U.S. patent application number 13/956669 was filed with the patent office on 2014-08-21 for methods of maintaining and using a high concentration of dissolved copper on the surface of a useful article.
This patent application is currently assigned to PMX Industries Inc.. The applicant listed for this patent is PMX Industries Inc.. Invention is credited to Thomas D. Johnson, Richard Pratt, Timothy Suh.
Application Number | 20140230510 13/956669 |
Document ID | / |
Family ID | 38779320 |
Filed Date | 2014-08-21 |
United States Patent
Application |
20140230510 |
Kind Code |
A1 |
Pratt; Richard ; et
al. |
August 21, 2014 |
METHODS OF MAINTAINING AND USING A HIGH CONCENTRATION OF DISSOLVED
COPPER ON THE SURFACE OF A USEFUL ARTICLE
Abstract
A method for maintaining and using a high concentration of
dissolved copper on a surface of a useful article by providing a
copper surface without coatings thereon, which increase the wetting
angle and which isolate the copper surface and which has a surface
roughness between 2 and 50 micro inches Ra, so as to kill microbes
thereon.
Inventors: |
Pratt; Richard; (Mt. Vernon,
IA) ; Johnson; Thomas D.; (Marion, IA) ; Suh;
Timothy; (Cedar Rapids, IA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
PMX Industries Inc. |
Cedar Rapids |
IA |
US |
|
|
Assignee: |
PMX Industries Inc.
Cedar Rapids
IA
|
Family ID: |
38779320 |
Appl. No.: |
13/956669 |
Filed: |
August 1, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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11751507 |
May 21, 2007 |
8522585 |
|
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13956669 |
|
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60747948 |
May 23, 2006 |
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Current U.S.
Class: |
72/39 |
Current CPC
Class: |
C22C 9/04 20130101; A61L
2/238 20130101; A01N 25/08 20130101; C22C 9/00 20130101; C22F 1/08
20130101; A61P 31/02 20180101; B21B 45/00 20130101; A61K 31/30
20130101; Y10T 428/12993 20150115; Y02A 50/30 20180101; A01N 59/20
20130101; Y02A 50/473 20180101; A01N 59/20 20130101; A01N 25/34
20130101; A01N 2300/00 20130101 |
Class at
Publication: |
72/39 |
International
Class: |
B21B 45/00 20060101
B21B045/00 |
Claims
1-11. (canceled)
12. A useful product configured for providing a solution with
continuously replenishing copper dissolved therein, the useful
product comprising: a. a mass of solid copper alloy having a copper
alloy contact surface; wherein the copper alloy contact surface has
a predetermined surface roughness characteristic and an associated
predetermined characteristic for killing microbes; b. said copper
alloy contact surface being free of any barrier coating thereon
which covers said copper alloy contact surface, isolates said
copper alloy contact surface from exposure to atmospheric oxygen
and further provides said copper alloy contact surface with an
increased wetting angle; c. said copper alloy contact surface being
a surface configured to provide a continuous source of copper; d.
said mass of solid copper alloy being deployed such that said
copper alloy contact surface is configured to facilitate exposure
to contact with a human hand or contaminated particles and cause a
reduction in live harmful pathogens disposed on said copper alloy
contact surface; wherein said step of directing placement comprises
the steps of: manufacturing a useful object from said mass of solid
copper alloy and advising users that said useful object has
anti-microbial properties.
13. The method of claim 12 wherein said useful object is a coin
minted by a government and released for distribution.
14. (canceled)
15. A method of killing live microbes by providing anti-microbial
consumer products: providing a useful consumer product that
performs a useful function that has a contact surface thereon,
which is configured to be touched by a portion of a human hand
during operation of the useful consumer product and while
performing the useful function; wherein said useful consumer
product is one of: a door knob; a cooking utensil; door push plate;
wherein said contact surface comprises a copper alloy contact
surface having a roughness characteristic of between 2 and 50 micro
inches Ra; wherein said contact surface is free of any coating
which isolates said contact surface from atmospheric oxygen; and
deploying said consumer product so as to receive live microbes
thereon to reduce over time a quantity of live microbes on the
contact surface, at least based in part upon said copper alloy
contact surface.
16. The method of killing microbes of claim 15 wherein said useful
consumer product is a door knob and wherein said copper alloy
contact surface has a roughness characteristic of between 6 and 14
micro inches Ra.
17. The method of killing microbes of claim 15 wherein said useful
consumer product is a door push plate and wherein said copper alloy
contact surface is free of any coating applied thereto, which tends
to increase a wetting angle of the copper alloy contact
surface.
18. The method of killing microbes of claim 15 wherein said useful
consumer product is a cooking utensil.
19. A method of killing microbes by providing an anti-microbial
building product: providing a useful building product that performs
a useful function that has a contact surface thereon which is
configured to be contacted by living harmful microbes while
performing the useful function; wherein said contact surface
comprises a copper alloy contact surface having a roughness
characteristic of between 2 and 50 micro inches Ra; wherein said
contact surface is free of any coating which isolates said contact
surface from atmospheric oxygen; and deploying said useful building
product so as to come in contact with live microbes and to reduce
over time a quantity of live microbes on the contact surface, at
least based in part upon said copper alloy contact surface.
20. The method of killing microbes by providing anti-microbial
building product of claim 19 wherein said anti-microbial building
product is duct work for a heating and ventilation system and
wherein said copper alloy contact surface has a roughness
characteristic of between 4 and 36 micro inches Ra.
21. A method of reducing transmission of disease comprising the
steps of: providing a copper alloy surface on a door at a location
that is designed to be contacted by a human hand when the door is
being opened; said copper alloy surface having a surface roughness
of 6 to 14 micro inches Ra and being free of any coating thereon,
which tends to increase a wetting angle of the copper alloy
surface; and deploying the door in a hospital.
