Grease-repelling paper

Abstract

A grease-repelling paper comprising a base paper layer and at least one side of the base paper layer, a cover layer consisting substantially of a natural or synthetic grease-repelling polymer and further ingredients, namely solvents or waxes, the cover layer in addition to cover layer material selected from natural or synthetic grease-repelling polymer, namely a polyacrylate, an acrylic / styrene copolymer or a modified and / or derivatised starch, between 15 and 50 parts by weight, as well as at least one further constituent, namely polyvalent alcohol selected from sugar alcohols namely glycerol, sorbitol, polyethylene glycol and / or a substance selected from natural aluminas, aluminium oxide, kaolin or talc. The invention also relates to a method for producing the grease-repelling paper.

Description

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a grease-repelling paper comprising a base paper layer as well as, on at least one side of the base paper layer, a cover layer consisting substantially of a natural or synthetic, grease-repelling polymer as well as, optionally, further ingredients, such as solvents or waxes, as well as to a method for producing a grease-repelling paper in which a base layer of an at least one-sided coating is surface-coated with a cover layer consisting substantially of a natural or synthetic grease-repelling polymer as well as, optionally, further ingredients such as solvents or waxes.

[0002] Grease-repelling papers or grease-repelling cartons are used for a wide variety of applications, for example in the food sector to package fatty products such as cheese or to place ready-prepared food such as French fries, etc. in packaging that is able to repel the high fat content of this substance rather than directly absorb it, so that neither grease stains occur on the paper used for the packaging nor does a user touching the packaging come into direct contact with the grease. The same applies to grease-repelling cartons, which are surface-treated in the same way as the grease-repelling papers to give them a grease-repelling finish. Such cartons are often used in the packaging of, for example, greased machine parts, but they can also be used in the food sector, for example to provide dimensionally stable packaging for fatty foods or foods prepared in grease.

[0003] In order to make a paper or cardboard surface grease-repelling, a surface coating must be applied to such a paper or cardboard, which grease-repelling coating in the past was often formed from fluorine-containing chemicals or mixtures containing them. An example of grease-repelling papers that have a surface coating with such fluorine-containing chemicals is described in EP 3 301 220 A1, according to which, in addition to an anionic fluorine-containing chemical, a starch component or starch mixture is also contained in the surface coating material. The disadvantage of such fluorine-containing surface coating materials is, on the one hand, that they are no longer authorised for food contact or that there are recommendations for their non-use in the food sector and, on the other hand, the fact that, for environmental reasons, there are always regulations requiring the replacement of fluorine-containing chemicals with other suitable substances. Recently, for example, surface coating materials have been launched on the market that do not contain any fluorine-containing chemicals, such as mixtures of polyacrylates or polymethacrylates and waxes. These substances can be used to produce grease-repelling surface coatings, but due to their high proportion of organic chemicals, they can cause difficulties during application and, in particular, storage in that they generally have to be applied at relatively high temperatures, require long drying times and often remain sticky, so that they are not only difficult to work with but often form either rather stiff and thus brittle surfaces or permanently sticky surfaces in the dried state; they can also foam during application and thus tend to form non-homogeneous coatings and other such problems.

[0004] For example, WO 2016 / 000830 describes a fluorine-free, water-repellent composition which, in addition to polyacrylates, also contains other substances such as blocked isocyanates, polysiloxanes, melamine resins and the like. However, similar compositions are also available on the market with fluorine content and must therefore not be used in the food sector.

[0005] Lastly, it has recently been found that compositions containing derivatised starches or starches modified by temperature treatment and other substances such as waxes are particularly suitable as barrier compositions which can prevent the migration of fats through the cellulosic substrates.

[0006] WO 2019 / 189229 refers to paper barrier materials in which several cover layers are applied to the paper in order to form either a grease barrier and / or a gas barrier. This document shows that a coating containing a small amount of starch is overlaid by a cover layer of polymers.

[0007] WO 2018 / 200790 A1 discloses a grease-repelling paper made from unbleached kraft paper, in which a cover layer is applied to at least one base paper layer. The coating materials for the base paper substantially comprise polymers.

[0008] For example, EP 3 825 368 A1 describes a coating composition containing starch and a synthetic latex polymer for forming a grease barrier layer. However, latex polymers usually suffer from the disadvantage of remaining sticky even after processing, so that the application of such a grease barrier layer can only be sensibly carried out on one side of the paper, wherein even in this case the sticking together of several paper layers, in particular on a reel spool, cannot be avoided due to the direct contact of at least two paper layers.SUMMARY OF THE INVENTION

[0009] The present invention now aims to provide paper with grease-repelling properties, in which the disadvantages of the prior art, in particular sticking together of the paper layers during or after manufacture and during storage, can be avoided, and furthermore to be able to provide an elastic, flexible, in particular durable barrier layer which is absolutely fluorine-free and can therefore be used in the food sector.

[0010] To solve this problem, the present invention is substantially characterised in that the cover layer contains, as a natural or synthetic polymer, a polyacrylate, an acrylic / styrene copolymer or a modified and / or derivatised starch, in that the cover layer contains, in addition to the cover layer material, between 15 and 50 parts by weight of surface starch, in particular between 20 and 30 parts by weight of surface starch as well as, optionally, at least one further constituent, such as a polyvalent alcohol selected from sugar alcohols such as glycerol, sorbitol, polyethylene glycol and / or a substance selected from natural aluminas, aluminium oxide, kaolin or talc. Since the cover layer, in addition to the cover layer material selected from a natural and synthetic grease-repelling polymer as well as, optionally, further ingredients, also contains between 15 and 50 parts by weight, in particular between 20 and 30 parts by weight of surface starch as well as, optionally, a further constituent, such as a polyvalent alcohol, selected from sugar alcohols, such as glycerol, sorbitol and / or polyethylene glycol or a substance selected from a natural alumina, aluminium oxide, kaolin or talc, it is surprisingly possible to eliminate the disadvantages of the prior art, in particular the formation of a sticky surface coating that is difficult to dry and to provide a grease-repelling surface coating that is easy to apply, dries quickly and is not sticky or does not remain sticky, i.e. does not tend to block. Due to this surprising reduction in the tendency of the formed grease-repelling layer to stick or block, such a grease-repelling paper can be applied on conventional coating systems, i.e. either on the paper machine itself or offline, without the compelling need to increase the drying capacity of the paper machine or the coating unit or in particular to extend the drying distance. In this way, a significant energy saving can be achieved by applying a coating material containing, in addition to commercially available and common cover layer materials, between 15 and 50 parts by weight, and in addition between 20 and 30 parts by weight of surface starch. Surprisingly, this type of grease-repelling cover layer has a KIT value according to TAPPI T 559 cm-12 between 3 and 8 on the flat sheet and a KIT value according to TAPPI T 559 cm-12 on edges or folds, wherein the fold is produced with a forward and immediately following backward rolling movement with the metal roller used for testing the cobbs according to ISO 535:2014, between 2 and 6, which is substantially the same as a KIT value according to TAPPI T 559 cm-12 of papers coated only with a conventional and commercially available natural or synthetic grease-repelling polymer.

