JP2021073532A - Light diffusion plate laminated body - Google Patents

Abstract

To provide a light diffusion plate laminated body capable of improving the uniformity of luminance of light emitted from a light source.SOLUTION: A light diffusion plate laminated body 10 includes: a plurality of laminated light diffusion plates 43; and recesses 52a provided as an air layer between the adjacent light diffusion plates 43. At least one of the plurality of light diffusion plates 43 has a concavo-convex shape on one of its surfaces and the concavo-convex shape is formed by providing polygonal pyramids without space on the surface of the light diffusion plate 43.SELECTED DRAWING: Figure 3

Description

The present invention relates to a light diffusing plate laminate used in a backlight unit.

In recent years, flat displays such as liquid crystal displays and plasma displays have been widely used as display devices because they are space-saving and have high definition. Of these, liquid crystal displays are attracting attention and are being developed because they are more power-saving and have high definition.

The liquid crystal display device includes, for example, a thin film transistor (hereinafter referred to as “TFT”) substrate and a color filter (color filter, hereinafter referred to as “CF”) substrate arranged so as to face each other, and a TFT substrate. It is a non-emission type display device provided with a liquid crystal display panel composed of a liquid crystal layer enclosed between the CF substrate and a liquid crystal display panel, and a backlight provided on the back side of the liquid crystal display panel. Then, in the CF substrate, each sub-pixel constituting the pixel is provided with, for example, a colored layer colored in red, green, or blue.

Further, as the backlight, an edge light type (side light type) or a direct type backlight unit that does not use a light guide sheet is provided on the lower surface side of the liquid crystal layer. The direct type backlight unit includes, for example, a light source composed of an optical sheet group consisting of a prism sheet or the like arranged facing the light incident side of the liquid crystal display panel, a diffusion sheet, an LED, or the like, and has a back surface. A light source, a diffusion sheet, and an optical sheet group are disclosed in order from the side (see, for example, Patent Document 1).

Japanese Unexamined Patent Publication No. 2011-129277

Here, in the backlight unit described in Patent Document 1, the diffusion sheet is composed of a transparent resin and transparent fine particles dispersed in the transparent resin, and the difference in refractive index between the transparent resin and the transparent fine particles. However, in the direct backlight unit in which the light source is arranged directly under the screen, the difference in brightness between the portion directly under the light source and the portion between the light sources is large. It has been difficult to sufficiently improve the uniformity of the brightness of the light emitted from the light source.

Therefore, the present invention has been made in view of this point, and provides a light diffusing plate capable of improving the uniformity of the brightness of the light emitted from the light source in the direct type backlight unit. The purpose.

In order to achieve the above object, in the light diffusing plate laminate of the present invention, a plurality of light diffusing plates containing a light diffusing agent are laminated in a resin matrix, and an air layer is provided between adjacent light diffusing plates. One surface of at least one light diffusing plate has a concavo-convex shape, and the concavo-convex shape is a polygonal cone arranged without gaps on the surface of the light diffusing plate.

According to the present invention, in the direct type backlight unit, the light from the light source can be uniformly surface-emitted, so that the uniformity of the brightness of the light emitted from the light source can be improved.

It is sectional drawing of the liquid crystal display device which concerns on 1st Embodiment of this invention. It is sectional drawing for demonstrating the backlight unit in the liquid crystal display device which concerns on 1st Embodiment of this invention. It is sectional drawing for demonstrating the backlight unit in the liquid crystal display device which concerns on 2nd Embodiment of this invention. It is sectional drawing for demonstrating the light diffusing plate which concerns on 2nd Embodiment of this invention. In the light diffusing plate according to the second embodiment of the present invention, while shifting the minute region having a predetermined projected area along the virtual plane, the surface having the uneven shape included in the minute region is approximated by a plane, and the plane is approximated. It is a figure which shows an example of how the inclination angle of the approximate plane is obtained. In the light diffusing plate according to the second embodiment of the present invention, while shifting the minute region having a predetermined projected area along the virtual plane, the surface having the uneven shape included in the minute region is approximated by a plane, and the plane is approximated. It is a figure which shows another example of finding the inclination angle of the approximate plane. It is a figure which shows the state that the light incident from a light source is reflected by the light diffusing plate which concerns on 2nd Embodiment of this invention. It is sectional drawing for demonstrating the backlight unit in the liquid crystal display device which concerns on a modification. It is a figure which shows the luminance distribution of a light source. It is a figure which shows the distribution in the x direction among the luminance distributions shown in FIG.

(First Embodiment)
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a cross-sectional view of a liquid crystal display device according to a first embodiment of the present invention, and FIG. 2 is a cross-sectional view for explaining a backlight unit in the liquid crystal display device according to the first embodiment of the present invention. It is a figure.

As shown in FIG. 1, the liquid crystal display device 1 includes a liquid crystal display panel 2 in which a plurality of pixels are arranged in a matrix, and a front surface side of the liquid crystal display panel 2 (the upper surface side in the drawing, which is the liquid crystal display device 1). The first polarizing plate 3 (hereinafter, may be simply referred to as "polarizing plate 3") attached to the viewer side) and the back surface side (rear surface side, the lower surface side in the drawing) of the liquid crystal display panel 2. The second polarizing plate 4 (hereinafter, may be simply referred to as "polarizing plate 4") attached to the liquid crystal display device 1 (the side opposite to the viewer side) and the liquid crystal display panel 2 are provided on the back surface side. It is equipped with a polarized light unit 5.

As shown in FIG. 1, the liquid crystal display panel 2 includes a TFT substrate 6 which is a first substrate, a CF substrate 7 which is a second substrate arranged to face the TFT substrate 6, and a TFT substrate 6 and a CF substrate 7. A sealing material provided in a frame shape for adhering the liquid crystal layer 8 provided between the two to each other and the TFT substrate 6 and the CF substrate 7 and enclosing the liquid crystal layer 8 between the TFT substrate 6 and the CF substrate 7. (Not shown).

The TFT substrate 6 and the CF substrate 7 are each formed in a rectangular plate shape. Further, the liquid crystal display device 1 includes a plurality of photo spacers (not shown) for regulating the thickness (that is, cell gap) of the liquid crystal layer 8.

The TFT substrate 6 has, for example, an insulating substrate such as a glass substrate or a plastic substrate, a plurality of gate lines provided on the insulating substrate so as to extend parallel to each other, and extend parallel to each other in a direction orthogonal to each gate line. To cover the plurality of source lines provided in the above, each gate line and each intersecting portion of each source line, that is, a plurality of TFTs provided for each sub-pixel Pr, Pg and Pb, and each TFT. A protective film provided, a plurality of pixel electrodes provided in a matrix on the protective film and connected to each TFT, and an alignment film provided so as to cover each pixel electrode (all not shown) are provided. ing.

The CF substrate 7 includes an insulating substrate such as a glass substrate or a plastic substrate, a common electrode provided on the insulating substrate, and an alignment film (all not shown) provided so as to cover the common electrode.

The liquid crystal layer 8 is made of a nematic liquid crystal material having electro-optical characteristics.

<Backlight unit>
As shown in FIG. 2, the backlight unit 5 is a direct type backlight unit in which a light source 22 is arranged on the back surface side of the light diffusing plate 23, and irradiates light rays toward the back surface of the light diffusing plate 23. On the light source 22, the light diffusing plate 23 that collects and diffuses the light incident from the back surface side, the Quantum Dot sheet 25 superimposed on the front surface side of the light diffusing plate 23, and the front surface side of the quantum dot sheet 25. A prism sheet 24 to be arranged and a reflective polarizing film 26 arranged on the surface side of the prism sheet 24 are provided.

The "back surface" referred to here means the back surface of the backlight unit 5 facing the front surface when the exit surface of the backlight unit 5 is the front surface.

<Light source>
The light source 22 is arranged on a surface parallel to the light emitting surface of the backlight unit 5 and emits light toward the light emitting surface side, and the direct type method is adopted in the present embodiment. .. As the light source 22, for example, a light emitting diode (LED) can be used. As the light source 22, a plurality of light emitting diodes arranged along the back surface of the light diffusing plate 23 may be used.

