Coated paper as a packaging material with a semi-crystalline coating color layer.

Abstract

The present application relates to a coated paper comprising a base paper and at least one semi-crystalline coating color layer having amorphous and crystalline regions applied indirectly or directly onto the base paper, wherein the amorphous regions comprise one or more natural polymers and / or one or more derivatives of natural polymers; the crystalline regions comprise one or more crystallizable organic compounds; and the permeability of at least one gas through the coated paper is reduced compared to the base paper. The present application further relates to a coating color utilized for the method of producing the coated paper, a method of production, and packaging for food products.

Description

[Technical field]

[0001] The present invention relates to coated papers with high barrier properties for use as food packaging materials. [Background technology]

[0002] Packaging accounts for a large proportion of global plastic waste pollution, thus spurring the search for alternatives made from biodegradable materials.

[0003] Food packaging in particular poses a challenge, as it requires good barrier properties against oxygen, water vapor, and microorganisms.For example, food packaging materials are often made from plastics, such as polyethylene terephthalate (PET), polyvinyl chloride (PVC), polyethylene (PE), and polypropylene (PP), which have good barrier properties as well as low weight and high mechanical stability.

[0004] Paper-based packaging materials have many advantages when compared to plastic materials, such as renewable, recyclable and compostable. However, their application is often limited due to poor barrier properties and high sensitivity to moisture. To improve the barrier properties, aluminum and petroleum-based polymers such as PE, EVOH and PVC derivatives can be laminated to paper-based packaging materials. However, such coatings complicate waste separation and therefore recycling, and reduce compostability. Therefore, the use of barrier layers based on natural bio-based polymers or alternatives to conventional metal- or plastic-based layers is highly desirable from an ecological point of view.

[0005] Examples of natural polymers that have been tested for packaging applications include chitosan, hemicellulose, microfibrillated cellulose, starch, etc. However, many of the natural polymers are hydrophilic, and films made from such materials are often hygroscopic, which leads to a partial loss of barrier properties under high humidity.

[0006] In forest and agricultural economics, there is a great interest in the secondary processing of by-products and waste products, for example lignin.

[0007] For example, lignin is used in papermaking. For example, WO 2021 / 191097 A1 describes a method for producing paper. The method comprises a wet stage and a dry stage. The wet stage comprises the creation of a fiber suspension comprising fibers in water, the fibers being selected from the group of lignocellulose, hemicellulose, and cellulose. In the wet stage, an additive is added comprising enzymatically oxidized lignin. It is intended to achieve an improvement in the moisture resistance of the paper, in particular the pressure resistance under moisture. Furthermore, it is proposed to add fatty acids, such as stearic acid, to the enzymatically oxidized lignin.

[0008] Lignin is a suitable hydrophobic biopolymer for use as a barrier layer in paper, but research has so far been limited. Coating color layers based on lignin alone do not have sufficient barrier properties. Thus, the prior art has undergone various experiments to improve the properties of lignin to a degree that it remains sufficiently airtight in humid environments such as food packaging.

[0009] US Patent No. 9,902,815 B2, as well as the academic publication Hult et al. 2013 by the same authors, describe a method for esterifying lignin with fatty acids, in particular with a mixture of tall oil and fatty acids, the main components of which are unsaturated fatty acids such as oleic acid, linoleic acid and linolenic acid, which are reacted with lignin to obtain various degrees of esterification.

[0010] In addition to esterification of lignin with tall oil, Hult et al. also embody softwood lignin and hardwood lignin containing palmitic acid and lauric acid. As such, it can be shown that lignin esterified with long chain palmitic acid has better barrier properties against water vapor than lignin esterified with lauric acid. The best barrier performance can be achieved by a layer consisting of hardwood lignin esterified with palmitic acid.

[0011] DE 10 2017 108 577 A1 relates to a coating comprising at least one polymer and at least one crystallizable material, as well as a method for producing the same, in which the polymer melts at a temperature of at most 10° C. at the melting temperature of the crystallizable material. 12 mPa s. In that way, a superhydrophobic and reproducible layer is obtained. However, this layer has very poor gas barrier properties. Summary of the Invention

[0012] The present invention is based on the surprising finding that the barrier effect of coating colour layers, especially those based on natural polymers such as lignin or lignin stearates, can be significantly improved by inducing semi-crystalline, i.e. both crystalline and amorphous, regions. This is achieved by adding crystallizable organic compounds to the coating colour, for example stearic acid. The coated paper of the present invention produced with such coating colours has a barrier effect sufficient for application in the food industry and is nevertheless biodegradable and recyclable.

[0013] The present invention therefore relates to a coated paper comprising a base paper and, indirectly or directly applied onto the base paper, at least one semi-crystalline coating color layer having amorphous and crystalline regions: the amorphous region comprises one or more naturally occurring polymers and / or one or more derivatives of naturally occurring polymers; the crystalline regions comprise one or more crystallizable organic compounds; and The coated paper has at least one gas permeability that is reduced compared to the base paper.

[0014] The semi-crystallization induced by the invention is realized by a coating color which contains, by way of example, a fatty acid as crystallizable organic compound, in combination with a derivative of a natural polymer, in particular lignin.The invention therefore relates, according to a second aspect, to a coating color for coating paper, comprising at least one solvent, at least one crystallizable organic compound and at least one natural polymer and / or derivative of a natural polymer, the crystallizable organic compound is selected from fatty acids, hydroxy fatty acids, or dicarboxylic acids, or their esters, amides, or salts; the natural polymer is selected from polysaccharides such as alginate, agar, cutin, suberin, lignin, cellulose, chitosan, and starch, carbohydrates such as natural rubber and balata, proteins such as collagen, keratin, fibroin, nucleic acids, lipids, polylactic acid (PLA), polyhydroxybutyric acid (PHB), and polyhydroxyalkanoates (PHAs); and The solvent is selected from water, tetrahydrofuran (THF), toluol, ethyl acetate, and alcohol.

[0015] The crystallization of the coating color layer of the coated paper, which is of importance here, depends in particular on the method applied to produce the coated paper. Thus, according to a third aspect, the present invention relates to a method for producing a coated paper having a base paper and a semi-crystalline coating color layer, comprising the following steps: a) preparing a coating color according to the second aspect by melt dispersion, high pressure dispersion, or spray drying of the components, followed by mechanical dispersion; b) preparing the base paper; c) applying a coating color to the base paper; and d) curing the coating color while forming a semi-crystalline coating color layer.

[0016] According to a fourth aspect, the present invention relates to packaging for food products comprising a coated paper according to the first aspect. [Brief description of the drawings]

[0017] [Figure 1] FIG. 1 shows the elgram of kraft lignin, with the number-average molar mass Mn and the weight-average molar mass Mw indicated. [Diagram 2] Figure 2 shows the 31P-NMR spectrum of kraft lignin. Signal A: internal standard, signal group B: aliphatic and phenolic hydroxy groups, signal C: carboxy group. [Diagram 3] Figure 3 shows the 31P-NMR spectrum of lignin esters. Signal A: internal standard, signal group B: hydroxyl group, signal C: carboxyl group. [Figure 4] FIG. 4 shows the IR spectra of lignin stearate (bottom) in comparison with kraft lignin extract (top) and stearic acid (middle). [Diagram 5] FIG. 5 shows the 1H-NMR-spectra of lignin stearate with the solvent CDCl3. [Figure 6] FIG. 6 shows the results of the determination of the water vapor permeability WVTR of papers coated with various coating colours (according to the invention) in dependence on the crystallised wax / crystallised fatty acid ratio. [Figure 7A] Figure 7A shows a scanning electron micrograph of the surface of the lignin stearate-stearic acid coating at EHT=10 kV, WD=6.3 mm, and 100,000x magnification. WD stands for “working distance,” the distance between the objective lens of the scanning electron microscope and the specimen being examined. EHT stands for “high tension,” the high pressure applied to accelerate electrons in the scanning electron microscope. [Figure 7B]Figure 7B shows a close-up of a 4 μL water droplet on a lignin-stearate-stearic acid coating, taken with a Data Physics OCA35 with a tiltable table under constant temperature and humidity (23 °C, 50% relative humidity). Software: SCA 4.5.2 Build 1052. The contact angle is 103°. [Figure 8A] FIG. 8A shows a scanning electron photograph of the surface of the AKD-CSE3 coating at EHT=10 kV, WD=6.44 mm, and a magnification of 100,000×. [Figure 8B] Figure 8B shows a close-up of a 4 μL water droplet on the AKD-CSE3 coating, taken with a Dataphysics OCA35 with a tiltable table under constant temperature and humidity (23 °C, 50% relative humidity). Software: SCA 4.5.2 Build 1052. The contact angle is 159° ± 3°. [Figure 9] Figure 9 shows a graph of the sliding angle of a water droplet on a lignin-stearate-stearic acid coated surface as a function of the water droplet volume. [Figure 10] Figure 10 shows a graph of the water vapor transmission rate (WVTR) of coated papers with various lignin stearate-fatty acid coatings in grams per square meter per day as a function of the fatty acid ratio, where fatty acid is the ratio of stearic acid to suberic acid. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] definition

[0019] The term "color coating" within the scope of the present invention, in accordance with the general understanding in the field of paper technology, denotes a coating material, which comprises or consists of binders, additives and possibly pigments or matrix pigments, which is applied ("coated") to the surface of the paper by means of a dedicated coating device for the surface treatment or modification of the base paper. Papers produced in this way are called "coated papers".