[0011] Since the cover layer of the grease-repelling paper contains, as natural or synthetic polymer, a polyacrylate, an acrylic / styrene copolymer or a modified and / or derivatised starch, it is possible on the one hand to keep the grease barrier of the coating in the range of a medium grease resistance, i.e. in the range of a KIT value according to TAPPI T 559 between and 3 and 8, and on the other hand, by adding surface starch in an amount of between 15 and 50% by weight, to provide both grease-repelling surface coatings which are inexpensive to produce and to avoid problems associated with the grease-repelling surface coatings according to the prior art based substantially exclusively on natural or synthetic polymers, such as polyacrylates, acrylic / styrene copolymers and possibly waxes, i.e. in particular to avoid a long drying time of the grease-repelling surface coating and thus to be able to ensure a significant energy saving in the formation of the surface coating.

[0012] Surface starch refers to a starch without any special functionality, i.e. without any derivatisation and without any additives. Conventional surface starches are selected from potato starch, maize starch, wheat starch, rice starch, sweet potato starch or manioc starch as well as mixtures of two of these. The surface starch may be a native starch or may also be partially pre-formed. The surface starches have no grease-repelling properties, i.e. they have no barrier effect against fats and / or oils and are used in the paper industry, for example, as a carrier medium for sizing agents. When using surface starch on a paper surface in this way, it is possible to increase the concentration of sizing agents on the paper surface by using the surface starch, thereby making the paper hydrophobic but by no means grease-repelling. The surface starch used is therefore usually a starch that is as inexpensive to produce as possible and as untreated as possible, i.e. not derivatised.

[0013] The term “surface coating” or “grease-repelling surface coating” according to the present invention always means a surface coating or grease-repelling surface coating which is absolutely free of any fluorine content.

[0014] In this context, a natural polymer is understood to mean in particular a modified starch, either a derivatised starch or a starch to which other substances that change its properties have been added. The properties of the starch derivatives relevant for the respective desired application are determined either by the choice of substituents or, on the other hand, by the molecular composition of the starch derivatives. This is achieved in a manner known per se by the fact that molecular degradation of the macromolecules often takes place during starch derivatisation, so that, depending on the desired application, greater or lesser degradation of the macromolecules is sought in order to obtain a starch derivative with specific properties. The commercially available grease-repelling natural polymers used together with surface starch in conjunction with the present invention are often such derivatised starches which have been made grease-repelling by a special treatment or a corresponding additive. Despite the fact that their starting material was also a starch corresponding to the surface starch, they are not comparable with it in terms of their properties, molecular weight, composition or manufacturing costs. Well-known grease-repelling starch products on the market include Perfectafilm B3085 (Perfectafilm is a trademark of Coöperative AVEBE U.A.), which is a modified starch, Stabilys EVO 280 (Stabilys is a trademark of Roquette Freres, Société Anonyme), which is a thermally treated starch, and Amyloseal (Amyloseal is a trade name of Cargill Deutschland GmbH), a copolymer of starch and a vinyl acetate / ethylene copolymer.

[0015] Lastly, a crosslinking compound such as PAE (polyaminoamide-epichlorohydrin resins) can be added to the grease-repelling surface coating to be produced in order to keep the grease-repelling properties of the paper high on the one hand and to further improve its wet strength on the other. Cross-linking compounds react with the surface starch via an esterification reaction by being used in an amount of about 5% by weight of the amount of starch, which not only reduces the weight of the grease-repelling coating to be applied, but above all increases the viscosity of the coating solution, which favours the curling (rolling tendency) of the paper between its production and its actual use and thus favours the winding of the grease-repelling paper produced onto parent rolls or even smaller rolls.

[0016] Synthetic polymers that form a grease-repelling surface on paper or cardboard are understood here to be exclusively fluorine-free chemicals or polymers. Preferably, these are acrylic-based polymers, such as Cartaseal SCR liq M1000, Cartaseal VWF and Cartaseal VWAF (Cartaseal is a trademark of Archroma IP GmbH, Germany), acrylic / styrene copolymer, such as Joncryl HPB 1701 (Joncryl is a trademark of BASF Corporation), CHT Coat 2293 or CHT Coat 250 (CHT is a trademark of CHT Germany GmbH).DETAILED DESCRIPTION OF THE INVENTION

[0017] Since, in accordance with a development of the invention, the grease-repelling paper is characterised in that the base paper used is a paper selected from kraft paper or NSSC paper comprising both softwood and hardwood pulp fibres, wherein in particular between 5 and 80% of the total weight of the pulp fibres, more preferably between 5 and 50% of the total weight of the pulp fibres, are hardwood pulp fibres, even more preferably between 5 and 30% of the total weight of the pulp fibres are hardwood pulp fibres, it is possible to provide a grease-repelling paper which has a particularly tear-resistant and stable base paper, so that packaging produced therefrom can not only be made grease-repelling, but in particular is sufficiently stable and tear-resistant to also be used for heavier objects, for example hinges, machine parts or the like, which need to be greased, without fear of tearing the base paper or the grease-repelling paper. At the same time, such a base paper can be used to produce grease-repelling paper or cardboard suitable for packaging foodstuffs due to the absence of additives that are questionable for use in the food sector.

[0018] If, in accordance with a development of the invention, an unbleached kraft paper is used as the base paper, it is possible to provide a base paper that is free from harmful chemicals, in particular chemicals that are questionable for use in the food sector, and can therefore be used unconditionally in the food sector, just like the grease-repelling surface coating. Preferably, such unbleached base papers have a kappa value according to ISO 302:2015 of between 38 and 60. Furthermore, such unbleached kraft paper as a base paper is preferably made from more than 90% primary pulp fibres in order to be able to reliably prevent any entry of impurities that are not permitted or are disruptive in the food sector.

[0019] Since, in accordance with a development of the invention, the grease-repelling paper is formed in such a way that the cover layer contains up to 15 parts by weight, in particular up to 10 parts by weight of the total weight of the cover layer of glycerol, wherein the parts by weight of glycerol relate to the total weight of the surface coating, it is possible to prevent the grease-resistant surface coating from drying out and thus to avoid the formation of a fragile or brittle coating of which the grease-repelling properties would no longer be guaranteed, for example in the area of creases, cracks or rubbed or chipped areas. In particular, the addition of glycerol makes it possible to provide better processability and better foldability of a grease-repelling paper according to the present invention. The grease barrier properties of the paper are not influenced per se by the addition of glycerol, sugar alcohols or polyethylene glycols, but merely ensure that the coating does not dry out too much and thus become brittle.

