Inorganic hydrophilic coating solution, hydrophilic coating film obtained therefrom, and member using same

Abstract

An inorganic hydrophilic coating solution including (a) an aqueous solution containing an amorphous silicate compound obtained by hydrolyzing and condensing a tetrafunctional silicon compound having a purity of 99.0 mass % or greater in an aqueous medium in the presence of a basic compound at a temperature within a range from normal temperature to 170? C., (b) water, and optionally, (c) not more than 30 mass % of an alcohol, a ketone, or a surfactant, where the concentration of the solid fraction derived from the aqueous solution containing the amorphous silicate compound is 0.01 to 2.0 mass % and the pH is 5 to 8; an inorganic hydrophilic coating film formed from a dried and cured product of the inorganic hydrophilic coating solution; a member having a substrate and the inorganic hydrophilic coating film formed on the surface of the substrate; and a cover panel for a solar cell module including the member.

Claims

1. An inorganic hydrophilic coating solution comprising: (a) an aqueous solution comprising water and an amorphous silicate compound obtained by hydrolyzing and condensing a tetrafunctional silicon compound having a purity of 99.0 mass% or greater in an aqueous medium in the presence of an organic ammonium salt represented by structural formula (2) shown below:
R.sup.2.sub.4N.sup.+X.sup.?(2) wherein R.sup.2 is independently at each instance selected from the group consisting of methyl, ethyl, propyl, isopropyl and butyl, and X represents a hydroxyl group (OH), and an amount added of the organic ammonium salt in the hydrolysis and condensation is 100 mol % to 500 mol % relative to the amount of the tetrafunctional silicon compound, at a temperature within a range from 10 to 170? C., wherein the tetrafunctional silicon compound is: an amorphous silica having an SiO.sub.2 content of 99.0 mass % or greater, a content of each of Na.sub.2O, K.sub.2O, Fe.sub.2O.sub.3, CaO, SO.sub.3, MgO, and P.sub.2O.sub.5 of 0.1 mass% or less, and a primary particle size of 500 nm or less, or tetraethyl orthosilicate; and (b) optionally, not more than 30 mass % of an alcohol, a ketone, a surfactant, or a mixture of two or more thereof, wherein a concentration of a solid fraction derived from the aqueous solution comprising the amorphous silicate compound is 0.01 to 2.0 mass %, and a pH is 5 to 8, wherein in a spectrum obtained by performing a .sup.29Si-NMR measurement of the aqueous solution comprising the amorphous silicate compound, when a surface area ratio of a peak attributable to a Q.sub.n structure, wherein n of Q.sub.n is an integer of 0 to 4, relative to all peaks is used to calculate a molar ratio R.sub.n, wherein Q.sub.0 is an uncondensed silicate monomer, Q.sub.1 is a monocondensate of a silicate monomer, Q.sub.2 is a dicondensate of a silicate monomer, Q.sub.3 is a tricondensate of a silicate monomer, and Q.sub.4 is a tetracondensate of a silicate monomer, and R.sub.n, wherein n of R.sub.n is an integer of 0 to 4, is a molar ratio of silicon atoms within the Q.sub.n structure relative to all silicon atoms within the aqueous solution comprising the amorphous silicate compound, then the relationships shown below are satisfied: (R.sub.0+R.sub.1+R.sub.2+R.sub.3)?90 mol %, R.sub.3?40 mol %, and R.sub.4?5 mol %.

2. The inorganic hydrophilic coating solution of claim 1, wherein a contact angle with water of a coating film obtained by drying and curing the inorganic hydrophilic coating solution is not more than 20?.

3. The inorganic hydrophilic coating solution of claim 1, further comprising: (d) microparticles selected from the group consisting of metal oxide particles, metal chalcogenide particles and organometallic complex particles, wherein the microparticles have n- type semiconductor properties and have a primary particle size of 1 to 100 nm.

4. The inorganic hydrophilic coating solution of claim 3, wherein the microparticles comprise microparticles selected from the group consisting of titanium dioxide particles and tungsten trioxide particles.

5. The inorganic hydrophilic coating solution of claim 3, wherein at least one metal selected from the group consisting of vanadium, manganese, iron, cobalt, nickel, copper, zinc, niobium, molybdenum, ruthenium, rhodium, palladium, silver, tin, tungsten, platinum, and gold, a compound of one of these metals, or a combination thereof is supported on the microparticles.

6. The inorganic hydrophilic coating solution of claim 1, wherein the organic ammonium salt is at least one organic ammonium salt selected from the group consisting of tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, and ethyltrimethylammonium hydroxide.

7. The inorganic hydrophilic coating solution of claim 1, wherein the amount added of the organic ammonium salt is 200 mol % to 500 mol % relative to the amount of the tetrafunctional silicon compound.

8. The inorganic hydrophilic coating solution of claim 1, wherein the hydrolysis and condensation is performed at a temperature within a range from 80 to 130? C.

9. An inorganic hydrophilic coating film obtained by drying and curing the inorganic hydrophilic coating solution of claim 1.

10. A member comprising a substrate, and the hydrophilic coating film of claim 9 disposed on a surface of the substrate.

11. The member of claim 10, wherein the substrate comprises a glass, a polycarbonate, an acrylic, a polyester, or a fluorine based substrate.

12. A cover panel comprising the member of claim 10, wherein the cover panel is suitable for a solar cell module.

Description

EXAMPLES

(1) Specifics of the present invention are described below based on a series of examples and comparative examples. However, the present invention is in no way limited by these examples.

Example 1

(2) For the tetrafunctional silicon compound, a high-purity fumed silica (not a commercially available product, an amorphous silica manufactured by Shin-Etsu Chemical Co., Ltd. having a primary particle size of not more than 500 nm) having the properties shown in the table below (units: mass %) was used.

(3) TABLE-US-00002 TABLE 1 SiO.sub.2 Fe.sub.2O.sub.3 Total carbon MgO SO.sub.3 Na.sub.2O K.sub.2O CaO P.sub.2O.sub.5 Cl.sup.? 99.04 <0.01 0.01 <0.01 0.03 <0.01 <0.01 0.10 0.008 <0.01

(4) The above fumed silica, water, and tetramethylammonium hydroxide (25 mass % aqueous solution, manufactured by Toyo Gosei Co., Ltd.) were mixed so that the ratio of silica : tetramethylammonium hydroxide=1:2 (molar ratio) and the silica content of the system at the start of the reaction was 5 mass %, and the mixture was then stirred under heating at 110? C. for 2 hours. The resulting solution was diluted with water to obtain a solid fraction concentration of 0.5 mass %, and was then adjusted to a pH of 7.0 using an ion exchange resin (product name: Dowex 50W-X8, manufactured by Dow Coming Corporation), thus obtaining a coating solution (solid fraction concentration: 0.5 mass %).

Example 2

(5) Tetraethyl orthosilicate (purity: 99.9 mass % or higher, manufactured by Tama Chemicals Corporation, hereafter sometimes referred to as TEOS), water, tetramethylammonium hydroxide (25 mass % aqueous solution, manufactured by Toyo Gosei Co., Ltd.) and acetone (manufactured by Wako Pure Chemical Industries, Ltd., special grade) were mixed so that the ratio of tetramethylammonium hydroxide: tetraethyl orthosilicate=4:1 (molar ratio), and so that at the start of reaction, the tetraethyl orthosilicate content of the system was 15 mass % and the acetone content was 42 mass %, and the mixture was then stirred at normal temperature for 5 hours, yielding a white precipitate. The solvent was removed from the system, the precipitate was recovered, and following washing with acetone, the precipitate was redissolved in water, diluted with water to obtain a solid fraction concentration of 0.5 mass %, and then adjusted to a pH of 7.0 using an ion exchange resin (product name: Dowex 50W-X8, manufactured by Dow Corning Corporation), thus obtaining a coating solution (solid fraction concentration: 0.5 mass %).

Example 3

(6) A photocatalyst Sagan Coat TO sol (product name: TO-85, a dispersion of Anatase-type titanium oxide, manufactured by Kon Corporation) was added to the coating solution of Example 1 in sufficient amount that the ratio of the solid fraction within the coating solution obtained in Example 1: TiO.sub.2=90:10 (mass ratio), thus preparing a coating solution.

Example 4

(7) A photocatalyst Sagan Coat TO sol (product name: TO-85, a dispersion of Anatase-type titanium oxide, manufactured by Kon Corporation) was added to the coating solution of Example 2 in sufficient amount that the ratio of the solid fraction within the coating solution obtained in Example 2: TiO.sub.2=90:10, thus preparing a coating solution.

Comparative Example 1

(8) With the exception of using a commercially available colloidal silica (purity: 20 mass %, product name: Snowtex OS, manufactured by Nissan Chemical Industries, Ltd.) instead of the high-purity fumed silica used in Example 1, a coating solution (solid fraction concentration: 0.5 mass %) was prepared in the same manner as Example 1.

Comparative Example 2

(9) With the exception of using a commercially available silicate hydrolyzed solution (purity: 10 mass %, product name: HAS-10, manufactured by Colcoat Co., Ltd.) instead of the tetraethyl orthosilicate used in Example 2, a coating solution (solid fraction concentration: 0.5 mass %) was prepared in the same manner as Example 2.

Comparative Example 3

(10) A commercially available peroxo titanic acid aqueous solution (product name: PTA-85, manufactured by Kon Corporation) was simply diluted with water to prepare a coating solution (solid fraction concentration: 0.5 mass %).

Comparative Example 4

(11) A commercially available product (product name: TPX-85, manufactured by Kon Corporation) composed of a mixture of an aqueous solution of peroxo titanic acid and an Anatase-type titanium oxide was simply diluted with water to prepare a coating solution (solid fraction concentration: 0.5 mass %).

(12) [.sup.29Si-NMR Measurements]

(13) The coating solutions prepared in Examples 1 and 2 and Comparative Examples 1 and 2 were each subjected to a .sup.29Si-NMR measurement, and in each of the thus obtained spectra, the surface area ratio of each peak attributable to a Q.sub.n structure (wherein n is an integer of 0 to 4) relative to all of the peaks was used to calculate a molar ratio R.sub.n (wherein n is as defined above) of silicon atoms within the Q.sub.n structure relative to all of the silicon atoms within the coating solution. At this time, a previously prepared calibration curve illustrating the relationship between the above surface area ratio and R.sub.n was used.

(14) [Application of Coating Solutions]

(15) The coating solution was applied to a substrate formed from a PET (polyethylene terephthalate) film (thickness: 50 ?m) that had been cut to A4 size and subjected to a corona discharge treatment, and the coating solution was then dried by heating to prepare a coating film having a thickness of approximately 200 nm. The conditions for the heated drying involved heating at 70? C. for 30 minutes.

(16) [Normal Temperature Curing Time]

(17) Following formation of the coating film, the film was left to stand at normal temperature, and a dry Kimwipe was used to scrub the film. The time at which this operation no longer resulted in the generation of visually detectable blemishes on the coating film was specified as the normal temperature curing time.

(18) Coating films obtained by performing the normal temperature curing described above were used for the following tests.

(19) [Film Thickness Measurement]

(20) The film thickness was measured using a thin film measurement device F-20 (product name, manufactured by Filmetric, Inc.).

(21) [Water Contact Angle]

(22) The water contact angle for the coating film was measured at normal temperature using a contact angle meter CA-A (product name, manufactured by Kyowa Interface Science Co., Ltd.). Measurement of the water contact angle was also performed for a coating film that had been left in a dark place for one month. Moreover, the water contact angle was also measured for a coating film that had been exposed outdoors for one month.

(23) [Water Film Formation after One Month Exposure]

(24) A coating film that had been exposed outdoors for one month was brought into contact with water, and an evaluation was made, against the following criteria, as to whether or not a water film is formed on the surface of the coating film.

(25) O: a water film was formed uniformly.

(26) ?: a water film was formed, but was not uniform.

(27) x: the coating film repelled the water, and a water film was not formed.

(28) [Total Light Transmittance, Haze]

(29) These were measured using a digital haze meter NDH-20D (manufactured by Nippon Denshoku Industries Co., Ltd.). The measurement of diagonally incident light was preformed with the test sample inclined at an angle of 45?.

(30) [Visually Detectable External Appearance Anomalies]

(31) The surface on which the coating film was provided was observed at all angles from the normal direction relative to the surface through to a direction parallel to the surface, and visual confirmation was made as to whether interference color appeared, or whether cloudiness occurred due to reflection.

(32) [Film Adhesion]

(33) Testing was performed in accordance with the cross-cut tape peeling test of JIS K 5400 8.5, and the number of residual blocks was recorded. A higher number indicates superior adhesion.

