JPH05302173A - Hydrophilic coating film and method for forming the same - Google Patents

Abstract

PURPOSE:To provide a coating film capable of keeping hydrophilicity and corrosion resistance for a long term by applying a solution containing an alkoxide of silicon and an inorganic material having a prescribed particle diameter on a substrate and firing. CONSTITUTION:The alkoxide of silicon (e.g. tetraethoxysilane, tetraisopropoxysilane or the like) and the inorganic material (selected from titanium dioxide, chromium oxide or iron oxide) having <=5mum average particle diameter are prepared. A mixture of solution obtained by dissolving the alkoxide of silicon in an organic solvent such as alcohols with the inorganic material is applied on the surface of the substrate and fired. And the hydrophilic coating film containing the inorganic material having <=5mum average particle diameter and silica is obtained. The coating film is used for a fin in the evaporator of the heat exchanger of an air conditioner or the like.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a metal base material used for fins and the like in evaporators of heat exchangers such as room air conditioners and car air conditioners, and in particular hydrophilicity that maintains corrosion resistance and hydrophilicity for a long period of time. Regarding coating.

[0002]

2. Description of the Related Art Generally, in heat exchangers, particularly evaporators of air conditioners, the surface temperature of the fins is below the dew point of the atmosphere, so that water is condensed on the surfaces of the fins. Such adhesion of water causes various problems such as a decrease in heat exchange performance due to an increase in flow resistance of heat-exchanged air, generation of noise due to air blowing, and water droplet scattering. ..

[0003] For the purpose of solving these problems, it is common practice to impart hydrophilicity to the surface of the fins to improve the flow of adhering water to prevent the air passage from being blocked. There is. For example, in JP-A-50-38645, the surface of aluminum is dipped in a solution containing an alkali metal carbonate and an alkali metal chromate to be coated, and further an alkali metal oxide and silicon dioxide are contained. A method of dipping in a solution to form a continuous, rough, porous and hydrophilic coating on an aluminum surface is disclosed.

Japanese Patent Application Laid-Open No. 62-235477 discloses that
A method of forming a hydrophilic film by coating the surface of aluminum with a solution containing an alkali metal silicate, an inorganic curing agent, and a water-soluble organic polymer compound is disclosed.

Japanese Patent Application Laid-Open No. 62-272099 discloses that
A method of imparting hydrophilicity by immersing the surface of a part made of aluminum in an aqueous medium containing a compound having a silanol group and polyvinylpyrrolidone is disclosed.

In JP-A-1-208475, a chromate treatment is applied, and then an aqueous solution of an alkali metal silicate containing orthophosphoric acid is applied, and then an orthophosphoric acid solution is applied, followed by heating and drying. A method for forming a hydrophilic coating by the above is disclosed.

As described above, the specific methods described in the published patent specifications have been clarified. However, all of the methods use the affinity of the alkali metal silicate with water as a fundamental principle, and are required for practical use. In order to improve the durability of the coating film, it can be said that the durability is improved by adding an inorganic curing agent or an organic polymer component. At the same time, it has also been attempted to make the surface of the substrate porous in advance to enhance the adhesion between the hydrophilic film and the substrate.

The hydrophilicity imparted by utilizing the characteristics of the alkali metal silicate has achieved its purpose sufficiently and is widely used in practice.
However, if such a hydrophilic coating is kept in contact with water for a long time, the portion of the coating that exhibits the hydrophilic function disappears due to the excellent solubility of the alkali metal silicate in water. This can cause problems. In addition, when used in a highly closed space such as a car air conditioner, carbon dioxide or organic substances contained in the breath of the human body reacts with alkali metal silicates to cause changes in the membrane due to the formation of carbonates or organic decomposition products. It is also a problem to generate an offensive odor. Further, in the case where the organic polymer compound is used as a part of the constituent material of the coating film, although it is not exposed to such a high temperature under normal use conditions, there is concern about the heat resistance for a long period of time.

