Patent Application
20210015103
The present disclosure relates to a method for producing metal particles exhibiting biocidal properties and using these particles as antimicrobial additives to produce articles or films with a coating having antimicrobial properties, and articles produced by the method.
United States Patent Publication No. 2015/0099095A1 discloses thermally sprayed alloys of for example copper which exhibit highly effective antimicrobial properties when the alloys are thermally sprayed to form a coat onto surfaces. However a problem with adapting such antimicrobial coats to many of the touch surfaces within a health care environment is the number of substrates and surfaces that need to be coated. Much work has gone into adding various antimicrobial ion agents to coatings and polymers but this approach has met with limited success as the ion activity is normally short lived. For example, in the case of silver ions being used, the silver ions must be present within a solution or contact with a human body and the antimicrobial activity is unable to last the lifetime of the products intended use. Having a long lasting inexpensive antimicrobial that could be added to everything from paints to plastics to hard and soft surfaces would be greatly advantageous in many environments.
Disclosed herein is a method of producing biocidal metal particles, comprising:
thermally spraying, into a collection system, a feed material having a metal mixture comprising about 2% to about 96 wt. % Cu, about 2 to about 96 wt. % Zn, and about 1 to about 40 wt. % Ni, under conditions to give particles with a size in a range from about 1 to about 50 microns; and collecting the sprayed metal particles, and wherein said collected sprayed metal particles are characterized in that they have an amorphous solid structure and exhibit biocidal properties.
In an embodiment, the feed material has a metal mixture comprising about 62.5 to about 66 wt. % Cu, about 16 to about 18 wt. % Zn, and about 17 to about 19 wt. % Ni.
In an embodiment, the feed material has a metal mixture comprising about 65 wt. % Cu, 17 wt. % Zn, and 18 wt. % Ni.
The feed material may include trace amounts of Iron (Fe) and Manganese (Mn) of up to about 0.5% of each.
The produced metal particles are characterized by having a composition as measured by EDX to be about 25.49 wt. % Cu, about 67.86 wt. % Zn, and about 6.66 wt. % Ni.
The produced metal particles are characterized by having a composition, as measured by elemental analysis, of about 54.7 wt. % Cu, about 34.1 wt. % Zn, and about 11.2 wt. % Ni, wherein during the elemental analysis the particles are dissolved in an acid solution and resulting metal ions are identified and quantified inductively coupled plasma emission spectroscopy (ICP).
In an embodiment the particles are produced under conditions to give particles with a size in a range from about 5 to about 10 microns.
The particles may be produced using twin arc thermal spraying, and wherein the feed material may be in a form of a wire.
In an embodiment, the metal particles exhibiting biocidal properties may be mixed with a polymer precursor to form a mixture, followed by polymerizing the polymer precursor to form a polymer containing the metal particles, and treating the polymer to expose metal particles on at least one surface of the polymer.
The polymer may be a thermoset polymer, and wherein the thermoset polymer may be any one or combination of an epoxy, phenolic resin, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyester thermoset, urea formaldehyde, acrylics, epoxies, silicone, alkyd polymer, urethane polymer and polyvinyl fluoride polymer.
The polymer may be a thermoplastic polymer, and the thermoplastic polymer being any one of polyurethane, polyethylene, polystyrene, polypropylene, nylon, acrylonitrile butadiene styrene, acrylonitrile styrene, ethylene vinyl acetate, methacrylic acid methyl ester, polyamide, polyacetal, polybutylenes terephthalate, polycarbonate, polyphenylene sulfide, liquid crystalpolymer, polyphenylene oxide, polysulfone, polyether sulfone, polyethylene terephthalate, polyether ether ketone, and any composites and combinations thereof.
Treating the polymer to expose the metal particles on at least one surface includes may include any one or combination of mechanically abrading the surface, chemically etching the surface, sand blasting the surface, tumbling the article, vibe bowl and thermal treatment to remove any polymer overcoating the metal particles.
Once the metal particles on at least one surface are exposed, the surface may be polished.
The metal particles may be mixed with a liquid, cream and/or emulsion.
A further understanding of the functional and advantageous aspects of the present disclosure can be realized by reference to the following detailed description and drawings.