[0020] By "coated paper" is meant within the context of the present invention a base paper which comprises one or more layers applied by coating, i.e. coating color layers. As layers of the paper substrate which are thus coated, functional layers and structure-forming layers come into consideration.

[0021] The term "coating colour" is used in the present invention as a generic term for any covering material, preparation and / or solution that can be applied in the paper industry to treat, modify or process the surface of paper. By "coating colour layer" is understood the coating colour that has been applied to the base paper and cured.

[0022] "Paper" is a flat material consisting essentially of fibres of plant origin and formed by dewatering a fibre suspension on a screen. The resulting fibre fleece is pressed and dried. Within the scope of the present invention, the flat materials "paperboard" and "cardboard", which are produced in a similar manner, are also included under paper. The only distinction made between paper, paperboard and cardboard is by basis weight, with cardboard having a basis weight of 600 g / m 2 and the paperboard has a square meter weight of more than 150 and 600 g / m 2 and the paper has a square meter weight of 150 g / m 2 With a square meter weight of:

[0023] The synonymous concepts "semicrystalline" and "quasicrystalline" generally refer to solids, and layers in particular, that contain both crystalline and amorphous domains, with a semicrystalline layer typically containing multiple individual amorphous and crystalline domains.

[0024] The term "crystallization" is synonymous with "degree of crystallinity" or "degree of crystallinity" and refers to the proportion of crystalline matter in a semicrystalline solid. Common techniques for determining the degree of crystallinity in polymers are density measurements, dynamic differential scanning calorimetry (DSC), X-ray diffraction (XRD), infrared spectroscopy or NMR spectroscopy. The measurements determined depend on the measurement technique applied. In the present invention, the crystallization of the coating color is determined by XRD measurements.

[0025] The concept "natural polymer" is synonymous with "biochemical biopolymer", a polymer synthesised in the cells of living organisms. Natural polymers are therefore also biodegradable. Natural polymers are in particular natural polymers within the meaning of Guideline (EU) 2019 / 904 of the European Parliament and of the Council of 5 June 2019 on the reduction of the impact of certain plastic products on the environment (see Article 3(1) thereof, exceptions in the definition of plastics).

[0026] The term "derivatives of natural polymers" refers in the present invention to polymers resulting from the secondary processing of biopolymers. These are also called chemically modified polymers. Examples of derivatives of natural polymers are lignin derivatives, such as lignin esters, cellulose derivatives, and starch derivatives.

[0027] By "crystallizable organic compound" is understood in the context of the present invention an organic compound which is capable of depositing on a crystal nucleus in a substance-specific regular form to form seed crystals or crystals.

[0028] "Melting temperature" (T m ) is understood to mean the temperature at which a substance melts, i.e. passes from a solid to a liquid aggregate state. The melting temperature of polymers and crystallizable materials can be determined by dynamic differential scanning calorimetry as specified in DIN EN ISO 11357-3:2013. A heating or cooling rate of 10 K / min is preferably applied here.

[0029] "Glass transition temperature" (T G ) is the temperature at which a polymer or plastic (but only fully or partially amorphous polymers) passes from a liquid or rubber-elastic flexible state to a glassy or hard-elastic brittle state, and is therefore also called the "softening temperature". At this temperature the polymer has a viscosity of 1012 mPas. For polymers that do not have a melting temperature, the glass transition temperature is used instead of the melting temperature. The glass transition temperature can be determined, for example, by differential scanning calorimetry (DSC) as specified in DIN EN ISO 11357-2:2014.

[0030] By "contact angle" of a droplet on a surface is understood in the present invention the angle that the intersection line between the base of the droplet and the surface forms with the horizontal, which is measured in degrees and depends on various factors such as the surface tension of the liquid and the properties of the surface.

[0031] "Rolling angle" is understood in the present invention as the inclination angle of a surface when a liquid drop rolls off the surface. It usually serves to characterize superhydrophobic surfaces with very high contact angles, where the liquid drop is approximately spherical. When the contact angle is relatively small, the liquid drop can move off the surface, but usually first deforms and then slides on the surface. Under a rolling angle of 180°, even when the water drop hangs down, it does not roll off but adheres to the coating color layer.

[0032] In the present invention, a surface is referred to as "superhydrophobic" if it has a contact angle with water of 145° or more, preferably 150° or more. At such a high contact angle, typically only about 2-3% of the water droplet surface comes into contact with the superhydrophobic surface; that is, such surfaces have extremely low wettability. Moreover, superhydrophobic surfaces are characterized by a sliding angle below 10°.

[0033] Coated paper and coating color

[0034] The present invention relates to a coated paper comprising a base paper and at least one semi-crystalline coating color layer having amorphous and crystalline regions, applied indirectly or directly onto the base paper: the amorphous region comprises one or more naturally occurring polymers and / or one or more derivatives of naturally occurring polymers; the crystalline regions comprise one or more crystallizable organic compounds; and The permeability of the coated paper to at least one gas is reduced compared to the base paper.

[0035] In one embodiment of the coated paper, the permeability of at least one gas under equal total coating weight is less than the permeability of a coated paper having the same base paper and either a coating color layer made of a natural polymer or its derivatives or a coating color layer made of a crystallizable organic compound.

[0036] The coating color layer reduces the permeability of the coated paper to at least one gas compared to the base paper. This gas is oxygen (O 2 ), nitrogen (N 2 ), carbon dioxide (CO 2 ), methane (CH 4 ), hydrogen (H 2 ), water vapor, or a mixture thereof, such as air. In particular, the water vapor transmission rate (WVTR) is reduced.

[0037] The inventors have found that the barrier performance or permeability in the present system, especially the WVTR, depends on crystallization. Without wishing to be bound by theory, such an effect is based on the fact that crystallites formed from crystallizable components are embedded in an amorphous matrix of natural polymers. The crystallites are impermeable to gases, especially to polar molecules such as water in the vapor phase, due to their high packing density. To permeate a thin semi-crystalline coating color layer, the gas must "bypass the crystallites" and travel a longer path, which directly reduces the permeability coefficient, so that the semi-crystalline layer acts as a water vapor barrier. This theory behind the effect is also supported by a computer-aided model described by Muller-Plathe for diffusion in filled semi-crystalline polymers (see Muller-Plate's Habilitation Thesis, ETH Zurich, 1993, p. 67ff.).

[0038] Pure layers of natural polymers, such as lignin, clearly show higher permeabilities, as do pure layers of crystallizable organic compounds, such as stearic acid layers, which have open areas due to the free volumes between the crystallite structures through which gases can permeate.

[0039] By selecting the crystallization in this way, it is possible to adjust the permeability, and in particular the WVTR, for each system according to the invention. Below 10% crystallization, semi-crystalline systems usually have little measurable effect on the WVTR of the coated paper compared to a comparable non-crystalline layer. In one embodiment, the crystallization of the semi-crystalline coating color layer is in the range of 10% to 90%. Crystallization above 90% usually does not lead to a change in the barrier behavior, but rather to various structural defects such as defects in the film's integrity. The crystallization may be, for example, 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%, 74%, 76%, 78%, 80%, 82%, 84%, 86%, 88%, or 90%. In one preferred embodiment, the crystallization is in the range of 10% to 40%. Above 40%, only a small reduction in gas permeability is possible. In a particularly preferred embodiment, the crystallization is in the range of 15% to 25%.

