Note: Descriptions are shown in the official language in which they were submitted.
COATING P~OCESS A~D PRODIJCT
.
The present invention relates to a process for eoating
a substratum such as a cloth or fabrle wlth a water resistant
composition to produce a weather-proof fabrle reslstant to
exposure to the weather and sunlight.
Water-proof coatings are well ]cnown and have been used
on fabrie and eloth for a number of years. Sueh eoatings
however, are generally used with elo-thes, eanvas tarps and the
like. There is presently a requirement for a waterproof
eoating to be used on highly transparent or translueent
10 flexible material sueh as fabrie ancl clo-th, in either
permanent or removable struetures. Such an application of a
water-proof material is in a building system such as that
diselosed in my eo-pending patent appllcation relating to a
canopy system for a bullding, Canadian Patent Applieation
15 Serial No. 352286.
In the past, water-proof eoatings have been used on
yarns, fabries and the like, ~ithout any speclfic preparation
to the~ yarns and fabries before the eoating step. The
coatings have previously been applied to the fabric by
20 spraying, dipping, brushing, flow coating, transfer coating
and sometimes by laminating. It is common practice to employ
two or more layers of coatings to improve the product quality.
In rnost cases the coating does not pene-trate the yarns, but,
rather adheres to the surfaee of the eloth. Thus, especially
25 with multi-filament yarns, there is often air, moisture and
perhaps other eontaminants trapped within the yar~s thus
coated over~
It was observed that in dip eoating processes where
-fabrics woven of multi-filamented yarns are drawn through a
.,
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~.7~ B~9
bath of low viscosity coa-ting resin the final produc-t shows
many flaws in the coating due to air bubbles. This air is
brought in-to the bath with the Eabric since i-t is entrained
within the yarns. As the fabric leaves the hath some of the
5 bubbles are picked up, and upon dryiny and curing, leave
voids and pinholes in the coating. The faster the rate of
fabric travel through the ~ath the more serious this problem
becomes. ~lowever slower rates of coating will increase the
cost per unit. Therefore a trade-off may be necessary
10 between the cos-t and the quality of the coated product. -
Furthermore, it was noted tha-t the serviceabili-ty of
the coated product, when exposed to weathering and sunlight,
is impaired due, in part, to the presence of air and moisture
,
trapped in the material by the coating. Chemical reactions
15 that cause weakening and embrittlement of the yarn filaments
take place in the presence of oxygen, moisture and other
impurities. Exposure to sunlight, especially the ultra-
violet rays thereof, initiates these degradation reactions in
the presence of such impurities.
The high tensile strength yarns are composed of very
fine rnulti filaments. Such types of fabric ma-terials are
therefore especially susceptible to degradation reactions
because a very large surface area is exposed to the
contaminates. Thus although glass is known to be very stable
25 under weathering, fiberglass fabrics are embrittled, weakened
-and yellowed rather rapidly if not protected by a coating
material. If the coating develops fine fissures known as
"crazing" due -to fatigue, then water and moisture can reach
the fiberglass and wick along the yarns. This is the usual
30 mode of failure of composites with fiberglass reinforcements
embeded in thermo-se-tting polyester resin.
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The mode of failure oE hydrocarbon synthe-tic fibers
is similar to that of glass fibers as described a~ove. There
~ is however, in addition -to the adsorbtion of water into the
; yarn, the absorption of moisture by the polymer itself.
5 These fibers have an affinity for mois:ture, and tend to have
a low to-medium moisture content. The presence o~ the
moisture at the sites of chemical degradation reactions is
especially important for decomposition and deterioration on
exposure to ultraviolet light. Thus Eor these fabrics their
10 s-tability under weathering is improved by preventing -entrap-
ment of air and moisture in the yarns as previously discussed,
and also by preventing the normal moisture regain of the
fibers.
Similarly as for synthetics, it is important for
15 fabrics composed of natural fibers to prevent the entrapment
of air and~moisture in the yarns and to prevent the normal
moisture regain of the fibers in order -to achieve stability
and long service life under exposure to weathering and
sunlight.
