JPH05286738A - Formation of titanium dioxide optical thin film - Google Patents

Abstract

PURPOSE:To apply a transparent ornament of uniform and clear colors on the surface of a rugged body or on the inner surface of a transparent vessel. CONSTITUTION:Titanium tetrachloride and glycerol are thermally condensed to synthesize a water-soluble titanium ester, tin chloride is dissolved in 2:1 to 1:9 molar ratio of Ti/Sn, and pure water is added to obtain the aq. dil. soln. A body with the surface cleaned is dipped in the dil. soln. which is boiled to deposit the hydrolyzate on the surface, and the surface is coated with a film of the mixture of titanium dioxide and tin oxide. Alternatively, a soln. contg. tiatnium and tin is applied on the body surface and baked to obtain the oxide coating film. The surface is pretreated in this way. The body is then heated in a film forming soln. prepared by adding a minute amt. of polycarboxylic acids to an aq. soln. of titanium tetrachloride acidified with hydrochloric acid, and the formed titanium dioxide is deposited on the pretreated surface.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a titanium dioxide optical thin film mainly for decorative use, and relates to glass, ceramics,
The purpose is to give gloss and color (hereinafter referred to as "iris") generated on the surface of plastic or the like by the phenomenon of light interference, but it is also applicable to optical applications.

[0002]

2. Description of the Related Art As a method for forming a titanium dioxide film on a concave surface, there are disclosed in JP-A-4-34502 and JP-A-4-345.
There is a method of scattering vapor deposition of titanium dioxide disclosed in ^No. 03, which performs vapor deposition in the presence of oxygen and argon gas in a vacuum of about 10 ¹ to 10 ³ Pa. The titanium dioxide film obtained by this method has a refractive index of 2.3, which is clearly lower than rutile titanium dioxide having a refractive index of 2.6 or more, and can be estimated to be anatase type. The concave surface that can be formed is a smooth open curved surface. The inventor of the present invention has disclosed Japanese Patent No. 1432039 (Japanese Patent Publication No. 61-191
8) disclosed a method for forming a titanium dioxide optical thin film by an aqueous solution reaction, and disclosed a method for forming a titanium dioxide thin film in which the optical thickness was controlled in Japanese Patent No. 1641229 (Japanese Patent Publication No. 03-7754). An object whose surface is coated by heating in an aqueous solution containing an iron salt is heated in a hydrochloric acid-acidic aqueous solution of titanium tetrachloride to deposit titanium dioxide produced by a thermal hydrolysis reaction on the coated surface. , To form a thin film of titanium dioxide. The latter is the object whose surface is coated by heating in an aqueous solution containing a water-soluble titanium ester, and which is heated in a strongly acidic aqueous solution of a tetravalent titanium salt to deposit titanium dioxide produced by thermal hydrolysis on the coated surface. Then, a thin film of titanium dioxide is formed. In all of these methods, a target object is heated in an aqueous solution containing an iron salt and / or a water-soluble titanium ester to coat the surface of the object, and then heated in an acidic aqueous solution of a tetravalent titanium salt to be subjected to thermal hydrolysis. Titanium dioxide produced by decomposition is deposited on the coating-treated surface to form a thin film of titanium dioxide by an aqueous solution reaction without using a vacuum.

