Method for producing a heat-sealable paper

Abstract

The present invention relates to a method for producing a heat-sealable paper in which a heat-sealable coating based on a heat-sealable polymer is applied to a paper web and the paper web is subsequently rolled onto the application of the heat-sealable coating and which is characterized in that the heat-sealable coating contains a synthetic or semi-synthetic wax whose melting point is above the maximum drying temperature of the paper web to be rolled up.

Description

[0001] The invention relates to a process for producing heat-sealable paper, in which a heat-sealable coating based on a heat-sealable polymer is applied to a paper web, and the paper web is subsequently rolled up onto the application of the heat-sealable coating. The invention particularly relates to a heat-sealable coating composition used in the production of the heat-sealable paper. Such heat-sealable coating compositions contain an antiblocking agent to prevent the paper web from sticking to itself during rolling or subsequent storage. Known antiblocking agents include, for example, platelet-shaped pigments based on kaolin.

[0002] Heat-sealable packaging papers are suitable for the production of bag packaging and filling of dry goods, such as pudding powder or vanilla sugar, but also for the packaging of other everyday items, such as screws or sewing utensils.

[0003] The current state of the art involves the production of heat-sealable paper using a two- or three-pass process on a paper machine, possibly a coating machine, and then a film laminating or extrusion line. Previous attempts to produce heat-sealable paper using a single-pass process directly on a paper machine with an integrated coating unit have failed due to the limited application weight and the strong tendency of the hot paper web to block in the post-dryer and / or reel sections.

[0004] WO 2018 / 200783 A1 shows a method for producing a heat-sealable paper having the features of the preamble of claim 1. Further prior art is discussed in US 5 336 528 A, WO 2017 / 024211 A1 and US 4 196 247 A.

[0005] The aim of this invention is to develop a heat-sealable paper that can be produced in a 1-pass process (online process) on a paper machine with an integrated coating unit (for example a film press) and a conventional paper drying in the after-drying section (for example air-turn, IR radiators and steam-heated cylinders) and can be rolled up without blocking at 50°C to 65°C.

[0006] This object is achieved by a method having the features of claim 1. According to the invention, the heat-sealing line contains wax in the disperse phase of at least one first wax type, wherein the melting point of the at least one first wax type is above the maximum drying temperature of the paper web to be rolled up. In a further embodiment, the melting temperature of the at least one wax type is above the melting point of the heat-sealable polymer.

[0007] The invention proposes a synthetic or semi-synthetic wax as an antiblocking agent, which is present in the heat-sealable coating composition as a dispersed phase. The wax of the at least one first wax type in the dispersed phase is largely spherical in shape with a diameter of 1-6 µm. The addition of at least one first wax type in dispersed form reduces the stickiness of the heat-sealable coating composition at temperatures below the melting point of the heat-sealable polymer. The cause of this phenomenon has not yet been researched, but one explanation could be that during the drying process, the wax spheres largely retain their shape and form a perceptible spacer layer, while the polymer dries as a film and is largely distributed between the wax spheres.In this way, the wax balls prevent the dried polymer film from coming into direct contact with the paper web lying above it during winding, and at best only have point-like contact.

[0008] With previously known heat-seal coating compositions, the paper temperature had to be strictly limited during winding to prevent deposits on the drying cylinders of the coating dryer and blocking of the paper web after winding. With the heat-seal coating composition according to the invention, winding can take place in the range of 50°C to 65°C without blocking.

[0009] There is also a further advantage from an energy point of view, because during the production of heat-sealable paper, the paper does not have to be cooled below 50 degrees Celsius as is usual before it can be wound up.

[0010] According to the invention, the wax contains a second wax type whose melting point lies between the maximum drying temperature of the paper web to be rolled up and the melting point of the first wax type. Preferably, the melting point of the second wax type is chosen between the melting temperature of the heat-sealable polymer and the melting point of the first wax type.

[0011] Surprisingly, it has been shown that a wax type with a melting point close to the melting point of the heat-sealable polymer improves the heat-sealability of the coating and can simultaneously act as an anti-blocking agent. By improving the heat-sealability of the coating, however, the weight fraction of the heat-sealable polymer in the coating can be reduced, so that the tendency to block is reduced simply by reducing the polymer content in the coating. However, the addition of the second wax type largely, ideally completely, compensates for the reduced heat-sealability of the coating.