<Light diffuser>
The light diffusing plate 23 has a function of condensing (condensing and diffusing) the light incident from the back surface side while diffusing it toward the normal direction side, in order to uniformly surface-emit the light from the light source 22. belongs to.

The light diffusing plate 23 is provided on the surface side of the light source 22 at a distance from the light source 22, and as shown in FIG. 2, the light diffusing agent 40 is dispersed in the resin matrix 37.

Since the resin matrix 37 of the light diffusing plate 23 needs to transmit light rays, it is formed mainly of a transparent, particularly colorless and transparent synthetic resin. The main component of the resin matrix 37 is not particularly limited, and examples thereof include polyethylene terephthalate, polyethylene naphthalate, acrylic resin, polycarbonate, polystyrene, polyolefin, cellulose acetate, weather-resistant vinyl chloride, and polyimide.

The light diffusing agent 40 of the light diffusing plate 23 is a particle having a property of diffusing light rays, and is roughly classified into an inorganic filler and an organic filler. Examples of the inorganic filler include silica, magnesium silicate, aluminum hydroxide, aluminum oxide, zinc oxide, barium sulfide, or a mixture thereof. Specific materials for the organic filler include, for example, silicone-based diffusing agents such as silicone powder, acrylic resin, acrylonitrile resin, polyurethane, polyvinyl chloride, polystyrene, polyamide, and polyacrylonitrile. The silicone-based diffuser is a spherical fine particle having a siloxane bond, for example, a silicone resin, a silicone rubber, a silicone composite powder which is a spherical powder in which the surface of a spherical silicone rubber powder is coated with a silicone resin, or a combination thereof. Is. Of these, silicone composite powder is preferable.

The shape of the light diffusing agent 40 is not particularly limited, and examples thereof include a spherical shape, a cubic shape, a needle shape, a rod shape, a spindle shape, a plate shape, a scale shape, and a fibrous shape, and among them, excellent light diffusing property. Spherical beads are preferred.

When spherical beads are used, the average particle size D50 of the light diffusing agent 40 based on the volume-based particle size distribution is preferably 0.8 μm or more and 30 μm or less.

<Quantum dot sheet>
The quantum dot sheet 25 has a function of converting light emitted from a light source 22 (for example, blue light) into light having a wavelength of an arbitrary color (for example, green or red) as an emission peak wavelength by the quantum dots. It is a thing.

The quantum dot sheet 25 includes a quantum dot layer containing quantum dots and a binder resin, and a pair of barrier films (both not shown) formed on the light entering surface and the light emitting surface of the quantum dot layer.

The quantum dot sheet 25 converts, for example, blue light having a wavelength of 450 nm into green light having a wavelength of 540 nm and red light having a wavelength of 650 nm. Therefore, by using a light source that emits blue light having a wavelength of 450 nm, the blue light is partially converted into green and red by the quantum dot sheet 25, and the light transmitted through the quantum dot sheet 25 becomes white light.

<Prism sheet>
The prism sheet 24 has a function of refracting light rays incident from the back surface side in the normal direction side.

The prism sheet 24 is provided between the quantum dot sheet 25 and the reflective polarizing film 26, and needs to transmit light rays. Therefore, the prism sheet 24 is formed of a transparent, particularly colorless and transparent synthetic resin as a main component. There is. The prism sheet 24 has a base material layer 35 and a row of protrusions composed of a plurality of convex prism portions 36 laminated on the surface of the base material layer 35. The ridge prism portion 36 is laminated in a stripe shape on the surface of the base material layer 35. The convex prism portion 36 is a triangular columnar body whose back surface is in contact with the front surface of the base material layer 35.

The lower limit of the thickness of the prism sheet 24 (the height from the back surface of the base material layer 35 to the apex of the convex prism portion 36) is preferably 35 μm, more preferably 50 μm. On the other hand, the upper limit of the thickness of the prism sheet 24 is preferably 200 μm, more preferably 180 μm.

Further, the lower limit of the pitch P (see FIG. 2) of the convex prism portion 36 in the prism sheet 24 is preferably 12 μm, more preferably 20 μm. On the other hand, the upper limit of the pitch P of the convex prism portion 36 in the prism sheet 24 is preferably 100 μm, more preferably 60 μm.

The apex angle of the convex prism portion 36 is preferably 85 ° or more and 95 ° or less. Further, as the lower limit of the refractive index of the convex prism portion 36, 1.5 is preferable, and 1.55 is more preferable. On the other hand, the upper limit of the refractive index of the convex prism portion 36 is preferably 1.7.

In FIG. 2, two prism sheets 24 are provided, but two prism sheets may be bonded together to form one.

<Reflective polarizing film>
The reflective polarizing film 26 transmits only the first linearly polarized light component (for example, P-polarized light) in the light emitted from the prism sheet 24, and the second linearly polarized light component orthogonal to the first linearly polarized light component. It has a function of reflecting (for example, S-polarized light) without absorbing it.

Then, the reflected second linearly polarized light component is reflected again to be in a state where the polarized light is eliminated, and in this state, it is incident on the reflective polarizing film 26 again, and the reflective polarizing film 26 In the light incident again, only the first linearly polarized light component is transmitted, and the second linearly polarized light component orthogonal to the first linearly polarized light component is not absorbed and is reflected again.

Then, the above-mentioned steps in the reflective polarizing film 26 are repeated, and the polarization direction of the first linearly polarized light component (transmission axis component) in the reflective polarizing film 26 and the transmission axis direction of the polarizing plate 4 of the liquid crystal display panel 2 are set. By matching, all the light emitted from the backlight unit 5 can be used for image formation on the liquid crystal display panel 2.

As the reflective polarizing film 26, a commercially available film (for example, manufactured by 3M Japan Ltd., trade name: DBEF (registered trademark)) can be used.

Here, in the present embodiment, as shown in FIG. 2, two light diffusing plates 23 are laminated in the thickness direction X of the backlight unit 5, and an air layer 30 is formed between the adjacent light diffusing plates 23. The feature is that the light diffusing plate laminate 10 provided with the above is provided.

With such a configuration, the difference in refractive index between the light diffusing agent 40 and the air layer 30 of the light diffusing plate 23 causes light reflection and scattering at the interface between the light diffusing agent 40 and the air layer 30. The diffusion performance of the entire light diffusing plate 23 is improved, and the light from the light source 22 can be uniformly surface-emitted. As a result, in the direct type backlight unit 5, it is possible to improve the uniformity of the brightness of the light emitted from the light source 22.

Further, in the present embodiment, it is preferable that the separation distance D between the light source 22 and the light diffusing plate laminate 10 is 10 mm or less in the thickness direction X of the backlight unit 5.

This is because when the separation distance D is larger than 10 mm, the brightness is lowered and the thickness of the backlight unit 5 becomes too large, which makes it difficult to reduce the thickness.

The separation distance D is preferably 8 mm or less, more preferably 7 mm or less, from the viewpoint of reducing the thickness of the backlight unit 5 and improving the brightness to save power.

The content of the light diffusing agent in the entire light diffusing plate 23 is preferably 0.3% by mass or more and 8.0% by mass or less. If it is less than 0.3% by mass, the content of the light diffusing agent is small, so that the light diffusing property of the light diffusing agent may not be sufficiently obtained, and if it is larger than 8.0% by mass, it may not be sufficiently obtained. This is because there may be a disadvantage that both the brightness and the uniformity of the brightness are lowered.

(Second Embodiment)
Next, a second embodiment of the present invention will be described. FIG. 3 is a cross-sectional view for explaining the backlight unit in the liquid crystal display device according to the present embodiment, and FIG. 4 is a cross-sectional view for explaining the light diffusing plate according to the present embodiment. Since the overall configuration of the liquid crystal display device is the same as that of the first embodiment described above, detailed description thereof will be omitted here. Further, the same components as those in the first embodiment are designated by the same reference numerals, and the description thereof will be omitted.

As shown in FIGS. 3 to 4, in the present embodiment, instead of the above-mentioned light diffusing plate 23, a light diffusing plate 43 having a pyramid shape is provided.

