U.S. patent application number 14/901139 was filed with the patent office on 2016-05-12 for coated fabrics.
The applicant listed for this patent is BRENNAN ENTERPRISE LIMITED. Invention is credited to Wayne John Hanison.
Application Number | 20160130747 14/901139 |
Document ID | / |
Family ID | 48999232 |
Filed Date | 2016-05-12 |
United States Patent
Application |
20160130747 |
Kind Code |
A1 |
Hanison; Wayne John |
May 12, 2016 |
COATED FABRICS
Abstract
A fabric has a coating which comprises an elastomeric, heat
curable silicone rubber composition containing a porous inorganic
filler. The filler is at sufficiently high loading to produce a
percolated porous structure, the percolated porous structure being
permeable to water vapour.
Inventors: |
Hanison; Wayne John; (Oldham
lancashire, GB) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
BRENNAN ENTERPRISE LIMITED |
Lancashire |
|
GB |
|
|
Family ID: |
48999232 |
Appl. No.: |
14/901139 |
Filed: |
June 24, 2014 |
PCT Filed: |
June 24, 2014 |
PCT NO: |
PCT/GB2014/051928 |
371 Date: |
December 28, 2015 |
Current U.S.
Class: |
442/76 ; 156/278;
427/358; 428/304.4 |
Current CPC
Class: |
D06N 3/0063 20130101;
D06N 2209/123 20130101; D06N 2209/128 20130101; D10B 2401/02
20130101; D06N 3/128 20130101 |
International
Class: |
D06N 3/00 20060101
D06N003/00; D06N 3/12 20060101 D06N003/12 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 28, 2013 |
GB |
1311647.0 |
Claims
1. A coated fabric, comprising: a coating comprises an elastomeric,
heat curable silicone rubber composition containing a porous
inorganic filler at sufficiently high loading to produce a
percolated porous structure, the percolated porous structure being
permeable to water vapour.
2. The coated fabric of claim 1, wherein a fabric is selected from
the group consisting of knitted, woven non-woven, and combinations
thereof.
3. The coated fabric of claim 1, wherein a fabric is selected from
the group consisting of cotton, polyester, polyamide, and
combinations thereof.
4. The coated fabric of claim 1, wherein the silicone rubber
composition is selected from the group consisting of polysiloxane
(condensation), peroxide, additional cured silicone, and
combinations thereof.
5. The coated fabric of claim 1, wherein the silicone rubber
composition comprises a filler or combination of fillers with a
porosity in the range from 2 nm to 1 .mu.m.
6. The coated fabric of claim 5, wherein the silicone rubber
composition comprises a filler or combination of fillers with a
mean pore size of substantially -0.5 .mu.m.
7. The coated fabric of claim 1, wherein the porous filler is
selected from the group consisting of kaolinite, amorphous silica,
diatomaceous earth, zeolites, metal organic frameworks, porous
carbon blacks, montmorillonite clay, and combinations thereof.
8. The coating fabric of claim 1, wherein the porous filler
comprises natural diatomaceous earth.
9. The coating fabric of claim 8, wherein the porous filler
comprises natural diatomaceous earth which is calcined.
10. The coating fabric of claim 8, wherein the porous filler
comprises natural diatomaceous earth which is flux-calcined.
11. The coated fabric of claim 8, wherein the particle size range
of filler is in the range from 5 to 100 .mu.m.
12. The coated fabric of claim 11, wherein the particle size range
of filler is an average pore size of substantially 11 .mu.m.
13. The coated fabric of claim 1, wherein one or more additional
fillers are incorporated into the formulation for improving the
rheological properties of the coating compound, and for improving
the physical properties of the cured coating itself.
14. The coated fabric of claim 13, wherein the reinforcing filler
or rheology modifying filler is selected from a group consisting of
calcium carbonate, barium carbonate, talc, mica, hydrotalcite,
calcium sulphate, barium sulphate, aluminium hydroxide, magnesium
hydroxide, calcium oxide, magnesium oxide, titanium oxide, zinc
oxide, and combinations thereof.
