US6436420B1

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United States Patent

US006436420

BI

(2) (10) Patent No.: US 6,436,420 B1
Antelman (45) Date of Patent: Aug. 20, 2002
(54) HIGH PERFORMANCE SILVER (LID) OXIDE 4,101,719 A * 7/1978 Uetani et al. ...... .. 429/206
ANTIMICROBIAL TEXTILE ARTICLES 4,410,593 A 10/1983 Tomibe et al. 428/389
. 5,211,855 A 5/1993 Antelman. ... 210/758
(75) Inventor: Marvin S. Antelman, Rehovot (IL) 5,271,952 A 12/1993 Liang et al. 427/2
. . 5,336,499 A 8/1994 Antelman 424/405
(73) Assignee: Marantech Holding, LLC, East 5,458,906 A 10/1995 Liang « 427/2.31
Providence, RI (US) 5,676,977 A * 10/1997 Antelman 424/618
(*) Notice: Subject to any disclaimer, the term of this . .
patent is extended or adjusted under 35 * cited by examiner
US.C. 154(b) by 0 days.
(21) Appl. No.: 09/477,883 Primary Examiner—Thurman K Page
. Assistant Examiner—Liliana Di Nola-Baron
(22) Filed Jan. 5, 2000 (74) Attorney, Agent, or Firm—Pennie & Edmonds, LLP
(51) sees .. AOIN 25/34 57 ABSTRACT
(52) a 424/404, 424/443; 424/449; 67)
_ 424/402; 424/618; 514/495; 210/758; 210/764 Fibrous textile articles possessing enhanced antimicrobial
(8) Field of Search .... +. 210/758, 764; properties are prepared by the deposition or interstitial
424/404, 618, 402, 443, 449, 514/495 precipitation of tetrasilver tetroxide (Ag,O,) crystals within
(56) References Cited the interstices of fibers, yarns and/or fabrics forming such

U.S. PATENT DOCUMENTS

2,791,518 A 5/1957 Stokes et al... 117/120

articles.

19 Claims, No Drawings

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US 6,436,420 B1

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HIGH PERFORMANCE SILVER (1,11) OXIDE
ANTIMICROBIAL TEXTILE ARTICLES

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to textile articles possessing anti-
microbial properties and a method for their preparation.

2. Description of Related Art

Textile articles which have been treated to render such
articles microbicidal to microorganisms coming in contact
with the article are known in the prior art. Such articles
include those made from paper, fibers, woven and non-
woven textiles and like fabrics which are designed for use in
environments such as hospitals, food processing plants,
laboratories and other areas where maintenance of germ-free
conditions is essential.

For example, U.S. Pat. No. 2,791,518 discloses a method
of imparting microbicidal properties to articles such as
textiles by immersing the article in a first aqueous solution
containing a water-soluble basic nitrogen compound
(ammonia) and a monovalent silver salt soluble in said
solution, followed by a second immersion in a second
solution containing a second salt capable of ion exchange
with the silver salt such that a monovalent silver salt
precipitate is formed within the article. The formed silver
precipitate is sparingly water soluble and imparts microbi-
cidal properties to the articles so treated.

Similarly, U.S. Pat. No. 5,271,952 discloses a method of
treating fibers to render them electrically conductive as well
as anti-bacterial comprising immersing the fibers in a bath
comprising an aqueous solution of a source of divalent
copper ions, a reducing agent, sodium thiosulfate and a
source of iodide ions, whereby copper iodide is adsorbed
into the fibers. Similar techniques for rendering fibers con-
ductive or resistant to bacteria involving the use of copper
compounds are disclosed in U.S. Pat. Nos. 4,410,593 and
5,458,906.

It has also been disclosed that materials such as chlori-
nated hydantions may be grafted to textiles for the purpose
of imparting antimicrobial properties, ie Williams et al,
218” ACS National Meeting (1999) Abstracts, Cell 32;
C&EN September 6, page 36. However, textiles so treated
tend to suffer severe diminishment of antimicrobial proper-
ties after as few as 5 hours of laundering and are UV
unstable over long durations of exposure.