[0003]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
Since the method of No. 39 utilizes a thermal hydrolysis reaction of titanium tetrachloride, which is an essentially homogeneous reaction, the production of titanium dioxide occurs uniformly in the solution, and therefore the titanium dioxide on the coated surface is Since the titanium dioxide precipitate particles are formed in the solution at the same time as the formation of the thin film, the solution gradually becomes turbid, making it difficult to directly observe the growth of the titanium dioxide thin film. It is not transparent and a slight cloudiness is observed. That is, the formation of a completely transparent titanium dioxide thin film has a very narrow range of conditions, and therefore has poor reproducibility.
Further, in the method disclosed in Japanese Patent No. 164229, the growth of the titanium dioxide thin film is very slow, and particularly when an acidic aqueous solution of titanium tetrachloride in hydrochloric acid is used, precipitation is remarkable and the growth is further slowed down. In any case, if a sulfuric acid aqueous solution of a tetravalent titanium salt is used, the turbidity generation can be suppressed within a range that does not significantly impair the transparency of the solution, and the titanium dioxide thin film formed is transparent. Since it becomes an anatase type crystal, the gloss is obviously inferior to that in the case of using an aqueous solution of titanium tetrachloride in hydrochloric acid. The present invention is
The object of the present invention is to improve the above-mentioned drawbacks of Japanese Patent No. 1432039 and to grow a completely transparent optical thin film of rutile type titanium dioxide on the surface of an arbitrary shape with good reproducibility while maintaining the transparency of the solution.

[0004]

[Patent Document 1] Said Patent No. 143203
As a result of detailed examination of the conditions for pretreatment of the object surface in No. 9, the pretreatment using a dilute aqueous solution containing a water-soluble titanium ester and tin chloride produces a transparent rutile titanium dioxide without any coloring due to absorption of light. Succeeded in growing an optical thin film. Furthermore, even when a dilute aqueous solution containing titanium tetrachloride and tin chloride is applied to the surface of an object and then heated to 300 ° C. or higher and baked, the solution is applied by heating in an acidic hydrochloric acid solution of titanium tetrachloride. It was found that a transparent rutile-type titanium dioxide optical thin film was formed on the surface. However, there was no great difference in the tendency of the solution to become turbid due to the formation of a precipitate during the reaction, and it was difficult to eliminate the trace cloudiness of the titanium dioxide thin film that was generated along with it. This deficiency was solved by making a trace amount of polycarboxylic acid coexist in an acidic aqueous solution of titanium tetrachloride. That is, when a water-soluble polycarboxylic acid obtained from a polymerizable carboxylic acid such as acrylic acid coexists, the solution is kept transparent without precipitation even when an acidic hydrochloric acid aqueous solution of titanium tetrachloride is heated, and When there is a surface pretreated according to the above in the solution or a surface coated with the mixed aqueous solution of titanium tetrachloride and tin chloride and baked, the formation of a titanium dioxide thin film proceeds and a completely transparent titanium dioxide optical thin film is formed. I have found that.

The molar ratio of titanium dioxide to tin oxide in the mixed oxide film containing titanium dioxide and tin oxide formed as a pretreatment layer on the surface of the object is preferably in the range of 1: 1 to 1: 9. If the proportion of titanium dioxide is too large, the growth rate will be slow, which will affect the transparency of the titanium dioxide thin film formed, and tin oxide alone will be less effective. In the case of applying a solution, a combination of titanium tetrachloride and stannic chloride is the most convenient solution for forming a film, but since it is oxidized to a mixed oxide containing titanium dioxide and tin oxide, titanium trichloride is used. And stannic chloride or stannous chloride, or a combination using an organic titanium compound and / or an organic tin compound. When a film of a mixed oxide containing titanium dioxide and tin oxide is formed by a thermal hydrolysis reaction in an aqueous solution, a combination of a water-soluble titanium ester and tin chloride, preferably stannic chloride is used. In this case, the form of water-soluble titanium ester is indispensable, and it is difficult to form a uniform titanium dioxide thin film with a combination of titanium tetrachloride and stannic chloride. The concentration of titanium and tin in the aqueous solution is titanium 5 to 30 μm.
ol / l, tin is preferably in the range of 25 to 50 μmol / l, and used as a 10 ^{4 to} 7 × 10 ³ N hydrochloric acid acidic solution.
In the case of a heat-resistant object such as glass or ceramics, the coating film formed in this manner can improve adhesion by baking at a temperature of 300 ° C. or higher which does not exceed the softening point or melting point of the surface layer. The baking process is not essential for forming the titanium dioxide thin film.