22. A useful product configured for providing a solution with
continuously replenishing copper dissolved therein, the useful
product comprising: a. a mass of solid copper alloy having a copper
alloy contact surface; wherein the copper alloy contact surface has
a surface roughness characteristic and an associated characteristic
for killing microbes; b. said copper alloy contact surface being
free of any barrier coating thereon which covers said copper alloy
contact surface and isolates said copper alloy contact surface from
exposure to atmospheric oxygen; c. said copper alloy contact
surface being a surface configured to provide a source of copper;
d. said mass of copper alloy being deployed such that said copper
alloy contact surface is configured to facilitate exposure to
contact with a human hand or contaminated particles and cause a
reduction in live harmful pathogens disposed on said copper alloy
contact surface; wherein said step of directing placement comprises
the steps of: manufacturing a useful object from said mass of solid
copper alloy and advising users that said useful object has
anti-microbial properties.
23. A method of reducing transmission of disease comprising the
steps of: providing a copper alloy surface on a useful object at a
location that is designed to be contacted by a human hand when the
useful object is operated; said copper alloy surface having a
surface roughness of 6 to 14 micro inches Ra and being free of any
coating thereon, which tends to increase a wetting angle of the
copper alloy surface; and deploying the useful object in a
hospital.
Description
[0001] The invention claims the benefit of priority of U.S.
Provisional Patent Application No. 60/747,948, "METHODS OF
PRODUCTION AND USE OF ANTI-MICROBIAL COPPER", filed on May 23,
2006.
FIELD OF THE INVENTION
[0002] The invention relates generally to methods for increasing
the concentration of dissolved copper ions and copper containing
molecules in solutions disposed on copper and copper alloy surfaces
and thereby enhancing the antimicrobial properties of such copper
alloy surfaces. Particularly, it relates to methods which can be
practiced on an industrial scale prior to fabrication into
semi-finished and finished goods, as well as treatments which can
be applied after fabrication.
BACKGROUND OF THE INVENTION
[0003] Copper and copper alloys have been used for millennia as
some of mankind's primary technological materials. Their
combination of ease of manufacture, recyclability, resistance to
overall corrosion, and their availability on a variety of
attractive colors and finishes have made them the preferred
material for coinage, as well as a variety of artistic and
architectural applications where these properties are important.
Electrical and thermal conductivity greater than nearly all
competitive materials combined with useful strength, formability,
and relatively low cost have made these materials vital to the
electronics industry.
[0004] Copper is an essential trace mineral, vital to the health
and proper functioning of human metabolism, as well as other life
forms at very low concentrations.
[0005] Copper sheathing of ships' hulls was used by the British
Navy beginning in the 18.sup.th century to prevent attack by teredo
(shipworm) and to prevent attachment of marine weeds and organisms
such as barnacles to wooden-hulled ships. The beneficial effects
were due to slow dissolution of the copper surface in contact with
seawater. Also, copper and copper compounds have been used in
paints for ships' hulls made of a variety of materials for their
effectiveness in preventing fouling of ships' bottoms by marine
organisms. These antifouling properties are tied to the release of
copper ions from the affected surface, resulting in a
microenvironment at the surface which is toxic to such organisms
and preventing attachment of these organisms to the affected
surface. Marine microorganisms may be affected by as little as 1
part per billion copper (1 ppb Cu).
[0006] Recent studies have shown that copper alloy surfaces are
effective at decreasing the viability of microorganisms such as
salmonella, listeria, and E. coli which cause food-borne illnesses.
Such surfaces are also effective at reducing viability of
microorganisms tied to secondary infections in health care
facilities, such as staphylococcus aureus, legionella, and
others.
[0007] Traditionally, copper alloy products are produced with a
bright surface protected from oxidation by a variety of treatments.
Copper and copper alloys will naturally form a thin oxide layer in
contact with the atmosphere, consisting primarily of cuprous oxide
(Cu.sub.2O) at normal temperatures; in environments containing
sulfur, there is an increased proportion of cupric oxide (CuO) and
cupric sulfide (CuS). This layer will grow thicker over time,
eventually obscuring the bright surface and causing the surface to
darken. Dark films of oxides and/or sulfides on the surface are
considered "dirty" and objectionable, unless used deliberately for
specific decorative or architectural purposes. A great deal of
effort and research has gone into methods of preventing such films
from forming and of removing them when they do form. Application of
surface treatments (anti-tarnish films, stain inhibitors, or
polymer coatings) which slow the transport of oxygen to the copper
alloy surface also slows formation of oxide films. These and other
methods are well known to those skilled in the art.
[0008] Since the antimicrobial properties of copper, copper alloys
and copper compounds have been known for some time, there have been
a number of patents issued for materials and processes making use
of these properties. As noted above, copper sheathing has been used
for centuries to prevent biofouling of ship hulls; more recently,
static underwater structures such as oil platforms have been
similarly protected. Galvanic corrosion between the steel of the
platforms and the protective copper sheathing has limited the
usefulness of this method, but Miller (U.S. Pat. No. 4,987,036;
January 1991) discloses a method of creating a substantially
continuous coating by placement of numerous small platelets of
copper adhered to the structure with an electrically insulating
material. Inoue (U.S. Pat. No. 5,338,319; February 1995) discloses
a related method for coating the inside of a resin pipe with a
beryllium-containing copper alloy. Both methods involve contact
with seawater.
[0009] Another patent (Miyafuji U.S. Pat. No. 6,313,064; November
2001) makes use of a Cu--Ti alloy where the titanium (and possibly
other alloying elements) preferentially oxidizes. Although this
does rely on a deliberate surface treatment to produce oxides and
available ions at the metal surface, these oxides and ions include
other and more reactive elements than just copper sulfides and
oxides and copper ions.
