U.S. patent application number 13/243645 was filed with the patent office on 2012-01-19 for medical devices and processes for preparing same.
This patent application is currently assigned to BOSTON SCIENTIFIC SCIMED, INC.. Invention is credited to Robert E. Burgmeier, Scott Schewe, Jan Weber.
Application Number | 20120013043 13/243645 |
Document ID | / |
Family ID | 34063236 |
Filed Date | 2012-01-19 |
United States Patent
Application |
20120013043 |
Kind Code |
A1 |
Weber; Jan ; et al. |
January 19, 2012 |
MEDICAL DEVICES AND PROCESSES FOR PREPARING SAME
Abstract
Medical balloons comprising a predetermined pattern of
conductive materials and methods of making the same.
Inventors: |
Weber; Jan; (Maastricht,
NL) ; Schewe; Scott; (Eden Prairie, MN) ;
Burgmeier; Robert E.; (Plymouth, MN) |
Assignee: |
BOSTON SCIENTIFIC SCIMED,
INC.
Maple Grove
MN
|
Family ID: |
34063236 |
Appl. No.: |
13/243645 |
Filed: |
September 23, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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10622621 |
Jul 18, 2003 |
8025637 |
|
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13243645 |
|
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Current U.S.
Class: |
264/317 |
Current CPC
Class: |
A61B 2018/00839
20130101; B29C 35/08 20130101; A61B 2017/00243 20130101; A61B
18/1492 20130101; A61B 2218/002 20130101; C08G 73/10 20130101; B29C
33/3842 20130101; B29C 33/52 20130101; A61M 25/1027 20130101; B29C
2033/525 20130101; A61B 2018/00065 20130101; A61B 2018/00351
20130101; A61B 2018/00797 20130101; A61M 25/1029 20130101; A61M
25/1038 20130101; A61B 2018/1407 20130101; B29C 2035/0827 20130101;
B29C 41/10 20130101; B29C 41/14 20130101; A61B 2018/00577 20130101;
B29L 2031/7542 20130101 |
Class at
Publication: |
264/317 |
International
Class: |
B29C 41/42 20060101
B29C041/42 |
Claims
1-20. (canceled)
21. A process for forming a medical balloon comprising: a)
providing a removable shape form that defines the shape of the
medical balloon; b) depositing at least one layer of a polymer
composition on the shape-form; c) applying conductive fibers or a
conductive wire on the polymer composition in a predetermined
pattern; and d) removing the shape-form.
22. The process of claim 21 wherein said depositing is selected
from spray, print, dip or brush deposition.
23. The process of claim 21 wherein said polymer composition
comprises a curable polymer.
24. The process of claim 21 wherein said balloon comprises a
multilayer structure said at least one first layer of said polymer
composition comprises an elastic polymer composition and further
comprising at least one second layer comprising a second polymer
composition that is less compliant.
25. The process of claim 21 wherein said conductive fibers are
sprayed as a mixture with a curable composition.
26. The process of claim 21 wherein said pattern is a spiral
pattern, radial stripes, longitudinal stripes, and spots.
27. The process of claim 21 wherein any intervening space between
said pattern of said conductive fibers is non-conductive.
28. The process of claim 21 comprising spiraling or coil winding
said conductive wire on said surface of said polymer
composition.
29. The process of claim 21 further comprising: (e) providing at
least one second polymer composition that comprises a polymer blend
which is different than said first polymer blend, said second
polymer blend comprises said conductive fibers; and (f) applying
said second polymer blend on said shape form to create transitions
within said balloon wherein a predetermined pattern of conductive
fibers and the intervening space between said pattern of said
conductive fibers is non-conductive.
30. The method of claim 29 wherein said pattern comprises axial
rings, circumference strips or spiral.
31. The method of claim 29 wherein said applying is spraying,
dipping, brushing or printing.
32. The method of claim 29 wherein said applying step is spraying,
said spraying is conducted with at least two spray heads.
33. The process of claim 33 wherein said second polymer composition
is curable.
34. A medical balloon formed from at least one polymer composition,
the medical balloon comprising a predetermined pattern of
conductive regions comprising conductive fibers, intervening
regions between said pattern of conductive regions are
non-conductive.
35. The medical balloon of claim 34 wherein said pattern comprises
spiral, spots, axial stripes or longitudinal stripes.
36. The medical balloon of claim 34 wherein said at least one
polymer composition is curable.
37. The medical balloon of claim 34 wherein said balloon comprises
a multilayer structure comprising a first layer and a second layer,
said first layer comprising said at least on polymer composition,
said at least one polymer composition is an elastic polymer
composition, said second layer comprising a polymer composition
that is less compliant.
38. A medical balloon formed from at least one polymer composition,
the medical balloon comprising conductive wire, said conductive
wire is spirally wrapped about said balloon.
39. The medical balloon of claim 38 wherein said at least one
polymer composition is curable.
40. The medical balloon of claim 38 wherein said balloon comprises
a multilayer structure comprising a first layer and a second layer,
said first layer comprising said at least on polymer composition,
said at least one polymer composition is an elastic polymer
composition, said second layer comprising a polymer composition
that is less compliant.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is claims priority to U.S. patent
application Ser. No. 10/622,621 filed Jul. 18, 2003, the entire
contents of which are hereby incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] Many medical devices comprising polymers, such as diagnostic
and balloon catheters, are currently being manufactured utilizing
conventional thermoplastic polymer thermoforming techniques such as
extrusion, injection molding, stretch blow molding, and the like.
Within these processes, one softens or melts the polymer and
reshapes it into the desired shape. Although these thermoforming
processes are well developed, pressures exist to shrink the size of
such medical products. At the same time the diversity of local
functional properties within the device is increasing.
Consequently, an increasing number of complex processing steps have
to be taken to get to the desired result.
[0003] Balloon molding from thermoplastic polymer compositions
comprising reinforcements is difficult due to the fact that most
types of reinforcing agents are unlikely to deform during the blow
molding process. Dip molding balloons is possible, but due to the
fact the inner shape has to be removed from within the balloon,
this is not the most suitable way to produce a reinforced
balloon.
[0004] High tensile strengths are important in angioplasty balloons
because they allow for the use of high pressure in a balloon having
a relatively small wall thickness. High pressure is often needed to
treat some forms of stenosis. Small wall thicknesses enable the
deflated balloon to remain narrow, making it easier to advance the
balloon through the arterial system. Similar factors are important
in catheter shaft materials.
[0005] One of the disadvantages of blow molding balloons is that
the cone sections have a thicker wall than the central section.
This results in a large balloon profile during folding. A variety
of techniques have been offered to reduce cone thickness, but they
are not always suitable for a given balloon.
[0006] Because of these factors, fabrication techniques for such
device components are not adequate to keep reducing size,
increasing device complexity, and/or implementing new devices.
Consequently there is a need for new fabrication techniques to
provide a wider range of local functional properties at the same
time allow further size reductions.
[0007] Curable compositions, dispensed or applied in liquid form,
and subsequently cured have some uses in conventional fabrication
of catheter devices, typically in adhesive or coating applications.
However, prior to the inventions described herein they have not
obtained widespread use.
[0008] Devices formed of cured polyimide materials have been
described in several documents. Polyimide polymers, known for their
high strength at very high temperatures are typically formed by
heating polyamide-acid precursor polymer material to a curing
temperature where amide and acid groups along the polymer condense
to form cyclic imide groups in the backbone polymer chain. This
technique is used to form balloons in Euteneuer, U.S. Pat. No.
4,952,357. This fabrication method, however, is unsuited to many
device forming applications because of the high temperatures
required for curing the polyimide. Further, while polyimide has
excellent strength properties, the resulting polymers have
relatively poor flexibility, elongation and softness. Still
further, the manufacturing procedure uses HF to dissolve a glass
substrate upon which the polyamide-acid is formed by deposition
from solution. The glass substrate formation and subsequent HF
destruction thereof is a relatively dangerous and expensive
process.
[0009] Polyimide tubing used for catheter shafts is described in
U.S. Pat. No. 4,976,720, Machold et al, but with no discussion of
how it is made.
[0010] U.S. Pat. No. 5,100,381, Burns, describes angioplasty
catheters with shaft portions made of polyimide or
polyimide-polytetrafluoroethylene composite material.
