JP5029789B2 - Optical sheet and display device including the optical sheet - Google Patents

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, and in particular, improves transmittance and viewing angle characteristics. The present invention relates to an optical sheet that can be used, and a display device including the optical sheet.

  In a display device such as a television using 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 has a role of providing a high-quality image to an observer. For this purpose, the optical sheets are arranged in parallel along the sheet surface, and are arranged between the prism parts that transmit the image light from the PDP and the prism parts, and the contrast is improved by appropriately blocking or reflecting the image light and external light. And a light absorption part that suppresses ghosts (Patent Document 1, etc.).

  The shape of the light absorbing portion is substantially triangular in cross section as in Patent Document 1, and the portion corresponding to the bottom is directed to the image source side. The bottom portion is linear.

JP 2006-189867 A

  According to such a form of the light absorbing portion, the image light that has reached the bottom portion of the light absorbing portion is normally absorbed by the light absorbing portion. However, it is preferable that the image light is transmitted to the observer side as much as possible, thereby improving the brightness of the image. On the other hand, since the light absorption part is indispensable for improving the contrast and suppressing the ghost as described above, it should be avoided to easily change the ratio and shape thereof.

  In view of such problems, it is an object of the present invention to provide an optical sheet that can improve transmittance and viewing angle characteristics while maintaining contrast, 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, provided with a plurality of layers arranged on the viewer side from the image source (2) and controlling the light emitted from the image source and emitting it to the viewer side. 20), wherein at least one of the plurality of layers is arranged in parallel along the sheet surface so as to transmit light, and between the prism portions. Are optical functional sheet layers (11, 21) having light absorbing portions (13, 13,..., 23, 23,...) Arranged in parallel so as to be able to absorb light. Among them, at least one of the sides on the layer surface side of the optical function sheet layer has depressions (16, 26) in a curve or broken line shape in the sheet thickness direction, and the light absorption part is only a material constituting the light absorption part. In the transmittance measurement of the formed 6 μm thick sheet, the transmittance was 40 It solves the problems by providing an optical sheet according to claim which is configured to have a light absorbing performance such that 70%.

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

  In a second aspect of the present invention, the material forming the light absorbing portion (13, 23) in the optical sheet (10, 20) according to the first aspect has a refractive index Nb, and is in contact with the light absorbing portion at the recessed portion. When the region has a refractive index Na, there is a relationship of Nb ≧ Na between Nb and Na.

  Invention of Claim 3 has the hollow (16, 26) of the light absorption part (13, 13, ..., 23,23, ...) in the optical sheet (10, 20) of Claim 1 or 2. The length (B) of the side is 10 to 50% with respect to the pitch (A) in which the light absorption parts are arranged in parallel.

  According to a fourth aspect of the present invention, in the cross section in the sheet thickness direction of the optical sheet (10, 20) according to any one of the first to third aspects, the prism portion (12) of the optical functional sheet layer (11, 21) is provided. , 12,... 22, 22,... Are trapezoids having a short upper base on one sheet surface side and a long lower base on the other sheet surface side, and light absorbing portions (13, 13,..., 23, 23,...) Is a triangle whose base is the side having the depression (16, 26).

  Here, the side having the depression in the “triangle” is not a straight line, but even in this case, the side having the depression is a concept of one side of the triangle.

  The invention according to claim 5 is the prism portion (12) of the optical function sheet layer (11, 21) in the sheet thickness direction cross section of the optical sheet (10, 20) according to any one of claims 1-3. , 12,..., 22, 22,... Are trapezoids having a short upper base on one sheet surface side and a long lower base on the other sheet surface side, and light absorbing portions (13, 13,..., 23, 23). ,... Is characterized by a trapezoidal shape having a long lower base on the side having the depressions (16, 26) and a short upper base on the other sheet surface side.

  Here, in the “trapezoid” of the light absorbing portion, the lower bottom having a depression is not a straight line, but even in this case, the lower bottom having the depression is a concept of a lower trapezoid.

  The invention according to claim 6 is provided between the upper and lower bases of the prism portions (12, 12,..., 22, 22,...) In the optical sheet (10, 20) according to claim 4 or 5. The hypotenuse of the trapezoid provided is characterized by being greater than 0 degree and less than or equal to 10 degrees with respect to the normal of the sheet surface.

  The invention according to claim 7 is the upper bottom and bottom of the prism portion (12, 12,..., 22, 22,...) Of the optical sheet (10, 20) according to any one of claims 4 to 6. The trapezoid hypotenuse provided between the base and the bottom is formed by a polygonal line or a curved line.

