JP5206653B2 - Method for producing porous silica film and method for producing laminated substrate - Google Patents

Description

  The present invention relates to a porous silica film, a laminated substrate having the porous silica film, a production method thereof, and an electroluminescence element.

  One of the most promising next-generation electronic displays is an organic EL display. As shown in FIG. 1, this organic EL display is a self-luminous display having an electroluminescence element 1 in which at least a transparent substrate 2, a transparent electrode (anode) 3, an electroluminescence layer 4 and a cathode 5 are laminated in this order. . In this electroluminescence element, holes injected from the transparent electrode 3 as an anode and electrons injected from the cathode 5 are recombined in the electroluminescence layer 4, and the emission center is excited by the recombination energy to emit light. It has the light emission principle.

  In the organic EL display, it is preferable that the light emitted from the electroluminescence layer 4 is efficiently extracted to the transparent substrate 2 side. However, as shown in FIG. 7 is guided light 12 that is totally reflected at the interface with 7 and travels while being totally reflected in the surface direction inside the transparent substrate 2. With this guided light 12, the light extraction efficiency extracted from the transparent substrate 2 (the ratio of the light generated in the electroluminescence layer 4 being extracted outside the electroluminescence element 1) is as low as about 20%, which is an improvement over the prior art. It has been requested.

  To solve such a problem, as shown in FIG. 3, a low refractive index layer 6 is provided on the electroluminescent layer 4 side of the transparent substrate 2, and the light 11 having a large emission angle is refracted by the low refractive index layer 6, thereby It has been studied to reduce generation and improve light extraction efficiency. For example, Patent Document 1 below describes an electroluminescence element having a low refractive index layer having a refractive index of 1.01 to 1.3 formed by a silica airgel film technique.

  Non-Patent Document 1 below describes that a porous silica film produced by a sol-gel method is used as a high-efficiency light extraction window material for an electroluminescence element. This porous silica film is a low refractive index layer having a refractive index of 1.196 to 1.335, and the maximum value of surface irregularities is described as 7 nm.

JP 2002-278477 A (paragraph numbers 0010 to 0012)

ULVAC Technical Journal, Issue 57, September 2002, pages 34-36

  Since the low refractive index layer described in Patent Document 1 is manufactured by a method in which a volatile supercritical liquid such as carbon dioxide is phase-separated from silica and then evaporated, coarse pores are formed in the low refractive index layer. There are many, and even on the film surface of the low refractive index layer, the maximum unevenness is in a form exceeding about 400 nm. When a transparent electrode forming an anode is formed on a low refractive index layer having such surface irregularities, the surface morphology of the transparent electrode is greatly influenced by the surface irregularities of the low refractive index layer, and thus the transparent electrode has protrusions and depressions. As a result, there has been a problem that a short circuit or the like occurs between the cathodes facing each other with the electroluminescence layer interposed therebetween, and the quality of the electroluminescence element is deteriorated.

  On the other hand, the porous silica film described in Non-Patent Document 1 has a small maximum surface irregularity and does not cause a problem of quality deterioration based on the surface irregularity. However, due to its production method, it is fired at a high temperature (usually 500 ° C. or higher). As a result, the obtained film was hard and brittle. In addition, when adhesion to the substrate is required, there is a problem that sufficient adhesion cannot be obtained, and even if it adheres to some extent, volume change (thermal expansion / contraction, volume shrinkage, etc.) during film formation There was also a problem that it was easy to break.

  The present invention has been made to solve the above-mentioned problems, and a first object is to improve the brittleness of the porous silica having a low refractive index that does not adversely affect other laminated materials as described above. A second object of the present invention is to provide a laminated substrate having a porous silica film that does not adversely affect other laminated materials as described above, has good adhesion to the substrate, and does not easily crack. In particular, the third object is to provide a method for manufacturing the porous silica film and the laminated substrate described above, and the fourth object is to reduce the occurrence of short circuits that impair the reliability, and to improve the light extraction efficiency. The object is to provide a good electroluminescent device.

  In the course of earnest research in order to solve the above problems, the present inventors have conducted hydrolysis and dehydration condensation reactions (hereinafter referred to as hydrolysis condensation reactions or sol-forms) of alkoxysilanes on a substrate such as a glass substrate. When a porous silica film having a low refractive index is formed using a gel method), an organic compound having a relatively low hydrophilicity such as n-butanol (this organic compound is converted into a hydrophilic organic film). After forming a film using a water-containing organic solution containing a compound)), and washing the film with a water-soluble organic solvent such as a lower alcohol, the hydrophilic organic compound in the film is extracted, The inventors have found that a porous silica film having a low refractive index in which a desired pore structure is formed in the film can be formed, and also found that the surface thereof is extremely smooth, and reached the present invention.

Method for producing a porous silica film and the laminated substrate to achieve the above Symbol purpose is as follows.

The method for producing a porous silica membrane according to the present invention includes a step of forming a primary membrane from a hydrous organic solution containing a raw material compound mainly composed of alkoxysilanes that undergo hydrolysis and dehydration condensation, and the primary membrane is formed. A step in which a hydrous organic solution undergoes a hydrolysis reaction and a dehydration condensation reaction to form an intermediate film, a step of pre-drying the intermediate film, and a step of bringing a water-soluble organic solvent into contact with the intermediate film after the pre-drying , the step of post-drying the intermediate film in contact with a water-soluble organic solvent, and a step of the intermediate film after post-drying further promotes hydrolytic condensation reaction to form a porous silica film, only contains the The hydrous organic solution contains a hydrophilic organic compound having a boiling point of 80 ° C. or higher, and the weight ratio of the organic solvent to the hydrophilic organic compound having a boiling point of 80 ° C. or higher in the hydrous organic solution is 5/5 to 2/8. To

In the method for producing a porous silica film according to the present invention , the relative dielectric constant of a hydrophilic organic compound having a boiling point of 80 ° C. or higher is preferably 20 or lower.

In the method for producing a porous silica film according to the present invention , the relative dielectric constant of the organic solvent contained in the water-containing organic solution is preferably 23 or more.

The method for producing a laminated substrate according to the present invention is characterized in that, in the above-described method for producing a porous silica film according to the present invention , the hydrated organic solution is applied onto a substrate to form a primary film. At this time, the substrate is preferably transparent.

According to the manufacturing method of the porous silica film according to the present invention described above mentioned, after forming the intermediate layer, by treatment in order before drying → contact with a water-soluble organic solvent → post-drying → dry heat, above The porous silica film according to the present invention can be formed. Moreover, according to the manufacturing method of the laminated substrate mentioned above, the laminated substrate of this invention which has the outstanding characteristic mentioned above can be manufactured, and the laminated substrate manufactured by this method can be applied preferably for electroluminescent elements.

According to the porous silica film of the present invention, unlike the conventional porous silica film, its brittleness is improved, and the obtained film has a low refractive index and a maximum surface roughness of 100 nm or less. Therefore, for example, when this porous silica film is used as a low refractive index layer for an electroluminescence element, generation of guided light can be reduced and light extraction efficiency can be improved, and further on the low refractive index layer. Even if the transparent electrode is formed, the transparent electrode can be prevented from being protruded or depressed.

  Further, according to the laminated substrate of the present invention, since the porous silica film having the above effect is formed on the substrate, for example, when this laminated substrate is applied to an electroluminescence element, the porous silica film and the substrate are in close contact with each other. A laminated substrate that is superior in performance and can improve the light extraction efficiency by reducing the generation of guided light, and further, even when a transparent electrode is mounted on the low refractive index layer, no protrusion or depression occurs on the transparent electrode. can do. As a result, the multilayer substrate of the present invention can be preferably applied to an electroluminescent element having excellent reliability.

  According to the method for producing a porous silica membrane of the present invention, an extremely simple means of incorporating a hydrophilic organic compound into a water-containing organic solution that is a raw material liquid and extracting the hydrophilic organic compound with a water-soluble organic solvent is provided. There is an advantage that it can be formed simply by adding. Moreover, after forming the intermediate film, the porous silica film having the above-described excellent characteristics can be formed by processing in the order of pre-drying → contact with a water-soluble organic solvent → post-drying → high-temperature drying. Furthermore, according to the method for producing a laminated substrate of the present invention, a laminated substrate having a porous silica film can be produced only by simple steps excellent in productivity, such as application of raw materials, surface treatment with chemicals, and drying.

