U.S. patent application number 12/762574 was filed with the patent office on 2010-10-28 for selectively permeable protective structure and methods for use.
This patent application is currently assigned to E. I. DU PONT DE NEMOURS AND COMPANY. Invention is credited to John Chu Chen, Donna Lynn Visioli.
Application Number | 20100273379 12/762574 |
Document ID | / |
Family ID | 42341531 |
Filed Date | 2010-10-28 |
United States Patent
Application |
20100273379 |
Kind Code |
A1 |
Chen; John Chu ; et
al. |
October 28, 2010 |
SELECTIVELY PERMEABLE PROTECTIVE STRUCTURE AND METHODS FOR USE
Abstract
An article comprising a selectively permeable protective
structure wherein the article is wrapped or covered with the
structure and a method for limiting damage to the article due to
corrosion or mold growth, comprising wrapping or covering the
article in the selectively permeable protective structure. The
selectively permeable structure comprises a membrane having a
moisture vapor permeation value of at least 200 g-mil/m.sup.2/24 h
and barrier to liquid water, and optionally a supporting
substrate.
Inventors: |
Chen; John Chu; (Hockessin,
DE) ; Visioli; Donna Lynn; (Lower Gwynedd,
PA) |
Correspondence
Address: |
E I DU PONT DE NEMOURS AND COMPANY;LEGAL PATENT RECORDS CENTER
BARLEY MILL PLAZA 25/1122B, 4417 LANCASTER PIKE
WILMINGTON
DE
19805
US
|
Assignee: |
E. I. DU PONT DE NEMOURS AND
COMPANY
Wilmington
DE
|
Family ID: |
42341531 |
Appl. No.: |
12/762574 |
Filed: |
April 19, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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61172036 |
Apr 23, 2009 |
|
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Current U.S.
Class: |
442/59 ;
427/398.1; 428/221; 428/319.9; 525/190 |
Current CPC
Class: |
B32B 27/12 20130101;
B32B 2307/412 20130101; C08L 23/0876 20130101; B32B 2307/558
20130101; C08L 23/0869 20130101; B32B 27/322 20130101; B32B
2264/102 20130101; B32B 2307/406 20130101; B32B 2307/75 20130101;
C08L 23/0876 20130101; Y10T 428/249921 20150401; B32B 27/304
20130101; B32B 27/08 20130101; B32B 5/026 20130101; B32B 27/06
20130101; Y10T 442/20 20150401; B32B 5/022 20130101; B32B 27/10
20130101; B32B 2250/42 20130101; B32B 2260/021 20130101; B32B
2307/734 20130101; B32B 2262/06 20130101; B32B 2262/062 20130101;
B32B 2307/50 20130101; B32B 2553/00 20130101; B32B 5/024 20130101;
B32B 27/40 20130101; B32B 27/18 20130101; B32B 2307/546 20130101;
Y10T 428/249993 20150401; B32B 5/08 20130101; B32B 27/327 20130101;
B32B 2307/554 20130101; B32B 2262/0261 20130101; B32B 2262/0253
20130101; B32B 2262/101 20130101; B32B 2307/7265 20130101; C08L
2205/03 20130101; B32B 2262/106 20130101; B32B 27/306 20130101;
B32B 2264/108 20130101; B32B 2307/304 20130101; C08L 2666/02
20130101; C08L 2666/02 20130101; B32B 2262/0269 20130101; C08L
23/0869 20130101; B32B 27/20 20130101; B32B 27/308 20130101; B32B
27/32 20130101; B32B 2270/00 20130101; B32B 2260/046 20130101; B32B
3/266 20130101; B32B 27/36 20130101; B32B 2262/14 20130101; B32B
2262/0276 20130101; B32B 2307/72 20130101; B32B 2264/104 20130101;
C08K 5/09 20130101; B32B 2262/08 20130101; C08L 2205/02 20130101;
B32B 2307/724 20130101 |
Class at
Publication: |
442/59 ; 525/190;
428/221; 428/319.9; 427/398.1 |
International
Class: |
D04H 13/00 20060101
D04H013/00; C08L 31/02 20060101 C08L031/02; B32B 3/26 20060101
B32B003/26; D03D 15/00 20060101 D03D015/00; B05D 3/00 20060101
B05D003/00 |
Claims
1. A selectively permeable structure wherein The structure has a
moisture vapor transmission rate of at least 50 g/m.sup.2/24 h; the
structure comprises or is produced from a selectively permeable
membrane, or permeable layer, and optionally a substrate; the
permeable membrane or permeable layer has a moisture vapor
permeation value of at least 200 g-mil/m.sup.2/24 h and a
water-entry pressure of at least 150 cm H.sub.2O; the permeable
membrane or permeable layer comprises or is produced from, based on
the weight of the membrane or layer, (a) 30 to 50% of an organic
acid-modified ionomer, (b) 1 to 30% of a dicarboxylic acid
derivative-derived polymer, and (c) one or more non-ionomeric
ethylene-containing polymers; the organic acid-modified ionomer is
a blend, based on the weight of the blend, of 70 to 97% of an
ethylene acid copolymer or the ionomer of the acid copolymer and 3
to 30% of an organic acid or salts thereof; the ethylene acid
copolymer has the formula of E/X/Y; E represents copolymerized
units of ethylene; X is present in about 2 to about 35 weight % of
the copolymer and represents copolymerized units of at least one
C.sub.3 to C.sub.8 .alpha.,.beta.-ethylenically unsaturated
carboxylic acid; and Y is present in 0 to about 35 weight % of the
copolymer and represents copolymerized units of alkyl acrylate or
alkyl methacrylate; at least 50% of the combined acidic groups in
the acid copolymer and the organic acid are neutralized to salts
with metal ions; at least 50% of the metal ions are alkali metal
ions; and the ethylene-containing polymer does not comprise a
dicarboxylic acid derivative and a carboxylic acid derivative.
2. The article of claim 1 wherein the organic acid is an acid
having 4 to 36 carbon atoms, or salts thereof; the dicarboxylic
acid derivative-derived polymer comprises 0.1 to 15%, based on the
weight of the polymer, of at least one dicarboxylic acid anhydride
unit or dicarboxylic acid monoalkyl ester unit; and the
ethylene-containing polymer is selected from the group consisting
of polyethylene homopolymer, copolymer of ethylene and an
.alpha.-olefin, copolymer of ethylene and a diolefin, copolymer of
ethylene and vinyl acetate, copolymer of ethylene and acrylic
ester, copolymer of ethylene and methacrylic ester, copolymer of
ethylene and carbon monoxide, or combinations of two or more
thereof.
3. The structure of claim 2 wherein the structure comprises the
substrate; the permeable membrane or permeable layer is coextruded
with, impregnated with, incorporated with, laminated with, or
coated on, a supporting substrate; the substrate comprises textile
or porous sheet material; the permeable membrane or permeable layer
is a nonporous monolithic membrane; and the dicarboxylic acid
derivative-derived polymer is selected from the group consisting of
ethylene/maleic acid monoalkyl ester copolymer, an ethylene/maleic
anhydride copolymer, terpolymer of ethylene/alkyl
(meth)acrylate/maleic anhydride, terpolymer of ethylene/alkyl
(meth)acrylate/maleic acid monoalkyl ester, ethylene homopolymer or
copolymer containing repeat units derived from maleic anhydride or
maleic acid monoalkyl ester, and combinations of two more
thereof.
4. The structure of claim 3 further comprising a layer including
fabrics of aramid, glass fiber, or combinations thereof.
5. The structure of claim 3 wherein the substrate is one or more
porous films, flash spun non-woven fabrics, woven fabrics of
synthetic fibers, natural fibers, scrims, or filter materials.
6. The structure of claim 5 wherein the substrate is one or more
flash spun polypropylene, flash spun polyester, or woven fabrics of
synthetic fibers.
7. The structure of claim 3 wherein the structure comprises the
substrate having impregnated therein, or laminated or coated
thereon the permeable membrane.
8. The structure of claim 7 wherein at least 50% of the metal ions
are sodium ions.
9. The structure of claim 7 wherein at least 50% of the metal ions
are potassium ions.
10. The structure of claim 7 wherein the substrate is one or more
porous films, flash spun non-woven fabrics, woven fabrics of
synthetic fibers, natural fibers, scrims, filter materials, or
combinations of two or more thereof.
11. The structure of claim 9 wherein the substrate is flash spun
polypropylene, flash spun polyester, woven fabric of synthetic
fiber, natural fiber, or combinations of two or more thereof.
12. An article comprising a selectively permeable protective
membrane and a substrate wherein the protective membrane is
extrusion coated, laminated, or adhesive-bonded, to the substrate;
the article is wrapped or covered with the membrane, has a moisture
vapor transmission rate of at least 50 g/m.sup.2/24 h; the membrane
has a moisture vapor permeation value of at least 200
g-mil/m.sup.2/24 h and a water-entry pressure of at least 150 cm
H.sub.2O; the membrane comprises or is produced from, based on the
weight of the membrane, (a) 30 to 45% of an organic acid-modified
ionomer, (b) 1 to 30% of a dicarboxylic acid derivative-derived
polymer, and (c) one or more non-ionomeric ethylene-containing
polymers; the organic acid-modified ionomer is a blend, based on
the weight of the blend, of 70 to 90% or of 70 to 97% of an
ethylene acid copolymer or the ionomer of the acid copolymer and 3
to 30% of an organic acid or salts thereof each having 4 to 36
carbon atoms; the ethylene acid copolymer is derived from ethylene,
about 2 to about 35% of at least one C.sub.3 to C.sub.8
.alpha.,.beta.-ethylenically unsaturated carboxylic acid, and 0 to
about 35% of alkyl (meth)acrylate; at least 50% of the combined
acidic groups in the acid copolymer and the organic acid are
neutralized to salts with metal ions; at least 50% of the metal
ions are alkali metal ions; and the ethylene-containing polymer
does not comprise a dicarboxylic acid derivative and a carboxylic
acid derivative.