  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 straight lines. And it is preferable that the angle | corner which each obtained straight line and the normal line of a sheet | seat surface make is more than 0 degree | times and below 10 degree | times.

  The invention according to claim 8 is a light-absorbing particle having an average particle diameter of 1 μm or more in the light-absorbing part (13, 13,...) Of the optical sheet (10) according to any one of claims 1 to 7. 15, 15, ...).

  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.

  In a ninth aspect of the present invention, a material for forming the prism portion (12, 12,..., 22, 22,...) In the optical sheet (10, 20) according to any one of the first to eighth aspects is provided. When the material having the refractive index Np and the light absorbing portion (13, 13,..., 23, 23,...) Has the refractive index Nb, there is a relationship of Np ≧ Nb between Np and Nb. The Np and Nb have a value of 1.49 to 1.56.

  According to a tenth aspect of the present invention, the prism portion and the light absorbing portion of the optical functional sheet layer in the optical sheet (30) according to any one of the first to ninth aspects have a predetermined cross section in the longitudinal direction. In addition to being formed to extend, two optical function sheet layers are stacked (11, 31), and the two optical function sheet layers are stacked so that the longitudinal direction of one and the other is perpendicular to each other. Features.

  The invention according to claim 11 is arranged such that the depressions (16, 26) in the optical sheet (10, 20) according to any one of claims 1 to 10 are exposed on one sheet surface side. It is characterized by that.

  The invention described in claim 12 has at least one action selected from the electromagnetic shielding, toning, antireflection, and antiglare on the optical sheet (10, 20) according to any one of claims 1-11. The above-mentioned problems are solved by providing an optical sheet characterized in that a layer having a layer is laminated.

  The invention according to claim 13 is provided with an image source (2) and the optical sheet (10, 20) according to any one of claims 1 to 12, wherein the optical sheet is an optical functional sheet layer. The above-mentioned problem is solved by providing a display device (1) characterized in that the layer surface on the side where the depressions (16, 26) are provided is arranged on the image source side.

  According to the present invention, it is possible to improve the transmittance and viewing angle characteristics while maintaining the contrast as compared with the conventional optical sheet.

It is the figure which showed the cross section of the optical sheet 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 concerning a modification. It is the figure which expanded and showed a part of optical sheet concerning the example whose light absorption part is trapezoid. It is the figure which showed the cross section of the optical sheet concerning 2nd 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 showed the cross section of the optical sheet concerning 3rd embodiment, and represented the layer structure typically. It is the figure which showed the cross section of the optical sheet concerning 4th 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 showed the layer structure of PDP and an optical sheet part in the scene where the optical sheet was attached to the glass panel type plasma television. It is the figure which showed the layer structure of PDP and an optical sheet part in the scene where the optical sheet was attached to the plasma television of a direct bonding system. It is a figure which shows the example of an optical path. It is another figure which shows the example of an optical path. It is a figure explaining the measuring method of a total light transmittance and a diffuse reflectance.

  The above 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 the optical sheet 10 according to the first embodiment. 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 17 as a base material layer, and an adhesive layer 18. 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 sheet thickness direction cross section of the optical sheet 10, and light absorbing sections 13, 13,... Disposed between the prism sections 12, 12,. … And. 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.

  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 value of the refractive index Np is not particularly limited, but is preferably 1.49 to 1.56 from the viewpoint of the availability of the applied material. 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,. Therefore, the light absorbing portions 13, 13,... Have a substantially triangular shape with the upper base side of the prism portions 12, 12,... As the base side and the apex opposite thereto as the lower base side of the prism portions 12, 12,. Become. 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 binder material filled in the binder part 14 is made of a material having a refractive index Nb equal to or lower than the refractive index Np of the prism parts 12, 12,. The value of the refractive index Nb is not particularly limited, but is preferably 1.49 to 1.56 from the viewpoint of the availability of the applied material. The difference in refractive index between Np and Nb is not particularly limited, but is preferably 0 to 0.06. 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.

  Due to the relationship between the refractive index difference and the incident angle of the image light, a part of the image light can be totally reflected at the interface without entering the light absorbing portions 13, 13,. Since it is provided, it is possible to provide a bright image.