[0012] According to the invention, the melting point of the first type of wax is selected in a range between 105 and 164 degrees Celsius and in particular between 115 and 164 degrees Celsius or between 156 and 164 degrees Celsius.

[0013] In a further aspect of the invention, the melting point of the second wax type is selected in a range from 86 to 164 degrees Celsius, preferably between 100 to 150 degrees Celsius, particularly preferably between 100 and 121 degrees Celsius and in particular between 100 and 115 degrees Celsius or at 105 degrees Celsius.

[0014] For the sake of clarity, it should be noted that adding only the second wax type, i.e., without the first wax type, can lead to improvements of the same, greater, or lesser magnitude than adding the first wax type. However, particularly advantageous results can be achieved by a coordinated dosage of the first and second wax types.

[0015] For this purpose, in a further aspect of the invention, based on 100% by weight of the heat-sealable polymer, the weight fraction of the first wax type is selected in a range from 2% to 25% by weight when the first wax type is used alone in the wax mixture, and in the range from 2% to 15% by weight when the first and second wax types are used in the wax mixture, preferably at 5% by weight.

[0016] The inventive use of the amount of the first wax type, or of the second wax type, or of a mixture of the first and second wax types, exceeds the amount usually used of less than 1% for paper applications in which waxes are used for purposes other than that of an antiblocking agent.

[0017] In a further aspect of the invention, the first type of wax is based on ethylene acrylic acid. Ethylene acrylic acid wax is a synthetic wax with a relatively low melting temperature, i.e., a melting temperature close to the melting temperature of the heat-sealable polymer. It has been shown that the use of this wax, in addition to acting as an anti-blocking agent, also improves the sealing strength of the heat-seal coating.

[0018] In a further aspect of the invention, the heat seal coating is applied to the paper web as a single coat with a basis weight in a range of 2g / m 2< to 7g / m 2<. In the prior art, however, the coat applications of the heat seal coating are greater than 7 - 10 g / m 2<. In the prior art, these relatively large coat applications increase blocking. A lower application of 2g / m 2< to 7g / m 2< is possible because both the proportion of the usual antiblocking agents can be reduced and by supporting the heat sealability, in particular by a type of wax with a melting point close to the melting temperature of the heat sealable polymer, the heat sealability of the coating slip can be improved to such an extent that the proportion of the heat sealable polymer can also be reduced.

[0019] The amount of coating applied can also be reduced if a particularly dense base paper is used as the base paper through high refining and the use of a hydrophobic agent as a substrate, which ensures that the coating remains particularly well on the paper surface.

[0020] A further aspect of the invention is that the weight proportion of the second type of wax in the heat seal line, based on 100% weight proportion of the polymer, is in the range of 3% to 10%, preferably 6%.

[0021] A further aspect of the invention is that the second wax type, or if only one wax type is used, the first wax type, is a synthetic wax based on secondary fatty acid amide waxes. PE or PP waxes are also suitable for the second wax type. As synthetic waxes, these waxes have a relatively high melting point compared to the melting point of the heat-sealable polymer.

[0022] A further aspect of the invention is that the heat seal coating additionally contains 5% to 40% by weight of a platelet-shaped pigment based on kaolin, based on 100% by weight of the heat sealable polymer.

[0023] A further aspect of the invention is that the heat seal line additionally contains 0.1% to 1% by volume of acrylate copolymer based on 100% by weight of the heat sealable polymer.

[0024] A further aspect of the invention is that the heat seal coating additionally contains 0.01% to 0.2% by volume of fatty alcohols based on 100% by weight of the heat sealable polymer.

[0025] A further aspect of the invention is that the heat-sealable polymer consists of at least polyolefin or polypropylene ethylene acrylate polymers, or polyethylene polymers.

[0026] A further aspect of the invention is that a front side coating with a coating application quantity of between 2g / m 2< and 8g / m 2< is applied to the opposite side of the paper web.

[0027] A further aspect of the invention is that the front coating contains 20 to 80 percent by weight of a platelet-shaped pigment based on kaolin and 80 to 20 percent by weight of modified starch. Modifications of the front coating can also be directed toward other properties, such as improving gravure printing properties.

[0028] A manufacturing process for a heat-sealable paper comprises the following process steps: production of a base paper in a paper machine with a basis weight (according to EN ISO 536) of 30 g / m 2 < to 150 g / m 2 < ; direct application of a heat-seal coating according to one of the process steps described above; and winding up the paper web.

