Heat-extracted paper

Abstract

A water vapor permeable and hot water resistant paper made essentially from cellulose and manufacturing additives necessary for cellulose production, such as acid and / or base-based pH adjusters, the paper containing only cellulose having a length-weighted average fiber length of at least 2.0 mm, particularly at least 2.5 mm, the cellulose forming the paper being ground to a consistency of 30-35% by high-consistency grinding and optionally to a consistency of 4-6% by low-consistency grinding, the fines content of the paper being set to a value less than 6.5%, the pH value being set within the quasi-neutral range, particularly below 7.5, preferably between 6.6 and 7.4, and the machine direction elongation of the paper being 3% or less.

Description

[Technical field]

[0001] The present invention relates to a water vapour permeable and hot water resistant paper made essentially from cellulose and production additives necessary for cellulose production, such as pH value adjusters based on acids and / or bases, or made essentially from cellulose and production additives essential for cellulose production, such as pH value adjusters based on acids and / or bases. [Background technology]

[0002] Specialized water-vapor-permeable and hot-water-resistant papers, also called hot-extraction papers, for use as coffee filters, tea filters or for other applications must meet certain requirements, especially when used in the food sector. Not only the raw materials used (in this case wood chips or cellulose), but also the additives, can be finely standardized and selected from a very small number of specific substances.

[0003] The list of additives in this case varies depending on the chosen application and in particular requires that after hot water extraction, the total dry residue of the extract is 10 mg / dm 2 and in particular additives commonly used in paper production must be significantly reduced.

[0004] In this connection it became clear that the requirements differ depending on the subsequent use and that a paper suitable for making tea, for example, cannot be used as a cook-in bag.

[0005] However, besides conventional coffee and tea filters, many special papers are also known in the art and can be used, i.e. may be used, for example for the production of drinking cups sold for holding hot coffee or hot tea or soup. Thus, for example, EP1985437A1 discloses a method in which paper is processed into drinking cups etc., in which the paper can be used immediately after formation in the food sector, for example for hot coffee or hot tea.

[0006] In addition to conventional coffee filters, the demand for capsules of this kind has increased in recent years, since machines capable of brewing coffee or tea by receiving capsules containing coffee to be brewed are increasingly used not only in the industrial market but also in the home. The use of these machines generates a very large number of used plastic or metal capsules or both, which are currently mostly thrown away or are considered special waste. Since the problem of plastic waste, which is found in the most inaccessible places such as the middle of the ocean, is increasing everywhere, this growing problem must be reduced as much as possible by disposing of plastics to be recycled. Since metal capsules, especially aluminum capsules, are very expensive and their production requires high energy consumption, a new type of container for capsule-based coffee machines is needed, which allows coffee to be brewed using capsules filled with coffee, without using capsules that have to be treated costly and without risking the environment.

[0007] EP0422898A1 discloses an optimized design for a coffee capsule comprising two rolls of filter paper, one of which can be stretched by at least 3%, and the other paper, which forms the top surface of the capsule, is impregnated with a sealant such as polyethylene or polypropylene to make it sealable.

[0008] Furthermore, there is an increasing demand for containers containing pre-made foods, such as soup containers, yogurt pots and their lids, as well as containers for baking mixes, for example, where the product is ready for immediate consumption or can be completed within the package itself. In order to protect the environment, plastic containers or container lids are becoming more and more unpopular, and especially paper containers are becoming ever more sought-after alternatives. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] European Patent Application Publication No. 1985437 [Patent Document 2] European Patent Application Publication No. 0422898 Summary of the Invention [Problem to be solved by the invention]

[0010] It is an object of the present invention to provide a water vapour permeable and hot water resistant paper which is suitable for the production of sachets for heat extractable consumables such as milk, tea, cocoa, flavourings, as well as hot beverage containers such as soup containers, lids for tea and coffee capsules, etc., or also for the production of containers, lids or packaging for hot preparations of a wide variety of foods, and further which can be used directly for the packaging of a wide variety of liquid, creamy or paste-like foods. [Means for solving the problem]

