U.S. patent application number 14/829003 was filed with the patent office on 2015-12-10 for anti-microbial coated devices and methods for making same.
The applicant listed for this patent is POLYPROTEC TECHNOLOGIES. Invention is credited to Derrick G. Arnold, Bradley F. Johnson, Jack F. Johnson, Robert J. Robinson.
Application Number | 20150351445 14/829003 |
Document ID | / |
Family ID | 44476713 |
Filed Date | 2015-12-10 |
United States Patent
Application |
20150351445 |
Kind Code |
A1 |
Arnold; Derrick G. ; et
al. |
December 10, 2015 |
ANTI-MICROBIAL COATED DEVICES AND METHODS FOR MAKING SAME
Abstract
An anti-microbial coated device includes a device sized and
configured for use in a microbe-contaminating environment. The
device includes a substrate having a surface configured to be
exposed in the microbe contaminating environment. A cold-sprayed
anti-microbial coating is deposited on at least a portion of the
surface of the substrate. The anti-microbial coating includes fused
metal particles and having a thickness in a range from 100 nm to 1
mm.
Inventors: |
Arnold; Derrick G.; (Sandy,
UT) ; Johnson; Jack F.; (Sandy, UT) ;
Robinson; Robert J.; (Raleigh, NC) ; Johnson; Bradley
F.; (West Jordan, UT) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
POLYPROTEC TECHNOLOGIES |
South Jordan |
UT |
US |
|
|
Family ID: |
44476713 |
Appl. No.: |
14/829003 |
Filed: |
August 18, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12954243 |
Nov 24, 2010 |
9109292 |
|
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14829003 |
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61308007 |
Feb 25, 2010 |
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Current U.S.
Class: |
426/323 |
Current CPC
Class: |
A23L 3/3589 20130101;
A23L 3/001 20130101; C23C 30/00 20130101; A23L 3/3598 20130101;
A23L 3/3454 20130101; A23V 2002/00 20130101; C23C 24/04 20130101;
A23L 3/358 20130101 |
International
Class: |
A23L 3/00 20060101
A23L003/00 |
Claims
1. A method for minimizing contamination of food products using an
anti-microbial food processing apparatus, comprising: providing a
food processing facility including food processing machinery having
structure that contacts food materials during food processing, the
food processing facility comprising one or more surfaces having a
substrate comprising a polymer, a natural fiber, or concrete, the
substrate having a cold-sprayed anti-microbial coating deposited on
at least a portion of the surface area, the anti-microbial coating
comprising a continuous layer of copper having a thickness in a
range from 100 nm to 5 mm; exposing the anti-microbial coating to a
microbial load, the antimicrobial coating at least partially
killing the microbial load.
2. A method as in claim, wherein the anti-microbial coating
includes brass silver, alloys thereof, or combinations thereof.
3. A method as in claim, wherein anti-microbial coating is allowed
to kill at least 95% of the microbial load.
4. A method as in claim 1, wherein the surface includes a portion
of a floor or a countertop.
5. A method as in claim 1, wherein the floor comprises a polymer
and/or concrete.
6. A method as in claim 1, wherein the surface includes a portion
of a floor or a countertop.
7. A method as in claim 1, wherein the surface is on a food
processing apparatus selected from the group consisting of
blenders, agitators, mixers, liquifier, paddle blenders, ribbon
blenders, screw blenders, mixing bowls, pulpers, juice extractors,
filters, evaporators, pumps, driers, boilers, homogenizers,
refrigerators, peelers, grinder, emulsifier, slicers,
disintigrator, comminution apparatus, washer, molder, chiller,
centrifuge, dicer, shredder, wrapping apparatus, pasturizer,
cutter, conveyor, compactor, chopper, caser, blower, blancher, bin,
lidder, hopper, mill, sheeter, tenderizer, or container.
8. A method as in claim 1, wherein the anti-microbial coating has a
thickness in a range from 500 nm to 5 mm.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application is a continuation of U.S. patent
application Ser. No. 12/954,243, filed Nov. 24, 2010, which claims
the benefit of U.S. Provisional Patent Application Ser. No.
61/308,007 filed Feb. 25, 2010 entitled ANTI-MICROBIAL DEVICES AND
METHODS FOR MAKING SAME, which is hereby incorporated by reference
in its entirety.
BACKGROUND OF THE INVENTION
[0002] 1. The Field of the Invention
[0003] The present invention relates to anti-microbial coated
substrates and methods for making anti-microbial coated substrates
using cold spray and methods of use.
[0004] 2. The Related Technology
[0005] It is well known that microbial contamination can occur by a
person touching the same surface as another person. Devices that
are known to transfer microbes through touch include door handles,
toilet handles, waste container, utensils, water faucet and other
products which come into contact with human beings.
[0006] One approach to reducing the communication of microbes
between people is to coat the surface of such devices with an
antimicrobial coating. The microbes transferred from one person to
the surface are killed or substantially reduce in number by the
anti-microbial agents on the surface of the device. This limits the
undesired transfer of the microbes to other people who may come
into contact with the device.
[0007] Numerous products have been developed with antimicrobial
coatings to prevent transmission of microbes. One common approach
has been to mix an antimicrobial metal with a resin and apply it to
the surface of the device where the device is susceptible to
contamination. However, these coatings tend to have problems with
adhesion to many substrates. Also, these resins tend to encapsulate
the antimicrobial metal and reduce its ability to effectively kill
microbes.
BRIEF SUMMARY
[0008] The present invention relates to devices coated with an
antimicrobial coating and methods for making the antimicrobial
coated devices using cold spraying. The antimicrobial coating is
formed from an antimicrobial metals such as copper or silver. The
antimicrobial metal is provided as a powder and cold sprayed onto
an exposed surface of the device. The high impact involved in cold
spraying causes the antimicrobial metal particles to fuse together
to form the antimicrobial coating. Antimicrobial particles striking
the surface of the device may also be fused to the surface of the
device, thereby creating excellent adhesion between the
antimicrobial coating and the device. In addition, cold spraying
allows for an extremely thin and continuous layer of antimicrobial
metal. The thinness of the antimicrobial coating minimizes changes
in the physical properties of the device while still providing the
desired antimicrobial benefits.
