Laminated light diffusion sheet, backlight unit, liquid crystal display device, and information apparatus

Abstract

To prevent reduction in luminance and luminance uniformity while improving handleability of a light diffusion sheet, during assembly of a backlight unit using a plurality of light diffusion sheets.SOLUTION: A laminated light diffusion sheet 100 includes a first light diffusion sheet 101 in which a plurality of recesses 22 formed into a substantially reverse polygonal pyramid or a substantially reverse polygonal pyramid trapezoid are arranged on a first surface 101a, and a second light diffusion sheet 102 laminated to the first surface 101a of the first light diffusion sheet 101. A lamination part of the first light diffusion sheet 101 and the second light diffusion sheet 102 has a peeling strength of 5.0 g weight / 25 mm or more. When the capacity of the recesses 22 is defined as V0 and the volume of air gaps remaining in the recesses 22 as Va, Va / V0 is 40% or more and 100% or less in an area of the first light diffusion sheet 101 excluding a peripheral part of the first surface 101a.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present disclosure relates to a laminated light diffusing sheet, a backlight unit, a liquid crystal display device, and an information device.

Background Art

[0002] As a display device for various information devices such as laptop PCs, televisions, monitors, smartphones, and tablet terminals, liquid crystal display devices are widely used. As the backlight of a liquid crystal display device, two types have been adopted: a direct-lit type in which a light source is arranged behind a liquid crystal panel, and a light guide plate type.

[0003] While the thickness reduction of liquid crystal display devices has been actively promoted, many liquid crystal display devices adopting a light guide plate type have been proposed as those suitable for thickness reduction. In that case, various light diffusing sheets have been used from the viewpoint of improving the in-plane luminance uniformity in order to suppress the image such as the arrangement shape of light sources on the light guide surface from remaining due to a moire (interference fringe) phenomenon or the like.

[0004] In recent years, due to the convenience of being able to individually control the ON / OFF of each LED light source within the same screen, etc., the direct-lit type has become the mainstream as the backlight of liquid crystal display devices.

[0005] When adopting a direct - type backlight, in order to eliminate the image of light sources such as LEDs (Light Emitting Diodes) on the light - emitting surface and improve the in - plane luminance uniformity, a light - diffusing sheet is used. The light - diffusing sheet is usually used by laminating multiple sheets, and it is known that as the number of laminated sheets increases, the luminance uniformity in the display screen improves. On the other hand, as the number of optical sheets including the light - diffusing sheet increases, when assembling the backlight unit, the handling of the optical sheets becomes complicated. That is, from the perspective of optical performance, by optimizing the laminated structure of the optical sheets used in the backlight unit, the desired performance can be obtained. However, from the perspective of manufacturing, there is a risk of problems in the individual handling and assembly of multiple optical sheets.

[0006] Problems associated with an increase in the number of optical sheets include, for example, in addition to an increased risk of damaging the optical sheet when removing the protective film of the optical sheet, the time required for the process of removing the protective film from each individual optical sheet may increase. Also, the time required for the process of inserting each individual optical sheet into the display frame of the liquid - crystal display device to form a laminate of optical sheets increases, and the possibility of the optical sheet being damaged in this process also increases. These problems become factors in reducing the yield rate, that is, reducing the production yield, and increasing the manufacturing cost of the backlight unit.

[0007] Patent Document 1 discloses a packaging method of binding optical films before inserting them into the display frame. This binding facilitates the handling of the films, reduces the number of processes required for assembling the display device, reduces the possibility of damaging the films, and can increase the production yield.

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0009] However, Patent Document 1 discloses that by laminating a brightness enhancing film, the handleability is improved, and by controlling the thickness of the adhesive layer, the peel strength is controlled while suppressing a decrease in brightness, or the brightness is controlled while suppressing a decrease in peel strength. However, with regard to the lamination of diffusion films, no measures for suppressing a decrease in performance are disclosed.

[0010] In a light diffusion sheet, improving brightness and brightness uniformity is always a required issue. While the brightness uniformity improves by increasing the number of light diffusion sheets used in a backlight unit, the brightness generally tends to decrease. Also, as the number of light diffusion sheets to be handled increases, the yield tends to decrease as described above.

[0011] An object of the present disclosure is to suppress a decrease in brightness and brightness uniformity while improving the handleability of a light diffusion sheet when assembling a backlight unit using a plurality of light diffusion sheets.

Means for Solving the Problems

[0012] In order to achieve the above object, as a result of intensive studies by the inventors of the present application, it has been found that in the lamination of light diffusion sheets in which a plurality of substantially inverted pyramidal concave portions are arranged, an adhesive material or the base material of another light diffusion sheet enters the concave portions, and as a result, a decrease in brightness and brightness uniformity occurs. Furthermore, the inventors of the present application have found that by ensuring that the ratio of the voids remaining in the concave portions in the laminated state is 40% or more of the volume of the concave portions, a decrease in brightness and brightness uniformity can be suppressed to a practical level.

[0013] Specifically, the laminated light diffusion sheet according to the present disclosure includes a first light diffusion sheet in which a plurality of recesses formed in a substantially inverted pyramid or substantially inverted truncated pyramid shape are arranged on a first surface, and a second light diffusion sheet bonded to the first surface of the first light diffusion sheet. The peeling strength at the bonding portion between the first light diffusion sheet and the second light diffusion sheet is 5.0 g weight / 25 mm or more. When the volume of the recess is V0 and the volume of the void remaining in the recess is Va, Va / V0 is 40% or more and 100% or less in a region excluding the peripheral portion of the first surface of the first light diffusion sheet.

[0014] According to the laminated light diffusion sheet of the present disclosure, since the first light diffusion sheet and the second light diffusion sheet are bonded together with a peeling strength of 5.0 g weight / 25 mm or more, the handleability of the light diffusion sheet during the assembly of the backlight unit can be improved. Further, in the first surface (active area directly below the display screen excluding the peripheral portion) of the first light diffusion sheet in which the recesses formed in a substantially inverted pyramid or substantially inverted truncated pyramid shape are arranged, since (the volume Va of the void remaining in the recess) / (the volume V0 of the recess) is 40% or more, it is possible to suppress a decrease in luminance and luminance uniformity due to the bonding.

[0015] In the present disclosure, the "light diffusion sheet" shall include a plate-shaped "light diffusion plate" and a film-shaped "light diffusion film".

[0016] Further, in the present disclosure, the "optical sheet" means a sheet having various optical functions such as diffusion, light collection, refraction, and reflection, and the "light diffusion sheet" is one of the "optical sheets".

[0017] Further, in the present disclosure, in consideration of the fact that it is difficult to form geometrically precise inverted pyramid or inverted truncated pyramid recesses by ordinary shape transfer techniques, the notations "substantially inverted pyramid" or "substantially inverted truncated pyramid" are used, but it goes without saying that these notations include shapes that can be regarded as true or substantially inverted pyramids or inverted truncated pyramids.

[0018] In the laminated light diffusing sheet according to the present disclosure, when the peel strength measured at 85 ° C. is 10 g weight / 25 mm or more, a laminated light diffusing sheet having sufficient heat resistance can be obtained.

[0019] In the laminated light diffusing sheet according to the present disclosure, when the peel strength measured at 85 ° C. is 100 g weight / 25 mm or more, a laminated light diffusing sheet having excellent heat resistance can be obtained.

[0020] In the laminated light diffusing sheet according to the present disclosure, the bonding portion may be the entire surface, the peripheral portion, or a plurality of dot-shaped or linear regions on the first surface of the first light diffusing sheet. That is, in the laminated light diffusing sheet according to the present disclosure, the peel strength between the first light diffusing sheet and the second light diffusing sheet is 5.0 g weight / 25 mm or more, and for the recesses arranged on the first surface of the first light diffusing sheet, (the volume Va of the voids remaining in the recesses) / (the volume V0 of the recesses) is 40% or more. If the bonding is performed, the bonding portion is not particularly limited.

[0021] In the laminated light diffusing sheet according to the present disclosure, the concave portion is formed in a substantially inverted quadrangular pyramid or a substantially inverted quadrangular frustum shape, the thickness of the first light diffusing sheet is 30 μm or more and 1000 μm or less, and the portion of the first light diffusing sheet where the concave portion is provided and other portions may be integrally formed of the same material. If the concave portion is formed in a substantially inverted quadrangular pyramid or a substantially inverted quadrangular frustum shape, the cutting accuracy of the mold (metal roll) used in the manufacturing process is improved. When the thickness of the first light diffusing sheet is 30 μm or more, the effect of improving the luminance uniformity is easily obtained. On the other hand, when the thickness of the first light diffusing sheet is less than 30 μm, the concave portion easily penetrates the sheet, making stable processing difficult. When the thickness of the first light diffusing sheet is 1000 μm or less, the backlight unit, that is, the liquid crystal display device can be thinned. However, generally, an optical sheet having a thickness exceeding 500 μm has sufficient rigidity even with a single sheet, so that handling during the assembly of the backlight unit becomes easy without bonding to other optical sheets. When the portion where the concave portion is provided (concave-shaped portion) and other portions (base material portion) in the first light diffusing sheet are integrally formed of the same material, it is possible to prevent the concave-shaped portion from peeling off from the base material portion in a reliability test or the like.

[0022] For example, in a light diffusing sheet in which a UV curable resin is shaped and laminated on a base film to provide a concave-shaped portion, the concave-shaped portion may peel off from the base film in a reliability test or the like. On the other hand, in a light diffusing sheet in which the base material portion and the concave-shaped portion are integrally formed, such as an extrusion molded product or a compression molded product, it is possible to prevent the concave-shaped portion from peeling off from the base material portion in a reliability test or the like. Further, generally, in an optical sheet bonded to another optical sheet, stress tends to concentrate at the bonding portion due to the bonding effect accompanying the bonding. However, if the base material portion and the concave-shaped portion are not integrally formed, there also occurs a problem that the base material portion and the concave-shaped portion are easily peeled off due to the difference in the linear expansion coefficient of each portion.

[0023] In the laminated light diffusion sheet according to the present disclosure, when the concave portion is formed in a substantially inverted quadrangular pyramid or a substantially inverted frustum of a quadrangular pyramid, a plurality of other concave portions formed in a substantially inverted quadrangular pyramid or a substantially inverted frustum of a quadrangular pyramid are arranged on one surface of the second light diffusion sheet, the other surface of the second light diffusion sheet is a flat surface or a matte surface, and the first surface of the first light diffusion sheet and the other surface of the second light diffusion sheet may be bonded together. By doing so, a laminated light diffusion sheet capable of exhibiting an excellent effect of improving luminance uniformity can be obtained relatively easily.

[0024] In the laminated light diffusing sheet according to the present disclosure, on one surface of the second light diffusing sheet, a plurality of other recesses formed in a substantially inverted pyramid or a substantially inverted truncated pyramid shape are arranged, and the arrangement direction of the recesses may be different from the arrangement direction of the other recesses. By doing so, even if there is a variation in Va / V0 (hereinafter, also referred to as "spatial volume ratio") in each recess, it is possible to suppress the occurrence of mottled patterns on the display screen and the decrease in luminance and luminance uniformity. In this case, the recesses and the other recesses may be formed in a substantially inverted quadrangular pyramid or a substantially inverted truncated quadrangular pyramid, a substantially inverted triangular pyramid or a substantially inverted truncated triangular pyramid, or a substantially inverted hexagonal pyramid or a substantially inverted truncated hexagonal pyramid. By doing so, it becomes easy to regularly arrange the recesses and the other recesses two-dimensionally. Further, when the arrangement direction of the recesses is different from the arrangement direction of the other recesses by 8° or more, it is possible to further suppress the occurrence of mottled patterns on the display screen. Note that the upper limit of the angle difference between the arrangement direction of the recesses and the arrangement direction of the other recesses varies depending on the shape of the inverted pyramid or the inverted truncated pyramid. When the shapes of the recesses and the other recesses are an inverted quadrangular pyramid or an inverted truncated quadrangular pyramid, the angle difference is preferably 82° or less, and more preferably 75° or less. That is, when the shapes of the recesses and the other recesses are an inverted quadrangular pyramid or an inverted truncated quadrangular pyramid, since the arrangement relationship between the recesses and the other recesses is the same when the angle difference is 8° and when the angle difference is 82°, a similar mottled pattern suppressing effect can be obtained. Further, when the shapes of the recesses and the other recesses are an inverted triangular pyramid or an inverted truncated triangular pyramid, the angle difference is preferably 52° or less, and more preferably 45° or less. That is, when the shapes of the recesses and the other recesses are an N-sided pyramid or an N-sided truncated pyramid (N is an integer of 3 or more), the angle difference is preferably [(180°×(N - 2) / N) - 8°] or less, and more preferably [(180°×(N - 2) / N) - 15°] or less.

[0025] In the laminated light diffusing sheet according to the present disclosure, when Va / V0 is 50% or more, it is possible to further suppress the decrease in luminance and luminance uniformity caused by bonding.

[0026] In the laminated light diffusion sheet according to the present disclosure, the first light diffusion sheet and the second light diffusion sheet may be bonded together by an OCA (optically clear adhesive). By doing so, the bonding operation can be easily performed.

[0027] In the laminated light diffusion sheet according to the present disclosure, the first light diffusion sheet and the second light diffusion sheet may be bonded together by an ink containing an ultraviolet curable resin. By doing so, the thickness of the adhesive layer for bonding the first light diffusion sheet and the second light diffusion sheet can be changed depending on the type of ink. However, compared with the case of bonding by OCA, the process of irradiating ultraviolet rays (UV) or the like to cure the ink increases.

[0028] In the laminated light diffusion sheet according to the present disclosure, the first light diffusion sheet and the second light diffusion sheet may be bonded together by laser welding using an infrared absorber. By doing so, sufficient peel strength can be obtained even when, for example, only the four corners of the sheet are bonded. However, compared with the case of bonding by OCA, the process of irradiating an infrared laser for welding increases.

