Light condensing-auxiliary film, edge-lit type backlight unit having light condensing-auxiliary film mounted thereon, and liquid crystal display device having edge-lit type backlight mounted thereon

Abstract

[Problem] To provide an optical film element in which self-moire is not visually recognized by the naked eye while entirely being constituted of a transparent resin without using fine particles for light diffusion, and which has high front-luminance without luminance unevenness in a light-outputting surface of a backlight when mounted on an edge-lit type backlight. [Solution] This light condensing-auxiliary film is inserted between a light-outputting surface of a light guide plate in an edge-lit type backlight unit which uses a dispersion-type LED point light source and a light-entering surface of a brightness enhance film (BEF). The light condensing-auxiliary film is characterized by being provided with: an optical waveguide layer which is formed of a translucent base film; a light extraction layer which is formed on one surface of the optical waveguide layer and has a plurality of unit recessed parts of an inverted quadrangular pyramid shape; and a light introduction layer which is formed on the other surface of the optical waveguide layer and has a plurality of unit triangular prisms extending in parallel in one direction. The light condensing-auxiliary film is also characterized in that: the light extraction layer constitutes a light-outputting surface; prism surfaces of the plurality of unit triangular prisms constituting the light introduction layer constitute a light-entering surface; the direction of ridge lines of the plurality of unit recesses intersects the direction of ridge lines of the plurality of unit triangular prisms at an angle of 42°-48°; none of the light extraction layer, the optical waveguide layer, and the light introduction layer contains fine particles for light diffusion; and self-moire due to the plurality of unit recesses and the plurality of unit triangular prism lenses is not visually recognized by the naked eye.

Description

A light-condensing auxiliary film, an edge-light type backlight unit incorporating the light-condensing auxiliary film, and a liquid crystal display device incorporating the edge-light type backlight.

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

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

[0003] The basic components of such edge-lit backlights using white LED point light sources are a light source, a light guide plate, a light propagation characteristic adjustment film (known by various names depending on its main function, such as a light shaping sheet or simply a light diffusion film), and a brightness enhancement film (BEF). BEFs are generally commercially available (mainly manufactured by 3M), and manufacturers of backlights, light guide plates, and light propagation characteristic adjustment films have rarely developed alternatives to BEFs. In such a configuration, diffuse white light from the light source (white LED) generally enters the light guide plate horizontally from the side of the light guide plate. The light is reflected and diffused by light diffusion dots arranged below the light guide plate, changing (deflecting) its propagation direction. The functional characteristics of the light guide plate are controlled so that the light is emitted from the top surface of the light guide plate (the surface facing the BEF) as light with a Gaussian-like peak in light intensity angular distribution. 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 and the like, 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 (light diffusion film) that assists the light diffusion function is inserted between this light guide plate and the BEF (see, for example, Figure 1 of Patent Document 1).

[0004] In recent years, the number of pixels has increased dramatically as LCD panels have become smaller. This has resulted in a significant decrease in the transmittance of light from the light source, resulting in poor front-view brightness at LCD panels. In edge-lit backlights, the aforementioned light guide plate function is said to reduce brightness unevenness compared to direct-type backlights. The desired optical characteristics are focused on the strength of the front-view brightness at the backlight. To address this issue, edge-lit backlights equipped with white LED light sources have been gaining attention, and vigorous efforts have been made to improve light guide plates for such backlights. Such improved light guide plates have optimally arranged light-reflecting dots on their underside, and optical elements that function to focus light reflected by the dots are formed on their upper surface (the light-exiting surface), and these optical elements are arranged in a unique spatial configuration not previously seen. As a result, the light emitted from the light-exiting surface of the optical elements arranged on the upper surface of the light guide plate has relatively strong directionality compared to the light emitted from conventional pseudo-surface light emitters. However, even with such light guide plates, the propagation direction and shape of the light emitted from them do not optimally match with a light-condensing film known as a BEF (Brightness Enhancement Film), which causes scattering losses during the light propagation process and means that the front brightness of the backlight does not fully meet market needs.

[0005] The present applicant has previously manufactured and sold light diffusion films for backlights, and has separately invented and filed a patent application for a novel optical film (light diffusion film) for direct-type point light sources (Japanese Patent Application No. 2023-78133). This invention focuses on the interrelationship between the refractive indexes of the layers of a three-layer film containing light-diffusing particles and a triangular prism layer on the light incident surface side. This invention is for direct-type point light sources, not edge-lit backlights, but the applicant gained various insights during the process of developing it.

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

[0007] Furthermore, through computer simulations and the like, the inventors have found that the optical characteristics required of an optical film element in the above-mentioned special usage environment (i.e., an environment in which the element is inserted between a light guide plate and a BEF) are such that the light emitted from the light guide plate is condensed while changing the angle of its propagation direction so that the light is incident on the BEF at an angle optimal for the BEF, and that this minimizes the loss of light quantity during the light propagation path and increases the front luminance from the backlight.

[0008] Based on the above findings, material design was considered 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 was necessary to minimize the haze value of the optical film element inserted between the light guide plate and the BEF. It also became clear that in order to satisfy this requirement, it was necessary to completely avoid the use of commonly used light-diffusing fine particles, which lead to an increase in the haze value.

[0009] On the other hand, the present applicant has accumulated various knowledge in the manufacturing process of optical films that use light-diffusing particles but are suitable for low-cost mass production, such as the invention described in Japanese Patent Application No. 2023-78133, and that include a triangular prism layer on the light incident surface side. Based on this knowledge, in the course of extensive research, the applicant has discovered a potential problem that, while recent light guide plates are capable of more efficient light guide and light extraction, using a scattering film on an efficient light guide plate can result in additional scattering loss. Furthermore, after considering currently available mass production technologies that most faithfully satisfy the above requirements while being the lowest cost, the applicant has come up with the idea that in order to achieve the function of concentrating light emitted from a light guide plate while changing the angle of its propagation direction with the fewest number of optical elements, which leads to the lowest cost, a combination of controlling the refractive index of the material used in 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 edge-lit backlights that does not contain any light-diffusing microparticles, the inventors investigated prior patent documents and found that optical film elements with such a basic configuration have a problem of moiré fringes appearing due to a self-moiré phenomenon that occurs in a single optical film element, as taught in, for example, Patent Document 1 (International Publication No. WO2010 / 029910).

[0011] Under the above background, the present invention aims to provide a film optical element that is inserted between the light guide plate and BEF of an edge-lit backlight, and that can or is expected to solve the following problems (satisfy the required characteristics): 1) The number of elements that make up the film optical element is as small as possible. 2) None of the elements that make up the film optical element contain light-diffusing microparticles. 3) Desired optical characteristics can be obtained while being configured so that self-moiré is not visible to the naked eye. 4) It is suitable for mass production using a roll-to-roll method and is low cost.

