GB2502241A - Packaging Material having barrier layer comprising inorganic particles in water soluble polymer - Google Patents

Abstract

The packaging material comprises a paper substrate 1, a sealant layer 2 applied to the paper 1 and a barrier layer 3. The barrier layer 3 is preferably an oxygen or water vapour barrier, and it comprises a water soluble polymer containing inorganic particles. The water soluble polymer is polyvinyl alcohol (PVA) and/or the particles are clay. The preferred sealant layer 2 comprises polysaccharide (e.g. starch, carboxy-methyl cellulose (CMC), or chitosan), polyvinyl alcohol (PVOH), polyethylene vinyl alcohol (EVOH), polyester, (e.g. polylactic acid (PLA)), acrylic polymer (e.g. acrylonitrile butadiene styrene copolymer (ABS)), polyolefin or polyamide, and a crosslinking agent.

Description

Packaging Material & Method for Marnifacturing the Same The present invention relates to packaging for food, pharmaceuticals, electronics and the Uke. In particular, the invention relates to improved packaging materia's, which are sustainahie and biodegradab'e and have reduced oxygen and moisture permeability, and methods for manufacturing the same.

Foods, pharmaceuticals, electronics and many other products are susceptible to degradation due to oxidation and/or the presence of moisture, with resulting io short shelf life. Therefore, when packaging such items, it is normal practice to use packaging materials that prevent oxygen and/or moisture entering the package, so as to increase the shelf life of these products.

Generally packaging films, which have been modified accordingly so as to afford i such barrier properties, are used to protect these products. Commonly used films for such applications are oriented polyester or nylon film. Barrier properties are afforded in these films by solution coating or extruding barrier resins such as p&yvinyfldene chloride (PVDC) or p&yviny alcohol (PVOH) onto or with the film, or depositing a coating of materi&s such as aluminium, aluminium oxide and silicone dioxide onto the film, to protect against ingress of oxygen. Modified oriented p&ypropylene (OPP) and ethy' viny' akohol copolymer (EVOH) film coextruded with other protective films are &so used.

All of these films have the desired effect of producing the required barrier properties and thus extending the shelf life of the packaged products in an adequate manner. However, all of these films are petroleum based and are a finite resource.

Aluminium foil, which also may be used for the desired protective purposes, offers an alternative to petroleum-based films. However, like petroleum-based films, aluminium foil is non-biodegradable.

There is increasing demand from the market p'ace to have such packaging materia's made from sustainable, biodegradable and non-oH based raw materials. Consequently, there are films now available which are made from poly(lactic acid) (PLA) and other such natural sustainable-based polymers.

These natural films, however, have other disadvantages, such as moisture sensitivity and ack of barrier performance and they are expensive.

Manufacturing such packaging materials out of paper would clearly fit the green' requirement. However, paper is virtually destroyed by the presence of moisture and it is totally porous to oxygen and the like. It is consequently not a suitable material for protecting any product against the ingress of oxygen or moisture, when used alone. I0

Various attempts have been made in the past to provide a barrier materid using paper, the most notable of which is the application of heavy coatings of chitosan on super calendared and highly beaten pulp papers to achieve a good resistance to oxygen at o% relative humidity (RH). However, such papers have a poor resistance to oxygen at higher RHs (such as those found in fridges and the Uke, where the packaged product may be stored) and they are very expensive to produce.

In general practice, the methodology used to achieve high barrier papers is to laminate the given paper to a high barrier film such as the films described above.

International Publication No. WO 2010/069451, for example, discloses a laminate of a paper-based core layer, outermost and innermost liquid-tight, heat-sealable layers of polyolefin and, applied onto the inner side of the core layer, an oxygen gas barrier layer formed from a polymer binder (such as PVOH, EVOH, PVDC, a polysaccharide or a polyester) dispersed or dissolved in an aqueous or solvent-based medium together with inorganic particles, preferably laminar in shape, dispersed in the same medium. The laminate also comprises a watcr vapour barrier layer positioned between the oxygen gas barrier layer and o the innermost po]y&efin ayer, comprising inorganic fiBer partides distributed within a p&ydlefin-based matrix p&yrner.

