JPH06322589A - Surface treatment of aluminum inside member of rice cooker - Google Patents

Abstract

PURPOSE:To prevent mottled tarnishing and spot stains, etc., from being generated on the surfaces of aluminum inside members of a rice cooker by forming an anodic oxide film having a specified thickness on the surface of each of the inside members in the alkaline electrolytic bath. CONSTITUTION:The surface of each of the aluminum inside members which are constituents of the inside parts of the rice cooker such as the inner lid, inner pot is subjected to anodic oxidation by using an alkaline electrolytic bath to form an anodic oxide film having >=3mum thickness on the surface of the inside member and if necessary, the oxide film is subjected to boiling water sealing treatment in hot water of about 98 deg.C for about 30min. In the rice cooker inside members of which are thus surface-treated, the mottled tarnishing the spot stains, etc., are not generated on the surfaces of the inside members even at the time of performing the rice cooking many times repeatedly and therefore the pitting and/or local corrosion, etc., which are caused by and progress from the above tarnishing and stains, etc., can be prevented from occurring.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for surface-treating an aluminum member constituting an inner portion such as an inner lid or an inner pot (inner pot) of a rice cooker such as an electric rice cooker or a gas rice cooker. In particular, spot-like discoloration or spots (spots) on the surface of the aluminum inner member due to repeated rice cooking
The present invention relates to a surface treatment method capable of preventing the occurrence of

[0002]

2. Description of the Related Art Conventionally, JIS 1 has been used as a member constituting an inner surface of a rice cooker such as an inner lid or an inner pot of the rice cooker.
A pure aluminum-based aluminum material typified by the No. 000 series is used, and recently, as described below, the far-infrared radiation effect is used.
Attempts have also been made to use an aluminum alloy such as -Mn-based or Al-Fe-based for the inner lid and the like.

By the way, when such an aluminum material (including both pure aluminum and aluminum alloy) is used for an inner lid or an inner pot of a rice cooker, the surface is hardened to prevent corrosion or scratches. As a surface treatment for coloring or the like, anodizing treatment is usually performed to form an anodized film (so-called alumite film).

Recently, Al-Si and Al-Mn have been used.
It has been found that when anodizing treatment is applied to the surface of a base material made of aluminum alloy such as aluminium, Al-Fe, etc., the alumite coating spontaneously develops black to gray color and exhibits good far infrared radiation characteristics. Therefore, attempts have been made to obtain the far-infrared radiation effect by subjecting the inner lid of the rice cooker to the anodic oxidation treatment using these aluminum alloys.

Conventionally, as a method of anodizing the aluminum inner member of the rice cooker as described above, a so-called acidic alumite film is usually formed by using an acidic electrolytic bath such as a sulfuric acid acidic bath or an oxalic acid acidic bath. Met.

Generally, after the anodizing treatment using the acidic electrolytic bath as described above, the sealing treatment is usually performed using high temperature boiling water or the like. Of the inner members of the rice cooker, in particular, the inner pot is usually coated with a resin such as Teflon resin or silicone resin on the surface of the acid alumite coating in order to prevent the cooked rice from sticking. On the other hand, the inner lid is generally not coated with a resin and is often used as an acidic alumite coating.

[0007]

As described above, in the case of an aluminum inner member of a conventional rice cooker in which an acidic alumite film is formed by using an acidic electrolytic bath, particularly in the case of an inner lid not coated with a resin, As cooking rice is repeated,
Spot-like discoloration or spot-like stains are generated on the surface, and pitting and partial corrosion often occur when the number of times of use is further increased. It should be noted that such discoloration and stains usually occur relatively early after the start of use of a new rice cooker. On the other hand, when a resin coating is applied on the surface of the acid alumite film, such problems as spotted discoloration do not occur while the resin coating layer remains, but repeated use many times. If the resin coating layer is peeled off as a result, a problem similar to the above occurs at the peeled portion.

The reason why the above-mentioned mottled discoloration, mottled spots, etc. occur at a relatively early stage is presumed as follows according to experiments and studies conducted by the present inventors.

That is, when rice is cooked in the rice cooker, hot water and steam near 100 ° C. flow in the pot, and the water-soluble components contained in the rice, such as water, are contained in the hot water. Mineral components such as Ca, P, and K are eluted, and the pasty substance of rice, which is composed of sugar fibers, is eluted, and hot water and steam containing these various substances are filled in the pan, It will be in continuous contact with the inner wall surface of the lid or the like.