SUMMARY OF THE INVENTION

The invention provides a fibrous textile article containing
an antimicrobial agent selected from the group consisting of
tetrasilver tetroxide and derivatives thereof interstitially
deposited within said article, said agent present in said
article in an amount sufficient to impart antimicrobial prop-
erties to said article.

The invention also provides a process for imparting
antimocrobial properties to a fibrous textile article compris-
ing:

a. providing an aqueous solution containing a water

soluble silver salt;

b. contacting said article with said solution for a period of
time sufficient to uniformly wet said article with said
solution;

c. immersing said wetted article in a bath containing a
second aqueous solution containing a strong alkali and
a water soluble oxidizing agent and heating said bath

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for a period of time sufficient to interstitially precipitate
tetrasilver tetroxide within said article; and

d. removing said article from said bath.

Textile articles prepared in accordance with this
invention, particularly woven and non-woven hydrophilic
fabrics, exhibit outstanding antimicrobial resistance with
respect to pathogens such as bacteria, viruses, yeast and
algae, are resistant to degradation upon exposure to sunlight
(ultraviolet light) and maintain their excellent antimicrobial
properties even after a number of launderings.

DETAILED DESCRIPTION OF THE
INVENTION

Imparting antimicrobial properties to fiber and its derived
textile products is achieved in the instant invention by
interstitial deposition of the molecular crystal compound
tetrasilver tetroxide, i.e., silver (I, II) oxide. Said silver
moiety is the subject of several patents. U.S. Pat. No.
5,336,499, the disclosure of which is incorporated herein by
reference, describes the anti-pathogenic properties of said
silver oxide of formula Ag,O, and also the mechanism of
operation of the molecular device, based on a unique crystal
having two monovalent silver (Ag I) ions and two trivalent
silver (Ag IID) ions in the molecule. The mechanism of
killing pathogens described in the patent is based on the
differential silver electronic activity between Ag (I) and Ag
(IID resulting in electrocution of pathogens, followed by
binding chelation of pathogenic surfaces.

USS. Pat. No. 5,211,855 also discloses the use of Ag,O,
crystals to kill pathogens in utilitarian water bodies such as
swimming pools.

An antimicrobial spectrum of Ag,O, is to be found in a
published article written by the instant inventor in the annual
R&D issue of Soap Cosmetics Chemical Specialties 1994,
70, 3 p. 52-59 entitled “Silver (IL, II) Disinfectants”, shown
in Table 1. The spectrum is based on specifications of the
Association of Official Analytical Chemists (AOAC).

TABLE 1

Antimicrobial Spectrum of Ag,O_

MICROORGANISM MIC* (PPM)
Gram Negatives

Escherichia coll 10231 2.50
Escherichia coll 25254 2.50
Enterobacter cloacae 13047 2.50
Pseudomonas aeruginosa 9027 1.25-2.50
Gram Positives

Bacillus subtilis 6633 5.00
Micrococcus lutena 9341 1.25-2.50
Staphylococcus aureus 0927 2.50-5.00
Staphylococcus aureus 27543 5.00
Staphylococcus epidermidis 12228 0.625
Sireptococeus agalactiae 27956 1.25-5.00
Streptococcus faeciunt 10541 5.00
Streptococeus-pyogenes T958 2.50
Yeast and Mold

Candida albicans 16404 2.50-5.0
Saccharomyces cerevisiae 2601 1.25

“MIC = Miniinal Inhibitory Concentration.

In said article, reference is made to the fact that monova-
lent silver is more anti-pathogenic than mercury which is
more anti-pathogenic than copper, based on their oligody-
namic activity as articulated by J. G. Horsfal in his “Prin-
ciples of Fungicidal Action” (Chronica Botanica 1956). The

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relative efficacy of metallic moieties against pathogens has
been called the Horsfal series, and is as follows:

Ag>Hg>Cu>Cd>Cr>Ni>Co>Zn>Fe>Ca

The present inventor has found that with respect to a
Horsfal series dedicated to silver, the relative efficacy
against pathogens is as follows:

Ag,O,>Ag(IID>Ag(ID>Ag(D

The term “fibrous textile article” as used herein is
intended to encompass a wide variety of materials including
paper, natural or synthetic fibers, threads and yarns made
from materials such as cotton, rayon, wool, jute, nylon,
polyesters, polyacetates, polyacrylics as well as cellulosics
in general. More particularly, the term refers to fibers woven
into a fabric such as knitting, and non-woven hydrophilic
fabrics or webbing used in anti-pathogenic applications such
as in the medical field, hospitals, biotechnology and food.
and dairy processing. Exemplary textile products of this
genre include bandages, gauze, bandage pads, skin patches,
work clothes (both disposable and reusable), bed sheets,
masks, dust cloths, safety belts, surgical gowns, ambulance
blankets, stretchers, filter materials, diapers, underwear,
pajamas, video display terminal screens and the like.

For some antimicrobial applications, Ag ,O,, crystals may
be deposited within the interstices of fibrous articles by
simply soaking the article in an aqueous dispersion of the
crystals or by combining the crystals with a carrier medium
and applying this composition to the fibrous article. This
method of physical incorporation of the crystals is useful
where the article is composed of low density or loosely
associated fibers such as bandage pads, gauze pads and
loosely non-woven products, and particularly laminated
products wherein the treated fibrous article is subsequently
sandwiched between one or two peelable layers which tend
to keep the crystals trapped in the fibrous article until ready
for use. Also, antimicrobial paper products may be made by
simply mixing an aqueous dispersion of the Ag.,O, crystals
with paper pulp prior to calendaring the pulp.

However, physical incorporation of the crystals is less
effective where the treated article is a fiber or yarn or a
higher density woven or non-woven fabric, since the pre-
formed crystals can not sufficiently penetrate into the inter-
stices of such articles. In such cases, deposition of Ag,O,
material via interstitial precipitation is preferred.

Interstitial precipitation of Ag,O, material is accom-
plished by first providing an aqueous solution of a monova-
lent water soluble silver salt such as the nitrate perchlorate,
acetate, methanesulfonate or fluoride, most preferably silver
nitrate. Next the article to be treated, e.g., a fiber, yarn of a
woven or non-woven fabric, is thoroughly wetted with this
solution such that the article absorbs solution on fiber
surfaces as well at one or more of the interstices between
fibrils forming the fiber, between fibers forming the yarn or
non-woven fabric, or between the weft and woof yarns
present in woven fabrics. Wetting may be accomplished by
uniformly spraying the article or more preferably by dipping
the article in a bath of the silver salt solution for a period of
time sufficient for the article to absorb the requisite amount
of silver salt solution.

Next the wetted article is optionally squeezed to remove
excess solution and immersed in a heated bath containing a
second aqueous solution comprising a strong alkali and a
water soluble oxidizing agent, and heated for a period of
time sufficient to cause reaction leading to the interstitial
precipitation of tetrasilver tetroxide (Ag,,O,) crystal material

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in the interstices of the fibrous article. Suitable alkalis for
this purpose include sodium or potassium hydroxide, with
sodium hydroxide most preferred. Suitable oxidizing agents
include alkali metal persulfates, permanganates or
hypochlorites, but sodium and more preferably potassium
persulfate is the preferred oxidizer. Reaction in the bath is
accomplished by heating at a temperature of at least 85° C.,
more preferably at least 90° C. for a period of time sufficient
to maximize yield of Ag,O,, generally from about 30
seconds to about 5 minutes. After the reaction is completed,
the treated article is removed from the bath and may be
washed several times with water to remove soluble inpuri-
ties or unreacted reagant.

The quantity of Ag,O, material present in the resulting
article will generally be a function of the quantity of silver
salt sorbed by the article, which can vary depending on the
nature of the article, e.g., loose vs. tight weave fabrics or
whether the fiber is natural or synthetic, the former being
more absorbtive of the silver salt solution.