[0012] International Patent Publication No. WO2010 / 029910

[0013] Therefore, the present inventors have conducted extensive research to provide an optical film element (hereinafter referred to as a light-concentrating auxiliary film) that is low-cost, does not contain any light-diffusing fine particles, has a configuration in which self-moiré is not visible to the naked eye, has a front luminance high enough for practical use as a backlight, and has luminance unevenness controlled to a level that is practical for practical use. The development of the light-concentrating auxiliary film according to the present invention is premised on the absence of any light-diffusing fine particles, and such an optical film is so transparent that haze is not visible, so that countermeasures against self-moiré are a major issue. However, the present inventors have conducted extensive research based on the reverse idea that, in theory, even if self-moiré occurs, it should not be visible to the naked eye if the distance between the moiré lines at that time is equal to or less than a predetermined distance, and as a result have completed the present invention.

[0014] That is, the first invention is a light-concentrating auxiliary film to be inserted between the light exit surface of a light guide plate and the light entrance surface of a brightness enhancement film (BEF) in an edge-lit backlight unit that uses discrete LED point light sources, the light-concentrating auxiliary film comprising: a light guide layer made of a translucent base film; a light extraction layer formed on one surface of the light guide layer and having a plurality of unit concave portions in the shape of an inverted square pyramid; and a light introduction layer formed on the other surface of the light guide layer and having a plurality of unit triangular prisms extending parallel to one direction, the light extraction layer constituting the light exit surface, the prism surfaces of the plurality of unit triangular prisms constituting the light introduction layer constituting the light entrance surface, none of the light extraction layer, the light guide layer, and the light introduction layer contain light-diffusing microparticles, 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, and the light-concentrating auxiliary film is characterized in that (Equation 1) |D1-D2|≦200 μm In the above equation 1, D1 and D2 satisfy the following equations 2a and 2b, respectively: (Equation 2a) D1=|P1m×δ1÷(δ1-P1m)| (Equation 2b) D2=|P1m×δ2÷(δ2-P1m)| In the above equations 2a and 2b, P1m>P2m, P1m satisfies the following equation 3a, and P2m satisfies the following equation 3b: (Equation 3a) P1m= P1×sin(0.25×π) (Equation 3b) P2m= P2÷2 In the above equations 2a and 2b, 1) For δ1, the absolute value of the difference between P1m and the value obtained by dividing P1m by P2m (rounding up to the nearest integer) is δa, and P1m is set to P2m. 1) When the absolute value of the difference between P1m and the value obtained by multiplying the integer part (rounded down to the nearest integer) of P1m divided by P2m is δa, and the absolute value of the difference between P1m and the value obtained by multiplying the integer part (rounded up to the nearest integer) of P1m divided by P2m is δb, 2) δ2 is the sum of P1m and the smaller of δa and δb, when the absolute value of the difference between P1m and the value obtained by multiplying the integer part (rounded down to the nearest integer) of P1m divided by P2m is δa, and the absolute value of the difference between P1m and the value obtained by multiplying the integer part (rounded down to the nearest integer) of P1m divided by P2m is δb, and the smaller of δa and δb is doubled and this value is compared to the larger of δa and δb.

[0015] A second invention is a light-collection auxiliary film to be interposed between the light exit surface of a light guide plate and the light entrance surface of a brightness enhancement film (BEF) in an edge-lit backlight unit using discrete LED point light sources, the light-collection auxiliary film comprising: a light guide layer made of a light-transmitting base film; a light extraction layer formed on one surface of the light guide layer and having a plurality of unit concave portions shaped like an inverted square pyramid; and a light introduction layer formed on the other surface of the light guide layer and having a plurality of unit triangular prisms extending parallel to one direction, the light extraction layer constituting the light exit surface, and prism surfaces of the plurality of unit triangular prisms constituting the light introduction layer constituting the light entrance surface, none of the light extraction layer, the light guide layer, and the light introduction layer contain light-diffusing particles, the intersection angle between the direction of the ridge lines of the plurality of unit concave portions and the direction of the ridge lines of the plurality of unit triangular prisms is within a range of 42° to 48°, and moire patterns caused by the plurality of unit concave portions and the plurality of unit triangular prisms are not visible to the naked eye. The light-condensing auxiliary film is characterized by the above.

[0016] A third invention is characterized in that in the second invention, 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 is characterized in that, in the first or third invention, 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-condensing 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 is characterized in that, in the ninth invention, the plurality of point light sources are arranged 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.

[0025] The light-concentrating auxiliary film of the present invention does not contain any light-diffusing fine particles, and is expected to function as an optical film element that suppresses the appearance of self-moiré (visible to the naked eye), has a front luminance high enough for practical use as a backlight, and has luminance unevenness controlled to a level that is practical for practical use. Furthermore, it can be manufactured using a roll mold using a roll-to-roll method suitable for mass production, which is expected to increase the ease of manufacturing and reduce manufacturing costs. Furthermore, these factors are expected to reduce the costs of edge-lit backlight units and liquid crystal display devices that incorporate the light-concentrating auxiliary film of the present invention.

[0026] In the following drawings, elements with the same reference numbers are the same.

[0033] Figure 1 is a conceptual diagram showing a cross section of a light-concentrating assist film according to the present invention.

[0034] Figure 2 is a conceptual diagram showing a front view (a) and cross sections (b and c) of a light extraction layer 100 on the light-exiting surface side of a light-concentrating assist film 10 according to the present invention. Reference numeral 200 indicates a unit recess (void), 220 indicates a ridge line, 240 indicates the deepest point of the unit recess (the center point of the recess, also called the inverted apex because it is the apex of an inverted pyramid), and 260 indicates a solid portion defining the unit recess.

[0035] Figure 2 is a conceptual diagram showing a front view (a) and cross section (b) of an array of unit triangular prisms 300 constituting the light-introduction layer 120 on the light-incident surface side of a light-concentrating assist film 10 according to the present invention. Reference numeral 300 indicates a unit triangular prism, 320 indicates a ridge line of the unit triangular prism, and 340 indicates a valley line formed by adjacent unit triangular prisms. 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 of the light concentrating assist film 10 of the present invention and the longitudinal direction of unit triangular prisms (protrusions) constituting the light introduction layer 120 on the light incident 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. (a) of the figure shows a case where these two directions intersect at 45°. (c) of the figure shows this state in a simplified alternative representation. (c) of the figure shows a state where the light extraction layer 100 is on top and the light introduction layer 120 is on the bottom. (b) and (d) of the figure show states where the intersection angles are 42° and 48°, respectively. This is a reference diagram of a known, general roll-to-roll manufacturing system. Although outside the scope of the present invention, this is intended to explain the preferred range of the unevenness of the surface of the light concentrating assist film of the present invention, and therefore reference numbers are omitted for components other than the main components. 1 is a conceptual diagram of a general method for manufacturing a roll mold by a cutting method, which is used to manufacture the light-concentrating assisting 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 mold having a thin metal film 680 (typically copper metal) formed on its surface at an apex angle θ, and (b) is an enlarged cross-sectional view of the single crystal diamond 660 cutting the thin film 680.(Although outside the scope of the present invention, this is for the purpose of explaining the preferred range of the uneven surface shape of the light-concentrating assisting film of the present invention, and therefore reference numbers are omitted for components other than the main components.) Figure 7(a) is a conceptual diagram of the cross section of an example of an edge-lit backlight equipped with light-concentrating assisting film 10 of the present invention. Reference number 700 indicates a liquid crystal panel, reference number 720 indicates the entire two-layer orthogonally stacked BEF and the light diffusion film laminated thereon, reference number 10 indicates the light-concentrating assisting film of the present invention, reference number 740 indicates a light guide plate unit having a reflective sheet on the underside, and reference number 760 indicates white LEDs. Note that the white LEDs 760 are discretely arranged in a row along the side of light guide plate unit 740 in the depth direction of the page. Figure 7(b) is a conceptual diagram showing the stacking state of each layer with the liquid crystal panel 700 of Figure 7(a) removed. The stacking is performed in the following order from bottom to top: a reflective sheet 744, a light guide plate 742, a light concentrating assist film 10 of the present invention, a two-sheet cross-stacked BEF 724, and a light diffusing film 722. 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 in the following order from bottom to top: a reflective sheet 744, a light guide plate 742, and a light concentrating assist film 10 of the present invention. Multiple white LEDs 760 are arranged on the side of the light guide plate 732. This figure shows a contour diagram of the light exit surface of a light concentrating assist film of the present invention when the shape characteristics and refractive index combinations are as listed in Table 1. The optical axis of the light emitted from the white LED in this case is parallel to a straight line passing through the center of the circular area of ​​the contour diagram and extending horizontally from left to right on the page. This is a conceptual diagram showing a method for visually determining self-moiré. FIG. 10A is a conceptual diagram of the measurement conditions when the judgment result is ◯, and FIG. 10B is a conceptual diagram of the measurement conditions when the judgment result is Δ or ×.

