Color-stable, antimicrobial, porous glass powder and process for producing such a powder at high temperatures and use thereof

Abstract

A color-stable, antimicrobial glass powder obtained by partial ion exchange at a temperature of 300° C. to 350° C. and an exchange time of 1 to 120 minutes, is formed of a mixture of porous glass particles having micropores and macropores made of borosilicate glass continuously foamed by extrusion having a Fe.sub.2O.sub.3 content <0.2 wt %, in which the obtained glass foam is subsequently comminuted by dry grinding to average particle sizes of 1.0 to 8.0 μm. The mixture includes color stabilizers containing 0.1% to 0.2% of ammonium ions and antimicrobial metal ions from dissolved metal salts, wherein the metal ions may be silver and/or zinc and/or copper ions. A method for the production of a color-stable, antimicrobial glass powder and applications for using the color-stable, antimicrobial glass powder are also provided.

Claims

1. A color-stable, antimicrobial glass powder having characteristics of having been obtained by partial ion exchange at a temperature of 300° C. to 350° C. and an exchange time of 1 to 120 minutes, the glass powder comprising a mixture of: porous glass particles having micropores and macropores made of borosilicate glass having characteristics of continuously foaming by extrusion having a Fe.sub.2O.sub.3 content <0.2 wt % and characteristics of subsequently comminuting an obtained glass foam by dry grinding to average particle sizes of 1.0 to 8.0 μm; ammonium nitrate forming 0.1% to 0.2% ammonium ions in the porous glass particles at the parameters described above; and antimicrobial metal ions from dissolved metal salts, the metal ions being at least one of silver or zinc or copper ions.

2. The color-stable, antimicrobial, porous glass powder according to claim 1 being used in polymers, silicones, paints, plasters or cosmetic products in quantities of 0.1 to 20.0 wt % to achieve an antimicrobial effect.

3. The color-stable, antimicrobial, porous glass powder according to claim 2, wherein the polymers are formed by two or more polymers or contain polymerisates having elastic characteristics of rubber.

4. The color-stable, antimicrobial, porous glass powder according to claim 2, wherein the polymers are compounds containing additional fillers, aggregates or coloring agents.

5. The color-stable, antimicrobial, porous glass powder according to claim 2, wherein the glass powder used in polymers form antimicrobially equipped polymers used to produce antimicrobially equipped molded parts, film or fibers.

6. The color-stable, antimicrobial, porous glass powder according to claim 2 wherein the silicones are damp-proof silicones.

7. The color-stable, antimicrobial, porous glass powder according to claim 1 being used in starting materials of polymers, including polymerizable or curable monomers or polymerizable or curable prepolymers or polymerizable or curable polymers.

8. The color-stable, antimicrobial, porous glass powder according to claim 1 being used in polymers, silicones, paints, plasters or cosmetic products in quantities of 0.1 to 20.0 wt % to achieve an antimicrobial effect, with a moisture absorption at 23° C. and 50% relative humidity being ≥0.2 wt %.

9. The color-stable, antimicrobial, porous glass powder according to claim 1 being used in paints and plasters in quantities of 0.1 to 20.0 wt % to achieve an antimicrobial effect and being water vapor permeable.

10. A method for the production of a color-stable, antimicrobial glass powder, the method comprising the following steps: carrying out a partial ion exchange at a temperature of 300° C. to 350° C. and an exchange time of 1 to 120 minutes; and providing a mixture of: porous glass particles having micropores and macropores made of borosilicate glass continuously foamed by extrusion having a Fe.sub.2O.sub.3 content <0.2 wt %, and subsequently comminuting an obtained glass foam by dry grinding to average particle sizes of 1.0 to 8.0 μm; ammonium nitrate as a color stabilizer forming 0.1% to 0.2% ammonium ions in porous glass particles at a temperature of 300° C. to 350° C. and an exchange time of 1 to 120 minutes; and antimicrobial metal ions from dissolved metal salts, the metal ions being at least one of silver or zinc or copper ions.

Description

DESCRIPTION OF THE INVENTION

Examples

(1) The invention is illustrated below with some examples in detail, but the invention is not to be construed as being limited to those examples.

(2) Production of the Porous Glass Particles

(3) A glass foam was produced from borosilicate glass of the chemical composition described above, using water vapour (2.5 grams per kilogram of molten glass) as a leavening agent in the single-screw extruder at a molten glass temperature of 880° C.