[0009]

In order to solve the above-mentioned problems, the present inventors did not use an organic compound as a constituent material of a coating film, and the hydrophilicity thereof does not substantially change for a long period of time. As a result of extensive studies on a method of forming a coating on a metal surface, a coating containing an inorganic substance having an average particle size of 5 μm or less and at least silica has hydrophilicity required for practical use and severe conditions such as heating water. In the present invention, they have found that they are stable for a long time, and have reached the present invention.

That is, the present invention is a hydrophilic coating containing an inorganic substance having an average particle size of 5 μm or less and at least silica, and is applicable to an inorganic substance having an average particle size of 5 μm or less and at least an organic solvent such as alcohols. A solution of a soluble silicon oxide or an alkoxide of silicon dissolved in an organic solvent or a hydrolyzate thereof is applied to a substrate and dried,
It is a method for forming a hydrophilic coating film containing an inorganic substance having an average particle diameter of 5 μm or less and at least silica by firing.

By the way, applying a metal alkoxide to the surface of a base material and baking it has been variously studied for various purposes, and has been utilized for various purposes. Seems to be similar to the method described in (1), but also has the completely opposite purpose, that is, the purpose of imparting antifouling property by making the surface of the substrate hydrophobic. Therefore, in the present invention, it is necessary to use a film-forming solution having a specific composition containing a metal alkoxide, which is an inorganic substance having an average particle size of 5 μm or less and at least a soluble silicon that can be silica when fired. Or it must be a mixture containing a silicon alkoxide.

The coatings of the present invention do not use alkali metal silicates, of course, nor alkali metals, and do not suffer from long term stability in water due to their elution. The coating film of the present invention is a hydrophilic film having high mechanical strength, porosity, and long-term stability. It is recognized that the surface of the coating film is covered with fine irregularities as shown in FIG. 1, and it is considered that these irregularities are involved in the development of hydrophilicity. However, only the unevenness due to the fine particles observed in FIG. 1 does not contribute to the hydrophilicity of the present invention, but rather, finer pores or cracks which are difficult to confirm in FIG. 1 are hydrophilic. It is considered to be the main cause. The cause of the generation of these fine pores is not clear, but the solid component does not shrink even though the silica component shrinks when the film is formed by firing, so that the film is formed while leaving partial stress. In addition, it is considered that such fine pores are generated on the surface with a large density.

In a porous material having pores, water permeates inside due to its own surface tension, and the macro has a low contact angle when a liquid is brought into contact with the surface, or a water droplet is dropped on the surface. It is observed that it shows hydrophilicity as a spread. The coating film of the present invention exhibits hydrophilicity due to such a mechanism and, at the same time, has hydrophilicity mainly due to the surface energy of the film itself mainly made of silicon.

The composition of the inorganic substance having an average particle size of 5 μm or less in the present invention is preferably 3 to 40 wt%, and more preferably 10 to 30 wt%. Here, wt% of each component is defined as wt% when all components are oxides. When it is 3 wt% or less, the film does not form sufficient unevenness and the fine pores described above, and does not exhibit desired hydrophilicity, and when it is 40 wt% or more, the strength of the film becomes low and the particles come off. Therefore, it is not preferable in handling.

The average particle diameter of the solid content in the present invention is 5
The inorganic substance having a particle size of μm or less may be any substance that does not exhibit substantially solubility in alcohol or water.
Calcium carbonate, TiO ₂ (rutile, anatase), rouge, α-iron oxide, γ-iron oxide, magnetite, chromium oxide, manganese dioxide, mineral fast yellow, naples yellow, cadmium red, cadmopone, barium sulfate, zinc oxide, lithopone. Pigments such as, mica, silica particles, alumina, talc, SiC, Si ₃ N ₄ , BN, T
Ceramic fine particles such as iN, SiC, Si ₃ N ₄ , B
Fibrous substances such as N ceramic whiskers, asbestos, glass wool, quartz wool, alumina wool, silica-alumina wool, potassium titanate, and the like can be used, and finely divided pigments are preferable. The distribution of the particle size of the fine particles does not have to be particularly narrow, and it is preferable that the distribution is as wide as 0.05 to 5 μm. In the case of a fibrous substance, the diameter is preferably about 0.05 to 5 μm, and the length is preferably 100 μm or less.

