Micro LED display device

Abstract

To provide a micro LED display device with excellent luminous efficiency and suppressed color mixture.SOLUTION: A micro LED display device according to the present invention includes a micro LED array substrate including a plurality of micro LEDs, a sealing portion that seals the plurality of micro LEDs, a low refractive index layer, and a plurality of wavelength conversion layers formed by partitioning in this order from the back side, and each of the wavelength conversion layers is formed such that a pair of layers corresponds to one micro LED in a thickness direction, and the refractive index of the low refractive index layer is lower than the refractive index of the sealing portion and the refractive index of the wavelength conversion layer, and a difference between the refractive index of the low refractive index layer and the refractive index of the sealing portion is 0.10 or more, and a difference between the refractive index of the low refractive index layer and the refractive index of the wavelength conversion layer is greater than or equal to 0.10.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a micro LED display device. [Background technology]

[0002] In recent years, micro LED displays configured by arranging micro LEDs in pixels arranged in a matrix have been developed as new display devices (e.g., Patent Document 1 and Patent Document 2). As a micro LED display, a display has been proposed that includes a micro LED array substrate configured by arranging a plurality of micro LEDs and an array of wavelength conversion layers (fluorescent light-emitting layers) provided on the micro LED array substrate, which absorb light from the micro LEDs and convert the emission wavelength of the light into red, green, and blue wavelengths, respectively (e.g., Patent Document 2). In such a micro LED display, a micro LED and a wavelength conversion layer are paired for each subpixel. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2020-43073 [Patent Document 2] Special Publication No. 2016-523450 Summary of the Invention [Problem to be solved by the invention]

[0004] In the micro LED display described above, there is a problem that light from the micro LED leaks to sub-pixels other than the one corresponding to the micro LED (adjacent sub-pixels, surrounding sub-pixels), resulting in color mixing.In addition, there is a problem that light is scattered within the wavelength conversion layer and returns to the back side, resulting in insufficient luminous efficiency.

[0005] An object of the present invention is to provide a micro LED display device that has excellent luminous efficiency and suppresses color mixing. [Means for solving the problem]

[0006] The micro LED display device of the present invention comprises a micro LED array substrate including a plurality of micro LEDs, a sealing portion for sealing the plurality of micro LEDs, a low refractive index layer, and a plurality of wavelength conversion layers formed in a partitioned manner, in this order from the micro LED array substrate side, wherein each wavelength conversion layer is formed to correspond to one micro LED in the thickness direction and form a pair, and the refractive index of the low refractive index layer is lower than the refractive index of the sealing portion and the refractive index of the wavelength conversion layer, the difference between the refractive index of the low refractive index layer and the refractive index of the sealing portion is 0.10 or more, and the difference between the refractive index of the low refractive index layer and the refractive index of the wavelength conversion layer is 0.10 or more. In one embodiment, the refractive index of the low refractive index layer is 1.25 or less. In one embodiment, the low refractive index layer is a porous layer made of a porous material formed by chemically bonding fine particles together. In one embodiment, the sealing portion is made of an adhesive. In one embodiment, the individual wavelength conversion layers are spaced apart by partition walls. In one embodiment, the micro LED is a blue LED or an ultraviolet LED. In one embodiment, the micro LED display device further comprises a color filter disposed on the surface of the wavelength conversion layer opposite to the low refractive index layer. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide a micro LED display device that has excellent luminous efficiency and suppresses color mixing. [Brief explanation of the drawings]

[0008] [Figure 1]1 is a schematic cross-sectional view of a micro LED display device according to one embodiment of the present invention; FIG. [Figure 2] FIG. 1(a) is a schematic cross-sectional view showing a configuration used in an example, and FIG. 1(b) is a schematic cross-sectional view showing a configuration used in a comparative example. DETAILED DESCRIPTION OF THE INVENTION

[0009] A. Micro LED display device FIG. 1 is a schematic cross-sectional view of a micro LED display device according to one embodiment of the present invention. The micro LED display device 100 according to this embodiment includes a micro LED array substrate 10 including a plurality of micro LEDs 11, an encapsulation unit 20 for encapsulating the micro LEDs 11, a low-refractive index layer 30, and a plurality of wavelength conversion layers 40 formed in sections, in this order from the micro LED array substrate side. Typically, the micro LED array substrate 10 includes a drive substrate 12 and a plurality of micro LEDs 11 arranged in an array (matrix) on the drive substrate 12. Each wavelength conversion layer 40 is formed to correspond to one micro LED 11 in the thickness direction and form a pair. Typically, one subpixel includes one wavelength conversion layer 40 and one micro LED 11. Red, green, and blue subpixels can be formed by transmitting light from the micro LEDs 11 through the wavelength conversion layer 40. In the case of a subpixel that directly utilizes light from a micro LED (for example, when a blue subpixel is formed using a blue LED), the wavelength conversion layer may be omitted or replaced with another layer (for example, a light diffusion layer). In one embodiment, each wavelength conversion layer is separated by a partition 50 (light-shielding layer).

[0010] In one embodiment, the low refractive index layer 30 is formed on the entire surface of the encapsulating portion 20 opposite to the micro LED array substrate 10. In another embodiment, the low refractive index layer 30 is provided directly on the encapsulating portion 20 (i.e., without any other layer therebetween).

[0011] The refractive index of the low refractive index layer 30 is lower than the refractive index of the sealing portion 20 and the refractive index of the wavelength conversion layer 40. The difference between the refractive index of the low refractive index layer 30 and the refractive index of the sealing portion 20 is 0.10 or more. In addition, the difference between the refractive index of the low refractive index layer 30 and the refractive index of the wavelength conversion layer 40 is 0.10 or more.

[0012] In the present invention, a low-refractive index layer is disposed between the encapsulation portion and the wavelength conversion layer, thereby creating a refractive index difference between the layers. As a result, at least a portion of the light emitted from the micro LED and scattered within the wavelength conversion layer to return to the rear surface can be reflected at the interface between the wavelength conversion layer and the low-refractive index layer and emitted toward the viewing side. This results in improved luminous efficiency. Furthermore, at least a portion of the light emitted obliquely from the micro LED and unable to reach the corresponding wavelength conversion layer (the wavelength conversion layer within the same subpixel) but traveling toward the periphery is reflected at the interface between the low-refractive index layer and the encapsulation portion and returned to the rear surface. This results in reduced color mixing. Micro LED display devices according to embodiments of the present invention are advantageous in that they not only have high resolution but also higher brightness and a wider color gamut than conventional displays.

[0013] B. Low refractive index layer The refractive index of the low refractive index layer is preferably 1.30 or less, more preferably 1.25 or less, even more preferably 1.20 or less, and particularly preferably 1.15 or less. The lower the refractive index of the low refractive index layer, the better, and the lower limit is, for example, 1.07 or more (preferably 1.05 or more). In this specification, the refractive index refers to the refractive index measured at a wavelength of 550 nm.

[0014] As described above, the difference between the refractive index of the low refractive index layer and the refractive index of the sealing portion is 0.10 or more. The difference between the refractive index of the low refractive index layer and the refractive index of the sealing portion is preferably 0.20 or more, more preferably 0.30 or more. Within this range, the above-mentioned effects become significant. The upper limit of the difference between the refractive index of the low refractive index layer and the refractive index of the sealing portion is, for example, 0.50 (preferably 0.70).

[0015] As described above, the difference between the refractive index of the low refractive index layer and the refractive index of the wavelength conversion layer is 0.10 or more. The difference between the refractive index of the low refractive index layer and the refractive index of the wavelength conversion layer is preferably 0.20 or more, more preferably 0.30 or more. Within such a range, the above-mentioned effects become significant. The upper limit of the difference between the refractive index of the low refractive index layer and the refractive index of the wavelength conversion layer is, for example, 0.50 (preferably 0.70).

[0016] The thickness of the low refractive index layer is preferably 0.01 μm to 1000 μm, more preferably 0.05 μm to 100 μm, still more preferably 0.1 μm to 80 μm, and particularly preferably 0.3 μm to 50 μm.

[0017] The low-refractive index layer may have any suitable configuration. In one embodiment, the low-refractive index layer has voids. The low-refractive index layer may be preferably formed by coating, printing, or the like. Materials constituting the low-refractive index layer include, for example, materials described in International Publication No. 2004 / 113966, Japanese Patent Application Laid-Open No. 2013-254183, and Japanese Patent Application Laid-Open No. 2012-189802. Specific examples include silica-based compounds; hydrolyzable silanes and their partial hydrolyzates and dehydration condensates; organic polymers; silicon compounds containing silanol groups; activated silica obtained by contacting silicate with acid or ion-exchange resin; polymerizable monomers (e.g., (meth)acrylic monomers and styrene-based monomers); curable resins (e.g., (meth)acrylic resins, fluorine-containing resins, and urethane resins); and combinations thereof. The low-refractive index layer may be formed by coating or printing a solution or dispersion of such materials.

