U.S. patent application number 10/830608 was filed with the patent office on 2004-10-28 for functionalization of porous materials by vacuum deposition of polymers.
Invention is credited to Mikhael, Michael G., Yializis, Angelo.
Application Number | 20040213918 10/830608 |
Document ID | / |
Family ID | 33303278 |
Filed Date | 2004-10-28 |
United States Patent
Application |
20040213918 |
Kind Code |
A1 |
Mikhael, Michael G. ; et
al. |
October 28, 2004 |
Functionalization of porous materials by vacuum deposition of
polymers
Abstract
A porous substrate is pretreated in a plasma field and a
functionalizing monomer is immediately flash-evaporated, deposited
and cured over the porous substrate in a vacuum vapor-deposition
chamber. By judiciously controlling the process so that the
resulting polymer coating adheres to the surface of individual
fibers in ultra-thin layers (approximately 0.02-3.0 .mu.m) that do
not extend across the pores in the material, the porosity of the
porous substrate is essentially unaffected while the fibers and the
final product acquire the desired functionality. The resulting
polymer layer is also used to improve the adherence and durability
of metallic and ceramic coatings.
Inventors: |
Mikhael, Michael G.;
(Tucson, AZ) ; Yializis, Angelo; (Tucson,
AZ) |
Correspondence
Address: |
QUARLES & BRADY STREICH LANG, LLP
ONE SOUTH CHURCH AVENUE
SUITE 1700
TUCSON
AZ
85701-1621
US
|
Family ID: |
33303278 |
Appl. No.: |
10/830608 |
Filed: |
April 23, 2004 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
60465719 |
Apr 25, 2003 |
|
|
|
Current U.S.
Class: |
427/446 ;
428/304.4 |
Current CPC
Class: |
Y10T 428/24999 20150401;
B05D 3/144 20130101; D06M 14/18 20130101; B01D 67/0072 20130101;
Y10T 428/249956 20150401; B01D 2239/0414 20130101; B01D 2325/30
20130101; C23C 8/20 20130101; Y10T 428/249987 20150401; B01D
2325/04 20130101; D06M 10/025 20130101; B01D 39/18 20130101; C23C
30/00 20130101; B05D 1/60 20130101; D04H 1/42 20130101; B01D
2239/1291 20130101; B01D 39/2065 20130101; B01D 67/0088 20130101;
B01D 2325/36 20130101; B01D 2239/0428 20130101; B01D 2239/045
20130101; B05D 3/142 20130101; C23C 8/02 20130101; C23C 28/00
20130101; B01D 39/2017 20130101; B01D 2239/0457 20130101; D06M
10/08 20130101; B01D 2239/0478 20130101; B01D 2239/0492 20130101;
Y10T 428/249953 20150401; B01D 2239/10 20130101; B01D 67/009
20130101; B01D 71/022 20130101; B01D 2239/065 20130101; B01D
2325/38 20130101; C23C 8/80 20130101; B01D 39/1623 20130101; B01D
71/02 20130101; B01D 2325/26 20130101; B01D 2239/0241 20130101;
B01D 2239/0421 20130101 |
Class at
Publication: |
427/446 ;
428/304.4 |
International
Class: |
C23C 004/00 |
Claims
We claim:
1. A process for functionalizing a porous substrate to impart a
particular functionality to the substrate while retaining its
permeability, comprising the following steps: (a) flash evaporating
a monomer having said functionality in a vacuum chamber to produce
a vapor; (b) condensing the vapor on the porous substrate to
produce a film of said monomer on the porous substrate; and (c)
curing the film to produce a functionalized polymeric layer on the
porous substrate; wherein said condensing step is carried out under
vapor-density and residence-time conditions that limit said
polymeric layer to a maximum thickness of about 3.0 .mu.m.
2. The process of claim 1, further including the step of
pretreating said substrate in a plasma field within about one
second prior to the condensation step.
3. The process of claim 1, further including the step of vacuum
depositing an inorganic layer over said polymeric layer.
4. The process of claim 3, wherein said inorganic layer is selected
from the group consisting of metals and ceramics.
5. The process of claim 2, further including the step of vacuum
depositing an inorganic layer over said polymeric layer.
6. The process of claim 5, wherein said inorganic layer is selected
from the group consisting of metals and ceramics.
7. The process of claim 3, further including the steps of flash
evaporating and condensing a second film of monomer on said
inorganic layer, and the further step of curing the second film to
produce a second polymeric layer on the inorganic layer.
8. The process of claim 4, further including the steps of flash
evaporating and condensing a second film of monomer on said
inorganic layer, and the further step of curing the second film to
produce a second polymeric layer on the inorganic layer.
9. The process of claim 5, further including the steps of flash
evaporating and condensing a second film of monomer on said
inorganic layer, and the further step of curing the second film to
produce a second polymeric layer on the inorganic layer.
10. The process of claim 6, further including the steps of flash
evaporating and condensing a second film of monomer on said
inorganic layer, and the step of curing the second film to produce
a second polymeric layer on the inorganic layer.
11. The process of claim 1, wherein said porous substrate comprises
a porous material selected from the group consisting of
polypropylene, polyethylene, fluoro-polymers, polyester, nylon,
rayon, paper, wool, cotton, glass fibers, carbon fibers,
cellulose-based fibers, and metals; and said monomer is a
fluorinated monomer to provide a water and oil repellency
functionality.
12. The process of claim 11, wherein said monomer comprises a color
additive.
13. The process of claim 11, wherein said monomer comprises a
biocide additive.