[0029] A heat seal coating composition according to the invention is defined in claim 13.

[0030] The temperature difference between the melting point of the synthetic or semi-synthetic wax and the maximum drying temperature of the paper web to be rolled up should be in a range between 1 and 60 degrees Celsius and in particular between 5 and 30 degrees Celsius and in particular between 5 and 15 degrees Celsius.

[0031] Another aspect of the heat seal coating is that the melting point of the first type of wax is in a range of 100 to 110 degrees Celsius, preferably 105 degrees Celsius.

[0032] A further aspect of the invention is that the heat seal coating composition, based on 100% by weight of the heat sealable polymer, the weight fraction of the second wax type is in the range of 2% to 15% by weight, preferably 5% to 6% by weight.

[0033] A further aspect of the invention is that the second type of wax is based on ethylene acrylic acid.

[0034] A further aspect of the invention is that the wax of the heat seal coating composition present in the disperse phase contains a second type of wax whose weight proportion, based on 100% weight proportion of the polymer, is in the range of 3% to 10%, preferably 6%, wherein the second type of wax has a lower melting point than the first type of wax, preferably a melting point in the range of 100 degrees Celsius to 110 degrees Celsius and wherein the second type of wax is based on secondary fatty acid amide waxes.

[0035] In a further aspect of the invention, the heat seal coating composition contains 5% to 40% by weight of a platelet-shaped pigment based on kaolin; 0.1% to 1% by volume of acrylate copolymer; 0.01% to 0.2% by volume of fatty alcohols; the heat sealable polymer consists of at least polyolefin or polypropylene-ethylene-acrylate polymers, or polyethylene polymers.

[0036] A further aspect of the invention also includes the arrangement for producing a heat-sealable paper web comprising a paper machine for producing a base paper web, a coating device for applying a heat-sealable coating composition according to one of the above coating compositions, a coating device for applying a reverse side coating composition, a drying device and a reel-up for winding up the paper web.

[0037] The invention will now be explained by means of examples and the Figure 1 described. The only Figure 1shows the manufacturing steps for producing a paper with a heat seal line.

[0038] The starting point, or process step 1, is the production of a base paper in a paper machine with a basis weight (according to EN ISO 536) between 30 g / m² and 150 g / m². In order to achieve the required high sealing strengths and qualities with the smallest possible application of heat-sealable coating, it is generally advantageous to produce a dense base paper with highly refined pulp. The refined pulp preferably has a freeness of 40 - 65 degrees Schopper Riegler (according to EN ISO 5267-1 / 2). The base paper preferably has a pulp composition of bleached pulp with a proportion of long fibers of 10% - 80% and short fibers of 20% to 90%. If necessary, the base paper is treated with a wet strength agent, such as polyamidoamine-epichlorohydrin resin, at a usage rate between greater than 0 L / t and 18 L / t.

[0039] In a further process step 2, a heat-sealing coating is then applied directly to one side of the base paper using a film press as a single coating, preferably with a basis weight of 2 g / m 2 - 7 g / m 2 , and then dried. The properties of the high-quality paper pulp complement the innovative composition of the heat-sealing coating, which is why the applied heat-sealing coating, at 2 g / m 2 to 7 g / m 2 , can be significantly less than the conventionally applied coatings of 10 g / m 2 , which also helps prevent blocking of the wound paper web.

[0040] The heat-sealable coating is applied to one side and comprises the following basic coating components: a heat-sealable binder, such as modified starch or a synthetic binder based on styrene butadiene or polyacrylate; a pigment, preferably platelet-shaped, such as kaolin; a mixture of synthetic and semi-synthetic waxes; optionally, a lubricant, such as a calcium stearate or PE-based one, which improves printability; optionally, a rheological aid; and optionally, a defoamer. The following table shows the weight proportions of the individual components of the formulation as absolutely dry for an exemplary embodiment: Table 1 function Chemical basis Melting point degrees Celsius Weight percentage absolutely dry heat-sealable polymer polyolefins, 85 100 First wax type as an anti-blocking agent Wax based on secondary fatty acid amide waxes, so-called ethylene bistereamide waxes 140 - 150 3 - 6 - 10 Second type of wax as an anti-blocking agent to improve heat sealing properties Synthetic wax based on ethylene acrylic acid 105 2 - 5 - 15 Antiblocking agents Platelet-shaped pigment based on kaolin - 5 - 40 Rheology setting Acrylate copolymer - 0,1 - 1,0 Defoamers Fatty alcohols - 0,01 - 0,2

