(12) Patent Application Publication (10) Pub. No.: US 2012/0237686 A1 Chen Et Al

US 20120237686A1 (19) United States (12) Patent Application Publication (10) Pub. No.: US 2012/0237686 A1 Chen et al. (43) Pub. Date: Sep. 20, 2012

(54) ANTIMICROBIAL GLAZE AND PORCELAIN (60) Provisional application No. 60/679,620, filed on May ENAMEL VADOUBLE LAYER GLAZE WITH 9, 2005. HIGH ZINC CONTENT Publication Classification (75) Inventors: Zheng Chen, Flemington, NJ (US); (51) Int. Cl. James Michael McHale, BOSD 3/02 (2006.01) Hillsborough, NJ (US) BSD L/02 (2006.01) (73) Assignee: Ideal Standard International (52) U.S. Cl...... 427/38O BVBA, Brussels (BE) (57) ABSTRACT (21) Appl. No.: 13/486,802 A cost-effective and practical antimicrobial glaze system and glazing process is disclosed herein. The antimicrobial glazef (22) Filed: Jun. 1, 2012 enamel may comprise at least two layers: a base layer and a 9 top layer. The base layer may contain a typical or normal O O glaze widely used in sanitary ware, having a low level of Zinc Related U.S. Application Data oxide. The base layer glaze may be directly sprayed on the (62) Division of application No. 1 1/920,111, filed on Nov. clay body Surface. A thin top glaze layer is sprayed on top of 19, 2008, filed as application No. PCT/US2006/ the base glaze layer and the top layer may contain a high level 017366 on May 5, 2006. of Zinc oxide. Patent Application Publication Sep. 20, 2012 Sheet 1 of 2 US 2012/023768.6 A1

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ANTIMICROBAL, GLAZE AND PORCELAN 1100° C. This approach can provide good antibacterial effi ENAMEL VADOUBLE LAYER GLAZE WITH cacy, but in practice, the level of silver required to obtain this HGH ZNC CONTENT effect results in an unacceptably large increase in the cost of the glaze. For example, a typical toilet and tank combination CROSS-REFERENCE TO RELATED contains about 6.5 lbs of glaze. Due to the relatively high APPLICATIONS vapor pressure of silver and its compounds at temperatures above 1200° C., at least 2 wt % of an antimicrobial silver 0001. This is a divisional application of U.S. application compound is needed to impart strong antimicrobial efficacy Ser. No. 1 1/920,111, which was filed on Nov. 19, 2008, which to the fired sanitary ware body. The cost of antimicrobial is national phase filing under section 371 of PCT/US2006/ silver compounds is roughly S100/lb, which at 2% loading 017366, filed on May 5, 2006, which claims the benefit of U.S. Provisional Application No. 60/679,620, filed on May 9, results in an added cost of S13 pertoilet and tank combo. This 2005, each of which is incorporated herein by reference in its cost requires a price increase for antimicrobial sanitary ware entirety. that is well beyond what many consumers in the Americas and Europe are willing to pay for the feature. Additionally, a large part of the silver in the glaze vaporizes and condenses on the INCORPORATION BY REFERENCE walls of the kiln, which over time can build up to troublesome 0002 All documents cited or referenced herein (“herein levels and result in manufacturing downtime, thereby further cited documents'), and all documents cited or referenced in increasing the cost of manufacturing these pieces. Thus, there herein cited documents, together with any manufacturer's is a need for a more cost effective means than using silver for instructions, descriptions, product specifications, and product producing antimicrobial sanitary ware for these markets. sheets for any products mentioned herein or in any document 0006. Of the other metals that have strong oligodynamic incorporated by reference herein, are hereby incorporated effects, Zinc is most Suited for use in Sanitary ware applica herein by reference, and may be employed in the practice of tions. Mercury, lead, and bismuth present toxicity and/or the invention. environmental issues, whereas iron and copper compounds would eliminate the possibility of producing white pieces. FIELD OF THE INVENTION Zinc oxide is already used as a flux material in