JP2004256727A - Method for producing photocatalytic coating solution and photocatalytic coating solution - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing a photocatalytic coating solution curable in a short time at normal temperature after applying to a substrate and forming a photocatalytic coating film resistant to peeling and provide the photocatalytic coating solution. <P>SOLUTION: The method for the production of the photocatalytic coating solution comprises a step to form a wet gel by adding dimethylformamide to an organic solvent, mixing with a titanium alkoxide, adding an acid catalyst and stirring for ≥48 hr to form the wet gel by sol-gel reaction, a step to dissolve the wet gel by adding an organic solvent containing lactic acid to the wet gel, and a titanium dioxide dispersing step to disperse anatase titanium dioxide powder in the wet gel solution. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

【００４１】
表１に示すように、市販塗料１〜市販塗料５の鉛筆引っかき値硬度は、「２Ｂ」や「ＨＢ」によっても塗膜の破れやすり傷が生じものもあり、最も評価の高い市販塗料４で「４Ｈ」という鉛筆引っかき値であった。これに対し、本願の実施例１〜実施例４の場合、鉛筆引っかき値はいずれも最上位の「６Ｈ」以上であり、いずれのコーティング膜も剥離は生じなかった。
【００４２】
また、碁盤目法および碁盤目テープ法の評価の場合、市販塗料では、市販塗料２を除いて概ね６〜８の評価であった。評価「８」は切り傷の交点にわずかな剥がれがあって、正方形の一目一目には剥がれがなく、欠損部の面積は全正方形面積の５％以内の場合である。これに対し、本願の実施例１〜実施例４の場合、いずれも最高評価の１０点であり、切り傷は細くて滑らかであり、一目一目に剥がれが観察されなかった。
【００４３】
従って、本実施例のコーティング膜は、市販塗料に比べて、塗膜の抵抗性が高くて剥離しにくい性質を備えていることが認められ、光触媒である二酸化チタンを保持する性能にも優れていると言える。また、１年以上保管した光触媒性コーティング溶液であってもコーティング膜の抵抗性に遜色はなく、長期間の保管安定性に優れていると言える。
【００４４】
『試験２：耐水性試験』
つぎに、コーティング膜の耐水性を試験した。実施例１〜実施例４の光触媒性コーティング溶液によりディップコーティグした試験片を４８時間水中に置いた後に膜の状態を確認した。その結果を表２に示す。
【００４５】
【表２】

【００４６】
表２に示すように、各実施例の溶液によるコーティング膜は、いずれも異常が認められず、剥離なども生じなかった。また、コーティング膜の抵抗性についても鉛筆引っかき値は「６Ｈ」であり、最高硬度を示した。従って、本実施例により成膜したコーティング膜は、耐水性に優れていることがわかる。
【００４７】
『試験３：大腸菌殺菌試験』
つぎに、コーティング膜の大腸菌殺菌試験を行った。実施例１〜実施例３の各光触媒性コーティング溶液を５０ｍｍ×５０ｍｍのガラス板上にコートし、常温にて４時間乾燥させて試験片とした。また、比較のためにコーティングを施さないガラス板の試験片を比較例１および比較例２として準備した。
【００４８】
試験を行うに当たり、まず大腸菌の試験液を作成した。大腸菌試験液は、液凍結保存してあった大腸菌液から０．１ｍｌを採取して液体培地５０ｍｌに加え、３７℃にて２４時間培養し、この培養液を菌数が約３０万個程度になるように調製した。一方、オートクレープにより濾紙と各試験片を充分殺菌しておく。そして、クリーンベンチ内にて滅菌済シャーレに菌の乾燥を防ぐ目的で濾紙を敷き、その上に試験片を置く。濾紙には滅菌水０．５ｍｌを染み込ませる。試験片上に調製した大腸菌試験液を０．５ｍｌ滴下し、滅菌したポリエチレンフィルムを被せてシャーレに蓋をして乾燥を防ぐようにする。このようにして大腸菌が付着された試験片を作成した。
【００４９】
各試験片に対し、２０Ｗの紫外線ランプを使用して紫外線量が１ｍｗ／ｃｍ^２に調整された紫外線を１時間照射した。この紫外線照射後、各試験片を滅菌ポリエチレン袋に入れて滅菌水５ｍｌで洗浄した。この洗浄液をもとに１０、１００、１０００、１００００倍に希釈する。希釈した液をそれぞれ滅菌済みの寒天培地に０．５ｍｌ滴下し、蓋をした後に３７℃で４８時間培養し、目視にて大腸菌のコロニーカウントを行った。この結果を表３に示す。
【００５０】
【表３】

【００５１】
表３に示すように、試験液１および試験液２には、約３０万個の大腸菌が存在していた。紫外線を１時間照射することにより、比較例１および比較例２では、それぞれ約５２０００個および約４６０００個までしか減少していないが、各実施例ではほとんど死滅した。従って、各実施例により成膜したコーティング膜は大腸菌殺菌効果に優れていることがわかる。
【００５２】
さらに、光源が存在しない場所での効果を確認するため、銀微粉末を混入させた光触媒性コーティング溶液を作成して、大腸菌殺菌試験を行った。銀微粉末は、１０ｎｍのＡＴＯＭＹＢＡＬＬ（触媒化成工業株式会社製）を使用し光触媒性コーティング溶液の全重量に対して１．０重量％加えた。この銀微粉末を混入した光触媒性コーティング溶液をガラス板上にコートして常温にて４時間乾燥させた。これに対し、前述の手順に従って大腸菌を滴下し、紫外線を照射せずに大腸菌殺菌試験を行った。この結果を表４に示す。
【００５３】
【表４】

【００５４】
表４に示すように、銀微粉末を入れた各実施例の溶液により成膜されたコーティング膜は、約３０万個存在していた大腸菌が８３０、９３０、９２０個にまで減少し、光源が無くても殺菌効果が発揮する。
【００５５】
『試験４：ジメチルホルムアミドの光触媒分解性能に及ぼす影響を確認する試験』
本発明に係る光触媒性コーティング溶液においてジメチルホルムアミドの添加の有無が光触媒の分解反応にどれ程寄与しているを確認する試験を行った。試験には、メチレンブルー退色試験と、アセトアルデヒドガス分解性能試験を行った。
【００５６】
まず、メチレンブルー退色試験について説明する。このメチレンブルー退色試験では、実施例１により製造した光触媒性コーティング溶液と、ジメチルホルムアミドを添加しないで製造した光触媒性コーティング溶液を比較例３とし、これらを縦横６０ｍｍのガラス板上にコートして乾燥させることにより試験片を作成した。メチレンブルー退色試験では、濃度が２０μｍｏｌ／Ｌのメチレンブルーを吸着用液とし、１０μｍｏｌ／Ｌのメチレンブルーを試験用液とした。
【００５７】
そして、各試験片上に液漏れを防ぐシリコングリスを塗ったポリエチレン製の円筒を置いて、このポリエチレン製の円筒にメチレンブルーの吸着用液を入れて２４時間放置し、コーティング膜にメチレンブルーを充分吸着させる。その後、ポリエチレン円筒内のメチレンブルー液を試験用のものに入れ替える。このように準備を整えた後、２０Ｗの紫外線ランプを使用して１ｍｗ／ｃｍ^２の紫外線をコーティング膜上に照射し、２０分毎にメチレンブルーの吸収波長のピークである６６４ｎｍの吸光度を測定した。この測定には株式会社島津製作所製のＵＶ−１６０Ａを使用した。吸光度とメチレンブルー溶液濃度とは比例関係にあることから、測定した吸光度を濃度に換算した。この結果を図２に示す。
【００５８】
図２は、横軸に紫外線を照射する時間経過を示し、縦軸にメチレンブルー試験液の濃度を示すグラフである。図２に示すように、紫外線照射後２０分経過後のメチレンブルー試験液の濃度は９．８４μｍｏｌ／Ｌであったが、１８０分経過後、ジメチルホルムアミドを未添加の比較例３では、８．８５μｍｏｌ／Ｌまで減少し、ジメチルホルムアミドを添加した実施例１では、７．１４μｍｏｌ／Ｌまで減少した。いずれもメチレンブルーを分解していることが認められるが、ジメチルホルムアミドを含む方がより分解性能に優れていることがわかる。さらに、この図２で求めた濃度の各点を最小二乗法で直線近似した傾きを分解示数として求めた。分解示数は数値が高いほど性能がよいことを意味し、有機化合物の分解性能の目安とされる。その結果、比較例３のジメチルホルムアミド未添加の場合、分解示数は５．６であったのに対し、実施例１のジメチルホルムアミドを添加した場合、分解示数は１６．４であり、約３倍の格差があった。したがって、ジメチルホルムアミドを添加することによって有機化合物の光触媒性能が向上することが確認された。
