Optical member, and backlight unit and image display device using the same

Abstract

The present application provides an optical member with excellent brightness uniformity. The optical member of the present application comprises: a light guide plate having an end surface on which light from a light source is incident, an exit surface from which the light after incidence is emitted, and a light extraction pattern provided on a side opposite to the exit surface; and a reflection plate attached to the light guide plate via a double-sided adhesive film. The double-sided adhesive film has, in order from the light guide plate side, a first adhesive layer, a low-refractive layer, and a second adhesive layer. In the optical member, the outer edge of the light guide plate is located closer to the outside than the outer edge of the double-sided adhesive film, and the outer edge of the double-sided adhesive film is located closer to the outside than the outer edge of the light extraction pattern.

Description

TECHNICAL FIELD

[0001] The present application relates to an optical member, and a backlight unit and an image display device using the same. BACKGROUND

[0002] In a backlight unit of an image display device (representatively, a liquid crystal display device), a technique is known in which a light guide plate and a reflection plate are laminated with a low-refractive layer interposed therebetween. According to such a technique, it has been reported that the light use efficiency is higher by interposing the low-refractive layer than in the case of simply laminating with an adhesive alone. However, even with such a technique, there is a case where light is emitted near the light-incident surface of light from a light source, and the uniformity of brightness is insufficient.

[0003] PRIOR ART DOCUMENTS

[0004] PATENT DOCUMENTS

[0005] Patent Document 1: Japanese Patent Application Laid-Open No. 10-62626 SUMMARY

[0006] PROBLEMS TO BE SOLVED BY THE INVENTION

[0007] The present application has been achieved in order to solve the above-described conventional problems, and a main object thereof is to provide an optical member capable of realizing a backlight unit having excellent uniformity of brightness.

[0008] MEANS FOR SOLVING PROBLEMS

[0009] The optical member of the embodiment of the present application includes a light guide plate having an end surface on which light from a light source is incident, an emission surface from which the light after incidence is emitted, and a light extraction pattern provided on a side opposite to the emission surface, and a reflection plate attached to the light guide plate with a double-sided adhesive film interposed therebetween. The double-sided adhesive film has, in order from the light guide plate side, a first adhesive layer, a low-refractive layer, and a second adhesive layer. In the optical member, the outer edge of the light guide plate is located more outward than the outer edge of the double-sided adhesive film, and the outer edge of the double-sided adhesive film is located more outward than the outer edge of the light extraction pattern.

[0010] In one embodiment, the maximum value of the distance between the outer edge of the light guide plate and the outer edge of the light extraction pattern is set as A, and the maximum value of the distance between the outer edge of the light guide plate and the outer edge of the double-sided adhesive film is set as B, and the optical member satisfies the relationship of A > 2B.

[0011] According to another aspect of the present application, there is provided a backlight unit. The backlight unit includes a light source, the optical member described above disposed with the end surface opposite to the light source, and a housing that accommodates the light source and the optical member.

[0012] According to a further aspect of the present application, there is provided an image display device having the above-described backlight unit and an image display panel disposed on the side of the light-exit surface of the light guide plate.

[0013] Effects of the Invention

[0014] According to the present application, in an optical member in which a light guide plate and a reflection plate are integrated via a double-sided adhesive film including a low-refractive layer, by configuring such that the outer edge of the light guide plate is located closer to the outside than the outer edge of the double-sided adhesive film, and the outer edge of the double-sided adhesive film is located closer to the outside than the outer edge of the light-exit pattern of the light guide plate, a backlight unit having excellent uniformity of brightness can be achieved. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 is a cross-sectional schematic view of an optical member of one embodiment of the present application.

[0016] Figure 2 is a top view schematic view illustrating the relationship between the outer edge of the light guide plate, the outer edge of the double-sided adhesive film, and the outer edge of the light-exit pattern in the optical member of the embodiment of the present application.

[0017] Figure 3 is a cross-sectional schematic view of a backlight unit of one embodiment of the present application.

[0018] SYMBOL EXPLANATION

[0019] 10 light guide plate

[0020] 10a end surface

[0021] 10b light-exit surface

[0022] 10c light-exit pattern

[0023] 20 double-sided adhesive film

[0024] 21 first adhesive layer

[0025] 22 low-refractive layer

[0026] 23 second adhesive layer

[0027] 24 substrate

[0028] 30 reflection plate

[0029] 100 optical member

[0030] 120 light source

[0031] 140 housing

[0032] 141 front surface portion

[0033] 142 back surface portion

[0034] 200 back light unit DETAILED DESCRIPTION

[0035] Hereinafter, embodiments of the present application will be described, but the present application is not limited to these embodiments.

[0036] A. Overall structure of optical member

[0037] Figure 1 is a cross-sectional view of an optical member according to an embodiment of the present application. The illustrated optical member 100 has a light guide plate 10, and a reflection plate 30 which is attached to the light guide plate 10 via a double-sided adhesive film 20. The double-sided adhesive film 20 has, in order from the light guide plate 10 side, a first adhesive layer 21, a low-refractive layer 22, and a second adhesive layer 23. In actual use, a base material 24 is provided between the low-refractive layer 22 and the second adhesive layer 23. More specifically, the low-refractive layer 22 can be formed on the surface of the base material 24, and the first adhesive layer 21 and the second adhesive layer 23 can be disposed on both sides of the laminate of the base material 24 and the low-refractive layer 22.

