JP5909393B2 - Photocatalyst dispersion and coating liquid - Google Patents

Description

  The present invention relates to a photocatalyst dispersion that exhibits photocatalytic activity when irradiated with light.

  When a semiconductor is irradiated with ultraviolet rays, electrons having a strong reducing action and holes having a strong oxidizing action are generated, and molecular species in contact with the semiconductor are decomposed by the redox action. Such an action is called a photocatalytic action, and by utilizing this photocatalytic action, organic compounds and NOx in atmospheric substances can be decomposed. Such a photocatalytic semiconductor is called a photocatalyst, and it has been proposed to use the photocatalyst in various forms for the purpose of deodorization, gas treatment, water treatment, antibacterial action and antifouling, utilizing the characteristics of the photocatalyst. ing. In addition, the photocatalyst has a property of being hydrophilized by light irradiation, and the hydrophilized photocatalyst has a property of repelling oily dirt, for example. Utilizing this property, a dispersion containing a photocatalyst is used as a coating agent to be applied onto a substrate or a coating film formed on the substrate. It has been performed that the cleaning property and the easy cleaning property are imparted to the surface of the substrate or the coating film.

  The dispersion containing a photocatalyst generally contains a dispersant for stably dispersing the photocatalyst as fine particles in a dispersion medium. When the photocatalyst is titanium oxide and the dispersion medium is an aqueous medium (medium consisting of water or water and a water-soluble organic solvent), nitric acid, hydrochloric acid, monophosphoric acid and polyphosphoric acid, and salts thereof are used as the dispersing agent. Is known to be used (Patent Document 1, paragraph 0004).

JP 2008-93630 A

  When the photocatalyst is titanium oxide, when an inorganic acid such as nitric acid or a salt of an inorganic acid is used as the dispersant, when the dispersion containing the photocatalyst is used as the coating agent, the flexibility of the coating agent film is small, There is an inconvenience that workability is lowered. In addition, a dispersant containing an inorganic acid or a salt of an inorganic acid is hardly decomposed or deteriorated by photocatalysis. This may lead to inconvenience that the photocatalyst is buried in the film of the coating agent when the dispersion is applied as a coating agent on the surface of the substrate or the coating film, and the photocatalytic action cannot be sufficiently exhibited. . Therefore, the present inventors examined the possibility of stably dispersing the photocatalyst using a polymer as a dispersant in order to avoid such inconvenience. As a result, when a specific resin is used as a dispersant, the present inventors have found that an aqueous dispersion having good dispersibility of the photocatalyst and hardly causing the disadvantages described above can be obtained, and the present invention has been devised. .

  The present invention provides a photocatalyst dispersion containing photocatalyst particles, an aqueous medium and a water-soluble amphoteric polymer, wherein the photocatalyst particles are dispersed in the aqueous medium. In this photocatalyst dispersion, the amphoteric polymer functions as a dispersant for the photocatalyst particles. The photocatalyst particles are preferably titanium oxide.

  The photocatalyst dispersion of the present invention is an aqueous dispersion in which a photocatalyst is dispersed in an aqueous medium, and is characterized in that an amphoteric polymer is used as a dispersant. The amphoteric polymer allows the photocatalyst to be dispersed in the dispersion medium in the form of relatively small particles, thereby improving the dispersion stability in the dispersion of the photocatalyst, and when applied and used like a coating agent, Make the coating flexible. Further, since the amphoteric polymer is appropriately decomposed by the photocatalytic action of the photocatalyst, the photocatalyst dispersion of the present invention containing this as a dispersant is used as a coating agent or the like to form a photocatalyst during use. Is exposed, allowing the photocatalytic action and the hydrophilizing action to be exerted continuously over a certain period of time.

  The photocatalyst dispersion of the present invention contains photocatalyst particles, an aqueous medium and an amphoteric polymer, and the photocatalyst particles are dispersed in the aqueous medium. Hereinafter, the components contained in the photocatalyst dispersion of the present invention will be described.

