Coated structure, sheet product and use thereof

Abstract

The present invention relates to a coating structure for a sheet-like substrate containing cellulose fibers. The coating structure comprises at least a first coating layer and a second coating layer, wherein the second coating layer is arranged in direct contact with the first coating layer. At least the first coating layer or the second coating layer is a barrier coating layer, and the barrier coating layer comprises at least one water-soluble cellulose derivative selected from any one of alkyl cellulose, hydroxyalkyl alkyl cellulose, hydroxyalkyl cellulose and mixtures thereof, and a plasticizer.

Description

Technical Field

[0001] The invention relates to a coated structure, a sheet-like product and the use thereof according to the preambles of the appended independent claims. Background Art

[0002] Various coatings can be applied to the surface of paper or board in order to improve their properties. Grease barrier properties are particularly important for paper and board used for products for packaging purposes. The coating applied to the surface of paper or board should provide an effective barrier to prevent leakage of the contents of the package, and / or protect the packaged contents from contamination and / or contact with the surrounding environment. For packaging materials for food and consumable liquids, barrier requirements are particularly stringent.

[0003] Coatings used for packaging purposes should have good resistance to creasing and folding. The coating should not crack when the paper or board is folded into a box or wrapped around a product. Cracks may reduce or even completely destroy the barrier properties of the coating.

[0004] Fluorochemicals or synthetic petroleum-based polymers have been conventionally used in coating compositions to provide the desired barrier properties and crack resistance at the same time. For environmental reasons, it is desirable to find effective alternatives to these petroleum-based chemicals. The alternatives should be sustainable and based on renewable bio-based sources. Conventional bio-based components used in coating formulations, such as starch, generally do not perform well in barrier coatings. They generally make the coating brittle or inflexible, which results in cracking of the coating when folded. In addition, the bio-based components should preferably be derived from non-food chain sources, which starch and starch derivatives cannot meet. Therefore, new alternatives are needed that can solve the problems currently encountered.

[0005] Furthermore, barrier coatings for packaging should also meet recyclability requirements. It is desirable to collect paper and board packaging for recycling and repulping. Many conventional barrier coatings are problematic for repulping and / or require special process arrangements when repulping. Coatings applied to paper and board should meet recycling requirements, for example they should not interfere with the repulping process. Summary of the invention

[0006] The object of the present invention is to minimize or, if possible, even eliminate the disadvantages existing in the prior art.

[0007] Another object of the present invention is to provide coated structures and sheet products which are based on renewable materials and are readily biodegradable and / or repulpable.

[0008] It is yet another object of the present invention to provide coated structures and sheet products which provide good grease barrier properties.

[0009] It is yet another object of the present invention to provide barrier coating structures that can be used to create coatings that are resistant to cracking when creased and / or folded.

[0010] These objects are achieved with the invention having the features presented below in the characterizing part of the independent claim.Some preferred embodiments of the invention are given in the dependent claims. DETAILED DESCRIPTION

[0011] Where applicable, the embodiments mentioned herein relate to all aspects of the invention, even if not always mentioned individually.

[0012] A typical coating structure for a sheet-like substrate comprising cellulosic fibers and / or lignocellulosic fibers according to the present invention comprises at least a first coating layer and a second coating layer, wherein the second coating layer is arranged in direct contact with the first coating layer, and at least the first coating layer or the second coating layer is a barrier coating layer, the barrier coating layer comprising:

[0013] - at least one water-soluble cellulose derivative selected from any one of alkyl cellulose, hydroxyalkyl alkyl cellulose, hydroxyalkyl cellulose and mixtures thereof, and

[0014] -Plasticizers.

[0015] A typical use of the coating structure according to the invention is to provide a grease barrier when applied to sheet products comprising cellulosic and / or lignocellulosic fibers.

