Light condensation assist film, edge-light type backlight unit equipped with the same, and liquid crystal display device equipped with edge-light type backlight

Abstract

To provide an optical film element which is composed entirely of transparent resin without using light-diffusing fine particles, in which self moire is not visually recognized with naked eyes, the optical film element which eliminates brightness unevenness on a light emission surface of a backlight and has high frontal brightness when being mounted on the edge-light type backlight.SOLUTION: A light condensation assist film 10 that is inserted between a light emission surface of a light guide plate and a light incidence surface of a brightness enhancement film in an edge-light type backlight unit that uses discrete type LED point light sources comprises: a light waveguide layer 110 that is made of a transparent substrate film; a light extraction layer 100 that is formed on one surface of the light waveguide layer and has multiple unit recesses in an inverted quadrangular pyramid shape; and a light introduction layer 120 that is formed on the other surface of the light waveguide layer and has multiple unit triangular prisms extending in parallel to one direction. The light extraction layer constitutes the light emission surface. The prism surfaces of the multiple unit triangular prisms that constitute the light introduction layer constitute the light incidence surface.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a light-condensing auxiliary film intended for use in an edge-light type backlight, an edge-light type backlight unit incorporating the light-condensing auxiliary film, and a liquid crystal display device incorporating the edge-light type backlight. [Background technology]

[0002] Liquid crystal display devices are widely used in various information devices, and can be broadly categorized into direct-lit and edge-lit types based on their basic structure. In the former type, the light source is placed on the rear side of the backlight unit mounted on the liquid crystal display device, while in the latter type, the light source is placed on the side of the light guide plate that constitutes part of the backlight unit (commonly referred to as edge-lit backlights). Edge-lit backlights are classified into CCFL (cold cathode fluorescent lamp) type and white LED point light source type based on the type of light source used, with white LED point light source types becoming mainstream in line with the recent trend towards smaller size, lighter weight, and more efficient power consumption.

[0003] The basic components of such edge-lit backlights with white LED point light sources are the light source, light guide plate, light propagation characteristic adjustment film (which is called by various names depending on its main function, and is sometimes called Light Shaping Sheet or simply Light Diffusion Film), and BEF (Brightness Enhance Film). BEF is generally a commercially available product (mainly made by 3M), and it has not been seen that backlight manufacturers, light guide plate manufacturers, and light propagation characteristic adjustment film manufacturers have developed substitutes for this BEF. In this type of configuration, the functional characteristics of the light guide plate are controlled so that the diffuse white light from the light source (white LED) enters horizontally from the side of the light guide plate, and its propagation direction is changed (deflected) by reflection and diffusion by the light diffusion dots arranged under the light guide plate, and the light is emitted from the top surface of the light guide plate (the surface facing the BEF) as light with a light intensity peak with a light intensity angular distribution similar to a Gaussian distribution type. This control method varies from company to company and is close to know-how. In the case of backlights in large liquid crystal panels mounted on liquid crystal TVs, etc., it is said that the degree of diffusion is not sufficient with just the light emitted from the exit surface of this light guide plate, so a film that assists the light diffusion function (light diffusion film) is inserted between this light guide plate and the BEF (for example, see Figure 1 of Patent Document 1).

[0004] In recent years, the number of pixels has increased dramatically with the miniaturization of liquid crystal panels, which has resulted in a sharp decline in the transmittance of light from the light source, resulting in a problem of poor front luminance on the liquid crystal panel. In such edge-lit backlights, it is said that luminance unevenness is less likely to occur compared to direct-type backlights due to the above-mentioned light guide plate function, and the required optical characteristics are focused on the strength of front luminance in the backlight. In order to solve this problem, edge-lit backlights equipped with white LED light sources are gaining attention, and at the same time, improvements to light guide plates for such types of backlights are being vigorously pursued. As such improved light guide plates, dots for light reflection are optimally arranged on the lower surface side, and optical elements that have the function of concentrating light reflected by the dots are formed on the upper surface of the light exit surface side, and a light guide plate has been proposed in which the optical elements form a special spatial arrangement not seen in the past. As a result, the light emitted from the light exit surface side of the optical elements arranged on the upper surface of the light guide plate has a relatively strong directivity compared to the light emitted from the conventional pseudo-surface light emitter. However, even with such light guide plates, the propagation direction and shape of the light emitted from them have not yet been optimally matched with a light-collecting film known as a BEF (Brightness Enhancement Film), resulting in scattering losses during the light propagation process and resulting in the front brightness of the backlight not fully meeting market needs.

[0005] By the way, the applicant has been manufacturing and selling light diffusion films for backlights, and has invented and filed a patent application for a new optical film (light diffusion film) for direct-type point light sources (Patent Application No. 2023-78133). This invention focuses on the interrelationship between the refractive indexes of each layer of a three-layer structure film that contains light-diffusing particles and includes a triangular prism layer on the light incident surface side. This invention is for direct-type point light sources and not for edge-lit backlights, but various findings have been obtained in the process of making the invention.

[0006] This time, the applicant received a request to develop a new light diffusion film for edge-light type backlight units against the background described above, and considered developing a new light diffusion film for edge-light type backlight units by utilizing the technical idea of ​​the above invention, and conducted repeated interviews. As a result, the applicant discovered for the first time that the propagation direction and shape of the light emitted from the top surface of the latest type light guide plate described above did not optimally match with a light collecting film called a BEF (Brightness Enhancement Film).

[0007] Furthermore, through computer simulations, etc., it was found that the optical characteristics required of the optical film element in the above-mentioned special usage environment (i.e., an environment in which it is inserted between a light guide plate and a BEF) are such that the light emitted from the light guide plate is concentrated while changing the angle of its propagation direction so that it is incident on the BEF at an angle that is optimal for the BEF, and that this makes it possible to minimize the loss of light in the light propagation path and increase the front brightness from the backlight.

[0008] Based on the above findings, while considering material design based on the properties required for desirable optical film elements, it became clear that in order to increase the front brightness from the backlight, it is necessary to at least minimize the haze value of the optical film element inserted between the light guide plate and the BEF, and that in order to meet this requirement, it is necessary to completely avoid using the commonly used light-diffusing microparticles that lead to an increase in the haze value.

[0009] On the other hand, the applicant has various knowledge accumulated in the manufacturing process of an optical film that uses light diffusing particles as in the invention described in Japanese Patent Application No. 2023-78133 by the applicant, but is suitable for mass production at low cost and includes a triangular prism layer on the light incident surface side. In the course of research based on such knowledge, the applicant discovered a potential problem that recent light guide plates are capable of more efficient light guide and light extraction, and that if a film using scattering is used on an efficient light guide plate, scattering loss will occur there. Furthermore, as a result of considering a technology that most faithfully satisfies the above-mentioned requirements while being the lowest cost among the currently available mass production technologies, the applicant came up with the idea that in order to achieve the function of concentrating light emitted from the light guide plate while changing the angle of its propagation direction with the fewest number of optical elements so as to achieve the lowest cost, the combination of controlling the refractive index of the material used for the optical film element inserted between the light guide plate and the BEF and controlling the surface shape of the optical film element is optimal.

[0010] Therefore, in the course of conducting extensive research to develop an optical film element for use in edge-lit backlights that does not contain any light-diffusing microparticles, the researchers examined prior patent documents and found that optical film elements with such a basic configuration have a problem with the appearance of moire fringes due to a self-moire phenomenon that occurs in a single optical film element, as taught in, for example, Patent Document 1 (International Publication WO2010 / 029910).

[0011] Against the above background, the present invention aims to provide a film-like optical element to be inserted between the light guide plate and BEF of an edge-lit backlight, which can or is expected to solve the following problems (satisfy the required characteristics): 1) The number of elements constituting the film-like optical element is as small as possible. 2) The elements constituting the film-like optical element do not contain any light-diffusing particles. 3) The desired optical characteristics can be obtained while making the self-moiré invisible to the naked eye. 4) It is suitable for mass production using the roll-to-roll method and is low cost. [Prior art documents] [Patent documents]

[0012] [Patent Document 1] International Patent Publication No. WO2010 / 029910 Summary of the Invention [Problem to be solved by the invention]

[0013] Therefore, the present inventor has conducted intensive research to provide an optical film element (hereinafter, referred to as a light-collecting auxiliary film) that is low-cost, does not contain any light-diffusing fine particles, has a structure in which self-moire is not visible to the naked eye, has a front luminance high enough to be practically usable as a backlight, and has luminance unevenness controlled to a level that is practically usable. In developing the light-collecting auxiliary film according to the present invention, it is premised on the fact that it does not contain any light-diffusing fine particles, and in the case of such an optical film, the film is so transparent that haze is not visible, so that the biggest issue is how to deal with self-moire. However, the present inventor conducted intensive research based on the reverse idea that, in theory, even if self-moire occurs, if the distance between the moire lines at that time is less than a predetermined distance, it should not be visible to the naked eye, and as a result, the present invention has been completed.