  Here, in the binder part 14, the side that is arranged on the left side in FIG. 1 and FIG. 2, that is, the side that corresponds to the bottom side of the light absorbing unit 13 that is arranged on the short upper base side of the prism parts 12, 12,. A curved (arc) -shaped recess 16 is formed so as to be convex toward the apex facing the side. Accordingly, the binder portion 14 is particularly thin at the end portions 16a and 16b of the recess 16. Moreover, the site | part which contact | connects the light absorption part 13 via the said hollow 16 has refractive index Na, and it is preferable that it is Na <= Nb in relation to above-described Nb. As will be described later, the difference between Na and Nb varies depending on the layer structure of the optical sheet. When the Na portion is an air layer, Na is 1.0, so the difference is the difference between Na and Nb. . On the other hand, when a pressure-sensitive adhesive layer is disposed here, from the viewpoint of the refractive index of the pressure-sensitive adhesive, the difference between the Na and Nb is usually in the range of 0 to 0.01 and may be about 0.003. Many. As a result, even the image light incident on the bottom side can be transmitted to the viewer side to provide a bright image. In this case, since the image light is emitted with the angle changed by refraction, the viewing angle characteristics can be improved. A specific optical path will be described later.

  The depth of the depression 16 indicated by C in FIG. 2 is defined by the distance from the upper bottom surface of the prism portions 12, 12,... To the deepest part of the depression 16. This distance is not particularly limited, but is preferably 2 to 4% with respect to the thickness of the optical function sheet layer 11 from the viewpoint of manufacturing and performance. Therefore, when the thickness of the optical function sheet layer 11 is 100 μm, the distance is preferably 2 to 4 μm. Further, in the present embodiment, the recess 16 has a curved (arc) shape, but may have a polygonal line shape.

  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 are colored to a predetermined concentration with pigments such as carbon or dyes such as red, blue, and yellow. Yes. 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 setting 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 width of the bottom side of the light absorbing portions 13, 13,... Shown by B in FIG. 1 is not particularly limited as long as the required optical performance can be obtained. It is preferable that it is 10 to 50% with respect to the pitch of the light absorption parts 13, 13,. If the ratio is less than 10%, the light absorption effect is small, and contrast reduction and ghosting become remarkable. On the other hand, if the ratio is larger than 50%, the light absorption effect increases and the screen is often darkened due to the decrease in transmittance. It is.

  Further, the angle θ (see FIG. 2) 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 is not particularly limited. From the viewpoint of appropriate external light and image light absorption and reflection by the portions 13, 13,..., It is preferably greater than 0 degree and not greater than 10 degrees, and more preferably greater than 0 degree and not greater than 6 degrees.

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 substantially 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. is doing. Further, the light absorbing particles 15 ′, 15 ′,... And the recess 16 ′ are provided in the modification as well as the light absorbing particles 15, 15,.

These angles θ ₁ and θ ₂ are in a relationship of θ ₁ > θ ₂ and both are preferably in the range of greater than 0 degrees and less than or equal to 10 degrees for the same reason as described above. A more preferable angle is greater than 0 degree and 6 degrees or less. Further, the two oblique sides 13a ', 13b' intersect at a position separated into _{T 1} and _{T 2} in the thickness direction (left-right direction) of the optical functional sheet layer 11 '. 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 triangular has been described and described, but the shape of the light absorbing portion is not limited to this and may be trapezoidal. 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 on the upper base side of the prism portions 12 ″, 12 ″,. (Upper bottom) can be arranged on the lower bottom side of the prism portions 12 ″, 12 ″,. Here, the length of the upper base indicated by F in FIG. 4 is preferably 2 to 25 μm.

  Returning to FIG. 1, another configuration of the optical sheet 10 will be described. The PET film layer 17 is a film layer serving as a base for forming the optical functional sheet layer 11 on the PET film layer 17 and is formed mainly of PET. The PET film layer 17 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 in appropriate amounts. Examples of general additives include phenol-based antioxidants, lactone-based stabilizers, and the like.