15. The coated fabric of claim 1, wherein the silicone rubber
composition comprises from 50 to 150 parts by weight of porous
filler per 100 parts by weight silicone rubber.
16. The coated fabric of claim 1, wherein the silicone rubber
composition comprises catalyst.
17. The coated fabric of claim 16, wherein the catalyst is selected
from a group consisting of organo-tin, platinum, peroxide, and
combinations thereof.
18. The coated fabric of claim 16, wherein the silicone rubber
composition comprises from 0.5 to 7.0 parts by weight of the
catalyst per 100 parts by weight (solid) silicone rubber.
19. The coated fabric of claim 1, wherein the silicone rubber
composition comprises an adhesion promoter.
20. The coated fabric of claim 19, wherein the adhesion promoter
comprises at least one of an organosilicon compound containing an
epoxy group, and an organosilicon compound containing a vinyl
acetoxy group.
21. The coated fabric of claim 19, wherein the silicone rubber
composition comprises from 2.25 to 4.5 parts by weight of adhesion
promoter per 100 parts by weight silicone rubber.
22. The coated fabric of claim 1, wherein the silicone rubber
composition comprises a solvent.
23. The coated fabric of claim 22, wherein the solvent comprises an
aromatic or aliphatic organic solvent.
24. The coated fabric of claim 22, wherein the solvent is selected
from a group consisting of toluene, xylene, hexane, heptanes, and
combinations thereof.
25. The coated fabric of claim 22, wherein the silicone rubber
composition comprises from 200 to 400 parts by weight of solvent
per 100 parts by weight (solid) silicone rubber.
26. The coated fabric of claim 1, wherein the silicone rubber
composition comprises at least one anti-microbial agent.
27. The coated fabric of claim 1, wherein the silicone rubber
composition comprises at least one insect repellent agent.
28. The coated fabric of claim 1, wherein the coated fabric is
breathable and waterproof.
29. The coated fabric of claim 1, having a coating weight of 70-100
gsm of the silicone rubber composition on the fabric.
30. A coated fabric structure, comprising a coated fabric
comprising a coating which comprises an elastomeric, heat curable
silicone rubber composition containing a porous inorganic filler at
sufficiently high loading to produce a percolated porous structure,
the percolated porous structure being permeable to water vapour;
the coated fabric in combination with one or more further
fabrics.
31. The coated fabric structure of claim 30, wherein adhesive is
coated onto the coated fabric to laminate a second fabric to
produce a trilaminate structure, wherein the adhesive coating has a
coating weight of adhesive of 5-20 gsm.
32. A method of making a coated fabric comprising: providing a
coated fabric comprising a coating which comprises an elastomeric,
heat curable silicone rubber composition containing a porous
inorganic filler at sufficiently high loading to produce a
percolated porous structure, the percolated porous structure being
permeable to water vapour; wherein the silicone rubber composition
is coated onto the base fabric using a knife-over roller
technique.
33. A method of making a coated fabric of claim 32, wherein a
second fabric is laminated to an adhesive layer on the base fabric
to provide a trilaminate coated fabric.
Description
[0001] The invention relates to coated fabrics and in particular to
waterproof, breathable coated textiles that can be used, for
example, in the manufacture of protective and leisure clothing,
bags and luggage.
[0002] Waterproof, breathable coating and laminates for textiles
are well known in the prior art, the terms "waterproof" and
"breathable" relating to the coating or laminate being impervious
to liquid water and permeable to water vapour respectively. This
imparts a high degree of comfort to the wearer, preventing
condensation of sweat inside the garment while providing a
waterproof barrier to keep the wearer dry in all types of
weather.
[0003] Materials sold under the registered trade mark GORE-TEX are
based on an expanded polytetrafluoroethylene membrane (e.g. U.S.