[0038] The light guide plate 10 has an end surface 10a on which light from a light source is incident, an exit surface 10b from which the light after the incidence is emitted, and a light extraction pattern 10c provided on the side opposite to the exit surface 10b. That is, typically, the light guide plate 10 is of an edge light type in which light is incident from the end surface 10a. More specifically, the light guide plate 10 guides the light incident to the end surface 10a from the light source to the side of the end surface 10a opposite to the end surface 10a while the light is subjected to a reflection action or the like inside, and slowly emits the light from the exit surface 10b in the process of the light guide. The light extraction pattern 10c can contribute to the reflection action or the like in the light guide. As the light extraction pattern, for example, a white dot, a concave-convex shape, or the like can be given. The light extraction pattern 10c can be formed, for example, by printing such as silk screen printing, injection molding, laser processing, and embossing. Typically, an exit pattern is provided on the exit surface 10b. As the exit pattern, for example, a concave-convex shape can be given. Typically, the light guide plate 10 is a plate-like object composed of a thermoplastic resin, a thermosetting resin, or a photocurable resin. As the resin constituting the light guide plate, for example, a (meth)acrylic resin, a polycarbonate resin, a cyclic olefin resin, a styrene resin, and a copolymer resin thereof can be given.

[0039] As the reflection plate 30, any appropriate reflection plate can be used. For example, the reflection plate can be a specular reflection plate or a diffuse reflection plate. As specific examples of the reflection plate, a resin sheet (e.g., an acrylic plate) having a high reflectance, a metal sheet or foil such as an aluminum sheet, a stainless steel sheet, or the like, an evaporation sheet in which aluminum, silver, or the like is evaporated on a substrate such as a resin film of polyester or the like, a laminate of a substrate such as a resin film of polyester or the like and a metal foil of aluminum or the like, and a resin film in which holes (pores) are formed in the interior can be given. By providing the reflection plate 30, the light utilization efficiency of the backlight unit can be improved.

[0040] In the embodiment of the present application, as shown in Figure 2 the outer edge of the light guide plate 10 is located closer to the outside than the outer edge of the double-coated adhesive film 20, and the outer edge of the double-coated adhesive film 20 is located closer to the outside than the outer edge of the light extraction pattern 10c of the light guide plate 10. In other words, in the optical member, the outer edge of the double-coated adhesive film 20 is not made to protrude from the outer edge of the light guide plate 10, and the outer edge of the light extraction pattern 10c is not made to protrude from the outer edge of the double-coated adhesive film 20. If such a configuration is adopted, light leakage can be significantly suppressed, and as a result, an optical member that enables a backlight unit having excellent uniformity of brightness can be obtained.

[0041] As shown in Figure 2 the light guide plate 10 and the double-coated adhesive film 20 each have a substantially rectangular shape in plan view. The light extraction pattern 10c has a given pattern in plan view, as shown in Figure 2 the outer edge of the patterned region can be substantially rectangular. In one embodiment, the length of the long side of the light guide plate 10 is longer than the length of the long side of the double-coated adhesive film 20, and the length of the short side of the light guide plate 10 is longer than the length of the short side of the double-coated adhesive film 20; and the length of the long side of the double-coated adhesive film 20 is longer than the length of the long side of the light extraction pattern 10c, and the length of the short side of the double-coated adhesive film 20 is longer than the length of the short side of the light extraction pattern 10c. If such a configuration is adopted, the protrusion of the outer edge as described above can be prevented well. That is, in the case where the light guide plate 10 and the double-coated adhesive film 20, and / or the double-coated adhesive film 20 and the light extraction pattern 10c are the same size, the protrusion of the outer edge as described above occurs even if the attachment is slightly off, but by the sizes thereof, the protrusion can be prevented well. In one embodiment, when the maximum value of the distance between the outer edge of the light guide plate 10 and the outer edge of the light extraction pattern 10c is set as A (mm), and the maximum value of the distance between the outer edge of the light guide plate 10 and the outer edge of the double-coated adhesive film 20 is set as B (mm), the optical member satisfies the relationship of A > 2B. If such a configuration is adopted, the protrusion of the outer edge as described above can be prevented even better.

[0042] The double-sided adhesive film will be described in detail below. For the light guide plate and reflector, a structure known in the industry can be used, therefore, descriptions other than those described above are omitted.

[0043] B. Double-sided adhesive film

[0044] B-1. Overview of Double-Sided Adhesive Film

[0045] As described in section A above, the double-sided adhesive film comprises a first adhesive layer 21, a low-refractive-index layer 22, a substrate 24 used in actual application, and a second adhesive layer 23 from the light guide plate 10 side. The porosity of the low-refractive-index layer 22 is, for example, 40% by volume or more. The storage modulus of the first adhesive layer at 23°C is, for example, 1.0 × 10⁻⁶. 5 (Pa)~1.0×10 7 (Pa), the storage modulus of the second adhesive layer at 23°C is, for example, 1.0 × 10⁻⁶. 5 (Pa) and below. By increasing the storage modulus of the first adhesive layer adjacent to the low-refractive-index layer as described above, adhesive ingress into the voids of the low-refractive-index layer can be prevented. Therefore, the refractive index of the low-refractive-index layer can be maintained at a low level, thereby preserving its effect. Furthermore, by reducing the storage modulus of the second adhesive layer, which is another adhesive layer, as described above, damage to the low-refractive-index layer caused by vibration can be suppressed. The effect of suppressing damage to the low-refractive-index layer caused by vibration is particularly significant when the optical component is used in automotive and / or recreational applications.

[0046] In one embodiment, the ratio of the thickness of the low-refractive-index layer to the total thickness of the adhesive layer present in the double-sided adhesive film is, for example, 0.10% to 5.00%, preferably 0.11% to 4.50%, and more preferably 0.12% to 4.00%. If the thickness ratio is within such a range, damage to the low-refractive-index layer caused by vibration can be suppressed more effectively. More specifically, in automotive and / or recreational applications, where significant vibrations exist not only longitudinally but also laterally, damage to the low-refractive-index layer due to lateral strength differences is particularly well suppressed.

