JP2013041303A - Optical sheet and display device with optical sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical sheet capable of improving view angle characteristics and suppressing an occurrence of ghost, and a display device with the optical sheet.SOLUTION: At least one layer of a plurality of layers is an optical function sheet layer including prism sections that are juxtaposed along a sheet surface in such a manner as transmitting light, and light absorbing sections that are juxtaposed between the prism sections in such a manner as absorbing light. In a sheet thickness-directional cross section, the prism section is defined as a trapezoid in which a part to face a plasma display panel side is a short upper base and the opposite side of the upper base is the long lower base. When the prism section is formed of a material with a refractive index Np and the light absorbing section is formed of a material with a refractive index Nb, a difference in the refractive indices expressed by Np-Nb is less than 0.01.

Description

  The present invention relates to an optical sheet that is disposed closer to an observer than an image source and can appropriately control image light and external light, and a display device including the optical sheet. The present invention relates to an optical sheet capable of suppressing ghost generation and a display device including the optical sheet.

  In a display device using a flat-plate image source such as a plasma display panel (hereinafter sometimes referred to as “PDP”), an optical sheet is disposed on the viewer side of the PDP. This optical sheet is provided in order to provide high quality image light to the observer. Therefore, the optical sheet is arranged in parallel along the sheet surface, and is arranged between the prism portion that transmits the image light from the PDP and the prism portion, and appropriately blocks or reflects the image light and external light to improve the contrast. And a light absorption part that suppresses ghosts (Patent Document 1, etc.).

  According to the invention described in Patent Document 1, the refractive index difference between the prism portion and the light absorbing portion is 0.05 or less. As an example where the difference is small, the critical angle at which total reflection occurs when the difference in refractive index is 0.01 is shown.

JP 2006-189867 A

  However, in the invention described in Patent Document 1, no consideration is made on a refractive index difference smaller than this, and other conventional optical sheets have not been studied for a refractive index difference smaller than this.

  On the other hand, the demands on the performance of optical sheets, particularly the improvement of viewing angle characteristics and the suppression of ghost generation have been further increased recently, and it is often necessary to provide an optical sheet that places importance on these.

  In view of the above problems, it is an object of the present invention to provide an optical sheet that can further improve viewing angle characteristics and suppress the occurrence of ghosts as compared to the conventional art, and a display device including the optical sheet.

  The present invention will be described below. In order to facilitate understanding of the present invention, reference numerals in the accompanying drawings are appended in parentheses, but the present invention is not limited to the illustrated embodiment.

  The invention according to claim 1 is an optical sheet (10, comprising a plurality of layers arranged on the viewer side from the plasma display panel (2) and controlling the light from the plasma display panel to be emitted to the viewer side. 20, 30), and at least one of the plurality of layers absorbs light between the prism portions and the prism portions (12, 12,...) Arranged in parallel along the sheet surface so as to transmit light. The optical functional sheet layer (11) having light absorbing portions (13, 13,...) That are arranged in parallel, and the prism portion has a short portion that should face the plasma display panel side in the sheet thickness direction cross section. Np-Nb when the bottom and the upper base are trapezoids having a long lower base, the prism portion is formed of a material having a refractive index Np, and the light absorbing portion is formed of a material having a refractive index Nb. In the table Refractive index difference to be to solve the above problems by providing an optical sheet being smaller than 0.01.

  As for invention of Claim 2, the light absorption part (13,13, ...) in the optical sheet (10,20,30) of Claim 1 was formed only with the material which comprises this light absorption part. In the measurement of the transmittance of a sheet having a thickness of 6 μm, the light absorption performance is such that the transmittance is 40 to 70%.

  Here, “transmittance” means the ratio of luminance before and after placing the sheet to be measured, and takes a value of 100% at the maximum.

  According to a third aspect of the present invention, in the cross section in the sheet thickness direction of the optical sheet (10, 20, 30) according to the first or second aspect, the light absorption portion (13, 13,...) It is a triangle having a base on the sheet surface side.

