Water-based barrier coating of natural substances for paper, paperboard or molded pulp

Abstract

The present invention relates to a natural, depolymerized powdered polymer and mixtures thereof and aqueous solutions prepared therefrom for the production of barrier coatings on paper, paperboard or molded pulp. The barrier coating is used to reduce diffusion of oxygen, mineral oil and edible oil and fatty substances through paper, paperboard or molded pulp.

Description

Technical Field

[0001] The invention relates to natural, depolymerized powdered polymers and mixtures thereof and aqueous solutions prepared therefrom for use in preparing barrier coatings on paper, paperboard or molded pulp. The barrier coatings are used to reduce the diffusion of oxygen, mineral and edible oils and fatty substances through paper or paperboard. Background Art

[0002] There is an extensive prior art for applying barrier coatings on paper, paperboard or molded pulp. To date, the vast majority of patent applications are related to the use of petrochemical-based film-forming materials. For example, mention may be made here of WO 2012 / 163821 entitled "Paper and paperboard packaging with a barrier coating comprising a polymer mixture".

[0003] WO 2021 / 005451 A1 describes a multilayer system with a barrier effect. The first layer is a so-called polysaccharide-based biobarrier. Guar gum is explicitly mentioned as a possible coating component. However, no further information or examples are provided about the use of guar gum to coat paper. Furthermore, no test results are provided for the barrier effect of the produced paper coating.

[0004] WO 2021 / 171016 A1 describes the use of alginate cross-linked with CaCl2 as a natural barrier coating. Guar gum and other polysaccharides are listed as thickeners to improve the elasticity of the barrier coating. Although preferred natural polysaccharides are given with viscosities of 200 cP to 10,000 cP, the necessary concentration data for these measurements are lacking. For example, in Example 1, a polysaccharide solution with a viscosity of 10,000 mPa·s was applied. However, no information is provided on barrier properties or application weights.

[0005] WO 2021 / 228695 A1 describes a paper-based packaging material having a barrier coating bonded directly to a carrier paper as a first coating. Guar gum and carrageenan are mentioned in a list of different synthetic and natural polymers on page 10 of the patent application and in claim 2. Examples of the application of guar gum or carrageenan or of the barrier effect of these two polysaccharides are missing.

[0006] Due to the increasing demand for environmentally friendly and sustainable solutions, paper, paperboard or molded pulp manufacturers are working on environmentally friendly barrier coatings to protect the end product from external influences. Examples include preventing the migration of mineral oils from paper or paperboard into the end product or prolonging the long-lasting freshness of the packaged product by excluding oxygen. Another purpose is to protect consumers from greasy fingers or soiled clothing, for example, caused by contamination from greasy food.

[0007] Sustainable solutions include solvent-free, water-based coatings and the elimination of the use of plastic or aluminum foil as well as fluorinated chemicals. Due to the growing discussion about microplastics in the environment, European Regulation (EU) 2019 / 904 was finally adopted in July 2021. This means that in the future, water-based coatings will have to abandon the use of synthetic polymers.

[0008] The cited prior art has various disadvantages, since only aqueous coating systems having a viscosity of at most 1,500 mPa·s (measured with a Brookfield viscometer at 20 rpm) can be applied with the common coating devices on paper machines, such as size or film presses, engraved rolls, blade coaters, doctor blade coaters, air knives, curtain coaters or spray applications, etc. Often, even viscosities <500 mPa·s are necessary.

[0009] According to European Regulation (EU) 2019 / 904, which came into force on July 3, 2021, for paper, paperboard or molded pulp intended for single use, barrier coatings are now only permitted if they consist of natural, unmodified polymers. At the same time, polymers identical to natural polymers produced by fermentation processes are also not permitted. In general, this regulation is referred to as the "Single-Use Plastics Directive", or SUPD for short. This abbreviation will also be used frequently in the following text.

[0010] Aqueous solutions of cold-water soluble polysaccharides generally have very high viscosities. For example, a 1 wt.% aqueous solution of guar gum has a viscosity between 4000 and 8000 mPa·s. Alginates have a slightly lower viscosity, but 2 wt.% solutions are also generally between 3000 and 7000 mPa·s. Both viscosity values ​​are measured under the conditions given above. Due to the high viscosity, obviously only highly diluted solutions can be used. This leads to a drastic reduction in the application volume and the associated barrier effect.

[0011] The second major drawback of the cited prior art is the lack of test results to determine the barrier effect. There is no published results for oxygen, mineral oil, edible oil or grease barrier in any application.

