Antimicrobial glaze and porcelain enamel via double layer glaze with high zinc content

Abstract

A cost-effective and practical antimicrobial glaze system and glazing process is disclosed herein. The antimicrobial glaze/enamel may comprise at least two layers: a base layer and a top layer. The base layer may contain a typical or normal glaze widely used in sanitary ware, having a low level of zinc oxide. The base layer glaze may be directly sprayed on the clay body surface. A thin top glaze layer is sprayed on top of the base glaze layer and the top layer may contain a high level of zinc oxide.

Claims

1. A multilayer antimicrobial glaze/enamel, comprising: a base glaze layer, wherein the base glaze layer comprises less than about 8.0 percent by weight ZnO; and a top glaze layer, wherein the top glaze layer comprises about 8.0 percent by weight to about 35.0 percent by weight ZnO, wherein the base glaze layer is between about 300 m and 1000 m in thickness; wherein the top glaze layer is between about 25 m and 250 m in thickness; wherein relative thicknesses and concentrations of the top glaze layer and base glaze layer are such that a total concentration of the multilayer antimicrobial glaze/enamel is less than about 5.0 percent by weight ZnO; and wherein the multilayer antimicrobial glaze/enamel is substantially free of surface defects.

2. The multilayer antimicrobial glaze/enamel of claim 1 wherein the base glaze layer is between about 300 m and 600 m in thickness after firing.

3. The multilayer antimicrobial glaze/enamel of claim 1 wherein the top glaze layer is between about 25 m and 150 m in thickness after firing.

4. The multilayer antimicrobial glaze/enamel of claim 3 wherein the top glaze layer is between about 100 m and 200 m in thickness after firing.

5. The multilayer antimicrobial glaze/enamel of claim 1 wherein the top glaze layer also includes a source of ions of Hg, Ag, Cu, Fe, Pb, and/or Bi.

6. A multilayer antimicrobial glaze or enamel comprising a base glaze layer and a top glaze layer, comprising: a base glaze layer comprising after firing: about 40 to about 70 weight % SiO2, about 0 to about 15 weight % Al2O3, about 0 to about 15 weight % ZrO2, about 0 to about 6 weight % ZnO, about 0 to about 20 weight % CaO, about 0 to about 20 weight % TiO2, about 7.0 to about 15.0 weight % opacifier and about 0 to about 20 weight % B2O3; and a top glaze layer comprising after firing: about 3 to 15 weight % Al.sub.2O.sub.3 about 40 to 70 weight % SiO.sub.2 about 11 to 35 weight % ZnO about 0 to 20 weight % other fluxes; wherein the base glaze layer is between about 300 m and 1000 m in thickness; wherein the top glaze layer is between about 25 m and 250 m in thickness; wherein relative thicknesses and concentrations of the top glaze layer and base glaze layer are such that a total concentration of the multilayer antimicrobial glaze/enamel is less than about 5.0 percent by weight ZnO; and wherein the multilayer antimicrobial glaze or enamel is substantially free of surface defects.

7. The multilayer antimicrobial glaze/enamel of claim 6 wherein the top glaze layer also includes a source of ions of Hg, Ag, Cu, Fe, Pb, Bi, and/or a rare earth element.

8. A multilayer antimicrobial glaze or enamel comprising: a base glaze layer; and a top glaze layer, wherein the top about 10 m of the top glaze layer contains about 11.0 percent by weight to about 35.0 percent by weight ZnO; wherein the percent by weight of ZnO in the top about 10 m of the top glaze layer is greater than the percent by weight of ZnO in the base glaze layer and the percent by weight of ZnO lower than the top about 10 m of the top glaze layer; wherein relative thicknesses and concentrations of the top glaze layer and base glaze layer are such that a total concentration of the multilayer antimicrobial glaze/enamel is less than about 5.0 percent by weight ZnO; and wherein the multilayer antimicrobial glaze/enamel is substantially free of surface defects.

9. The multilayer antimicrobial glaze/enamel of claim 8 wherein the top glaze layer also includes a source of ions of Hg, Ag, Cu, Fe, Pb, and/or Bi.

10. A multilayer antimicrobial glaze/enamel, comprising: a base glaze layer, wherein the base glaze layer comprises less than about 8.0 percent by weight ZnO; and a top glaze layer, wherein the top glaze layer comprises about 8.0 percent by weight to about 35.0 percent by weight ZnO, wherein the top glaze layer comprises a top surface and a bottom surface; and wherein the bottom surface is adjacent to the base glaze layer, wherein the base glaze layer is between about 300 m and 1000 m in thickness; wherein the top glaze layer is between about 25 m and 250 m in thickness; wherein relative thicknesses and concentrations of the top glaze layer and base glaze layer are such that a total concentration of the multilayer antimicrobial glaze/enamel is less than about 5.0 percent by weight ZnO; and wherein the multilayer antimicrobial glaze/enamel is substantially free of surface defects.

