WO2012018273A1 - Procedure for the production and use of porcelain stoneware tiles with antibacterial activity - Google Patents

Abstract

The present invention describes the production process to obtain porcelain stoneware tiles with antibacterial action. The material promotes the bacteria's death, while all the other required technological characteristics, particularly the chemical resistance and anti-staining properties, are assured. The product is made from a porcelain stoneware paste with a black ceramic pigment containing iron and chromium in its composition; the deposition, by jet spraying, of a small layer of a transparent glaze (typically used to enhance the surface characteristics) and the firing schedule is similar to that used to obtain similar products. Once fired, a chemical (sodium nitrate and silver nitrate solution) and thermal (at 4300C) treatment is optionally carried out. Under optimized conditions the material shows effective antibacterial action: killing of 77% S. Aureus bacteria and 81% E. Coli bacteria, i.e., the survival percentage of the tested bacteria is only about 20%.

Description

 DESCRIPTION

PROCEDURE FOR OBTAINING AND USING 6TH PORCELAIN WITH

 ANTI-BACTERIAL ACTION

The present invention relates to the process of obtaining porcelain stoneware with antibacterial action, that is, which promotes the killing of bacteria without detriment to other important product characteristics, namely the high chemical resistance and anti-stain properties.

The antibacterial action, proven by determining the survival rate of Gram-positive, Staphylococcus aureus, and Gram-negative Escherichia Coli bacteria, is achieved through the use of a ceramic pigment and chemical and heat treatment.

The antimicrobial effect achieved only works when bacteria are in direct contact with the ceramic tiles.

Since the pigment used is already commonly used in these products for aesthetic effects, the added cost of this material with antibacterial properties comes only from the costs associated with chemical and heat treatment.

The developed product has anti-stain characteristics, belonging to class 5 (ISO 10545-14 standard) and is chemically resistant, being classified by ISO 10545-13 as UA, ULA and UHA for all agents. tested chemicals, except for the 18% (v / v) hydrochloric acid solution, which promotes a slight chemical attack on its surface (UHB).

BACKGROUND OF THE INVENTION

List of found documents

N. Kalantari, S. Ghaffari, Evaluation of toxicity of heavy metals for Escherichia Coli growth, Iran. J. Environ. Health Know. Eng., 5, (3), 173-178, 2008.

R. Narayanan, M.J. Mchale, Antimicrobial glaze and acid resistant porcelain for enameled steel products, WO / 2006/133075.

I. Birky, J.V. ood, Monolithic ceramic material including an antimicrobial material, WO 0014029, 2000.

I. Akira, T. Mitsuo, I. Series, Antibacterial ceramic product and its production, JP 8290985, 1996.

N. Hiroshi, A. Kiminori, S. Muniteru, Antimicrobial calcium phosphate based ceramics, JP 4288006, 1992.

S. Shuji, A. Kiminori, F. Keijiro, Inorganic antimicrobial agent and production thereof, JP 4013605, 1992.

state of art

The pathogenic organisms are present in the most diverse means so the possibility of having Anti-bacterial surfaces, as an obstacle to bacterial growth, is a very attractive solution for a wide range of applications, from hospital to home, school, etc.

Ceramic materials are widely used in the interior finishing of buildings, so the development of ceramic floors and tiles with antibacterial properties is a significant asset.

Given the technical characteristics of porcelain stoneware, in particular its very low porosity and high chemical resistance, this product is suitable for developing this functionality.

The antimicrobial effect of silver has been known since ancient times. Greco-Pomegranate civilizations have found that algae did not grow in copper and silver containers that contained water for human consumption, unlike in clay containers.

This action was named by Pelkzar et al. [1] as an oligodynamic effect and was defined as the ability of small quantities of certain metals to have a lethal effect on bacteria.

One of the issues of environmental and health concern that arises is the toxicity of heavy metals.

