Optical laminates and methods for manufacturing optical laminates

Abstract

This invention provides an optical laminate that achieves reduced thickness while maintaining excellent optical performance, and a method for manufacturing the optical laminate. The optical laminate according to an embodiment of this invention comprises: a transparent layer with a thickness of 20 μm or less; a porous layer disposed directly on one side of the transparent layer in a predetermined pattern along its thickness direction, and having a refractive index of 1.25 or less; an adhesive layer disposed opposite to the transparent layer and in contact with the porous layer; and an adhesive layer disposed opposite to the transparent layer and covering the porous layer.

Description

[Technical Field]

[0001] This invention relates to an optical laminate and a method for manufacturing an optical laminate. [Previous Technology]

[0002] It is known to attach an optical laminate containing a low-refractive-index layer with a refractive index lower than that of the light guide plate to a light guide plate for propagating light, so as to arbitrarily control the propagation of light in the light guide plate. The industry is researching the patterning of this low-refractive-index layer to give the optical laminate a light extraction function. For example, an optical laminate has been proposed that includes a substrate and a variable refractive-index extraction layer disposed on the substrate. The variable refractive-index extraction layer includes a first region selectively printed with a first material with a relatively low refractive index and a second region formed by coating the first material with a second material with a relatively high refractive index (see, for example, Patent Document 1). The optical laminate described in Patent Document 1 has an adhesive layer formed on the surface of the substrate opposite to the variable refractive-index extraction layer, and is attached to the light guide plate by means of the adhesive layer. In recent years, the applications of optical products with light guide plates have become increasingly diversified, and there is a desire for miniaturization of optical products and, consequently, thinner optical laminates attached to light guide plates. However, the optical laminate described in Patent Document 1 includes a substrate on which the first substance is selectively printed, making it difficult to achieve a thinner optical laminate. Although studies have been conducted on thinning the substrate or peeling and removing the substrate from the variable refractive index extraction layer, thinning the substrate is more difficult from the perspective of manufacturing stability of the optical laminate. If the substrate is peeled off, the variable refractive index extraction layer may be damaged. Furthermore, if the substrate is peeled off and an adhesive layer is directly applied to the variable refractive index extraction layer, the optical performance of the variable refractive index extraction layer cannot be adequately maintained. [Prior Art Documents] [Patent Documents]

[0003] Patent Document 1: International Publication No. 2014 / 031726 [Summary of the Invention]

[0004] [The problem the invention aims to solve]

[0005] This invention was made to solve the aforementioned prior problems, and its main objective is to provide an optical laminate that can achieve thinner thickness while maintaining excellent optical performance, and a method for manufacturing the optical laminate. [Technical Means for Solving the Problem]

[0006] An optical laminate according to an embodiment of the present invention comprises: a transparent layer having a thickness of 20 μm or less; a porous layer having a predetermined pattern directly disposed on one side of the transparent layer in the thickness direction and having a refractive index of 1.25 or less; an adhesive layer disposed opposite to the transparent layer on the side opposite to the porous layer and in contact with the transparent layer; and an adhesive layer disposed opposite to the transparent layer on the side opposite to the adhesive layer and covering the porous layer. In one embodiment, the transparent layer has a barrier function that inhibits the penetration of components constituting the adhesive layer into the porous layer. In one embodiment, the porosity of the transparent layer is less than the porosity of the porous layer. In one embodiment, the adhesive layer comprises an adhesive having a storage elastic modulus of 1.0 × 10⁵ Pa or more at 23°C. Another embodiment of the present invention provides a method for manufacturing an optical laminate comprising the following steps: forming a transparent layer with a thickness of 20 μm or less on a substrate; patterning a porous layer with a refractive index of 1.25 or less on the side of the transparent layer opposite to the substrate; forming an adhesive layer covering the porous layer from the side opposite to the transparent layer; peeling the substrate from the transparent layer; and forming an adhesive layer on the side of the transparent layer opposite to the porous layer. In one embodiment, the peeling force when peeling the substrate from the transparent layer is 1 N / 25 mm or less. [Effects of the Invention]

[0007] According to an embodiment of the present invention, an optical laminate that can achieve thinning while maintaining excellent optical performance can be realized.

Implementation Method

[0009] Embodiments of the present invention will be described below, but the present invention is not limited to these embodiments. First, the general structure of the optical laminate will be described, and then the constituent elements of the optical laminate will be described in detail.

[0010] A. Overall Structure of Optical Stack Figure 1 is a schematic cross-sectional view of an optical stack according to one embodiment of the present invention; Figure 2 is a schematic cross-sectional view of an optical article having the optical stack of Figure 1. The optical stack 100 in the example figures includes: a transparent layer 1 with a thickness of 20 μm or less; a porous layer 2 directly disposed in a predetermined pattern on one side of the transparent layer 1 in the thickness direction, and having a refractive index of 1.25 or less; an adhesive layer 4 disposed opposite to the transparent layer 1 on the side opposite to the porous layer 2 and in contact with the transparent layer 1; and an adhesive layer 3 disposed opposite to the transparent layer 1 on the side opposite to the adhesive layer 4 and covering the porous layer 2. In this configuration, the transparent layer is disposed between the porous layer and the adhesive layer, and the thickness of the transparent layer is 20 μm or less, thus achieving a thinner optical stack and maintaining the refractive index of the porous layer below the aforementioned upper limit. Therefore, the excellent optical performance of the optical stack can be sufficiently maintained. The thickness of the transparent layer 1 is preferably 10 μm or less, more preferably 5 μm or less, and even more preferably 4 μm or less, typically 0.1 μm or more. The porous layer 2 is typically characterized by having internal voids. The refractive index of the porous layer 2 is preferably less than 1.20, more preferably 1.19 or less, and even more preferably 1.18 or less, typically 1.10 or more. Unless otherwise specified, the refractive index refers to the refractive index measured at a wavelength of 550 nm.

