Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Adhesive outermost layer
Reexamination Certificate
2000-12-29
2002-10-08
Seidleck, James J. (Department: 1771)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Adhesive outermost layer
C428S349000, C428S3550RA, C428S3550EN, C428S3550AC, C428S412000, C428S421000, C428S423100, C428S426000, C428S457000, C428S478200, C428S474400, C428S480000, C428S492000, C428S500000, C428S532000, C428S537100, C428S537500, C428S688000, C522S084000, C522S182000, C522S184000, C522S173000, C522S174000, C522S178000, C522S150000, C524S804000, C524S816000, C524S819000, C524S820000, C524S821000, C524S823000, C524S827000, C524S832000, C524S833000
Reexamination Certificate
active
06461728
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to pressure sensitive adhesives formed using gamma irradiation, methods of using the pressure sensitive adhesives, and articles containing the pressure sensitive adhesives.
BACKGROUND OF THE INVENTION
The advantage of acrylic polymers as viscoelastic bases for pressure-sensitive adhesives (PSAs) are well known. Pressure-sensitive adhesives have been used for more than half a century for a variety of marking, holding, protecting, sealing, and masking purposes. Fundamentally, PSAs require a delicate balance of viscous and elastic properties, which result in a 4-fold balance of adhesion, cohesion, stretchiness, and elasticity. In essence, PSA products have sufficient cohesiveness and elasticity so that, despite their tackiness, they can be handled with the fingers and can typically be removed from smooth surfaces without leaving a substantial amount of residue.
There are several methods presently in use for the preparation of PSAs. These methods include a variety of polymerization methods including batch, hot melt, solution, thermal emulsion, suspension, ultra-violet (UV)-initiated bulk, and UV-initiated on-web polymerization techniques. Monomer and initiator residues produced in some of these methods can prevent the attainment of desirable levels of properties (e.g., peel adhesion and shear strength) and some of these methods are relatively slow.
For example, acrylic polymer compositions can be used to make PSAs by solution polymerization. The solution polymerization methods generally use relatively large amounts of organic solvents. Polymers in solvent may be difficult to handle and transport due to the volume of the solvent and the potential release of volatile organic compounds (VOCs) into the atmosphere. Using solvents also necessitates high heat or vacuum to remove the solvent from the polymer.
SUMMARY OF THE INVENTION
Generally, the present invention relates to pressure sensitive adhesives formed using gamma irradiation. One embodiment is a pressure sensitive adhesive comprising a polymeric reaction product formed by gamma ray irradiation of an emulsion composition. The emulsion composition comprises water; (meth)acrylate monomer material; polar, free-radically polymerizable material that is copolymerizable with the (meth)acrylate monomer material; and at least one emulsifier. Yet another embodiment is like the first embodiment, as described above, wherein the polymeric reaction product is formed in the absence of any initiator selected from the group consisting of photoinitiators and thermal initiators.
Another embodiment is a pressure sensitive adhesive-forming emulsion composition comprising a polymeric reaction product formed by gamma irradiation of a composition. The composition comprising water; (meth)acrylate monomer material; polar, free-radically polymerizable material that is copolymerizable with the (meth)acrylate monomer material; and at least one emulsifier.
Yet another embodiment is a method of making a pressure sensitive adhesive, the method comprising the steps of: forming an emulsion composition comprising water, (meth)acrylate monomer material, polar, free-radically polymerizable material that is copolymerizable with the (meth)acrylate monomer material, and at least one emulsifier; and irradiating at least a portion of the emulsion composition with gamma rays to initiate polymerization of the emulsion composition. An additional embodiment is the method described above and further comprising the step of removing at least a portion of the water from the emulsion composition after irradiating at least a portion of the emulsion composition. A further embodiment is the method, as described above, wherein the step of irradiating at least a portion of the emulsion composition comprises irradiating the emulsion composition substantially uniformly.
An additional embodiment is an article comprising: a substrate; and a pressure sensitive adhesive disposed on at least one surface of the substrate, the pressure sensitive adhesive comprising a polymeric reaction product formed by gamma irradiation of an emulsion composition comprising water, (meth)acrylate monomer material, polar, free-radically polymerizable material that is copolymerizable with the (meth)acrylate monomer material, and at least one emulsifier.
Another embodiment is a pressure sensitive adhesive which is a polymeric reaction product of a composition. The composition comprises: water; (meth)acrylate monomer material; polar, free-radically polymerizable material that is copolymerizable with the (meth)acrylate monomer material; and an emulsifier. The polymeric reaction product has a shear strength of at least 5000 minutes at room temperature using a 1 kg weight and a peel adhesion of at least 45 N/dm at, at least room temperature. In another embodiment, the shear strength was at least 10,000 minutes. In yet another embodiment, the peel adhesion was at least 50 N/dm. In another embodiment, the peel adhesion was at least 50 N/dm and the shear strength was at least 10,000 minutes.
The above summary of the present invention is not intended to describe each disclosed embodiment or every implementation of the present invention. The detailed description which follows more particularly exemplifies these embodiments.
DETAILED DESCRIPTION
The present invention is believed to be applicable to pressure sensitive adhesives, methods of using the pressure sensitive adhesives, and articles containing the pressure sensitive adhesives. In particular, the present invention is directed to pressure sensitive adhesives formed by gamma irradiation, methods of using the pressure sensitive adhesives, and articles containing the pressure sensitive adhesives. While the present invention is not so limited, an appreciation of various aspects of the invention will be gained through a discussion of the examples provided below.
At least some embodiments of both the pressure sensitive adhesives of the invention and the methods of the invention to make pressure sensitive adhesives offer advantages not available currently. Water-based latex pressure sensitive adhesives of the invention can have excellent adhesive properties including a satisfactory range of both peel adhesion and shear strength performance. Some embodiments are particularly useful in applications that are adversely impacted if initiator residue is present in the adhesive. The method of making pressure sensitive adhesives can enable the use of higher solids emulsions. This can result in less need to adjust emulsion viscosity for a subsequent coating operation and lower energy cost to dry the applied adhesive coating.
Generally, the pressure sensitive adhesives of the invention are formed by gamma radiation polymerization of an emulsion containing water; (meth)acrylate monomer material; polar, free-radically copolymerizable material that is copolymerizable with the (meth)acrylate monomer material; and an emulsifier. Other components can also be added for particular application or to obtain desired properties including, for example, other copolymerizable materials, tackifying agents, crosslinking agents, free radical initiators, plasticizers, dyes, pigments, antioxidants, UV stabilizers, thickening agents, electro-conductivity agents, reflective agents, antistatic agents, inorganic materials, biocides (bactericides, fungicides), bioactive agents, pharmaceutical aids, releasable agents, cosmetic agents, rheology modifiers, and the like. The pressure sensitive adhesives can, if desired, have good peel adhesion, good shear strength, or a combination of these properties.
The terms “(meth)acrylate” or “(meth)acrylates” are used throughout this application and are meant to include both acrylate(s) and methacrylate(s).
The amounts of each component in the emulsion are typically present in a number of parts per 100 parts of the combined (meth)acrylate monomer material; polar, free-radically copolymerizable material; and any other copolymerizable material. Henceforth this basis is called the total free-radically copolymerizable material.
Leisinger Karen J.
Tran Thu-Van T.
Weiss Douglas E.
3M Innovative Properties Company
McClendon Sanza L.
Seidleck James J.
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