The polycarboxylic acid is conveniently obtained by polymerizing an unsaturated carboxylic acid such as acrylic acid, methacrylic acid or itaconic acid, but may be a polyester containing a large amount of carboxyl groups. Using a tribasic acid such as citric acid alone does not have any effect, but the effect can be obtained by heating and condensing with glycerol or the like to form a polycarboxylic acid. As a result of comparison with acrylic acid, the effect was recognized even with an average composition close to that of a decamer and in a wide range of higher polymerization degree. Even if a hydrophobic component such as methyl methacrylate is mixed in the polymer, it is effective if the polymer is water-soluble. To obtain a water-soluble polymer,
Benzoyl peroxide or AIBN (azobisisobutyronitrile) is used for monomers such as acrylic acid and methacrylic acid.
It is polymerized by a polymerization initiator such as and is dissolved in water.
The weight ratio of the polymerization initiator to the monomer is preferably in the range of 1/10 to 1/100, but may be lower. Since the polymerization reaction is explosive due to the large amount of catalyst,
It is convenient to carry out in an amount of 5 g or less. The polycarboxylic acid thus obtained is added to a hydrochloric acid-acidified titanium tetrachloride aqueous solution in a trace amount, and a thermohydrolysis reaction is allowed to proceed by putting an object having the pretreated surface and heating the surface, A transparent thin film of titanium dioxide with a gloss is formed.

The use concentration of polycarboxylic acid is very low,
Micromolar order is sufficient. If the concentration is too high, the thermal hydrolysis reaction is completely suppressed and no change occurs even if heating is continued at 100 ° C. The optimum concentration varies depending on the acid concentration and titanium concentration of the reaction solution, but in the range of the conditions of Japanese Patent No. 1432039, the carboxylic acid equivalent is preferably between 10 ⁶ and 10 ⁵ mol. It can be confirmed by comparison with the case where the titanium dioxide optical thin film thus formed is of the rutile type in comparison with the case where the film is formed under the condition of sulfuric acid acidity. That is, when the surface coated with the mixed oxide film containing titanium dioxide and tin oxide as described above is heated in a sulfuric acid-acidic titanium salt aqueous solution to undergo a thermal hydrolysis reaction, the titanium dioxide thin film formed has a gloss. Compared with the case of heating in an aqueous hydrochloric acid solution of titanium tetrachloride in the presence of the above polycarboxylic acid, it is clearly inferior and the effect as an iris film is low.
On the other hand, once a glossy thin film is formed in a hydrochloric acid-acidified titanium tetrachloride aqueous solution, rutile crystal growth continues as it is, even if the reaction solution is switched to a sulfuric acid-acidified titanium salt aqueous solution and the reaction is continued. An optical thin film with excellent saturation can be obtained. Therefore, if the initial film formation is performed in a hydrochloric acid-acidified titanium tetrachloride aqueous solution containing a polycarboxylic acid, the growth can be continued even if it is continued, or if the film formation reaction solution is switched to a sulfuric acid-acidified titanium salt aqueous solution. The object of the invention is fully achieved.

[0008]

The reason why the mixed oxide film of titanium dioxide and tin oxide exhibits an excellent effect as compared with the mixed oxide film of titanium dioxide and iron oxide in Japanese Patent No. 1432039 is that iron oxide is easily dissolved in hydrochloric acid. On the other hand, tin oxide seems to be difficult to dissolve in hydrochloric acid, but German Patent DE2522
According to the description of 572C2, tin oxide has a catalytic effect of converting anatase into rutile, and therefore, when titanium dioxide is deposited on a mixed oxide film of titanium dioxide and tin oxide, a rutile type thin film is easily formed. It is understood that it can be obtained. That is, when the surface coated with such a coating is immersed in an aqueous hydrochloric acid solution of titanium tetrachloride to carry out the thermal hydrolysis reaction of titanium tetrachloride, the mixed oxide on the surface serves as nuclei to form the rutile titanium dioxide epitaxial layer. It is thought that various growth will proceed. The mechanism by which the presence of polycarboxylic acid suppresses the formation of precipitates in the reaction solution without hindering the formation of a titanium dioxide thin film is unknown, but such an action does not occur under the condition of sulfuric acid acidity. Tribasic acid,
Nucleation in the reaction solution is a stereochemistry of polycarboxylic acid because it has no effect with simple polybasic acids such as tetrabasic acid, and it has an effect at a very low concentration compared to the ion concentration of existing titanium. It is considered that the crystal growth of titanium dioxide proceeds selectively only on the coating surface on which nuclei are already present, which is prevented by the selective blocking effect. In the case of a single layer film 2.
In the rutile type having a refractive index of 6 or more and the anatase type having a refractive index of 2.3, it can be easily confirmed by calculation that the maximum reflectance is 1.3 times or more that of the latter. Therefore, the rutile type titanium dioxide film of the present invention has a larger difference between the maximum reflectance and the minimum reflectance as compared with the prior art, exhibits a clearer interference color, and has a remarkably excellent iris effect.