[0047] B-2. Substrate

[0048] The substrate is typically made of a film or a plate of a resin, preferably a transparent resin. As representative examples of such a resin, thermoplastic resins, reactive resins (e.g., ionizing radiation-curable resins) can be given. As specific examples of the thermoplastic resins, polymethyl methacrylate (PMMA), polyacrylonitrile, and the like (meth)acrylic resins, polycarbonate (PC) resins, polyester resins such as PET, cellulose-based resins such as triacetyl cellulose (TAC), cyclic polyolefin-based resins, styrene-based resins can be given. As specific examples of the ionizing radiation-curable resins, epoxy acrylate-based resins, urethane acrylate-based resins can be given. These resins can be used alone or in combination of two or more.

[0049] The thickness of the substrate is, for example, 10 μm to 100 μm, preferably 10 μm to 50 μm.

[0050] The refractive index of the substrate is preferably 1.47 or more, more preferably 1.47 to 1.60, further preferably 1.47 to 1.55. If it is in such a range, the image display unit can be introduced without adversely affecting the light guided from the light guide plate.

[0051] B-3. Low-refractive layer

[0052] The low-refractive layer typically has voids inside. The void fraction of the low-refractive layer is, as described above, 40 vol% or more, typically 50 vol% or more, preferably 70 vol% or more, more preferably 80 vol% or more. On the other hand, the void fraction is, for example, 90 vol% or less, preferably 85 vol% or less. By making the void fraction in the above range, the refractive index of the low-refractive layer can be brought to an appropriate range. The void fraction is a value calculated from the value of the refractive index measured using an ellipsometer by using Lorentz-Lorenz's equation.

[0053] The refractive index of the low-refractive layer is preferably 1.30 or less, more preferably 1.20 or less, further preferably 1.15 or less. The lower limit of the refractive index can be, for example, 1.01. If it is in such a range, very excellent light use efficiency can be achieved in the laminated structure of the light guide plate obtained via the optical laminate of the double-sided adhesive layer and the surrounding member. Unless otherwise specified, the refractive index refers to the refractive index measured at a wavelength of 550 nm. The refractive index is a value measured by the method described in "(1) Refractive index of low-refractive layer" in the following Examples.

[0054] The low-refractive-index layer can employ any appropriate configuration as long as it has the above-described desired void ratio and refractive index. The low-refractive-index layer can be preferably formed by coating or printing, or the like. As a material constituting the low-refractive-index layer, for example, the materials described in International Publication No. 2004 / 113966, Japanese Patent Application Publication No. 2013-254183, and Japanese Patent Application Publication No. 2012-189802 can be employed. Specifically, for example, the following can be mentioned: a silicon dioxide-based compound; a hydrolyzable silane-based compound, and a partial hydrolyzate and a dehydration condensate thereof; an organic polymer; a silane alcohol group-containing silicon compound; active silica obtained by bringing a silicate with an acid, an ion exchange resin; a polymerizable monomer (for example, a (meth)acrylic monomer, and a styrene monomer); a curable resin (for example, a (meth)acrylic resin, a fluorine-containing resin, and a urethane resin); and a combination thereof. The low-refractive-index layer can be formed by coating or printing, or the like, of a solution or a dispersion of such a material.

[0055] The size of the voids (pores) in the low-refractive-index layer refers to the diameter of the long axis of the voids (pores) and the diameter of the short axis. The size of the voids (pores) is, for example, 2 nm to 500 nm. The size of the voids (pores) is, for example, 2 nm or more, preferably 5 nm or more, more preferably 10 nm or more, and further preferably 20 nm or more. On the other hand, the size of the voids (pores) is, for example, 500 nm or less, preferably 200 nm or less, and more preferably 100 nm or less. The size of the voids (pores) is, for example, in the range of 2 nm to 500 nm, preferably 5 nm to 500 nm, more preferably 10 nm to 200 nm, and further preferably 20 nm to 100 nm. The size of the voids (pores) can be adjusted to a desired size according to the purpose and use, or the like. The size of the voids (pores) can be quantified by the BET test method.

[0056] The size of the voids (pores) can be quantified by the BET test method. Specifically, 0.1 g of a sample (the formed void layer) is put in a capillary of a specific surface area measuring device (manufactured by Micromeritics Corporation: ASAP2020), and the gas in the void structure is degassed by performing 24-hour reduced pressure drying at room temperature. Then, the adsorption isotherm is plotted by adsorbing nitrogen to the above sample, and the fine pore distribution is calculated. Thus, the void size can be evaluated.

[0057] The haze of the low-refractive-index layer is, for example, less than 5%, and preferably less than 3%. On the other hand, the haze is, for example, 0.1% or more, and preferably 0.2% or more. The range of the haze is, for example, 0.1% or more and less than 5%, and preferably 0.2% or more and less than 3%. The haze can be measured by the method described below, for example. Note that the haze is an index of the transparency of the low-refractive-index layer.

[0058] The void layer (low refractive index layer) was cut to a size of 50 mm x 50 mm, and set in a haze meter (manufactured by Murakami Color Research Laboratory Co., Ltd.: HM-150), and the haze was measured. The haze value was calculated by the following formula.

[0059] Haze (%) = [Diffuse transmittance (%) / Total light transmittance (%) ] x 100 (%)

[0060] As the low refractive index layer having a void inside as described above, for example, a low refractive index layer having a porous layer and / or an air layer in at least a part thereof can be given. The porous layer typically contains an aerogel, and / or a particle (for example, a hollow particle and / or a porous particle). The low refractive index layer can preferably be a nanoporous layer (specifically, a porous layer in which 90% or more of the micropores have a diameter in the range of 10 -1 nm to 10 3 nm).

