JPH08229107A - Improving method of antibacterial performance of copper-containing stainless steel - Google Patents

Abstract

PURPOSE: To produce a stainless steel with higher antibacterial performance without impairing appearance, machinability and the like. CONSTITUTION: A stainless steel containing 0.3wt.% or more of Cu or work thereof is dipped into an acid solution and a surface denatured layer is removed to expose a skin layer part rich in Cu. The acid solution herein used is the one containing not-oxidizing or reducing acid and the surface layer part is adjusted to 0.10 at.% or more of Cu concentration to secure excellent antibacterial performance. Thus, excellent antibacterial performance can be developed by the dipping treatment using the acid solution even fo ra material from which the antibacterial performance is already lost by grinding, working or the like.

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 antibacterial property of Cu-containing stainless steel used as various sanitary equipment, medical equipment, food-related equipment, base material and the like.

[0002]

2. Description of the Related Art Stainless steel having excellent corrosion resistance is widely used as various sanitary equipment, medical equipment, food-related equipment, base materials and the like. However, due to the propagation of various bacteria,
There is an increasing tendency to be concerned about the adverse effects of bad odors and slime on human bodies, animals, products and the like. Especially in kitchens, medical institutions, buildings where many people gather, where cleanliness is required, there is a strong demand for materials that are resistant to various bacteria. In order to meet this type of requirement, 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 are disclosed in JP-A-5-228202. 6-10191, etc.

[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 are eluted and the appearance is deteriorated, and the original antibacterial action is impaired. Be done. In addition, when the antibacterial agent is exhausted, the remaining film is rather a nutrient for miscellaneous bacteria, which also promotes the growth of miscellaneous bacteria. In the case where the composite plating containing the antibacterial agent component is applied, there is a drawback that the adhesion of the plating layer is not sufficient and the workability is deteriorated. In addition, the appearance may be deteriorated due to dissolution, wear, and defects of the film, and the antibacterial action may be decreased. Moreover, since the antibacterial agent is used in all the methods, the eluted antibacterial agent may have a harmful effect on the human body and the environment. Therefore, it is desired to impart antibacterial properties to the stainless steel itself, instead of coating the antibacterial agent component.

The present inventors have investigated and studied stainless steels satisfying such required characteristics. As a result, it has been clarified that stainless steel having excellent antibacterial property for a long period of time can be obtained by adding copper to the stainless steel. Japanese Patent Application Nos. 7-21291 and 7-21292
Filed as an issue. The Cu-containing stainless steel forms a Cu-rich surface layer portion, and exhibits antibacterial properties by Cu ions eluted from the surface layer portion. However, in the process of processing stainless steel into products, various types of polishing and machining are often applied to stainless steel, and the surface layer may deteriorate depending on the conditions of polishing and machining, and the original excellent antibacterial properties may not be exhibited. is there. The present invention is a further improvement of the Cu-containing stainless steel exhibiting such good antibacterial property, and the surface layer portion of the stainless steel which has been deteriorated by polishing or machining is removed to expose the surface having a high Cu concentration. Thus, the purpose of the present invention is to restore the antibacterial property easily at a relatively low manufacturing cost, without impairing the various characteristics such as the beautiful appearance and workability peculiar to stainless steel.

[0005]

In order to achieve the object, the method of improving the antibacterial property of the present invention comprises 0.3% by weight or more of C.
It is characterized in that stainless steel containing u or a processed product thereof is immersed in an acidic solution to remove the surface-altered layer to expose the Cu-rich surface layer portion. As the acidic solution, an acidic solution containing a non-oxidizing or reducing acid such as sulfuric acid, hydrofluoric acid or oxalic acid is used, and the pH is preferably adjusted to 2.5 or less.
Stainless steel or its processed product is immersed in this acidic solution. By the acid immersion, the surface-altered layer generated by polishing or processing is removed, and the surface layer portion having a Cu concentration of 0.10 atomic% or more effective for antibacterial properties is exposed.