[0018] The porosity of the low refractive index layer having voids is preferably 35% by volume or more, more preferably 38% by volume or more, and particularly preferably 40% by volume or more. Within this range, a low refractive index layer with a particularly low refractive index can be formed. The upper limit of the porosity of the low refractive index layer is, for example, 90% by volume or less, preferably 75% by volume or less. Within this range, a low refractive index layer with excellent strength can be formed. The porosity is a value calculated from the refractive index measured with an ellipsometer using the Lorentz-Lorenz's formula.

[0019] The size of the voids (holes) in the low refractive index layer refers to the diameter of the long axis of the voids (holes) out of the diameter of the long axis and the diameter of the short axis. The size of the voids (holes) is, for example, 2 nm to 500 nm. The size of the voids (holes) 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 voids (holes) is, for example, 500 nm or less, preferably 200 nm or less, and more preferably 100 nm or less. The size of the voids (holes) ranges, for example, from 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 voids (holes) can be adjusted to a desired size depending on the purpose and application.

[0020] The size of the voids (pores) can be quantified using the BET test method. Specifically, 0.1 g of the sample (the formed void layer) is placed in the capillary of a specific surface area measuring device (Micromeritics: ASAP2020), and then dried under reduced pressure at room temperature for 24 hours to remove the gas from the void structure. Nitrogen gas is then adsorbed onto the sample, and an adsorption isotherm is plotted to determine the pore distribution. This allows the void size to be evaluated.

[0021] 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 haze ranges, for example, from 0.1% to less than 5%, preferably from 0.2% to less than 3%. The haze can be measured, for example, by the following method. The haze is an index of the transparency of the low refractive index layer. The void layer (low refractive index layer) is cut to a size of 50 mm x 50 mm, and is set in a haze meter (Murakami Color Research Laboratory: HM-150) to measure the haze. The haze value is calculated using the following formula. Haze (%) = [Diffuse transmittance (%) / Total light transmittance (%)] x 100 (%)

[0022] Examples of the low refractive index layer having voids therein include a porous layer and / or a low refractive index layer having an air layer at least in a part thereof. The porous layer typically contains aerogel and / or particles (e.g., hollow fine particles and / or porous particles). The low refractive index layer is preferably a nanoporous layer (specifically, a layer in which 90% or more of the micropores have a diameter of 10 -1 nm~10 3 The porous layer may be in the range of 100 nm.

[0023] Any suitable particles may be used as the particles. The particles are typically made of a silica-based compound. Examples of particle shapes include spherical, plate-like, needle-like, string-like, and bunch-of-grapes shapes. Examples of string-like particles include particles in which multiple spherical, plate-like, or needle-like particles are strung together like beads, short fiber-like particles (e.g., the short fiber-like particles described in JP 2001-188104 A), and combinations thereof. String-like particles may be linear or branched. Examples of bunch-of-grapes-like particles include particles in which multiple spherical, plate-like, and needle-like particles aggregate to form a bunch of grapes. The particle shape can be confirmed, for example, by observation with a transmission electron microscope.

[0024] 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 in this range, the breakage prevention effect of the present invention becomes remarkable. Furthermore, the desired thickness ratio can be easily achieved.

[0025] The low refractive index layer can be typically formed by coating or printing as described above. With such a configuration, the low refractive index layer can be continuously provided by roll-to-roll printing. Any appropriate printing method can be adopted. Specifically, the printing method may be a plate-based printing method such as gravure printing, offset printing, or flexographic printing, or a plateless printing method such as inkjet printing, laser printing, or electrostatic printing.

[0026] An example of a specific configuration of the low refractive index layer will be described below. The low refractive index layer of this embodiment is composed of one or more types of structural units that form a fine void structure, and the structural units are chemically bonded to each other via catalytic action. Examples of the shape of the structural units include particulate, fibrous, rod-like, and flat-plate-like. The structural units may have only one shape, or may have a combination of two or more shapes. In one embodiment, the low refractive index layer is a void layer made of a porous body formed by chemically bonding fine particles to each other. The following mainly describes the case where the void layer is made of a porous body formed by chemically bonding fine particles to each other.

[0027] Such a void layer can be formed, for example, by chemically bonding microporous particles together in the void layer-forming step. In an embodiment of the present invention, the shape of the "particles" (e.g., the microporous particles) is not particularly limited and may be, for example, spherical or another shape. In an embodiment of the present invention, the microporous particles may be, for example, sol-gel beaded particles, nanoparticles (hollow nanosilica nanoballoon particles), nanofibers, etc. The microporous particles typically include inorganic substances. Specific examples of inorganic substances include silicon (Si), magnesium (Mg), aluminum (Al), titanium (Ti), zinc (Zn), and zirconium (Zr). These may be used alone or in combination of two or more. In one embodiment, the microporous particles are, for example, microporous particles of a silicon compound, and the porous body is, for example, a silicone porous body. The microporous particles of the silicon compound include, for example, a pulverized gel silica compound. Another example of a low-refractive-index layer having at least a porous layer and / or an air layer is a void layer made of a fibrous material such as nanofibers, which are entangled to form voids. The method for producing such a void layer is not particularly limited, and can be the same as that for the void layer of a porous body in which microporous particles are chemically bonded to each other. Further examples include void layers made of hollow nanoparticles or nanoclay, and void layers made of hollow nanoballoons or magnesium fluoride. The void layer may be made of a single constituent material or a plurality of constituent materials. The void layer may be made of a single constituent material or a plurality of constituent materials.

[0028] In this embodiment, the porous structure of the porous body may be, for example, an open-cell structure, in which the pores are interconnected. An open-cell structure refers to, for example, the three-dimensional interconnection of the pores in the silicone porous body, and can also be described as a state in which the internal voids of the pore structure are interconnected. Having an open-cell structure in a porous body can increase the porosity. However, when closed-cell particles (particles with individual pore structures) such as hollow silica are used, an open-cell structure cannot be formed. On the other hand, when silica sol particles (pulverized gel-like silicon compound that forms a sol) are used, the particles have a three-dimensional dendritic structure, and the dendritic particles settle and deposit in the coating film (coated film of a sol containing a pulverized gel-like silicon compound), thereby easily forming an open-cell structure. The low refractive index layer more preferably has a monolithic structure in which the open-cell structure includes a distribution of multiple pores. The monolithic structure refers, for example, to a hierarchical structure including a structure with nano-sized voids and an open-cell structure in which the nano-voids are aggregated. When forming a monolithic structure, for example, it is possible to achieve both membrane strength with fine pores and high porosity with coarse open-cell pores. Such a monolithic structure can be preferably formed by controlling the pore distribution of the resulting pore structure in the gel (gel silicon compound) prior to pulverization into silica sol particles. In addition, for example, when pulverizing the gel silicon compound, the monolithic structure can be formed by controlling the particle size distribution of the pulverized silica sol particles to a desired size.

[0029] The low refractive index layer contains, for example, pulverized gel compounds as described above, and the pulverized compounds are chemically bonded together. The form of the chemical bond between the pulverized compounds in the low refractive index layer is not particularly limited, and examples thereof include cross-linking, covalent bonding, and hydrogen bonding.

[0030] The gel form of the gel-like compound is not particularly limited. "Gel" generally refers to a solidified state in which solutes have an aggregated structure due to their mutual interaction, losing their independent mobility. The gel-like compound may be, for example, a wet gel or a xerogel. In general, a wet gel refers to a compound containing a dispersion medium in which the solute has a uniform structure, while a xerogel refers to a compound from which the solvent has been removed and in which the solute has a network structure with voids.

[0031] The gelling compound may be, for example, a gelling product obtained by gelling a monomer compound.Specifically, the gelling silicon compound may be, for example, a gelling product obtained by bonding monomer silicon compounds to each other, specifically, a gelling product obtained by bonding monomer silicon compounds to each other by covalent bonds, hydrogen bonds or intermolecular forces.The covalent bonds may be, for example, bonds formed by dehydration condensation.

[0032] The volume average particle diameter of the pulverized material in the low refractive index layer is, for example, 0.10 μm or more, preferably 0.20 μm or more, and more preferably 0.40 μm or more. On the other hand, the volume average particle diameter is, for example, 2.00 μm or less, preferably 1.50 μm or less, and more preferably 1.00 μm or less. The volume average particle diameter ranges, for example, from 0.10 μm to 2.00 μm, preferably from 0.20 μm to 1.50 μm, and more preferably from 0.40 μm to 1.00 μm. The particle size distribution can be measured, for example, using a particle size distribution evaluation device such as a dynamic light scattering method or a laser diffraction method, or an electron microscope such as a scanning electron microscope (SEM) or a transmission electron microscope (TEM). The volume average particle diameter is an index of the particle size variation of the pulverized material.