[0012] Aqueous solutions of enzymatically decomposed starch have been used in the paper industry for a long time. Although this application complies with European Regulation (EU) 2019 / 904 (SUPD), starch coatings exhibit two serious disadvantages. First, the natural starch coating is very hard and brittle and breaks immediately when the paper is folded during subsequent applications. This completely destroys any barrier effect that may have existed. A second disadvantage is the insufficient barrier effect against oxygen and hydrophobic substances, such as mineral and edible oils, and fatty substances.

[0013] EP 0 030 443 describes a water-soluble phosphorylated guar gum product and a method for producing the same. The phosphorylated guar gum product is very suitable for the surface treatment of paper. The guar gum product is chemically modified and thus does not comply with European Regulation (EU) 2019 / 904. The phosphorylated guar gum can be produced by depolymerizing guar gum under alkaline conditions in the presence of an oxidizing agent. The depolymerized guar gum is then used as a starting material for the production of phosphorylated guar gum.

[0014] US2014 / 0243518 A1 discloses a method for preparing cationic galactomannan. It is generally described that the galactomannan can be used in the paper industry, but no further details are given. The cationic galactomannan is chemically modified.

[0015] EP 2492 395A1 describes an oil and fat resistant treatment composition. The oil and fat resistance is achieved by fluorocarbon resin, guar gum and inorganic phosphate. It is disclosed that the use of fluorocarbon resin is essential for obtaining this resistance. The use of such fluorinated chemicals is not environmentally friendly and sustainable. Summary of the invention

[0016] In contrast, the object of the present invention is to provide a barrier coating for non-petrochemical based paper or paperboard using natural, unmodified polymers and mixtures thereof and aqueous solutions prepared therefrom. The barrier coating is intended to reduce the diffusion of oxygen, mineral and edible oils and fatty substances through paper or paperboard.

[0017] Thus, in a first embodiment of the invention, there is provided a barrier coating for paper, board or moulded pulp for reducing the diffusion of oxygen, mineral and edible oils and fatty substances through the paper, board or moulded pulp, the coating being based on naturally depolymerised powdered polymers and mixtures thereof.

[0018] The natural powdery polymer is a polysaccharide, preferably selected from polygalactomannans, such as guar gum, tara gum, sesbania gum or locust bean gum, alginate or carrageenan. These polymers are completely of natural origin and are not chemically modified. Similar polymers produced by possible fermentation processes, such as xanthan gum, Weilan, etc., are not included in the subject matter of the present invention.

[0019] According to the invention, the barrier coating for paper, paperboard or molded pulp is intended, on the one hand, to protect the goods to be packaged from external influences and, on the other hand, to ensure pleasant use by the consumer.

[0020] Paper and board are made from fibrous materials, which today are obtained primarily from the raw material wood. The most important fibrous materials are pulp, mechanical wood pulp and waste paper pulp. Paper and board are flat materials formed by dewatering a fiber suspension (pulp) on wires. The resulting fiber web is compacted and dried.

[0021] The difference between paper and board, among other things, lies in their mass per unit area. In layman's terms, the basis weight is 150g / m 2 Up to 600g / m 2 The material in this range is called cardboard. Cardboard is usually thicker and stiffer than paper.

[0022] Molded pulp is a packaging material made from recycled paper and cellulose paper. Pulp can be made from materials such as recycled cardboard, paperboard and newspaper. In fact, any paper-based product can be used. This includes items that have been made from molded pulp, have completed their use and need to be recycled again.

[0023] There are four basic types of molded pulp. Thick-walled molded pulp has rough edges and is used to carry goods from one place to another. Injection molding is used to smooth or finish a thick-walled mold on at least one side of its thinner version. Thermoformed fiber molds are heated molds that are made using a three-dimensional mold and vacuum forming. The last type, processed pulp, takes one of the other three forms and is finished by adding imprints, coatings, or sometimes seeds.

[0024] The exact process for making molded paper pulp depends on the desired functionality and size. The production of the pulp itself is a common process for all types. In fact, a basic pulp can be used to produce all four basic types. The paper product is fed into a shredder, which breaks the product into small pieces. Hot water is then added to make a semi-liquid pulp. The pulp is then passed through a filter to remove any non-paper materials, such as plastic.

