JPH09249981A - Production of copper-containing stainless steel improved in antibacterial property - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a stainless steel excellent in antibacterial properties and surface quality by immersing a Cu-contg. stainless steel into an acidic soln. contg. hydrochloric acid and nitric acid with specified concns. and allowing a surface layer in which the concn. of Cu is specified to expose. SOLUTION: A stainless steel contg., by weight, >=0.3% Cu or the worked product thereof is immersed to an acidic soln. having 0.2 to 5.0% hydrochloric acid concn. and 1.0 to 20.0% nitric acid concn. In this way, a surface layer part having >=0.10 atomic % Cu concn. is formed, and excellent antibacterial properties can be obtd. Hydrochloric acid in the acidic soln. gives an effect of increasing the Cu concn. in the surface layer part. In the case the stainless steel is immersed into the hydrochloric acid-contg. acidic soln., the surface layer part exposes after the breaking of a passive film, but, when the passive film is reformed, there may occur the case in which impurities are accumulated on the base materal to color the surface. In the case nitric acid is present in this system, impurities are dissolved away at the time of repassivation, so that the surface state characteristic of the stainless steel free from coloring can be obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to kitchen equipment, electric appliances,
The present invention relates to a method for producing stainless steel or a processed product thereof, which is used for applications requiring antibacterial properties in a wide range of fields such as building materials, various machines, and chemical equipment.

[0002]

2. Description of the Related Art Since various equipment used in kitchen equipment, hospitals, and pipes for handrails of transportation means such as buses and trains are required to have corrosion resistance in a general environment, SUS is required.
The stainless steel represented by 304 is mainly used. However, nosocomial infection due to Staphylococcus aureus has become a problem in recent years, and there is a demand for improved hygiene even in an environment used by an unspecified number of people such as buses and trains. Along with this, maintenance-free materials with functions such as antibacterial properties that do not stop at the properties of general structural materials as materials used for various machines and instruments and do not require infection prevention such as regular disinfection. Materials are desired. In order to meet this kind of demand, there is a method of coating and laminating a resin containing an antibacterial agent on the surface of stainless steel, a method of plating an antibacterial agent component in a matrix, and the like.
8202, JP-A-6-10191 and the like.

[0003]

When a resin containing an antibacterial agent is applied and laminated on the surface of stainless steel, the metallic luster peculiar to stainless steel is lost and the commercial value is lowered. Moreover,
The antibacterial film is damaged during processing and during use, such as cracking, chipping, and abrasion, and when exposed to a humid atmosphere, the antibacterial components elute and the appearance is degraded, as well as the original antibacterial action is impaired. Be done. Further, when the antibacterial agent is exhausted, the remaining film rather serves as nutrients for miscellaneous bacteria and promotes reproduction. In the case of applying a composite plating mixed with an antibacterial agent component, the adhesion of the plating layer is not sufficient, and there is a drawback that the workability is reduced. In addition, the appearance may be deteriorated due to dissolution, wear, and defects of the film, and the antibacterial action may be reduced. In addition, since the antibacterial agent is used in any of the methods, the eluted antibacterial agent may have an adverse effect on the human body or the environment. Therefore, it is desired to impart antibacterial property to the stainless steel itself instead of the method of coating the antibacterial agent component.

The present inventors have investigated and studied stainless steels satisfying such required characteristics. As a result, it was found that by adding Cu to the stainless steel, a stainless steel having excellent antibacterial property maintained for a long period of time can be obtained, and Japanese Patent Application Nos. 7-21291 and 7-2
No. 1292, etc. Cu-containing stainless steel is C
C that forms a u-rich surface layer and elutes from this surface layer
Antibacterial properties are expressed by u ions. However, in the process of processing stainless steel into products, various types of polishing and machining are often performed, and the surface layer may deteriorate depending on the conditions of polishing and machining, and the original excellent antibacterial properties may not be exhibited. . INDUSTRIAL APPLICABILITY The present invention further improves Cu-containing stainless steel exhibiting good antibacterial properties and removes the surface layer portion of the stainless steel that has been deteriorated by polishing or machining to expose the surface layer portion having a high Cu concentration. It is an object of the present invention to obtain stainless steel which is beautiful and has stable antibacterial properties easily and stably at a relatively low manufacturing cost without deteriorating various characteristics such as appearance and workability.

[0005]

In order to achieve the object, the manufacturing method of the present invention uses a stainless steel containing 0.3% by weight or more of Cu or a processed product thereof with a hydrochloric acid concentration of 0.2 to 5.0.
It is characterized in that it is immersed in an acidic solution having a wt% and nitric acid concentration of 1.0 to 20.0 wt% to expose a surface layer portion having a Cu concentration of 0.10 atomic% or more. A mixed acid solution of hydrochloric acid and nitric acid removes the surface-altered layer caused by polishing and machining, stabilizes the surface quality of stainless steel, and exposes the surface layer portion with a Cu concentration of 0.10 atomic% or more, which is effective for antibacterial properties. To do.

