JP2012103290A - Optical sheet, backlight unit and liquid crystal display device - Google Patents

Abstract

An optical sheet having both an effect of improving luminance and an effect of concealing unevenness is provided.
An optical sheet according to the present invention includes a base film 2 having optical transparency and a plurality of unit lenses formed on one surface of the base film 2 and having a substantially trapezoidal shape in a cross section perpendicular to the base film 2. 3 and a diffusion layer 5 that is formed on the top surface 4 of the unit lens 3 and diffuses and reflects light. Thereby, it is possible to obtain an optical sheet having both the effects of concealing unevenness and improving luminance at a high level.
[Selection] Figure 1

Description

  The present invention relates to an optical sheet used in a backlight unit such as a liquid crystal display device, the backlight unit, and a liquid crystal display device.

  Liquid crystal display devices are used in a wide range of fields such as cellular phones, PDA terminals, digital cameras, televisions, personal computer displays, and digital photo frames. The liquid crystal display device is a display device including a liquid crystal panel and a backlight unit on the back surface thereof, and displays an image by supplying light from the backlight unit to the liquid crystal panel. As the backlight unit, two types, an edge light type and a direct type, are generally used.

  The edge-light type backlight unit includes a light guide plate having a cold cathode tube as a linear light source or an LED as a point light source arranged on a side surface, and an optical sheet such as a reflection sheet or a diffusion sheet. Light incident on the light guide plate from the side surface propagates while being totally reflected between the light output surface and the reflection surface, which are the two main surfaces of the light guide plate, and hits white dots that promote light scattering formed on the reflection surface. And exit from the light exit surface. The light guide plate emits light having a substantially uniform illuminance distribution on the entire light exit surface of the light guide plate based on such a principle. Here, since it is not preferable that white dots on the reflecting surface are observed as luminance unevenness from the light emitting surface of the light guide plate, it is usual to use an optical sheet between the light emitting surface of the light guide plate and the liquid crystal display panel. An edge light type backlight unit is suitable for thinning a liquid crystal display device.

  The direct-type backlight unit includes a light source disposed directly under the liquid crystal panel and an optical sheet such as a reflection sheet or a diffusion sheet. In order to use a plurality of cold-cathode tubes and LEDs as the light source so that sufficient luminance can be obtained in the screen, an area overlapping the light source (area corresponding to the upper part of the light source) and an area not overlapping the light source (between the light sources) Difference in brightness (brightness unevenness). In order to eliminate such luminance unevenness, it is essential to use an optical sheet between the light source and the liquid crystal display panel. The direct-type backlight unit can increase the light use efficiency.

  In order to eliminate luminance unevenness due to white dots on the reflection surface of the light guide plate in the above-described edge light type backlight unit, and to eliminate luminance unevenness due to differences in position with respect to multiple light sources in the direct type backlight unit, luminance unevenness concealment (Hereinafter, it is also simply referred to as “unevenness concealment”). It is necessary to use a plurality of optical sheets such as bead-coated light diffusion sheets in a stacked manner.

  However, a sheet with high unevenness concealment has a low light transmittance and often causes a reduction in luminance. In recent years, a method for efficiently using limited light for the purpose of increasing the definition of an image due to the development of liquid crystal display technology and reducing power consumption has been sought.

  In view of the above background, there is a demand for an optical member having both the effects of concealing unevenness and improving luminance.

  For example, in Patent Document 1, a microlens array arranged periodically and in a matrix is formed on at least one of a light incident surface and a light emitting surface, and a microlens on the surface on which the microlens array is formed is formed. An optical element having a surface roughness expressed by a center line arithmetic average roughness Ra of 0.1 μm or more and 2 μm or less is disclosed for the non-planar portion.

  Further, in Patent Document 2, a linear prism shape having an apex angle of 50 to 150 degrees is formed on the surface, and fine irregularities having a surface roughness (Ra) of 0.2 to 20 μm are provided on the prism surface. A diffuser plate is disclosed.

JP 2009-223192 A JP 2008-242002 A

  Patent Document 1 describes an optical element having two regions having different shapes, that is, a microlens that exhibits light condensing properties and a flat surface portion having a specific surface roughness that exhibits light diffusibility. However, the condensing effect of the microlens is smaller than that of the prism, and does not show a sufficient brightness enhancement effect. Furthermore, if the ratio of the plane portion between the microlenses is increased in order to improve the unevenness concealing property, the luminance decreases.

  In addition, as described in Patent Document 2, when fine irregularities are formed on the entire prism surface, the prism irregularities having an angle suitable for condensing decrease due to the fine irregularities, and the condensing effect is reduced. .

  As described above, with the conventional technology, it has been extremely difficult to simultaneously obtain both the effects of concealing unevenness and improving luminance.

  This invention is made | formed in view of this point, and it aims at providing the optical sheet which can acquire the effect of both non-uniformity concealment property and a brightness improvement with a high level.

  The optical sheet of the present invention includes a base film having light transmittance, a plurality of unit lenses formed on one surface of the base film and having a substantially trapezoidal shape in a cross section perpendicular to the one surface of the base film, And a diffusion layer formed on the top surface of the unit lens.

  According to this configuration, by having the slope suitable for condensing and the diffusion layer for diffusing and reflecting the light, it is possible to obtain both the effects of concealing unevenness and improving the luminance at a high level.

  In the optical sheet of the present invention, the plurality of unit lenses may be composed of a plurality of parallel light-transmitting members having a prismatic shape extending in a specific direction. The unit lens may be formed of a light transmissive member having a substantially frustum shape.

