NZ333393A - Sheet material for microwave food package comprising a susceptor layer of metal particles - Google Patents

Abstract

The specification describes a sheet material (1) having: (i) a substrate (2) of porous sheet material usually paper or other non-woven cellulosic fiber material used in the packaging industry (ii) a coating material (4) on the substrate. The coating material is able withstand the migration of susceptor metal particles (iii) the susceptor layer (5) is applied by a printing process and in the presence of a liquid carrier (iv) a food contactable plastic layer (7) which overlies the susceptor metal particles. The bags or packages may optionally contain printed material.

Description

...NEW ZEALAND" PATENTS ACT, 1953 No: 333393 Date: 15 December 1998 COMPLETE SPECIFICATION "MICROWAVE FOOD PACKAGING" We, AEP INDUSTRIES (NZ) LIMITED, a company duly incorporated under the laws of New Zealand of 100 Carbine Road, Mt Wellington, Auckland, New Zealand do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: ^intellectual property of n.z. 1 H DEC 1999 RECEIVED The present invention relates to microwave food packaging and/or materials and methods suitable therefore.

The use of microwave energy to heat and cook food is now common place. High frequency electromagnetic radiation generated within a microwave oven will heat food. However it does not adequately brown the outside of the food. Browning of food is often desirable.

Conventional methods of cooking food, using a thermal oven, does heat the exterior of such food products, resulting in the browning of the surfaces for example pastry. It has therefore been desirable for foods heated by microwave energy to resemble foods cooked by conventional methods.

Common methods of increasing the browning of pastry food for cooking in a microwave is to cook the food within packaging which has a microwave interactive layer disposed between plies of food contactable or other strength providing packaging material.

The microwave interactive layer between such plies absorbs at least some of microwave energy which is then converted into heat which is then able to be transferred conductively or radiantly to the food.

It is therefore an object of the present invention to provide microwave food packaging and/or materials and methods for forming such, which will at least provide the public with a useful choice.

Accordingly the present invention broadly consists in a sheet material comprising or including (i) a substrate of a substantially porous sheet material, (ii) a coating material on all or part(s) of a first surface of said substrate, said coating being of a material resistant to the migration therethrough of susceptor metal particles, (iii) a susceptor layer of particles of said susceptor metal on at least part(s) of the coating material of step (ii), said particles having been applied thereto by a printing process when the susceptor metal particles were in the presence of a liquid carrier, and (iv) a food contactable plastics layer overlying at least the susceptor metal particles (and preferably also any exposed first surface of said substrate and any exposed coating of (ii)), and (v) optionally, printed material on the second surface of the substrate registerable for bag or package making purposes to the area(s) of the susceptor layer to enable machine manufacture of such bags or packaged by reference to the printed material for the purpose of appropriate positioning of the susceptor layer into the wall(s) of a bag or package.

In a second aspect the present invention consists in a package is formed by heat sealing the food contactable layers of the two opposite and machine directioned edges of a feed stock of said sheet material together, and subsequent separating from said sheet material by the heat seal cutting separation of discrete bags from said sheet material.

In a further aspect the present invention consists in a method of manufacturing a sheet material suitable for the packaging of microwave heatable foods comprising (i) taking a substrate of a substantially porous sheet material, (ii) applying a coating material on all or part(s) of a first surface of said substrate, said coating being of a material resistant to the migration therethrough of susceptor metal particles, (iii) applying a susceptor layer of particles of said susceptor metal on at least part(s) of the coating material of step (ii), said particles having been applied thereto by a printing process when the susceptor metal particles were in the presence of a liquid carrier, and (iv) applying a food contactable plastics layer overlying at least the susceptor metal particles (and preferably also any exposed first surface of said substrate and any exposed coating of step (ii)), and (v) optionally, applying printed material (whether prior or subsequent or intermediate of steps (ii) to (iv)) on the second surface of the substrate registerable for bag or package making purposes to the area(s) of the susceptor layer to enable machine manufacture of such bags or packaged by reference to the printed material for the purpose of appropriate positioning of the susceptor layer into the wall(s) of a bag or package.

Preferably said substrate is paper or a non-woven sheet of cellulosic fibres.

Preferably said coating material has been applied as a fluid system to said first surface of said substrate.

Preferably said substrate is a paper of between 35 to 65gsm.

Preferably said paper is a 39gsm BK paper.

Preferably said coating material is a primer.

Preferably said primer is of a kind which provides a barrier layer to reduce the absorbing effect of the susceptor metal particles into said paper.

Preferably said primer is a high solids primer.

Preferably said primer is based on an alcohol soluble nitrocellulose blended with a low molecular weight high acid value acrylic resin SAIB (sucrose acetate iso buterate) and pigmented with calcium carbonate.

