Note: Descriptions are shown in the official language in which they were submitted.
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METHOD FOR MANUFACTURING SOLID ELASTOMERIC GELS
Field of the Invention
The present invention relates to the m~nllf~ct~lre of solid elastomeric gels
and to the formation of pads including layers of such gels.
BackPround
o Pads including layers of solid elastomeric gels such as those described in
U.S. Patent No. 3,676,387 have been proven to be highly effective in reducing the
affect of pressure points on portions of a person supported on the pads, therebyreducing tissue infl~mm~tion (e.g., "bed sores") and loss of circulation to
e~Ll~nlilies due to restriction of blood flow.
U.S. Patent Applications Nos. 08/253,510 filed June 3, 1994, and
08/324,734 filed October 18, 1994, describe wrist rests adapted to be used by a
computer operator which include covered layers of solid elastomeric gel on whichthe wrists of the computer operator may be supported. The layers of solid
elastomeric gel in those pads retain their shape and provide a conformable contour
that distributes the weight of a users hands and/or rOl eal ~lls across a broad surface
area.
Heretofore, the solid elastomeric gels used in such pads have been made in
batch processes and subsequently molded to a desired shape. U.S. Patent No.
3,676,387 describes batch processes for making several gel constructions, each of
2~ which processes includes placing a polymer and a plasticizer such a mineral oil in a
heated vessel, mixing the polymer and plasticizer under medium to high shear for a
determined time, and then emptying the vessel. Such batch processes typically
require long mixing times and can cause mechanical degradation due to agitation
and or can thermal degradation of the polymers due to oxidation. Stabilizers maybe added to reduce thermal degradation, but they are limited in their effectiveness
and add cost to the process.
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Disclosure of the Invention
The present invention provides a method for making solid elastomeric gels
more quickly and with less mechanical and thermal degradation than is possible with
the batch process described above; together with improved methods for forming
pads that include layers of solid elastomeric gel.
Generally, the method according to the present invention is for making solid
elastomeric gel from copolymer and plasticizer and includes the steps of (1 )
providing an extruder having multiple infeed sections each followed by a mixing
section along a barrel of the extruder; (2) introducing the copolymer into one of the
o infeed sections of the operating extruder, (3) heating and shearing the copolymer in
a subsequent mixing section, (4) introducing the plasticizer to the copolymer
through at least one of the feeding sections in a pattern and at a rate that produces
solid elastomeric gel at room te,--pela~lre that will retain its shape after repeated
compression and decompression of the gel, and (5) ejecting the gel from the
extruder.
The ejecting step may include ejecting the gel through a die to form a length
of the gel having a predetermined cross section, and the method may further include
(6) cutting the extruded gel into lengths to form pieces of the gel with uniform cross
sections that can be used in pads.
Alternatively, the method can further include the steps of (6) providing a die
having a cavity defined by a cavity surface with a predetermined shape and a
support surface around the periphery of the cavity; (7) forming a preliminary
structure including (a) a rigid base portion adapted to engage the support surface of
the die, that has inner and outer surfaces and an inlet passageway communicatingbetween those surfaces; and (b) a thermoplastic sheet having a periphery ~tt~çhed to
the periphery of the base portion with the sheet extending over its inner surface to
define a chamber between the thermoplastic sheet and the inner surface of the base
portion, which chamber has a volume less than the volume of the cavity; and (8)
positioning the base portion against the support surface of the die with the
thermoplastic sheet positioned in the cavity at a position spaced from the cavity
surface. The ejecting step may then include ejecting the gel through the inlet
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passageway into the chamber to thermally deform the sheet into intim~te
engagement against the cavity surface and to form, when the gel has cooled, a pad
includinçJ a piece of solid elastomeric gel having a surface covered by the polymeric
sheet that corresponds in shape to the cavity surface.
s
Brief Description of the Drawing
The present invention will be further described with reference to the
accompanying drawing wherein like reference numerals refer to like parts in the
several views, and wherein:
o Figure I is a schematic view of an extruder used in the method according to
the present invention;
Figure 2 is an enlarged fragmentary view of portions of the screws from the
extruder illustrated in Figure l;
Figure 3 is a sectional view taken approximately along line 3-3 of Figure 2;
Figure 4 is a sectional view taken approximately along line 4-4 of Figure 2,
Figure 5 is a schematic view illustrating a first modification of the method
illustrated in Figure l;
Figure 6 is an enlarged sectional view of a die used in the method
modification illustrated in Figure 5;
Figure 7 is an enlarged perspective view of a piece of solid elastomeric gel
made using the method modification illustrated in Figure 5;
Figures 8 and 9 are sectional views illustrating a second modification of the
method illustrated in Figure 1, and
Figure 10 is a perspective view of a pad made using the second method
2~ modification illustrated in Figures 8 and 9.
