Pressure sensitive adhesive tape

Details Pressure sensitive adhesive tape Pressure sensitive adhesive tape

1998-02-02

2001-03-13

Zirker, Daniel (Department: 1771)

Stock material or miscellaneous articles

Web or sheet containing structurally defined element or...

Adhesive outermost layer

Reexamination Certificate

active

06200677

ABSTRACT:

The present invention relates to a pressure sensitive adhesive tape.
It is conventional to bind wires and cables together using adhesive tape made from a polymeric material. The constituent polymers of such tapes are generally halogenated in order to provide the necessary flame retardance. For example, many tapes are made from polyvinyl chloride (PVC). The main problem of PVC and other halogenated polymers is that upon combustion a large volume of toxic, acidic and highly corrosive hydrogen halide smoke is liberated. In addition there has recently been much debate surrounding the environmental damage caused during the manufacture and disposal of PVC products. Hence there is a need for a halogen-free, recyclable adhesive tape. Ideally the adhesive tape should be suitable for a wide range of automotive and industrial applications and should exhibit sufficient flexibility, softness, flame retardancy and have acceptable unwind and handling properties. Most non-PVC adhesive tapes have no flame retardant properties. Those that do tend to be inflexible. The flexibility of the tape is now a crucial consideration as a common use for such tapes is to bind together the wires and cables of vehicle wiring harnesses. As these harnesses increase in complexity they include increasing numbers of wires which must be received through small holes in the vehicle body.
Thus the flexibility of the harness during installation and in service should not be unduly restricted by the adhesive tape. Such flexibility is frequently achieved by the use of plasticisers having a relatively low molecular weight with respect to that of the host polymer. Certain of these plasticisers have been shown to be carcinogenic. Furthermore, plasticisers in general present problems due to their tendency to migrate from the film into the adhesive, resulting in changes in adhesive performance.
The present invention seeks to provide a recyclable, flexible, pressure sensitive adhesive tape having no halogen component and not being prone to the problems caused by plasticiser migration, but which has acceptable flame retardant properties.
According to the present invention there is provided a pressure sensitive adhesive tape comprising a tape body coated on one side thereof with an adhesive, the tape body comprising the following components:
(a) from 40% to 85% wt. of at least one copolymer of olefin with vinyl- or acrylic esters (hereinafter called “copolymer a”);
(b) from 0% to 20% wt. of low density (less than 0.9 g cm
3
) polyethylene;
(c) from 20% to 55% wt. of inorganic filler and/or flame retardant consisting of any of the following either alone or in combination: aluminum trihydrate filler, zinc borate, an organic polyphosphate, polyammonium phosphate or magnesium hydroxide; and
(d) from 0% to 5% wt. of a silane coupling agent.
The tapes of the invention are sufficiently flexible and soft for most applications and have good unwinding and handling properties such that the tapes are suitable for both automatic and manual wrapping. Sufficient flame retardancy is also exhibited to satisfy the standard tests UL510 and ISO 3795, even though the tapes do not comprise any halogenated components.
The “copolymer a” component of the tape may comprise any of the following either alone or in combination: ethylene vinyl acetate copolymer (EVA), ethylene-methyl acetate (EMA) or ethylene-butyl acetate (EBA). The preferred component is EVA.
The “copolymer a” component of the tape renders the tape with its good flexibility. The “copolymer a” preferably has a low melt flow index (MFI), i.e. an MFI value of less than 6. This reduces the tendency for stress cracks to occur in the tape, especially at higher temperatures. The “copolymer a” preferably comprises at least two vinyl acetate copolymers having different melt flow indexes. In a particularly preferred embodiment of the invention the first of said copolymers has an MFI of between 4 and 7, and ideally 6, and the second has an MFI of from 0.5 to 1, and ideally 0.75, the two copolymers being present in a ratio having a range from 3 to 1.5:1 and ideally being 2:1 (first polymer:second polymer).
The low density polyethylene is more compatible with the filler than the “copolymer a” and ensures a more homogeneous distribution of the filler.
The fillers and/or flame retardants have a low surface area so as to enhance flexibility. Fillers having a BET value of substantially 4 are preferred.
The composition may further optionally comprise from 5% to 45% wt. of the plastomer polypropylene. Polypropylene is added in order to raise the temperature rating of the tape.
The film may be manufactured by any conventional technique, for example melt blowing. It is noted that PVC cannot be melt blown and therefore must be cast or calandered. Thus the tape of the invention is less expensive to manufacture.
The adhesive of the tape may comprise any standard adhesive for such tapes including, for example, solvent or water based or powder coated acrylic, polyurethane or polyester adhesives or natural rubber based adhesives. Heat curable adhesives are preferred.
The tapes are free of halogenated materials such as PVC. The tapes are also preferably free of plasticisers, which are prone to migration and have been shown to be carcinogenic.
The tapes are also resistant to conditions which are conventionally found in motor vehicle engines, such wires being subjected to high temperatures and contact with water and fluids such as petrol, diesel, oil, salt solution and anti freeze.
The tapes of the present invention have a temperature rating of between 105° and 130°.


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