[0011] U.S. Pat. No. 6,024,722, Rau et al, applies thermoplastic
polyimide to the art of balloon catheter construction, i.e., to
catheter shafts, guide catheters, infusion catheters and balloons.
Use of this material, however, is subject to the same limitations
already recognized for the general class of thermoplastic
polymers.
[0012] U.S. Pat. No. 5,145,942, Hergenrother, et al, describes
methyl-substituted polyimide polymers which are thermoplastic, but
curable to a crosslinked state by irradiation with UV or exposure
to temperatures in excess of 275.degree. C. The UV irradiation
process, however, appears to be very slow (100 hrs at 0.21
watts/cm.sup.2 to cure films of 1.7 and 2.4 mils (0.04-0.06 mm).
Thus use of this material for forming medical devices appears to
offer few or no benefits compared to other polyimides, while at the
same time incurring further processing disadvantages.
[0013] In addition to condensation from polyamide-acid polymers, it
has been proposed to form a polyimide from a bis-maleimide compound
by Diels Alder cycloaddition, however these reactions are also run
at temperatures in excess of 200.degree. C. More recently it has
been proposed to prepare polyimides by diene cycloadditions which
are catalyzed by UV irradiation, near or even below ambient
temperatures.
SUMMARY OF THE INVENTION
[0014] The present invention, in one aspect, pertains to processes
for forming articles, particularly medical devices, from radiation
curable compositions in which pattern-wise curing is used to form
the device or coatings thereon. The devices may be polymer devices,
or metal or ceramic devices containing polymer surfaces (coatings).
In a further aspect, the invention pertains to a device so
formed.
[0015] An aspect of the invention is the use of ice (frozen water),
wax, polyvinyl alcohol, or another readily fluidizable solid
material, to produce a substrate having a desired device shape, for
instance a balloon shape, depositing a curable polymer-forming
composition onto the outside of the shape. Spray, print or dip
deposition may be used. After deposition, one can direct UV or
other cure inducing energy at the deposited layer to cure the
polymer in the device shape, followed by a fluidizing step to get
rid of the fluidizable material.
[0016] In a further aspect, the invention pertains to a mold form
for a medical device which is formed of a material which melts at a
temperature below 100.degree. C., preferably at or below 50.degree.
C., and especially at or below ambient temperature (about
22.degree. C.).
[0017] In some embodiments the inventive process allows for varied
fabrication techniques, for instance applying a liquid curable
formulation to a substrate of fluidizable material pattern-wise or
uniformly, and/or curing by irradiating pattern-wise, sequentially
or uniformly, as appropriate to the device being built. The curable
formulation can be varied on-the-fly to change the physical
properties of the device as desired. Moreover, the substrate may be
altered, for instance to change fluidization properties of melt
point or solubility, or to leave behind material such as fibers
which may provide desired bridging structures or other desirable
connections between portions of the device through the volume
occupied by the substrate.
[0018] In a further aspect, the invention pertains to processes for
forming medical devices from radiation curable compositions which
cure to form polyimide polymers below about 50.degree. C.
[0019] The process also allows for tailoring of physical properties
to the demands of the article being formed.
[0020] Other aspects of the invention are described in the detailed
description below and in the claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] FIG. 1 is a perspective view of a balloon catheter using a
balloon of the present invention.
[0022] FIGS. 2A-2C illustrate a preferred method of forming a
dilatation balloon of the present invention.
[0023] FIGS. 3A and 3B illustrate a balloon formed in a normal
deflated state and inflated in a pressurized state.
[0024] FIG. 4 is a schematic side sectional view of a wire which
may be used to prepare an ice or wax form mold useful for preparing
a catheter shaft in the method of the present invention.
[0025] FIG. 5 is a view as in FIG. 4 with an ice or wax mold formed
over the wire.
[0026] FIG. 6 is a view as in FIG. 5 with the form further modified
to provide a balloon shape at the distal end.
[0027] FIG. 7 is a view as in FIG. 6 with the form further modified
to provide a longitudinal hole in the balloon form passing through
the cone walls of the balloon form.
[0028] FIG. 8 is a side section view of a balloon for a rapid
exchange catheter from the modified form of FIG. 8.
[0029] FIG. 9 is a perspective view of a balloon for a rapid
exchange catheter which may be prepared in accordance with the
invention.
[0030] FIG. 10 is a cross-sectional view of a catheter shaft
prepared in accordance with an embodiment of the invention.
[0031] FIGS. 11A-C are side-section schematic views illustrating
the steps of preparing a self-retracting balloon in accordance with
an embodiment of the invention.
[0032] FIGS. 12A and 12 B, respectively, show a side view of a
balloon formed with an axial curve and an ellipsoid cross-sectional
distal tube on which such balloon may be mounted.
[0033] FIG. 13 is a schematic depiction of a process in accordance
an embodiment of the invention, viewed in cross-section, for
preparing a balloon having a chamber structure adapted to carry and
dispense a drug at the treatment site.
[0034] FIG. 14 is a perspective view of a stent in expanded
configuration which may be made in accordance with the
invention.
DETAILED DESCRIPTION OF THE INVENTION
[0035] All published documents, including all US patent documents,
mentioned anywhere in this application are hereby expressly
incorporated herein by reference in their entirety. Any copending
patent applications, mentioned anywhere in this application are
also hereby expressly incorporated herein by reference in their
entirety.
[0036] Some embodiments of the present invention are directed to
processes for forming medical devices, especially those deployed
and operated through various vascular channels, to devices obtained
from such processes and to novel modified polyimide polymers useful
therein.
[0037] Referring to FIG. 1 there is shown a catheter 10 comprising
an elongated tube 12 with a balloon 14 mounted at the end thereof.
The balloon is made of a cured polymeric material in accordance
with the invention hereof.
[0038] FIGS. 2A-2C illustrate one method of the present invention
for forming a balloon 14. As shown in FIG. 2A, a substrate 30 is
provided having an exterior surface of configuration which will
determine the inner surface of balloon 14. This exterior surface
configuration corresponds to the desired interior surface
configuration of balloon 14 when balloon 14 is fully inflated. In
at least some cases the exterior surface of the substrate 30 will
also substantially determine the outer surface of the balloon,
since the polymerizable material applied thereto will typically be
very thin. The substrate is made of a solid material which can be
readily fluidized under conditions do not destroy the integrity of
the formed device (here the balloon).
[0039] In preferred embodiments of the present invention, substrate
30 is ice or another meltable material, such as a wax,
characterized by a melting point of about 100.degree. C. or less,
preferably about 50.degree. or less. In some embodiments, however,
higher melting points may be used, or the substrate material may be
fluidizable by another mechanism such as dissolution with water or
another solvent which does not substantially attack the formed
device under the substrate fluidization conditions employed. An
example of such a material is a water soluble polyvinyl alcohol
(PVA) manufactured by Environmental Polymers of Irlam, UK, and sold
under the trademark Depart.TM.. Depart.TM. polymer compositions
have melting temperatures of from about 185.degree. C. and
210.degree. C. and can be altered to become fully soluble in
ambient to hot water, for instance 20-80.degree. C. More detailed
information on the Depart.TM. product can be found in Materials
World, Vol. 10, No 8, pp 36-38, August 2002. Thus, references to
ice and/or wax in specific embodiments herein should be taken to be
illustrative embodiments which can be readily modified to employ
alternate fluidizable materials such as the Depart.TM. PVA
compositions and other readily fluidizable materials.
[0040] The substrate 30 may also be a composite material comprising
solid particles which are not fluidizable, for instance strength
reinforcing inorganic particles, in a solid matrix of fluidizable
material. In some cases it will be desirable that, upon
fluidization of the matrix material, the particulate material can
be removed the formed device together with the matrix material.
However, as described more fully herein, in some cases it may be
desirable to leave behind non-fluidizable components of the
substrate 30, such as fibers or other particulate material, when
the fluidizable material is removed. When left behind such
components can provide bridging structures between multiple layers
or other features as described herein.
[0041] As shown in FIG. 2A, substrate 30 has a proximal waist
section 34, a balloon section 36 of greater outside diameter, and a
distal tip section 38 of reduced outside diameter.