[0061] As the particle, any appropriate particle can be used. The particle is typically formed of a silica-based compound. As the shape of the particle, for example, a spherical shape, a plate shape, a needle shape, a string shape, and a grape cluster shape can be given. As the string-shaped particle, for example, a particle in which a plurality of particles having a spherical shape, a plate shape, or a needle shape are connected in a rosary shape; a short fiber-shaped particle (for example, a short fiber-shaped particle described in Japanese Patent Application Laid-Open No. 2001-188104), and a combination thereof can be given. The string-shaped particle can be a straight chain shape or a branched shape. As the grape cluster-shaped particle, for example, a particle in which a plurality of spherical, plate, and needle-shaped particles are agglomerated into a grape cluster shape can be given. The shape of the particle can be confirmed by observation using, for example, a transmission electron microscope.

[0062] The thickness of the low refractive index layer is preferably in the range of 0.2 μm to 5 μm, and more preferably in the range of 0.3 μm to 3 μm. If the thickness of the low refractive index layer is in this range, the damage prevention effect of the present application becomes significant. Furthermore, the above-described desired thickness ratio can be easily achieved.

[0063] Hereinafter, an example of a specific configuration of the low refractive index layer will be described. The low refractive index layer of the present embodiment contains one or more structural units that form a fine void structure, and the structural units are chemically bound together by catalysis. As the shape of the structural unit, for example, a particle shape, a fiber shape, a rod shape, and a flat plate shape can be given. The structural unit can have only one shape, or can have two or more shapes in combination. Hereinafter, the case in which the low refractive index layer is a void layer of a porous body in which the above-described microporous particles are chemically bound together will be mainly described.

[0064] Such a void layer can be formed by, for example, causing the microporous particles to chemically bond to each other in the void layer forming step. Note that in the embodiments of the present application, the shape of the "particles" (e.g., the microporous particles described above) is not particularly limited, and can be, for example, spherical or another shape. In addition, in the embodiments of the present application, the microporous particles described above can be, for example, sol-gel bead-like particles, nanoparticles (hollow nanosilica / nano hollow sphere particles), nanofibers, or the like. The microporous particles typically include an inorganic substance. As specific examples of the inorganic substance, silicon (Si), magnesium (Mg), aluminum (Al), titanium (Ti), zinc (Zn), and zirconium (Zr) can be given. These can be used alone or in combination with two or more. In one embodiment, the microporous particles described above are, for example, microporous particles of a silicon compound, and the porous body described above is, for example, a silicone porous body. The microporous particles of the silicon compound include, for example, a pulverized body of a gel-like silica compound. In addition, as other forms of the low-refractive layer having a porous layer and / or an air layer in at least a portion thereof, for example, a void layer formed of a fibrous substance such as a nanofiber, the fibrous substance being entangled with each other to form voids and form a layer can be given. The manufacturing method of such a void layer is not particularly limited, and is the same as in the case of the void layer of the porous body in which the microporous particles described above are chemically bonded to each other, for example. Furthermore, as other forms, a void layer using hollow nanoparticles, a nanoclay, a void layer using hollow nanohollow spheres, magnesium fluoride can be given. The void layer can be a void layer formed of a single constituent substance or a void layer formed of a plurality of constituent substances. The void layer can be constituted of a single form described above or can be constituted of a plurality of forms described above.

[0065] In the present embodiment, the porous structure of the porous body can be, for example, a continuous bubble structure in which the pore structures are continuous. In the case of a continuous bubble structure, for example, in the above-described silicone porous body, it refers to a state in which the pore structures are three-dimensionally connected, and can also be said to be a state in which the internal voids of the pore structures are continuous. By providing the porous body with a continuous bubble structure, the void ratio can be increased. On the other hand, in the case of using individual bubble particles (particles each having a pore structure) such as hollow silica, it is not possible to form a continuous bubble structure. On the other hand, in the case of using, for example, silica gel particles (pulverized products of a gel-like silicon compound that forms a sol), since the particles have a three-dimensional dendritic structure, the dendritic particles can settle and deposit in a coating film (a coating film of a sol containing pulverized products of a gel-like silicon compound), and thus a continuous bubble structure can be easily formed. The low-refractive-index layer more preferably has a monolithic structure in which a plurality of pore distributions are included. The monolithic structure refers to a hierarchical structure, which includes, for example, a structure in which nano-sized fine voids are present, and a continuous bubble structure in which such nano voids are aggregated. In the case of forming a monolithic structure, for example, the fine voids can be used to impart strength to the film, and the coarse continuous bubble voids can be used to impart a high void ratio, so that both the film strength and the high void ratio can be achieved. Such a monolithic structure is preferably formed by controlling the pore distribution of the void structure generated in a gel (a gel-like silicon compound) in a stage prior to pulverization into silica gel particles. In addition, for example, by controlling the particle size distribution of the silica gel particles after pulverization to be a desired size when the gel-like silicon compound is pulverized, a monolithic structure can be formed.

[0066] The low-refractive-index layer contains, for example, as described above, pulverized products of a gel-like compound, and the pulverized products are chemically bonded to each other. The form of the chemical bonding (chemical bond) of the pulverized products to each other in the low-refractive-index layer is not particularly limited, and examples thereof include a cross-linking bond, a covalent bond, and a hydrogen bond.

[0067] The volume average particle diameter of the above-described pulverized products in the low-refractive-index layer is, for example, 0.10 μm or more, preferably 0.20 μm or more, and more preferably 0.40 μm or more. On the other hand, the volume average particle diameter is, for example, 2.00 μm or less, preferably 1.50 μm or less, and more preferably 1.00 μm or less. The range of the volume average particle diameter is, for example, 0.10 μm to 2.00 μm, preferably 0.20 μm to 1.50 μm, and more preferably 0.40 μm to 1.00 μm. The particle size distribution can be measured by, for example, a particle size distribution evaluation device such as a dynamic light scattering method, a laser diffraction method, and the like, and an electron microscope such as a scanning electron microscope (SEM), a transmission electron microscope (TEM), and the like. Note that the volume average particle diameter is an index of the deviation of the particle size of the pulverized products.

