The present invention concerns biodegradable packages which are capable of storing substances which require protection from outside contamination from moisture, light and Oxygen. Such packages are particularly suitable for storing foodstuffs such as potato crisps, biscuits and cakes but can find many other applications. It will be appreciated that packaging foodstuffs in such a manner so as to provide a relatively long shelf life conflicts with the desire to make the packaging biodegradable. Even potato crisps contain a degree of moisture and if the bag allows this to pass through the packet walls the quality of the crisps will degrade. Additionally if the packaging allows moisture to penetrate this will also degrade any foodstuffs within the packaging. Thus the core of the problem faced by attempts to develop a biodegradable food package is that of providing an oxygen, light and moisture barrier ^' in the biodegradable packaging material yet can be mass produced using known heat sealing techniques.

The physical properties of biodegradable, compostable co-polyester films such as "Ecoflex", "MaterBi" or Mitsubishi "GSPLA" are less affected by short term moisture exposure and when sealed to themselves give good seal strength and seal integrity. However, these materials are intrinsically soft and extensible and do not have the necessary differential thermoplastic properties to form an effective package on typical modern high speed pack form filling lines using conventionally heated flat or crimp sealing jaws. In addition they have moderate to poor gas and water permeability properties rendering them unsuitable for packaging moisture sensitive products which may require modified gas atmospheres in the pack.

In addition the packaging industry has used Physical Vapour Deposition (PVD) of metals on oil based polymeric films in an attempt to give high gas, moisture and light barriers: However this procedure has been unable to provide a combination of bio-degradability, with good barrier resistance to moisture and gas.

United States Patent Application No. US 2004/0076778 biodegradable bags for packing foods which may include paper and a metallised and/or ceramic barrier layer in a heat sealable laminated wall structure. However the laminated structures disclosed in this specification have a number of drawbacks in view of the extensive use of such materials in the manufacture of foodstuff packages. In particular because of the relatively low unit price of such packages any savings in the amount of material used per package can have very substantial implications.

It is one concern of the present invention to provide a laminated biodegradable packaging material which is heat sealable, relatively simple to manufacture and affords good protection against moisture and air penetration.

Aspects of the present invention are set out in the independent claims of this specification.

In order that the present invention may be more readily understood embodiments thereof will now be described by way of example and with reference to the accompanying drawings in which:

Figure 1 shows cross sections through a preferred embodiment of a laminated heat-sealable packaging material according to the present invention and two other variants;

Figure 3 shows plan a view of a web of laminated material according to the present invention prior to the formation of individual bags;

Figure 4 is a section through two laminated materials according to the present invention which have been heat sealed together such as at the end of a bag;

Figures 5 a is flow diagrams showing stages in the manufacture of manufacture of laminated material in accordance with an aspect of the present invention;

Figure 5b shows stages in a printing process;

Figure 6 is a cross section through another embodiment of a heat-sealable packaging material according to the present invention;

Figures 7, 8 and 9 are very high resolution photographs giving an insight to the present invention, and Figure 10 is a flow diagram showing steps in the manufacture of the material of Figure 6.

Referring now to Figure 1 of the accompanying drawings this shows an embodiment of a laminated material according to the present invention and two other variants. The laminated material shown in in this embodiments has a layer 1 of a biodegradable polymer. An important features of this layer is that it can be readily used for heat sealing a package and accordingly must have good heat seal ability and accordingly a relatively low melting point - preferably below 125degC. It is known that a wide range of suitable biodegradable polymers are available. One preferred biodegradable polymer is Polybutylene Succinate. In a preferred embodiment this layer is 25um thick though a potential thickness range is from 5μ to 50μ

An important feature of this embodiment is the use of a particular type of cellulosic based super calendered papers such as Glassine or even certain types of high quality tracing paper. Thus in Figure 1 layer 2 is a layer of this type. The question as to what constitutes super calendered paper will be discussed later in this specification. This is despite the fact that most cellulosic based structures such as Kraft or Glassine, although biodegradable, are not heat-sealable or nor do they have good gas barrier properties and also suffer from significant moisture sensitivity. However, they are suitable for packing pre-made bags products such as morning goods and food products with a short shelf life. However the natural and sustainable origin of cellulosic papers makes them ideal for composting and their non-thermoplastic behaviour ideal for a heat resistant outer layer in a laminated film structure manufactured by a heat sealing process. The problem is how to combine such natural cellulosic material with a barrier component so as to achieve a combination capable of providing a heat sealable laminate which provides a good barrier against oxygen, moisture and light and which is inexpensive and the manufacture of which can be readily automated. This is particularly important in the packaging and retailing of foodstuffs which have very large production runs and which retail for a low unit cost.