[0025] Molding pulp, used to make products such as egg cartons and beverage carriers, is poured onto a lubricated metal mold. A vacuum pump then draws the pulp onto the mold, distributing it evenly across the mold. Once the pulp is formed, it is placed in an oven to dry. The length of time it takes for a pulp mold to dry depends on its size and thickness.

[0026] Oxygen protection:

[0027] Removing oxygen prolongs the freshness and shelf life of packaged food. This means that food waste can be reduced by extending the shelf life across the value chain (i.e. transport, retail and consumer).

[0028] Preventing Mineral Oil Contamination:

[0029] The use of recycled paper in the production of paper, board or moulded pulp introduces contamination with mineral oil components, which come from printed waste paper, for example. These problems are mainly caused by two mineral oil components, namely saturated mineral oil hydrocarbons MOSH (mineral oil saturated hydrocarbons) and aromatic mineral oil hydrocarbons MOAH (mineral oil aromatic hydrocarbons). Even at room temperature, the volatile components of these components evaporate and are incorporated into the packaging material. Barrier coatings are applied to paper and board to prevent these components from being transferred from the packaging material to the packaged goods.

[0030] Happy end-users:

[0031] Paper and paperboard with a grease and oil barrier are used extensively in the fast food industry. For example, hamburger wrappers are equipped with a fat barrier. The fat from the hamburger meat does not pass through the paper and get on the hands of the customer. The corresponding folding boxes for larger hamburgers are also equipped with a fat barrier, which also prevents fat from seeping out.

[0032] The object to be solved is in particular to provide an aqueous, low-viscosity coating solution of a natural, unmodified polysaccharide with a solids content of more than 10 wt.%. Furthermore, the coating of paper, board or molded pulp produced from this solution should comply with European Regulation (EU) 2019 / 904 and have an excellent barrier effect against oxygen, mineral oils, edible oils and fats. Furthermore, the applied coating must be sufficiently flexible to retain the barrier effect even after folding.

[0033] Thus, in a first embodiment of the invention, there is provided a barrier coating for paper, board or moulded pulp for reducing the diffusion of oxygen, mineral and edible oils and fatty substances through the paper, board or moulded pulp, the coating being based on naturally depolymerised powdered polymers and mixtures thereof.

[0034] The barrier coating of the present invention is based on a natural, depolymerized powdered polymer. In the meaning of the present invention, "based on" means in particular that the natural, depolymerized powdered polymer is the main functional component of the barrier coating. In particular, the amount of polymer in the barrier coating may be in the range of 85 wt.% to 100 wt.%, more particularly, in the range of 90 to 100 wt.%, or 95 wt.% to 100 wt.%, or 99 wt.% to 100 wt.%. The barrier coating may consist entirely of the natural, depolymerized powdered polymer and mixtures thereof.

[0035] In the meaning of the present invention, "natural polymer" means in particular that the polymer is obtained from nature and is used without any further chemical modification (except depolymerization). In particular, the natural polymers have not been synthetically functionalized in any way (e.g. with cations or anions) before they are used in the barrier coating. The only modification of the polymers included according to the present invention is depolymerization, i.e. shortening of the polymer chains. When the polymers are depolymerized, no such chemical modification is carried out.

[0036] The barrier coating of the invention is particularly free of further modified polymers, in particular halogenated polymers. In particular, the barrier coating can consist entirely of compounds that comply with European Regulation (EU) 2019 / 904 (SUPD).

[0037] Surprisingly, it has now been found that from more or less strongly depolymerized natural polysaccharides such as guar gum, alginates or carrageenans, low-viscosity solutions having a polymer solids content of more than 10 wt.% and a viscosity of preferably up to 5000 mPa·s (measured with a Brookfield at room temperature, 20 revolutions per minute), in particular up to 2000 mPa·s, further preferably below 1,500 mPa·s (measured with a Brookfield at room temperature, 20 revolutions per minute) can be produced. Papers coated with these polymer solutions comply with European Regulation (EU) 2019 / 904 (SUPD), have excellent barrier properties against oxygen, mineral oils, edible oils and fats, and have excellent flexibility.

[0038] Another advantage is that it is simple to prepare aqueous solutions from depolymerized natural polysaccharides. For the starting polysaccharide, stirring of the aggregates with a high shear effect is necessary in order to dissolve the powder in water without agglomeration. The depolymerized polysaccharide can be easily dissolved in water using a magnetic stirrer.