  As will be described later (see FIG. 10), the pressure-sensitive adhesive layer 18 is provided with a pressure-sensitive adhesive that adheres the optical sheet to another layer or the like in order to place the optical sheet 10 on the image output side from the PDP 2 of the plasma television 1. Is a layer. The material of the pressure-sensitive adhesive used for the pressure-sensitive adhesive layer 18 is not particularly limited as long as it transmits light and can appropriately bond the optical sheet 10 to the other. 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 described above is manufactured as follows, for example. A liquid material serving as a material for the prism portions 12, 12,... Next, the prism parts 12, 12 are cured by irradiating with ultraviolet rays in a state where the material to be the prism parts 12, 12,... Is sandwiched between the roll mold forming the prism part shape and the PET film. , ... are formed. Then, between the prism portions 12, 12,..., A liquid material in which black light-absorbing particles 15, 15,. The light absorbing portions 13, 13,... Are formed by curing. At this time, the sheet surface on the bottom side of the binder portion 14 is scanned so that the tip of the blade comes into contact before irradiating with ultraviolet rays. As a result, a part of the bottom side of the resin that becomes the binder portion 14 is scraped off, and depressions 16, 16,... Are formed by irradiation with ultraviolet rays. In this way, the optical function sheet layer 11 is manufactured. Further, the pressure-sensitive adhesive layer 18 is laminated on the optical function sheet layer 11 and the PET film layer 17 thus manufactured.

  FIG. 5 is a diagram schematically showing the layer structure of the optical sheet 20 according to the second embodiment. The optical sheet 20 includes an optical function sheet layer 21, a PET film layer 27 as a base material layer, and an adhesive layer 28. Each of the above layers extends in the rear / front direction of the paper while maintaining the cross section shown in FIG. FIG. 6 shows an enlarged view focusing on one light absorbing portion 23 and the prism portions 22 and 22 adjacent thereto in the optical function sheet layer 21.

  Unlike the light absorbing portions 13, 13,... Of the optical sheet 10, the optical sheet 20 emits light by filling the light absorbing portions 23, 23,... With black or other colored photocurable resin. It is formed so that it can be absorbed. In this case, after forming the prism portion as described above, the light absorbing portions 23, 23,... Can be formed. Further, in the same manner as the optical sheet 10, a recess 26 is formed on the bottom sides of the light absorbing portions 23, 23,. Such a configuration of the optical sheet 20 can also provide the optical sheet of the present invention.

  FIG. 7 is a cross-sectional view of the optical sheet 30 according to the third embodiment, schematically showing the layer configuration. The optical sheet 30 is configured such that another optical functional sheet layer 31 is sandwiched between the optical functional sheet layer 11 and the PET film layer 17 of the optical sheet 10 of the first embodiment. At this time, the prism portion 32 and the light absorbing portion (not shown in the drawing) extend in a direction orthogonal to the prism portions 12, 12,... And the light absorbing portions 13, 13,. Be placed. Accordingly, the prism portions 32 and the light absorbing portions of the optical function sheet layer 31 are alternately arranged in parallel in the back / front direction of the drawing in FIG.

  FIG. 8 is a cross-sectional view of the optical sheet 40 according to the fourth embodiment, schematically showing the layer configuration. FIG. 9 is an enlarged view of one light absorbing portion 43 of the optical sheet 40, prism portions 42 and 42 adjacent to the light absorbing portion 43, and a part of the adhesive layer 48. The optical sheet 40 includes an optical function sheet layer 41, a PET film layer 47 as a base material layer, and an adhesive layer 48. Each of the above layers extends in the back / front direction of the paper while maintaining the cross section shown in FIG.

  Unlike the above-described optical sheet 10 and the like, the optical sheet 40 is provided with an adhesive layer 48 on one surface of the optical function sheet layer 41. Accordingly, the optical function sheet layer 41 is disposed between the PET film layer 47 and the pressure-sensitive adhesive layer 48. By adopting such a layer structure, it is possible to provide a so-called direct-tension type video apparatus in which the optical sheet 40 is directly attached to the video source. Details will be described later.

  Here, as shown in FIG. 9, in this embodiment, the recess 46 is in contact with the adhesive layer 48. Here, when the pressure-sensitive adhesive is a material having the above-described refractive index Na, an optical sheet having the effects of the present invention can be obtained.

  In the optical sheets 10, 20, 30, and 40 described above, the base material layer is not necessarily made of PET, and other than that, polybutylene terephthalate resin (PBT) or polytrimethylene terephthalate (PTT) resin "Polyester resin" such as 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.

  Furthermore, the optical sheet of the present invention includes a film layer for blocking electromagnetic waves, a film layer for correcting color tone, a film layer for cutting neon lines, a film layer for cutting infrared rays, a film layer for preventing reflection, and a film for preventing charging. A functional film layer such as a layer or a film layer for the purpose of antiglare may be provided.

  Next, a configuration when the optical sheet 10 as described above is attached to the plasma television 1 as a display device will be described. FIG. 10 is a diagram schematically showing a configuration of the glass filter type plasma television 1 in which the optical sheet 10 is laminated on the image output side of the PDP 2 through the glass layer 6. In FIG. 10, 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 sheets 20 and 30.

