Method for producing gel for forming low refractive index film, method for producing coating liquid for forming low refractive index film, and method for producing low refractive index film

Abstract

To provide a method for producing a gel and a coating liquid capable of forming a low refractive index film having both a very low refractive index and an allowable haze value.SOLUTION: A method for producing a gel for forming a low refractive index film according to an embodiment of the present invention includes a gelation step of gelating a raw material of the gel in a gel production solvent, and includes introducing fine bubbles into the gel production solvent. In one embodiment, the fine gas bubbles in the gel production solvents each have a median size D50 of 200nm or less and a half-width of 400nm or less. The method for producing a coating liquid for forming a low refractive index film according to the embodiment of the present invention includes a solvent replacement step of replacing a gel production solvent in a mixed liquid containing a gel obtained by the method for producing a gel for forming a low refractive index film with another solvent.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing a gel for forming a low refractive index film, a method for producing a coating liquid for forming a low refractive index film, and a method for producing a low refractive index film. [Background technology]

[0002] In an optical laminate, optical design according to the refractive index of each layer constituting the optical laminate is important. Therefore, providing a layer with a controlled refractive index in the optical laminate is of great significance in the optical design of the optical laminate. A low refractive index layer, in which the refractive index is lowered by a void structure, is known as a layer with a controlled refractive index that can be provided in an optical laminate. Here, in order to realize new optical designs, a low refractive index layer having a refractive index even lower than that currently achievable is desired. However, when an attempt is made to further lower the refractive index of the low refractive index film (porous film) constituting the low refractive index layer, there is a problem that haze may increase. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-182490 Summary of the Invention [Problem to be solved by the invention]

[0004] The present invention has been made to solve the above-mentioned conventional problems, and its main object is to provide a method for producing a gel and a coating liquid that can form a low refractive index film that has both a very low refractive index and an acceptable haze value. [Means for solving the problem]

[0005] [1] A method for producing a low refractive index film-forming gel according to an embodiment of the present invention includes a gelling step of gelling a gel raw material in a gel production solvent, and also includes introducing fine bubbles into the gel production solvent. [2] In the above [1], the median diameter D50 of the fine bubbles is 200 nm or less, and the half-value width of the bubble diameter distribution is 400 nm or less. [3] In the above [1] or [2], the raw material of the gel contains a hydrolyzable silane. [4] In any one of the above [1] to [3], the raw material of the gel contains a compound represented by the following formula (1): [ka] In formula (1), X is 2 or 3, R 1 and R 2 are each a linear or branched alkyl group, R 1 and R 2 may be the same or different, R 1 may be the same or different when X is 2, R 2 may be the same or different from each other. [5] In any one of the above [1] to [4], the solvent for producing the gel is dimethyl sulfoxide. [6] According to another aspect of the present invention, there is provided a method for producing a coating solution for forming a low refractive index film, the method comprising a solvent substitution step of substituting a solvent for producing the gel in a mixed solution containing the gel obtained by any one of the production methods [1] to [5] above with another solvent. [7] In the above [6], the production method further includes a gel crushing step of crushing the gel lumps. [8] In the above [7], the gel crushing step includes a coarse crushing step of crushing the gel mass to a size of 15 cm or less, and a fine crushing step of crushing the coarsely crushed gel to a size of 2.00 μm or less, the coarse crushing step being carried out before the solvent substitution step, and the fine crushing step being carried out after the solvent substitution step. [9] In any one of the above [6] to [8], the production method further includes an aging step of aging the gel before the solvent substitution step.

[10] In the above [9], the maturing step includes incubating the gel in the mixed solution at 30°C or higher.

[11] According to yet another aspect of the present invention, there is provided a method for producing a low refractive index film, which comprises applying and heating a coating liquid for forming a low refractive index film obtained by any one of the production methods [6] to

[10] above.

[12] In the above

[11] , the refractive index of the obtained low refractive index film is less than 1.20, and the haze is less than 2%. [Effects of the Invention]

[0006] According to an embodiment of the present invention, a method for producing a gel and a coating liquid that can form a low refractive index film that has both a very low refractive index and an acceptable haze value can be provided. DETAILED DESCRIPTION OF THE INVENTION

[0007] Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to these embodiments.

[0008] A. Manufacturing method of low refractive index film forming gel A-1. Overview of manufacturing method A method for producing a low refractive index film-forming gel according to an embodiment of the present invention includes a gelation step of gelling a gel raw material in a gel-producing solvent, and in an embodiment of the present invention, the method includes introducing fine bubbles into the gel-producing solvent.

[0009] The gel raw material may be a compound that can be gelled directly, or a precursor of such a compound. When the gel raw material is a compound that can be gelled directly, a mixed solution containing the gel raw material, a gel-producing solvent, and a gelling catalyst is prepared, and the compound is gelled in the mixed solution (essentially, the gel-producing solvent). When the gel raw material is a precursor, a mixed solution containing the precursor, a gel-producing solvent, and, for example, a catalyst for hydrolysis of the precursor is prepared. For example, a compound that can be gelled can be produced by hydrolyzing the precursor. That is, a compound that can be gelled is produced from the precursor in the mixed solution (essentially, the gel-producing solvent), and the compound is gelled. In either case, fine bubbles are introduced into the gel-producing solvent in which gelling occurs. Note that, in this specification, the term "solvent" encompasses a dispersion medium. That is, "solvent" refers to a liquid that can dissolve and / or disperse a specific substance.

[0010] Below, the raw materials for the gel and gelation will be explained, followed by a description of the solvent for producing the gel and the introduction of microbubbles.

