Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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METHOD FOR L~MINATING FOAM BODIES
I~CLUDING A REINFORCING SCRIM
The present invention resides in an improved
method for the preparation of laminated synthetic
resinous thermoplastic foam bodies which incorporate a
reinforcing scrim therein.
More particularly, the present invention
resid~s in an improved method for the preparation of
thermoplas~ic ~oam laminates wherein an undesirable
bowing or curvature of the laminate is avoided.
Frequently, it is desired to laminate bodies
of synthetic resinous thermoplastic fo~m together by
passing a heated blade therebetween to heat-plastify
adjacent surfaces o~ the bodies. The adjacent surfaces
are then pre~sed toyether to fuse the surfaces together
to provide a laminated body of the desired size. For
many processes, it is desirable to incorporate within
such a laminate a reinforcing scrim such as a glass
fiber reinforcing scrim. Such laminates may be employed
for the insulation of cryogenic vessels by the so-called
spiral generation technique. Such a technique is dis-
closed in U.S. Patent Nos. 4,017,346 and 4,050,607. An
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apparatus for preparing laminates suitable for the spiral
generation process is set forth in ~nited S-tates Patent No.
4,049,852 while various configurations of laminates suitable for
the spiral generation process are set forth in United States Patent
Nos. 3,919,034; 3,924,039; and 3,954,539. OEtentimes, such
laminates, after preparation, show a somewhat cur~ed configuration
along the longitudinal axis. The reason for the development of
such undesired curvature ~as not understood and when it occurred it
was frequently in an undesired direction which necessitated extra
mechanical manipulation of the laminate, also referred to in the
art as a billet or log, in order to have it conform to the desired
configuration. In the thermal insulation for cyrogenic vessels,
undesired mechanically induced tensila stresses in the insulation
should be avoided in order to minimize the possibility of the
insulating laminate cracking under thermal stress.
The invention resides in a generally continuous method
for the preparation of an elongate laminate from a plurality of
foam bodies formed from a synthetic resinous thermoplastic material
having a reinforcing scrim embedded between said foam bodies,
including the steps of heating adjacent surfaces of adjacent foam
bodies to a temperature sufficient to plasticize the foam body
surfaces, contacting the adjacent heated and plasticized surfaces
of the foam bodies, and cooling the plasticized surfaces to form a
rigid bond between the foam bodies incorporating the reinforcing
scrim therein, the reinforcing scrim being positioned relative to
the major surfaces of a planar heating element during the heating
of the adjacent foam surfaces whereby a first portion of the scrim
is in frictional contact with one surface of the heating element
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and a second portion of the scrim is in frictional contact with
an opposite surface of the heating element, to thereby obtain a
laminate exhibiting a desired degree of curvature.
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The invention further resides in a continu-
ous method for the preparation of an elongate laminate
of synthetic resinous, thermoplastic foam body incor-
porating a reinforcing scrim therein, wherein adjacent
foam surfaces of adjacent foam bodies are heated by
means of a generally planar heating element having
first and second oppo~ed heating surfaces to a temper-
ature sufficient that on contact of the adjacent foam
surfaces and ~ooling thereof, a rigid bond is achieved
between the bodies the improvement which comprises pass-
ing the reinforcing scrim, the scrim being in the form
of one scrim folded over the heating element or the
scrim comprising two separate portions, a portion dis-
posed on each of the major heating surfaces, over the
major surfaces uf ~he planar heating element during
the heating of the adjacent foam surfaces to thereby
obtain a lamina~e exhibiting a d~sixed degree of curva-
ture.
The method of the present invention will
become more apparent from the following specification
taken in co~nection with ~he drawing wherein:
~ igure 1 is a schematic side view of a
lami~ation apparatus in acccrdan e with the invention;
Figure 2 is a top view of the lamination
apparatus of Figure l;
Figure 3 is a partly-disassembled heating
blade assembly as used in the apparatus of the invention;
Figure 4 is a sectional view of the heating
blade of the ~ssembly of Figure 3 showing the passage
of a reinforcing scrim therethrough; and
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Figure 5 is a sectional view of an embodiment
of the present invention in which a pair of heating
blades are employed.
In Figures 1 and 2 there is schematically
depicted a laminating apparatus 10 comprising in coopera-
tive combination a frame and support means (not shown).
Supported on the frame is a supply roll 11 for dispensing
therefrom a reinforcing scrim 12. The reinforcing
scrim 12 extends between a first series of foam bodies
formed from a synthetic resinous material 13 arranyed
in end to-end relationship and a second series of foam
bodies 14 also formed from a synthetic resinous material.