  In addition, according to the multilayer substrate and the electroluminescent device of the present invention, since there are few residual organic components, particularly when used for an electroluminescent device, the change with time is small and the stability is excellent, and the light extraction efficiency is high. A good electroluminescent element can be provided.

It is sectional drawing which shows an example of an electroluminescent element structure. It is sectional drawing which shows an example of the electroluminescent element which does not have a low refractive index layer. It is sectional drawing which shows an example of the electroluminescent element which has a low-refractive-index layer.

Embodiments of the present invention will be described below.
(1) Porous silica film and laminated substrate having the same The porous silica film of the present invention has a refractive index of 1.10 to 1.35, a maximum surface irregularity of 100 nm or less, and thermogravimetry- The mass spectrum analysis is characterized in that a peak of at least one substance among alcohols having 1 to 4 carbon atoms is given in a higher temperature range than the boiling point of the substance at 760 mmHg. Moreover, the laminated substrate of this invention has the porous silica film 6 which concerns on this invention on the board | substrate 2, as shown in FIG.

(Porous silica membrane)
The refractive index of the porous silica film of the present invention is 1.10 to 1.35. This refractive index is an average refractive index in the entire depth direction determined by an ellipsometer measurement based on ASTM D-542, and is represented by a value with respect to sodium D line (589.3 nm) at 23 ° C. The porous silica film has a lower refractive index as its porosity is higher. Therefore, as the refractive index is reduced, the generation of guided light can be suppressed and the light extraction efficiency can be improved, but the refractive index is 1.10. If it is less than 1, mechanical strength may be insufficient due to high porosity. Considering these points, the preferable lower limit of the refractive index is 1.13, more preferably 1.15. On the other hand, when the refractive index exceeds 1.35, generation of guided light may not be sufficiently suppressed. Considering these points, the preferable upper limit of the refractive index is 1.30, more preferably 1.27.

  The silica film having the refractive index described above has an average pore diameter of 1 to 50 nm, and from the viewpoint of light transmittance and mechanical strength of the film, the upper limit value of the average pore diameter is preferably 40 nm, 30 nm Is more preferable, and 20 nm is most preferable. On the other hand, the lower limit value of the average pore diameter is preferably 2 nm, more preferably 3 nm, from the viewpoints of light transmittance and refractive index. If the average hole diameter is less than 1 nm, the refractive index increases and the generation of guided light cannot be suppressed, and the light extraction efficiency cannot be sufficiently improved. The average pore diameter is evaluated by analyzing an observation image using a transmission electron microscope (TEM) or a scanning electron microscope (SEM).

  There are no particular restrictions on the shape of the pores of the porous silica film of the present invention, and examples of possible shapes include closed cells, tunnels, and communication holes in which closed cells communicate with each other. A communication hole in which closed cells communicate with each other is preferable. The average pore diameter in the case of a communication hole in which tunnels or closed cells communicate with each other is defined as an average value of their widths.

  The porous silica film has a maximum unevenness of the surface of 100 nm or less, preferably 50 nm or less, and more preferably 30 nm or less. In addition, the lower limit of the maximum value of the surface unevenness is practically about 10 nm. The surface irregularities are measured using an atomic force microscope (AFM). Specifically, arbitrary five places on the surface of the given porous silica film are selected, and an area of 100 μm square is observed and evaluated by AFM. Further, the maximum value of the surface unevenness can also be determined by analyzing an electronic image photograph of a cross section by SEM. In this case, an electron microscope photograph with an electron beam acceleration voltage of 5 kV and an observation magnification of 1000 to 10,000 times can be taken and determined by the difference between the crest and trough of the cross section. In addition, as a SEM observation sample, the laminated substrate when this porous silica film was formed on the substrate was used as a sample, and mechanical shock was applied in a state where the sample was cooled and embrittled with liquid nitrogen. The brittle fracture surface was used. As this brittle fracture surface, a sample which was not deposited on a thin film of a conductive material such as metal or carbon, which is generally used for the purpose of improving the conductivity of the sample surface, was used.

  In addition, on the surface of the porous silica film, a granular structure having a diameter of 1 to 300 nm is observed by surface shape observation with an atomic force microscope. Furthermore, as a result of measuring the porosity of the porous silica film by spectroscopic ellipsometry with a measurement light wavelength range of 250 to 850 nm, it is confirmed that it is 30 to 80%.

The porous silica film of the present invention is mainly composed of a silicon oxide (SiO ₂ ) composition. The silica film has a SiOx composition (provided that the silicon atom-carbon atom bond exists in a part of the silica composition by a method such as copolymerization of organic silanes in silica synthesis by a sol-gel method, for example. Is a positive number greater than 0 and less than 2.

  This silica film may contain any chemical composition containing a positive element (sometimes abbreviated as an additional composition). For example, yttrium oxide, lanthanum oxide, cerium oxide, praseodymium oxide, samarium oxide, europium oxide, gadolinium oxide, terbium oxide, dysprosium oxide, holmium oxide, erbium oxide, thulium oxide, titanium oxide, zirconium oxide, chromium oxide, manganese oxide, Transition metal oxide compositions such as iron oxide, cobalt oxide, nickel oxide, copper oxide, zinc oxide, cadmium oxide, gallium oxide, indium oxide, germanium oxide, tin oxide, lead oxide; lithium oxide, sodium oxide, potassium oxide, oxide Alkali metal oxide compositions such as rubidium and cesium oxide; alkaline earth metal compositions such as magnesium oxide, calcium oxide, strontium oxide and barium oxide; boron oxide composition; aluminum oxide composition; It can be. In addition, known inorganic glass compositions such as chalcogenide glass compositions and fluoride glass compositions can also be mentioned.

  The silicon oxide composition constituting the silica film is contained in such a ratio that the ratio of silicon to all positive elements including silicon is 50 to 100 mol%. When the silicon content is less than 50 mol%, the refractive index of the porous silica film may become extremely large, or the mechanical strength of the porous silica film may be extremely lowered. A preferable lower limit is 70 mol%, more preferably 80 mol%, and most preferably 90 mol%, and a higher-quality porous silica film is formed as the silicon content is higher.

  The chemical composition of the porous silica film having such a composition can be specified by thermogravimetric-mass spectrum (TG-MS) analysis of a mechanically scraped sample. The porous silica membrane of the present invention has been identified by TG-MS analysis as having a peak of at least one substance among alcohols having 1 to 4 carbon atoms given in a higher temperature range than the boiling point of the substance at 760 mmHg. The

  The porous silica film thus identified has reduced brittleness and improved mechanical properties, and is excellent in adhesion to a substrate serving as a base substrate when the porous silica film is formed. The reason for this is not clear at the present time, but the alkoxy group having 1 to 4 carbon atoms and / or alcohols remaining in the porous silica film has an appropriate mechanical strength and adhesion to the substrate. It is thought that it has brought. At this time, the alcohol is preferably methanol or ethanol. In the TG-MS analysis, the reason why the peak of lower alcohols having 1 to 4 carbon atoms appears at a temperature higher than the boiling point of the substance at 760 mmHg is that the pore diameter of the porous silica film of the present invention is uniform and very high. Because of its small size, it takes energy larger than usual for the lower alcohol molecules to escape out of the porous silica film, or there are alcohols having 1 to 4 carbon atoms, and this is combined with porous silica. It is presumed that some kind of interaction such as hydrogen bonding works between the membrane. Such a phenomenon is considered to correlate closely with the excellent characteristics (for example, light transmittance, mechanical strength, etc.) of the porous silica film of the present invention.

The total carbon concentration in the porous silica membrane is preferably 0.1 to 10% by weight (synonymous with mass%). When the total carbon concentration exceeds 10% by weight, the organic matter substantially remains, so that the release of the remaining organic matter occurs with time. For example, when it is used for an electroluminescence device, the emission characteristics The stability over time deteriorates. On the other hand, when the total carbon concentration is less than 0.1% by weight, the mechanical strength of the porous silica film may be extremely lowered. The upper limit of the total carbon concentration of the porous silica membrane is preferably 8% by weight, more preferably 5% by weight , and the lower limit is preferably 0.2% by weight, more preferably 0.3% by weight. . The total carbon concentration of the porous silica membrane is measured by using a commercially available total carbon concentration measuring device (for example, TOC5000 manufactured by Shimadzu Corporation), and in the gas generated when the test sample of the porous silica membrane is heated to 1450 ° C. It is determined by analyzing the amount of carbon.