[0039] The natural, depolymerized powdered polymer of the present invention preferably has a high degree of depolymerization. In a particularly preferred embodiment, the degree of depolymerization is such that the viscosity of a 2 wt.% aqueous solution of the natural depolymerized powdered polymer is in the range of 1 mPa·s to 100 mPa·s, more preferably in the range of 1 mPa·s to 50 mPa·s, in particular in the range of 1 mPa·s to 20 mPa·s (measured with Brookfield at room temperature, 20 revolutions per minute).

[0040] Natural polymers in powder form are:

[0041] a) Polysaccharides from the group of polygalactomannans.

[0042] Galactomannans are reserve polysaccharides obtained from the endosperm of seeds of various leguminous plants. They are uniform chains of β-1,4-linked mannopyranosidic glycosides with side chains of α-1,6-linked galactosidic residues. The weight ratio of mannose to galactose varies in various leguminous plants.

[0043] The most important representative of these polysaccharides is guar gum. It is obtained from the seeds of the guar bean shrub (Cyamopsis tetragonoloba L.). It grows in India, Pakistan, the United States (Texas, Arizona) and northern Australia. The weight ratio of mannose to galactose in guar gum is ideally 2:1. The molecular weights available are 50,000 to 8,000,000.

[0044] Another important representative of galactomannan is locust bean gum. It is obtained from the seeds of the carob tree (Ceratonia Siliqua L.). It is grown in the Mediterranean region. The ideal weight ratio of mannose to galactose in locust bean gum is 4:1. The molecular weight provided is 50,000 to 3,000,000.

[0045] In recent years, tara gum from the seeds of the tara tree (Caesalpinia Spinosa L.) in Peru, Ecuador and Kenya and cassia gum from the seeds of the cassia shrub (Cassia tora and Cass obtusifolia) in India have gained attention. The ideal weight ratio of mannose to galactose is 3:1 for tara gum and 5:1 for cassia gum. The molecular weight of cassia gum is 200,000 to 300,000; no value is given in the literature for tara gum.

[0046] Sesbania gum also belongs to the class of polygalactomannans. The main growing area is India, but commercial qualities are also known from Egypt. Like guar gum, the weight ratio of mannose to galactose in sesbania gum is also ideally 2:1. Its molecular weight is 2,000,000 g / mol to 3,000,000 g / mol. There is no information on the distribution of the galactose side groups.

[0047] Molecular weight values ​​were taken from Cassia gum, Chemical and Technical Assessment (CTA) and Characterization of galactomannans from the endosperm of leguminous plants of the genus Sesbania (subfamily Faboideae).

[0048] According to the present invention, from the group of polygalactomannans, guar gum and locust bean gum are preferred, among which guar gum is particularly preferred.

[0049] b) Alginic acid is mainly found in marine brown algae as a cell wall component (up to 40 wt.% of dry matter); it consists of cellulose-like filaments (degree of polymerization about 1000) and has similar supporting functions. Alginic acid is a carboxyl group (C6H8O6) n A polysaccharide consisting of a mixture of two uronic acids, β-D-mannuronic acid and α-L-guluronic acid, linked in alternating proportions by 1,4-glycosidic bonds to form linear chains. These chains contain longer segments (blocks) of only one uronic acid (MMM- or GGGG-), or the two basic elements appear alternately (-GMGMG-); the carboxyl groups are not esterified. The molecular weight ranges from 30,000 to 200,000 Daltons (180 to 900 uronic acid units). Salts of alginic acid are called alginates.

[0050] c) The polysaccharide carrageenan also comes from algae.

[0051] Carrageenan is a sulfated galactan extracted from red algae seen as flower clusters. Carrageenan is precipitated from hot water extracts of the algae. Carrageenan is a colorless to sandy powder with a molecular weight between 100,000 and 800,000 Daltons and a sulfate content of about 25 wt.%, which is easily soluble in warm water. Carrageenan is divided into three main components, namely kappa-type, iota-type and lambda-type, each with different properties.

[0052] Information on alginic acid and carrageenan is taken from Thieme Encyclopedia of Chemistry Online (retrieved February 2022).

[0053] It is clear from the information on polygalactomannan, alginic acid and carrageenan that these polysaccharides are polymers of natural origin.

[0054] In the case of addition of acid, depolymerization and / or hydrolysis of the polysaccharide takes place in the powder form. After hydrolysis, the decomposed polysaccharide is neutralized with a base to a neutral pH range.

[0055] Preferably, the depolymerization is carried out in the absence of agents which could react with the polymer and chemically modify it. It is particularly preferred that no oxidizing agent is used during the depolymerization and that the depolymerization is carried out entirely by applying an acid.

