EP3821074B1 - Heat-sealable barrier paper - Google Patents

Description

The present invention relates to a heat-sealable barrier paper comprising or consisting of a) a backing paper, having a front side and a back side opposite the front side, b) a first barrier layer arranged on the front side of the backing paper, consisting of or comprising a binder and a pigment, and c) a second barrier layer arranged on the first barrier layer, consisting of or comprising an acrylate copolymer and a wax. The present invention also relates to the use of a barrier paper according to the invention as packaging and to a method for producing a barrier paper according to the invention. Further aspects of the present invention emerge from the following description and the claims.

Groceries that are offered in bulk, such as sausage, cheese or baked goods, are usually handed over to customers in packaging for reasons of hygiene or to keep them fresh. High demands are placed on the packaging, especially in the case of fatty foods. When conventional paper-based packaging is used, fat from the food can penetrate the packaging material in the case of food containing fat. This can cause the packaging material to soften and tear, or contamination of other items with the grease when you come into contact with the packaging.

A wood-free, greaseproof "sandwich paper" is often used to package fatty foods, which has a certain grease resistance due to the greasy grinding of the fibers. However, the grease resistance of these sandwich papers is often not sufficient.

A greasy grind is achieved with wide, widely spaced knives or basalt stone sizing over a long grind time. The fibers are not cut, but crushed. The result is a strongly swelling fiber slime, a slippery, greasy substance that drains only slowly on the paper machine. The paper gains high density but loses opacity. It becomes glassy translucent. When the fiber is shortened, it is referred to as "greasy-long". More shortened fibers are referred to as "sleazy-short". If the substrate is mainly made from greasy, short fibers, it only has a low tear resistance and resistance to tear propagation.

A composite packaging material is often used as a grease-resistant alternative to greaseproof paper. A composite packaging material can consist, for example, of a composite material formed from paper and a plastic and/or aluminum foil. If there is no polyethylene (PE) coating, fluorocarbons can be used as water repellent chemicals. For example, paper is coated on one side with polyethylene, often in an energy-intensive extrusion process, or with aluminum foil. These composite packaging materials are characterized by high grease resistance. However, if these composite packaging materials are used for paper recycling, these materials disrupt the recycling process considerably. Due to the film layer, the composite packaging materials cannot be fiberized sufficiently well during the recycling process and so-called wet-strength specks form. The specks are the remains of the plastic or aluminum foil to which paper fibers are still attached. The necessary separation of the flakes in the pulp preparation process results in a not inconsiderable loss of pulp, which is withdrawn from the process. These specks have to be laboriously removed during the recycling process. It is also not possible to compost these composites, since the plastic or aluminum foils used do not biodegrade.

In the DE 10 2014 119 572 A1 describes a packaging paper for foodstuffs with a weight per unit area between 20 g/m ² and 40 g/m ² and with a mass fraction of filler which is less than 20% based on the mass of the uncoated paper having. The packaging paper has a coating on at least one side, which comprises a vegetable oil encapsulated in a polymer, talc and a binder.

In the U.S. 2007/000971 A1 describes a sealable paper consisting of a base paper, which may be printed on its front side, and comprising a water vapor barrier layer consisting of a mixture of acrylic polymers and less than 5% by weight wax. On the back of the base paper, the paper may have a sealable layer made from a natural or synthetic latex.

WO 2010/042162 A1 describes a coated paper or board with a multi-layer coating, the multi-layer coating comprising a first water vapor barrier layer, a biopolymer barrier layer and a second water vapor barrier layer.

WO 2019/121733 A1 describes a barrier paper comprising a) a paper substrate and b) a barrier layer arranged on the front side of the paper substrate, the barrier layer comprising or consisting of a polymeric binder and a wax based on a vegetable oil.

WO 00/24967 A1 describes a barrier paper with a polymer-containing barrier layer and a metal layer applied to the barrier layer.

WO 94/26513 A1 describes a recyclable paper stock coated on the surface with a water-based emulsion coating.

Packaging always consists of different components, i.e. the packaging material and the packaging aid. The goods that are packaged are referred to as packaged goods. Packaging aids are materials that increase the strength of the packaging or make it possible in the first place, such as nails, adhesive tape, staples and strapping that ensure the crates and boxes stay together. Packaging aids also include labels such as labels on beverage bottles, banderoles on cans and closures of bottles and jars, means of identification (e.g. warning labels), desiccants, security means (e.g. seals) or cushioning materials (corner pads, air cushions). etc.). Packaging is the designation for the container in which the packaged goods (goods) are packed. For example, the following packaging materials are used A distinction is made between: box, crate, crate, sack, can, barrel, glass, bottle, canister, bag, shrink hood, etc. Packaging materials are materials from which the packaging is made. Such typical packaging materials include, for example, wood, glass, metal, paper and plastic. Cardboard is a term for packaging made of corrugated cardboard.

The object of the present invention is to provide a packaging material that can be fed into paper recycling without the recycling process being adversely affected by the formation of specks or other rejects, such as foils. In addition, the packaging material should be designed in such a way that it is suitable for contact with food and has low water and water vapor permeability and high fat resistance.

An additional object of the present invention is to design the barrier paper so that it is heat-sealable. In addition, it is desirable that it biodegrade, i. H. composted.

