JP3340149B2 - Hydrophilic coating and method for forming the coating - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydrophilic film which maintains corrosion resistance and hydrophilicity for a long period of time on a metal substrate used as a fin in a heat exchanger such as a room air conditioner or a car air conditioner. .

[0002]

2. Description of the Related Art Generally, in a heat exchanger, particularly in an evaporator of an air conditioner, water is condensed on the fin surface because the surface temperature of the fin becomes lower than the dew point of the atmosphere. Such adhesion of moisture causes various problems such as a decrease in heat exchange performance due to an increase in flow resistance of air to be exchanged, generation of noise due to air blowing, and scattering of water droplets. .

[0003] In order to solve these problems, it is generally practiced to impart a hydrophilic property to the surface of the fin to improve the flow of the attached water so as to prevent the air flow path from being blocked. I have. For example, JP-A-50-38645 discloses that an aluminum surface is immersed in a solution containing an alkali metal carbonate and an alkali metal chromate, coated, and further contains an alkali metal oxide and silicon dioxide. A method is disclosed for dipping in a solution to form a continuous, coarse, porous and hydrophilic coating on an aluminum surface.

[0004] Japanese Patent Application Laid-Open No. Sho 62-235777 discloses that
There is disclosed a method of forming a hydrophilic film by coating an aluminum surface with a solution containing an alkali metal silicate, an inorganic curing agent, and a water-soluble organic polymer compound.

[0005] JP-A-62-272099 describes that
A method for imparting hydrophilicity by immersing a surface of a component made of aluminum in an aqueous medium containing a compound having a silanol group and polyvinylpyrrolidone is disclosed.

JP-A-1-208475 describes that a chromate treatment is applied, 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. Accordingly, a method for forming a hydrophilic film is disclosed.

As described above, specific methods described in the specification of the published patent have been clarified. However, all of the methods are based on the affinity of the alkali metal silicate with water, which is the fundamental principle, and are practically required. In order to improve the durability of the film to be formed, it can be said that the durability is improved by adding an inorganic curing agent or an organic polymer component. At the same time, attempts have been made to enhance the adhesion between the hydrophilic film and the substrate by making the surface porous in advance.

[0008] Such hydrophilicity imparted by utilizing the properties of alkali metal silicate sufficiently fulfills its purpose and is widely used in practical use.
However, if such a hydrophilic coating is kept in contact with water for a long period of time, the portion of the coating exhibiting the hydrophilic function disappears due to the excellent solubility of the alkali metal silicate in water. May cause problems. In addition, when used in a highly enclosed space such as a car air conditioner, the film changes due to the formation of carbonates or organic decomposition products due to the reaction between the carbon dioxide gas or organic substance contained in human breath and the alkali metal silicate. It is also a problem that an unpleasant odor is caused by the odor. Further, those in which an organic polymer compound is used as a part of the constituent material of the coating film are not exposed to such a high temperature under ordinary use conditions, but remain uneasy in heat resistance over a long period of time.

[0009]

Means for Solving the Problems In order to solve the above-mentioned problems, the present inventors did not use an organic compound as a constituent material of a film and did not substantially change its hydrophilicity over a long period of time. After extensive studies on the method of forming a coating on a metal surface, a coating comprising an inorganic substance having an average particle diameter of 5 μm or less and at least silica is required to have hydrophilicity necessary for practical use and severe conditions, for example, heating water. The present invention was also found to be stable over a long period of time.

That is, the present invention provides a silica coating having a thickness of 0.1 to 10 μm formed on the outermost surface of a substrate,
The silica coating is formed from a solution in which an alkoxide of silicon is dissolved in an organic solvent or a hydrolyzate thereof or a solution in which silicon oxide soluble in an organic solvent is dissolved in an organic solvent or a hydrolyzate thereof, and Average particle size 5μ
m is 3 to 40% by weight of an inorganic substance, and is a hydrophilic silica coating characterized by having fine pores or cracks as well as irregularities caused by the inorganic substance on the surface of the silica coating.

By the way, the application of a metal alkoxide to the surface of a substrate and sintering have been conventionally studied for various purposes and utilized for various purposes. However, there is also a method which is completely opposite to the above-mentioned method, that is, has a purpose of imparting an 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 composed of an inorganic substance having an average particle diameter of 5 μm or less, and at least soluble silicon which can become silica when calcined. Or a mixture containing a silicon alkoxide.