[0011] In one embodiment, a portion of one side of the transparent layer 1 in the thickness direction may be exposed from the porous layer 2. This exposed portion is in contact with the adhesive layer 3. Therefore, the adhesive layer 3 is in contact with both the porous layer 2 and the transparent layer 1. This suppresses the peeling of the transparent layer 1 relative to the porous layer 2 during the processing of the laminate prior to processing. The refractive index of the adhesive layer 3 is typically greater than that of the porous layer 2. The refractive index of the adhesive layer 3 is greater than 1.25, preferably 1.4 or more, and typically less than 1.7.

[0012] In one embodiment, the transparent layer 1 is a barrier layer 1a that has the function of inhibiting the penetration of the components constituting the adhesive layer 4 into the porous layer 2. Therefore, the increase in the refractive index of the porous layer can be stably suppressed. The adhesive layer 4 can be an adhesive layer or an adhesive layer.

[0013] In one embodiment, the porosity of the transparent layer 1 is less than that of the porous layer 2. With this configuration, the barrier performance of the transparent layer 1 can be sufficiently ensured, and the entry of the adhesive or bonding agent constituting the bonding layer into the voids of the porous layer can be stably suppressed. The porosity of the transparent layer 1 is, for example, 15% by volume or less, preferably 10% by volume or less, and at least 1% by volume. The porosity of the porous layer 2 is, for example, more than 10% by volume, preferably 20% by volume or more, more preferably 30% by volume or more, and even more preferably 35% by volume or more, and for example, 60% by volume or less, preferably 55% by volume or less, more preferably 50% by volume or less, and even more preferably 45% by volume or less. If the porosity is within this range, the refractive index of the porous layer can be set to an appropriate range, and the specified mechanical strength can be ensured. The porosity is calculated using the Lorentz-Lorenz formula based on the refractive index value measured by an ellipsometry.

[0014] In one embodiment, the adhesive layer 3 comprises an adhesive having a storage modulus of elasticity of 1.0 × 10⁵ (Pa) or higher at 23°C. Preferably, the storage modulus of elasticity of the adhesive constituting the adhesive layer 3 is 1.1 × 10⁵ (Pa) or higher, and more preferably 1.2 × 10⁵ (Pa) or higher. If the storage modulus of elasticity of the adhesive is at or above the aforementioned lower limit, the entry of the adhesive constituting the adhesive layer into the voids of the porous layer can be suppressed. Therefore, the increase in the refractive index of the porous layer can be suppressed more stably. The storage modulus of elasticity is determined by reading the value at 23°C under conditions of 1 Hz at a temperature ranging from -50°C to 150°C within a temperature range of -50°C to 150°C, measured at a heating rate of 5°C / minute, according to the method described in JIS K 7244-1 "Plastics - Test Method for Dynamic Mechanical Properties". The upper limit of the storage elastic modulus of the adhesive constituting adhesive layer 3 at 23°C is typically below 100 × 10⁵ (Pa).

[0015] The following provides a detailed description of the transparent layer, the porous layer, the adhesive layer, and the adhesive layer.

[0016] B. Transparent Layer Transparent layer 1 allows light to pass through. The total light transmittance of transparent layer 1 is, for example, 70% to 100%, preferably 80% to 99%. If the total light transmittance of the transparent layer is within the above range, excellent transparency of the optical laminate as a whole can be achieved. As a result, adverse effects in the application of the optical laminate can be suppressed.

[0017] As long as light can pass through, the transparent layer 1 can be of any suitable composition. Examples of transparent layer 1 include resin films and inorganic films. Examples of resin film materials include: polyvinyl alcohol (PVA); (meth)acrylic resins such as polymethyl methacrylate (PMMA); polyvinyl acetal resin; thermoplastic resins with polar groups such as polycarbonate resin, polyaryl ester resin, and polyurethane resin; and thermo- or UV (ultraviolet) curable resins such as acrylic hard coating resins, epoxy hard coating resins, and polysiloxane hard coating resins. Furthermore, (meth)acrylic refers to acrylic and / or methacrylic resins. The resin film materials can be used alone or in combination. Also, the above-mentioned resin film can be composed solely of resin, or other substances can be added to modify the physical properties of the resin film. Specifically, examples include adding boric acid compounds or silane compounds to introduce a cross-linking structure into the PVA.

[0018] Examples of inorganic thin film materials include SiO2, ZTO (Zinc Tin Oxide), ITO (Indium Tin Oxide), IZO (Indium Zinc Oxide), TiO2, Si, ZnO, AZO (Aluminum Zinc Oxide), Al2O3, MgO, MgF2, and SiN. Inorganic thin film materials can be used alone or in combination.

[0019] C. Porous Layer A porous layer 2 is directly disposed on one side of the transparent layer 1 in the thickness direction and has a predetermined pattern shape. The porous layer 2 typically has a plurality of openings 21 defining the pattern. In one embodiment, the porous layer 2 has a gradient pattern in which the ratio of openings per unit area increases as it faces a predetermined direction orthogonal to the thickness direction of the transparent layer 1. The openings 21 can adopt any suitable shape and size. When the porous layer 2 has a gradient pattern, openings 21 of the same size can be distributed in a manner that becomes sparser as they face the predetermined direction, or the size of the openings 21 can be changed in a manner that increases as they face the predetermined direction.