Pat. No. 3,953,583) to produce a microporous membrane that can be
laminated to a fabric. The pores in the membrane are 20,000 times
larger than a water molecule allowing the passage of vapour, while
the extremely low surface energy of the membrane imparts high
waterproofing properties.
[0004] Microporous coatings based on polyurethanes are also known
in the art, as described by U.S. Pat. Nos. 4,560,611, 5,520,998,
5,626,950 and 5,692,936. These are produced by direct coating a
polyurethane solution onto a fabric, then coagulating the solution
to produce a network of micropores in the polymer structure.
[0005] Another group of coatings are based on hydrophilic
polyurethanes. These are usually directly coated onto a fabric, and
rely on the incorporation of hydrophilic segments in the polymer
chains. Water molecules from perspiration are therefore able to
diffuse from inside the clothing of the wearer through the polymer
layer via a step-wise process and transported to the outside
environment. The functionality of these hydrophilic layers relies
on a humid environment building up inside the breathable garment.
The higher the humidity inside the garment, the faster the rate of
diffusion of water molecules through the polymeric layer. These
types of polyurethane coatings usually contain both hydrophilic and
hydrophobic segments to incorporate breathability and
waterproofness respectively.
[0006] There are a number of problems associated with both the
microporous membranes and the hydrophilic coatings. The performance
of microporous membranes can deteriorate over time due to
contamination of the pores by soil, detergents and body oils.
Blocking of the pores in this manner reduces the breathability of
the membrane and can also alter the surface chemistry of the
membrane, resulting in the increased likelihood of liquid water
penetration. Gore attempted to resolve this problem by the
application of a very thin layer of hydrophilic polyurethane on top
of the microporous PTFE as a protective layer to prevent the
microporous layer from contaminants.
[0007] There are also problems associated with hydrophilic based
polyurethane breathable coatings. The main one is their
susceptibility to swelling in water. By their very nature, water
molecules are attracted to the hydrophilic segments in the polymer.
Water molecules are therefore able to "solvate" the hydrophilic
segments within the polymer and swell the membrane. This can impart
to a "clammy" feeling to the wearer as well as a loss of coating
strength. In severe cases it can lead to a loss of adherence to the
fabric itself, causing delamination. This is quite common when the
garment is subjected to harsh aqueous environments.
[0008] The present invention has been made from a consideration of
the above.
[0009] According to the present invention there is provided a
coated fabric, wherein the coating comprises an elastomeric, heat
curable silicone rubber composition containing a porous inorganic
filler at sufficiently high loading to produce a percolated porous
structure, the percolated porous structure being permeable to water
vapour.
[0010] In a percolated system a gas is able to pass through the
porous structure via a series of holes or pathways. The invention
achieves porosity throughout the rubber coating. The very nature of
the inorganic filler used in the formulation is that of particles
containing a plurality of micron and sub-micron pores as an
integral part of its structure. In the silicone rubber formulation,
below a certain level of filler these particles are not in close
proximity to each other. However, when a certain level, or amount
of filler is incorporated into the rubber matrix, a mixed matrix
compound is achieved where the porous particles are in sufficiently
close proximity to each other to allow the passage of water vapour
through each porous particle straight through the continuous mixed
matrix coating i.e. the "percolation threshold" is reached to
produce a true percolated structure throughout the mixed
rubber/filler matrix. For any given system, below the "percolation
threshold" a continuous connected component does not exist, but
above the percolation threshold there exists a connected component
to scale of the system size. Unlike other percolated systems, the
invention tends not to allow the passage of liquid water (up to a
hydrostatic head pressure of at least 2000 mm) due to the very
hydrophobic nature and low surface energy of the silicone
rubber.
[0011] In its simplest terms, the "percolated structure" of the
proposed invention can be described by the interconnectedness of
the porous filler particles throughout the mixed matrix compound
that gives rise to continuous connected porous pathways to allow
the passage of water vapour molecules throughout the rubber matrix,
giving rise to its breathability.
