U.S. patent application number 16/444414 was filed with the patent office on 2019-10-03 for patterned silicone coating.
The applicant listed for this patent is KCI USA, INC.. Invention is credited to Deborah ADDISON, Risham AMJAD, Patrick Joseph BROSNAN, Sally STEPHENS, Gary STREET, Ian TEET.
Application Number | 20190298582 16/444414 |
Document ID | / |
Family ID | 44147134 |
Filed Date | 2019-10-03 |
United States Patent
Application |
20190298582 |
Kind Code |
A1 |
ADDISON; Deborah ; et
al. |
October 3, 2019 |
PATTERNED SILICONE COATING
Abstract
A method of applying a patterned coating of a silicone adhesive
to a substrate sheet, comprising the steps of pattern coating a
silicone precursor composition onto the substrate, followed by
thermally curing the precursor composition coated on the substrate.
The precursor composition is a viscous fluid, and the pattern
coating is performed by suitably modified block printing, intaglio
printing or screen printing methods. Also provided are coated
substrates obtainable by the methods of the invention, and wound
dressings comprising such coated substrates.
Inventors: |
ADDISON; Deborah; (Via
Lancaster, GB) ; STEPHENS; Sally; (Skipton, GB)
; BROSNAN; Patrick Joseph; (Bingley, GB) ; STREET;
Gary; (West Yorkshire, GB) ; TEET; Ian;
(Kelbrooke, GB) ; AMJAD; Risham; (Manchester,
GB) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
KCI USA, INC. |
San Antonio |
TX |
US |
|
|
Family ID: |
44147134 |
Appl. No.: |
16/444414 |
Filed: |
June 18, 2019 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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15225536 |
Aug 1, 2016 |
10357406 |
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16444414 |
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14111626 |
Jan 23, 2014 |
9433534 |
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PCT/GB2012/050822 |
Apr 13, 2012 |
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15225536 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B05D 1/322 20130101;
A61F 13/025 20130101; C09J 7/22 20180101; C09J 7/38 20180101; C09J
2483/00 20130101; C09J 2301/302 20200801; A61F 13/0206 20130101;
A61F 13/0276 20130101; Y10T 428/24802 20150115; C09J 183/04
20130101; C09J 2423/106 20130101; C09J 7/26 20180101; B05D 3/0254
20130101; A61F 13/0283 20130101; C09J 5/06 20130101; B05D 1/28
20130101; C09J 2475/006 20130101 |
International
Class: |
A61F 13/02 20060101
A61F013/02; C09J 7/26 20060101 C09J007/26; C09J 7/22 20060101
C09J007/22; B05D 1/28 20060101 B05D001/28; C09J 5/06 20060101
C09J005/06; B05D 3/02 20060101 B05D003/02; C09J 7/38 20060101
C09J007/38; B05D 1/32 20060101 B05D001/32 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 15, 2011 |
GB |
1106491.2 |
Claims
1. A wound dressing, comprising: a backing sheet comprising a
semipermeable polyurethane film; a pattern of silicone adhesive
printed on a first surface of the backing sheet; and an absorbent
island adhered to the backing sheet by the pattern of silicone
adhesive.
2. The wound dressing of claim 1, wherein the absorbent island
comprises a polyurethane foam.
3. The wound dressing of claim 1, wherein the pattern of silicone
adhesive comprises an open network of adhesive.
4. The wound dressing of claim 3, wherein the open network of
adhesive defines a plurality of regions of adhesive that are
separated from one another by portions of the backing sheet along
which no silicone adhesive is provided.
5. The wound dressing of claim 1, wherein the pattern of silicone
adhesive is printed directly on the first surface of the backing
sheet such that the silicone adhesive directly contacts the
polyurethane film.
6. A wound dressing, comprising: a backing sheet comprising a film;
an absorbent island adhered to the lower surface of the backing
sheet; and a plurality of silicone adhesive structures printed on a
lower surface of the backing sheet; wherein each adhesive structure
is separated from an adjacent silicone adhesive structure by a
portion of the lower surface of the backing sheet along which no
silicone adhesive is provided.
7. The wound dressing of claim 6, wherein the silicone adhesive
structures are bonded directly to the backing sheet.
8. The wound dressing of claim 6, wherein the backing sheet
comprises a hydrophilic material.
9. The wound dressing of claim 6, wherein each silicone adhesive
structure has a diameter of at least 2 mm.
10. The wound dressing of claim 6, wherein the silicone adhesive
structures are printed on the lower surface of the backing sheet
such that a density of silicone adhesive along the lower surface of
the backing sheet is from approximately 20 grams to approximately
350 grams of silicone adhesive per square meter.
11. The wound dressing of claim 6, wherein the backing sheet has a
surface area from approximately 1 cm2 to approximately 1000
cm2.
12. The wound dressing of claim 6, wherein the entirety of an outer
periphery of each adhesive structure is surrounded by portions of
the lower surface of the backing sheet along which no silicone
adhesive is provided.
13. A wound dressing, comprising: a backing sheet having a first
surface configured to be attached to a patient; an absorbent layer;
and a pattern of silicone adhesive printed on the first surface of
the backing sheet; wherein the pattern of silicone adhesive is
bonded to and directly contacts the first surface of the backing
sheet.
