Oil-resistant filter wrapping paper

[0001] The present invention relates to the field of paper manufacture for tobacco products. In particular, it relates to wrapping paper for tobacco product filters, the method of its production, and the tobacco product for which such wrapping paper is used.

Background of the invention and related art [0002] A standard filter cigarette consists of a cylindrical, round or oval tobacco rod surrounded by cigarette paper, a filter plug formed in the same way, which is surrounded by filter wrapping paper, and a mouthpiece paper, usually glued with all the filter wrapping paper and with part of the cigarette paper surrounding the tobacco and thus joins the filter plug with the tobacco rod.

[0003] The filter plug itself can be made of various materials, cellulose acetate fibers are often used, partly in combination with activated carbon particles. Wrapping paper surrounding the filter plug is usually adhered to the surface of the filter plug in one or more narrow strip-shaped areas. This area, or these areas, usually extends or extends along a direction parallel to the axis of symmetry of the filter plug. Also, the filter wrapping paper is usually glued to itself along a narrow seam to prevent the filter plug from detaching. Many different adhesives are used in the art for this purpose, but polyvinyl acetate or hot melt adhesives are often used.

[0004] Typical filter wrapping papers in the relatively low and medium air permeability range consist of wood cellulose, with a mixture of long or short fibers depending on the desired properties of the paper. Typically, these papers also contain mineral fillers, such as, for example, calcium carbonate, kaolin, talc, titanium dioxide or other mineral fillers and mixtures thereof. Other additives, such as wet strength agents, may additionally or alternatively be used to obtain special properties.

[0005] For example, fillers such as calcium carbonate, sodium acetate and magnesium carbonate have been used for tobacco wrapping paper described in patent application EP 03752844 A2. Also in the patent application WO 2009/006570 A2, in addition to magnesium oxide, calcium carbonate as a second filler for the production of tobacco wrapping paper is mentioned. Another example of the use of a filler is given in patent document DD 145863 A3, in which calcium carbonate is primarily used as a cigarette paper filler.

[0006] The production of such wrapping paper for filters takes place in paper machines, for example in flat screen paper machines.

[0007] Cellulose fibers used in paper production are usually divided into long and short fibers, with the long fibers generally being derived from coniferous wood, such as pine or spruce, more than 2 mm in length, while short fibers are from wood from trees deciduous, such as birch, beech or eucalyptus, and usually have a length less than 2 mm, often about 1 mm.

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[0008] In the first stage of paper production, cellulose is dissolved in water and then ground in a milling aggregate, the so-called conical mill. Separately, short and long fibers are milled separately. The level of milling of cellulose is determined by measuring the degree of milling, for example according to ISO 5267 ("Pulps. Determination of drainability - Part 1: SchopperRiegler method" - "Pulps. Determination of dehydration susceptibility - Part 1: Method

Schopper-Riegler "). The result is given in Schopper-Riegler degrees (° SR). Typically, long-fiber cellulose for use in filter wrapping paper is ground to a grinding degree of 50-70 ° SR.

[0009] Short-fiber cellulose is generally much less finely ground and reaches a grinding degree from 15 ° SR to 40 ° SR. Grinding of short-fiber cellulose can also be completely omitted. [0010] Examples of the degree of milling that is used to produce wrapper paper for filters or to combine the filter part and the cigarette part are given in patent applications EP 0758695 A2 and EP 0758532 A2. For fiber lengths from 0.8 to 2 mm, grinding ratios from 14 ° SR to 72 ° SR are used. In US Patent Application 5,979460, cellulose ester fibers with a typical fiber length of 3 to 7 mm are milled to a milling degree of 30 to 60 ° SR to form a layer that is wound on a cigarette filter. Further examples of grinding degrees for wrapping paper for filters or mouthpiece covering paper are given in patent documents EP 03752844 A2 and DD 145863 A3, in which grinding degrees from 92 ° SR to 94 ° SR and from 91 ° SR to 92 ° SR are used.

[0011] After adding fillers, such as, for example, calcium carbonate, kaolin, talc, titanium dioxide or other mineral fillers or mixtures thereof, the suspension of fibers and fillers flows from the headbox of the paper machine to a sieve, where it can be dehydrated by various means, for example by gravity or a vacuum. Then the wet fiber layer moves through the pressing section, where it is dried by mechanical pressing against the dryer. Finally, the fiber layer passes through the drying section, in which it is dried by contact with cylinders heated by steam, for example. Then the finished paper can be wound. Further processing steps can be carried out in the paper machine, for example sizing in sizing presses or coating presses, applying watermarks, extrusion, impregnation, etc.