(Laminated substrate having porous silica film)
The laminated substrate of the present invention has the porous silica film 6 according to the present invention on the substrate 2. The porous silica film is as described above.

  When the laminated substrate of the present invention is used for, for example, an electroluminescence element, it is preferable that the substrate is transparent. The substrate constituting the laminated substrate has a refractive index of 1.4 to 1.9, preferably 1.45 to 1. 70, more preferably 1.47 to 1.65, and most preferably 1.48 to 1.60. This refractive index is an average refractive index in the entire depth direction determined by an ellipsometer measurement based on ASTM D-542, and is represented by a value with respect to sodium D line (589.3 nm) at 23 ° C. As the substrate having such a refractive index, a transparent substrate made of a general-purpose material can be used. For example, various types of shot glass such as BK7, SF11, LaSFN9, BaK1, and F2, synthetic fused silica glass, optical crown glass, low expansion borosilicate glass, sapphire, soda glass, alkali-free glass, polymethyl methacrylate and cross-linked Examples thereof include acrylic resins such as acrylate, aromatic polycarbonate resins such as bisphenol A polycarbonate, styrene resins such as polystyrene, amorphous polyolefin resins such as polycycloolefin, and synthetic resins such as epoxy resins. Of these, shot glass such as BK7 and BaK1, synthetic fused silica glass, optical crown glass, low expansion borosilicate glass, soda glass, alkali-free glass, acrylic resin, aromatic polycarbonate resin, and amorphous polyolefin resin are preferable. BK7 shot glass, synthetic fused silica glass, optical crown glass, low expansion borosilicate glass, soda glass, alkali-free glass, acrylic resin, and aromatic polycarbonate resin are particularly preferred.

  In the laminated substrate of the present invention, the thickness of the substrate is usually 0.1 to 10 mm. The lower limit of the substrate thickness is preferably 0.2 mm, more preferably 0.3 mm, from the viewpoint of mechanical strength and gas barrier properties. On the other hand, the upper limit value of the thickness of the substrate is preferably 5 mm, more preferably 3 mm, from the viewpoint of lightness and light transmittance.

  Regarding the transmittance of the substrate, the transmittance of the laminated substrate is 80% or more at the sodium D-line wavelength (589.3 nm) when measured by the transmittance of the laminated substrate combined with the porous silica film described later. Is more preferable, 85% or more is more preferable, and 90% or more is still more preferable.

(Method for producing porous silica film and laminated substrate)
The porous silica film is formed by the following process. (A) a step of preparing a raw material liquid for forming a porous silica film; (b) a step of forming a primary film from the raw material liquid; (c) an intermediate film is formed by increasing the molecular weight of the formed primary film. (D) a step of bringing a water-soluble organic solvent into contact with the intermediate membrane to form a porous silica membrane, (e) a step of washing the porous silica membrane, and (f) a step of drying the porous silica membrane. (Ki) Silylation step. Hereinafter, each step will be described.

(A) a step of preparing a raw material liquid for forming a porous silica film;
The raw material liquid for forming the porous silica film is a hydrous organic solution containing a raw material compound that is mainly composed of alkoxysilanes and can be increased in molecular weight by hydrolysis reaction and dehydration condensation reaction.

  The water-containing organic solution that is a raw material liquid contains alkoxysilanes, a hydrophilic organic solvent, water, and a catalyst that is added as necessary.

  Examples of alkoxysilanes include tetramethoxysilane, tetraethoxysilane, tetra (n-propoxy) silane, tetraisopropoxysilane, tetra (n-butoxy) silane, and the like, trimethoxysilane, triethoxysilane, and methyl. Trialkoxysilanes such as trimethoxysilane, methyltriethoxysilane, phenyltrimethoxysilane, phenyltriethoxysilane, dialkoxysilanes such as dimethyldimethoxysilane, dimethyldiethoxysilane, diphenyldimethoxysilane, diphenyldiethoxysilane, bis (Trimethoxysilyl) methane, bis (triethoxysilyl) methane, 1,2-bis (trimethoxysilyl) ethane, 1,2-bis (triethoxysilyl) ethane, 1,4-bis (tri Toxylsilyl) benzene, 1,4-bis (triethoxysilyl) benzene, 1,3,5-tris (trimethoxysilyl) benzene and the like, in which two or more trialkoxysilyl groups are bonded, 3- Aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-glycidyloxypropyltrimethoxysilane, 3-glycidyloxypropyltriethoxysilane, 3-mercaptopropyltrimethoxysilane, 3-acryloyloxypropyltrimethoxysilane, An alkyl group substituted on a silicon atom, such as 3-carboxypropyltrimethoxysilane, has a reactive functional group, and may be a partial hydrolyzate or oligomer.

  Among these, tetramethoxysilane, tetraethoxysilane, trimethoxysilane, triethoxysilane, tetramethoxysilane, or tetraethoxysilane oligomer is particularly preferable. In particular, tetramethoxysilane oligomers are most preferably used because of their reactivity and controllability of gelation.

  Furthermore, monoalkoxysilanes having 2 to 3 hydrogen, alkyl groups, or aryl groups on silicon atoms can be mixed with the alkoxysilanes. By mixing monoalkoxysilanes, the resulting porous silica membrane can be hydrophobized to improve water resistance. Examples of monoalkoxysilanes include triethylmethoxysilane, triethylethoxysilane, tripropylmethoxysilane, triphenylmethoxysilane, triphenylethoxysilane, diphenylmethylmethoxysilane, diphenylmethylethoxysilane, and the like. The mixing amount of monoalkoxysilanes is desirably 70 mol% or less of the total alkoxysilanes. If the mixing amount exceeds 70 mol%, gelation may not occur.

  Further, fluorinated alkyls such as (3,3,3-trifluoropropyl) trimethoxysilane, (3,3,3-trifluoropropyl) triethoxysilane, pentafluorophenyltrimethoxysilane, pentafluorophenyltriethoxysilane When an alkoxysilane having a group or a fluorinated aryl group is used in combination, excellent water resistance, moisture resistance, stain resistance and the like may be obtained.

  In this raw material solution, the oligomer may be a cross-linked or cage molecule (such as silsesquioxane). Practically, as the upper limit of the degree of condensate contained in the water-containing organic solution, the transparency of the solution is preferably in the range of 90 to 100% as the light transmittance at a wavelength of 400 nm, 23 ° C. and an optical path length of 10 mm, for example. Used. The lower limit of the light transmittance of the solution is preferably 92% or more, more preferably 95% or more.

  In addition, when applying the above-described raw material liquid, it is necessary that a certain degree of high molecular weight (that is, a state in which condensation has progressed to some extent) has already been achieved. It is preferable that high molecular weight is achieved to such an extent that insoluble matter cannot be formed. The reason is that if there are visible insolubles in the raw material solution before coating, large surface irregularities can be surely produced and the film quality is lowered.

  As the organic solvent, those having the ability to mix alkoxysilanes constituting the raw material liquid, water, and a hydrophilic organic compound having a boiling point of 80 ° C. or higher, which will be described later, are preferably used. Usable organic solvents include alcohols such as monohydric alcohols having 1 to 4 carbon atoms, dihydric alcohols having 1 to 4 carbon atoms, polyhydric alcohols such as glycerin and pentaerythritol; diethylene glycol, ethylene glycol monomethyl ether, ethylene Glycol dimethyl ether, 2-ethoxyethanol, propylene glycol monomethyl ether, propylene glycol methyl ether acetate and the like, ethers or esterified products of the above alcohols; ketones such as acetone and methyl ethyl ketone; formamide, N-methylformamide, N-ethylformamide, N , N-dimethylformamide, N, N-diethylformamide, N-methylacetamide, N-ethylacetamide, N, N-dimethylacetamide, N, N-di Tylacetamide, N-methylpyrrolidone, N-formylmorpholine, N-acetylmorpholine, N-formylpiperidine, N-acetylpiperidine, N-formylpyrrolidine, N-acetylpyrrolidine, N, N′-diformylpiperazine, N, N Amides such as' -diformylpiperazine and N, N'-diacetylpiperazine; Lactones such as γ-butyrolactone; Ureas such as tetramethylurea and N, N'-dimethylimidazolidine; Dimethylsulfoxide and the like . These water-soluble organic solvents may be used alone or as a mixture. Among these, preferable organic solvents in terms of film-forming properties (particularly volatile) on the substrate include acetone, methyl ethyl ketone, monohydric alcohols having 1 to 4 carbon atoms, and the like. Among these, methanol, ethanol, n-propanol, isopropyl alcohol, and acetone are more preferable, and methanol or ethanol is most preferable.