[0029] Another laminated light diffusion sheet according to the present disclosure is a laminated light diffusion sheet including a first light diffusion sheet having a plurality of recesses formed in a substantially inverted pyramid or substantially inverted truncated pyramid shape arranged on a first surface, and a second light diffusion sheet bonded to the first surface of the first light diffusion sheet, wherein the peel strength at the bonding portion between the first light diffusion sheet and the second light diffusion sheet is 5.0 g weight / 25 mm or more, and a plurality of other recesses formed in a substantially inverted pyramid or substantially inverted truncated pyramid shape are arranged on one surface of the second light diffusion sheet, and the arrangement direction of the recesses is different from the arrangement direction of the other recesses.

[0030] According to another laminated light diffusing sheet according to the present disclosure, since the first light diffusing sheet and the second light diffusing sheet are bonded together with a peel strength of 5.0 g weight / 25 mm or more, the handleability of the light diffusing sheet can be improved during the assembly of the backlight unit. Further, since the arrangement direction of the concave portions in the first light diffusing sheet is different from the arrangement direction of the other concave portions in the second light diffusing sheet, even if there is a variation in the spatial volume ratio Va / V0 in each concave portion of the first light diffusing sheet, it is possible to suppress the occurrence of a mottled pattern on the display screen and a decrease in luminance and luminance uniformity. In this case, the concave portion and the other concave portion may be formed in a substantially inverted quadrangular pyramid or a substantially inverted quadrangular pyramid frustum, a substantially inverted triangular pyramid or a substantially inverted triangular pyramid frustum, or a substantially inverted hexagonal pyramid or a substantially inverted hexagonal pyramid frustum. By doing so, it becomes easy to regularly arrange the concave portion and the other concave portion two-dimensionally. Further, when the arrangement direction of the concave portion is different from the arrangement direction of the other concave portion by 8° or more, it is possible to further suppress the occurrence of a mottled pattern on the display screen. Incidentally, the upper limit of the angular difference between the arrangement direction of the concave portion and the arrangement direction of the other concave portion varies depending on the shape of the inverted pyramid or the inverted pyramid frustum. When the shapes of the concave portion and the other concave portion are an inverted quadrangular pyramid or an inverted quadrangular pyramid frustum, the angular difference is preferably 82° or less, and more preferably 75° or less. That is, when the shapes of the concave portion and the other concave portion are an inverted quadrangular pyramid or an inverted quadrangular pyramid frustum, since the arrangement relationship between the concave portion and the other concave portion is the same when the angular difference is 8° and when the angular difference is 82°, a similar mottled pattern suppressing effect can be obtained. Further, when the shapes of the concave portion and the other concave portion are an inverted triangular pyramid or an inverted triangular pyramid frustum, the angular difference is preferably 52° or less, and more preferably 45° or less. That is, when the shapes of the concave portion and the other concave portion are an N-sided pyramid or an N-sided pyramid frustum (N is an integer of 3 or more), the angular difference is preferably [(180°×(N - 2) / N) - 8°] or less, and more preferably [(180°×(N - 2) / N) - 15°] or less.

[0031] The backlight unit according to the present disclosure is a backlight unit incorporated in a liquid crystal display device and guiding the light emitted from a light source toward a display screen, and includes the laminated light diffusion sheet according to the present disclosure or another laminated light diffusion sheet between the display screen and the light source. Therefore, it is possible to suppress a decrease in luminance and luminance uniformity while improving the handleability of the light diffusion sheet when assembling the backlight unit using a plurality of light diffusion sheets.

[0032] In the backlight unit according to the present disclosure, a color conversion sheet that converts the wavelength of the light emitted from the light source may be further provided between the display screen and the light source. By doing so, it is not necessary to use an expensive white light source as the light source, so the cost of the backlight unit can be reduced. The arrangement position of the color conversion sheet is not particularly limited as long as it is between the display screen and the light source. For example, the color conversion sheet may be arranged between the light source and the laminated light diffusion sheet or another laminated light diffusion sheet, or between the display screen and the laminated light diffusion sheet or another laminated light diffusion sheet.

[0033] In the backlight unit according to the present disclosure, the content of the light diffusing agent in the first light diffusion sheet is not particularly limited as long as the light diffusion effect due to reflection and refraction in the concave portion formed in a substantially inverted pyramid or a substantially inverted truncated pyramid shape is not impaired. For example, it may contain 0 parts by mass or more and 10 parts by mass or less of the light diffusing agent with respect to 100 parts by mass of the matrix resin.

[0034] The liquid crystal display device according to the present disclosure includes the backlight unit according to the present disclosure and a liquid crystal display panel. Therefore, it is possible to suppress a decrease in luminance and luminance uniformity while improving the handleability of the light diffusion sheet when assembling the backlight unit using a plurality of light diffusion sheets. The same effect can also be obtained in an information device including the liquid crystal display device according to the present disclosure.

[0035] Further, it is preferable that the first light diffusion sheet is formed of the same material for the concave portion and the base material portion so that the concave portion and the base material portion do not cause interfacial peeling in reliability tests or the like. In particular, it is preferable that the concave portion and the base material portion are integrally formed by a method such as extrusion molding or compression molding.

[0036] In the first light diffusion sheet, the arrangement pitch of the concave portions is preferably 30 μm or more and 1000 μm or less, and the width of the boundary portion between adjacent concave portions is preferably 25% or less of the arrangement pitch. Specifically, in order to reduce the area ratio of the boundary portion, the width of the boundary portion is 25% or less, preferably 20% or less, more preferably 15% or less of the arrangement pitch. However, in order to avoid a decrease in wear resistance, the width of the boundary portion is 0.5% or more, preferably 1.0% or more of the arrangement pitch. In the present disclosure, the "boundary portion between the concave portions" means the "width of the flat portion intentionally arranged between the concave portions" when the concave portions are arranged at intervals, and means the "width of the curved portion at the top of the ridge line partitioning the concave portions" when the concave portions are arranged without gaps.

[0037] In the first light diffusion sheet, when the arrangement pitch is 1000 μm or less, an increase in the thickness of the first light diffusion sheet can be suppressed, and the backlight unit can be made thinner.

[0038] In the first light diffusion sheet, when the width of the boundary portion is the width of the curved portion at the top of the ridge line partitioning the concave portions, in other words, when the concave portions are arranged without gaps, the luminance uniformity can be improved as compared with the case where the concave portions are arranged at intervals. In this case, the concave portions are formed in a substantially inverted quadrangular pyramid or a substantially inverted quadrangular frustum shape, the ridge line extends in the first direction and the second direction, the arrangement pitch is the average value of the first arrangement pitch of the concave portions in the first direction and the second arrangement pitch of the concave portions in the second direction, and the width of the boundary portion may be the average value of the width occupied by the curved portion at the top of the ridge line in the first direction and the width occupied by the curved portion at the top of the ridge line in the second direction. Thereby, the formation of the concave portions can be easily performed.

[0039] In the first light diffusion sheet, when the angle formed by the wall surface of the concave portion and the sheet surface of the first light diffusion sheet is 40 degrees or more and 65 degrees or less, a sufficient effect of improving luminance uniformity can be obtained by the concave portion.

[0040] In the first light diffusion sheet, when the concave portion is provided only on the first surface and the second surface of the first light diffusion sheet is a flat surface or a matte surface, it is possible to obtain an effect of improving luminance uniformity while suppressing wear and damage on the second surface.

Advantages of the Invention

[0041] According to the present disclosure, it is possible to suppress a decrease in luminance and luminance uniformity while improving the handleability of the light diffusion sheet when assembling the backlight unit using a plurality of light diffusion sheets.

Brief Description of the Drawings

[0042]

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Mode for Carrying Out the Invention

[0043] (Embodiment) Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. Note that the scope of the present disclosure is not limited to the following embodiments and can be arbitrarily changed within the scope of the technical idea of the present disclosure.

[0044] <Liquid Crystal Display Device> As shown in FIG. 1, the liquid crystal display device 50 of the present embodiment includes a liquid crystal display panel 5, a first polarizing plate 6 attached to the lower surface of the liquid crystal display panel 5, a second polarizing plate 7 attached to the upper surface of the liquid crystal display panel 5, and a backlight unit 40 provided on the back side of the liquid crystal display panel 5 via the first polarizing plate 6. The liquid crystal display panel 5 includes a TFT substrate 1 and a CF substrate 2 provided to face each other, a liquid crystal layer 3 provided between the TFT substrate 1 and the CF substrate 2, and a sealing material (not shown) provided in a frame shape for enclosing the liquid crystal layer 3 between the TFT substrate 1 and the CF substrate 2.

[0045] The shape of the display screen 50a of the liquid crystal display device 50 as viewed from the front (above in FIG. 1) is, in principle, rectangular or square, but is not limited thereto, and may be a shape in which the corners of the rectangle are rounded, an elliptical shape, a circular shape, a trapezoidal shape, or any shape such as an automobile instrument panel.

[0046] In the liquid crystal display device 50, in each sub-pixel corresponding to each pixel electrode, a voltage of a predetermined magnitude is applied to the liquid crystal layer 3 to change the alignment state of the liquid crystal layer 3. As a result, the transmittance of light incident from the backlight unit 40 through the first polarizing plate 6 is adjusted. The light with the adjusted transmittance is emitted through the second polarizing plate 7 and an image is displayed.

[0047] The liquid crystal display device 50 of the present embodiment is used as a display device incorporated in various information devices (for example, in-vehicle devices such as car navigation systems, personal computers, mobile phones, portable information terminals such as notebook computers and tablets, portable game machines, copiers, ticket vending machines, automated teller machines, etc.).

[0048] The TFT substrate 1 includes, for example, a plurality of TFTs provided in a matrix on a glass substrate, an interlayer insulating film provided to cover each TFT, a plurality of pixel electrodes provided in a matrix on the interlayer insulating film and connected to the plurality of TFTs respectively, and an alignment film provided to cover each pixel electrode. The CF substrate 2 includes, for example, a black matrix provided in a lattice pattern on a glass substrate, a color filter including a red layer, a green layer, and a blue layer provided between the respective lattices of the black matrix, a common electrode provided to cover the black matrix and the color filter, and an alignment film provided to cover the common electrode. The liquid crystal layer 3 is composed of a nematic liquid crystal material containing liquid crystal molecules having electro-optical characteristics. The first polarizing plate 6 and the second polarizing plate 7 include, for example, a polarizer layer having a polarization axis in one direction and a pair of protective layers provided so as to sandwich the polarizer layer.

[0049] <Backlight unit> As shown in FIG. 2, the backlight unit 40 of the present embodiment mainly includes a plurality of light sources 42 and a laminated light diffusion sheet 100 provided above the plurality of light sources 42. The laminated light diffusion sheet 100 has a structure in which a lower first light diffusion sheet 101 and an upper second light diffusion sheet 102 are bonded together by an adhesive member 111. The first light diffusion sheet 101 and the second light diffusion sheet 102 are bonded together by attaching or applying, for example, an OCA (Optical Clear Adhesive) film, an ink containing an ultraviolet curable resin, an ink containing an infrared absorber, etc. to the bonding surface of the first light diffusion sheet 101 or the second light diffusion sheet 102.

[0050] In the example shown in FIG. 2, the plurality of light sources 42 are blue light sources and are two-dimensionally arranged on the reflection sheet 41. A wavelength selection sheet 43 and a color conversion sheet 44 are arranged between the plurality of light sources 42 and the laminated light diffusion sheet 100. The wavelength selection sheet 43 is arranged below the color conversion sheet 44. The wavelength selection sheet 43 selectively transmits light having the emission wavelength of the light source 42 and reflects light having other wavelengths. The color conversion sheet 44 converts the color of the light emitted by the light source 42.

[0051] On the upper side of the laminated light diffusion sheet 100, a brightness enhancement sheet 47 is arranged in order to improve the brightness. The type of the brightness enhancement sheet 47 is not particularly limited as long as it can increase the brightness of the light emitted from the light source 42. In the example shown in FIG. 2, as the brightness enhancement sheet 47, the lower first prism sheet 45 and the upper second prism sheet 46 are arranged with their respective prism extension directions orthogonal to each other.

[0052] Although not shown, a polarizing sheet may be provided on the upper side of the brightness enhancement sheet 47. The polarizing sheet improves the brightness of the display screen 50a by preventing the light emitted from the backlight unit 40 from being absorbed by the first polarizing plate 6 of the liquid crystal display device 50.

[0053] In the present disclosure, the “light diffusion sheet” shall include a plate-shaped “light diffusion plate” and a film-shaped “light diffusion film”. Further, the “optical sheet” means a sheet having various optical functions such as diffusion, condensing, refraction, and reflection, and the “light diffusion sheet”, “reflection sheet”, “brightness enhancement sheet”, etc. are included in the “optical sheet”.

[0054] Hereinafter, each component of the backlight unit 40 will be described.

[0055] [Reflection Sheet] The reflection sheet 41 is composed of, for example, a film made of white polyethylene terephthalate resin, a silver vapor deposition film, or the like.

[0056] [Light Source] The type of the light source 42 is not particularly limited, and for example, it may be an LED element, a laser element, etc., and an LED element may be used from the viewpoints of cost, productivity, etc. In order to adjust the light emission angle characteristics of the LED element serving as the light source 42, a lens may be attached to the LED element. The light source 42 may have a rectangular shape in plan view, and in that case, the length of one side may be 10 μm or more (preferably 50 μm or more) and 10 mm or less (preferably 5 mm or less, more preferably 1 mm or less). The number of arrangements of the light source 42 is not particularly limited either, but when a plurality of light sources 42 are arranged dispersedly, it is preferable to arrange them regularly on the reflection sheet 41. Arranging regularly means arranging with a certain regularity, and for example, the case where the light sources 42 are arranged at equal intervals corresponds to this. When the light sources 42 are arranged at equal intervals, the center-to-center distance between two adjacent light sources 42 may be 0.5 mm or more (preferably 2 mm or more) and 20 mm or less.

[0057] In the present embodiment, for example, as shown in FIG. 3, a plurality of light sources 42 each made of an LED element are arranged in a two-dimensional array with a certain interval. In other words, the plurality of light sources 42 are arranged along two directions orthogonal to each other.