[0006]

[Function] The inventors of the present invention have found that Cu is formed on the surface of a stainless steel material.
It was found that an excellent antibacterial property is obtained when a surface layer portion having a high concentration is formed, and for that purpose, it is necessary to include 0.3% by weight or more of Cu in the raw material steel for the purpose of the above application. Revealed in. When Cu is contained in stainless steel, Cu is concentrated in the passivation film on the surface of stainless steel or Cu-based oxide is generated. The concentrated Cu or Cu-based oxide is ionized as an extremely small amount of Cu ions by a slight amount of water adhering to the surface of the stainless steel in a humid environment in which bacteria easily grow. Cu ionized
Efficiently inactivates by reacting with the respiration and metabolic enzymes of cells, and kills bacteria and other bacteria. Such an antibacterial effect is
When the Cu content in the steel is 0.3% by weight or more, the concentration of Cu concentrated on the surface is rapidly increased, which is remarkable. However, in the process of processing stainless steel into products and the like, polishing processing such as mechanical polishing and electrolytic polishing may be performed on stainless steel. The Cu-rich surface layer portion may be deteriorated by polishing and may not exhibit sufficient antibacterial properties at the product stage. The antibacterial property due to Cu may disappear depending on the processing conditions even during bending or drawing.

The inventors of the present invention further investigated and studied the stainless steel with the antibacterial property disappeared, and found that it contained an acid containing 0.2 to 5.0% by weight of hydrochloric acid and 1.0 to 20.0% by weight of nitric acid. Immersion of stainless steel or its processed product in a solution removes the altered surface layer to obtain stable surface quality, and the surface Cu concentration is 0.10 atomic% or more, which is excellent antibacterial property. Have been found to be restored. The stainless steel targeted by the present invention contains 0.3% by weight or more of C.
It contains u. Cu is an essential alloying element for imparting excellent antibacterial properties. Cu content 0.3% by weight
If it does not satisfy the condition, even if it is dipped in an acidic solution, Cu is not sufficiently concentrated in the passivation film and excellent antibacterial property cannot be obtained.
However, even if Cu is excessively contained, the effect of improving the antibacterial property is saturated and the material properties such as hot workability and toughness are rather deteriorated. Therefore, 0.3 to 5.0% by weight, preferably 0.1.
Cu is included in the range of 3 to 4.0% by weight.

Components other than Cu include Cr, Ni, C, Si, and Mn, which are usually contained in stainless steel. The contents of these alloying elements differ depending on the steel type,
C: 0.005 to 0.50% by weight, Si: 0.1 to 3.
0% by weight, Mn: 0.1 to 4.0% by weight, Ni: 0.0
5 to 15.0% by weight, Cr: 10.0 to 25.0% by weight
It is adjusted to. Further, as property improving elements, Mo: 0.05 to 4.0% by weight, which is effective for improving corrosion resistance, and Ti, Nb, V, and Zr which are carbonitride forming elements are 0.01 to respectively.
It is also possible to add 1.0 wt%, 0.0005 to 0.02 wt% each of B, Ca, and a rare earth element effective for improving hot workability.

Hydrochloric acid in the acidic solution acts to increase the Cu concentration in the surface layer. This is because hydrochloric acid destroys the passive film and elutes the extreme surface layer of the base material, and in this state, a passive state containing a relatively large amount of Cu is reformed, and as a result, C of the surface layer portion is formed.
It is presumed that the u concentration will increase. In order to effectively increase the Cu concentration, it is necessary to set the hydrochloric acid concentration to 0.2% by weight or more. However, when the concentration of hydrochloric acid exceeds 5.0% by weight, a surface Cu concentration sufficient to exert antibacterial properties can be obtained in an extremely short time, but at the same time, the surface quality deteriorates, so that industrially stable operation is possible. It will be difficult. From the viewpoint of workability and economy, the concentration of hydrochloric acid is preferably 5.0% by weight or less. Nitric acid in an acidic solution is effective in maintaining good surface quality after immersion. That is, when stainless steel is dipped in an acidic solution containing hydrochloric acid, the surface layer of the base metal is exposed after the passivation film is destroyed, but impurities are generated when the passivation film is re-formed after that. It may accumulate on the surface and cause the surface to be colored. When nitric acid is present in this system, impurities are dissolved and removed during repassivation, so that the original surface state of stainless steel without coloring can be obtained. When the concentration of hydrochloric acid is in the range of 0.2 to 5.0% by weight, the effect of improving the surface quality becomes remarkable when the concentration of nitric acid is 1.0% by weight or more. However, even if the nitric acid is added in excess of 20.0% by weight, the effect is saturated.