In general, the quantity of alkali present in the second bath
should be sufficient to maintain a strongly basic pH, ie.,
about 13+, and providing a slight molar excess of silver salt
over oxidizing agent is suitable to complete the reaction.
Thus the content of tetrasilver tetroxide interstitially pre-
cipitated within any given fibrous article may be controlled
by varying the concentration of the silver salt in the solution
used to first wet the article and appropriately adjusting the
quantities of alkali and oxidizing agent present in the
immersion solution at approximately stoichiometric levels.

The term “derivatives of Ag,O,” is intended to include
Ag,O, reaction products prepared by reacting Ag,O, with
suitable water soluble acids to give the corresponding Ag
(ID salts, e.g., reactions with fluoroboric acid or phosphoric
acid to give the Ag (II) fluoroborate or phosphate, as
disclosed in U.S. Pat. No. 5,107,295. Also included are
divalent silver nitrate and divalent silver halides prepared by
reacting Ag,O, with nitric acid or the corresponding
haloacids, e.g. HBr, HI or HCI as disclosed in U.S. Pat. No.
5,078,902. Trivalent silver derivatives such as Ag (III)
biguanide prepared in accordance with U.S. Pat. No. 5,223,
149 are also included.

Textile articles containing such derivatives would be
prepared by further contacting the Ag,O, containing article
in an additional step with an aqueous solution containing up
to stoichiometric amounts of the appropriate reagant(s)
sufficient to convert at least a portion of the Ag,O, to the Ag
(ID) or Ag (IID) derivative.

Textile articles containing such derivatives are less pre-
ferred for the purposes of this invention because some
derivatives may be generally more water soluble than
Ag,O,, require a further processing step in their manufac-
ture and are less effective as antimicrobial agents than
Ag,O, as shown in the silver Horsfal series described above.
However, the Ag(II) or Ag(III) derivatives of Ag,O, are
useful as antimicrobial agents in fabrics which are designed
for a single use such as bandages or disposable garments.

The content of the Ag,O, or its derivatives (based on
weight PPM silver) in the fabric may preferably range from
as little as 0.5 weight PPM up to about 50,000 weight PPM,
based on the weight of the textile article. The minimum
content should be sufficient to kill pathogens from which
protection is sought, whereas the maximum content is dic-
tated by factors such as economy and affect on fabric
properties. Generally speaking, the higher the silver content,
the more effective will be the antimicrobial properties of the
fabric. For most applications, silver content in the range of
from about 30 to about 10,000 weight PPM will provide
satisfactory antimicrobial properties.

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Antimicrobial properties are evaluated in accordance with
this invention using the Association of Official Analytical
Chemists (AOAC) test method 972.04, which is used pri-
marily to evaluate the bacteriostatic activity of laundry
additive disinfectants. In this test, a square or rectangular
sterile swatch of fabric is pressed into a petri dish containing
a layer of nutrient agar which has been inoculated with a
pathogen. Following a fixed period of incubation, each
fabric sample is evaluated by measuring the clear zones
adjacent the four sides of each test swatch as an index of
antimicrobial activity. The presence of clear zones along all
four sides of the swatch is indicative of antimicrobial
activity, rated 4/4. The width of the clear zones in millime-
ters is reasonably indicative of the degree of antimicrobial
activity.

The following examples are illustrative of the invention.

EXAMPLE 1

A swatch of virgin nylon webbing was immersed in an
aqueous solution containing dissolved silver nitrate at a
concentration of about 100 PPM silver maintained at room
temperature. After 30 seconds immersion time, the swatch
was removed from this solution and immersed in a hot
aqueous solution containing 7.2 g/liter each of NaOH and.
sodium persulfate, which solution is then boiled for one
minute (95-100° C.). The swatch was then removed from
the boiling solution, washed with water and dried. There was
perceived a hardly visible tan coating on the swatch fibers.
The content of Ag,O, in the fabric swatch, measured as
silver, was 89 weight PPM as verified by gravimetric analy-
sis.

EXAMPLES 2-6

Example 1 was repeated except that the concentration of
silver nitrate in the first solution and reagants in the second
solution were varied to provide the following Ag content in
the fabric swatch:

SOLUTION (PPM Ag) _ FABRIC (PPM Ag)

Ex2 890 35*
Ex 3 890 541
Ex 4 10,000 3970
Ex5 10,000 9140
Ex 6 10,000 9670

“Nylon fabric for this test was of a tighter weave than that used in
Example 1 which accounts for the lower silver take up.

