TECHNICAL FIELD The present invention is directed to a coated fibre based material comprising a fibre based substrate comprising microfibrillated cellulose and having at least first and second barrier coatings formed thereon, to articles such as paper products, particularly food grade packaging, formed from said coated material, and to methods of preparing said coated material and paper products.

BACKGROUND

Packaging for perishable goods such as foodstuffs, particularly food wrap and bag/pouch packaging and the like, is commonly derived from polymeric substrates. One such product is biaxially oriented polypropylene (BOPP) film. It is used in a variety of forms suitable for food packaging, labels and stationery. However, the polymeric components of such films are relatively expensive and the films are not readily recyclable. A further recent concern in the food packaging industry is the migration of mineral oil derived from printing inks or recycled paper pulp used in the production of direct contact food packaging cartons and indirect contact food packaging containers used for transport and storage of food and to date polypropylene barriers have been found not to work or not to work efficiently. Another issue concerns the printability of polymer-based films for packaging manufactures seeking accurate illustration printing by techniques such as rotogravure printing and flexographic printing, and the replacement of polymeric packaging with standard fibre based products (having better printability) is problematic physically due to their relatively low strength and therefore higher weight requirement.

Thus, there is a need for new materials to address one or more of the aforementioned problems.

SUMMARY OF THE INVENTION In accordance with a first aspect, there is provided a coated fibre based material comprising: a fibre based substrate comprising microfibrillated cellulose and having at least first and second barrier coatings formed thereon. In accordance with a second aspect, there is provided an article, paper product or food- grade-packaging formed or formable from the coated fibre based material according to the first aspect of the present invention.

In accordance with a third aspect, there is provided an intermediate fibre based material formable into the coated fibre based material of the first aspect of the present invention, said intermediate fibre based material comprising a fibre based substrate and having one or other of the first and second barrier coatings as defined in the first aspect of the present invention, formed on a surface of the fibre based substrate. In accordance with a fourth aspect, there is provided a method of preparing a coated fibre based material, comprising : providing or obtaining a fibre based substrate according to the first aspect of the present invention; applying a first barrier coating according to the first aspect of the present invention to the fibre based substrate; and applying a second barrier coating according to the first aspect of the present invention to the fibre based substrate.

BRIEF DESCRIPTION OF THE FIGURES

Figure 1 is a schematic depiction of one illustrative embodiment of the present invention.

Figure 2 is a schematic depiction of a second illustrative embodiment of the present invention. Figure 3 is a schematic depiction of a third illustrative embodiment of the present invention.

Figure 4 is a schematic depiction of a fourth illustrative embodiment of the present invention. Figure 5 is a schematic depiction of a cross-section of a yoghurt pot having a lid formed from the coated fibre based material according to an illustrative embodiment of the present invention. Figure 6 is a graph showing moisture pick-up for a coated paper according to exemplary embodiments of the present invention and a series of comparative coated papers.

DETAILED DESCRIPTION

As used herein "co-processed inorganic particulate material" refers to inorganic particulate material produced by the methods for microfibrillating fibrous substrates comprising cellulose in the presence of an inorganic particulate material as described herein.

By microfibrillating is meant a process in which microfibrils of cellulose are liberated or partially liberated as individual species or as smaller aggregates as compared to the fibres of the pre-microfibrillated pulp. Typical cellulose fibres (i.e., pre-microfibrillated pulp) include larger aggregates of hundreds or thousands of individual cellulose microfibrils. By microfibrillating the cellulose, particular characteristics and properties, including but not limited to the characteristic and properties described herein, are imparted to the microfibrillated cellulose and the compositions including the microfibrillated cellulose. As used herein, "non-microfibrillated cellulose" refers to fibrous material which is of a form suitable for making paper therefrom, for example paper pulp, and which is not prepared by the microfibrillating process described herein. Exemplary fibrous materials are described later. Unless otherwise stated, the particle size properties referred to herein for the inorganic particulate materials are as measured by the well known conventional method employed in the art of laser light scattering, using a Malvern Mastersizer S machine as supplied by Malvern Instruments Ltd (or by other methods which give essentially the same result). In the laser light scattering technique, the size of particles in powders, suspensions and emulsions may be measured using the diffraction of a laser beam, based on an application of Mie or Frauenhofer theory. Such a machine provides measurements and a plot of the cumulative percentage by volume of particles having a size, referred to in the art as the 'equivalent spherical diameter' (e.s.d), less than given e.s.d values. The mean particle size d ₅₀ is the value determined in this way of the particle e.s.d at which there are 50% by volume of the particles which have an equivalent spherical diameter less than that d ₅₀ value.

Alternatively, where stated, particle size properties referred to herein for the inorganic particulate materials are as measured in a well known manner by sedimentation of the particulate material in a fully dispersed condition in an aqueous medium using a Sedigraph 5100 machine as supplied by Micromeritics Instruments Corporation, Norcross, Georgia, USA (telephone: +1 770 662 3620; web-site: www.micromeritics.com), referred to herein as a "Micromeritics Sedigraph 5100 unit". Such a machine provides measurements and a plot of the cumulative percentage by weight of particles having a size, referred to in the art as the 'equivalent spherical diameter' (e.s.d), less than given e.s.d values. The mean particle size d ₅₀ is the value determined in this way of the particle e.s.d at which there are 50% by weight of the particles which have an equivalent spherical diameter less than that d ₅₀ value. Unless otherwise stated, particle size properties of the microfibrillated cellulose materials are as measured by the well known conventional method employed in the art of laser light scattering, using a Malvern Mastersizer S machine as supplied by Malvern Instruments Ltd (or by other methods which give essentially the same result). Details of an exemplary procedure used to characterise the particle size distributions of mixtures of inorganic particle material and microfibrillated cellulose using a Malvern Mastersizer S machine are provided in WO-A-2010/131016 at page 40, line 32 to page 41 , line 34.

Unless otherwise stated, "barrier coating" refers to a coating or coating applied to the surface of a fibre based substrate such as, for example, paper, to modify or enhance the rate at which one or more of oxygen, moisture, grease (including, for example, mineral oil derived from recycled pulp and/or printing inks) and aromas pass (i.e., transmitted) through said fibre based substrate. The barrier coating composition may therefore stop, slow down or ameliorate (i.e., decrease) the rate at which one or more of oxygen, moisture, grease and aromas pass through the fibre based substrate. Unless otherwise stated, "functional coating" refers to a coating or coatings applied to a barrier coated fibre based material such as, for example, barrier coated paper, to modify or enhance one or more of gloss, coverage, brightness, strength , print receptivity or printability (including, for example, print gloss, snap, print density, picking speed or percent missing dots). Certain embodiments of the functional coating of the present invention may therefore be said to provide or enhance print receptivity or printability of a barrier coated fibre based material. Further, if the functional coating comprises a platy inorganic particulate material, as defined herein, it may also enhance a barrier property of the coated fibre based material.

Fibre based substrate

The fibre based substrate comprises microfibri Hated cellulose (as defined herein). The fi bre based substrate further comprises non-microfibrillated cellulose. The microfibrillated cellulose and non-microfibrillated cellulose may or may not be derived from the same cellulose-based material. The weight ratio of microfibrillated cellulose to non-microfibrillated cellulose may be from about 1 :99 to about 99:1 , for example from about 1 :99 to about 90: 10, or from about 1 :99 to about 80:20, or from about 1 :99 to about 70:30, or from about 1 :99 to about 60:40, or from about 1 :99 to about 50:50, or from about 1 :99 to about 45:55, or from about 1 :99 to about 40:60, or from about 1 :99 to about 35:65, or from about 1 :99 to about 30:70, or from about 1 :99 to about 25:75, or from about 1 :99 to about 20:80, or from about 1 :99 to about 15:85, or from about 1 :99 to about 10:90, or from about 1 :99 to about 5:95. The weight ratio of microfibrillated cellulose to non-microfibrillated cellulose may be from 5:95 to about 50:50, or from about 5:95 to about 45:55, or from about 5:95 to about 40:60, or from about 5:95 to about 35:65, or from about 5:95 to about 30:70, or from about 5:95 to about 25:75, or from about 5:95 to about 20:80, or from about 5:95 to about 15:85, or from about 5:95 to about 10:90. The weight ratio of microfibrillated cellulose to non-microfibrillated cellulose may be from 10:90 to about 50:50, or from about 10:90 to about 45:55, or from about 10:90 to about 40:60, or from about 10:90 to about 35:65, or from about 10:90 to about 30:70, or from about 10:90 to about 25:75, or from about 10:90 to about 20:80, or from about 10:90 to about 15:85. The weight ratio of microfibrillated cellulose to non-microfibrillated cellulose may be from 15:85 to about 50:50, or from about 15:85 to about 45:55, or from about 15:85 to about 40:60, or from about 15:85 to about 35:65, or from about 15:85 to about 30:70, or from about 15:85 to about 25:75, or from about 1 5 : 85 to about 20:80. The weight ratio of m icrofibrillated cell ulose to non- microfibrillated cellulose may be from 20:80 to about 50:50, or from about 20:80 to about 45:55, or from about 20:80 to about 40:60, or from about 20:80 to about 35:65, or from about 20:80 to about 30:70, or from about 20:80 to about 25:75.

The fibre based substrate may comprise other optional components suitable for making paper products. The fibre based substrate may comprise a polymeric material, other than the cellulose- derived components described above. For example, the polymeric material may be one or more of polymethylmethacrylate, polyacetal, polycarbonate, polyacrylonitrile, polybutadiene, polystyrene, polyacrylate, polypropylene, epoxy polymers, unsaturated polyesters, polyurethanes, polycyclopentadienes and copolymers thereof, and liquid rubbers, such as silicones. In an embodiment, the fibre based substrate comprises less than about 5 % by weight polymeric material, based on the total weight of the fibre based substrate, for example, less than about 2 % by weight, or less than about 1 % by weight. In another embodiment, the fibre based substrate is substantially free of polymeric material. In another embodiment, the fibre based substrate is free of polymeric material.

In an embodiment, the microfibrillated cellulose is obtainable by a method comprising microfibrillating a fibrous substrate comprising cellulose in a suitable environment, advantageously an aqueous environment, by grinding in the presence of a grinding medium which is to be removed after the completion of grinding. The grinding is carried out in the absence of grindable inorganic particulate material. A grindable inorganic particulate material is a material which would be ground in the presence of the grinding medium. In an embodiment, the grinding is performed in a tower mill, a screened grinder, a stirred medial mill, or stirred media detritor. Suitable methods for preparing microfibrillated cellulose are described in WO-A-201 0/1 31016, see in particular pages page 33, line 17 to page 40, line 24, the entire contents of which are hereby incorporated by reference.