[0009] In a preferred embodiment, the antimicrobial device is a
food processing apparatus that includes a food processing machine
part having structure that contacts food. The anti-microbial
coating may be applied to at least a portion of the surface area of
the structure that contacts the food. The antimicrobial coating
reduces microbial contamination on the food processing equipment,
thereby allowing the equipment to produce healthy cleaner products
and/or to operate for longer periods of time without being shut
down for cleaning.
[0010] These and other objects and features of the present
invention will become more fully apparent from the following
description and appended claims, or may be learned by the practice
of the invention as set forth hereinafter.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] To further clarify the above and other advantages and
features of the present invention, a more particular description of
the invention will be rendered by reference to specific embodiments
thereof which are illustrated in the appended drawings. It is
appreciated that these drawings depict only illustrated embodiments
of the invention and are therefore not to be considered limiting of
its scope. The invention will be described and explained with
additional specificity and detail through the use of the
accompanying drawings in which:
[0012] FIG. 1 illustrates a conveyor system having an
anti-microbial coated conveyor belt;
[0013] FIG. 2 illustrates a cold spray system for coating a device
according to the methods of the present invention; and
[0014] FIG. 3 illustrates a process for applying a cold-spray
coating to an auger according to one embodiment of the
invention.
DETAILED DESCRIPTION
[0015] In one embodiment, a method for manufacturing an
antimicrobial coated device may include providing a device sized
and configured for use in a microbe-contaminating environment and
having a surface configured to be exposed in the microbe
contaminating environment. A cold-spraying apparatus is used to
cold spray an anti-microbial metal powder onto the surface to form
an anti-microbial coating. The coated area includes at least
apportion of the area of the device that benefits from having an
anti-microbial surface, such as those portion of the device that
have exposed surfaces susceptible to contamination.
[0016] The device to be coated is selected according to a need to
maintain a sanitary surface on the device during use. There are
many devices designed and/or configured to be used in direct
contact with people and/or items that need to remain sanitary in
order to minimize communication of microbes. Examples of categories
of devices that can be coated according to the method disclosed
herein include, but are not limited to, food processing equipment,
food services equipment, medical equipment, dental equipment,
safety equipment, boating equipment, and combinations of these.
[0017] Food processing equipment is equipment that is used to
process, prepare, and/or package food materials and products for
human consumption. Examples of food processing equipment includes,
but are not limited to, a conveyor, a blender, an agitator, a
mixer, a liquifier, a paddle blender, a ribbon blender, a screw
blender, a mixing container, a pulper, a juice extractor, a filter,
an evaporator, a pump, a drier, a boiler, a homogenizer, a
refrigerator, a peeler, a grinder, an emulsifier, a slicer, a
disintigrator, a comminution apparatus, a washer, a shape molder, a
chiller, a centrifuge, a dicer, a shredder, a wrapping apparatus, a
pasteurizer, a cutter, a conveyor, a compactor, a chopper, a caser,
a blower, a blancher, a bin, a lidder, a hopper, a mill, a sheeter,
a tenderizer, or a container.
[0018] The foregoing food processing apparatuses (and similar
devices used in processing food materials) include machine parts
having structure that contacts food. The machine parts may be a
blade, a panel, a paddle, a prop, an auger, a bowl, a belt, a drum,
a scraper, a lid, a tube, a roller, a disk, a liner, a duct, or the
like. The structure provided by these machine parts come in contact
with food material as the apparatus moves, manipulates, and/or
supports the food materials during food processing.
[0019] In one embodiment, the machine part may be a conveyor belt,
which provides a surface that supports food material as the food is
conveyed from one location in a food processing facility to another
location. The conveyor belt may have a planar surface or a varied
surface. Typically conveyor belts that have a planar surface may be
used for horizontal conveyance and conveyor belts with a varied
surface can be used in as an elevator conveyor. FIG. 1 illustrates
an example of an elevator type conveyance apparatus 100, which
include a conveyor belt 102 positioned within housing 104. A motor
106 operates a drive mechanism 208 to cause conveyor belt 102 to
advance in the upward direction 110. Belt 102 forms a continuous
loop and rotates in a circular manner according to known methods in
the conveyor belt art.
[0020] Conveyor belt 102 includes a plurality of ridges 112 that
separate a plurality of flat areas 114 where food material can be
loaded. The ridges 112 prevent food material on flat areas 114 from
sliding downward. The conveyor belt 102 is flanked laterally by
housing railing 116. Railing 116 minimizes food material falling
off on the sides of conveyor belt 102. Conveyor Apparatus also
includes a hopper 120 having raised sidewalls or paneling that
define a temporary storage space that is unloaded by rotation of
the conveyor belt 102.
[0021] The parts of conveyor apparatus 100 provide a substrate for
an anti-microbial coating. For example, the antimicrobial cold
spray coating may be on the ridges 112, flat areas 114, inside
surface 122 of railing 122, and/or the inside surface 124 of the
sidewalls of hopper 120. The cold sprayed coating may have a
thickness in a range from 100 nm to 5 mm, or 500 nm to 5000
microns, or 1 micron to 3000 microns, or 5 microns to 1000 microns
and may include copper, brass, silver, an alloy of these, or a
combination of these. In other embodiments, any of the foregoing
ranges of coating thickness may have upper limits less 3 mm, 2 mm,
1 mm, 500 microns, 100 microns, or 50 microns. The surfaces of the
railing 116, conveyor belt 102, and/or hopper 120 are used to move
and transport food material and the food material comes into
contact with these surfaces, thereby providing these surfaces with
a food source of organic material for microbial consumption. In
addition, these surfaces are exposed to microbial loads from
airborne microbes and/or microbes in the food material. The food
materials are maintained sanitary for extended periods of time due
to the anti-microbial coating killing microbes that might otherwise
propagate on the surfaces of the conveyor apparatus.