[0040] The coating color used to form the semi-crystalline coating color layer preferably does not contain crystalline components, and the crystallizable organic compound is preferably not present as crystals in the coating color. In some circumstances, for example in an aqueous solvent, fatty acid molecules may be present as crystals to a small extent, especially when the fatty acid is melted in the presence of water, dispersed and cooled. Such a state is referred to in the present case as substantially non-crystalline. In one embodiment, the crystallizable organic compound is present in the coating color in a substantially non-crystalline form, i.e. it is not a coating color that contains crystalline filler material in an amorphous binder. Such a coating color layer is also referred to as a granular crystalline coating color layer, in order to distinguish it from the semi-crystalline coating color layer according to the present invention. That is, the semi-crystalline according to the present invention is not granular crystalline. The crystallization preferably occurs only upon application of the coating color layer. In one embodiment, the crystalline regions are formed during application of the coating color to the base paper. In another embodiment, the crystalline regions are formed when the coating color hardens. In one embodiment, the crystalline regions are formed both during application of the coating color to the base paper and during hardening of the coating color.

[0041] The coating color of the present invention allows for the realization of coated papers with high barrier performance, in particular with very low WVTR. In one embodiment, the WVTR is 10±1 g m -2 Based on the weight per unit area of ​​coating color of 40g m -2 d -1 not exceed.

[0042] Such WVTR is clearly lower than that of comparable systems of the prior art. Indeed, Hult et al. (2013) also reported a WVTR of 40 g m for a layer containing lignin palmitate. -2 d -1However, this layer was not measured under standard conditions, i.e., 23°C and 50% humidity. In contrast, in the present invention, the WVTR is measured at 38°C and over 90% humidity. The non-crystalline layer, consisting of lignin palmitic acid, has a WVTR of 200 g m2 when the tropical conditions of 38°C and over 90% humidity are selected. -2 d -1 This will result in a WVTR that exceeds 100%.

[0043] The WVTR of the coated paper according to the present invention is, for example, 40 g m -2 d -1 , 38g·m -2 d -1 , 36g·m -2 d -1 , 34g·m -2 d -1 , 32g·m -2 d -1 , 30g·m -2 d -1 , 28g·m -2 d -1 , 26g·m -2 d -1 , 24g·m -2 d -1 , 22g·m -2 d -1 , 20g·m -2 d -1 , 18g·m -2 d -1 , 16g·m -2 d -1 , 14g·m -2 d -1 , 12g·m -2 d -1 , 10g·m -2 d -1 , 8g·m -2 d -1 , 6g·m -2 d -1 , 4g·m -2 d -1 , 2g·m -2 d -1 , 1g·m -2 d -1By selecting the appropriate components of the coating color and adjusting the crystallization, it is possible to obtain a coating weight of 20 g m -2 d -1 Not to exceed 10 g m -2 d -1 It is possible to achieve a WVTR not exceeding 100%.

[0044] The melting temperature T of at least one crystallizable organic compound m is the glass transition temperature T of at least one natural polymer and / or at least one derivative of a natural polymer g It is preferable that it is lower than .

[0045] This is important to prevent the formation of nanostructured surface structures that would make the surface superhydrophobic but also gas-permeable, especially to water vapor. As shown in Example 7, superhydrophobic surfaces made of polymers and crystallizable organic compounds known from the prior art, in which the melting temperature of the crystallizable organic compound is above the glass transition temperature of the polymer, can withstand temperatures of up to 400 g m -2 d -1 Accordingly, as can be seen from Example 9, even in the system according to the present invention having a derivative of a natural polymer, i.e., lignin stearate and a fatty acid, the use of a fatty acid such as suberic acid having a melting temperature higher than the glass transition temperature of the lignin stearate leads to results that are clearly inferior in terms of water vapor barrier performance to the use of a fatty acid such as stearic acid having a melting temperature lower than the glass transition temperature of the lignin stearate.

[0046] Therefore, the melting temperature T of at least one crystallizable organic compound m is the glass transition temperature T of at least one natural polymer and / or derivative of a natural polymer. g For example, the melting temperature T of the crystallizable organic compound should be at least 1°C lower than the melting temperature T mis the glass transition temperature T of at least one natural polymer and / or derivative of a natural polymer by 1° C., 2° C., 3° ​​C., 4° C., 5° C., 7° C., 10° C., 12° C., 15° C., 17° C., 20° C., 22° C., 25° C., 30° C., 35° C., 40° C., 45° C., 50° C., 55° C., 60° C., 65° C., 70° C., 75° C., or 80° C. g The opening should be greater than 1° C. to ensure that no partially superhydrophobic surface is produced. In one embodiment, the melting temperature T m is the glass transition temperature T of at least one natural polymer and / or derivative of a natural polymer. g In one embodiment, the melting temperature T m is the glass transition temperature T of at least one natural polymer and / or derivative of a natural polymer. g In one embodiment, the melting temperature T m is the glass transition temperature T of at least one natural polymer and / or derivative of a natural polymer. g In one embodiment, the melting temperature T m is the glass transition temperature T of at least one natural polymer and / or derivative of a natural polymer. g The melting temperature of stearic acid is at least 30°C lower than the glass transition temperature T g In one embodiment, the melting temperature T m is the glass transition temperature T of at least one natural polymer and / or derivative of a natural polymer. g at least 50°C lower.

[0047] Thereby, the surface of the coating color layer is not superhydrophobic. That is, the coating color layer has a contact angle with water not exceeding 150°. The contact angle may be, for example, 80°, 85°, 90°, 95°, 100°, 105°, 110°, 115°, 120°, 125°, 130°, 135°, 140°, or 145°. Even if it exceeds 145°, the surface is still considered to be superhydrophobic. Therefore, it is preferred that the contact angle does not exceed 145°. In one embodiment, the contact angle does not exceed 130°. In one embodiment, the contact angle does not exceed 115°.

[0048] Furthermore, the coating color layer preferably has a rolling angle of more than 10° for a water drop of 4 μL volume. The rolling angle may be, for example, 10°, 15°, 20°, 25°, 30°, 35°, 40°, 45°, 50°, 55°, 60°, 65°, 70°, 75°, 80°, 85°, 90°, 95°, 100°, 105°, 110°, 115°, 120°, 125°, 130°, 135°, 140°, 145°, 150°, 155°, 160°, 165°, 170°, 175°, 180°. In one embodiment, the rolling angle is greater than 20°. In one embodiment, the rolling angle is greater than 40°. In one embodiment, the rolling angle is greater than 60°.

[0049] In one embodiment, the ratio of the crystallizable organic compound to the total mass of the coating color layer is in the range of 1-60 wt%. Below 1 wt%, no measurable crystallization can occur and the entire coating color layer remains amorphous. If more than 60% of the crystallizable organic compound is used, the film may become too non-uniform and may have holes that limit the barrier performance. For example, the crystalline organic compound can be 1%, 2%, 4%, 5%, 6%, 8%, 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%, or 60% by weight in the coating color layer. The present invention can show through experiments that the barrier performance does not increase consistently with increasing crystallization. Rather, for example, for the crystallizable organic compound stearic acid, the minimum value of WVTR is obtained at a weight ratio of approximately 30% relative to the total mass of the coating color layer. If the content exceeds 50% by weight, usually no improvement in barrier performance can be expected. If the content is below 3% by weight, only slight crystallization that has little effect on barrier performance can be achieved. In one embodiment, the proportion of the crystalline organic compound is in the range of 3 to 50% by weight. In one embodiment, the proportion of the crystalline organic compound is in the range of 5 to 40% by weight. In one embodiment, the proportion of the crystalline organic compound is in the range of 25 to 35% by weight.

[0050] The crystallizable organic compounds are preferably branched, at least partially linear, hydrocarbons, the accumulation of homogeneous chains of such linear hydrocarbons allowing the formation of crystals or crystallites.

[0051] The crystallizable organic compounds usable according to the invention are, for example, 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, as well as their dicarboxylic acid esters, dicarboxylic acid amides, or salts of dicarboxylic acids. Examples of dicarboxylic acids usable according to the invention are tetradicarboxylic acids, hexadicarboxylic acids, octadicarboxylic acids, icosanediacids, or docosanediacids. The crystallizable organic compound is preferably not starch. The crystallizable organic compound is preferably not suberic acid, especially when the natural polymer is lignin or lignin stearate.

[0052] The fatty acids used as crystallizable organic compounds may be saturated or unsaturated fatty acids containing 12 to 40 carbon atoms. Examples of saturated fatty acids are lauric acid, myristic acid, palmitic acid, margaric acid, stearic acid, aratic acid, behenic acid, lignoceric acid, cerotic acid, montanic acid, melissic acid, lacteric acid, gedaic 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, cetoleic acid, erucic acid, and nervonic acid. Examples of unsaturated fatty acids are linoleic acid (LA), alpha-linolenic acid (ALA), gamma linolenic acid (GLA), calendullic 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, (clup(no)donic acid), (DPA-3) docosahexaenoic acid (cervonic acid, clupanodonic acid, DHA), and tetracosahexaenoic acid (nisinic acid).