【００５９】
つぎに、アセトアルデヒドガス分解性能試験について説明する。ジメチルホルムアミドを添加した実施例１と、未添加の比較例３とについて、アセトアルデヒドガスの分解性能の違いを調べた。まず、実施例１および比較例３の各溶液を３×１０ｍｍのガラス板上にコートして試験片を作成した。一方、容量１００ｍｌのスクリュー瓶中にアセトアルデヒドガスを注入し濃度が１０００ｐｐｍとなるようにする。このスクリュー瓶の中に試験片を置く。そして、各試験片に対して２０Ｗ紫外線ランプを使用して２ｍｗ／ｃｍ^２の紫外線を照射し、紫外線照射開始から１０分おきにスクリュー瓶中のガスを採取し、ガスクロマトグラフＧＣ−１４Ｂ（株式会社島津製作所製）を使って、アセトアルデヒドガスおよび分解により発生する二酸化炭素ガスを測定した。二酸化炭素の理論発生値はアセトアルデヒドガスが分解された量の２倍となる。この結果を図３および図４に示す。
【００６０】
図３は、時間経過に対するアセトアルデヒドガスの濃度を示すグラフであり、分解により減少する量がわかる。図３に示すように、実施例１および比較例３の各試験片では、いずれも１０００ｐｐｍのアセトアルデヒド量が時間に比例して減少し、５０分経過したとき、ジメチルホルムアミド未添加の比較例３では、アセトアルデヒド濃度が５５４ｐｐｍ以下にまで減少し、ジメチルホルムアミドを添加した実施例１では、ほぼ０ｐｐｍにまで減少することができた。このようにいずれの試験片もアセトアルデヒドガス分解性能が認められるが、ジメチルホルムアミドを添加した場合の方が２倍以上の速度で分解が進行する。
【００６１】
図４は、時間経過に対する二酸化炭素の濃度を示すグラフであり、アセトアルデヒドガスを分解して発生する二酸化炭素量がわかる。図４に示すように、実施例１および比較例３の各試験片では、いずれも時間経過に伴って二酸化炭素の濃度が増加し、５０分経過したとき、ジメチルホルムアミド未添加の比較例３では、二酸化炭素濃度が７７３ｐｐｍとなり、ジメチルホルムアミドを添加した実施例１では、２０００ｐｐｍとなった。図３および図４を比較してわかるように、アセトアルデヒドガスの分解により発生する二酸化炭素は、実施例１の場合、ほぼ理論発生値に沿って分解量に対して２倍量となっている。また比較例３の場合も、分解量に対して約１．５倍量となっている。
【００６２】
以上のことからジメチルホルムアミドを混合した光触媒性コーティング溶液の方が、有機化合物および有機ガスの分解性能に優れていることが確認された。
【００６３】
『試験５：常温硬化確認試験』
つぎに、本実施例１〜実施例４の光触媒性コーティング溶液が、常温で硬化するのに要する時間を調べる試験を行った。また、比較のため、前述した試験１において比較試料とした常温硬化型の塗料である市販塗料１〜市販塗料５に関しても同様の試験を行った。試験に当たって、各溶液をそれぞれ基材に塗布し、１時間ごとに塗膜の抵抗性に関する鉛筆引っかき値を求めた。この結果を表５に示す。
【００６４】
【表５】

【００６５】
表５に示すように、市販塗料の場合、常温で１時間経過時点で鉛筆引っかき値は「２Ｂ」であり、その後徐々に硬化するが、５時経過しても市販塗料２では鉛筆引っかき値が「Ｂ」、市販塗料１および市販塗料５では「ＨＢ」、市販塗料３および市販塗料４では「Ｈ」であった。これに対して実施例１〜実施例４の場合、１時間経過したときにはすでに鉛筆引っかき値が「Ｈ」の硬度を示すまでに乾燥硬化し、常温にて４時間以上経過すれば、鉛筆引っかき値が「６Ｈ」以上の硬度に到達した。このように本実施例は、４時間という短時間で硬化できることが確認され、市販の塗料に比べても格段に速く乾燥し、高い硬度が得られることが認められた。
【００６６】
『試験６：コーティング膜の耐候試験』
実施例１から実施例４の光触媒性コーティング溶液により成膜したコーティング膜の耐候試験を行った。この耐候試験では、７０ｍｍ×３０ｍｍの基板上に各実施例の光触媒コーティング溶液を塗布した試験片を耐候試験機にて３０００時間試験を行った。試験機はＱ−ＳＵＮキセノンアーク方式耐候試験機（Ｑ−ＬＡＢ製）を使用し、キセノンランプにて紫外線を照射するとともに、定期的にシャワーで水がかけられる状況下で２４時間連続駆動により耐候促進試験が進められた。参考基準によると８００時間の試験で約１年経過した状態に相当するとされる。この結果、３０００時間経過しても各コーティング膜に目視で確認できるひび割れや剥離は認められなかった。
【００６７】
以上のような本実施形態によれば、４〜５時間程度で常温硬化ができるため現場施工が容易となる。また、成膜されたコーティング膜は、耐水性や耐候性に優れており、膜強度が高いため長期間光触媒二酸化チタン粒子を保持できて効果を発揮できる。
【００６８】
さらに、ジメチルホルムアミドを混入することにより、一層有機化合物や有機ガスの分解性能が向上する。また、銀微粉末を添加することにより夜や光源が少ない場所であっても殺菌効果を保持できるし、乳酸を混入することにより光触媒性コーティング溶液は保存安定性が向上し、少なくとも１年以上保存しても優れた光触媒性能を発揮するコーティング膜を形成できる。
【００６９】
また、光触媒性コーティング溶液には、シリコン系の物質を使用せず、チタンアルコキシドや二酸化チタン粉末を使用するため、溶液の製造は撹拌のみであり、複雑な反応工程や反応制御を必要とせず容易に製造できる。
【００７０】
なお、本発明に係る光触媒性コーティング溶液の製造方法およびこれによる溶液は、前述した実施形態に限定されるものではなく、適宜変更することができる。
【００７１】
【発明の効果】
以上説明したように本発明によれば、短時間で常温硬化ができて耐水性や耐候性、抵抗性に優れた光触媒性コーティング膜を形成することができる。
【図面の簡単な説明】
【図１】本発明に係る光触媒性コーティング溶液の製造方法を示すフロー図である。
【図２】本発明に係る実施例のジメチルホルムアミド添加の有無の効果を確認するメチレンブルー退色試験の結果を示すグラフである。
【図３】本実施例におけるジメチルホルムアミド添加の有無の効果を確認するアセトアルデヒドガス分解性能試験の結果を示すグラフである。
【図４】図３においてアセトアルデヒドガス分解により発生する二酸化炭素量を示すグラフである。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for producing a photocatalytic coating solution for forming a photocatalytic coating by subjecting a surface of a substrate to a coating treatment and curing at room temperature, and to a photocatalytic coating solution.
[0002]
[Prior art]
The photocatalyst generates electrons and holes when the surface is irradiated with ultraviolet rays, and these electrons and holes react with environmental pollutants and malodorous substances to decompose, thereby achieving various functions such as antifouling, deodorizing, and antibacterial. Demonstrate. Photocatalysts include metal oxides such as titanium oxide, tin oxide, tungsten oxide, and zinc oxide, and metal sulfides such as cadmium sulfide and copper sulfide.Of these, titanium oxide, particularly anatase-type titanium oxide has a photocatalytic activity. It is known to be excellent.
[0003]
