Light-condensing auxiliary film, side-light-type backlight unit on which light-condensing auxiliary film is mounted, and liquid crystal display device on which side-light-type backlight is mounted

Abstract

Provided is an optical film requirement that does not use fine particles for light diffusion, is entirely composed of a transparent resin, and has a self-moire pattern that cannot be visually recognized by the naked eye, said optical film requirement having high front brightness without luminance unevenness on the light emission surface of a backlight when mounted on an edge-light backlight. A light-collecting auxiliary film inserted between the light emission surface of a light guide plate and the light incidence surface of a brightness enhancement film (BEF) in an edge-light backlight unit using discrete LED point light sources, the light-collecting auxiliary film being characterized by comprising: an optical waveguide layer comprising a light-transmitting base film, and a light-collecting layer comprising a light-transmitting base film, the light-collecting auxiliary film being interposed between the light emission surface of the light guide plate and the light incidence surface of the brightness enhancement film (BEF), the light-collecting auxiliary film being interposed between the light-emitting surface of the light guide plate and the light incidence surface of the brightness enhancement film (BEF); a light extraction layer that is formed on one surface of the optical waveguide layer and has a plurality of inverted rectangular pyramid-shaped unit recesses; and a light introduction layer formed on the other surface of the optical waveguide layer and having a plurality of unit triangular prisms extending in parallel in one direction, the light extraction layer constituting a light emission surface, and prism surfaces of the plurality of unit triangular prisms constituting the light introduction layer constituting a light incidence surface. The direction of the ridge lines of the plurality of unit recesses and the direction of the ridge lines of the plurality of unit triangular prisms intersect at an angle of 42 DEG to 48 DEG, and the light extraction layer, the optical waveguide layer, and the light introduction layer do not contain fine particles for light diffusion. The self-moire pattern generated by the plurality of unit recesses and the plurality of unit triangular prism lenses cannot be visually recognized by naked eyes.

Description

Technical Field

[0001] The present invention relates to a light-concentrating auxiliary film for use in a side-lit backlight, a side-lit backlight unit equipped with the light-concentrating auxiliary film, and a liquid crystal display device equipped with the side-lit backlight. Background Technology

[0002] Liquid crystal displays (LCDs) are widely used in various information devices, but based on their basic structure, they can be broadly classified into direct-lit and edge-lit types. In the former, the light source is located on the back side of the backlight unit mounted on the LCD, while in the latter, the light source is located on the side of the light guide plate that constitutes part of the backlight unit (commonly referred to as an edge-lit backlight). Edge-lit backlights, depending on the type of light source used, include CCFL (cold cathode fluorescent lamp) and white LED point light source types. With the recent trends of miniaturization, weight reduction, and power efficiency, white LED point light source types are becoming the mainstream.

[0003] The basic components of a typical white LED point light source type side-lit backlight are a light source, a light guide plate, a light propagation characteristic adjustment film (which has various names depending on its main function, some called Light Shaping Sheet or simply light diffusion film), and a BEF (Brightness Enhancement Film). For the BEF, commercially available products are commonly used (3M's products are the mainstream), and to date, no alternatives have been developed by backlight manufacturers, light guide plate manufacturers, or light propagation characteristic adjustment film manufacturers. In this configuration, the functional characteristics of the light guide plate are typically controlled so that the diffused white light from the light source (white LED) enters horizontally from the side of the light guide plate, and its propagation direction is changed (deflected) by the reflection and diffusion of light diffusion points arranged under the light guide plate. This causes the light to exit from the upper surface of the light guide plate (the side facing the BEF) with a Gaussian intensity distribution peak. The method of control varies from company to company and is almost a know-how. In the case of a backlight used in a large LCD panel such as an LCD TV, it can be said that the diffusion of light emitted from the light guide plate alone is insufficient. Therefore, a film (light diffusion film) is inserted between the light guide plate and the BEF to assist in the light diffusion function (for example, see Patent Document 1). Figure 1 ).

[0004] In recent years, with the miniaturization of LCD panels and the dramatic increase in pixel count, the transmittance of light from the light source has decreased drastically, resulting in insufficient brightness on the front side of the LCD panel. In edge-lit backlights, thanks to the function of the aforementioned light guide plate, brightness unevenness is less likely to occur compared to direct-lit backlights. The required optical characteristics are focused on the intensity of the backlight's front brightness. To address this issue, edge-lit backlights equipped with white LED light sources are attracting attention, and improvements to light guide plates for this type of backlight are being actively pursued. One such improved light guide plate proposes a design where a light-reflecting point is optimally positioned on the lower surface, and an optical element with the function of focusing the light reflected from that point is formed on the upper surface of the light-emitting surface. Furthermore, this optical element is configured in a unique spatial arrangement not previously seen. As a result, the light emitted from the light-emitting surface of the optical components located on the upper surface of the light guide plate has a stronger directionality compared to the light emitted from the pseudo-planar light source in the past. However, even with such a light guide plate, the propagation direction and shape of the light emitted from it do not achieve optimal matching with the light-concentrating film known as BEF (Brightness Enhancement Film). Therefore, scattering loss occurs during light propagation, and the front brightness of the backlight does not fully meet market demands.

[0005] However, the applicant has been manufacturing and selling light diffusion films for backlights, and has also invented a novel optical film (light diffusion film) for direct-lit point light sources and filed a patent application (Japanese Patent Application No. 2023-78133). This invention focuses on the relationship between the refractive indices of each layer of a three-layer structure film containing light-diffusing microparticles and a triangular prism layer on the light-incident surface. While this invention is for direct-lit point light sources and not for side-lit backlights, various knowledge was gained in the process of completing it.

[0006] In this instance, the applicant accepted a commission to develop a new light diffusion film for a side-lit backlight unit, as described in the aforementioned background. The applicant conducted research and repeated investigations to effectively utilize the technical concepts of the aforementioned invention to develop a novel light diffusion film for a side-lit backlight unit. As a result, it was discovered for the first time that the propagation direction and shape of light emitted from the upper surface of the aforementioned latest light guide plate did not optimally match the light-concentrating film known as BEF (Brightness Enhancement Film).

[0007] Furthermore, through computer simulations, it was discovered that for the optical characteristics required by the optical film in the aforementioned special operating environment (i.e., the environment where it is inserted between the light guide plate and the BEF), it is important to focus the light emitted from the light guide plate and change its propagation direction at an angle that is optimal for the BEF, thereby minimizing the loss of light in the light propagation path and enhancing the front brightness from the backlight.

[0008] Based on the knowledge described above, in the process of studying material design based on the desired characteristics of the optical film, it was determined that in order to enhance the front brightness from the backlight, it is necessary to minimize the haze value of the optical film inserted between the light guide plate and the BEF. It was also determined that in order to meet this requirement, it is necessary to completely avoid using commonly used light-diffusing particles that would cause an increase in haze value.

[0009] On the other hand, as described in the applicant's Japanese Patent Application No. 2023-78133, the applicant possesses various knowledge accumulated in the process of manufacturing an optical film that, while using light-diffusing microparticles, is suitable for mass production at low cost and includes a triangular prism layer on the light-incident surface. Based on this knowledge, during repeated research, the following potential problem was discovered: Recent light guides have enabled more efficient waveguide and light extraction. Even with efficient light guides, scattering losses still occur if a scattering film is used on them. Furthermore, among currently available mass production technologies, research was conducted on the technology that most faithfully meets the above requirements while having the lowest cost. It was concluded that, in order to achieve the function of focusing light emitted from the light guide and changing its propagation direction using the fewest possible optical components in a way that facilitates achieving the lowest cost, the optimal solution is a combination of controlling the refractive index of the material used in the optical film component inserted between the light guide and the BEF and controlling the shape of the surface of the optical film component.

[0010] Therefore, in the process of repeatedly studying optical film components that are completely free of light-diffusing particles for use in side-lit backlights, existing patent documents were studied, and it was found that in such optical film components with such basic structure, for example, as taught in Patent Document 1 (International Patent Publication No. WO2010 / 029910), there is a problem of moiré stripes caused by self-moiré patterns generated in a single optical film component.

[0011] The object of the present invention is, in the above context, to provide a film-shaped optical element that is inserted between the light guide plate and the BEF of a side-lit backlight, which can solve or is expected to solve the following problems (meet the required characteristics).

[0012] 1) The number of components constituting the film-like optical element should be as small as possible.

[0013] 2) The components constituting the film-like optical elements do not contain any light-diffusing particles.

[0014] 3) To obtain the desired optical properties by constructing a structure that is not visually recognizable to the naked eye, such as a moiré pattern.

[0015] 4) Suitable for mass production in roll-to-roll mode, with lower cost.

[0016] Existing technical documents

[0017] Patent documents

[0018] Patent Document 1: International Patent Publication No. WO2010 / 029910 Summary of the Invention

[0019] The problem the invention aims to solve

[0020] Therefore, the inventors conducted repeated and in-depth research to provide an optical film component (hereinafter referred to as a light-concentrating auxiliary film) that is low in cost, completely free of light-diffusing particles, has a moiré pattern that is not visually discernible to the naked eye, and provides a practically usable brightness for the front of the backlight, with brightness unevenness controlled to a practical level. Furthermore, in developing the light-concentrating auxiliary film of this invention, since it was based on the premise of being completely free of light-diffusing particles, such an optical film would be so transparent that haze would be imperceptible to the naked eye. Therefore, countermeasures against moiré patterns became the biggest challenge. The inventors believed that even if moiré patterns theoretically occurred, if the spacing between the moiré lines was less than a predetermined distance, they should be imperceptible to the naked eye. Based on this reverse thinking, repeated and in-depth research was conducted, resulting in the completion of this invention.

