JP2954868B2 - Method for improving antibacterial properties of Cu-containing stainless steel - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for improving the antibacterial properties of stainless steel used as various sanitary equipment, medical equipment, food-related equipment and equipment, and the like.

[0002]

2. Description of the Related Art Stainless steel has been widely used in various sanitary equipment, medical equipment, food-related equipment and equipment, etc., utilizing its excellent corrosion resistance. Conventionally, materials are selected with emphasis on material properties such as corrosion resistance and strength.
Contamination, bad smell, slimming, etc. caused by propagation of various bacteria
In recent years, where there is a growing tendency to be concerned about adverse effects on products and the like, antibacterial properties are required in addition to conventional properties. In particular, medical equipment, medical institutions,
In buildings and the like where a large number of people gather, it is desired to develop a material that is resistant to various bacteria. In order to meet this kind of demand, a method of coating and laminating a resin containing an antimicrobial agent on the surface of stainless steel, a method of plating an antimicrobial component in a matrix, and the like are disclosed in JP-A-5-228202 and JP-A-5-228202. -10191 publication.

When a resin containing an antibacterial agent is applied and laminated on the surface of stainless steel, the excellent metallic luster inherent to stainless steel is impaired, and the commercial value is reduced. Moreover, the antibacterial coating is liable to be damaged during processing or use, such as breakage or abrasion, and the antibacterial component elutes when exposed to a humid atmosphere. As a result, not only the appearance deteriorates, but also the original antibacterial action is impaired. In addition, when the antibacterial agent is depleted, the remaining film becomes a nutrient for various bacteria, which in turn promotes the propagation of various bacteria. 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 the dissolution, abrasion, chipping or the like of the film, and the antibacterial action may be reduced. In either method,
Since the antibacterial agent is used, the eluted antibacterial agent may have an adverse effect on the human body and the environment. Therefore, it is desired to provide the stainless steel itself with antibacterial properties instead of the method of coating the antibacterial component.

[0004]

The present inventors have investigated and studied stainless steel satisfying such required characteristics. As a result, it has been clarified that when Cu is contained in stainless steel, a stainless steel which maintains excellent antibacterial properties over a long period of time can be obtained, and has been proposed in Japanese Patent Application Laid-Open Nos. 8-193218 and 8-193219. Cu-containing stainless steel forms a Cu-rich surface layer, and exhibits antibacterial properties by Cu ions eluted from the surface layer. However, in the process of processing stainless steel into products, various types of polishing and mechanical processing are often performed, and depending on the conditions of polishing and mechanical processing, the surface layer may be degraded and the original excellent antibacterial properties may not be exhibited. The present invention has been devised to solve such a problem, and based on the fact that the antibacterial property of stainless steel proposed in the earlier application is improved by Cu content,
By removing the surface layer of stainless steel that has been deteriorated by polishing and machining, and exposing the surface with a high Cu concentration, it is relatively inexpensive without impairing the various properties such as beautiful appearance and workability peculiar to stainless steel. An object of the present invention is to easily and stably recover stable antibacterial properties at a production cost.

[0005]

According to the present invention, there is provided a method for improving antibacterial properties, which comprises at least 0.1 to 30.0% by weight of stainless steel containing 0.3% by weight or more of Cu or a processed product thereof. Immersion in an acidic solution containing H ₂ SO ₄ and Cu ions of 50 to 5000 ppm to reduce the Cu concentration of the surface layer to 0.1
It is characterized by increasing to 0 atomic% or more. The pickling solution to be used is added Cu ions 50~5000ppm to 0.1 to 30.0 wt% solution of H ₂ SO _4. The added Cu ions exhibit an effect of stabilizing the surface quality after pickling, as compared with a case where stainless steel is immersed in an H ₂ SO ₄ pickling solution. By this acid immersion, the surface altered layer generated by polishing or processing is removed, and C effective for antibacterial property is removed.
A surface portion having a u concentration of 0.10 atomic% or more is formed.