[0058] When a blue light source is used as the light source 42, the blue light source may emit light with x < 0.24 and y < 0.18 in the chromaticity coordinates of CIE1931, for example. Further, when a white light source is used as the light source 42, the white light source is composed of an LED element with a peak wavelength in the blue region, an LED element with a peak wavelength in the green region, and an LED element with a peak wavelength in the red region, and may emit light with 0.24 < x < 0.42 and 0.18 < y < 0.48 in the chromaticity coordinates of CIE1931, for example. When a white light source is used as the light source 42, the wavelength selection sheet 43 and the color conversion sheet 44 may not be arranged.

[0059] [Wavelength Selection Sheet and Color Conversion Sheet] The wavelength selection sheet 43 selectively transmits light having the emission wavelength of the light source 42 (for example, blue light) and reflects light having other wavelengths. The color conversion sheet 44 converts light from the light source 42 (for example, blue light) into light having a peak wavelength of an arbitrary color (for example, green or red). The color conversion sheet 44 converts, for example, blue light with a wavelength of 450 nm into green light with a wavelength of 540 nm and red light with a wavelength of 650 nm. In this case, when the light source 42 that emits blue light with a wavelength of 450 nm is used, the blue light is partially converted into green light and red light by the color conversion sheet 44, so the light transmitted through the color conversion sheet 44 becomes white light. As the color conversion sheet 44, for example, a QD (quantum dot) sheet, a fluorescent sheet, or the like may be used. Since the wavelength selection sheet 43 is disposed below the color conversion sheet 44, the light whose wavelength has changed by the color conversion sheet 44 can only advance above the color conversion sheet 44.

[0060] In the example shown in FIG. 2, the wavelength selection sheet 43 and the color conversion sheet 44 are disposed between the light source 42 and the laminated light diffusion sheet 100. Instead, they may be disposed between the laminated light diffusion sheet 100 and the brightness enhancement sheet 47.

[0061] [Brightness Enhancement Sheet] The first prism sheet 45 and the second prism sheet 46 that constitute the brightness enhancement sheet 47 are, for example, films in which a plurality of groove stripes having an isosceles triangle cross-section are formed adjacent to each other, and the apex angle of the prism sandwiched between a pair of adjacent groove stripes is formed to be about 90°. Here, each groove stripe formed in the first prism sheet 45 and each groove stripe formed in the second prism sheet 46 are arranged to be orthogonal to each other. The first prism sheet 45 and the second prism sheet 46 may be integrally formed. As the first prism sheet 45 and the second prism sheet 46, for example, a PET (polyethylene terephthalate) film with a prism shape formed using a UV-curable acrylic resin may be used.

[0062] [Laminated Light Diffusion Sheet]< [Configuration of Light Diffusion Sheet]< The laminated light diffusing sheet 100 has a first light diffusing sheet 101 and a second light diffusing sheet 102 having the same structure. The thicknesses of the first light diffusing sheet 101 and the second light diffusing sheet 102 are, for example, 30 μm or more and 1000 μm or less. Each of the first light diffusing sheet 101 and the second light diffusing sheet 102 has a base material layer 21. The base material layer 21 is preferably composed of, for example, polycarbonate as a base material (matrix resin) and does not contain a diffusing agent, but may contain, for example, about 10 parts by mass or less of a diffusing agent with respect to 100 parts by mass of the base material. Known materials can be appropriately used as the diffusing agent.

[0063] On the first surface 101a of the first light diffusing sheet 101 and the first surface 102a of the second light diffusing sheet 102 (in the example shown in FIG. 2, the first surfaces 101a and 102a are light emitting surfaces), a plurality of recesses 22 are provided. The plurality of recesses 22 are formed in a substantially inverted pyramid or a substantially inverted truncated pyramid shape. In this example, the plurality of recesses 22 are formed in a substantially inverted regular quadrangular pyramid shape. The plurality of recesses 22 have substantially the same shape within the range of machining errors. Adjacent recesses 22 are partitioned by a ridge line 23.

[0064] Specifically, as shown in FIG. 4, substantially inverted quadrangular pyramid-shaped (inverted pyramid-shaped) recesses 22 are arranged in a two-dimensional matrix on the first surface 101a of the first light diffusing sheet 101 and the first surface 102a of the second light diffusing sheet 102. In other words, the recesses 22 are arranged along two directions orthogonal to each other. Adjacent recesses 22 are partitioned by a ridge line 23. The ridge line 23 extends along the two directions in which the recesses 22 are arranged. The center (the apex of the inverted pyramid) of the recess 22 is the deepest part of the recess 22. In FIG. 4, for simplicity, an example in which the recesses 22 are arranged in a 5×5 matrix is illustrated, but the actual number of arrangements of the recesses 22 is much larger. In the two-dimensional arrangement of the recesses 22, the recesses 22 may be provided on the first surface 101a (102a) without gaps, or may be provided at a predetermined interval. Also, as long as the light diffusing effect is not impaired, some of the recesses 22 may be randomly arranged.

[0065] In this embodiment, in both the first light diffusion sheet 101 and the second light diffusion sheet 102, the recesses 22 are provided in the base material layer 21. In other words, the sheet portion (concave-shaped portion) where the recesses 22 are provided and the other sheet portion (base material portion) are integrally formed of the same material. The first light diffusion sheet 101 and the second light diffusion sheet 102 are integrally formed by, for example, transferring the shape of the recesses to a molten or softened sheet material using a method such as pressing with two rolls or in a press machine. Thereby, it is possible to prevent the concave-shaped portion from peeling off from the base material portion in a reliability test or the like.

[0066] The arrangement pitch of the recesses 22 is set to, for example, about 20 μm or more. The arrangement pitch of the recesses is basically in a proportional relationship with the thickness of the light diffusion sheet in which the recesses are provided. When a thin light diffusion sheet is bonded to another light diffusion sheet, the rigidity of the thin light diffusion sheet increases, making it easier to handle during the assembly of the backlight unit or the like. Even in the case of a thick light diffusion sheet, when it is bonded to another light diffusion sheet, the number of parts during the assembly of the backlight unit or the like decreases, so the labor of assembly can be reduced. From the above viewpoints, in the first light diffusion sheet 101 and the second light diffusion sheet 102, the arrangement pitch of the recesses 22 is set to 30 μm or more and 500 μm or less, preferably 50 μm or more and 300 μm or less, more preferably 50 μm or more and 200 μm or less.

[0067] The angle formed by the wall surface of the recess 22 (the inclined surface of a substantially inverted pyramid or a substantially inverted truncated pyramid) and the sheet surface of the first light diffusion sheet 101 and the second light diffusion sheet 102 (the virtual mirror surface without the recess 22) is set to, for example, 40 degrees or more and 65 degrees or less, preferably 45 degrees or more and 60 degrees or less, more preferably 47 degrees or more and 55 degrees or less. In other words, the apex angle of the recess 22 is set to, for example, 50 degrees or more and 100 degrees or less, preferably 60 degrees or more and 90 degrees or less, more preferably 70 degrees or more and 86 degrees or less.

[0068] The second surface 101b of the first light diffusion sheet 101 and the second surface 102b of the second light diffusion sheet 102 may be flat surfaces (mirror surfaces), but may also be matte surfaces in order to improve diffusibility. In the example shown in FIG. 2, the second surface 101b of the first light diffusion sheet 101 and the second surface 102b of the second light diffusion sheet 102 are arranged so as to be incident surfaces, but instead, the second surface 101b of the first light diffusion sheet 101 and the second surface 102b of the second light diffusion sheet 102 may be arranged so as to be emission surfaces. Alternatively, one of the second surface 101b of the first light diffusion sheet 101 and the second surface 102b of the second light diffusion sheet 102 may be an incident surface and the other may be an emission surface.

[0069] In addition, in the laminated light diffusion sheet 100 of the present embodiment, the first light diffusion sheet 101 and the second light diffusion sheet 102 having the same structure are bonded together, but instead, the first light diffusion sheet 101 and the second light diffusion sheet 102 having different structures may be bonded together. For example, the dimensions, shapes, and arrangement pitches of the recesses 22 provided in the second light diffusion sheet 102 may be different from the dimensions, shapes, and arrangement pitches of the recesses 22 provided in the first light diffusion sheet 101. Alternatively, the surface shape of the second surface 102b of the second light diffusion sheet 102 may be different from the surface shape of the second surface 101b of the first light diffusion sheet 101. Alternatively, the second light diffusion sheet 102 may not be provided with the recesses 22.

[0070] [Bonding of Light Diffusion Sheets] In the laminated light diffusion sheet 100 of the present embodiment, the first surface 101a (concave pyramid forming surface) of the first light diffusion sheet 101 and the second surface 102b (matte surface) of the second light diffusion sheet 102 are bonded together. The peel strength at the bonding portion between the first light diffusion sheet 101 and the second light diffusion sheet 102 is 5.0 g wt / 25 mm or more, preferably 10.0 g wt / 25 mm or more, more preferably 100 g wt / 25 mm or more, and even more preferably 140 g wt / 25 mm or more.

[0071] The bonding portion between the first light diffusion sheet 101 and the second light diffusion sheet 102 may be the entire surface of the first surface 101a, or may be the peripheral portion of the first surface 101a (the end portion excluding the active area directly below the display screen 50a). Alternatively, a plurality of dot-shaped or linear regions on the first surface 101a of the first light diffusion sheet 101 may be bonded to the second surface 102b of the second light diffusion sheet 102.

[0072] The first light diffusion sheet 101 and the second light diffusion sheet 102 may be bonded together by an OCA film serving as the bonding member 111. In this case, after attaching the OCA film to the entire surface of the second surface 102b of the second light diffusion sheet 102, the first surface 101a of the first light diffusion sheet 101 may be bonded to the OCA film.

[0073] The first light diffusion sheet 101 and the second light diffusion sheet 102 may be bonded together by applying an ink containing an ultraviolet curable resin (UV curable ink) serving as the bonding member 111 to the second surface 102b of the second light diffusion sheet 102 and then bringing the first surface 101a of the first light diffusion sheet 101 into contact with the second surface 102b of the second light diffusion sheet 102 and performing ultraviolet irradiation. In this case, the UV curable ink may be applied to the entire surface of the second surface 102b of the second light diffusion sheet 102, or the UV curable ink may be applied to a plurality of dot-shaped or linear regions on the second surface 102b of the second light diffusion sheet 102. The dot-shaped or linear regions to which the UV curable ink is applied may have a predetermined area and shape, may be regularly arranged, or may be randomly arranged. Alternatively, the UV curable ink may be applied to the peripheral portion along the four side edges of the second surface 102b of the second light diffusion sheet 102.

[0074] The first light diffusing sheet 101 and the second light diffusing sheet 102 may be bonded by applying ink containing an infrared absorber to the four corners (the corner parts of the peripheral part) of the second surface 102b of the second light diffusing sheet 102, and then bringing the first surface 101a of the first light diffusing sheet 101 into contact with the second surface 102b of the second light diffusing sheet 102 and performing infrared laser irradiation. In this case, the base material layers 21 at the four corners of the first light diffusing sheet 101 and the second light diffusing sheet 102 are heat-sealed to form an adhesive member 111. An infrared absorber may remain in the adhesive member 111.

[0075] By the way, when the first light diffusing sheet 101 and the second light diffusing sheet 102 are bonded together, a part of the adhesive material or the base material layer 21 of the second light diffusing sheet 102 may enter the concave portion 22 on the first surface 101a of the first light diffusing sheet 101.

[0076] On the other hand, the laminated light diffusing sheet 100 of the present embodiment is characterized in that when the volume of the concave portion 22 is V0 and the volume of the void remaining in the concave portion 22 is Va, on the first surface 101a (the active area directly below the display screen 50a excluding the peripheral portion) of the first light diffusing sheet 101, the bonding is performed so that Va / V0 is 40% or more, preferably 50% or more. Thereby, it is possible to suppress the decrease in luminance and luminance uniformity caused by the bonding of the first light diffusing sheet 101 and the second light diffusing sheet 102 to a practical level. For example, when only the peripheral portion of the first surface 101a of the first light diffusing sheet 101 is bonded to the second light diffusing sheet 102, Va / V0 becomes 100% which is the upper limit.

[0077] In the laminated light diffusion sheet 100 of this embodiment, the first light diffusion sheet 101 and the second light diffusion sheet 102 are arranged and bonded with their respective first surfaces 101a and 102a as the light-emitting surfaces, that is, the first light diffusion sheet 101 and the second light diffusion sheet 102 are arranged in the same direction. In this case, it is preferable that Va / V0 is 55% or more. Further, by arranging and bonding the first light diffusion sheet 101 and the second light diffusion sheet 102 in the same direction, compared with the case where the first light diffusion sheet 101 and the second light diffusion sheet 102 are arranged and bonded in different directions, for example, when bonding the first surface 101a of the first light diffusion sheet 101 and the first surface 102a of the second light diffusion sheet 102, the bonding becomes easier.

[0078] Incidentally, the second light diffusion sheet 102 may be a light diffusion sheet of a type different from the first light diffusion sheet 101, for example, a light diffusion sheet having irregularities provided with resin beads or the like on the sheet surface. Also in this case, when bonding the light diffusion sheet to the first surface 101a of the first light diffusion sheet 101, it is important to ensure that the recess 22 in the first surface 101a is not filled with an adhesive material or resin beads, so as to secure Va / V0 of 40% or more.

[0079] <Variations of the laminated light diffusion sheet> In the configuration example of the backlight unit 40 shown in FIG. 2, the laminated light diffusion sheet 100 is constituted by two light diffusion sheets, namely, a first light diffusion sheet 101 and a second light diffusion sheet 102. Alternatively, as in the modification shown in FIG. 5, the laminated light diffusion sheet 100 may be constituted by three light diffusion sheets, namely, a first light diffusion sheet 101, a second light diffusion sheet 102, and a third light diffusion sheet 103. In this case, the third light diffusion sheet 103 may have the same structure as the first light diffusion sheet 101 and the second light diffusion sheet 102. That is, a plurality of recesses 22 formed in a substantially inverted regular square pyramid may be provided on the first surface 103a (the light-emitting surface in the example shown in FIG. 5) of the third light diffusion sheet 103. The second surface 103b of the third light diffusion sheet 103 may be a matte surface. In the modification shown in FIG. 5, the laminated light diffusion sheet 100 has a structure in which the lower first light diffusion sheet 101 and the middle second light diffusion sheet 102 are bonded together by an adhesive member 111, and the middle second light diffusion sheet 102 and the upper third light diffusion sheet 103 are bonded together by an adhesive member 112. The second light diffusion sheet 102 and the third light diffusion sheet 103 are bonded together by attaching or applying, for example, an OCA film, an ink containing an ultraviolet curable resin, an ink containing an infrared absorber, etc. to the bonding surface of the second light diffusion sheet 102 or the third light diffusion sheet 103, in the same manner as the bonding of the first light diffusion sheet 101 and the second light diffusion sheet 102 in the above-described embodiment shown in FIG. 2.