On the other hand, the surface of the alumite coating generally has a porous structure having a large number of pores. Particularly in the case of an acidic alumite coating formed by using an acidic electrolytic bath, the sulfuric acid electrolytic bath used for anodizing treatment or Anions of the electrolytic solution such as an oxalic acid electrolytic bath, for example, sulfate ions (SO ₄ ²⁻ ) and oxalate ions (COOH ⁻ ) are surrounded by pores on the surface as sulfate radicals and oxalate radicals. There is. This has been confirmed from the collection analysis of gas from the surface by heating, the detection result of S by an X-ray microanalyzer, and the like.

If the inner lid of a rice cooker on which an acidic alumite film having such a film structure is formed is exposed to the hot and humid atmosphere in the pan during rice cooking, it will remain in the pores due to thermal expansion and wetting. The anion such as sulfate ion and oxalate ion appears on the surface of the film from the corrosive acid radical such as sulfate and oxalate. These acidic anions directly react with hot water and various substances contained therein as described above immediately on the surface of the alumite film to generate white to yellowish white spots and discolored parts on the surface of the alumite film. I will end up. When the number of cooked rice is further increased, the discolored portion and the spot-shaped portion are the starting points, and pitting and partial corrosion proceed.

The above-mentioned mottled discoloration and mottled spots themselves do not affect the function of the rice cooker,
Since it occurs relatively early after the start of use of the new rice cooker, it may give the user of the rice cooker anxiety and distrust, and damage the commercial value. Therefore, it is strongly desired to prevent the occurrence. There is. Further, when trying to utilize the far infrared radiation effect of an anodized film such as an Al-Si alloy, the far infrared radiation characteristics may be impaired due to a change in the coating surface color tone due to discoloration, or the far infrared radiation characteristics may be non-uniform. May become. In addition, these Al-
Anodized films such as Si alloys are black due to spontaneous coloring
It usually has a gray color tone, but if the discoloration or stains described above occur in this case, the discoloration or stains will be greater than in the case of a pure aluminum-based anodic oxide film with a silver tone. It is noticeable and gives a bad appearance.

The present invention has been made in view of the above circumstances, and the aluminum-made inner member such as the inner lid and the inner pot of the rice cooker has the above-described spot-like discoloration and spot-like stains even if the rice is repeatedly cooked. It is an object of the present invention to provide a method of performing a surface treatment so as not to occur.

[0014]

[Means for Solving the Problems] As described above, the cause of spot-like discoloration and spot-like stains on the inner lid and pot of a conventional rice cooker is that the acidic electrolytic bath during anodizing treatment causes acidity. Since it is estimated that corrosive acid radicals remain in the pores of the alumite film, if anodizing treatment is performed under the conditions that such acid radicals do not remain in the pores of the alumite film, We believe that discoloration and spots can be prevented, and as a result of various experiments and studies, we found that discoloration and spots actually occurred by using an alkaline electrolytic bath that does not have corrosive acid radicals as the electrolytic solution in anodizing treatment. The inventors have found that the above can be prevented and have completed the present invention.

Specifically, according to the present invention, when surface-treating an inner member made of aluminum which constitutes an inner portion such as an inner lid or an inner pot of a rice cooker, an alkaline electrolytic bath is provided on the surface of the inner member made of aluminum. It is characterized in that it is subjected to anodizing treatment to form an anodized film having a thickness of 3 μm or more.

[0016]

In the method of the present invention, as the electrolytic bath at the time of anodizing treatment, instead of the acidic electrolytic bath used in the conventional method, an alkaline electrolytic bath is used to form an alumite film (using an alkaline electrolytic bath as described above). The alumite film thus formed is referred to as "alkaline alumite film").

As the alkaline electrolytic bath for the anodizing treatment, a bath based on NaOH or Na ₃ PO _{4 is used.}
The base and the bath further include a bath which is based on Na ₂ CO _3, but many of them both were added to other slight additive main component, such as NaOH, to any of these alkaline electrolytic bath Even when subjected to anodizing using, when used as an inner member of a rice cooker, the occurrence of spot-like discoloration and spot-like stains as described above is extremely small, and eventually pitting or the like starting from the discoloration point or the like. It was also found that the occurrence of partial corrosion was extremely small. The reason is estimated as follows.