Therefore, conventionally, various techniques for forming a photocatalytic film on a substrate using titanium oxide have been proposed. For example, there is a technique of sintering titanium oxide particles coated on a base material or firing a hydrolyzable titanium oxide film by a sol-gel method to form a photocatalytic film. There is also a technique of forming a photocatalytic film on a substrate using titanium oxide as a binder.
[0004]
However, in the conventional technology of sintering titanium oxide particles or firing titanium oxide by a sol-gel method to form a photocatalytic film, it is necessary to fire at a high temperature of 500 ° C. or more. There is an inconvenience that the substrate on which the film can be coated is limited. Also, in the technology of forming a photocatalytic film using titanium oxide as a binder, a heat treatment is required after coating a base material with a coating agent to suppress the separation of titanium oxide even at a high temperature, even if the temperature is not high. Further, since the silicon binder covers the surface of the titanium dioxide particles with a silicon film, the contact between the excited electrons and holes and the organic compound to be decomposed is hindered.
[0005]
On the other hand, a technique of forming a photocatalytic film by curing at room temperature without performing heat treatment has also been proposed. For example, Japanese Patent Application Laid-Open No. 2000-129174 discloses that titanium oxide, an organomonosilane containing a methyl group, and HLB (Hydrophile-Lipophile Balance) are used to form a photocatalytic coating film only by drying at room temperature. A photocatalytic coating composition comprising 0 to 17.0 nonionic surfactant and a solvent has been proposed (Patent Document 1).
[0006]
[Patent Document 1]
JP 2000-129174 A
[0007]
[Problems to be solved by the invention]
However, the photocatalytic coating cured at room temperature is generally easily peeled off from the substrate, which causes disadvantages such as a powder falling phenomenon and a decrease in photocatalytic activity. Further, in the invention described in the above-mentioned publication, organomonosilane which is a silicon compound has high reactivity, and may be solidified in a container during application by spraying. Further, in the case of a silicon-based material, it may take one week to one month to completely solidify even if it is hardened at room temperature. The above-mentioned photocatalytic paint has a low stability and a problem in terms of storage and life because the hydrolysis and condensation reactions proceed slowly but slowly. Further, since the resin is crosslinked and hardened, the volume shrinkage is large, and the coating film may be broken by shrinkage stress. On the other hand, the sterilization performance of the photocatalytic film cannot be expected to be effective at places where a sufficient light source is not secured, such as at night.
[0008]
The present invention has been made in order to solve such a problem, and can be performed at room temperature in a short time after application to a substrate, and can form a photocatalytic coating film that is difficult to peel off. It is an object of the present invention to provide a method for producing a photocatalytic coating solution and a photocatalytic coating solution.
[0009]
[Means for Solving the Problems]
The feature of the method for producing a photocatalytic coating solution according to the present invention is that dimethylformamide is added to an organic solvent and titanium alkoxide is added and mixed, and after adding an acid catalyst, the mixture is stirred for 48 hours or more to obtain a wet gel by sol-gel reaction. Forming a wet gel, dissolving the wet gel by adding an organic solvent containing lactic acid, and dispersing the wet gel solution by adding anatase type titanium dioxide powder to the wet gel solution. And a dispersing step.