[0016] Typical sheet products according to the present invention include:

[0017] - a substrate comprising cellulose fibers and / or lignocellulose fibers and having a first major surface and a second major surface parallel to each other, and

[0018] A coating structure according to the invention applied to at least the first or second large surface of a substrate.

[0019] A typical use of the sheet product according to the invention is in the manufacture of food service packaging.

[0020] It has now been unexpectedly found that a double-layer coating structure comprising at least one barrier layer formed by a specific water-soluble cellulose derivative and a plasticizer can effectively act as a grease barrier, especially against liquid greases or oils, and sometimes even as a mineral oil barrier. The use of a water-soluble cellulose derivative makes the coating structure easy to repulp and reduces the need for components from non-renewable sources. The water-soluble cellulose derivative is a bio-based component, but is derived from a favorable renewable non-food source. In addition, it has been found that the simultaneous use of a specific water-soluble cellulose derivative and a plasticizer unexpectedly improves the performance of the coating structure, making it less viscous and reducing the risk of blocking. In addition, the cracking tendency of the coating structure is significantly reduced, which improves the conversion performance of the obtained coating structure.

[0021] The coating structure according to the present invention comprises at least the first coating layer and the second coating layer. The first coating layer is applied directly on the surface of the sheet substrate comprising cellulose fibers and / or lignocellulose fibers. This means that the coating structure is preferably free of pre-coating and top coating, and is only composed of the first coating layer and the second coating layer, wherein the first coating layer is in contact with the surface of the substrate, and the second coating layer forms the outer surface of the coating layer and subsequently forms the outer surface of the substrate. In some embodiments, before applying the first coating layer, for example, a layer of hydrophobic surface slurry (size) can be applied to the surface of the sheet substrate, but preferably, the first coating layer is applied directly to the surface of the sheet substrate, and the substrate does not contain any pre-existing treatment layer, such as a surface slurry layer. The sheet substrate may include an internal slurry. The first coating layer and the second coating layer may be applied on the substrate surface using any conventional surface sizing or coating technology or a combination thereof. For example, the first coating layer may be applied using a surface sizing device, and the second coating layer may be applied by using a coating device such as a scraper or a rod coating device.

[0022] The second coating layer is arranged in direct contact with the first coating layer, which means that the second coating layer is directly applied on the surface of the first coating layer, in immediate and close contact with the first coating layer. Therefore, the coating structure does not have any intermediate layer between the first coating layer and the second coating layer.

[0023] The coating structure may include two or more first coating layers and / or two or more second coating layers. Preferably, if the coating structure includes multiple first coating layers and / or multiple second coating layers, the first coating layers are preferably chemically identical to each other and the second coating layers are preferably chemically identical to each other. Chemically identical means that the coating layers are made of the same components of the same amount, i.e., the coating layers are made by using the same coating formulation. The coating weight within multiple first coating layers and / or multiple second coating layers can vary.

[0024] According to a preferred embodiment, the first coating layer and the second coating layer are identical to each other and they are both barrier coating layers. Using two identical coating layers can enable each individual layer to use a lower coating weight while still obtaining the desired barrier effect. In addition, when the coating structure includes two or more identical coating layers, the risk of coating defects can be minimized.

[0025] According to one embodiment, the first coating layer and the second coating layer are different from each other. For example, the first coating layer may contain a different water-soluble cellulose derivative and / or plasticizer than the second coating layer. In this way, the properties of the coating structure can be tailored to meet even very specific needs, such as barrier properties to be achieved.

[0026] The coating weight of the first coating layer and the second coating layer can be freely selected according to the desired end use and the desired barrier properties. According to one embodiment of the present invention, the first coating layer may have a coating weight of 2-30 g / m 2 , preferably 3-20g / m 2 , more preferably 5-15g / m 2 The coating weight of the second coating layer may be 0.5-20 g / m 2 , preferably 0.5-15g / m 2 , more preferably 0.5-10g / m 2 Typically, the first coating layer may have a higher coating weight than the second coating layer.