  A hydrophilic organic compound having a boiling point of 80 ° C. or higher has a hydrophilic functional group such as a hydroxyl group, a carbonyl group, an ether bond, an ester bond, a carbonate bond, a carboxyl group, an amide bond, a urethane bond, or a urea bond in the molecular structure. It is an organic compound. The hydrophilic organic compound may have a plurality of hydrophilic functional groups among them in the molecular structure. The boiling point here is a boiling point under a pressure of 760 mmHg. When a hydrophilic organic compound having a boiling point of less than 80 ° C. is used, the porosity of the porous silica film may be extremely reduced. Preferable examples of the hydrophilic organic compound having a boiling point of 80 ° C. or higher include alcohols having 3 to 8 carbon atoms, polyhydric alcohols having 2 to 6 carbon atoms, and phenols. More preferred hydrophilic organic compounds include alcohols having 3 to 8 carbon atoms, diols having 2 to 8 carbon atoms, triols having 3 to 8 carbon atoms, and tetraols having 4 to 8 carbon atoms. More preferable hydrophilic organic compounds include alcohols having 4 to 7 carbon atoms such as n-butanol, isobutyl alcohol, t-butyl alcohol, n-pentanol, cyclopentanol, n-hexanol, cyclohexanol, benzyl alcohol, C2-C4 diols such as ethylene glycol, propylene glycol, 1,4-butanediol, C3-C6 triols such as glycerol and trishydroxymethylethane, C4 such as erythritol and pentaerythritol -5 tetraols. In this hydrophilic organic compound, if the number of carbon atoms is too large, the hydrophilicity may decrease too much.

  A catalyst is mix | blended as needed. Examples of the catalyst include substances that promote the hydrolysis and dehydration condensation reactions of the alkoxysilanes described above. Specific examples include acids such as hydrochloric acid, nitric acid, sulfuric acid, formic acid, acetic acid, oxalic acid and maleic acid; amines such as ammonia, butylamine, dibutylamine and triethylamine; bases such as pyridine; Lewis such as acetylacetone complex of aluminum Acids; and the like.

  Examples of the metal species of the metal chelate compound used as the catalyst include titanium, aluminum, zirconium, tin, and antimony. Specific examples of the metal chelate compound include the following.

  Examples of aluminum complexes include di-ethoxy mono (acetylacetonato) aluminum, di-n-propoxy mono (acetylacetonato) aluminum, di-isopropoxy mono (acetylacetonato) aluminum, di-n-butoxy. Mono (acetylacetonato) aluminum, di-sec-butoxy mono (acetylacetonato) aluminum, di-tert-butoxy mono (acetylacetonato) aluminum, monoethoxy bis (acetylacetonato) aluminum, mono-n -Propoxy bis (acetylacetonato) aluminum, monoisopropoxy bis (acetylacetonato) aluminum, mono-n-butoxy bis (acetylacetonato) aluminum, mono-sec-butoxy bi (Acetylacetonato) aluminum, mono-tert-butoxy bis (acetylacetonato) aluminum, tris (acetylacetonato) aluminum, diethoxy mono (ethylacetoacetate) aluminum, di-n-propoxy mono (ethylacetoacetate) ) Aluminum, diisopropoxy mono (ethyl acetoacetate) aluminum, di-n-butoxy mono (ethyl acetoacetate) aluminum, di-sec-butoxy mono (ethyl acetoacetate) aluminum, di-tert-butoxy mono (Ethyl acetoacetate) aluminum, monoethoxy bis (ethyl acetoacetate) aluminum, mono-n-propoxy bis (ethyl acetoacetate) aluminum, monoisoprop Xy-bis (ethyl acetoacetate) aluminum, mono-n-butoxy bis (ethyl acetoacetate) aluminum, mono-sec-butoxy bis (ethyl acetoacetate) aluminum, mono-tert-butoxy bis (ethyl acetoacetate) Examples thereof include aluminum chelate compounds such as aluminum and tris (ethylacetoacetate) aluminum.

  Titanium complexes include triethoxy mono (acetylacetonato) titanium, tri-n-propoxy mono (acetylacetonato) titanium, triisopropoxy mono (acetylacetonato) titanium, tri-n-butoxy mono (acetyl). Acetonato) titanium, tri-sec-butoxy mono (acetylacetonato) titanium, tri-tert-butoxy mono (acetylacetonato) titanium, diethoxy bis (acetylacetonato) titanium, di-n-propoxy bis (Acetylacetonato) titanium, diisopropoxy bis (acetylacetonato) titanium, di-n-butoxy bis (acetylacetonato) titanium, di-sec-butoxy bis (acetylacetonato) titanium, di-tert -Butoxy bis (ace Ruacetonate) titanium, monoethoxy tris (acetylacetonato) titanium, mono-n-propoxy tris (acetylacetonato) titanium, monoisopropoxy tris (acetylacetonato) titanium, mono-n-butoxy tris (acetyl) Acetonato) titanium, mono-sec-butoxy-tris (acetylacetonato) titanium, mono-tert-butoxy-tris (acetylacetonato) titanium, tetrakis (acetylacetonato) titanium, triethoxy mono (ethylacetoacetate) titanium , Tri-n-propoxy mono (ethyl acetoacetate) titanium, triisopropoxy mono (ethyl acetoacetate) titanium, tri-n-butoxy mono (ethyl acetoacetate) titanium, tri-sec-butyl Xy mono (ethyl acetoacetate) titanium, tri-tert-butoxy mono (ethyl acetoacetate) titanium, diethoxy bis (ethyl acetoacetate) titanium, di-n-propoxy bis (ethyl acetoacetate) titanium, diiso Propoxy bis (ethyl acetoacetate) titanium, di-n-butoxy bis (ethyl acetoacetate) titanium, di-sec-butoxy bis (ethyl acetoacetate) titanium, di-tert-butoxy bis (ethyl acetoacetate) Titanium, monoethoxy tris (ethyl acetoacetate) titanium, mono-n-propoxy tris (ethyl acetoacetate) titanium, monoisopropoxy tris (ethyl acetoacetate) titanium, mono-n-butoxy tris (ethyl acetoacetate) Acetate) titanium, mono-sec-butoxy tris (ethyl acetoacetate) titanium, mono-tert-butoxy tris (ethyl acetoacetate) titanium, tetrakis (ethyl acetoacetate) titanium, mono (acetylacetonate) tris (ethyl aceto) Acetate) titanium, bis (acetylacetonato) bis (ethylacetoacetate) titanium, tris (acetylacetonato) mono (ethylacetoacetate) titanium and the like.

  In addition to these catalysts, weak alkaline compounds such as basic catalysts such as ammonia may be used. In this case, it is preferable to appropriately adjust the silica concentration, the organic solvent species, and the like. Moreover, when preparing a water-containing organic solution, it is preferable not to increase the catalyst concentration in a solution rapidly. Specific examples include a method of mixing alkoxysilanes and a part of an organic solvent, then mixing water, and finally mixing the remaining organic solvent and base.

  In particular, hydrochloric acid that is highly volatile and easy to remove and Lewis acids such as acetylacetone complex of aluminum are preferable. The addition amount of the catalyst is usually 0.001-1 mol, preferably 0.01-0.1 mol, with respect to 1 mol of alkoxysilanes. When the addition amount of the catalyst exceeds 1 mol, a precipitate composed of coarse gel particles is generated, and a uniform porous silica film may not be obtained.

  The raw material liquid for forming the porous silica film of the present invention is formed by blending the above-mentioned raw materials. The blending ratio of the alkoxysilanes is preferably 10 to 60% by weight and more preferably 20 to 40% by weight with respect to the whole raw material liquid. When the compounding ratio of alkoxysilanes exceeds 60% by weight, the porous silica film may be broken during film formation. On the other hand, when the compounding ratio of alkoxysilanes is less than 10% by weight, the hydrolysis reaction and the dehydration condensation reaction are extremely slow, and the film formability may be deteriorated (film unevenness).