Preferably said primer is applied to said paper at a film weight of between 1.5-2.5gsm (preferably approximately 2gsm)(dry).

Preferably said primer coating consists, when being applied, of, SAIB at substantially 19.80% by weight CaC03 at substantially 19.25% by weight Nitro cellulose at substantially 10.45% by weight Cyclic ketone substantially 4.00% by weight Acrylic at substantially 4.00% by weight the remainder being a solvent such as a suitable blend of alcohol and ester.

Preferably said primer is applied to said substrate flexographically either in line or out of line.

Preferably said substrate is provided on said first surface with a complete cover of said coating.

Preferably said susceptor layer applied to at least part of said coating material is, when being applied, an ink and is pattern applied to said coating on selective regions thereof.

Preferably said susceptor layer contains a said susceptor metal of aluminium in a composite resin matrix comprising nitrous cellulose and acrylic resin.

Preferably said susceptor layer consists of, aluminium at substantially 30% by weight, hydrognated ester resin at substantially 5% by weight, cellulose asotate propionate at substantially 6.88% by weight, and acrylic at substantially 2.5% by weight, and remainder being a suitable carrier.

Preferably said susceptor layer is applied to at least part of said coating material at 0.9-1.6gsm (dry).

Preferably said susceptor layer is applied to said coating material at approximately 1.2gsm (dry).

Preferably said susceptor layer is applied to selective areas of said coating material in one pass.

Preferably said susceptor layer is applied to selective areas of said coating material as an additional pass.

Preferably said susceptor layer is applied to selective areas of said coating material by direct gravure and this may be either an in line or out of line process.

Preferably said susceptor layer is applied to selective areas of said coating material using gravure engraved images.

Preferably said susceptor layer is applied to selective areas of said coating material flexographically.

Preferably coating material is applied to said substrate to at least underlie said susceptor layer.

Preferably said food contactable plastic layer is applied to overlie all of said coating material.

Preferably said food contactable plastics layer is a heat sealable polyester.

Preferably said food contactable plastics layer may be of a multi-ply sheet material wherein at least its exposed surface is of a heat sealable and food contactable polyester.

Preferably said food contactable plastics layer is adhesive laminated to overlie at least said coating material to provide both the food contactable feature of said sheet material and to provide a heat sealable capability for the formation of packages from said sheet material.

Preferably said adhesive is thermally stable (up to the likely heating temperature of the sheet material by microwave energy) and is laminated to said heat sealable polyester.

Preferably said sealing component is amorphous polyester using a two part isocyanate adhesive yielding a dry weight of approximately 3gsm.

Preferably said adhesive is applied to the polyester on one side thereof to be bonded to said susceptor side of said substrate of substantially porous sheet material.

Preferably said printed material on said second surface of said substrate is applied to said substrate at regions to allow the registrability of said sheet material in respect of the location of the regions of said susceptor layer.

Preferably said printed material on said second surface allows for machine registrability of the region(s) of said susceptor layer both in the machine direction of said sheet material and in a direction lateral thereto.

Preferably said sheet material is provided in a reel form, from which it can be dispensed for the manufacture of said microwave package.

Preferably regions of said sheet material are bonded in a manner to define a containment region for the receipt and containment of food such that at the bonded regions of said sheet material anyone or more of said "layers" (i) to (v), save for the microwave susceptor layer, are present.

In still a further aspect the present invention consists in a package formed from a material as herein described.

In still a further aspect the present invention consists in a method of forming a pack comprising i) taking from a feed stock (preferably a rolled feed stock) of a sheet material as herein before described, ii) advancing in a substantially continuous manner, said feed stock past a manipulation means to bring together two machine direction edges of said food contactable material of said sheet material, iii) joining said two edges together, iv) heat sealing and separating in a direction substantially transverse to the machine direction, of discrete packs from the distal end of said edge joined feed stock, wherein subsequent to the taking of said sheet material from said feed stock said method also includes the registering by register apparatus of the location of said susceptor material preferably with reference to said coating on said second surface of said substrate such register apparatus being in communication with subsequent steps such that joints formed by said joining of said two edges and/or said heat sealing and separation of discrete packs, have no susceptor coating present at, at least one of the joined edges.

Preferably said taking of said sheet material from said feed stock involves the rolled dispensing of such sheet material from a feed stock by a suitable means (whether it is a powered or non powered roller or whether sheet material is drawn by drawing means from said feed stock roll or other.

Preferably said manipulation means folds said feed stock in a manner such that said two machine direction edges of said food contactable material are brought together substantially face to face.

Preferably said joining of said two edges is achieved by the heat sealing of the two machine direction edges of said food contactable material, such sealing forming an elongate and substantially continuous seam.

Preferably said register apparatus is an electronic optical sensor which is communication with the apparatus to achieve said heat sealing and separation of discrete packs.