[0010] Many patents have been issued for copper-containing biocides
for use on agricultural produce and in water treatment. Copper
salts and compounds provide a strong source of antimicrobially
effective copper ions, but the relatively high solubility of the
compounds results in short periods of effectiveness before the
copper is washed away. Many of the patents focus on methods to
decrease the release of copper into solution and increase the
effective lifetime of the treatment. Examples of this type of
product are given in Cook (U.S. Pat. No. 7,163,709; January 2007),
Back (U.S. Pat. No. 6,638,431; October 2003), Stainer (U.S. Pat.
No. 5,171,350; December 1992), and Denkewicz (U.S. Pat. No.
6,217,780; April 2001). These treatments may be applied to a
variety of surfaces, but they do not make use of a permanent,
inherently antimicrobial copper or copper alloy surface to act as a
long-term source of copper ions.
[0011] Another method used to make metallic mill products (such as
metal sheet or strip in coils) with an antimicrobial surface is to
coat the surface with a solution, paint, or polymer containing an
antimicrobial agent and dry or cure the coating in place. The
antimicrobial agent may be metallic particles, non-metallic
particles carrying antimicrobial metal ions, glass particles
containing such ions, and/or particles of metal salts or similar
compounds. The classic example of these methods is the
"HealthShield" product line from AK Steel (Myers, et al.; U.S. Pat.
No. 6,929,705; August 2005), consisting of a metallic substrate
coated with a resin formulation carrying inorganic zeolites and
oxides which in turn carry metal ions or compounds for
antimicrobial effect. Other similar products (directly using metal
compounds or salts) are disclosed in Lyon (U.S. Pat. No. 6,042,877;
March 2000) and Zlotnik (U.S. Pat. No. 5,066,328; November 1991),
although this list is by no means exhaustive. While these coatings
may be applied to a number of different substrates, either before
or after fabrication into finished articles, the antimicrobial
properties of these items are due to the coating alone and do not
rely on the metallic article itself as a permanent source of
antimicrobial ions.
[0012] Yet another method of forming antimicrobial articles and
surfaces also involves the use of particles of metal powders,
metal-ion containing salts and other compounds, and metal-ion
carrying particles similar to those noted above, but blended
throughout a bulk polymer or similar moldable substance. McDonald
(U.S. Pat. No. 6,797,743; September 2004) discloses such a polymer,
also used as a coating on a substrate item; Kiik (U.S. Pat. No.
6,585,813; July 2003) discloses a related formulation used to fight
algae growth on blended asphalt roofing shingles and other items
used in the building trades. Again, the anti-microbial properties
are due to the copper- or other metal-containing particles, and not
due to the bulk of the material itself. Also, the effectiveness of
these materials is limited by the total concentration of
anti-microbial metal particles and compounds which can be blended
into the matrix, and by transport of these effective ions through
the matrix to the useful surface, where an uncoated metal surface
presents the effective ions directly at the surface with minimal
transport and concentration limited only by the solubility of the
metal in the solution of interest.
[0013] One disadvantage of the traditional method of supplying
copper surfaces free of oxidation and treated to prevent further
oxidation is that a clean, bare, bright copper surface is generally
hydrophobic, minimizing or preventing contact between the surface
and water or aqueous solutions. Treatments normally applied to
prevent further oxidation are generally even more hydrophobic than
the original copper surface, both directly minimizing physical
transport of oxygen to the copper surface and preventing formation
of adsorbed films of water on the surface which can assist
transport of oxygen to the surface and copper ions from the
surface.
[0014] A further disadvantage of such treatments is that clean,
bare, bright copper in the metallic, non-ionized state is nearly
insoluble in water. Oxidation of copper provides copper ions which
can be assimilated into aqueous solutions or into body fluid
residues to provide antimicrobial properties. Without such copper
ions available for transport, an antimicrobially active surface
would need to develop naturally. Not only can these
natural/atmospheric processes be slow to occur, but the reactions
required are variable in reaction time, dependent on the nature of
prior commercial treatment, environmental conditions, and,
therefore, are difficult to predict. One interested in ensuring
that a surface is active at the time it is placed in service would
benefit from the stated invention(s), as they ensure the surface is
predictably active at the time it is placed in service. It is,
therefore, difficult to predict the antimicrobial activity of these
naturally formed surfaces.
[0015] Prior art does not address the effects of manufacturing
methods necessary to create commercially useful articles and how
those stated antimicrobial surfaces could be changed in processing.
The invention is directed to the problem of creating a repeatably
and renewably active surface at the time an article is placed in
service which provides copper ions available for assimilation into
aqueous solutions or body fluid residues for antimicrobial
properties, which can be produced on semi-finished goods or
finished articles during or after manufacture.
SUMMARY OF THE INVENTION
[0016] In one embodiment, the present invention creates a specific
surface finish on copper and copper-alloy surfaces by any of a
variety of methods, which may be followed by chemical treatment to
increase concentrations of dissolved copper ions in solutions in
contact with the surfaces and thereby enhance the microbial
properties of the surfaces. The surface finish may be produced by
cold rolling with work rolls of suitable finish; by grinding with
suitable abrasives; by brushing or buffing with or without
abrasives; by impacting the surface with grit or shot of suitable
size and velocity; by controlled chemical etching; and a number of
other different processes. The purpose of the specific surface
finish is to enhance wetting of the copper alloy surface by water,
aqueous solutions, and/or bodily fluids to enhance dissolution of
copper and copper ions into said fluids for antimicrobial
effect.
[0017] In one embodiment, the chemical treatment involves the use
of a degreasing treatment during mill coil processing to remove
oils, greases, waxes, and other surface contaminants which will
interfere with wetting of the surface by aqueous solutions or
bodily fluids. It may also involve further treatment of the
degreased surface with diluted acid, possibly with the addition of
an oxidizing agent, followed by a water rinse. This further
treatment is used to change the oxidation state of the copper or
copper alloy surface to enhance takeup of copper ions from the
surface into solutions in contact with the surface.