(4) TABLE-US-00003 TABLE 3 Chemical composition of the borosilicate glass for the example Oxides Content in wt % Na.sub.2O 9.91 K.sub.2O 2.91 MgO 0.57 CaO 2.52 Al.sub.2O.sub.3 5.52 SiO.sub.2 57.7 B.sub.2O.sub.3 10.9 Fe.sub.2O.sub.3 0.12 ZnO 4.32 BaO 4.94 F.sub.2 0.42

(5) The determination of the chemical glass composition (ISO 52340) is made via atomic absorption spectroscopy (AAS) or X-ray fluorescent analysis.

(6) As a next step, the glass foam was coarse-crushed in a roll type crusher with a punched screen of 7 mm down to glass foam particles of ≤7 mm. After that, they were crushed to a mean particle size of 3.0 μm in a combined grinding and separating process (ball mill)—(particle size distribution: d.sub.10=0.9 μm; d.sub.50=2.9 μm; d.sub.75=5.0 μm; d.sub.90=7.2 μm and d.sub.99<12.0 μm).

(7) The particle size distribution was determined by means of laser diffraction in accordance with DIN ISO 1332-1. D.sub.50 is the particle size where 50 percent of the particles are smaller or equal to the specified value.

(8) The ph value of the porous glass particles was determined in a 10% aqueous solution at ambient temperature in accordance with DIN EN ISO 787-9. In deviation from the standard, the eluate was produced from 10 g glass powder and 90 g distilled water, however. The glass particles were now filtered, and the filtrate was measured concerning both ph value and conductivity, using the pH laboratory kit including a conductivity electrode (Hach Lange GmbH).

(9) The content of moisture in the glass particles was determined in accordance with ISO 787-2 after 2 hours of drying in the recirculation unit at 105° C.

(10) The following values were determined for the porous borosilicate glass powder of a d.sub.50 of 2.9 μm used in the examples: pH: 10.3 Conductivity: 0.7 mS/cm Residual moisture: 0.4%.
Production of the Color-Stable, Antimicrobial, Porous Glass Particles

(11) 12.5 g silver nitrate (very pure, for synthesis, silver content 63.5%) and 15 grams of ammonium nitrate) were solved in 14 ml of distilled water. This was done with a heatable magnetic stirrer as the solvent action runs highly endothermally.

(12) 237.5 g of the porous glass particles of a d.sub.50 of 2.9 μm were put into a plastic bowl. The porous glass particles were mixed in a laboratory agitator at low speeds (400 to 600 min.sup.31 1). The solution of silver nitrate and ammonium nitrate was then slowly added by drops into the bowl with the porous glass particles, always agitating the mixture.

(13) Once the complete solution was filled in, the mixture was stirred for another 10 minutes.

(14) The mixture was evenly distributed on a stainless steel sheet, the thickness of the layer being <1 cm. The filled layer was covered with a lid and put into the furnace that was preheated to 330° C. When the setpoint temperature of 330° C. was reached, the sheet remained in the furnace at 330° C. for another 45 minutes. The sheet was taken out of the furnace, and after a cooling period of 30 minutes approximately the color-stable, antimicrobial, porous glass particles could be removed from the sheet. After that, the dried, color-stable, antimicrobial, porous glass powder was deagglomerated in a toothed colloid mill KK 100.

(15) The next step was the production of eluates from the color-stable, antimicrobial, porous glass particles.

(16) In deviation from the standard DIN EN ISO 787-14, 10 grams of the glass particles were eluated in 90 g of distilled water. The glass particles were filtered and additionally centrifuged before the analysis in order to separate any floating matter. The filtrate was measured concerning both ph value and conductivity, using the pH laboratory kit including conductivity electrode (Hach Lange GmbH).

(17) The ph value of the filtrate was 7.9, its conductivity 10.0 mS/cm. The silver ion content in the eluate was determined using the photometer DR 2800 (make Hach Lange GmbH) and the cuvette test LCK 354. The eluate had a silver content of 0.47 mg/l. The moisture content of the color-stable, antimicrobial, porous glass particles was determined in accordance with ISO 787-2 after 2 hours of drying in the recirculation unit at 105° C. and was 0.21%.