13. The article of claim 12 wherein the dicarboxylic acid
derivative-derived polymer is a dipolymer of ethylene and a maleic
acid monoalkyl ester, a dipolymer of ethylene and maleic anhydride,
terpolymer of ethylene/alkyl (meth)acrylate/maleic anhydride,
terpolymer of ethylene/alkyl (meth)acrylate/maleic acid monoalkyl
ester, ethylene homopolymer or copolymer containing repeat units
derived from maleic anhydride or maleic acid monoalkyl ester, or
combination of two or more thereof; the ethylene-containing polymer
is selected from the group consisting of polyethylene homopolymer,
copolymer of ethylene and an .alpha.-olefin, copolymer of ethylene
and a diolefin, copolymer of ethylene and vinyl acetate, copolymer
of ethylene and acrylic ester, copolymer of ethylene and
methacrylic ester, copolymer of ethylene and carbon monoxide, or
combinations of two or more thereof; and the substrate is textile
or porous sheet material; the substrate and the selectively
permeable structure are in overlying fashion; and the membrane is a
nonporous monolithic membrane.
14. The article of claim 13 wherein the dicarboxylic acid
derivative-derived polymer comprises 0.1 to 15%, based on the
weight of the polymer, of at least one dicarboxylic acid anhydride
unit or maleic acid monoalkyl ester unit.
15. The article of claim 14 wherein the article further comprises a
layer including fabrics of aramid, glass fiber, or combinations
thereof.
16. The article of claim 14 wherein the substrate is selected from
the group consisting of porous film, flash spun non-woven fabric,
woven fabric of synthetic fiber, natural fiber, scrim, filter
material, and combinations of two or more thereof; and at least 50%
of the metal ions are sodium ions or potassium ions.
17. The article of claim 14 wherein the substrate is selected from
the group consisting of flash spun polypropylene, woven fabric of
synthetic fiber, natural fiber, and combinations of two or more
thereof and at least 50% of the metal ions are sodium ions or
potassium ions.
18. The article of claim 17 further comprising at least one heat
insulation layer, cushioning layer, or textile layer.
19. A method comprising preparing a first composition comprising an
organic acid-modified ionomer; melt blending the first composition
with one or more non-ionomeric ethylene-containing polymers to
provide a second composition; melt blending the second composition
with a dicarboxylic acid derivative-derived polymer to provide a
molten third composition; contacting a substrate with the molten
third composition to adhere, embed, or impregnate the molten
composition to the substrate or adhere, embed, or impregnate the
substrate to the molten third composition to provide the multilayer
structure; and cooling the multilayer structure to allow the molten
third composition to cool and solidify; wherein the organic
acid-modified ionomer, the ethylene-containing polymer, the
dicarboxylic acid derivative-derived polymer, and the substrate are
each as recited in claim 1.
20. The method of claim 19 wherein the dicarboxylic acid
derivative-derived polymer is selected from the group consisting of
dipolymer of ethylene and an alkyl acrylate, ethylene homopolymer
or copolymer, and combinations thereof; the ethylene-containing
polymer is selected from the group consisting of polyethylene
homopolymer, dipolymer of ethylene and an .alpha.-olefin, copolymer
of ethylene and a diolefin, a second ethylene-containing copolymer,
or combinations of two or more thereof; the second
ethylene-containing polymer is produced from copolymerization of
ethylene with at least one polar monomer selected from the group
consisting of vinyl acetate, acrylic ester, and carbon monoxide;
and the substrate is textile or porous sheet material; the
substrate and the selectively permeable structure are in overlying
fashion; and the membrane is a monolithic membrane.
Description
[0001] This application claims the benefit of U.S. Provisional
Application No. 61/172,036, filed Apr. 23, 2009, now pending, the
entire disclosure of which is incorporated herein by reference.
[0002] This invention relates to a selectively permeable structure
for covering objects during transportation and storage and to a
method for reducing damage to an article due to corrosion or mold
growth. It also relates to a method for preparing the selectively
permeable structure.
BACKGROUND
[0003] Equipment is often wrapped or packaged with film or fabric
tarpaulins, hoods or other covers to prevent surface damage during
transportation and storage. These covers may be prepared from high
barrier (highly moisture impermeable) films and fabrics (see, e.g.,
http://www.heritagepackaging.com/productservices/barrierpackaging/bpbasic-
s/bp basics.htm).
[0004] Many relatively small items are shipped on pallets, that is,
platforms that are easily moved by forklifts or small cranes.
Pallets provide convenience in loading and unloading goods from
shipping containers, and in moving smaller amounts of goods over
shorter distances, such as within warehouses, or to deliver a
retail quantity. The small items may be unpackaged or packaged, for
example in bags or boxes, when they are placed on the pallets.
[0005] A loaded pallet must have integrity and stability, so that
the goods are not damaged or lost during shipping. To provide the
necessary integrity and stability, the pallet and its load have
been typically wrapped together in film, for example overlapping
layers of polyethylene stretch wrap that may be applied by machine
or by hand. See, e.g., US RE38429. Other generally practiced
methods of providing integrity and stability to loaded pallets
include wrapping the pallet and its load in heat shrinkable film,
encasing the loaded pallet in a sheath or "hood" which may be heat
shrinkable or stretchable, and containing the goods in a single
carton or box. These methods are sometimes referred to,
individually or collectively, as "pallet unitizing".
[0006] Using barrier films for wrapping small objects or articles
in sealed bags is generally suitable since the object may be dried
before being sealed in the bags and/or drying agents may be
included inside the sealed bags. This approach is less suitable for
large objects such as vehicles, boats, motors, machinery,
industrial goods, pallets or containers holding smaller articles,
and other bulky equipment because the covers are typically not
hermetically sealed around the object and thorough drying of the
object may not be feasible. This may be especially problematic
during storage or when shipping by ship or railroad, because the
large objects may be exposed to adverse weather conditions for long
periods of time. Atmospheric moisture and/or rain may enter the
space under the cover and be trapped and condense. With high
barrier covers, there is no way for water to permeate back outside
the cover, resulting in a buildup of moisture inside the cover,
leading to the possibility of corrosion.
[0007] Large amounts of money are lost each year because of
corrosion of, for example, iron, steel, and other metals. There are
many factors affecting corrosion rate including moisture, oxygen,
and salt presence. A common corrosion occurs due to electrochemical
reactions at high humidity conditions. For example, when iron is
exposed to moist air, it reacts with oxygen to form rust (iron
oxide). The result of corrosion may be the formation of metal oxide
that flakes off easily, causing extensive pitting thereby causing
structural weakness and disintegration of the metal. Corrosion can
also affect other properties of metal parts such as reducing
conductivity or increasing surface roughness so that moving parts
become unable to move freely.
[0008] In addition to corrosion of metals, mold growth may occur in
the condensed moisture on the surface of the equipment.
[0009] Using a film or cover with a high water vapor transmission
rate can prevent condensation of water inside the cover by allowing
equilibration of the trapped moisture back into the surrounding
atmosphere. Using such a film prevents or reduces rust formation
and corrosion and reduces the opportunity for mold growth.
[0010] Various permeable materials having a wide range of
mechanical and transport properties are known. Depending upon the
particular application in which the permeable material is to be
employed, however, certain combinations of properties are required.
For a protective cover application, it is desirable that the
material transports water vapor, but blocks the transport of liquid
water or other fluids, and be lightweight and flexible over a broad
temperature range. A need exists for a material that can be a
flexible, solid material with membrane characteristics that
facilitate the transport of water vapor, for example, from
equipment inside a cover to the atmosphere and block entry of
liquids such as water, oil or corrosive fluids.
[0011] Various references describe semipermeable materials produced
from a variety of polymers that may be useful for protective
covers. See e.g., U.S. Pat. No. 6,579,948. Recently protective
fabrics comprising a selectively permeable membrane comprising
organic acid-modified ionomer compositions have been disclosed
(U.S. Pat. No. 7,514,380).
[0012] Many previous permeable membranes are microporous (i.e.,
permeable due to the presence of microscopic pores through which
vapor can pass). Microporous membranes, which may be laminated on
or between nonwoven textiles, have increased permeability, but may
not provide adequate barriers to liquids because of their
nonselective permeability. Liquids under pressure may be able to
penetrate the pores. Most microporous films are biaxially oriented,
so only a small amount of shrinkage is possible, and they cannot be
shrunk without losing their porosity. They may also have low tear
strength and their surfaces may be easily fouled, thereby losing
permeability.
[0013] Because no single material has emerged which satisfies all
of the technical requirements and that presents a cost-effective
alternative, it is desirable to provide a selectively permeable
membrane or structure or layer that displays a combination of
mechanical properties, low temperature flexibility, selective
transport, ease of processability, and cost-effectiveness, so as to
render it suitable for use as a protective cover for objects that
limits corrosion and/or mold growth.