[0021] That is, the first technical solution is a light-concentrating auxiliary film, which is inserted between the light-emitting surface of the light guide plate and the light-incident surface of the brightness enhancement film (BEF) in a side-lit backlight unit using discrete LED point light sources. The light-concentrating auxiliary film is characterized by comprising: a light waveguide layer composed of a transparent substrate film; a light extraction layer formed on one side of the light waveguide layer, having a plurality of unit recesses in the shape of an inverted quadrangular pyramid; and a light guide layer formed on the other side of the light waveguide layer, having a plurality of unit triangular prisms extending parallel in one direction. The light extraction layer constitutes the light-emitting surface, and the prism surfaces of the plurality of unit triangular prisms constituting the light guide layer constitute the light-incident surface. The light extraction layer, the light waveguide layer, and the light guide layer all contain no light-diffusing particles. The relationship between the spacing P1 of the plurality of unit recesses and the spacing P2 of the plurality of unit triangular prism lenses is P1>P2, satisfying all of the following conditions:

[0022] (Mathematical Formula 1) |D1-D2|≤200μm

[0023] In the above mathematical expression 1, D1 and D2 satisfy the following mathematical expressions 2a and 2b, respectively.

[0024] (Mathematical formula 2a) D1=|P1m×δ1÷(δ1-P1m)|

[0025] (Mathematical formula 2b) D2=|P1m×δ2÷(δ2-P1m)|

[0026] In the above mathematical expressions 2a and 2b, P1m > P2m, P1m satisfies the following mathematical expression 3a, and P2m satisfies the following mathematical expression 3b.

[0027] (Mathematical formula 3a) P1m = P1 × sin(0.25 × π)

[0028] (Mathematical expression 3b) P2m = P2 ÷ 2

[0029] In the above mathematical expressions 2a and 2b,

[0030] 1) When the absolute value of the difference between P1m and P1m is denoted as δa, and the absolute value of the difference between P2m and P1m obtained by multiplying the integer part (rounded up) of P1m by P2m, and P1m obtained by multiplying the integer part (rounded down) of P1m by P2m, and P1m obtained by P1m obtained by multiplying the absolute value of P1m by P2m, the sum of the smaller of δa and δb and P1m is δ1.

[0031] 2) When the absolute value of the difference between P1m and P1m is δa (the integer part of the value obtained by dividing P1m by P2m and carrying over the decimal part), and the absolute value of the difference between P1m and P2m is δb (the integer part of the value obtained by dividing P1m by P2m and carrying over the decimal part), the smaller of δa and δb is set to twice the value. When comparing the value of this twice-multiplied value with the larger of δa and δb, the sum of the smaller value and P1m is δ2.

[0032] The second technical solution is a light-concentrating auxiliary film, which is inserted between the light-emitting surface of the light guide plate and the light-injecting surface of the brightness enhancement film (BEF) in a side-lit backlight unit using discrete LED point light sources. The light-concentrating auxiliary film is characterized in that...

[0033] This light-concentrating auxiliary film possesses:

[0034] The optical waveguide layer is composed of a transparent substrate film;

[0035] A light extraction layer, formed on one face of the optical waveguide layer, has multiple unit recesses in the shape of an inverted square pyramid; and

[0036] A light-guiding layer, formed on the other side of the optical waveguide layer, has multiple unit triangular prisms extending parallel in one direction.

[0037] The light extraction layer constitutes the light emission surface.

[0038] The prism surfaces of the multiple unit triangular prisms constituting the light guiding layer form the light incident surface.

[0039] The light extraction layer, the light waveguide layer, and the light guiding layer all contain no light diffusion particles.

[0040] The angle between the direction of the edge line of the plurality of unit concave portions and the direction of the edge line of the plurality of unit triangular prisms is in the range of 42° to 48°.

[0041] The moiré pattern generated by the plurality of unit recesses and the plurality of unit triangular prisms is not visually perceptible to the naked eye.

[0042] According to the second technical solution, the third technical solution is characterized in that the relationship between the distance P1 of the plurality of unit recesses and the distance P2 of the plurality of unit triangular prism lenses is P1>P2.

[0043] According to the first or third technical solution, the fourth technical solution is characterized in that the apex angle of the plurality of unit recesses is less than 100°.

[0044] According to the fourth technical solution, the fifth technical solution is characterized in that when the refractive index of the resin constituting the light extraction layer is set to n1, the refractive index of the resin constituting the light guiding layer is set to n2, and the refractive index of the resin constituting the optical waveguide layer is set to n0, the relationship n0≥n1 and n0≥n2 exists.

[0045] According to the fifth technical solution, the sixth technical solution is characterized in that 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.

[0046] According to the sixth technical solution, the seventh technical solution is characterized in that the apex angle of the plurality of triangular prisms is less than 95°.

[0047] According to the seventh technical solution, the eighth technical solution is characterized in that the apex angle of the plurality of unit recesses is above 80° and below 95°.

[0048] The ninth technical solution is a side-lit backlight unit, which has multiple point light sources, a light guide plate and a brightness enhancement film (BEF). The side-lit backlight unit is characterized in that at least one light-concentrating auxiliary film of any one of the first to eighth technical solutions is inserted between the light guide plate and the brightness enhancement film (BEF).

[0049] According to the 9th technical solution, the 10th technical solution is characterized in that the plurality of point light sources are arranged on at least one edge side of the light guide plate.

[0050] The 11th technical solution is a liquid crystal display device, characterized in that the liquid crystal display device includes the side-lit backlight unit and the liquid crystal display panel of the 10th technical solution.

[0051] The effects of the invention

[0052] The light-concentrating auxiliary film of the present invention is completely free of light-diffusing particles and can be expected to function as an optical film element that suppresses the appearance of self-moiré patterns (to a degree that can be visually recognized by the naked eye) and controls the front brightness of the backlight to a level that can withstand practical use, and controls the brightness unevenness to a level that can withstand practical use.

[0053] Furthermore, it is possible to use roller dies to manufacture in a roll-to-roll manner suitable for mass production, which increases the ease of manufacturing and can be expected to reduce manufacturing costs.

[0054] Furthermore, this can lead to cost reductions in side-lit backlight units equipped with the light-concentrating auxiliary film of the present invention, as well as in liquid crystal display devices. Attached Figure Description

[0055] In the figures described below, the constituent elements marked with the same reference numerals are the same constituent elements.

[0056] Figure 1 This is a conceptual diagram showing a cross-section of the light-concentrating auxiliary film of the present invention.

[0057] Figure 2 (a) is a conceptual diagram of the front view of the light extraction layer 100 on the light emitting side of the light-concentrating auxiliary film 10 of the present invention. Figure 2 (b) and Figure 2 (c) is a conceptual cross-sectional view of the light extraction layer 100 on the light emitting side of the light-concentrating auxiliary film 10 of the present invention. Reference numeral 200 indicates a unit recess (void), reference numeral 220 indicates a ridge line, reference numeral 240 indicates the deepest point of the unit recess (which is the center point of the recess, the apex of the inverted pyramid, and therefore called the inverted apex), and reference numeral 260 indicates the solid portion that divides the unit recess.

[0058] Figure 3 (a) is a conceptual diagram of the front view showing the array of unit triangular prisms 300 constituting the light guiding layer 120 on the light incident surface side of the light concentrating auxiliary film 10 of the present invention. Figure 3 (b) is a conceptual cross-sectional view showing an array of unit triangular prisms 300 constituting the light guiding layer 120 on the light incident surface side of the light concentrating auxiliary film 10 of the present invention. Reference numeral 300 denotes a unit triangular prism, reference numeral 320 denotes the edge of a unit triangular prism, and reference numeral 340 denotes the valley line formed by adjacent unit triangular prisms.

[0059] Figure 4 This is a diagram showing the relationship between the arrangement direction of the unit recesses 200 (generally inverted pyramids) of the light extraction layer 100 constituting the light emitting surface side of the light-concentrating auxiliary film 10 of the present invention and the length direction of the unit triangular prisms (convex strips) of the light guiding layer 120 constituting the light emitting surface side. In this diagram, the valley lines 340 in the array of unit triangular prisms 300 of the light guiding layer 120 are shown as dashed lines. Figure 4 In (a), the case where these two directions intersect at 45° is shown. Figure 4 In (c), the state is represented using a simplified alternative representation. Figure 4 In (c), it indicates that the light extraction layer 100 is on top and the light introduction layer 120 is on the bottom. Figure 4 (b) and Figure 4 (d) indicates the states where the cross angles are 42° and 48° respectively.

[0060] Figure 5This is a reference diagram of a commonly known roll-to-roll manufacturing system. Although outside the scope of this invention, it is used to illustrate a preferred range of the surface irregularities of the light-concentrating auxiliary film of this invention, and therefore reference numerals are omitted except for the main components.

[0061] Figure 6 This is a conceptual diagram of a typical method for manufacturing the roller mold used in the production of the light-concentrating auxiliary film 10 of the present invention by means of a cutting method. Figure 6 (a) is a conceptual diagram showing the cutting of a roller with a thin film 680 of metal (usually copper) formed on its surface using a cutting tool 640 with a single crystal diamond 660 at the front end and a vertex angle θ. Figure 6 (b) is an enlarged view of the single-crystal diamond 660 cutting the thin film 680, showing a cross-sectional view. (Although outside the scope of the invention, it is a drawing used to illustrate a preferred range of the surface irregularities of the light-concentrating auxiliary film of the invention, therefore reference numerals are omitted except for the main constituent elements.)

[0062] Figure 7 (a) is a cross-sectional conceptual diagram of an example of a side-lit backlight equipped with the light-concentrating auxiliary film 10 of the present invention. Reference numeral 700 indicates a liquid crystal panel, reference numeral 720 indicates the entirety of two orthogonally overlapping BEF sheets and a light-diffusing film stacked thereon, reference numeral 10 indicates the light-concentrating auxiliary film of the present invention, reference numeral 740 indicates a light guide plate unit having a reflective sheet on its lower surface side, and reference numeral 760 indicates a white LED. Furthermore, the white LEDs 760 are arranged in a discrete row along the side of the light guide plate unit 740 in the depth direction of the paper. Figure 7 (b) is in the removal Figure 7 The concept diagram showing the stacked state of each layer is shown after the liquid crystal panel 700 in (a). In the stack, the reflective sheet 744, the light guide plate 742, the light focusing auxiliary film 10 of the present invention, two orthogonally overlapping BEF 724, and the light diffusion film 722 are stacked sequentially from the bottom to the top.