  In the optical sheet of the present invention, the area occupied by the diffusion layer in a plan view from a direction perpendicular to the one surface of the base film may be 5% or more and 70% or less of the entire area of the base film.

  According to this configuration, it is possible to balance the effect of high unevenness concealment and the effect of improving luminance.

  In the optical sheet of the present invention, the unit lens may have an inclination angle of 15 ° to 60 °. In the optical sheet of the present invention, the reflectance at 550 nm of the diffusion layer may be 3% or more and 15% or less.

  According to this configuration, the effect of improving the luminance can be sufficiently enhanced.

  In the optical sheet of the present invention, the diffusion angle of the diffusion layer may be not less than 0.1 degrees and not more than 150 degrees.

  According to this configuration, the unevenness concealing property can be sufficiently improved.

  In the optical sheet of the present invention, the surface of the diffusion layer may have an uneven structure. In the optical sheet of the present invention, the concavo-convex structure may be a concavo-convex structure formed using a speckle pattern by interference exposure. In the optical sheet of the present invention, the unit lens and the diffusion layer may be provided integrally.

  The backlight unit of the present invention comprises the above optical sheet. In addition, a liquid crystal display device of the present invention includes the backlight unit.

  The optical sheet of the present invention can obtain both the effects of concealing unevenness and improving luminance at a high level, and can provide high luminance while suppressing uneven luminance of the backlight unit.

It is a cross-sectional schematic diagram of one Embodiment of the optical sheet which concerns on embodiment. It is a plane schematic diagram of an embodiment of an optical sheet according to the embodiment. (A) and (b) are cases where the unit lens is a prismatic shape with a substantially trapezoidal cross-sectional shape, and (c) is an abbreviation that the unit lens has a quadrangular shape when viewed from the vertical direction on the paper surface. This is a case of a quadrangular frustum shape, and (d), (e), and (f) are cases where the unit lens is a substantially truncated cone shape whose shape viewed from the vertical direction on the paper surface is circular. It is explanatory drawing for demonstrating the definition of a diffusion angle. It is a microscope picture (300 times) which shows the surface shape of an example of the optical sheet which concerns on embodiment. It is a cross-sectional schematic diagram of other embodiment of the optical sheet which concerns on embodiment. It is a cross-sectional schematic diagram which shows the preparation methods of the optical sheet which concerns on embodiment. It is a cross-sectional schematic diagram which shows the preparation methods of the optical sheet which concerns on embodiment. It is a figure which shows the structural example of the direct type | mold backlight unit which concerns on embodiment. It is a figure which shows the structural example of the edge light type backlight unit which concerns on embodiment. It is a cross-sectional schematic diagram of the liquid crystal display device which concerns on embodiment. FIG. 6 is a diagram illustrating a cross-sectional shape per unit lens of Examples 1 and 2 and Comparative Example 4;

  As in Patent Document 1, in the case where the region showing the light condensing property and the region showing the light diffusing property are provided separately, the light passing through the region showing the light condensing property and the region showing the light diffusing property are Since the light that has passed through is independent, the light condensing region is reduced to increase the unevenness concealing property, and the light diffusing region is not required to be increased to improve the light condensing property. Must not. That is, the improvement in unevenness concealment and the improvement in luminance are in a trade-off relationship, and if one is increased, the other is decreased. Further, as in Patent Document 2, even if a light-collecting structure and a light-diffusing structure are formed in the same region, a light-diffusing structure is created in the entire light-collecting structure. If it is included, the proportion of the structure suitable for light collection decreases, and the light collection performance decreases.

  The present inventors pay attention to this point, and by providing a diffusion layer that has not only light diffusibility but also brightness enhancement effect, it is possible to obtain both the effects of unevenness concealment and brightness enhancement at a high level. I found. And the structure which has the slope which has an angle suitable for condensing, and the diffusion layer (diffusion area | region) which diffuses and reflects light moderately was devised. In such a structure, not only the light can be collected properly by the slope, but also the brightness enhancement effect can be obtained, and the light is also appropriately reflected and diffused by the diffusion layer, so that the brightness improvement and the unevenness concealment improvement effect are further improved. Is obtained. The reason for improving the luminance by the diffusion layer is that the light reflected by the diffusion layer is condensed again on the slope because the diffusion layer has an appropriate reflectance. That is, the essence of the present invention has a slope as a region exhibiting light condensing property and a diffusion layer as a region exhibiting light diffusibility and reflectivity on the base film, so that it is properly condensed on the slope. The brightness improvement effect obtained by this, the light that was not collected is reflected by the diffusion layer, and the brightness improvement effect that is obtained by collecting again from the slope of the unit lens, and the light that was not reflected is moderately An object of the present invention is to provide an optical sheet having an effect of concealing unevenness by being diffused. Note that the boundary between the diffusion layer and the lens may not be clear, and the diffusion layer and the lens may be integrated. Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 is a schematic cross-sectional view of an optical sheet 1 according to an aspect of the present invention (hereinafter also referred to as “this embodiment”) as viewed from a cross section perpendicular to a light incident surface (light exit surface). FIG. 2 is a schematic plan view of the optical sheet 1 according to the present embodiment when viewed from directly above the main surface having the unit lens 3 (in a direction perpendicular to the main surface). Here, FIG. 1 corresponds to a cross section taken along the line AA ′ of FIGS. 2A, 2C, and 2D, for example.