However, whilst such laminates can be effective for long-term packaging, they are complex and expensive to manufacture. For example, in the formation of the laminate described in WO 2010/069451, the oxygen gas barrier layer is formed by liquid film coating of a liquid gas barrier composition onto the paper-based core layer, and subsequent drying. The thickness of this layer means that a substantial amount of energy is needed to dry it, which significantly increases the cost of the packaging.

Oriented packaging films are commonly manufactured using a two-step process whereby an extruded film is stretched in a first direction, for example using a so-called MDI machine. After exiting the MDI machine, the film may or may not be chemically treated using an "in-line" coater, for example, to improve the adhesion properties of the film. Then, the film is stretched in a second direction, io perpendicular to the first direction, i.e. in a transverse direction. This may be done in a so-called TDI machine.

Thus, it is known in the art to apply coatings "in-line" on a film production line.

The coating may be applied immediately after the film is extruded and before the films are stretched, or between the two stretching steps, that is, between the MDI machine and the TDI machine.

Because a film produced by the above-discussed method is generally stretched by a factor of between 4 and 60 times, the thickness of the coating in the final product will generally be very thin, normally between 0.05 and 0.3 microns in thickness. Thus, most barrier coatings applied in this conventional way do not exhibit sufficient barrier properties. The use of PVDC, for example, does not improve the barrier properties of the film significantly enough for the coated films to be commercially viable.

There is thus a requirement for a packaging material, which is sustainable, biodegradable and would not strain the earth's food and non-renewable resources, and which offers reduced oxygen and moisture permeability. The packaging material should typically be capable of being hermeticafly seded to o maintain the internal package atmosphere and extend the shelf life of the packaged product. There is also a need to provide packaging material which is cheap and easy to manufacture.

Thus, a novel method of manufacture, making use of readily available and renewable raw materials, that is economical and results in the production of a packaging material that exhibits high oxygen and moisture barrier properties, In a first aspect, the invention provides a packaging material comprising a paper substrate, a sealant layer and a barrier layer, wherein the sealant layer is applied to the paper substrate.

In a second aspect, the invention provides a method of making a packaging material comprising applying a sealant layer to a paper substrate and applying a io barrier layer.

The inventors have found that it is surprisingly possible to provide a paper substrate with ultra-high barrier performance against both oxygen and moisture, using an arrangement of the first aspect and a method of the second aspect.

Previous'y, manufacturers of packaging material have apphed a barrier layer direcfly to a paper substrate, which, as the inventors have found, has caused barrier performance to be both unpredictable and unreliable. As described herein, the inventors have developed a packaging material and an associated method of manufacture which overcome this problem.

The basis of the invention, in the first and second aspects, is to provide a substrate made of paper, and modify it by the addition of a sealant layer. A barrier layer is subsequently added to the sealant layer, resulting in ultra-high barrier performance.

The standard way to define barrier performance is by measuring the oxygen transmission rate (OTR) and moisture vapour transmission rate (MVTR) through the substrate under given conditions.

OTR is the steady state rate at which oxygen gas permeates through a substrate at specified conditions of temperature and relative humidity. It is defined as the amount of oxygen (in cubic centimetres, cc or cm) that would pass through one square metre (i m2) of the substrate with ioo% oxygen at atmospheric pressure on one side of the substrate, and an alternate gas at atmospheric pressure on the other side of the substrate, in 24 hours. Values are hence expressed as cms/m2/24 h in metric (or SI) units.

