JPH09295912A - Production of antimicrobial ceramics - Google Patents

Abstract

PROBLEM TO BE SOLVED: To economically obtain antimicrobial ceramics excellent in persistence of antimicrobial effects and strength by blending a specific amount of a specified ingredient therein. SOLUTION: The antimicrobial ceramics are obtained by granulating a blend containing 100 pts.wt. fly ash and 1-15 pts.wt. pulverized coal, baking the resultant granulated blend, then converting the surface layer of the prepared ceramics into a zeolite according to an alkali hydrothermal synthesis and further supporting an antimicrobial metallic ion (e.g. silver) thereon by the ion exchange. The resultant antimicrobial ceramics are a spherical product having 1-20mm diameter. When the alkali hydrothermal synthesis is carried out, a zeolite- forming assistant (e.g. sodium aluminate) is preferably added into an aqueous solution of an alkali (e.g. NaOH). The ion exchange reaction is preferably conducted in a reactional solution at 40-80 deg.C and about pH7 for 5-24hr. The content of the antimicrobial metallic ion in the zeolite support material is preferably about 0.5-15wt.%.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing antibacterial ceramics having excellent durability and strength of antibacterial effect.

[0002]

2. Description of the Related Art It has a strong antibacterial property against metal ions such as silver ion, copper ion and zinc ion, and this property has an oligodynamic effect.
Also known as Then, by supporting this antibacterial metal ion on zeolite, an antibacterial ceramics that can be used safely and in a wide range of applications has been developed.
For example, JP-A-59-37956 and JP-A-60-18
As it can be seen in 1002.

[0003]

The antibacterial ceramics are required to have not only a high antibacterial effect but also the antibacterial effect lasting for a long period of time. However, although the conventional zeolite-based antibacterial ceramics are excellent in the antibacterial effect at the initial stage of use, there is a problem that the antibacterial effect is inferior in sustainability.

Zeolites include natural zeolites and synthetic zeolites. Natural zeolite is inferior in ion exchange function to synthetic zeolite. On the other hand, synthetic zeolite generally uses sodium silicate and sodium aluminate as starting materials, so that the manufacturing cost is extremely high.

Further, in order to use the antibacterial ceramics in the fields of filters and carriers, it is necessary to granulate fine powdery zeolite. However, mixing of the binder added during granulation causes a problem in that the antibacterial effect is deteriorated due to the blockage of the pores of the zeolite structure and the strength of the granulated product.

An object of the present invention is to provide a method for obtaining inexpensive antibacterial ceramics which is excellent in durability and strength of antibacterial effect.

[0007]

According to the present invention, a spherical ceramic obtained by granulating a mixture containing 100 parts by weight of fly ash and 1 to 15 parts by weight of pulverized coal into spherical particles and firing the mixture is subjected to alkaline hydrothermal synthesis. This is a method for producing antibacterial ceramics, characterized in that the surface layer is made into zeolite and the antibacterial metal ions are carried by ion exchange.

Fly ash is mainly coal ash obtained by collecting with an electric dust collector of a pulverized coal combustion boiler of a coal-fired power plant. These are vitrified, spherical fine particles containing SiO ₂ and Al ₂ O ₃ as main components and melted at high temperature.

According to the present invention, the fly ash is blended with a specific amount of pulverized coal, granulated, and then fired to form a ceramic, which is then made into zeolite, and further, an antibacterial metal ion is carried, thereby maintaining the antibacterial effect. The antibacterial ceramics having the properties, strength and economy are obtained.

In the present invention, the pulverized coal blended in the granulated material burns when firing the granulated material, and has the function of promoting the sintering of the granulated material. As a result, the antibacterial ceramics obtained according to the present invention exhibits excellent strength that is not easily damaged even when an external force is applied during use.

Further, in the firing step of the granulated product, a large number of fine pores are generated due to the burning of the pulverized coal. These pores are maintained even after the formation of zeolite. The fly ash that does not contain pulverized coal also has fine pores, but the fine pores formed by the burning of pulverized coal have a larger diameter.