[0068] The type of the gel-like compound is not particularly limited. As the gel-like compound, for example, a gel-like silicon compound can be given.

[0069] In addition, in the low refractive index layer (void layer), for example, it is preferable that silicon atoms contained form siloxane bonds. As a specific example, the proportion of unbound silicon atoms (i.e., residual silanol) among all silicon atoms contained in the void layer is, for example, less than 50%, preferably 30% or less, and more preferably 15% or less.

[0070] Hereinafter, an example of a method of forming such a low refractive index layer will be described.

[0071] Typically, the method includes a precursor forming step of forming a precursor of a void structure as a low refractive index layer (void layer) on a resin film, and a cross-linking reaction step of inducing a cross-linking reaction inside the precursor after the precursor forming step. The method further includes a containing liquid preparation step of preparing a containing liquid (hereinafter sometimes referred to as a "microparticle-containing liquid" or simply a "containing liquid") containing microparticles, and a drying step of drying the containing liquid, in which the microparticles in the dried body are chemically bonded to each other to form the precursor in the precursor forming step. The containing liquid is not particularly limited, and is, for example, a suspension containing microparticles. Note that, hereinafter, a case in which the microparticles are a pulverized product of a gel-like compound and the void layer contains a porous body (preferably, a silicone porous body) of the pulverized product of the gel-like compound will be mainly described. Note that, in a case other than the case in which the microparticles are a pulverized product of a gel-like compound, a low refractive index layer can also be formed in the same manner.

[0072] According to the above-described method, a low refractive index layer (void layer) having, for example, a very low refractive index can be formed. The reason therefor can be inferred as follows, for example. However, this inference is not limiting on the method of forming a low refractive index layer.

[0073] The above-described pulverized product is obtained by pulverizing a gel-like silicon compound, and thus the three-dimensional structure of the gel-like silicon compound before pulverization is formed in a state of being dispersed in a three-dimensional basic structure. Further, in the above-described method, by applying the pulverized product of the gel-like silicon compound to a resin film, a precursor of a porous structure based on the three-dimensional basic structure can be formed. That is, according to the above-described method, a new porous structure (three-dimensional basic structure) based on the application of the pulverized product, which is different from the three-dimensional structure of the gel-like silicon compound, can be formed. Thus, in the finally obtained void layer, a low refractive index that functions to the same extent as an air layer, for example, can be achieved. In addition, in the above-described method, the pulverized products are chemically bonded to each other, and thus the three-dimensional basic structure can be immobilized. Thus, although the finally obtained void layer is a structure having voids, sufficient strength and flexibility can be maintained.

[0074] The detailed circumstances of the specific configuration of the low refractive index layer and the method of forming the same are described in, for example, International Publication No. 2019 / 151073. The description of this publication is incorporated herein by reference.

[0075] B-4. First Adhesive Layer

[0076] The first adhesive layer has a hardness such that the adhesive constituting the first adhesive layer will not penetrate into the voids of the low refractive index layer under normal conditions. As described above, the storage modulus of the first adhesive layer at 23°C is 1.0 × 10⁻⁶. 5 (Pa)~1.0×10 7 (Pa), for example, 1.1 × 10 5 (Pa) or above, 1.2×10 5 (Pa) or above, 1.3×10 5 (Pa) or above, 1.4×10 5 (Pa) or above, 1.5×10 5 (Pa) or above, 1.6×10 5 (Pa) or above, 1.7×10 5 (Pa) or above, 1.8×10 5 (Pa) or above, 1.9×10 5 (Pa) or above or 2.0×10 5 (Pa) or higher, and 1.0 × 10 7 (Pa) below, 5.0×10 6 (Pa) or less, 1.0×10 6 (Pa) or below or 5.0×10 5 (Pa) or less, preferably 1.3 × 10 5 (Pa)~1.0×10 6 (Pa), more preferably 1.5 × 10 5 (Pa)~5.0×10 5 (Pa). The storage modulus is determined as follows: based on the method described in JIS K7244-1 "Plastics - Test method for dynamic mechanical properties", the measurement is performed at a frequency of 1 Hz in the range of -50℃ to 150℃ at a heating rate of 5℃ / min, and the value at 23℃ is read.

[0077] As the adhesive constituting the first adhesive layer, any appropriate adhesive having the characteristics described above can be used. As the adhesive, an acrylic adhesive (acrylic adhesive composition) can be typically cited. The acrylic adhesive composition typically contains a (meth)acrylic polymer as a main component (base polymer). In the solid content of the adhesive composition, the (meth)acrylic polymer may, for example, be contained in the adhesive composition at a rate of 50% by weight or more, preferably 70% by weight or more, and more preferably 90% by weight or more. The (meth)acrylic polymer contains an alkyl (meth)acrylate as a monomer unit as a main component. Note that the (meth)acrylate refers to an acrylate and / or a methacrylate. As the alkyl group of the alkyl (meth)acrylate, a linear or branched alkyl group having 1 to 18 carbon atoms can be cited, for example. The average number of carbon atoms of the alkyl group is preferably 3 to 9. As the monomer constituting the (meth)acrylic polymer, in addition to the alkyl (meth)acrylate, a carboxyl group-containing monomer, a hydroxyl group-containing monomer, an amide group-containing monomer, an aromatic ring-containing (meth)acrylate, a heterocyclic ring-containing (meth)acrylate, and the like can be cited as a copolymerizable monomer. The copolymerizable monomer is preferably a hydroxyl group-containing monomer and / or a heterocyclic ring-containing (meth)acrylate, and more preferably an N-acryloylmorpholine. The acrylic adhesive composition can preferably contain a silane coupling agent and / or a crosslinking agent. As the silane coupling agent, an epoxy group-containing silane coupling agent can be cited, for example. As the crosslinking agent, an isocyanate-based crosslinking agent, a peroxide-based crosslinking agent, and the like can be cited, for example. Details of such an adhesive layer or acrylic adhesive composition are described in, for example, Japanese Patent No. 4140736, the disclosure of which is incorporated herein by reference.