SUMMARY OF THE INVENTION
[0014] An article or package comprises or is produced from a
selectively permeable protective structure wherein the structure
comprises, consists essentially of, or is produced from a
selectively permeable membrane; the membrane can comprise, consist
essentially of, or be produced from a composition comprising,
consisting essentially of, or produced from
[0015] (a) 30 to 50 weight %, based on the combination of (a), (b)
and (c), of a blended combination of
[0016] (1) 70 to 90 weight %, based on the combination of (1) and
(2), of one or more ethylene acid copolymers or ionomers of the
acid copolymers such as one having the formula of E/X/Y wherein E
represents copolymerized units of ethylene, X is present in about 2
to about 35 weight % of the copolymer and represents copolymerized
units of at least one C.sub.3 to C.sub.8
.alpha.,.beta.-ethylenically unsaturated carboxylic acid, and Y is
present in 0 to about 35 weight % of the copolymer and represents
copolymerized units of alkyl acrylate or alkyl methacrylate;
[0017] (2) 3 to 30 weight %, based on the combination of (1) and
(2), of one or more organic acids such as one having from 4 to 36
carbon atoms, or salts thereof; wherein at least 50% of the
combined acidic groups in the acid copolymer and the organic acid
are nominally neutralized to salts with metal ions; wherein at
least 50% of the metal ions are alkali metal ions;
[0018] (b) one or more, preferably non-ionomeric,
ethylene-containing polymers such as polyethylene homopolymers,
dipolymers of ethylene and an .alpha.-olefin, dipolymers of
ethylene and a diolefin, and ethylene copolymers (or dipolymers)
obtained from copolymerization of ethylene with at least one polar
monomer selected from the group consisting of vinyl acetate,
acrylic ester, methacrylic ester and carbon monoxide, wherein the
ethylene-containing polymer does not comprise a dicarboxylic acid
derivative, and
[0019] (c) 1 to 30 wt %, based on the combination of (a), (b) and
(c), of a dicarboxylic acid derivative-derived polymer such as one
comprising 0.1 to 15 wt % of dicarboxylic acid derivative, for
example, an anhydride, an ethylene/alkyl acrylate/methacrylic acid
or acrylic acid terpolymer, an ethylene/maleic acid monoalkyl ester
copolymer, or combination of two or more thereof; wherein (a), (b)
and (c) total 100 wt %.
[0020] The membrane may have a moisture vapor permeation value
(MVPV) of at least 200 g-mil/m.sup.2/24 h and high water-entry
pressure; and the selectively permeable structure has a moisture
vapor transmission rate (MVTR) of at least 30 g/m.sup.2/24 h or at
least 30 g/m.sup.2/24 h. The MVPV is measured at 37.8.degree. C.
and 100% relative humidity according to ASTM F-1249.
[0021] A method for limiting damage to an article due to corrosion
or mold growth, comprising wrapping or covering the article in a
selectively permeable protective structure wherein the structure
can be the same as that disclosed above.
[0022] A method for preparing a selectively permeable multilayer
structure or article comprising or consisting essentially of:
[0023] 1) preparing a first composition comprising, consisting
essentially of, or consisting of
[0024] (i) one or more ethylene acid copolymers; and
[0025] (ii) one or more organic acids; wherein at least 50% of the
combined acidic groups in the acid copolymer and the organic acid
are nominally neutralized to salts with metal ions and at least 50%
of the metal ions are alkali metal ions;
[0026] 2) melt blending the first composition with one or more
non-ionomeric ethylene-containing polymers selected from the group
consisting of polyethylene (PE) homopolymers, copolymers of
ethylene and an .alpha.-olefin, copolymers of ethylene and a
diolefin, and ethylene copolymers obtained from copolymerization of
ethylene with at least one polar monomer selected from the group
consisting of vinyl acetate, acrylic ester, methacrylic ester and
carbon monoxide, wherein ethylene-containing polymer does not
comprise a dicarboxylic acid derivative, to provide a second
composition;
[0027] (3) melt blending the second composition with a polymer
comprising 0.1 to 15 weight % of a dicarboxylic acid derivative
selected from the group consisting of maleic anhydride, citraconic
anhydride, itaconic anhydride, tetrahydrophthalic anhydride,
monoalkyl esters of maleic acid, fumeric acid, citraconic acid,
itaconic acid or tetrahydrophthalic acid, and combinations thereof,
to provide a third composition in a molten condition;
[0028] 4) contacting a substrate with the molten third composition
to adhere, embed, or impregnate the melted composition to the
substrate or adhere, embed, or impregnate the substrate to the
molten third composition to provide a coated substrate with the
third composition in a molten condition;
[0029] 5) cooling the coated substrate to allow the molten third
composition to cool and solidify.
DETAILED DESCRIPTION OF THE INVENTION
[0030] The entire disclosures of all references are incorporated
herein by reference Tradenames or trade marks are shown in upper
case. The word(s) following the verb "is" can be a definition of
the subject.
[0031] "(Meth)acrylic acid" includes methacrylic acid and/or
acrylic acid and "(meth)acrylate" includes methacrylate and/or
acrylate.
[0032] "Selectively permeable" means permeation is allowed only to
certain molecules in a specific state such as vapor or gas and not
to other molecules or in a different state such as liquid or solid.
Such molecules can be dissolved or dispersed in the matrix of
certain materials such as a film or sheet of the composition
disclosed herein and thereafter be diffused or migrated through the
material.
[0033] A selectively protective permeable membrane or layer may be
coextruded with, impregnated with, incorporated with, laminated
with, adhesive-bonded to, coated on, or otherwise adhered to, a
supporting substrate as discussed hereinbelow. The permeable
membrane or layer preferably is non-porous.
[0034] The selectively permeable membrane may have MVPV of at least
200, at least 800, at least 900, at least 1200, at least 2000, at
least 4,000 g-mil/m.sup.2/24 h, or even higher. MVPV is an
indicator of the permeability of the composition that makes up the
membrane, by measuring moisture permeation of the membrane, which
may be a film or sheet that is normalized to 1 mil thickness.
[0035] Selectively permeable protective covers may have MVTR of at
least 30, at least 50, at least 100, at least 500, or at least 1000
g/m.sup.2/24 h, or even higher. MVTR measures total moisture vapor
transmitted through a film during a unit time, disregarding the
structure thickness. For a membrane of a given composition and
MVPV, MVTR decreases as the thickness increases.
[0036] A selectively permeable protective structure provides a
combination of mechanical properties, low temperature flexibility,
selective transport, ease of processability, and
cost-effectiveness.
[0037] The composition can be formed into a monolithic or
continuous membrane that functions as a selectively permeable
barrier. Monolithic continuous membranes, in contrast to
microporous membranes, have high water-entry pressure and are
waterproof and liquidproof. High water-entry pressure refers to
>150 cm (or >250 cm or >500 cm) H.sub.2O hydrostatic head,
as described in DIN EN20811:92.
[0038] Therefore, monolithic membranes provide barriers to liquids
such as water, while still allowing permeability to water vapor
under appropriate conditions. A monolithic barrier is also
effective at preventing exposure to liquids such as water,
solvents, oils, corrosive fluids and the like, or particulates or
solids, including dust, irritants, mold spores, allergens, pollen,
animal dander, hair and the like.
[0039] The selectively permeable membrane may be selective to
liquid penetrants depending on the size and polarity of the
penetrants, i.e., has selectivity so as to be capable of allowing
water to diffuse through at a higher rate than virtually all
organic liquids having a molecular weight higher than that of
methanol.
[0040] The selectively permeable protective structure may be
prepared by preparing a first composition comprising one or more
ethylene acid copolymers; and one or more organic acids wherein at
least 50% of the combined acidic groups in the acid copolymer and
the organic acid are nominally neutralized to salts with metal ions
and at least 50% of the metal ions are alkali metal ions; melt
blending the first composition with an ethylene-containing polymer
and a dicarboxylic acid derivative-containing copolymer to provide
a molten composition; contacting a substrate with the molten
composition to adhere, embed, or impregnate the melted composition
to the substrate or adhere, embed, or impregnate the substrate to
the third composition to provide a coated substrate; and cooling
the coated substrate to allow the molten composition to cool and
solidify. The components of the composition and the methods used to
prepare the selectively permeable protective structure are
described more fully below.
[0041] The acid copolymers used to make the compositions are
preferably "direct" or "random" acid copolymers. "Direct"
copolymers are polymers polymerized by adding all monomers
simultaneously, as distinct from a graft copolymer, where another
monomer is grafted onto an existing polymer, often by a subsequent
free radical reaction.
[0042] Examples of X include unsaturated acids such as acrylic acid
or methacrylic acid. Preferably X is from 5 to 25 weight % of the
E/X/Y copolymer.
[0043] Notable are E/X/Y copolymers wherein Y is 0 weight % of the
polymer (that is, an E/X dipolymer). When present, Y is present in
at least 0.1 weight %, or about 2 to about 35 weight % of the E/X/Y
copolymer.
[0044] Examples of Y include alkyl acrylate, alkyl methacrylate, or
combinations thereof wherein the alkyl groups have from 1 to 8, or
1 to 4, carbon atoms. Y is a softening comonomer (softening means
that the polymer is made less crystalline).
[0045] Ethylene acid copolymers may be produced by any methods
known to one skilled in the art such as use of "co-solvent
technology" disclosed in U.S. Pat. No. 5,028,674.
[0046] Specific acid copolymers include ethylene/acrylic acid
dipolymers, ethylene/methacrylic acid dipolymers, and
ethylene/acrylic acid/n-butyl acrylate, ethylene/methacrylic
acid/n-butyl methacrylate, ethylene/acrylic acid/iso-butyl
acrylate, ethylene/methacrylic acid/iso-butyl methacrylate,
ethylene/acrylic acid/methyl acrylate, ethylene/methacrylic
acid/methyl methacrylate, ethylene/acrylic acid/ethyl acrylate and
ethylene/methacrylic acid/ethyl methacrylate terpolymers, or
combinations of two or more thereof. An ethylene/methacrylic acid
dipolymer of note comprises 19 weight % of copolymerized units of
methacrylic acid.
