US20100038266A1

US20100038266A1 - Packaging Laminate

Info

Publication number: US20100038266A1
Application number: US12/516,972
Authority: US
Inventors: Hans Hällström; Susanne Gratz; Fredrik Solhage
Original assignee: Akzo Nobel NV
Current assignee: Akzo Nobel NV
Priority date: 2006-12-01
Filing date: 2007-11-29
Publication date: 2010-02-18
Also published as: CA2671041A1; US20100047404A1; US20100048768A1; WO2008066489A1; NO20092461L; PL2087171T3; EP2087171A1; JP2010511798A; EP2086756A1; WO2008066488A1; NO20092462L; JP2010511797A; EP2086757A1; US8013041B2; EP2087171B1; JP2010511796A; CA2671038A1; WO2008066487A1; CA2671102A1; JP5070294B2

Abstract

The invention relates to a packaging laminate comprising at least one base layer of paper or paper board and at least one liquid barrier layer, said paper or paper board comprising expanded or unexpanded expandable thermoplastic microspheres. The invention further relates to the production and use of a packaging laminate and a package for food or beverage products and its production.

Description

The present invention relates to a packaging laminate, its production and use, and a package for food products and its production.
Packaging laminate comprising at least one layer of paper or paper board is widely used for packaging containers for food products. Examples of such laminate are disclosed in e.g. WO 02/090206, WO 97/02140, WO 97/02181 and WO 98/18680.
Finished packaging containers can be produced from packaging laminates with modern packing and filling machines that form, fill and seal the packages. In connection with the forming and filling of the package, the packaging laminate may be treated with a disinfectant such as aqueous hydrogen peroxide. When food is packed for a long shelf-life, the entire package may be treated in a retort at high temperature and super-atmospheric pressure, for example by hot steam, and then rapidly cooled by direct contact with water. In either of these cases liquid or moisture may penetrate into the paper or paper board layer where the edges are freely exposed. Various attempts to solve this problem have been disclosed.
The previously mentioned WO 02/090206 discloses that the paper or paper board should be rendered hydrophobic by stock sizing with an aqueous dispersion of alkyl ketene dimer.
WO 03/021040 discloses a paperboard for packages composed of one or more layers with a top layer of bleached kraft pulp having a gloss value of 15-50%, a minimal gloss variation, a density in the range of 700 to 850 kg/m³and being hydrophobic from a sizing agent treatment of each layer.
WO 2005/003460 discloses a package intended for thermal treatment comprising a fibre-based packaging material treated with a hydrophobic size and comprising one or more layers for reduced water penetration outside and/or inside the fibre substrate. The fibre substrate is treated with a combination of a wet-strength size, a hydrophobic size and an aluminium and/or calcium compound.
WO 03/106155 discloses a way of forming a container from a packaging laminate to protect the edges against moisture penetration.
WO 2004/056666 discloses a certain heating cycle for packages to minimise edge penetration of moisture.
JP Laid Open No. 2002-254532 describes containers of heat insulating paper containing thermoplastic microspheres. It is disclosed that the edge wick is improved by disabling expansion of the microspheres at the edges of the paper.
Other disclosures relating to the use of thermoplastic microspheres in paper for various application include U.S. Pat. Nos. 3,556,934, 4,133,688, 5,125,996 and 6,379,497, JP Patent 2689787, JP Laid Open No. 2003-105693, WO 01/54988, WO 2004/099499, WO 2004/101888, WO 2004/113613 and WO 2006/068573, US Patent Appln. Publ. No. 2001/0038893, and Ö, Söderberg, “World Pulp & Paper Technology 1995/96, The International Review for the Pulp & Paper Industry” p. 143-145.
Various sizing formulations are disclosed in e.g. U.S. Pat. Nos. 4,654,386, 5,969,011, 6,093,217, 6,165,259, 6,306,255, 6,444,024, 6,485,555, 6,692,560, 6,818,100 and 6,846,384.
An object of the invention is to provide a package for food products made from a packaging laminate with high resistance against penetration of liquid or moisture at the edges of the laminate.
A further object of the invention is to provide a paper or paper board containing packaging laminate with properties suitable for such a package.
It has been found that these objects can be achieved by including expanded or unexpanded expandable thermoplastic microspheres in the paper or at least at the edges of the paper.
Thus, one aspect of the invention concerns a packaging laminate comprising at least one base layer of paper or paper board, at least one liquid barrier layer and at least one gas barrier layer, said paper or paper board comprising, preferably at least at the edges thereof, expanded or unexpanded expandable thermoplastic microspheres.
Another aspect of the invention concerns a process for the production of a packaging laminate comprising a step of applying at least one liquid barrier layer and at least one gas barrier layer to a sheet or web of paper or paper board comprising, preferably at least at the edges thereof, expanded or unexpanded expandable thermoplastic microspheres.
Still another aspect of the invention concerns use of a packaging laminate as defined above for the production of sealed packages for food or beverage products.
A further aspect of the invention concerns a process for the production of a sealed package comprising the steps of forming a container from a packaging laminate, filling the container with a food or beverage product, and sealing the container, wherein said packaging laminate comprises at least one base layer of paper or paper board and at least one liquid barrier layer, and preferably at least one gas barrier layer, said paper or paper board comprising, preferably at least at the edges thereof, expanded or unexpanded expandable thermoplastic microspheres.
Still a further aspect of the invention concerns a sealed package for food or beverage products made of a packaging laminate comprising at least one base layer of paper or paper board and at least one liquid barrier layer, and preferably at least one gas barrier layer, said paper or paper board comprising, preferably at least at the edges thereof, expanded or unexpanded expandable thermoplastic microspheres.
In one embodiment the package is suitable for packaging of food or beverages that do not need to be heat treated after the package has been filled and sealed. Usually such packages are used for beverages like milk, juice and other soft drinks, and the packaging laminate used therefore will herein be referred to as liquid packaging laminate or liquid packaging board. Desirable properties of a liquid packaging laminate includes ability to withstand liquid contents of the package as well as liquid disinfectants like aqueous hydrogen peroxide solutions.
In another embodiment the package is suitable for food or beverages where the filled and sealed package is heat treated to increase the shelf life of the content. Such packages can be used for all kinds of food products, particularly those traditionally being packed in tin cans, and will herein be referred to as retortable packages and the material therefore as retortable packaging laminate or retortable board. Desired properties of a retortable packaging laminate include ability to withstand treatment with saturated steam at a high temperature and pressure, for example from about 110 to about 150° C. at a time from about 30 minutes to about 3 hours.
The packaging laminate of the invention comprises one or several base layers of paper or paper board, usually comprising cellulosic fibres. Preferably, the paper or paper board base layer has a grammage from about 30 to about 2250 g/m²or from about 50 to about 1500 g/m³, most preferably from about 65 to about 500 g/m²or from about 100 to about 300 g/m². The density is preferably from about 100 to about 1200 kg/m³, most preferably from about 150 to about 1000 kg/m³or from about 200 to about 900 kg/m³.
The paper or paper board may be made from various kinds of pulps, such as bleached or unbleached pulps based on virgin and/or recycled fibres. The pulp may be based on fibres from chemical pulp such as sulphate, sulphite and organosolve pulps, mechanical pulp such as thermo-mechanical pulp (TMP), chemo-thermo-mechanical pulp (CTMP), refiner pulp and ground wood pulp, from both hardwood and softwood, and can also be based on recycled fibres, optionally from de-inked pulps (DIP), and mixtures thereof. The paper or paper board may comprise one or several plies from the same or different kinds of pulp. Examples of multi ply combinations include bleached chemical pulp top/DIP, CTMP or mechanical pulp middle/bleached chemical pulp back; bleached chemical pulp top/DIP, CTMP or mechanical pulp middle/mechanical pulp back; bleached chemical pulp top/DIP, CTMP or mechanical pulp middle/unbleached chemical pulp back; and bleached chemical pulp top/unbleached chemical pulp back, the top side optionally being coated and the back side optionally being coated. The top side refers to the side intended to face the outside of the finished package. In multi ply paper or paper board at least one ply comprises thermoplastic microspheres. In paper or paper board with three or more plies, preferably at least one of the middle plies comprises thermoplastic microspheres.
In a single ply paper or paper board the grammage is preferably from about 50 to about 1500 g/m², most preferably from about 100 to about 700 g/m²or from about 150 to about 500 g/m². The density is preferably from about 100 to about 1200 kg/m³, most preferably from about 150 to about 1000 kg/m³or from about 200 to about 800 kg/m³.
In a two plies paper or paper board the grammage, per ply, is preferably from about 25 to about 750 g/m², most preferably from about 50 to about 400 g/m²or from about 100 to about 300 g/m². The total grammage is preferably from about 50 to about 1500 g/m², most preferably from about 100 to about 800 or from about 200 to about 600 g/m². The total density is preferably from about 300 to about 1200 kg/m³, most preferably from about 400 to about 1000 kg/m³or from about 450 to about 900 kg/m³.