The raw materials of the components other than the solid content used for forming the coating film of the present invention may be metal compounds capable of forming oxides substantially by firing treatment, such as Si, Al,
Compounds such as Zr, Pb, Zn, Fe, B, Ti, Sn, etc., and generally, chlorides, oxychlorides, nitrates, sulfates, organic acid salts, hydroxides, alkoxy compounds or the like of the metal. These hydrates or hydrolysates are mentioned. 2 selected from these and other metals
It is also possible to use more than one species at the same time. Specific compounds are listed below for the main metals, but similar compounds can be generally used for other metals.

The alkoxide of silicon in the present invention has the general formula Si (OR ¹ ) (OR ² ) (OR ³ ) (OR ⁴ ), S
iCl (OR ¹ ) (OR ² ) (OR ³ ), SiCl ₂ (OR
¹ ) (OR ² ) or SiCl ₃ (OR ¹ ) (wherein R ¹ , R ² , R ³ and R ⁴ are methyl group, ethyl group, normal propyl group, isopropyl group, normal butyl group, secondary butyl group) , A methoxyethyl group, an ethoxyethyl group or a phenyl group), or a hydrolyzate thereof, particularly tetraethoxysilane, tetramethoxysilane, tetraisopropoxysilane, tetranormal Propoxysilane, tetranormalbutoxysilane, tetratertiarybutoxysilane and the like or hydrolysates thereof are preferred.

The silicon oxide soluble in organic solvents such as alcohols in the present invention is generally known as colloidal silica, but when dissolved in alcohols, it is dissolved or uniformly dispersed. Anything can be used.

Al source materials AlCl ₃ , Al ₂ (SO ₄ )
Al such as ₃ , Al (NO ₃ ) ₃ , aluminum laurate, aluminum stearate, and aluminum naphthenate
Salt or hydrous salt thereof, or polyaluminum chloride, hydroxide of Al such as boehmite, or general formula Al (OR ¹ ) (OR ² ) (OR ³ ), AlCl (OR ¹ ) (
OR ² ), AlCl ₂ (OR ¹ ) (wherein R ¹ , R ² ,
R ³ represents any of a methyl group, an ethyl group, an isopropyl group, a normal butyl group, a secondary butyl group, a methoxyethyl group, an ethoxyethyl group or a phenyl group. )
Alkoxy compounds represented by, especially triethoxy aluminum, triisopropoxy aluminum, trinormal propoxy aluminum, tri-secondary butyl aluminum, chlorodiisopropoxy aluminum, chlorodisecondary butyl aluminum, dichloroisopropoxy aluminum, dichlorosecondary butyl Aluminum etc. are mentioned.

Ti source materials such as TiCl ₄ and TiO Cl
Ti salts such as ₂ , Ti (NO ₃ ) ₄ and TiO (NO ₃ ) ₂ or their hydrated salts, or the general formula Ti (OR ¹ ) (OR
² ) (OR ³ ) (OR ⁴ ), TiCl (OR ¹ ) (OR ² ) (OR
³ ), TiCl ₂ (OR ¹ ) (OR ² ), or TiCl ₃ (OR ¹ ).
(In the formula, R ¹ and R ² are a methyl group, an ethyl group, a normal propyl group, an isopropyl group, a normal butyl group,
A secondary butyl group, a methoxyethyl group, an ethoxyethyl group, or a phenyl group is shown. Among the alkoxy compounds represented by), tetraethoxy titanium, tetranormal propoxy titanium, tetraisopropoxy titanium, tetranormal butoxy titanium, chlorotriethoxy titanium, dichlorodinormal butoxy titanium, trichloro normal butoxy titanium, etc. or dibutoxy titanium acetyl. Examples include acetonate and isopropoxydititanium octylene glycolate.