[0041] In the next process step (3), a pigmented coating is applied directly to the opposite side to compensate for curl and adjust other required paper properties, such as achieving a barrier against grease and mineral oils and / or achieving printability with gravure or flexographic inks. The coating application rates for this reverse coating range from 0.8 g / m² to 8 g / m². Table 2 function Chemical basis Melting point degrees Celsius Weight percentage absolutely dry pigment Platelet-shaped pigment based on kaolin - 20 - 80 binder Modified starch - 80 - 20

[0042] The main advantage of the proposed composition of the heat seal coating is that the heat sealable paper can be produced in a single operation because the risk of blocking during winding of the heat sealable paper is significantly reduced.

[0043] It is, of course, also possible to perform these last two process steps in reverse order, i.e., applying the back coating first, followed by the heat seal coating. The next process step, step 4, involves rolling up the paper web, preferably at a temperature range of 50°C to 65°C.

[0044] The heat-sealable paper produced in this way exhibits good heat-sealability. By selecting a suitable binder, the heat-sealable paper can also be designed for good recycling, allowing it to be reused in the waste paper cycle. The back coating can be used to achieve "special properties," such as a barrier against grease / mineral oils or printability with gravure / flexographic printing.

[0045] Using the described procedure, the following sealing forces can be achieved in a seal pull test: Table 3 Seal seam peel test Sealing temperature °C Hottack N / 45mm Coldtack N / 45mm 90 14,0 13,8 100 14,6 13,4 110 14,4 13,6 120 11,7 14,2 130 7,6 14.3 140 2,1 12,2

[0046] Cold tack, a cold peel test, and hot tack, a hot peel test, are well-known methods for measuring adhesive strengths. Table 3 shows that the tensile strengths for hot tack are higher than for cold tack at sealing temperatures between 90°C and 110°C, but drop rapidly above these temperatures. With cold tack, the maximum achievable tensile strengths are somewhat lower than with hot tack, but remain largely constant over a temperature range of 90°C to 130°C, with a maximum at approximately 130°C. High peel strengths for hot tack enable rapid processing of the seal, for example, in bag production and bag packaging.

[0047] The following paper properties were measured for a 50 g / m 2< heat-sealable paper with a one-sided heat-seal line and a one-sided line for printing and barrier, produced according to the described manufacturing process: Table 4 Test parameters Value Basis weight (EN ISO 536) 50,00 g / m 2 Thickness (EN 20534) 53,40 µm Absolute water content (DIN EN 20 287) 6,08 % Smoothness Bekk OS (ISO 5627) 100,40 s Smoothness Bekk SS (ISO 5627) 90,40 s Porosity according to Bendtsen (ISO 5636-3) (150WG) 0,0 ml / min Cobb water 60 OS (EN 20535) 13,90 g / m 2 Cobb water 60 SS (EN 20535) 25,23 g / m 2 Cobb-Unger 120 OS 2,08 g / m 2 Cobb-Unger 120 SS 1,00 g / m 2 sizing 14,00 min Sizing factor 2,10 Ash (ISO 1762) 2,70 % Mullen burst pressure (ISO 2758) 297,50 kPa Longitudinal breaking strength (EN ISO 1925 2 / 3) 67,70 N / 15mm Breaking force transverse (EN ISO 1925 2 / 3) 38,05 N / 15mm Taber stiffness longitudinal 0,74 pcm Taber stiffness transverse 0,42 pcm White with UV on OS (ISO 2470) 82,86 Color coordinate system on OS L* (ISO 5631-1 / 2) 95,78 Color coordinate on OS a*(ISO 5631-1 / 2) -0,04 Color coordinate on OS b*(ISO 5631-1 / 2) 5,32 Grease DIN level OS 0,0 Level Grease DIN grade SS 4,0 Level

[0048] The following are examples of a laboratory study demonstrating the reduction in tackiness of heat-sealable polymers with the addition of waxes. The basis was a 50 g / m² ash-free paper sample from the paper machine. This sample was coated with bleached, branded pulp made of 2 / 3 long fiber and 1 / 3 short fiber, with a dosage of wet strength agent based on polyamine amide epichlorohydrin resin. DIN A4 sheets were coated on one side with various formulations using a hand doctor blade in the laboratory. The heat-sealable polymers used are listed in the following table. The heat-sealable polymers are commercially available aqueous dispersions with varying solid contents. Table 5 Heat seal polymer used Chemistry Polyolefin Polyethylene acrylate Polyethylene vinyl acetate Commercial form aqueous polyolefin dispersion aqueous polyethylene acrylate dispersion aqueous polyethylene vinyl acetate dispersion Solids content (FG) % Commercial product 56 30 50 pH value of the merchandise 9,9 9,5 4-5