  According to a fourth aspect of the present invention, in the cross section in the sheet thickness direction of the optical sheet (10, 20, 30) according to the first or second aspect, the light absorbing portion (13, 13,...) The trapezoid has a long lower base on the sheet surface side and a short upper base on the sheet surface side which is the lower base side of the prism portion.

  According to a fifth aspect of the present invention, there is provided an optical sheet (10, 20, 30) according to any one of the first to fourth aspects, wherein the prism portion (12, 12,. The oblique side of the trapezoid included in the above is characterized in that it is larger than 0 degree and not larger than 10 degrees with respect to the normal of the sheet surface.

  The invention according to claim 6 is characterized in that the hypotenuse in the optical sheet (10, 20, 30) according to claim 5 is formed of a polygonal line or a curve.

  Here, when the hypotenuse has a curved shape, the angle formed by the curve and the normal of the sheet surface is obtained as follows. The curve is divided into 10 equal parts in the sheet thickness direction, and the end points of the obtained curves are connected to obtain a straight line. And the angle which each straight line obtained and the normal line of a sheet surface make is all greater than 0 degree and 10 degrees or less.

  The invention according to claim 7 has an average particle diameter of 1 μm or more in the light absorbing portion (13, 13,...) In the optical sheet (10, 20, 30) according to any one of claims 1 to 6. It contains light absorbing particles.

  Here, “average particle size of 1 μm” in the case of “average particle size of 1 μm or more” is intended for particles having a particle size of 0.5 μm or more and smaller than 1.5 μm in the particle size measurement by the weight distribution method. In the particle size distribution, it means that the standard deviation is 0.3 or more.

  The invention according to claim 8 is characterized in that Np and Nb in the optical sheet (10, 20, 30) according to any one of claims 1 to 7 have a value of 1.49 to 1.56. And

  In the invention according to claim 9, the prism portion and the light absorbing portion of the optical function sheet layer in the optical sheet according to any one of claims 1 to 8 have a predetermined cross section and extend in the longitudinal direction. In addition, two optical function sheet layers are stacked, and the two optical function sheet layers are stacked so that the longitudinal directions of one and the other are perpendicular to each other.

  Invention of Claim 10 is equipped with a plasma display panel and the optical sheet as described in any one of Claims 1-9 arrange | positioned at the image light emission side of a plasma display panel, It is characterized by the above-mentioned. The above-described problem is solved by providing a display device.

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to provide an optical sheet which can improve a viewing angle characteristic compared with the past, and can suppress generation | occurrence | production of a ghost, and a display apparatus provided with this optical sheet.

It is the figure which showed the cross section of the optical sheet of this invention concerning 1st embodiment, and represented the layer structure typically. It is the figure which expanded and showed a part of optical sheet shown in FIG. It is the figure which expanded and showed a part of optical sheet of this invention concerning a modification. It is the figure which expanded and showed a part of optical sheet of this invention concerning the example whose light absorption part is trapezoid. It is the figure which showed the cross section of the optical sheet of this invention concerning 2nd embodiment, and represented the layer structure typically. It is the figure which showed the cross section of the optical sheet of this invention concerning 3rd embodiment, and represented the layer structure typically. It is the figure which showed typically the layer structure of PDP and an optical sheet in the scene where the optical sheet of this invention was attached to the plasma television. It is the figure which showed typically the layer structure of PDP and an optical sheet in the scene where the optical sheet of this invention was attached to the plasma television of another form. It is a figure for demonstrating the optical path of image light. It is a figure for demonstrating the optical path of the image light which causes a ghost image. It is a graph which shows the relationship between a viewing angle and relative brightness | luminance among the results of an Example.

  The above-described operation and gain of the present invention will be clarified from embodiments for carrying out the invention described below. Hereinafter, the present invention will be described based on embodiments shown in the drawings.