[0020] The total light transmittance of the porous layer 2 is, for example, 85% to 99%, preferably 87% to 98%, and even more preferably 89% to 97%. The haze of the porous layer 2 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. By placing such a porous layer in a specified position, excellent overall transparency of the optical laminate can be achieved. The haze can be measured, for example, by the following method: The porous layer is cut into 50 mm × 50 mm pieces and placed in a haze meter (manufactured by Murakami Color Technology Research Institute Co., Ltd.: HM-150) to measure the haze. The haze value is calculated by the following formula: Haze (%) = [diffuse transmittance (%) / total light transmittance (%)] × 100 (%)

[0021] The thickness of the porous layer 2 is, for example, 30 nm to 5 μm, more preferably 200 nm to 4 μm, even more preferably 400 nm to 3 μm, and even more preferably 600 nm to 2 μm. If the thickness of the porous layer is within this range, the porous layer can effectively exhibit total internal reflection for light in the visible to infrared region.

[0022] The porous layer 2 can be of any suitable composition as long as it possesses the aforementioned desired characteristics. The porous layer is preferably formed by coating or printing. Materials constituting the porous layer may be, for example, those described in International Patent Publication No. 2004 / 113966, Japanese Patent Application Publication No. 2013-254183, and Japanese Patent Application Publication No. 2012-189802. Silicon compounds may be cited as representative examples. Examples of silicon compounds include: silicon dioxide compounds; hydrolyzable silanes, and their partially hydrolysates and dehydration condensates; silicon compounds containing silanol groups; and active silicon dioxide obtained by contacting silicates with acids or ion exchange resins. Examples also include: organic polymers; polymerizable monomers (e.g., (meth)acrylic monomers and styrene monomers); curable resins (e.g., (meth)acrylic resins, fluorinated resins, and urethane resins). These materials can be used alone or in combination. Porous layers can be formed by coating or printing solutions or dispersions of such materials.

[0023] The size of the pores in the porous layer refers to the major axis diameter of the pores, between their major and minor axis diameters. The size of the pores is, for example, 2 nm to 500 nm. The size of the pores 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 pores is, for example, 500 nm or less, preferably 200 nm or less, and even more preferably 100 nm or less. The range of 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 pores can be adjusted to the required size depending on the purpose and application.

[0024] The size of the pores can be quantified using the BET (Brunauer-Emmett-Teller) test. Specifically, 0.1 g of sample (the formed pore layer) is placed in the capillary of a surface area measuring device (manufactured by Micromeritics: ASAP2020), and then dried under reduced pressure at room temperature for 24 hours to degas the gas within the pore structure. Furthermore, by adsorbing nitrogen onto the sample, an adsorption isotherm is plotted to determine the pore distribution. This allows for the evaluation of the pore size.

[0025] As the aforementioned porous layer with internal voids, examples include porous layers having at least a portion of 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 porous layer is preferably a nanopore layer (specifically, a porous layer where more than 90% of the micropores have a diameter in the range of 10⁻¹ nm to 10³ nm).

[0026] Any suitable particle can be used as the aforementioned particle. The particles typically include silicon dioxide compounds. Examples of particle shapes include spherical, plate-like, needle-like, string-like, and grape-like. Examples of string-like particles include beads formed by multiple particles having spherical, plate-like, or needle-like shapes strung together, short fibrous particles (e.g., the short fibrous particles described in Japanese Patent Application Publication No. 2001-188104), and combinations thereof. String-like particles can be linear or branched. Examples of grape-like particles are multiple spherical, plate-like, and needle-like particles aggregated into a grape-like shape. The shape of the particles can be confirmed, for example, by observation using a transmission electron microscope.

[0027] An example of the specific structure of the porous layer will be described below. The porous layer of this embodiment includes one or more structural units that form a fine pore structure, and these structural units are chemically bonded to each other through a catalytic action. Examples of the shape of the structural units include particle-like, fibrous, rod-like, and plate-like shapes. The structural units may have only one shape, or they may combine two or more shapes. Hereinafter, the porous layer will be mainly described as a pore layer of a porous body in which the above-mentioned fine pore particles are chemically bonded to each other.

[0028] In the void layer formation step, such a void layer can be formed, for example, by chemically bonding microporous particles (porous particles) together. Furthermore, in embodiments of the present invention, the shape of the "particles" (e.g., the aforementioned microporous particles) is not particularly limited; for example, they can be spherical or other shapes. Also, in embodiments of the present invention, the aforementioned microporous particles can be, for example, sol-gel beaded particles, nanoparticles (hollow nano-silica / nano-balloon particles), nanofibers, etc. Microporous particles typically include inorganic materials. Specific examples of inorganic materials include silicon (Si), magnesium (Mg), aluminum (Al), titanium (Ti), zinc (Zn), and zirconium (Zr). These can be used alone or in combination of two or more. In one embodiment, the aforementioned microporous particles are, for example, microporous particles (porous particles) of silicon compounds, and the aforementioned porous body is, for example, a polysiloxane porous body. The aforementioned microporous particles of silicon compounds include, for example, pulverized gel-like silicon compounds. Furthermore, as another form of a porous layer having at least a portion of a porous layer and / or an air layer, a void layer may be formed by comprising fibrous materials such as nanofibers, wherein the fibrous materials are intertwined to form voids and thus form a layer. The method for manufacturing this void layer is not particularly limited; for example, it can be the same as the case of a void layer of a porous body in which the aforementioned microporous particles are chemically bonded together. As another form, examples include void layers using hollow nanoparticles or nanoclay, void layers formed using hollow nanoballoons or magnesium fluoride. A void layer may be a void layer containing a single constituent material or a void layer containing multiple constituent materials. A void layer may contain a single of the aforementioned forms or multiple of the aforementioned forms.