14. The process of claim 11, wherein said monomer comprises a
brominated monomer to provide a fire retardant functionality.
15. The process of claim 1, wherein said porous substrate comprises
a porous material selected from the group consisting of
polypropylene, polyethylene, polyester, nylon, rayon, paper,
cotton, wool, glass fibers, carbon fibers, cellulose-based fibers,
and metals; and said monomer is functionalized with a functional
group selected from the group of hydroxyl, carboxyl, sulfonic,
amino, amido, or ether to provide a hydrophilic functionality.
16. The process of claim 15, wherein said monomer comprises a color
additive.
17. The process of claim 15, wherein said monomer comprises an
biocide additive.
18. The process of claim 15, wherein said monomer comprises a
brominated material to provide a fire-retardant functionality.
19. The process of claim 15, wherein said monomer comprises an
acrylated acetyl acetonate monomer to provide a metal-chelating
functionality.
20. The process of claim 1, wherein said porous substrate comprises
a porous material selected from the group consisting of
polypropylene, polyethylene, fluoro-polymers, polyester, nylon,
rayon, paper, cotton, wool, glass fibers, carbon fibers,
cellulose-based fibers and metals; and said monomer includes a
sulfonic acid group to provide a proton-conductivity
functionality.
21. The process of claim 1, wherein said porous substrate comprises
a porous material selected from the group consisting of
polypropylene, polyethylene, fluoro-polymers, polyester, nylon,
rayon, paper, wool, cotton, glass fibers, carbon fibers, cellulose
based fibers, and metals; said monomer includes a sulfonic acid
group; and further comprising the step of co-depositing metallic
lithium over said monomer prior to the curing step to provide a
polymer electrolyte with ion-conductivity functionality.
22. The process of claim 3, wherein said porous substrate comprises
a porous material selected from the group consisting of
polypropylene, polyethylene, fluoro-polymers, polyester, nylon,
rayon, paper, wool, cotton, glass fibers, carbon fibers,
cellulose-based fibers and metals; and said metal layer provides a
low-emissivity functionality.
23. The process of claim 7, wherein said porous substrate comprises
a porous material selected from the group consisting of
polypropylene, polyethylene, fluoro-polymers, polyester, nylon,
rayon, paper, wool, cotton, glass fibers, carbon fibers, cellulose
based fibers and metals; and said metal layer provides a
low-emissivity functionality.
24. A porous substrate produced by the process of claim 1, wherein
said monomer incorporates a hydrophilic and oleophilic
functionality.
25. A porous substrate produced by the process of claim 1, wherein
said monomer incorporates a hydrophilic electrostatic dissipation
functionality.
26. A porous substrate produced by the process of claim 1, wherein
said monomer incorporates a hydrophobic and oleophobic
functionality.
27. A porous substrate produced by the process of claim 1, wherein
said monomer incorporates a color.
28. A porous substrate produced by the process of claim 1, wherein
said monomer incorporates a biocide functionality.
29. A porous substrate produced by the process of claim 1, wherein
said monomer incorporates a fire-resistant functionality.
30. A porous substrate produced by the process of claim 1, wherein
said monomer incorporates a metal-chelating functionality.
31. A porous substrate produced by the process of claim 1, wherein
said monomer incorporates a proton-conductivity functionality.
32. A porous substrate produced by the process of claim 1, wherein
said monomer incorporates an ion-conductivity functionality.
33. A porous substrate produced by the process of claim 1, wherein
said monomer incorporates a pH-sensing functionality.
34. A porous substrate produced by the process of claim 1, wherein
said monomer incorporates a scent-emission functionality.
35. A porous substrate with increased wet tensile strength produced
by the process of claim 1.
36. A porous substrate with increased chemical resistance produced
by the process of claim 1.
37. A porous substrate with increased abrasion resistance produced
by the process of claim 1.
38. A porous substrate with a reduced friction coefficient produced
by the process of claim 1.
39. A porous substrate with two sides and corresponding opposite
functionalities produced by the process of claim 1.
40. A porous substrate produced by the process of claim 3, wherein
said inorganic layer is metallic to provide electrical
conductivity, low-emissivity and electrostatic dissipation
functionalities.
41. A porous substrate produced by the process of claim 5, wherein
said inorganic layer is metallic to provide electrical
conductivity, low-emissivity and electrostatic dissipation
functionalities.
Description
[0001] RELATED APPLICATION
[0002] This application is based on U.S. Provisional Application
Serial No. 60/465,719, filed on Apr. 25, 2003.
BACKGROUND OF THE INVENTION
[0003] 1. Field of the Invention
[0004] This invention is related in general to the
functionalization of the surface of materials for the purpose of
improving their properties for particular applications. In
particular, it pertains to a combined
plasma-treatment/vapor-deposition process for functionalizing
paper, membranes, and other woven and non-woven porous
materials.
[0005] 2. Description of the Related Art
[0006] The term "functionalization" and related terminology are
used in the art and herein to refer to the process of treating a
material to alter its surface properties to meet specific
requirements for a particular application. For example, the surface
energy of a material may be treated to render it particularly
hydrophobic or hydrophilic as may be desirable for a given use.
Thus, surface functionalization has become common practice in the
manufacture of many materials because it adds value to the end
product. In order to achieve such different ultimate results,
functionalization may be carried out in a variety of ways ranging
from wet chemistry to various forms of vapor deposition, vacuum
metallization and sputtering.