The foam bodies 13 and 14 have adjacent surfaces with
the scrim 12 disposed therebetween. A first pair of
15 feed rolls 15 and 16 con~ey the foam bodies 13, 14 and
the scrim 12 toward a second pair of pressure or feed
rolls 18 and 19. ~djacent the feed rolls 18 and 19 and
remote from the feed rolls 15 and 16 is a heating blade
or platen assembly 21. It is preferred to support the
scrim 12 between roll 11 and blade assembly 21 with a
smooth sheet metal plate (not shown) ~o prevent wrinkling
or folding of the scrim. The blade assembly 21 includes
a heating element or blade 22 which passes be~ween the
foam bodies 13 and 14 and raises the temperature of the
adjacent surfaces of the foam bodies 13 and 14 to a
temperature sufficient to heat-plastify and collapse
the foam material. The foam bodies 13 and 14 are
remo~ed from the region of the blade assembly 21 by
first and second pairs of draw rolls 23, 24 and 25, 26.
The draw rolls force the heated surfaces o the foam
bodies together, to thereby encapsulate the scrim
within the heat plastified collapsed foam and between
the foam bodies. It will be understood that the heat
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plasticized material of the foam bodies will readily
pass or flow through the mesh or open spaces provided
between the strands of the scrim to meld into each
other to thereby unite into a combined layer of the
plasticized material with the scrim embedded in the
meld. Upon cooling, the plasticized material with the
reinforcing scrim substan~ially centrally disposed
therein is rigidified to permanently fuse the foam
bodies to each other.
In Figure 3 there is depicted a view of a
heating blade assembly 21 having an electrical resis-
tance heating element 22 of generally flat planar
configuration. The heating element 22 is perforated in
regions where the maximum generation of heat is desired
and may be of a substantially square or r~ctangular
conXiguration. The thickness of the heating element is
not critical provided that the thickness is sufficient
to provide adequate strength during use and provided
-that the voltage applied to the plate will produce a
current flow sufficient to heat the plate to a tempera-
ture sufficient to plasticize or melt the adjacent
surfaces of the foam bodies. In a preferred embodiment,
the heating element is shaped in a serpentine configuration,
somewhat as illustrated in Figure 3. Such serpentine
heating elements are well ~nown in th art. The heating
element 22 is supported within a first frame or support
membar 32 and is suitably insulated therefrom. The
heating element is affi~ed to the support member 32 by
means of screws 33 which are also electrically insulated
from the heating element 22. Remotely disposed from
~he first support member 32 is a second support member
34, of which the bottom half only is shown. The heating
element 22 is eiectrically insulated from the support
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member 34 by means of insulating material 36 such as a
glass cloth-siloxane resin laminate.
A sectional view through the heating element
22 is depicted in Figure 4 wherein a reinforcing scrim
12a is shown passing through a central ~ransversely
disposed slot 37 of the element 22. sy passing the
reinforcing scrim 12a through the centrally disposed
slot of the heating element, the frictional drag on
adjacent surfaces of the foam bodies being laminated is
approximately equalized such that the tendency for the
resultant laminate to warp is substantially reduced.
In Figure 5 there is depicted a sectional
view of an alternate heating assembly 40 suitable for
the practice o~ the present invention. The heating
assembly 40 comprises a first electrical resistance
heating element 41 and a like heating element 42 in
spaced apart parallel face-to-face relationship with
element 41. Preferably, the heating elements have a
serpentine configuration such as is illustrated for the
heating element of Figure 3. Con~igurations for the
heating element other than the preferred serpentine
shape may be used and will be readily apparent to
persons skilled in the art. Thus, a single reversely
bent or U-shaped element could be satisactorily employed
in the practice of the invention. Heating elements ~1
and 42 are separated by a plurality of spacers 43 of
like discoidal configuration. The spacers 43 are
disposed at the terminal ends or xeverse bénds in the
heating elements and correspond in location generally
to the support members 32 and 34 of Figure 3. Thus,
the heating elements of Figure 5 are, ln essence, two
heating elements such as are depicted in Figures 3 and
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4 but are positioned in a spaced-apart relat.ionship
from each other to provide a path for a reinforcing
scrim 12b to be passed therebetween. Preferably, the
heating elements for use in the practice of the inven-
tion have major opposed parallel faces and have athickness not greater than one-quarter inch and prefer-
ably about 3/16 of an inch.
