GB1579832A

GB1579832A - Flexible pouches and bags

Info

Publication number: GB1579832A
Application number: GB20774/76A
Authority: GB
Original assignee: Mardon Flexible Packaging Ltd; British American Tobacco Co Ltd
Current assignee: British American Tobacco Investments Ltd; Lawson Mardon Flexible Ltd
Priority date: 1976-05-19
Filing date: 1976-05-19
Publication date: 1980-11-26
Also published as: DE2722621A1; AU510452B2; AU2525477A; CA1126221A; NL7705439A

Description

(54) IMPROVEMENTS RELATING TO FLEXIBLE POUCHES AND BAGS (71) We, BRITISH-AMERICAN TOBACCO COMPANY LIMITED, of Westminster House, 7, Millbank, London. S.W. 1., a Company incorporated under the laws of Great Britain, and MARDON FLEXIBLE PACKAGING LIMITED, of P.O. Box 3, Norton Hill Factory, Midsomer Norton, Bath, Somerset, a Company incorporated under the laws of Great Britain, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method in which it is to be performed, to be particularly described in and by the following statement: This invention concerns improvements relating to flexible pouches and bags, hereinafter referred to as pouches, and is concerned with improvements upon or modifications of pouches described and claimed in the Specification of Patent No. 1,254,444.

In that Patent, a flexible pouch is claimed comprising two layers of heat-sealable thermoplastic plastics materials adherent to opposite surfaces of a layer of metal foil, the materials of the said two layers having different melting points and having limited compatibility with each other and the pouch being sealed, where it will require to be opened, at a line or lines of contact between surfaces of different layers of the plastics materials. Limited compatibility is defined as meaning compatibility such that seals produced between surfaces of the two materials on melting the said surfaces under predetermined conditions of temperature, time and pressure are, although hermetic, capable of being peeled open. Also in the present specification and claims, the term limited compatibility is used with the meaning so defined.

The present invention seeks to provide improvements or modifications offering additional advantages of versatility, practical utility and, in some cases, reduction of cost.

According to the invention, a flexible pouch comprises a laminate of two layers of heat-sealable thermoplastic plastics material permanently adherent to opposite surfaces of an intermediate layer, such intermediate layer not being a layer of metal foil and the materials of the said two layers having different melting points and having limited compatibility (as hereinbefore defined) with each other and the pouch being heat-sealed, where it will require to be opened, at a line or lines of contact between a surface of one of the thermosplastics materials and a surface of the other of those materials.

The selection of intermediate layer will depend upon the requirements imposed by the intended contents of the pouch and the intended mode of use. Factors to be considered in this connection, apart from cost, are the required barrier properties with respect to humidity and, in some cases, to light and heat conditions, the required strength and rigidity or flexibility of the pouch, the balance of desirability of transparency for attractively displaying the contents and/or printed matter within the pouch against that of opacity for protecting the contents against ill effects of exposure to light. With these and other factors, hereinafter referred to, in mind, the following choices are open: A pouch is thus made from a laminate comprising two layers of thermoplastic materials permanently adherent to opposite surfaces of an intermediate layer or "core" of non-metallic material.This intermediate layer may be transparent, for example in the form of a film of transparent celllulosic or plastic material, which may be coated or uncoated as hereinafter described.

Use may be made of an opaque intermediate layer, which may be a vacuum metallised and/or otherwise opaque-coated or uncoated film of cellulosic or plastics material.

An intermediate layer of paper of paper board, which may be coated or uncoated and/or vacuum metallised, may be employed.

An intermediate layer may be provided which is adapted for contributing positively to the maintenance of required moisture conditions in the pouch, for example a layer of paper or plastics material loaded with a salt capable of keeping the equilibrium moisture content of, in particular, tobacco within a narrow range required for protection of the contents of the pouch, particularly optimum smoking quality.

In all cases, the outer layers of thermoplastics materials of limited compatibility may be polyolefin materials having different melting points, a difference within a range of 5 to 500C being appropriate in the case of polyethylene materials. Suitably, the material forming the outside of the pouch will have the higher melting point.