1. a) einem Trägerpapier, aufweisend eine Vorderseite und eine der Vorderseite gegenüberliegende Rückseite,
2. b) einer auf der Vorderseite oder Rückseite des Trägerpapiers angeordneten ersten Barriereschicht, bestehend aus oder umfassend ein Bindemittel und ein Pigment, und
3. c) einer auf der ersten Barriereschicht angeordneten zweiten Barriereschicht, bestehend aus oder umfassend ein Acrylat-Copolymer und ein Wachs,

• wobei das Wachs in der zweiten Barriereschicht ein, zwei, drei oder mehr als drei Alkane enthält oder daraus besteht ausgewählt aus der Gruppe bestehend aus Heneicosan, Docosan, Tricosan, Tetracosan, Pentacosan, Hexacosan, Heptacosan, Octacosan, Nonacosan, Triacontan, Hentriacontan, Dotriacontan, Tritriacontan, Tetratriacontan, Pentatriacontan, Hexatriacontan, Heptatriacontan, Octatriacontan und Nonatriacontan,
• wobei das Acrylat-Copolymer in der zweiten Barriereschicht ein Copolymer ist, hergestellt unter Verwendung von zwei, drei, vier, fünf, sechs oder sämtlichen Monomeren ausgewählt aus der Gruppe bestehend aus Acrylsäuremethylester, Methacrylsäuremethylester, Acrylsäurebutylester, Methacrylsäurebutylester, Acrylsäure-2-ethylhexylester, Methacrylsäure-2-ethylhexylester und Styrol
  und
• wobei das Bindemittel in der ersten Barriereschicht ein (Meth)Acrylatpolymer oder (Meth)Acrylat-Copolmyer ist.

These objects are achieved according to the invention by a heat-sealable barrier paper comprising or consisting of

1. a) a backing paper, having a front side and a back side opposite the front side,
2. b) a first barrier layer arranged on the front or back of the backing paper, consisting of or comprising a binder and a pigment, and
3. c) a second barrier layer arranged on the first barrier layer, consisting of or comprising an acrylate copolymer and a wax,

• wherein the wax in the second barrier layer contains or consists of one, two, three or more than three alkanes selected from the group consisting of heneicosane, docosane, tricosane, tetracosane, pentacosane, hexacosane, heptacosane, octacosane, nonacosane, triacontane, hentriacontane, dotriacontane , tritriacontane, tetratriacontane, pentatriacontane, hexatriacontane, heptatriacontane, octatriacontane and nonatriacontane,
• wherein the acrylate copolymer in the second barrier layer is a copolymer prepared using two, three, four, five, six or all of the monomers selected from the group consisting of methyl acrylate, methyl methacrylate, butyl acrylate, butyl methacrylate, 2-ethylhexyl acrylate, methacrylic acid -2-ethylhexyl ester and styrene
  and
• wherein the binder in the first barrier layer is a (meth)acrylate polymer or (meth)acrylate copolymer.

Surprisingly, it has been shown in our own investigations that the combination of a first barrier layer, consisting of or comprising a binder and a pigment, and a second barrier layer, consisting of or comprising an acrylate copolymer and a wax, to extremely low water vapor permeability and to leads to particularly high water and grease resistance. At the same time, the barrier paper is recyclable because no foils are used, in particular no plastic or aluminum foils are used. During defibration in the recycling process, a barrier paper according to the invention forms a pulp without specks or other rejects being formed. The barrier paper according to the invention can thus be completely fed into paper recycling. Thanks to the combination of acrylate copolymer and wax in the second barrier layer, the barrier paper is also heat-sealable.

In barrier papers according to the invention, the use of extruded, bonded foils or metal foils vapor-deposited or bonded on is completely dispensed with, since the individual layers of the barrier paper according to the invention are produced by the application of dispersions. The individual layers of the barrier paper according to the invention are not extruded.

The wax in the second barrier layer is a saturated hydrocarbon wax.

Our own investigations have shown that when waxes from saturated hydrocarbons are used, barrier papers with particularly high grease resistance and water resistance can be obtained. In addition, it has been shown that acrylate copolymers are particularly compatible with waxes from saturated hydrocarbons and therefore a uniform and stable second barrier layer can be formed. Particularly in the case of heat sealing, when the barrier layer is heated to temperatures above 90° C., no undesired demixing or cluster formation takes place with a mixture of acrylate copolymer and wax from saturated hydrocarbons.

Barrier papers are preferred according to the invention, the wax having a melting point above 40.degree. C., preferably above 50.degree. C., particularly preferably above 60.degree.

Our own investigations have shown that very good results can be obtained when using waxes with a melting point of over 30 °C. Surprisingly, however, it could be shown that when waxes with a melting point of more than 40° C. are used, the resistance of the barrier papers to mechanical stress can be increased. This resistance is further increased with even higher melting points of the waxes. Our own investigations have also shown that the optimal melting point of the wax is in the range of 60 to 80 °C if the barrier papers are also to be used at temperatures between 6 °C and 30 °C. If the barrier papers are also to be used at higher temperatures, it may make sense to use a wax with a higher melting point.

According to the invention, preference is given to barrier papers in which the wax has a melting point of less than 100.degree. C., preferably less than 90.degree. C., particularly preferably less than 80.degree.

According to the invention, preference is given to barrier papers in which the wax has a melting point in the range from 40° C. to 100° C., preferably in the range from 50° C. to 90° C., particularly preferably in the range from 60° C. to 80° C.

Barrier papers are preferred according to the invention, the proportion by mass of the wax in the second barrier layer being 5 to 60%, preferably 15 to 50%, particularly preferably 20 to 40%, based on the total mass of the second barrier layer.

In an alternative embodiment, barrier papers are preferred, the proportion by mass of the wax in the second barrier layer being 5 to 60%, preferably 10 to 60%, particularly preferably 15 to 60%, based on the total mass of the second barrier layer.