[0027] The coating structure of the present invention comprises at least one barrier coating layer. This means that the coating structure comprises at least two coating layers, at least one of which is a barrier coating layer. At least the first coating layer or the second coating layer in the coating structure is a barrier coating layer. According to the present invention, the first coating layer can be a barrier coating layer or the second coating layer can be a barrier coating layer. It is also possible that according to the present invention, both the first coating layer and the second coating layer are barrier coating layers. The present invention provides the possibility of optimizing the barrier properties of the coating structure by selecting the number and position of the barrier layers in the coating structure.

[0028] The barrier coating layer according to the present invention comprises at least one water-soluble cellulose derivative selected from the group consisting of: any one of alkyl cellulose, hydroxyalkyl alkyl cellulose, hydroxyalkyl cellulose and mixtures thereof. The water-soluble cellulose derivative may preferably be selected from the group consisting of: any one of methyl cellulose, hydroxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, (hydroxyethyl) methyl cellulose and (hydroxypropyl) methyl cellulose and mixtures thereof. Preferably, the water-soluble cellulose derivative is methyl cellulose, (hydroxypropyl) methyl cellulose or hydroxyethyl cellulose, more preferably hydroxyethyl cellulose. It has been observed that when one of the specified water-soluble cellulose derivatives is present in the barrier coating layer, the layer is more flexible and less prone to cracking when creased or folded. In addition, the specified cellulose derivative provides an increased dry solids content for the coating formulation, making it easier to apply to the surface of the substrate to be coated and providing better film-forming properties.

[0029] In particular the use of (hydroxypropyl)methylcellulose makes it possible to provide coatings which exhibit mineral oil barrier properties and are therefore also suitable for technical applications.

[0030] Cellulose derivatives suitable for use in the present invention are water-soluble at least at room temperature (+21° C.). In the context of the present invention, the term "water-soluble cellulose derivative" means a cellulose derivative which dissolves in water without gel formation. At a temperature of +21° C., an unsaturated solution (in water) of a water-soluble cellulose derivative does not contain solid particles and it can be filtered through a filter with an opening of 100 microns. Methylcellulose and (hydroxypropyl)methylcellulose become water-insoluble in hot water (about +75° C.), but they are still suitable for use in the present invention and can even provide limited water barrier properties, especially for hot liquids, for coating layers in addition to grease barrier properties.

[0031] The barrier coating layer comprising the water-soluble cellulose derivative, ie, the first coating layer and / or the second coating layer is preferably formed without using an organic solvent. The barrier coating layer is generally formed by using an aqueous solution of the water-soluble cellulose derivative without an organic solvent.

[0032] The first coating layer and the second coating layer may both be barrier coating layers comprising chemically identical water-soluble cellulose derivatives. Alternatively, the first coating layer and the second coating layer may both be barrier coating layers, wherein the first barrier coating layer comprises a first water-soluble cellulose derivative and the second barrier coating layer comprises a second water-soluble cellulose derivative. The first water-soluble cellulose derivative and the second water-soluble cellulose derivative are different from each other and are selected from any one of alkyl cellulose, hydroxyalkyl alkyl cellulose, hydroxyalkyl cellulose and mixtures thereof.

[0033] The barrier coating layer (i.e., the first coating layer and / or the second coating layer) may comprise a water-soluble cellulose derivative in an amount of 50-99 wt-%, preferably 60-97 wt-%, more preferably 70-95 wt-% or 80-95 wt-%, calculated from the total solids content of the barrier coating layer. Using the present invention, coated structures can be produced in which the content of bio-based components is high while maintaining key barrier and crack resistance properties at least at acceptable levels.