[0014] That is, the first invention is A light-collecting auxiliary film that is inserted between a light-emitting surface of a light guide plate and a light-incident surface of a brightness enhancement film (BEF) in an edge-light type backlight unit that uses discrete LED point light sources, an optical waveguide layer made of a light-transmitting substrate film; a light extraction layer formed on one surface of the optical waveguide layer and having a plurality of unit recesses each having an inverted square pyramid shape; a light introduction layer formed on the other surface of the optical waveguide layer and having a plurality of unit triangular prisms extending in parallel in one direction; the light extraction layer constitutes a light exit surface, a prism surface of each of the plurality of unit triangular prisms constituting the light introduction layer constitutes a light incidence surface; None of the light extraction layer, the optical waveguide layer, and the light introduction layer contains light diffusing fine particles, The light-collecting assistance film is characterized in that the relationship between the pitch P1 of the plurality of unit recesses and the pitch P2 of the plurality of unit triangular prism lenses is P1>P2, and all of the following conditions are satisfied: (Math 1) |D1-D2|≦200 μm In the above formula 1, D1 and D2 satisfy the following formulas 2a and 2b, respectively: (Math 2a) D1 = |P1m × δ1 ÷ (δ1-P1m)| (Math 2b) D2 = |P1m × δ2 ÷ (δ2-P1m)| In the above formulas 2a and 2b, P1m>P2m, P1m satisfies the following formula 3a, and P2m satisfies the following formula 3b, (Math 3a) P1m= P1×sin(0.25×π) (Number 3b) P2m= P2÷2 In the above formulas 2a and 2b, 1) δ1 is the sum of P1m and the smaller of δa and δb, where δa is the absolute value of the difference between P1m and the integer part (rounded up to the nearest integer) of the value obtained by dividing P1m by P2m and multiplying the result by P2m, and δb is the absolute value of the difference between P1m and the integer part (rounded down to the nearest integer) of the value obtained by dividing P1m by P2m and multiplying the result by P2m, 2) δ2 is the sum of P1m and the smaller of δa and δb, where δa is the absolute value of the difference between P1m and the integer part (rounded up to the nearest integer) obtained by dividing P1m by P2m and multiplying that value by P2m, and δb is the absolute value of the difference between P1m and the integer part (rounded down to the nearest integer) obtained by dividing P1m by P2m and multiplying that value by P2m.

[0015] The second invention is A light exit surface of a light guide plate in an edge-lit backlight unit using discrete LED point light sources; A light-collecting auxiliary film that is interposed between a light incident surface of a brightness enhancement film (BEF), an optical waveguide layer made of a light-transmitting substrate film; a light extraction layer formed on one surface of the optical waveguide layer and having a plurality of unit recesses each having an inverted square pyramid shape; a light introduction layer formed on the other surface of the optical waveguide layer and having a plurality of unit triangular prisms extending in parallel in one direction; the light extraction layer constitutes a light exit surface, a prism surface of each of the plurality of unit triangular prisms constituting the light introduction layer constitutes a light incidence surface; None of the light extraction layer, the optical waveguide layer, and the light introduction layer contains light diffusing fine particles, an intersection angle between the direction of the ridges of the plurality of unit recesses and the direction of the ridges of the plurality of unit triangular prisms is within a range of 42° to 48°; Moire caused by the plurality of unit recesses and the plurality of unit triangular prisms is not visible to the naked eye. The light-condensing auxiliary film is characterized by the above.

[0016] The third invention is The second invention is characterized in that the relationship between the pitch P1 of the plurality of unit concave portions and the pitch P2 of the plurality of unit triangular prism lenses is P1>P2.

[0017] A fourth invention according to the first or third invention is characterized in that the apex angles of the plurality of unit recesses are less than 100°.

[0018] The fifth invention is characterized in that, in the fourth invention, when the refractive index of the resin constituting the light extraction layer is n1, the refractive index of the resin constituting the light introduction layer is n2, and the refractive index of the resin constituting the optical waveguide layer is n0, the relationships n0≧n1 and n0≧n2 hold.

[0019] A sixth invention is characterized in that in the fifth invention, the range of the refractive index n1 is 1.50≦n1≦1.64, and the range of the refractive index n2 is 1.50≦n2≦1.64.

[0020] A seventh invention is characterized in that, in the sixth invention, the apex angles of the plurality of triangular prisms are 95° or less.

[0021] An eighth invention is characterized in that in the seventh invention, the apex angles of the plurality of unit recesses are equal to or greater than 80° and equal to or less than 95°.

[0022] The ninth invention is an edge-lit backlight unit having a plurality of point light sources, a light guide plate, and a brightness enhancement film (BEF), characterized in that at least one light-collecting auxiliary film according to any one of the first to eighth inventions is inserted between the light guide plate and the brightness enhancement film (BEF).

[0023] A tenth invention according to the ninth invention is characterized in that the plurality of point light sources are disposed on at least one edge side of the light guide plate.

[0024] An eleventh aspect of the present invention is a liquid crystal display device comprising the edge-light type backlight unit according to the tenth aspect of the present invention and a liquid crystal display panel. Effect of the Invention

[0025] The light-concentrating auxiliary film of the present invention does not contain any light-diffusing microparticles, and is expected to function as an optical film element that suppresses the appearance of self-moiré (visible to the naked eye), while providing a front brightness as a backlight that is high enough for practical use, and with brightness unevenness controlled to a level that is practical for practical use. Furthermore, by using a roll mold, it will be possible to manufacture the material using a roll-to-roll method that is suitable for mass production, which is expected to increase the ease of manufacturing and reduce manufacturing costs. Furthermore, these factors are expected to contribute to cost reduction in edge-light type backlight units incorporating the light-collecting auxiliary film of the present invention, and further in liquid crystal display devices. [Brief description of the drawings]

[0026] In the following drawings, components with the same reference numbers are the same components. [Figure 1] FIG. 2 is a conceptual diagram showing a cross section of a light-concentrating auxiliary film according to the present invention. [Diagram 2] 1A and 1B are schematic diagrams showing a front view and cross-sectional views of a light extraction layer 100 on the light exit surface side of a light concentrating assistance film 10 according to the present invention. Reference number 200 indicates a unit recess (void), 220 indicates a ridge line, 240 indicates the deepest point of the unit recess (which is the center point of the recess and the apex of an inverted pyramid, and is therefore called the inverted apex), and 260 indicates a solid portion that defines the unit recess. [Diagram 3] 1A and 1B are schematic diagrams showing a front view and a cross-sectional view of an array of unit triangular prisms 300 constituting the light introduction layer 120 on the light incident surface side of the light concentrating auxiliary film 10 according to the present invention. Reference numeral 300 denotes a unit triangular prism, 320 denotes a ridge line of the unit triangular prism, and 340 denotes a valley line formed by adjacent unit triangular prisms. [Figure 4] FIG. 1 is a diagram showing the relationship between the arrangement direction of unit recesses 200 (approximately inverted pyramids) constituting the light extraction layer 100 on the light exit surface side in the light concentrating auxiliary film 10 of the present invention and the longitudinal direction of unit triangular prisms (protruding strips) constituting the light introduction layer 120 on the light entrance surface side. In the same figure, the valley lines 340 in the array of unit triangular prisms 300 in the light introduction layer 120 are shown by dashed lines. FIG. (a) shows a case where these two directions intersect at 45°. FIG. (c) shows this state in another simplified representation. FIG. (c) shows a state where the light extraction layer 100 is placed on top and the light introduction layer 120 is placed on the bottom. FIG. (b) and FIG. (d) show a state where this intersection angle is 42° and 48°, respectively. [Diagram 5] This is a reference diagram of a known general roll-to-roll manufacturing system. Although it is outside the scope of the present invention, since it is for explaining a preferred range of the uneven shape of the surface of the light-concentrating auxiliary film of the present invention, reference numbers are omitted for components other than the main components. [Figure 6]This is a conceptual diagram of a general method for manufacturing a roll die by a cutting method for use in manufacturing the light-concentrating auxiliary film 10 of the present invention. (a) is a conceptual diagram showing a cutting tool 640 having a single crystal diamond 660 at its tip, cutting a roll die having a thin metal film 680 (usually copper metal) formed on its surface at an apex angle θ, and (b) is an enlarged view and cross-sectional view of the single crystal diamond 660 cutting the thin film 680. (Although it is outside the scope of the present invention, reference numbers are omitted for components other than the main components because it is intended to explain the preferred range of the uneven shape of the surface of the light-concentrating auxiliary film of the present invention.) [Figure 7] FIG. 7(a) is a conceptual diagram of a cross section of an example of an edge-lit backlight equipped with the light-collecting auxiliary film 10 of the present invention. Reference number 700 indicates a liquid crystal panel, reference number 720 indicates the entire two-sheet orthogonally stacked BEF and the light-diffusing film laminated thereon, reference number 10 indicates the light-collecting auxiliary film of the present invention, reference number 740 indicates a light guide plate unit having a reflecting sheet on the lower surface side, and reference number 760 indicates a white LED. The white LEDs 760 are arranged in a row in a discrete manner in the depth direction of the paper along the side surface of the light guide plate unit 740. FIG. 7(b) is a conceptual diagram showing the stacking state of each layer with the liquid crystal panel 700 in FIG. 7(a) removed. The stacking is performed in the order of a reflecting sheet 744, a light guide plate 742, the light-collecting auxiliary film 10 of the present invention, a two-sheet orthogonally stacked BEF 724, and a light-diffusing film 722 from the bottom to the top. [Figure 8] This is a conceptual diagram of the optical elements used in measuring the light intensity peaks (using Mini-Diff V2) in the examples and comparative examples. The stacking is performed by stacking a reflecting sheet 744, a light guide plate 742, and the light concentrating assistance film 10 of the present invention from bottom to top. A plurality of white LEDs 760 are arranged on the side of the light guide plate 732. [Figure 9] This shows a contour diagram of the light emission surface of a light concentrating auxiliary film of the present invention when the combination of shape characteristics and refractive index is as shown in Table 1. In this case, the optical axis of the light emitted from the white LED is parallel to a straight line that passes through the center of the circular area of ​​this contour diagram and runs horizontally from left to right on the paper. [Figure 10] 11 is a conceptual diagram showing a method for determining self-moiré by the naked eye. Fig. 11(a) is a conceptual diagram of the measurement conditions when the determination result is O, and Fig. 11(b) is a conceptual diagram of the measurement conditions when the determination result is △ or ×. BEST MODE FOR CARRYING OUT THEINVENTION

[0027] (Implementation) The present invention will be described in detail below with reference to the embodiments and drawings. Note that the present invention is not limited to the following embodiments and can be arbitrarily modified within the scope of the object and spirit of the present invention.

