Note: Descriptions are shown in the official language in which they were submitted.
~z~
The present invention relates to a process for manufac-
turing sealant coated articles. More partlcularly, the present
invention relates to a process for manufacturing a heat recover-
able polymeric article, a portion of which article possesses
sealant properties.
Heat shrinkable tubing with a sealant coating on its
interlor surface has been used for many years in a variety of
commercial applications. For example, sealant line heat shrink-
able tubing is used to insulate and seal electrical connectionsand to environmentally protect welded joints in pipe lines. Such
sealant lined heat recoverable tubings are described in Wetmore,
U.S. Patent Number 3,297,819. Similarly, sealant coated, longi-
tudinally heat shrinkable tape has been applied to metallic
pipes, pipe ~oints and the like to provide corrosion protection.
Because of their relatively low viscosities and gener-
ally high tack, conventional sealant compositions do not readily
lend themselves to processing in thermoplastic extrusion equip-
ment. Heretofore, the best known process for manufacturing
lengths of internally sealant coated heat shrlnkable tubing
entailed a costly separate coating step, which frequently had to
be manually carried out on a discrete piece basis. In this prior
art process, flexible, heat shrinkabls tubing such as that
described in Currie, U.S. Patent Number 2,027,962 and in Cook et
al., U.S. Patent Number 3~Q86,242 is internally coated with a
sealant applied with a brush or swab. Prior to application, the
sealant composition is typically thinned with a solvent or heated
to render it more fluid.
In contrast to the difficult problems encountered when
coating a sealant material on the interior surface of a tubular
article, a sealant layer can be applied to one surface of a lon-
gitudinally heat recoverable backing tape with relative ease.
However, such a heat shrinkable tape fabrication process is not
particularly efficient as it requires at least two relatively
-- 2 --
~ Z~ ~8 ~7
slow speed s-teps, one to produce the backlng, and another sepa-
rate step carried out subsequent to cross-linking the backing, to
apply the coating thereto, again by swabbing or brushing.
The present invention provides novel and an efficient
process for manu~acturing a sealant coated, dimensionally heat
recoverable article.
The present invention also provides a unitary shaped
article which is dimensionally heat recoverable and possesses a
tacky, sealant material uniformly disposed along its extruded
length.
The present invention again provides a melt processable
polymeric composition which, when sub;ected to radiation, is
readlly converted into an effective tacky sealant composition.
The present invention overcomes many of the disadvan-
tages associated with sealant coated, dimensionally heat recover-
able articles and the processes for their manufacture as known inthe prior art. It does so by providing a novel process for manu-
facturing such articles which includes the steps of extruding a
first radiation cross-linkable polymer composition and also
extrudlng (preferably substantially slmultaneously) a second
radiation convertible polymer composition to afford a unitary
shaped article having a first configuration in which the article
possesses portions formed respectively of the first and second
compositions; and then exposing the shaped article to a source of
radiation to initiate the formation of chemical bonds between
adjacent polymer chains in the first composition, and to induce
chemical change in the second composition, thereby transforming
said second composition from a melt ~e.g. extrusion) processable
composition to a tacky, sealant composition. The article in said
first configuration may be rendered dimensionally heat recover-
able by the step of distorting it at a temperature below thecrystalline melt temperature of the cross-linkable composition
, ~ ,
~ ~ 2~ ~7
into a second conEiguration either prior to the step of exposing
the article to a source of radiatlon or alternatively~ subsequent
to the irradiation step, by the steps of heating the artlcle to
about the crystalline melt temperature of the first composltion;
distorting the article into a stretched second configuration; and
then cooling the article while
, . ..p
.
~26~138~7
main-taining it in the second configuration thereby providing an
ar-ticle recoverable to or towards its first configuration upon
subsequen-t heating.