Detailed Description
Referring now to Figures I through 4 there is illustrated a method according
to the present invention for making solid elastomeric gel from copolymer and
30 plasticizer. Generally, that method includes the steps of ( I ) providing a twin screw
extruder 10 (e.g., a Werner Pfleiderer Model ZSK 30 twin screw co-rotating
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extruder) that has multiple infeed sections I la, I lb, l lc and I ld into whichmaterial may be fed through hoppers 16, each of which infeed sections 11 a, 11 b,
l l c and 11 d is followed by a mixing section 12 along a barrel 13 of the extruder;
(2) introducing the copolymer into one of the infeed sections (e.g., 11 a) of the
s extruder 10, (3) heating and shearing the copolymer in a subsequent mixing section
12; (3) introducing the plasticizer to the copolymer through at least one of theinfeed sections l lb, l l c and 1 I d in a pattern and at a rate to produce solid
elastomeric gel that at room temperature that will retain its shape after repeated
compression and decompression cycles of the gel; and (4) ejecting the solid
elastomeric gel from the extruder 10.
Figure 2 illustrates portions of twin screws 14 in the extruder 10 at two of
the infeed and mixing sections l la, l lb, and 12 ofthe twin screw extruder 10.
Figures 3 and 4 illustrate the cross sectional shapes of the twin screws 14 at the
mixing and infeed sections respectively. While the specific pitch and type of mixing
and infeed sections used is not critical, those sections should be selected to provide
sufficient residence time in the various sections to accomplish homogeneous mixing
and plasticizing of the copolymer.
The polymer is introduced into the first infeed section 11 a of the barrel 13,
and is then heated to between 200 and 350 degrees Fahrenheit in the following
short mixing section 12. Plasticizer is introduced at the second infeed section 1 lb
and is then heated to a temperature in the range of 200 to 350 degrees Fahrenheit in
the next mixing section 12. The mixture then passes through another mixing
section l lc heated to a temperature in the range of 250 to 350 degrees Fahrenheit.
The barrel 13 and the screws 14 may include any number of infeed and mixing
sections 11 and 12 needed to achieve the desired softness for the solid elastomeric
gel. After the final mixing section 11, the mixed gel is passed through a cooling
feed section 15 to reduce the temperature, and thereby increase the viscosity of the
molten gel so that it can be fed either ( I ) into a storage container (not shown) for
later processin~, or (2) through a profile extrusion die 21 as will be explained below
with reference to Figures 5 through 7, or (3) into an injection mold or die 30 as will
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also be explained below with reference to Figures 8 through 10, or (4) into a form-
fill-seal device to fill a flexible sleeve with the gel to form a pad of a desired shape.
Figures 5 through 7 illustrate a first modification of the method illustrated inFigures 1 through 4 that can be used to make pieces 20 of the solid elastomeric gel
with uniform cross sections (see Figure 7) that can be used in pads. To make such
pieces 20 of solid elastomeric gel, the molten gel from the extruder 10 is pushed
through a profile extrusion die 21 onto a conveyor 25 where the at least partially
cooled and solidified gel extruded through the die 21 is cut into lengths by a cutting
device 22 to form the pieces 20 of the gel with uniform cross sections that can be
0 used in pads.
Figure 6 illustrates details ofthe profile extrusion die 21 which has an inlet
port 23 into which molten gel is fed from the extruder 10 at a temperature and rate
that allows the periphery of the gel to conform to the shape of an outlet orifice 24
of the die 21 and, upon being exposed to room temperature air, to solidify to anextent that its peripheral shape in cross section is retained upon further cooling.
The profile extrusion die 21 includes a central temperature control section having
openings 27 through which heated or cooled liquids or air may circulated or electric
heaters may be positioned to help provide temperature control for the gel passing
through the die 21.