; 20 The failure of such compositions of material is
- caused primarily by the deterioration of the protective
coating which after a certain time in service allows the sub-
stratum to be exposed to oxygen and mois-ture from the
atmosphere. However, it is apparent that the material is
25 often exposed to the said impurities by their entrapment
within the material by the coating. Further, it is known
that the degradation reactions produce reactive agents, so
that these reactions are self sustaining and propaga-ting.
Therefore the material rnay be well on the way to its
30 deterioration from wi-thin before the coating that protects
from outside agents loses its effec-tiveness.
In general, wa-ter-proof coatings have been placed on
yarns, fabrics and sheet material such as films and sheet
cast or extruded material, and the like, without any specific
prepara-t:ion of these subs-tra-tum materials before the coating
5 step. Thus existing moisture is entrapped within these
substratums to the extent of their affinity for adsorption
and absorption of moisture. Furthermore, air and other
contaminants can be trapped in the substratum by the coating.
The resul-t i-s often tha-t when ultraviolet light hits this
10 coated fabric~ decompositlon and deterioration of the fabric
- occurs at least partially d~e to the impurities, mois-ture and
air trapped beneath the waterproof coating.
Review of the past art indicates tha-t no specific
effort has been made to avoid the presence of moisture in the
15 fibers of a substratum or to avoid the presence of moisture,
air and contaminants adjacent to the filiments of the yarns
as a means of producing fabric or cloth substratums wi-th
improved stability and durability when exposed to sunlight
and to the weather.
The presence of the said impurities in the fabric is
not considered ln the coating of high viscosity resins onto
fabric since they cannot penetrate the yarns but, rather,
over-coat the fabrics. Therefore these coatings are usually
applied by flow coating. A good quality product is obtained
25 by spreading the coating with a knife blade supplied with air
pressure. Since the coatings are usually pigmented and
otherwise treated for improved weatherability the ultra-
violet radiation does not act upon the fabric substratum.
The presence of -the said impurities in the fabric has
30 been considered in the coating of low viscosity resins on-to
fabric to the extent that it has been recognized that -the air
within the fabric will cause flaws in the final produc-t as a
result of the air forming bubbles i.n. the low viscosity resin.
- To avoid this problem of bubbles produced as the fabric moves
through low viscosity resins it was found tha-t the coating
5 res Ln will not produce bubbles if the resin is transported at
the same rate of travel as that of -the fabric. This method
is typical of the "transfer type" coa-ting process. The low
viscosity resin, transported on a moving belt or wheel,
:~ contacts the fabric and wicks into it, while moving at the
lO same speed as the fabric. Wetting the fabric by contact or
spraying and allowing time for penetration and then dip
coating in a resin bath will reduce :Eoaming in the bath. This
method is described in Canadian Patent No. 998,300 and US
3,843,386. Dip coating may be avoided altogether if
15 successive transfer coa-ting runs can build up a sufficiently
; ~ thick coating over the fabric.
Previously, the above mentioned art has been employed
to produce opaque products and thus the role of the said
: impurities entrapped in the material as agents for the
20 degradation of the fabric has not been important/ slnce the
~ ultraviolet light which inltiates the degradation reactions
does not reach the fabric substratum. There is presently a
need for architectural fabrics of high transparency or
translucency for capture of solar energy by the buildings and
25 for natural illumination within -the building. It is there-
fore the object of the present invention to produce novel
. products wherein a clear, hi.ghly transparent and mois-ture
resistant composition penetrates and surrounds yarn filaments
avoiding entrapment of air or other contaminants adjacent to
30 the fibers, and avoiding the natural moisture regain and the
presence of other volatile contaminants as can exist in the
in the fibers. The moisture resistance of the composition
used on the fabric is such as to prevent the fabric's natural
affinity for moisture from attractlng the moisture from the
environment through the coating and into the fibers. Thus the
5 permeability of the coating to water vapour is very low.
The present invention provides a coating process for
a fabric or cloth wherein moisture, air and impurities are
first removed. The fabric then makes a pass through a
coating bath which can employ resins of any specific viscosi-
10 ty, which are clear when curred and do not absorb moisturenor deteriorate when exposed to weathering and sunlight. A
preferred resin for use in this process is available from
ow Corning Corporation under the trade mark "R-4~3117
conformal coating" or any other resin type having equivalent
. :
15 characteristics can also be used.