[0011] A-2. Gel raw materials The raw material for the gel may typically be a silicon compound. The silicon compound may be subjected to gelation as it is, or may be a precursor of the silicon compound to be subjected to gelation. When the raw material for the gel is a precursor of a silicon compound to be subjected to gelation, the precursor may be a hydrolyzable silane. The hydrolyzable silane may be, for example, a compound represented by the following formula (1):

[0012] [ka]

[0013] In the above formula (1), X may be, for example, 2, 3, or 4, and may also be, for example, 3 or 4; R 1 and R 2 are each a linear or branched alkyl group, R 1 and R2 may be the same or different, R 1 may be the same or different when X is 2, R 2 may be the same or different from each other.

[0014] More specifically, the above R 1 and R 2 The number of carbon atoms in each of these may be, for example, 1 to 6, or may be, for example, 1 to 4, or may be, for example, 1 to 2. Therefore, specific examples of the linear alkyl group include a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, and a hexyl group, and specific examples of the branched alkyl group include an isopropyl group and an isobutyl group.

[0015] Specific examples of the silicon compound (hydrolyzable silane) represented by the above formula (1) include compounds represented by the following formula (1') in which X is 3. In the following formula (1'), R 1 and R 2 are the same as in the above formula (1). 1 and R 2 When is a methyl group, the silicon compound (hydrolyzable silane) is methyltrimethoxysilane (hereinafter also referred to as "MTMS").

[0016] [ka]

[0017] A compound that can be subjected to gelation (silicon compound) can be produced by hydrolyzing the hydrolyzable silane in a mixed solution containing the hydrolyzable silane, a gel-producing solvent, and a hydrolysis catalyst. The silicon compound obtained by hydrolysis of the hydrolyzable silane can be represented, for example, by the following formula (2). The silicon compound can typically be gelled by a dehydration condensation reaction.

[0018] [ka]

[0019] R in the above formula (2) 1 and X are as described above in relation to formula (1).

[0020] Specific examples of the silicon compound represented by the above formula (2) include compounds represented by the following formula (2') in which X is 3. In the following formula (2'), R 1 is as explained in relation to the above formula (1). 1 When is a methyl group, the silicon compound is tris(hydroxy)methylsilane.

[0021] [ka]

[0022] A-3.Gelling A-3-1. Hydrolysis of hydrolyzable silanes When the raw material for the gel is a precursor (e.g., a hydrolyzable silane such as MTMS), a compound that can be subjected to gelation (a silicon compound) can be produced by hydrolyzing the hydrolyzable silane in a mixture containing the hydrolyzable silane, a solvent for producing the gel, and a catalyst for hydrolysis.

[0023] Any appropriate hydrolysis method can be adopted depending on the purpose. Representative examples of hydrolysis catalysts include acid catalysts. Specific examples of acid catalysts include oxalic acid and acetic acid. Specifically, the hydrolysis reaction can be carried out by slowly adding an aqueous solution of oxalic acid dropwise to a solution of the precursor in a solvent for gel production at room temperature, followed by stirring for approximately 30 minutes. When hydrolyzing a precursor (e.g., a hydrolyzable silane such as MTMS), it is preferable to hydrolyze the precursor so that substantially no alkoxy groups remain. Such hydrolysis can more efficiently perform subsequent gelation, aging, and heating and fixation after the formation of a low refractive index film. The amount of catalyst added to the precursor in the hydrolysis reaction can be appropriately set depending on the purpose. The amount of catalyst added may be, for example, 0.00001 to 0.03 mol, or, for example, 0.00005 to 0.02 mol, or, for example, 0.0001 to 0.01 mol, per 1 mol of precursor.

[0024] A-3-2. Gelation of silicon compounds As described above, the method for producing a low-refractive-index film-forming gel according to an embodiment of the present invention includes a gelation step in which a gel raw material is gelled in a gel-producing solvent. As described above, the gel raw material may be a silicon compound that is directly subjected to gelation, or a precursor of such a silicon compound (e.g., a hydrolyzable silane such as MTMS). Specifically, gelation can be carried out by subjecting the silicon compound to a dehydration condensation reaction in a mixture containing the silicon compound, a gel-producing solvent, and a gelation catalyst. When the gel raw material is a precursor of a silicon compound, the silicon compound is obtained by hydrolysis of the precursor, as described above in Section A-3-1, and the obtained silicon compound is subjected to gelation. The hydrolysis of the precursor and the gelation of the silicon compound can be carried out consecutively. The gelation of a silicon compound will be described below.

[0025] The gelation of silicon compounds can be carried out, for example, by a dehydration condensation reaction between silicon compounds. The dehydration condensation reaction is preferably carried out in the presence of a gelation catalyst. A typical example of the gelation catalyst is a dehydration condensation catalyst. Specific examples of the dehydration condensation catalyst include acid catalysts such as hydrochloric acid, oxalic acid, and sulfuric acid, and base catalysts such as ammonia, potassium hydroxide, sodium hydroxide, and ammonium hydroxide. A base catalyst is preferred. The amount of the gelation catalyst added relative to the silicon compound in the dehydration condensation reaction can be appropriately set depending on the purpose. The amount of the gelation catalyst added may be, for example, 0.01 to 10 mol, or may be, for example, 0.05 to 7 mol, or may be, for example, 0.1 to 5 mol, per 1 mol of the silicon compound.

[0026] Any appropriate solvent may be used as the gel-producing solvent as long as the effects of the embodiments of the present invention can be obtained. In one embodiment, the gel-producing solvent may have, for example, a boiling point of 130°C or higher. In one embodiment, the gel-producing solvent may be, for example, a water-soluble solvent. In this specification, the term "water-soluble solvent" refers to a solvent that can be mixed with water in any ratio.

