Note: Descriptions are shown in the official language in which they were submitted.
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UV-CUR.A.BLE SUPERABSORBENT COATINGS
TECHNICAL FIELD AND INDUSTRIAL
APPLICABILITY OF THE INVENTION
The present invention relates to a high strength superabsorbent coating
capable of
rapidly absorbing water, which is suitable for coating a variety of articles
requiring a
water-resistant surface, including, but not limited to, reinforced or molded
products, as
well as reinforcing materials used in the manufacture of such products. More
specifically,
the coating is formed from a non-aqueous composition comprising a water-
swellable
polymer powder and a liquid UV-curable resin. The coating composition may
further
include a viscosity-modifying agent.
The inventive concept also relates to articles coated with the superabsorbent
coating composition, including reinforced and molded products and fibrous
reinforcing
materials; as well as methods of applying such coatings. The coating of this
invention
demonstrates a high level of water absorption, and provides an excellent
spreading and
coating ability when applied to a substrate.
BACKGROUND OF THE INVENTION
Deterioration caused by the invasion of moisture beneath the exposed surfaces
of articles
used in outdoor environments is a well-known problem. This deterioration
includes
oxidative deterioration caused by reaction of water with the surfaces of
reinforcing fibers
used in these articles, as well as water-induced corrosion. liz marine
environments, for
example, the problems associated with waterlogging are particularly compounded
by the
salinity of the environment. The presence of salt in such aqueous environments
hastens
the oxidative decomposition. In non-saline environments, for example in
environments
having high atmospheric humidity, water-resistant coatings are necessary to
protect the
structures and equipment surfaces from moisture-induced decomposition.
Articles affected by the deterioration described above include items having a
surface exposed to high moisture or humidity. Examples of such articles
include
reinforced rods and cables, such as fiber optic or telecommunications cables.
These
telecommunications cables are often used in situations where they are buried
underground
or submerged in water over long periods. As such, protection from water damage
is
critical to the structural integrity of these cables and to the success of the
functions they
are intended to perform. A telecommunications cable, for example, may include
a core
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comprising a glass rod that acts as a stiffening or reinforcing member. This
rod
contributes to the rigidity of the cable. When water penetrates to contact the
core element
of the cable, corrosion or chemical deterioration of the cable infrastructure
may result.
In order to combat the problems associated with this waterlogging damage,
several
strategies have been devised in an attempt to provide water resistance to
cables and other
reinforced articles, and to protect their sensitive inner surfaces from
contact with water or
water vapor present in the surrounding environment. These techniques for
making water-
repellent articles have included wrapping the articles in a protective
sheathing material; or
sealing the surface to be protected. Sealing tech~uques may include chemically
manipulating the surface layer of the article to render it resistant to water-
absorption, or
applying a repellent coating.
The technique of covering the surface with a protective sheatlung material is
conventional. It includes for example, using a wrap or tape made of an
impervious
polymer with water-blocking ability, or treating the wrapping material with an
emulsion
or solution of a water-blocl~ing polymer. The sheathing process does not
require
application of a chemical compound or treatment to the surface of the article;
rather the
protection is derived only from the coverage by the sheathing material.
Coatings used to repel water traditionally have been composed of substances
that
are both insoluble and impenetrable to water, and therefore presented a
physical barrier to
encroaching moisture. Such barrier coatings have included materials such as
greases or
gels. In the case of cables, for example, these coatings are applied by
extrusiomnder
pressure. There are however, certain drawbacks associated with this type of
coating.
Greases or gels are difficult to handle because of their slipperiness, and
they contribute an
unpleasant feel to the coated article. This is an important factor to be
considered in the
manufacturing process, particularly because it affects the ease of handling of
the cable
during splicing operations. Greases and gels also undergo changes in viscosity
at low or
high temperatures. These viscosity changes may affect the freeze/thaw
performance and
therefore the stability of the coating. Poor performance in these respects
therefore affects
the stable performance of the cables.
More recently, greaseless, water-resistant dry coatings have been devised
which,
of themselves, have some degree of water-absorbing capacity. This ability to
absorb
water allows the coating to absorb the moisture contacting the article, while
preventing
direct contact with the sensitive surfaces. The absorbent component in these
dry
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waterblocking coatings is a dry, granulated superabsorbent polymer that swells
and
absorbs upon contact with water. The superabsorbent polymers are usually
characterized
in terms of their swell rate, swell capacity and gel strength. Traditional
uses for these dry
superabsorbent polymers have primarily included personal hygiene product
articles, food
packaging articles and chemical spill cleanup compositions, however recent
experimentation has included using these dry polymers to form coatings for
other articles
such as reinforced cables. For example, United States Patent 5,689,601 to
Hager
discloses a dry waterblocking coating for reinforcing fiber articles using a
powdered or
granulated water-soluble dry bloclcing ingredient encased in one or more thin
layers of a
sheathing polymer. This casing restricts the degree of water absorption that
can be
achieved by the granular polyner, and accordingly the swell capacity of this
coating is
limited.
