CN116686102A - Micro LED display device - Google Patents

Abstract

The present invention provides a micro LED display device having excellent luminous efficiency and suppressed color mixing. The micro LED display device of the present invention includes 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 divided wavelength conversion layers formed sequentially from the back side. Each of the wavelength conversion layers is formed in a group corresponding to one micro LED in the thickness direction, the refractive index of the low refractive index layer is lower than the refractive index of the sealing part and the refractive index of the wavelength conversion layer, and the low refractive index layer The difference between the refractive index of the index layer and the sealing portion is 0.10 or more, and the difference between the refractive index of the low refractive index layer and the wavelength conversion layer is 0.10 or more.

Description

Micro LED display device

Technical Field

The present invention relates to a micro LED display device.

Background Art

In recent years, as a new type of display device, a micro LED display configured by configuring micro LEDs in pixels arranged in a matrix is being developed (for example, Patent Document 1, Patent Document 2). As a micro LED display, a display having a micro LED array substrate configured by configuring a plurality of micro LEDs and an array of wavelength conversion layers (fluorescent light emitting layers) provided on the micro LED array substrate has been proposed, wherein the array of wavelength conversion layers (fluorescent light emitting layers) absorbs light from the micro LEDs and converts the emission wavelength of the light into wavelengths of red, green, and blue light, respectively (for example, Patent Document 2). In such a micro LED display, the micro LED and the wavelength conversion layer are grouped for each sub-pixel.

Prior art literature

Patent Literature

Patent Document 1: Japanese Patent Application Publication No. 2020-43073

Patent Document 2: Japanese Patent Application No. 2016-523450

Summary of the invention

Problem to be solved by the invention

In the micro-LED display as described above, there is a problem of color mixing caused by light from the micro-LED leaking to sub-pixels other than those corresponding to the micro-LED (adjacent sub-pixels, peripheral sub-pixels). In addition, there is also a problem of not being able to obtain sufficient luminous efficiency due to light returning to the back side due to scattering in the wavelength conversion layer.

An object of the present invention is to provide a micro LED display device having excellent luminous efficiency and suppressed color mixing.

Solutions to the problem

The micro-LED display device of the present invention comprises, in order from the micro-LED array substrate side: the 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 by division, wherein each wavelength conversion layer 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 greater than 0.10, and the difference between the refractive index of the low refractive index layer and the refractive index of the wavelength conversion layer is greater than 0.10.

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 void layer formed of a porous body, and the porous body is composed of fine particles chemically bonded to each other.

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

In one embodiment, the wavelength conversion layers are isolated from each other 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 includes a color filter disposed on a surface of the wavelength conversion layer opposite to the low refractive index layer.

Effects of the Invention

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

BRIEF DESCRIPTION OF THE 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 a configuration provided in an example, and FIG. 2 (b) is a schematic cross-sectional view showing a configuration provided in a comparative example.

Explanation of symbols

10 Micro LED Array Substrate

11. Micro LED

12. Driver board

20 Sealing part

30 Low refractive index layer

40 wavelength conversion layer

100 Micro LED Display Devices

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: a micro-LED array substrate 10 including a plurality of micro-LEDs 11, a sealing portion 20 for sealing the plurality of micro-LEDs 11, a low refractive index layer 30, and a 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-LED 11 in the thickness direction. Typically, one wavelength conversion layer 40 and one micro-LED 11 are included in one sub-pixel. By allowing light from the micro-LED 11 to pass through the wavelength conversion layer 40, red, green, and blue sub-pixels can be formed. It should be noted that, for the case of a sub-pixel that directly utilizes light from a micro-LED (for example, a case where a blue LED forms a blue sub-pixel), the wavelength conversion layer can be omitted at this location, or replaced by other layers (for example, a light diffusion layer). In one embodiment, each wavelength conversion layer may be isolated and arranged 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 opposite to the micro LED array substrate 10. In another embodiment, the low refractive index layer 30 is directly provided on the sealing portion 20 (ie, without other layers).

The refractive index of the low refractive index layer 30 is lower than the refractive index of the sealing part 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 part 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.

In the present invention, a low refractive index layer is arranged between the sealing part and the wavelength conversion layer, thereby generating a refractive index difference between the layers. As a result, at least a portion of the light emitted from the micro-LED and returned to the back side after being scattered in the wavelength conversion layer 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. In addition, at least a portion of the light emitted from the micro-LED in an oblique direction and failing to reach the corresponding wavelength conversion layer (the wavelength conversion layer in the same sub-pixel) and heading toward its periphery will be reflected at the interface between the low refractive index layer and the sealing part and returned to the back side. As a result, color mixing is suppressed. In addition to high precision, the micro-LED display device of the embodiment of the present invention is also advantageous in terms of high brightness and wide color gamut compared to existing displays.

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 preferred it is, and its 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 550nm.

As mentioned above, the difference between the refractive index of low-refractive index layer and the refractive index of sealing portion is more than 0.10. The difference between the refractive index of low-refractive index layer and the refractive index of sealing portion is preferably more than 0.20, more preferably more than 0.30. If it is such a scope, then the above-mentioned effect becomes remarkable. The upper limit of the difference between the refractive index of low-refractive index layer and the refractive index of 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 it is such a range, the above effect becomes 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).

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

The low refractive index layer can adopt any appropriate composition. In one embodiment, the low refractive index layer has a gap. The low refractive index layer can be preferably formed by coating or printing. As the material constituting the low refractive index layer, for example, the materials described in International Publication No. 2004/113966, Japanese Patent Publication No. 2013-254183, and Japanese Patent Publication No. 2012-189802 can be used. Specifically, for example, silicon dioxide compounds; hydrolyzable silanes, and their partial hydrolyzates and dehydrated condensates; organic polymers; silicon compounds containing silanol groups; active silica obtained by contacting silicates with acids and ion exchange resins; polymerizable monomers (for example, (meth) acrylic monomers, and styrene monomers); curable resins (for example, (meth) acrylic resins, fluorine-containing resins, and carbamate resins); and combinations thereof. The low refractive index layer can be formed by coating or printing a solution or dispersion of such a material.

The voidage of the low-refractive index layer with space is preferably more than 35 volume %, more preferably more than 38 volume %, particularly preferably more than 40 volume %.If it is such a scope, then a low-refractive index layer with particularly low refractive index can be formed.The upper limit of the voidage of low-refractive index layer is, for example, below 90 volume %, preferably below 75 volume %.If it is such a scope, then a low-refractive index layer with excellent intensity can be formed.Voidage is the value of the refractive index measured by utilizing ellipsometer, the value obtained by calculating voidage by Lorentz-Lorenz ' sformula (Lorentz-Lorenz equation).

The size of the void (hole) in the low refractive index layer refers to the diameter of the long axis of the void (hole) and the diameter of the short axis. The size of the void (hole) is, for example, 2nm to 500nm. The size of the void (hole) is, for example, more than 2nm, preferably more than 5nm, more preferably more than 10nm, and further preferably more than 20nm. On the other hand, the size of the void (hole) is, for example, less than 500nm, preferably less than 200nm, and more preferably less than 100nm. The range of the size of the void (hole) is, for example, 2nm to 500nm, preferably 5nm to 500nm, more preferably 10nm to 200nm, and further preferably 20nm to 100nm. The size of the void (hole) can be adjusted to a desired size according to the purpose and use.

