DE102022200463A1 - Coated papers with a semi-crystalline coating color layer as packaging material - Google Patents

Abstract

The application relates to a coated paper, comprising a base paper and at least one semi-crystalline coating color layer applied directly or indirectly to the base paper and having amorphous areas and crystalline areas, the amorphous areas containing one or more natural polymers and/or one or more derivatives of natural polymers; wherein the crystalline regions comprise one or more crystallizable organic compounds; and wherein the permeability of at least one gas through the coated paper is reduced compared to the base paper. The application also relates to the coating color used to manufacture the coated paper, the manufacturing process and packaging for food.

Description

FIELD OF THE INVENTION

The invention relates to a coated paper with a high barrier performance for use as a packaging material for food.

BACKGROUND OF THE INVENTION

Packaging accounts for a large proportion of global plastic waste pollution, which is why the search for alternatives made from biodegradable materials is being driven forward.

The packaging of food is a particular challenge because it requires good barrier properties against oxygen, water vapor and microorganisms. Packaging materials for food often consist of plastics, for example polyethylene terephthalate (PET), polyvinyl chloride (PVC), polyethylene (PE) and polypropylene (PP), since these have good barrier properties, low weight and high mechanical stability.

Paper-based packaging materials have many advantages over plastic materials, such as renewability, recyclability and compostability. However, their application is limited due to the often poor barrier properties and high sensitivity to moisture. In order to improve the barrier properties, the paper-based packaging material can be laminated with aluminum or petroleum-based polymers such as PE, EVOH and PVC derivatives. However, these coatings complicate waste sorting and therefore recycling, and reduce compostability. Therefore, the use of barrier layers based on naturally bio-based polymers or the replacement of the conventional metal or plastic-based layer is very desirable from an ecological point of view.

Examples of natural polymers that have been tested for packaging applications are chitosan, hemicelluloses, microfibrillated cellulose and starch. However, many of the natural polymers are hydrophilic and the films made from these materials are often hygroscopic, resulting in a partial loss of their barrier properties at high humidity.

In forestry and agriculture there is great interest in the further processing of by-products and waste products such as lignin. Although lignin, as a hydrophobic biopolymer, suggests itself for use as a barrier layer on paper, research is still poor. However, a coating color layer based on lignin alone does not have sufficient barrier properties. For this reason, various attempts have been made in the prior art to improve the properties of lignin to such an extent that they remain sufficiently tight even in a humid environment, such as in food packaging.

US 9,902,815 B2 and the scientific paper Hult et al. edited by the same authors. 2013 describe processes for the esterification of lignin with fatty acids, in particular the lignin is esterified with a mixture of tall oil fatty acids. The main components of this mixture are unsaturated fatty acids such as oleic acid, linoleic acid and linolenic acid, which have been reacted with the lignin to various degrees of esterification.

Besides the esterification of lignin and tall oil, Hult et al. also reacted softwood and hardwood lignin with palmitic acid and lauric acid. It could be shown that the lignin esterified with the long-chain palmitic acid had better barrier properties against water vapor than the lignin esterified with lauric acid. The best barrier performance was achieved with a layer of hardwood lignin esterified with palmitic acid.

SUMMARY OF THE INVENTION

The present invention is based, inter alia, on the surprising finding that the barrier effect of a coating color layer based on a natural polymer, for example lignin or lignin stearate, can be significantly increased by inducing semicrystallinity, ie both crystalline and amorphous areas. This is achieved by adding a crystallizable organic compound, for example stearic acid, to the coating color. One made with this coating color layer Coated paper according to the invention has an adequate barrier effect for use in the food industry and is nevertheless biodegradable and recyclable.

• • wobei die amorphen Bereiche ein oder mehrere natürliche Polymere und/oder ein oder mehrere Derivate von natürlichen Polymeren enthalten
• • wobei die kristallinen Bereiche eine oder mehrere kristallisierbare organische Verbindungen umfassen; und
• • wobei die Permeabilität wenigstens eines Gases durch das gestrichene Papier im Vergleich zum Basispapier reduziert ist.

Consequently, the present invention relates to a coated paper, comprising a base paper and at least one semi-crystalline coating color layer applied directly or indirectly to the base paper and having amorphous areas and crystalline areas:

• • wherein the amorphous regions contain one or more natural polymers and/or one or more derivatives of natural polymers
• • wherein the crystalline regions comprise one or more crystallizable organic compounds; and
• • wherein the permeability of at least one gas through the coated paper is reduced compared to the base paper.

• • wobei die kristallisierbare organische Verbindung ausgewählt ist aus Fettsäuren, Hydroxyfettsäuren oder Dicarbonsäuren oder deren Estern, Amiden oder Salzen;
• • wobei das natürliche Polymer ausgewählt ist aus Polysacchariden wie Alginat, Agar-Agar, Cutin, Suberin, Lignin, Cellulose, Chitosan, und Stärke, Kohlenwasserstoffen wie Kautschuk oder Balata, Proteinen wie Kollagen, Keratin, Fibroin, Nukleinsäuren, Lipiden, Polylactid (PLA), Polyhydroxybutyrat (PHB), und Polyhydroxyalkonoat (PHA); und
• • wobei das Lösungsmittel ausgewählt ist aus Wasser, Tetrahydrofuran (THF), Toluol, Ethylacetat, und Alkoholen.

The induced semi-crystallinity according to the invention was achieved, for example, with a coating color containing a fatty acid as a crystallizable organic compound in combination with the derivative of a natural polymer, in particular lignin. Consequently, according to a second aspect, the invention relates to a coating color for coating papers, containing at least one solvent, at least one crystallizable organic compound and at least one natural polymer and/or derivative of a natural polymer,

• • wherein the crystallizable organic compound is selected from fatty acids, hydroxy fatty acids or dicarboxylic acids or their esters, amides or salts;
• • wherein the natural polymer is selected from polysaccharides such as alginate, agar-agar, cutin, suberin, lignin, cellulose, chitosan, and starch, hydrocarbons such as rubber or balata, proteins such as collagen, keratin, fibroin, nucleic acids, lipids, polylactide (PLA ), polyhydroxybutyrate (PHB), and polyhydroxyalconoate (PHA); and
• • wherein the solvent is selected from water, tetrahydrofuran (THF), toluene, ethyl acetate, and alcohols.

1. a) Herstellen einer Streichfarbe nach einem dem zweiten Aspekt durch Schmelzdispergierung, Hochdruckdispergierung, oder Sprühtrocknung und anschließender mechanischer Dispergierung der Komponenten;
2. b) Bereitstellen eines Basispapiers;
3. c) Auftrag der Streichfarbe auf das Basispapier, und
4. d) Aushärtung der Streichfarbe unter Ausbildung der semikristallinen Streichfarbenschicht.

The crystallinity of the coating color layer in the coated paper, which is essential here, depends in particular on the process used to produce the coated paper. Consequently, according to a third aspect, the invention relates to a method for producing a coated paper with a base paper and a semi-crystalline coating color layer, comprising the steps:

1. a) production of a coating color according to the second aspect by melt dispersion, high-pressure dispersion, or spray drying and subsequent mechanical dispersion of the components;
2. b) providing a base paper;
3. c) application of the coating color to the base paper, and
4. d) curing of the coating color with formation of the semi-crystalline coating color layer.

According to a fourth aspect, the invention relates to packaging for foodstuffs comprising the coated paper according to the first aspect.

character list

• 1 Figure 12 shows an elugram of Kraft lignin labeling the number average molar mass Mn and the weight average molar mass Mw.
• 2 Figure 1 shows a ³¹ P NMR spectrum of Kraft lignin. Signal A: internal standard, signal group B: aliphatic and phenolic hydroxy groups, signal C: carboxy group
• 3 shows a ³¹ P-NMR spectrum of the lignin ester. Signal A: internal standard, signal group B: hydroxy groups, signal group C: carboxy groups.
• 4 shows an IR spectrum of lignin stearate (bottom) in comparison with the educt Kraft lignin (top) and stearic acid (middle).
• 5 shows a 1H-NMR spectrum of lignin stearate with the solvent CDCl3.
• 6 shows the results of determining the water vapor permeability of the papers coated with different coating colors (according to the invention) as a function of the proportion of crystallizing wax/fatty acid

DETAILED DESCRIPTION OF THE INVENTION

definitions

In the context of the present invention and in accordance with the general understanding in the field of paper technology, the term "coating color" refers to paints containing or consisting of binders, additives and optionally pigments or matrix pigments that are applied to the paper surface with special coating devices for surface finishing or -modification of a base paper can be applied ("coated"). Papers made in this way are referred to as "coated papers".

