U.S. patent application number 10/454348 was filed with the patent office on 2003-11-20 for thermoplastic articles exhibiting high surface-available silver.
Invention is credited to Dankel, Robert, Haas, Geoffrey, Laridon, Erik.
Application Number | 20030215521 10/454348 |
Document ID | / |
Family ID | 21774109 |
Filed Date | 2003-11-20 |
United States Patent
Application |
20030215521 |
Kind Code |
A1 |
Laridon, Erik ; et
al. |
November 20, 2003 |
Thermoplastic articles exhibiting high surface-available silver
Abstract
Improvements in increasing the amount of surface-available
silver in thermoplastic articles comprising certain
silver-containing antimicrobial agents. Such an invention requires
the incorporation of a sufficient amount of a carboxylic acid salt
within the thermoplastic article simultaneously with the necessary
silver-containing antimicrobial agent. Certain carboxylic acid
salts are standard acid scavengers and lubricants for certain
thermoplastic applications; however, the amounts required within
this inventive thermoplastic article are in excess of that commonly
added within such articles, and the types of acid scavengers
possibly added within such target thermoplastic articles are
preferably neutralized hydrotalcite compounds, thereby permitting
the carboxylic acid salt to function in the inventive manner.
Surprisingly, such a high amount of such standard salts, as well as
potentially other non-standard salts, present within the target
thermoplastic cause the release of greater amounts of silver to the
target article's surface, thereby permitting a greater degree of
antimicrobial activity, among other potential benefits for such an
increase in surface-available silver. Methods of producing such
inventive thermoplastics are also encompassed within this
invention.
Inventors: |
Laridon, Erik; (Heverlee,
BE) ; Haas, Geoffrey; (Spartanburg, SC) ;
Dankel, Robert; (Taylors, SC) |
Correspondence
Address: |
Wiliam S. Parks
P.O. Box 1927
Spartanburg
SC
29304
US
|
Family ID: |
21774109 |
Appl. No.: |
10/454348 |
Filed: |
June 4, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10454348 |
Jun 4, 2003 |
|
|
|
10015872 |
Dec 12, 2001 |
|
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Current U.S.
Class: |
424/604 ;
424/486; 424/618 |
Current CPC
Class: |
A61K 33/38 20130101;
A61K 33/42 20130101 |
Class at
Publication: |
424/604 ;
424/618; 424/486 |
International
Class: |
A61K 033/42; A61K
033/38; A61K 009/14 |
Claims
What I claim is:
1. A styrenic thermoplastic article comprising at least one
silver-containing antimicrobial agent and exhibiting a
surface-available amount of silver compound of at least 0.80
micrograms of silver/square decimeters of said surface, as measured
by a salt-extraction test of 24 hours at room temperature.
2. The styrenic thermoplastic article of claim 1 wherein said at
least one silver-containing antimicrobial agent is an inorganic
silver-containing compound.
3. The styrenic thermoplastic article of claim 2 wherein said
inorganic silver-containing antimicrobial agent is selected from
the group consisting of silver zirconium phosphates, silver
glasses, silver zeolites, and any mixtures thereof.
4. The styrenic thermoplastic article of claim 3 wherein said
inorganic silver-containing antimicrobial agent is silver zirconium
phosphate.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of co-pending application
10/015,872, filed on Dec. 12, 2001.
FIELD OF THE INVENTION
[0002] This invention relates to improvements in increasing the
amount of surface-available silver in thermoplastic articles
comprising certain silver-containing antimicrobial agents. Such an
invention requires the incorporation of a sufficient amount of a
carboxylic acid salt within the thermoplastic article
simultaneously with the necessary silver-containing antimicrobial
agent. Certain carboxylic acid salts are standard acid scavengers
and lubricants for certain thermoplastic applications; however, the
amounts required within this inventive thermoplastic article are in
excess of that commonly added within such articles, and the types
of acid scavengers possibly added within such target thermoplastic
articles are preferably neutralized hydrotalcite compounds, thereby
permitting the carboxylic acid salt to function in the inventive
manner. Surprisingly, such a high amount of such standard salts, as
well as potentially other non-standard salts, present within the
target thermoplastic cause the release of greater amounts of silver
to the target article's surface, thereby permitting a greater
degree of antimicrobial activity, among other potential benefits
for such an increase in surface-available silver. Methods of
producing such inventive thermoplastics are also encompassed within
this invention.