Thus, in one aspect thereof the present invention pro-
vides a process for manufacturing a sealant coated dimensionally
heat-recoverable laminated sheet comprising the steps of: select~
ing a first polymer composition comprising a radiation cross-
linkable polymer; forming a second polymer composition by admix-
ing a thermoplastic component and a rubber component in propor-
tions such that the composition comprises 30 to 95% of the ther-
moplastic component and 5 to 70% of the rubber component, said
second composition being radiation convertible to a sealant com-
position; extruding said first and second polymer compositions to
form a unitary laminated sheet possessing two layers formed
respectively of said first and second polymer compositions and
being in a first configuration; deforming said sheet at a temper-
ature below the crystalline melt temperature of said first compo-
sition into a second configuration; and exposing said sheet to a
source of radiation to initiate the formation of chemical bonds
between ad;acent polymer chains in said first composition, and to
induce chemical change in said second composition, thersby con-
verting said second composition from a melt processable composi-
tion to a sealant composition and rendering said first composi-
tion recoverable towards said first configuration upon subsequentheating. Suitably the laminated sheet is stretched along its
longitudinal axis.
In a further aspect thereof the present invention pro-
30 ; vides a process for manufacturing a sealant coated, dimensionally
heat-recoverable dual layer tubular article comprising the steps
of: selecting a first polymer composition comprising a radiation
cross-linkable polymer; forming a second polymer composition by
I admixing a thermoplastic component and a rubber component in pro-
portions such that the composition comprises 30 to 95% of the
thermoplastic component and 5 to 70% of the rubber cornponent,
- 5 -
~Z62887
said second composition being radiation convertible to a sealant
composition; extruding said first and second polymer compositions
to form a unitary dual layer tubular article possessing an outer
tubular layer formed from said first radiation cross-linkable
polymer composition disposed concentrically around an inner tubu-
lar layer formed from said second radiation convertible polymer
composition and being in a first configuration; e~posing said
article to a source of radiation to initiate the formation of
chemical bonds between adjacent polymer chains in said first com-
position, and to induce chemical change in said second composi-
tion, thereby converting said second composition from a melt pro-
cessable composition to a sealant composition; heating said art-
icle to about the crystalline melt temperature of said first com-
position; deforming said article into a second configuration; and
cooling said article while maintaining it in said second conflgu-
ration thereby rendering it recoverable towards said first con-
figuration upon subsequent heating. Suitably said dual layer
tubular article is deformed by uniform radial expansion.
In a stili further aspect thereof the present invention
provides a process for manufacturing a sealant coated dimension~
ally heat-recoverable dual layer tubular article comprising the
steps of: selecting a first polymer composition comprising a
radiation cross-linkable polymer; forming a second polymer compo-
sition by admixing a thermoplastic component and a rubber compo-
nent in proportions such that the composition comprises 30 to 95%
of the thermoplastic component and 5 to 70% of the rubber compo-
nent, said second composition being radiation convertible to a
sealant composition; ~ e ~ ~ said first and second polymer com-
positions to form a unitary dual layer tubular article possessingan outer tubular layer formed from said first radiation cross-
linkable polymer composition disposed concentrically around an
inner tubular layer formed from said second radiation convertible
polymer composition and being in a first configuration; deforming
35 j said article at a temperature below the crystalline melt tempera-
ture of said first composition into a second configuratlon; and
- 5a -
~ Z~2~387
exposing said article to a source of radiation to initlate the
formation of chemical bonds between ad~acent polymer chains in
said first composition, thereby converting said second composi-
tion from a melt processable composition to a sealant composition
and rendering said first composition recoverable towards said
first configuration upon subsequent heating. Suitably the dual
layer tubular article is deformed by uniform radial expansion.
In a further aspect thereof the present invention pro-
vides a process for manufacturing a sealant coated, dimensionally
heat-recoverable laminated sheet comprising the steps of: select-
ing a first polymer composition comprising a radiation cross-
linkable polymer; forming a second polymer composition by admix-
ing a thermoplastic component and a rubber component in propor-
tions such that the composition comprises 30 to 95% of the ther-
moplastic component and 5 to 70% of the rubber component, said
second composition being radiation convertible to a sealant com-
position; extruding said first and second polymer compositions to
form a unitary laminated sheet possessing two layers formed
respectively of said first and second compositions and being in a
first configuration; exposing said sheet to a source of radiation
to initiate the formation of chemical bonds between ad~acent
polymer chains in said first composition, and to induce chemical
change in said second composition, thereby converting said second
composition from a melt processable composition to a sealant com-
position; heating said sheet to about the crystalline melt tem-
perature of said first composition; deforming said sheet into a
second configuration; and cooling said sheet while maintaining it
in said second configuration thereby rendering it recoverable
towards said first configuration upon subsequent heating. Suit-
ably said laminated sheet is stretched along its longitudinal
axis.
