Method for producing a base paper

Abstract

The invention relates to a method for producing a base paper, in which a cellulose pulp containing substantially both softwood and hardwood components, as well as optionally additives, is subjected to a grinding step, and at least one compacting step is carried out, in which method: an optionally bleached cellulose pulp, consisting of 55 to 80 parts by weight, in particular 60 to 80 parts by weight of hardwood primary cellulose and 25 to 45 parts by weight, in particular 30 to 40 parts by weight of softwood primary cellulose, as well as up to 3 parts by weight of filler, is provided; the cellulose pulp is obtained by mixing one pulp made from hardwood and one pulp made from softwood; either each pulp that makes up the cellulose pulp is separately ground to a degree of refinement of 39 to 45 °SR according to ISO 5267-1:1999 for the pulp made from hardwood and 35 to 41 °SR according to ISO 5267-1:1999 for the pulp made from softwood, or the pulp obtained by mixing the pulp made from hardwood and the pulp made from softwood is ground to a degree of refinement of 39 to 42 °SR; the mixed pulp is subjected to dewatering; a formed sheet is calendered on at least one side; and optionally at least one impregnation is applied to at least one side. The invention also relates to a base paper produced according to the method.

Description

[0001] METHOD FOR PRODUCING A BASE PAPER

[0002] The present invention relates to a process for producing a base paper, in which a pulp containing essentially both softwood and hardwood components and optionally additives is subjected to a refining step and at least one compaction step is carried out, as well as a base paper produced according to this process.

[0003] Paper, especially for packaging purposes, is used for a wide variety of materials and objects, and in recent times there have been increasing attempts to replace plastic packaging with paper packaging. In order to meet the respective requirements and in particular to achieve the material properties of plastic packaging, the paper used must have appropriate surface properties, strength, and barrier properties against moisture, grease, and / or gases. In addition, it must be able to hold the packaged goods safely and reliably without the paper tearing, being punctured, becoming so saturated in humid environments that it no longer has any stability or tear resistance, etc.Until now, the papers used for this purpose were usually coated with relatively thick polymer materials such as polyethylene, polylactic acid, polypropylene, and the like. This combined effect provided a combination of the positive properties of the paper used and the positive properties of plastic packaging, while simultaneously reducing the amount of plastic required for the respective packaging. However, for environmental reasons, particularly recycling reasons, such packaging is no longer appropriate, and there are increasing attempts to provide packaging or packaging materials that essentially require no non-recyclable plastics, or that contain only such small amounts of plastic, particularly biodegradable plastic, that sustainable and, in particular, compostable or fully recyclable packaging can be provided.Regardless of the requirements placed on such papers, such as a certain degree of stretchability, air permeability or air resistance, in order to be able to fill powdered materials quickly and reliably, as well as to maintain a certain degree of resistance to tearing of the paper or a product made from it when dropped, etc., it is an essential prerequisite for many papers that they have at least temporary resistance to penetration by moisture and / or grease, which has so far been achieved mainly by applying a plastic coating to one or both sides of the paper.The thicker or denser such a coating is, the less suitable such paper is for recycling or, in particular, composting and must be disposed of with residual waste as it is no longer suitable for the production of recycled paper. Another possibility for achieving resistance of a paper to moisture and / or grease is to seal at least one paper surface using pressure, by smoothing the surface by applying pressure using rollers. In this process, particularly when a relatively high pressure is applied, the surface pores present in the paper are closed and the paper surface is thus perfectly prepared for the application of grease and / or moisture barrier layers.Such surface smoothing can be achieved, for example, by using a so-called supercalender, which is a calender that has a large number of nips arranged one behind the other. The disadvantage of using a supercalender is that treating a base paper in such a system weakens the paper so much that it is no longer usable for packaging purposes. Another possibility or a supplementary possibility to prevent such penetration of moisture and / or grease into or through the paper is to produce a so-called filled paper, in which a relatively large amount of additives such as carboxymethyl cellulose (CMC), microfibrillated cellulose (MFC) or nanofibrillated cellulose (NFC) orContains fillers, which additives fill the pores inside the paper and thus close them, which is why penetration of moisture or grease, for example, is prevented or greatly reduced. Furthermore, such papers are often made exclusively from hardwood pulp, as their surfaces can be smoothed more easily and thus have better prerequisites for the subsequent application of a coating. However, in terms of their mechanical properties, such as the tensile strength index, such papers are significantly poorer than, for example, kraft papers made from softwood. Due to these poorer mechanical properties, they are therefore only ill-suited for use in the packaging sector, especially when other special properties, such as resistance to moisture or the like, are required.