In the context of the present invention, a “coated paper” is understood to mean a base paper which comprises one or more layers applied by coating, ie coating color layers. Possible layers of such a coated paper substrate are functional layers and structure-forming layers (such as leveling layers for smoothing the surface).

According to the invention, the term “coating color” is used as a generic term for all spreadable coating compositions, preparations and/or solutions in the paper industry for treating, modifying or finishing a paper surface. “Coating color layer” means the coating color that has been applied to the base paper and has hardened.

"Paper" is a flat material consisting essentially of fibers of plant origin and formed by dewatering a fiber suspension on a wire. The resulting fiber fleece is compacted and dried. In the context of this invention, the two-dimensional materials “cardboard” and “cardboard” produced in the same way are also subsumed under paper. Distinguishes between paper, board and paperboard only on the basis of basis weight, where paperboard has a grammage greater than 600 g/ ^m2 , paperboard has a grammage greater than 150 and less than or equal to 600 g/ ^m2 and paper has a grammage of less than or equal to 150 g/m ² .

The synonymous terms "semicrystalline" and "partially crystalline" generally refer to a solid and in particular a layer which contains both crystalline and amorphous areas (domains). A semi-crystalline layer usually contains a large number of individual amorphous and crystalline areas.

The term "crystallinity" is synonymous with "degree of crystallinity" or "degree of crystallization" and describes that portion of a partially crystalline solid that is crystalline. The most common methods for determining the degree of crystallization in polymers are density measurement, differential scanning calorimetry (DSC), X-ray diffraction (XRD), IR spectroscopy or NMR spectroscopy. The measured value determined depends on the measurement method used. According to the invention, the crystallinity of the coating color is determined by means of XRD measurements.

The term "natural polymer", synonymous with "biogenic biopolymer" is a polymer that is synthesized in the cell of a living being. The natural polymer is therefore also biodegradable. The natural polymer is in particular a natural polymer within the meaning of Directive (EU) 2019/904 of the European Parliament and of the Council of June 5, 2019 on reducing the impact of certain plastic products on the environment (see Article 3 No.1 Exclusion in the definition of plastic).

According to the invention, the term “derivatives of natural polymers” is understood to mean polymers produced by the further processing of biopolymers. These are also referred to as chemically modified polymers. Examples of derivatives of natural polymers are lignin derivatives, e.g., lignin esters, cellulose derivatives and starch derivatives.

According to the invention, a “crystallizable organic compound” is to be understood as meaning those organic compounds which attach themselves to a crystallization nucleus in a regular, substance-specific form and can form a nucleus or crystal.

Coated paper and paint

• • wobei die amorphen Bereiche ein oder mehrere natürliche Polymere und/oder ein oder mehrere Derivate von natürlichen Polymeren enthalten;
• • wobei die kristallinen Bereiche eine oder mehrere kristallisierbare organische Verbindungen umfassen; und
• • wobei die Permeabilität wenigstens eines Gases durch das gestrichene Papier im Vergleich zum Basispapier reduziert ist.

The present invention relates to a coated paper, comprising a base paper and at least one semi-crystalline coating color layer applied directly or indirectly to the base paper and having amorphous areas and crystalline areas:

• • wherein the amorphous regions contain one or more natural polymers and/or one or more derivatives of natural polymers;
• • wherein the crystalline regions comprise one or more crystallizable organic compounds; and
• • wherein the permeability of at least one gas through the coated paper is reduced compared to the base paper.

According to one embodiment of the coated paper, the permeability of at least one gas is lower than the permeability of a coated paper with the same base paper and a coating color layer made of the natural polymer or its derivative and a coating color layer made of the crystallizable organic compound for the same total application quantity.

By means of the coating color layer, the permeability of at least one gas through the coated paper is reduced in comparison to the base paper. This can be oxygen (O ₂ ), nitrogen (N ₂ ), carbon dioxide (CO ₂ ), methane (CH ₄ ), hydrogen (H ₂ ), water vapor or a mixture thereof, for example air. In particular, the water vapor transmission rate (WVTR) is reduced.

The inventors have found that the barrier performance or permeability, in particular the WVTR, is directly dependent on the crystallinity in the system according to the invention. Without wishing to be bound by theory, this effect is based on the embedding of crystallites formed from the crystallizable component in an amorphous matrix of natural polymer. The crystallites are impermeable to gases, especially polar molecules such as water in the vapor phase, due to the high packing density. In order to permeate through the thin, semi-crystalline coating color layer, the gases have to take a further route “around the crystallites”, which directly reduces the permeation coefficient and the semi-crystalline layer thus acts as a water vapor barrier. This theory behind the effect is also supported by the computer-aided model described by Müller-Plathe for diffusion through semi-crystalline and filled polymers (see Müller-Plate habilitation thesis ETH Zurich 1993, page 67 ff.).

Pure layers of natural polymer, e.g. lignin, show a significantly higher permeability, as do pure layers of crystallizable organic compound stearic acid layers, which have open areas due to free volumes between the crystallite structures through which gases can permeate.

The permeability, in particular the WVTR, can thus be adjusted for each system according to the invention by selecting the crystallinity. Below 10% crystallinity, a semi-crystalline system typically has little measurable impact on the WVTR of the coated paper compared to a comparable non-crystalline layer. According to one embodiment, the crystallinity of the semi-crystalline coating color layer is in the range from 10% to 90%. A crystallinity above 90% does not generally lead to any change in the barrier effect, but to various structural disadvantages, such as disrupting the integrity of the film. For example, the crystallinity can be 10%, 12%, 14%, 16%, 18%, 20%, 22%, 24%, 26%, 28%, 30%, 32%, 34%, 36%, 38%, 40 %, 42%, 44%, 46%, 48%, 50%, 52%, 54%, 56%, 58%, 60%, 62%, 64%, 66%, 68%, 70%, 72%, Apply for 74%, 76%, 78%, 80%, 82%, 84%, 86%, 88%, or 90%. In a preferred embodiment, the crystallinity ranges from 10% to 40%. A slight reduction in gas permeability can still be achieved above 40%. In a particularly preferred embodiment, the crystallinity ranges from 15% to 25%.

The coating color that is used to form the semi-crystalline coating color layer preferably contains no crystalline elements, and the crystallizable organic compound is also preferably not present in the coating color in crystalline form. It is therefore not a coating color comprising crystalline fillers in amorphous binders. The crystallinity preferably only occurs with the application of the coating color layer. According to one embodiment, the crystalline areas form during the application of the coating color to the base paper. In a further embodiment, the crystalline areas form during the hardening of the coating color. According to one embodiment, the crystalline areas form both during the application of the coating color to the base paper and during the curing of the coating color.

A coated paper with a high barrier performance, in particular a very low WVTR, can be achieved with the coating color according to the invention. According to one embodiment, the WVTR is not more than 40 gm ^{-2 d -1} at a basis weight of the coating color of 10 ± 1 gm ^-2 .

This WVTR is significantly lower than comparable prior art systems. Although Hult et al. 2013 also described a WVTR of 40 g m ^-2 d ^-1 for a layer with lignin palmitic acid ester. However, this was measured under standard conditions, i.e. at 23 °C and 50 % humidity. According to the invention, on the other hand, the WVTR is measured at 38° C. and over 90% atmospheric humidity. A non-crystalline layer of lignin palmitic acid ester would have a WVTR of over 200 g·m ^-2 ·d ^-1 under the chosen tropical conditions of 38 °C and over 90 % humidity.