[0049] The waxes used for this invention to prevent deposits in the drying of the paper machine and to prevent blocking of the paper web after winding on the drum without prior cooling of the paper web are shown in Table 6. Table 6 Waxes used to prevent deposits in the drying process and to prevent blocking in the reel after winding Chemistry Semi-synthetic wax, amide wax based on ethylenebistearamide Synthetic wax, polyethylene wax Synthetic wax, polypropylene wax Vegetable wax, soy wax Melting point °C 140-150 115-121 156-164 68 Average particle size h µm 5 4 6 1 charge non-ionic non-ionic non-ionic anionic

[0050] The different formulations are listed in the following Tables 7, 8 and 9. The parts refer to the dry matter of the respective coating color component.

[0051] First, Table 7 shows formulations V1-0, V1-1, V1-2, V1-3, and V1-4 with polyolefin as heat seal polymer Table 7 Recipe ingredient V1-0 V1-1 V1-2 V1-3 V1-4 Heat seal polymer Type Polyolefin Heat seal polymer parts 100 100 100 100 100 kaolin parts 0 25 25 25 25 Copolymer wax parts 0 20 20 20 20 Amide wax parts 0 20 0 0 0 PE wax parts 0 0 20 0 0 PP wax parts 0 0 0 20 0 Soy wax parts 0 0 0 0 20

[0052] Table 8 below shows formulations V2-0, V2-1, V2-2, V23, and V2-4 with polyethylene acrylate as heat seal polymer Table 8 Recipe ingredient V2-0 V2-1 V2-2 V2-3 V2-4 Heat seal polymer Type Polyethylene acrylate Heat seal polymer parts 100 100 100 100 100 kaolin parts 0 25 25 25 25 Copolymer wax parts 0 20 20 20 20 Amide wax parts 0 20 0 0 0 PE wax parts 0 0 20 0 0 PP wax parts 0 0 0 20 0 Soy wax parts 0 0 0 0 20

[0053] Table 9 shows formulations V3-0, V3-1, V3-2, and V3-3 with polyethylene vinyl acetate as the heat-seal polymer. Since neither copolymer wax nor soy wax is compatible with polyethylene vinyl acetate, the proportions of the other waxes were increased compared to the previous formulations. Table 9 Recipe ingredient V3-0 V3-1 V3-2 V3-3 Heat seal polymer Type Polyolethylenevinyl acetate Heat seal polymer parts 100 100 100 100 kaolin parts 0 25 25 25 Copolymer wax parts 0 0 0 0 Amide wax parts 0 25 0 0 PE wax parts 0 0 25 0 PP wax parts 0 0 0 25 Soy wax parts - - - -

[0054] The application weights were adjusted so that the laboratory sheets without wax and pigments had the same application weight of heat-sealable polymer as the laboratory sheets with wax and pigments. Therefore, the laboratory sheets with wax and pigments had a higher overall application weight. The coated laboratory sheets were then tested for tack and heat-seal properties. Two tests were used to evaluate tack. In the first test, the tack of the paper surface is assessed by manual tactile testing with the fingers. The laboratory sheets were evaluated for tack immediately after the coating had dried while still warm, using a grading system. The higher the grade, the stickier the coated surface. The following grading scale was used: 10 = very tacky; 8 = noticeably tacky; 6 = noticeable tackiness; 4 = tackiness no longer noticeable; 2 = definitely not tacky.

[0055] In a test developed by the applicant, hereinafter referred to as the adhesive force test, the slip force of the coated side of a laboratory sheet on a hot plate is determined. The laboratory sheet is placed with the coated side onto the hot plate. A 1 kg weight measuring 5 cm x 5 cm x 5 cm is placed on top of the laboratory sheet, exerting a pressure of 0.4 N / cm² on the laboratory sheet. A spring force gauge is then attached to the laboratory sheet with an adhesive strip. The laboratory sheet is then manually pulled across the 60°C hot plate at a constant speed (0.3 m / min) using the spring force gauge. The slip force can therefore be determined directly on the spring force gauge. The higher the measured force, the stickier the paper surface.

