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
2000-12-29
2002-09-24
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...
C525S073000, C525S075000, C525S077000, C525S078000, C525S080000, C525S085000, C525S191000, C525S203000, C525S205000, C525S212000, C525S218000, C525S221000, C525S222000, C525S225000, C525S238000, C525S240000, C525S241000, C428S343000, C428S3550EN, C428S3550CN, C428S3550AC, C428S375000, C442S327000, C442S361000
Reexamination Certificate
active
06455634
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to polymer blends comprising at least one (meth)acrylate polymer and at least one amorphous propylene-derived polymer that exhibit pressure sensitive adhesive properties. The pressure sensitive adhesives are useful in preparing a wide variety of articles.
BACKGROUND OF THE INVENTION
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. Of these, (meth)acrylate-based polymer PSAs have evolved as a preferred class of PSA due to their optical clarity, permanence of properties over time, and versatility of adhesion levels, to name just a few of the their benefits. It is known to prepare PSAs comprising mixtures of certain (meth)acrylate-based polymers with certain other types of polymers.
European Patent Application No. 0 254 002 (Sumitomo Chemical Co. Ltd.) describes PSAs comprising at least one elastomer (e.g., natural rubber, styrene-butadiene rubber, and acrylic rubber), at least one tackifier, and an ethylene-propylene copolymer having such a low molecular weight that the intrinsic viscosity is not more than 0.5. The ethylene-propylene copolymer is obtainable by oxidative degradation of a corresponding ethylene-propylene copolymer containing 30-60 weight % of propylene. The amount of ethylene-propylene copolymer is in the range of 5-40 parts by weight based on 100 parts by weight of the elastomer. It is taught that the PSA therein is ordinarily dissolved in toluene or the like, coated on a substrate, and then dried to remove the solvent.
U.S. Pat. No. 5,202,361 (Zimmerman et al.) teaches another approach to preparing PSAs using certain (meth)acrylate polymers in combination with certain alpha-olefin polymers. Specifically, the alpha-olefins have a glass transition temperature (Tg) of about −70° C. to about −10° C. and a weight average molecular weight of about 25,000 to about 5,000,000. Furthermore, at least 60 mole % of the olefin monomers used to prepare the alpha-olefin polymers have 6 to 18 carbon atoms. The PSAs purportedly have good adhesion to both low and high energy surfaces. It is taught that the alpha-olefin polymer is dissolved in a mixture of free-radically polymerizable monomers and a photoinitiator/crosslinker. The liquid composition is then coated on a substrate and cured by irradiating the composition using ultraviolet radiation.
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. Among useful PSAs described therein are acrylics and poly alpha-olefins. 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, which are melt processable, as having a substantially continuous domain (generally the PSA) and a substantially fibrillous to schistose domain (generally the thermoplastic material). Tackifiers may be added.
PCT Publication No. WO 96/25,469 (Minnesota Mining and Manufacturing Co.) describes PSAs that are a blend of about 5 to 95 weight percent of an acrylic PSA and about 5 to about 95 weight percent of a thermoplastic elastomeric copolymer. The thermoplastic elastomeric materials are materials that contain at least two segments, i.e., a hard segment and a soft segment. Useful thermoplastic elastomeric materials include styrene-(ethylene-propylene) block copolymers, polyolefin-based thermoplastic elastomeric materials represented by the formula —(CH
2
CHR)x, where R is an alkyl group containing 2 to 10 carbon atoms, and polyolefins based on metallocene catalysis, such as an ethylene/1-octene copolymer. The blends are melt processable.
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, farther adhesives for adequately adhering to low surface energy surfaces, especially those adhesives that perform without comprising adherence to high surface energy substrates, are desired. Similarly, adhesives with improved adherence to high surface energy substrates are beneficial.
It is also desired that any such new adhesives will allow for broad formulation latitude and tailorability for particular applications. For example, in some applications it is desirable to have a hot-melt processable composition, as opposed to those compositions that are coated on a substrate and subsequently dried or cured. It is also preferred to use (meth)acrylate polymers in such adhesives, due to their desirable properties. The present invention addresses these motivating factors.
SUMMARY OF THE INVENTION
PSA blends of the invention are particularly useful for adhering to both relatively high and low surface energy materials. PSA blends of the invention are capable of providing adequate or improved peel adhesion to such substrates. Surprisingly, in preferred embodiments of the invention, peel adhesion to low surface energy substrates, such as polypropylene, is enhanced as compared to peel adhesion of the (meth)acrylate polymer without the propylene-derived polymer to low surface energy substrates or peel adhesion of the propylene-derived polymer without the (meth)acrylate polymer to low surface energy substrates. This enhancement is even possible in some embodiments without causing detrimental effects in peel adhesion to high surface energy substrates. According to other aspects of the invention, peel adhesion to high surface energy substrates, such as glass, is enhanced as compared to peel adhesion of the (meth)acrylate polymer without the propylene-derived polymer to high surface energy substrates or peel adhesion of the propylene-derived polymer without the (meth)acrylate polymer to high surface energy substrates. Useful shear strengths are also realizable using the blends of this invention.
Certain embodiments of the invention provide substrates with the pressure sensitive adhesive composition at least partially applied thereon. Other embodiments of the invention provide fibers and microfiber webs comprising the pressure sensitive adhesive composition.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Pressure sensitive adhesive (PSA) blends of the present invention comprise at least one (meth)acrylate polymer and at least one propylene-derived polymer. Terms used throughout to assist in describing the invention are defined in turn below.
“Polymer” refers to macromolecular materials having at least five repeating monomeric units, which may or may not be the same. The term “polymer”, as used herein, encompasses homopolymers and copolymers. Copolymers of the invention refer to those polymers derived from at least two chemically different monomers. Included within the definition of copolymers are traditional copolymers derived from at least five monomers, which include only two chemically different types of monomers, as well as terpolymers, which i
Bennett Greggory S.
Joseph Eugene G.
Khandpur Ashish K.
3M Innovative Properties Company
Nutter Nathan M.
Pribnow Scott R.
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