[0033] The type of gel compound is not particularly limited. Examples of gel compounds include gel silicon compounds. Hereinafter, a case where the gel compound is a gel silicon compound will be described as an example, but the present invention is not limited thereto.

[0034] The crosslinked bond is, for example, a siloxane bond. Examples of siloxane bonds include T2 bonds, T3 bonds, and T4 bonds, as shown below. When the void layer (low refractive index layer) has siloxane bonds, it may have any one type of bond, any two types of bonds, or all three types of bonds. The higher the ratio of T2 and T3 among the siloxane bonds, the more flexible the gel will be, and the more the inherent properties of the gel can be expected. On the other hand, the higher the ratio of T4, the more easily the film strength will be expressed. Therefore, it is preferable to change the ratios of T2, T3, and T4 depending on the purpose, application, desired properties, etc.

[0035] [ka]

[0036] In addition, in the low refractive index layer (void layer), for example, it is preferable that the silicon atoms contained therein are siloxane-bonded. Specifically, the proportion of unbonded silicon atoms (i.e., residual silanols) among all silicon atoms contained in the void layer is, for example, less than 50%, preferably 30% or less, and more preferably 15% or less.

[0037] When the gel compound is a gel silicon compound, the monomeric silicon compound is not particularly limited. Examples of the monomeric silicon compound include compounds represented by the following formula (1). When the gel silicon compound is a gel in which the monomeric silicon compounds are bonded to each other by hydrogen bonds or intermolecular forces as described above, the monomers of formula (1) can be hydrogen-bonded to each other via their respective hydroxyl groups, for example.

[0038] [ka]

[0039] In formula (1), X is, for example, 2, 3 or 4, preferably 3 or 4. R 1 is, for example, a straight-chain or branched alkyl group. 1The number of carbon atoms is, for example, 1 to 6, preferably 1 to 4, and more preferably 1 or 2. Examples of the linear alkyl group include a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, and a hexyl group, and examples of the branched alkyl group include an isopropyl group and an isobutyl group.

[0040] Specific examples of the silicon compound represented by formula (1) include compounds represented by the following formula (1') in which X is 3. In the following formula (1'), R 1 is the same as in formula (1), and is, for example, a methyl group. 1 When X is a methyl group, the silicon compound is tris(hydroxy)methylsilane. When X is 3, the silicon compound is, for example, a trifunctional silane having three functional groups.

[0041] [ka]

[0042] Another specific example of the silicon compound represented by formula (1) is a compound in which X is 4. In this case, the silicon compound is, for example, a tetrafunctional silane having four functional groups.

[0043] The monomeric silicon compound may be, for example, a hydrolyzate of a silicon compound precursor. The silicon compound precursor may be, for example, any precursor that can produce a silicon compound by hydrolysis, and a specific example thereof is a compound represented by the following formula (2):

[0044] [ka]

[0045] In the formula (2), X is, for example, 2, 3, or 4. R 1 and R 2 are each independently a linear or branched alkyl group, R 1 and R2 may be the same or different, R 1 may be the same or different when X is 2, R 2 may be the same or different from each other.

[0046] X and R 1 is, for example, X and R in formula (1) 1 is the same as R 2 is, for example, R in formula (1) 1 The following example can be used.

[0047] A specific example of the silicon compound precursor represented by formula (2) is a compound represented by the following formula (2') in which X is 3. In the following formula (2'), R 1 and R 2 are the same as in equation (2). 1 and R 2 When is a methyl group, the silicon compound precursor is trimethoxy(methyl)silane (hereinafter also referred to as "MTMS").

[0048] [ka]

[0049] The monomeric silicon compound is preferably a trifunctional silane, for example, because of its low refractive index. Furthermore, the monomeric silicon compound is preferably a tetrafunctional silane, for example, because of its excellent strength (e.g., scratch resistance). Only one type of monomeric silicon compound may be used, or two or more types may be used in combination. For example, the monomeric silicon compound may contain only a trifunctional silane, only a tetrafunctional silane, or both a trifunctional silane and a tetrafunctional silane, or may further contain other silicon compounds. When two or more types of silicon compounds are used as the monomeric silicon compound, the ratio thereof is not particularly limited and can be set appropriately.

[0050] An example of a method for forming such a low refractive index layer will be described below.

[0051] This method typically includes a precursor-forming step of forming a void structure on a resin film, which serves as a precursor for a low-refractive index layer (void layer), and a crosslinking reaction step of inducing a crosslinking reaction within the precursor after the precursor-forming step. This method further includes a liquid-containing step of preparing a liquid containing microporous particles (hereinafter sometimes referred to as a "microporous particle-containing liquid" or simply "containing liquid") and a drying step of drying the liquid containing the microporous particles. In the precursor-forming step, the microporous particles in the dried body are chemically bonded to form a precursor. The liquid containing the microporous particles is not particularly limited, and may be, for example, a suspension containing microporous particles. The following description will primarily focus on the case where the microporous particles are a pulverized gel compound and the void layer is a porous body (preferably a silicone porous body) containing the pulverized gel compound. However, the low-refractive index layer can also be formed in a similar manner when the microporous particles are other than a pulverized gel compound.

[0052] According to the above method, for example, a low refractive index layer (void layer) having a very low refractive index is formed. The reason for this is presumed to be as follows. However, this presumption does not limit the method for forming the low refractive index layer.

[0053] Since the above-mentioned pulverized material is obtained by pulverizing a gel silicon compound, the three-dimensional structure of the gel silicon compound before pulverization is dispersed in the three-dimensional basic structure. Furthermore, in the above-mentioned method, a precursor of a porous structure based on the three-dimensional basic structure is formed by coating the crushed material of the gel silicon compound on a resin film. In other words, according to the above-mentioned method, a new porous structure (three-dimensional basic structure) different from the three-dimensional structure of the gel silicon compound is formed by coating the crushed material. Therefore, in the finally obtained void layer, for example, a low refractive index that functions to the same extent as an air layer can be realized. Furthermore, in the above-mentioned method, the crushed material is chemically bonded to each other, so the three-dimensional basic structure is fixed. Therefore, the finally obtained void layer can maintain sufficient strength and flexibility despite having a void structure.

[0054] Furthermore, in the above method, the precursor formation step and the crosslinking reaction step are performed as separate steps. In addition, the crosslinking reaction step is preferably performed in multiple stages. By performing the crosslinking reaction step in multiple stages, for example, the strength of the precursor can be further improved compared to performing the crosslinking reaction step in a single stage, thereby obtaining a low-refractive index layer that combines high porosity and strength. The mechanism behind this is unclear, but it is speculated, for example, as follows. As described above, if film strength is improved by using a catalyst or the like simultaneously with the formation of a porous layer, the progress of the catalytic reaction increases the film strength but reduces the porosity. This is thought to be because, for example, the progression of the crosslinking reaction between microporous particles by the catalyst increases the number of crosslinks (chemical bonds) between the microporous particles, which strengthens the bonds but condenses the entire porous layer, resulting in a decrease in porosity. In contrast, by performing the precursor formation step and the crosslinking reaction step as separate steps and performing the crosslinking reaction step in multiple stages, it is thought that the number of crosslinks (chemical bonds) can be increased without significantly changing the overall morphology of the precursor (for example, without causing significant overall condensation). However, these are only examples of possible mechanisms and do not limit the method for forming the low refractive index layer.

[0055] In the precursor formation process, for example, particles having a certain shape are layered to form a precursor for the porous layer. At this stage, the strength of the precursor is very weak. Then, for example, a photo- or thermally activated catalytic reaction is used to generate a product (e.g., a strong base catalyst generated from a photobase generator) that can chemically bond the microporous particles together (first stage of the crosslinking reaction process). To efficiently advance the reaction in a short time, further heat aging (second stage of the crosslinking reaction process) is performed, which is thought to further promote the chemical bonding (crosslinking reaction) between the microporous particles and improve strength. For example, if the microporous particles are microporous particles of a silicon compound (e.g., a pulverized body of a gel-like silica compound) and residual silanol groups (Si-OH groups) are present in the precursor, the residual silanol groups are thought to chemically bond together through a crosslinking reaction. However, this explanation is also an example and does not limit the method for forming the low refractive index layer.