[0027] Examples of gel-producing solvents include dimethyl sulfoxide (DMSO), N-methylpyrrolidone (NMP), N,N-dimethylacetamide (DMAc), dimethylformamide (DMF), γ-butyrolactone (GBL), acetonitrile (MeCN), and ethylene glycol monoethyl ether (EGEE). These may be used alone or in combination of two or more. Furthermore, for example, a mixed solvent obtained by mixing these solvents or a combination thereof with an alcoholic solvent (e.g., isopropyl alcohol, isobutyl alcohol, n-butyl alcohol, pentanol [n-pentyl alcohol]) may be used as the gel-producing solvent. Preferred examples of gel-producing solvents include N-methylpyrrolidone, dimethyl sulfoxide, dimethylformamide (DMF), γ-butyrolactone, N,N-dimethylacetamide, and combinations thereof.

[0028] The ratio of the gel raw materials (substantially silicon compounds) in the gel-producing solvent can be appropriately set depending on the purpose, the type of gel raw materials, the type of gel-producing solvent, etc. Specifically, the gel raw materials can be used in a ratio of, for example, 1 to 50 parts by weight, for example, 3 to 30 parts by weight, or for example, 5 to 10 parts by weight, relative to 100 parts by weight of the gel-producing solvent.

[0029] The gelation conditions can be appropriately set depending on the purpose, the type of gel raw material, the type of gel-producing solvent, etc. When the gel raw material is a silicon compound, the treatment temperature for the mixed solution containing the gel raw material and the gel-producing solvent can be, for example, 20°C to 30°C, or, for example, 22°C to 28°C, or, for example, 24°C to 26°C; the treatment time can be, for example, 1 minute to 60 minutes, or, for example, 5 minutes to 40 minutes, or, for example, 10 minutes to 30 minutes. Such treatment temperatures and treatment times can appropriately gel the silicon compound. More specifically, the dehydration condensation reaction of the silicon compound grows siloxane bonds, forming primary particles of the silicon compound. As the reaction progresses, the primary particles are strung together in a beaded pattern, producing a gel with a three-dimensional structure.

[0030] The form of the gel obtained by gelation may be any appropriate form as long as the effects of the embodiments of the present invention can be obtained. The term "gel" generally refers to a solidified state in which solutes lose their independent mobility due to interactions between the solutes and have an aggregated structure. Examples of gel forms include wet gels and xerogels. A wet gel refers to a structure in which the solutes that constitute the gel skeleton are integrated with the solvent contained therein, and the solute surface is wetted by the solvent. A xerogel refers to a structure in which the solute has a network structure with voids after the solvent has been removed. The gelled silicon compound (gel-like silicon compound) may preferably be a wet gel.

[0031] The amount of residual silanol groups in the gelled silicon compound (gel silicon compound) may be any appropriate amount as long as the effects of the present invention can be obtained. The amount of residual silanol groups may be expressed, for example, as the number of moles of residual silanol groups. The number of moles of residual silanol groups is typically the proportion of residual silanol groups when the number of moles of alkoxy groups in the raw material of the gel (silicon compound or its precursor) is taken as 100. The number of moles of residual silanol groups may be, for example, 50% or less, for example, 40% or less, or for example, 30% or less, or may be, for example, 1% or more, for example, 3% or more, or for example, 5% or more. The range of the number of moles of residual silanol groups may be, for example, 1% to 50%, for example, 3% to 40%, or for example, 5% to 30%.

[0032] A-4. Introduction of microbubbles In an embodiment of the present invention, as described above, microbubbles are introduced into a gel-producing solvent. That is, in an embodiment of the present invention, gelation of a gel raw material (substantially, a silicon compound) is carried out in the gel-producing solvent into which microbubbles have been introduced, as described in the above section A-3-2.

[0033] Any appropriate method for introducing microbubbles can be employed as long as it achieves the effects of the embodiments of the present invention. Examples of the introduction method include (i) a method for crushing bubbles by shearing the liquid, and (ii) a method for precipitating gas dissolved in the liquid. Specific examples of method (i) include a swirling flow liquid method, a micropore method, a static mixer method, an ejector method, and a Venturi method. The swirling flow liquid method typically generates a high-speed swirling flow in a gas-containing solvent to crush bubbles. The micropore method typically miniaturizes bubbles using microscopic gas dispersion holes. In this case, it is preferable to add a surfactant to the solvent. This is because reducing the gas-liquid interfacial tension allows the use of very small gas dispersion holes, thereby generating finer bubbles. The static mixer method typically crushes the gas using obstacles while the gas-containing solvent is moving through a pipeline. The ejector and Venturi types typically create a sudden pressure change in the flow path of the gas-containing solvent to crush the bubbles. Specific examples of method (ii) include the pressure dissolution deposition method and the heated deposition method. The pressure dissolution deposition method typically involves rapidly depressurizing a gas-saturated solution under pressure to precipitate bubbles. The heated deposition method typically involves rapidly heating a gas-saturated solution at room temperature to precipitate bubbles. The method for introducing fine bubbles can be appropriately selected depending on the purpose and the desired bubble size and bubble size distribution of the fine bubbles. In one embodiment, the pressure dissolution deposition method can be used.

[0034] Preferably, the median diameter D50 of the microbubbles introduced into the gel-producing solvent (generated in the gel-producing solvent) is 200 nm or less, and the half-value width of the bubble size distribution is 400 nm or less. Such a configuration of the microbubbles can provide a gel and a coating solution capable of forming a low-refractive-index film that combines a very low refractive index with an acceptable haze value. The median diameter D50 of the microbubbles is more preferably 150 nm or less, even more preferably 100 nm or less, particularly preferably 75 nm or less, and especially preferably 50 nm or less. The median diameter D50 of the microbubbles can be, for example, 10 nm or more, or, for example, 20 nm or more. The half-value width of the bubble size distribution is more preferably 300 nm or less, even more preferably 200 nm or less, particularly preferably 150 nm or less, and especially preferably 100 nm or less. The half-value width of the bubble size distribution can be, for example, 30 nm or more, or, for example, 50 nm or more. By gelling the gel raw materials in a gel-producing solvent containing such microbubbles, voids of a size theoretically large enough to prevent scattering (e.g., several tens of nanometers) can be formed in the final pulverized gel product. It is estimated that these voids can result in a low-refractive-index film that combines a very low refractive index with an acceptable haze value. However, this mechanism is merely speculation and does not limit or constrain the present invention. The median diameter D50 of the microbubbles and the half-width of the bubble size distribution can be measured, for example, by dynamic light scattering (DLS).

