Backlight unit and image display device

Abstract

The present application provides a backlight unit with excellent uniformity of brightness. The backlight unit of the present application comprises: a light source; a light guide plate disposed opposite the light source and having an end surface on which light from the light source is incident and an exit surface through which the light after being incident is emitted; a reflection plate attached to the back surface side of the light guide plate via a double-sided adhesive film; and a housing that accommodates the light source, the light guide plate, and the reflection plate and has a front surface portion and a back surface portion. 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. The backlight unit is configured in such a manner that light from the light source is not incident between the low-refractive layer and the reflection plate, or in such a manner that light incident from the light source between the low-refractive layer and the reflection plate is not emitted from the exit surface of the light guide plate.

Description

Technical Field

[0001] This invention relates to backlight units. Background Technology

[0002] In the backlight unit of an image display device (typically a liquid crystal display device), a technique is known of laminating a light guide plate and a reflector with a low-refractive-index layer in between. According to this technique, it has been reported that by using a low-refractive-index layer in between, the light utilization efficiency is higher compared to simply using adhesives for lamination. However, even with this technique, there are still issues such as light exiting near the incident surface of the light source and insufficient uniformity of brightness.

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 10-62626 Summary of the Invention

[0006] The problem that the invention aims to solve

[0007] The present invention was made to solve the above-mentioned existing problems, and its main objective is to provide a backlight unit with excellent brightness uniformity.

[0008] Problem Solving Methods

[0009] A backlight unit according to an embodiment of the present invention includes: a light source; a light guide plate disposed opposite to the light source and having an incident end face from the light source and an exit face from which incident light exits; a reflector plate attached to the back side of the light guide plate via a double-sided adhesive film; and a housing that houses the light source, the light guide plate, and the reflector plate, and has a front portion and a back portion. The double-sided adhesive film has, in sequence from the light guide plate side, a first adhesive layer, a low-refractive-index layer, and a second adhesive layer. The backlight unit is configured such that light from the light source does not incident between the low-refractive-index layer and the reflector plate, or that light incident from the light source between the low-refractive-index layer and the reflector plate does not exit from the exit face of the light guide plate.

[0010] In one embodiment, the light source side end face of the double-sided adhesive film is substantially flush with the light source side end face of the reflector.

[0011] In one embodiment, the backlight unit has a light-shielding printed portion near the light source side end of the reflector.

[0012] In one embodiment, the backlight unit has a light-shielding part selected from a light-shielding strip, a solidified or cured coating film of a light-shielding resin solution, and a light-shielding molded body on the light source side end face of the low refractive index layer.

[0013] In one embodiment, the reflector has an extension that extends closer to the light source than the double-sided adhesive film. The extension is provided with a light-shielding part selected from a light-shielding tape, a solidified or cured coating film of a light-shielding resin solution, and a light-shielding molded body.

[0014] In one embodiment, the low-refractive-index layer and the reflector have protrusions extending closer to the light source than the light guide plate. In another embodiment, a reflective layer is further provided on the protrusion of the low-refractive-index layer.

[0015] In one embodiment, at the light source side end of the light guide plate, the double-sided adhesive film and the reflector are further away from the light source than the end face of the light guide plate to form a given gap. A light-shielding part selected from light-shielding tape, solidified or cured coating film of light-shielding resin solution, and light-shielding molded body is provided in the gap.

[0016] In one embodiment, the backlight unit forms a given gap at the light source side end of the light guide plate, where the end face of the double-sided adhesive film and the reflector is further away from the light source than the end face of the light guide plate. A protrusion with a shape suitable for the gap is provided at a position on the housing corresponding to the gap on the back side.

[0017] In one embodiment, the light source is an LED light source.

[0018] According to other aspects of the present invention, an image display device can be provided. This image display device includes: the aforementioned backlight unit, and an image display panel disposed on the emission surface side of the aforementioned light guide plate.

[0019] The effects of the invention

[0020] According to the present invention, a backlight unit with excellent brightness uniformity can be achieved by configuring a backlight unit comprising a light guide plate and a reflector bonded together by a double-sided adhesive film having a low refractive index layer in such a way that light does not incident from the light source side end face of the low refractive index layer. Attached Figure Description

[0021] Figure 1 This is a cross-sectional schematic diagram of a backlight unit according to one embodiment of the present invention.

[0022] Figure 2 It can be used Figure 1 A cross-sectional schematic diagram of the double-sided adhesive film of the backlight unit.

[0023] Figure 3(a) to (c) are partial cross-sectional schematic diagrams illustrating specific examples of the light-shielding structure in the embodiments of the present invention.

[0024] Figure 4 This is a partial cross-sectional schematic diagram illustrating another specific example of the light-shielding structure in an embodiment of the present invention.

[0025] Figure 5 (a) and (b) are partial cross-sectional schematic diagrams illustrating yet another specific example of the light-shielding structure in an embodiment of the present invention.

[0026] Symbol Explanation

[0027] 10 Light Source

[0028] 20 Light guide plates

[0029] 30. Housing

[0030] 31 Front

[0031] 32 Back side

[0032] 40 Double-sided adhesive film

[0033] 41 First adhesive layer

[0034] 42 Low Refractive Index Layer

[0035] 43 Second adhesive layer

[0036] 44 Substrate

[0037] 50 reflector

[0038] 52 Light-shielding printing layer

[0039] 60 shading part

[0040] 100 backlight units Detailed Implementation

[0041] The embodiments of the present invention will be described below, but the present invention is not limited to these embodiments.

[0042] A. Overall structure of the backlight unit

[0043] Figure 1 This is a cross-sectional schematic diagram of a backlight unit according to one embodiment of the present invention; Figure 2 It is used for Figure 1A cross-sectional schematic diagram of the double-sided adhesive film of the backlight unit is shown in the figure. The backlight unit 100 illustrated in the figure includes: a light source 10, a light guide plate 20, a housing 30, a double-sided adhesive film 40, and a reflector 50. The back side of the light guide plate 20 is bonded to the reflector 50 through the double-sided adhesive film 40. The housing 30 has a front portion 31 and a back portion 32, and houses the light source 10, the light guide plate 20, and the reflector 50. The back portion 32 is box-shaped with an opening at the top (front side), and the front portion 31 protrudes inward from the back portion at a pair of ends opposite to the back portion 32. Typically, the front portion 31 and the back portion 32 are typically bonded together. With this configuration, the housing 30 can fit the light guide plate 20 and the reflector 50. Typically, any suitable optical component (not shown) can be mounted (supported) on the front portion (the inwardly protruding portion). Examples of optical components include, for example, diffusers and prisms. Multiple diffuser sheets and / or prism sheets can be mounted. It should be noted that the housing 30 in the example figure is the rear side portion of the housing that houses the entire image display device.

[0044] The light source 10 is disposed opposite to the end face 20a of the light guide plate on one end side of the light guide plate 20. Therefore, typically, the backlight unit is an edge light. Typically, the light source 10 is surrounded by a reflector (not shown). Any suitable configuration can be used as the light source. Specific examples include light-emitting diodes (LEDs), cold cathode fluorescent lamps (CCFLs), external electrode fluorescent lamps (EEFLs), and hot cathode fluorescent lamps (HCFLs). In one embodiment, an LED light source can be used. Typically, the LED light source can be configured by arranging LEDs (point light sources) in a row.

[0045] The light guide plate 20 has an end face 20a from which light from the light source is incident and an exit face 20b from which the incident light exits. The end face 20a of the light guide plate 20 is disposed opposite to the light source 10. More specifically, the light guide plate 20 guides light to the end side opposite to the end face 20a while internally reflecting light incident from the light source 10, and slowly emits light from the exit face 20b during this light guiding process. Typically, an exit pattern is provided on the exit face 20b. Examples of exit patterns include, for example, a concave-convex shape. Furthermore, typically, a light extraction pattern is provided on the side of the light guide plate opposite to the exit face. Examples of light extraction patterns include, for example, a white dot. It should be noted that any suitable configuration can be used as the light guide plate. As for the material constituting the light guide plate, any suitable material can be used as long as it can efficiently guide the light irradiated from the light source. Examples of materials constituting the light guide plate include acrylic resins such as polymethyl methacrylate (PMMA), polycarbonate (PC) resin, polyethylene terephthalate (PET) resin, and styrene resin. In one embodiment, the back side of the light guide plate 20 can be attached to a flexible printed circuit board for a light source via any suitable mechanism (e.g., adhesive tape).

[0046] The double-sided adhesive film 40 has, sequentially from the light guide plate 20 side, a first adhesive layer 41, a low refractive index layer 42, and a second adhesive layer 43. In practical use, a substrate 44 is disposed between the first adhesive layer 41 and the low refractive index layer 42. More specifically, the low refractive index layer 42 can be formed on the surface of the substrate 44, and the first adhesive layer 41 and the second adhesive layer 43 are disposed on both sides of the laminate of the substrate 44 and the low refractive index layer 42.

[0047] As the reflector 50, any suitable reflector can be used. For example, the reflector can be a specular reflector or a diffuse reflector. Specific examples of reflectors include resin sheets with high reflectivity (e.g., acrylic sheets), thin metal sheets or foils such as aluminum or stainless steel, vapor-deposited sheets with aluminum, silver, etc., deposited on a substrate such as a polyester resin film, laminates of a substrate such as a polyester resin film and metal foils such as aluminum, and resin films with pores (voids) formed inside. By providing the reflector 50, the light utilization efficiency of the backlight unit can be improved.

[0048] In embodiments of the present invention, the backlight unit 100 is configured such that light from the light source does not incident between the low-refractive-index layer 42 and the reflector 50, or such that light incident from the light source between the low-refractive-index layer 42 and the reflector 50 does not exit from the exit surface 20b of the light guide plate 20. In this specification, such a configuration is referred to as a "light-shielding structure." By providing a light-shielding structure, light leakage near the incident surface of light from the light source can be significantly suppressed, resulting in a backlight unit with excellent brightness uniformity.

[0049] The light-shielding structure and the double-sided adhesive film 40 will be described in detail below.

[0050] B. Light-shielding structure

[0051] Figure 3 (a)~ Figure 3 (c) are partial cross-sectional schematic diagrams illustrating specific examples of the light-shielding structure. Figure 3 (a) and Figure 3 In the example shown in (b), the light source side end face of the double-sided adhesive film 40 is substantially flush with the light source side end face of the reflector 50 (i.e., the end faces are in the same position).

[0052] exist Figure 3 In the example shown in (a), a light-shielding printing portion 52 is provided near the light source side end of the reflector 50. The light-shielding printing layer is typically a solid colored layer, preferably a black colored layer. The total light transmittance of the light-shielding printing layer with a thickness of 3 μm to 5 μm is preferably 0.01% or less, more preferably 0.008% or less. The lower the total light transmittance of the light-shielding printing layer, the more preferred it is; its lower limit can be, for example, 0.001%. When the total light transmittance of the light-shielding printing layer is within such a range, excellent light-shielding function can be achieved. The thickness of the light-shielding printing layer is preferably 3 μm to 5 μm. With such a thickness, it is easy to achieve the desired total light transmittance (resulting in light-shielding function) by appropriately selecting the constituent materials.