[0020] Substantially no change in the KIT values according to TAPPI T 559 compared to grease-repelling surface coatings of papers produced from conventional, commercially purchasable, even fluorine-free surface coating materials based on natural or synthetic grease-repelling polymers can be provided in accordance with the invention, since the cover layer of such a grease-repelling paper is formed from 50 to 80 parts by weight of the natural or synthetic polymer or a modified and / or derivatised starch, 15 to 50 parts by weight of surface starch, in particular 20 to 30 parts by weight and up to 15 parts by weight of glycerol. By adding 15 to 50 parts by weight, in particular 20 to 30 parts by weight of surface starch, it is possible to keep the KIT value substantially unchanged, wherein it has been found that with additions of surface starch in the amount of up to 25 parts by weight, a change in the KIT value, in particular a reduction in the KIT value compared to a grease-repelling surface coating of a paper made of conventional, commercially available, natural or synthetic, fluorine-free polymers is not observable. A slight decrease in the KIT value according to TAPPI T 559 can be observed for surface starches in the surface coating material that exceed 25% by weight. Surprisingly, however, this type of surface coating not only makes it possible to provide a grease-repelling paper with good grease-repelling properties, but in particular to avoid the disadvantages of the prior art, namely to provide a surface coating that does not tend to block and that is not sticky, so that paper can be applied to rolls or reels without sticking. In particular, this makes it possible to provide a paper that can be dried quickly and can therefore be produced either directly on the paper machine or externally without having to extend the drying section compared to a conventional surface coating system.

[0021] Grease-repelling papers according to the invention can be produced here in a very wide grammage range, namely between 25 g / m2 and 250 g / m2, wherein coatings are applied in quantities of 2 to 6 g / m2 and side of the paper, preferably between 3 and 5 g / m2. The coating can be applied to one or both sides, which is in contrast to the coatings according to the prior art, as these can usually only be applied to one side due to their poor drying properties and their tendency to be sticky.

[0022] The Gurley value according to ISO 5636-5:2013 of the base paper can be in a wide range, such as between 9 s and 150 s, preferably around 20 s to 50 s, and the Cobb value 60 s according to ISO 535:2014 of the coating can usually be between 15 and 30 g / m2, preferably 20 to 28 g / m2.

[0023] It is surprising that the physical variables that otherwise have a significant influence on the paper properties, such as Gurley (air permeability) and degree of sizing, smoothness (expressed as Bendtsen roughness), have a much smaller influence on the coating result when the coating according to the invention is used, which is why a significantly greater variety of base papers with different degrees of sizing and air permeability can be used when the coating according to the invention is used.

[0024] A further aim of the invention is to provide a method for producing a grease-repelling paper in which a conventional paper machine or conventional coating device can be used without requiring excessive energy input for drying or an excessive drying time.

[0025] To solve this problem, the method according to the invention is substantially characterised in that the cover layer containing, in addition to the cover layer material selected from a natural or synthetic, grease-repelling polymer, such as a polyacrylate, an acrylic / styrene copolymer or a modified and / or derivatised starch, also between 15 and 50 parts by weight, in particular between 20 and 30 parts by weight of surface starch as well as, optionally, at least one further constituent, such as a polyvalent alcohol or an alumina containing cover layer is applied by means of a coating process selected from a single-sided coating process, such as a doctor blade coating process, curtain coating process, gravure roll coating process, a single- or double-sided coating process, such as a film press coating process or a double-sided coating process, such as a film or glue press coating process, and is then subjected to at least one-stage drying by means of IR, roller or hot air drying at temperatures between 65 and 95° C., in particular 70 to 90° C., at a drying capacity per metre of paper web width of 500 to 650 kW / m, preferably 530 to 620 kW / m, particularly preferably 500 to 600 kW / m.

[0026] Surprisingly, with such a process it is possible to apply the grease-repelling cover layer to the base paper using a conventional coating process selected from single-sided coating processes, doctor blade coating processes, curtain coating processes, gravure roll coating processes or even a double-sided coating process, such as a film or size press coating process, in such a way that the grease-repelling coating formed can be prevented from sticking to a non-coated paper side or another side. By subsequently subjecting the coating material to an at least single-stage drying process by means of infrared roller or hot air drying at temperatures between 65 and 95° C., in particular 70 to 90° C., at a drying capacity per metre of paper web width of 500 to 650 kW / m, preferably 530 to 620 kW / m, particularly preferably 500 to 600 kW / m or, in the case of a paper machine running at a speed of between 500 and 1000 m / min, a drying capacity of 0.5 to 1.3 kW·min / m2, preferably 0.53 to 1.24 kW·min / m2, in particular 0.55 to 1.2 kW·min / m2, it is possible to dry the grease-repelling coating quickly and completely without it remaining sticky, so that this grease-repelling surface coating can surprisingly be provided with a conventional coating process with extremely reduced energy consumption of up to 60% less compared to the formation of grease-repelling coatings according to the prior art. In addition, any drying process can be used without fear of further polymerisation or derivatisation of the surface coating material.

[0027] According to a development, the method according to the invention is carried out in such a way that the grease-repelling surface coating, in addition to a natural or synthetic, grease-repelling polymer, such as a polyacrylate, an acrylic / styrene copolymer or a modified and / or derivatised starch and the surface starch is additionally applied with up to 15 parts by weight, in particular up to 10 parts by weight of the total weight of the cover layer of glycerol, by means of barrier coating and is subjected to drying in a roller dryer. The presence of up to 15 parts by weight, in particular up to 10 parts by weight of the total weight of the cover layer of glycerol makes it possible to provide a grease-repelling barrier layer or surface layer in a drying process, such as in a roller dryer, which surprisingly does not dry out completely, but also does not remain sticky and thus does not tend to form cracks or fissures or to stick the layers together. Despite the addition of glycerol to the surface coating, such papers provided with a grease-repelling surface coating have KIT values according to TAPPI T 559 on the flat sheet in a medium range between 3 and 8, without any reduction compared to grease-repelling coatings that do not contain glycerol. Instead of glycerol, other sugar alcohols or polyethylene glycols can be used, for example. At the same time, in order to improve the surface smoothness of the grease-repelling paper and in particular to improve its gliding properties, other substances such as kaolin, talc, natural alumina or synthetic alumina can be added to the surface coating material in quantities of up to 3 parts by weight of the total weight of the surface coating material. Surprisingly, however, it has been shown that only natural aluminas, synthetic aluminas, aluminium oxide, kaolin or talc, which preferably contain a platelet-like structure, can be used. Substances with a spherical structure, such as calcium carbonate, are not suitable as agents for maintaining the surface smoothness in conjunction with the present invention.