The coatings of the present invention do not use alkali metals as well as alkali metal silicates and do not suffer from long-term lack of stability in water due to their dissolution. The coating of the present invention is a hydrophilic coating having high mechanical strength, being porous, and capable of maintaining long-term stability. It was recognized that the surface of the coating was covered with fine irregularities as shown in FIG. 1, and it is considered that these irregularities contributed to the development of hydrophilicity. However, not only the irregularities caused by the fine particles observed in FIG. 1 do not contribute to the hydrophilicity of the present invention, but rather finer pores or cracks which are difficult to confirm in FIG. Probable cause. Although the cause of the generation of these fine pores is not clear, since the silica component shrinks when the film is formed by firing, the solid content does not shrink, so that the film is formed while partially leaving a stress. In addition, it is considered that such fine pores are generated at a large density on the surface.

In a porous substance having pores, water penetrates into the interior due to its own surface tension, and macroscopically, the contact angle is low when a liquid is brought into contact with the surface, or water drops are dropped on the surface. It is observed that it shows hydrophilicity as the time spread. The film of the present invention exhibits hydrophilicity due to such a mechanism and, at the same time, has hydrophilicity due to the surface energy of the film itself mainly composed of silicon.

In the present invention, the composition of the inorganic substance having an average particle diameter of 5 μm or less in the coating is preferably 3 to 40% by weight, more preferably 10 to 30% by weight. Here, the wt% of each component is the weight% when all the components are converted to oxides. When the content is 3 wt% or less, the film does not form sufficient unevenness and the above-mentioned fine pores, does not exhibit desirable hydrophilicity, and when the content is 40 wt% or more, the strength of the film is reduced and particles are peeled off. Therefore, it is not preferable in handling.

In the present invention, the average particle diameter of the solid content of 5
The inorganic substance having a particle size of μm or less may be any substance that does not substantially exhibit solubility in alcohol or water.
Calcium carbonate, TiO ₂ (rutile, anatase), petiole, α-iron oxide, γ-iron oxide, magnetite, chromium oxide, manganese dioxide, mineral fast yellow, naples yellow, cadmium red, cadmopon, barium sulfate, zinc oxide, lithopone Such as pigments, mica, silica particles, alumina, talc, SiC, Si ₃ N ₄ , BN, T
Ceramic fine particles such as iN, SiC, Si ₃ N ₄ , B
N-type ceramic whiskers, asbestos, glass wool, quartz wool, alumina wool, silica alumina wool, fibrous substances such as potassium titanate, and mixtures thereof can be used, and finely divided pigments are preferred. The distribution of the particle diameter of the fine particles does not need to be particularly narrow, and it is more preferable that the distribution is as wide as about 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 material of the components other than the solid content used to form the coating of the present invention may be a metal compound which can substantially form an oxide by a baking treatment.
Compounds such as Zr, Pb, Zn, Fe, B, Ti, and Sn, 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 simultaneously. Specific compounds for the main metals are listed below, but similar compounds can be generally used for other metals.

The alkoxide of silicon in the present invention is represented by 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 ) (where R ¹ , R ² , R ³ , R ⁴ 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.) Or a hydrolyzate thereof, particularly tetraethoxysilane, tetramethoxysilane, tetraisopropoxysilane, tetranormal Propoxy silane, tetra-n-butoxy silane, tetra-tertiary-butoxy silane, or the like or a hydrolyzate thereof is 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 should do.

AlCl ₃ , Al ₂ (SO ₄ )
₃ , Al (NO ₃ ) ₃ , aluminum such as aluminum laurate, aluminum stearate, aluminum naphthenate, etc.
Salt thereof, or a hydrate salt or poly aluminum chloride, hydroxides of Al, such as boehmite or the general formula ^{Al, (OR 1) (OR} 2) (OR 3), AlCl (OR 1) (
OR ² ), AlCl ₂ (OR ¹ ) (where R ¹ , R ² ,
R ³ represents any one of a methyl group, an ethyl group, an isopropyl group, a normal butyl group, a secondary butyl group, a methoxyethyl group, an ethoxyethyl group and a phenyl group. )
In particular, an alkoxy compound represented by triethoxyaluminum, triisopropoxyaluminum, trinormal propoxyaluminum, trisecondary butylaluminum, chlorodiisopropoxyaluminum, chlorodisecondarybutylaluminum, dichloroisopropoxyaluminum, dichlorosecondarybutyl Aluminum and the like can be mentioned.

TiCl ₄ , TiO Cl
₂ , Ti (NO ₃ ) ₄ , TiO (NO ₃ ) _2, etc., or a hydrated salt thereof, or a 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 )
(Wherein R ¹ and R ² represent a methyl group, an ethyl group, a normal propyl group, an isopropyl group, a normal butyl group,
Shows any of a secondary butyl group, a methoxyethyl group, an ethoxyethyl group and a phenyl group. Among the alkoxy compounds represented by), tetraethoxytitanium, tetranormalpropoxytitanium, tetraisopropoxytitanium, tetranormalbutoxytitanium, chlorotriethoxytitanium, dichlorodinorbutoxytitanium, trichloronormalbutoxytitanium, etc. or dibutoxytitanium acetyl Examples include acetonate and isopropoxydititanium octylene glycolate.