Antibacterial ceramics based on metal ions are
When used, a part of the metal ions supported on the zeolite forms a metal salt. This metal salt has no antibacterial properties,
It gradually accumulates in the fine pores of zeolite and inhibits the diffusion of antibacterial metal ions in the pores. The antibacterial ceramics obtained by the present invention has a large pore size of fine pores formed by burning of pulverized coal, which makes it difficult to cause clogging of fine pores due to the deposition of metal salts and stabilizes the diffusion of antibacterial metal ions. Continuation seems to affect the persistence of the antibacterial effect.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The fly ash used as a starting material in the present invention varies depending on the place of coal production or the state of beneficiate, but generally, SiO ₂ : 40 to 70 wt%, A
_{l 2 O 3: 20~40wt%,} Fe 2 O 3: 5~10wt
%, Other minor components: Na ₂ O, K ₂ O, CaO, Mg
It has chemical components including O and the like. The particle size is 15 ~
70 μm. According to JIS-6201, 44 μm
In the present invention, 75% of which passes through the standard sieve is defined as fly ash. However, the present invention is not limited to this because the fly ash is granulated and used, and fly ash that does not pass through the standard sieve of 44 μm can also be used. .

With respect to 100 parts by weight of this fly ash,
Pulverized coal is blended in an amount of 1 to 15 parts by weight, more preferably 3 to 6 parts by weight, and granulated. For this granulation, for example, water is added as a binder to the entire mixture by about 1 to 5% by weight, and the mixture is kneaded with a wheel type kneader such as a Simpson mill, fret or melanger, and then rolled or pressurized. Mold by any method such as.

The particle size of the pulverized coal is preferably about the same as the particle size of the fly ash, for example, 1 to 100 μm. If the particle size is too large, the pores of the ceramic become large and the strength becomes poor, which is not preferable. The shape and size of the granulated product can be arbitrarily determined depending on the use of the antibacterial agent, for example, a spherical product having a diameter of 1 to 20 mm.

The granulated material is calcined at a calcining temperature of, for example, 1000 ° C. or higher, preferably 1200 ° C., and spontaneous combustion of pulverized coal is promoted to effect self-combustion.

A method for making fly ash into zeolite by alkali hydrothermal synthesis is disclosed in JP-A-59-35019,
It is known from JP-A 64-24014 and JP-A 2-229709. In the present invention, this known alkaline hydrothermal synthesis method can be applied to the method of making the surface layer of the ceramic obtained by firing the granulated product of fly ash into zeolite.

It is preferable that the ceramic is washed with an acidic solution to dissolve and remove impurities such as iron before it is made into zeolite. This acidic solution uses something other than hydrochloric acid. Washing with hydrochloric acid is not preferable because chlorine remaining in the fly ash forms a chloride in the subsequent ion exchange reaction step and inhibits antibacterial properties.

The alkaline hydrothermal synthesis is carried out by heating and stirring ceramics in an alkaline aqueous solution. As the alkaline aqueous solution, for example, a sodium hydroxide solution is used. Further, sodium aluminate or the like may be added to this alkaline aqueous solution as a zeolite-forming auxiliary component.

Zeolite is a crystalline aluminosilicate, and its composition formula is x (M ₂ , M ') O.Al ₂ O ₃ .ySi.
O ₂ · zH ₂ O (M and M ′ are monovalent and divalent metals,
x, y, and z are represented by the molar ratio of each component), and the structure is such that a SiO ₂ tetrahedron is a matrix and Si and a part thereof are A
The tetrahedron substituted with l forms a three-dimensional network structure via oxygen atoms. Peculiar cavities and pores are formed depending on the bonding method, and the fine pore diameter is 3 to 10 Å. Then, a zeolite in which a tetravalent SiO ₄ tetrahedron centered at tetravalent Si ⁴ ₊ and an AlO ₄ tetrahedron centered at trivalent Al ³ ₊ are bonded is a negatively charged AlO ₄ tetrahedron part. In order to neutralize the cations, the equivalent amount of cations is easily bound, and the cation exchange function is exerted.

Zeolization occurs not in the whole area of the ceramic structure but in the surface layer having a depth of about 1 mm in contact with the alkaline aqueous solution. Therefore, the inside has a double structure of fly ash and the surface layer is zeolite.