14. The wound dressing of claim 13, wherein the first surface of
the backing sheet to which the pattern of silicone adhesive is
bonded comprises a hydrophilic material.
15. The wound dressing of claim 13, wherein the first surface of
the backing sheet comprises a center portion that is free of
adhesive.
16. The wound dressing of claim 15, wherein the pattern of silicone
adhesive defines a margin that extends between an outer periphery
of the center portion and an outer perimeter of the backing
sheet.
17. The wound dressing of claim 16, wherein the margin extends
about the entirety of the outer periphery of the center
portion.
18. The wound dressing of claim 16, wherein the margin has a width
from approximately 1 cm to approximately 4 cm.
19. The wound dressing of claim 14, wherein the hydrophilic
material comprises a polyurethane or a hydrocolloid.
20. The wound dressing of claim of claim 13, wherein prior to the
wound dressing being attached to a patient, a cover sheet including
a plurality of raised, folded tabs is adhered to the first surface
of the backing layer by the silicone adhesive.
Description
CROSS-REFERENCE TO RELATED PATENT APPLICATIONS
[0001] This application is a divisional of U.S. patent application
Ser. No. 15/225,536, filed on Aug. 1, 2016, which is a divisional
of U.S. patent application Ser. No. 14/111,626, filed Jan. 23,
2014, now U.S. Pat. No. 9,433,534, which is a US national stage
application under 35 U.S.C. .sctn. 371 of International Application
No. PCT/GB2012/050822, filed Apr. 13, 2012, which claims the
benefit of priority to GB Application No. 1106491.2, filed Apr. 15,
2011, each of which is incorporated herein by reference in its
entirety.
SUMMARY
[0002] The present invention relates to methods of providing
patterned coatings of silicone adhesives on sheet-like substrates,
in particular on medical substrates such as wound dressings.
[0003] Silicone pressure-sensitive adhesives are known for use in
medical products such as wound dressings. The silicone adhesives
have high medical acceptability and are capable of being sterilized
by conventional methods such as autoclaving, gamma and ethylene
oxide without loss of properties. A drawback of the silicone
adhesives is that they have limited oxygen and moisture
permeability. This means that a continuous coating of the silicone
adhesive on, for example, a wound dressing backing sheet, results
in poor breathability of the resulting wound dressing. It is
therefore desirable to provide a discontinuous silicone adhesive
layer to maintain breathability of the dressing.
[0004] Soft silicone adhesives are prepared from a fluid
polymerizable precursor mixture that is coated onto a substrate,
for example by dip-coating or coating process, followed by thermal
curing. The precursor composition is desirably a solventless
composition. The resulting soft silicone adhesives are generally
soft and tacky, but generally solvent free, and therefore readily
repositionable on the skin.
[0005] Hitherto, discontinuous silicone adhesive layers have been
provided by coating the silicone adhesive precursor onto an open
mesh substrate, such as a gauze, so that the apertures of the
substrate remain open after coating with the precursor, followed by
curing of the coated substrate. The resulting silicone
adhesive-coated, open mesh structure can then be applied to a
suitable substrate such as a semipermeable wound dressing backing
sheet. Coated mesh silicone adhesive structures of this type are
described, for example, in EP-A-0251810.
[0006] US-A-20050233072 describes a method of applying a pattern
coating of hydrogel forming polymer onto a substrate, comprising
moving the substrate through a slot coater that applies a patterned
coating of a low-viscosity polymerizable and/or crosslinkable
polymer precursor material to the substrate, followed by
polymerizing the coating downstream of the coater.
[0007] However, it has not previously been suggested to pattern
coat a silicone adhesive directly onto a substrate such as a
backing sheet. This may be because the silicone adhesive precursor
is viscous and solvent-free, and therefore cannot be used in
conventional pattern coating methods such as screen printing or
slot coating. Furthermore, silicone compositions are generally
incompatible with common hydrophilic wound dressing materials,
whereby they adhere relatively weakly to such materials unless a
primer coating is applied between the substrate and the silicone
adhesive. This further hinders conventional pattern coating with
silicone adhesives.
[0008] In a first aspect, the present invention provides a method
of applying a patterned coating of a silicone adhesive to a
substrate sheet, comprising the steps of pattern coating a silicone
precursor composition onto the substrate, followed by thermally
curing the precursor composition coated on the substrate.
[0009] In a first embodiment, the step of pattern coating is
performed by the steps of coating the silicone prepolymer
composition onto an apertured support layer having holes and lands
to provide a coated apertured support layer, followed by applying
the coated support layer to the substrate sheet, followed by
removing the coated apertured support layer to leave a patterned
layer of the silicone composition on the substrate sheet. This
method results in a pattern of the silicone on the substrate sheet
that substantially corresponds to the pattern of lands on the
support layer. The support layer may be removed before or after the
step of curing the silicone.
[0010] In a second embodiment, the step of pattern coating is
performed by providing a mold having a base surface and recesses in
said surface corresponding to the desired adhesive pattern, filling
said recesses with said silicone prepolymer composition, applying
said substrate sheet to said base surface so that it contacts the
prepolymer mixture in the recesses, curing said prepolymer mixture
in contact with the substrate sheet, and removing the substrate
sheet and silicone layer from the mold. In other words, this
embodiment covers various forms intaglio printing of the silicone
prepolymer onto the substrate. The pattern of recesses can be
connected to form a connected layer of the silicone with apertures,
or the recesses may be separated from each other on the surface of
the mold so that separate areas of silicone are deposited on the
support sheet. The process may be carried out in discontinous
fashion using a plurality of flat molds, or in continuous fashion
using an intaglio roller.
