FIELD OF INVENTION

The present invention relates to packaging and more particularly concerns packages comprising organic synthetic polymers.

BACKGROUND OF THE INVENTION AND PRIOR ART

Product packaging is regarded by today's industry as an essential part of product marketing. In many cases the package is the only visible part of the product and it is evident that the appearance of the package may indeed attract the consumer's attention to the product. However, apart from aesthetic and marketing considerations, the package must fulfil a major role, i.e product protection, preferably without impairing the flexible handling and storage of the packed product.

Polymers in general and plastic materials in particular are used in manufacturing packages, due to their strength, lightness and the ease in which a variety of forms can be produced using these materials. Some of these materials are basically transparent and some are colourless and thus an enormous range of colours can be obtained by addition of dyes and

pigments. These materials are also compatible with other materials, and can easily be combined with such to produce, for example, laminates of various types.

One major problem, in manufacturing suitable packages in general, and food packages in particular, is to find a compromise between the strength of the package and its quick controlled and convenient opening.

Achieving this compromise is highly important for packages used in food industries in general, and for snacks in particular.

In addition, it is desirable to be able to control the direction of the opening of the package. There has hitherto not been proposed any simple means to control the opening direction of the package and in most cases when the package is opened, it does not continue to hold the product efficiently.

It is the object of the present invention to provide a package wherein the direction of the opening of the package is predetermined.

DESCRIPTION OF THE INVENTION

According to the present invention, there is provided a package made essentially of film material having a portion which can be torn to open said package, at least said portion being constituted by a mono-oriented film having one or more polymeric layers which are mono-oriented, said layers having an axis, as herein defined, that determines the orientation of the intended opening tear.

Mono-orientation is achieved by stretching a film in one direction. The direction in which the film has been stretched to achieve the mono-orientation will be referred to herein as "axis". A mono-oriented film is generally relatively resistant to tears in a direction perpendicular to the axis and has a low resistance to tears in a direction parallel thereto.

Consequently, when tearing such a film this tear will tend to form in a direction essentially parallel to that of the axis.

As known, in most cases polymeric films and consequently packages made therefrom have a higher tearing resistance at their edges. A common known solution to this problem is to add a strip or tape or to make a slit or a cut in the edge of the polymer film which predetermine the initial tearing of the package. However, in none of these cases is the direction of the tear ensured.

According to the present invention, the package has inherent means which facilitate the tearing open of the package and which determine the orientation of the tear. Means for predetermining the initial tearing similar to the ones mentioned above may also be included in the package.

By another aspect of the present invention there is provided a method of preparing a package made essentially of film material and having a poπion which is intended to be torn for opening the package, the method comprising forming and fusing one or more films made wholly or partially of a polymeric material to obtain said package, the method being character¬ ized in that at least one of said films is mono-oriented and at least said portion is formed therefrom, the axis of the mono-oriented film being essentially parallel to the orientation of the intended tear.

The mono-oriented film may have a single polymeric mono- oriented layer or may have a plurality of such layers. In the latter case the axis of all mono-oriented polymeric layers should be essentially parallel to one another. The mono-oriented film may also be a laminate of mono- oriented polymeric layers and layers made of other materials, e.g. non- transparent materials such as aluminium foil, metalized polymer film, paper and the like, or transparent materials such as polyethylenes, polypropylenes, polyesters, polyamides and other thermoplastic polymers, as well as polyimides.

Mono-oriented polymeric films may be prepared from polymers such as polyolefins, polyesters, polyamides, other thermoplastics and mixtures of different polymers as well as polyimides. Some preferred polymers are linear low density polyethylene (LLDPE), high density polyethylene (HDPE), polypropylene or a combination thereof. A particu¬ larly preferred polymer is a mixture of LLDPE and HDPE, a mixture of about 85% LLDPE and 15% of HDPE being the most preferred. A mono- oriented polymeric film is prepared by stretching a prepared polymeric film in only one direction. The stretching of a polymeric film may for example be by a factor of about 5 to 9. with a stretching factor of about 7-8 being preferred. (The stretching factor is the ratio between the length of a unit film after stretching to its length prior to stretching).

The mono-oriented film of the present invention whether consisting of a single or a plurality of mono-oriented polymeric layers may be prepared by one continuous process on a single machine or may be performed in discreet steps on various machines.

Printing or pigmentation, if desired, may be performed on the mono-oriented polymeric film or on any of the materials to which the mono-oriented polymeric film is laminated. The printing or the impregna- tion may be performed by any of a number of methods known per se.

Preparation of a package with the mono-oriented film is generally as known per se and may be carried out on conventional machines used in the art for manufacturing packages from film material. The mono-oriented film may form the entire package or may form a part thereof including the portion wherein the opening by tearing is intended. The orientation of the mono-oriented film in the package will be such that its axis will be parallel to the direction of the desired tear.

In accordance with the present invention there is thus provided a package in which the opening by tearing is enabled by an inherent

characteristic of the packaging material. The package may thus be opened in a controlled manner without tearing the package apart, thus retaining its structure and avoiding loss or spillage of the package material during the opening process. This characteristic is very important for a host of packaged products, such as foods and snack products, pharmaceuticals, chemicals, etc. This is particularly the case where the packaged product is in the form of a liquid or a powder or where this product consists of very small items such as small electronic parts and the like.