[0080] Note that although the laminated light diffusion sheet 100 of this modification is constituted by three light diffusion sheets, the laminated light diffusion sheet 100 may be constituted by four or more light diffusion sheets.

[0081] Also, in the laminated light diffusion sheet 100 of this modification, the second surfaces 101b to 103b of the first to third light diffusion sheets 101 to 103 are arranged to be the light-incident surfaces. Alternatively, the second surfaces 101b to 103b of the first to third light diffusion sheets 101 to 103 may be arranged to be the light-emitting surfaces. Or, one or two of the second surfaces 101b to 103b of the first to third light diffusion sheets 101 to 103 may be arranged to be the light-incident surfaces, and the others may be arranged to be the light-emitting surfaces.

[0082] Also, in the laminated light diffusing sheet 100 of the present embodiment, the first to third light diffusing sheets 101 to 103 having the same structure are bonded together. Instead of this, the first to third light diffusing sheets 101 to 103 having different structures from each other may be bonded together. Alternatively, only one of the first to third light diffusing sheets 101 to 103 may have a structure different from the other two. For example, the dimensions, shapes, and arrangement pitches of the recesses 22 provided in the second light diffusing sheet 102 and / or the third light diffusing sheet 103 may be different from the dimensions, shapes, and arrangement pitches of the recesses 22 provided in the first light diffusing sheet 101. Alternatively, the surface shape of the second surface 102b of the second light diffusing sheet 102 and / or the surface shape of the second surface 103b of the third light diffusing sheet 103 may be different from the surface shape of the second surface 101b of the first light diffusing sheet 101. Alternatively, the recesses 22 may not be provided in the second light diffusing sheet 102 and / or the third light diffusing sheet 103.

[0083] <Variations of the light diffusing sheet> In the example shown in FIG. 2 or FIG. 5, a plurality of recesses 22 are formed on the first surfaces 101a to 103a of the first to third light diffusing sheets 101 to 103. In addition to this, a plurality of other recesses similar to the recesses 22 may also be formed on the second surfaces 101b to 103b of the first to third light diffusing sheets 101 to 103.

[0084] The plurality of recesses 22 may be formed in a substantially inverted pyramid or a substantially inverted truncated pyramid shape. The plurality of recesses 22 may be regularly two-dimensionally arranged. As the "inverted pyramid (truncated pyramid)", a triangular pyramid (truncated pyramid), a quadrangular pyramid (truncated pyramid), or a hexagonal pyramid (truncated pyramid) that can be two-dimensionally arranged without gaps is preferable. In the manufacturing process such as extrusion molding or injection molding when providing the recesses 22, a mold (metal roll) is used. Considering the accuracy of the cutting operation on the surface of this mold (metal roll), an inverted quadrangular pyramid (truncated pyramid) may be selected as the "inverted pyramid (truncated pyramid)".

[0085] In the present disclosure, in consideration of the fact that it is difficult to form geometrically precise inverted pyramids or frustums of inverted pyramids by ordinary shape transfer techniques, the notations "substantially inverted pyramid" or "substantially frustum of inverted pyramid" are used, but it goes without saying that these notations include shapes that can be regarded as true or substantially inverted pyramids or frustums of inverted pyramids. Further, "substantially" means that approximation is possible. For example, "substantially quadrangular pyramid" refers to a shape that can be approximated to a quadrangular pyramid. Also, shapes deformed from "inverted pyramid" or "frustum of inverted pyramid" within the range of inevitable shape variations due to processing accuracy in industrial production are also included in "substantially inverted pyramid" or "substantially frustum of inverted pyramid".

[0086] When a plurality of recesses 22 are regularly two-dimensionally arranged, the plurality of recesses 22 may be provided without gaps over the entire surface of the first to third light diffusion sheets 101 to 103, or a flat portion having a predetermined width may be provided between the recesses 22.

[0087] The first to third light diffusion sheets 101 to 103 may be composed of a base material layer 21 that does not contain a diffusing agent, for example, a base material layer 21 made of clear polycarbonate. When the base material layer 21 contains a diffusing agent, the material of the diffusing agent is not particularly limited. As inorganic particles, for example, silica, titanium oxide, aluminum hydroxide, barium sulfate, etc. may be used, and as organic particles, for example, acrylic, acrylonitrile, silicone, polystyrene, polyamide, etc. may be used. From the viewpoint of the light diffusion effect, the particle size of the diffusing agent may be, for example, 0.1 μm or more (preferably 1 μm or more) and 10 μm or less (preferably 8 μm or less). The first to third light diffusion sheets 101 to 103 preferably do not contain a diffusing agent from the viewpoints of the effects of reflection and refraction by a substantially inverted pyramid shape and the light diffusion effect by the diffusing agent. However, with 100 parts by mass of the material (matrix) constituting the base material layer 21, the content of the diffusing agent may be, for example, 0.1 part by mass or more (preferably 0.3 part by mass or more) and 10 parts by mass or less (preferably 8 parts by mass or less). The difference between the refractive index of the diffusing agent and the refractive index of the matrix of the base material layer 21 may be 0.01 or more, preferably 0.03 or more, more preferably 0.05 or more, still more preferably 0.1 or more, and most preferably 0.15 or more. When the difference between the refractive index of the diffusing agent and the refractive index of the matrix of the base material layer 21 is less than 0.01, the diffusion effect by the diffusing agent becomes insufficient.

[0088] The resin serving as the matrix of the base material layer 21 is not particularly limited as long as it is a material that transmits light. For example, acrylic, polystyrene, styrene acrylic, polycarbonate, MS (methyl methacrylate·styrene copolymer) resin, polyethylene terephthalate, polyethylene naphthalate, cellulose acetate, polyimide, etc. may be used.

[0089] The thicknesses of the first to third light diffusion sheets 101 to 103 are not particularly limited. However, considering the effect of lamination, for example, it may be 1 mm or less (preferably 800 μm or less, more preferably 500 μm or less, still more preferably 300 μm or less) and 30 μm or more (preferably 50 μm or more, more preferably 70 μm or more). When the thickness of the first to third light diffusion sheets 101 to 103 exceeds 1 mm, it becomes difficult to achieve the thinning of the liquid crystal display. On the other hand, when the thickness of the first to third light diffusion sheets 101 to 103 is less than 30 μm, it becomes difficult to form a film while imparting an uneven shape.

[0090] <Manufacturing method of light diffusion sheet> Hereinafter, the manufacturing method of the first to third light diffusion sheets 101 to 103 will be described. The manufacturing method of the first to third light diffusion sheets 101 to 103 is not particularly limited. For example, an extrusion molding method, a compression molding method, a transfer method using a UV curable resin or a thermosetting resin, an injection molding method, etc. may be used, but it is preferable to use an extrusion molding method, a compression molding method, an injection molding method, etc. that can be integrally molded with the same material. When extruding the first to third light diffusion sheets 101 to 103, for example, the line speed is preferably 2 m / min or more and 50 m / min or less (more preferably 3 m / min or more and 40 m / min or less), and the compression line pressure is preferably 50 kgf / cm or more and 1000 kgf / cm or less (more preferably 100 kgf / cm or more and 800 kgf / cm or less, still more preferably 200 kgf / cm or more and 500 kgf / cm or less). Incidentally, when the line speed exceeds 50 m / min, the cooling of the resin for the light diffusion sheet is insufficient, and the shape transfer rate is likely to decrease. On the other hand, when the line speed is less than 2 m / min, the productivity is likely to decrease, and the shape transfer rate also decreases. Also, when the compression line pressure exceeds 1000 kgf / cm, it may exceed the mechanical strength of the manufacturing equipment. On the other hand, when the compression line pressure is less than 50 kgf / cm, the shape transfer rate is likely to decrease.

[0091] The procedure for manufacturing a single-layer light diffusion sheet having an uneven shape on its surface using an extrusion molding method is as follows. First, pellet-shaped plastic particles (diffusion agents may be added) are fed into a single-screw extruder and melted and kneaded while being heated. Then, the molten resin extruded by a T-die is sandwiched between two metal rolls and cooled, and then conveyed using guide rolls. In the case of a relatively thin film, it is wound into a roll by a winder and then cut to a predetermined size, and in the case of a relatively thick sheet, it is cut into a single-sheet flat plate by a sheet cutter to produce a light diffusion sheet. Here, by sandwiching the molten resin using a metal roll having a shape with the desired uneven shape inverted on its surface, the inverted shape on the roll surface is transferred to the resin, so that the desired uneven shape can be imparted to the surface of the light diffusion sheet. Also, since the shape transferred to the resin does not necessarily have 100% of the shape of the roll surface transferred, the shape of the roll surface may be designed by calculating backward from the transfer degree.

[0092] When manufacturing a two-layer light diffusion sheet having an uneven shape on its surface using an extrusion molding method, for example, pellet-shaped plastic particles necessary for forming each layer are fed into each of two single-screw extruders, and then the same procedure as described above is carried out for each layer, and the layers produced are laminated.

[0093] Alternatively, a two-layer light diffusion sheet having an uneven shape on its surface may be produced as follows. First, pellet-shaped plastic particles necessary for forming each layer are fed into each of two single-screw extruders and melted and kneaded while being heated. Then, the molten resin for each layer is fed into a single T-die, laminated within the T-die, and the laminated molten resin extruded by the T-die is sandwiched between two metal rolls and cooled. Then, the laminated molten resin is conveyed using guide rolls, wound into a roll and then cut, or made into a sheet and cut into a single-sheet flat plate by a sheet cutter to produce a two-layer light diffusion sheet having an uneven shape on its surface.

[0094] <Shape of the ridge line defining the concave portion of the light diffusion sheet> Hereinafter, further features of the first to third light diffusion sheets 101 to 103, specifically, features of the shape of the ridge lines 23 partitioning the recesses 22 from each other, will be described taking the first light diffusion sheet 101 as an example with reference to FIGS. 6 to 15.

[0095] As shown in FIG. 6, on the first surface 101a of the first light diffusion sheet 101, a plurality of recesses 22 formed, for example, in a substantially inverted regular square pyramid shape are provided. The plurality of recesses 22 may be formed in a substantially inverted regular square frustum shape. The center 22a of the recess 22 is the deepest part of the recess 22. The plurality of recesses 22 are arranged along the X direction (first direction) and the Y direction (second direction) orthogonal to each other. Adjacent recesses 22 are partitioned by a ridge line 23. The ridge line 23 extends along the X direction and the Y direction.

[0096] In the first light diffusion sheet 101, the ridge line 23 may have a shape recessed between the intersection points 23a of the ridge line 23 with respect to the straight lines Lx and Ly connecting the intersection points 23a of the ridge line 23. The maximum height difference d between the straight lines Lx and Ly connecting the intersection points 23a and the ridge line 23 may be 1 μm or more and 30 μm or less, preferably 1.5 μm or more and 20 μm or less, more preferably 2.5 μm or more and 10 μm or less.

[0097] In the first light diffusion sheet 101, the ridge line may be recessed between all the intersection points 23a of the ridge line, or the ridge line 23 may not have a recessed shape between some of the intersection points 23a.

[0098] FIG. 7 shows an example of the shape when the ridge line 23 extending in the X direction along the Ax - Bx line in FIG. 6 is viewed from a direction parallel to the sheet surface and perpendicular to the X direction, and FIG. 8 shows an example of the shape when the ridge line 23 extending in the Y direction along the Ay - By line in FIG. 6 is viewed from a direction parallel to the sheet surface and perpendicular to the Y direction. As shown in FIG. 7, with respect to the straight line Lx connecting the intersections 23a of the ridge line 23 in the X direction, the ridge line 23 may have a concave shape between the intersections 23a. In this case, taking the arrangement pitch in the X direction of the recess 22 as Px, the ridge line 23 extending in the X direction has, for example, the lowest point 23b at a position of Px / 2 (half pitch) from the intersection 23a, and the distance (maximum height difference) from the straight line Lx to the lowest point 23b is dx. Also, as shown in FIG. 8, with respect to the straight line Ly connecting the intersections 23a of the ridge line 23 in the Y direction, the ridge line 23 may have a concave shape between the intersections 23a. In this case, taking the arrangement pitch in the Y direction of the recess 22 as Py, the ridge line 23 extending in the Y direction has, for example, the lowest point 23b at a position of Py / 2 (half pitch) from the intersection 23a, and the distance (maximum height difference) from the straight line Ly to the lowest point 23b is dy.

[0099] When the recess 22 is formed in an inverted regular square pyramid shape, the arrangement pitch Px in the X direction of the recess 22 is equal to the interval (horizontal distance) between the intersections 23a in the X direction, and the arrangement pitch Py in the Y direction of the recess 22 is equal to the interval (horizontal distance) between the intersections 23a in the Y direction.

[0100] Taking the average value of the maximum height difference dx in the X direction and the maximum height difference dy in the Y direction as the maximum height difference d, the maximum height difference d may be set to 1 μm or more and 30 μm or less, preferably 1.5 μm or more and 20 μm or less, more preferably 2.5 μm or more and 10 μm or less.

[0101] The concave shape of the ridge line 23 between the intersection points 23a is not particularly limited. For example, as shown in FIG. 9, with respect to the straight line L connecting the intersection points 23a, the ridge line 23 may be recessed in a substantially arc shape (FIG. 9(A)), a substantially parabolic shape (FIG. 9(B)), a substantially triangular shape (FIG. 9(C)), or a substantially trapezoidal shape (FIG. 9(D)) between the intersection points 23a. Further, the ridge line 23 may have a shape that is recessed substantially symmetrically about the lowest point of the ridge line 23 between the intersection points 23a with respect to the straight line L connecting the intersection points 23a of the ridge line 23.