[0028] Throughout this specification, 1) In the present invention, "light focusing" means collecting (concentrating) diffused light from a light source, for example, light emitted from a light guide plate, and deflecting and propagating it in any direction. However, the meaning of "focusing" here is not strict, and it also includes cases where a phenomenon of slight partial diffusion occurs depending on the characteristics of the incident light, such as the direction of incident light and its intensity angular distribution. 2) "Film" refers not only to film in the strict sense defined by thickness, but also to thicker materials usually called sheets. 3) "Self-moiré" refers to moiré (moiré fringes) that occurs in a single transparent film-like optical element (or optical film element). There are parallel moiré and rotational moiré, but in the present invention, since there is a fact that rotational moiré did not appear in any of the examples within the scope of the configuration (it is not visible to the naked eye), the moiré mentioned below means parallel moiré. Note that in the present invention, when a moiré phenomenon that is visible to the naked eye is observed, it is said that moiré appears, and when it is not visible, it is said that moiré does not appear, and this is not said from a theoretical standpoint. 4) "Convex stripe" means a convex protrusion that extends continuously in one direction with the same cross-sectional shape, and "concave stripe" means a concave depression that extends in one direction with the same cross-sectional shape. In this case, "one direction" does not necessarily mean a direction defined by a continuous straight line, but may also include a direction defined by a continuous curve. 5) "Approximately parallel" means that the ridges of multiple convex ribs or the valleys of multiple concave ribs are substantially parallel from a practical standpoint, and "substantially" as used herein means within a range that does not impede the achievement of the object of the present invention. 6) An "approximately square pyramid" or "approximately inverted pyramid" refers not only to a true inverted square pyramid, but also to one that is substantially an inverted square pyramid from a practical standpoint and can be regarded as an inverted square pyramid or an inverted pyramid within the range of unavoidable variation in shape resulting from the processing accuracy of industrial production. For example, an "inverted square pyramid trapezoid" with a flat apex is included in the category of "approximately inverted polygonal pyramid" if it has a small apex area, as long as it does not impede the achievement of the object of this invention. 7) "Refractive index" refers to the refractive index measured at a wavelength of 589 nm using an Atago Appe refractometer (NAR-1T SOLID). In the following, it is represented by the symbol nD. The refractive index is expressed as a number with two decimal places, but in this case, the value does not necessarily mean that the number with two decimal places is zero, but includes values ​​that are less than the number one unit above the second decimal place and exceed the number one unit below it. 8) "Apex angle" refers to the apex angle shown in Figures 2 and 3. The angle was measured by magnifying the transfer surface 2400 times using a laser microscope (Keyence VKX-1000). Although the apex angle does not have a decimal point, this does not mean that the value after the decimal point is zero, and includes values ​​rounded off to one digit below the indicated value.

[0029] The light-collecting auxiliary film according to the present invention is a film-like optical element (optical film element) that is inserted between a light guide plate (also called a light guide sheet or light guide film) and a BEF (Brightness Enhancement Film) in an edge-lit backlight, collects light emitted from the upper surface of the light guide plate, and deflects (sometimes called raising) the propagation direction of the collected light to the optimal direction for the BEF. The main features of the present invention are that it can achieve this function only with a special combination of surface shape and refractive index without relying on volume diffusion (e.g., light diffusion by light-diffusing fine particles) (i.e., without using light-diffusing fine particles), and can suppress or avoid self-moire that generally appears when light-diffusing fine particles are not used, and can be mass-produced by a roll-to-roll method. The following is a detailed description.

[0030] 1. Overall structure of the light-collecting auxiliary film FIG. 1 shows a conceptual diagram of a cross-sectional structure of a light-concentrating assisting film 10 according to the present invention. As shown in the figure, the light-concentrating assisting film 10 according to the present invention has a three-layer structure of a light extraction layer 100, a light guide layer 110, and a light introduction layer 120, and each layer is integrated by being in close contact with each other. Here, the light extraction layer 100 constitutes the light exit surface (upper side of the paper), and the light introduction layer 120 constitutes the light entrance surface (lower side of the paper). That is, the light-concentrating assisting film 10 has the light introduction layer 120 on the side facing the light guide plate (not shown) (the side closer to the light guide plate), and has the light extraction layer 100 on the opposite side from the light guide plate (not shown) (the side farther from the light guide plate). In the figure, solid lines extending horizontally between these layers are drawn, giving the impression that a clear, flat boundary surface is formed between each layer, but these boundaries do not necessarily need to be flat, and some intermixing between them is permitted within a range that does not affect the achievement of the object of the present invention. In particular, if the refractive indexes of the layers through the boundary surface are the same, they can be treated as optically the same in the present invention, so in such a case, some intermixing is permitted. In this embodiment, the light extraction layer 100 is the light exit surface and the light introduction layer 130 is the light entrance surface, but instead, the light extraction layer 100 may be the light entrance surface and the light introduction layer 130 may be the light exit surface as long as it does not affect the achievement of the object of the present invention.

[0031] 2. Shape characteristics of each layer that composes the light-collecting auxiliary film (Shape characteristics of the light extraction layer) The light extraction layer 100, which is the light exit surface of the light concentrating assistance film, is composed of an array of units having a plurality of unit recesses 200 each having a substantially inverted quadrangular pyramid shape (inverted pyramid shape). Note that, for convenience, the terms "unit recess" and "inverted pyramid" are used interchangeably in this specification, and since both refer to a void portion, for convenience, the void portion of a recess and the solid portion defining the void portion are used interchangeably below, and these terms should be interpreted appropriately depending on the context of the scene in which they are used.

[0032] FIG. 2(a) shows a front view of one section of the light extraction layer 100. The front view of one section in which 12 of the unit recesses 200 constituting the light extraction layer 100 are two-dimensionally arranged is shown in the figure, but this is for the sake of explanation only, and in reality, a large number of inverted pyramid-shaped unit recesses 200 that are too small to be seen with the naked eye are formed. The upper end (the upper end on the front side of the paper) of the inverted pyramid-shaped unit recess 200 forms a rectangular ridge 220, but this ridge 220 is merely a conceptual line, and its width is preferably as close to zero as practically possible. In the present invention, the distance between each line formed by connecting the ridges 220 of each unit recess 200 in the same direction is called the pitch (reference number 230) (P1) of the unit recess 200.

[0033] The center point of the area occupied by the unit concave portion 200 in the figure is located directly above the bottom center point 240 of the unit concave portion 200. This bottom center point 240 is also the apex of the inverted pyramid that constitutes the unit concave portion 200 including it, and so will hereinafter be referred to as the "inverted pyramid apex" for convenience. Lines connecting the inverted pyramid apex 240 to each corner of the rectangular base of the inverted pyramid 200 are shown in the figure, but these lines are also merely conceptual, and it is preferable that their widths be as close to zero as practically achievable.

[0034] Moreover, it is preferable that the exposed surface (slope of the inverted pyramid) of each unit concave portion 200 is a mirror surface as much as practically achievable, in order to suppress the occurrence of unnecessary scattering and minimize the loss of the transmitted light when the light is deflected and concentrated in a predetermined direction due to the difference in refractive index at the boundary between this exposed surface and air.

[0035] 2(b) shows a cross-sectional view of a cross section passing through the bottom center point 240 (the apex of the inverted pyramid) of each unit concave portion 200 in the vertical direction of the paper, and (c) shows a cross-sectional view of a cross section passing through the left and right direction of the paper. In each cross-sectional view, the parts hatched with dots indicate solid parts, and the white parts indicate void parts (i.e., exposed parts). The solid line extending vertically on the right side of the cross-sectional view of FIG. 2(b) is a conceptual line and indicates a plane (the upper end surface on the light emission side) passing through the upper end of the light extraction layer 100, and the solid line extending horizontally is also a conceptual line and indicates the boundary between each unit concave portion 200, but since the solid parts of each unit concave portion 200 are all formed of the same material, this boundary is also merely conceptual. The solid lines extending horizontally in the cross-sectional view of Figure 2 (c) are conceptual lines and indicate a plane passing through the upper end of the light extraction layer 100 (the upper end surface on the light emission side), and the solid lines extending vertically indicate the boundaries between each of the unit recesses 200; however, since the solid portions of each of the unit recesses 200 are all formed of the same material, these boundaries are also merely conceptual.

[0036] The apex angle of the unit concave portion 200 in the present invention refers to the angle (θ1) shown in the cross-sectional view of Fig. 2(b) or (c). That is, in a cross-section passing through the center points 240 (vertex of the inverted pyramid) of the bottoms of two unit concave portions 200 arranged adjacent to each other and having a common edge line and perpendicular to the common edge line, the apex angle (reference number 250) (θ1) of a triangular region 260 (triangular region 260 hatched with dots in Fig. 2(b)) occupied by the solid parts of adjacent unit concave portions 200. In the present invention, as shown in Fig. 2(b), the top view of the unit concave portion 200 is a regular square, so that the angle of this apex angle (θ1) is the same in both the vertical and horizontal directions of the paper, which is clear when Fig. 2(b) and (c) are compared.