[0012] Patent applications EP 0758695 A2 and EP 0758532 A2, for example, describe a process step that includes impregnation with alkaline agents applied to a dried paper web for making filter paper or paper connecting the filter part to the cigarette. To this end, substances such as alkali metal hydroxides, carbonates and bicarbonates, which are water-soluble, are used. Also in patent document DD 145863 A3 is impregnation of cigarette paper to which mixtures of alkali metal salts, alkaline earth metal salts of acetic acid, tartaric acid, citric acid and nitric acid were used.

[0013] Finished wrapper paper for filters typically has a roll form with a width corresponding to the width of the paper machine. This roll is then cut most often into narrower rolls, so-called bobbins, whose width is adapted to the circumference of the filter plug and the desired width

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EP 2 551 407 B1. A typical bobbin is approximately 5,000 to 6,000 m long and 25 to 27 mm wide. Significant differences in the length and width of the bobbin are possible to match the wide range of commercially available cigarette filters. In addition, it is assumed that the width of the bobbin is roughly an integral multiple of the width needed for the production of the filter plug, because filter production machines can simultaneously produce several filter rods in parallel, usually two.

[0014] In some cigarettes, one or more mechanical breakable capsules are inserted into the filter plug. These capsules contain a liquid, generally an oil, with flavoring agents such as, for example, menthol. The smoker is therefore able to crush this capsule (s) by pressing the filter plug, for example, with the fingers, and thereby activate the flavors. The released flavorings then give the aroma of smoke flowing through the filter plug and the cigarette mouthpiece, and therefore the smoker can smell it. Thus, the smoker can enjoy the taste sensations of the cigarette by destroying the capsules. Such a filter cigarette is described, for example, in US Patent Document 2008/142028.

[0015] Fluid leaking from damaged capsules, however, tends to permeate through the filter wrapper paper and through the mouthpiece cover paper, which causes stains to be seen on the outside of the cigarette. These spots are noticeable to the smoker and affect the appearance of the cigarette.

[0016] Such stains can be prevented by creating a certain oil barrier in the filter paper. The ability of paper to produce an oil barrier, hereinafter referred to as "oil resistance", is determined by means of the standard test used in papermaking and paper processing industry according to the TAPPI standard T 559 cm-02 "Test of fat and paper resistance." In this test, drops of 12 different test liquids are applied to the paper, sorted in ascending order of wettability, and it is determined which test fluids penetrate the reverse side of the paper. The test result is KIT level, which records which test fluid has leaked to the other side of the paper first. It is represented by a number from 1 to 12, with higher values ​​corresponding to a higher oil retaining effect. In the event of leakage at the first test fluid, the result is given as "<1". For filter wrapping paper intended for the above use, to avoid the formation of stains on the cigarette, a KIT level of about 5 was sufficient.

[0017] One way to give paper such an oil barrier or "oil-resistant" function is to coat the wrapping paper for filters with a fluorinated hydrocarbon that gives the paper oil repelling properties. For example, these fluorinated hydrocarbons are often used in paper packaging for foodstuffs, but in many countries they are not approved for use in cigarettes. In addition, the coating may make it difficult to stick the filter wrap paper.

[0018] In addition to fluorinated hydrocarbons, it has also been proposed to use specially modified starch products, specifically starch octenyl succinate, to impregnate papers intended for food packaging, see WO 2008/100688. However, these starches have the disadvantage that in order to achieve the desired effect they must be applied to

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Relatively large amounts of paper. A sufficient effect could only be obtained after applying more than about 80 kg of this starch product to a ton of paper.

[0019] Using the proposed method for wrapping paper for filters, this indicator ₂ as a rule, it would be much more than 2 g / m2. This would adversely increase not only material costs, but also energy demand for drying.

[0020] Also CA 2467601 describes the application of starch products to obtain oil resistance. A composition containing modified starch, an agent for increasing mechanical flexibility, for example glycol and an agent for adjusting rheological behavior has been proposed there. Although an improvement in the mechanical flexibility of the coating can be achieved in this way, according to this patent document, in order to provide sufficient oil resistance, it would also require applying more than 75 kg of this composition per ton of paper. Therefore, here too, material costs and associated costs of materials and energy for drying paper are relatively high. Besides, the result could only be obtained for₂ paper with a weight of over 37 g / m2, which corresponds to a spread of at least 2.78 g / m2. However, it is by no means obvious that the effect described in this patent document can also be easily transferred to wrapping paper for filters, which has a much lower basis weight. In addition, the use of glycols in cigarette papers is not permitted in some countries.