[0102] As a feature of the first light diffusing sheet 101, when the arrangement pitch of the recesses 22 is P and the dimension occupied by the curved portion at the top of the ridge line 23 in the arrangement direction of the recesses 22 is Wr, the ratio Wr / P needs to be 0.25 (25%) or less, preferably 0.2 (20%) or less, and more preferably 0.15 (15%) or less. However, in order to avoid a decrease in abrasion resistance, the ratio Wr / P should be 0.005 (0.5%) or more, preferably 0.01 (1.0%) or more.

[0103] In the present disclosure, when the recesses 22 are arranged without gaps as shown in FIG. 6, the "curved portion at the top of the ridge line 23" is regarded as the "boundary portion between the recesses 22". When the recesses 22 are arranged at intervals, the "flat portion intentionally arranged between the recesses 22" is regarded as the "boundary portion between the recesses 22".

[0104] FIG. 10 shows an example of the cross-sectional configuration of the first light diffusing sheet 101 along the Cx - Dx line in FIG. 6, and FIG. 11 shows an example of the cross-sectional configuration of the first light diffusing sheet 101 along the Cy - Dy line in FIG. 6. Specifically, FIG. 10 shows the cross-sectional configuration when the first light diffusing sheet 101 is cut by a plane passing through the centers 22a of the recesses 22 adjacent to each other in the X direction and the midpoint between the intersection points 23a on the ridge line 23 located between the recesses 22 and perpendicular to the sheet surface. FIG. 11 shows the cross-sectional configuration when the first light diffusing sheet 101 is cut by a plane passing through the centers 22a of the recesses 22 adjacent to each other in the Y direction and the midpoint between the intersection points 23a on the ridge line 23 located between the recesses 22 and perpendicular to the sheet surface.

[0105] In the cross-sectional configuration shown in FIG. 10, the distance (horizontal distance) between the centers 22a of the recesses 22 adjacent to each other in the X direction is equal to the arrangement pitch Px of the recesses 22 in the X direction. The dimension occupied by the curved portion (boundary portion) at the top of the ridge line 23 in the X direction is Wrx. The dimensions occupied by the straight portions of the respective wall surfaces (the inclined surfaces of the inverted square pyramids) of the recesses 22 adjacent to each other across the ridge line 23 in the X direction are Wsx1 and Wsx2. The angle formed between the wall surface (the inclined surface of the inverted square pyramid) of the recess 22 and the sheet surface in the X direction is θx. The height from the center 22a of the recess 22 to the apex (the midpoint between the intersection points 23a) of the ridge line 23 (the ridge line 23 extending in the Y direction) is Hx.

[0106] In the cross-sectional configuration shown in FIG. 11, the distance (horizontal distance) between the centers 22a of the recesses 22 adjacent to each other in the Y direction is equal to the arrangement pitch Py of the recesses 22 in the Y direction. The dimension occupied by the curved portion (boundary portion) at the top of the ridge line 23 in the Y direction is Wry. The dimensions occupied by the straight portions of the respective wall surfaces (the inclined surfaces of the inverted square pyramids) of the recesses 22 adjacent to each other across the ridge line 23 in the Y direction are Wsy1 and Wsy2. The angle formed between the wall surface (the inclined surface of the inverted square pyramid) of the recess 22 and the sheet surface in the Y direction is θy. The height from the center 22a of the recess 22 to the apex (the midpoint between the intersection points 23a) of the ridge line 23 (the ridge line 23 extending in the X direction) is Hy.

[0107] When the recess 22 is formed as an inverted square pyramid, it is necessary to set the ratio Wr / P, where P is the average value of the arrangement pitch Px and the arrangement pitch Py, and Wr is the average value of the dimension Wrx and the dimension Wry, to 0.25 (25%) or less, preferably 0.2 (20%) or less, and more preferably 0.15 (15%) or less.

[0108] FIG. 12 shows an example of the results of measuring the shape and dimensions of the X-direction ridge line shown in FIG. 7 with a laser microscope. FIG. 13 shows an example of the results of measuring the shape and dimensions of the Y-direction ridge line shown in FIG. 8 with a laser microscope. FIG. 14 shows an example of the results of measuring the shape, dimensions, and angles of the cross-sectional configuration shown in FIG. 10 with a laser microscope. FIG. 15 shows an example of the results of measuring the shape, dimensions, and angles of the cross-sectional configuration shown in FIG. 11 with a laser microscope. In addition, in the measurement of the maximum values (maximum height differences) dx and dy of the distances between the straight lines Lx and Ly connecting the intersections 23a of the ridge line 23 and the ridge line 23, the maximum values of the lengths of the perpendiculars drawn perpendicularly from the points on the ridge line 23 to the straight lines Lx and Ly were defined as dx and dy. Also, in the measurement of the array pitches Px and Py, the "horizontal distance between the intersections 23a" in each of the X direction and the Y direction was obtained as Px and Py. In this way, even with the method of measuring the "horizontal distance between the intersections 23a", the array pitches Px and Py can be obtained easily and accurately.

[0109] <Features of the Embodiment (Including Modification Examples)> As described above, the laminated light diffusing sheet 100 of the present embodiment includes a first light diffusing sheet 101 in which a plurality of recesses 22 formed in a substantially inverted pyramid or substantially inverted truncated pyramid shape are arranged on the first surface 101a, and a second light diffusing sheet 102 bonded to the first surface 101a of the first light diffusing sheet 101. The peel strength at the bonding portion between the first light diffusing sheet 101 and the second light diffusing sheet 102 is 5.0 g weight / 25 mm or more. When the volume of the recess 22 is V0 and the volume of the void remaining in the recess 22 is Va, Va / V0 is 40% or more and 100% or less in the region excluding the peripheral portion of the first surface 101a of the first light diffusing sheet 101.

[0110] According to the laminated light diffusing sheet 100 of the present embodiment, since the first light diffusing sheet 101 and the second light diffusing sheet 102 are bonded together with a peel strength of 5.0 g / 25 mm or more, the handleability of each light diffusing sheet 101 and 102 can be improved during the assembly of the backlight unit 40. Further, in the first surface 101a (the active area directly below the display screen 50a excluding the peripheral edge portion) of the first light diffusing sheet 101 in which the concave portions 22 formed in a substantially inverted pyramid or a substantially inverted truncated pyramid shape are arranged, since (the volume Va of the void remaining in the concave portion 22) / (the volume V0 of the concave portion 22) is 40% or more, a decrease in luminance and luminance uniformity due to bonding can be suppressed.

[0111] In addition, in the laminated light diffusing sheet where Va / V0 is 40% or more, when the peel strength at the bonding portion between the first light diffusing sheet and the second light diffusing sheet is 100 g / 25 mm or more, preferably 140 g / 25 mm or more, the handleability of each light diffusing sheet 101 and 102 can be further improved during the assembly of the backlight unit 40.

[0112] In the laminated light diffusing sheet 100 of the present embodiment, when the peel strength measured at 85°C is 10 g / 25 mm or more, a laminated light diffusing sheet 100 with sufficient heat resistance can be obtained.

[0113] In the laminated light diffusing sheet 100 of the present embodiment, when the peel strength measured at 85°C is 100 g / 25 mm or more, a laminated light diffusing sheet 100 with excellent heat resistance can be obtained.

[0114] In addition, in the laminated light diffusing sheet 100 of the present embodiment, when the peel strength measured at 85°C is 140 g / 25 mm or more, a laminated light diffusing sheet with even better heat resistance can be obtained.

[0115] In the laminated light diffusing sheet 100 of the present embodiment, the bonding portion of the light diffusing sheets 101 and 102 may be the entire surface, the peripheral portion, or a plurality of dot-shaped or linear regions on the first surface 101a of the first light diffusing sheet 101. That is, in the laminated light diffusing sheet 100 of the present embodiment, the peeling strength between the first light diffusing sheet 101 and the second light diffusing sheet 102 is 5.0 g weight / 25 mm or more, and for the recesses 22 arranged on the first surface 101a of the first light diffusing sheet 101, if the bonding is performed such that (the volume Va of the voids remaining in the recesses 22) / (the volume V0 of the recesses 22) is 40% or more, the bonding portion is not particularly limited.

[0116] In the laminated light diffusing sheet 100 of the present embodiment, the recesses 22 are formed in a substantially inverted quadrangular pyramid or a substantially inverted quadrangular frustum shape. The thickness of the first light diffusing sheet 101 is 30 μm or more and 1000 μm or less. The portion of the first light diffusing sheet 101 where the recesses 22 are provided and the other portions may be integrally formed of the same material. If the recesses 22 are formed in a substantially inverted quadrangular pyramid or a substantially inverted quadrangular frustum shape, the cutting accuracy of the mold (metal roll) used in the manufacturing process is improved. When the thickness of the first light diffusing sheet 101 is 30 μm or more, the effect of improving the luminance uniformity is easily obtained. On the other hand, when the thickness of the first light diffusing sheet 101 is less than 30 μm, the recesses 22 are likely to penetrate the sheet, making stable processing difficult. When the thickness of the first light diffusing sheet 101 is 1000 μm or less, the backlight unit 40, that is, the liquid crystal display device 50 can be made thinner. Generally, an optical sheet with a thickness exceeding 500 μm has sufficient rigidity even when used alone, so the handling during the assembly of the backlight unit becomes easier without bonding to other optical sheets. When the portion (concave-shaped portion) where the recesses 22 are provided and the other portions (base material portions) of the first light diffusing sheet 101 are integrally formed of the same material, it is possible to prevent the concave-shaped portion from peeling off from the base material portion in a reliability test or the like.

[0117] For example, in a light diffusion sheet in which a UV curable resin is shaped and laminated on a base film to provide a concave portion, the concave portion may peel off from the base film in a reliability test or the like. On the other hand, in a light diffusion sheet in which the base portion and the concave portion are integrally formed, such as an extrusion molded product or a compression molded product, it is possible to prevent the concave portion from peeling off from the base portion in a reliability test or the like. Further, generally, in an optical sheet bonded to another optical sheet, stress tends to concentrate at the bonding portion due to the bonding effect accompanying the bonding. However, if the base portion and the concave portion are not integrally formed, there also occurs a problem that the base portion and the concave portion are likely to peel off due to the difference in the linear expansion coefficients of the respective portions.

[0118] In the laminated light diffusion sheet 100 of the present embodiment, when the concave portion 22 of the first light diffusion sheet 101 is formed in a substantially inverted quadrangular pyramid or a substantially inverted quadrangular frustum shape, a plurality of concave portions 22 formed in a substantially inverted quadrangular pyramid or a substantially inverted quadrangular frustum shape are arranged on the first surface 102a of the second light diffusion sheet 102, the second surface 102b of the second light diffusion sheet 102 is a flat surface or a matte surface, and the first surface 101a of the first light diffusion sheet 101 and the second surface 102b of the second light diffusion sheet 102 may be bonded together. By doing so, a laminated light diffusion sheet 100 that can exhibit an excellent effect of improving luminance uniformity can be obtained relatively easily.

[0119] In the laminated light diffusion sheet 100 of the present embodiment, when Va / V0 is 50% or more, a decrease in luminance and luminance uniformity due to bonding can be further suppressed.

[0120] In the laminated light diffusion sheet 100 of the present embodiment, the first light diffusion sheet 101 and the second light diffusion sheet 102 may be bonded together by an OCA (optical clear adhesive). By doing so, the bonding operation can be easily performed.

[0121] In the laminated light diffusion sheet 100 of the present embodiment, the first light diffusion sheet 101 and the second light diffusion sheet 102 may be bonded together with an ink containing an ultraviolet curable resin. By doing so, the thickness of the adhesive layer for bonding the first light diffusion sheet 101 and the second light diffusion sheet 102 can be changed depending on the type of ink. However, compared with the case of bonding with an OCA, the process of irradiating ultraviolet rays (UV) or the like to cure the ink increases.

[0122] In the laminated light diffusion sheet 100 of the present embodiment, the first light diffusion sheet 101 and the second light diffusion sheet 102 may be bonded together by laser welding using an infrared absorber. By doing so, sufficient peel strength can be obtained even when, for example, only the four corners of the sheet are bonded. However, compared with the case of bonding with an OCA, the process of irradiating an infrared laser for welding increases.

[0123] The backlight unit 40 of the present embodiment is incorporated into the liquid crystal display device 50, guides the light emitted from the light source 41 toward the display screen 50a, and includes the laminated light diffusion sheet 100 of the present embodiment described above between the display screen 50a and the light source 41. Therefore, it is possible to suppress a decrease in luminance and luminance uniformity while improving the handleability of the light diffusion sheets 101 and 102 during the assembly of the backlight unit 40 using a plurality of light diffusion sheets 101 and 102.

[0124] In the backlight unit 40 of the present embodiment, a color conversion sheet 44 that converts the wavelength of the light emitted from the light source 41 may be further provided between the display screen 50a and the light source 41. By doing so, it is not necessary to use an expensive white light source as the light source 41, so the cost of the backlight unit 40 can be reduced. Note that the arrangement position of the color conversion sheet 44 is not particularly limited as long as it is between the display screen 50a and the light source 41. For example, the color conversion sheet 44 may be arranged between the light source 41 and the laminated light diffusion sheet 100, or between the display screen 50a and the laminated light diffusion sheet 100.

[0125] In the backlight unit 40 of the present embodiment, the content of the light diffusing agent in the first light diffusing sheet 101 is not particularly limited as long as the light diffusing effect due to reflection and refraction in the concave portion 22 formed in a substantially inverted pyramid or substantially inverted frustum shape is not impaired. For example, it may contain 0 parts by mass or more and 10 parts by mass or less of the light diffusing agent with respect to 100 parts by mass of the matrix resin.

[0126] The liquid crystal display device 50 of the present embodiment includes the above-described backlight unit 40 of the present embodiment and a liquid crystal display panel 5. Therefore, it is possible to suppress a decrease in luminance and luminance uniformity while improving the handleability of the light diffusing sheets 101 and 102 during the assembly of the backlight unit 40 using a plurality of light diffusing sheets 101 and 102. The same effect can be obtained in the information device including the liquid crystal display device 50 of the present embodiment.