The advantages of the present invention will become
apparent to those skilled in the art when the following descrip-
tion of the best mode contemplated for practiclng the invention
- 5b -
2~387
is read in conjunction with the accompanyi.ng drawing wherein llke
reference charac-ters refer to the same or similar elements and in
which:
Figure 1 is a perspectlve view of an extruded tubular
article formed from two concentrically disposed polymer composi-
tions;
Figure 2 is a perspective view of a sealant lined heat
recoverable sleeve formed in accordance with the process of the
invention;
Figure 3 is a perspective view of an extruded sheet
article formed from two layers of polymer compositions;
Figure 4 is a perspective view of a sealant coated,
longitudinally heat shrinkable polymeric tape produced in accor-
dance with the process of the invention;
Figure 5 is a block flow diagram of a preferred
sequence of process steps employed in the practice of the inven-
tion;
- 5c -
28iS7
MPO767
--6--
and
Figure 6 is a block flow diagram of another preferred
sequence of process steps employecl in the practice of the
invention.
DETAILED DESCRIPTIO~ OF A E'RBFER~ED EMBODIMENT
. . ~
Referring now generally to the several figures,
and specifically to Figure 1, there is shown an extruded
two layer tubular article 10. The outer layer 1 is formed
from a radiation cross-linkable polymer composition. The
inner layer 2 is formed from a radiation convertible polymer
~- composition. Both polymer compositions are ~ l-y
easily processable in conventional thermoplastic
extrusion equipment. It is to be understood that there are
a variety of alternative manufacturing processes that can be
1~ employed to form the extruded tubular article 10 For
example the radiation convertible polymer composition used
to form the inner layer 2 can be extruded as a tube and
wound onto a take up reel. Subsequently, the radiation
cross-linkable polymer composition used to form the outer
layer 1 can be extruded over the inner layer 2 to form the
tubular article 10. Alternatively, if two extruders are
available, the extrusion of each of the two polymer
compositions can be performed "in line" thereby eliminating
the need to handle the tubing twice. Typically, in such a
process the radiation convertible polymer composition would
be extruded into a tube, run through a water bath, dri~d,
2i3137
MPO767
--7--
and fed into the back of a second extruder which would apply
the outer layer of the radiation cross-linkable polymer
composition.
Another, and preferable manufacturing process for fabri-
cating the tubular article 10 employs a pair of extruders
which simultaneously feed the two polymer compositions into
a co-extrusion head where in the two polymer compositions
meet and form the dual layer tubular article 10 substan-
tially simultaneously. Co-extrusion is the preferred fabri-
cation technique for tubular article 10 because it makes iteasier to control such product perameters as for example,
wall thickness and concentricity.
The possibilities for manufacturing process variations
in the extruding step can be seen by reference to Figure 3
wherein a two layered laminated sheet article 30 is shown
with the first radiation cross-linkable polymer composition
forming an outer layer 1 and the second radiation convertible
polymer composition forming an inner layer 2. For example,
either polymer composition could be extruded in a first pass
and the other composition laminated to the first sheet in a
subsequent e~trusion pass. Alternatively, the sheet article
30 can be formed in a single pass using in line extrusion
techniques. Another process variation entails separately
extruding layers of each composition and laminating them
together in a separate bonding operation. Preferably, a
substantially simultaneous co-extrusion process is used to
form the laminated sheet article 30. Because of the
~2887
MPO767
--8--
multiplicity of extrusion process variations that can be
used to form shaped articles, as used herein the process
step called "extruding" is intended to include multiple pass
extrusions, in line extrusions, sl1bsequent laminations of
previously extruded components, and simultaneous extrusions
made with co-extrusion tooling.
Two pr-t~e~é process variations are available to impart
the property of heat recoverability to those portiorls of a
shaped article formed from the first, i.e. radiation cross-
linkable, polymer composition. These process variations areshown diagrammatically in Figures 5 and 6. In general,
although not invariably, higher recovery ratios can be
obtained by using the process shown in Figure 5. This pro-
cess is described in greater detail in the Cook et al. U.S.
