Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2002-09-03
2004-05-25
Moore, Margaret G. (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S088000, C525S098000, C525S100000, C525S123000, C525S191000, C525S222000, C525S241000
Reexamination Certificate
active
06740711
ABSTRACT:
This invention relates to the use of hot melt pressure sensitive adhesives which adhere well to human and other mammalian skin, and are useful in a variety of medical device products, as well as in industrial and consumer pressure sensitive adhesive products.
The requirements for skin contact pressure sensitive adhesives are stringent. They must adhere well to the skin during a variety of environmental conditions and they must also be removable without leaving any residue on the skin, and without causing significant trauma to the skin. Formulation of such adhesives often involves adding a plasticising additive, such as a tackifier or plasticiser, in order to vary one or other properties of the adhesive such as tack, adhesion cohesive strength etc. Many such additives are of relatively low molecular weight, and as such can contribute negative characteristics to the formulation. In particular, such additives can migrate out of the adhesive, and can adversely affect backing and carrier materials, or can remain on the substrate after removal of the adhesive tape.
Pressure sensitive hot melt adhesives are useful in that they can be processed without the concomitant need to evaporate quantities of solvent or water, and thus have advantages over comparable solution and emulsion pressure sensitive adhesives. With the use of hot melt pressure sensitive adhesives, there are reduced environmental concerns, and reduced costs of dealing with those concerns, because no solvent needs to be recovered or incinerated. As far as emulsion adhesives are concerned, the energy associated with the removal of water, with its high latent heat of evaporation, is saved with the use of hot melt pressure sensitive adhesives. However, it has been found difficult in the past to develop suitable hot melt pressure sensitive adhesives that adhere effectively and safely to human skin, and this has limited the opportunities for cost savings that the hot melt processing promises.
There have been many efforts to develop adhesives that fulfil these criteria. For example U.S. Pat. No. 5,559,165 discloses adhesives for skin use that comprise a high molecular weight block copolymer and 60 to 95 parts of a liquid diluent, for example mineral oil. But the mineral oil inherent in these compositions is capable of migration, to a degree determined in part by the nature of the backing material. Again, U.S. Pat. No. 5,891,957 describes adhesive compositions for skin adhesion and bandage applications comprising a styrene-isoprene-styrene triblock or multiarm copolymer and low-molecular weight styrene-isoprene diblock copolymers having a styrene content of 10-25%. In this case the low molecular weight styrene-isoprene diblock copolymer is functioning as the plasticiser. But the problem with such materials is that, although the compositions are said to provide a pressure sensitive adhesive free of migrating chemicals, they are difficult to process, long times being necessary to incorporate the low molecular weight styrene-isoprene diblock copolymers. This is because of the energy necessary to break down the physical crosslinks in the triblock or multiarm copolymer rubber, due to the association of the glassy styrene residues of each polymer chain.
The present invention consists in a pressure sensitive hot melt adhesive comprising one or more pressure sensitive adhesive matrices and optionally tackifiers and/or plasticisers, characterised in that the adhesive also contains an effective amount of trans-polyoctenamer. The adhesives show reduced migration, tendency, staining tendency, improved compatibility of ingredients and ease of processing and can be used on mammalian skin as components of medical devices, as well as in industrial and consumer products.
The trans-polyoctenamer should constitute at least 0.5 wt. % of the total formulation, preferably at least 2 wt. % and more preferably at least 5 wt. %. The preferred formulations contain 5 to 40 wt. % of this component, more preferably 10 to 30 wt. %.
We have made the surprising discovery that if trans-polyoctenamer, a polymeric rubber, is blended with elastomers that are well-known in the art to provide the basis of pressure sensitive adhesive materials, the resulting formulation behaves as though it is a plasticised formulation. Such formulations perform as pressure sensitive adhesives without the concomitant drawbacks of conventional plasticisers such as migration. Processing of such pressure sensitive adhesive formulations incorporating the trans-polyoctenamer is greatly facilitated.
The benefits of using the trans-polyoctenamer are (a) improved compatibility of different ingredients, (b) improved processibility of the formulation, so that significantly lower blending times and/or lower mixing temperatures are possible so that for example temperature sensitive ingredients can be more readily incorporated and (c) improved adhesion.
Formulations according to the present invention may be based upon any suitable pressure sensitive adhesive material or blend of material. The adhesive matrix may be based on for example polyisobutylene, butyl rubber, polyacrylates, polyurethanes, silicone gum, natural gum rubber, SBR rubber or polyvinyl ether. Thermoplastic elastomers such as styrene-isoprene-styrene block copolymers and styrene-ethylene/propylene-styrene block copolymers may be used, and these may require optional tackifiers and plasticisers. Blends or mixtures of elastomers may be more easily employed, because one of the unique characteristics of trans-polyoctenamer is its ability to act as a compatibilising agent. Conventional additives such as tackifiers, and antioxidants may be present to modify, adjust and stabilise the adhesive and other properties of the matrix.
Trans-polyoctenamer is a crystalline metathesis polymer of cyclooctene with predominantly trans-isomeric double bonds. It is said to contain a mixture of linear polymer and macrocyclic groups within each polymer chain. The trans-polyoctenamer is exemplified by the materials Vestenamer 6213 and 8012, which are available from Hüls AG. The polymer as available from Hüls AG is said to contain 15% by weight of cyclic oligomers and 85% of acyclic polymer. The crystallinity of the polymer is thermally reversible and reforms very rapidly on cooling the polymer below its melting point. While the inventors do not wish to be bound by any particular theory of action, it is believed that the high ring content in the polymer chains serves to aid compatibility between otherwise incompatible elastomers. Also, the polymer crystallinity and the high ring content increases the amount of network formation within the permanently tacky pressure sensitive adhesive continuous phase. Further, the low content of double bonds in the polymer improves the thermal and oxidative stability of the formulation, while the low viscosity of molten trans-polyoctenamer aids the processing of these materials.
Particularly suitable as bases for the pressure sensitive adhesives of the invention are rubbers such as linear or radial A-B-A block copolymers or mixtures of these A-B-A block copolymers with simple A-B block copolymers. These block copolymers can be based on styrene-butadiene, styrene-isoprene, and hydrogenated styrene-diene copolymers such as styrene ethylene-butylene.
Suitable styrene-diene copolymers for the practice of the invention are exemplified by a-blend of linear styrene/isoprene/styrene triblock copolymer and linear styrene/isoprene diblock copolymer. Such a material is available from Shell Chemical as Kraton D-1161 and has a bound styrene content of about 15% and a diblock content of 17%. A second example is a blend of linear styrene/isoprene/styrene triblock copolymer and linear styrene/isoprene diblock copolymer available from Shell Chemical as Kraton D-1117 and which has a bound styrene content of about 17% and a diblock content of 33%.
An example of a suitable hydrogenated styrene-diene copolymer is a thermoplastic elastomer comprising a blend of clear linear triblock and diblock copolymer based on styrene and ethylene/butylene,
Dhaeze Kristine
Lipman Roger David Arnold
Avery Dennison Corporation
Christie Parker & Hale LLP
Moore Margaret G.
Zimmer Marc S
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