DISCUSSION OF THE PRIOR ART
[0003] There has been a great deal of attention in recent years
given to the hazards of bacterial contamination from potential
everyday exposure. Noteworthy examples of such concern include the
fatal consequences of food poisoning due to certain strains of
Eschericia coli being found within undercooked beef in fast food
restaurants; Salmonella contamination causing sicknesses from
undercooked and unwashed poultry food products; and illnesses and
skin infections attributed to Staphylococcus aureus, yeast, and
other unicellular organisms. With such an increased consumer
interest in this area, manufacturers have begun introducing
antimicrobial agents within various household products and
articles.
[0004] Silver-containing inorganic microbiocides have recently been
developed and utilized as antimicrobial agents on and within a
plethora of different substrates and surfaces. In particular, such
microbiocides have been adapted for incorporation within plastic
compositions and fibers in order to provide household and consumer
products which inherently exhibit antimicrobial characteristics.
Although such silver-based agents provide suitable antimicrobial
properties within thermoplastic articles, and other types of
articles, there are certain limitations as to the potential
antimicrobial efficacy of such thermoplastic articles. Such
limitations are apparently due to relatively low amounts of
surface-available silver within and/or on such thermoplastic
articles. Without intending to be bound to any specific scientific
theory, it, is believed that such low surface-available amounts of
silver are the result of the inability of a sufficient amount of
the integrated silver compounds to migrate to the thermoplastic
surface. Such a result is observed for standard thermoplastics
comprising silver-containing antimicrobials. Thus, there exists a
need to provide efficacious amounts of silver-containing
antimicrobial agents within thermoplastic compositions that exhibit
such heretofore unattainable high levels of surface-available
silver compounds, thereby providing more effective antimicrobial
activity, among other potential desirable characteristics as a
result thereof.
[0005] Past plastic compositions and articles comprising
silver-containing antimicrobial agents include U.S. Pat. No.
5,405,644 to Ohsumi et al., which includes the addition of certain
triazoles, U.S. Pat. No. 4,938,955 to Niira, deceased et al. (also
including benzotriazole stabilizers), U.S. Pat. No. 5,750,609 to
Nosu et al., which discloses an ultraviolet protective agent for
incorporation within a variety of compositions, such as films,
fibers, cosmetics, and the like, comprising a zinc-based
hydrotalcite which acts solely as an ultraviolet absorber. However,
these particular methods and plastics have proven to be costly
(with the high expense of benzotriazoles initially), particularly
since relatively high concentrations of the expensive stabilizing
compounds are required, and do not provide any appreciable increase
of available silver on the surface of such articles. Also, as these
stabilizers are not thermally stable, they introduce additional
processing complications. As such, there is no teaching or fair
suggestion within the prior art which pertains to the needed
improvement in increasing the amounts of surface-available silver
compounds on target thermoplastics.
DESCRIPTION OF THE INVENTION
[0006] It is thus an object of the invention to provide an increase
in the amount of surface-available silver to actual thermoplastic
articles (containers, plaques, films, fibers, and the like). A
further object of the invention is to provide such an increase
through the utilization of acceptable, commercially available,
components for thermoplastic formulations. Another object of the
invention is to provide a highly efficacious antimicrobial
thermoplastic article. Yet another object of this invention is to
provide a cost-effective method of increasing the amount of
surface-available silver on such target inventive thermoplastic
articles and thereby reducing the amount of active silver remaining
within the target resin itself.
