JP2011170180A - Optical sheet, backlight unit, and display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical sheet which has high scratch-resistance and is not scratched even when used in combination with a sheet having optical functionality, and which has concealing property required for concealing shade nonuniformity, a scratch of a light diffuser plate, or the like. <P>SOLUTION: The optical sheet 25 which is used for illumination light path control to control a light path of light incident from a light source and emit light, and in which a functional sheet 2 having other optical function is laminated on a light emitting face side, has an optical shape for focusing or diffusing the light on the light emitting face, and the optical shape has a plurality of microlenses 100 which are arranged independently and form substantially hemisphere shapes, and a light deflection element 110 that is arranged between the microlenses 100 and extends along the light emitting face, and only top portions of the microlenses 100 are made to abut on the functional sheet 2. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an optical sheet, a backlight unit, and a display device used for optical path control.

  Liquid crystal display devices using liquid crystal panels are widely used not only for image display means for mobile phones, personal digital assistants, and personal computer displays, but also for televisions as home appliances.・ Image display devices for large-size information appliances that have been difficult with Ray Tube (CRT) televisions are also spreading to general households. In addition, in order to make better use of the advantages of liquid crystal display devices, not only large-size products but also products that support high brightness, thinness, and weight reduction are being supplied to the market at high speed.

  Many of such liquid crystal display devices have a built-in light source, and a backlight unit including a light source is provided on the back side of the liquid crystal panel in order to obtain the brightness necessary for displaying an image. The configuration is arranged. As the light source used in this backlight unit, a light source typified by a cold cathode tube or a light emitting diode (LED) is arranged on the side surface of the liquid crystal display device, and it is made of resin with excellent light transmittance. A “light guide plate light guide method” (so-called edge light method) that performs multiple reflections in a flat light guide plate is also known, and an image display element and a light source disposed on the back side of a liquid crystal display device There is known a “direct type” having a configuration in which a light diffusing plate and an optical film having a strong light scattering property are arranged so that a cold-cathode tube or an LED is not directly visible.

  In the liquid crystal display device as described above, suppression of power consumption for the purpose of reducing energy consumption as part of countermeasures for global environmental problems has become a major issue. In the case of a liquid crystal display device, the power consumption of the backlight serving as the light source is the largest, and efforts to suppress the power consumption of the backlight are widely performed.

  As one of these efforts, attempts have been made to reduce power consumption by reducing the number of cold cathode tubes, which are light sources, and the effect of reducing power consumption is widely recognized by society. However, reducing the number of cold-cathode tubes will increase the brightness unevenness (lamp image) that is the brightness of the light source, and the lamp image will not be completely erased by the countermeasures by the combination of the light diffusion plate and the optical sheet so far. It has become difficult. When diffusing particles are increased in the light diffusing plate in order to erase the lamp image, it is difficult to obtain the luminance necessary for image display by lowering the total light transmittance of the light diffusing plate. In this case, a desired luminance can be obtained by increasing the intensity of light from the cold cathode tube as a light source, but there is a problem that power consumption increases.

  In addition, a liquid crystal display device using an LED light source has been proposed in expectation of reduction in power consumption. In this liquid crystal display device, the direct light method in which the LED light source is arranged on the back side of the liquid crystal display device and the edge light method in which the LED light source is arranged on the side surface side of the liquid crystal display device are adopted, and the contrast ratio is improved as compared with the conventional case. Products are being introduced to the market. However, there still remains a problem that heat generation around the LED light source cannot be suppressed and a desired luminance cannot be obtained.

  That is, in order to suppress heat generation and reduce power consumption, it is effective to reduce the number of LED light sources, but in this case, it is difficult to obtain the required luminance. Further, there remains a problem of brightness unevenness that is light and dark of the light source and visibility of the LED light source, and further, it is necessary to improve the visibility of the pattern for uniform brightness provided on the light guide plate. In this regard, attempts have been made to improve the characteristics of the light diffusing plate and the optical sheet, and to ensure the required luminance and make the luminance uniform by combining them optimally.

  In the above optical sheet, conventionally, as a method for improving the light use efficiency of the light source, a method of collecting diffused light from the backlight unit by the optical sheet and improving the front luminance has been adopted. A brightness enhancement film (BEF: Brightness Enhancement Film), which is a registered trademark of the company, is widely used as an optical sheet. This BEF is a sheet in which unit prisms having a triangular cross section are arranged at a constant pitch in one direction on the upper surface of a transparent substrate, condensing light from “off-axis”, This light is redirected “on-axis” or “recycled” towards the viewer. Thus, when light incident from the flat surface of the substrate exits from the prism surface, the light is collected in the front direction, and the luminance in the front direction can be improved.

  Here, the optical sheet used in the liquid crystal display device has various functions such as not only improving luminance by improving light utilization efficiency but also removing unevenness of the light source, securing the viewing area of the display, and maintaining the rigidity of the display. Is required. Therefore, in order to realize desired optical characteristics, a plurality of layers are often stacked on the light diffusion plate (on the liquid crystal panel side). However, when this BEF is used as an optical sheet, the vertical viewing angle is very narrow with respect to the horizontal viewing angle because the BEF vertical light is refracted by the prism surface and emitted in the normal direction. There is a problem, and furthermore, since the top of the prism is sharp, there is a drawback that scratches are likely to occur when contacting the optical sheet or functional member disposed on the prism or a liquid crystal panel.

  Attempts have been made to reduce the number of optical sheets to be used while compensating for these drawbacks and maintaining equivalent optical characteristics and environmental characteristics. For example, Patent Document 1 describes a method of imparting a diffusing function to the condensing function of a prism by dispersing diffusible fine particles in the prism lens. Further, in Patent Document 2, by arranging microlenses randomly on a base material, light incident from the back surface is condensed by the microlens and emitted forward, and the same optical performance is achieved with fewer optical sheets than in the past. A method for achieving the above has been proposed.

