In particular, the invention relates to a laminate for use in forming resealable packaging.

Various types of resealable packaging are known. Some incorporate mechanical means for resealing, such as zippers. Other types of resealable packaging comprise laminates that include pressure sensitive adhesive layers, such adhesive allowing sealed packaging to be opened and then closed and resealed.

A commonly used resealable packaging material uses a laminate comprising a pressure sensitive adhesive layer sandwiched between a substrate layer comprising, for example, a polyester film and a sealable polythene layer. The polythene layer of this laminate can be heat-sealed to a structure that is also made of polythene, such as a container or tray. Alternatively, the above described laminate is folded and the polythene layer is heat-sealed to itself to form a bag.

In operation, in order to open packaging sealed using the laminate, the laminate is peeled away from rest of the packaging. This peeling action causes the layers making up the laminate to become separated. The sealable polythene layer remains attached to the rest of the packaging, thereby exposing the pressure sensitive adhesive layer which remains attached to the substrate layer. The exposed pressure sensitive adhesive layer can subsequently be reattached to the sealable film, thereby resealing the packaging.

However, there are problems associated with packaging comprising this type of known laminate. In order to make it easy to open and consumer friendly, the sealable polythene layer has to be thin, preferably within the range of 15 to 20 microns. This allows the layer to be easily separated from the pressure sensitive adhesive layer upon opening the packaging. However, when such a thin film is used, the polythene sealable layer tends to laminate and cracks form on the film as it is separated from the pressure sensitive adhesive. These cracks are called"piping"and

this is where narrow areas of the film laminate forming"pipes"of between 0.25 to 4 mm diameter between the polythene and the pressure sensitive adhesive. This is detrimental to the desired resealing function of the laminate and is clearly not acceptable.

It has been attempted to overcome this problem by using a thicker layer of polythene, the layer being in the region of 40-50 microns thick. This increases the rigidity of the polythene so that it cannot convolute and form pipes or cracks in the packaging. However, the use of such a thicker layer of polythene in the laminate leads to other problems. The packaging formed from the laminate is much more difficult to open. Furthermore, the use of the thicker polythene layer requires special sealing dies to be installed on machines handling the laminate. In addition, making the polythene thicker may not actually solve the problem of the adhesion between the polythene and the pressure sensitive adhesive. The tendency for the polythene layer to laminate still exists, frequently leading to packaging not being properly sealed so that it has a tendency to leak, especially during transit.

The current invention seeks to provide a solution to this problem without the use of thicker polythene films in the laminate.

In a first aspect of the present invention, there is provided a laminate for use in packaging comprising a layer of pressure sensitive adhesive sandwiched between a substrate layer and a sealable layer, wherein the sealable layer comprises polypropylene and is sealable to other packaging material or itself.

In a preferred embodiment, the polypropylene is a homo-polymer, a co-polymer or a metalocene polymer of either type.

The laminates according to the first aspect of the present invention do not suffer from the disadvantages experienced with known laminates having a polythene sealable layer. The polypropylene sealable layer has a high adhesion to the pressure sensitive adhesive and does not allow cracks or pipes to form in the laminate.

Indeed, a laminate according to the present invention can have a sealable layer with a thickness of 50 microns or less.

Where the sealable layer is made up of just polypropylene, the laminate can be fused to polypropylene materials, such as polypropylene containers. However, such a laminate cannot be fused to some other materials, such as polythene. Therefore, in a further preferred embodiment, the sealable layer comprises a coextrusion with at least 2 layers, the layer adjacent the pressure sensitive adhesive being polypropylene.

The material at the exposed side of the sealable layer will be selected for its ability to fuse to whatever material the laminate is to be fused to.

Thus, for example, a laminate, which is to be fused to a polythene container, may include a sealable layer comprising polypropylene, a mixture of polypropylene and polythene, and then polythene. The polythene may be selected from the group consisting of LDPE, MDPE, LLDPE, LMDPE, VLLDPE and Metalocene PE.

Alternatively, the coextrusion could comprise polypropylene, a mixture of polypropylene and a plastomer, and then the plastomer. Preferably, the plastomer is Exxon Exact@ or Dow Affinity@.