[0035] In the manner described above, a low refractive index film-forming gel can be obtained. The low refractive index film-forming gel can typically be obtained as a mixed liquid containing the gel and a gel-producing solvent.

[0036] So far, gelation using a silicon compound has been described, but it goes without saying that the raw material for the gel is not limited to a silicon compound. Any appropriate material that can be used in the above-mentioned method for producing a gel and the method for producing a coating liquid described later can be used as the raw material for the gel.

[0037] B. Manufacturing method of coating liquid for forming low refractive index film B-1. Overview of manufacturing method A method for producing a coating liquid for forming a low refractive index film according to an embodiment of the present invention includes a solvent substitution step of substituting the solvent for producing the gel in a mixed liquid containing the gel obtained by the production method described in the above item A with another solvent.

[0038] The gel obtained by the manufacturing method described in the above item A is typically in the form of clumps in the mixed solution. Therefore, the manufacturing method of a coating solution for forming a low refractive index film may further include a gel crushing step of crushing the gel clumps. The gel crushing step typically includes a coarse crushing step and a fine crushing step. The gel crushing step may be performed before or after the solvent substitution step. In one embodiment, the coarse crushing step may be performed before the solvent substitution step, and the fine crushing step may be performed after the solvent substitution step.

[0039] The method for producing a coating liquid for forming a low refractive index film may further include an aging step of aging the gel before the solvent substitution step or the coarse pulverization step.

[0040] The aging step, the solvent substitution step, and the gel crushing step will be described in this order below.

[0041] B-2. Aging process Any suitable conditions for the aging treatment in the aging step can be adopted as long as the effects of the embodiments of the present invention can be obtained. The aging treatment can be performed, for example, by incubating a gelled silicon compound (gel silicon compound) in a mixed liquid at a predetermined temperature. The aging treatment can further grow the primary particles of a gel silicon compound having a three-dimensional structure, thereby increasing the size of the particles themselves. As a result, the contact state at the neck portions where particles contact each other can be increased, for example, from point contact to surface contact. A gel silicon compound that has undergone the above-mentioned aging treatment can, for example, increase the strength of the gel itself, thereby further improving the strength of the three-dimensional basic structure of the pulverized product obtained by pulverization, as described below. This can prevent the pore size of the void structure in which the three-dimensional basic structure is deposited from shrinking due to solvent evaporation during the drying process after coating when a low refractive index film is formed using the resulting coating liquid.

[0042] The temperature of the aging treatment may be, for example, 30°C or higher, for example, 35°C or higher, or for example, 40°C or higher, and may be, for example, 80°C or lower, for example, 75°C or lower, or for example, 70°C or lower. The temperature range of the aging treatment may be, for example, 30°C to 80°C, for example, 35°C to 75°C, or for example, 40°C to 70°C. The aging treatment time may be, for example, 5 hours or higher, for example, 10 hours or higher, or for example, 15 hours or higher, and may be, for example, 50 hours or lower, for example, 40 hours or lower, or for example, 30 hours or lower. The aging treatment time range may be, for example, 5 hours to 50 hours, for example, 10 hours to 40 hours, or for example, 15 hours to 30 hours. The aging treatment conditions are preferably set so as to increase the size of the primary particles in the gel-like silicon compound and increase the contact area of ​​the neck portions. The aging treatment temperature is preferably determined taking into account, for example, the boiling point of the solvent in the mixed liquid. For example, if the temperature of the aging treatment is too high, the solvent will volatilize excessively, and the resulting coating liquid will be concentrated, which may cause problems such as closure of the pores in the three-dimensional void structure.If the temperature of the aging treatment is too low, the effect of aging will not be sufficient, and temperature fluctuations will increase over time in the mass production process, which may result in the formation of a low-refractive index film of inferior quality.

[0043] Preferably, the reaction product after gelation (specifically, the mixed liquid containing the gel and the solvent for producing the gel) can be subjected to the aging treatment as it is.

[0044] The number of moles of residual silanol groups contained in the gel-like silicon compound after aging treatment is as explained in Section A-3-2 above regarding the silicon compound after gelation. If the number of moles of residual silanol groups is too high, it may not be possible to maintain a sufficient void structure. If the number of moles of residual silanol groups is too low, sufficient crosslinking may not occur, and the strength of the resulting low refractive index film may be insufficient. Note that while the above explanation is given as an example of residual silanol groups, if a silicon compound modified with various reactive functional groups is used as the raw material for the gel, the same may apply to such functional groups.

[0045] B-3. ​​Solvent substitution process As described above, the solvent substitution step involves substituting the gel-producing solvent with another solvent. By substituting the gel-producing solvent with another solvent, a more uniform coating film can be formed when the resulting coating liquid is used to form a coating film.