[0006]

According to the investigation and research conducted by the present inventors, as described in the above-mentioned prior application specification, when a surface layer having a high Cu concentration is formed on the surface of a stainless steel material, excellent antibacterial properties are obtained. It was found that it was necessary to include 0.3% by weight or more of Cu in the base steel. When Cu is contained in the stainless steel, Cu is concentrated and a Cu-based oxide is generated in the passive film on the stainless steel surface. The concentrated Cu or Cu-based oxide is ionized as a very small amount of Cu ions by a small amount of water adhering to the surface of the stainless steel in a humid environment where bacteria can easily propagate. The ionized Cu reacts with the cell's respiratory and metabolic enzymes to inactivate the cells and metabolic enzymes. As a result, bacteria and germs are killed. Cu content of 0.3% by weight in steel
Above, the concentration of Cu concentrated on the surface rapidly increases, and such an antibacterial effect becomes remarkable. However, in a process of processing stainless steel into a product or the like, there is a case where a polishing process such as mechanical polishing or electrolytic polishing is performed on the stainless steel.
The Cu-rich surface layer, which is effective for antibacterial properties, is deteriorated by this polishing, and may not exhibit sufficient antibacterial properties at the product stage. Further, the antibacterial property may be lost depending on processing conditions such as bending and drawing.

Therefore, the present inventors have further investigated and studied the stainless steel having lost the antibacterial property, and
When immersing stainless steel in an acidic solution containing 0.0% by weight of H ₂ SO ₄ and Cu ions at a concentration of 50 to 5000 ppm, the Cu concentration on the surface of the stainless steel was increased to 0.10 atomic% or more, and excellent. It has been found that the antibacterial properties are restored. The stainless steel targeted by the present invention contains 0.3% by weight or more of Cu. Cu is an alloy element indispensable for imparting excellent antibacterial properties. 0.3% by weight
When the Cu content is less than 3, even if stainless steel is immersed in an acidic solution, Cu is not sufficiently concentrated in the passive film, and excellent antibacterial properties cannot be obtained. In this respect, in order to obtain effective antibacterial properties, Cu content of 0.3% by weight or more is required. However, even if Cu is excessively contained, the antibacterial property improving effect is saturated, and material properties such as hot workability and toughness are rather deteriorated. Therefore, in the stainless steel targeted by the present invention, the Cu content is preferably adjusted to a range of 0.3 to 5.0% by weight, more preferably 0.3 to 4.0% by weight.

[0008] As alloy components other than Cu, there are Cr, Ni, C, Si, Mn and the like usually contained in stainless steel. The content of these alloy elements differs depending on the steel type, but 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:
It is adjusted to 0.1 to 15.0% by weight and Cr to 10.0 to 25.0% by weight. As the property improving element, Mo: 0.05 to 4.0% by weight which is effective for improving the corrosion resistance, and each of Ti, Nb, V, and Zr, which are carbonitride forming elements, are 0.0
01-0.5% by weight, B, C effective for improving hot workability
a, rare earth metal may be contained in each of 0.0005 to 0.02% by weight.

[0009] The concentration of H ₂ SO ₄ in the acidic solution is set at 0.1 from the viewpoint of ensuring a sufficient surface Cu concentration to exhibit antibacterial properties.
1% by weight or more is required. As the H ₂ SO ₄ concentration increases, the time to obtain a sufficient surface Cu concentration to exhibit antibacterial properties is shortened. However, at a high H ₂ SO ₄ concentration exceeding 30.0% by weight, the surface quality deteriorates at the same time, and industrially stable operation cannot be performed. Further, from the viewpoints of workability and economy, an H ₂ SO ₄ concentration of 30.0% by weight or less is preferable. The mechanism by which the antimicrobial properties of stainless steel are restored by immersion in an H ₂ SO ₄ -containing acidic solution is not clear, but one possibility is considered as follows. When the stainless steel containing Cu is immersed in the acidic solution, the passivation film is destroyed and the extreme surface layer of the base material is eluted, and in this state, the passivation film containing a relatively large amount of Cu is reformed. As a result, it is inferred that the Cu concentration in the surface layer increases.