ZrCl is used as a Zr raw material._Four, ZrO
Cl₂ , Zr (NO₃)_Four , ZrO (NO₃)₂, Stearin
Zirconium acid, zirconium naphthenate, 2-ethyl
Zirconium hexanoate, zirconium acetylaceto
Zr salt such as nato or hydrous salt thereof, or general
Formula Zr (OR¹) (OR²) (OR³) (OR^Four), ZrCl
(OR¹) (OR²) (OR³), ZrCl₂(OR¹) (OR²)
Or ZrCl₃(OR ¹) (However, in the formula R¹ , R² Hame
Cyl group, ethyl group, normal propyl group, isopropyl
Group, normal butyl group, secondary butyl group, methoxy
Any of ethyl group, ethoxyethyl group or phenyl group
Indicates ) Among the alkoxy compounds represented by
Laethoxyzirconium, tetra-normal propoxydi
Ruconium, tetraisopropoxyzirconium, Tet
Rannormal butoxy zirconium, chlorotriethoxy
Zirconium, dichlorodinormal butoxyzirconium
And trichloro normal butoxy zirconium, etc.
Be done.

In the present invention, since silicon is the main component of film formation, film-forming property, adhesion of the film to the substrate,
Although the stability of the film is excellent, it is also effective to add a compound of zinc or lead, which becomes a corresponding oxide when baked, if necessary.

The concentration of the coating chemical solution used for forming the hydrophilic film is 0. 1 as the concentration of metal other than solid content in the solution.
1 to 5 mol / l is preferable, but 0.4 to 2 mol / l
l is more preferred. If the concentration is lower than 0.1 mol / l, the film formed in one coating operation becomes thin, and the number of times of repeated coating increases, which is not preferable in practice. On the other hand, when it is higher than 5 mol / l, it is not preferable because a large crack that causes peeling may occur in the film due to choking (powder blowing phenomenon) or extreme volume contraction. However, it is not always necessary that this concentration condition be satisfied, and adjustment is possible depending on the types of additives and solvents.

Alcohols are preferably used as the solvent for adjusting the concentration, and methanol, ethanol, i-propanol, n-propanol, n-butanol, i-butanol, t-butanol, methoxyethanol, ethoxyethanol, ethylene glycol are used. And the like, and it is also possible to use a combination of two or more of these.

The thickness of the hydrophilic coating obtained at this time is 0.
1 to 10 μm is preferable, and 0.3 to 5 μm is more preferable. Since the pore volume is almost proportional to the film thickness, the film thickness is 0.1μ
A film thinner than m has an insufficient effect of imparting hydrophilicity to the metal surface, while a film thicker than 10 μm is not sufficient in the effect of generating irregularities due to fine particles, and peeling easily occurs, which is not preferable. The hydrophilic film can be formed by a single application or a plurality of times.

The chemical solution is applied onto the substrate by a dipping method, a spray method, a roller coating method, a flow coating method, a screen printing method, a brush coating method or the like. The type of metal having a hydrophilic surface is selected in consideration of usage conditions based on thermal conductivity, chemical stability, mechanical strength, etc.
Aluminum, aluminum alloy, copper, brass, stainless steel, etc. are preferable, and their shape is generally a plate shape or a hollow coil shape, but imparts hydrophilicity to a laminated or composite of various metals. Of course it is possible.

In the coating method of the present invention, it is useful to subject the surface of the substrate to various pretreatments. Mechanical polishing, electropolishing, acid cleaning, alkali cleaning, water cleaning or degreasing cleaning with an organic solvent is effective for any metal. In the case of aluminum or aluminum alloy, well-known techniques in the art, such as alumite treatment, chromate treatment or chemical conversion treatment with a phosphate such as zinc, titanium or zirconium is used for the purpose of improving corrosion resistance and adhesion of coating film. You can also do it. Further, in a range not departing from the object of the present invention, pretreatment with an organic polymer compound may be applicable in some cases.