11. The multilayer antimicrobial glaze/enamel of claim 10, wherein the top surface of the top glaze layer is adjacent to an ambient environment.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) These and other objects and features are illustrated and described in the following specification to be read in conjunction with the sheets of drawings in which:

(2) FIG. 1 is a chart comparing the antimicrobial efficacy of ceramic tile samples with thin top glaze layers containing 6.0, 10.0, and 15.0 weight percent zinc oxide relative to a ceramic control tile with no top layer. The top glaze layers of the samples compared in FIG. 1 are approximately 150 m thick.

(3) FIG. 2 is a chart comparing the antimicrobial efficacy test results of ceramic tile samples that have top layers containing 10.0 weight percent zinc oxide at a thickness of 150 m and 300 m. The efficacy is reported relative to ceramic control tiles with no top layer glaze.

DETAILED DESCRIPTION OF THE INVENTION

(4) The antimicrobial glaze/enamel of the present invention is made of at least two layers: a base layer and a top layer. The base layer consists of typical glaze materials that are widely used in sanitary ware manufacture. The base layer glaze is sprayed directly onto the clay body surface. The top layer contains a high level of zinc oxide (ZnO). The level of ZnO in the top layer is between about 8.0 wt % to about 35.0 wt %, preferably about 10.0 wt % to about 25.0 wt %. The top layer thickness may be in the range between about 25 m to about 250 m, and preferably about 25 to about 150 m in order to achieve good glaze quality.

(5) A typical glaze formula, an example of which is 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 the base glaze layer is preferably in the range of about 300 m to about 600 m. With about 0 wt % to about 8.0 wt % ZnO in the base layer, the glaze can be made free of pits and other surface irregularity defects. The base layer is then dried or fired. After firing a typical base glaze layer composition may be that shown in Table 2.

(6) TABLE-US-00001 TABLE 1 Typical glaze formula used in base layer. Raw Materials Formula (wt %) Feldspar 32.0-42.0 Whiting 8.0-18.0 ZnO 0-8.0 Talc 0-3.0 Frit 0-10.0 Silica 13.0-23.0 Opacifier 7.0-15.0 Clay 0-12.0 Other <10.0

(7) TABLE-US-00002 TABLE 2 Typical composition of base glaze after firing. Chemical Ingredients Formula (wt %) SiO2 40-70 Al2O3 0-15 ZrO2 0-15 ZnO 0-8 CaO 0-20 TiO2 0-20 B2O3 0-20 Others (e.g., K2O, 0-20 Na2O, MgO, Li2O)

(8) After the base layer is dried or fired, preferably dried in air at a temperature below about 200 C., a second, top glaze layer with a higher ZnO level than the base layer is sprayed on the top of the base layer. To avoid the formation of surface defects, the thickness of the top glaze layer is maintained at 25 m to 250 m. To achieve sufficient antimicrobial efficacy, the ZnO level in the top glaze layer glaze is between about 8.0 wt % and about 35.0 wt %.

(9) An example of a top glaze layer formula after firing is listed in Table 3. In order to reduce the possibility of the top glaze layer forming pits and other surface defects, that layer is kept thin and more exposed to air circulation. The surface of the top glaze layer is smooth, uniform, and has a high gloss. For optimal efficacy, surface appearance, and gloss, the top layer thickness needs to be in the range of about 25 m to about 250 m, preferably about 100 m to about 200 m. After finishing spraying of the top glaze layer, the parts can be sent to kiln for firing at normal firing temperature, typically around 1200 C.

(10) TABLE-US-00003 TABLE 3 Top layer glaze composition (after firing) Raw Materials Formula (wt %) Al.sub.2O.sub.3 8 SiO.sub.2 61 ZnO 25 Other Flux 6

(11) Because only a thin layer contains high levels of ZnO, the total ZnO content in the overall glaze is less than about 5.0 wt %. As the cost of ZnO is about $1/lb, a glaze system that requires about 5.0% ZnO can be manufactured at about 1/50.sup.th of the cost of a glaze with about 2.0 wt % of antimicrobial silver compound. The zinc-based glaze will give equal or better antimicrobial performance because the surface of the glaze in contact with bacteria can have a zinc content that is orders of magnitude higher than the silver content in commercially available antimicrobial chinaware.

(12) To summarize the present invention, the antimicrobial glaze/enamel is made of at least two layers: a base layer and a top layer. The base glaze layer consists of typical or normal glaze which is widely used in sanitary ware, and preferably has low levels of ZnO; about 0-8.0 wt %. An example of a base glaze layer composition after firing is shown in Table 3. The base glaze layer is preferably between 300 m and 1000 m thick after firing.

