Field of invention

The invention is on the evolution of single fast firing technology producing ceramic tiles with Anti-Microbial properties and the method of producing nano-particles of materials with anti-microbial characters to be infused in the glaze. More specifically, this invention pertains to ceramic glazing compositions that impart built in antimicrobial characteristics to ceramic floors and walls. These antimicrobial characteristics are developed by bacteriostatic and bactericidal actions of nano-particles of certain inorganic compounds and the method of production of such nano-particles.

Abstract of the invention

The present invention is related to manufacturing of germ free tiles for floor and wall using a specially formulated anti-microbial glaze.

The present invention discloses the glaze composition comprising of frits, a plurality of combination of borates of calcium, magnesium and zinc which have the antimicrobial property, which is built in to the glaze.

The present invention also discloses the addition of magnesium in the form of Talc/Dolomite. Besides this, addition of Zinc oxide in the glaze further brings inbuilt stability of antimicrobial property.

With the above glaze composition of antimicrobial property, the invention further discloses the final infusion of Zinc oxide nano-particles to the glaze making the glaze composition fool proof to fight against the bacteria's.

Ceramic surfaces produced using the said glaze composition with high intense antimicrobial property/anti-bacterial efficacy have been tested with respect to Japanese Standards JIS Z2801-2000 and proved germ free.

Background of the invention

Bacteria have flourished on earth for over three billion years they were here first, long before most other species. We didn't know anything about them until the late 17th century, when for the first time the Dutch scientist Antonie Philips Van Leeuwenhoek, who saw these "animalcule", while squinting at some samples in the recently invented microscope. He was looking at scrapings from inside the human mouth. At least six different types live in human mouths, despite human efforts to destroy them. The oceans are filled with bacteria. Each gram of dirt can have as many as two and half billion bacteria in it. Bacteria have been found four miles below the earth surface. There is sketchy evidence for small bacteria floating 25 miles up in the stratosphere. Scientist estimate that the total mass of the earth's bacteria outweighs all of the plants, animals and other living things combined.

Most bacteria reproduce using a process called "Binary Fission". To do this, a single bacterium will grow to twice its normal size and then split in to two "Daughter Cells". These two new cells are exact copies of the original bacterium.

Some bacteria have been found 2 miles underground in a South American gold mine surviving on is radioactive emission from the rocks. Arthur W.Anderason found Deinococcus radiodurans can handle radiation exposure nearly 10,000 times the fatal dose for humans.

Bacteria grow in various shapes and sizes. Some are little rod shaped critters, some spherical, and they can even be spiral shape. Bacteria have taken two distinct evolutionary pathways, and most remarkable thing about them is their ubiquitous diet, which can vary from metallic substrates to solar and from deep in the earth to occupying important strata of the oceans. There are estimated 75 to 100 trillion cells in the human body. It is believed by scientists that there are more bacteria in our body than number of cells in our body. One species of bacteria (pseudomonas natriegens) can reach puberty in about 10 min after they are born. In theory, a single organism can produce 1 billion little clones between lunch and dinner. Under extreme magnification the unlovable E.Coli "food Poisoning" look very much like our computer mouse. When they move it on out, they whip their tails for propulsion. This microbe can cover 25 times the length of their body in a second if a horse could do that it would be galloping at over 130 miles per hour.

Bacteria and their relatives, the archaea, number at least five billion trillion trillion. If you could stop time long enough line them up nose to tail in a straight line they would stretch from here to the edge of the known universe (about ten billion light years away).If all of the water was sucked out of our body, 10% of what was left by weight would be bacteria.

Stubborn bacteria can cling on to even clean looking floor mopped with a brand new mop or sponge.

Boric acid has been used for over 20 years to preserve urine while in transit for bacteriological examination. It has been suggested that it may be toxic for some urinary pathogens. To investigate this several strains of bacteria and fungi commonly found in urine were exposed to different concentration of boric acid in nutrient broth. Viable counts were made at the outset and at intervals for up to 24 hours at room temperature to detect bacteriostatic or bactericidal effects. At concentration between 10 to 20gms/l boric acid was bacteriostatic or fungistatic for very nearly all the common urinary pathogens. At 10gms/l boric acid was weakly bactericidal for some strains of acinetobacter calcoaceticus and pseudomonas aeruginosa, though higher concentrations were bacteriostatic only. Group B streptococci varied in their response to boric acid, but for most of them 10 or 20gms/l were satisfactorily bacteriostatic. It is concluded that boric acid is rarely toxic, and when it is, the effect is usually sufficient delayed to be of only theoretical importance.