Some sanitary ware glaze systems, albeit at levels that are too low to yield 0003. The present invention relates to antimicrobial sani any significant antimicrobial effect. For example, Japanese tary ware, in particular, the ceramic glaze layer. The invention Patent Application 10-227686 relates to an antimicrobial provides for a cost-effective and practical antimicrobial glaze glaze formulation that contains 6-20 wt % of zinc compounds System and glazing process. measured as Zinc oxide. The inventors state that at least 6 wit % of Zinc compounds is necessary to obtain consistent anti BACKGROUND OF THE INVENTION microbial efficacy. Using Such a large amount of Zinc in a sanitary ware glaze system, although it might provide anti 0004. The oligodynamic effect is the term given to the microbial properties at a cost much lower than that obtainable ability of small amounts of heavy metals to exert a lethal through the use of silver compounds, presents manufacturing effect on bacteria (from the Greek: oligos, Small; dynamis, issues that severely limit the practicality of this approach. power). The effectiveness of heavy metals as antimicrobials is Such a sanitary ware glaze system having more than 6 wt % believed to be due to the high affinity of cellular proteins for Zinc oxide, will begin to Suffer severe pitting and Surface metallic ions. Bacteria cells die due to the cumulative effects irregularity defects. These defects become even more severe of ions within the cell, even if the concentration of ions in a if the circulation of air in the kiln is not sufficient. Solution is miniscule. Metals that generally show a strong oligodynamic effect are (in order of decreasing strength) 0007 Similar needs and issues exist for antimicrobial por Hg-Ag-Cu-Zn-Fe-Pb>Bi. Among these metals, silver and celain enamel systems. Whereas glazes are glass coatings Zinc have been used in materials for various applications and applied to ceramic Substrates (bodies), porcelain enamel is industries, such as materials for use in medical devices, food the general term applied to Such glass coatings on metallic processing products, textiles, and sanitary ware. Oligody Substrates. For example, porcelain enamels are widely namic elements other than silver and Zinc, either due to applied to steel and cast iron bodies in the manufacture of human toxicity or some incompatibility with the intended sinks, bathtubs, hot water heaters, cookware, and some appli matrix material (e.g. changes in color), are rarely used as aCCS, antimicrobial agents in material applications. Compared to Zinc, silver and its salts exert a much stronger antimicrobial SUMMARY OF THE INVENTION effect against common bacteria Such as Staphylococcus Aureus and Escherichia coli. Zinc oxide, however, generally 0008. Therefore, there remains a need for a cost-effective shows much better efficacy than silver against various fungi. and practical (from a manufacturing viewpoint) approach to Another practical factor from a manufacturing standpoint is providing sanitary ware with antimicrobial properties. The that silver is far more expensive than Zinc, with a market price invention described herein provides a solution to this prob over 100 times greater per unit weight compared to zinc. lem. A cost-effective and practical antimicrobial glazef 0005 U.S. Pat. Nos. 5,807,641 and 5,882,808 relate to enamel system and glazing process can be achieved by the antimicrobial sanitary ware produced by adding silver com herein described glazing technology, employing at least two pounds to the ceramic glaze layer. The silver is added to the glaze layers. glaze slurry as a salt or oxide. The glaze slurry is applied to the 0009. The antimicrobial glaze/enamel of the present ceramic body and fired at a temperature generally exceeding invention is made of at least two layers: a base layer and a top US 2012/023768.6 A1 Sep. 20, 2012 layer. The base layer consists of typical glaze materials that are widely used in sanitary ware manufacture. The base layer TABLE 1-continued glaze is