[0046] The other solvent may typically be the solvent for the resulting coating liquid. Any appropriate solvent may be used as the solvent for the coating liquid as long as the effects of the embodiments of the present invention can be obtained. In one embodiment, the other solvent has affinity with the gel-producing solvent and can dissolve the gelling catalyst (dehydration condensation catalyst) contained in the mixed liquid, the alcohol component that is a by-product of gelation (dehydration condensation reaction), water, etc. Examples of the solvent for the coating liquid include organic solvents. The organic solvent may be, for example, a solvent with a boiling point of 130°C or less. Specific examples of such solvents include isopropyl alcohol (IPA), ethanol, methanol, n-butanol, 2-butanol, isobutyl alcohol, pentyl alcohol, propylene glycol monomethyl ether (PGME), methyl cellosolve, and acetone. The solvent for the coating liquid may be used alone or in combination of two or more. Preferred are isopropyl alcohol (IPA), ethanol, n-butanol, 2-butanol, isobutyl alcohol, pentyl alcohol, propylene glycol monomethyl ether (PGME), and methyl cellosolve, which have low volatility at room temperature and can provide a coating liquid with excellent stability.

[0047] Any suitable combination of the gel-producing solvent and other solvent (solvent for the coating liquid) can be adopted as long as the effects of the embodiment of the present invention can be obtained. Specific examples of combinations include DMSO and IPA, DMSO and ethanol, DMSO and isobutyl alcohol, and DMSO and n-butanol.

[0048] Any suitable method can be used for solvent substitution. Solvent substitution can be carried out, for example, as follows. First, a gel (typically a gel-like silicon compound) obtained as described in Section A above and optionally subjected to the aging treatment described in Section B-2 above is contacted with or immersed in the other solvent. More specifically, by adding the other solvent to a mixture containing a gel-like silicon compound and a gel-producing solvent, the gel-like silicon compound can be contacted (essentially immersed) in the other solvent. This allows the gelling catalyst (dehydration condensation catalyst) contained in the mixture, alcohol components that are by-products of gelation (dehydration condensation reaction), water, etc., to be dissolved in the other solvent. Next, the solvent that has contacted the gel (essentially the gel-producing solvent and the other solvent) is discarded, and the gel is contacted with or immersed in a new other solvent. This procedure is repeated until the amount of gel-producing solvent remaining in the gel-containing mixture reaches a predetermined amount (e.g., 0.5 g / ml or less). The contact time of the gel with the other solvent per session may be, for example, 0.5 hours or more, for example, 1 hour or more, or for example, 1.5 hours or more, or for example, 10 hours or less. A typical example of such an operation is decantation. Alternatively, the other solvent may be continuously supplied to the mixed solution containing the gel until the remaining amount of the gel-producing solvent in the mixed solution reaches a predetermined amount. The temperature during contact between the gel and the other solvent may be, for example, 20°C to 70°C, or may be, for example, 25°C to 65°C, or may be, for example, 30°C to 60°C. A high temperature during contact has the advantage that solvent substitution proceeds quickly and the amount of solvent required for substitution can be reduced. A temperature during contact at or near room temperature has the advantage that undesired denaturation of the gel can be suppressed.

[0049] B-4. Gel crushing process As described above, the gel obtained by the manufacturing method described in Section A is typically in the form of clumps in the mixed solution. Therefore, by crushing the gel clumps, a coating solution capable of forming a low refractive index film can be obtained. As described above, the gel crushing step typically includes a coarse crushing step and a fine crushing step. The coarse crushing step typically includes crushing the gel clumps to a size of 15 cm or less; the fine crushing step typically includes crushing the coarsely crushed gel to a size of 2.00 μm or less. In one embodiment, the coarse crushing step can be performed before the solvent substitution step, and the fine crushing step can be performed after the solvent substitution step. That is, in a manufacturing method for a coating solution for forming a low refractive index film according to an embodiment of the present invention, the following procedure can be used, for example: (i) coarsely crushing the gel clumps to a size of 15 cm or less, (ii) replacing the gel-production solvent in the mixed solution containing the coarsely crushed gel and the gel-production solvent with another solvent, and (iii) finely crushing the coarsely crushed gel in the mixed solution containing the coarsely crushed gel and the other solvent to a size of 2.00 μm or less.

[0050] As described above, in the coarse pulverization step, the gel mass is pulverized to a size of 15 cm or less. By performing the coarse pulverization step before the solvent substitution step, the gel-producing solvent in the gel is more likely to dissolve into other solvents in the solvent substitution step, making it easier to reduce the amount of gel-producing solvent remaining in the gel. The shape of the gel after coarse pulverization can be any appropriate shape as long as the effect of coarse pulverization is obtained. The shape can typically be a three-dimensional shape such as granules. The size of the gel after coarse pulverization can be, for example, 10 cm or less, or, for example, 5 cm or less, or, for example, 0.005 cm or more, or, for example, 0.01 cm or more, or, for example, 0.02 cm or more. Here, "size" refers to the length of the longest part of the three-dimensional shape. Any appropriate method can be used for coarse pulverization. Examples of coarse pulverization methods include crushing and cutting using general physical forces.

[0051] In the fine pulverization step, the coarsely pulverized gel is pulverized to a size of 2.00 μm or less, as described above. By pulverizing the gel, a new three-dimensional sol structure can be obtained. This three-dimensional sol structure allows the coating liquid to form a low refractive index film with a predetermined void structure.

[0052] The volume average particle diameter of the gel (pulverized gel) after pulverization can be, for example, 1.50 μm or less, or, for example, 1.00 μm or less, or, for example, 0.05 μm or more, or, for example, 0.10 μm or more, or, for example, 0.20 μm or more, or, for example, 0.40 μm or more. The volume average particle diameter can range, for example, from 0.05 μm to 2.00 μm, or, for example, from 0.20 μm to 1.50 μm, or, for example, from 0.40 μm to 1.00 μm. The volume average particle diameter is an index of the size and variation of the pulverized gel in the coating liquid. The volume average particle diameter can be measured, for example, by a particle size distribution evaluation device such as a dynamic light scattering method or a laser diffraction method, or by an electron microscope such as a scanning electron microscope (SEM) or a transmission electron microscope (TEM).