Our own investigations have surprisingly shown that with a wax mass fraction of less than 5%, the barrier properties against fat, oil and moisture decrease disproportionately, while with a wax mass fraction of more than 60%, excellent barrier properties can be obtained, but the mechanical resistance of the barrier layer decreases disproportionately. Our own investigations have shown that particularly good barrier papers with optimal barrier and mechanical properties can be obtained if the proportion of wax is 20 to 40%. Our own investigations have also shown that the heat-sealability of the barrier paper decreases sharply if the proportion of wax mass is less than 5%.

1. a) mindestens 5 %, 6 %, 7 %, 8 %, 9 %, 10 %, 11 %, 12 %, 13 %, 14 %, 15 %, 16 %, 17 %, 18 %, 19 % oder 20 % beträgt, bezogen auf die Gesamtmasse der zweiten Barriereschicht, wobei die Anteile mit steigenden Werten weiter bevorzugt sind,
   und/oder
2. b) maximal 60 %, 59 %, 58 %, 57 %, 56 %, 55 %, 54 %, 53 %, 52 %, 51 %, 50 %, 49 %, 48 %, 47 %, 46 %, 45 %, 44 %, 43 %, 42 %, 41 % oder 40 %, beträgt, bezogen auf die Gesamtmasse der zweiten Barriereschicht, wobei die Anteile mit sinkenden Werten weiter bevorzugt sind. Sämtliche Kombinationen der oben unter a) aufgeführten Mindestwerte mit den oben unter b) aufgeführten Maximalwerte sind dabei möglich.

Barrier papers are therefore preferred according to the invention, the proportion by mass of the wax

1. a) at least 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19% or 20% is, based on the total mass of the second barrier layer, the proportions with increasing values being more preferred,
   and or
2. b) maximum 60%, 59%, 58%, 57%, 56%, 55%, 54%, 53%, 52%, 51%, 50%, 49%, 48%, 47%, 46%, 45% , 44%, 43%, 42%, 41% or 40%, based on the total mass of the second barrier layer, the proportions with decreasing values being more preferred. All combinations of the minimum values listed under a) above with the maximum values listed under b) above are possible.

According to the invention, preference is given to barrier papers in which the wax based on saturated hydrocarbons contains or consists of one, two, three or more than three alkanes selected from the group consisting of hexacosane, heptacosane, octacosane, nonacosane and triacontane. Barrier papers are particularly preferred according to the invention, wherein the saturated hydrocarbon-based wax is an octacosane-based wax.

According to the invention, the acrylate copolymer in the second barrier layer is particularly preferably a copolymer with an average molar mass in the range from 50,000 to 150,000 g/mol, preferably in the range from 80,000 to 130,000 g/mol, particularly preferably in the range of 90,000 up to 100,000 g/mol. The mean molar mass is determined with the aid of gel permeation chromatography (GPC) with tetrahydrofuran (THF; tetramethylene oxide; 1,4-epoxybutane; oxacyclopentane) as the solvent, polystyrene as the standard and detection using an RI detector (refractive index detector).

Our own investigations have shown that acrylate copolymers with an average molar mass of more than 50,000 g/mol or more than 80,000 g/mol form a particularly stable second barrier layer, especially if they are mixed with wax.

According to the invention, the acrylate copolymer in the second barrier layer is a copolymer produced using two, three, four, five, six or all of the monomers selected from the group consisting of methyl acrylate, methyl methacrylate, butyl acrylate, butyl methacrylate, 2-acrylic acid ethylhexyl ester, 2-ethylhexyl methacrylate and styrene.

The properties of the resulting acrylate copolymer can be optimized by selecting the monomers used to prepare the acrylate copolymer. Our own investigations have surprisingly shown that an acrylate copolymer made from methyl acrylate, methyl methacrylate, butyl acrylate, butyl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate and/or styrene has particularly good barrier properties and is combined with the wax or In particular, it is compatible with the wax based on saturated hydrocarbons. Without wishing to be bound by any theory, it is currently assumed that the compatibility of wax and acrylate copolymer is a result of the optimally matching polarities of both substances. If the differences between the polarities of the binder and wax are too great, compatibility decreases and segregation can even occur. Own investigations have shown that acrylate copolymers and wax, and in particular acrylate copolymers from the monomers described above are prepared with wax based on saturated hydrocarbons have an optimal ratio of the polarities of both substances.

In addition to methyl acrylate, methyl methacrylate, butyl acrylate, butyl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate and styrene, other monomers may have been used to produce the acrylate copolymer or the copolymer was produced from two, three, four, five, six or all monomers selected from the group consisting of methyl acrylate, methyl methacrylate, butyl acrylate, butyl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate and styrene.

According to the invention, the acrylate copolymer is particularly preferably a random copolymer. Acrylate copolymers can, for example, also be produced as block copolymers. However, it has been shown that when block acrylate copolymers are used, phases are formed in which blocks of the same monomer units agglomerate. This phase formation in block copolymers can be disadvantageous according to the invention.

It is preferred according to the invention if the mass fraction of the acrylate copolymer, which is present in the second barrier layer in addition to the wax, is 40 to 95% in the second barrier layer, preferably 50 to 85%, particularly preferably 60 to 80%, based on the total mass of the second barrier layer.

Our own investigations have shown that a content of acrylate copolymer, which is present in the second barrier layer alongside the wax, below a mass fraction of 40% leads to barrier papers in which the mechanical resistance of the second barrier layer decreases disproportionately. With an acrylate copolymer content of more than 95% by mass, the mechanical resistance of the second barrier layer is sufficiently high, but it has been shown that the barrier properties against fat, oil and moisture decrease disproportionately. Our own investigations have shown that particularly good barrier papers with optimal barrier and mechanical properties can be obtained if the content of acrylate copolymer is 20 to 40% by mass.