[0011] In a third embodiment, the method comprises providing a mold
sheet having upper and lower surfaces and a pattern of apertures
extending between the upper and lower surfaces, filling the
apertures with the fluid silicone prepolymer composition,
contacting one of said upper or lower surfaces with the support
sheet so that said support sheet contacts said fluid silicone
prepolymer composition in said apertures, curing the silicone
prepolymer composition in contact with the support sheet, and
removing the mold sheet. The step of curing may be carried out
before or after the step of curing. This method resembles screen
printing, but the apertures in the mold sheet are substantially
larger than the apertures conventionally used for printing screens
so that the viscosity of the silicone precursor does not hinder
printing. The process may be carried out in discontinous fashion
using a plurality of flat mold sheets, or in continuous fashion
using an apertured roller as described in more detail below.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] The invention will now be described in more detail with
reference to the accompanying drawings, in which:
[0013] FIG. 1 shows a mesh suitable for use as a support layer in
the block printing embodiments according to the present
invention;
[0014] FIG. 2 shows a flat mold suitable for use in a batch
intaglio printing method according to the present invention;
[0015] FIG. 3 shows a schematic view of a roller intaglio printing
method according to the present invention;
[0016] FIG. 4 shows a schematic view of a roller screen printing
method according to the present invention;
[0017] FIG. 5 shows a cross-section through the roller of FIG.
4;
[0018] FIG. 6 shows a perspective view of a silicone-adhesive
pattern coated substrate according to the present invention;
[0019] FIG. 7 shows a perspective view partially cut away of a
wound dressing according to the present invention; and
[0020] FIG. 8 shows the wound dressing of FIG. 7 packaged in a
microorganism-impermeable container.
DETAILED DESCRIPTION
[0021] As noted above, in a first aspect the present invention
provides a method of applying a patterned coating of a silicone
adhesive to a substrate sheet, comprising the steps of pattern
coating a silicone precursor composition onto the substrate,
followed by curing the precursor composition coated on the
substrate.
[0022] The pattern of silicone adhesive may be any regular or
irregular pattern. In certain embodiments the pattern has
translational symmetry along at least one axis, for example along
two or three axes. In certain embodiments, the pattern is in the
form of a network of adhesive coating, such as a mesh pattern or a
honeycomb pattern. In other embodiments the pattern consist of a
plurality of islands, dots, or patches of adhesive separated by
adhesive-free regions of the substrate. In yet other embodiments,
the pattern may be in the form of an adhesive-coated margin or
annulus surrounding an adhesive-free area, for example for the
production of adhesive-bordered dressings. In any event, the
adhesive pattern suitably covers from about 10% to about 90% of the
area of the coated surface of the substrate, for example from about
20% to about 50% of said area. The patterning of the adhesive is
macroscopic, for example the minimum width dimension of any coated
area is suitably greater than about 2 mm. The density of the
coating is suitably from about 20 gsm to 350 gsm, more suitably
from about 30 gsm to about 250 gsm.
[0023] The substrate sheet suitably provides a protective covering,
cushioning, mechanical support and/or liquid absorbency, for
example in a wound dressing. Suitably, the substrate sheet is
formed from a material that is hydrophilic, suitably a material
that does not swell or dissolve significantly in water or wound
fluid. Suitably, the substrate sheet has an uncompressed thickness
of from about 0.2 mm to about 15 mm, for example from about 0.5 mm
to about 5 mm.
[0024] The substrate sheet may be any of the layers conventionally
used to form layers over a wound contacting layer in a laminated
wound dressing, for example absorbent layers or backing layers. In
certain embodiments, the substrate sheet is a backing layer in the
form of a sheet of continuous semipermeable or impermeable polymer.
In other embodiments the substrate sheet may be an absorbent layer
for example a hydrophilic foam, a sponge, a film, or a textile
layer. The textile may be nonwoven, knitted or woven,
[0025] The curing of the silicone prepolymer in situ achieves
strong bonding between the silicone adhesive and substrate sheet
surfaces that are normally incompatible with and non-adherent to
silicone, including hydrophilic surfaces such as polyurethane or
hydrocolloid surfaces. This bonding is suitably achieved without
the use of a silicone primer to improve adhesion, i.e. it is direct
bonding between the silicone and the material of the substrate
sheet.
[0026] In particular embodiments, the substrate sheet is (a) a
semipermeable or impermeable polymer film, or (b) a hydrophilic
foam sheet, or (c) a nonwoven web.
[0027] Suitable semipermeable or impermeable polymer films for the
substrate sheet include any of the semipermeable films
conventionally used to form a backing sheet of wound dressings. The
films are suitably continuous, i.e. they do not comprise
macroscopic apertures that would allow passage of wound fluid.