[0012] The silicone composite solution can be coated on a natural
or synthetic fabric which may be woven, nonwoven or knitted and
comprise, for example, polyester or polyamide. The coating process
may involve direct coating onto the fabric substrate. The coated
fabric of the invention comprises a waterproof, breathable coated
textile that can be used for the manufacture of a variety of
articles, such as protective and leisure clothing, bags and
luggage.
[0013] Silicone rubber exhibits gas permeability due to the zero
energy of rotation about the silicon-oxygen bond in the backbone
chain. Together with the plurality of methyl groups on the outside
of the polymer chains (which in turn impart water repellent
properties), intermolecular interaction is very low causing a large
free volume between polymer chains, allowing the diffusion of gas
molecules through the polymer matrix. However the level of
permeability of silicone rubber alone is not sufficient to produce
a water proof, breathable membrane on its own. The coated fabric of
the invention therefore incorporates a porous filler which by
creating a percolated structure within the silicone rubber
composition, complements the permeable properties of the silicone
rubber to produce a truly water-vapour permeable, liquid water
impermeable membrane.
[0014] For the proposed invention of a waterproof, breathable
silicone rubber composite coated onto a textile surface, it is
proposed that different construction of coated fabric can be
produced according to the end use. Single fabric coated structures
are proposed along with multi fabric layer structures. The silicone
rubber coating may be provided between adjacent fabrics in a
multilayer structure and/or on the exterior of the structure. Some
possible embodiments of the invention are mentioned below:--
1. Single texture (2-layer) comprising one fabric (e.g.
polyester/polyamide (Nylon)) coated on one side with the silicone
composite. This would be the most basic construction, intended for
example for use in the manufacture of hiking, walking and camping
jackets. 2. Double texture (tri-laminate) comprising an outer layer
fabric (e.g. polyester/polyamide (Nylon)) laminated to a second,
inner liner fabric (polyester) with the silicone composite layer in
between. This would be a more durable fabric intended for example
for water sport surface suits, dry suits and sailing/yachting
suits/jackets. It is envisaged that this durable fabric
construction can also be used in heavy duty work wear, for example,
for outdoor workers. 3. Double texture (tri-laminate) fabric
constructed from an outer fabric and an inner fabric (e.g.
polyamide, polyester/polyamide (Nylon)) with the silicone coating
in between. This type of construction would be useful for
applications where durability and fire retardance are required.
[0015] The silicone rubber coating is a solution based formulation
that is ideally coated directly onto a fabric. The silicone rubber
composition contains the following polysiloxane and solid filler.
Optionally the silicone rubber contains any of catalyst, adhesive
and/or adhesion promoter and a solvent.
[0016] In one embodiment of the invention the various components of
the rubber coating may be included as follows:--
TABLE-US-00001 Compound Parts (g) (A) Silicone 100 rubber (solid)
(B) filler 50-150; optionally 80-120 (C) catalyst 0.5-7.0 (depends
on silicone cure system).sup.1 (D) adhesive/adhesion 2.25-4.50
promoter (E) Solvent 200-400.sup.2 .sup.1the above formulation may
be based on a condensation, peroxide or addition cured silicone,
which will determine the type and quantity of catalyst (organotin,
peroxide or platinum type). .sup.2the solvent level is based on phr
of solid rubber to produce a solution of 35-50% solids. A pre mixed
silicone polymer solution in toluene may also be used, which would
reduce the amount of additional solvent needed
[0017] The breathable silicone rubber coating of the invention has
advantages over breathable polyurethane systems in as much that it
is non-swelling in aqueous environments with no loss of adhesion in
tri-laminate constructions. As it is an inherent property of
silicone rubber, the coating also has excellent resistance to
ageing (e.g. no hydrolysis, another issue with PU systems) and
excellent flexibility and low temperature performance.
[0018] The breathable silicone rubber composite has an extremely
porous nature due to the high porosity of the diatomaceous earth
filler that is used in the silicone formulation. The high porosity
and surface area of the composite raises the possibility of extra
functionality being designed into the breathable coating.