[0042] As shown in FIG. 2B, film 40 of a radiation curable
composition is deposited on the exterior surface of deposition
substrate 30. This step can be performed, for example, by dipping
deposition substrate 30 into a solution of the curable composition,
or, if the composition has a low viscosity, into the neat
composition, withdrawing the substrate 30, allowing the solvent to
evaporate, if present, and then irradiating the resulting film to
produce the cured film 40 on deposition substrate 30 at a
temperature below the melting temperature of substrate 30. The
curable composition may also be applied by spraying. Multiple
depositions and cure steps may be used to build the thickness of
the cured material to a desired thickness. In some embodiments,
each deposition formed with this technique may be from about
0.00001 inches (0.25 .mu.m) to about 0.001 inches (25.4 .mu.m)
thick, suitably about 0.0001 inches (2.5 .mu.m) thick. In some
embodiments of the present invention, repeated dip coatings and
radiation curing is performed until the desired thickness of film
40 has been formed. For some balloon embodiments the final wall
thickness may be on the order of about 0.0001 inches (2.5 .mu.m) to
about 0.002 inches (50 .mu.m), for instance about 0.0002 inches to
about 0.001 inches (5-25 .mu.m). Other balloons may desirably have
thicker or thinner walls, for instance if a balloon wall is
formulated with a porous outer layer to carry and deliver a drug
load, the desired total wall thickness might be substantially
greater than 50 .mu.m.
[0043] The next step in the process is the removal of deposition
substrate 30 from within the cured polymer film 40. When the
substrate material is fluidizable by melting, removal is preferably
achieved by simply heating the assembly of deposition substrate 30
and cured film 40 to a temperature above the melting point of
substrate 30. The deposition substrate melts and flows out leaving
the cured film device. For instance if the substrate 30 is made of
ice, the assembly may be heated by exposing it to ambient
temperatures for a period of time. In the case where substrate 30
is fluidizable by selective dissolution, the assembly may be
immersed in a suitable solvent for a period of time, and/or a
solvent flow may be directed at the substrate to effect dissolution
and removal of the substrate. The material used to form the
substrate may be collected and reused if desired. Following removal
of the substrate the desired device is obtained, in this case a
balloon.
[0044] The substrate 30 may be readily formed by filling a
corresponding female mold with water or melted wax and then
lowering the temperature below the freezing point of the substrate
material employed. Forming the deposition substrate 30 from ice or
wax provides many advantages over the process employed in U.S. Pat.
No. 4,952,357 to form polyimide balloons. The substrate material is
cheaper, more easily recycled, and no toxic or corrosive material
is needed.
[0045] The present invention has several important advantages in at
least some embodiments. First, it offers extremely thin walls, and
therefore is extremely well suited for low profile catheters and
balloons. Second, the process of the present invention, as
illustrated in FIGS. 2A-2C, offers close control over the inside
diameter tolerances of balloon 14. Third, the method of the present
invention, unlike other balloon fabrication techniques, can be used
to obtain desired wall thickness profile desired, whether that be
thinner cones, relief patterned surfaces or the like. Fourth, the
method can be used to optimize the properties of the polymer
material deposited for different areas of the device. Fifth, very
complex device structures can easily be produced.
[0046] In the embodiment of the method of the present invention
described in FIGS. 2A-2C, substrate 30 has a surface configuration
which corresponds to the desired shape of the balloon in a fully
inflated condition. Conversely, the surface configuration of
substrate 30 can correspond to the desired shape of the balloon in
a deflated condition (or in a partially inflated condition). This
latter embodiment is particularly advantageous for ensuring that
the balloon has a minimum profile when deflated by making the shape
of the deflated balloon predictable. By using this embodiment,
creasing and heat setting characteristics may not be required.
FIGS. 3A and 3B illustrate an example of this embodiment. FIG. 3A
is a cross section of balloon 50 in a deflated condition, which has
been defined by substrate 52 having three lobes 54A-54C. As a
result, balloon 50 has three corresponding lobes 56A-56C when
deflated. FIG. 3B shows the fully inflated state of balloon 5.
[0047] The ice or wax form can also be prepared by mechanical or
thermal processing of a body of such material, such as a rod or
cube shape, into the desired balloon or other shape. For instance,
both ice and wax, at a suitable low temperature, can be readily
sculpted mechanically or using a laser.
[0048] Considering all of the foregoing, balloons may be readily
manufactured which have, for example, diameters of about 1.5-25 mm,
lengths of about 5-200 mm, wall thicknesses of about 0.0003-0.03
inches, in some embodiments from about 0.0003-0.003 inches, and to
any of the typical ranges for balloon dimensions and strengths as
typically utilized in the medical industry heretofore.
[0049] For any given catheter construction, the balloon may be
bonded to a shaft which may be formed of polyester, polyamide such
as nylon 10, nylon 6/10, nylon 11 nylon 12, or mixtures there of,
polyethylene, thermoset polyimide, polyetheramide block copolymer,
such as the ester-linked polyetheramides sold under the trade mark
PEBAX.RTM., polyetherester block copolymer such as sold under the
ARNITEL.RTM. and HYTREL.RTM. trademarks, or anything else known in
the art. In another embodiment, however, the balloon may be formed
integral with the shaft or a portion thereof.
[0050] Deposition techniques can be varied according to the
characteristics desired. General dip and spray coating techniques
maybe used. Moreover, much more sophisticated techniques can be
used. Using multiple layers to build up the balloon, the balloon
can be provided with site specific characteristics while still
providing a balloon whose overall property profile is not
substantially comprised. For instance, in one embodiment the
curable composition is applied with an applicator employing one or
more computer controlled spray heads similar to ink jet print
heads. Different curable formulations may be provided via multiple
spray heads, allowing the cured formulation to be varied on-the-fly
i.e., as it is being applied, in the manner of printing different
colors. In this way, for instance the innermost layer of the waist
area may be formulated to provide tacky cured properties which
facilitate subsequent bonding to a shaft, while, in the expandable
portion of the balloon, the same innermost layer is formulated to
minimize tack so as to avoid blocking adhesion. Likewise, the
outermost surface may be formulated to provide softness and/or
lubricity without tackiness. In this way two or more different
polymer blends may be created on-the-fly in order to create
transitions within the balloon or other device in relation to
stiffness, softness, hydrophilicity, tack, tensile strength,
elongation and/or MRI for fluoroscopic visibility.
[0051] The cured outer layer polymer material may be rendered
hydrophilic by using curable compounds having hydrophilic
side-branch or main moieties. Such moieties may be anionic or
cationic groups or polyethylene oxide blocks. This is particularly
advantageous when the base resin property is generally very
hydrophobic, as is true for instance for polyimides.
[0052] Accordingly, one can spray (using for example a high
definition ultrasonic spray nozzle) spiral patterns of stiff
polyester onto or into soft polyester to form a shaft. One can
apply (e.g. by spray, dipcoat, brush, etc.) a nanoclay containing
polymer in any pattern in conjunction to the same solution
containing no filler. One can do the same using a radiopaque
(Barium salt, Tungsten salt) or various magnetic substances, i.e.
ferromagnetic, paramagnetic superparamagnetic, or diamagnetic
substances (e.g. dysprosium or gadolinium salts). One can use 2, 3
or more curable compositions in any pattern (e.g. separated in
axial (rings), circumference (stripes) or radial (layers)
direction). Alternatively, or at the same time, one can also mix
multiple polymers during spraying to obtain a gradual
transition.
[0053] A very precise spray technology which can be used in the
invention is by means of ultrasonic spraying. Suitable ultrasonic
spray systems are available from Sono-Tek Corp., Milton N.Y., and
are described at http://www.sono-tek.com/. Other technologies to
make very precise lines or features are electrohydrodynamic
printing, such as is available at Princeton University Ceramic
Materials Laboratory and described at
http://www.princeton.edu/.about.cml/html/research/ehdp.html; and
picoliter dispensers described at
http://www.microdrop.de/html/about.html and available from
Microdrop GmbH, Norderstedt Germany.
[0054] Besides being suitable for applying the radiation curable
composition, these techniques can be employed to modify the
fluidizable form before application. For instance, structures can
be made in ice on top of the a more basic ice form and the result
employed as the substrate which is then covered by the radiation
curing formulation. In this way basic forms can be easily modified
to provide a variety of products with different structural
features. A particular example has as its objective a balloon
having a bumpy surface and a uniform wall thickness. A standard
balloon mold ice form prepared in accordance with the invention can
be modified by applying bumps to the surface at specific locations
using water in a subfreezing environment. Subsequent application of
a radiation curable formulation to the modified ice form, followed
by curing, can be employed to provide the objective balloon.