[0063] Figure 8 This is a conceptual diagram of the optical components used in the light intensity peak measurement (using Mini-Diff V2) of the embodiments and comparative examples. In the stack, a reflective sheet 744, a light guide plate 742, and the light-concentrating auxiliary film 10 of the present invention are stacked from bottom to top. A plurality of white LEDs 760 are arranged on the side of the light guide plate 732.

[0064] Figure 9This is a contour map showing the light-emitting surface of the light-concentrating auxiliary film when the combination of its shape characteristics and refractive index is described in Table 1. In this case, the optical axis of the light emitted from the white LED passes through the center of the circular region of the contour map and is parallel to a straight line traveling horizontally from left to right on the paper.

[0065] Figure 10 This is a conceptual diagram representing a method for judging moiré patterns by visual inspection. Figure 10 (a) is a concept diagram of the measurement conditions when the judgment result is ○. Figure 10 (b) is a conceptual diagram of the determination conditions when the judgment result is △ or ×. Detailed Implementation

[0066] (Implementation Method)

[0067] The present invention will now be described in detail with reference to the embodiments and accompanying drawings. However, the present invention is not limited to the following embodiments, and can be modified arbitrarily within the scope of the purpose and spirit of the present invention.

[0068] In addition, throughout the entire manual,

[0069] 1) In this invention, "light focusing" refers to focusing diffused light from a light source, such as light emitted from a light guide plate, and deflecting it in any direction to propagate it. However, the meaning of "light focusing" here is not strict and also includes the phenomenon of slight local diffusion caused by the characteristics of the direction, intensity, and angle distribution of the incident light.

[0070] 2) “Membrane” includes not only membranes in the strict sense defined by thickness, but also thicker membranes that are usually referred to as sheets.

[0071] 3) "Self-moiré" refers to moiré patterns (moiré fringes) generated in a transparent single-film optical element (or optical film element). Parallel moiré patterns and rotational moiré patterns exist, but in this invention, given that rotational moiré patterns (which are not visually perceptible to the naked eye) do not appear in any embodiment within their constituent range, the moiré pattern referred to below is a parallel moiré pattern. Furthermore, in this invention, the phenomenon of moiré patterns that are visually perceptible to the naked eye is referred to as the appearance of moiré patterns, and the phenomenon that is not visually perceptible is referred to as the absence of moiré patterns, rather than from a principle-based perspective.

[0072] 4) "Convex stripe" refers to a convex protrusion that extends continuously in one direction with the same cross-sectional shape, while "concave stripe" refers to a concave depression that extends in one direction with the same cross-sectional shape. In this case, "one direction" is not necessarily only defined by a continuous straight line, but can also include the direction defined by a continuous curve.

[0073] 5) "Substantially parallel" means that the edges of the multiple convex strips or the valleys of the concave strips are substantially parallel from a practical point of view. Here, "substantially" means within the scope of achieving the purpose of the present invention.

[0074] 6) “Approximately square pyramid” or “approximately inverted pyramid” includes not only true inverted square pyramids, but also cases that can be regarded as inverted square pyramids or inverted pyramids from a practical point of view, within the range of unavoidable shape deviations caused by the processing precision in industrial production. For example, with regard to the “inverted frustum” with a flat top, the inverted frustum with a smaller top area is also included in “approximately inverted pyramid” to the extent that it does not impede the achievement of the purpose of the present invention.

[0075] 7) "Refractive index" refers to the refractive index measured at a wavelength of 589 nm using an Abbe refractometer (NAR-1T SOLID) manufactured by ATAGO CO.,LTD. It is hereinafter represented by the symbol nD. The refractive index is expressed with two decimal places, but this does not necessarily mean that the value after the second decimal place is zero. Rather, it includes all values ​​from one unit below to one unit above the second decimal place.

[0076] 8) "Vertex" refers to Figure 2 and Figure 3 The apex angle is shown. Furthermore, for the angle, the transfer surface was measured at 2400x magnification using a laser microscope (Keyence VKX-1000). For the apex angle, there is no decimal point notation, but this does not mean the value after the decimal point is zero; it also includes values ​​rounded to the nearest hundredth place less than the displayed value.

[0077] The light-concentrating auxiliary film of the present invention is a film-shaped optical element (optical film element) inserted between a light guide plate (also called a light guide sheet or light guide film) and a BEF (Brightness Enhancement Film) in a side-lit backlight. It is used to concentrate light emitted from the upper surface of the light guide plate and deflect the propagation direction of the concentrated light in a direction most suitable for the BEF (sometimes also called lifting). The main feature of the present invention is that, without relying on volume diffusion (e.g., light diffusion based on light-diffusing particles) (i.e., without using light-diffusing particles), this function can be achieved solely through a special combination of surface shape and refractive index. Furthermore, it can suppress or avoid self-moiré patterns that typically occur without using light-diffusing particles, and can be mass-produced using a roll-to-roll method. Details will follow.

[0078] 1. Overall structure of the light-concentrating auxiliary film

[0079] exist Figure 1 The figure shows a conceptual cross-sectional view of the light-concentrating auxiliary film 10 of the present invention. As shown in the figure, the light-concentrating auxiliary film 10 of the present invention has a three-layer structure consisting of a light extraction layer 100, a light waveguide layer 110, and a light guide layer 120, with each layer tightly bonded together and integrated. Here, the light extraction layer 100 constitutes the light emission surface (the upper side of the paper), and the light guide layer 120 constitutes the light injection surface (the lower side of the paper). That is, the light-concentrating auxiliary film 10 has a light guide layer 120 on the side facing the light guide plate (not shown) (the side closer to the light guide plate), and a light extraction layer 100 in the opposite direction to the light guide plate (not shown) (the side away from the light guide plate). In the figure, solid lines extending horizontally between these layers are shown, giving the impression of flat and clearly defined boundary surfaces between the layers. However, these boundary surfaces do not necessarily need to be flat, and slight interlacing between them is allowed within the scope of achieving the purpose of the present invention. In particular, if the refractive indices of the layers separated by the boundary surface are the same, they can be optically treated as the same layer in this invention, thus allowing for slight staggering. Furthermore, in this embodiment, the light extraction layer 100 is designated as the light emitting surface and the light guiding layer 130 as the light receiving surface. However, alternatively, if it does not affect the achievement of the objectives of this invention, the light extraction layer 100 can be designated as the light receiving surface and the light guiding layer 130 as the light emitting surface.

[0080] 2. Shape characteristics of each layer constituting the light-concentrating auxiliary film

[0081] (Shape characteristics of the light extraction layer)

[0082] The light extraction layer 100, which serves as the light emitting surface of the light-concentrating auxiliary film, is composed of an array of units having a plurality of unit recesses 200 that are approximately inverted quadrangular pyramidal in shape (inverted pyramidal in shape). Furthermore, for convenience, the terms "unit recess" and "inverted pyramid" are used interchangeably in this specification, both referring to a void portion. Therefore, for convenience, the void portion of the recess and the solid portion that defines the void portion are also used interchangeably, and they are appropriately replaced according to the context of the usage.

[0083] exist Figure 2Figure (a) shows a front view of a section of the light extraction layer 100. The figure illustrates a section formed by a two-dimensional arrangement of 12 of the plurality of unit recesses 200 constituting the light extraction layer 100, but this is merely for illustration; in reality, numerous inverted pyramid-shaped unit recesses 200, so small as to be invisible to the naked eye, are formed. The upper ends (the upper ends facing the front of the paper) of the inverted pyramid-shaped unit recesses 200 form quadrilateral ridges 220, but these ridges 220 are merely conceptual lines, and their width is preferably infinitely close to zero in practice. In this invention, the distance between the lines formed by joining the ridges 220 of each unit recess 200 in the same direction is called the spacing of the unit recesses 200 (reference numeral 230) (P1).

[0084] The center point of the area occupied by the unit recess 200 in the figure is located directly above the bottom center point 240 of the unit recess 200. This bottom center point 240 is also the apex of the inverted pyramid that constitutes the unit recess 200 including the bottom center point 240, and is therefore referred to as the "vertical pyramid apex" for convenience. In this figure, a line is shown connecting the corners of the quadrilateral at the base of the inverted pyramid 200 to the apex 240 of the inverted pyramid, but this line is only a conceptual line, and its width is preferably as close to zero as possible in practice.

[0085] Furthermore, in practice, the exposed surfaces (the slopes of the inverted pyramid) in each unit recess 200 are preferably as mirror-like as possible. This is to suppress the generation of unnecessary scattering and minimize the loss of transmitted light when the light is deflected and concentrated in a specified direction by the difference in refractive index at the boundary between the exposed surface and the air.

[0086] Figure 2 (b) represents a sectional view obtained by cutting along the vertical direction of the paper through the bottom center point 240 (the apex of the inverted pyramid) of each unit recess 200. Figure 2 (c) represents a sectional view obtained by cutting along the left and right sides of the paper through the bottom center point 240 (the apex of the inverted pyramid) of each unit recess 200. In each sectional view, shaded areas marked with dots represent solid areas, and white areas represent open areas (i.e., exposed areas). Figure 2 The solid line extending longitudinally on the right side of the cross-sectional view in (b) is a conceptual line representing the plane (upper end face of the light emitting surface side) passing through the upper end of the light extraction layer 100. The solid line extending laterally is also a conceptual line representing the boundary between each unit recess 200. However, since the solid portions of each unit recess 200 are all formed of the same material, this boundary is also only conceptual. Figure 2The solid lines extending laterally in the cross-sectional view of (c) are conceptual lines representing the plane passing through the upper end of the light extraction layer 100 (the upper end face of the light emission surface side), and the solid lines extending longitudinally represent the boundaries between each unit recess 200, but since the solid portions of each unit recess 200 are all formed of the same material, the boundaries are also only conceptual.