JP-A-10-246805 JP 2006-301528 A

  By the way, the optical sheet described in Patent Document 1 has a diffusing function in addition to a condensing function. However, since the diffusing fine particles are dispersed in the prism, the light collected on the front surface is caused by the diffusing fine particles. It diffuses again, and the amount of light in the front direction decreases. Further, there is a problem that glare due to refraction and reflection at a specific angle of the lens is visually recognized. Furthermore, since the tip of the prism is sharp, scratches are likely to occur on the back surface of the optical sheet placed on the top and the functional sheet having a different optical function, and foreign matter due to contact or friction is generated. It also has the problem of doing.

  In particular, optical sheets and functional sheets that are used in a stacked state may be used with their four sides fixed to the frame of the device when placed in a liquid crystal display device, but they are fixed without moving completely inside the device. However, it may come into contact with other optical sheets or optical members having functionality, and may be rubbed and scratched due to vibration during conveyance or movement. Further, when driving the liquid crystal display device, the optical sheet and the optical member having functionality are warmed by the heat generated from the light source, and as a result, expansion and contraction depending on the physical properties specific to the material to be formed occurs in the plane. Since changes and flexures occur, it may be rubbed and scratched by contact with other optical sheets or optical members having functionality.

  As a measure to improve the scratch resistance and prevent the generation of foreign matter, it is sometimes used to round the prism top, but the width to cut the prism top and the front luminance are inversely proportional, so it is desirable In order to achieve the scratch resistance, the front luminance is lowered.

  On the other hand, since the optical sheet described in Patent Document 2 has a hemispherical lens, even if it comes into contact with an optical sheet or a functional sheet that is used in a stacked manner, it is slippery because of its rounded structure. It has the characteristic that it is hard to be damaged. However, since a gap is generated between adjacent microlenses, light that passes through the microlens and is refracted and scattered at the interface between the microlens and the air layer and collected on the front surface can be formed between the adjacent microlenses. There is a problem that light emitted without being refracted and scattered from the gap is generated, and a bright spot and a bright line are visually recognized due to a luminance difference between these lights.

  The present invention has been made in view of such problems, and has high scratch resistance that is not damaged even when used in combination with a light condensing / diffusion characteristic and a sheet having a plurality of functionalities. Furthermore, it is an object of the present invention to provide an optical sheet having a concealing property necessary for concealing light / dark unevenness of a light source and a scratch on a light diffusing plate, a backlight unit including the optical sheet, and a display device. .

In order to solve the above problems, the present invention proposes the following means.
In other words, the optical sheet according to the present invention is used for illumination optical path control that emits light by controlling the optical path of light incident from the light source, and a functional sheet having other optical functions is laminated on the light exit surface side. An optical sheet having an optical shape for condensing or diffusing light on a light exit surface, wherein the optical shape is a substantially hemispherical microlens arranged independently of each other, and these microlenses And a plurality of light deflection elements extending along the light emitting surface, and only the tops of the microlenses are configured to contact the functional sheet, respectively. And

  According to the optical sheet having such a feature, only the smooth top of the microlens that slides easily and is not easily damaged is brought into contact with the functional sheet, and the tip of the light deflecting element having a linear structure that is easily damaged is the functional sheet. They are arranged apart from each other without contacting the Therefore, it is possible to improve the scratch resistance of the light emitting surface, and at the same time, it is possible to provide an optical sheet having both the optical characteristics of the substantially hemispherical microlens and the light deflection element having a linear structure.

  In the optical sheet, the protrusion height of the microlens is H1, the amount of deflection between the pair of microlenses of the functional sheet that contacts at least the pair of microlenses is H2, and the light deflection element It is preferable that the relationship of H3 <H1-H2 is satisfied when the protrusion height of H3 is H3.

  Thereby, it is possible to reliably avoid contact between the tip of the light deflection element and the functional sheet. Therefore, it is possible to avoid a decrease in optical characteristics due to the tip of the light deflection element being crushed, and to prevent the functional sheet from being damaged by the tip of the light deflection element.

Furthermore, in the engineering sheet, it is preferable that the area of the top of the microlens that contacts the functional sheet in a plan view is set to a range of 10% or less of the bottom area of the microlens.
Thus, by reducing the contact area of the functional sheet with respect to the microlens, it is possible to suppress the occurrence of friction scratches due to contact.

Moreover, in the said optical sheet, it is preferable that the fine uneven | corrugated shape is provided to the surface of the said micro lens and the said optical deflection | deviation element. Furthermore, it is preferable that this fine uneven | corrugated shape is an unevenness | corrugation whose surface roughness Ra is the range of 0.1 micrometer-10 micrometers.
By providing fine irregularities on the light emitting surface side in this way, it is possible to further enhance the scratch resistance on the light emitting surface side, and at the same time, increase the light diffusion function to improve the viewing angle and concealment. Can be achieved.

Furthermore, in the optical sheet, a plurality of substantially hemispherical protrusions may be formed on the light incident surface.
Thereby, the scratch resistance of the light incident surface of the optical sheet can be improved, and the light diffusibility can be enhanced by the light being refracted by the projection. As a result, the viewing angle can be increased and the concealability can be improved.

Moreover, in the said optical sheet, it is preferable that the fine uneven | corrugated shape is provided to the surface of the said light-incidence surface. Furthermore, it is preferable that this fine uneven | corrugated shape is an unevenness | corrugation whose surface roughness is the range of 0.5 micrometer-5 micrometers.
By providing fine irregularities on the light incident surface side in this way, it is possible to improve the scratch resistance on the light incident surface side, and at the same time, increase the light diffusion function to increase the viewing angle and improve the concealability. It becomes possible to plan.

The backlight unit according to the present invention includes any one of the optical sheets described above and a light source that irradiates light to the light incident surface of the optical sheet.
Furthermore, the display device according to the present invention includes the backlight unit and an image display unit that defines a display image according to transmission / light-shielding in pixel units and displays an image by light irradiation from the backlight unit. It is characterized by having.