While Figure 5 illustrates feeding molten gel directly from the extruder 10
into the profile extrusion die 21, solid elastomeric gel made using the extruder 10 or
by a batch process at an earlier time may be made molten and fed through the
profile extrusion die 21 using means other than the extruder 10, such as a melt
pump (not shown)
Figures 8 through 10 illustrate a second modification of the method
illustrated in Figures I through 4 that can be used to make pads including pieces 28
of the solid elastomeric gel with precise predetermined peripheral shapes. That
method further includes the steps of providing the die 30 (Figures 8 and 9) having a
cavity defined by a cavity surface 32 with a predetermined shape, and a support
surface 34 around the periphery of the cavity. A preliminary structure is formedthat includes a rigid base portion 35 (e.g., of polystyrene plastic) adapted to engage
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the support surface 34 of the die 30, having inner and outer surfaces 36 and 37, and
having an inlet passageway 38 and small air vents (not shown) communicating
between its inner and outer surfaces 36 and 37. Also provided is a thermoplasticsheet 40 having a periphery 41 attached to the periphery of the base portion 35 with
the sheet 40 extending over the inner surface 36 to define a chamber 42 between the
thermoplastic sheet 40 and the inner surface 36 ofthe base portion 35, which
chamber 42 has a volume less than the volume ofthe cavity in the die 30 between
the inner surface 36 and the cavity surface 32. The base portion 35 is positioned
and may be clamped if necessary against the support surface 34 of the die 30 with
o the thermoplastic sheet 40 positioned in the cavity at a position spaced from the
cavity surface 32 (Figure 8). The molten gel is then injected by the extruder 10through the inlet passageway 38 into the chamber 42 to thermally deforrn the sheet
40 into intim~te engagement against the cavity surface 32 (Figure 9). When the gel
has cooled there is formed a pad 44 including the 28 piece of solid elastomeric gel
having a surface very precisely corresponding in shape to the cavity surface 32 and
overlaid by the sheet 40. The sheet 40 also corresponds very precisely to the cavity
surface 32, has an inner surface coextensive with the top and side surfaces of said
layer of gel, and is smooth and free of wrinkles.
The sheet 40 can be a laminate of an inner oil impervious therrnoplastic
polymeric film and an outer conformable layer that provides a pleasing surface
texture for contact by a persons hands and arms. As an example, a polyurethane
blown microfiber web l~min~ted to a polyurethane film has been found quite
suitable. Such a laminate is described in U.S. Patent Application No. 08/490,464,
filed June 14, 1995, Attorney Docket No. 51823USA9A.
The sheet 40 can be attached to the base portion 35 by heat sealing or other
means, such as are described in U.S. Patent Applications Nos. 08/253,510 filed June
3, 1994, and 08/324,734 filed October 18, 1994.
While, as described above, molten gel can be fed directly from the extruder
10 into the chamber 42, solid elastomeric gel made using the extruder 10 or by abatch process at an earlier time may be made molten and fed into the chamber 42
using means other than the extruder 10, such as by a melt pump (not shown).
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Example 1:
Solid elastomeric gel has been produced by the following continuous
extrusion process.
A copolymer commercially designated "Kraton (t.m.) 1107" and available
from Shell Petroleum Company was introduced into a first infeed section l la of the
co-rotating twin screw extruder 10. The screw design of the extruder 10 was suchthat multiple mixing sections 12 each followed different multiple infeed sections 11
along the barrel 13 of the extruder 10. The copolymer introduced in the extrudero was heated and sheared in the first mixing section 12 immediately following its
introduction into the first infeed section 11 a. Mineral oil plasticizer similar to that
described in U.S. Patent No. 3,676,387 was introduced at approximately a 1: 1 ratio
by weight with the copolymer at the second infeed section 11 b of the extruder 10.
Additional plasticizer was introduced at the third infeed section l l c at a ratio of
5 about 3: I by weight with the copolymer, and still additional plasticizer introduced at
the fourth infeed section at a ratio of about 4: I by weight with the copolymer. The
extruder 10 was fed with copolymer and plasticizer at a rate that produced 50
pounds per hour of the gel.
For purposes of comparison, solid elastomeric gel was also produced by the
20 following batch process.
A 75 gallon heated kettle was filled with the same ratio of the copolymer
"Kraton (t.m.) 1107" and the mineral oil plasticizer described above to which was
added a small amount of"Irgonox (t.m.) 1076 stabilizer. The mixture was agitatedat medium shear for 8 hours.
2~ The solid elastomeric gels produced by the above two processes were
analyzed using gel permeatation chromatography analysis ("gpc") to compare the
percentages of tri-block and di-block copolymers in the gels, and thereby compare
the amount of thermal and/or mechanical degradation the gels had undergone in
their manufacturing processes (i.e., tri-block copolymers degrade to di-block
30 copolymers, so that the level of di-block copolymers in the gel is an indication of
the amount of degradation that has occurred in the manufacturing process). The gel
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made by the extrusion process contained 66.7 percent tri-block copolymers and
33.1 percent di-block copolymers, whereas the gel made by the batch process
contained 52.7 percent tri-block copolymers and 47.3 percent di-block copolymerswhich indicated that significantly less thermal degradation had occurred in the
5 extrusion process than in the batch process.
The present invention has now been described with reference to one
embodiment together with several modifications thereof. It will be apparent to
those skilled in the art that many changes can be made in the embodiment and
modifications described above without departing from the scope of the present
o invention. Thus the scope of the present invention should not be limited to the
methods and structures described in this application~ but only by the methods and
structures described by the language of the claims and the equivalents of those
methods and structures.