Possibilities include:
[0019] a) incorporation of essential oil anti-microbial agents into
the silicone composite. The large internal volume of the porous
filler particles may be able to act as a "reservoir" for essential
oils that would be released slowly over time to impart
antimicrobial properties to the breathable fabric. This would be
extremely advantageous for garments that are susceptible to
bacterial and fungal growth which causes unpleasant odours.
[0020] b) Similarly, insect repellent agents could also be
incorporated into the filler particles. This would be advantageous
for hiking and camping clothing in areas where a high population of
insects is present.
[0021] The above areas are only possible due to the large porous
internal volume of the filler particles. Traditional waterproof,
breathable coatings fashioned from microporous PTFE, polyurethane
and hydrophilic solid polyurethane membranes do not have this
large, internal free volume to act as a reservoir for additional
functional materials. This is one other distinct advantage that the
present invention has over prior art breathable materials.
[0022] The invention will now be described further by way of
example only with reference to the accompanying drawing:--
[0023] FIG. 1 which shows a schematic diagram of a tri-laminate
waterproof breathable construction of the invention and the water
vapour evaporation pathway therethrough.
[0024] Referring to the drawing a coated fabric 10 comprises a
first woven fabric 11 having a plain weave construction made from
polyamide. This is direct coated on one side thereof with a
silicone rubber composition 12. The silicone rubber composition has
the following components:--
(A) a polysiloxane 13 that can be cross-linked by polyaddition,
polycondensation or free radical means catalysed by platinum,
organotin or peroxide compounds respectively. (B) a porous filler
14. In one embodiment this comprises natural diatomaceous earth (or
diatomite) which is a soft siliceous sedimentary rock crumbled into
a fine powder. The porous filler, while typically natural
diatomaceous earth, may also be calcined and flux-calcined.
Calcination is the heat treatment of a material in the presence of
air or oxygen. Flux-calcination is the heat treatment of a material
in the presence of a fluxing agent. (C) a catalyst (not shown),
which can be either an organo-tin compound, platinum catalyst or
peroxide. For the current formulation, C14-010, an organo-tin
catalyst commercially available from Itac Ltd can be typically
used. (D) additionally (not shown), a mixture of
glycidoxypropyltrimethoxysilane and vinyltriacetoxysilane adhesion
promoter, such as the commercially available SYL-OFF 297 from Dow
Corning. This is also supplied under the product code C14-025 from
Itac Ltd. (E) an aromatic or aliphatic solvent (not shown) to
adjust the solids content of the coating solution. Toluene is
typically used for this purpose, although SPB2 (a mixture of hexane
and heptane) can also be used. The ratio of mixing the components
A-E is set out below.
TABLE-US-00002 Compound Parts (g) (A) C14-007 100 (30% solids
solution in toluene) (B) Celtix filler 15-45 (C) C14-010 1.75-3.50
(D) C14-025 2.25-4.50 (E) Solvent 10-50
[0025] A second plain weave fabric 15 also made form polyamide is
situated on the other side of the coating such that the silicone
coating is sandwiched between the two fabrics.
[0026] If using a polycondensation cure silicone rubber such as
that mentioned above, excess moisture in the filler should be
removed prior to mixing. Natural diatomaceous earth contains around
8% by weight of moisture that is held by the filler. Excessive
moisture can interfere with the condensation reaction, leading to
insufficient crosslinking and poor physical properties. The
diatomaceous earth filler should therefore ideally be dried at
temperatures of 100-120.degree. C. for a minimum of 16 hours prior
to mixing. Alternatively, a molecular sieve compound can be added
to the coating formulation that will remove the moisture from the
filler, thus obviating the necessity to pre-dry the filler before
mixing the compound. If the latter alternative is to be employed,
the molecular sieve compound needs to be added to the coating
formulation and thoroughly mixed and left to stand for not less
than two hours before coating onto the fabric. A typical molecular
sieve compound employed for this purpose is a porous, crystalline
aluminosilicate powder such as those marketed under the brand name
"Sylosiv".