The preparation of a package and a mono-oriented polymeric film to be used therein will be described in the following bv reference to specific embodiments, it being understood that the invention is not limited thereto.

Preparation of mono-oriented polyethylene film. A mono-oriented polymeric film is prepared by a continuous extrusion process followed by a stretching process and a high volt, discharge treatment (an electrical surface treatment of films intended to prepare the surface for lamination and/or printing). This may be performed on a single machine, consisting of a feeding unit, an extruder equipped with a round die and a temperature control unit, an air cooling ring for cooling the material exiting from the die and a stretching unit which comprises oil heated rollers equipped with a system controlling both the heating and the turning speed of said rollers. The machine also includes a high voltage discharge treatment unit as well as a system which enables the exact rolling of the obtained film.

Pellets or granules of a mixture of 85% of LLDPE and 15% HDPE are introduced to the extruder through the feeding system. These pellets and/or granules are heated, molded and compressed by a screw inside the cylinder which is kept at 175-200° and exit as a homogeneous tube

through the die which is kept at 200°. Adaptors and connectors of the system are kept at 185°C. The emerging tube is cooled and expanded by air through an air ring forming a polyethylene balloon of about 0.2 mm width. The polyethylene balloon is slit on a slitting table to form an open polymeric film and then attached to the roller system.

This polymeric film passes then through the stretching system. The stretching system comprises several heating rollers, the first one of which is heated to about 100°C, and the last one to about 125°, and a stretching roller which stretches the film emerging from the 125° heating roller. The ratio of roller velocities is adjusted so as to achieve a stretching factor of about 8. In this process the thickness of the polyethylene film is reduced from about 150-200 μm to about 25 μm. After the stretching the film is passed over an annealing roller and then over a cooling roller which cools the film to room temperature. After the stretching process is completed, the polymeric film is passed through the high voltage discharge treatment unit to prepare it for lamination and/or printing.

The obtained mono-oriented polyethylene film has the following physical characteristics: Density 0.941 gr/cm ³ ; ultimate tensile strength 320 p.s.i.

Preparation of mono-oriented polypropylene film

The same apparatus and process is applied for the preparation of mono-oriented polypropylene film by just changing the temperature of the different parts in the system and adapting the stretching velocities. The following parameters are used to prepare mono-oriented PP film: cylinder temperature 220°C, adaptors and connectors 220°C , die 220°C. The temperature of the rollers of the stretching system is from 110°C to 135°. The stretching is performed at 135°C by adjusting the ratio of velocities of the rollers so as to achieve a stretching factor of about 7. The obtained

propylene film has the following physical characteristics: Density 0.91 gr/cm ³ ; ultimate tensile strength 285 P.S.I.

Lamination of mono-oriented polyethylene film with polyethylene and polyester films.

A laminate is prepared by wet combining a mono-oriented polyethylene film of 25μm thickness, prepared according to the above procedure with a polyethylene film (40 μm) and a polyester film (12 μm) using a polyurethane adhesive (30% in ethylmethylketone). The wet combining process is briefly as follows: the polyurethane adhesive is applied on both sides of the polyester film and then the coated polyester film is passed through a four-section oven for evaporation of the solvent, (the temperature of the four sections of the oven being set to 60°C, 80°C, 85° and 100°); as soon as the polyester film exits from the oven the mono- oriented poly-ethylene film and the PE film are pressed against the opposite sides of the polyester film, thus producing a laminate having a polyeste. layer sand-wiched between the mono-oriented polyethylene film and the polyethylene film. The pressing system includes two pre-heating rolls and two pressing rolls which are heated to a temperature of about 120°C. The obtained laminate has a delamination resistance of 2-4

N/mm ³ at room temperature.

Preparation of package comprising a mono-oriented polyethylene film.

A package is prepared from the above obtained laminate, which package consists of two portions of an elongated film folded and fused to one another in which the axis of the mono-oriented film is oriented so that its axis is transverse with respect to the longitudinal axis of the package. The laminate is folded so that the inner layers are PE (non-mono-oriented)

layers. In this manner, the package may be easily opened by tearing and the tear will thus be transverse-wise.

For preparation of the package, the laminate is introduced into a machine in which the film is folded along its longitudinal axis so that an open sleeve is obtained. In this sleeve the axis of the mono-oriented film is parallel to the fold. This open sleeve is passed through a fusing system in which strips which are perpendicular to the longitudinal axis of the laminate are heated (180°, 5s) and pressed and consequently the two films fuse to one another at said strips. Thereby, a packaging unit is formed, the length of which is essentially half of the width of the original laminate and its width being the distance between two consecutive fused strips. Cutting to individual packaging unit and sealing of the still open end is usually performed when introducing into the package the product to be contained therein. In order to facilitate opening of the package, a small cut or a slit may be introduced into the edge of the final package so as to serve as .-. tearing initiation point.