[0022] Other anti-microbial coated devices, including but not
limited to other food processing equipment, can have machine parts
such as tubes, chambers, panels, exposed surfaces, and flexible or
rigid fixed or moving parts that contact food in a similar manner
as the machine parts described with reference to FIG. 1 and can
have a cold-spray anti-microbial coating to reduce microbial
contamination.
[0023] For example, the machine part may be a drum having interior
walls that move food materials inside the drum as the drum rotates.
The interior surfaces of the drum may include a cold sprayed
anti-microbial coating as described herein. The machine part may be
a scraper having a rigid flat surface that can include a
cold-sprayed anti-microbial coating. The machine part may be a
blade having a rigid flat surface includes a cold-sprayed
anti-microbial coating. The machine part may be a prop used to
agitate or mix a fluid. The prop may have all or a portion of its
exposed surface coated with a cold-sprayed anti-microbial coating.
The machine part may be a paddle that is rotated to perform mixing
or blending. The paddle may have an exposed surface that when
rotated pushes food material. The exposed surface of the paddle may
be coated with a cold-sprayed anti-microbial coating. The machine
part may be an auger having flighting, the surface of which is
coated with a cold-sprayed antimicrobial coating. The machine part
may be a bowl or other container where food materials are held for
mixing and the interior surface of the bowl (i.e., the surface of
the bowl or container the comes into contact with the food) may be
coated with a cold-sprayed anti-microbial coating. The machine part
may be a lid that covers a container, bowl, or other chamber. The
inside surface of the lid may be coated with the cold-sprayed,
anti-microbial coating. The machine part may be a tube or other
conduit and the interior surface (i.e., the surface in contact with
food material traveling in the tube) may be coated with a
cold-sprayed anti-microbial coating. The machine part may be a disk
that rotates to cut, chop, blend, or otherwise manipulate a food
material can have flat exposed surfaces that contact food during
use and the surfaces may be coated with the cold-sprayed
anti-microbial coating. The machine part may be a liner to a
chamber that is removable for cleaning or servicing purposes. The
liner may have a cold sprayed anti-microbial coating on an exposed
surface (i.e., the surface that is exposed to the interior of a
chamber when the liner is installed in the device).
[0024] Those skilled in the art will recognize that the list of
food processing apparatuses, machine parts, and structures above
and/or the other devices disclosed herein and their structures are
not an exhaustive list of devices, machine parts and/or structures
that can include a cold-sprayed anti-microbial coating according to
the invention.
[0025] Those skilled in the art will also recognize that the
devices, machine parts, and/or structures disclosed herein do not
necessarily have the entire exposed surface coated with the
anti-microbial coating. Because there is a cost associated with the
coating, the particular amount of the surface area that is coated
will often be selected to minimize cost while minimizing the
potential threat of contamination. Thus, the anti-microbial coating
may be applied to portions of the devices and/or machines parts in
locations where exposure to contamination is highest, such as
locations where organic particulates are likely to collect or be
constantly present and/or where moisture is present, and/or where
airborne microbes are likely to come into contact with organic
material.
[0026] As mentioned above, the present invention includes
anti-microbial devices other than food processing devices. The
cold-sprayed anti-microbial device can be applied to a part or
structure of food service equipment, medical equipment, dental
equipment, safety equipment, boating equipment, and combinations of
these.
[0027] Food services equipment is equipment that comes into contact
with food and beverage products for human consumption. Examples of
food services equipment includes, but is not limited to, food
processing conveyor belts, refrigerators, ice makers, ice scoops,
food storage structures, soda dispensers, grocery carts, food
storage structures, water bottles, drinking fountains, sinks,
faucets, appliances, egg cartons, countertops, flooring, and the
like. These devices can have surfaces that may be prone to
microbial contamination. Example illustrations of some of these
devices can be found in U.S.Pat. Nos. 7,025,282, 7,552,597,
7,263,856, 7,350,369, 7,393,032, 7,207,576, 7,527,174, 7,188,847,
7,287,487, 7,178,523, 7,594,706, 7,604,001, 7,314,307, 7,238,921,
7,264,189, 7,388,174, and 6,959,496, which are hereby incorporated
by reference for their teaching, illustration, and use of the
structure of food services devices.
[0028] The foregoing devices all have surfaces that can benefit
from an antimicrobial coating according to the invention. The
inside surfaces of refrigerators, including paneling, shelving,
and/or drawers, can have spilled food and/or water condensation
that harbors microbes. The refrigerator may be a commercial
refrigerator located in a business establishment or personal
refrigerators located in a person's home. The paneling or shelving
of food storage structures such as those found in home pantries or
grocery store food displays can be susceptible to microbial growth.
Ice makers tend to have wet surfaces on, around, and/or in the
storage compartment and/or opening of the storage compartment for
ice, which can be contaminated with microbes. The handle portion
and/or scoop of an ice scoops used to retrieve ice can be
susceptible to microbial contamination due to the exposure to
people's hands and moisture from the ice storage. Soda dispensers
can accumulate microbes on the dispenser spouts and/or supporting
trays where soda cups are placed to be filled with soda. Grocery
carts can be exposed to microbes on their handle portions where
people grasp the cart to push it and/or the basket portion where
food products can be temporarily stored during shopping.
[0029] Additional examples of surfaces on food services equipment
that can be coated with an anti-microbial coating according to the
invention include surfaces of water bottles including the water
bottle opening, the cap, the interior surface, and/or the exterior
surface of the bottle. The buttons or levers used to dispense water
from a drinking fountain may be prone to contamination from
touching. In addition the surface of the receptacle of a drinking
fountain provides a wet environment for growing microbes. Similarly
sinks and faucets in commercial establishments and/or homes are
prone to contamination on the surfaces of the handles, spouts,
and/or receptacles where water, human contact, and sources of
organic material are typically present. Kitchen appliances such as
blenders, toasters, food processors, rice cookers, knives, cooking
utensils, and/or serving utensils, may have handles and/or exterior
surfaces that may be prone to microbial contamination. The upper
surface of indoor flooring in homes or commercial establishments
where food is prepared, stored, and/or transported may also be
susceptible to microbial contamination. The surface of egg cartons
used to transport eggs can be contaminated on surfaces configured
to be in contact with the eggs.