In a paper or paper board of three or more plies the outer plies preferably have a grammage from about 10 to about 750 g/m², most preferably from about 20 to about 400 g/m²or from about 30 to about 200 g/m². The density of the outer layers is preferably from about 300 to about 1200 kg/m³, most preferably from about 400 to about 1000 kg/m³or from about 450 to about 900 kg/m³. The centre, or non-outer, ply or plies preferably have a grammage from about 10 to about 750 g/m², most preferably from about 25 to about 400 g/m²or from about 50 to about 200 g/m². The density of the centre, or non-outer ply or plies are preferably from about 10 to about 800 kg/m³, most preferably from about 50 to about 700 kg/m³or from about 100 to about 600 kg/m³. The total grammage is preferably from about 30 to about 2250 g/m², most preferably from about 65 to about 800 g/m²or from about 110 to about 600 g/m². The total density is preferably from about 100 to about 1000 kg/m³, most preferably from about 200 to about 900 kg/m³or from about 400 to about 800 kg/m³.
An embodiment of a retortable packaging laminate comprises a base layer of a double ply paper or paper board made from bleached and unbleached, respectively, softwood kraft pulp. However, other combinations of single or multi ply paper or paper board of various compositions can also be employed.
An embodiment of a liquid packaging laminate comprises a base layer of a three plies paper or paper board, of which preferably at least the middle ply comprises thermoplastic microspheres. Examples of combinations of plies include those mentioned above.
The paper or paper board is preferably sized, most preferably stock sized, with a hydrophobic sizing agent. In multiply paper or paper board, this means that at least one ply is sized. Such a ply may or may not comprise thermoplastic microspheres. Preferred sizing agents include cellulose reactive sizes such as ketene dimers or multimers like alkyl or alkenyl ketene dimers (AKD), succinic anhydrides like alkyl or alkenyl succinic anhydrides (ASA), and mixtures thereof. Other useful sizing agents include cellulose non-reactive sizes such as rosin, starch and other polymeric sizes like copolymers of styrene with vinyl monomers such as maleic anhydride, acrylic acid and its alkyl esters, acrylamide, etc. The same or different sizing agent may be used for different plies in the paper or paper board. For example, it is possible to use AKD or ASA in one or more plies and rosin in one or more other plies. The amount of sizing agent used is preferably from about 0.1 to about 10 kg/tonne paper, more preferably from about 0.3 to about 5 kg/tonne paper and most preferably from about 0.5 to about 4.5 kg/tonne paper or from about 2 to about 4 kg/tonne paper.
Preferred ketene dimers have the general formula (I):
where R¹and R²represent the same or different saturated or unsaturated hydrocarbon groups such as alkyl, alkenyl, cycloalkyl, aryl or aralkyl. The hydrocarbon groups may be branched or straight chained and do preferably have from 6 to 36 carbon atoms, most preferably from 12 to 20 carbon atoms. Examples of hydrocarbon groups include branched and straight chained octyl, decyl, dodecyl, tetradecyl, hexadecyl, octadecyl, eicosyl, docosyl, tetracosyl, phenyl, benzyl, beta-naphthyl, cyclohexyl and hexadecyl groups. Useful ketene dimers include those prepared from organic acids such as montanic acid, naphthenic acid, 9,10-decylenic acid, 9,10-dodecylenic acid, palmitoleic acid, oleic acid, ricinoleic acid, linoleic acid, stearic acid, isostearic acid, eleostearic acid, naturally occurring mixtures of fatty acids found in coconut oil, babassu oil, palm kernel oil, palm oil, olive oil, peanut oil, rape oil, beef tallow, lard, whale blubber, and mixtures of any of the above named fatty acids with each other. Depending on the hydrocarbon groups, the ketene dimers may be solid or liquid at room temperature (25° C.).
In most cases the sizing agent is included in a formulation also comprising a natural polymer such as starch or a synthetic polymer. A suitable sizing formulation is preferably an aqueous dispersion with a preferred dry content from about 5 to about 40 wt %, most preferably from about 15 to about 30 wt %. Preferably from about 50 to about 99 wt %, most preferably from about 75 to about 95 wt % of the dry content of the formulation is made up of a sizing agent as described above.
It has been found that unexpectedly good results are achieved if a sizing agent, particularly a ketene dimer or multimer, an alkyl succinic anhydride a rosin or a mixture thereof, is included in a sizing formulation also comprising an acrylamide based polymer, particularly a charged and most preferably a cationic acrylamide based polymer. However, also anionic, amphoteric and non-ionic acrylamide based polymers may be used. The amount of acrylamide based polymer is preferably from about 1 to about 50 wt %, most preferably from about 5 to about 30 wt % or from about 10 to about 20 wt %, based on the dry content of the sizing agent.
A sizing formulation may also comprise other commonly used additives such as compounds acting as dispersants, emulsifiers or stabilisers, examples of which include organic compounds like naphthalene sulphonate, lignosulphonate, quaternary ammonium compounds and salts thereof, celluloses and derivates thereof and inorganic compounds like polyaluminium compounds such as polyaluminium chloride, polyaluminium sulphate or polyaluminium silicate sulphate. Other additives include various kinds of biocides and defoaming agents. Useful additives in sizing formulations are also described in, for example, U.S. Pat. No. 6,165,259, U.S. Pat. No. 5,969,011, U.S. Pat. No. 6,306,255 and U.S. Pat. No. 6,846,384. The amount of organic compounds acting as dispersants, emulsifiers or stabilisers may, for example, be from about 0.1 to about 10 wt % of the dry content. The amount of polyaluminium compounds may, for example, be from about 0.1 to about 10 wt % of the dry content. The amount of biocide may, for example, be from about 0.01 to about 2 wt % of the dry content.
Preferred acrylamide based polymers have a weight average molecular weight of at least about 10000 or at least about 50000. In most cases the molecular weight is preferably at least about 100000 or at least about 500000. In most cases it is preferred that the molecular weight is no more than about 50 millions or no more than about 20 millions or no more than about 5 millions.
Useful acrylamide based polymers may be obtainable by polymerising acrylamide or acrylamide based monomers, preferably in combination with one or more ethylenically unsaturated cationic, potentially cationic, anionic or potentially anionic monomers. The term “potentially cationic monomer”, as used herein, refers to a monomer bearing a potentially ionisable group which becomes cationic when included in a polymer on application to the cellulosic suspension. The term “potentially anionic monomer”, as used herein, refers to a monomer bearing a potentially ionisable group becoming anionic when included in a polymer on application to the cellulosic suspension.
Examples of acrylamide and acrylamide based monomers include methacrylamide, N-alkyl (meth)acrylamides such as N-methyl (meth)acrylamide, N-ethyl (meth)acrylamide, N-n-propyl (meth)acrylamide, N-isopropyl (meth)acrylamide, N-n-butyl (meth)acrylamide, N-t-butyl (meth)acrylamide and N-isobutyl (meth)acrylamide; N-alkoxyalkyl (meth)acrylamides such as N-n-butoxymethyl (meth)acrylamide, and N-isobutoxymethyl (meth)acrylamide; N,N-dialkyl (meth)acrylamides such as N,N-dimethyl (meth)acrylamide; and, dialkylamino-alkyl (meth) acrylamides.
Useful ethylenically unsaturated cationic and potentially cationic monomers are preferably water soluble. Examples of such monomers include diallyldialkyl ammonium halides, e.g. diallyldimethyl ammonium chloride and cationic monomers represented by the general structural formula (II):
wherein R₁is H or CH₃; R₂and R₃are, independently of each other, H or, preferably, a hydrocarbon group, suitably alkyl, having from 1 to 3 carbon atoms, preferably 1 to 2 carbon atoms; A is O or NH; B is an alkyl or alkylene group having from 2 to 8 carbon atoms, suitably from 2 to 4 carbon atoms, or a hydroxy propylene group; R₄is H or, preferably, a hydrocarbon group, suitably alkyl, having from 1 to 4 carbon atoms, preferably 1 to 2 carbon atoms, or a substituent containing an aromatic group, suitably a phenyl or substituted phenyl group, which can be attached to the nitrogen by means of an alkylene group usually having from 1 to 3 carbon atoms, suitably 1 to 2 carbon atoms, suitable R₄including a benzyl group (—CH₂—C₆H₅); and X⁻ is an anionic counter ion, usually a halide like chloride.
Examples of useful monomers represented by the general structural formula (II) include quaternary monomers obtainable by treating dialkylaminoalkyl (meth)acrylates, e.g. dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate and dimethylamino-hydroxypropyl (meth)acrylate, or dialkylaminoalkyl (meth)acrylamides, e.g. dimethylamino-ethyl (meth)acrylamide, diethylaminoethyl (meth)acrylamide, dimethylaminopropyl (meth)-acrylamide, and diethylaminopropyl (meth)acrylamide, with methyl chloride or benzyl chloride. Preferred cationic monomers of the general formula (II) include dimethylaminoethyl acrylate methyl chloride quaternary salt, dimethylaminoethyl methacrylate methyl chloride quaternary salt, dimethylaminoethyl acrylate benzyl chloride quaternary salt and dimethyl-aminoethyl methacrylate benzyl chloride quaternary salt.
Examples of useful co-polymerisable anionic and potentially anionic monomers include ethylenically unsaturated carboxylic acids and salts thereof such as (meth)acrylic acid and salts thereof; ethylenically unsaturated sulphonic acids and salts thereof such as 2-acrylamido-2-methylpropanesulphonate, sulphoethyl-(meth)acrylate, vinylsulphonic acid and salts thereof, styrenesulphonate, and paravinyl phenol (hydroxy styrene) and salts thereof. Any salts may be used, such as those of sodium or other alkali metals.
Amphoteric acrylamide based polymers may be obtained by polymerising a mixture comprising one or more akrylamide based monomers, one or more ethylenically unsaturated anionic or potentially anionic monomers and one or more water-soluble ethylenically unsaturated cationic or potentially cationic monomers. Examples of suitable anionic and potentially anionic monomers include those mentioned above.