  FIG. 1 is a diagram schematically showing a layer structure of a cross section of an optical sheet 10 according to the first embodiment of the present invention. In FIG. 1, some repetitive symbols may be omitted for the sake of clarity (the same applies to the following drawings). The optical sheet 10 includes an optical function sheet layer 11, a PET film layer 16 as a base material layer, and an adhesive layer 17. Each of the layers extends in the back / front direction of the paper while maintaining the cross section shown in FIG. Each layer will be described below.

  The optical functional sheet layer 11 includes prism sections 12, 12,... That are substantially trapezoidal in the thickness direction cross section of the optical sheet 10, and a light absorbing section 13, disposed between the prism sections 12, 12,. 13, and so on. FIG. 2 shows an enlarged view focusing on one light absorbing portion 13 and the prism portions 12 and 12 adjacent thereto. The optical function sheet layer 11 will be described with reference to FIGS. 1 and 2 and the drawings appropriately shown.

  The prism portions 12, 12,... Are elements having a substantially trapezoidal cross section arranged such that one sheet surface side is an upper base and the other sheet surface side is a lower base. The prism parts 12, 12,... Are made of a light transmissive resin having a refractive index of Np. This is usually formed of, for example, epoxy acrylate having a characteristic of being cured by ionizing radiation, ultraviolet rays or the like. The size of Np is not particularly limited, but is preferably 1.49 to 1.56 from the viewpoint of availability of applicable materials.

  Accordingly, the image light is provided to the observer by transmitting the image light through the prism portions 12, 12,.

  The light absorbing parts 13, 13,... Are parts disposed between the prism parts 12, 12,. The light absorbing parts 13, 13,... Have a substantially triangular shape with the upper base side of the prism parts 12, 12,. . The light absorption parts 13, 13,... Include a binder part 14 filled with a substance having a refractive index of Nb, and light absorption particles 15, 15,... Mixed in the binder part 14.

  The external light is incident on and absorbed by the light absorbing portions 13, 13,..., So that the influence of the external light on the image light can be reduced and the contrast can be improved.

  The binder material filled in the binder part 14 is made of a material having a refractive index Nb. Although the magnitude | size of Nb is not specifically limited, From a viewpoint of the availability of the material to apply, it is preferable that it is 1.49-1.56. The material used as the binder material is not particularly limited, and examples thereof include urethane acrylate having characteristics of being cured by ionizing radiation, ultraviolet rays, and the like.

  Here, the difference between Np and Nb in the optical sheet 10 of the present invention is configured such that Np−Nb is smaller than 0.01. As a result, it is possible to improve viewing angle characteristics and suppress the occurrence of ghosts. The reason will be described in detail later.

  The light-absorbing particles 15, 15,... Are preferably particles having an average particle diameter of 1 μm or more from the viewpoint of availability and handling, and this is colored to a predetermined concentration with a pigment such as carbon or a dye such as red, blue, or yellow. Has been. For this, for example, commercially available colored resin fine particles can be used. The refractive index Nr of the light absorbing particles 15, 15,... Is not particularly limited.

  Here, the light absorption performance of the light absorbing portions 13, 13,... Can be adjusted as appropriate depending on the purpose. However, in the transmittance measurement of a sheet having a thickness of 6 μm formed only from the material constituting the light absorbing portion, It is preferable that the light absorption performance is such that the rate is 40 to 70%. The means for adjusting the transmittance to 40 to 70% is not particularly limited, and examples thereof include adjusting the content of light absorbing particles and light absorbing performance.

  Further, the angle θ of the oblique sides (two sides extending in the sheet thickness direction) of the light absorbing portions 13, 13,... With respect to the sheet surface normal can be changed according to the purpose and is not particularly limited. However, in the case of a normal display device, from the viewpoint of appropriately reflecting and absorbing external light and image light, it is preferably greater than 0 degree and 10 degrees or less, and more preferably greater than 0 degrees and 6 degrees or less. preferable.