[0056] The above method includes a step of preparing a liquid containing microporous particles. When the microporous particles are a pulverized product of a gel-like compound, the pulverized product can be obtained, for example, by pulverizing the gel-like compound. By pulverizing the gel-like compound, the three-dimensional structure of the gel-like compound is destroyed and dispersed into a three-dimensional basic structure, as described above. An example of preparing the pulverized product is as follows.

[0057] The gelation of the monomer compounds can be achieved, for example, by hydrogen bonding or intermolecular bonding between the monomer compounds. Examples of the monomer compounds include silicon compounds represented by the above formula (1). Since the silicon compound of formula (1) has a hydroxyl group, hydrogen bonding or intermolecular bonding can occur between the monomers of formula (1), for example, via the respective hydroxyl groups.

[0058] Alternatively, the silicon compound may be a hydrolysate of the silicon compound precursor, for example, it may be produced by hydrolyzing the silicon compound precursor represented by the above formula (2).

[0059] The method for hydrolyzing the monomer compound precursor is not particularly limited and can be, for example, a chemical reaction in the presence of a catalyst. Examples of catalysts include acids such as oxalic acid and acetic acid. The hydrolysis reaction can be carried out, for example, by slowly adding dropwise an aqueous solution of oxalic acid to a mixture (e.g., a suspension) of a silicon compound and dimethyl sulfoxide at room temperature, followed by stirring for approximately 30 minutes. When hydrolyzing the silicon compound precursor, for example, by completely hydrolyzing the alkoxy groups of the silicon compound precursor, subsequent gelation, aging, and heating and fixation after pore structure formation can be carried out more efficiently.

[0060] The gelation of the monomer compound can be carried out, for example, by a dehydration condensation reaction between monomers. The dehydration condensation reaction is preferably carried out, for example, in the presence of a catalyst, and examples of the catalyst include acid catalysts such as hydrochloric acid, oxalic acid, and sulfuric acid, and base catalysts such as ammonia, potassium hydroxide, sodium hydroxide, and ammonium hydroxide. The dehydration condensation catalyst is preferably a base catalyst. In the dehydration condensation reaction, the amount of catalyst added relative to the monomer compound is not particularly limited. For example, the catalyst can be added in an amount of preferably 0.1 to 10 moles, more preferably 0.05 to 7 moles, and even more preferably 0.1 to 5 moles, relative to 1 mole of the monomer compound.

[0061] The gelation of the monomer compound is preferably carried out in, for example, a solvent. The ratio of the monomer compound to the solvent is not particularly limited. Examples of the solvent include dimethyl sulfoxide (DMSO), N-methylpyrrolidone (NMP), N,N-dimethylacetamide (DMAc), dimethylformamide (DMF), γ-butyrolactone (GBL), acetonitrile (MeCN), ethylene glycol ethyl ether (EGEE), etc. The solvent may be used alone or in combination of two or more. The solvent used for gelation is hereinafter also referred to as "gelation solvent."

[0062] The gelation conditions are not particularly limited. The treatment temperature for the solvent containing the monomer compound is, for example, 20°C to 30°C, preferably 22°C to 28°C, and more preferably 24°C to 26°C. The treatment time is, for example, 1 minute to 60 minutes, preferably 5 minutes to 40 minutes, and more preferably 10 minutes to 30 minutes. When a dehydration condensation reaction is carried out, the treatment conditions are not particularly limited, and these examples can be used. By carrying out gelation, for example, siloxane bonds grow and primary silica particles are formed, and as the reaction progresses, the primary particles are strung together like beads to produce a gel with a three-dimensional structure.

[0063] The gel-like compound obtained by gelation is preferably subjected to an aging treatment after the gelation reaction. The aging treatment, for example, can further grow the primary particles of the gel having a three-dimensional structure obtained by gelation, thereby increasing the size of the particles themselves, and as a result, the contact state at the neck portions where the particles are in contact with each other can be changed from point contact to surface contact (increasing the contact area). For example, the strength of the gel that has been aged increases, and as a result, the strength of the three-dimensional basic structure after pulverization can be improved. This can prevent the pore size of the void structure in which the three-dimensional basic structure is deposited from shrinking due to solvent evaporation during the drying process, for example, in the drying process after coating the pulverized material.

[0064] The aging treatment can be carried out, for example, by incubating the gel compound at a predetermined temperature for a predetermined time. The aging temperature is, for example, 30°C or higher, preferably 35°C or higher, and more preferably 40°C or higher. On the other hand, the aging temperature is, for example, 80°C or lower, preferably 75°C or lower, and more preferably 70°C or lower. The aging temperature range is, for example, 30°C to 80°C, preferably 35°C to 75°C, and more preferably 40°C to 70°C. The aging time is, for example, 5 hours or longer, preferably 10 hours or longer, and more preferably 15 hours or longer. On the other hand, the aging time range is, for example, 50 hours or shorter, preferably 40 hours or shorter, and more preferably 30 hours or shorter. The aging time range is, for example, 5 hours to 50 hours, preferably 10 hours to 40 hours, and more preferably 15 hours to 30 hours. The aging conditions can be optimized, for example, to increase the silica primary particle size and the contact area of the neck portion. Furthermore, it is preferable to take into consideration the boiling point of the solvent used; for example, if the aging temperature is too high, the solvent will volatilize excessively, which may cause problems such as the pores in the three-dimensional void structure being closed due to the increased concentration of the coating liquid (gel liquid). On the other hand, for example, if the aging temperature is too low, not only will the aging effect not be fully obtained, but temperature fluctuations will increase over time in the mass production process, which may result in a low refractive index layer with inferior properties.

[0065] The aging treatment can use, for example, the same solvent as that used in the gelation treatment. Specifically, it is preferable to subject the reaction product (i.e., the solvent containing the gel-like compound) after the gelation treatment to the aging treatment as is. The number of moles of residual silanol groups contained in the gel (gel-like compound, for example, gel-like silicon compound) that has undergone the aging treatment after gelation is, for example, 50% or less, preferably 40% or less, and more preferably 30% or less. On the other hand, the number of moles of residual silanol groups is, for example, 1% or more, preferably 3% or more, and more preferably 5% or more. The range of the number of moles of residual silanol groups is, for example, 1% to 50%, preferably 3% to 40%, and more preferably 5% to 30%. For the purpose of increasing the hardness of the gel, for example, a lower number of moles of residual silanol groups is preferable. If the number of moles of silanol groups is too high, for example, the pore structure may not be maintained until the precursor of the silicone porous body is crosslinked. On the other hand, if the number of moles of silanol groups is too low, for example, in the process of preparing a microporous particle-containing liquid (e.g., a suspension) and / or in a subsequent process, the pulverized gel compound may not be crosslinked, and sufficient film strength may not be imparted. The number of moles of residual silanol groups is, for example, the proportion of residual silanol groups when the number of moles of alkoxy groups in the raw material (e.g., a monomer compound precursor) is taken as 100. While the above is an example of silanol groups, for example, when a monomer silicon compound is modified with various reactive functional groups, the same matters and conditions may also be applied to each functional group.

[0066] After the monomer compound is gelled in the gelling solvent, the resulting gelled compound is pulverised. For example, the pulverisation may be carried out by directly pulverising the gelled compound in the gelling solvent, or by replacing the gelling solvent with another solvent and then pulverising the gelled compound in the other solvent. Furthermore, for example, if the catalyst and solvent used in the gelling reaction remain after the aging step, causing gelation of the liquid over time (pot life) and a reduction in drying efficiency during the drying step, it is preferable to replace them with another solvent. Hereinafter, the other solvent will also be referred to as the "pulverising solvent".

[0067] The grinding solvent is not particularly limited, and for example, an organic solvent can be used. Examples of organic solvents include solvents with a boiling point of, for example, 130°C or less, preferably 100°C or less, and more preferably 85°C or less. Specific examples include isopropyl alcohol (IPA), ethanol, methanol, butanol, propylene glycol monomethyl ether (PGME), methyl cellosolve, acetone, dimethylformamide (DMF), isobutyl alcohol, etc. The grinding solvent may be used alone or in combination of two or more.

[0068] The combination of the gelling solvent and the grinding solvent is not particularly limited, and examples thereof include combinations of DMSO and IPA, DMSO and ethanol, DMSO and methanol, DMSO and butanol, DMSO and isobutyl alcohol, etc. By replacing the gelling solvent with the grinding solvent in this way, for example, a more uniform coating film can be formed in the coating film formation described below.