[0004] Finally, there are papers used in the packaging sector that can provide a certain moisture and grease barrier due to their relatively high basis weight, their multi-layer structure, or the use of barrier materials such as coatings or impregnations. The disadvantage of these papers is that their production requires a high level of raw material input and the use of additional coatings or surface treatment processes. Therefore, such papers are generally disadvantageous due to both the high material consumption and the resulting high energy consumption during their production.

[0005] In the course of investigations, the applicant has found that the above-mentioned problems in the production of papers with certain barrier properties, such as moisture-resistant and / or grease-resistant papers, essentially arise from the fact that the base papers used in the production of such papers are not optimally suited to achieving a corresponding barrier property, which is why not all properties of the desired end product, such as filler content, basis weight, mechanical properties and / or barrier properties, can be optimized.

[0006] The present invention now aims to provide a process for producing a base paper which, on the one hand, can be produced in a particularly energy-efficient manner and, on the other hand, is particularly well suited as a base paper for the subsequent application of moisture-resistant and / or grease-repellent coatings or surface treatment steps.

[0007] To achieve this object, the process according to the invention for producing a base paper is essentially characterized in that an optionally bleached cellulose pulp consisting of 55 to 80 parts by weight, in particular 60 to 80 parts by weight, of hardwood primary cellulose and 25 to 45 parts, in particular 30 to 40 parts by weight, of softwood primary cellulose and up to 3 parts by weight of filler is provided, that the cellulose pulp is obtained by mixing one pulp each made from hardwood and one from softwood, that either each pulp forming the cellulose pulp is subjected to separate refining to a degree of freeness of 39 to 45 °SR in accordance with ISO 5267-1:1999 for the pulp made from hardwood primary cellulose or35 to 41 °SR according to ISO 5267-1:1999 for the pulp from softwood primary pulp or which is subjected to refining to a freeness of 39 to 42 °SR by mixing the pulp obtained from hardwood primary pulp and the pulp from softwood primary pulp, that the mixed pulp is subjected to dewatering, that a formed sheet is calendered at least on one side and optionally at least on one.

[0008] By providing an optionally bleached cellulose pulp consisting of 55 to 80 parts by weight, in particular 60 to 80 parts by weight, of hardwood primary cellulose and 25 to 45 parts, in particular 30 to 40 parts by weight, of softwood primary cellulose as well as up to 3 parts by weight of filler, it is possible to optimally utilize the advantageous properties of hardwood primary cellulose and softwood primary cellulose, such as good strength properties and good printability, without having to use, or in above-average amounts, conventional process chemicals such as cationic polymers and the like. By using only small amounts of filler, namely up to 3 parts by weight.-Parts succeed in saving drying energy, and in addition, the non-swellable filler further contributes to either the compaction of the sheet or the surface smoothness, which is why base paper produced in this way can not only serve as the basis for packaging papers suitable for use in the food industry, but can also be produced with significantly lower energy consumption than conventional base or base papers. Thus, base paper produced from a pulp with this composition exhibits good strength properties on the one hand, and at the same time, due to the high proportion of hardwood primary pulp, it is possible to produce extremely thin base papers, i.e., papers with a low basis weight while simultaneously offering good printability and smoothness.State-of-the-art base papers used to produce grease and / or moisture barrier papers typically have significantly higher basis weights and lower mechanical strengths. Surprisingly, it is irrelevant in this context whether the pulp is bleached or unbleached; it has only been found to be essential that the base paper produced according to the present process contains a higher proportion by weight of hardwood primary pulp than of softwood primary pulp. In this context, primary pulp means that only virgin fibers or reject fibers directly from the paper machine are used, and no recycled paper is used.

[0009] In the context of this text, a raw paper or base paper is understood to be a finished and ready-to-use paper, which can also be subjected to further treatment, such as impregnation and / or coating. After such further treatment, this paper is

[0010] Raw paper as defined in the present application produces a packaging paper.