[0010]
Further, the feature of the method for producing a photocatalytic coating solution according to the present invention is that, with respect to the weight of the photocatalytic coating solution, dimethylformamide is added to 40 to 50% by weight of propanol in an amount of 3.0 to 4.0% by weight, 4.0 to 5.0% by weight of tetrapropyl titanate is added and mixed, and 1.0 to 1.5% by weight of 0.1 to 1.0 mol / L nitric acid is added, followed by stirring for 48 hours or more to obtain a sol. A wet gel forming step of forming a wet gel by a gel reaction, and a wet gel dissolving step of adding and dissolving 40 to 50% by weight of propanol containing 0.8 to 1.5% by weight of lactic acid to the wet gel. A titanium dioxide dispersion step of adding 0.9 to 1.5% by weight of anatase type titanium dioxide powder to the wet gel solution and dispersing it.
[0011]
According to such a method, the sol-gel reaction proceeds slowly over a long period of time in the wet gel generation step, so it is estimated that the gel molecules can grow two-dimensionally, and the coating is hard to be cracked and peeled off. A film is formed.
[0012]
In the present invention, in the wet gel formation step, it is preferable to stir for 65 to 75 hours after adding the acid catalyst. This shortens the time until solution production while ensuring the performance of the coating film.
[0013]
Further, in the present invention, silver powder may be added in the titanium dioxide dispersion step. According to this, the sterilizing effect of the coating film can be exhibited even in a situation where a sufficient light source cannot be secured, such as at night.
[0014]
Further, the photocatalytic coating solution according to the present invention is characterized in that it is a solution obtained by any of the above-described methods for producing a photocatalytic coating solution, and according to this solution, in a short time after application to the substrate Forming a coating film that is completely cured at room temperature and hardly peels off, and has an excellent photocatalytic effect.
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of a method for producing a photocatalytic coating solution and a photocatalytic coating solution according to the present invention will be described with reference to the drawings.
[0016]
The method for producing a photocatalytic coating solution of the present embodiment mainly includes a wet gel generating step of generating a wet gel so that molecules grow in a two-dimensional network, and a wet gel dissolving step of dissolving the wet gel in an organic solvent. And a titanium dioxide dispersion step of adding and dispersing titanium dioxide powder to the wet gel solution, and producing a photocatalytic coating solution through each of these steps.
[0017]
The wet gel forming step includes a dimethylformamide mixing step of adding dimethylformamide to the organic solvent and stirring and mixing, a titanium alkoxide mixing step of adding titanium alkoxide and stirring and mixing, and an acid catalyst mixing step of adding an acid catalyst and stirring and mixing. It is done through. In the acid catalyst mixing step, it is preferable to stir slowly over time so that the molecules of the wet gel are two-dimensionally bonded to form a network. If it grows three-dimensionally, the two-dimensional molecular connection between molecules becomes weak, the adhesion to the substrate is poor, and the film can be peeled off only by rubbing with a finger. For this reason, in the prior art, a primer film or the like is formed as a base film between the base material and the photocatalytic film, but in the present embodiment, it is not necessary to form a primer film because a two-dimensional network is formed. Under normal conditions, it is necessary to stir for about 48 hours or more, preferably 60 hours to 100 hours, more preferably 65 hours to 75 hours in order to shorten the production time while securing the film forming performance. Stir.
[0018]
Dimethylformamide is used as an additive in the sol-gel method. However, the reason for adding dimethylformamide in the conventional sol-gel method is to suppress cracking when drying the gel. In other words, conventionally, when a wet gel is dried, a difference in shrinkage between the surface layer and the inside causes a tensile stress or a capillary force to shrink the surface layer to act on the surface layer. To add dimethylformamide. However, in the present invention, as a result of an experiment, the compound is added for the purpose of improving the effect of decomposing an organic compound by a photocatalyst.
[0019]
Examples of the organic solvent include ethanol, methanol, a propanol isomer, a butanol isomer, methyl cellosolve, ethyl cellosolve, and butyl cellosolve. Examples of the titanium alkoxide include tetramethyl titanate, tetraisopropyl titanate, tetra-n-butyl titanate, tetraethoxy titanate, and tetra-2-ethylhexyl titanate. Further, examples of the acid catalyst include nitric acid and hydrochloric acid. An alkaline catalyst such as ammonia is not preferable because a sol-gel reaction does not occur.
[0020]
The wet gel dissolving step is a step in which an organic solvent containing lactic acid is added to the wet gel generated in the wet gel generating step, followed by stirring and dissolving. It is preferable that the organic solvent is sufficiently stirred and dissolved until the organic solvent becomes transparent. The same organic solvent as that used in the above-mentioned wet gel forming step is used. Lactic acid acts as a chelating agent to produce a chelate compound, so that the hydrolysis and polycondensation reaction of the polymer in the photocatalytic coating solution is controlled, and long-term storage is possible.
[0021]
The titanium dioxide dispersion step is a step of adding anatase-type titanium dioxide powder to the wet gel solution prepared in the wet gel dissolution step and sufficiently dispersing the powder by a dispersion treatment. Ultrasonic waves acted on the dispersion treatment. Sufficient dispersion improves long-term storage. In the present embodiment, a nano-sized silver fine powder may be added during the titanium dioxide dispersion step. The silver fine powder can exert a bactericidal effect even when a sufficient light source cannot be secured at night or the like. In addition, by making the size nano, it is easy to dissolve, and the surface area can be increased to enhance the sterilizing effect.
[0022]
Next, preferred contents of the titanium alkoxide, dimethylformamide, acid catalyst, lactic acid, anatase type titanium dioxide powder, and organic solvent in the present embodiment will be described. The inventors prepared a photocatalytic coating solution by changing the content of each composition in order to determine an appropriate content, coated the solution on a substrate, and observed.
[0023]
First, the content of titanium alkoxide was examined. Titanium alkoxide is selected from tetrapropyl titanate, and 1.78% by weight or less, 2.67% by weight, 4.0% by weight, 5.0% by weight, 6.22% by weight based on the total weight of the photocatalytic coating solution. , 8.88% by weight, and more than 13% by weight.