[0030] Another category of device that can be coated with an
anti-microbial coating according to the invention includes medical
devices. Medical equipment that can be coated with the
antimicrobial coating includes surgical equipment, diagnostic
equipment (e.g., MRI machines and optical scanners), trays,
hospital countertops, operating tables, hospital flooring,
operating rooms, hospital room beds, toilets, sinks, and/or
showers, wheelchairs, crutches, stethoscopes, and medical supplies
such as tubing and adhesive bandages. Example illustrations of
these devices can be found in U.S. Pat. Nos. 7,541,812, 7,355,617
7,296,652, 7,242,308, 7,600,274, 7,172,421, 7,254,850, 7,318,242,
7,490,619, and 7,334,440, which are hereby incorporated by
reference for their teaching, illustration, and use of the
structure of medical devices.
[0031] Examples of surfaces of the surgical equipment that may be
prone to contamination include the surfaces of the handle portion
and/or surfaces intended to contact the patient, such as a cutting
surface of a scalpel. Examples of surfaces of an MRI machine that
may be susceptible to contamination include the upper surface of
the table upon which the patient lies. Optical scanning equipment
may have surfaces for resting a person's chin and/or surfaces that
come into contact with a person's face. Medical trays have surfaces
that come into contact with bodily fluids and/or hospital food.
Hospital countertops have an upper surface that may be exposed to
bodily fluids or tissues and/or food that may contaminate the
surface thereof. Operating tables may have straps, railing, and/or
other surfaces that may be exposed to contamination. The present
invention also includes coating the surface of hospital flooring
and/or bed structures.
[0032] Yet another category of devices that may include an
antimicrobial coating include dental devices. Examples of dental
devices include curing lights, drilling equipment, endodontic
reciprocating hand pieces, packing devices, toothbrushes, dental
chairs, aspiration devices, sinks, faucets and the like. Examples
of dental devices can be found in U.S. Pat. Nos. 7,144,250 and
5,339,482, which are hereby incorporated by reference for their
teaching, illustration, and use of dental devices.
[0033] Other devices that can be coated include boating equipment.
Boating equipment is constantly being exposed to microbes in the
water being navigated. These microbes often grow on the surfaces of
the boat and can cause fouling. Examples of surfaces on boating
equipment that can be contaminated include, but are not limited to,
the hull of the boat, the boat propeller, the boat carpeting or
other flooring, and/or the boat seat cushions. Examples boating
structures that can be coated are described in U.S. Pat. No.
7,302,906 and US Publication 2008/0166493, which are hereby
incorporated herein by reference for their teaching, illustration,
and use of boating devices. Yet other devices that can be coated
include playground equipment, patio cover, tape or adhesive, toilet
seat, portable toilet, exercise equipment, garbage cans, baby
changing station, sports equipment, shoe insert, safety harness,
safety mat, or a combination thereof.
[0034] Playground equipment can be coated on the surfaces where
people hang our grasp, such as the rungs of a ladder. Patio covers
can be coated on the fabric covering, which has a tendency to
collect water during rain storms and/or exposure to sprinklers and
are in high humidity environments. Tape and other adhesive devices
can be coated on an upper surface story lower surface. Toilet seats
can be coated on the upper surface configured to make contact with
that person. Exercise equipment can be coated with the
antimicrobial coating on the surface of the bench, bars, and/or
handles that allow users to group the exercise equipment. A shoe
insert can be coated on the upper surface that is configured to
make contact with the foot of a person. Baby changing station may
include the antimicrobial coating on the surface of planar
surfaces, railings, and/or the cushioning of the baby changing
station. Safety harnesses may have the antimicrobial coating
applied to the surface of the straps of the harness. Athletic mats
or safety nets may have the antimicrobial coating applied to the
impact surface, particularly surfaces that come into contact with
the feet of the person using the mat. Example illustrations of
these devices can be found in U.S. Pat. Nos. 7,463,885, 7,252,232,
7,523,857, 7,231,673, 7,585,019, 7,316,237, 7,563,205, 7,426,765,
7,426,765, 7,588,114, 7,384,098, 7,367,074, and 6,774,067, which
are hereby incorporated by reference for their teaching,
illustration, and use of devices that are used in microbe
contaminating environments.
[0035] As mentioned above, the methods of the invention include
cold spraying an antimicrobial powder onto at least a portion of
the surface of the device that is to be exposed to the microbe
contaminating environment. The cold spraying process utilizes an
apparatus for accelerating fine solid particles (e.g., having a
size from about 1-50 .mu.m) to supersonic speeds (e.g., in a range
of 300-1,200 m/sec) and directing the particles against the surface
of the device to be coated. When the particles strike the substrate
surface, the kinetic energy of the particles is transformed into
plastic deformation of the particles, and a bond is formed between
the particles and the target surface. This process forms a dense
antimicrobial coating with little or no thermal effect on the
underlying substrate surface. The cold spray processing allows
formation of dense, low-oxide-content deposits of anti-microbial
materials on a variety of substrates, in air and at near-ambient
temperatures.
[0036] The anti-microbial coating is applied to the surface of the
material so as to minimize the thickness of the anti-microbial
coating while maximizing anti-microbial action. The thickness of
the anti-microbial coating may be in a range from 100 nm to 5 mm,
or in a range from 500 nm to 5000 microns, or 1 micron to 3000
microns, or 5 microns to 1000 microns.