  As can be seen from FIG. 1 and FIG. 2, the optical sheet 1 of this embodiment includes a base film 2 having optical transparency and a cross-sectional shape in one direction perpendicular to the base film 2 formed on one surface of the base film 2. Includes a plurality of unit lenses 3 each having a substantially trapezoidal shape, and a diffusion layer 5 that is formed on the top surface 4 of the unit lens 3 and diffuses and reflects light from the light source.

  The unit lens 3 is a light transmissive member having an inclined surface 7 having a predetermined angle and a flat surface, and is made of a material such as resin or glass. The unit lens 3 has a function of refracting light and condensing light on its slope.

  In the unit lens 3, from the viewpoint of improving luminance, an inclination angle (when the height from the bottom surface to the top surface of the unit lens is h, the slope angle at a height of h / 2 from the bottom surface is meant. That is, in this specification, the inclination angle is included in the inclination angle) is preferably 15 ° or more and 60 ° or less. The inclination angle is more preferably 20 ° or more and 50 ° or less, and further preferably 20 ° or more and 45 ° or less.

  Here, as the inclination angle, a value measured using a fine shape measuring instrument ET4000 manufactured by Kosaka Laboratory Ltd. is used. The measurement conditions are, for example, an X pitch of 3 μm, a Y pitch of 3 μm, and a Z magnification of 2000 times. From the height data and the measurement pitch obtained in such a measurement, a tilt angle is calculated using a trigonometric function. However, the method for measuring the tilt angle is not limited to this.

  The diffusion layer 5 is, for example, a layer having a large number of fine uneven structures near the surface (see FIG. 1). The diffusion layer 5 is not limited to having a fine concavo-convex structure as long as appropriate diffusion and reflection of light can be realized. For example, a layer containing fine particles as a light diffusing agent may be used as the diffusion layer 5.

  The reflectance of the diffusion layer 5 is preferably 3% or more and 15% or less for the light having a wavelength of 550 nm from the viewpoint of enhancing the luminance enhancement effect. More preferably, it is 10% or less. The reflectivity is obtained when light is incident on the surface opposite to the surface on which the diffusion layer is formed in the optical sheet 1 from a direction inclined by 5 ° from the perpendicular to the surface (that is, the incident angle to the substrate surface). Is the specular reflectance at a wavelength of 550 nm. The reflectance can be measured using, for example, MPC-2200 manufactured by Shimadzu Corporation. However, the reflectance measurement method is not limited to this.

  In the state where both the unit lens 3 and the diffusion layer 5 exist, it is difficult to accurately measure the reflectance of the diffusion layer 5. For this reason, here, the reflectance of the diffusion layer 5 formed under the same conditions on the base film 2 not having the unit lens 3 is defined as the reflectance of the diffusion layer 5 in the optical sheet 1.

  The diffusion angle of the diffusion layer 5 is preferably not less than 0.1 ° and not more than 150 ° from the viewpoint of improving the unevenness concealing property. More preferably, it is 15 ° or more. In the diffusion layer 5 having a fine concavo-convex structure, the diffusion angle can be controlled by the height difference of the fine concavo-convex structure, the interval of the concavo-convex.

  As the diffusion layer 5, any of an isotropic diffusion layer that can obtain substantially the same diffusion angle regardless of the measurement direction and an anisotropic diffusion layer that has a different diffusion angle depending on the measurement direction can be used. For example, the anisotropic diffusion layer is a diffusion layer 5 having different diffusion angles when the diffusion angles are measured in two orthogonal directions. Further, the diffusion angle of the diffusion layer 5 may be different for each measurement position in the sheet surface.

  The diffusion angle described in this specification is an emission angle (half-value angle) at which the intensity in the distribution of the transmitted light intensity with respect to the emission angle with the emission angle of the transmitted diffused light as the x-axis and the intensity as the y-axis is half the peak intensity. (FWHM: Full Width Half Maximum), which is shown in FIG. As shown in FIG. 3 (b), the diffusion angle is set in the diffusion layer 5 as shown in FIG. On the other hand, it can be obtained by measuring the outgoing angle distribution of the transmitted light intensity of light incident from the normal direction.

  In the state where both the unit lens 3 and the diffusion layer 5 exist, it is difficult to accurately measure the diffusion angle of the diffusion layer 5. For this reason, here, the diffusion angle of the diffusion layer 5 formed under the same conditions on the base film 2 not having the unit lens 3 is defined as the diffusion angle of the diffusion layer 5 in the optical sheet 1.

  The base film 2 is a light-transmitting base material made of a material such as resin or glass. In particular, the light transmittance of the base material alone is preferably 75% or more. In addition, about the material of the base film 2, etc., if it can permeate | transmit the target light suitably, it will not specifically limit.

  With the optical sheet 1 having the above-described configuration, it is possible to obtain both effects of concealing unevenness and improving luminance at a high level.

  Here, although the optical sheet 1 in which the unit lens 3 and the diffusion layer 5 are separated is shown, the present invention is not limited to this. The unit lens 3 and the diffusion layer 5 may be integrated. In this case, a diffusion region is provided on the top surface 4 of the unit lens 3. Here, “separate” means that the boundary between the unit lens 3 and the diffusion layer 5 is clear, and “integral” means that the boundary between the unit lens 3 and the diffusion layer 5 is clear. Means that it does not exist.