[0034] In addition to the water-soluble cellulose derivative, the barrier coating comprises a plasticizer. The plasticizer is incorporated into the barrier coating between the water-soluble cellulose derivative chains, wherein the plasticizer separates the chains and controls their movement in the barrier coating. The selected plasticizer is preferably suitable for food packaging purposes, which means, for example, that phthalates are excluded. The plasticizer can be selected from the group comprising the following: polyols, such as sorbitol, mannitol, ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, propylene glycol or polyethylene glycol; fatty acids; monosaccharides, ethanolamines; triethanolamine; alkyl citrates, urea; lecithin and glycerol. According to a preferred embodiment, the plasticizer can be selected from sorbitol, polyethylene glycol or glycerol. Typically, the incorporation of plasticizers into the barrier coating makes the barrier coating too sticky, which may easily lead to blocking problems. It has now been unexpectedly observed that when the barrier coating comprises a water-soluble cellulose derivative, the viscosity of the barrier coating comprising a plasticizer is significantly reduced. This means that a coating can be obtained in which crack resistance and barrier properties can be balanced with flexibility in order to obtain a coated structure with optimal properties for the desired purpose.

[0035] The barrier coating may comprise plasticizer in an amount of 1-50 wt-%, preferably 3-40 wt-%, more preferably 5-30 wt-% or 5-20 wt-%, calculated on the total solids content of the barrier coating.

[0036] According to a preferred embodiment of the present invention, at least the barrier coating may further comprise inorganic pigment particles. The inorganic mineral pigment may be selected from kaolin, talc, calcium carbonate or any mixture thereof, preferably calcium carbonate, such as ground calcium carbonate or precipitated calcium carbonate. The particle size D50 of the inorganic pigment particles may be <5 μm. According to one embodiment, the barrier coating may comprise inorganic mineral particles, wherein at least 45% of the inorganic mineral particles have a particle size of <2 μm. The addition of inorganic mineral pigments may further improve the barrier properties obtained. It has been unexpectedly observed that water-soluble cellulose derivatives increase the flexibility of the barrier coating in a manner that allows a large amount of inorganic pigment particles to be incorporated into the barrier coating. This may not only improve the barrier properties, but also make the production of the coated structure more economical.

[0037] The first coating layer and the second coating layer may both comprise inorganic mineral particles, whether or not they are barrier coating layers according to the present invention. The inorganic mineral particles, their type and / or amount in the first coating layer and the second coating layer may be the same or different. Preferably, the first coating layer and the second coating layer comprise the same inorganic mineral particles, even though their amount may be different in the first coating layer and the second coating layer.

[0038] According to a preferred embodiment, at least the second coating layer applied directly on the one or more first coating layers can be a barrier coating layer comprising inorganic pigment particles, preferably calcium carbonate particles. In this case, the first coating layer can act as a sealing layer, which reduces or prevents the barrier coating layer from penetrating into the surface of the substrate to be coated.

[0039] According to one embodiment of the present invention, the water-soluble cellulose derivative may be selected from alkyl cellulose, such as methyl cellulose, wherein the barrier coating layer may contain 5-20 wt-%, preferably 7-17 wt-%, more preferably 7-15 wt-% of inorganic pigment particles, calculated from the total dry solid content of the barrier coating layer. For example, the barrier coating layer may contain 50-90 wt-%, preferably 60-90 wt-% or 75-87 wt-% of alkyl cellulose such as methyl cellulose, 5-20 wt-%, preferably 7-17 wt-% or preferably 7-15 wt-% of inorganic pigment particles, and 5-30 wt-%, preferably 5-25 wt-% or 5-20 wt-% of plasticizer, the total amount of the components totaling 100%.

