JP6044827B2 - Method for producing metal product having fluororesin coating - Google Patents

Description

  The present invention relates to a method for producing a metal product having a fluororesin coating on the surface, and is obtained by coating the fluororesin coating on a metal substrate of a cooking container such as a rice cooker, a heat retaining jar, or a mochi rice cooker. The present invention relates to a method for manufacturing a metal product.

  Conventionally, containers such as a pot for an electromagnetic heating rice cooker and a pot for an electromagnetic cooker used for an electromagnetic heating cooker are made of a magnetic metal plate such as iron or stainless steel that has a heat generation function and an aluminum or aluminum alloy plate that has a heat conduction function. It is manufactured by press molding such as deep drawing with a composite material (aluminum plate) as a base material and an aluminum plate as an inner side. On the outer surface side of the aluminum plate, a water-repellent fluororesin coating is used to prevent sticking (non-adhesive) of cooked rice and other cooked food in the container, to prevent contamination of the inner surface, and to prevent rust, etc. Forming on the inner surface is performed.

In the case of the inner pot of a rice cooker, washing of the rice may be performed in the inner pot, so that the fluororesin coating has few coating film defects such as pinholes, and the adhesion of the coating to the metal substrate is sufficient. It is required to be.
However, although the fluororesin is excellent in non-adhesiveness, chemical resistance, heat resistance, etc., it has been difficult to paint the fluororesin directly on the metal surface because of its low affinity with other substances.

  For this reason, conventionally, in order to improve the adhesion between the metal surface and the fluororesin coating layer, the metal surface is subjected to a surface roughening treatment such as electrolytic etching treatment or sand blast treatment, and then a water-based paint in which the fluororesin is dispersed is applied. After that, it is baked to form a fluororesin film (see Patent Documents 1 to 3).

  Further, in Patent Document 4, since aluminum has poor etching properties, a large number of deep pits are generated on the etched surface. When a tetrafluoroethylene resin dispersion is applied to this and dried and baked, the resin thickness around the pits is reduced. In consideration of the fact that it becomes small and pinholes are likely to occur, after etching the surface of aluminum or aluminum alloy, after applying a fluororesin dispersion and drying or sintering, an inorganic pigment is contained as a second layer thereon It is described that the provision of a fluororesin layer drastically reduces pinholes on the resin surface and improves the corrosion resistance of materials with poor etching properties.

However, as described in Patent Document 4, the etching method requires a ground treatment in order to eliminate pinholes, resulting in an increase in the number of processes.
Further, the sandblast method requires a large apparatus, and it is not easy to uniformly roughen the surface of the metal substrate.

Japanese Patent Laid-Open No. 06-015465 Japanese Patent Laid-Open No. 9-237777 Japanese Patent Laid-Open No. 10-7773 Japanese Patent No. 2861172

  In view of the above problems, the present invention provides a method for producing a metal product having a surface of a metal substrate that is roughened without using an etching method or a sandblasting method, and having a fluororesin coating having excellent adhesion on the surface of the metal substrate. The purpose is to provide.