Preferably register apparatus is also in communication with the apparatus for joining said two longitudinal edges together however said feed stock is preferably manufactured such that no susceptor coating is present at its two machine direction edges.

This invention may also be said broadly to consist in the parts, elements and features referred to or indicated in the specification of the application, individually or collectively, and any or all combinations of any two or more of said parts, elements or features, and where specific integers are mentioned herein which have known equivalents in the art to which this invention relates, such known equivalents are deemed to be incorporated herein as if individually set forth.

The invention consists in the foregoing and also envisages constructions of which the following gives examples.

One preferred form of the present invention will now be described with reference to the accompanying drawings in which; Figure 1 is a sectional view through part of a sheet material of the present invention, Figure 2 is a sectional view through an alternative but more complex version of the present invention, Figure 3 is a sectional view through part of a sheet material of yet an alternative but more complex version of the present invention, Figure 4 is a sectional view through the sheet material as shown in figure 1 wherein an additional layer is provided, Figure 5 is a sectional view at a seam of a package formed from the sheet material of the present invention, Figure 6 is a plan view of a continuous feed stock sheet material of the present invention illustrating patches of microwave susceptor regions, Figure 7 is a perspective view of part of a feed stock sheet material of the present invention wherein the layers comprising of the sheet material have been shown in partial exploded view, Figure 8 is a sectional view through a package formed from the sheet material wherein there is provided a back seal, Figure 9 is a sectional view through a package formed from sheet materials wherein there is provided a side seal, Figure 10 is a perspective view of an example of steps which may be present in a process for forming a package of sheet material from the present invention wherein the sheet material has been shown in a partially inflated form for the sake of showing locations of the seams, but such an inflated form would not normally be present in a process to manufacture such packaging.

The invention in its most preferred form is show in cross-section through a portion of the sheet material in figure 1. This sheet material 1 comprises or includes a substrate 2 which has there on a coating material 4 on all or part of a first surface 3 thereof.

In the most preferred form the coating material is applied to the entire first surface of said substrate 2. However and as can be seen in figures 2 & 4 the coating material may be applied to selective areas of the first surface of said substrate.

Onto at least parts of the coating material 4 a susceptor layer 5 may be applied. The susceptor layer is applied to coating material such that the coating material underlies the susceptor layer to provide a barrier to the absorption of susceptor particles into the substrate. The presence of susceptor particles within the substrate is undesirable as the substrate during microwave cooking provides a degree of insulation between heat generated on the or towards the first surface of said substrate and a second surface 6 of said substrate. Hence to provide a barrier to the absorption of susceptor particles into the substrate and hence increase the separation between energised susceptor material (during micro-cooking) and the second surface of said substrate, the sheet material of the present invention includes said coating material which is of a material which reduces the extent of absorption of susceptor particles into the paper. The minimising of the absorbing effect of the susceptor layer into the paper by the provision of the coating, also increases the suscpetors energy potential.

As can be seen with reference to figures 1 - 5 a coating material (whether provided to fully cover the first surface of said substrate or not) is provided to be in disposed between said substrate and the susceptor layer.

The desirable insulating characteristics of the substrate 2 make it desirable that the substrate be at or towards the outer periphery of the package formed from the sheet material of the present invention. As a result of the insulating nature of the substrate, and because of a lack of presence of susceptor material therein the removal of packages from a micro-oven after it having been energised by electromagnetic radiation can be achieved with little discomfort to the user. The energised (and still warm or hot) susceptor material immediately after being energised by electromagnetic radiation is partially insulated by the substrate to the hands or fingers of the user.

The susceptor layer is preferably applied to at least parts of said coating material by a printing process. The susceptor layer includes a susceptor metal such as for example aluminium particles. It is well known that aluminium particles are microwave interactive and in the presence of electromagnetic radiation they are energised and as a result increase in temperature. It will be appreciated by a person skilled in the art that the present invention should not be limited to there being a presence of merely one layer between the substrate and the susceptor layer. Several layers including a coating layer which reduces the extent of migration of susceptor particles into the paper, may be present between the first surface of said substrate and the susceptor layer.

In order to ensure that the side of the sheet material to be adjacent the food material to be packaged in packages therefrom is of a food contactable nature (both at ambient and elevated temperatures) the regions of the susceptor layer are covered with a food contactable plastics layer 7 (whether of a single ply or multi-ply layer) to separate the susceptor layer from the containment region and hence any food product within the containment region of packages made from the sheet material of the present invention. With reference to figures 1 and 2 in preferred forms the food contactable plastics layer also covers any exposed first surface of the substrate (figure 2) and also any exposed coating material (figure 1). For manufacturing simplicity the most preferred form is shown in figure 1 however as shown in figure 3 food contactable plastics layer may be provided to selective regions to overlie merely the susceptor layer(s).