Generally, either dry or fluid coatings for reinforced fibers, strands and
articles,
such as cables that are made from these fibrous materials, are applied to the
surface of the
fibrous material and then cured before further processing, if any, occurs. The
means of
applying coatings, in general, differs depending on whether a fluid coating is
used or
whether a solid particulate coating is being applied. In the case of dry
coatings, the
coating process using granulated water-blocking agents involves several time-
consuming
and labor-intensive steps that are directly related to the use of a granulated
or powdered
polymer. These steps include the need for one or more treatments with a
binding resin,
and one or more applications of powdered resin at powder-coating stations
using
apparatus such as a fluidized bed. Alternatively, fluid coatings containing an
absorbent
polymer may be used.
A drawback of aqueous coatings is the time required to set and cure the
coating
after it is applied. Conventional coating processes which require heating, for
example in
ovens, or air-drying, require additional processing time. This results in
increased
processing costs.
There exists in the art then, a need for a waterblocking coating composition
for
application to reinforced articles or reinforcing materials, which possesses
high capacity
for water absorption and a concurrent, rapid swell rate. Moreover, it is
desired that such a
coating be capable of curing quickly and effectively, without a costly and
time-consuming
process.
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SLTMMARY OF THE INVENTION
It has now surprisingly been discovered that a highly absorbent waterblocking
coating having an excellent water swelling capacity and a rapid swell rate can
be fonned
from a non-aqueous coating composition comprising a non-aqueous liquid UV-
curable
resin and a water-swellable polymer. The coatings containing this water-
swellable
polymer are capable of substantially instantaneous water absorption when
exposed to
aqueous environments.
In one aspect, this invention includes a method of providing water resistance
to the
surface of an article comprising:
a) preparing a non-aqueous liquid coating composition comprising a water-
swellable polymer and a W curable resin;
b) applying the non-aqueous liquid coating composition to the surface of the
article to form a coated surface; and
c) exposing the coated surface to UV light and curing the non-aqueous liquid
coating to form a water-absorbing, water-resistant coating layer comprising a
water-swellable polymer on the surface of the article.
DETAILED DESCRIPTION OF THE PREFERRED
EMBODIMENTS OF THE INVENTION
The composition of this invention is suitable for forming a water-swellable
coating on the surface of articles or materials requiring surfaces that are
resistant to water,
and therefore protects the material underlying the surfaces that are treated
with the
coating.
The term "article", as it is used herein, is specifically intended to include
any
product or material having a surface that requires a water-resistant coating
to protect the
underlying structure from deterioration caused by exposure to moisture. Such
articles
include molded composite articles, laminates, sheets, reinforcing fiber
materials known in
the art, and products made using one or more of these fiber materials, either
collectively
or dispersed within a matrix of any type. The term also includes articles
manufactured
using reinforced fiber products, such as structural materials or equipment.
As water contacts the coated surface of the article to be protected, the
coating of
the invention absorbs water and swells in volume. By absorbing the water, the
coating
effectively wicks away the moisture and thus prevents it from contacting the
inner
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surfaces of the protected article. As a result, the sensitive inner surfaces
remain dry and
are protected from waterlogging deterioration. The coatings of this invention
uniquely
achieve water resistance protection by absorbing water to prevent moisture
penetration
beneath the coating layer.
The water-swellable polymer used in the coatings of this invention may be
selected from any such polymer capable of forming a non-aqueous solution for
use in the
coating mixture, and which, upon cure, has a swell capacity and swell rate
that enables
absorption of water followed by desorption without loss of the polymer itself
when the
coating is dried. Preferably, such a polymer is in powdered or particulate
form. The
water-swellable polymer for use in the present invention may, for example, be
selected
from the group of polymers possessing the required ability to absorb and
desorb quantities
of water. The coatings comprising the highly absorbent water swellable polymer
of the
present invention would absorb significantly lv.gher quantities of water,
demonstrating
swell rates of up to 75% of the dry weight or more. A desirable content of
water-swellable
polymer in the coating composition is in the range of from 5-70% weight.