[0053] In one embodiment, the fatty acid used as the crystallizable organic compound has 16-18 carbon atoms and 0 or 1 double bond. In one embodiment, the fatty acid is selected from margaric acid, stearic acid, palmitic acid, linoleic acid, α-linoleic acid, γ-linoleic acid. In one embodiment, the crystallizable organic compound is stearic acid or its amide or salt.

[0054] The fatty acid salts according to the present invention are chromium(III) chloride complexes containing fatty acids, as well as aluminum, calcium, sodium, potassium and ammonium salts. Preferred fatty acid salts are monovalent salts consisting of sodium, potassium or ammonium ions.

[0055] The at least one crystallizable organic compound may be present in the coating color as a fatty acid mixture or as a wax. As wax, according to the invention, in particular carnauba wax, candelilla wax, beeswax and Japan wax come into consideration.

[0056] In 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 linolenic acid, a mixture of stearic acid, palmitic acid, and linolenic acid, a mixture of stearic acid, oleic acid, and linolenic acid, a mixture of stearic acid, oleic acid, and linolenic acid, a mixture of stearic acid, linoleic acid, and linolenic acid.

[0057] According to the invention, the proportion of natural polymer or its derivatives relative to the total mass of the coating color layer may be in the range of 40-99% by weight. In this case, only one polymer or its derivative may be used, or a mixture of natural polymers, a mixture of derivatives of natural polymers, or a mixture of natural polymers and derivatives of natural polymers may be used. Without wishing to be bound by theory, the natural polymer or its derivatives is involved in the formation of amorphous regions on the one hand and crystalline regions on the other hand. In this case, it is believed that the natural polymer forms an amorphous matrix in which the crystalline regions are embedded. The proportion of natural polymer depends on the proportion of crystallizable organic compounds and the possible presence of other components. For example, the natural polymer or derivative thereof may have a proportion of 40%, 42%, 44%, 46%, 48%, 50%, 52%, 54%, 56%, 58%, 60%, 62%, 64%, 66%, 68%, 70%, 72%, 74%, 76%, 78%, 80%, 82%, 84%, 86%, 88%, 90%, 92%, 94%, 96%, 98%, or 99% by weight. In one embodiment, the proportion of natural polymer is in the range of 50-95% by weight. In one embodiment, the proportion of natural polymer is in the range of 60-90% by weight. In one embodiment, the proportion of natural polymer is in the range of 65-75% by weight.

[0058] Natural polymers that can be used according to the invention are, for example, hydrocarbons such as natural rubber and balata, proteins such as collagen, keratin, fibroin, nucleic acids, polysaccharides such as alginates, agar, cutin, suberin, lignin, cellulose, chitosan, and starch, lipids, polylactic acid (PLA), polyhydroxybutyric acid (PHB), and polyhydroxyalkanoates (PHAs). Derivatives according to the invention are cellulose derivatives such as methylcellulose (MC), hydroxypropylmethylcellulose (HPMC), methylhydroxyethylcellulose (MHEC), methylated starch, ethylated starch; starch derivatives such as hydroxyethyl starch, hydroxypropyl starch, carboxymethyl starch, starch formate, starch acetate, starch propionate, or starch butyrate, suberin derivatives, cutin derivatives, or lignin derivatives. These natural polymers and their derivatives are considered to be suitable for forming an amorphous matrix around a crystallizable organic compound. The crystallizable organic compounds are preferably not identical to naturally occurring polymers and their derivatives, and therefore the crystalline and amorphous regions of the coating color layer of the present invention are not different states of one substance.

[0059] Fatty acids are absolutely of no concern to the human organism and are listed on the food additive list under the name E 570, i.e. suitable for food ("dual-use additives"). This is an advantage for their use in food packaging materials, such as coated paper according to the invention, since due to (relatively long-term) contact migration of substances from the packaging into the food may possibly occur.

[0060] In one embodiment, the natural polymer is suberin. Suberin is a plant biopolymer stored in the cell wall. Suberized cells are found in the secondary epidermis as well as in underground plant organs. Suberin derives its name from the cork oak (Quercus suber). Suberin can be classified into two different domains: polyphenolic and polyaliphatic. In the polyaliphatic fraction, dicarboxylic acids, hydroxy acids, long chain fatty acids and hydroxycinnamic acids are found. Current research further leads to the suggestion that glycerol is also a very potent bond monomer. The phenolic proportion shows similarities to lignin, where the proportion of monolignols is clearly lower than that of lignin. Based on the ester bonds of suberin, the model of the chemical structure of suberin is similar to that of lignin fatty acid esters, which suggests that the results presented here can be transferred to suberin.

[0061] In one embodiment, the natural polymer is lignin. Lignin is a polymeric aromatic substance of lignifying plants, filling the spaces between the cell membranes to make them lignified. Lignin can be considered as a polymeric derivative of phenylpropane, consisting of a structure that can be attributed to coumaryl alcohol, coniferyl alcohol, or sinapyl alcohol, depending on the type of tree (MR about 5000-10000). The lignins of different types of trees or plants (grass, broadleaf or coniferous) differ in the percentage proportion of each alcohol. These components are reticulated with each other in various ways (ether and C-C bonds), thus forming a three-dimensional network. Furthermore, in addition to the diversity of each individual lignin molecule, the lignins of different types of trees or plants are also differentiated by the proportion of alcohols or phenyl groups derived therefrom: coniferous lignins mainly contain coniferyl units (approximately 90%), which have guaiacyl groups (3-methoxy-4-hydroxy-phenyl groups), and are therefore called G lignin. Hardwood lignins contain varying proportions of guaiacyl and sinapyl moieties containing syringyl (3,5-methoxy-4-hydroxy-phenyl) groups. The syringyl proportion can be between 5 and 65 percent. The resulting lignin is called GS lignin. Lignins from partially lignified grasses and other monocotyledonous plants are characterized by a high proportion of coumaryl moieties, approximately 15 to 35 percent, which form para-hydroxy-phenylpropane, forming HGS lignin with a similar proportion of syringyl and 50 to 70 percent of guaiacyl.

[0062] According to the present invention, the lignin may be obtained from a coniferous tree, a broadleaf tree, a herbaceous plant, or an annual plant. In one embodiment, it is a lignin obtained from a coniferous tree. In another embodiment, it is a lignin obtained from a broadleaf tree.

[0063] Various methods for obtaining lignin are known to those skilled in the art, including the Kraft process, the Sulfite process, the Soda-Antrachinon process, the GRANIT process, the Alcell process,TM The methods include the Kraft process, and the Organocel process. In one embodiment, this is lignin obtained from softwoods by the Kraft process. These methods are summarized in Nitz et al. 2001. In one embodiment, this is lignin obtained from hardwoods by the Kraft process.

[0064] In one embodiment, the derivative of a natural polymer is an ester of a natural polymer. Esters of natural polymers suitable for the present invention are cellulose esters, starch esters, cutin esters, suberin esters, and lignin esters. In one embodiment, it is an ester of lignin and one or more fatty acids, hydroxy fatty acids, or dicarboxylic acids.

[0065] The acid used for esterification of lignin preferably has a similar chain length and a similar degree of branching to the acid used as the crystallizable organic compound. The chain lengths of both acids should not differ by more than 8 C atoms. Preferably, the chain lengths should not differ by more than 5 C atoms. It is especially preferred that the difference in chain length should not exceed 3 atoms. Additionally, the number of double bonds, i.e. the degree of saturation, between the acid used for esterification of lignin and the acid used as the crystallizable organic compound should match.

[0066] In one embodiment, the coating color or coating color layer comprises an ester of a natural polymer, the fatty acid being identical to at least one fatty acid used as the crystallizable organic compound. The selection of the same fatty acid provides the best prerequisites for the formation of crystals in the semi-crystalline coating color layer. In one embodiment, the coating color or coating color layer comprises a lignin fatty acid ester, the fatty acid being identical to at least one fatty acid used as the crystallizable organic compound. A further advantage of using the same fatty acid is that surplus fatty acids that did not react during esterification can be utilized, thereby saving one method step. In one embodiment, the crystallizable organic compound is stearic acid and the derivative of a natural polymer is lignin stearate.