[0011] To solve this problem, the water vapor permeable and hot water resistant paper is a paper that contains substantially only cellulose having a length-weighted average fiber length of at least 2.0 mm, in particular at least 2.5 mm, the cellulose forming the paper being ground to a consistency of 30-35% by high-concentration grinding and optionally to a consistency of 4-6% by low-concentration grinding, the proportion of fines in the paper being set to a value less than 6.5%, the pH value being set within the pseudo-neutral range, in particular at a pH value below 7.5, preferably between 6.6 and 7.4, and the machine direction elongation of the paper being less than or equal to 3%. By selecting a paper containing cellulose having a length-weighted average fiber length of at least 2.0 mm, in particular at least 2.5 mm, it is possible to produce a paper having a substantially higher tensile strength or burst strength compared to conventional papers. Furthermore, the proportion of fines in the water vapor permeable and hot water resistant paper is set to less than 6.5%, so that on the one hand the required air permeability of the paper is guaranteed and on the other hand the pore size of the paper can be selectively adjusted. Adjusting the pH value in the quasi-neutral range, i.e. to values ​​below 7.5 and preferably within the range of 6.6-7.4, means that the paper is not only suitable as a hot extract for hot drinks and soups, but it can also be used, for example, for hot extractable food supplements or directly for the production of containers and / or lids for such liquid, creamy or paste-like foods. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Since the cellulose from which the paper is made is cellulose that has been subjected to high consistency grinding and optionally low consistency grinding, it is possible to substantially increase the elongation of the paper in the cross direction compared to the longitudinal elongation, and it is further possible to ensure the removal of shives that are customarily contained therein when unbleached cellulose is used. According to the invention, the cellulose from which the paper is made has therefore been subjected to high consistency grinding at a consistency between 30% and 35% and, optionally, further low consistency grinding at a consistency between 4% and 6%.

[0013] Within the framework of the present application, when the term "paper" is chosen, this refers to a "water vapor permeable and hot water resistant paper" which can be used both as a container or its components and as a lid, in particular for liquid, creamy or paste-like foods, before, after or during their production, and which can also conventionally be used as a heat extraction paper, for example for the preparation of coffee, etc.

[0014] For a particularly good flat paper that also has the necessary strength properties, the elongation properties are substantially set so that the ratio between the breaking strain in the machine direction (MD) and the breaking strain in the cross direction (CD) is 1:5.5 or less, in particular 1:4.5 or less.

[0015] Furthermore, the limitation of the elongation of the water vapor permeable and hot water resistant paper, in particular the breaking strain in the machine direction to not more than 3%, preferably to a value between 1.5% and 3%, ensures good flatness despite the relatively large elongation in the cross direction, up to 9.5%, which is due to the cellulose fibers, and therefore makes it possible to produce papers suitable for example for soup containers, coffee capsules, lids or tops for containers for dairy products or even as containers for baking mixes. Dimensionally stable and strong papers can be formed which do not tear and whose fiber structure is not destroyed even when high temperatures and pressures are used, so that, despite this small elongation in the machine direction, this type of paper can provide the paper structure required for thermal extraction (including under pressure).

[0016] Cellulose having a length-weighted average fiber length of at least 2.5 mm refers to cellulose having an average fiber length of 2.5 mm, where the deviation from the average value is as small as possible, preferably no more than +0.8 mm, in particular no more than +0.4 mm, and particularly preferably no more than +0.2 mm.

[0017] By using cellulose with a length-weighted average fiber length of at least 2.0 mm, in particular 2.5 mm, the proportion of fines made of cellulose fibers with very short fiber lengths is suppressed. This type of paper makes it possible in particular to achieve uniform properties, which are suitable for use as tops for coffee capsules at high pressure, etc., without any risk of undesirable fines or ballast material getting into the beverage produced by the capsules etc. Taking into account the fact that there are very detailed regulations for the production of hot beverages, the skilled person will immediately understand that not only must the legal requirements be taken into account as to which components may have a water vapor permeable and hot water resistant paper, and in particular as to what amount of production additives or extractives from the added substances are contained in the final product, but also that it must be ensured that the paper is virtually free of additives that are not strictly required to be contained therein, and in particular that the number of added substances must be limited, taking into account also the fact that no impurities originating from the cellulose itself can get into the beverage produced. In this case, particular attention should be paid to the fact that this paper does not contain aluminum and is therefore permitted for applications requiring contact with food.