  Water is blended 0.01 to 10 times, preferably 0.05 to 7 times, more preferably 0.07 to 5 times the weight of the alkoxysilane to be used. When the blending amount of water is less than 0.01 times the weight of the alkoxysilanes, the degree of progress of hydrolysis condensation reaction becomes insufficient, and the film may become cloudy. On the other hand, when the amount of water exceeds 10 times the weight of the alkoxysilanes, the surface tension of the raw material liquid becomes extremely large, and the film formability may deteriorate (liquid repelling, etc.).

  Water is necessary for hydrolysis of alkoxysilanes, and is important from the viewpoint of improving the film forming property of the target porous silica film. Therefore, when the preferable amount of water is defined by the molar ratio with respect to the amount of alkoxide groups, the amount of water is 0.1 to 1.6 mol times, especially 0.3 to 1.2 mol times the amount of 1 mol of alkoxide groups in alkoxysilane. In particular, the amount is preferably 0.5 to 0.7 mole times.

  Water may be added at any time after the alkoxysilanes are dissolved in an organic solvent, but it is desirable to add water after sufficiently dispersing the alkoxysilanes, catalyst and other additives in the solvent. Most preferred.

  The purity of the water to be used may be one that has undergone either or both of ion exchange and distillation. When the porous silica film of the present invention is used in an application field that particularly dislikes minute impurities such as semiconductor materials and optical materials, a porous silica film with a higher purity is required, and thus distilled water is further ion-exchanged. It is desirable to use ultrapure water. In this case, for example, water passed through a filter having a pore size of 0.01 to 0.5 μm may be used.

  When a hydrophilic organic compound having a boiling point of 80 ° C. or higher is used in the water-containing organic solution, the content of the hydrophilic organic compound having a boiling point of 80 ° C. or higher is equal to the total content of the organic solvent and the hydrophilic organic compound having a boiling point of 80 ° C. or higher. On the other hand, it is important that the amount is not more than a specific amount. The content of the hydrophilic organic compound having a boiling point of 80 ° C. or higher with respect to the total content is 90% by weight or less, preferably 85% by weight or less.

  If the blending ratio of the hydrophilic organic compound having a boiling point of 80 ° C. or higher is too small, the porosity of the porous silica film becomes extremely small, and it may be difficult to achieve a low refractive index of the porous silica film. In general, the total content of the organic solvent and the hydrophilic organic compound having a boiling point of 80 ° C. or higher is preferably 30% by weight or more, more preferably 50% by weight or more, and particularly preferably 60% by weight or more. On the other hand, when the blending ratio of the hydrophilic organic compound exceeds 90% by weight of the total content, the coating film may become cloudy during the film formation or the porous silica film may be broken. Therefore, the content of the hydrophilic organic compound having a boiling point of 80 ° C. or higher in the water-containing organic solution is 30% to 90% by weight, particularly 50% to 85% by weight, particularly 60% to 85% by weight of the total content. % Or less is preferable.

  The atmospheric temperature in the preparation of the coating liquid and the mixing order are arbitrary, but in order to obtain a uniform structure formation in the coating liquid, water is preferably mixed last. Moreover, in order to suppress the extreme hydrolysis and condensation reaction of silicon alkoxide in the coating solution, the coating solution should be adjusted at a temperature range of 0 to 60 ° C., particularly 15 to 40 ° C., particularly 15 to 30 ° C. Is preferred.

  At the time of liquid preparation, the stirring operation of the coating liquid is arbitrary, but it is more preferable to stir with a stirrer for each mixing.

  Further, after the coating solution is prepared, the solution is preferably aged in order to hydrolyze and dehydrate and condense silicon alkoxides. During this aging period, it is preferable that the hydrolyzed condensate of silicon alkoxides to be generated is in a more uniformly dispersed state in the coating solution, and therefore it is preferable to stir the solution.

  The temperature during the aging period is arbitrary, and in general, it may be heated at room temperature or continuously or intermittently. Among them, it is preferable to perform rapid heat aging in order to form a three-dimensional nanoporous structure by a hydrolytic condensate of silicon alkoxides. Further, when heat aging is performed, heat aging immediately after adjusting the coating solution is preferable, and within 15 days after adjusting the coating solution, more preferably within 12 days, particularly within 3 days, and particularly within 1 day, it is preferable to start heating aging.

  Specifically, accelerated aging is preferably performed at 40 to 70 ° C. for 1 to 5 hours. At that time, in order to obtain a uniform porous structure, stirring is preferably performed. In particular, accelerated aging for 2 to 3 hours at a temperature in the vicinity of 60 ° C. is preferable from the viewpoint of porosity.

  The viscosity of the raw material liquid is 0.1 to 1000 centipoise, preferably 0.5 to 500 centipoise, more preferably 1 to 100 centipoise, and it is preferable from the viewpoint of production to use a raw material liquid having a viscosity in this range.

(A) a step of forming a primary film from a raw material liquid;
The primary film is formed by applying a water-containing organic solution, which is a raw material liquid, on a substrate. Examples of the substrate include semiconductors such as silicon and germanium, compound semiconductors such as gallium-arsenic and indium-antimony, substrates such as ceramics and metals, and transparent substrates such as glass substrates and synthetic resin substrates.

  When the porous silica film of the present invention is formed on a substrate, the properties of the substrate surface may affect the properties of the porous silica film. Therefore, not only the cleaning of the substrate surface but also the surface treatment of the substrate may be performed in some cases. Examples of the substrate surface cleaning include immersion treatment in acids such as sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, alkalis such as aqueous sodium hydroxide, and mixed liquids having oxidizing properties such as hydrogen peroxide and concentrated sulfuric acid, hydrochloric acid, and ammonia. It is done. In particular, from the viewpoint of adhesion to a porous silica film, it is more preferable to perform a surface treatment with acids such as sulfuric acid and nitric acid on a silicon substrate and a transparent glass substrate.

  Examples of means for applying the raw material liquid include a casting method in which the raw material liquid is extended onto the substrate using a bar coater, an applicator or a doctor blade, a dip method in which the substrate is immersed in the raw material liquid, and a spin coating method. Well known. Of these means, the casting method and the spin coating method are preferably employed because the raw material liquid can be uniformly applied.

  When the raw material liquid is applied by the casting method, the casting speed is 0.1 to 1000 m / min, preferably 0.5 to 700 m / min, and more preferably 1 to 500 m / min.

  The rotation speed in the place where the raw material liquid is applied and formed by the spin coating method is 10 to 100,000 rotations / minute, preferably 50 to 50,000 rotations / minute, and more preferably 100 to 10,000 rotations / minute.

  In the dip coating method, the substrate may be dipped in the coating solution and pulled up at an arbitrary speed. The pulling speed at this time is preferably 0.01 to 50 mm / sec, more preferably 0.05 to 30 mm / sec, and particularly preferably 0.1 to 20 mm / sec. Although there is no restriction | limiting in the speed | rate which immerses a board | substrate in a coating liquid, It may be preferable to immerse a board | substrate in a coating liquid at a speed | rate comparable as a raising speed | rate. The substrate may be immersed for an appropriate time until the substrate is immersed in the coating solution and pulled up. The duration is usually 1 second to 48 hours, preferably 3 seconds to 24 hours, more preferably 5 seconds to 12 hours. It's time.

  The atmosphere during coating may be air or an inert gas such as nitrogen or argon, and the temperature is usually 0 to 60 ° C., preferably 10 to 50 ° C., more preferably 20 to 40 ° C. The humidity is usually 5 to 90%, preferably 10 to 80%, more preferably 15 to 70%. Since the dip coating method has a lower drying speed than the spin coating method, there is a tendency to form a stable film with less distortion by the sol-gel reaction after coating. Therefore, the film structure may be preferably controlled by the surface treatment of the substrate.

  The film forming temperature is 0 to 100 ° C., preferably 10 to 80 ° C., more preferably 20 to 70 ° C.

(C) a step in which the applied film is polymerized to form an intermediate film;
The applied film has a high molecular weight, and an intermediate film is formed. This reaction is called a so-called sol-gel method, and the elementary reaction consists of two elementary reactions, a hydrolysis reaction of alkoxysilanes and a dehydration condensation reaction between silanol groups generated by the hydrolysis reaction.

  The hydrolysis reaction is caused by adding water, but the water can be added as an aqueous alcohol solution or as water vapor without being particularly limited. If water is added rapidly, depending on the type of alkoxysilane, the hydrolysis reaction and the dehydration condensation reaction occur too quickly, and precipitation may occur. Therefore, in order to prevent such precipitation, take sufficient time to add water, make the alcohol solvent coexist in a state where water is added uniformly, and add water at a low temperature. It is preferable to use means such as inhibiting the reaction alone or in combination.