According to the optical sheet of the present invention, it is possible to improve the scratch resistance of the light emitting surface, and at the same time, to exhibit the optical characteristics of the substantially hemispherical microlens and the light deflection element. Therefore, an optical sheet having high scratch resistance and concealment can be provided.
Further, according to the backlight unit and the display device according to the present invention, since the optical sheet is provided, it is possible to exhibit high luminance without luminance unevenness while having high scratch resistance.

It is a longitudinal cross-sectional view of the display apparatus which concerns on embodiment. It is a longitudinal cross-sectional view of the optical sheet and functional sheet of the display apparatus which concern on embodiment. FIG. 3 is an enlarged view of FIG. 2. It is the longitudinal cross-sectional view of the optical sheet of the display sheet which concerns on embodiment, and a functional sheet, and the top view of an optical sheet. It is a longitudinal cross-sectional view of the optical sheet of the display sheet which concerns on embodiment, a functional sheet, and a light diffusing plate. It is a longitudinal cross-sectional view which shows the other structure of the display apparatus which concerns on embodiment. It is a figure which shows the cross-sectional shape of an optical deflection | deviation element.

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.
1 to 6 are examples of schematic cross-sectional views illustrating the configuration of the optical sheet, the backlight unit, and the display device according to the present embodiment, and their usage, and the scales or ratios of the respective parts do not match the actual ones. . Moreover, it is not limited to the aspect shown in these drawings.

  As shown in FIG. 1, a display device 70 according to an embodiment of the present invention includes a liquid crystal display configured by providing an image display element 35 on a backlight unit 55 that irradiates light to an observer side. This is a device that emits display light whose display is controlled by an image signal from the image display element 35 toward the viewer side F, thereby displaying a planar image. In the following, the upper direction in FIG. 1 is referred to as the observer side or the front side, and the lower direction is referred to as the back side.

The image display element 35 includes two polarizing plates (polarizing films) 31 and 33 and a liquid crystal panel 32 sandwiched between them. The liquid crystal panel 32 is configured, for example, by filling a liquid crystal layer between two glass substrates.
The light K emitted from the backlight unit 55 is incident on the liquid crystal panel 32 via the polarizing plate 33 on the back side and is emitted to the viewer side via the polarizing plate 31 on the viewer side.

  The image display element 35 is preferably an element that displays an image by transmitting / blocking light in pixel units. If the image is displayed by transmitting / blocking light in pixel units, the optical sheet 25 improves the luminance toward the viewer side and reduces the viewing angle dependency of the light intensity. It is possible to display an image with high image quality by effectively using the light with reduced image quality.

  The image display element 35 is preferably a liquid crystal display element. A liquid crystal display element is a typical element that transmits / shields light in pixel units and displays an image, and can improve image quality and reduce manufacturing cost compared to other display elements. Can do.

  The display device 70 is a liquid crystal display device including the image display element 35 as described above. However, as long as the display device 70 includes at least the backlight unit 55, a projection screen device, a plasma display, an EL display, or the like is used. The type of the image display unit that displays an image using the light from the backlight unit 55 as display light is not limited.

The backlight unit 55 is configured by laminating and arranging the light source unit 45, the light diffusion plate 50, the optical sheet 25, and the functional sheet 2 in this order.
Note that the number of functional sheets 2 is not limited to a single sheet, and a plurality of sheets may be provided.

The light source unit 45 supplies light toward the front side, and a direct type is adopted in the present embodiment. The light source unit 45 has a configuration in which a plurality of light sources 41 are arranged in a lamp house (reflecting plate) 43.
As the light source 41, for example, a plurality of linear light sources can be employed. As these linear light sources, fluorescent lamps, cold cathode fluorescent lamps (CCFLs), EEFLs, or LEDs arranged continuously in a linear form can be used.

  The reflector 43 is disposed so as to cover the back side and the side of the plurality of light sources 41, and on the side opposite to the observer side F and the side of the light emitted from the light source 41 in all directions. It plays the role of reflecting the emitted light and emitting it to the viewer side F. As a result, the light H emitted to the observer side F can be approximated as light emitted from the light source 41 in all directions. Thus, the use efficiency of light is improved by using the reflecting plate 43. The reflection plate 43 may be any member that reflects light with high efficiency. For example, a general reflection sheet, reflection plate, or the like can be used.

The light diffusing plate 50 is, for example, a member formed by dispersing a light diffusing region in a transparent resin into a plate shape, and plays a role of diffusing light emitted from the light source unit 45.
As the transparent resin, a thermoplastic resin, a thermosetting resin or the like can be used. For example, a polycarbonate resin, an acrylic resin, a fluorine acrylic resin, a silicone acrylic resin, an epoxy acrylate resin, a polystyrene resin, a cycloolefin polymer, Methyl styrene resin, fluorene resin, polyethylene terephthalate (PET), polypropylene, acrylonitrile polystyrene copolymer, and the like can be used.

  The light diffusion region is preferably made of light diffusion particles. This is because suitable diffusion performance can be easily obtained. As the light diffusing particles, transparent particles made of an inorganic oxide or a resin can be used.

The functional sheet 2 is a sheet made of resin, and is a kind of optical sheet having a function different from that of the optical sheet 25 of the present embodiment, which will be described in detail later, and is laminated on the light emitting side of the optical sheet 25. Are arranged as follows. The light incident surface of the functional sheet 2 has a flat shape, and optical shapes such as various lenses and prisms are formed on the light emitting surface side to provide a desired optical function. In the present embodiment, the optical shape on the light exit surface of the functional sheet 2 is omitted, but examples include optical shapes such as a triangular prism array, a cylindrical array, and a microlens.
The functional sheet 2 may be a light diffusing plate whose main function is to diffuse light in addition to such a configuration.