[0007] Textiles, non-woven products and paper substrates are
fiber-based porous materials with inherent properties derived from
the nature of the fibers. Synthetic and natural fibers (for
example, polypropylene, nylon, polyethylene, polyester, cellulosic
fibers, wool, silk, and other polymers and blends) can be shaped
into different products with a great range of mechanical and
physical properties. In addition, the porosity of these materials
usually serves a necessary function, such as gas and/or liquid
permeation, particulate filtration, liquid absorption, etc.
Therefore, any subsequent treatment designed to further modify the
chemical properties of the fibers by appropriately functionalizing
them must be carried out, to the extent possible, without affecting
the porosity of the material. This has heretofore been virtually
impossible when such functionalization results from the deposition
of polymers.
[0008] A variety of wet chemical processes have been used
traditionally to treat with polymers and functionalize fibers that
are otherwise inert or have limited surface functionality. These
processes involve the immersion of the fibrous material in liquids
or fluid foams designed to coat individual fibers and impart
specific functionalities while retaining the material's porosity
and ability to breathe. In spite of the many claims made in
commercial products, though, it is clear that such wet-chemistry
processes at best materially reduce the porosity of the substrate
or, in the worst cases, essentially plug the interstices between
fibers. Therefore, the functionalization of porous materials by
wet-chemistry polymer deposition has produced the desired results
in terms of surface functionality, but with the attendant serious
deterioration of the mechanical characteristics of the underlying
porous substrate.
[0009] Thus, prior-art processes for functionalizing porous
materials by coating the fibers with a polymer film have produced
unsatisfactory results because of loss of porosity. In addition,
these solvent-based and water-based processes for woven and
non-woven fabrics, paper and other porous materials (like open- and
closed-cell plastic foams) have been increasingly facing
environmental challenges and constraints that result in higher
end-product costs. In some cases, producers have actually withdrawn
from the market coatings that present potential health hazards,
such as the fluoro and chloro monomer materials used to
functionalize products for hydrophobic/oleophobic and biocide
properties, respectively.
[0010] Therefore, there is a pressing need for new coating
technologies that are suitable for porous materials, are safe to
implement, do not utilize solvents, and do not effect the
mechanical and functional properties of the porous substrate. While
polymers applied by vacuum deposition have been used successfully
in the art to impart particular functional properties to
non-porous, non-permeable substrates, no attempt was historically
made to so functionalize porous materials because the vacuum
deposition process was believed to be likely to exacerbate the pore
plugging problem.
[0011] For example, the vacuum deposition of a polymer coating by
flash evaporation of a monomer and its subsequent polymerization by
radiation curing in a vacuum chamber has been used widely with a
variety of monomers, such as free-radical polymerizable acrylates,
cationic polymerizable epoxies and vinyl monomers, to control the
surface energy of the resulting products and introduce desirable
characteristics. Without limitation, these include hydrophobicity,
oleophobicity, hydrophilicity, oleophilicity, fire resistance,
biocidicity, color, anti-stain, antistatic, and sensor properties.
In all cases, the substrate is exposed to a dense fog of vaporized
monomer under conditions that cause its immediate condensation and
curing on the substrate's surface. Therefore, it stood to reason to
believe that these conditions would favor the accumulation of
monomer droplets in the pores of a porous substrate and cause it to
become impermeable. This invention is based on the surprising
discovery that, when appropriately controlled, vacuum deposition
can be use successfully to functionalize porous materials while
retaining their permeability properties.
BRIEF SUMMARY OF THE INVENTION
[0012] In view of the foregoing, this invention is directed at a
process that is suitable for functionalizing a broad range of
porous substrates, including synthetic and natural fabrics, fibers
and non-woven materials. Because of the fibrous nature of these
substrates and their general commercial uses, the invention is
directed particularly at maintaining the breathability of the
materials, providing durability in the coatings and prolonged
resistance to washing and cleaning, and selectively treating one or
both sides of the fabric material. The invention also aims at a
process that is compatible with the use of existing equipment and
with the application of other coating layers, including various
additives and catalysts currently utilized in the art.
[0013] Therefore, according to one aspect of the invention, a
porous substrate is pretreated in a plasma field and a
functionalizing monomer is immediately flash-evaporated, deposited
and cured over the substrate in a vacuum vapor-deposition chamber.
We discovered that it is possible to control the process so that
the resulting polymer coating adheres to the surface of individual
fibers in ultra-thin layers (approximately 0.02-3.0 .mu.m,
depending on the size of the pores) that do not extend across the
pores in the material. As a result, the porosity of the substrate
is essentially unaffected while the fibers and the final product
acquire the desired functionality.
[0014] The vapor deposition of metals and/or ceramics has also been
used in the art to produce a great variety of functionalized
products. For example, metal-coated substrates provide increased
reflectivity and indium-titanium-oxide (ITO) coated materials
provide electrical conductivity. Metal, ceramic and polymer layers
have been deposited on non-porous substrates separately or in
combination to produce different effects, as may be desirable for
particular applications.
[0015] Therefore, according to another aspect of the invention,
multiple layers of polymeric and metallic and/or ceramic materials
are vapor deposited in a single process to impart additional
functional properties to the porous substrate. For example, while
it has been known to deposit metal layers directly on fabrics in
order to add reflectivity, the resulting coated products have
exhibited low durability and poor resistance to abrasion (i.e., the
metal particles do not form an even layer over the microscopically
rough fiber surfaces and metal flakes tend to separate from the
fabric). According to the invention, a polymer layer is first
deposited to produce a smooth thin layer over the fibers and a
metal layer is then deposited over the resulting improved
substrate. This process yields a smoother fiber surface for
receiving the metal deposition, which prevents cracking and
separation of the outer metal layer. If necessary, depending on the
intended use, an additional polymeric protective layer can yet be
added over the metallic film without materially affecting the
overall permeability of the fabric.