sprayed directly onto the clay body Surface. The top layer contains a high level of zinc oxide (ZnO). The level of Typical glaze formula used in base layer. ZnO in the top layer is between about 8.0 wt % to about 35.0 Raw Materials Formula (wt %) wt %, preferably about 10.0 wt % to about 25.0 wt %. The top Silica 130-23.O layer thickness may be in the range between about 25um to Opacifier 7.O-1S.O about 250 um, and preferably about 25um to about 150 um in Clay O-12.O order to achieve good glaze quality. Other <10.O 0010. These and other embodiments are disclosed or are obvious from and encompassed by, the following Detailed Description. TABLE 2

BRIEF DESCRIPTION OF THE DRAWINGS Typical composition of base glaze after firing. Chemical Ingredients Formula (wt %) 0011. These and other objects and features are illustrated and described in the following specification to be read in SiO, 40-70 Al2O3 O-15 conjunction with the sheets of drawings in which: ZrO2 O-15 0012 FIG. 1 is a chart comparing the antimicrobial effi ZnO O-8 cacy of ceramic tile samples with thin top glaze layers con CaO O-2O TiO2 O-2O taining 6.0, 10.0, and 15.0 weight percent Zinc oxide relative B2O3 O-2O to a ceramic control tile with no top layer. The top glaze layers Others (e.g., K2O, Na2O, MgO, Li2O) O-2O of the samples compared in FIG. 1 are approximately 150 um thick. 0013 FIG. 2 is a chart comparing the antimicrobial effi 0016. After the base layer is dried or fired, preferably dried cacy test results of ceramic tile samples that have top layers in air at a temperature below about 200° C., a second, top containing 10.0 weight percent Zinc oxide at a thickness of glaze layer with a higher ZnO level than the base layer is 150 um and 300 lum. The efficacy is reported relative to sprayed on the top of the base layer. To avoid the formation of ceramic control tiles with no top layer glaze. surface defects, the thickness of the top glaze layer is main tained at 25um to 250 um. To achieve sufficient antimicrobial efficacy, the ZnO level in the top glaze layer glaze is between DETAILED DESCRIPTION OF THE INVENTION about 8.0 wt % and about 35.0 wt %. 0017. An example of a top glaze layer formula after firing 0014. The antimicrobial glaze/enamel of the present is listed in Table 3. In order to reduce the possibility of the top invention is made of at least two layers: a base layer and a top glaze layer forming pits and other surface defects, that layer is layer. The base layer consists of typical glaze materials that kept thin and more exposed to air circulation. The Surface of are widely used in sanitary ware manufacture. The base layer the top glaze layer is Smooth, uniform, and has a high gloss. glaze is sprayed directly onto the clay body Surface. The top For optimal efficacy, Surface appearance, and gloss, the top layer contains a high level of zinc oxide (ZnO). The level of layer thickness needs to be in the range of about 25 um to ZnO in the top layer is between about 8.0 wt % to about 35.0 about 250 um, preferably about 100 um to about 200 um. wt %, preferably about 10.0 wt % to about 25.0 wt %. The top After finishing spraying of the top glaze layer, the parts can be layer thickness may be in the range between about 25um to sent to kiln for firing at normal firing temperature, typically about 250 um, and preferably about 25 to about 150 um in order to achieve good glaze quality. around 1200° C. 0015. A typical glaze formula, an example of which is TABLE 3 listed in Table 1, is used as the first layer (base layer), and may be sprayed on the clay body surface directly. The thickness of Top layer glaze composition (after firing the base glaze layer is preferably in the range of about 300 um to about 600 um. With about 0 wt % to about 8.0 wt % ZnO in Raw Materials Formula (wt %) the base layer, the glaze can be made free of pits and other Al2O3 8 surface irregularity defects. The base layer is then dried or SiO2 61 ZnO 25 fired. After firing a typical base glaze layer composition may Other Flux 6 be that shown in Table 2.