This invention is a manufacturing method of a metal product including the process of forming the film containing a fluororesin as described below.
(1) forming an aluminum film on a metal substrate by electroplating;
Forming a coating film using a fluororesin-containing paste on the aluminum film;
Drying the coating film;
After drying the coating film, baking the coating film to form a fluororesin film;
I have a,
The electrolytic solution used in the electroplating method comprises a molten salt added such that 1,10-phenanthroline is 0.2 g / L or more and 0.5 g / L or less as an additive.
A method for producing a metal product having a fluororesin coating.
With the configuration (1), a metal product having a fluororesin film having excellent adhesion on the surface of the metal substrate can be produced.
(2) The surface roughness of the surface of the aluminum film formed by electroplating is a metal having the fluororesin coating according to (1) having an arithmetic average roughness (Ra) of 0.1 to 1.0 μm. Product manufacturing method.
With the configuration (2), the aluminum film formed by the electroplating method has a rough surface, so that the adhesion between the metal material surface and the fluororesin film is improved.
(3) The method for producing a metal product having the fluororesin coating according to (1) or (2), wherein the metal substrate is made of one selected from the group consisting of iron, stainless steel, copper or aluminum.
With the configuration (3) above, it is possible to manufacture a metal product such as a cooking container for cooking.
(4) The metal substrate is a bonding material made of plate-shaped iron, stainless steel, or copper and plate-shaped aluminum, and an aluminum film is formed on the aluminum side of the bonding material by electroplating (1). Or the manufacturing method of the metal product which has a fluororesin film as described in (2).
With the configuration of (4) above, it is possible to make use of the characteristics of each of the bonded metals.
(5) The molten salt is either in the molten salt, or a molten salt containing aluminum chloride及beauty A Le kills pyridinium chloride containing aluminum chloride and alkyl imidazolium chloride, the alkyl imidazolium chloride and alkyl group in the alkyl pyridinium chloride The method for producing a metal product having a fluororesin coating according to any one of the above (1) to (4), wherein the number of carbon atoms possessed is 1-5.
With the configuration ( 5 ), an aluminum film can be efficiently formed on the metal substrate.
(6) the molten salt method for producing a metal product having a fluororesin coating according to any one of aluminum chloride, and 1-ethyl-3-methyl imidazolium chloride Tona Ru (1) (5) .
With the configuration ( 6 ) above, the surface of the aluminum film formed on the metal substrate can be efficiently roughened.
( 7 ) The overvoltage value at the time of aluminum electrodeposition is controlled to be −110 mV or more and −150 mV or less by adjusting the amount of 1,10-phenanthroline added , according to any one of (1) to (6) above. A method for producing a metal product having a fluororesin coating.
With the configuration ( 7 ) above, the surface of the aluminum film formed on the metal substrate can be uniformly roughened.

  According to the method for producing a metal product of the present invention, it is possible to obtain a metal product having a fluororesin film excellent in adhesiveness with a metal substrate on the metal substrate.

It is a figure which shows the relationship between an overvoltage and additive concentration. It is a figure which shows an example of the apparatus which implements the process of manufacturing an aluminum film on the metal base material in this invention.

The method for producing a metal product of the present invention comprises a step of forming an aluminum film on a metal substrate by electroplating, a step of forming a coating film containing a fluororesin on the aluminum film, and a coating containing the fluororesin. It consists of a step of firing the film to form a fluororesin coating.
In the step of forming the aluminum film, a roughened aluminum film is formed on the metal substrate, and the fluororesin film is formed on the roughened aluminum film, thereby bonding the aluminum film and the fluororesin film. And the peel resistance of the fluororesin coating is improved.
Below, each said process is demonstrated.

[Aluminum film forming process]
(Metal base material)
An electroplating method is used to form an aluminum film on the metal substrate.
As a metal substrate, plate-like iron, iron alloy (stainless steel, etc.), nickel, nickel alloy, copper, copper alloy, aluminum, aluminum alloy or iron, iron alloy, nickel, nickel alloy, copper, copper alloy and plate-like A bonding material bonded with aluminum can be used.
However, when the substrate surface is made of aluminum, an aluminum oxide film is usually present on the surface of the aluminum, so the adhesion between the aluminum plating film and the substrate aluminum is not good, so the aluminum film is easy to peel off. Become. Therefore, it is preferable to form the aluminum film by subjecting the base material after the oxide film present on the surface of the aluminum base material to be removed by reverse electrolysis or the like to the molten salt electrolysis treatment.
In the reverse electrolysis treatment, the oxide film on the surface of the aluminum substrate is eluted in the molten salt by performing an electrolytic treatment using the aluminum substrate having an oxide film as an anode in a molten salt electrolytic bath.