[0029] In this embodiment, the porous structure of the porous body can be, for example, a bubble-like structure formed by continuous pore structures. A bubble-like structure refers, for example, to a state in which the pore structures of the aforementioned polysiloxane porous body are three-dimensionally connected, or in other words, the internal voids of the pore structure are continuous. By having a bubble-like structure, the porosity of the porous body can be increased. However, when using individual bubble particles (particles each having a pore structure), such as hollow silica, a bubble-like structure cannot be formed. On the other hand, when using silica sol particles (a pulverized material of a gel-like silica compound forming a sol), since these particles have a three-dimensional dendritic structure, a bubble-like structure can be easily formed by the sedimentation and deposition of these dendritic particles in a coating film (a coating film containing pulverized gel-like silica compounds). The porous layer is more preferably a monolithic structure with a bubble-like structure comprising a plurality of fine pores. Monolithic structures, for example, refer to hierarchical structures comprising nanoscale micropores and interconnected bubble structures formed by these nanoscale micropores. In the formation of monolithic structures, for example, the micropores can impart film strength, while the larger interconnected bubble structures impart a higher porosity, thus achieving a balance between film strength and high porosity. This type of monolithic structure is preferably formed by controlling the pore distribution of the generated void structure within the gel (gel-like silicone compound) in the stage prior to pulverizing it into silicone sol particles. Furthermore, for example, monolithic structures can be formed by controlling the particle size distribution of the pulverized silicone sol particles to the desired size during the pulverization of the gel-like silicone compound.

[0030] The porous layer, for example as described above, contains fragments of a gel-like compound, which are chemically bonded to each other. The form of the chemical bonding (chemical bond) between the fragments in the porous layer is not particularly limited, and examples include cross-linking, covalent bonding, and hydrogen bonding.

[0031] The volume average particle size of the above-mentioned pulverized material in the porous layer is, for example, 0.05 μm or more, preferably 0.10 μm or more, and more preferably 0.11 μm or more. On the other hand, the volume average particle size is, for example, 1.00 μm or less, preferably 0.90 μm or less, and more preferably 0.50 μm or less. The range of the volume average particle size is, for example, 0.05 μm to 1.00 μm, preferably 0.10 μm to 0.90 μm, and more preferably 0.11 μm to 0.55 μm. The particle size distribution can be measured, for example, by a particle size distribution evaluation device such as dynamic light scattering method or laser diffraction method, and an electron microscope such as scanning electron microscope (SEM) or transmission electron microscope (TEM). Furthermore, the volume average particle size is an indicator of the deviation of the particle size of the pulverized material.

[0032] There are no particular limitations on the types of gel-like compounds. For example, gel-like silicone compounds can be cited as examples of gel-like compounds.

[0033] Furthermore, in the porous layer (void layer), the contained silicon atoms are preferably bonded with siloxane bonds. As a specific example, the proportion of unbonded silicon atoms (i.e., residual silanols) among all the silicon atoms contained in the void layer is, for example, less than 50%, preferably less than 30%, and more preferably less than 15%.

[0034] D. Adhesive Layer Adhesive layer 4, as detailed below, is provided for attaching the optical laminate 100 to an optical component (typically a light guide plate 10). Adhesive layer 4 is disposed on the side of the transparent layer 1 opposite to the porous layer 2. Since adhesive layer 4 does not contact the porous layer 2, its configuration is not particularly limited and any suitable configuration can be adopted. As mentioned above, adhesive layer 4 can be an adhesive layer or an adhesive layer. When adhesive layer 4 is an adhesive layer, adhesive layer 3 is designated as the first adhesive layer 3, and adhesive layer 4 is designated as the second adhesive layer 4a for distinction. For example, (meth)acrylic adhesives can be used as the adhesive constituting the second adhesive layer 4a. The thickness of the second adhesive layer 4a is, for example, 5 μm or more and 200 μm or less, preferably 100 μm or less. Examples of adhesives constituting the adhesive layer include thermosetting adhesives and UV-curing adhesives. The thickness of the adhesive layer is, for example, 0.1 μm to 200 μm.

[0035] E. Adhesive Layer (First Adhesive Layer) The adhesive layer 3, as detailed later, is provided for attaching the optical laminate 100 to the optical component. That is, the optical laminate 100 has two adhesive surfaces capable of connecting two optical components. In one embodiment, the adhesive layer 3 covers the porous layer 2 in an embedded manner and contacts the transparent layer 1 through the opening 21 of the porous layer 2.

[0036] As the adhesive constituting adhesive layer 3, any suitable adhesive can be used as long as it has the characteristics described above. An acrylic adhesive (acrylic adhesive composition) is representatively exemplified as an adhesive. The acrylic adhesive composition typically contains a (meth)acrylic polymer as the main component (base polymer). In the solid composition of the adhesive composition, the (meth)acrylic polymer may be contained in the adhesive composition at a ratio of 50% by mass or more, preferably 70% by mass or more, and more preferably 90% by mass or more. As a monomer unit, the (meth)acrylic polymer contains an alkyl (meth)acrylate as the main component. Furthermore, (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. In addition to alkyl methacrylates, other monomers constituting (meth)acrylate polymers may include carboxyl-containing monomers, hydroxyl-containing monomers, amide-containing monomers, aromatic ring-containing (meth)acrylates, and heterocyclic (meth)acrylates, etc., as comonomers. The comonomers are preferably hydroxyl-containing monomers and / or heterocyclic (meth)acrylates, and more preferably N-acrylamide. 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-based crosslinking agents and peroxide-based crosslinking agents. Details of such adhesive layers or acrylic adhesive compositions are described, for example, in Patent No. 4140736, the description of which is incorporated herein by reference.