[0037] The preferred shape of the unit recess (single recess having an approximately inverted square pyramid shape) 200 is a square shape at its upper end, with the length of one side being 19 μm to 65 μm, preferably 29 μm to 55 μm, and more preferably 39 μm to 45 μm. If it is within such a range, it is expected that the desired single recess having an approximately inverted square pyramid shape can be cut with a single crystal diamond tip in the manufacturing process of the roll mold. Moreover, the preferred depth of the unit recess (single recess having an approximately inverted square pyramid shape) 200 is 11 μm to 39 μm, preferably 12 μm to 33 μm, and more preferably 16 μm to 27 μm. The above ranges of the length of one side and the depth are preferred ranges determined based on evaluation of the optical properties of the light-collecting auxiliary film 10.

[0038] The thickness of the light extraction layer 100 composed of the unit recesses 200 (single recesses of approximately inverted square pyramid shape) is a value slightly greater than the value of the depth of the unit recesses 200. This "+α" corresponds to the thickness of a portion called "residual film" (integrated with the light extraction layer and made of the same material as the light extraction layer) in the industry, which is used to slightly increase the height of the inverted vertex of the unit recesses 200 from the upper surface (light-emitting surface) of the optical waveguide layer 110 disposed below the unit recesses 200, and is about 1 to 3 μm. If there is no residual film, the shape of the unit recesses 200 (especially the inclined surface) is easily deformed, and this value is obtained from the empirical rule that it is difficult to accurately maintain the shape of the unit recesses 200 during mass production. Specifically, the thickness of the light extraction layer 100 is 12 μm to 42 μm, preferably 13 μm to 36 μm, and more preferably 17 μm to 30 μm.

[0039] The apex angle of the unit recess 200 is less than 100°, and is preferably 80° to 95°, and more preferably 85° to 95°, but the upper and lower limits here are preferred values ​​determined from the viewpoints of the desired optical properties and the manufacturing costs of the roll mold described below.

[0040] When the shape of the upper end of the unit recess 200 is square, the length of one side is the same as the pitch (P1), and the solid portion 260 formed by connecting two adjacent unit recesses 200 is perpendicular to a plane passing through the vertices 240 of each unit recess 200 and has a triangular shape in a cross section passing through those vertices, with the length of the base being the same as the pitch (P1).

[0041] (Refractive index of the light extraction layer) The refractive index n1 of the resin (resin after curing) constituting the light extraction layer satisfies n0≧n1, preferably 1.50≦n1≦1.64, in relation to the refractive index n2 of the resin (resin after curing) constituting the light introduction layer described below and the refractive index n0 of the optical waveguide layer (layer between the light extraction layer and the light introduction layer) described below. The upper and lower limits here are preferred values ​​determined from the viewpoints of desired optical properties and the following viewpoints.

[0042] When using a UV-curable resin as described below as a material, if the refractive index nD is 1.58 or more, it is common to add nanofillers such as TiO2 and ZrO2 to the resin to increase the refractive index, but the nanofillers themselves that give the high refractive index are basically expensive, so the paint tends to become very expensive, which is not practically preferable. Furthermore, if the refractive index nD is 1.64 or more, the amount of nanofiller added becomes too large, the viscosity increases, and unevenness (unevenness in film thickness, etc.) tends to occur when applying the monomer to the base film, and the nanofiller also tends to aggregate, which tends to cause turbidity in the coating film, which tends to reduce the transmittance, which is not practically preferable. In addition to these practical problems, if the refractive index is increased from the resin composition side without using TiO2 or ZrO2, there is a practical problem that the coating film tends to become very brittle, making it difficult to handle the film after molding (it is easily scratched).

[0043] On the other hand, in order to lower the refractive index nD to 1.52 or less, it is common to add a nanofiller such as BaF2 to the monomer or to incorporate fluorine into the monomer molecule to lower the refractive index; however, either method is expensive and has practical problems in that the coating is too soft, making it difficult to handle the film after shaping (curing).

[0044] (Materials and formation method of light extraction layer) Basically, any resin can be suitably used as long as it is a UV-curable transparent resin and has the refractive index specified by the present invention. Note that "transparent" does not mean transparent in the strict sense, but means a state in which the haze value is low (for example, 2 to 3% or less) and can be said to be practically transparent. A known roll-to-roll continuous manufacturing method (see reference diagram in FIG. 5) is suitably adopted for manufacturing, and the resins constituting the light extraction layer and the light introduction layer, respectively, are applied in an uncured state onto one side of the base film or base sheet constituting the optical waveguide layer to form a coating layer, and a roll mold having a fine uneven pattern (pyramid-shaped uneven pattern) formed on its surface is pressed against the surface of the coating layer to transfer the uneven pattern of the roll mold, and ultraviolet rays (UV rays) are sequentially irradiated onto the transferred portion to suitably form the coating layer. The principle of the process for transferring the uneven pattern of a roll mold can also be used in the microimprinting process of plastic films, so it is also possible to form the light extraction layer and light introduction layer with the desired surface shapes by microimprinting on the surface of a three-layer film in which transparent thermoplastic resin films that constitute the light extraction layer and light introduction layer, respectively, are previously bonded to a base film that constitutes the optical waveguide layer, thereby forming a light extraction layer and a light introduction layer.

[0045] (Basic functions of the light extraction layer) The function of the light extraction layer is to further raise the light from the optical waveguide layer described below (making the direction of the light closer to vertical) and make it enter the BEF at an incident angle that is favorable for the BEF, thereby contributing to improving the front-side brightness through a synergistic effect with the BEF.

[0046] (Shape characteristics of the light introduction layer) The light introduction layer 120, which is the light incidence surface of the light-collecting auxiliary film, is composed of a triangular prism layer 30 having a plurality of unit triangular prisms 300 extending in a predetermined direction. FIG. 3(a) shows a top view of one section of the light introduction layer 130. The top view of one section in which four of the unit triangular prisms 300 constituting the light introduction layer 130 are arranged in parallel is shown in the figure, but this is for the sake of explanation only, and in reality, an extremely large number of unit triangular prisms 300 with a width so thin that they cannot be seen with the naked eye are formed. The apex of the unit triangular prism 300 constitutes a ridge line 310, but this ridge line 310 is merely a conceptual line, and its width is preferably as close to zero as practically achievable. In the present invention, the distance between each ridge line 310 of each unit triangular prism 300 is called the pitch (reference number 330) (P2) of the unit triangular prisms 300.

[0047] In the figure, a boundary line is drawn between each adjacent unit triangular prism 300, but this boundary line is merely a conceptual line, and it is preferable that the width of the boundary line be as close to zero as practically achievable.

[0048] Moreover, it is preferable that the exposed surface (the slope of the triangular prism) of each triangular prism 300 is a mirror surface as much as practically achievable. This is to minimize the loss of light due to unnecessary scattering when the light is deflected and concentrated in a specified direction due to the difference in refractive index at the boundary between this exposed surface and air.

[0049] 3(b) shows a cross-sectional view in a cross section perpendicular to the longitudinal direction of each unit triangular prism 300. In this cross-sectional view, the dotted hatched portions indicate solid portions, and the white portions indicate void portions (i.e., exposed portions).

[0050] The apex angle (reference number 350) of unit triangular prism 300 in the present invention refers to the angle (θ2) shown in the cross-sectional view of Fig. 3(b). That is, it refers to the apex angle (θ2) of the solid portion of the triangle (portion hatched with dots) in the cross-section of unit triangular prism 300 appearing in the same figure. In the present invention, as shown in the same figure, it is preferable that the shape of unit triangular prism 300 in the cross-section perpendicular to the longitudinal direction is an isosceles triangle.

[0051] The preferred shape of the unit triangular prism 300 is an isosceles triangle (including an equilateral triangle) in a cross section perpendicular to its longitudinal direction (the direction of the ridge line), with a height h of 3 μm to 24 μm, preferably 4 μm to 21 μm, more preferably 5 μm to 16 μm, and P2 of 7 μm to 27 μm, preferably 9 μm to 22 μm, more preferably 11 μm to 18 μm. However, it is not limited to an isosceles triangle, but the reason why an isosceles triangle is preferred is that it is easy to cut the desired array of unit triangular prisms from single crystal diamond in the manufacturing process of the roll mold. In addition, these numerical ranges are determined by minimizing the manufacturing cost of the roll mold described later, and are obtained from a practical viewpoint.

[0052] The thickness of the light introduction layer composed of unit triangular prisms 300 is the height h of the unit triangular prism plus a value. This +α corresponds to the thickness of what is called in the industry a "residual film" (integrated with the light introduction layer and made of the same material as the light introduction layer) on the bottom surface of the unit triangular prism, and is a value of about 1 to 3 μm. This value was obtained from experience, stating that if this residual film does not exist, the cross-sectional shape of the unit triangular prisms will tend to be distorted, making it difficult to accurately maintain that shape during mass production.

[0053] The apex angle (reference number 350) of the unit triangular prism 300 is preferably 60° to 95°, more preferably 70° to 95°, and most preferably 80° to 93°. This value is determined from the viewpoints of desired optical characteristics and the manufacturing costs of a roll mold, which will be described later.

[0054] (Refractive index of the light introduction layer) The refractive index n2 of the resin (cured resin) of the light introduction layer composed of the array of unit triangular prisms 300 satisfies n0≧n2, and preferably 1.50≦n2≦1.64, in relation to the refractive index n1 of the resin (cured resin) of the above-mentioned light extraction layer and the refractive index n0 of the optical waveguide layer (layer between the light extraction layer and the light introduction layer) described below. The upper and lower limits here are preferred values ​​determined from the viewpoint of desired optical properties and practical issues pointed out in the explanation of the light extraction layer 100.