[0009]

EXAMPLES The present invention will be described in more detail below by taking the case of forming a titanium dioxide optical thin film on the surface of glass as an example. In Examples 1 to 6 below, the window glass plate was wiped with an alkaline aqueous solution and then washed with water to clean the surface, and an optical thin film of titanium dioxide was formed using the one pretreated as follows.
That is, a water-soluble titanium ester is prepared by heating titanium tetrachloride and glycerol in accordance with the description in Japanese Patent No. 1432039, and pure water is added to the titanium concentration of about 35 m.
Dilute to a mol / l aqueous solution. Hydrochloric acid was further added to this aqueous solution so that the titanium concentration was about 25 mmol / l and the hydrochloric acid concentration was about 3.35 N.
Dissolve 1 g to obtain a stock solution of the pretreatment liquid. 250 with pure water
Immerse the glass plate in the diluted solution twice and boil it for about 30 minutes to hydrolyze it, then gently wash it with pure water and dry it. Bake and cut into pieces that fit into test tubes. Prepare the film-forming reaction solution as follows, add an appropriate amount of polycarboxylic acid,
Heated in a test tube with a glass plate pretreated as described above. Stock solution composition: Titanium tetrachloride 10 g Hydrochloric acid (36.46%) 330 ml Pure water 1000 ml Ti concentration 52.8 mmol / l HCl concentration about 3.87 N Reaction solution composition: Stock solution 20 ml Pure water 500 ml Ti concentration about 2 mmol / l HCl concentration about 0 For 15N polycarboxylic acid, glycerol citrate, polyacrylic acid, polymethacrylic acid, acrylic acid-itaconic acid copolymer, and methyl methacrylate-acrylic acid copolymer were prepared as follows, and added to the reaction solution having the above composition. In addition, a thin film of titanium dioxide was formed. Example 1 3.0 g of citric acid was dissolved in 1.0 g of glycerol, and about 0.7 g was heated until dehydrated to obtain a resin-like solid substance.
Dissolve in 0 ml of pure water. The COOH equivalent of this solution was estimated from the dehydration amount to be about 910 μmol / ml.
This is further diluted 1000 times, and 0.44 ml is added to 50 ml of the reaction solution having the above composition to obtain a film formation reaction solution containing a polycarboxylic acid having an estimated effective COOH equivalent of about 8 μmol / ml. Example 2 0.1 g of AIBN was dissolved in 1.0 g of acrylic acid, 1 ml of pure water was added, and the mixture was heated in a hot water bath to polymerize and further heated in saturated steam for 60 minutes, and then dissolved in pure water. And the total amount 3
It is set to 0 g. COOH equivalent is 410 by alkali titration
It was estimated to be around μmol / ml. KMn0 ₄ was detected unsaturated bond by, but is determined residual monomer is hardly present. A solution diluted with pure water by a factor of 500 was added 0.49 ml to 50 ml of the reaction solution, and CO was added.
The film-forming reaction liquid contains a polycarboxylic acid having an OH equivalent of about 8 μmol / ml. Example 3 0.1 g of AIBN was dissolved in 2.0 g of methacrylic acid,
1 ml of pure water is added and the mixture is heated in a hot water bath to polymerize and further heated in saturated steam for 60 minutes, then dissolved in pure water to a total amount of 30 g. COOH equivalent is about 7 by alkali titration
It was estimated to be 50 μmol / ml. KMn0 ₄ was detected unsaturated bond by, but is determined residual monomer is hardly present. 0.48 ml of a solution obtained by adding pure water and diluting 900 times was added to 50 ml of the reaction solution, and CO
The film-forming reaction liquid contains a polycarboxylic acid having an OH equivalent of about 8 μmol / ml. Example 4 0.1 g of AIBN was dissolved in 1.0 g of acrylic acid, 1 ml of pure water was added, and 0.9 g of itaconic acid was added and dissolved to heat and polymerize in a water bath, and saturated water vapor was added. After heating for 60 minutes in it, dissolve in pure water and total 30g
And COOH equivalent is about 920μ by alkali titration
It was estimated to be mol / ml. KMn0 ₄ by results in significant residual monomers detected unsaturated bond is detected,
When converted into COOH equivalents, the values were so small that they could be ignored. This is further diluted 1000 times, and 0.44 ml is added to 50 ml of the reaction solution having the above composition, and COOH or the like is added to about 8 times.