That is, the alkaline alumite film obtained by anodizing in an alkaline electrolytic bath is
It has been found that, unlike the acidic alumite coating obtained by anodizing in an acidic electrolytic bath, corrosive acid radicals (anions) of the electrolytic solution do not remain in the pores of the alumite coating. To remain in the pores of the alkaline alumite film is mostly OH ^- is, therefore be exposed directly to such an alkaline alumite film to harsh high temperature wet heat atmosphere containing various substances in the cooker, sulfate ions Corrosive anions such as oxalate and oxalate ions do not float from inside the pores of the coating to the coating surface and do not react on the coating surface.Therefore, there is no risk that the coating surface will discolor or stain. Along with this, pitting and partial corrosion starting from the color change point are prevented.

Here, as the alkaline electrolytic bath, the above-mentioned NaOH-based bath or Na ₃ PO.
A bath based on ₄ , a bath based on Na ₂ CO ₃ , and the like can be used, but the bath is not limited thereto.

The thickness of the alkaline alumite coating formed using the alkaline electrolytic bath is 3 μm or more.
The thickness of the alumite coating itself has almost no effect on the above-described spot-like discoloration and spot-like spots, but if the thickness is less than 3 μm, the original purpose of forming the alumite coating is corrosion resistance and scratch resistance. Etc. cannot be obtained sufficiently. The upper limit of the thickness of the alkaline alumite coating is not particularly specified, but it is usually preferably about 8 μm or less from the viewpoint of economy and the like.

On the other hand, the conditions for the anodizing treatment using an alkaline electrolytic bath are not particularly limited, and they are DC electrolysis, AC electrolysis, AC / DC vertical electrolysis at normal bath concentration, normal bath temperature and normal current density. Anodizing treatment may be performed by current electrolysis or the like.

The material of the inner member of the rice cooker on which the alkaline alumite film is to be formed may be aluminum or an aluminum alloy, and the specific type is not particularly limited, but in general, an inner lid or Pure aluminum alloys such as JIS 1100 alloy are often used for the inner pot, and recently Al-Si alloys and Al-Mn alloys have been used for the purpose of obtaining a far infrared radiation effect.
The use of a system alloy, an Al-Fe system alloy, etc. for the inner lid has been studied, and the method of the present invention can be applied to any of these aluminum materials.

Further, in general, in the case of the inner pot, the surface of the alumite film is often coated with a resin such as Teflon resin or silicone resin. In the case of the inner member obtained by the present invention, the surface of the alkaline alumite film is coated with the resin. Of course, coating may be applied. In this case, even if the resin coating layer is peeled off due to long-term use or the like, it is possible to prevent discoloration or stains at the peeled portion. Among the inner members of the rice cooker, the same acid alumite coating as before is formed on the inner pot coated with resin, and the alkaline alumite coating according to the present invention is formed only on the inner lid not coated with resin. Of course, you can do that.

[0024]

Example In a 1.5 liter electric rice cooker, a pure aluminum material made of JIS 1100 alloy was used for the inner pot and the inner lid. The inner lid was formed with a common sulfuric acid bath to form an acidic alumite film having a thickness of 20 μm, and the acidic alumite film on the inner surface side of the inner pot was coated with a Teflon resin coating having a thickness of 30 μm. On the other hand, for the inner lid,
Anodizing treatment was performed by the following six methods A to F to form an alumite coating (however, A was not treated). A: Anodizing treatment was not performed (comparative example). B: Anodizing treatment was performed according to a conventional method using a general sulfuric acid electrolytic bath to form an acidic alumite film having a thickness of 8 μm (conventional method-comparative example). C: Using a general oxalic acid electrolytic bath, anodizing treatment was performed according to a conventional method to form an acidic alumite film having a thickness of 8 μm (conventional method-comparative example). D: Using a 0.1 molar NaOH bath, anodizing treatment was performed by direct current electrolysis with a current density of 2 A / dm ² at a bath temperature of 15 ° C. to form an alkaline alumite film having a thickness of 8 μm. E: Using a 0.2 molar Na ₃ PO ₄ bath, bath temperature 15
Anodizing treatment was performed by direct current electrolysis with a current density of 2 A / dm ² at ℃ to form an alkaline alumite film having a thickness of 8 μm. F: Using a 0.1 molar Na ₂ CO ₃ bath, bath temperature 15
Anodizing treatment was performed by direct current electrolysis with a current density of 3 A / dm ² at ℃ to form an alkaline alumite film having a thickness of 8 μm.