[0024]
As a result, when manufactured at 1.78% by weight, the gelation reaction took about 300 hours, and the coating film did not have the ability to hold the titanium powder. When produced at 1.78% by weight or less, almost no reaction occurred. In the case of manufacturing at 2.67% by weight, gelation was completed in about 140 hours, but the titanium dioxide of the coating film was peeled off in about one week. When manufactured at 4.0% by weight, gelation was completed in about 80 hours, and the wet gel was transparent and a transparent solution was produced even after dissolution. The coating film formed with this solution had no cracks or peeling, and the solution itself had a life of one year or more. Further, in the case of manufacturing at 5.0% by weight, gelation was completed in about 70 hours, the wet gel was transparent, and the solution after dissolution was also transparent. The coated film had no cracking or peeling and had a solution life of more than one year. On the other hand, when it was manufactured at 6.22% by weight, gelation and film formation occurred in about 12 hours, but fine cracks occurred and the life of the coating film became several months. When produced at 8.88% by weight, gelation occurs in about one hour, but the film cracked and peeled off severely even when applied to equipment. Furthermore, when it was produced at 13% by weight or more, it reacted and precipitated immediately after mixing.
[0025]
Therefore, when the titanium alkoxide is tetrapropyl titanate, it is preferable to contain the titanium alkoxide in a range of at least 4.0% by weight to 5.0% by weight based on the total weight of the photocatalytic coating solution. If the titanium alkoxide is less than 4.0% by weight, the gelation reaction takes a long time, and the titanium dioxide powder may peel off and fall off. If the titanium alkoxide exceeds 5.0% by weight, the coating film may be cracked and peeled off.
[0026]
Next, the content of the acid catalyst was examined. As the acid catalyst, 0.1 mol / L nitric acid is selected, and 0.5% by weight or less, 0.7% by weight, 1.0% by weight, 1.5% by weight, 2% by weight or less based on the total weight of the photocatalytic coating solution. A photocatalytic coating solution was prepared with a variation of 0.0 wt% and 3.0 wt%. As a result, when 0.5% by weight or less was added, the gelation reaction of the solution hardly proceeded. When 0.7% by weight was added, the gelling reaction took about 300 hours, but the photocatalytic effect of the coating film was good. When 1.0% by weight is added, gelation is completed in about 96 hours, the wet gel is transparent and a transparent solution is formed even after dissolution, the coating film is not cracked or peeled, and the life of the solution is 1 year or more. there were. In addition, when manufactured at 1.5% by weight, gelation is completed in about 60 hours, the wet gel is transparent and a transparent solution can be formed even after dissolution, the coating film has no cracking or peeling, and the life of the solution is one year. That was all. When 2.0% by weight was added, gelation occurred in about 24 hours, but the titanium powder peeled off in about one week. When 3.0% by weight was added, the reaction proceeded at once as soon as the titanium alkoxide was added, and a precipitate was formed.
[0027]
Further, the concentration of the acid catalyst was also examined. When the concentration was less than 0.1 mol / L, the photocatalytic performance of the coated photocatalytic film was reduced to about 1/2. When the concentration exceeded 1.0 mol / L, the photocatalytic coating solution became cloudy. When the concentration is 0.5 mol / L, there is no problem in the performance of the coating film, but the wet gel becomes translucent. If the concentration is from 0.1 mol / L to 1.0 mol / L, the result of the nitric acid content described above is recognized.
[0028]
Therefore, when the acid catalyst is nitric acid, the concentration is 0.1 mol / L to 1.0 mol / L, and the concentration is in the range of 1.0% to 1.5% by weight based on the total weight of the photocatalytic coating solution. It is preferable to include them. If the amount of nitric acid is less than 1.0% by weight, the gelation reaction may take a long time or the reaction may hardly proceed. If the content of nitric acid exceeds 1.5% by weight, the titanium powder may be easily peeled off from the coating film, or a precipitate may be formed during the gelation reaction. When the concentration of nitric acid is less than 0.1 mol / L, the photocatalytic performance of the coated photocatalyst film is deteriorated. When the concentration exceeds 1.0 mol / L, the photocatalytic coating solution may become cloudy and not solidified.
[0029]
Further, it is preferable that dimethylformamide is contained in a range of 3.0% by weight to 4.0% by weight based on the total weight of the photocatalytic coating solution. If the amount of dimethylformamide is less than 3.0% by weight, the photocatalytic performance may decrease. If the amount of dimethylformamide greatly exceeds 4.0% by weight, the base material may be dissolved when applied to plastic.
[0030]
It is preferable that lactic acid is contained in the range of 0.8% by weight to 1.5% by weight based on the total weight of the photocatalytic coating solution. If the lactic acid content is less than 0.8% by weight, the action as a chelating agent is weakened, and the control of the hydrolysis and polycondensation reaction of the polymer becomes insufficient, so that the solution may not be stored for a long time. On the other hand, if the lactic acid content exceeds 1.5% by weight, the lactic acid is difficult to dry, so that the coated film may take a long time to dry or may not be dried in some cases.
[0031]
Further, the anatase type titanium dioxide powder is preferably contained in a range of 0.9% by weight to 1.5% by weight based on the total weight of the photocatalytic coating solution. If the amount of the anatase type titanium dioxide powder is less than 0.9% by weight, the photocatalytic reaction becomes insufficient, and the decomposition performance of the organic compound may be reduced. On the other hand, when the amount of the anatase type titanium dioxide powder exceeds 1.5% by weight, the coating film cannot hold the titanium dioxide powder, and there is a possibility of powder falling off.
[0032]
Further, the organic solvent is preferably contained in the range of 40% by weight to 50% by weight based on the total weight of the photocatalytic coating solution. If it is less than 40% by weight, the solution concentration becomes too high, and the coating film may be cracked or peeled off when applied to a substrate. If it exceeds 50% by weight, the solution concentration becomes thin and the strength of the coating film decreases. There is a possibility that the titanium dioxide powder falls and cannot be retained.
[0033]
Next, various performance tests were performed on examples of the coating film obtained by curing the photocatalytic coating solution of the present embodiment at room temperature. The present invention will be described in more detail with reference to the following examples, but the present invention is not limited thereto.
[0034]
[Example 1]
The photocatalytic coating solution of Example 1 of the present invention was prepared by adding 3.0% by weight of dimethylformamide and 4.0% by weight of tetrapropyl titanate to 45.0% by weight of 1-propanol, and adding 0.1 mol / L of nitric acid. Was added and stirred for about 100 hours to prepare a wet gel. Then, 1.0% by weight of lactic acid and 45.0% by weight of 1-propanol are added to the wet gel and stirred to dissolve the wet gel. Then, after dissolving, 1.0% by weight of anatase type titanium dioxide powder (manufactured by Nippon Aerosil Co., Ltd.) was added, and the mixture was dispersed by ultrasonic waves to prepare a photocatalytic coating solution of Example 1.