Preferably, the
amount of the water-swellable polymer is from about 44% by weight to about 70%
by
weight based on the total weight of the composition. An example of a suitable
water-
swellable polymer is a polyacrylate powder commercially available under the
trade name
"AP80HS", from Emerging Technologies Inc.
The UV-curable resin that is included in the coating composition of the
present
invention is suitably a liquid, non-aqueous resin that is capable of curing
rapidly and
effectively upon exposure to ultraviolet light. Such liquid, non-aqueous
resins may be
selected from UV-curable epoxides, polyethers, polyesters, polyurethanes,
acrylates, and
combinations thereof. Preferably, the W-curable resin is a solvent-free
polyacrylate
resin that is typically liquid at room temperature. While the resin should be
a liquid, its
viscosity will, however, vary as a function of temperature. Preferably, the UV-
curable
resin is a liquid at or above ambient temperature. An example of such a resin
is a
polyacrylate sold under the trade name "500 VINCH" by Zeon Technologies Inc.
The UV-curable resin may be included in the coating composition at a
concentration of from about 30% by weight to about 9S% by weight, based on the
total
weight of the composition. Preferably, the concentration of UV-curable resin
is from
about 35% by weight to about 56% by weight.
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The compositions used to form the coatings of the present invention further
comprises one or more photoinitiators, which initiate cross-linking of the ITV-
curable
resin during the curing process. Examples of photoinitiators include "IRGACURE
651"
or "IRGACURE ~ 19" which are phenyl ketone photoinitiators available
commercially
from Ciba Specialty chemicals. Depending on the commercial formulation of the
LTV-
curable resin that is selected, the photoinitiator may be included in the
formulation. For
example, 500 VINCH UV-curable resin is sold as a combined formulation
containing a
UV-curable polyacrylate and one or more photoinitiators. The coating
composition may
also include one or more additives conventionally known for use in surface
coating
materials. For example, colorants, viscosity modifying agents, surface-active
agents, and
lubricants may be added to the formulation. The amount of any such additives
may
readily be selected according to the desired effect of the additive in the
composition.
The coating compositions may be formed by combining the water-swellable
polymer powder with the liquid ITV-curable resin and the photoinitiator.
Preferably, the
ingredients may be combined at room temperature; however, the resin may be pre-
heated
before it is combined with the other ingredients. For example, the resin may
be heated to a
temperature ranging from room temperature up to about 150°F
(66°C) before mixing.
The mixture may be blended by any suitable means. In one preferred embodiment,
a
blend of 50% by weight of a water-swellable polymer powder, such as a
polyacrylate
powder, is combined with 50% of a liquid UV-curable resin, such as acrylate
resin. The
coatings formed from this combination were observed to provide maximum water-
swell
capacity.
The coating composition of the invention may be applied to fibers, rovings,
rods,
cables and any other articles in need of water-blocking protection. The
coating
composition may be applied to coat these articles by conventional means,
including
flooding, dipping, spraying any other known means. Where the articles to be
protected is
a reinforcing strand or roving, the composition may suitably be applied by
means
including, but not limited to, dip-draw immersion followed by passage through
a stripper
die.
Where the coating composition is to be applied to a reinforcing strand or
roving,
the strand or roving may be first sized with an appropriate sizing composition
that is
compatible with the ingredients in the coating composition. The step of sizing
before
applying the coating is preferred because it reduces mechanical abrasion,
Which can cause
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breakage of the fiber filaments in the strand or roving, and fuzz build-up on
processing
machinery.
The water resistant properties of the coatings of the present invention are
obtained
by curing the non-aqueous composition, after it has been applied on the
surface of the
article, by exposure to ultraviolet (UV) light. Curing by exposure to UV light
permits
fast, efficient formation of the coating without the need for equipment such
as ovens,
which consume larger amounts of energy, and which may require longer curing
times.
During the curing process, crosslinking occurs between the polymer chains,
thereby
allowing the coating containing the polymers to form a hardened layer, which
protects the
underlying coated article by absorbing water as it contacts the coated
surface. Suitably, at
least one layer of the coating composition is applied to one or more surfaces
of the article
to form a coated surface. The coated surface is then exposed to UV radiation
at a
wavelength of from about 200 to about 450 nanometers. The frequency of
radiation is
selected based on the curing requirements for the UV-curable resin. For
example, where
500 VINCH polyacrylate is used, a preferred frequency for curing the coating
is about
350 nanometers. The UV radiation may be supplied by any suitable UV light
source that
provides radiation of the desired frequency. For example, a light box sold
under the
brand name "FUSION" may be used.