[Photocatalyst particles]
As the photocatalyst, a compound that exhibits a photocatalytic action by ultraviolet rays or visible rays can be used. For example, as a photocatalyst, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Tc, Re, Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, Pt, Cu, Ag , One or more of metal elements such as Au, Zn, Cd, Ga, In, Tl, Ge, Sn, Pb, Bi, La, Ce, nitride, sulfide, oxynitride, Examples thereof include oxysulfides, nitrofluorides, oxyfluorides, oxynitrofluorides, and the like. Among these, titanium oxide is particularly preferably used as a photocatalyst. As used herein, titanium oxide includes a small amount (for example, 1 mol% or less with respect to Ti) of metal ions or nitrogen, and a small amount (for example, 1 mol% or less with respect to Ti) of other metal oxidation. The thing which carries a thing is included.

  In the photocatalyst dispersion of the present invention, the photocatalyst is present in the form of particles. The photocatalyst particles present in the dispersion preferably have dimensions such that the particle diameter (median diameter) is 10 nm or more and 500 nm or less as measured by a dynamic light scattering method. It is difficult to disperse fine particles having a particle diameter of less than 10 nm in the dispersion. When the particle diameter exceeds 500 nm, the particles are likely to precipitate, and the stability of the dispersion over time decreases. In order to obtain such an average particle size, the photocatalyst dispersion is prepared using a powder photocatalyst having a primary particle size (particle size before preparing the dispersion) in the range of 5 nm to 500 nm. Is preferred. Such photocatalysts are sold, for example, under the trade names ST-01, ST-21, ST-31, ST-41, and MPT-623 from Ishihara Sangyo Co., Ltd. SSP-25, SSP-20, SSP-M, STA-100A, STR-100N, STR-100A, STR-100W are sold under the trade names AMT-100, AMT-600, TKP- 101, TKP-102, and sold by Sumitomo Chemical Co., Ltd. under the trade names PC-101 and TP-S201 (both are titanium oxide).

  The photocatalyst particles are preferably contained in an amount of 1 to 60% by weight when the total weight of the dispersion is 100% by weight. If the ratio of the photocatalyst particles is small, it is difficult to obtain photocatalytic action. If the ratio of the photocatalyst particles is large, the viscosity of the dispersion becomes high and handling becomes difficult, and the stability over time decreases and the photocatalyst particles aggregate. It becomes easy to do.

[Aqueous medium]
The aqueous medium is water or a solvent containing water as a main component and a water-soluble organic solvent. In general, ion-exchanged water is used as water. Examples of the water-soluble organic solvent include methyl alcohol, ethyl alcohol, isopropanol, butanol, ethylene glycol, diethylene glycol, propylene glycol, glycerin, methyl soloselve, ethyl soloselve, butyl cellosolve, ethyl carbitol, butyl carbitol, methyl carbitol, Examples include propylene glycol monomethyl ether, propylene glycol monoethyl ether, acetone, and 2-butanone. When an aqueous medium has a water-soluble organic solvent, it is preferable to use a water-soluble organic solvent in the ratio of 0-100 weight part with respect to 100 weight part of water.

  The aqueous medium is preferably contained in an amount of 50 to 99% by weight when the total weight of the dispersion is 100% by weight. If the ratio of the aqueous medium is small, the dispersion may have a high viscosity and may be difficult to handle. If the ratio of the aqueous medium is large, the concentration of the photocatalyst particles will be low, so that the photocatalytic action is difficult to obtain.

[Water-soluble amphoteric polymer]
An amphoteric polymer refers to a polymer having both cationic and anionic groups. The amphoteric polymer may optionally contain units having nonionic groups. The zwitterionic polymer is, for example, a polymer obtained by polymerizing a monomer having an amino group (including a cyclic amino group) as a cationic group and a monomer having a carboxylic acid group or a sulfonic acid group as an anionic group. The zwitterionic polymer may be obtained by polymerizing a nonionic monomer in addition to a monomer having a cationic group and a monomer having an anionic group.