As shown in FIG. 4, the light diffusing plate 43 has a resin matrix 51 and a concave-convex shape layer 52 formed on the resin matrix 51. Like the resin matrix 37 described above, the resin matrix 51 is composed of, for example, polycarbonate as a base material, and contains, for example, about 0.5 to 4% by mass of a light diffusing agent 51a with respect to 100% by mass of the base material. To do. As the light diffusing agent 51a, a known material can be appropriately used. The concave-convex shape layer 52 is made of, for example, clear polycarbonate, and for example, inverted pyramid-shaped recesses 52a (corresponding to the above-mentioned air layer 30) are two-dimensionally arranged on the surface of the concave-convex shape layer 52. The apex angle θ of the recess 52a is, for example, 90 °, and the arrangement pitch p of the recess 52a is, for example, about 100 μm. The light diffusing plate 43 may have a one-layer structure containing a light diffusing agent and having an uneven shape on the surface. As described above, the light diffusing plate 43 is not limited to the form shown in FIG. For example, the light diffusing plate may have a one-layer structure provided with an uneven shape, or may have a structure of three or more layers including a layer having an uneven shape. Further, the uneven shape layer is not limited to the one in which the inverted pyramid-shaped concave portions are arranged two-dimensionally as described above, and the uneven shape may be arranged at random.

Further, at least one surface of the light diffusing plate 43 has an uneven shape, and a minute region having a predetermined projected area with respect to the virtual plane of the light diffusing plate 43 is two-dimensionally shifted along the virtual plane. When a surface having an uneven shape included in a minute area at each position of the virtual plane is approximated by a plane and the inclination angle formed by the plane approximated by the plane with the virtual plane of the light diffusing plate 43 is obtained, each position is obtained. The ratio of the total area of the minute region having an inclination angle of 30 ° or more to the total area of the minute region of is 30% or more.

Here, the virtual plane of the light diffusing plate 43 means a flat surface that remains after virtually removing irregularities on the light diffusing plate 43. More specifically, the "virtual plane" means a virtual plane provided horizontally so as to be in contact with the deepest portion of the concave and convex recesses. However, "horizontal" here means parallel to the horizontal plane of the light diffusing plate 43, and does not mean horizontal in a strict sense. For example, when the surface of the light diffusing plate 43 opposite to the surface on which the unevenness is provided is a flat surface or a shape close to a flat surface, the virtual surface may be provided so as to be parallel to this surface.

_{FIG. 5A shows a minute region (for example, R 1} , R1) at each position while shifting a minute region having a predetermined projected area along the virtual plane (P) of the light diffusing plate 43 (specifically, the concave-convex shape layer 52). Surfaces having an uneven shape (for example, S ₁ , S ₂ , S ₃ , ...) Included in R ₂ , R _{3, ...)} ) Is approximated to a plane, and the plane (for example, V ₁ , V ₂ , V ₃ , ... ) Is calculated (for example, θ ₁ , θ ₂ , θ ₃ , ...). In FIG. 5A, for the sake of simplicity, the minute region is shifted according to each slope of the unevenness, but in reality, as shown in FIG. 5B, the minute region is two-dimensionally irrespective of the state of the unevenness. I will shift it. At this time, the minute region after the shift may overlap with the minute region before the shift.

According to the present embodiment described above, the micro-region having a predetermined projected area with respect to the virtual plane of the light diffusing plate 43 is shifted along the virtual plane, and has a concave-convex shape included in the micro-region at each position. When the plane is approximated to the plane and the inclination angle of the plane that is approximated to the plane is obtained, the ratio of the total area of the minute region having the inclination angle of 30 ° or more to the total area of the minute region at each position is 30% or more. The uneven shape is controlled so as to be. Therefore, as shown in FIG. 6, for example, a plurality of light sources 22 arranged in a two-dimensional manner on a reflective sheet (for example, a film made of a white polyethylene terephthalate resin, a silver vapor deposition film, or the like) 41. Reflection of light incident on the light diffusing plate 43, specifically, multiple reflection in the light diffusing plate 43, or multiple reflection between the reflection sheet 41 on which the light source 22 is placed and the light diffusing plate 43. Etc. will be promoted. As a result, even if the distance between the light source 22 and the light diffusing plate 43 becomes small in the direct type backlight unit 9 in which a plurality of light sources 22 such as LEDs are arranged, the area between each light source 22 and the light source on the light emitting surface is reduced. It is possible to sufficiently suppress the occurrence of uneven brightness between the two.

In the present embodiment, the number of light sources 22 arranged is not particularly limited, but when a plurality of light sources 22 are arranged in a distributed manner, it is preferable to arrange them regularly on the reflective sheet 41. The regular arrangement means that the light sources are arranged with a certain rule, and for example, the case where the light sources 22 are arranged at equal intervals is applicable. When the light sources 22 are arranged at equal intervals, the distance between the centers of two adjacent light sources 22 may be 0.5 mm or more (preferably 2 mm or more) and 20 mm or less. Further, when the distance between the centers of two adjacent light sources 22 is 0.5 mm or more, a phenomenon (luminance unevenness) in which the brightness is smaller than that of other regions in the region between the adjacent light sources 22 is likely to occur. Therefore, the usefulness of applying the present embodiment is increased.

Further, the uneven shape formed on the surface of the light diffusing plate 43 may not be a uniform shape due to restrictions on processing accuracy in industrial production, and may have some variation (FIG. 5A). reference). In this case, the inclination angle of the surface (approximate plane) of each minute region on the surface of the light diffusing plate 43 provided with the uneven shape varies in the range of 0 to 90 degrees. When the variations are totaled, the uneven shape is controlled so that 30% or more of them have an inclination angle of 30 degrees or more. In particular, when the light diffusing plate 43 is formed using a plastic film, it is difficult to make the shape of the concave portion or the convex portion formed on the surface of the light diffusing plate 43 uniform. The advantage of applying this embodiment on the premise that the angles vary is great.

Further, in the present embodiment, the upper surface of the light diffusing plate 43 (the surface on the prism sheet 24 side) is provided with an uneven shape (recessed portion 52a), but the uneven shape is provided on at least one surface of the light diffusing plate 43. Just do it. That is, uneven shapes may be provided on the lower surface (the surface on the light source 22 side) or both sides (upper surface and lower surface) of the light diffusing plate 43.

The uneven shape provided on the surface of the light diffusing plate 43 is not particularly limited as long as the inclination angle of the surface of the minute region can be measured by a method described later or the like, and for example, the pitch, arrangement, shape, etc. are random. It may have a matte shape or a shape in which a plurality of convex portions and concave portions are regularly arranged two-dimensionally.

Further, the uneven shape provided on the surface of the light diffusing plate 43 may include a shape that can be approximated to a polygonal weight or a polygonal pyramid. Here, as the "polygonal pyramid", a triangular pyramid, a quadrangular pyramid, or a hexagonal pyramid that can be arranged without a gap on the surface of the light diffusion plate 43 is preferable. By arranging a shape that can be approximated to a polygonal weight or a polygonal pyramid on the surface of the light diffusing plate 43 without gaps, it is possible to reduce the area of the portion of the light diffusing plate 43 in the virtual plane where the inclination angle is 0 °. Further, a mold (metal roll) is used in a manufacturing process such as extrusion molding or injection molding when providing an uneven shape on the surface of the light diffusion plate 43, and the accuracy of the cutting work on the surface of the mold (metal roll) is improved. In consideration, a square pyramid may be selected as the "polygonal pyramid".

Examples of the shape of the convex portion include a hemisphere (upper half), a cone, a triangular pyramid, a quadrangular pyramid, a hexagonal pyramid, and the like, and examples of the shape of the concave portion include a hemisphere (lower half), an inverted cone, and an inverted cone. Examples thereof include a triangular pyramid, an inverted quadrangular pyramid, and an inverted hexagonal pyramid.

