CN116686102A

CN116686102A - Micro LED display device

Info

Publication number: CN116686102A
Application number: CN202180088243.3A
Authority: CN
Inventors: 吉川贵博; 服部大辅; 森岛谅太
Original assignee: Nitto Denko Corp
Current assignee: Nitto Denko Corp
Priority date: 2021-03-31
Filing date: 2021-12-10
Publication date: 2023-09-01
Also published as: TW202240881A; WO2022209031A1; JP2022155737A; KR20230161930A

Abstract

The invention provides a micro LED display device with excellent luminous efficiency and suppressed color mixing. The micro LED display device of the present invention comprises, in order from the back surface side, a micro LED array substrate including a plurality of micro LEDs, a sealing portion sealing the plurality of micro LEDs, a low refractive index layer, and a plurality of wavelength conversion layers formed by division, each of the wavelength conversion layers being formed so as to correspond to one of the micro LEDs in a group in a thickness direction, the refractive index of the low refractive index layer being 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 being 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 being 0.10 or more.

Description

Micro LED display device

Technical Field

The invention relates to a micro LED display device.

Background

In recent years, as a new display device, development of a micro LED display in which micro LEDs are arranged in pixels arranged in a matrix has been advanced (for example, patent document 1 and patent document 2). As a micro LED display, a display has been proposed which includes a micro LED array substrate configured by disposing a plurality of micro LEDs and an array of wavelength conversion layers (fluorescent light emitting layers) provided on the micro LED array substrate, the array of wavelength conversion layers (fluorescent light emitting layers) absorbing light from the micro LEDs and converting the emission wavelength of the light into wavelengths of red, green, and blue lights, respectively (for example, patent document 2). In such a micro LED display, the micro LEDs are formed in groups with the wavelength conversion layer for each subpixel.

Prior art literature

Patent literature

Patent document 1: japanese patent application laid-open No. 2020-43073

Patent document 2: japanese patent application laid-open No. 2016-523450

Disclosure of Invention

Problems to be solved by the invention

In the micro LED display as described above, there is a problem in that light from the micro LED leaks to sub-pixels (adjacent sub-pixels, peripheral sub-pixels) other than the sub-pixels corresponding to the micro LED, and color mixing occurs. In addition, there is a problem that light returning to the back surface side is generated due to scattering in the wavelength conversion layer, and sufficient luminous efficiency cannot be obtained.

The invention provides a micro LED display device with excellent luminous efficiency and suppressed color mixing.

Means for solving the problems

The micro LED display device of the present invention comprises, in order from the micro LED array substrate side: the micro LED array substrate includes a plurality of micro LEDs, a sealing portion sealing the plurality of micro LEDs, a low refractive index layer, and a plurality of wavelength conversion layers formed by division, each of the wavelength conversion layers being formed in a group corresponding to one of the micro LEDs in a thickness direction, a refractive index of the low refractive index layer being lower than a refractive index of the sealing portion and a refractive index of the wavelength conversion layer, a difference between the refractive index of the low refractive index layer and the refractive index of the sealing portion being 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 being 0.10 or more.

In one embodiment, the low refractive index layer has a refractive index of 1.25 or less.

In one embodiment, the low refractive index layer is a void layer formed of a porous body, and the porous body is formed by chemically bonding fine particles to each other.

In one embodiment, the sealing portion is formed of an adhesive.

In one embodiment, the wavelength conversion layers are arranged in a spaced apart relationship by a spacer.

In one embodiment, the micro LED is a blue LED or an ultraviolet LED.

In one embodiment, the micro LED display device further includes a color filter disposed on a surface of the wavelength conversion layer opposite to the low refractive index layer.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the present invention, a micro LED display device having excellent light emission efficiency and suppressed color mixing can be provided.

Drawings

Fig. 1 is a schematic cross-sectional view of a micro LED display device according to an embodiment of the present invention.

Fig. 2 (a) is a schematic cross-sectional view showing the constitution of the example, and (b) is a schematic cross-sectional view showing the constitution of the comparative example.

Symbol description

10. Micro LED array substrate

11. Micro LED

12. Driving substrate

20. Sealing part

30. Low refractive index layer

40. Wavelength conversion layer

100. Micro LED display device

Detailed Description

A. Micro LED display device

Fig. 1 is a schematic cross-sectional view of a micro LED display device according to an embodiment of the present invention. The micro LED display device 100 of the present embodiment includes, in order from the micro LED array substrate side: the micro LED array substrate 10 including the plurality of micro LEDs 11, the sealing portion 20 sealing the plurality of micro LEDs 11, the low refractive index layer 30, and the plurality of wavelength conversion layers 40 formed by division. Typically, the micro LED array substrate 10 includes a driving substrate 12 and a plurality of micro LEDs 11 arranged in an array (matrix) on the driving substrate 12. Each wavelength conversion layer 40 is formed in a group corresponding to one micro LED11 in the thickness direction. Typically, one wavelength conversion layer 40 and one micro LED11 are each included in one sub-pixel. By transmitting light from the micro LED11 through the wavelength conversion layer 40, red, green, and blue sub-pixels can be formed. In the case of a subpixel that directly uses light from a micro LED (for example, in the case of a blue subpixel formed from a blue LED), the wavelength conversion layer may be omitted or replaced with another layer (for example, a light diffusion layer) at this location. In one embodiment, each wavelength conversion layer may be arranged in isolation by a partition wall 50 (light shielding layer).

In one embodiment, the low refractive index layer 30 is formed on the entire surface of the sealing portion 20 on the opposite side of the micro LED array substrate 10. In one embodiment, the low refractive index layer 30 is directly (i.e., without sandwiching other layers) provided on the sealing portion 20.

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. 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.

In the present invention, a low refractive index layer is disposed between the sealing portion and the wavelength conversion layer, thereby generating a refractive index difference between the layers. As a result, at least a part of the light emitted from the micro LED and to be scattered in the wavelength conversion layer and returned to the back surface side can be reflected at the interface between the wavelength conversion layer and the low refractive index layer and emitted to the visible side. As a result, the luminous efficiency is improved. At least a part of light emitted from the micro LED obliquely and not reaching the corresponding wavelength conversion layer (wavelength conversion layer in the same subpixel) and directed to the periphery thereof is reflected at the interface between the low refractive index layer and the sealing portion and returned to the back surface side. As a result, color mixing is suppressed. In addition to high definition, the micro LED display device of the embodiment of the present invention is advantageous in terms of high brightness and wide color gamut as compared to the existing display.

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, further preferably 1.20 or less, and particularly preferably 1.15 or less. The lower the refractive index of the low refractive index layer, the more preferable, the lower limit thereof is, for example, 1.07 or more (preferably 1.05 or more). In the present specification, the refractive index means a refractive index measured at a wavelength of 550 nm.

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. If the range is such, the above effect becomes remarkable. 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).

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. If the range is such, the above effect becomes remarkable. 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).

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

The low refractive index layer may take any suitable form. In one embodiment, the low refractive index layer has voids. The low refractive index layer may be preferably formed by coating or printing or the like. As a material constituting the low refractive index layer, for example, it is possible to use: international publication No. 2004/113966, japanese patent application laid-open No. 2013-254183, and Japanese patent application laid-open No. 2012-189802. Specifically, examples thereof include: a silica-based compound; hydrolyzable silanes, partial hydrolysates thereof, and dehydration condensates thereof; an organic polymer; silicon compounds containing silanol groups; an active silica obtained by contacting a silicate with an acid and an ion exchange resin; polymerizable monomers (e.g., a (meth) acrylic monomer, a styrene monomer); 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 a material.

The void ratio 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. If the refractive index is within such a range, a low refractive index layer having a particularly low refractive index can be formed. The upper limit of the void ratio of the low refractive index layer is, for example, 90% by volume or less, preferably 75% by volume or less. If the refractive index is in this range, a low refractive index layer having excellent strength can be formed. The void fraction is a value obtained by calculating the void fraction from Lorentz-Lorenz' sformula (Lorentz-Lorenz equation) based on the value of the refractive index measured by an ellipsometer.