Standard test conditions are 73 °F (23 °C) and o% RH. However, since many food products have ioo% RH when packed in a container, and the fridges that packaged products are often stored in are generafly at 50% RH, measuring the OTR at a fixed RH in the range of 75-80% RH is more appropriate in the field to which the present invention relates. It is necessary to define the level of RH because there are polymers such as PVOH that have an excellent oxygen barrier performance at o% RH, but very poor barrier performance at 75% RH, for example. As described herein, the OTR measurement is measured at 23 °C and 75% RH.

Moisture transmission, referred to as moisture vapour transmission rate (MVTR), is measured in a similar way and it is the amount of moisture (in grammes, g) that would pass through one square metre (i m2) of the substrate in 24 hours at 38 °C and 90% RH. Values are hence expressed as g/m2/24 h in metric (or SI) units.

Table 1 shows the OTR and MVTR for commonly used barrier substrates, measured at the above-defined conditions.

Table 1

Substrate OTR MVTR (cm3/rn2/24 h) (g/rn2/24 h) Standard printing paper Over 50,000 Totafly porous micron polythene film 5,000 1-5 12 micron polyester film 140 10-20 micron OPP film 800 10-20 12-PVDC coated Polyester 8 1-2 Metalised polyester film 2 1-2 Special metalised OPP jo 1 micron PE-EVOH-PE 10-25 10-30 Aluminium oxide coated PET film 2 1-2 5i02 coated film 1 1 Aluminium foil (pin hole free) In general, substrates that have an OTR of 10 cms/m2/24 h or less are used for packaging oxygen sensitive products such as, for example, meat. For potato crisps and such like where the moisture transmission rate is more critica', metalised OPP is used to achieve an acceptable shelf life. Polyethylene (PE), which has a very good MVTR, has a poor OTR and is therefore not used on its own for oxygen-sensitive products.

Ideally, therefore, any new barrier material should have an OTR and MVTR of no more than 20 cm3 org /m2/24 h, if it is to be used as a barrier substrate for food, pharmaceutical, electronic or other packing operations. As described herein, the inventors have developed a packaging material that demonstrates a superior level of performance in this regard.

is The packaging materia's of the first aspect comprise a paper substrate, typically provided as a layer of paper or paperboard. Any suitable paper may be used, such as super c&endared and highly beaten pulp papers as have previously been used in this field or any conventional paper or paperboard of suitable packaging quality. Examples of suitable papers include MG Brown Kraft, MG Bleached Kraft, claycoated papers generally used for high definition printing, compressed papers such as Printopaque as produced by Billerud, and greaseproof and vegetable parchment papers that are generally available in the market place.

The packaging materials of the first aspect further comprise a sealant layer, which is applied to the paper substrate, i.e. the sealant layer is in direct contact with the paper substrate. The purpose of the sealant layer is primarily to seal any pores in the paper and to create a smooth surface on the upper side, or both sides, of the paper, rendering it suitable for receiving a barrier layer. It also functions as an oxygen barrier material. PreferaHy, therefore, the sea'ant layer provides a continuous and complete covering over the desired surface of the paper substrate.

The seathnt layer can be made of any synthetic or natura' polymer type material, or a combination of one or more polymers and any other product. For example, it can be made of polysaccharide, starch, PVOH, EVOH, PLA, chitosan, carboxy-methyl cellulose, acrylic polymer, acrylic butadiene styrene (ABS), polyolefin, polyester, polyamide or any known polymer or material. Such materials are typically provided in solution form. Alternatively they may be applied as an extrusion coating with ioo% polymer or mixture thereof.

In a preferred embodiment, a natural product such as starch, chitosan or the like is used. This has the advantage of producing a biodegradable, sustainable packaging material. Such materials, when used in the sealant layer of the described packaging material, enhance the barrier performance of the paper substrate at low RH. I0

In another preferred embodiment, the sealant thyer is made of PVOH, EVOH or such like. These materials are synthetic, but also easily degradable. PVOH has been found to better control the ultimate barrier performance. It is produced with different degrees of hydrolysis and at different molecular weights. Any is PVOH grade may be used in the seathnt layer. The critical factor is to app'y a sufficient weight of the seathnt to create a smooth surface for the barrier layer.