[0056] In particular, mineral acids (e.g. hydrochloric acid, sulfuric acid, nitric acid, sulfamic acid, methanesulfonic acid, phosphoric acid and others) and carboxylic acids (e.g. citric acid, tartaric acid, lactic acid, formic acid, gluconic acid and others) can be used as acids. In general, acids with a pKa value of <4.5 can be used. Preferably, methanesulfonic acid, phosphoric acid, citric acid and lactic acid are used for the hydrolysis. Methanesulfonic acid and citric acid are particularly preferred.

[0057] All common alkalis, in particular aqueous alkali solutions (such as caustic soda and caustic potash solutions), as well as ammonia or amines, can be used for neutralization. Preference is given to sodium hydroxide and potassium hydroxide, particular preference to sodium hydroxide.

[0058] The extent of hydrolysis can be controlled by the amount and concentration of acid used, the duration of the acid treatment and the temperature of the treatment.

[0059] The viscosity of the aqueous solution of the powdered sample was measured after a swelling time of 2 hours using a Brookfield rotational viscometer (RVT model). The measurement was carried out at room temperature (22° C.±2° C.) and at the specified rotational speed per minute (rpm).

[0060] The viscosity of the powdered depolymerized polysaccharide measured as a 10 wt.% aqueous solution at 20 rpm is at most 5000 mPa·s. A viscosity of at most 2,000 mPa·s is preferred, and a viscosity of at most 1,500 mPa·s is particularly preferred. The viscosity may particularly be in the range of 10 mPa·s to 1000 mPa·s, 10 mPa·s to 250 mPa·s or 10 mPa·s to 200 mPa·s.

[0061] According to the invention, the carrier substrate paper, paperboard or moulded pulp is coated with an aqueous polysaccharide solution.

[0062] The coating of paper and board substrates can be carried out either "in-line" directly on the paper machine during paper and board production or "off-line" in a separate coating process downstream.

[0063] Coating processes known to the person skilled in the art are suitable for coating, for example a size press or film press, engraved roll, knife coater, blade coater, air knife, curtain coater, etc., and also spray devices.

[0064] The barrier coating is applied to at least one side of the carrier substrate, forming at least one layer in the case of a multilayer barrier coating. The area application weight based on the dry coating is preferably 0.3 g / m 2 Up to 10g / m 2 .

[0065] Another preferred feature of the invention is the mixing of the depolymerized and / or hydrolyzed polysaccharides with one another, as well as the addition of other pulverulent additives: thus, nonionic polygalactomannans can be mixed with anionic polysaccharides based on alginate and / or carrageenan.

[0066] For example, the mixing ratio is within the following range:

[0067] Polygalactomannan is 10wt.% to 100wt.%,

[0068] 0 wt. % to 20 wt. % of alginate and / or carrageenan,

[0069] Other powdered additives are 0 wt.% to 10 wt.%.

[0070] In this sense, it is particularly preferred that the powdered additive is selected from sodium gluconate, trisodium citrate, sodium lactate, potassium / sodium tartrate, sorbitol and / or sucrose, and mixtures thereof.

[0071] According to the invention, the aqueous polymer solution for coating paper, board or molded pulp can consist entirely of the pulverulent polysaccharide dissolved in water for use. However, it may also contain other additives known per se, such as wetting agents, defoamers, plasticizers, fillers, sizing agents (e.g. AKD = alkylated ketene dimer), hydrophobic agents (e.g. wax emulsions), levelers, thickeners or dyes. The amount of other additives may be in the range of 0 wt.% to 15 wt.%, preferably 0 wt.% to 10 wt.%, more preferably 0 wt.% to 5 wt.%, in particular 0 wt.% to 1 wt.%. In a preferred embodiment, the barrier coating according to the invention consists of the aforementioned natural depolymerized pulverulent polymer and the aforementioned additives in the aforementioned amounts. DETAILED DESCRIPTION

[0072] Preparation of depolymerized polysaccharides

[0073] Preparation of hydrolyzed guar gum

[0074] In a heatable 25-liter horizontal reactor from Drais, 3500 g of 200-mesh guar gum were introduced at room temperature and the reactor was sealed. Under stirring, 678 g of a mixture of isopropanol (580 g) and water (118 g) were injected and stirred for 5 minutes. Then 360 g of water (40 g), isopropanol (100 g) and MSA (220 g) was added and the reactor contents were heated to 80° C. within 60 minutes. Stirring was performed at this temperature for 60 minutes. Subsequently, neutralization was achieved by injecting a mixture of 768 g of NaOH 50 wt.% (128 g), water (190 g) and isopropanol (450 g), and the hydrolysis was stopped. Excess isopropanol / water was distilled off under vacuum to a residual moisture of <10%. The dried reaction product was then ground and sieved through a 500 μm sieve.