[0067] The synthesis of esters of natural polymers can be carried out according to the principle of Schotten-Baumann esterification (see Example 2). Suitable reaction conditions are well known to those skilled in the art and can be taken from Example 2. For example, lignin stearate can be obtained by reaction of stearic acid chloride with kraft lignin.

[0068] The lignin stearates utilized for the production of coated paper according to the present invention may have a degree of esterification of at least 40%. The degree of esterification may be, for example, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90% or 95%. In an embodiment, the degree of esterification is at least 90%.

[0069] Furthermore, lignin stearate has a softening temperature T in the range of 70 to 140°C. gAbove 140°C, problems may arise in industrial applications, since problems in processing (melt dispersion, drying, film formation) are expected. Below about 70°C, the matrix remains too soft after drying, which may result in, for example, "sticking" during winding of the paper web and subsequent delamination of the coating when the web is unwound. This temperature may be, for example, 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. More preferably, the lignin stearate has a softening temperature T in the range of 120-140°C. g has.

[0070] The coating color layer may contain one or more fillers, such as protective colloids or fillers, depending on the application and requirements. Protective colloids are particularly suitable for keeping the particles stable in aqueous dispersions and thus allowing a uniform coating of the paper. Suitable protective colloids are polyvinyl alcohols, polysorbates, PEG alkoxylates, and sorbitan fatty acid esters (SPAN). Suitable fillers are pigments, in particular nanoclays. Nanoclays are accelerators for crystallization.

[0071] The natural polymers or their derivatives and the crystallizable organic compounds used may also contain impurities resulting from their preparation or production. Impurities that may come into consideration are, for example, unesterified lignin polymers or polysaccharides such as cellulose or xylene. These impurities preferably make up only a small proportion of the coating color and thus of the resulting coating color layer. In one embodiment, the proportion of impurities in the coating color layer relative to the total mass of the coating color layer is below 1% by weight.

[0072] In one embodiment, the coating color is free of synthetic polymers that are petroleum-based and not biodegradable, except for unavoidable impurities.

[0073] Based on the materials present in the coating color layer, the coated paper is biodegradable. "Biodegradable" refers to the ability of organic chemicals to be degraded biologically, i.e. by living organisms or their enzymes. In the ideal case, such chemical transformation proceeds to complete mineralization, but may also stop in the case of decomposition-stable transformation products. The OECD guidelines for the testing of chemicals are generally accepted and are also applied within the framework of chemical authorization. The test of the OECD test series 301 (AF) proves the ready biodegradability under aerobic conditions. Different test methods can be applied for soluble or sparingly soluble substances as well as for volatile substances. "Biodegradable" or "biologically degradable" in the sense of the present invention refers to a paper that has a biodegradability of at least 40% measured according to OECD 301 F or at least 20% measured according to OECD 302 C (MITI-II-test) and thus has an essential or fundamental degradability. This corresponds to the limit value for OECD 302 C according to the "Revised Introduction to the OECD Guidelines for testing of Chemicals, section 3, Part 1, dated 23 March 2006". Microcapsule walls are also referred to as rapidly biodegradable in this case if they exceed a limit value of at least 60% as measured according to OECD 301 F.

[0074] In one embodiment, the coated paper is readily biodegradable according to OECD 301.

[0075] In addition, coated papers are recyclable. Paper recycling refers to the pretreatment of waste paper, used board and cardboard in paper industry plants by dissolving them, in order to produce new paper, board and cardboard from them again. To a small extent, recycled waste paper is first used to produce waste paper stock, which is then used for the production of new paper. Printing ink removal or deinking (from the English ink = "printing ink", "ink") is a key process in paper recycling to remove printing ink from printed waste paper. The recyclability can be evaluated, for example, by the INGEDE-Methode 11. The coated paper according to the invention achieves a deinking score of more than 50 according to the INGEDE-Methode 11. A deinking score of more than 70 is preferred.

[0076] The components of the coatable layer used according to the invention enable the coated paper to be approved for direct or indirect food contact, in particular suitable for approval according to the European Food Safety Authority guidelines.

[0077] Basically, any kind of paper can be considered as the base paper for the coated paper, i.e. cardboard, paperboard or even normal paper. For packaging foodstuffs, low basis weight papers are often considered, since they are flexible and material-saving. It is precisely in such papers that the coating color layer according to the invention leads to a significant improvement in the barrier properties.

[0078] In one embodiment, the base paper is 150 g · m -2 The basis weight is, for example, 150 g · m -2 , 145g · m -2 , 140g · m 2 , 135g · m -2 , 130g · m -2 , 125g · m-2 , 120g · m -2 , 115g · m -2 , 110g · m -2 , 105g · m -2 , 100g · m -2 , 95g · m -2 , 90g · m -2 , 85g · m -2 , 80g · m -2 , 75g · m -2 , 70g · m -2 , 65g · m -2 , 60g · m -2 , 55g · m -2 , 50g · m -2 , 45g · m -2 , 40g · m -2 , 35g · m -2 Or 30g · m -2 In one embodiment, the basis weight is 100 g · m -2 In one embodiment, the basis weight is less than 80 g · m -2 In one embodiment, the basis weight is 50 to 80 g · m -2 is within the range.

[0079] The coated paper may include further layers in addition to the semi-crystalline coating color layer. In one embodiment, the coated paper includes further layers selected from a coating color, an ink, a sealing medium, and an adhesive.

[0080] This further layer may be disposed on top of the semi-crystalline coating color layer, between the base paper and the semi-crystalline coating color layer, or on the side of the base paper facing the semi-crystalline coating color layer.

[0081] That is, the semi-crystalline coating color layer may be applied directly onto the base paper. In this case, the semi-crystalline coating color layer is in direct contact with the base paper. Indirect application means that one or more layers are between the coating color and the base paper.

[0082] The further layer may in particular reduce the permeability of the coated paper to at least one gas compared to the base paper, or form a barrier against liquids or viscous substances such as fats, oils, hydrocarbons, etc.

[0083] The other layer is, in particular, a) at least one hydrophobic polymer, which may be based, for example, on polyacrylate, styrene / butadiene copolymer, and / or polyolefin, b) at least one hydrophilic polymer, which may be based, for example, on polyvinyl alcohol, c) at least one inorganic pigment, such as a flake pigment, e.g. a layered silicate such as kaolin; d) at least one inorganic pigment and a binder; e) may contain amorphous and crystalline regions, such as the coating color composition of the present invention; f) may comprise 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, low molecular weight polyolefins, polyterpenes, and mixtures thereof; g) reducing or preventing the migration of substances, in particular hydrophobic substances, such as those mentioned in point e) above, thereby making it possible to prevent or reduce the migration of substances, for example from an underlying layer, into food, in particular into fat-containing food, h) may comprise or consist of at least one metal, such as aluminum, gold, and / or a metal oxide, such as aluminum oxide, in particular a metal coating layer; i) may be at least heat sealable or cold sealable; j) may include at least one adhesive; k) It may comprise or consist of at least one thermoplastic material, in particular as a heat-sealable material.

[0084] The base paper may be a base paper that is coated on one or both sides or it may be an uncoated base paper.

[0085] The coated base paper is surface-treated with a binder-containing coating color. The binder-applying material is a coating color that may be based on starch, starch derivatives, chalk, kaolin, casein, or plastic dispersions. This allows the base paper to obtain a more sealed, smooth, and stable surface.

[0086] However, uncoated base paper may be surface treated, up to a maximum of 5 g / m 2 The pigment may include

[0087] For use as food packaging, paper requires a certain tear strength or breaking load. In one embodiment, the coated paper has a breaking load in the fiber direction based on width of 3.0 to 6.0 kN·m -1 The breaking load in the direction of the fiber based on the width is, 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 In one embodiment, the breaking load in the fiber direction relative to the width is 3.5 to 5.5 kN m -1 In one embodiment, the breaking load in the fiber direction based on the width is in the range of 4.0 to 5.0 kNm -1 is within the range.

[0088] The semi-crystallization induced by the invention is achieved by a coating color which contains, by way of example, a fatty acid as a crystallizable organic compound, in particular in combination with a derivative of a natural polymer, lignin.The invention therefore relates in a second aspect to a coating color for coating paper, which comprises at least one solvent, at least one crystallizable organic compound and at least one natural polymer and / or derivative of a natural polymer.