According to the invention, it is particularly preferred if the mass fraction of the acrylate copolymer in the second barrier layer is 40 to 95% and the mass fraction of Wax in the second barrier layer is 5 to 60% and it is even more preferred if the mass fraction of the acrylate copolymer in the second barrier layer is 50 to 85% and the mass fraction of the wax in the second barrier layer is 15 to 50% and it is even more preferred if the mass fraction of the acrylate copolymer in the second barrier layer is 60 to 80% and the mass fraction of the wax in the second barrier layer is 20 to 40%.

In addition to the acrylate copolymer, other polymers or additives can also be contained in the second barrier layer. It is preferred according to the invention if the second barrier layer consists of acrylate copolymer, wax and a mass fraction of at most 10%, preferably at most 5%, of other substances that are not acrylate copolymer or wax, based on the total mass of the second barrier layer.

A heat-sealable barrier paper according to the invention is preferred, the mass per unit area of the second barrier layer being in the range from 2.5 to 7.4 g/m ² , preferably in the range from 2.8 to 6.5 g/m ² , particularly preferably in the ranges from 2.9 to 5.2 g/m ² .

A heat-sealable barrier paper according to the invention is preferred, wherein the second barrier layer is a dispersion layer.

In the context of the present invention, a dispersion layer is understood as meaning a layer which has been produced from a dispersion, usually an aqueous dispersion. It is therefore preferred according to the invention if the second barrier layer was produced from a dispersion. In a dispersion layer, the individual polymer molecules are not distributed homogeneously, but can be present in separate phases in some cases, with individual phases being able to be present separately from one another. It is spoken of a quasi close order. The presence of phases is a result of the manufacturing process in which the layers are made from a dispersion in which the polymers are already present in disperse phases. After removing the dispersion medium, mostly water, no film is formed.

In the context of the present invention, a film is understood to mean a very thin (<1 mm) sheet of metal or plastic which has constant strength along its entire dimension and contains a long-range order of the molecular structure. at The constant strength of plastic films is a result of the polymer molecules that are homogeneously distributed in the film. The main characteristic of plastic films is their ability to be wrapped on or around objects and to conform to their shape. A heat-sealable barrier paper according to the invention is preferred, the first barrier layer and/or the second barrier layer not being in the form of a film.

The main difference between a foil and a dispersion layer according to the present invention is that a foil is also stable as a stand-alone layer, i.e. without a carrier paper, while a dispersion layer is not stable as a stand-alone layer, i.e. not without a carrier medium.

A heat-sealable barrier paper according to the invention is preferred, wherein the pigment in the first barrier layer is an organic pigment, an inorganic pigment or a mixture of organic pigment and inorganic pigment.

A heat-sealable barrier paper according to the invention is particularly preferred, wherein the pigment in the first barrier layer is an inorganic pigment selected from the list consisting of calcined kaolin, kaolin, kaolinite, magnesium silicate hydrate, silica, bentonite, calcium carbonate, aluminum hydroxide, alumina and boehmite.

A heat-sealable barrier paper according to the invention is particularly preferred, where the pigment in the first barrier layer is in the form of flakes.

Our own investigations, in which non-platelet-shaped pigments were compared with platelet-shaped pigments, have surprisingly shown that the use of platelet-shaped pigments leads to particularly good properties in the first barrier layer or in the corresponding barrier paper. When using flake-form pigments in the first barrier layer, the individual flakes of the pigment are stacked on top of each other in an offset manner, resulting in a very dense layered structure that has a high barrier effect. Pigments that are not in the form of platelets do not form these layered structures. Platelet-shaped (also referred to as flake-shaped or flake-like) is understood to mean particles that have a significantly larger diameter than thickness.

It is particularly preferred according to the invention if the flake-form pigment has a (preferably average) aspect ratio of 5 to 100, preferred from 15 to 100, more preferably from 20 to 80. The aspect ratio (also called "aspect ratio" or "shape factor") is the quotient between the diameter and the thickness of the flake of the inorganic pigment before mixing with the other components. An aspect ratio of 15 means that the diameter of the platelet is 15 times greater than the thickness of the platelet.

A heat-sealable barrier paper according to the invention is preferred, the proportion by mass of the pigment in the first barrier layer being 5 to 60%, preferably 15 to 40%, particularly preferably 20 to 40%, based on the total mass of the first barrier layer.

A heat-sealable barrier paper according to the invention is preferred, wherein the binder in the first barrier layer is an acrylate polymer or acrylate copolymer.

In the heat-sealable barrier paper according to the invention, the binder in the first barrier layer is a (meth)acrylate polymer or (meth)acrylate copolymer.

A heat-sealable barrier paper according to the invention is preferred, wherein the binder in the first barrier layer is not an ethylene-vinyl alcohol copolymer (EVOH) or polyvinyl alcohol (PVOH).

A heat-sealable barrier paper according to the invention is preferred, wherein the binder in the first barrier layer is an anionic acrylate polymer or an anionic acrylate copolymer.

A heat-sealable barrier paper according to the invention is preferred, wherein the binder in the first barrier layer is an anionic (meth)acrylate polymer or an anionic (meth)acrylate copolymer.

In the context of the present invention, a (meth)acrylic polymer is understood to mean a polymer that can be prepared from methacrylic acid, acrylic acid or a mixture of methacrylic acid and acrylic acid as monomers.

In the context of the present invention, a (meth)acrylic copolymer is understood to mean a copolymer composed of methacrylic acid or acrylic acid and at least one another monomer or can be prepared from a mixture of methacrylic acid and acrylic acid and at least one other monomer.