[0078] The thickness of the first adhesive layer is preferably 3 μm to 30 μm, and more preferably 5 μm to 10 μm. If the thickness of the first adhesive layer is in this range, the following advantages are obtained: sufficient adhesion is obtained, and the influence of the adhesive layer thickness on the overall thickness is small. Furthermore, the desired thickness ratio described above can be easily achieved.

[0079] B-5. Second Adhesive Layer

[0080] The second adhesive layer is formed of any appropriate adhesive. In one embodiment, the second adhesive layer is formed of an adhesive having flexibility that can absorb the transmission of vibrations to suppress breakage of the low refractive index layer. As described above, the storage modulus of the second adhesive layer at 23°C is, for example, 1.0 x 10 5 (Pa) or less, for example, 1.0 x 10 5 (Pa) or less, 9.5 x 10 4 (Pa) or less, 9.0 x 10 4 (Pa) or less, 8.5 x 104 (Pa) below, 8.0×10 4 (Pa) below, 7.5×10 4 (Pa) or below, or 7.0×10 4 (Pa) or less, and 1.0 × 10 3 (Pa) or above, 5.0×10 3 (Pa) or above, 1.0×10 4 (Pa) or above, or 5.0 × 10 4 (Pa) or higher, preferably 5.0 × 10⁻⁶. 3 (Pa)~9.0×10 4 (Pa) or less, more preferably 1.0 × 10 4 (Pa)~8.5×10 4 (Pa).

[0081] As the adhesive constituting the second adhesive layer, any suitable adhesive can be used as long as it has the properties described above. Acrylic adhesives (acrylic adhesive compositions) are representative examples of adhesives. Acrylic adhesive compositions are as described in section B-4 above. However, the adhesive constituting the second adhesive layer preferably does not contain heterocyclic (meth)acrylates as comonomers. Furthermore, the weight-average molecular weight (Mw) of the base polymer in the adhesive composition is preferably 2,000,000 or less, more preferably 5,000 to 1,600,000. Details of the second adhesive layer or the acrylic adhesive composition constituting the second adhesive layer are described, for example, in Japanese Patent Application Laid-Open No. 2016-190996, the contents of which are incorporated herein by reference.

[0082] The thickness of the second adhesive layer is preferably 5 μm to 300 μm, more preferably 10 μm to 200 μm. If the thickness of the second adhesive layer is within this range, it can mitigate impact and reduce damage to the low-refractive-index layer, especially during lateral vibration, and can reduce strain within the structure generated during image display device assembly. As a result, it can reduce brightness unevenness during image display. Furthermore, the aforementioned desired thickness ratio can be easily achieved.

[0083] C. Backlight unit

[0084] The optical components described in items A and B above can be applied to backlight units (especially edge-lit backlight units). Therefore, embodiments of the present invention also include such backlight units. Figure 3is a cross-sectional view of a backlight unit according to an embodiment of the present application. The backlight unit 200 includes a light source 120, the optical member 100 described in items A and B disposed opposite the light source 120 on an end surface 10a of the light guide plate 10, and a housing 140 that houses the light source 120 and the optical member 100.

[0085] The light source 120 is disposed opposite the end surface 10a of the light guide plate on one end portion side of the light guide plate 10. Thus, the backlight unit is typically an edge light type. The light source 120 is typically surrounded by a reflector not shown. As the light source, any appropriate configuration can be used. As specific examples, a light emitting diode (LED), a cold cathode fluorescent lamp (CCFL), an external electrode fluorescent lamp (EEFL), and a hot cathode fluorescent lamp (HCFL) can be used. In one embodiment, an LED light source can be used. The LED light source can typically be configured by arranging LEDs (point light sources) in a row.

[0086] The housing 140 has a front portion 141 and a back portion 142, and houses the light source 120 and the optical member 100. The back portion 142 is a box shape open on the upper side (front side), and the front portion 141 protrudes inward from the back portion on a pair of end portions opposite the back portion 142. The front portion 141 is typically integrated with the back portion 142 by being bonded thereto. With this configuration, the housing 140 can house the optical member 100.

[0087] D. Image display device

[0088] The backlight unit of item C described above can be applied to an image display device (e.g., a liquid crystal display, etc.). Thus, embodiments of the present application also include such an image display device. The image display device includes the backlight unit described in item C, and an image display panel disposed on the light exit surface side of the light guide plate.

[0089] Embodiments

[0090] The present application will be specifically described below by way of examples, but the present application is not limited to these examples. Note that the measurement methods of each characteristic are described below. Also, unless otherwise specified, "%" and "parts" in the examples are based on weight.

[0091] (1) Refractive index of low refractive layer

[0092] After forming the low refractive index layer on the acrylic film, it was cut into a size of 50 mm x 50 mm, and was attached to the surface of a glass plate (thickness: 3 mm) with an adhesive layer interposed therebetween. The central portion (diameter of about 20 mm) of the back surface of the glass plate was painted over with a black marker, and a sample was obtained in which no reflection occurred on the back surface of the glass plate. The sample was set in an ellipsometer (manufactured by J. A. Woollam Japan, Inc.: VASE), and the refractive index was measured at a wavelength of 550 nm and an incident angle of 50 to 80 degrees.