The packaging formed from the sheet material of the present invention avoids the $33393 presence of susceptor material in at least one (and preferably both) of the plies at the seams which maybe formed. With reference to figure 5 where a seam is defined by for example the heat seal joining of edges of a sheet of the present invention, the sheet material at the seam does not include a susceptor layer.

To aid in the manufacturing of packages from the sheet material of the present invention, and to ensure that during such manufacturing there is a registrability of the sheet material and more specifically the machine registrability of the location of susceptor material within the sheet material, there is preferably provided on a second surface of said substrate, indicia (preferably printed material) in known locations with respect to the locations of the regions of the susceptor layer. With reference to figure 7, a substantially continuous sheet material of the present invention includes indicia such as printing provided on the second surface of said substrate to be used to determine the location of regions of the susceptor layer in the sheet material. The printing of machine readable indicia on the second surface of the substrate in locations may for example either overlie each of the regions of the susceptor material, or alternatively are in known locations in respect of the regions of the susceptor material, to allow the machine determination of the location of the regions of susceptor material. Hence any packages formed by said machine can be made to avoid the presence in at least one of the sheets at the ply, of a susceptor material.

With reference to figure 7, in machine direction Z, dimensions X and Y, indicate the distance of a leading and trailing edge of a region of susceptor material to allow a machine manufacturing packaging from the sheet material to determine where any seams of packaging are to be formed. Likewise in a direction lateral to the machine direction, indicia may be provided on the second surface of the substrate to determine widthwise, the boundaries of the regions of susceptor material in the sheet material of the present invention.

In figures 8 and 9 there are shown examples of how a feed stock sheet material of the present invention may be joined at seams 9 to define an elongate enclosed region of material. In figure 8 the preferred process involves the folding of a continuous sheet of material such as in part shown in figure 6, to bring its edge regions 10 together for bonding to each other.

In figure 9 an alternative is illustrated.

The printed material 11 which is preferably provided on the second surface of the substrate in the preferred form provides registrability of the location of susceptor material along the elongate direction of the feed stock sheet material of the present invention. Such registrability in this direction is desirable to determine where the formation of seals in a direction lateral to the machine direction is to be provided. Packages from the sheet Intellectual Property Office of NZ 2 3 FEB 2001 material of the present invention may be manufactured, without any registrability of the lateral location of the susceptor regions, if the edge regions 10 inherently do not have susceptor regions present. However the present invention may also be extended to include the registrability of susceptor regions lateral to the machine direction of the feed stock sheet material of the present invention. This may be desirable where there is a slitting of the sheet material in a longitudinal direction and to ensure such slitting occurs to define slit edges of sheet material where no susceptor region is present.

With reference to figure 10 the sheet material of the present invention has been brought together to overlie (in a food contactable layer to food contactable layer condition) and it can be seen how the feed stock sheet material may first be joined at sealing stations 12 to form an enclose region defined by boundaries substantially in accordance to this section shown in figure 9.

In the preferred form the food contactable layer is of a heat sealable material such as a polyester and hence the sealing stations 12, are heat sealers. The longitudinally sealed sheet material is then most preferably heat sealed and separated to define discrete packages 13. A lateral heat seal and separating operation 14 preferably achieves the heat seal and separation of the discrete packages so as to define a discrete package which has both edge and bottom sealing and provides an open mouth for subsequent filling with a food material. It will however be appreciated that the present invention is not limited to the formation of packages in this sequence and it is also envisaged that the sheet material of the present invention may be used for the provision of packages of food created by a known form, fill and seal method.

As rolled feed stock of sheet material to be processed by a package forming machine is not necessarily going to be identical for each different type of package, it is desirable for the machine to easily to be able to determine the location of the susceptor regions within the sheet material. It is to this extent that the sheet material of the present invention is preferably made where the printed material on the second surface of the substrate is in known locations in respect of the regions of susceptor material. The printed material is then able to be read by a detection device 14 as the sheet material passes through the machine to form packages form the sheet material of the present invention and is able to communicate with the necessary components of the machinery to ensure that discrete packages are formed where susceptor material is not present at any of the seams which are formed. Such a detection device 14 may for example be a photocel of optic fibre eye unit. It will be appreciated that the presence of printed material is optional but highly desirably especially in situations where the presence and location of the susceptor regions can not be otherwise easily determined.