[0053] A light-blocking printed layer can be formed by any suitable printing method using any appropriate ink or coating. Specific examples of printing methods include: gravure printing, offset printing, screen printing, and transfer printing from transfer sheets.

[0054] Typically, the inks or coatings used contain binders, colorants, solvents, and any suitable additives that may be used as needed. Examples of binders include: chlorinated polyolefins (e.g., chlorinated polyethylene, chlorinated polypropylene), polyester resins, urethane resins, acrylic resins, vinyl acetate resins, vinyl chloride-vinyl acetate copolymers, and cellulose resins. The binder resin can be used alone or in combination of two or more. In one embodiment, the binder resin is a thermopolymerizable resin. Compared to photopolymerizable resins, thermopolymerizable resins require less dosage, thus allowing for a greater dosage of colorant (colorant content in the colored layer). As a result, particularly in the case of forming a black colored layer, a colored layer with very low total light transmittance and excellent light-blocking function can be formed. In one embodiment, the binder resin is a (meth)acrylic resin, preferably an acrylic resin containing a polyfunctional monomer (e.g., pentaerythritol triacrylate) as a copolymer component. By using an acrylic resin containing a polyfunctional monomer as a copolymer component, a colored layer with a suitable elastic modulus can be formed.

[0055] As colorants, any suitable colorant can be used depending on the purpose. Specific examples of colorants include: inorganic pigments such as titanium dioxide, zinc oxide, carbon black, iron black, iron oxide red, molybdenum chrome red, ultramarine, cobalt blue, chrome yellow, and titanium yellow; organic pigments or dyes such as phthalocyanine blue, indanthrene blue, isoindolinone yellow, benzidine yellow, quinacridone red, polyazo red, dinaphthalene-containing benzene red, and aniline black; metallic pigments containing flake-like foils of aluminum, brass, etc.; and pearlescent pigments (pearl pigments) containing flake-like foils of titanium dioxide coated with mica, basic lead carbonate, etc. In the case of forming a black colored layer, carbon black, iron black, and aniline black can be used appropriately. In this case, it is preferable to use colorants in combination. The reason is that they can form a colored layer that absorbs visible light uniformly over a wide range without color (i.e., completely black). For example, in addition to the colorants mentioned above, azo compounds and / or quinone compounds can be used. In one embodiment, the colorant contains carbon black as the main component and other colorants (e.g., azo compounds and / or quinone compounds). With this configuration, a colorless coloring layer with excellent stability over time can be formed. In the case of forming a black coloring layer, the colorant can be used in a ratio preferably 50 to 200 parts by weight relative to 100 parts by weight of the binder resin. In this case, the carbon black content in the colorant is preferably 80% to 100%. By using the colorant (especially carbon black) in such a ratio, a coloring layer with very low total light transmittance and excellent stability over time can be formed.

[0056] exist Figure 3In the example shown in (b), a light-shielding portion 60 is provided on the light-source side end face of the low-refractive-index layer 42. The light-shielding portion 60 only needs to be optically provided on the light-source side end face of the low-refractive-index layer 42; practically, it can be provided on the light-source side end face of the double-sided adhesive film 40 (or a double-sided adhesive film other than the first adhesive layer), or on the light-source side end face of the double-sided adhesive film 40 (or a double-sided adhesive film other than the first adhesive layer) and the light-source side end face of the reflector 50. Examples of light-shielding portions 60 include: light-shielding strips, solidified or cured films of light-shielding resin solutions, and light-shielding molded bodies. Typically, a light-shielding strip has a light-shielding substrate and an adhesive layer or bonding agent layer. Typically, the light-shielding substrate is a resin film containing a colorant. As the colorant, a resin film containing a colorant can be used. Figure 3 (a) illustrates the colorant. Typically, the light-shielding substrate is a black band. In one embodiment, the solidified or cured film of the light-shielding resin solution coating is the same as the light-shielding printed layer described above. The light-shielding resin solution can, for example, be the ink or coating that forms the light-shielding printed layer described above. In another embodiment, the light-shielding resin solution may contain any suitable thermoplastic resin as a binder. Due to the formation location, the light-shielding portion is formed by coating and solidifying or curing such ink or coating without printing. As the name suggests, the light-shielding molded body is a molded body of the light-shielding resin. Typically, the light-shielding resin comprises a base resin (binder) and a colorant. The light-shielding molded body can, for example, be a box-shaped or plate-shaped object. The total light transmittance of the light-shielding portion at a thickness of 3 μm to 5 μm is the same as described above, preferably 0.01% or less, more preferably 0.008% or less. The lower the total light transmittance of the light-shielding portion, the more preferred it is; its lower limit can be, for example, 0.001%.

[0057] exist Figure 3 In the example shown in (c), the reflector 50 has an extension 54 that extends closer to the light source than the double-sided adhesive film 40, and a light-shielding part 60 is provided in the extension 54.