As shown in FIGS. 1 and 2, the shape of the optical function sheet layer 11 is such that the prism portions 12, 12,... Have a substantially trapezoidal cross section, and are formed between the light absorbing portions 13, 13, ... has a triangular cross-section. However, if the light can be controlled appropriately, these shapes are not particularly limited, and appropriate shapes are appropriately adopted. FIG. 3 shows a modification. FIG. 3 is a view corresponding to FIG. 2 and shows one light absorbing portion 13 ′ in the optical function sheet layer 11 ′ and prism portions 12 ′ and 12 ′ arranged on both sides thereof. As can be seen from FIG. 3, the hypotenuse in the cross section of the light absorbing portion 13 ′ (the hypotenuse of the prism portions 12 ′ and 12 ′) is not from one hypotenuse, but two oblique sides 13a ′, 13a ′, 13b ′, and 13b ′. It is composed of That is, the cross section has a polygonal oblique side. Specifically, the oblique sides 13a ′ and 13a ′ arranged on the upper base (short side bottom) side (left side of the paper surface) of the prism portions 12 ′ and 12 ′ have an angle θ ₁ with respect to the normal of the sheet surface of the optical sheet. Have. On the other hand, the oblique sides 13b ′ and 13b ′ arranged on the lower bottom (long side bottom) side (right side of the sheet) of the prism portions 12 ′ and 12 ′ have an angle θ ₂ with respect to the normal of the sheet surface of the optical sheet. doing.

It is preferable that the angles θ ₁ and θ ₂ have a relationship of θ ₁ > θ ₂ and both are in the range of greater than 0 degree and less than 10 degrees. A more preferable angle is greater than 0 degree and 6 degrees or less. Further, the two oblique sides 13a ′ and 13b ′ intersect in the thickness direction of the optical function sheet layer 11 ′ (left and right direction in the drawing) at a position divided into T1 and T2. T ₁ and T ₂ are preferably the same size.

  The modification is an example constituted by two hypotenuses, but may be formed in a polygonal line shape in the cross section by comprising more hypotenuses. Furthermore, this may be curved.

  In the present embodiment, the case where the light absorbing portion is substantially triangular has been described and described, but the shape of the light absorbing portion is not limited to this, and may be a trapezoid. FIG. 4 shows the light absorbing portion 13 ″ of the optical functional sheet layer 11 ″ of the optical sheet and the prism portions 12 ″ and 12 ″ adjacent thereto in the example where the light absorbing portion is trapezoidal. Here, as shown in FIG. 4, the light absorbing portion 13 ″ has a trapezoidal shape. At this time, the long base (lower base) of the trapezoid is the upper base side of the prism portion 12 ″, and the short base (upper base) is the prism portion. It can be placed on the bottom side of 12 ″. Here, the length of the upper base indicated by B in FIG. 4 is preferably in the range of 2 to 25 μm.

  Returning to FIG. 1, another configuration of the optical sheet 10 will be described. The PET film layer 16 is a film layer serving as a base for forming the optical functional sheet layer 11 on the PET film layer 16 and is formed mainly of PET. The PET film layer 16 only needs to contain PET as a main component, and may contain other resins. Here, the main component means 50% by mass or more based on the whole PET film layer. Various additives may be added. Examples of general additives include phenol-based antioxidants, lactone-based stabilizers, and the like.

  As will be described later, the pressure-sensitive adhesive layer 17 is a layer in which a pressure-sensitive adhesive for adhering the optical sheet 10 to another sheet or member disposed in the plasma television 1, for example, is disposed. The material of the pressure-sensitive adhesive used for the pressure-sensitive adhesive layer 17 is not particularly limited as long as it transmits light and can appropriately bond the optical sheet 10 to other materials. Examples thereof include an acrylic copolymer, and the adhesive strength thereof is, for example, about several N / 25 mm to 20 N / 25 mm.

