JP2000061193A - Washing tank improved in mildewproofing property - Google Patents

Abstract

PROBLEM TO BE SOLVED: To impart antimicrobial and mildewproofing properties to the stainless steel itself which is used for a washing tank by utilizing a photocatalyst effect of ZnO. SOLUTION: This washing tank 2 is constituted by using the ferritic stainless steel contg. 16.0 to 20.0% Cr and 0.4 to 2.0% Cu and/or 0.4 to 3.0% Mo at need as a base material, applying a galvanizing layer on the outer flank facing a water tank 1 and forming a ZnO layer on the front layer of this galvanizing layer. A method of mounting a light transparent cap 3 at a washing machine or arranging a photoirradiation light source 4 between the water tank 1 and the washing tank 2, etc., is adopted in order to enhance the photocatalyst effect of the ZnO.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a washing tub which has good antibacterial properties and does not cause black mold.

[0002]

2. Description of the Related Art A fully automatic washing machine has a double structure in which a washing tub is installed in a plastic tub or a plastic-coated steel tub. If this type of washing machine is used for a long period of time, mold may occur between the water tub and the washing tub, depending on the usage conditions and structure. Therefore, the bleach for washing machines, which dissolves mold in water, is used, or mold generated by disassembly cleaning is removed. However, the bleaching agent needs to be added every few months, and the decomposition is expensive. In order to suppress the growth of microorganisms, it is also adopted in part to construct a washing tub with plastic or a plastic-coated steel plate mixed with an antibacterial / antifungal agent. However, as a practical problem, it has been pointed out that after a certain period of time, the antibacterial / antifungal agent is exhausted and its effect is weakened.

By the way, as a material for a washing tub, stainless steel has been evaluated for its high-class feeling and beauty, and the washing tub has been made of stainless steel, and is now widely used. Stainless steel is essentially resistant to fungi and mold and can be said to be an effective material for preventing mold. However, there is a strong demand for laundry that is safe to the human body without being contaminated by pathogenic bacteria and the like, and it has been desired to impart antibacterial properties to stainless steel itself. Therefore, the applicant of the present invention has introduced a stainless steel washing tub provided with an antibacterial property by forming a concentrated layer of TiO ₂ functioning as a photocatalyst on the surface of stainless steel in Japanese Patent Application Laid-Open No. 9-38377.

[0004]

Originally, stainless steel is considered to be a material that is resistant to mold and is effective as a measure against mold. However, even in the case of a stainless steel washing tub, black molds are occasionally found on the outer surface of the washing tub, that is, on the water tub side of the washing machine, depending on the conditions of use. The generation of black mold greatly impairs the cleanliness of the washing machine, which in turn reduces the commercial value of the washing machine. Also, recently
More advanced measures against pathogenic bacteria and fungi are required in various fields. Also for washing machines, it is strongly required to finish laundry that is safe for human body without being contaminated with pathogenic bacteria and mold, and a washing tub with stainless steel itself having antibacterial and antifungal properties is desired. There is.

[0005]

The present invention has been devised in order to meet such a requirement, and utilizes that the surface ZnO of the zinc plating layer formed on the surface of stainless steel acts as an antibacterial / mold. However, by using galvanized stainless steel as a material for washing tubs and aquariums, it is possible to sustain the antibacterial and antifungal functions semipermanently, and to provide a stainless steel washing tub that is safe for the human body and the environment. To aim. In order to achieve the object, the washing tub of the present invention is made of Cr
A ferritic stainless steel having a content of 16.0 to 20.0% by weight is used as a base material, and at least an outer surface facing a water tank is provided with a zinc plating layer, and ZnO is formed on a surface layer of the zinc plating layer.
It is characterized in that a layer is formed.

The stainless steel used contains 0.4 to 2.0% by weight of Cu and / or 0.4 to 2.0 as other alloying components.
It may contain 3.0% by weight of Mo. A galvanized layer is formed on the surface of stainless steel with a coating weight of 5 to 40 g / m ² . ZnO, which is effective as a photocatalyst, is generated on the surface layer of the galvanized layer. In order to enhance the photocatalytic action of ZnO, a light-transmissive lid is attached to the washing machine,
Alternatively, it is adopted to arrange a light source for light irradiation between the water tank and the washing tank.