[0058] Figure 4 This is a partial cross-sectional schematic diagram illustrating another specific example of a light-shielding structure. Figure 4In the example shown, the low-refractive-index layer 42 and the reflector 50 have protrusions extending closer to the light source than the light guide plate 20. Optically, it is sufficient for the low-refractive-index layer 42 to have protrusions; however, structurally, as shown in the example, the substrate 44, the second adhesive layer 43, and the reflector 50 can also have protrusions to support the protrusions of the low-refractive-index layer 42. Preferably, the protrusions extend to a position corresponding to the emitting surface of the light source (e.g., an LED). More preferably, as shown, a reflective layer 70 is provided at the protrusions. With such a structure, light emitted from the light source can be reflected by the low-refractive-index layer, thus preventing light from incident on the adhesive layer and the substrate. It should be noted that the details of the reflective layer 70 will be described below.

[0059] exist Figure 4 In the example shown, as described above, a reflective layer 70 is preferably provided further at the protrusion of the low-refractive-index layer 42 (represented as the first adhesive layer 41 in the figures). By providing a reflective layer, light leakage from the light source near the incident surface can be suppressed more effectively. The reflective layer can be of any suitable configuration. For example, it can be the reflective plate described in section A above for reflective plate 50, or it can be a metal vapor-deposited film. The reflectivity of the reflective layer is preferably 80% to 100%, more preferably 95% to 100%. As long as the first adhesive layer 41 has a protrusion as shown in the example, the reflective layer 70 can be adhered to the first adhesive layer 41. If the first adhesive layer 41 does not have a protrusion, the reflective layer 70 can be adhered to the protrusion of the low-refractive-index layer through any suitable adhesive layer or bonding agent layer, or it can be formed directly on the protrusion of the low-refractive-index layer.

[0060] Figure 5 (a) and Figure 5 (b) are partial cross-sectional schematic diagrams illustrating yet another specific example of a light-shielding structure. Figure 5 In the example shown in (a), at the light source side end of the light guide plate 20, the end faces of the double-sided adhesive film 40 and the reflector 50 are located further away from the light source 10 than the end face of the light guide plate 20. This creates a gap on the back side of the light source side end of the light guide plate 20. In the example shown, a light-shielding portion 60 is provided in this gap. As described above, examples of the light-shielding portion 60 include a light-shielding strip, a solidified or cured film of a light-shielding resin solution coating, and a light-shielding molded body. The light-shielding molded body preferably has a shape suitable for the shape of the gap. With such a structure, tilting or positional shift of the light guide plate 20 can be prevented.

[0061] exist Figure 5 In the example shown in (b), it is also similar to Figure 5 Similarly, in the example shown in (a), a gap is formed on the back side of the light guide plate 20 at the light source side end. Figure 5In the example shown in (b), a protrusion 36 is provided on the back side 32 of the housing 31 at a position corresponding to the gap. The housing has light-shielding properties, therefore, the protrusion 36 can function as a light-shielding structure. The protrusion 36 preferably has a shape that suits the shape of the gap and can substantially support the light guide plate.

[0062] C. Double-sided adhesive film

[0063] C-1. Overview of Double-Sided Adhesive Film

[0064] As described in section A above, the double-sided adhesive film 40 has a first adhesive layer 41, a low refractive index layer 42, a substrate 44 as needed, and a second adhesive layer 43 from the light guide plate 20 side.

[0065] C-2. Substrate

[0066] Typically, the substrate 44 can be made of a film or sheet of resin (preferably a transparent resin). Examples of such resins include thermoplastic resins and reactive resins (e.g., ionizing radiation-curing resins). Specific examples of thermoplastic resins include: polymethyl methacrylate (PMMA), (meth)acrylic resins such as polyacrylonitrile, polycarbonate (PC) resins, polyester resins such as PET, cellulose resins such as cellulose triacetate (TAC), cyclic polyolefin resins, and styrene resins. Specific examples of ionizing radiation-curing resins include epoxy acrylate resins and urethane acrylate resins. These resins can be used alone or in combination of two or more.

[0067] The thickness of the substrate is, for example, 10 μm to 100 μm, preferably 10 μm to 50 μm.

[0068] The refractive index of the substrate is preferably 1.47 or higher, more preferably 1.47 to 1.60, and even more preferably 1.47 to 1.55. If it falls within this range, the light can be introduced into the image display unit without adversely affecting the light emitted from the light guide plate.

[0069] C-3. Low Refractive Index Layer

[0070] Typically, the low-refractive-index layer 42 has voids within it. The porosity of the low-refractive-index layer is, for example, 40% or more, typically 50% or more, preferably 70% or more, and more preferably 80% or more. On the other hand, the porosity is, for example, 90% or less, preferably 85% or less. By keeping the porosity within the above range, the refractive index of the low-refractive-index layer can be made to reach an appropriate range. The porosity is a value obtained by calculating the porosity using the Lorentz-Lorenz formula based on the refractive index value measured using an ellipsometry.

[0071] The refractive index of the low-refractive-index layer is preferably 1.30 or less, more preferably 1.20 or less, and even more preferably 1.15 or less. The lower limit of the refractive index can be, for example, 1.01. Within such a range, very excellent light utilization efficiency can be achieved in the backlight unit. 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 the Low-Refractive-Index Layer” of the following embodiment.

[0072] The low-refractive-index layer can be constructed using any suitable configuration as long as it possesses the desired porosity and refractive index. The low-refractive-index layer is preferably formed by coating or printing. Materials constituting the low-refractive-index layer can be, for example, those described in International Patent Application Publication No. 2004 / 113966, Japanese Patent Application Publication No. 2013-254183, and Japanese Patent Application Publication No. 2012-189802. Specifically, examples include: silica compounds; hydrolyzable silanes, their partially hydrolysates and dehydration condensates; organic polymers; silicon compounds containing silanol groups; active silica obtained by contacting silicates with acids or ion-exchange resins; polymerizable monomers (e.g., (meth)acrylic acid monomers and styrene monomers); curable resins (e.g., (meth)acrylic acid resins, fluorinated resins, and urethane resins); and combinations thereof. The low-refractive-index layer can be formed by coating or printing onto a solution or dispersion of such materials.