Patent referenced above.
For selected applications, modest expansion and asso-
ciated recovery are frequently adequate. For example, in
the manufacture and use of sealant coated heat recoverable
tape used to protectively wrap metallic pipelines, a longi-
tudinal expansion and associated recovery of lO to 20% issufficient. The process shown diagrammatically in Figure 6
allows sealant coated heat shrinkable tape to be manufac-
tured at lower cost than heretofore thought possible. The
preferred manufacturing process employing the present inven-
tion involves the co-extrusion of the first and second
polymer compositions to form the laminated sheet article 30
shown in Figure 3. The sheet 30 passes over a chilled
~LZ~;2~
MP0767
_g_
calendar roll (not shown) which is typically part of a three
roll stack of the type well known to those skilled in the
art of polymer sheet extrusion. rrhe sheet 30 is sub-
sequently passed through a set of calendar rolls (also not
S shown) which axe rotating at dif~erent surface velocities to
impart the desired amount of longitudinal stretch (typisally
10 to 20%) to the sheet. Before the sheet is wound on to a
ta~e up reel, the edges are trimmed to produce a tape of
uniform width. At this point, the sheet is very easy to
handle because the layer formed from the second radiation
convertible polymer composition does not exhibit significant
tack, self adhesion or other properties which would make
handling awkward. Manufacture of the heat shrinkable,
sealant coated tape 40 is completed by exposing the sheet to
a source of radiation to thereby cross-link the first
polymer composition and form cross-lin~ed outer layer 3
shown in Figure 4 and simultaneously convert the second
polymer composition into a tacky sealant composition shown
as sealant layer 4 in Figure 4.
The preferred source of radiation is ionizing radiation
such as high energy electrons such as those produced by an
electron beam generator~ However, it is to be understood
that other sources of radiation can also be suitably
employed, preferably other sources of ionizing rad.iationO A
sheet of release paper (not shown) can suitably be disposed
between adjacent layers of the sealant coated tape as it
leaves the electron beam and is wound onto a ta~e-up reel to
facilitate subsequent handling of the product.
2~387
MPO767
--10--
~ s has been heretofore indicated, the present invention
entails the discovery of a novel and superior process for
the fabrication of heat recoverable sealant coated articles.
In addition, my invention entails the discovery that certain
materials when subjected to irradi.ation at a dose level of
from about 2 to about 50 megarads, preferably 5 to 20
meqarads, are transformed from extrusion processible
thermoplastics into tacky sealants.
As used herein the term "sealant" connotes an adhesive
material which is used for filling voids and interstices to
provide a seal against moisture, dust, solvents and/or other
fluids. Sealant compositions are viscid, water resistant
macromolecular compositions resembling Newtonian fluids in
exhibiting both viscous and elastic response to stress.
They usually, although not invariably, exhibit (in the sense
of A~TM 1146) second order cohesive blocking (and preferably
second order adhesive blocking to substrates such as metals
as well) at a temperature between room temperature and the
crystalline melt or glass transition temperature or range of
the sealant composition. They will preferably have a
cohesive strength qPnerally of the same order as their adhe-
sive strength. Conventional sealant compositions usually
comprise mixtures of elastomers, or mixtures of
thermoplastic polymers, or both, and include both mastics
and hot melt sealants as described in Bullman, Adhesives
Age, November 1976, pages 25-28. Mastics generally
consist of mixtures of substantially non-crystalline
materials, for example, bituminous materials, elastomers, or
~Z62~3~37
MPO767
thermoplastic polymers. Sealants, including those prepared
according to the instant invention, frequently contain inert
fibrous or powdered fillers, tackifiers, stabilizers and/or
antirads.
A generally suitable method for determining the
viscosity of sealant materials is set forth in ASTM D-3570
(Procedure A or B).