The particulate grinding medium may be of a natural or a synthetic material. The grinding medium may, for example, comprise balls, beads or pellets of any hard mineral, ceramic or metallic material. Such materials may include, for example, alumina, zirconia, zirconium silicate, aluminium silicate or the mullite-rich material which is produced by calcining kaolinitic clay at a temperature in the range of from about 1300°C to about 1800°C. For example, in some embodiments a Carbolite® grinding media is preferred. Alternatively, particles of natural sand of a suitable particle size may be used.

Generally, the type of and particle size of grinding medium to be selected for use in certain embodiments of the present invention may be dependent on the properties, such as, e.g., the particle size of, and the chemical composition of, the feed suspension of material to be ground. Preferably, the particulate grinding medium comprises particles having an average diameter in the range of from about 0.5 mm to about 6 mm. In one embodiment, the particles have an average diameter of at least about 3 mm.

The grinding medium may comprise particles having a specific gravity of at least about 2.5. The grinding medium may comprise particles have a specific gravity of at least about 3, or least about 4, or least about 5, or at least about 6.. The grinding medium (or media) may be present in an amount up to about 70% by volume of the charge. The grinding media may be present in amount of at least about 10% by volume of the charge, for example, at least about 20 % by volume of the charge, or at least about 30% by volume of the charge, or at least about 40 % by volume of the charge, or at least about 50% by volume of the charge, or at least about 60 % by volume of the charge.

The fibre based substrate may further comprise co-processed inorganic particulate material. In this embodiment, the inorganic particulate material is co-processed with a fibrous substrate comprising cellulose during the preparation of said microfibrillated cellulose. In an advantageous embodiment, the microfibrillated cellulose is obtainable by a method comprising microfibrillating a fibrous substrate comprising cellulose in a suitable environment, advantageously an aqueous environment, in the presence of said inorganic particulate material. In a further embodiment, the microfibrillating step comprises grinding the fibrous substrate comprising cellulose in the presence of the inorganic particulate material. The grinding may be performed in a tower mill, a screened grinder, a stirred media mill or a stirred media detritor. Suitable methods for preparing microfibrillated cellulose in the presence of an inorganic particulate material are described in WO-A-2010/131016, see in particular page 9, line 19 to page 22, line 12, the entire contents of which are hereby incorporated by reference.

In this embodiment, a particulate grinding medium may be present. As described above, by grinding medium is meant a medium other than the inorganic particulate material which is co-ground with the fibrous substrate comprising cellulose. The particulate grinding medium, when present, may be of a type, form and size as described above in connection with the embodiment in which grinding is carried out in the absence of grindable inorganic particulate material.

The fibrous substrate comprising cellulose may be derived from any suitable source, such as wood, grasses (e.g., sugarcane, bamboo) or rags (e.g., textile waste, cotton, hemp or flax). The fibrous substrate comprising cellulose may be in the form of a pulp (i.e., a suspension of cellulose fibres in water), which may be prepared by any suitable chemical or mechanical treatment, or combination thereof. For example, the pulp may be a chemical pulp, or a chemithermomechanical pulp, or a mechanical pulp, or a recycled pulp, or a papermill broke, or a papermill waste stream, or waste from a papermill, or a combination thereof. The cellulose pulp may be beaten (for example in a Valley beater) and/or otherwise refined (for example, processing in a conical or plate refiner) to any predetermined freeness, reported in the art as Canadian standard freeness (CSF) in cm ³ . CSF means a value for the freeness or drainage rate of pulp measured by the rate that a suspension of pulp may be drained. For example, the cellulose pulp may have a Canadian standard freeness of about 10 cm ³ or greater prior to being microfibrillated. The cellulose pulp may have a CSF of about 700 cm ³ or less, for example, equal to or less than about 650 cm ³ , or equal to or less than about 600 cm ³ , or equal to or less than about 550 cm ³ , or equal to or less than about 500 cm ³ , or equal to or less than about 450 cm ³ , or equal to or less than about 400 cm ³ , or equal to or less than about 350 cm ³ , or equal to or less than about 300 cm ³ , or equal to or less than about 250 cm ³ , or equal to or less than about 200 cm ³ , or equal to or less than about 150 cm ³ , or equal to or less than about 100 cm ³ , or equal to or less than about 50 cm ³ . The cellulose pulp may then be dewatered by methods well known in the art, for example, the pulp may be filtered through a screen in order to obtain a wet sheet comprising at least about 10% solids, for example at least about 15% solids, or at least about 20% solids, or at least about 30% solids, or at least about 40% solids. The pulp may be utilised in an unrefined state; that is to say without being beaten or de watered, or otherwise refined. Likewise, the non-microfibrillated cellulose, i.e., fibrous material which is of a form suitable for making paper therefrom and which is not prepared by the microfibrillating process described herein, may be derived from any suitable source, such as wood, grasses (e.g., sugarcane, bamboo) or rags (e.g., textile waste, cotton, hemp or flax). The fibrous material may be in the form of a pulp (i.e., a suspension of cellulose fibres in water), which may be prepared by any suitable chemical or mechanical treatment, or com bi nation thereof. For example , the pu lp may be a chem ical pulp, or a chemithermomechanical pulp, or a mechanical pulp, or a recycled pulp, or a papermill broke, or a papermill waste stream, or waste from a papermill, or a combination thereof. The cellulose pulp may be beaten (for example in a Valley beater) and/or otherwise refined (for example, processing in a conical or plate refiner) to any predetermined freeness, reported in the art as Canadian standard freeness (CSF) in cm ³ . CSF means a value for the freeness or drainage rate of pulp measured by the rate that a suspension of pulp may be drained. For example, the cellulose pulp may have a Canadian standard freeness of about 10 cm ³ or greater prior to being microfibrillated. The cellulose pulp may have a CSF of about 700 cm ³ or less, for example, equal to or less than about 650 cm ³ , or equal to or less than about 600 cm ³ , or equal to or less than about 550 cm ³ , or equal to or less than about 500 cm ³ , or equal to or less than about 450 cm ³ , or equal to or less than about 400 cm ³ , or equal to or less than about 350 cm ³ , or equal to or less than about 300 cm ³ , or equal to or less than about 250 cm ³ , or equal to or less than about 200 cm ³ , or equal to or less than about 150 cm ³ , or equal to or less than about 100 cm ³ , or equal to or less than about 50 cm ³ . The cellulose pulp may then be dewatered by methods well known in the art, for example, the pulp may be filtered through a screen in order to obtain a wet sheet comprising at least about 10% solids, for example at least about 15% solids, or at least about 20% solids, or at least about 30% solids, or at least about 40% solids. The pulp may be utilised in an unrefined state; that is to say without being beaten or dewatered, or otherwise refined.

The fibrous substrate comprising cellulose may be added to a grinding vessel or homogenizer in a dry state. For example, a dry paper broke may be added directly to the grinder vessel. The aqueous environment in the grinder vessel will facilitate the formation of a pulp.

The grinding may be carried out in one or more stages. For example, a coarse inorganic particulate material may be ground in the grinder vessel to a predetermined particle size distribution, after which the fibrous material comprising cellulose is added and the grinding continued until the desired level of microfibrillation has been obtained.

In one embodiment, the mean particle size (d ₅₀ ) of the inorganic particulate material is reduced during the co-grinding process. For example, the d ₅₀ of the inorganic particulate material may be reduced by at least about 10%, for example, the d ₅₀ of the inorganic particulate material may be reduced by at least about 20%, or reduced by at least about 30%, or reduced by at least about 40%, or reduced by at least about 50%, or reduced by at least about 60%, or reduced by at least about 70%, or reduced by at least about 80%, or reduced by at least about 90%. For example, an inorganic particulate material having a d ₅₀ of 2.5 pm prior to co-grinding and a d ₅₀ of 1.5 pm post co-grinding will have been subject to a 40% reduction in particle size. In embodiments, the mean particle size of the inorganic particulate material is not significantly reduced during the co-grinding process. By 'not significantly reduced' is meant that the d ₅₀ of the inorganic particulate material is reduced by less than about 10%, for example, the d ₅ o of the inorganic particulate material is reduced by less than about 5%.

The fibrous substrate comprising cellulose may be microfibrillated in the presence of an inorganic particulate material to obtain microfibrillated cellulose having a d ₅₀ ranging from about 5 pm to about 500 pm, as measured by laser light scattering, for example, from about 15 pm to about 400, or from about 20 pm to about 300, or from about 25 to about 250 pm, or from about 30 pm to about 150 pm, or from about 50 pm to about 140 pm, or from about 70 pm to about 130 pm, or from about 50 to about 120 pm. The fibrous substrate comprising cellulose may be microfibrillated in the presence of an inorganic particulate material to obtain microfibrillated cellulose having a d ₅₀ of equal to or less than about 400 pm, for example equal to or less than about 300 pm, or equal to or less than about 200 pm, or equal to or less than about 150 pm, or equal to or less than about 125 pm, or equal to or less than about 100 pm, or equal to or less than about 90 pm, or equal to or less than about 80 pm, or equal to or less than about 70 pm, or equal to or less than about 60 pm, or equal to or less than about 50 pm, or equal to or less than about 40 μηι, or equal to or less than about 30 μηι, or equal to or less than about 20 pm, or equal to or less than about 10 pm.

The fibrous substrate comprising cellulose may be microfibrillated in the presence of an inorganic particulate material to obtain microfibrillated cellulose having a modal fibre particle size ranging from about 0.1-500 pm and a modal inorganic particulate material particle size ranging from 0.25-20 pm. The fibrous substrate comprising cellulose may be microfibrillated in the presence of an inorganic particulate material to obtain microfibrillated cellulose having a modal fibre particle size of at least about 0.5 pm, for example at least about 10 pm, or at least about 50 pm, or at least about 100 pm, or at least about 150 pm, or at least about 200 pm, or at least about 300 pm, or at least about 400 pm.

The fibrous substrate comprising cellulose may be microfibrillated in the presence of an inorgan ic particulate material to obtai n microfibri llated cellulose having a fibre steepness equal to or greater than about 10, as measured by Malvern. Fibre steepness (i.e., the steepness of the particle size distribution of the fibres) is determined by the following formula: Steepness = 100 x (d ₃₀ /d ₇ o)

The microfibrillated cellulose may have a fibre steepness equal to or less than about 100. The microfibrillated cellulose may have a fibre steepness equal to or less than about 75, or equal to or less than about 50, or equal to or less than about 40, or equal to or less than about 30. The microfibrillated cellulose may have a fibre steepness from about 20 to about 50, or from about 25 to about 40, or from about 25 to about 35, or from about 30 to about 40.