In this zeolite-made ceramic,
Supports antibacterial metal ions. Antibacterial metal ions are
Examples include silver, copper, zinc, mercury, tin, lead, bismuth, cadmium, chromium and thallium. From the viewpoint of high antibacterial property and safety, silver, copper and zinc ions are preferable.

Silver ions are silver nitrate, silver sulfate, silver perchlorate,
Copper acetate, such as silver acetate, diammine silver nitrate, and diammine silver sulfate, copper nitrate, copper perchlorate, copper acetate, potassium tetracyanocuprate, copper sulfate, etc., zinc ion is zinc nitrate,
Examples include zinc sulfate, zinc perchlorate, zinc thiocyanate, and zinc acetate.

In order to obtain a sufficient antibacterial property, it is appropriate that the antibacterial metal ion is contained in the zeolite carrier in an amount of about 0.5 to 15 wt%. Moreover, as a preferable condition of the ion exchange reaction, the reaction is carried out in a reaction solution having a pH of about 7 and 40 to 80 ° C. for 5 to 24 hours.

By this ion exchange reaction, some or all of the ion-exchangeable metal ions in the zeolite are replaced with antibacterial metal ions. After the ion exchange reaction,
Filtration, washing with water and drying are carried out in the usual manner.

The antibacterial ceramics thus obtained can be used in various fields. For example, it can be used as an antibacterial / mildew / algae control agent for water and soil.

Specific applications include water purifiers, cooling towers, water tanks, tanks, fresh fish, water purification agents for aquaculture,
Examples thereof include cultivating soil for potted plants and soil improving agents therefor, but are not limited thereto, and can be used in all fields in which it is necessary to prevent the generation / proliferation of microorganisms such as general bacteria, fungi, fungi, and algae.

[0028]

EXAMPLES Examples of the present invention and comparative examples are shown below.
Table 1 shows the chemical component values of the raw fly ash used in each example.

[0029]

[Table 1]

Example 1 To 100 parts by weight of fly ash A shown in Table 1 was added 7 wt% by adding water to a composition consisting of 4 parts by weight of pulverized coal.
After kneading with frets, pan-type rolling granulation produces an average particle size of 3 m
It was granulated into a spherical shape of m. This granulated product was fired at 1200 ° C. for 1 hour to produce a spherical ceramic.

1 kg of this ceramic was put in 1.5 liters of diluted sulfuric acid (volume: 10%) heated to 80 ° C.
After allowing to stand for a period of time, the dissolved components were washed off with water. Next, 1 Kg of the washed spherical fly ash and 1 liter of a 3N sodium hydroxide aqueous solution were mixed and stirred, and then the solution was heated to 85 ° C. to carry out hydrothermal synthesis reaction for 3 hours to achieve zeolite formation. After being made into zeolite, it was filtered, washed with water and dried.

Next, 1 liter of water was added to 1 kg of the ceramic after the zeolite formation, and further concentrated nitric acid was added to adjust the pH to 7. Furthermore, the concentration of 0.2
0.75 liter of a mol / liter silver nitrate aqueous solution was added, and the mixture was stirred at 70 ° C. for 8 hours, and silver ions were supported on the ceramics by ion exchange. After that,
It was filtered, washed with water, and dried at 120 ° C.

Example 2 10% by weight of water was externally added to a mixture of 100 parts by weight of fly ash B shown in Table 1 and 10 parts by weight of pulverized coal, and the mixture was kneaded with frets, followed by rolling in a pan mold. The particles were granulated into a spherical shape having an average particle size of 8 mm. After that, firing was carried out under the same conditions as in Example 1 above, and further, an antibacterial ceramic was obtained by making zeolite and carrying silver ions.

Example 3 In Example 1, to 1 liter of a 3N sodium hydroxide aqueous solution, 250 g of sodium aluminate dissolved in 1.2 liter of water was further added as a zeolite-forming auxiliary component with stirring. An antibacterial ceramic was obtained under the same conditions except that this was used as an alkaline aqueous solution used for zeolite formation.

Comparative Example 1 Fly ash A shown in Table 1 was externally added with 7% by weight of water (without blending pulverized coal), and then kneaded and molded under the same conditions as in Example 1 above. Furthermore, antibacterial ceramics were obtained by making zeolite and supporting silver ions.

