Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Compositions to be polymerized by wave energy wherein said...
Reexamination Certificate
1998-11-13
2002-01-15
Berman, Susan W. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Compositions to be polymerized by wave energy wherein said...
C522S110000, C522S111000, C522S112000, C522S113000, C522S148000, C522S158000, C522S159000, C522S161000, C522S120000, C522S121000, C522S046000, C522S036000, C522S039000, C522S149000, C526S348000, C526S348200, C526S348300, C526S348400, C526S348500, C526S348600, C526S348700
Reexamination Certificate
active
06339112
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to radiation curable compositions comprising at least one metallocene polyolefin. The radiation curable compositions are useful for a variety of applications, particularly as coatings and adhesives. The radiation curable composition may comprise a single metallocene polyolefin, or blend thereof. The ultraviolet curable compositions further comprise at least one photoinitiator and/or at least one photoinduced coupling agent. For pressure sensitive adhesive applications, the radiation curable composition also preferably comprises other ingredients such as a tackifying resins and plasticizers.
BACKGROUND OF THE INVENTION
A continuing need in the coatings and adhesive art, particularly for pressure-sensitive adhesives (PSA's), is the achievement of better control over various mechanical and process properties so that adhesives can be “tailor-made” for specific, highly demanding end-use applications such as packaging, medical, and masking tapes. These applications require a proper balance of properties, and this balance changes with the particular end-use. Similarly, laminating adhesives and coatings are needed which have low volatile content, immediate cure, and excellent adhesion to a variety of substrates, particularly film.
With the discovery of Ziegler-Natta catalysts, it became possible to polymerize &agr;-olefin monomers to high molecular weight. The homopolymers of the C
6
-C
10
&agr;-olefins were naturally tacky and therefore good candidates for PSA's since they had low toxicity, good aging, and favorable oxidative stability. These homopolymers are chemically inert, resistant to plasticizer migration, and relatively inexpensive. Such homopolymers, however, exhibit poor cohesive strength, lacking the shear adhesion necessary for high performance PSA's.
There are several patents directed toward adhesive compositions comprising Ziegler-Natta catalyst derived polymerized &agr;-olefin monomers. Initially, such amorphous polyolefins were used alone or combined with other ingredients to produce hot melt adhesives. Since the amorphous polyolefins used for hot melt adhesives tended to exhibit diminished rather than enhanced shear strength upon exposure to radiation, new combinations of &agr;-olefin monomers that cross-link upon being exposed to radiation were developed.
For example, U.S. Pat. No. 5,112,882, issued to Babu, May 12, 1992; U.S. Pat. No. 5,209,971 issued to Babu, May 11, 1993, as well as WO 93/11184, published Jun. 10, 1993 and EP 0 620 247 A2 published Oct. 19, 1994, teach pressure sensitive adhesive compositions comprising one or more poly(&agr;-olefin) homopolymers, copolymers, terpolymers and tetrapolymers derived from monomers containing 6 to 10 carbon atoms and photoactive crosslinking agents; whereas U.S. Pat. No. 5,298,708, issued to Babu, Mar. 29, 1994, is directed toward a microwave-active tape employing the adhesive composition of the '882 patent.
U.S. Pat. No., 5,202,361, issued to Zimmerman et al., Apr. 13, 1993, teaches radiation-curable, tackifier free compositions containing a blend of certain acrylate esters and monoethylenically-unsaturated copolymerizable monomers, certain &agr;-olefin polymers, and a photoinitiator.
U.S. Pat. No. 5,407,970, issued to Peterson et al., Apr. 18, 1995, teaches adhesive compositions comprising terpolymers C
6
to C
10
unsaturated &agr;-olefin monomers, C
2
to C
5
&agr;-olefin monomers, polyene monomers and an effective amount of photoactive cross-linking agent.