The monomer mixture for preparing the acrylamide based polymer may also comprise one or more polyfunctional crosslinking agents in addition to the above-mentioned ethylenically unsaturated monomers. The presence of a polyfunctional crosslinking agent in the monomer mixture improves polymer's capability of being dispersed in water. The polyfunctional crosslinking agents can be non-ionic, cationic, anionic or amphoteric. Examples of suitable polyfunctional crosslinking agents include compounds having at least two ethylenically unsaturated bonds, e.g. N,N-methylene-bis(meth)acrylamide, polyethyleneglycol di(meth)acrylate, N-vinyl (meth)acrylamide, divinylbenzene, trialkylammonium salts and N-methylallyl(meth)acrylamide; compounds having an ethylenically unsaturated bond and a reactive group, e.g. glycidyl (meth)acrylate, acrolein and methylol(meth)acrylamide; and compounds having at least two reactive groups, e.g. dialdehydes like glyoxal, diepoxy compounds and epichlorohydrin. Suitable water-dispersible polymers can be prepared using at least 4 molar parts per million of polyfunctional crosslinking agent based on monomers present in the monomer mixture, or based on monomeric units present in the polymer, preferably from about 4 to about 6000 molar parts per million, most preferably from 20 to 4000. Examples of useful water-dispersible polymers include the acrylamide based polymers disclosed in U.S. Pat. No. 5,167,766.
The ratio between acrylamide or acrylamide based monomers and charged or potentially charged monomers is selected to obtain an acrylamide based polymer with a suitable charge density. For a cationic acrylamide based polymer the charge density is preferably from about 0.1 to about 11 meq/g or from about 0.5 to about 10 meq/g, most preferably from about 0.6 to about 8 meq/g or from about 1 to about 5 meq/g. In some cases the charge density of a cationic acrylamide based polymer is preferably from about 3 to about 8 meq/g. For an anionic acrylamide based polymer the charge density is preferably from about 0.5 to about 10 meq/g, most preferably from about 2 to about 8 meq/g.
The paper or paper board may further comprise a wet strength agent that is added to the stock before dewatering. Suitable wet strength agents include resins of polyamine epihalohydrin, polyamide epihalohydrin, polyaminoamide epihalohydrin, urea/formaldehyde, urea/melamine/formaldehyde, phenol/formaldehyde, polyacrylic amide/glyoxal condensate, polyvinyl amine, poly-urethane, polyisocyanate, and mixtures thereof, of which polyaminoamide epichlorohydrin (PAAE) is particularly preferred. The amount of wet strength agent is preferably from about 0.1 to about 10 kg/tonne paper, most preferably from about 0.5 to about 5 kg/tonne paper.
It is particularly preferred that at least one of a sizing agent, preferably a ketene dimer, and a wet strength agent, preferably polyaminoamide epihalohydrin, is added to the stock when producing the paper or paper board.
The paper or paper board may also contain other additives commonly used in paper making and added to the stock before dewatering. Such additives may include one or more fillers, e.g. mineral fillers like kaolin, china clay, titanium dioxide, gypsum, talc, chalk, ground marble or precipitated calcium carbonate. Other commonly used additives may include retention aids, aluminium compounds, dyes, optical brightening agents, etc. Examples of aluminium compounds include alum, aluminates and polyaluminium compounds, e.g. polyaluminium chlorides and sulphates. Examples of retention aids include cationic polymers, anionic inorganic materials in combination with organic polymers such as acrylamide based polymers, e.g. bentonite in combination with cationic organic polymers or silica-based sols in combination with cationic organic polymers or cationic and anionic organic polymers.
Examples of cationic organic polymers useful in retention aids include, for example, those described in WO 2006/068576 and WO 2006/123989. In an embodiment the cationic organic polymer comprises one or more aromatic groups of the same or different types. The aromatic groups can be present in the polymer backbone (main chain) or in a substituent group that is attached to the polymer backbone. Examples of suitable aromatic groups include aryl, aralkyl and alkaryl groups such as phenyl, phenylene, naphthyl, xylylene, benzyl and phenylethyl; nitrogen-containing aromatic (aryl) groups such as pyridinium and quinolinium, as well as derivatives of these groups such as benzyl. Examples of cationically charged groups that can be present in the cationic polymer as well as in monomers used for preparing the cationic polymer include quaternary ammonium groups, tertiary amino groups and acid addition salts thereof.
The packaging laminate comprises at least one, preferably at least two liquid barrier layers on each side of the paper or paper board base layer(s). A liquid barrier layer may be made of any material that show no or insignificant permeability to water. Suitable materials include polymers of polyethylene like high density or linear low density polyethylene, polypropylene, PVC, polyesters like polyethylene terephthalate, and physical or mechanical mixtures thereof. Also co-polymers can be used, such as co-polymers of ethylene and propylene. The liquid barrier layer(s) can be applied in any known ways, such as various lamination methods or the like.
The packaging laminate may further comprise a gas barrier layer, preferably between the base layer and a liquid non-permeable layer intended to face the inside of the package. Any material that show no or insignificant permeability to molecular oxygen can be used. Examples of materials include metal foils like aluminium foils, silica coating, e.g. applied in a coating composition comprising colloidal silica and optionally various additives as described in WO 2006/065196, or produced by plasma deposition. Other possible materials include polymers like polyvinyl alcohol or co-polymers of ethylene and vinyl alcohol. The gas barrier layer can be applied in any known ways, such as various laminating methods or the like.
Usually there are separate layers for providing liquid and gas barriers, respectively, but in an embodiment a liquid barrier layer and a gas barrier layer is provided by a single layer of a material having both liquid and gas barrier properties.
The thermoplastic microspheres in the paper or paper board are preferably expanded and are added to the stock during the production of the paper or paper board, either as pre-expanded microspheres or as unexpanded thermally expandable microspheres that preferably are expanded by heating during the paper or paper board production process, for example during a drying stage where heat is applied, or in a separate process step, for example in a cylinder heater or laminator. The microspheres may be expanded when the paper or paper board still is wet or when the paper or paper board is fully or almost fully dried. The microspheres are preferably added in the form of an aqueous slurry thereof, that optionally may contain other additives desirable to supply to the stock. The amount of thermoplastic microspheres added is preferably from about 1 to about 100 kg/tonne paper, most preferably from about 1 to about 50 kg/tonne paper or from about 4 to about 40 kg/tonne paper.
Thermally expandable thermoplastic microspheres as referred to herein preferably comprise a thermoplastic polymer shell encapsulating a propellant. The propellant is preferably a liquid having a boiling temperature not higher than the softening temperature of the thermoplastic polymer shell. Upon heating, the propellant increases the internal pressure at the same time as the shell softens, resulting in significant expansion of the microspheres. Both expandable and pre-expanded thermoplastic microspheres are commercially available under the trademark Expancel® (Akzo Nobel) and are marketed in various forms, e.g. as dry free flowing particles, as an aqueous slurry or as a partially dewatered wet-cake. They are also well described in the literature, for example in U.S. Pat. Nos. 3,615,972, 3,945,956, 4,287,308, 5,536,756, 6,235,800, 6,235,394 and 6,509,384, in US Patent Applications Publication 2005/0079352, in EP 486080 and EP 1288272, in WO 2004/072160, WO 2007/091960 and WO 2007/091961 and in JP Laid Open No. 1987-286534, 2005-213379 and 2005-272633.
The thermoplastic polymer shell of the thermoplastic microspheres is preferably made of a homo- or co-polymer obtained by polymerising ethylenically unsaturated monomers. Those monomers can, for example, be nitrile containing monomers such as acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, α-ethoxyacrylonitrile, fumaronitrile or crotonitrile; acrylic esters such as methyl acrylate or ethyl acrylate; methacrylic esters such as methyl methacrylate, isobornyl methacrylate or ethyl methacrylate; vinyl halides such as vinyl chloride; vinyl esters such as vinyl acetate, vinyl ethers such as alkyl vinyl ethers like methyl vinyl ether or ethyl vinyl ether, other vinyl monomers such as vinyl pyridine; vinylidene halides such as vinylidene chloride; styrenes such as styrene, halogenated styrenes or α-methyl styrene; or dienes such as butadiene, isoprene and chloroprene. Any mixtures of the above mentioned monomers may also be used.
The propellant of the thermoplastic microspheres may comprise hydrocarbons such as propane, butane, isobutane, n-pentane, isopentane, neopentane, hexane, isohexane, neohexane, heptane, isoheptane, octane or isooctane, or mixtures thereof. Aside from them, other hydrocarbon types can also be used, such as petroleum ether, or chlorinated or fluorinated hydrocarbons, such as methyl chloride, methylene chloride, dichloroethane, dichloroethylene, trichloroethane, trichloroethylene, trichlorofluoromethane, perfluorinated hydrocarbons, etc.
Expandable thermoplastic microspheres suitable for the invention preferably have a volume median diameter from about 1 to about 500 μm, more preferably from about 5 to about 100 μm, most preferably from about 10 to about 50 μm. The temperature at which the expansion starts, referred to as T_start, is preferably from about 60 to about 150° C., most preferably from about 70 to about 100° C. The temperature at which maximum expansion is reached, referred to as T_max, is preferably from about 90 to about 180° C., most preferably from about 115 to about 150° C.
Pre-expanded thermoplastic microspheres suitable for the invention preferably have a volume median diameter from about 10 to about 120 μm, most preferably from about 20 to about 80 μm. The density is preferably from about 5 to about 150 g/dm³, most preferably from about 10 to about 100 g/dm³. Even though pre-expanded thermoplastic microspheres are commercially available as such, it is also possible to provide them by thermal on-site expansion of unexpanded expandable thermoplastic microspheres, for example just before they are added to the stock, which is facilitated if the expandable microspheres have a T_startbelow about 100° C. so steam can be used as a heating medium.
The invention will be further described in connection with the following Examples that, however, should not be interpreted as limiting the scope of the invention. Unless otherwise stated, all parts and percentages refer to parts and percent by weight.
In the Examples, one or more of the following products were used:


ST 1:	Cationic starch based biopolymer modified with 2,3-
	hydroxypropyl trimethyl ammonium chloride to D.S. 0.042,
	the polymer having a cationic charge density of about
	0.28 meq/g.
ST 2:	Cationic starch based biopolymer modified with 2,3-
	hydroxypropyl trimethyl ammonium chloride to D.S. 0.02,
	the polymer having a cationic charge density of about
	0.14 meq/g.
ST 3:	Cationic starch based biopolymer modified with 2,3-
	hydroxypropyl trimethyl ammonium chloride to D.S. 0.035,
	the polymer having a cationic charge density of about
	0.23 meq/g.
WS 1:	PAAE wet strength agent (Eka WS XO)
WS 2:	PAAE wet strength agent (Eka WS 320)
SA 1:	Sizing formulation with AKD and 10 wt % based on the AKD
	of cationic polymer prepared by polymerising 90 mole %
	acrylamide and 10 mole % dimethylaminoethyl acrylate
	methyl chloride quaternary salt and having a weight average
	molecular weight of about 1 million and cationic charge
	density of about 1.2 meq/g.
SA 2:	AKD sizing agent stabilised with starch (Eka DR 28 HF)
SA 3:	AKD sizing agent stabilised with starch (Eka DR C223)
MS 1:	Expancel ™ expandable microspheres (461WU20) with
	average particle size 6-9 μm
MS 2:	Expancel ™ pre-expanded microspheres (461WE20) with
	average particle size 20-30 μm
MS 3:	Expancel ™ expandable microspheres (820SL40) with
	average particle size 10-16 μm
MS 4:	Expancel ™ expandable microspheres (551DUX12), fraction
	with average particle size 4-6 μm
PL 1:	Cationic acrylamide-based polymer prepared by
	polymerisation of 90 mole % acrylamide and 10 mole %
	dimethylaminoethyl acrylate methyl chloride quaternary salt
	and having a weight average molecular weight of about 6
	million and a cationic charge of about 1.2 meq/g.
PL 2:	Cationic acrylamide-based polymer prepared by
	polymerisation of 90 mole % acrylamide and 10 mole %
	dimethylaminoethyl acrylate benzyl chloride quaternary salt,
	and having a weight average molecular weight of about 6
	million and cationic charge of about 1.2 meq/g.
NP 1:	Anionic inorganic condensation polymer of silicic acid in the
	form of colloidal aluminium-modified silica sol having an S
	value of <35 and containing silica-based particles with a
	specific surface area of about 700 m²/g.