[0047] Ionomers are obtained by neutralization of an acid
copolymer. Neutralizing agents including metal cations such as
sodium or potassium ions are used to neutralize at least some
portion of the acidic groups in the acid copolymer. Unmodified
ionomers are prepared from the acid copolymers such as those
disclosed in U.S. Pat. No. 3,264,272. "Unmodified" refers to
ionomers that are not blended with any material that has an effect
on the properties of the unblended ionomer. The acid copolymers may
be used to prepare unmodified, melt processable ionomers by
treatment with a metal compound. The unmodified ionomers may be
nominally neutralized to any level such as about 15 to about 90% or
about 40 to about 75% of the acid moieties.
[0048] The organic acids may be monobasic, having fewer than 36
carbon atoms, or salts thereof. The acids are optionally
substituted with from one to three substituents independently
selected from the group consisting of C.sub.1-C.sub.8 alkyl, OH,
and OR.sup.1 in which each R.sup.1 is independently C.sub.1-C.sub.8
alkyl, C.sub.1-C.sub.6 alkoxyalkyl or COR.sup.2; and each R.sup.2
is C.sub.1-C.sub.8 alkyl.
[0049] Examples of organic acids include C.sub.4 to C.sub.36 (e.g.,
C.sub.34, C.sub.4-26, C.sub.6-22, or C.sub.12-22) acids. At high
neutralization such as greater than 80%, up to 100% nominal
neutralization (i.e., sufficient metal compound is added such that
all acid moieties in the copolymer and organic acid are nominally
neutralized), volatility is not an issue and organic acids with
lower carbon content may be used, though it is preferred that the
organic acid (or salt) be non-volatile (not volatilize at
temperatures of melt blending of the agent with the acid copolymer)
and non-migratory (not bloom to the surface of the polymer under
normal storage conditions (ambient temperatures)). Examples of
organic acids include, but are not limited to, caproic acid,
caprylic acid, capric acid, lauric acid, stearic acid, isostearic
acid, arachidic acid, behenic acid, erucic acid, oleic acid, and
linoleic acid. Organic (fatty) acids include palmitic acid, stearic
acid, oleic acid, erucic acid, behenic acid, isostearic acid,
12-hydroxystearic acid, or combinations of two or more thereof.
Saturated organic acids, such as stearic acid, arachidic acid, and
behenic acid, may be preferred.
[0050] Organic acids may be commercially available as a mixture of
named organic acid(s) and a number of structurally different
organic acids of varying lesser amounts. When a composition
comprises a named acid, other unnamed acids may be present at
levels conventionally known to be present in commercial supplies of
the named acid. For example, a commercially available mixture of
acids includes 90 weight % of a mixture of arachidic acid (C.sub.20
acid) and behenic acid (C.sub.22 acid) with 6 weight % of C.sub.18
acids and 4 weight % of other acids.
[0051] Salts of any of these organic acids may include the alkali
metal salts, such that the metal ions present in the final
composition comprise at least 50% of alkali metal ions, including
lithium, sodium, potassium salts and/or cesium salts, preferably
sodium salts or potassium salts.
[0052] The amount of basic metal compound capable of neutralizing
acidic groups may be provided by adding the stoichiometric amount
of the basic compound calculated to neutralize a target amount of
acid moieties in the acid copolymer and organic acid(s) in the
blend (herein referred to as "% nominal neutralization" or
"nominally neutralized"). Thus, sufficient basic compound is made
available in the blend so that, in aggregate, the indicated level
of nominal neutralization could be achieved. Greater than 50%, 60%,
70%, 80% or 90% (or even 100%) of the total acidic groups in the
E/X/Y copolymers and organic acids may be nominally neutralized
with metal ions; and the metal ions comprise at least 50 mole %
alkali metal ions, preferably sodium or potassium. Small amounts of
salts of alkaline earth metal and/or transition metal ions may be
present in addition to the alkali metals.
[0053] Metal compounds may include compounds of alkali metals, such
as lithium, sodium, potassium, or cesium or combinations of such
cations. Examples include sodium, potassium, cesium or any
combination of sodium, potassium, and/or cesium, optionally
including small amounts of other cations such as other alkali metal
ions, transition metal ions or alkaline earth ions. Metal compounds
of note include formates, acetates, nitrates, carbonates,
hydrogencarbonates, oxides, hydroxides or alkoxides of the ions of
alkali metals, especially sodium and potassium, and formates,
acetates, nitrates, oxides, hydroxides or alkoxides of the ions of
alkaline earth metals and transition metals. Of note are sodium
hydroxide, potassium hydroxide, sodium acetate, potassium acetate,
sodium carbonate and potassium carbonate.
[0054] The ethylene acid copolymers or unmodified ionomers may be
mixed with organic acids or salts thereof and/or metal compounds,
by any means known to one skilled in the art, to prepare a blended
modified ionomer composition comprising (1) and (2) as described
above.
[0055] It is substantially melt-processable and may be produced by
combining one or more ethylene acid copolymers, one or more
monobasic carboxylic acids or salts thereof, and basic compound(s)
to form a mixture; and heating the mixture under a condition
sufficient to produce the composition. Heating may be carried out
under a temperature in the range of from about 80 to about 350,
about 100 to about 320, or 120 to 300.degree. C. under a pressure
that accommodates the temperature for a period from about 30
seconds to about 2 or 3 hours. For example, the composition may be
produced by melt-blending an acid copolymer and/or ionomer thereof
with one or more organic acids or salts thereof; concurrently or
subsequently combining a sufficient amount of a basic metal
compound capable of neutralization of the acid moieties to nominal
neutralization levels greater than 50, 60, 70, 80, 90%, to near
100%, or to 100%. A salt-and-pepper blend of components may be
heated or the components may be melt-blended in an extruder. For
example, a twin-screw extruder may be used to mix and treat the
acid copolymer and the organic acid (or salt) with the metal
compound at the same time. It is desirable that the blending is
conducted so that the components are intimately mixed, allowing the
basic metal compound to neutralize the acidic moieties.
[0056] Treatment of acid copolymers and organic acids with metal
compounds in this manner (concurrently or subsequently), such as
without the use of an inert diluent, may produce a composition
without loss of processability or properties such as toughness and
elongation to a level higher than that which would result in loss
of melt processability and properties for the ionomer alone.
[0057] The selectively permeable modified ionomer composition also
comprises one or more ethylene-containing polymers. Blending with
such polymers may provide better processability, improved
toughness, strength, flexibility, and/or compatibility of the blend
when used as a monolayer structure or when adhering to a substrate.
Desirably, the modified ionomer combination of (1) and (2) is
prepared and subsequently blended with additional
ethylene-containing polymers to prepare the final selectively
permeable composition. However, in some embodiments the
ethylene-containing polymer may be melt blended with the components
of the organic acid-modified ionomer during its preparation. That
is, preparing the organic acid modified ionomer and blending with
the ethylene-containing polymer may be conducted simultaneously in
a single process operation. A salt-and-pepper blend of the organic
acid-modified ionomer and the ethylene-containing polymer may be
heated above their melting temperatures and mixed or the components
may be melt-blended in an extruder.
[0058] The ethylene-containing polymers may include polyethylene
(PE) homopolymers and copolymers. PE homopolymers and copolymers
may be prepared by a variety of methods, for example, the
well-known Ziegler-Natta catalyst polymerization (e.g., U.S. Pat.
No. 4,076,698 and U.S. Pat. No. 3,645,992), metallocene catalyzed
polymerization, VERSIPOL catalyzed polymerization and by free
radical polymerization. The polymerization may be conducted as
solution phase processes, gas phase processes, and the like.
Examples of PE polymers may include high density PE (HDPE), linear
low density PE (LLDPE), low density PE (LDPE), very low or ultralow
density PEs (VLDPE or ULDPE), lower density PE made with
metallocene having high flexibility and low crystallinity (mPE).
Metallocene technology is described in, for example, U.S. Pat. Nos.
5,272,236, 5,278,272, 5,507,475, 5,264,405, and 5,240,894.
[0059] The density of PE may range from about 0.865 g/cc to about
0.970 g/cc. Linear PE may incorporate .alpha.-olefin comonomers
such as butene, hexene or octene to decrease density to within the
density range so described. For example, a copolymer may comprise a
major portion (by weight) of ethylene that is copolymerized with
another .alpha.-olefin having 3-20 carbon atoms and up to about 20%
by weight of the copolymer. Other .alpha.-olefins are propylene,
1-butene, 1-hexene, 4-methyl-1-pentene, 1-octene, 1-decene,
1-tetradecene, 1-octadecene, or in combinations of two or more. Of
note are metallocene polyethylenes comprising ethylene/octene
copolymers.
[0060] The PE copolymer may also be an ethylene propylene elastomer
containing a small amount of unsaturated compounds having a double
bond. The term "PE" when used herein is used generically to refer
to any or all of the polymers comprising ethylene described
above.
[0061] Ethylene copolymers having small amounts of a diolefin
component such as butadiene, norbornadiene, hexadiene and isoprene
are also generally suitable. Terpolymers such as
ethylene/propylene/diene monomer (EPDM) are also suitable.