[0007] Accordingly, this invention encompasses a thermoplastic
article comprising at least one silver-containing antimicrobial
agent, optionally at least one acid scavenger compound, and from
0.1% to 1.25% by weight, preferably from about 0.2 to about 1.0%,
more preferably from about 0.2 to about 0.5%, and most preferably
about 0.3% by weight of at least one carboxylic acid salt component
other than or in excess of said optional at least one acid
scavenger compound. Furthermore, this invention also encompasses a
method of forming a thermoplastic article comprising the steps of
providing a thermoplastic polymer, introducing at least one
silver-containing antimicrobial agent, optionally at least one acid
scavenger compound, and from at least 0.1% to 1.25% by weight,
preferably from about 0.2 to about 1.0%, more preferably from about
0.2 to about 0.5%, and most preferably about 0.3% by weight of at
least one carboxylic acid salt component other than or in excess of
said optional at least one acid scavenger compound, melting said
resultant mixture of polymer, silver-containing antimicrobial
agent, and at least one carboxylic acid salt, and cooling said
molten mixture in a desired shaped thermoplastic article. Also,
this invention encompasses a polyolefin article comprising at least
one silver-containing antimicrobial agent and exhibiting a
surface-available amount of silver of at least 0.25 micrograms of
silver/square decimeter (or a styrenic thermoplastic article
exhibiting an amount of at least 0.80 micrograms of silver/square
decimeter in terms of surface-available silver) of said surface, as
measured by a salt-extraction test for 24 hours at room
temperature. Nowhere within the prior art has such a specific
plastic article or method of making thereof been disclosed,
utilized, or fairly suggested to produce a thermoplastic article
with such desirable increased surface-available silver
characteristics.
[0008] The term "surface-available silver" is intended to encompass
the phenomenon of the detectable presence of available silver,
either as metals or ions, on the target article's surface or,
possibly from a distance very close to such surface but imbedded
therein until extracted out with relative ease. Detection in this
instance is accomplished through a particular method, as eluded to
above, wherein the sample article is immersed within an extracting
solution, such as, as one example, a mixed salt solution (in this
instance a sodium-potassium-phosphate buffer solution) for at least
twenty-four hours at room temperature. After such time, the extract
solution is then analyzed through, for example, and without
intended limitation, Inductive Coupled Plasma spectroscopy
(hereinafter referred to as ICP) for the presence of silver therein
which would have been removed from the target thermoplastic during
the extraction process. The detection of such silver thus indicates
the availability of silver at or near the article's surface and
thus correlates to an increase in activity in relation to the
availability of such silver in such a manner.
[0009] The closest art all involves the presence of
silver-containing antimicrobial agents within thermoplastics, but
do not concern the need for or possibility of increasing such
desirable surface-available silver compounds. Such prior art is
discussed above.
[0010] Any plastic in which a silver-based antimicrobial agent may
be properly incorporated can be utilized in this invention. For
instance, and without intending any limitations therein,
polyolefins, such as polyethylene, polypropylene, and polybutylene,
styrenics, such as polystyrene, ABS, and the like, and polyesters,
such as polyethylene terephthalate, may be utilized within this
invention. Preferably, the plastic is a thermoplastic that can be
molded into different shapes and sizes upon extrusion a molding
with the silver-containing antimicrobial and the required excess
amount of carboxylic acid salts. Thus, polyolefins, particularly
polypropylene, and styrenics, particularly polystyrene, are
preferred. Furthermore, such plastics preferably may be colored to
provide other aesthetic features for the end user. Thus, the
plastic may also comprise colorants, such as, for example,
poly(oxyalkylenated) colorants, pigments, dyes, and the like, too.
Other additives may also be present, including antistatic agents,
brightening compounds, nucleating agents, clarifying agents,
lubricants, flame retardants, antioxidants, UV stabilizers,
fillers, and the like.
[0011] The preferred silver-containing antimicrobial is an
inorganic silver-containing compound, including, without
limitation, inorganic compounds such as silver zirconium phosphates
available from Milliken & Company under the tradename
ALPHASAN.RTM. RC-2000, RC-5000, and RC-7000, although any
silver-containing inorganic antimicrobial agent may also be
utilized within the inventive plastic article (for instance, as
mere examples, a silver substituted zeolite available from Shingawa
under the tradename ZEOMIC.RTM., and silver-containing glasses,
such as IONPURE.RTM. from Ishizuka Glass under the tradename
IONPURE.RTM., as well as AMP.RTM. T558 and MICROFREE.RTM., both
available from DuPont, as well as JMAC.RTM., available from Johnson
Mathey). Generally, such an antimicrobial is added in an amount of
from about 0.01 to 10% by total weight of the target plastic
composition; more preferably from about 0.05 to about 2.0%; and
most preferably from about 0.5 to about 2.0%.