[0087] The apex angle of the unit recess 200 in this invention refers to Figure 2 (b) or Figure 2 The angle (θ1) shown in the cross-sectional view of (c). That is, in the cross-section passing through the bottom center point 240 (vertical pyramid apex) of each of the two unit recesses 200 arranged adjacent to each other and having a shared edge and orthogonal to the shared edge, it refers to the triangular region 260 occupied by the solid parts of the unit recesses 200 adjacent to each other. Figure 2 In (b), the vertex angle (reference numeral 250) (θ1) of the shaded triangle region 260) is marked by a dot. In this invention, as shown in the figure, the top view of the unit recess 200 is a regular quadrilateral, so the angle of the vertex angle (θ1) is the same in both the longitudinal and transverse directions of the paper, which can be determined by comparing (b) and (c) of the figure.

[0088] Regarding the preferred shape of the unit recess (a generally inverted square pyramid-shaped single recess) 200, its upper end is square, and the length of one side is 19 μm to 65 μm, preferably 29 μm to 55 μm, and more preferably 39 μm to 45 μm. Within this range, it is expected that the desired generally inverted square pyramid-shaped single recess can be machined using a single-crystal diamond cutting tool during the die-making process. Furthermore, the preferred depth of the unit recess (a generally inverted square pyramid-shaped single recess) 200 is 11 μm to 39 μm, preferably 12 μm to 33 μm, and more preferably 16 μm to 27 μm. The aforementioned ranges of side length and depth are preferred ranges determined based on the evaluation of the optical properties of the light-concentrating auxiliary film 10.

[0089] The thickness of the light extraction layer 100, which is composed of unit recesses 200 (generally inverted square pyramidal single recesses), is obtained by slightly adding α to the depth of the unit recesses 200. This +α corresponds to the thickness of what is known in the art as a "residual film" (integrated with the light extraction layer and made of the same material as the light extraction layer) that slightly raises the height of the inverted vertex of the unit recesses 200 from the upper surface (light-emission side) of the optical waveguide layer 110 (described later) located below it, and is approximately 1 to 3 μm. This value is obtained according to the rule of thumb that without this residual film, the shape of the unit recesses 200 (especially the bevel) is easily deformed, making it difficult to accurately maintain the shape of the unit recesses 200 during mass production. Specifically, the thickness of the light extraction layer 100 is 12 μm to 42 μm, preferably 13 μm to 36 μm, and more preferably 17 μm to 30 μm.

[0090] The apex angle of the unit recess 200 is less than 100°, preferably 80°~95°, more preferably 85°~95°, but the upper and lower limits here are preferred values ​​obtained from the viewpoint of desired optical characteristics and the manufacturing cost of the roller mold described later.

[0091] When the upper end of the unit recess 200 is square, the length of one side is the same as the spacing (P1). The solid part 260 formed by connecting two adjacent unit recesses 200 is triangular in the cross section that is perpendicular to the plane passing through the vertex 240 of each unit recess 200 and passes through its vertex, and the length of its base is the same as the spacing (P1).

[0092] (Refractive index of the light extraction layer)

[0093] Regarding the refractive index n1 of the resin constituting the light extraction layer (cured resin), in the relationship between the refractive index n2 of the resin constituting the light guiding layer (cured resin) and the refractive index n0 of the optical waveguide layer (layer between the light extraction layer and the light guiding layer), which will be described later, n0 ≥ n1, preferably 1.50 ≤ n1 ≤ 1.64. The upper and lower limits here are preferred values ​​derived from the viewpoint of desired optical properties and the following viewpoint.

[0094] When using the UV-curable resin described below as a material, if the refractive index nD is 1.58 or higher, high refractive index nanofillers such as TiO2 and ZrO2 are usually added to the resin to achieve this. However, since high refractive index nanofillers are generally expensive, the coatings can become very costly, making this a practically undesirable practice. Furthermore, if the refractive index nD is 1.64 or higher, the amount of nanofiller added becomes excessive, increasing viscosity and easily causing unevenness (unequal film thickness) when coating the monomer onto the substrate film. It also easily leads to the aggregation of nanofillers, resulting in a cloudy coating and consequently, reduced transmittance, making this a practically undesirable practice. In addition to these practical problems, if the refractive index is increased from the resin composition side without using TiO2 or ZrO2, the coating film tends to become very brittle, making the processing of the shaped film difficult (easily damaged), which is a practical problem.

[0095] On the other hand, conversely, in order to reduce the refractive index nD to below 1.52, it is usually achieved by adding nanofillers such as BaF2 to the monomer or by introducing fluorine into the monomer molecule. However, in either case, the price has to be increased. As the coating is too soft, there are practical problems such as the difficulty in handling the film after shaping (after curing).

[0096] (Materials and formation methods of the light extraction layer)

[0097] Basically, any resin can be preferably used if it is a UV-curable transparent resin with the refractive index specified in this invention. Furthermore, "transparent" as used here does not refer to transparency in the strict sense, but rather to a state where the haze value is low (e.g., below 2-3%), which can practically be described as transparent. In manufacturing, a known roll-to-roll continuous manufacturing method (see [reference]) can be preferably used. Figure 5 (Referencing the diagram), resins constituting the light extraction layer and the light guiding layer are coated in an uncured state onto one side of a substrate film or sheet constituting the waveguide layer to form a coating layer. A roller with a finely patterned (pyramid-shaped) concave-convex pattern is pressed onto the surface of the coating layer, thereby transferring the concave-convex pattern of the roller. The transferred area is then irradiated with ultraviolet light (UV rays), which can better form the coating. Furthermore, the principle of the process of transferring the concave-convex pattern of the roller can also be applied to the micro-imprinting process of plastic films. Therefore, for the formation of the light extraction layer and the light guiding layer, it is also possible to consider forming the light extraction layer and the light guiding layer with the desired surface shape by micro-imprinting the surface of a three-layer structure film. The three-layer structure film is formed by pre-bonding transparent thermoplastic resin films constituting the light extraction layer and the light guiding layer respectively onto the substrate film constituting the waveguide layer.

[0098] (Basic functions of the light extraction layer)

[0099] The function of the light extraction layer is to further lift the light from the optical waveguide layer (described later) (to make the direction of the light further closer to the vertical direction) and inject it into the BEF at a preferred incident angle for the BEF, thereby helping to improve the front brightness through the synergistic effect with the BEF.

[0100] (Shape characteristics of the light-guiding layer)

[0101] The light guiding layer 120, which serves as the light-concentrating auxiliary film, is composed of a triangular prism layer 30 having a plurality of unit triangular prisms 300 extending in a predetermined direction. Figure 3 Figure (a) shows a top view of a section of the light guiding layer 130. The figure illustrates a section consisting of four unit triangular prisms 300 arranged side-by-side, but this is merely for illustration; in reality, numerous unit triangular prisms 300 are formed, their widths so fine as to be 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 possible in practice. In this invention, the distance between the ridges 310 of each unit triangular prism 300 is referred to as the spacing between the unit triangular prisms 300 (reference numeral 330) (P2).

[0102] In this figure, a boundary line is shown between each adjacent unit triangular prism 300, but this boundary line is only a conceptual line, and its width is preferably as close to zero as possible in practice.

[0103] Furthermore, in practice, the exposed surfaces (the inclined surfaces of the triangular prisms) in each triangular prism 300 are preferably mirror surfaces. This is to minimize the loss of light due to unnecessary scattering when the light is deflected and concentrated in a specified direction by the difference in refractive index at the boundary between the exposed surface and the air.

[0104] Figure 3 (b) represents a sectional view of each unit triangular prism 300, orthogonal to the length direction. In this sectional view, the shaded parts marked by dots represent solid parts, and the white parts represent gaps (i.e., exposed parts).

[0105] The apex angle (reference numeral 350) of the unit triangular prism 300 in this invention refers to Figure 3 The angle (θ2) shown in the cross-sectional view of (b) refers to the apex angle (θ2) of the solid portion (the shaded portion marked by a dot) of the triangle in the cross-section of the unit triangular prism 300 shown in the figure. In this invention, as shown in the figure, the shape of the cross-section orthogonal to the length direction of the unit triangular prism 300 is preferably an isosceles triangle.

[0106] The preferred shape of the unit triangular prism 300 is an isosceles triangle (including an equilateral triangle) in a cross-section orthogonal to its length direction (the direction of the prism line), with a height h of 3μm to 24μm, preferably 4μm to 21μm, more preferably 5μm to 16μm, and P2 of 7μm to 27μm, preferably 9μm to 22μm, more preferably 11μm to 18μm. However, while not limited to an isosceles triangle, it is preferred because it facilitates machining of the desired array of unit triangular prisms using single-crystal diamond during the manufacturing process of the roller mold. Furthermore, these numerical ranges are derived from a practical point of view, with the aim of minimizing the manufacturing cost of the roller mold as described later.

[0107] The thickness of the light-guiding layer composed of the unit triangular prism 300 is obtained by slightly adding α to the value of the height h of the unit triangular prism. This +α corresponds to the thickness of the portion of the bottom surface of the unit triangular prism, referred to in the art as the so-called "residual film" (which is integral with the light-guiding layer and is made of the same material as the light-guiding layer), and is approximately 1 to 3 μm. This value is obtained according to the following rule of thumb: without this residual film, the cross-sectional shape of the unit triangular prism is easily deformed, and it becomes difficult to accurately maintain its shape during mass production.

[0108] The apex angle (reference numeral 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 an preferred value derived from the viewpoint of desired optical characteristics and the manufacturing cost of the roller mold, which will be discussed later.