The WVTR of the coated paper according to the invention can be, for example, 40 g m ^-2 d ^-1 , 38 g m ^-2 d ^-1 , 36 g m ^-2 d ^-1 , 34 g m ^-2 d ^{- 1} , 32 gsm ^-2 d ^-1 , 30 gsm ^-2 d ^-1 , 28 gsm ^-2 d ^-1 , 26 gsm ^-2 d ^-1 , 24 gsm ^-2 · d ^-1 , 22 g · m ^-2 · d ^-1 , 20 g · m ^-2 · d ^-1 , 18 g · m ^-2 · d ^-1 , 16 g · m ^-2 · d ^-1 , 14 g m ^-2 d ^-1 , 12 g m ^-2 d ^-1 , 10 g m ^-2 d ^-1 , 8 g m ^-2 d ^-1 , 6 g m ^{- 2.d -1} , 4 g.m ^-2 .d ^-1 , 2 g.m ^-2 .d ^-1 , 1 g.m ^-2 .d ^-1 . By choosing suitable components of the coating color and adjusting the crystallinity, a WVTR of no more than 20 gm ^-2 .d ^-1 , or even no more than 10 gm ^-2 .d ^{-1 ,} can be achieved.

According to one embodiment, the proportion of the crystallizable organic compounds, based on the total mass of the coating color layer, is in the range from 1 to 60% by weight. Below 1% by weight, no measurable crystallinity can be generated, but the entire coating color layer remains amorphous. If more than 60% crystallizable organic compound is used, the film becomes too inhomogeneous and holes can form, which limit the barrier performance. For example, the crystalline organic compound can have a proportion of 1% by weight, 2% by weight, 4% by weight, 5% by weight, 6% by weight, 8% by weight, 10% by weight , 12 wt%, 14 wt%, 16 wt%, 18 wt%, 20 wt%, 22 wt%, 24 wt%, 26 wt%, 28 wt%, 30 wt%, 32 wt%, 34 wt%, 36 wt%, 38 wt%, 40 wt%, 42 wt%, 44 wt% %, 46%, 48%, 50%, 52%, 54%, 56%, 58%, or 60% by weight % in the coating color layer. The inventors were able to show experimentally that barrier performance does not increase consistently with increasing crystallinity. Rather, for example for the crystallizable organic compound stearic acid, a minimum of the WVTR is obtained with a proportion of around 30% by weight, based on the total mass of the coating color layer. Generally, no increase in barrier performance is to be expected above 50% by weight. Below 3% by weight, only a low level of crystallinity can be achieved, which hardly affects the barrier performance. According to one embodiment, the proportion of the crystalline organic compound is in the range from 3 to 50% by weight. According to one embodiment, the proportion of the crystalline organic compound is in the range from 5 to 40% by weight. According to one embodiment, the proportion of the crystalline organic compound is in the range from 25 to 35% by weight.

The crystallizable organic compounds are preferably at least partially chain hydrocarbons, which are preferably branched. The addition of similar chains of such chain-like hydrocarbons allows crystal or crystallite formation.

Examples of crystallizable organic compounds that can be used according to the invention are fatty acids, fatty acid amides, fatty acid esters, salts of fatty acids, hydroxy fatty acids, hydroxy fatty acid amides, hydroxy fatty acid esters, salts of hydroxy fatty acids, or dicarboxylic acids and their dicarboxylic esters, dicarboxylic acid amides or salts of dicarboxylic acids. Examples of dicarboxylic acids which can be used according to the invention are tetradecanedioic acid, hexadecanedioic acid, octadecanedioic acid, icosanedioic acid or docosanedioic acid.

The fatty acid used as the crystallizable organic compound can be a saturated or unsaturated fatty acid having 12 to 40 carbon atoms. Examples of saturated fatty acids are lauric acid, myristic acid, palmitic acid, margaric acid, stearic acid, arachidic acid, behenic acid, lignoceric acid, cerotic acid, montanic acid, melissic acid, lacceric acid, geddic acid. Examples of unsaturated fatty acids are myristoleic acid, palmitoleic acid, margaroleic acid, petroselinic acid, oleic acid (OA), elaidic acid, vaccenic acid, gadoleic acid, gondoic acid, cetolic acid, erucic acid, and nervonic acid. Examples of unsaturated fatty acids are linoleic acid (LA), α-linolenic acid (ALA), γ-linolenic acid (GLA), calendulic acid, punicic acid, alpha-eleostearic acid, beta-eleostearic acid, stearidonic acid, arachidonic acid, eicosapentaenoic acid (timnodonic acid, EPA), docosadienoic acid, docosatetraenoic acid (adrenic acid, ADA), docosapentaenoic acid, (clupa(no)donic acid), (DPA-3) docosahexaenoic acid (cervonic acid, clupanodonic acid, DHA) and tetracosahexaenoic acid (nisic acid).

According to one embodiment, the fatty acid used as the organic compound to crystallize has 16 to 18 carbon atoms and 0 or 1 double bond. According to one embodiment, the fatty acid is selected from margaric acid, stearic acid, palmitic acid, linoleic acid, α-linolenic acid, γ-linoleic acid. According to one embodiment, the crystallizing component is stearic acid or its amide or salt.

Fatty acid salts according to the invention are chromium(III) chloride complexes with fatty acids, as well as aluminium, calcium, sodium, potassium and ammonium salts. Preferred fatty acid salts are monovalent salts of sodium, potassium or ammonium ions.

The at least one crystallizable organic compound can be present in the coating color as a fatty acid mixture or wax. According to the invention, suitable waxes include carnauba wax, candelilia wax, beeswax and Japan wax.

According to one embodiment, the fatty acid mixture is a mixture of stearic acid, palmitic acid, oleic acid, linoleic acid and/or linolenic acid. Further examples of fatty acid mixtures are a mixture of stearic acid, palmitic acid and oleic acid, a mixture of stearic acid, linoleic acid and linolenic acid, a mixture of stearic acid, palmitic acid and linoleic acid, a mixture of stearic acid, palmitic acid and linolenic acid, a mixture of stearic acid, oleic acid and linoleic acid, a mixture of stearic acid, oleic acid and linolenic acid, a mixture of stearic acid, linoleic acid and linolenic acid,

According to the invention, the proportion of the natural polymers or their derivatives, based on the total mass of the coating color layer, can be in the range from 40 to 99% by weight. Only one polymer or its derivative can be used, but also mixtures of natural polymers, mixtures of derivatives of natural polymers or mixtures of natural derivatives and derivatives of natural polymers. Without wishing to be bound by theory, the natural polymers or their derivatives form the amorphous areas on the one hand and are involved in the formation of the crystalline areas on the other. It is assumed that the natural polymers form the amorphous matrix in which the crystalline areas are embedded. The proportion of the natural polymers depends on the proportion of the crystallizable organic compound(s) and the presence of other possible components. For example, the natural polymers or their derivatives can have a proportion of 40% by weight, 42% by weight, 44% by weight, 46% by weight, 48% by weight, 50% by weight, 52% by weight -%, 54 wt%, 56 wt%, 58 wt%, 60 wt%, 62 wt%, 64 wt%, 66 wt%, 68 wt% , 70 wt%, 72 wt%, 74 wt%, 76 wt%, 78 wt%, 80 wt%, 82 wt%, 84 wt%, 86 wt% -%, 88% by weight, 90% by weight, 92% by weight, 94% by weight, 96% by weight, 98% by weight, or 99% by weight. According to one embodiment, the proportion of the natural polymers is in the range from 50 to 95% by weight. According to one embodiment, the proportion of the natural polymers is in the range from 60 to 90% by weight. According to one embodiment, the proportion of the natural polymers is in the range from 65 to 75% by weight.