[0062] The ethylene-containing polymer may include ethylene
copolymers obtained from copolymerization of ethylene with at least
one polar monomer such as ethylene/vinyl acetate copolymer (EVA),
ethylene/acrylic ester copolymers, ethylene/methacrylic ester
copolymers, ethylene/vinyl acetate/CO copolymers, ethylene/acrylic
ester/CO copolymers, and/or mixtures of any of these.
[0063] EVA includes copolymers derived from the copolymerization of
ethylene and vinyl acetate or the copolymerization of ethylene,
vinyl acetate, and an additional comonomer. The vinyl acetate
comonomer may have 2 to 45 or 6 to 30 weight % derived from vinyl
acetate. An EVA may have a melt flow rate, measured in accordance
with ASTM D-1238, of from 0.1 to 60 g/10 or 0.3 to 30 g/10 minutes.
A mixture of two or more different EVAs may be used.
[0064] Ethylene/alkyl (meth)acrylate copolymer includes copolymers
of ethylene and one or more C.sub.1-8 alkyl (meth)acrylates.
Examples of alkyl (meth)acrylates include methyl acrylate, ethyl
acrylate and butyl acrylate. Examples of the copolymers include
ethylene/methyl acrylate copolymer ethylene/ethyl acrylate
copolymer, ethylene/butyl acrylate copolymer, or combinations of
two or more thereof. Alkyl (meth)acrylate may be incorporated into
an ethylene/alkyl (meth)acrylate copolymer at 2 to 45, 5 to 45, 10
to 35, or 10 to 28 weight %.
[0065] Ethylene/alkyl (meth)acrylate copolymers may be prepared by
processes well known to one skilled in the art using either
autoclave or tubular reactors. See, e.g., U.S. Pat. Nos. 2,897,183,
3,404,134, 5,028,674, 6,500,888, and 6,518,365. Because the methods
for making an ethylene/alkyl (meth)acrylate copolymer are well
known, the description of which is omitted herein for the interest
of brevity. Tubular reactor produced ethylene/alkyl (meth)acrylate
copolymers are commercially available from E. I. du Pont de Nemours
and Company, Wilmington, Del. (DuPont) such as ELVALOY.RTM. AC. The
ethylene/alkyl (meth)acrylate copolymers may vary significantly in
molecular weight and the selection of the melt index (MI) grade of
polymer may be made by balancing the properties of the
ethylene/alkyl (meth)acrylate copolymer with those of the
neutralized organic acid and ethylene acid copolymer to provide the
desired mix of permeability and structural properties needed for a
specific variable permeability construction. A mixture of two or
more different ethylene/alkyl (meth)acrylate copolymers may be
used. Of note is a composition wherein at least one ethylene/alkyl
(meth)acrylate copolymer is present in up to 15 weight %.
[0066] Small amounts (from 1 or 5 weight % to about 15 weight %) of
a dicarboxylic acid derivative-derived polymer or ethylene acid
copolymers are used to facilitate blending of the modified ionomer
combination and the ethylene-containing copolymer to provide
improved mechanical properties. As noted above, for best
permeability and mechanical performance, it is desirable for the
combination of (1) and (2) to be prepared prior to blending with
the additional ethylene-containing polymer and the dicarboxylic
acid derivative-derived polymer.
[0067] A dicarboxylic acid derivative-derived polymer may be used
in the composition, comprising a copolymer having a dicarboxylic
acid anhydride unit derived from an unsaturated dicarboxylic acid
anhydride, including units obtained from maleic anhydride,
citraconic anhydride, itaconic anhydride, tetrahydrophthalic
anhydride, or combinations of two or more thereof. The modified
copolymer may be obtained by known techniques, such as a grafting
process in which a polymer selected from an ethylene homopolymer or
copolymer (e.g. PE), a polypropylene homopolymer or copolymer, an
EVA or an ethylene/alkyl (meth)acrylate copolymer, as disclosed
above, is dissolved in an organic solvent with an unsaturated
dicarboxylic acid anhydride and a radical generator, followed by
heating with stirring; and a process in which all the components
are fed to an extruder to provide a maleic-anhydride grafted
ethylene copolymer. Grafting processes provide copolymers with from
0.1 to 3 weight % of anhydride units in which the anhydride unit is
in a moiety pendant from the backbone of the polymer. These graft
copolymers are available commercially from DuPont under the
FUSABOND or BYNEL brand names. A graft copolymer of note is an
ethylene/methyl acrylate copolymer having 24 weight % copolymerized
methyl acrylate units (prior to grafting) grafted with 1.8 weight %
of maleic anhydride.
[0068] A dicarboxylic acid derivative-derived polymer also may be
readily obtained by a high-pressure free radical process, in which
an olefin comonomer and a comonomer such as maleic anhydride are
directly copolymerized to provide a copolymer in which atoms from
the anhydride unit comprise a portion of the polymer backbone. A
suitable high-pressure process is described, for example, in U.S.
Pat. No. 4,351,931. This process allows for preparation of
copolymers with greater than 3 wt %, for example, about 4 or 5 wt %
to about 15 wt %, of anhydride units. These copolymers include
olefin/maleate copolymers such as ethylene/maleic anhydride
copolymers.
[0069] Other dicarboxylic acid derivative-derived polymers can
include, for example, an ester of a dicarboxylic acid such as
maleic acid monoalkyl ester, also known as ethyl hydrogen maleate.
Such polymers can include copolymers of ethylene and maleic acid
monoethyl ester having from about 5 to about 10, or from about 6 to
about 9 wt % of maleic acid monoethyl ester.
[0070] These dicarboxylic acid derivative-derived polymers used to
facilitate blending include ethylene/maleic acid monoalkyl ester
dipolymers; and ethylene/maleic acid monoalkyl ester/n-butyl
(meth)acrylate, ethylene/maleic acid monoalkyl ester/methyl
(meth)acrylate, ethylene/maleic acid monoalkyl ester/ethyl
(meth)acrylate terpolymers, or combinations thereof. These
copolymers may be readily obtained by a high-pressure free radical
process, in which an olefin comonomer and the maleic acid monoalkyl
ester comonomer are directly copolymerized to provide a copolymer
in which atoms from the maleic acid monoalkyl ester unit comprise a
portion of the polymer backbone. Additional alkyl acrylate or alkyl
methacrylate comonomers may also be copolymerized to prepare the
terpolymers listed. A suitable high-pressure process is described,
for example, in U.S. Pat. No. 4,351,931. This process allows for
preparation of copolymers with from about 4 or 5 weight % to about
15 weight %, of maleic acid monoethyl ester units. A maleic acid
monoalkyl ester of note is maleic acid monoethyl ester, also known
as ethyl hydrogen maleate. Copolymers of note include copolymers of
ethylene and maleic acid monoethyl ester having from about 5 to
about 10, or from about 6 to about 9 weight % of copolymerized
units of maleic acid monoethyl ester.
[0071] The modified ionomer combination of (1) and (2) may be
prepared, melt blended with the ethylene-containing polymer and
then melt blended with the dicarboxylic acid derivative-containing
polymer. However, in some embodiments the organic acid-modified
ionomer may be prepared and melt blended with the
ethylene-containing polymer and the dicarboxylic acid
derivative-containing polymer at the same time. That is, blending
the organic acid-modified ionomer with the ethylene-containing
polymer and the dicarboxylic acid derivative-containing polymer may
be conducted simultaneously in a single process operation. A
salt-and-pepper blend of the organic acid-modified ionomer, the
ethylene-containing polymer and the dicarboxylic acid
derivative-containing polymer may be heated above their melting
temperatures and mixed or the components may be melt-blended in an
extruder, either after pre-blending a pellet blend or by feeding
the components to the extruder in metered amounts.
[0072] When blending polymeric resins the higher flow or lower
viscosity resin tends to flow more readily relative to other lower
flow resins. This melt rheology effect tends to facilitate the
higher flow resin to disperse and distribute more effectively in
the blend during the melt blending process and enable more
effective distribution at the interface with higher melt shear
field. Depending on the blending and extrusion conditions, the
ethylene-containing polymer and the dicarboxylic acid
derivative-containing polymer components may be concentrated near
the surface of the extrudate, providing improved adhesion to the
substrate.
[0073] The composition may additionally comprise from 0.01 to 15,
0.01 to 10, or 0.01 to 5, weight %, based on the total composition
weight, of additives including plasticizers, stabilizers including
viscosity stabilizers and hydrolytic stabilizers, primary and
secondary antioxidants, ultraviolet ray absorbers, anti-static
agents, dyes, pigments or other coloring agents, inorganic fillers,
fire-retardants, lubricants, reinforcing agents such as glass fiber
and flakes, synthetic (for example, aramid) fiber or pulp, foaming
or blowing agents, processing aids, slip additives, antiblock
agents such as silica or talc, release agents, tackifying resins,
or combinations of two or more thereof. These additives are
described in the Kirk Othmer Encyclopedia of Chemical
Technology.
[0074] The additives may be incorporated into the composition by
any known process such as by dry blending, extruding a mixture of
the various constituents, the conventional masterbatch technique,
or the like.
[0075] The composition can further comprise a fire retardant such
as a chemical additive including, but not limited to, phosphorous
compounds, antimony oxides, and halogen compounds, particularly
bromine compounds, and others well known in the art. A loading of
such additives can be between 20 to 30, or about 25% (of the final
air-dried composition or air-dried film weight).
[0076] The compositions may also comprise fillers, fibers, or pulps
in added quantities that may be up to 30 to 40 weight % of the
total composition. These materials may provide reinforcement or
otherwise modify the mechanical properties of the composition,
without negatively impacting the selective permeability of the
composition. Fillers include, for example, inorganic materials such
as carbon black, TiO.sub.2, calcium carbonate (CaCO.sub.3). Fibers,
including chopped fibers, include glass fibers, aramid fibers,
carbon fibers and the like. Pulps include, for example aramid
micropulps (micropulp has a volume average length from about 0.01
to about 100 micro-meters).