To provide during and subsequent to the cooking of food material within the Intellectual Property Office of NZ 2 3 FEB 2001 packaging, the desirable strength and insulation characteristics for the substrate, the substrate is preferably a non woven sheet of cellulosic fibres such as for example paper or paperboard. The sheet material of the present invention is preferably formed by applying to the paper a coating material in a fluid system. Such may be for example achieved by a printing process and is preferably in a manner to provide an overall coating to the first surface of the paper. The coating material is preferably a high solids primer of a kind which provides a barrier layer to reduce the absorbing effect of the subsequent application thereon of the susceptor layer. The primer is in the preferred form applied to the paper by flexography but alternatively may be applied by gravure. To provide a suitable barrier to the absorbing effect of susceptor particles, the primer is preferably based on an alcohol soluble nitrocellulose blended with a low molecular weight high acid value acrylic resin, SAIB and pigmented with calcium carbonate. Preferably after the coating layer is applied, printing is applied to the non coated side of the paper. Register of the susceptor then takes place either in line or as an additional process.

It will be appreciated that the sheet material of the present invention, as it may be used for the heating of different kinds of food, is able to be manufactured with different shaped and sized regions of susceptor layer to provide different heating characteristics of the food within the microwave. In the preferred form the susceptor layer is pattern applied to the primer. The susceptor layer is applied thereto by a printing process when susceptor metal particles are present in a liquid carrier. The preferred form of the application of the susceptor layer is by direct gravure. This may be either an in line or out of line process. The susceptor metal particles are preferably of an aluminium (preferably of a leafing aluminium). These particles are as part of the susceptor layer in its liquid condition when applied present in a composite resin matrix comprising nitrous cellulose and acrylic resin. The metal particles are preferably applied to the coating material in one pass however alternately, (but with the selection of the materials herein described, unnecessary), may be applied to the coating material in an additional pass.

Subsequently the coating is allowed to dry, which in all cases is preferably achieved by solvent volatilisation and extraction to a level of less than 15mg/m2 this is preferably achieve by employing a convection heat/air flow drying system.

The susceptor layer is then preferably applied to known locations in respect of the printing on the other surface of the paper or is the printing applied in respect to known locations of the susceptor material.

Subsequent to the application of the regions of susceptor material to the primer, a food contactable plastics layer is provided to at least overlie the susceptor metal particles and preferably also any exposed first surface of the paper and any exposed primer. In the preferred form as shown in figure 1 the food contactable plastics layer is applied as a blanket coating to provide a separation layer between food to be packaged in packages formed from the sheet material and any of the undesirable substances in the sheet material (such as the susceptor material). The food contactable plastics material is preferably a single ply material however in alternative forms it may be a multi-ply material. The food contactable material as well as providing a layer to separate the food from any harmful or any undesirably substances in the sheet material, also provides the function of sealability to like or similar material by for example heat sealing. In the alternative form where the food contactable material may be of a multiply layer it is preferable that at least the exposed layer of the food contactable material also functions to provide the heat sealable feature.

It will however be appreciated by a person skilled in the art that alternative sealing methods may be achieved such as adhesive sealing or the like and in such instances the food contactable material does not require to have heat sealable characteristics.

A material which may be suitable as the food contactable plastics layer is a heat sealable polyester. Further preferred details of materials will be described herein after by way of examples.

Claims (76)

WHAT WE CLAIM IS:

1. A sheet material comprising or including (i) a substrate of a substantially porous sheet material, (ii) a coating material on all or part(s) of a first surface of said substrate, said coating being of a material resistant to the migration therethrough of susceptor metal particles, (iii) a susceptor layer of particles of said susceptor metal on at least part(s) of the coating material of step (ii), said particles having been applied thereto by a printing process when the susceptor metal particles were in the presence of a liquid carrier, and (iv) a food contactable plastics layer overlying at least the susceptor metal particles (and preferably also any exposed first surface of said substrate and any exposed coating of (ii)), and (v) optionally, printed material on the second surface of the substrate registerable for bag or package making purposes to the area(s) of the susceptor layer to enable machine manufacture of such bags or packaged by reference to the printed material for the purpose of appropriate positioning of the susceptor layer into the wall(s) of a bag or package.

2. A sheet material as claimed in claim 1 wherein said substrate is paper or a non-woven sheet of cellulosic fibres.

3. A sheet material as claimed in claim 1 or 2 wherein said coating material has been applied as a fluid system to said first surface of said substrate.

4. A sheet material as claimed in anyone of claims 1 to 3 wherein said substrate is a paper of between 35 to 65gsm.

5. A sheet material as claimed in claim 4 wherein said paper is a 39gsm BK paper.

6. A sheet material as claimed in anyone of claims 1 to 5 wherein said coating i \ material1 is a primer.

7. A sheet material as claimed in claim 6 wherein said primer is of a kind which provides a barrier layer to reduce the absorbing effect of the susceptor metal particles into said paper.