The film-forming reaction solution contains μmol / ml polycarboxylic acid. Example 5 0.05 g of AIBN was dissolved in a mixed solution of 0.1 g of methyl methacrylate and 0.6 g of acrylic acid, 1 ml of pure water was added, and the mixture was heated in a hot water bath to polymerize, and further in saturated steam.
After continuing heating for a minute, it is dissolved in pure water to a total amount of 30 g.
COOH equivalent is about 400μmol / by alkali titration
It was estimated to be ml. KMn0 ₄ was detected unsaturated bond by, but is determined residual monomer is hardly present. The reaction solution 5 was prepared by adding pure water and diluting it 500 times.
Add 0.5 ml to 0 ml, COOH equivalent is about 8 μm
The film-forming reaction solution contains ol / ml of polycarboxylic acid. Example 6 Polyacrylic acids having different degrees of polymerization were prepared by varying the amount of the polymerization initiator in the range of up to 30 times the acrylic acid / AIBN ratio in Example 2, and each had a COOH equivalent of about 8 μm.
A film forming reaction solution containing mol / ml of polycarboxylic acid was prepared. As described above, the glass plate pretreated as described above using the film-forming reaction solutions of Examples 1 to 6 was placed and
A thermal hydrolysis reaction was carried out by heating in a water bath at 0 ° C. In each case, the liquid did not become turbid, and a gloss appeared on the surface of the glass plate in about 10 to 12 minutes, and a completely transparent titanium dioxide optical thin film showing a yellow interference color was obtained in about 30 minutes. If the reaction is further continued, the interference colors of pink, purple, blue, and green appear as the thin film grows.
Similar to the description in No. 2039, but the liquid remained transparent until the end. All the above examples can be directly applied to glass or ceramics of any shape and size. For example, it is possible to easily form a desired iris film on the surface of a ceramic having a surface with a complicated uneven pattern, the surface of a glass work having a three-dimensional shape, or the inner surface of a glass bulb or a glass bottle by the same procedure. Example 7 A letter was written on a clean glass plate with a pretreatment stock solution prepared by dissolving stannic chloride in the water-soluble titanium ester, and the mixture was baked at 360 ° C., and the reaction was carried out for about 2 hours with the composition of Example 1. As a result of continuing, a green iris color character appeared on a colorless transparent background, and the liquid was kept transparent. Comparative Example 1 A similar reaction was carried out using a film-forming reaction solution containing no polycarboxylic acid, but the reaction solution gradually became cloudy as the gloss was developed, and after 30 minutes the solution became completely opaque, and the formed dioxide was generated. Fogging was observed in the titanium thin film. Comparative Example 2 Instead of polycarboxylic acid, a simple carboxylic acid, that is, tartaric acid, citric acid, lactic acid, succinic acid, acetic acid, oxalic acid,
A similar reaction was carried out using a film-forming reaction solution in which organic acids such as phthalic acid, maleic acid, glycolic acid, and ethylenediaminetetraacetic acid were added in various proportions, but without disturbing the formation of a titanium dioxide thin film. The turbidity of the liquid could not be prevented. Comparative Example 3 Writing letters on the glass surface with an aqueous solution of stannic chloride, 360
After baking at 0 ° C. and continuing the reaction with the composition of Example 1 for 30 minutes, a glossy film of titanium dioxide was formed around the characters, but the liquid became translucent and turbid. .. Comparative Example 4 3 ml of 50% sulfuric acid and 1 drop of an aqueous solution of titanium tetrachloride having a concentration of 3.5 mol (about 0.05 m in a 100 ml volumetric flask).
1) was added and the pretreated glass plate was treated in a solution made up to 100 ml with pure water. The titanium dioxide film obtained was clearly inferior in gloss to those of Examples 1 to 6, The iris effect was also insufficient. On the other hand, when the silver-white titanium dioxide film formed in Example 1 was treated with the same solution, clear interference colors of yellow, pink, purple, blue, and green were developed depending on the treatment time, and it was strong. It was accompanied by luster.