[0035]
[Example 2]
In Example 2, 4.0 wt% of dimethylformamide and 5.0 wt% of tetrapropyl titanate were added to 45.0 wt% of 2-propanol, and 1.5 wt% of 0.1 mol / L nitric acid was added. And stirred for about 100 hours to produce a wet gel. Then, 1.5% by weight of lactic acid and 41.5% by weight of 2-propanol are added to the wet gel and stirred to dissolve the wet gel. Then, after dissolving, 1.5% by weight of anatase type titanium dioxide powder (manufactured by Nippon Aerosil Co., Ltd.) was added, and the mixture was subjected to ultrasonic dispersion treatment to prepare a photocatalytic coating solution of Example 1.
[0036]
[Examples 3 and 4]
In Examples 3 and 4, the photocatalytic coating solutions of Examples 1 and 2 were stored in a closed state at room temperature for one year or more.
[0037]
"Test 1: Test on resistance of coating film"
First, in order to examine the resistance of the coating film of each example, a pencil scratch test and an adhesion test were performed in accordance with the general paint test method of JIS K5400. In the pencil scratch test, the hardness of the coating film is examined using a pencil scratch tester, and is represented by a pencil concentration symbol. A scratch tester manufactured by Sepro was used as the tester. Regarding the pencil hardness, the density symbol 9H is the hardest, 6B is the softest, and the harder is the higher. The criterion for this evaluation is to judge whether or not the coating film has been scratched two or more times in five tests in the case of evaluating the scratch. For example, when scratches are not recognized two or more times at 1H and scratches are recognized at least two times at 2H, 1H is the pencil scratching value. Note that “scratch” may be evaluated based on “tear”.
[0038]
In addition, the adhesion test was performed by a crosscut method and a crosscut tape method. The grid method is to visually observe the adhesion state of the coating film generated when a cut that penetrates the coating film and reaches the bare ground in a grid pattern. The crosscut-shaped cut is made with a cutter using a cutter guide. In addition, the cross-cut tape method is to make a cut in a grid pattern that penetrates the coating film and reaches the bare ground, and then rubs an adhesive tape specified by JIS with an eraser on the cross-cut and completely adheres and peels off Of the coating film is visually observed. The crosscut method and the crosscut tape method are evaluated on a scale of 0 to 10 according to the state of peeling. For example, “0” indicates a case where the area of peeling is 65% or more of the entire square area, and “6” indicates that there is peeling on both sides of the cut and at the intersection, and the area of the defective portion is 5 to 15% of the total square area. "10" indicates that each cut is thin and smooth on both sides, and there is no peeling at the intersection of the cut and each square.
[0039]
Table 1 shows the results of Examples 1 to 4 for Test 1 as described above. For comparison, a similar test was performed on five other competitor products that are generally marketed as room temperature-curable photocatalytic paints. The results are also shown. Commercially available paint 1 is a resin-curable paint containing anatase-type titanium dioxide, and is coated in two layers. Commercial paint 2 is an anatase type titanium dioxide water-soluble sol paint. Commercial paint 3 is a fluororesin paint containing anatase-type titanium dioxide powder. Commercial paint 4 is a two-layer coating, the lower layer is an organic-inorganic hybrid paint, and the upper layer is an anatase type titanium dioxide sol. The commercially available paint 5 is a two-pack type, one is an inorganic binder paint, and the other is a brookite-type titanium dioxide water-soluble sol paint.
[0040]
[Table 1]

[0041]
As shown in Table 1, the commercial paint 1 to commercial paint 5 had a pencil scratch hardness of "2B" or "HB", in which the paint film was easily torn or scratched. The pencil scratch value was “4H”. On the other hand, in the case of Examples 1 to 4 of the present application, the pencil scratching values were all “6H” or more at the top, and no peeling occurred in any of the coating films.
[0042]
In addition, in the case of the cross-cut method and the cross-cut tape method, the evaluation of the commercially available paint was generally 6 to 8 except for the commercially available paint 2. In the evaluation “8”, there was slight peeling at the intersection of the cuts, no peeling at a glance of the square, and the area of the defective portion was within 5% of the total square area. On the other hand, in the case of Examples 1 to 4 of the present application, the score was 10 points of the highest evaluation, the cut was fine and smooth, and no peeling was observed at a glance.
[0043]
Therefore, it is recognized that the coating film of this example has a property that the coating film has high resistance and is hardly peeled off as compared with a commercially available coating material, and also has excellent performance of retaining titanium dioxide as a photocatalyst. It can be said that there is. In addition, even if the photocatalytic coating solution is stored for one year or more, it can be said that the coating film has the same resistance as the coating film and has excellent long-term storage stability.
[0044]
"Test 2: Water resistance test"
Next, the water resistance of the coating film was tested. The test pieces dip-coated with the photocatalytic coating solutions of Examples 1 to 4 were placed in water for 48 hours, and the state of the film was confirmed. Table 2 shows the results.
[0045]
[Table 2]

[0046]
As shown in Table 2, no abnormality was observed in any of the coating films formed by the solutions of the examples, and no peeling occurred. The pencil scratch value of the coating film was also “6H”, indicating the highest hardness. Therefore, it is understood that the coating film formed according to this example has excellent water resistance.
[0047]
"Test 3: Escherichia coli sterilization test"
Next, an Escherichia coli sterilization test of the coating film was performed. Each of the photocatalytic coating solutions of Examples 1 to 3 was coated on a 50 mm × 50 mm glass plate and dried at room temperature for 4 hours to obtain test pieces. For comparison, test pieces of a glass plate without coating were prepared as Comparative Examples 1 and 2.
[0048]
In conducting the test, a test solution of Escherichia coli was first prepared. Escherichia coli test solution is prepared by collecting 0.1 ml of the Escherichia coli solution which has been frozen and stored, adding it to 50 ml of liquid medium, and culturing at 37 ° C. for 24 hours. It was prepared as follows. On the other hand, the filter paper and each test piece are sufficiently sterilized by autoclave. Then, filter paper is laid on the sterilized petri dish in a clean bench for the purpose of preventing the bacteria from drying, and a test piece is placed thereon. The filter paper is impregnated with 0.5 ml of sterile water. 0.5 ml of the prepared E. coli test solution is dropped on the test piece, covered with a sterilized polyethylene film and covered with a petri dish to prevent drying. Thus, a test piece to which Escherichia coli was attached was prepared.