It has been found by the inventors that sealant weights of at east 2 g/m2, preferably between 2 and 50 g/m2, more preferably between 2 and 25 g/m2, and most preferably between 2 and 15 g/rn2 are advantageous, dependent on the grade of PVOH used. Super hydrolysed grades have the higher water resistance and, thus, lower sealant weights may be employed for the same. These grades with higher molecular weights are preferred as they are more effective in sealing the paper surface.

It has been found by the inventors that highly hydrolysed grades of PVOH, preferably with higher molecular weights and generally hydrolysed to 98-99% level, achieve a high oxygen barrier when used alone, albeit at low humidity.

The sealant layer can be cross linked to achieve a more durable resin. Cross linking agents are numerous and include such chemicah as silanes, glyoxa, melamine resins and so on.

The skilled person will realise that the foregoing lists of materia's for use in the sealant layer are not exhaustive, but purely illustrative.

The sealant layer, however, typically does not comprise inorganic particles, such as clay minerals, in addition to the polymer type material. As above, its primary purpose is to seal off and smooth the pores in the paper surface before applying a barrier layer (which barrier ayer preferably does inchide such inorganic particles), and its composition reflects this. If inorganic particles are included in the sealant layer they may improve the ultimate barrier performance but, for the purposes of the invention described herein, it is not necessary for such particles to be included in this layer of the packaging material.

io The packaging materia's of the first aspect further comprise a barrier layer. The purpose of the barrier ayer is primarily to prohibit the ingress of moisture and oxygen into the sealant layer. It may therefore be thought of as a moisture and oxygen barrier layer. Use of such a barrier layer enables the use of a moisture-sensitive sealant layer such as, for example, a sealant layer that has a high oxygen barrier function, but only at thw RH (such as PVOH, as hereinbefore described). Preferably, therefore, the barrier layer provides a continuous and complete covering over the seahint ayer. Preferab'y, the barrier thyer is applied to the sealant layer, such that it is in direct contact with the sealant layer.

In a preferred embodiment, the barrier layer comprises, or consists of, inorganic stratified, or platelet-like, particles dispersed in a water-soluble polymer or PVDC solution. The polymer can be any of PVOH, ethylene-vinyl alcohol, a polysaccharide such as hydroxyethylcellulose and the like, or any combination thereof. The preferred resin is PVOH.

The inorganic particles can be platelet-like materials such as natural or synthetic clay (such as kaolinite, vermiculite, halloysite, montmorillonite and such like), mica (synthetic and natural) and such like. All these platelet-like materials should swell in the presence of water and form intimate mixtures with the high o hydrogen bonding p&ymers that they are dispersed in.

Dispersions of phitelet-like materials in a high hydrogen polymer, rather than PVDC sohitions, are preferred in the invention. Such dispersions are weB known in the art and numerous articles can be found describing the same.

One method for producing the preferred hybrid solutions is to first produce a water/alcohol based solution of the polymer and, once dissolved, to add the inorganic partides to the solution.

Once the barrier layer has been applied and dried, the platelet-like materials form a sheet-type formation in the p&ymer, and prevent oxygen and water molecu'es from passing through. This creates a tortuous path through the ayer for these mo'ecules, which have to find spaces between the platelets in order to pass through the layer. This creates a barrier function.

In genera], these pateet-Bke materials need to have a high aspect ratio (meaning the ratio of thickness to the length). Preferably, the aspect ratio for these partic'es should be more than 200:1, such as more than oo:i, more than 5o0:i, more than 600:1 or more than 750:1.

The ratio of particles to p&ymer in the barrier thyer is ideally 20-40:80-60, but it can be anything from io:o to 60:40. The solids content of the solution can be from 1% to 15%.