  The optical sheet 10 is manufactured as follows, for example. A liquid material serving as a material for the prism portion is applied to one surface side of the PET film layer 16. Next, the prism portions 12, 12,... Are formed by irradiating with ultraviolet rays in a state where the material to be the prism portion is sandwiched between the roll mold for forming the prism portion shape and the PET film. . Then, between the prism portions 12, 12,..., A transparent resin liquid material serving as a material for the binder portion in which black light-absorbing particles are dispersed is filled, and excess material is removed by squeegeeing the ultraviolet light. It is cured by irradiation. Thereby, the light absorption parts 13, 13,... Are formed.

  FIG. 5 is a cross-sectional view of the optical sheet 20 of the present invention according to the second embodiment, schematically showing the layer configuration. The optical sheet 20 is configured such that another optical functional sheet layer 21 is sandwiched between the optical functional sheet layer 11 and the PET film layer 16 of the optical sheet 10 of the first embodiment. At this time, the prism portion 22 and the light absorbing portion (not shown in the drawing) are arranged so as to be orthogonal to the prism portions 12, 12,... And the light absorbing portions 13, 13,. Accordingly, the prism portions 22 and the light absorbing portions of the optical function sheet layer 21 are alternately arranged in parallel in the back / front direction of the drawing. Since the configuration of each layer provided in the other optical sheet 20 is the same as that of each configuration in the optical sheet 10, the description thereof is omitted here.

  FIG. 6 is a view schematically showing the layer structure of the optical sheet 30 of the present invention according to the third embodiment. The optical sheet 30 includes an optical function sheet layer 11, a PET film layer 16 as a base material layer, and an adhesive layer 17. Each of the above layers extends in the back / front direction of the paper while maintaining the cross section shown in FIG.

  The optical sheet 30 is characterized in that the pressure-sensitive adhesive layer 17 is provided on one surface side of the optical function sheet layer 11 and on the side opposite to the surface on which the PET film layer 16 is disposed. Even if the pressure-sensitive adhesive layer 17 is arranged in this manner, the optical sheet of the present invention can be obtained. About each layer with which the optical sheet 30 is provided, since it is common in the description in the optical sheet 10, description is abbreviate | omitted here. Such a layer configuration of the optical sheet 30 enables the optical sheet 30 to be directly attached to the PDP 2 (see FIG. 8) and stacked as will be described later.

  About the base material layer comprised in the optical sheets 10, 20, and 30 of the present invention described above, PET is not necessarily used as a material, and other than that, polybutylene terephthalate resin (PBT) or polytrimethylene terephthalate ( A “polyester resin” such as a PTT resin can be used. In the present embodiment, it has been described that a resin having PET as a main component is a preferable material from the viewpoint of mass productivity, price, availability, etc. in addition to performance.

  Further, the optical sheet of the present invention includes a layer that blocks electromagnetic waves, a layer that blocks infrared rays, a layer that blocks neon lines, a layer that corrects color tone, a layer that prevents reflection, a layer that prevents charging, and an antiglare layer Etc. may be provided.

  Next, a configuration when the optical sheet 10 of the present invention as described above is attached to the plasma television 1 as a display device will be described. FIG. 7 is a diagram schematically showing a layer structure of the PDP 2 and the optical sheet 10 when the optical sheet 10 is disposed on the image output side of the PDP 2 and the PDP 2 and the optical sheet 10 are provided in the plasma television 1. . In FIG. 7, the right side of the drawing is the observer side. Although the case where the optical sheet 10 is applied will be described here, the same applies to the optical sheet 20.

  As shown in FIG. 7, the optical sheet 10 of the present invention is arranged on the viewer side with a gap indicated by A with respect to the PDP 2 that is the image source. Further, on the viewer side of the pressure-sensitive adhesive layer 17, various layers (3, 4, 5) having functions of the glass plate 6 and AS, AR, and AG are provided. Here, “AS” is an abbreviation of “antistatic” and means an antistatic function. “AR” is an abbreviation for “anti-reflection” and a function for suppressing light reflectance, and “AG” is an abbreviation for “anti-glare” and is a function that can prevent glare on the prism surface.