[0055] The spraying process allows the precise definition of the
wall thickness on all sides of the balloon and, as such, one can
achieve an even wall thickness in cone and central section or even
a thinner wall thickness in the cone section. To spray with
accurate precision (spatial as well as allowing rapid changes in
flow rate) one can use ultrasonic spray nozzles as described
above.
[0056] The substrate shapes can be made in a
polytetrafluoroethylene (PTFE) coated clampshell mold, over a
similarily coated corewire, or by any other suitable means. By
including a metal central corewire through an ice shape, one can
use electrostatic spraying as a means to get a very homogeneous
layer. A metal core wire can also be used as a resistance heater to
facilitate melting of the form after the device has been formed and
cured.
[0057] One way to include an axial reinforcement in the device
being formed is to spray more material along several stripes
parallel to the central axis. Such stripes can be used to reinforce
the longitudinal balloon body region under the blade pad of a
cutting balloon as described in U.S. Pat. No. 5,320,634, Vigil et
al, for example.
[0058] The process can also be used to produce preform shapes of
balloon parisons, where the parison would be used in a conventional
blow molding step. Ideal balloon preform shapes and preferential
thicknesses could be achieved by multiple step spraying of the
polymer coating.
[0059] Composites may also be prepared by the inventive processes.
For instance: [0060] Spiral or coil wind a wire or fiber made out
of SPECTRA.RTM., KEVLAR.RTM. or other, polyimide, polyester, ultra
high molecular weight polyethylene, glass, flexible ceramic, or
metallic material around a balloon shaped ice or wax form, and then
spray on the photocurable composition and cure. In some embodiments
an underlayer of the photocurable composition is applied and cured
first. [0061] Small stripes of a stiff material may be put onto the
ice or wax, keeping them in place by mechanically pining, e.g.
using push pins at the end, or by making the stripe material wet on
the inside so that it freezes against the mold, spraying the
photocurable composition, and curing to produce a shape in which
the stripe is embedded in the balloon or other device being formed.
[0062] A braided sock made out of a fiber material can be slid over
the ice or wax form, or over a cured layer already applied to the
form, followed by spraying and photocuring. [0063] Strips of
"Bucky" paper, made out of carbon nanotubes, may be laid on the ice
or wax form, or over a cured layer already applied to the form,
followed by spraying and photocuring.
[0064] As, already noted, various fillers, optionally
functionalized, maybe included in the polymer composition. The
filler particles may have a fibrous, spherical, plate-like, or
amorphous shape. Radiopaque and paramagnetic materials are among
the types of fillers which may be used. Reinforcing particles may
be employed. Particles of carbon, clay, silica, alumina, or liquid
crystal polymer, are examples. Nanofillers, for instance nanoclays,
nano ceramics and carbon nanofibers and tubes, characterized by a
diameter of about 100 nm or less, are particular examples. Such
particles are sufficiently small that they do not substantially
reduce optical clarity of the composition and will not obstruct the
passage of UV light through the solution as they are smaller then
the wavelengths being used.
[0065] With conventional thermoplastic polymer processes it is very
difficult to obtain a high dispersion of nanoparticles. In the case
of the present invention where very low viscosity compositions may
be employed, the mixing and dispersion can be accomplished much
easier.
[0066] Drugs may be incorporated into the curing formulations,
directly or carried on the fillers. This will lock them in the
polymer matrix after curing. As the curing is done at room
temperature, a wide range of pharmaceutical substances may be used.
Such substances may be localized on the device to specific tissue
or fluid contact areas so as to maximize beneficial effects while
minimizing side effects and/or compromising the physical properties
of the device. Some drugs may be incorporated into the interior of
fillers such as nanotubes, rather than, or in addition to, being
incorporated thereon. Stents are particular examples of devices
where drugs maybe desirably incorporated.
[0067] Using multi-head spray printing techniques as described
above, compositions comprising such reinforcing agents may be
applied in a pattern-wise manner, with intervening space filled by
relatively unreinforced compositions in order to provide the end
product with a desired combination of physical properties such as
balloon burst strength, burst profile, compliance, compliance curve
profile, and elastic stress response.
[0068] The curing radiation is preferably UV source, that is one
having a significant output in at least a portion of the range of
about 150 to about 400 nm. Broad or narrow spectrum sources may be
employed.
[0069] As an alternative to changing the formulation on-the-fly, or
in addition thereto, cured properties may be modified by
pattern-wise curing. For instance, a UV laser, or a focused
broadband UV source, may be directed at a curable coating in an
overlapping helical or mesh pattern until the entire layer has been
cured. Curing in such a manner may substantially alter the physical
properties of the layer relative to curing by applying the
requisite irradiation in a substantially uniform manner.
[0070] After the composition has cured, the assembly is heated to
melt and drain the water or wax form. In the case of ice forms, in
order to get rid quickly of the water, one might use microwave
heating, as the absorption rate of microwaves in water is much
higher than for polymers.
[0071] Radiation curing formulations may also be utilized to
produce complex devices on simple substrates. Stent devices are a
particular example. Another example is a balloon having an outer
surface which has a raised pattern to engage a stent during
inflation so as to prevent slippage. Such complex structures can be
obtained by pattern-wise application of one or more layers of
curable material, using a pattern which leaves voids at appropriate
positions, or by pattern-wise curing of a uniformly applied
coating. Using optical systems and masks, one can cure only
specific areas after which one can wash of the non-cured material
in adjacent areas. Details to sub-micron level can be created as UV
light can be focused to within this range. One way to get
homogeneous illumination of a tubular structure is to focus a
parallel expanded light beam into a conical mirror in which the
tubular structure (balloon or shaft) is oriented along the central
axis.
[0072] The following are specific modifications which may be
employed in forming balloons: [0073] A polyester or polyimide
balloon can be produced with an equal wall thickness in core, cone
and waist section using a spraying process in conjunction with
dissolvable lost-wax mold made out of ice, wax, salt. After or
during spraying one can irradiate with UV to form the polymer.
Rotating the mold will cause the solvent to spread out. [0074]
Spraying stripes in a straight pattern or spiral can make a striped
balloon. This for example could be used for the cutting balloon as
they require material underneath the knives that doesn't extend in
axial direction as this would break the adhesive bond between the
blade and the polymer [0075] Outer surface bumps can be created at
the transition of the cone and body of a balloon, spaced so as to
be exposed when the balloon is deflated and folded for insertion
into the vascular system of a patient. A stent can then be crimp
mounted over the folded body portion between the bumps such that
the bumps prevent the crimped stent from sliding off. By
appropriate shaping, such bumps can also improve cross-ability of
the catheter/balloon/stent assembly, e.g. by tapering the diameter
from the folded balloon to the diameter of the crimped stent.
[0076] Also applicable to catheter/balloon/stent assemblies, a
hydrophilic polymer forming composition can be sprayed and cured on
the outer surface of the balloon cone sections while a hydrophobic
polymer forming composition is used on the core section so as to
improve stent securement. [0077] Instead of producing a very smooth
outer surface in the core section, one can also produce a textured
pattern to improve stent securement. This can be done by for
example by utilizing an ultrasonic spray nozzle which can spray
little "dots" in a predefined pattern. [0078] A multilayer balloon
with a soft outer layer may be produced. [0079] One can also spray
a layer or a pattern on top of existing balloons made by
conventional methods. [0080] A tapered balloon or even a tapered
curved balloon can be made quite easily.
[0081] Still further applications of the present invention include
the following: [0082] Imagewise patterned application of a curable
composition on a solid tubular form of a fluidizable material, or
patterned curing, may be used to prepare stents in accordance with
the invention. The curable compositions used may include organic or
inorganic reinforcing agents such as fibers or other particles of
liquid crystal polymers, metals, carbon, nanotubes, silicas, or the
like. Property profiles may be varied longitudinally or radially by
altering compositions in accordance with the particular property
profile desired. [0083] Portions of a device, such as metal stent
struts structures, may be applied to in the shape-form before
application of the curable composition, or applied to a first cured
layer before application of a second layer of curable composition
over the structures. Upon curing, such structures become embedded
in the formed device. [0084] A tubular graft of continuous material
may be formed on a tubular shape-form, but with reinforcing
structures pattern sprayed into the graft material in a manner
analogous to the balloon reinforcing strategy described above.