The shape of the convex portion may be, for example, a substantially hemisphere (upper half), a substantially cone, a substantially triangular pyramid, a substantially quadrangular pyramid, a substantially hexagonal pyramid, or the like. (Lower half), substantially inverted cone, substantially inverted triangular pyramid, substantially inverted quadrangular pyramid, substantially inverted hexagonal pyramid, and the like. Here, "abbreviation" means that it can be approximated, and for example, "substantially quadrangular pyramid" means a shape that can be approximated to a quadrangular pyramid. However, considering the accuracy of industrial production, the convex and concave parts are approximately hemisphere (upper half or lower half), approximately cone (approximately inverted cone), approximately triangular pyramid (approximately inverted triangular pyramid), and approximately quadrangular pyramid (abbreviated). It may be a deformed shape from an inverted quadrangular pyramid), and there may be unavoidable shape variations due to processing accuracy in industrial production.

When a plurality of convex portions and concave portions are regularly arranged two-dimensionally on the surface of the light diffusing plate 43, the plurality of convex portions and concave portions may be provided on the entire surface of the light diffusing plate 43 without gaps. It may be provided at regular intervals (pitch) or at random intervals.

Further, in the present embodiment, if the inclination angle of the surface of the light diffusing plate 43 having an uneven shape can be obtained for each minute region, the method of calculating the inclination angle is not particularly limited, but for example, The following calculation method may be used.

(Procedure 1) Using a laser microscope VK-100 manufactured by KEYENCE, the surface shape of the light diffuser plate 43 is measured at a magnification of 400 times, and automatic tilt correction is performed to obtain 768 pixels in length and 1024 pixels in width. The height data of 522.6 μm × 697 μm) is collected as a CSV file. The height measurement can be performed, for example, as follows. First, the focus position is changed stepwise to acquire a plurality of confocal images to be measured, and then light is emitted for each pixel based on the relationship between the discrete focus position (Z) and the photodetection intensity (I). The intensity change curve (IZ curve) is estimated, and the peak position, that is, the height is obtained from the IZ curve.

(Procedure 2) The height data (digit) collected in step 1 is converted into height data (μm) using the Z calibration value.

(Procedure 3) Using the height data obtained in step 2, the data of a minute area of 4 pixels in length × 4 pixels in width (area (projected area of the light diffusing plate 43 with respect to the virtual plane) is 7.29 μm ² ). Based on this, a plane that approximates the sheet surface included in the minute region is calculated by a known mathematical method.

(Procedure 4) The angle formed by the approximate plane calculated in step 3 with the virtual plane of the light diffusing plate 43 (that is, the plane having a height of 0) is calculated and used as the inclination angle of the minute region.

(Procedure 5) Procedures 3 and 4 are carried out for 500,000 or more (specifically, 779,280) minute areas while shifting the minute areas by 1 pixel in the vertical or horizontal direction.

(Procedure 6) The ratio of the total area of the minute region having an inclination angle of 30 ° or more to the total area of the minute region of 500,000 points or more measured in step 5 (hereinafter, simply "the area having the inclination angle of 30 ° or more". ”) Is calculated.

The calculation of the "ratio of the area having an inclination angle of 30 ° or more" is performed in a target range of 0.5 mm square or more in consideration of processing variations and the like (522.6 μm in procedure 1). It is preferable to obtain it from the height data (in the range of × 697 μm). Of course, in order to improve the data accuracy, it goes without saying that a plurality of target ranges of 0.5 mm square or more may be set, or height data may be acquired with the entire surface of the sheet as the target range. As the target range expands, the number of "small regions" for calculating the tilt angle also increases. There is no particular upper limit to the number of "micro regions" as long as there is no problem in terms of resources such as measurement and data processing. For example, when two target ranges of 0.5 mm square or more are set, the number of "micro regions" is also doubled. Further, even if the target range has the same size, if the number of pixels included in the range increases, the number of "micro regions" also increases. That is, the number of "micro regions" for which the inclination angle is calculated is determined by the size of the target range, the number of pixels included in the target range, the area of the minute region described later, and the like. However, when the target range is 0.5 mm square or more in consideration of processing variations, etc., in order to accurately grasp the uneven shape, at least 100,000 points or more (preferably 300,000 points or more, more preferably 500,000 points or more). The inclination angle may be calculated for a minute region (more than a portion).

Further, in the above-mentioned calculation method of the tilt angle, the tilt angle is calculated while shifting a minute area of 4 pixels in the vertical direction and 4 pixels in the horizontal direction by 1 pixel in the vertical direction or the horizontal direction. The tilt angle may be calculated while shifting a minute area of size by 2 pixels in the vertical direction or the horizontal direction. Alternatively, the tilt angle may be calculated while shifting a minute region having a larger size (for example, 8 pixels in the vertical direction and 8 pixels in the horizontal direction) by 4 pixels in the vertical direction or the horizontal direction. That is, the pixel size of the minute region and the pixel pitch of shifting the minute region can be arbitrarily set as long as the uneven shape can be grasped accurately.

Further, the area of a minute region (projected area of the light diffusing plate with respect to the virtual plane) in the measurement of the tilt angle is not particularly limited as long as it is a sufficiently small area where the reflection characteristics of light from a small light source can be evaluated microscopically. However, in consideration of measurement accuracy, performance of measuring equipment, etc., 0.1 mm ² or less (preferably 0.01 mm ² or less, more preferably 0.001 mm ² or less, still ^{more preferably 0.0001 mm 2} (100 μm ² ) or less). ) (The area of 7.29 μm ² in step 3).

Further, in the present embodiment, since the light diffusing plate 43 has the resin matrix 51 containing the light diffusing agent 51a, the light diffusing in the light diffusing plate 43 is promoted. It is possible to further suppress the uneven brightness between the two.

The material of the light diffusing agent 51a contained in the resin matrix 51 is not particularly limited, but the inorganic particles include, for example, silica, titanium oxide, aluminum hydroxide, barium sulfate and the like, and the organic particles include, for example, acrylic and acrylonitrile. Silicone, polystyrene, polyamide and the like may be used.

The particle size of the light diffusing agent 51a may be, for example, 0.1 μm or more (preferably 1 μm or more) and 10 μm or less (preferably 8 μm or less) from the viewpoint of the light diffusing effect.

Regarding the content of the light diffusing agent 51a, from the viewpoint of the light diffusing effect, the material (matrix) constituting the resin matrix 51 is 100% by mass, for example, 0.1% by mass or more (preferably 0.3% by mass or more). ) 10% by mass or less (preferably 8% by mass or less).

The difference between the refractive index of the light diffusing agent 51a and the refractive index of the matrix of the resin matrix 51 is 0.01 or more, preferably 0.03 or more, more preferably 0.05 or more, still more preferably 0.1 or more, and most. It may be preferably 0.15 or more. If the difference between the refractive index of the light diffusing agent 51a and the refractive index of the resin matrix 51 is less than 0.01, the diffusing effect of the light diffusing agent 51a becomes insufficient.

The main component of the resin matrix 51 is not particularly limited as long as it is a material that transmits light, but for example, acrylic, polystyrene, polycarbonate, MS (methylmethacrylate / styrene copolymer) resin, polyimideterephthalate, polyethylene naphthalate, etc. Cellulole acetate, polyimide or the like may be used.

The thickness of the light diffusing plate 43 of the present embodiment is not particularly limited, but is, for example, 3 mm or less (preferably 2 mm or less, more preferably 1.5 mm or less, still more preferably 1 mm or less) and 0.1 mm or more. May be good. If the thickness of the light diffusing plate 43 exceeds 3 mm, it becomes difficult to achieve a thin liquid crystal display. On the other hand, if the thickness of the light diffusing plate 43 is less than 0.1 mm, it becomes difficult to exert the above-mentioned effect of improving the brightness uniformity.

When the light diffusing plate 43 of the present embodiment has a multi-layer structure (the resin matrix 51 of the lower layer and the concave-convex shape layer 52 of the upper layer), the thickness of the layer (concave-convex shape layer 52) provided with the uneven shape on the surface is , Has a thickness greater than the maximum height or depth of the concave-convex shape. For example, in the case of a layer provided with a convex portion (or concave portion) having a height (or depth) of 20 μm, the thickness is made larger than 20 μm.