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

[0028] Throughout this specification, the following terms are used: 1) "Light concentration" in this invention 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 "concentration" here is not strict and includes cases where slight partial diffusion occurs depending on characteristics such as the direction of incident light and the intensity angular distribution. 2) "Film" refers not only to films in the strict sense defined by thickness, but also to thicker materials commonly referred to as sheets. 3) "Self-moiré" refers to moiré (moiré fringes) that occur in a single transparent film-like optical element (or optical film element). Moiré can be divided into parallel moiré and rotational moiré. In this invention, rotational moiré did not appear (it was not visible to the naked eye) within the scope of the configuration in any of the examples. Therefore, the moiré referred to below refers to parallel moiré. In this invention, the term "appearance of moiré" refers to a moiré phenomenon visible to the naked eye, and "non-appearance of moiré" refers to a moiré phenomenon that is not visible to the naked eye, and is not used from a theoretical standpoint. 4) "Convex stripes" refers to convex protrusions that extend continuously in one direction with the same cross-sectional shape, and "concave stripes" refers to concave depressions that extend in one direction with the same cross-sectional shape. In this case, "one direction" does not necessarily refer to a direction defined by a continuous straight line, but may also include a direction defined by a continuous curve. 5) "Approximately parallel" refers to the ridge lines of multiple convex stripes or the valley lines of multiple concave stripes being 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) "Approximately square pyramid" or "approximately inverted pyramid" refers not only to true inverted square pyramids, but also to those that are essentially inverted square pyramids from a practical standpoint and can be considered to be inverted square pyramids or inverted pyramids within the range of unavoidable shape variations resulting from processing accuracy in industrial production. For example, even in the case of an "inverted square pyramid trapezoid" with a flat apex, if the apex area is small, it is considered to be included in the "approximately inverted polygonal pyramid" as long as it does not hinder the achievement of the objectives of this invention.7) "Refractive index" refers to the refractive index measured using an Atago Appe refractometer (NAR-1T SOLID) at a measurement wavelength of 589 nm. Hereinafter, it is represented by the symbol nD. The refractive index is expressed as a number with two decimal points, but in this case, this does not necessarily mean that the number after the second decimal point is zero. It includes values ​​from less than the number one unit above to more than the number one unit below the second decimal point. 8) "Apex angle" refers to the apex angle shown in Figures 2 and 3. The angle was measured using a laser microscope (Keyence VKX-1000) with the transfer surface magnified 2400 times. Although the apex angle does not include decimal points, this does not mean that the number after the decimal point is zero. It also includes values ​​rounded to the nearest decimal point.

[0029] The light-concentrating assist 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 brightness enhancement film (BEF) in an edge-lit backlight. The film collects light emitted from the upper surface of the light guide plate and deflects (sometimes referred to as tilting) the collected light in the optimal direction for the BEF. The present invention achieves this function without relying on volume diffusion (e.g., light diffusion by light-diffusing particles) (i.e., without using light-diffusing particles) but with a special combination of surface shape and refractive index. Furthermore, the film can suppress or avoid the self-moiré pattern that typically appears when light-diffusing particles are not used. It can also be mass-produced using a roll-to-roll process. This will be described in detail below.

[0030] 1. Overall Configuration of Light Concentrating Assist Film FIG. 1 shows a conceptual diagram of the cross-sectional configuration of a light concentrating assist film 10 according to the present invention. As shown in the figure, the light concentrating assist film 10 according to the present invention has a three-layer configuration: a light extraction layer 100, a light guide layer 110, and a light introduction layer 120, which are closely attached to each other and integrated. Here, the light extraction layer 100 forms the light exit surface (the upper side of the drawing), and the light introduction layer 120 forms the light entrance surface (the lower side of the drawing). That is, the light concentrating assist film 10 has the light introduction layer 120 facing the light guide plate (not shown) (the side closer to the light guide plate) and the light extraction layer 100 facing away 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 give the impression of forming clear, flat boundaries between the layers. However, these boundaries do not necessarily need to be flat, and some degree of inter-layer ...

[0031] 2. Shape characteristics of each layer constituting the light concentration assist film (Shape characteristics of the light extraction layer) The light extraction layer 100, which is the light exit surface of the light concentration assist 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" will be used interchangeably in this specification, and since both refer to void portions, for convenience, the void portion of a recess and the solid portion defining that void portion will be used interchangeably below, and these terms will be interpreted appropriately depending on the context of the situation in which they are used.

[0032] 2A shows a front view of one section of the light extraction layer 100. While this figure shows a front view of one section in which 12 of the unit concave portions 200 constituting this light extraction layer 100 are two-dimensionally arranged, this is for illustrative purposes only; in reality, an extremely large number of inverted pyramid-shaped unit concave portions 200 are formed, each so small that they are invisible to the naked eye. The upper ends (the upper ends facing the page) of the inverted pyramid-shaped unit concave portions 200 form a rectangular ridge line 220, but this ridge line 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 ridge lines 220 of each unit concave portion 200 in the same direction is referred to as the pitch (reference numeral 230) (P1) of the unit concave portions 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 therefore will be referred to as the "inverted pyramid apex" below for convenience. Although the figure shows lines connecting the inverted pyramid apex 240 with each corner of the rectangular base of the inverted pyramid 200, these lines are also merely conceptual lines, and it is preferable that their width be as close to zero as practically achievable.