Natural polymers that can be used according to the invention are, for example, hydrocarbons such as rubber or balata, proteins such as collagen, keratin, fibroin, nucleic acids, polysaccharides such as alginate, agar-agar, cutin, suberin, lignin, cellulose, chitosan, and starch, lipids, polylactide (PLA) , polyhydroxybutyrate (PHB), and polyhydroxyalconoate (PHA). Derivatives according to the invention are cellulose derivatives such as methyl cellulose (MC) and hydroxypropylmethyl cellulose (HPMC), methyl hydroxyethyl cellulose (MHEC), starch derivatives such as methylated starch, ethylated starch; Hydroxyethyl starch, hydroxypropyl starch, carboxymethyl starch, starch formate, starch acetate, starch propionate, or starch butyrate, suberin derivatives, cutin derivatives, or lignin derivatives. It is believed that these natural polymers and their derivatives are capable of forming an amorphous matrix around a crystallizable organic compound.

The fatty acids are considered absolutely harmless for the human organism and are listed under the designation E 570 on the list of ingredients for food, so they are suitable for food ("dual-use substance"). This is an advantage for use in packaging materials for foodstuffs, such as the coated paper according to the invention, since the (prolonged) contact may result in mass transfer from the packaging to the foodstuff.

According to one embodiment, the natural polymer is suberin. Suberin is a plant biopolymer that is embedded in cell walls. Suberinized cells are found both in the secondary closure tissue and in subterranean plant organs. Suberin is named after the cork oak (Quercus suber}. Suberin can be divided into two different domains: a polyphenolic and a polyaliphatic domain. In the polyaliphatic fraction, dicarboxylic acids, hydroxy acids ren, long-chain fatty acids and hydroxycinnamic acids found. Current research also provides evidence that glycerol is also a very prominent monomer of the compound. The phenolic part shows a similarity to lignin. However, the proportion of monolignoles is significantly lower than that of lignin. Due to the ester linkages in suberin, the model of the chemical structure of suberin appears to be similar to the model of the chemical structure of lignin fatty acid esters, suggesting that the results presented here can be extrapolated to suberin.

According to one embodiment, the natural polymer is lignin. Lignin is a high-molecular, aromatic substance that fills the spaces between the cell membranes in woody plants and turns them into wood. Lignin can be regarded as a higher-molecular (MR approx. 5000 to 10000) derivative of phenylpropane which, depending on the type of wood, is composed of structures which can be traced back to coumaryl alcohol, coniferyl alcohol or sinapyl alcohol. The lignin of different types of wood or plants (grasses, deciduous or coniferous trees) differs in the percentage of alcohol. The components are crosslinked in a variety of ways (ether and C-C bonds) and thus form a three-dimensional network. In addition to the variability of each individual lignin molecule, the lignin of different wood and plant species also differs in the proportion of alcohols or the phenyl residues derived from them: softwood lignin contains predominantly coniferyl units (about 90%), which have a guaiacyl residue (3-methoxy -4-hydroxy-phenyl radical) and is therefore referred to as G-lignin. Hardwood lignin contains varying proportions of guaiacyl residues and sinapyl elements containing a syringyl residue (3,5-methoxy-4-hydroxy-phenyl residue). The syringyl content can be between 5 and 65 percent, the resulting lignins are called GS lignins. The lignin of the partially woody grasses and other monocots is characterized by a high proportion of about 15 to 35 percent cumaryl elements, which form the para-hydroxyphenylpropane and, together with an equal amount of syringyl and a guaiacyl proportion of 50 to 70 percent, the HGS -form lignins

According to the invention, the lignin can be obtained from conifers, deciduous trees, grass plants or annual plants. According to one embodiment, the lignin is obtained from softwoods. According to a further embodiment, it is lignin made from deciduous trees.

Various processes for obtaining lignin are known to those skilled in the art and include the Kraft process, the sulfite process, the soda anthraquinone process, the GRANIT process, the Alcell™ process and the Organocell process. According to one embodiment, the lignin is obtained from softwoods using the Kraft process. These methods are described in Nitz et al. summarized in 2001. According to one embodiment, the lignin is obtained from hardwoods using the Kraft process.

According to one embodiment, the derivative of a natural polymer is an ester of a natural polymer. Esters of natural polymers which are suitable according to the invention are cellulose esters, starch esters, cutin esters, suberin esters and lignin esters. According to one embodiment, it is an ester of lignin and one or more fatty acids, hydroxy fatty acids or dicarboxylic acids.

The acid used for the esterification of the lignin preferably has a similar chain length and degree of branching as the acid used as the crystallized component. The chain length of the two acids should not differ by more than 8 carbon atoms. The chain length preferably differs by no more than 5 carbon atoms. The difference in chain length is particularly preferably not more than 3 carbon atoms. In addition, the number of double bonds, i.e. the degree of saturation, should match between the acid used for the esterification of the lignin and the acid used as the crystallizable organic compound.

According to one embodiment, the coating color or the coating color layer contains an ester of a natural polymer, the fatty acid being identical to at least one fatty acid used as a crystallizing component. The selection of identical fatty acids offers the best conditions for the formation of the crystals in the semi-crystalline coating color layer. According to one embodiment, the coating color or the coating color layer contains a lignin fatty acid ester, the fatty acid being identical to at least one fatty acid used as a crystallizing component. Another advantage of using identical fatty acids is that the excess fatty acid that did not react during the esterification can be used. This saves one process step. In one embodiment, the crystallizable organic compound is stearic acid and the natural polymer derivative is lignin stearate.

The synthesis of the ester of the natural polymer can be carried out according to the principle of a Schotten-Baumann esterification (see example 2). Suitable reaction conditions are known to those skilled in the art and can be found in example 2. For example, the lignin stearate can be obtained by reacting stearic acid chloride with Kraft lignin.

The lignin stearate used according to the invention to produce the coated paper can have an esterification number of at least 40%. The esterification number can be, for example, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90% or 95%. According to the embodiment, the esterification number is at least 90%.

Furthermore, the lignin stearate preferably has a softening point _Tg in the range from 70 to 140.degree. Above 140 °C, there might be problems in the technical application, since the processing (melt dispersion, drying and filming) would probably be problematic. Below about 70 °C, the matrix can still remain too soft after drying and, for example, when the paper webs are rolled up, the coating can “stick” and later detach when the webs are unwound. For example, the temperature can be 70°C, 75°C, 80°C, 85°C, 90°C, 95°C, 100°C, 105°C, 110°C, 120°C, 125°C, 130° C, 135 °C or 140 °C. Even more preferably, the lignin stearate has a softening point _Tg in the range 120-140°C.

Depending on the area of application and the requirements, the coating color layer can contain one or more other ingredients, for example a protective colloid or a filler. Protective colloids are particularly suitable for keeping the particles stable in aqueous dispersion and thus enabling the paper to be coated homogeneously. Suitable protective colloids are polyvinyl alcohol, polysorbates, PEG alkoxylates and sorbitan fatty acid esters (SPAN). Suitable fillers are in particular pigments such as nanoclay. Nanoclay is used as an accelerator for crystallization.

Both the natural polymer used or its derivative and the crystallized organic compound can contain impurities that are caused by extraction or production. Possible impurities are, for example, non-esterified lignin polymers, but also polysaccharides such as celluloses and xylans. These impurities preferably make up only a very small part of the coating color and thus of the resulting coating color layer. According to one embodiment, the proportion of impurities in the coating color layer, based on the total mass of the coating color layer, is below 1% by weight.

According to one embodiment, apart from unavoidable impurities, the coating color does not contain any synthetic polymer that is petroleum-based and non-biodegradable.

Coated paper is biodegradable due to the materials present in the coating color layer. "Biodegradability" refers to the ability of organic chemicals to be broken down biologically, i.e. by living beings or their enzymes. In the ideal case, this chemical metabolism proceeds completely up to mineralization, but it can also stop in the case of transformation products that are stable in degradation. The guidelines for the testing of chemicals from the OECD, which are also used in the context of chemical approval, are generally recognised. The tests of the OECD test series 301 (A-F) demonstrate rapid and complete biodegradation (ready biodegradability) under aerobic conditions. Different test methods are available for readily or poorly soluble as well as for volatile substances. Biodegradable" or "biodegradable" in the sense of the present invention refers to papers that have a biodegradability measured according to OECD 301 F of at least 40% or measured according to OECD 302 C (MITI-II test) of at least 20% and thus have a exhibit inherent or fundamental degradability. This corresponds to the limit value for the OECD 302 C according to "Revised Introduction to the OECD Guidelines for testing of Chemicals, Section 3, Part 1, dated 23 March 2006". From a limit value of at least 60% measured according to OECD 301 F microcapsule walls are also referred to herein as rapidly biodegradable.