[0093] (2) Uniformity of luminance

[0094] The backlight units obtained in the examples and comparative examples were lit, and the uniformity of luminance was confirmed by visual observation. The evaluation was performed according to the following criteria.

[0095] O: uniform luminance throughout

[0096] X: light leakage was confirmed, and the luminance was not uniform.

[0097] [Production Example 1] Preparation of coating liquid for forming low refractive index layer

[0098] (1) Gelation of silicon compound

[0099] A mixed liquid A was prepared by dissolving 0.95 g of methyltrimethoxysilane (MTMS) as a precursor of a silicon compound in 2.2 g of dimethyl sulfoxide (DMSO). To the mixed liquid A, 0.5 g of an oxalic acid aqueous solution at 0.01 mol / L was added, and stirring was performed at room temperature for 30 minutes, whereby the MTMS was hydrolyzed to produce a mixed liquid B containing a trihydroxymethylsilane.

[0100] After 0.38 g of 28% by weight ammonia water and 0.2 g of pure water were added to 5.5 g of DMSO, the above mixed liquid B was further added, and stirring was performed at room temperature for 15 minutes, whereby the trihydroxymethylsilane was gelled to produce a mixed liquid C containing a gelled silicon compound.

[0101] (2) Ripening treatment

[0102] The mixed liquid C containing a gelled silicon compound, which was prepared as described above, was directly incubated at 40°C for 20 hours, and a ripening treatment was performed.

[0103] (3) Pulverization treatment

[0104] Next, the gelled silicon compound subjected to the maturation treatment as described above was crushed into a granular shape of several mm to several cm in size with a spatula. Next, 40 g of isopropyl alcohol (IPA) was added to the mixed solution C, and after gentle stirring, the gel was allowed to stand at room temperature for 6 hours to perform a solvent and catalyst decantation. Solvent replacement was performed by repeating the same decantation treatment three times, and a mixed solution D was obtained. Next, the gelled silicon compound in the mixed solution D was subjected to a pulverization treatment (high-pressure medium-free pulverization). The pulverization treatment (high-pressure medium-free pulverization) was performed using a homogenizer (SMT Co., Ltd., trade name "UH-50") for 2 minutes at 50 W and 20 kHz after weighing 1.85 g of the gelled compound in the mixed solution D and 1.15 g of IPA in a 5-cc screw bottle.

[0105] The gelled silicon compound in the mixed solution D was pulverized by this pulverization treatment, and thus the mixed solution D' became a sol liquid of the pulverized product. The volume average particle diameter representing the particle size deviation of the pulverized product contained in the mixed solution D' was confirmed by a dynamic light scattering type nano-trace particle size analyzer (Upa-EX150 type, manufactured by Nikkiso Co., Ltd.), and the result was 0.50 to 0.70. Further, 0.062 g of a 1.5% by weight concentration MEK (methyl ethyl ketone) solution of a photobase generator (Wako Pure Chemical Industries, Ltd.: trade name WPBG266) and 0.036 g of a 5% concentration MEK solution of bis(trimethoxysilyl)ethane were added to 0.75 g of the sol liquid (mixed solution C') at a ratio of 1.5% by weight of the photobase generator and 5% by weight of bis(trimethoxysilyl)ethane, and a coating liquid for a low-refractive layer was obtained.

[0106] [Manufacturing Example 2] Preparation of an adhesive constituting a first adhesive layer

[0107] In a four-necked flask equipped with a stirring blade, a thermometer, a nitrogen gas introducing tube, and a condenser, 90.7 parts of butyl acrylate, 6 parts of N-acryloylmorpholine, 3 parts of acrylic acid, 0.3 parts of 2-hydroxybutyl acrylate, and 0.1 part by weight of 2,2'-azobisisobutyronitrile as a polymerization initiator were added together with 100 g of ethyl acetate, and nitrogen gas was introduced while slowly stirring to perform nitrogen gas replacement. After the liquid temperature in the flask was maintained at around 55°C, a polymerization reaction was performed for 8 hours to prepare an acrylic polymer solution. With respect to 100 parts of the solid content of the obtained acrylic polymer solution, 0.2 parts of an isocyanate crosslinking agent (CORONATE L manufactured by Japan Polyurethane Industries, Inc., an adduct of trimethylolpropane with toluene diisocyanate), 0.3 parts of benzoyl peroxide (NYPER BMT manufactured by NOF Corporation), and 0.2 parts of γ-glycidoxypropylmethoxysilane (KBM-403 manufactured by Shin-Etsu Chemical Co., Ltd.) were mixed to prepare an acrylic adhesive solution. Next, the acrylic adhesive solution was applied to one side of a polyethylene terephthalate (PET) film (manufactured by Mitsubishi Chemical Polyester Film Co., Ltd., thickness: 38 μm) on which a silicone treatment had been performed, in such a manner that the thickness of the dried adhesive layer would be 20 μm, and drying was performed at 150°C for 3 minutes to form an adhesive layer. The storage modulus of the obtained adhesive was 1.3 x 104Pa. 5 Pa.