Embodiments of the disclosure will now be described, by way of example only, with reference to the drawings, in which:
Without limitation, the majority of the systems described herein are directed to a thermal spray system and collection of metal particles produced by the thermal spray method. A surprising property of these metal particles is that they exhibit significant biocidal properties for killing various bacteria, viruses and the like. As required, embodiments of the present disclosure are disclosed herein. However, the disclosed embodiments are merely exemplary, and it should be understood that the disclosure may be embodied in many various and alternative forms.
The figures are not to scale and some features may be exaggerated or minimized to show details of particular elements while related elements may have been eliminated to prevent obscuring novel aspects. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present disclosure. For purposes of teaching and not limitation, the illustrated embodiments are directed to a method of producing biocidal metal particles, and articles of manufacture produced using these particles.
As used herein, the term “about”, when used in conjunction with ranges of dimensions, velocities, temperatures or other physical properties or characteristics is meant to cover slight variations that may exist in the upper and lower limits of the ranges of dimensions as to not exclude embodiments where on average most of the dimensions are satisfied but where statistically dimensions may exist outside this region. For example, in embodiments of the present disclosure dimensions of components of a thermal spray system are given but it will be understood that these are non-limiting.
As used herein the term “polymer” means any thermoset polymer, any thermoplastic polymer, any plastic and rubber.
In an embodiment, metal droplets are collected via an electric arc wire spray process. A functional schematic of the process is shown in
The particle temperature may be measured optically by two-color pyrometry to determine an optimal spray distance depending on melting point of the sprayed metal, as shown in
It will be appreciated by those skilled in the art that many other methods of thermal spray deposition may be used and it is understood that the present disclosure is not restricted to the use of the twin arc spray process to produce the metal droplets, although it is the most cost effective and robust process and thus is a preferred embodiment. Other types of thermal spray such as flame spray, plasma spray, high-velocity oxygen-fuel spray, kinetic or cold spray, may be used in place of the wire arc spray gun 10 of
For the collection of the metal particles, in-flight particle conditions such as temperature, velocity, size and number of particles are measured for the particular metal being deposited along the centerline of the particulate plume by a sensor at various spray distances. Since particles in-flight are cooled by ambient air, substantially all particles will solidify after travelling a certain distance. Based on these measurements one can determine at what distance from the surface of the substrate or plenum being applied the particle temperature is close to its melting point but are not yet solidified and are still in a molten phase. As a result, a set of spray parameters such as spray distance and torch input power for specific metallic materials can be established. This set of parameters will allow the metal particles to be collected in plenum 18. The parameters are chosen to produce the metal particles with a sizes in a selected size range. The data shown in
Broadly, present method of producing biocidal amorphous metal particles includes thermally spraying, into a collection system, a feed material having a metal mixture comprising about 2% to about 96 wt. % Cu, about 2 to about 96 wt. % Zn, and about 1 to about 40 wt. % Ni. The feed material is thermally sprayed under conditions to give particles with a size in a range from about 1 to about 50 microns. The metal particles are collected and may be subject to a screening or filtering step to remove particles greater than 50 microns. As noted above, using a mixed metal feed material with Copper (Cu), Zinc (Zn) and Nickel (Ni) in the aforementioned ranges provides metal particles characterized in that they exhibit biocidal properties, as will be described by way of example hereinafter.
For the metal mixture feed material disclosed herein the spray distance was from about 270 to 300 mm. The spray distance is defined as a distance from nozzle or tip of the spray gun to the substrate or plenum.
In order to maintain the rapid cooling of the particles cooling can be provided, for example, by air jets directed to the spray area. The air flow rate will depend on several parameters including the distance of the air nozzle from the substrate surface or plenum
Without being limited by any theory, it is believed that there is a direct correlation between the resulting crystallinity of the sprayed metal alloy particles and the degree to which the molten particles cool and in this regard improved biocidal efficacy with the amorphous structure.
Studies by the inventors have shown that particle velocity is also a useful parameter in producing the biocidal metal particles. The inventor's studies of the wire-arc process show that the metal particles acceleration continues to distances 170-200 mm depending on the process parameters, primarily on atomizing gas flow rate and the metal density. At longer spray distances for collection of particles velocities may be adjusted by increasing of atomizing gas flow rate or using spray guns which provide higher particle velocities.