[0055] (Material and Formation Method of Light Introduction Layer) The material used is basically the same as the material of the light extraction layer 100 described above, and any resin that is a UV-curable transparent resin and has the refractive index specified by the present invention can be suitably used. Note that "transparent" here does not mean transparent in the strict sense, but means a state in which the haze value is low (for example, 2 to 3% or less) and can be said to be practically transparent. A known roll-to-roll continuous manufacturing method (see reference diagram in FIG. 5) is suitably adopted for manufacturing, and the resins constituting the light extraction layer and the light introduction layer, respectively, are applied in an uncured state onto one side of the base film or base sheet constituting the optical waveguide layer to form a coating layer, and the surface of the coating layer is pressed against a roll mold on which a fine uneven pattern (an uneven pattern having protrusions in the shape of triangular ridges in cross section) is formed to transfer the uneven pattern of the roll mold, and the transferred portion is successively irradiated with ultraviolet light (UV rays) to form the coating layer. The principle of the process for transferring the uneven pattern of a roll mold can also be used in the microimprinting process of plastic films, so it is also possible to form the light extraction layer and light introduction layer with the desired surface shapes by microimprinting on the surface of a three-layer film in which transparent thermoplastic resin films that constitute the light extraction layer and light introduction layer, respectively, are previously bonded to a base film that constitutes the optical waveguide layer, thereby forming a light extraction layer and a light introduction layer.

[0056] (Basic functions of the light introduction layer) Without limiting the technical scope of the present invention in any way, the light introduction layer 120 has the function of deflecting (raising) the light from a light guide plate (not shown) with an exit angle of 70° to 80° so that the light approaches the vertical direction, and propagating the light to the optical waveguide layer 110 described below.

[0057] (Optical Waveguide Layer Characteristics) The optical waveguide layer 110 of the light collecting auxiliary film 10 constitutes an intermediate layer between the light extraction layer 100 and the light introduction layer 120. The optical waveguide layer 110 does not contain any light diffusing fine particles. From the viewpoint of the light transmittance of the optical waveguide layer 110, the resin constituting the optical waveguide layer 110 is preferably a transparent resin such as polyethylene terephthalate (PET), polycarbonate (PC), polymethyl methacrylate (PMMA), or styrene-methyl methacrylate copolymer, the refractive index of which is suitable for the present invention, but from the viewpoints of reliability and availability, a transparent optical PET film is preferably used. The optical PET film used in the present invention is preferably one whose surface is easily adhesive by plasma treatment, chemical treatment, or the like.

[0058] The thickness of the light guide layer 110 is naturally determined from the relationship between the total thickness required for the light collecting auxiliary film 10, the thickness of the light extraction layer 100, and the thickness of the light introduction layer 120. From the viewpoint of improving the front brightness, it is preferable to make it as thin as possible, but since some cure shrinkage occurs when the UV-curable resin applied to both sides of the base film that becomes the light guide layer cures, it is preferable to have a thickness that can withstand this cure shrinkage, and the lower limit is preferably about 15 μm to 20 μm in view of the thickness of the light extraction layer and the light introduction layer. On the other hand, the upper limit is preferably about 200 μm in view of the total thickness required for the light collecting auxiliary film 10.

[0059] The refractive index of the plastic constituting the optical waveguide layer 110 is determined by the type of plastic used, and the numerical range of the refractive index is automatically determined. In the present invention, however, as described above, an optical PET film is preferably used, and the nominal refractive index in this case is 1.58.

[0060] This optical waveguide layer 110 functions as a so-called base film in the manufacturing process of the light concentrating auxiliary film 10 of the present invention, and is configured to transmit light to the light extraction layer 100 without reducing the amount of light incident from the optical waveguide layer 110 as much as possible after the light extraction layer 100 and the light introduction layer 120 are formed on both sides of the optical waveguide layer 110, and an optical PET film (optical polyethylene terephthalate film) can be suitably used. The optical PET film is surface-treated to an extent that does not affect the optical properties of the bulk of the film in order to improve the adhesive strength when a different resin is applied and bonded thereon. This surface treatment process is not included in the manufacturing process of the light concentrating auxiliary film 10 of the present invention, and therefore a commercially available optical PET film is suitably used as the optical waveguide layer 110 of the light concentrating auxiliary film 10.

[0061] (Interrelationship between the arrangement direction of unit recesses in the light extraction layer and the arrangement direction of unit triangular prisms in the light introduction layer) 4 shows the relationship (intersection angle) between the arrangement direction of unit recesses 200 (approximately inverted pyramids) constituting the light extraction layer 100 on the light exit surface side in the light concentrating assistance film 10 of the present invention and the longitudinal direction of unit triangular prisms (convex stripes) constituting the light introduction layer 120 on the light entrance surface side. In the figure, the valley lines 340 in the array of unit triangular prisms 300 in the light introduction layer 120 are shown by dashed lines. The figure shows a case where these two directions intersect at 45°. This value of 45° does not need to be an exact value, and a slight error is acceptable as long as the object of the present invention can be achieved.

[0062] (Interrelationship between the pitch of the light extraction layer (P1) and the pitch of the light introduction layer (P2)) Controlling the relationship between the pitch (P1) of the light extraction layer and the pitch (P2) of the light introduction layer is important in suppressing the appearance of self-moiré. Although the general moiré phenomenon, i.e., the moiré phenomenon between different optical elements, is well known, there seems to be no prior art document in the technical field of edge-lit backlights that addresses the problem of eliminating the self-moiré phenomenon that occurs only within one optical element itself. Note that although the above-mentioned Patent Document 1 addresses the problem of eliminating the moiré phenomenon, the moiré phenomenon is not a self-moiré phenomenon.

[0063] The inventor expressed the relationship between the pitch (P1) of the light extraction layer and the pitch (P2) of the light introduction layer as a mathematical formula that predicts the appearance of a general moire phenomenon, and inserted the actual values ​​of P1 and P2, respectively, and discovered that the predicted results did not match the actual measured results.

[0064] Therefore, the inventor conducted extensive research and found that, under conditions in which the arrangement direction of the unit recesses 200 in the light extraction layer 100 intersects with the arrangement direction of the unit triangular prisms 300 in the light introduction layer 130, when the actual values ​​of P1 and P2 are inserted into the following moiré equation, which the inventor discovered independently, the predicted results and the actual measured results match well, and that when these relationships satisfy all of the following conditions, it is possible to suppress the self-moiré phenomenon, as will be clear from the examples described below. That is, the light concentrating assistance film of the present invention that suppresses the self-moire phenomenon is characterized in that the relationship between the pitch (P1) of the light extraction layer and the pitch (P2) of the light introduction layer is P1>P2, and all of the above conditions are satisfied. (Math 1) | D1-D2|≦200 μm In the above formula 1, D1 and D2 satisfy the following formulas 2a and 2b, respectively: (Math 2a) D1 = |P1m × δ1 ÷ (δ1-P1m)| (Math 2b) D2 = |P1m × δ2 ÷ (δ2-P1m)| In the above formulas 2a and 2b, P1m>P2m, P1m satisfies the following formula 3a, and P2m satisfies the following formula 3b, (Math 3a) P1m= P1×sin(0.25×π) (Number 3b) P2m= P2÷2 In the above formulas 2a and 2b, 1) δ1 is the sum of P1m and the smaller of δa and δb, where δa is the absolute value of the difference between P1m and the integer part (rounded up to the nearest integer) of the value obtained by dividing P1m by P2m and multiplying the result by P2m, and δb is the absolute value of the difference between P1m and the integer part (rounded down to the nearest integer) of the value obtained by dividing P1m by P2m and multiplying the result by P2m, 2) δ2 is the sum of P1m and the smaller of δa and δb, where δa is the absolute value of the difference between P1m and the integer part (rounded up to the nearest integer) obtained by dividing P1m by P2m and multiplying that value by P2m, and δb is the absolute value of the difference between P1m and the integer part (rounded down to the nearest integer) obtained by dividing P1m by P2m and multiplying that value by P2m.

[0065] (Interrelationship of refractive index of each layer) In the light focusing assistance film of the present invention, the relationship between the refractive index n2 of the light extraction layer (the refractive index of the resin constituting the light extraction layer), the refractive index n0 of the optical waveguide layer that is in planar contact with it (the refractive index of the resin constituting the optical waveguide layer), and the refractive index n1 of the light introduction layer that is in planar contact with the opposite surface of the light extraction layer (the refractive index of the resin constituting the light introduction layer) is n0≧n1 and n0≧n2, and preferably the refractive index n1 is in the range of 1.50≦n1≦1.64 and the refractive index n2 is in the range of 1.50≦n2≦1.64.

[0066] 3. Roll mold that supports the manufacturing process of light-collecting auxiliary film The present invention has as its object the solution of the problem of reducing the cost of the light concentrating auxiliary film, but it goes without saying that the manufacturing cost of the light concentrating auxiliary film reflects the upstream costs of the manufacturing process. From this viewpoint, the roll-to-roll method is preferably adopted for manufacturing the light concentrating auxiliary film of the present invention, as described in detail below, and a roll mold is preferably used for this method. Since this roll mold is a precision part that requires advanced manufacturing technology, its cost greatly affects the manufacturing cost of the light concentrating auxiliary film. Therefore, the influence and constraints on the shape of the light concentrating auxiliary film of the present invention caused by the roll mold used for manufacturing the light concentrating auxiliary film will be described below. However, the scope of the present invention is not limited to the contents described below, and the manufacturing of the light concentrating auxiliary film of the present invention is not limited to the use of the following roll mold.