[0012] The carboxylic acid salt may be any such salt based upon
monovalent, bivalent, or trivalent metal ions and from
C.sub.1-C.sub.40 in carbon chain length. Preferably, such at least
one carboxylic acid salt is selected from the group consisting of
at least one C.sub.1-C.sub.40 carboxylic acid compound neutralized
by at least one cation selected from the group consisting of
monovalent metal ions, bivalent ions, and trivalent metal ions.
Such ions include, without limitation, monovalents such as alkali
metals (e.g., sodium, potassium, lithium, and like) bivalents such
as alkaline earth metals (e.g., calcium, barium, strontium,
magnesium, cadmium, rubidium, and the like), zinc, tin (II), iron
(II), such as aluminum, for example. It appears that the bi- and
tri-valents provide the best overall thermoplastic article from
both a surface-available silver compound standpoint and an
aesthetic perspective because discoloration appears to be a greater
problem with monovalents than for the others. However, such
discoloration is greater for the larger-sized monovalent metal ions
(e.g., sodium and potassium) for some undetermined reason. Although
such compounds do appear to brown or yellow the target inventive
resins to a certain extent, such colors may also be acceptable, or
even desired, for certain reasons as well, thus the utilization of
such carboxylic acid salts is not completely discouraged, and thus
remains possible within the invention. Preferably, also, said
carboxylic acid salt is preferably selected from the group
consisting of alkali metal acetates, alkali metal stearates,
alkaline earth metal acetates, alkaline earth metal stearates, zinc
stearate, tin (II) stearate, aluminum stearate (as well as di- and
tri-stearate), and any mixtures thereof (although other chain
lengths, including myristates, behenates, oleates, palmitates, and
the like, may also be utilized, these stearates and acetates are
non-limiting preferred examples for this invention). Most
preferred, though again, non-limiting, is calcium stearate, due to
its advantages in processing as well as ultimate efficacy within
the finished target thermoplastic article, as shown below. As noted
above, the carboxylic acid salt should be added in amounts of from
about 0.1% to 1.25% by weight, preferably from about 0.2 to about
1.0%, more preferably from about 0.2 to about 0.5%, and most
preferably about 0.3% by weight of the total polymer component.
Such amounts are in excess of any other acid scavenger compounds
that are present within the target polymer itself (and preferably
none of the carboxylic acid salts are utilized as acid scavengers
in addition to this inventive purpose). In any event, such amounts
are generally well in excess of standard additive amounts for acid
scavenging carboxylic acid salts (such as calcium stearate, as one
example) utilized within thermoplastic articles. Surprisingly,
then, it has been found that such excess amounts of carboxylic acid
salts are instrumental in providing the highly desirable increase
in surface-available silver compounds on the target thermoplastic
articles comprising silver-containing antimicrobial agents. It is
not fully understood why such an addition of excess amount works in
such a manner; however, the presence of too much carboxylic acid
salt (e.g., greater than the maximum amount noted above, such as
about 1.3% by weight of the total polymer component and above, as
well as, in some circumstances, even amounts within the possible
range of proportions noted above) exhibits a sharp reduction in
such surface-available silver compounds and thus cannot function
properly (and, in fact, results in an amount of such silver
compounds well below that for a control of thermoplastic comprising
only the silver-containing antimicrobial agent and no carboxylic
acid salt at all). Again, such a selection criteria for the
necessary carboxylic acid salt is highly unexpected to provide what
is believed to provide a much-improved antimicrobial thermoplastic
article ultimately.
[0013] As noted below, the basic procedures followed in producing
the inventive antimicrobial plastic article comprise standard
plastic formation techniques. There are two basic methods of
incorporating additives (such as silver-containing antimicrobials
and the necessary carboxylic acid salts, for example) within
polymer articles. One method is to dry blend a mixture of polymer,
additives, antimicrobials, and carboxylic acid salt; melting the
dry mix into a molten formulation which is then eventually cooled
and cut into pellets; the pellets are then introduced within an
injection molding machine, or other similar type of processing
equipment, and ultimately cooled into a shaped article.
Alternatively, one may mix conventional resin pellets and a
masterbatch concentrate containing the antimicrobial and carboxylic
acid salt additives and molding in conventional molding equipment.