[0006]

The present inventors have found that when a surface layer portion having a high Cu concentration is formed on the surface of a stainless steel material, an excellent antibacterial property can be obtained. It was clarified in the above-mentioned prior application that it is necessary to contain Cu in an amount of at least%. When Cu is added to stainless steel, Cu is concentrated or Cu-based oxide is generated in the passivation film on the surface of stainless steel. The concentrated Cu or Cu-based oxide is ionized as an extremely small amount of Cu ion by a slight amount of water adhering to the surface of stainless steel in a wet environment where it is easy to propagate recently.
Ionized Cu efficiently and strongly reacts with the respiratory and metabolic enzymes of cells, and inactivates the cells and metabolic enzymes. As a result, bacteria have recently been killed. Such an antibacterial effect becomes remarkable when the Cu content in the steel becomes 0.3% by weight or more because the concentration of Cu concentrated on the surface sharply increases. However, in the process of processing stainless steel into a product or the like, polishing processing such as mechanical polishing or electrolytic polishing may be performed on stainless steel. Due to this polishing process, the Cu-rich surface layer portion may be deteriorated, and sufficient antibacterial properties may not be exhibited at the product stage. The antibacterial property may disappear depending on the processing conditions even in bending or drawing.

[0007] Therefore, the present inventors further investigated and studied the stainless steel from which the antibacterial property disappeared, and as a result, the stainless steel was immersed in an acidic solution containing a non-oxidizing or reducing acid and having its pH properly adjusted. By doing so, it was found that when the Cu concentration on the surface becomes as high as 0.10 atomic% or more, the excellent antibacterial property is restored. Among the acidic solutions, dilute sulfuric acid aqueous solution, hydrofluoric nitric acid aqueous solution, oxalic acid aqueous solution, etc. are particularly effective in improving antibacterial properties. The antibacterial recovery effect becomes more remarkable when the temperature of the acidic solution is raised. The stainless steel targeted by the present invention contains 0.3% by weight or more of Cu. C
u is an alloying element essential for imparting excellent antibacterial properties. If the Cu content is less than 0.3% by weight, excellent antibacterial properties cannot be obtained because Cu is not sufficiently concentrated in the passivation film even when immersed in an acidic solution. In this respect, a Cu content of 0.3% by weight or more is necessary to obtain effective antibacterial properties. 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, the Cu content in the stainless steel of the present invention is preferably 0.3.
To 5.0% by weight, more preferably 0.3 to 2.0
Adjust to the range of weight%.

When the Cu concentration on the surface is lowered by polishing, processing, etc., stainless steel is added to an acidic solution containing a non-oxidizing acid such as phosphoric acid, sulfuric acid, hydrofluoric nitric acid or an acidic solution containing a reducing acid such as oxalic acid. When is dipped, the Cu concentration in the surface layer portion increases and the antibacterial property is recovered. On the other hand, when immersed in an acidic solution containing only an oxidizing acid such as nitric acid, the Cu concentration on the surface of the steel material does not change significantly, and the antibacterial property remains low.
The mechanism by which the antibacterial properties are restored by a non-oxidizing or reducing acidic solution is not clear, but one possible reason is as follows. When stainless steel is immersed in an acidic solution containing only an oxidizing acid, the stainless steel surface is only oxidized without elution, and Cu is not concentrated in the passivation film on the steel surface. On the other hand, when stainless steel is immersed in a non-oxidizing or reducing acid solution, the passivation film is destroyed and the very surface layer of the base steel elutes, and in this state the passivation containing a relatively large amount of Cu. The film reforms.
As a result, it is presumed that the Cu concentration in the surface layer portion becomes high. Of the acidic solutions that can improve antibacterial properties,
Especially dilute sulfuric acid aqueous solution, hydrofluoric nitric acid aqueous solution and oxalic acid aqueous solution,
It has a strong antibacterial recovery action, is relatively inexpensive, and alleviates the problem of post-treatment.

With an acidic solution having a low acid concentration and a pH higher than 2.5, even if the stainless steel is immersed in an acidic solution containing a non-oxidizing acid or a reducing acid, the passivation film is less likely to be destroyed. Cu is not sufficiently concentrated in the film. Therefore, the pH of the acidic solution is preferably 2.5 or less. The lower the pH of the acidic solution, the stronger the action of concentrating Cu, and the better antibacterial property is exhibited by immersion for a relatively short time. However, in an acidic solution having an excessively low pH, the stainless steel surface is corroded or discolored by the acid, impairing the original beautiful appearance of the stainless steel. Therefore, the acidic solution used in the present invention is preferably adjusted to have a pH range of 0 to 2.5. If the pH of the acidic solution is 2.5 or less, the Cu concentration in the surface layer portion can be increased even at a temperature near room temperature. However, the higher corrosion resistance of stainless steel, the longer the dipping time required for increasing the Cu concentration in the surface layer portion. In this case, by raising the temperature of the acidic solution, the reactivity between the acidic solution and the surface of the stainless steel can be enhanced, Cu concentration by the acidic solution can be promoted, and the immersion time can be shortened. The effect of raising the temperature becomes remarkable when the acidic solution is heated to 50 ° C. or higher. Further, the upper limit temperature of the acidic solution may be the boiling point or lower, but it is preferably 80 ° C. or lower in consideration of economical efficiency.