[0053] The particle size distribution of the pulverized gel product may be any suitable one as long as the effect of fine pulverization is obtained. The particle size distribution of the pulverized gel product may be such that particles with a particle size of 0.4 μm to 1 μm are present in an amount of, for example, 50% to 99.9% by weight, for example, 80% to 99.8% by weight, or for example, 90% to 99.7% by weight, and / or such that particles with a particle size of 1 μm to 2 μm are present in an amount of, for example, 0.1% to 50% by weight, for example, 0.2% to 20% by weight, or for example, 0.3% to 10% by weight. The particle size distribution can be measured, for example, using the particle size distribution evaluation device described above or an electron microscope.

[0054] Any suitable method for pulverization can be used as long as it produces the desired pulverized gel product. Specific examples of pulverization means include pulverization devices that use cavitation, such as ultrasonic homogenizers and high-speed rotation homogenizers, and wet-type pulverization devices that cause oblique collisions of liquids at high pressure. In embodiments of the present invention, media-less pulverization devices such as homogenizers are preferred over media-based pulverization devices, such as ball mills. Media-based pulverization devices typically physically destroy the void structure of the gel during pulverization, while media-less pulverization devices typically use high-speed shear force to peel off the relatively weakly bonded silica particle bonding surfaces already encapsulated in the three-dimensional structure of the gel.

[0055] Any appropriate conditions for the pulverization can be adopted as long as the desired pulverized gel product is obtained. For example, it is preferable to apply a momentary high-speed flow to pulverize the gel without volatilizing the solvent. More specifically, it is preferable to pulverize the gel so as to obtain a pulverized gel product having the particle size variation (e.g., volume average particle size or particle size distribution) described above. If the pulverization workload (e.g., pulverization time, intensity) is insufficient, coarse particles remain, resulting in the failure to form the desired pores and increased appearance defects, which may prevent the production of a high-quality low-refractive-index film. If the pulverization workload is too high, the resulting pulverized gel product will be excessively fine, and as a result, the pore size of the resulting low-refractive-index film may be too small, making it impossible to achieve the desired porosity.

[0056] The number of moles of residual silanol groups contained in the pulverized gel is as explained above in Section A-3-2 regarding the silicon compound after gelation.

[0057] In this way, a coating liquid for forming a low refractive index film containing the pulverized gel and a solvent can be obtained. As described above, the pulverized gel is very fine, so the coating liquid for forming a low refractive index film can typically be a sol liquid (a dispersion of the pulverized gel).

[0058] B-5. Coating liquid for forming low refractive index films In the coating solution for forming a low refractive index film, the ratio (concentration) of the pulverized gel material to the solvent can be appropriately set depending on the purpose and the desired properties of the low refractive index film. This ratio can be, for example, 0.3% (v / v) to 50% (v / v), or, for example, 0.5% (v / v) to 30% (v / v), or, for example, 1.0% (v / v) to 10% (v / v). If the concentration of the pulverized gel material is too high, the fluidity of the coating solution may decrease, which may cause aggregates and / or coating streaks in the coating film, resulting in an insufficient quality of the resulting low refractive index film. If the concentration of the pulverized gel material is too low, the time required to dry the solvent may be excessively long, and the residual solvent concentration in the coating film immediately after drying may be high, which may result in a decrease in porosity.

[0059] The shear viscosity of the coating solution for forming a low refractive index film can be appropriately set depending on the purpose and the desired properties of the low refractive index film. For example, at a shear rate of 10,000 1 / s, the viscosity can be, for example, 100 cPa·s or less, or, for example, 10 cPa·s or less, or, for example, 1 cPa·s or less. If the shear viscosity is too high, aggregates and / or coating streaks may occur in the coating film, resulting in an insufficient quality of the resulting low refractive index film. If the shear viscosity is too low, the wet thickness of the coating film may not be sufficiently thick, and a low refractive index film of the desired thickness may not be obtained.

[0060] The coating solution for forming a low refractive index film may further contain a catalyst capable of promoting the crosslinking reaction between the pulverized gel particles during the formation of the low refractive index film, and a substance capable of generating the catalyst. That is, these may be added to the coating solution for forming a low refractive index film prepared as described in Section B-4. Examples of the catalyst include photoactive catalysts and thermally active catalysts. Examples of substances capable of generating a catalyst (catalyst generators) include photocatalyst generators and thermal catalyst generators. Examples of photocatalyst generators include photobase generators (catalysts that generate a basic catalyst upon light irradiation) and photoacid generators (substances that generate an acidic catalyst upon light irradiation). The amount of catalyst added may be, for example, 0.001 mol to 0.5 mol, for example, 0.005 mol to 0.3 mol, or for example, 0.01 mol to 0.1 mol per mol of the pulverized gel particle. The amount of catalyst generator added may be, for example, 0.001 mol to 0.5 mol, or may be, for example, 0.005 mol to 0.3 mol, or may be, for example, 0.01 mol to 0.1 mol, relative to 1 mol of the pulverized gel product.

[0061] C. Low refractive index film At least one embodiment of the present invention relates to a method for producing a coating liquid for forming a low refractive index film. Accordingly, the coating liquid obtained by an embodiment of the present invention can be used to form a low refractive index film. That is, a method for producing a low refractive index film can also be included in an embodiment of the present invention. A low refractive index film can typically be formed by applying a coating liquid and heating (including drying). Heating can chemically bond the pulverized gel particles together. The chemical bond can be, for example, a cross-linking bond (typically, a dehydration condensation reaction of residual silanol groups contained in the pulverized gel particles). The heating temperature is, for example, 20°C or higher, preferably 50°C or higher. Meanwhile, the heating temperature is, for example, 200°C or lower, preferably 150°C or lower. The heating time is, for example, 10 seconds or longer. Meanwhile, the heating time is, for example, 24 hours or shorter, preferably 1 hour or shorter, more preferably 30 minutes or shorter, and even more preferably 10 minutes or shorter.