[0010]

As described above, according to the present invention, by the thermal hydrolysis reaction of titanium tetrachloride, which is a homogeneous reaction in an aqueous solution, titanium dioxide and tin oxide are retained in the presence of polycarboxylic acid while maintaining the transparency of the liquid. Since the crystal growth of titanium dioxide is carried out on the surface coated with the mixed oxide film, there is no problem of liquid pooling in the recesses, which is unavoidable by the coating method, even if the shape of the object surface is uneven. Further, unlike the case of diffusion vacuum deposition, it can be easily formed on a surface close to a closed curved surface such as the inner surface of a glass bottle. Therefore, according to the present invention, a completely transparent rutile titanium dioxide optical thin film having a uniform thickness and an arbitrary thickness is formed on a surface of a wide range of objects made of a wide range of materials such as glass, ceramics and plastics, and its size is substantially limited. It can be easily formed without the need for a vacuum device and has high reproducibility. As described above, the method of the present invention does not require expensive equipment and is industrially advantageous, and since it can be carried out with a simple chemical experiment tool, it can be applied as a hobby craft. Also, since there is no precipitation, the titanium in the solution is consumed only for the growth of the titanium dioxide film, so that a significantly higher growth rate can be obtained than in the case of Japanese Patent No. 1432039. Since the reaction solution is kept transparent, it is easy to visually observe the growth of the thin film using a transparent reaction container, and thus the film thickness can be easily controlled. Once the glossy film is formed, the rutile titanium dioxide optical thin film grows while maintaining its crystalline form even if the reaction solution is switched to sulfuric acid-acidified one and continues to grow. Does not have to be a problem. In this way, it is possible to easily form a uniform iris film on the inner surface of a glass container having a complicated shape, and thus it is possible to obtain a new decorative effect that cannot be realized by the vapor deposition method or the coating method. For example, the decorative iris color light ray reflector disclosed in JP-A-3-12830 can be easily realized. Open to the public 6
By combining the method for forming a silicate film disclosed in 3--14877, it is possible to easily achieve the formation of a multilayer film having more excellent saturation.

Claims (1)

[Claims] 1. A thermal hydrolysis reaction is carried out by heating an object having a surface coated with a film of a mixed oxide containing titanium dioxide and tin oxide in the presence of polycarboxylic acid in an acidic aqueous solution of titanium tetrachloride in hydrochloric acid. By a thermal hydrolysis reaction of a strongly acidic tetravalent titanium salt aqueous solution, characterized in that it comprises an initial film-forming step of depositing titanium dioxide generated by the method on the coated surface to form a glossy thin film of rutile-type titanium dioxide. Method for forming titanium dioxide optical thin film.