In such an acidic solution, the Cu concentration is 0.1.
The stainless steel is immersed under the condition that 0 atomic% or more of the surface layer portion is formed. When the Cu concentration in the surface layer portion is 0.10 atomic% or more, 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 are exhibited even in a normal environment in about 12 hours. As described above, stainless steel is immersed in an acidic solution that contains a non-oxidizing acid or reducing acid and is appropriately adjusted in concentration, temperature, etc. during production / processing of the product, or during use of the product. As a result, the Cu concentration becomes 0.
A surface layer portion having a height of 10 atomic% or more is formed. Therefore, even if the antibacterial property is lost, excellent antibacterial property can be imparted relatively easily and inexpensively without impairing the original appearance of stainless steel.

[0011]

【Example】

Example 1: Various stainless steels having the components shown in Table 1 were smelted, and an annealed plate having a thickness of 1 mm was manufactured from a steel ingot of 100 kg through hot rolling, solution heat treatment, cold rolling and annealing. In Table 1, Group A is a steel according to the present invention, and Group B is a comparative steel having a Cu content outside the range specified in the present invention.

[0012]

[Table 1]

After wet-polishing about 20 μm of the surface of the annealed material with # 400 emery paper, the pH was adjusted to 0.2.
Further, an acidic solution treatment material was prepared by immersing in a sulfuric acid aqueous solution having a liquid temperature of 70 ° C. for 60 seconds and washing with pure water. The surface Cu concentration of each as-polished stainless steel and each stainless steel treated with an acidic solution were measured and subjected to an antibacterial test. 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. Staphylococc for antibacterial test
us aureus IFO 12732 (Staphylococcus aureus) and Pseudomonas aerugino
3 for each sa (Pseudomonas aeruginosa) in normal broth medium
Culture was performed at 5 ° C for 16 to 20 hours with shaking to prepare a culture solution.
The bacterial solution was prepared by diluting the culture solution 20,000 times with sterile phosphate buffer. 1 ml of the bacterial solution was dropped on the surface of each stainless steel polishing material and the surface of the acidic solution immersion material.
Stored at 5 ° C for 12 hours. After storage, the cells were washed out with SCDLP medium, and the number of viable cells in the obtained liquid was measured by the pour plate culture method (culture at 35 ° C. for 2 days) using standard agar medium. When using this test method, 24
It can be said that the material having a stronger antibacterial property is obtained as the number of viable bacteria after the lapse of time decreases. In addition, in order to confirm that there was no abnormality in the test, the bacterial solution was directly dropped on a glass petri dish as a reference, and the number of bacteria was measured in the same manner. The test results are evaluated as highly reliable when there is no significant increase or decrease in the reference viable cell count. As shown in Table 2, the viable cell count at the start was not significantly different between the polished stainless steel surface and the stainless steel surface treated with the acidic solution.

[0014]

[Table 2]

As shown in Table 3 showing the test results, all the stainless steels in the polished state had low surface Cu concentration and were inferior in antibacterial property. However, according to the present invention, A
After immersion treatment of the stainless steels of the group with an acidic solution, the surface Cu concentration was 0.10 atomic% or more, and excellent antibacterial properties were exhibited. On the other hand, in the B group stainless steel having a Cu content of less than 0.3% by weight, the surface Cu concentration is 0.1 even after the immersion treatment with the same acidic solution.
Below 0 atom%, the antibacterial properties remained low. As is clear from this comparison, it was confirmed that the Cu content needs to be increased to the range specified in the present invention in order to secure the excellent antibacterial property after the immersion treatment with the acidic solution. Further, when each stainless steel of Group A was immersed in an acidic solution and examined for appearance such as surface gloss, no difference was detected as compared with the polished surface.