Conventional sealants, as previously indicated, are
generally not suitable for extrusion processing because of
their high degree of tackiness and low melt strength. My
invention overcomes this problem and permits rapid and
facile extrusion in that a thermoplastic organic polymeric
material (the sealant precursor) is available in the form of
relatively free flowing pellets which do not adhexe to each
s~ 15 other and which do not slump or otherwise ~ fie their
pellet configuration prior to entrance into the extruder
barrel. As previously indicated, a particularly advan-
tageous process of the instant invention for fabricating the
sealant coated, heat recoverable articles involves coextru-
sion of the polymer which is to be rendered heat recoverable
and the polymer which is convertible into a sealant. To be
suitable for coextrusion with a thermoplastic of the type
suitable for radiation cross-linking (to enable the ther-
moplastic to be made heat recoverable), the co-extrudate
(i.e. the precursor polymer which is radiation convertible
to a sealant) should have a viscosity ranging from about O.l
to about 106 poise, preferably 102 to 104 poise, at its
MPO767
-12-
extrusion temperature. The extrusion temperature of the co-
extrudate will conventionally be approximately equal to the
melting point of the thermoplastic.
Conventional sealants are tac~y, exhibit severe slump
and generally have unsuitable viscosities for extrusion,
much less coextrusion with thermoplastics. It is for this
reason that as heretofore indicated, conventional sealants
ordinarily require separate, relatively expensive procedures
to apply them as a coating ~frequently solvent diluted) onto
thermoplastic articles.
I have discovered certain polymeric compositions (i.e.
sealant precursors), which prior to irradiation have low
tackiness, exhibit little slump and have viscosities which
permit facile extrusion or coe~trusion. The sealant
precursor compositions useful in the practice of the instant
invention can be processed on high speed compounding equip-
ment for thermoplastics to produce free flowing pellets.
These pellets can be extruded or, alternatively, coextruded
with another polymeric material (i.e. a radiation
cross-linkable thermoplastic) to form a unitary article
which is heat recoverable. Exposing the formed article to
irradiation crosslinks the thermoplastic and transforms the
sealant precursor into a tacky sealant material. The visco-
sity of the sealant precursor will suitably be greater
before irradiation than after. This is desirable since a
relatively high viscosity for the sealant precursor
simplifies coextrusion, and low viscosity after irradiation
improves the wettability of the sealant.
~L262~313~7
MPO767
-13-
Another advantageous property of the compositions of the
Co r~, f~, o~ C n t ~ r o~o o ~ f ~
instant invention lS that by ad]usting their ~mp~ ~ion I
can ensure that they exhibit cohesive and adhesive
blocking of either the first or t:he second degree after
irradiation. Second degree blocking connotes that if
opposing surfaces are pressed together and then separated
there will be a transfer of sealant material. First degree
blocking connotes the situation where no transfer of
material occurs. Blocking is defined in greater detail in
ASTM Method D-1146. First degree adhesive blocking is
advantageous in that it allows tubular articles with an
interior sealant coating to slide freely along a pipe or
cable, and tape articles to be applied as a pressure sen-
sitive tape. Unwinding of the sealant coated tape to adjust
position is also possible prior to heat recovery. Second
degree adhesive bloc~ing is characteristic of mastic type
materials which manifest self sealing and reduced craft
sensitivity. Another benefit of my sealants is that they
have good load bearing characteristics and~not creep at high
ambient temperatures.
The sealant precursors of ~he instant invention contain
as essential components a thermoplastic (Component A) and a
rubber ~Component B). Other conventional constituents of
sealants such as stabilizers, antirads, inorganic and/or
organic fillers and tackifiers may also be present if
desired.
Based on the combination of Components A and B only
Component A will comprise 30 to 95% of the combination
.
387
MPO767
-14-
(preferably 50 to 90%) and Component B correspondingly 5 to
70% (preferably 10 to 50%).
As heretofore indicated, the sealants of the instant
invention can be "tailored" so as to manifest, after irra-
diation, either first or second order blocking dependingupon the requirements of the application. Although the pre-
cise ratio of Component A/Componerlt B required to afford a
sealant manifesting first order blocking will vary depending
upon the chemical nature and molecular weight of Components
A and ~, I have found that if the ratio of A : B is > 2.5 :
1 the sealant will ordinarily manifest first order blocking.
If the ratio A : B is < 2.5 : 1 the sealant will obviously
manifest second order blocking.