Suitably, the substrate sheet in these embodiments is also
microorganism-impermeable. Suitable continuous conformable
substrate sheets of this type will suitably have a moisture vapor
transmission rate (MVTR) of the substrate sheet alone of 300 to
35000 g/m.sup.2/24 hrs, suitably 500 to 25000 g/m.sup.2/24 hrs at
37.5.degree. C. at 100% to 10% relative humidity difference
(measured before coating with the silicone adhesive). It has been
found that such moisture vapor transmission rates allow the wound
under the dressing to heal under moist conditions without causing
the skin surrounding the wound to macerate. The substrate sheet
thickness in these embodiments is suitably in the range of 10 to
1000 micrometers, more suitably 100 to 500 micrometers.
[0028] Suitable polymers for forming the substrate sheet in these
embodiments include polyurethanes and poly alkoxyalkyl acrylates
and methacrylates. Suitably, the substrate sheet in these
embodiments comprises a continuous layer of a high density blocked
polyurethane foam that is predominantly closed-cell. A suitable
backing sheet material is the polyurethane film available under the
Registered Trade Mark ESTANE 5714F. Also suitable are elastomeric
polymeric esters such as Du Pont HYTREL (Registered Trade
Mark).
[0029] Suitable hydrophilic foam sheets for use as the substrate
sheet include polyurethane foams, carboxylated butadiene-styrene
rubber, polyacrylate, polyvinylic or cellulosic foams. The
hydrophilic foam may be open-cell or closed-cell. Suitably, the
foam comprises a polyurethane, and more suitably it comprises at
least 50% by weight of one or more polyurethanes, for example at
least 75% by weight thereof.
[0030] The hydrophilic polyurethane foam materials are formed by
reacting particular diisocyanates or isocyanate-capped prepolymers
with suitable chain extending compounds having amine and/or alcohol
multiple functionality. Chain terminating compounds such as
mono-amines or monohydric alcohols may be included in the reaction
mixture. Water may be included in the reaction mixture, since it
reacts with isocyanate to liberate carbon dioxide for foaming the
mixture.
[0031] The hydrophilic foams used in the substrate sheets of the
invention may also have the property of swelling and expanding when
water is absorbed. The degree of swelling of the hydrophilic foams
on complete saturation with an aqueous medium is typically at least
100% (expressed in terms of increase in volume), and suitably at
least 200%. Preferred foams swell by 400 to 800%. Despite this high
degree of swelling, however, the foams of the invention retain
their integrity even after absorption of large quantities of water.
Typically, the cells of the hydrophilic foams have an average
diameter in the range 0.1 to 0.6 mm. Suitably hydrophilic foams are
as described in EP-A-0541391. These foam layers are available from
Systagenix Wound Management under the Registered Trade Marks TIELLE
and HYPOL.
[0032] Suitably, the basis weight of the hydrophilic foam when used
as a substrate sheet in the materials of the present invention is
from 0.2 to 1.5 kg/m.sup.2, more suitably 0.5 to 1.0
kg/m.sup.2.
[0033] Suitable textiles for use as the substrate sheet include any
of those conventionally used for absorbent products, including
cellulose woven or nonwoven webs, or cellulose derivatives such as
viscose, rayon or oxidized regenerated cellulose. In certain
embodiments, the fabric comprises at least about 10 wt. % of
hydrogel-forming absorbent fibers based on the dry weight of the
fabric, for example, the fabric comprises at least about 20 wt. %
of the hydrogel-forming fibers, for example from about 30 wt. % to
about 50 wt. % of such fibers.
[0034] The term "hydrogel-forming fibers" refers to fibers that can
absorb at least about twice their own weight of water, suitably at
least about four times their own weight of water, to form a
hydrogel. The fibers are normally insoluble in water. Suitable
materials for the hydrogel-forming fibers include alginates,
carboxymethylcelluloses, hydroxyethyl-celluloses, polyacrylates,
and hyaluronates. Suitable materials are calcium alginate and
sodium carboxymethylcellulose and mixtures thereof.
[0035] Suitably, the fabric comprises at least about 10 wt. % based
on the dry weight of the fabric of substantially
non-water-absorbent textile fibers, and suitably it comprises at
least about 20 wt. % of such fibers, for example from about 30 wt.
% to about 60 wt. % of such fibers. Suitable non-absorbent textile
fibers include polyamide fibers such as nylon fibers, polyolefin
fibers, and viscose fibers.
[0036] In some embodiments, the absorbent layer is similar to those
described in WO03/053584. That is to say, the absorbent layer
comprises or consists essentially of a nonwoven fabric made up of a
mixture of from about 10 wt. % to about 90 wt. % of
hydrogel-forming absorbent fibers and from about 90 wt. % to about
10 wt. % of nonabsorbent textile fibers. In certain embodiments, at
least some of the non-absorbent textile fibers are coated with
metallic silver (Ag.sup.0) as an antimicrobial agent. Suitably, the
amount of silver in the fabric is from about 0.1% to about 10 wt.
%, based on the dry weight of the fabric. Textiles of this kind are
available from Systagenix Wound Management under the Registered
Trade Mark SILVERCEL.
[0037] The basis weight of the textile substrate sheet may be in
the range of 50-500 g/m.sup.2, such as 100-400 g/m.sup.2. The
uncompressed thickness of the textile layer may be in the range of
from 0.5 mm to 10 mm, such as 1 mm to 4 mm. The free (uncompressed)
liquid absorbency measured for physiological saline may be in the
range of 5 to 30 g/g at 25.degree. C.