[0018] In one embodiment, the chemical treatment of the surface
specifically does not include application of tarnish inhibitors
such as benzotriazole (BTA) or tolytriazole (TTA), or of films of
oils, waxes, or other substances used to inhibit wetting of the
surface by water, aqueous solutions, or bodily fluids or to slow or
prevent transport of oxygen or sulfur to contact with the copper or
copper alloy surface. Such applications inhibit takeup of copper
ions from the treated surface and decrease the antimicrobial
properties of the surface.
[0019] Accordingly, the present invention comprises a useful
article comprising a copper alloy surface configured to
continuously provide a source of copper to be dissolved in high
concentrations into a solution disposed on the copper alloy
surface.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] FIG. 1 shows measured contact angle as a function of process
and alloy. The contact angle is higher for commercial treatments
with anti-tarnishing agents such as BTA, TTA, and oil than it is
for either of the invented processes listed. A commercially treated
surface with an oil film has the highest contact angle and least
wetting by water. A surface treated with acid and an oxidizing
agent such as hydrogen peroxide (Process 2) exhibits a low-contact
angle and good wetting. This pattern holds for all alloy families
listed (copper, red brasses, and yellow brasses).
[0021] FIG. 2 shows the relationship between copper evolution
(dissolution) into aqueous solution and contact angle as a function
of surface treatment process. The copper evolution increases with
decreasing contact angle, showing that wetting between the surface
and the solution (low-contact angles) is important for increased
copper evolution and thus antimicrobial effect.
[0022] FIG. 3 shows copper evolution/content in solution as a
function of process route and surface finish. All invention
processes show increased copper in solution compared to normal
commercial processing with BTA as a tarnish inhibitor. For surface
finish "A" (the preferred embodiment), certain process routes show
dramatic increases in copper evolution into solution. The
combination of Process 5 and Finish A showed the highest copper
release of methods tested.
[0023] FIG. 4 shows inactivation rates for E. coli exposed on
surfaces treated by invention Process 2 compared with normal
commercially processed material with BTA as a tarnish inhibitor.
This process shows a 3 log.sub.10 reduction in CFU (99.9% reduction
in active bacteria) after only 30 minutes exposure, with complete
inactivation after 45 minutes. Commercial material shows only a
slight reduction after 90+ minute's exposure.
[0024] FIG. 5 shows results for treatment by invention Process 4.
This process shows a 3 log.sub.10 reduction in CFU after 45 minutes
exposure, with complete inactivation after 60 minutes. Commercial
material shows only a slight reduction after 90+ minute's
exposure.
[0025] FIG. 6 shows results for treatment by invention Process
5.
[0026] This process shows a slightly lower (2 log.sub.10) reduction
in CFU after 45 minutes exposure, with complete inactivation after
the same 60 minutes. Commercial material shows only a slight
reduction after 90+ minute's exposure.
[0027] FIG. 7 compares commercially processed material with BTA and
rolled material with a residual oil film and no further processing.
Both "commercial conditions" exhibit substantially low rates of
inactivation of the bacteria through the tested times when compared
to the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0028] The invention can better be understood by reference to the
following detailed description wherein numerous exemplary processes
are described. Numerous abbreviations are used throughout. To aid
in the understanding, some of the abbreviations are described and
listed in Table 1 below. These definitions relate to numerous
matters, including but not limited to detailed definitions of
materials, material characteristics, tests procedures, innovative
manufacturing and surface treatment processes and other processes
of the present invention.
TABLE-US-00001 TABLE 1 Process Conditions/Definitions Finish A =
6-14 Ra rolled, typically 10 Ra Finish B = 2-5 Ra rolled, typically
4 Ra Finish C = 18-40 Ra rolled, typically 28 Ra MILL OIL =
As-rolled; remnants of rolling lubricant. NOT degreased; starting
point for other conditions. DG = Degrease using commercial solution
DRY = Forced air dry PKL = 10-20% H.sub.2SO.sub.4 + 1-3%
H.sub.2O.sub.2 RT = Age 72 hours @ 25.degree. C. in air FURN1 =
Furnace treat 2 hours @ 200.degree. C. in air FURN2 = Furnace treat
5 minutes @400.degree. C. in air Process 1 DG + DRY Process 2 DG +
PKL + DRY Process 3 DG + DRY + RT Process 4 DG + DRY + FURN1
Process 5 DG + PKL + DRY + FURN2
[0029] 1) Contact Angle Studies--Surface Wetting by Aqueous
Solution
[0030] One measure of the effectiveness of the treatments according
to the present invention is to determine the contact angle between
the treated surface and the top surface of a water drop sitting on
the surface ("sessile drop"). In this detailed description, the
contact angle is defined as the angle of incidence between the
solid surface and the liquid, both in the presence of air.
Physically, this corresponds to the angle between the solid surface
itself and a plane tangent to the droplet surface at the point of
contact between solid, liquid, and air. This contact angle is
related to surface interface energies and the chemical bonding of
the surfaces involved, as seen by wettability of the surface by
various fluids and adhesion between surfaces. These surface
energies (and contact angles) are in turn related to such
controllable factors as surface roughness (Ra); the chemistry of
the base surface itself; the presence or absence of surface films
or layers of oxides, sulfides, etc. (and their type); and the
thickness of such surface films.