[0018] For further improvement in the food suitability of the water vapor permeable and hot water resistant paper, unbleached paper without shives is used. To achieve shive-free paper, the cellulose forming the paper is subjected to high-consistency grinding during paper production, in particular in the range of 130-190 kWh / t, preferably around 170 kWh / t, which makes it possible to remove all shives from the cellulose, but at the same time to avoid excessive stretching of the cellulose fibers in the cross direction. Shives constitute artifacts on the paper surface and therefore have a detrimental effect on the subsequent processing. Shives in the paper structure should be removed both in terms of appearance and in terms of strength. The method for determining the shive content is described in Tappi T275 - Somerville shive content. The paper according to the invention is considered herein to have less than 0.01% shive fragments at 0.15 mm slit width, measured according to Tappi T275.

[0019] Surprisingly, it is possible to produce water vapour permeable and hot water resistant papers, which can be produced without the addition of production additives, such as defoamers, precipitation inhibitors, starches, adhesion promoters, tackifiers, fillers etc., and which can nevertheless be produced on modern high speed paper machines, exhibiting machine speeds of up to 900 m / min, without the machine being operated substantially below its maximum speed. Usually the machine speed can only be accelerated through the addition of production additives known from the prior art, but this can be prevented through specially selected ingredients and their digestion and processing.

[0020] According to the invention, a water vapor permeable and hot water resistant paper is therefore developed in which only inorganic acids and inorganic bases, such as sulfuric acid (H2SO4) and caustic soda (NaOH), are used as pH value adjusters during its production. In this case, it is important that the chlorine content is kept particularly low in order to avoid the introduction of easily soluble chlorine into the final product by the hot water during extraction. Likewise, the nitrogen content in the water extract must be limited, since a higher nitrogen content can alter the flavor of beverages, baked cakes, etc. prepared with the paper. The content of nitrogen compounds separable at 220°C is determined photometrically by Kjeldal digestion according to DIN 38406-E5-1:1983-10 and is preferably limited to less than 0.025 mg / g dry matter.

[0021] According to the development of the invention, the cellulose is selected from cellulose from coniferous trees selected from the group including fir, spruce, pine, larch and Douglas fir. Coniferous trees are known to have high fiber length and are particularly commonly used in the production of paper, which must have high tensile strength. According to the invention, an attempt is made to select cellulose that is not only length-weighted, but also preferably derived from one and the same type of wood or from a mixture of two different woods, for example spruce and pine.

[0022] According to the development of the present invention, cellulose is selected for the water vapor permeable and hot water resistant paper so that not more than 15%, preferably not more than 10%, in particular about 5% of the cellulose from coniferous trees is replaced with cellulose from deciduous trees selected from the group including beech, oak, aspen, poplar, acacia, alder, maple, chestnut, dogwood, sycamore, lime and eucalyptus, or a mixture of two or more of them. In order to keep the properties of the paper substantially unchanged, not more than 15%, preferably not more than 10%, in particular about 5% of the cellulose can be replaced by cellulose from deciduous trees having shorter fiber length than that from coniferous trees. Despite this replacement, it is possible according to the present invention to maintain the breaking strain properties of the water vapor permeable and hot water resistant paper in particular.

[0023] This type of paper according to the invention has a density of 40 to 100 g / m 2 , preferably 50 to 80 g / m 2 The basis weight in this case is selected depending on the intended application, such as the heat or pressure to be applied for extraction, or the required time and type of application, and is often approximately 60 to 80 g / m 2 is within the range.

[0024] Since this is obviously suitable for any requirements for the extraction of food and beverages, according to the development of the present invention, the water vapor permeable and hot water resistant paper is selected such that the chlorine content of the hot water extract from the paper is below 0.7 mg / l and the aluminum content of the hot water extract from the paper is below 0.1 mg / l. In particular, the lowering of the aluminum content originating from additives and the low chlorine content allow the water vapor permeable and hot water resistant paper to be used in the food and beverage sector.