In present studies, biocidal metal particles were collected by means of a non-limiting exemplary dry dust collection plenum system 18 in which the thermally sprayed metal feed material is sprayed into the dry dust collector plenum from a distance of 12″ to 24″ from the nozzle of the twin arc gun to plenum, which then leads through 20 to 50 feet of 12″ duct for rapid cooling of particles in a dry dust collector. The particle-laden gases enter through a side intake of the dust collector's hopper, under vacuum or pressure. The gases are then filtered through cartridges and exit through the venturi into the clean air plenum. The clean air can either be channeled outside or re-circulated depending on the application. The metal particles are then deposited into a 50 gallon drum for processing to separate particles to give the metal particles in the desired micron sizes.
Particles with sizes from about 1 micron to about 50 microns represent a broad range and a preferred range of particle sizes is from about 5 microns to about 10 microns. As will be discussed in the Examples hereinafter, the metal particles themselves exhibit very high efficacy as biocidal agents. In addition, when in incorporated into other materials articles of manufacture can be produced having biocidal properties. The biocidal metal particles produced in accordance with the present disclosure may be incorporated into any material amenable to being produced in a way that can incorporate the metal particles. Such materials include, but are not limited to, polymers, plastics, rubbers, and any liquids, creams and emulsions to mention just a few.
Non-limiting examples of making articles of manufacture include mixing the metal particles exhibiting biocidal properties with a polymer precursor to form a mixture, polymerizing the polymer precursor to form a polymer containing the metal particles, and treating the polymer to expose metal particles on at least one surface of the polymer. Once polymerized at least one surface (or more) are treated to give a polymer product with a surface having metal particles at least partially exposed to provide a biocidal polymer based product.
In an example, in the case of injection molding, the inner surfaces of the mold may be sprayed with a solution containing the amorphous metal particles such that when a polymer material is extruded, the powders come of the inner surface of the mold and are embedded in the surfaces of the molded article whereupon they can be exposed by any one of several methods discussed herein.
The polymer may be any one or combination of acrylics, epoxies, silicone, alkyd polymers, urethane polymers and polyvinyl fluoride polymers.
The polymer may be a thermoplastic polymer, with the thermoplastic polymer being any one of polyurethane, polyethylene, polystyrene, polypropylene, nylon, acrylonitrile butadiene styrene, acrylonitrile styrene, ethylene vinyl acetate, methacrylic acid methyl ester, polyamide, polyacetal, polybutylenes terephthalate, polycarbonate, polyphenylene sulfide, liquid crystalpolymer, polyphenylene oxide, polysulfone, polyether sulfone, polyethylene terephthalate, polyether ether ketone, and any composites and combinations thereof.
The polymer may be a thermoset polymer, with the thermoset polymer being any one of an epoxy, phenolic resins, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyester thermosets, urea formaldehyde and any composites and combinations thereof.
The polymer encapsulating the metal particles may be treated to partially expose the metal particles at one or more surfaces of the object. This treatment may include any one or combination of mechanically abrading the surface, chemically etching the surface, sand blasting the surface, tumbling the article, vibe bowl to give a vibratory finishing, as well as by thermal treatment to remove any polymer overcoating the metal particles. Once the surface(s) have been treated, the article may be polished on the exposed surfaces.
When a rubberized article is produced, the metal particles exhibiting biocidal properties with a liquid rubber precursor to form a mixture are mixed with a liquid rubber precursor which is then cured to form a rubberized article of manufacture, treating at least once surface of the article to partially expose metal particles.
Acrylic coatings are available in air drying or thermosetting compositions, acrylics are relatively high cost materials. Epoxy coatings have excellent resistance to wear and chemicals. They are relatively expensive and are only available in thermosetting or two part (catalyst activated) compositions with relatively short pot lives. They are good for severe indoor applications, but can degrade rapidly and darken in a few months of exterior service.
Silicone coatings provide the best potential for coatings which must operate at elevated temperatures. Ultraviolet absorbing compounds can be added to prevent darkening of the silicone during exterior exposures.
Alkyd coatings are slow drying and baking is required when applying the alkyd coatings.
Urethane coatings may be used but color degradation on exterior exposure has been a problem with urethane coatings.
Polyvinyl fluoride films (Tedlar) may be applied by roll bonding with an adhesive. Tedlar films have been used to protect sheet copper in exterior applications.
A mixed metal feed material was used to produce metal particles for study of the chemical, physical and biocidal of the produced metal particles.
The mixed metal feed material comprised about 65 wt. % Cu, about 17 wt. % Zn, and about 18 wt. % Ni. It will be appreciated that the alloys of the mixed metal feed material may include trace amounts of other materials, for example trace amounts of Iron (Fe) and Manganese (Mn) of about 0.5% each were detected in the starting alloy.