[0011] According to the invention, the process is conducted such that the cellulose pulp is obtained by mixing one hardwood pulp and one softwood pulp. Therefore, according to the invention, one hardwood pulp and one softwood pulp are produced separately, which are then mixed after their production or after a separate milling step for each of the two pulps.

[0012] By conducting the process in such a way that either each pulp forming the cellulose pulp is subjected to separate refining to a degree of 39 to 45 °SR for the pulp from hardwood or 35 to 41 °SR for the pulp from softwood, or by subjecting the pulp obtained by mixing the pulp from hardwood and the pulp from softwood to a degree of 39 to 42 °SR, it is possible to ensure that a compaction of a sheet produced from this cellulose pulp which is particularly suitable for subsequent coating of the base paper can be achieved, while at the same time the degree of refining is adjusted in such a way that shortening of the fibres contained in the cellulose pulp does not occur, which would therefore impair the mechanical properties of a base paper produced therefrom.Furthermore, the above-mentioned refining levels ensure that the base paper can be produced in an energy-efficient manner due to the still moderate refining and drying energy required. If, as is possible with the present invention, the softwood pulp and the hardwood pulp are refined separately, the respective pulp fibers can be taken into account even more precisely by adjusting the refining level, and in particular, fiber shortening and destruction of the fiber sheath can be more reliably avoided.

[0013] By further conducting the process such that the pulp is refined to a degree of beating in the range of 42°SR, and subsequently subjecting the mixed pulp to dewatering, for example, on a Fourdrinier screen, the dewatering step is slowed down somewhat. On the other hand, however, this method makes it possible to optimize the density and, in particular, the homogeneous product properties of a paper produced in this way without having to expend an excessive amount of drying energy during the drying process, just as it does not require the application of excessively high pressure in a subsequent calendering step. Thus, surprisingly, the softwood components used make it possible to achieve cloudiness or sheet formation in the paper while simultaneously fully retaining the good mechanical properties.By conducting the process in this way, not only can the product properties be optimized in terms of mechanical properties and density, but the process can also be carried out with significantly reduced energy consumption, both in terms of electrical energy and steam consumption.

[0014] By further conducting the process such that a sheet formed after dewatering the pulp is calendered on at least one side and, if appropriate, at least one impregnation is applied to at least one side, a compacted surface is achieved that is smooth on at least one side, but still has sufficient porosity to prevent, for example, complete exclusion of air from objects packaged in the base paper. Using such a process, for example, a base paper with an air resistance (Gurely), measured according to ISO 5636-5:2013, in the range of approximately 150 to 300 s can be achieved, whereby a base paper produced in this way is optimally suited for subsequent coating despite air permeability, which has a positive effect on energy consumption during the production process.If necessary, such packaging paper can be impregnated and / or coated at least once on at least one side, whereby the impregnations and / or coatings can be selected and applied depending on the intended use. Surprisingly, this process allows any impregnations or coatings applied to penetrate or be pressed into the paper to a certain extent, whereby not only is a packaging paper with outstanding mechanical properties achieved from the base paper, but such good grease and / or moisture resistance of the paper can also be ensured while simultaneously ensuring low chemical consumption for such coatings and / or impregnations.The low amount of chemicals required also enables the chemicals to be firmly anchored to the paper surface, which is why coatings formed in this way are surprisingly less prone to flaking. Due to the structure of the paper surface of the base paper produced using the process according to the invention, it is possible to use small amounts of coating chemicals. This ensures that, unlike grease and / or moisture-resistant packaging papers according to the state of the art, the maximum amounts of coating chemicals specified by law are not exceeded and that the use of the base paper and also of a coated packaging paper based on it is possible and permitted in the food sector. Paper produced in this way can therefore be used as packaging for vegetables, meat, ice cream or the like.be used without it softening or fat contained in the packaged food penetrating the paper.