[0067] The roll mold used in the examples of the present invention was prepared by a lathe processing method described in detail below, but other possible methods include a photolitho-etching processing method, an electron beam processing method, and a direct laser processing method. However, the photolitho-etching processing method and the electron beam processing method are not preferable because they are expensive to prepare a rolled and large-area mold, and from a practical point of view, they go against one of the objectives of the present invention, which is to reduce costs. In addition, there may be cases where a large area can be achieved by lowering the accuracy of the concave-convex shape of the mold, but the accuracy of the shape obtained by pressing a low-precision mold to transfer the concave-convex shape is also low, and it is considered that it is not practical for the manufacture of optical films that require a high-precision surface shape. Regarding the direct laser processing method, it may be possible to use it in light of the fact that laser processing machines have become faster in recent years, but since the laser spot diameter is at least about 10 μm, this processing method is also considered to be not practical for the manufacture of optical films that require a high-precision surface shape. For these reasons, it is considered that at present, lathe cutting processing, which is highly accurate and cost-effective, can be suitably used as a processing method that contributes to reducing costs, which is one of the objectives of the present invention.

[0068] (Roll mold manufacturing method) 6 is a conceptual diagram of a general method for manufacturing a roll die by a cutting method for use in manufacturing the light concentrating assist film 10 of the present invention. (a) is a conceptual diagram showing cutting a roll die having a thin metal film 680 (usually copper metal) formed on its surface at an apex angle θ with a cutting tool 640 having a single crystal diamond bit 660 at its tip, and (b) is an enlarged cross-sectional view of the single crystal diamond bit 660 cutting the thin film 680. (Although outside the scope of the present invention, reference numbers are omitted for components other than the main components because this is for the purpose of explaining the preferred range of the uneven shape of the surface of the light concentrating assist film of the present invention.)

[0069] First, a metal film of copper or nickel is formed (mainly by electrolytic plating) on ​​the surface of a metal drum (usually iron or SUS) that will become a core roll of a predetermined size. The film thickness at this time is about 300 to 500 μm. In parallel with this, the single crystal diamond at the tip of the diamond bite (tool) is processed into a desired shape (in this embodiment, an isosceles triangle with an apex angle θ). Next, the single crystal diamond processed in this way is attached to the tip of a shank and the surface is polished to the desired shape. At this time, the shank is created in a shape that matches the cutting machine.

[0070] For example, when a copper film is formed on the surface, the manufacturing of a roll die by lathe cutting is generally performed as follows. First, the copper film formed on the surface of the metal drum in the above process is cut off in a line shape at high speed with a single crystal diamond tip having a specified tip angle (the position of the single crystal diamond tip is fixed and the roll die is rotated at high speed), thereby carving multiple concave stripes extending parallel to one direction on the surface. After this is done for one revolution of the drum, the position of the single crystal diamond tip is moved horizontally (in the direction along the axis of the drum) by a distance equivalent to the pitch (P), and the same operation is performed for another revolution, and this is repeated. Therefore, the smaller the diameter of the drum (the shorter the length of the cutting process line), the less wear is caused to the tip and side surface of the single crystal diamond tip, which in turn suppresses unnecessary scattering and reduces processing costs.

[0071] The concave stripes at this time correspond to the resin convex stripes that are pressed into the concave stripes in the roll-to-roll manufacturing process, and the size of these convex stripes, as described in detail in the examples below, is a triangular cross-sectional convex strip with a depth of the order of 9 μm to 21 μm and a base of the order of 18 μm to 42 μm, and therefore the size of the pointed end of the single crystal diamond tip that penetrates the copper plating layer is also of the same order, and since the optical performance of the light focusing auxiliary film of the present invention depends on the accuracy of the surface shape, the cutting process requires high-precision control.

[0072] In addition, if the apex angle of the tip of the single crystal diamond tip is obtuse, for example, 100° or more, the tip cannot grip (bite) sufficiently during the cutting process, and the tip of the single crystal diamond tip slides on the copper-plated surface, causing the single crystal diamond tip to vibrate, reducing the smoothness of the slope of the protrusion formed on the mold. As a result, the smoothness of the slope of the inverted pyramid and the slope of the triangular prism decreases. This also imposes practical restrictions on the size of the protrusion (and the size of the inverted pyramid and triangular prism that are created by transferring it).

[0073] Furthermore, the surface shape of the light extraction layer and light introduction layer formed on the surface of the final light focusing auxiliary film is determined by the triangular cross-sectional convex stripes or square pyramidal (pyramidal) protrusions formed on this drum mold, and the intersection (transition) between one surface and the adjacent surface of this surface shape needs to be as sharp (narrow) as possible due to the optical properties required of the light focusing auxiliary film, so the tip shape of the single crystal diamond tip used requires nanometer-order precision.

[0074] Regarding the ease of processing when forming the uneven strips on the surface of the mold, when forming a triangular prism layer on the light incident surface side of the light collecting auxiliary film of the present invention, the unit triangular prism strip is most easily processed with an apex angle of 90° (base angle 45°), and it is particularly easy to process a symmetrical shape. If the apex angle is more acute than 90°, problems are likely to occur in the durability of the bit, which is not preferable because it increases the difficulty of processing. On the other hand, if the apex angle is more obtuse than 90°, the cutting performance of the bit (single crystal diamond chip) becomes poor (the bit does not bite into the deposited copper metal film well), so the bit vibrates and the finish of the processed surface tends to become poor. For this reason, the apex angle of the pointed end of the single crystal diamond tip functioning as a bit (in the case of the present invention, that is, the apex angle of the unit triangular prism formed on the light incident surface side of the light focusing auxiliary film) is preferably 60° or more and 130° or less, more preferably 80° or more and 100° or less, and even more preferably 80° or more and 95° or less, and in any of these values, it is preferable that the angle error is ±1°.

[0075] When forming a unit recess of a substantially inverted quadrangular pyramid shape (substantially inverted pyramid shape) on the light exit surface side of the light-collecting auxiliary film of the present invention, the conditions of die processing are stricter and more difficult than when forming a unit triangular prism. The reason for this is the following process. That is, when cutting a protrusion corresponding to the recess of an inverted pyramid, first, in the first step, the tip of a single crystal diamond chip is pressed against (bites into) the surface of the copper-plated drum while rotating the drum to form a ridge of a concave strip with a triangular cross section. Next, in the second step, the ridge of a concave strip with a triangular cross section is formed in a similar manner in a direction perpendicular to the direction of the ridge of the concave strip formed in the first step. As a result, an inverted pyramidal unit recess is formed at the intersection of the concave strip formed in the first step and the concave strip formed in the second step, and the part that is not cut off by cutting becomes a pyramidal (pyramidal) protrusion. In this second step, the load applied to the tip of the single crystal diamond tip is not a static load, but a repeated impact load. In other words, repeated impact loads are applied when the tip passes alternately through the solid and void parts of the concave strip formed in the first step. For this reason, the processing conditions are stricter than in the case of the unit triangular prism described above, and durability problems of the bit are more likely to occur. For this reason, if the apex angle (in the case of the present invention, that is, the apex angle of the unit recess having an approximately inverted square pyramid shape (approximately inverted pyramid shape) formed on the light exit surface side of the light focusing auxiliary film) is acuter than 90°, the difficulty of processing increases, and similarly, if it is an obtuse angle of 100° or more, the difficulty of processing increases. Therefore, such an apex angle is preferably 70° or more and 130° or less, and more preferably 80° or more and 100° or less, and in any of these numerical values, the angle error is preferably ±1°.

[0076] (Backlight unit and liquid crystal display device equipped with the light-collecting auxiliary film of the present invention) FIG. 7(a) is a conceptual diagram of a cross section of a liquid crystal display device 70 equipped with the light-concentrating auxiliary film of the present invention. Reference number 700 indicates a liquid crystal panel unit, reference number 720 indicates a laminated unit of two orthogonally stacked BEFs (reference number 724 in FIG. 7(b)) and a light diffusion film (reference number 722 in FIG. 7(b)) laminated thereon, reference number 10 indicates the light-concentrating auxiliary film of the present invention, reference number 740 indicates a light guide plate unit having a reflective sheet on the lower surface side, and reference number 760 indicates a white LED. The white LEDs 760 are discretely arranged in a row along the side surface of the light guide plate unit 740 in the depth direction of the paper. The light-concentrating auxiliary film 10 of the present invention is inserted between the upper surface (light exit surface) of the light guide plate unit 740 and the laminated unit 720. This light-concentrating auxiliary film 10 has the function of collecting light from the upper surface (light exit surface) of the light guide plate unit 740 and deflecting (changing) its propagation direction to a more vertical direction (toward the top of the paper), thereby changing the light propagation characteristics to match as closely as possible to the two-sheet orthogonally stacked BEF (reference number 724 in Figure 7(b)) stacked on top of it.

[0077] Fig. 7(b) is a conceptual diagram showing the stacking state of each layer with the liquid crystal panel unit 700 in Fig. 7(a) removed. The layers are stacked in the order of a reflecting sheet 744, a light guide plate 742, a light concentrating assistance film 10 of the present invention, two orthogonally stacked BEFs 724, and a light diffusing film 722 from bottom to top.