As a Zr raw material, ZrCl is used._Four, ZrO
Cl_Two , Zr (NO_Three)_Four , ZrO (NO_Three)_Two, Stearin
Zirconium, zirconium naphthenate, 2-ethyl
Zirconium hexanoate, zirconium acetylacetate
Zr salts such as nath or their hydrated salts, or general
The expression Zr (OR¹) (OR^Two) (OR^Three) (OR^Four), ZrCl
(OR¹) (OR^Two) (OR^Three), ZrCl_Two(OR¹) (OR^Two)
Or ZrCl_Three(OR ¹) (Where R¹ , R^Two Hame
Tyl group, ethyl group, normal propyl group, isopropyl
Group, normal butyl group, secondary butyl group, methoxy
Either an ethyl group, an ethoxyethyl group or a phenyl group
Indicates Of the alkoxy compounds represented by
Laethoxyzirconium, tetranormal propoxydi
Ruconium, tetraisopropoxy zirconium, tet
Lanomaltoxy zirconium, chlorotriethoxy
Zirconium, dichlorodinalbutoxyzirconium
And trichloronormal butoxyzirconium
Can be

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

The concentration of the coating solution used for forming the hydrophilic film is 0.1% as the concentration of metals other than solids in the solution.
1-5 mol / l is preferred, but 0.4-2 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 required for repeated coating increases, which is not practically preferable. On the other hand, when it is higher than 5 mol / l, it is not preferable because a large crack may be generated in the film due to chalking (powder phenomena) or extreme volume shrinkage, which may cause peeling. However, the concentration condition does not always have to be the same, and adjustment can be made depending on the types of additives and solvents.

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

The thickness of the hydrophilic film obtained at this time is 0.1 mm.
It is preferably from 1 to 10 μm, more preferably from 0.3 to 5 μm. Since the pore volume is almost proportional to the film thickness,
When the film is thinner than m, the effect of imparting hydrophilicity to the metal surface is not sufficient. On the other hand, when the film is thicker than 10 μm, the effect of generating irregularities due to the fine particles is not sufficient, and peeling tends to occur, which is not preferable. The hydrophilic film can be formed by one application or a plurality of applications.

The application of the chemical solution onto the substrate is performed by a method such as a dipping method, a spray method, a roller coating method, a flow coating method, a screen printing method, or a brush coating method. The type of metal having a hydrophilic surface is selected in consideration of use conditions based on thermal conductivity, chemical stability, mechanical strength, etc.
Aluminum, aluminum alloys, copper, brass, stainless steel, etc. are preferred, and their shapes are generally plate-like or hollow coil-like, but they impart hydrophilicity to laminated or composite materials of various metals. Of course it is also possible.

In the coating method of the present invention, it is useful to perform various pretreatments on the surface of the substrate. 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, alumite treatment, chromate treatment, or chemical conversion treatment with a phosphate such as zinc, titanium, zirconium, etc., which are well known in the art, are used for the purpose of improving corrosion resistance and coating adhesion. You can also. Further, pretreatment with an organic polymer compound may be applicable in some cases without departing from the object of the present invention.

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

Hereinafter, the present invention will be described in more detail with reference to Examples.

[0030]

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

This coating solution was placed in a 500 cc glass beaker, and 50 × 100 × 0.2 mm SU was poured into the beaker.
A sample piece made of S304 is charged, and then the sample piece is 4 mm /
withdraw from the coating solution at a constant speed of
After drying at 70 ° C for 20 minutes,
It was calcined at 50 ° C. for 20 minutes and cooled to room temperature.

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

The following evaluation test was performed on the coated sample, and the hydrophilicity and chemical stability of the film were confirmed. Acid resistance test: 1% by weight in a glass 1L beaker
The sample was immersed in the hydrochloric acid solution, and left at room temperature for 24 hours. After a lapse of time, the sample was washed with running water, and the surface state was visually observed. The evaluation was as follows: ○: no change was observed, ×: crack or peeling was observed.
, And the middle was △.

Solvent resistance test: Acetone was placed in a glass 1L beaker, and the sample was immersed in the beaker.
Left for 4 hours. After a lapse of time, the sample was washed with running water, and the surface state was visually observed. In the evaluation, ○ indicates no change, X indicates cracks or peeling, and △ indicates the middle.