EXAMPLE 1

The centre layer of liquid packaging board with a grammage of approximately 120 g/m²was produced in a Dynamic sheet former (Formette Dynamic, supplied by Fibertech AB, Sweden), from a stock based on 100% unbleached chemical thermomechanical pulp (CTMP) fibres with a stock consistency of 0.5% and a neutral pH.
Paper sheets were formed in the Dynamic Sheet Former by pumping the stock from the mixing chest through a traversing nozzle into the rotating drum onto the water film on top of the wire, draining the stock to form a sheet, pressing and drying the sheet.
Additions to the stock were made at the following times (in seconds) before pumping:
90 s, Cationic starch
75 s, PAAE wet strength agent
60 s, AKD sizing agent
45 s, Expancel™ microspheres
30 s, Cationic polymer
15 s, Anionic silica sol
0 s, Pumping
The paper board sheets were pressed and dried in a cylinder dryer at 140° C., causing heat treatment of the microspheres in either wet or dry paper web surrounding and expansion of at least the unexpanded microspheres. Two different drying methods were used:
Wet heat treatment: pre-drying 2 min 105° C. (still wet)+final drying 140° C.
Dry heat treatment: drying 10 min 105° C. (dry)+final drying 140° C.
Sample were prepared by laminating the board material with PVC and cutting 75×25 mm pieces.
The raw edge penetration (REP) of the samples was tested with two methods:
1. REP Water: Water 80° C., 3 hrs
2. REP H₂O₂: Aqueous 35% hydrogen peroxide, 70° C., 10 min
The results at wet heat treatment are shown in Table 1 while the results at dry heat treatment are shown in Table 2. The addition levels are calculated as dry product on dry stock system, except for the silica based particles that are calculated as SiO₂based on dry stock system.