(18) The proof that and if so, how many ammonium ions were in the glass particles doped with silver nitrate and ammonium nitrate, was carried out, on the qualitative side, by the blue discoloration of a universal indicator, and on the quantitative side, with a cuvette test in accordance with the standard method of the ISO 7150-1, DIN 38406 E5.

(19) Description of the Test Arrangement for a Qualitative Determination of Ammonium Ions:

(20) The product is presented in a watch-glass. ph paper is glued into a second watch-glass, using a few drops of water. When some drops of concentrated sodium hydroxide solution have been added, the watch-glass with the pH paper is slipped over the other glass (simulation of a micro gas chamber). After a short period, the ph paper discolors and reaches the alkaline zone (in the present case, it gets blue).

(21) All products analysed to date, to which ammonium nitrate has been introduced, showed a positive qualitative reaction.

(22) Description of the Test Arrangement for the Quantitative Determination of Ammonium Ions:

(23) As ammonium ions are excellently soluble in water, we have used a cuvette test made by Hach Lange GmbH.

(24) The cuvette test is available in 3 different concentration levels (47-130 mg/l, 2.0-47.0 mg/l and 0.015-2.0 mg/l). This is a standardized method in accordance with ISO 7150-1, DIN 38406 E5-1. It is the principle of this measurement that ammonium ions will react to hypochlorite ions and salicylate ions in the presence of sodium nitroprusside as catalyzer to become indophenol blue, at a pH value of 12.6. Primary amines are also detected and result in multiple findings. A 1000-fold surplus of urea is no interference.

(25) The intensity of the indophenol blue coloration is measured with a photometer DR 2800, also made by Hach Lange GmbH.

(26) An analysis is performed of a 10 percent aqueous eluate which after filtration and centrifugation is subjected to the chemical reaction described above, in a cuvette provided with a bar code.

(27) The values thus determined are presented in Table 4. The results make clear what proportions of ammonium can be detected in the individual products.

(28) TABLE-US-00004 Tempering time/ Temperature pH LF Ag+ NH.sub.4 NH.sub.4NO.sub.3 Duration Item Sample value (mS/cm) (mg/l) (mg/l) (g/assay) (min) ° C. 1) TROVOguard B-K3-040309 8.75 6.93 0.42 1.05 400 45 330 Charge No. 22-02-16- S40-An6-KR7-K3 2) TROVOguard B-K3-040306 7.9 8.95 0.44 1.11 600 45 330 Charge No. 23-02-16- S42-An6-KR7-K3 3) TROVOguard B-K3-040310 7.7 9 0.46 1.09 600 45 330 Charge No. 15-11-S35- An0-KR6-K3-ZnO10 4) TROVOguard B-K3-040306 7.7 10 0.49 1.27 600 45 330 Charge No. 15-07-S35- AnO-KR6-K3 5) TROVOguard B-K2-040301 8.4 10.2 0.43 1.74 600 5 330 Charge No. 15-11-S39- An3-KR4-K2

(29) Contrary to the schools of thought and discussions with chemical engineers, a share of 0.1 to 0.2% of ammonium ions can be detected in the modifed glass particles obtained at temperatures of 33° C. with ammonium nitrate, where in case of smaller particles, cf. item 5 in Table 4, a particle with the mean particle size of 2 μm had a higher ammonium ion content than in the items 1-4 of the variations with a mean particle size of 3 μm. If the particles are smaller, both the silver ion exchange and the ammonium ion exchange are achieved with shorter tempering periods, as the surface available for exchange is larger.

(30) Example of Comparison Without Ammonium Nitrate

(31) The same method was used to produce the antimicrobial, porous glass particles used for comparison which are not color-stable. No ammonium nitrate was used here. In this case, the ph value of the eluate was 9.9, the conductivity 4.1 mS/cm and the silver content 0.35 mg/l. It was possible to prove the antimicrobial effect of this product in a plaster over a period of approximately 4 years in an outdoor field test, where the plaster underwent heavy discoloration, however. In façade paints, the antimicrobial effect of these silver-doped, porous glass particles has also been proved in an outdoor test over a period of 24 months, where strong discoloration occurred as well.