[0038] Suitably, the silicone precursor composition is
substantially or completely solvent-free. For example, the
precursor composition may comprise less than about 10 wt. % of
solvent, typically less than about 1 wt. % of solvent. The term
"solvent" is used in its usual sense, that is to say organic and/or
aqueous liquid solvents or diluents that do not foam part of the
final adhesive polymer composition. Suitably, the precursor
composition is a viscous fluid, for example a fluid having a
viscosity of at least about 1 Pa s, typically about 2 Pa s to about
20 Pa s at 20.degree. C.
[0039] Suitably, the silicone composition is a so-called soft skin
adhesive silicone elastomer. Such silicones can be made by an
addition reaction (hydrosilylation) between (a) a vinyl functional
polydimethyl siloxane, such as bis-dimethyl vinyl PDMS, and (b) a
hydrogen functional siloxane, such as dimethyl, methylhydrogen
siloxane copolymers, hydrogen dimethylsiloxy terminated PDMS. The
cure reaction is catalyzed by a hydrosilylation catalyst, such as a
noble metal catalyst, suitably a platinum catalyst. Suitably the
silicone prepolymer composition further comprises a polymerization
inhibitor that is evaporated from said composition during said step
of thermally partially curing, for example 2-methyl-3-butyn-2-ol.
The polymerization inhibitor is suitably present in an amount of
from about 0.001 wt. % to about 1 wt. %, for example from about
0.01 wt. % to about 0.1 wt. % before curing.
[0040] Silicone skin adhesive compositions are suitably supplied as
two-part systems: Part A contains at least the vinyl prepolymer and
the catalyst, while Part B contains the vinyl prepolymer and the
SiH siloxane cross linker. The components are mixed immediately
before use, optionally with addition of the polymerization
inhibitor, to form the adhesive precursor composition.
[0041] In embodiments, the silicone coating composition comprises
or consists essentially of the following components:
[0042] (A) a diorganopolysiloxane having at least 2 alkenyl groups
in each molecule;
[0043] (B) an organohydrogenpolysiloxane having at least 2
silicon-bonded hydrogen atoms in each molecule, in a quantity
sufficient for the ratio between the number of moles of
silicon-bonded hydrogen atoms in this component and the number of
moles of alkenyl groups in component (A) to have a value of from
about 0.6:1 to about 20.1,
[0044] (C) optionally a platinum group metal catalyst suitably in a
quantity providing 0.1 to 500 weight parts as platinum group metal
per 1,000,000 weight parts component (A); and
[0045] (D) a volatile polymerization inhibitor, suitably selected
from: alkyne alcohols such as 2-methyl-3-butyn-2-ol,
3,5-dimethyl-1-hexyn-3-ol, and phenylbutynol; ene-yne compounds
such as 3-methyl-3-penten-1-yne and 3,5-dimethyl-3-hexen-1-yne;
tetramethyltetrahexenyl-cyclotetrasiloxane; and benzotriazole.
[0046] The diorganopolysiloxane, component (A), used in the instant
invention is the base component of the total composition. This
diorganopolysiloxane must contain at least 2 alkenyl groups in each
molecule in order for this composition to cure into a rubbery
elastic silicone rubber coating composition.
[0047] The diorganopolysiloxane (A) comprises essentially
straight-chain organopolysiloxane with the average unit formula
R.sub.nSiO.sub.(4-n)/2, wherein R is selected from substituted and
unsubstituted monovalent hydrocarbon groups and n has a value of
1.9 to 2.1. R may be exemplified by alkyl groups such as methyl,
ethyl, propyl, and others; alkenyl groups such as vinyl, allyl, and
others; aryl groups such as phenyl, and others; and haloalkyl
groups such as 3,3,3-trifluoropropyl and others. The
diorganopolysiloxane (A) should have a viscosity at 25.degree. C.
of at least 100 centipoise (1 d Pas). When such factors as the
strength of the silicone rubber coating membrane, and blendability
are taken into account, the viscosity of diorganopolysiloxane (A)
at 25.degree. C. is preferably from 1,000 centipoise (1 d Pas) to
100,000 centipoise (100 Pas). The diorganopolysiloxane (A) may be
exemplified by dimethylvinylsiloxy-endblocked
dimethylpolysiloxanes, dimethylvinylsiloxy-endblocked
dimethylsiloxane-methylvinylsiloxane copolymers, and
dimethylvinyl-siloxy-endblocked
dimethylsiloxane-methylphenylsiloxane copolymers.
[0048] Component (B), an organopolysiloxane that contains at least
2 silicon-bonded hydrogen atoms in each molecule, is a crosslinker
for the composition of the instant invention. The
organopolysiloxane (B) may be exemplified by
trimethylsiloxy-endblocked methyl-hydrogenpolysiloxanes,
trimethylsiloxy-endblocked dimethylsiloxanemethylhydrogen-siloxane
copolymers, dimethylphenylsiloxy-endblocked
methyiphenylsiloxanemethyl-hydrogensiloxane copolymers, cyclic
methylhydrogenpolysiloxanes, and copolymers that contain the
dimethylhydrogensiloxy unit and SiO4/2 unit. The
organohydrogenpolysiloxane (B) should be added in a quantity that
the ratio between the number of moles of silicon-bonded hydrogen
atoms in this organohydrogenpolysiloxane and the number of moles of
alkenyl groups in component (A) has a value of 0.6:1 to 20:1.
