Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2000-12-21
2002-12-03
Nutter, Nathan M. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S240000, C428S500000, C428S343000, C428S3550EN
Reexamination Certificate
active
06489400
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to polymer blends comprising ethylene/propylene-derived copolymers and certain other propylene-derived polymers that exhibit pressure-sensitive adhesive properties. The pressure-sensitive adhesives are useful in preparing a wide variety of articles.
BACKGROUND OF THE INVENTION
A wide variety of references describe blends of &agr;-olefin polymers (i.e., those polymers derived from at least one &agr;-olefin monomer) that are used in hot-melt adhesives and heat-sealing films. However, these references do not teach formulation of such adhesives so that they possess the balance of properties (e.g., shear, peel, and tack) requisite of PSAs. For example, see U.S. Pat. No. 3,492,372 (Flanagan); U.S. Pat. No. 3,798,118 (Jones); U.S. Pat. No. 3,900,694 (Jurrens); U.S. Pat. No. 4,178,272 (Meyer, Jr. et al.); U.S. Pat. No. 4,761,450 (Lakshmanan et al.); U.S. Pat. No. 4,857,594 (Lakshmanan et al.); U.S. Pat. No. 4,957,968 (Adur et al.); U.S. Pat. No. 5,397,843 (Lakshmanan et al.) ; and U.S. Pat. No. 5,834,562 (Silvestri et al.). Further examples include Japanese Patent Publication Nos. 60-120775; 55-069637; 48-066638; and 73-027739.
Pressure-sensitive adhesive (PSA) compositions are well known to those of ordinary skill in the art to possess properties including the following: (1) aggressive and permanent tack, (2) adherence with no more than finger pressure, (3) sufficient ability to hold onto an adherend, and (4) sufficient cohesive strength. Materials that have been found to function well as PSAs are polymers designed and formulated to exhibit the requisite viscoelastic properties resulting in a desired balance of tack, peel adhesion, and shear holding power. Obtaining the proper balance of properties is not a simple process.
The most commonly used polymers for preparing PSAs are natural rubber-, synthetic rubber- (e.g., styrene/butadiene copolymers (SBR) and styrene/isoprene/styrene (SIS) block copolymers), and various (meth)acrylate- (e.g., acrylate and methacrylate) based polymers. With the exception of several (meth)acrylate- and certain &agr;-olefin-based polymers, which are inherently tacky, these polymers are typically blended with appropriate tackifiers to render them pressure-sensitive.
PSA compositions comprising polymers derived from &agr;-olefin monomers are known. Often, such compositions include a single &agr;-olefin polymer, typically a copolymer, which is usually blended with a tackifier. Blending an &agr;-olefin-derived polymer with another polymer when preparing PSAs is known, however. Yet, the relative proportions of the polymers and the physical characteristics of the polymers in these blends is typically not specified.
For example, see European Patent Application No. 0 178 062 (Uniroyal, Inc.) teaches hot melt pressure-sensitive thermoplastic elastomeric adhesive compositions comprising blends of thermoplastic elastomeric polymers made from ethylene and propylene (e.g., those comprising crystalline polypropylene moieties and essentially amorphous elastomeric ethylene-propylene copolymer moieties having a melting point of at least 150° C. as measured by differential thermal analysis), tackifiers, and other optional additives, such as plasticizers, fillers, and stabilizers. Amorphous polypropylene having a ring-and-ball softening point of 149-154° C. is mentioned as an example of a suitable plasticizer. Plasticizers can comprise 5-50% by weight of the total adhesive.
Also see U.S. Pat. Nos. 3,954,697 and 4,072,812 (McConnell et al.), which teach single component, hot-melt, pressure-sensitive adhesives based on copolymers derived from propylene and 40-60 mole % (based on the copolymer) higher olefin monomers. The copolymers may be used alone or in mixture with other materials, including compatible tackifiers, amorphous polypropylene and amorphous block ethylene/propylene-derived copolymers.