[0021] In the case of filter wrapping papers, which are generally much lighter and thinner than food wrapping papers, larger amounts of applications of these starch products are needed in relation to the paper pulp at the outset, because the papers because of their low weight and their weight low thickness, therefore, have less oil resistance and therefore, that due to the light weight, the weight per unit weight of wrapping paper for filters occurs on a relatively much larger surface.

[0022] However, applying a large amount of starch products also has other negative effects in addition to additional costs. For example, heavily starch coated papers tend to produce dust, which increases the number of cleaning cycles on machining machines and reduces their efficiency.

Brief description of the invention [0023] The object of the invention is to provide wrapping paper for filters that can be produced at a low cost, yet it has sufficient oil resistance and has favorable mechanical properties for further processing.

[0024] This object is achieved by means of filter wrapping paper according to claim 1. 1 and the method of its production according to claim 11. Further preferred embodiments are given in the dependent claims.

[0025] The filter wrapping paper of the invention contains a proportion of long cellulose fibers at least 30% by weight, preferably at least 40% by weight based on the total amount of paper fibers. In addition, filter wrapping paper is distinguished by a combination of the following three features:

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EP 2 551 407 B1 (i) the degree of grinding of long cellulose fibers is from 80 ° SR to 100 ° SR, preferably from 85 ° SR to 95 ° SR according to ISO 5267 by the Schopper-Riegler method, (ii) the wrapping paper for filters has a filler content in an amount of 10 wt.%, preferably <8 wt.%, and particularly preferably <6 wt.% based on the total weight of the paper, and (iii) the filter wrapping paper is impregnated with a material that is suitable for forming an aqueous composition, in particular an aqueous solution or suspension.

[0026] The inventors have found that by combining these features it is possible to produce filter wrap paper which has a KIT level according to TAPPI T 559 cm-02 of at least 4, usually even or more. This is even the case when filter wrapping paper as the starting material,₂ i.e. before impregnation, it has a very low basis weight of 15-35 g / m2.

[0027] From the inventors' point of view, this is a surprising and unpredictable result that between these three characteristics (i) to (iii) there is a very obvious synergistic effect.

For the combination of only two of the above-mentioned features (i) to (iii) does not have this positive effect, which is presented in more detail below based on comparative examples. Furthermore, the inventors' research indicates that this particular technical effect is only obtained by combining the three specific features mentioned above.

[0028] As mentioned above, the wrapping paper for the filters according to the invention shows sufficient ₂ oil resistance at relatively low basis weights from 15 to 35 g / m compared to the raw material without impregnation. Pre-impregnated paper with a basis weight of 20-30 g / m, particularly preferably 20-25 g / m, has been found to be preferred. Such filter paper may have an average air permeability of ISO 2965 of less than 12,000 cm / (cm min kPa), preferably less than 8,000 cm / (cm min kPa). The effect according to the invention can also be achieved₂ in heavier filter papers. However, also in filter papers above 35 g / m it is possible to produce in a different, traditional way sufficient oil resistance, in a range other than that preferred here, for which the state of the art according to the inventors' knowledge does not yet have any truly satisfactory solution.

[0029] By impregnation and the optional subsequent application of the material described below, the weight of the finished wrapping paper for filters is increased. Preferred ranges for finished wrapping paper for filters are 15.5-24.0 g / m, preferably 20.5-39.0 g / m and particularly preferably 20.5-34.0 g / m².

[0030] The appropriate amount of coating of the impregnation material can be determined experimentally in such a way that it gives the desired oil resistance. The share of impregnation material₂ relative to the basis weight of the finished filter paper, however, is 0.5-3.0 g / m, preferably 1.0-2.5 g / m, and particularly preferably 1.3-2.0 g / m.

[0031] As mentioned above, the filter wrapping paper of the invention is impregnated with a material suitable for forming an aqueous composition, especially an aqueous solution or

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Suspensions. This aqueous solution or suspension can then be used for impregnation to incorporate the material into paper, while the aqueous component after impregnation evaporates or evaporates. Starch or a starch derivative, preferably hydrolyzed starch, especially maltodextrin, has proved to be the preferred impregnation material.