[0016]

[Table 3]

Example 2: With respect to the stainless steel of test No. A1 listed in Table 1, the sample surface was wet-polished with # 400 emery paper and then subjected to immersion treatment using various acidic solutions as shown in Table 4. did. In Table 4, the acid concentration pH of the acidic solution described as <0 indicates that the measured pH value was less than 0. The surface Cu concentration after the immersion treatment was different depending on the type of the acidic solution used and the immersion conditions.
The antibacterial property of each test piece subjected to the immersion treatment with an acidic solution is
Tested under the same conditions as in Example 1. Table 5 showing test results
As can be seen in FIG.
The u concentration was 0.1 atomic% or more, and excellent antibacterial properties were obtained. In particular, it can be seen that when the surface Cu concentration exceeds 0.3 atomic%, extremely excellent antibacterial properties are obtained. Further, the action of thickening Cu in the surface layer is greater in the sulfuric acid aqueous solution, the oxalic acid aqueous solution, and the hydrofluoric nitric acid aqueous solution than in the hydrochloric acid aqueous solution and the phosphoric acid aqueous solution, and the higher the temperature of the acidic solution, the more C
u Concentration became remarkable. On the other hand, when the pH exceeds 2.5 as in the comparative method Q1, R1 or the like, or when the pH is 2.5 or less as in the comparative method R3, T1 or the like, the temperature of the solution is low or the immersion time is short. When it was time, the surface Cu concentration did not reach 0.10 atomic% or more, and the antibacterial property was insufficient. From this test result, in order to obtain excellent antibacterial properties,
By using an acidic solution containing a non-oxidizing or reducing acid as specified in the present invention, and adjusting the pH, the temperature of the solution, the immersion time, etc., the surface Cu concentration is 0.10 atomic%
It was confirmed that the above needs to be done. The surface of the stainless steel after the immersion treatment with the acidic solution according to the present invention had almost the same appearance as the polished state.

[0018]

[Table 4]

[0019]

[Table 5]

Example 3 Using a 1 mm thick annealed pickling material obtained from the stainless steels of test Nos. A2 and B1 listed in Table 1, a portion having a length of 640 mm and a width of 440 mm was deepened by press forming. A sink for sink with a height of 180 mm was manufactured. After that, the inner surface of the sink was subjected to rough polishing and buffing in the same manner as a normal product to obtain a final product, and a plurality of these were manufactured. A part of the side surface was cut out from the final product obtained and further immersed in an acidic solution, and the surface Cu concentration and the antibacterial property on the surface that was inside the sink were investigated. Table 6 shows the immersion conditions of the acidic solution and the investigation results. As can be seen from Table 6, in the sink prepared in the test number A2 which was not subjected to the immersion treatment with the acidic solution, the surface layer was Cu.
No enrichment was detected. When this sink was dipped according to the present invention, the surface Cu concentration was increased to 0.5
When it reached 1 atom%, almost complete bactericidal action was exhibited. On the other hand, the sink made of the stainless steel of the test number B1 having a Cu content outside the range specified in the present invention shows a remarkable increase in the surface Cu concentration even when immersed in an acidic solution having a relatively low pH. The antibacterial property was also low. As is clear from this comparison, it is confirmed that even a polished product is provided with excellent antibacterial properties by immersion treatment of stainless steel having a Cu content within the range specified in the present invention. Was done.

[0021]

[Table 6]

[0022]

As described above, in the present invention, by treating stainless steel containing 0.3% by weight or more of Cu with an acidic solution, the Cu concentration in the surface layer is reduced to 0.1.
It has been raised to over 0 atom%. As a result, excellent antibacterial properties are imparted to the materials and products whose original antibacterial properties have been reduced by polishing, processing, use as products, etc. without impairing the material properties and appearance. The stainless steel obtained in this way can be used as a material or processed product that has excellent antibacterial properties for a long period of time and is safe for the human body and the environment.
It is used in a wide range of applications such as Western tableware, kitchen equipment, medical equipment, sanitary equipment, various food manufacturing / transporting equipment, bathtubs, washing tubs, door knobs, pipes, etc.

 ─────────────────────────────────────────────────── --- Continuation of the front page (72) Inventor Rishi Kikuchi 4976 Nomuraminami-cho, Shinnanyo-shi, Yamaguchi Prefecture Steel Research Laboratory, Nisshin Steel Co., Ltd. (72) Inventor Seiichi Isozaki 4976 Nomuraminami-cho, Shinnanyo-shi, Yamaguchi Prefecture Shin Steel Co., Ltd. Steel Research Laboratory

Claims (3)

[Claims] 1. An antibacterial property of a Cu-containing stainless steel, which comprises immersing a stainless steel containing 0.3% by weight or more of Cu or a processed product thereof in an acidic solution to remove a surface alteration layer to expose a Cu-rich surface layer portion. How to improve. 2. A method for improving antibacterial property of Cu-containing stainless steel, wherein the acidic solution according to claim 1 is an acidic solution containing a non-oxidizing or reducing acid. 3. The Cu concentration in the surface layer portion according to claim 1 is 0.
A method for improving the antibacterial property of Cu-containing stainless steel containing 10 atomic% or more.