The size of the voids (holes) in the low refractive index layer refers to the diameter of the major axis of the voids (holes) and the diameter of the major axis of the minor axis. The size of the voids (pores) is, for example, 2nm to 500nm. The size of the voids (pores) is, for example, 2nm or more, preferably 5nm or more, more preferably 10nm or more, and still more preferably 20nm or more. On the other hand, the size of the voids (pores) is, for example, 500nm or less, preferably 200nm or less, and more preferably 100nm or less. The size of the voids (pores) is, for example, in the range of 2nm to 500nm, preferably 5nm to 500nm, more preferably 10nm to 200nm, still more preferably 20nm to 100nm. The size of the voids (pores) can be adjusted to a desired size according to the purpose, use, and the like.

The size of the voids (pores) can be quantified by the BET test method. Specifically, 0.1g of a sample (a void layer formed) was put into a capillary tube of a specific surface area measuring apparatus (ASAP 2020, manufactured by Memerorelix Co., ltd.) and then dried under reduced pressure at room temperature for 24 hours to degas the gas in the void structure. Then, adsorption isotherms were drawn by adsorbing nitrogen gas to the sample, and pore distribution was determined. Thereby, the void size can be evaluated.

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 is, for example, in the range of 0.1% or more and less than 5%, preferably 0.2% or more and less than 3%. Haze can be measured, for example, by the method described below. Haze is an index of transparency of a low refractive index layer.

The void layer (low refractive index layer) was cut into a size of 50mm×50mm, and the resultant was set in a haze meter (HM-150, manufactured by Toku Kogyo Co., ltd.) to measure haze. Regarding the haze value, calculation was performed by the following formula.

Haze (%) = [ diffuse transmittance (%)/total light transmittance (%) ] ×100 (%)

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

Any suitable particle may be used as the particles. The particles are typically formed from a silica-based compound. Examples of the shape of the particles include: spherical, plate-like, needle-like, string-like, and grape-like. Examples of the rope-like particles include: a plurality of particles having a spherical, plate-like, or needle-like shape connected into a beaded particle; short fiber-like particles (for example, short fiber-like particles described in Japanese patent application laid-open No. 2001-188104), and combinations thereof. The string-like particles may be linear or branched. Examples of the grape cluster-shaped particles include: the plurality of spherical, plate-like, and needle-like particles are aggregated to form a grape cluster-like particle. The shape of the particles can be confirmed by observation using, for example, a transmission electron microscope.

The thickness of the low refractive index layer is preferably 0.2 μm to 5 μm, more preferably 0.3 μm to 3 μm. If the thickness of the low refractive index layer is in such a range, the breakage preventing effect of the present invention becomes remarkable. Further, the above-described desired thickness ratio can be easily achieved.

Typically, the low refractive index layer may be 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 may be in any suitable manner. The printing method may be a printing method having a format such as gravure printing, offset printing, or flexographic printing, or a printing method having no format such as inkjet printing, laser printing, or electrostatic printing.

An example of a specific structure of the low refractive index layer will be described below. The low refractive index layer of the present embodiment comprises one or more structural units that form a fine void structure, the structural units being chemically bonded to each other by catalytic action. Examples of the shape of the structural unit include: particulate, fibrous, rod-like, and flat-plate-like. The structural unit may have only one shape, or may have two or more shapes in combination. In one embodiment, the low refractive index layer is a void layer formed of a porous body in which fine particles are chemically bonded to each other. Hereinafter, a case of a void layer formed of a porous body formed by chemically bonding fine particles to each other will be mainly described.

Such a void layer can be formed by, for example, chemically bonding microporous particles to each other in the void layer forming step. In the embodiment of the present invention, the shape of the "particles" (for example, the microporous particles) is not particularly limited, and may be, for example, spherical or other shapes. In addition, in the embodiment of the present invention, the microporous particles may be, for example, sol-gel beaded particles, nanoparticles (hollow nanosilica/hollow nanosphere particles), nanofibers, or the like. Microporous particles typically comprise inorganic materials. Specific examples of the inorganic substance include: silicon (Si), magnesium (Mg), aluminum (Al), titanium (Ti), zinc (Zn), zirconium (Zr). These may be used alone or in combination of two or more. In one embodiment, the microporous particles are microporous particles of a silicon compound, and the porous body is a silicone porous body. The microporous particles of the silicon compound include, for example, a pulverized product of a gel-like silica compound. In addition, as other forms of the low refractive index layer having a porous layer and/or an air layer in at least a part thereof, for example, there are included: the void layer is formed by fibrous materials such as nanofibers, which intertwine to form voids and form a layer. The method for producing such a void layer is not particularly limited, and is similar to the case of a void layer of a porous body in which the microporous particles are chemically bonded to each other, for example. In addition, as another form, there are exemplified a void layer using hollow nanoparticles, nanoclay, and a void layer formed using hollow nanohollow spheres, magnesium fluoride. The void layer may be a void layer formed of a single constituent substance or may be a void layer formed of a plurality of constituent substances. The void layer may be formed of a single one or a plurality of the above forms.

In the present embodiment, the porous structure of the porous body may be, for example, a foam-connected structure in which the porous structure is continuous. The foam structure is, for example, a state in which the pore structures are three-dimensionally connected to each other in the silicone porous body, and may be a state in which internal voids of the pore structures are continuous. By providing the porous body with a continuous bubble structure, the void ratio can be improved. In the case of single-bubble particles (particles each having a pore structure) such as hollow silica, a continuous bubble structure cannot be formed. On the other hand, in the case of using, for example, silica gel particles (crushed product of gel-like silicon compound forming a sol), since the particles have a three-dimensional dendritic structure, sedimentation and deposition of the dendritic particles occur in a coating film (coating film of sol containing crushed product of gel-like silicon compound), whereby a continuous bubble structure can be easily formed. The low refractive index layer more preferably has a monolithic structure in which the continuous bubble structure includes a plurality of pore distributions. The monolithic structure represents a hierarchical structure including, for example, a structure in which fine voids of a nanometer size exist, and a foam-linked structure in which such nano voids are aggregated. In the case of forming a monolithic structure, for example, a film strength can be provided by fine voids, and a high void fraction can be provided by coarse continuous foam voids, thereby achieving both the film strength and the high void fraction. Such a monolithic structure is preferably formed by controlling the pore distribution of the void structure formed in the gel (gel-like silicon compound) at the early stage of pulverization into silica gel particles. In addition, for example, when the gel-like silicon compound is pulverized, the particle size distribution of the silica gel particles after pulverization is controlled to a desired size, whereby a monolithic structure can be formed.

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

The gel form of the gel-like compound is not particularly limited. "gel" generally refers to a state in which solutes lose their independent mobility due to interaction and aggregate, and solidify. The gel-like compound may be, for example, a wet gel or a xerogel. In general, wet gel means a gel containing a dispersion medium and having a uniform structure of a solute in the dispersion medium, and xerogel means a gel having a network structure in which a solvent is removed and a solute has voids.

Examples of the gel-like compound include a gelled product obtained by gelling a monomer compound. Specifically, examples of the gel-like silicon compound include: specific examples of the gelled product obtained by bonding the silicon compounds of the monomers to each other include gelled products in which covalent bonds, hydrogen bonds, and intermolecular forces are formed between the silicon compounds of the monomers. Examples of the covalent bond include a bond formed by dehydration condensation.

The volume average particle diameter of the pulverized product 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 is, for example, in the range of 0.10 μm to 2.00. Mu.m, preferably 0.20 μm to 1.50. Mu.m, more preferably 0.40 μm to 1.00. Mu.m. The particle size distribution can be measured by a particle size distribution evaluation device such as a dynamic light scattering method or a laser diffraction method, an electron microscope such as a Scanning Electron Microscope (SEM) or a Transmission Electron Microscope (TEM), or the like. The volume average particle diameter is an index of the variation in particle size of the pulverized product.

The kind of the gel-like compound is not particularly limited. The gel-like compound may be, for example, a gel-like silicon compound. Hereinafter, a case where the gel-like compound is a gel-like silicon compound will be described as an example, but the present invention is not limited thereto.