The coating film formed by various methods has a thickness of 50-
A metal having an excellent hydrophilic surface can be obtained by drying and calcination at 200 ° C. for 5 to 30 minutes and calcining in an electric furnace at 300 ° C. or higher for 10 to 60 minutes. The upper limit of the firing temperature is not particularly limited, but for stainless steel, it is preferably about 500 ° C or lower.

The present invention will be described in more detail with reference to the following examples.

[0030]

Example 1 Into a 2 L three-necked flask equipped with a stirrer, 500 g of an ethanol solution of tetraethoxysilane at 20.0 wt% in terms of SiO ₂ (manufactured by Colcoat Co., Ltd.) was placed, and 3
About 1 cc of 5% hydrochloric acid and 50 cc of water were added, and the mixture was stirred under reflux at 50 ° C. for 3 hours. Then, with stirring, 16.7 g of rutile-type titanium oxide having an average particle size of 0.2 μm was charged, and 70% of ethanol and 3 parts of methoxyethanol were added so that the concentration of SiO ₂ became 1.0 mol / l.
A white coating solution was prepared by diluting with 0% mixed solvent of about 1100 cc.

This coating solution was placed in a 500 cc glass beaker, into which a SU of 50 × 100 × 0.2 mm was placed.
A sample piece made of S304 was charged, and then the sample piece was 4 mm /
Withdraw from the coating solution at a constant speed of sec, in air,
Dry at 70 ° C for 20 minutes, then in an electric furnace in air 1
It was calcined at 50 ° C. for 20 minutes and cooled to room temperature.

Then, the same coating and drying are repeated again, and thereafter, from 200 ° C. to 4 ° C. at a rate of 5 ° C./min.
The temperature was raised to 50 ° C., the temperature was maintained for 20 minutes, the sample was taken out of the electric furnace and allowed to cool, whereby a sample piece on which a white film was formed was obtained. A scanning electron micrograph of the surface of the coating is shown in FIG.

The following evaluation test was conducted on the coated sample to confirm the hydrophilicity and chemical stability of the film. Acid resistance test: 1% by weight in a glass 1L beaker
A hydrochloric acid solution was added, the sample was immersed therein, and left at room temperature for 24 hours. After the lapse of time, the sample was washed with running water, and the surface condition was visually observed. The evaluation is ○ when no change is observed, and × when cracks or peeling are recognized.
And the middle was marked with Δ.

Solvent resistance test: A 1 L beaker made of glass was charged with acetone, and the sample was immersed in the beaker, and the mixture was allowed to stand at room temperature for 2 hours.
It was left for 4 hours. After the lapse of time, the sample was washed with running water, and the surface condition was visually observed. In the evaluation, those showing no change were evaluated as ◯, those showing cracks or peeling were evaluated as ×, and the middle was evaluated as Δ.

Water cracking test: A sample was immersed in a beaker containing distilled water for 10 seconds and quickly pulled up to evaluate how water was cut off. The case where no wet portion was observed was marked with X, and the middle thereof was marked with Δ.

Measurement of wet spread: 5 μl of distilled water was gently dropped on the surface of the sample with a microsyringe, and the spread of the water drop after 5 seconds was measured with a caliper. In addition, in the warm water immersion test as a hydrophilicity accelerated test, for changes over time, it was immersed in distilled water at 45 ° C, taken out of the tank after a predetermined time elapsed, then dried at 80 ° C until a constant weight was obtained, and cooled to room temperature. Then, the above measurement was performed.

The results of each measurement are shown in Table 1. It is clear that the film has extremely excellent hydrophilicity as compared with the comparative example in the wet spreadability test and the water cracking test.