[0037] The anti-microbial coating can be applied in specific areas
as desired. Also, the anti-microbial coating can be applied in
cracks and crevices and other locations where microbial growth may
be problematic.
[0038] The surface area of the anti-microbial coating may depend on
the particular device being coated. However, in many embodiments,
the surface area may be at least on the order of a surface area
that one would grab or handle or work on. In one embodiment, the
surface area may be at least 50 cm.sup.2, at least 200 cm.sup.2, or
at least 1000 cm.sup.2. In other embodiments the surface area may
be much larger. For example where a conveyor belt in a food
processing plant is coated or the interior surface of the
refrigerator, countertops, flooring, wall paneling, the surface
area to be coated may be greater than 1.0 m.sup.2, greater than 5
m.sup.2, or greater than 10 m.sup.2. In one embodiment of
antimicrobial coating the surface area in a range from 0.5 m.sup.2
to 200 m.sup.2, 1.0 m.sup.2 to 100 m.sup.2, or 2.0 m.sup.2 to 50
m.sup.2.
[0039] The type of material onto which the anti-microbial coating
is cold-sprayed can be any solid material including, but not
limited to metal, metal alloy, ceramic, organic polymers, natural
fibers, natural materials such as wood, and composites such as
concrete. The area that is cold sprayed includes at least a portion
of the surface of the device that benefits from anti-microbial
properties. As mentioned, the anti-microbial coating can be applied
to an exposed surface susceptible to contamination, a handle or
other member of the device that is specifically configured to be
grasped or manipulated by a person, or a working surface configured
to come into contact with microbes or a working surface that
provides a particularly rich environment for propagating
microbes.
[0040] In one embodiment, the surface to which the anti-microbial
is applied is of a flexible substrate. If desired, the flexibility
of the substrate in the location of the anti-microbial coating may
have a flexural strength less than 40 MPa, less than 20 MPa, or
even less than 10 MPa as measured according to ASTM D790. The
substrate may have the foregoing flexibility even after the
anti-microbial coating is applied. This is typically achieved by
maintaining a relatively thin anti-microbial coating (e.g., less
than 2000 microns or even less than 1000 microns).
[0041] There are significant advantages to the cold spray process.
Because the process occurs essentially at room temperature, copper,
which is a reactive metal can be applied in an open-air environment
with little or no oxidation. Also, nearby undamaged surface is not
exposed to extreme temperature or chemical conditions used in
conventional thermal deposition techniques. This allows for
polymeric materials and low melting point materials to be coated
with the anti-microbial coatings. Because the anti-microbial
coating is applied at ambient pressure, no vacuum chamber is
required.
[0042] The deposition rate can be relatively high, thereby allowing
large surface areas to be coated. The deposition rate can be in a
range from 0.5 g to 50 g per minute, more preferably 1 g to 10 g
per minute, depending on the nozzle size and spray gas flow rate.
The surface area of the antimicrobial coating can be almost any
size and is typically at least as large as the surface area of
objects designed to be handled by a person.
[0043] The antimicrobial powders include one or more metals having
antimicrobial properties. Examples of suitable antimicrobial metals
include silver, copper, zinc, mercury, tin, lead, bismuth, cadmium,
chromium, cobalt, nickel, thallium, combinations of these and
alloys of these. Preferred metals include copper and/or silver.
Other metals may be blended with the antimicrobial metals to
achieve desired mechanical and/or aesthetic properties. For example
additional metals that can be used include aluminum, iron,
vanadium, stainless steel, aluminum-zinc alloy and the like. In one
embodiment the antimicrobial metal powder (e.g., copper and/or
silver) may be cold sprayed with a second metal to produce a
desired coating color and/or applied using an oxygenated carrier
case to oxidize some or all of the metals in the metal powder to
create a desire hue or color. For example, when copper is applied
to a substrate the coating color may be copper orange. When silver
is applied the coating color may be a shiny to pearl white silver.
However when copper is applied with an oxygen carrier gas the
coating may be a green color. By blending different volumes of
powder the color can be changed. Adding 2% iron by volume to silver
may produce a pink hue color coating. Adding silver to copper may
give a peach hue color coating.
[0044] The antimicrobial metal powder is comprised of a plurality
of metal particles characterized by an average particle size in a
range from 5 nm to 50 .mu.m, more preferably 10 nm to 10 .mu.m, and
most preferably 20 nm to 1 .mu.m. The size of the particles may be
selected to achieve a desired grain size in the resulting coating.
The anti-microbial coatings may have a particularly small grain
size due to the very small metal particles from which they are
derived. The metal particles tend to produce coatings with grain
sizes of similar scale because cold spray processing temperatures
are much lower than the metal melting point, which avoids grain
growth conditions.
[0045] Metal powders suitable for preparing the antimicrobial
coatings are commercially available. Cold spray coating devices
useful to practice the method of the invention are commercially
available from Ktech Corporation, ASB Industries, Barberton Ohio,
and the Obninsk Center for Powder Spraying in Russia.
[0046] FIG. 2 shows a schematic of a cold spray apparatus useful
for practicing the method of the invention. Compressed gas from a
gas supply is supplied along a pneumatic line 201 in the direction
202 via shut-off and control valve 203, gas distributor 204, hose
205, and valve 206, pre-heated to a desired temperature with an
in-line heater 207 and directed to a mixing chamber 210 via hose
208. Metal powder including an anti-microbial metal is added to one
of multiple feed hoppers 220, 221 and 222, which are controlled by
valves 217, 218, and 219, respectively. The other two hoppers can
hold steel balls and glass beads for cleaning and shot-peening
processes, respectively. In normal operation only one hopper valve
is open for a specific process. Usually the agglomerate is put into
hopper 220 that is controlled by valve 217. In the coating process,
compressed gas enters the hopper 220 and carries the anti-microbial
powder, via valve 217, to mixing chamber 210 through hose 223. In
the mixing chamber 210, the anti-microbial metal powder is mixed
with the heated pressurized gas to provide a particle-gas stream.