[0069] The method for pulverizing the gel-like compound is not particularly limited and can be performed using, for example, an ultrasonic homogenizer, a high-speed rotation homogenizer, or other grinding devices that utilize the cavitation phenomenon. While media-based grinding devices such as ball mills physically destroy the void structure of the gel during grinding, cavitation-based grinding devices such as homogenizers use a media-less method, which uses high-speed shear force to peel off the relatively weakly bonded silica particle interfaces already embedded in the three-dimensional gel structure. This allows the resulting three-dimensional gel structure to retain a void structure with a certain range of particle size distribution, and can re-form the void structure formed by deposition during coating and drying. The grinding conditions are not particularly limited; for example, it is preferable to apply a momentary high-speed flow to grind the gel without volatilizing the solvent. For example, grinding is preferably performed to obtain a pulverized product with the above-mentioned particle size variation (e.g., volume average particle size or particle size distribution). If the amount of work, such as the grinding time and intensity, is insufficient, for example, coarse particles will remain, making it impossible to form dense pores, and there will be an increase in appearance defects, making it impossible to achieve high quality.On the other hand, if the amount of work is too much, for example, the particles will be finer than the desired particle size distribution, and the void size accumulated after coating and drying will be fine, which may prevent the desired porosity from being obtained.

[0070] In this manner, a liquid (e.g., a suspension) containing microporous particles (pulverized gel-like compound) can be prepared. Furthermore, a liquid containing microporous particles and a catalyst can be prepared by adding a catalyst that chemically bonds the microporous particles to each other after or during the preparation process of the liquid containing microporous particles. The catalyst may be, for example, a catalyst that promotes cross-linking between the microporous particles. The chemical reaction that chemically bonds the microporous particles to each other preferably utilizes a dehydration condensation reaction of residual silanol groups contained in silica sol molecules. By promoting the reaction between the hydroxyl groups of the silanol groups with a catalyst, continuous film formation that hardens the pore structure in a short time is possible. Examples of catalysts include photoactive catalysts and thermally active catalysts. Photoactive catalysts can chemically bond (e.g., cross-link) the microporous particles to each other without heating, for example, during the precursor formation process. This reduces the overall shrinkage of the precursor during the precursor formation process, thereby maintaining a higher porosity. Furthermore, a catalyst-generating substance (catalyst generator) may be used in addition to or instead of the catalyst. For example, in addition to or instead of a photoactive catalyst, a substance that generates a catalyst by light (photocatalyst generator) may be used, or in addition to or instead of a thermally active catalyst, a substance that generates a catalyst by heat (thermal catalyst generator) may be used. Examples of photocatalyst generators include photobase generators (substances that generate a basic catalyst by light irradiation) and photoacid generators (substances that generate an acidic catalyst by light irradiation), and photobase generators are preferred.Examples of photobase generators include 9-anthrylmethyl N,N-diethylcarbamate (trade name WPBG-018), (E)-1-[3-(2-hydroxyphenyl)-2-propenoyl]piperidine (trade name WPBG-027), 1-(anthraquinon-2-yl)ethyl imidazolecarboxylate (trade name WPBG-140), 2-nitrophenylmethyl 4-methacryloyloxypiperidine-1-carboxylate (trade name WPBG-165), and 1,2-diisopropyl-3-[bis(dimethylamino)methylene]guanidium. Examples of photoacid generators include 2-(3-benzoylphenyl)propionate (trade name WPBG-266), 1,2-dicyclohexyl-4,4,5,5-tetramethylbiguanidium n-butyltriphenylborate (trade name WPBG-300), and 2-(9-oxoxanthen-2-yl)propionic acid 1,5,7-triazabicyclo[4.4.0]dec-5-ene (Tokyo Chemical Industry Co., Ltd.), and a compound containing 4-piperidinemethanol (trade name HDPD-PB100, manufactured by Heraeus Chemical). All of the above-mentioned product names containing "WPBG" are trade names of Wako Pure Chemical Industries, Ltd. Examples of photoacid generators include aromatic sulfonium salts (trade name SP-170, manufactured by ADEKA), triarylsulfonium salts (trade name CPI101A, manufactured by San-Apro), and aromatic iodonium salts (trade name Irgacure 250, manufactured by Ciba Japan). Furthermore, the catalyst that chemically bonds the microporous particles together is not limited to a photoactive catalyst or a photocatalyst generator, but may be, for example, a thermally active catalyst or a thermal catalyst generator such as urea. Examples of the catalyst that chemically bonds the microporous particles together include base catalysts such as potassium hydroxide, sodium hydroxide, and ammonium hydroxide, and acid catalysts such as hydrochloric acid, acetic acid, and oxalic acid. Among these, base catalysts are preferred.The catalyst or catalyst generator that chemically bonds microporous particles together can be used, for example, by adding it to a sol particle liquid (e.g., a suspension) containing the pulverized material (microporous particles) just before coating, or by using it as a mixed liquid in which the catalyst or catalyst generator is mixed with a solvent. The mixed liquid may be, for example, a coating liquid in which the catalyst or catalyst generator is directly added to the sol particle liquid and dissolved therein, a solution in which the catalyst or catalyst generator is dissolved in a solvent, or a dispersion in which the catalyst or catalyst generator is dispersed in a solvent. The solvent is not particularly limited, and examples thereof include water, a buffer solution, etc.

[0071] Furthermore, for example, a cross-linking auxiliary agent may be added to the gel-containing liquid to indirectly bond the pulverized gel particles together. This cross-linking auxiliary agent penetrates between the particles (the pulverized gel particles) and the particles and the cross-linking auxiliary interact or bond with each other, making it possible to bond particles that are somewhat distant from each other, thereby efficiently increasing strength. A multi-cross-linking auxiliary agent is preferred. Specifically, the multi-cross-linking silane monomer may have, for example, two to three alkoxysilyl groups, and the chain length between the alkoxysilyl groups may be from one to ten carbon atoms, and may also contain elements other than carbon. Examples of the crosslinking auxiliary include bis(trimethoxysilyl)ethane, bis(triethoxysilyl)ethane, bis(trimethoxysilyl)methane, bis(triethoxysilyl)methane, bis(triethoxysilyl)propane, bis(trimethoxysilyl)propane, bis(triethoxysilyl)butane, bis(trimethoxysilyl)butane, bis(triethoxysilyl)pentane, bis(trimethoxysilyl)pentane, bis(triethoxysilyl)hexane, bis(trimethoxysilyl)hexane, bis(trimethoxysilyl)-N-butyl-N-propyl-ethane-1,2-diamine, tris-(3-trimethoxysilylpropyl)isocyanurate, and tris-(3-triethoxysilylpropyl)isocyanurate. The amount of the crosslinking aid to be added is not particularly limited, but is, for example, 0.01 to 20% by weight, 0.05 to 15% by weight, or 0.1 to 10% by weight relative to the weight of the pulverized silicon compound.

[0072] Next, a liquid containing microporous particles (e.g., a suspension) is applied onto the plugged portion (coating step). Coating can be performed using, but is not limited to, various coating methods described below. A coating film containing microporous particles and a catalyst can be formed by directly applying a liquid containing microporous particles (e.g., a pulverized gel silica compound) onto the plugged portion. The coating film can also be referred to as a coating layer. By forming a coating film, for example, the pulverized material, whose three-dimensional structure has been destroyed, settles and deposits, creating a new three-dimensional structure. For example, the liquid containing microporous particles does not need to contain a catalyst that chemically bonds the microporous particles together. For example, as described below, the precursor formation step can be performed after or while spraying a catalyst that chemically bonds the microporous particles onto the coating film. However, the liquid containing microporous particles may contain a catalyst that chemically bonds the microporous particles together, and the catalyst contained in the coating film chemically bonds the microporous particles together to form a precursor for the porous body.

[0073] The solvent (hereinafter also referred to as "coating solvent") is not particularly limited, and for example, an organic solvent can be used. Examples of organic solvents include solvents with a boiling point of 150°C or less. Specific examples include IPA, ethanol, methanol, n-butanol, 2-butanol, isobutyl alcohol, pentanol, etc., and the same solvent as the grinding solvent can also be used. When the method for forming a low refractive index layer includes a step of grinding a gel compound, for example, the grinding solvent containing the ground product of the gel compound may be used as is in the coating film formation step.

[0074] In the coating step, for example, a pulverized sol dispersed in a solvent (hereinafter also referred to as "sol particle liquid") is preferably coated onto the sealing portion. For example, the sol particle liquid is coated onto the sealing portion, dried, and then chemically crosslinked, thereby continuously forming a porous layer having a certain level of film strength or higher. Note that "sol" in the embodiments of the present invention refers to a state in which silica sol particles with a nano-three-dimensional structure that retains part of the porous structure are dispersed in a solvent and exhibit fluidity by pulverizing the three-dimensional structure of the gel.