In 1969 Porter and Brodie's described the use of boric acid at a concentration of 18gms/l to preserve urine while in transit for bacteriological examination. Although urine is a culture medium, they showed that when boric acid was added the number of any bacteria present did not change significantly for up to 48hrs at room temperature, and other cellular elements remained substantially intact. They claimed this effective bacteriostatic allowed the numerical criteria for the laboratory diagnosis of Urinary tract infection (UTI) to be applied despite delay in performing the examination, this cheap and simple way to increase accuracy in the diagnosis of bacteriuria and pyuria has not been widely adopted. Ten years after the introduction of boric acid for the preservation of urine only a quarter of a group of 64 laboratories in England and Wales were using it.

The relative lack of interest is perhaps explained by the small no of publications that describe the use of boric acid, and the suggestion in some of them, that it is occasionally bactericidal.

The field of providing products with built in antimicrobial protection has grown tremendously over the past several years. What once started out as a premium or novel option for high end consumer products and medical devices has now grown in to a main stream characteristic found in many consumer products. Consumers can go to any home improvement center and see many, if not hundreds of products that claim some degree of resistance to microbiological growth or contamination. Some major retailers have specific section devoted to such antimicrobial products. Antibacterial products have been introduced in to plastics, textiles, liquids, metal coatings, and an array of other types of materials. However, there remain several areas of consumers and commercial products in which development of commercially viable antimicrobial products has proven difficult/One such area is ceramic coatings. Ceramic coatings are commonly used in products that store, treat or transport water and liquid waste. Ceramic toilets, urinals, bidets, bathrooms basins, flooring tiles and other bathroom fixtures are probably the most common example of such products.

Ceramic products used to collect and transport water are often stained by scum and films of biologic origin eg: bacteria, fungus, mold, mildew etc. As on today, the primary method of removing biological scum and film from these ceramic products has been to abrade the ceramic surface in the presence of topical cleaning agent. This process is time consuming and provides little or no protection against future growth. Some cleaning agent can damage the surface of the ceramic product. Therefore, there is great interest in the development of ceramic coating that have built in protection against the growth and proliferation of microbes.

A few such built in antimicrobial coating are describes in the ceramic literature but they have not seen commercial success. Existing technology are somewhat limited, for example: The high temperatures used in ceramic firing processes typically preclude the use of organic antimicrobial agents. Inorganic antimicrobial silver based materials are too expensive. Zinc oxide is known as having antimicrobial characteristic and has been used in the preparation of ceramic glazing compositions. However, Zinc oxide alone is an antimicrobial agent has not shown antimicrobial efficacy sufficient for control of microbial growth and proliferation on ceramic surfaces. Accordingly, there is a need for a low cost ceramic coating that has built in antimicrobial protection.

Another interesting inorganic compound, Magnesium oxide which also acts as an antibacterial agent against commonly found bacteria, spores and virus. The other important environmental remediation aspect of MgO includes its potential to scavenge fluoride from drinking water and this property has been known for more than 70 years. Nano crystalline particles of MgO produce antibacterial activities which have been tested by treating Escherichia coli and staphylococcus aureus cultures with 1mg/1 ml of the nano particles.

Magnesium oxide is obtained by thermal decomposition of Magnesium silicate, Magnesium carbonate. Talc (magnesium silicate) and Dolomite (Magnesium + Calcium carbonate) are used in the glazes/frits for ceramic coating. The bactericidal activity has been tested on the gram positive staphylococcus aureus bacteria as well as gram negative E.Coli bacteria. All the bactericidal experiments were conducted using nano crystalline MgO. The smaller particles are more active in killing the bacteria. According to our proposed mechanism, the MgO is responsible for the formation of an active oxygen species, which is active on the cell membrane as well as inside the bacterial cell.

Thus, one object of the present invention is to provide a new and useful antimicrobial ceramic coating that can impart antimicrobial characteristics in a wide range of ceramic products.

A still further object of the invention is to provide this ceramic coating at a cost that is acceptable to the market place. Furthermore, this antimicrobial ceramic coating should be safe to humans, exhibit commercially acceptable antimicrobial properties, and most importantly, be compatible with existing ceramic production process. To overcome all these hurdles patent documents US8003217, US5807641 and US20110070275 listed in the prior art discloses the use of certain anti-microbial materials infused in to glaze composition which are either costly or in a different composition and application.