At this time, 50 to 5000 pp is added to the acidic solution.
By adding m Cu ions, a high quality surface without surface roughness is formed stably. That is, H ₂ SO
_When stainless steel is immersed in an acidic solution containing ₄ , the passivation film is destroyed in the active region, and then the surface layer of the base material is eluted. When exposed to the active region for a long time or immersed in a high-concentration acidic solution, the elution amount of the stainless steel increases, the surface skin becomes rough, and the surface quality deteriorates. On the other hand, Cu
When ions are present in the acidic solution, the potential rises to the vicinity of the passive region, so that elution of the base material does not occur rapidly,
Surface roughness is suppressed. H ₂ SO ₄ concentration 0.1-3
In the range of 0.0% by weight, the effect of improving the surface quality is small when the addition amount of Cu ions is less than 50 ppm.
Even if Cu ions are added in excess of 00 ppm, the effect of improving the surface quality is saturated. The immersion time in the acidic liquid is preferably 10 seconds or more for stable industrial operation, and is preferably 1 hour or less from an economic viewpoint. The temperature of the acidic solution is preferably from room temperature to 80 ° C. in consideration of workability.

In such an acidic solution, a Cu concentration of 0.1
The stainless steel is immersed under the condition that a surface portion of 0 atomic% or more is formed. When the Cu concentration in the surface layer is 0.10 atomic% or more, preferably 0.20 atomic% or more, excellent antibacterial properties are imparted to stainless steel. Thereby, sufficient antibacterial properties can be obtained in about 12 hours under a normal environment. As described above, by immersing stainless steel in an acidic solution under conditions where the concentration, immersion time, temperature, etc. are appropriately adjusted according to the situation during production and processing of the product or during use of the product, the Cu concentration is reduced. Is increased to 0.10 atomic% or more. Therefore, even if the material has lost its antibacterial properties, it is possible to relatively easily and inexpensively recover the antibacterial properties without impairing the original appearance of stainless steel.

[0012]

【Example】

Example 1: 12 kg of various stainless steels whose components are shown in Table 1 were melted in a high-frequency vacuum melting furnace. Steel type numbers 1 to 4 in Table 1 are austenitic stainless steels,
It is a steel whose u content is changed in the range of 0.2 to 2.0% by weight. Steel type numbers 5 and 6 each have a Cu content of 0.1.
Ferritic stainless steel adjusted to 2% by weight and 0.4% by weight. Steel Nos. 7 and 8 are martensitic stainless steels whose Cu content was adjusted to 0.2% by weight and 0.5% by weight, respectively.

[0013]

As for stainless steels of steel types Nos. 1-4, a hot-rolled sheet having a thickness of 3.8 mm is formed by hot rolling, the hot-rolled sheet is annealed at 1150 ° C. × soak for 1 minute, and then cold-rolled. To produce a cold-rolled sheet having a thickness of 1 mm.
Minutes of finish annealing. The surface of each test piece cut out from the annealed plate was subjected to wet polishing using # 400 emery paper to polish it by about 20 μm to obtain a test material. For stainless steels of steel types Nos. 4 and 5, a hot-rolled sheet having a thickness of 3.6 mm was formed by hot rolling, batch-annealed at 860 ° C. × soaking for 6 hours, and then cold-rolled into a cold-rolled sheet having a thickness of 1 mm. Rolled plates are manufactured and 87
Finish annealing was performed at 0 ° C. × soaking for 1 minute. The surface of each test piece cut out from the annealed plate was made approximately # 20 with # 400 emery paper.
A wet polishing was performed to polish μm to obtain a test material. For stainless steels of steel types Nos. 7 and 8, the sheet thickness was 3.
A 6 mm hot-rolled sheet was subjected to batch annealing at 860 ° C. × soaking for 6 hours, then a cold-rolled sheet having a thickness of 1 mm was produced by cold rolling, and subjected to finish annealing at 780 ° C. × soaking for 1 minute. . The surface of each test piece cut out from the annealed plate was subjected to wet polishing using # 400 emery paper to polish it by about 20 μm to obtain a test material.

