Note: Descriptions are shown in the official language in which they were submitted.
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sAcKGRouND OF THE INVENTION
The present invention relates in ~eneral to pressure
sensitive calenderable, adhesives and in particular to such
adhesives based on thermoplastic rubbers having improved strength
characteristics, processability, as well as outstanding tack and
adhesion, and low creep, etc. properties.
As is known in the art and practiced industrially,
relatively effective pressure sensitive adhesives, hereinafter
also designated p.s.a. can be prepared from various types of
organic, synthetic, polymeric substances such as triblock
copolymers e.g. styrene-diolefin - styrene types and available
commercially in the form of styrene-isoprene-styrene and styrene-
butadiene-styrene triblock polymers.
The former type is usually preferred for use as a con-
tact adhesive while the latter type is preferably used for heat
activated adhesives. In general, the base elastomer materials
used in adhesive formulations, whether of the synthetic or
natural rubber type are not of the cross linked type and are
accordingly soluble in the usual solvents employed in adhesives
manufacture. Being of an essentially amorphorus nature, however,
the strength as well as other important properties characteriz-
ing the product upon blending with the usual additives is often
inadequate for the adhesion problem at hand.
PRIOR ART
Fairly recent developments in polymer technology
have enabled the preparation of unusually high strength resinous
materials which are highly crystalline, Polymers of this type
as typified by crystalline homo-and copolymers of ethylene
and propylene these in combination with rubbery alpha-olefin
copolymers to produce thermoplastic rubbers which may or may not
be partially cured, are described for uses not reIevant to the
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present application in the United States patents 3,758,643;
3,B06,558 and 3,835,201.
United States patent 4,072,735 discloses hot melt ad-
h~sives based on an ethylene-propylene rubber with tackifying
resin and a large amount of polybutylene
GENERAL DESCRIPTION OF THF. INVENTION
In accordance with the present invention, it has
been discovered that polymer compositions of a thermoplastic
"crystalline"olefinic polymer component combined with a rubbery
olefin copolymer component car, in accordance with the limitations
to be hereinafter discussed in detail, be utilized in the prepar-
ation of pressure sensitive adhesive compositions having manifold
beneficial properties and particularly, tack, adhesion, creep
and the like and in addition are readily calenderable.
Thus, paramount among the objects of the present inven-: .
tion is to provide an adhesive composition having the aforemen-
tioned as well as other improved properties, the product adhesive
having significantly improved overall functionally and
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,
thus eminently suitable for use in a wide variety of environments
under diverse conditions of heat, humidity, physical stress and
the like.
Attainment of the foregoing objects is made possible in
accordance with the present invention which in its broader aspects
provides a pressure sensitive adhesive, calendarable composition
comprising a rubbery copolymer of ethylene and at least one other
copolymerizable mono~lefin of the formula CH2=CHR wherein R is
alkyl of 1 to 12 carbons with or without at least one copolymer-
izable polyene, said rubbery copolymer containing from about 10
to 100% by weight, preferably from 20 - 67% by weight, based on
the copolymer, of crystalline polymer of ethylene, propylene or
crystalline copolymers of ethylene and propylene and sufficient
tackifying agent to provide a tackifier: rubbery copolymer
weight ratio of from about 1.2:1 to 8:1.
In a further aspect, the invention provides an adhesive
article comprising the composition coated on a base such as a
flexible, film forming polymeric substance including thermoplastic
resins such as polyethylene, polyester, etc.
One of the truly surprising aspects of the present
invention is the fact that the aforedescribed composition of
rubbery and crystalline polymer components could be formulated
to provide effective adhesive having the highly desirable strength
properties normally characteristic of a crystalline thermoplastic
polymeric material and yet the ease of processability, and
superior tack, adhesion and creep properties normally character-
istic of a rubbery, essentially amorphous polymeric material.
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The use, in an adhesive composition, of a thermoplastic polymeric
substance having a significant degree of crystallinity and par-
ticularly in the relatively large amounts prescribed herein,
would normally be contraindicated, primarily due to the inertness
and insolubility ordinarily attributed to such materials. It
was thus unexpected to fine that the "thermoplastic rubber"
described herein could be effectively plasticized with tackifying
agents as will be described to provide a truly superior adhesive
product.
The improvements described herein obtain where the
rubbery copolymer is any one of those described in United States
patents 3,758,643; 3,806,558 and 3,835,201 and whether the rubbery
copolymer as provided for incorporation with the crystalline
polymer is or is not partially cured. Thus, in United States
3,758,643, the amorphous rubbery copolymer is prepared by
copolymerizing two or more monoolefins of the formula CH2=CHR
wherein R is alkyl of 1 to 12 carbons. A small amount of at
least one copolymerisable polymer may be added to provide
unsaturation in the copolymer. The polyene may be a conjugated
or preferably non-conjugated diene such as dicyclo-pentadiene as
described in United States 3,758,643. Moreover, trienes as well
as dienes may be used. The polyene may be used in amounts up to
about 20% by weight of the copolymer rubber. Partial curing of
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the rubbery copolymer, effected with the usual curatives of the
free radical or cross linking type as explained in column 3
of the patent, is carried out to a gel, i.e. insolubles content
at least 10% in excess of the original gel content of the rubber
and preferably at least 20% in excess and more preferably at
least 30% in excess as measured in cyclohexane. In general,
the gel content will be at least 30% but less than 90%. The
gel is that portion of the rubber which is insoluble in the
cyclohexane and is measured by immersing a sample o~ the material
in the solvent for 48 hours at 73F, taking an aliquot of the
solution and determining the concentration of solute by evapor-
ating the solvent. The partially cured rubber can be blended
with the crystalline polymex material e.g. poly-propylene on a
roll mill, in a Banbury mixer or in an extruder. As explained
in the patent, polypropylene is somewhat superior having
highly crystalline isotactic and syndiotactic form.
As described in United States 3,806,558, the afore-
described procedure can be modified to a one step process by
effecting partial cure of the rubber in the presence of the
~0 crystalline polymer component while the blend is undergoing masti-
cation
As described in United States 3~835~201 treatment of
the copolymer rubber with curative is rendered unnecessary pro-
vided the copolymer rubber be typified in having certain speci-
fied rheological characteristics, specifically a relatively high
value of a viscosity parameter designated "zero shear viscosity".
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The latter, also called steady flow viscosity, is defined as
the melt viscosity at zero shear rate and can be determined from
stress relaxation data or from shear creep data in the manner
fully described in United States 3,835,201. The patent further
describes "branching index" as a further qualifying test.
In any event, any of the thermoplastic rubber compo-
sition described in the foregoing 3,758,643; 3,806,558 and
3,835,201 patents may be used to advantage herein~
Tackifiers useful herein include hydrocarbon resins
such as amorphous polypropylene; poly terpenes such as those
commercially available under the trade name designations.
Wingtack* supplied by Goodyear, eg. Wingtack 10, Wingtack 95;
hydrogenated rosin esters such as those commercially available
from Hercules under the trade name designation Hercolyn*D; the
glycerol or pentaerythritol esters of rosin acids available
commercially from Hercules under the trade name designations,
respectively, PermalynxA-115* and Foral*85 and the zinc salts of
rosin acids such as Pexate resins available commercially from
Hercules. ~any of the foregoing tackifiers are available in
various grades, differing, for example~ in molecular weight,
softening point etc. In any event~ the characteristics of the
product adhesive will differ somewhat depending upon the nature
and quantity of the tackifier used. In accordance with a
particularly preferred embodiment of the invention~ the tacki-
fiers are used in combination comprising two or more thereof.
* Trade Mark
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Particularly, worthy of mention in this regard are the combina-
tion of different polyterpenes and specifically those available
commercially as Wingtack 10 and Wingtack 95 in approximately
equal weight amounts as we11 as combinations of hydrogenated
rosin esters (Hercolyn D) and polyterpenes (Wingtack 95)
respecti~ely in weight ratios of, for example 83:71 82:99 and
62:134.
The tackiEier is added in amounts sufficient to yield
a tackifier: rubbery copolymer weight ratio of from about 1.2:1
to 8:1 and preferably from about 1.2:1 to 6:1 with a range of
1 5:1 to 4.5:1 being most preferred.
The compositions herein can be conveniently prepared
by mixing the thermoplastic rubber material and tackifier on a
rubber mill the rolls being preheated to elevated temperature
e.g. 275-350F. As blending occurs, the roll temperature is
preferably reduced to less than about 200F e.g. 175F. The
resultant adhesive composition can be applied to a suitable
base by pressing same to the desired thickness between a piece
of Mylar* film, for example, and a release paper sheet to pro-
duce an adhesive article, Alternatively, the thermoplastic
rubber may be blended with minor amounts of the tackifier in
a Banbury mill, completion of the compounding being thereafter
e~fected by adding the remaining tackifier on the rubber mill.
Since the present adhesive compositions are readily calender-
able, compounding on the rubber mill is greatly facilitated.
* Trade Mark
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The following examples are given for purposes of
illustration only and are not to be interpreted as necessarily
limiting the invention. All quantities are by weight unless
otherwise indicated.
EXAMPLE 1
-
The thermoplastic rubber (TPR) used in this example
is that described in Example 1, run no. 4 of United States
3,758,643 comprising partially cured ethylene-propylene copoly-
mer rubber, 90 parts, (masterbatch) combined with 10 parts of
crystalline polypropylene.
A mixture of 200 parts of the above TPR, 250 parts
Wingtack 95 and 250 parts Wingtack 10 are mixed on a rubber
mill with rolls preheated to 310F. As the tackifier level
increases during the blending, the rolls are lowered in temper-
ature to 170F. A sample of the final mixture, containing 72%
tackifier by weight is pressed between a piece of Mylar film
and a sheet of release paper at 170F to obtain a film of about
2 mils thickness. The adhesive gives a Probe Tack value (100 g
load, 0.1 second) of 720.
EXAMPLES 2, 3 and 4
; .
The TPR used in these Examples is that described in
Example 1, run no. 8 of United States 3,758,643 comprising
partially cured ethylene-propylene copolymer rubber, 70 parts
(masterbatch) combined ~ith 30 parts of crystalline polypropylene.
A series of adhesives is prepared by initially blending the TPR
with minor amounts of tackifiers on the rubber and then complet~
ing the compounding by adding additional tackifier on the rubber
mill.
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The compositions of the products and the physical properties
obtained when coated on Mylar film to thickness of 2.3, l.9
and 1.6 mil respectively are given below:
Composition Properties
Adhes~lon
ExampleTPR Hercolyn D Wingtack 95 T (a)TO Steel(b~reeP(C)
No. (parts)(parts) (parts)
2.) lO0 83 71 386 46 lO0
3.) lO0 82 99 480 54 83
4.) lO0 62 134 252 65 50
(a) tested under ASTM-D 2979
(b) tested under AST~l-D 1000
(c) tested by flat bar heated to 150F; adhere 1 in2
of end of adhesive tape to flat bar in vertical position and
attach l kilogram weight to free end of tape; creep det~rmined
electronically and given as time in hours for tape to move down
bar 0.5 inches.
EXAMPLE~ 5
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The TPR used in this Example is that described in
United States 3,806,558, Example l, run no. 8, comprising ethy-
lenepropylene copolymer, 60 parts combined with crystalline poly-
propylene, 40 parts. An adhesive prepared as in Examples 2-4
has the following composition.
Ingredient Parts
TPR 100
Wingtack-lO 88
Wingtack 95 78
X _ g
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This adhesive, spread to a thickness of 2.2 mils on ~ylar back-
ing gives the following values when tested as described in the
previous Examples:
tack: 202
ashesion to
steel: 40
creep: 66
EXA~IPLE 6
The TPR used in this Example is that described in
United States 3,835,201. Example ~o. 1 comprising an 80/20 blend
of monoolefin copolymer elastomer with crystalline polypropylene.
An adhesive is prepared as described in Examples 2-4 of the
following composition:
IngredientParts
TPR 100
l~ingtack 10 77
Foral 85 66
This composition when tested as described in the foregoing
Examples at a mass thickness of 3,2 mils gives the following
results.
ashesion to steel: 78 ounces/inch
flat bar creep time: 72 hours/0.5 in.
Results similar to those described in the preceding Examples
are obtained when the procedures described therein are repeated
utilizing other tackifiers and TPR materials described herein
and varying the concentrations thereof within the limits herein-
~0 before delineated.
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