Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2003-02-06
2004-07-06
Szekely, Peter (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C524S059000
Reexamination Certificate
active
06759454
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to polymer modified bituminous compositions having improved phase stability, heat aging and viscosity characteristics. In particular, the invention relates to compositions containing a novel anionic block copolymer where one of the blocks is a controlled distribution copolymer of a conjugated diene and a mono-alkenyl arene having a specific arrangement of the monomers in the copolymer block.
BACKGROUND OF THE INVENTION
Naturally occurring or petroleum derived bitumen is a useful material for many applications. However, bitumen by itself often cannot meet the performance requirements for applications such as paving, roofing felts and water-proofing membranes. Therefore, approaches have been developed whereby polymers are added to the bitumen to increase properties such as low temperature flexibility and high temperature softening point. Improvements in either the low temperature or high temperature properties result in an increased temperature range of practical use. In some polymer-modified bitumen compositions the polymer is especially effective and these property increases occur simultaneously. In addition to improvements in temperature range of use, improvements in fatigue resistance, thermal cracking and rutting resistance can be achieved.
Of particular utility in the field of polymer-modified bituminous compositions are anionic vinyl aromatic—conjugated diene block copolymers. U.S. Pat. No. 4,129,541 teaches the use of radial styrene—butadiene block copolymers to improve the low temperature flexibility and stress crack resistance of bitumen for cold temperature coating applications.
The limited compatibility, however, of polymers with bitumen components often leads to unstable blends and thereby results in variable and/or inferior properties.
A variety of approaches have been taken to improve the compatibility of anionic block copolymers with bitumen. The technology disclosed in U.S. Pat. No. 4,145,322 teaches the use of sulfur crosslinking agents in conjunction with anionic block copolymers. The crosslinked compositions exhibit excellent high and low temperature characteristics. Importantly, the addition of anionic triblock copolymers changed the inherent character of bitumen from viscous to visco-elastic.
Further improvements in the sulfur crosslinking approach were taught in U.S. Pat. No. 5,773,496 wherein combinations of anionic block and radial, or multi-armed, copolymers were used in blends with bitumen. Because of the relatively high amounts of diblock copolymer, crosslinking by sulfur was necessary to attain property improvements, particularly improvements in force ductility. In U.S. Pat. No. 6,429,241 approaches to improved properties were taught whereby a relatively high amount of sulfur crosslinking of an anionic triblock copolymer/bitumen blend was achieved by a process utilizing incremental addition of the copolymer and crosslinker.
While leading to property improvements, the approach of crosslinking to stabilize anionic block copolymer/bitumen blends has the drawback of requiring extra materials (i.e., the crosslinking agents) and extra process steps for incorporating these agents. This process has the further drawback of resulting in either weak products or highly gelled products when the crosslinking agent is improperly used. Further undesirable features of sulfur crosslinking is the generation of hydrogen sulfide during processing which presents environmental and health risks.
Another approach to improved property sets through the formation of stable polymer-modified bituminous compositions is by the use of compatibilizers. U.S. Pat. No. 5,331,028 teaches the use of a glycidated ethylene copolymer as a compatibilizer for SBS/bitumen blends. In this technology, the functionalized ethylene copolymer is reacted with the bitumen to form a bituminous component more receptive to anionic block copolymer blending.
Other functionalized polymers useful as block copolymer—bitumen compatibilizers such as epoxidized polydienes have been taught in U.S. Pat. No. 5,451,619 and polar polymers such as functionalized polyethylene in U.S. Pat. No. 6,100,317.
Incorporation of compatibilizing polymers to stabilize anionic block copolymer—bitumen blends has led to significant property improvements. However, this approach requires the addition of a third component which is often expensive. Further, the processes for preparation of the blends can be generally complex because of steps required to produce the compatibilizer or those required for blending into the bitumen composition.
Simpler approaches whereby the anionic block copolymer composition or structure is modified during its initial manufacture are attractive from a process and cost point of view. U.S. Pat. No. 4,530,652 and U.S. Pat. No. 5,854,335 teach the modification of the butadiene rubber block of anionic block copolymers to achieve enchanced compatibility and performance. In particular, the rubber midblock is modified to increase the 1,2-addition of the butadiene during polymerization. The increased compatibility achieved by this approach results in improved retention of properties after heat aging, increased flexibility and improved high temperature flow resistance.
It has now been found that anionic block copolymers having a controlled distribution rubber block comprising alkenyl arene and conjugated diene monomer units have excellent compatability with bitumen. Such block copolymers and methods for making them are described in above referenced U.S. Provisional Patent Application Serial No. 60/355,210 and in copending, commonly owned U.S. patent application Ser. No. 10/359,981, now published as US2003/0176582 A1. Further, the performance characteristics of such compositions are attractive for a variety of applications such as paving, roofing felts, water-proofing membranes, asphaltic adhesives, mopping asphalts, carpet backings, sound-deadening and coatings.
SUMMARY OF THE INVENTION
The present invention is a bituminous composition comprising:
I) from about 75 percent to about 99.5 percent bitumen; and
II) from about 0.5 percent to about 25 percent weight of a block copolymer having at least one A block and at least one B block wherein:
a) each A block is a mono-alkenyl arene homopolymer block and each B block is a controlled distribution copolymer block of at least one conjugated diene and at least one mono-alkenyl arene;
b) each A block having a number average molecular weight between about 3,000 and about 60,000 and each B block having a number average molecular weight between about 30,000 and about 300,000;
c) each B block comprises terminal regions adjacent to the A blocks that are rich in conjugated diene units and one or more regions not adjacent to the A blocks that are rich in mono-alkenyl arene units;
d) the total amount of mono-alkenyl arene in the block copolymer is about 20 percent weight to about 80 percent weight; and
e) the weight percent of mono-alkenyl arene in each B block is between about 10 percent and about 75 percent.
The block copolymer of the present invention may be unsaturated or selectively, partially or fully saturated by hydrogenation. The advantages of the present invention are bituminous compositions of increased compatibility having improved heat aging characteristics and broad service temperatures. Specific applications of this composition are paving formulations, roofing felts, water-proofing membranes, asphaltic adhesives, mopping asphalts, pipe coatings and carpet backings.
DETAILED DESCRIPTION OF THE INVENTION
The present invention offers bituminous compositions comprising novel anionic block copolymers. The novel anionic block copolymers result from the copolymerization of alkenyl arenes and dienes as part of a mono alkenyl arene/conjugated diene block copolymer. Surprisingly, the combination of (1) a unique control for the monomer addition and (2) the use of diethyl ether or other modifiers as a component of the solvent (which will be referred to as “distribution agents”) results in a certain characteristic distribution
Handlin, Jr. Dale L.
Kluttz Robert Q.
Stephens Keith E.
Willis Carl L.
KRATON Polymers U.S. LLC
Masse Michael A.
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