[0032] The invention is not limited to these materials, however. Alternatively, one or more of the following substances may also be used for the impregnation material: gelatin, shellac, collodion, acacia, agar-agar, tragacanth, locust bean gum, guar gum, carboxymethyl starch, alginic acid and its salts, especially sodium alginate, alginate potassium and calcium alginate or cellulose derivatives, in particular methyl cellulose and carboxymethyl cellulose and its sodium, potassium, calcium or magnesium compounds.

[0033] As described above, a special feature of the wrapping paper for the filters of the invention is that a relatively low proportion of fillers is used. However, fillers may be present, even if they have a relatively low proportion, and are preferably mineral fillers, especially calcium carbonate, kaolin, talc, titanium dioxide or a mixture of two or more of these fillers.

[0034] Although already with the paper impregnation described above - in combination with the especially high degree of milling of long fiber cellulose and the relatively low proportion of fillers - a sufficiently high oil resistance can be obtained for most applications, it is possible to increase the oil resistance by applying additional oil if necessary an additional layer of material, in particular by printing or spraying. This additional layer of material can be applied in principle to both sides of the wrapping paper for filters. It is, however, preferred to apply it at least to the side that faces the filter plug during use. In contrast to impregnation, in which material is introduced into the paper, the optional additional layer of material is essentially limited to the surface of the already impregnated paper and is therefore referred to herein as the "coating".

[0035] The proportion of the additional layer of material in the basis weight of the finished wrapping paper for the filters in the area under consideration is preferably 1.0-6.0 g / m, in particular 2.0-4.0 g / m. In this case, the restriction "in the area under study" means that there is not necessarily a need for additional material to coat the entire surface of the wrapping paper for the filters. In the applications described in more detail below, this is the case when the additional coating material is primarily used to provide a self-adhesive effect.

[0036] The material of the subsequent coating layer is preferably also suitable for forming an aqueous composition, especially an aqueous solution or suspension. Oxidized starch has proven particularly advantageous. However, all the materials listed above in connection with impregnation are also possible.

[0037] A preferred material for impregnation and / or an additional coating layer is one which, after moisturizing, glues the wrapping paper to the filters with itself, with a filter plug and / or with a mouthpiece cover paper, without using another adhesive. As will be explained in more detail below on the basis of embodiments, impregnation and optional additional coating not only serves to increase oil resistance, but it gives

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In the case of filter paper, self-adhesive action as a particular further advantage. For this purpose, the impregnation material or the additional coating material only needs to be moistened and thus partly dissolved, after which it can be glued to the second part of the wrapping paper for filters, with a filter plug or with a mouthpiece cover paper. This self-adhesive result can be created by means of impregnation alone, however, thanks to the additional material coating it is further strengthened. In the event that impregnation alone is sufficient to create oil resistance, the application of additional material, i.e. coatings, to those selected areas that serve as the place of gluing can be limited if the filter wrapping paper is glued with itself, with a filter plug or with mouthpiece cover paper.

[0038] In the method of production of the filter paper according to the invention, pre-paper is first produced which has the above features (i) and (ii). The pre-paper is then impregnated with a suitable material in the aqueous composition, especially in the aqueous solution or suspension. This impregnation can be carried out, for example, in a size press of a paper machine. Alternatively, impregnation can be carried out by applying the water-based composition on both sides in a paper press coating machine or by means of a double-sided roller applicator.

[0039] After impregnation and drying, the wrapping paper for the filters can be coated - as has already been said, optionally - with additional material. The preferred method of coating is intaglio printing. Further suitable coating methods are flexographic printing, spraying or coating by means of a coating press or rollers. It is characteristic here, however, that the material is applied to the surface and not introduced into the paper structure, as in the case of impregnation, for example in a size press.

Description of preferred embodiments [0040] It has turned out that by means of special fiber treatment, appropriate selection of paper composition and by impregnation of paper with an aqueous composition, a surprising synergistic effect is obtained, which allows all the previously described requirements to be realized simultaneously. This should be illustrated by the following examples.