(32) Example of Color Tests in Plaster

(33) A laboratory mixer was used to blend the color-stable, antimicrobial, porous glass particles claimed by the invention into a silicone resin plaster in a concentration of 1.0, 2.0 and 4.0 wt % (samples 1.1, 1.2 and 1.3). A laboratory mixer was used to blend the color-stable, antimicrobial, porous glass particles claimed by the invention into a silicone resin plaster in a concentration of 1.0, 2.0 and 4.0 wt % (samples V1, V2 and V3).

(34) For the comparison of the different colors, a plaster sample without argentiferous, antimicrobial, porous glass particles was used (V0). The plaster samples were applied to plastic plates, with a thickness of the layer of ca. 2.0 mm.

(35) These samples were stressed in various manners in order to get figures for a long-term behaviour. The first set of samples was only dried at ambient temperature.

(36) A second set of samples was stored in the laboratory for 5 weeks.

(37) With the third set of samples, the sample sheets were inclined at a 90 degree angle in a southerly direction, and left exposed to the prevailing climatic situation for 10 weeks.

(38) A fourth set of samples was exposed to alternatingly UV light and humidity at high temperatures in the QUV test for 10 days. A lamp was used here which realises the best possible simulation of insolation in the critical short-wave UV range between 365 nm and the solar energy limit of 295 nm. The radiation peak was at 340 nm.

(39) The colors were compared using the method of the CIELAB color space in order to determine color differences between a reference sample (V.0—zero sample without glass particles) and the comparison samples (samples with argentiferous glass particles and samples with argentiferous glass particles and ammonium). The underlying color model is described in EN ISO 11664-4.

(40) The model of the CIELAB color space has three axes in order to represent the color differences mathematically. The brightness axis L with a range between L=0 for black and L=100 for white, arranged in the model vertically to the color axes, running through the zero point. The a axis (da value) describes the green and red content of a color, where negative values are green and positive values red. The b axis (db value) describes the blue and yellow content of a color, where negative values are blue and positive values yellow.

(41) The value dE mathematically defines the total color difference between two samples with the formula:
dE=√{square root over (dL.sup.2+da.sup.2+db.sup.2)}

(42) Tables 5 and 6 include the sample V.0, which is the comparison sample each for the plaster without antimicrobial glass powder.

(43) For comparison purposes, this sample was also exposed to the various storage methods and compared afterwards with the samples containing silver-doped glass powder stored in the same way.

(44) The samples in Table 5, V.1 to V.3, are plasters produced without ammonium nitrate, which are equipped with the silver-doped glass particles (comparison).

(45) The samples 1.1 to 1.3 in Table 6 are plasters produced with ammonium nitrate, which are equipped with the silver-doped glass particles. In each case, samples of the plaster were mixed with 1.0, 2.0 and 4.0 wt % of the argentiferous glass particles and then applied to plastic plates.

(46) TABLE-US-00005 TABLE 5 Color differences of plaster with silver-doped glass powder without ammonium nitrate (comparison) Content of silver-doped glass powder without ammonium Color difference to the sample V.0 Name nitrate dE dL da db Examination After drying condition Sample V.0 without Sample V.1 1% 2.59 −2.51 0.52 −0.34  Sample V.2 2% 4.51 −4.43 0.73 −0.46  Sample V.3 4% 6.93 −6.83 1.13 −0.26  Examination 5 weeks in the lab condition Sample V.0 without 0.14  0.13 −0.03  Sample V.1 1% 0.11 −0.10 0.04 Sample V.2 2% 0.24 −0.13 0.19 Sample V.3 4% 0.85 −0.43 0.71 Examination 10 weeks in weather at 90° angle condition Sample V.0 without 0.46 −0.07 −0.45  Sample V.1 1% 2.31 −1.75 1.48 Sample V.2 2% 4.05 −2.54 3.12 Sample V.3 4% 5.18 −3.34 3.90 Examination 10 days QUV 340 mm condition Sample V.0 ohne 0.20  0.19 −0.07  Sample V.1 1% 5.54 −2.25 5.05 Sample V.2 2% 8.31 −3.54 7.44 Sample V.3 4% 9.38 −4.64 8.07