[0049] The platinum group metal catalyst, component (C), used in
the compositions is a curing catalyst. The platinum group metal
catalyst (C) may be exemplified by platinum micropowder, platinum
black, chloroplatinic acid, platinum tetrachloride, olefin
complexes of chloroplatinic acid, alcohol solutions of
chloroplatinic acid, complexes between chloroplatinic acid and
alkenylsiloxanes, rhodium compounds, and palladium compounds. The
platinum group metal catalyst (C) should be added generally at 0.1
to 500 weight parts as platinum group metal per 1,000,000 weight
parts component (A), and is preferably used at 1 to 50 weight parts
as platinum group metal per 1,000,000 weight parts component (A).
The reaction will not develop adequately at less than 0.1 weight
parts, while additions in excess of 500 weight parts are
uneconomical.
[0050] The step of curing the silicone adhesive precursor normally
comprises thermal curing to at least partially cure the silicone.
The thermal curing is suitably performed continuously by passing
the coated substrate through an oven. Suitable thermal curing
conditions include exposure to a temperature of from about
80.degree. C. to about 200.degree. C., for example about
120.degree. C. to about 180.degree. C. for a time of from about 1
minute to about 10 minutes, for example about 1.5 minutes to about
5 minutes. Especially suitable conditions are
110.degree.-150.degree. C. for 2 to 6 minutes. The elevated
temperature results in evaporation of the polymerization inhibitor
(when present) from the silicone composition and therefore in
polymerization of the silicone. The resulting material is
chemically polymerized and dimensionally stable, but may be capable
of further curing by ionizing radiation as explained further
below.
[0051] The thermally cured material may then be subjected to a
final cure with ionizing radiation. The ionizing radiation is
suitably selected from e-beam radiation and gamma radiation. A
variety of procedures for E-beam and gamma ray curing are
well-known. The cure depends on the specific equipment used, and
those skilled in the art can define a dose calibration model for
the specific equipment, geometry, and line speed, as well as other
well understood process parameters. The final cure may form part of
the final sterilization by irradiation of the products of the
invention. Suitably, the method of the invention further comprises
the step of packaging the material in a microorganism-impermeable
container prior to the step of further curing with ionizing
radiation, whereby the step of further curing also sterilizes the
material.
[0052] Commercially available electron beam generating equipment is
readily available. For example, a Model CB-300 electron beam
generating apparatus (available from Energy Sciences, Inc.
(Wilmington, Mass.). Generally, a support film (e.g., polyester
terephthalate support film) runs through a chamber. Generally, the
chamber is flushed with an inert gas, e.g., nitrogen while the
samples are e-beam cured. Multiple passes through the e-beam
sterilizer may be needed.
[0053] Commercially available gamma irradiation equipment includes
equipment often used for gamma irradiation sterilization of
products for medical applications. Cobalt 60 sources are
appropriate. Total absorbed doses are suitably from 20 to 60 kGy,
more suitably from about 35 to 50 kGy and dose rates are suitably
about 7 to 8 kGy/hour.
[0054] The step of further curing with ionizing radiation is also
effective to bond the silicone adhesive more strongly to the
surface of the substrate layer. This is thought to be due to the
ionizing radiation forming covalent bonds between the silicone and
the substrate layer material.
[0055] The final cured silicone adhesive coating is suitably gel-
or elastomer-like, substantially hydrophobic, and moderately
adherent (tacky). This coating is therefore suitable for direct
application to and removal from wounds without excessive trauma,
and/or for repositionable application to skin.
[0056] In a first embodiment, the step of pattern coating is
performed by the steps of coating the silicone prepolymer
composition onto an apertured support layer having holes and lands
to provide a coated apertured support layer, followed by applying
the coated support layer to the substrate sheet, followed by
removing the coated apertured support layer to leave a patterned
layer of the silicone composition on the substrate sheet. This
method results in a pattern of the silicone on the substrate sheet
that substantially corresponds to the pattern of lands on the
support layer. Thus, the method resembles block printing in that
the coated apertured support layer is used as a printing block to
print a pattern of silicone prepolymer onto the substrate.
[0057] The support layer may be removed before or after the step of
curing the silicone. Suitably, the support layer has a surface that
is relatively non-adherent to the silicone adhesive, for example a
perfluorocarbon surface.
[0058] The support layer may be a mesh or web or fabric suitably
formed from a woven, nonwoven or knitted textile, or it may be a
molded mesh, or it may be an apertured continuous film. A typical
perforated plastic sheet substrate layer is shown in FIG. 1.
[0059] The size and shape of the apertures in the support layer
generally correspond to the desired adhesive-free areas of the
silicone coated substrate. The apertures generally have an aspect
ratio of from 1:1 to 5:1, and preferably from 1:1 to 2:1. For
example, the apertures may be approximately circular or
approximately square. The apertures suitably have an average
diameter of from about 2 to about 4 mm, and more suitably from
about 3 to about 5 mm. The open area of the support may for example
be from about 30% to about 90%, for example from about 50% to about
80%.
[0060] The support sheet is suitably formed from any medically
acceptable material, such as cellulose, polyolefins, polyesters, or
polyamides.