U.S. Pat. No. 4,143,858 (Schmidt, III et al.) teaches amorphous polyolefin homopolymers and copolymers useful in hot-melt PSAs. The amorphous polyolefin polymers may also be blended with up to 20 weight % crystalline polyolefins. The adhesives therein may be used alone or in mixture with other materials such as amorphous polypropylene, amorphous block ethylene/propylene-derived copolymer, etc.
It is also noteworthy that many references describing blends of &agr;-olefin derived polymers with other polymers teach blending &agr;-olefin-derived polymers with other polymers that are rubber-based, containing conjugated dienes. For example, see U.S. Pat. No. 5,859,114 (Davis et al.), where a major amount of an ethylene-propylene-diene terpolymer is blended with a minor amount of at least one fully saturated adhesive-enhancing polymer miscible therewith and at least one tackifier. Examples of adhesive-enhancing polymers taught to be useful therein include: ethylene-vinyl acetate copolymers, ethylene-vinyl chloride copolymers, ethylene-octene copolymers, ethylene-butene copolymers, and propylene-butene-ethylene terpolymers. As described in U.S. Pat. No. 5,504,136 (Davis et al.), ethylene-propylene copolymers, such as those typically having an ethylene content of about 45-65% by weight, are also mentioned as having utility as the adhesive-enhancing polymer in a related invention.
PCT Publication No. WO 98/33,858 (American Tape Co.) describes PSAs comprising a natural or synthetic rubber and a thermoplastic polyolefin blend of ethylene/propylene rubber, hydrogenated polyisoprene, and polypropylene. Each of the constituents making up the thermoplastic polyolefin blend has a relatively low molecular weight (3,000-10,000). The PSA composition also includes a tackifier.
PCT Publication No. WO 97/23,577 (Minnesota Mining and Manufacturing Co.) describes blended PSAs that include at least two components. The first component is a PSA. For example, PSAs useful in the invention include tackified natural rubbers, synthetic rubbers, tackified styrene block copolymers, polyvinyl ethers, acrylics, poly-&agr;-olefins (described as being predominantly amorphous), and silicones. The second component is a thermoplastic material or elastomer. For example, thermoplastic materials useful in the invention include isotactic polypropylene and ethylene/propylene copolymers. It is also taught that useful thermoplastic materials are essentially immiscible in the PSA component at use temperatures. The Abstract describes the blends therein as having a substantially continuous domain (generally the PSA) and a substantially fibrinous to schistose domain (generally the thermoplastic material). Tackifiers may be added.
UK Pat. Application No. GB 2 041 949 (The Kendall Company) discloses PSAs comprising (1) a rubbery copolymer of ethylene, a C
3
-C
14
monoolefin and, optionally, a non-conjugated diene, (2) a polymer of a crystalline ethylene or propylene, and (3) a tackifying agent.
Many compositions derived from diene monomers are relatively unstable over time, such as for example, when exposed to weathering or higher temperatures (e.g., such as when hot-melt processing the compositions). Furthermore, many such compositions are relatively non-polar and do not adhere adequately to both relatively high surface energy substrates and low surface energy substrates. “Low surface energy substrates” are those that have a surface energy of less than 45 mJ/m
2
, more typically less than 40 mJ/m
2
or less than 35 mJ/m
2
. Included among such materials are polyethylene, polypropylene, acrylonitrile-butadiene-styrene, and polyamide.
Ways to effectively adhere to low surface energy materials is a challenge that those of ordinary skill in the art are attempting to overcome. Many times improvements in adherence to low surface energy substrates compromises adherence to higher surface energy substrates or compromises shear strength of the adhesive. As such, further adhesives for adequately adhering to low surface energy surfaces are desired. It is also desired that any such new adhesives will allow for broad formulation latitude and tailorability for particular applications.
It would als
Bennett Greggory S.
Khandpur Ashish K.
Siedle Allen R.
3M Innovative Properties Company
Nutter Nathan M.
Pribnow Scott R.
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