[0034] Furthermore, it is preferable that the exposed surface (slope of the inverted pyramid) of each unit concave portion 200 is as mirror-finished as practically achievable, in order to suppress the occurrence of unnecessary scattering and minimize the loss of transmitted light when 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 taken along a plane 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 FIG. 2(c) shows a cross-sectional view taken along a plane passing through the left and right direction of the paper. In each cross-sectional view, the hatched areas indicate solid portions, and the white areas indicate void portions (i.e., exposed portions). The solid line extending vertically on the right side of the cross-sectional view of FIG. 2(b) is a conceptual line that indicates a plane passing through the upper end of the light extraction layer 100 (the upper end surface on the light emission surface side), and the solid line extending horizontally is also a conceptual line that indicates the boundary between each unit concave portion 200. However, because the solid portions 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 surface side), and the solid lines extending vertically indicate the boundaries between each unit recess 200, but since the solid parts of each unit recess 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 Figure 2(b) or (c). That is, in a cross-section that passes through the center points 240 of the bottoms (vertices of the inverted pyramids) of two unit concave portions 200 arranged adjacent to each other and having a common ridge line and is perpendicular to the common ridge line, the apex angle (reference numeral 250) (θ1) of a triangular region 260 (the triangular region 260 hatched with dots in Figure 2(b)) occupied by the solid portions of adjacent unit concave portions 200. In the present invention, as shown in the figure, the top view of the unit concave portion 200 is a regular square, so the angle of this apex angle (θ1) is the same in both the vertical and horizontal directions of the paper, which is clear from a comparison of Figures 2(b) and 2(c).

[0037] The preferred shape of the unit recess (single recess having a substantially inverted square pyramidal shape) 200 is a square 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. Within these ranges, it is expected that the desired single recess having a substantially inverted square pyramidal shape can be cut using a single crystal diamond tip during the manufacturing process of the roll mold. Furthermore, the preferred depth of the unit recess (single recess having a substantially inverted square pyramidal shape) 200 is 11 μm to 39 μm, preferably 12 μm to 33 μm, and more preferably 16 μm to 27 μm. The ranges of the side length and depth are preferred ranges determined based on evaluation of the optical properties of the light-concentrating assistance film 10.

[0038] The thickness of the light extraction layer 100 composed of unit recesses 200 (single recesses each having a substantially inverted square pyramid shape) is the depth of the unit recesses 200 plus a value of α. This α corresponds to the thickness of what is referred to in the industry as a "residual film" (integrated with the light extraction layer and made of the same material as the light extraction layer) to slightly raise the height of the inverted vertex of the unit recess 200 from the upper surface (light-emitting surface) of the optical waveguide layer 110 (described below) located below it, and is approximately 1 to 3 μm. This value was obtained based on the empirical rule that, without this residual film, the shape of the unit recess 200 (especially the slope) is easily deformed, making it difficult to accurately maintain the shape of the unit recess 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°, preferably 80° to 95°, and more preferably 85° to 95°, but the upper and lower limit values ​​here are preferred values ​​determined from the viewpoint of the desired optical properties and the manufacturing cost 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 the plane passing through the vertices 240 of each unit recess 200 and has a triangular shape in a cross section passing through those vertices, and the length of its base is the same as the pitch (P1).

[0041] (Refractive Index of Light Extraction Layer) The refractive index n1 of the resin (cured resin) constituting the light extraction layer satisfies the relationship between the refractive index n2 of the resin (cured resin) constituting the light introduction layer (described later) and the refractive index n0 of the optical waveguide layer (layer between the light extraction layer and the light introduction layer) (described later), and is preferably n0≧n1, and is preferably 1.50≦n1≦1.64. The upper and lower limits here are preferred values ​​determined from the viewpoint of desired optical properties and the following points of view.

[0042] When using UV-curable resins (see below) with a refractive index of nD = 1.58 or higher, adding nanofillers such as TiO2 or ZrO2 to the resin is a common method of increasing the refractive index. However, because the nanofillers themselves are generally expensive, this approach makes the coating very expensive, which is undesirable in practice. Furthermore, when the refractive index is nD = 1.64 or higher, the amount of nanofiller added becomes too high, increasing viscosity and resulting in unevenness (e.g., uneven film thickness) when applying the monomer to the substrate film. This also increases the likelihood of nanofiller aggregation, leading to cloudiness in the coating film and reduced transmittance, which is undesirable in practice. In addition to these practical issues, increasing the refractive index from the resin composition without using TiO2 or ZrO2 creates a practical problem: the coating film tends to become very brittle, making the film difficult to handle after molding (e.g., 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, but in either case, it is inevitably expensive and there are practical problems in that the coating film is too soft, making it difficult to handle after shaping (curing).

[0044] (Material and Forming Method of the Light Extraction Layer) Essentially, 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" here does not refer to transparency in the strict sense, but rather to a state in which the haze value is low (e.g., 2-3% or less) and can be considered practically transparent. A known roll-to-roll continuous manufacturing method (see the reference diagram in FIG. 5 ) is suitably employed for production. The resins constituting the light extraction layer and the light introduction layer, respectively, are applied in an uncured state onto one side of a substrate film or substrate sheet constituting the optical waveguide layer to form a coating layer, and a roll mold having a fine uneven pattern (a pyramidal uneven pattern) formed on its surface is pressed against the surface of the coating layer to transfer the uneven pattern of the roll mold. The transferred portion is then sequentially irradiated with ultraviolet light (UV rays). The principle of the process for transferring the uneven pattern of a roll mold can also be used in the microimprinting process for plastic films, so it is possible to form the light extraction layer and light introduction layer with the desired surface shape by microimprinting on the surface of a three-layer structure 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.

[0045] (Basic Function of Light Extraction Layer) The function of the light extraction layer is to further raise the light from the optical waveguide layer described below (to bring the direction of the light closer to the vertical direction) and make it incident on the BEF at an incident angle that is favorable for the BEF, thereby contributing to an improvement in front brightness through a synergistic effect with the BEF.

[0046] (Shape Characteristics of the Light Introduction Layer) The light introduction layer 120, which serves as the light entrance surface of the light concentrating assist film, is composed of a triangular prism layer 30 having a plurality of unit triangular prisms 300 extending in a predetermined direction. Figure 3(a) shows a top view of one section of the light introduction layer 130. While this figure shows a top view of one section in which four of the unit triangular prisms 300 constituting this light introduction layer 130 are arranged side by side, this is for illustrative purposes only; in reality, a large number of unit triangular prisms 300 are formed, each so narrow that they are invisible to the naked eye. The apex of each unit triangular prism 300 forms a ridge 310, but this ridge 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 310 of each unit triangular prism 300 is referred to as the pitch (reference numeral 330) (P2) of the unit triangular prisms 300.

[0047] In the figure, a boundary line is drawn between adjacent unit triangular prisms 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] Furthermore, it is preferable that the exposed surface (the slope of the triangular prism) of each triangular prism 300 be as mirror-finished as practically possible, in order to minimize the loss of light due to unnecessary scattering 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.

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

[0050] In the present invention, the apex angle (reference numeral 350) of the unit triangular prism 300 refers to the angle (θ2) shown in the cross-sectional view of Figure 3(b). That is, it refers to the apex angle (θ2) of the solid portion of the triangle (the portion hatched with dots) in the cross-section of the unit triangular prism 300 shown in the same figure. In the present invention, as shown in the same figure, it is preferable that the shape of the cross-section perpendicular to the longitudinal direction of the unit triangular prism 300 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, and more preferably 5 μm to 16 μm, and P2 of 7 μm to 27 μm, preferably 9 μm to 22 μm, and more preferably 11 μm to 18 μm. While not limited to an isosceles triangle, the reason an isosceles triangle is preferred is that it is easier to cut the desired array of unit triangular prisms from single-crystal diamond during the roll mold manufacturing process. Furthermore, these numerical ranges are determined by minimizing the manufacturing costs of the roll mold, as described below, and are obtained from a practical perspective.