[0031] In this invention, the solid surface in question is a
permanent metallic surface of copper alloy, either as part of a
bulk metal object or as a thinner layer (but still permanent)
deposited on a substrate. "Copper alloy" is used herein to refer to
any copper containing alloy including just copper itself. The
contact angle measurements discussed herein were performed with a
single standard fluid, lab-quality filtered deionized/reverse
osmosis water (DI/RO water) which had been boiled to minimize and
stabilize the dissolved gas content of the liquid. Measure-ments
were made on a variety of metallic surfaces treated according to
the invention processes, using the sessile drop method. The actual
measurements of contact angle were made using a real-time capture
camera/microscope setup. Drop Shape Analysis system). Measurements
were taken every second for one minute after dosing the surface
with 0.003 ml of the "standard water" noted above. The final
contact angle after 60 seconds of contact was selected as the
standard for comparison in this study; this helped minimize
variability in measurements due to vibration of the test setup,
lighting conditions, and air currents.
[0032] Results of contact angle measurements are shown in FIG. 1.
Commercially processed material with an oil film remaining on the
surface has the highest contact angle and thus poorest wetting by
the water used for the test. This is expected, since it is a common
observation that "oil and water do not mix". Commercial surfaces
treated with hydrophobic tarnish inhibitors tolytriazole (TTA) and
benzotriazole (BTA) also exhibit high contact angles and poor
wetting, meaning that water (and aqueous solutions such as bodily
fluids and many cleaners) will not contact the surface so treated.
These results show a similar pattern for different copper alloys,
although the actual data varies; results for copper, red brass and
yellow brass are given in FIG. 1. Surfaces treated by the first
process of the invention, hereafter "Process 1", show a
consistently lower contact angle than standard commercial processes
for each alloy tested, and surfaces treated by the second invention
process, hereafter "Process 2", show contact angles dramatically
lower yet.
[0033] 2) Copper Evolution Testing on Treated Surfaces Using
Simulated Body Fluids [Immersion in Artificial Sweat]
[0034] As a further measure of the effectiveness of copper alloy
surfaces treated according to the invention, tests were performed
to determine rates of copper evolution from the metallic surface in
simulated bodily fluids. Since one of the primary uses of such
treated surfaces is in prevention of cross-contamination between
infected and un-infected hospital personnel, touch surfaces such as
push plates and door handles contacted by the skin of the hands
(and thus by fluids such as sweat) are of particular interest. A
search of the published literature shows a great deal of interest
in metal evolution in human sweat, in large part due to incidents
of contact dermatitis. As such, there are a number of formulations
of "artificial sweat", although there are few in published standard
test methods and these appear to be primarily directed at testing
for nickel (Table 2). Common to nearly all of the formulations
investigated is the presence of salts, lactic acid, and some
nitrogen-containing substance simulating the amino acid residues
found in actual sweat. The proportions vary widely, although most
are similar to commonly used blood plasma extenders, and many
formulations include other substances (such as sulfides, ammonia,
or ammonia salts) which would be expected to react strongly with
copper surfaces.
TABLE-US-00002 TABLE 2 Artificial Sweat Formulations ISO EN JIS
RL-1 Component 3160-2 1811 Unknown1 Denmark Unknown2 L0848D Japan2
(PMX) NaCl 20 g/l 0.50% 7.5 g/l 4.5 g/l 0.30% 19.9 g/l 17.0 g/l 6.0
g/l KCl 1.2 g/l 0.3 g/l 0.3 g/l Urea 0.10% 1.0 g/l 0.2 g/l 0.20%
1.7 g/l 1.0 g/l 2.0 g/l C.sub.3H.sub.6O.sub.3 15 g/l 0.10% 1.0 ml/l
0.20% 1.7 g/l 4.0 g/l Lactic Acid NH.sub.4Cl 17.5 g/l.sup. 0.4 g/l
0.2 g/l Acetic Acid 5 g/l Na.sub.2SO.sub.4 0.3 g/l 0.10% Na2S 0.8
g/l CH.sub.3OH 1500 ml.sup. Methanol NaC.sub.3H.sub.5O.sub.3 3.1
g/l Sodium lactate pH 4.7 6.6 4.57 not 4.5 not not not specified
specified specified specified adjusted by NaOH NH4OH not not not
not not not specified specified specified specified specified
specified
[0035] One artificial sweat formulation selected for this testing
is found in JIS L0848D, which includes both NH.sub.4Cl (ammonium
chloride) and Na.sub.2S (sodium sulfide). Both of these would be
expected to significantly corrode copper surfaces, as well as being
somewhat toxic to micro-organisms in their own right. Subsequent
testing with this formulation showed unexpected corrosion and
formation of insoluble films of CuS (copper sulfide). This
corrosion product would be difficult to analyze for by the selected
technique, as well as being in a non-bioavailable form and thus
ineffective from an antimicrobial standpoint, so testing with this
formulation was discontinued. The other composition used is a
compromise between other less aggressive formulations found in the
literature, and is based on readily available medical supplies.
This formula (referred to as "RL-1") is made by taking Lactated
Ringer's solution (a common blood plasma extender used in cases of
severe dehydration or blood loss) and adding urea in quantities
adequate to simulate the amino acid residues and protein breakdown
products normally found in actual sweat. The final composition is
also given in Table 2.
[0036] Copper samples were exposed to artificial sweat by two
methods (immersion and sessile drop). Immersion testing consisted
of placing a treated metal coupon into a large test tube with a
known quantity of the selected sweat formulation (generally 15 ml,
sufficient to completely cover the sample). The tube was agitated
for the desired exposure time, after which it was removed from the
tube and rinsed down into the tube with a known quantity of
lab-quality filtered deionized/reverse osmosis water (DI/RO water).