[0049]
For each test piece, the amount of ultraviolet light was 1 mw / cm using a 20 W ultraviolet lamp. ² Was adjusted for 1 hour. After this ultraviolet irradiation, each test piece was placed in a sterilized polyethylene bag and washed with 5 ml of sterilized water. Dilute 10, 100, 1000, 10000 times based on this washing solution. 0.5 ml of each diluted solution was added dropwise to a sterilized agar medium, and after capping, the cells were cultured at 37 ° C. for 48 hours, and colonies of Escherichia coli were counted visually. Table 3 shows the results.
[0050]
[Table 3]

[0051]
As shown in Table 3, the test solution 1 and the test solution 2 contained about 300,000 E. coli. Irradiation with ultraviolet light for one hour reduced only about 52,000 and about 46,000 in Comparative Examples 1 and 2, respectively, but almost died in each Example. Therefore, it can be seen that the coating films formed according to the respective examples are excellent in the E. coli sterilizing effect.
[0052]
Further, in order to confirm the effect in a place where no light source is present, a photocatalytic coating solution mixed with silver fine powder was prepared and subjected to an E. coli sterilization test. The silver fine powder was added in an amount of 1.0% by weight based on the total weight of the photocatalytic coating solution using 10 nm ATOMYBALL (manufactured by Catalyst Chemical Industry Co., Ltd.). The photocatalytic coating solution mixed with the silver fine powder was coated on a glass plate and dried at room temperature for 4 hours. On the other hand, Escherichia coli was dropped in accordance with the above-mentioned procedure, and an Escherichia coli sterilization test was performed without irradiation with ultraviolet rays. Table 4 shows the results.
[0053]
[Table 4]

[0054]
As shown in Table 4, in the coating film formed by the solution of each example containing silver fine powder, about 300,000 E. coli were reduced to 830, 930, and 920, and the light source was reduced. Even without it, a bactericidal effect is exhibited.
[0055]
"Test 4: Test to confirm the effect of dimethylformamide on photocatalytic degradation performance"
A test was conducted to confirm how much the presence or absence of dimethylformamide in the photocatalytic coating solution according to the present invention contributed to the decomposition reaction of the photocatalyst. For the test, a methylene blue discoloration test and an acetaldehyde gas decomposition performance test were performed.
[0056]
First, the methylene blue discoloration test will be described. In this methylene blue discoloration test, the photocatalytic coating solution prepared according to Example 1 and the photocatalytic coating solution prepared without adding dimethylformamide were used as Comparative Example 3, which were coated on a 60 mm long and horizontal glass plate and dried. Thus, a test piece was prepared. In the methylene blue discoloration test, methylene blue having a concentration of 20 μmol / L was used as an adsorption solution, and 10 μmol / L methylene blue was used as a test solution.
[0057]
Then, a polyethylene cylinder coated with silicon grease to prevent liquid leakage is placed on each test piece, and a methylene blue adsorption solution is put in the polyethylene cylinder and left for 24 hours to sufficiently adsorb methylene blue on the coating film. . After that, the methylene blue liquid in the polyethylene cylinder is replaced with the one for the test. After preparation as described above, 1 mw / cm using a 20 W ultraviolet lamp. ² Was irradiated on the coating film, and the absorbance at 664 nm, which is the peak of the absorption wavelength of methylene blue, was measured every 20 minutes. For this measurement, UV-160A manufactured by Shimadzu Corporation was used. Since the absorbance was proportional to the methylene blue solution concentration, the measured absorbance was converted to a concentration. The result is shown in FIG.
[0058]
FIG. 2 is a graph in which the abscissa indicates the time lapse of ultraviolet irradiation and the ordinate indicates the concentration of the methylene blue test solution. As shown in FIG. 2, the concentration of the methylene blue test solution 20 minutes after ultraviolet irradiation was 9.84 μmol / L, but after 180 minutes, 8.85 μmol in Comparative Example 3 in which dimethylformamide was not added. / L, and in Example 1 to which dimethylformamide was added, it decreased to 7.14 μmol / L. It can be seen that all of them decompose methylene blue, but it is clear that the one containing dimethylformamide has more excellent decomposition performance. Further, a gradient obtained by linearly approximating each point of the density obtained in FIG. 2 by the least square method was obtained as a decomposition index. The higher the numerical value of the decomposition index, the better the performance, and it is a measure of the decomposition performance of the organic compound. As a result, when the dimethylformamide of Comparative Example 3 was not added, the decomposition index was 5.6, whereas when the dimethylformamide of Example 1 was added, the decomposition index was 16.4. There was a threefold difference. Therefore, it was confirmed that the photocatalytic performance of the organic compound was improved by adding dimethylformamide.
[0059]
Next, an acetaldehyde gas decomposition performance test will be described. Example 1 in which dimethylformamide was added and Comparative Example 3 in which dimethylformamide was not added were examined for differences in acetaldehyde gas decomposition performance. First, each solution of Example 1 and Comparative Example 3 was coated on a 3 × 10 mm glass plate to prepare a test piece. On the other hand, acetaldehyde gas is injected into a screw bottle having a capacity of 100 ml so that the concentration becomes 1000 ppm. Place the test specimen in the screw bottle. Then, using a 20 W ultraviolet lamp for each test piece, 2 mw / cm ² Irradiate with UV light, collect the gas in the screw bottle every 10 minutes from the start of UV irradiation, and use gas chromatograph GC-14B (manufactured by Shimadzu Corporation) to remove acetaldehyde gas and carbon dioxide gas generated by decomposition. It was measured. The theoretical generation value of carbon dioxide is twice the amount of the decomposition of acetaldehyde gas. The results are shown in FIGS. 3 and 4.
[0060]
FIG. 3 is a graph showing the concentration of the acetaldehyde gas with respect to the passage of time, and shows the amount reduced by the decomposition. As shown in FIG. 3, in each of the test pieces of Example 1 and Comparative Example 3, the amount of acetaldehyde of 1000 ppm decreased in proportion to time, and when 50 minutes had elapsed, Comparative Example 3 in which dimethylformamide was not added was used. , The acetaldehyde concentration was reduced to 554 ppm or less, and in Example 1 to which dimethylformamide was added, the concentration could be reduced to almost 0 ppm. As described above, acetaldehyde gas decomposing performance is observed in all of the test pieces, but the decomposition proceeds at twice or more the rate when dimethylformamide is added.