The immersion time in the acidic solution is preferably 10 seconds or more for industrially stable operation, and is preferably 1 hour or less from the economical point of view. The temperature of the acidic solution is preferably room temperature or higher and 80 ° C. or lower in consideration of workability. The concentration of the acidic solution, the immersion time, the temperature, etc. are appropriately adjusted when the product is produced and processed, or according to the situation during use of the product. When stainless steel is immersed in such an acidic solution, a surface layer portion having a Cu concentration of 0.10 atomic% or more is formed, and excellent antibacterial properties are obtained. The Cu concentration in the surface layer portion is preferably 0.20 atomic% or more. As a result, sufficient antibacterial properties can be obtained in about 12 hours even under a normal environment. Therefore, even if the material loses its antibacterial properties,
The excellent antibacterial property is recovered relatively easily and inexpensively without impairing the original appearance of stainless steel.

[0011]

Example 12 kg of various stainless steels having the components and compositions shown in Table 1 were melted in a high frequency vacuum melting furnace. Steels A to D according to the present invention are austenitic stainless steels with varying Cu content in the range 0.4 to 3.4% by weight. In this type of steel, a steel ingot is hot-rolled into a hot-rolled sheet having a thickness of 3.8 mm, annealed at 1150 ° C for 1 minute soaking, and then cold-rolled to a cold sheet having a thickness of 1 mm. Manufactured into rolled sheets. Then, after finish annealing of 1050 ° C. × soaking for 1 minute, the surface of each sample was wet-polished with # 400 emery paper for about 20 μm to obtain a test material. Steels E and F according to the invention are ferritic stainless steels, C
The u contents were 0.5% by weight and 0.4% by weight, respectively. In this type of steel, a steel ingot is hot-rolled to a plate thickness of 3.6.
mm hot-rolled sheet, batch annealing at 860 ° C x soaking 6
After hot-rolled sheet annealing for 1 hour, cold rolled sheet thickness 1m
m cold rolled sheet. Then, after finishing annealing of 870 ° C. × soaking for 1 minute, the surface of each sample was wet-polished with # 400 emery paper for about 20 μm to obtain a test material. Steels GI according to the present invention are martensitic stainless steels with Cu contents of 0.6% by weight, 2.1% by weight and 0.7% by weight, respectively. In this type of steel, a steel ingot is hot-rolled into a hot-rolled steel sheet having a thickness of 3.6 mm, batch-annealed at 860 ° C for 6 hours soaking, and then cold-rolled. It was manufactured into a 1 mm cold-rolled sheet. Next, after finish annealing of 780 ° C. × soaking for 1 minute, the surface of each sample was wet-polished with # 400 emery paper for about 20 μm to obtain a test material. Comparative examples steels J and K are austenitic stainless steels, L are ferritic stainless steels, M and N are martensitic stainless steels,
In each case, the Cu content is less than 0.3% by weight.

[0012]

The stainless steels A to I according to the invention are listed in Table 2.
The surface-altered layer was removed by immersing in an acidic solution under the conditions shown in.

[0014]

For each as-polished stainless steel and each stainless steel treated with an acidic solution, the surface Cu concentration was measured and the antibacterial property was investigated. Further, the surface quality was judged by visual observation. The surface Cu concentration was calculated using the relative sensitivity index from the integrated intensity of each peak by irradiating the sample surface after degreasing with Mgkα X-ray using an X-ray electron spectroscopy analyzer. For antibacterial tests, Staphylococ
us aureus and Pseud
Each of Omonas aeruginosa (Pseudomonas aeruginosa) was shake-cultured in a normal broth medium at 35 ° C. for 16 to 24 hours to prepare a culture solution. The culture solution was diluted 20,000 times with sterile phosphate buffer solution to prepare a bacterial solution. 1 ml of the bacterial solution was dropped on the surface of each stainless steel polishing material and acidic solution immersion material, and stored at 25 ° C. for 24 hours. After storage, the test piece was washed off with 9 ml of SCDLP medium (manufactured by Nippon Pharmaceutical Co., Ltd.), and the number of viable cells was counted on the obtained liquid by a pour plate method (cultured at 35 ° C. for 2 days) using a standard agar medium. . As a reference, the bacterial solution was directly dropped on a sterilized petri dish, and the number of viable bacteria was counted in the same manner. Test results are evaluated as reliable when there is no significant increase or decrease in the reference viable cell count. According to this test method, it can be said that a material having a higher antibacterial property is obtained as the viable cell count after 24 hours is decreased from the viable cell count before the start of the test. As an antibacterial index, a sterilization rate calculated by the following formula of 95% or more was evaluated as antibacterial. The viable cell count at the start of the test was
5.0 × 10 ⁵ for Staphylococcus aureus and 5.1 for Pseudomonas aeruginosa
It was × 10 ⁵ . Sterilization rate = {(the number of viable cells at the start of the test)-(the number of viable cells after 24 hours)} / (the number of viable cells at the start of the test) x 100 (%)