The grinding is suitably performed in a grinding vessel, such as a tumbling mill (e.g. , rod, ball and autogenous), a stirred mill (e.g. , SAM or IsaMill), a tower mill, a stirred media detritor (SMD), or a grinding vessel comprising rotating parallel grinding plates between which the feed to be ground is fed.

The fibrous substrate comprising cellulose and inorganic particulate material may be present in the aqueous environment at an initial solids content of at least about 4 wt %, of which at least about 2 % by weight is fibrous substrate comprising cellulose. The initial solids content may be at least about 10 wt%, or at least about 20 wt %, or at least about 30 wt %, or at least about at least 40 wt %. At least about 5 % by weight of the initial solids content may be fibrous substrate comprising cellulose, for example, at least about 10 %, or at least about 15 %, or at least about 20 % by weight of the initial solids content may be fibrous substrate comprising cellulose.

As the suspension of material to be ground may be of a relatively high viscosity, a suitable dispersing agent may preferably be added to the suspension prior to grinding. The dispersing agent may be, for example, a water soluble condensed phosphate, polysilicic acid or a salt thereof, or a polyelectrolyte, for example a water soluble salt of a poly(acrylic acid) or of a poly(methacrylic acid) having a number average molecular weight not greater than 80,000. The amount of the dispersing agent used would generally be in the range of from 0.1 to 2.0% by weight, based on the weight of the dry inorganic particulate solid material. The suspension may suitably be ground at a temperature in the range of from 4°C to 100°C.

Other additives which may be included during the microfibrillation step include: carboxymethyl cellulose, amphoteric carboxymethyl cellulose, oxidising agents, 2,2,6,6-Tetramethylpiperidine-1 -o xy I (TE M PO) , TE M PO d erivatives , a nd wood degrading enzymes.

The pH of the suspension of material to be ground may be about 7 or greater than about 7 (i.e., basic), for example, the pH of the suspension may be about 8, or about 9, or about 10, or about 1 1. The pH of the suspension of material to be ground may be less than about 7 (i.e., acidic), for example, the pH of the suspension may be about 6, or about 5, or about 4, or about 3. The pH of the suspension of material to be ground may be adjusted by addition of an appropriate amount of acid or base. Suitable bases included alkali metal hydroxides, such as, for example NaOH. Other suitable bases are sodium carbonate and ammonia. Suitable acids included inorganic acids, such as hydrochloric and sulphuric acid, or organic acids. An exemplary acid is orthophosphoric acid.

The amount of inorganic particulate material and cellulose pulp in the mixture to be co- ground may vary in a ratio of from about 99.5:0.5 to about 0.5:99.5, based on the dry weight of inorganic particulate material and the amount of dry fibre in the pulp, for example, a ratio of from about 99.5:0.5 to about 50:50 based on the dry weight of inorganic particulate material and the amount of dry fibre in the pulp. For example, the ratio of the amount of inorganic particulate material and dry fibre may be from about 99.5:0.5 to about 70:30. In an embodiment, the ratio of inorganic particulate material to dry fibre is about 80:20, or for example, about 85: 15, or about 90:10, or about 91 :9, or about 92:8, or about 93:7, or about 94:6, or about 95:5, or about 96:4, or about 97:3, or about 98:2, or about 99: 1 . In a preferred embodiment, the weight ratio of inorganic particulate material to dry fibre is about 95:5. In another preferred embodiment, the weight ratio of inorganic particulate material to dry fibre is about 90: 10. In another preferred embodiment, the weight ratio of inorganic particulate material to dry fibre is about 85:15. In another preferred embodiment, the weight ratio of inorganic particulate material to dry fibre is about 80:20. The total energy input in a typical grinding process to obtain the desired aqueous suspension composition may typically be between about 100 and 1500 kWht ^"1 based on the total dry weight of the inorganic particulate filler. The total energy input may be less than about 1000 kWht ^"1 , for example, less than about 800 kWht ^"1 , less than about 600 kWht ^"1 , less than about 500 kWht ^"1 , less than about 400 kWht ^"1 , less than about 300 kWht ^"1 , or less than about 200 kWht ^"1 . As will be apparent, the total energy input per tonne of dry fibre in the fibrous substrate comprising cellulose will be less than about 10,000 kWht ^"1 , for example, less than about 9000 kWht ^"1 , or less than about 8000 kWht ^"1 , or less than about 7000 kWht ^"1 , or less than about 6000 kWht ^"1 , or less than about 5000 kWht ^"1 , for example less than about 4000 kWht-1 , less than about 3000 kWht ^"1 , less than about 2000 kWht ^"1 , less than about 1500 kWht ^"1 , less than about 1200 kWhf ¹ , less than about 1000 kWht ^"1 , or less than about 800 kWht ^"1 . The total energy input varies depending on the amount of dry fibre in the fibrous substrate being microfibrillated, and optionally the speed of grind and the duration of grind. Microfibrillation of the fibrous substrate comprising cellulose may be effected under wet conditions in the presence of the inorganic particulate material by a method in which the mixture of cellulose pulp and inorganic particulate material is pressurized (for example, to a pressure of about 500 bar) and then passed to a zone of lower pressure. The rate at which the mixture is passed to the low pressure zone is sufficiently high and the pressure of the low pressure zone is sufficiently low as to cause microfibrillation of the cellulose fibres. For example, the pressure drop may be effected by forcing the mixture through an annular opening that has a narrow entrance orifice with a much larger exit orifice. The drastic decrease in pressure as the mixture accelerates into a larger volume (i .e. , a lower pressure zone) induces cavitation which causes microfibrillation. In an embodiment, microfibrillation of the fibrous substrate comprising cellulose may be effected in a homogenizer under wet conditions in the presence of the inorganic particulate material. In the homogenizer, the cellulose pulp-inorganic particulate material mixture is pressurized (for example, to a pressure of about 500 bar), and forced through a small nozzle or orifice. The mixture may be pressurized to a pressure of from about 100 to about 1000 bar, for example to a pressure of equal to or greater than 300 bar, or equal to or greater than about 500, or equal to or greater than about 200 bar, or equal to or greater than about 700 bar. The homogenization subjects the fibres to high shear forces such that as the pressurized cellulose pulp exits the nozzle or orifice, cavitation causes microfibrillation of the cellulose fibres in the pulp. Additional water may be added to improve flowability of the suspension through the homogenizer. The resulting aqueous suspension comprising microfibrillated cellulose and inorganic particulate material may be fed back into the inlet of the homogenizer for multiple passes through the homogenizer. The inorganic particulate material may be a naturally platy mineral, such as kaolin. As such, homogenization not only facilitates microfibrillation of the cellulose pulp, but also facilitates delamination of the platy particulate material.

As described later, a platy particulate material, such as kaolin, is understood to have a shape factor of at least about 10, for example, at least about 15, or at least about 20, or at least about 30, or at least about 40, or at least about 50, or at least about 60, or at least about 70, or at least about 80, or at least about 90, or at least about 100. Shape factor, as described below, is a measure of the ratio of particle diameter to particle thickness for a population of particles of varying size and shape as measured using the electrical conductivity methods, apparatuses, and equations described in U.S. Patent No. 5,576,617.

A suspension of a platy inorganic particulate material, such as kaolin, may be treated in the homogenizer to a predetermined particle size distribution in the absence of the fibrous substrate comprising cellulose, after which the fibrous material comprising cellulose is added to the aqueous slurry of inorganic particulate material and the combined suspension is processed in the homogenizer as described above. The homogenization process is continued, including one or more passes through the homogenizer, until the desired level of microfibrillation has been obtained. Similarly, the platy inorganic particulate material may be treated in a grinder to a predetermined particle size distribution and then combined with the fibrous material comprising cellulose followed by processing in the homogenizer. An exemplary homogenizer is a Manton Gaulin (APV) homogenizer.

After the microfibrillation step has been carried out, the aqueous suspension comprising microfibrillated cellulose and inorganic particulate material may be screened to remove fibre above a certain size and to remove any grinding medium. For example, the suspension can be subjected to screening using a sieve having a selected nominal aperture size in order to remove fibres which do not pass through the sieve. Nominal aperture size means the nominal central separation of opposite sides of a square aperture or the nominal diameter of a round aperture. The sieve may be a BSS sieve (in accordance with BS 1796) having a nominal aperture size of 150pm, for example, a nominal aperture size 125pm , or 106pm, or 90pm, or 74pm, or 63pm, or 53pm, 45pm, or 38pm. In one embodiment, the aqueous suspension is screened using a BSS sieve having a nominal aperture of 125pm. The aqueous suspension may then be optionally dewatered.

For use in certain embodiments of the fibre based substrate of the present invention, the microfibrillated cellulose and co-processed inorganic particulate material may be provided in the form of an aqueous slurry or damp pressed cake.

In certain embodiments in which the microfibrillation is conducted in the absence of grindable inorganic particulate material, the fibrous substrate comprising cellulose may be microfibrillated to obtain microfibrillated cellulose having a d ₅₀ ranging from about 5 to pm about 500 pm, as measured by laser light scattering. The fibrous substrate comprising cellulose may be microfibrillated to obtain microfibrillated cellulose having a d ₅ o of equal to or less than about 400 pm, for example equal to or less than about 300 pm, or equal to or less than about 200 pm, or equal to or less than about 150 pm, or equal to or less than about 125 pm, or equal to or less than about 100 pm, or equal to or less than about 90 pm, or equal to or less than about 80 pm, or equal to or less than about 70 pm, or equal to or less than about 60 pm, or equal to or less than about 50 pm, or equal to or less than about 40 μηη, or equal to or less than about 30 pm, or equal to or less than about 20 pm, or equal to or less than about 10 pm.

The fibrous substrate comprising cellulose may be microfibrillated to obtain microfibrillated cellulose having a modal fibre particle size ranging from about 0.1-500 pm. The fibrous substrate comprising cellulose may be microfibrillated to obtain microfibrillated cellulose having a modal fibre particle size of at least about 0.5 pm, for example at least about 10 pm, or at least about 50 pm, or at least about 100 pm, or at least about 150 pm, or at least about 200 pm, or at least about 300 pm, or at least about 400 pm.

The fibrous substrate comprising cellulose may be microfibrillated to obtain microfibrillated cellulose having a fibre steepness equal to or greater than about 10, as measured by Malvern. Fibre steepness (i.e., the steepness of the particle size distribution of the fibres) is determined by the following formula:

Steepness = 100 x (d ₃ o/d ₇ o)

The microfibrillated cellulose may have a fibre steepness equal to or less than about 100. The microfibrillated cellulose may have a fibre steepness equal to or less than about 75, or equal to or less than about 50, or equal to or less than about 40, or equal to or less than about 30. The microfibrillated cellulose may have a fibre steepness from about 20 to about 50, or from about 25 to about 40, or from about 25 to about 35, or from about 30 to about 40.