[0028] The invention is explained in greater detail below with reference to practical examples.

[0029] For these examples, three different base papers, as defined below in Table 1, were produced as the base material and used in laboratory coating tests.

[0030] The following base paper qualities S11, S12 and S13 were used for coating tests with a Sumet® laboratory coating machine (Sumet® is a trademark of Frohnweiser Consulting GmbH, Germany).TABLE 1Base papersPaper propertyStandardUnitDirectionS11S12S13Paper compositionKraft1,KraftNSSC2unbleachedbleachedPulp types (HW% by80% SW40% SW80%hardwood; SW softwood)weight20% HW60% HWHW,20%SWGrammageISOg / m239.139.628.7536: 2019Air permeability GurleyISO 5636-s29.286.519.45: 2013Cobb value 60sISOg / m2smooth211925535: 2014sideCobb value 60sISOg / m2rough232129535: 2014sideBendtsen roughnessISO 8791-ml / minsmooth7136522: 2013sideBendtsen roughnessISO 8791-ml / minrough5121643012: 2013sideBekk roughnessISOssmooth2476545075627: 1995sideBekk roughnessISOsrough1441.523.65627: 1995side(1Kraft is a base paper produced using the Kraft process;2NSSC is a base paper produced using the neutral sulphite semi-chemical process)

[0031] After coating, which was carried out as shown in Table 2 below, the KIT values of the various coated papers were determined according to the methods described in TAPPI T 559. The KIT values according to TAPPI T 559 shown in Table 2 were achieved in the coating tests:TABLE 2one-FoldingsidedFoldingkit[1] / Totalkitaway2-sidedapplicationKit valuetowardfromCoating formulationBase paper[2]Supplier[g / m2]flatnesscoatingcoatingWithout coatingS11—0111Cartaseal3 pureS111Archroma4.326-73375T Cartaseal VWF; 25T starch4;S111Archroma4.2963-4410T glycerol;100T Cartaseal VWF; 10TS111Archroma2.274-52-32glycerol;100T Cartaseal VWF; 10TS111Archroma4.3465-65-6glycerol;75T 2020IW001-2 pureS111BASF4.1965575T 2020IW001-2; 25T Starch;S111BASF4.245-64-5410T PEG300100T 2020IW001-2; 10T PEG300S111BASF2.2654-53-4100T 2020IW001-2; 10T PEG300S111BASF4.0764-5475T 2020IW001-2; 25T starch;S111BASF4644-510T glycerol;100T 2020IW001-2; 10T Glycerol;S111BASF2.34654100T 2020IW001-2; 10T glycerol;S111BASF4.5876675T Cartaseal VWF; 25T starchS111Archroma4.157-83-4475T 2020IW001-2; 25T starchS111BASF3.866-72-33-4100T 2020IW001-2S111BASF3.98622-375T Cartaseal VWF; 25T starch;S111Archroma3.07522-310T glycerol65T Cartaseal VWF; 35T starch;S111Archroma3.824-52-3310T glycerol75T Cartaseal VWF; 25T starch;S112Archroma7.998-97-8610T glycerol75T Cartaseal VWF; 25T starch;S111Archroma / 4.0553350T kaolin; 10T glycerolAKWWithout coatingS12—0111Cartaseal VWF pureS122Archroma6.127-84475T Cartaseal VWF; 25T starch;S121Archroma4.0682210T glycerol75T Cartaseal VWF; 25T starch;S122Archroma8.0983-43-410T glycerolWithout coatingS13—0111Cartaseal VWF pureS132Archroma4.06843-475T Cartaseal VWF; 25T starch;S131Archroma2.977-822-310T glycerol75T Cartaseal VWF; 25T starch;S132Archroma5.9298710T glycerol75T Cartaseal VWF; 25T starch;S131Archroma4.078-94510T glycerol75T Cartaseal VWF; 25T starch;S132Archroma8.1410 9810T glycerol(3(Cartaseal is a trademark of Archroma IP GmbH, Germany;4starch in this context means a surface starch)

[0032] From the KIT values according to TAPPI T 559 shown in Table 2, it can be seen that an addition of up to 35 parts by weight of surface starch to a commercially available material forming a grease-repelling coating causes almost no deterioration in the grease-repelling properties of the coated paper, while at the same time, surprisingly, a product could be obtained of which the surface coating is neither sticky nor difficult to dry. Furthermore, the surface coating according to the invention does not significantly increase the drying time for the formed grease-repelling surface coating or even possibly reduces it and thus achieves equally significant energy savings in the formation of the surface coating.

Examples

Embodiment Construction

[0017]Since, in accordance with a development of the invention, the grease-repelling paper is characterised in that the base paper used is a paper selected from kraft paper or NSSC paper comprising both softwood and hardwood pulp fibres, wherein in particular between 5 and 80% of the total weight of the pulp fibres, more preferably between 5 and 50% of the total weight of the pulp fibres, are hardwood pulp fibres, even more preferably between 5 and 30% of the total weight of the pulp fibres are hardwood pulp fibres, it is possible to provide a grease-repelling paper which has a particularly tear-resistant and stable base paper, so that packaging produced therefrom can not only be made grease-repelling, but in particular is sufficiently stable and tear-resistant to also be used for heavier objects, for example hinges, machine parts or the like, which need to be greased, without fear of tearing the base paper or the grease-repelling paper. At the same time, such a base paper can be us...

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a grease-repelling paper comprising a base paper layer as well as, on at least one side of the base paper layer, a cover layer consisting substantially of a natural or synthetic, grease-repelling polymer as well as, optionally, further ingredients, such as solvents or waxes, as well as to a method for producing a grease-repelling paper in which a base layer of an at least one-sided coating is surface-coated with a cover layer consisting substantially of a natural or synthetic grease-repelling polymer as well as, optionally, further ingredients such as solvents or waxes.

[0002] Grease-repelling papers or grease-repelling cartons are used for a wide variety of applications, for example in the food sector to package fatty products such as cheese or to place ready-prepared food such as French fries, etc. in packaging that is able to repel the high fat content of this substance rather than directly absorb it, so that neither grease stains occur on the paper used for the packaging nor does a user touching the packaging come into direct contact with the grease. The same applies to grease-repelling cartons, which are surface-treated in the same way as the grease-repelling papers to give them a grease-repelling finish. Such cartons are often used in the packaging of, for example, greased machine parts, but they can also be used in the food sector, for example to provide dimensionally stable packaging for fatty foods or foods prepared in grease.