[0075] The concentration of the pulverized material in the coating solvent is not particularly limited and is, for example, 0.3% (v / v) to 50% (v / v), preferably 0.5% (v / v) to 30% (v / v), and more preferably 1.0% (v / v) to 10% (v / v). If the concentration of the pulverized material is too high, for example, the fluidity of the sol particle liquid may be significantly reduced, which may cause aggregates and coating streaks during coating. If the concentration of the pulverized material is too low, for example, not only may it take a considerable amount of time to dry the solvent from the sol particle liquid, but also the amount of residual solvent immediately after drying may be high, which may reduce the porosity.

[0076] The physical properties of the sol are not particularly limited. The shear viscosity of the sol is, for example, 100 cPa·s or less, preferably 10 cPa·s or less, and more preferably 1 cPa·s or less, at a shear rate of 10,000 1 / s. If the shear viscosity is too high, for example, coating streaks may occur, and problems such as a decrease in the transfer rate of gravure coating may occur. Conversely, if the shear viscosity is too low, for example, the wet coating thickness during coating may not be thick enough, and the desired thickness may not be obtained after drying.

[0077] The amount of the pulverized material to be applied is not particularly limited and can be appropriately set depending on, for example, the desired thickness of the silicone porous body (and consequently, the low refractive index layer). As a specific example, when forming a silicone porous body having a thickness of 0.1 μm to 1000 μm, the amount of the pulverized material to be applied is 100 μm per square meter of the coated surface. 2The coating weight is, for example, 0.01 μg to 60,000 μg, preferably 0.1 μg to 5,000 μg, and more preferably 1 μg to 50 μg per coating. The preferred coating weight of the sol particle liquid is difficult to define uniquely because it depends on factors such as the liquid concentration and coating method. However, considering productivity, it is preferable to coat as thin a layer as possible. If the coating weight is too high, for example, there is a high possibility that the solvent will be dried in a drying oven before volatilizing. This may result in the nano-pulverized sol particles settling and accumulating in the solvent, causing the solvent to dry before forming a void structure, inhibiting the formation of voids and significantly reducing the porosity. On the other hand, if the coating weight is too thin, there is a high risk of coating cissing.

[0078] Furthermore, the method for forming a low refractive index layer further includes, for example, a precursor-forming step of forming a void structure, which is a precursor of the void layer (low refractive index layer), as described above. The precursor-forming step is not particularly limited, but for example, the precursor (void structure) may be formed by a drying step of drying a coating film prepared by coating a microporous particle-containing liquid. The drying treatment in the drying step not only removes the solvent (solvent contained in the sol particle liquid) in the coating film, but also causes the sol particles to settle and deposit during the drying treatment, forming a void structure. The temperature for the drying treatment is, for example, 50°C to 250°C, preferably 60°C to 150°C, and more preferably 70°C to 130°C. The time for the drying treatment is, for example, 0.1 to 30 minutes, preferably 0.2 to 10 minutes, and more preferably 0.3 to 3 minutes.

[0079] The drying process may be, for example, natural drying, heat drying, or reduced-pressure drying. Among these, heat drying is preferred when industrial continuous production is assumed. The heat drying method is not particularly limited, and for example, a general heating means can be used. Examples of heating means include a hot air blower, a heating roll, and a far-infrared heater. Furthermore, the solvent used is preferably a solvent with low surface tension in order to prevent shrinkage stress caused by solvent evaporation during drying and the resulting cracking of the porous layer (porous silicone body). Examples of the solvent include lower alcohols such as isopropyl alcohol (IPA), hexane, and perfluorohexane. Furthermore, a small amount of a perfluoro-based surfactant or a silicone-based surfactant may be added to the IPA or the like to reduce the surface tension.

[0080] Furthermore, as described above, the method for forming a low refractive index layer includes a crosslinking reaction step in which a crosslinking reaction occurs within the precursor after the precursor formation step. In this crosslinking reaction step, a basic substance is generated by light irradiation or heating, and the crosslinking reaction step is multi-stage. In the first stage of the crosslinking reaction step, for example, microporous particles are chemically bonded together by the action of a catalyst (basic substance). This fixes, for example, the three-dimensional structure of the pulverized material in the coating film (precursor). In conventional fixation by sintering, high-temperature treatment, for example, at 200°C or higher, induces dehydration condensation of silanol groups and the formation of siloxane bonds. In this formation method, by reacting various additives that catalyze the above-mentioned dehydration condensation reaction, a void structure can be continuously formed and fixed, for example, at a relatively low drying temperature of around 100°C and in a short treatment time of less than a few minutes.

[0081] The chemical bonding method is not particularly limited, and can be appropriately determined depending on the type of gel silicon compound, for example.Specifically, chemical bonding can be performed by chemical cross-linking between pulverized materials, and also, for example, when inorganic particles such as titanium oxide are added to the pulverized material, it is possible to chemically cross-link the inorganic particles and the pulverized material.In addition, when supporting a biocatalyst such as an enzyme, it is also possible to chemically cross-link the pulverized material with a site other than the catalytic active site.Therefore, the method for forming a low refractive index layer can be applied not only to a void layer (silicone porous body) formed between sol particles, but also to an organic-inorganic hybrid void layer, a host-guest void layer, etc.

[0082] The stage at which the chemical reaction in the presence of the catalyst is carried out (occurs) in the method for forming a low refractive index layer is not particularly limited, and it may be carried out, for example, in at least one stage of the multi-stage crosslinking reaction process. For example, in the method for forming a low refractive index layer, as described above, the drying process may also serve as the precursor formation process. Alternatively, for example, a multi-stage crosslinking reaction process may be carried out after the drying process, and in at least one of the stages, the microporous particles may be chemically bonded to each other by the action of the catalyst. For example, when the catalyst is a photoactive catalyst as described above, the microporous particles may be chemically bonded to each other by light irradiation in the crosslinking reaction process to form a precursor of the porous body. Furthermore, when the catalyst is a thermally active catalyst, the microporous particles may be chemically bonded to each other by heating in the crosslinking reaction process to form a precursor of the porous body.

[0083] The chemical reaction can be carried out, for example, by irradiating or heating a coating film containing a catalyst previously added to a sol particle liquid (e.g., a suspension), or by spraying a catalyst onto the coating film and then irradiating or heating it, or by irradiating or heating it while spraying the catalyst. The integrated light amount in the light irradiation is not particularly limited, and is, for example, 200 mJ / cm2 in terms of a wavelength of 360 nm. 2 ~800mJ / cm 2 and preferably 250 mJ / cm 2 ~600mJ / cm 2 and more preferably 300 mJ / cm2 ~400mJ / cm 2 In order to prevent insufficient effect due to insufficient irradiation amount resulting in insufficient decomposition due to light absorption by the catalyst, the irradiation amount is set to 200 mJ / cm 2 The above integrated light intensity is preferred. The conditions for the heat treatment are not particularly limited. The heating temperature is, for example, 50°C to 250°C, preferably 60°C to 150°C, and more preferably 70°C to 130°C. The heating time is, for example, 0.1 to 30 minutes, preferably 0.2 to 10 minutes, and more preferably 0.3 to 3 minutes. Alternatively, the step of drying the coated sol particle liquid (e.g., suspension) as described above may also serve as a step of carrying out a chemical reaction in the presence of a catalyst. That is, in the step of drying the coated sol particle liquid (e.g., suspension), the pulverized particles (microporous particles) may be chemically bonded together by a chemical reaction in the presence of a catalyst. In this case, the coated film may be further heated after the drying step to further firmly bond the pulverized particles (microporous particles). Furthermore, it is believed that a chemical reaction in the presence of a catalyst may also occur in the step of preparing a microporous particle-containing liquid (e.g., suspension) and the step of applying the microporous particle-containing liquid. However, this assumption does not limit the method for forming the low refractive index layer. Furthermore, the solvent used is preferably one with low surface tension, for example, to prevent shrinkage stress caused by solvent evaporation during drying and the resulting cracking of the void layer. Examples of suitable solvents include lower alcohols such as isopropyl alcohol (IPA), hexane, and perfluorohexane.

[0084] In the method for forming a low refractive index layer, the crosslinking reaction process is performed in multiple stages, which can further improve the strength of the porous layer (low refractive index layer) compared to, for example, a single-stage crosslinking reaction process. Hereinafter, the second and subsequent stages of the crosslinking reaction process may be referred to as the "aging process." In the aging process, for example, the precursor may be heated to further promote the crosslinking reaction within the precursor. The phenomenon and mechanism that occur in the crosslinking reaction process are unclear, but are, for example, as described above. For example, in the aging process, the heating temperature is lowered to cause the crosslinking reaction while suppressing the shrinkage of the precursor, thereby improving strength and achieving both high porosity and strength. The temperature in the aging process is, for example, 40°C to 70°C, preferably 45°C to 65°C, and more preferably 50°C to 60°C. The time for the aging process is, for example, 10 hours to 30 hours, preferably 13 hours to 25 hours, and more preferably 15 hours to 20 hours.