[0037] The thickness of the adhesive layer 3 is, for example, 3 μm to 30 μm, preferably 5 μm to 10 μm. If the thickness of the adhesive layer is within this range, sufficient adhesion can be achieved, and the optical laminate can be made thinner.

[0038] F. Method for Manufacturing an Optical Stack Next, a method for manufacturing an optical stack according to one embodiment will be described. Figures 3(a) to 3(e) are schematic cross-sectional views illustrating a method for manufacturing an optical stack according to one embodiment of the present invention. A method for manufacturing an optical stack according to one embodiment includes the following steps: forming a transparent layer 1 with a thickness of 20 μm or less on a substrate 5; patterning a porous layer 2 with a refractive index of 1.25 or less on the side of the transparent layer 1 opposite to the substrate 5; forming an adhesive layer 3 on the side opposite to the transparent layer 1, covering the porous layer 2; peeling the substrate 5 from the transparent layer 1; and forming an adhesive layer 4 on the side of the transparent layer 1 opposite to the porous layer 2.

[0039] In this method, as shown in FIG3(a), firstly, the transparent layer 1 is formed on the substrate 5 using any suitable method. The substrate 5 is not particularly limited in its composition as long as it can stably support the transparent layer 1 and the porous layer 2 in a patterned manner. Any suitable resin film can be used as the substrate 5. Specific examples of materials that form the main component of the resin film include: cellulose-based resins such as triacetyl cellulose (TAC); polyester-based resins such as polyethylene terephthalate (PET); polyvinyl alcohol-based resins; polycarbonate-based resins; polyamide-based resins; polyimide-based resins; polyether-based resins; polyether-based resins; polystyrene-based resins; polyvinyl chloride-based resins; polyolefin-based resins; (meth)acrylic acid-based resins; and acetate-based resins. Examples of suitable resins include thermosetting or UV-curing resins such as (meth)acrylate, urethane, (meth)acrylate urethane, epoxy, and polysiloxane. An inorganic thin film, such as a copper oxide film, can be deposited on the surface of the substrate 5. The thickness of the substrate 5 is, for example, greater than 5 μm, preferably 10 μm or more, and for example, less than 100 μm.

[0040] When the transparent layer 1 comprises a resin film, a solution containing the resin film material is coated onto the substrate 5, and the coating is dried to form the transparent layer 1 (resin film). Alternatively, a separately prepared transparent layer (resin film) may be attached to the substrate. When the transparent layer 1 comprises an inorganic thin film, the inorganic thin film material is deposited onto the substrate 5 by a film-forming method such as sputtering to form the transparent layer 1 (inorganic thin film).

[0041] Subsequently, as shown in FIG3(b), the porous layer 2 is patterned on the side of the transparent layer 1 opposite to the substrate 5 using any suitable method. That is, the porous layer 2 is patterned on the transparent layer 1 while the transparent layer 1 is supported by the substrate 5. Therefore, the patterning of the porous layer 2 can be stably implemented.

[0042] In one embodiment, this step typically includes the following steps: a precursor formation step for forming a porous structure on a transparent layer as a precursor of a porous layer (void layer); and a cross-linking reaction step for inducing a cross-linking reaction inside the precursor after the precursor formation step. This step further includes a containing liquid preparation step for preparing a containing liquid containing microporous particles (hereinafter sometimes referred to as "microporous particle containing liquid" or simply "containing liquid"), and a drying step for drying the containing liquid, wherein in the precursor formation step, the microporous particles in the dried body are chemically bonded to each other to form the precursor. The containing liquid is not particularly limited, for example, it is a suspension containing microporous particles. Furthermore, the following mainly describes the case where the microporous particles are a pulverized gel-like compound, and the void layer is a porous body (preferably a polysiloxane porous body) containing the pulverized gel-like compound. However, porous layers can also be formed when the microporous particles are not pulverized gel-like compounds.

[0043] According to the above method, for example, a porous layer (void layer) with a very low refractive index can be formed. The reason for this is, for example, as follows. However, this speculation does not limit the method of forming the porous layer.

[0044] The aforementioned pulverized material is obtained by pulverizing a gel-like silicon compound, and therefore the three-dimensional structure of the gel-like silicon compound before pulverization is dispersed into a three-dimensional basic structure. Furthermore, in the above method, by coating or printing the pulverized gel-like silicon compound onto a transparent layer, a precursor of a porous structure based on a three-dimensional basic structure can be formed. That is, according to the above method, a new porous structure (three-dimensional basic structure) obtained by coating the pulverized material, which is different from the three-dimensional structure of the gel-like silicon compound, can be formed. Therefore, in the finally obtained porous layer, for example, a low refractive index that functions to the same extent as an air layer can be achieved. Furthermore, in the above method, since the fragments are chemically bonded to each other, the three-dimensional basic structure is fixed. Therefore, although the finally obtained porous layer is a structure with pores, sufficient strength and flexibility can be maintained. Details of the specific composition and formation method of the porous layer are described, for example, in International Publication No. 2019 / 151073. The information contained in that bulletin is incorporated herein by reference.

[0045] In one embodiment, this step is performed by printing the aforementioned microporous particles containing liquid into a predetermined pattern. Examples of printing methods include inkjet printing, gravure printing, and screen printing.

[0046] Subsequently, as shown in FIG3(c), an adhesive layer 3 covering the porous layer 2 is formed by any suitable method. In one embodiment, the adhesive constituting the adhesive layer 3 is applied to a resin film and dried. After the adhesive layer 3 is formed on the resin film, the adhesive layer 3 is attached to the porous layer 2 and the transparent layer 1 in a manner that embeds the porous layer 2.