[0016] As detailed below, similar advantages are obtained by
combining polymers with ceramics, which also tend to break up and
separate from the substrate when deposited directly over fibers.
Various other purposes and advantages of the invention will become
clear from its description in the specification that follows and
from the novel features particularly pointed out in the appended
claims. Therefore, the invention consists of the features
hereinafter illustrated in the drawings, fully described in the
detailed description of the preferred embodiments and particularly
pointed out in the claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1 is a schematic representation of a modified vacuum
chamber according to the invention.
[0018] FIG. 2 is a scanning electron microscope (SEM) picture of an
uncoated non-woven polypropylene fabric used to produce an
oleophobic filter medium.
[0019] FIG. 3 is an SEM picture of the same non-woven polypropylene
fabric of FIG. 2 after coating by monomer vacuum deposition
according to the invention.
[0020] FIG. 4 is a schematic representation of a vacuum chamber
equipped with plasma pretreatment, a flash evaporation/condensation
station, a monomer radiation-curing station, and a metal or ceramic
vapor deposition station for the sequential deposition of multiple
layers over a porous substrate according to the invention.
[0021] FIG. 5 is a schematic representation of the same chamber of
FIG. 4 with an additional in-line vacuum deposition station
following the metal/ceramic deposition unit.
[0022] FIG. 6 illustrates the functionalizing properties of the
invention on a porous non-woven polypropylene filter medium. The
lower portion shows the oleo-philic (left) and hydrophobic (right)
properties of the uncoated material. The middle portion shows the
medium's oleophobic property acquired after coating with a
TEFLON.RTM.-like polymer (a fluorinated acrylate). The top portion
shows the hydrophilic property acquired after coating with a
wetting polymer (a carboxylic acid functionalized acrylate).
[0023] FIG. 7 is a flow chart of the basic steps of the process of
the invention.
[0024] FIG. 8 is a flow chart of the steps involved in a second
embodiment of the invention.
[0025] FIG. 9 is a flow chart of the steps involved in a third
embodiment of the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION
[0026] The invention lies in the discovery that utilizing the
process of vacuum deposition to functionalize a porous substrate
with a polymeric film makes it possible to control the thickness of
the deposited layer and avoid the problem of pore plugging
encountered when functionalization is carried out by wet chemistry.
The invention also lies in the discovery that coating individual
fibers of a porous substrate with a thin polymer layer produces a
surface that is better adapted for receiving the subsequent
deposition of metal or ceramic layers. Surprisingly, when deposited
over an underlying polymer layer already used to coat individual
fibers, metals and ceramics are found to be much more resistant to
breakage and separation than heretofore possible using prior-art
deposition techniques. Without limitation, porous substrates to
which this invention applies consist of polypropylene,
polyethylene, fluoro-polymers, polyester, nylon, rayon, paper,
wool, cotton, glass fibers, carbon fibers, cellulose based fibers,
and metals.
[0027] For the purposes of this disclosure, the term "porous" is
used in a macroscopic sense with reference to any substrate through
which fluids can easily permeate under normal conditions. These
include, for example, paper, textiles, woven or non-woven fabrics,
solid foams, membranes and similar materials exhibiting
permeability properties typically associated with these products.
"Porous" is not intended to cover materials which, though they
exhibit structural porosity, are not used functionally as permeable
substrates. The term "condensation" refers to a phase-change
process from gas to liquid (and subsequently solid) obtained upon
contact with a surface having a temperature lower than the dew
point of the gas at a given operating pressure. For the purposes of
the invention, such a surface is the substrate subjected to vapor
deposition which has been either pre-chilled or is in contact with
a cold drum in the vacuum chamber. Finally, the term "monomer" is
intended to include also oligomers and blends of monomers or
oligomers capable of flash evaporation in a vacuum chamber.
[0028] In its preferred embodiment, the invention is practiced by
first pretreating the porous substrate in a plasma field and then
immediately subjecting it to the deposition of a thin layer of
vaporized monomer in a vacuum deposition process under conditions
that prevent the formation of condensate blocking the pores of the
substrate. The monomer film is subsequently polymerized by exposing
it to an electron-beam field or other radiation-curing process. The
monomer is flash-evaporated and condensed on the porous substrate
in conventional manner but, in order to retain the structural
porosity and the related functional properties of the substrate,
the residence time of the substrate within the deposition zone of
the vacuum chamber is controlled to ensure that a very thin film is
deposited relative to the size of the pores in the substrate. Thus,
monomer penetration within the porous structure of the substrate
produces a coating of individual fibers (or pore walls) without
sealing the openings between fibers. This is achieved by
controlling the vapor density and the speed of the moving substrate
to limit the thickness of the coating to about 0.02 to 3 .mu.m.
[0029] Vacuum plasma has been used for some time to pretreat as
well as to finish treating products of vapor deposition processes.
Pretreatment is used to clean and activate the substrate. These
functions are attributed to the plasma ablation of contaminants and
the generation of free radical and ionic species, respectively.
Plasma finishing treatment has been shown to have chemical and
physical effects that are useful in improving the outcome of
vapor-deposition processes. For example, plasma for hydrocarbon
gases and other functional monomer vapors that polymerize on the
vapor-deposited surface may be added (plasma grafting and
polymerization) to produce specific results, such as hydrophilic
and hydrophobic surfaces.