(13) The base glaze layer is sprayed directly on the clay body surface. The top glaze layer material contains high ZnO levels in the range of between about 6.0 wt % and about 35.0 wt %, preferably about 10.0 wt % to about 25.0 wt %. Other ingredients in the top layer may include, but are not limited to, Al.sub.2O.sub.3, SiO.sub.2, and other oxides, such as, but not limited to, K.sub.2O, Na.sub.2O, Li.sub.2O, MgO, CaO, B.sub.2O.sub.3, BaO, MoO, SnO, and SrO The top layer's thickness needs to be controlled in the range of between about 25 m to about 250 m, and preferably from about 25 m to about 150 m in order to achieve good glaze quality.

(14) In another embodiment, a top glaze layer is sprayed and fired to a thickness of between about 25 m and 250 m in which the top 10 m of the top glaze layer have between 8.0 wt % and 15.0 wt % ZnO, but due to diffusion between the top glaze layer and the bottom glaze layer the overall wt % ZnO in the top layer is less than 8.0 wt %.

(15) In another embodiment, oligodynamic elements or compounds other than zinc are added to increase the antimicrobial efficacy of the glaze or enamel, including but not limited to Hg, Ag, Cu, Fe, Pb, Bi, and/or a rare earth element or elements.

(16) The invention will now be further described by way of the following non-limiting examples.

EXAMPLES

Example 1

(17) A series of ceramic tiles were prepared with base layer compositions according to Table 1 and top layer compositions containing 6.0 wt %, 10.0 wt %, 15.0 wt %, and 25.0 wt % ZnO. The base layer was sprayed to give a post-fire thickness of approximately 450 m. After allowing approximately 5 minutes for the base layer to dry in ambient air, the top layer was sprayed on to the base layer to a post-fire thickness of approximately 150 m. The tiles were then fired in air at a temperature of 1215 C. for a soak time of 45 minutes. Upon cooling and removal from the furnace, the samples were subjected to antimicrobial efficacy testing in accordance with the procedures outlined in the Japanese Standard JIS Z2801. A ceramic tile with the identical base layer and no top layer was prepared at the same time and used as the control tile. The results of these tests are shown in Table 4 and FIG. 1. The results indicate that the sample with 6 wt % ZnO in the top layer has little of no efficacy against Staph Aureus relative to the control tile with no top layer glaze. The sample with top layer glaze containing 10 wt % ZnO exhibited significantly improved antimicrobial efficacy compared to the 6.0 wt % ZnO glaze, with a roughly Log 2.0 reduction relative to the control tile. The sample with top layer glaze containing 15.0 wt % ZnO exhibited a Log 3.8 reduction relative to the control tile. This corresponds to a reduction in Staph Aureus count of 99.98% over the 24 hour test period. Additionally, the antimicrobial efficacy of the sample having 25.0 wt % ZnO in the top layer (not shown) exhibited a >Log 3.0 reduction against Staph Aureus. However, the cosmetic quality of the glaze began to suffer from surface defects due to the high ZnO content.

Example 2

(18) Additional sample tiles were prepared according to the procedure given in Example 1, with the exception that the post-fire thickness of the top layer was varied from 150 m to 300 m. These samples were then subjected to antimicrobial efficacy testing in accordance with the procedures outlined in the Japanese Standard JIS Z2801. FIG. 2 shows the difference in antimicrobial efficacy against Staph Aureus of samples with a 10 wt % ZnO top glaze layer at different thickness. The efficacy is improved when the thickness is increased from 150 m to 300 m.

(19) TABLE-US-00004 TABLE 4 Bacteria counts (in colony forming units/cm.sup.2) during JIS Z2801 testing of samples described in Example 1. Contact time against Staph Aureus ZnO level in top glaze layer 0 hours 24 hours Control Tile (0% ZnO) 6.5 10.sup.3 8.3 10.sup.3 6.0 wt % ZnO, 150 m 6.5 10.sup.3 4.0 10.sup.3 10.0 wt % ZnO, 150 m 6.5 10.sup.3 8.3 10.sup.1 15.0 wt % ZnO, 150 m 6.5 10.sup.3 1.1 10.sup.0

(20) Having thus described in detail the preferred embodiments of the present invention, it is to be understood that the invention defined by the above paragraphs is not to be limited to the particular details set forth in the above description. Many apparent variations thereof are possible without departing from the spirit or scope of the present invention.

(21) In this application, terms such as comprises, comprised, comprising and the like, can have the meaning attributed to it in U.S. patent law; e.g., they can mean includes, included, including, and the like; and terms such as consisting essentially of and consists essentially of, have the meaning ascribed to them in U.S. patent law, e.g., they allow for elements not explicitly recited, but exclude elements that are found in the prior art or that affect a basic or novel characteristic of the invention.

(22) Citation or identification of any document in this application is not an admission that such document is available as prior art to the present invention.