  Monomers having a cationic group include, for example, monoallylamine, N-methylallylamine, N, N-dimethylallylamine, N-cyclohexylallylamine, N, N- (methyl) cyclohexylallylamine, N, N-dicyclohexylallylamine, diallylamine, N- Methyl diallylamine, N-benzyl diallylamine, diallyl dimethyl ammonium chloride, diallyl dimethyl ammonium bromide, diallyl dimethyl ammonium iodide, diallyl dimethyl ammonium methyl sulfate, diallyl methyl benzyl ammonium chloride, diallyl methyl benzyl ammonium bromide, diallyl methyl benzyl ammonium iodide , Diallylmethylbenzylammonium methyl sulfate, diallyldibenzylammonium chloride, diallyldibenzyl bromide Ammonium iodide diallyl dibenzyl ammonium, methyl sulfate diallyl dibenzyl ammonium and the like. Some or all of these cationic group-containing monomers may form an addition salt, and can be used in the form of, for example, hydrochloride, sulfate, amide sulfate, or the like. The monomer having an anionic group is, for example, maleic acid, citraconic acid or itaconic acid, or a sodium salt, potassium salt or ammonium salt thereof. Sulfur dioxide is mentioned as a nonionic monomer contained in an amphoteric polymer.

  Alternatively, the amphoteric polymer may be obtained by polymerizing a monomer having a cation group and an anion group in a molecule and a nonionic monomer. A monomer having a cation group and an anion group in one molecule is, for example, carboxybetaine, and a nonionic monomer that is polymerized therewith is, for example, alkyl methacrylate.

  The amphoteric polymer is preferably one that gives an acidic aqueous solution when dissolved in water. The acidic aqueous solution is obtained by stably dispersing the photocatalyst particles. When the amphoteric polymer does not give an acidic aqueous solution, it is preferable to use a pH adjuster to make the dispersion acidic, specifically, pH 1 to 5.

Specific examples of amphoteric polymers include styrene-acrylic acid-acrylic acid dialkylamino ester polymers, allylamine-maleic acid copolymers, N, N-diallylamine-maleic acid copolymers, and vinylpyridine-acrylic acid copolymers. , Aminoethyl methacrylate-methacrylic acid copolymer, 2-vinylpyridine-maleic acid copolymer, 4-vinylpyridine-maleic acid copolymer, 2-vinylpyridine-itaconic acid copolymer, n-methylaminoethyl methacrylate -Acrylic acid copolymer, 4-vinylpyridine-itaconic acid copolymer, n-methylallylamine-itaconic acid copolymer and 4-vinylpyridine-fumaric acid copolymer, N-methacryloyloxyethyl-N, N- Dimethylammonium-α-N-methylcarboxybetaine metac Le acid alkyl ester copolymer (alkyl chain C _1-18), and methacryloyloxyethyl dimethyl betaine chloride methacryloyloxyethyl trimethylammonium betaine 2-hydroxyethyl methacrylate copolymer, and the like. In particular, allylamine-maleic acid copolymer and N, N-diallylamine-maleic acid copolymer, and N-methacryloyloxyethyl-N, N-dimethylammonium-α-N-methylcarboxybetaine / methacrylic acid alkyl ester copolymer A compound (the alkyl chain is C _1-18 ) is preferably used. In the present invention, an N, N-diallylamine-maleic acid copolymer obtained by introducing sulfur disulfide as a nonionic monomer is also preferably used.

  Amphoteric polymers preferably used in the present invention include, for example, trade names PAS410C (diallylaminate-maleic acid copolymer) and PA-84 (maleic acid-diallyldimethylammonium chloride) from Nitto Boseki Co., Ltd. (Nittobo). Sulfur dioxide copolymer) and also sold by Mitsubishi Chemical Corporation under the trade name Yuka Former (eg Yuka Former 510, Yuka Former 204WL).

  The reason why good dispersibility of the photocatalyst particles can be obtained when the amphoteric polymer is used as a dispersant is not clear. The reason for this is that, for example, when the photocatalyst is titanium oxide that has not been surface-treated and the pH of the amphoteric polymer aqueous solution is equal to or lower than the isoelectric point of the photocatalyst, the titanium oxide has a positive charge in the aqueous solution. Being charged, the anionic group of the amphoteric polymer is adsorbed to this positive charge and adsorbed to titanium oxide, and the cationic group is ion-dissociated in an acidic aqueous solution to ensure solubility in water. I think that may be mentioned. Further, since the isoelectric point of titanium oxide is generally 5 to 6, it is considered that the solubility of titanium oxide is ensured by such a mechanism when the aqueous solution of the amphoteric polymer gives an acidic aqueous solution. However, this reason is only a presumed reason and does not limit the present invention.