[0109] (Refractive index of the light-guiding layer)

[0110] Regarding the refractive index n2 of the resin (cured resin) of the light-guiding layer composed of an array of unit triangular prisms 300, in the relationship between the refractive index n1 of the resin (cured resin) of the light-extraction layer and the refractive index n0 of the light waveguide layer (the layer between the light extraction layer and the light-guiding layer) described later, n0 ≥ n2, preferably 1.50 ≤ n2 ≤ 1.64. These upper and lower limits are preferred values ​​derived from the viewpoint of desired optical properties and the practical problems pointed out in the description of the light extraction layer 100.

[0111] (Materials and formation methods of the light-guiding layer)

[0112] The material used is essentially the same as that of the light extraction layer 100 described above, which is a UV-curable transparent resin. Any resin can preferably be used if it has the refractive index specified in this invention. Furthermore, the term "transparent" here does not refer to transparency in the strict sense, but rather to a state where the haze value is low (e.g., below 2-3%), which can practically be described as transparent. In manufacturing, a known roll-to-roll continuous manufacturing method (see [reference]) is preferred. Figure 5 (Referencing the diagram), resins constituting the light extraction layer and the light guiding layer are coated in an uncured state onto one side of a substrate film or sheet constituting the waveguide layer to form a coating layer. A roller with a fine embossed pattern (a raised, triangular-sectioned pattern) is pressed onto the surface of the coating layer, thereby transferring the embossed pattern of the roller. The transferred area is then irradiated with ultraviolet light (UV rays), which allows for better formation. Furthermore, the principle of transferring the embossed pattern of the roller can also be applied to the micro-imprinting process of plastic films. Therefore, for the formation of the light extraction layer and the light guiding layer, it is also possible to consider forming the light extraction layer and the light guiding layer with the desired surface shape by micro-imprinting the surface of a three-layer structure film. The three-layer structure film is formed by pre-bonding transparent thermoplastic resin films constituting the light extraction layer and the light guiding layer respectively onto the substrate film constituting the waveguide layer.

[0113] (Basic functions of the light-guiding layer)

[0114] Without limiting the scope of the invention in any way, the light guide layer 120 functions to deflect (lift) light from the light guide plate (not shown) at an emission angle of 70° to 80° in a near-vertical direction and propagate it to the light waveguide layer 110 described later.

[0115] (Characteristics of optical waveguide layer)

[0116] The optical waveguide layer 110 of the light-concentrating auxiliary film 10 forms an intermediate layer between the light extraction layer 100 and the light guiding layer 120. The optical waveguide layer 110 is completely free of light-diffusing particles. From the viewpoint of light transmittance of the optical waveguide layer 110, it is preferable that the resin constituting the optical waveguide layer 110 is a transparent resin such as polyethylene terephthalate (PET), polycarbonate (PC), polymethyl methacrylate (PMMA), or styrene-methyl methacrylate copolymer, and that its refractive index is suitable for the present invention. However, from the viewpoints of reliability and availability, a transparent optical PET film can be used more preferably. Furthermore, for the optical PET film used in the present invention, a film whose surface is easily bonded by plasma treatment, chemical treatment, etc., can be used more preferably.

[0117] Regarding the thickness of the optical waveguide layer 110, it is naturally determined based on the relationship between the overall thickness required for the optical focusing auxiliary film 10, the thickness of the aforementioned light extraction layer 100, and the thickness of the aforementioned light guiding layer 120. From the viewpoint of improving frontal brightness, it is preferable to have a thickness as thin as possible. However, since the UV-curable resin coated on both sides of the substrate film that forms the optical waveguide layer undergoes some curing shrinkage during curing, it is preferable to have a thickness that can counteract this curing shrinkage. Depending on the thickness of the light extraction layer and the light guiding layer, its lower limit is preferably about 15 μm to 20 μm. On the other hand, based on the relationship with the overall thickness required for the optical focusing auxiliary film 10, its upper limit is preferably about 200 μm.

[0118] Regarding the refractive index of the plastic constituting the optical waveguide layer 110, the range of refractive index values ​​is naturally determined by the type of plastic used. However, in this invention, as described above, an optical PET film with a nominal refractive index of 1.58 can be used more preferably.

[0119] Regarding the optical waveguide layer 110, its configuration is such that, during the manufacturing process of the optical focusing auxiliary film 10 of the present invention, it functions as a so-called substrate film. After the light extraction layer 100 and the light guiding layer 120 are formed on its two sides respectively, it performs the function of allowing light to pass through the light extraction layer 100 with minimal reduction in the amount of light incident from the optical waveguide layer 110. Therefore, an optical PET film (optical polyethylene terephthalate film) can be preferably used. For the optical PET film, in order to improve the adhesion when coating and bonding different resins, the optical PET film is surface-processed within a range that does not affect the optical properties of the film body. This surface-processing process is not included in the manufacturing process of the optical focusing auxiliary film 10 of the present invention; therefore, commercially available products can be preferably used for the optical PET film constituting the optical waveguide layer 110 of the optical focusing auxiliary film 10.

[0120] (The relationship between the arrangement direction of the unit concave portion of the light extraction layer and the arrangement direction of the unit triangular prism of the light guiding layer)

[0121] exist Figure 4 The figure illustrates the relationship (intersection angle) between the arrangement direction of the unit recesses 200 (generally inverted pyramids) of the light extraction layer 100 constituting the light emitting surface side and the length direction of the unit triangular prisms (convex strips) of the light guiding layer 120 constituting the light emitting surface side. In this figure, the valley lines 340 in the array of unit triangular prisms 300 of the light guiding layer 120 are illustrated with dashed lines. The figure shows the intersection of these two directions at 45°. This 45° value may not be exact; some error is permissible within the scope necessary to achieve the objectives of this invention.

[0122] (The relationship between the spacing of the light extraction layer (P1) and the spacing of the light guiding layer (P2))

[0123] To suppress the occurrence of self-moiré patterns, controlling the relationship between the spacing of the light extraction layer (P1) and the spacing of the light guiding layer (P2) is crucial. While common moiré patterns, i.e., moiré patterns between different optical components, are well-known, in the field of side-lit backlights, no prior art has been found that addresses the problem of eliminating self-moiré patterns occurring only within a single optical component. Furthermore, while Patent Document 1 addresses the problem of eliminating moiré patterns, this moiré pattern is not a self-moiré pattern.

[0124] The inventors used a mathematical formula to predict the occurrence of typical moiré patterns to express the relationship between the spacing of the light extraction layer (P1) and the spacing of the light guide layer (P2). They attempted to insert the actual values ​​of P1 and P2 respectively, and found that the predicted results did not match the measured results.

[0125] Therefore, the inventors conducted repeated and in-depth research and found that, under the condition that the arrangement direction of the unit recesses 200 of the light extraction layer 100 intersects with the arrangement direction of the unit triangular prisms 300 of the light guiding layer 130, when the actual values ​​of P1 and P2 are inserted into the following moiré pattern discovered by the inventors, the predicted results match the measured results well. As can be seen from the embodiments described later, when their relationship satisfies all of the following conditions, the self-moiré phenomenon can be suppressed.

[0126] That is, in the light-concentrating auxiliary film of the present invention that suppresses self-moiré phenomenon, the relationship between the spacing (P1) of the light extraction layer and the spacing (P2) of the light guiding layer is P1>P2, satisfying all of the following conditions.

[0127] (Mathematical Formula 1) |D1-D2|≤200μm

[0128] In the above mathematical expression 1, D1 and D2 satisfy the following mathematical expressions 2a and 2b, respectively.

[0129] (Mathematical formula 2a) D1 = |P1m × δ1 ÷ (δ1 - P1m)|

[0130] (Mathematical expression 2b) D2 = |P1m × δ2 ÷ (δ2 - P1m)|

[0131] In the above mathematical expressions 2a and 2b, P1m > P2m, P1m satisfies the following mathematical expression 3a, and P2m satisfies the following mathematical expression 3b.

[0132] (Mathematical formula 3a) P1m = P1 × sin(0.25 × π)

[0133] (Mathematical expression 3b) P2m = P2 ÷ 2

[0134] In the above mathematical expressions 2a and 2b,

[0135] 1) When the absolute value of the difference between P1m and P1m is denoted as δa, and the absolute value of the difference between P2m and P1m obtained by multiplying the integer part (rounded up) of P1m by P2m, and P1m obtained by multiplying the integer part (rounded down) of P1m by P2m, and P1m obtained by P1m obtained by multiplying the absolute value of P1m by P2m, the sum of the smaller of δa and δb and P1m is δ1.

[0136] 2) When the absolute value of the difference between P1m and P1m is δa (the integer part of the value obtained by dividing P1m by P2m and carrying over the decimal part), and the absolute value of the difference between P1m and P2m is δb (the integer part of the value obtained by dividing P1m by P2m and carrying over the decimal part), the smaller of δa and δb is set to twice the value. When comparing the value of this twice-multiplied value with the larger of δa and δb, the sum of the smaller value and P1m is δ2.

[0137] (The relationship between the refractive indices of each layer)

[0138] Furthermore, in the light-concentrating auxiliary film of the present invention, 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 planarly attached to it (the refractive index of the resin constituting the optical waveguide layer), and the refractive index n1 of the light guide layer that is planarly attached to the side opposite to the side where the light extraction layer is located (the refractive index of the resin constituting the light guide layer) are related as follows: n0 ≥ n1 and n0 ≥ n2. Preferably, the range of refractive index n1 is 1.50 ≤ n1 ≤ 1.64, and the range of refractive index n2 is 1.50 ≤ n2 ≤ 1.64.

[0139] 3. Roller mold supporting the fabrication of light-concentrating auxiliary films

[0140] This invention also aims to address the issue of reducing the cost of light-concentrating auxiliary films, but the manufacturing cost of these films naturally reflects upstream costs in the manufacturing process. From this perspective, in the manufacturing of the light-concentrating auxiliary film of this invention, as detailed below, a roll-to-roll method is preferably employed, in which a roller mold is preferably used. This roller mold is a precision component requiring highly advanced manufacturing technology, and therefore its cost significantly impacts the manufacturing cost of the light-concentrating auxiliary film. Therefore, the following explains the influence and limitations on the shape of the light-concentrating auxiliary film of this invention caused by the roller mold used in its manufacturing. However, the scope of this invention is not limited to the following description, and the manufacturing of the light-concentrating auxiliary film of this invention is not limited to the use of the roller mold described below.