[0077] The polymer composition can be formed or incorporated into a
film or sheet. Films may be made by known techniques such as
casting the polymer composition onto a flat surface or into a film,
extruding the molten polymer composition through an extruder to
form a cast film, or extruding and blowing the polymer composition
film to form an extruded blown film.
[0078] The films may have a thickness of from 1 to 2500 .mu.m, with
the preferred thickness for many protective cover applications
being about 5 to 10 mils thick, or about 120 to 250 .mu.m
thick.
[0079] The protective structures can be in the form of, for
example, tarpaulins, covers, and the like. The membrane from the
composition can be present as a layer of material added to the
protective structure, or as one component of a fabric incorporated
into the protective structure. Generally, a layer of the
composition and a supporting substrate, as described in greater
detail below, may be arranged in overlaying or overlapping fashion
to provide a protective structure. When used with a substrate, the
selectively permeable composition may have a thickness from about
10 to about 250 .mu.m. The membrane composition can be converted
and applied to a substrate by a variety of techniques and
processes.
[0080] The composition may be applied to a substrate in molten
condition by, for example but not limitation, extrusion coating to
a substrate or lamination of two substrate layers by means of an
inner layer of the composition applied in molten form to adhere the
substrates together. In some embodiments the polymer composition
can be coated directly on a substrate utilizing fabric impregnation
and coating techniques. For example, the selectively permeable
composition is a coating applied directly on the substrate (via
extrusion coating, spraying, painting or other appropriate
application methods). Such coating can be applied using spreading
methods known in the art such as with a rubber doctor blade or with
a slit extrusion machine.
[0081] The composition can be applied to one side or both sides of
a textile substrate. In the case where the substrate is coated or
laminated on one side, the composition may be applied to the side
that is directly exposed to the environment to provide a
liquid-impermeable outer surface. Alternatively, in applications
where mechanical wear or abrasion is likely, the composition may be
applied to the side of the textile substrate opposite the side
exposed to the mechanical wear to afford protection of the
polymeric composition.
[0082] In other embodiments the composition can be impregnated in a
substrate or the substrate can be impregnated in the polymer.
[0083] The selectively permeable composition may be formed at least
partially in the substrate by impregnating the substrate with the
composition by applying the molten composition to the substrate and
then cooling the composition while it is in contact with the pores
of the substrate.
[0084] The composition can be dispersed throughout the substrate
such as a loosely woven fabric where the composition fills gaps in
the substrate and does not just adhere on the surface of a
substrate. The substrate can be impregnated inside the selectively
permeable membrane through lamination or coextrusion process to
have the permeable compositions on both sides of the substrate.
[0085] The composition can also be accommodated between two layers
of textiles in a sandwich-like manner. Several layer assemblies can
also be assembled one above the other. For example, the
configuration can comprise the selectively permeable membrane
layer, a substrate layer, another selectively permeable membrane
layer, another substrate layer, and so on, depending upon desired
applications of the protective structure. Other configurations can
comprise variations of the aforementioned sandwich configuration,
including a plurality of selectively permeable membrane layers, a
plurality of substrate layers, and so forth, including mixtures
thereof.
[0086] The membrane from the composition can be present as a layer
of material added to the protective structure, or as one component
of a fabric incorporated into the protective structure. Coated
fabrics, used previously as tarpaulins or other covers, may have at
least one wear resistant outer layer that generally needs high
flexibility, high resistance to marring from wear, abrasion,
scuffing, and scratching, high mechanical strength and toughness.
Coating compositions preferably exhibit good adhesion to fabrics
and other substrates such as plastic films and cellulosic materials
such as paper or paperboard. They also desirably exhibit good melt
processability, good colorability, good printability, and high
transparency and/or gloss. Previous coating compositions for these
applications include plasticized or flexible polyvinyl chloride.
The composition described herein provides a superior coating
composition to previous coating materials because it is selectively
permeable.
[0087] The composition can be in the form of a film or sheet and
the film is mechanically held or fastened in overlaying fashion
adjacent to the textile. Mechanical fastening includes the use of
fasteners such as snaps, zippers, hook-and-loop fasteners and the
like. Mechanical fastening also includes stitching or quilting
using threads or fibers.
[0088] The selectively permeable membrane may be attached or
adhered to the substrate by use of a compatible adhesive placed
between the membrane layer and the substrate. To maintain water
vapor permeability of the structure, in some embodiments the
adhesive is present as a discontinuous layer between the membrane
layer and the substrate, and in many cases, it may be applied as a
series of adhesive dots that cover for example about 10 to about 40
percent of the substrate surface. The adhesive also may be applied
selectively near the edges of the membrane and the substrate.
[0089] The selectively permeable membrane may also be attached to
the substrate by heat sealing or high frequency (HF) welding. The
laminate can be heat sealed (thermally bonded) using any known
method, included heated presses and calenders and the like, or by
applying heat to the layers and then subsequently pressing them
together without additional heat. In each case, the softened layer
or component subsequently bonds the film structure to the
substrate. In either heat sealing or HF welding, the bonding of the
film to the substrate may be continuous across the entire area of
the film and substrate or it may be discontinuous. Discontinuous
bonding may be accomplished by application of heat or HF radiation
to selected portions of the area where the film overlays the
substrate.
[0090] A selectively permeable composition as described herein can
be prepared as a powder with granular sizes of up to 600,
alternatively up to 400, alternatively up to 200 .mu.m in size. A
powder composition can comprise granules that vary in size from
about 100 to about 600 .mu.m. The average particle size in a powder
composition can be from about 150 to about 200 .mu.m. The
compositions can be milled, pulverized or otherwise processed by
methods known in the art to provide a desired particle size
suitable for application to a substrate.
[0091] The powder can be applied to a substrate by a technique such
as powder scattering, wherein the powder is evenly distributed
across a working width of a substrate and thereafter melted,
smoothed, and cooled to provide a uniform coating of the
composition on the substrate.
[0092] The laminate can further comprise a layer of
adhesion-promoting or contaminant blocking substance that is
selectively permeable, which could also be an abrasion resistant
polymer, positioned adjacent to the selectively permeable layer.
For example, this substance may contain urethane functionality and
can be about 2.5 to 12 .mu.m thick. Other polymers that can be used
in this layer include a variety of elastomers, reactive materials,
and adhesives. Preferably the adhesion promoting polymer layer is
present as a film, however, the layer can be a coating or an
impregnation of the substrate. This additional adhesion promoting
polymer layer is especially useful when the laminate is made by
combining the layers of the laminate by thermal pressing, bonding,
calendaring and the like. In this case, the layer of abrasion
resistant polymer should be compatible with the selectively
permeable layer so that when the items are thermally pressed they
adhere together.
[0093] The substrate may be any material providing support, shape,
esthetic effect, protection, surface texture, bulk volume, weight,
or combinations of two or more thereof to enhance the functionality
and handability of the structure.
[0094] A substrate can be a vehicle to aid in incorporating the
selectively permeable composition or provide mechanical support for
the membrane so that permeability is not hindered. Preferably a
substrate has water vapor diffusion that is greater than the water
vapor diffusion of the selectively permeable membrane so that the
water vapor diffusion characteristics of the structure are
essentially provided by the selectively permeable composition. That
is, the substrate does not substantially affect the passage of
water vapor through the layered structure, and for example, may
have a measured MVTR of at least 1.8, 4, 5, or even 10,
Kg/m.sup.2/24 hours.
[0095] Any support or substrate meeting these desired
characteristics may be used with the selectively permeable
composition. Examples include a textile or porous sheet material.
Sheets made from synthetic fiber spun fabrics, such as nonwoven
textiles, may be used as a textile substrate. Cloth that is woven,
knitted or the like is also suitable as a textile substrate. A
fabric may comprise flame retardant(s), filler(s), or additive(s)
disclosed above.
[0096] For example, a fabric may comprise a 50% nylon-50% cotton
blend woven fabric (also known as NYCO) such as those by Bradford
Dyeing Association, Inc., in Bradford, R.I. A fabric of note is a
polyester woven fabric from Millikin and Company (Spartanburg,
S.C.).
[0097] While the substrate has been described generally as a
textile, the substrate can be any other material that is capable of
accommodating thereon one or a plurality of layers or accommodating
therein a dispersion of the selectively permeable composition.
[0098] Cellulosic materials such as paper webs (for example Kraft
or rice paper), materials made from synthetic fiber spun fabrics,
nonwoven textiles, microporous films, or even perforated films
having large percentages of open areas such as perforated PE films,
may be used as materials for the substrate(s), for example. These
materials may be reinforced with fibers. Microporous films of note
may be prepared from polypropylene, polyethylene or combinations
thereof. They may be monolayer or multilayer films (for example,
three-layer films comprising an inner layer of polypropylene
between two outer layers of polyethylene). Microporous films are
available from Celgard, LLC, Charlotte, N.C. under the CELGARD
tradename.
[0099] Suitable polymers for a microporous film are (1) linear
ultrahigh molecular weight polyethylene having an intrinsic
viscosity of at least 18, preferably 18 to 39, deciliters/gram, (2)
linear ultrahigh molecular weight polypropylene having an intrinsic
viscosity of at least 6 deciliters/gram, and (3) mixtures of (1)
and (2).