[0007]

The present inventors have paid attention to an oxide semiconductor having a photocatalytic function, which is known as a non-consumable antibacterial agent, in order to impart antibacterial and antifungal properties to the stainless steel itself constituting the washing tub. When exposed to sunlight, fluorescent light, ultraviolet rays, etc., the photocatalyst changes oxygen into active oxygen, decomposes enzymes of pathogenic bacteria, and kills bacteria. The photocatalytic reaction requires irradiation of light, but unlike other antibacterial agents, it has the advantage that the antibacterial action lasts semipermanently. Although various oxides are known as oxide semiconductors exhibiting a photocatalytic action, ZnO is most effective in imparting antibacterial properties to stainless steel for washing tubs. Moreover, ZnO also has a deterrent effect on the generation and reproduction of black mold.

In the present invention, Z which exhibits a photocatalytic action
A method of galvanizing stainless steel was used to form the nO layer. Ordinary galvanized steel sheet is subjected to chromate treatment, phosphate treatment, etc. immediately after plating in order to prevent corrosion and oxidation of the plated layer. However, in the present invention, since it is used in the ZnO state, it remains galvanized. Stainless steel plate is used. When a galvanized stainless steel sheet is left in the atmosphere, the surface of the zinc plated layer is oxidized in a short period of time, and a ZnO layer is formed. Also,
When steam is sprayed on the stainless steel plate immediately after it leaves the plating bath in the plating process, the generation of ZnO is promoted.
Of course, ZnO is produced as a corrosion product from the galvanized layer that exhibits a sacrificial anticorrosive action even during use of the washing tub. ZnO adheres to the surface of the galvanized layer and is effective not only for antibacterial and antifungal properties but also for corrosion protection of stainless steel itself.

It is desired that the inner surface of the washing tub contacting the laundry has the gloss of stainless steel itself in appearance. Also, since the inner surface of the washing tub is in direct contact with the laundry, if the zinc plating layer is formed on the inner surface side, the zinc plating layer may be scraped off due to friction with clothes during washing, which may stain the laundry. is there. In this respect, it is preferable to remove the galvanized layer on the inner surface of the washing tub, or to galvanize only one surface of the stainless steel plate at the time of plating. In the present invention, since the metal Zn itself of the plating layer is not used, a particularly large amount of plating adhesion is not required. Basically, it is important that ZnO, which is a corrosion product of plating, adheres to the surface of stainless steel, and the amount of adhesion of 5 to 30 g / m ² that is used in ordinary electroplating is sufficient. . In addition, single-sided plating is desirable in order to secure the luster of stainless steel on the inner surface that contacts laundry.

The single-sided plating may be hot dipping, but industrially electroplating is suitable. As one-sided electroplating, a method of insulating one side of a stainless steel plate with an adhesive tape, a method of keeping the water level of the electrolytic solution constant and contacting only one side of the stainless steel plate, a stainless steel plate which is shallowly immersed in the electrolytic solution in the electrolytic cell There is a method in which the electrolytic solution is continuously jetted onto the upper surface of the steel plate to push the electrolytic solution to the side surface, and only the lower surface of the stainless steel plate facing the anode is plated while preventing the plating of the upper surface of the stainless steel plate. When the galvanized layer of the single-sided plated stainless steel plate is the outer surface of the washing tub, the stainless steel surface is exposed on the inner surface side of the washing tub. There is no mold problem on the inner surface of the washing tub, but it is desirable that it has antibacterial properties. Therefore, in the present invention, Cu and Mo
Addition of to give the stainless steel antibacterial properties.

Cu is an element which exhibits antibacterial properties by itself, and is added to ferritic stainless steel to form a fine intermetallic compound by heat treatment during steel production (for example, 800 ° C. × 24 hours → cooling in a furnace). When deposited in steel, persistent antibacterial properties are developed with or without light irradiation. The improvement of antibacterial property becomes remarkable when 0.4 wt% or more of Cu is added. However, if a large amount of Cu exceeding 2.0% by weight is added, the hot workability at the time of steel production deteriorates. Mo
Is an element that improves the corrosion resistance of stainless steel and does not require addition in normal use. However, in an area where the quality of tap water is poor, a chlorine-based bleaching agent exceeding an appropriate concentration may be used in a complicated manner, or the laundry may be left in a washing tub for a long time after the bleaching agent is added. In such cases, there is a risk of pitting corrosion in the stainless steel washing tub,
Stainless steel with Mo added as needed is used. It also has the effect of promoting precipitation of the Cu phase during heat treatment. The amount of Mo added is set in the range of 0.4 to 3.0% by weight in order to secure the required corrosion resistance. 0.
If the Mo content is less than 4% by weight, the effect of addition on the improvement of corrosion resistance is not remarkable. On the other hand, when the Mo content exceeds 3.0% by weight, the cost is increased and the steel material is hardened to deteriorate the formability.

