Stock material or miscellaneous articles – Layer or component removable to expose adhesive
Reexamination Certificate
2002-02-13
2004-04-20
Ahmad, Nasser (Department: 1772)
Stock material or miscellaneous articles
Layer or component removable to expose adhesive
C428S041300, C428S212000, C428S213000, C428S214000, C428S35500R, C525S089000, C525S094000
Reexamination Certificate
active
06723407
ABSTRACT:
The invention relates to strippable systems comprising at least one pressure sensitive adhesive based on at least one block copolymer.
For the residueless and nondestructive redetachment of self-adhesive tapes by stretching parallel to their bond plane, very particular requirements are imposed on such self-adhesive tapes (also referred to below as strippable self-adhesive tapes). First, such adhesive tapes must be highly extensible, since it is only the stretching deformation which allows the desired detachment from the substrate. Further, such self-adhesive tapes need high cohesion, so that they do not tear under the tensile stress which is necessary in the detachment process. Of special significance is the requirement that the stretching of the self-adhesive tapes on detachment is accompanied by a significant loss of tack. Only such a loss of tack ensures that the stretched self-adhesive strip during the detachment process does not stick in the stretched state to one of the bond partners in the extended state. Absent such a loss of tack, self-adhesive tapes bonded in this way could in many cases no longer be nondestructively removable from the joint.
BACKGROUND OF THE INVENTION
Self-adhesive tapes redetachable residuelessly and nondestructively by extensive stretching in their bond plane from a wide variety of substrates find broad application in the reversible adhesive sticking of articles which are light to moderately heavy, particularly in the home and office sectors. The strippable self-adhesive tape products described in the patent literature make use of single-layer and multilayer constructions. Single-layer products are described, for example, in DE 33 31 016 A1. The multilayer product constructions can be subdivided into those for which the adhesive strip tensile strength that is required for the residueless and nondestructive detachment process is mediated essentially by a backing sheet or a foam material backing—examples of aforementioned self-adhesive tapes can be found, inter alia, in U.S. Pat. No. 4,024,312, WO 92/11332, WO 92/11333, WO 95/06691, and DE 195 31 696 A1—and those for which the tensile strength is mediated substantially by way of the pressure sensitive adhesive. Examples of the latter products are described, inter alia, in DE 196 49 727 A1, DE 196 49 728 A1, DE 196 49 729 A1, DE 197 20 145 A1, and DE 198 20 858 A1. DE 197 08 366 A1 describes multilayer strippable self-adhesive tapes which are composed of a plurality of layers and comprise styrene block copolymers as base elastomer. Reference below to styrene block copolymers shall be taken to mean the class of materials comprising block copolymers composed of at least one polystyrene block and at least one polydiene block (or a partially or fully hydrogenated analog thereof). As compared with DE 33 31 016 A1, such multilayer construction makes it possible in particular to exert selective control over selected parameters which are significant properties for strippable self-adhesive tapes, such as the stripping force, the adhesion, and also the aging stability with respect, for example, to ozonolysis.
Specific embodiments and applications of aforementioned strippable self-adhesive tapes are described in DE42 22 849A1, DE44 28 587A1, DE44 31 914A1, DE 198 42 864 A1, DE 198 42 865 A1, DE 199 38 693 A1, and WO 98/03601 A1, and also in DE 42 33 872 A1, DE 195 11 288 A1, U.S. Pat. No. 5,672,402 A, and WO 94/21157 A1.
While the patent literature presented above describes a large number of different pressure sensitive adhesive systems examples including those based on natural rubber/resin blends, on styrene block copolymer/resin blends, and on random acrylic copolymers, it is nevertheless the case that commercially available strippable self-adhesive tapes use exclusively pressure sensitive adhesives based on styrene block copolymer/resin blends as, for instance, do the products Command® Adhesive from Minnesota Mining and Manufacturing Co. Inc., St. Paul (USA), the tesa® Powerstrips® from Beiersdorf AG, Hamburg (D), and Plastofix® Formula Force 1000 from Plasto S. A. (F). Apart from the tesa® Powerstrips® Deco, which comprise polymers based on saturated elastomer blocks, these systems use styrene block copolymers based on polymer blocks which are unsaturated in the elastomer block.
Advantages of such styrene block copolymer based pressure sensitive adhesives for use in strippable self-adhesive tapes are:
their very high extensibility. Elongations at break are generally greater than 400%, preferably greater than 600%, with particular preference greater than 800%.
the simultaneously very low stress values at moderate degrees of stretching in the range between about 200% and 400% elongation, which, among other things, allow very low detachment forces (stripping forces).
their tensile strength, which despite high extensibility and low stress values at abovementioned average degrees of stretching is very high and which constitutes an essential prerequisite for the residueless and nondestructive redetachment process, especially if the pressure sensitive adhesive itself contributes to the tensile strength of the self-adhesive tape.
their ability to exhibit when being stretched a significantly reduced tack, which is an essential prerequisite for an absence of sticking to one of the substrates while in the stretched state during removal from the joint. Self-adhesive strips which do stick in this way on extension can in many cases no longer be removed nondestructively from a joint by further stretching.
the outstanding bond strengths they can achieve on a variety of substrates having a very wide range of polarities.
Advantages of single-layer strippable self-adhesive tapes based on styrene block copolymers are the simple construction of the product, which is obtainable by a very simple, cost-effective production process; the realization of a wide thickness range; the possibility in principle of producing transparent adhesive tapes, especially tapes with water-clear transparency; and, for the production of punched products, a simple and readily manageable punching process. Advantages of multilayer self-adhesive tapes, consisting of a plurality of styrene block copolymer based layers, are their easy obtainability by coextrusion and the wide variability of layer thicknesses and layer compositions, which allows substantially independent control of surface properties (adhesion) and volume properties (cohesion).
Disadvantages of styrene block copolymer based pressure sensitive adhesives, when using systems which utilize unsaturated polymer chains in the elastomer block, e.g., when using styrene-isoprene-styrene (SIS) and styrene-butadiene-styrene (SBS) block copolymers, include the poor aging stability with respect to ultraviolet radiation and also to thermooxidative degradation and to ozonolysis. Accordingly, it is completely impossible to utilize the advantage of self-adhesive tapes possessing water-clear transparency, because the pressure sensitive adhesive has to be protected from the incidence of light. This is done, for example, by means of light-absorbing additives such as titanium dioxide, whose compounding leads to nontransparent products. It is true that the aging stability of styrene block copolymers containing chemically saturated elastomer blocks, examples being the hydrogenated analogs of SBS and SIS, styrene-ethylene/butylene-styrene (SEBS) and styrene-ethylene/propylene-styrene (SEPS), is much improved, they therefore typically need no light-absorbing additives, and so can be processed more easily to water-clear products. A disadvantage found, however, is typically that the good balance between bond strength and low redetachment forces, which SIS and SBS based pressure sensitive adhesives are known to exhibit, is not achieved. At the same time, in the absence of plasticizers (e.g., liquid resins, aliphatic oils), which are desirable for many formulations, the selection of sufficiently compatible tackifier resins in comparison, say, to SIS is markedly restricted.
A further disadvantage of strippable self-adhe
Dollase Thilo
Husemann Marc
Lühmann Bernd
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