[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 of α. This α corresponds to the thickness of what is known in the industry as 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 approximately 1 to 3 μm. This value was obtained based on the empirical rule that if this residual film were not present, the cross-sectional shape of the unit triangular prism would likely 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 the desired optical properties and the manufacturing costs of the roll mold, which will be described later.

[0054] (Refractive Index of Light Introduction Layer) The refractive index n2 of the resin (cured resin) of the light introduction layer composed of an array of unit triangular prisms 300 satisfies n0≧n2, preferably 1.50≦n2≦1.64, in relation to the refractive index n1 of the resin (cured resin) of the light extraction layer described above 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 perspective of the desired optical properties and the practical issues pointed out in the explanation of the light extraction layer 100.

[0055] (Materials and Formation Method of the Light Introduction Layer) The materials used are basically the same as those of the light extraction layer 100 described above. 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" here does not refer to transparency in the strict sense, but rather to a state in which the haze value is low (e.g., 2 to 3% or less) and can be considered practically transparent. A known roll-to-roll continuous manufacturing method (see the reference diagram in FIG. 5 ) is suitably employed for production. The resins constituting the light extraction layer and the light introduction layer, respectively, are applied in an uncured state onto one side of a substrate film or substrate sheet constituting the optical waveguide layer to form a coating layer. A roll mold having a fine uneven pattern (an uneven pattern having triangular ridge-like protrusions in cross section) formed on its surface is pressed against the surface of the coating layer to transfer the uneven pattern of the roll mold. The transferred portion is then sequentially irradiated with ultraviolet light (UV rays). The principle of the process for transferring the uneven pattern of a roll mold can also be used in the microimprinting process for plastic films, so it is possible to form the light extraction layer and light introduction layer with the desired surface shape by microimprinting on the surface of a three-layer structure 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.

[0056] (Basic Function of 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) light emitted from a light guide plate (not shown) at 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] (Characteristics of the Light Guide Layer) The light guide layer 110 of the light concentrating assistance film 10 constitutes an intermediate layer between the light extraction layer 100 and the light introduction layer 120. The light guide layer 110 does not contain any light diffusing particles. From the viewpoint of the light transmittance of the light guide layer 110, the resin constituting the light guide layer 110 is preferably a transparent resin such as polyethylene terephthalate (PET), polycarbonate (PC), polymethyl methacrylate (PMMA), or styrene-methyl methacrylate copolymer, with a refractive index suitable for the present invention. However, from the viewpoints of reliability and availability, a transparent optical PET film is preferably used. Note that 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 overall thickness required for the light concentrating assistance film 10 and the thickness of the above-mentioned light extraction layer 100 and light introduction layer 120. From the viewpoint of improving front brightness, it can be said that the thinner the layer, the better. However, since some cure shrinkage occurs when the UV-curable resin applied to both sides of the base film that forms the light guide layer cures, it is preferable for the thickness to be thick enough to withstand this cure shrinkage, and the lower limit is preferably about 15 μm to 20 μm in view of the thicknesses of the light extraction layer and light introduction layer. On the other hand, the upper limit is preferably a maximum of about 200 μm in view of the relationship with the overall thickness required for the light concentrating assistance 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 light guide layer 110 functions as a so-called base film in the manufacturing process of the light concentrating assist film 10 of the present invention. After the light extraction layer 100 and the light introduction layer 120 are formed on both sides of the light guide layer 110, respectively, the light guide layer 110 is configured to transmit light to the light extraction layer 100 without reducing the amount of light incident from the light guide layer 110 as much as possible. For this purpose, an optical-grade PET film (optical-grade polyethylene terephthalate film) can be suitably used. The optical PET film is surface-treated to a degree that does not affect the optical properties of the bulk of the film in order to improve adhesive strength when a different resin is applied and bonded thereto. This surface treatment process is not included in the manufacturing process of the light concentrating assist 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 assist 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) Figure 4 shows the relationship (intersection angle) between the arrangement direction of unit recesses 200 (approximately inverted pyramids) that make up 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) that make up the light introduction layer 120 on the light incident 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 45° value 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 (P1) of the light extraction layer and the pitch (P2) of the light introduction layer) Controlling the interrelationship between the pitch (P1) of the light extraction layer and the pitch (P2) of the light introduction layer is important in suppressing the occurrence of self-moiré. While the general moiré phenomenon, i.e., the moiré phenomenon occurring between different optical elements, is well known, there appears 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 a single optical element. While the aforementioned Patent Document 1 addresses the problem of eliminating the moiré phenomenon, the moiré phenomenon in question is not a self-moiré phenomenon.

[0063] The inventors 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 moiré phenomenon, and when they inserted the actual values ​​of P1 and P2, respectively, they discovered that the predicted results did not match the actual measured results.

[0064] Therefore, the present inventors conducted extensive research and found that, under the condition that 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 formula independently discovered by the present inventors, the predicted results and the actual measured results agree 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 concentration assistance film of the present invention that suppresses the self-moiré 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. (Equation 1) |D1-D2|≦200 μm In the above equation 1, D1 and D2 satisfy the following equations 2a and 2b, respectively: (Equation 2a) D1=|P1m×δ1÷(δ1-P1m)| (Equation 2b) D2=|P1m×δ2÷(δ2-P1m)| In the above equations 2a and 2b, P1m>P2m, P1m satisfies the following equation 3a, and P2m satisfies the following equation 3b: (Equation 3a) P1m= P1×sin(0.25×π) (Equation 3b) P2m= P2÷2 In the above equations 2a and 2b, 1) For δ1, the absolute value of the difference between P1m and the value obtained by dividing P1m by P2m (rounding up to the nearest integer) is δa, and P1m is calculated by multiplying the result by P2m. 1) When the absolute value of the difference between P1m and the value obtained by multiplying the integer part (rounded down to the nearest integer) of P1m divided by P2m is δa, and the absolute value of the difference between P1m and the value obtained by multiplying the integer part (rounded up to the nearest integer) of P1m divided by P2m is δb, 2) δ2 is the sum of P1m and the smaller of δa and δb, when the absolute value of the difference between P1m and the value obtained by multiplying the integer part (rounded down to the nearest integer) of P1m divided by P2m is δa, and the absolute value of the difference between P1m and the value obtained by multiplying the integer part (rounded down to the nearest integer) of P1m divided by P2m is δb, and the smaller of δa and δb is doubled and this value is compared to the larger of δa and δb.

[0065] (Relationship between Refractive Indexes of Each Layer) In the light concentration assistance film according to 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 Supporting the Manufacturing Method of Light Concentrating Assist Film One of the objects of the present invention is to solve the problem of reducing the cost of light concentrating assist films, but it goes without saying that the manufacturing cost of a light concentrating assist film reflects the costs upstream in the manufacturing process. From this perspective, a roll-to-roll method is preferably adopted for manufacturing the light concentrating assist film of the present invention, as described in detail below, and a roll mold is preferably used for this method. Because this roll mold is a precision part that requires advanced manufacturing technology, its cost significantly affects the manufacturing cost of the light concentrating assist film. Therefore, the following describes the effects and restrictions on the shape of the light concentrating assist film of the present invention that arise from the roll mold used to manufacture the light concentrating assist film. However, the scope of the present invention is not limited to the content described below, and the manufacturing of the light concentrating assist film of the present invention is not limited to the use of the roll mold described below.