The aforementioned molding steps may be performed preferably with
injection molding equipment; however, other plastic-forming
operations may also be utilized such as, and without limitation,
blow molding, fiber extrusion, film formation, compression molding,
rotational molding, and the like. These alternative plastic
article-forming operations would be well understood and appreciated
by one of ordinary skill in this art. The composition may then be
processed and fabricated by any number of different techniques,
including, without limitation, injection molding, injection blow
molding, injection stretch blow molding, injection rotational
molding, extrusion, extrusion blow molding, sheet extrusion, film
extrusion, cast film extrusion, foam extrusion, thermoforming (such
as into films, blown-films, biaxially oriented films), thin wall
injection molding, and the like into a fabricated article. For
styrenics, such a procedure generally entails the utilization of
pelletized polymers including antioxidant, lubricant, and the like,
additives previously incorporated therein, to which powdered
antimicrobial and carboxylic acid salt components may then be mixed
therewith. The resultant solid pellets can then be melted by a
heated screw during melting and mixing of the molten components
prior to extrusion, or other process step.
[0014] Other additives may also be used in the composition of the
present invention, provided they do not interfere with the primary
benefits of the invention. It may even be advantageous to premix
these additives or similar structures with the silver-containing
antimicrobial agent(s) and carboxylic acid salts in order to reduce
their melting points and thereby enhance dispersion and
distribution during melt processing. Such additives are well known
to those skilled in the art, and include nucleating agents,
plasticizers, lubricants, catalyst neutralizers, antioxidants,
light stabilizers, colorants, acid scavengers, and the like. Some
of these additives may provide further beneficial property
enhancements, including improved aesthetics, easier processing, and
improved stability to processing or end use conditions.
[0015] In particular, it is contemplated that the acid scavengers
utilized herein are primarily not the same carboxylic acid salts as
needed for the desired increase in surface-available silver on the
target thermoplastic article. Thus, as one example, dihydrotalcite
types (such as, primarily, through without limitation, DHT4-A from
Kyowa Chemical Industry Co., Ltd.) are preferred for this purpose,
thereby permitting any carboxylic acid salts to be utilized
primarily for the aforementioned inventive silver-generating
purpose.
[0016] The compositions of the present invention are suitable as
additives to improve the antimicrobial efficacy, and any other
characteristic for which surface-available silver is highly
desirable, of packaging materials and container materials for
cosmetics, food-stuffs, films, thermoformed articles (drinking
cups, for example), thick-walled storage containers, medical
applications (syringes, intravenous bags, gloves, and the like),
food processing equipment (conveyors belts, and the like) and other
similar and typical end-uses for which antimicrobial thermoplastics
are highly desired, particularly because they provide excellent
efficacy for such film, sheet, or other similar fabricated
thermoplastic articles without deleterious affecting such an
article's physical properties.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0017] The following examples are indicative of the preferred
embodiment of this invention:
[0018] Antimicrobial Thermoplastic Article Production
[0019] Thermoplastic articles were produced in accordance with the
different compositions listed below (all such compositions weighed
1000 g prior to molding):
HOMOPOLYMER POLYPROPYLENE COMPOSITION TABLE
[0020]
1 Component Amount Polypropylene homopolymer (Himont Profax .RTM.
6301 to 1000 g NT, from Basell) Irganox .RTM. B215, Antioxidant
(from Ciba Specialty 1500 ppm Chemicals) DHT4-A, Acid Scavenger 400
ppm Silver-Containing Antimicrobial Agent (type noted as noted
below below) Carboxylic Acid Salt (type noted below) as noted
below
HIGH DENSITY POLYETHYLENE COMPOSITION TABLE
[0021]
2 Component Amount High Density Polyethylene (DOW .RTM. 8454N,
commercial to 1000 g resin comprising a pre-produced formulation of
polymer with antioxidants and acid scavengers) Silver-Containing
Antimicrobial Agent (type noted as noted below below) Carboxylic
Acid Salt (type noted below) as noted below
LINEAR LOW DENSITY POLYETHYLENE COMPOSITION TABLE
[0022]