~; Another object of the process is to attain high rates
of fabric travel while producing a product of excellent
~i ~ quality. Thls is achieved by preventing air entrainment into
;~ the bath and by the specific method employed for the resin
20 bath.
A further object of the process is to obtain control
over volatiles released during the process. These volatiles
can be recovered and liquified for reuse thus preventing
pollution which is a common problem in prior coating proces- -
25 ses.
In one embodiment a process is defined as shown in
Figure 1, wherein the process consists of multiple stages of
fabric travel, first, through a liquid bath and then
immediately into a vacuum chamber. In one embodiment of the
30 invention two such stages are employed. The fabric(9), in
the off loom condition and with no pretreatments is taken from
a pay-out reel(7) and run through the entire machinery to be
attached to the take-up reel(8) where -the coated fabric(10)
, is taken up as a finished product in a roll. In the first
stage the fabric enters the first bath(l) -through a slit(6),
5 the lips of the slit being fabricated of low fric-tion and
abrasion resistant material. The fabric passes through the
first bath chamber(l) and exits through another slit(6) into
the first vacuum'chamber(2). Similarly the fabric(9), leaves
the first vacuum chamber(2),through another sli.t(6) proceeding
10 directly into the second bath chamber(3? and -thence through '
another slit(6) into the second vacuum chamber(4) and'exiting
by a final-exit slit(6).
The purpose of -the first bath(l) is primarily to serve
as a seal-against entry of air into the first vacuum
15,chamber(2) in which a high vacuum is sustalned. Wa-ter or some
other liquid or solution is constantly fed to the chamber
which provides that the overflow is returned for resupply.
It is preferable that this liquid is quite ho-t so as to heat
the fibers to as high a temperature as is consistant with
.
20 safeguarding their physical properties. Thus the travel
distance and the temperature of the bath(l) is to be deter-
mined according to the type of ma-terial. Then, when the
fabric(9) leaves the bath(l) and enters the first vacuum
chamber(2) the liquid will flash oef as will t,he absorbèd
25 mo'isture due to the high temperature of -the fibers and high
vacuum maintained in this chamber(2). It is provided that the
first vacuum chamber can be portioned off into regions of
progressively higher vacuum by means of pai.rs of soft rubber
rollers or some other device.
Any air entering the first vacuum chamber(2) in the
yarn is instantly released from the yarn and removed by the
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vacuum pump. Also since the liquid feed -to bath(l) can be
pressurized the liquid will tend to wick out the incoming slit
counter directionwise to the fabric travel so that air in the
yarn will be largely displaced by the liquid before the
5 yarn(9) travels into the bath(l). Cross flow of the bath(l)
liquid through the fabric can further assist to remove air and
physical impurities from the fabric(9). The bath(l) supply
and recycle circuits should ~herefore be fitted appropriately
with filters and de-airing holding tanks.
The first bath(l) also may serve some pretreatment of
the yarns such as heat setting to provide shrink resistance,
or provide some chemical modification of the fibers or any
combination of such uses including dying and the like prior to
coating. The liquids employed in the first bath(l) must
1~ howe~er be highly volatile so as not to remain in the yarns on
entering the first vacuum chamber. Thus there is no inter-
ference from the ~irst bath that reduces the effectiveness of
the release of absorbed moisture from the Eibers.
Therefore, according to the method of the present
~- 20 invention there will not exist any moisture in the fibers of
the fabric(9) nor any mois-ture or air in the yarns, except in
very small traces. And any such small traces of vapours will
be easily displaced by liquid coating bath(3), which,
supplied under pressure will penetrate completely and fill
25 the voids in the yarn, surrounding every filament. In the
embodiment of the invention as we are now describing, the
second bath chamber(3) is the coating chamber(3). The coating
liquid supply should be at such a flow rate -that a cross flow
exists with an over-flow from the bath(3) which is
30 resupplied. In this circuit a de-airing holding tank is used.
The coating liquid is supplied under pressure to cause a
certain amount of counter direction flow and such that the
coating liquld is extruded from the coa-tlng charnber(3) in-to
the second vacuum chamber at a rate correspondlny to the
fabric ra-te of travel. The exit slit(6) can have hard edged
5 lips or hard rollers to nip back the coa-ting resin and allow
a specific thickness of the coating film over the surface of
the fabric. A predetermined nip pressure controls the
quantity of resin remaining on the fabric.