  The optical sheet 25 includes a substantially sheet-like base material 90, a substantially hemispherical microlens 100 and a linear structure light deflection element 110 disposed on the light emitting surface side of the base material 90, and the base material 90. And a substantially hemispherical protrusion 120 disposed on the light incident surface.

The substantially hemispherical microlens 100 and the light deflecting element 110 having a linear structure on the light exit surface side improve the luminance by condensing the light H incident through the light diffusion plate 50 according to its shape. Have a role.
On the other hand, the projection 120 having a substantially hemispherical shape on the light incident surface side is mainly intended to prevent the occurrence of scratches due to contact with or rubbing with the light diffusion plate 50.
In addition, this optical sheet 25 can be used not only for a liquid crystal device but for any one that performs optical path control, such as a rear projection screen, a solar cell, an organic or inorganic EL, and an illumination device.

  Further, since the optical sheet 25 is provided with a fine uneven shape on the light emitting surface side or the light incident surface side, the viewing angle can be expanded by diffusing with the light H from the light source 41 by the fine uneven shape. . Furthermore, when observing the light source 41 side from the observer side F through the image display element 35, the luminance unevenness, the lamp image, the light / dark difference, and the like due to the light source 41 are reduced, and uniform light in the screen is observed on the observer side. F can be injected. Further, it is possible to prevent a predetermined pattern provided for the purpose of reducing the lamp image on the front or back surface of the light diffusing plate 50 or a structure showing a required function from being seen through the observer side F. You can also

  3 and 4 are diagrams illustrating a cross-sectional structure of the optical sheet 25 according to the embodiment. A substantially hemispherical microlens 100 and a light deflecting element 110 having a linear structure are provided on the light exit surface side, and a substantially hemispherical microlens 100 with reference to a valley of the light deflecting element 110 having a linear structure. The protrusion height H1 is set to be higher than the protrusion height H3 of the light deflection element 110 having a linear structure.

  As described above, the protrusion height H1 of the microlens 100 is set to be larger than the protrusion height H3 of the light deflection element 110, so that the functional sheet 2 laminated on the light emitting surface of the optical sheet 25 is 2 and 3, the light incident surface is in contact with the top of the microlens 100. Thereby, the light deflection element 110 and the functional sheet 2 are separated from each other.

  Here, the functional sheet 2 is made of a transparent resin and has a slight elasticity. Therefore, when contacting the microlens 100 as described above, as shown in FIGS. 2 and 3, the functional sheet 2 that contacts the pair of adjacent microlenses 100, 100 has the pair of microlenses. The vicinity of the middle of the distance L between 100 and 100 is bent so as to be convex toward the optical sheet 25 side.

  In the optical sheet 25 of the present embodiment, when the deflection amount of the functional sheet 2 is H2 (see FIG. 3), the protrusion height of the microlens 100 is set so that the relationship of H3 <H1-H2 is established. The height H1 and the protrusion height H3 of the light deflection element 110 are designed respectively. That is, the dimension obtained by subtracting the protrusion height H3 of the light deflection element 110 from the protrusion height H1 of the microlens 100 is designed to be smaller than the deflection amount H2 of the functional sheet 2.

  Here, the deflection amount H2 of the functional sheet 2 is determined by the characteristics of the polymer material of the resin used (particularly, the elastic modulus that varies depending on the temperature), the environment in which the display device 70 is placed, and the heating during use. It is calculated as the maximum amount of deflection found under the assumption of the environment. Thereby, the light deflecting element 110 having a linear structure provided on the light incident surface side of the functional sheet 2 and the light emitting surface side of the optical sheet 25 does not come into contact under any use environment. Therefore, it is possible to prevent the functional sheet 2 from being damaged by friction by the light deflecting element 110 having a linear structure.

  Further, the deflection amount H2 of the functional sheet 2 depends on the interval L between the pair of microlenses 100, and the deflection amount H2 increases as the interval L increases. In the present embodiment, the microlenses 100 may be arranged at regular intervals represented by a square arrangement or a hexagonal arrangement, or may be a random arrangement in which the intervals L are not uniform.

  Note that the interval L between the microlenses 100 in the aligned arrangement varies depending on the area ratio occupied by the microlenses 100 in the light exit surface, that is, the area ratio indicated by the microlenses 100 in plan view. When the area ratio of the microlens 100 is high, the interval L is narrowed, and when the area ratio is low, the interval L is increased. That is, the area ratio of the microlens 100 influences the optical characteristics of the optical sheet 25. When the area ratio of the microlens 100 is set high, the viewing angle is widened, but the luminance tends to decrease. . On the other hand, when the area ratio of the microlens 100 is set low, the luminance is improved, but the viewing angle tends to be narrow.

  In addition, the random arrangement in which the intervals L of the microlenses 100 are non-uniform is advantageous in that the occurrence of interference fringes with the regular structures of the image display element 35 and the functional sheet 2 is prevented. have. Further, in this random arrangement, unlike in the case of the arrangement arrangement, the locations where the distance L of the microlenses 100 where the deflection amount H2 of the functional sheet 2 is the maximum are also randomly arranged. For this reason, when the area ratio of the microlens 100 is low, the interval L between the microlenses 100 becomes large. Therefore, when creating the random arrangement data, it is necessary to set a numerical value of the maximum interval L. Arise. In the optical sheet 25 of the present embodiment, the maximum deflection amount H2 is found from the maximum interval L in this random arrangement, and the area ratio, diameter, width, and height of the substantially hemispherical microlens 100 and the light deflection element 110 are found. It is necessary to set the specifications.