[0100] The microporous film may include a finely divided,
particulate, substantially water-insoluble, inorganic filler, for
example a siliceous filler, which is distributed throughout the
matrix and which is present in amount 50 to 90%, particularly 50 to
85%, by weight of the film. The filler may be silica, precipitated
silica, or silica having an average ultimate particle size of less
than 0.1 .mu.m and may occupy 35 to 80% of the total volume of
microporous film. Because they have a relatively narrow range of
pore sizes, films may be made by extruding a polymeric composition
which contains an inorganic filler and a processing oil, e.g. a
paraffinic oil, naphthenic oil or aromatic oil, uniformly
distributed therein; followed by extraction of the processing oil,
e.g. with trichloroethylene. Some films are disclosed, for example,
in U.S. Pat. Nos. 4,937,115 and 3,351,495 and films are sold by PPG
Industries under the tradename TESLIN.
[0101] Specific examples of porous or perforated films include a
porous PE film having a porosity of about 55% and a pore size of
about 0.25 microns, available under the tradename CELGARD K878 from
Hoechst Celanese Corp; a porous PE film available under the
tradename MSX 1137P from 3M Co.; and a filled porous PE film
available under the designation Van Leer 10.times. from Van Leer
Corp. TESLIN SP7 is a filled porous PE films containing about 60%
silica, having a thickness of about 0.18 mm (0.007 inch), a tear
strength measured as described above of about 90 g, a porosity of
about 65%, an average pore size of about 0.1 micron and a largest
pore size of 4 to 10 microns. TESLIN X457 is similar to TESLIN SP7
but is more porous. TESLIN SP10 is similar to TESLIN SP7 but has a
thickness of about 0.25 mm (0.010 inch). All three TESLIN films are
available from PPG Industries. A perforated high density
polyethylene film, 0.11 mm (4.5 mil) thick, with an open area of
about 36%, is available under the tradename DELNET from Applied
Extrusion Technologies.
[0102] A substrate can be a porous sheet material comprising a
fluoropolymer. A substrate can be sheet material made with expanded
polytetrafluoroethylene that is available from many companies,
including W. L. Gore & Associates of Wilmington, Del. Other
porous substrates include porous or microporous polyurethane films,
certain flash spun non-woven fabrics, such as flash spun
polypropylene, and other spun bonded polymer fabrics, filter
materials from companies such as Millipore, nano- or micro-fiber
structures, natural or synthetic fibers, other related supports
that add dimensional stability, or combinations of two or more
thereof.
[0103] The protective structure may further comprise other layers
such as adhesive layers, thermal insulation layers, cushioning
layers, absorptive layers, reactive layers, and the like.
[0104] Insulation layers and cushioning layers may comprise an
organic thermoplastic fiber-based material comprising, e.g.,
polyester, polyethylene or polypropylene. For example, the thermal
insulating or cushioning layer is a fiberfill batt comprising
polyester. A fiberfill batt sold as THERMOLITE ACTIVE ORIGINAL by
DuPont is suitable. Alternatively, the thermal insulating layer may
comprise melt-blown fibers, such as melt-blown polyolefins, sold as
THINSULATE, by 3M. They may also include other materials such as
fiberglass batts.
[0105] The mechanical properties and ease of processing of the
selectively permeable composition, and its ability to transport
water vapor and block liquids, combined with a support substrate
render protective structures thereof applicable for covering or
enclosing articles during transport and storage.
[0106] A variety of structural configurations may be used to
produce the package. For example, the variably permeable multilayer
structure may be in the form of a flexible sheet of material. The
sheet material may be wrapped around an article to be protected
from corrosion in the same way conventional plastic films are used.
Some structural configurations are as follows.
[0107] (1) Films or sheets of material comprising the selectively
permeable structure that may be wrapped around or draped over the
object(s) being packaged.
[0108] For example, the object, which may be a piece of equipment
or a pallet and its load, may be wrapped in overlapping layers of
film that may be applied by machine or by hand. These films may be
relatively long and narrow and dispensed from rolls. The film may
be stretchable or heat shrinkable. Wrapping an object with a linear
stretch wrapping film by a machine, for example may be done by
placing the object on a turntable and rotating it as the film is
fed horizontally and its position is varied vertically to wrap the
object in overlapping layers. The film may also be applied
manually, as by an operator with a hand-held film dispenser who
walks around the loaded pallet until a sufficient amount of film is
applied.
[0109] A heat shrinkable film can be wrapped around an object and
heat applied to it so that it shrinks to conform tightly around the
object.
[0110] Other examples include substantially flat rectangular sheets
having similar length and width that may be draped and optionally
mechanically fastened in place (for example, with straps, ropes,
elastic bands or the like) over the object, such as tarpaulins and
the like.
[0111] These package forms may be preferred when a large variety of
objects of different size and shape are to be packaged at a given
time or location.
[0112] (2) Bags, pouches, hoods or sheathes comprised completely of
the selectively permeable structure described herein or which
comprise other materials such as other polymeric materials, woven
or nonwoven textiles and the like and have windows, patches or
areas thereon which comprise the selectively permeable
structure.
[0113] These packaging forms are prepared from sheets or films that
are formed into a concave shape that can accommodate the object to
be packaged.
[0114] They include heat shrinkable hoods and pallet stretch hoods.
Pallet stretch hoods are elastic sheaths that are stretched to fit
over a pallet and its load. The pallet stretch hood then contracts,
due to its elastic properties, and the forces of contraction
provide integrity and stability to the loaded pallet.
[0115] These package forms may be preferred when a large number of
objects of similar size and shape are to be packaged at a given
time or location.
[0116] (3) Rigid or semi-rigid or flexible structures such as tubs,
boxes, bins and the like, comprised completely of the selectively
permeable structure or comprised in part of other materials having
one or more windows of the variably permeable multilayer structure
thereon.
[0117] (4) Lidding material comprised completely of the selectively
permeable structure or comprised in part of other materials having
one or more windows of the selectively permeable structure thereon.
The lidding material may be used in combination with rigid or
semi-rigid or flexible structures such as tubs, boxes, bins and the
like to prepare a package comprising the selectively permeable
structure.
[0118] (5) Patches of the selectively permeable structure over
designed openings of packages to provide the desired
permeability.
[0119] (6) Packages in which the selectively permeable structure is
covered by a removable protective cover that allows a user to
expose the selectively permeable structure to the environment at an
appropriate time. For example, the protective cover may comprise a
material with low adhesion to the selectively permeable structure
that may be peeled away from the surface of the selectively
permeable structure when desired. Alternatively, the cover may be
removable material that overlays the selectively permeable
structure, but is not adhered to it, in a package. For example, the
protective cover may be a lid, flap or patch of protective (such as
barrier) material that may be removed when desired. The protective
cover may also be placed over a patch or window of the selectively
permeable structure in a package.
[0120] This form of protective cover may provide extra protection
of equipment during rain or other inclement weather, after which
the barrier flap is removed to allow for moisture to vent through
the selectively permeable membrane.
[0121] Numerous variations of these structures are also possible
and such structures will become apparent to those skilled in the
art upon reading this disclosure.
[0122] In the method for limiting damage to an article due to
corrosion or mold growth, the article can be wrapped or covered in
a selectively permeable protective structure disclosed above and
the wrapping or covering may or may not be hermetic.
[0123] The following Examples are presented to demonstrate and
illustrate, but are not meant to unduly limit the scope of, the
invention.
EXAMPLES
[0124] MI, the mass rate of flow of a polymer through a specified
capillary under controlled conditions of temperature and pressure,
was determined according to ASTM 1238 at 190.degree. C. using a
2160 g weight, in g/10 minutes.
[0125] For samples with high water permeability (>100
g/m.sup.2-24 h), the water vapor transmission tests were conducted
on a Mocon PERMATRAN-W 101K, following ASTM D6701-01, at
37.8.degree. C. at 100% relative humidity. For the other samples,
the transmission tests were conducted on a Mocon PERMATRAN-W 700,
following ASTM F1249-01. Moisture vapor permeation values (MVPV) on
film samples are reported in g-mil/m.sup.2-24 h while MVTR are
reported in g/m.sup.2-24 h. The compositions had MVPV of at least
800 (or at least 1200) g-mil/m.sup.2/24 h.
[0126] Another method for determining material "breathability," or
evaporative resistance, uses a Guarded Sweating Hotplate Test
according to ASTM F1868, ISO 11092.
[0127] In order to illustrate the moisture permeance associated
with a film layer involving a selectively permeable composition as
described herein, extrusion cast films are prepared from the
materials listed below.
Materials Used
[0128] EAC-2: a dipolymer of ethylene, and methacrylic acid (19 wt
%), MI=300. EAC-3: a terpolymer of ethylene, n-butyl acrylate (23.5
wt %) and methacrylic acid (9 wt %), having an MI of 200. EAC-4: a
terpolymer of ethylene, n-butyl acrylate (28 wt %) and acrylic acid
(6.2 wt %), having an MI of 200. EAC-5: a terpolymer of ethylene,
n-butyl acrylate (15.5 wt %) and acrylic acid (8.5 wt %), having an
MI of 60. EAC-6: a terpolymer of ethylene, n-butyl acrylate (15.5
wt %) and acrylic acid (10.5 wt %), having an MI of 60. ABA: A
mixture containing 90 wt % of a mixture of arachidic acid and
behenic acid with 6 weight % C.sub.18 acids and 4 wt % other acids
commercially available under the tradename Hystrene.RTM. 9022 from
Chemtura. PE-1: low density polyethylene available under the
designation DPE 1640 from DuPont Performance Elastomers mPE-1: a
metallocene polyethylene; density=0.920 g/cc; MI=5 g/10 min. mPE-2:
a metallocene polyethylene; density=0.895 g/cc; MI=3 g/10 min.
mPE-3: a metallocene polyethylene; density=0.895 g/cc; MI=1 g/10
min. mPE-4: a metallocene PE; density=0.920 g/cc: MI=1 g/10 min.
mPE-5: a metallocene PE; density=0.870 g/cc; MI=5 g/10 min. mPE-6:
a metallocene PE; density=0.920 g/cc; MI of 3 g/10 min. mPE-7: a
metallocene PE; density=0.895 g/cc; MI of 5 g/10 min. mPE-8: a
metallocene PE; density=0.870 g/cc; MI of 3 g/10 min. mPE-9: a
metallocene PE; density=0.870 g/cc; MI of 1 g/10 min. EMA-1: an
ethylene/methyl acrylate copolymer with 24 weight % copolymerized
methyl acrylate units (remainder ethylene), with MI of 2 g/min.