The laminate material shown in Figure 1 includes a barrier layer 3. Preferably this coating is carried out by a chemical vapour deposition process. In the present embodiment layer 3 is preferably of aluminium. However alternative materials can be aluminium oxide or silicon oxide such as S1O2. Additionally layer 3 may be ceramic and selected from oxides such as those of Calcium, Zinc, Silicon or Boron or a mixture of Aluminium or one of its oxides with one of these ceramics. The thickness range for this barrier layer is from 0.01 microns to 0.15 microns. A preferable thickness is 0.26 microns. However the direct superimposition of aluminium onto paper has the problem that many paperscontain sulphites or other chemicals which will eventually corrode the aluminium and destroy the integrity of the packaging. It is for this reason that super calendered paper such as Glassine (RTM) are used. Another advantage of using such paper is that it is extremely smooth. As the barrier coating is very thin this helps to prevent the formations of miniature bridges or ridges in the barrier layer which can degrade its performance. However the direct combination of a super calendered paper layer with an aluminium layer still presents the problem that any moisture inevitably absorbed by the paper will cause its fibres to swell which in turn causes the very thin aluminium layer to fracture

In accordance with another important feature the laminated structure shown in Figure 1 has an additional layer 4 of a lacquer. One preferred lacquer is an acrylic lacquer such as that formed by a polymerisation in a mixture of water and monomers of acrylic, styrene plus surfactants, stabilisers etc. Such copolymers are are BIM BA8853 manufactured by BIM BA AB of Finland and a

MICHELMANN product of USA. these are styrene/acrylic copolymers. To these copolymer suspensions are added sub-micron sized fillers to provide a more tortuous path length to water and gas molecules. Such fillers are manufactured by Nanograde in Switzerland. The purpose of this layer is to reduce still further the possibility of absorbed moisture in layer 2 degrading the barrier properties of layer 3. One way in which this additional layer acts unexpectantly is that it can form a very thin lattice-like structure which can fill any cavities in the surface of layer 1 left after the initial calendering. The lacquer should be designed to not affect biodegradability. Whilst it has been found that water-based lacquers are effective it is also possible to employ and lacquers or lacquer-like materials which after application evapourate so as to deposit the suspended filler particles on the metallised layer. Other suitable lacquers which can be used in the present embodiment are based on polyvinyl alchohol. One such lacquer is known as GOHSENOL (RTM) manufactured by The Nippon Synthetic Chemical Industry co ltd. Another potential lacquer is a recently announced amorphous PVOH by the same company called Nichigo G-Polymer. Suitable materials for the filler particles are Talc, Bentonite, Kaolinite. Other examples of filler particles have been described in respect of the first embodiment. A suitable amount for the filler particles is 30% of the weight of the lacquer (30% w/w). However depending on the nature of the lacquer and the sizes of the particles this ratio could lie between 10 - 50%.

This lacquer layer 4 is shown in schematically in Figure 1 as about to be applied to the paper layer

2 which would otherwise have been the outer layer an the final manufactured package. Of course the paper layer 3 is capable of supporting printing and this is shown as a print layer 5. The actual positioning of this lacquer layer in respect of the other layers of the laminate can be varied 2. This is shown in the other two variants la and lb in Figure 1. However the location of layer 3 as shown shown in Figure 1 is preferred.

Referring now to Figures 2, 2a and 2b these show cross sections of bags made from laminated material of the kind described with reference to the main embodiment and the variants shown in Figure 1. The sealant layer 1 in each of these three cross sections is on the inner side of the bag so that it is this side that any product within the finally sealed bag will contact . Figure 2a illustrates a sealed bag in which two flaps of the laminated material have been heat sealed together using opposed sealant layers to complete the sealing of the open ends of the bag, Figure 2b shows the two flaps before heat sealing. In Figure 3a it will be seen that the final seal has been made by heat welding layer 1 of the laminate to its outer side which is of course remote from the sealant layer 1.

This latter method of sealing the individual bags is slightly more economical than the method shown in Figure 2a as it will be appreciated that the Figure 2c method enables more bags to be produced for a given length of webbing.

Once a bag has been manufactured, filled with product and sold tearing open the package will expose the biodegradable sealant layer and also cause a degree of delamination to occur in the laminated structure of the packaging material. This in turn allows moisture to invade the material and start its decomposition.