  The area ratio of the above-described substantially hemispherical microlens 100 is a specification value determined from the optical characteristics required for the optical sheet 25, and this area ratio sets the number of arranged microlenses 100 and the diameter in the light exit surface. It becomes a numerical value determined by doing. Here, the diameter of the microlens 100 that determines the area ratio of the microlens 100 is desirably set to 50 μm or more and 200 μm or less. When the diameter exceeds 200 μm, the microlens 100 itself is easily visible, which leads to the appearance of unevenness, roughness, and bright spots on the light exit surface. On the other hand, when the diameter of the microlens 100 is 50 μm or less, the height of the light deflecting element 110 having a linear structure is limited to a small size. Will cause a decline. Note that the shape seen from the upper surface of the substantially hemispherical microlens 100, that is, the shape in plan view, is preferably substantially circular, and may be other shapes such as an elliptical shape.

The area ratio of the microlens 100 is desirably set within a range of 10% to 60% of the light exit surface in the preferable diameter of the microlens 100 described above. When the area is 10% or less, the number of the substantially hemispherical microlenses 100 that exist independently decreases, and the effect of hardly scratching the light emitting surface indicated by the microlens 100 is reduced. Further, since the distance L between the microlenses 100 becomes too wide, the light deflection element 110 and the microlens 100 are liable to come into contact with each other, and the shape, width, and protruding height of the light deflection element 110 having a linear structure are increased. This is not preferable because H3 is greatly limited. Further, when the area ratio of the light deflecting element 110 having the linear structure is increased, there is a possibility that interference fringes are likely to be generated with the regular structure of the image display element 35 or the functional sheet 2. Furthermore, in the expansion of the viewing angle, which is another effect of the microlens 100, the effect is reduced by reducing the number.
The area of the microlens 100 is the area value in the projected shadow of the light emitting surface in plan view, that is, the area value of the bottom surface of the microlens 100 on the plane including the valleys of the light deflection element 110 having a linear structure. Show.

  On the other hand, when the area ratio of the microlens 100 is 60% or more, the effect of hardly scratching the light exit surface is greatly improved. However, since the area ratio of the light deflecting element 110 is relatively lowered, the effect of increasing the concentration of light by the light deflecting element 110 to improve the brightness is reduced, and as a result, the entire optical sheet 25 is reduced. This leads to a decrease in the optical characteristics. Further, when the microlenses 100 are randomly arranged, it is easy to have some regularity in the arrangement, and the image display element 35 or the functional sheet 2 having a regular structure is likely to generate interference fringes. This is not preferable.

  The shape of the microlens 100 is good when it comes into contact with the functional sheet 2 and its small contact area leads to the functional sheet 2 being hardly scratched. Therefore, as for the shape of the microlens 100, it is desirable that the shape of the top part to be contacted is close to a hemisphere. Furthermore, it is preferable that the area in contact with the light incident surface of the functional sheet 2 laminated on the light emitting surface is 10% or less of the bottom area of the microlens 100. Thereby, it becomes possible to suppress the occurrence of frictional flaws due to contact.

  The protrusion height H1 of the microlens 100 is desirably increased in order to improve the light condensing property and improve the luminance. When the aspect ratio is a value obtained by dividing the protrusion height H1 of the microlens 100 by the diameter, the value is preferably 40% or more. As a result, the cross-sectional shape becomes closer to a hemispherical shape, and as a result, the tip portion of the microlens is likely to have a rounded shape that is less likely to be scratched.

  As shown in FIG. 6A, the light deflection element 110 preferably has a triangular prism shape in cross section perpendicular to the extending direction. The reason is that the lens can be easily molded and the brightness is improved by controlling the direction of the emitted light. Further, a convexly curved lens shape as shown in FIG. This is because the emission performance can be improved because the exit surface can be set at various angles. The convexly curved lens shape may be an aspherical shape as shown in FIG. 6C, and the reason is that the diffusion performance can be increased because the radius of curvature of the apex can be reduced. It is done. Furthermore, a curved triangular prism as shown in FIG. 6D may be used, and the light emission surface can be set at various angles, so that the diffusion performance is improved. The light deflection element 110 may be configured by combining a plurality of the above-described cross-sectional shapes. This is because the optical performance can be expected to be improved by combining the condensing and diffusing effects of two or more light deflection elements.

  The width and height of the light deflection element 110 are determined by the relationship with the microlens 100, and the width is preferably 20 μm or more and 150 μm or less. In the case of 20 μm or less, the luminance is reduced due to the diffraction effect of light, and it is difficult to maintain high shape accuracy when processing and shaping the light deflection element 110, leading to a reduction in luminance. Further, when the thickness is 150 μm or more, the height and area ratio of the light deflection element 110 are increased, so that the light incident surface side of the functional sheet 2 that is laminated and disposed on the light emitting surface may be damaged. There is sex. Further, it is not preferable because the image display element 35 or the functional sheet 2 has a regular structure and interference fringes are easily generated, and the viewing angle is narrowed.

  On the other hand, the protrusion height H3 of the light deflection element 110 is desirably set in the range of 20% to 60% of the protrusion height H1 of the microlens 100. When the protruding height H3 of the light deflecting element 110 is less than 20% of the protruding height H1 of the microlens 100, the width and height of the light deflecting element 110 itself are reduced, causing a decrease in luminance as described above. there is a possibility. In addition, when it exceeds 60%, there is a possibility that the functional sheet 2 laminated on the light emitting surface is in contact with the light incident surface side and may be damaged, or the image display element 35 or the functional sheet. 2 is not preferable because the structure having the regularity of 2 and interference fringes are likely to be generated, and the viewing angle is narrowed.

  The microlens 100 and the light deflection element 110 that have been described so far can be formed on a highly transparent sheet-like substrate 90 using an electron beam curable resin typified by a UV curable resin. As an example, there is a technique in which the microlens 100 and the light deflection element 110 are UV molded using a mold in which the microlens 100 and the light deflection element 110 having dimensions designed in advance are formed. Here, as a material of the highly transparent sheet, PET (polyethylene terephthalate), PC (polycarbonate), PMMA (polymethyl methacrylate), COP (cycloolefin polymer), acrylonitrile styrene copolymer, acrylonitrile polystyrene copolymer And so on.