[0067] The roll mold used in the examples of the present invention was prepared by the lathe processing method described in detail below. Other possible methods include photolithography etching, electron beam processing, and direct laser processing. However, photolithography etching and electron beam processing are undesirable because they require high costs for producing rolled and large-area molds, which, from a practical standpoint, goes against the goal of cost reduction, one of the objectives of the present invention. While it may be possible to increase the area by reducing the precision of the mold's concave-convex shape, the precision of the shape obtained by pressing a low-precision mold against the mold to transfer the concave-convex shape will also be low, making this method impractical for the production of optical films requiring high-precision surface shapes. Regarding direct laser processing, while it may be possible to use it given the recent increase in the speed of laser processing machines, the laser spot diameter is at least about 10 μm, so this processing method is also impractical for the production of optical films requiring high-precision surface shapes. For these reasons, it is currently believed that lathe cutting, which is highly accurate and cost-effective, is the most suitable processing method for achieving cost reduction, one of the objectives of the present invention.

[0068] (Method of Manufacturing Roll Mold) Figure 6 is a conceptual diagram of a general method of manufacturing a roll mold by a cutting method to be used in manufacturing the light concentrating assist film 10 of the present invention. (a) is a conceptual diagram showing a roll mold having a thin metal film 680 (typically copper metal) formed on its surface being cut at an apex angle θ by 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, 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, and therefore reference numbers are omitted for components other than the main components.)

[0069] First, a metal film of copper or nickel is formed (mainly by electrolytic plating) on ​​the surface of a metal drum (typically made of iron or SUS) that will serve as a core roll of a specified size. The film thickness at this time is approximately 300 to 500 μm. In parallel with this, the single crystal diamond at the tip of the diamond cutting tool is machined into the desired shape (in this example, an isosceles triangle with an apex angle θ). Next, the machined single crystal diamond is attached to the tip of a shank, and the surface is polished to the desired shape. The shank is then created in a shape that matches the cutting machine.

[0070] Taking the example of a case where a copper film is formed on the surface, the manufacture of a roll mold by lathe cutting is generally carried out as follows. First, the copper film formed on the surface of the metal drum in the above process is cut off linearly at high speed with a single crystal diamond tip having a predetermined tip angle (the position of the single crystal diamond tip is fixed and the roll mold is rotated at high speed), thereby carving multiple concave lines extending parallel to one direction into the surface. After this is done around one circumference of the drum, the position of the single crystal diamond tip is moved laterally (in the direction along the drum axis) by a distance corresponding to the pitch (P), and the same operation is carried out for another circumference, and this process is repeated. Therefore, the smaller the diameter of the drum (the shorter the length of the cutting line), the less wear on the tip and side surface of the single crystal diamond tip, which reduces unnecessary scattering and reduces processing costs.

[0071] The concave strips at this time correspond to the resin convex strips that are pressed into the concave strips in the roll-to-roll manufacturing process, and the size of these convex strips, as described in the examples detailed 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, so the size of the pointed end of the single crystal diamond tip that bites into the copper plating layer is also of this order, and since the optical performance of the light-concentrating auxiliary film of the present invention depends on the accuracy of the surface shape, the cutting process requires high-precision control.

[0072] Furthermore, if the apex angle of the tip of the single crystal diamond tip is obtuse, for example, 100° or more, the tip cannot sufficiently grip (bite) during the cutting process, and the tip of the single crystal diamond tip slides on the copper-plated surface, causing vibration of the single crystal diamond tip and 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 is reduced. 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 shapes of the light extraction layer and light introduction layer formed on the surface of the final light-concentrating auxiliary film are determined by the triangular cross-sectional convex strips 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-concentrating auxiliary film, so the tip shape of the single-crystal diamond chip used requires nano-order precision.

[0074] Regarding 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-concentrating auxiliary film of the present invention, a unit triangular prism strip with an apex angle of 90° (base angle 45°) is the easiest to process, and it is particularly easy to process a symmetrical shape. Apex angles more acute than 90° are likely to cause problems with the durability of the cutting tool, making processing more difficult, which is undesirable. Conversely, a apex angle more obtuse than 90° reduces the cutting performance of the cutting tool (single-crystal diamond chip) (poor penetration into the deposited copper metal film), which causes vibration of the cutting tool and tends to result in a poor finish on the processed surface. For this reason, the apex angle of the tip of the single crystal diamond tip that functions 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-concentrating auxiliary film of the present invention, the conditions for mold 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 the protrusion corresponding to the inverted pyramid recess, first, in the first step, while rotating the drum, the tip of a single-crystal diamond tip is pressed against (engaged in) the copper-plated drum surface to form a ridge of a triangular cross-section recessed strip. Next, in the second step, a similar operation is performed to form a ridge of a triangular cross-section recessed strip in a direction perpendicular to the direction of the ridge of the recessed strip formed in the first step. As a result, at the intersection of the concave strip formed in the first step and the concave strip formed in the second step, an inverted pyramidal (inverted pyramidal) unit recess is formed, and the part that is not cut off by cutting becomes a convex part in the shape of a pyramid. However, the load that is applied to the tip of the single crystal diamond tip in this second step is not a static load, but a repeated impact load. That is, when passing through the solid part and the void part of the concave strip formed in the first step alternately, a repeated impact load is applied. For this reason, the processing conditions are more severe than in the case of the unit triangular prism described above, and the durability problem of the bit is 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-concentrating auxiliary film) is more acute than 90°, the difficulty of processing increases, and if it is an obtuse angle of 100° or more, the difficulty of processing similarly 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 values, the angle error is preferably ±1°.

[0076] (Backlight unit and liquid crystal display device equipped with the light concentrating assist film of the present invention) Figure 7(a) is a conceptual cross-sectional view of a liquid crystal display device 70 equipped with the light concentrating assist 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 Figure 7(b)) and a light diffusion film (reference number 722 in Figure 7(b)) laminated thereon, reference number 10 indicates the light concentrating assist film of the present invention, reference number 740 indicates a light guide plate unit having a reflective sheet on its lower surface, and reference number 760 indicates white LEDs. The white LEDs 760 are discretely arranged in a row along the side of the light guide plate unit 740 in the depth direction of the paper. The light concentrating assist 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 assistance 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) the propagation direction of the light in 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-layer orthogonally stacked BEF (reference number 724 in Figure 7(b)) that is stacked on top of it.

[0077] 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 stacking is performed in the following order from bottom to top: a reflective sheet 744, a light guide plate 742, a light-condensing assistance film 10 of the present invention, two orthogonally stacked BEFs 724, and a light-diffusing film 722.