[0003] In order to make a paper or cardboard surface grease-repelling, a surface coating must be applied to such a paper or cardboard, which grease-repelling coating in the past was often formed from fluorine-containing chemicals or mixtures containing them. An example of grease-repelling papers that have a surface coating with such fluorine-containing chemicals is described in EP 3 301 220 A1, according to which, in addition to an anionic fluorine-containing chemical, a starch component or starch mixture is also contained in the surface coating material. The disadvantage of such fluorine-containing surface coating materials is, on the one hand, that they are no longer authorised for food contact or that there are recommendations for their non-use in the food sector and, on the other hand, the fact that, for environmental reasons, there are always regulations requiring the replacement of fluorine-containing chemicals with other suitable substances. Recently, for example, surface coating materials have been launched on the market that do not contain any fluorine-containing chemicals, such as mixtures of polyacrylates or polymethacrylates and waxes. These substances can be used to produce grease-repelling surface coatings, but due to their high proportion of organic chemicals, they can cause difficulties during application and, in particular, storage in that they generally have to be applied at relatively high temperatures, require long drying times and often remain sticky, so that they are not only difficult to work with but often form either rather stiff and thus brittle surfaces or permanently sticky surfaces in the dried state; they can also foam during application and thus tend to form non-homogeneous coatings and other such problems.

[0004] For example, WO 2016 / 000830 describes a fluorine-free, water-repellent composition which, in addition to polyacrylates, also contains other substances such as blocked isocyanates, polysiloxanes, melamine resins and the like. However, similar compositions are also available on the market with fluorine content and must therefore not be used in the food sector.

[0005] Lastly, it has recently been found that compositions containing derivatised starches or starches modified by temperature treatment and other substances such as waxes are particularly suitable as barrier compositions which can prevent the migration of fats through the cellulosic substrates.

[0006] WO 2019 / 189229 refers to paper barrier materials in which several cover layers are applied to the paper in order to form either a grease barrier and / or a gas barrier. This document shows that a coating containing a small amount of starch is overlaid by a cover layer of polymers.

[0007] WO 2018 / 200790 A1 discloses a grease-repelling paper made from unbleached kraft paper, in which a cover layer is applied to at least one base paper layer. The coating materials for the base paper substantially comprise polymers.

[0008] For example, EP 3 825 368 A1 describes a coating composition containing starch and a synthetic latex polymer for forming a grease barrier layer. However, latex polymers usually suffer from the disadvantage of remaining sticky even after processing, so that the application of such a grease barrier layer can only be sensibly carried out on one side of the paper, wherein even in this case the sticking together of several paper layers, in particular on a reel spool, cannot be avoided due to the direct contact of at least two paper layers.SUMMARY OF THE INVENTION

[0009] The present invention now aims to provide paper with grease-repelling properties, in which the disadvantages of the prior art, in particular sticking together of the paper layers during or after manufacture and during storage, can be avoided, and furthermore to be able to provide an elastic, flexible, in particular durable barrier layer which is absolutely fluorine-free and can therefore be used in the food sector.

[0010] To solve this problem, the present invention is substantially characterised in that the cover layer contains, as a natural or synthetic polymer, a polyacrylate, an acrylic / styrene copolymer or a modified and / or derivatised starch, in that the cover layer contains, in addition to the cover layer material, between 15 and 50 parts by weight of surface starch, in particular between 20 and 30 parts by weight of surface starch as well as, optionally, at least one further constituent, such as a polyvalent alcohol selected from sugar alcohols such as glycerol, sorbitol, polyethylene glycol and / or a substance selected from natural aluminas, aluminium oxide, kaolin or talc. Since the cover layer, in addition to the cover layer material selected from a natural and synthetic grease-repelling polymer as well as, optionally, further ingredients, also contains between 15 and 50 parts by weight, in particular between 20 and 30 parts by weight of surface starch as well as, optionally, a further constituent, such as a polyvalent alcohol, selected from sugar alcohols, such as glycerol, sorbitol and / or polyethylene glycol or a substance selected from a natural alumina, aluminium oxide, kaolin or talc, it is surprisingly possible to eliminate the disadvantages of the prior art, in particular the formation of a sticky surface coating that is difficult to dry and to provide a grease-repelling surface coating that is easy to apply, dries quickly and is not sticky or does not remain sticky, i.e. does not tend to block. Due to this surprising reduction in the tendency of the formed grease-repelling layer to stick or block, such a grease-repelling paper can be applied on conventional coating systems, i.e. either on the paper machine itself or offline, without the compelling need to increase the drying capacity of the paper machine or the coating unit or in particular to extend the drying distance. In this way, a significant energy saving can be achieved by applying a coating material containing, in addition to commercially available and common cover layer materials, between 15 and 50 parts by weight, and in addition between 20 and 30 parts by weight of surface starch. Surprisingly, this type of grease-repelling cover layer has a KIT value according to TAPPI T 559 cm-12 between 3 and 8 on the flat sheet and a KIT value according to TAPPI T 559 cm-12 on edges or folds, wherein the fold is produced with a forward and immediately following backward rolling movement with the metal roller used for testing the cobbs according to ISO 535:2014, between 2 and 6, which is substantially the same as a KIT value according to TAPPI T 559 cm-12 of papers coated only with a conventional and commercially available natural or synthetic grease-repelling polymer.

[0011] Since the cover layer of the grease-repelling paper contains, as natural or synthetic polymer, a polyacrylate, an acrylic / styrene copolymer or a modified and / or derivatised starch, it is possible on the one hand to keep the grease barrier of the coating in the range of a medium grease resistance, i.e. in the range of a KIT value according to TAPPI T 559 between and 3 and 8, and on the other hand, by adding surface starch in an amount of between 15 and 50% by weight, to provide both grease-repelling surface coatings which are inexpensive to produce and to avoid problems associated with the grease-repelling surface coatings according to the prior art based substantially exclusively on natural or synthetic polymers, such as polyacrylates, acrylic / styrene copolymers and possibly waxes, i.e. in particular to avoid a long drying time of the grease-repelling surface coating and thus to be able to ensure a significant energy saving in the formation of the surface coating.

[0012] Surface starch refers to a starch without any special functionality, i.e. without any derivatisation and without any additives. Conventional surface starches are selected from potato starch, maize starch, wheat starch, rice starch, sweet potato starch or manioc starch as well as mixtures of two of these. The surface starch may be a native starch or may also be partially pre-formed. The surface starches have no grease-repelling properties, i.e. they have no barrier effect against fats and / or oils and are used in the paper industry, for example, as a carrier medium for sizing agents. When using surface starch on a paper surface in this way, it is possible to increase the concentration of sizing agents on the paper surface by using the surface starch, thereby making the paper hydrophobic but by no means grease-repelling. The surface starch used is therefore usually a starch that is as inexpensive to produce as possible and as untreated as possible, i.e. not derivatised.