[0030] We found that, when coupled with the vacuum deposition of
monomers over fibrous substrates, plasma pretreatment produces the
additional unexpected effect of preventing the formation of monomer
droplets (an effect referred to as "beading" in the art) over the
substrate. This discovery is particularly advantageous to prevent
the plugging of pores in fabrics, paper and other porous materials
being coated with functionalizing monomers. Therefore, the
combination of plasma pretreatment with vapor deposition is much
preferred in carrying out the invention.
[0031] As illustrated in FIG. 1, in order to practice the invention
a conventional vacuum chamber 10 is modified to enable the serial
plasma-field pretreatment, vapor deposition, and radiation curing
of a porous substrate in a continuous process. Typically, the
porous substrate 12 (like paper or fabric) is processed entirely
within the vacuum chamber 10 while being spooled continuously
between a feed reel 14 and a product reel 16. The substrate 12 is
first passed through a cold compartment 18 to chill it to a
temperature sufficiently low to ensure the subsequent
cryocondensation of the monomer vapor. The substrate is then passed
through a plasma pretreatment unit 20 and immediately thereafter
(within no more than a few seconds, preferably within milliseconds)
through a flash evaporator 22, where it is exposed to the monomer
vapor for the deposition of a thin liquid film over the cold
substrate. The monomer film is then polymerized by radiation curing
through exposure to an electron beam unit 24 and passed downstream
through another (optional) cooled compartment 18. As is well known
in the art, instead of pre-chilling the substrate 12 being
processed, a rotating cold drum (typically kept at -20.degree. C.
to 30.degree. C.) in contact with the substrate past the evaporator
22 may be used to effect the condensation of the monomer vapor.
[0032] We found that the monomer feed to the evaporator unit 22 and
the speed of the spooling substrate can be judiciously tailored to
ensure the three-dimensional coverage of the porous structure of
the substrate 12 while limiting the thickness of the film deposited
over the substrate fibers. For example, feeding a fluoro-acrylate
monomer at a rate of about 40 ml/minute to the flash evaporator 22
and moving the substrate 12 (1.2 meter wide) through the chamber at
a speed of about 100 meters per minute produces the formation of a
substantially uniform film about 0.5-.mu.m thick over the
polypropylene fibers of a typical filter medium with pores about
20-40 .mu.m wide. As a result, the porosity of the medium is not
significantly affected, but the material is thoroughly
functionalized to exhibit oleophobic properties.
[0033] FIGS. 2 and 3 illustrate SEM pictures of such a non-woven
filter medium before and after coating, respectively, according to
the invention. The micrographs show no evidence of polymer
obstruction between the fibers and, in fact, air permeation tests
showed no significant difference between the two samples. This
resulted from the conformal (i.e., shaped to conform to the
structure of individual fibers) deposition of the liquid monomer
from a vapor phase state over the surface of the fibers, in
contrast to conventional liquid-based methods that exhibit very
limited levels of conformal deposition. The smooth and pliable
nature of the polymer surface covering each fiber after vapor
deposition is believed to be the reason for the greater adhesion
and resistance to breakage of metallic and/or ceramic layers whey
they are further used to cover the fibers.
[0034] In general, we found that thin polymer coatings (0.1 .mu.m
or less) designed to alter the chemical functionality of a porous
substrate have no significant effect on gas permeability. Thicker
coatings, designed to provide physical protection against wear and
tear, have only a minor effect on breathability. As illustrated in
Table 1 below for three different fabrics treated with the process
of the invention, air permeability appears to be (and remain after
treatment) simply a function of the weight of the material (i.e.,
the coarseness of the weave), rather than of the polymer coating.
Each material in the table (A-cotton, B-polyester, C-wool)
consisted of a woven fabric coated with as much as 2-3 .mu.m of
vacuum deposited acrylate polymer prior to metallization. This
relatively thick polymer coating enhanced the abrasion resistance
and washability properties of the metallized fabrics but did not
materially affect the permeability of the material.
1 TABLE 1 Basis weight Air permeability Material (OZ/Y.sup.2)
(CFM/M.sup.2) A-uncoated cotton 5.83 39.6 A-coated cotton 6.06 38.9
B-uncoated polyester 6.76 16.0 B-coated polyester 6.90 15.5
C-uncoated wool 3.38 118.7 C-coated wool 3.54 108.6
[0035] Based on these results, it is clear that the invention
provides an environmentally friendly vacuum-based process that
utilizes solvent-free and water-free monomers and produces
high-quality polymer coatings that do not effect the functional
porosity of the substrate. The coating process can be implemented
in conventional vacuum coating plants and can be combined with
in-line plasma treatment and metallization to create unique and
high value-added products. The common feature of all embodiments of
the invention is coating of the fibers or voids in the porous
substrate produced by flash evaporation and radiation curing of a
monomer to produce a conforming, thin, polymer layer that
functionalizes the surface of a porous material with virtually no
effect on its permeability or breathability.
[0036] Various tests have shown that the process can be used
successfully to functionalize surfaces of woven and non-woven
fabrics, paper, membranes and foam substrates. Properties such as
oil and water repellency and wettability, release, antibacterial
and other chemical functionalities are easily achievable with ultra
thin polymer coatings (less than 0.2 .mu.m). Thicker polymer
layers, of the order of 0.2-3 .mu.m, have been used to provide
thermo-mechanical properties such as heat sealing, abrasion
resistance and chemical resistance against moisture, acids, bases
and organic solvents. Such thin coatings of multifunctional
acrylates, monoacrylates, vinyls, epoxies and various other
oligomers can be deposited over a substrate traveling at speeds as
high as 1000 ft/min. This high productivity, combined with
relatively low monomer material costs, results in a very economical
and cost effective functionalization process.