With respect to each of the polished stainless steels, the surface Cu concentration was measured, and the antibacterial property and the surface quality were investigated. The surface quality was determined by visual observation. The surface Cu concentration was calculated using a 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 spectrometer. For antibacterial tests, Staphylococcus aure
us (Staphylococcus aureus) and Pseudomonas
aeruginosa (Pseudomonas aeruginosa) was cultured with shaking in a normal broth medium at 35 ° C for 16 to 20 hours to prepare a culture solution. The culture was sterilized with phosphate buffer solution for 20 years.
The bacterial solution was prepared by diluting 000-fold. 1 ml of the bacterial solution is dropped on the surface of the abrasive of each stainless steel, and the temperature is 25 ° C.
For 24 hours. After saving, SCDLP (Soybe
an Casein Digest Broth wi
the Lecithin and Polysorba
te 80, manufactured by Nippon Pharmaceutical Co., Ltd.), and the resulting solution was subjected to a pour culture method (3) using a standard agar medium.
(Cultivation at 5 ° C for 2 days). Further, in order to confirm that there was no abnormality in the test, a bacterial solution was directly dropped on a sterilized glass petri dish as a control, and the number of viable bacteria was similarly counted.

In this test method, when there is no significant change in the number of viable bacteria serving as a control, the test result can be evaluated as having high reliability. And, it can be said that the more the viable count after 24 hours is smaller than the viable count before the start of the test, the more excellent the antibacterial property. As an antibacterial index, a sterilization rate of 95% or more calculated by the following equation was evaluated as antibacterial. Sterilization rate (%) = [viable cell count at start of test × (1−change rate of control / 100) −viable count at 24 hours] / viable count at start of test × (1−change rate of control) / 100) × 100 Rate of change (%) of control = (viable cell count at start of test−viable cell count after 24 hours) / viable cell count at start of test × 100

[0017]

As shown in Table 2 showing the results of the investigation, the as-polished material had a sterilization rate of less than 95%, regardless of the Cu content, and was determined to have no antibacterial properties. In addition, in the as-polished material, the surface Cu concentration was 0.10 atomic% or less in any of the test pieces. Therefore, the same stainless steel abrasive was kept at a temperature of 50 ° C. with a H ₂ SO ₄ concentration of 30% and a Cu ion concentration of 5000 p.
immersion in an acidic solution of pm for 1 hour. The surface Cu concentration, antibacterial property and surface quality of each test piece after the immersion treatment were similarly examined.

[0019]

As can be seen from Table 3 showing the results of the investigation, the steel types No. 1,5 and Cu having a Cu content of less than 0.3% by weight were used.
In No. 7, the surface Cu concentration was 0.10 even when immersed in an acidic solution.
Atomic%, the antibacterial test with Staphylococcus aureus and Pseudomonas aeruginosa showed a low sterilization rate. On the other hand, the material Cu
Steel grade numbers 2 to 4,6, whose content is 0.3% by weight or more
In No. 8, the surface layer Cu content was low and did not exhibit antibacterial properties as shown in Table 2 in the polished state, but the surface layer Cu content became 0.10 atomic% or more by immersion treatment in an acidic solution. . As a result, as shown in Table 3, excellent antibacterial properties with a sterilization rate of 90% or more were exhibited. Also, the surface of the stainless steel after the immersion treatment was maintained at a good quality. From the above results, it was confirmed that when the Cu content of the material was 0.3% by weight or more, the antibacterial property was improved by immersion in an acidic solution containing H ₂ SO ₄ and Cu ions. . A stainless steel of steel type number 2 (Cu content: 0.3% by weight) is immersed for a short time in an acidic solution in which the H ₂ SO ₄ concentration and the Cu ion concentration are variously varied, and the surface Cu concentration, antibacterial property and surface quality are immersed. The effect of the concentration of H ₂ SO _{4 and the} concentration of Cu ions on the concentration was investigated. The examination results are shown in Tables 4 and 5 in comparison with the as-polished material.