The particle-gas stream is accelerated into a supersonic jet by
passing through a Laval nozzle, 211. Thus, the particle-gas stream
obtains sufficient velocity in the direction 212 for the
anti-microbial metal powder to deposit anti-microbial metal
particles onto the surface of a device 214, forming a coating 213.
The device 214, can be translated with an X-Y translation stage
(not shown) that allows control of the area of the deposition.
[0047] To cover large surface areas, the cold-spray apparatus may
be moved relative to the part being coated and/or the part can be
moved relative to cold-spray apparatus. By moving the cold-spray
apparatus and/or the part relative to one another, any size of
substrate can be coated and parts that have curved surfaces may
also be coated. The particular movement of the cold spray apparatus
and the part to be coated will depend on the shape and size of the
part. For example, where the part is a belt, the belt may be
rotated in a similar manner as belts are rotated. The cold spray
apparatus may remain in a fixed position until one or more complete
rotations are made to coat a portion of the belt. The cold spray
device can then be moved lateral to the direction of rotation and
being coating another section of the belt until the entire belt is
coated.
[0048] In some cases, the surface to be coated is on the inside of
a chamber and the cold spraying apparatus may not fit within the
chamber. In other embodiments, the part to be coated may be to
large or cumbersome to coat when assembled. In these cases, the
part can be coated in pieces and then assembled. With reference to
FIG. 1, the walls of hopper 120 may be coated as three separate
flat pieces and then assembled to make hopper 120. Other devices
that have interior surfaces such as drums, conduits, mixing
chambers, and the like can be manufactured in a similar manner.
[0049] The present invention also includes applying the cold spray
coating to curved and/or convoluted structures. FIG. 3 illustrates
a schematic showing coating the flighting of an auger. In this
embodiment, a cold spraying device 300 is positioned to coat the
flighting structure 310 of auger 312. The cold spraying apparatus
300 includes a nozzle 302 configured to spray the anti-microbial
powder. The sprayed powder forms a spray stream 304. The spray
stream 304 has a particular width 306 that is determined in part by
the distance of apparatus 300 from part 312. In one embodiment the
spray stream 306 can have a width 306 that is substantially the
same as the width of the flighting. Alternatively, spray apparatus
300 may have a width 306 that is less than the width of the
flighting. In this case, apparatus 300 may be moved laterally
(i.e., in a direction from the center of the flighting toward the
outside of the flighting or vice versa) to cover the width of the
flighting. In addition, auger 312 can be rotated as indicated by
arrow 314. Rotation of auger 312 can be carried out using an
electric motor 316 and drive shaft 318, which is coupled to the
shaft of auger 312. To maintain the spray stream positioned on
flighting 310, the auger 312 (and optionally motor 316) may be
advanced as indicated by arrow 320 while auger 312 is rotated.
Alternatively, cold-spray apparatus 300 may be advanced in the
direction opposite arrow 320. By controlling the movement of auger
312 relative to cold spraying apparatus 300 and vice versa, a
complicated spray pattern can be easily projected onto the surface
of flighting 310. Similar techniques may be used to coat devices,
parts, and structures of any of the devices described herein.
[0050] The pressurized gas accelerant in some cases can be an
important parameter in cold spray processing. Typically in cold
spray processes, helium, or a mixture of helium and nitrogen, is
used to accelerate particles with a size range of from 5 to 50
.mu.m. Helium is preferred in some cases because it has a very high
sonic velocity, and larger particles can achieve V.sub.c using it
as an accelerant. Other gases including nitrogen, air, argon and
the other noble gases, carbon dioxide and mixtures thereof can also
be used effectively depending upon the ductility of the material,
particle size and gas temperatures.
[0051] The method of the invention can be accomplished using
nitrogen, argon, or mixtures thereof, as the primary accelerating
gas. Air can also be used in cases where the reactivity of oxygen
is not an issue. Preferred gases for the invention are argon, air,
nitrogen and mixtures thereof. The compressed gas usually has a
working pressure of 70 to 700 psi, depending upon the metal or
alloy to be coated, nozzle type and the properties of the work
piece. Preferably, the gas has a working pressure of 90 to 300 psi.
The gas stream is heated, usually to a working temperature of 30 to
600.degree. C., and preferably 200 to 400.degree. C., before it
enters the mixing chamber, 110. The heated gas allows for a higher
velocity to be achieved in the supersonic jet and keeps the gas
from rapidly cooling and freezing once it expands past the throat
of the nozzle. U.S. Pat. No. 6,722,584, Kay, et al, hereby
incorporated by reference, describes a convenient commercial source
of a heating element, a Monel.TM. 400 tube, wound in the form of a
coil, and powered by a welding power supply.
[0052] The rate of addition of anti-microbial powder to the mixing
chamber is controlled by the hopper valve, 117. The material hopper
can be configured in several ways to deliver precise amounts of
powder to the mixing chamber. One configuration, delivers precise
amounts of powder that is picked up by a non-heated compressed gas
stream and delivered to the mixing chamber. The rate of addition of
powder is a primary parameter used in controlling the rate of
deposition of metal particles on the surface of the device. The
optimal addition rate depends upon several parameters including the
gas flow rate, the loading of metal powder, the type of material
and thickness of the coating desired. The optimal addition rate is
determined empirically using several trials for each material. With
a fixed device translation speed or jet translation speed, an
optimal addition rate is that suitable for forming a uniform and
desired thickness coating in one pass. The particle addition can be
driven by a gas stream through a hose from powder hopper to the
mixing chamber, while the addition rate is adjusted by a hopper
valve 117. Alternatively, several passes of the jet over the
surface of the device can be made.
[0053] The particle-gas stream provided in the mixing chamber 110,
accelerates by passing through a Laval nozzle, 111, to form a
supersonic jet that is directed at a work piece to be coated. The
exit port of the nozzle is some working distance from the work
piece, preferably 10 to 30 mm and most preferably 15 to 25 mm. An
X-Y translation stage can move the device and the rate of movement
can control (at least in part) the deposition rate. Alternatively,
the mixing chamber and Laval nozzle, together control the area of
deposition, and the rate of movement controls the deposition per
unit area. Repeated scanning of the work piece often can give more
uniform coatings than a single pass.
