Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Compositions to be polymerized by wave energy wherein said...
Patent
1995-08-23
1999-05-11
Berman, Susan W.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Compositions to be polymerized by wave energy wherein said...
522 34, 522 35, 522114, 522121, 522125, 522182, 522904, 526328, 5263285, C08J133/08;133/10
Patent
active
059028360
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention describes a viscoelastomeric material with high shear at ambient and elevated temperatures prepared from a blend of ethylenically unsaturated monomers. A process for making this material is also described.
2. Background Information
Pressure sensitive adhesives (PSAs) made by photopolymerizing an alkyl acrylate and a polar copolymerizable monomer are known in the art. See, e.g., U.S. Pat. Nos. RE 24,906; 4,181,755; 4,364,972; and 4,243,500. Acrylic-based PSAs exhibit good adherence to high energy (i.e., polar) substrates such as metal and painted steel surfaces but generally exhibit lower adhesion to low energy (i.e., nonpolar) substrates such as polyethylene and polypropylene.
Solvent-processed acrylic PSA compositions can be crosslinked by adding a polyfunctional crosslinking agent that reacts with a reactive group which is described a solvent-processed crosslinked acrylic PSA with excellent cohesion that is the reaction product of (a) a polyisocyanate, prepared by reacting (1) an acrylic copolymer having a molecular weight between 1,000 and 30,000 and from 1.7 to 5.0 functional groups that can react with an isocyanate group with (2) a diisocyanate, so that the ratio of isocyanate groups per coreactive functional group is about 2:1, and (b) an adherent copolymer comprising functional groups that can react with an isocyanate group. Like any solvent processing technique, however, the preparation of thick adhesives is difficult because the solvent causes bubbling in the adhesive and the emission of solvent vapors into the atmosphere is undesirable.
To avoid environmental pollution, manufacturing processes that do not require the use of volatile solvents have become of great interest. An early step in this direction for the manufacture of PSA tape was the process described in Belgium Patent No. 675,420. In this process, flexible carriers are coated with acrylic monomers, or mixtures of such monomers with copolymerizable compounds, with the possible addition of a thickening and/or initiating agent, and the monomers are polymerized directly on the carrier using ultraviolet radiation.
Hot melt coating a PSA composition eliminates the necessity of solvent processing. To hot melt process an adhesive composition, the composition must be uncrosslinked during the coating process; however, to achieve a PSA with balanced properties (i.e., peel and shear adhesion), the composition must be crosslinked. In hot melt coating processes, this is usually done by exposure to high energy radiation (e.g., E-beam or high intensity ultraviolet radiation). When high intensity ultraviolet radiation is used, a photoactive crosslinking species such as benzophenone is generally added to the composition. However, this often results in PSAs that display cure gradients. Additionally, thicker sections of PSA compositions cannot be cured this way.
A more efficient method of photocrosslinking involves incorporating hydrogen abstracting moieties into the polymer backbone prior to coating. Such polymers can be hot melt coated and subsequently cured by conventional irradiation techniques. This process is typified by U.S. Pat. No. 4,737,599 where a PSA with good adhesion to skin is described. That process is much more efficient than the high intensity irradiation method described immediately above, but the preparation of a thick PSA section that does not display a cure gradient is not described.
The cohesive strength of an acrylic PSA can be increased without unduly affecting its compliance by utilizing a photoactive crosslinking agent in conjunction with a photoinitiator. See, e.g., U.S. Pat. Nos. 4,181,752; 4,329,384; 4,330,590; 4,391,687, and 5,202,361. Useful photoactive crosslinking agents include various aldehydes, quinones, and particularly certain chromophore-substituted halomethyl-s-triazines (because they provide desirably shortened reaction times and somewhat greater tolerance to oxygen over the non-halomethyl-containing agents), although their use can result in evol
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Babu Gaddam N.
Bennett Greggory S.
Chen Kejian
Vesley George F.
Winslow Louis E.
Berman Susan W.
Knecht III Harold C.
Minnesota Mining and Manufacturing Company
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