As noted above, the grinding is performed in the presence of a grinding medium. In an embodiment, the grinding medium is a coarse media comprising particles having an average diameter in the range of from about 1 mm to about 6 mm, for example about 2 mm, or about 3 mm, or about 4 mm, or about 5 mm.

In another embodiment, the grinding media has a specific gravity of at least about 2.5, for example, at least about 3, or at least about 3.5, or at least about 4.0, or at least about 4.5, or least about 5.0, or at least about 5.5, or at least about 6.0. As described above, the grinding medium (or media) may be in an amount up to about 70% by volume of the charge. The grinding media may be present in amount of at least about 10% by volume of the charge, for example, at least about 20 % by volume of the charge, or at least about 30% by volume of the charge, or at least about 40 % by volume of the charge, or at least about 50% by volume of the charge, or at least about 60 % by volume of the charge.

In one embodiment, the grinding medium is present in amount of about 50% by volume of the charge.

By "charge" is meant the composition which is the feed fed to the grinder vessel. The charge includes water, grinding media, the fibrous substrate comprising cellulose and any other optional additives (other than as described herein). The fibrous substrate comprising cellulose may be present in an aqueous environment at an initial solids content of at least about 1 wt %. The fibrous substrate comprising cellulose may be present in the aqueous environment at an initial solids content of at least about 2 wt %, for example at least about 3 wt %, or at least about at least 4 wt %. Typically the initial solids content will be no more than about 10 wt%.

For use in certain embodiments of the present invention, the microfibrillated cellulose prepared in the absence of grindable inorganic particulate material may be provided in the form of an aqueous slurry or damp pressed cake. The fibre based substrate may also contain other additives commonly used in papermaking, for example, a n on-ionic, cationic or an anionic retention aid or microparticle retention system in an amount in the range from about 0.1 to 2% by weight, based on the dry weight of the microfibrillated cellulose and inorganic particulate material. It may also contain a sizing agent which may be, for example, a long chain alkylketene dimer, a wax emulsion or a succinic acid derivative. The fibre based substrate may also contain dye and/or an optical brightening agent. The fibre based substrate may also comprise dry and wet strength aids such as, for example, starch or epichlorhydrin copolymers. One advantage in utilising microfibrillated cellulose is that in provides high tensile strength, thus enabling a very strong and very lightweight paper base to be produced, which may also contain highly opacifying minerals, such as the co-processed inorganic particulate materials described below). Thus, in an advantageous embodiment, the fibre based substrate is in the form of a paper base or sheet having a relatively low base weight. For example, in one embodiment, the base weight is from about 10 gsm to about 50 gsm. In other embodiments, the paper base or sheet has a base weight of from about 20 gsm to about 40 gsm, or from about 30 gsm to about 40 gsm, or from about 25 gsm to about 40 gsm, or from about 25 gsm to 35 gsm.

- co-processed inorganic particulate material

In certain embodiments of the present invention, co-processed inorganic particulate material is included in the fibre based substrate. The co-processed inorganic particulate material may serve the purpose of functional filler, extender filler or opacifying agent, i.e., to increase, decrease or otherwise modify the opacity of the coated fibre based material.

The inorganic particulate material may, for example, be an alkaline earth metal carbonate or sulphate, such as calcium carbonate, magnesium carbonate, dolomite, gypsum, a hydrous kandite clay such as kaolin, halloysite or ball clay, an anhydrous (calcined) kandite clay such as metakaolin or fully calcined kaolin, talc, mica, perlite or diatomaceous earth, or magnesium hydroxide, or aluminium trihydrate, or combinations thereof.

I n an embodiment, the inorganic particulate material is an alkaline earth metal carbonate, for example, calcium carbonate. The inorganic particulate material may be ground calcium carbonate (GCC) or precipitated calcium carbonate (PCC), or a mixture of GCC and PCC. In another embodiment, the inorganic particulate material is a naturally platy mineral, for example, kaolin. The inorganic particulate material may be a mixture of kaolin and calcium carbonate, for example, a mixture of kaolin and GCC, or a mixture of kaolin and PCC, or a mixture of kaolin, GCC and PCC.

The particulate calcium carbonate used in certain embodiments of the present invention may be obtained from a natural source by grinding . Ground calcium carbonate (GCC) is typically obtained by crushing and then grinding a mineral source such as chalk, marble or limestone, which may be followed by a particle size classification step, in order to obtain a product having the desired degree of fineness. Other techniques such as bleaching, flotation and magnetic separation may also be used to obtain a product having the desired degree of fineness and/or colour. The particulate solid material may be ground autogenously, i.e. by attrition between the particles of the solid material themselves, or, alternatively, in the presence of a particulate grinding medium comprising particles of a different material from the calcium carbonate to be ground. These processes may be carried out with or without the presence of a dispersant and biocides, which may be added at any stage of the process.

Precipitated calcium carbonate (PCC) may be used as the source of particulate calcium carbonate in the present invention, and may be produced by any of the known methods available in the art. TAPPI Monograph Series No 30, "Paper Coating Pigments", pages 34-35 describes the three main commercial processes for preparing precipitated calcium carbonate which is suitable for use in preparing products for use in the paper industry, but may also be used in the practice of the present invention. In all three processes, a calcium carbonate feed material, such as limestone, is first calcined to produce quicklime, and the quicklime is then slaked in water to yield calcium hydroxide or milk of lime. In the first process, the milk of lime is directly carbonated with carbon dioxide gas. This process has the advantage that no by-product is formed, and it is relatively easy to control the properties and purity of the calcium carbonate product. In the second process the milk of lime is contacted with soda ash to produce, by double decomposition, a precipitate of calcium carbonate and a solution of sodium hydroxide. The sodium hydroxide may be substantially completely separated from the calcium carbonate if this process is used commercially. In the third main commercial process the milk of lime is first contacted with ammonium chloride to give a calcium chloride solution and ammonia gas. The calcium chloride solution is then contacted with soda ash to produce by double decomposition precipitated calcium carbonate and a solution of sodium chloride. The crystals can be produced in a variety of different shapes and sizes, depending on the specific reaction process that is used. The three main forms of PCC crystals are aragonite, rhombohedral and scalenohedral, all of which are suitable for use in the present invention, including mixtures thereof. Wet grinding of calcium carbonate involves the formation of an aqueous suspension of the calcium carbonate which may then be ground, optionally in the presence of a suitable dispersing agent. Reference may be made to, for example, EP-A-614948 (the contents of which are incorporated by reference in their entirety) for more information regarding the wet grinding of calcium carbonate.

Kaolin clay used in certain embodiments of this invention may be a processed material derived from a natural source, namely raw natural kaolin clay mineral. The processed kaolin clay may typically contain at least about 50% by weight kaolinite. For example, most commercially processed kaolin clays contain greater than about 75% by weight kaolinite and may contain greater than about 90%, in some cases greater than about 95% by weight of kaolinite.

Kaolin clay used in certain embodiments of the present invention may be prepared from the raw natural kaolin clay mineral by one or more other processes which are well known to those skilled in the art, for example by known refining or beneficiation steps.

For example, the clay mineral may be bleached with a reductive bleaching agent, such as sodium hydrosulfite. If sodium hydrosulfite is used, the bleached clay mineral may optionally be dewatered, and optionally washed and again optionally dewatered, after the sodium hydrosulfite bleaching step.

The clay mineral may be treated to remove impurities, e. g. by flocculation, flotation, or magnetic separation techniques well known in the art. Alternatively the clay mineral used in the first aspect of the present invention may be untreated in the form of a solid or as an aqueous suspension.

The process for preparing the particulate kaolin clay used in certain embodiments of the present invention may also include one or more comminution steps, e.g., grinding or milling. Light comminution of a coarse kaolin is used to give suitable delamination thereof. The comminution may be carried out by use of beads or granules of a plastic (e. g. nylon), sand or ceramic grinding or milling aid. The coarse kaolin may be refined to remove impurities and improve physical properties using well known procedures. The kaolin clay may be treated by a known particle size classification procedure, e.g., screening and centrifuging (or both), to obtain particles having a desired d ₅₀ value or particle size distribution.

The particle size distribution of the inorganic particulate materials will be that which is suitable for use in paint. Suitable particle sizes are described below in connection with the primary pigment and extender pigment.

In one embodiment, the inorganic particulate material used during the microfibrillating step may have a particle size distribution in which at least about 10% by weight of the particles have an e.s.d of less than 2 pm, for example, at least about 20% by weight, or at least about 30% by weight, or at least about 40% by weight, or at least about 50% by weight, or at least about 60% by weight, or at least about 70% by weight, or at least about 80% by weight, or at least about 90% by weight, or at least about 95% by weight, or about 100% of the particles have an e.s.d of less than 2 pm.

The amount of co-processed inorganic particulate material in the fibre based substrate composition of certain embodiments of the present invention may range from about 0.1 to about 80 % by weight, based on the total weight of the fibre based substrate. In certain embodiments, the amount of co-processed inorganic particulate material in the fibre based substrate may be from about 0.2 to about 70 % by weight, for example, from about 0.2 to about 60% by weight, for example, from about 0.2 to about 50 % by weight, for example, from about 0.3 to about 50 % by weight, for example, from about 0.4 to about 40 % by weight, for example, from about 0.4 to about 30 % by weight, or from about 0.4 to about 20 % by weight. In certain embodiments, amount of co- processed inorganic particulate material in the fibre-based material is at least about 0.5 % by weight, for example, at least about 1 % by weight, or at least about 5 % by weight, or at least about 10 % by weight, or at least about 15 % by weight, or at least about 20 % by weight, or at least about 25 % by weight, or at least about 30 % by weight, or at least about 35 % by weight, or at least about 40 % by weight, or at least about 45 % by weight, or at least about 50 % by weight.

Because in certain embodiments in which co-processed inorganic particulate material is included in the fibre based substrate along with the microfibrillated cellulose this means the amount of inorganic particulate material (as described later) that would otherwise have been added separately to the fibre based substrate (e.g., as functional filler, extender filler or opacifying agent) may be reduced. In certain embodiments, the co-processed inorganic particulate material constitutes all of the inorganic particulate material comprised in the fibre based substrate.