  Here, it is preferable that the AG layer is disposed closest to the viewer in view of its properties, and AR and AG may be formed of a single film having both properties. Further, as various layers provided as examples, various layers of AS, AR, and AG are given as examples, but other layers having other functions can be provided as necessary. Examples thereof include a layer that blocks electromagnetic waves, a layer that blocks infrared rays, a layer that blocks neon wires, and a toning layer.

  FIG. 8 shows a case where the optical sheet 30 is applied in another example of the plasma television 1 ′. FIG. 8 is a view corresponding to FIG. 7, in which the optical sheet 30 is arranged on the image output side of the PDP 2, and the layer structure of the PDP 2 and the optical sheet 30 when the PDP 2 and the optical sheet 30 are provided in the plasma television 1 ′. FIG. In FIG. 8, the right side of the drawing is the observer side.

  As can be seen from FIG. 8, in the plasma television 1 ′, the optical sheet 30 is directly laminated on the image output side of the PDP 2 by the arrangement of the adhesive layer 17 of the optical sheet 30. This is referred to as a so-called direct attachment method, and the display device can be further thinned. Even with the direct pasting method, the display device of the present invention can be obtained.

  Next, the optical path will be described. In general, it is known that light incident on an interface of substances having different refractive indexes is refracted. And as seen in Snell's law, the degree of refraction is due to the difference in refractive index between the two substances that form the interface, and depending on the difference and the angle of incident light, total reflection at the interface does not occur. Well known. In the optical sheet, the interface between the binder portions 14 and 114 and the prism portions 12 and 112 (hereinafter sometimes simply referred to as “interface”) becomes a problem.

  FIG. 9 is a diagram for explaining the optical path of the image light. FIG. 9 (a) is an example of the present invention, and FIG. 9 (b) is a diagram for explaining a conventional example, both of which include one light absorbing portion 13, 113 and prism portions 12, 12 adjacent thereto. 112 and 112 are shown. In the optical sheet 10 of the present invention, since the refractive index difference between the binder portion 14 and the prism portion 12 is suppressed to be smaller than 0.01 as described above, total reflection hardly occurs. Thus, as shown in FIG. 9A, even if the image light Le10 is incident at a shallow angle with respect to the interface (image light incident at φ3 with respect to the normal of the interface), the image light Le10 is It enters into the light absorption part 13, becomes light Lk10, and is absorbed by the light absorption particles 15, 15,. Here, even if the refractive index difference (Np−Nb) is negative, total reflection does not occur regardless of the magnitude of the difference, and the same effect as described above is obtained.

On the other hand, since the refractive index difference of the conventional optical sheet is larger than that of the optical sheet 10, as shown in FIG. 9B, the image light Le110 incident on the interface at a shallow angle (relative to the normal of the interface). The image light incident at φ3 is totally reflected and emitted to the viewer as light Lf110 (image) indicated by a broken line. At this time, since the interface is inclined at a predetermined angle with respect to the normal of the sheet surface, the light Lf110 is emitted at an angle closer to the normal of the sheet surface than the light Le110. That is, the light emitted after being totally reflected at the interface is converted to an angle close to the normal of the sheet surface and emitted. Then, the light Le101 that normally passes through the prism portion 112, which is light that is originally near the normal line of the sheet surface, is combined with the light Le101 and the like, and only the image at a viewing angle close to the front tends to be bright. This causes a phenomenon in which the brightness is suddenly lowered at an angle deviated from the front, which is a cause of uneven brightness (non-uniformity) in the screen.
However, according to the optical sheet 10 of the present invention, as described above, light that may be emitted in a form close to the normal line of the sheet surface can be absorbed, so that this phenomenon is suppressed (viewing angle characteristics). Improvement), it is possible to reduce the brightness unevenness in the screen (improve uniformity).