[0073] The size of the voids (pores) in the low refractive index layer refers to the diameter of the major axis of the void (pore) and the diameter of the minor axis. The size of the void (pore) is, for example, 2 nm to 500 nm. The size of the void (pore) is, for example, 2 nm or more, preferably 5 nm or more, more preferably 10 nm or more, and even more preferably 20 nm or more. On the other hand, the size of the void (pore) is, for example, 500 nm or less, preferably 200 nm or less, and even more preferably 100 nm or less. The range of the void (pore) size is, for example, 2 nm to 500 nm, preferably 5 nm to 500 nm, more preferably 10 nm to 200 nm, and even more preferably 20 nm to 100 nm. The size of the void (pore) can be adjusted to the desired size according to the purpose and application. The size of the void (pore) can be quantified by the BET test method.

[0074] The size of the pores can be quantified using the BET test method. Specifically, 0.1 g of the sample (the formed pore layer) is placed in the capillary of a surface area measuring device (McMerrittek: ASAP2020), and then subjected to reduced pressure drying at room temperature for 24 hours to degas the gas within the pore structure. Then, by adsorbing nitrogen onto the sample and plotting adsorption isotherms, the pore distribution can be determined. The pore size can then be evaluated.

[0075] The haze of the low-refractive-index layer is, for example, less than 5%, preferably less than 3%. On the other hand, the haze is, for example, 0.1% or more, preferably 0.2% or more. The range of haze is, for example, 0.1% or more and less than 5%, preferably 0.2% or more and less than 3%. Haze is an indicator of the transparency of the low-refractive-index layer, and can be measured, for example, by the method described below. It should be noted that haze is an indicator of the transparency of the low-refractive-index layer.

[0076] The void layer (low refractive index layer) was cut into 50mm × 50mm pieces and placed in a haze meter (Murakami Color Technology Research Institute Co., Ltd.: HM-150) to measure the haze. The haze value was calculated using the following formula.

[0077] Haze (%) = [Diffuse transmittance (%) / Total transmittance (%)] × 100 (%)

[0078] As a low-refractive-index layer with internal voids, examples include low-refractive-index layers having at least a porous layer and / or an air layer. The porous layer typically comprises aerogels, and / or particles (e.g., hollow microparticles and / or porous particles). The low-refractive-index layer can preferably be a nanoporous layer (specifically, more than 90% of the micropores have a diameter of 10...). -1 nm~10 3 Porous layers in the nm range).

[0079] As the aforementioned particles, any suitable particles can be used. The particles are typically formed from silica-based compounds. Examples of particle shapes include spherical, plate-like, needle-like, rope-like, and grape-like shapes. Examples of rope-like particles include: multiple particles having spherical, plate-like, or needle-like shapes linked together to form a beaded structure; short fibrous particles (e.g., the short fibrous particles described in Japanese Patent Application Publication No. 2001-188104); and combinations thereof. Rope-like particles can be linear or branched. Examples of grape-like particles include: multiple spherical, plate-like, and needle-like particles aggregated to form grape-like clusters. The shape of the particles can be confirmed by observation using, for example, a transmission electron microscope.

[0080] The thickness of the low-refractive-index layer is preferably 0.2 μm to 5 μm, more preferably 0.3 μm to 3 μm. When the thickness of the low-refractive-index layer is within this range, excellent total internal reflection can be achieved, resulting in excellent light guiding function.

[0081] The specific composition and formation method of the low-refractive-index layer are described in detail in, for example, International Publication No. 2019 / 151073. The contents of that publication are incorporated herein by reference.

[0082] C-4. First Adhesive Layer

[0083] The first adhesive layer 41 can be made of any suitable adhesive. The first adhesive layer can be the same as or different from the second adhesive layer described later. The thickness of the first adhesive layer is preferably 5 μm to 200 μm, more preferably 10 μm to 150 μm.

[0084] C-5. Second adhesive layer

[0085] The second adhesive layer 43 has a hardness such that the adhesive constituting the adhesive layer will not penetrate into the voids of the low refractive index layer under normal conditions. The storage modulus of the second adhesive layer at 23°C is, for example, 1.0 × 10⁻⁶. 5 (Pa)~1.0×10 7 (Pa), preferably 1.3 × 10 5 (Pa)~1.0×10 6 (Pa), more preferably 1.5 × 10 5 (Pa)~5.0×10 5 (Pa). By ensuring that the storage modulus of the second adhesive layer adjacent to the low-refractive-index layer is within the range described above, it is possible to prevent the adhesive constituting the second adhesive layer from entering the voids of the low-refractive-index layer. Therefore, the refractive index of the low-refractive-index layer can be maintained at a low level, and this effect can be preserved. 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, within a range of -50°C to 150°C, at a heating rate of 5°C / min, and the value at 23°C is recorded.