[0016]

As shown in Table 3 showing the test results, test numbers 1 to 8 in which austenitic stainless steel was immersed in an acidic solution having a hydrochloric acid concentration of 0.3 to 4.5% by weight and a nitric acid concentration of 2 to 18% by weight. Then, the surface Cu concentration becomes 0.36 to 1.87 atom% by the dipping treatment, and the sterilization rate becomes 98 to 1
It exhibited an excellent antibacterial property of 00%. In addition, the surface after pickling was not roughened and the surface quality was good. In the test numbers 9 to 12 in which the ferritic stainless steel was immersed in an acidic solution having a hydrochloric acid concentration of 0.3 to 4.0% by weight and a nitric acid concentration of 10 to 18% by weight, the surface Cu concentration was decreased by the immersion treatment for a short time and a long time. The content was 0.41 to 1.58 atom%, and the sterilization rate was 95 to 100%, which showed excellent antibacterial properties. In addition, the surface after pickling was not roughened and the surface quality was good.

In Test Nos. 13 to 18 in which the ferritic stainless steel was immersed in an acidic solution having a hydrochloric acid concentration of 0.2 to 4.5% by weight and a nitric acid concentration of 10% by weight, the surface Cu concentration was increased by the immersion treatment for a relatively long time. 0.21 to 0.38 atom%
Thus, the sterilization rate was 98 to 100%, indicating excellent antibacterial properties. In addition, the surface after pickling was not roughened and the surface quality was good. For comparison, comparative steels J to N having a Cu content of less than 0.3% by weight were immersed in an acidic solution having a hydrochloric acid concentration and a nitric acid concentration specified in the present invention, and similarly test pieces were prepared. Further, a stainless steel having a Cu content of 0.3% by weight or more as a component was immersed in an acidic solution that did not satisfy the conditions specified in the present invention, and a test piece was similarly prepared. Table 4 shows the pickling conditions at this time.

[0019]

The surface Cu concentration, antibacterial property and surface quality of the as-polished test pieces and the pickled test pieces were similarly examined.

[0021]

As can be seen in Table 5 showing the survey results,
Test Nos. 19 to 23 in which stainless steel having a Cu content of less than 0.3 wt% was pickled with an acidic solution having a hydrochloric acid concentration of 0.3 to 4.5 wt% and a nitric acid concentration of 5 to 15 wt% Even when immersed for a long time, the surface Cu concentration is 0.06 ~
As low as 0.08 atom%, the sterilization rate is as low as 0-10%,
No improvement in antibacterial properties was observed. On the other hand, even when the Cu content was 0.3% by weight or more, when the hydrochloric acid concentration and the nitric acid concentration were out of the ranges specified in the present invention, the surface Cu concentration was high and the antibacterial property was poor, but the surface quality was poor. . From the comparison between Table 5 and Table 3, in order to obtain stainless steel excellent in both antibacterial property and surface quality, the Cu content is 0.3% by weight.
The above stainless steel is used, and the hydrochloric acid concentration is 0.2 to
It was confirmed that the combination of pickling with an acidic solution of 5.0 wt% and nitric acid concentration of 1.0 to 20.0 wt% was significant.

[0023]

As described above, in the present invention, the stainless steel containing 0.3% by weight of Cu is immersed in an acidic solution having a specified hydrochloric acid concentration and nitric acid concentration to form the altered layer in the surface layer portion. By removing and exposing the surface layer portion having a Cu concentration of 0.10 atomic% or more, a stainless steel excellent in antibacterial property and surface quality is obtained. By this, polishing, processing,
Even if the antibacterial property is lost due to its use as a product, it is possible to impart excellent antibacterial property without impairing the material properties and appearance. The stainless steel thus obtained has excellent antibacterial properties for a long period of time and is a safe material for the human body and the environment, and is used as a cutting tool, Western tableware, kitchen equipment, medical equipment, sanitary equipment, and various food products. It is used in a wide range of applications such as manufacturing and transportation equipment, bathtubs, washing tubs, hot water storage tanks, door knobs, and pipes.

Front Page Continuation (72) Inventor Rishi Kikuchi 3-4-1, Marunouchi, Chiyoda-ku, Tokyo Nisshin Steel Co., Ltd.

Claims (1)

[Claims] 1. A stainless steel containing 0.3% by weight or more of Cu or a processed product thereof is immersed in an acidic solution having a hydrochloric acid concentration of 0.2 to 5.0% by weight and a nitric acid concentration of 1.0 to 20.0% by weight. A method for producing Cu-containing stainless steel having improved antibacterial properties, which comprises exposing a surface layer portion having a Cu concentration of 0.10 atomic% or more.