AOAC antipathogenic tests on these textiles were per-
formed by an independent laboratory which was licensed by
a State environmental regulatory body. The marker organ-
isms used in conformity with AOAC test method 972.04
were Pseudemonas Aeroginosa (PA) as the Gram negative
bacteria marker, and Staphylococcus Aureus (SA) for Gram
positive bacteria.

The tests were conducted in terms of inhibition of cultures
of the bacteria. Two swatches were used for the tests in
contact with the cultures. The swatches were 1.5 inches wide
and weighed about 69 mg./cm?. Each swatch had four sides,
and two swatches were used with each representative culture
so that a total of eight trials were reflected with each
bacterium. An 8/8 inhibition would indicate 100% efficacy.
However, the test protocol went beyond the specifications of
the AOAC method insofar that the actual average inhibition
zone width in millimeters was recorded for both swatches
tested. These results were then combined with the afore-

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mentioned anti-microbial spectrum shown in Table 1 which
includes the marker bacteria of the AOAC tests, and extrapo-
lated. The conclusion was that the preferred embodiments of
the invention were 100% effective against all of the
microbes shown in Table 1 and against salmonella and the
AIDS virus based on the previous independent results
obtained with silver (I, II) oxide.

Representative results with nylon fabric are shown in
Table 2. Generally, the degree of microbial activity varies
directly with the silver concentration. In addition to the high
performance anti microbial properties of the fabrics, they
withstood wear and could be considered permanent insofar
that tested fabrics withstood 100 hours of laundering and
600 hours of ultra violet exposure. Laundering is evaluated
using hot water and detergent using the standard test of the
American Association of Textile Chemists (AATC).

TABLE 2

Antimicrobial Performance of Precipitated Ag,O,

Inhibition Inhibition
Example Silver -Zone-SA Zone-PA Inhibition
Number PPM (mm) (mm) Index

1 89 3.2 13 5/8

2 35 18 2.0 8/8

3 S41 55 5.1 3/8

4 3970 5.8 2.6 3/8

5 9140 58 28 gs

6 9670 6.1 48 8/8

EXAMPLE 7

An independent medical researcher in Israel obtained a
very virulent strain of Staph from a patient at the Shaarei
Tzedek Hospital in Jerusalem. The patient subsequently died
from infection. This strain was evaluated as more virulent
than any of the other Staph microorganisms listed in Table
1 by the pathology staff at the hospital. This Staph strain was
utilized as the Staph source, and the otherwise exact test
protocol described above was repeated. The silver concen-
tration of the test swatch was found to be 9,138 PPM. Only
one test swatch was used for the Staph evaluation. It tested
at 4/4 with a much diminished average inhibition zone of
0.50 mm, which was to be expected for the more virulent
strain. The values were extrapolated for all Gram positive
bacteria listed in Table 1. It was concluded that precipitated
Ag,O, was capable of inhibiting all of the listed Gram
positive bacteria. The extrapolation took into consideration
a theoretical calculation of the reduction of the Staph
inhibition zone, were the conventional Staph aureus organ-
isms to display the listed MIC range of 2.5—5.0 PPM. Since
the inhibition zone is inversely proportional to the MIC, one
can calculate that the MIC for the virulent Staph strain was
40.5-61.0 PPM. By applying the same reasoning to the
Gram Negative microorganisms for their PA marker, one can
claim inhibition as well for all Gram Negative bacteria listed
in Table 1 by Ag,O,.