The size of the voids (pores) can be quantified by the BET test method. Specifically, after 0.1 g of the sample (the void layer formed) is put into the capillary of the specific surface area measuring device (made by MacMeretic: ASAP2020), the gas in the void structure is degassed by drying under reduced pressure at room temperature for 24 hours. Then, the adsorption isotherm is drawn by adsorbing nitrogen on the above sample to obtain the pore distribution. In this way, 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 range of the haze is, for example, 0.1% or more and less than 5%, preferably 0.2% or more and less than 3%. The haze can be measured, for example, by the method described below. It should be noted that the haze is an indicator of the transparency of the low refractive index layer.

The void layer (low refractive index layer) was cut into a size of 50 mm×50 mm, and placed in a haze meter (HM-150 manufactured by Murakami Color Research Laboratory Co., Ltd.) to measure the haze value. The haze value was calculated by the following formula.

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

As the low refractive index layer having voids inside, for example, a low refractive index layer having a porous layer and/or an air layer in at least a portion thereof can be cited. The porous layer typically includes aerogels and/or particles (e.g., hollow microparticles and/or porous particles). The low refractive index layer may preferably be a nanoporous layer (specifically, a porous layer in which 90% or more of the micropores have a diameter within the range of 10 ^-1 nm to 10 ³ nm).

As the above-mentioned particles, any appropriate particles can be used. The particles are typically formed of a silicon dioxide compound. As the shape of the particles, for example, spherical, plate-like, needle-like, rope-like, and grape-like. As rope-like particles, for example, a plurality of particles having a spherical, plate-like, or needle-like shape are connected to form a rosary-like particle; short fiber-like particles (for example, short fiber-like particles described in Japanese Patent Gazette No. 2001-188104), and combinations thereof can be listed. Rope-like particles can be straight-chain or branched. As grape-like particles, for example, a plurality of spherical, plate-like, and needle-like particles are condensed to form grape-like particles. 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 within this range, the damage prevention effect of the present invention becomes significant. In addition, the above-mentioned desired thickness ratio can be easily achieved.

Typically, the low refractive index layer can be formed by coating or printing as described above. If it is such a structure, the low refractive index layer can be continuously provided by roll-to-roll. Printing can be performed in any appropriate manner. The printing method can be a printing method with a plate such as gravure printing, offset printing, flexographic printing, or a printing method without a plate such as inkjet printing, laser printing, or electrostatic printing.

Below, an example of the specific composition of the low refractive index layer is described. The low refractive index layer of the present embodiment contains one or more structural units that form a fine void structure, and the structural units are chemically combined with each other through catalysis. As the shape of the structural unit, for example: particle-shaped, fibrous, rod-shaped, and flat. The structural unit can have only one shape, or it can be combined to have two or more shapes. In one embodiment, the low refractive index layer is a void layer formed by a porous body composed of fine particles chemically combined with each other. Below, the situation of the void layer formed by a porous body composed of fine particles chemically combined with each other is mainly described.

Such a void layer can be formed by, for example, chemically bonding microporous particles to each other in the void layer forming process. It should be noted that, in an embodiment of the present invention, the shape of the "particles" (for example, the above-mentioned microporous particles) is not particularly limited, for example, it can be spherical or other shapes. In addition, in an embodiment of the present invention, the above-mentioned microporous particles can be, for example, sol-gel beaded particles, nanoparticles (hollow nano-silica/nano hollow sphere particles), nanofibers, etc. The microporous particles typically include inorganic substances. As specific examples of inorganic substances, silicon (Si), magnesium (Mg), aluminum (Al), titanium (Ti), zinc (Zn), and zirconium (Zr) can be cited. They can be used alone or in combination of two or more. In one embodiment, the above-mentioned microporous particles are, for example, microporous particles of silicon compounds, and the above-mentioned porous body is, for example, an organosilicon porous body. The microporous particles of the above-mentioned silicon compound, for example, include a pulverized body of a gel-like silica compound. In addition, as other forms of low refractive index layers having a porous layer and/or an air layer in at least a portion, there are, for example, void layers formed by fibrous materials such as nanofibers, which are entangled with each other to form voids and form a layer. The method for making such a void layer is not particularly limited, for example, it is the same as the case of the void layer of a porous body in which the above-mentioned microporous particles are chemically bonded to each other. In addition, as other forms, void layers using hollow nanoparticles and nanoclays, void layers formed using hollow nano hollow spheres and magnesium fluoride can be listed. The void layer can be a void layer formed by a single constituent substance, or it can be a void layer formed by multiple constituent substances. The void layer can be composed of a single form mentioned above, or it can be composed of multiple forms mentioned above.

In the present embodiment, the porous structure of the porous body can be, for example, a continuous bubble structure formed by a continuous pore structure. As for the continuous bubble structure, for example, in the above-mentioned organic silicon porous body, it refers to the state in which the pore structure is three-dimensionally connected, and it can also be said that the internal voids of the pore structure are continuous. By making the porous body have a continuous bubble structure, the porosity can be increased. However, when using single bubble particles such as hollow silica (particles each having a pore structure), a continuous bubble structure cannot be formed. On the other hand, when using, for example, silica gel particles (a crushed product of a gel-like silicon compound forming a sol), since the particles have a three-dimensional tree-like structure, the tree-like particles will settle and precipitate in the coating film (a coating film of a sol containing a crushed product of a gel-like silicon compound), thereby easily forming a continuous bubble structure. The low refractive index layer is more preferably a monolithic structure in which the continuous bubble structure includes a plurality of pore distributions. The monolithic structure represents a hierarchical structure, which includes, for example, a structure in which nano-sized fine voids exist, and a continuous bubble structure formed by the aggregation of such nano-voids. In the case of forming a monolithic structure, for example, fine voids can be used to impart strength to the membrane, and coarse interconnected voids can be used to impart high porosity, thereby achieving both membrane strength and high porosity. Such a monolithic structure can preferably be formed by controlling the pore distribution of the void structure generated in the gel (gel-like silicon compound) at the pre-stage of crushing into silica gel particles. In addition, for example, when crushing the gel-like silicon compound, the particle size distribution of the crushed silica gel particles is controlled to a desired size, so that a monolithic structure can be formed.

The low refractive index layer, for example, comprises a pulverized product of a gel-like compound as described above, and the pulverized products are chemically bonded together. The form of chemical bonding (chemical bond) between the pulverized products in the low refractive index layer is not particularly limited, and examples thereof include cross-linking bonds, covalent bonds, and hydrogen bonds.

The gel morphology of the gel-like compound is not particularly limited. "Gel" generally refers to a state in which the solute has lost its independent mobility due to interaction and has aggregated, and has solidified. The gel-like compound can be, for example, a wet gel or a dry gel. It should be noted that, in general, a wet gel refers to a gel containing a dispersion medium and in which the solute adopts a uniform structure, and a dry gel refers to a gel in which the solvent is removed and the solute adopts a mesh structure with voids.