Examples 1-8: Insufficient oil resistance of standard and modified filter wrapping paper and obtaining oil resistance by the invention ₂ [0041] Several wrapping papers were produced for filters with a basis weight of about 23 g / m, containing about 60% long-fiber cellulose and about 40% short-fiber cellulose, both percentages refer to pure pulp and a variable filler content from 0-10% relative to the total paper weight. Precipitated calcium carbonate (PCC) was used as the filler. [0042] In addition to the filler content, the degree of milling of long fiber cellulose also changes. In Table 1, 'normal' means long-fiber cellulose with a standard grinding degree of 50 to 70 ° SR, whereas in the variants of long-fiber cellulose with a high degree of grinding ('intensive')

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The long fiber cellulose was ground to a 93 ° SR milling degree in a double disc mill. Paper impregnation, if carried out, takes place in a sizing press of a paper machine using a 10-15% aqueous suspension of short-chain hydrolyzed starch (Eliane MD2 maltodextrin from Avebe, available for example via Brenntag CEE GmbH) and thus after drying, about 1-2 g of this starch per square meter of paper remains in the paper structure, which is also referred to below as "coating weight", although in this case it is not strictly speaking "coating" in the sense of coating, but impregnation. Unless otherwise stated, all percentages refer to weight percentages.

[0043] For the preparation of the starch suspension, 150 kg of this starch product were mixed in 800 liters of tap water at room temperature, mixing with a standard mixer, and after about 5-15 minutes of mixing, made up to 1000 kg of tap water.

[0044] The amount of starch added to the paper by impregnation was determined as the difference in basis weight determined according to ISO 536 before and after impregnation.

[0045] All papers in terms of their oil resistance were tested according to TAPPI T 559 cm-02, with 9 tests on each paper. The range of values ​​obtained and all other results of this test are summarized in Table 1.

Table 1: oil resistance of standard, modified and coated wrapping paper for filters

<td></td><td colspan="2">Wrapping paper for filters</td><td colspan="2">Impregnation</td><td>Oil resistance</td>

<td>No.</td><td>Cellulose long fiber Grinding</td><td>Content filler [%]</td><td>Starch suspension [%]</td><td>Coating weight [g / m²]</td><td>KIT level</td>

<td> 1</td><td>normal</td><td> 10</td><td>lack</td><td> 0</td><td> &lt;1</td>

<td> 2</td><td>intensive</td><td> 10</td><td>lack</td><td> 0</td><td> &lt;1</td>

<td> 3</td><td>normal</td><td> 0</td><td>lack</td><td> 0</td><td> 1</td>

<td> 4</td><td>intensive</td><td> 0</td><td>lack</td><td> 0</td><td> 1-2</td>

<td> 5</td><td>normal</td><td> 10</td><td> 12</td><td> 1.5</td><td> &lt;1</td>

<td> 6</td><td>intensive</td><td> 10</td><td> 12</td><td> 1.5</td><td> &lt;1</td>

<td> 7</td><td>normal</td><td> 0</td><td> 12</td><td> 1.5</td><td> 1-2</td>

<td> 8</td><td>intensive</td><td> 0</td><td> 10</td><td> 1.2</td><td> 5-6</td>

[0046] Example 1 describes standard filter wrapping paper and shows that standard filter wrapping paper does not have sufficient oil resistance.

[0047] In Example 2, long fiber cellulose was ground intensively, resulting in a more compact paper structure. Despite this, no improvement in oil resistance is achieved.

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[0048] In Example 3 no filler was used. This action also results in a denser paper structure, but the oil resistance is also slightly improved.

[0049] Example 4 shows that also the combination of long fiber cellulose with a high degree of grinding and the lack of filler does not result in any sufficient improvement in oil resistance.

[0050] Examples 5-7 show the same papers as in examples 1-3, but with additional impregnation of a starch suspension. Although the amount of starch coating roughly corresponds to the amount proposed in WO 2008/100688 or CA 2467601, and therefore at least a slight improvement in oil resistance would be expected, this cannot be confirmed experimentally.

[0051] It can therefore be concluded from examples 1-7 that the low basis weight and low thickness of the filter wrapping papers is a particular problem in order to obtain oil resistance which cannot be eliminated by methods known in the art.

[0052] Surprisingly, the inventors have found, however, that by combining all means, and thus:

- by using long-fiber cellulose with a high degree of milling,

- by reducing the amount of filler and

- by impregnation with a starch suspension, a synergistic effect can be achieved that cannot be obtained only by simply layering the individual shares of these agents. Since the measurements show for the paper from example 8 the KIT level 5-6, while for none of the examples 1-7, which also used two of the described measures, a KIT level greater than 2 was obtained. However, the KIT level 5-6 already provides sufficient oil resistance.

[0053] It should also be noted that in example 8 KIT 5-6 can be achieved by impregnating only 1.2 g of starch per square meter of paper, while impregnating with 1.5 g of starch per square meter of paper in examples 5- 7 is not causing any significant improvement yet.