[0086] 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 typically contain a (meth)acrylate polymer as the main component (base polymer). In the solid component of the adhesive composition, the (meth)acrylate polymer may, for example, be contained in the adhesive composition at a proportion of 50% by weight or more, preferably 70% by weight or more, more preferably 90% by weight or more. The (meth)acrylate polymer contains an alkyl (meth)acrylate as a monomer unit as the main component. It should be noted that (meth)acrylate refers to acrylates and / or methacrylates. As the alkyl group of the (meth)acrylate, examples include linear or branched alkyl groups having 1 to 18 carbon atoms. The average number of carbon atoms in the alkyl group is preferably 3 to 9. As monomers constituting the (meth)acrylate polymer, in addition to (meth)acrylate, examples include carboxyl-containing monomers, hydroxyl-containing monomers, amide-containing monomers, aromatic ring (meth)acrylates, heterocyclic (meth)acrylates, and other comonomers. The comonomer is preferably a hydroxyl-containing monomer and / or a heterocyclic (meth)acrylate, more preferably N-acryloylmorpholine. The acrylic adhesive composition may preferably contain a silane coupling agent and / or a crosslinking agent. Examples of silane coupling agents include, for example, epoxy-containing silane coupling agents. Examples of crosslinking agents include, for example, isocyanate crosslinking agents and peroxide crosslinking agents. Details of such adhesive layers or acrylic adhesive compositions are described, for example, in Japanese Patent No. 4140736, which is incorporated herein by reference.

[0087] The thickness of the second adhesive layer is preferably 3 μm to 30 μm, more preferably 5 μm to 10 μm. If the thickness of the second adhesive layer is within this range, it has the advantage of sufficient adhesion and minimal impact of the thickness of the second adhesive layer on the overall thickness.

[0088] D. Image display device

[0089] The aforementioned backlight unit can be suitably used in image display devices (e.g., liquid crystal displays). Therefore, embodiments of the present invention also include such an image display device. The image display device includes: the backlight unit described above, and an image display panel disposed on the emission surface side of a light guide plate.

[0090] Example

[0091] The present invention will now be specifically described through examples, but the present invention is not limited to these examples. It should be noted that the methods for measuring each characteristic are as described below. Furthermore, unless otherwise specified, "%" and "parts" in the examples are based on weight.

[0092] (1) Refractive index of the low-refractive-index layer

[0093] After forming a low-refractive-index layer on the acrylic film, it was cut into 50mm × 50mm pieces and bonded to the surface of a glass plate (thickness: 3mm) through an adhesive layer. The central part of the back side of the glass plate (approximately 20mm in diameter) was filled with black marker, resulting in a sample that does not reflect light from the back side of the glass plate. The refractive index of the sample was measured using an ellipsometry (JAWoollam Japan: VASE) at a wavelength of 550nm and an incident angle of 50–80 degrees.

[0094] (2) Uniformity of brightness

[0095] The backlight units obtained in the embodiments and comparative examples were lit, and the uniformity of brightness was confirmed by visual observation. The evaluation was conducted according to the following criteria.

[0096] ○: Overall uniformity of brightness

[0097] ×: Confirms light leakage from the light source near the incident surface.

[0098] [Manufacturing Example 1] Preparation of Coating Solution for Forming Low Refractive Index Layers

[0099] (1) Gel formation of silicon compounds

[0100] Mixture A was prepared by dissolving 0.95 g of methyltrimethoxysilane (MTMS), a precursor of silicon compounds, in 2.2 g of dimethyl sulfoxide (DMSO). 0.5 g of a 0.01 mol / L aqueous solution of oxalic acid was added to mixture A, and the mixture was stirred at room temperature for 30 minutes, thereby hydrolyzing MTMS to produce mixture B containing trihydroxymethylsilane.

[0101] After adding 0.38 g of 28% ammonia and 0.2 g of pure water to 5.5 g of DMSO, the above mixture B was further added, and the mixture was stirred at room temperature for 15 minutes to gel the trihydroxymethylsilane, thereby obtaining a mixture C containing a gel-like silicon compound.

[0102] (2) Aging treatment

[0103] The mixture C containing the gel-like silicon compound prepared as described above was directly incubated at 40°C for 20 hours to perform a curing treatment.

[0104] (3) Crushing process

[0105] Next, the gel-like silicon compound, after being cured as described above, was broken into particles ranging from several mm to several cm in size using a scraper. Then, 40 g of isopropanol (IPA) was added to mixture C, and after gentle stirring, it was allowed to stand at room temperature for 6 hours to allow the solvent and catalyst in the gel to be decanted. Solvent replacement was achieved by performing the same decantation process three times, yielding mixture D. Next, the gel-like silicon compound in mixture D was subjected to a high-pressure, medium-free grinding process. The grinding process (high-pressure, medium-free grinding) was performed using a homogenizer (SMT Corporation, trade name "UH-50"). 1.85 g of the gel-like compound and 1.15 g of IPA from mixture D were weighed into a 5 cc screw-top bottle, and then ground for 2 minutes at 50 W and 20 kHz.

[0106] Through this pulverization process, the gel-like silicon compound in the above-mentioned mixture D is pulverized, thereby forming a sol solution of pulverized material in mixture D'. The volume average particle size, representing the particle size deviation, of the pulverized material contained in mixture D' was confirmed using a dynamic light scattering nano-trajectory particle size analyzer (manufactured by Nikkiso Corporation, UPA-EX150 type), and the result was 0.50 to 0.70. Furthermore, relative to 0.75 g of this sol solution (mixture C'), 0.062 g of a 1.5 wt% MEK (methyl ethyl ketone) solution of photoalkali-generating agent (Wako Pure Chemical Industries Co., Ltd.: trade name WPBG266) and 0.036 g of a 5 wt% MEK solution of bis(trimethoxysilyl)ethane were added to obtain a coating solution for forming a low refractive index layer.