The total amount of artificial sweat used was noted for calculation
of dilution factors to determine actual concentration of copper in
the original exposure. The sessile drop method ("drop" testing)
consisted of pipetting a small quantity of the test solution onto
the top surface of a treated coupon held horizontally, exposing for
the desired time, then dumping the droplet into a test tube and
rinsing the coupon into the tube with a known quantity of DI/RO
water. The quantity of solution which could be used for the initial
droplet exposure was limited by the surface tension of the solution
on the treated coupon. This method (while similar to the subsequent
biological test exposure procedure) had less copper surface area
exposed to the solution, required greater dilutions to provide
sufficient volume for ICP testing, did not permit agitation of the
solution on the surface, and resulted in greater variability of the
test results than the immersion test method. Copper evolution
results presented here are all by the immersion technique.
[0037] The exposed and diluted solutions were analyzed for copper
content by inductively coupled plasma spectroscopy (ICP) on an IRIS
Intrepid II XSP Dual View spectroscope from Thermo Electron
Corporation. The copper detection limit for this machine was 1.3
parts per billion (PPB). This is of the same order as the minimum
toxicity limit for copper in anti-fouling applications in seawater
(1 PPB), so the presence of any detectable copper in solution would
be expected to indicate some antimicrobial effect, with greater
effects at higher Cu concentrations. Dilution levels were used to
re-normalize the analyzed concentrations back to the values
appropriate during the actual exposures. Analysis was also
performed for other elements (Al, Zn, Ni, and Ag) as a check on
consistency of testing by ICP.
[0038] FIG. 2 shows a comparison between contact angle measurements
for various process treatments and the copper evolution into
solution from coupons treated by the same processes. For normal
commercial processes, there is a generally low rate of copper
evolution, and there are indications that what copper does show up
is tightly bound and not available for microorganisms. For surfaces
treated by the processes of the invention, there is a strong
correlation between contact angle and copper evolution; as the
contact angle decreases (indicating better wetting of the surface),
the copper evolution increases dramatically.
[0039] Results of copper evolution into solution from treated
coupons immersed in artificial sweat RL-1 for various processing
routes and surface finishes are given in FIG. 3. Copper contents in
solution for all processes associated with this invention are
higher than the results obtained from standard commercial
processing of strip with a benzotriazole (BTA) tarnish inhibitor
coating. For surface finishes B and C, results follow a similar
pattern for all processes tested (2-6 times increase in Cu content
over the standard commercial process). For surface finish A (the
preferred embodiment), results are similar to other surface
finishes for some invention process routes, but other preferred
process routes (Process 2 and Process 5) show dramatic
improvements, from 15 times to 25+ times increases in copper
content in solution.
[0040] 3) Microbiological Testing--Inactivation of Bacteria Exposed
on Treated Copper Alloy Surfaces
[0041] A further confirmation of the antimicrobial effectiveness of
the processes of the invention is actual testing with biological
agents to show the rates at which such agents are inactivated by
contact with treated surfaces. The test method used is a
modification of an ASTM-approved method for the evaluation of the
antimicrobial effectiveness of sanitizers on inanimate, nonporous,
non-food-contact surfaces. The method used consisted of: [0042] 1)
Preparing a standard culture of the micro-organisms to be tested;
[0043] 2) Securing samples of the desired materials, and/or
treating the samples according to the desired test conditions (the
processes of the invention and standard materials for comparison);
[0044] 3) Exposing the treated samples to a known quantity of the
cultured organisms for the desired test time; [0045] 4) Placing the
exposed coupon in a quantity of an appropriate neutralizing
solution (which will neither encourage nor discourage further
growth of the organisms and will neutralize further effect of the
tested surface) and ultrasonically treating the coupon to suspend
any surviving organisms into the neutralizing solution; [0046] 5)
Removing the test coupon from the neutralizing solution to further
ensure stopping of the antimicrobial effects of the copper alloy
surface; [0047] 6) Diluting the neutralizer solution (with
surviving micro-organisms) to an appropriate level to give
readily-countable results after exposure, and exposing a known
quantity of the diluted solutions on Petri dishes coated with a
suitable growth medium for the organisms selected; [0048] 7)
Incubating the exposed plates (prepared Petri dishes) to encourage
growth of countable colonies, followed by counting the colonies on
individual plates; [0049] 8) And calculating (based on the known
quantities of solutions transferred and dilution levels) the number
of colony-forming units (CFU's) in the original solution used to
remove the surviving organisms from the exposed surface; [0050] 9)
To provide baseline data for comparison, a matching quantity of the
original standard culture is treated by identical techniques
(except for exposure to the copper alloy surface), plated,
incubated and counted by the same methods.
[0051] Duplicate coupons of alloy C11000 with surface finish A
(.about.10 Ra) were tested for each test condition, and all
dilutions were also plated in duplicate to minimize the effects of
variations in biological laboratory preparation techniques. All
exposures in this study were performed using Escherichia coli (ATCC
11229) obtained from the American Type Culture Collection (ATCC),
Manassas, Va. Similar results are expected using other organisms of
interest, such as Staphylococcus aureus and Salmonella enterica,
which have been implicated in outbreaks of hospital-acquired
(nosocomial) infections and food poisoning. Stock cultures were
incubated for at least 48 hours before use, to ensure vigorous
growth of the organisms. Twenty micro-liters of stock culture were
used for inoculation of the treated coupons, and the survivors were
suspended in 20 ml of Butterfield's buffer solution (0.6 mM
KH.sub.2PO.sub.4 monopotassium phosphate in DI/RO water) as a
neutralizing agent. The same buffer was also used for subsequent
dilutions, and final growth plates were inoculated with 20 ml of
the diluted suspensions. The growth medium for the stock cultures
of E. coli was Difco.TM. Nutrient Broth (beef extract and peptone)
and the medium for the Petri dishes (plate medium) was Difco.TM.
Nutrient Agar, both from Becton, Dickinson and Company, Sparks, Md.