3 Component Amount Linear Low Density Polyethylene (DOWLEX .RTM.
2552-E, to 1000 g commercial resin comprising a pre-produced
formulation of polymer with antioxidants and acid scavengers)
Silver-Containing Antimicrobial Agent (type noted as noted below
below) Carboxylic Acid Salt (type noted below) as noted below
POLYSTYRENE COMPOSITION TABLE
[0023]
4 Component Amount Polystyrene (DOW Styron .RTM. 660-71, commercial
resin to 1000 g comprising a pre-produced formulation of polymer
with antioxidants and acid scavengers) Silver-Containing
Antimicrobial Agent (type noted as noted below below) Carboxylic
Acid Salt (type noted below) as noted below
[0024] The polypropylene articles were produced by first mixing the
polypropylene fluff together with the other components as listed to
form a solid mixture of all such components. The solid mixture was
then introduced within a hopper for further melting on a standard
heated screw extruder. The molten mixture thus mixed thoroughly,
and pelletized before being finally molded into a desired shape,
into which they were then cooled into desired configurations for
further use, in this case as plaques.
[0025] The polyethylene and polystyrene articles were all produced
by taking pre-produced pellets of the (commercially available)
polymer with other additives already provided, except the necessary
silver-containing antimicrobial agents and the accompanying
carboxylic acid salts. These powdered components were then mixed
prior to melting with the aforementioned pellets to form a similar
solid mixture for further melt extruding and mixing via a heated
screw extruder. The molded articles were also plaques that were
then cooled sufficiently to form the desired solid articles for the
purpose of further testing and analysis.
[0026] Of course, although screw extruding and molding techniques
were followed to form plaques in this preferred instance, it should
be evident that any techniques standard within the thermoplastic
article production industry to form any solid articles of such
broadly defined polymeric articles may be followed as well.
[0027] The specific compositions produced conform with the
particulars set forth in the Table below in terms of type of
polymer (from above) (PP indicates from the Homopolymer
Polypropylene Compositions Table, HDPE from the High Density
Polyethylene Table, LLDPE from the Linear Low Density Polyethylene
Table, and PS from the Polystyrene Table), type of
silver-containing antimicrobial agent (generally, and non-limiting,
in an amount of 10000 ppm, or about 1% by weight of the total
polymer content of RC-2000 and RC-5000 are ALPHASAN.RTM.
silver-containing compounds, and ZEOMIC.RTM., is a zeolite-based
compound, as noted above), and type of carboxylic acid salt (and
amount) (CaSt is calcium stearate, Aldi-St is aluminum distearate,
MgAc is magnesium acetate, with like labels for others salts
tested) as listed:
THERMOPLASTIC ARTICLE FORMULATION TABLE
[0028]
5 Polymer Carboxylic Acid Example # Type Silver-Containing Agent
Salt (in ppm) 1 PP RC-5000 (10000 ppm) MgSt (3000 ppm) 2 PP RC-5000
(10000 ppm) CaSt (3000 ppm) 3 PP RC-5000 (10000 ppm) BaSt (3000
ppm) 4 PP RC-5000 (10000 ppm) CdSt (3000 ppm) 5 PP RC-5000 (10000
ppm) Sn(II)St (3000 ppm) 6 PP RC-2000 (10000 ppm) MgSt (3000 ppm) 7
PP RC-2000 (10000 ppm) CaSt (3000 ppm) 8 PP RC-2000 (10000 ppm)
BaSt (3000 ppm) 9 PP RC-2000 (10000 ppm) ZnSt (3000 ppm) 10 PP