The conformation and manner of production of the pouch may be as described and illustrated in our aforesaid Specification.

Ways of carrying the invention into effect will now be more fully described by way of example: Example 1, transparent intermediate layer: a). For the production of a transparent flexible pouch, a sheet material of tripleply construction was prepared which consisted of an intermediate transparent layer of 44.5 g/m2 polyvinylidene chloride copolymer-coated cellulosic film, supplied by British Cellophane Limited as 445 MXXT/A Cellophane (Registered Trade Mark), laminated by 2 glum2 of polyurethane-based adhesive to polyethylene films, both of which were 50mym thick, one having a melting range of 100-105 C and the other a melting range of 105-125"C, the material of the layer forming the outside of the pouch having a higher melting point than that of the inner layer.The coating, present on both sides of the intermediate layer, comprised 1.5 to 2.5 g/m2 of a copolymer of vinylidene chloride/acrylonitrile acrylate.

From this material" a pouch was produced, the conformation of the blank and manner of production being as described and illustrated in the aforesaid Specification.

Thus the pouch possessed a seal which, although hermetic, was capable of being peeled open.

Such a pouch, while possessing effective barrier properties, allows the contents to be clearly seen. Due to the flexibility of the pouch, possible danger of damage during storage and transit are reduced, and the pouch has a good appearance and soft feel.

Deformation and loss of appearance when the contents are packaged under reduced air pressure was avoided. Finally a reduction in cost can be achieved.

b). As an alternative intermediate transparent layer, use was made of a 32.5 glm2 uncoated cellulose film supplied by British Cellophane Limited as 325P Cellophane.

(R.T.M.) c). Another intermediate transparent layer employed was of 18 mym thick polyvinylidene chloride co-polymer-coated oriented polypropylene, supplied by I.C.I. Limited as Propafilm 'C' (Registered Trade Mark).

d). Finally an intermediate transparent ]ayer of 20 mym nylon - 6 film was used.

The materials of b) to d) provided properties similar to those obtained with a), but b), apart from transparency, had lowerbarrier properties, while d) gave additional toughness.

Example 2, opaque intermediate layer: a) A sheet material was prepared which consisted of a 36.5 glm? film of polyvinylidene chloride co-polymer-coated cellulosic film suppied by British Cellophane Limited as 365 MXXT/A Cellophane (R.T.M.) on which aluminium metal had been deposited on both sides by vacuummetallisation to a thickness giving an optical density (inverse of logarithm of light transmitted) of 2.54, the metallised film forming the intermediate layer in a lamination between two polyethylene films of different melt range as described under Example 1 a).

Aluminium may be deposited on one side only of the film.

b) An alternative intermediate layer consisted of a 44.5 g/m2 white opaque polyvinylidene chloride co-polymer-coated cellulosic film supplied by British Cellophane Limited as 445 MXXB/A.

c) As another intermediate layer, use was made of a 12 mym film of polyethylene terephthallate metallised on one side to give an optical density of 3.5 - 4.0.

In addition to advantages with respect to barrier properties, appearance and other features referred to above under 1 a), a metallic or other opaque appearance can be obtained at low cost. Especially the in terinediate layer of 2 b) can be printed upon.

Example 3, opaque intermediate layer of paper or paper-board: a) An opaque sheet material was prepared which consisted of an intermediate layer of 100 g/m2 clay-coated paper, known as Clan Label and supplied by the Inveresk Paper Company Limited, in a lamination between two polyethylene films of different melt range as previously described.

b) The intermediate layer consisted of 52 glum2 plastic paper of the kind known as Tyvek (Registered Trade Mark) supplied by the DuPont Company.

In addition to opacity, such intermediate layers afford stiffness or rigidity, together, with good properties against mechanical damage in conjunction with low cost. An especially attractive appearance is provided by 1 b).