  As shown in FIG. 10, the optical sheet 10 is laminated on the image output surface of the PDP 2 that is the image source. At this time, a gap indicated by E in FIG. 10 is formed between the optical sheet 10 and the PDP 2 and is usually filled with air. More specifically, the optical sheet 10 is attached to the PDP 2 side of the glass layer 6 with the adhesive layer 18. Various layers (3, 4, 5) having AS, AR, and AG functions are provided on the viewer side of the glass layer 6. Here, “AS” is an abbreviation of “anti-static” and an anti-static function, and “AR” is an abbreviation of “anti-reflection” and a function of suppressing light reflectance. “AG” is an abbreviation for “anti-glare” and can prevent glare on the prism surface.

  Here, various layers of AS, AR, and AG have been exemplified as other layers provided, 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. The same applies to the display devices described below.

  FIG. 11 is a diagram for explaining a scene in which the optical sheet 40 is attached to a plasma television 1 ′ that is a display device. The plasma television 1 'is a so-called direct pasting method in which the optical sheet 40 is directly laminated on the image output side of the PDP 2' without using a glass panel. Accordingly, the optical sheet 40 is provided by being attached to the PDP 2 ′ by the adhesive layer 48. Various layers (3, 4, 5) having AS, AR, and AG functions are provided on the viewer side of the PET film layer 47.

  Next, the optical path will be described. FIG. 12 is a diagram showing an example of an optical path by paying attention to one light absorbing portion 13, 113 and the prism portions 12, 12, 112, 112 adjacent thereto. 12A shows the optical sheet 10, and FIG. 12B shows the optical sheet 110 of the conventional example. As can be seen from FIG. 12 (a), the light L11 and L12 incident on the end of the bottom side (indentation 16) of the light absorbing portion 13 is reflected by the prism portion 12, due to the interface shape of the binder portion 14 and the refractive index difference described above. Proceed to spread to 12 side. Accordingly, the light L11 and the light L12 are transmitted through the optical sheet 10 despite being incident on the light absorbing portion 13, and reach the observer as image light. Thereby, the transmittance can be improved. In addition, since the light is refracted and transmitted as described above, the viewing angle characteristics can be improved.

  On the other hand, as can be seen from FIG. 12B, the light L111 and L112 incident on the bottom end portion of the light absorbing portion 113 of the conventional optical sheet 110 travel straight through the binder 114 without being refracted, and the light absorbing particles 115. , 115 will be absorbed.

  FIG. 13 shows an example of an optical path in the case where the light absorbing portion of the optical sheet is filled with black or other colored photocurable resin so as to be able to absorb light. FIG. 13A shows an example of the optical sheet 20, and FIG. 13B shows an example of the conventional optical sheet 120. As can be seen from FIG. 13 (a), the light L21 and L22 incident on the end of the bottom (indentation 26) of the light absorbing portion 23 is converted into the prism portion 22 by the interface shape and refractive index difference with the light absorbing portion 23. It progresses so that it may spread to 22 side. At this time, although the light absorbing portion 23 is formed so as to be able to absorb light, the light L21 and L22 travel through the portion where the light absorbing portion 23 is thinned, so that some of the light is absorbed by the prism portions 22 and 22. Can penetrate. As a result, the light L21 and L22 passes through the optical sheet 20 even though it enters the light absorbing portion 23, and reaches the observer as image light. Therefore, the transmittance can be improved. Further, as described above, since the light is refracted and transmitted, it is possible to provide image light having a good viewing angle characteristic.

  On the other hand, as can be seen from FIG. 13B, the lights L121 and L122 incident on the bottom edge of the light absorbing portion 123 of the conventional optical sheet 120 travel straight through the light absorbing portion 123 without being refracted. It will be absorbed by the absorber 123.

  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.

  In the example, the depth (C in FIG. 2) was changed, and the transmittance, viewing angle, and contrast at that time were measured. This will be specifically described below.

<Test sample>
As a test sample, an optical sheet in which the depth of the depression in the light absorbing portion was changed was produced. Table 1 shows the details.

  The optical sheet shown in Table 1 was subjected to performance tests for total light transmittance, viewing angle characteristics, and contrast.

<Viewing angle characteristics>
The viewing angle characteristic obtains the relative luminance at each viewing angle, and the viewing angle becomes a relative luminance of 1/2 relative to the relative luminance at the front (viewing angle is 0 degree), and the viewing angle becomes a relative luminance of 1/3. Its performance was evaluated by obtaining the corners.
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).