RC-2000 (10000 ppm) CdSt (3000 ppm) 11 PP RC-2000 (10000 ppm)
Sn(II)St (3000 ppm) 12 PP ZEOMIC (10000 ppm) NaSt (3000 ppm) 13 PP
ZEOMIC (10000 ppm) CaSt (3000 ppm) 14 PP RC-5000 (10000 ppm) LiSt
(100 ppm) 15 PP RC-5000 (10000 ppm) MgSt (1000 ppm) 16 PP RC-5000
(10000 ppm) MgSt (2431 ppm) 17 PP RC-5000 (10000 ppm) MgSt (10000
ppm) 18 PP RC-5000 (10000 ppm) CaSt (1000 ppm) 19 PP RC-5000 (10000
ppm) CaSt (1514 ppm) 20 PP RC-5000 (10000 ppm) CaSt (10000 ppm) 21
PP RC-5000 (10000 ppm) BaSt (100 ppm) 22 PP RC-5000 (10000 ppm)
BaSt (300 ppm) 23 PP RC-5000 (10000 ppm) BaSt (1000 ppm) 24 PP
RC-5000 (10000 ppm) BaSt (10000 ppm) 25 PP RC-5000 (10000 ppm) CdSt
(100 ppm) 26 PP RC-5000 (10000 ppm) CdSt (300 ppm) 27 PP RC-5000
(10000 ppm) CdSt (1000 ppm) 28 PP RC-5000 (10000 ppm) CdSt (10000
ppm) 29 PP RC-5000 (10000 ppm) Sn(II)St (100 ppm) 30 PP RC-5000
(10000 ppm) Sn(II)St (300 ppm) 31 PP RC-5000 (10000 ppm) Sn(II)St
(1000 ppm) 32 PP RC-5000 (10000 ppm) AlSt (100 ppm) 33 PP RC-5000
(10000 ppm) AlSt (300 ppm) 34 PP RC-5000 (10000 ppm) AlSt (1000
ppm) 35 PP RC-5000 (10000 ppm) AlSt (3000 ppm) 36 PP RC-5000 (10000
ppm) Aldi-St (100 ppm) 37 PP RC-5000 (10000 ppm) Aldi-St (300 ppm)
38 PP RC-5000 (10000 ppm) Aldi-St (1000 ppm) 39 PP RC-5000 (10000
ppm) Aldi-St (3000 ppm) 40 PP RC-5000 (10000 ppm) Altri-St (100
ppm) 41 PP RC-5000 (10000 ppm) Altri-St (300 ppm) 42 PP RC-5000
(10000 ppm) Altri-St (1000 ppm) 43 PP RC-5000 (10000 ppm) Altri-St
(3000 ppm) 44 HDPE RC-5000 (10000 ppm) LiSt (10000 ppm) 45 HDPE
RC-5000 (10000 ppm) NaSt (3000 ppm) 46 HDPE RC-5000 (10000 ppm)
NaSt (10000 ppm) 47 HDPE RC-5000 (10000 ppm) KSt (10000 ppm) 48
HDPE RC-5000 (10000 ppm) MgSt (3000 ppm) 49 HDPE RC-5000 (10000
ppm) MgSt (10000 ppm) 50 HDPE RC-5000 (10000 ppm) CaSt (3000 ppm)
51 HDPE RC-5000 (10000 ppm) CaSt (10000 ppm) 52 HDPE RC-5000 (10000
ppm) BaSt (3000 ppm) 53 HDPE RC-5000 (10000 ppm) BaSt (10000 ppm)
54 HDPE RC-5000 (10000 ppm) ZnSt (3000 ppm) 55 HDPE RC-5000 (10000
ppm) CdSt (3000 ppm) 56 HDPE RC-5000 (10000 ppm) Sn(II)St (3000
ppm) 57 LLDPE RC-5000 (10000 ppm) LiSt (3000 ppm) 58 LLDPE RC-5000
(10000 ppm) NaSt (3000 ppm) 59 LLDPE RC-5000 (10000 ppm) MgSt (3000
ppm) 60 LLDPE RC-5000 (10000 ppm) CaSt (3000 ppm) 61 LLDPE RC-5000
(10000 ppm) BaSt (3000 ppm) 62 LLDPE RC-5000 (10000 ppm) ZnSt (3000
ppm) 63 LLDPE RC-5000 (10000 ppm) CdSt (3000 ppm) 64 LLDPE RC-5000
(10000 ppm) Sn(II)St (3000 ppm) 65 PS RC-5000 (10000 ppm) CaSt
(3000 ppm)
[0029] Each article was produced after the initial polymer and
additives were first blended in a Kenwood mixer for 5 minutes at
low speed. All samples were then melt-compounded on a Killion
single screw extruder at a ramped temperature from about
205.degree. to 230.degree. C. through four heating zones. The melt
temperature upon exit of the extruder die was about 230.degree. C.
The screw had a diameter of 2.54 cm and a length/diameter ratio of
32:1. Upon melting the molten polymer was filtered through a 300
mesh (48 micron) screen (with an output of about 1 kilogram/10
minutes, about 115 rpm). The individual plaques of the target
polypropylene, HDPE, LLDPE, and polystyrene were then made through
molding in an Arburg 25 ton injection molder. The plaques had
dimensions of about 50 mm X 70 mm X 1.00 mm (with surface area of
about 0.71 dm.sup.2), and were made in a mold having a polished
mirror finish. The mold cooling circulating water was controlled at
a temperature of about 30 +/-1.degree. C.