[0085] Stent, graft or balloon structures may be provided with drug
retaining chambers, for instance as described herein in connection
with FIG. 13. [0086] Polyester Stent grafts can be sprayed using
this technology. [0087] By incorporating low volatile nano- or
micro-sized particles in the solution one is able to create porous
structures. Heating the layer while UV-curing at the same time will
force the volatile particles to form micro- or nano-channels to the
surface. So one can use this to create a double layer balloon with
a drug in between the two layers that is being forced out during
expansion of the balloon. One can also spray such a layer on top of
a drug containing polymer. [0088] Catheter shafts can be formed
using the same techniques and variations described for balloons.
Consequently, one can produce both braided and non-braided shafts
with different compositions of polymers, or having braided proximal
portions and non- [0089] Thickness measurement during spraying and
curing. It would be advantageous to build in a laser thickness
measurement system during spraying to provide a feedback system.
braided distal portions.
[0090] FIG. 4 depicts a wire 60 which may be used to generate a
suitable shaft form. A layer of water or molten wax is applied to
the wire, for instance by dip coating, and then cooled to solidify.
This cycle may be repeated as needed to build up the form to the
desire diameter, as shown at numeral 65 in FIG. 5. The radiation
curing formulation is then applied and cured as described. Melting
and removing the wax or ice form provides clearance to remove the
wire. As an alternative to ice or wax forms, shafts can be sprayed
directly on non-stick PTFE or silver coated mandrel wires.
[0091] Balloons and shafts can also be formed integrally, i.e., in
one piece. FIG. 6 depicts an integral shaft and balloon form 70,
obtained by placing the distal end of an ice or wax form 65 of FIG.
5 in a balloon-shaped mold form and molding the balloon form
portion 75 thereover. The integral shaft and balloon are then
formed over form 70 in the manner already described.
[0092] Tandem balloons can be prepared in a simple manner. Instead
of one balloon form as shown in FIG. 6, the shaft form 65 may be
modified to include two or more balloons form shapes, spraying and
curing as before.
[0093] FIGS. 7, 8 and 9 depict a more complex balloon form that can
be prepared by modification of the form 70 of FIG. 5. This balloon
can be used in a rapid exchange catheter system.
[0094] Current rapid exchange catheters entail two lumens over at
least a portion of the catheter to provide fluid access to the
balloon on the one hand and guidewire passage on the other hand.
This dual lumen concept restricts the fluid access to and from the
balloon chamber, which lead to increased inflation- and deflation
times. It also adds to the overall profile of the system as there
are four walls in cross section. Within U.S. Pat. No. 5,409,458
(Khairkhahan et al.) and U.S. Pat. No. 5,549,553 (Resseman,
Stivland and Blaeser) two designs have been proposed to resolve
this issue by attaching the guidewire lumen to the wall of the
balloon. U.S. Pat. No. 5,409,458 shows a one-sided flattened
balloon design were the guidewire lumen is glued against the
exterior of the flat side. U.S. Pat. No. 5,549,553 shows a balloon
in which the guidewire runs through part of the balloon wall.
[0095] Both solutions are not ideal as they force the guidewire to
one side of the balloon during inflation. This makes them both
unsuitable to be used as stent deployment systems. First of all
because the pressure they generate on the stent is non-uniform
along the circumference, this due to the guidewire being forced
between the balloon inflation chamber and the stent. Secondly,
because of the guidewire being forced into the vessel wall by the
balloon, the guidewire also presses into the vessel wall on both
the distal as well as proximal side of the dilatation area during
dilatation. Generally one wants a smooth transition between the
distended region of the vessel and the undistended regions
immediately distal and proximal thereto.
[0096] An alternative solution to the problem of designing balloons
for rapid exchange catheters, especially those used to place
stents, is a further aspect of the present invention. The inventive
balloon has a guidewire channel through the balloon as shown in
FIG. 9. Instead of having the pressure chamber on one side of the
guidewire, as in the above patents, FIG. 9 depicts a balloon 80,
having a longitudinal axis 82, a central body portion 84 and
proximal and distal tapering cone portions 86, 87. A longitudinal
guidewire channel 85 is provided entering and emerging through the
tapered cone walls 86, 87. With this design the pressure chamber
entirely surrounds the guidewire channel 85. Consequently, the
pressure on the guidewire channel is equally exerted from all
directions. Therefore the guide wire channel is not forced against
the wall of the balloon during inflation and the pressure on the
stent is equally distributed.
[0097] One way to produce such a balloon starts from a form as
shown in FIG. 6. An axially extending hole 90, spaced radially out
from the axis at a distance less than the outer wall is then
drilled through the balloon portion 75 of ice form 70 to produce
the modified form as shown in FIG. 7. Dipping or spraying the
photocurable composition, and subsequent radiation curing produces
a balloon 96 having an integrally formed off-axis longitudinal
guidewire channel 95. Radiation curing of the photocurable
composition may be accomplished, for instance, by irradiating
through the ice form or by directing a beam obliquely along hole 90
Curing the composition film and melting the ice or wax will leave a
balloon shape as shown in FIG. 8 where the wall of the balloon
extends through the length of the hole. It is of course also
possible to generate this hole during the production of the ice
shape by having a wire in place during the freezing process and
removing the wire later on. If one uses a metal wire for this, one
can easily release it out of the ice shape by sending an electric
current through it, heating the wire.
[0098] Another way to form the guide wire channel 95 of the balloon
as in FIG. 9 uses a separately formed tube which is inserted into
the hole 90 of the form 70 of FIG. 7 before the outside of the form
70 is coated and cured. Such tube may be formed in the manner
described herein, or by any other means, and may be the same
material as the rest of the balloon or a different material. The
tube may be formed with fibers extending outward beyond the
thickness of the tube at its ends in order to improve bond strength
between balloon outer wall and the separately formed guide wire
channel.
[0099] A balloon as in FIG. 9 formed by embedding a tube of some
other material through the hole 90 prior to spraying may be
desirable if one wishes to use the system as a stent delivery
system. If the tube 95 is too thin or too elastic, it may be
squeezed closed during crimping of a stent. If one integrates a
tube out of some stiff material in the balloon construction, this
potential problem can be overcome.
[0100] In a variation on the balloon of FIG. 9, more longitudinal
channels through out the balloon are provided and left open such
that the inflated balloon still allows the flow of blood through
the system.
[0101] Spraying and curing the balloon also offers a way to produce
the combined shaft and balloon construction in a single run. This
can be done for example by taking a mandrel and producing a thin
layer of ice or wax over the entire length. Secondly, the form of
the balloon is added in ice on the end. The hole in the balloon
shape as described above is drilled, and then the entire system is
sprayed with the curable composition. Next one cures the
composition and melts the ice or wax form.
[0102] In another embodiment of the invention, using a PTFE coated
wire mandrel, with a moon-shape cross section, it is possible to
prepare dual lumen shafts outer over a long length. Once more, a
thin layer of ice is provided over the mandrel then a pre-formed
tube forming the inner is placed in the inner rounding of the moon
and the whole structure is sprayed with the curable composition and
then cured. After melting the ice, the mandrel can be easily
removed. FIG. 10 shows a section view of a shaft 100 produced in
this way. The shaft has an outer wall 102, an inner wall 104, an
outer lumen 106 and an inner lumen 108. The inner wall 104 is
formed of the tube inserted into the moon curved substrate form,
i.e. after the PTFE coated wire has been coated with the
fluidizable substrate material, while the outer is formed of the
subsequently applied UV cured polymer.
[0103] FIGS. 11A-C illustrate yet another embodiment of the
invention. In FIG. 11A, a basic balloon form 110 of ice or other
fluidizable solid is shown. To the form 110 have been applied
circumferential bands 112 and 114. The bands 112 and 114 are
elastic materials which have been stretched from their rest
diameter to reach their diameter on the form. The elastic material
may be silicone or other rubbery material, but is one to which the
cured polymer film formed of the curable composition will adhere.
The curable composition 116 is then applied by spray or other
technique, over the entire form, including over the bands 112 and
114, as shown in FIG. 11B, and then cured to form a balloon with
the bands 112 and 114 embedded therein. In FIG. 11C, when the
fluidizable form has been removed, the composite balloon is
stressed by the bands 112, 114 to collapse to their rest position.