Figure 3 of the accompanying drawings shows a web 10 of laminated material as viewed from above the sealant layer 1. Each rectangle, represents the surface area of a single bag. The vertical and cross lines represent areas of the web which are to be heat sealed together whilst the horizontal lines represent both seal and cut lines The cutting and sealing processes for making bags from this web 10 is well known and involves initially passing the web over a cylindrical former before seal of the kind shown in Figure 2 are applied and individual bags are cut from the web

. Figure 4 shows two sheets of the material of Figure 1 heat-welded together as in the two welded flaps shown in Figure 2a, the laminated material having the same reference numerals as have been used in Figure 1. Cleave points which occur when the bag is opened are shown at 11. These cleave points are due to the interply bond strength being less than the textile strength of the paper layer 2. In this figure it will be seen that a region 12 is shown where the actual heat sealing has taken place.

In order to accelerate the decomposition process of a used bag the paper layer 3 can be impregnated prior to the lamination process with a suitable hydrophilic substance. Suitable hydrophilic substances are amino acids, peptides, nucleic acids, fats, poly saccharrides, vitamins and trace minerals. It is possible to impregnate the whole of layer 3 with hydrophilic material or only to impregnate the borders of layer 3 at the strips where heat sealing is carried out.

Turning now to Figure 5a this shows the first part of a processing flow which leads to the laminated material shown in Figure 1. Thus Figure 5a shows a mill 30 for manufacturing rolls of paper one of which is shown at A. The roll A is then taken to a calendering station 31 having a plurality of rollers. The calendering station is of a known kind and compresses and smooths the paper in roll A to generated a super calendered roll B of in the range of 20 to 100 gsm. Roll B is then fed into a plasma coater 32 where the calendered paper is coated with the barrier layer 3. It is well known that thin films of materials such as aluminium or those alternatives which have already been described can be deposited onto thin films using plasma coaters. The roll of laminated paper and barrier layer which has been produced in the plasma coater is shown at D and is fed as a web through a coating section 34, a drying section 35, an extrusion section 36 and thence to a chilled roller 37 to produce a triple laminated web of material in a roll F, the three layers being the sealant layer 1, the paper layer 2 and the barrier layer 3.

Figure shows the final stages of the manufacture of the laminated material. The first of these stages gives two alternative routes for printing on layer 2 of the laminated material contained in the roll F. One of these alternatives is shown at 40 which illustrates a flexograph printing press and the other at 41 which shows a gravure offset printing press. The printed roll G is then coated with the acrylic layer in a rotary coater shown at 43.

Naturally if a laminated material according to either of the alternative variants shown in Figure 1 is required than the ordering of the sections described can be varied appropriately. Additionally the layer 2 can impregnated with hydrophilic material in an appropriate manner either after the milling stage, or the calendering stage or before the final application of the lacquer.

Referring now to Figure 6 of the accompanying drawings this figure is a cross section through an embodiment of a packaging material in accordance with the present invention. It will be seen that in the embodiment of Figure 6 has in fact been simplified with respect to the previously described embodiment. In this figure layer 100 shows a heat seal layer which has been printed on a layer 200 in any suitable known manner. Layer 300 is a layer of a super calendered cellulosic material as in the previously described embodiment and such as Glassine or Kraft paper. Preferably this paper is again between 30 to 60 gsm and will be white filled or natural. Cellulose based structures such Kraft or Glassine papers as already mentioned are not heat-sealable or nor do they have gas barrier properties and suffer from significant moisture sensitivity. However, they are suitable for packing premade bags products such as morning goods and food products with a short shelf life. Thus although the natural and sustainable origin of cellulosic papers makes them ideal for composting and their non-thermoplastic behaviour ideal for the outer layer in a laminated film structure their permeability to moisture and gases limits their use for packaging materials which are sensitive to gas and moisture permeation.

Attempts to improve the barrier effect provided by calendered or super calendered papers such as glassine or Kraft have involved the application of a lacquer to the paper. However such treatment of the paper still leads to an inadequate barrier effect. This can be appreciated from Figure 7 of the accompanying drawings. This figure is a high resolution photograph showing a non-calendered paper layer which has been treated with a metallised layer of aluminium by Physical Vapour Deposition (PVD). However this photograph reveals a multitude of cracks and voids due to the significant dimensional changes in the paper due to associated moisture gain or loss. Thus any improvement in barrier qualities is marginal so that this metallising technique on paper technique has previously used for decorative qualities.