  As the hydrolytic condensation reaction of alkoxysilanes by the sol-gel method proceeds, the condensation product of alkoxysilanes gradually increases in molecular weight. In the hydrolysis-condensation reaction, phase separation that may be caused by a change in phase equilibrium may occur. In the present invention, the composition of the raw material liquid, the alkoxysilanes used, and the hydrophilic organic compound having a boiling point of 80 ° C. or higher The degree of hydrophilicity is controlled so that phase separation occurs on the nanometer scale. As a result, the separated phase of the hydrophilic organic compound is formed on the substrate while being held in the gel network of the alkoxysilane condensate, thereby forming an intermediate film.

  For this reason, it is important to control the hydrophilicity of a hydrophilic organic compound having a boiling point of 80 ° C. or higher. When the hydrophilic organic compound is represented by a relative dielectric constant, it is preferably 10 to 20, more preferably 13 to 19 can be defined.

  From the viewpoint of balancing the degree of hydrophilicity, it is desirable that the water-containing organic solution as the raw material solution contains an organic solvent (specifically, methanol, ethanol, etc.) having a relative dielectric constant of 23 or more. In particular, when the weight ratio of the organic solvent having a relative dielectric constant of 23 or more and the hydrophilic organic compound having a boiling point of 80 ° C. or more (weight of the organic solvent / weight of the hydrophilic organic compound) is in the range of 5/5 to 2/8. Furthermore, the desired phase separation behavior is achieved. The weight ratio is most preferably 4/6 to 2/8.

  In forming the intermediate film, for example, by pre-drying the coating film applied on the substrate, the solvent concentration in the thin film can be reduced and a partial condensation reaction of silica can be performed. As a result, the three-dimensional network structure in the film is fixed and promoted, and surface smoothness is obtained.

  The pre-drying of the intermediate film may be any of pressurization, reduced pressure, and normal pressure, and the temperature is not limited, but the effect of the pre-drying has at least two phases of silica hydrogel part and solution part inside the intermediate film. It is presumed that a phase separation structure is formed. Such a phase separation structure includes a sea-island structure, a structure composed of a rod-like dispersed phase and a continuous phase, a lamellar structure, a structure composed of communication holes and a continuous phase, IPN (Inter-penetrating network), bi-continuous (Bi-continuous), and the like. Any structure such as an interpenetrating structure called may be used. In order to form such a phase separation structure, that is, to promote a partial crosslinking reaction of silica, it is preferable to control temperature and humidity. Specifically, the temperature is usually 0 to 60 ° C., preferably 10 to 50 ° C., more preferably 20 to 40 ° C., and the relative humidity of the atmosphere is usually 5 to 95%, preferably 10 to 90%, more preferably. Is 15 to 80%, and most preferably 25 to 60%. The predrying time is usually 30 seconds to 60 minutes, preferably 1 to 30 minutes.

(D) A step of forming a porous silica membrane by bringing a water-soluble organic solvent into contact with the intermediate membrane (extraction step);
By bringing a water-soluble organic solvent into contact with the intermediate film, the hydrophilic organic compound in the intermediate film is extracted and removed, and water in the intermediate film is removed. The water present in the intermediate film is not only dissolved in the organic solvent but also adsorbed on the inner wall of the film constituent material. Therefore, in order to effectively remove the water in the intermediate film, the organic solvent Control the water content in it. Therefore, the content of water in the organic solvent is 0 to 10% by weight, preferably 0 to 5% by weight, and more preferably 0 to 3% by weight. If the dehydration is not sufficiently performed, the pores may collapse and disappear or become smaller in the subsequent heating or drying process of the film.

  As the means for extracting and removing the hydrophilic organic compound in the intermediate film, for example, immersing the intermediate film in a water-soluble organic solvent, washing the surface of the intermediate film with a water-soluble organic solvent, Examples thereof include spraying a water-soluble organic solvent on the surface and spraying water-soluble organic solvent vapor on the surface of the intermediate film. Of these, dipping means and cleaning means are preferred. Although the contact time between the intermediate film and the water-soluble organic solvent can be set in the range of 1 second to 24 hours, the upper limit of the contact time is preferably 12 hours and more preferably 6 hours from the viewpoint of productivity. On the other hand, the lower limit of the contact time is preferably 10 seconds and more preferably 30 seconds because the hydrophilic organic compound having a boiling point of 80 ° C. or higher and water must be sufficiently removed.

  As the contact treatment liquid, polar solvents are preferable, and among them, monohydric alcohols, polyhydric alcohols, ketones, ethers, esters, amides, or two or more hydrophilic solvents are preferable. When combining two or more kinds of hydrophilic solvents, they may be used in combination or may be combined by treating each solvent alone. Furthermore, the same kind of contact treatment liquid can be repeatedly acted on.

  In terms of making the porous silica film of the present invention porous, the contact treatment solvent is preferably a water-soluble organic solvent having a relative dielectric constant of 15 or more and a boiling point of 300 ° C. or less, specifically, methanol. Monohydric alcohols such as ethanol, polyhydric alcohols such as ethylene glycol, and ketones such as acetone and ethyl methyl ketone are preferred. Of these, monohydric alcohols such as methanol, ethanol, iso-propanol, n-butanol, and 1-pentanol are preferable, and monohydric alcohols having 4 or less carbon atoms are particularly preferable.

  In addition, before this extraction process, after the extraction process, or simultaneously with the extraction process, the intermediate film can be brought into contact with acids or bases. By carrying out like this, the hydrolysis condensation reaction of alkoxysilanes in the surface layer of an intermediate body film | membrane can be accelerated | stimulated. As a result, the surface layer of the intermediate film is preferable because it is very smooth and has high hardness. Preferable acids to be contacted include acids that are easily vaporized such as hydrogen chloride, formic acid, acetic acid, and trifluoroacetic acid. Preferred bases include ammonia, methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine, triethylamine, n-propylamine, isopropylamine, n-butylamine, cyclopentylamine, cyclohexylamine, and the like. 6 or less monoamines may be mentioned.

  As a method for bringing the intermediate film into contact with acids or bases, liquids or solutions or vapors of acids or bases are used. Moreover, acids or bases can be dissolved in the above-mentioned water-soluble organic solvent used in the extraction step, and contacted simultaneously with the extraction step.

(E) a step of cleaning the porous silica membrane;
You may add the washing | cleaning process of a porous silica film at the arbitrary time of the formation process of a porous silica film. The cleaning is performed by spraying the cleaning liquid on the porous silica film, immersing the porous silica film in the cleaning liquid, or casting the cleaning liquid on the porous silica film. Examples of the cleaning liquid include water, weakly acidic aqueous solution, weakly alkaline aqueous solution, alcohols having 1 to 4 carbon atoms, ketones such as acetone and methyl ethyl ketone, hydrophilic ethers such as diethyl ether and tetrahydrofuran, and water such as methyl acetate and ethyl acetate. May be exemplified by partially miscible esters, and a preferable cleaning liquid is water. In particular, it is preferable to add a washing step for the purpose of removing the acids or bases after the contacting step with the acids or bases.

(F) a step of drying the porous silica membrane;
The drying step is performed for the purpose of removing volatile components remaining in the porous silica membrane and / or for the purpose of promoting the hydrolysis condensation reaction of alkoxysilanes. The drying temperature is 20 to 500 ° C., preferably 30 to 400 ° C., more preferably 50 to 350 ° C., and the drying time is 1 minute to 50 hours, preferably 3 minutes to 30 hours, more preferably 5 minutes to 15 hours.

  The drying method can be performed by a known method such as blow drying or drying under reduced pressure, and may be combined. It should be noted that since the drying is too strong and the volatile components are removed rapidly, cracks are generated in the porous silica film, so that a gentle drying method such as blow drying is preferable. After the blast drying, vacuum drying for the purpose of sufficiently removing volatile components can be added.

  In order to form a more stable membrane structure with less distortion, a method in which the porous silica membrane is dried in multiple stages at different treatment temperatures after the step of contacting the intermediate membrane with the water-soluble organic solvent, that is, First, drying may be performed under low temperature conditions (post-drying), and then drying at a temperature as described above (high-temperature drying).