Sterilization (where appropriate) was by means of steam autoclave
(preferred), dry heat in an oven at 200-400.degree. C. (where
required for certain test conditions), or by immersion of
instruments in 99%+ isopropyl alcohol. Plate counts were performed
manually by visual examination of the exposed plates after 48 hours
incubation. Plates exhibiting 20-300 colonies (at a particular
dilution) were used for counting where possible; lower count plates
were used at low dilutions where necessary.
[0052] For the purposes of this study, the absolute numbers of
bacteria (CFU's) remaining on the coupons after exposure are not as
important as the rate of reduction (percentage or log.sub.10
decrease) from the original baseline number. EPA efficacy data
requirements state that a 99.9% reduction in numbers of organisms
(3 log.sub.10 reduction in CFU) be obtained as compared to the
baseline to be considered effective, so this was the trigger level
sought in the study. The exposure time required for a 3 log.sub.10
reduction in CFU was determined and compared to similar data from
other studies of the antimicrobial effectiveness of copper alloys
not treated by the methods of this invention.
[0053] Results of microbiological exposure testing are presented in
FIG. 4 through FIG. 7. In all cases, results of exposures using one
of the processes of the invention are compared against exposures of
samples treaded using normal commercial processing and coated with
BTA as a tarnish inhibitor film, a normal condition for copper
alloy mill products. FIG. 4 shows the results of treatment by
invention Process 2 (DG+PKL). Surfaces treated by this process show
a 3 log.sub.10 reduction in CFU (99.9% reduction in active
bacteria) after only 30 minutes exposure, with complete
inactivation after 45 minutes. Commercially processed material with
a BTA coating shows only a 2 log.sub.10 reduction in CFU after 90
minutes exposure (the longest used in this study). In a 2005 study,
Michels et al. shows complete inactivation of a different strain of
E. coli after 90 minutes, although surface finish and presence of
any anti-tarnish films is not reported.
[0054] FIG. 5 shows results of biological exposures using invention
Process 4 (DG+PKL+FURN1). Surfaces treated by this process show a 3
log.sub.10 reduction in CFU at slightly more than 45 minutes, with
complete inactivation after 60 minutes exposure.
[0055] FIG. 6 shows results of biological exposures using invention
Process 5 (DG+PKL+FURN2). Surfaces treated by this process show a
lower reduction in CFU at 45 minutes (only 2 log.sub.10 reduction),
but a sharp transition and complete inactivation after the same 60
minutes exposure. All three of the preferred processes tested show
a significantly faster reduction in active CFU's (40-60% less time
to 3 log.sub.10 reduction and 30-50% less time to complete
inactivation) compared to previously published data.
[0056] FIG. 7 shows a comparison between the standard final
commercial processing (including BTA as a tarnish inhibitor) and
material rolled, but not cleaned or coated, with a residual film of
rolling mill lubricant. These two conditions show similar behavior,
with low rates of inactivation of the exposed bacteria (only 1-1.5
log.sub.10 reduction in CFU after 60-90 minutes). Contact angle
studies showed both of these conditions had poor wetting and high
contact angles, and the mill oil samples had the highest contact
angle studied.
[0057] One embodiment of the invention shall be further described
by reference to the following example:
[0058] Copper alloy strip is processed to the desired thickness,
annealed to soften and cleaned by normal processes to remove oxides
from the strip prior to final rolling. Work rolls with surfaces
intended to give the desired surface finish are loaded into the
rolling mill stand; the strip in coil form is loaded into the
rolling mill and rolled to the final thickness in one or more
passes. The surface finish required on the work rolls to result in
the desired surface finish will depend on the alloy, incoming
hardness, incoming surface finish, reduction pass schedule, and
other factors known to those skilled in the art. The desired
surface finish of the rolled strip should be between 2 and 50 micro
inches Ra; preferably this finish should be between 4 and 36 micro
inches Ra; and most preferably between 6 and 14 micro inches Ra.
Following rolling, the strip in coil form is loaded onto a
semi-continuous cleaning line and the residual rolling lubricants
removed using a commercial degreasing solution, rinsed with water
(without application of a hydrophobic tarnish inhibitor), and dried
with hot air. The dried strip discharging from the cleaning line is
formed back into a coil for ease of transport. Slitting to final
width and packaging for shipment should be performed with minimal
delays to prevent excess atmospheric oxidation of the uncoated
strip which may be visually objectionable to the customer. Normal
tarnishing and slight oxidation of the strip surface is expected as
part of the process and may be beneficial to antimicrobial
properties of the strip. Cleaning may be performed either with or
without brushing or buffing, as needed to further refine the
surface finish.
[0059] A further embodiment of the invention shall be described by
reference to the following example:
[0060] Copper alloy strip is processed to the desired
ready-to-finish thickness, annealed to soften and cleaned by normal
processes to remove oxides from the strip prior to final rolling.
Work rolls with surfaces intended to give the desired surface
finish are loaded into the rolling mill stand; the strip in coil
form is loaded into the rolling mill and rolled to the final
thickness in one or more passes. The surface finish required on the
work rolls to result in the desired surface finish will depend on
the alloy, incoming hardness, incoming surface finish, reduction
pass schedule, and other factors known to those skilled in the art.
The desired surface finish of the rolled strip should be between 2
and 50 micro inches Ra; preferably this finish should be between 4
and 36 micro inches Ra; and most preferably between 6 and 14 micro
inches Ra. Following rolling, the strip in coil form is loaded onto
a semi-continuous cleaning line and the residual rolling lubricants
removed using a commercial degreasing solution, rinsed with water,
treated with a solution of acid appropriate to reduce or dissolve
metal oxides such as nitric, sulfuric, phosphoric, hydrochloric or
similar. Many commercial formulations rely on concentrations of
sulfuric acid, typically <30% (to which may be added an
oxidizing agent such as hydrogen peroxide), followed by rinsing
with water (without application of a hydrophobic tarnish
inhibitor), and drying with hot air. The sulfuric acid
concentration is preferably <25%, and more preferably 10-20%.