U.S. Pat. No. 5,559,164, issued to Babu, Sep. 24, 1996, teaches compositions radiation curable to pressure sensitive adhesives comprising one or more copolymers of &agr;-olefin of which 90.1 to 99 mole percent are one or more straight chain &agr;-olefins, having 2 to 10 carbon atoms of which at least 55% have 6 to 10 carbon atoms, and 9.9 to 0.1 mole percent are one or more &agr;-olefins having 6 to 20 carbon atoms and at least one methylidyne; an effective amount of a photoactive hydrogen abstracting agent; and optionally a tackifying resin.
“Metallocene polyolefins” have recently been introduced. Metallocene polyolefins are homogeneous linear and substantially linear ethylene polymers prepared using single-site or metallocene catalysts.
Tse et al., U.S. Pat. No. 5,530,054, claims a hot melt adhesive composition consisting essentially of: (a) 30-70 wt-% of a copolymer of ethylene and about 6 to about 30 wt-% of a C
4
to C
20
&agr;-olefin produced in the presence of a catalyst composition comprising a metallocene and an alumoxane and having an M
w
of from about 20,000 to about 100,000; and (b) a hydrocarbon tackifier which is selected from a recited list. Exemplified are compositions consisting of 45 wt-% of ethylene/butene-1 copolymer having a specific gravity of either 0.898 g/cm
3
or 0.901 g/cm
3
.
Tse et al, U.S. Pat. No. 5,548,014, claims a hot melt adhesive composition comprising a blend of ethylene/&agr;-olefin copolymers wherein the first copolymer has a M
w
from about 20,000 to about 39,000 and the second copolymer has a M
w
from about 40,000 to about 100,000. Each of the hot melt adhesives exemplified comprises a blend of copolymers, contains 45 wt-% copolymer, with at least one of the copolymers having a polydispersity greater than 2.5. Furthermore, the lowest density copolymer exemplified has a specific gravity of 0.894 g/cm
3
.
Lakshmanan et al., U.S. Pat. No. 5,397,843, teaches blended polymer compositions comprising an admixture of a copolymer of ethylene and an &agr;-olefin and an amorphous polypropylene and/or amorphous polyolefin, or mixtures thereof. The single &agr;-olefin exemplified is “Flexomer 9042” from Union Carbide, having a 1-butene content of 15 wt-%, a melt index of 5.0 g/10 min., a crystallinity level of 26% and a density of 0.900 g/cm
3
. The “Flexomer” polyolefin depicted in the examples is believed to a have a polydispersity greater than 2.5.
Hence, metallocene polyolefins also found utility for use in finished hot melt adhesive compositions. Although such compositions are believed to be a substantial improvement over the amorphous polyolefins prepared using Ziegler-Natta catalysts, such compositions continue to suffer from poor shear adhesion strength.
There exists a need for adhesive compositions having improved shear strength that can be produced from commercially available materials. The present inventors have now discovered that adhesive compositions based on metallocene polyolefins may be radiation cured to enhance their adhesive properties, particularly shear strength. The resulting adhesive compositions are relatively inexpensive in comparison to the radiation curable compositions of the prior art, since it is not necessary for the adhesive manufacturer to first polymerize the &agr;-olefins. Further, the novel adhesive compositions are surmised to exhibit a balance of properties which is superior to those which have been previously attained.
SUMMARY OF THE INVENTION
The present invention describes metallocene polyolefin-based compositions that consistently crosslink to a reproducible extent upon exposure to a radiation source, thus substantially improving the properties of such compositions, such as the cohesive strength. Surprisingly, the metallocene polyolefin employed may have a significantly lower comonomer content relative to the &agr;-olefin based radiation curable compositions of the prior art. Further, the applicants have found that certain commercially available grades of metallocene polyolefins exhibit a significant increase in static shear upon exposure to radiation while concurrently retaining or improving the peel values.
Accordingly, the present invention is a radiation curable composition comprising at least one metallocene polyolefin. The radiation curable composition may comprise a single metallocene polyolefin or blends thereof. Preferably, the radiation curable composition comprises from about 15 wt-% to 100 wt-% of a metallocene polyolefin having a comonomer content ranging from about 10 mole-% to about 20 mole-%. The co
Acevedo Margarita
Baetzold John P.
Kauffman Thomas F.
Berman Susan W.
H.B. Fuller Licensing & Financing Inc.
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