  Further, the material used for the microlens 100 and the light deflection element 110 is preferably a transparent resin made of a thermoplastic resin. For example, polycarbonate resin, acrylic resin, fluorine acrylic resin, silicone acrylic resin, epoxy acrylate resin, polystyrene Examples thereof include resins, cycloolefin polymers, methylstyrene resins, fluorene resins, PET, polypropylene, acrylonitrile styrene copolymers, acrylonitrile polystyrene copolymers, and the like. It can also be formed by an extrusion molding method using these materials, an injection molding method, or a hot press molding method.

  The microlens 100 and the light deflection element 110 can be used by adding inorganic fine particles or organic fine particles for the purpose of improving diffusibility. Examples include acrylic particles, styrene particles, styrene acrylic particles and cross-linked products thereof, melamine-formalin condensate particles, polyurethane particles, polyester particles, silicone particles, fluorine particles, copolymers thereof, smectites. , Clay compound particles such as kaolinite, talc, inorganic oxide particles such as silica, titanium oxide, alumina, silica alumina, zirconia, zinc oxide, barium oxide, strontium oxide, calcium carbonate, barium carbonate, barium chloride, barium sulfate, Examples thereof include inorganic fine particles such as barium nitrate, barium hydroxide, aluminum hydroxide, strontium carbonate, strontium chloride, strontium sulfate, strontium nitrate, strontium hydroxide, and glass particles.

  The microlens 100 and the light deflection element 110 are preferably those to which an ultraviolet absorber is added. By adding the ultraviolet absorber, it is possible to suppress the deterioration of the microlens 100 and the light deflection element 110 due to the ultraviolet rays irradiated from the light source 41 due to the ultraviolet rays, thereby extending the life. Examples of the ultraviolet absorber include benzotriazole compounds such as 2- (2′-hydroxy-5′-methylphenyl) benzotriazole, benzophenone compounds such as 2-hydroxy-4-methoxybenzophenone, and 4-t- Salicylic acid ester compounds such as butylphenyl salicylate, oxalic acid anilide compounds such as 2-ethoxy-2′-ethyl oxalic acid bisanilide, and cyanoacrylates such as ethyl-2-cyano-3,3-diphenylacrylate A system or the like can be used.

  The surface of the microlens 100 and the light deflection element 110 may be further provided with a fine uneven shape. This is because the fine uneven shape can further enhance the diffusion characteristics. At this time, it is desirable that the surface roughness Ra (arithmetic average roughness) is set in a range of 0.1 μm to 10 μm. It is difficult to obtain a diffusion effect with a fine concavo-convex shape of less than 0.1 μm, and a fine concavo-convex shape of over 10 μm may cause a significant decrease in luminance, and at the same time, the top of the microlens 100 is not easily scratched. This is because the damage is prevented and the damage prevention effect is reduced. As a method for forming the fine uneven shape, for example, a method of roughening the surface of a mold in which the shapes of the microlens 100 and the light deflecting element 110 are previously formed is etched or sandblasted, and the microlens 100 and the light deflecting element 110 are formed. Examples include a method of further cutting a fine uneven shape on a mold whose shape has been formed first.

  On the other hand, a substantially hemispherical protrusion 120 as shown in FIG. 5 is preferably provided on the light incident surface side of the optical sheet 25. Generation of scratches due to contact or rubbing with the light diffusion plate 50 on the light incident surface side can be prevented. Further, since a gap due to the protrusion 120 is generated, it is possible to suppress the occurrence of Newton rings. The protrusions 120 are desirably formed in a range that does not hinder the incidence of light from the light source 41, and the area ratio for installing the substantially hemispherical protrusions 120 in the light incident surface is in the range of 1% to 20%. It is desirable to be set to. If it is 1% or less, the effect of preventing the occurrence of scratches due to contact or rubbing cannot be obtained. On the other hand, if it is 20% or more, the light from the light source 41 is prevented from being taken into the optical sheet 25, which causes a decrease in luminance.

  Furthermore, the protrusion 120 formed on the light incident surface side of the optical sheet 25 preferably has a diameter set in a range of 20 μm to 200 μm. When the diameter is 20 μm or less, the effect of preventing the occurrence of scratches due to contact and rubbing is too low, and it is not desirable because it is difficult to process and mold. On the other hand, in the case of 200 μm or more, there is a possibility that the protrusion 120 may be visually observed, and that there is a high possibility that the incidence of light from the light source 41 is hindered and the luminance is lowered. Moreover, although the protrusion height of the protrusion 120 depends on its diameter, it is desirable that the aspect ratio value obtained by dividing the height by the diameter is between 0.1 and 0.3. This is because if the height is too low, the effect of preventing the occurrence of scratches due to contact or rubbing cannot be obtained, and if it is too high, the incidence of light from the light source 41 is hindered and the luminance is lowered. . The shape of the protrusion 120 as viewed from above may be circular or substantially circular, and may be elliptical, triangular, quadrangular, or polygonal with rounded corners.

  The protrusion 120 is preferably provided with a fine uneven shape on the light incident surface side of the optical sheet 25. As a result, it is possible to suppress the generation of scratches due to contact and rubbing and the generation of Newton rings, and it is possible to improve the concealability. Therefore, a predetermined pattern provided for the purpose of reducing the lamp image on the front surface or the back surface of the light diffusion plate 50 or a necessary function is provided at the same time as reducing luminance unevenness due to the light source, lamp image, brightness difference and the like. It is possible to suppress the structure to be seen from the viewer side F.

  The surface roughness Rz (ten-point average roughness) of the fine unevenness in the fine unevenness on the surface of the protrusion 120 is preferably set in the range of 0.5 μm to 5 μm. Difficulty and concealment effects are difficult to obtain with a fine uneven shape of less than 0.5 μm, and a fine uneven shape of more than 5 μm may cause a significant decrease in brightness, and at the same time, the top of the protrusion 120 is not easily damaged. It may cause a reduction in damage prevention effect. As a method for forming the fine uneven shape, for example, a method of roughening the surface of the mold on which the protrusion 120 is first formed by etching or sand blasting, etc., or further cutting the fine uneven shape on the mold on which the protrusion 120 is previously formed. And the like.