- inorganic particulate material other than co-processed inorganic particulate material

In another embodiment, the fibre based substrate comprises inorganic particulate material other than the co-processed inorganic particulate material described above. In certain embodiments, said other inorganic particulate material constitutes all of the inorganic particulate material in the fibre based substrate.

The (non-co-processed) inorganic particulate material may, for example, be an alkaline earth metal carbonate or sulphate, such as calcium carbonate, magnesium carbonate, dolomite, gypsum, a hydrous kandite clay such as kaolin, halloysite or ball clay, an anhydrous (calcined) kandite clay such as metakaolin or fully calcined kaolin, talc, mica, perlite or diatomaceous earth, or magnesium hydroxide, or aluminium tri hydrate, or combinations thereof.

In one embodiment, the mean particle size (d ₅₀ ) of the inorganic particulate material (and the co-processed inorganic particulate material described above) may be from about 0.1 pm to about 20 pm, as determined by Sedigraph. For example, the d ₅₀ may be from about 0.2 pm to about 15 pm, or from about 0.3 pm to about 12 pm, or from about 0.4 pm to about 10 pm, or form about 0.6 pm to about 10 pm, or from about 0.8 pm to about 10 pm, or from about 1 pm to about 10 pm, or from about 1.5 pm to about 10 pm, or from about 2 pm to about 10 pm, or from about 2.5 to about 10 pm. The d ₅ o of the inorganic particulate material may be up to about 9 pm, for example, up to about 8 pm, or up to about 7 pm, or up to about 6 pm, or up to about 5 pm, or up to about 4 pm, or up to about 3 pm, or up to about 2 pm, or up to about 1 pm. The amount of inorganic particulate material in the fibre based substrate composition of the present invention may range from about 0.1 to about 80 % by weight, based on the total weight of the fibre based substrate. In embodiments, the amount of inorganic particulate material in the fibre based substrate may be from about 0.2 to about 70 % by weight, for example, from about 0.2 to about 60% by weight, for example, from about 0.2 to about 50 % by weight, for example, from about 0.3 to about 50 % by weight, for example, from about 0.4 to about 40 % by weight, for example, from about 0.4 to about 30 % by weight, or from about 0.4 to about 20 % by weight. In embodiments, amount inorganic particulate material in the fibre-based material is at least about 0.5 % by weight, for example, at least about 1 % by weight, or at least about 5 % by weight, or at least about 10 % by weight, or at least about 15 % by weight, or at least about 20 % by weight, or at least about 25 % by weight, or at least about 30 % by weight, or at least about 35 % by weight, or at least about 40 % by weight, or at least about 45 % by weight, or at least about 50 % by weight. In further embodiments, the total amount of inorganic particulate material (i.e. , the combined amount of co-processed inorganic particulate material and non-co-processed inorganic particulate material) in the fibre based substrate may from about 0.1 to about 80 % by weight, based on the total weig ht of the fibre based substrate. I n embodiments, the amount of inorganic particulate material in the fibre based substrate may be from about 0.2 to about 70 % by weight, for example, from about 0.2 to about 60% by weight, for example, from about 0.2 to about 50 % by weight, for example, from about 0.3 to about 50 % by weight, for example, from about 0.4 to about 40 % by weight, for example, from about 0.4 to about 30 % by weight, or from about 0.4 to about 20 % by weight. In embodiments, amount inorganic particulate material in the fibre-based material is at least about 0.5 % by weight, for example, at least about 1 % by weight, or at least about 5 % by weight, or at least about 10 % by weight, or at least about 1 5 % by weight, or at least about 20 % by weight, or at least about 25 % by weight, or at least about 30 % by weight, or at least about 35 % by weight, or at least about 40 % by weight, or at least about 45 % by weight, or at least about 50 % by weight.

In an embodiment, the weight ratio of the co-processed inorganic particulate material to non-co-processed inorganic particulate material in the fibre based substrate is from about 1 :1 to about 1 :30, for example, from about 1 :1 to about 1 :20, or from about 1 : 1 to about 1 : 15, or from about 1 : 1 to about 1 : 10, or from about 1 : 1 to about 1 :7, or from about 1 :3 to about 1 :6, or about 1 : 1 , or about 1 :2, or about 1 :3, or about 1 :4, or about 1 :5. In other embodiments, the weight ratio of the co-processed inorganic particulate material to non-co-processed inorganic particulate material in the fibre based substrate is from about 30: 1 to about 1 :1 , for example, from about 20:1 to about 1 :1 , or from about 15:1 to about 1 :1 , or from about 10: 1 to about 1 : 1 , or from about 7: 1 to about 1 :1 , from about 6:1 to about 3:1 , or about 2:1 , or about 3:1 , or about 4: 1 or about 5:1.

Barrier coatings

In accordance with the first aspect of the invention, the fibre based substrate has at least first and second barrier coatings formed thereon.

The barrier property may be selected from the rate at which one or more of oxygen, moisture, grease (including, for example, mineral oil derived from recycled pulp and/or printing inks) and aromas pass (i.e. , transmitted) through the coated fibre based material. The barrier coating composition may therefore slow down or ameliorate (i.e., decrease) the rate at which one or more of oxygen, moisture, grease and aromas pass through the coated fibre based material.

In an embodiment, the fibre based substrate is disposed between (i.e., sandwiched by) said first and second barrier coatings. Thus, in accordance with the illustrated embodiment shown in Figure 1 , the coated fibre based material (100) comprises a fibre based substrate (101 ) having a first barrier coating form on a first surface (102) of the fibre based substrate and the second barrier coating (105) is formed an opposing surface (104) of the fibre based substrate (101 ).

In one embodiment, one or both of the first and second barrier coatings comprise a platy inorganic particulate material.

A platy inorganic particulate material is considered to have relatively high shape factor. An inorganic particulate material of high shape factor is considered to be more "platy" than inorganic product of low shape factor. "Shape factor", as used herein, is a measure of the ratio of particle diameter to particle thickness for a population of particles of varying size and shape as measured using the electrical conductivity methods, apparatuses, and equations described in U.S. Patent No. 5,576,617, which is incorporated herein by reference. As the technique for determining shape factor is further described in the '617 patent, the electrical conductivity of a composition of an aqueous suspension of orientated particles under test is measured as the composition flows through a vessel. Measurements of the electrical conductivity are taken along one direction of the vessel and along another direction of the vessel transverse to the first direction. Using the difference between the two conductivity measurements, the shape factor of the particulate material under test is determined. The platy inorganic particulate material may, for example, be an alkaline earth metal sulphate, such as gypsum, a hydrous kandite clay such as kaolin, halloysite or ball clay, an anhydrous (calcined) kandite clay such as metakaolin or fully calcined kaolin, talc, mica, perlite or diatomaceous earth, or magnesium hydroxide, or aluminium tri hydrate, or combinations thereof.

A preferred platy inorganic particulate material is aluminosilicate, particularly kaolin. Hereafter, certain embodiments of the present invention may tend to be discussed in terms of kaolin, and in relation to aspects where the kaolin is processed and/or treated. The present invention should not be construed as being limited to such embodiments.

The shape factor of the kaolin may suitably be equal to or greater than about 10. For example, the shape factor may be equal or greater than about 20, or equal or greater than about 30, or equal or greater than about 40, or equal or greater than about 50, or equal or greater than about 60 or about 70. The shape factor may be equal or greater than about 80, for example equal or greater than about 90 or about 100, for example up to about 1 10 or about 150. For example, the shape factor may lie in one or more of the following ranges: 25 to 150; 20 to 1 10; 30 to 150; 30 to 1 10; 40 to 150; 40 to 1 10; 50 to 150; 50 to 1 10; 60 to 150; 60 to 1 10; 70 to 150; 70 to 1 10; 80 to 150; 80 to 120; 90 to 150; 90 to 1 10. The kaolin may be prepared in accordance with the methods described above. Exemplary barrier coating compositions and methods of preparation are described in WO-A-03/022933, the entire contents of which are incorporated herein by reference.

The kaolin particles may have a mean particle size (d ₅₀ by Sedigraph) ranging from about 0.1 pm to about 10 pm, such as a d ₅ o ranging from about 0.25 pm to about 8 pm, for example, from about 0.25 pm to about 6 pm, or from about 0.25 pm to about 4.0 pm, or from about 0.25 pm to about 3.0 pm, or from about 0.25 to about 2.0 pm, or from about 0.1 pm to about 2.0 pm, or from about 0.1 pm to about 1.5 pm, or from about 0.1 pm to about 1.0 pm. For example, the d ₅₀ can be about 0.4 pm, or about 0.5 pm, or about 0.6 pm, or about 0.7 pm, or about 0.8 pm, or about 0.9 pm, or about 1.0 μηι, or about 1.1 μηι _> or about 1.2 μιη, or about 1.3 μιη, or about 1.4, μηη, or about 1.5 μηι, or about 1.6 μιη, or about 1.7 μιτι, or about 1.8 μηι, or about 1.9 μιτι, or about 2.0 μηι. In an embodiment, the inorganic particulate of the first barrier coating has a shape factor greater than (i.e. , is more platy than) the inorganic particulate of the second barrier coating. For example, the first barrier coating may comprise kaolin having a shape factor of greater than or equal to about 90, for example, greater than or equal to about 100, and the second barrier coating may comprise kaolin having a shape factor of less than about 70, for less than or equal to about 60. In one embodiment, the first barrier coating comprises kaolin having a shape factor of about 100 and the second barrier coating comprises kaolin having a shape factor of about 60. In such embodiments, the kaolin may be the only platy inorganic particulate material in each barrier coating.

The steepness of the particle size distribution (psd) of the platy inorganic particulate material, for example, platy kaolin, according to certain embodiments of the present invention, often referred to as narrowness of the psd, refers to the slope of the psd curve. Thus in some cases the psd of the kaolin may be steep and in other cases it may be broad. Steepness, as used herein, is measured as 100 times the ratio of d ₃₀ to d ₇₀ , where d ₃₀ is the value of the particle e.s.d. less than which there are 30 % by weight of the particles and d ₇₀ is the value of particle e.s.d. less than which there are 70 % by weight of the particles as determined from the psd (by Sedigraph). Thus, in certain embodiments, the platy kaolin may have a steepness of from about 10 to about 50, for example, from about 15 to about 45, or from about 20 to about 40, or from about 25 to about 40, or from about 30 to about 45, or from about 30 to about 40, or from about 25 to about 35, or from about 25 to about 30, or from about 30 to about 35.