[0015] According to a further development of the method according to the invention, the method is carried out in such a way that the softwood pulp and the hardwood pulp are each subjected to a separate refining process and subsequently mixed, and that the fiber length of a mixture of hardwood pulp and softwood pulp is adjusted to an average length-weighted fiber length according to ISO 16065-2:2014 of 1.00 mm to 1.35 mm. With this type of process, the fiber length of the hardwood pulp fiber is not shortened during refining, and that of the softwood portion also remains essentially unchanged, so that overall a homogeneous pulp is achieved with a slightly longer average length-weighted fiber length compared to pulps made exclusively from hardwood. Packaging paper made from this type of base paper still has the positive mechanical properties of the long-fiber orSoftwood pulp fibers and, surprisingly, due to the larger hardwood content in the pulp, it is also possible to produce a mechanically strong packaging paper with good printability and favorable surface properties from the base paper without the need for excessive amounts of coating chemicals, which nevertheless has ventilation or air permeability, for example when filled with powdery or granular goods. It is irrelevant whether the base paper according to the invention is used directly or whether a packaging paper made from the base paper and having a surface treatment, such as calendering or impregnation, is used. In the context of the present invention, pulps are understood to mean pulps produced by the kraft process.By carrying out the dewatering of the mixed cellulose pulps at a paper machine speed of 700 m / s to 850 m / s, as corresponds to a further development of the method according to the invention, this ensures, on the one hand, that the cellulose pulp is dewatered sufficiently quickly and, on the other hand, taking into account the selected high degree of refining, the machine speed only needs to be reduced to a justifiably small extent compared to that used in the production of packaging papers with unrefined or only slightly refined papers, with refining degrees in the range of 22 °SR. What is surprising in this context is that the machine speed can be kept relatively high compared to pulps with only a low degree of refining and, despite this, good dewatering and homogeneous sheet formation can be achieved.Surprisingly, it has been shown that, due to the use of softwood fibers, which, for example, allows a reduction in the basis weight of the base paper according to the invention while simultaneously maintaining the required mechanical strength, the dewatering rate of the paper machine can even be increased by about 5% when using the blended cellulose pulps, despite the relatively high degree of freeness. The filler content of up to 3% used according to the invention also contributes to this, promoting dewatering or drying while nevertheless not having a negative effect on the mechanical strength.

[0016] By carrying out the method according to a further development thereof in such a way that the at least one-sided calendering of a sheet of base paper formed after dewatering, for example on a Fourdinier or any other wire section with a bottom and top former, is carried out with a hardnip calender, preferably a hardnip calender heated to a maximum of 150 °C, more preferably a maximum of 90 °C, at a line load of 50 to 200 kN / m, more preferably 70 to 120 kN / m, it is possible, on the one hand, to ensure good smoothness and thus printability of a packaging paper produced from the base paper or also of the base paper itself, and, in particular, to achieve a mechanical surface finishing, in particular surface compaction of the paper, which reduces the porosity on the surface thereof to such an extent that a coating or coating applied subsequently, if necessary, is not required.Impregnation can penetrate the paper structure not too deeply, but at least to a small extent, and can therefore be carried out with significantly reduced chemical consumption compared to non-calendered papers. At the same time, good printability of the surface is achieved, whereby the consumption of printing inks and dyes can also be reduced due to the small surface pores.

[0017] According to a further development of the invention, the process is carried out in such a way that the base paper is calendered on both sides. With double-sided calendering, it is possible to smooth both surfaces of the paper to such an extent that the base paper produced in this way can already be used for packaging applications without the additional application of a coating and / or impregnation. Thus, calendering makes it possible to

[0018] Bendtsen roughness of the paper (measured according to ISO 8791-2.2013) to values ​​in the range of 60 to 150 ml / min, preferably about 120 ml / min, compared to non-calendered paper, which has a Bendtsen roughness in the range of up to 900 ml / min. As is the case with a further development of the present invention, the process is carried out in such a way that, before or after calendering, a coating of at least one side of the base paper with surface starch and sizing agent, in particular in a total application quantity of 0.8 to 2 g / m 2is carried out, such a process not only makes it possible to impart additional strength and dimensional stability to the paper produced in this way, but above all also makes it possible to significantly improve its printability, surprisingly without there being any risk of bleeding or running of the printing inks used when using the base paper itself or a packaging paper made from it. According to a development of the process according to the invention, both sides of the base paper are each coated with at least one layer, in particular with different coating materials, selected from polyolefins such as polyethylene or polypropylene, starches and modified starches, acrylates, polyalcohols such as polyvinyl alcohol, ethylene-vinyl alcohol or polylactic acid.By applying at least one such additional coating to both sides of the base paper, a further improvement in the grease and / or moisture resistance and, where appropriate, also a gas barrier property against oxygen and aromas of a packaging paper produced from the base paper is achieved.