In some situations, it may be desirable for the laminate according to the present invention to have the pressure sensitive adhesive layer and sealable layer overlaying only a portion of the substrate layer. Thus, for example, if the laminate is used to close an opening in a container, a laminate could be used wherein the pressure sensitive adhesive and sealable layers are only present in those regions within which the laminate is to contact and be fused to the container.

In a yet further preferred embodiment, the substrate layer of the laminate has barrier properties. For example, the substrate layer could prevent egress of liquids from one side of the laminate to the other, or it could be impervious to microbes.

The substrate layer might be made from polyester, nylon or polypropylene, paper, cellophane or other plastic film.

According to a second aspect of the invention, the laminate according to the first aspect of the invention is manufactured using the following method. Firstly, the pressure sensitive adhesive layer is applied to the substrate layer, preferably by extrusion or hotmelt coating. Next, the sealable layer is applied to the pressure sensitive adhesive. This is preferably done by extrusion, hotmelt coating or solution coating.

In a preferred embodiment, the adhesion of a sealable layer to a pressure sensitive adhesive layer is improved by calendering the sealable layer in the conventional way once it has been applied to the layer of pressure sensitive adhesive.

The thickness of the sealable layer applied to the pressure sensitive adhesive is preferably between 3 and 40 microns.

According to a third aspect of the present invention, the laminate according to the first aspect is used to form a sealable packaging. In one embodiment, this is done by fusing the laminate to a container to render said container sealable. In this embodiment, the laminate may be used to cover the opening of the container, the sealable layer being fused to the container material around the edges of the opening.

When the container is to be opened, the laminate is peeled from the container, whereupon the sealable layer remains in contact with the container whilst the other layers of the laminate are peeled away. This means that the pressure sensitive adhesive becomes exposed and may be used to re-attach the laminate in its original position, sealing the container once again.

In an alternative embodiment, the laminate may be used to form a sealable bag. To do this, two or more sheets of the laminate according to the first aspect of the invention are fused along their edges, the sealable layers of the laminates being arranged to lie adjacent to one another so they can fuse together. To open a sealable bag, the laminates are pulled apart, so that they separate at one of the sealed edges. This results in the layers of one of the laminates separating to expose the pressure sensitive adhesive layer. This exposed adhesive layer may then be reattached to rest of other laminate, thereby resealing the bag. Such a sealable bag

may also be made from a single sheet of laminate, folded so that the sealable layers lie next to one another and fused along the open edges.

In order that the first aspect of the invention may be better understood, two embodiments thereof will now be described by way of illustration only and with reference to the accompanying drawings, wherein: Figure 1 shows a laminate wherein the sealable layer comprises polypropylene; and Figure 2 shows a laminate wherein the sealable layer comprises a triple coextrusion.

Figure 1 shows a cross-sectional view of the laminate 11, according to the present invention. The pressure sensitive adhesive layer 13 is sandwiched between a substrate layer 12 and a polypropylene sealable layer 14. In Figure 2, the laminate 21 is made up of a substrate layer 22, a layer of pressure sensitive adhesive 23 and a sealable layer 24. In this laminate, the sealable layer 24 is a coextrusion of polypropylene 25, a heat sealable polymer 27, such as polythene, selected to bond to packaging material and a mixture 26 of the polypropylene and the heat sealable polymer positioned between them.

When the laminate 11 is used to seal a container, the sealable layer 14 is heat-fused to the container material. In order to open the container, the laminate is peeled from the container. This peeling action separates the sealable layer 14 from the rest of the laminate, thereby exposing the pressure sensitive layer 13 which remains attached to the substrate layer 12. This allows the container to be re-sealed, as the exposed pressure sensitive adhesive 13 can be re-attached to the sealable layer 14, returning the laminate to its original configuration, sealing the container.

When the laminate 21 is used to seal a container, the sealable layer 24 is heat-fused to the container material. In order to open the container, the laminate is peeled from the container. This peeling action separates the sealable layer 24, comprising the three layers 25,26 and 27, from the rest of the laminate, thereby exposing the pressure sensitive layer 23 which remains attached to the substrate layer 22. This allows the container to be re-sealed, as the exposed pressure sensitive adhesive 23 can be re-attached to the sealable layer 24, returning the laminate to its original configuration, sealing the container.