The first and second barrier coatings may be provided for application in the form a slurry, for example, an aqueous slurry. The solids content of the slurry may be from about 10 % to about 90 %, for example, from about 20 % to about 80 %, or from about 30 % to about 70 %, or from about 40 % to about 70 %, or from about 50 % to about 70 %, for from about 40 % to about 60 %, for from about 45 % to about 65 %, or from about 55 % to about 65 %. The first and second barrier coatings may be applied in sufficient amounts to form coatings have the desired coating weight. For example, the total coat weight of each of the first and/or second barrier coating, considered separately, may be up to about 20 gsm, for example, up to about 18 gsm, or up to about 16 gsm, or up to about 14 gsm, or about to about 12 gsm, or about to about 10 gsm, or up to about 9 gsm, or up to about 8 gsm, or up to about 7 gsm, or up to about 6 gsm, or up to about 5 gsm, or up to about 4 gsm or up to about 3 gsm, or up to about 2 gsm. In an embodiment, the total coat weight is at least about 1 gsm, for example, at least about 2 gsm, or at least about 3 gsm, or at least about 4 gsm.

In certain embodiments, first barrier coating comprises at least two barrier layers which are applied sequentially to the fibre based substrate. The at least two barrier layers may have the same composition, e.g., both layers comprising a platy kaolin of the same shape factor, or may have different compositions, e.g., each layer comprises a platy kaolin of different shape factor, or each layer comprises a different platy inorganic particulate material, which may or may not have the same shape factor. The coat weight of each barrier layer may vary provided the total coat weight of the first barrier coating layer is within the total coat weight described above. For example, a first barrier layer may be applied having a coat weight of about 5 gsm and second barrier layer having a coat weight of 5 gsm may be applied to the first barrier layer, giving a total coating weight of 10 gsm. The ratio of coat weight of the first and second barrier layers of the first barrier coating may range from about 1 : 10 to about 10:1 , for example, from about 1 :9 to about 9:1 , or from about 1 :8 to about 8:1 , or from about 7:1 to about 1 :7, or from about 1 :6 to about 6: 1 , or from about 1 :5 to about 5:1 , or from about 1 :4 to about 4: 1 , or from about 1 :3 to about 3:1 , or from about 1 :2 to about 2: 1 , or about 1 :1.

Thus, in accordance with the illustrated embodiment shown in Figure 2, the coated fibre based material (200) comprises a fibre based substrate (201 ) having a first barrier coating comprising two barrier layers (203a and 203b) sequentially formed on a first surface (202) of the fibre based substrate (201 ) and a second barrier coating (205) formed on a second opposing surface (204) of the fibre based substrate. Barrier layers (203a) and (203b) may both have coat weights of about 5 gsm.

The first and/or second barrier coatings may comprise non-platy inorganic particulate materials, for example, inorganic particulate material having a shape factor less than 10, for example, less than about 8, or less than about 6, or less than about 4, or less than about 2 , or about 1 . In certain embodiments, non-platy inorganic particulate materials include alkaline earth metal carbonates, such as calcium carbonate, magnesium carbonate, and dolomite.

In a further embodiment, the first and/or second barrier coating comprises one or more binding or cobinding agents. For example, latex, which may, optionally, be carboxylated, including: a styrene-butadiene rubber latex; an acrylic polymer latex; a polyvinyl acetate latex; or a styrene acrylic copolymer latex, starch derivatives, sodium carboxymethyl cellulose, alcohol-based binder, and proteins.

By "alcohol" is meant an organic compound in which a hydroxy I functional group (-OH) is bonded to a carbon atom. An alcohol-based binder is therefore a composition or compound which contains a hydroxyl functional group bonded to a carbon atom, which is capable of functioning as a binder in a barrier coating which is suitable for coating paper products and the like. The alcohol-based binder may comprise a primary alcohol having the general formula RCH ₂ OH, a secondary alcohol having the general formula RR'CHOH, a tertiary alcohol having the general formula RR'R"COH, or a combination thereof. R, R', and R" stand for alkyl groups having from one to twenty carbon toms. The alcohol-based binder may comprise primary, secondary and/or tertiary alcohol groups, which may be attached to a polymer backbone. In an embodiment, the alcohol-based binder is a polymer comprising a carboniferous backbone having hydroxyl functional groups appended therefrom. Advantageously, the polymer may be polyvinyl alcohol.

In one advantageous embodiment, the first barrier coating comprises a platy inorganic particulate material and an alcohol-based binder as described above. The platy inorganic particulate material may be kaolin having a shape factor of at least about 50, for example, at least about 60, or at least about 70, or at least about 80, at least about 90, or at least about 100, or at least about 1 10, or at least about 120. The kaolin may have a shape factor no greater than about 150. The kaolin particles may have a mean particle size (d ₅ o by Sedigraph) ranging from about 0.1 pm to about 2.0 pm, such as a d ₅ o ranging from about 0.25 pm to about 1.0 pm. The alcohol-based binder may be polyvinyl alcohol. Polyvinyl alcohol may be obtained by conventional methods know in the art, such as, for example by partial or complete hydrolysis of polyvinyl acetate to remove acetate groups. Thus, a person of skill in the art will understand that polyvinyl alcohol obtained by hydrolysis of polyvinyl acetate may contain pendant acetate groups as well as pendant hydroxy groups. Thus, in embodiments, the polyvinyl alcohol is derived from partially or fully hydrolysed polyvinyl acetate. The extent of hydrolysis may be such that at least about 50 mole % of the acetate groups are hydrolysed, for example, at least about 60 mole % of the acetate groups are hydrolysed, for example, at least about 70 mole % of the acetate groups are hydrolysed, for example, at least about 80 mole % of the acetate groups are hydrolysed, for example, at least about 85 mole % of the acetate groups are hydrolysed, for example, at least about 90 mole % of the acetate groups are hydrolysed, for example, at least about 95 mole % of the acetate groups are hydrolysed or, for example, at least about 99 mole % of the acetate groups are hydrolysed. In another embodiment, the polymer is a copolymer of polyvinyl alcohol and other monomers, such as, for example, acetate and acrylate. The weight ratio of the platy inorganic particulate material, e.g., kaolin, to alcohol-based binder, e.g., polyvinyl alcohol, may be from about 90: 10 to about 10:90, for example, from about about 80:20 to about 20:80, or from about 70:30 to about 30:70, or from about 60:40 to about 40:60, or about 50:50. In an embodiment, the first and/or second barrier coating is applied in two separate barrier layers, as described above. In one embodiment, the total coat weight of the two separate barrier layers taken together is less than about 20 gsm, or less than about 15 gsm, or less than about 12 gsm, or about 10 gsm. In an embodiment, the first and second barrier layers have the same coat weight.

In another advantageous embodiment, the second barrier coating comprises a platy inorganic particulate material and a latex binder. The platy inorganic particulate material may be kaolin having a shape factor of at least about 10, for example, at least about 20, or at least about 30, or at least about 40, at least about 50, or at least about 60. The kaolin may have a shape factor no greater than about 150, for example less than about 100, or less than about 90, or less than about 80, or less than about 70. The kaolin may have a shape factor of from about 20 to about 80, for example, from about 30 to about 70, or from about 40 to about 70, or from about 50 to about 70, or from about 50 to about 65, or from about 55 to about 65. The kaolin particles may have a mean particle size (d ₅₀ by Sedigraph) ranging from about 0.1 μηι to about 2.0 μηι, such as a d ₅₀ ranging from about 0.25 m to about 1 .0 pm. The latex binder may be a styrene-butadiene rubber latex; an acrylic polymer latex; a polyvinyl acetate latex; or a styrene acrylic copolymer latex. Advantageously, the latex binder is a styrene- butadiene rubber latex. The second barrier coating may additionally comprise other co-binders including, for example, starch and/or carboxymethyl cellulose.

In an embodiment, the moisture vapour transmission rate (MVTR) of a coated fibre based material according to the present invention is lower than a second MVTR of a coated fibre based material devoid of microfibrillated cellulose (as defined herein).

In a further embodiment, the second barrier coating has another functional coating disposed thereon. The functional coating may provide or enhance one or more of gloss, coverage, brightness, strength, print receptivity or printability, for example, flexographic printability, or gravure printability, including rotogravure printability, or offset printability. The function coating may also enhance one or more barrier properties of the coated fibre based substrate.

Thus, in accordance with the illustrated embodiment shown in Figure 3, the coated fibre based material (300) comprises a fibre based substrate (301) having a first barrier coating comprising two barrier layers (303a and 303b) sequentially formed on a first surface (302) of the fibre based substrate (301 ), a second barrier coating (305) formed on a second opposing surface (304) of the fibre based substrate, and a functional coating (307) formed on an upper surface (306) of the second barrier coating. In an embodiment, the functional coating comprises inorganic particulate material having a shape factor of at least about 20, and wherein at least about 80 % by weight of the inorganic particulate material has an e.s.d (by Sedigraph) of less than about 1.0 pm and the amount of inorganic particulate material having an e.s.d of less than about 0.25 pm ranges from about 25 % to about 60% by weight.

The inorganic particulate material may, for example, be an alkaline earth metal carbonate or sulphate, such as calcium carbonate, magnesium carbonate, dolomite, gypsum, a hydrous kandite clay such as kaolin, halloysite or ball clay, an anhydrous (calcined) kandite clay such as metakaolin or fully calcined kaolin, talc, mica, perlite or diatomaceous earth, or magnesium hydroxide, or aluminium trihydrate, or combinations thereof.

A preferred inorganic particulate material is aluminosilicate, particularly kaolin. Hereafter, certain embodiments of the present invention may tend to be discussed in terms of kaolin, and in relation to aspects where the kaolin is processed and/or treated. The invention should not be construed as being limited to such embodiments.

In an embodiment, the kaolin has a shape factor of at least about 30, or at least about 40, or at least about 50, or from about 20 to about 60, from about 40 to 50, or from about 30 to 40.

In an embodiment, at least about 94% by weight of the kaolin has an e.s.d of less than about 2 pm, for example, at least about 95% by weight, or least about 96% by weight, or at least about 97 %, or at least about 98 % by weight of the kaolin has an e.s.d of less than about 2 pm. In an embodiment, the amount of the kaolin having an e.s.d of less than about 2 pm ranges from about 94% to about 99% by weight. In an embodiment, at least about 85% by weight of the kaolin has an e.s.d of less than about 1 pm, for example, at least about 88% by weight of the kaolin has an e.s.d of less than about 1 pm, or at least about 92% by weight of the kaolin has an e.s.d of less than about 1 urn.

In an embodiment, the amount of the kaolin having an e.s.d of less than about 0.25 pm ranges from about 35% to about 50% by weight.