The second vacuum chanber(4) is provided for the
lO drying and curring of the resin. A preferred embodiment
employs a low vacuum with an inert atmosphere such-as
nitrogen. The low vacuum assist the evapouration of the
volatiles from the coating resin so that curring can begin.
Direct or infrared radlant heating can be employed for
lS promoting the fast curring of the thermo-setting resin.
: The penetration of the resin into the fabric provides
improved adhesion. Pressure, and elevated temperature
assists high viscosity resins to properly penetrate the
fabric. Since the fabric can travel quite quickly through
20 the coating chamber(3) a very short in-terval exposure to
high temperatures often will not harm the fabric subs-tratum.
This is especially tr~le for glass fabrics which can be
exposed briefly to temperatures exceeding 1000 F and also
for polyesters and some other syn-thetic fabrics which can be
25 exposed briefly to temperatures exceeding ~00F. Thus the
method of coating application of the present invention
provides that thermoplastic materials can be supplied to the
coating chamber(3) as a hot melt. This method may also
employ volatile solvents to assist in loweriny the
30 temperature of the mel-t or improving the viscosity. ~rhe
volatiles can then be recovered and liqulfied by exhausting
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them from the second vacuum chamber(4). A low vacuum will
assist the evaporation of the solvents.
- In another embodiment the coatiny is a liquid resin,
supplied at room temperature to the coating chamber(3), which
.5 cures by means of thermo-setting mechanism. There~ore upon
exiting from the coating chamber(3) the fabric may enter a two
: or three stage curing chamber(4) as is common practice with
coating resins. The use of a catalyst and elevated
. temperature can allow the coated fabric -to exit and be taken-
10 up on a reel within 30 minutes of travel time within thecuring chamber.
The method herein of utilizing the baths as seals
against entry of air into the process improves the quality of
the resulting product but also at the same time preven-ts
15 exposure. of the process volatiles to the environment, and
contains them for collection and reuse. This has both
environmental and economic benefits. Many of the solvents. or
treatments that could be employed evolve very toxic volatiles
which pollute the environmen-t and are not easily eliminated
20 or removed from the exhaust of coating process employed in
-- the prior art.
In a further embodiment a 3 or 4 stage process is
visualized including pretreatment bath for substratum
preparation, coating, secondary coating and post coati.ng
25 treatments.
By way of example, metalic ions may be deposited on
opposite si.des of the coated fabric by reaction in seccessive
bath and vacuum chambers following after the coating stage.
The final exit from the mechanism is through a slit
30 or through a pair of resilient surface rollers, or through a
final bath with the dr~ving following in the open air. This
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last bath could be used for a final wa-ter cooling, fixing or
washing bath or other purpose. The material is then taken up
on a reel
The present invention prodcues improved products by a
5 novel coating process for various types of compositions that
are already known and used. The improved product is a fabrie
with no moisture, air bubbles or impurities trapped between
the fabric and the coating resin. Mositure which normally
exist in the fibers is removed before the coating,and the
10 cured resin coating has a laek of affinlty for water, thus
moisture eannot reaeh the fibers and normal moisture regain
of the fibers lS prevented. Known eompositions that ean
benefit by improved properties and process technology of this
invention include glass fabric coated with silicone resin or poly-
15 tetrafluoroethylene polymers. The invention relates to novelcompositions that are provided stability against ultraviolet
; degradation on exposure to weathering, which stability is
provided by means of the process. The novel compositions
include synthetic and natural fibers having low to medium
20 normal moisture regain, for example polyester fabrics, coated
over with a polysiloxane resin such as is available from Dow
Corning under the trade name R-4-3117 conformed coating
silieone resin.
The present-invention offers improved process teeh-
25 nology for produets other than~the transparent or translucent
architectural Eabrics as discussed above. Indeed any eoating
on a substratum ean advantageously employ the process
deseribed. Thus films, slit and woven films, scrims, non-
wovens, knits, tube-knit and tube-woven goods of any
30 deseription can advantageously be coated by means of a process
embodying this invention, the scope of the process being
limited only by the claims.