  Next, the planar pattern of the optical sheet 1 of the present embodiment will be described with reference to FIG. FIG. 2 shows a top surface 4, a bottom line or a bottom surface 6, and a slope 7 therebetween in order to easily show the planar pattern shape. The bottom line or the bottom surface 6 is a line or surface connecting points where the height of the lens is lowest. The unit lens 3 is preferably a plurality of parallel light-transmitting members having a prismatic shape extending in a specific direction, particularly when the direction of light to be collected is limited to one direction. (FIG. 2 (a), (b)). This is because, when the unit lens 3 has such a shape, the light viewing angle can be maintained without condensing light in a direction other than the specific direction. Or when the condensing direction is not limited, it is preferably a light transmissive member having a substantially frustum shape that is scattered at intervals (FIGS. 2C, 2D, and 2E). (F)). This is because by making the unit lens 3 into a substantially frustum shape that is scattered at intervals, the inclined surface exists isotropically, and light in any direction can be collected.

  Here, the optical sheet 1 in FIG. 2A uses a plurality of unit lenses 3 made of a prismatic light-transmitting member that is long in the vertical direction of the paper and has substantially the same width in the horizontal direction of the paper. Further, in the optical sheet 1 of FIG. 2A, the plurality of unit lenses 3 extend substantially parallel to each other. On the other hand, the optical sheet 1 in FIG. 2B uses a plurality of unit lenses 3 made of a prismatic light transmissive member that is long in the vertical direction of the paper and has different widths in the horizontal direction of the paper. In addition, also in the optical sheet 1 of FIG.2 (b), the several unit lens 3 is extended in the substantially parallel mutually.

  In addition, a plurality of unit lenses 3 made of a light-transmitting member having a truncated pyramid shape are used in the optical sheet 1 of FIG. On the other hand, in the optical sheet 1 of FIGS. 2D, 2E, and 2F, a plurality of unit lenses 3 made of a light-transmitting member having a truncated cone shape are used.

  2A, 2C, and 2D, the size (width and diameter in plan view) of the plurality of unit lenses 3 and the interval between the unit lenses 3 are used. Are approximately equal. On the other hand, in the optical sheet 1 of FIG. 2B, FIG. 2E, and FIG. 2F, the size (width and diameter in plan view) of the plurality of unit lenses 3 and the unit lenses 3 to each other. The spacing is different.

  In the optical sheet 1 of the present embodiment, the unit lenses 3 are regularly arranged (FIGS. 2A, 2C, 2D, and 2E), and the arrangement regularity is low (FIG. 2). 2 (b), (f)) may be used. Further, the size (width and diameter in plan view) of the unit lens 3 may be non-uniform in the plane (FIGS. 2B, 2E, and 2F). However, the top surface of the unit lens 3 when viewed in plan from directly above the optical sheet 1 (in a direction perpendicular to one main surface of the base film 2) in order to balance the effect of high unevenness concealment and the effect of improving luminance. 4 is preferably 5% to 70% of the entire base film 2 (the entire optical sheet 1). The height of the unit lens 3 is preferably 15 to 150 μm, and the pitch (interval between unit lenses) is preferably 40 to 500 μm.

  FIG. 4 is a photomicrograph of the optical sheet 1 actually produced. In FIG. 4, the optical sheet 1 whose sectional shape perpendicular to one principal surface of the base film 2 corresponds to FIG. 1 and whose plan view from the direction perpendicular to the one principal surface of the base film 2 corresponds to FIG. Is shown. As described above, the unit lens includes a plurality of unit lenses having a substantially trapezoidal cross section in one direction perpendicular to one surface of the base film 2, and a diffusion layer that is formed on the top surface of the unit lens and diffuses light from the light source. As a result, the effect of improving the luminance can be enhanced while ensuring high unevenness concealment.

  FIG. 5 is a schematic cross-sectional view of another embodiment of the optical sheet 1 as viewed from a cross section perpendicular to the light incident surface (light emitting surface). As shown here, the slope of the unit lens 3 is not necessarily a flat surface (that is, the cross section is a straight line), and may be a curved surface (that is, the cross section is a curve) (FIG. 5B). (C), (e), (f)). However, in order to obtain higher luminance, the slope angle (θ (0) to θ (N)) forming the slope of the unit lens is 15 ° or more and 60 ° or less (preferably 20 ° or more and 50 ° or less, more preferably It is preferable that the slope region that falls within the range of 20 ° to 45 ° is wide. That is, it is preferable that the area of the slope having the slope angle within the above range is wide.

  Further, the top surface 4 of the unit lens 3 is not necessarily a flat surface, and may be a curved surface (that is, its cross section is a curved line) (FIG. 5D). In this case, the surface of the diffusion layer 5 is also a slightly curved surface. Here, the slightly curved surface refers to a curved surface whose tangent is within ± 10 ° with respect to one main surface of the optical base film 2. The angle is calculated, for example, using a trigonometric function from the height data and measurement pitch obtained by measuring the surface shape of the slope with a stylus using a fine shape measuring machine ET4000 manufactured by Kosaka Laboratory Ltd. it can.

  Specifically, in FIG. 5A, the slope of the unit lens 3 is a flat surface, and the top surface 4 of the unit lens 3 is also a flat surface. In FIG. 5B, the slope of the unit lens 3 is a curved surface having a predetermined curvature, and the center of curvature exists outside the unit lens 3. That is, the unit lens 3 has a slope angle that is small at the skirt portion and large at the tip portion. In addition, in FIG.5 (b), the top surface 4 is a plane.