According to one embodiment, the coated paper has ready biodegradability according to OECD 301

In addition, the coated paper is recyclable. Paper recycling is the dissolving and processing of waste paper, used cardboard and cardboard in plants of the paper industry with the aim of producing new paper, cardboard and cardboard from it. To a small extent, waste paper pulp is first produced from the recovered paper as pulp, which is only later used to produce new pulp paper is used. Ink removal or deinking is the key process in paper recycling to remove ink from printed waste paper. The evaluation of the recyclability can be carried out with the INGEDE method 11, for example. The coated paper according to the invention achieves a deinkability score of over 50 using the INGEDE method 11. The deinkability score is preferably over 70.

With the components of the contestable layer used according to the invention, the coated paper can be approved for direct or indirect food contact. In particular, it is suitable for approval in accordance with the guidelines of the European Food Safety Authority.

In principle, all types of paper can be used as the base paper for the coated paper, i.e. cardboard, cardboard or normal paper. Paper with a low grammage is often required for food packaging, as it is flexible and saves on material. It is precisely with such papers that the coating color layer according to the invention leads to a strong increase in the barrier performance.

According to one embodiment, the base paper has a basis weight of less than 150 ^g m ^-2 The basis weight can be, for example, 150 g m ^-2 , 145 g m ^-2 , 140 g m ^-2 , 135 g m ^-2 , 130 g.m ^-2 , 125 g.m ^-2 , 120 g.m ^-2 , 115 g.m ^-2 , 110 g.m ^-2 , 105 g.m ^-2 , 100 g.m ^-2 , 95 g m ^-2 , 90 g m ^-2 , 85 g m ^-2 , 80 g m ^-2 , 75 g m ^-2 , 70 g m ^-2 , 65 g m ^-2 , 60 g m ^-2 , 55 gm ^-2 , 50 gm ^-2 , 45 gm ^-2 , 40 gm ^-2 , 35 gm ^-2 or 30 gm ^-2 . According to one embodiment, the weight per unit area is below 100 g·m ^-2 . According to one embodiment, the basis weight is below 80 g·m ^-2 . According to one embodiment, the basis weight is in the range from 50 to 80 gm ^-2 .

The coated paper can contain further layers in addition to the semi-crystalline coating color layer. According to one embodiment, the coated paper contains a further layer selected from a coating color, an ink, a sealing medium and an adhesive.

The further layer can be arranged on the semi-crystalline coating color layer, between base paper and semi-crystalline coating color layer or on the side of the base paper opposite the semi-crystalline coating color layer.

The semi-crystalline coating color layer can therefore be applied directly to the base paper. In this case, the semi-crystalline coating color layer is in direct contact with the base paper. Indirect application means that there are one or more layers between the coating color and the base paper.

Further layers can in particular further reduce the permeability of at least one gas through the coated paper compared to the base paper or form barriers for liquids or viscous substances such as fats, oils, hydrocarbons.

1. a) mindestens ein hydrophobes Polymer umfassen, z.B. auf Basis eines Polyacrylats, eines Styrol-/Butadien-Copolymers und/oder eines Polyolefins
2. b) mindestens ein hydrophiles Polymer umfassen, z.B. Basis eines Polyvinylalkohols
3. c) mindestens ein anorganisches Pigment umfassen, z.B. ein plättchenförmiges Pigment, z.B. ein Schichtsilikat wie Kaolin,
4. d) mindestens ein anorganisches Pigment und ein Bindemittel umfassen,
5. e) amorphe und kristalline Bereiche umfassen, z.B. die erfindungsgemäße Streichfarbenzusammensetzung,
6. f) Stoffe enthalten oder daraus bestehen, die ausgewählt sind aus der Gruppe lipophile Stoffe, Paraffine, insbesondere Hartparaffine, Wachse, insbesondere mikrokristalline Wachse, Wachse auf Basis von pflanzlichen Ölen oder Fetten, Wachse auf Basis von tierischen Ölen oder Fetten, pflanzliche Wachse, tierische Wachse, niedermolekulare Polyolefine, Polyterpene und deren Mischungen,
7. g) den Übergang von Stoffen, insbesondere von hydrophoben Stoffen, verringern oder verhindern, z.B. von Stoffen gemäß vorstehendem Punkt e) um beispielsweise den Übergang von Stoffen aus darunterliegenden Schichten auf ein Lebensmittel, insbesondere ein fetthaltiges Lebensmittel, zu verhindern oder zu verringern,
8. h) mindestens ein Metall, z.B. Aluminium, Gold, und/oder ein Metalloxid, z.B. Aluminiumoxid, umfassen oder daraus bestehen, insbesondere eine metallisierte Schicht sein,
9. i) mindestens heiß- oder kaltsiegelbar sein,
10. j) mindesten seinen Klebstoff umfassen,
11. k) mindestens ein thermoplastisches Material, insbesondere als heißsiegelbares Material, umfassen oder daraus bestehen.

A further layer can in particular:

1. a) comprise at least one hydrophobic polymer, for example based on a polyacrylate, a styrene/butadiene copolymer and/or a polyolefin
2. b) comprise at least one hydrophilic polymer, for example based on a polyvinyl alcohol
3. c) comprise at least one inorganic pigment, for example a platelet-shaped pigment, for example a sheet silicate such as kaolin,
4. d) comprise at least one inorganic pigment and a binder,
5. e) include amorphous and crystalline areas, for example the coating color composition according to the invention,
6. f) contain or consist of substances selected from the group consisting of lipophilic substances, paraffins, in particular hard paraffins, waxes, in particular microcrystalline waxes, waxes based on vegetable oils or fats, waxes based on animal oils or fats, vegetable waxes, animal waxes Waxes, low-molecular polyolefins, polyterpenes and their mixtures,
7. g) reduce or prevent the transfer of substances, in particular hydrophobic substances, e.g. of substances according to point e) above, for example to prevent or reduce the transfer of substances from underlying layers to a food, in particular a fatty food,
8. h) comprise or consist of at least one metal, e.g. aluminum, gold, and/or a metal oxide, e.g. aluminum oxide, in particular be a metallized layer,
9. i) be at least heat-sealable or cold-sealable,
10. j) include at least its adhesive,
11. k) comprise or consist of at least one thermoplastic material, in particular as a heat-sealable material.

The base paper can be a base paper coated on one or both sides or an uncoated base paper.

In the case of coated base paper, the surface is finished with a coating color containing a binder. Coating color is used as the material for the binder application, the main component of which can be starch, starch derivatives, chalk, kaolin, casein or plastic dispersion. This gives the base paper a more closed, smoother and more stable surface.

However, uncoated base paper can also be surface-treated and contain up to 5 g/m ² of pigments.

For use as packaging in the food sector, the paper needs a certain tear strength or breaking strength. According to one embodiment, the coated paper has a width-related breaking strength in the fiber direction in the range from 3.0 to 6.0 kN·m ^-1 . The width-related breaking strength in fiber direction can be, for example, 3.0 kN m ^-1 , 3.2 kN m ^-1 , 3.4 kN m ^-1 , 3.5 kN m ^-1 , 3.6 kN m ^{- 1} , 3.8 kN m ^-1 , 4.0 kN m ^-1 , 4.2 kN m ^-1 , 4.4 kN m ^-1 , 4.5 kN m ^-1 , 4.6 kN m ^-1 , 4.8 kN m ^-1 , 5.0 kN m ^-1 , 5.2 kN m ^-1 , 5.4 kN m ^-1 , 5.5 kN m ^-1 , 5.6 kN m ^-1 , 5.8 kN m ^-1 , 6.0 kN m ^-1 . According to one embodiment, the broad-based breaking strength in the fiber direction is in the range from 3.5 to 5.5 kN m ^-1 . According to one embodiment, the broad-based breaking force in the fiber direction is in the range from 4.0 to 5.0 kN m ^-1 .