Further studies were conducted to ascertain the crystallinity of the metal particles.
In order to characterize the size distribution and material composition of the metal dust particles and their distributions in polymer composites, we have prepared samples of the particles alone and samples of particle-epoxy composites and analyzed these samples by Scanning Electron Microscope (SEM) and Energy-dispersive X-ray spectroscopy (EDX), Zeiss Leo 1530 at Waterloo Advanced Technology Laboratory (WATLAB).
More particularly, all collected metal particles were cleaned with water and ethanol before use. The pure metal particle samples were prepared by adhering the particles with double-sided conductive tapes on SEM stubs. The particle-epoxy composite samples were prepared by mixing 20 wt. % metal particles in epoxy solution, which is composed of D.E.R 331 Epoxy Resin and D.E.H. 24 Curing Agent at 100:13 weight ratio, depositing a drop of the mixture on SEM stubs, and curing the mixture at 150° C. for 90 minutes. As metal particles tend to be covered by polymers in a metal-polymer composite due to the difference in surface energies, some of the composite samples were roughened by sand paper to remove their surface layers and reveal their bulk cross-sections. All samples were coated with a 10 nm layer of gold by vacuum deposition to enhance conductivity before analyzing with SEM. The images of the samples from SEM were processed with a commercial software, SPIP 6.5, in order to determine the distribution of particle size and other properties.
The size distribution of the thermally sprayed metal particles from the SEMs of the pure metal particle samples is shown in
Error bars are not visible in the plots as the standard deviations are very small. The result indicates that the vast majority (>90%) of the particles are in the range between 5 to 10 pm in diameter. However, in terms of area, these particles only occupy around 25% of the total area, where the most of the remaining areas (˜50%) are covered by particles in the range between 10 to 50 μm. There a few larger granular metal pieces which are likely compacted clumps or agglomerations of the fine powder material.
Concurrently with these SEM measurements, the composition of these pure metal particles was measured by EDX to be 25.49 wt. % Copper (Cu), 67.86 wt. % Zinc (Zn), and 6.66 wt. % Nickel (Ni). This is very different from the composition of the raw metal feed material of the thermo-spraying process (where the composition of the feed is about 65 wt. % Cu, 17 wt. % Zn, and 18 wt. % Ni). As EDX detects the composition of materials with a penetration depth about 2 microns, which is smaller than the typical size of the metal particles, this difference in composition is likely because the surface and the bulk composition of the dust particles are different. In addition, the EDX measurement is looking at local point surfaces and may not be representative of the overall bulk sample. This variation between the surface and the bulk of the dust particle could be a result of the rapid cooling from the thermal spraying process. When the metal particles are measured by elemental analysis, where the particles are dissolved in acid and the resulting ions are identified, and quantified using inductively coupled plasma emission spectroscopy (ICP), the composition of the metal particles was determined to be 54.7% Cu, 34.1% Zn, and 11.2% Ni, which is closer to the raw feed material of 65 wt. % Cu, 17 wt. % Zn, and 18 wt. % Ni than observed from the EDX measurements.
For the composite samples, the surface was completely covered by epoxy, with no dust particles visible in SEM. However, once we removed a surface layer of the sample by roughening, the cross-section of the composite revealed that the metal particles covered approximately 0.396±0.034% of the cross-sectional area.
A variety of example studies, presented below, have been carried out to examine characteristics of products obtained using methods of the disclosure, which can aid in optimizing parameters to obtain a suitable particle size and composition for its intended use.
Twenty millilitres of Luria Broth (LB) media was inoculated with DH5o strain of Escherichia coli (E. coli) and was placed in a 37° C. shaking incubator for 6 hours in a 50 mL Falcon tube. The tube was removed from the incubator and the optical density 600 (OD600) of the culture was measured to be 2.3. A 1g aliquot of the metal dust particles were added to each of two 50 mL Falcon tubes for parallel ‘high’ (3 mL) and a ‘low’ (1 mL) bacteria assay. Luria Broth (LB) media was added to each of the two Falcon tubes containing the metal dust particles (17 mL in the ‘High’ tube and 19 mL in the ‘Low’ tube).