This aids in obtaining a small deflated profile. Bands placed as
depicted here, or in other configurations may also be used to alter
balloon distension curves.
[0104] A modification of the balloon of FIG. 11C uses a first
polymer layer, sprayed over the form and cured, before the bands
112, 114 are applied. Suitably, the bands employed in this
embodiment are also over-coated and cured as described previously,
so that they are encapsulated by the sprayed polymer. This
technique avoids the necessity of maintaining a strong adhesive
bond between the cured polymer forming the balloon body and the
elastic bands. In further modifications of this balloon or the
balloon of FIG. 11C, the bands 112, 114 may be made of a
non-compliant material to change balloon compliance. The cured
polymer forming the body of the balloon may be a compliant,
semi-compliant or non-compliant material.
[0105] FIGS. 12A and 12B depict another balloon embodiment which
can be obtained in accordance with the invention. Instead of a
symmetric balloon mold along the axial axis, balloon 120 is curved
along the direction of the balloon axis 122. As most of the
arteries are curved, this would actually be advantageous in many
cases. One way to be able to direct the balloon and catheter shaft
in the direction of the curvature of the vessel would be to use an
ellipsoid shaped cross-section for the inner lumen 124, as shown in
FIG. 12B. By going through a curvature this would align the shaft
with the curvature.
[0106] Another embodiment of the invention uses a first ice shape
mold, spraying at least a first layer over this ice layer and
curing the layer(s) to form a proto-balloon. The ice form is then
melted, but the water is kept in the proto-balloon and that water
is actually pressurized to expand the proto-balloon to a second
diameter. The expanded diameter can be only slightly larger than
the diameter of the first ice-shape mold. Keeping the pressure on
to maintain expanded diameter, the water is refrozen to fixate the
expanded shape, after which at least one second layer is sprayed on
the proto-balloon and cured. In this way one can build in a
negative pressure in the balloon layer which would help to
strengthen the balloon and allows creating different
distension/pressure curves. The cycle of melting the form,
pressurizing the cured balloon, refreezing the form material
applying a further layer and curing the further layer may be
repeated any number of times, until the desired balloon thickness
is obtained. In this embodiment adhesion between the first and
second layers can be enhanced if the first layer is formed with
reinforcing fibers extending outwardly. Upon application and curing
of the second layer, the fibers become embedded in both layers.
[0107] FIG. 13 schematically depicts another balloon-forming
process according to the invention, in which the balloon is
provided hollow chamber structures which can be used to carry and
dispense drugs at a treatment site. After a first layer of curable
composition has been applied to a substrate form 130 and cured to
produce balloon inner layer 132, positive chamber forms 136 are
applied to the balloon. A second layer 135 is then sprayed over the
balloon covering the chamber forms except for stem regions 134, and
cured. Layer 135 may be formed from the same or a different
composition from that used to form the inner layer 136. After
curing the second layer 135, the chamber forms are removed to yield
a balloon 140 which includes hollow chambers 142 therein, opening
to the outer surface. These pockets can be filled with one or more
drugs prior to dilatation. During dilatation the drugs are squeezed
out of the chambers as the balloon is pressurized against the
vessel wall.
[0108] In another embodiment of the invention one can build a
double layer balloon having a chamber between the two layers by
depositing a first polymer-forming layer, curing the first layer,
spraying an additional ice (wax) layer on top of the first polymer
layer, covering the additional ice (wax) layer with a second
polymer-forming layer, leaving open one or more channels for the
water or wax to disappear, and then curing the second layer. In
this way, one can build double layered balloons without a contact
between the layers. Or if one only partly covers the first layers,
one might create a contact point between the first and second
layer, for example to fill with drugs etc. Fibers may be sprayed in
the first polymer layer, the fibers being dimensioned so that they
stick out of the first polymer layer. If one sprays a thin layer of
water on the first polymer layer covering only part of the fibers
(in other words, the fibers stick through the ice layer as well as
the first polymer layer), and then sprays a top-polymer layer, a
connection between the first and second polymer layer can be
created. This technique can also be used with electrically
conductive wires or fibers to provide electrical connection between
separated layers.
[0109] In an example of a still further embodiment of the
inventions described herein, one can incorporate long fibers in the
ice mold that run from one surface to another part of the surface
of an object and stick out on both ends. Spraying the polymer over
this shape will embed the ends of the fibers in the polymer layer.
Melting the ice will leave the fiber connection between the two
points of the surface intact. One or more fibers can connect all
kind of points between the surface. For example, providing a
longitudinally extending stripe in the ice mold comprising fibers
which extend 90 degrees with the longitudinal axis, and just beyond
the ice mold surface at both ends of the fibers, followed by spray
and cure of the curable formulation to embed the fibers in opposite
ends will produce a balloon which grows from a circular shape to an
elliptical shape when the pressure in the balloon further expands
as the expansion in the fiber orientation is restricted.
[0110] In another example, a balloon similar to the previous
example except that one connects all the fibers only on one end to
the balloon surface, such that the fiber ends are incorporated into
the balloon wall, while guiding the other end to the proximal
section of the balloon. Following the same procedure one ends up
with a balloon were a bunch of fibers sticks out on the proximal
part of the balloon. These fibers may be connected to the catheter
shaft, for example to a ring in the catheter shaft. The fibers are
made out of a highly elastic material and are readily elongated
under the during the inflation of the balloon. When the balloons is
deflated, the fibers contract and they will help deflate the
balloon. If fibers are distributed in the balloon wall at least
predominately along a desired folding pattern, for instance along
three or more longitudinally extending stripes, the fiber
contraction will assist in refolding the balloon for safe
retraction.
[0111] Alternatively, one could connect such single-end surface
embedded fibers (non-compliant this time) all the way to the
proximal side of the catheter, and allow the physician to determine
the expansion of the balloon by connecting the fibers for example
to a rotating device which would increase or decrease the length of
the fibers as it is rotated. Depending on the number of fibers and
their distribution along the surface, expansion characteristics of
the balloon could be altered on the fly, to change balloon expanded
diameters along a portion of the balloon length, e.g. to focalize
dilation pressure over a smaller balloon length; to provide
different cross sectional balloon configurations e.g. elliptical or
polygonal cross-sections along some or all of the balloon length;
to bend the balloon; and/or to control the balloon refold.
[0112] Another device can be built using the inventive method is a
double layered balloon structure (using a first elastic layer,
followed by an additional ice layer, followed by a second
non-compliant layer, leaving a void between the two layers, which
may optionally be supported by fiber connections between the
layers, as previously described. Microchannels through the second
layer may be formed-in-place or cut by UV-laser ablation. After
removing the intermediate ice layer the resulting the intermediate
chamber may be filled with encapsulated drugs. The encapsulation
may be designed to break as a function of the external pressure. In
other words, raising the internal pressure of the balloon would
expand the elastic inner membrane against the outer non-compliant
balloon, squeezing the intermediate drug layer. Once the pressure
would pass a certain threshold, the encapsulation would snap and
release a burst of the drug that would be injected in the vessel
wall through the micro-channels. Of course one could use multiple
drugs in multiple types of spheres exploding at different pressure
levels.
[0113] FIG. 14 depicts a stent 150 in expanded form. The stent may
be formed on a shape form of ice or other fluidizable material,
e.g. by imagewise spraying of a curable composition on a tubular
form, followed by curing the sprayed composition. The stent
material may be a composite as previously described.
[0114] As previously described, the invention may use a composition
which is radiation curable to a solid polymer at a temperature
below the melting point of the fluidizable substrate form material,
suitably less than 100.degree. C. In the case of ice forms, the
material should be radiation curable below 0.degree. C. Radiation
curing compositions of (meth)acrylate esters (i.e. acrylates,
methacrylates and mixtures thereof) are well known and may be used
in the invention. A wide variety of cured properties are available
from such compositions. Unless e-beam sources are used, such
compositions typically employ a photoinitiator.
[0115] The radiation curable compounds, such as those which are
initiated with UV or visible light radiation, may be monomeric,
oligomeric, prepolymeric, or polymeric in nature. Mixtures of such
compounds are typically used. Typically the compositions are
liquids prior to curing in order facilitate application of the
composition, and then a solid after being exposed to radiation such
as UV or visible light radiation.