Given that the treatment of ordinary paper with a metallised layer provided marginally improved barrier qualities it would seem reasonable the treating calendered paper and particularly super calendered paper would provide substantially improved barrier qualities over metallised paper. However as can be seen from Figure 8 this is actually not the case. Figure 8 shows the surface of a layer of super calendered glassine paper which has been metallised in a similar manner to the ordinary paper layer of Figure 7. Even though the super calendered paper offers a substantially smoother surface finish, less sulphate residue and should accordingly be more suitable for the metallisation process it will be seen that the metal is still highly porous and accordingly has inadequate barrier properties.

However in the present embodiment it is the metallised layer 400 which is has been treated with a soluble lacquer or lacquer-like substances which already been described rather than the cellulosic layer. Again in accordance with a favoured variant of the present invention this lacquer layer 500 additionally contains filler particles which may be either organic or in-organic but preferably are of sub-micron size. It is believed that these filler particles help in reducing the porosity of the metal in the metallised layer 400 and provide a more arduous path length against the permeation through the layer of metal for any gas or moisture which attempts to permeate through the layer. In addition the lacquer helps protect the cellulose fibres of the layer 300 from swelling caused by moisture, thus helping maintaining the integrity of the metallised layer in environments which contain moisture.

This can be appreciated from Figure 9 which is another photograph taken at the same resolution as Figures 7 and 8 and shows a metallising layer of aluminium which has been treated with a soluble lacquer containing submicron-sized filler particles. It will be seen that the effect of the application of the soluble lacquer and filler particles and the subsequent evaporation of the lacquer that the filler particles act to clog the pores which can be seen in Figures 7 and 8 so as to further densify the metal.

It has also been found that soluble lacquers are substantially more effective than solventless coatings which can be applied by extrusion coating. It is believed that this advantage is provided by the improved deposition of the filler particles as the lacquer evaporates. In this embodiment a suitable lacquer for layer 400 is known as BIM BA8853. Other suitable lacquers which can be used in the present embodiment are based on polyvinyl alchohol. One such lacquer is known as GOHSENOL (RTM) manufactured by The Nippon Synthetic Chemical Industry co ltd. Another potential lacquer is a recently announced amorphous PVOH by the same company called Nichigo G-Polymer. Suitable materials for the filler particles are Talc, Bentonite, Kaolinite. Other examples of filler particles have been described in respect of the first embodiment. A suitable amount for the filler particles is 30% of the weight of the lacquer (30% w/w). However depending on the nature of the lacquer and the sizes of the particles this ratio could lie between 10 - 50%.

The final layers in the material are layer 200, which is a suitable print design, and layer 100 which consists of a heat-sealable lacquer. This lacquer in the present embodiment is a water-based acrylic lacquer which can be applied in a number of known different ways. These include Gravure, cylinder, Flexo offset, ' K ¹ bar, knife bar, or spray coating and an example of such printing techniques and equipment has already been shown in Figure 5a

In a finished packaging bag, layer 5 could be the inner layer of the bag. The manufacture of an example of a packaging bag using modern heat sealing techniques has already been described.

In order to improve the bio-degradability of the cellulosic layer 3 may be either impregnated during the manufacture of the material with a hydrophilic material or treated with such a material prior to the manufacture of the actual laminated film.As the result of tearing a packet manufactered from a bio degradable material of the kind just described the cellulose layer will exposed the the ambient atmosphere and in particular to moisture which wil cause its now exposed fibres to exapnd in initiate the degrading process.

It will also be appreciated that the layer 500, if not itself heat sealable could be coated with a heat sealable layer of a bio degradable material. Accordingly if both sides of the final laminate are coated with heat sealbable material. If these two outer sides are labelled A and B the two sides can be sealed together in three diferrent configurations, namely A to B, A to A and B to B Referring now to Figure 10 of the accompanying drawings this figure shows a simple flow diagram repesenting steps in the manufacture of the laminated material which has been just described. Thus in Step 10 there is manufacxtured a roll of paper from suitable celulose material. In Step 11, as in the first embodiment, this paper is milled to generate super calendered paper. Similarly in Step 12 the calendered paper is metallised. However in the next Step 13 the metallised layer so generated is coated with a polar-based lacquer containing sub-micron sized particles. Once the coating material applied in Step 13 has dried additional treatments such as printing can be carried out to provide the final product.