Examples 9-20: Applicability of the invention in the field of typical filter wrapping papers [0054] The following examples show that the observed synergistic effect is not strongly dependent on the properties of the paper, but can be used across the entire spectrum of typical filter wrapping papers.

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EP 2 551 407 B1

Table 2: Oil resistance of coated wrapping paper for filters

<td></td><td colspan="3">Paper</td><td>Impregnation</td><td>Oil resistance</td>

<td>No.</td><td>Weight [G / m²)</td><td>Long fiber [%]</td><td>Content filler [%]</td><td>Weight₂coatings [g / m]</td><td>KIT level</td>

<td> 9</td><td> 20</td><td> 55</td><td> 2</td><td> 1.2</td><td> 4-5</td>

<td> 10</td><td> 25</td><td> 55</td><td> 2</td><td> 1.3</td><td> 5-6</td>

<td> 11</td><td> 30</td><td> 55</td><td> 2</td><td> 1.4</td><td> 8-9</td>

<td> 12</td><td> 25</td><td> 30</td><td> 2</td><td> 1.2</td><td> 4-5</td>

<td> 13</td><td> 25</td><td> 45</td><td> 2</td><td> 1.3</td><td> 6-7</td>

<td> 14</td><td> 25</td><td> 70</td><td> 2</td><td> 1.4</td><td> 6-8</td>

<td> 15</td><td> 25</td><td> 55</td><td> 4</td><td> 1.3</td><td> 6-7</td>

<td> 16</td><td> 25</td><td> 55</td><td> 6</td><td> 1.3</td><td> 6-7</td>

<td> 17</td><td> 25</td><td> 55</td><td> 8</td><td> 1.2</td><td> 4-6</td>

<td> 18</td><td> 25</td><td> 55</td><td> 2</td><td> 1.5</td><td> 5-7</td>

<td> 19</td><td> 25</td><td> 55</td><td> 2</td><td> 1.7</td><td> 6-8</td>

<td> 20</td><td> 25</td><td> 55</td><td> 2</td><td> 2.0</td><td> 8-9</td>

[0055] In Examples 9-11, it is noted that increasing basis weight is beneficial for oil resistance, and therefore, with increasing basis weight, either a higher KIT level is achieved with the same coating weight in impregnation, or the same KIT level can be maintained at lower basis weight for impregnation. The procedure can be carried out with similar results 22 for wrapping papers for filters with a basis weight from about 15 g / m to about 35 g / m. Based on these 22 examples, the basis weight is preferably selected, however, in the range from 20 g / m to 30 g / m, 22 and particularly preferably in the range from 20 g / m to 25 g / m. Basis weight means the weight of the pre-impregnated filter wrap paper, which is also referred to below as "basis weight₂ Output ". Also at a basis weight exceeding 35 g / m, the described effect can be achieved, however, other known methods can be used for such papers to obtain oil resistance.

[0056] In Examples 12-14, the content of high-fiber long fiber cellulose is changed at a constant fiber weight. As expected, it turns out that the oil resistance increases as the content of long-fiber cellulose increases, because long-fiber cellulose with a high degree of grinding affects the denser structure of the paper. In order to obtain sufficient oil resistance, the content of long fiber cellulose relative to the total pulp weight of the paper should be at least 30%, preferably at least 40%. In principle, nothing prevents you from using up to 100% long fiber cellulose. However, the benefits in the field of oil resistance with very high proportions of long fiber cellulose increase not so much

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EP 2 551 407 B1 as much as with small shares. Since long-fiber cellulose is usually more expensive than short-fiber cellulose, and in addition milling is also associated with energy costs, the ideal share of long-fiber cellulose for individual applications is also the result of economic calculations.

[0057] Regarding the milling of long fiber cellulose, the effect is from a milling degree of about 80 ° SR, however, the range from 85 ° SR to 95 ° SR is preferred. As the tensile strength of the paper also decreases as the milling increases, the milling of long fiber cellulose cannot be arbitrarily intensive. The upper limit of the degree of milling of long fiber cellulose is set to 100 ° SR.