<Contrast>
The contrast was a value obtained by dividing the total light transmittance by the diffuse reflectance. FIG. 14 illustrates a method for measuring the total light transmittance and the diffuse reflectance. As shown in FIG. 14A, the total light transmittance is the ratio of the omnidirectional light in the integrating sphere to the irradiated light for all the light transmitted through the optical sheet. On the other hand, the diffuse reflectance is defined by the omnidirectional diffuse reflectance obtained by excluding the 45-degree specular reflected light component from the total light diffuse reflectance. In the measurement, as shown in FIG. 14B, a standard white plate is arranged on the back side of the optical sheet, and the 45-degree specular reflection light is excluded, and the omnidirectional light in the integrating sphere at that time is detected by a detector. To do so.

  The results will be described below. Table 2 shows the results.

  As can be seen from Table 2, although a slight decrease in contrast is observed with an increase in the depth of the depression, the improvement in transmittance and viewing angle characteristics is more remarkable than this. In this sense, the present invention can provide an optical sheet that can improve transmittance and viewing angle characteristics while maintaining contrast, and a display device including the sheet.

  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 encompassed by.

1 Plasma TV (display device)
2 Plasma display panel (video source)
10, 20, 30, 40 Optical sheet 11, 21, 31, 41 Optical function sheet layer 12, 22, 32, 42 Prism part 13, 23, 33, 43 Light absorbing part 14, 34, 44 Binder part 15, 35, 45 Light-absorbing particles 16, 26, 46 Recesses 17, 27, 47 PET film layer (base material layer)
18, 28, 48 Adhesive layer

Claims (13)

An optical sheet that is disposed on the viewer side from the video source, and includes a plurality of layers that control the light emitted from the video source and emit the light to the viewer side,
An optical functional sheet in which at least one of the plurality of layers has a prism portion arranged in parallel along the sheet surface so as to transmit light, and a light absorbing portion arranged in parallel so as to absorb light between the prism portions. With layers
Of the sides of the light absorbing portion in the sheet thickness direction cross section, at least one of the sides that become the layer surface side of the optical function sheet layer has a depression in a curve or a broken line shape in the sheet thickness direction,
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. An optical sheet characterized by that.   When the material forming the light absorbing portion has a refractive index Nb and the portion in contact with the light absorbing portion in the hollow portion has a refractive index Na, there is a relationship of Nb ≧ Na between Nb and Na. The optical sheet according to claim 1.   The length of the side which has the said hollow of the said light absorption part is 10 to 50% with respect to the pitch with which the said light absorption part is paralleled, The optical sheet of Claim 1 or 2 characterized by the above-mentioned. In the sheet thickness direction cross section,
The prism portion of the optical function sheet layer is a trapezoid having a short upper base on one sheet surface side and a long lower base on the other sheet surface side,
The optical sheet according to any one of claims 1 to 3, wherein the light absorbing portion is a triangle having a side having the depression as a base. In the sheet thickness direction cross section,
The prism portion of the optical function sheet layer is a trapezoid having a short upper base on one sheet surface side and a long lower base on the other sheet surface side,
4. The optical device according to claim 1, wherein the light absorbing portion has a trapezoidal shape having a long lower base on the side having the depression and a short upper base on the other sheet surface side. Sheet.   6. The trapezoid hypotenuse 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 of the sheet surface. The optical sheet according to 1.   The optical sheet according to any one of claims 4 to 6, wherein the hypotenuse of the trapezoid formed between the upper base and the lower base of the prism portion is 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.   When the material forming the prism portion has a refractive index Np and the material forming the light absorbing portion has a refractive index Nb, there is a relationship of Np ≧ Nb between the Np and Nb, and the Np Nb is a value of 1.49-1.56, The optical sheet as described in any one of Claims 1-8 characterized by the above-mentioned.   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 9, wherein the functional sheet layer is laminated so that the longitudinal direction is perpendicular to one and the other.   The optical sheet according to any one of claims 1 to 10, wherein the depression is disposed so as to be exposed on one sheet surface side.   The optical sheet according to any one of claims 1 to 11, further comprising a layer having at least one action selected from electromagnetic wave shielding, toning, antireflection, and antiglare. . An image source, and the optical sheet according to any one of claims 1 to 12, are provided,
The display device, wherein the optical sheet is arranged such that a layer surface of the optical functional sheet layer on which the depression is provided is on the image source side.

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