[0040] According to another embodiment of the present invention, the water-soluble cellulose derivative is preferably selected from hydroxyalkyl cellulose or hydroxyalkyl alkyl cellulose, such as hydroxyethyl cellulose or (hydroxypropyl) methyl cellulose, wherein the barrier coating layer may contain an amount of 20-60 wt-%, preferably 30-55 wt-%, more preferably 40-50 wt-% of inorganic pigment particles, calculated from the total dry solid content of the barrier coating layer. For example, the barrier coating layer may contain 20-60 wt-%, preferably 30-55 wt-% or 40-50 wt-% of hydroxyalkyl alkyl cellulose such as hydroxyethyl cellulose or (hydroxypropyl) methyl cellulose, 20-50 wt-%, preferably 35-50 wt-% or 30-50 wt-% of inorganic pigment particles, and 5-30 wt-%, preferably 10-30 wt-% or 15-26 wt-% of plasticizer, the total amount of the components totaling 100%. The use of hydroxyalkyl cellulose or hydroxyalkyl alkyl cellulose enables the use of high levels of inorganic pigment particles in the barrier coating without degrading coating properties such as crack resistance.

[0041] Starch can increase the brittleness of the coating structure and reduce the resistance of the coating structure to cracking. Therefore, the amount of starch is preferably minimized in the coating structure according to the present invention. More preferably, the first coating layer and the second coating layer of the coating structure do not contain starch.

[0042] According to one embodiment of the present invention, the first coating layer of the coating structure may contain carboxymethyl cellulose, provided that the second coating layer is a barrier coating layer according to the present invention and does not contain carboxymethyl cellulose. According to another preferred embodiment of the present invention, the first coating layer and the second coating layer of the coating structure are completely free of carboxymethyl cellulose.

[0043] According to one embodiment of the present invention, at least the barrier coating layer may further comprise an additional coating adhesive, preferably polyvinyl alcohol. The weight average molecular weight of the polyvinyl alcohol may be <100,000 g / mol, preferably <90,000 g / mol. Polyvinyl alcohol particularly suitable for use as an additional coating adhesive may have a weight average molecular weight of ≤70,000 g / mol, preferably 13,000-70,000 g / mol. The polyvinyl alcohol may be at least partially hydrolyzed. When used as an additional coating adhesive, polyvinyl alcohol may improve both the film formation and the water vapor and mineral oil barrier properties of the coating layer. Polyvinyl alcohol may also reduce the blocking tendency of the obtained coating structure. According to one embodiment, the first coating layer and / or the second coating layer does not contain polyvinyl alcohol.

[0044] According to another embodiment, the coating layer may contain one or more of the following additives: a thickener, a crosslinking agent, a lubricant, an alkyl ketene dimer, an alkenyl succinic anhydride, and a dispersant. Preferably, the first coating layer and the second coating layer do not contain animal-based additives and / or components, such as animal-based chitosan or gelatin. Excluding animal-based additives makes the coating structure suitable for food service packaging products for all consumer groups, regardless of their religion or ideology.

[0045] The coating structure may further comprise one or more additional coating layers applied on the surface of the second coating layer. The additional coating layer may be different from the second coating layer.

[0046] According to a preferred embodiment, the coating structure does not contain additives that are synthetic polymers. In particular, the coating structure may be free of styrene-based synthetic polymers, such as styrene-butadiene or styrene-acrylate latex. Excluding synthetic polymers can improve the biodegradability and / or compostability of the coating structure and make it more environmentally friendly, even if the final consumer disposes in an incorrect manner. Excluding styrene-based polymers also makes the coating structure safe to produce. In particular, according to one embodiment of the present invention, the coating structure does not contain any layer of laminated polymer film. This improves the repulpability and compostability of the coating structure.

[0047] The substrate used for the coated structure according to the present invention may comprise cellulose fibers and / or lignocellulose fibers. Cellulose fibers or lignocellulose fibers may be obtained by any conventional pulping method, including chemical, mechanical, chemi-mechanical pulping methods. The substrate may also comprise or consist of recycled fibers. The substrate has a first large surface and a second large surface parallel to each other, and is generally in the form of a fiber web. The substrate may have a fiber weight of 25-800 g / m 2 , preferably 30-700g / m 2 , more preferably 40-500g / m 2 The coating structure may be applied to at least the first major surface and / or the second major surface of the substrate by using any conventional surface sizing technique or coating technique, such as rod coating, knife coating, spray coating or curtain coating.