The cross-linking bond is, for example, a siloxane bond. Examples of the siloxane bond include a T2 bond, a T3 bond, and a T4 bond described below. In the case where the void layer (low refractive index layer) has a siloxane bond, any one bond, any two bonds, or all three bonds may be present. The more the ratio of T2 to T3 in the siloxane bond, the more flexible the gel is, and the original properties of the gel can be expected. On the other hand, the greater the ratio of T4, the more likely the film strength is exhibited. Therefore, it is preferable to change the ratio of T2, T3, and T4 according to the purpose, use, desired characteristics, and the like.

[ chemical formula 1]

In addition, in the low refractive index layer (void layer), for example, silicon atoms contained therein preferably form siloxane bonds. Specifically, the proportion of unbound silicon atoms (i.e., residual silanol) in all silicon atoms contained in the void layer is, for example, less than 50%, preferably 30% or less, and more preferably 15% or less.

In the case where the gel-like compound is a gel-like silicon compound, the silicon compound of the monomer is not particularly limited. The monomeric silicon compound may be, for example, a compound represented by the following formula (1). When the gel-like silicon compound is a gelled product in which hydrogen bonds or intermolecular forces are formed between the silicon compounds of the monomers as described above, hydrogen bonds may be formed between the monomers of formula (1) via the hydroxyl groups, for example.

[ chemical formula 2]

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

Specific examples of the silicon compound represented by the formula (1) include compounds represented by the following formula (1') in which X is 3. In the following formula (1'), R ¹ In the same manner as in the case of formula (1), for example, methyl is used. At R ¹ In the case of methyl, the silicon compound is a trihydroxymethyl silane. In the case where X is 3, the silicon compound is, for example, a trifunctional silane having 3 functional groups.

[ chemical formula 3]

As another specific example of the silicon compound represented by the formula (1), a compound wherein X is 4 is given. In this case, the silicon compound is, for example, a tetrafunctional silane having 4 functional groups.

The monomeric silicon compound may also be, for example, a hydrolysate of a silicon compound precursor. The silicon compound precursor may be any one that can produce a silicon compound by hydrolysis, and specific examples thereof include a compound represented by the following formula (2).

[ chemical formula 4]

In the above formula (2), X is, for example, 2, 3 or 4,

R ¹ r is R ² Each independently is a linear or branched alkyl group,

R ¹ r is R ² May be the same or different from each other,

in the case where X is 2, R ¹ May be the same as or different from each other,

R ² may be the same or different from each other.

X and R ¹ For example, X and R in formula (1) ¹ The same applies. R is R ² For example, R in formula (1) may be cited ¹ Is an example of (a).

Specific examples of the silicon compound precursor represented by the formula (2) include, for example: a compound represented by the following formula (2') wherein X is 3. In the following formula (2'), R ¹ R is R ² Each of which is the same as that of the formula (2). At R ¹ R is R ² In the case of methyl, the silicon compound precursor is trimethoxy (methyl) silane (hereinafter also referred to as "MTMS").

[ chemical formula 5]

The silicon compound of the monomer is preferably a trifunctional silane, for example, from the viewpoint of excellent low refractive index. In addition, for example, from the viewpoint of excellent strength (e.g., scratch resistance), the silicon compound of the monomer is preferably a tetrafunctional silane. The silicon compounds of the monomer may be used alone or in combination of two or more. For example, the silicon compound as the monomer may contain only trifunctional silane, may contain only tetrafunctional silane, may contain both trifunctional silane and tetrafunctional silane, and may further contain other silicon compounds. In the case of using two or more kinds of silicon compounds as the silicon compounds of the monomers, the ratio thereof is not particularly limited and may be appropriately set.

An example of a method for forming such a low refractive index layer is described below.

Typically, the method comprises: a precursor forming step of forming a void structure as a precursor of a low refractive index layer (void layer) on the resin film; and a crosslinking reaction step of causing a crosslinking reaction inside the precursor after the precursor forming step. The method further comprises the steps of: a step of preparing a liquid containing microporous particles (hereinafter, sometimes referred to as "microporous particle liquid containing" or simply "liquid containing"); and a drying step of drying the liquid-containing material, wherein in the precursor forming step, the microporous particles in the dried material are chemically bonded to each other to form a precursor. The liquid is not particularly limited, and is, for example, a suspension containing microporous particles. Hereinafter, a porous body (preferably, a silicone porous body) in which the microporous particles are pulverized gel-like compounds and the void layer contains pulverized gel-like compounds will be described mainly. In the case where the microporous particles are not pulverized of a gel-like compound, the low refractive index layer may be formed in the same manner.

According to the above method, a low refractive index layer (void layer) having a very low refractive index, for example, can be formed. The reason for this is presumed to be as follows, for example. However, this assumption is not limited to the method of forming the low refractive index layer.

The above-mentioned pulverized product is obtained by pulverizing a gel-like silicon compound, and therefore, the three-dimensional structure of the gel-like silicon compound before pulverization is formed in a state dispersed in the three-dimensional basic structure. Further, in the above method, a precursor of a porous structure based on a three-dimensional basic structure can be formed by applying a pulverized product of a gel-like silicon compound to a resin film. That is, according to the above-described method, a new porous structure (three-dimensional basic structure) based on the application of the pulverized material, which is different from the three-dimensional structure of the gel-like silicon compound, can be formed. Therefore, the void layer to be finally obtained can have a low refractive index functioning to the same extent as the air layer, for example. In addition, in the above method, the crushed materials are chemically bonded to each other, and thus, the three-dimensional basic structure can be immobilized. Therefore, even though the resulting void layer is a structure having voids, sufficient strength and flexibility can be maintained.

In the above method, the precursor forming step and the crosslinking reaction step may be performed as different steps. In addition, the crosslinking reaction step is preferably performed in multiple steps. By performing the crosslinking reaction step in multiple steps, for example, the strength of the precursor can be further improved as compared with the case of performing the crosslinking reaction step in one step, and a low refractive index layer having both high void ratio and strength can be obtained. The mechanism is not clear, but it is assumed that the following is, for example. That is, when the film strength is increased by a catalyst or the like while forming the void layer as described above, there is a problem that the film strength is increased but the void ratio is decreased due to progress of the catalyst reaction. This is considered to be due to, for example, that the number of crosslinks (chemical bonds) between microporous particles increases by the crosslinking reaction between microporous particles with a catalyst, and thus the bonds become strong, but the entire void layer is coagulated, and the void fraction decreases. In contrast, it is considered that by performing the precursor forming step and the crosslinking reaction step in different steps and performing the crosslinking reaction step in multiple steps, the number of crosslinks (chemical bonds) can be increased (for example, almost no coagulation of the whole) and almost no morphology change of the whole precursor can be caused, for example. However, these are merely examples of a mechanism that can be presumed, and the method of forming the low refractive index layer is not limited.

In the precursor forming step, for example, particles having a predetermined shape are stacked to form a precursor of the void layer. The strength of the precursor at this point in time is very weak. Then, for example, by a photo-or thermally active catalytic reaction, a product (for example, a strong base catalyst generated from a photo-alkaline agent or the like) capable of chemically bonding the microporous particles to each other is generated (first stage of the crosslinking reaction process). It is considered that, in order to perform the reaction more efficiently in a short time, the chemical bonding (crosslinking reaction) between the microporous particles proceeds further and the strength is improved by further performing the heat aging (second stage of the crosslinking reaction step). It is considered that, for example, the microporous particles are microporous particles of a silicon compound (for example, crushed pieces of a gel-like silica compound), and when residual silanol groups (si—oh groups) are present in the precursor, the residual silanol groups are chemically bonded to each other by a crosslinking reaction. However, this description is also an example, and the method of forming the low refractive index layer is not limited.

The method includes a liquid-containing preparation step of preparing a liquid containing microporous particles. In the case where the microporous particles are pulverized products of gel-like compounds, the pulverized products are obtained by, for example, pulverizing the gel-like compounds. By pulverizing the gel-like compound, as described above, the three-dimensional structure of the gel-like compound is broken and dispersed in the three-dimensional basic structure. An example of the preparation of the pulverized product is as follows.

Gelation of the monomer compounds may be carried out by, for example, causing the monomer compounds to form hydrogen bonds with each other, or forming intermolecular forces. Examples of the monomer compound include: the silicon compound represented by the above formula (1). Since the silicon compound of formula (1) has a hydroxyl group, hydrogen bonds or intermolecular forces may be formed between the monomers of formula (1) via, for example, the respective hydroxyl groups.