However, it has been shown that for macroscopic life forms silver is the least toxic element with no contraindication when used at low concentrations [2]

In contrast, silver and osmium are the most toxic elements to microscopic beings because fungot toxicity, within the same group of the periodic table, increases with increasing atomic weight [3].

Due to its intense antibacterial activity silver and its salts are used in water treatment or placed in organic matrices for various uses, from clothing to medical-surgical devices [4].

The mechanisms of antibacterial action of silver ions are closely related to the thiol group (sulfhydryl - SH) [3-4], which is made up of proteins, which in turn are responsible for enzymatic activity.

The addition of silver ions to a medium containing bacteria causes the phosphate ions to release from the bacteria.

Thus, the bacteria's plasma or its cytoplasmic membrane, which is associated with important enzymes, becomes a target for silver ions [5].

The effects caused by the addition of silver ions to E. coli bacterial enzymes are the inhibition of bacterial growth and the deposition of silver ions on precipitates and cell walls as precipitates [6].

The bacterial cell grows in size and the cytoplasmic membrane, cytoplasmic content and other Cell layers have anomalies in the structure.

Finally, silver ions interact with nucleic acids, causing the bacterium to lose its reproductive capacity and thus limit its proliferation [6].

In the case of S. aureus bacteria the addition of silver ions also causes damage. The walls and membranes separate, which results in the release of their cellular content into the surrounding medium.

There is also a decrease in cytoplasm density and heterogeneity.

It is common to find dense or precipitated particles around damaged cells.

The chromium ion is considered biologically important for all levels of living organisms; in particular trivalent chromium plays an important role in controlling carbohydrate and lipid metabolism in cells [7].

Despite causing inhibition of bacterial growth and decreased pathogenicity, chromium ion can interact with iron in the metabolism of living organisms [8].

Iron is an essential nutrient for life forms because of its activity in electron transport in the reactions of biological systems. However, their insolubility and reactivity give rise, respectively, to availability and toxicity problems in bacterial cells [9].

High amounts of iron are extremely toxic and can lead to antimicrobial effects [8].

Kalantari and Ghaffari [8] evaluated the influence of chromium and iron on the growth of E. coli bacteria and found that the presence of Cr ³⁺ ion had an inhibitory effect and could reduce it to 38% (solution with a concentration of chromium ions of 0.5 mM / L).

In a culture of E. coli bacteria, the addition of solutions with high iron ion concentration (1 mM / L) promotes a reduction in their growth.

Fe (III) reduced it to 31.3% and Fe (II) completely inhibited it [8].

These authors also found that the combined action of iron and chromium ions is extremely effective in inhibiting the growth of E. coli.

The addition to the culture medium of a solution containing 0.1 mM / L Fe ³⁺ and Fe ²⁺ and 0,5 mM / L Cr ³⁺ promotes a drastic inhibition of bacterial growth, which is only 8%.

Thus, high concentrations of Fe ²⁺ inhibit bacterial growth; chromium, although only partially inhibitory when acting alone, combined with iron becomes lethal to E. coli because salts of chromium will promote the precipitation of iron inside the cell, causing its death.

References :

[1] RJ Luckens, Structure activity relationship, In Kleinzellar, A., Springer, GF, Wittmann HG (ed.), Molecular Biology, Biochemistry and Biophysics, Chemist of Fungicidal Action, Springer - Verlang, New York, 10, 76- 90, 1971.

[2] A. Goetz, Water sanitation with silver. J. American Water Works Association, 35, 579-584, 1943.

[3] M.J. Pelkzar et al. Microbiology: Concepts and Applications, São Paulo: MAKRON Books do Brasil, 2, 517, 1996.

[4] A. Tucci, A. Nanetti, L. Malmusi, G. Timellini, Microbiological Ceramic Surfaces for Hospital Environments, Industrial Ceramics, 12, 7-10, 2007.