A heat-sealable barrier paper according to the invention is preferred, wherein the binder in the first barrier layer is a copolymer prepared using one, two, three or all of the monomers selected from the group consisting of butyl methacrylate, butyl acrylate, methacrylonitrile, acrylonitrile, α-methylstyrene and styrene.

A heat-sealable barrier paper according to the invention is preferred, wherein the binder in the first barrier layer is a copolymer made using butyl acrylate, acrylonitrile and styrene.

A heat-sealable barrier paper according to the invention is preferred, the mass per unit area of the first barrier layer being in the range from 1.5 to 6.4 g/m ² , preferably in the range from 1.8 to 5.5 g/m ² , particularly preferably in the ranges from 1.9 to 4.2 g/m ² .

In addition to the binder and the pigment, other polymers or additives can also be contained in the second barrier layer. It is preferred according to the invention if the first barrier layer consists of an acrylate polymer or acrylate copolymer, a pigment and a mass fraction of at most 5%, preferably at most 2.5% of other substances (e.g. additives) that are not acrylate polymers or acrylate -Copolymers or pigments, based on the total mass of the second barrier layer.

In the context of the present invention, the term carrier paper is used as a generic term, which also includes carrier cardboard and carrier cardboard. A backing paper is a flat material that essentially consists of fibers, mostly of vegetable origin, and is formed by dewatering a fiber suspension. The basis weight should not be restricted by the term backing paper.

A heat-sealable barrier paper according to the invention is preferred, wherein the carrier paper is a paper, cardboard or paperboard. If the backing paper is cardboard, it can be solid cardboard or corrugated cardboard (e.g. B. single shaft or double shaft) may be formed. It is also possible for the heat-sealable barrier paper according to the invention to be in the form of an outer liner, inner liner or intermediate liner of corrugated board.

A heat-sealable barrier paper according to the invention is particularly preferred, wherein the carrier paper is a paper with a basis weight in the range from 30 to 150 g/m ² , a board with a basis weight above 150 g/m ² and less than 225 g/m ² or a paperboard with a basis weight of more than 225 g/m ² .

A heat-sealable barrier paper according to the invention is very particularly preferred, the carrier paper being a paper with a basis weight in the range from 25 to 80 g/m ² , preferably with a basis weight in the range from 30 to 60 g/m ² , particularly preferably with a basis weight in the range of 35 to 50 g/m ² .

A heat-sealable barrier paper according to the invention is preferred, the base paper containing no organic or inorganic pigments. In one embodiment, the carrier paper is base paper.

A barrier paper according to the invention is preferred, the carrier paper containing a cellulose with a Schopper-Riegler degree in the range from 24 to 54°SR, preferably in the range from 29 to 49°SR, particularly preferably in the range from 34 to 44°SR.

A heat-sealable barrier paper according to the invention is preferred, the carrier paper having a short-fiber pulp with a Schopper-Riegler grade of at least 30°SR and/or a long-fiber pulp with a Schopper-Riegler grade of at least 24°SR.

A barrier paper according to the invention is preferred, the carrier paper comprising or consisting of a cellulose which comprises a short-fiber cellulose and a long-fiber cellulose. A mass ratio between short-fiber pulp and long-fiber pulp in the range from 2:1 to 1:2, preferably in the range from 1.5:1 to 1:1.5, particularly preferably about 1:1 is preferred.

Our own investigations have shown that the combination of a short-fiber pulp and a long-fiber pulp with the Schopper-Riegler grades used according to the invention leads to a particularly dense paper which has a very high barrier effect against fat. This barrier effect can be improved even further if the Schopper-Riegler degree is in the ranges marked as preferred or particularly preferred or has the values marked as preferred or particularly preferred.

Our own investigations have shown that particularly good properties of the resulting barrier paper are obtained if the carrier paper is made from a mixture of a short-fiber cellulose and a long-fiber cellulose and this mixture is leveled again before the carrier substrate is manufactured in order to achieve the desired schopper -Riegler degree in the range from 24 to 54°SR, preferably in the range from 29 to 49°SR, particularly preferably in the range from 34 to 44°SR. The short-fiber and long-fiber cellulose used before grinding can have a Schopper-Riegler degree that is outside the preferred range. The Schopper-Riegler grade of the short-fiber pulp and long-fiber pulp used is preferably smaller before the beating than after the beating.

In one embodiment, the barrier paper according to the invention is a barrier paper, the short-fiber pulp consisting entirely or partially, preferably at least to a mass fraction of more than 50%, based on the total mass of the short-fiber pulp, of fibers from hardwoods, preferably made of birch fibers, beech fibers or eucalyptus fibers and the long-fiber pulp consists entirely or partially, preferably at least more than 50%, based on the total mass of the long-fiber pulp, of fibers from coniferous trees, preferably pine fibers, spruce fibers or fir fibers.

A heat-sealable barrier paper according to the invention is preferred, the carrier paper comprising a proportion by mass of at least 70% short-fiber pulp, preferably between 70 and 75% short-fiber pulp, based on the total mass of short-fiber pulp and long-fiber pulp.

A heat-sealable barrier paper according to the invention is preferred, wherein the carrier paper consists of fresh fibers or has a mass fraction of greater than or equal to 50%, preferably greater than or equal to 80%, particularly preferably greater than 95% fresh fibers, based on the total mass of the fibers in the backing paper.

In the context of the present invention, fresh fibers are understood as meaning a pulp which is obtained directly from the plant starting material (usually wood or grass). Fresh fibers are to be distinguished from recycled fibers that have previously been used at least once in other paper or cardboard products, i.e. that consist of waste paper, waste cardboard and/or waste cardboard.

