Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Adhesive outermost layer
Reexamination Certificate
1998-05-29
2001-01-23
Morris, Terrel (Department: 1771)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Adhesive outermost layer
C522S112000, C522S157000, C522S158000, C522S160000, C522S161000
Reexamination Certificate
active
06177190
ABSTRACT:
TECHNICAL FIELD
This invention relates to pressure-sensitive adhesive compositions, and, more particularly, to pressure-sensitive adhesive compositions formed from at least two polymeric materials at least one of which is a poly(1-alkene) based pressure-sensitive adhesive, to methods for making such pressure-sensitive adhesive compositions, and to tapes and articles including such pressure-sensitive adhesive compositions.
BACKGROUND OF THE INVENTION
Pressure-sensitive adhesive tapes are used for many diverse applications including, for example, marking, holding, protecting, sealing and masking purposes. These tapes comprise a backing, or other substrate, and a pressure-sensitive adhesive. Pressure-sensitive adhesives used in pressure-sensitive adhesive tapes generally adhere with no more than applied finger pressure and often stay tacky for months or years. Pressure-sensitive adhesives exert a strong holding force and should be removable from a smooth surface without leaving a residue.
In the medical field, pressure-sensitive adhesive tapes may be used, for example, to secure a wound dressing or to restrict movement of a joint or limb. It is important that the pressure-sensitive adhesive tape adhere well to skin without causing skin damage on removal.
Electrical tapes typically comprise a pressure-sensitive adhesive applied to a plasticized polyvinyl chloride backing or a polyethylene or rubber film backing. Electrical tape is used to insulate, hold, reinforce and protect electrical wires. Other uses include identifying wires in electrical circuitry, and protecting terminals during manufacture of electrical circuit boards.
Packaging applications require a large variety of tapes for uses such as closing packages, protecting labels, sealing packages from moisture, and strapping and bundling loose parts. Packaging tapes are subjected to continuous shear and low angle peel forces. Generally, if the adhesive mass is of low cohesive strength, it fails in shear; if the shear resistance is improved by adding firmness to the adhesive, it has a tendency to be less tacky and fail adhesively.
Pressure-sensitive adhesives require a delicate balance of viscous and elastic properties which result in a four-fold balance of adhesion, cohesion, stretchiness and elasticity. Pressure-sensitive adhesives generally comprise polymers that are inherently tacky or polymers that are tackified by the addition of tackifying resins.
Major classes of pressure-sensitive adhesives include tackified natural rubbers; synthetic rubbers such as butyl rubber; and tackified linear, radial, star, branched and tapered block copolymers such as styrene-butadiene, styrene-ethylene/butylene and styrene-isoprene; polyvinyl ethers; acrylics, especially those having long chain alkyl groups; poly(1-alkene)s (also referred to as poly-&agr;-olefins); and silicones.
Polyolefin catalyst systems (i.e., Ziegler-Natta (ZN) and metallocene) have made it possible to synthesize high molecular weight poly(1-alkene) pressure-sensitive adhesives including homopolymers of C
6
to C
10
poly(1-alkenes).
Another type of poly(1-alkene) material, by-products of isotactic polypropylene that are described as atactic copolymers of C
3
-C
6
and C
3
-C
8
with molecular weights up to 50,000, have found uses as hot melt adhesives. These copolymers also make pressure-sensitive adhesives when mixed with tackifiers.
Pressure-sensitive adhesives comprising blends of poly(1-alkenes) and flow-control agents are used to protect surfaces such as automobile paint finishes and may be removed without leaving residue.
Radiation crosslinking of poly(1-alkene) homopolymer or copolymer compositions (both Ziegler Natta-catalyzed and metallocene-catalyzed) has been accomplished.