Comparative Example 2 Water was added in an amount of 7% by weight to a composition prepared by adding 0.5 parts by weight of pulverized coal to 100 parts by weight of fly ash A shown in Table 1, and the same procedure as in Example 1 was followed. Under the same conditions, antibacterial ceramics were obtained by kneading, molding, forming zeolite and supporting silver ions.

Comparative Example 3 Moisture 7% by weight by external application to a composition prepared by adding 20 parts by weight of pulverized coal to 100 parts by weight of fly ash A shown in Table 1.
And then kneading under the same conditions as in Example 1 above.
An antibacterial ceramic was obtained by molding, further forming zeolite and supporting silver ions.

Comparative Example 4 Commercially available spherical synthetic zeolite (A type, 4 manufactured by Tosoh Corp.)
.About.8 mesh) was used to carry silver ions by ion exchange under the same conditions as in Example 1 to obtain spherical antibacterial ceramics.

Table 2 shows the antibacterial activity of the non-acting product and Table 3 shows the antibacterial activity of the product after 1 year of action. The evaluation of the antibacterial activity of the non-acting products in Table 2 was performed by the shake flask method. That is, the antibacterial ceramics 0.
25 g was put in an Erlenmeyer flask containing 250 ml of phosphate buffer, and the test bacterial suspension was added to this at 10 ⁵ CFU / ml, and the Erlenmeyer flask was shaken at 25 ± 5 ° C. After the passage of time, the number of viable bacteria was measured.

In order to evaluate the sustainability of the antibacterial effect shown in Table 3, the spherical antibacterial ceramics obtained in each example were passed through tap water (containing 0.4 ppm of chlorine) for one year. Thereafter, the filtered, washed and dried spherical antibacterial ceramics were tested by the shake flask method described above.

The strain used in this test was Escherichia coli IF.
O-12734, the medium is Mueller Hinton 2 (BBL). Table 4 shows the results of testing the fine pores of the non-acting product and the strength of the product after passing water for one year. The fine pores were measured by mercury porosimetry. For strength, the presence or absence of disintegration was visually observed.

[0042]

[Table 2]

[0043]

[Table 3]

[0044]

[Table 4]

As shown in the results of Tables 2 and 3, the antibacterial ceramics obtained from the examples of the present invention show an excellent antibacterial action and, at the same time, are remarkably excellent in durability. Also, from the strength test results in Table 4, there is strength that can withstand long-term use in water. On the other hand, Comparative Example 1 in which the pulverized coal is not blended in the granulated product and Comparative Example 2 in which the blending ratio of the pulverized coal is less than the range of the present invention are both inferior in sustainability of the antibacterial effect. Comparative Example 1 is also inferior in strength.

In Comparative Example 3 in which the proportion of pulverized coal is more than the limited range of the present invention, the structure is excessively porous and the strength is poor.
Comparative Example 4 uses a synthetic zeolite and is inferior in durability and strength of antibacterial effect.

[0047]

As shown by the results of the above examples, the ceramics obtained by the present invention have excellent antibacterial activity,
The antibacterial effect is excellent in durability. Moreover, it maintains its strength even after long-term use in water. Therefore, for example, it is possible to provide an antibacterial ceramic suitable for long-term use in a place in contact with moisture. Further, since the starting material is fly ash, which is an industrial waste, not only can the manufacturing cost be reduced, but it is also preferable in terms of resource saving and recycling.

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Claims (3)

[Claims] 1. Fly ash 100 parts by weight and pulverized coal 1
Antibacterial ceramics characterized by granulating a mixture containing ˜15 parts by weight and firing the resulting ceramic to make the surface layer into a zeolite by alkali hydrothermal synthesis, and further carrying antibacterial metal ions by ion exchange. Manufacturing method. 2. The method for producing an antibacterial ceramic according to claim 1, wherein a zeolite-forming promoter is added to an alkaline aqueous solution for performing alkaline hydrothermal synthesis. 3. The method for producing an antibacterial ceramic according to claim 1, wherein the ceramic is a spherical product having a diameter of 1 to 20 mm.