Chemically Componen~ A may be defined as a thermoplastic
polymer. Thermoplastics are materials which differ from
thermosets or elastomers in that when subjected to heat they
do not cure or set but rather soften to a flowable state in
which they can be forced from a heated cavity such as an
extruder head. Suitable polymers include copolymers of
ethylene, propylene, vinyl chloride and vinylidene fluoride
and copolymers thereof with each other and/or with one or
more other copolymerizable olefinic co-monomers such as
vinyl acetate, methyl and ethyl acrylate, halogenated
ethylenes and halogenated propylenes; styrene-diene block
copolymers, polyamides, and polyesters.
Component B of the sealant has been described as a
"rubber". As used herein the term "rubber" is intended to
~l2~ 37
MPO767
-15-
encompass not merely natural and synthetic rubber but also
those synthetic rubber like materials exhibiting elastomeric
or rubber like properties. Suitable rubbers for Component B
include polyisobutylene, butyl rubber, brominated or
chlorinated butyl rubber and epichlorohydrin rubber. A cri-
tical requirement of Component B is that it undergo chain
scission when subjected to irradiation since this chain
scission is believed to be the mechanism whereby the melt
processable sealant precursor is transformed into a tacky
sealant. Radiation generally has the effect of causing
cross-linking of rubbers so it is essential that the rubbers
of the instant invention have a scission/cross-linking ratio
at 20C of > ~
The practice of the invention is illustrated by the
following example in which all parts are by weight.
Example I
The properties of an irradiated sealant prepared
according to the teaching of the present invention
(Formulation B) compared to those of a typical conventional
mastic type sealant (Formulation ~) in Ta~le 1. TMA flow
temperature and T-peel data show the superior load bearing
capability of Composition B. Finally, blocking and tack
data of Composition B show first degree blocking with the
sealant manifesting good tack. Irradiation was at a dose
level of ~ and 1~ megarads. Irradiation at 8 megarads of
Formulation A results in a fall off in T-peel values.
~26Z1~387
MPO767
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TABLE I
Weight %
Composition _ A_ B
Butyl Rubber 50.0 ----
Atactic Polypropylene 50.0 ----
Butyl Rubber ---- 15.0
Ethylene/Vinylacetate
Thermoplastic ---- 18.5
Ethylene/Vinylacetate/
Methacrylic Acid
Thermoplastic Terpolymer 50.0
Tackifier (Hydrogenated hydrocarbon) 15.0
Antirad 1.0
Antioxidant 0.5
PROPERTIES
Composition _ A B B B
Radiation Dose (Mrads) _ 0 0 816
IMA 50% Flow Temperature (C) 23 >60>60 65
T-Peel (PLI)
Polyethylene to Polyethylene 1 1010 10
Polyethylene/Ethylene vinyl
acetate to Polyethylene/Ethylene2 >15>15 >15
vinyl acetate
Dynamic Viscosity ~t 90C, 400
radian/ sec. (10 poise) 1.8 2.2 2.0 1.9
~628~37
MP0767
-17-
Melt Flow at 150~C, 2160gm
(gm/lOmin.~* >200 54 67 82
Falling Ball Tack (cm of roll) 0 12 9 7
*Note that material having melt flow values in excess of 200
and high tack makes coextrusion inconvenient or impossible.
However, within such outer limit the greater the melt flow
the less the craft sensitivity.
EXAMPLE II
The properties of adhesive compositions with elastomer
content varying from lO to 25 wt.~ are shown in Table 2. T-
peel and melt flow data show the load bearing capabilities
of these adhesives and the improvements in flow after
irradiation.
EXAMPLE 2
Weight %
Composition C D E F
Butyl Rubber lQ lS 20 25
Ethylene/Vinyl Acetate
Thermoplastic Copolymer 23 18 13 8
Ethylene/Vinyl Acetate
Methacrylic Acid Thermoplastic
Terpolymer 50 50 50 50
Hydrogenated Hydrocarbon
Tackifier 15 lS 15 15
Antirad
Antioxidant 0.5 0.5 0.5Q.5
MP0767
Proeerties
T-Peel (PLl)
PolyethyIene/Ethylene vinyl acetate
to Polyethylene/Ethylene vinyl
acetate, 10 Mrads 13 14 9 7
Melt Flow at 150C, 2160gm
(gm/10 min.)
0 Mrads 59 4949 32
10 Mrads S9 6462 63
20 Mrads 48 5867 83