  The amphoteric polymer is preferably contained in an amount of 1 to 40% by weight when the total weight of the dispersion is 100% by weight. When the amount of the amphoteric polymer is too small, the photocatalyst particles cannot be sufficiently dispersed, and the dispersibility of the photocatalyst particles may be lowered. When the amount of the amphoteric polymer is too large, the viscosity of the dispersion is increased, the handling property is deteriorated, and the cost is increased.

[Other ingredients]
The photocatalyst dispersion of the present invention may further contain other components other than the above, if necessary. Other components include, for example, pH adjusters, antiseptic and fungicides, surfactants, chelating agents, leveling agents, binder resins (which may be in the form of solutions or emulsions), binders, antifoaming agents and thickening agents. One or more additives selected from agents. Other ingredients are added in amounts that can impart the desired properties to the dispersion. The proportion of other components in the dispersion is not particularly limited, and is appropriately selected depending on the use of the dispersion. For example, when the dispersion is used as a coating agent, the other components are preferably contained in a proportion of 50% by weight or less when the total weight of the dispersion is 100% by weight. When the proportion of other components is large, the proportion of any one or more of the above components in the dispersion decreases, and the film obtained by coating the dispersion does not exhibit a predetermined photocatalytic action. Or the viscosity of a dispersion may become high and it may become difficult to implement coating.

[Production method]
Next, a method for producing the photocatalyst dispersion of the present invention will be described. In the photocatalyst dispersion of the present invention, a photocatalyst, an amphoteric polymer, and other components added as necessary are added to an aqueous medium, and a known dispersion apparatus, specifically, a medium agitating disperser, rolling It can be produced by a method of dispersing the photocatalyst using an apparatus such as a ball mill, a vibrating ball mill, or a jet mill. In the case of using a medium agitating type disperser as the disperser, a bead having a diameter of 2.0 mm or less is generally used as the medium (media), which is generally made of zirconia, alumina, or glass. Dispersion is carried out until the photocatalyst has an average particle size in the aforementioned range.

[Usage]
The photocatalyst dispersion of the present invention has a photocatalytic film or hydrophilicity on the surface of a substrate such as glass, plastic, metal, ceramics and concrete and a coating film formed on the surface of the substrate. It can be used to form a film. The photocatalyst dispersion for forming such a film can also be referred to as a coating agent. Such a film can be formed by a known method such as spin coating, air knife coating, reverse roll coating, die coating, spray coating, or brushing. When applying the photocatalyst dispersion of the present invention to the surface of a coating film (coating film), in order to improve the adhesion between the coating agent and the coating film, the undercoating agent is applied and then the coating agent is applied. You can do it.

  When the photocatalyst dispersion of the present invention is applied as a coating agent to the substrate surface or the coating film surface formed on the substrate surface to form a coating layer, the substrate surface becomes hydrophilic by light irradiation. Easy to repel oily dirt. Therefore, the photocatalyst dispersion of the present invention can impart good drip-proofing properties, antifouling / antifogging properties, self-cleaning properties, and easy cleaning properties to the substrate surface.

  Alternatively, the photocatalyst dispersion of the present invention can be used for a dye-sensitized solar cell. Specifically, the photocatalyst dispersion of the present invention may be used for coating on a transparent electrode (negative electrode) of a dye-sensitized solar cell. In this case, the photocatalyst dispersion of the present invention is preferably used with a higher viscosity than when used as a coating agent. The viscosity may be increased by adding a thickener. The photocatalyst dispersion may be premixed with a dye.