Examples of gel-like compounds include gelled products obtained by gelling monomeric compounds. Specifically, examples of the gel-like silicon compound include gelled products obtained by bonding monomeric silicon compounds to each other, and as a specific example, gelled products obtained by bonding monomeric silicon compounds to each other by covalent bonds, hydrogen bonds, or intermolecular forces. Examples of covalent bonds include bonds based on dehydration condensation.

The volume average particle size of the above-mentioned 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 size is, for example, 2.00 μm or less, preferably 1.50 μm or less, and more preferably 1.00 μm or less. The range of the volume average particle size is, for example, 0.10 μm to 2.00 μm, preferably 0.20 μm to 1.50 μm, and more preferably 0.40 μm to 1.00 μm. The particle size distribution can be measured by, for example, a particle size distribution evaluation device such as a dynamic light scattering method and a laser diffraction method, and an electron microscope such as a scanning electron microscope (SEM) and a transmission electron microscope (TEM). It should be noted that the volume average particle size is an indicator of the deviation of the particle size of the pulverized material.

The type of gel-like compound is not particularly limited. Examples of the gel-like compound include gel-like silicon compounds. The following description will be made by taking the case where the gel-like compound is a gel-like silicon compound as an example, but the invention is not limited thereto.

The above-mentioned cross-linking bond is, for example, a siloxane bond. As the siloxane bond, for example, the T2 bond, T3 bond, and T4 bond shown below can be cited. When the void layer (low refractive index layer) has a siloxane bond, it can have any one bond, any two bonds, or all three bonds. In the siloxane bond, the more the ratio of T2 and T3, the more flexible it is, and the original properties of the gel can be expected. On the other hand, the more the ratio of T4, the easier it is to show film strength. Therefore, it is preferred to change the ratio of T2, T3, and T4 according to the purpose, use, desired properties, etc.

[Chemical formula 1]

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

When the gel-like compound is a gel-like silicon compound, the silicon compound of the monomer is not particularly limited. As the silicon compound of the monomer, for example, the compound represented by the following formula (1) can be cited. When the gel-like silicon compound is a gelled product in which the silicon compounds of the monomers form hydrogen bonds or intermolecular forces with each other as described above, the monomers of formula (1) can form hydrogen bonds, for example, via their respective hydroxyl groups.

[Chemical formula 2]

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

As a specific example of the silicon compound represented by formula (1), for example, a compound represented by the following formula (1') in which X is 3 can be cited. In the following formula (1'), R ¹ is the same as in the case of formula (1), for example, a methyl group. When R ¹ is a methyl group, the silicon compound is trihydroxymethylsilane. When X is 3, the silicon compound is, for example, a trifunctional silane having three functional groups.

[Chemical formula 3]

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

The silicon compound as a monomer may be, for example, a hydrolyzate of a silicon compound precursor. The silicon compound precursor may be any one that can generate a silicon compound by hydrolysis, and specific examples thereof include compounds represented by the following formula (2).

[Chemical formula 4]

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

^R1 and ^R2 are each independently a linear or branched alkyl group,

^R1 and ^R2 may be the same or different.

When X is 2, ^R1 may be the same or different from each other.

^R2 may be the same as or different from each other.

X and ^R1 are, for example, the same as X and ^R1 in formula (1). ^R2 can refer to the examples of ^R1 in formula (1).

As a specific example of the silicon compound precursor represented by formula (2), for example, a compound represented by the following formula (2') in which X is 3 can be cited. In the following formula (2'), ^R1 and ^R2 are the same as in the case of formula (2). When ^R1 and ^R2 are methyl groups, the silicon compound precursor is trimethoxy(methyl)silane (hereinafter also referred to as "MTMS").

[Chemical formula 5]

From the perspective of, for example, excellent low refractive index, the silicon compound of the monomer is preferably a trifunctional silane. In addition, for example, from the perspective of excellent strength (for example, scratch resistance), the silicon compound of the monomer is preferably a tetrafunctional silane. The silicon compound of the monomer can be used only one, or two or more can be used in combination. For example, as a silicon compound of the monomer, it can contain only trifunctional silane, it can contain only tetrafunctional silane, it can also contain both trifunctional silane and tetrafunctional silane, and it can further contain other silicon compounds. In the case of using two or more silicon compounds as the silicon compound of the monomer, the ratio is not particularly limited and can be appropriately set.

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

Typically, the method includes: a precursor forming step of forming a void structure as a precursor of a low refractive index layer (void layer) on a resin film; and a cross-linking reaction step of initiating a cross-linking reaction inside the precursor after the precursor forming step. The method further includes: a liquid containing liquid (hereinafter sometimes referred to as "microporous particle containing liquid" or simply "containing liquid") containing microporous particles; and a drying step of drying the containing liquid, in which the microporous particles in the dried body are chemically bonded to each other to form a precursor. The containing liquid is not particularly limited, and is, for example, a suspension containing microporous particles. It should be noted that the following is mainly described for the case where the microporous particles are a pulverized product of a gel-like compound and the void layer contains a porous body (preferably a silicone porous body) of a pulverized product of a gel-like compound. It should be noted that in the case where the microporous particles are other than a pulverized product of a gel-like compound, the low refractive index layer can also be formed in the same manner.

According to the above method, for example, a low refractive index layer (void layer) having a very low refractive index can be formed. The reason for this can be speculated as follows, for example. However, this speculation does not limit the method for forming the low refractive index layer.

The above-mentioned pulverized material is obtained by pulverizing a gel-like silicon compound, and therefore, the three-dimensional structure of the gel-like silicon compound before pulverization is formed in a state dispersed in the three-dimensional basic structure. Furthermore, in the above-mentioned method, by coating the pulverized material of the gel-like silicon compound on a resin film, a precursor of a porous structure based on the three-dimensional basic structure can be formed. That is, according to the above-mentioned method, a new porous structure (three-dimensional basic structure) based on the coating of the pulverized material, which is different from the three-dimensional structure of the gel-like silicon compound, can be formed. Therefore, in the void layer finally obtained, for example, a low refractive index that functions to the same extent as an air layer can be achieved. In addition, in the above-mentioned method, chemical bonds are formed between the pulverized materials, and therefore, the three-dimensional basic structure can be fixed. Therefore, although the void layer finally obtained is a structure with voids, sufficient strength and flexibility can be maintained.

In addition, in the above-mentioned method, the above-mentioned precursor formation process and the above-mentioned cross-linking reaction process can be carried out as different processes. In addition, it is preferred to carry out the cross-linking reaction process in multiple steps. By carrying out the cross-linking reaction process in multiple steps, for example, compared with carrying out the cross-linking reaction process in one step, the intensity of the precursor can be further improved, thereby obtaining a low-refractive index layer that takes into account high void ratio and intensity. Its mechanism is still unclear, but for example, it can be inferred as follows. That is, when utilizing catalysts etc. to improve film strength while forming the void layer as described above, due to the carrying out of the catalyst reaction, there is a problem that the void ratio is reduced although the film strength is improved. This can be considered to be attributed to, for example, by utilizing catalysts to carry out the cross-linking reaction of microporous particles each other, the cross-linking (chemical bonding) number of microporous particles each other increases, thus, bonding becomes strong, but the void layer as a whole condenses, and the void ratio is reduced. In contrast, it can be considered that by carrying out the precursor formation process and the cross-linking reaction process in different processes and carrying out the cross-linking reaction process in multiple steps, the cross-linking (chemical bonding) number can be increased (for example, almost no overall coagulation occurs), and almost no change in the form of the precursor as a whole is caused. However, these are only examples of mechanisms that can be inferred, and do not limit the formation method of the low refractive index layer.