The heating element 22 of Figure 3 is preferably
prepared from a perforated stainless steel sheet having
a thickness of about 1/8 inch and the heating element
40 of Fi~ure 5 is prepared from perforated stainless
steel sheets each having a thickness of about 1/16 of
an inch ànd spaced about 1/16 of an inch apart to
permit the passage therebetween of the reinforcing
1~ scrim 12b. For the lamination of polystyrene foam
having a density of about two (2) pounds per cubic
foot, the heating elements are heated to a temperature,
as indicated by a thermocouple manually positioned on
the surface of the heating element to a temperature of
about 600F. A convenient source of electrical power
for the heating element is an alternating current or
direct current welding power supply.
The method of the present invention is useful
with any synthetic resinous thermoplastic foam material
which is heat-weldable and provides laminates having a
minimum warp or curvature. The reinforcing scrim may
be wider, narrower or egual in width to the faces of
the foam bodies being laminated depending on the desired
end use. The scrim may be continuous as depic~ed in
Figures 1 and 2 or consist of a plurality of overlapping
joined lengths. Conveniently, short lengths are joined
at each end of a scrim section by a transversely extending
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pressure sensitive adhesive tape or other desired
securing means. In the preparation of elongate
laminates for use in the application of thermal insula-
tion by the so-called spiral generation process, it is
S highly desirable to maintain the curvature of the
laminate at a value which is equal to or less than the
curvature of the vessel wall to which it is applled.
The pre~ent invention is particularly suited
~or the pre~aration of laminated foam bodies of a
synthetic resinous thermoplastic material for use in
the insulation of cryogenic vessels. A typical laminate
might comprise 5 pieces or planks of foam; for example,
one 2 by 8 inch plank laminated to four 2 by 6 inch
planks wherein the 2 by 6 inch planks are stacked four
high, and one of the edges of each 2 by 6 inch plank is
heat sealed to one face of the 2 by 8 inch plank to
provide an 8 inch by 8 i~ch square laminate having a
reinforcing scrim encapsulated in the sealed inner face
of the 2 by 8 inch plank. A simpler laminate might
comprise two 4 by a inch planks in welded ace~to-face
engagement with a reinforcing scrim therebetween. In
the preparation of laminates, a substantial problem has
been observed in that wA~n two planks are laminated
together by the use of a hot blade, and a scrim is
supplied and em~edded within the weld between the two
planks, an undesirable curvature or warpage is obtained
in the resulting laminate. The present invention
substantially reduces or eliminates such undesired
curvature or warpage.
In its broadest application, it has been
discovered that by passing the scrim through a planar
heating assembly, the curvature or warpage o~ the
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laminate is substantially and signiflcantly reduced.
The mechanism by which this reduction in curvature is
obtained is believed to be basically due to the balancing
of frictional forces against each other on the opposed
faces of the foam bodies to be joined.
By passing the scrim through an elec~rically
heated blade or between a pair of such blades, the
frictional drag on the foam bodies being laminated is
equalized. The ~ond be~wee~ the foam bodies is obtained
by heating the adjacent faces of foam bodies to plastify,
i.e., to soften or melt the material and then contacting
such heated foam faces under pressure. Heating of the
scrim itself has little or no effect on the degree of
bonding between the foam bodies. When a foam body is
pushed or pulled through a heating assembly and the
foam bodies to be laminated move relatlve to the heated
blade or blade , friction is developed between the
faces of the foam bodies contacting the fixed blade or
blades. When a single blade is used, for example, in
such a lamination procedure, one has the choice of
placing a reinforcing scrim to be encapsulated in the
weld line on one side or the other of the heated blade.
Accordingly, on one side o the blade, the foam body is
in direct contact with the heating blade and on the
other side of the blade, the reinforcing scrim is in
direct contact with the blade and, accordingly, the
frictional forces are different on opposite sides of
the heating blade.
Rectangular foam bodies to be laminated, as in
the apparatus of Figures 1 and 2, are bonded, that is,
heat sealed or welded across the entire contiguous
surfaces of the foam bodies. As the ad~acent faces of
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the foam bodies are heated to a tempera-ture at which
they will bond to each other, the scrim is encapsulated
or embedded therein. A portion of the scrim would only
be free to move in the event that a foam surface to be
laminated has voids therein such as grooves, cut-outs
and the like.
It is apparent from the foregoing specification
that the present invention is intended to be illustrative
and is not to be construed as being restrictive or
otherwise limiting excepting as it is set forth and
defined in the appended claims.
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