In another embodiment, the barrier ayer is formed from a plasma deposition of aluminium, aluminium oxide, silicon dioxide or other such inorganic particles onto the sealant layer as described above.

The skilled person will realise that the foregoing lists of materials for use in the barrier layer are not exhaustive, but purely illustrative.

The thickness of the barrier layer is typically between 0.5 and 3 microns, optionally 1-2 microns or 2-3 microns, but preferably 0.5-1 microns. The thickimss can be more than 3 microns, but it becomes uneconomical to dry thicker coats. The barrier coating can be ess than o. microns thick, but barrier performance is thereby reduced.

In afi cases, however, the packaging materials of the first aspect of the invention comprise a sealant layer topped by a barrier layer as described above. -10-

It is possible that the packaging materials may include one or more further layers in addition to the paper substrate, sealant layer and barrier layer as hereinbefore described. For example, to make the combination of the paper substrate, sealant thyer and barrier ayer, which may convenienfly be referred to as barrier paper', functional for heat sealing or cold sealing, other layers will need to be applied. These other layers are not relevant to the invention described herein, other than to provide it with further functionality as a packaging material. Suitable layers, including heat sealable' and cold sealable' layers, will be known in the art. I0

However, the se&ant thyer will be in direct contact with the paper substrate, whichever arrangement is employed. Preferably, the barrier layer will also be in direct contact with the sealant layer; for example, no intermediate bonding layer will be found between the barrier layer and the sealant layer. Thus, any layers in is addition to the foregoing three layers will typically be located on top of the barrier layer or on the opposite side of the paper substrate to the se&ant and barrier layers.

In preferred embodiments, the barrier paper contains only the paper substrate, sealant layer and barrier layer as hereinbefore described, i.e. it consists of only these three layers, arranged as described.

Naturally, packaging materials having a sealant layer provided to both sides of the paper substrate are also envisaged and encompassed. A barrier layer is then suitably provided on top of each sealant layer. In this arrangement, the barrier paper consists of five layers. Other layers may be deposited in addition to these five layers. However, again, the sealant layer will be in direct contact with the paper substrate, whichever arrangement is employed. Preferably, the barrier ayer wifl also be in direct contact with the scalant layer.

Preferably, therefore, the barrier paper comprised in the packaging materials of the first aspect consists of no more than five layers, for examp'e, it preferably consists of three ayers, arranged as described. -11-

In a second aspect, there is provided a method of manufacturing a packaging material, comprising applying a sealant layer to a paper substrate and applying a barrier layer.

The paper substrate, sealant layer and barrier layer may be prepared as hereinbefore described.

There is no restriction in the way the sealant layer is applied to the paper substrate. It can be applied as a solution by direct gravure, offset gravure, io reverse gravure and by spray, curtain or any other form of coating. It can &so be applied by ioo% resin by extrusion coating, whether by direct extrusion or by means of hot melt methods with or without slot die. Preferably, it is applied so as to cover the desired surface of the paper substrate, i.e. it forms a complete and continuous covering.

More than one coat of the seathnt layer maybe applied. If the coating is solution-based, a first coat has to be dried before a second coat is applied. The critical factor is to apply a sufficient weight of the sealant to create a smooth surface for the barrier layer.

Once applied the sealant layer may be dried.

The barrier layer is preferably applied to the sealant layer, such that it is in direct contact with the sealant layer. Preferably, it is applied over the entire surface of the sealant layer, i.e. it forms a complete and continuous covering over the sealant layer.

In one embodiment, the barrier layer is applied as a plasma deposition of aluminium, aluminium oxide, silicon dioxide or other such inorganic particles.

Once appbed the barrier ayer is dried to achieve a ioo% sofids layer.

Mternatively the seathnt ayer can be overcoated using conventiona' equipment to vaporise aluminium, aluminium oxide, silicon dioxide or the like to form a continuous inorganic layer on top of the sealant layer, so achieving a moisture or oxygen barrier as described above.