When the coatings of the invention are applied to the surfaces of reinforcing
fiber
strands and cured, they demonstrate a swell capacity of up to about 75% the
initial dry
weight of the water-swellable polymer. Preferably, the swell capacity for this
type of
application is from about 40% up to about 60% by weight, based on the initial
dry weight
of the water-swellable polymer.
Glass fiber reinforced articles comprising the water resistant coating herein
described may be used in applications where exposure to water or water vapor
is likely,
and where the formation of a durable, resilient, flexible coating with good
waterproofing
properties is desired. The following examples are representative of, but are
in no way
limiting as to the scope of this invention.
EXAMPLES
Exemplary coating compositions were prepared by combining a water-swellable
polyacrylate polymer powder, AP80HS, and 500 VINCH polyacrylate, a non-aqueous
liquid UV curable resin, in various proportions. The polymer powder and UV-
curable
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resin were combined and blended to form a homogenous dispersion. The strands
of
"ADVANTEX R2SH" or "TYPE-E" glass strand, which are pre-sized glass rovings
commercially available from Owens Corning, were passed through a bath
containing the
coating composition to impregnate the strands. After impregnating, the strands
were
S passed through a stripper die of desired orifice size to control the amount
of coating
composition deposited on the surface of the strand. The coated strand was then
cured by
exposure to UV light for a period of from about 0.1 second to about S seconds
as it was
passed through an array of UV ovens. The wavelength of the ultraviolet light
in the UV
ovens was about 36S nanometers.
Example 1
In this example, a coating composition for IJV curing was formulated by mixing
a
blend of a superabsorbent polyacrylate and a UV-acrylate in the proportions
listed below:
9S% weight of S00 VINCH W acrylate made by Zeon Technologies; and
1S S% weight of AP 80HS supplied by Emerging Technologies.
Example 2
In this coating composition, the same ingredients were combined as follows:
86% weight of S00 VINCH ITV acrylate; and
14% weight of AP 80HS.
Example 3
An exemplary coating composition was developed according to the following
formulation:
2S 75.7% weight of S00 VINCH UV acrylate; and
24.3% weight of AP 80HS.
Example 4
In this example, a coating composition for W curing was formulated by the
following formulation:
64.9% weight of S00 V1NCH UV; and
35.1% weight of AP 80HS.
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Example 5
In this coating composition, the ingredients were combined as follows:
56% weight of 500 VINCH IJV acrylate; and
44% weight of AP 80HS.
Example 6
In this coating composition, the ingredients were combined as follows:
45% weight of 500 VINCH UV acrylate; and
45% weight of AP 80HS.
Example 7
In this coating composition, the ingredients were combined as follows:
50% weight of 500 V1NCH UV acrylate; and
50% weight of AP 80HS.
Example 8
In this coating composition, the ingredients were combined as follows:
30% weight of 500 VINCH IJV acrylate; and
70% weight of AP 80HS.
Example 9
The coatings of Examples 1- 8 were investigated to determine their swell
capacity in water when applied to reinforcing fiber materials. Strands of
ADVANTEX
R.25H and TYPE-E glass reinforcing fibers were coated with the coating
composition of
each of Examples 1- 8. The glass was sized with an aminosilane before the
coating was
applied. For each sample, the swell capacity, determined as the percentage
swell over
time calculated based on the total weight of coating and fiber, was measured.
The results
obtained are included in Table 1:
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TABLE 1
ExamplesThe com osition The swell
blended wei
ht %
AP80HSa SOOVINCH capacity
1 5 95 21
2 14 86 30
3 24.3 75.7 30
4 35.1 64.9 40
44 56 58
6 45 45 29.6
7 50 50 48
8 70 30 43.8
Superabsorbent polyacrylate, Emerging Technologies Inc.
UV acrylate, by Zeon Technologies Inc.
Swell capacity was measured as the percentage change in weight
of the coated strand after 1 minute.
The observed results indicate that a significant amount of water absorption
could
be achieved, for example where the proportions of either the superabsorbent
polymer or
the UV curable polymer are in a concentration of from about 30% by weight to
about
70% by weight, respectively.
Having described and exemplified the invention, it should be appreciated that
the
following claims are not to be so limited but are to be afforded a scope
commensurate
with the wording of each element of the claim and equivalents thereof.
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