[0075] The viscosity of the obtained product (HG-1) compared with the starting guar gum is shown in Table 1.

[0076] Raw materials used:

[0077] From BASF MSA = methanesulfonic acid 70 wt.%.

[0078] Guar Gum 200 Mesh:

[0079] Specifications: Particle size: at least 96% passing 200 mesh sieve.

[0080] Polygalactomannan content: at least 82wt.%,

[0081] 1 wt.% Viscosity after 2 hours: at least 5,000 mPa·s as measured with Brookfield (RVT model) at room temperature and 20 rpm.

[0082] Preparation of hydrolyzed alginate

[0083] In a 25-liter horizontal reactor from Drais, 3500 g of 40 mesh alginate was placed at room temperature and the reactor was closed. While stirring, a mixture of 650 g of isopropanol (600 g) and water (50 g) was injected and stirred for 5 minutes. Then a mixture of 138 g of water (15 g), isopropanol (100 g) and 50% (23 g) of citric acid was injected and the reactor contents were heated to 80° C. within 60 minutes. Stir at this temperature for 60 minutes. Subsequently, neutralization was achieved by injecting a mixture of 754.5 g of NaOH 50 wt.% (14.5 g), water (190 g) and isopropanol (550 g), and hydrolysis was stopped. Excess isopropanol / water was distilled off under vacuum to a residual moisture content of <10%. The dried reaction product was then ground and sieved with a 500 μm sieve.

[0084] The viscosity of the obtained product (HA-1) is compared with that of the starting alginate and is shown in Table 1.

[0085] Raw materials used:

[0086] Alginate 40 mesh:

[0087] Specifications: Particle size: at least 95% passing through 40 mesh sieve.

[0088] 2wt.% Viscosity after 2 hours: at least 3,500 mPa·s measured with Brookfield (RVT type) at room temperature and 20 rpm

[0089] 2 wt.% pH: 7.0 to 8.5.

[0090] Preparation of powdered blends from depolymerized polysaccharides

[0091] A simple powdered mixture was prepared from the two hydrolyzed polysaccharides in the following weight ratio.

[0092] a) PM-1 = 95% HG-1 + 5% HA-1

[0093] b)PM-2=90% HG-1+10% HA-1

[0094] Table 1 also shows the viscosity of the two polysaccharide mixtures.

[0095] As a comparative example, Table 1 shows the G2 30.226 as the viscosity of enzymatically hydrolyzed starch.

[0096] Preparation of aqueous solution:

[0097] a) Starting polysaccharide

[0098] The aqueous solution must be prepared on an aggregate with high shear forces. A Dispermat (type AE 04) from VMA Getzmann is used for this purpose.

[0099] Place the necessary amount of soft water (hardness level <5° dH) in a suitable container. Immerse the toothed disc of the Dispermat (diameter = 70 mm). Set the stirrer speed to 500 rpm initially. Then sprinkle in the powder slowly. As soon as an increase in viscosity is noticed, increase the speed to 1000 rpm. During dissolution, take care to ensure that no undissolved gel lumps are formed. After complete addition, continue stirring for 5 minutes. Measure the viscosity after a swelling time of 2 hours.

[0100] b) Depolymerized guar gum or alginate

[0101] Aqueous solutions of hydrolyzed polysaccharides can be easily prepared without the need for high gravity aggregation.

[0102] Place the required amount of soft water in a beaker. Add a magnetic stirring bar, place the beaker on a commercial magnetic stirrer, turn on the stirrer at medium speed, and sprinkle the powder into the water. To speed up the dissolution, the water can be heated to 40°C to 50°C. After the powder has completely dissolved, measure the viscosity also after 2 hours. If necessary, cool the solution to 22°C ± 2°C.