In the precursor formation process, for example, particles with a certain 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 light or thermally active catalytic reaction, a product (for example, a strong base catalyst produced by a photobase generator, etc.) that can form a chemical bond between microporous particles will be produced (the first stage of the cross-linking reaction process). It can be considered that in order to react more efficiently in a short time, by further heating aging (the second stage of the cross-linking reaction process), the chemical bonding (cross-linking reaction) between microporous particles will be further carried out, and the strength will be improved. It can be considered that, for example, the microporous particles are microporous particles of silicon compounds (for example, a pulverized body of a gel-like silica compound), and when there are residual silanol groups (Si-OH groups) in the precursor, the residual silanol groups will form chemical bonds through cross-linking reactions. However, this description is also an example and does not limit the formation method of the low refractive index layer.

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

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

Alternatively, the silicon compound may be a hydrolyzate of the silicon compound precursor, and may be produced, for example, by hydrolyzing the silicon compound precursor represented by the above formula (2).

The method for hydrolyzing the monomer compound precursor is not particularly limited, and for example, it can be carried out by a chemical reaction in the presence of a catalyst. Examples of the catalyst include acids such as oxalic acid and acetic acid. The hydrolysis reaction can be carried out as follows: for example, an aqueous solution of oxalic acid is slowly dropped into a mixed solution (e.g., a suspension) of a silicon compound and dimethyl sulfoxide at room temperature and 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 groups of the silicon compound precursor, the subsequent gelation/ripening/heating/immobilization after the void structure is formed can be carried out more effectively.

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 in the presence of a catalyst, and examples of the catalyst include acid catalysts such as hydrochloric acid, oxalic acid, and sulfuric acid, and dehydration condensation catalysts such as alkaline catalysts such as ammonia, potassium hydroxide, sodium hydroxide, and ammonium hydroxide. As a dehydration condensation catalyst, an alkaline catalyst is preferably used. In the dehydration condensation reaction, the amount of the catalyst added relative to the monomer compound is not particularly limited. For example, relative to 1 mole of the monomer compound, the catalyst can be preferably added in an amount of 0.1 to 10 moles, more preferably 0.05 to 7 moles, and further preferably 0.1 to 5 moles.

The gelation of the monomer compound is preferably carried out in, for example, a solvent. There is no particular restriction on the ratio of the monomer compound to the solvent. 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), and the like. The solvent may be used alone or in combination of two or more. Hereinafter, the solvent used in the gelation is also referred to as a "solvent for gelation".

There is no particular restriction on the conditions for gelation. 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. In the case of a dehydration condensation reaction, the treatment conditions are not particularly limited, and the above examples can be cited. By gelation, for example, siloxane bonds can be grown to form primary silica particles, and by further reacting, the primary particles can be connected to each other in a beaded shape to form a gel with a three-dimensional structure.

Preferably, the gel-like compound obtained by gelation is subjected to a aging treatment after the gelation reaction. Through 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 (increasing the contact area). For the gel after the aging treatment, for example, the strength of the gel itself increases, and as a result, the strength of the three-dimensional basic structure after the pulverization can be improved. Thus, for example, in the drying process after the pulverized material is applied, the pore size of the void structure formed by the accumulation of the three-dimensional basic structure can be suppressed from shrinking due to the volatilization of the solvent during the drying process.

The aging treatment can be carried out, for example, by incubating the gel-like compound at a given temperature for a given time. The aging temperature is, for example, above 30°C, preferably above 35°C, and more preferably above 40°C. On the other hand, the aging temperature is, for example, below 80°C, preferably below 75°C, and more preferably below 70°C. The range of the aging temperature 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, above 5 hours, preferably above 10 hours, and more preferably above 15 hours. On the other hand, the aging time is, for example, below 50 hours, preferably below 40 hours, and more preferably below 30 hours. The range of the aging time is, for example, 5 hours to 50 hours, preferably 10 hours to 40 hours, and more preferably 15 hours to 30 hours. It should be noted that the aging conditions can be optimized, for example, in order to obtain an increase in the size of the primary particles of silica and an increase in the contact area of the neck. In addition, the boiling point of the solvent used is preferably considered. For example, when the aging temperature is too high, the solvent will volatilize excessively, and the concentration of the coating liquid (gel liquid) may be concentrated, which may cause undesirable conditions such as closure of the pores of the three-dimensional void structure. On the other hand, when the aging temperature is too low, not only will the effect of aging not be fully obtained, but it will also increase the temperature deviation over time in the mass production process, and a low refractive index layer with poor characteristics may be formed.

The aging treatment can use the same solvent as, for example, the gelation treatment. Specifically, it is preferred to directly perform the aging treatment on the reactant after the gelation treatment (that is, the solvent containing the gel-like compound). The number of moles of residual silanol groups contained in the gel (gel-like compound, such as a gel-like silicon compound) after the aging treatment after the gelation is completed is, for example, less than 50%, preferably less than 40%, and more preferably less than 30%. On the other hand, the number of moles of residual silanol groups is, for example, more than 1%, preferably more than 3%, and more preferably more than 5%. 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, the lower the number of moles of residual silanol groups, the more preferred. When the number of moles of silanol groups is too high, the void structure may not be maintained until, for example, the precursor of the organosilicon porous body is cross-linked. On the other hand, when the number of moles of silanol groups is too low, for example, in the process of making a microporous particle-containing liquid (e.g., a suspension) and/or in the subsequent process, it is possible that the crushed material of the gel-like compound cannot be cross-linked, and sufficient film strength cannot be given. It should be noted that the number of moles of residual silanol groups is, for example, the ratio of residual silanol groups when the number of moles of alkoxy groups of the raw material (e.g., a monomer compound precursor) is set to 100. It should be noted that the above is an example of a silanol group. For example, when a silicon compound of a monomer is modified with various reactive functional groups, the same matters and conditions can also be applied to each functional group.

After the monomer compound is gelled in a gelling solvent, the obtained gelled compound is crushed. The crushing can be performed directly on the gelled compound in the gelling solvent, for example, or the gelling solvent can be replaced with other solvents and then the gelled compound in the other solvent is crushed. In addition, for example, when the catalyst and solvent used in the gelling reaction remain after the aging process, thereby causing the liquid to gel over time (pot life) and the drying efficiency during the drying process is reduced, it is preferably replaced with other solvents. Hereinafter, the above-mentioned other solvents are also referred to as "crushing solvents".

The pulverizing solvent is not particularly limited, and for example, an organic solvent may be used. As the organic solvent, a solvent having a boiling point of, for example, 130° C. or less, preferably 100° C. or less, and more preferably 85° C. or less may be cited. Specific examples include isopropyl alcohol (IPA), ethanol, methanol, butanol, propylene glycol monomethyl ether (PGME), methyl cellosolve, acetone, dimethylformamide (DMF), isobutyl alcohol, and the like. The pulverizing solvent 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 and IPA, DMSO and ethanol, DMSO and methanol, DMSO and butanol, DMSO and isobutanol, etc. By replacing the gelling solvent with the pulverizing solvent in this way, for example, in the coating film formation described later, a more uniform coating film can be formed.