[0025] In particular, the water vapor permeable and hot water resistant paper is developed to be further calendered if necessary, so that the desired surface smoothness of this type of paper is reliably maintained or achieved. The optional step of calendering, in particular by means of a soft nip or long nip calender, and particularly preferably by means of a shoe calender, smooths the surface of the paper, but at the same time does not have too great a negative effect on the burst strength, elongation properties in the machine direction and the Gurley value. The selection of a shoe length of 50 to 170 mm in the shoe calender, for example a nip pressure of up to 10 MPa, a surface temperature of the calender rollers of up to 280° C., has a positive effect on the desired smoothing behavior and printability of the water vapor permeable and hot water resistant paper. When soft nip or long nip calenders, and especially shoe calenders, are used, it is advisable to ensure that the line load of the calender rollers does not exceed a value of 350 kN / m, preferably a value of 250 kN / m, and particularly preferably a value of 250 kN / m, in order to avoid excessive compression of the paper, so that the desired smoothness and printability of the paper can be achieved. In the case of long nip calenders, and especially shoe calenders, the value of the line load should not exceed 700 kN / m, preferably 600 kN / m, and particularly preferably 500 kN / m.

[0026] According to the development of the present invention, sulfate-treated unbleached cellulose is used for the water vapor permeable and hot water resistant paper.The use of unbleached cellulose means that the use of bleaching agents, which would otherwise be necessary, is avoided, which substantially improves the overall suitability of this paper as a free-standing pouch or lid for hot extraction containers or other containers in the food and beverage field and food additive field.

[0027] In accordance with the development of the present invention, the bending stiffness index in the machine direction is set to 70 to 600 Nm 6 / kg 3 , especially 170~400Nm 6 / kg 3 and particularly preferably 200 to 280 Nm6 / kg 3 By adjusting the tear resistance index to a value between 10.0 mN.m and 10.0 mN.m, it is ensured that the paper is flexible enough not to tear during use, while the stiffness is sufficient even for the production of, for example, stand-alone pouches. The adjustment of the specific tear resistance index is important in this context. In correspondence with the development of the present invention, this is substantially the same in the longitudinal and transverse directions and is between 10.0 mN.m and 10.0 mN.m. 2 / g~13.0mN.m 2 / g.

[0028] Finally, in order to reliably avoid the absorption of water by this type of water vapor permeable and hot water resistant paper and thereby the dampening of the product contained therein, and / or to guarantee a corresponding flavor protection, the invention has been developed to ensure that this paper has a coated design. At least one coating is applied to this paper, which must effectively stick to the water vapor permeable and hot water resistant paper according to the invention and cannot be accidentally peeled off, and in accordance with the development of the invention, the surface energy of this paper is 33 mJ / m 2 More than 35 mJ / m 2 More than 38 mJ / m 2 The surface energy is adjusted to be greater than 3 mJ / m. The surface energy in this case is considered to be the sum of the polar and dispersive parts of the paper and the layers of the paper close to the surface. The surface energy was determined using a Kruss measuring instrument; water and diiodomethane were used as test liquids. The difference in surface energy between the top side and the screen side of the paper is preferably less than 3 mJ / m. 2 , particularly preferably 2 mJ / m 2 In this way, it can be ensured that when a coating is applied, both sides of the paper behave equally, so that the coating does not accidentally peel off on one side, for example. The surface energy of the paper comes from the cellulose used and the production additives that are absolutely essential in the paper machine. Its adjustment is therefore possible, for example, via the selection of the cellulose.

[0029] The paper coating may for example be selected from one of the following methods: laminating, pasting or extrusion coating, or extrusion pasting, dispersion coating or metallizing. The coating materials used for the formation of this type of coating are mainly plastics that meet the requirements laid down under the legislation for foodstuffs for thermal extraction or thermal preparation, except for the metallizing process, and the whole composite of paper and coating(s) must comply with these requirements. Biodegradable or compostable plastics, such as polylactic acid or polyvinyl alcohol, are particularly preferred. However, in each case other corresponding materials, such as polyethylene or polypropylene, may also be used. One or both sides of the paper may be coated, and various numbers and types of plastics or materials may be used for the coating. The thickness of the corresponding layers is adapted to the respective material and other desired barrier properties and is between 5 and 25 μm, in particular between 7 and 20 μm per layer, not more than approximately 50 μm in total.

