Package with tear tape and method of forming same

Details Package with tear tape and method of forming same Package with tear tape and method of forming same

1996-09-27

2001-05-08

Ahmad, Nasser (Department: 1772)

Stock material or miscellaneous articles

Sheet facing and longitudinally noncoextensive with web or...

C206S242000, C206S245000, C206S264000, C206S273000, C264S171130, C428S042200, C428S043000, C428S352000, C428S35500R, C428S192000, C428S194000, C428S910000

Reexamination Certificate

active

06228458

ABSTRACT:

CROSS-REFERENCES TO RELATED APPLICATIONS
This application is a convention application of United Kingdom Patent Application No. 9520015.0 filed Sep. 28, 1995 and United Kingdom Patent Application No. 9609656.5 filed May 9,1996. Priority is claimed under 35 U.S.C. 119.
FIELD OF THE INVENTION
This invention relates to tapes and is concerned with tear tapes for hermetically sealed packages and more particularly, but not exclusively, packages based on flow wrap or vacuum wrapping methods as used in, for example, the coffee, cold meat, pre-packed cheese, and cigarette industries.
BACKGROUND OF THE INVENTION
It is well known that tear tapes are effective in opening various types of consumer packaging, especially those formed from packaging material using non-hermetic wrapping techniques such as roll wrapping and standard envelope wrapping. However, traditional tear tapes based on uncoated films, wax coated films, single surface hot melt coated films or those that use pressure sensitive adhesive/release coatings are unsuitable for hermetically sealed packages since their presence significantly reduces the efficiency of the end seals thereby allowing ingress of air, moisture and/or bacteria which, in the case of packaging for food products such as cheese, will reduce shelf life.
For example, with tear tapes incorporating a pressure sensitive adhesive coating and a release coating an opposite surfaces of a film, the tear tape is adhered to the packaging material by means of the pressure sensitive adhesive and the packaging material is then suitably wrapped around the product to be packaged. In a flow wrapping process, the packaging material is overlapped to form a tube including a side seal, the product is inserted into the tube, the tube is then closed by forming the end seals with the tear tape sandwiched between the layers of packaging material joined to form the end seals. As a consequence of the presence of the release coating on the tear tape, the end seal efficiency is significantly reduced. Similarly, in the case of tear tapes based on a film coated on one surface only with a hot melt coating, the end seal efficiency is reduced where the packaging material and the non-coated film surface are in contact. In both cases, gaps are also formed at both edges of the tear tape due to the physical size of the tear tape sandwiched between layers of the packaging material at the end seals.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a tear tape which, in addition to facilitating the opening of a hermetically sealed package, will also maintain the seal integrity when integrated into the package.
According to one aspect of the present invention there is provided, in combination, packaging material suitable for forming a hermetically sealed package and a tear tape attached thereto, which tear tape includes (i) a surface capable of sealing to the packaging material under the conditions required for sealing together portions of the packaging material to form the end seals of the package and (ii) a surface bonded to the packaging material and formed of a component which flows under said conditions.
In a particularly preferred embodiment, the tear tape includes a substrate formed from an oriented base film of thermoplastic plastics material. One surface of the base film may carry a layer of plastics material capable of sealing to the packaging material under the conditions required for sealing together portions of the packaging material to form the end seals of the package (hereinafter referred to as the sealing layer). The plastics material has a lower softening or melting point than the melting point of the tear tape base film and the packaging material and it may be applied to the substrate by, for example, co-extrusion. The other surface of the tear tape base film may be coated with a layer of, for example, a hot melt adhesive which bonds the tear tape to the packaging material along the whole length of the package and which flows, under the conditions required to seal the packaging material together when forming the end seals of the package, to seal the tear tape at the end seals (hereinafter referred to as the bonding layer).
Preferably, the tear tape is produced in the form of traverse wound reels containing from for example 3000-120,000 meters of tape 1.5-15 mm wide. In use, the bonding layer, for example, the hot melt adhesive surface of the tear tape is applied to the inside surface of the packaging material by the application of heat or heat and pressure across the whole length of the packaging material including that portion of the material intended to form the hermetic seal at the end of the package. The packaging material is then folded and overlapped to form the side seal of the package, the product is inserted, and the end seals are formed to encapsulate the product and, as a result, the sealing layer is adhered to the packaging material portion forming the end seals of the package. The hermetic seal of the package is maintained by the action of the hot melt adhesive (the bonding layer) flowing around the tear tape edges when the end seal is formed by heat and pressure. Hot melt adhesive transfer from the film surface to the tape edges eliminates gaps in the seal which would otherwise enable the ingress of air, moisture or bacteria. The flowing action of the hot melt adhesive and the seal integrity are ensured by appropriately controlling the following factors: tear tape base film thickness, hot melt adhesive viscosity, hot melt adhesive coating weight, and the temperature and pressure of the sealing jaws needed to seal together the portions of the packaging material when forming the end seal of the package.
The nature of the packaging material is dependent on the nature of the product to be packaged but generally the packaging material will be based on polyethylene, polyethylene terephthalate or polyamide. Typical examples are, for cooked meats an LDPE/PVDC/LDPE multi-layer material or a PVDC coated PET (15 microns)/LDPE material; for peanuts a metallised PET (12.5 microns)/LDPE (50 microns) material; for bacon a cast polyamide (Nylon) (20 microns)/LDPE (50 microns) material; and, for cheese, a cast polyamide (50 microns)/LDPE (70 microns) material. LDPE is low density polyethylene, PVDC is polyvinylidene chloride, and PET is polyethylene terephthalate. All these packaging films are designed to provide gas and moisture barriers.
According to another aspect of the present invention there is provided a tear tape for use in the aforementioned combination, which tear tape comprises:
(i) a film having a thickness of from 20 to 60 microns and a width of from 1 to 20mm and formed of oriented polypropylene or oriented polyester (polyethylene terephthalate),
(ii) a sealing layer of thickness of from 5 to 40 microns provided on one surface of the film to enable the tear tape to be sealed to polyethylene-, polyethylene terephthalate-, or polyamide-based filmic packaging material, said sealing layer having a softening or melting point which is less than the melting point of the film and being formed from polyethylene, ethylene/vinyl acetate copolymer, polyvinylidene chloride, polyamide or wax, and
(iii) a bonding layer provided on the opposite surface of the film at a coating weight of from 5 to 50 gram per square meter, said bonding layer having a softening or melting point which is less than the melting point of the film, less than or equal to the softening point or melting point of the sealing layer, and is from 70 to 120° C. (Ring and Ball), having a viscosity of from 500 to 4000 centipoises at 160° C. (Brookfield, Spindle No.9, 5 r.p.m.), and being formed of polyethylene, ethylene/vinyl acetate copolymer, polyvinylidene chloride, polyamide or wax.
According to a further aspect of the present invention there is provided a tear tape for use in the aforementioned combination, which tear tape comprises:
(i) a film having a thickness of from 20 to 60 microns and a width of from 1 to 20mm and formed from oriented polyethylene, and
(ii) a bonding layer provide

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