There is no particular limitation on the method for pulverizing the gel-like compound, and it can be performed by, for example, an ultrasonic homogenizer, a high-speed rotary homogenizer, or other pulverizing devices utilizing the cavitation phenomenon. Devices that perform medium pulverization, such as ball mills, for example, physically destroy the void structure of the gel during pulverization. In contrast, cavitation pulverizing devices such as homogenizers are, for example, medium-free, and therefore utilize high-speed shear forces to peel off the relatively weakly bound silica particle bonding surfaces that have been enclosed in the three-dimensional structure of the gel. Thus, the obtained three-dimensional structure of the gel can maintain, for example, a void structure having a particle size distribution within a certain range, so that the void structure caused by the accumulation during coating/drying can be re-formed. There are no particular limitations on the pulverization conditions, and it is preferred that the gel be pulverized by instantaneously imparting a high-speed flow without causing the solvent to volatilize. For example, it is preferred to pulverize in a manner that forms a pulverized product having a particle size deviation (e.g., volume average particle size or particle size distribution) as described above. If the amount of work such as pulverization time/intensity is insufficient, for example, coarse particles may remain, and dense pores may not be formed, and appearance defects may increase, and high quality may not be obtained. On the other hand, if the amount of work is too much, for example, particles may become finer than the desired particle size distribution, and the size of the voids accumulated after coating/drying may become fine, and the desired porosity may not be obtained.

As described above, a liquid (e.g., a suspension) containing microporous particles (a crushed product of a gel-like compound) can be manufactured. Furthermore, a liquid containing microporous particles and a catalyst can be manufactured by adding a catalyst that chemically binds the microporous particles to each other after manufacturing the liquid containing the microporous particles or during the manufacturing process. The catalyst can be, for example, a catalyst that promotes the crosslinking of the microporous particles to each other. As a chemical reaction that chemically binds the microporous particles to each other, it is preferred to utilize the dehydration condensation reaction of the residual silanol groups contained in the silica gel molecules. By utilizing a catalyst to promote the reaction of the hydroxyl groups of the silanol groups to each other, continuous film formation that solidifies the void structure can be performed in a short time. As a catalyst, for example, a photoactivated catalyst and a thermally activated catalyst can be cited. According to the photoactivated catalyst, for example, in the precursor formation process, the microporous particles can be chemically bound to each other (e.g., forming crosslinks) without heating. Thus, for example, it is not easy to cause the shrinkage of the precursor as a whole in the precursor formation process, so a higher porosity can be maintained. In addition, a substance (catalyst generator) that produces a catalyst can be used in addition to or instead of a catalyst. For example, a substance that generates a catalyst by light (photocatalyst generator) may be used in addition to or instead of a photoactivated catalyst, and a substance that generates a catalyst by heat (thermal catalyst generator) may be used in addition to or instead of a thermally activated catalyst. Examples of the photocatalyst generator include photobase generators (substances that generate a basic catalyst by light irradiation), photoacid generators (substances that generate an acidic catalyst by light irradiation), and the like, preferably photobase generators. Examples of the photobase generator include 9-anthrylmethyl N,N-diethylcarbamate (trade name WPBG-018), (E)-1-[3-(2-hydroxyphenyl)-2-propenoyl]piperidine (trade name WPBG-027), 1-(anthraquinone-2-yl)ethylimidazolecarboxylate (trade name WPBG-030), and 1-(anthraquinone-2-yl)ethylimidazolecarboxylate (trade name WPBG-040). imidazolecarboxylate, trade name WPBG-140), 2-nitrophenylmethyl 4-methacryloyloxypiperidine-1-carboxylate (trade name WPBG-165), 2-(3-benzoylphenyl)propionic acid 1,2-diisopropyl-3-[bis(dimethylamino)methylene]guanidine salt (trade name WPBG-266), n-butyltriphenylboronic acid 1,2-dicyclohexyl-4,4,5,5-tetramethylbiguanidine salt (trade name WPBG-300), and 2-(9-oxo- 1,5,7-triazabicyclo[4.4.0]dec-5-ene (Tokyo Chemical Industry Co., Ltd.), a compound containing 4-piperidinol (trade name HDPD-PB100: manufactured by Heraeus), etc. It should be noted that the above-mentioned trade names containing "WPBG" are all trade names of Wako Pure Chemical Industries, Ltd. Examples of the photoacid generator include aromatic sulfonium salts (trade name SP-170: ADEKA Corporation), triaryl sulfonium salts (trade name CPI101A: San-Apro Co., Ltd.), aromatic iodine Salt (trade name Irgacure250: Ciba Japan Co., Ltd.), etc. In addition, the catalyst that chemically binds the microporous particles to each other is not limited to photoactivated catalysts and photocatalyst generators, but may also be, for example, thermally activated catalysts or thermal catalyst generators such as urea. Catalysts that chemically bind the microporous particles to each other include, for example, alkali catalysts such as potassium hydroxide, sodium hydroxide, ammonium hydroxide, acid catalysts such as hydrochloric acid, acetic acid, oxalic acid, etc. Among these, alkali catalysts are preferred. The catalyst or catalyst generator that chemically binds the microporous particles to each other can be used, for example, by adding it to a sol particle liquid (such as a suspension) containing the crushed material (microporous particles) just before coating, or it can be used in the form of a mixed liquid formed by mixing the catalyst or catalyst generator with a solvent. The mixed liquid can be, for example, a coating liquid obtained by directly adding it to the sol particle liquid and dissolving it, a solution obtained by dissolving the catalyst or catalyst generator in a solvent, or a dispersion obtained by dispersing the catalyst or catalyst generator in a solvent. The solvent is not particularly limited, and examples thereof include water, a buffer solution, and the like.

In addition, for example, a cross-linking auxiliary agent for indirectly bonding the above-mentioned pulverized products of the gel to each other can be further added to the gel-containing liquid. The cross-linking auxiliary agent enters between the particles (the above-mentioned pulverized products), and the particles and the cross-linking auxiliary agent interact or bind to each other, thereby allowing particles that are a certain distance away from each other to be able to bind to each other, thereby efficiently improving the strength. As the above-mentioned cross-linking auxiliary agent, a multi-cross-linked silane monomer is preferred. Specifically, the above-mentioned multi-cross-linked silane monomer has, for example, 2 or more and 3 or less alkoxysilyl groups, and the chain length between the alkoxysilyl groups can be 1 or more and 10 or less carbon atoms, and can also contain elements other than carbon. Examples of the crosslinking auxiliary agent 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 cross-linking auxiliary agent added is not particularly limited, and 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 product of the silicon compound.