  In FIG. 5C, the slope of the unit lens 3 is a curved surface having a predetermined curvature, and the center of curvature exists inside the unit lens 3. That is, the unit lens 3 has a large slope angle at the skirt portion and a small tip portion. In addition, in FIG.5 (c), the top surface 4 is a plane. In FIG. 5D, the slope of the unit lens 3 is a flat surface. On the other hand, the top surface 4 is a curved surface (slightly curved surface) having a predetermined curvature, and the center of curvature exists inside the unit lens 3. Similarly, the surface of the diffusion layer 5 is a curved surface (slightly curved surface) having a predetermined curvature.

  5A, 5B, 5C, and 5D show the case where a layer made of a resin containing fine particles as a light diffusing agent is used as the diffusion layer 5. FIG. However, the same applies to the case where a layer having fine irregularities is used.

  In FIG. 5 (e), the slope of the unit lens 3 is a curved surface having a predetermined curvature, and the center of curvature exists outside the unit lens 3. That is, the unit lens 3 has a slope angle that is small at the skirt portion and large at the tip portion. The top surface 4 is a flat surface. The shape of the unit lens 3 in FIG. 5 (f) is the same as that in FIG. 5 (e). The difference between FIG. 5E and FIG. 5F is the pattern of the fine concavo-convex structure provided in the diffusion layer 5. That is, in FIG. 5E, the pattern of the fine concavo-convex structure is substantially the same in the sheet surface, whereas in FIG. 5F, the pattern of the fine concavo-convex structure is different in the sheet surface. As shown in FIG. 5 (f), the diffusion angle in the sheet surface can be varied by varying the pattern of the fine concavo-convex structure in the sheet surface.

  5E and 5F show the case where a layer having fine irregularities is used as the diffusion layer 5, but a layer made of a resin containing fine particles as a light diffusing agent may also be used. It is the same.

  In the present specification, the expression of substantially trapezoid includes the cross-sectional shape of the unit lens 3 shown in FIGS. 5 (a) to 5 (f). That is, the unit lens 3 includes those whose slopes and top surfaces 4 are curved surfaces.

  The diffusion layer 5 can be obtained by the following method. For example, a light diffusibility of the top surface of a unit lens is produced by forming a laminated body in which a diffusion layer made of a resin containing fine particles as a light diffusing agent is laminated on a base material, and processing the laminated body to form a unit lens shape. Is obtained. It is desirable that the fine particles have a refractive index different from that of the substrate. In this case, the top surface of the unit lens has a flat shape.

  Alternatively, a light diffusion property may be imparted to the top surface of the unit lens by forming a diffusion layer having a concavo-convex structure on the surface of the substrate and processing it to form a unit lens shape.

  Thus, it is more preferable to provide a concavo-convex structure on the surface of the base material to form a diffusion layer because the optical sheet 1 of the present embodiment can be produced only by transferring the shape to the base material.

  The uneven structure is, for example, a structure in which a plurality of concave portions or convex portions are provided on the surface. The shape of the concave portion or the convex portion may be any one of a substantially conical shape, a substantially spherical shape, a substantially ellipsoidal shape, a substantially lenticular lens shape, a substantially parabolic surface shape, or a reverse shape thereof. Or may be arranged irregularly. Further, the concave portions or the convex portions may be connected by a continuous curved surface. Furthermore, a random structure in which irregular irregularities are connected by a continuous curved surface can be preferably used. This random structure is preferably a fine three-dimensional structure obtained by exposing and developing a photosensitive material. In particular, a fine three-dimensional structure (hereinafter, this three-dimensional structure) obtained by exposing and developing a photosensitive material using speckle patterns generated by interference in the space after the coherent light passes through the diffusion plate. Is also sometimes referred to as “speckle pattern”).

  The concavo-convex structure preferably has a low regularity of at least one of height and pitch from the viewpoint of uniform light output and moire suppression. As a specific size of the concavo-convex structure, the average value is preferably 1 to 100 μm, more preferably 1 to 50 μm, and the aspect ratio is preferably 0.5 to 3. The pitch is defined as an interval between the convex portions. The aspect ratio is defined by the ratio (height / width) between the height of the convex portion and the width of the convex portion at a position ½ of the height of the convex portion. Here, a convex part points out a part higher than the average height of a shape.

  The optical sheet 1 having the speckle pattern as the diffusion layer 5 can be manufactured by using, for example, the following method.

  First, a diffusion layer sub-master mold 8a having a speckle pattern on the entire surface of one surface of a sheet-like substrate is produced (FIG. 6A). As a method for forming a non-uniform concavo-convex structure using a speckle pattern, a method based on the method of JP-T-2003-525472 (International Publication No. 01/065469) can be applied.

  The speckle pattern includes, for example, a speckle pattern generated by a predetermined light source, a mask having a variable size and shape opening provided in an optical path of light projected from the light source, and light projected from the light source. Using a recording plate and a diffusion plate that diffuses light from the light source between the mask and the plate, and changing the size and shape of the opening of the mask, the diffusibility of the diffusion plate, and the distance between each component Can be formed.

  The speckle pattern thus obtained is recorded on the photosensitive resin or photoresist applied on the plate, and is developed to develop a submaster for the diffusion layer in which irregularities derived from the speckle pattern are formed. A mold 8a is obtained. By attaching a metal to the diffusion layer submaster mold 8a by a method such as electroforming, a mold 9a having a non-uniform uneven shape derived from the speckle pattern can be manufactured (FIG. 6B).