-12 -The sealant layer and barrier layer may be applied during the production of the packaging materia' itseff.

The sealant layer and barrier layer may be applied in line, or separately, onto the surface of the paper substrate. The sealant layer and barrier layer can be applied to one side of the paper only. Alternatively they can be applied to both sides of the paper. In a preferred embodiment, however, only a sealant ayer and a barrier layer are applied to one or both sides of the paper substrate.

In an embodiment, addition& thyers may be appfied, but the se&ant layer wifi always be applied directly to the paper substrate. Preferably, the barrier layer is applied directly to the sealant layer.

is Preferably the packaging materia' is not formed from a laminate. The packaging materia' is not formed by himinating a paper substrate to a high barrier ifim, as is knos%m in the art.

Whichever arrangement is employed, the resultant packaging material demonstrates excellent OTR and MVTR, even under high humidity. This is because the invention makes use of a sealant layer, formed from PVOH, for example, as herein described, which achieves a high oxygen barrier when used alone, aTheit at low humidity (for example, 0%); barrier performance may diminish at high humidity (above 6o% RH). Such a seabnt layer may not achieve a reliable moisture barrier, however. According'y, a barrier layer is deposited on the sealant layer, which prevents moisture ingress and, therefore, maintains the sealant ayer at low RH. The barrier layer a'so advantageously reduces oxygen permeability. When combined, the barrier layer and the sealant aycr act synergistically, resifiting in an cxccflcnt barrier to both moisture and oxygen.

Furthermore, even under &ongation as may be generated with pulling and roBing tensions that may be appUed during manufacture, the seaThnt and barrier layers are applied to the paper substrate with high adhesion, providing good printability and the ability to laminate on one or both surfaces of the paper.

-13 -The packaging materials of the first aspect, and provided by the methods of the second aspect, are thus different to known packaging materials as hereinbefore discussed, which are prepared by laminating a paper ayer to a high barrier film.

In this regard, the packaging materia's described herein comprise a sealant ayer disposed between a paper substrate and a barrier layer. The sealant layer in this arrangement seals any pores in the paper and acts as an oxygen barrier, whilst the barrier layer prohibits the ingress of moisture and passage of oxygen into the sealant layer; the two layers act surprisingly synergistically to result in ultra-high barrier performance. There is no such synergy in the known laminates.

io Moreover, the barrier layer used in the present invention is preferab'y only 0.5-1 microns thick, whereas the barrier layer in known laminates is over 10 microns thick. The thinner barrier layer used in the present invention requires significantly less drying time, which means less energy is needed during manufacture, making it a more economical process. Manufacture also does not involve the separate production steps that are required in known processes to manufacture the known barrier films in the first place. Thus, the methods of the second aspect offer a novel and simpUfied manufacturing process compared to traditional processes.

The packaging materials of the first aspect, producible by the methods of the second aspect, thus achieve an OTR of no more than 100 cm3/m2/24 h, preferably no more than 50 cm3/m2/24 h, more preferably no more than 20 cmd/m2/24 h and most preferably no more than 10, 5, 1 or even 0.5 cm3/m2/24 h (measured at 23 °C and 75% RH).

The packaging materials of the first aspect, producible by the methods of the second aspect, also achieve an MVTR of no more than 100 g/m/24 h, preferably no more than 50 g/m2/24 h, more preferably no more than 20 cm3/m2/24 h and most preferably no more than 10, 5, 1 or even o. g/m2/24 h (measured at 38 °C and at 90% RH).

Whilst the coatings known in the art have been found by the inventors to be unreliable and unpredictahie in their barrier performance (which is believed to be a result of direct appUcation of the barrier layer onto the paper substrate), providing a sealant ayer between the paper substrate and barrier layers in the present invention has been found to overcome such problems.

-14 -Thus, in a third aspect of the invention, there is provided a packaging material obtained or obtainable by a method according to the second aspect.