[0061]
FIG. 4 is a graph showing the concentration of carbon dioxide over time, and shows the amount of carbon dioxide generated by decomposing acetaldehyde gas. As shown in FIG. 4, in each of the test pieces of Example 1 and Comparative Example 3, the concentration of carbon dioxide increased with the passage of time, and when 50 minutes had elapsed, Comparative Example 3 in which dimethylformamide was not added was used. , The carbon dioxide concentration became 773 ppm, and in Example 1 to which dimethylformamide was added, it became 2000 ppm. As can be seen by comparing FIGS. 3 and 4, in the case of Example 1, the amount of carbon dioxide generated by the decomposition of the acetaldehyde gas is twice the amount of the decomposition substantially along the theoretical generation value. Also, in the case of Comparative Example 3, the amount was about 1.5 times the decomposition amount.
[0062]
From the above, it was confirmed that the photocatalytic coating solution mixed with dimethylformamide was superior in the decomposition performance of the organic compound and the organic gas.
[0063]
"Test 5: Room temperature curing test"
Next, a test was conducted to determine the time required for the photocatalytic coating solutions of Examples 1 to 4 to cure at room temperature. For comparison, the same test was carried out with respect to the commercially available paints 1 to 5 which are cold-curable paints used as comparative samples in Test 1 described above. In the test, each solution was applied to a substrate, and a pencil scratch value relating to the resistance of the coating film was determined every hour. Table 5 shows the results.
[0064]
[Table 5]

[0065]
As shown in Table 5, in the case of the commercial paint, the pencil scratch value was “2B” after 1 hour at room temperature, and then gradually cured. "B", "HB" for the commercial paints 1 and 5, and "H" for the commercial paints 3 and 4. On the other hand, in the case of Examples 1 to 4, when one hour has passed, the pencil scratch value has already been dried and hardened until the hardness of “H” is indicated. Reached a hardness of “6H” or more. As described above, it was confirmed that the present example could be cured in a short time of 4 hours, and it was recognized that the composition dried much faster than the commercially available paint and that high hardness was obtained.
[0066]
"Test 6: Weather test of coating film"
A weather resistance test was performed on the coating films formed using the photocatalytic coating solutions of Examples 1 to 4. In this weather resistance test, a test piece obtained by applying the photocatalyst coating solution of each example on a 70 mm × 30 mm substrate was subjected to a 3000 hour test using a weather resistance tester. The testing machine used a Q-SUN xenon arc type weathering tester (manufactured by Q-LAB), irradiating ultraviolet rays with a xenon lamp, and running continuously for 24 hours under a condition where water was sprinkled regularly with a shower. Accelerated testing proceeded. According to the reference standard, this is equivalent to a state in which about one year has passed in an 800-hour test. As a result, even after lapse of 3000 hours, cracks and peeling which could be visually confirmed were not observed in each coating film.
[0067]
According to the present embodiment as described above, room temperature curing can be performed in about 4 to 5 hours, so that on-site construction is facilitated. Further, the formed coating film is excellent in water resistance and weather resistance, and has high film strength, so that it can hold the photocatalytic titanium dioxide particles for a long period of time and exhibit the effect.
[0068]
Further, by mixing dimethylformamide, the decomposition performance of organic compounds and organic gases is further improved. In addition, by adding silver fine powder, the bactericidal effect can be maintained even at night or in a place where the light source is small, and the storage stability of the photocatalytic coating solution is improved by mixing lactic acid, and the storage time is at least one year. Thus, a coating film exhibiting excellent photocatalytic performance can be formed.
[0069]
The photocatalytic coating solution uses titanium alkoxide and titanium dioxide powder without using any silicon-based substance, so the solution is manufactured only by stirring, and does not require complicated reaction steps or reaction control. Can be manufactured.
[0070]
The method for producing a photocatalytic coating solution according to the present invention and the resulting solution are not limited to the embodiments described above, and can be changed as appropriate.
[0071]
【The invention's effect】
As described above, according to the present invention, a photocatalytic coating film that can be cured at room temperature in a short time and is excellent in water resistance, weather resistance, and resistance can be formed.
[Brief description of the drawings]
FIG. 1 is a flowchart showing a method for producing a photocatalytic coating solution according to the present invention.
FIG. 2 is a graph showing the results of a methylene blue discoloration test for confirming the effect of the presence or absence of dimethylformamide in the examples according to the present invention.
FIG. 3 is a graph showing the results of an acetaldehyde gas decomposition performance test for confirming the effect of the presence or absence of dimethylformamide in this example.
FIG. 4 is a graph showing the amount of carbon dioxide generated by acetaldehyde gas decomposition in FIG.

Claims (5)

Wet gel forming step of adding dimethylformamide to the organic solvent and adding and mixing titanium alkoxide, stirring the mixture for 48 hours or more after adding the acid catalyst to form a wet gel by a sol-gel reaction,
A wet gel dissolving step of adding and dissolving an organic solvent containing lactic acid to the wet gel,
A titanium dioxide dispersion step of adding and dispersing an anatase type titanium dioxide powder to the wet gel solution. Based on the weight of the photocatalytic coating solution, 40 to 50% by weight of propanol are added with 3.0 to 4.0% by weight of dimethylformamide, and 4.0 to 5.0% by weight of tetrapropyl titanate are added and mixed. A wet gel forming step of adding a nitric acid of 0.1 to 1.0 mol / L at 1.0 to 1.5% by weight and then stirring for 48 hours or more to form a wet gel by a sol-gel reaction;
A wet gel dissolving step of adding and dissolving 40 to 50% by weight of propanol containing 0.8 to 1.5% by weight of lactic acid to the wet gel;
A titanium dioxide dispersion step of adding 0.9 to 1.5% by weight of anatase type titanium dioxide powder to the wet gel solution and dispersing the wet gel solution. 3. The method for producing a photocatalytic coating solution according to claim 1, wherein in the wet gel forming step, stirring is performed for 65 to 75 hours after adding the acid catalyst. The method for producing a photocatalytic coating solution according to any one of claims 1 to 3, wherein silver powder is further added in the titanium dioxide dispersion step. A photocatalytic coating solution produced by the method for producing a photocatalytic coating solution according to claim 1.

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