Example 4. humidity-control layer: a) An intermediate layer is made of absorbent paper impregnated with a saturated solution of sodium chloride for maintaining in the pouch an atmosphere such that tobacco stored therein has a moisture content of substantially 12.5% throughout its period of storage prior to sale and consumption. The other layers are of polyethylene film such as is described under 1 a). The permeability of the inner layer, i.e. the layer facing the contents of the pouch or pack, should be such as to allow the exchange of water vapour between the contents and the salt. The outer layer, i.e. the layer between the salt and the atmosphere, should be substantially less permeable than the inner layer. The permeability can be controlled for example by varying the thickness of the layers.

The relative humidity maintained is determined by the particular salt used, but will vary with ambient temperature and the salt must be chosen with this in mind. The quantities of salt and water in the paper determine the period of protection, but this protection will vary also with the ambient relative humidity and the permeability of the polyethylene. The salt will give up or adsorb moisture depending on the ambient vapour pressure.

b) A pouch of size 157mm x 127mm, with a flap 157mm x 85mm, is made of three layers. The outer layer of the pouch is made from 150 micron thick polyethy- lene having a moisture-vapour transmission rate (M.V.T.R.) of 2.5 g/m2/24hr at 38"C, 90% relative humidity (R.H.). The central layer is of an 80 g/m2 absorbent paper, of dimensions 150mm x 335mm, which has been impregnated with l.lg of dry sodium chloride. In addition, the paper layer contains 1.5 millilitres of water. The inner layer is made from a copolymer of vinylacetate (12%) and ethylene (88%) having a M.V.T.R. of 50 g/m2/24hr at 38"C, 90% R.H. The central layer is fully enclosed on all edges by the plastics layers and may be laminated to their inner sides.This system will maintain within the pouch an RH of 75.1% at 25"C, with a rate of change in RH with temperature equal to 0.02% RH per degree centigrade change of temperature.

The pouch would be used to contain 50g of pipe tobacco at a moisture content of 20%, the RH required to maintain this moisture content being 75%. It would be hermetically sealed and the seal at its mouth would be peelable by virtue of the differential sealing properties of the dissimilar plastics layers.

In storage, the pouch would maintain the moisture content of the tobacco at 20% for different periods depending on the actual storage conditions. For, example, at 35% RH 38"C, the level of 20% would be maintained for about five weeks before the tobacco began to lose moisture at a rate dictated by the M.V.T.R. of the outside plastics layer. At 90% RH 38 C, the 20% level would be mainlained for approximately 13 weeks before the tobacco began to gain moisture at a rate dictated by the degree of unsaturation of the enclosed saltsolution/paper layer.

WHAT WE CLAIM IS: 1. A flexible pouch comprising a laminate of two layers of heat-sealable thermoplastic plastics material permanently adherent to opposite surfaces of an intermediate layer, such intermediate layer not being a layer of metal foil and the materials of the said two layers having different melting points and having limited compatibility (as hereinbefore defined) with each other and the pouch being heat-sealed, where it will require to be opened, at a line or lines of contact between a surface of one of the thermoplastics materials and a surface of the other of those materials.

2. A pouch according to claim 1, wherein the said two layers are of polyolefin materials.

3. A pouch according to claim 1, wherein the said two layers are of polyethylene materials.

4. A pouch according to any one of claims 1 to 3, wherein the intermediate layer is of transparent material.

5. A pouch according to claim 4, wherein the intermediate layer is a film of transparent, coated or uncoated, cellulosic or plastics material.

6. A pouch according to claim 5, wherein the material of the intermediate layer is coated with a co-polymer material.

7. A pouch according to claim 6, wherein the intermediate layer is of oriented polypropylene coated with polyvinylidene chloride co-polymer.

8. A pouch according to claim 5, wherein the intermediate layer is a film of nylon 6 6 material.

9. A pouch according to any one of claims 1 to 3, wherein the intermediate layer is of opaque material.

10. A pouch according to claim 9, wherein the intermediate layer is of a material which has been vacuum-metallised on one or both surfaces.