[0047] Next, as shown in FIG3(d), the substrate 5 is peeled off from the transparent layer 1. The peel force when peeling the substrate 5 from the transparent layer 1 is preferably 1 N / 25 mm or less, more preferably 0.8 N / 25 mm or less. The peel force is measured, for example, by the following method. A 50 mm × 140 mm strip of the laminated film of the substrate 5 and the transparent layer 1 is sampled, and the substrate 5 side of the sample is fixed to a glass plate with double-sided tape. An acrylic adhesive layer (20 μm thick) is laminated onto a PET film (T100: manufactured by Mitsubishi Resin Film Co., Ltd.), and an adhesive tape piece cut into 25 mm × 100 mm is laminated onto the transparent layer side of the laminated film to perform lamination with the PET film. Then, the sample is clamped in an Autograph tensile testing machine (manufactured by Shimadzu Corporation: AG-Xplus) with a clamping distance of 100 mm, and a tensile test is performed at a tensile speed of 0.3 m / min. The average test force of the 50 mm peel test is defined as the adhesive peel strength, i.e., the adhesive force. Furthermore, the adhesion force can also be measured using the same method. In this invention, there is no clear distinction between "adhesive force" and "adhesion force". In one embodiment, the adhesive layer 3 contacts the transparent layer 1 through the opening 21 of the porous layer 2, thus preventing the transparent layer 1 from peeling off from the porous layer 2 as the substrate 5 is peeled away.

[0048] Subsequently, as shown in FIG3(e), an adhesive layer 4 is formed on the side of the transparent layer 1 opposite to the porous layer 2 using any suitable method. In one embodiment, an adhesive or bonding agent constituting the adhesive layer 4 is applied to a resin film and dried to form the adhesive layer 4 on the resin film, and then the adhesive layer 4 is attached to the transparent layer 1. Alternatively, an adhesive or bonding agent can be applied to the transparent layer and dried to form the adhesive layer.

[0049] An optical laminate consisting of an adhesive layer, a porous layer, a transparent layer, and an adhesive layer is manufactured by means of the above method.

[0050] G. Application of the Optical Stack The optical stack of the present invention can be typically applied to an optical article 200 having a light guide plate 10, which can extract light propagating within the light guide plate 10 to another optical component. In one embodiment, as shown in FIG2, the optical stack 100 is attached to the light guide plate 10 via an adhesive layer 4. Although not shown, other optical components are attached to the adhesive layer 3 of the optical stack 100. The light guide plate 10 can typically propagate light incident from the light source 11 (typically an LED (Light Emitting Diode)) in a predetermined direction (left-right direction in FIG2). The porous layer 2 is preferably configured such that a portion with a relatively small opening area is located on the side of the light guide plate 10 near the light source 11, and a portion with a relatively large opening area is located on the opposite side from the light source 11. In this way, the optical stack 100 can uniformly extract light from the light guide plate 10 and propagate the extracted light to another optical component. Furthermore, as described above, the optical laminate 100 is thinned, thus suppressing color shift. [Example]

[0051] The present invention will be specifically described below by way of examples, but the present invention is not limited to these examples. Furthermore, the methods for measuring each characteristic are as follows. Also, unless otherwise specified, "%" and "parts" in the examples are mass standards.

[0052] (1) Refractive Index Before the adhesive layer is bonded to the porous layer, after the porous layer is formed, it is cut into 25 mm × 50 mm sizes, and then the cut pieces are bonded to the surface of a glass plate (thickness: 3 mm) by adhesive. The central part of the back of the glass plate (about 20 mm in diameter) is covered with black marking ink to make a sample that does not reflect on the back of the glass plate. The refractive index of the sample is measured in an ellipsometry (manufactured by JAWoollam Japan: VASE) at a wavelength of 550 nm and an incident angle of 50 to 80 degrees. On the other hand, the refractive index measurement in the composition of the adhesive is performed by attaching the adhesive layer to the formed porous layer, using a prism coupler (manufactured by Metricon) to incident a laser (λ = 407 nm) from the transparent layer side, calculating the refractive index at 407 nm based on the measured value of the total internal reflection angle, and converting the refractive index at 550 nm based on the wavelength dispersion of the refractive index calculated separately by an ellipsometry (manufactured by JAWoollam).

[0053] (2) Optical Durability The optical laminates obtained in each embodiment and each comparative example were placed in an oven at 65°C and 95%RH (relative humidity) for 1000 h of heating and humidification durability test. The degree of refractive index increase from the initial value after the above heating and humidification durability test was measured. Laminates with an increase of less than 0.05 were marked as ×, and laminates with an increase of more than 0.05 were marked as ×. The results are shown in Table 1.