[0048] According to a preferred embodiment, the resulting sheet product coated with the coating structure may have a TAPPI 559 KIT test value of at least 8, preferably at least 10, more preferably at least 12. The KIT test value measures the repellency of the coating layer to oil and grease, and the measurement is performed according to standard TAPPI method T-559pm-96.

[0049] According to a preferred embodiment, the obtained sheet product coated with the coating structure may have a thickness of <100 g / m 2 The mineral oil barrier HVTR value of 1000 g / d is 1000 g / cm2. The hexane vapor transmission rate (HVTR) value used is obtained by using a test method developed by BASF. In the test, hexane is placed in a measuring cup covered by the barrier sample and the evaporation of hexane through a known area is measured. The test method is well known to those skilled in the art.

[0050] According to a preferred embodiment, at 23°C and 50% relative humidity, the obtained sheet product coated with the coating structure may have a water vapor barrier WVTR value of <100 g / m 2 The WVTR value can be measured by using the standard methods of ASTM F-1249, ISO 15105-2, ISO 15106-3, and DIN 53122-2.

[0051] The sheet product coated with the coating structure can be used to make food service packaging or liquid packaging. Typical examples of food service packaging are packaging for fast food, ready meals, sandwiches, bakery products such as cookies, donuts, etc.

[0052] In this context, all weight-% values ​​given for the various components are calculated from the total dry solids content of the coating layer, if not stated otherwise.

[0053] experiment

[0054] Some embodiments of the invention are described in the following non-limiting examples.

[0055] Preparation of cellulose derivative solution

[0056] The cellulose derivative used was dissolved in water. The cellulose derivative was dissolved at a maximum solids content, which resulted in a cellulose derivative solution with a Brookfield viscosity of less than 1000 mPas at room temperature. The dissolution procedure is described below, and the properties of the cellulose derivative used and the cellulose derivative solution obtained are described in Table 1.

[0057] Methylcellulose (MEC); (Hydroxypropyl) methylcellulose (HPMC): Heat 1 / 3 of the total amount of water used to near boiling temperature and add the cellulose derivative powder under mixing to avoid lumps. Place the obtained suspension in an ice bath and continue mixing until all the cellulose derivative powder has dissolved. Add the remaining amount of the total amount of water under mixing.

[0058] Hydroxyethyl Cellulose (HEC) : The cellulose derivative powder is added to water under mixing and the obtained suspension is heated to 60°C and kept at this temperature until dissolution of the derivative is complete.

[0059] Table 1 Properties of the obtained cellulose derivative solutions.

[0060]

[0061] *Viscosity measurement temperature given in brackets

[0062] Coating preparation and measurement

[0063] The coating formulations used in the examples were prepared by mixing using a Diaf dissolver.

[0064] A Brookfield DV-E (Brookfield GmbH, Lorch, Germany) viscometer was used to measure the bulk viscosity of the coating formulations immediately after their preparation. Different spindles were used depending on the viscosity range of the respective sample. The measurements were carried out at 100 rpm.

[0065] Laboratory coating tests were performed using a draw down coater K control coater (RK Print Coat Instruments, Litlington, UK) with different winding rods and coating speeds. The samples were dried using an InfraRR IR dryer for 60 seconds. All samples were double coated. The substrate used in the coating tests was virgin fiber-based paperboard with a basis weight of 295 g / m 2A barrier coating is applied to the uncoated bottom side of the substrate.

[0066] The coating weight of the coated substrate was determined by weighing the coated sample and the uncoated base paper and the coating weight was obtained by the weight difference. The samples were subjected to a simple conversion test, including sample creasing using a Cyklos CPM 450 creasing and perforation unit. Creases and folds were performed in the machine direction and in the cross direction. The creased samples were dyed by using methyl red dissolved in ethanol. For folding, a Cobb roller was used to provide uniform folding pressure.