11. A pouch according to claim 9 or 10, wherein the said material is a coated cellulosic material.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. In addition to opacity, such intermediate layers afford stiffness or rigidity, together, with good properties against mechanical damage in conjunction with low cost. An especially attractive appearance is provided by 1 b). Example 4. humidity-control layer: a) An intermediate layer is made of absorbent paper impregnated with a saturated solution of sodium chloride for maintaining in the pouch an atmosphere such that tobacco stored therein has a moisture content of substantially 12.5% throughout its period of storage prior to sale and consumption. The other layers are of polyethylene film such as is described under 1 a). The permeability of the inner layer, i.e. the layer facing the contents of the pouch or pack, should be such as to allow the exchange of water vapour between the contents and the salt. The outer layer, i.e. the layer between the salt and the atmosphere, should be substantially less permeable than the inner layer. The permeability can be controlled for example by varying the thickness of the layers. The relative humidity maintained is determined by the particular salt used, but will vary with ambient temperature and the salt must be chosen with this in mind. The quantities of salt and water in the paper determine the period of protection, but this protection will vary also with the ambient relative humidity and the permeability of the polyethylene. The salt will give up or adsorb moisture depending on the ambient vapour pressure. b) A pouch of size 157mm x 127mm, with a flap 157mm x 85mm, is made of three layers. The outer layer of the pouch is made from 150 micron thick polyethy- lene having a moisture-vapour transmission rate (M.V.T.R.) of 2.5 g/m2/24hr at 38"C, 90% relative humidity (R.H.). The central layer is of an 80 g/m2 absorbent paper, of dimensions 150mm x 335mm, which has been impregnated with l.lg of dry sodium chloride. In addition, the paper layer contains 1.5 millilitres of water. The inner layer is made from a copolymer of vinylacetate (12%) and ethylene (88%) having a M.V.T.R. of 50 g/m2/24hr at 38"C, 90% R.H. The central layer is fully enclosed on all edges by the plastics layers and may be laminated to their inner sides.This system will maintain within the pouch an RH of 75.1% at 25"C, with a rate of change in RH with temperature equal to 0.02% RH per degree centigrade change of temperature. The pouch would be used to contain 50g of pipe tobacco at a moisture content of 20%, the RH required to maintain this moisture content being 75%. It would be hermetically sealed and the seal at its mouth would be peelable by virtue of the differential sealing properties of the dissimilar plastics layers. In storage, the pouch would maintain the moisture content of the tobacco at 20% for different periods depending on the actual storage conditions. For, example, at 35% RH 38"C, the level of 20% would be maintained for about five weeks before the tobacco began to lose moisture at a rate dictated by the M.V.T.R. of the outside plastics layer. At 90% RH 38 C, the 20% level would be mainlained for approximately 13 weeks before the tobacco began to gain moisture at a rate dictated by the degree of unsaturation of the enclosed saltsolution/paper layer. WHAT WE CLAIM IS:

1. A flexible pouch comprising a laminate of two layers of heat-sealable thermoplastic plastics material permanently adherent to opposite surfaces of an intermediate layer, such intermediate layer not being a layer of metal foil and the materials of the said two layers having different melting points and having limited compatibility (as hereinbefore defined) with each other and the pouch being heat-sealed, where it will require to be opened, at a line or lines of contact between a surface of one of the thermoplastics materials and a surface of the other of those materials.

12. A pouch according to claim 9 or 10,

wherein the intermediate layer is of paper or paper board.

13. A pouch according to any one of the preceding claims, wherein the intermediate layer is of paper or plastics material loaded with a salt capable of keeping the moisture condition of the interior of the pouch within predetermined limits.

14. A pouch according to any one of claims 1 to 12 and containing tobacco to be protected, wherein the intermediate layer is of paper or plastics material loaded with a salts capable of keeping the moisture condition of the said tobacco within predetermined limits required for the protection thereof.

15. A pouch according to claim 1 and substantially as hereinbefore described with reference to any one of the Examples.