[0056] Additionally, smoothness was determined using the Bekk smoothness test. The smoothness of the coated side of the laboratory sheets was measured using a smoothness meter.

[0057] The heat-sealability property was also determined using a test developed by the applicant, in which the laboratory sheets are sealed using a hand-held welding device. The heat-sealing strength of the seal seam was determined using a strength tester, in which the force required to pull the paper strips apart at the seal seam was determined using a strength testing device. The seal seam on the laboratory sheets was created using a hand-held welding device from Kopp SZ IG, in which the laboratory sheets were welded from coated side to coated side by manually pressing the welding tongs together at 135°C for 5 seconds. The heat-sealing strength was then determined using an FPG 7 / 18 strength testing device from Kögel. The paper strips were clamped into the tensile testing device, and the force required to pull the paper strips apart at their seal seam was measured.

[0058] The results of the laboratory tests are shown in Tables 10, 11, and 12 below. The results of Table 10 correspond to the formulations shown in Table 7, the results of Table 11 correspond to the formulations shown in Table 8, and the results of Table 12 correspond to the formulations shown in Table 9. Table 10 V1-0 V1-1 V1-2 V1-3 V1-4 Heat seal polymer Type Polyolefin Line application g / m 2 6 8 8 8 8 Smoothness according to Bekk s 35 ±10 20 ±10 20 ±5 20 ±5 25 ±10 Sensory stickiness note 8 2 3 3 3 Adhesive strength test N 8 3 5 5 5 Heat sealing strength N / 15mm 3,1 2,8 2,8 3,0 3,0 Table 11 V2-0 V2-1 V2-2 V2-3 V2-4 Heat seal polymer Type Polyethylene acrylate Line application g / m 2 4 6 6 6 6 Smoothness according to Bekk s 30 ±5 15 ±5 20 ±5 15 ±5 20 ±5 Sensory stickiness note 6 2 3 3 2 Adhesive strength test N 6 3 4 4 3 Heat sealing strength N / 15mm 3,0 2,8 3,0 3,2 2,6 Table 12 V3-0 V3-1 V3-2 V3-3 Heat seal polymer Type Polyolethylenevinyl acetate 8 8 8 Smoothness according to Bekk s 30 ±5 25 ±5 20 ±5 15 ±5 Sensory stickiness note 10 2 3 3 Adhesive strength test N 12 3 4 4 Heat sealing strength N / 15mm 3,0 2,9 3,1 2,9 Evaluation of the results:

[0059] The applied heat-sealable polymers showed a sticky surface without the addition of wax / pigments, which, as expected, leads to problems during dosing in a paper machine with integrated film press and subsequent contact drying on hot cylinders.

[0060] Without the addition of wax / pigments in the coating, sticking or blocking in the paper roll can be observed during the subsequent winding of the paper web without prior cooling of the paper web.

[0061] By adding waxes and pigments to formulations containing heat-sealable polymers according to the invention, a significant reduction in tack was determined based on laboratory results. In particular, the tack test showed a significant decrease in tack, ranging from 6-10 without wax / without pigments to 2-3 with wax / with pigments. Furthermore, the adhesion test showed a decrease in tack due to a reduction in slip force to values of 3-5 N compared to values of 6-12 N without wax / without pigments. As the values for the determined heat-sealing forces show, the heat-sealing forces can be largely maintained despite the added waxes.

[0062] Surprisingly, differences in the coatings were also found using the Bekk smoothness test. The results show a trend in the smoothness values. The handsheets without wax / without pigments showed higher smoothness than the handsheets with wax / with pigments. One interpretation of smoothness for stickiness is that the higher the smoothness, the more tightly the paper surface is sealed. This results in higher air resistance on the paper surface and is an indication of greater stickiness of the paper surface. These values with regard to stickiness reduction allow the justified expectation that the coating applied to the paper web in the paper machine can be produced without deposits on the drying cylinders and without blocking the wound paper web.

[0063] However, soy wax is considered an exception. Due to its low melting point on the hot drying cylinder, it is not possible to avoid deposits in combination with the heat-sealable polymers. Therefore, the semi-synthetic and synthetic waxes of the invention are considered more suitable for preventing deposits and clogging of the paper roll.