[0067] The water resistance of the coated substrates was tested using the Cobb 60 test according to standard ISO 535.

[0068] The water vapor barrier properties WVTR of the coated substrates were measured using a Systech Permeation Analyzers M7002 instrument.

[0069] The hexane vapor transmission rate of the coated substrate was determined by using the cup method. 20 grams of hexane was placed in a metal cup. The coated substrate was placed on top of the cup between two liners, with the coated side facing down. The sample was fastened to the cup using a metal frame. The weight loss was recorded for 24 hours.

[0070] The grease barrier properties of a coated substrate are given as a KIT value.

[0071] The blocking test was performed at a temperature of 40°C and a pressure of 150 bar for 4 hours. The coated sample was coated with a barrier coating on one side and a top side coating on the other side. The barrier coated sample was placed against the top side coating in the test. The ratings for the blocking test results are shown in Table 2.

[0072] Table 2 Blocking test levels used in the examples.

[0073]

[0074]

[0075] Example 1: Effects of different plasticizers on coating properties

[0076] The effect of different plasticizers was tested with low molecular weight hydroxypropyl methylcellulose HPMC. Glycerol, sorbitol and polyethylene glycol were selected as plasticizers. The coating formulation contained 20 wt-% plasticizer and 80 wt-% HPMC. All samples were double coated.

[0077] The coating weights and barrier properties obtained are shown in Table 3. Good film formation was obtained with all plasticizers tested.

[0078] Table 3 Coating weight and barrier properties of samples of Example 1.

[0079]

[0080] From Table 3, it can be seen that all coating layers with different plasticizers show good grease barrier properties.

[0081] Example 2: Effect of adding inorganic pigments on coating properties

[0082] The effect of inorganic pigment addition of the following cellulose derivatives was tested: hydroxypropylmethylcellulose HPMC, methylcellulose MEC and hydroxyethylcellulose HEC. Ground calcium carbonate (HydroCarb60, Omya) was used as inorganic pigment. All coating formulations contained 20 wt-% plasticizer. In coating formulations containing HPMC or HEC, the plasticizer was PEG300; in coating formulations containing MEC, the plasticizer was D-sorbitol. The amounts of cellulose derivatives and inorganic pigments in the coating formulations are shown in Table 4. All samples were double coated.

[0083] The coating weights and barrier properties obtained are shown in Table 4.

[0084] Table 4 Coating formulations, achieved coating weights and barrier properties of samples of Example 2.

[0085]

[0086] As can be seen in Table 4, none of the HPMC or HEC samples tested showed cracking at the crease up to 30 wt-% pigment loading. For the coated structure with a double coating of HPMC and HEC, a KIT value of 12 was obtained for all pigment addition levels. The HPMC and HEC samples showed good grease barrier properties.

[0087] The MEC samples containing 10 wt-% inorganic pigments showed no cracking at the creases, whereas the MEC samples with higher inorganic pigment contents showed some cracking at the creases.For the double coated coated structures with MEC, KIT values ​​of 7-8 were obtained for all pigment addition levels.

[0088] Example 3: Coated structure with large amounts of inorganic pigments and additional binder

[0089] Higher pigment content in the coating structure was tested with hydroxyethylcellulose and hydroxypropylmethylcellulose coating formulations. Ground calcium carbonate GCC (HydroCarb 60, Omya) was used as an inorganic pigment. The influence of the presence of additional binders in the coating layer was also tested. The coating formulations used to make the coating layer are presented in Table 5.

[0090] Table 5 Coating formulations used in Example 3

[0091]

[0092] The resulting coating weights and barrier properties of the double coated samples are shown in Table 6. HVTR values ​​< 100 g / m 2 Demonstrates good barrier properties to mineral oils.

[0093] Table 6 Coating formulations, obtained coating weights and barrier properties of samples of Example 3.