[0107] [Manufacturing Example 2] Preparation of the adhesive constituting the first adhesive layer

[0108] In a four-necked flask equipped with a stirring blade, thermometer, nitrogen inlet tube, and 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 parts by weight of 2,2'-azobisisobutyronitrile (2,2'-azobisisobutyronitrile) as a polymerization initiator, along with 100g of ethyl acetate, were added together. After nitrogen purging was performed by slowly stirring and introducing nitrogen gas, the liquid temperature in the flask was maintained at around 55°C, and the polymerization reaction was carried out for 8 hours to prepare an acrylic polymer solution. An acrylic adhesive solution was prepared by mixing 100 parts of the solids component of the obtained acrylic polymer solution with 0.2 parts of isocyanate crosslinking agent (CORONATE L, manufactured by Nippon Polyurethane Kogyo Co., Ltd., an adduct of trimethylolpropane and toluene diisocyanate), 0.3 parts of benzoyl peroxide (NYPER BMT, manufactured by Nippon Yushi Co., Ltd.), and 0.2 parts of γ-epoxypropoxypropylmethoxysilane (KBM-403, manufactured by Shin-Etsu Chemical Co., Ltd.). Next, the acrylic adhesive solution was coated onto one side of a silicone-treated polyethylene terephthalate (PET) film (manufactured by Mitsubishi Chemical Polyester Film Co., Ltd., thickness: 38 μm) to achieve a 20 μm thickness after drying, and then dried at 150°C for 3 minutes to form an adhesive layer. The resulting adhesive had a storage modulus of 1.3 × 10⁻⁶ at 23°C. 5 Pa.

[0109] [Manufacturing Example 3] Preparation of the adhesive constituting the second adhesive layer

[0110] In a four-necked flask equipped with a stirring blade, thermometer, nitrogen inlet tube, and condenser, 99 parts of butyl acrylate, 1 part of 4-hydroxybutyl acrylate, 0.1 parts of 2,2'-azobisisobutyronitrile (2,2'-azobisisobutyronitrile) as a polymerization initiator, and 100 parts of ethyl acetate were added together. After nitrogen purging by slowly stirring, the liquid temperature in the flask was maintained at approximately 55°C, and the polymerization reaction was carried out for 8 hours to prepare an acrylic polymer solution. Relative to 100 parts of the solid content of the obtained acrylic polymer solution, 0.1 parts of isocyanate crosslinking agent (Takenate D110N, trimethylolpropanebenzene diisocyanate, manufactured by Mitsui Takeda Chemical Co., Ltd.), 0.1 parts of benzoyl peroxide (NYPER BMT, manufactured by Nippon Yushi Co., Ltd.), and 0.2 parts of γ-glycidoxypropylmethoxysilane (KBM-403, manufactured by Shin-Etsu Chemical Co., Ltd.) were added to prepare an acrylic adhesive composition solution. Next, the solution of the above acrylic adhesive composition was coated onto one side of a polyethylene terephthalate membrane (separator: Mitsubishi Chemical Polyester Membrane Co., Ltd., MRF38) treated with an organosilicon release agent, and dried at 150°C for 3 minutes, forming an adhesive layer with a thickness of 20 μm on the surface of the separator. The resulting adhesive had a storage modulus of 8.2 × 10⁻⁶ at 23°C. 4 Pa.

[0111] [Manufacturing Example 4] Fabrication of Double-Sided Adhesive Film

[0112] The low-refractive-index layer forming coating liquid prepared in Manufacturing Example 1 was applied to a substrate (acrylic film) with a thickness of 30 μm. The wet thickness of the coating layer (thickness before drying) was approximately 27 μm. The coating layer was dried by treating it at a temperature of 100°C for 1 minute, forming a low-refractive-index layer (thickness 0.9 μm) on the substrate. The porosity of the resulting 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 with a structure of first adhesive layer / low-refractive-index layer / substrate / second adhesive layer was produced.

[0113] [Example 1]

[0114] The backlight unit was removed from a commercially available liquid crystal display device (manufactured by KING JIM Corporation, trade name "XMC10"). The light guide plate was then removed from the removed backlight unit (essentially a housing). Meanwhile, using black ink (manufactured by PILOT Corporation, CD / DVD marker black MFD-15EU-B), a 1.5mm wide light-shielding printing layer was formed on the light source side of a commercially available reflector (manufactured by Toray Industries, Inc., trade name "Lumirror (registered trademark) #225E6SR"). That is, a light-shielding printing layer was provided as shown... Figure 3 The light-shielding structure shown in (a) is obtained by bonding the light guide plate and the reflector plate with the light-shielding printed layer together with the double-sided adhesive film obtained in Manufacturing Example 4. At this time, the light guide plate is bonded to the first adhesive layer. The resulting laminate is then placed back into the housing to manufacture the backlight unit. The resulting backlight unit is evaluated in (2) above. The results are shown in Table 1.