Next, a liquid (e.g., a suspension) containing microporous particles is applied to the sealing portion (coating process). The coating can be, for example, various coating methods described later, and is not limited thereto. A coating film containing microporous particles and a catalyst can be formed by directly applying a liquid containing microporous particles (e.g., a crushed product of a gel-like silica compound) to the sealing portion. The coating film may also be referred to as a coating layer, for example. By forming a coating film, for example, the crushed product after the three-dimensional structure is destroyed settles/sediments, thereby constructing a new three-dimensional structure. It should be noted that, for example, the liquid containing microporous particles may not contain a catalyst that chemically binds the microporous particles to each other. For example, as described later, after the catalyst that chemically binds the microporous particles to each other is sprayed on the coating film, or while spraying, a precursor formation process is performed. However, the liquid containing microporous particles may also contain a catalyst that chemically binds the microporous particles to each other, and the microporous particles are chemically bound to each other through the action of the catalyst contained in the coating film to form a precursor of a porous body.

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

In the coating process, for example, a sol-like crushed material (hereinafter also referred to as "sol particle liquid") dispersed in a solvent is preferably applied to the sealing portion. For the sol particle liquid, by, for example, applying it to the sealing portion and drying it, and then performing the above-mentioned chemical crosslinking, continuous film formation of a void layer having a film strength above a certain level can be achieved. It should be noted that the "sol" in the embodiment of the present invention refers to a state in which silica gel particles of a nano three-dimensional structure that retain a part of the void structure are dispersed in a solvent by crushing the three-dimensional structure of the gel, thereby showing 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). When the concentration of the pulverized material is too high, for example, the fluidity of the sol particle liquid is significantly reduced, and agglomerates/coating streaks may be caused during coating. When the concentration of the pulverized material is too low, for example, not only does it take a considerable amount of time to dry the solvent of the sol particle liquid, but the residual solvent immediately after drying also increases, and thus the porosity 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. When the shear viscosity is too high, for example, coating streaks may occur, and a reduction in the transfer rate of gravure coating may be observed. On the contrary, when the shear viscosity is too low, for example, the wet coating thickness during coating may not be increased, and the desired thickness may not be obtained after drying.

There is no particular limitation on the amount of the pulverized material to be applied, and for example, it can be appropriately set according to the desired thickness of the organic silicon porous body (ultimately the low refractive index layer). As a specific example, in the case of forming an organic silicon porous body with a thickness of 0.1 μm to 1000 μm, the amount of the pulverized material applied is, for example, 0.01 μg to 60,000 μg per 1 ^m2 area of the coating surface, preferably 0.1 μg to 5000 μg, and more preferably 1 μg to 50 μg. The preferred amount of the sol particle liquid to be applied is related to, for example, the concentration of the liquid, the coating method, etc., and is therefore difficult to define uniquely, but if productivity is taken into consideration, it is preferably applied in as thin a layer as possible. When the amount of application is too much, for example, the possibility of being dried in a drying furnace before the solvent evaporates becomes high. As a result, the nano-pulverized sol particles settle/sediment in the solvent, and the solvent dries before the void structure is formed, which may hinder the formation of voids and lead to a significant reduction in the void ratio. On the other hand, if the coating amount is too thin, the risk of coating cavities being generated may become high.

In addition, the method for forming a low refractive index layer includes, for example, a precursor forming step of forming a void structure as a precursor of a void layer (low refractive index layer) as described above. The precursor forming step is not particularly limited, and the precursor (void structure) can be formed by, for example, a drying step of drying a coating film made by coating a microporous particle-containing liquid. Through the drying treatment in the drying step, for example, not only the solvent in the above-mentioned coating film (the solvent contained in the sol particle liquid) can be removed, but also the sol particles can be precipitated/deposited during the drying treatment to form a void structure. The temperature of 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 of the drying treatment is, for example, 0.1 minute to 30 minutes, preferably 0.2 minute to 10 minutes, and more preferably 0.3 minute to 3 minutes.

The drying treatment may be, for example, natural drying, heat drying, or reduced pressure drying. Among them, in the case of industrial continuous production as a prerequisite, heat drying is preferably adopted. The method of heat drying is not particularly limited, for example, a common heating mechanism may be used. As the heating mechanism, for example, a hot air device, a heating roller, a far infrared heater, etc. may be cited. In addition, regarding the solvent used, for the purpose of suppressing the generation of shrinkage stress accompanying solvent volatilization during drying and the crack phenomenon of the void layer (organic silicon porous body) caused thereby, a solvent with low surface tension is preferably used. As the solvent, for example, lower alcohols represented by isopropyl alcohol (IPA), hexane, perfluorohexane, etc. may be cited. In addition, a small amount of perfluoro surfactants or organosilicon surfactants may be added to the above-mentioned IPA, etc. to reduce the surface tension.

Further, the formation method of the low refractive index layer is as described above, including a cross-linking reaction process in which a cross-linking reaction occurs inside the precursor after the precursor formation process, in which an alkaline substance is generated by illumination or heating, and the cross-linking reaction process is a plurality of stages. In the first stage of the cross-linking reaction process, for example, microporous particles are chemically bonded to each other by the action of a catalyst (alkaline substance). Thus, for example, the three-dimensional structure of the crushed material in the coating film (precursor) is immobilized. In the case of immobilization using existing sintering, for example, by performing a high temperature treatment of more than 200°C, dehydration condensation of silanol groups and the formation of siloxane bonds are induced. In this formation method, by reacting various additives that catalyze the above-mentioned dehydration condensation reaction, for example, a void structure can be continuously formed and immobilized at a relatively low drying temperature of about 100°C and a short processing time of less than several minutes.

There is no particular limitation on the method of chemical bonding, and for example, it can be appropriately determined according to the type of gel-like silicon compound. As a specific example, chemical bonding can be carried out by chemical cross-linking of the pulverized materials, for example, in the case where inorganic particles such as titanium oxide are added to the pulverized materials, it is also possible to consider chemically forming cross-links between the inorganic particles and the pulverized materials. In addition, it also includes the case where biocatalysts such as enzymes are loaded, and the case where a site different from the catalyst active site is formed with the pulverized materials. Therefore, for the formation method of the low refractive index layer, it is possible to consider not only the application expansion to the void layer (organic silicon porous body) formed by the sol particles, but also the application expansion to the organic-inorganic hybrid void layer, the host-guest void layer, etc.

The chemical reaction in the presence of the above-mentioned catalyst is not particularly limited at which stage in the formation method of the low refractive index layer is carried out (occurred), for example, it is carried out in at least one stage of the cross-linking reaction process of the above-mentioned multiple stages. For example, in the formation method of the low refractive index layer, the drying process can also be used as the precursor formation process as described above. In addition, for example, a cross-linking reaction process of multiple stages can also be carried out after the drying process, and in at least one stage thereof, the microporous particles are chemically bonded to each other by the action of the catalyst. For example, as described above, when the catalyst is a photoactivated catalyst, in the cross-linking reaction process, the microporous particles can be chemically combined with each other by illumination to form a precursor of a porous body. In addition, when the catalyst is a thermally activated catalyst, in the cross-linking reaction process, the microporous particles can be chemically combined with each other by heating to form a precursor of a porous body.