  By using this mold 9a, a diffusion layer in which a non-uniform concavo-convex structure derived from speckle patterns is formed on a predetermined transparent film using, for example, an ultraviolet curable resin can be formed. Below, the said predetermined | prescribed transparent film in which the diffused layer was formed is called the film 8b with a diffused layer pattern (FIG.6 (c)).

Subsequently, a part of the obtained film 8b with the diffusion layer pattern is cut and removed by machining to form a replication mold 8c (FIG. 6D). The replica 8c is processed so that a pattern made of a frustum-shaped unit lens remains. Thereafter, a master mold 9b is manufactured by depositing metal on the replica mold 8c by a method such as electroforming by a method based on the method of JP-T-2003-525472 (International Publication No. 01/065469) ( FIG. 7 (a)).

  For example, the master sheet 9b is pressed by being superimposed on the base film 2 coated with an ultraviolet curable resin, and the ultraviolet curable resin is cured, whereby the optical sheet 1 of the present embodiment can be manufactured (FIG. 7B). . The concavo-convex structure can be provided on one or both of the incident surface and the exit surface of the optical sheet. From the viewpoint of improving the luminance, the main concavo-convex structure is preferably on the exit surface, More preferably, the surface is smooth. In general, when the optical sheet 1 is laminated, a very small amount of beads may be applied to the incident surface within a range that does not significantly affect the optical characteristics in order to prevent damage. Such a case is also included in the smooth surface.

  Next, a backlight unit using the optical sheet 1 of the present embodiment described above will be described. 8 and 9 are diagrams showing a schematic configuration of the backlight unit according to the present embodiment.

  The backlight unit of this embodiment has the optical sheet 15 of this embodiment. The backlight unit includes a direct type (FIG. 8) in which the light sources 11 and 12 are arranged directly below the image display surface, and an edge light having the light source plate 10 and the light source 12 disposed on the side surface of the light guide plate 10. Any of the molds (FIG. 9) can be suitably used. The optical sheet 15 of the present embodiment is preferably disposed with the unevenness forming surface side as a light exit surface. Moreover, it is preferable that a reflection sheet 13 for reflecting light is used below the light sources 11 and 12. As long as the backlight unit has the above-described configuration, another optical sheet, a diffusion sheet, or the like may be further disposed. For example, between the light sources 11 and 12 and the optical sheet 15 of the present embodiment. A configuration in which the diffusion plate 14 is provided (FIG. 8) or a configuration in which the prism sheet 17 and the reflective polarizing sheet 18 are placed on the optical sheet 15 (FIG. 9B) can be employed. As the light source, a linear light source 11 such as a cold cathode fluorescent lamp (CCFL) or a point light source 12 such as an LED (light emitting diode) or a laser can be used.

  As the diffusing plate 14, various materials can be used as long as they can diffuse light. For example, polystyrene, acrylic resin, polycarbonate, cycloolefin polymer, or the like added with an organic polymer or inorganic fine particles having an effect of diffusing light can be used. These diffusing plates 14 have the effect of diffusing light and making light from the lower light source uniform. Further, the diffusion plate 14 may have an uneven shape on the surface. These may be added with an organic polymer or inorganic fine particles as necessary. A diffusion plate 14 in which two or more components of resin are mixed and stretched to form a sheet can also be used.

  The light guide plate 10 is a flat member whose base material is a transparent resin material having a certain refractive index, such as an acrylic resin such as methyl methacrylate resin, a polycarbonate resin, a polyolefin resin, or a cycloolefin resin. is there. The light guide plate 10 has a reflecting portion such as a reflective dot or a concavo-convex shape so that light incident from a light incident surface (one or a plurality of side end surfaces) is emitted from a light emitting surface substantially orthogonal to the side end surface. Have As the reflective part, silk printing method with reflective dots printed with white ink, molding method with irregularities on the base material surface by injection molding using stamper, and base material and reflector are pasted with dot-like adhesive material A reflective dot produced by an adhesive dot method, a dot method by groove processing, or the like is preferably used. The shape of the side end face of the light guide plate 10 is a taper type, a rectangular type, or the like. The light guide plate 10 used in the present invention may be a light guide plate made of a single plate or a light guide plate made of a plurality of block light guide plates.

  As the reflection sheet 13, various materials can be used as long as they can reflect light. For example, a resin such as polyester or polycarbonate is foamed and fine air particles are put inside to form a sheet, a sheet formed by mixing two or more resins, and a resin layer with a different refractive index is laminated. The sheet | seat etc. which were done can be used. In addition, the reflective sheet 13 may have an uneven shape on the surface. As these, those having inorganic fine particles added to the surface can be used as necessary.

  As the surface shaping type diffusion sheet, a sheet in which spherical beads of acrylic resin are coated on a sheet of polyester resin, triacetyl cellulose, polycarbonate, or the like can be used. In addition, as the surface-shaped diffusion sheet, a sheet in which a fine concavo-convex structure made of an ultraviolet curable resin is transferred onto a sheet of polyester resin, triacetyl cellulose, polycarbonate, or the like can be used. Such a surface-shaped diffusion sheet has a function of condensing the light diffused by the diffusion plate 14 as well as the effect of diffusing and uniformizing the light. By using the surface-shaped diffusion sheet in combination with the optical sheet 15 of this embodiment, it is possible to reduce luminance unevenness, reduce the thickness of the light source unit, and reduce the number of light sources.

