2362587 SHEET MATERIALS AND METHODS FOR MANUFACTURING THE SAME The present
invention relates to sheet materials and to methods for their manufacture. In particular, the invention relates to a sheet material comprising a resealable substrate layer.
Resealable packages are currently constructed by incorporating zippers or other mechanical devices, or by using pressure sensitive adhesive as part of the packaging.
In the latter case, a thin polythene film is laminated to a carrier film such as, for example, a polyester film with pressure sensitive adhesive. The polythene layer of this laminate can then be sealed to a structure that is also made of polythene such as a container, tray or bag. In operation, the carrier film can be peeled away from the polythene layer which is attached to the structure, thereby exposing the pressure sensitive adhesive layer. Because the pressure sensitive adhesive layer is exposed, the carrier film can then be returned to its original position by way of the pressure sensitive adhesive and hence, the structure is resealed.
The above laminate uses a thin polythene layer as the layer via which it seals to other structures. However, this polythene layer is only suitable for sealing to polythene and as such, the structure to which it fuses must be made of polythene or laminated with a polythene layer. Although it is economical to incorporate this laminate into a bag made of polythene or to seal two pieces' of the laminate to one another in order to made a bag, this is not the case if it is to he fused to, for example, a container, as containers made of polythene or laminated with polythene are relatively expensive.
In addition, a lot of trays and containers are made of APET or PVC but at present no resealable laminate is available which will fuse to these material. There are PET films available which will fuse to these materials, and these films could be incorporated into the laminate structure described above and then fused to, for example, an APET container. However, such laminates are not resealable because the thinnest PET films currently available are 12 microns thick. Because of their thickness, they do not break at the edge where they seal with the container or tray when peeled. Upon peeling back the carrier film you are, therefore, left with either an intact or badly shredded PET film covering your container or tray.
The current invention seeks to provide an improved sheet material, which overcomes the disadvantages of the resealable larninates already in use by being reclosable and sealable to mono-materials such as APET, CPET, GPET, PVC, PS, ABS, PC etc.
Accordingly, in a first aspect of the invention, there is provided a sheet material comprising a substrate layer carrying a laminate of an adhesive layer and a sealable layer, wherein the sealable layer is preferably a lacquer and the adhesive layer provides a means whereby the substrate layer can be repeatedly detached from and reattached to the sealable layer by way of the adhesive layer. In a preferred embodiment, the sealable layer is less than 15 microns thick and fusible to another article preferably, by heat sealing. The other article is preferably made of APET, PVC or polystyrene. If the article is made of APET or PVC a co- polyester resin based sealable layer can be used. Alternatively, if the article consists of polystyrene an acrylic or polycarprolactone sealable layer is used. In a preferred embodiment, the adhesive layer is a pressure sensitive adhesive which can either have a stronger affinity to the substrate layer than to the sealable layer, a stronger affinity to the sealable layer than to the substrate layer or an equal affinity to the substrate layer and to the sealable layer. In most circumstances, the adhesive layer and sealable layer will overlay at least a part of, if not all of, the substrate layer. In a preferred embodiment, the substrate layer acts as a barrier between one side of the sheet material and the other. For example, the substrate layer could prevent egress of liquids, be impervious to microbes etc or act as a filter by only allowing the passage of certain things. The material for the substrate layer is chosen according to the intended use of the sheet material, for example polyester, nylon, polypropylene, paper, cellophane or other plastic films can be used as well as other suitable materials which will be readily apparent to those skilled in the art.
According to a second aspect of the invention, there is provided a sheet material as described above but further comprising an intermediate layer between the adhesive layer and the sealable layer. This intermediate layer is preferably made of PET (between 2-10 microns thick), PE (between 10-30 microns thick), OPP (between 415 microns thick), aluminium foil (between 4-50 microns thick) or cast or blown polypropylene film (between 10-50 microns thick).
In a third aspect of the present invention, there is provided a method of forming a sheet material, comprising:
(a) applying the sealable layer to one side of the substrate layer and the adhesive layer to the other side of the substrate layer; (b) transferring the sealable layer from one side of the substrate layer to which it is attached in (a) to the other side, so that it is now attached to the adhesive layer.
In a specific embodiment, the sealable layer is applied to the substrate layer with additives that facilitate the transfer of the sealable layer from the substrate layer to the adhesive layer. The sealable layer can be transferred to the adhesive layer by bringing the sealable layer and the adhesive layer into direct contact with each other so that the sealable layer detaches from the substrate layer and attaches instead to the adhesive layer. In a preferred embodiment the sealable layer is transferred to the adhesive layer by rolling up the substrate layer with the adhesive layer on one side and the sealable layer on the other side. This rolling up can be done under tension and into a reel.
According to a fourth aspect of the present invention, there is provided a method of forming a sheet material, comprising applying an adhesive layer to a substrate layer and then a sealable layer to the adhesive layer wherein the adhesive layer is preferably applied to the substrate layer by extrusion, gravure roll coating, Mayer bar coating, or hot melt coating and the sealable layer is preferably applied to the adhesive layer by extrusion, hot meh coating or by conventional coating by solution.
In a fifth aspect of the present invention, there is provided a method of forming a sheet material comprising applying an adhesive layer to a substrate layer, an intermediate layer to the adhesive layer and then a sealable layer to the second layer. In this case, the adhesive layer is preferably applied to the substrate layer by extrusion or hot melt coating, the intermediate layer is preferably laminated to the layer and the sealable layer is preferably applied to the intermediate layer as an extrusion, hot melt or as a conventional coating.