Alternatively, the silicon compound may be a hydrolysate of the silicon compound precursor, and for example, the silicon compound precursor represented by the formula (2) may be hydrolyzed to produce the silicon compound precursor.

The method of hydrolysis of the monomer compound precursor is not particularly limited, and may be performed by a chemical reaction in the presence of a catalyst, for example. Examples of the catalyst include: oxalic acid, acetic acid, and the like. The hydrolysis reaction may be performed as follows: for example, an aqueous solution of oxalic acid is slowly added dropwise to a mixed solution (e.g., suspension) of a silicon compound and dimethyl sulfoxide at room temperature, and the mixture is mixed, and then the mixture is stirred for about 30 minutes. When the silicon compound precursor is hydrolyzed, for example, by completely hydrolyzing the alkoxy group of the silicon compound precursor, the subsequent gelation/curing/heating/immobilization after formation of the void structure can be more effectively performed.

Gelation of the monomer compound may be performed by, for example, dehydration condensation reaction between monomers. The dehydration condensation reaction is preferably carried out in the presence of a catalyst, for example: acid catalysts such as hydrochloric acid, oxalic acid and sulfuric acid, and dehydration condensation catalysts such as alkali catalysts such as ammonia, potassium hydroxide, sodium hydroxide and ammonium hydroxide. As the dehydration condensation catalyst, a base catalyst is preferable. In the dehydration condensation reaction, the amount of the catalyst to be added to the monomer compound is not particularly limited. For example, the catalyst may be added preferably in an amount of 0.1 to 10 moles, more preferably in an amount of 0.05 to 7 moles, still more preferably in an amount of 0.1 to 5 moles, relative to 1 mole of the monomer compound.

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-dimethylacetamide (DMAc), dimethylformamide (DMF), gamma-butyrolactone (GBL), acetonitrile (MeCN), ethylene Glycol Ethyl Ether (EGEE), and the like. The solvent may be used alone or in combination of two or more. Hereinafter, the solvent used for gelation is also referred to as "gelation solvent".

The condition of gelation is not particularly limited. The treatment temperature for the solvent containing the monomer compound is, for example, 20 to 30 ℃, preferably 22 to 28 ℃, more preferably 24 to 26 ℃. The treatment time is, for example, 1 to 60 minutes, preferably 5 to 40 minutes, and more preferably 10 to 30 minutes. In the case of carrying out the dehydration condensation reaction, the treatment conditions are not particularly limited, and the above examples can be cited. By performing gelation, for example, siloxane bonds can be grown to form silica primary particles, and by further performing reaction, the primary particles can be connected to each other in the form of beads to form a gel of a three-dimensional structure.

The gel-like compound obtained by gelation is preferably subjected to a curing treatment after the gelation reaction. By the aging treatment, for example, the primary particles of the gel having a three-dimensional structure obtained by gelation can be further grown, and the size of the particles themselves can be increased, and as a result, the contact state of the necks where the particles are in contact with each other can be changed from point contact to surface contact (increase in contact area). The strength of the gel itself after the aging treatment is increased, for example, and as a result, the strength of the three-dimensional basic structure after the pulverization can be improved. Thus, for example, in the drying step after the pulverized product is applied, shrinkage of the pore size of the void structure formed by the three-dimensional basic structure being stacked can be suppressed as the solvent in the drying step volatilizes.

The curing treatment may be performed, for example, by incubating the gel-like compound at a given temperature for a given time. The curing temperature is, for example, 30℃or higher, preferably 35℃or higher, and more preferably 40℃or higher. On the other hand, the curing temperature is, for example, 80℃or less, preferably 75℃or less, and more preferably 70℃or less. The curing temperature is, for example, in the range of 30℃to 80℃and preferably 35℃to 75℃and more preferably 40℃to 70 ℃. The curing time is, for example, 5 hours or more, preferably 10 hours or more, and more preferably 15 hours or more. On the other hand, the aging time is, for example, 50 hours or less, preferably 40 hours or less, and more preferably 30 hours or less. The curing time is, for example, 5 to 50 hours, preferably 10 to 40 hours, more preferably 15 to 30 hours. The curing conditions may be optimized so as to obtain an increase in the size of the primary particles of silica and an increase in the contact area of the neck portion, for example. Further, it is preferable to consider the boiling point of the solvent used, for example, if the curing temperature is too high, the solvent may be excessively volatilized, and the concentration of the coating liquid (gel liquid) may cause defects such as pore closure of the three-dimensional void structure. On the other hand, for example, when the curing temperature is too low, not only the effect due to curing is not sufficiently obtained, but also the temperature deviation with time of the mass production process increases, and a low refractive index layer having poor characteristics may be formed.

The curing treatment may use the same solvent as, for example, the gelation treatment. Specifically, it is preferable to directly subject the gel-treated reactant (i.e., the solvent containing the gel-like compound) to the aging treatment. The molar number of residual silanol groups contained in the gel (gel-like compound, for example, gel-like silicon compound) after completion of 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 molar number of the residual silanol groups is, for example, 1% or more, preferably 3% or more, and more preferably 5% or more. The molar amount of the residual silanol groups is, for example, 1% to 50%, preferably 3% to 40%, and more preferably 5% to 30%. For the purpose of improving the hardness of the gel, for example, the lower the number of moles of residual silanol groups, the more preferable. If the molar amount of silanol groups is too high, the void structure may not be maintained until, for example, the precursor of the silicone porous body is crosslinked. On the other hand, if the molar number of silanol groups is too low, for example, in the step of producing a microporous particle-containing liquid (for example, suspension) and/or in the subsequent step, there is a possibility that the pulverized product of the gel-like compound cannot be crosslinked and sufficient film strength cannot be imparted. The molar number of the residual silanol groups is, for example, the ratio of the residual silanol groups when the molar number of the alkoxy groups of the raw material (for example, the monomer compound precursor) is 100. The silanol groups are examples, and for example, when the silicon compound of the monomer is modified with various reactive functional groups, the same matters and conditions as those of the functional groups may be applied.

The monomer compound is gelled in a solvent for gelation, and then the resulting gel-like compound is pulverized. The pulverization may be performed, for example, by directly pulverizing the gel-like compound in the solvent for gelation, or by replacing the solvent for gelation with another solvent and then pulverizing the gel-like compound in the other solvent. In addition, for example, when the catalyst used in the gelation reaction and the solvent used remain after the aging step, the gelation of the liquid with time (pot life) is caused and the drying efficiency in the drying step is reduced, it is preferable to replace the catalyst with another solvent. Hereinafter, the other solvent is also referred to as "solvent for pulverization".

The solvent for pulverization is not particularly limited, and for example, an organic solvent can be used. The organic solvent may have a boiling point of, for example, 130℃or less, preferably 100℃or less, and more preferably 85℃or less. Specific examples thereof include isopropyl alcohol (IPA), ethanol, methanol, butanol, propylene Glycol Monomethyl Ether (PGME), methyl cellosolve, acetone, dimethylformamide (DMF), and isobutanol. The pulverizing solvents may be used alone or in combination of two or more.

The combination of the gelling solvent and the pulverizing solvent is not particularly limited, and examples thereof include: combinations of DMSO with IPA, DMSO with ethanol, DMSO with methanol, DMSO with butanol, DMSO with isobutanol, and the like. By replacing the gelation solvent with the pulverization solvent in this manner, for example, in the formation of a coating film described later, a more uniform coating film can be formed.