[0062] The refractive index of the low refractive index film is preferably less than 1.20, more preferably 1.13 to 1.19, even more preferably 1.14 to 1.18, and particularly preferably 1.15 to 1.17. A low refractive index film having such an extremely low refractive index can be realized by using the low refractive index film-forming gel and coating liquid obtained by the manufacturing method of an embodiment of the present invention. The refractive index refers to a refractive index measured at a wavelength of 550 nm, unless otherwise specified.

[0063] The haze of the low refractive index film is preferably less than 5%, more preferably less than 3%, and even more preferably less than 2%. Meanwhile, the haze may be, for example, 0.1% or more, or even 0.2% or more. The low refractive index film-forming gel and coating solution obtained by the manufacturing method of the embodiment of the present invention can achieve a low refractive index film having such an extremely low refractive index as described above while maintaining the haze within such an acceptable range. The haze can be calculated, for example, from the following formula using a value measured with a haze meter (e.g., "HM-150" manufactured by Murakami Color Research Laboratory Co., Ltd.): Haze (%) = [Diffuse transmittance (%) / Total light transmittance (%)] x 100 (%)

[0064] The total light transmittance of the low refractive index film is preferably 85% to 99%, more preferably 87% to 98%, and even more preferably 89% to 97%. Excellent transparency can be achieved in an optical laminate using the low refractive index film. The total light transmittance can be measured, for example, using the above-mentioned haze meter.

[0065] The thickness of the low refractive index film is preferably 0.3 μm to 10 μm, more preferably 1.0 μm to 8.0 μm, even more preferably 1.5 μm to 7.0 μm, particularly preferably 2.0 μm to 6.0 μm, and especially preferably 2.5 μm to 5.0 μm. Such a very thin low refractive index film can be obtained by the low refractive index film-forming gel and coating liquid obtained by the production method of the embodiment of the present invention.

[0066] The porosity of the low-refractive-index film is preferably 20% to 60% by volume, more preferably 25% to 55% by volume, even more preferably 30% to 50% by volume, and particularly preferably 35% to 45% by volume. The low-refractive-index film-forming gel and coating solution obtained by the manufacturing method of an embodiment of the present invention can produce a low-refractive-index film with a lower refractive index while maintaining the same porosity. Here, the porosity is a value calculated from the refractive index measured with an ellipsometer using the Lorentz-Lorenz formula. [Example]

[0067] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. The methods for measuring each property are as follows. Unless otherwise specified, "%" and "parts" in the examples are by weight.

[0068] (1) Median diameter D50 of fine bubbles and half-width of bubble size distribution For the gel-producing solvents used in the examples and comparative examples, the median bubble diameter D50 and the half-width of the bubble size distribution were measured using a dynamic light scattering particle size distribution analyzer (manufactured by Entegris, product name "Nicomp N3000").

[0069] (2) Thickness The thickness was measured using an interference film thickness meter (manufactured by Otsuka Electronics Co., Ltd., product name "MCPD-3000").

[0070] (3) Refractive index The acrylic film / low refractive index film laminates obtained in the Examples and Comparative Examples were cut to a size of 25 mm x 50 mm. The cut laminates were attached to the surface of a glass plate (thickness: 3 mm) via an adhesive. The center of the back surface of the glass plate (diameter: approximately 20 mm) was filled in with black marker to create a sample that was not reflective on the back surface of the glass plate. The sample was placed in an ellipsometer (JA Woollam Japan: VASE), and the refractive index was measured at a wavelength of 550 nm and an incident angle of 50 to 80 degrees.

[0071] (4) Haze value The acrylic film / low refractive index film laminates obtained in the examples and comparative examples were cut to a predetermined size to prepare test samples. The total light transmittance and diffuse transmittance of the test samples were measured using a haze meter (e.g., "HM-150" manufactured by Murakami Color Research Laboratory Co., Ltd.), and the haze value was calculated using the following formula. Haze (%) = [Diffuse transmittance (%) / Total light transmittance (%)] x 100 (%)

[0072] [Example 1] (1) Introduction of microbubbles into the gel production solvent Microbubbles were generated in dimethyl sulfoxide (DMSO) using a pressure dissolution deposition type microbubble generator (Living Energy, product name "LE3FS"). The median diameter D50 of the microbubbles in DMSO was 45 nm, and the half-width of the bubble size distribution was 90 nm.

[0073] (2) Gelation of silicon compounds (preparation of gel for forming low refractive index films) 2.2 g of DMSO with microbubbles generated as described above was prepared, and 0.95 g of methyltrimethoxysilane (MTMS), a precursor of a silicon compound, was dissolved in this to prepare mixed solution A. 0.5 g of a 0.01 mol / L aqueous solution of oxalic acid was added to mixed solution A, and the mixture was stirred at room temperature for 30 minutes to hydrolyze the MTMS, producing mixed solution B containing tris(hydroxy)methylsilane. To 5.5 g of DMSO (in which fine bubbles were generated in the same manner as above), 0.38 g of 28 wt % ammonia water and 0.2 g of pure water were added, and then the above mixed solution B was further added and stirred at room temperature for 15 minutes to gel the tris(hydroxy)methylsilane, thereby obtaining mixed solution C containing a gel-like silicon compound. In this way, a gel for forming a low refractive index film was obtained.

[0074] (3) Aging treatment The mixed solution C containing the gel-like silicon compound prepared as above was incubated as is at 40° C. for 20 hours for aging treatment.