[0038]

[Table 1]

Example 2 In a 2 L three-necked flask equipped with a stirrer, 500 g of an ethanol solution of tetraethoxysilane of 20.0 wt% in terms of SiO ₂ was placed, and about 1 cc of 35% hydrochloric acid and 50 parts of water were added thereto.
cc was added and the mixture was stirred at 50 ° C. for 3 hours under reflux.
Then, while stirring was charged isopropanol solution 42.8g of Nissan Chemical Co., Ltd. in terms of SiO ₂ 30.0 wt% of colloidal silica, further Dainichi Seika Co. of black pigment # 9590 (CuO, Fe ₂ 8.6 g of a mixture of O, Cr ₂ O _{3 and the} like having a particle size of 0.5 to ₂ μm) was added, and the concentration of SiO ₂ and pigment was 1.0 mo.
A black coating solution was prepared by diluting the mixture with about 1300 cc of a mixed solvent of 80% ethanol and 20% isopropanol so as to be 1 / l.

This coating solution was placed in a 500 cc glass beaker, into which a SU of 50 × 100 × 0.2 mm was placed.
A sample piece made of S304 was charged, and then the sample piece was 4 mm /
Withdraw from the coating solution at a constant speed of sec, in air,
Dry at 70 ℃ for 20 minutes, then further 150 in air by electric furnace
It was calcined at 20 ° C. for 20 minutes and cooled to room temperature.

Then, the same coating and drying are repeated again, and thereafter, from 200 ° C. to 4 ° C. at a rate of 5 ° C./min.
When the temperature was raised to 50 ° C., the temperature was maintained for 20 minutes, the sample was taken out of the electric furnace and allowed to cool, a sample piece having a black coating film was obtained.

The coated sample was subjected to the same evaluation test as in Example 1 to confirm the hydrophilicity and chemical stability of the film. The results are shown in Table 1. It is clear that the film has extremely excellent hydrophilicity as compared with the comparative example in the wet spreadability test and the water cracking test.

Examples 3, 4, 5 By the same method as in Example 1, the raw materials shown in each column of Table 1,
The same table shows the results of forming a coating film using a solvent and performing the same evaluations as in Example 1. Rouge has a particle size of 0.4-0.8 μm
And Fe ₂ O ₃ was used as the component, and chromia having a particle diameter of 0.2 to 1 μm was used. In any case, it is clear that the film has extremely excellent hydrophilicity in comparison with the comparative example in the wettability and water cracking test.

Comparative Example 1 Tetraethoxysilane (manufactured by Colcoat) was adjusted to a concentration of 1.0 mol / l in a 20.0 wt% SiO ₂ equivalent ethanol solution, and a film was formed in the same manner as in Example 1. The results are shown in Table 1.

Comparative Example 2 The same film formation as in Example 1 was performed using a 1.0 mol / l aqueous solution of No. 3 silicic acid. The results are shown in Table 1.

Comparative Example 3 By the same method as in Example 1, a coating film was formed with calcium carbonate having a particle size of 5 to 10 μm as a solid content. The resulting coating peeled off easily and a stability test could not be performed.

[0047]

As is apparent from Table 1 showing the results of the examples, the coating film of the present invention has the hydrophilicity and water flowability required for condensers of heat exchangers, etc. Since it does not contain silicates or organic substances, it has the effect of exhibiting hydrophilicity that does not change its performance over a long period of time even under severe usage conditions.

[Brief description of drawings]

FIG. 1 is a scanning electron micrograph of the sample of Example 1.

─────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] March 8, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] Brief description of the drawing

[Correction method] Change

[Correction content]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a scanning electron micrograph of the thin film formed on the substrate of Example 1.

Claims (4)

[Claims] 1. A hydrophilic coating comprising an inorganic substance having an average particle size of 5 μm or less and at least silica. 2. The hydrophilic coating according to claim 1, wherein the inorganic substance is a mixture or a single substance containing at least one selected from titanium dioxide, chromium oxide and iron oxide. 3. A heat exchanger or an evaporator, wherein at least a part of the metal surface has the hydrophilic coating according to claim 1 or 2. 4. A hydrophilic coating film, characterized in that a solution containing at least an alkoxide of silicon and an inorganic substance having an average particle size of 5 μm or less is applied to the surface of a substrate and baked to form a solution. Production method.