[0019] For a further improvement of the moisture and / or grease resistance, the process is essentially carried out in such a way that before or after calendering and before coating, an impregnation, preferably two-sided impregnation of the base paper is carried out by applying and pressing in a dispersion or solution selected from starches or modified starches, acrylates, polyalcohols, such as polyvinyl alcohol with at least 1.5 g / m 2 , preferably at least 2.0 g / m 2is carried out. With such further impregnation of the surface of the paper, it is possible to further improve the surface properties of such a paper and, in particular, to further seal the pores of the packaging paper made from the base paper. Such additional impregnation is carried out according to the invention in small amounts of at least 1.5 g / m 2applied. This can involve impregnation with a starch solution, which also improves the mechanical strength of the base paper. This type of process makes it possible to provide the paper with a better barrier effect across its entire cross-section. Surprisingly, it has been shown that if a surface coating is also applied, a synergistic effect can be achieved. A synergistic effect in the sense that the paper is overall more robust during processing than if only the improvements in the properties of two individual surface treatment processes are added together. It has been shown that the achieved barrier effect is less damaged by folding, kinking, gluing, etc. during processing or in use than if only a surface coating had been applied.The process according to the invention thus surprisingly makes it possible to provide a base paper which has a smooth surface, is easy to print on and has surprisingly good mechanical properties. In terms of its surface smoothness, the paper is comparable to conventional translucent papers, such as glassine papers, and can replace them, which is surprising given the high softwood content in the paper. At the same time, the base paper can be produced without the addition of process additives, such as cationic retention polymers and the like, which further favors the use of either the base paper itself or a packaging paper made from it in the food sector. Due to the large amount or the large weight proportion of up to 45 weight.-Parts of softwood pulp fibers, it is surprisingly possible to impart mechanical properties to the base paper that almost correspond to the mechanical properties of kraft paper made exclusively from softwood. Through the intensive refining of the softwood pulp as well as the moderate refining of the hardwood pulp to °SR values ​​in the range of 40, not only is maximum compaction in the subsequent calendering step achieved to values ​​in the range of up to 900 kg / m³. 3 of the resulting base paper, but surprisingly, the good mechanical properties achieved by the addition of the long-fibered softwood can be maintained at the same time.

[0020] A base paper produced by the process according to the invention is essentially characterized in that the base paper has an ash content of less than 4% and a content of fines with a size of < 0.2 mm of less than 36% as well as a specific tear resistance index according to ISO 1974:2012 of > 8 mN.m 2 / g in machine direction and > 9 mN,m 2 / g in the transverse direction. The extremely low ash content in the base paper ensures that it is essentially free of production aids such as cationic retention polymers. Furthermore, the content of fines with a size of < 0.2 mm is less than 36%, ensuring that the paper is sufficiently refined to be highly compacted, which results in a final density of the base paper according to the invention of approximately 900 kg / m 3and, on the other hand, this fines content ensures that excessive energy expenditure is not required during the paper manufacturing process and that excessive slowing of the paper machine at the press to, for example, values ​​below 800 m / min can be avoided, which higher fines contents would undoubtedly cause. By providing a base paper produced according to the process according to the invention, it has surprisingly been found that a specific tear resistance index of this paper according to ISO 1974:2012 > 8 mN.mVg in the machine direction and > 9 mN.mVg in the transverse direction can be achieved. Such a paper is surprisingly tear-resistant despite a low basis weight, especially compared to papers made from hardwood pulp, and can therefore be used in applications in which it is essential that packaging made from it does not tear accidentally.It should be taken into account that the paper does not tear further if a hole or similar structure has formed in it. This property, which is also retained in packaging papers made from it, is particularly important and advantageous, since known packaging papers, which are made solely from hardwood pulp, for example, exhibit only very low tear resistance.

[0021] As a further development of the invention, the base paper is designed in such a way that it has a basis weight of between 50 g / m 2 and 135 g / m 2 and has a tensile strength index according to ISO 1924-3:2005, which at a basis weight of 50 g / m 2At least 80 Nm / g, it is possible to produce a paper with a high tensile strength index combined with low material consumption, resulting in a significant saving in energy and material during production. Basis weights in the range of 50 g / m 2 up to 135 g / m 2 are to be described as low or very low for the packaging of moist or greasy items and, particularly when such items are stored or kept in a frozen state, for example, are usually not sufficient to ensure that the paper does not soften or tear over time.