[0027] The formulation should be mixed in a mechanical mixing
device, such as a Z-blade mixer. Components (A) and (B) should be
thoroughly mixed in the first instance for 20-30 mins to produce a
homogenous "dough" mix, followed by components (C), (D) and (E).
The complete formulation should then be mixed for a further 20-30
mins until a completely homogenous solution is produced. Measured
solids content of the solution should be 35-45%. After the final
mix, the formulation will have a useable pot life of 8 hours.
[0028] The water vapour pathway is in the direction of arrows
A.
[0029] The invention will now be described further with reference
to the following examples.
EXAMPLE 1
Tri-Laminate Coated Fabric (as Shown in FIG. 1)
[0030] The silicone composite solution can be coated on a synthetic
woven or knitted fabric e.g. polyester or nylon using direct
coating (knife over roller) method. A multiple number of passes is
required in order to achieve a coating weight of 70-100 gsm.
Ideally a coating weight of around 85 gsm should be achieved. It is
usual for at least three coating passes to be needed to achieve
this weight. It is important to ensure the temperature is at a
temperature that enables evaporation of the solvent, but is not too
high as to cause premature cross-linking of the silicone composite.
As a guide, a temperature of 60-80.degree. C. should be maintained
in the heated spreading chest. The uncoated side of the fabric will
function as the "inner" lining of the waterproof, breathable
fabric.
[0031] After the last coating of the silicone composite has been
applied, a final coating of silicone based pressure sensitive
adhesive (PSA) is required in order to laminate the coated fabric
to an "outer" layer fabric to produce a tri-laminate construction.
A commercial grade PSA from Dow Corning known as DC7358 (a peroxide
cured adhesive) can be used for this purpose. Peroxide (typically
dibenzoyl peroxide) needs to be premixed into the adhesive solution
at a level between 0.5-2%. A light coating of adhesive (between
5-20 gsm depending on the level of adhesion required) is then
applied over the silicone coating, the solvent is allowed to
evaporate through the heated chest (temperature must not be over
75.degree. C. or premature crosslinking of the adhesive will
occur). The coated fabric is then laminated through two pressurised
rollers against a second, uncoated fabric to produce the
tri-laminate construction. The laminated fabric can then be cured
off-line. The fabric coating can be cured for 30-45 min at a
temperature of 120-140.degree. C. Lower temperatures down to
100.degree. C. can be used for longer curing times of up to 6
hours.
[0032] The tri-laminate water proof breathable fabric can be used
(but not limited to) garments for water sport and marine
applications such as surface suits, dry suits, sailing garments,
etc.
EXAMPLE 2
Single Coated Fabric
[0033] The single coated fabric is manufactured in a similar way to
the tri-laminate. On this occasion the coated fabric serves as the
outer fabric shell as opposed to the inner layer fabric, and the
fabric is not then laminated to another fabric. There is therefore
no need to apply a silicone adhesive layer. However, due to the
non-stick properties of silicone rubber, it is necessary to apply a
breathable, low melting point thermoplastic top coat on the
breathable silicone layer in order to facilitate the adhesion of
seam sealing tapes. A polyurethane coating solution such as
Larithane BTH231 can be used for this purpose. Swelling effects of
the polyurethane are not as critical as the fabric is not laminated
to another outer fabric, where loss of peel adhesion could become
an issue.
[0034] Water vapour transmission rate (breathability):
[0035] The breathability of the fabric has been internally tested
according to BS7209 "Water vapour permeable apparel fabrics". A
circular test piece of the fabric is fixed over the rim of a
circular aluminium dish that contains a measured amount of
distilled water. The outside surface of the rim of the dish is then
sealed so that the only pathway water vapour can take is through
the fabric. The total weight of the dish, fabric and water is
measured, whereupon the dish is then placed on a circular turntable
that rotates to prevent a microclimate of humid air above the
surface of the fabric. The dish is then left in atmospheric
conditions of 65% relative humidity and 20.degree. C. for at least
16 hours. The weight of the whole test dish is then measured to
calculate the loss of water in the form of vapour through the dish.