8. A sheet material as claimed in claims 6 or 7 wherein said primer is a high solids primer.

9. A sheet material as claimed in anyone of claims 6 to 8 wherein said primer is based on an alcohol soluble nitrocellulose blended with a low molecular weight high acid value acrylic resin SAIB (sucrose acetate iso buterate) and pigmented with calcium carbonate. -14-

10. A sheet material as claimed in anyone of claims 6 to 9 wherein said primer is applied to said paper at a film weight of between 1.5-2.5gsm (preferably approximately 2gsm)(dry).

11. A sheet material as claimed in anyone of claims 6 to 10 wherein said primer coating consists, when being applied, of, SAIB at substantially 19.80% by weight CaC03 at substantially 19.25% by weight Nitro cellulose at substantially 10.45% by weight Cyclic ketone substantially 4.00% by weight Acrylic at substantially 4.00% by weight the remainder being a solvent such as a suitable blend of alcohol and ester.

12. A sheet material as claimed in anyone of claims 6 to 11 wherein said primer is applied to said substrate flexographically either in line or out of line.

13. A sheet material as claimed in anyone of claims 1 to 12 wherein said substrate is provided on said first surface with a complete cover of said coating.

14. A sheet material as claimed in anyone of claims 1 to 13 wherein said susceptor layer applied to at least part of said coating material is, when being applied, an ink and is pattern applied to said coating on selective regions thereof.

15. A sheet material as claimed in anyone of claims 1 to 14 wherein said susceptor layer contains a said susceptor metal of aluminium in a composite resin matrix comprising nitrous cellulose and acrylic resin.

16. A sheet material as claimed in anyone of claims 1 to 15 wherein said susceptor layer consists of, aluminium at substantially 30% by weight, hydrognated ester resin at substantially 5% by weight, cellulose asotate propionate at substantially 6.88% by weight, and acrylic at substantially 2.5% by weight, and remainder being a suitable carrier.

17. A sheet material as claimed in anyone of claims 1 to 16 wherein said susceptor layer is applied to at least part of said coating material at 0.9-1.6gsm (dry).

18. A sheet material as claimed in anyone of claims 1 to 17 wherein said susceptor layer is applied to said coating material at approximately 1.2gsm (dry).

19. A sheet material as claimed in anyone of claims 1 to 18 wherein said susceptor layer is applied to selective areas of said coating material in one pass.

20. A sheet material as claimed in anyone of claims 1 to 19 said susceptor layer is applied to selective areas of said coating material as an additional pass.

21. A sheet material as claimed in anyone of claims 1 to 20 wherein said susceptor -15- layer is applied to selective areas of said coating material by direct gravure and this may be either an in line or out of line process.

22. A sheet material as claimed in anyone of claims 1 to 21 wherein said susceptor layer is applied to selective areas of said coating material using gravure engraved images.

23. A sheet material as claimed in anyone of claims 1 to 18 wherein said susceptor layer is applied to selective areas of said coating material flexographically.

24. A sheet material as claimed in anyone of claims 1 to 23 coating material is applied to said substrate to at least underlie said susceptor layer.

25. A sheet material as claimed in anyone of claims 1 to 24 wherein said food contactable plastic layer is applied to overlie all of said coating material.

26. A sheet material as claimed in anyone of claims 1 to 25 wherein said food contactable plastics layer is a heat sealable polyester.

27. A sheet material as claimed in anyone of claims 1 to 25 wherein said food contactable plastics layer may be of a multi-ply sheet material wherein at least its exposed surface is of a heat sealable and food contactable polyester.

28. A sheet material as claimed in claims 1 to 27 wherein said food contactable plastics layer is adhesive laminated to overlie at least said coating material to provide both the food contactable feature of said sheet material and to provide a heat sealable capability for the formation of packages from said sheet material.

29. A sheet material as claimed in claim 28 wherein said adhesive is thermally stable (up to the likely heating temperature of the sheet material by microwave energy) and is laminated to said heat sealable polyester.

30. A sheet material as claimed in claim 29 wherein said sealing component is amorphous polyester using a two part isocyanate adhesive yielding a dry weight of approximately 3gsm.

31. A sheet material as claimed in anyone of claims 28 to 30 wherein said adhesive is applied to the polyester on one side thereof to be bonded to said susceptor side of said substrate of substantially porous sheet material.

32. A sheet material as claimed in anyone of claims 1 to 31 wherein said printed material on said second surface of said substrate is applied to said substrate at regions to allow the registrability of said sheet material in respect of the location of the regions of said susceptor layer.

33. A sheet material as claimed in claims 1 to 32 wherein said printed material on said second surface allows for machine registrability of the region(s) of said susceptor layer both in the machine direction of said sheet material and in a direction lateral thereto.

34. A sheet material as claimed in anyone of claims 1 to 33 wherein said sheet material is provided in a reel form, from which it can be dispensed for the manufacture -16- of said microwave package.