[0030] The water vapor permeable and hot water resistant paper is preferably used unbleached, although the use of bleached paper is in principle also possible, but due to the bleaching agents used in the production process it is less preferred than the use of natural brown paper.

[0031] The water vapour permeable and hot water resistant paper can be used in processes for producing capsules for tea and / or coffee preparations and / or tops for closures for yoghurt and milk products, or for the production of autonomous pouches for soup or hot beverage preparations, which may contain, for example, components that are additionally dissolved in the hot beverage if required, such as milk powder, tea, chocolate etc.

[0032] The invention is explained in more detail below with the aid of exemplary embodiments. With regard to the measurement of the variables used for the description of the properties of the produced products, the following criteria have been used for their measurement or determination, which are not listed separately below:

[0033] [Table 1] EXAMPLES

[0034] Example 1 Production of a first water vapor permeable and hot water resistant paper in accordance with the present invention. Unbleached sulfated kraft cellulose with a kappa number of 42, produced exclusively from 80%-81% spruce and 19%-20% pine wood, was used to produce water vapor permeable and hot water resistant paper. The pH was adjusted down using only 98% sulfuric acid in a sack paper machine operated pseudo-neutral at a maximum speed of over 1000 m / min (504 m / min was operated specifically for paper production). The resulting white water has a pH value of 6.2 to approximately 7.5. Chemicals normally used during paper production, such as alum, starch, precipitation inhibitors, defoamers, talc or other sizing agents, should not be used and any residual amounts of these materials in the produced paper can be ensured by closing the corresponding additional openings in the plant at least one hour before the start of the production of water vapor permeable and hot water resistant paper. Similarly, the fiber getter is transferred to another paper machine or other waste container to avoid contamination of paper with short fibers. This changeover is carried out several hours, preferably around 3 hours, before the start of production. In this case, the paper machine is operated in such a way that the waste paper itself, the dry waste and the scraps are not fed back into the stock during paper production. These streams are led into a so-called intermediate container during production.

[0035] The base material is subjected to a high-consistency grinding and then a low-consistency grinding, where the consistency is set between 30% and 35% for the high-consistency grinding and between 4% and 6% for the low-consistency grinding. Furthermore, the tension in the cross direction and the low-consistency grinding are controlled according to the porosity arrival (Gurley) over 17 to 20 seconds for the high-consistency grinding. In the above-mentioned exemplary embodiment, the specific grinding load during the high-consistency grinding is between 160 and 180 kWh / t and during the low-consistency grinding is between 120 and 145 kWh / t.

[0036] The paper machine is provided with a long screen of the Fourdrinier screen section. The paper is pressed in the press section using two conventional nips and a shoe press with pressure in the first nip of 55 kN / m, the second nip of 75 kN / m and a shoe pressure at a pressure of 500 kN / m. The water vapor permeable and hot water resistant paper is dried in the dryer section using slalom drying. Drying continues until the target value of 7% residual moisture is reached.

[0037] The paper produced by this method has the following: 17s air permeability (Gurley) 207Nm 6 / kg 3 Bending stiffness index 61g / m 2 Basis weight of, and 1.92% strain at break in machine direction 6.25% strain at break in the cross direction.

[0038] To test the properties, a hot extract was made from 2 g of paper using 100 ml of water by boiling in reduced water for 1 hour according to the ISO 6588-2:2012 standard, without the buffer / potassium chloride solution specified in the standard.

[0039] The fiber material was filtered off and the chlorine in the filtrate was determined by ion chromatography and the aluminum ions by atomic absorption spectrometry. It was demonstrated that a chlorine content of 0.62 mg / l and an aluminum content of 0.079 mg / l were achieved. A pH value of 6.8 was determined in the filtrate.

[0040] The cellulose had a fiber length of 2.47 mm, a fines percentage of 6.48% (fraction 0.05-0.5 mm) and a shive fiber content of 0.005%.

[0041] The surface energy of the upper side is 40 mJ / m 2 and the screen side is 42 mJ / m 2 It was.