(Electroplating)
A molten salt electrolyte is used as the electrolyte used for electroplating.
As the molten salt, an organic molten salt or an inorganic molten salt can be used.
As the organic molten salt, an organic molten salt which is a eutectic salt of an organic halide and an aluminum halide can be used. As the organic halide, an imidazolium salt and a pyridinium salt (such as butylpyridinium chloride (BPC)) are used. Etc. can be used.
Of these, an imidazolium salt is preferable, and a salt containing an imidazolium cation having an alkyl group (having 1 to 5 carbon atoms) at the 1,3-positions is preferably used. In particular, aluminum chloride-1-ethyl-3-methylimidazolium chloride (AlCl _3- EMIC) type molten salt is most preferably used because it is highly stable and hardly decomposes. The temperature of the molten salt bath is 10 ° C to 100 ° C, preferably 25 ° C to 45 ° C. The lower the temperature, the narrower the current density range that can be plated, and the higher the temperature exceeding 100 ° C., the higher the heating cost.
As the pyridinium salt, butylpyridinium chloride (BPC) or the like can be used.

As the inorganic molten salt, an eutectic salt of an alkali metal halide and an aluminum halide (AlCl ₃ —XCl (X: alkali metal)) can be used. Such an inorganic molten salt generally has a higher melting temperature than an organic salt bath such as an imidazolium salt bath, but is less restricted by environmental conditions such as moisture and oxygen, and can be put into practical use at a low cost overall. .
However, in the present invention, an additive may be added to the molten salt as described later. However, since the inorganic molten salt has a high melting point, it is necessary to increase the temperature of the plating solution, and the additive volatilizes and decomposes at a high temperature. Since there is a possibility, it is preferable to use an organic molten salt that melts at a low temperature.

The composition of the molten salt electrolyte is such that the aluminum film formed on the substrate has a rough surface.
When the molten salt electrolyte does not contain other components in addition to the molten salt, the aluminum film has a rough surface. However, since a uniform rough surface can be obtained by adding additives such as benzene, xylene, pyridinebenzotriazole, polystyrene, 1,10-phenanthroline to the molten salt, it is preferable to add these additives.
However, when the concentration of these additives in the electrolytic solution increases, the surface of the aluminum film approaches a mirror surface and a specific surface roughness cannot be obtained. Therefore, the amount of addition needs to be a certain value or less.

In order to improve the adhesion to the fluororesin coating, the surface roughness of the aluminum film is preferably an arithmetic average roughness (Ra) of 0.1 to 1.0 μm. Further, the ten-point average roughness (Rz) may be 0.1 to 1.0 μm.
In order to achieve the above-mentioned specific surface roughness, it is necessary to control the addition amount to a certain value or less even when the additive is not added or even when the additive is added. The amount added varies depending on the type of additive, but when AlCl ₃ -EMIC is used as the molten salt, 1,10-phenanthroline is particularly preferably used, but the concentration in the electrolyte is 0.2 g / L or more. It is preferably 0.5 g / L or less.

In the case where the additive is added, a part of the additive is taken into the plating film during the plating step, so that the concentration of the additive in the electrolytic solution decreases as the plating progresses. Therefore, in order to make the roughness of the plating film surface uniform, it is necessary to maintain the concentration of the additive in the electrolytic solution within a predetermined setting range.
For this reason, it is necessary to monitor the concentration of the additive in the electrolytic solution, but in the present invention, the overvoltage is measured, and the additive is added to the electrolytic solution so that an overvoltage within a predetermined range can be obtained based on the measured value. Add to. Monitoring may be performed continuously or at intervals.

  The overvoltage is an absolute value of a potential difference between a theoretical potential (equilibrium electrode potential) at which an aluminum electrodeposition reaction occurs and an electrode potential when the aluminum electrodeposition reaction actually proceeds. Since the absolute value of this potential difference reflects the concentration of the additive, the concentration of the additive in the electrolytic solution is controlled by adjusting the amount of additive added so that the overvoltage is within a predetermined range. Can do.