  In the post-drying, drying may be performed under any of pressure, reduced pressure, and normal pressure. The drying temperature is preferably dried at a temperature lower than the temperature at which the silica skeleton derived from the silica hydrogel part in the phase separation structure generated in the pre-drying is denatured, and is generally 0 to 100 ° C, particularly 10 to 70 ° C. 15-50 degreeC is preferable and drying time is 30 second-60 minutes normally, Preferably it is 1 minute-30 minutes.

  Furthermore, in the post-drying, the hydrophilic solvent content in the region in the range of 5% of the film thickness, preferably in the range of 3% in the film depth direction from the film surface is set to 30% by weight or less, and then the temperature is increased. It is preferable to perform drying. As a result, the film structure change can be reduced and deformation of the film such as cracking and warping can be suppressed.

  The purpose of high-temperature drying is to remove unnecessary solvents and additives in the porous silica membrane and to cure the membrane. For example, an oven furnace, a vacuum dryer, a hot plate, or the like can be used for the heat drying. The drying time is usually 10 seconds to 48 hours, preferably 30 seconds to 24 hours, more preferably 1 minute to 12 hours, and the drying temperature is usually 100 to 370 ° C, preferably 130 to 350 ° C, more preferably. 150-320 ° C. High temperature drying may be performed under any of pressure, reduced pressure, and normal pressure.

(G) silylation step;
It is preferable to treat the obtained porous silica membrane with a silylating agent. By treating with a silylating agent, hydrophobicity is imparted to the porous silica film, and the pores can be prevented from being contaminated by impurities such as alkaline water. Examples of the silylating agent include trimethylmethoxysilane, trimethylethoxysilane, dimethyldimethoxysilane, dimethyldiethoxysilane, methyltrimethoxysilane, methyltriethoxysilane, dimethylethoxysilane, methyldiethoxysilane, dimethylvinylmethoxysilane, and dimethyl. Alkoxysilanes such as vinylethoxysilane, diphenyldimethoxysilane, diphenyldiethoxysilane, phenyltrimethoxysilane, phenyltriethoxysilane, trimethylchlorosilane, dimethyldichlorosilane, methyltrichlorosilane, methyldichlorosilane, dimethylchlorosolane, dimethylvinylchlorosilane , Methyl vinyl dichlorosilane, methyl chloro disilane, triphenyl chloro silane, methyl diphenyl chloro Chlorosilanes such as silane, diphenyldichlorosilane, hexamethyldisilazane, N, N′-bis (trimethylsilyl) urea, N-trimethylsilylacetamide, dimethyltrimethylsilylamine, diethyltriethylsilylamine, trimethylsilylimidazole and other silazanes, (3, 3,3-trifluoropropyl) trimethoxysilane, (3,3,3-trifluoropropyl) triethoxysilane, pentafluorophenyltrimethoxysilane, pentafluorophenyltriethoxysilane, etc. And alkoxysilanes having a group. Silylation is performed by applying a silylating agent to the porous silica film, immersing the porous silica film in the silylating agent, or exposing the porous silica film to the vapor of the silylating agent. Can do.

(Electroluminescence element)
As shown in FIG. 1, the electroluminescent element of the present invention has the above-described laminated substrate, and is characterized in that at least a transparent electrode, an electroluminescent layer, and a cathode are laminated in this order on the laminated substrate. is there.

  In particular, since the electroluminescent device of the present invention has a smooth porous silica film having a maximum surface irregularity of 100 nm or less, there is no protrusion or depression of the transparent electrode formed on the porous silica film, and the anode and There is no short circuit between the two. Furthermore, since it has a laminated substrate with a porous silica film that has good adhesion to the substrate and is less likely to crack, the brittleness of the porous silica film, which has the effect of improving the light extraction efficiency, has been improved, and the low refractive index In addition, since the maximum value of the surface unevenness is 100 nm or less, an electroluminescence element excellent in reliability and light extraction efficiency is obtained.

  (A) The transparent electrode functions as an anode of the electroluminescence element. As the transparent electrode, a composite oxide thin film such as indium oxide added with tin (commonly referred to as ITO) or zinc oxide added with aluminum (commonly referred to as AZO) is preferably used. In particular, ITO is preferable.

The transparent electrode is formed by a vacuum film formation process such as vapor deposition or sputtering. The larger the light transmittance in the visible light wavelength region of the formed transparent electrode, the better, for example, 50 to 99%. A preferred lower limit is 60%, more preferably 70%. The electrical resistance of the transparent electrode is preferably as small as the sheet resistance value, but is usually 1 to 100Ω / □ (= 1 cm ² ), and the upper limit is preferably 70Ω / □, more preferably 50Ω / □. Further, the thickness of the transparent electrode is usually 0.01 to 10 μm as long as the above-described light transmittance and surface resistance value are satisfied. From the viewpoint of conductivity, the lower limit is preferably 0.03 μm, and 0.05 μm. Is more preferable. On the other hand, from the viewpoint of light transmittance, the upper limit is preferably 1 μm, and more preferably 0.5 μm. Such a transparent electrode is formed in a pattern necessary as an electrode of an electroluminescence element by a photolithography method or the like.

(B) The electroluminescent layer is formed by a material that exhibits a light emission phenomenon when an electric field is applied. The material includes activated zinc oxide ZnS: X (where X is Mn, Tb , Cu, an activation element of Sm, _{etc.), CaS:. Eu, SrS} : Ce, SrGa 2 S 4: Ce, CaGa 2 S 4: Ce, CaS: Pb, BaAl 2 S 4: conventionally such as Eu Inorganic EL materials used, 8-hydroxyquinoline aluminum complexes, aromatic amines, low molecular dye organic EL materials such as anthracene single crystals, poly (p-phenylene vinylene), poly [2-methoxy-5 Organic E of conjugated polymers such as-(2-ethylhexyloxy) -1,4-phenylenevinylene], poly (3-alkylthiophene), and polyvinylcarbazole Substances, and organic EL materials are conventionally used. The thickness of the electroluminescence layer is usually 0.01 to 1 μm, preferably 0.03 to 0.5 μm, and more preferably 0.05 to 0.2 μm. The electroluminescent layer can be formed by a vacuum film formation process such as vapor deposition or sputtering.

  (C) The cathode is provided so as to face the above-mentioned transparent electrode and sandwich the electroluminescence layer, and is aluminum, tin, magnesium, indium, calcium, gold, silver, copper, nickel, chromium, palladium, platinum, magnesium- It is formed of a silver alloy, a magnesium-indium alloy, an aluminum-lithium alloy, or the like. In particular, it is preferable to form with aluminum. The thickness of the cathode is usually 0.01 to 1 μm, preferably 0.03 to 0.5 μm, and more preferably 0.05 to 0.3 μm. The cathode can be formed by a vacuum film formation process such as vapor deposition or sputtering.

  (D) A hole injection layer and a hole transport layer can be further laminated between the electroluminescence layer and the transparent electrode, and an electron injection layer and an electron are interposed between the electroluminescence layer and the cathode. A transport layer can be further laminated. Moreover, you may apply well-known layers other than these.

  Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples.

Example 1
MKC silicate MS51 (6.6 g, manufactured by Mitsubishi Chemical Corporation, MKC silicate is a registered trademark), which is a methoxysilane oligomer having a polymerization degree distribution of alkoxysilanes of about 2 to 20 and a peak average degree of polymerization of 3 to 4. Methanol (2.9 g) as an organic solvent, n-butanol (9.8 g) as a hydrophilic organic compound having a boiling point of 80 ° C. or higher, and a 5 wt% methanol solution (1.3 g) of an aluminum acetylacetonate complex as a catalyst And water (1.4 g) were mixed, stirred at 60 ° C. for 2.5 hours, and then allowed to stand at room temperature for 2.5 days to prepare a raw material liquid which was a water-containing organic solution. Therefore, the weight ratio of methanol and n-butanol contained in this raw material liquid was 3: 7.

  This raw material liquid was applied onto a glass substrate (thickness 0.7 mm) having a refractive index of 1.5 at 23 ° C. at a sodium D-line wavelength to form a primary film. Application of the raw material solution was performed by spin coating at a rotation speed of 3000 rpm for 20 seconds at room temperature and in the atmosphere, and left for 10 minutes to obtain an intermediate film.

