion performance is degraded, especially if the
vertex portion of the prism is embedded, the light condensation
performance is degraded considerably.
[0067] On the other hand, in the case of the laminated prism sheet
configuration according to the present invention as shown in FIG. 4
(2), the height of the prism column 12 at the surface of the lower
prism sheet 11 is not uniform and the first prism column 12a and
the second prism column 12b higher than the first prism column 12a
are periodically arranged in parallel and only the first prism
column 12a is configured to be adhered to the adherence layer 23 at
the back surface of the upper prism sheet 21 laminated to the
surface. And the second prism column 12b with a low height is not
adhered to the adherence layer 23 at the back surface and
consequently the light condensation of the second prism column 12b
is preserved as it is. Therefore, the laminated prism sheet
configuration according to the present invention shows little
deterioration in comparison with the conventional configuration and
it turns out that the light condensation/diffusion performance is
excellent as a whole prism system.
[0068] FIG. 5 shows the cross sectional schematics of the laminated
optical sheet according to the present invention. The laminated
optical sheet according to the present invention consists of the
lower diffusion sheet 2, the lower prism sheet 11 and the upper
prism sheet 21 with a light diffusion function being laminated onto
the light-guiding plate 30.
[0069] The first convex portion having the first height and the
second convex portion having the second height lower than the first
height are arranged in parallel on the lower diffusion sheet 2.
Between the neighboring first convex portions, one or more second
convex portions are disposed. In the case of FIG. 5, the convex
portions are configured in parallel with the second convex portions
being continuously arranged with one first linear convex
portion.
[0070] A part of the first convex portion is adhered to the
adherence layer 13 at the back surface of the lower prism sheet 11
laminated to the surface of the lower diffusion sheet 2 and the
second convex portion is not adhered. Also, a diffusion layer 4 of
the convex portion with a random or a uniform height are formed at
the back surface of the lower diffusion sheet 2.
[0071] At the surface of the upper prism sheet 21, a prism layer 22
whereon prism columns of uniform height and width are arranged in
parallel is formed and a diffusion layer of a convex portion with
uniform height is formed at the back surface and at the same time
an adhesion layer 23 is formed. And at the lower prism sheet 11, a
prism layer 12 whereon a plural number of the first prism columns
having the first height and a plural number of the second prism
columns having the second height lower than the first height is
formed and the vertex portion of the first prism column at the
lower prism sheet 11 is adhered to the adherence layer 23 at the
back surface of the upper prism sheet 21 and the vertex portion of
the second prism column is not adhered.
Embodiment 1
[0072] (Prototype Evaluation Result)
[0073] Four kinds of prototypes (No. 1.about.4) were prepared by
adhering the lower prism sheet and the diffusion sheet, and the
enlarged cross sectional photographs and the measurement results of
brightness performance thereof are shown in FIG. 10 and FIG. 11,
respectively.
[0074] The enlarged cross sectional photographs shows the cross
sectional view of the adhered sheet enlarged by 2000 times.
[0075] In the prototype 1, the height of the convex portion was not
enough and the adhesive layer buried the diffusion portion almost
entirely, resulting in the degradation of the diffusion
performance. And in the prototypes No. 2 and No. 3, the lamination
became possible while keeping the diffusion performance because the
height of the vertex portion is larger than the thickness of the
adhesion layer and excellency in diffusion performance could be
conformed. Note that the prototype No. 4 did not reveal the problem
in diffusion performance, but the vertex portion thrusted into the
upper prism sheet because the pressure at the time of adhesion was
too strong (refer to the enlarged photograph) and resultantly the
brightness drop became big.
Embodiment 2
[0076] FIG. 13 shows the cross sectional configuration of the
diffusion sheet in embodiment 2.
[0077] As is shown in FIG. 13, the diffusion sheet 1a having a
convex portion, similarly as the diffusion sheet 1 in FIG. 1, has
the diffusion layer 3 of a minute concave-convex shape thereon the
first concave portion 3a having the first height and the second
concave portion 3b having the height lower than the first height
are periodically positioned in parallel, and the diffusion layer 4
having the concave portion 4a of uniform or random height is
fainted at the back surface of the diffusion sheet 2.