The backing paper, the first barrier layer and the second barrier layer can also contain the additives customarily used in papermaking, such as sizing agents, pigments (in addition to the pigments already described above), optical brighteners, biocides, dispersing agents, release agents, antifoams, retention aids, Fixing agents, flocculants, deaerators, wetting agents, leveling agents, slime control agents or thickeners. The additives are usually used to adjust the properties of the coating compositions used to produce the respective layer (e.g. defoamers or retention aids) or to adjust the properties of the resulting layer (e.g. optical brighteners).

A barrier paper according to the invention is preferred, with the backing paper having further layers on the back. For example, the back can be coated with a starch layer, preferably modified starch, particularly preferably modified corn starch. The properties of the barrier paper can be improved by a coating on the back. For example, it is thus possible to ensure that the barrier paper can be printed on the back.

A barrier paper according to the invention is preferred, the barrier paper having a migration value of MOSH (mineral oil saturated hydrocarbons) and MOAH (mineral oil aromatic hydrocarbons) of at least less than 2 mg/kg, preferably less than or equal to 0.6 mg/kg, more preferably less than or equal to 0.4 mg/kg. The migration is preferably determined by using modified polyphenylene oxides (MPPO) ( ^Tenax® ) according to DIN EN 14338:2004-03. Here, the modified polyphenylene oxide (MPPO; Tenax ^® ) is regarded as a substitute food test. Here, the second barrier layer of the packaging system according to the invention is covered with modified polyphenylene oxide (MPPO; ^Tenax® ) and at 40° C. for 10 days in a conventional oven stored. After storage, the polyphenylene oxide (MPPO; Tenax ^® ) is extracted with hexane for chromatography. The migration value of MOSH and MOAH in this extract is determined using GC-FID.

A barrier paper is preferred according to the invention, the barrier paper on the second barrier layer having a grease permeability with turpentine oil according to Tappi 454 om-10 of at least 1300 s, preferably at least 1500 s, particularly preferably at least 1800 s.

According to the invention, a barrier paper is preferred, wherein the barrier paper on the second barrier layer has a water resistance of greater than 240 s, preferably greater than 400 s, particularly preferably greater than 600 s, determined based on Tappi 454 om-10.

A barrier paper is preferred according to the invention, the barrier paper having a water vapor permeability according to DIN 53122-1 at a climate of 23° C. and 85% humidity of less than or equal to 300 g/(m ² d), preferably less than or equal to 250 g/(m ² d ), particularly preferably less than or equal to 125 g/(m ² d).

Surprisingly, it has been shown that the barrier paper according to the invention not only has a very high resistance to grease, but also low water vapor permeability. Low water vapor permeability in packaging is desirable for food, since the packaged food does not dry out prematurely and stays fresh for longer.

A barrier paper is preferred according to the invention, the barrier paper having a grease permeability of at least level 5, preferably at least level 3, particularly preferably at least level 1; measured according to method DIN 53116.

Our own investigations have shown that barrier papers according to the invention can have a KIT value of over 12 and thus exhibit excellent bed resistance, which is in the same range as the grease resistance of barrier papers coated with plastic or aluminum foil.

A barrier paper is preferred according to the invention, the barrier paper preferably having a sealing strength of greater than or equal to 3.0 N/15 mm at 500 kPa, 150° C. and 1 s has a sealing strength of greater than or equal to 3.5 N/15mm, particularly preferably greater than or equal to 4.2 N/15mm.

According to the invention, a barrier paper is preferred, the weight per unit area of the barrier paper being in the range from 30 to 800 g/m ² , preferably in the range from 35 to 600 g/m ² , particularly preferably in the range from 40 to 250 g/m ² .

A barrier paper is preferred according to the invention, wherein the barrier paper is a paper with a basis weight in the range of 30 to 150 g/m ² , a board with a basis weight of more than 150 g/m ² and less than 225 g/m ² or a Cardboard with a mass per unit area of more than 225 g/m ² .

A barrier paper is preferred according to the invention, the barrier paper on the second barrier layer having a Bekk smoothness determined according to ISO 5627 in the range from 100 to 1200 s, preferably in the range from 125 to 1000 s, more preferably in the range from 125 to 800 s In this case, Bekk smoothness is not determined on both sides of the barrier paper, but only on the second barrier layer of the barrier paper.

Our own investigations have shown that barrier papers with the Bekk smoothness described above have particularly good properties. With a Bekk smoothness of less than 100 s, the paper often has a structure that is too coarse, so that a decrease in water and/or grease resistance or an increase in water vapor permeability can often be observed. In fact, the low smoothness of the paper shows an increase in the surface area, so that diffusion processes are favored. Our own investigations have also shown that with Bekk smoothnesses of more than 1200 s no significant improvement in the properties can be obtained.

According to the invention, a barrier paper is preferred that has no further layer on the second barrier layer.

1. a) von weniger als 30 km quer zur Faserrichtung aufweist
   und/oder
2. b) von weniger als 20 km längs zur Faserrichtung aufweist.

A barrier paper is preferred according to the invention, the barrier paper having a breaking length according to Hoyer

1. a) less than 30 km across the grain
   and or
2. b) less than 20 km along the grain.

A barrier paper is preferred according to the invention, the barrier paper containing no fluorine-containing compounds, in particular no fluorinated organic compounds.

A heat-sealable barrier paper according to the invention is preferred, the barrier paper not containing a layer consisting exclusively of natural rubber or synthetic rubber (e.g. styrene-butadiene rubber, butadiene rubber, ethylene-propylene copolymer, polyether amides, epoxy rubber, urethane rubber, silicone rubber or polysulfide rubber).

Another aspect of the present invention relates to the use of a barrier paper according to the invention as packaging material, in particular for food, electronic products, agricultural products (e.g. seeds, fertilizers), animal feed, washing powder, pharmaceutical products, building materials (e.g. cement, gypsum, powdered paste) or cosmetics.