According to a sixth aspect of the present invention, there is provided the sheet material used as a packaging material or as part of a packing, preferably wherein the packaging is a bag, and the sheet material is fused to itself, or a lid for a container or a tray, wherein the sheet material is not fused to itself, but is preferably fused to the container or tray. The packaging material or package can be used for packaging food, pharmaceuticals or other consumables.
In a seventh aspect of the present invention, there is provided a package article comprising a sheet material.
In order that the invention may be better understood, an embodiment thereof will now be described by way of illustration only and with reference to the accompanying drawings, wherein:
Figure 1 shows a piece of conventional resealable material; Figure 2 shows a piece of sheet material in accordance with the invention in its first aspect; Figure 3 shows a sheet material in accordance with a second aspect of the invention; Figure 4 illustrates the steps involved in the method, in accordance with a third aspect of the present invention, used to produce the sheet material in accordance with the invention in its first aspect.
Figure 5 shows a bag in accordance with a sixth aspect of the present invention, made of the sheet material in accordance with the invention in its first aspect.
Figure 6 shows a tray with a resealable lid in accordance with a sixth aspect of the present invention, made from sheet material in accordance with the invention in its first aspect; and Figure 7 shows a tray with a sealing film in accordance with a sixth aspect of the 5 invention, being peeled away.
Figure 1 shows a piece of conventional resealable film 2 comprising a thin polythene film 8 laminated to a substrate layer 4 by way of a pressure sensitive adhesive layer 6. When the film 2 is fused to, for example, a polythene tray by way of the thin Polythene film 8, the substrate layer 4 can be peeled off the container thereby exposing the pressure sensitive adhesive layer 6. The substrate layer 4 can then be placed back over the container, and is held in place by the pressure sensitive adhesive layer 6, so that the container is resealed.
The sheet material 10, shown in Figure 2, is in accordance with the first aspect of the present invention. The adhesive layer 12 is composed of a lacquer which is chosen depending upon the type of container to which the material 10 is to be fused. For example, if the container is made of a PET or PVC a co-polyster resin based lacquer can be used. However, if the container is made of polystyrene an acrylic or polycarolactone lacquer can be used. On top of the adhesive layer 12 is a pressure sensitive adhesive layer 14 and on top of that is a substrate layer 16 that is capable of acting as a barrier between one side of the material 10 and the other. The substrate layer 16, which can be made from, for example, polyester, nylon, polypropylene, paper, cellophane or other plastic film, can be detached from the container to which the material 10 is fused by way of the lacquer 12 thereby exposing the pressure sensitive adhesive 14. Exposing the pressure sensitive adhesive 14 in this way means that the substrate layer 16 can now be replaced and held in place by the pressure sensitive adhesive 14.
Figure 3 shows another piece of sheet material 18, which is in accordance with the second aspect of the present invention. In this particular case, the material further comprises a intermediate layer 20 between the adhesive layer 14 and the sealable layer 12. This intermediate layer can be made from, for example, PET, PE, OPP, aluminium foil or cast or blown polypropylene. The sheet material 18 is reseable in the same way as the sheet material 10 shown in Figure 2.
Figure 4 illustrates the steps involved in one of the methods used to produce the material 10 shown in Figure 2. Initially, the sealable layer 12 is attached to one side, and the adhesive layer 14 to the other side, of the substrate layer 16 in order to produce the sheet material 22. The sheet material 22 is then wound up to produce the reel 24. In the reel 24 the sealable layer 12 and the adhesive layer 14 are brought into contact. The bond between the sealable layer 12 and the substrate layer 16 is weaker than the bond which is now able to form between the sealable layer 12 and adhesive layer 14. Finally therefore, when the reel 24 is unwound the sheet material 10 results. Thus, the sheet material 10 produced by this method comprises the adhesive layer 14 sandwiched between the substrate layer 16 and the sealable layer 12.
The sheet material 10, in Figure 2 and the sheet material 18, in Figure 3 can both be used to produce the resealable bag 26 shown in Figure 5. In Figure 5, the bag shown is composed of sheet material 10 whereby the adhesive layer 14 and the sealable layer 12 overlay completely the substrate layer 16. However, the adhesive layer 14 and the sealable layer 12 can only overlay the part of the substrate layer 16 which fuses to the other sheet. In either case fusing the sealable layers 12 of two pieces of sheet material 10 produces the bag 26. In addition, a bag could also be produced from one piece of sheet material 10 ( or 18) by folding the material and then fusing the sealable layers 12 along the edges which come together. The bag 26 can be used to house something in the space 28.
The resealable container 32 shown in Figure 6 comprises of sheet material 10 (but could equally comprise the sheet material 18, shown in Figure 3). The sealable layer 12 of the sheet material 10 fuses with the container 3 0 at the point 3 1. Again, the adhesive layer 14 and the sealable layer 12 are shown completely overlaying the substrate layer 16. However, the adhesive layer 14 and the sealable layer 12 may only overlay part of the substrate layer 16, preferably just the part of the substrate layer which is aligned with the bp 31 of the container 30 when the container is closed.
Figure 7, shows the resealable container 32, in Figure 6, being opened. In this particular case the sealable layer 12 breaks at position 34 due to its stronger affinity for the container 30 than for the adhesive layer 14. Equally however, the adhesive layer 14 could also break at a similar position to the sealable layer 12 and hence also remain behind on the container 30. Both of the above could also occur when the bag 26 in Figure 5 was opened.