[0061] The support sheet is coated with the silicone adhesive
prepolymer composition by any suitable means, such as dip-coating
or roller coating. Air or another gas may be blown through the
coated support to ensure that the apertures are open before
applying the coated support to the substrate. The support sheet is
suitably then lifted off the substrate to leave a pattern of
silicone adhesive prepolymer on the substrate, which is then cured.
In other embodiments, the curing is carried out with the support
sheet on the substrate, followed by lifting the support sheet off
the cured silicone. The latter embodiments require, of course, that
the cured silicone adhesive is less adherent to the support than to
the substrate.
[0062] In a second embodiment, the step of pattern coating is
performed by providing a mold having a base surface and recesses in
said surface corresponding to the desired adhesive pattern, filling
said recesses with said silicone prepolymer composition, applying
said substrate sheet to said base surface so that it contacts the
prepolymer mixture in the recesses, curing said prepolymer mixture
in contact with the substrate sheet, and removing the substrate
sheet and silicone layer from the mold. In other words, this
embodiment covers various forms intaglio printing of the silicone
prepolymer onto the substrate.
[0063] The pattern of recesses can be connected to form a connected
layer of the silicone with apertures, or the recesses may be
separated from each other on the surface of the mold so that
separate areas of silicone are deposited on the support sheet. The
depth of the recesses is suitably from about 0.1 mm to about 2 mm,
for example about 0.2 mm to about 1 mm. The mold is suitably formed
from metal or polymer.
[0064] The recesses are suitably filled with the silicone
prepolymer composition by flooding the mold with the prepolymer
composition, followed by wiping with e.g. a doctor blade to remove
the prepolymer from the base surface of the mold outside the
recesses. Curing of the prepolymer is performed after printing, as
described above.
[0065] The process may be carried out in discontinous fashion using
a plurality of flat molds, or in continuous fashion using an
intaglio roller. A suitable flat mold is shown in FIG. 2. The mold
1 is formed of polytetrafluoroethylene, and comprises a flat base
surface 2 having recesses 3 formed therein by any suitable method
such as injection molding or machining. The recesses 3 in this
embodiment have substantially constant depth of about 0.5 mm. The
recesses 3 are filled with the silicone prepolymer composition 4 by
flooding the mold with the prepolymer composition, followed by
wiping the base surface 2 with a doctor blade (not shown) to remove
excess prepolymer. Substrate layer 6 is laid on top of the base
surface 2, optionally with application of pressure, and is then
peeled away to provide the substrate layer having patterned
silicone adhesive prepolymer thereon. Curing is then carried
out.
[0066] A suitable roller method is shown in FIG. 3. In these
embodiments, the roller 10 is formed having recesses 12 in its
outer surface as hereinbefore described. The prepolymer is applied
in a continuous layer to the outside surface of the intaglio roller
10 by a transfer roller 14. A doctor blade 16 wipes the outer
surface of the intaglio roller leaving the apertures filled with
the prepolymer. The coated roller is then applied to the moving
substrate 18 to print the prepolymer onto the substrate 18,
followed by curing.
[0067] In a third embodiment, the method of the present invention
comprises providing a mold sheet having upper and lower surfaces
and a pattern of apertures extending between the upper and lower
surfaces, filling the apertures with the fluid silicone prepolymer
composition, contacting one of said upper or lower surfaces with
the support sheet so that said support sheet contacts said fluid
silicone prepolymer composition in said apertures, curing the
silicone prepolymer composition in contact with the support sheet,
and removing the mold sheet. The step of curing may be carried out
before or after the step of removing the mold sheet.
[0068] This method resembles screen printing, but the apertures in
the mold sheet are substantially larger than the apertures in
conventional printing screens so that the viscosity of the silicone
precursor does not hinder printing. Suitably, the thickness of the
mold sheet is from about 0.1 mm to about 2 mm, for example from
about 0.2 mm to about 1 mm. The mold sheet may for example be a
perforated metal sheet, a perforated plastic sheet, or a textile
sheet having large apertures. The open area of the mold sheet is
suitably from about 10% to about 90% of the total area, for example
from about 10% to about 50% of the total area of the mold
sheet.
[0069] Suitably, the apertures in the mold sheet are filled with
the silicone adhesive prepolymer composition by flooding the mold
sheet with prepolymer, followed by wiping excess prepolymer from
the surfaces of the mold sheet, for example with a doctor blade.
The step of flooding the mold sheet with prepolymer is suitably
pertained while one of the surfaces of the mold sheet is in contact
with the substrate sheet.
[0070] The process may be carried out in discontinuous fashion
using a plurality of flat mold sheets, or in continuous fashion
using an apertured roller. A suitable roller method is shown in
FIG. 5. In these embodiments, the screen printing roller 20 is
formed from a mold sheet material as hereinbefore described. The
prepolymer is pumped into channel 22 inside the roller so that it
is fed selectively to the apertures of the roller 20 that are in
contact with the substrate sheet 24. The position of the channel 22
is fixed as the roller rotates, so that one edge 26 of the channel
acts as a doctor blade to wipe the inside surface of the roller
after the apertures have been filled with the prepolymer. A
concentric channel 28 may be provided that is fed with compressed
air (or other compressed gas) to ensure that the prepolymer in the
apertures is transferred to the substrate sheet 24 as the roller
rotates. The printed substrate sheet is then cured.