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 irradiating or heating the coating film after spraying the catalyst, or irradiating or heating while spraying the catalyst. The cumulative light amount during irradiation is not particularly limited, and is, for example, 200mJ/ ^cm2 to 800mJ/ ^cm2 , preferably 250mJ/ ^cm2 to 600mJ/ ^cm2 , and more preferably 300mJ/ ^cm2 to 400mJ/ ^cm2 , based on a wavelength of 360nm. From the viewpoint of preventing insufficient irradiation, inability to perform decomposition based on light absorption of the catalyst, and insufficient effect, a cumulative light amount of 200mJ/ ^cm2 or more 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 process of drying the sol particle liquid (e.g., suspension) after coating as described above can also be simultaneously used as a process for performing a chemical reaction in the presence of a catalyst. That is, in the process of drying the sol particle liquid (e.g., suspension) after coating, the crushed materials (microporous particles) can be chemically combined with each other by a chemical reaction in the presence of a catalyst. In this case, the crushed materials (microporous particles) can be more strongly combined with each other by further heating the coating film after the drying process. Furthermore, it can be inferred that the chemical reaction in the presence of a catalyst sometimes also occurs in the process of making a microporous particle-containing liquid (e.g., suspension) and the process of coating a microporous particle-containing liquid. However, this speculation does not limit the method for forming a low refractive index layer. In addition, with regard to the solvent used, for example, for the purpose of suppressing the generation of shrinkage stress accompanying the volatilization of the solvent during drying and the cracking phenomenon of the void layer caused by this, a solvent with low surface tension is preferred. For example, lower alcohols represented by isopropyl alcohol (IPA), hexane, and perfluorohexane can be mentioned.

In the formation method of the low refractive index layer, by making the cross-linking reaction process into multiple stages, for example, compared with the case where the cross-linking reaction process is one stage, the strength of the void layer (low refractive index layer) can be further improved. Hereinafter, the process after the second stage of the cross-linking reaction process is sometimes referred to as an "aging process". In the aging process, for example, by heating the precursor, the cross-linking reaction can be further promoted inside the precursor. The phenomenon and mechanism occurring in the cross-linking reaction process are not yet clear, but for example as described above. For example, in the aging process, by making the heating temperature low, the cross-linking reaction occurs while suppressing the shrinkage of the precursor, the strength can be improved, and the high void ratio and strength can be taken into account. 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.

The low refractive index layer formed as described above is excellent in strength and can be formed into a porous body in a roll shape, for example, which has advantages such as good production efficiency and easy handling.

The low refractive index layer (void layer) thus formed can be further laminated with other films (layers) to form a laminated structure having a porous structure. In this case, the components in the laminated structure can be laminated via a binder or adhesive, for example.

The specific structure and formation method of the low refractive index layer are described in detail in, for example, International Publication No. 2019/151073. The description of this publication is incorporated herein by reference.

C. Micro LED Array Substrate

As the micro LED array substrate, any micro LED array substrate having any appropriate structure may be used. Representatively, 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 .

Micro LED refers to an LED having a chip size of, for example, 1 μm square to 100 μm square.

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

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

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, acrylic resins, etc. In addition, the sealing portion may also be formed of molten glass. Examples of glass constituting the sealing portion include acrylic glass, crown glass, flint glass, borosilicate glass, etc.

The sealing portion may be formed of an adhesive or a bonding agent. In one embodiment, the sealing portion is formed of a bonding agent.

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

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

The light transmittance (23°C) of the sealing portion at a wavelength of 590nm can be, for example, 80% or more, preferably 85% or more, and more preferably 90% or more. In addition, 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 further preferably 80% or more. In addition, 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 further 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 further preferably 1.45 to 1.80.

The thickness of the sealing portion is preferably less than 200 μm, more preferably less than 150 μm, further preferably less than 100 μm, and particularly preferably less than 50 μm. If the thickness of the sealing portion is reduced, the effect of suppressing color mixing becomes significant. The lower limit of the thickness of the sealing portion is, for example, 10 μm. It should be noted that the thickness of the sealing portion can be the distance from the surface on the low refractive index layer side of the micro LED to the surface on the micro LED side of the sealing portion.

E. Wavelength conversion layer

The wavelength conversion layer is a layer that absorbs the 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 sub-pixel can be formed by a wavelength conversion layer that absorbs the excitation light from the micro-LED and emits red light, and a green sub-pixel can be formed by a wavelength conversion layer that absorbs the excitation light and emits green light. In addition, in the case of using an ultraviolet LED, a red sub-pixel can be formed by a wavelength conversion layer that is excited by ultraviolet light and emits red light, a green sub-pixel can be formed by a wavelength conversion layer that is excited by ultraviolet light and emits green light, and a blue sub-pixel can be formed by a wavelength conversion layer that is excited by ultraviolet light and emits blue light.

In one embodiment, the wavelength conversion layer includes 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 can be used. As such a material, resins, organic oxides, and inorganic oxides can be cited. The matrix material is preferably a resin. The resin can be a thermoplastic resin, a thermosetting resin, or an active energy ray-curable resin (for example, an electron beam-curable resin, an ultraviolet-curable resin, or a visible light-curable resin). Preferably, it is a thermosetting resin or an ultraviolet-curable resin, and more preferably a thermosetting resin. The resin can be used alone or in combination (for example, blended, copolymerized).

In one embodiment, quantum dots can be used as phosphor particles. Quantum dots can control the wavelength conversion characteristics of the wavelength conversion layer. Specifically, by appropriately combining and using quantum dots with different luminescent center wavelengths, a wavelength conversion layer that realizes light with a desired luminescent center wavelength can be formed. The luminescent center wavelength of quantum dots can be adjusted according to the material and/or composition, particle size, shape, etc. of the quantum dots. As quantum dots, for example, quantum dots with a luminescent center wavelength in a band ranging from 600nm to 680nm (hereinafter referred to as quantum dots A), quantum dots with a luminescent center wavelength in a band ranging from 500nm to 600nm (hereinafter referred to as quantum dots B), and quantum dots with a luminescent center wavelength in a band ranging from 400nm to 500nm (hereinafter referred to as quantum dots C). Quantum dot A is excited by excitation light (light from a micro LED) and emits red light, quantum dot B emits green light, and quantum dot C emits blue light. By appropriately combining them, when light of a given wavelength is incident and passed through the wavelength conversion layer, light with a luminescent center wavelength in a desired band can be realized.

The quantum dots may be made of any suitable material. The quantum dots may preferably be made of an inorganic material, more preferably an inorganic conductor material or an inorganic semiconductor material. Examples of semiconductor materials include semiconductors of Group II-VI, Group III-V, Group IV-VI, and Group IV. 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, Si ₃ N ₄ , Ge ₃ N ₄ , Al ₂ O ₃ , (Al, Ga, In) ₂ (S, Se, Te) ₃ , and Al ₂ CO. These semiconductor materials may be used alone or in combination of two or more. The quantum dot may contain a p-type dopant or an n-type dopant.

The size of the quantum dot can be any appropriate size according to the desired emission wavelength. The size of the quantum dot is preferably 1nm to 10nm, more preferably 2nm to 8nm. If the size of the quantum dot is in such a range, the green and red colors respectively show distinct luminescence, and high color reproducibility can be achieved. For example, green light can emit light when the size of the quantum dot is about 7nm, and red light can emit light at about 3nm. The size of the quantum dot is the average particle size when the quantum dot is, for example, a true spherical shape, and is the size along the smallest axis in the shape when it is a shape other than this. It should be noted that, as the shape of the quantum dot, any appropriate shape can be adopted according to the purpose. As specific examples, true spherical, scaly, plate-like, ellipsoidal, and irregular shapes can be cited.

