CA1126221A - Flexible pouches and bags - Google Patents

Abstract

A B S T R A C T

A flexible pouch comprises two layers of heat-sealable thermoplastics material applied to opposite surfaces of an intermediate layer other than a layer of metal foil or to surfaces of each other, the materials of the said two layers having limited compatibility 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 materials. An intermediate layer may be of transparent or opaque material or of a material loaded with a salt capable of keeping the moisture condition of contents of a pouch within limites required for their protection.

Description

llZti~21 ., , This invention conc~rns improvements relating to flexible pouches and bags, hereinafter referred to as pouches, and is concerned with improvements upon pouches described and claimed in the Specification of Canadian Patent No. 935,790.
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 cf 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 temp-erature, time and pressure are, although hermetic, capable of being peeled open. Also in the pre~ent specification and ~laims, the term limited compatib lity is ueed with the meaning so defined.
The present invention seeks to provide improvements or mod-ifications offering addltional advantages of versatility, practical utility and, in some cases, reduction of cost of a flexible pouch comprising a laminate of two layers of heat-sealable thermoplastic plastics material permanently adherent to opposite surfaces of an intermediate layer.
The selection of intermediate layer will depend upon the requirements imposed by the intended contents of the pouch and ., , ~26~2~

-2-the intended made of use. Factors to be considered in this connection, apart from cost, are the required barrier properties with respect to humidity and, in somc cases, to light and heat conditions, the required s.trength and rigidity or flexibility of the pouch, the balance of desirability of transparency for attractiuely 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:
The intermediate layer may be transparent, for example in the form of a filrn of transparent cellulosic or plastic material, ~hich may be coated or uncoated as hereinafter described.
An opaque intermediate layer may be a vacuum metallised and/or otherwise opaque-coated.or uncoated film of cellulosic or plastics material or a layer of paper or paper~board, which may be coated or uncoated and/or vacuum metallised, may be employed.

T~e intermediate layer is adapted for con~ributing positively to the maintenancë of required moisture-conditions in the -pourch, and comprises, for example, a layer .
of paper or plastics material loaded with a salt capable of keeping the equilibrium mo:.sture content of, in particular, tobacco within a narrow range required for protection of the contents of the pouch, particularly optimum smcking quality.
A flexi~l~ pouch in accordance with th0 invention comprises a laminate of two layers of heat-sealable thermoplastics material permanently adherent to oppasite surfares of an inter-mediate flexible barrier layer of sheet material of the group `'` llZ6ZZ~

consisting of cellulosic and plasticg ~aterials, the materials of the said two layers having different melting points and having limited compatibility 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 said thermoplastics materials and a surface of the other of those materials, the said intermediate layer being loaded with a salt capable of keeping the moisture condition of the contents of the pouch within pre- .
determined limits required for the protection of the .said contents, that layer of the two layers of thermoplastics material which is on the inside of the pouch being permeable to water vapour to permit exchange of water vapour between the said salt and the contents of the pouch, while the other of the said two layers, which is on the outside of the pouch,is permeable to water vapour but substantially less so than the said layer on the inside.
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 50C 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:
An intermediate humidity-control layer was made of absorbent paper impregnated with a saturated solution of sodium chloride for ';q - - , .. , ... , . , .. .. ~. .....
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maintaining in the pouch an at~osphere such that tobacco stored of therein has a moisture content/substantially 12.5¢~ throughout its period of stora~e prior to'sale and consumption. The other layers were of polyethylene film such as i5 described under Ta) below. 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.
From the laminate material a pouch was produced. Ihe conform-ation of the blank and manner of production were as described and illustrated in the aforesaid Specification. Thus the pouch possessed a seal which, although hermetic, was capable of being peeled open.
The relative humidity maintained in the pouch is determined by the particular salt used, but will vary with ambient temp-erature 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.
Example 2:
A pouch of size 157mm x 127mm with a flap 157mm x 85mm is made of three laysrs. The outer layer of the pouch is made ' ' i ' ' ~ I