This measurement of weight loss is then calculated to calculate the
"water vapour transmission rate" (WVTR) in units of g/m.sup.2/24
hours. The weight loss of water vapour through the test fabric is
also measured against that from a reference fabric to calculate the
water vapour permeability index (WVPI), quoted as a percentage of
the reference fabric.
[0036] The waterproof breathable fabric as described in this
specification will typically have a WVTR of 400-650 g/m2/24 hours,
more typically around 500 g/m.sup.2/24 hours and a WVPI of 50-90%,
more typically around 75%.
[0037] Hydrostatic Head pressure rating (waterproofness):
[0038] This is described as the water pressure required to leak
(penetrate) through the fabric. This is determined by carrying out
test BS3424-26, which subjects a test piece of fabric to pressure
from either a column of water or water pressurised from a
compressor. Any fabric that can withstand a pressure equivalent to
a column height of 1000 mm is deemed "waterproof" although in
practice ratings of 2,000-20,000 mm are expected from quality
products.
[0039] The waterproof breathable fabric as described in this
specification demonstrated a hydrostatic head rating of at least
2,000 mm according to internal tests.
[0040] Peeling (adhesion) strength--tri-laminate only.
[0041] The peeling strength is simply the force required to peel
the laminated fabrics apart, as measured on a tensometer. The test
piece is a 50 mm wide strip of the fabric with both face and back
fabrics delaminated from each other. The force in N/50 mm is then
measured that is required to peel the fabrics apart.
[0042] The tri-laminate fabric as described previously typically
has a peeling strength of 4-8 N/50 mm, more typically around 6 N/50
mm. The peeling strength will remain unaffected after the test
piece has been immersed in a 2% salt water solution for 24
hours.
[0043] It is to be understood that the above described embodiments
are by way of illustration only. Many modifications and variations
are possible.
Some possible modifications and variations are set out below. a)
The invention contemplates the optional addition of a thixotropic
filler such as fumed silica to the base silicone rubber
formulation. This would alter the rheological properties by
increasing the viscosity of the coating formulation and reduce
"strike-through" of the solution through the fabric. This leads to
reducing the degree of coating penetration through the fabric
leading to a better appearance and handle of the coated fabric. b)
An improvement in adhesion of silicone rubber to the fabric may
optionally be achieved by applying a pre-treatment of an organic
silane compound to the fabric prior to applying the rubber coating.
The silane pre-treatment would typically be applied by a dipping
technique into a silane solution followed by drying to evaporate
the solvent. c) As discussed previously the diatomaceous earth
filler may be dried prior to mixing into the rubber formulation, as
excess moisture present in the filler disrupts the condensation
cross-linking reaction. The addition of a molecular sieve compound
into the rubber/filler solution 2-3 hours prior to coating removes
the moisture from within the coating solution, thus eliminating any
requirement to pre-dry the filler. d) One or more blowing agents
may be used to increase the porosity of the adhesive. Increasing
the elastomer content of the adhesive may improve the peel
strength. d) While the currently preferred porous filler used to
create a percolated porous structure is natural diatomaceous earth,
there are a range of other porous fillers which may be used in
place of or in combination with diatomaceous earth. Such fillers
may include kaolinite, amorphous silica, zeolites, metal organic
frameworks, porous carbon blacks and montmorillonite clay. e)
Additional fillers may be incorporated into the composite
formulation to improve the physical properties of the composite
coating. These include, either alone, or in combination, any of
calcium carbonate, barium carbonate, talc, mica, hydrotalcite,
calcium sulphate, barium sulphate, aluminium hydroxide, magnesium
hydroxide, calcium oxide, magnesium oxide, titanium oxide, and zinc
oxide.
* * * * *