FIG. 1 shows the relationship between overvoltage and additive concentration when AlCl ₃ -EMIC is used as the molten salt and 1,10-phenanthroline (in the figure, “phen”) is used as the additive. In addition, the density | concentration of 1, 10-phenanthroline is shown with the mass with respect to a plating solution.
When AlCl ₃ -EMIC is used as the molten salt and 1,10-phenanthroline is used as the additive, the additive concentration is preferably such that the overvoltage is −110 mV to 0 mV, and is −110 mV to −150 mV. More preferred.
A specific surface roughness can be obtained when the overvoltage is -110 mV to 150 mV.

FIG. 2 is a view showing a configuration of an apparatus for maintaining the concentration of the additive in the molten salt electrolyte at a set value.
As shown in FIG. 1, the electrolytic solution whose additive has been reduced by electrodeposition overflows from the plating tank 1, is continuously returned to the recovered electrolytic solution tank 21, and then sent to the replenisher storage tank 22. An additive storage tank 23 is connected to the raw material dissolution tank 22, and a supply valve 24 is controlled by a control signal from a control device 25 that sends a control signal based on an overvoltage signal, and a predetermined amount of additive is added from the additive storage tank 23. Is supplied to the recovered electrolyte tank 21 to adjust the additive concentration in the electrolyte. Next, the electrolytic solution is supplied from the replenisher storage tank 22 to the electrolytic tank 1 after removing solids in the liquid by the filter 26. Further, since the liquid temperature rises due to electrolysis, a cooling device may be provided to cool the electrolytic solution.

  In the measurement of the overvoltage, the potential difference between the voltage between the aluminum substrate (cathode) and the anode in the electrolytic cell and the theoretical potential (equilibrium electrode potential), that is, the overvoltage is taken out as an electric signal, and this overvoltage and the set voltage are used as the control device 25. Then, the amount of the additive supplied to the replenisher storage tank 22 is controlled by adjusting the opening of the additive supply valve so that the overvoltage becomes a set value.

If moisture or oxygen is mixed in the molten salt, the molten salt will deteriorate or plating will not be performed properly. Therefore, electrolysis is performed in an inert gas atmosphere such as nitrogen or argon, and in a sealed environment. It is preferable.
Specifically, the electrolytic solution is stirred by covering the plating bath surface of the electrolytic cell and bubbling an inert gas from the bottom of the electrolytic cell, and water and oxygen contained in the electrolytic solution are driven out. The space above the liquid surface is a nitrogen gas atmosphere. Further, instead of the lid, a shielding plate may be suspended on the surface of the electrolytic solution to shut out the outside air, or an inert gas may be supplied from above the electrolytic cell.

  In the aluminum plating method of this invention, it is preferable to perform electroplating, adjusting so that the temperature of the said plating bath may be 60 to 120 degreeC. By setting the temperature of the plating bath to 60 ° C. or higher, the viscosity of the plating bath can be sufficiently lowered, and the plating efficiency can be improved. Moreover, volatilization of aluminum chloride can be suppressed by setting it to 120 degrees C or less. The temperature of the plating bath is more preferably 60 ° C to 100 ° C, and further preferably 60 ° C to 80 ° C.

[Fluorine resin coating film forming process]
In order to form the fluororesin coating film, first, a paste-like fluororesin coating material in which a fluororesin component and an inorganic pigment added as necessary are dispersed in an aqueous dispersion medium as a solid content is prepared.
The fluororesin used in the present invention may be in any form such as aqueous dispersion or powder, but is particularly preferably an aqueous dispersion.
In order to improve the dispersibility of the solid content, it is preferable to add a surfactant to the aqueous dispersion as appropriate. Further, in use, the dispersion of the fluororesin is stirred by a stirrer (mixer), and the aggregated particles are pulverized and refined.