[0037] When further combined with the vapor deposition of metal
and/or ceramic layers, the process of the invention affords
improvements in a wide range of multifunctional products. FIG. 4
illustrates schematically a vacuum chamber 30 that includes a
station 32 for depositing metals and ceramics (such as a sputtering
unit or a reactive electron-beam evaporation unit). Note that in
the process illustrated in this figure the porous substrate 12 is
chilled by contact with a cold drum 34 for the condensation step.
If desirable, additional layers may be deposited sequentially in
line by adding further deposition units. For example, a transparent
polymer layer may be further used to coat the metal layer already
deposited on the fabric (over the initial thin polymer film of the
invention) in order to protect the metal and prevent abrasion while
retaining the reflectivity of the fabric. In such a case, as shown
in FIG. 5, an additional flash evaporation unit 36, followed by a
second radiation curing unit 38, would be utilized after the
metallization stage.
[0038] It is anticipated that such a combination of layers can be
used advantageously in the production of a variety of improved
products. For example, metallized fabrics are used for decoration
and to achieve energy savings in the production of roll, vertical,
and horizontal blinds. Similarly, breathable insulation in the form
of metallized paper and non-woven polymers is widely used in
construction to reflect heat while minimizing the formation of mold
and mildew. Metallized fabrics are used to decorate garments and
paper for labels. They are also used as clothing liners and in
camping gear, such as sleeping bags and tents, to improve
insulation without affecting weight and breathability. The same
advantages are desirable in blankets and tapes for medical
applications, in fire protective suits designed to reflect infrared
radiation in a multitude of military applications (jackets, shirts,
garments, tents and tarps used to reduce infrared signature), in
garments for workers in microwave and radar communication
industries, and in clothing for electro-magnetic interference (EMI)
testing personnel.
[0039] Metallized fabrics are also widely used in the automotive
industry to provide engine and exhaust-heat insulation, and filter
media (such as functionalized the non-woven polypropylene used to
produce electrostatically charged filter systems and air filters
with EMI shielding properties). Foams and fabrics are metallized to
produce electromagnetic shields for gasket materials, cable
shields, covers and liners for motors, avionic boxes, cable
junctions, antennas, portable shielded rooms, window drapery, wall
coverings and electrostatic dissipating garments. The performance
of the porous materials used in all of these applications can be
materially improved by the initial deposition of a first thin-film
polymer layer according to the present invention.
[0040] A great variety of paper, as well as woven and non-woven
fabrics, were coated according to the invention with different
polymer formulations designed to serve specific applications. The
coated materials were subjected to surface microscopic
investigation. The data showed in all cases that condensing a
flash-evaporated monomer vapor on the plasma pretreated fibers
produces a homogeneous thin liquid layer that covers the entire
surface of each individual fiber without connecting fiber to fiber
and blocking the pores. The following examples illustrate these
applications of the invention (all percentages are by weight).
EXAMPLE 1
Hydrophobic/Oleophobic Coating
[0041] A melt-blown polypropylene nonwoven fabric was
functionalized with a hydrophobic/oleophobic fluorinated acrylate
polymer coating to create a repellent surface. The monomer was
flash evaporated at about 100 Millitorr. The fabric was pretreated
in a plasma field and within one second it was exposed to the
monomer vapor for condensation while traveling at a speed of about
50 meters/minute. The condensed monomer layer was cured in-line by
electron beam radiation within 100 milliseconds. A polymer coating
thickness of about 0.1 .mu.m resulted from the run, which was found
to provide adequate repellency for water and oil with a surface
energy of about 27 dyne/cm. The functionalized fabric repelled both
water-based and oil-based fluids while substantially retaining the
original permeability of the fabric. The coated materials showed
high performance as electrostatic charged filter media. The same
coating process with the same fluoro-acrylate monomer was repeated
on nonwoven polyethylene, paper, fluoro-polymers, polyester fibers,
nylon fibers, rayon fibers, wool fabrics, and cotton fabrics.
Similar water/oil repellency results were obtained with all kinds
of fabric materials where the functionalizing monomer was deposited
in thicknesses ranging from 0.02 to 3.0 .mu.m. In addition to water
and oil repellency, the coated materials showed a lower coefficient
of friction, which produced a silky feel in the coated fabrics. In
a similar experiment at a higher speed (200 meter/minute), the
functionalized coating was restricted to the exposed surface of the
fabric material. The back side of the coated web retained its
original properties. (It is noted that the option of selectively
coating only one side of the web is another unique characteristic
for the process of the invention.) As illustrated in FIG. 6
(left-center side), these coating formulations produced the desired
repellent characteristics in these fabrics without loss oil
repellency properties of the treated fabric remained substantially
unaltered after 10 wash cycles.
2TABLE 2 Durability of Water and Oil Repellent Fluoro-Polymer
Coatings Water/Alcohol Oil Repellency Test* Repellency Test* 10
Wash 10 Wash Fabrics Samples Un-washed cycles Un-washed cycles
Cotton Uncoated 1 1 1 1 Coated 6 4 5 3 Poly- Uncoated 3 3 1 1 ester
Coated 6 5 6 4 Nylon Uncoated 3 3 1 1 Coated 6 5 6 4 *Number 1 is
the lowest repellency and 6 is the highest.