[0058] Finally, in examples 15-17 the filler content (in this case precipitated calcium carbonate) in the filter paper is changed. The increasing content of calcium carbonate or similar fillers loosens the paper structure and deteriorates the oil resistance, and therefore, as can be deduced from example 6, in any case, a content of calcium carbonate less than 10%, preferably however less than 8% and particularly preferably less than 6%. You can also completely dispense with the filler. Since, on the one hand, calcium carbonate is cheaper than cellulose, and on the other hand, in order to obtain sufficient resistance to oil, however, with higher filler content it is necessary to use possibly more starch for impregnation, the specific choice of filler content - within the limits specified here - results to a large extent from economic calculation.

[0059] Finally, as shown in examples 10 and 18-20, the amount of starch applied to the paper during impregnation can be changed. It turns out that as the coating weight increases, the oil resistance increases, however, as with long fiber cellulose content, the improvement in oil resistance at higher basis weights does not increase as much as at low weights. Basis weights from 0.5 g / m to 3 g / m have proved to be suitable, such as from

2 2 2

1.0 g / m to 2.5 g / m, particularly preferred from 1.3 g / m to 2.0 g / m.

[0060] In addition to the impregnation provided herein in the examples by means of a suspension of short chain hydrolyzed starch, the invention can be achieved by impregnation also with other water-based compositions, for example solutions or suspensions. As an alternative to short-chain hydrolyzed starch, for example, gelatin, shellac, collodion, acacia, agar-agar, tragacanth, locust bean gum, guar gum, in addition starch and starch derivatives such as carboxymethyl starch or alginic acid and its salts, in in particular sodium alginate, potassium alginate and calcium alginate, and cellulose derivatives such as methyl cellulose and carboxymethyl cellulose and their sodium, potassium, calcium or magnesium compounds. Mixtures that contain one or more of these substances can also be used. When choosing a specific substance or mixture of substances, statutory provisions should be taken into account, in addition to suitability for use.

[0061] Since the possibility of improving oil resistance by impregnation with increasing amounts of starch is technically limited, it is proposed in further embodiments of the invention to apply an additional further aqueous composition after impregnation to the paper surface. The aqueous composition may contain starch or a starch derivative that may be

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EP 2 551 407 B1 the same that is also used for impregnation. In many cases, however, another substance or mixture of substances is chosen that can be better used in selected coating methods, for example due to rheological behavior requirements.

[0062] A comparable effect can also be achieved, for example, with gelatin, shellac, collodion, acacia, agar-agar, tragacanth, locust bean gum, guar gum, and in addition with starch and starch derivatives such as carboxymethyl starch or with alginic acid and its salts, in particular sodium alginate, potassium alginate and calcium alginate, and by means of cellulose derivatives such as methyl cellulose or carboxymethyl cellulose and their sodium compounds, potassium, calcium or magnesium.

[0063] There are no restrictions regarding the type of coating method. Standard printing methods such as gravure or flexography can be used, but it is also possible to spray the composition, as can one-sided coating with a coating press or roller. It is significant, however, that the material is applied to the surface and not introduced into the paper structure, as in impregnation, for example in a size press. In order to conceptually differentiate from the "impregnation" mentioned above, the coating additionally provided for the impregnation is called "coating". This term should be understood broadly and should only show that the additional material is applied for the most part on already impregnated paper instead of the paper structure.

[0064] In the examples below, the previously impregnated papers from Examples 9-20 were additionally completely printed (i.e. coated) with an approximately 20% aqueous composition, specifically an aqueous suspension of oxidized starch (Perfectamyl A5760 from Avebe) by standard intaglio printing. In this case, an additional 3 g of oxidized starch was applied per square meter of printed paper surface.

Table 3: resistance of printed and impregnated wrapping paper for filters

<td rowspan="2">Example No.</td><td rowspan="2">Impregnated paper as example no</td><td colspan="2">KIT level</td>

<td>Before printing</td><td>After printing</td>

<td> 21</td><td> 9</td><td> 4-5</td><td> 6-8</td>

<td> 22</td><td> 10</td><td> 5-6</td><td> 8-9</td>

<td> 23</td><td> 12</td><td> 4-5</td><td> 6-8</td>

<td> 24</td><td> 17</td><td> 4-6</td><td> 7-9</td>

[0065] In Examples 21-24, it is noted that, by printing, it is generally possible to achieve a further improvement in oil resistance by 2-3 points, with the oil resistance measurement being carried out on the printed side. However, when used for a cigarette, it is recommended that, although it is not necessary for the printed side to be directed towards the filter plug. [0066] The amount of fillers of the aqueous composition applied by gravure in addition to the aforementioned impregnation brings verifiable effects in the range from 1.0 to

2

6.0 g / m2 of printed surface, however, the range from 2.0 to 4.0 g / m2 of printed is preferred

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EP 2 551 407 B1 surface. The coating weights given relate to dried paper, i.e. after the water has evaporated or evaporated from the applied aqueous composition. Also with other coating methods it can be expected that with an amount of 1.0 to 6.0 g / m2, preferably 2.0 to 4.0 g / m2, an effect at least approximately comparable to that of gravure printing can be achieved , because the oil resistance obviously depends more on the grammage of the coating than on the type of coating method.