[0022] Such a tensile strength index ensures that the paper can withstand a wide variety of stresses, such as the storage of packaged goods in a stacked state, the dropping of a bag together with packaged goods, etc., without tearing. A further improvement in the extensibility of the base paper can be achieved by subjecting the softwood pulp to high-consistency refining, which has a surprisingly positive effect on the extensibility of the base paper in the transverse direction, but at the same time has only an extremely small effect on the degree of refining of the base paper. Finally, an improved extensibility in the machine direction of the

[0023] Base paper can be achieved by microcreping it, for example, on a Clupak machine. The TEA index according to ISO 1924-3:2005 of such a base paper is 1.1 to 2.3 J / g in the machine direction and 1.5 to 2.0 J / g in the cross direction. By further developing the base paper so that the air resistance value (Gurley) of the uncoated base paper according to ISO 5636-5:2013 is between 150 and 300 s, it is possible to maintain a certain low air permeability of the base or base paper.By developing the packaging paper in such a way that it is coated on both sides, in particular by providing both surfaces with at least one layer of an identical and / or different coating, the base paper and also a packaging paper produced from it can be given further advantageous properties, such as excellent printability, different resistance to moisture and grease on both sides of the paper, smoothness and the like.

[0024] These tailor-made properties of the base paper according to the invention can be further refined by, as corresponds to a further development of the invention, forming the paper in such a way that the coatings on both surfaces differ from one another, in particular with regard to the amount, composition and physical / chemical properties of the coating agent. As corresponds to a further development of the invention, applying a further coating consisting of surface starch and sizing agent to at least one side makes it possible not only to significantly improve the printability of the paper, but also to further increase the strength and dimensional stability of the paper. The coating with starch and sizing agent can be applied before or after calendering, but further coatings orIf several layers of coatings are provided to produce packaging paper from the base paper, the coating which gives the paper grease or moisture resistance should be provided as the outermost layer.

[0025] The invention is explained in more detail below using exemplary embodiments (or a schematic drawing of the inventive method). These show:

[0026] Example 1: Process for producing the base paper in two grammages according to the invention (Paper 1 and Paper 2)

[0027] Process description: .

[0028] A bleached pulp consisting of 42% primary softwood pulp was refined at a refining capacity of 297 kWh / t, resulting in a softwood pulp freeness of 41 °SR. Furthermore, 58% of a bleached primary hardwood pulp was used, which was subjected to a refining capacity of 97 kWh / t, resulting in a hardwood pulp freeness of 44 °SR. The auxiliaries were added in the approach flow system of the paper machine. The pH was set to 8.1, cationic starch with a cationization degree DS of 0.05 was added at a rate of 11 kg / t dry paper, and alkenylsuccinic anhydride was used as a sizing agent at a rate of 2.35 kg / t dry paper.

[0029] Furthermore, calcium carbonate was added as a filler at a rate of 25 kg / t of dry paper. No cationic retention polymer was added. Surprisingly, the two different pulp types could be mixed without problems, and the process additives could also be added in the conventional way. Surprisingly, no deterioration in the effect of the process additives was observed.

[0030] Consistency of the pulp at the headbox was 0.315%. Dewatering took place on the wire section with a top and bottom former at a wire speed of 820 m / min, and in a press section with four nips, with the line pressure in the three nips being 48 kN / m, 95 kN / m, and 115 kN / m, and in the shoe press nip 600 kN / m. Despite the high softwood content, the sheet was well formed, and the resulting sheet had extremely homogeneous properties and, above all, a uniform surface, despite the use of two different fiber types. The paper was pre-dried and coated in a coating unit with 1 g / m 2Surface thickness was treated. The resulting coating was also surprisingly homogeneous. The coated paper was smoothed immediately before winding in a single hardnip calender at 60 kN / m and 85°C and then finally wound with a final residual moisture content of 7%. The speed at the calender was 865 m / min.

[0031] Under the conditions mentioned, base papers were produced in two grammages - Paper 1 with 77 and Paper 2 with 101 g / m 2 , The data on screen speed and speed at the pope are average values ​​from the operation with both grammages.