[0127] In addition, it is preferable that the first light diffusing sheet 101 is formed of the same material for the concave portion and the base material portion so that the concave portion and the base material portion do not cause interfacial peeling in a reliability test or the like. In particular, it is preferable that the concave portion and the base material portion are integrally formed by a method such as extrusion molding or compression molding.

[0128] In the first light diffusing sheet 101, the arrangement pitch of the concave portions 22 is preferably 30 μm or more and 1000 μm or less, and the width of the boundary portion between adjacent concave portions 22 is preferably 25% or less of the arrangement pitch. Specifically, in order to reduce the area ratio of the boundary portion, the width of the boundary portion is 25% or less, preferably 20% or less, more preferably 15% or less of the arrangement pitch. However, in order to avoid a decrease in abrasion resistance, the width of the boundary portion is 0.5% or more, preferably 1.0% or more of the arrangement pitch. In the present disclosure, the "boundary portion between the concave portions 22" means the "width of the flat portion intentionally arranged between the concave portions 22" when the concave portions 22 are arranged at intervals, and means the "width of the curved portion at the top of the ridge line 23 partitioning the concave portions 22" when the concave portions 22 are arranged without gaps.

[0129] In the first light diffusion sheet 101, when the array pitch is 1000 μm or less, an increase in the thickness of the first light diffusion sheet 101 can be suppressed, and the backlight unit 40 can be made thinner.

[0130] In the first light diffusion sheet 101, when the width of the boundary portion is the width of the curved portion at the top of the ridge line 23 that partitions the recesses 22 from each other, in other words, when the recesses 22 are arranged without gaps, the luminance uniformity can be improved as compared with the case where the recesses 22 are arranged with an interval. In this case, the recess 22 is formed in a substantially inverted quadrangular pyramid or a substantially inverted quadrangular frustum shape, the ridge line 23 extends in the first direction and the second direction, the array pitch is the average value of the first array pitch of the recess 22 in the first direction and the second array pitch of the recess 22 in the second direction, and the width of the boundary portion may be the average value of the width occupied by the curved portion at the top of the ridge line 23 in the first direction and the width occupied by the curved portion at the top of the ridge line 23 in the second direction. Thereby, the recess 22 can be easily formed.

[0131] In the first light diffusion sheet 101, when the angle formed by the wall surface of the recess 22 and the sheet surface of the first light diffusion sheet 101 is 40 degrees or more and 65 degrees or less, a sufficient luminance uniformity improvement effect can be obtained by the recess 22.

[0132] In the first light diffusion sheet 101, when the recess 22 is provided only on the first surface 101a and the second surface 101b of the first light diffusion sheet 101 is a flat surface or a matte surface, the luminance uniformity improvement effect can be obtained while suppressing wear and damage on the second surface 101b.

[0133] Still, in the first light diffusing sheet 101, where the ridge line 23 (the opening edge of the recess 22) partitioning the recess 22 causes wear and damage, if the ridge line 23 has a shape that is recessed between the intersection points 23a of the ridge line 23, wear and damage are less likely to occur even when used in overlap with other optical sheets or other light diffusing sheets. Also, the dimension Wr occupied by the curved portion at the top of the ridge line 23 in the arrangement direction of the recesses 22 is suppressed to 25% or less of the arrangement pitch P of the recesses. For this reason, since the top of the ridge line 23 can maintain a steep shape, even if the ridge line 23 is recessed between the intersection points 23a, the luminance uniformity is less likely to decrease. Also, when the maximum height difference d between the straight line connecting the intersection points 23a and the ridge line 23 is 1 μm or more, the scratch resistance is improved, and when the maximum height difference d is 30 μm or less, a decrease in luminance uniformity can be suppressed. In particular, when the maximum height difference d is 1.5 μm or more and 20 μm or less, both the scratch resistance and the luminance uniformity can be further improved, and when the maximum height difference d is 2.5 μm or more and 10 μm or less, both the scratch resistance and the luminance uniformity can be further improved.

[0134] (Example) Hereinafter, the examples will be described together with comparative examples and reference examples.

[0135] <Light diffusing sheet used> Table 1 shows the configuration, optical characteristics, etc. of samples of the light diffusing sheet (hereinafter referred to as "light diffusing sheet #1") with inverted square pyramid-shaped recesses formed, used in the examples, comparative examples, and reference examples. In Table 1, the "width Wr of the ridge line" means the "width of the curved portion at the top of the ridge line", that is, the "width of the boundary portion between the recesses".

[0136]

Table 1

[0137] The light diffusion sheet #1 used in the examples, comparative examples, and reference examples was prepared as follows. First, an aromatic polycarbonate resin with a melt mass flow rate of 15 g / 10 min measured in accordance with ISO 1133 was fed into an extruder, melt-kneaded, and then the resin was extruded from a T-die. Thereafter, as one of the two metal rolls, a roll having the shape shown in FIGS. 16(A) and (B) ((B) is a shape view seen from the X-Y cross-sectional direction of (A)) (a pyramid shape of a regular square pyramid with a height of 50 μm, a length (pitch) of one side of the square at the bottom of the regular square pyramid of 100 μm, and an apex angle of 90 degrees) on its surface was used as a casting roll, and as the other roll, a roll having a random mat shape (surface roughness Ra = 2.1 μm) on its surface was used as a pressing roll. The molten resin extruded from the T-die was sandwiched between the two rolls and cooled while transferring the shape. Thus, a single-layer light diffusion sheet #1 with a thickness of 90 μm was prepared by an extrusion molding method.

[0138] As shown in Table 1, the light diffusion sheet #1 does not contain a diffusing agent and has a concave portion (inverted square pyramid) with a pyramid shape height (depth) H of 43 μm that depends on the height of the regular square pyramid on the roll on one surface (the first surface), and the other surface (the second surface) is a mat surface with a surface roughness Ra = 1.4 μm. It is a single-layer polycarbonate sheet. Further, in the obtained light diffusion sheet #1, the pitch P (length of one side of the square pyramid bottom surface) of the inverted square pyramid, the apex angle, the width Wr of the ridge line, and Wr / P are 100 μm, 90 degrees, 16 μm, and 16%, respectively, and the light transmittance, light reflectance, and haze at a wavelength of 450 nm are 94%, 12%, and 94%, respectively.

[0139] <Measurement of the Arrangement Pitch, Apex Angle, Ridge Line Width, and Height of the Inverted Square Pyramid> The shape measurement of the recesses (inverted square pyramids) formed on the surface of the light diffusing sheet #1 shown in Table 1 was performed using a laser microscope. Specifically, a 50 mm square test piece was cut out from the light diffusing sheet #1 obtained by extrusion molding, and the array pitches Px and Py (the horizontal distance between the intersections 23a in the X and Y directions) of the recesses 22 shown in FIGS. 7 and 8 were measured, and the array pitch P was determined as the average value thereof. Further, the angles θx and θy (the angles formed between the wall surface of the recess 22 (the slope of the inverted regular square pyramid) and the sheet surface in the X and Y directions) shown in FIGS. 10 and 11 were measured, and the apex angle (apex angle = 180 degrees - (θx + θy)) was determined based on the average value thereof. Further, the dimensions Wrx and Wry (the dimensions occupied by the curved portions at the tops of the ridge lines 23 in the X and Y directions) shown in FIGS. 10 and 11 were measured, and the width Wr of the ridge line was determined as the average value thereof. Incidentally, the unit of the ratio Wr / P of the width Wr to the array pitch P is %. Further, the heights Hx and Hy (the height from the center 22a of the recess 22 to the apex of the ridge line 23) shown in FIGS. 10 and 11 were measured, and the height H of the inverted square pyramid was determined as the average value thereof.

[0140] <Calculation of V0 (volume of the recess having an inverted square pyramid shape)> V0 (volume of the recess having an inverted square pyramid shape) can be calculated from the above-described shape measurement results of the recess, specifically, the height H of the inverted square pyramid and the array pitch P of the recess. Specifically, while observing the recess having an inverted square pyramid shape (pyramid shape) with a microscope, the recess is cut along one of the ridge lines of the recess and passing through the bottom of the recess (the apex of the pyramid), and by measuring H and P for the cross section, V0 can be calculated more accurately. Also, for the laminated light diffusing sheet, after peeling off the two laminated light diffusing sheets and separating them into individual light diffusing sheets, the bonding surface of the sheet is observed, and by measuring H and P for the pyramid shape of the recess, V0 can be calculated more accurately.

[0141] <Measurement of the surface roughness (Ra) of the light diffusing sheet> The surface roughness of the matte surface of the light diffusing sheet #1 shown in Table 1 was measured using an SJ-210 manufactured by Mitutoyo Corporation in accordance with JIS B 0601 using a test piece cut out to a size of 50 mm square.

[0142] <Measurement of Optical Properties> The light transmittance and light reflectance of the light diffusion sheet #1 at a wavelength of 450 nm shown in Table 1 were measured using a V-670 manufactured by JASCO Corporation with a test piece cut out to a size of 50 mm square. The haze was measured using an HZ-2 manufactured by Suga Test Instruments Co., Ltd. in accordance with JIS K 7361:2000. The measurement of optical properties was carried out with the surface having the concave portion formed in an inverted square pyramid as the incident surface.

[0143] <Fabrication of Laminated Light Diffusion Sheet and Measurement of Va / V0 (Spatial Volume Ratio)> Two light diffusion sheets #1 cut out to a size of 300 mm in length and 200 mm in width were bonded together by the method described below to fabricate laminated light diffusion sheets for each of the examples, comparative examples, and reference examples. The measurement of the spatial volume ratio (Va / V0) on the bonding surface of the two light diffusion sheets #1 constituting the laminated light diffusion sheet was carried out as follows. Note that V0 (the volume of the concave portion in the shape of an inverted square pyramid) can be calculated from the above-described measurement results of the shape of the concave portion, specifically, the height H of the inverted square pyramid and the arrangement pitch P of the concave portions. Also, Va is the volume of the voids (spaces where the sheet base material and the adhesive do not exist) remaining in the concave portions in the laminated light diffusion sheet after bonding. The spatial volume ratio (Va / V0) may be calculated as an average value for a plurality of randomly extracted concave portions.

[0144] In Example 1, MHM-FWD25 manufactured by Nikkai Shinwa Co., Ltd. was used as the OCA, and two light diffusion sheets #1 were bonded together. The bonding method was as follows: First, in the first step, an OCA with a thickness of 25 μm was attached to the matte surface of the first light diffusion sheet #1, and then the surface having the concave portion in the shape of an inverted square pyramid of the second light diffusion sheet #1 was brought into contact with the surface to which the OCA was attached on the first light diffusion sheet #1 and bonded together.

[0145] In this case, as shown in Fig. 17, since the OCA layer (adhesive member 111) is substantially horizontal with respect to the sheet surface of the second light diffusing sheet #1 (first light diffusing sheet 101), the shape of the gap 121 remaining in the recess (recess 22) also becomes a shape close to a regular square pyramid. That is, the shape of the gap 121 is substantially similar to the inverted square pyramid shape of the recess before lamination. Therefore, after laminating the two light diffusing sheets #1, the laminated light diffusing sheet is cut by a microtome with two planes passing through the center (deepest part) of the recess with an inverted square pyramid shape and perpendicular to the ridge lines of the inverted square pyramid (that is, the X cross-section and Y cross-section perpendicular to the X direction and Y direction shown in Fig. 6). The shapes of the X cross-section and Y cross-section are observed with a laser microscope, and the heights hax and hay of the gap 121 without the OCA layer in the recess in the X cross-section and Y cross-section are measured, and the average value ha of hax and hay is obtained. Next, using the calculation formula for the volume of a square pyramid, the space volume ratio Va / V0 (%) = (ha / H) 3 ×100 is calculated. Fig. 18 is a photograph showing the cross-sectional configuration of the laminated light diffusing sheet of Example 1. In Figs. 17 and 18, the same elements as those of the laminated light diffusing sheet 100 of the embodiment shown in Figs. 2, 4, etc. are denoted by the same reference numerals.

[0146] In Examples 2 to 4 and Comparative Example 1, two light diffusing sheets #1 were laminated using an ink containing a UV curable resin. As the ink containing a UV curable resin, a UV curable acrylic urethane-based light transmissive ink was used, and screen printing was used for printing. In addition, after applying the ink containing a UV curable resin, the two light diffusing sheets #1 were sandwiched and crimped with a rubber roll in a state where the bonding surfaces of the two light diffusing sheets #1 were overlapped, and then the ink was cured by ultraviolet irradiation.

[0147] Specifically, in Examples 2 and 3, an ink containing a UV-curable resin was printed on the entire matte surface of the first light diffusion sheet #1, with a thickness of 10 μm in Example 2 and 20 μm in Example 3. Then, the surface of the second light diffusion sheet #1 having the concave portions of the inverted square pyramids was bonded to the surface of the first light diffusion sheet #1 on which the ink was printed. In Comparative Example 1, an ink containing a UV-curable resin was printed on the entire surface of the second light diffusion sheet #1 having the concave portions of the inverted square pyramids so that the concave portions were almost 100% filled. Then, the matte surface of the first light diffusion sheet #1 was bonded to the surface of the second light diffusion sheet #1 on which the ink was printed (the surface having the concave portions of the inverted square pyramids). In Example 4, along the four edges of the matte surface of the first light diffusion sheet #1 cut out in a size of 300 mm × 200 mm, an ink containing the aforementioned UV-curable resin was printed with a width of 1.7 mm in the range from the four edges to 1.7 mm in the direction of the center of the sheet, with a thickness of 10 μm. Then, the surface of the second light diffusion sheet #1 having the concave portions of the inverted square pyramids was bonded to the surface of the first light diffusion sheet #1 on which the ink was printed. In Examples 2 to 4 and Comparative Example 1, after bonding the two light diffusion sheets #1, ultraviolet rays were irradiated to cure the ink containing the UV-curable resin, and then the above-described optical physical properties were measured and the peel strength described below was measured.