The photocatalytic action of ZnO is exhibited when it is irradiated with sunlight, fluorescence, ultraviolet light or the like. Above all, ultraviolet irradiation is effective for manifesting a photocatalytic action. However, in a usual washing tub, since the upper part is covered with an opaque plastic lid, the washing tub is less likely to be exposed to external light. In the washing tub of the present invention utilizing the photocatalytic action of ZnO, when external light such as sunlight or indoor fluorescent lamp is used as the light source,
A transparent plastic lid is used so that ultraviolet rays can pass through the tank. However, when sunlight or the like is used to activate ZnO, the antifungal action depends on the amount of solar radiation on that day. On the other hand, by incorporating the irradiation light source inside the washing machine, it is possible to secure a necessary light amount without being affected by a natural phenomenon. For example,
As shown in FIG. 1, an irradiation light source 4 such as a fluorescent lamp of about 5 W, a mercury lamp or the like is arranged inside the lid 3 at a position facing between the water tub 1 and the washing tub 2 to form the washing tub 2. Z of steel
The nO surface is irradiated with the irradiation light source 4. In this case, it is desirable to connect the control circuit to the irradiation light source 4 so that the irradiation light source 4 is turned on for several hours after the power switch for washing / dehydrating is turned off.

[0013]

EXAMPLES As shown in Table 1, Example 1 of the present invention and Comparative Example 1
Then, a stainless steel (SUS430JIL) cold rolled sheet having a surface finish of 2B and a sheet thickness of 0.8 mm was used. Invention Example 1
Then, one surface of the stainless steel plate was electrogalvanized with an adhesion amount of 30 g / m ² , and in Comparative Example 1, the cold rolled plate itself was used. In the invention example 2, C: 0.010% by weight,
Si: 0.06% by weight, Cr: 17.7% by weight, Nb:
0.42% by weight, Cu: 1.46% by weight, N: 0.00
A ferritic stainless steel containing 8% by weight was heat-treated in the manufacturing process, and one surface of a BA finishing material in which a Cu-rich phase was precipitated was electrogalvanized with an adhesion amount of 10 g / m ² .

A test piece was cut out from each stainless steel plate,
It was subjected to a mold resistance test. In mold resistance test, test bacteria
As Cladosporium cladospor
Using ioides IFO 6348 (black mold), try
Test bacteria in potato dextrose agar at 25 ℃ for 10 days
After culturing for 10 days, the spores (conidia) are
A spore suspension was prepared by suspending in sucrose peptone medium.
Place the test piece in a Petri dish with the galvanized layer on top
And test piece surface area 9 cm ² 0.5 ml per spore
Sprinkle the suspension evenly, cover the petri dish with a temperature of 30
Culturing was carried out at a temperature of ℃ and a relative humidity of 97 ℃. When culturing,
A 15W fluorescent lamp at a position 20 cm away from the
Then, the influence of the presence or absence of irradiation of the fluorescent lamp was investigated.

The growth state of the hyphae generated on the surface of the test piece every one week from the start of the culture is measured according to JIS Z2911 (199).
2) Judgment was made according to the method for displaying mold resistance results in “Test method for mold resistance”. Mold growth became remarkable from 3 weeks after the start of the test, and as shown in Table 1, in Comparative Example 1, black mold was clearly observed. On the other hand, in Examples 1 and 2 of the present invention in which the galvanized layer was provided, a slight black mold was observed only after 4 weeks from the start of the test even when the fluorescent lamp was not irradiated. Furthermore, the present invention example 1 irradiated with a fluorescent lamp
In Nos. 2 and 3, the development of black mold was not observed, and excellent mold resistance was confirmed. Further, as is clear from Table 1, it can be seen that ZnO has some influence on the improvement of the antifungal property even when the light is shielded. It is generally said that the photocatalyst does not exhibit its function in the light-shielded state. However, the improvement of the antifungal property shown in Table 1 is that the Zn metal ionizes and dissolves from the zinc plating layer directly under the ZnO layer, and the toxicity of Zn ⁺² It is speculated that this contributed to the fungicide.