[0032] belle 1:

[0033]

[0034] The resulting base papers were then coated on both sides in the next process steps. The base papers were then coated on both sides using a rotogravure process with a water-based coating from Michelman's Michem® Coat series, each with a weight of 6 g / m 2 and 4 g / m 2 The applied quantity is coated. The paint formulation used creates a grease barrier. The achieved kit values ​​according to Tappi T 559 were 4 g / m 2 Application at 10-11 and at 6 g / m 2 at 11-12.

[0035] In a further experiment, the same base papers were also rotogravured on one side with 4 g / m 2 with a Michem® Coat product and on the other side with 4 g / m 2coated with a VaporCoat® product. The grease barriers achieved were again Kit 10-11 for the side treated with Michem® Coat. The water vapor transfer rate at 23 °C and 50% relative humidity according to ISO 2528'2017 for the other paper side, which was coated with VaporCoat®, was 12 g / m². 2 .d. The same test was carried out with Gervalux 100gsm paper. The achieved grease barrier was Kit 11 and the water vapor transfer rate was 10 g / m 2 . d. Taking into account the variability of the measurement methods, the results can be considered equivalent. However, with a packaging paper produced according to the invention, better mechanical properties such as longitudinal tensile strength index or tear propagation resistance index can be achieved, while using approximately 20% less paper.

[0036] Raw paper 3 according to the invention

[0037] Process description:

[0038] A bleached pulp consisting of 40% softwood primary pulp was subjected to refining at a refining rate of 243 kWh / t, resulting in a softwood pulp freeness of 35 °SR. A further 60% of a bleached hardwood primary pulp was used, which was subjected to a refining rate of 78 kWh / t, resulting in a hardwood pulp freeness of 39 °SR. The auxiliaries were added in the approach flow system of the paper machine. The pH was set to 8.1, cationic starch with a cationization degree DS of 0.05 was added at a rate of 10.4 kg / t dry paper, and alkenylsuccinic anhydride was used as a sizing agent at a rate of 2.67 kg / t dry paper. Calcium carbonate was added as fillers at a rate of 10 kg / t and bentonite at a rate of 1.7 kg / t dry paper. No cationic retention polymer was added. The pulp consistency at the headbox was 0.39%.Dewatering took place in the wire section with a top and bottom former at a wire speed of 770 m / min and in a press section with four nips. The line pressure in the three nips was 48 kN / m, 95 kN / m, and 115 kN / m, and in the shoe press nip, 600 kN / m. The kraft paper was pre-dried and coated in a coating unit at 2 g / m. 2 The surface was treated with a special calendering system and smoothed immediately before winding in a single hardnip calender at 100 kN / m and 85°C. The final moisture content was then wound up with a final residual moisture content of 7%. The speed at the pole was 811 m / min.

[0039] The paper obtained in this way had a grammage of 80 g / m 2 and had the following properties: Table 2:

[0040] Raw paper 4 according to the invention

[0041] Process description: A bleached pulp consisting of 27% primary softwood pulp was refined with a 73% primary hardwood pulp at a refining capacity of 141-174 kWh / t, resulting in a pulp mixture with a freeness of 40-41 °SR. The auxiliaries were added in the approach flow of the paper machine. The pH was adjusted to 8.1, cationic starch with a cationization degree DS of 0.05 was added at a rate of 8.1 kg / t of dry paper, and sizing agents were used.

[0042] Alkenylsuccinic anhydrides were used at a rate of 3.8 kg / t of dry paper. Bentonite was added as a filler at a rate of 2.4 kg / t of dry paper. No cationic retention polymer was added. The consistency of the pulp at the headbox was 0.15%. Dewatering took place on the wire section with a top and bottom former at a wire speed of 770 m / min and in a press section with four nips, with the line pressure in the three nips being 52 kN / m, 98 kN / m, and 120 kN / m, and in the shoe press nip at 600 kN / m. The kraft paper was pre-dried and coated in a coating unit with 2 g / m 2 Surface thickness, containing 1.6 kg / t alkenylsuccinic anhydride as a sizing agent, was treated and smoothed immediately before winding in a single hardnip calender at 100 kN / m and 85 °C. Finally, it was wound up with a final residual moisture content of 7%. The speed at the pole was 815 m / min.