[0094]

[0095]

[0096] From the results in Table 6, it can be seen that both HPMC and HEC gave good grease barrier as well as mineral barrier properties. In addition, the blocking results were good and the coating did not crack during creasing.

[0097] Example 4: Coated structure with high content of inorganic pigments

[0098] The coating formulations were tested with hydroxyethylcellulose and hydroxypropylmethylcellulose coating formulations with up to 50 wt-% inorganic pigment content in the coating structure. Ground calcium carbonate GCC (HydroCarb 60, Omya) was used as the inorganic pigment. The influence of the presence of an additional binder in the coating layer was also tested. The coating formulations used to make the coating layer are presented in Table 7.

[0099] Table 7 Coating formulation for Example 4

[0100]

[0101] The resulting coating weights and barrier properties of the double coated samples are shown in Table 8.

[0102] From the results in Table 8, it can be seen that the coating formulation has good grease barrier as well as mineral barrier properties. In addition, the blocking results are good.

[0103] Table 8 Coating formulations, obtained coating weights and barrier properties of samples of Example 4.

[0104]

[0105] Although the present invention has been described with reference to what currently appear to be the most practical and preferred embodiments, it should be understood that the present invention is not limited to the above-described embodiments, but the present invention is intended to cover various modifications and equivalent technical solutions within the scope of the appended claims.

Claims

1. A coating structure for a sheet-like substrate comprising cellulose fibers and / or lignocellulose fibers, the coating structure comprising at least a first coating layer and a second coating layer, wherein: The second coating layer is arranged in direct contact with the first coating layer, wherein at least the first coating layer or the second coating layer is a barrier coating layer, and wherein the barrier coating layer comprises: - 60-99 wt-% of at least one water-soluble cellulose derivative selected from the group consisting of any one of methylcellulose, hydroxymethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, (hydroxyethyl)methylcellulose and mixtures thereof, - 1-40 wt-% of a plasticizer, the plasticizer being a polyol selected from the group consisting of sorbitol, mannitol, ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, propylene glycol or polyethylene glycol, and - Inorganic pigment particles in the following amounts: When the water-soluble cellulose derivative is selected from alkylcellulose, the inorganic pigment particles in an amount of 5-20 wt-%, or When the water-soluble cellulose derivative is selected from hydroxyalkyl cellulose or hydroxyalkyl alkyl cellulose, the inorganic pigment particles are present in an amount of 20-60 wt-%, Wherein, the percentage is calculated from the total solids content of the barrier coating layer.

2. The coating structure according to claim 1, characterized in that: The barrier coating layer comprises the water-soluble cellulose derivative in an amount of 60-97 wt-%, calculated on the total solid content of the barrier coating layer.

3. The coating structure according to claim 1, characterized in that: The barrier coating layer comprises the plasticizer in an amount of 3-40 wt-%, calculated on the total solids content of the barrier coating layer.

4. The coating structure according to claim 1, characterized in that: The first coating layer and the second coating layer are barrier coating layers.

5. The coating structure according to claim 1, characterized in that: The first coating layer has a thickness of 2-30 g / m 2 The coating weight of the second coating layer is 0.5-20g / m 2 coating weight.

6. Use of a coating structure according to any one of claims 1 to 5 for providing a grease barrier when applied to a sheet-like product comprising cellulosic and / or lignocellulosic fibers.

7. Flake products, including: - a substrate comprising cellulose fibers and / or lignocellulose fibers and having a first major surface and a second major surface parallel to each other, and - A coating structure according to any one of claims 1 to 5 applied on at least the first large surface or the second large surface of the substrate.

8. The product according to claim 7, characterized in that The substrate has a thickness of 25-800 g / m 2 Weight.

9. The product according to claim 7 or 8, characterized in that The product has a KIT test value of at least 8 and / or <100 g / m 2 / d mineral oil barrier HVTR value.

10. Use of a sheet-like product according to any one of claims 7 to 9 for the manufacture of food service packaging.

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