TABLE 1

(wet heat treatment)

					Retention
	ST 1	WS 1	SA 1	MS	system	REP H₂O₂
Test No.	(kg/t)	(kg/t)	(kg/t)	(kg/t)/Type	PL 1/NP 1	(kg/m²)

1 (Ref.)	5	—	0.5	—	0.3/0.3	15.22
2 (Ref.)	5	—	4	—	0.3/0.3	2.08
3	5	—	0.5	4/MS 1	0.3/0.3	13.05
4	5	1	0.5	4/MS 1	0.3/0.3	9.10
5	5	—	4	4/MS 1	0.3/0.3	1.35
6	5	—	4	40/MS 1	0.3/0.3	1.42
7	5	—	4	4/MS 2	0.3/0.3	1.16
8	5	—	4	40/MS 2	0.3/0.3	1.63

TABLE 2

(dry heat treatment)

					Retention	REP
Test	ST 1	WS 1	SA 1	MS	system	Water
No.	(kg/t)	(kg/t)	(kg/t)	(kg/t)/Type	PL 1/NP 1	(kg/m²)

1 (Ref.)	5	—	0.5	—	0.3/0.3	10.18
2 (Ref.)	5	—	4	—	0.3/0.3	4.00
3	5	—	0.5	4/MS 1	0.3/0.3	9.93
4	5	1	0.5	4/MS 1	0.3/0.3	9.54
5	5	—	4	4/MS 1	0.3/0.3	3.82
6	5	—	4	40/MS 1	0.3/0.3	3.25
7	5	—	4	4/MS 2	0.3/0.3	3.32
8	5	—	4	40/MS 2	0.3/0.3	3.55

EXAMPLE 2

The centre layer of liquid packaging board was produced in an XPM (experimental paper machine), with the same pulp as used in Example 1, at a pH of 8.0. Additions to the stock were made in the following order:
Cationic starch 1, 50%
PAAE wet strength agent
Expancel™ microspheres
Cationic starch 2, 50%
AKD sizing agent
Cationic polymer
Anionic silica sol
The paper web was dried at maximum 100° C. in the XPM (maximum drying temperature 100° C.). The microspheres were subjected to dry heat treatment at 140° C. in a cylinder dryer. Samples were prepared and tested as in Example 1, with the exception that the aqueous hydrogen peroxide was only 30%. The results are shown in Table 3 with addition levels calculated as in Example 1.

TABLE 3

				Retention	REP	REP
Test	ST 1	SA 1	MS	system	Water	H₂O₂
No.	(kg/t)	(kg/t)	(kg/t)/Type	PL 1/NP 1	(kg/m²)	(kg/m²)

1 (Ref.)	3 + 3	—	—	0.15/3	13.99	21.31
2 (Ref.)	3 + 3	0.5	—	0.15/3	13.06	20.82
3 (Ref.)	3 + 3	1	—	0.15/3	6.22	14.62
4 (Ref.)	3 + 3	4	—	0.15/3	4.08	7.01
5	3 + 3	0.5	4/MS 1	0.15/3	11.96	19.95
6	3 + 3	0.5	20/MS 1	0.15/3	11.47	20.17
7	3 + 3	0.5	40/MS 1	0.15/3	11.71	20.44
8	3 + 3	4	4/MS 1	0.15/3	3.54	4.90
9	3 + 3	4	20/MS 1	0.15/3	3.44	5.23
10	3 + 3	4	40/MS 1	0.15/3	3.76	5.36
11	3 + 3	0.5	4/MS 2	0.15/3	11.06	19.96
12	3 + 3	0.5	20/MS 2	0.15/3	11.22	18.47
13	3 + 3	0.5	40/MS 2	0.15/3	11.55	20.31
14	3 + 3	4	4/MS 2	0.15/3	3.64	5.54
15	3 + 3	4	20/MS 2	0.15/3	3.64	6.99
16	3 + 3	4	40/MS 2	0.15/3	2.66	7.38
17	3 + 3	0.5	4/MS 3	0.15/3	12.59	20.12
18	3 + 3	0.5	20/MS 3	0.15/3	12.37	19.65
19	3 + 3	0.5	40/MS 3	0.15/3	12.83	23.14
20	3 + 3	4	4/MS 3	0.15/3	3.53	5.00
21	3 + 3	4	20/MS 3	0.15/3	4.23	5.01
22	3 + 3	4	40/MS 3	0.15/3	4.10	6.16

EXAMPLE 3

The centre layer of liquid packaging board was produced and tested for REP in water as in Example 2. The results are shown in Table 4.

TABLE 4

							REP
		SA		MS	PL		water
Test	ST 1	(kg/t)/	WS 2	(kg/t)/	(kg/t)/	NP 1	(kg/
No.	(kg/t)	Type	(kg/t)	Type	Type	(kg/t)	m²)

1 (Ref.)	3 + 3	—	—	—	0.15/PL 1	3	10.80
2 (Ref.)	3 + 3	2/SA 2	—	—	0.15/PL 1	3	4.06
3 (Ref.)	3 + 3	2/SA 1	—	—	0.15/PL 1	3	3.80
4 (Ref.)	3 + 3	2/SA 1	1	—	0.15/PL 1	3	3.66
5	3 + 3	2/SA 1	—	40/MS 1	0.15/PL 1	3	3.56
6	3 + 3	2/SA 1	1	20/MS 1	0.15/PL 1	3	3.42
7	3 + 3	2/SA 2	—	40/MS 2	0.15/PL 1	3	3.65
8	3 + 3	2/SA 1	—	40/MS 2	0.15/PL 1	3	3.12
9	3 + 3	2/SA 1	1	20/MS 2	0.15/PL 1	3	3.53
10	3 + 3	2/SA 2	—	40/MS 3	0.15/PL 1	3	3.69
11	3 + 3	2/SA 1	—	40/MS 3	0.15/PL 2	3	3.26
12	3 + 3	2/SA 1	1	20/MS 3	0.15/PL 1	3	3.49
13	3 + 3	2/SA 1	1	40/MS 3	0.15/PL 1	3	2.90

EXAMPLE 4

Retortable board with a grammage of approximately 250 g/m²was produced in a PFI sheet former, supplied by Hamjern Maskin A/S, Norway, from a stock based on 100% bleached softwood kraft fibres and having a stock consistency of 1.88%. Additions to the stock were made at the following times (in seconds) before dewatering:
75 s, AKD sizing agent
60 s, Expancel™ microspheres
45 s, Cationic starch
30 s, Cationic polymer
15 s, Anionic silica sol
0 s, Dewatering
The paper board sheets were pressed and dried in a cylinder dryer at 140° C., causing heat treatment of the microspheres in wet paper web surrounding and expansion of at least the unexpanded microspheres. The following method was used:
Wet heat treatment: cylinder drum 1 h 85° C. (still wet)+final drying 140° C. Samples were prepared as in Example 1 and the raw edge penetration (REP) was tested by treatment with steam in an autoclave 60 min at 130° C. and 2 bar. The autoclave was a Certoclav TT 121, supplied by Certoclav Sterilizer GmbH, Austria. The results are shown in Table 5 with addition levels calculated as in Example 1.