The method for manufacturing the light diffusing plate 43 is not particularly limited, but for example, an extrusion molding method, an injection molding method, or the like may be used. The procedure for manufacturing the single-layer light diffusing plate 43 having an uneven shape on the surface by using the extrusion molding method is as follows. First, pellet-shaped plastic particles to which a diffusing agent has been added (in addition, pellet-shaped plastic particles to which no diffusing agent has been added may be mixed) are put into a uniaxial extruder and melted while being heated. After kneading, the molten resin extruded by the T-die is sandwiched between two metal rolls to cool it, then conveyed using a guide roll and cut into single-wafered flat plates by a sheet cutter to diffuse light. The plate 43 is manufactured. Here, by sandwiching the molten resin using a metal roll having an inverted shape of the desired uneven shape on the surface, the inverted shape of the roll surface is transferred to the resin, so that the desired uneven shape is transferred to the surface of the diffusion sheet. Can be shaped. Further, since the shape transferred to the resin does not necessarily mean that the shape of the roll surface is 100% transferred, the shape of the roll surface may be designed by back calculation from the degree of transfer.

When the light diffusing plate 43 having a two-layer structure having an uneven shape on the surface is manufactured by using the extrusion molding method, for example, pellet-shaped plastic particles required for forming each layer are applied to each of the two single-screw extruders. After charging, the same procedure as described above may be carried out for each layer, and the produced sheets may be laminated.

Alternatively, pellet-shaped plastic particles necessary for forming each layer are put into each of the two single-screw extruders, melted and kneaded while heating, and then the molten resin to be each layer is put into one T-die. Then, the laminated molten resin is laminated in the T-die, and the laminated molten resin extruded by the T-die is sandwiched between two metal rolls to be cooled, then conveyed using a guide roll, and single-wafered by a sheet cutter machine. A light diffusing plate 43 having a two-layer structure having an uneven shape on the surface may be produced by cutting it into a flat plate.

Further, in the present embodiment, as the backlight unit 9, a direct type backlight unit in which a plurality of light sources 22 are dispersedly arranged on the back side of the display screen 60 of the liquid crystal display device 1 is used. Therefore, in order to reduce the size of the liquid crystal display device 1, it is necessary to reduce the distance between the light source 22 and the light diffusing plate 43. However, if this distance is reduced, a phenomenon (luminance unevenness) in which the brightness of the display screen 60 of the portion located on the region between the distributed light sources 22 is smaller than that of the other portions is likely to occur.

On the other hand, as described above, using the light diffusing plate 43 having the uneven shape of the present invention on the surface is useful for suppressing the uneven brightness. In particular, in view of the thinning of small and medium-sized liquid crystal displays in the future, the distance between the light source 22 and the light diffusing plate 43 is 15 mm or less, preferably 10 mm or less, more preferably 5 mm or less, further preferably 2 mm or less, and ultimately 0 mm. In this case, the usefulness of the present invention is considered to be even more remarkable.

The above embodiment may be modified as follows.

In the first embodiment, the two light diffusing plates 23 are laminated in the thickness direction X of the backlight unit 5, but as in the backlight unit 50 shown in FIG. 7, three lights are used. The light diffusing plate laminated body 10 in which the diffusing plates 23 are laminated may be provided. In this case, as shown in FIG. 7, two layers of air layers 30 are provided between the adjacent light diffusion plates 23.

And even in such a configuration, the same effect as the above-mentioned backlight unit 5 can be obtained.

Further, the above-mentioned reflective polarizing film 26 may be provided between the light source 22 and the light diffusing plate laminate 10. With such a configuration, it is possible to promote light mixing between the light source 22 and the light diffusing plate laminate 10 without increasing the separation distance D, and to make the light distribution even more uniform.

Further, as described above, the light diffusing plate 43 of the second embodiment is provided with the concave-convex shape layer 52 having a surface provided with the concave-convex shape of the present invention on the resin matrix 51. Alternatively, the light diffusing plate 43 may be configured with a one-layer structure containing a diffusing agent and having an uneven shape on the surface. Alternatively, the light diffusing plate 43 may be configured with a structure of three or more layers including the resin matrix 51 and the concave-convex shape layer 52. Alternatively, the resin matrix 51 and the concave-convex shape layer 52 may be configured as independent light diffusing plates, and both may be laminated or arranged separately. In the latter case, the concave-convex shape layer 52 may be arranged on the light source 22 side. Alternatively, the light diffusing plate 43 may be composed of only the resin matrix 51, and the uneven shape of the present invention may be provided on the lower surface of the prism sheet 24.

Hereinafter, the present invention will be described based on examples. The present invention is not limited to these examples, and these examples can be modified or modified based on the gist of the present invention, and these examples are excluded from the scope of the present invention. is not it.

(Example 1)
First, the direct type backlight unit shown in FIG. 2 was prepared. A light emitting diode (manufactured by Cree, trade name: XPGDRY-L1-0000-00501) was used as the light source. Further, as a light diffusing plate laminate, two light diffusing plates (thickness: 0.5 mm) in which polycarbonate is mixed with silicone-based fine particles as a light diffusing agent and one side has a matte surface and the other side has a mirror surface. An air layer was provided between the light diffusing plates by laminating, and the matte surface was directed toward the surface side. In addition, a quantum dot sheet (manufactured by Hitachi Kasei Co., Ltd.) and two prism sheets (manufactured by 3M Japan Ltd., trade name: BEF-2) are used, and the top of the prism row is the surface in each case. They were arranged so as to project to the side and the ridgelines of the prism rows were orthogonal to each other. As the reflective polarizing film, a commercially available film (manufactured by 3M Japan Ltd., trade name: DBEF (registered trademark)) was used.

Further, the separation distance D between the light source and the light diffusing plate laminate is set to 2.0 mm, and the blending amounts of the light diffusing agent with respect to the entire light diffusing plate are 0.8% by mass, 3.0% by mass, and 8. It was set to 0% by mass.

<Evaluation of brightness uniformity>
Next, in the prepared backlight unit, the light emitting diode was turned on, and the two-dimensional luminance distribution was measured using a two-dimensional color luminance measuring device (manufactured by Highland, trade name: RISA-COLOR / ONE). Then, the resulting two-dimensional intensity distribution (plan view), and obtains the brightness B _{r = 0 mm} at the center position indicating the maximum luminance, the luminance B _{r = 5mm} in the position of the radius of 5mm from the center position, the luminance ratio _{Br = 5 mm} / _{Br = 0 mm} was determined. The higher the luminance ratio _{Br = 5 mm} / _{Br = 0 mm} , the higher the diffusivity of the luminance distribution and the more uniform the luminance of the light emitted from the light source. The above results are shown in Table 1.

<Examination of the separation distance between the light source and the light diffusing plate laminate>
Next, in the above-mentioned backlight unit, the separation distance D between the light source and the light diffusing plate laminate is set to 1.5 mm, 2.0 mm, 2.8 mm, 3.7 mm, 5.0 mm, and 7.0 mm. At the same time, the blending amount of the light diffusing agent with respect to the entire light diffusing plate was set to 3.0% by mass.

Then, by evaluating the uniformity of the brightness described above, the separation distance between the light source and the light diffusing plate laminate was examined. The above results are shown in Table 2.

(Example 2)
As the light diffusing plate laminate, one in which two layers of air layers are provided between the light diffusing plates by laminating three of the above-mentioned light diffusing plates (thickness: 0.3 mm) is used, and further, the light diffusing plate FIG. 7 is the same as in Example 1 except that the blending amounts of the light diffusing agent with respect to the whole are set to 0.3% by mass, 0.8% by mass, 3.0% by mass, and 8.0% by mass. The direct type backlight unit shown in is prepared.

Next, in the same manner as in Example 1 described above, the uniformity evaluation of the brightness and the separation distance between the light source and the light diffusing plate laminate were examined. The above results are shown in Tables 1 and 2.

(Comparative Example 1)
Instead of the above-mentioned light diffusing plate laminate, a light diffusing plate composed of only one of the above-mentioned light diffusing plates (thickness: 1.0 mm) and not provided with an air layer is used, and further, a light diffusing plate is used. Directly below in the same manner as in Example 1 except that the blending amount of the light diffusing agent was set to 0.3% by mass, 0.8% by mass, 3.0% by mass, and 8.0% by mass. A type backlight unit was prepared.