[0141] The roller mold used in the embodiments of the present invention is prepared by the lathe machining method detailed below. However, other conceivable methods include photolithography, electron beam machining, and direct laser machining. However, photolithography and electron beam machining increase costs in the fabrication of large-area roller molds, which, from a practical point of view, contradicts the cost reduction objective of the present invention and is therefore not preferred. Furthermore, the possibility of achieving large area by reducing the precision of the mold's concave-convex shape has been considered, but when transferring the concave-convex shape using a mold with low pressing precision, the resulting shape precision is also low, making it impractical for manufacturing optical films requiring high-precision surface shapes. Regarding direct laser machining, in recent years, given the increasing speed of laser processing machines, it has become possible to use direct laser machining. However, since the laser spot diameter is originally at least around 10 μm, this machining method is also considered impractical for manufacturing optical films requiring high-precision surface shapes. Therefore, for machining methods that contribute to cost reduction, one of the objectives of the present invention, it is currently considered that high-precision and cost-effective turning machining is currently the most suitable option.

[0142] (Manufacturing method of roller mold)

[0143] Figure 6 This is a conceptual diagram of a typical method for manufacturing the roller mold used in the production of the light-concentrating auxiliary film 10 of the present invention by means of a cutting method. Figure 6 (a) is a conceptual diagram showing the cutting of a roller with a thin film 680 of metal (usually copper) formed on its surface by a cutting tool 640 having a single-crystal diamond tip 660 at the front end and a apex angle θ. Figure 6 (b) is an enlarged view showing the single-crystal diamond cutting tip 660 cutting the thin film 680, and is a cross-sectional view. (Although outside the scope of the present invention, it is a drawing used to illustrate a preferred range of the surface irregularities of the light-concentrating auxiliary film of the present invention, and therefore reference numerals are omitted except for the main constituent elements.)

[0144] First, a copper-nickel metal film (primarily electroplated) is formed on the surface of a metal roller (typically iron or SUS) of a specified size. The film thickness is approximately 300-500 μm. Simultaneously, the single-crystal diamond at the tip of a diamond cutting tool is machined into the desired shape (in this embodiment, an isosceles triangle with a vertex angle θ). Next, the machined single-crystal diamond is bonded to the tip of the shank, and the surface is ground to achieve the desired shape. The shank is then shaped to match the cutting machine.

[0145] Taking the formation of a copper film on the surface as an example, the roller mold is manufactured using turning as follows: First, using a single-crystal diamond cutting tool with a specified tip angle, the copper film formed on the surface of the metal roller in the above process is linearly removed at high speed (the position of the single-crystal diamond cutting tool is fixed and the roller mold is rotated at high speed), thereby etching multiple recessed strips extending parallel in one direction on the surface. After performing this operation around one revolution of the roller, the position of the single-crystal diamond cutting tool is moved laterally (along the axis of the roller) by a distance equivalent to the spacing (P), and the same operation is performed again around one revolution, and this operation is repeated. Therefore, the smaller the diameter of the roller (the shorter the length of the cutting line), the less wear on the tip and sides of the single-crystal diamond cutting tool, and correspondingly, excess scattering can be suppressed and processing costs can be reduced.

[0146] At this time, the concave strip corresponds to the convex strip of resin that is pressed into the concave strip during the roll-to-roll manufacturing process. The dimensions of the convex strip, as described in the detailed embodiments below, are those of a triangular cross-section with a depth of 9μm to 21μm and a base of 18μm to 42μm. Therefore, the size of the tip of the single-crystal diamond blade that cuts into the copper plating layer is also of this size. In the light-concentrating auxiliary film of the present invention, its optical performance is affected by the accuracy of the surface shape, so the cutting process requires high-precision control.

[0147] Furthermore, if the apex angle of the single-crystal diamond cutting tool tip is obtuse, for example, greater than 100°, sufficient bite (cutting) of the tool cannot be ensured during the cutting process. The tip of the single-crystal diamond cutting tool slides on the copper-plated surface, causing vibration of the tool and reducing the smoothness of the beveled surface of the protrusion formed in the mold. As a result, the smoothness of the beveled surface of the inverted pyramid and the triangular prism is reduced. From a practical point of view, this is also limited by the size of the protrusion (and the size of the inverted pyramid and triangular prism obtained by transferring it).

[0148] Furthermore, the surface shapes of the light extraction layer and light guiding layer formed on the surface of the final light-concentrating auxiliary film are influenced by the triangular convex strips or pyramidal protrusions formed in the roller mold. The intersection (transition) of one surface with the adjacent surface in this surface shape needs to be as sharp (narrow) as possible in terms of the optical properties required by the light-concentrating auxiliary film. Therefore, the tip shape of the single-crystal diamond blade used requires nanometer-level precision.

[0149] Regarding the ease of machining when forming irregular strips on the surface of the mold, in the case of forming a triangular prism layer on the light-injection side of the light-concentrating auxiliary film of the present invention, the apex angle of each triangular prism strip is 90° (base angle 45°), especially when it is a bilaterally symmetrical shape. When the apex angle is an acute angle smaller than 90°, the durability of the cutting tool is prone to problems, thus increasing the machining difficulty, and is therefore not preferred. Conversely, when the apex angle is an obtuse angle larger than 90°, the sharpness of the cutting tool (single-crystal diamond insert) deteriorates (the cutting depth relative to the formed copper metal film deteriorates), thus increasing the tendency for cutting tool vibration to occur and deteriorate the quality of the machined surface. Therefore, the apex angle of the tip of the single-crystal diamond cutting tool that functions as a cutting tool (in the case of the present invention, that is, the apex angle of the unit triangular prism formed on the light-injection surface side of the light-concentrating 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. In these values, the angle error is preferably ±1°.

[0150] When a unit recess in the shape of a roughly inverted square pyramid (roughly inverted pyramid) is formed on the light-emitting side of the light-concentrating auxiliary film of the present invention, the mold processing conditions become more stringent and difficult compared to the case of forming a unit triangular prism. The reason for this is the following process: First, as a first step, while rotating the drum, the tip of a single-crystal diamond cutting tool is pressed (cut into) the surface of the copper-plated drum to perform cutting, thereby forming a ridge of a concave strip with a triangular cross-section. Next, as a second step, in a direction orthogonal to the direction of the ridge of the concave strip formed in the first step, the same action is performed to form a ridge of a concave strip with a triangular cross-section. As a result, the intersection of the concave strip formed in step 1 and the concave strip formed in step 2 creates an inverted quadrangular pyramid (inverted pyramid) unit concave portion, while the portion not removed by cutting becomes a quadrangular pyramid (pyramidal) protrusion. However, the load applied to the tip of the single-crystal diamond cutting tool in this step 2 is not a static load, but a repeated impact load. That is, repeated impact loads are applied as the tool alternately passes through the solid and void portions of the concave strip formed in step 1. Therefore, compared to the case of the unit triangular prism described above, the machining conditions become more stringent, and tool durability problems are more likely to occur. Therefore, when the apex angle (in the case of the present invention, that is, the apex angle of the unit concave portion of the approximately inverted square pyramid (approximately inverted pyramid) formed on the light-emitting side of the light-concentrating auxiliary film) is an acute angle less than 90°, the processing difficulty increases. Similarly, when it becomes an obtuse angle of 100° or more, the processing difficulty also increases. Therefore, such an apex angle is preferably 70° or more and 130° or less, more preferably 80° or more and 100° or less. In these values, the angle error is preferably ±1°.

[0151] (Backlight unit and liquid crystal display device equipped with the light-concentrating auxiliary film of the present invention)

[0152] Figure 7 (a) is a conceptual cross-sectional view of a liquid crystal display device 70 equipped with the light-concentrating auxiliary film of the present invention. Reference numeral 700 denotes a liquid crystal panel unit, and reference numeral 720 denotes two orthogonally overlapping BEF (button-free) panels. Figure 7 (b) reference numeral 724) and the light diffusion film stacked thereon ( Figure 7In (b) of the figure, reference numeral 722 indicates the stacked unit, reference numeral 10 indicates the light-concentrating auxiliary film of the present invention, reference numeral 740 indicates the light guide plate unit having a reflective sheet on the lower surface side, and reference numeral 760 indicates the white LED. Furthermore, the white LEDs 760 are arranged in a discrete row along the side of the light guide plate unit 740 in the depth direction of the paper. The light-concentrating auxiliary film 10 of the present invention is inserted between the upper surface (light emitting surface) of the light guide plate unit 740 and the stacked unit 720. This light-concentrating auxiliary film 10 has the following function: by concentrating the light from the upper surface (light emitting surface) of the light guide plate unit 740 and further deflecting its propagation direction in the vertical direction (the direction of the upper side of the paper) (changing the propagation direction), the light propagation characteristics are changed to be orthogonally overlapping with the two sheets BEF (beam-effect transistors) stacked thereon. Figure 7 (b) The attached figure (724) matches the state as closely as possible.

[0153] Figure 7 (b) is to remove Figure 7 The concept diagram showing the stacking state of each layer is shown after the liquid crystal panel unit 700 in (a). In the stack, the reflective sheet 744, the light guide plate 742, the light focusing auxiliary film 10 of the present invention, two orthogonally overlapping BEF 724, and the light diffusion film 722 are stacked sequentially from the bottom to the top.

[0154] (Evaluation method of the light-concentrating auxiliary film of the present invention)

[0155] exist Figure 8 The image shows, conceptually, the stacked structure for evaluating the properties of the light-concentrating auxiliary film 10 of the present invention. (Removal) Figure 7 (b) shows two orthogonally overlapping BEF724 and light diffusion film 722 and illustrates the stacking of each layer, in which, from the bottom to the top, are reflective sheet 744, light guide plate 742, and light focusing auxiliary film 10 of the present invention.