[0042] Example 2 Production of a second water vapor permeable and hot water resistant paper according to the present invention. Unbleached sulfated kraft cellulose with a kappa number of 41, produced exclusively from 80%-81% spruce and 19%-20% pine wood, was used to produce water vapor permeable and hot water resistant paper. The pH was adjusted down using only 98% sulfuric acid in a sack paper machine operated pseudo-neutral at a maximum speed of over 1000 m / min (operated at approximately 504 m / min specifically for paper production). The resulting white water has a pH value of 6.2 to approximately 7.5. Chemicals normally used in paper production, such as alum, starch, precipitation inhibitors, defoamers, talc or sizing agents, should not be used and any residual amounts of these materials in the produced paper can be ensured by closing the corresponding additional openings in the plant at least one hour before paper production begins. Similarly, to avoid contamination of the water vapor permeable and hot water resistant paper with short fibers, the fiber getter is transferred to another paper machine or other waste container. This changeover is carried out several hours, preferably around 3 hours, before the start of production. In this case, the paper machine is operated in such a way that the waste paper itself, the dry waste and the scraps are not fed back into the stock during paper production. These streams are led into a so-called intermediate container during production.

[0043] The base material is subjected to a high-consistency grinding and then a low-consistency grinding, where the consistency is set between 30% and 35% for the high-consistency grinding and between 4% and 6% for the low-consistency grinding. Furthermore, the tension in the cross direction and the low-consistency grinding are controlled according to the porosity arrival (Gurley) over 17 to 20 seconds for the high-consistency grinding. In the above-mentioned exemplary embodiment, the specific grinding load during the high-consistency grinding is between 160 and 180 kWh / t and during the low-consistency grinding is between 120 and 145 kWh / t.

[0044] The paper machine is provided with a long screen, in particular the Fourdrinier screen section. The paper is pressed in a press section using two conventional nips and a shoe press with a pressure in the first nip of 55 kN / m, the second nip of 75 kN / m and a shoe pressure at a pressure of 500 kN / m. The water vapor permeable and hot water resistant paper is dried in the dryer section using slalom drying. Drying continues until a target value of 7% residual moisture is reached.

[0045] The paper produced by this method has the following: 15.1s air permeability (Gurley) 237Nm 6 / kg 3 Bending stiffness index 65g / m 2 Basis weight of, and 1.77% strain at break in machine direction The fracture strain in the cross direction is 7.69%.

[0046] To test the properties, a hot extract was made from 2 g of paper using 100 ml of water by boiling in reduced water for 1 hour according to the ISO 6588-2:2012 standard, without the buffer / potassium chloride solution specified in the standard.

[0047] The fiber material was filtered off and the chlorine in the filtrate was determined by ion chromatography and the aluminum ions by atomic absorption spectrometry. It was demonstrated that a chlorine content of 0.66 mg / l and an aluminum content of 0.052 mg / l were achieved. A pH value of 6.7 was determined in the filtrate.

[0048] The cellulose had a fiber length of 2.62 mm, a fines percentage of 5.19% (fraction 0.05-0.5 mm) and a shive fiber content of 0.005%.

[0049] The surface energy of the upper side is 39 mJ / m 2 and the screen side is 41 mJ / m 2 It was.

[0050] Example 3 A third method for producing water vapor permeable and hot water resistant paper according to the present invention. Bleached sulfuric kraft cellulose with a kappa number of less than 5, produced from 56%-60% spruce, 25%-29% pine and 15% birch, was used to produce water vapor permeable and hot water resistant paper. The pH was adjusted down using only 98% sulfuric acid in a sack paper machine operated pseudo-neutral at a maximum speed of approximately 900 m / min (operated at approximately 620 m / min specifically for paper production). The resulting white water has a pH value of 6.7 to approximately 6.9. Chemicals normally used in paper production, such as alum, starch, precipitation inhibitors, defoamers, talc or sizing agents, should not be used and any residual amounts of these materials in the produced paper can be ensured by closing the corresponding additional openings in the plant at least one hour before paper production begins. Similarly, the fiber getter is transferred to another waste container to avoid contamination of paper with short fibers. This changeover is carried out several hours, preferably approximately 3 hours, before the start of production. In this case, the paper machine is operated in such a way that the waste paper itself, the dry waste and the scraps are not fed back into the stock during paper production: these streams are led into a so-called intermediate container during production.