[0148] In Examples 2 and 3, as shown in FIG. 19, a phenomenon was observed in which the UV curable resin (adhesive member 111) adsorbed near the ridge line (ridge line 23) of the concave portion (concave portion 22) having an inverted square pyramid shape. This adsorption phenomenon is considered to be caused by surface tension. As a result, the shape of the void 121 remaining in the concave portion 22 became different from that of a regular square pyramid. Therefore, as described below, the void 121 was divided into shape portions for which volume calculation was possible, and the volume of the void 121 was obtained from the sum of the volumes of the respective shape portions. That is, after bonding two light diffusion sheets #1 together, the laminated light diffusion sheet was cut with a microtome using two planes passing through the center (deepest part) of the concave portion having an inverted square pyramid shape and perpendicular to the ridge line of the inverted square pyramid (that is, an X cross section and a Y cross section perpendicular to the X direction and the Y direction shown in FIG. 6). The shapes of the X cross section and the Y cross section were observed with a laser microscope, and in the X cross section and the Y cross section, the heights ha1x and ha1y of the height range in the concave portion where the UV curable resin did not enter were measured, and the average value ha1 of ha1x and ha1y was obtained. Thereby, the volume A (triangular cross section) of the regular square pyramid portion having the height ha1 was obtained. Also, in the X cross section and the Y cross section, the heights ha2x and ha1y and the widths (the base lengths of the regular square pyramid having the height ha1) wx and wy of the height range in the concave portion where the UV curable resin partially entered were measured, and the average value ha2 of ha2x and ha2y was obtained. Thereby, the volume B (quadrangular cross section) of the rectangular parallelepiped portion having the height ha2, the width wx, and the wy was obtained. Next, the space volume ratio Va / V0 (%) = (volume A + volume B) / V0 × 100 was calculated. FIG. 20 is a photograph showing the cross-sectional configuration of the laminated light diffusion sheet of Example 2. In FIGS. 19 and 20, the same elements as those of the laminated light diffusion sheet 100 of the embodiment shown in FIGS. 2 and 4 are denoted by the same reference numerals.

[0149] In Comparative Example 1, since Va = 0, the space volume ratio Va / V0 (%) = 0 (%). In Example 4, there was no printing ink in the active area (the area where optical physical properties were measured) except for the peripheral portion of the sheet, and Va = V0. Therefore, Va / V0 (%) = 100 (%).

[0150] In Example 5, an infrared-absorbing ink was prepared by mixing 75% by mass of a UV-curable resin (INKJET-CLC-K-01) manufactured by Natco and 25% by mass of a solar radiation shielding dispersion (YMW-D20) manufactured by Sumitomo Metal Mining Co., Ltd., which is an infrared absorber. Two light diffusion sheets #1 cut into a size of 300 mm × 200 mm were bonded together at the four corners. Heat welding was performed by irradiating an infrared laser using a semiconductor laser (L13920-511(M)) manufactured by Hamamatsu Photonics K.K.

[0151] Specifically, the aforementioned infrared-absorbing ink was dot-printed in a grid pattern on the four corner portions (10 mm square portions) of the matte surface of the first light diffusion sheet #1. The dots were circular dots with a diameter of 50 μm, and the distance between the centers of two adjacent dots was 100 μm. Thereafter, with the surface having the inverted square pyramid-shaped concave portion of the second light diffusion sheet #1 in contact with the surface of the first light diffusion sheet #1 on which the ink was printed, while pressing the two light diffusion sheets #1 from above and below with glass plates, an infrared laser (output 50 W, spot diameter 1.6 mm) was irradiated for 500 milliseconds to bond the two light diffusion sheets #1 together.

[0152] In Example 5, there is no printed ink in the active area (the area where optical physical properties are measured) except for the peripheral portion of the sheet, and Va = V0, so Va / V0 (%) = 100 (%).

[0153] In Reference Example 1, the two light diffusion sheets #1 were laminated such that the matte surface of the first light diffusion sheet #1 was in contact with the surface having the inverted square pyramid-shaped concave portion of the second light diffusion sheet #1 without bonding the two light diffusion sheets #1 together. Therefore, in Reference Example 1, Va = V0, so Va / V0 (%) = 100 (%).

[0154] In Examples 6 to 10, in the same manner as in Example 1, two light diffusion sheets #1 were bonded together using an OCA. Specifically, in Example 6, an OCA with a thickness of 50 μm was attached to the matte surface of the first light diffusion sheet #1 using Aron Tack MF-29 manufactured by Toyo Gosei Co., Ltd. In Example 7, an OCA with a thickness of 25 μm was attached to the matte surface of the first light diffusion sheet #1 using Aron Tack MF-29 manufactured by Toyo Gosei Co., Ltd. In Example 8, an OCA with a thickness of 50 μm was attached to the matte surface of the first light diffusion sheet #1 using Aron Tack MF-25 manufactured by Toyo Gosei Co., Ltd. In Example 9, an OCA with a thickness of 25 μm was attached to the matte surface of the first light diffusion sheet #1 using Aron Tack MF-25 manufactured by Toyo Gosei Co., Ltd. In Example 10, an OCA with a thickness of 50 μm was attached to the matte surface of the first light diffusion sheet #1 using MHM-FWD50 manufactured by Nikkei Shinwa Co., Ltd. In Examples 6 to 9, the two light diffusion sheets #1 were bonded together while heating at a temperature of 60°C.

[0155] In Examples 11 to 13, in the same manner as in Example 7, two light diffusion sheets #1 were bonded together using an OCA. Specifically, an OCA with a thickness of 25 μm was attached to the matte surface of the first light diffusion sheet #1 using Aron Tack MF-29 manufactured by Toyo Gosei Co., Ltd. Next, the two light diffusion sheets #1 were bonded together without heating at room temperature of 23°C in Example 11, while heating at a temperature of 30°C in Example 12, and while heating at a temperature of 40°C in Example 13.

[0156] <Measurement of Peel Strength> The peel strength at the bonding location of the two light diffusion sheets #1 that make up the laminated light diffusion sheet (Examples 1 to 13, Comparative Example 1) after bonding was measured as follows. From each sample of the laminated light diffusion sheet, a test piece with a width of 25 mm and a length of 150 mm was cut out. Using a peel tester (IPTS-5N) manufactured by IMADA, while peeling the two light diffusion sheets #1 from each other in the 180-degree direction at a peel rate of 1000 mm / min, the peel strength was measured. In Example 4, as described above, an ink containing a UV curable resin was printed linearly with a width of 1.7 mm along the four edges of the first light diffusion sheet #1 for bonding. However, a test piece with a width of 25 mm was cut out in a direction perpendicular to the linear printed ink to measure the peel strength. In Example 5, a test piece with a width of 25 mm was cut out so as to include the entire spot portion welded with an infrared laser to measure the peel strength.

[0157] <Measurement of Peel Strength at 85°C> The peel strength at 85°C at the bonding location of the two light diffusion sheets #1 that make up the laminated light diffusion sheet (Examples 6 to 13) after bonding was measured as follows. From each sample of the laminated light diffusion sheet, a test piece with a width of 25 mm and a length of 100 mm was cut out. After holding the test piece in an 85°C atmosphere for 10 minutes, using a tensile tester (Autograph AGX-V) manufactured by Shimadzu Corporation, while peeling the two light diffusion sheets #1 from each other in the 180-degree direction at a peel rate of 50 mm / min in an 85°C atmosphere, the peel strength was measured.

[0158] <Heat Cycle Test> A heat cycle test (reliability test) was conducted on the laminated light diffusion sheets (Examples 6 to 13) after lamination. In the heat cycle test, after putting samples of each laminated light diffusion sheet into a low-temperature constant temperature and humidity chamber (PL-1KP) manufactured by ESPEC, first, the samples were cooled to -40°C, then held at -40°C for 1 hour, then the inside of the low-temperature constant temperature and humidity chamber was heated to 85°C over 40 minutes, then held at 85°C for 1 hour, then the inside of the low-temperature constant temperature and humidity chamber was cooled to -40°C over 40 minutes, then held at -40°C for 1 hour, and then the inside of the low-temperature constant temperature and humidity chamber was heated to 85°C again over 40 minutes. This cooling and heating heat cycle was repeated 96 times.

[0159] <Measurement of Luminance and Luminance Uniformity> In the examples, reference examples, and comparative examples, the measurement of luminance and luminance uniformity was carried out with the configuration of the backlight unit 40 shown in FIG. 2. The laminated light diffusion sheet 100 obtained by laminating two light diffusion sheets #1 was arranged such that the surfaces (the first surfaces 101a and 102a) having the inverted square pyramid-shaped recesses 22 became the light-emitting surfaces (facing the luminance improvement sheet 47). As the plurality of light sources 42, as shown in FIG. 21, an LED array in which 20 LEDs in the vertical direction and 20 LEDs in the horizontal direction were arranged on the reflection sheet 41 was used. Specifically, as the LED array, an array of Cree blue LEDs (XPGDRY-L1-0000-00501) serving as the light source 42 arranged at a pitch of 3.5 mm × 4.5 mm was used. On the light sources (LEDs) 42 arranged in an array, a wavelength selection sheet 43, a color conversion sheet 44, the sample to be evaluated (the laminated light diffusion sheet 100 after lamination), and a luminance improvement sheet 47 (two prism sheets 45 and 46 whose prism extension directions are orthogonal) were arranged, and the measurement of luminance and luminance uniformity was carried out.

[0160] In the measurement of luminance uniformity, first, using the LED array shown in Fig. 21, in the sheet stacking structure of the aforementioned backlight unit 40, the two-dimensional luminance distribution was measured for the surface of the luminance improvement sheet 47 on the uppermost layer using an SR-5000WS manufactured by Topcon Technohouse Co., Ltd. Then, for the actually measured luminance values of all 65,536 pixels (256 pixels × 256 pixels) in the region R of 12 vertical × 9 horizontal light sources 42 (LEDs) among the LED arrays shown in Fig. 21, the average value and the standard deviation were calculated. This average value was used for the evaluation of luminance, and the luminance uniformity was calculated using the average value and the standard deviation of luminance according to the following formula: Luminance uniformity = (Average value of luminance (cd / m 2 )) ÷ (Standard deviation of luminance (cd / m 2 )) The higher the numerical value of the luminance uniformity obtained in this way, the more uniform the luminance indicates.

[0161] <Evaluation and Comprehensive Evaluation of Luminance and Luminance Uniformity> The evaluation of the luminance and luminance uniformity of the examples, comparative examples, and reference examples was carried out according to the following criteria using relative luminance (%) and relative luminance uniformity (%). Note that the relative luminance (%) and relative luminance uniformity (%) are the values of luminance and luminance uniformity measured in Reference Example 1 (laminated without laminating two light diffusion sheets #1), and are calculated as relative values with the value of Reference Example 1 set to 100% by dividing the values of luminance and luminance uniformity measured in each example and comparative example.

[0162] Excellent: Relative value is 90% or more (excellent laminated light diffusion sheet) Good: Relative value is 80% or more and less than 90% (practicable laminated light diffusion sheet) Not acceptable: Relative value is less than 80% (laminated light diffusion sheet with significant deterioration of optical performance due to lamination).

[0163] Also, the comprehensive evaluation of the examples, comparative examples, and reference examples was carried out according to the following criteria.

[0164] Excellent: Peel strength is 5 g weight / 25 mm or more, and both luminance and luminance uniformity are excellent Good: The peel strength is 5 g weight / 25 mm or more, and both the luminance and the luminance uniformity are good. One is good and the other is excellent. Not acceptable: The peel strength is less than 5 g weight / 25 mm, or at least one of the luminance and the luminance uniformity is not acceptable.

[0165] <Evaluation of Examples 1 to 5, Comparative Example 1, and Reference Example 1> In Examples 1 to 5, Comparative Example 1, and Reference Example 1, as described above, a laminated light diffusion sheet was constructed using two sheets of the light diffusion sheet #1 shown in Table 1 cut out into a rectangle of 200 mm × 300 mm, and the relationship between the spatial volume ratio (Va / V0) and the optical physical properties (measurement values of luminance and luminance uniformity, etc.) was evaluated. The results are shown in Table 2 together with the characteristics such as the dimensions, physical properties, bonding method, and peel strength of each laminated light diffusion sheet.

[0166]

Table 2

[0167] As shown in Table 2, in Examples 1 to 5, in the laminated light diffusion sheet in which two sheets of the light diffusion sheet #1 with the reverse square pyramid-shaped recesses arranged at a pitch of 100 μm are bonded together, since the bonding is performed so that the spatial volume ratio (Va / V0) becomes 40% or more, as a result, the effectiveness of the voids in the recesses is maintained, and it can be seen that the luminance is not impaired and the luminance uniformity is also good. In particular, when the spatial volume ratio (Va / V0) is 50% or more (preferably 55% or more), excellent luminance and luminance uniformity are obtained.

[0168] On the other hand, in Comparative Example 1, since the reverse square pyramid-shaped recesses are filled with an ink having a refractive index higher than that of air so that the spatial volume ratio (Va / V0) becomes less than 40%, the light diffusion effect by the reverse square pyramid-shaped recesses is lost, and a laminated light diffusion sheet with low luminance uniformity is obtained.

[0169] As can be seen from the evaluation results of Reference Example 1, when the two light diffusion sheets #1 are not bonded together, the spatial volume ratio (Va / V0) is 100%, and since the light diffusion effect due to the concave portions in the shape of an inverted square pyramid is not adversely affected, good luminance and luminance uniformity can be obtained. However, since the two light diffusion sheets #1 are not bonded together (i.e., the peel strength is 0), the handleability during the assembly of the backlight unit deteriorates.

[0170] <Evaluation of Examples 6 to 10> Regarding Examples 6 to 10 as well, similar to Examples 1 to 5, the relationship between the spatial volume ratio (Va / V0) and the optical properties (measurement values of luminance and luminance uniformity, etc.) was evaluated. Further, as additional evaluations, the measurement of the peel strength at 85°C and the heat cycle test were carried out. The results are shown in Table 3.