[0156] The specific evaluation methods are described in the detailed examples below.

[0157] <Example>

[0158] The following describes the embodiments.

[0159] 1. Fabrication of the light extraction layer of the light-concentrating auxiliary film

[0160] (Substrate film)

[0161] For the substrate film used, an optical PET film with a thickness of 50 μm was used (e.g., DIAFOIL T600E50 manufactured by Mitsubishi Chemical Corporation). Furthermore, if the effect does not vary from manufacturer to manufacturer, then as long as certain specific characteristics are present, it can be used optimally.

[0162] (UV-cured resin)

[0163] For the UV-curable resin used, a UV-curable resin obtained by adding a photoinitiator to a UV-curable acrylate monomer (97 wt%) was used, and it was formulated so that the refractive index nD after curing is the value shown in the table below. The refractive index nD is shown as the value measured using an Abbe refractometer (ATAGO CO.,LTD. NAR-1T SOLID).

[0164] (Roller mold)

[0165] The shape characteristics of the unit concavity were used to make Figure 2 The shape characteristics shown are such that the apex angle (θ1) and spacing (P1) are as described in Table 1 below, and the surface of the roller mold is uneven (the thickness of the copper metal film on the surface is 300μm~500μm).

[0166] (Film-forming method)

[0167] Basically, a roll-to-roll film-making method commonly used is employed. Specifically, a roll of substrate film is placed in the aforementioned roll-to-roll manufacturing system and the system is started. Next, using the conventional method in roll-to-roll manufacturing, an acrylic-based UV-curable resin, prepared in a manner such that its cured refractive index is the value listed in the table below, is continuously coated onto the substrate film to form a coating layer. A roller is then pressed sequentially onto the coated film and irradiated with ultraviolet light (UV rays) to cure it, forming a light extraction layer. A double-layer film with a light extraction layer formed on one side is then produced and rolled up (the first roll is produced). Regarding the apex angle (θ1) and spacing (P1) at this point, the transfer surface is magnified 2400 times using a laser microscope (Keyence VKX-1000) to confirm that the apex angle (θ1) and spacing (P1) have been transferred.

[0168] 2. Fabrication of the light-guiding layer of the light-concentrating auxiliary film

[0169] The same UV-curing resin used was the same as that used in the light extraction layer described above. The refractive index after curing was also measured using an Abbe refractometer (ATAGO CO.,LTD. NAR-1T SOLID). A different type of roller was used, whose surface pattern could form a triangular prism array composed of multiple ridges with isosceles triangular cross-sections.

[0170] 3. Judgment Method

[0171] 1) Methods for identifying moiré patterns

[0172] Essentially based on visual inspection. Holding one end of the light-concentrating auxiliary film sample of this invention with the fingers of one hand, extending the arm of that hand, and shielding it against an indoor fluorescent light, determine whether the moiré pattern can be visually identified with the naked eye. The specific method of judgment is as follows... Figure 10 As shown in the conceptual diagram. In a dark room, holding the end of the light-concentrating auxiliary film 10 of the present invention with one hand, the film is vertically placed between the naked eye 1010 and the fluorescent lamp 1020, which is about 60 cm away from the naked eye. The transmitted moiré pattern is visually confirmed from the light extraction layer (the layer with the inverted pyramid shape) side. Next, the film is placed directly below the film and positioned so that the center of the film, after being set to horizontal, is at an angle of about 30 cm relative to the same fluorescent lamp 1020 and the naked eye 1010. The angled light from the fluorescent lamp 1020 is obliquely irradiated onto the surface of the light extraction layer of the film, and the reflected moiré pattern is confirmed by its reflection. At this time, the case where neither the transmitted moiré pattern nor the reflected moiré pattern can be visually identified is marked as ○.

[0173] Next, in this determination, if moiré patterns (transmitted moiré patterns and / or reflected moiré patterns) can be visually identified, the center of the film (refer to) is configured such that it is placed horizontally above the light guide plate 742 (including the light reflector 744) of the backlight unit used in the brightness measurement. Figure 8 The stacked diagram is located at a position approximately 30 cm tilted relative to the naked eye at the same angle as described above. Further judgment is made by visual inspection. In either the case where the light extraction layer (inverted pyramid layer) is facing upwards or the case where the light guiding layer (triangular prism layer) is facing upwards, the case where the moiré pattern (transmission moiré pattern) cannot be visually identified is set as △, and the case where it can be visually identified is set as ×.

[0174] Furthermore, the relationship between the arrangement direction of the unit concave portions of the light extraction layer (the same direction as the ridge line) and the arrangement direction of the unit triangular prisms of the light guiding layer (the same direction as the ridge line) is as follows: Figure 4 As shown. Additionally, the cross-sectional shape of the solid portion of two adjacent unit recesses at this time ( Figure 2 The cross-sectional shape shown) and the cross-sectional shape of the unit triangular prism ( Figure 3 The cross-sectional shapes shown are all isosceles triangles.

[0175] 2) Evaluation method for front brightness

[0176] A 9-inch side-lit backlight unit using white LEDs as the light source (structural reference). Figure 7 (b) The light-concentrating auxiliary film of the present invention was mounted and evaluated. For the two orthogonally overlapping BEFs, 3M's BEF-4DT was used, and for the light-diffusing film stacked on them, the applicant's D159GS was used.

[0177] The white LED has a maximum power supply voltage of 17V and is driven by a constant current of 200mA.

[0178] A 5cm square area centered on the center point of the backlight unit's emission surface was divided into 64×64 cells (each cell is approximately 0.78mm square). The shutter speed was set to Auto (high dynamic range sampling mode), and measurements were taken. The average of the luminance values ​​of the 64×64=4096 points was taken as the front luminance value. The luminance meter used was a HI-LAND two-dimensional luminance and colorimetry measuring device (ACE3-2000).

[0179] Furthermore, in the following evaluation method, the direction of the optical axis of the light emitted from the white LED disposed on the side of the light guide plate of the side-lit backlight is parallel to the direction (length direction) of the edge line of the unit triangular prism of the light guiding layer of the light-concentrating auxiliary film of the present invention disposed on the light guide plate. Moreover, the orientation characteristics of the light emitted from the upper surface of the light guide plate mounted on the side-lit backlight unit to the light-concentrating auxiliary film of the present invention are such that when the combination of the shape characteristics and refractive index of the light-concentrating auxiliary film of the present invention is the value listed in Table 1 below, the contour map of the light emitting surface of the light-concentrating auxiliary film becomes... Figure 9 The contour plot shown illustrates the orientation characteristics of light.

[0180] [Table 1]

[0181]

[0182] 2. The shape characteristics, refractive index, and optical properties of the light-concentrating auxiliary films used in the examples and comparative examples are shown in the following summary table.

[0183] 1) Judgment results of moiré patterns

[0184] [Table 2]

[0185] (At a cross angle of 45°: the cross angle was measured using a microscope (VHX-8000) manufactured by Keyence Corporation.)

[0186]

[0187] (Note 1: The calculation in the above calculation results refers to the calculation first designed by the inventor based on the calculation formula described in the specification and claims regarding the self-moiré pattern under the following conditions: 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 guiding layer (the same direction as the ridge line) intersect each other at 45°, and the cross-sectional shape of the solid portion of two adjacent unit recesses ( Figure 2 The cross-sectional shape shown in the figure) and the cross-sectional shape of the unit triangular prism ( Figure 3 The cross-sectional shapes shown are all isosceles triangles.

[0188] (Note 2: The marks ○, △, and × in the Moiré pattern judgment result column refer to the actual judgment results based on the judgment method described in the chapter on the self-moiré pattern judgment method above.)

[0189] Next, the results of actually judging that no self-moiré pattern appeared even when the cross angle was varied by 3.0° from 45.0° will be compared with the calculation results obtained by the above calculation formula and recorded in the following table.

[0190] [Table 3]

[0191] (For cross angles of 42.0°, 45.0°, and 48.0°: The cross angles were measured using a Keyence microscope (VHX-8000). Furthermore, the cross angles are...) Figure 4 (The shown intersection angle.)

[0192]

[0193] (Note 1: The calculation in the above calculation results refers to the calculation first designed by the inventor based on the calculation formula described in the specification and claims regarding the self-moiré pattern under the following conditions: 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 guiding layer (the same direction as the ridge line) intersect each other at 42.0°, 45.0°, and 48.0° respectively, and the cross-sectional shape of the solid portion of two adjacent unit recesses ( Figure 2 The cross-sectional shape shown in the figure) and the cross-sectional shape of the unit triangular prism ( Figure 3 The cross-sectional shapes shown are all isosceles triangles.

[0194] (Note 2: The marks ○, △, and × in the "Measured Moiré Pattern Judgment Result" column refer to the actual judgment results based on the judgment method described in the section on self-moiré pattern judgment.)

[0195] 2) The result of judging the front brightness of the light emitting surface of the side-lit backlight equipped with the light-concentrating auxiliary film of the present invention.

[0196] In the table below, the refractive index of the light extraction layer is n1 = 1.52, and the refractive index of the light guiding layer is n2 = 1.52. Additionally, the refractive index of the waveguide layer is n0 = 1.58, and its thickness is 50 μm. The thickness of the residual films of both the light extraction and light guiding layers is 1 μm. Furthermore, in all the following results, brightness unevenness is not visually perceptible to the naked eye.

[0197] [Table 4]

[0198]

[0199] (Note: For the optical simulator used in the optical simulation, Synopsys' LightTools (lighting design software) was employed. The parameters used in the simulation were set so that the error between the measured and simulated values ​​would be consistent with the values ​​in Table 6 described later, to ensure the reasonableness of the simulated values.)

[0200] When observing the above overview, it is clear that in the group of embodiments and the group of comparative examples, with the apex angle of the light extraction layer between 100° and 110° as the boundary, the front brightness of the group of comparative examples tends to decrease.