[0051] The base material is subjected to a high-consistency grinding and then a low-consistency grinding, where the consistency is set between 30% and 35% for the high-consistency grinding and between 4% and 6% for the low-consistency grinding. Furthermore, the tension in the cross direction and the low-consistency grinding are controlled according to the porosity arrival (Gurley) over 17 to 20 s. In the above-mentioned exemplary embodiment, the specific grinding load during high-consistency grinding is between 70 and 80 kWh / t and during low-consistency grinding is 40 to 50 kWh / t.

[0052] The paper machine is provided with a long screen, in particular the Fourdrinier screen section. The paper is produced in the press section using three nips, with a first nip of 60 kN / m, a second nip of 90 kN / m and a third nip of 95 kN / m. The paper is dried in the dryer section using slalom drying. Drying continues until a target value of 7% residual moisture is reached.

[0053] The paper produced by this method has the following: 19.2s air permeability (Gurley) 83Nm 6 / kg 3 Bending stiffness index 100g / m 2 Grammage 2.12% strain at break in machine direction The fracture strain in the cross direction is 7.83%.

[0054] To test the properties, a hot extract was made from 2 g of paper using 100 ml of water by boiling in reduced water for 1 hour according to the ISO 6588-2:2012 standard, without the buffer / potassium chloride solution specified in the standard.

[0055] The fiber material was filtered off and the chlorine in the filtrate was determined by ion chromatography and the aluminum ions by atomic absorption spectrometry. It was demonstrated that a chlorine content of 0.69 mg / l and an aluminum content of 0.038 mg / l were achieved. A pH value of 6.8 was determined in the filtrate.

[0056] The cellulose had a fiber length of 2.33 mm, a fines fraction of 6.24% (fraction 0.05-0.5 mm) and a shive fiber content of 0.001%.

[0057] The surface energy of the upper side is 44 mJ / m 2 and the screen side is 46 mJ / m 2 It was.

[0058] Example 4 A fourth method for producing water vapor permeable and hot water resistant paper according to the present invention. Unbleached sulfated kraft cellulose with a kappa number of 44, produced exclusively from 80%-81% spruce and 19%-20% pine wood, was used to produce a water vapor permeable and hot water resistant paper. The pH was adjusted down using only 98% sulfuric acid in a sack paper machine operated pseudo-neutral at a maximum speed of approximately 900 m / min (operated at approximately 605 m / min specifically for paper production). The resulting white water has a pH value of 6.6 to approximately 7.1. Chemicals normally used in paper production, such as alum, starch, precipitation inhibitors, defoamers, talc or sizing agents, should not be used and any residual amounts of these materials in the paper produced can be ensured by closing the corresponding additional openings in the plant at least one hour before paper production begins. Similarly, to avoid contamination of paper with short fibers, the fiber getter is transferred to another paper machine or other waste container. This changeover is carried out several hours, preferably approximately 3 hours, before the start of production. In this case, the paper machine is operated in such a way that the waste paper itself, the dry waste and the scraps are not fed back into the stock during the production of the water vapor permeable and hot water resistant paper: these streams are led into a so-called intermediate container during production.

[0059] The base material is subjected to a high-consistency grinding and then a low-consistency grinding, where the consistency is set between 30% and 35% for the high-consistency grinding and between 4% and 6% for the low-consistency grinding. Furthermore, the tension in the cross direction and the low-consistency grinding are controlled according to the porosity arrival (Gurley) over 17 to 20 seconds for the high-consistency grinding. In the above-mentioned exemplary embodiment, the specific grinding load during the high-consistency grinding is between 170 and 190 kWh / t and during the low-consistency grinding is between 90 and 120 kWh / t.

[0060] The paper machine is equipped with a long screen, in particular a Fourdrinier screen section. The paper is produced in a press section using three nips, with a first nip of 70 kN / m, a second nip of 90 kN / m and a third nip of 105 kN / m.

[0061] The paper is dried in the dryer section using slalom drying. Drying is continued until a target value of 7% residual moisture is reached.