  The protrusion 120 formed on the light incident surface side of the optical sheet 25 can be formed by performing both surface processing simultaneously on the front and back surfaces in the extrusion forming process for forming the microlens 100 and the light deflection element 110 on the light emitting surface side. It can also be obtained by bonding sheets obtained by separate processing.

  In addition, you may give the process which provides discontinuous microprotrusion on the light-incidence surface side of the optical sheet 25 instead of a mat | matte process. Examples of the method for forming such irregularities include mat processing and embossing. According to these methods, it is possible to obtain a fine uneven shape by pressing the transparent resin softened by heating to the uneven member to transfer the shape of the member, and then curing the transparent resin. it can. As another method, transparent particles having a particle size of about 30 to 100 μm may be blended in a molten transparent resin, and the transparent particles may be extruded to the outermost layer side to cause unevenness on the surface. When this method is used, it is preferable that the refractive indexes of the transparent resin and the transparent particles are equal.

  The thickness of the optical sheet 25 of the present invention is preferably in the range of 50 μm to 600 μm, although it varies depending on the material and material used, the environment used and the situation. When the thickness is 50 μm or less, the size of the microlens 100 and the light deflection element 110 to be formed is limited, and it becomes difficult to exhibit the required optical characteristics. In addition, since the strength of the sheet itself cannot be obtained, bending or deformation due to heat or the like is likely to occur, resulting in a problem that wrinkles or luminance unevenness is likely to occur. On the other hand, when the thickness is 600 μm or more, inconvenience occurs in handling such as a decrease in transmittance of the entire optical sheet, an increase in material cost, and an increase in weight in the molding process.

  As described above, since the optical sheet 25 of the present invention has a structure in which the above-described microlens 100 on the light emitting surface side and the light deflection element 110 are combined, the light of the optical sheet 25 is laminated when the functional sheets 2 are laminated. Generation | occurrence | production of the damage | wound by a contact or a rubbing can be prevented in the light-incidence surface of the output surface and the functional sheet 2. That is, it is possible to provide an optical sheet 25 that has scratch resistance and has the optical characteristics of the microlens 100 and the light deflection element 110 at the same time.

Further, by imparting a fine uneven shape to the light emitting surface side of the optical sheet 25 and providing a substantially hemispherical protrusion 120 and fine unevenness to the light incident surface side, the scratch resistance on the light incident surface side is improved. At the same time, it is possible to enhance the light diffusing function and increase the viewing angle and concealment.
Furthermore, by combining this optical sheet 25 with the functional sheet 2 or the light diffusing plate 50, it is possible to emit a liquid crystal display image excellent in luminance, viewing angle, and concealment in the viewer side direction. A backlight unit 55 and a display device 70 can be provided.

  As described above, the display device 70 has a configuration in which the image display element 35 is a liquid crystal display element and uses the light K whose light collection and diffusion characteristics are improved by the backlight unit 55 described above. Thus, the luminance of the observer side F is improved and the distribution of the light intensity in the viewing angle direction is smoothed to reduce the uneven brightness of the lamp image and the light diffusing plate 50, thereby making the image of the entire screen uniform. Obtainable.

  As described above, the embodiment in the present embodiment has been described in detail. However, without departing from the technical idea of the present embodiment, the present invention is not limited thereto, and some design changes and the like are possible.

  Hereinafter, in an Example, the optical characteristic evaluation of the optical sheet 25 and the display apparatus 70, the abrasion test of the optical sheet 25 and the functional sheet 2, and its evaluation are demonstrated.

Example 1
As the substantially hemispherical microlens 100 on the exit surface side, a square-shaped hemispherical microlens 100 having an area ratio of 40%, a diameter of 100 μm, and a lens height (projection height H1) of 48 μm, and a linear structure As the optical deflecting element 110, a mold was fabricated in which a prism with a vertex angle of 90 ° having a width of 30 μm and a lens height (projection height H3) of 15 μm was formed. Then, using this mold, an approximately hemispherical microlens 100 made of a UV curable resin (refractive index = 1.52) on a PET substrate (Toyobo Co., Ltd.) having a thickness of 250 μm and an optical deflection element having a linear structure. 110 was formed to produce an optical sheet 25. Note that the prisms having a linear structure were arranged in a line in the horizontal direction when viewed from the observer side.

(Example 2)
The light emitting surface side of the optical sheet 25 produced in Example 1 was roughened by blasting to produce an optical sheet 25 having a light emitting surface with a surface roughness Ra of 3 to 4 μm.

(Example 3)
The light incident surface side of the optical sheet 25 produced in Example 1 was roughened by blasting to produce an optical sheet 25 having a surface roughness Rz of 1 to 2 μm in Rz.

Example 4
The light incident surface side of the optical sheet 25 obtained by roughening the lens surface produced in Example 2 by blasting is roughened by blasting so that the surface roughness of the light incident surface is 1 to 2 μm in Rz. An optical sheet 25 was produced.

(Comparative Example 1)
Using the same UV curable resin as the above-mentioned four types of optical sheets 25, an optical sheet in which only a prism having a width of 30 μm, a height of 15 μm, and an apex angle of 90 ° is formed on the same PET substrate by the same method is produced. did.

(Comparative Example 2)
As a comparative example, evaluation was performed using a microlens sheet incorporated in a commercially available liquid crystal television.

(Optical evaluation)
The display device of this example was evaluated by the following measurement method.
(Front brightness evaluation)
The produced four types of optical sheets 25 were placed on the light diffusion plate 50, and a display device 70 having an image display element 35 on the observer side was assembled. The brightness of the center of the screen was measured under the same conditions using a spectral radiance meter (SR-3A: manufactured by Topcon Technohouse Co., Ltd.) with the screen of this display device being displayed as all white.