[0054] [Manufacturing Example 1] Preparation of Coating Solution for Porous Layer Formation (1) Gelification of Silicon Compound 0.95 g of methyltrimethoxysilane (MTMS), a precursor of the silicon compound, was dissolved in 2.2 g of dimethyl sulfoxide (DMSO) to prepare mixture A. 0.5 g of 0.01 mol / L oxalic acid aqueous solution was added to mixture A, and the mixture was stirred at room temperature (23°C) for 30 minutes to hydrolyze MTMS and generate mixture B containing tris(hydroxy)methylsilane. 0.38 g of 28% by weight ammonia and 0.2 g of pure water were added to 5.5 g of DMSO, and then mixture B was added. The mixture was stirred at room temperature (23°C) for 15 minutes to gel the tris(hydroxy)methylsilane and obtain mixture C containing gel-like silicon compound. (2) Curing treatment: The mixture C containing the gel-like silicon compound prepared as described above was directly cured at 40°C for 20 hours. (3) Pulverization treatment: Subsequently, the gel-like silicon compound cured as described above was pulverized into particles of several mm to several cm in size using a scraper. Then, 40 g of isobutanol (IBA) was added to the mixture C, and after gentle stirring, it was allowed to stand at room temperature for 6 hours to decant the solvent and catalyst in the gel. Solvent replacement was performed by performing the same decanting treatment 3 times to obtain the mixture D. Subsequently, the gel-like silicon compound in the mixture D was pulverized (high pressure, medium-free pulverization). The pulverization process (high-pressure, media-free pulverization) was performed using a homogenizer (SMT Corporation, trade name "UH-50"). 1.85 g of the gel-like compound and 1.15 g of IBA from mixture D were weighed and placed in a 5 cc screw-top bottle, then pulverized at 50 W and 20 kHz for 2 minutes. This pulverization process pulverized the gel-like silicone compound in mixture D, thus producing a sol solution E of pulverized material. The volume average particle size, representing the particle size deviation, of the pulverized material in sol solution E was confirmed using a dynamic light scattering Nanotrac particle size analyzer (Nikkiso Corporation, UPA-EX150 model), and the result was 0.10 μm to 0.30 μm. Furthermore, relative to 0.75 g of sol solution E, 0.062 g of a 1.5% by mass concentration MEK (methyl ethyl ketone) solution of photoalkali-generating agent (Wako Pure Chemical Industries, Ltd.: trade name WPBG266) and 0.036 g of a 5% concentration MEK solution of bis(trimethoxysilyl)hexane were added to obtain a coating solution for forming a porous layer.

[0055] [Manufacturing Example 2] Preparation of the first adhesive layer: 90.7 parts of butyl acrylate, 6 parts of N-acrylamide, 3 parts of acrylic acid, 0.3 parts of 2-hydroxybutyl acrylate, 0.1 parts by weight of 2,2'-azobisisobutyronitrile (as polymerization initiator), and 100 g of ethyl acetate were added to a four-necked flask equipped with a stirrer, a thermometer, a nitrogen inlet tube, and a condenser. While stirring slowly, nitrogen was introduced to replace the nitrogen. 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. To prepare an acrylic adhesive solution, relative to 100 parts of the solids content of the obtained acrylic polymer solution, 0.2 parts of isocyanate crosslinking agent (Coronate L, an adduct of trimethylolpropane toluene diisocyanate, manufactured by Nippon Polyurethane Industry Co., Ltd.), 0.3 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 mixed. Then, the acrylic adhesive solution was coated onto one side of a polysiloxane-treated polyethylene terephthalate (PET) film (manufactured by Mitsubishi Chemical Polyester Film Co., Ltd., thickness: 38 μm) to form a 10 μm adhesive layer after drying. The film was dried at 150°C for 3 minutes to form the first adhesive layer. The storage modulus of the resulting adhesive was 1.3 × 10⁵ Pa.

[0056] [Manufacturing Example 3] Preparation of the second adhesive layer: 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 to a four-necked flask equipped with a stirrer, a thermometer, a nitrogen inlet tube, and a condenser. While stirring slowly, nitrogen was introduced to replace the nitrogen. The liquid temperature in the flask was maintained at around 55°C, and the polymerization reaction was carried out for 8 hours to prepare a solution of acrylic polymer. To a solid content of 100 parts relative to the obtained acrylic polymer solution, 0.1 parts of isocyanate crosslinking agent (Takenate D110N, trimethylolpropane dimethyl diisocyanate, manufactured by Mitsui Takeda Chemical Co., Ltd.), 0.1 parts of benzoyl peroxide (Nyper BMT, manufactured by Nippon Yushu 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. Subsequently, the above acrylic adhesive composition solution was coated onto one side of a polyethylene terephthalate film (release film: manufactured by Mitsubishi Chemical Polyester Film Co., Ltd., MRF38) treated with a polysiloxane release agent, and dried at 150°C for 3 minutes to form a second adhesive layer with a thickness of 12 μm on the surface of the release film. The resulting adhesive had a storage modulus of elasticity of 8.2 × 10⁴ Pa.

[0057] [Example 1] After coating a substrate (PET resin film) with an aqueous solution of polyvinyl alcohol (PVA), the coating was dried. This formed a PVA layer as a transparent layer on the substrate. The thickness of the PVA layer was 3 μm. Then, the porous layer forming coating liquid of Manufacturing Example 1 was patterned by gravure printing on the side of the PVA layer opposite to the substrate, and the coating was dried. This formed a patterned porous layer on the PVA layer. The pattern of the porous layer had a gradually increasing opening ratio per unit area in the width direction. The refractive index of the porous layer was 1.19. The thickness of the porous layer was 0.9 μm. Then, the first adhesive layer obtained in Manufacturing Example 2 was attached to the porous layer. Then, the PET substrate was peeled from the PVA layer at a peel angle of 180° and a peel speed of 300 mm / min. The peel force was measured using an Autograph tensile testing machine. The results are shown in Table 1. Next, the second adhesive layer obtained in Manufacturing Example 3 was attached to the side of the PVA layer opposite to the porous layer. An optical laminate having a first adhesive layer / porous layer / transparent layer / second adhesive layer was thus obtained.

[0058] [Example 2] An aqueous solution of polymethyl methacrylate (PMMA) was used instead of an aqueous solution of PVA to form a PMMA layer as a transparent layer on a substrate. Otherwise, an optical laminate was obtained in the same manner as in Example 1.