[0062] The paper produced by this method has the following: Air permeability of 18.7s (Gurley) 422Nm 6 / kg 3 Bending stiffness index 40g / m 2 Grammage 2.28% strain at break in machine direction The fracture strain in the cross direction is 8.21%.

[0063] To test the properties, a hot extract was made from 2 g of paper using 100 ml of water by boiling in reduced water for 1 hour according to the ISO 6588-2:2012 standard, without the buffer / potassium chloride solution specified in the standard.

[0064] The fiber material was filtered off and the chlorine in the filtrate was determined by ion chromatography and the aluminum ions by atomic absorption spectrometry. It was demonstrated that a chlorine content of 0.59 mg / l and an aluminum content of 0.071 mg / l were achieved. A pH value of 6.7 was determined in the filtrate.

[0065] The cellulose had a fiber length of 2.51 mm, a fines percentage of 5.45% (fraction 0.05-0.5 mm) and a shive fiber content of 0.005%.

[0066] The surface energy of the upper side is 37 mJ / m 2 and the screen side is 39 mJ / m 2 It was.

Claims

1. A water vapor permeable and hot water resistant paper made essentially from cellulose and production additives necessary for cellulose production based on acids and / or bases, the paper containing only cellulose having a length weighted average fiber length of at least 2.0 mm, in particular at least 2.5 mm, the cellulose forming the paper being ground to a consistency of 30-35% by high consistency grinding and optionally to a consistency of 4-6% by low consistency grinding, the proportion of fines consisting of cellulose fibers in the paper being set to a value of less than 6.5%, the pH value being set within the pseudo-neutral range, in particular to a pH value below 7.5, and the elongation in the machine direction of the paper being less than 3%.

2. The paper described in claim 1, wherein the pH value is set to a pH value between 6.6 and 7.

4.

3. 3. Paper according to claim 1 or 2, in which the ratio of breaking strain in the machine direction (MD) to breaking strain in the cross direction (CD) is at most 1:5.5, in particular at most 1:4.

5.

4. 4. Paper according to any one of claims 1 to 3, wherein the cellulose is selected from cellulose derived from conifers selected from the group comprising fir, spruce, pine, larch and Douglas fir or a mixture of two or more thereof.

5. 5. The paper of claim 4, wherein up to 15% of the cellulose from conifers is replaced by cellulose from deciduous trees selected from the group including beech, oak, aspen, poplar, acacia, alder, maple, chestnut, dogwood, sycamore, lime and eucalyptus or a mixture of two or more thereof.

6. The paper according to claim 5, wherein up to 10%, in particular approximately 5%, of the cellulose from coniferous trees is replaced by cellulose from deciduous trees selected from the group comprising beech, oak, aspen, poplar, acacia, alder, maple, chestnut, dogwood, sycamore, lime and eucalyptus or a mixture of two or more thereof.

7. The paper according to any one of the preceding claims, wherein the paper has a basis weight between 40 and 100 g / m 2 .

8. The paper of claim 7, wherein the paper has a basis weight of between 50 and 80 g / m 2 .

9. Paper according to any one of the preceding claims, having an air permeability according to Gurley between 15s and 25s, in particular between 17s and 20s.

10. The paper according to any one of claims 1 to 9, wherein the chlorine content of the water extract from the paper is less than 0.7 mg / l and the aluminium content of the water extract from the paper is less than 0.1 mg / l.

11. 70 to 600 Nm ６ / kg ３ , especially 170 to 400 Nm ６ The paper according to any one of claims 1 to 10, having a bending stiffness index in the machine direction of 1 / kg 3 .

12. Paper according to any one of the preceding claims, wherein the paper is optionally calendered, in particular in a soft nip or long nip calender, and in particular in a shoe calender.

13. The surface energy of the paper is 33 mJ / m ２ The paper according to any one of claims 1 to 12, wherein the thickness is adjusted to exceed 14. The paper of claim 13, wherein the surface energy of the paper is adjusted to exceed 35 mJ / m 2 .

15. Use of the water vapour permeable and hot water resistant paper according to any one of claims 1 to 14 in a process for the production of foodstuff containers selected from sachets, paper lids for coffee capsules, yoghurt pots or soup containers, or containers for baking mixes.

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