The method for pulverizing the gel-like compound is not particularly limited, and may be carried out by, for example, an ultrasonic homogenizer, a high-speed rotary homogenizer, or other pulverizing apparatus utilizing cavitation. In contrast to a device for pulverizing media such as a ball mill, which physically breaks the void structure of the gel during pulverization, a cavitation-type pulverizing device such as a homogenizer is, for example, a non-media type, and therefore, the bonded silica particle junction surface, which is relatively weakly bonded and has been embedded in the gel three-dimensional structure, is peeled off by a high-speed shearing force. Thus, the resulting gel three-dimensional structure can maintain a void structure having a certain range of particle size distribution, for example, and can reform a void structure due to accumulation at the time of coating/drying. The conditions for pulverization are not particularly limited, and for example, it is preferable that the gel is pulverized without causing volatilization of the solvent by instantaneously imparting a high-speed flow. For example, it is preferable to crush the particles so as to form crushed materials having the above-described particle size deviation (for example, volume average particle diameter or particle size distribution). If the work amount such as the pulverizing time and the strength is insufficient, coarse particles may remain, for example, and not only dense fine pores may not be formed, but also appearance defects may increase, and high quality may not be obtained. On the other hand, if the work amount is excessive, for example, particles finer than the desired particle size distribution may be formed, and the void size formed by deposition after coating/drying may become fine, so that the desired void fraction may not be obtained.

As described above, a liquid (e.g., a suspension) containing microporous particles (pulverized product of gel-like compound) can be produced. Further, a liquid containing microporous particles and a catalyst can be produced by adding a catalyst that chemically bonds microporous particles to each other after the production of the liquid containing microporous particles or in the production step. The catalyst may be, for example, a catalyst that promotes cross-linking of microporous particles to each other. As a chemical reaction for chemically bonding the microporous particles to each other, a dehydration condensation reaction using residual silanol groups contained in the silica gel molecule is preferable. By promoting the reaction of the hydroxyl groups of the silanol groups with each other by the catalyst, a continuous film formation for curing the void structure can be performed in a short time. Examples of the catalyst include: photoactivated catalysts and thermally activated catalysts. According to the photoactivated catalyst, for example, in the precursor forming process, microporous particles can be chemically bonded to each other (e.g., form cross-links) without heating. Thus, for example, shrinkage of the entire precursor is less likely to occur in the precursor forming step, and thus a higher void fraction can be maintained. In addition, a substance that generates a catalyst (catalyst generating agent) may be used in addition to or in place of the catalyst. For example, a substance that generates a catalyst by light (photocatalyst generator) may be used in addition to or instead of the photoactivated catalyst, and a substance that generates a catalyst by heat (thermal catalyst generator) may be used in addition to or instead of the thermally activated catalyst. Examples of the photocatalyst generator include: photobase generators (substances that generate alkaline catalysts by irradiation), photoacid generators (substances that generate acidic catalysts by irradiation), and the like, are preferable. Examples of the photobase generator include: 9-Anthracene methyl N, N-diethylcarbamate (9-anthracenemethyl N, N-diethyl arbamate, trade name WPBG-018), (E) -1- [3- (2-hydroxy) Phenyl) -2-propenoyl]Piperidine ((E) -1- [3- (2-hydroxyphenyl) -2-propenoyl)]Piperidine, trade name WPBG-027), 1- (anthraquinone-2-yl) ethyl imidazole carboxylate (1- (anthraquinon-2-yl) ethyl imidazolecarboxylate, trade name WPBG-140), 2-nitrophenylmethyl 4-methacryloxypiperidine-1-carboxylate (trade name WPBG-165), 1, 2-diisopropyl-3- [ bis (dimethylamino) methylene-2- (3-benzoylphenyl) propanoate]Guanidine salt (trade name WPBG-266), 1, 2-dicyclohexyl-4, 5-tetramethyldiguanidine salt of n-butyltriphenylborate (trade name WPBG-300), and 2- (9-oxo)Ton-2-yl) propionic acid 1,5, 7-triazabicyclo [4.4.0]Dec-5-ene (Tokyo chemical Co., ltd.), a compound containing 4-piperidinemethanol (trade name HDPD-PB100: manufactured by Heraeus Co., ltd.), and the like. The trade names including "WPBG" are trade names of light pure chemical industry corporation. Examples of the photoacid generator include: aromatic sulfonium salt (trade name SP-170: ADEKA Co., ltd.), triarylsulfonium salt (trade name CPI101A: san-Apro Co.), aromatic iodine->Salts (trade name Irgacure250: ciba Japanese Co., ltd.) and the like. The catalyst that chemically bonds the microporous particles to each other is not limited to the photoactivated catalyst and the photocatalyst generator, and may be, for example, a thermally activated catalyst or a thermal catalyst generator such as urea. Catalysts which chemically bond microporous particles to each other can be exemplified by, for example: base catalysts such as potassium hydroxide, sodium hydroxide, and ammonium hydroxide, acid catalysts such as hydrochloric acid, acetic acid, and oxalic acid, and the like. Among these, a base catalyst is preferable. The catalyst or catalyst generator in which the microporous particles are chemically bonded to each other may be used, for example, by being added to a sol particle solution (for example, suspension) containing crushed materials (microporous particles) immediately before application, or may be used in the form of a mixed solution in which the catalyst or catalyst generator is mixed with a solvent. The mixed liquid may be obtained by directly adding and dissolving the mixed liquid in a sol particle liquid The obtained coating liquid, a solution obtained by dissolving the catalyst or the catalyst generator in a solvent, or a dispersion obtained by dispersing the catalyst or the catalyst generator in a solvent. The solvent is not particularly limited, and examples thereof include water and buffers.

In addition, for example, a crosslinking auxiliary agent for indirectly binding the crushed products of the gel to each other may be further added to the gel-containing liquid. The crosslinking auxiliary agent is introduced into the particles (the crushed material) and the particles and the crosslinking auxiliary agent are respectively interacted or combined, so that the particles which are separated from each other by a certain distance can be combined, and the strength can be improved efficiently. The crosslinking assistant is preferably a multi-crosslinking silane monomer. Specifically, the multi-crosslinking silane monomer has, for example, an alkoxysilyl group of 2 to 3, and the chain length between the alkoxysilyl groups may be 1 to 10 carbon atoms, or may contain an element other than carbon. Examples of the crosslinking auxiliary agent include: bis (trimethoxysilyl) ethane, bis (triethoxysilyl) ethane, bis (trimethoxysilyl) methane, bis (triethoxysilyl) propane, bis (trimethoxysilyl) propane, bis (triethoxysilyl) butane, bis (trimethoxysilyl) butane, bis (triethoxysilyl) pentane, bis (trimethoxysilyl) pentane, bis (triethoxysilyl) hexane, bis (trimethoxysilyl) -N-butyl-N-propyl-ethane-1, 2-diamine, tris (3-trimethoxysilylpropyl) isocyanurate, tris (3-triethoxysilylpropyl) isocyanurate, and the like. The amount of the crosslinking auxiliary added is not particularly limited, and is, for example, 0.01 to 20 wt%, 0.05 to 15 wt%, or 0.1 to 10 wt% based on the weight of the pulverized product of the silicon compound.

Next, a liquid (for example, a suspension) containing microporous particles is applied to the sealing portion (application step). The coating may be performed by various coating methods described later, for example, and is not limited thereto. The coating film containing the microporous particles and the catalyst can be formed by directly coating a liquid containing the microporous particles (for example, pulverized product of gel-like silica compound) on the sealing portion. The coating film may also be referred to as a coating layer, for example. By forming the coating film, for example, the crushed material after the three-dimensional structure is broken down is settled and deposited, thereby constructing a new three-dimensional structure. For example, the liquid containing microporous particles may not contain a catalyst for chemically binding microporous particles to each other. For example, as described later, the precursor forming step may be performed after the catalyst for chemically bonding the microporous particles to each other is blown to the coating film or while blowing. However, the microporous particle-containing liquid may contain a catalyst that chemically bonds microporous particles to each other, and a precursor that chemically bonds microporous particles to each other by the action of the catalyst contained in the coating film to form a porous body.

The solvent (hereinafter also referred to as "coating solvent") is not particularly limited, and for example, an organic solvent may be used. Examples of the organic solvent include: a solvent having a boiling point of 150 ℃ or less. Specific examples include: IPA, ethanol, methanol, n-butanol, 2-butanol, isobutanol, pentanol, etc., and the same solvent as the pulverizing solvent may be used. In the case where the method for forming the low refractive index layer includes a step of pulverizing the gel-like compound, for example, a solvent for pulverizing the pulverized product containing the gel-like compound may be directly used in the step of forming the coating film.