(47) TABLE-US-00006 TABLE 6 Color differences of plaster with silver-doped glass powder with ammonium nitrate (patent claim) Content of silver-doped glass powder with ammonium Color difference to V-0 Name nitrate dE dL da db Examination After drying condition Sample V.0 without Sample 1.1 1% 0.83 −0.75 0.15 0.33 Sample 1.2 2% 1.13 −1.06 0.22 0.35 Sample 1.3 4% 2.37 −2.22 0.47 0.72 Examination 5 weeks in the lab condition Sample V.0 without 0.05  0.01 0.05 Sample 1.1 1% 0.08  0.06 0.03 Sample 1.2 2% 0.20 −0.17 0.06 Sample 1.3 4% 0.38 −0.37 −0.07  Examination 10 weeks in weather at 90° angle condition Sample V.0 without 0.42 −0.17 −0.38  Sample 1.1 1% 0.23 −0.17 0.16 Sample 1.2 2% 1.23 −0.32 1.18 Sample 1.3 4% 2.51 −0.34 2.48 Examination 10 days QUV 340 mm condition Sample V.0 without 0.31 −0.28 0.13 Sample 1.1 1% 0.33 −0.25 0.18 Sample 1.2 2% 1.24 −0.22 1.21 Sample 1.3 4% 2.20 −0.82 2.04

(48) TABLE-US-00007 TABLE 7 Assessment scale for color differences Extent of color difference Evaluation 0 No noticeable difference 1 Very small, just noticeable difference 2 Small, but distinctly noticeable difference 3 Moderate difference 4 Considerable difference 5 Very large difference

(49) The plaster samples 1.1 to 1.3 with the glass particles produced by using silver nitrate and ammonium nitrate show significantly lower color differences than the samples V1 to V3 with the glass particles produced using silver nitrate.

(50) If you consider the fact that the human eye is unable to notice color differences lower than a difference value of 1 (cf. Table 7), no sample of sample 1.1 presents a visible color difference. The values are sometimes even under the reference values of the sample without argentiferous glass particles.

(51) The quantity used, namely 1.0 wt % of the color-stable, antimicrobial, porous glass particles of this sample will suffice for most applications, corresponding to a silver ion content in the plaster of around 300 ppm.

(52) With the samples with 2.0 and 4.0 wt % of the argentiferous glass powder, there are large differences between the comparison samples V2 and V3, on the one hand, and the samples 1.2 and 1.3 on the other hand. The discoloration of the plaster by silver ions is increased by 100% to 400% if you do not use any ammonium nitrate.

(53) The sample of the color-stable, antimicrobial, porous glass particles produced in the example was subjected to a long-term release of silver ions, by producing and analysing multiple eluates.

(54) The first eluate was produced from 20 g color-stable, antimicrobial, porous glass particles suspended in 180 g of distilled water. The glass particles were filtered off, and dried in the recirculation unit at 105° C. for 2 hours. The filtered matter was centrifuged before the analysis in order to separate any floating matter.

(55) The filtrate was measured concerning both ph value and conductivity, using a pH laboratory kit including a conductivity electrode (Hach Lange GmbH).

(56) The silver ion content of the filtrate was determined using the photometer DR 2800 (Hersteller Hach Lange GmbH) and the cuvette test LCK 354. The dried glass particles were again eluated in distilled water in the mass ratio 1:9, after which the glass particles were filtered off and dried. A number of 5 eluates in total were produced according to this pattern, and analysed.

(57) TABLE-US-00008 TABLE 8 pH value and conductivity of the multiple eluates of color-stable, antimicrobial, porous glass particles according to the claims of the invention Quantity used Color-stable, antimicrobial, porous glass Distilled Eluate particles water Conductivity Ag.sup.+ No. in g in g pH in mS/cm in mg/l 1 20.00 180.00 7.9 9.9 0.48 2 19.93 179.37 8.0 1.0 0.39 3 19.68 177.12 8.1 0.15 0.26 4 19.08 171.72 7.8 0.07 0.12 5 17.04 153.36 7.6 0.12 0.08

(58) The release of silver ions from the color-stable, antimicrobial, porous glass particles is even sufficiently high after 5 eluates to achieve an antimicrobial effect. 0.235 grams of silver were in total liberated with the 5 eluates made of the color-stable, antimicrobial, porous glass particles. If you consider the quantity of used silver of 0.635 grams, the calculation shows that only 37% of the silver was liberated under these extreme test conditions, which means that the antimicrobial effect will continue for a longer period.