[0021]

[0022]

As shown in Table 4 (Test No. 1), the as-polished material had a low surface Cu concentration and did not exhibit antibacterial properties. When this abrasive was immersed in acidic solutions of various Cu ion concentrations at an H ₂ SO ₄ concentration of less than 0.1% by weight (test numbers 2, 8, 14, 20), the surface layer had a Cu concentration of 0.06 to 0. The sterilization rate is also 59 because it is as low as 0.08 atomic%.
% Or less, indicating that the antibacterial properties have not been improved. On the other hand, those immersed in an acidic solution having a H ₂ SO ₄ concentration of 0.1% by weight or more (test numbers 3 to 7, 9 to
13, 15, 19, 21 to 25), the surface layer Cu concentration was as high as 0.14 to 0.21 atomic% regardless of the Cu ion concentration, and exhibited excellent antibacterial properties with a sterilization rate of 97 to 100%. However, when the Cu ion concentration was as low as 30 ppm (Test Nos. 3 to 7), the surface became extremely rough and could not be commercialized. In an acidic solution in which the H ₂ SO ₄ concentration and the Cu ion concentration were variously changed, steel type No. 2 (Cu content was 0.1%) was added.
(3% by weight) stainless steel was immersed for a relatively long time, and the effects of the H ₂ SO ₄ concentration and the Cu ion concentration on the surface Cu concentration, antibacterial property and surface quality were investigated. The examination results are shown in Tables 6 and 7 in comparison with the as-polished material.

[0024]

[0025]

As shown in Table 6 (Test No. 31), the as-polished material had a low surface Cu concentration and did not show antibacterial properties. This abrasive is used at an H ₂ SO ₄ concentration of 0.1% by weight.
In the samples immersed in acidic solutions having various Cu ion concentrations of less than (test numbers 32, 38, 44, and 50), the sterilization rate was 25% or less because the surface Cu concentration was as low as 0.05 to 0.09 atomic%. , Indicating that the antibacterial property has not been improved. On the other hand, those immersed in an acidic solution having a H ₂ SO ₄ concentration of 0.1% by weight or more (Test Nos. 33 to 3)
7, 39-43, 45-49, 51-55)
The surface Cu concentration is 0.13 to 0.22 regardless of the ion concentration.
Atomic% was high and exhibited excellent antibacterial properties with a sterilization rate of 96 to 100%. However, when the Cu ion concentration was as low as 30 ppm (Test Nos. 33 to 37), the surface became extremely rough and could not be commercialized.

As can be seen from test number 43,
_{In the case} of an acidic solution containing 2 ppm of Cu ions at a concentration of 40 wt% and containing 50 ppm of ₂ SO ₄ , it was possible to commercialize the product, but surface roughness was partially generated. On the other hand, as shown in Test Nos. 49 and 55, in an acidic solution containing H ₂ SO _{4 at a} concentration of 40% by weight and containing a high concentration of Cu ions, surface roughening does not occur and at least 50 ppm of Cu ions are contained. The surface quality was found to be stable. From the above results,
A stainless steel containing 0.3% by weight or more of Cu or a processed product thereof is mixed with 0.10 to 30.0% by weight of H ₂ SO ₄ and 50%.
When immersed in an acidic solution containing up to 5000 ppm of Cu ions, it is confirmed that the surface altered layer generated by polishing and processing is removed, and a surface layer having a Cu concentration of 0.10 atomic% or more effective for antibacterial properties is formed. Was. As a result, it is found that the antibacterial property is restored without impairing the surface quality.

Example 2: 12 kg of various stainless steels having the components shown in Table 8 were melted in a high-frequency vacuum melting furnace. Steel type symbols A to G are austenitic stainless steels in which the Cu content is changed in the range of 0.3 to 3.4% by weight. Each ingot was hot-rolled into a hot-rolled sheet having a thickness of 3.8 mm, and then subjected to hot-rolled sheet annealing at 1150 ° C and soaking for 1 minute. Next, a cold-rolled sheet having a thickness of 1 mm was manufactured by cold rolling,
Finish annealing was performed at 50 ° C. × soaking for 1 minute. A test piece was cut out from each of the annealed stainless steel plates, and wet-polished using # 400 emery paper to polish it by about 20 μm to obtain a test material. The steel symbols H and I are ferritic stainless steels having Cu contents of 0.4% by weight and 0.5% by weight, respectively. Each ingot was hot rolled into a hot-rolled sheet having a thickness of 3.6 mm by hot rolling, and subjected to batch annealing at 860 ° C. × soaking for 6 hours.
A cold-rolled sheet having a thickness of 1 mm is manufactured by cold rolling, and 870 ° C.
× Finish annealing with soaking for 1 minute. A test piece was cut out from each of the annealed stainless steel plates, and wet-polished using # 400 emery paper to polish it by about 20 μm to obtain a test material.

The steel symbols J to L are martensitic stainless steels having a Cu content of 0.6% by weight, 2.1% by weight and 0.7% by weight, respectively. Each ingot was hot-rolled into a hot-rolled sheet having a thickness of 3.6 mm by hot rolling, and subjected to batch annealing at 860 ° C. × soaking for 6 hours, and then cold-rolled to produce a cold-rolled sheet having a thickness of 1 mm. Finish annealing was performed at 780 ° C. × 1 minute soaking. A test piece was cut out from each of the annealed stainless steel plates, and wet-polished using # 400 emery paper to polish it by about 20 μm to obtain a test material. In the comparative examples, the steel symbols M and N are austenitic stainless steel, the steel symbol O is a ferritic stainless steel, and the steel symbols P and Q are martensitic stainless steels, each having a Cu content of less than 0.3% by weight.

[0030]

For each of the polished stainless steel and each of the stainless steels treated with the acidic solution, the Cu concentration of the surface layer was measured in the same manner as in Example 1, and the antibacterial properties and the surface quality were investigated. H ₂ SO ₄ concentration and Cu according to the invention
When stainless steel is immersed in an acidic solution of ion concentration,
The surface layer Cu concentration, antibacterial property and surface quality as shown in Tables 9 and 10 were obtained. Test Nos. 1 to 6 used an austenitic stainless steel abrasive, and H ₂ SO ₄ was 0.15 to 0.15.
25.0% by weight, Cu ion concentration 60-5000pp
This is an example of immersion for a short time in an acidic solution changed in the range of m. The immersion resulted in a surface layer Cu concentration of 0.26 to 1.57 atomic%, and a very excellent antibacterial property with a sterilization rate of 97 to 100% was obtained. Also, the surface after the immersion treatment was of good quality without rough skin. Test numbers 7-14 use austenitic stainless steel abrasives and H ₂ SO
₄ 0.2 to 20.0% by weight, Cu ion concentration 50 to
This is an example of immersion in an acidic solution changed in a range of 3000 ppm for a long time. By immersion, the surface Cu concentration is 0.13
1.58 atomic%, sterilization rate 98-100%
Very good antibacterial properties were obtained. Also, the surface after the immersion treatment was of good quality without rough skin.

Test Nos. 15 to 18 use a ferrite stainless steel abrasive and adjust H ₂ SO ₄ to 0.1 to 25.
This is an example of immersion for a long time in an acidic solution in which the concentration of Cu ion is changed in the range of 50 to 5000 ppm at 0% by weight. By immersion, the surface layer Cu concentration became 0.21 to 0.38 atomic%, and a very excellent antibacterial property with a sterilization rate of 98 to 100% was obtained. Also, the surface after the immersion treatment was of good quality without rough skin. Test Nos. 19 to 24 used martensitic stainless steel abrasives, H ₂ SO ₄ of 0.1 to 25.0% by weight, and Cu ion concentration of 50 to 45.
This is an example of immersing in an acidic solution changed in the range of 00 ppm for a long time. Surface Cu concentration by immersion is 0.19 ~
It was 1.45 atomic%, and a very excellent antibacterial property with a sterilization rate of 97 to 100% was obtained. Also, the surface after the immersion treatment was of good quality without rough skin.

[0033]

[0034]

As a comparative test, when steels M to Q having a Cu content of less than 0.3% by weight were immersed in an acidic solution having an H ₂ SO ₄ concentration and a Cu ion concentration according to the present invention, the Cu content was reduced. When the concentration of H ₂ SO ₄ or the concentration of Cu ions in the acidic solution is out of the range specified in the present invention at 0.3% by weight or more, the surface Cu concentration, antibacterial property and surface quality after the pickling treatment are shown. 11 and Table 12. Test numbers 31 to
No. 40 uses an abrasive of stainless steel M to Q having a Cu content of less than 0.3% by weight, and has an H ₂ SO ₄ concentration of 2.5 to 3%.
0.0% by weight, Cu ion concentration 300 ~ 4500ppm
This is an example of immersion treatment for 100 to 3600 seconds in an acidic solution changed in the range of (1) to (3). In this case, even if immersed for a relatively long time, the Cu concentration in the surface layer is limited to 0.01 to 0.09 atomic%,
It showed a sterilization rate of ９１91%. This indicates that a Cu content of 0.3% by weight or more is necessary for improving the antibacterial property. Test numbers 41, 44-46, 49-51
Since an acidic solution having a low H ₂ SO ₄ concentration of less than 0.10% by weight was used, the surface Cu concentration after the immersion treatment was 0.0%.
As low as 3 to 0.09 atomic%, sufficient antibacterial properties could not be obtained. Test numbers 42, 43, 47 and 48 are H ₂ SO
_{4 This} is an example in which stainless steel having a Cu content of 0.3% by weight or more was immersed in an acidic solution having a concentration of 5.0% by weight or 40.0% by weight and a Cu ion concentration adjusted to 10 ppm.
In this case, the antibacterial property was sufficiently improved, but the surface roughness was remarkable, and the product could not be used as a product utilizing the surface unique to stainless steel.

[0036]

[0037]

[0038]

As described above, in the present invention, the Cu content of the stainless steel used and the H content of the acidic solution are used.
The specified combination of the ₂ SO ₄ concentration and the Cu ion concentration raises the surface Cu concentration of the effective antibacterial property to 0.10 atomic% or more without causing roughening of the stainless steel after the treatment with the acidic solution. . Therefore, even after the original antibacterial property is lost by polishing, processing, use as a product, or the like, it is possible to impart excellent antibacterial property without impairing the material properties and appearance. The stainless steel obtained in this way can be used as a material that exhibits excellent antibacterial properties over a long period of time and is safe for the human body and the environment, such as cutlery, western tableware, kitchen appliances, various furnishings, medical equipment, sanitary goods, and various foods. Used in a wide range of fields such as manufacturing and transport containers, bathtubs, washing machines, hot water tanks, doorknobs, pipes, etc.

Continued on the front page (72) Inventor Rishi Kikuchi 4976 Nomura Minamicho, Shinnanyo-shi, Yamaguchi Nisshin Steel Engineering Co., Ltd. (72) Inventor Tomoaki Toyohara 4976 Nomuraminamicho, Shinnanyo-shi, Yamaguchi Nisshin (56) References JP-A-63-143267 (JP, A) JP-A-63-235482 (JP, A) JP-A-3-79773 (JP, A) JP-B-51-2054 (JP, B1) (58) Fields investigated (Int. Cl. ⁶ , DB name) C23C 22/00 A61L 2/16 C22C 38/00 302 C22C 38/16

Claims (1)

(57) [Claims] 1. A stainless steel containing 0.3% by weight or more of Cu or a processed product thereof containing 0.1 to 30.0% by weight of H ₂ SO.
_A method for improving the antibacterial property of a Cu-containing stainless steel, comprising immersing in an acidic solution containing ₄ and 50 to 5000 ppm of Cu ions to increase the Cu concentration in the surface layer to 0.10 atomic% or more.