Next, in the same manner as in Example 1 described above, the uniformity evaluation of the luminance and the examination of the separation distance between the light source and the light diffusing plate were carried out. The above results are shown in Tables 1 and 2.

As shown in Table 1, a plurality of (2 or 3) light diffusing plates are laminated in the thickness direction of the backlight unit, and an air layer is provided between adjacent light diffusing plates. _{In Examples 1 and 2 using the laminated body, the brightness ratio Br = 5 mm} / _{Br = 0 mm} is higher than that in Comparative Example 1 in which the air layer is not provided, and the diffusivity of the brightness distribution is high. It is high, and it can be seen that the uniformity of the brightness of the light emitted from the light source is improved.

In particular, in Examples 1 and 2 in which the content of the light diffusing agent in the entire light diffusing plate is 0.3% by mass or more and 8.0% by mass or less, the light emitted from the light source is compared with Comparative Example 1. It can be seen that the uniformity of the brightness of is improved.

_{Further, as shown in Table 2, in Examples 1 and 2, the brightness ratio Br = 5 mm} / when the distance D between the light source and the light diffusing plate laminate is 7 mm or less as compared with Comparative Example 1. _{It can be seen that Br = 0 mm} is high, the luminance distribution is highly diffusive, and the uniformity of the luminance of the light emitted from the light source is improved.

Next, the present invention using a light diffusing plate having a pyramid shape will be described based on examples.

In addition, the calculation of the inclination angle of the surface having the uneven shape in the light diffusing plate of each example and the calculation of the "ratio of the area having the inclination angle of 30 ° or more" in the light diffusing plate of each example are described above. The methods of steps 1 to 6 were used.

Further, the evaluation of the luminance uniformity in each example is performed by the following procedure in order to make a universal evaluation in consideration of the influence of the light emission characteristics of the LED used as the light source and the arrangement of the LEDs. First, after turning on one LED, a light diffuser plate to be evaluated is placed at a certain distance from the LED, and two prism sheets are laminated on the LED so that the ridgelines of each are orthogonal to each other. The two-dimensional plane brightness of the LED image is measured from the upper side of the polarizing sheet in a state where the polarizing sheet (for example, DBEF series manufactured by 3M) is placed on the polarizing sheet, and the change in brightness depending on the distance from the center of the LED is obtained. .. FIG. 8 shows a two-dimensional luminance distribution of an LED image obtained by using RISACOLOR manufactured by HI-LAND for the above-mentioned two-dimensional luminance measurement. Next, a brightness change curve is extracted along a straight line passing through the LED center point (white line extending in the x-axis direction in FIG. 8), and as shown in FIG. 9, the horizontal axis is the distance from the LED center and the vertical axis is the vertical axis. It is represented by a graph in which the relative brightness is set to 1 and the graph width in the horizontal axis direction when the relative brightness is 0.5 is obtained as FWHM (Full Width at Half Maximum). The larger the FWHM, the larger the spread of light and the improved the luminance uniformity. Therefore, the luminance uniformity in each example is evaluated using the FWHM.

Further, polycarbonate (refractive index 1.59) was used as the base resin (matrix) of the light diffusing plate of each example, and silicone (refractive index 1.43) was used as the diffusing agent added to the base resin. That is, in the light diffusing plate of each example, the difference in refractive index between the base resin and the diffusing agent is 0.16.

(Example 3)
The method for manufacturing the light diffusing plate of Example 3 is as follows. First, a base resin and a diffusing agent resin are mixed and a film is formed by extrusion molding, and then one of the two metal rolls is a roll having a matte shape (Ra: 4.5 μm) with a random surface. A roll having a pyramid shape is used as one roll, and both rolls are crimped to a resin film to transfer the surface shape of each roll, and a random mat (embossed mat) shape is formed on one side and a concave pyramid shape is formed on the other side. A single-layer light diffusing plate (thickness: 0.15 mm) was produced.

Table 3 shows the surface shape of the light diffusing plate of Example 3 thus produced. Further, the "ratio of the area having an inclination angle of 30 ° or more" of the concave pyramid-shaped surface of the light diffusing plate of Example 3 was 90%.

Next, the direct type backlight unit shown in FIG. 3 was prepared. A light emitting diode (manufactured by Cree, trade name: XPGDRY-L1-0000-00501) was used as the light source. Further, as the light diffusing plate laminate, one in which an air layer is provided between the light diffusing plates by laminating two of the above-mentioned light diffusing plates is used, and as shown in Table 3, the concave pyramid-shaped surface is on the back surface side ( It turned to the incoming light side). In addition, a quantum dot sheet (manufactured by Hitachi Kasei Co., Ltd.) and two prism sheets (manufactured by 3M Japan Ltd., trade name: BEF-2) are used, and the top of the prism row is the surface in each case. They were arranged so as to project to the side and the ridgelines of the prism rows were orthogonal to each other. As the reflective polarizing film, a commercially available film (manufactured by 3M Japan Ltd., trade name: DBEF (registered trademark)) was used.

Further, the separation distance D between the light source and the light diffusing plate laminate was set to 1.0 mm and 2.0 mm. Then, the FWHM was measured by the above-mentioned method, and the brightness uniformity was evaluated. The above results are shown in Table 3.

(Example 4)
The FWHM was measured and the brightness uniformity was evaluated in the same manner as in Example 3 described above, except that the orientation of the light diffusing plate produced in Example 3 was changed to the orientation shown in Table 3. The above results are shown in Table 3.

(Example 5)
The FWHM was measured and the brightness uniformity was evaluated in the same manner as in Example 3 described above, except that the orientation of the light diffusing plate produced in Example 3 was changed to the orientation shown in Table 3. The above results are shown in Table 3.

(Comparative Example 3)
The method for manufacturing the light diffusing plate of Comparative Example 3 is as follows. First, a base resin and a diffusing agent resin are mixed and a film is formed by extrusion molding, and then one of the two metal rolls is a roll having a matte shape (Ra: 4.5 μm) with a random surface. A mirror surface roll is used as one roll, and both rolls are pressure-bonded to a resin film to transfer the surface shape of each roll. A single-layer light diffusing plate having a random mat shape on one side and a mirror surface on the other side (thickness: 0.3 mm) was prepared.

Table 3 shows the surface shape of the light diffusing plate of Comparative Example 3 produced in this way. Further, the "ratio of the area having an inclination angle of 30 ° or more" of the concave pyramid-shaped surface of the light diffusing plate of Comparative Example 3 was 25%.

Then, instead of the light diffusing plate produced in Example 3, one light diffusing plate of this Comparative Example was used and arranged in the orientation shown in Table 3, in the same manner as in Example 3 described above. The FWHM was measured and the brightness uniformity was evaluated. The above results are shown in Table 3.

(Comparative Example 4)
The FWHM was measured and the brightness uniformity was evaluated in the same manner as in Comparative Example 3 described above, except that the orientation of the light diffusing plate produced in Comparative Example 3 was changed to the orientation shown in Table 3. The above results are shown in Table 3.

(Comparative Example 5)
The method for manufacturing the light diffusing plate of Comparative Example 5 is as follows. First, a base resin and a diffusing agent resin are mixed and a film is formed by extrusion molding, and then one of the two metal rolls is a roll having a matte shape (Ra: 4.5 μm) with a random surface. A mirror surface roll is used as one roll, and both rolls are pressure-bonded to a resin film to transfer the surface shape of each roll. A single-layer light diffusing plate having a random mat shape on one side and a mirror surface on the other side (thickness: 0.1 mm) was prepared.

Table 3 shows the surface shape of the light diffusing plate of Comparative Example 5 thus produced. Further, the "ratio of the area having an inclination angle of 30 ° or more" of the concave pyramid-shaped surface of the light diffusing plate of Comparative Example 5 was 25%.

Then, instead of the light diffusing plate produced in Example 3, three light diffusing plates of this comparative example were used and arranged in the orientation shown in Table 3, in the same manner as in Example 3 described above. The FWHM was measured and the brightness uniformity was evaluated. The above results are shown in Table 3.

(Comparative Example 6)
The FWHM was measured and the brightness uniformity was evaluated in the same manner as in Comparative Example 5 described above, except that the orientation of the light diffusing plate produced in Comparative Example 5 was changed to the orientation shown in Table 3. The above results are shown in Table 3.