According to the invention, the use of a barrier paper according to the invention as an inner bag, inlay or inner lining of a packaging box is particularly preferred. A suitability is also seen in particular for bulk goods, free-flowing, lumpy and/or powdery packaged goods. The goods that are packaged are referred to as packaged goods.

According to the invention, the use of a barrier paper according to the invention as food packaging material, in particular inlay, inner bag, stand-up pouch, tray cover, wrapping paper, backing paper, cake slice, blister packaging, intermediate and/or separating paper, is particularly preferred.

According to the invention, it is particularly preferred to use it for wrapping, placing under, interposing, covering and/or separating dry, moist and/or frozen foodstuffs, such as baked goods, pre-baked rolls, baking ingredients, fruit, vegetables, roasted and/or deep-fried goods, snack goods, sandwiches , bread, burgers, rice, noodles, frozen fries, frozen creamed vegetables, breaded schnitzel, meat products, fish products, ready meals, baking mixes, mashed potatoes, packet soups, instant noodle dishes, sausage products, salad bundles, salad bowls and/or cheese.

A further aspect of the present invention relates to packaging, in particular food packaging, comprising a barrier paper according to the invention.

1. a) Reduzierung der Wasserdampfdurchlässigkeit nach DIN 53122-1 auf einen Wert von kleiner gleich 300 g/(m²d)
   und/oder
2. b) Reduzierung der Fettdurchlässigkeit mit Terpetinöl nach Tappi 454 auf einen Wert von mindestens 1300 s.

Another aspect of the present invention relates to a use of a heat-sealable barrier paper according to the invention in packaging, preferably in food packaging, for

1. a) Reduction of water vapor permeability according to DIN 53122-1 to a value of less than or equal to 300 g/(m ² d)
   and or
2. b) Reduction of the fat permeability with turpetine oil according to Tappi 454 to a value of at least 1300 s.

1. (i) Herstellen oder Bereitstellen eines Trägerpapiers
2. (ii) Herstellen oder Bereitstellen eines ersten Barrierestrichs umfassend ein Bindemittel und ein Pigment
3. (iii) Auftragen des hergestellten oder bereitgestellten ersten Barrierestrichs auf eine Seite des Papiersubstrats und anschließendes Trocknen des Barrierestrichs, sodass eine erste Barriereschicht resultiert
4. (iv) Herstellen oder Bereitstellen eines zweiten Barrierestrichs umfassend ein Acrylat-Copolymer und ein Wachs
   und
5. (v) Auftragen des hergestellten oder bereitgestellten zweiten Barrierestrichs auf die in Schritt iii hergestellte erste Barriereschicht und anschließendes Trocknen des zweiten Barrierestrichs, sodass eine zweite Barriereschicht resultiert.

A further aspect of the present invention relates to a method for producing a barrier paper (10), preferably a barrier paper according to the invention, comprising the following steps

1. (i) Making or providing a backing paper
2. (ii) producing or providing a first barrier coating comprising a binder and a pigment
3. (iii) applying the prepared or provided first barrier coat to one side of the paper substrate and then drying the barrier coat, resulting in a first barrier layer
4. (iv) producing or providing a second barrier coat comprising an acrylate copolymer and a wax
   and
5. (v) Application of the second barrier coating produced or provided to the first barrier coating produced in step iii and subsequent drying of the second barrier coating, so that a second barrier coating results.

A further aspect of the present invention relates to a heat-sealable barrier paper produced by a method according to the invention.

Within the scope of the present invention, several of the aspects described above as preferred are preferably realized simultaneously; the combinations of such aspects and the corresponding features resulting from the appended claims are particularly preferred.

With regard to the coating composition used in a method according to the invention for producing a barrier paper, reference is made here to the statements on the composition of the individual layers. The coating compositions are designed in such a way that the layers present in a barrier paper according to the invention result therefrom. The coating compositions are usually in the form of an aqueous dispersion and contain the constituents or compounds (e.g. monomers or crosslinking agents) present in the individual layers, which react to form the constituents.

In addition, the coating compositions can also contain the additives customarily used in papermaking, such as biocides, dispersants, release agents, defoamers or thickeners, which are added to adjust the properties of the coating composition and which usually remain in the layer produced from the coating composition. In this case, additives customarily used in papermaking can be used in the customary amounts.

To apply the coating composition to the base paper or a layer already present on the base paper (e.g. first barrier layer), the person skilled in the art knows various techniques which are referred to as brushing, for example: blade coating, coating with a film press, cast coating, curtain coating ("curtain coating "), squeegee painting, air knife painting or spray painting. All of these known, aforementioned painting techniques are suitable for applying the coating composition according to the invention to a backing paper, preferably a backing paper which comprises one or more precoats or intermediate coats or which also does not comprise any precoat or intermediate coat. According to the invention, preference is given to curtain coating ("curtain coating") or application by means of a roller blade (roller blade coating).

The invention is further illustrated below by means of an example.

Example:

A backing paper was used which was made from a 1:1 mixture of short-fiber and long-fiber pulp with a beating of 39° SR on a paper machine, a paper web provided with resin sizing in the mass and having a basis weight of 40 g/m ² . The paper substrate produced was calendered at a line load of 80 kN/m and a temperature of 80.degree.

A first barrier coating, which was present as an aqueous dispersion, was applied to the produced base paper using an air brush, and this barrier coating was then dried using IR and air drying, resulting in a first barrier layer with a weight per unit area of 3 g/m ² . The composition of the first barrier coat (excluding water) is given in Table 1.