35. A microwave food package of a sheet material as claimed in anyone of claims 1 to 34 wherein regions of said sheet material are bonded in a manner to define a containment region for the receipt and containment of food such that at the bonded regions of said sheet material anyone or more of said "layers" (i) to (v), save for the microwave susceptor layer, are present.

36. A microwave food package of a sheet material as claimed in claim 3 5 wherein said package is formed by heat sealing the food contactable layers of the two opposite and machine directioned edges of a feed stock of said sheet material together, and subsequent separating from said sheet material by the heat seal cutting separation of discrete bags from said sheet material. fyi. A method of manufacturing a sheet material suitable for the packaging of microwave heatable foods comprising (i) taking a substrate of a substantially porous sheet material,

V- (ii) applying a coating material on all or part(s) of a first surface of said substrate, said coating being of a material resistant to the migration therethrough of susceptor metal particles, (iii) applying a susceptor layer of particles of said susceptor metal on at least part(s) of the coating material of step (ii), said particles having been applied thereto by a printing process when the susceptor metal particles were in the presence of a liquid carrier, and (iv) applying a food contactable plastics layer overlying at least the susceptor metal particles (and preferably also any exposed first surface of said substrate and any exposed coating of step (ii)), and (v) optionally, applying printed material (whether prior or subsequent or intermediate of steps (ii) to (iv)) on the second surface of the substrate registerable for bag or package making purposes to the area(s) of the susceptor layer to enable machine manufacture of such bags or packaged by reference to the printed material for the purpose of appropriate positioning of the susceptor layer into the wall(s) of a bag or package.

38. A method of manufacturing as claimed in claim 37 wherein said coating material is applied as a fluid system to said first surface of said substrate.

39. A method of manufacturing as claimed in claims 37 or 38 wherein said coating material is a primer.

40. A method of manufacturing as claimed in claim 39 wherein said primer is of a kind which provides a barrier layer to reduce the absorbing effect of the susceptor metal particles into said paper. -17-

41. A method of manufacturing as claimed in claims 39 or 40 wherein said primer is a high solids primer.

42. A method of manufacturing as claimed in any one of claims 39 to 41 wherein said primer is based on an alcohol soluble nitrocellulose blended with a low molecular weight high acid value acrylic resin SAIB (sucrose acetate iso buterate) and pigmented with calcium carbonate.

43. A method of manufacturing as claimed in any one of claims 39 to 42 wherein said primer is applied to said paper at a film weight of between 1.5-2.5gsm (preferably approximately 2gsm)(dry).

44. A method of manufacturing as claimed in any one of claims 39 to 43 wherein said primer coating consists, when being applied, of, SAIB at substantially 19.80% by weight CaC03 at substantially 19.25% by weight Nitro cellulose at substantially 10.45% by weight Cyclic ketone substantially 4.00% by weight Acrylic at substantially 4.00% by weight the remainder being a solvent such as a suitable blend of alcohol and ester.

45. A method of manufacturing as claimed in any one of claims 39 to 44 wherein said primer is applied to said substrate flexographically either in line or out of line.

46. A method of manufacturing as claimed in any one of claims 37 to 45 wherein said substrate is provided on said first surface with a complete cover of said coating.

47. A method of manufacturing as claimed in any one of claim 37 to 46 wherein said susceptor layer applied to at least part of said coating material is, when being applied, an ink and is pattern applied to said coating on selective regions thereof.

48. A method of manufacturing as claimed in any one of claims 37 to 47 wherein said susceptor layer contains a said susceptor metal of aluminium in a composite resin matrix comprising nitrous cellulose and acrylic resin.

49. A method of manufacturing as claimed in any one of claims 37 to 48 wherein said susceptor, in a form when being applied, consists of, aluminium at substantially 30% by weight, hydrognated ester resin at substantially 5% by weight, cellulose asotate propionate at substantially 6.88% by weight, and acrylic at substantially 2.5% by weight, and remainder being a suitable carrier.

50. A method of manufacturing as claimed in any one of claims 37 to 49 wherein said susceptor layer is applied to at least part of said coating material at 0.9-1.6gsm (dry).

51. A method of manufacturing as claimed in any one of claims 37 to 50 wherein said -18- susceptor layer is applied to said coating material at approximately 1.2gsm (dry).

52. A method of manufacturing as claimed in any one of claims 37 to 51 wherein said susceptor layer is applied to selective areas of said coating material in one pass.

53. A method of manufacturing as claimed in any one of claims 37 to 52 wherein said susceptor layer is applied to selective areas of said coating material as an additional pass.

54. A method of manufacturing as claimed in any one of claims 37 to 53 wherein said susceptor layer is applied to selective areas of said coating material by direct gravure and this may be either an in line or out of line process.

55. A method of manufacturing as claimed in any one of claims 37 to 54 wherein said susceptor layer is applied to selective areas of said coating material using gravure engraved images.