[5] W.J. Schreurs, H. Rosenberg, Effect on silver ions on transport and retention of phosphate by Escherichia Coli, J. Bacteriol., 152, 7-13, 1982.

[6] WK Jung, HC Koo, KW im, S. Shin, SH Kim, YH Park Antibacterial activity and mechanism of action of the silver ion in Staphylococcus aureus and Escherichia coli, Appl. Environ. Microbiol., 74 (7) 2171-2178, 2008. [7] V. Juturu, JR Komorowski, Chromium supplements, glucose and insulin responses, Am. J. Clin. Nutr., 78 (1) 192-193, 2003.

[8] N. Kalantari, S. Ghaffari, Evaluation of toxicity of heavy metals for Escherichia Coli growth, Iran. J. Environ. Health Sci. Eng., 5 (3) 173-178, 2008.

[9] S.C. Andrews, Iron storage in bacteria, Adv. Icrob. Physiol., 40, 281-351, 1998.

Differences between published works and the present invention

The antimicrobial effect of silver, chromium and iron is known and the existence of ceramic material with antibacterial properties is also a reality.

However, this work is innovative because the antimicrobial effect of chromium and iron has only been tested in solution and there is no report of its application to ceramic materials which have the particularity of being subjected to high temperatures during processing. (1200 ° C), which promote the densification of the material and the occurrence of chemical reactions.

In this invention one takes advantage of the fact that these metal elements are part of the composition of ceramic pigments which are commonly used to stain porcelain stoneware pastes. Other ceramic pigments used to obtain porcelain stoneware with other colors may also impart antibacterial properties to the ceramic material.

The ceramic material with antibacterial properties that is currently on the market was developed by an Italian group (Fiandre and Iris Ceramic) (Active Clean Air & Antibacterial Ceramic - http: // www. Active- ceramic.com/; PCT / IB2009 / 006002).

In this product the antimicrobial effect comes from the presence on the product surface of a material with photocatalytic properties: Ti0 ₂ .

Thus, for the material to have antibacterial properties it needs radiation.

In the present invention it is only necessary for the bacteria to be in direct contact with the material.

DESCRIPTION OF THE INVENTION

The name of porcelain stoneware is sufficient to define the origins and characteristics of this product.

In ceramic terminology, stoneware is synonymous with a very compact material consisting of several crystalline phases dispersed in a glass matrix.

The adjective porcelain has an etymological root in the term porcelain. According to ISO 10545-3 this type of material has a water absorption of less than 0.5%. However, most manufacturers rely on products with even lower water absorption (<0.05%).

Thus, this material does not require a glaze to waterproof its surface and it is possible to polish it if a shiny surface is desired.

Another important feature of this product is that even if abrasion occurs, although its abrasion resistance is quite high, there is no discontinuity of its characteristics as there is no distinct surface part from the interior part.

The novelty of this product comes from the fact that it has combined the ancient knowledge of the antimicrobial effect of some heavy metals, namely silver, iron and chromium with a relatively new ceramic product, porcelain stoneware which has excellent technical characteristics. .

This material is suitable for indoor or outdoor applications, high traffic sites, etc.

The antimicrobial effect of the material with the addition of only 2.5% black ceramic pigment translates into a 51% efficacy for E. coli bacteria.

The 81% increase comes from chemical (with silver salts) and thermal treatments.

In any case, the isolated use of the ceramic dye already reduces the amount of E. coli bacteria in half, without any extra costs for black porcelain stoneware.

Example

Materials:

- Porcelain stoneware paste whose composition is (% by weight): 66.20% Si0 ₂ ; 19.42% A1 ₂ 0 ₃ ; 1.06% Fe ₂ 0 ₃ ; 0.65% CaO; <0.50% MgO; 2.02% Na ₂ 0; 2.36% K ₂₀ ; 0.38% TiO ₂ ; <0.30 MnO; > 0.50 P ₂ 0 ₅ .