Example 25: sizing wrapping paper for filters [0067] Both the impregnation itself, as well as in combination with an additional surface coating ("coating") allow to obtain wrapping paper for filters that is self-adhesive or with a filter plug, without the need for additional adhesives. All you need to do is apply a small amount of water to a part of the paper surface or the entire surface. Regarding water, there are no special requirements, it can be above all ordinary tap water as well as demineralized water. The temperature of the water is also not particularly important for gluing, preferably it is in the range of 15 ° C to 60 ° C.

[0068] The wetted surface is then brought under slight mechanical pressure to contact the surface to be glued and dried for a short time, preferably at elevated temperature, for example around 60 ° C. Temperatures that allow rapid drying, preferably above 40 ° C, particularly preferably above 50 ° C, are preferred. However, one should not choose a temperature that is high enough to cause thermal decomposition of the paper, therefore it should generally be below 105 ° C, preferably below 90 ° C.

[0069] Particular importance in the production of cigarette filters is to obtain very minimal adhesive strength very quickly to prevent the filter from tearing off in further processing steps or the wrapping paper separating from the filter. In this case, the gluing takes place in such a way that the glue joint is about 2 mm wide and is located in the machine direction of the wrapping paper for the filters. Where the wrapping paper for the filter is glued together, gluing occurs between the top side and the sieve side of the wrapping paper for the filter.

[0070] In order to reproduce this process in the laboratory, each paper of examples 10, 11, 14 and 22 is tested for its stickiness. In addition to the paper from Example 10 and its printed version from Example 22, which roughly corresponds to the average wrapping paper for filters, the papers from Examples 11 and 14 were also selected, because due to the higher basis weight or due to the higher proportion of long-fiber cellulose, they have higher tensile strength.

[0071] For the test, two paper strips 15 mm wide in the machine direction and a length in the transverse direction sufficient according to ISO 1924-2 to measure the tensile strength were first prepared. On the upper side of the first strip, along about 2 mm in width, in the machine direction of the paper, and therefore a straight strip located in parallel

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To the short side of the strip, water was brushed. Then the paper strip was brought into contact with the sieve side of the second strip in such a way that the gluing of both strips resulted in a straight strip 15 mm wide, but now longer. The gluing site was loaded with a flat metal body heated to a temperature of about 60 ° C for about 1 second by manual pressure. Immediately afterwards, the glued paper web was subjected to a tensile strength measurement based on ISO 1924-2. In this case, a strand of paper was gripped at both ends and stretched to break. During the experiments, it was observed whether there was a break at the place of gluing or elsewhere on the paper strip. Four strips were tested on each paper.

[0072] It turns out that, with the exception of the paper in Example 11, in three or more of the four stripes tested, no breakage occurs at the point of gluing. Therefore, the adhesive strength is already greater than the tensile strength of the paper itself, so it is assumed that the adhesive bond strength is sufficient for machining. In example 11 this was not the case, because the paper did not break at one point only in four attempts. However, due to the higher tensile strength of this paper, it is also assumed in this case that the adhesive strength for the machine production of filters from this paper is sufficient.

[0073] If sufficient paper resistance to oil is to be obtained after paper impregnation, but the adhesive strength is not sufficient for machining, it is proposed that the composition intended to be applied to the surface or "coating" not be applied to the entire surface, but only to some parts of it. These partial areas can in principle have any shape, but are matched to the shape of the surface to be glued. The shaping of these partial areas is preferably carried out in a manner which also up until now in the manufacture of the filter corresponded to areas of the wrapping paper of the filter equipped with an adhesive.

[0074] The composition is usually applied and preferably on these partial areas of the paper side that faces the filter plug. However, it is also possible to plan these partial areas on the other side of the paper or on both sides of the paper, for example if additional bonding of the filter wrap paper to the mouthpiece cover paper is to be achieved at a later stage of cigarette production.

[0075] The features described above can have meaning in any combination.

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EP 2 551 407 B1