[0085] The low refractive index layer formed as described above has excellent strength, and can be made into a roll-shaped porous body, for example, which has the advantages of high production efficiency and ease of handling.

[0086] The low refractive index layer (void layer) thus formed may be further laminated with another film (layer) to form a laminate structure including a porous structure. In this case, each component of the laminate structure may be laminated via, for example, a pressure-sensitive adhesive or adhesive.

[0087] The specific configuration and formation method of the low refractive index layer are described in detail in, for example, International Publication No. 2019 / 151073, the disclosure of which is incorporated herein by reference.

[0088] C. Micro LED array substrate The micro LED array substrate may have any suitable configuration. Typically, as shown in Fig. 1, a micro LED array substrate 10 includes a drive substrate 12 and a plurality of micro LEDs 11 arranged in a matrix on the drive substrate 12.

[0089] A micro LED refers to an LED with a chip size of, for example, 1 μm square to 100 μm square.

[0090] In one embodiment, the plurality of micro LEDs may be a single type of micro LED, hi one embodiment, the micro LED is a blue LED or an ultraviolet LED.

[0091] The driving board can be configured to switch and drive each micro LED individually, and driving boards are well known to those skilled in the art, so a description thereof will be omitted here.

[0092] D. Sealing part The sealing portion may be formed of any suitable transparent material. Examples of materials constituting the sealing portion include epoxy resins, silicone resins, and acrylic resins. The sealing portion may also be formed of molten glass. Examples of glass constituting the sealing portion include acrylic glass, crown glass, flint glass, and borosilicate glass.

[0093] The seal may be made of an adhesive or pressure sensitive adhesive, hi one embodiment, the seal is made of a pressure sensitive adhesive.

[0094] Any appropriate adhesive can be used as the adhesive, for example, water-based adhesives such as isocyanate-based, polyvinyl alcohol-based, gelatin-based, vinyl latex-based, water-based polyurethane, and water-based polyester, and curable adhesives such as ultraviolet-curable adhesives and electron beam-curable adhesives.

[0095] Any appropriate pressure-sensitive adhesive can be used as the pressure-sensitive adhesive. Examples include rubber-based, acrylic-based, silicone-based, urethane-based, vinyl alkyl ether-based, polyvinyl alcohol-based, polyvinylpyrrolidone-based, polyacrylamide-based, and cellulose-based pressure-sensitive adhesives. Among these, acrylic pressure-sensitive adhesives are preferably used because of their excellent optical transparency, adhesive properties, weather resistance, heat resistance, and the like.

[0096] The sealed portion may have a light transmittance (23°C) of, for example, 80% or more, preferably 85% or more, and more preferably 90% or more at a wavelength of 590 nm. The average light transmittance of the sealed portion at a wavelength of 450 nm to 500 nm is preferably 70% or more, more preferably 75% or more, and even more preferably 80% or more. The average light transmittance of the sealed portion at a wavelength of 500 nm to 780 nm is preferably 80% or more, more preferably 85% or more, and even more preferably 90% or more.

[0097] The refractive index of the sealing portion is preferably 1.40 or more, more preferably 1.40 to 2.00, and even more preferably 1.45 to 1.80.

[0098] The thickness of the encapsulating portion is preferably 200 μm or less, more preferably 150 μm or less, even more preferably 100 μm or less, and particularly preferably 50 μm or less. The thinner the encapsulating portion, the more pronounced the effect of suppressing color mixing. The lower limit of the encapsulating portion thickness is, for example, 10 μm. The thickness of the encapsulating portion may be the distance from the surface of the micro LED on the low refractive index layer side to the surface of the encapsulating portion on the micro LED side.

[0099] E. Wavelength conversion layer The wavelength conversion layer is a layer that absorbs excitation light from the micro LED and emits a predetermined color. When a blue LED is used as the micro LED, a red subpixel can be formed by a wavelength conversion layer that absorbs the excitation light from the micro LED and emits red light, and a green subpixel can be formed by a wavelength conversion layer that absorbs the excitation light and emits green light. When an ultraviolet LED is used, a red subpixel can be formed by a wavelength conversion layer that is excited by ultraviolet light and emits red light, a green subpixel can be formed by a wavelength conversion layer that is excited by ultraviolet light and emits green light, and a blue subpixel can be formed by a wavelength conversion layer that is excited by ultraviolet light and emits blue light.

[0100] In one embodiment, the wavelength conversion layer contains phosphor particles. The wavelength conversion layer typically contains a matrix and phosphor particles dispersed in the matrix. Any appropriate material can be used as the material constituting the matrix (hereinafter also referred to as the matrix material). Examples of such materials include resins, organic oxides, and inorganic oxides. The matrix material is preferably a resin. The resin may be a thermoplastic resin, a thermosetting resin, or an active energy ray-curable resin (e.g., an electron beam-curable resin, an ultraviolet ray-curable resin, or a visible light-curable resin). A thermosetting resin or an ultraviolet ray-curable resin is preferred, and a thermosetting resin is more preferred. The resins may be used alone or in combination (e.g., blended or copolymerized).

[0101] In one embodiment, quantum dots may be used as the phosphor particles. The quantum dots can control the wavelength conversion characteristics of the wavelength conversion layer. Specifically, by appropriately combining quantum dots with different central emission wavelengths, a wavelength conversion layer that achieves light with a desired central emission wavelength can be formed. The central emission wavelength of the quantum dots can be adjusted by the material and / or composition, particle size, shape, etc. of the quantum dots. Known quantum dots include quantum dots with a central emission wavelength in the wavelength range of 600 nm to 680 nm (hereinafter referred to as quantum dot A), quantum dots with a central emission wavelength in the wavelength range of 500 nm to 600 nm (hereinafter referred to as quantum dot B), and quantum dots with a central emission wavelength in the wavelength range of 400 nm to 500 nm (hereinafter referred to as quantum dot C). Quantum dot A emits red light when excited by excitation light (light from a micro LED), quantum dot B emits green light, and quantum dot C emits blue light. By appropriately combining these, when light of a predetermined wavelength is made to enter and pass through the wavelength conversion layer, light having a central emission wavelength in a desired wavelength band can be realized.

[0102] The quantum dots can be made of any suitable material. Preferably, the quantum dots can be made of inorganic materials, more preferably inorganic conductive materials or inorganic semiconductor materials. Semiconductor materials include, for example, II-VI, III-V, IV-VI, and IV semiconductors. Specific examples include Si, Ge, Sn, Se, Te, B, C (including diamond), P, BN, BP, BAs, AlN, AlP, AlAs, AlSb, GaN, GaP, GaAs, GaSb, InN, InP, InAs, InSb, ZnO, ZnS, ZnSe, ZnTe, CdS, CdSe, CdSeZn, CdTe, HgS, HgSe, HgTe, BeS, BeSe, BeTe, MgS, MgSe, GeS, GeSe, GeTe, SnS, SnSe, SnTe, PbO, PbS, PbSe, PbTe, CuF, CuCl, CuBr, CuI, SiN, GeN, AlO, (Al, Ga, In)(S, Se, Te), and AlCO. These may be used alone or in combination of two or more. The quantum dots may contain a p-type dopant or an n-type dopant.

[0103] The size of the quantum dots can be any appropriate size depending on the desired emission wavelength. The size of the quantum dots is preferably 1 nm to 10 nm, more preferably 2 nm to 8 nm. When the size of the quantum dots is within this range, both green and red light can be emitted sharply, achieving high color rendering. For example, green light can be emitted when the quantum dots are about 7 nm in size, and red light can be emitted when the quantum dots are about 3 nm in size. The size of the quantum dots is the average particle size when the quantum dots are, for example, spherical, or the dimension along the smallest axis of the shape when the quantum dots have any other shape. The shape of the quantum dots can be any appropriate shape depending on the purpose. Specific examples include spherical, flake, plate, ellipsoidal, and irregular shapes.

[0104] The quantum dots can be blended in a ratio of preferably 1 to 50 parts by weight, more preferably 2 to 30 parts by weight, per 100 parts by weight of the matrix material. If the blending amount of quantum dots falls within this range, a display with excellent hue balance across all RGB can be provided.

[0105] Details of quantum dots are described in, for example, JP 2012-169271 A, JP 2015-102857 A, JP 2015-65158 A, JP 2013-544018 A, JP 2013-544018 A, and JP 2010-533976 A, the disclosures of which are incorporated herein by reference. Commercially available quantum dots may be used.

[0106] In another embodiment, the phosphor particles are particles that exhibit luminescence due to their composition, such as sulfide, aluminate, oxide, silicate, nitride, YAG, and terbium aluminum garnet (TAG) based materials.