[0059] [Example 3] An ethanol solution of polyvinyl acetal was used instead of an aqueous solution of PVA to form a polyvinyl acetal layer as a transparent layer on a substrate. Otherwise, an optical laminate was obtained in the same manner as in Example 1.

[0060] [Example 4] A substrate with a CuO sputtered film deposited on a polyethylene terephthalate (PET) film was prepared. A SiO2 layer as a transparent layer was formed on the CuO sputtered film. Otherwise, an optical laminate was obtained in the same manner as in Example 1.

[0061] [Example 5] The porous layer forming coating liquid of Manufacturing Example 1 was patterned by inkjet printing instead of gravure printing. Otherwise, an optical laminate was obtained in the same manner as in Example 1.

[0062] [Comparative Example 1] The porous layer forming coating liquid of Manufacturing Example 1 was patterned on a substrate (cyclic olefin (COP) film; ZF16; manufactured by Zeon Corporation, Japan) with a thickness of 100 μm by gravure printing, and then the coating was dried. This formed a patterned porous layer on the substrate. Next, the first adhesive layer obtained in Manufacturing Example 2 was attached to the porous layer. Then, the substrate was peeled off from the porous layer, and the second adhesive layer obtained in Manufacturing Example 3 was attached to its peeled surface. An optical laminate having the structure of a first adhesive layer / porous layer / second adhesive layer was obtained by the above method.

[0063] [Comparative Example 2] The porous layer forming coating liquid of Manufacturing Example 1 was patterned on a substrate (acrylic resin film) with a thickness of 30 μm by gravure printing, and then the coating was dried. This formed a patterned porous layer on the substrate. Next, the first adhesive layer obtained in Manufacturing Example 2 was attached to the porous layer. Then, the second adhesive layer obtained in Manufacturing Example 3 was attached to the side of the substrate opposite to the porous layer. An optical laminate having the structure of a first adhesive layer / porous layer / substrate / second adhesive layer was obtained in this manner.

[0064] [Table 1] Table 1 No. Example 1 Example 2 Example 3 Example 4 Example 5 Comparative Example 1 Comparative Example 2 First adhesive layer Material Manufacturing Example 2 Manufacturing Example 2 Manufacturing Example 2 Manufacturing Example 2 Manufacturing Example 2 Manufacturing Example 2 Manufacturing Example 2 Thickness [μm] 10 10 10 10 10 10 10 Porous layer Material Manufacturing Example 1 Manufacturing Example 1 Manufacturing Example 1 Manufacturing Example 1 Manufacturing Example 1 Manufacturing Example 1 Manufacturing Example 1 Printing methods Intaglio ink jet Intaglio Intaglio Thickness [μm] 0.9 0.9 0.9 0.9 0.9 0.9 0.9 transparent layer Material PVA PMMA Polyvinyl acetal SiO2 PVA acrylic acid Thickness [μm] 3 3 3 1 3 30 Second adhesive layer Material Manufacturing Example 3 Manufacturing Example 3 Manufacturing Example 3 Manufacturing Example 3 Manufacturing Example 3 Manufacturing Example 3 Manufacturing Example 3 Thickness [μm] 12 12 12 12 12 12 12 Peeling force [N / 25 mm] 0.1 0.1 0.1 0.5 0.1 - - Total thickness [μm] 25 25 25 twenty three 25 twenty two 52 Optical durability ×

[0065] As clearly shown in Table 1, according to embodiments of the present invention, by providing a transparent layer with a thickness of less than 20 μm between the patterned porous layer and the adhesive layer, a thinner thickness can be achieved in the optical laminate, and excellent optical durability can be achieved. [Industrial Applicability]

[0066] The optical laminate of the present invention can be used in various optical products, and is particularly suitable for optical products with light guide plates. [Simplified Explanation of the Diagram]

[0008] FIG1 is a schematic cross-sectional view of an optical laminate according to one embodiment of the present invention. FIG2 is a schematic cross-sectional view of an optical article having the optical laminate of FIG1. ​​FIG3(a) to FIG3(e) are schematic cross-sectional views for illustrating a method of manufacturing an optical laminate according to one embodiment of the present invention.

Claims

1. An optical laminate comprising: a transparent layer having a thickness of 20 μm or less; a porous layer having a gradient pattern directly disposed on one side of the transparent layer in the thickness direction and having a refractive index of 1.25 or less; an adhesive layer disposed opposite to the transparent layer and in contact with the porous layer; and an adhesive layer disposed opposite to the transparent layer and covering the porous layer.

2. The optical laminate of claim 1, wherein the transparent layer has a barrier function that inhibits the penetration of the components constituting the adhesive layer into the porous layer.

3. The optical laminate as claimed in claim 2, wherein the porosity of the transparent layer is less than the porosity of the porous layer.

4. An optical laminate as claimed in any one of claims 1 to 3, wherein the adhesive layer comprises an adhesive having a storage elastic modulus of 1.0 × 10⁵ (Pa) or higher at 23°C.

5. A method for manufacturing an optical laminate, comprising the following steps: forming a transparent layer with a thickness of 20 μm or less on a substrate; patterning a porous layer with a refractive index of 1.25 or less on the side of the transparent layer opposite to the substrate; forming an adhesive layer on the side opposite to the transparent layer, covering the porous layer; peeling the substrate from the transparent layer; and forming an adhesive layer on the side of the transparent layer opposite to the porous layer, wherein the pattern formed by the patterning is a gradient pattern.

6. The method for manufacturing an optical laminate as claimed in claim 5, wherein the peeling force when peeling the substrate from the transparent layer is 1 N / 25 mm or less.

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