According to a fourth aspect of the invention, there is provided a packaging container containing a packaging material according to the first aspect or third aspect.

According to a fifth aspect of the invention, there is provided a use of a io packaging materi& according to the first aspect or third aspect, or a packaging container according to the fourth aspect, to protect a product from degradation due to oxidation and/or the presence of moisture.

For a better understanding of the invention, and to show how embodiments of the same may be carried into effect, reference will now be made, by way of examp'e only, to the accompanying drawings, in which: Figures 1 and 2 each show a schematic cross-sectional view of a packaging material in accordance with an embodiment of the first aspect of the present invention.

Figure 3 shows OTR performance data for a packaging material of the first aspect of the invention, produced according to a method of the second aspect of the invention.

Figure i shows a paper substrate 1 having a sealant layer 2 applied thereto, which sealant layer 2 provides a smooth surface on which a barrier layer 3 is deposited.

In the illustrated embodiment, the paper substrate 1 is provided as a layer of paper, formed from conventional paper of packaging quabty grade.

The sea'ant layer 2 is made of super hydrolysed grade PVOH, appfled as a coating on the paper substrate 1. The coating weight is 2-15 g/m2. The sealant layer 2 forms a continuous and complete covering on a first surface of the paper substrate 1. A smooth surface is created by the sealant layer 2, once dried.

-15 - The barrier layer 3 comprises inorganic platelet-like particles of clay or platelet-like inorganic particles dispersed in the water-soluble polymer, PVOH. The plat&et-Hke materia's swefi in the presence of water and form intimate mixtures with the PVOH. The barrier layer 3 is deposited on the sealant layer 2 as a continuous and complete covering over the sealant layer 2, and allowed to dry.

The sealant layer 2 provides a high oxygen barrier, functioning at low RH. The barrier layer 3 prohibits the ingress of moisture into the sealing layer 2, even at io high RH. It also reduces oxygen permeability. This combination of materia's, applied to the paper substrate 1 as shown, thus enhances the overafi final barrier performance of the packaging material.

Figure 2 shows an alternative arrangement of a packaging material of the first aspect of the invention. In this arrangement, a substrate layer 2, as described for Figure 1, is appfied to both sides of the paper substrate 1. A barrier thyer 3, as described for Figure 1, is apphed to each of the sea'ant layers 1. This combination of materials, applied to the paper substrate 1 as shown, further enhances the overall final barrier performance of the packaging material.

Permutations and combinations of any of the various described embodiments of the invention can be used, whilst retaining the desired basic properties of the packaging materials and/or methods of manufacture described herein.

Example

A packaging material of the first aspect, produced according to a method of the second aspect, was assessed for OTR performance. The test was carried out at 23 °C and 75% RH (average) using standard Mocon equipment and a standard method.

The results are shown in Figure 3. As ilhistrated in the graph, the OTR was found to be 0.387 cms/m2/24 h. -16 -Aspects (A) of the invention are listed below.

Al. A packaging material comprising a paper substrate, a seathnt layer and a barrier layer, wherein the sealant ayer is applied to the paper substrate.

2. The packaging material of Al, wherein the sealant layer seals and/or smoothes any pores in the paper substrate.

3. The packaging material of Al or 2, wherein the sealant layer is made of one or more synthetic or natural pcilymers sdected from the group consisting of p&ysaccharides, starch, PVOH, EVOH, PLA, chitosan, carboxy-methy cellifiose, acrylic polymer, ABS, polyolefin, polyester and polyamide.

4. The packaging material of any one of Al, 2 or 3, wherein the sealant layer further comprises a cross-Bnking agent.

5. The packaging material of any one of Al or 2-4, wherein the sealant layer has a weight of between 2 and 15 g/m2.

6. The packaging material of any one of Al or 2-5, wherein the barrier layer is applied to the sealant layer.

7. The packaging material of any one of Al or 2-6, wherein the barrier layer is a moisture barrier layer.

8. The packaging material of any one of Al or 2-7, wherein the barrier layer comprises inorganic particles dispersed in a water soluble polymer solution.