[0013] The term “surface coating” or “grease-repelling surface coating” according to the present invention always means a surface coating or grease-repelling surface coating which is absolutely free of any fluorine content.

[0014] In this context, a natural polymer is understood to mean in particular a modified starch, either a derivatised starch or a starch to which other substances that change its properties have been added. The properties of the starch derivatives relevant for the respective desired application are determined either by the choice of substituents or, on the other hand, by the molecular composition of the starch derivatives. This is achieved in a manner known per se by the fact that molecular degradation of the macromolecules often takes place during starch derivatisation, so that, depending on the desired application, greater or lesser degradation of the macromolecules is sought in order to obtain a starch derivative with specific properties. The commercially available grease-repelling natural polymers used together with surface starch in conjunction with the present invention are often such derivatised starches which have been made grease-repelling by a special treatment or a corresponding additive. Despite the fact that their starting material was also a starch corresponding to the surface starch, they are not comparable with it in terms of their properties, molecular weight, composition or manufacturing costs. Well-known grease-repelling starch products on the market include Perfectafilm B3085 (Perfectafilm is a trademark of Coöperative AVEBE U.A.), which is a modified starch, Stabilys EVO 280 (Stabilys is a trademark of Roquette Freres, Société Anonyme), which is a thermally treated starch, and Amyloseal (Amyloseal is a trade name of Cargill Deutschland GmbH), a copolymer of starch and a vinyl acetate / ethylene copolymer.

[0015] Lastly, a crosslinking compound such as PAE (polyaminoamide-epichlorohydrin resins) can be added to the grease-repelling surface coating to be produced in order to keep the grease-repelling properties of the paper high on the one hand and to further improve its wet strength on the other. Cross-linking compounds react with the surface starch via an esterification reaction by being used in an amount of about 5% by weight of the amount of starch, which not only reduces the weight of the grease-repelling coating to be applied, but above all increases the viscosity of the coating solution, which favours the curling (rolling tendency) of the paper between its production and its actual use and thus favours the winding of the grease-repelling paper produced onto parent rolls or even smaller rolls.

[0016] Synthetic polymers that form a grease-repelling surface on paper or cardboard are understood here to be exclusively fluorine-free chemicals or polymers. Preferably, these are acrylic-based polymers, such as Cartaseal SCR liq M1000, Cartaseal VWF and Cartaseal VWAF (Cartaseal is a trademark of Archroma IP GmbH, Germany), acrylic / styrene copolymer, such as Joncryl HPB 1701 (Joncryl is a trademark of BASF Corporation), CHT Coat 2293 or CHT Coat 250 (CHT is a trademark of CHT Germany GmbH).DETAILED DESCRIPTION OF THE INVENTION

[0017] Since, in accordance with a development of the invention, the grease-repelling paper is characterised in that the base paper used is a paper selected from kraft paper or NSSC paper comprising both softwood and hardwood pulp fibres, wherein in particular between 5 and 80% of the total weight of the pulp fibres, more preferably between 5 and 50% of the total weight of the pulp fibres, are hardwood pulp fibres, even more preferably between 5 and 30% of the total weight of the pulp fibres are hardwood pulp fibres, it is possible to provide a grease-repelling paper which has a particularly tear-resistant and stable base paper, so that packaging produced therefrom can not only be made grease-repelling, but in particular is sufficiently stable and tear-resistant to also be used for heavier objects, for example hinges, machine parts or the like, which need to be greased, without fear of tearing the base paper or the grease-repelling paper. At the same time, such a base paper can be used to produce grease-repelling paper or cardboard suitable for packaging foodstuffs due to the absence of additives that are questionable for use in the food sector.

[0018] If, in accordance with a development of the invention, an unbleached kraft paper is used as the base paper, it is possible to provide a base paper that is free from harmful chemicals, in particular chemicals that are questionable for use in the food sector, and can therefore be used unconditionally in the food sector, just like the grease-repelling surface coating. Preferably, such unbleached base papers have a kappa value according to ISO 302:2015 of between 38 and 60. Furthermore, such unbleached kraft paper as a base paper is preferably made from more than 90% primary pulp fibres in order to be able to reliably prevent any entry of impurities that are not permitted or are disruptive in the food sector.

[0019] Since, in accordance with a development of the invention, the grease-repelling paper is formed in such a way that the cover layer contains up to 15 parts by weight, in particular up to 10 parts by weight of the total weight of the cover layer of glycerol, wherein the parts by weight of glycerol relate to the total weight of the surface coating, it is possible to prevent the grease-resistant surface coating from drying out and thus to avoid the formation of a fragile or brittle coating of which the grease-repelling properties would no longer be guaranteed, for example in the area of creases, cracks or rubbed or chipped areas. In particular, the addition of glycerol makes it possible to provide better processability and better foldability of a grease-repelling paper according to the present invention. The grease barrier properties of the paper are not influenced per se by the addition of glycerol, sugar alcohols or polyethylene glycols, but merely ensure that the coating does not dry out too much and thus become brittle.

[0020] Substantially no change in the KIT values according to TAPPI T 559 compared to grease-repelling surface coatings of papers produced from conventional, commercially purchasable, even fluorine-free surface coating materials based on natural or synthetic grease-repelling polymers can be provided in accordance with the invention, since the cover layer of such a grease-repelling paper is formed from 50 to 80 parts by weight of the natural or synthetic polymer or a modified and / or derivatised starch, 15 to 50 parts by weight of surface starch, in particular 20 to 30 parts by weight and up to 15 parts by weight of glycerol. By adding 15 to 50 parts by weight, in particular 20 to 30 parts by weight of surface starch, it is possible to keep the KIT value substantially unchanged, wherein it has been found that with additions of surface starch in the amount of up to 25 parts by weight, a change in the KIT value, in particular a reduction in the KIT value compared to a grease-repelling surface coating of a paper made of conventional, commercially available, natural or synthetic, fluorine-free polymers is not observable. A slight decrease in the KIT value according to TAPPI T 559 can be observed for surface starches in the surface coating material that exceed 25% by weight. Surprisingly, however, this type of surface coating not only makes it possible to provide a grease-repelling paper with good grease-repelling properties, but in particular to avoid the disadvantages of the prior art, namely to provide a surface coating that does not tend to block and that is not sticky, so that paper can be applied to rolls or reels without sticking. In particular, this makes it possible to provide a paper that can be dried quickly and can therefore be produced either directly on the paper machine or externally without having to extend the drying section compared to a conventional surface coating system.

