Stock material or miscellaneous articles – Layer or component removable to expose adhesive
Reexamination Certificate
1999-12-13
2004-04-27
Ahmad, Nasser (Department: 1772)
Stock material or miscellaneous articles
Layer or component removable to expose adhesive
C428S041300, C428S423100, C428S423300, C428S906000, C428S920000, C428S921000
Reexamination Certificate
active
06726971
ABSTRACT:
INTRODUCTION
This invention relates to pressure-sensitive adhesive tape and, more particularly, to polyurethane adhesive tape which is both clear and thermally stable or flame retardant.
BACKGROUND
Pressure sensitive adhesive tapes, including both roll tape and sheet forms, have long been prepared both as general purpose tapes and as specialty tapes. For applications where optical clarity or adhesive bond longevity is required, acrylic or silicone pressure-sensitive adhesives have traditionally been used. In certain applications, however, such traditional materials do not meet the performance and cost requirements. In particular, for example, various aeronautical applications are found to require pressure-sensitive adhesive tape which meet requirements for low flamability. More specifically, certain applications, especially certain aeronautical applications call for pressure-sensitive adhesive tape having maximum average burn extinguishing time of 15 seconds, maximum average burn length of 8 inches and maximum average drip extinguishing time of 5 seconds, measured in accordance with BSS 7230 Method F2 (12 seconds vertical) published by Boeing Company, (Seattle, Wash., U.S.A.) and set forth in substantial portion as test method 6, below.
Existing tapes meeting such stringent requirements have been found to have shortcomings in other respects. Most notably, it has now been recognized that pressure-sensitive adhesive tape meeting the above-stated thermal stability requirements would and other physical property requirements would also advantageously be substantially clear or transparent. In addition, in certain applications the substantially clear, thermally stable tape must also meet physical property requirements such as weight, elongation, tensile strength, peel,strength, water vapor impermeability, environmental resistance, moisture absorption and puncture resistance. A self-adhesive tape is described in U.S. Pat. No. 5,807,637, which is said to be capable of gap-bridging sealing functions and to form bonds which are stable at both high and low temperatures. Specifically, a double-sided tape is described, based on a cross-linked, non-foam polyurethane substrate. The adhesive compositions suggested for this double-sided tape are known adhesive compositions based on rubber or acrylate chemistry. A high quantity of fillers are employed, however, which are said to contribute to the permanent bond strength achieved by the double sided tape. Fillers such as carbon black, chalk, zinc oxide and the like are disclosed which would render the tape non-transparent. In addition, the cross-linked polyurethane employed in U.S. Pat. No. 5,807,637 would be expected to render the tape undesirably brittle. Adhesive tape employing a polyurethane acrylate layer is described in U.S. Pat. No. 5,858,495 to have a high degree of three-dimensional cross-linking, with resulting brittleness sufficient to prevent removal of the tape from a substrate except in small segments. The pressure sensitive adhesive tape of U.S. Pat. No. 5,858,495 also employs pigment, such that it would not be substantially transparent.
It is an object of the present invention to provide substantially clear adhesive tape which is thermally stable, that is, meeting the above-stated specifications for flame retardancy. It is an object of at least preferred embodiments of the invention to also meet certain physical property requirements. These and other objects of the present invention will be better understood from the following disclosure of the invention and detailed description of certain preferred embodiments.
SUMMARY
In accordance with one aspect, the present invention provides thermally stable, clear, pressure-sensitive adhesive tape comprising a clear polyether-based polyurethane backing film and clear, polyether-based polyurethane pressure-sensitive adhesive coated on one side of the backing film. The polyurethane backing film and/or the polyurethane adhesive incorporates flame retardant effective to render the tape substantially flame retardant. As used here and in the appended claims, the term “flame retardant” means that the pressure-sensitive adhesive tape disclosed here meets the above-stated requirements for thermal stability, specifically, having maximum average burn extinguishing time of 15 seconds, maximum average burn length of 8 inches and maximum average drip extinguishing time of 5 seconds, measured in accordance with BSS 7230 Method F2 (12 seconds vertical) published by Boeing Company and set forth in substantial part as Test Method 6, below. Preferably, both the polyurethane backing film and the solvent based polyurethane incorporate a flame retardant additive.
The term “clear” or “substantially clear” as used here and in the appended claims, means that the PSA tape disclosed here, as applied to the substrate, is substantially transparent, preferably being sufficiently transparent for a person applying the tape to a substrate to view the perimeter of any air bubbles trapped between the tape and the substrate, to which it has been applied, and to view a gap or seam in the underlying substrate through the applied tape and read 12 point OCRA Extended typeface printing. Although the PSA tape disclosed here most preferably is colorless, it optionally may be tinted with color and, nevertheless, be substantially transparent, that is, “clear” as that term is used here.
It will be recognized by those skilled in the art, i.e., those skilled in the field of pressure-sensitive adhesives tapes, that the present invention represents a useful technological advance. More specifically, as further discussed below in connection with certain preferred embodiments, the clear polyurethane backing film and clear, pressure sensitive polyurethane adhesive coated on one side of the polyurethane backing film provides performance characteristics meeting the requirements of certain end use applications, including certain aeronautical applications. In particular, certain preferred embodiments of the adhesive tapes disclosed here provide advantageous performance both in being applied to a substrate and in subsequent performance. More particularly, as noted above, the pressure-sensitive adhesive tapes disclosed here meet the thermal stability requirements applicable to certain aeronautical applications, as well as uses such as floor panel joint protection, galley area floor membrane and lead edge protection. Moreover, it is a particular advantage of the adhesive tapes disclosed here, that they are clear, that is, substantially transparent. This enables air bubbles trapped under the tape to be viewed during application of the tape, so that the air bubbles can be removed to provide better adhesive bonding of the tape to the substrate. In addition, it is possible to view through the tape to observe the location of a seam or gap or the like being sealed by application of the tape, such that the tape can be better centered or otherwise positioned along the seam as it is applied. In addition, it is possible to view through the tape to observe alignment marks or part identification numbers as an additional safeguard to proper assembly of the structure. Additional features and advantages of the invention will be better understood from the following detailed description of certain preferred embodiments.
DETAILED DESCRIPTION OF CERTAIN PREFERRED EMBODIMENTS
The preferred embodiments described here in detail have a clear polyether-based polyurethane backing film. Most preferably, the backing film is a mono-layer backing, that is, a backing formed as a single layer of clear, substantially non-crosslinked polyether-based polyurethane rather than being constructed as a laminate of multiple layers. Suitable materials for the backing film include, for example, polyurethane X-1656 from Deerfield Urethane, Inc. Whately, Mass. and Stevens Urethane, Holyoke, Mass. Other suitable polyether-based polyurethanes for the clear backing film of the PSA tapes disclosed here are commercially available or can be prepared in accordance with known materials, equipment and
Tyco Adhesives LP
Tyco Healthcare Group LP
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