Embossed film having controlled tear

Details Embossed film having controlled tear Embossed film having controlled tear

1999-12-14

2002-08-13

Boykin, Terressa M. (Department: 1711)

Stock material or miscellaneous articles

Web or sheet containing structurally defined element or...

Adhesive outermost layer

Reexamination Certificate

active

06432527

ABSTRACT:

BACKGROUND
This invention relates to an oriented, embossed film, which may be used as a backing in an adhesive tape. The film is easily and readily hand-tearable without the use of cutting tools or a dispenser and provides a substantially straight, non-curling edge when torn.
Many adhesive tapes, particularly those used for packaging and sealing require backings having relatively high tensile strengths. For this reason, various types of Kraft paper, plastic films and cloths that have considerable tensile strength have been used in the construction of adhesive tapes. Thus to remove a length of tape from a roll, an auxiliary cutting tool or surface is often required, making a taping process less convenient.
Many adhesive tapes have a longitudinally oriented film backing. The orientation of the film backing significantly improves the tensile strength of the tape, but renders it extremely difficult to hand tear a length of tape cleanly and transversely. Such oriented films tend to stretch unduly, not conform well, and tear along the axis of orientation.
Many tapes use paper treated with moisture-resistant polymer as a backing. Paper is a surprisingly expensive material, and its cost is increased by the several treatments to which it is subjected in making the tape suitable for many uses. Further, even treated paper retains a moisture-sensitivity that occasionally weakens it sufficiently to cause it to fail. Also, paper is comparatively stiff so that the tape does not flex or conform well to many surfaces.
Cloth-backed tapes can be more attractive, flexible, and tear-resistant than paper but cloth is expensive, special treatments are required to prevent the penetration of adhesive through it, and there is a tendency for it to ravel. Various types of nonwoven tape backings, including the so-called “spun-bonded” polymeric backings are less expensive to make and more ravel-resistant than woven cloth, but their thickness, tear-resistance, etc., are not uniform and their open nature makes application of adhesive coating difficult and expensive.
SUMMARY
The present invention provides a film that is inexpensive to manufacture, uses readily available materials which may be processed using conventional equipment, and is tearable (capable of being torn) in the cross-web (transverse) direction and optionally in the longitudinal (machine) direction. The film, when used as a backing for adhesive tapes, possesses good mechanical properties, such as tensile strength, low stretch or creep, and a reduced tendency to inadvertently split along the direction of orientation. The tape is suitable in medical, industrial and commercial applications.
Thus, the present invention provides an embossed, uniaxially oriented film comprising a major amount of a semi-crystalline first polymer component, a minor amount of a second polymer component having a yield point less than that of the first polymer component, and an embossed pattern providing predetermined tearability in a direction substantially transverse to the direction of orientation. Preferably the film comprises a continuous phase of the first polymer component and a discontinuous phase of the second polymer component.
The present invention also provides an adhesive article comprising the embossed, uniaxially oriented film and a layer of adhesive on at least one major surface of the film. The adhesive layer may be coated on the embossed (patterned) or unembossed (smooth) surface of the film. Preferably the adhesive layer is on the embossed (patterned) surface and preferably the adhesive is a pressure-sensitive adhesive.
Further, the present invention provides a process for preparing an embossed, oriented film that comprises providing a film comprising a melt-processed polymer blend comprising a semicrystalline first polymer component and a second polymer component having a yield point less than the first polymer component, orienting the film, and embossing the oriented film with a pattern to impart tearability in a direction substantially transverse to the direction of orientation. Optionally a pattern may be chosen that will impart tearability in the longitudinal direction as well.


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