[0016]

[0017] In addition, trials cut from each stainless steel plate
An antibacterial test was performed using the test piece. In the antibacterial test,
Pathogens cultivated in Iyon medium with shaking at 35 ° C for 16 to 20 hours
Sex Escherichia coli IFO3
301 and Staphylococcus aureus
aureus 1FO12732 culture solution
Prepare a test bacterial solution by diluting 20,000 times with acid buffer
did. Surface area of test piece 25 cm² 1 ml of test bacterial solution
After dropping and storing at 25 ° C for 24 hours,
The number of bacteria was measured. In Invention Example 1, the ZnO layer was used as the test surface.
And is placed at a position 20 cm away from the test piece 15
Illuminated with a W fluorescent lamp. In the present invention example 2, the zinc plating layer
Irradiate fluorescent light with the uncoated stainless steel surface as the test surface.
Omitted. Further, in Comparative Example 1, the test was conducted in a light-shielded state.
As can be seen from the test results in Table 2, the number of viable bacteria in Comparative Example 1
Was not measurable, but both of the invention examples 1 and 2
Effective against both pathogenic E. coli and S. aureus
Antibacterial properties were shown. Above all, the Cu-rich phase is precipitated
In the present invention example 2 which has the above
It has a bactericidal action.

[0018]

Further, a strip test piece of 30 mm × 100 mm was cut out from the galvanized stainless steel of Example 1 of the present invention and attached to three outer surfaces of a washing tub used in an actual washing machine with an adhesive, The state of actual use was monitored. As detergent, use powder soap with a high tendency to generate mold,
In order to add moisture to the inside of the washing machine, steam was introduced from the humidifier after the washing was completed, and environmental conditions were set so that molds could grow easily. After 3 months, the washing tub was taken out from the washing machine and the outer surface of the washing tub was observed. Soap powder began to adhere to the outer surface, and growth of black mold was detected in that area. However, generation of black mold was not detected at all in the portion to which the test piece of Inventive Example 1 was attached. From this,
It is confirmed that the stainless steel washing tub according to the present invention exhibits excellent antifungal properties.

The action of ZnO described above is the same as that of the washing tub 2.
It can be applied to the inner surface of the water tank 1 as well.

[0021]

As described above, the washing tub of the present invention uses stainless steel having ZnO on the surface as a material. The ZnO layer has an excellent anti-bacterial effect against bacteria, black mold, malodor, etc. that tend to occur and propagate in a washing tub exposed to a humid atmosphere, and has an antibacterial effect, so the interior of the washing machine can be cleaned for a long time. To maintain. Also, as a base material, C
When u-added stainless steel is used, the antibacterial property is further improved. In this way, since the stainless steel itself is provided with antibacterial / antifungal effects, antifungal and antibacterial treatment is not required after processing into a washing tub. Moreover, the antibacterial and antifungal action is
Since it uses a non-consumable photocatalyst, it lasts semipermanently and can be used for a long time in a washing machine.

[Brief description of drawings]

[Figure 1] Washing machine with galvanized stainless steel plate used for the washing tub and incorporating an irradiation light source

[Explanation of symbols]

1: Water tank 2: Washing tank 3: Lid 4: Irradiation light source

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Toshiro Nagoshi             4976 Nomura-Minami-cho, Shinnanyo-shi, Yamaguchi Nissin             Steel Research Laboratory F term (reference) 3B155 AA01 AA08 CB06 DC18

Claims (5)

[Claims] 1. A Cr content of 16.0 to 20.0% by weight.
A basin of ferritic stainless steel as a base material, a zinc plating layer is formed on at least an outer surface facing a water tub, and a ZnO layer is formed on a surface layer of the zinc plating layer. 2. The ferritic stainless steel according to claim 1 contains 0.4 to 2.0% by weight of Cu and / or 0.4 to 2.0% by weight.
A washing tub with an improved antifungal property containing 3.0% by weight of Mo. 3. The washing tub with improved antifungal properties according to claim 1 or 2, wherein the galvanized layer is formed at a coating weight of 5 to 40 g / m ² . 4. A light-transmissive lid body is provided.
3. A washing tub with improved antifungal properties according to any one of 3 above. 5. The washing tub with improved antifungal properties according to claim 1, wherein a light source for irradiating light is provided between the water tub and the washing tub.