These and other objects are achieved by the claimed invention, which is one embodiment is an antimicrobial ceramic glazing composition comprising.

a) Fritted glaze is a fused mass at 1400°C containing borates of calcium, magnesium, zinc etc. Here a good amount of raw materials like boric acid, borax pentahydrate, dolomite, feldspar, quartz, calcite, china clay, zinc oxide etc. have been used.

b) Along with the above mentioned pre melted glaze which is also called a frit, we
proposed the use of 3 to 4% talc powder and 1 to 4 % zinc oxide in the base glaze composition along with other basic raw materials like quartz, feldspar, calcite, alumina, corundum, china clay etc.

c) The glaze composition composed of a) and b) will be treated with 0.3 to 0.7% Zinc oxide nano particles. These nano particles of Zinc oxide are obtained by fine wet grinding in high alumina ball mills to achieve 100 to 500 Nano meter particles size.

In a further embodiment, the invention is a ceramic article that exhibits antimicrobial properties. The ceramic articles according to the invention have two portion ie body & glaze. The glaze comprises of frit, basic raw materials and Infusion of Zinc oxide nano particles as mentioned above. Thus the glaze contains sufficient and acceptable level of antimicrobial efficacy.

Summary of the invention

The present invention is a ceramic glaze coating for achieving germ free antimicrobial activity on ceramic tiles. The present invention further discloses a method of glaze coating embedded with multiple ingredients having antimicrobial activity on ceramic body with primary coating of engobe.

The glaze coating comprising,

1) Fritted glaze embedded with borates of calcium, magnesium, zinc etc.
2) Antimicrobial activity from MgO and presence of ZnO.
3) Infusion treatment of Nano Zinc Oxide antimicrobial activity at 0.3 to 0.7% dosage along with the glaze.

Detailed description of the invention

The invention particularly relates to antimicrobial treatment to ceramic glaze coating applied on engobe and ceramic body.

Brief description of the process

Body preparation

We have two methods of body preparation. 1st a wet process and 2nd a dry process. The main purpose of both the process is to achieve fine ground clay / minerals particles.

We use 70 to 80% plastic clay raw materials and 20 to 30% minerals. The role of plastic clay is to bring binding strength and the role of minerals is to act as a fluxing agent. The composition is designed on such a way that its physical, chemical and thermal properties of a biscuit tile are achieved. Physical means its working abilities at press stage, and it should have enough strength at green/dry stage for the safe transportation till it reaches the firing zone. Before the powder is pressed it is subjected for thorough magnetic separation to avoid the iron particles is the body, otherwise it result in black specks in the finished tile surface.

The chemistry of the tile should have Si02- 60 to 65%; Al203- 16 to 20%; Fe203- 6 to 10%; CaO- 1 to 2%; MgO- 1 to 2%; Na20- 0.5 to 1%; K20- 1.5 to 2.5% and LOI- 6 to 8%. The thermal properties should meet the classifications as per the Bureau of Indian standards. (Reference Fig 1. Flow chart for slip house and Fig.2. Flow chart of milling plant)

Brief Description of the Drawings

Fig.1. Flow Chart of Slip house for wet process Fig.2. Flow chart of milling plant for dry process Fig.3. Flow chart of Press and Drier Fig.4. Flow Chart of Glaze Preparation Fig.5. Glaze Line flow chart Fig.6. Firing Curve

Press Stage
After a minimum 24hrs of ageing, the powder is conveyed to press hopper through a vibrosieve. The powder is pressed in the hydraulic press of capacity 1700 to 2080 tons and above to a definite size with 250 to 300 Kgs/Cm2 specific pressure. To remove the moisture content in the green tiles the tiles are conveyed to Dryer with a temp around 200°C - 250°C and a cycle of 20 to 25min. The exit tile moisture content will be below 1% and surface temp from 90 to 100°C. Now the tiles are ready for glazing. (Reference Fig 3. Flow chart for Press and Driver)

Glaze Preparation

Table 1: List of minerals for frit Preperation

The above composition is fused in a rotary /continual kiln at 1400°C for a cycle of 4 -5hrs. The fused mass will be quenched in water to form the frit crystals. It is called a pre-melted glaze useful in fast firing technology for producing ceramic tiles. (Reference Fig 4. Flow chart for Glaze Preparation)

Table 2 : List of minerals for Engobe and base glaze composition

Preparation of Zinc Oxide Nano particles

The mechanical milling is only a technique to produce of Zinc Oxide nano particles in low temperature, large scale and simple wet process.

The technique has proved to be an effective and simple without involving high temperature. In this technique powder particles are trapped between highly kinetic colliding balls and the inner surface of the wall, which causes repeated deformation & destruction results the formation of fine, dispersed particles. The mixture ratio of the grinding media and ZnO powder is around 10:1 by weight percentage. This material is ground for 24hours by wet grinding and dried in the oven with temperature 100°C till it gets dried. This powder has particle size distribution from 100nm to 500nm.

Infusion of Nano Zinc Oxide particles at 0.3 to 0.7% to the above said glaze composition.

Kiln department

The equipment / device used for firing of green ceramic coated tiles is called kiln. The kiln is divided in to six zones.
a) Pre-drier zone: Here the temperature is maintained from room temp to 300°C in this zone the moisture content is totally eliminated.

b) Pre-heating zone: Here the temperature will be from 300 °C to 900 °C all inorganic incompatible matter will get combusted and allotropic transformation of a to B quartz takes place.

c) Heating zone: Here the temperature will be from 900 °C to 1150°C in this zone the sintering process starts due to decomposition of kaolinite to Meta kaolinite, formation of Al-Si spinal structure, formation of amorphous silica and formation of mullite phase. Here the ceramic coating gets fused to the ceramic body making surface impervious.

d) Rapid cooling zone: Here the temperature drastically reduced from 1150 °C to 1050°C by blowing of cold air which leads to quenching of tile.

e) Slow cooling zone: Here the temperature is brought from 1050 °C to 900 °C. The stability of the ceramic coating surface, squareness of the tile and the warpage of the tile will be determined be slow cooling.

f) Final cooling zone: Here the temperature will be brought down from 900 °C to 150°C

(Reference Fig 5. Glaze Line flow chart and Reference Fig 6. Firing Curve)

What is claimed is

1) A method of ceramic glaze coating composition comprising:

a) engobe composition application;

b) the base glaze composition application;

c) print application;

2) The method of ceramic glaze coating of claim 1, wherein said base glaze
composition application comprising:

a) Fritted glaze embedded with borates of calcium, magnesium, zinc etc;
b) Antimicrobial activity from MgO and presence of ZnO;
c) Vaccination treatment of Nano Zinc Oxide antimicrobial activity at 0.3 to 0.7% dosage along with the glaze;

3) The method of base glaze composition of claim 2, wherein beside frits, glaze composition contains 3 to 5% of talc powder which contains magnesium oxide after decomposition of magnesium silicate.

4) The method of base glaze composition of claim 2, wherein besides frits, talc and other basic raw materials like quartz, feldspar, calcite, alumina, china clay, zircosil, there are 1 to 4% zinc oxide has been used.

5) The method of base glaze composition of claim 4, wherein said composition is also infused by zinc oxide nano particles of size 100nm to 500nm with 0.3 to 0.7% dosages.

6) The method of base glaze composition of claim 2, wherein said plurality of combination of borates of calcium, magnesium and zinc oxide nano particles which provides to build the antimicrobial protection to the ceramic tiles.

7) The method of base glaze composition of claim 6, wherein said zinc oxide nano particles has been produced by the method of mechanical milling heated in a low temperature, large scale and simple wet process.

8) The method of preparing zinc oxide nano-particles of claim 7, wherein said powder particles are trapped between highly kinetic colliding balls and the inner surface of the wall which causes repeated deformation and destruction results the formation of fine and dispersed particles.

9) The method of preparing zinc nano- particles of claim 8, wherein said grinding media and zinc oxide powder particles ratio is 10:1.

10) The method of preparing zinc oxide nano- particles of claim 8, wherein said powder material has to be ground for 24 hours by wet grinding and dried in the oven with temperature 100 degree centigrade till it gets dried.

11) The method of preparing zinc oxide nano- particle of claim 8, wherein said grounded powder has particle size distribution from 100nm to 500nm.

12) The method of ceramic glaze coating composition of claim 1, wherein said test organism staphylococcus aureus antimicrobial activity stays at >99.00%.

13) The method of ceramic glaze coating composition of claim 1, wherein said test organism Escherichia Coli anti-bacterial activity stays at >2.00 and bacterial killing stays at >99.00%.

14) The method of ceramic glaze coating composition of claim 1, wherein said standard antimicrobial value log reduction S >2.0 and microbial reduction percentage >90%.