TABLE 1. 0018. Because only a thin layer contains high levels of ZnO, the total ZnO content in the overall glaze is less than Typical glaze formula used in base layer. about 5.0 wt %. As the cost of ZnO is about S1/lb, a glaze system that requires about 5.0% ZnO can be manufactured at Raw Materials Formula (wt %) about /so" of the cost of a glaze with about 2.0 wt % of Feldspar 32.0-42.O Whiting 80-18.0 antimicrobial silver compound. The zinc-based glaze will ZnO O-8.0 give equal or better antimicrobial performance because the Talc O-3.0 Surface of the glaze in contact with bacteria can have a Zinc Frit O-1O.O content that is orders of magnitude higher than the silver content in commercially available antimicrobial chinaware. US 2012/023768.6 A1 Sep. 20, 2012

0019. To summarize the present invention, the antimicro 3.0 reduction against Staph Aureus. However, the cosmetic bial glazefenamel is made of at least two layers: a base layer quality of the glaze began to Suffer from Surface defects due to and a top layer. The base glaze layer consists of typical or the high ZnO content. normal glaze which is widely used in sanitary ware, and preferably has low levels of ZnO; about 0-8.0 wt %. An Example 2 example of a base glaze layer composition after firing is shown in Table 3. The base glaze layer is preferably between 0025. Additional sample tiles were prepared according to 300 Lum and 1000 um thick after firing. the procedure given in Example 1, with the exception that the 0020. The base glaze layer is sprayed directly on the clay post-fire thickness of the top layer was varied from 150 um to body Surface. The top glaze layer material contains high ZnO 300 Lum. These samples were then subjected to antimicrobial levels in the range of between about 6.0 wt % and about 35.0 efficacy testing in accordance with the procedures outlined in wt %, preferably about 10.0 wt % to about 25.0 wt %. Other the Japanese Standard JIS Z2801. FIG.2 shows the difference ingredients in the top layer may include, but are not limited to, in antimicrobial efficacy against Staph Aureus of Samples Al-O, SiO, and other oxides, such as, but not limited to. with a 10 wt % ZnO top glaze layer at different thickness. The KO, NaO, LiO, MgO, CaO. B.O. BaO, MoC), SnO, and efficacy is improved when the thickness is increased from 150 SrO The top layer's thickness needs to be controlled in the um to 300 um. range of between about 25 um to about 250 lum, and prefer ably from about 25um to about 150 um in order to achieve TABLE 4 good glaze quality. Bacteria counts (in colony forming units/cm) during JIS Z2801 0021. In another embodiment, a top glaze layer is sprayed testing of samples described in Example 1. and fired to a thickness of between about 25um and 250 um in which the top 10um of the top glaze layer have between 8.0 Contact time against wt % and 15.0 wt % ZnO, but due to diffusion between the top Staph Aureus glaze layer and the bottom glaze layer the overall wt % ZnO ZnO level in top glaze layer O hours 24 hours in the top layer is less than 8.0 wt %. Control Tile (0% ZnO) 6.5 x 10 8.3 x 10 0022. In another embodiment, oligodynamic elements or 6.0 wt % ZnO, 150 m 6.5 x 10 4.0 x 10 compounds other than Zinc are added to increase the antimi 10.0 wt % ZnO, 150 m 6.5 x 10 8.3 x 10 crobial efficacy of the glaze or enamel, including but not 15.0 wt % ZnO, 150 m 6.5 x 10 1.1 x 109 limited to Hg, Ag, Cu, Fe, Pb, Bi, and/or a rare earth element or elements. 0026. Having thus described in detail the preferred 0023 The invention will now be further described by way embodiments of the present invention, it is to be understood of the following non-limiting examples. that the invention defined by the above paragraphs is not to be limited to the particular details set forth in the above descrip EXAMPLES tion. Many apparent variations thereof are possible without departing from the spirit or scope of the present invention. Example 1 0027. In this application, terms such as “comprises.” “comprised,” “comprising and the like, can have the mean 0024. A series of ceramic tiles were prepared with base ing attributed to it in U.S. Patent law; e.g., they can mean layer compositions according to Table 1 and top layer com “includes.” “included,” “including, and the like; and terms positions containing 6.0 wt %, 10.0 wt %, 15.0 wt %, and 25.0 Such as "consisting essentially of and “consists essentially wt % ZnO. The base layer was sprayed to give a post-fire of have the