The quantum dots are preferably blended in an amount of 1 to 50 parts by weight, more preferably 2 to 30 parts by weight, relative to 100 parts by weight of the matrix material. If the blending amount of the quantum dots is within this range, a display having excellent RGB color balance can be provided.

The details of quantum dots are described in, for example, Japanese Patent Application Laid-Open No. 2012-169271, Japanese Patent Application Laid-Open No. 2015-102857, Japanese Patent Application Laid-Open No. 2015-65158, Japanese Patent Application No. 2013-544018, Japanese Patent Application No. 2013-544018, and Japanese Patent Application No. 2010-533976, and the contents of these publications are incorporated herein by reference. Commercially available quantum dots may also be used.

In another embodiment, the phosphor particles are particles that emit light derived from their composition. Examples of such phosphor particles include sulfide, aluminate, oxide, silicate, nitride, YAG, and terbium aluminum garnet (TAG) based materials.

In addition, as the phosphor particles, the following red phosphors and green phosphors can be used. As the red phosphor, for example, a composite fluoride phosphor activated by Mn ⁴⁺ can be cited. A composite fluoride phosphor refers to a coordination compound that includes at least one coordination center (e.g., M described later), is surrounded by fluoride ions that act as ligands, and is charge-compensated by counter ions (e.g., A described later) as needed. Specific examples thereof include 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⁺ . 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. Preferably, the phosphor is a composite fluoride phosphor having a coordination number of 6 at the coordination center. The details of such a red phosphor are described in, for example, Japanese Patent Application Laid-Open No. 2015-84327, the entire contents of which are incorporated herein by reference.

As a green phosphor, for example, a compound containing a solid solution of SiAlON having a β _- type _Si3N4 crystal structure as a main component can be cited. It is preferable to perform a treatment such that the amount of oxygen contained in such SiAlON crystal reaches a specific amount (for example, 0.8 mass %) or less. By performing such a treatment, a green phosphor having a narrow peak width and emitting bright light can be obtained. The details of such a green phosphor are described in, for example, Japanese Patent Publication No. 2013-28814. The entire description of the publication is cited in this specification as a reference.

The thickness of the wavelength conversion layer is preferably 5 μm to 100 μm, and more preferably 30 μm to 50 μm. When the thickness of the wavelength conversion layer is within such a range, excellent conversion efficiency and durability are achieved.

As described above, in one embodiment, each wavelength conversion layer is isolated and configured by a 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, and 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 fully suppressed. By reducing the width of the partition wall, a micro LED display device with excellent luminous efficiency can be obtained.

As described above, in the case of forming a sub-pixel that directly utilizes light from a micro-LED (for example, in the case of forming a blue sub-pixel by a blue LED), the wavelength conversion layer can be replaced with a light diffusion layer at this location. It is preferred that the light scattering layer contains light scattering particles. Examples of materials constituting the light scattering particles include aluminum oxide, zirconium oxide, titanium oxide, barium sulfate, and the like.

In one embodiment, the micro LED display device further comprises a color filter disposed on a side of the wavelength conversion layer (and/or light diffusion layer) opposite to the low refractive index layer. The color filter may be configured to have any appropriate configuration corresponding to the color development of the sub-pixel. In one embodiment, in each sub-pixel, a color filter capable of cutting off the color development except for the desired color may be configured. For example, in red sub-pixels and green sub-pixels, a color filter capable of cutting off the color development of blue may be used.

Example

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

[Example 1]

For the configuration shown in FIG2(a), i.e., a configuration in which a red phosphor and a green phosphor are arranged as wavelength conversion layers, and a blue LED is arranged directly below the green phosphor via a low refractive index layer (refractive index: 1.20) and a sealing portion (refractive index: 1.50), the brightness of red light emission and the brightness of green light emission based on optical simulation were obtained. The wavelength conversion layers are all layers formed by adding 10% by weight of wavelength conversion particles (refractive index 1.80) to a base portion (refractive index 1.47). The refractive index of the wavelength conversion layers is 1.50.

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

The thickness of the wavelength conversion layer of each RGB is set to 100μm, and the width is set to 100μm. The width of the partition wall arranged between each RGB is set to 50nm. LEDs are arranged at positions relative to each wavelength conversion layer. In this simulation, for the purpose of investigating the influence of color mixing, only the LED corresponding to the wavelength conversion layer of Green is arranged, and a sealing part (adhesive layer) is arranged between the LED and the wavelength conversion layer. The thickness of the sealing part between the LED and the wavelength conversion layer is shown in Table 1. The thickness of the low refractive index layer is set to 1.0μm. In addition, this size is assumed to be 78 inches at 4K resolution (3840x2160). The partition wall is arranged between the wavelength conversion layers at 50.0μm, and the transmittance is set to 0%. In addition, a photoreceiver is arranged on each pixel.

[Comparative Example 1]

For the structure shown in Figure 2(b), that is, a red phosphor and a green phosphor are arranged as wavelength conversion layers, and a blue LED is arranged directly below the green phosphor via a sealing portion (a low refractive index layer is not arranged), the brightness of the red light and the brightness of the green light were calculated based on optical simulation.

＜Evaluation＞

The ratio of the brightness in Example 1 to the brightness in Comparative Example 1 (100%) 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 structure, the green phosphor and the blue LED constitute a sub-pixel for green color display, so the brightness of green light emission > the brightness of red light emission. Moreover, the greater the brightness difference between green light emission and red light emission, the greater the color mixing suppression effect.

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

[Table 1]

Seal thickness Green glow Red glow 25μm 99% 14% 75μm 119% 38% i25μm 126% 88%

[Example 2]

For the configuration shown in FIG2(a), i.e., a configuration in which a red phosphor and a green phosphor are arranged as wavelength conversion layers, and a blue LED is arranged directly below the green phosphor via a low refractive index layer and a sealing portion (the thickness between the LED and the wavelength conversion layer: 75 μm) (the wavelength conversion layer has a thickness of 100 μm and a width of 100 μm, the partition wall has a thickness of 50 μm, and the low refractive index layer has a thickness of 1.0 μm), the brightness of the red light emission and the brightness of the green light emission were calculated based on optical simulation.

[Comparative Example 2]

For the structure shown in Figure 2(b), that is, a red phosphor and a green phosphor are arranged as wavelength conversion layers, and a blue LED is arranged directly below the green phosphor via a sealing portion (thickness 75μm) (no low refractive index layer is arranged), the brightness of the red light and the brightness of the green light were calculated based on optical simulation.

＜Evaluation＞

The ratio of the brightness in Example 2 to the brightness in Comparative Example 2 (100%) is shown in Table 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 calculated for each refractive index setting.

As is clear from Table 2, in the present invention, by providing a low refractive index layer, unnecessary red light emission can be suppressed and color mixing can be preferably suppressed.

[Table 2]

Claims (7)

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.