  As the prism sheet 17, an optical sheet in which prism rows having a substantially triangular shape, a substantially trapezoidal shape, and a substantially elliptical shape are arranged in an array on the surface can be used. A shape obtained by rounding the top of the cross-sectional shape can be preferably used from the viewpoint of improving scratch resistance. These prism sheets can be used in a form in which a prism array made of an ultraviolet curable resin is transferred onto a base material sheet such as a polyester resin, triacetyl cellulose, or polycarbonate. Since such a prism sheet 17 exhibits retroreflectivity, it has a function of collecting incident light to the front. By using this prism sheet in combination with the optical sheet 15 of the present invention, luminance unevenness can be reduced, and the light source unit can be made thinner and the number of light sources can be reduced.

  As the reflective polarizing sheet 18, a sheet having a function of separating linearly polarized light from natural light or polarized light can be used. As a sheet | seat which isolate | separates linearly polarized light, the film etc. which permeate | transmit one of the linearly polarized light orthogonal to an axial direction, and reflect the other are mentioned, for example. Specifically, as the reflective polarizing sheet, a resin having a large birefringence retardation (polycarbonate, acrylic resin, polyester resin, etc.) and a resin having a small birefringence retardation (cycloolefin polymer, etc.) are alternately laminated. A sheet obtained by laminating and uniaxially stretching, a sheet (DBEF, manufactured by 3M Co., Ltd.) having a structure in which several hundred layers of birefringent polyester resin are laminated can be used.

  These backlight units can be used as a liquid crystal display device by combining with a liquid crystal display panel.

  Next, a liquid crystal display device using the backlight unit of the present embodiment described above will be described.

  FIG. 10 is a cross-sectional view of a liquid crystal display device using an edge light type backlight unit. The liquid crystal display device using the backlight unit of the present embodiment includes a liquid crystal display panel 118 that performs display by adjusting light transmission of the surface light source device, and the above-described backlight unit disposed on the back surface of the liquid crystal display panel. Have In the liquid crystal display device, the backlight unit is stored in the backlight chassis 119. The light guide plate 10 of the backlight unit has white dots 113. The liquid crystal display panel 118 includes a liquid crystal layer, two glass plates 1181 sandwiching the liquid crystal layer, and a polarizing plate 1182 provided on the front and back of the glass plate 1181.

  The backlight unit according to the present embodiment has both luminance unevenness suppression and high luminance. Therefore, by using the backlight unit of the present embodiment for a liquid crystal display device, it is possible to increase the luminance of the liquid crystal display device while ensuring the uniformity of display of the liquid crystal display device (uniformity of luminance).

Next, examples and comparative examples performed for clarifying the effects of the present invention will be described, but the present invention is not limited thereto.
Example 1

  In this example, the characteristics of the backlight unit using the optical sheet having the slope shape shown in FIG. 11 were evaluated. In other words, the optical sheet of this example has a unit lens pitch of 250 μm, a height of 40 μm, an inclination angle of 40 °, and a top lens occupying 45% of the top surface when viewed from above the optical sheet. A diffusion layer having a diffusing angle (FWHM) having a concavo-convex structure derived from speckles is formed on the surface. That is, the ratio of the area occupied by the entire diffusion layer when viewed in plan from directly above the optical sheet is 45%. At this time, the reflectance of the diffusion layer 5 at 550 nm is 6%. In addition, since the uneven structure derived from speckle is sufficiently smaller than the dimension of the unit lens, it hardly appears in FIG.

  The pitch, height, and slope angle of the unit lenses in the optical sheet of this example were measured with a fine shape measuring instrument ET4000 manufactured by Kosaka Laboratory. Moreover, the ratio of the area occupied in the entire diffusion layer when viewed in plan from directly above the optical sheet was calculated by taking a micrograph. The diffusion angle shown in the present example is an angle measured with an LD 8900 after entering light from a surface having a fine concavo-convex structure. For example, when 5 ° is indicated, it indicates that the FWHM in any direction is an isotropic optical sheet of 5 °. Further, in the case of 30 × 10 °, an anisotropic optical sheet in which the diffusion angle in the direction in which the diffusion angle is minimum is 10 ° and the diffusion angle in the direction in which the diffusion angle is maximum is 30 °. Represents something. The reflectance is a reflectance measured by MPC-2200 when the specular reflectance is incident on the back surface of the surface having a fine concavo-convex structure at an incident angle of 5 °. Table 1 shows each parameter.

[Brightness improvement]
As shown in FIG. 9B, the reflection sheet 13 is disposed under the light guide plate 10, the optical sheet of this embodiment is disposed as the optical sheet 15 on the light guide plate 10, and the prism sheet 17 and The reflective polarizing sheets 18 were sequentially arranged to configure the backlight unit for luminance evaluation of this example. In addition, about optical members other than an optical sheet, ie, white LED, the reflective sheet 13, the light-guide plate 10, the prism sheet 17, and the reflective polarizing sheet 18, what was used for KDL-32EX700 by SONY is used, respectively. .

  A two-dimensional color luminance meter (CA-2000) manufactured by Konica Minolta Sensing Co., Ltd. was installed 75 cm away from the backlight unit, and the average value measured in a circle with a diameter of 35 mm in the center of the backlight unit was defined as the luminance. . The luminance change rate (%) is calculated from the luminance of this example and the luminance of Comparative Example 1 described later, and is shown in Table 1 as an index representing the luminance improvement.