meaning ascribed to them in U.S. Patent law, thickness of approximately 450 Lum. After allowing approxi e.g., they allow for elements not explicitly recited, but mately 5 minutes for the base layer to dry in ambient air, the exclude elements that are found in the prior art or that affect top layer was sprayed on to the base layer to a post-fire a basic or novel characteristic of the invention. thickness of approximately 150 lum. The tiles were then fired 0028 Citation or identification of any document in this in air at a temperature of 1215° C. for a soak time of 45 application is not an admission that such document is avail minutes. Upon cooling and removal from the furnace, the able as prior art to the present invention. samples were Subjected to antimicrobial efficacy testing in accordance with the procedures outlined in the Japanese What is claimed is: Standard JIS Z2801. A ceramic tile with the identical base layer and no top layer was prepared at the same time and used 1. A method of producing an antimicrobial ceramic glaze as the control tile. The results of these tests are shown in Table or porcelain enamel product, comprising the steps of: 4 and FIG.1. The results indicate that the sample with 6 wt % applying a base glaze material onto a ceramic body to form ZnO in the top layer has little of no efficacy against Staph a base glaze layer; Aureus relative to the control tile with no top layer glaze. The applying a top glaze material onto the base glaze layer, sample with top layer glaze containing 10 wt % ZnO exhib wherein the top glaze material is comprised of more than ited significantly improved antimicrobial efficacy compared about 8.0 percent by weight and less than about 35.0 to the 6.0 wt % ZnO glaze, with a roughly Log 2.0 reduction percent by weight ZnO; and relative to the control tile. The sample with top layer glaze firing the top glaze material in a kiln to create a top glaze containing 15.0 wt % ZnO exhibited a Log 3.8 reduction layer. relative to the control tile. This corresponds to a reduction in 2. The method of claim 1 wherein the base glaze layer is Staph Aureus count of 99.98% over the 24 hour test period. fired in a kiln prior to application of the top glaze material. Additionally, the antimicrobial efficacy of the sample having 3. The method of claim 1 wherein the base glaze material is 25.0 wt % ZnO in the top layer (not shown) exhibited a >Log applied by spray coating. US 2012/023768.6 A1 Sep. 20, 2012

4. The method of claim 1 wherein the base glaze material is applying a top glaze material directly to the base glaze applied to an after-firing thickness of between about 300 um layer wherein the top glaze material contains more than and 1000 Lum. about 8.0 percent by weight and less than about 35.0 5. The method of claim 1 wherein the top glaze material is percent by weight ZnO; and applied by spray coating. firing the top glaze material in a kiln to create a top glaze 6. The method of claim 1 wherein the top glaze material is layer of thickness between about 25um and 250 um after applied to an after-firing thickness of between about 25 um firing. 11. The method of claim 10 wherein the base glaze material and 250 lum. is fired in a kiln prior to application of the top glaze material. 7. The method of claim 1 wherein the top glaze material is 12. The method of claim 10 wherein the base glaze material applied to an after-firing thickness of between about 100 um is applied to the ceramic body by spray coating. and 200 um. 13. The method of claim 10 wherein the top glaze material 8. The method of claim 1 wherein the base glaze material is is applied to the base glaze layer by spray coating. air dried prior to application of the top glaze material. 14. The method of claim 10 wherein the top glaze layer is 9. The method of claim 1 wherein the top glaze layer also of thickness between about 25um and 150 um after firing. includes a source of ions of Hg, Ag, Cu, Fe, Pb, Bi, and/or a 15. The method of claim 10 wherein the base glaze material rare earth element. is air dried prior to application of the top glaze material. 10. A method of producing an antimicrobial ceramic glazef 16. The method of claim 10 wherein the top glaze layer also enamel product, comprising the steps of: includes a source of ions of Hg, Ag, Cu, Fe, Pb, Bi, and/or a applying a base glaze material onto a ceramic body to form rare earth element. a base glaze layer of thickness between about 300 um and 1000 um after firing: