Note: Descriptions are shown in the official language in which they were submitted.
lOt~ 4~
This :invention relates to synthetic hydrocarbon-
derived resins and to their preparation. This
invention especially relates to reslns suitable for use
in pressure sensitive adhesives derived from a
manipulati~e combination of diolefins, olefins and
a-methyl styrene.
Valuable resins can be prepared by polymerizing a
diolefin/olefin mixture characterized by a principal
backbone of piperylene and 2-methyl-2-butene. Such
resins, when polymerized with aluminum chloride, are
especially valuable for use in adding tack to various
rubbers for adhesive purposes.
However~ such resins are many times inadequate
for effectively enhancing the tack of various unvulcanized
bIock copolymers for pressure sensitive adhesive
purposes. Pressure sensitive adhesives demand a tailored
balance of cohesive and adhesive forces to yield
effective shear, peel and tack values uncommon to
ordinary building-tack rubbery materials. ~imply
increasing the 2-methyl-2-butene, or decreasing the
piperylene, content of the backbone has been found to be
insufficiently effective in most cases.
Therefore, it is an object of this invention
to provide an improved hydrocarbon-derived resin having a
primary diolefin/olefin backbone for pressure sensitive
tack-imparting purposes.
In accordance with this invention, a hydrocarbon-
derived resin, suitable as a rubber tackifier, is
prepared b~ the method which comprises reacting in the
--1 i4~alS~
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presence of an aliphatic hydrocarbon solvent and a
catalyst selected from aluminum chloride and ethyl
aluminum dichloride, a monomer mixture comprised of
88 to about 98 weight percent of a di.olefin/olefin
mixture of a weight ratio in the range of about 0.6/1
to about l.L~/l and, correspondlngly, aboutl2 to about 2,
preferably about 9 to about 3, weight percen-t a-methyl
styrene~ ~here said diolefin comprises at least 95
weight percent piperylene and up to about 5 weight percent
10 isoprene based on the diolefin~ and where said olefin
comprises. at least one olefin selected ~rom 2-methyl-2-
butene~ 2-methyl-1-butene~ 2-methyl-2-pentene and
2-methyl-1-pentene, preferably at least about 90 weight
percent 2-methyl-2-butene or 2-methyl-2-pentene based on
the olefin. A 800C to 100C softening point is typical.
In the practice of this invention, it is preferred
that the diolefin is essentially piperylene and that the
olefin is essentially 2-methyl-2-butene.
In further practice of this inven.tion, in order
to provide effective enhancement of the tack by the
a-methyl styrene, it is required in the resin that~ as
the amount of a-methyl styrene increases, the diolefin/
olefin ratio increases. Thus, for example, as a-methyl
styrene increases from 2 percent tol2 percent, the
diolefin/olefin ratio should correspondingly increase
about 0.6/1 to about l.L~/l. In this regard, it is
preferred that the amount of a-methyl styrene ranges
from 3 to about 9 weight percent and the diolefin/olefin
ratio correspondingly ranges from about 0.8/1 to about 1/1.
~ 9 ~
The resins of this invention are prepared by
reacting the manipulated monomers in the presence of an
aliphatic solvent~ and aluminum chloride or ethyl
aluminum dichloride, at a temperature in the range of
about OoC to about 100C, preferably in the range of
about 10C to about 50oC. The reaction can be conducted
batch wise or as a continuous processD The reaction can
be conducted at atmospheric pressure or above or below
atmospheric pressure. Generally, the autogenous
pressure developed by the reaction can be used.
Representative of various aliphatic solvents are
saturated hydrocarbons containing 3 to about 8 carbon
atoms? representative of which are n-butane, isobutane,
n-pentane, isopentane, n-hexane, isohexane5 n-heptane
and isoheptane. Hexane and heptane are preferred. It
is understood that unreacted hydrocarbons in the
polymerization mixture can also act as a solvent.
Generally sufficient solvent is used to provide a
solution containing 70 weight percent monomers or resin,
although higher or lower concentrations can usually be
used.
Generally the reaction can be conducted over a
period of time in the range of about 30 to about 120
minutes, although shorter or longer times can be used.
The resin is generally recovered by deactivating
the catalyst with a material selected from water, an
alcohol such as methanol~ isopropanol and butanol and/or
lime, filtering the product and steam stripping the filtrate
to remove volatiles. Then the resin can be mi~ed with
~ Q
various rubbers as tackifiers.
The resin of this invention has been found to be
particularly useful for mixing with unvulcanized
elastomeric block copolymers for the purpose of forming
pressure sensitive adhesives. Particularly representative
of such copolymers are unvulcanized e]astomeric block
copolymers having the general configuration A - B - A
wherein each A is a non-elastomeric polystyrene block
having an average molecular weight in the range of about
5~000 to about 30~000 and a glass transition temperature
above about 25C, the total block A content being about
10 to about 50, preferably about 12 to about 307 weight
percent of the copolymer and B is an elastomeric polymer
block selected from 1~4-addition polymers o~ isoprene, as
a diene polymer, having an average molecular weight
~ in the range of about 50,000 to about 150,000 and a glass
; transitlon temperature below about 10C, said copolymer
having a tensile strength at 25OC in excess of 200 pounds
per squar~ inch. Thus, such unvulcanized elastomeri~
block copolymer comprises non-elastomeric terminal
polymer blocks and internal elastomeric polymer blocks.
Generally it is preferred that the dif~erence between
glass transition temperatures of the end blocks and
middle blocks be at least 40OC and more preferably at
least about 100C.
~he block copolymers can conveniently be prepared
by first polymerizing styrene with a lithium based
initiator. Various lithium based initiators can be used
such as, for example, lithium metal, alkyl lithium
~4--
4~.~
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compounds, lithium hydrocarbyls and organolithium
amides. ~lkyl lithium compounds are preferred.
Particularly pre~erred are branched chain, preferably
secondary~ alkyl li-thi~so Such alkyl li-thiums
especially include secondary butyl lithium, isobu-tyl
lithium, isoamyl lithium and secondary amyl li-thium
Af-ter polymerizing s-tyrene to an average molecular
weight of about 5,000 to about 30,000, the isoprene as
the diene monomer and additional amounts of styrene
are added to the polymerization mixture. The polymeriza-
tion is then continued to provide an elastomeric non-
conjugated diene polymer block followed ~y a non-elastomer
block polymer of the styrene.
Such a polymerization, to form the block copolymer~
is generally conducted at a temperature in the range o~
about 20C. to about 65C. in an inert hydrocarbon solvent
such as an aliphatic or aromatic hydrocarbon.
When preparing pressure sensitive adhesives,
generally the tackifying resin is mixed with the block
copolymer in an amount of about 30 to about 25 weight
percen-t of the tackifying resin, based on the block
copolymer. If desired, the mixture can conveniently
be formed by mixing the tackifying resin and bl~ck
copolymer in the presence of a volatile organlc
hydrocarbon solvent such as toluene, benzene, hexane,
heptane and octane. In this manner, the adhesive
mixture, with solvent, is simply applied to a substrate
surface, partially drying the application, and con-
; tacting said subs-trate surface with the adhesive
~ --5--
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mixture therebetween and drying said adhesive.
Alternatively, a pressure sensitive adhesive tape
can be provided by applying the resin/block copolymer
solution to a flexible substrate and drying the mixture~
The practice of this invention is more fully
illustrated by reference to the following example which
is intended to be representati~e rather than limiting
of the scope of the in~ention. Unless otherwise indicated,
all parts and percentages are by weight.
EXAMPLE I
A series of experiments was conducted, identified
herein as ~xperiments A-~I and Experiment A-A. In these
experiments, various amounts of piperylene and 2-methyl-
2-hutene, along with heptane, were charged to reactors.
15 Additionally, various amounts of a-methyl styrene along
with alumi~um trichloride were also charged to the
reactors. The polymerization reactions were conducted
at temperatures in the range of about 27C to about
30C for about 120 minutes. The catalyst was
20 deactivated with mathanol and lime. The resin was
simply recovered by filtering the product and steam
stripping the filtrate to remove volatiles.
The parameters and results of the experiments A-H
are more clearly shown in the following Table 1~ as well
25 as the tackifying ability of the resins when mixed with
an unvulcanized block copolymer of styrene-isoprene-
styrene in an amount of50 parts resin per 50 parts
block copolymer. Note that, as the ratio of piperylene
~PIP) to 2-methyl-2-butene (2MB2) is increased, the
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percent a-methyl styrene must also be increased to
achieve the same tack value. It is equally important
to note that by operation of this invention, tack values
can be maintained while 2-methyl-2-but;ene content is
5 actually reduced. Experiment A-A is included to more
clearly demonstrate that this type of resin has little,
if any, effect upon enhancing the tack of a butadiene/
styrene-type rubber. Experiment A shows that with
a-methyl styrene, the tack is substantially reduced by a
great magnitude.
TABLE 1
Monomer Wt % Tack
Ratio alpha (Rolling
Pip/ methyl So~teningBall)
Exp2MB2 styrene2 ~13(inches~
A-A1.0 6.3 90.5No tack
A 1.0 0 100.518 12
B .6 2 9 88 1.26
C ~ 3.o 98 5~93
D loO 6~3 90.5 1.68
E 1.0 6.2 92.0 1.58
F .6 8.6 85.5 .7
G 1.4 9.1 94 1.09
H 1.0 12.L~ 88 .8
1 Experiment A-A used a 1,3-butadiene/styrene emulsion
polymerized elastomeric copolymer
2 Based on piperylene, 2-methyl-2-butene and a-methyl
styrene. The piperylene/2-methyl-2-butene/a-methyl
styrene actually, in additio~, about 22 percent
2-pentene, 1 percent isoprene, 3.5 percent cyclo-
pentene and 1.5 percent other hydrocarbons containing
5 to 6 carbon atoms.
3 Ring and Ball softening point tASTM E 28-58 T)
.
SQ long as the basic piperylene/said olefin
backbone is maintained, the polymerization monomer
mixture can be modified by containing up to about 15
weight percent, preferably only up to about 10 weight
percent, piperylene dimers, piperylene trimers, or
other unsaturated hydrocarbons containing 5 to 6 carbon
atoms. Representative of such hydrocarbons, which may
take place i~ the polymerization reaction, include
those, in addition to the 2-methyl-2-butene, selected
from 2-methyl-1-butene, 2~3-dimethyl-L-butene~
2,3-dimethyl-2-butene~ 2-methyl-1-pentene, 2-methyl-2-
pentene, cyclopentene and 1,3-cyclopentadiene. It is
understood that other hydrocarbons containing ~ to 6,
more generally 5 to 6, carbon atoms can be present
which act more as diluents than reactants. Representative
of typical hydrocarbons which have been found to be
~resent are 3~3~dimethyl-1-butene~ l-pentene, 2-pentene,
3-methyl-2-pentene, 4-methyl-1-pentene, 2-he~ene and
cyclohexene.
While certain representative embodiments and
details have been shown for the purpose of illustrating
the inventlon, it will be apparent to those having
skill in this art that various changes and modifications
may be made therein ~Jithout departing from the spirit
or scope of the invention.