After the anodic oxidation treatment of B to F, boiling water sealing was performed in hot water of 98 ° C. for 30 minutes.

Each of the inner lids A to F treated as described above was actually assembled in a rice cooker in combination with the inner pot described above, and the rice cooking experiment was repeated to find the state of discoloration or corrosion of the inner lid surface. I checked. In the rice cooking experiment, 1 liter of white rice was cooked at one time, and the surface of the inner lid on the side in contact with the cooked rice was observed with the naked eye after the completion of rice cooking, and examined for discoloration, stains, pinholes, corrosion, etc. For the sake of accuracy, the surface of the inner lid was lightly washed with tap water and a sponge scrubbing brush every three times. The survey results are shown in Table 1 below.

[0027]

[Table 1]

As is apparent from Table 1, in the case of the inner lids (Samples D to F) of the present invention in which the alkaline alumite coating was formed by using the alkaline electrolytic bath according to the method of the present invention, the untreated inner lid ( Compared with the sample A) and the inner lid (sample B, C) on which an acidic alumite film was formed by using an acidic electrolytic bath according to the conventional method, the number of times of cooking rice until discoloration or stains was significantly increased. It can be seen that the number of times rice is cooked before the occurrence of corrosion is significantly increased. Therefore, even if the number of times of rice cooking is repeated, discoloration and stains are extremely unlikely to occur, and corrosion resistance is also significantly improved.

[0029]

According to the surface treatment method of the present invention, since the aluminum inner member such as the inner lid of the rice cooker is anodized by the alkaline electrolytic bath, the pores of the anodized film are not corroded by the electrolytic solution. The surface of the aluminum inner member of the rice cooker treated by the method of the present invention, for example, the surface of the inner lid, does not retain acid radicals, and thus the surface of the inner lid contains various substances such as mineral components in the pan during rice cooking. Even if it is directly exposed to the atmosphere, the corrosive anions floating on the surface of the film from the pores of the anodic oxide film directly react with the above substances and hot water, etc., causing discoloration or stains on the film surface. Therefore, even if the rice is repeatedly cooked, a patchy discolored pattern or spotted spots are not generated, and the appearance is less likely to be damaged. Fear less corrosion as a point to or progression, thus it is possible to significantly increase the commercial value of the rice cooker according to the method of the present invention.

Even when the resin coating is further applied to the surface of the anodic oxide coating as in an inner pot, if the anodic oxidation treatment is performed according to the method of the present invention, the peeled portion is peeled off after peeling the resin coating layer. It can prevent discoloration and stains, and the anodic oxide film formed by using an alkaline electrolytic bath has more detailed irregularities, so it has good adhesion to resin coating layers such as Teflon resin and silicone resin. Therefore, peeling of the resin coating layer is less likely to occur, and the thickness of the resin coating layer can be made thinner than in the past to reduce the cost.

Further, in the case of an inner member such as an inner lid utilizing the far infrared radiation effect using an Al-Si type alloy, an Al-Mn type alloy, an Al-Fe type alloy, or the like, spontaneous coloration by anodizing treatment is carried out. It is usually to make the color tone of the coating surface black to gray, so that white to yellow discoloration and spots are extremely conspicuous, but if the method of the present invention is applied in this case, Similar to the above, it is possible to prevent the occurrence of discoloration and stains, and not only that, but it is also possible to prevent the occurrence of a situation where the far-infrared radiation characteristics deteriorate or become uneven due to the change in color tone due to discoloration or stains, for a long period of time. Good far infrared radiation characteristics can be maintained.

 ─────────────────────────────────────────────────── ─── Continued front page (72) Inventor Shuichi Matsumoto 1-5-1 Kiba, Koto-ku, Tokyo Inside Fujikura Ltd. (72) Inventor Kenzo Okada 4-3-18 Nihombashi Muromachi, Chuo-ku, Tokyo Sky Inside Aluminum Co., Ltd. (72) Kenji Nomoto 4-3-18 Nihombashi Muromachi, Chuo-ku, Tokyo Inside Sky Aluminum Co., Ltd.

Claims (1)

[Claims] 1. When surface-treating an aluminum inner member that constitutes an inner portion of an inner lid, an inner pot or the like of a rice cooker, the surface of the aluminum inner member is anodized using an alkaline electrolytic bath. And forming an anodized film having a thickness of 3 μm or more on the surface of the inner member made of aluminum in the rice cooker.