TABLE 5

Test	ST 1	SA 1	MS	Retention system	REP vapour
No.	(kg/t)	(kg/t)	(kg/t)/Type	PL 1/NP 1	(kg/m²)

1 (Ref.)	7	—	—	0.5/0.45	1.15
2 (Ref.)	7	0.75	—	0.5/0.45	0.55
3	7	0.75	5/MS 2	0.5/0.45	0.44
4	7	0.75	40/MS 2	0.5/0.45	0.28
5	7	0.75	5/MS 1	0.5/0.45	0.40
6	7	0.75	10/MS 3	0.5/0.45	0.43
7	7	0.75	40/MS 3	0.5/0.45	0.40
8	7	0.75	10/MS 4	0.5/0.45	0.40

EXAMPLE 5

Retortable board was produced as in Example 4, but with a stock based on 100% unbleached softwood kraft fibres and a stock consistency of 1.75%. Additions to the stock were made at the following times (in seconds) before dewatering:
75 s, AKD sizing agent
65 s, PAAE, wet strength agent
55 s, Expancel™ microspheres
45 s, Cationic starch
30 s, Cationic polymer
15 s, Anionic silica sol
0 s, Dewatering
The paper board sheets were pressed and dried in a cylinder dryer at 160° C., causing heat treatment of the microspheres in dry or wet paper web surrounding and expansion of at least the unexpanded microspheres. The following methods were used:
Dry heat treatment: cylinder drum 3 hrs 85° C. (dry)+final drying 160° C.
Wet heat treatment: cylinder drum 1 hr 85° C. (dry)+final drying 160° C.
Samples were prepared and tested as in Example 1 and the raw edge penetration, REP, was tested with two different methods;
1. REP Vapour: Steam autoclave 130° C., 60 min, 2 bar
2. REP H₂O₂: Aqueous 35% hydrogen peroxide, 70° C., 10 min
The results at dry heat treatment are shown in Table 6 while the results at wet heat treatment are shown in Table 7, with addition levels calculated as in Example 1.

TABLE 6

(dry heat treatment)

					Retention
					system	REP	REP
Test	ST 2	SA 1	WS 1	MS 1	PL 1/NP 1	Vapour	H₂O₂
No.	(kg/t)	(kg/t)	(kg/t)	(kg/t)	(kg/t)	(kg/m²)	(kg/m²)

1 (Ref.)	7	—	—	—	0.5/0.45	2.14	7.64
2 (Ref.)	7	0.375	—	—	0.5/0.45	0.60	2.04
3 (Ref.)	7	—	2		0.5/0.45	0.45	8.37
4 (Ref.)	7	—	—	5	0.5/0.45	2.75	7.32
5	7	0.375	—	5	0.5/0.45	0.41	2.17
6	7	—	2	5	0.5/0.45	0.40	6.43
7	7	0.375	2	5	0.5/0.45	0.44	2.34
8 (Ref.)	7	0.75	—	—	0.5/0.45	0.77	0.92
9 (Ref.)	7	0.75	2	—	0.5/0.45	0.49	1.30
10	7	0.75	—	5	0.5/0.45	0.47	0.85

TABLE 7

(wet heat treatment)

					Retention system	REP
Test	ST 2	SA 1	WS 1	MS 1	PL 1/NP 1	H₂O₂
No.	(kg/t)	(kg/t)	(kg/t)	(kg/t)	(kg/t)	(kg/m²)

1 (Ref.)	7	—	—	—	0.5/0.45	10.19
2 (Ref.)	7	0.375	—	—	0.5/0.45	3.08
3 (Ref.)	7	—	2	—	0.5/0.45	5.30
4 (Ref.)	7	—	—	5	0.5/0.45	8.93
5	7	0.375	—	5	0.5/0.45	2.77
6	7	—	2	5	0.5/0.45	4.13
7	7	0.375	2	5	0.5/0.45	2.42
8 (Ref.)	7	0.75	—	—	0.5/0.45	1.29
9 (Ref.)	7	0.75	2	—	0.5/0.45	2.06
10	7	0.75	—	5	0.5/0.45	1.21

EXAMPLE 6

Retortable board was produced as in Example 4 but with a stock consistency of 2.1%. Additions to the stock were made at the following times (in seconds) before dewatering:
75 s, AKD sizing agent
60 s, Expancel™ microspheres
45 s, Cationic starch
30 s, Cationic polymer
15 s, Anionic silica sol
0 s, Dewatering
The paper board sheets were pressed and dried in a cylinder dryer, causing heat treatment of the microspheres in wet paper web surrounding and expansion of at least the unexpanded microspheres. The following methods were used:
1. cylinder drum 2 h 70° C. (still wet)+final drying 140° C.
2. cylinder drum 2 h 70° C. (still wet)+final drying 160° C.
Samples were prepared as in Example 4 and the raw edge penetration, REP, was tested with two different methods;
1. REP vapour: Steam autoclave 130° C., 60 min, 2 bar
2. REP water: Water 80° C., 3 hrs
REP vapour was tested for the samples dried at 140° C. and REP water for the samples dried at 160° C.
The results are shown in Table 7 with addition levels calculated as in Example 1.

TABLE 8

				Retention		REP
Test	ST 1	SA 1	MS	system	REP vapour	water
No.	(kg/t)	(kg/t)	(kg/t)/Type	PL 1/NP 1	(kg/m²)	(kg/m²)

1 (Ref.)	7	—	—	0.5/0.45	2.21	9.21
2 (Ref.)	7	0.75	—	0.5/0.45	0.53	2.30
3	7	0.75	5/MS 2	0.5/0.45	0.45	1.61
4	7	0.75	10/MS 2	0.5/0.45	0.45	1.27
5	7	0.75	20/MS 2	0.5/0.45	0.44	1.57
6	7	0.75	40/MS 2	0.5/0.45	0.27	1.05
7	7	0.75	10/MS 3	0.5/0.45	0.44	1.82

EXAMPLE 7

Retortable board was produced as in Example 6. Additions to the stock were made at the following times (in seconds) before dewatering:
75 s, AKD sizing agent
60 s, Expancel™ microspheres
45 s, Cationic starch
30 s, Cationic polymer
15 s, Anionic silica sol
0 s, Dewatering
The paper board sheets were pressed and dried in a cylinder dryer, causing heat treatment of the microspheres in wet paper web surrounding and expansion of at least the unexpanded microspheres. The following method was used:
Wet heat treatment: cylinder drum 2 h 70° C. (still wet)+final drying 140° C.
Samples were prepared and tested as in Example 1. The results are shown in Table 8 with addition levels calculated as in Example 1.