[Unevenness concealment]
As shown in FIG. 9A, the reflection sheet 13 is disposed under the light guide plate 10, and the optical sheet of the present embodiment is disposed as the optical sheet 15 on the light guide plate 10. The backlight unit was configured. In addition, about optical members other than an optical sheet, ie, white LED, the reflective sheet 13, and the light-guide plate 10, what was used for KDL-32EX700 by a SONY company was used, respectively. Table 1 shows the results of visual evaluation of unevenness concealment, with ○ indicating that the reflective dots formed of white dots on the light guide plate 10 are not visible, and x indicating that the dots are visible.

(Example 2)
In this example, instead of the optical sheet in Example 1, the area occupied by the diffusion layer is 45% of the total when viewed in plan from directly above the sheet, and the diffusion angle (FWHM) of the diffusion layer having a concavo-convex structure derived from speckle The characteristics were evaluated using a backlight unit in which an optical sheet having a 60 × 1 ° and a reflectance of 8% was disposed so that the diffusion layer diffuses light in a direction parallel to the LED array. Other parameters of the optical sheet are the same as those in the first embodiment. That is, the cross-sectional shape of the unit lens has a slope shape shown in FIG. The measurement method and evaluation method for each parameter are the same as in Example 1. The measurement results and evaluation results are shown in Table 1.

(Comparative Example 1)
In this comparative example, instead of the optical sheet in Example 1 or Example 2, the characteristics were evaluated using a backlight unit in which TDF-127 (manufactured by Toray Industries, Inc.), which is an isotropic diffusion sheet, was disposed at the same position. . The evaluation method is the same as in Example 1. The evaluation results are shown in Table 1.

(Comparative Example 2)
In this comparative example, instead of the optical sheet in Example 1 or Example 2, the characteristics were evaluated using a backlight unit in which an isotropic diffusion sheet having an FWHM of 30 ° and a reflectance of 6% was disposed at the same position. . The measurement method and evaluation method for each parameter are the same as in Example 1. The measurement results and evaluation results are shown in Table 1.

(Comparative Example 3)
In this comparative example, instead of the optical sheet in Example 1 or Example 2, light is diffused in the direction parallel to the LED array in the same position with an anisotropic diffusion sheet having FWHM 60 × 1 ° and a reflectance of 8%. The characteristics were evaluated using the backlight unit arranged as described above. The measurement method and evaluation method for each parameter are the same as in Example 1. The measurement results and evaluation results are shown in Table 1.

(Comparative Example 4)
In this comparative example, instead of the optical sheet in Example 1 or Example 2, when viewed in plan from directly above the sheet, the area occupied by the top surface is 45% of the entire surface, and the cross-sectional shape of the unit lens is shown in FIG. The characteristics were evaluated using a backlight unit in which an optical sheet having no diffusion layer on the top surface was disposed at the same position. The measurement method and evaluation method for each parameter are the same as in Example 1. The measurement results and evaluation results are shown in Table 1.

  As shown in Table 1, the optical sheets of Example 1 and Example 2 in which the diffusion layer and the slope having the light collecting function are fused are compared with the diffusion sheets of Comparative Examples 1 to 3 having no light collecting slope. As a result, the effect of improving brightness is high, and the unevenness concealing property is high and the brightness is high as compared with the optical sheet of Comparative Example 4 that has a slope having a light collecting function but no diffusion layer. In the optical sheets of Example 1 and Example 2, it has a slope suitable for condensing, and further, the light that has not been collected is also collected again through reflection, and the brightness enhancement effect is obtained at a high level, This is because light is diffused appropriately by the diffusion layer, so that the unevenness concealing property can be obtained at a high level.

  The optical sheet of the present invention is suitably used for backlights of various display devices.

DESCRIPTION OF SYMBOLS 1 Optical sheet 2 Base film 3 Unit lens 4 Top surface 5 Diffusion layer 6 Bottom line or bottom surface 7 Slope 10 Light guide plate 11 Linear light source
12 Point Light Source 13 Reflective Sheet 14 Diffuser 15 Optical Sheet 17 Prism Sheet 18 Reflective Polarizing Sheet

Claims (12)

A base film having optical transparency;
A plurality of unit lenses formed on one surface of the base film and having a substantially trapezoidal cross-sectional shape perpendicular to the one surface of the base film;
An optical sheet comprising: a diffusion layer that is formed on a top surface of the unit lens and diffuses light collected by the unit lens.   2. The optical sheet according to claim 1, wherein the plurality of unit lenses include a plurality of parallel light-transmitting members having a prismatic shape extending in a specific direction.   The optical sheet according to claim 1, wherein the unit lens is made of a light transmissive member having a substantially frustum shape.   The planar area from the direction perpendicular | vertical to the said one surface of the said base film WHEREIN: The area which the said diffusion layer occupies is 5% or more and 70% or less of the area of the said whole base film, The any one of Claims 1-3 characterized by the above-mentioned. The optical sheet according to claim 1.   The optical sheet according to claim 1, wherein the unit lens has an inclination angle of 15 ° to 60 °.   The optical sheet according to any one of claims 1 to 5, wherein a reflectance at 550 nm of the diffusion layer is 3% or more and 15% or less.   The optical sheet according to any one of claims 1 to 6, wherein a diffusion angle of the diffusion layer is 0.1 degrees or more and 150 degrees or less.   The optical sheet according to claim 1, wherein the surface of the diffusion layer has an uneven structure.   The optical sheet according to claim 8, wherein the concavo-convex structure is a concavo-convex structure formed using a speckle pattern formed by interference exposure.   The optical sheet according to claim 1, wherein the unit lens and the diffusion layer are provided integrally.   A backlight unit comprising the optical sheet according to claim 1.   A liquid crystal display device comprising the backlight unit according to claim 11.