On the other hand, the ghost image is as follows. FIG. 10 is a diagram for explaining the optical paths of the light beams Lg20 and Lg120 that may cause a ghost image. FIG. 10 (a) is an example of the present invention, and FIG. 10 (b) is a diagram for explaining a conventional example, both of which include one light absorbing portion 13, 113 and prism portions 12, 12 adjacent thereto. 112 and 112 are shown. The light Lg 120 also undergoes total reflection under the same conditions as the image light.
The ghost image is reflected from the sheet surface, the sheet interface, the PDP surface, etc. before the image light emitted from a pixel having a PDP reaches the observer, and is viewed from the prism portion at a position separated from the certain pixel. Is one of the causes of the occurrence. That is, the lights Lg20 and Lg120 shown in FIG. 10 reach the light beam Lg20 and Lg120 that have arrived here due to repeated reflection of image light emitted from the pixels located at spaced positions above the paper surface.

  On the other hand, in the optical sheet 10 of the present invention, since the difference in refractive index between the binder part 14 and the prism part 12 is suppressed to be smaller than 0.01 as described above, total reflection hardly occurs. Accordingly, as shown in FIG. 10A, even if the light Lg20 that causes the ghost image is incident on the interface at a shallow angle (incident at φ3 with respect to the normal of the interface), this is converted into the light absorbing portion as the light Lk20. 13 and is absorbed by the light-absorbing particles 15, 15,. Here, even if the refractive index difference (Np−Nb) is negative, total reflection does not occur regardless of the magnitude of the difference, and the same effect as described above is obtained.

  On the other hand, in the conventional optical sheet, as shown in FIG. 10B, the light Lg120 (image light incident at φ3 with respect to the normal of the interface) that can be a ghost image incident on the interface at a shallow angle is totally reflected. Then, the light Lf120 indicated by the broken line is emitted to the viewer side. Therefore, this is recognized by the observer as a ghost image.

  As described above, according to the optical sheet 10 of the present invention, since a part of light that can cause a ghost image can be absorbed before it is provided to an observer, generation of a ghost image can be suppressed. It becomes possible.

  As described above, the optical sheet of the present invention and the display device including the optical sheet can further improve the viewing angle characteristics and the ghost generation as compared with the related art.

  Examples of the optical sheet having the above configuration will be described below in more detail. However, the present invention is not limited to the scope of the examples.

  As an example, viewing angle characteristics and ghosts were evaluated in each optical sheet in which the refractive index difference between the prism portion and the binder portion was changed. The conditions and results will be described below.

<Test sample>
As a test sample, an optical sheet having a different refractive index difference between the prism portion and the binder portion was manufactured. Table 1 shows the details.

  Here, the refractive index difference is a value obtained by subtracting the refractive index Nb of the binder portion from the refractive index Np of the prism portion.

<Viewing angle characteristics>
The viewing angle characteristics were measured by measuring the relative luminance at each viewing angle. Here, the viewing angle means the angle between the normal line of the screen from the center of the screen and the line of sight toward the center of the screen. The sign of the viewing angle is positive in the upper part of FIG. 1 and negative in the lower part of the figure. The relative luminance means the ratio (ratio) of the luminance when the optical sheet is arranged when the luminance when the optical sheet is not arranged is 100%. The measurement was performed for each angle with an automatic variable angle photometer (Murakami Color Research Laboratory, GP-500).

<Ghost evaluation>
The presence or absence of the ghost image was visually evaluated. The case where there was no or little ghost occurrence was marked with “◯”, and the case where ghost occurrence was evident was marked with “X”.

  The results are shown in Table 2 and FIG. In FIG. 11, the figure of the refractive index difference is represented, and the graph corresponding to this is indicated by an arrow.

  Here, the viewing angle characteristics in Table 2 were determined as follows. Based on the relationship between the obtained viewing angle and the relative luminance, the difference between the maximum relative luminance and the minimum relative luminance within the range of ± 10 ° in the front view (that is, centering on the viewing angle of 0 °) is 10%. The case where it is within the range is “◯”, and the case where it is larger than 10% is “x”. The uniformity of the screen is evaluated by observing the screen from a position separated from the screen by a predetermined distance in the normal direction of the screen. The distance is relative to the height of the screen (vertical size). Usually it is 3 times. According to this condition, at the observation position, the angle formed by the center front of the screen and the upper and lower ends of the screen is approximately ± 10 degrees. Therefore, it is appropriate to make the above determination.

