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.

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˜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˜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˜5 μm.

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˜0.1) and w.sub.1:w.sub.2=1:y (y being 1.0˜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˜0.6 mm; an air layer having thickness of 1˜100 μm 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

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˜0.6 mm. Also, the height difference Δd.sub.3 is 1˜100 μm.

[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 Δd.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˜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] Δd 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