  Examples of the fluororesin used for forming the fluororesin coating include polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether (PFA), and ethylene. -Fluororesin such as tetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), or ethylene-chlorotrifluoroethylene copolymer (ECTFE). These may be used alone or in combination of two or more. Of these, PTFE, PFA, and FEP are used alone or in combination of two or more, since the film has good non-adhesiveness.

  The fluororesin coating film may be formed by coating a fluororesin paint after forming the metal substrate. After coating the fluororesin paint on the metal substrate on the flat plate, the obtained fluororesin coating is applied. You may press-mold into the shape of a rice cooker inner pot.

[Fluorine resin film forming process]
The fluororesin coating film formed on the metal substrate is then subjected to a heat treatment or the like to evaporate and volatilize the liquid medium, and then subjected to a sintering process to become a fluororesin coating film. Although sintering temperature changes with kinds of fluororesin, in the case of PTFE, it is 250-300 degreeC.

  EXAMPLES Hereinafter, although this invention is demonstrated in detail based on an Example, these Examples are illustrations and the metal porous body of this invention is not limited to these. The scope of the present invention is defined by the scope of the claims, and includes meanings equivalent to the scope of the claims and all modifications within the scope.

Evaluation methods of physical properties of the fluororesin coating films prepared in Examples and Comparative Examples are as follows.
(1) Surface roughness Arithmetic mean roughness (Ra) etc. were measured by the method prescribed | regulated by JISB0601-1994.

(2) Adhesive strength (180 ° peel strength)
After fusing one end of the FEP tape to the coating surface, make a notch penetrating to the metal base with a width of 1.5 cm in the fused part, and pull the other end not fused in the direction of 180 ° The strength at the time of peeling was determined. The force required for peeling off per 1 cm width is defined as the 180 ° peel strength (kg / cm) of the coating film.

(3) Pinhole Degree A pinhole degree is defined as a current value when a solution of 1000 g of water, 110 g of isopropyl alcohol, 12.5 g of sodium chloride, and 0.1 g of phenolphthalein is applied at a voltage of 30 V for 30 seconds. .

(4) Corrosion resistance The actual cooking rice test was conducted 500 times to evaluate the presence or absence of corrosion. The case where corrosion sites were observed by visual observation was evaluated as corrosion (x), and the case where corrosion sites were not observed was evaluated as no corrosion (◯).

[ Reference Example 1 ]
(Formation of aluminum film)
A stainless steel plate was used as the metal substrate.
The stainless steel plate is connected to the cathode side, the counter electrode aluminum plate (purity 99.99%) is connected to the anode side, and nitrogen is bubbled from the bottom of the electrolytic cell at a flow rate of 0.5 L / min. Was plated to form an aluminum film having a thickness of 10 μm on the substrate.
The electrolysis conditions are as follows.
Molten salt composition: 33mol% EMIC-66mol% AlCl 3
Additive: None Liquid temperature: 45 ° C
Current density: 2 A / dm ² (DC current)
Setting overvoltage: -120 mV to -150 mV
Table 1 shows the surface roughness of the aluminum film.

(Formation of fluororesin coating film)
Disperse 329 g of powder made of PFA spherical particles having an average particle size of about 20 μm (MP102 manufactured by du Pont) in a liquid medium in which 309 g of water and 62 g of a surfactant (Octapol 80 manufactured by Sanyo Chemical Industries, Ltd.) are mixed. 300 g of a PFA dispersion (AD-2-CR manufactured by Daikin Industries, Ltd.) consisting of 47% by weight of PFA spherical particles having an average particle size of 0.4 μm, 6% by weight of a surfactant, and 47% by weight of water was added. Fluorine resin paint was prepared by thoroughly mixing.
The fluororesin paint was coated on the aluminum film of the stainless steel plate so that the coating thickness was 2 μm to form a fluororesin coating film.