(photocatalyst)
A titanium oxide photocatalyst was prepared as a photocatalyst (product name ST-01, manufactured by Ishihara Sangyo Co., Ltd.).
(Dispersant)
The following six types of resins were prepared as dispersants.
<Amphoteric polymer>
Diallylaminate-maleic acid copolymer (manufactured by Nitto Boseki Co., Ltd., trade name PAS-410C, concentration 40%)
Maleic acid-diallyldimethylammonium chloride-sulfur dioxide copolymer (manufactured by Nitto Boseki Co., Ltd., trade name PAS-84, concentration 30%)
N-methacryloyloxyethyl-N, N-dimethylammonium-α-N-methylcarboxybetaine / methacrylic acid alkyl ester copolymer (manufactured by Mitsubishi Chemical Corporation, trade name Yukaformer 510, concentration 18%)
<Cationic polymer>
Diallyldimethylammonium chloride polymer (Nitto Boseki Co., Ltd., trade name PAS-H-10L, concentration 28%)
Polyethyleneimine (Nippon Shokubai Co., Ltd., trade name Epomin SP-012)
<Anionic polymer>
Ethylene-maleic anhydride copolymer (Vertellus Specialties Inc., trade name ZEMAC E-400)

  In Example 4, in order to adjust the pH of the dispersion to acidic, 12N hydrochloric acid (hydrochloric acid content: 37% by weight) (special grade reagent: manufactured by Wako Pure Chemical Industries, Ltd.) was prepared. In Comparative Example 3, sodium hydroxide having a sodium hydroxide content of 97% by weight (special grade reagent: manufactured by Wako Pure Chemical Industries, Ltd.) was prepared in order to dissolve the anionic polymer in water.

(Examples 1-2, Comparative Examples 1-3)
A photocatalyst, a dispersant, and water (ion exchange water) as an aqueous medium are mixed and stirred at a ratio shown in Table 1, and then a bead mill made of zirconia having a diameter of 0.5 mm is used as a medium by a medium stirring type disperser. The photocatalyst was dispersed to obtain a photocatalyst dispersion. The pH of each of the obtained dispersions, the particle diameter of the photocatalyst particles in the dispersion, and the temporal stability of the dispersion were evaluated by the following procedure.

(PH)
Measurement was performed using a pH meter.
(Photocatalyst particle diameter)
The particle diameter (median diameter) of the photocatalyst particles in the photocatalyst dispersion was measured by a dynamic light scattering method. For the measurement, LB550 manufactured by Horiba Ltd. was used.
(Stability over time)
The dispersion was placed in a glass bottle and allowed to stand at room temperature for 6 months, and then the state was visually observed and evaluated according to the following criteria.
○: There is no precipitation. Alternatively, the photocatalyst particles are precipitated but easily redispersed when shaken.
X: The photocatalyst particle | grains have settled and it does not re-disperse even if it shakes.

  The evaluation results are shown in Table 1.

  As shown in Table 1, all of Examples 1 to 4 in which the amphoteric polymer was used as a dispersant had a small photocatalyst particle size, and exhibited good dispersibility and stability over time. In Comparative Examples 1 to 3 in which a polymer having only a cationic group or only an anionic group was used as a dispersant, the photocatalyst had a large particle size and poor dispersibility, and therefore was inferior in stability over time. .

  The photocatalyst dispersion of the present invention ensures good dispersibility by using an amphoteric polymer as a dispersant, is useful as a coating agent, and is used for adsorbing a dye in a dye-sensitized solar cell. It can be used as a titanium oxide layer.

Claims (4)

A photocatalyst dispersion comprising photocatalyst particles, an aqueous medium and a water-soluble amphoteric polymer, wherein the photocatalyst particles are dispersed in the aqueous medium ,
The amphoteric polymer is N-methacryloyloxyethyl-N, N-dimethylammonium-α-N-methylcarboxybetaine / methacrylic acid alkyl ester copolymer (the alkyl chain has 1 to 18 carbon atoms), or N, N A diallylamine-maleic acid copolymer or a copolymer in which sulfur dioxide is further polymerized;
Photocatalyst dispersion . The photocatalyst dispersion according to claim 1, wherein the pH is acidic. The photocatalyst dispersion according to claim 1 or 2 , wherein the photocatalyst particles are titanium oxide photocatalyst particles. The coating liquid containing the photocatalyst dispersion of any one of Claims 1-3 .