EXAMPLE 2
Hydrophilic Coating
[0042] A melt-blown polypropylene nonwoven fabric was coated with a
hydrophilic acrylate polymer film functionalized with hydroxyl,
carboxyl, sulfonic, amino, amido and ether groups (in separate
tests) to create a water absorbent surface. The monomer was flash
evaporated at about 10 Millitorr. The fabric was pretreated in a
plasma field and within one second it was exposed to the monomer
vapor for condensation while traveling at a speed of about 30
meters/minute. The condensed monomer layer was cured in-line by
electron beam radiation within 150 milliseconds. A polymer coating
thickness of about 0.1 .mu.m resulted from the run, which was found
to provide adequate wettability in all cases by water with a
surface energy of about 70-72 dyne/cm. The functionalized fabrics
absorbed water while substantially retaining the original
permeability of the fabrics. The coated materials showed high
performance as water absorbent media. The same coating process with
the same hydrophilic acrylate monomers was repeated on nonwoven
polyethylene, fluoro-polymers, polyester fibers and fluoropolymer
fabrics. Similar results were obtained with all kinds of fabric
materials with monomer layers ranging from 0.1 to 3.0 .mu.m. In a
similar experiment at a higher speed (200 meter/minute), the
functionalized coating was restricted to the exposed surface of the
fabric material. The back side of the coated web kept its original
properties. FIG. 6 illustrates water tests on the surface of a
non-woven polypropylene filter medium used in the examples, before
and after coating, as detailed above. Before coating, the material
was hydrophobic, as seen at the bottom-right portion of the
picture. After functionalization according to the invention, the
material became clearly hydrophilic, as illustrated at the
top-right portion of the picture by the water drop absorbed into
the fabric. Thus, these coated substrates can be used
advantageously for diapers, filters, battery separators and ion
transport membranes. Table 3 below shows three water-strike tests
for non-woven polypropylene coated with two hydrophilic
acrylate-based formulations (Sigma 1033 and Sigma 1032 coatings).
Filter paper, which is known to be highly absorbing, was used as
the reference control material (because untreated diaper
material--polypropylene--is known to be hydrophobic).
3TABLE 3 Water strike test for non-woven polypropylene (NW PP).
Time in seconds required for complete absorption of a ten-gram
portion of DI water 1.sup.st 2.sup.nd 3.sup.rd Average Material
strike strike strike time Uncoated 89.36 64.36 65.92 73.21 NW PP
Filter paper 3.15 6.98 7.35 5.83 control 1033 coating on 4.71 6.29
5.99 5.66 PP 1032 2.7 6.77 7.05 5.51 coating on PP Note that coated
polypropylene is as effective as the highly absorbing filter
paper.
EXAMPLE 3
Hydrophobic/Oleophobic Colored Coating
[0043] The same experiment as in Example 1 was repeated with 3-5%
organic dyes (e.g., disperse red) mixed in the fluorinated acrylate
monomer. The coated substrates showed the same levels of water and
oil repellency, measured at about 6 and 5 on the Dupont.RTM.
Teflon.RTM. Repellency Test, respectively, with the color added to
the coating. The intensity of the color can be controlled by
monitoring either the amount of organic dye or the thickness of the
coating.
EXAMPLE 4
Hydrophilic Colored Coating
[0044] The same experiment as in Example 2 was repeated with 3-5%
organic dyes (e.g., Malachite green) mixed in the hydrophilic
acrylate monomer. The coated substrates showed a colored surface
with comparably high water absorption.
EXAMPLE 5
Hydrophobic/Oleophobic Biocide Coating
[0045] The same experiment as in Example 1 was repeated with 2-4%
organic antibacterial additive (e.g., chlorinated aromatic
compound) in the fluorinated acrylate monomer. The coated
substrates showed water and oil repellency with antibacterial
properties as indicated below.
4 Results (Zone Size) Staphylococcus Klebsiella Pneumoniae Sample
identification (13 mm) (13 mm) Control uncoated paper no inhibition
to no inhibition to growth growth complete inhibition Both side
Coated paper complete inhibition
EXAMPLE 6
Hydrophilic Biocide Coating
[0046] The same experiment as in Example 2 was repeated with 3-5%
organic antibacterial additive (e.g., chlorinated aromatic
compound) in the hydrophilic acrylate monomer. The coated
substrates showed antibacterial properties and high water
absorption.
EXAMPLE 7
Fire Retardant Coatings
[0047] The same experiments as in Example 1 and 2 were repeated
with 5-20% brominated compound in the diacrylate monomer. The
coated substrates showed fire resistance properties with
hydrophobic/oleophobic and hydrophilic properties comparable to
those of Examples 1 and 2.
EXAMPLE 8
Color Changing Sensing Coatings
[0048] The same experiments as in Example 1 and 2 were repeated
with 5-20% of a pH indicator compound, such as phenol phthaleine,
in the diacrylate monomer. The resulting coated substrates changed
color reversibly with corresponding changes in the environment's
pH. The same experiments were repeated using 5-30% heat-sensitive
molecules, such as 4-pentyl-4-cyanobiphenyl, which produces a
change in color from clear to grey when the temperature reaches
about 50 degrees C. The coated materials changed color with changes
in the temperature of the environment.