[0089] As explained for the coating color layer of the coated paper according to the first embodiment, the crystallizable organic compound is preferably selected from fatty acids, hydroxy acids or dicarboxylic acids, or their esters, amides or salts. Furthermore, the crystallizable organic compound is present in amorphous form in the coating color. Since the coating color is the starting material for forming the coating color layer, the definition of the crystallizable organic compound in the first embodiment of the invention applies here as well.

[0090] The natural polymers are in particular selected from hydrocarbons such as natural rubber and balata, proteins such as collagen, keratin, fibroin, nucleic acids, polysaccharides such as alginates, agar, cutin, suberin, lignin, cellulose, chitosan and starch, lipids, polylactic acid (PLA), polyhydroxybutyric acid (PHB) and polyhydroxyalkanoates (PHAs). For the natural polymers or derivatives the definition of the natural polymer or derivative in the first aspect of the invention applies here as well.

[0091] However, unlike the coating color layer, the coating color additionally comprises at least one solvent. Suitable solvents are water, tetrahydrofuran (THF), toluol, ethyl acetate, and alcohols such as ethanol and isopropanol. The solvent is preferably water.

[0092] In one embodiment, the fatty acid in the ester of the natural polymer, particularly in the lignin ester, is the same as at least one fatty acid utilized as the crystallizable organic compound, in one embodiment, the crystallizable organic compound is stearic acid and the derivative of the natural polymer is lignin stearate.

[0093] Based on the solvent proportion, the proportion of the natural polymer and / or its derivative in the coating color is different from the proportion in the coating color layer. In one embodiment, the proportion of the natural polymer and / or its derivative in the total mass of the coating color is in the range of 6-30% by weight. This proportion may be, for example, 6%, 8%, 10%, 12%, 14%, 16%, 18%, 20%, 22%, 24%, 26%, 28%, or 30% by weight. In one embodiment, this proportion is in the range of 8-25% by weight. In another embodiment, this proportion is in the range of 15-25% by weight.

[0094] In one embodiment, the proportion of the crystallizable organic compound relative to the total mass of the coating color is in the range of 2-15% by weight. This proportion may be, for example, 2%, 4%, 6%, 8%, 10%, 12%, 13%, 14%, or 15% by weight. In one embodiment, this proportion is in the range of 4-12% by weight. In one embodiment, this proportion is in the range of 5-8% by weight.

[0095] In one embodiment, the proportion of the solvent to the total mass of the coating color is in the range of 60-95%. This proportion may be, for example, 60%, 62%, 64%, 66%, 68%, 70%, 72%, 74%, 76%, 78%, 80%, 82%, 84%, 86%, 88%, 90%, 92%, 94% or 95% by weight. In one embodiment, this proportion is in the range of 70-90% by weight. In one embodiment, this proportion is in the range of 75-85% by weight.

[0096] At a solids content of 10% by weight, i.e. at a solvent content of 90% by weight, the proportion of polymer is preferably in the range of 6.5% to 7.5% by weight and the proportion of crystallizable organic compounds is preferably in the range of 2.5% to 3.5% by weight. At a solids content of 15% by weight, i.e. at a solvent content of 85% by weight, the proportion of polymer is preferably in the range of 9.8% to 11.3% by weight and the proportion of crystallizable organic compounds is preferably in the range of 3.8% to 5.3% by weight. At a solids content of 25% by weight, i.e. at a solvent content of 75% by weight, the proportion of polymer is preferably in the range of 16.3% to 18.8% by weight and the proportion of crystallizable organic compounds is preferably in the range of 6.3% to 8.8% by weight. At a solids content of 30% by weight, i.e. at a solvent content of 70% by weight, the polymer content is preferably in the range of 16.3% to 18.8% by weight and the crystallizable organic compound content is preferably in the range of 6.3% to 8.8% by weight. At a solids content of 40% by weight, i.e. at a solvent content of 60% by weight, the polymer content is preferably in the range of 26.0% to 30.0% by weight and the crystallizable organic compound content is preferably in the range of 10·0% to 14.0% by weight.

[0097] Manufacturing method

[0098] The crystallization of the semi-crystalline coating color layer in the coated paper of interest here depends in particular on the method applied for producing the coated paper. Thus, according to a third aspect, the present invention relates to a method for producing a coated paper having a base paper and a semi-crystalline coating color layer, comprising the following steps: a) preparing a coating color according to the second aspect by melt dispersion, high pressure dispersion, or spray drying of the components, followed by mechanical dispersion; b) preparing the base paper; c) applying a coating color to the base paper; and d) curing the coating color while forming a semi-crystalline coating color layer.

[0099] In one embodiment, application of the coating color to the base paper is preferably carried out by a curtain or blade method.

[0100] As explained with respect to the crystallization of the coating color layer of the coated paper of the present invention based on the first embodiment, the method of the present invention makes it possible to adjust the crystallization of the semi-crystalline coating color layer by the proportion of the crystallizable organic compound relative to the total mass of the coating color layer.

[0101] In addition, the curing temperature, curing time, and curing pressure also have an effect on crystallization.

[0102] In one embodiment of the method, the curing temperature is in the range of 20-300° C. In one embodiment of the method, the curing temperature is in the range of 120-140° C.

[0103] In one embodiment of the method, the curing time is in the range of 10 seconds to 15 minutes. In one embodiment of the method, the curing time is in the range of 1 to 3 minutes.

[0104] In one embodiment of the method, the curing pressure is in the range of 0.2 bar to 3 bar. In one embodiment of the method, the curing pressure is in the range of 0.9 bar to 1.1 bar.

[0105] As coated paper is produced through the process described above, the present invention is also directed to coated paper produced by the process according to the second aspect.

[0106] packaging

[0107] According to a fourth aspect, the present invention relates to packaging for food products comprising a coated paper according to the first aspect.

[0108] This may be, for example, a package of dry food, a package of food sold cold requiring further cooking, a package containing portion-sized food for more than one person, or a package of portion-sized food sold as more than one unit.

[0109] Packaging that comes into consideration is, for example, a stand-up bag packaging, a tube bag packaging, or a paper wrapper, etc. In one embodiment, the packaging is a tube bag packaging.

[0110] Working Example

[0111] Example 1 - Characterization of lignin The main focus of lignin characterization is its molar mass and the number of hydroxyl groups. Molar Mass The determination of the molar mass is carried out by GPC.

[0112] Instrument parameters-GPC4

[0113] [Table 1]

[0114] [Table 2]

[0115] standard [Table 3]

[0116] FIG. 1 shows an example of the kraft lignin used. Number average molar mass Mn: 1000g * m -2* d -1 Weighted average molar mass Mw: 5000g * m -2* d -1

[0117] Hydroxy group number The number of hydroxy groups can be determined using titration and 31P-NMr.

[0118] Titration: The OH number of the kraft lignin (KL) is determined in accordance with DIN EN ISO 4629-1.

[0119] 31P-NMR spectroscopy Phosphorylation of lignin derivatives is carried out according to the rules of Granata et al. To do so, 25 mg of dry lignin is dissolved in 150 μL of DMF. After dissolution, 100 μL of pyridine and 200 μL of a solution of the internal standard endo-N-hydroxy-5-norbomen-2,3-dicarboximide (25.0 mmol in pyridine / CDCl3 1.6:1) are added. * L-1) and 50 μL of a solution of chromium(III)-acetylacetonate (32.64 mmol / L in pyridine / CDCl3 1.6:1) are added. The solution is flushed with argon for a few minutes, followed by the addition of 150 μL of the phosphite reagent 2-chloro-4,4,5,5-tetramethyl-1,3,2-dioxophosphorane (0.944 mmol) and 300 μL of CDCl3 under an argon atmosphere. The solution thus obtained is placed in an NMR tube which is flushed with argon.

[0120] From the integration of the signals, the amount of hydroxyl groups can be calculated. For the kraft lignin shown in Figure 2, the amount of hydroxyl groups is 6.18 mmol / g and the amount of carboxyl groups is 0.5 mmol / g.

[0121] Example 2 - Preparation of esterified lignin Lignin stearate was synthesized from stearic acid chloride and kraft lignin based on the principle of Schotten-Baumann esterification.

[0122] [ka]

[0123] Lignin was dissolved in dry 1,4-dioxane (50 g / L) (N 2After about 1 hour, stearic acid chloride (2.8 g per g lignin) and pyridine (0.25 g per g lignin) were added. The reaction was stirred at 80° C. for 6 hours.

[0124] The reaction solution was subsequently stirred in 3 L of water for 2 h. The precipitate was filtered (Po.2), washed with water and dried at 40° C. in a vacuum drying cabinet.