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

[0079] <Examples> Examples will be described below. 1. Creation of light extraction layer of light concentrating assist film (Base film) The base film used was an optical PET film (e.g., Diafoil T600E50 manufactured by Mitsubishi Chemical Corporation) with a thickness of 50 μm. Note that as long as the effect does not differ depending on the manufacturer, any film having certain properties can be suitably used.

[0080] (UV-curable resin) The UV-curable resin used was a UV-curable acrylate monomer (97 wt%) to which a photoinitiator was added, and was formulated so that the refractive index nD after curing would be 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 (thickness of the copper metal thin film on the surface was 300 μm to 500 μm) was used, in which the shape characteristics of the unit recesses were as shown in FIG. 2 and the surface irregularities had apex angles (θ1) and pitches (P1) that were the values ​​shown in Table 1 below.

[0082] (Film Production Method) A commonly used roll-to-roll film production method was basically employed. Specifically, a roll of substrate film was placed in the roll-to-roll production system described above, and the system was started. Next, an acrylate-based UV-curable resin formulated to have a post-curing refractive index as listed in the table below was continuously applied to the substrate film using a method commonly used in roll-to-roll production to form a coating layer. A roll mold was then pressed against the coating film, irradiated with ultraviolet (UV) light, and cured to form a light extraction layer. A two-layer film with a light extraction layer formed on one side was then produced, and wound up (a first roll was produced). The apex angle (θ1) and pitch (P1) were confirmed to have been transferred using a laser microscope (Keyence VKX-1000) to magnify the transfer surface 2400 times.

[0083] 2. Preparation of the light introduction layer of the light concentration assist film The UV curable resin used was the same as that used for the light extraction layer described above. 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 texture pattern capable of forming a triangular prism array consisting of multiple ridges with an isosceles triangular cross section.

[0084] 3. Evaluation Method 1) Evaluation Method for Self-Moiré The evaluation was primarily visual. One end of a sample of the light-concentrating assist film of the present invention was held with the fingers of one hand, and the arm of that hand was extended and held up to an indoor fluorescent light. The evaluation was based on whether moiré was visible to the naked eye. The specific evaluation method is as shown in the conceptual diagram in Figure 10. In a darkroom, the end of the light-concentrating assist film 10 of the present invention was held in one hand, and the film was held vertically midway between the naked eye 1010 and a fluorescent lamp 1020 approximately 60 cm away from the naked eye. Visual confirmation of transmission moiré was performed from the light extraction layer (layer having an inverted pyramid). Next, the film was brought directly below the film's position, and the center of the horizontally positioned film was positioned approximately 30 cm diagonally from the same fluorescent lamp 1020 and the naked eye 1010. Oblique light from the fluorescent lamp 1020 was directed obliquely onto the surface of the film's light extraction layer, and reflective moiré was confirmed by the reflection. In this case, if neither transmission nor reflection moiré is visible, it is marked as ○. Next, if moiré (transmission moiré and / or reflection moiré) is visible in this judgment, 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 horizontally (see the stacking diagram in Figure 8) so that it is approximately 30 cm diagonally from the naked eye 1010 at the same angle as above, and further judgment is made visually. If moiré (transmission moiré) is not visible in either the case where the light extraction layer (inverted pyramid layer) is facing up or the light introduction layer (triangular prism layer) is facing up, it is marked as △, and if it is visible, it is marked as ×. Note that the relationship between the arrangement direction of the unit recesses 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 addition, the cross-sectional shape of the solid portions of the two adjacent unit recesses (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 assist film of the present invention was mounted on a 9-inch edge-lit backlight unit (see FIG. 7(b) for the configuration) using a white LED as a light source and evaluated. The two orthogonally stacked BEFs used here were BEF-4DT manufactured by 3M, and the light-diffusing film laminated on top was D159GS manufactured by Tsujiden Co., Ltd., a company owned by the present applicant. The white LEDs were driven at a constant current of 200 mA with a maximum power supply voltage of 17 V. A 5 cm square area centered on the center point of the emission surface of the backlight unit was divided into 64 x 64 cells (each cell was approximately 0.78 mm square), and measurements were taken with the shutter speed set to Auto (high dynamic sampling mode). The average of the front luminance values ​​at 64 x 64 = 4096 points was taken as the front luminance value. 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 light emitted from the white LEDs arranged on the side surface of the light guide plate of the edge-lit backlight is parallel to the direction (longitudinal direction) of the ridge lines of the unit triangular prisms in the light introduction layer of the light concentrating auxiliary film of the present invention arranged on the light guide plate. The light 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, when the shape characteristics and refractive index of the light concentrating auxiliary film of the present invention were combined as shown in Table 1 below, were such that the contour diagram on the light exit surface of the light concentrating auxiliary film was as shown in Figure 9.

[0086] 2. The shape characteristics, refractive index and optical characteristics of the light-condensing auxiliary films used in the examples and comparative examples were evaluated as shown in the table below. 1) Self-moiré evaluation results (Note 1: The calculation in the above calculation results is based on a formula devised by the present inventor and described in the specification and claims for self-moiré under the following conditions: the arrangement direction of the unit concave portions in the light extraction layer (same direction as the ridge line) and the arrangement direction of the unit triangular prisms in the light introduction layer (same direction as the ridge line) intersect at 45° with each other; and the cross-sectional shape of the portion formed by the solid portions of two adjacent unit concave portions (the cross-sectional shape shown in FIG. 2) and the cross-sectional shape of the unit triangular prisms (the cross-sectional shape shown in FIG. 3) are both isosceles triangles.) (Note 2: The symbols ○, △, and × in the moiré evaluation result column respectively represent the actual evaluation results obtained by the evaluation method explained in the section on self-moiré evaluation method above.)

[0087] Next, the table below shows a comparison of the results of actual determination using the above-mentioned determination method and the calculation results obtained using the above-mentioned calculation formula, showing that no self-moiré appears even when the intersection angle is varied by 3.0° above or below 45.0°. (Note 1: The calculation in the above calculation results is based on a formula devised by the present inventor and described in the specification and claims for self-moiré under the condition that the arrangement direction of the unit concave portions in the light extraction layer (same direction as the ridge line) and the arrangement direction of the unit triangular prisms in 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 formed by the solid portions of two adjacent unit concave portions (the cross-sectional shape shown in FIG. 2) and the cross-sectional shape of the unit triangular prisms (the cross-sectional shape shown in FIG. 3) are both isosceles triangles.) (Note 2: The symbols ○, △, and × in the column for measured moiré evaluation results respectively refer to the actual evaluation results obtained by the evaluation method described in the section on self-moiré evaluation method above.)

[0088] 2) Evaluation results of front luminance at the light exit surface of an edge-lit backlight equipped with the light concentrating assist 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, and 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 both 1 μm. In the results below, no brightness unevenness was visible to the naked eye in any case. (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, thereby ensuring the validity of the simulation values.)

[0089] Looking at the above table, it is clearly evident that 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°, compared to the example group and the comparative example group.

[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 and its 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 was both 1 μm. In the results below, no brightness unevenness was visible to the naked eye in any case. (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, thereby ensuring the validity of the simulation values.)

[0091] Looking at the above table, it is clearly evident that 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°, compared to the example group and the comparative example group.

