Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
2000-03-31
2001-09-18
Mayes, Curtis (Department: 1734)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C156S272600, C156S277000, C053S396000, C053S425000, C053S476000
Reexamination Certificate
active
06290801
ABSTRACT:
BACKGROUND OF THE INVENTION
Cold seal packages have openings that are sealed under the application of pressure without the need for the application of elevated temperatures. Cold seal packaging can be used to package a variety of goods, including comestibles, pharmaceuticals, and medical supplies. They typically utilize cold seal adhesives such as natural rubber (also referred to as latex rubber). Such cold seal adhesives are differentiated from heat seal adhesives in that heat seal adhesives typically require both elevated temperature and pressure for activation. Cold seal adhesives are used as an alternative in packaging because heat seal adhesives have limitations in manufacturing. For example, heat seal adhesives require additional time for thermal diffusion to activate them.
Natural rubber (or latex rubber) has several disadvantages. Of particular concern is that it can initiate an allergic response in people. It is believed that certain people become sensitized to allergens in natural rubber over repeated exposure to natural rubber and, thus, exhibit increasingly severe allergic responses upon each exposure. This is particularly significant in the medical area where both health care workers and chronically ill patients are repeatedly and directly exposed to products, such as natural rubber gloves, tubing, and the like. To a lesser extent, medical packaging for wound dressings and bandages may also contain natural rubber in the cold seal adhesives used in packaging. Other disadvantages of natural rubber include discoloration upon aging and an unpleasant odor.
Synthetic cold seal adhesives have been incorporated into packaging to overcome the disadvantages associated with natural rubber. For example, U.S. Pat. No. 4,442,259 (Isgur et al.) describes the use of aqueous based polyurethanes in cold seal packaging applications. U.S. Pat. No. 5,616,400 (Zhang) describes a cold seal adhesive for use in forming packages. The cold seal adhesive is formed from a polyurethane ionomer, wherein overlapping coatings of the cold seal adhesive are pressed together forming an envelope enclosing an item packaged. That is, the seal is formed between the same substrates and same adhesives with no difference in adhesion at the two interfaces between the layer of adhesive and the substrates.
While these patents have described the adhesive characteristics of these synthetic cold seal materials, the opening characteristics of packaging remain an important consideration. This is of particular concern in packaging pharmaceutical and medical supplies to maintain sterility within the package. Evidence of tampering or breach of the cold seal are important features of such packaging. However, a competing interest is also opening the bond formed in a package with a cold seal material. For example, it is desirable that the package be easily opened with controlled predictable motion and force resulting in a decreased likelihood of spillage of the package contents.
Thus, what is yet needed is a cold seal package which exhibits sufficient bond strength and yet is easily opened and preferably provides evidence of prior opening.
SUMMARY OF THE INVENTION
Methods for making a cold seal package and cold seal packages are provided by the present invention. A cold seal package generally includes constructions wherein two substrates, which can be two discrete portions of a contiguous sheet material, for example, are sealingly engaged to one another, preferably, to form a sealed enclosure for placement of an article therein. The two sealing portions of the substrate(s) can be generally easily and cleanly peeled apart without substantial damage to the substrate(s). Furthermore, the sealing portions of the substrate(s) cannot typically be resealed, or refastened, once peeled apart, thereby forming a substantially “non-refastenable cold seal.” By this it is meant that after initially sealing, opening, and then again engaging the sealing portions of the substrate(s), a very small or nonexistent force would be required for reopening the package.
This non-refastenable cold seal can be formed, for example, between two sealing portions of the substrate(s) and two layers of contact adhesive, which may be the same or different. The bond formed at the interface of the two layers of contact adhesive is typically a substantially permanent bond (referred to herein as a cold seal bond or a cold seal adhesive bond). That is, upon opening the package of the present invention at the cold seal, the layers of adhesive are not separated from each other. The bond formed at the interface of a layer of the contact adhesive and one of the substrates (i.e., the anchor substrate) is also typically a permanent bond, whereas the bond formed at the interface of a layer of the contact adhesive and the other substrate (i.e., the transfer substrate) is a peelable and nonrefastenable bond. The bond at the interface of the layer of the contact adhesive and the transfer substrate is peelable as a result of a layer of a release coating on the surface of the transfer substrate. The peelability may result from release of the adhesive and the release coating from the transfer substrate, or portions thereof, or from release of just the adhesive with the release coating remaining on the transfer substrate.
In one embodiment, the present invention provides a method for making a cold seal package comprising the steps of: applying a first substantially natural latex rubber-free contact adhesive to an anchor surface to form an anchor contact adhesive coating; applying a release coating composition to a transfer surface to form a release-coated transfer surface; applying a second substantially natural latex rubber-free contact adhesive to the release-coated transfer surface to form a transfer contact adhesive coating; and contacting the anchor contact adhesive coating with the transfer contact adhesive coating, each of which are at a temperature of about 50° C. or less, to form a substantially non-refastenable cold seal between the anchor surface and the release-coated transfer surface; wherein, upon peeling the anchor and transfer surfaces apart, substantially all of the anchor contact adhesive coating and the transfer contact adhesive coating that formed the cold seal remain on the anchor surface. It will be understood that there may be other portions of the transfer contact adhesive that were not used in forming the cold seal that remain on the transfer substrate depending on the coating patterns of the contact adhesive layers and release coating.
The first substantially natural latex rubber-free contact adhesive and the second substantially natural latex rubber-free contact adhesive may be the same contact adhesive or they may be different contact adhesives. Preferably, the contact adhesives have an open time of at least about 24 hours at a temperature of about 50° C. or less. The first and second substantially natural latex rubber-free contact adhesives preferably each comprise a material selected from the group of a polychloroprene, a polyurethane, a styrene-isoprene copolymer, a styrene-butadiene copolymer, a polyimide, a polyvinyl chloride, a nitrocellulose, a polyisoprene, an acrylonitrile-butadiene-isoprene terpolymer, a butadiene-methacrylonitrile copolymer, a polyethylene-vinyl acetate copolymer, a polyacrylate, and mixtures thereof. Preferably, at least one of the first and second substantially natural latex rubber-free contact adhesives is formed from an aqueous polyurethane dispersion.
Preferably and advantageously for enhanced adhesion of the contact adhesive, the anchor surface is treated prior to applying the first substantially natural latex rubber-free contact adhesive. This step of treating the anchor surface preferably involves corona treating the anchor surface, although other treatment techniques can be used, such as flame treatment or coating with a primer, for example.
Upon applying the release coating composition to a transfer surface, preferably and advantageously, a substantially continuous release coating is formed. By this it is m
Delmore Michael D.
Krampe Stephen E.
3M Innovative Properties Company
Gwin Doreen S. L.
Mayes Curtis
LandOfFree
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