The induced semi-crystallinity according to the invention was achieved, for example, with a coating color containing a fatty acid as a crystallizable organic compound in combination with the derivative of a natural polymer, in particular lignin. Consequently, according to a second aspect, the invention relates to a coating color for coating papers, containing at least one solvent, at least one crystallizable organic compound and at least one natural polymer and/or derivative of a natural polymer.

As described with regard to the coating color layer in the coated paper according to the first aspect, the crystallizable organic compound is preferably selected from fatty acids, hydroxy acids or dicarboxylic acids or their esters, amides or salts. Since the coating color is the starting material for the formation of the coating color layer, the definitions of the crystallizable organic compound in the first aspect of the invention also apply here.

The natural polymer is selected in particular from hydrocarbons such as rubber or balata, proteins such as collagen, keratin, fibroin, nucleic acids, polysaccharides such as alginate, agar-agar, cutin, suberin, lignin, cellulose, chitosan, and starch, lipids, polylactide (PLA) , polyhydroxybutyrate (PHB), and polyhydroxyalconoate (PHA). The definitions of the natural polymer or the derivative in the first aspect of the invention also apply here to the natural polymer or the derivative.

In contrast to the coating color layer, however, the coating color also contains at least one solvent. Suitable solvents are water, tetrahydrofuran (THF), toluene, ethyl acetate, and alcohols such as ethanol or isopropanol. The solvent is preferably water.

According to one embodiment, at least one fatty acid in the ester of the natural polymer, in particular in the lignin ester, is identical to at least one fatty acid used as a crystallizable organic compound. In one embodiment, the crystallizable organic compound is stearic acid and the natural polymer derivative is lignin stearate.

Due to the proportion of solvents, the proportion of natural polymers and/or their derivatives in the coating color differs from the proportion in the coating color layer. According to one embodiment, the proportion of the natural polymers and/or their derivatives, based on the total mass of the coating color, is in the range from 6 to 30% by weight. The proportion can be, for example, 6% by weight, 8% by weight, 10% by weight, 12% by weight, 14 wt%, 16 wt%, 18 wt%, 20 wt%, 22 wt%, 24 wt%, 26 wt%, 28 wt%, or 30 wt% .-%, lay. According to one embodiment, the proportion is in the range from 8 to 25% by weight. According to a further embodiment, the proportion is in the range from 15 to 25% by weight.

According to one embodiment, the proportion of the crystallizable organic compounds, based on the total mass of the coating color, is in the range from 2 to 15% by weight. The proportion can be, for example, 2% by weight, 4% by weight, 6% by weight, 8 10%, 12%, 13%, 14%, or 15% by weight. According to one embodiment, the proportion is in the range from 4 to 12% by weight. According to one embodiment, the proportion is in the range from 5 to 8% by weight.

According to one embodiment, the proportion of the solvent, based on the total mass of the coating color, is in the range from 60 to 95% by weight. The proportion can be, for example, 60% by weight, 62% by weight, 64% by weight, 66% by weight, 68% by weight, 70% by weight, 72% by weight, 74% by weight -%, 76 wt%, 78 wt%, 80 wt%, 82 wt%, 84 wt%, 86 wt%, 88 wt%, 90 wt% 92%, 94% or 95% by weight. In one embodiment, the proportion is in the range from 70 to 90% by weight. In one embodiment, the proportion ranges from 75 to 85% by weight.

With a dry content of 10% by weight, ie a solvent content of 90% by weight, the proportion of polymer is preferably in the range from 6.5% by weight to 7.5% by weight and the proportion of crystallizable organics Compound in the range of 2.5% to 3.5% by weight. With a dry content of 15% by weight, ie a solvent content of 85% by weight, the proportion of polymer is preferably in the range from 9.8% by weight to 11.3% by weight and the proportion of crystallizable organics Compound in the range of 3.8% to 5.3% by weight. With a dry content of 25% by weight, ie a solvent content of 75% by weight, the proportion of polymer is preferably in the range from 16.3% by weight to 18.8% by weight and the proportion of crystallizable organics Compound in the range of 6.3% to 8.8% by weight. With a dry content of 30% by weight, ie a solvent content of 70% by weight, the proportion of polymer is preferably in the range from 16.3% by weight to 18.8% by weight and the proportion of crystallizable organics Compound in the range of 6.3% to 8.8% by weight. With a dry content of 40% by weight, ie a solvent content of 60% by weight, the proportion of polymer is preferably in the range from 26.0% by weight to 30.0% by weight and the proportion of crystallizable organics compound in the range of 10.0% to 14.0% by weight.

production method

1. a) Herstellen einer Streichfarbe nach einem dem zweiten Aspekt durch Schmelzdispergierung, Hochdruckdispergierung, oder Sprühtrocknung und anschließender mechanischer Dispergierung der Komponenten;
2. b) Bereitstellen eines Basispapiers;
3. c) Auftrag der Streichfarbe auf das Basispapier, und
4. d) Aushärtung der Streichfarbe unter Ausbildung der semikristallinen Streichfarbenschicht.

The essential here crystallinity of the semi-crystalline coating color layer in the coated paper is dependent in particular on the process used to produce the coated paper. Consequently, according to a third aspect, the invention relates to a method for producing a coated paper with a base paper and a semi-crystalline coating color layer, comprising the steps:

1. a) production of a coating color according to the second aspect by melt dispersion, high-pressure dispersion, or spray drying and subsequent mechanical dispersion of the components;
2. b) providing a base paper;
3. c) application of the coating color to the base paper, and
4. d) curing of the coating color with formation of the semi-crystalline coating color layer.

According to one embodiment, the coating color is applied to the base paper, preferably by means of a curtain or doctor blade method.

As stated in the first aspect with regard to the crystallinity of the coating color layer of the coated paper according to the invention, the method according to the invention can be used to adjust the crystallinity of the semicrystalline coating color layer by the proportion of crystallizable organic compounds based on the total mass of the coating color.

In addition, the curing temperature, curing time and curing pressure have an impact on the crystallinity.

According to one embodiment of the method, the curing temperature is in the range from 20 to 300°C. According to one embodiment of the method, the curing temperature is in the range from 120 to 140°C.

According to one embodiment of the method, the curing time is in the range from 10 s to 15 minutes. According to one embodiment of the method, the curing time is in the range from 1 to 3 minutes.

According to one embodiment of the method, the curing pressure is in the range from 0.2 bar to 3 bar. According to one embodiment of the method, the curing pressure is in the range from 0.9 bar to 1.1 bar.

Packaging

According to a fourth aspect, the invention relates to packaging for foodstuffs comprising the coated paper according to the first aspect.

This may be, for example, packaging for dried food, food sold cold that requires further preparation, packaging containing food in single-serving portions for more than one person, or packaging containing food in single-serving portion sizes for more than one person unit is sold, act.

Stand-up pouch packaging, tubular pouch packaging or packaging paper can be used as packaging, for example. According to one embodiment, the packaging is a tubular bag packaging.

EXAMPLES

Example 1 - Characterization of Lignin

The main focus of the characterization of the lignin lies in the molar mass of the lignin and the number of hydroxyl groups.

molar mass

The molar mass is determined by means of GPC

Device parameters - GPC 4

Flow 1mL/min Temperature RI detector 35°C injection volume sample 100µL injection volume internal 20µL default Injection Volume System Test 20µL Injection volume standards 20µL guard column PSS MCX 5µm 8×50mm main pillar PSS MCX 1000Å and MCX 100000Å 5µm) 8x300mm Eluent/ solvent buffer NaCl 0.1 mol/L + NaOH 0.1 mol/L Internal standard Ethylene Glycol (1µL in 1mL Eluent) System test/ floor count 2-3 µL ethylene glycol in 1mL eluent

standards

Poly(styrenesulfonic acid) sodium salt single standard from PSS 1 mg in 1 mL eluent

In 1 an example of a used Kraft lignin is shown.
Number average molar mass Mn: 1000 g*m ^-2 *d ^-1
Weight average molar mass Mw: 5000 g*m ^-2 *d ^-1

hydroxy group number

The number of hydroxy groups can be determined by titration and by 31P-NMR.

titration:

The OH number of Kraft lignin (KL) is determined according to DIN EN ISO 4629-1.