In the coating step, for example, a sol-like pulverized product (hereinafter also referred to as "sol particle liquid") dispersed in a solvent is preferably applied to the sealing portion. For example, the sol particle solution is applied to the sealing portion and dried, and then subjected to the chemical crosslinking, whereby a continuous film formation of a void layer having a film strength of a certain level or higher can be achieved. In the present embodiment, "sol" refers to a state in which silica gel particles having a nano three-dimensional structure in which a part of a void structure is maintained are dispersed in a solvent by pulverizing the three-dimensional structure of a gel, thereby exhibiting fluidity.

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 solution is significantly reduced, and aggregates and coating streaks may be caused during coating. If the concentration of the pulverized material is too low, for example, not only it takes a considerable time to dry the solvent of the sol particle solution, but also the residual solvent immediately after drying increases, and thus the void fraction may be reduced.

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 10001/s. If the shear viscosity is too high, for example, coating streaks may occur, and a decrease in transfer rate of gravure coating may be observed. In contrast, when the shear viscosity is too low, for example, the wet coating thickness at the time of coating may not be increased, and a desired thickness may not be obtained after drying.

The application amount of the pulverized product is not particularly limited, and may be appropriately set according to the thickness of a desired silicone porous body (eventually, a low refractive index layer), for example. Specifically, in the case of forming a porous organosilicon body having a thickness of 0.1 μm to 1000 μm, the average of the coating amount of the pulverized material per 1m ² The surface area of the coating layer is, for example, 0.01 to 60000. Mu.g, preferably 0.1 to 5000. Mu.g, and more preferably 1 to 50. Mu.g. The preferable application amount of the sol particle liquid is difficult to be uniquely defined in terms of, for example, the concentration of the liquid, the application method, and the like, but is preferably applied in a thin layer as much as possible in view of productivity. When the coating amount is too large, for example, the solvent may be dried in a drying oven before volatilization. As a result, the nano-sized sol particles are deposited in the solvent, and the solvent is dried before the void structure is formed, which may hinder the formation of voids and greatly reduce the void ratio. On the other hand, if the coating amount is too thin, the risk of occurrence of coating shrinkage cavity may become high.

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

The drying treatment may be, for example, natural drying, heating drying, or reduced pressure drying. Among them, in the case of industrial continuous production, heat drying is preferably employed. The method of heat drying is not particularly limited, and for example, a usual heating mechanism may be used. Examples of the heating means include: a heater, a heating roller, a far infrared heater, etc. In addition, regarding the solvent to be used, a solvent having a low surface tension is preferable in order to suppress the occurrence of shrinkage stress accompanying volatilization of the solvent during drying and the cracking phenomenon of the void layer (the silicone porous body) caused thereby. Examples of the solvent include: lower alcohols such as isopropyl alcohol (IPA), hexane, and perfluorohexane. In addition, a perfluoro-type surfactant or a silicone-type surfactant may be added to the IPA or the like in a small amount to reduce the surface tension.

Further, the method for forming the low refractive index layer includes a crosslinking reaction step of causing a crosslinking reaction to occur in the precursor after the precursor forming step, in which an alkaline substance is generated by irradiation or heating, and the crosslinking reaction step is a plurality of steps, as described above. In the first stage of the crosslinking reaction process, for example, microporous particles are chemically bonded to each other by the action of a catalyst (alkaline substance). Thereby, for example, the three-dimensional structure of the pulverized material in the coating film (precursor) is immobilized. In the case of immobilization by conventional sintering, for example, dehydration condensation of silanol groups and formation of siloxane bonds are induced by high-temperature treatment at 200 ℃. In the present method, by reacting various additives that catalyze the dehydration condensation reaction, for example, a void structure can be continuously formed at a low drying temperature of about 100 ℃ and a short treatment time of less than several minutes, and immobilization can be achieved.

The method of chemical bonding is not particularly limited, and may be appropriately determined depending on the kind of the gel-like silicon compound, for example. As a specific example, the chemical bonding may be performed by, for example, chemically crosslinking the pulverized materials with each other, but, for example, when inorganic particles such as titanium oxide are added to the pulverized materials, it is also conceivable to chemically crosslink the inorganic particles with the pulverized materials. In addition, the case where a biocatalyst such as an enzyme is supported and the case where a site different from the catalyst active site is chemically crosslinked with the pulverized product are also included. Therefore, for the method of forming the low refractive index layer, it is possible to consider not only application expansion to, for example, a void layer (silicone porous body) formed of sol particles, but also application expansion to an organic-inorganic hybrid void layer, a host-guest void layer, or the like.

The stage in the method of forming the low refractive index layer at which the chemical reaction is performed (generated) in the presence of the catalyst is not particularly limited, and is, for example, performed at least in one of the crosslinking reaction steps of the plurality of stages. For example, in the method of forming the low refractive index layer, the drying step may be also referred to as a precursor forming step. In addition, for example, a crosslinking reaction step may be performed in a plurality of stages after the drying step, and the microporous particles may be chemically bonded to each other by the action of a catalyst in at least one stage. For example, in the case where the catalyst is a photoactivated catalyst as described above, in the crosslinking reaction step, the microporous particles may be chemically bonded to each other by light to form a precursor of the porous body. In addition, in the case where the catalyst is a heat-activated catalyst, in the crosslinking reaction step, the microporous particles may be chemically bonded to each other by heating to form a precursor of the porous body.

The chemical reaction may be performed by, for example, irradiating or heating a coating film containing a catalyst previously added to a sol particle solution (for example, a suspension), irradiating or heating the coating film after spraying the catalyst, or irradiating or heating the coating film while spraying the catalyst. The cumulative light amount in the light is not particularly limited, and is, for example, 200mJ/cm in terms of wavelength of 360nm ² ～800mJ/cm ² Preferably 250mJ/cm ² ～600mJ/cm ² More preferably 300mJ/cm ² ～400mJ/cm ² . From the viewpoint of preventing insufficient irradiation amount, failure to proceed decomposition by light absorption by the catalyst, and insufficient effect, it is preferably 200mJ/cm ² The above accumulated light amount. The conditions of the heat treatment are not particularly limited. The heating temperature is, for example, 50℃to 250℃and preferably 60℃to 150℃and more preferably 70℃to 130 ℃. 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 solution (for example, suspension) as described above may be performed simultaneously as the step of performing the chemical reaction in the presence of the catalyst. That is, in the step of drying the coated sol particle liquid (for example, suspension), the crushed materials (microporous particles) can be chemically bonded to each other by a chemical reaction in the presence of a catalyst. In this case, the crushed materials (microporous particles) can be more strongly bonded to each other by further heating the coating film after the drying process. Further, it is presumed that the chemical reaction in the presence of the catalyst may occur in the step of preparing the microporous particle-containing liquid (for example, suspension) and the step of applying the microporous particle-containing liquid. However, this assumption is not limited to the method of forming the low refractive index layer. In addition, regarding the solvent to be used, for example, a solvent having a low surface tension is preferable for the purpose of suppressing the occurrence of shrinkage stress accompanying volatilization of the solvent at the time of drying and the cracking phenomenon of the void layer caused thereby. Examples include: lower alcohols such as isopropyl alcohol (IPA), hexane, and perfluorohexane.

In the method for forming the low refractive index layer, the strength of the void layer (low refractive index layer) can be further improved by the crosslinking reaction step being performed in a plurality of stages, for example, compared to the case where the crosslinking reaction step is performed in one stage. Hereinafter, the steps subsequent to the second stage of the crosslinking reaction step may be referred to as "aging step". In the aging step, for example, the precursor is heated, whereby the crosslinking reaction can be further promoted in the precursor. The phenomenon and mechanism occurring in the crosslinking reaction step are not clear, but are, for example, as described above. For example, in the aging step, by setting the heating temperature to a low temperature, the precursor is suppressed from shrinking and the crosslinking reaction is caused to occur, whereby the strength can be improved and both the high void fraction and the strength can be achieved. The temperature in the aging step is, for example, 40 to 70 ℃, preferably 45 to 65 ℃, more preferably 50 to 60 ℃. The time for performing the aging step is, for example, 10 to 30 hours, preferably 13 to 25 hours, and more preferably 15 to 20 hours.