[0171]

Table 3

[0172] As shown in Table 3, in Examples 6 to 10, in the laminated light diffusion sheet in which two light diffusion sheets #1 with concave portions in the shape of an inverted square pyramid arranged at a pitch of 100 μm are bonded together, since they are bonded together so that the spatial volume ratio (Va / V0) becomes 40% or more, as a result, the effectiveness of the voids in the concave portions is maintained, and it can be seen that the luminance is not impaired and the luminance uniformity is also good.

[0173] Also, in Examples 6 to 9, the peel strength at 85°C is as high as 100 g weight / 25 mm or more. When the appearance of the laminated light diffusion sheet before and after the heat cycle test was confirmed, no generation of bubbles was observed even after the heat cycle test at -40°C to 85°C, and it can be seen that it is a laminated light diffusion sheet with good heat resistance. On the other hand, in Example 10, the peel strength at 85°C is 4 g weight / 25 mm, generation of bubbles was confirmed at the 11th cycle of the heat cycle test, and at the completion of 96 cycles, the bubbles had greatly expanded.

[0174] <Evaluation of Examples 11 to 13> For Examples 11 to 13, similar to Examples 6 to 10, the relationship between the spatial volume ratio (Va / V0) and optical properties (measurement values such as luminance and luminance uniformity) was evaluated. Further, as additional evaluations, measurement of the peel strength at 85°C and a heat cycle test were conducted. The results are shown in Table 4.

[0175]

Table 4

[0176] As shown in Table 4, in Examples 11 to 13, in the laminated light diffusing sheet in which two sheets of the light diffusing sheet #1 with concave portions in an inverted square pyramid shape arranged at a pitch of 100 μm are bonded together, since they are bonded together so that the spatial volume ratio (Va / V0) becomes 40% or more, as a result, the effectiveness of the voids in the concave portions is maintained, and it can be seen that the luminance is not impaired and the luminance uniformity is also good.

[0177] Also, as shown in Table 4, in Examples 11 to 13, even when the peel strength at 85°C is 10 g weight / 25 mm, 20 g weight / 25 mm, and 40 g weight / 25 mm respectively, no generation of bubbles was observed after the heat cycle test at -40°C to 85°C. According to Examples 11 to 13, it can be seen that if the peel strength at 85°C is 10 g weight / 25 mm or more, a laminated light diffusing sheet with no impaired luminance, good luminance uniformity, and sufficient heat resistance can be obtained.

[0178] (Other Embodiments) As described above, embodiments (including modified examples and examples. The same shall apply hereinafter) of the present disclosure have been described, but the present disclosure is not limited to the above-described embodiments only, and various modifications are possible within the scope of the disclosure. That is, the description of the above-described embodiments is merely illustrative in nature and is not intended to limit the present disclosure, its applications, or its uses.

[0179] For example, the configuration (layer structure, material, etc.) of the laminated light diffusion sheet is not limited to the configuration of the laminated light diffusion sheet 100 of the foregoing embodiment as long as it is a laminated light diffusion sheet including "a first light diffusion sheet in which a plurality of recesses formed in a substantially inverted pyramid or substantially inverted truncated pyramid shape are arranged on a first surface, and a second light diffusion sheet bonded to the first surface of the first light diffusion sheet, the peeling strength at the bonding location being 5.0 g weight / 25 mm or more, and the spatial volume ratio (Va / V0) being 40% or more".

[0180] Also, the configuration of the backlight to which the laminated light diffusion sheet is applied and the liquid crystal display device including the backlight is not limited to the configuration of the backlight unit 40 and the liquid crystal display device 50 of the foregoing embodiment as long as they include "a first light diffusion sheet in which a plurality of recesses formed in a substantially inverted pyramid or substantially inverted truncated pyramid shape are arranged on a first surface, and a second light diffusion sheet bonded to the first surface of the first light diffusion sheet, the peeling strength at the bonding location being 5.0 g weight / 25 mm or more, and the spatial volume ratio (Va / V0) being 40% or more".

[0181] In the foregoing embodiment, when the first light diffusion sheet 101 and the second light diffusion sheet 102 are bonded together with an OCA (optically clear adhesive), an OCA film is attached to the bonding surface. Instead of this, OCA may be applied to the bonding surface.

[0182] Incidentally, the inventors of the present application have found that, due to variations in the ratio (spatial volume ratio Va / V0) of the voids remaining in each recess in a state where a light diffusion sheet in which a plurality of substantially inverted pyramid-shaped recesses are arranged is bonded to another light diffusion sheet, a mottled pattern occurs on the display screen of the liquid crystal display device, resulting in a decrease in luminance and luminance uniformity. Furthermore, the inventors of the present application have found that when a light diffusion sheet in which a plurality of substantially inverted pyramid-shaped recesses are arranged is bonded to another light diffusion sheet, if the other light diffusion sheet also has a plurality of other substantially inverted pyramid-shaped recesses arranged therein and the arrangement direction of the other recesses is different from the arrangement direction of the recesses, the occurrence of the mottled pattern can be suppressed.

[0183] FIG. 22 shows an example of the arrangement direction of the concave portions of the first light diffusion sheet 101 and the second light diffusion sheet 102 that constitute the laminated light diffusion sheet 100 in the backlight unit 40 shown in FIG. 2. FIG. 22 shows a part of each of the first light diffusion sheet 101 and the second light diffusion sheet 102. As shown in FIG. 22, the arrangement direction D1 of the inverted pyramid-shaped concave portions 22 of the first light diffusion sheet 101 (that is, the direction D1 in which the ridge lines 23 partitioning the concave portions 22 of the first light diffusion sheet 101 extend) and the arrangement direction D2 of the inverted pyramid-shaped concave portions 22 of the second light diffusion sheet 102 (that is, the direction D2 in which the ridge lines 23 partitioning the concave portions 22 of the second light diffusion sheet 102 extend) are different. Note that the ridge lines 23 partitioning the concave portions 22 of the first light diffusion sheet 101 extend in the X direction and the Y direction that are orthogonal to each other, and the arrangement direction D1 is the X direction.

[0184] In an actual manufacturing process, after bonding the sheet base material that becomes the first light diffusion sheet 101 and the sheet base material that becomes the second light diffusion sheet 102 so that the arrangement directions of the concave portions 22 of each sheet are different, it is cut to a size suitable for the backlight unit 40 to form the laminated light diffusion sheet 100. Therefore, the end sides of the first light diffusion sheet 101 and the second light diffusion sheet 102 that constitute the laminated light diffusion sheet 100 are aligned.

[0185] Table 5 shows the results of visually checking the presence or absence of mottled patterns while changing the angle formed by the arrangement directions of the concave portions of each sheet in the bonding of the two light diffusion sheets #1 in the above-described Example 1.

[0186]

Table 5

[0187] As shown in Table 5, when the arrangement direction D1 of the concave portions 22 of the first light diffusion sheet 101 is different from the arrangement direction D2 of the concave portions 22 of the second light diffusion sheet 102, even if there is a variation in the spatial volume ratio Va / V0 in each concave portion 22 of the first light diffusion sheet 101, it has been found that the occurrence of moiré patterns and the reduction in luminance and luminance uniformity can be suppressed. Specifically, in order to suppress the reduction in luminance and luminance uniformity, the arrangement direction D1 of the concave portions 22 of the first light diffusion sheet 101 and the arrangement direction D2 of the other concave portions 22 of the second light diffusion sheet 102 are preferably different by 5° or more and 85° or less, more preferably different by 8° or more and 82° or less, and even more preferably different by 15° or more and 75° or less. Further, in a configuration where the arrangement direction D1 of the concave portions 22 of the first light diffusion sheet 101 is different from the arrangement direction D2 of the concave portions 22 of the second light diffusion sheet 102, even when the spatial volume ratio (Va / V0) of the concave portions 22 of the first light diffusion sheet 101 is less than 40%, practically sufficient luminance and luminance uniformity may be obtained.

[0188] In addition, the shapes of the concave portions 22 of the first light diffusion sheet 101 and the concave portions 22 of the second light diffusion sheet 102 are not limited to substantially inverted square pyramids, and may be substantially inverted square frustums, substantially inverted triangular pyramids or substantially inverted triangular frustums, or substantially inverted hexagonal pyramids or substantially inverted hexagonal frustums, etc. By doing so, it becomes easy to regularly arrange the concave portions 22 of the first light diffusion sheet 101 and the concave portions 22 of the second light diffusion sheet 102 two-dimensionally.

Explanation of Reference Numerals

[0189] 1 TFT substrate 2 CF substrate 3 Liquid crystal layer 5 Liquid crystal display panel 6 First polarizing plate 7 Second polarizing plate 21 Base material layer 22 Concave portion 22a Center 23 Ridge line 23a Intersection point 23b Lowest point 40 Backlight unit 41 Reflective sheet 42 Light source 43 Wavelength selection sheet 44 Color conversion sheet 45 First prism sheet 46 Second prism sheet 47 Brightness enhancement sheet 50 Liquid crystal display device 50a Display screen 100 Laminated light diffusion sheet 101 First light diffusion sheet 101a First surface 101b Second surface 102 Second light diffusion sheet 102a First surface 102b Second surface 103 Third light diffusion sheet 103a First surface 103b Second surface 111 Adhesive member 112 Adhesive member 121 Gap

Claims

1. A laminated light diffusion sheet including a first light diffusion sheet having a first surface on which a plurality of recesses each having a substantially inverted polygonal pyramid shape or a substantially inverted polygonal pyramid frustum shape are arranged, and a second light diffusion sheet bonded to the first surface of the first light diffusion sheet, a peel strength at a bonding location between the first light diffusion sheet and the second light diffusion sheet is 5.0 g / 25 mm or more; When the volume of the recess is V0 and the volume of a void remaining in the recess is Va, Va / V0 is 40% or more and 100% or less in a region excluding a peripheral portion of the first surface of the first light diffusion sheet. Laminated light diffusion sheet.

2. The peel strength measured at 85° C. is 10 g / 25 mm or more. The laminated light-diffusing sheet according to claim 1 .

3. The peel strength measured at 85° C. is 100 g / 25 mm or more. The laminated light-diffusing sheet according to claim 1 .

4. The bonding portion is the entire surface of the first surface of the first light diffusing sheet, the peripheral portion, or a plurality of dot-like or linear regions. The laminated light-diffusing sheet according to claim 1 .

5. The recess is formed in a substantially inverted quadrangular pyramid or a substantially inverted truncated quadrangular pyramid shape, The thickness of the first light diffusing sheet is 30 μm or more and 1000 μm or less, the portion in which the recess is provided and the other portion of the first light diffusion sheet are integrally formed from the same material; The laminated light-diffusing sheet according to claim 1 .

6. A plurality of other recesses each having a substantially inverted pyramid shape or a substantially inverted trapezoidal pyramid shape are arranged on one surface of the second light diffusing sheet, The other surface of the second light diffusing sheet is a flat surface or a matte surface, the first surface of the first light diffusion sheet and the other surface of the second light diffusion sheet are bonded together; The laminated light-diffusing sheet according to claim 5 .

7. A plurality of other recesses each having a substantially inverted pyramid shape or a substantially inverted pyramid frustum shape are arranged on one surface of the second light diffusing sheet, The arrangement direction of the recesses is different from the arrangement direction of the other recesses. The laminated light-diffusing sheet according to claim 1 .

8. The recess and the other recess are formed in a substantially inverted square pyramid or a substantially inverted square frustum, a substantially inverted triangular pyramid or a substantially inverted triangular frustum, or a substantially inverted hexagonal pyramid or a substantially inverted hexagonal frustum. The laminated light-diffusing sheet according to claim 7 .

9. The arrangement direction of the recesses differs from the arrangement direction of the other recesses by 8° or more. The laminated light-diffusing sheet according to claim 7 .

10. The Va / V0 is 50% or more. The laminated light-diffusing sheet according to claim 1 .

11. The first light diffusion sheet and the second light diffusion sheet are bonded together by an OCA (optically transparent adhesive). The laminated light-diffusing sheet according to claim 1 .

12. the first light diffusion sheet and the second light diffusion sheet are bonded together by ink containing an ultraviolet curable resin; The laminated light-diffusing sheet according to claim 1 .

13. The first light diffusion sheet and the second light diffusion sheet are bonded to each other by laser welding using an infrared absorbing agent. The laminated light-diffusing sheet according to claim 1 .

14. A laminated light diffusion sheet including a first light diffusion sheet having a first surface on which a plurality of recesses each having a substantially inverted polygonal pyramid shape or a substantially inverted polygonal pyramid frustum shape are arranged, and a second light diffusion sheet bonded to the first surface of the first light diffusion sheet, a peel strength at a bonding location between the first light diffusion sheet and the second light diffusion sheet is 5.0 g / 25 mm or more; A plurality of other recesses each having a substantially inverted pyramid shape or a substantially inverted pyramid frustum shape are arranged on one surface of the second light diffusing sheet, The arrangement direction of the recesses is different from the arrangement direction of the other recesses. Laminated light diffusion sheet.

15. The recess and the other recess are formed in a substantially inverted square pyramid or a substantially inverted square pyramid truncated shape, a substantially inverted triangular pyramid or a substantially inverted triangular pyramid truncated shape, or a substantially inverted hexagonal pyramid or a substantially inverted hexagonal pyramid truncated shape. The laminated light-diffusing sheet according to claim 14 .

16. The arrangement direction of the recesses differs from the arrangement direction of the other recesses by 8° or more. The laminated light-diffusing sheet according to claim 14 .

17. A backlight unit that is incorporated in a liquid crystal display device and guides light emitted from a light source toward a display screen, The laminated light diffusing sheet according to any one of claims 1 to 16 is provided between the display screen and the light source. Backlight unit.

18. a color conversion sheet between the display screen and the light source for converting the wavelength of light emitted from the light source; The backlight unit according to claim 17.

19. The color conversion sheet is disposed between the light source and the laminated light diffusion sheet, or between the display screen and the laminated light diffusion sheet. The backlight unit according to claim 18.

20. The first light diffusion sheet contains 0 parts by mass or more and 10 parts by mass or less of a light diffusion agent relative to 100 parts by mass of a matrix resin. The backlight unit according to claim 17.

21. A backlight unit according to claim 17; A liquid crystal display panel. LCD display device.

22. A liquid crystal display device comprising the liquid crystal display device according to claim 21. Information equipment.

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