31P NMR spectroscopy

The phosphorylation of the lignin derivatives is carried out according to the instructions of Granata et al. carried out. For this purpose, 25 mg of the dry lignin are first dissolved in 150 µL DMF. After dissolving, 100 µL of pyridine, 200 µL of a solution of the internal standard endo-N-hydroxy-5-norbomene-2,3-dicarboximide (25.0 mmol*L-1 in pyridine/CDCl3 1.6:1) and 50 µL of a solution of chromium(III) acetylacetonate (32.64 mmol/L, in pyridine/CDCl3 1.6:1) are added. Argon is flushed through the solution for a few minutes and then 150 µL of the phosphitylation reagent 2-chloro-4,4,5,5-tetramethyl-1,3,2-dioxophospholane (0.944 mmol) and 300 µL CDCl3 are added under an argon atmosphere. The solution thus obtained is transferred to an argon-purged NMR tube.

The amount of hydroxy groups can be calculated from the integrals of the signals.
For that in error! Reference source not found. Kraft lignin shown gives a hydroxy group amount of 6.18 mmol/g and a carboxy group amount of 0.5 mmol/g.

Example 2 - Preparation of Esterified Lignins

The synthesis of the lignin stearate was carried out according to the principle of a Schotten-Baumann esterification of the stearic acid chloride with Kraft lignin.

Lignin was dissolved in dry 1,4-dioxane (50 g/L) (N ₂ atmosphere). After about one hour, the stearic acid chloride (2.8 g per 1 g lignin) and pyridine (0.25 g per 1 g lignin) are added. The reaction was stirred at 80°C for 6 h.

The reaction solution was then poured into 3 L of water and stirred for 2 hours. The precipitate is filtered off (Po.2), washed with water and dried at 40° C. in a vacuum drying cabinet.

The solid was added to 1 L of ethanol and heated to boiling for 6 h. After cooling to room temperature, the mixture was centrifuged (4,700 rpm, 10 min). The supernatant was decanted off and the solid was again placed in 200 mL ethanol, stirred at 60° C. for about 1 h, allowed to cool to room temperature and centrifuged. This step was repeated about 2 to 3 times.

The solid is dried at 40° C. in a vacuum drying cabinet. To remove any insoluble residues, the solid is dissolved in a little THF, the solution is centrifuged, the decanted solution is spun off in a rotary evaporator and the product is obtained in this way.

The synthetic procedure was repeated with stearic acid amide from Croda, candelilla wax and carnauba in place of the stearic acid.

Example 3 - Characterization of the lignin esters

The most important factor characterizing the lignin ester is the degree of esterification. This was determined by means of ³¹ P NMR spectroscopy and by means of titration.

³¹ P NMR spectroscopy

The degree of esterification can be calculated from the mole fractions of the hydroxyl groups of the lignin ester (nLE) and the Kraft lignin (nKL) used. The total amount of hydroxyl groups nKL (-OH and -COOH) in the Kraft lignin used is 6.68 mmol per gram of lignin (see example 1). The amount of hydroxyl groups in the lignin ester can be determined analogously. The spectrum obtained is 3 shown.

The amount of substance of hydroxy groups (-OH) is therefore: 1.10 mmol*g ^-1 The amount of substance of carboxyl groups (-COOH): 0.09 mmol*g ^-1 The total amount of substance n _LE of hydroxy groups (-OH and -COOH): 1.19mmol*g ^-1

$$E=1-\left(\frac{\mathrm{1,19}}{\mathrm{6,68}}\right)=\mathrm{0,82}=82\%$$

The degree of esterification E is as follows: $$E=1-\left(\frac{n_{LE}}{n_{KL}}\right)$$

$$E=1-\left(\frac{\mathrm{1:19}}{6.68}\right)=0.82=82\%$$

Titration according to DIN EN ISO 4629-1:2016

softening temperature

The softening point of the lignin ester is determined optically. A small amount of powdered lignin esters is placed on a watch glass and placed in a convection oven. The oven temperature is increased in 10°C increments and the temperature at which the powder melts into a droplet is noted.
The softening point of lignin stearate is around 130°C

IR spectroscopy

4 Figure 1 shows the IR spectrum of lignin stearate compared to Kraft lignin and stearic acid. The successful conversion can be recognized by the signal at 1750 cm ^-1 , which represents the C=O oscillation of an ester. In comparison, the C=O oscillation of the acid is at 1700 cm ^-1 .

1H NMR spectroscopy

5 shows the 1H-NMR spectrum of lignin stearate.

Example 4 - Coating Color Production

A) Coating color based on organic solvents

The solids content of a coating color was between 10 and 25 percent by weight. 1 g of a mixture of lignin stearate and stearic acid (e.g. 7:3) was weighed into a 5 mL vessel with a lid and dissolved in 3 mL of a mixture of THF (tetrahydrofuran) and EA (ethyl acetate) (1:2).

The preparation was repeated with stearic acid amide, carnauba wax and candelilla wax in place of stearic acid. Depending on the wax used, the solvent mixture was varied in order to ensure solubility and subsequent wettability on the paper to be coated. The lignin stearate/carnauba wax and lignin stearate/candelilla wax coating colors were prepared in a 2:1 mixture of THF/EE.

B) Water-based coating color with spray-dried lignin

The solids content of a coating color was between 10 and 25 percent by weight. 3.75 g of spray-dried lignin stearate-stearic acid mixture (1:1) was dispersed in 15 mL of a solution of 1% SPAN-60 in water using an ultrathorax. 5 mL of the dispersion was placed in a 25 mL speed mixer beaker. A hole was punched in the lid of the cup. The dispersion was degassed in a speed mixer at 800 rpm and a pressure of 30 mbar for four minutes.

The preparation was repeated with stearic acid amide, carnauba wax and candelilla wax in place of stearic acid.

Example 5 - Production of coated papers

An RK K303 Multicoater (see 6 , Table 1) used.

The base paper was placed on the waste paper in such a way that the standard K-bar to be clamped rests on the base paper. The corresponding bar is clamped in the Multicoater. A weight was placed on the paper behind the stick. The desired spreading speed was set (from organic medium 10-20 m/min, from aqueous dispersion 3 m/min). The coating color (approx. 3-5 mL) was applied to the paper with a pipette in front of the stick in the width of the paper and the coating process was started. The rod drove over the paper and distributed the coating color evenly on it.

After coating, the paper was transferred to a cardboard backing, fixed at the corners to prevent it from rolling up and dried in the oven at 130 °C for 10 minutes (organic medium: evaporation of the solvent in room air, the coating melted at 130 °C for approx. 3 minutes). Table 1 Coating area : max. 350x440 mm substrate size max. 350x580 mm waste paper rolls : 375mm width x 150mm Standard K-Bars wet film application wire gauge mm K303 rod #0 4 0.05 K303 rod #1 6 0.08 K303 rod #2 12 0.16 K303 rod #3 24 0.31 K303 rod #4 40 0.51 K303 rod #5 50 0.64 K303 rod #6 60 0.76 K303 rod #7 80 1 K303 rod #8 100 1.27 K303 rod #9 120 1.5

Example 6 - Determination of the water vapor permeability of the coated papers

The water vapor permeability is determined based on DIN 53122-1 as a gravimetric method.

Round test specimens with a diameter of 6.3 cm are punched out of the papers to be examined. A desiccant (e.g. silica gel beads) is placed in a measuring vessel. A sealing ring is placed on the edge of the vessel, the test specimen is placed on the sealing ring with the side of the water vapor barrier facing the drying agent, another sealing ring and a metal ring are placed on the test specimen. The jar is sealed with a lid having a hole 5.7 cm in diameter. The diagram of such a measurement setup in cross section can be seen in the figure.