[0078] (Method of evaluating the light-collecting auxiliary film of the present invention) Fig. 8 conceptually shows the stacking configuration when evaluating the characteristics of the light concentrating assist film 10 of the present invention. The stacking of each layer is shown by removing the two orthogonally stacked BEF 724 and the light diffusion film 722 in Fig. 7(b), and the stacking from bottom to top is the reflection sheet 744, the light guide plate 742, and the light concentrating assist film 10 of the present invention. Specific evaluation methods etc. will be described in detail in the Examples below.

[0079] <Example> Examples will be described below. 1. Creating a light extraction layer for the light-collecting auxiliary film (Base film) The substrate film used was an optical PET film (e.g., Diafoil T600E50 manufactured by Mitsubishi Chemical Corporation) with a thickness of 50 μm. If the effect does not differ depending on the manufacturer, any film having certain characteristics can be used suitably.

[0080] (UV curing resin) The UV-curable resin used was a UV-curable acrylate monomer (97 wt%) with a photoinitiator added, and was mixed so that the refractive index nD after curing was the value shown in the table below. The refractive index nD is the value measured using an Appe refractometer (NAR-1T SOLID, manufactured by Atago Co., Ltd.).

[0081] (Roll mold) A roll mold (with a surface copper metal thin film thickness of 300 μm to 500 μm) was used, which has surface irregularities such that the shape characteristics of the unit recesses are as shown in FIG. 2 and the apex angle (θ1) and pitch (P1) are the values ​​shown in Table 1 below.

[0082] (Film forming method) Basically, a commonly used roll-to-roll film production method was adopted. Specifically, a roll of the base film was set in the roll-to-roll manufacturing system described above, and the system was started. Next, an acrylate-based UV-curable resin, which was mixed so that the refractive index after curing would be the value listed in the table below, was continuously applied to the base film in a prescribed manner that is common to the roll-to-roll method to form a coating layer, while a roll mold was pressed against the coating film in sequence, and ultraviolet light (UV rays) was irradiated to cure it and form a light extraction layer, creating a two-layer film with the light extraction layer formed on one side, which was then wound up (the first roll was created). The apex angle (θ1) and pitch (P1) at this time were confirmed to have been transferred by magnifying the transfer surface 2400 times using a laser microscope (Keyence VKX-1000).

[0083] 2. Creation of the light introduction layer of the light-collecting auxiliary film The UV curable resin used was the same as that used for the light extraction layer. The refractive index after curing was also measured in the same manner using an Appe refractometer (NAR-1T SOLID manufactured by Atago Co., Ltd.). The roll mold used was a different roll mold that had a surface uneven pattern capable of forming a triangular prism array consisting of multiple ridges with an isosceles triangular cross section.

[0084] 3.Judgment method 1) How to determine self-moiré Basically, it was visual. One end of a sample of the light-collecting assisting film of the present invention was held with the fingers of one hand, the arm of the hand was extended, and the film was held up to an indoor fluorescent light, and it was judged whether moire was visible to the naked eye. The specific judgment method is as shown in the conceptual diagram in FIG. 10. In a dark room, the end of the light-collecting assisting film 10 of the present invention was held with one hand, and the film was held vertically between the naked eye 1010 and the fluorescent light 1020 about 60 cm away from the naked eye, and the transmission moire was visually confirmed from the light extraction layer (layer having an inverted pyramid) side. Next, the film was brought directly under the position of the film and arranged so that the center of the horizontal film was located about 30 cm diagonally from the same fluorescent light 1020 and the naked eye 1010, and the oblique light from the fluorescent light 1020 was applied obliquely to the surface of the light extraction layer of the film, and the reflection moire was confirmed by the reflection. At this time, if neither the transmission moire nor the reflection moire was visible, it was marked as ○. Next, if this judgment reveals that moiré (transmission moiré and / or reflection moiré) is visible, the film is placed horizontally on the light guide plate 742 (including the light reflector 744) of the backlight unit used in the brightness measurement, and the center of the film is placed (see the stacking diagram in Figure 8) at a distance of approximately 30 cm diagonally from the naked eye 1010 at the same angle as above, and a further judgment is made visually. In either case, when the light extraction layer (inverted pyramid layer) is facing up, or when the light introduction layer (triangular prism layer) is facing up, if no moiré (transmission moiré) is visible, it is marked as △, and if it is visible, it is marked as ×. In this case, the relationship between the arrangement direction of the unit concave portions of the light extraction layer (the same direction as the ridge line) and the arrangement direction of the unit triangular prisms of the light introduction layer (the same direction as the ridge line) is as shown in Figure 4. In this case, the cross-sectional shape of the portion formed by the solid portions of two adjacent unit concave portions (the cross-sectional shape shown in Figure 2) and the cross-sectional shape of the unit triangular prism (the cross-sectional shape shown in Figure 3) were both isosceles triangles.

[0085] 2) Evaluation method for front luminance The light-collecting auxiliary film of the present invention was mounted on a 9-inch edge-lit backlight unit (see FIG. 7(b) for the configuration) that uses a white LED as a light source, and evaluated. The two-sheet orthogonally stacked BEF used here was BEF-4DT manufactured by 3M, and the light-diffusing film laminated on top of that was D159GS manufactured by Tsujiden Co., Ltd., the same applicant as above. The white LED was driven at a constant current of 200 mA with a maximum power supply voltage of 17 V. A 5cm square area centered on the center point of the backlight unit's emission surface was divided into 64 x 64 cells (each cell is approximately 0.78mm square), and measurements were taken with the shutter speed set to Auto (high dynamic sampling mode). The front luminance value was calculated by averaging the front luminance values ​​of 64 x 64 = 4096 points. The luminance measuring device used was a two-dimensional luminance and chromaticity measuring device (ACE3-2000) manufactured by Hyland. In the following evaluation method, the direction of the optical axis of the light emitted from the white LED arranged on the side of the light guide plate of the edge-lit backlight is parallel to the direction (longitudinal direction) of the ridge of the unit triangular prism of the light introduction layer of the light concentrating auxiliary film of the present invention arranged on the light guide plate. The orientation characteristics of the light emitted from the upper surface of the light guide plate mounted on this edge-lit backlight unit toward the light concentrating auxiliary film of the present invention were such that, when the combination of the shape characteristics and refractive index of the light concentrating auxiliary film of the present invention was as shown in Table 1 below, the contour diagram on the light exit surface of the light concentrating auxiliary film was as shown in Figure 9. [Table 1]

[0086] 2. The shape characteristics, refractive index and optical characteristics of the light-collecting auxiliary films used in the examples and comparative examples were as shown in the table below. 1) Self-moiré judgement results [Table 2] (Note 1: The calculation in the above calculation result is based on a formula devised by the present inventor for the first time and described in the specification and claims for self-moiré under the condition that the arrangement direction of the unit concave portions of the light extraction layer (same direction as the ridge line) and the arrangement direction of the unit triangular prisms of the light introduction layer (same direction as the ridge line) intersect at 45° with each other, and the cross-sectional shape of the portion made up of the solid portions of two adjacent unit concave portions (cross-sectional shape shown in FIG. 2) and the cross-sectional shape of the unit triangular prisms (cross-sectional shape shown in FIG. 3) are both isosceles triangles.) (Note 2: The symbols ○, △, and × in the Moiré Judgment Result column each represent the actual judgment result according to the judgment method as explained in the Self-Moiré Judgment Method section above.)

[0087] Next, the results of actually determining that no self-moiré occurs even when the intersection angle is changed by 3.0° up or down from 45.0° are shown in the table below, comparing the results actually determined using the above-mentioned determination method with the calculation results obtained using the above-mentioned formula. [Table 3] (Note 1: The calculation in the above calculation result is based on a formula devised by the present inventor for the first time and described in the specification and claims for self-moiré under the condition that the arrangement direction of the unit concave portions of the light extraction layer (same direction as the ridge line) and the arrangement direction of the unit triangular prisms of the light introduction layer (same direction as the ridge line) intersect at 42.0°, 45.0°, and 48.0° to each other, respectively, and the cross-sectional shape of the portion made up of the solid portions of two adjacent unit concave portions (cross-sectional shape shown in FIG. 2) and the cross-sectional shape of the unit triangular prisms (cross-sectional shape shown in FIG. 3) are both isosceles triangles.) (Note 2: The symbols ○, △, and × in the column for the measured moiré evaluation results respectively refer to the actual evaluation results according to the evaluation method explained in the section on self-measured moiré evaluation methods above.)

[0088] 2) Evaluation results of front luminance at the light exit surface of an edge-lit backlight equipped with the light-condensing auxiliary film of the present invention In the table below, the refractive index of the light extraction layer was n1 = 1.52, and the refractive index of the light introduction layer was n2 = 1.52. The refractive index of the optical waveguide layer was n0 = 1.58, the thickness was 50 μm, and the thickness of the residual film of the light extraction layer and the residual film of the light introduction layer were both 1 μm. In the results below, in all cases, the brightness unevenness was not visible to the naked eye. [Table 4] (Note: For the optical simulation, an optical simulator, LightTools lighting design software manufactured by Synopsys, was used. The parameters used in the simulation were set so that the error between the actual measured values ​​and the simulated values ​​was the value shown in Table 6 below, to ensure the validity of the simulation values.)

[0089] From the above table, it is clearly seen that, between the example group and the comparative example group, the front brightness of the comparative example group tends to decrease when the apex angle of the light extraction layer is between 100° and 110°.