 - Black ceramic pigment (2,5% by weight) with an average composition estimated by SEM / EDS as (% atomic): chrome 36,8%; iron 44.2%; aluminum 8.8%; magnesium 6.0%; titanium 0.8%; and oxygen 3.4%.

 - Transparent commercial glaze consisting of a single crystalline phase (estimated by XRD)

Ba ₀ .8 (Al _{1. 6} Si ₂ .4Oe). Its chemical composition is (% by weight): 47,2% SiO ₂ ; 16.8% Al ₂ 0 ₃ ; 24.3 BaO; 5.4% CaO; 6.3% Na ₂ 0.

After conformation and drying of the material the transparent commercial glaze as an aqueous suspension was spray applied onto the material (about 130 g / m ² with a density of 1280 g / l).

Its main function is to fill the microporosity on the surface of parts to improve stain resistance.

The material was then baked in an industrial roller oven with a 90 minute cycle and a maximum temperature of 1210 ° C. After baking, about 20 g / m ² of an aqueous solution with 98% sodium nitrate and 2% silver nitrate (weight percentages) was also spray applied.

The material was then heat treated at 430 ° C.

Bacterial reduction assessment:

In this evaluation two bacterial strains were used: Staphylococcus aureus (NCTC 6871) and Escherichia coli (ATCC 25922).

For growth of each of the indicator strains in liquid medium, 10 ml of a Tryptic Soy Broth (TSB) culture medium solution was pipetted into a test tube.

With the aid of a lamp, a loop was sterilized by approaching the flame.

It was expected to cool slightly and the cells were collected in the solid medium (from the 2 culture collections) into the TSB test tubes, which were closed and identified.

To promote cell growth they were placed on a shaker for 24 hours at a constant temperature of 37 ° C and under agitation (150 rpm).

In one conical flask, 0.7 ml of the inoculum was added to a sterile potassium hydrogen phosphate buffered solution (70 ml) (pH 7.2), which constituted the culture medium. test.

To estimate the initial number of viable cells, an aliquot was taken to make decimal serial dilutions which were then plated (100 μΐ on each plate) into TSA-containing petri dishes.

These plates were then incubated at 37 ° C for 24h, at which time the colony forming units (CFU) were analyzed and counted.

CFU determinations were made in triplicate using at least two dilutions.

To perform the bacterial reduction evaluation test, the test samples were added to the test culture medium and incubated for 1 h with shaking at 20 ° C.

After incubation, viable cell counts were performed by determining CFU / ml as described for the initial cell count (at least five replicates were performed for each assay to ensure the reliability of the results).

The reduction (R) of colony forming units (CFU) was quantified by the equation:

R = (Co - C) x 100 / Co where Co represents the CFU number in the test with the control sample and C translates the CFUs obtained with the test material. The reduction rate obtained for the developed material was 81.1% for E. Coli bacteria and 77.8% for S. Aureus bacteria.

Stain Resistance:

The developed material has a high class 5 stain resistance (ISO 10545-14) for all staining agents tested (green chromium; olive oil and iodine solution).

This means that 24 hours after staining, the stain can be removed with running water without leaving a trace.

Chemical resistance:

Chemical resistance has been tested according to ISO 10545-13:

 - household chemicals (ammonium chloride, 100 g / l);

 - chemicals for use in swimming pools (sodium hypochlorite solution, 20 mg / l);

 - low concentration acids and bases: hydrochloric acid solution, 3% (v / v); potassium hydroxide, 30 g / l; citric acid, 100 g / l;

 - high concentration acids and bases: hydrochloric acid solution, 18% (v / v); potassium hydroxide, 100 g / l and lactic acid, 5% (v / v).

The developed material has an antacid behavior (UA, ULA and UHA), except for an 18% (v / v) hydrochloric acid solution, which causes slight attack. surface chemical (UHB)

(L and H mean that the concentration of the chemical agent used is respectively low and high; It translates that, after contact with the chemical solutions, the product shows no surface defect, ie, does not suffer chemical attack.)