[0021] Grease-repelling papers according to the invention can be produced here in a very wide grammage range, namely between 25 g / m2 and 250 g / m2, wherein coatings are applied in quantities of 2 to 6 g / m2 and side of the paper, preferably between 3 and 5 g / m2. The coating can be applied to one or both sides, which is in contrast to the coatings according to the prior art, as these can usually only be applied to one side due to their poor drying properties and their tendency to be sticky.

[0022] The Gurley value according to ISO 5636-5:2013 of the base paper can be in a wide range, such as between 9 s and 150 s, preferably around 20 s to 50 s, and the Cobb value 60 s according to ISO 535:2014 of the coating can usually be between 15 and 30 g / m2, preferably 20 to 28 g / m2.

[0023] It is surprising that the physical variables that otherwise have a significant influence on the paper properties, such as Gurley (air permeability) and degree of sizing, smoothness (expressed as Bendtsen roughness), have a much smaller influence on the coating result when the coating according to the invention is used, which is why a significantly greater variety of base papers with different degrees of sizing and air permeability can be used when the coating according to the invention is used.

[0024] A further aim of the invention is to provide a method for producing a grease-repelling paper in which a conventional paper machine or conventional coating device can be used without requiring excessive energy input for drying or an excessive drying time.

[0025] To solve this problem, the method according to the invention is substantially characterised in that the cover layer containing, in addition to the cover layer material selected from a natural or synthetic, grease-repelling polymer, such as a polyacrylate, an acrylic / styrene copolymer or a modified and / or derivatised starch, also between 15 and 50 parts by weight, in particular between 20 and 30 parts by weight of surface starch as well as, optionally, at least one further constituent, such as a polyvalent alcohol or an alumina containing cover layer is applied by means of a coating process selected from a single-sided coating process, such as a doctor blade coating process, curtain coating process, gravure roll coating process, a single- or double-sided coating process, such as a film press coating process or a double-sided coating process, such as a film or glue press coating process, and is then subjected to at least one-stage drying by means of IR, roller or hot air drying at temperatures between 65 and 95° C., in particular 70 to 90° C., at a drying capacity per metre of paper web width of 500 to 650 kW / m, preferably 530 to 620 kW / m, particularly preferably 500 to 600 kW / m.

[0026] Surprisingly, with such a process it is possible to apply the grease-repelling cover layer to the base paper using a conventional coating process selected from single-sided coating processes, doctor blade coating processes, curtain coating processes, gravure roll coating processes or even a double-sided coating process, such as a film or size press coating process, in such a way that the grease-repelling coating formed can be prevented from sticking to a non-coated paper side or another side. By subsequently subjecting the coating material to an at least single-stage drying process by means of infrared roller or hot air drying at temperatures between 65 and 95° C., in particular 70 to 90° C., at a drying capacity per metre of paper web width of 500 to 650 kW / m, preferably 530 to 620 kW / m, particularly preferably 500 to 600 kW / m or, in the case of a paper machine running at a speed of between 500 and 1000 m / min, a drying capacity of 0.5 to 1.3 kW·min / m2, preferably 0.53 to 1.24 kW·min / m2, in particular 0.55 to 1.2 kW·min / m2, it is possible to dry the grease-repelling coating quickly and completely without it remaining sticky, so that this grease-repelling surface coating can surprisingly be provided with a conventional coating process with extremely reduced energy consumption of up to 60% less compared to the formation of grease-repelling coatings according to the prior art. In addition, any drying process can be used without fear of further polymerisation or derivatisation of the surface coating material.

[0027] According to a development, the method according to the invention is carried out in such a way that the grease-repelling surface coating, in addition to a natural or synthetic, grease-repelling polymer, such as a polyacrylate, an acrylic / styrene copolymer or a modified and / or derivatised starch and the surface starch is additionally applied with up to 15 parts by weight, in particular up to 10 parts by weight of the total weight of the cover layer of glycerol, by means of barrier coating and is subjected to drying in a roller dryer. The presence of up to 15 parts by weight, in particular up to 10 parts by weight of the total weight of the cover layer of glycerol makes it possible to provide a grease-repelling barrier layer or surface layer in a drying process, such as in a roller dryer, which surprisingly does not dry out completely, but also does not remain sticky and thus does not tend to form cracks or fissures or to stick the layers together. Despite the addition of glycerol to the surface coating, such papers provided with a grease-repelling surface coating have KIT values according to TAPPI T 559 on the flat sheet in a medium range between 3 and 8, without any reduction compared to grease-repelling coatings that do not contain glycerol. Instead of glycerol, other sugar alcohols or polyethylene glycols can be used, for example. At the same time, in order to improve the surface smoothness of the grease-repelling paper and in particular to improve its gliding properties, other substances such as kaolin, talc, natural alumina or synthetic alumina can be added to the surface coating material in quantities of up to 3 parts by weight of the total weight of the surface coating material. Surprisingly, however, it has been shown that only natural aluminas, synthetic aluminas, aluminium oxide, kaolin or talc, which preferably contain a platelet-like structure, can be used. Substances with a spherical structure, such as calcium carbonate, are not suitable as agents for maintaining the surface smoothness in conjunction with the present invention.

[0028] The invention is explained in greater detail below with reference to practical examples.

[0029] For these examples, three different base papers, as defined below in Table 1, were produced as the base material and used in laboratory coating tests.

[0030] The following base paper qualities S11, S12 and S13 were used for coating tests with a Sumet® laboratory coating machine (Sumet® is a trademark of Frohnweiser Consulting GmbH, Germany).TABLE 1Base papersPaper propertyStandardUnitDirectionS11S12S13Paper compositionKraft1,KraftNSSC2unbleachedbleachedPulp types (HW% by80% SW40% SW80%hardwood; SW softwood)weight20% HW60% HWHW,20%SWGrammageISOg / m239.139.628.7536: 2019Air permeability GurleyISO 5636-s29.286.519.45: 2013Cobb value 60sISOg / m2smooth211925535: 2014sideCobb value 60sISOg / m2rough232129535: 2014sideBendtsen roughnessISO 8791-ml / minsmooth7136522: 2013sideBendtsen roughnessISO 8791-ml / minrough5121643012: 2013sideBekk roughnessISOssmooth2476545075627: 1995sideBekk roughnessISOsrough1441.523.65627: 1995side(1Kraft is a base paper produced using the Kraft process;2NSSC is a base paper produced using the neutral sulphite semi-chemical process)