[0090] In the table below, the refractive index of the light extraction layer was n1 = 1.58, and the refractive index of the light introduction layer was n2 = 1.52. The refractive index of the optical waveguide layer was n0 = 1.58, the thickness was 50 μm, and the thickness of the residual film of the light extraction layer and the residual film of the light introduction layer were both 1 μm. In the results below, in all cases, the brightness unevenness was not visible to the naked eye. [Table 5] (Note: For the optical simulation, an optical simulator, LightTools lighting design software manufactured by Synopsys, was used. The parameters used in the simulation were set so that the error between the actual measured values ​​and the simulated values ​​was the value shown in Table 6 below, to ensure the validity of the simulation values.)

[0091] From the above table, it is clearly seen that, between the example group and the comparative example group, the front brightness of the comparative example group tends to decrease when the apex angle of the light extraction layer is between 100° and 110°.

[0092] The above simulations were all performed using an optical simulator (LightTools lighting design software manufactured by Synopsys), and the validity of the above simulation values ​​was ensured by setting various parameters so that the error (error from the actual measurement) between the actual measurement value of front luminance and the simulation value was within 1%, as shown in the following Table 6. In this case, the refractive index n0 of the optical waveguide layer was 1.58, the thickness was 50 μm, and the thickness of the remaining film of the light extraction layer and the remaining film of the light introduction layer were each 1 μm. [Table 6]

[0093] The table below shows the frontal luminance measured at the exit surface of the light concentrating auxiliary film when the light concentrating auxiliary film of the present invention has an apex angle of 80° for the inverted pyramid of the light extraction layer, an apex angle of 90° for the triangular prism (isosceles triangle) of the light introduction layer, and the refractive index of each layer changed to the value shown in the table (the residual film of the light extraction layer and the residual film of the light introduction layer are each approximately 1 μm thick), placed horizontally on a light guide plate such that the frontal luminance at the exit surface of the light guide plate is 749.9 cd / m2. [Table 7]

[0094] The table below shows the frontal luminance measured at the exit surface of the light concentrating auxiliary film when the light concentrating auxiliary film of the present invention has an apex angle of 90° for the inverted pyramid of the light extraction layer, an apex angle of 90° for the triangular prism (isosceles triangle) of the light introduction layer, and the refractive index of each layer changed to the value shown in the table (the residual film of the light extraction layer and the residual film of the light introduction layer are each approximately 1 μm thick), placed horizontally on a light guide plate such that the frontal luminance at the exit surface of the light guide plate is 749.9 cd / m2. [Table 8]

[0095] The present invention has been described in detail above based on representative embodiments, examples, and comparative examples, but various variations can be adopted without departing from the scope of the object and spirit of the present invention. [Industrial Applicability]

[0096] According to the present invention, a light-concentrating auxiliary film having the following characteristics can be obtained. 1) The light-collecting auxiliary film has a small number of elements. 2) The elements constituting the light-collecting auxiliary film do not contain any light-diffusing particles. 3) The appearance of self-moiré can be suppressed while obtaining desired optical characteristics. 4) It is suitable for mass production using the roll-to-roll method and is low cost. As a result of the above, it is expected that the manufacturing costs of edge-lit backlight units incorporating the light-concentrating auxiliary film of the present invention will be reduced, and further that it is expected that the demand for reducing the costs of liquid crystal display devices incorporating the same will be met. [Explanation of symbols]

[0097] 10 Light-collecting auxiliary film 100 Light extraction layer 110 Optical waveguide layer 120 Optical introduction layer 200 unit recess (approximately inverted pyramid) 220 Ridge line of unit recess (approximately inverted pyramid) 230 Pitch of unit recess (approximately inverted pyramid) (P1) 240 Bottom center point of unit recess 250 The apex angle (θ1) of the triangular solid area occupied by the solid parts of adjacent unit recesses 260 Triangular solid area occupied by the solid parts of adjacent unit recesses 300 unit triangular prism 320 Unit Triangular Prism Edges 330 unit triangular prism pitch (P2) 340 Valley lines formed by adjacent unit triangular prisms 350 Unit triangular prism apex angle (θ2) 500 Known common roll-to-roll manufacturing systems (for reference) 520 UV curing resin to be applied 540 Roll mold 560 Unwinding roll 562 Winding Roll 580 UV irradiation device 620 Roll mold 640 Cutting tool shank 660 Single crystal diamond 680 Workpiece to be cut (copper plated layer) 700 LCD Panel 720 BEF (two crossed sheets) and light diffusion film (manufactured by the applicant) 722 Light diffusion film (manufactured by applicant) 724 BEF (2-piece cross type) 740 Light guide plate unit (light reflecting sheet and light guide plate) 742 Light guide plate 744 Light Reflective Sheet 760 Discrete White LED 1010 naked eye 1020 Indoor fluorescent lamp

Claims

1. A light exit surface of a light guide plate in an edge-lit backlight unit using discrete LED point light sources; A light-condensing auxiliary film that is inserted between a light incident surface of a brightness enhancement film (BEF), an optical waveguide layer made of a light-transmitting substrate film; a light extraction layer formed on one surface of the optical waveguide layer and having a plurality of unit recesses each having an inverted square pyramid shape; a light introduction layer formed on the other surface of the optical waveguide layer and having a plurality of unit triangular prisms extending in parallel in one direction; the light extraction layer constitutes a light exit surface, a prism surface of each of the plurality of unit triangular prisms constituting the light introduction layer constitutes a light incidence surface; None of the light extraction layer, the optical waveguide layer, and the light introduction layer contains light diffusing fine particles, The relationship between the pitch P1 of the plurality of unit recesses and the pitch P2 of the plurality of unit triangular prism lenses is P1>P2. A light-condensing auxiliary film characterized by satisfying all of the following conditions: (Math. 1) | D1−D2|≦200 μm In the above formula 1, D1 and D2 satisfy the following formulas 2a and 2b, respectively: (Math 2a) D1 = |P1m × δ1 ÷ (δ1 - P1m)| (Math 2b) D2 = |P1m × δ2 ÷ (δ2 - P1m)| In the above formulas 2a and 2b, P1m>P2m, P1m satisfies the following formula 3a, and P2m satisfies the following formula 3b, (Math. 3a) P1m= P1× sin(0.25×π) (Math 3b) P2m= P2÷2 In the above formulas 2a and 2b, 1) δ1 is the sum of P1m and the smaller of δa and δb, where δa is the absolute value of the difference between P1m and the integer part (rounded up to the nearest integer) of the value obtained by dividing P1m by P2m and multiplying the result by P2m, and δb is the absolute value of the difference between P1m and the integer part (rounded down to the nearest integer) of the value obtained by dividing P1m by P2m and multiplying the result by P2m, 2) δ2 is the sum of P1m and the smaller of δa and δb, where δa is the absolute value of the difference between P1m and the integer part (rounded up to the nearest integer) of P1m divided by P2m and P2m multiplied by P2m, and δb is the absolute value of the difference between P1m and the integer part (rounded down to the nearest integer) of P1m divided by P2m and P2m multiplied by P1m, and the resulting value is doubled and compared to the larger of δa and δb.

2. A light exit surface of a light guide plate in an edge-lit backlight unit using discrete LED point light sources; A light-condensing auxiliary film that is inserted between a light incident surface of a brightness enhancement film (BEF), an optical waveguide layer made of a light-transmitting substrate film; a light extraction layer formed on one surface of the optical waveguide layer and having a plurality of unit recesses each having an inverted square pyramid shape; a light introduction layer formed on the other surface of the optical waveguide layer and having a plurality of unit triangular prisms extending in parallel in one direction; the light extraction layer constitutes a light exit surface, a prism surface of each of the plurality of unit triangular prisms constituting the light introduction layer constitutes a light incidence surface; None of the light extraction layer, the optical waveguide layer, and the light introduction layer contains light diffusing fine particles, an intersection angle between a direction of ridgelines of the plurality of unit concaves and a direction of ridgelines of the plurality of unit triangular prisms is within a range of 42° to 48°; Moire caused by the plurality of unit recesses and the plurality of unit triangular prisms is not visible to the naked eye. A light-condensing auxiliary film.

3. The relationship between the pitch P1 of the plurality of unit recesses and the pitch P2 of the plurality of unit triangular prism lenses is P1>P2.

3. The light-condensing assisting film according to claim 2.

4. The apex angle of each of the unit recesses is less than 100°.

4. The light-condensing assisting film according to claim 1 or 3.

5. The light-collection assist film according to claim 4, characterized in that when the refractive index of the resin constituting the light extraction layer is n1, the refractive index of the resin constituting the light introduction layer is n2, and the refractive index of the resin constituting the optical waveguide layer is n0, the relationships n0≧n1 and n0≧n2 hold.

6. 6. The light-collecting assistance film according to claim 5, wherein the refractive index n1 is in the range of 1.50≦n1≦1.64, and the refractive index n2 is in the range of 1.50≦n2≦1.

64.

7. The apex angle of the plurality of unit triangular prisms is 95° or less. The light-condensing assisting film according to claim 6 .

8. The apex angle of each of the unit recesses is equal to or greater than 80° and equal to or less than 95°.

8. The light-concentrating auxiliary film according to claim 7.

9. An edge-light type backlight unit having a plurality of point light sources, a light guide plate, and a brightness enhancement film (BEF), At least one light-condensing assist film according to any one of claims 1 to 8 is interposed between the light guide plate and the brightness enhancement film (BEF). The edge-light type backlight unit is characterized by the above.

10. The plurality of point light sources are disposed on at least one edge side of the light guide plate.

10. The edge-light type backlight unit according to claim 9.

11. The edge-light type backlight unit according to claim 10; Equipped with an LCD display panel A liquid crystal display device characterized by the above-mentioned.

Images