(Comparative Example 7)
The method for manufacturing the light diffusing plate of Comparative Example 7 is as follows. First, a base resin and a diffusing agent resin are mixed and a film is formed by extrusion molding, and then one of the two metal rolls is a roll having a matte shape (Ra: 4.5 μm) with a random surface. A mirror surface roll is used as one roll, and both rolls are pressure-bonded to a resin film to transfer the surface shape of each roll. A single-layer light diffusing plate having a random mat shape on one side and a mirror surface on the other side (thickness: 0.15 mm) was prepared.

Table 3 shows the surface shape of the light diffusing plate of Comparative Example 7 produced in this way. Further, the "ratio of the area having an inclination angle of 30 ° or more" of the concave pyramid-shaped surface of the light diffusing plate of Comparative Example 7 was 25%.

Then, instead of the light diffusing plate produced in Example 3, two light diffusing plates of this Comparative Example were used and arranged in the orientation shown in Table 3, in the same manner as in Example 3 described above. The FWHM was measured and the brightness uniformity was evaluated. The above results are shown in Table 3.

(Comparative Example 8)
The FWHM was measured and the brightness uniformity was evaluated in the same manner as in Comparative Example 7 described above, except that the orientation of the light diffusing plate produced in Comparative Example 7 was changed to the orientation shown in Table 3. The above results are shown in Table 3.

As shown in Table 3, in the thickness direction of the backlight unit, a plurality of (two) light diffusing plates having concave pyramid-shaped surfaces are laminated, and an air layer is provided between adjacent light diffusing plates. In Examples 3 to 5 using the diffuser plate laminate, the FWHM value is higher and the luminance distribution is more diffusive than in Comparative Examples 3 to 8 in which the concave pyramid-shaped surface is not provided. It can be seen that the uniformity of the brightness of the light emitted from the light source is improved.

(Example 6)
As a light diffusing plate laminate, three light diffusing plates (thickness 0.2 mm and light diffusing) in which silicone-based fine particles are mixed as a light diffusing agent and one side has a matte surface and the other side has a mirror surface are mixed. One sheet has a light diffusing agent compounded in an amount of 3.0% by mass with respect to the entire plate, and two sheets have a thickness of 0.15 mm and a light diffusing agent compounded in an amount of 0.8 mass% with respect to the entire plate. Sheets) The same as in Example 1 except that two air layers are provided between the light diffusing plates by laminating, and the one having a total thickness of 0.5 mm is used with the matte surface facing the surface side. Then, the direct type backlight unit shown in FIG. 7 was prepared. Two light diffusing plates having a thickness of 0.15 mm were arranged on the front surface side, and a light diffusing plate having a thickness of 0.2 mm was arranged on the back surface side thereof.

Next, the uniformity evaluation of the brightness was performed in the same manner as in Example 1 described above. The above results are shown in Table 4.

(Example 7)
As a light diffusing plate laminate, two light diffusing plates (thickness 0.2 mm and light diffusing) in which silicone-based fine particles are mixed as a light diffusing agent and one side has a matte surface and the other side has a mirror surface. One sheet having a light diffusing agent compounded in an amount of 3.0% by mass based on the entire plate, and one having a thickness of 0.15 mm and a light diffusing agent compounding amount of 0.8% by mass based on the entire plate. Sheets) The same as in Example 1 except that one air layer is provided between the light diffusing plates by laminating, and the one having a total thickness of 0.35 mm is used with the matte surface facing the surface side. Then, the direct type backlight unit shown in FIG. 2 was prepared. A light diffusing plate having a thickness of 0.15 mm was arranged on the front surface side, and a light diffusing plate having a thickness of 0.2 mm was arranged on the back surface side thereof.

Next, the uniformity evaluation of the brightness was performed in the same manner as in Example 1 described above. The above results are shown in Table 4.

(Example 8)
As a light diffusing plate laminate, two light diffusing plates (thickness 0.1 mm and light diffusing) in which silicone-based fine particles are mixed as a light diffusing agent and one side has a matte surface and the other side has a mirror surface are mixed. One sheet having a light diffusing agent compounded in an amount of 3.0% by mass based on the entire plate, and one having a thickness of 0.1 mm and a light diffusing agent compounding amount of 0.8% by mass based on the entire plate. Sheets) The same as in Example 1 except that one air layer is provided between the light diffusing plates by laminating, and the one having a total thickness of 0.2 mm is used with the matte surface facing the surface side. Then, the direct type backlight unit shown in FIG. 2 was prepared. A light diffusing plate having a thickness of 0.1 mm and a blending amount of a light diffusing agent of 0.8% by mass is arranged on the front surface side, and a light diffusing agent having a thickness of 0.1 mm and a blending amount of the light diffusing agent is 3. A 0% by mass light diffuser was placed.

Next, the uniformity evaluation of the brightness was performed in the same manner as in Example 1 described above. The above results are shown in Table 4.

(Example 9)
As a light diffusing plate laminate, two light diffusing plates (thickness 0.1 mm and light diffusing) in which silicone-based fine particles are mixed as a light diffusing agent and one side has a matte surface and the other side has a mirror surface are mixed. One sheet with a light diffusing agent compounded in an amount of 3.0% by mass with respect to the entire plate, and one having a thickness of 0.05 mm and a light diffusing agent compounded in an amount of 0.8 mass% with respect to the entire plate. Sheets) The same as in Example 1 except that one air layer is provided between the light diffusing plates and the total thickness is 0.15 mm, and the matte surface is directed toward the surface side. Then, the direct type backlight unit shown in FIG. 2 was prepared. A light diffusing plate having a thickness of 0.05 mm was arranged on the front surface side, and a light diffusing plate having a thickness of 0.1 mm was arranged on the back surface side thereof.

Next, the uniformity evaluation of the brightness was performed in the same manner as in Example 1 described above. The above results are shown in Table 4.

(Example 10)
As a light diffusing plate laminate, three light diffusing plates (thickness: 0.05 mm) in which silicone-based fine particles are mixed as a light diffusing agent and one side has a matte surface and the other side has a mirror surface. One sheet has a light diffusing agent compounded in an amount of 3.0% by mass with respect to the entire plate, and two sheets have a thickness of 0.05 mm and a light diffusing agent compounded in an amount of 0.8 mass% with respect to the entire plate. Sheets) The same as in Example 1 except that two air layers are provided between the light diffusing plates and a total thickness of 0.15 mm is used with the matte surface facing the surface side. Then, the direct type backlight unit shown in FIG. 7 was prepared. Two light diffusing plates having a thickness of 0.05 mm and a light diffusing agent compounding amount of 0.8% by mass are arranged on the front surface side, and the light diffusing agent compounding amount is 0.05 mm on the back surface side. A 3.0% by mass light diffuser was placed.

Next, the uniformity evaluation of the brightness was performed in the same manner as in Example 1 described above. The above results are shown in Table 4.

(Example 11)
As a light diffusing plate laminate, two light diffusing plates (thickness: 0.05 mm) in which silicone-based fine particles are mixed as a light diffusing agent and one side has a matte surface and the other side has a mirror surface. One sheet with a light diffusing agent compounded in an amount of 3.0% by mass with respect to the entire plate, and one having a thickness of 0.05 mm and a light diffusing agent compounded in an amount of 0.8 mass% with respect to the entire plate. Sheets) The same as in Example 1 except that one air layer is provided between the light diffusing plates by laminating, and the one having a total thickness of 0.1 mm is used with the matte surface facing the surface side. Then, the direct type backlight unit shown in FIG. 2 was prepared. A light diffusing plate having a thickness of 0.05 mm and a blending amount of a light diffusing agent of 0.8% by mass is arranged on the front surface side, and a light diffusing agent having a thickness of 0.05 mm and a blending amount of the light diffusing agent is 3. A 0% by mass light diffuser was placed.

Next, the uniformity evaluation of the brightness was performed in the same manner as in Example 1 described above. The above results are shown in Table 4.