G-1: an ethylene/methyl acrylate copolymer having 24 wt %
copolymerized methyl acrylate units (prior to grafting) grafted
with 1.8 wt % of maleic anhydride. EMAME-1: an ethylene/maleic acid
monoethyl ester dipolymer with 6 wt % maleic acid monoethyl
ester.
[0129] Employing a Werner & Pfleiderer single-screw extruder, a
composition containing 80 weight % of EAC-2 and 20 weight % of ABA
was nominally neutralized to 93-97% with potassium hydroxide
(Composition A). Composition A has MI of 0.6 g/10 min. Composition
A was extruded through a film die to prepare a cast film with 2-mil
thickness and the film properties summarized in Table 1.
[0130] Similarly, a composition containing 90 weight % of EAC-1 and
10 weight % of sodium stearate based on the combined weight of
EAC-1 and sodium stearate was nominally neutralized to 73% with
sodium hydroxide (Composition B). Composition B has MI of 2.4 g/10
min.
TABLE-US-00001 TABLE 1 Properties of Composition A 2% Tensile
Modulus MD TD Average (psi) 25400 18300 21850 Elmendorf
Tear-notched (ASTM1922) Unnotched (g/mil) 9.07 20.6 14.84 (g/mm)
348 790 569 Tensile properties (2 inch/min) Tensile strength (psi)
1600 1100 1350 Elongation at break (%) 290 149 219.5 WVTR
(mil-g/m.sup.2-day) 12721
[0131] Composition A is subsequently melt compounded with
polyethylenes (PE-1 and mPE-1 through mPE-9 as listed above) and
G-1 to prepare compositions containing 35 wt % of Composition A, 10
wt % of G-1 and 55 wt % of polyethylene. Additional compositions
include those containing 30 wt % of Composition A, 15 wt % of G-1
and 55 wt % of polyethylene; 35 wt % of Composition A, 15 wt % of
G-1 and 50 wt % of polyethylene; 40 wt % of Composition A, 10 wt %
of G-1 and 50 wt % of polyethylene; or 45 wt % of Composition A, 10
wt % of G-1 and 45 wt % of polyethylene.
[0132] Similarly, Composition A was melt blended with the
polyethylenes listed and EMAME-1 to provide compositions containing
35 wt % of Composition A, 5 wt % of EMAME-1 and 60 wt % of
polyethylene; 30 wt % of Composition A, 10 wt % of EMAME-1 and 60
wt % of polyethylene; 30 wt % of Composition A, 15 wt % of EMAME-1
and 55 wt % of polyethylene; 45 wt % of Composition A, 5 wt % of
EMAME-1 and 50 wt % of polyethylene; or 45 wt % of Composition A,
10 wt % of EMAME-1 and 45 wt % of polyethylene.
[0133] The compounded blends are extruded through a film die to
prepare cast films with 2-mil thickness.
[0134] Composition A and Composition B were melt compounded with
EMA-1 and G-1 by preparing salt-and-pepper pellet blends with the
amounts shown in Table 2 and passing the pellet blends through two
single screw extruders in an Egan extrusion coating machine
equipped with a feed block to combine the melt from the two
extruders. The extrusion conditions are summarized below.
TABLE-US-00002 TABLE 2 Weight % in blend Example Composition A
Composition B EMA-1 G-1 C1 35 0 65 0 1 35 0 55 10 C2 40 0 60 0 2 40
0 50 10 2A 40 0 50 10 C3 45 0 55 0 3 45 0 45 10 C4 0 40 60 0 4 0 40
50 10 C5 0 50 50 0 5 0 50 40 10
[0135] The compositions listed in Table 2 were extrusion coated
onto white unprinted woven polyester fabric commercially available
from Milliken and Company (Spartanburg, S.C.) that had been corona
treated at 5 kW. Coating was done at 75 feet/min line speed,
75.degree. F. chill roll and nip roll pressure of 100 psi.
TABLE-US-00003 TABLE 3 Peel Target Coating Melt Temp Strength Delay
WVTR Example Thickness (mils) (.degree. F.) (g/in) (hrs)
(g/m.sup.2-day) C1 3 531 702 24 155 1 4 476 1322 24 116 C2 3 472
930 24 2 3 473 1167 24 234 2A 3 485 893 24 268 C3 3 472 439 24 239
3 3 486 769 24 353 C4 3 484 570 72 111 4 3 485 803 24 133 C5 3 481
419 72 157 5 3 486 302 24 190
[0136] The adhesion of the coating to the fabric was tested
according to ASTM F904-84 and summarized in Table 3. In Table 3,
"Delay" indicates the time after extrusion coating before the peel
test was conducted. Examples 1-4, compositions containing the
maleic anhydride graft copolymer G-1, all provided better adhesion
to the fabric than the corresponding compositions C.sub.1-C.sub.4,
not containing G-1. The MIs of EMA-1 and G-1 are higher than the MI
of Composition A, so they may be concentrated near the surface of
the extrudate, thereby improving adhesion to the substrate.
Extrusion melt temperature may influence the adhesion of the
coating as demonstrated by Examples 2 and 2A. Lower extrusion
temperatures may be desirable to provide enhanced adhesion.
Composition B has MI more nearly matching EMA-1 and G-1. A blend of
Composition B, EMA-1 and G-1 does not show enhanced adhesion under
the extrusion conditions tested.
[0137] The WVTR was measured according to ASTM method D-6701-01 and
summarized in Table 3. Permeability may be enhanced when the maleic
anhydride graft copolymer is included in the blend.
Moisture Vapor Transmission Rate (MVTR) of Multilayer Structure
[0138] This is measured by a method derived from the Inverted Cup
method of MVTR measurement [ASTM E 96 Procedure BW, Standard Test
Methods for Water Vapor Transmission of Fabrics (ASTM 1999)]. A
vessel with an opening on top is charged with water and the opening
is covered first with a moisture vapor permeable (liquid
impermeable) layer of expanded-PTFE film ("ePTFE"), and then with
the sample for which the MVTR is to be measured, and finally by
woven fabric overlayer [NYCO 50:50 nylon/cotton blend, 6.7
oz/yd.sup.2 (0.23 kg/m.sup.2) treated with durable water repellant
finish]. The three layers are sealed in place, inverted for 30
minutes to condition the layers, weighed to the nearest 0.001 g,
and then contacted with a dry stream of nitrogen while inverted.
After 19 h at 23.degree. C., the sample is reweighed and the MVTR
calculated (kg/m.sup.224 h) by means of the following equation:
MVTR=1/[(1/MVTR.sub.obs)-(1/MVTR.sub.mb)]
where MVTR.sub.obs is the observed MVTR of the experiment and
MVTR.sub.mb is the MVTR of the ePTFE moisture barrier (measured
separately). The values are the average of results from three
replicate samples.
Corrosion Test
[0139] The following test is performed to evaluate the corrosion
protection performance of films prepared from compositions with
different permeation values.
[0140] A small wooden cage was designed with a lower open platform
to support a carbon steel test coupon (2 inch.times.4 inch) and an
upper open platform to support a small aluminum dish. Above the
upper platform was a framework to support a headspace. The cage was
designed so that air could circulate freely throughout the internal
volume defined by the cage. Three cages are prepared, one for each
test film.
[0141] Bags are prepared from the test films in Table 6 by folding
and heat sealing the edges together so that the internal volume of
each bag fits loosely around the cage with enough extra material so
that the opening could be closed by rolling over. Each test film is
2 mils thick.
[0142] For the test, the steel test coupons are polished with 600
grit grinding paper and cleaned with acetone. The coupons are
labeled and pictures are taken before the test for comparison after
the test. A test coupon is placed in the lower platform of each
cage. A small sponge is placed in the aluminum dish in each cage
and 30 g of water is adsorbed into each sponge. A test bag is
placed around the cage and the opening rolled over and taped and
held shut with a spring clamp. The opening is not hermetically
sealed but free air exchange between the air inside and outside the
bag through the opening is prevented. The test packages (cage
inside closed bag) are placed in an oven set at 60.degree. C. After
68 hours in the oven, the test packages are removed from the oven
and visually inspected before opening to qualitatively assess the
amount of moisture present inside the package. The packages are
opened and the test coupons removed and assessed for the amount of
surface corrosion on the upper and lower surfaces. Using ADOBE
PHOTOSHOP 7.0, color photographs of the coupons are transformed
into black-and-white images in which corroded areas are transformed
to black and noncorroded areas are transformed to white. The
fractional area of black (as a percentage) of the total area of the
coupon is calculated according to standard procedures in the
software.
* * * * *
References