TABLE 9

Test	ST 1	SA 1	MS	Retention system	REP H₂O₂
No.	(kg/t)	(kg/t)	(kg/t)/Type	PL 1/NP 1	(kg/m²)

1 (Ref.)	7	—	—	0.5/0.45	23.17
2 (Ref.)	7	0.75	—	0.5/0.45	0.88
3	7	0.75	5/MS 2	0.5/0.45	0.70
4	7	0.75	5/MS 1	0.5/0.45	0.67
5	7	0.75	10/MS 3	0.5/0.45	0.68
6	7	0.75	10/MS 4	0.5/0.45	0.77

EXAMPLE 8

Retortable board, in two plies, with a grammage of approximately 290 g/m²was produced in a Dynamic Sheet Former (Formette Dynamic, supplied by Fibertech AB, Sweden), using 50% from a stock based on 100% unbleached softwood kraft fibres and a stock consistency of 0.5% to form the bottom ply, and using 50% from a stock based on 100% bleached softwood kraft fibres and a stock consistency of 0.5% to form the top ply. In both stocks the conductivity was 1.5 mS/cm and the pH was around neutral.
Paper sheets were formed in the Dynamic Sheet Former by pumping the stock from the mixing chest through a traversing nozzle into the rotating drum onto the water film on top of the wire, draining the stock to form a sheet, pressing and drying the sheet. The stocks were added sequentially to form the two plies in the Retortable board.
Additions to each of the stocks were made at the following times (in seconds) before pumping:
90 s, Cationic starch
75 s, PAAE, wet strength agent
60 s, AKD sizing agent
45 s, Expancel™ microspheres
30 s, Cationic starch
15 s, Anionic silica sol
0 s, Pumping
The paper board sheets were pressed and oven dried, causing heat treatment of the microspheres in wet paper web surrounding and expansion of at least the unexpanded microspheres. The following method was used:
Dry heat treatment: drying 20 min 105° C. (dry)+final drying 10 min 105° C. Samples were prepared as in Example 1 and the raw edge penetration, REP, was tested with:
REP vapour+water: Steam autoclave 130° C., 60 min, 2 bar+Water 6° C., 10 min The bending resistance was measured according to SCAN P 29:95, by using a L&W Bending Resistance Tester, Type 16D, supplied by Lorentzon&Wettre, Sweden. The bending resistance index was calculated by dividing the bending resistance with the cubic of the grammage. The results are shown in Table 9 with addition levels calculated as in Example 1.

TABLE 9

				MS				Bending
			SA	(kg/			REP	resistance
Test	ST 2	WS 1	(kg/t)/	t)/	ST 3	NP 1	vapour	index
No.	(kg/t)	(kg/t)	Type	Type	(kg/t)	(kg/t)	(kg/m²)	(Nm⁶/kg³)

1	7	—	—	—	3	—	4.57	15.9
(Ref.)
2	7	—	4/SA 3	—	3	0.45	1.28	15.1
(Ref.)
3	7	—	4/SA 1	—	3	0.45	1.07	15.4
(Ref.)
4	7	4	—	—	3	0.45	4.43	16.7
(Ref.)
5	7	4	4/SA 1	—	3	0.45	1.08	15.5
(Ref.)
6	7	—	4/SA 1	4/	3	0.45	0.84	16.0
				MS 3
7	7	—	4/SA 1	10/	3	0.45	0.92	16.4
				MS 3

It appears that it was possible to obtain both low raw edge penetration and high bending resistance.

Claims

1. A retortable packaging laminate comprising at least one base layer of sized paper or paper board, at least one liquid barrier layer and at least one gas barrier layer, said paper or paper board comprising expanded or unexpanded expandable thermoplastic microspheres.

2. The retortable packaging laminate as claimed in claim 1, having ability to withstand treatment with saturated steam at from about 110 to about 150° C. at a time from about 30 minutes to about 3 hours.

3. The retortable packaging laminate as claimed in claim 2, wherein the paper or paper board is made of pulp from softwood.

4. The retortable packaging laminate as claimed in claim 3, comprising a base layer of a double ply paper or paper board made from bleached and unbleached, respectively, softwood kraft pulp.

5. The retortable packaging laminate as claimed in claim 1, wherein the paper or paper board is sized with a formulation comprising a sizing agent selected from the group consisting of ketene dimers and multimers, succinic anhydrides and rosins, and also comprising an acrylamide based polymer.

6. The retortable packaging laminate as claimed in claim 5, wherein the acrylamide based polymer is cationic.

7. The retortable packaging laminate as claimed in claim 1, wherein the paper or paper board comprises a wet strength resin.

8. The retortable packaging laminate as claimed in claim 7, wherein the wet strength resin is selected from the group consisting of polyamine epihalohydrines, polyamide epihalohydrines and polyaminoamide epihalohydrins.

9. The retortable packaging laminate as claimed in claim 1, wherein the thermoplastic microspheres are expanded.

10. The retortable packaging laminate as claimed in claim 9, wherein the thermoplastic microspheres have been added as pre-expanded thermoplastic microspheres.

11. The retortable packaging laminate as claimed in claim 9, wherein the thermoplastic microspheres have been added as unexpanded thermally expandable microspheres being expanded during the production of the paper or paper board, said paper or paper board still being wet during the expansion.

12. The retortable packaging laminate as claimed in claim 9, wherein the thermoplastic microspheres have been added as unexpanded thermally expandable microspheres during the production of the paper or paper board, said paper or paper board being fully or almost fully dried during the expansion.

13. A process for the production of a retortable packaging laminate comprising a step of applying at least one liquid barrier layer and at least one gas barrier layer to a sheet or web of retortable paper or paper board comprising expanded or unexpanded expandable thermoplastic microspheres.

14. (canceled)

15. A sealed package for food or beverage products made of a retortable packaging laminate comprising at least one base layer of sized paper or paper board, at least one liquid barrier layer and at least one gas barrier layer, said paper or paper board comprising expanded or unexpanded expandable thermoplastic microspheres.

16. A process for the production of a sealed package comprising the steps of forming a container from a retortable packaging laminate comprising at least one base layer of sized paper or paper board, at least one liquid barrier layer and at least one gas barrier layer, said paper or paper board comprising expanded or unexpanded expandable thermoplastic microspheres, filling the container with a food or beverage product, and sealing the container.

17. The process as claimed in claim 16, further comprising heat treating the filled and sealed package.