[0030] Analyses for Surface-Available Silver
[0031] Each article was then exposed to an extract solution at room
temperature for 24 hours (or more, as listed below). In each
instance below, the extract solution used was a sodium-potassium
phosphate buffer solution, although any salt solution (e.g., sodium
chloride, calcium chloride, and the like) could also be utilized as
the test extract solution as long as proper silver extraction is
permitted with such solutions. Controls with silver antimicrobial
but no carboxylic acid salt were tested as comparisons.
[0032] The extraction procedure and analyses involved first
producing a standard plot of different silver concentrations within
a nitric acid solution. The silver preparations were prepared by
first weighing out 1000 ppm of silver into 100 mL volumetric flask
and adding 0.5 mL of a 5% nitric acid solution to the flask to the
fill line (to produce a 1 ppm silver standard). A further dilution
of 10 g of the 1 ppm preparation into a 100 mL volumetric flask and
then adding the remainder of 5% nitric acid solution (to produce a
100 ppb standard. A final 500 ppb standard was then prepared in
similar fashion with 5 g of the 100 ppb standard used. The
concentrations were then measured by utilization of inductively
coupled plasma spectroscopy for such silver content. The results
were then plotted for comparison with the eventual silver content
of the extract solutions below.
[0033] The extract solution a 1 X strength solution of a
sodium-potassium-phosphate solution (initially about 145 g of
sodium phosphate mixed with about 71 g of potassium phosphate
diluted in a 1 liter volumetric flask with deionized water, with a
subsequent dilution of 100 mL of this first solution to 1000 mL
with deionized water). The treated plaques were then individually
placed within a sealed plastic bag with a sufficient amount of the
extract solution to fully immerse the sample. The bag was then
placed and placed on an orbital shaker at 140 rpm and kept at room
temperature for 24 hours. After that time, 9.5 mL of the resultant
extract solution was then placed into a 15 mL vial with 0.5% of 70%
nitric acid added. The resultant test extract solution was then
subjected to ICP spectroscopy and the resulting measurements of
silver concentration were then plotted against the standards,
above. The measurements for the above plaque samples are as
follows:
EXPERIMENTAL SILVER EXTRACTION TABLE
[0034]
6 Example # Amount of Silver Detected ({circle over (3)}
g/dm.sup.2) 1 0.25 2 0.33 3 0.29 4 0.52 5 0.32 6 0.90 7 1.10 8 0.92
9 0.78 10 0.92 11 0.63 12 0.82 13 0.90 14 0.19 15 0.22 16 0.23 17
0.21 18 0.26 19 0.34 20 0.50 21 0.25 22 0.27 23 0.22 24 0.32 25
0.26 26 0.25 27 0.33 28 0.41 29 0.21 30 0.23 31 0.25 32 0.22 33
0.21 34 0.26 35 0.25 36 0.27 37 0.26 38 0.30 39 0.27 40 0.29 41
0.25 42 0.26 43 0.25 44 0.23 45 0.30 46 0.33 47 0.40 48 0.54 49
0.31 50 0.81 51 0.73 52 0.36 53 0.31 54 0.57 55 0.70 56 0.44 57
0.31 58 0.29 59 0.37 60 0.85 61 0.34 62 0.45 63 0.52 64 0.26 65
1.09 Control (PP) 0.17 (RC-5000)(1%) Control (PP) 0.69
(RC-2000)(1%) Control (PP) 0.58 (ZEOMIC)(1%) Control (HDPE) 0.22
(RC-5000)(1%) Control (LLDPE) 0.16 (RC-5000)(1%) Control (PS) 0.62
(RC-5000)(1%)
[0035] Thus, unexpectedly, in comparison with the controls, the
inventive articles exhibit increases (in differing degrees) of
available silver at the surfaces thereof, particularly in
polyolefin for silver zirconium phosphate types (RC-5000, RC-2000)
of at least 0.25 .mu.g/dm.sup.2, for silver zeolite of at least
0.75, and for styrenics any silver-containing antimicrobial of at
least 0.80.
[0036] There are, of course, many alternative embodiments and
modifications of the present invention which are intended to be
included within the spirit and scope of the following claims.
* * * * *