[0103] Table 1: Brookfield viscosity measured after 2 hours swelling time, expressed in mPa·s

[0104]

[0105] 1)= G2 30.226

[0106] Preparation of paper coating

[0107] Paper with the following specifications was used to test the barrier effect:

[0108] Paper A:

[0109] ■Untreated, bleached virgin fiber paper

[0110] ■Weight per unit area = 50g / m 2

[0111] Bendtsen porosity = 253 mL / min

[0112] Paper B:

[0113] ■Untreated, bleached virgin fiber paper

[0114] ■Basic weight = 40g / m 2

[0115] Bendtsen porosity = 17.5 mL / min

[0116] Implementation of paper coating

[0117] An automatic film applicator from Byk Instruments (model: AG-2150) equipped with a profile blade (crease = 24 μm) was used as coating device. The speed of the blade during coating was 500 mm / s.

[0118] For coating, the paper was cut to A4 size. The paper was clamped in a fixture, a doctor blade was inserted, and the aqueous coating solution was applied in front of the doctor blade with a pipette. After applying the solution, the coating device was immediately started. The paper was then dried in a drying oven at 80°C for 5 minutes.

[0119] Method for determination of coating weight (dry)

[0120] Before coating, the paper to be coated was weighed using a commercial top loading laboratory balance (precision: 0.01 g). The wet paper was weighed again immediately after coating. After drying, the coated area was measured with a ruler. The solid content of the coating solution was determined using a Mettler-Toledo drying balance, HC103 moisture analyzer. Based on the data obtained, the dry coating weight was calculated using the following formula.

[0121] Coating area A, Dry coating quality,

[0122] The calculated result is given with an accuracy of one decimal place.

[0123] Measurement of barrier effect

[0124] a) Barrier test for gaseous mineral oil components.

[0125] The method used was similar to Test Method 2 on page 12 of WO 2012 / 163821.

[0126] The instrument used for this test is an EZ-Cup Vapometer 68-3000 from Thwing-Albert Instruments. Other than that, the procedure is the same. The results for HVTR (Hexane Vapor Transmission Rate) are expressed in grams lost per square meter of paper surface per day (g / m 2 ·d) given.

[0127] b) Barrier test for grease and oil

[0128] To test this property, there is a standardized method by the "Technical Association of the Pulp and Paper Industry", or Tappi for short. The method number is Tappi T 559 and is called "Test method for resistance of paper and paperboard to grease and oil".

[0129] The method, often referred to as the kit test, describes a procedure for testing the repellency and / or resistance to absorption of paper or paperboard treated with a fluorochemical sizing agent. The fluorochemical can render the paper lipophobic and hydrophobic by reducing its surface energy. This is achieved by treating the fiber surface without forming a continuous film. The test was originally developed to allow paper manufacturers to determine when the applied fluorochemical was absorbed by the paper and the approximate resistance level. To do this, production samples were tested with a series of numbered agents (with varying surface tension and viscosity or "aggressiveness"), which were contained in bottles in a specially designed kit. The highest numbered (most aggressive) solution that remained on the paper surface without causing damage was given a "kit rating" (hence the term "kit test"). This concept is the basis for the current classical method.

[0130] For barrier coatings that do not use fluorinated chemicals, this method is not very interesting. Therefore, a simple and practical test method was developed. In the test, a paper container is folded up and commercially available sunflower oil (brand: Gut & Günstig Sunflower Oil from EDEKA) is poured into it. After certain time intervals, it is evaluated whether the oil penetrates the paper. This test is referred to by the simple term "boat test".

[0131] "Boat Test" Steps

[0132] The substrate to be tested (paper or cardboard) is cut to a size of 7 x 7 cm. A strip 1 cm wide on each side is folded at a 90° angle so that the coated side is on the inside. The resulting corner is folded on both sides to form a square container, the so-called "boat".

[0133] Now place the "boat" made on the grey cardboard and mark the contact surface on the corners of the cardboard. Dark spots will easily appear on the underlying cardboard as the oil penetrates the paper. Pour 9 ml of commercial sunflower oil into the boat. Visual assessment is carried out after 10 minutes, 60 minutes and 24 hours. The results are expressed as a percentage of penetration relative to the total area of ​​the boat.

[0134] c) Flexibility evaluation of barrier coatings

[0135] To determine this, the "boat test" described above is modified. After the paper has been cut to size (7 x 7 cm), the first step is to fold the paper diagonally. The paper is folded 180° along the crease and the edge is gently scraped with a scraper. The paper is then unfolded and the method described above is performed. The result is given as the percentage of penetration in the crease.

[0136] d) Determination of oxygen barrier

[0137] The oxygen permeability was determined according to DIN 53380-3.

[0138] Measuring area is 5cm 2 .

