Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Compositions to be polymerized by wave energy wherein said...
Reexamination Certificate
2000-09-08
2002-09-10
Seidleck, James J. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Compositions to be polymerized by wave energy wherein said...
C522S008000, C522S035000, C522S904000, C522S150000, C522S153000, C522S157000, C522S178000, C522S182000, C522S184000, C522S114000, C522S113000, C522S120000, C522S121000, C522S125000, C526S328000, C526S328500
Reexamination Certificate
active
06448301
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
This invention relates to polymeric compositions that are processible and may be photochemically cured to produce crosslinked compositions useful in coating, sealants, adhesive and many other applications
BACKGROUND OF THE INVENTION
For coating, sealant and adhesive applications, much research has focused on acrylic pressure sensitive adhesives (PSAs), which exhibit good adherence to high energy (i.e., polar) substrates such as metal and painted steel surfaces and which have good performance properties at high temperatures (i.e., 100° C. or greater), are known in the art. Crosslinking acrylic compositions so as to form crosslinked PSAs is an area of much interest and research.
Solvent-processed acrylic PSA compositions can be crosslinked through the addition of polyfunctional crosslinking agents that react with functionalities within the polymer. See, e.g., Japanese Kokoku No. 58[1983]-046236. However, such processes result in the emission of solvent vapors.
The difficulty of additional processing steps, necessary to incorporate polyfunctional crosslinking agents into acrylic PSAs, can be avoided by the use of latent crosslinking reactions. This technique is exemplified in U.S. Pat. No. 4,812,541, where synergistic amounts of an N-vinyl lactam monomer and a glycidyl monomer are incorporated into an acrylate polymer to provide a high performance PSA; however, these latent crosslinked polyacrylates require post-curing that requires additional heat and/or time. Pendent functional group-containing polymers are also described in U.S. Pat. Nos. 4,908,229, 5,122,567, and 5,274,063.
The problems associated with solvent processing and crosslinking bulk-processed acrylate PSAs can be avoided through the use of actinic radiation processing. PSAs made by photopolymerizing an alkyl acrylate and a polar copolymerizable monomer (e.g., acrylic acid, N-vinyl pyrrolidone, etc.) are known in the art. See, e.g., U.S. Pat. Nos. RE 24,906, 4,181,752, 4,364,972, and 4,243,500. The cohesive strength of an acrylic PSA prepared in this manner can be increased if a photoactive crosslinking agent such as an aldehyde, a quinone, or a chromophore-substituted halomethyl-s-triazine is used in conjunction with a photoinitiator. See, e.g., U.S. Pat. Nos. 4,329,384, 4,330,590, 4,391,687, and 5,202,361. However, this type of photocrosslinking process is affected by the thickness of the composition.
In addition to actinic radiation processing, acrylate PSAs can be applied to substrates by solvent and hot-melt coating techniques. Although solvent coating techniques are widely used, hot-melt coating techniques provide some environmental and economical advantages. However, unlike solvent coating techniques where the polymer coating and crosslinking are performed simultaneously, hot-melt coating requires that coating and crosslinking be performed sequentially. This is due to competing considerations a polymer cannot be hot-melt coated effectively if it is crosslinked, yet the polymer needs to be crosslinked to achieve certain desirable performance properties (e.g., cohesive strength where the polymer is a PSA). Therefore, hot-melt coating is performed prior to crosslinking of the coated polymer.
Because hot-melt coating techniques involve high amounts of thermal energy and shear, the subsequent crosslinking procedure usually involves non-thermal energy sources. Electron beam (E-beam) and ultraviolet (UV) energy sources have been used traditionally, although E-beam techniques often are too energy intensive to be practical. Accordingly, much interest has been focused on UV radiation techniques.
U.S. Pat. No. 5,741,543 (Winslow et al.) describes a syrup polymer process in which a composition containing monomers is coated onto a substrate and crosslinked so as to form a PSA by means of polymerizing free radically polymerizable monomers from covalently attached pendent unsaturation in the polymer component of the composition. The coating can be carried out by a wide variety of industrial methods because the process of the invention allows for compositions with a wide degree of possible viscosities.
SUMMARY OF THE INVENTION
Briefly, the present invention provides novel melt-processible compositions prepared from a first polymer having a plurality of pendent polymerizable functional groups and a polymeric photoinitiator. The composition may further comprise a second component with co-reactive pendent polymerizable groups. The functional groups are reactive by free-radical addition (e.g. free radical addition to a carbon-carbon double bond). In addition, reactions involving polymeric reactants of the instant invention are controlled and precise in that they result in polymer-polymer coupling reactions only by reaction between the pendent free-radically polymerizable functional groups. The novel composition has been discovered to provide low shrinkage, low residual compositions whose properties are easily tailored to the desired end-uses. Residuals include monomers, solvents, or other volatile components.
In one aspect this invention provides crosslinkable composition comprising
a) a first component having a plurality of pendent free-radically polymerizable functional groups;
b) a polymeric photoinitiator, and
c) a residual content of less than 2.0 wt. %, preferably less than 1.0 wt. %, most preferably less than 0.1 wt. %,
wherein said composition is melt processible at temperatures of less than or equal to 100° C.
The first component is selected from:
1) a first polymer having a plurality of pendent polymerizable functional groups, and
2) a first polyfunctional compound having a plurality of pendent polymerizable functional groups.
The composition may further comprise a second component that may be selected from a second polymer having a plurality of pendent polymerizable functional groups, and a second polyfunctional compound having a plurality of pendent polymerizable functional groups.
In another aspect this invention provides a UV crosslinkable composition that produces no or minimal by-products, and that achieves crosslink density by chain-growth addition. This invention has several advantages. The composition is low in viscosity, readily melt processible and coatable, and has minimal residuals content such as solvents, monomers, plasticizers and/or viscosity modifiers. The compositions can rapidly and reliably be prepared without requiring specialized equipment and without generating concerns about potentially toxic or irritating unreacted low molecular weight monomeric species.
The compositions may be used as coatings, including hard surface coatings, clear coatings, powder coatings and pattern coatings; as adhesives, including pressure sensitive adhesives and hot melt adhesives; as sealants; as optical coatings; as blown microfibers (BMF); as high refractive index optical materials; as barrier films; in microreplication; as low adhesion backsizes, (LABs) and as release coatings.
As used herein, the term “melt processible” or simply “processible” is used to refer to polymer compositions that possess or achieve a suitable low viscosity for coating or extrusion at temperatures less than or equal to 100° C., using conventional extrusion equipment without the need for addition of solvents, monomers, plasticizers and/or viscosity modifiers and without the need for extraordinary pressures.
The crosslinked compositions are useful as adhesives, including pressure sensitive adhesives, as sealants, as foams and as coatings. In one embodiment the invention provides an adhesive article comprising the crosslinked composition coated on a substrate, such as a tape backing. The novel compositions of the present invention cure by means of polymerizable functional groups to form crosslinked compositions possessing tailorable properties such as shear, peel, release and strength through selection of the particular constituents, and by control of the crosslink density. The crosslink density is predetermined by the percentage of free-radically polymerizable functional groups incorporated into the
Abuelyaman Ahmed S.
Fansler Duane D.
Gaddam Babu N.
Heilmann Steven M.
Kavanagh Maureen A.
3M Innovative Properties Company
Kokko Kent S.
McClendon Sanza L.
Seidleck James J.
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