[0031] After coating, which was carried out as shown in Table 2 below, the KIT values of the various coated papers were determined according to the methods described in TAPPI T 559. The KIT values according to TAPPI T 559 shown in Table 2 were achieved in the coating tests:TABLE 2one-FoldingsidedFoldingkit[1] / Totalkitaway2-sidedapplicationKit valuetowardfromCoating formulationBase paper[2]Supplier[g / m2]flatnesscoatingcoatingWithout coatingS11—0111Cartaseal3 pureS111Archroma4.326-73375T Cartaseal VWF; 25T starch4;S111Archroma4.2963-4410T glycerol;100T Cartaseal VWF; 10TS111Archroma2.274-52-32glycerol;100T Cartaseal VWF; 10TS111Archroma4.3465-65-6glycerol;75T 2020IW001-2 pureS111BASF4.1965575T 2020IW001-2; 25T Starch;S111BASF4.245-64-5410T PEG300100T 2020IW001-2; 10T PEG300S111BASF2.2654-53-4100T 2020IW001-2; 10T PEG300S111BASF4.0764-5475T 2020IW001-2; 25T starch;S111BASF4644-510T glycerol;100T 2020IW001-2; 10T Glycerol;S111BASF2.34654100T 2020IW001-2; 10T glycerol;S111BASF4.5876675T Cartaseal VWF; 25T starchS111Archroma4.157-83-4475T 2020IW001-2; 25T starchS111BASF3.866-72-33-4100T 2020IW001-2S111BASF3.98622-375T Cartaseal VWF; 25T starch;S111Archroma3.07522-310T glycerol65T Cartaseal VWF; 35T starch;S111Archroma3.824-52-3310T glycerol75T Cartaseal VWF; 25T starch;S112Archroma7.998-97-8610T glycerol75T Cartaseal VWF; 25T starch;S111Archroma / 4.0553350T kaolin; 10T glycerolAKWWithout coatingS12—0111Cartaseal VWF pureS122Archroma6.127-84475T Cartaseal VWF; 25T starch;S121Archroma4.0682210T glycerol75T Cartaseal VWF; 25T starch;S122Archroma8.0983-43-410T glycerolWithout coatingS13—0111Cartaseal VWF pureS132Archroma4.06843-475T Cartaseal VWF; 25T starch;S131Archroma2.977-822-310T glycerol75T Cartaseal VWF; 25T starch;S132Archroma5.9298710T glycerol75T Cartaseal VWF; 25T starch;S131Archroma4.078-94510T glycerol75T Cartaseal VWF; 25T starch;S132Archroma8.1410 9810T glycerol(3(Cartaseal is a trademark of Archroma IP GmbH, Germany;4starch in this context means a surface starch)

[0032] From the KIT values according to TAPPI T 559 shown in Table 2, it can be seen that an addition of up to 35 parts by weight of surface starch to a commercially available material forming a grease-repelling coating causes almost no deterioration in the grease-repelling properties of the coated paper, while at the same time, surprisingly, a product could be obtained of which the surface coating is neither sticky nor difficult to dry. Furthermore, the surface coating according to the invention does not significantly increase the drying time for the formed grease-repelling surface coating or even possibly reduces it and thus achieves equally significant energy savings in the formation of the surface coating.

Examples

Embodiment Construction

[0017]Since, in accordance with a development of the invention, the grease-repelling paper is characterised in that the base paper used is a paper selected from kraft paper or NSSC paper comprising both softwood and hardwood pulp fibres, wherein in particular between 5 and 80% of the total weight of the pulp fibres, more preferably between 5 and 50% of the total weight of the pulp fibres, are hardwood pulp fibres, even more preferably between 5 and 30% of the total weight of the pulp fibres are hardwood pulp fibres, it is possible to provide a grease-repelling paper which has a particularly tear-resistant and stable base paper, so that packaging produced therefrom can not only be made grease-repelling, but in particular is sufficiently stable and tear-resistant to also be used for heavier objects, for example hinges, machine parts or the like, which need to be greased, without fear of tearing the base paper or the grease-repelling paper. At the same time, such a base paper can be us...

Claims

1. A grease-repelling paper comprising a base paper layer as well as, on at least one side of the base paper layer, a cover layer consisting substantially of a natural or synthetic, grease-repelling polymer as well as solvents or waxes, characterised in that the cover layer contains, as natural or synthetic polymer, a polyacrylate, an acrylic / styrene copolymer or a modified and / or derivatised starch, in that the cover layer contains, in addition to the cover layer material, between 15 and 50 parts by weight of surface starch as well as, at least one further constituent, a polyvalent alcohol selected from glycerol, sorbitol, polyethylene glycol and / or a substance selected from natural aluminas, aluminium oxide, kaolin or talc.

2. The grease-repelling paper according to claim 1, wherein the base paper used is a paper selected from kraft paper or NSSC paper comprising both softwood and hardwood pulp fibres, wherein between 5 and 80% of the total weight of the pulp fibres.

3. The grease-repelling paper according to claim 1, wherein an unbleached kraft paper is used as the base paper.

4. The grease-repelling paper according to claim 1, wherein the cover layer contains up to 15 parts by weight of the total weight of the cover layer, of glycerol.

5. The grease-repelling paper according to claim 1, wherein the cover layer is formed from 50 to 80 parts by weight of the natural or synthetic polymer or a modified and / or derivatised starch, 15 to 50 parts by weight of surface starch, and up to 15 parts by weight of glycerol.

6. The grease-repelling paper according to claim 1, wherein it has a KIT value according to TAPPI T 559 of between 3 and 8 on a flat sheet.

7. A method for producing a grease-repelling paper, in which a base layer of an at least one-side coating is surface-coated with a cover layer material consisting substantially of a natural or synthetic grease-repelling polymer as well as solvents or waxes, characterised in that the cover layer containing, in addition to the cover layer material selected from a natural or synthetic grease repellent polymer, namely a polyacrylate, an acrylic / styrene copolymer or a modified and / or derivatised starch, also between 15 and 50 parts by weight of surface starch and at least one further constituent, a polyvalent alcohol or an alumina, is applied by means of a coating process selected from single-sided coating processes, curtain coating processes, gravure roll coating processes, or two-sided film or size press coating processes, and then it is subjected to at least one-stage drying by means of IR, roll or hot air drying at temperatures between 65 and 95° C., at a drying capacity per metre of paper web width of 500 to 650 kWIm, or a drying capacity of 0.5 to 1.3 kW·min / m2, and with a paper machine running at a speed of between 500 and 1000 m / min.

8. The method according to claim 7, wherein the grease-repelling surface coating, in addition to the natural or synthetic grease-repelling polymer, a namely the polyacrylate, the acrylic / styrene copolymer or the modified and / or derivatised starch and the surface starch, is additionally applied with up to 15 parts by weight of the total weight of the cover layer of a glycerol-containing cover layer material by means of barrier coating and is subjected to drying in a roller dryer.