A second barrier coating, which was present as an aqueous dispersion, was applied to the first barrier layer produced using a volumetric doctor blade, and this barrier coating was then dried using IR and air drying, resulting in a second barrier layer with a basis weight of 4 g/m ² . The composition of the second barrier coat (excluding water) is given in Table 1.

The resulting barrier paper, which could be heat-sealed at 120° C., had a basis weight of 47 g/m ² and its properties were measured. The results are summarized in Table 2. Table 1: component trade name component mass fraction First barrier line (plus water): Polyacrylamide, anionically modified Sterocoll BL binder 0.01 to 0.10 aqueous polymer dispersion based on acrylic acid ester, carboxylic acids Sterocoll FS binder 1.0 to 2.5 anionic copolymer based on n-butyl acrylate, Acronal S505 binder 65 to 75 acrylonitrile and styrene kaolin Capim NP pigment 25 to 35 Second barrier line (plus water): Statistical acrylate copolymer made from methyl acrylate, butyl acrylate, 2-ethylhexyl acrylate and styrene as monomers in equal proportions by mass. acrylate copolymer barrier agent 70% octacosane octacosane wax 30% Characteristic value Unit determination method basis weight 47 ± 2 gsm ² ISO 536 thickness 63±5 µm EN 20534 breaking load longitudinal 55±5 N/15mm EN ISO 1924-2 breaking load across 20±4 N/15mm EN ISO 1924-2 tearing length lengthwise 10±2 km to Hoyer tear length across 3.5±1 km to Hoyer bursting strength 170±20 kPa EN ISO 2758 Fat resistance palm kernel fat top side 1 level DIN 53116 Grease resistance turpentine top + 1800 s Tappy 454 Water resistance top > 600 s Tappy 454 Water absorption Cobb ₃₀₀ topside < 1 gsm ² EN ISO 535 KIT test 12 Tappy 559 seal strength 4:5-5 N/15mm 500 kPa, 150 °C and 1 s water vapor permeability < 100 g/( ^m2* d) DIN 53122-1 (23 °C / 85 % RH) Smoothness according to Bekk: 150 seconds ISO 5627

Claims (11)

1. Heat-sealable barrier paper comprising or consisting of

   a) a carrier paper having a front side and a back side opposite the front side,

   b) a first barrier layer disposed on the front side of the carrier paper and consisting of or comprising a binder and a pigment, and

   c) a second barrier layer disposed on the first barrier layer and consisting of or comprising an acrylate copolymer and a wax,

   wherein the wax in the second barrier layer comprises or consists of one, two, three or more than three alkanes selected from the group consisting of heneicosane, docosane, tricosane, tetracosane, pentacosane, hexacosane, heptacosane, octacosane, nonacosane, triacontane, hentriacontane, dotriacontane, tritriacontane, tetratriacontane, pentatriacontane, hexatriacontane, heptatriacontane, octatriacontane, and nonatriacontane,

   wherein the acrylate copolymer in the second barrier layer is a copolymer prepared using two, three, four, five, six or all the monomers selected from the group consisting of methyl acrylate, methyl methacrylate, butyl acrylate, butyl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, and styrene
   and

   wherein the binder in the first barrier layer is a (meth)acrylate polymer or (meth)acrylate copolymer.
2. Heat-sealable barrier paper according to Claim 1, wherein the mass fraction of the wax in the second barrier layer is 5 to 60%, preferably 15 to 50%, more preferably 20 to 40%, based on the total mass of the second barrier layer.
3. Heat-sealable barrier paper according to any of the preceding claims, wherein the wax in the second barrier layer has a melting point of above 40°C, preferably of above 50°C, more preferably of above 60°C.
4. Heat-sealable barrier paper according to any of the preceding claims, wherein the binder in the first barrier layer is a copolymer prepared using one, two, three or all the monomers selected from the group consisting of butyl methacrylate, butyl acrylate, methacrylonitrile, acrylonitrile, α-methylstyrene, and styrene.
5. Heat-sealable barrier paper according to any of the preceding claims, wherein the pigment in the first barrier layer is an inorganic pigment selected from the list consisting of calcined kaolin, kaolin, kaolinite, hydrated magnesium silicate, silicon oxide, bentonite, calcium carbonate, aluminium hydroxide, aluminium oxide, and boehmite.
6. Heat-sealable barrier paper according to any of the preceding claims, wherein the mass fraction of the pigment in the first barrier layer is 5 to 60%, preferably 15 to 40%, more preferably 20 to 40%, based on the total mass of the first barrier layer.
7. Heat-sealable barrier paper according to any of the preceding claims, wherein the pigment in the first barrier layer is lamellar in form.
8. Heat-sealable barrier paper according to any of the preceding claims, wherein the barrier paper on the second barrier layer has a Bekk smoothness as determined to ISO 5627 in the range from 100 to 1200 s.
9. Use of a barrier paper according to any of Claims 1 to 8 as packaging material.
10. Use according to Claim 9 for

    a) reducing the DIN 53122-1 water vapour transmission rate to a level of less than or equal to 300 g/(m²d)
    and/or

    b) reducing the Tappi 454 fat permeability with turpentine to a level of at least 1300 s.
11. Method for producing a barrier paper, preferably a barrier paper according to any of Claims 1 to 8, comprising the following steps:

    (i) producing or providing a carrier paper

    (ii) producing or providing a first barrier coating comprising a binder and a pigment

    (iii) applying the produced or provided first barrier coating to one side of the paper substrate and then drying the barrier coating to give a first barrier layer

    (iv) producing or providing a second barrier coating comprising an acrylate copolymer and a wax
    and

    (v) applying the produced or provided second barrier coating to the first barrier layer produced in step iii and then drying the second barrier coating to give a second barrier layer.