[0075] (4) Coarse grinding and solvent replacement Next, the gel-like silicon compound aged as described above was crushed into granules of several mm to several cm in size using a spatula (coarse crushing). Next, 40 g of isopropyl alcohol (IPA) was added to the mixed solution C, and after light stirring, the mixture was left to stand at room temperature for 6 hours, and the solvent and catalyst in the gel were decanted. The same decantation process was repeated three times to replace DMSO with IPA (solvent replacement), and mixed solution D was obtained.

[0076] (5) Fine pulverization (preparation of coating liquid for forming low refractive index film) Next, the gel-like silicon compound in the mixed solution D was finely pulverized (high-pressure media-less pulverization). The finely pulverization (high-pressure media-less pulverization) was carried out using a homogenizer (manufactured by SMT Corporation, trade name "UH-50"), with 1.85 g of the gel-like compound in the mixed solution D and 1.15 g of IPA weighed into a 5 cc screw bottle, and the pulverization was carried out at 50 W and 20 kHz for 2 minutes. As described above, the gel-like silicon compound in the mixed solution D was pulverized, and the mixed solution D became a sol solution E of pulverized gel material. The volume average particle size, which indicates the particle size variation of the pulverized gel material contained in the sol solution E, was confirmed using a dynamic light scattering Nanotrac particle size analyzer (manufactured by Nikkiso Co., Ltd., UPA-EX150 model) and was found to be 0.50 μm to 0.70 μm. Furthermore, 0.015 g of a 1.5 wt % MEK (methyl ethyl ketone) solution of a photobase generator (Wako Pure Chemical Industries, Ltd., product name: WPBG266) and 0.005 g of a 5% MEK solution of a bis-crosslinking accelerator ((trimethoxysilyl)hexane) were added to 0.75 g of the sol solution E in a ratio of 0.015 g to 0.75 g of the sol solution E to obtain a coating solution for forming a low refractive index film.

[0077] (6) Formation of low refractive index film The low refractive index film-forming coating solution obtained as described above was applied to an acrylic film, and the coating film was heated at 100°C for 1 minute to form a low refractive index film on the acrylic film. The obtained low refractive index film had a thickness of 3.0 μm, a refractive index of 1.162, and a haze value of 0.16%. The results are shown in Table 1, along with the results of Comparative Example 1 described below.

[0078] [Comparative Example 1] Except for not generating microbubbles in the DMSO, a low refractive index film-forming gel and a low refractive index film-forming coating solution were obtained in the same manner as in Example 1. The median bubble diameter D50 of the DMSO in which microbubbles were not generated was 450 nm, and the half-value width of the bubble size distribution was 1200 nm. A low refractive index film was formed on an acrylic film in the same manner as in Example 1, except that this low refractive index film-forming coating liquid was used. The obtained low refractive index film had a thickness of 3.0 μm, a refractive index of 1.200, and a haze value of 0.10%. The results are shown in Table 1.

[0079] [Table 1]

[0080] As is clear from Table 1, the low refractive index films formed using the low refractive index film-forming gel and low refractive index film-forming coating liquid obtained in the examples of the present invention achieve an extremely low refractive index of 1.16 while maintaining a good haze value (transparency) of 0.16%. [Industrial Applicability]

[0081] The low-refractive-index film-forming gel and low-refractive-index film-forming coating liquid obtained by the manufacturing method of the embodiment of the present invention can be suitably used for forming a low-refractive-index film. The low-refractive-index film obtained using such a gel and coating liquid can be suitably used for various optical laminates.

Claims

1. A method for producing a low refractive index film-forming gel, A gelling step of gelling a gel raw material in a gel production solvent, introducing fine bubbles into the gel-producing solvent; Manufacturing method.

2. 2. The method for producing a low refractive index film-forming gel according to claim 1, wherein the median diameter D50 of the fine bubbles is 200 nm or less, and the half-value width of the bubble diameter distribution is 400 nm or less.

3. The method for producing a low refractive index film-forming gel according to claim 1 , wherein the raw material of the gel contains a hydrolyzable silane.

4. The method for producing a low refractive index film-forming gel according to claim 3, wherein the hydrolyzable silane contains a compound represented by the following formula (1): 【Chemistry 1】 In formula (1), X is 2 or 3; R １ and R ２ are each a linear or branched alkyl group, R １ and R ２ may be the same or different, R １ may be the same or different when X is 2, R ２ may be the same or different from each other.

5. The method for producing a low refractive index film-forming gel according to claim 3, wherein the solvent for producing the gel is dimethyl sulfoxide.

6. 6. A method for producing a coating solution for forming a low refractive index film, comprising a solvent substitution step of substituting a solvent for producing the gel in a mixed solution containing the gel obtained by the production method according to claim 1 with another solvent.

7. The method for producing a coating solution for forming a low refractive index film according to claim 6 , further comprising a gel crushing step of crushing the gel lumps.

8. The gel crushing step includes a coarse crushing step of crushing the gel mass to a size of 15 cm or less, and a fine crushing step of crushing the coarsely crushed gel to a size of 2.00 μm or less, The coarse pulverization step is carried out before the solvent substitution step, and the fine pulverization step is carried out after the solvent substitution step. The method for producing the coating liquid for forming a low refractive index film according to claim 7.

9. The method for producing a coating solution for forming a low refractive index film according to claim 8 , further comprising an aging step of aging the gel before the coarse pulverization step.

10. The method for producing a coating solution for forming a low refractive index film according to claim 9 , wherein the aging step comprises incubating the gel in the mixed solution at 30° C. or higher.

11. A method for producing a low refractive index film, comprising applying and heating the coating liquid for forming a low refractive index film obtained by the method according to claim 10.

12. The method for producing a low refractive index film according to claim 11, wherein the refractive index of the obtained low refractive index film is less than 1.20 and the haze is less than 2%.

Images