Since the low refractive index layer formed as described above is excellent in strength, for example, a rolled porous body can be produced, and there are advantages such as good production efficiency and easy handling.

The low refractive index layer (void layer) thus formed may be further laminated with other films (layers), for example, to produce a laminated structure having a porous structure. In this case, the respective constituent elements in the laminated structure may be laminated via an adhesive or an adhesive, for example.

Details of specific configurations and forming methods of the low refractive index layer are described in, for example, international publication No. 2019/151073. The disclosure of this publication is incorporated by reference into the present specification.

C. Micro LED array substrate

As the micro LED array substrate, any appropriately configured micro LED array substrate may be used. Typically, as shown in fig. 1, the micro LED array substrate 10 includes a driving substrate 12 and a plurality of micro LEDs 11 arranged in a matrix on the driving substrate 12.

Micro LEDs are LEDs with a chip size of, for example, 1 μm square to 100 μm square.

In one embodiment, as the plurality of micro LEDs, a single kind of micro LEDs may be used. In one embodiment, the micro LED is a blue LED or an ultraviolet LED.

The driving substrate may be configured to individually switch and drive the micro LEDs. The driving substrate is well known to those skilled in the art, and the description thereof is omitted here.

D. Sealing part

The seal may be formed of any suitable transparent material. Examples of the material constituting the sealing portion include: epoxy resins, silicone resins, acrylic resins, and the like. The sealing portion may be formed of molten glass. Examples of the glass constituting the sealing portion include: acrylic glass, crown glass, flint glass, borosilicate glass, and the like.

The seal may be formed of an adhesive or an adhesive. In one embodiment, the seal is formed of an adhesive.

As the adhesive, any suitable adhesive may be used. Examples include: and a curable adhesive such as an isocyanate-based adhesive, a polyvinyl alcohol-based adhesive, a gelatin-based adhesive, a vinyl-based latex-based adhesive, an aqueous polyurethane-based adhesive, an aqueous polyester-based adhesive, an ultraviolet-curable adhesive, and an electron beam-curable adhesive.

As the binder, any suitable binder may be used. Examples include: and adhesives such as rubbers, acrylic, silicone, urethane, vinyl alkyl ether, polyvinyl alcohol, polyvinyl pyrrolidone, polyacrylamide, and cellulose. Among them, acrylic adhesives are preferably used in view of excellent optical transparency and excellent adhesive properties, weather resistance, heat resistance, and the like.

The light transmittance (23 ℃) of the sealing portion at a wavelength of 590nm may be, for example, 80% or more, preferably 85% or more, and more preferably 90% or more. The average light transmittance of the sealing portion at a wavelength of 450nm to 500nm is preferably 70% or more, more preferably 75% or more, and still more preferably 80% or more. The average light transmittance of the sealing portion at a wavelength of 500nm to 780nm is preferably 80% or more, more preferably 85% or more, and still more preferably 90% or more.

The refractive index of the sealing portion is preferably 1.40 or more, more preferably 1.40 to 2.00, and still more preferably 1.45 to 1.80.

The thickness of the sealing portion is preferably 200 μm or less, more preferably 150 μm or less, further preferably 100 μm or less, particularly preferably 50 μm or less. If the thickness of the seal portion is reduced, the effect of color mixture suppression becomes remarkable. The lower limit of the thickness of the sealing portion is, for example, 10 μm. The thickness of the sealing portion may be a distance from the surface of the micro LED on the low refractive index layer side to the surface of the sealing portion on the micro LED side.

E. Wavelength conversion layer

The wavelength conversion layer is a layer that absorbs excitation light from the micro LED and emits light of a given color. In the case of using a blue LED as the micro LED, a red subpixel may be formed by a wavelength conversion layer that absorbs excitation light from the micro LED and emits red light, and a green subpixel may be formed by a wavelength conversion layer that absorbs the excitation light and emits green light. In the case of using an ultraviolet LED, a red subpixel may be formed by a wavelength conversion layer that emits red light when excited by ultraviolet light, a green subpixel may be formed by a wavelength conversion layer that emits green light when excited by ultraviolet light, and a blue subpixel may be formed by a wavelength conversion layer that emits blue light when excited by ultraviolet light.

In one embodiment, the wavelength conversion layer comprises phosphor particles. Typically, the wavelength conversion layer includes a matrix and phosphor particles dispersed in the matrix. As a material constituting the matrix (hereinafter also referred to as a matrix material), any appropriate material may be used. Examples of such a material include resins, organic oxides, and inorganic oxides. The base 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 curable resin, or a visible light curable resin). Preferably a thermosetting resin or an ultraviolet curable resin, more preferably a thermosetting resin. The resins may be used alone or in combination (e.g., blending, copolymerization).

In one embodiment, quantum dots may be used as the phosphor particles. The quantum dots are capable of controlling the wavelength conversion characteristics of the wavelength conversion layer. Specifically, by appropriately combining quantum dots having different emission center wavelengths, a wavelength conversion layer that realizes light having a desired emission center wavelength can be formed. The luminescence center wavelength of the quantum dot may be adjusted according to the material and/or composition, particle size, shape, etc. of the quantum dot. As quantum dots, for example, known are: a quantum dot having a luminescence center wavelength in a wavelength band ranging from 600nm to 680nm (hereinafter referred to as quantum dot A), a quantum dot having a luminescence center wavelength in a wavelength band ranging from 500nm to 600nm (hereinafter referred to as quantum dot B), and a quantum dot having a luminescence center wavelength in a wavelength band ranging from 400nm to 500nm (hereinafter referred to as quantum dot C). The quantum dot a is excited by excitation light (light from the micro LED) to emit red light, the quantum dot B emits green light, and the quantum dot C emits blue light. By appropriately combining these, when light of a given wavelength is made incident on and passes through the wavelength conversion layer, light having a luminescence center wavelength in a desired wavelength band can be realized.

The quantum dots may be composed of any suitable material. The quantum dots may preferably be composed of an inorganic material, more preferably an inorganic conductor material or an inorganic semiconductor material. Examples of the semiconductor material include: group II-VI, III-V, IV-VI, and IV semiconductors. Specific examples thereof include Si, ge, sn, se, te, B, C (including diamond) and 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, si ₃ N ₄ 、Ge ₃ N ₄ 、Al ₂ O ₃ 、(Al、Ga、In) ₂ (S、Se、Te) ₃ 、Al ₂ CO. These semiconductor materials may be used alone or in combination of two or more. Measuring amountThe sub-dots may contain p-type dopants or n-type dopants.

The size of the quantum dots may be any suitable size depending on the desired emission wavelength. The size of the quantum dot is preferably 1nm to 10nm, more preferably 2nm to 8nm. When the size of the quantum dot is in such a range, green and red each exhibit clear light emission, and high color reproducibility can be achieved. For example, green light may emit light at a quantum dot size of about 7nm, and red light may emit light at about 3 nm. The size of the quantum dot is an average particle diameter in the case of a spherical shape, for example, and is a size along the smallest axis in the other shapes. The shape of the quantum dot may be any suitable shape according to the purpose. Specific examples thereof include regular spherical, scaly, plate-like, elliptic, and irregular shapes.

The quantum dots may be blended in a proportion of preferably 1 to 50 parts by weight, more preferably 2 to 30 parts by weight, relative to 100 parts by weight of the base material. If the amount of quantum dots is in such a range, a display excellent in all RGB color balance can be provided.

Details of quantum dots are described in, for example, japanese patent application laid-open publication No. 2012-169271, japanese patent application laid-open publication No. 2015-102857, japanese patent application laid-open publication No. 2015-65158, japanese patent application laid-open publication No. 2013-544018, and japanese patent application laid-open publication No. 2010-533976, the descriptions of which are incorporated herein by reference. The quantum dot may be commercially available.

In another embodiment, the phosphor particles are particles that exhibit luminescence derived from their composition. Examples of such phosphor particles include: sulfide, aluminate, oxide, silicate, nitride, YAG, terbium Aluminum Garnet (TAG) based materials.