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from 150 micron thick polyethylene having a moisture-vapour transmission rate (M.V.T.R.) of 2.5 g/m2/24hr at 38C, 90O
relative humidity (R.H.). The central layer is of an 80 9/m2 absorbent paper, of dimens`ions 150mm x 335 mm, which has been impregnated with 1.19 of dry sodium chloride. In addition, the paper layer contains 1.5 millilitres of water. The inner layer is made from a copolymer of vinyl-acetate (12~) and ethylene (88~) having a M.~.T.R. of 50 9/m2/24 hr at 3ac, 9ooo 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 75~1o at 25C with a rate of change in RH with temperature equal to 0. 02o RH per degree centigrade change of temperature.
The pouch would be used to contain 50y of pipe tobacco at a moisture cont~nt of 20~, the RH required to maintain this moisture content being 75O. 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 condition~. For example, at 35O RH ~8C, 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 90O RH 3BC, the 20~ level would be maintained for approximately 13 weeks before the tobacco began to gain moisture at a rate dictated by the , , ~ . . ,,,, . , .. , ..... . . . .. . .. ... , ~ . . . . .

l~Z6Z21 degree of unsaturation of the enclosed salt-solution/paper layer.
Ta) For the production o~ a transparent flexible pouch, a sheet material of triple-ply construction was prepared which consisted of an intermediate transparent layer of 44.5 9/m2 polyvinylidene chloride co-polymer-coated cellulosic film, supplie by British Cellophane Limited as 445 MXXT/A cellophane laminated by 2 g/m2 of polyuretllane-based adhesive to polyethylene films, both of which were 5Cmym thick, one having a melting range of 100-105C and the other a melting range of 105-125C, 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 gtm2 of a copolymer of vinylldene chloride/
acrylonitrile/acry~ate.
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.
T b) As an alternative intermediate transparent layer, use was made of a 32.5 9/m2 uncoated cellulose film supplied by British Cellophane Limited as 325P cellophane.
Tc) Another intermediate transparent layer employed was of 18 mym thick polyvinylidene chloride co-polymer-coated oriented ~g-~ . ~ 6,e ~tl6 ti~
~ polypropylene, ~upplied by I.C.I. Limited ~ Propafilm 'C' .,'~;~ , ~ ~ ...., .:

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T d) Finally an intermediate transparent layer of 20 mym nylon - 6 film was used.
The materials ofTb) toTd) provi~ed properties similar to those obtained withTa),butTb), apart from transparency, had lower-barrier properties, whileTd) gave additional toughness.
For an opaque intermediate layer:-Oa) A sheet material was prepared which consiste~ of a36.5 9/m2 film o~ polyvinylidene chloride co-polymer-coated cellulosic film supplied by British CellGphane Limited as 365 MXXT/A cellophane on which aluminium metal had been deposited on both sides by ~acuum-metallisation to a thickness givir.g an optical density (inverse of logarithm of light trans mitted) of 2.5-4, the metallised film forming the intermediate layer in a lamination between two polyethy~ene films of different melt range as described under Example l.
Aluminium may be deposited on one side only of the film.
o b) An alternative opaque intermediate layer consisted of a 44.5 9/m2 white opaque polyvinylidene chloride co-polymer-coated cellulosic film supplied by British Cellophane Limited as 445 MXXB/A.
c) As another opaque 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 - 4Ø
In addition to advantages with respect to barrier properties, appearance and other features referred to above, a ~etallic or other opaque appearance can be obtained at low cost. Especially the intermediate layer of Ob) can be printed upon.

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Opaque intermediate laye.rs of paper or paper-board are also possible;-Od) An opaque sheet material was prepared whichconsisted of an intermediate layer of 100 g/m2 clay-coated paper, m~rketed-u~der-the trademark: Clan Label by the Inveresk Paper Company Limited, in a lamination between two polyethylene films of different melt range as previously described.
Oe) The intermediate layer consisted of 52 g/m2 plastic paper of the kind marketed under the trade mark Tyvek by the Dupont Company.
In addition to opacityl 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 Oe).

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Claims (2)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A flexible pouch comprising a laminate of two layers of heat-sealable thermoplastics material permanently adherent to opposite surfaces of an intermediate flexible barrier layer of sheet material of the group consisting of cellulosic and plastics materials, the materials of the said two layers having different melting points and having limited compatibility 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 said thermoplastics materials and a surface of the other of those materials, the said intermediate layer being loaded with a salt capable of keeping the moisture condition of contents of the pouch within predetermined limits required for the protection of the said contents, that layer of the two layers of thermoplastics material which is on the inside of the pouch being permeable to water vapour to permit exchange of water vapour between the said salt and the contents of the pouch, while the other of the said two layers, which is on the outside of the pouch is permeable to water vapour but substantially less so than the said layer on the inside.

2. A pouch according to claim 1, wherein the intermediate layer is of absorbent paper impregnated with sodium chloride, the layer on the outside is of a polyethylene material permeable to water vapour and the layer on the inside is of a thermo-plastics material more permeable to water vapour than the material of the outside layer.