[0054] The deposition efficiency of the process depends on the type
of the metal particles, nozzle type, substrate material, gas
temperature, and gas pressure, which affect the particle velocity.
Usually if the particle velocity is too low, the metal particles to
deform plastically, resulting in poor deposition efficiency. If the
particle velocity is too high, the hard spheres tend to abrade the
surface, removing coating rather than depositing it. Thus, for the
process of the invention, there is a minimum critical velocity (Vc)
and a maximum velocity (Vm) between which is an optimum velocity
(Vo) that, at a specific temperature, gives an optimum deposition
efficiency. In practical situations, monitoring gas pressure is
much easier than monitoring gas-particle stream velocity. Thus, gas
pressure and temperature are the parameters most often used to
control particle velocity; and too low or too high particle
velocity can result in low deposition efficiency.
[0055] The method of the invention can be used in combination with
pre-cleaning processes. For instance, the surface of the device can
be treated with a gas stream with entrained abrasive agent prior to
the coating process to remove contaminants and provide a fresh
surface for bonding. For the cleaning process, a second material
hopper, 121, communicating with the mixing chamber 110, may contain
the abrasive agent including those selected from the group: glass
spheres, sand, alumina, silicon carbide, and steel spheres.
[0056] The present invention also relates to method for minimizing
communication of contaminating microbes through contact with the
device. The method includes providing an anti-microbial coated
device as described above. The anti-microbial device includes a
substrate having a surface where at least a portion of the surface
is coated with a cold-sprayed anti-microbial coating. The
anti-microbial coating includes fused metal particles having a
thickness in a range from 200 nm to 1 mm. The surface of the
substrate is then exposed to a microbial load under conditions
suitable for microbial growth. The anti-microbial coating is
allowed to kill at least 90% of the microbial load, more preferably
at least 95%, and most preferably at least 99% of the microbial
load.
[0057] The devices can advantageously be used in conditions that
are amenable to microbial growth conditions without the adverse
affects of microbial contamination. Conditions in which the
anti-microbial coating can have a beneficial effect vary widely.
For example, the solute concentration of the surrounding
environment may affect microbial growth. In a hypotonic
environment, where the solute concentration inside is greater than
that outside of the cell, osmotic pressure will cause water to
enter the cell and eventually cause it to burst. Cells may try to
adjust to this situation by producing or taking in more solutes. In
a hypertonic environment, where the solute concentration is greater
outside than inside of the cell, water leaves the cell shrinking
the plasma membrane and dehydrating the cell. In this case the cell
will become inactive and stop growing.
[0058] The microbe contaminating environment may also include
sufficient water for microbial growth. Metabolic activity and
reproduction of cells require water. The transport of material such
as nutrients, wastes, toxic materials, and other compounds in and
out of the cell requires water. Water exists in two different
forms. Bound water has a physical bond to other compounds in the
growth environment and is not available for use in cellular
functions. Available water is free and available for microorganisms
to use. The degree of water availability for chemical activity and
growth is called the water activity (a.sub.w). The water activity
is equivalent to the ratio of the vapor pressure of the growth
medium to the vapor pressure of pure water. The values range
between zero and one. The activity of pure water is equal to
one.
[0059] Osmotic pressure, relative humidity, freezing point, and
boiling point affect the water activity. Water activity is
inversely proportional to osmotic pressure and directly
proportional to relative humidity. Increasing the solute
concentration and lowering the relative humidity would result in a
reduction in water activity. Microorganisms differ in their
abilities to grow at various water activities. Examples of minimum
water activities include, the following: for bacteria a.sub.w is at
least 0.9, for yeast, a.sub.w is at least 0.87, for molds, a.sub.w
is at least 0.8, for halophilic bacteria a.sub.w is at least 0.75,
for xerophilic molds a.sub.w is at least 0.65, and for osmophilic
yeasts a.sub.w is at least 0.60.
[0060] The pH in an environment may also affect cell growth. While
various different microorganisms have different maximum, minimum,
and optimum pH levels, the growth conditions in which the
antimicrobial coated devices of the invention are typically
configured to be used is in a range from pH 4 to pH 9.
[0061] Temperature also greatly affects the growth and function of
microorganisms. The temperatures above and below the tolerance of
the organism can prevent enzyme catalyzed reactions that are
important to cell function from taking place. The devices of the
invention may be configured and arranged for use in temperatures
ranging from 0.degree. C. to 40.degree. C. Microorganisms that can
grow at temperatures between 0 and 40.degree. C. include
Psychrotrophs and Mesophiles. Psychrotrophs typically grow at
temperatures between 0 and 30.degree. C. and are often a factor in
the spoilage of refrigerated foods. Mesophiles typically have
optimal temperature between 20 and 40.degree. C.
[0062] The gaseous environment surrounding microorganisms can have
a significant impact on their growth and metabolic system. The
devices of the invention may be configured and arranged for use in
environments that include oxygen. Those skilled in the art are
familiar with the environmental configurations that lead to cell
growth and increased contamination of a surface of a device.
[0063] The foregoing conditions are example conditions in which the
anti-microbial coated devices can be advantageously used to
minimize contamination in an otherwise microbial contaminating
environment.
[0064] The following examples illustrate example methods for making
antimicrobial coated devices and using the devices.
EXAMPLE 1
[0065] Example 1 teaches a method for making an anti-microbial
coated for use in food manufacturing. A conveyor belt having a
width of 24'' and a length of 25' is coated with a copper
anti-microbial coating. The conveyor belt is made from high density
polyethylene having a thickness of 1/8'' and a flexural stiffness
less than 20 MPa.