[0116] Examples of (meth)acrylate terminated radiation curable
compounds include, but are not limited to, epoxy (meth)acrylates,
urethane (meth)acrylates (aliphatic and aromatic), polyester
(meth)acrylates, acrylic (meth)acrylates, polycarbonate
(meth)acrylates and so forth and mixtures thereof. For spray
application, low viscosity compositions are preferred, suitably
viscosities of about 350 mPas or less, preferably about 150 mPas or
less. When higher viscosity components are used, reactive monomer
diluents and/or non-reactive solvents maybe used to reduce the
viscosity of the overall composition. Higher viscosity compositions
can be used with other application techniques such as dip or brush
coating.
[0117] The (meth)acrylate functional monomers typically range in
molecular weight from about 86 to about 500 and typically have
viscosities of 200 mPas or less at 25.degree. C. It may be
desirable to employ monomers in combination with oligomers to
provide desirable coating viscosities. When such monomers are
employed in combination with oligomers, they co-polymerize with the
oligomers and form an integral part of the cured coating. Generally
acrylate monomers are preferred over methacrylate monomers for
radiation curing. Other radiation curable ethylenically unsaturated
monomers can of course also be used alone or in mixture with
(meth)acrylate monomers.
[0118] Ethylenically unsaturated oligomers and prepolymers which
may be employed are typically viscous liquids at room temperature,
with viscosities which range from a few thousand to greater than
one million mPas at 25.degree. C. They typically have up to 20
acrylate groups per molecule, with two to six acrylate groups per
molecule probably the most common, and range in molecular weight
from about 500 to about 20,000, but can be as high as 200,000
g/mol. Oligomers typically provide film properties which are
superior to what can be achieved with monomers. Oligomers typically
include a carbon containing backbone to which the radiation-curable
functional group(s) is bound. Examples of suitable
carbon-containing backbones include, but are not limited to,
polyolefins such as polyethylene, polyesters, polyamides,
polycarbonates, polyurethanes, and so forth. The size of the
carbon-containing backbone can be selected to provide the desired
molecular weight.
[0119] Other suitable UV curable compositions include cationically
polymerizable compounds, most notably epoxies. Examples of
commercially available suitable UV curable epoxies include, but are
not limited to, UVACURE.RTM. 1500, 1530 and 1534 available from UCB
Radcure, SARCAT.RTM. K126 available from Sartomer, and so forth.
Vinyl ethers and styryloxy ethers are other cationically
polymerizable compounds which can be used.
[0120] Photoinitiators are advantageously employed in combination
with the radiation curable compounds. Photoinitiators typically
form free radical species when exposed to UV light. Photoinitiators
are typically used in amounts of about 0.5 wt. % to about 15 wt. %
of the UV formulation, more typically about 0.5 to 10%, desirably 1
to 7% and more desirably 3-5% by weight of the composition.
Typically this amount will be based on the binder composition,
particularly if the binder composition is prepared prior to mixing
with the magnetic material.
[0121] The photoinitiators are typically active in the UV/visible
range, approximately 250-850 nm, or some segment thereof. Examples
of photoinitiators, which initiate under a free radical mechanism,
include benzophenone, acetophenone, chlorinated acetophenone,
dialkoxyacetophenones, dialkylhydroxyacetophenones,
dialkylhydroxyacetophenone esters, benzoin, benzoin acetate,
benzoin alkyl ethers, dimethoxybenzoin, dibenzylketone,
benzoylcyclohexanol and other aromatic ketones, acyloxime esters,
acylphosphine oxides, acylphosphosphonates, ketosulfides,
dibenzoyldisulphides, diphenyldithiocarbonate and
diphenyl(2,4,6-trimethylbenzoyl) phosphine oxide.
[0122] The photoinitiators that may be used in combination with the
radiation curable compound include photoinitiators available
commercially from Ciba-Geigy Corp., Tarrytown, N.Y. under the
"IRGACURE" and "DAROCUR" tradenames, specifically "IRGACURE" 184
(1-hydroxycyclohexyl phenyl ketone), 907
(2-methyl-1-[4-(methylthio)phenyl]-2-morpholino propan-1-one), 369
(2-benzyl-2-N,N-dimethylamino-1-(4-morpholinophenyl)-1-butanone),
500 (the combination of 1-hydroxy cyclohexyl phenyl ketone and
benzophenone), 651 (2,2-dimethoxy-2-phenyl acetophenone) (e.g.,
"IRGACURE" 651), 1700 (the combination of
bis(2,6-dimethoxybenzoyl-2,4-,4-trimethyl pentyl phosphine oxide
and 2-hydroxy-2-methyl-1-phenyl-propan-1-one) and "DAROCUR" 1173
(2-hydroxy-2-methyl-1-phenyl-1-propane) and 4265 (the combination
of 2,4,6-trimethylbenzoyldiphenyl-phosphine oxide and
2-hydroxy-2-methyl-1-phenyl-propan-1-one); photoinitiators
available commercially from Union Carbide Chemicals and Plastics
Co. Inc., Danbury, Conn. under the "CYRACURE" tradename, such as
"CYRACURE" UVI-6974 (mixed triaryl sulfonium hexafluoroantimonate
salts) and UVI-6990 (mixed triaryl sulfonium hexafluorophosphate
salts); and the visible light [blue] photoinitiators,
dl-camphorquinone and "IRGACURE" 784DC. Of course, combinations of
these materials may also be employed herein.
[0123] If cationically polymerizable compounds are employed in the
radiation curable composition the photoinitiator is suitably a
cationic photoinitiator, a number of which are commercially
available.
[0124] The above lists are intended for illustrative purposes only
and are not intended to limit the scope of the present invention.
Such UV curing systems are known in the art.
[0125] Alternatively, x-ray, gamma ray or electron beam curing may
be employed. While a photoinitiator is typically employed in the
case of UV curing, it is usually not required when such high energy
sources are employed to cure the composition.
[0126] Another type of formulation which may be utilized in the
invention is a photo-activated Diels-Alder addition reaction of an
aromatic 2,5-dialkyl-1,4-diketone and a compound having two or more
(meth)acrylate or maleimide groups thereon, optionally with a chain
terminating mono-maleimide, or (meth)acrylate as illustrated by the
following equation (I):
##STR00001##
wherein X is a carbon linked organo group and Ar is an optionally
substituted aromatic moieity. X may comprise an aromatic group or
an aliphatic group, and may also contain hetero atoms such as O, N,
S, P, Cl, F and Si. X also may be a polymeric moiety. Examples of X
groups which can be used are arylene such as 1,3-phenylene,
1,4-phenylene,
##STR00002##
and substituted versions thereof; alkylene such as methylene,
ethylene, propylene, butylene, 1,6-hexamethylene, polyethylene,
polypropylene, and the like; alkylenearalkylene such as
methylenephenylenemethylene; alkyleneetheralkylene. Examples of
polymeric moieties include alkylene started polyethers, in which
the polyether is an aliphatic polyether moiety, for instance
polyoxyethylene (EO).sub.n, polyoxypropylene (PO).sub.n,
polyoxybutylene and copolymers thereof such as
(EO).sub.n(PO).sub.m, where n and m are positive numbers. X may
also be a carbon linked aromatic polyether moiety, aromatic or
aliphatic polyester, aromatic or aliphatic polyamide, polyurethane,
polyorganosiloxane, copolymers, especially block copolymers of any
of the above.