[0078] However, in contrast to the fact that a plural number of the
second convex portion 3b was disposed between one first convex
portion 3a and one first convex portion 3a in FIG. 1, the
embodiment here includes the three first convex portion 2a and a
plural number of the second convex portion 3b disposed among the
first convex portion 3a. By disposing many first convex portions
3a, it becomes possible to heighten the adhesion strength when the
diffusion sheet la is adhered to the upper layer sheet. Although
not illustrated in FIG. 13, the first convex portion 3a is disposed
linearly from the front side to the bottom side.
Embodiment 3
[0079] FIG. 14 represents a cross sectional configuration of the
adherence portion between the upper prism sheet 21 and the lower
prism sheet 11 according to embodiment 3. At the lower prism sheet
11, a plural number of the first prism column 12c having the first
height and the second prism column 12b having the second height
lower than the first height are disposed periodically. And the
vertex portion of the first prism column 12c of the lower prism
sheet 11 butts the adherence layer 23 at the back surface of the
upper prism sheet 21, while the vertex portion of the second prism
column 12b is arranged not to butt.
[0080] FIG. 15 shows an enlarged cross sectional view of the first
prism column in embodiment 3, showing the enlarged view of the C
portion in FIG. 14. Although luminance degradation occurs when the
prism column is buried in the adhesion layer, the vertex portion 25
of the first prism column 12c is only in contact with the adhesion
layer 23 as shown in FIG. 15, not penetrating. Therefore, the
abutting width to the adhesion layer 23 becomes wider. Because FIG.
15 is a cross sectional configuration, an abutting actually occurs
in plane. In this way, for the vertex portion of the prism column
being curved, a brightness performance degradation can be prevented
while enhancing the adhesion strength. Note that the vertex portion
of the second prism column 12b is round similarly as the vertex
portion 25 of the first prism column 12c, though not
illustrated.
[0081] Also, the curvature radius R at the vortex portion 25 of the
first prism column 12c is set at 3R. If the curvature radius at the
vertex portion is smaller than 2R, the vertex portion of the unit
prism is penetrated making brightness degradation obvious. Also, if
the curvature radius at the vertex portion is larger than 5R, the
original optical performance of the prism sheet becomes
unattainable.
Other Embodiments
[0082] In contrast to embodiment 3, at the lower prism sheet, only
the vertex portion of the plural number of the first prism column
having the first height may be made to be round while making the
vertex portion of the second prism column having an acute angle. By
mixing the prism columns with the vertex portion being in curved
shape and the prism columns with ones in sharp angle, it becomes
possible to improve both the front brightness and the viewing angle
brightness.
INDUSTRIAL APPLICATION POSSIBILITY
[0083] This invention is useful as an optical sheet composing a
back light unit of the liquid crystal panel.
EXPLANATION OF SIGNS
[0084] 1, 1a Diffusion sheet having a convex portion
[0085] 2 Diffusion sheet
[0086] 3a First convex portion
[0087] 3b Second convex portion
[0088] 3, 4, 24 Diffusion layer
[0089] 11 Lower prism sheet
[0090] 12, 22 Prism column
[0091] 12a, 12c First prism columns
[0092] 12b Second prism columns
[0093] 13, 23 Adhesion layer
[0094] 21 Upper prism sheet
[0095] 22a Prism columns
[0096] 25 Vertex portion
[0097] 30 Light-guiding plate
[0098] 32 Light source
[0099] 34 Reflective sheet
[0100] 40 Liquid crystal panel
[0101] 41, 43 Polarizing plates
[0102] 42, Liquid crystal cell
[0103] 50 Backlight unit
[0104] A, B, C Enlarged view
[0105] D Thickness
[0106] Interval
[0107] R Curvature radius
[0108] .DELTA.d Height difference
[0109] h.sub.1, h.sub.2, m.sub.1, m.sub.2 Height
[0110] w.sub.1, w.sub.2, k.sub.1, k.sub.2 Width
* * * * *