[0066] The conveyor belt is cold sprayed with a copper powder. The
copper powder has a mean particle size of 50 .mu.m. The copper
powder is sprayed at supersonic speeds at the surface of the
conveyor belt for a sufficient time to form a cold-sprayed copper
coating with a thickness of 3000 microns. Essentially the entire
upper surface of the conveyor belt is coated with a fine
anti-microbial copper coating.
[0067] The conveyor belt can be included in a food processing
conveyor apparatus (e.g., conveyor system 200). The food processing
conveyor apparatus includes a drive mechanism for rotating the
coated conveyor belt. The anti-microbial coating is typically
coated on the outside surface of the conveyor belt such that food
material disposed on the upper surface of the conveyor belt comes
into contact with the anti-microbial coating. The food processing
conveyor apparatus can be configured to transport food products
such as cereal. A method for using the conveyor apparatus and
coated conveyor belt includes operating the conveyor under standard
in an open environment in a food processing facility where the
conveyor belt comes into contact with food material (e.g., cereal)
and is exposed to airborn microbes or microbes in the food
materials. The antimicrobial coating is allowed to kill at least a
portion of the microbial load exposed on the anti-microbial
coating.
EXAMPLE 2
[0068] Example 2 is a hypothetical example illustrating the use of
an anti-microbial coated conveyor belt to kill microbes in a
microbial contaminating environment. As shown in Table 1, 13
different strains of microbes are prepared, including Salmonella
cultures, Listeria monocytogenes cultures, and mold cultures.
TABLE-US-00001 TABLE 1 Salmonella Composite Culture SRCC Number
Salmonella Heidelberg FSC-CC 1801 (ATCC 8326) Salmonella
Enteritidis FSC-CC 1395 (ATCC 13076) Salmonella Typhimurium FSC-CC
1397 (ATCC 13311) Salmonella Senftenberg FSC-CC 2470 (ATCC 43845)
Listeria monocytogenes Composite Culture FSC-CC Number Serotype
Listeria monocytogenes (Environmenatal 7 1/2 b isolate) Listeria
monocytogenes (Hot Dog isolate) 525 1/2 c Listeria monocytogenes
Scott A 1234 4b Listeria monocytogenes 2310 1/2 a Molds-Composite
Culture FSC-CC Number Penicillium citrinum 1123 Asperigillus niger
772 Asperigillus penicilloides 1260 Cladisporium cladosporoides
1374 Rhizopus oryzhae 2066
[0069] The strains of Salmonella are cultivated in tryptic soy
broth (TSB), individually, and incubated at 35.degree. C. for 18-24
h. The strains of L. monocytogenes are cultivated in tryptic soy
broth with 0.6% yeast extract (TSBYE), individually, and incubated
at 35.degree. C. for 18-24 h. A cell suspension is prepared for
each strain used in the inoculum. Cell suspensions are mixed to
prepare an inoculum, which contains approximately equal numbers of
cells of each strain. The composite cultures are then stored at
4.degree. C., (for up to 26 h) while the culture level is
determined by plating serial dilutions of the composite on tryptic
soy agar (TSA). The plates are incubated at 35.degree. C. for 24 h
prior to enumeration. Verification of Salmonella and L.
monocytogenes composite culture is conducted by streaking onto
xylose lysine desoxycholate (XLD) and modified oxford agar (MOX)
and incubating at 35.degree. C. for 18-24 h.
[0070] The mold strains are prepared on Potato Dextrose Agar (PDA)
with antibiotics, individually, and incubated for 5 days at
25.degree. C. under aerobic conditions. A cell suspension is
prepared for each strain used in the inoculum. Cell suspensions are
mixed to prepare an inoculum, which contains approximately equal
numbers of cells of each strain. The composite culture is then
stored at 4.degree. C. until use. The culture level is determined
by direct microscopic count. Broth cultures are stored at 4.degree.
C. prior to inoculation. Dilutions are prepared with Butterfield's
phosphate buffer. The composite cultures (0.5 ml) are evenly
distributed over the entire surface area of each coupon of
anti-microbial coated conveyor belt. Initial inoculation levels are
targeted at 10.sup.7 per coupon. After inoculation, samples are
stored at room temperature for 2 h and analyzed for counts.
Uncoated coupons are used as controls. The experimental protocol is
summarized below in Table 2 in which a total of 36 microbial
analyses are performed.
TABLE-US-00002 TABLE 2 Sam- pling Listeria Coating level time
monocytogenes Salmonella Mold 0 mm coating 0 hr 1-3 samples 4-6
samples 7-9 samples (control) 2 hr 10-12 samples 13-15 samples
16-18 samples 1 mm coating 2 hr 19-21 samples 22-24 samples 25-27
samples 3 mm coating 2 hr 28-30 samples 31-33 samples 34-36
samples
[0071] Coupons of anti-microbial coated conveyor belt (10
cm.times.10 cm) are placed in a sterile stomacher bag and rinsed
with 10 ml Neutralizing Buffer for 1 min to wash the inoculated
cells from the surface. Serial dilutions are performed using
Butterfield's phosphate buffer. All samples are analyzed by the
pour plate technique. Typical colonies are considered as
confirmatory. The methods of analysis is outlined below in Table
3.
TABLE-US-00003 Incubation Time/ Temperature/ Test Medium Atmosphere
Listeria Trypticase Soy Agar with 48 hours/30.degree. C./aerobic
monocytogenes Yeast Extract with Modified Oxford Agar overlay
Salmonella Trypticase Soy Agar with 48 hours/35.degree. C./aerobic
XLD overlay Mold Potato Dextrose Agar with 5 days/25.degree.
C./aerobic antibiotics
[0072] The present invention may be embodied in other specific
forms without departing from its spirit or essential
characteristics. The described embodiments are to be considered in
all respects only as illustrative and not restrictive. The scope of
the invention is, therefore, indicated by the appended claims
rather than by the foregoing description. All changes which come
within the meaning and range of equivalency of the claims are to be
embraced within their scope.
* * * * *