SUMMARY OF THE INVENTION
The present invention provides a radiation-curable pressure-sensitive adhesive composition, comprising:
(a) a pressure-sensitive adhesive component comprising at least one poly(1-alkene);
(b) about 2 to about 100 parts by weight, based on 100 parts by weight of said pressure-sensitive adhesive component, of a polymer component comprising at least one non-pressure-sensitive adhesive polymer having reactive sites for crosslinking; and
(c) a sufficient amount of at least one crosslinking agent to crosslink (a) and (b) to provide on curing a crosslinked pressure-sensitive adhesive composition with (i) shear strength at least 300% greater than, and peel adhesion not less than 80% of, that of a crosslinked composition consisting essentially of the reaction product of components (a) and (c), or with (ii) shear strength and peel adhesion each not less than 80% of those of a crosslinked composition consisting essentially of components (a) and (c) produced under (1) the same cure conditions including the same curing energy dose, except at a process speed that is at least 100% faster than the process speed for producing the crosslinked reaction product consisting essentially of components (a) and (c) or (2) the same process speed, but with cure conditions comprising a curing energy dosage that is at least 50% less than the curing energy dosage for producing the crosslinked reaction product consisting essentially of components (a) and (c). Optionally, the composition may further comprise tackifiers and/or other additives such as plasticizers and fillers.
Certain pressure-sensitive adhesive compositions according to the present invention will not necessarily have all of the beneficial physical properties defined in the previous paragraph. Such pressure-sensitive adhesive compositions may be further defined as radiation curable pressure-sensitive adhesive compositions comprising (a) a pressure-sensitive adhesive component comprising at least one poly(1-alkene) with an inherent viscosity of at least about 0.4 deciliters/gram (dL/g), (b) from about 2 to about 100 parts by weight, per 100 parts of the pressure-sensitive adhesive component, of a polymer component comprising at least one non-pressure-sensitive polymer having (i) a G′ of at least about 5×10
6
dynes/cm
2
at 1 Hz and at the use temperature, and (ii) a tertiary carbon content of about 1 to about 50 mole percent, based on the total moles of the polymer component, provided that if the tertiary carbon content of the polymer component is about 1 to about 10 mole percent, the shear viscosity of the polymer component is greater than about 500 Pa-s at 175° C., and (c) a radiation activatable crosslinking agent. Optionally, the pressure-sensitive adhesive composition may further comprise tackifiers and/or other additives.
Further provided is a method of making a radiation crosslinkable pressure-sensitive adhesive composition comprising melt mixing (i) a pressure-sensitive adhesive component having at least one poly(1-alkene) with an inherent viscosity greater than about 0.4 dL/g, (ii) about 2 to about 100 parts by weight, per 100 parts of said pressure-sensitive adhesive component, of a polymer component comprising at least one non-pressure-sensitive polymer having a G′ of at least about 5×10
6
dynes/cm
2
at 1 Hz at the use temperature and having a tertiary carbon content of about 1 to about 50 mole percent, based on the total moles of the polymer component, provided that if the tertiary carbon mole percent is from about 1 to about 10 mole percent, the polymer component has a shear viscosity greater than about 500 Pa-s at 175° C., and (iii) a radiation activatable crosslinking agent. A pressure-sensitive adhesive article can be made by (1) forming said composition into a shaped article, and (2) cooling, if needed, the shaped article. The shaped article may be a pressure-sensitive adhesive suitable for subsequent lamination to a surface or may be a pressure-sensitive adhesive layer on a substrate. The radiation crosslinkable pressure-sensitive adhesive may be exposed to radiation to create a partially or fully radiation crosslinked pressure-sensitive adhesive.
The method may be used to make poly(1-alkene) pressure-sensitive adhesives having improved shear properties and approximately equivalent peel
Brown Chad Everett
Gehlsen Mark David
Hyde Patrick Darby
Joseph Eugene Gregory
Kolpe Vasant Venugopal
3M Innovative Properties Company
Gover Melanie
Gupta Sharmistha
Morris Terrel
LandOfFree
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