(Abrasion evaluation)
The wear evaluation of this example and the comparative example was evaluated by the following measuring method.
(Gakushin style wear test)
The scratch resistance was evaluated using a Gakushin type abrasion tester under the following conditions. First, the surface of the optical sheet 25 to be evaluated on which the substantially hemispherical microlens 100 and the light deflecting element 110 having a linear structure are formed is fixed to the Gakushin abrasion tester as the upper surface, and then the functional sheet 2 to be laminated is used. Install the light diffusion sheet (Ewa product) with the back (light incident surface side) facing each other, pressurize under the condition that the load is 100 g / cm3, and light deflection of the substantially hemispherical microlens 100 and the linear structure The element 110 and the back surface of the diffusion sheet were rubbed by reciprocating 30 times at an amplitude of 50 mm and a speed of 120 mm / second, and the presence or absence of scratches and the degree of scratches on the rubbed surfaces were visually evaluated.

(Evaluation results)
Table 1 shows the measurement results of this example and the comparative example.

Example 1 has a front luminance of 489 cd / m ² and a vertical half-value angle of 36.7 °. In the Gakushin type abrasion test, scratches were found on the lens surface of the optical sheet and the back surface of the light diffusion sheet. It was not recognized and good results were obtained.
In Example 2, the front luminance was 467 cd / m ² , the vertical half-value angle of the visual field was 38.1 °, and although the luminance was slightly reduced, the viewing angle was improved. In the Gakushin abrasion test, no scratches were observed on the lens surface of the optical sheet and the back surface of the light diffusion sheet, and good results were obtained.
In Example 3, the front luminance was 477 cd / m ² , and the vertical half-value angle was 37.7 °. Although a slight decrease in luminance was observed, an improvement in the viewing angle was observed. In the Gakushin abrasion test, no scratches were observed on the lens surface of the optical sheet and the back surface of the light diffusion sheet, and good results were obtained.
In Example 4, the front luminance was 455 cd / m ² , the vertical half-value angle was 38.9 °, and a slight decrease in luminance was observed, but the viewing angle was improved. In the Gakushin abrasion test, no scratches were observed on the lens surface of the optical sheet and the back surface of the light diffusion sheet, and good results were obtained.

Comparative Example 1 has a front luminance of 501 cd / m ² and a vertical half-value angle of 28.5 °, which is high in brightness, but has a narrow viewing angle. In the Gakushin Abrasion Test, it was found that large streak-like scratches in the amplitude direction were observed on the lens surface of the optical sheet, and the prism top was shaved.
Comparative Example 2 has a front luminance of 434 cd / m ² and a vertical half-field angle of 47.3 °. The viewing angle is wide, but the luminance is lowered. In the Gakushin type abrasion test, no flaws were observed on the lens surface of the optical sheet and the back surface of the light diffusion sheet in the Gakushin type abrasion test, and good results were obtained.

  Therefore, from the evaluation results of the above-described examples and comparative examples, the light exit surface side and other functional sheet light are combined by combining the substantially hemispherical microlens 100 on the light exit surface side and the light deflection element 110 having a linear structure. An excellent optical sheet having both the optical characteristics of the substantially hemispherical microlens 100 and the light deflecting element 110 having a linear structure by imparting scratch resistance that can prevent the occurrence of scratches due to contact or rubbing to the incident surface side. It was found that it was possible to provide

H1 ... Projection height of micro lens H2 ... Deflection amount of functional sheet H3 ... Projection height L of light deflection element ... Micro lens interval 2 ... Functional sheet 25 ... Optical sheets 31, 33 ... Polarizing plate 32 ... Liquid crystal panel 35 ... Image display element 41 ... Light source 43 ... Reflector plate 45 ... Light source unit 50 ... Light diffusion plate 55 ... Backlight unit 70 ... Display device 90 ... Base material 100 ... Micro lens 110 ... Light deflection element 120 ... Projection.

Claims (10)

The optical sheet is used for illumination optical path control to control and emit an optical path of light incident from a light source, and a functional sheet having other optical functions is laminated on the light exit surface side,
The light exit surface has an optical shape for condensing or diffusing light,
The optical shape includes a plurality of substantially hemispherical microlenses arranged independently of each other, and a plurality of optical lenses arranged between the microlenses and extending along the light exit surface. ,
Only the top part of the said micro lens is comprised so that it may contact | abut to the said functional sheet, respectively, The optical sheet characterized by the above-mentioned.   The protrusion height of the microlens is H1, the amount of deflection between the pair of microlenses of the functional sheet that contacts at least the pair of microlenses is H2, and the protrusion height of the light deflection element is H3. The optical sheet according to claim 1, wherein a relationship of H3 <H1-H2 is established.   3. The optical device according to claim 1, wherein an area of a top portion of the microlens contacting the functional sheet in a plan view is set to a range of 10% or less of a bottom area of the microlens. Sheet.   The optical sheet according to any one of claims 1 to 3, wherein fine irregularities are provided on the surfaces of the microlens and the light deflection element.   The optical sheet according to claim 4, wherein the fine uneven shape is an unevenness having a surface roughness Ra in a range of 0.1 μm to 10 μm.   The optical sheet according to claim 1, wherein a plurality of substantially hemispherical protrusions are formed on the light incident surface.   The optical sheet according to claim 6, wherein a fine uneven shape is provided on a surface of the light incident surface.   The optical sheet according to claim 7, wherein the fine uneven shape is an uneven surface having a surface roughness in a range of 0.5 μm to 5 μm. The optical sheet according to any one of claims 1 to 8,
A backlight unit comprising: a light source that irradiates light to the light incident surface of the optical sheet. The backlight unit according to claim 9,
A display device comprising: an image display unit that defines a display image in accordance with transmission / shading in pixel units and displays an image by light irradiation from the backlight unit.

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