In an embodiment, the kaolin has a shape factor ranging from about 30 to about 50, for example, from about 40 to about 50, or from about 45 to about 50, at least about 96% by weight of the kaolin has an e.s.d of less than about 2 pm, at least about 80% by weight of the kaolin has an e.s.d of less than about 1 pm, and the amount of the kaolin having an e.s.d of less than about 0.25 pm ranges from about 35% to about 45% by weight.

The functional coating may additionally comprise one or more binders (as described herein), for example, a latex binder and/or starch. As with the first and second barrier coatings described above, the functional coating may be provided for application in the form a slurry, for example, an aqueous slurry. The solids content of the slurry may be from about 10 % to about 90 %, for example, from about 20 % to about 80 %, or from about 30 % to about 70 %, or from about 40 % to about 70 %, or from about 50 % to about 70 %, or from about 60 % to about 70.

Exemplary functional coating compositions and methods of preparation are described i n WO-A-2004/061014, the entire contents of which are incorporated herein by reference.

Certain embodiments of the present invention is also directed to an intermediate fibre based material which is formable into the coated fibre based material disclosed herein. The intermediate fibre based material comprising a fibre based substrate comprising microfibrillated cellulose, as disclosed herein, and having one or other of the first and second barrier coatings as disclosed herein formed on a surface of the fibre based substrate. In an embodiment, the fibre based substrate is a paper sheet having a base weight of from about 10 gsm to about 50 gsm, for example, a base weight of from about 20 gsm to about 40 gsm, or from about 30 gsm to about 40 gsm, or from about 25 gsm to about 40 gsm, or from about 25 gsm to 35 gsm. In a further embodiment, the first barrier coating comprises at least to barrier layers, as disclosed herein, sequentially formed on the fibre based substrate of the intermediate fibre based material. In a further embodiment, a functional coating, as disclosed herein, is disposed on the second barrier coating formed on a surface of the fibrous substrate of the intermediate fibre based material.

The barrier and/or functional coatings may contain one or more optional additional components, if desired. Such additional components, where present, are suitably selected from known additives for paper coating compositions. Some of these optional additives may provide more than one function in the coating composition. Examples of known classes of optional additives are as follows:

(a) one or more fillers, extenders or pigments: the compositions described herein can be used as sole fillers, extenders or pigments in the coating compositions, or may be used in conjunction with one or more other known fillers and extenders, including the inorganic particulate materials described above, or pigments, such as, for example, titanium dioxide, calcium sulphate, satin white, and so-called 'plastic pigment'. When a mixture of fillers, extenders and/or pigments is used, the total filler/extender/pigment solids content is preferably present in the composition in an amount of at least about 75wt% of the total weight of the dry components of the coating composition;

(b) one or more binding or cobinding agents: for example, latex, which may, optionally, be carboxylated, including: a styrene-butadiene rubber latex; an acrylic polymer latex; a polyvinyl acetate latex; or a styrene acrylic copolymer latex, starch derivatives, sodium carboxymethyl cellulose, polyvinyl alcohol, and proteins;

(c) one or more cross linkers: for example, in levels of up to about 5% by weight; e.g., glyoxals, melamine formaldehyde resins, ammonium zirconium carbonates; one or more dry or wet pick improvement additives: e.g., in levels up to about 2% by weight, e.g . , melamine resin, polyethylene emulsions, urea formaldehyde, melamine formaldehyde, polyamide, calcium stearate, styrene maleic anhydride and others; one or more dry or wet rub improvement and abrasion resistance additives: e.g., in levels up to about 2% by weight, e.g., glyoxal based resins, oxidised polyethylenes, melamine resins, urea formaldehyde, melamine formaldehyde, polyethylene wax, calcium stearate and others; one or more water resistance additives: e.g., in levels up to about 2% by weight, e.g., oxidised polyethylenes, ketone resin, anionic latex, polyurethane, SMA, glyoxal, melamine resin , urea formaldehyde, melamine formaldehyde, polyamide, glyoxals, stearates and other materials commercially available for this function;

(d) one or more water retention aids: for example, in levels up to about 2% by weight, e.g., sodium carboxymethyl cellulose, hydroxyethyl cellulose, PVOH (polyvinyl alcohol), starches, proteins, polyacrylates, gums, alginates, polyacrylamide bentonite and other commercially available products sold for such applications;

(e) one or more viscosity modifiers and/or thickeners: for example, in levels up to about 2% by weight; e.g. , acrylic associative thickeners, polyacrylates, emulsion copolymers, dicyanamide, triols, polyoxyethylene ether, urea, sulphated castor oil, polyvinyl pyrrolidone, CMC (carboxymethyl celluloses, for exam ple sod iu m carboxymethyl cellulose), sodium alginate, xanthan gum, sodium silicate, acrylic acid copolymers, HMC (hydroxymethyl celluloses), HEC (hydroxyethyl celluloses) and others;

(f) one or more lubricity/calendering aids: for example, in levels up to about 2% by weight, e.g., calcium stearate, ammonium stearate, zinc stearate, wax emulsions, waxes, alkyl ketene dimer, glycols; one or more gloss-ink hold-out additives: e.g., in levels up to about 2% by weight, e.g., oxidised polyethylenes, polyethylene emulsions, waxes, casein, guar gum, CMC, HMC, calcium stearate, ammonium stearate, sodium alginate and others;

(g) one or more dispersants: the dispersant is a chemical additive capable, when present in a sufficient amount, of acting on the particles of the particulate inorganic material to prevent or effectively restrict flocculation or agglomeration of the particles to a desired extent, according to normal processing requirements. The dispersant may be present in levels up to about 1 % by weig ht, and includes, for example, polyelectrolytes such as polyacrylates and copolymers containing polyacrylate species, especially polyacrylate salts (e.g., sodium and aluminium optionally with a group II condensed sodium phosphate, non-ionic surfactants, alkanolamine and other reagents commonly used for this function. The dispersant may, for example, be selected from conventional dispersant materials commonly used in the processing and grinding of inorganic particulate materials. Such dispersants will be well recognised by those skilled in this art. They are generally water-soluble salts capable of supplying anionic species which in their effective amounts can adsorb on the surface of the inorganic particles and thereby inhibit aggregation of the particles. The unsolvated salts suitably include alkali metal cations such as sodium. Solvation may in some cases be assisted by making the aqueous suspension slightly alkaline. Examples of suitable dispersants include: water soluble condensed phosphates, e.g., polymetaphosphate salts [general form of the sodium salts: (NaP0 ₃ )J such as tetrasodium metaphosphate or so-called "sodium hexametaphosphate" (Graham's salt); water-soluble salts of polysilicic acids; polyelectrolytes; salts of homopolymers or copolymers of acrylic acid or methacrylic acid, or salts of polymers of other derivatives of acrylic acid, suitably having a weight average molecular mass of less than about 20,000. Sodium hexametaphosphate and sodium polyacrylate, the latter suitably having a weight average molecular mass in the range of about 1 ,500 to about 10,000, are especially preferred;

(h) one or more antifoamers and defoamers: for example, in levels up to about 1 % by weight, e.g., blends of surfactants, tributyl phosphate, fatty polyoxyethylene esters plus fatty alcohols, fatty acid soaps, silicone emulsions and other silicone containing compositions, waxes and inorganic particulates in mineral oil, blends of emulsified hydrocarbons and other compounds sold commercially to carry out this function;

(i) one or more optical brightening agents (OBA) and fluorescent whitening agents (FWA): for example, in levels up to about 1 % by weight, e.g., stilbene derivatives; (j) one or more dyes: for example, in levels up to about 0.5% by weight; (k) one or more biocides/spoilage control agents: for example, in levels up to about 1 % by weight, e.g., oxidizing biocides such as chlorine gas, chlorine dioxide gas, sodium hypochlorite, sodium hypobromite, hydrogen, peroxide, peracetic oxide, ammonium bromide/sodium hypochlorite, or non-oxidising biocides such as GLUT (Glutaraldehyde , CAS No 90045-36-6), ISO (CIT/MIT) (Isothiazolinone, CAS No 55956-84-9 & 961 18-96-6), ISO (BIT/MIT) (Isothiazolinone), ISO (BIT) (Isothiazolinone, CAS No 2634-33-5), DBNPA, BNPD (Bronopol), NaOPP, CARBAMATE, THIONE (Dazomet).EDDM - dimethanol (O-formal), HT - Triazine (N-formal), THPS - tetrakis (O-formal), TMAD - diurea (N-formal), metaborate, sodium dodecylbenene sulphonate, thiocyanate, organosulphur, sodium benzoate and other compounds sold commercially for this function, e.g., the range of biocide polymers sold by Nalco;

(I) one or more levelling and evening aids: for example, in levels up to about 2% by weight, e.g., non-ionic polyol, polyethylene emulsions, fatty acid, esters and alcohol derivatives, alcohol/ethylene oxide, calcium stearate and other compounds sold commercially for this function;

(m) one or more grease and oil resistance additives: for example, in levels up to about 2% by weight, e.g . , oxidised polyethylenes, latex, SMA (styrene maleic anhydride), polyamide, waxes, alginate, protein, CMC, and HMC. Any of the above additives and additive types may be used alone or in admixture with each other and with other additives, if desired.

For all of the above additives, the percentages by weight quoted are based on the dry weight of inorganic particulate material (100%) present in the composition. Where the additive is present in a minimum amount, the minimum amount may be about 0.01 % by weight based on the dry weight of pigment.

In another embodiment, a further coating or printed layer, for example, an ink-based printed layer, is formed on the second barrier coating or, when present, on the functional coating disposed on the second barrier coating. An ink-based printed layer may comprise a colour way and/or graphical representation, e.g., a name, word, phrase, logo, symbol, design, image, signature or any combination of these elements.

Thus, in accordance with the illustrated embodiment shown in Figure 4, the coated fibre based material (400) comprises a fibre based substrate (401) having a first barrier coating comprising two barrier layers (403a and 403b) sequentially formed on a first surface (402) of the fibre based substrate (401 ), a second barrier coating (405) formed on a second opposing surface (404) of the fibre based substrate, a functional coating (407) formed on an upper surface (406) of the second barrier coating, and a ink-based layer (409) printed on the upper surface (408) of the functional coating (407).

The ink-based printed may be applied to the functional coating using any suitable printing method, including but not limited to, offset printing, flexographic printing, rotogravure, and the like. In an advantageous embodiment, the ink-based layer is applied using a flexographic printing technique.

The coating process may be carried out using standard techniques which are well known to the skilled person. The coating process may also involve calendaring or supercalendering the coated product.