[0127] Specific bismaleimide compounds which may be employed
include N,N'-m-phenylene bismaleimide, N,N'-ethylenebismaleimide,
N,N'-hexamethylenebismaleimide, N,N'-dodecamethylenebismaleimide,
N,N'-m-xylylenebismaleimide, N,N'-p-xylylenebismaleimide,
N,N'-1,3-bismethylenecyclohexanebismaleimide-,
N,N'-1,4-bismethylenecyclohexanebismaleimide,
N,N'-2,4-tolylenebismaleimide, N,N'-2,6-tolylenebismaleimide,
N,N'-3,3-diphenylmethanebismaleimide,
N,N'-4,4-diphenylmethanebismaleimide,
3,3-diphenylsulfonebismaleimide, 4,4-diphenylsulfonebismaleimide,
N,N'-4,4-diphenylsulfidebismaleimide,
N,N'-p-benzophenonebismaleimide, N,N'-diphenylethanebismaleimide,
N,N'-diphenyl ether bismaleimide,
N,N'-(methylene-ditetrahydrophenyl)bismaleimide,
N,N'-(3-ethyl)-4,4-diphenylmethanebismaleimide,
N,N'-(3,3-dimethyl)-4,4-diphenylmethanebismaleimide,
N,N'-(3,3-diethyl)-4,4-diphenylmethanebismaleimide,
N,N'-(3,3-dichloro)-4,4-diphenylmethanebismaleimide,
N,N'-tolidinebismaleimide, N,N'-isophoronebismaleimide,
N,N'-p,p'-diphenyldimethylsilylbismaleimide,
N,N'-benzophenonebismaleimid-e, N,N'-diphenylpropanebismaleimide,
N,N'-naphthalenebismaleimide, N,N'-m-phenylenebismaleimide,
N,N'-4,4-(1,1-diphenyl-cyclohexane)-bis-maleimide,
N,N'-3,5-(1,2,4-triazol)-bismaleimide,
N,N'-pyridine-2,6-diylbismaleimide,
N,N'-5-methoxy-1,3-phenylenebismaleimide,
1,2-bis(2-maleimidoethoxy)ethane,
1,3-bis(3-maleimidopropoxy)propane,
N,N'-hexamethylene-bis-dimethylmaleimide, N,N'-4,4'1-(diphenyl
ether)-bis-dimethylmaleimide,
N,N'-4,4'-(diphenylsulfone)-bis-dimethylmaleimide,
N,N'-bismaleimide of N,N'-4,4'-(diamino)-triphenylphosphate or the
like; an aromatic bismaleimide compound such as
2,2-bis[4-(4-maleimidophenoxy)phenyl]propane,
2,2-bis[3-chloro-4-(4-maleimidophenoxy)phenyl]propane,
2,2-bis[3-bromo-4-(4-maleimidophenoxy)phenyl]propane,
2,2-bis[3-ethyl-4-(4-maleimidophenoxy)phenyl]propane,
2,2-bis[3-propyl-4-(4-maleimidophenoxy)phenyl]propane,
2,2-bis[3-isopropyl-4-(4-maleimidophenoxy)phenyl]propane,
2,2-bis[3-butyl-4-(4-maleimidophenoxy)phenyl]propane,
2,2-bis[3-sec-butyl-4-(4-maleimidophenoxy)phenyl]propane,
2,2-bis[3-methoxy-4-(4-maleimidophenoxy)phenyl]propane,
1,1-bis[4-(4-maleimidophenoxy)phenyl]ethane,
1,1-bis[3-methyl-4-(4-maleimidophenoxy)phenyl]ethane,
1,1-bis[3-chloro-4-(4-maleimidophenoxy)phenyl]ethane,
1,1-bis[3-bromo-4-(4-maleimidophenoxy)phenyl]ethane,
1,1-bis[4-(4-maleimidophenoxy)-phenyl]methane,
1,1-bis[3-methyl-4-(4-maleimidophenoxy)-phenyl]methane,
1,1-bis[3-chloro-4-(4-maleimidophenoxy)-phenyl]methane,
1,1-bis[3-bromo-4-(4-maleimidophenoxy)-phenyl]methane,
3,3-bis[4-(4-maleimidophenoxy)phenyl]-pentane,
1,1-bis[4-(4-maleimidophenoxy)phenyl]propane,
1,1,1,3,3,3-hexafluoro-2,2-bis[4-(4-maleimidophenoxy)-phenyl]propane,
1,1,1,3,3,3-hexafluoro-2,2-bis[3,5-dimethyl-(4-maleimidophenoxy)phenyl]pr-
opane,
1,1,1,3,3,3-hexafluoro-2,2-bis[3,5-dibromo-(4-maleimido-phenoxy)phe-
nyl]-propane and 1,1,1,3,3,3-hexafluoro-2,2-bis-[3- or
5-methyl-(4-maleimidophenoxy)phenyl]propane, etc.
[0128] The aromatic 2,5-dialkyl-1,4-diketone used in the reaction
of equation (I) may also be varied widely in structure. Ar may be
the same or different and may be for instance phenyl and
substituted phenyls, e.g. R--C.sub.6H.sub.4--, where R is alkyl,
alkoxy, cyano, fluoro, hydroxyalkyl, and the like, and the alkyl
and alkoxy groups may have for instance 1-20 carbon atoms,
optionally interrupted with one or more ether oxygen atoms. Ar may
also be naphthyl and substituted naphthyl. Specific Ar groups may
be hydroxymethylphenyl, dimethoxyphenyl, diethoxyphenyl,
dodecylphenyl, dodecyloxyphenyl, 2-hydroxyethoxyphenyl, and
mixtures of these. In some cases it may be possible to substitute
an aliphatic group, for instance a 1-hydroxycyclohexyl group at the
Ar positions.
[0129] In equation (1) some or all of the bismaleimide compounds
may be replaced with compounds having three or more maleimide
groups, examples of which include, polyfunctional maleimide
compounds obtained by the reaction of maleic anhydride with
polyamine condensation products obtained by reacting aniline and
formalin, 3,4,4'-triaminodiphenylmethane, triaminophenol,
tris-(4-aminophenyl)-phosphate, tris(4-aminophenyl)-phosphate,
tris(4-aminophenyl)-thiophosphate, or other polyamines.
[0130] (Meth)acrylate and acrylamide compounds may also be
substituted for some or all of the maleimide compounds depicted in
equation (1). When compounds having multiple (meth)acrylate groups
are employed, the product is a polyester, rather than a polyimide.
Similarly if acrylamide compounds are employed the product is a
polyamide. Copolymers may be produced from mixtures of
bismaleimides with multi(meth)acrylates and/or
multiacrylamides.
[0131] Suitably the composition is formulated to have a ratio of
equivalents of maleimide and/or (meth)acrylate groups to diketone
compounds of from about 1:1 to about 4:1, more preferably about
1:2.
[0132] The group X may be modified to provide a softer, more
flexible cured polymer than has heretofore been available from
conventional polyimides. In particular, longer chain alkylene or
(poly)alkyleneoxy groups as X groups will enhance flexibility and
elongation properties of the polymer and may also provide improved
softness. Longer chain alkylene or (poly)alkyleneoxy groups on the
Ar moiety should also improve softness. Combining maleimide
compounds having different X groups and/or using combinations of
aromatic diketones allows for the properties of the cured polymer
to be modified such that flexibility, toughness and strength can be
optimally balanced.
[0133] While the traditional polyimides have been noted for their
strengths properties, high temperature performance has been
considered a major feature of the commercially available polymers.
Hence they have traditionally been prepared with very low to no
heteroatom content outside of the imide rings and aromatic rings
and with very high aromatic content. For the present invention the
device manufacturer can tailor the properties of the cured
properties either by selection of the bismaleimide, selection of
the aromatic diketone or by blending of materials or any
combination thereof.
[0134] As an alternative to radiation curing, a composition which
is curable upon mixing of two or more components may be employed,
the individual components being stable until mixed. The individual
components may be blended on-the-fly, so that the resulting
composition cures promptly as it is applied, but does not cure in
the application apparatus.
[0135] The above examples and disclosure are intended to be
illustrative and not exhaustive. These examples and description
will suggest many variations and alternatives to one of ordinary
skill in this art. All these alternatives and variations are
intended to be included within the scope of the claims, where the
term "comprising" means "including, but not limited to". Those
familiar with the art may recognize other equivalents to the
specific embodiments described herein which equivalents are also
intended to be encompassed by the claims. Further, the particular
features presented in the dependent claims can be combined with
each other in other manners within the scope of the invention such
that the invention should be recognized as also specifically
directed to other embodiments having any other possible combination
of the features of the dependent claims. For instance, for purposes
of claim publication and/or claim presentation timing requirements,
any dependent claim which follows should be taken as alternatively
written in a multiple dependent form from all prior and subsequent
claims which possess all antecedents referenced in such dependent
claim if such multiple dependent format is an accepted format
within the jurisdiction (e.g. each claim depending directly from
claim 1 should be alternatively taken as depending from any
previous claims). In jurisdictions where multiple dependent claim
formats are restricted, the subject matter of the dependent claims
should each be also taken as alternatively written in each singly
dependent claim format which creates a dependency from a prior or
subsequent antecedent-possessing claim other than the specific
claim listed in such dependent claim below.
* * * * *
References