[0108] [Manufacturing Example 3] Preparation of an adhesive constituting a second adhesive layer

[0109] In a four-necked flask equipped with a stirring blade, a thermometer, a nitrogen gas introducing tube, and a condenser, 99 parts of butyl acrylate, 1 part of 4-hydroxybutyl acrylate, 0.1 part of 2,2'-azobisisobutyronitrile as a polymerization initiator, and 100 parts of ethyl acetate were added, and nitrogen gas was introduced while slowly stirring to perform nitrogen gas replacement. After that, the liquid temperature in the flask was maintained at about 55°C, and a polymerization reaction was performed for 8 hours to prepare a solution of an acrylic polymer. With respect to 100 parts of the solid content of the obtained acrylic polymer solution, 0.1 part of an isocyanate crosslinking agent (Takenate D110N manufactured by Mitsui Takeda Chemical Co., Ltd., trimethylolpropane xylylenediisocyanate), 0.1 part of benzoyl peroxide (NYPER BMT manufactured by NOF Corporation), and 0.2 part of γ-glycidoxypropylmethoxysilane (KBM-403 manufactured by Shin-Etsu Chemical Co., Ltd.) were mixed to prepare a solution of an acrylic adhesive composition. Next, the solution of the acrylic adhesive composition was applied to one side of a polyethylene terephthalate film (separator: MRF38 manufactured by Mitsubishi Chemical Polyester Film Co., Ltd.) that had been treated with a silicone-based releasing agent, and drying was performed at 150°C for 3 minutes to form an adhesive layer having a thickness of 20 μm on the surface of the separator. The storage modulus of the obtained adhesive was 8.2 x 104Pa. 4 Pa.

[0110] [Manufacturing Example 4] Production of Double-Sided Adhesive Film

[0111] The coating solution for low refractive index layer formation prepared in Manufacturing Example 1 was applied to a substrate (acrylic film) having a thickness of 30 μm. The wet thickness (thickness before drying) of the applied layer was about 27 μm. The applied layer was dried by being subjected to treatment at a temperature of 100°C for 1 minute to form a low refractive index layer (thickness: 0.9 μm) on the substrate. The void ratio of the obtained low refractive index layer was 56%, and the refractive index was 1.15. Next, a first adhesive layer (thickness: 10 μm) made of the adhesive prepared in Manufacturing Example 2 was formed on the surface of the low refractive index layer, and a second adhesive layer (thickness: 28 μm) made of the adhesive prepared in Manufacturing Example 3 was further formed on the surface of the substrate. In this way, a double-sided adhesive film having a structure of first adhesive layer / low refractive index layer / substrate / second adhesive layer was produced.

[0112] [Example 1]

[0113] A backlight unit was taken out from a commercially available liquid crystal display device (manufactured by KING JIM Co., Ltd., trade name "XMC10"). A light guide plate was taken out from the taken-out backlight unit (essentially a housing). On the other hand, the double-coated adhesive film obtained in Production Example 4 was cut out in such a manner that the size thereof was smaller than the size of the light guide plate and larger than the size of a light extraction pattern provided to the light guide plate. Specifically, the size of the cut-out double-coated adhesive film was 119 mm x 176.5 mm, the size of the light guide plate was 120 mm x 179 mm, and the size of the light extraction pattern (essentially the outer edge of the patterned region) was 117 mm x 173 mm. The light guide plate was attached to a commercially available reflective plate (manufactured by Toray Industries, Inc., trade name "Lumirror (registered trademark) #225E6SR") with the double-coated adhesive film cut out to the above-mentioned size interposed therebetween, to thereby obtain an optical member. At this time, the light guide plate was attached to the first adhesive layer. Note that in the attachment, neither the outer edge of the double-coated adhesive film from the outer edge of the light guide plate nor the outer edge of the light extraction pattern from the outer edge of the double-coated adhesive film was confirmed. The obtained optical member was again incorporated into the housing, to thereby produce a backlight unit. The obtained backlight unit was subjected to the evaluation described in (2) above. The results are shown in Table 1.

[0114] [Comparative Example 1]

[0115] The double-coated adhesive film was cut out to the same size as the light guide plate, and an optical member and a backlight unit were produced in the same manner as in Example 1, except for this. Note that in the attachment, the outer edge of the double-coated adhesive film from the outer edge of the light guide plate was confirmed. The obtained backlight unit was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[0116] [Comparative Example 2]

[0117] The double-coated adhesive film was cut out to the same size as the light extraction pattern, and an optical member and a backlight unit were produced in the same manner as in Example 1, except for this. Note that in the attachment, the outer edge of the light extraction pattern from the outer edge of the double-coated adhesive film was confirmed. The obtained backlight unit was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[0118] [Table 1]

[0119]

[0120] As is clear from Table 1, according to the example of the present application, by adjusting the sizes of the light guide plate, the double-coated adhesive film, and the light extraction pattern of the light guide plate, and configuring such that the outer edge of the light guide plate is located more outward than the outer edge of the double-coated adhesive film and the outer edge of the double-coated adhesive film is located more outward than the outer edge of the light extraction pattern of the light guide plate, it is possible to realize a backlight unit excellent in uniformity of brightness.

[0121] Industrial Applicability

[0122] The optical member and the backlight unit of the present application can be suitably used for a backlight unit of an image display device, particularly a liquid crystal display device.

Claims

1. An optical component comprising: A light guide plate having an incident end face from a light source, an exit face for escaping the incident light, and a light extraction pattern disposed on a side opposite to the exit face; and A reflector is attached to the light guide plate through a double-sided adhesive film. The double-sided adhesive film, starting from the light guide plate side, sequentially comprises a first adhesive layer, a low refractive index layer, and a second adhesive layer. The outer edge of the light guide plate is located further outward than the outer edge of the double-sided adhesive film, and the outer edge of the double-sided adhesive film is located further outward than the outer edge of the light extraction pattern. When the maximum value of the distance between the outer edge of the light guide plate and the outer edge of the light extraction pattern is set as A, and the maximum value of the distance between the outer edge of the light guide plate and the outer edge of the double-sided adhesive film is set as B, the relationship A > 2B is satisfied.

2. A backlight unit, comprising: light source; The optical component of claim 1, whose end face is disposed opposite to the light source; and A housing that houses the light source and the optical components.

3. An image display device, comprising: The backlight unit as described in claim 2, An image display panel disposed on the emission surface side of the light guide plate.

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