  Regarding the viewing angle characteristics, as can be seen from FIG. 11 in particular, when the refractive index difference is 0.01 or more, it can be seen that the relative luminance suddenly increases in the range of the viewing angle of −15 to +15 degrees. On the other hand, in the optical sheet of the present invention (with a refractive index difference of less than 0.01), although the relative luminance is the highest near the front (near the viewing angle of 0 degree), it does not protrude here and is abrupt. There is no change. Thereby, the viewing angle characteristics are good, and the uniformity in the screen can be improved.

  Although the present invention has been described in connection with the most practical and preferred embodiments at the present time, the present invention is not limited to the embodiments disclosed herein, The invention can be appropriately changed without departing from the gist or concept of the invention that can be read from the claims and the entire specification, and an optical sheet accompanying such a change and a display device including the optical sheet are also included in the technical scope of the present invention. Must be understood as being.

1, 1 'Plasma TV (display device)
2 Plasma display panel (PDP, video light source)
DESCRIPTION OF SYMBOLS 10, 20, 30 Optical sheet 11, 21 Optical function sheet layer 12, 22 Prism part 13 Light absorption part 14 Binder part 15 Light absorption particle 16 PET film layer 17 Adhesive layer

Claims (10)

An optical sheet that is disposed on the viewer side from the plasma display panel, and includes a plurality of layers that emit light to the viewer side by controlling light from the plasma display panel,
At least one of the plurality of layers is
A prism portion arranged in parallel along the sheet surface so as to transmit light;
An optical functional sheet layer having a light absorbing portion arranged in parallel so as to be able to absorb light between the prism portions,
The prism portion has a trapezoidal shape in which a portion that should face the plasma display panel side in the sheet thickness direction cross section is a short upper base, and a side opposite to the upper base is a long lower base,
When the prism portion is formed of a material having a refractive index Np and the light absorbing portion is formed of a material having a refractive index Nb, a refractive index difference represented by Np−Nb is smaller than 0.01. An optical sheet.   The light absorbing portion is configured to have a light absorbing performance such that the transmittance is 40 to 70% in the transmittance measurement of a sheet having a thickness of 6 μm formed of only the material constituting the light absorbing portion. The optical sheet according to claim 1, wherein the optical sheet is provided. In the sheet thickness direction cross section,
The optical sheet according to claim 1, wherein the light absorbing portion is a triangle having a bottom side on a sheet surface side that is the upper bottom side of the prism portion. In the sheet thickness direction cross section,
The light absorbing portion is a trapezoid having a long lower bottom on the sheet surface side which is the upper bottom side of the prism portion and a short upper bottom on the sheet surface side which is the lower bottom side of the prism portion. The optical sheet according to claim 1 or 2.   5. The oblique side of the trapezoid provided between the upper base and the lower base of the prism portion is greater than 0 degree and less than or equal to 10 degrees with respect to the normal line of the sheet surface. The optical sheet according to any one of the above.   The optical sheet according to claim 5, wherein the hypotenuse comprises a polygonal line or a curved line.   The optical sheet according to claim 1, wherein the light absorbing portion contains light absorbing particles having an average particle diameter of 1 μm or more.   The optical sheet according to any one of claims 1 to 7, wherein Np and Nb have a value of 1.49 to 1.56.   The prism portion and the light absorbing portion of the optical function sheet layer are formed to have a predetermined cross section and extend in the longitudinal direction, and the two optical function sheet layers are laminated. The optical sheet according to any one of claims 1 to 8, wherein the functional sheet layer is laminated so that the longitudinal direction is perpendicular to one and the other. A plasma display panel;
A display device comprising: the optical sheet according to claim 1 disposed on an image light emitting side of the plasma display panel.

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