Thus, in a further aspect, there is provided a method of preparing a coated fibre based material, comprising: providing or obtaining a fibre based substrate as defined herein; applying a first barrier coating as defined herein to the fibre based substrate; and applying a second barrier coating as defined herein to the fibre based substrate. In an embodiment, the first and second barrier coatings are applied to opposing surfaces of the fibre based substrate such that the fibre based substrate is disposed between said first and second barrier coatings.

In accordance with certain embodiments described above, the first barrier coating comprises at least two barrier layers which are applied sequentially to the fibre based substrate.

In another embodiment, a functional coating as defined herein is applied to the second barrier coating.

In yet another embodiment, one or more of the first barrier coating, the second barrier coating, the first and second barrier layers of the first barrier coating, and the functional coating applied to the second barrier coating are applied using a printing technique. Suitable printing techniques are described later and include offset printing, flexographic printing or rotogravure printing. In yet another embodiment a further coating or printed layer, for example, an ink-based printed layer, is formed on the second barrier coating or, when present, on the functional coating disposed on the second barrier coating. The further coating or printed layer may be formed by a printing technique, for example, a printing technique selected from offset printing, flexographic printing or rotogravure printing.

Methods of coating paper and other sheet materials, and apparatus for performing the methods, are widely published and well known. Such known methods and apparatus may conveniently be used for preparing coated paper. For example, there is a review of such methods published in Pulp and Paper International, May 1994, page 18 et seq. Sheets may be coated on the sheet forming machine, i.e., "on-machine," or "off- machine" on a coater or coating machine. Use of high solids compositions is desirable in the coating method because it leaves less water to evaporate subsequently. However, as is well known in the art, the solids level should not be so high that high viscosity and leveling problems are introduced. The methods of coating may be performed using an apparatus comprising (i) an application for applying the coating composition to the material to be coated and (ii) a metering device for ensuring that a correct level of coating composition is applied. When an excess of coating composition is applied to the applicator, the metering device is downstream of it. Alternatively, the correct amount of coating composition may be applied to the applicator by the metering device, e.g., as a film press. At the points of coating application and metering, the paper web support ranges from a backing roll, e.g., via one or two applicators, to nothing (i.e., just tension). The time the coating is in contact with the paper before the excess is finally removed is the dwell time - and this may be short, long or variable.

The coating is usually added by a coating head at a coating station. According to the quality desired, paper grades are uncoated, single-coated, double-coated and even triple-coated. When providing more than one coat, the initial coat (precoat) may have a cheaper formulation and optionally coarser pigment in the coating composition. A coater that is applying coating on each side of the paper will have two or four coating heads, depending on the number of coating layers applied on each side. Most coating heads coat only one side at a time, but some roll coaters (e.g., film presses, gate rolls, and size presses) coat both sides in one pass. Examples of known coaters which may be employed include, without limitation, air knife coaters, blade coaters, rod coaters, bar coaters, multi-head coaters, roll coaters, roll or blade coaters, cast coaters, laboratory coaters, gravure coaters, kisscoaters, liquid application systems, reverse roll coaters, curtain coaters, spray coaters and extrusion coaters.

Water may be added to the solids comprising the coating composition to give a concentration of solids which is preferably such that, when the composition is coated onto a sheet to a desired target coating weight, the composition has a rheology which is suitable to enable the composition to be coated with a pressure (i.e., a blade pressure) of between 1 and 1.5 bar.

Calendering is a well known process in which paper smoothness and gloss is improved and bulk is reduced by passing a coated paper sheet between calender nips or rollers one or more times. Usually, elastomer-coated rolls are employed to give pressing of high solids compositions. An elevated temperature may be applied. One or more (e.g., up to about 12, or sometimes higher) passes through the nips may be applied.

In one advantageous embodiment, one or more of the barrier coatings and other functional coatings is printed on the fibre based substrate, e.g., printed on a surface of the fibre based substrate.

The printing may utilize a technique selected from offset printing, flexographic printing or rotogravure printing, thereby allowing the barrier coating to be applied to areas where it is required.

Offset printing is a widely used printing technique, as will be well understood by a person of ordinary skill in the art. The barrier coating compositions is transferred (or "offset") from a plate to a rubber blanket, then to the surface of the paper substrate. The paper substrate may be sheet-fed or web-fed. The web-fed process may be heatset or coldset.

Flexographic printing is a widely used printing technique, as will be well understood by a person of ordinary skill in the art. Using this technique the barrier coating composition is transferred from a first roll which is partially immersed in a tank comprising the barrier coating composition. The barrier coating composition is then transferred to the anilox roll (or meter roll) whose texture holds a specific amount of the barrier coating composition since it is covered with thousands of small wells or cups that enable it to meter the barrier coating composition to the printing plate in a uniform thickness evenly and quickly. The fibre based substrate is finally sandwiched between the plate and the impression cylinder to transfer the barrier coating. The coated substrate is then fed through a dryer, which allows the coating to dry. Advantageously, flexographic printing enables the first or second barrier coating composition to be applied in a series of thin layers (e.g., a series of two or more layers with a total coat weight of about 10 gsm) which has sufficient hold out to maintain good barrier properties (to liquid and/or vapour mineral oil transmission.

Rotogravure printing is a widely used printing technique, as will be well understood by a person of ordinary skill in the art.

Articles of manufacture and other paper products

Certain embodiments of the present invention is further directed to articles and paper products formed or formable from the coated fibre based material of the present invention. The term paper product, as used in connection with the present invention, should be understood to mean all forms of paper, including board such as, for example, white-lined board and linerboard, cardboard, paperboard, coated board and the like. There are numerous types of coated paper which may be made according to the present invention, including paper suitable for food packaging, perishable goods other than food, e.g. , pharmaceutical products and compositions, books, magazines, newspapers and the like, and office papers. The paper may be calendered or super calendered as appropriate. Advantageously, paper suitable for light weight coating (LWC), medium coating (MWC) or machine finished pigmentisation (MFP) may also be made according to the present methods.

Barrier coated papers products formed or formable from the coated fibre based material of the present invention include brown corrugated boxes, flexible packaging including retail and shopping bags, food and hygiene bags and sacks, milk and beverage cartons, boxes suitable for cereals and the like, self-adhesive labels, disposable cups and containers, envelopes, cigarette paper and bible paper. In an advantageous embodiment, barrier coated paper products formed or formable from the coated fibre based material of the present invention include food wrap, bags or pouches, and sealing members, e.g., lids, for dairy products such, as for example, tubs and pouches, and the like, suitable for yoghurt, fromage frais, single, double, pouring, whipped, clotted or sour cream, cheese, cottage cheese, creme freche, butter or margarine. In embodiments in which the coated fibre based material is formed into a sealing member for tubs, pots or cartons, for example, a tub, pot or carton suitable for containing a dairy product of the type described immediately above, and with reference to the non-limiting illustrative embodiment shown in Figure 5, the first barrier coating (503a; 503b) is orientated such that on sealing the tub or carton (500) with the sealing member (510) it faces the interior of the tub or carton (500), and the second barrier coating (505), optionally comprising a functional layer (507) and an ink-based layer (509), which is optionally a printed ink-based layer, faces outwards. In other embodiments, the food wrap is in the form of a packet for crisps (often referred to as potato chips in USA), biscuits, confectionary, and the like. In these embodiments, the first barrier faces the interior of the packet and proximate an area in which a foodstuff is to be contained.

In another advantageous embodiment in which the coated fibre based material of the present invention is formed or formable into a three-dimensional product suitable for food-grade packaging the first barrier coating faces the interior of the packaging and is proximate an area in which a foodstuff is to be contained.

Thus, certain embodiments of the coated fibre based material of the present invention enables the production of a desirably strong and lightweight paper (owing in part to the incorporation of microfibrillated cellulose in the fibre based substrate) having a desirable barrier to one or more of oxygen, moisture and/or grease, thereby protecting foodstuffs contained with the packaging (including protection from inks used to form an outer ink-based layer on the outermost surface of the second barrier coating or functional coating disposed thereon), and the further advantage of an outer surface having desirable printability.

Embodiments of the present invention will now be described by way of illustration only, with reference to the following examples. EXAMPLES

Example 1 A combination of kraft pulp and microfibrillated cellulose was used in various combinations from 100% kraft to 80% kraft/20% microfibrillated cellulose (mfc) to make a series of hand sheets using the Rapid Kothe with base weights ranging from 20-30 gsm, as detailed in Table 1. The hand sheets were circular having a diameter of about 20 cm.

Table 1.

The hand sheets were then coated as follows: 1. Precoat of 7 gsm of kaolin having a shape factor of 60 (100pts), latex (6pts), starch (4pts). This is the second barrier coating as it is described herein.

2. Topcoat of 10 gsm of a platy kaolin (100 parts), latex (10pts), carboxymethyl cellulose (O.Spts). This is the functional coating disposed on the second barrier coating as it is described herein.

3. Two separate coats of 5 gsm of 50:50 kaolin having a shape factor of

100:polyvinyl alcohol (Celvol2). This is the first barrier coating as it is described herein.

Coatings were applied using HDD methods. A circular guard was placed about the edge (at an ingress of about 2 mm) of the hand sheet to prevent seepage of colour around upper points on the circumference and under the coated sheet. The colour was applied in an arc at the top, and the selected HDD bar carefully drawn down. The precoat was applied first and dried vigorously. The topcoat was applied next in the same manner, followed by the two separate coats making up the first barrier coating. Example 2

A coated 30 gsm handsheet from Example 1 was tested for moisture pick-up using a Payne cup measurement. The coated paper was based on a fibre substrate having 80% kraft/20% microfibrillated cellulose. The dessicant was 10 g zeolite, dried at 150°C for two days. The chamber was a Gallenkamp environment chamber, at 24°C and 21 °C for the dry and wet, respectively, achieving 25°C and 71 % relative humidity (approaching BS3177 conditions). The paper was tested without overprint varnish and without heatseal.

A number of other papers were tested under the same conditions:

Paper A - a commercial 100 gsm hardwood/softwood sulphate pulp based paper coated on one face with a polyester film on the reverse face with polyolefin;

Paper B - a commercial 80 gsm paper coated on one face with a polyester film and on the reverse side with polyolefin;

Paper C - a commercial 95 gsm kraft paper (MG base) coated on one face with a polyester film on the reverse face with polyolefin. Payne cups were weighed without seal ring, paper diaphragm or clampscrews. Moisture pick up was determined after 24 and 48 hours.

Moisture pick-up for the 30 gsm paper and Paper A, Paper B and Paper C is shown in Figure 6.

The 80/20 kraft/microfibrillated cellulose 30 gsm handsheet had better (i.e., lower) MVTR than Paper A, Paper B and Paper C. This is very good for a paper having such a relatively low base weight of 30 gsm.