The aim of the present invention is to obtain a ceramic material for application as a floor or as a coating (porcelain stoneware) with excellent antibacterial properties without detriment to other important technical characteristics normally associated with this type of material, namely High chemical resistance, abrasion and anti-stain.

Moreover, part of the antibacterial action (51% reduction of E. coli bacteria) is achieved by the use of a raw material commonly used in the production of this type of products to achieve aesthetic effects (ceramic pigments) which implies absence. additional costs.

Increasing antibacterial action to 81% reduction already involves additional costs, which are expected to be reduced and the cost / benefit ratio is interesting.

The state of the art shows only antibacterial ceramic material acting only if irradiated by sunlight or ultraviolet.

Now developed material just needs to contact with the bacteria.

Although ceramic pigments are a common raw material in the processing of porcelain stoneware to obtain products with the most varied colors, their antibacterial action has never been thought of.

The present invention exploits exactly this new functionality of this type of raw material.

In addition to the tested pigment, there will be other commercial ceramic pigments that may give the ceramic material antibacterial properties, which should be explored in future actions.

The industrial production of the developed product is easy as it does not require any equipment beyond what the porcelain stoneware factories usually have.

The present invention has been tested for the indicated bacteria. However, the need to optimize its performance, extend its application to other bacteria and measure its reproducibility and longevity is not to be ruled out.

Claims

1. PROCEDURE FOR OBTAINING PORCELAIN GRAIN WITH ANTI-BACTERIAL ACTIVITY, HIGH CHEMICAL RESISTANCE AND STAINING characterized by involving the following steps:

 (a) Addition of black pigment to the porcelain stoneware paste of the composition (in% atomic): Chromium 35,6; Iron 42.8; Aluminum 8.5; Magnesium 5.8; Titanium 0.7 and Oxygen 6.6);

 (b) Atomization or filter-pressing of the paste obtained;

(c) material forming by dry pressing or extrusion;

 (d) drying;

(e) Spraying 130-150 g / m ² of a commercial clear glaze having a density of 1280-1300 g / l.

 (f) Cooking.

PROCEDURE FOR OBTAINING PORCELAIN GRAIN WITH ANTI-BACTERIAL ACTIVITY, HIGH CHEMICAL RESISTANCE AND STAINING, according to the preceding claim, characterized in that the ceramic pieces obtained have antibacterial activity which varies with the amount of black pigment used in the preparation. The composition of the paste was the reduction rate of E. coli bacteria from 77 and 63% and S. aureus bacteria from 81 and 67% to 2.5 and 0.5% (by weight) dye.

3. OBTAINING PARTS - CBRAMICS THAT HAVE ANTI-BACTERIAL PROPERTIES, HIGH CHEMICAL AND SPOT RESISTANCE characterized by involving the following steps:

(a) spraying 18-23 g / m ² of an aqueous solution of sodium nitrate and silver nitrate with a density of 1200-1220 g / l;

 (b) Heat treatment at 430 ° C.

Use of the ceramic parts obtained according to the preceding claims, characterized in that they reduce the number of E. coli and S. aureus bacteria when they are in direct contact with said parts.

USE OF CERAMIC PARTS, obtained according to the preceding claims, characterized in that they exhibit a high stain resistance achieving the removal of stains of green chromium, olive oil and iodine solution after cleaning with running water.

USE OF CERAMIC PARTS, obtained according to the preceding claims, characterized in that they have a high resistance to:

 - common household chemicals: ammonium chloride, 100 g / l;

chemicals for use in swimming pools: sodium hypochlorite solution, 20 mg / L; - acids and bases at low concentrations: hydrochloric acid solution (3% v / v), potassium hydroxide (30 g / l) and citric acid (100 g / l),

showing no surface defects upon contact.