[0115] [Example 2]

[0116] A commercially available light-shielding strip (manufactured by DIC Corporation, trade name "DAITAC LS-050H", width 0.5 mm) was attached to the end face of the double-sided adhesive film obtained in Manufacturing Example 4, thereby creating a light-shielding portion. That is, a light-shielding portion was created as shown in the image. Figure 3 (b) shows the light-shielding structure. The backlight unit was fabricated in the same manner as in Example 1, except that the double-sided adhesive tape was used. The resulting backlight unit was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[0117] [Example 3]

[0118] Except for extending the light source side end of the reflector by 2mm, similarly to Example 1, the light guide plate and the reflector are bonded together through a double-sided adhesive film to obtain a laminate. Next, two commercially available light-shielding tapes (manufactured by DIC Corporation, trade name "DAITAC LS-050H", 1.5mm wide black adhesive tape) are overlapped at the extended portion of the reflector and bonded to the end face of the low refractive index layer to form a light-shielding portion. That is, a light-shielding portion is formed as described above. Figure 3 (c) shows the light-shielding structure. A backlight unit was fabricated in the same manner as in Example 1, except that the laminated body was used. The resulting backlight unit was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[0119] [Example 4]

[0120] The low-refractive-index layer of the double-sided adhesive film, the substrate, the second adhesive layer, and the reflector are extended to positions corresponding to the emission surface of the light source (LED) of the backlight unit. Otherwise, the light guide plate and the reflector are bonded together with the double-sided adhesive film in the same manner as in Example 1, resulting in a laminate. That is, a laminate is formed as described in Example 1. Figure 4 The light-shielding structure shown is without a reflective layer. A backlight unit was fabricated in the same manner as in Example 1, except that the laminate was used. The resulting backlight unit was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[0121] [Example 5]

[0122] A gap is formed by positioning the end faces of the double-sided adhesive film and the reflector 2mm further away from the light source than the end face of the light guide plate. Otherwise, similar to Example 1, the light guide plate and the reflector are bonded together through the double-sided adhesive film to obtain a laminate. Next, five commercially available light-shielding strips (manufactured by DIC, trade name "DAITAC LS-050H", 1.5mm wide black adhesive strips) are overlapped and bonded at positions on the back of the housing corresponding to this gap, thereby creating a light-shielding portion. That is, a light-shielding portion is provided as described above. Figure 5 The light-shielding structure shown in (a) was used to fabricate a backlight unit by incorporating the aforementioned laminated body into the housing. The resulting backlight unit was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[0123] [Comparative Example 1]

[0124] The backlight unit was fabricated in the same manner as in Example 1, except that no light-shielding printed layer was formed on the reflector (i.e., no light-shielding structure was provided). The resulting backlight unit was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[0125] [Table 1]

[0126] Light-shielding structure Uniformity of brightness Example 1 Figure 3 (a) ○ Example 2 Figure 3 (b) ○ Example 3 Figure 3 (c) ○ Example 4 Figure 4 (Without a reflective layer) ○ Example 5 Figure 5 (a) ○ Comparative Example 1 none ×

[0127] As can be clearly seen from Table 1, according to the embodiments of the present invention, by setting a given light-shielding structure, a backlight unit with excellent brightness uniformity can be achieved.

[0128] Industrial applicability

[0129] The backlight unit of the present invention can be suitably used as a backlight unit for an image display device (especially a liquid crystal display device).

Claims

1. A backlight unit comprising: a light source; a light guide plate disposed opposite to the light source and having an end surface on which light from the light source is incident and an exit surface from which the light after the incidence is emitted; a reflection plate attached to a back surface side of the light guide plate via a double-sided adhesive film; and a housing which accommodates the light source, the light guide plate and the reflection plate and has a front surface portion and a back surface portion, 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, the backlight unit is configured in such a manner that light from the light source is not incident between the low-refractive layer and the reflection plate or in such a manner that light incident between the low-refractive layer and the reflection plate from the light source is not emitted from the exit surface of the light guide plate, the reflection plate has a projection portion which projects toward the light source side more than the double-sided adhesive film, and a light-blocking portion selected from a light-blocking tape, a solidified or cured product of a coated film of a light-blocking resin solution and a light-blocking molded product is provided in the projection portion.

2. The backlight unit according to claim 1, wherein the low-refractive layer and the reflection plate have a projection portion which projects toward the light source side more than the light guide plate.

3. The backlight unit according to claim 2, wherein a reflection layer is further provided in the projection portion of the low-refractive layer.

4. The backlight unit according to claim 1, wherein, at a light source side end portion of the light guide plate, an end surface of the double-sided adhesive film and the reflection plate is formed to be farther from the light source than an end surface of the light guide plate, a given gap portion is formed, and a light-blocking portion selected from a light-blocking tape, a solidified or cured product of a coated film of a light-blocking resin solution and a light-blocking molded product is provided in the gap portion.

5. A backlight unit comprising: a light source; a light guide plate disposed opposite to the light source and having an end surface on which light from the light source is incident and an exit surface from which the light after the incidence is emitted; a reflection plate attached to a back surface side of the light guide plate via a double-sided adhesive film; and a housing which accommodates the light source, the light guide plate and the reflection plate and has a front surface portion and a back surface portion, 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, the backlight unit is configured in such a manner that light from the light source is not incident between the low-refractive layer and the reflection plate or in such a manner that light incident between the low-refractive layer and the reflection plate from the light source is not emitted from the exit surface of the light guide plate, at a light source side end portion of the light guide plate, an end surface of the double-sided adhesive film and the reflection plate is formed to be farther from the light source than an end surface of the light guide plate, a given gap portion is formed, and a protrusion portion which is adapted to the shape of the gap portion is provided at a position of the back surface portion of the housing corresponding to the gap portion.

6. The backlight unit according to any one of claims 1 to 5, wherein the light source is an LED light source.

7. An image display device comprising: the backlight unit according to any one of claims 1 to 6, and an image display panel disposed on the exit surface side of the light guide plate. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​

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