(34) [Film Strength]

(35) Following preparation of each of the above coating films, each coating film was left to stand at normal temperature for at least 48 hours, and the coating film was then rubbed with a finger and scrubbed with a dry Kimwipe, and evaluated against the following criteria.

(36) O: no blemishes were formed.

(37) x: blemishes were formed.

(38) [Stain Resistance]

(39) The external appearance of a coating film that had been exposed outdoors for one month in the manner described above was inspected visually and evaluated against the following criteria.

(40) O: no change in the external appearance from the initial state.

(41) ?: not stained, but the film itself developed color interference, whitening, or both.

(42) x: water marks, rain spots, or both occurred.

(43) [Optical Properties]

(44) The optical properties of the coating film were evaluated against the following criteria.

(45) O: no detectable whitening or interference color, and no reduction in transparency when tilted.

(46) ?: whitening, interference color, or both were detected, but no reduction in transparency occurred when tilted.

(47) x: whitening, interference color, or both were detected, and a reduction in transparency occurred when tilted.

(48) The results of the above tests are shown in Table 2.

(49) TABLE-US-00003 TABLE 2 Exam- Exam- Compar- Exam- Exam- ple 3 ple 4 ative Compar- Compar- Compar- ple 1 ple 2 S T Example 1 ative ative ative S T method + method + Snowtex Example 2 Example 3 Example 4 method method TiO2 TiO2 OS HAS-10 PTA TPX-85 Main component(s) sili- sili- silicate + silicate + silica Sili- peroxo peroxo cate cate photo- photo- cate titanic titanic catalyst catalyst acid acid + photo- catalyst Compounds used silicate silicate silicate silicate silica Sili- peroxo peroxo (raw (raw (raw (raw cate titanic titanic material: material: material: material: acid silica) TEOS) silica) TEOS) acid Monomer ?Rn (n = 99 99 27 50 condensation 0.fwdarw.3)/mol % degree, molar R3/mol % 53 43 25 40 ratio R4/mol % <1 <1 73 10 Normal temperature curing time/hr 2 2 5 5 48< 1 48< 48< Initial water contact angle/deg 5 6 5 7 12 56 24 22 Water contact angle after 1 month 11 11 8 9 14 50 21 21 in dark/deg Water contact angle after 1 month <5 <5 <5 <5 6 45 19 15 exposure/deg Water film formation after 1 month 0 0 0 0 0 x ? 0 exposure Total light transmittance perpendicular +4.2 +4.0 +3.1 +3.2 3.1 +3.7 +0.6 ?3.7 (change relative to incident light substrate/? % 45? incident +4.2 +4.0 +2.9 +3.2 3.7 +1.2 +0.4 ?5.1 light Reduction in transparency upon none None none none none slight none slight diagonally incident light reduction reduction Haze (change relative perpendicular 0 0 ?0.1 ?0.1 +0.2 +0.8 ?0.1 ?0.1 to substrate)/? % incident light 45? incident 0 0 +0.1 +0.1 +0.3 +1.2 +0.6 +1.0 light Cloudiness upon diagonally none None none none none None slight slight incident light cloudiness cloudiness Visually detectable external none None none none none strong interference interference appearance anomalies inter- color + slight color + slight ference cloudiness cloudiness color Overall evaluations Film adhesion 100/100 100/100 100/100 100/100 5/100 5/100 90/100 90/100 Film strength 0 0 0 0 x 0 x x Stain resistance 0 0 0 0 ? x ? ? Optical properties 0 0 0 0 ? x x x OK OK OK OK durability stain external external NG resistance appearance appearance NG NG NG (Notes) S method: silicate obtained by hydrolysis and condensation of silica. T method: silicate obtained by hydrolysis and condensation of TEOS.

INDUSTRIAL APPLICABILITY

(50) The hydrophilic coating solution of the present invention is an inorganic hydrophilic coating solution, yet can form a film that can suppress light reflection and coherence, and has a substrate stain resistance function derived from the extremely high hydrophilicity. Moreover, the coating solution is stable in aqueous systems and neutral environments, and can form a coating film even by curing at normal temperature, meaning handling of the solution is safe and easy, during both industrial inline production and onsite operations, and therefore a strong and transparent hydrophilic coating can be applied easily, primarily to residential construction materials such as glass and exterior walls.