As the phosphor particles, the following red phosphor and green phosphor can be used. As the red phosphor, for example, mn can be mentioned ⁴⁺ An activated complex fluoride phosphor. The complex fluoride phosphor is a phosphor comprising at least one ligand A complex compound in which a center (for example, M described below) is surrounded by fluoride ions functioning as ligands and, if necessary, charge compensation is performed by a counter ion (for example, a described below). As a specific example thereof, A ₂ [MF ₅ ]:Mn ⁴⁺ 、A ₃ [MF ₆ ]:Mn ⁴⁺ 、Zn ₂ [MF ₇ ]:Mn ⁴⁺ 、A[In ₂ F ₇ ]:Mn ⁴⁺ 、A ₂ [M′F ₆ ]:Mn ⁴⁺ 、E[M′F ₆ ]:Mn ⁴⁺ 、A ₃ [ZrF ₇ ]:Mn ⁴⁺ 、Ba _0.65 Zr _0.35 F _2.70 ：Mn ⁴⁺ . Wherein A is Li, na, K, rb, cs, NH ₄ 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. Preferred is a complex fluoride phosphor having a coordination number of 6 in the coordination center. Details of such red phosphors are described in, for example, japanese patent application laid-open No. 2015-84327. The entire disclosure of this publication is incorporated by reference into this specification.

Examples of the green phosphor include a phosphor containing a phosphor having β -type Si ₃ N ₄ A compound comprising a solid solution of a sialon having a crystal structure as a main component. It is preferable to perform a treatment of making the amount of oxygen contained in such sialon crystals equal to or less than a specific amount (for example, 0.8 mass%). By performing such a treatment, a green phosphor having a narrow peak width and capable of emitting clear light can be obtained. Details of such green phosphors are described in, for example, japanese patent application laid-open No. 2013-28814. The entire disclosure of this publication is incorporated by reference into this specification.

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 such a range, the conversion efficiency and durability are excellent.

As described above, in one embodiment, the wavelength conversion layers are arranged in isolation by the partition wall (light shielding layer). The width of the partition wall (i.e., the interval between adjacent wavelength conversion layers) is preferably 0.1 μm to 100 μm, more preferably 1 μm to 50 μm. In the present invention, even if the width of the partition wall is narrow, color mixing can be sufficiently suppressed. By reducing the width of the partition wall, a micro LED display device excellent in light emission efficiency can be obtained.

As described above, in the case of configuring a subpixel directly using light from a micro LED (for example, in the case of forming a blue subpixel by a blue LED), the wavelength conversion layer may be replaced with a light diffusion layer at this location. The light scattering layer preferably contains light scattering particles. Examples of the material constituting the light scattering particles include alumina, zirconia, titania, and barium sulfate.

In one embodiment, the micro LED display device further includes a color filter disposed on a side of the wavelength conversion layer (and/or the light diffusion layer) opposite to the low refractive index layer. The color filter may be of any appropriate configuration in accordance with the color development of the subpixel. In one embodiment, a color filter capable of cutting off the color development other than the desired color may be arranged in each subpixel. For example, a color filter capable of cutting off the color development of blue may be used for the red subpixel and the green subpixel.

Examples

Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited to these examples.

Example 1

The structure shown in fig. 2 (a), in which red and green phosphors as wavelength conversion layers were arranged and blue LEDs were arranged directly under the green phosphor with a low refractive index layer (refractive index: 1.20) and a sealing portion (refractive index: 1.50) interposed therebetween, was obtained as luminance of red light emission and luminance of green light emission based on optical simulation. The wavelength conversion layers were each obtained by adding 10 wt% of wavelength conversion particles (refractive index 1.80) to the base portion (refractive index 1.47). The refractive index of the wavelength conversion layers was 1.50.

The optical characteristics in this example, and examples and comparative examples described later were calculated using Synopsys, inc. optical simulation software (Lighttools). The optical model used for the simulation is as follows.

The thickness of each wavelength conversion layer of RGB was set to 100. Mu.m, and the width was set to 100. Mu.m. The width of the partition wall disposed between each RGB was set to 50nm. LEDs are arranged at positions facing the wavelength conversion layers. In the present simulation, for the purpose of investigating the influence of color mixing, only LEDs corresponding to the wavelength conversion layer of Green were arranged, and a sealing portion (adhesive layer) was arranged between the LEDs and the wavelength conversion layer. The seal thickness between the LED and the wavelength conversion layer is shown in table 1. The thickness of the low refractive index layer was set to 1.0. Mu.m. In addition, this dimension is assumed to be 78 inches at 4K resolution (3840 x 2160). The spacer was arranged between the wavelength conversion layers at 50.0 μm, and the transmittance was set to 0%. Further, a light receiver is disposed in each pixel.

Comparative example 1

In the configuration shown in fig. 2 b, that is, the configuration in which the red phosphor and the green phosphor as the wavelength conversion layers are arranged and the blue LED is arranged directly under the green phosphor via the sealing portion (the low refractive index layer is not arranged), the luminance of the red light emission and the luminance of the green light emission based on the optical simulation were obtained.

< evaluation >

The ratio of the luminance in example 1 to the luminance (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, 125 μm, and the ratio of the above-mentioned luminance was obtained for each thickness setting.

In the above configuration, since the green phosphor and the blue LED constitute a subpixel for green color development, the luminance of green emission > the luminance of red emission, and the larger the luminance difference between green emission and red emission, the larger the color mixture suppression effect.

As is clear from table 1, in the present invention, by disposing the low refractive index layer, unnecessary red light emission can be suppressed, and color mixture can be desirably suppressed. In addition, such an effect becomes remarkable by appropriately setting the thickness of the sealing portion between the LED and the wavelength conversion layer.

TABLE 1

Thickness of seal part	Green light emission	Red light emission
			25μm	99％	14％
75μm	119％	38％
			i25μm	126％	88％

Example 2

The structure shown in fig. 2 (a), in which red phosphor and green phosphor as wavelength conversion layers were arranged with a low refractive index layer and a sealing portion (thickness between the LED and the wavelength conversion layer: 75 μm) interposed therebetween, and blue LED was arranged directly under the green phosphor (thickness of the wavelength conversion layer was 100 μm and width was 100 μm, thickness of the partition wall was 50 μm, thickness of the low refractive index layer was 1.0 μm), and brightness of red light emission and brightness of green light emission by optical simulation were obtained.

Comparative example 2

In the configuration shown in fig. 2 b, that is, the configuration in which the red phosphor and the green phosphor as the wavelength conversion layers are arranged and the blue LED is arranged directly under the green phosphor with the sealing portion (thickness 75 μm) (no low refractive index layer is arranged), the luminance of the red light emission and the luminance of the green light emission based on the optical simulation were obtained.

< evaluation >

The ratio of the luminance in example 2 to the luminance (100%) in comparative example 2 is shown in table 2. The refractive indices of the low refractive index layers were set to 1.10, 1.20, 1.25, and 1.30, and the above-mentioned luminance ratios at the respective refractive index settings were obtained.

As is clear from table 2, in the present invention, by disposing the low refractive index layer, unnecessary red light emission can be suppressed, and color mixture can be desirably suppressed.

TABLE 2

Claims

1. A micro LED display device is provided with, in order from a micro LED array substrate side:

the micro LED array substrate comprising a plurality of micro LEDs,

A sealing part for sealing a plurality of the micro LEDs,

Low refractive index layer

A plurality of wavelength conversion layers formed by division,

each of the wavelength conversion layers is formed in a group corresponding to one of the micro LEDs in the 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.

2. The micro LED display device of claim 1, wherein,

the low refractive index layer has a refractive index of 1.25 or less.

3. The micro LED display device according to claim 1 or 2, wherein,

the low refractive index layer is a void layer formed of a porous body composed of fine particles chemically bonded to each other.

4. The micro LED display device according to any one of the claims 1 to 3, wherein,

the seal is formed from an adhesive.

5. The micro LED display device according to any one of claims 1 to 4, wherein,

the wavelength conversion layers are arranged in isolation by partition walls.

6. The micro LED display device of any one of claims 1-5, wherein,

the micro LEDs are blue LEDs or ultraviolet LEDs.

7. The micro LED display device according to any one of claims 1 to 6, further comprising a color filter disposed on a surface of the wavelength conversion layer opposite to the low refractive index layer.