9. The packaging material of 8, wherein: (a) the inorganic particles are particles of natural or synthetic clay; and/or (b) the water s&uble polymer solution is a P\TOI1 solution.

to. The packaging material of any one of Al or 2-9, wherein the barrier layer is o.-i microns thick.

11. The packaging material of any one of Al or 2-10, wherein the sealant layer and/or the barrier layer provides a barrier to oxygen.

12. The packaging materia' of any one of Al or 2-11, having an oxygen transmission rate (OTR) of no more than 10 cms/m2/24 h. 13. The packaging material of any one of Al or 2-12, having a moisture vapour transmission rate (MVTR) of no more than 10 g/m2/24 h. Jo 14. A packaging material as hereinbefore described, and as shown in the accompanying drawings.

Al5. A method of making a packaging material comprising: (a) applying a sealant layer to a paper substrate; and s (b) applying a barrier layer.

16. The method of Al5, svherein step (b) comprises applying the barrier thyer to the sealant layer.

17. A method of making a packaging material with barrier properties, as hereinbefore described.

i8. A packaging material obtainable by the method of any one of A15, i6 or 17.

19. A packaging container containing the packaging material of any one of Al, 2-14 or iS.

20. Use of the packaging material of any one of Al, 2-14 or iS, or the packaging container of 19, to protect a product from degradation due to oxidation and/or the presence of moisture.

Claims (10)

1. -18 -Claims 1. A packaging material comprising a paper substrate, a sealant layer and a barrier layer, wherein the sealant layer is applied to the paper substrate, the banler layer comprises inorganic particles dispersed in a water soluble polymer solution and (a) the inorganic particles are particles of natural or synthetic clay and/or (b) the water soluble polymer solution is a PVOI-I solution.
2. 2. A packaging material as claimed in claim 1, wherein the sealant layer seals io and/or smoothes any pores in the paper substrate.
3. 3. A packaging material as claimed in claim 1 or 2, wherein the sealant layer is made of one or more synthetic or natural polymers selected from the group consisting of polysaccharides, starch, PVOI-I, EVOH, PLA, chitosan, carboxy-methyl is cellulose, acrylic polymer, ABS, polyolefin, polyester and polyamide.
4. 4. A packaging material as claimed in any one of claims 1-3, wherein the sealant layer further comprises a cross-linking agent.
5. 5. A packaging material as claimed in any one of claims 1-4, wherein the sealant layer has a weight of between 2 and 15 g/m2.
6. 6. A packaging material as claimed in any one of claims 1-5, wherein the barrier layer is applied to the sealant layer.
7. 7. A packaging material as claimed in any one of claims i-6, wherein the barrier layer is a moisture barrier layer.
8. 8. A packaging material as daimed in any onc of claims 1-7, wherein the barrier layer is 0.5-1 microns thick.
9. 9. A packaging material as claimed in any one of claims 1-8, wherein the sealant layer and/or the barrier layer provides a barrier to oxygen.
10. 10. A packaging material as claimed in any one of claims 1-9, having an oxygen transmission rate (OTR) of no more than 10 cms/m2/24 h. -19 -ii. A packaging material as claimed in any one of claims 1-10, having a moisture vapour transmission rate (MVTR) of no more than 10 g/m2/24 h. 12. A method of making a packaging material as claimed in any one of claims 1-11 comprising: (a) applying a sealant layer to a paper substrate; and (b) applying a barrier layer.Jo 13. A method as claimed in daim 12, wherein step (b) comprises applying the barrier thyer to the seathnt layer.14. A packaging container containing a packaging material as claimed in any one of claims 1-11.15. Use of a packaging material as daimed in any one of daims 1-11, or a packaging container as claimed in daim 14, to protect a product from degradation due to oxidation and/or the presence of moisture.