[0125] The solid was placed in 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 and the solid was placed in 200 mL of ethanol again, stirred at 60 °C for about 1 h, cooled to room temperature, and centrifuged. This step was repeated approximately 2-3 times.

[0126] The solid was dried in a vacuum drying cabinet at 40° C. To remove possible insoluble residues, the solid was dissolved in a small amount of THF, the solution was centrifuged, and the decanted solution was spun on a rotary evaporator, thus obtaining the product.

[0127] The synthesis procedure was repeated using Croda stearamide, candelilla wax, and carnauba in place of stearic acid.

[0128] Example 3 - Characterization of Lignin Esters The most important factor in characterizing lignin esters is the degree of esterification. 31 This was determined by P-NMR spectroscopy and titration.

[0129] 31 P-NMR spectroscopy The degree of esterification can be calculated from the ratio of the substance amount of hydroxyl groups between the lignin ester (nLE) and the kraft lignin (nKL) used. The total substance amount nKL of hydroxyl groups (-OH and -COOH) in the kraft lignin used is 6.68 mmol per gram of lignin (see Example 1). The substance amount of hydroxyl groups in the lignin ester can be determined in a similar manner. The spectrum obtained is shown in FIG. 3.

[0130] Therefore, the amount of hydroxyl group (-OH) is 1.10 mmol. * g -1 It is. The amount of carboxyl group (-COOH) is 0.09 mmol. * g -1 It is. Total amount of hydroxyl groups (-OH and -COOH) n LE is 1.19 mmol * g -1 It is.

[0131] The degree of esterification E is calculated as follows:

[0132]

number

[0133] Titration according to DIN EN ISO 4629-1:2016

[0134] Softening temperature The softening temperature of the lignin ester is determined visually. A small amount of powdered lignin ester is placed on a watch glass and placed in a ventilated oven. The oven temperature is increased in steps of 10 °C and the temperature at which the powder melts into flowing droplets is recorded. The softening temperature of lignin stearate is about 130°C.

[0135] Infrared spectroscopy Figure 4 shows the IR spectrum of lignin stearate in comparison with kraft lignin and stearic acid. The 1750 cm peak represents the C=O vibration of the ester. -1 Successful conversion can be recognized by looking at the nearby signal. In comparison, the C=O vibration of the acid is at 1700 cm -1 Located nearby.

[0136] 1H-NMR spectroscopy FIG. 5 shows the 1H-NMR spectrum of lignin stearate.

[0137] Example 4 - Coating Color Creation

[0138] A) Organic solvent-based coating colors The solids content of the coating color was 10-25 weight percent. 1 g of a mixture of lignin stearate and stearic acid (e.g., 7:3) was placed in a 5 mL container with a lid and dissolved in 3 mL of a mixture of tetrahydrofuran (THF) and ethyl acetate (EE) (1:2). The preparation was repeated using stearamide, candelilla wax, and carnauba wax instead of stearic acid. The solvent mixture was changed depending on the wax used to ensure solubility and subsequent wetting on the coated paper. Lignin stearate / carnauba wax and lignin stearate / candelilla wax coating colors were prepared in a 2:1 mixture of THF / EE.

[0139] B) Water-based coating colors containing spray-dried lignin The solids content of the coating color was 10-25 weight percent. 3.75 g of the 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 Speedmixer cup. A hole was punched in the lid of the cup. The dispersion was degassed in the Speedmixer at 800 rpm and 30 mbar pressure for 4 minutes. The preparation was repeated using stearamide, candelilla wax, and carnauba wax in place of stearic acid.

[0140] Example 5 - Preparation of coated paper An RK K303 multi-coater (see Table 1) was used to coat the paper. The base paper was placed on top of the broke paper (Makulaturpapier) so that the standard K bar to be clamped rested on top of the base paper. The corresponding bar was clamped in the multicoater. A weight was placed on the paper behind the bar. The desired coating speed was adjusted (10-20 m / min for organic media, 3 m / min for aqueous dispersions). The coating color (approximately 3-5 mL) was applied to the paper with a pipette in front of the bar and across the width of the paper, starting the coating process. The bar then moved over the paper, distributing the coating color evenly over it.

[0141] After coating, the paper was transferred onto a cardboard support, the corners were clamped to prevent curling, and dried in an oven at 130°C for 10 minutes (organic medium: evaporation of solvent into room air, melting of coating at 130°C for approximately 3 minutes).

[0142] [Table 4]

[0143] Example 6 - Determination of water vapor permeability of coated paper The water vapour permeability is determined gravimetrically in accordance with DIN 53122-1.

[0144] A circular specimen with a diameter of 6.3 cm is cut from the paper to be tested. A desiccant (e.g. silica gel pearls) is placed in the measuring vessel. A sealing ring is placed on the edge of the vessel, the specimen is placed on the sealing ring with the water vapor barrier side facing the desiccant, and the sealing ring and metal ring are placed on top of the specimen. The vessel is closed with a lid with a hole of 5.7 cm cross section. A schematic cross section of such a measuring structure can be seen in the drawing.

[0145] The measurement vessel thus prepared is placed in a climate chamber with a temperature of 38 °C and a relative humidity of > 90%. After approximately 16 hours of conditioning in the climate chamber, the measurement vessel is weighed. After 2-3 hours intervals, new weighing is carried out until at least three measurements have been obtained. Between each weighing, the measurement vessel is left in the climate chamber.

[0146] From the mass gain, the unit of grams per square meter per day (g * m -2* d -1 ) the water vapor permeability can be calculated. At least two specimens are measured for each barrier to be tested. a) Stearic acid b) Candelilla c) Carnauba d) Stearic acid amide The results for the coverage are shown in FIG.

[0147] Comparison with the method of Hult et al. (Measurement: Coatings made from aqueous dispersions with a dry content of 20% (spray-dried lignin) in a 1% SPAN-60 solution Tropical conditions 36.2+-20,0g * m -2 d -1 :(Two measurements: 50.4 and 22.1g * m -2 d -1 )The first value is presumably caused by a missing part.

[0148] Hult Compliant: 2.0+-0.1g * m-2 d -1 (Two measurements: 2.0 and 1.9 g * m -2 d -1 )

[0149] The pure lignin stearate-coated paper was 368.0 ± 10.6 g m -2 d -1 and provides almost no barrier effect against water vapor.

[0150] As the proportion of stearic acid was increased, the result was 17.1±1.0 g m -2 ·day -1 If the proportion of stearic acid is further increased, the WVTR increases again and the barrier performance deteriorates.

[0151] Thus, by using a composite of lignin stearate and stearic acid with a stearic acid content of 30% by weight, it is possible to achieve very good barrier performance against water vapor under tropical conditions.

[0152] Low WVTR values ​​were also achieved using wax b) candelilla wax, carnauba wax, and stearic acid. For candelilla wax, the minimum was also near 30% by weight, whereas for carnauba wax, the minimum was near 50% by weight.

[0153] Example 7 (comparison) - Examination of the surface structure and WVTR of superhydrophobic layers based on DE 10 2017 108 577 but not based on the invention In order to prove that the layer according to the invention is structurally distinct from the superhydrophobic layer according to DE 10 2017 108 577, a base paper was coated with a superhydrophobic layer according to DE 10 2017 108 577 according to Example 1. As base paper, a 100 mm thick paper sheet made of hardwood and softwood pulp with an overall basis weight of 63 g / m 2 First, polymer CSE was used. 3This was coated with an aqueous dispersion of alkyl-ketene-dimer (AKD) (Basoplast 2030 LC, BASF) of 10 g / m. The weight per unit area of ​​this coating was 10 g / m. 2 Polymer CSE 3 is a fully substituted cellulose ester of stearic acid (DS:3).

[0154] After complete drying, the substrates were heated to 120° C. for 5 minutes in a drying cabinet and subsequently cooled under laboratory conditions ((22±3° C. / 35% relative humidity, RF).

[0155] The melting temperature of AKD, as determined using dynamic differential scanning calorimetry (DSC), is -60°C, and the polymer CSE 3 The melting temperature of was -55°C.

[0156] After the coated paper had completely cooled, the crystallization of the wax resulted in a nanostructured superhydrophobic surface, which can be seen in the scanning electron micrograph (see FIG. 7A). The contact angle was determined at constant temperature and humidity (23°C, 50% relative humidity) using a Data Physics OCA35 with a tiltable table. From the photographs, the contact angle was calculated with the aid of the software SCA 4.5.2 Build 1052. No magnification was applied. The contact angle of a 4 μl water droplet was 159±3° (see FIG. 7B).