[0092] All of the above simulations were performed using an optical simulator (LightTools lighting design software manufactured by Synopsys), and the validity of the simulation values ​​was ensured by setting the various parameters so that the error (error from the actual measurement) between the actual front luminance value and the simulation value was within 1%, as shown in 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 was each 1 μm.

[0093] The table below shows the front brightness 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 is changed to the value shown in the table (the thickness of the remaining film of the light extraction layer and the remaining film of the light introduction layer is each approximately 1 μm), and the film is placed horizontally on a light guide plate whose exit surface has a front brightness of 749.9 cd / m2.

[0094] The table below shows the front brightness measured at the exit surface of the light concentrating auxiliary film when the light concentrating auxiliary film (the thickness of the remaining film of the light extraction layer and the remaining film of the light introduction layer is approximately 1 μm each) is placed horizontally on a light guide plate whose front brightness at the exit surface of the light guide plate is 749.9 cd / m2, and the apex angle of the inverted pyramid of the light extraction layer of the light concentrating auxiliary film of the present invention is set to 90°, the apex angle of the triangular prism (isosceles triangle) of the light introduction layer is set to 90°, and the refractive index of each layer is changed to the value shown in the table.

[0095] The present invention has been described in detail above based on typical embodiments and examples and comparative examples, but various variations can be adopted as long as they do not deviate from the scope of the object and spirit of the present invention.

[0096] The present invention provides a light-concentrating auxiliary film having the following characteristics: 1) The number of elements constituting the light-concentrating auxiliary film is small. 2) The elements constituting the light-concentrating auxiliary film do not contain any light-diffusing fine particles. 3) The desired optical characteristics are obtained while suppressing the appearance of self-moiré. 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 will be expected to meet the demand for lower costs for liquid crystal display devices incorporating such films.

[0097] 10 Light concentration assist film 100 Light extraction layer 110 Optical waveguide layer 120 Light introduction layer 200 Unit concave portion (approximately inverted pyramid) 220 Ridge line of unit concave portion (approximately inverted pyramid) 230 Pitch of unit concave portion (approximately inverted pyramid) (P1) 240 Center point of bottom of unit concave portion 250 Vertex angle (θ1) of triangular solid area occupied by solid portions of adjacent unit concave portions 260 Triangular solid area occupied by solid portions of adjacent unit concave portions 300 Unit triangular prism 320 Ridge line of unit triangular prism 330 Unit triangular prism pitch (P2) 340 Valley line formed by adjacent unit triangular prisms 350 Vertex angle (θ2) of unit triangular prism 500 Well-known general roll-to-roll manufacturing system (for reference) 520 UV curable resin to be applied 540 Roll mold 560 Unwinding roll 562 Take-up roll 580 UV irradiation device 620 Roll mold 640 Shank of cutting tool 660 Single crystal diamond 680 Workpiece to be cut (copper plated layer) 700 Liquid crystal panel 720 BEF (two crossed type) and light diffusion film (manufactured by applicant) 722 Light diffusion film (manufactured by applicant) 724 BEF (two crossed type) 740 Light guide plate unit (light reflection sheet and light guide plate) 742 Light guide plate 744 Light reflection sheet 760 Discrete white LED 1010 Naked eye 1020 Indoor fluorescent lamp

Claims

1. A light-concentrating auxiliary film to be inserted between the light exit surface of a light guide plate in an edge-lit backlight unit that uses discrete LED point light sources and the light entrance surface of a brightness enhancement film (BEF), comprising: a light guide layer made of a translucent base film; a light extraction layer formed on one surface of the light guide layer and having a plurality of unit concave portions shaped like an inverted square pyramid; and a light introduction layer formed on the other surface of the light guide layer and having a plurality of unit triangular prisms extending parallel to one direction, wherein the light extraction layer constitutes the light exit surface, and prism surfaces of the plurality of unit triangular prisms constituting the light introduction layer constitute the light entrance surface, none of the light extraction layer, the light guide layer, and the light introduction layer contain light diffusing microparticles, and 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, and wherein all of the following conditions are satisfied: (Equation 1) |D1-D2|≦200 μm In the above equation 1, D1 and D2 satisfy the following equations 2a and 2b, respectively. (Equation 2a) D1=|P1m×δ1÷(δ1-P1m)| (Equation 2b) D2=|P1m×δ2÷(δ2-P1m)| In the above equations 2a and 2b, P1m>P2m, P1m satisfies the following equation 3a, and P2m satisfies the following equation 3b. (Equation 3a) P1m=P1× sin(0.25×π) (Equation 3b) P2m=P2÷2 In the above equations 2a and 2b, 1) For δ1, 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 it by P2m is set to δa, and P1m is set to P2m. 1) δa is the absolute value of the difference between P1m and the integer part (rounded down) of P1m divided by P2m multiplied by P2m, and δb is the absolute value of the difference between P1m and the integer part (rounded up) of P1m divided by P2m, and δb is the absolute value of the difference between P1m and the integer part (rounded down) of P1m divided by P2m multiplied by P2m, and δb is the absolute value of the difference between P1m and the integer part (rounded down) of P1m divided by P2m multiplied by P2m, and P1m is the sum of P1m and the smaller of δa and δb, which is doubled.

2. A light-collection auxiliary film that is inserted between a light exit surface of a light guide plate in an edge-lit backlight unit that uses discrete LED point light sources and a light entrance surface of a brightness enhancement film (BEF), comprising: a light guide layer made of a light-transmitting base film; a light extraction layer formed on one surface of the light guide layer and having a plurality of unit concave portions shaped like an inverted square pyramid; and a light introduction layer formed on the other surface of the light guide layer and having a plurality of unit triangular prisms extending parallel to one direction, wherein the light extraction layer constitutes the light exit surface, and the prism surfaces of the plurality of unit triangular prisms that constitute the light introduction layer constitute the light entrance surface, none of the light extraction layer, the light guide layer, and the light introduction layer contain light-diffusing particles, the intersection angle between the direction of the ridge lines of the plurality of unit concave portions and the direction of the ridge lines of the plurality of unit triangular prisms is within a range of 42° to 48°, and moire caused by the plurality of unit concave portions and the plurality of unit triangular prisms is not visible to the naked eye. A light-condensing auxiliary film.

3. The light-condensing assistance film according to claim 2, wherein 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.

4. The light-condensing assistance film according to claim 1 or 3, characterized in that the apex angle of each of the plurality of unit recesses is less than 100°.

5. A light-concentrating auxiliary film as described in 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 relationship of n0≧n1 and n0≧n2 is satisfied.

6. The light-collecting auxiliary 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 light-condensing auxiliary film according to claim 6, wherein the apex angle of each of the plurality of unit triangular prisms is 95° or less.

8. The light-condensing auxiliary film according to claim 7, wherein the apex angle of each of the unit recesses is between 80° and 95°.

9. An edge-lit backlight unit having multiple point light sources, a light guide plate, and a brightness enhancement film (BEF), characterized in that at least one light-collection assist film according to any one of claims 1 to 8 is inserted between the light guide plate and the brightness enhancement film (BEF).

10. The edge-light type backlight unit according to claim 9, wherein the plurality of point light sources are arranged on at least one edge side of the light guide plate.

11. A liquid crystal display device comprising: the edge-light type backlight unit according to claim 10; and a liquid crystal display panel.

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