EXAMPLE 8

The method of Example 1 was repeated with larger
amounts of webbing utilizing one-foot lengths. Accordingly,
webbing was obtained having respectively 4730 and 9430
PPM of silver. These materials were dyed orange, and the
dye completely covered and hid the brown/black color
imparted to the virgin webbing by the tetroxide at these
relatively high levels. After dyeing, swatches of the webbing

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were cut from the master rolls and were then evaluated in the
same manner as described above by exposure to Staph
aureus. All swatches indicated an 8/8 score, with average
inhibition zones of 6.3 and 6.0 respectively for the 4730 and
9430 PPM samples. Lengths of the dyed webbing were
subjected to 100 hours of laundering in accordance with the
AATC method, after which bacteriostatic efficacy was again
evaluated. Visual inspection after laundering revealed frayed
webbing. Nevertheless, both materials exhibited an 8/8 score
with an improvement in inhibition zones to 7.0 for Staph
aureus. This indicated that the laundry wear tended to
expose fresh surface of tetroxide from the fabric interstices.
Swatches were again taken from these materials and
exposed to 600 hours of ultra violet light in a weathering
test. Evaluations of the UV exposed samples with Staph
aureus again indicated scores of 8/8 for both concentrations
of silver, with inhibition zones of 6.5 and 4.6, respectively
for the 4730 and 9430 PPM silver concentration webbing.
Accordingly, ultra violet exposure did not interfere with
bacteriostatic activity.

Comparative Example

Monovalent silver iodide was interstitially precipitated
within nylon fabric such that the fabric contained 4895 PPM
silver. Test swatches were prepared and evaluated against
SA and PA pathogens by the test procedure described above.
The Inhibition Index for SA was 7/8 and for PA was 0/8. In
addition, the SA inhibition zone was only about 0.5 mm.

Fabrics treated in accordance with this invention hold
promise for many antimicrobial applications ranging from
preventing jock itch when applied to athletic supporters to
preventing scabies and bed sores with treated bed sheets or
hospital gowns used in nursing homes and hospitals.

What is claimed is:

1. A fibrous textile article containing an antimicrobial
agent selected from the group consisting of tetrasilver
tetroxide and derivatives thereof interstitially deposited
within said article, said agent present in said article in an
amount sufficient to impart antimicrobial properties to said
article.

2. The article of claim 1 wherein said agent is tetrasilver
tetroxide.

3. The article claim 2 wherein said crystals are intersti-
tially deposited by interstitial precipitation.

4. The article of claim 3 wherein said textile article is a
woven or non-woven fabric.

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5. The article of claim 4 wherein said agent is present
within said fabric at a level in the range of about 0.5 to about
50,000 weight PPM, based on the weight of silver.

6. The article of claim 5 containing about 30 to about
10,000 PPM of said agent.

7. The article of claim 3 wherein said antimicrobial
properties are sufficient to yield microbial inhibition zones
extending beyond 1 mm of fabric swatch borders as mea-
sured by AOAC test 972.04.

8. The article of claim 4 wherein said fabric is capable of
withstanding at least 100 hours of laundering without sig-
nificant loss of antimicrobial efficacy.

9. The article of claim 4 wherein said fabric is capable of
withstanding at least 600 hours of exposure to ultraviolet
light without significant loss of antimicrobial efficacy.

10. A method for producing a textile article having
antimicrobial properties, comprising:

contacting the article with a first solution, the first solution

comprising silver; and

contacting the article with a second solution, the second

solution comprising an amount of oxidizing agent
sufficient to deposit an antimicrobially active amount of
tetrasilver tetroxide within the article.

11. The method of claim 10 wherein said silver comprises
silver nitrate.

12. The method of claim 10 wherein said second solution
comprises an amount of alkali sufficient to provide a pH of
at least about 13.

13. The method of claim 10 wherein said oxidizing agent
is potassium persulfate.

14. The method of claim 10 wherein said bath is heated to
a temperature in excess of 85° C.

15. The method of claim 10 wherein said article contains
from about 0.5 to about 50,000 weight PPM of precipitate,
based on the weight of silver.

16. The method of claim 15 wherein said article contains
about 30 to about 10,000 PPM of said precipitate.

17. A method for imparting antimicrobial properties to a
fibrous article, comprising:

providing an aqueous dispersion of Ag,O, crystals; and

contacting the article with the aqueous dispersion.

18. The method of claims 17, wherein the article com-
prises low density or loosely associated fibers.

19. The method of claim 18, wherein the article comprises

5 a bandage, gauze pad, or a laminated product.

Oe Oe