[0071] In a second aspect, the present invention provides a
substrate sheet having a patterned silicone adhesive coating
thereon, obtainable by a method according to the present
invention.
[0072] FIG. 6 shows a printed substrate sheet according to this
aspect of the invention. The substrate 30 is a semipermeable
polyurethane wound dressing backing sheet. The patterned silicone
adhesive 32 is in the form of an open network of adhesive formed by
block printing a mesh coated with the silicone prepolymer onto the
substrate followed by curing. In other embodiments, the adhesive
may be patterned as a continuous adhesive margin extending around
the perimeter of the substrate sheet, whereby the central region of
the substrate sheet is adhesive-free. The width of the adhesive
coated margin is suitably from about 1 cm to about 4 cm. The
adhesive-coated margin can then be used to attach the substrate
sheet to skin surrounding a wound.
[0073] In a further aspect, the present invention provides a wound
dressing comprising a substrate sheet according to the second
aspect of the invention.
[0074] Suitably, the wound dressing according to the present
invention is in the form of a piece having a total area of from
about 1 cm.sup.2 to about 1000 cm.sup.2, for example from about 5
cm.sup.2 to about 400 cm.sup.2.
[0075] The dressing may comprise one or more releasable cover
sheets over the adhesive pattern coated surface of the substrate to
protect the adhesive surface before use. The cover sheets may
comprise a film of polyethylene, polypropylene or fluorocarbons and
papers coated with these materials. Suitably, the cover sheet is a
release-coated paper sheet, such as a silicone release-coated paper
sheet. Examples of silicone-coated release papers are POLYSLIK
(Registered Trade Mark) supplied by H.P. Smith & Co., offered
in various formulations to control the degree of adhesion of the
paper to the silicone coated substrate surface.
[0076] In certain embodiments, the cover sheets may comprise two or
more parts, such as a first removable part having a first edge and
a second removable part that meets the first part along the first
edge. Suitably, along each of said edges where the parts meet, one
of the parts is folded back to provide a folded-back margin, and
the other part overlaps the said folded-back margin. This provides
an easy-to-grasp margin on each part in the region of overlap to
assist removal of the cover sheet by the care giver. In other
embodiments, the cover sheets may comprise three parts, for example
as described in detail in EP-A-0117632.
[0077] FIG. 7 shows a wound dressing according to this embodiment
of the invention. The wound dressing 40 is an island-type dressing
having a semipermeable polyurethane film backing sheet 42 that is
the substrate for a printed pattern 44 of silicone adhesive. An
absorbent island 46 of hydrophilic polyurethane foam is adhered
centrally on the backing sheet by the silicone adhesive. Release
coated cover sheets 48, 49 are applied over the wound facing side
of the dressing.
[0078] Suitably, the wound dressings of the invention are sterile
and packaged in a microorganism-impermeable container, such as a
pouch. FIG. 8 shows the wound dressing 40 of FIG. 7 packaged in a
microorganism-impermeable pouch 50.
[0079] Any feature disclosed herein in relation to any one or more
aspects of the invention may be present in any of the other aspects
defined herein. Likewise, any combination of the alternative
features described herein may be present in any of the aspects of
the invention. It will be understood that all such combinations and
features of the different aspects have not been described in detail
herein solely for reasons of brevity.
Example 1
[0080] A support mesh is coated with a fluid silicone adhesive
prepolymer composition. The support mesh is a polypropylene sheet
having a hexagonal (close packed) array of circular apertures of
diameter 8 mm and open area about 60%. The silicone prepolymer is
made by mixing Components Gel A and Gel B (Dow Corning products
Q7-9177) at a weight ratio of 50:50 at 25-40.degree. C. The mesh is
coated by transferring of mixture using either a roller or a
coating machine.
[0081] The silicone prepolymer composition on the support mesh is
gently pressed onto substrate sheet formed of 0.4 mm high-density
polyurethane foam formed from a blocked toluene di-isocyanate. The
coated substrate with the mesh in place is then cured at
110-150.degree. C. for 2 to 6 minutes. The support mesh is then
lifted off to leave a pattern of adhesive on the support sheet
corresponding to the pattern of lands on the support mesh. This
results in a substrate coated with a patterned silicone adhesive as
shown in FIG. 6.
[0082] Moisture vapour transfer rate (MVTR) was measured for the
resulting pattern coated adhesive sheets. For comparison, MVTR was
also measured for the semipermeable substrate layer without any
coating, and for the semipermeable substrate layer having a
continuous coating of the same silicone adhesive. The results were
as follows:
TABLE-US-00001 Material MVTR (g/m.sup.2/24 hr) Film Backing 12002.5
Film backing + continuous layer of silicone 311 Film backing +
patterned layer of silicone 8910.5
[0083] It can be seen that the silicone adhesive is substantially
impermeable to moisture, but that this drawback can be
substantially overcome by the use of the patterned adhesive
coating.
Example 2
[0084] The method of Example 1 is repeated with replacement of the
semipermeable film substrate by a hydrophilic polyurethane foam
substrate (TIELLE.RTM., produced by Systagenix Wound Management). A
similar printed adhesive pattern is achieved on the foam.
[0085] The above examples have been described by way of
illustration only. Many other embodiments falling within the scope
of the accompanying claims will be apparent to the skilled
reader.
* * * * *