[0107] Furthermore, the following red and green phosphors may be used as phosphor particles. 4+ A complex fluoride phosphor is a coordination compound that contains at least one coordination center (e.g., M, described below), is surrounded by fluoride ions that act as ligands, and is optionally charge-compensated by counter ions (e.g., A, described below). A specific example is A2[MF5]:Mn 4+ , A3[MF6]:Mn 4+ , Zn2[MF7]:Mn 4+ , A[In2F7]:Mn 4+ , A2[M´F6]:Mn 4+ , E[M´F6]:Mn 4+ , A3[ZrF7]:Mn 4+ , Ba 0.65 Zr 0.35 F 2.70 :Mn 4+Here, A is Li, Na, K, Rb, Cs, NH4, or a combination thereof. M is Al, Ga, In, or a combination thereof. M' is Ge, Si, Sn, Ti, Zr, or a combination thereof. E is Mg, Ca, Sr, Ba, Zn, or a combination thereof. A complex fluoride phosphor having a coordination number of 6 in the coordination center is preferred. Details of such red phosphors are described, for example, in JP 2015-84327 A. The disclosure of this publication is incorporated herein by reference in its entirety.

[0108] An example of a green phosphor is a compound containing, as a main component, a solid solution of sialon having a β-type Si3N4 crystal structure. Preferably, a process is carried out to reduce the oxygen content in such sialon crystal to a specific amount (e.g., 0.8% by mass) or less. By carrying out such a process, a green phosphor that emits sharp light with a narrow peak width can be obtained. Details of such a green phosphor are described, for example, in JP 2013-28814 A. The disclosure of this publication is incorporated herein by reference in its entirety.

[0109] The thickness of the wavelength conversion layer is preferably 5 μm to 100 μm, more preferably 30 μm to 50 μm. If the thickness of the wavelength conversion layer is in this range, the conversion efficiency and durability can be excellent.

[0110] As described above, in one embodiment, the wavelength conversion layers are spaced apart by partition walls (light-shielding layers). The width of the partition walls (i.e., the distance between adjacent wavelength conversion layers) is preferably 0.1 μm to 100 μm, more preferably 1 μm to 50 μm. In the present invention, sufficient color mixing can be suppressed even when the width of the partition walls is narrow. By narrowing the width of the partition walls, a micro LED display device with excellent luminous efficiency can be obtained.

[0111] As described above, when constructing a subpixel that directly utilizes light from a micro LED (for example, when forming a blue subpixel using a blue LED), the wavelength conversion layer can be replaced with a light diffusion layer in that location. The light scattering layer preferably contains light scattering particles. Examples of materials that constitute the light scattering particles include alumina, zirconium oxide, titanium oxide, and barium sulfate.

[0112] In one embodiment, the micro LED display device further includes a color filter disposed on the surface of the wavelength conversion layer (and / or light diffusion layer) opposite to the low refractive index layer. The color filter may have any suitable configuration depending on the color emitted by the subpixel. In one embodiment, a color filter is disposed in each subpixel to block colors other than the desired color. For example, a color filter that blocks blue color is used in the red and green subpixels. [Example]

[0113] The present invention will be specifically explained below with reference to examples, but the present invention is not limited to these examples.

[0114] [Example 1] The luminance of red and green light was determined by optical simulation for the configuration shown in Figure 2(a), in which red and green phosphors are arranged as wavelength conversion layers, and a blue LED is placed directly below the green phosphor via a low-refractive index layer (refractive index: 1.20) and a sealing layer (refractive index: 1.50). The wavelength conversion layers were each constructed by adding 10% by weight of wavelength-converting particles (refractive index: 1.80) to a matrix layer (refractive index: 1.47). The refractive index of each wavelength conversion layer was 1.50. The optical properties in this example and in the examples and comparative examples described later were calculated using optical simulation software (Lighttools) from Synopsys, Inc. The optical model used in the simulation is as follows: The thickness and width of each RGB wavelength conversion layer was 100 μm and 100 μm, respectively. The width of the partitions between each RGB layer was 50 nm. LEDs were placed opposite each wavelength conversion layer. In this simulation, to investigate the effects of color mixing, only the LED corresponding to the green wavelength conversion layer was placed, and a sealing section (adhesive layer) was placed between the LED and the wavelength conversion layer. The thickness of the sealing section between the LED and the wavelength conversion layer is shown in Table 1. The thickness of the low refractive index layer was 1.0 μm. The dimensions are based on a 78-inch display with 4K resolution (3840 x 2160). The partitions were placed 50.0 μm apart between the wavelength conversion layers, and the transmittance was set to 0%. A photodetector was placed above each pixel.

[0115] [Comparative Example 1] For the configuration shown in Figure 2(b), i.e., a configuration in which red and green phosphors are arranged as wavelength conversion layers and a blue LED is placed directly below the green phosphor via a sealing portion (without a low refractive index layer), the brightness of red and green light emissions was determined by optical simulation.

[0116] <Evaluation> The ratio of the brightness in Example 1 to the brightness (100%) in Comparative Example 1 is shown in Table 1. The thickness of the sealing portion between the LED and the wavelength conversion layer was set to 25 μm, 75 μm, and 125 μm, and the brightness ratio was calculated for each thickness setting. In the above configuration, the green phosphor and blue LED form a subpixel that emits green light, and therefore the relationship is such that the brightness of the green light emission is greater than the brightness of the red light emission, and the greater the difference in brightness between the green light emission and the red light emission, the greater the color mixing suppression effect. As is clear from Table 1, in the present invention, the provision of a low refractive index layer suppresses unwanted red light emission and effectively prevents color mixing. Furthermore, these effects become more pronounced by appropriately setting the thickness of the sealing portion between the LED and the wavelength conversion layer.

[0117] [Table 1]

[0118] [Example 2] The luminance of red light emission and the luminance of green light emission were determined by optical simulation for the configuration shown in Figure 2(a), i.e., a configuration in which red and green phosphors are arranged as wavelength conversion layers, and a blue LED is placed directly below the green phosphor via a low refractive index layer and a sealing portion (thickness between the LED and the wavelength conversion layer: 75 μm) (the wavelength conversion layer is 100 μm thick and 100 μm wide, the partition is 50 μm thick, and the low refractive index layer is 1.0 μm thick).

[0119] Comparative Example 2 For the configuration shown in Figure 2(b), i.e., a configuration in which red and green phosphors are arranged as wavelength conversion layers and a blue LED is placed directly below the green phosphor via a sealing portion (75 μm thick) (without a low refractive index layer), the brightness of red and green light emissions was determined by optical simulation.

[0120] <Evaluation> Table 2 shows the ratio of the brightness in Example 2 to the brightness (100%) in Comparative Example 2. The refractive index of the low refractive index layer was set to 1.10, 1.20, 1.25, and 1.30, and the brightness ratio was determined for each refractive index setting. As is clear from Table 2, in the present invention, by providing a low refractive index layer, unwanted red light emission is suppressed and color mixing is preferably suppressed.

[0121] [Table 2] [Explanation of symbols]

[0122] 10 Micro LED array board 11 Micro LED 12 Drive board 20 Sealing part 30 Low refractive index layer 40 Wavelength conversion layer 100 Micro LED display devices

Claims

1. a micro LED array substrate including a plurality of micro LEDs; an encapsulation portion that encapsulates the plurality of micro LEDs; a low refractive index layer; a plurality of wavelength conversion layers formed in sections, in this order from the micro LED array substrate side; Each wavelength conversion layer is formed to be paired with one of the micro LEDs in a thickness direction; the refractive index of the low refractive index layer is lower than the refractive index of the sealing portion and the refractive index of the wavelength conversion layer, the difference between the refractive index of the low refractive index layer and the refractive index of the sealing portion is 0.10 or more; the difference between the refractive index of the low refractive index layer and the refractive index of the wavelength conversion layer is 0.10 or more, the low refractive index layer has a thickness of 0.3 μm to 3 μm; the low refractive index layer is a porous layer made of a porous material formed by chemically bonding fine particles together; Micro LED display device.

2. 10. The micro LED display device of claim 1, wherein the refractive index of said low refractive index layer is less than or equal to 1.

25.

3. The micro LED display device according to claim 1 or 2, wherein the sealing portion is made of an adhesive.

4. 4. The micro LED display device of claim 1, wherein the individual wavelength conversion layers are spaced apart by partitions.

5. 5. The micro LED display device of claim 1, wherein the micro LEDs are blue or ultraviolet LEDs.

6. 6. The micro LED display device of claim 1, further comprising a color filter disposed on the surface of the wavelength conversion layer opposite the low refractive index layer.

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