The tubes were capped and inverted to form a colloidal solution of the metal dust particles. An aliquot of the bacteria was added to each tube (3 mL for ‘high’ and 1 mL for ‘low’ for a 20 mL final volume) containing the colloidal mixture of metal dust particles and the tubes were immediately capped and mixed by repeated inversion. Aliquots of 200uL of the re-suspended colloidal mixture were plated onto LB agar plates and at the following times after the addition of bacteria: 0 min. (removed after addition of the bacteria), 15 min., 60 min., 120 min. During the time-course, the tubes were shaken horizontally on a rotary platform shaker at room temperature at 60 rpm. At each time-point the tubes were put vertically in a rack for 3 minutes before the removal of the 200 uL aliquot of material for plating to allow for the colloid to settle slightly from the liquid. After the time-course had been completed, all plated were transferred to a 37° C. incubator overnight. The following day the plates were observed for bacterial growth.
The metal particles appeared to have little if any solubility in aqueous solutions. However rigorous solubility assays were not part of this study. The majority of the material did settle quickly to the bottom of the tube in a 20 mL volume (˜3 minutes) although some material did not settle as the liquid remained translucent. During the experiment, it was decided to allow for the tubes to rest vertically before removal of aliquots for testing in order to decrease the amount of the metal dust colloidal mixture being transferred to the LB agar plates, where the metal dust particles might have growth inhibiting activity that is outside of the scope of the present study. It was decided not to centrifuge the tubes during collection of these aliquots to remove colloid because that process would likely pellet the bacteria leading to artificially low colony numbers.
In conclusion, the metal particles produced in accordance with the present disclosure show remarkable bacteria-growth inhibitory activity on their own and have been observed to exhibit bactericidal activity as well as biocidal activity in general. It is likely however that the observed inhibition of growth is bactericidal as the colloidal structures were allowed to settle from the liquid before transfer to the LB-agar plates, and growth inhibition on the plates would have also been apparent in the 0 minutes time-point.
In other experiments with aluminum alloys, brass, and copper powders by themselves, it was observed over a period of 120 minutes that there was no bacteria-growth inhibitory activity suggesting these metal particles exhibited no efficacy as biocidal agents, whereas the mixed metal Cu, Zn, Ni, powders disclosed herein showed remarkable bactericidal activity showing complete colony forming unit (CFU) reduction.
In conclusion, the present metal particles based on Cu, Zn and Ni show remarkable bacteria-growth inhibitory activity and bactericidal activity whereas none of the above mentioned particles of thermally sprayed aluminum alloys, brass and copper exhibited no effect on bacterial growth.
A mixture of 5 wt % particles with Plascoat PPA 571 ES polymer coating was prepared and applied to a metal surface to form a coating. The antimicrobial activity of this coating was compared to the same polymer coating without the particles (control surface), in the following manner.
An aqueous suspension of live E. coli bacteria was prepared with at a concentration of 1.2×109 colony forming units (cfu) per mL, including 5% fetal bovine serum and 0.01% Triton X-100 to simulate the effects of a soiled surface. To 6.25 cm2 of each polymer-coated surface was applied 20 μL of this suspension, and it was allowed to stand for 30 minutes. Subsequently, the surface was washed with 5 mL of phosphate buffered saline and 100 μL of this washing solution was plated on standard plate count agar and incubated at 35° C. for 48 hours. The number of colony forming units was counted for each sample.
In comparison to the control surface (i.e. polymer coating without particles), the 5% particle laden surface reduced the viable bacterial count by 4.9×105 cfu/cm2 in 30 minutes of exposure time, corresponding to a 0.3 log reduction. This demonstrates that the particle-polymer mixture had a significant intrinsic biocidal activity due to the presence of the amorphous solid particles contained in the mixture.
As used herein, the terms “comprises”, “comprising”, “includes” and “including” are to be construed as being inclusive and open ended, and not exclusive. Specifically, when used in this specification including claims, the terms “comprises”, “comprising”, “includes” and “including” and variations thereof mean the specified features, steps or components are included. These terms are not to be interpreted to exclude the presence of other features, steps or components.
The foregoing description of the preferred embodiments of the disclosure has been presented to illustrate the principles of the disclosure and not to limit the disclosure to the particular embodiment illustrated. It is intended that the scope of the disclosure be defined by all of the embodiments encompassed within the following claims and their equivalents.
| Number | Date | Country | |
|---|---|---|---|
| 62270319 | Dec 2015 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 16064135 | Jun 2018 | US |
| Child | 16797113 | US |