56. A method of manufacturing as claimed in any one of claims 37 to 52 wherein said susceptor layer is applied to selective areas of said coating material flexographically.

57. A method of manufacturing as claimed in any one of claims 37 to 56 wherein coating material is applied to said substrate to at least underlie said susceptor layer.

58. A method of manufacturing as claimed in any one of claims 37 to 57 wherein said food contactable plastic layer is applied to overlie all of said coating material.

59. A method of manufacturing as claimed in any one of claims 37 to 58 wherein said food contactable plastics layer is a heat sealable polyester.

60. A method of manufacturing as claimed in any one of claims 37 to 59 wherein said food contactable plastics layer may be of a multi-ply sheet material wherein at least its exposed surface is of a heat sealable and food contactable polyester.

61. A method of manufacturing as claimed in any one of claims 37 to 60 wherein said food contactable plastics layer is adhesive laminated to overlie at least said coating material to provide both the food contactable feature of said sheet material and to provide a heat sealable capability for the formation of packages from said sheet material.

62. A method of manufacturing as claimed in claim 61 wherein said adhesive is thermally stable (up to the likely heating temperature of the sheet material by microwave energy) and is laminated to said heat sealable polyester.

63. A method of manufacturing as claimed in claim 62 wherein said sealing component is amorphous polyester using a two part isocyanate adhesive yielding a dry weight of approximately 3gsm.

64. A method of manufacturing as claimed in claims 62 or 63 wherein said adhesive is applied to the polyester on one side thereof to be bonded to said susceptor side of said substrate of substantially porous sheet material.

65. A method of manufacturing as claimed in any one of claims 37 to 64 wherein said printed material on said second surface of said substrate is applied to said substrate at -19- regions to allow the registrability of said sheet material in respect of the location of the regions of said susceptor layer.

66. A method of manufacturing as claimed in any one of claims 37 to 65 wherein said printed material on said second surface is applied in a manner which allows for machine registrability of the region(s) of said susceptor layer both in the machine direction of said sheet material and in a direction lateral thereto.

67. A method of manufacturing as claimed in any one of claims 37 to 66 wherein said sheet material is provided in a reel form, from which it can be dispensed for the manufacture of said microwave package.

68. A method of manufacturing as claimed in any one of claims 37 to 67 to form a package of the sheet material wherein regions of said sheet material are bonded in a manner to define a containment region for the receipt and containment of food such that at the bonded regions of said sheet material anyone or more of said "layers" (i) to (v), save for the microwave susceptor layer, are present.

69. A method of manufacturing as claimed in claim 68 wherein said package is formed by heat sealing the food contactable layers of the two opposite and machine directioned edges of a feed stock of said sheet material together, and subsequent separating from said sheet material by the heat seal cutting separation of discrete bags from said sheet material.

70. A package formed from a material as claimed in anyone of claims 1 to 36

71. A method of forming a pack comprising / ■'i) taking from a feed stock (preferably a rolled feed stock) of a sheet material as herein before described, ii) advancing in a substantially continuous manner, said feed stock past a manipulation means to bring together two machine direction edges of said food contactable material of said sheet material, / o iii) joining said two edges together, iv) heat sealing and separating in a direction substantially transverse to the machine direction, of discrete packs from the distal end of said edge joined feed stock, wherein subsequent to the taking of said sheet material from said feed stock said method also includes the registering by register apparatus of the location of said susceptor material preferably with reference to said coating on said second surface of said substrate such register apparatus being in communication with subsequent steps such that joints formed by said joining of said two edges and/or said heat sealing and separation of discrete packs, have no susceptor coating present at, at least one of the joined edges.

72. A method of forming a pack as claimed in claim 71 wherein said taking of said sheet material from said feed stock involves the rolled dispensing of such sheet material from a feed stock by a suitable means (whether it is a powered or non powered roller or -20- whether sheet material is drawn by drawing means from said feed stock roll or other.

73. A method of forming a pack as claimed in claims 71 or 72 wherein said manipulation means folds said feed stock in a manner such that said two machine direction edges of said food contactable material are brought together substantially face to face.

74. A method of forming a pack as claimed in claims 71 to 73 wherein said joining of said two edges is achieved by the heat sealing of the two machine direction edges of said food contactable material, such sealing forming an elongate and substantially continuous seam.

75. A method of forming a pack as claimed in claims 71 to 74 wherein said register apparatus is an electronic optical sensor which is communication with the apparatus to achieve said heat sealing and separation of discrete packs.

76. A method of forming a pack as claimed in claims 71 to 74 wherein said register apparatus is also in communication with the apparatus for joining said two longitudinal edges together however said feed stock is preferably manufactured such that no susceptor coating is present at its two machine direction edges. DATED THIS H:\library\patents\djj\ahb\392615.ahb