EXAMPLE 9
Flavored Coatings
[0049] The same experiments as in Example 1 and 2 were repeated
with 5-20% artificial fruit-flavor compounds in the diacrylate
monomer; for example, an ionone such as
4-(2,6,6-trimethyl-1-cyclohexen-1-yl)-3-buten-2-one is used to
confer a strawberry. The coated substrates exhibited a
corresponding emission of a fruity scent in addition to
hydrophobic/oleophobic and hydrophilic properties comparable to
those of Examples 1 and 2.
EXAMPLE 10
Wet Tensile Strength Coatings
[0050] The same experiments as in Example 1 and 2 were repeated at
a slower rate (<100 fpm) to allow the monomer vapor to penetrate
all the way through the fibers of paper material and coat the
entire available surface of individual fibers (retaining the
porosity if the material). The resulting coated paper exhibited a
high wet tensile strength in addition to hydrophobic/oleophobic and
hydrophilic properties comparable to those of Examples 1 and 2.
EXAMPLE 11
Chemical Resistant Coatings
[0051] The same experiments as in Example 1 and 2 were repeated
with a monomer that contained 5-40% triacrylate monomer in order to
increase cross-linking and the density of the coating, thereby
increase it chemical resistance. The coated substrates showed that
the addition of the triacrylate monomer increased the chemical
resistance to organic solvents as well as acid and base solutions
while retaining hydrophobic/oleophobic and hydrophilic properties
comparable to those of Examples 1 and 2.
EXAMPLE 12
Metal Chelating Coatings
[0052] The same experiments as in Example 2 were repeated with
10-20% acrylated acetyl acetonate monomer in the diacrylate
monomer. The coated substrates showed metal chelating properties by
bonding to metal ions (e.g., Cu, Pb, Cr). Accordingly, they were
tested successfully as filters for removing metal ions from
water.
EXAMPLE 13
Proton Conductor Coatings
[0053] As in the previous examples, porous polypropylene and
fluoropolymer films were coated with a sulfonated compound monomer
and then cured with an electron beam. The coated substrates
exhibited proton conductivity, thereby showing potential for use as
a fuel-cell membrane.
EXAMPLE 14
Ion Conductor Coatings
[0054] As in the previous examples, porous polypropylene and
fluoropolymer films were coated with a sulfonated compound that was
co-deposited with metallic lithium to form lithium sulfonate and
then cured with an electron beam. The coated substrates exhibited
lithium-ion conductivity, thereby showing potential for use as a
battery separator and electrolyte.
[0055] In addition to the foregoing examples, the ability to
deposit a polymer layer followed by metallization in line, as
illustrated in FIG. 5, offers some unique opportunities in the
production of metallized fabrics and paper. A top thin polymer
layer can provide abrasion and corrosion protection which is a
basic requirement for most metallized layers. For example, we have
shown that the washability of metallized fabrics can be prolonged
significantly when coated with a vacuum deposited acrylate layer
that has a thickness of about 1.0 .mu.m. Such thin polymer layers
have no practical effect on the fabric breathability and "comfort"
properties. Similarly, metallized fabrics for heat reflecting
applications can be protected with thin polymer layers that have
low infrared absorption in order to minimize heat absorption upon
exposure to high temperatures (low emissivity). Other
functionalizing polymer properties include controlling the surface
energy, which may be varied from high surface energy for improved
adhesion and wettability of the metallized material to low surface
energy for release applications and Teflon.RTM.-like
performance.
[0056] As illustrated by the examples above, coating formulations
have also been effectively functionalized with biocide compounds,
such as chlorinated molecules. A small amount of biocide is
evaporated simultaneously with the acrylate monomer and becomes
trapped in the matrix of the radiation cured host polymer. Such
coatings have been successfully deposited directly on fabric
substrates or over other polymer, metal or ceramic films. Colored
decorative coatings were similarly prepared and applied by
synthesizing functionalized organic dyes formulated in a binder and
applying them to white paper and non-woven webs.
[0057] This invention demonstrates that porous materials may be
functionalized by monomer vacuum deposition to produce desired
surface properties without significant loss of the original
characteristics of the substrate. Thus, vacuum deposited polymer
coatings on fabric and paper webs provide a real alternative to
conventional solvent- and water-based coating processes. Highly
functional coatings can be obtained that conformally coat the
fibers of these materials with little or no effect on porosity and
gas or liquid permeation. Coatings with submicron thickness can be
used to replace liquid-based fluoro treatments and wax impregnation
processes, which are facing environmental and recycleability
challenges. The totally enclosed conditions of a vacuum chamber are
environmentally friendly, permitting fluoro, chloro and other
hazardous-monomer formulations to be processed safely.
[0058] FIGS. 7, 8 and 9 are flow charts illustrating the basic
steps of the preferred embodiments of the invention for single,
double and triple layer applications, respectively. Various changes
in the details, steps and components that have been described may
be made by those skilled in the art within the principles and scope
of the invention herein illustrated and defined in the appended
claims. For example, while the invention has been described mainly
in terms of one-side coating, it is clear that the two sides of a
sheet-type substrate may be coated separately or on line to produce
different functionalities. For example, diaper material may be
functionalized to improve hydrophilicity on one side and produce
hydrophobicity on the opposite side, thereby producing a diaper
that is highly absorbent in the interior and repellent in the
exterior, as desirable for most uses.
[0059] Thus, while the present invention has been shown and
described herein in what is believed to be the most practical and
preferred embodiments, it is recognized that departures can be made
therefrom within the scope of the invention, which is not to be
limited to the details disclosed herein but is to be accorded the
full scope of the claims so as to embrace any and all equivalent
processes and products.
* * * * *