(Comparative Example 9)
Instead of the above-mentioned light diffusing plate laminate, a light diffusing plate in which silicone-based fine particles are mixed as a light diffusing agent and has a matte surface on one side and a mirror surface on the other side (light with a thickness of 0.5 mm). The amount of the light diffusing agent blended with respect to the entire diffusing plate is 0.8% by mass) It is composed of only one sheet and does not have an air layer, except that the matte surface is facing the surface side. , A direct type backlight unit was prepared in the same manner as in the first embodiment.

Next, the uniformity evaluation of the brightness was performed in the same manner as in Example 1 described above. The above results are shown in Table 5.

(Comparative Example 10)
A direct type backlight unit was prepared in the same manner as in Comparative Example 9 except that the blending amount of the light diffusing agent with respect to the entire light diffusing plate was changed to 3.0% by mass.

Next, the uniformity evaluation of the brightness was performed in the same manner as in Example 1 described above. The above results are shown in Table 5.

(Comparative Example 11)
Instead of the above-mentioned light diffusing plate laminate, a light diffusing plate in which silicone-based fine particles are mixed as a light diffusing agent and has a matte surface on one side and a mirror surface on the other side (light with a thickness of 0.35 mm). The amount of the light diffusing agent blended with respect to the entire diffusing plate is 0.8% by mass) It is composed of only one sheet and does not have an air layer, except that the matte surface is facing the surface side. , A direct type backlight unit was prepared in the same manner as in the first embodiment.

Next, the uniformity evaluation of the brightness was performed in the same manner as in Example 1 described above. The above results are shown in Table 5.

(Comparative Example 12)
A direct type backlight unit was prepared in the same manner as in Comparative Example 11 except that the blending amount of the light diffusing agent with respect to the entire light diffusing plate was changed to 3.0% by mass.

Next, the uniformity evaluation of the brightness was performed in the same manner as in Example 1 described above. The above results are shown in Table 5.

(Comparative Example 13)
Instead of the above-mentioned light diffusing plate laminate, a light diffusing plate in which silicone-based fine particles are mixed as a light diffusing agent and has a matte surface on one side and a mirror surface on the other side (light with a thickness of 0.2 mm). The amount of the light diffusing agent blended with respect to the entire diffusing plate is 0.8% by mass) It is composed of only one sheet and does not have an air layer, except that the matte surface is facing the surface side. , A direct type backlight unit was prepared in the same manner as in the first embodiment.

Next, the uniformity evaluation of the brightness was performed in the same manner as in Example 1 described above. The above results are shown in Table 5.

(Comparative Example 14)
A direct type backlight unit was prepared in the same manner as in Comparative Example 13 except that the blending amount of the light diffusing agent with respect to the entire light diffusing plate was changed to 3.0% by mass.

Next, the uniformity evaluation of the brightness was performed in the same manner as in Example 1 described above. The above results are shown in Table 5.

(Comparative Example 15)
Instead of the above-mentioned light diffusing plate laminate, a light diffusing plate in which silicone-based fine particles are mixed as a light diffusing agent and has a matte surface on one side and a mirror surface on the other side (light with a thickness of 0.15 mm). The amount of the light diffusing agent blended with respect to the entire diffusing plate is 0.8% by mass) It is composed of only one sheet and does not have an air layer, except that the matte surface is facing the surface side. , A direct type backlight unit was prepared in the same manner as in the first embodiment.

Next, the uniformity evaluation of the brightness was performed in the same manner as in Example 1 described above. The above results are shown in Table 5.

(Comparative Example 16)
A direct type backlight unit was prepared in the same manner as in Comparative Example 15 except that the blending amount of the light diffusing agent with respect to the entire light diffusing plate was changed to 3.0% by mass.

Next, the uniformity evaluation of the brightness was performed in the same manner as in Example 1 described above. The above results are shown in Table 5.

(Comparative Example 17)
Instead of the above-mentioned light diffusing plate laminate, a light diffusing plate in which silicone-based fine particles are mixed as a light diffusing agent and has a matte surface on one side and a mirror surface on the other side (light with a thickness of 0.1 mm). The amount of the light diffusing agent blended with respect to the entire diffusing plate is 0.8% by mass) It is composed of only one sheet and does not have an air layer, except that the matte surface is facing the surface side. , A direct type backlight unit was prepared in the same manner as in the first embodiment.

Next, the uniformity evaluation of the brightness was performed in the same manner as in Example 1 described above. The above results are shown in Table 5.

(Comparative Example 18)
A direct type backlight unit was prepared in the same manner as in Comparative Example 17, except that the blending amount of the light diffusing agent with respect to the entire light diffusing plate was changed to 3.0% by mass.

Next, the uniformity evaluation of the brightness was performed in the same manner as in Example 1 described above. The above results are shown in Table 5.

As shown in Tables 4 and 5, a plurality of (three) light diffusing plates are laminated in the thickness direction of the backlight unit, and an air layer is provided between adjacent light diffusing plates. In Example 6 using the body, although the total thickness is the same 0.5 mm, the brightness ratio B is compared with Comparative Examples 9 to 10 in which only one light diffusing plate is used and no air layer is provided. _{It can be seen that r = 5 mm} / _{Br = 0 mm} is high, the luminance distribution is highly diffusive, and the uniformity of the luminance of the light emitted from the light source is improved.

Similarly, Example 7 and Comparative Examples 11 to 12 (total thickness: 0.35 mm), Example 8 and Comparative Examples 13 to 14 (total thickness: 0.2 mm), and Examples 9 to 10 and Comparative Example 15 From the comparison between ~ 16 (total thickness 0.15 mm) and Example 11 and Comparative Examples 17-18 (total thickness 0.1 mm), a plurality of (2 or 3) light diffusers are laminated. In addition, in Examples 7 to 11 using the light diffusing plate laminate in which the air layer is provided between the adjacent light diffusing plates, the luminance distribution is highly diffusive and the brightness of the light emitted from the light source is uniform. Can be seen to be improving.

As described above, the present invention is particularly useful for a light diffusing plate laminate used in a liquid crystal display device.

1 LCD display device 2 LCD display panel 3 1st polarizing plate 4 2nd polarizing plate 5 Backlight unit 6 TFT substrate 7 CF substrate 8 LCD layer 9 Backlight unit 10 Light diffuser laminate 22 Light source 23 Light diffuser 24 Prism sheet 25 Quantum dot sheet 26 Reflective polarizing film 30 Air layer 35 Base material layer 36 Convex prism part 37 Resin matrix 40 Light diffuser 43 Light diffuser plate 50 Backlight unit 51 Resin matrix 51a Light diffuser 52 Concavo-convex shape layer 52a Concave D Separation distance between the light source and the laminated light diffuser X Backlight unit thickness direction θ Concave apex angle

Claims (6)

A plurality of light diffusing plates containing a light diffusing agent are laminated in the resin matrix, and an air layer is provided between the adjacent light diffusing plates.
Of the plurality of light diffusing plates, at least one surface of the light diffusing plate has an uneven shape.
The uneven shape is a light diffusing plate laminated body characterized by being polygonal pyramids arranged without gaps on the surface of the light diffusing plate. The light diffusing plate laminate according to claim 1, wherein the number of the light diffusing plates is two or three. The first or second aspect of the light diffusing plate, wherein the content of the light diffusing agent in the entire light diffusing plate is 0.3% by mass or more and 8.0% by mass or less. Light diffusing plate laminate. The light according to any one of claims 1 to 3, wherein the light diffusing plate has an average particle size of 0.8 μm or more and 30 μm or less of the light diffusing agent contained in the resin matrix. Diffuse plate laminate. The light diffusing plate laminate according to any one of claims 1 to 4, wherein the resin matrix is polycarbonate and the light diffusing agent is a silicone-based diffusing agent. The light diffuser has a flat surface that appears when the uneven shape is virtually removed as a virtual plane, and a minute region having a predetermined projected area with respect to the virtual plane is two-dimensionally formed along the virtual plane. When the surface having the uneven shape included in the minute region at each position of the virtual plane is approximated by a plane, and the inclination angle formed by the plane approximated by the plane and the virtual plane is obtained. The ratio of the total area of the minute region having the inclination angle of 30 ° or more to the total area of the minute region at each position is 30% or more. The light diffusing plate laminate according to any one item.

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