Hydrogen peroxide content (if used) is preferably <15% and more
preferably 0.5-3%. Other acids and oxidizing agents may be used as
well; this example is illustrative only and is not intended to
restrict application of the general principles embodied in this
invention. The dried strip discharging from the cleaning line is
formed back into a coil for ease of transport. Slitting to final
width and packaging for shipment should be performed with minimal
delays to prevent excess atmospheric oxidation of the uncoated
strip which may be visually objectionable to the customer. Normal
tarnishing and slight oxidation of the strip surface is expected as
part of the process and may be beneficial to antimicrobial
properties of the strip. Cleaning may be performed either with or
without brushing or buffing, as needed to further refine the
surface finish. The cleaning may be performed in a single
continuous cleaning line if equipment for both degreasing and acid
treatment is available; otherwise, these operations may be
performed on two separate cleaning lines. If performed on separate
cleaning lines, a hydrophobic tarnish inhibitor may be applied
before drying at the first line to provide surface protection to
the strip before acid treatment, but no such inhibitor is to be
applied following the final treatment step before slitting.)
[0061] A further embodiment of the invention shall be described by
reference to the following example:
[0062] Copper alloy strip is processed by normal commercial methods
to a desired surface finish of the rolled strip between 2 and 50
micro inches Ra; preferably this finish should be between 4 and 36
micro inches Ra; and most preferably between 6 and 14 micro inches
Ra. The strip may be shipped as-is or degreased, or (if desired for
subsequent forming processes) may be annealed to soften and cleaned
to remove oxides formed during the annealing process. Following
cleaning, the strip may be coated with a hydrophobic tarnish
inhibitor to preserve the surface condition and appearance of the
strip which is to be formed into finished parts by normal
commercial processes such as stamping, drawing, bending, coining,
etc. These methods are well known to those skilled in the art. The
strip is then formed into finished parts as desired.
[0063] Following forming and either before or after final assembly,
and prior to placement of the article into service, the article(s)
are cleaned with a commercial degreasing solution to remove
remnants of oils, waxes, and greases used as forming lubricants
and/or rinsed with water (without application of a hydrophobic
tarnish inhibitor), and/or dried with hot air. The articles should
not have been treated with coatings, lacquers, paints or other
polymer finishes prior to said treatment. Subsequent to the
degreasing treatment, they may also be treated with an acid
solution as noted above. Ex: Sulfuric acid<30% as noted above
(to which may be added an oxidizing agent such as hydrogen
peroxide) and/or rinsed with water (without application of a
hydrophobic tarnish inhibitor) and/or dried with hot air.
[0064] The formed parts may also be treated after degreasing to
deliberately change the oxidation state of the copper alloy
surface, increasing the bioavailability of the copper at the
surface to enhance the antimicrobial properties. This may be
accomplished by any of a number of methods, including exposure in
air (or a reactive atmosphere containing any of a number of
constituents such as O.sub.2, H.sub.2, N.sub.2, or compounds of Ag,
P, S, N, C, etc.) at temperatures from 0 C up to 500 C for various
times; by treatment with solutions of sulfides, halogens, salts and
dilute acids; by treatment with water to which oxygen has been
deliberately added; by treatment with solutions of hydrogen
peroxide or similar oxidizing agents; and other methods known to
those skilled in the art. The intent of this treatment is to make
the surface more chemically active, rather than the normal
commercial practices of preventing oxidation of copper alloy
surface.
[0065] It should be noted that the above examples are illustrative
only, and do not restrict the application of the principles behind
this invention. Other specific equipment may be used to achieve the
desired surface roughness or finish; other solutions may be used
for removal of oils, greases, and other surface films; different
acids and concentrations may be used, and oxidizing agents other
than hydrogen peroxide may be used as well. The principles of
creating a specific desired surface roughness or finish, and/or
subjecting the copper alloy surface to a commercial degreasing
treatment to remove hydrophobic surface films, and/or treating the
surface with acids and/or oxidizing agents to enhance the contact
angle between the treated surface and aqueous solutions and
increase the bioavailability of the copper in the treated surface,
and/or subjecting the surface to a suitable atmosphere and
temperature to further enhance the evolution of the copper ions,
and/or specifically excluding the used of hydrophobic protective
and tarnish-inhibiting films on the surface so treated for
antimicrobial effect are the fundamental portions of this
invention.
[0066] The copper and copper alloy surfaces of the present
invention could be used in numerous applications, including but not
limited to:
[0067] Medical instruments
[0068] Appliances
[0069] Lighting devices and controls
[0070] Plumbing fixtures
[0071] Hand tools
[0072] First Aid devices
[0073] Vehicle touch surfaces
[0074] Processing equipment for produce and meat processing
Packaging Agriculture [0075] Grain or food storage [0076]
Water/food dispensing [0077] Ear tags [0078] Dairy and meat
processing
[0079] Fast food and commercial restaurants
[0080] Cell phones and telecom
[0081] Computers (keyboards and peripherals)
[0082] Masks and breathing apparatus
[0083] Mold proofing in building products and construction.
[0084] Throughout this description the terms degreasing and
cleaning are used repeatedly. It should be understood that numerous
alternate ways of cleaning/degreasing the surface are contemplated
including but not limited to:
[0085] 1) Abrasively clean/grit blasting
[0086] 2) Cathodic cleaning/degreasing
[0087] 3) Anodic cleaning/chemical milling
[0088] 4) Electrolytically and electrochemically cleaning
[0089] 5) Application of ultrasonic or other acoustic
activation
[0090] 6) Ion milling for special medical applications
[0091] In one embodiment it may be preferred to do all of the
following:
[0092] Use ultrasonic+a andoic electrolytic clean+ and cathodic
chemical milling.
* * * * *