[0043] The resulting paper had a grammage of 61 g / m 2 and had the following features:

[0044] Table 3:

[0045] In summary, it can be seen that the production of the raw paper according to the invention only generates about 32 to 55% CO2E / T compared to common raw papers available on the market.

Claims

Patent claims 1. A process for producing a base paper, in which a cellulose pulp essentially containing both softwood and hardwood components and optionally additives is subjected to a refining step and at least one compacting step is carried out, characterized in that an optionally bleached cellulose pulp consisting of 55 to 80 parts by weight, in particular 60 to 80 parts by weight of hardwood primary cellulose and 25 to 45 parts, in particular 30 to 40 parts by weight of softwood primary cellulose and up to 3 parts by weight of filler is provided, that the cellulose pulp is obtained by mixing one pulp made from hardwood and one from softwood, that either each pulp forming the cellulose pulp is subjected to a separate refining to a freeness of 39 to 45 °SR in accordance with ISO 5267-T.1999 for the hardwood pulp or35 to 41 °SR according to ISO 5267-1:1999 for the pulp from softwood or which is subjected to refining to a degree of refining of 39 to 42 °SR by mixing the pulp from hardwood and the pulp from softwood, that the mixed pulp is subjected to dewatering, that a formed sheet is calendered on at least one side and optionally at least one impregnation is applied to at least one side.

2. The method according to claim 1, characterized in that the softwood pulp and the hardwood pulp are each subjected to a separate grinding process and subsequently mixed, and in that a fiber length of a mixture of hardwood pulp and softwood pulp is adjusted to an average length-weighted fiber length according to ISO 16065-2:2014 of 1.00 mm to 1.35 mm.

3. Process according to claim 1 or 2, characterized in that the dewatering of the mixed pulps is carried out at a screening speed of 700 to 900 m / s.

4. The method according to claim 1, 2 or 3, characterized in that the at least one-sided calendering of a sheet of the base paper formed after dewatering on the screen is carried out with a hardnip calender, preferably a hardnip calender heated to a maximum of 150 °C, more preferably a maximum of 90 °C, at a line load of 50 to 200 kN / m, more preferably 70 to 120 kN / m.

5. A method according to claim 4, characterized in that the base paper is calendered on both sides.

6. Method according to one of claims 1 to 5, characterized in that before or after calendering, a coating of at least one side of the base paper with surface thickness, in particular in an amount of 0.8 to 2 g / m 27. A method according to any one of claims 1 to 6, characterized in that both sides of the base paper are coated, in particular with different coating materials, selected from polyolefins, such as polyethylene or polypropylene, starches and modified starches, acrylates, polyalcohols, such as polyvinyl alcohol, ethylene-vinyl alcohol or polylactic acid, with at least one layer each, 8. Method according to one of claims 1 to 7, characterized in that before or after calendering and before coating, an impregnation, preferably double-sided impregnation of the base paper by applying and pressing in a dispersion, solution or solution selected from starches or modified starches, acrylates, polyalcohols, such as polyvinyl alcohol with at least 1.5 g / m 2 , preferably at least 2.0 g / m 2 is carried out, 9. Raw paper produced by a process according to one of claims 1 to 8, characterized in that the raw paper has an ash content of less than 4% and a content of fines with a size of < 0.2 mm of less than 36% and a specific tear resistance index according to ISO 1974:2012 of > 8 mN.mVg in the machine direction and > 9 mN.m 2 / g in the transverse direction.

10. Raw paper according to claim 9, characterized in that the raw paper has a basis weight according to ISO 536:2019 between 50 g / m 2 and 135 g / m 2 and has a tensile strength index according to ISO 1924-3:2005 of 80 to 105 kN / m in the machine direction and of 30 to 40 kN / m in the transverse direction.

11. Raw paper according to claim 9 or 10, characterized in that the air resistance value (Gurley) of the uncoated raw paper according to ISO 5636-5:2013 is between 100 and 300 s.

12. Raw paper according to claim 8, 9 or 10, characterized in that it is coated on both sides, in particular on both surfaces with at least one layer of the same or different coating.

13. Raw paper according to claim 12, characterized in that the coatings on both surfaces are different from each other, in particular with regard to the amount, composition composition and physical / chemical properties of the coating agent differ from one another.

14. Raw paper according to claim 12, characterized in that a further coating of surface starch is additionally applied to at least one side.

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