[0157] Example 8 - Examination of the surface structure and hydrophobicity of the paper according to the present invention A coating color based on a mixture of lignin stearate and stearic acid (7:3, i.e. 30% stearic acid proportion) was prepared according to Example 3. For this purpose, 1 g of this mixture was weighed into a 5 mL container with a lid and dissolved in 3 mL of a mixture of THF and EE (1:2).

[0158] This coating colour is applied to a pulp made of hardwood and softwood pulp with a total basis weight of 63 g / m 2 CCK coated paper was coated as described in Example 3 (coating application rate: 5 g / m2 After coating, the paper was transferred onto a cardboard support, corners were clamped to prevent curling, and dried in an oven at 130° C. for 10 minutes.

[0159] The glass transition temperature (T g ) is approximately 130°C. The melting temperature of stearic acid is 69°C, i.e., the T g Therefore, the formation of a superhydrophobic layer was not expected. This is supported by the scanning electron micrograph of the lignin stearate-stearic acid layer in Figure 8A, which shows a surface structure that is clearly different from that of the superhydrophobic layer.

[0160] The contact angle of a 4 μl water droplet was 103.2 ± 1.4° (see FIG. 8B). As expected based on the low contact angle, the rolling angle could not be easily determined. The rolling angle (RoA) of a 4 μL water droplet was not measurable because the instrument only allows for a tilt of 70°, at which no rolling was observed yet. Therefore, various drop volumes were applied and the rolling angle was determined. The results are shown in the graph in FIG. 9.

[0161] By fitting the curve, the theoretical sliding angle of a 4 μL water droplet on the lignin stearate-stearic acid layer was calculated (see Table 2). The calculated sliding angle of a 4 μL droplet is greater than 180°, meaning that no sliding will occur.

[0162] [Table 5]

[0163] Example 9 - Comparison of WVTR of coated papers according to the present invention To test the effect of the ratio of melting temperatures of crystallizable organic compounds on WVTR, coatings consisting of stearic acid or suberic acid as crystallizable organic compounds and lignin stearate as natural polymers were prepared as described in Example 8, with varying ratios of fatty acids. A mixture of THF and methanol (1:1) was used to prepare the suberin-containing coating color.

[0164] Stearic acid is T m The melting temperature of lignin stearate is 69°C, i.e., the glass transition temperature T g ~130℃. In contrast, the melting temperature of suberic acid, T m is T m ~140°C, which is above the glass transition temperature of lignin stearate.

[0165] Coating colors were prepared as described in Example 8, but with varying amounts of stearic or suberic acid: the fatty acid percentages were 20%, 30%, 40%, 50% or 60% by weight.

[0166] These coating colors were coated onto the corresponding base papers according to Example 8. Upon completion, the WVTR of the coated papers was determined as described in Example 6. The results are shown in FIG.

[0167] As can be seen from this graph, the suberic acid-lignin stearate coating has a minimum value of 200 g m at 30% by weight of suberic acid. -2 d -1 The coating containing stearic acid also had a WVTR value of 24 g m at 30 wt.%. -2 d -1 It was clearly below this.

[0168] Regarding further preferred embodiments of the device according to the invention, in order to avoid repetition, reference is made to the general part of the description as well as to the appended claims. Finally, it should be clearly pointed out that the above-described embodiments of the device according to the present invention are merely intended to verify the teachings of the patent application and are not intended to be limiting.

Claims

1. A coated paper comprising a base paper and at least one semi-crystalline coating layer having an amorphous region and a crystalline region, which is applied indirectly or directly onto the base paper, the amorphous region comprises one or more naturally occurring polymers and / or one or more derivatives of naturally occurring polymers; the crystalline regions comprise one or more crystallizable organic compounds; and A coated paper, wherein the permeability of the coated paper to at least one gas is reduced compared to the base paper.

2. The at least one crystallizable organic compound has a glass transition temperature T ｇ Lower melting temperature T ｍ The coated paper of claim 1 having

3. 2. The coated paper of claim 1, wherein the permeability of at least one gas is lower than the permeability of a coated paper having the same base paper and either a coating layer made of a natural polymer or a derivative thereof or a coating layer made of a crystallizable organic compound.

4. 4. The coated paper of claim 3, wherein the coating layer has a contact angle with water of not more than 130° and / or the coating layer has a sliding angle with a water droplet of 4 μL volume of more than 40°.

5. 2. The coated paper of claim 1, wherein the crystallization of the semi-crystalline coating layer is in the range of 10% to 40%.

6. At 38°C and humidity above 90%, and 10±1 g m －２ Based on the weight per unit area of ​​the coating of 40 g m －２ ・d －１ 2. The coated paper of claim 1, having a water vapor transmission rate (WVTR) of no more than 100 wt.

7. 2. The coated paper according to claim 1, wherein the proportion of the crystallizable organic compound relative to the total mass of the coating layer is in the range of 5 to 50% by weight.

8. 2. The coated paper according to claim 1, wherein the proportion of the natural polymer or its derivative relative to the total mass of the coating layer is in the range of 50 to 95% by weight.

9. 2. The coated paper of claim 1, wherein the at least one crystallizable organic compound is selected from fatty acids, hydroxy fatty acids, or dicarboxylic acids, or their esters, amides, or salts.

10. 2. The coated paper of claim 1, wherein the fatty acid is a saturated or unsaturated fatty acid containing from 12 to 40 carbon atoms.

11. 11. The coated paper of claim 10, wherein the at least one crystallizable organic compound is present in the coating as a fatty acid mixture or a wax, the wax being carnauba wax, candelilla wax, beeswax, and Japan wax, and the fatty acid mixture is a mixture consisting of stearic acid, palmitic acid, oleic acid, linoleic acid, and / or linolenic acid.

12. 2. The coated paper of claim 1, wherein the natural polymer is selected from the group consisting of proteins, peptides, nucleic acids, polysaccharides, lipids, polyhydroxyalkanoates (PHAs), cutin, suberin, lignin, cellulose, chitosan, and starch.

13. Coated paper as described in claim 12, wherein the natural polymer is selected from suberin and lignin.

14. Lignin can be obtained from coniferous trees, broad-leaved trees, herbaceous plants, or annual plants, and can be produced by the Kraft process, the sulfite process, the Soda-Antrachinon process, the GRANIT process, the Alcell process, etc. ＴＭ 14. The coated paper of claim 13, extracted by a method selected from the group consisting of a cellulose acetate method and an organocaloric method.

15. 15. The coated paper of claim 14, wherein the derivative of a natural polymer is an ester of a natural polymer.

16. Coated paper as described in claim 15, wherein the derivative of the natural polymer is an ester of lignin with one or more fatty acids, hydroxy fatty acids, or dicarboxylic acids.

17. 11. The coated paper of claim 10, wherein the at least one fatty acid in the lignin ester is the same as the at least one fatty acid utilized as the crystallizable organic compound.

18. 16. Coated paper according to claim 15, wherein the crystallizable organic compound is stearic acid and the derivative of a natural polymer is lignin stearate.

19. The coated paper has the following constituent features: the coated paper is biodegradable; the coated paper is recyclable; the coated paper is capable of being approved for direct or indirect food contact; The coated paper of claim 1 having at least one of:

20. 1. A coating for coating paper, comprising at least one solvent, at least one crystallizable organic compound, and at least one natural polymer and / or derivative of a natural polymer, the crystallizable organic compounds are as defined in accordance with any one of claims 9 to 11, the natural polymers and derivatives of natural polymers are as defined in accordance with any one of claims 12 to 15, and The coating, wherein the solvent is selected from water, tetrahydrofuran (THF), toluol, ethyl acetate, and alcohol.

21. Each of the following configuration requirements: the absence of crystallizable organic compounds in crystalline form; the proportion of the natural polymer and / or its derivative relative to the total mass of the coating is in the range of 6 to 30% by weight; the proportion of the crystallizable organic compound relative to the total mass of the coating is in the range of 2 to 15 wt. %; and the ratio of the solvent to the total mass of the coating is in the range of 60 to 90 wt. %; 21. The coating of claim 20, having at least one of:

22. 1. A method for producing a coated paper having a base paper and a semi-crystalline coating layer, comprising the steps of: a) preparing the coating of claim 20 by melt dispersion, high pressure dispersion, or spray drying of the components followed by mechanical dispersion; b) preparing a base paper; c) applying said coating to said base paper; and d) allowing the coating to cure while forming a semi-crystalline coating layer; A method comprising:

23. 10. Packaging for food products comprising the coated paper of claim 1.

Images