[0139] Barrier effect results

[0140] Table 2: Results of barrier effect test

[0141] Paper A:

[0142]

[0143] 1)= G2 30.226

[0144] Paper B:

[0145]

[0146] Table 3: Results of test c) on the flexibility of the barrier coating

[0147] Paper A:

[0148]

[0149]

[0150] 1)= G2 30.226

[0151] Paper B:

[0152]

[0153] 1)= G2 30.226

[0154] Table 4: Results of oxygen barrier effect Paper B:

[0155]

[0156] 1)= G2 30.226

[0157] The results showed that the hydrolyzed polysaccharide had superior barrier effect and flexibility compared with the coating of hydrolyzed starch.

Claims

1. A barrier coating for paper, paperboard or moulded pulp for reducing the diffusion of oxygen, mineral and edible oils and fatty substances through the paper, paperboard or moulded pulp, the barrier coating being based on naturally depolymerised pulverulent polymers and mixtures thereof.

2. The barrier coating according to claim 1, It is characterized in that The polymer is selected from polygalactomannans, in particular from guar gum, tara gum, sesbania gum, locust bean gum, alginates or carrageenan.

3. The barrier coating according to claim 1 or 2, further comprising additives or auxiliaries known per se, in particular wetting agents, defoamers, plasticizers, fillers, sizing agents, hydrophobic agents, levelers, thickeners or dyes, which in particular comply with European Regulation (EU) 2019 / 904.

4. The barrier coating according to claim 3, It is characterized in that The additive or auxiliary agent is selected from sodium gluconate, trisodium citrate, sodium lactate, potassium / sodium tartrate, sorbitol and / or sucrose, and mixtures thereof.

5. A method for preparing a barrier coating according to any one of claims 1 to 4, by depolymerizing and / or hydrolyzing a polymer in a powder state with the addition of an acid, and subsequently neutralizing the decomposed polymer with a base to a neutral pH range.

6. The method according to claim 5, It is characterized in that Use an acid with a pKa value < 4.

5.

7. The method according to claim 5 or 6, It is characterized in that Mineral acids, in particular hydrochloric acid, sulfuric acid, nitric acid, sulfamic acid, methanesulfonic acid and / or phosphoric acid; carboxylic acids, in particular citric acid, tartaric acid, lactic acid, formic acid and / or gluconic acid, and mixtures thereof are used as acids.

8. The method according to any one of claims 5 to 7, It is characterized in that Sodium hydroxide and potassium hydroxide, in particular sodium hydroxide solution and potassium hydroxide solution, are used as bases.

9. The method according to any one of claims 5 to 7, It is characterized in that An aqueous solvent is added to the depolymerized and / or hydrolyzed polymer under the action of shear forces.

10. The method according to claim 9, It is characterized in that The solids content of the polymer is adjusted to at least 10 wt.%.

11. The method according to any one of claims 5 to 10, It is characterized in that Additives or auxiliaries known per se, in particular wetting agents, defoamers, plasticizers, fillers, sizing agents, hydrophobic agents, levelers, thickeners or dyes, are added, which in particular comply with European Regulation (EU) 2019 / 904.

12. The method according to claim 11, It is characterized in that The additive or auxiliary agent is selected from sodium gluconate, trisodium citrate, sodium lactate, potassium / sodium tartrate, sorbitol and / or sucrose, and mixtures thereof.

13. The method according to any one of claims 5 to 12, It is characterized in that A viscosity in the range of at most 5,000 mPa·s (measured with a Brookfield at room temperature and 20 revolutions per minute), in particular a viscosity in the range of at most 2,000 mPa·s, is set.

14. Use of a coating solution obtainable by the process according to any one of claims 5 to 13 for coating paper or paperboard.

15. The use according to claim 14, which is carried out in-line on a paper machine during paper and board production, or off-line in a separate coating process downstream, in particular using known coating processes selected from size presses or film presses, engraved rolls, blade coaters, knife coaters, air knife and / or curtain coaters, and by spray application.

16. Paper, paperboard or moulded pulp comprising a barrier coating according to any one of claims 1 to 4.

17. Paper, paperboard or moulded pulp according to claim 16, comprising the barrier coating on at least one side of the paper or paperboard.

18. Paper, paperboard or moulded pulp according to claim 16 or 17, comprising at least one layer of a multi-layer barrier coating.

19. Paper, paperboard or moulded pulp according to any one of claims 16 to 18, It is characterized in that The area coating weight is 0.3 g / m based on dry coating. 2 Up to 10g / m 2 .

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