Water cracking test: The sample was immersed in a beaker containing distilled water for 10 seconds, and the water was removed immediately when the sample was pulled up. The case where no wet part was observed was evaluated as x, and the middle was evaluated as 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 the warm water immersion test as an accelerated hydrophilicity test, a change with time was immersed in distilled water at 45 ° C., taken out of the tank after a lapse of a predetermined time, then dried at 80 ° C. until a constant weight was obtained, and cooled to room temperature. Then, the above measurement was performed.

Table 1 shows the measurement results. It is clear that the coating has extremely superior hydrophilicity in comparison with the comparative example in the wet spreading property and the water cracking test.

[0038]

[Table 1]

Example 2 A 2L three-necked flask equipped with a stirrer was charged with 500 g of an ethanol solution of 20.0 wt% of tetraethoxysilane in terms of SiO ₂ , and about 1 cc of 35% hydrochloric acid and 50 ml of water.
cc was added and the mixture was stirred under reflux at 50 ° C. for 3 hours.
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 O, Cr ₂ O ₃ mixture having a particle size of 0.5~2μm such) was 8.6g turned further SiO ₂ and the concentration of the pigment it 1.0mo
The mixture was diluted with about 1300 cc of a mixed solvent of 80% ethanol and 20% isopropanol so as to be 1 / l to prepare a black coating solution.

This coating solution was placed in a 500 cc glass beaker, and 50 × 100 × 0.2 mm SU was poured into the beaker.
A sample piece made of S304 is charged, and then the sample piece is 4 mm /
withdraw from the coating solution at a constant speed of
After drying at 70 ° C for 20 minutes, furthermore,
Temporarily baked at 20 ° C. for 20 minutes and cooled to room temperature.

Then, the same coating and drying are repeated again, and thereafter, the temperature is further increased from 200 ° C. to 4 ° C. at a rate of 5 ° C./min.
The temperature was raised to 50 ° C., held for 20 minutes, taken out of the electric furnace, and allowed to cool, whereby a sample piece having a black film formed thereon 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 coating has extremely superior hydrophilicity in comparison with the comparative example in the wet spreading property and the water cracking test.

Examples 3, 4, 5 In the same manner as in Example 1, the starting materials shown in each column of Table 1 were prepared.
A coating was formed using a solvent, and the same evaluation as in Example 1 was performed. The results are shown in the same table. The petiole has a particle diameter of 0.4-0.8 μm
The component was regarded as Fe ₂ O _3, and chromia having a particle diameter of 0.2 to 1 μm was used. In each case, it is clear that the coating has extremely excellent hydrophilicity in comparison with the comparative example in the wet spreading property and the water cracking test.

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

Comparative Example 2 A coating was formed in the same manner as in Example 1 by using a 1.0 mol / l aqueous solution of No. 3 silicate. The results are shown in Table 1.

Comparative Example 3 A coating was formed in the same manner as in Example 1 except that calcium carbonate having a particle size of 5 to 10 μm was used as a solid content. The resulting coating was easily peeled off and could not be tested for stability.

[0047]

As is clear from Table 1 showing the results of the examples, the coating of the present invention has hydrophilicity and water flowability required for a condenser of a heat exchanger and the like. Since it does not contain silicates or organic substances, it has the effect of exhibiting hydrophilicity whose performance does not change over a long period of time even under severe use conditions.

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

Continuation of front page (56) References JP-A-63-171883 (JP, A) JP-A-3-42238 (JP, A) JP-A-61-91042 (JP, A) JP-A-4-309557 (JP) , A) (58) Field surveyed (Int. Cl. ⁷ , DB name) C23C 18/02 B05D 5/04 F28F 1/12

Claims (4)

(57) [Claims] A thickness of 0.1 formed on the outermost surface of a substrate
A silica coating having a mean particle size of 5 μm or less in the silica coating, which is formed from a solution in which an alkoxide of silicon is dissolved in an organic solvent or a hydrolyzate thereof. %, And having fine pores or cracks together with irregularities caused by an inorganic substance on the surface of the silica coating. 2. A thickness of 0.1 formed on the outermost surface of the substrate.
A silica coating having a mean particle size of 5 μm or less, wherein the silica coating is formed from a solution in which silicon oxide soluble in an organic solvent is dissolved in an organic solvent or a hydrolyzate thereof. A hydrophilic silica coating containing a substance in an amount of 3 to 40% by weight and having fine pores or cracks as well as irregularities caused by an inorganic substance on the surface of the silica coating. 3. An inorganic substance having a diameter of 0.05 to 5 μm and a length of
3. The hydrophilic silica coating according to claim 1, wherein the coating is a fibrous substance having a size of 100 μm or less . 4. A heat exchanger or an evaporator, wherein at least a part of a metal surface has the hydrophilic silica coating according to claim 1.