The measuring vessel prepared in this way is placed in a climatic chamber in which a temperature of 38 °C and relative humidity of >90% prevail. After conditioning in the chamber for around 16 hours, the measuring vessel is weighed. At intervals of 2-3 hours, new weighings are carried out until at least three measurement results are available. The measuring vessel is stored in the climatic chamber between the weighings.

1. a) Stearinsäure
2. b) Candelilla
3. c) Carnauba
4. d) Stearinsäureamid sind in 8 dargestellt.

The water vapor permeability in grams per square meter per day (g*m ^-2 *d ^-1 ) can be calculated from the mass gain. At least two test specimens are measured per barrier to be examined. The results for the coatings with

1. a) stearic acid
2. b) Candelilla
3. c) carnauba
4. d) stearic acid amide are in 8th shown.

Comparison to the measurement method of Hult et al. (measured: line from aqueous dispersion dry content 20% (spray-dried lignin) in 1% SPAN-60 solution) Tropical: 36.2 +- 20.0 g*m ^-2 d ^-1 (two measurements: 50.4 and 22, 1 g*m ^-2 d ^-1 . The first value is probably caused by defects)
According to Hult: 2.0 +- 0.1 g* ^-2 d ^-1 (two measurements: 2.0 and 1.9 g*m ^-2 d ^-1 )

With a WVTR of 368.0 ± 10.6 g m ^-2 day ^{-1 ,} the paper coated with pure lignin stearate has almost no barrier performance against water vapour. If the proportion of stearic acid is increased, a WVTR of 17.1 ± 1.0 g m ^-2 day ^-1 can be achieved at a proportion of 30%. If the proportion of stearic acid is further increased, the WVTR increases again and the barrier performance deteriorates.

By using the composite of lignin stearate and stearic acid with a stearic acid content of 30%, a very good barrier performance against water vapor can be achieved under tropical conditions.

With regard to further advantageous configurations of the device according to the invention, to avoid repetition, reference is made to the general part of the description and to the appended claims.

Finally, it should be expressly pointed out that the above-described exemplary embodiments of the device according to the invention only serve to explain the claimed teaching, but do not restrict it to the exemplary embodiments.

QUOTES INCLUDED IN DESCRIPTION

This list of documents cited by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent Literature Cited

• US 9902815 B2 [0007]

Claims (21)

Coated paper, comprising a base paper and at least one semi-crystalline coating color layer applied directly or indirectly to the base paper and having amorphous areas and crystalline areas: • wherein the amorphous regions contain one or more natural polymers and/or one or more derivatives of natural polymers; • wherein the crystalline regions comprise one or more crystallizable organic compounds; and • wherein the permeability of at least one gas through the coated paper is reduced compared to the base paper. Coated paper after claim 1 , wherein the permeability of at least one gas is lower than the permeability of a coated paper with the same base paper and a coating color layer made of the natural polymer or its derivative and a coating color layer made of the crystallizable organic compound. Coated paper according to one of the preceding claims, wherein the crystalline areas form during the application of the coating color to the base paper and/or the curing of the coating color. Coated paper according to any one of the preceding claims, wherein the crystallizing component in the coating color is not in crystalline form. Coated paper according to any one of the preceding claims, wherein the crystallinity of the semi-crystalline coating color layer is in the range from 10% to 90%, preferably in the range from 10% to 40%, particularly preferably in the range from 15% to 25%. Coated paper according to any one of the preceding claims, having a water vapor transmission rate (WVTR) of not more than 40 gm ^-2 d ^-1 , preferably not more than 20 gm ^-2 d ^-1 measured at 38°C and above 90% humidity and with a surface weight of the coating color of 10 ± 1 g m ^-2 . Coated paper according to one of the preceding claims, wherein the proportion of the crystallizable organic compounds, based on the total mass of the coating color layer, is in the range from 1 to 60% by weight, preferably in the range from 5 to 50% by weight, particularly preferably in the range from 10 to 40% by weight, very particularly preferably in the range from 25 to 35% by weight. Coated paper according to any one of the preceding claims, wherein the proportion of the natural polymers or derivatives thereof, based on the total mass of the coating color layer, is in the range from 40 to 99% by weight, preferably in the range from 50 to 95% by weight, particularly preferably in the range from 60 to 90% by weight, very particularly preferably in the range from 65 to 75% by weight. Coated paper according to one of the preceding claims, wherein at least one crystallizable organic compound is selected from fatty acids, hydroxy fatty acids or dicarboxylic acids or their esters, amides or salts. Coated paper according to any one of the preceding claims, wherein the fatty acids are preferably saturated or unsaturated fatty acids having 12 to 40 carbon atoms, more preferably fatty acids having 16 to 18 carbon atoms and 0 or 1 double bond, in particular the crystallizing component is stearic acid or its amide. Coated paper after claim 10 , wherein the at least one crystallizable organic compound is present as a fatty acid mixture or wax in the coating color, wherein the wax is preferably selected from carnauba wax, candelilia wax, beeswax, and Japan wax and the fatty acid mixture is preferably a mixture of stearic acid, palmitic acid, oleic acid, linoleic acid and/or linolenic acid is. Coated paper according to one of the preceding claims, wherein the natural polymers are selected from the group consisting of proteins, peptides, nucleic acids, polysaccharides, lipids, polyhydroxyalkonoates (PHA), cutin, suberin, lignin, cellulose, chitosan, and starch, is particularly preferred the natural polymer selected from suberin and lignin. Coated paper after claim 12 , wherein the lignin is obtained from conifers, deciduous trees, grass plants or annual plants, preferably from conifers or deciduous trees, and with a process selected from Kraft process, sulfite process, soda-anthraquinone process, GRANIT process, Alcell™ process and Organocell process, preferably lignin obtained from softwood or deciduous wood by means of the kraft process. Coated paper after claim 12 or 13 wherein the derivative of a natural polymer is the ester of a natural polymer, preferably a lignin ester, more preferably an ester of lignin and one or more fatty acids, hydroxy fatty acids or dicarboxylic acids. Coated paper after one of Claims 10 until 14 , wherein at least one fatty acid in the lignin ester is identical to at least one fatty acid used as a crystallizing component. Coated paper after one of Claims 10 until 15 wherein the crystallizable organic compound is stearic acid and the derivative of a natural polymer is lignin stearate. Coated paper according to one of the preceding claims, wherein the coated paper has at least one of the following features: • the coated paper is biodegradable, in particular it has easy biodegradability according to OECD 301; • the coated paper is recyclable; and • the coated paper can be approved for direct or indirect food contact, in particular according to the guidelines of the European Food Safety Authority. Coating color for coating papers, containing at least one solvent, at least one crystallizable organic compound and at least one natural polymer and/or derivative of a natural polymer; • wherein the crystallizable organic compound is/are defined according to claim 10 or 11 ; • wherein the natural polymer and the derivative of a natural polymer are according to any one of Claims 12 until 15 ; and • wherein the solvent is selected from water, tetrahydrofuran (THF), toluene, ethyl acetate, and alcohols, preferably the solvent is water. coating color after Claim 18 , having at least one of the following features: • the proportion of natural polymers and/or derivatives thereof, based on the total mass of the coating color, is in the range from 6 to 30% by weight, preferably in the range from 8 to 25% by weight, particularly preferably in the range of 10 to 15% by weight; the proportion of crystallizable organic compounds based on the total mass of the coating color is in the range from 2 to 15% by weight, preferably in the range from 4 to 12% by weight, particularly preferably in the range from 5 to 8% by weight, ; and • the proportion of the solvent, based on the total mass of the coating color, is in the range from 60 to 90% by weight, preferably in the range from 70 to 90% by weight, particularly preferably in the range from 75 to 85% by weight Method for producing a coated paper with a base paper and a semi-crystalline coating color layer, comprising the steps: a) producing a coating color according to one of claims 18 or 19 by melt dispersion, high-pressure dispersion, or spray drying and subsequent mechanical dispersion of the components; b) providing a base paper; c) application of the coating color to the base paper, preferably by means of a curtain or doctor blade method; and d) curing of the coating color with formation of the semi-crystalline coating color layer. Food packaging comprising the coated paper according to any one of Claims 1 until 17 .

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