Note: Descriptions are shown in the official language in which they were submitted.
~9~
~ield of t~e Invention
This invention relates to affixing a non-tacky,
flexible layer in sheet or tape form to a substrate by
applying a stretching elongation to the flexible layer
before application to the substrate whereby adhesion to
the substrate is obtained as well as self-bonding or
fusion of overlapping layers.
Back ~ound of the Invention
Many articles need to be coated for protection
from the environment. For example, metal surfaces may be
protected by covering with a coating layer, thereby
preventing chemical, oxidative or other attack of the
surface. The technology ~or the application of such
coatings is well known and includes application from
solution, by the application of a paint, or application as
a thin sheet or tape. In the application of such coatings
in the ~orm of sheet or tape, a separate adhesive layer is
generally used to achieve adhesion of the sheet to the
substrate and o~ overlapping layers of the sheet to each
other. In commercial wrapping operations, such as pîpe
wrapping, it is normal practice to use a sheet carrying
such an adhesive layer, and to stretch the sheet slightly,
up to about 5 percent, to ensure that it is wrapped
tightly around the pipe.
In electrical applications such as cable splices,
a tape in the form of a strip of ~lexible material is
stretched, and wrapped, usually spirally around an
electrical c~ble. The overlapping layers tend to fuse to
one another so that they can no longer be separated
readily. Earlier such tapes were based on natural rubber,
whereas later tapes which are described in the literature
are based on combinations of synthetic polymers. U.S.
Patent No. 2,569,541 issued to Harold E. Selby discloses
such compositions containing polyethylene, butyl rubber,
,., , ~
'
polyethylene and a tackifîer resin and requires that the
proportion of butyl rubber be below 25 percent, and a
tackifier is required to produce a composi~ion w'nich seals
readily. U.S. Patent No. 3,298,992 issued to H. M. Bond
et al discloses tape composi~ions containing specific
proportions of butyl rubber, polyisobutylene, a
chlorinated hydrocarbon resin and a high styrene copolymer
of butadiene and styrene. Generally these materials when
formed into a roll without a liner adhere together or fuse
so that after a short period of time it is impossible to
unwind them. To avoid this problem, self-adhering tapes
have been provided with a removable liner between
overlapping layers. Removal of the liner is time
consuming and may be difficult when it becomes tightly
adhered to the tape.
DISCLOSURE AND PRACTICE OF Il~VENTION
. . . ~
The present invention is based on the discovery
of certain compositions in sheet or tape form, which are
not tacky and therefore do not stick together when
overwrapped in the relaxed state, but which fuse and
produce a homogeneous body when subjected to a s~retching
elongation of at least about 50 percent and wrapped around
a substrate. The compositions comprise raw polymer
mixtures consisting of certain a~olefin polymers mixed in
specific proportions with an elastomeric polymer component
of which at least about 50 percent by weight is an
isobutylene-isoprene polymer, the balance being
polyisobutylene, an ethylene propylene polymer or natural
rubber. They are s~rong but can be readily stretched
without breaking. They have good ozone resistance and are
readily handleable over a wide temperature range. The
a -olefin polymers may be isotactic polypropylene or those
polyethylenes which are generally referred to as low
pressure polyethylene.
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A further aspect of the invention is the
surprising discovery that the presence of filler or
pigment in the tape increases the rate of fusion of
overlapping layers of the stretched, wrapped tape.
According to my discovery, there is provided the
proce,ss of affixing to a substrate a flexible layer having
insufficient tack to self-bond in the relaxed state, said
layer comprising a raw polymer mixture selected from the
group consisting oE (all parts being parts by weigh~)
(a) a mixture of from about 15 to about 30 parts of linear
low density polyethylene and from about 70 to about 85
parts of elas~omeric polymer9 and (b) a mixture of from
about 15 ~o about 25 parts of isotactic polypropylene and
from abou~ 75 to about 85 parts of elastomeric polymer,
said elastomeric polymer consisting of from about 50 to
100 par~s by weight of an isobutylene-isoprene polymer and
from 0 to about 50 parts by weight of one or more polymers
selected from (i) natural rubber, (ii) a homopolymer of
isobutylene having a molecular weight from abou~ 50,000 to
about 100,000 and ~iii) a polymer o~ ethylene and
propylene containing rom about 50 to about 65 percent by
weight ethylene, wherein said flexible layer is subjected
to a stretching elongation of at least about 50 percent
immediately prior to contact with the substrate, applying
the elongated layer to the substrate in a wrapping
operation and allowing overlapping layers of said flexible
layer to bond to and fuse with each other.
Further according to my discovery, there is
provided the proces,s of afixing to a substrate a flexible
layer having insufficient tack to self-bond in the relaxed
state9 said layer comprising a raw polymer mixture
selected from the group consisting of (all parts being
parts by weight) (a) a mixture of from about 15 to about
30 parts of linear low density polyethylene and from about
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,~:,,,., . . ~,
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2Z
70 to about 85 parts of elastomeric polymer, and (b) a
mixture of from about 15 to about 20 parts of isotactic
polypropylene and from about 80 to about ~5 parts of
elastomeric polymer, said raw polymer mixtures (a) and (b)
also containing from about 0.5 to about 20 parts by
weight, per 100 parts of total polymer, of one or more
filler or pigment, said elastomeric polymer consisting of
from about 50 to 100 parts by weignt of an isobutylene-
isoprene polymer and from 0 to about 50 parts by weight of
one or more polymers selected from (i) natural rubber and
(ii) a homopolymer of isobutylene having a molecular
weight of from about 50,000 to about 100,000, wherein said
flexible layer is subjected to a stretching elongation of
at least about 50 percent immediately prior to contact
with the substrate, applying the elongated layer to the
substrate in a wrapping operation and allowing overlapping
layers of said flexible layer to bond to and fuse with
each other.
The isobutylene-isoprene polymer may be selected
from a polymer containing from about 97 to about 99.5
weight percent of isobutylene and from about 0.5 to about
3 weight percent of isoprene or from a polymer containing
from about 0.5 to about 1.5 weight percent of chlorine or
from about 1.5 to about 2.5 weight percent of bromine and
from about 95 to about 99 weight percent of isobutylene
and from about 0.5 to about 3 weight percent of isoprene.
Such polymers are commercially available and have a
molecular weight, expressed as the Mooney viscosity, of
from about 30 to about 80 (~L 1+8 at 100C).
Polyisobutylene elastomer is available
commercially as various molecular weight products. It is
prepared using Friedel-Crafts catalysts at low temperature
and its manufac~ure is well known in the art.
Polyisobutylene preferred in the raw polymer mixture has a
~296~2
Staudinger molecular weigi~t of from about 50,000 to about
100,000, and especially from about 60,000 to about
80,000. Grades having higher molecular weights, for
example about 120,000 to about 135,000, result in very
strong tapes which are difficult to stretch and which do
not fuse satisfactorily at room temperature when stretched
and wrapped. On the other hand, very low molecular weignt
grades result in tapes which are tacky and difficult to
handle.
Elastomeric copolymers of ethylene and propylene
are well known to those skilled in the art and a variety
are available commercially. Suitable such copolymers
include EYR (ethylene-propylene rubber) and EPDM
(ethylene-propylene-terpolymer) containing by weight ~rom
about 50 percent to about 65 percent ethylene. The third
monomer which is used in a small amount in the production
o EPDM is a copolymerizable polyene. Those polyenes
which are generally used commercially are non-conjugated
dienes including 5-ethylidene-2-norbornene, 1,4 hexadiene
and cyclic dienes such as dic~clopentadiene.
The natural rubber is preferably selected from
the commercially available SMR grades.
Polyethylene is a well-known article of commerce
and a large number of grades are available. The old or
conventional grades are produced by a high pressure
process which operates at a pressure of from about 15,000
to 50,000 psi. The polymers produced in this process
contain a variety of short and long chain branches and
have densities falling in the range from about 0.91 to
0.94 gm/cm3. In the newer or low pressure processes the
polymer is produced either in gas phase 1uidized bed
reactors at pressures of abvut 100 to 300 p5 i or in liquid
phase reactors. In ~hese low pressure processes, the
ethylene units polymerize in a linear fashion and randomly
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61~2Z
spaced short branches or side chains are incorporated by
copolymerizing small amounts, up to about 20 percent by
weight, of ~ -olefins such as propylene, butene, hexene
and octene and the like. The frequency and length of the
side chains controls the density of the polymer. The term
linear low density polyethylene (LLDPE) is commonly used,
and when used herein is to be understood to mean the low
pressure produced copolymers having a density in the range
from ~.9l to 0.94 gm/cm3. They generally range in
10 molecular weight from about lO0,000 to 500,000 wi~h those
in the range from about lO0,000 to 300,000 being
preferred. These polymers have been found to be useful in
the practice of the invention, whereas the use of
polyethylene produced at high pressure results in tapes
which are weak and which tend ~o self-bond in the relaxed
state. LLDPE is available commercially in gradPs covering
a range of melt flow index, which is a measure of the
viscosity under melt flow conditions. Those preferred in
`the practice of the present invention fall within the
range from about 0.2 to about 5 according to ASTM-D-1238.
The polypropylene which can be used in ~he
practice of the present invention is preferably hi~hly
crystalline in which propylene is polymerized
predominantly in the isotactic configuration. It may also
contain a small proportion, up to about 15 percent by
weight, of the atactic configuration or of ano~her
copolymerized ~-olefin such as butene, pentene, hexene,
octene and the like. The term polypropylene is used
herein to include homopolymers of propylene as well as
such copolymers. A large number of grades of
polypropylene are available commercially covering a wide
range of melt flow index. The grades having a melt flow
index according to ASTM-D-1238 of from about 2 to about 12
are preferred.
~Z9~ 2
The relative proportions of thermoplastic polymer
and elastomeric polymer used in the present invention fall
within a narrow range. ~xpressed in parts per 100 of
total polymer in the compositions, the proportion of
linear low density polyethylene is rom about 15 to about
30 parts, preferably from about lS to about 25 parts. The
proportion of polypropylene is from about lS to about 25
parts, preferably from about lS to about 20 parts.
Proportions below the lower limits of the above ranges
result in sheets or tapes having a level of tack which
causes self adhesion when overlapped in the relaxed or
unstretched state, whereas proportions higher than the
upper limits result in products in which overlapping
layers do not fuse within a reasonable time at normal
temperatures when stretched and wrapped.
Filler or pigment may be included in the flexible
layer containing a linear low density polyethylene if
desired in an amount up to about 20 parts by weight, based
on 100 parts of total polymer. They may be selected from
those generally used in rubber compounds, exeL~plified by
carbon blac~, calcium carbonate, talc, aluminum powder,
titanium oxide and zinc oxide. The amount of a particular
filler or pigment which can be used without adversely
afecting the tensile and/or fusion properties of the
flexible layer can be readily determined by those skilled
in the art. It has surprisingly been found tha~ carbon
black and pigments, when present in the range from 5 to
about 20 parts by weight, actually appear to increase the
rate of fusion of overlapping layers of stretched wrapped
sheets or tapes. Thus, when the higher levels of a-olefin
polymer are used it is desirable to include carbon black
or pigment in the compositions. To achieve this effect it
is preferred to use ti~anium oxide or carbon black, the
preferred carbon black being a high abrasion or super
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abrasion furnace black. For electrical applications in
which conductivity is desired, it is desirable to also use
from about 10 to about 30 parts by weight per 100 parts of
total polymers of an electrically conducting carbon black
or metal powder, such as aluminum powder.
Other optional ingredients may be incorporated
into the flexible layer to achieve various performance
objectives. For example, there can be added antioxidants
and stabilizers, processing aids, lubricants and fire
10 retardants. The use of a separate tackifier is not
required.
The flexible layer is prepared by mixing
procedures well known in the art of processing of
synthetic rubbers using either a two roll mill or an
internal mixer. When using a two roll mill, the
thermoplastic polymer is added to the mill which has been
pre-heated to a suitable temperature generally in the
range of about 150 to about 170C and mixed until it
fluxes and forms a band on the mill rolls, which usually
takes about two minutes. The elastomeric polymer(s) and
any additives are then added to the mill and the mixing
continued until a uniform blend is obtained, which usually
takes a further five minutes. The mixture is taken off
the mill as strips of compound. Compound may also be
produced in bulk form using an internal mixer by adding
the polymers in any order to a preheated mixer and mixing
until a uniform compound is obtained, usually about 5
minutes. Sheets of the flexible layer may be prepared
such as by passing the compound ~hrough a calendar or an
extruder equipped with a sheet die. The thickness of the
sheets is not critical but generally is from about 0.1 to
about 5 mm. For most applications it is preferred to use
sheets having a thickness of from about 0.3 to about 3
mm. The fle~ible layer may be used in sheet for~ although
~96l~;~2
for a variety of applications it is desirably in tlle form
of a tape prod.lced by cutting the sheet to form tapes
l~aving the desired width.
The flexible layer, in sheet or tape form, is
applied to the substrate by subjecting it to a stretching
elongation in one direction of at least about 50 percent
and in the elongated state applying it to the substrate,
as for example in a wrapping action. Such stretching
results in the sheets or ~apes developing the ability to
self-bond and the overlapping layers adhere strongly to
each other. These layers have the appearance of a fused
sheet on or covering the substrate witnin a few hours of
application. In order to develop the self-bonding
properties required, the flexible layer is elongated by at
least about 50 percen~. The upper limit of elongation
depends on the composition of tne particular sheet or tape
and must be below the level which would cause rupture.
Preferably, I have found that an elongation of from about
75 percent to about 150 percent provides an optimum
balance between developing self-bonding properties and
avoiding rupture.
The process of my invention may be used in a wide
variety of applications such as splicing, encapsulation
and connection. Metal parts can be readily covered with
such a flexible layer for storage or environmental
reasons; for example a metal pylon may be so covered to
protect it when immersed in water. Minor repairs may be
made to existing covers of exposed parts, for example
underneath cars, trucks or other like vehicles. Damaged
boots on tie rod ends or rack and pinion steering
components may be readily repaired by covering with a
flexible layer in accordance with this invention. The
process may be used, particularl~ in the form of tapes, in
the electrical trade for splicing cables, and for
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repairing splices and damaged insulation especially in
cold weather environments.
The following examples illustrate the scope o~ my
invention.
Example 1
Sixty grams of each of four compounds of butyl
rubber and linear low density polyethylene were prepared
in a laboratory sized internal mixer in the relative
proportions (parts by weight) shown in Table 1. The butyl
rubber was POLYSAR Butyl 301 supplied by Polysar Limîted
and contained about 98.4 weight percent of isobu~ylene and
about 1.6 weight percent of isoprene and had a Mooney
viscosity (ML 1+12 at 125C) of about 55. The
polyethylene was DOWLEX~ 2045 supplied by Dow Chemical
having a Melt Index of 1.0 gm/10 min as determined by ASTM
Method D-1236 and a density of 0.92 as determined by ASTM
Method D-792. The internal mixer was preheated to about
160C and the polymers added and mixed for about 5
minutes. The compounds were sheeted out on a rubber mill
to a thickness of about 1.5 mm and tapes having a width of
0.6 centimeters cut from each sheet.
The degree of unstretched tack of the tapes was
determined by folding the tapes, pressing overlapping
layers together, and observing the degree of self-adhesion
8S the ease with which the layers could be hand
separated. ~ tape from each compound was elongated by 75
to 100 percent and wrapped around a metal rod. The
wrapping was examined after standing overnight at room
tempera~ure. The results are shown in Table I.
~ 30
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TARLE I
Compound/Ta~e No. l 2 3 4
Butyl rubber 90 80 75 70
Polyethylene lO 20 25 30
Carbon black 3 3 3 3
Antioxidant 9.05 0~05 0.05 0-05
Unstretc'ned tack ** * * Nil
Degree of Fusion High High High Partial
(Gvernight at R.T.)
* slight ~ layers separate under very light force0 ** moderate - layers separated without tearing but under
a firm force.
Notes:
Carbon Black - IRB #4 ~
Antioxidant - IRGANOX lOlO
ample 2
Using the procedure of Example 1, the compounds
shown in Table II were prepared and evaluated. The butyl
rubber and polyethylene were the same as used in Example
l. In comparing the properties o Tape No. 5 with Tape
No. 4 of Table I, it is seen that the presence of lO parts
of carbon black per lOO parts of total polymer results in
a higher level of fusion. Tape No. 7, which is outside
the scope of the invention, shows that for rep].acement of
part of the butyl rubber with EPD~, the addition of carbon
black essentially eliminates the fusion. Tapes No. 8 and
~, which are outside the scope of the invention, shows
that above the critical level of polyethylene the tape
will not fuse.
.
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TABLE_II
Com~ound/Ta~e No. 5 6 7 8 9
Butyl rubber 70 80 40 65 65
EPDM 585 ~ 40 -- -
Polyethylene 30 20 20 35 35
Carbon black lO l0 l0 lO 20
Unstretched Tack Nil Nil Nil Nil Nil
Degree of Fusion
(overnight at R.T.) High High Very low I~one None
Notes:
10 EPDM 585 - A copolymer of ethylene 9 propylene and
ethylene norbornene, containing about 62
percent ethylene, supplied by Polysar
Limited.
Carbon black - N-330 type
Example 3
Using ~he procedure of Example l, three compounds
containing 75 parts by weight of POLYSAR Butyl 301, 25
parts by weight of DOWLEX 2045 polyethylene and 0.05 parts
of IRGANOX l0l0 antioxldant were prepared and evaluated~
The first compound contained no additional material, the
second also contained 20 par~s of N~330 type carbon black
and the third contained 21.3 parts of TITANOX ALO titanium
oxide (parts being by weigh~ per l00 parts of total
polymer).
None of the tapes possessed unstretched tack.
After stretching and applying, on standing overnight the
inner layers of ~he wrapped tape from the first compound
had fused although a portion of the outer layer could ~e
unwrapped without tearing. The tapes from the second and
third compounds had fused so that the layers could not be
separated
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F~am2~e 4
A compound containing 48 grams of butyl rubber
and 12 grams of isotactic polypropylene was prepared and
evaluated using ~he procedure of Example 1. The butyl
rubber, Butyl 111, was supplied by Polysar Limited and
contained about 99.3 weight percent isobutylene and about
0.7 weight percent of isoprene and had a Mooney viscosity
~ML 1+8 at 100C) of about 70~ The polypropylene, PROFAX~
6524 was supplied by Hercules. Tapes prepared from the
compound had slight surface tack but wnen overlapped on
each other and pressed together did not bond and could be
readily separated. A strip was elongated by about 100
percent and wrapped around a metal rod. It clung tigntly
to the rod and overlapping layers adhered strongly to each
other and after 24 hours the overlapping layer had fused.
ample 5
Example 4 was repeated except that 15 grams of
the polypropylene and 45 grams of t~e butyl rubber were
used in preparing the compound. The unstretched tape had
negligible tack, whereas overlapping layers of the
elongated, wrapped tape self-bonded strongly. They could
be unwound aEter 24 hours but required the application of
significant force to do so.
ample_6
Example 4 was repeated except that instead of
butyl rubber, brominated butyl rubber was used containing
about 96.1 weight percent of isobutylene, about 1.8 weight
percent of isoprene and about 2.1 weight percent of
bromine and having a Mooney viscosity (ML 1+4 at 125C) of
about 52. The uns~retched t~pe had no significant tack
` wherea~ the overlapping layers of the elongated, wrapped
tape adhered fairly strongly to each other.
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Example_7
Using the procedure of Example 1, the compounds
shown in ~able III were prepared and evaluated. The
butyl rubber was POLYSAR Butyl 301 as used in E~ample 1,
and the polypropylene was the same as used in Example 3.
The carbon black was N-330 type. These results show the
criticality of the amount of polypropylene which may be
used in the invention, tapes No. 12 and 13 being outside
the scope of the invention.
TABLE III
Compound/Tape No. 10 11 12 13
Bu~yl rubber 80 75 75 70
Polypropylene 20 25 25 30
Carbon black -- 0 20 0
Unstretched tack v. slight nil nil nil
Degree of Fusion high low none none
ample 8
Using the procedure of Example 1, the compounds
shown in Table IV were prepared and evaluated. Tapes 14
and 15 had slight unstretched tack. On the other hand,
Tapes 16 and 17 which are outside the scope of the
invention were tacky and overlapping layers of unstretched
tapes tore when an effort was made to separate them. In
all cases, the stretched wrapped tapes had fused when
examined after standing at room temperature overnight.
TABLE IV
Compound/T~e No. 14 15 16 17
Butyl rubber 85 85 90 90
Shell RMT6100 15 -- 10 --
30 Esso PP00400 -- 15 -- 10
Carbon black 3 3 3 3
Antioxidant ~ 0.5 0.5 0.5 0.5
Un.stretched tack slight slight tacky tacky
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Notes:
_ _
Shell RMT6100 a~d Esso PP00400 - isotactic polypropylene
supplied by Shell Chemical and Esso Chemical,
respectively.
Carbon black - N-330 type
Antioxidant - IRGANOX 1010
Butyl rubber - as used in Example 1
ample 9
Using th~ procedure of Example 1, the compounds
shown in Table V were prepared and evaluated. The butyl
rubber was Butyl 301 and the polypropylene was PROFAX
6524, as used in previous examples. The elongated,
wrapped tapes prepared from all compounds had fused when
examined after standing overnight.
TABLE V
Compound/Tape_No. 18 19 20 21
__
Butyl rubber 40 40 42.5 40
Polyisobutylene 40
20 Natural rubber -- 40 -- --
EPDM 585 -- -- 42.5 --
EPDM 346 - -- -- 40
Polypropylene 20 20 15 20
Carbon black -- -- 3.0 --
Antioxidant -- - 0.05 --
Unstretched tacknil slight slight nil
Notes:
__
EPDM 585 - As used in Example 2.
EPDM 346 - A copolymer of ethylene, propylene and
ethylidene norbornene containing about 62
percent by weight ethylene, and supplied by
Polysar Limited.
Carbon black - N-330 type
Antioxidant - IRGANOX lOlO
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