[0064] The heat-sealability properties were not negatively affected by the addition of waxes and pigments. Very good heat-sealability was measured on the laboratory sheets. The study therefore concludes that the inventive addition of semi-synthetic and synthetic waxes with a high melting point to a formulation containing heat-sealable polymers can prevent deposits on the drying cylinder during coating drying and prevent blocking of the paper web after reeling at elevated temperatures in the range of 50°C to 60°C, thereby producing a heat-sealable paper with good heat-seal properties.

Claims

1. Method for producing a heat-sealable paper in which a heat-sealing coating, based on a heat-sealable polymer, is applied to a paper web and the paper web is subsequently rolled up onto the application of the heat-sealing coating, wherein the heat-sealing coating contains wax of a first type of wax in a dispersed phase, characterized in that the melting point of the first type of wax is above the maximum drying temperature of the paper web to be wound up and between 105 and 164 degrees Celsius, and the wax contains a second type of wax whose melting point is chosen between the maximum drying temperature of the paper web to be wound up and the melting point of the first type of wax.

2. The method according to claim 1, wherein the melting point of the second type of wax is selected between the melting temperature of the heat-sealable polymer and the melting point of the first type of wax.

3. The method according to claim 1 or 2, wherein the melting point of the second type of wax is selected in a range of 86 to 164 degrees Celsius.

4. The method according to any one of claims 1 to 3, wherein, based on 100% by weight of the heat-sealable polymer, the weight fractions of the first type of wax are selected in a range from 2% to 25% by weight when the first type of wax is used alone, and in a range from 2% to 15% by weight when the first and second type of wax are used.

5. The method according to any one of claims 2 to 4, wherein the weight fraction of the second type of wax, based on 100% by weight of the polymer, is selected in the range 3% to 10%.

6. The method according to any one of the preceding claims, wherein as first or second type of wax, a wax based on ethylene acrylic acid or secondary fatty acid amide waxes are selected.

7. The method according to any one of the preceding claims, wherein the heat-sealing coating additionally contains 5% to 40% by weight of a platelet-shaped pigment, based on kaolin, based on 100% by weight of the heat-sealable polymer.

8. The method according to any one of the preceding claims, wherein the heat-sealing coating additionally contains 0.1% to 1% by weight of acrylate copolymer, based on 100% by weight of the heat-sealable polymer and / or the heat-sealing coating additionally contains 0.01% to 0.2% by volume of fatty alcohols, based on 100% by weight of the heat-sealable polymer.

9. The method according to any one of the preceding claims, wherein the heat-sealable polymer consists of at least polyolefin or polypropylene ethylene acrylate polymers, or polyethylene polymers.

10. The method according to any one of the preceding claims, wherein a front coat contains 20 to 80% by weight of a platelet-shaped pigment, based on kaolin, and 80 to 20% by weight of modified starch.

11. The method according to any one of the preceding claims, wherein the maximum drying temperature of the paper web to be rolled up is between 80 and 100 degrees Celsius.

12. Manufacturing method of a heat-sealable paper with the following method steps: • production of a base paper in a paper machine with a basis weight of 30 g / m2 to 150 g / m2; • direct application of a heat-sealing coating according to any one of the method claims 1 to 11; • drying the heat-sealing coating • rolling up the paper web.

13. Heat-sealing coating composition, based on a heat-sealable polymer, wherein the heat-sealing coating composition contains a wax, comprising two types of wax, wherein the first type of wax is in the disperse phase and has a melting point which is above the temperature of a paper web to be wound up in a range of 105 to 164 degrees Celsius, and wherein the second type of wax has a melting point between the maximum drying temperature of the paper web to be wound up and the melting point of the first type of wax.

14. The heat-sealing coating composition according to claim 13, wherein the heat-sealing coating additionally contains at least one of the following components: • the second type of wax, which has a lower melting point than the first type of wax, wherein the second type of wax is based on secondary fatty acid amide waxes; • 5% to 40% by weight of a platelet-shaped pigment based on kaolin; • 0.1% to 1% by volume of acrylate copolymer; • 0.01% to 0.2% by volume of fatty alcohols; • the heat-sealable polymer which consists at least of polyolefin or polypropylene ethylene acrylate polymers, or polyethylene polymers.

15. Arrangement for producing a heat-sealable paper web, comprising: • paper machine for producing a raw paper web; • coating device for applying a heat-sealing coating composition according to any one of claims 13 or 14; • coating device for applying a counter-side coating compound; • drying device; • winding unit for winding up the paper web.

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