  The obtained intermediate film was immersed in 300 mL of methanol, which is a water-soluble organic solvent, for 5 minutes, dried, and then dried in an oven at 150 ° C. for 30 minutes to obtain a porous silica film.

The porous silica film thus obtained had a very flat surface, and the maximum surface irregularities measured by SEM and atomic force microscope were both 10 nm. From the refractive index measurement by ellipsometry, the refractive index of this porous silica film was 1.29. Further, the total carbon concentration in the porous silica film was 3%, and from the results of ¹³ C solid state NMR measurement, it was found that methanol was present and methoxy groups derived from the raw material methoxysilane oligomer were not substantially observed. . Moreover, as a result of TG-MS analysis, it was found that methanol contained in the film was released from the film at a temperature higher than the boiling point at 760 mmHg.

(Measurement)
Maximum surface roughness: The maximum surface roughness of the porous silica film is obtained by polishing the sample in cross section and taking a photo of the secondary electron image using a scanning electron microscope (SEM). It was determined by measuring the maximum value of the bottom and the bottom of the valley. SEM was observed using an JEOL JSM6320F scanning electron microscope at an acceleration voltage of 5 kV and magnifications of 10000 and 50000 times. In addition, the measurement with an atomic force microscope was performed by the above-described method (5 locations; 100 μm square region) using SPI300, DFM mode manufactured by Seiko Co., Ltd., and the evaluation result of the maximum value of the surface unevenness by SEM was verified.

  Refractive index: The refractive index of the porous silica film was measured in the wavelength range of 250 to 850 nm by spectroscopic ellipsometry (GES-5 manufactured by SOPRA), and analyzed using modeling.

  Total carbon concentration: The total carbon concentration of the porous silica membrane was measured by placing the sample in a total carbon concentration measuring apparatus, heating to 1450 ° C., and analyzing the amount of carbon in the gas generated. The total carbon concentration measuring device used was TOC5000 manufactured by Shimadzu Corporation.

Carbon source-derived analysis of carbon components: ¹³ C solid state NMR measurement was performed, and carbon source-derived analysis was performed.

  TG-MS analysis: The temperature was raised to 25 to 600 ° C. under a nitrogen stream, and the vaporized substance was detected with a mass spectrometer.

(Example 2)
Using the multilayer substrate of Example 1 described above, an electroluminescence element was manufactured by the following procedure. (A) An ITO layer (thickness: 0.16 μm) as a transparent electrode was formed on the surface of the porous silica film of the laminated substrate obtained in Example 1 by sputtering. The surface of the ITO layer was washed with an aqueous surfactant solution and ultrapure water and dried to remove moisture. (B) Next, this transparent electrode was patterned. For patterning, a photoresist material is applied on the entire surface by spin coating on a transparent electrode, exposed to a predetermined shape using an ultrahigh pressure mercury lamp (exposure intensity of 230 mJ / cm ² ), and then diluted with tetramethylammonium hydroxide in an aqueous solution. The unexposed photoresist material was dissolved and removed (developed) at (concentration: 2.4% by weight). The ITO exposed in the development was dissolved and removed (etched) with 6N hydrochloric acid at 45 ° C. After the etching, the remaining photoresist material that was hardly soluble upon exposure was peeled off. This peeling was performed by dipping in a concentrated tetramethylammonium hydroxide aqueous solution (concentration: 20% by weight). Then, it washed with ultrapure water. (C) Next, an interlayer insulating film was provided. The interlayer insulating film was provided in order to prevent a short circuit between the electroluminescent layer and the cathode to be formed after covering an excess portion of the patterned ITO with an insulating material (photoresist material). First, a photoresist material is applied to the entire surface by spin coating, and then exposed to a predetermined shape using an ultrahigh pressure mercury lamp (exposure intensity: 100 mJ / cm ² ), and then undiluted with the dilute aqueous solution of tetramethylammonium hydroxide. The photoresist material in the exposed area was dissolved and removed (developed). Then, washing with ultrapure water was performed. (D) ; Next, an electroluminescence layer was formed thereon. As the electroluminescence layer, an 8-hydroxyquinoline complex of aluminum (abbreviated as Alq3) was deposited with a thickness of about 200 nm. (E) A lithium fluoride (thickness: 0.5 nm) / aluminum layer (thickness: 80 nm) as a cathode was formed on the electroluminescence layer thus formed by vapor deposition. Here, lithium fluoride was used for the purpose of promoting electron injection.

(Comparative Example 1)
An electroluminescent device of Comparative Example 1 was prepared in the same manner as in Example 2 except that a commercially available glass substrate was used instead of the laminated substrate of Example 2. In addition, the maximum value of the surface unevenness of the glass substrate was about 10 nm.

(Performance evaluation of electroluminescence element)
When an electric field of 3 to 15 V was applied to the electroluminescent elements of Example 2 and Comparative Example 1, the emission intensity of emitted light to the outside of the electroluminescent element of Example 2 was about 1.2 times that of Comparative Example 1. In addition, the electroluminescent element of Example 2 was not damaged by a short circuit. From these results, it is considered that the electroluminescent element of Example 2 was able to form a transparent electrode with very few protrusions and depressions due to the excellent flatness of the porous silica film to be formed.

(Example 3)
In Example 1, a solvent in which the mixing ratio of methanol and n-butanol was 2: 8 was applied, pre-dried, immersed in ethanol for 5 minutes, and then subjected to secondary drying and high-temperature drying. The surface structure of this film formed a granular structure of about 100 nm excellent in smoothness, and the surface irregularities were 10 nm or less.

Example 4
In Example 2, a solvent in which the mixing ratio of methanol and n-butanol was 2: 8 was used. The surface structure of the film formed a granular structure of about 100 nm excellent in smoothness, and the surface unevenness was 10 nm or less.

(Example 5)
In Example 1, a solvent in which the mixing ratio of methanol and n-butanol was 7: 3 was used. Table 1 shows the film thickness, porosity, and refractive index calculated from the spectroscopic ellipsometry results for the obtained film.

(Example 6)
In Example 1, a solvent in which the mixing ratio of methanol and n-butanol was 3: 7 was used, and it did not include pre-drying, solvent contact step, and secondary drying. Minutes, dried. Table 1 shows the film thickness, porosity, and refractive index calculated from the spectroscopic ellipsometry results for the obtained film.

(Example 7)
In Example 6, a solvent having a mixing ratio of methanol and n-butanol of 2: 8 was used. The surface structure of this film formed a granular structure of about 100 nm excellent in smoothness, and the surface unevenness was 5 nm or less.

(Example 8)
In Example 3, methanol was used as a solvent instead of a mixed solvent. Table 1 shows the film thickness, porosity, and refractive index calculated from the spectroscopic ellipsometry results for the obtained film.

DESCRIPTION OF SYMBOLS 1 Electroluminescent element 2 Substrate 3 Transparent electrode 4 Light emitting layer 5 Cathode 6 Low refractive index layer (porous silica film)
7 Air 10 Multilayer substrate 11 Light with a large emission angle 12 Waveguide light

Claims (5)

A step of forming a primary film from a water-containing organic solution containing a raw material compound mainly composed of alkoxysilanes that undergoes a hydrolysis reaction and a dehydration condensation reaction;
A step in which the water-containing organic solution forming the primary film undergoes a hydrolysis reaction and a dehydration condensation reaction to form an intermediate film,
Pre-drying the intermediate film,
Contacting the water-soluble organic solvent with the intermediate film after pre-drying,
Post-drying the intermediate film in contact with the water-soluble organic solvent; and
Step of intermediate film after post-drying further promotes hydrolytic condensation reaction to form a porous silica film, only including,
The water-containing organic solution contains a hydrophilic organic compound having a boiling point of 80 ° C. or higher, and the weight ratio of the organic solvent to the hydrophilic organic compound having a boiling point of 80 ° C. or higher in the water-containing organic solution is 5/5 to 2/8. A method for producing a porous silica film, which is characterized. 2. The method for producing a porous silica film according to claim 1 , wherein a hydrophilic organic compound having a boiling point of 80 ° C. or more has a relative dielectric constant of 20 or less. The method for producing a porous silica film according to claim 1 or 2 , wherein the relative permittivity of the organic solvent contained in the water-containing organic solution is 23 or more. The method for producing a porous substrate according to any one of claims 1 to 3 , wherein a primary film is formed by applying the water-containing organic solution on the substrate. The method for manufacturing a laminated substrate according to claim 4 , wherein the substrate is transparent.

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