[0201] In the table below, the refractive index of the light extraction layer is n1 = 1.58, and the refractive index of the light guiding layer is n2 = 1.52. Additionally, the refractive index of the waveguide layer is n0 = 1.58, and its thickness is 50 μm. The thickness of the residual films of both the light extraction and light guiding layers is 1 μm. Furthermore, in all the following results, brightness unevenness is not visually perceptible to the naked eye.

[0202] [Table 5]

[0203]

[0204] (Note: For the optical simulator used in the optical simulation, Synopsys' LightTools (lighting design software) was employed. The parameters used in the simulation were set so that the error between the measured values ​​and the simulated values ​​would be consistent with the values ​​in Table 6 described later, to ensure the reasonableness of the simulated values.)

[0205] When observing the above overview, it is clear that in the group of embodiments and the group of comparative examples, with the apex angle of the light extraction layer between 100° and 110° as the boundary, the front brightness of the group of comparative examples tends to decrease.

[0206] All the above simulations were performed using an optical simulator (Synopsys LightTools lighting design software). Various parameters were set to ensure that the error between the measured and simulated front brightness values ​​(the error relative to the measured value) was within 1%, as shown in Table 6 below, thus ensuring the reasonableness of the simulated values. Furthermore, in this case, the refractive index n0 of the optical waveguide layer was 1.58, the thickness was 50 μm, and the thicknesses of the residual films of the light extraction layer and the light guiding layer were both 1 μm.

[0207] [Table 6]

[0208]

[0209] The following table shows the front brightness when the inverted pyramid of the light extraction layer of the light-concentrating auxiliary film of the present invention (the thickness of the residual film of the light extraction layer and the residual film of the light guiding layer are each about 1 μm) is horizontally placed on a light guide plate with a front brightness of 749.9 cd / m2 on the emission surface of the light guide plate, based on setting the apex angle of the inverted pyramid of the light extraction layer of the light guiding film of the present invention to 80° and the apex angle of the triangular prism (isosceles triangle) of the light guiding layer to 90°, and the front brightness of the emission surface of the light-concentrating auxiliary film is measured.

[0210] [Table 7]

[0211]

[0212] The following table shows the front brightness when the inverted pyramid of the light extraction layer of the light-concentrating auxiliary film of the present invention (the thickness of the residual film of the light extraction layer and the residual film of the light guiding layer are each about 1 μm) is horizontally placed on a light guide plate with a front brightness of 749.9 cd / m2 on the emission surface of the light guide plate, based on setting the apex angle of the inverted pyramid of the light extraction layer of the light-concentrating auxiliary film of the present invention to 90° and the apex angle of the triangular prism (isosceles triangle) of the light guiding layer to 90°, and the front brightness of the emission surface of the light-concentrating auxiliary film is measured.

[0213] [Table 8]

[0214]

[0215] The present invention has been described in detail above based on representative embodiments, examples, and comparative examples. However, various modifications may be made as long as they do not exceed the scope of the purpose and spirit of the present invention.

[0216] Industrial availability

[0217] According to the present invention, a light-concentrating auxiliary film having the following characteristics is obtained.

[0218] 1) The number of components constituting the light-concentrating auxiliary film is relatively small.

[0219] 2) The components constituting the light-concentrating auxiliary film contain no light-diffusing particles.

[0220] 3) It can suppress the occurrence of self-moiré patterns and obtain the desired optical properties.

[0221] 4) Suitable for mass production in roll-to-roll mode, with lower cost.

[0222] Based on the above results, it is expected that the manufacturing cost of the side-lit backlight unit equipped with the light-concentrating auxiliary film of the present invention can be reduced, and further, it is expected that the requirement for low cost of liquid crystal display devices equipped with the light-concentrating auxiliary film can be met.

[0223] Explanation of reference numerals in the attached figures

[0224] 10. Light-concentrating auxiliary film; 100. Light extraction layer; 110. Optical waveguide layer; 120. Light-guiding layer; 200. Unit concave portion (roughly inverted pyramid); 220. Edge of unit concave portion (roughly inverted pyramid); 230. Spacing (P1) of unit concave portions (roughly inverted pyramid); 240. Bottom center point of unit concave portion; 250. Vertex angle (θ1) of the solid region of the triangle occupied by the solid parts of adjacent unit concave portions; 260. Solid region of the triangle occupied by the solid parts of adjacent unit concave portions; 300. Unit triangular prism; 320. Edge of unit triangular prism; 330. Spacing (P2) of unit triangular prisms; 340. Valley line formed by adjacent unit triangular prisms; 350. Vertex angle (θ2) of unit triangular prism; 5 00. A known conventional roll-to-roll manufacturing system (reference); 520. Coated UV-curable resin; 540. Roller die; 560. Take-up roll; 562. Take-up roll; 580. UV irradiation device; 620. Roller die; 640. Shank of cutting tool; 660. Single crystal diamond; 680. Workpiece to be cut (copper plating); 700. Liquid crystal panel; 720. BEF (two-piece cross-type) and light diffusion film (manufactured by the applicant); 722. Light diffusion film (manufactured by the applicant); 724. BEF (two-piece cross-type); 740. Light guide plate unit (light reflector and light guide plate); 742. Light guide plate; 744. Light reflector; 760. Discrete white LED; 1010. Naked eye; 1020. Indoor fluorescent lamp.

Claims

1. A light-concentrating auxiliary film, which is inserted between the light-emitting surface of a light guide plate and the light-incident surface of a brightness enhancement film (BEF) in a side-lit backlight unit using discrete LED point light sources, characterized in that... This light-concentrating auxiliary film possesses: The optical waveguide layer is composed of a transparent substrate film; A light extraction layer, formed on one face of the optical waveguide layer, has multiple unit recesses in the shape of an inverted square pyramid; and A light-guiding layer, formed on the other side of the optical waveguide layer, has multiple unit triangular prisms extending parallel in one direction. The light extraction layer constitutes the light emission surface. The prism surfaces of the multiple unit triangular prisms constituting the light guiding layer form the light incident surface. The light extraction layer, the light waveguide layer, and the light guiding layer all contain no light diffusion particles. The relationship between the spacing P1 of the plurality of unit recesses and the spacing P2 of the plurality of unit triangular prism lenses is P1>P2, satisfying all of the following conditions: (Mathematical Formula 1) |D1-D2|≤200μm In the above mathematical expression 1, D1 and D2 satisfy the following mathematical expressions 2a and 2b, respectively. (Mathematical formula 2a) D1=|P1m×δ1÷(δ1-P1m)| (Mathematical formula 2b) D2=|P1m×δ2÷(δ2-P1m)| In the above mathematical expressions 2a and 2b, P1m > P2m, P1m satisfies the following mathematical expression 3a, and P2m satisfies the following mathematical expression 3b. (Mathematical formula 3a) P1m = P1 × sin(0.25 × π) (Mathematical expression 3b) P2m = P2 ÷ 2 In the above mathematical expressions 2a and 2b, 1) When the absolute value of the difference between P1m and P1m is denoted as δa, and the absolute value of the difference between P2m and P1m obtained by multiplying the integer part (rounded up) of P1m by P2m, and P1m obtained by multiplying the integer part (rounded down) of P1m by P2m, and P1m obtained by P1m obtained by multiplying the absolute value of P1m by P2m, the sum of the smaller of δa and δb and P1m is δ1. 2) When the absolute value of the difference between P1m and P1m is δa (the integer part of the value obtained by dividing P1m by P2m and carrying over the decimal part), and the absolute value of the difference between P1m and P2m is δb (the integer part of the value obtained by dividing P1m by P2m and carrying over the decimal part), the smaller of δa and δb is set to twice the value. When comparing the twice-valued value with the larger of δa and δb, the sum of the smaller value and P1m is δ2.

2. A light-concentrating auxiliary film, which is inserted between the light-emitting surface of a light guide plate and the light-incident surface of a brightness enhancement film (BEF) in a side-lit backlight unit using discrete LED point light sources, characterized in that... This light-concentrating auxiliary film possesses: The optical waveguide layer is composed of a transparent substrate film; A light extraction layer, formed on one face of the optical waveguide layer, has multiple unit recesses in the shape of an inverted square pyramid; and A light-guiding layer, formed on the other side of the optical waveguide layer, has multiple unit triangular prisms extending parallel in one direction. The light extraction layer constitutes the light emission surface. The prism surfaces of the multiple unit triangular prisms constituting the light guiding layer form the light incident surface. The light extraction layer, the light waveguide layer, and the light guiding layer all contain no light diffusion particles. The angle between the direction of the edge line of the plurality of unit concave portions and the direction of the edge line of the plurality of unit triangular prisms is in the range of 42° to 48°. The moiré pattern generated by the plurality of unit recesses and the plurality of unit triangular prisms is not visually perceptible to the naked eye.

3. The light-concentrating auxiliary film according to claim 2, characterized in that, The relationship between the distance P1 between the plurality of unit recesses and the distance P2 between the plurality of unit triangular prism lenses is P1>P2.

4. The light-concentrating auxiliary 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. The light-concentrating auxiliary film according to claim 4, characterized in that, When the refractive index of the resin constituting the light extraction layer is set to n1, the refractive index of the resin constituting the light guiding layer is set to n2, and the refractive index of the resin constituting the optical waveguide layer is set to n0, the following relationship exists: n0≥n1 and n0≥n2.

6. The light-concentrating auxiliary film according to claim 5, characterized in that, 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.

7. The light-concentrating auxiliary film according to claim 6, characterized in that, The apex angle of the plurality of unit triangular prisms is less than 95°.

8. The light-concentrating auxiliary film according to claim 7, characterized in that, The apex angle of the plurality of unit recesses is greater than 80° and less than 95°.

9. A side-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-concentrating auxiliary 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 side-lit backlight unit according to claim 9, characterized in that, The plurality of point light sources are disposed on at least one edge side of the light guide plate.

11. A liquid crystal display device, characterized in that, The liquid crystal display device includes the side-lit backlight unit and liquid crystal display panel as described in claim 10.

Images