(Formation of fluorine resin film)
Next, after drying said fluororesin coating film at 80 degreeC, it heated at 200 degreeC and the coating board which has a fluororesin film was obtained.
The coating plate thus obtained was deep-drawn by press molding to produce an inner pot for a rice cooker.

(Evaluation)
The adhesive force (180 ° peel strength) and pinhole of the obtained coated plate press-processed product were measured, and further, the actual cooking rice test was conducted 500 times to evaluate the presence or absence of corrosion. The results are shown in Table 1.

[Example 1 ]
In Reference Example 1 , an inner pot was produced in the same manner as in Reference Example 1 except that the conditions for forming the aluminum film were as follows.
Table 1 shows the results of evaluating the obtained aluminum film and the inner pot in the same manner as in Reference Example 1 .
Electrolyte composition: 33 mol% EMIC-66 mol% AlCl ₃
Additive: 1,10-phenanthroline Liquid temperature: 45 ° C
Current density: 2 A / dm ² (DC current)
Setting overvoltage: -120 mV to -140 mV

[ Reference Example 2 ]
In Reference Example 1 , an inner pot was produced in the same manner as in Reference Example 1 except that the conditions for forming the aluminum film were as follows.
The obtained aluminum film and inner pot were evaluated in the same manner as in Reference Example 1 and the results are shown in Table 1.
Electrolyte composition: 33 mol% EMIC-66 mol% AlCl ₃
Additive: Xylene Liquid temperature: 45 ° C
Current density: 2 A / dm ² (DC current)
Setting overvoltage: -120 mV to -140 mV

[Comparative Example 1]
In Reference Example 1 , an inner hook was produced in the same manner as in Reference Example 1 except that an aluminum film was not formed, and the inner hook was evaluated. The evaluation results are shown in Table 1.

DESCRIPTION OF SYMBOLS 1 Electrolysis tank 21 Recovery electrolyte tank 22 Replenishment liquid storage tank 23 Additive storage tank 24 Supply valve 25 Control apparatus 26 Filter

Claims (7)

Forming an aluminum film by electroplating on a metal substrate;
Forming a coating film using a fluororesin-containing paste on the aluminum film;
Drying the coating film;
After drying the coating film, baking the coating film to form a fluororesin film;
I have a,
The electrolytic solution used in the electroplating method comprises a molten salt added such that 1,10-phenanthroline is 0.2 g / L or more and 0.5 g / L or less as an additive.
A method for producing a metal product having a fluororesin coating.   The surface roughness of the surface of the aluminum film formed by electroplating is arithmetic mean roughness (Ra) of 0.1 to 1.0 µm. Production of a metal product having a fluororesin coating according to claim 1 Method.   The method for producing a metal product having a fluororesin coating according to claim 1 or 2, wherein the metal substrate is one selected from the group consisting of iron, stainless steel, copper, and aluminum.   The metal substrate is a bonding material made of plate-shaped iron, stainless steel, or copper and plate-shaped aluminum, and an aluminum film is formed on the aluminum side of the bonding material by electroplating. The manufacturing method of the metal product which has a fluororesin film of description. The molten salt is either molten salt containing molten salt, or aluminum chloride及beauty A Le kills pyridinium chloride containing aluminum chloride and alkyl imidazolium chloride,
The method for producing a metal product having a fluororesin coating according to any one of claims 1 to 4, wherein the alkyl group in the alkylimidazolium chloride and the alkylpyridinium chloride has 1 to 5 carbon atoms. . The molten salt method for producing a metal product having a fluororesin coating according aluminum chloride, and 1-ethyl-3-methyl imidazolium chloride Tona Ru claim 1 in any one of claims 5. The fluororesin film according to any one of claims 1 to 6, wherein an overvoltage value during aluminum electrodeposition is controlled to be -110 mV or more and -150 mV or less by adjusting an amount of 1,10-phenanthroline added. The manufacturing method of the metal product which has this.

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