Electrically conductive paper structure, method for producing the same and use thereof

Abstract

A method for producing an electrically conductive paper structure provided with through openings, containing cellulosic fibers and electrically conductive fibers, comprising providing a paper machine having a dewatering screen for producing a paper structure, the dewatering screen having inserts for creating through openings in the paper structure; providing a stock suspension containing cellulosic fibers, electrically conductive fibers, and water; conveying the stock suspension to the dewatering screen in order to deposit cellulosic fibers and electrically conductive fibers on the dewatering screen and in this way form a paper web; dewatering the paper web.

Description

[0001] The invention relates to an electrically conductive paper structure, a method for producing the same and the use of the electrically conductive paper structure.

[0002] Electrically conductive paper structures based, for example, on cellulose-containing fibers and electrically conductive fibers are known in the prior art, see, for example, WO 2020 / 224800 A1. It is thus generally known to equip flat paper substrates with conductive fibers, in particular metal fibers or graphitized carbon fibers or carbon fibers, or other materials that provide conductivity, e.g., carbon nanotubes, in such a way that electrical current flows through the flat paper substrate. Depending on the specific resistance, the paper substrate can be used for different purposes, e.g., as a heating element, as an element for electromagnetic shielding, or as an element for signal detection.

[0003] The electrically conductive paper structures known to date have the disadvantage, particularly when used as heating paper, that the installation and permanent attachment to walls, ceilings and floors leads to problems.

[0004] The present invention is therefore based on the object of providing an improved electrically conductive paper structure. In particular, the electrically conductive paper structure, when used as heating paper, should be easily applied and permanently attached to walls, ceilings, and floors.

[0005] This object is achieved by the combinations of features defined in the independent claims. Further developments of the invention are the subject of the dependent claims. Summary of the invention

[0006] 1. (First aspect of the invention) A method for producing an electrically conductive paper structure provided with through openings, containing cellulosic fibers and electrically conductive fibers, comprising: a) providing a paper machine having a dewatering screen for producing a paper structure, the dewatering screen having inserts for creating through openings in the paper structure; b) providing a stock suspension containing cellulosic fibers, electrically conductive fibers, and water; c) conveying the stock suspension to the dewatering screen to deposit cellulosic fibers and electrically conductive fibers on the dewatering screen and thus form a paper web; d) dewatering the paper web. 2.(Preferred embodiment) The process according to paragraph 1, wherein the provision of the stock suspension in step b) is carried out by first providing a stock suspension containing cellulose-containing fibers and water, optionally adding at least one chemical additive, and subsequently adding electrically conductive fibers. 3. (Preferred embodiment) The process according to paragraph 1 or 2, wherein the paper machine is a cylinder-shaped paper machine and, in addition, at least one continuous, electrically conductive thread is introduced into the stock suspension in the cylinder-shaped paper machine, wherein the thread is brought to the dewatering wire, namely a cylinder-shaped wire, in such a way that the thread is embedded in the fiber structure during the formation of the paper web. 4.(Preferred embodiment) Method according to one of paragraphs 1 to 3, wherein the inserts for creating through-openings in the paper structure are each formed in the shape of a motif, in particular in a round shape or in the shape of a polygon. 5. (Preferred embodiment) Method according to one of paragraphs 1 to 4, wherein the inserts for creating through-openings in the paper structure are based on plastic or metal. 6. (Second aspect of the invention) Electrically conductive paper structure with cellulose-containing fiber materials and electrically conductive fibers, wherein the electrically conductive paper structure is provided with through-openings, wherein the through-openings are obtainable during the production of the paper structure in the form of a paper web by means of a paper machine, and the paper machine has a dewatering screen provided with inserts for creating through-openings in the paper structure. 7.(Preferred embodiment) The electrically conductive paper structure according to paragraph 6, wherein the paper structure is obtainable by the process according to any one of paragraphs 1 to 5. 8. (Third aspect of the invention) Use of the electrically conductive paper structure according to paragraph 6 or 7 as a heating element, an electromagnetic shielding element, or a signal detection element. Detailed description of the preferred embodiments

[0007] The present invention is based on the idea of ​​providing an electrically conductive paper structure that can be easily applied and permanently fixed to walls, ceilings, and floors. The electrically conductive paper structure is provided with through-openings. The through-openings are obtainable during the production of the paper structure in the form of a paper web using a paper machine, and the paper machine has a dewatering screen provided with inserts for creating through-openings in the paper structure. Due to the presence of the through-openings, the electrically conductive paper structure according to the invention can be applied and permanently fixed to walls, ceilings, and floors in a simple and efficient manner by plastering, filling, or pouring. The through-openings advantageously improve the adhesion of the attached paper structure.Furthermore, the through-holes improve sound insulation when the paper is applied to a sound-insulating substrate, as well as the breathing ability—i.e., the air and moisture exchange—of the walls, ceilings, or floors equipped with the electrically conductive paper structure according to the invention. Furthermore, the holes increase the electrical resistance, which is advantageous for achieving low heating outputs. Another advantage is the lower material consumption. Furthermore, the holes reduce any tension, e.g., in combination with other papers, films, or the like, and thus prevent or reduce any bending, warping, or the like that may occur.

[0008] According to the present invention, the through-holes are created in a single work step during papermaking on the paper machine. Thus, no further work steps such as punching, mechanical cutting, laser cutting, or the like are required, meaning the creation of the through-holes is extremely cost-effective.

[0009] The electrically conductive paper structure according to the invention is preferably plastered with a suitable plaster. In construction, a pasty, usually granular, plaster that is applied wet is typically used.

[0010] The present invention is based on the production of banknote paper known in the prior art, in which the window or the through-opening is introduced directly into the paper machine, see, for example, WO 00 / 39391 A1. According to the present invention, the through-openings in the electrically conductive paper structure are produced by means of a dewatering screen, wherein the dewatering screen is provided with inserts suitable for producing through-openings in the paper structure. In particular, sufficiently high webs can be used as inserts. A dewatering screen known in the prior art with an insert suitable for producing a through-opening in the paper structure is shown, for example, in Figure 2 of WO 00 / 39391 A1. As a result of the presence of the sufficiently high webs on the dewatering screen, no paper can accumulate in the region of the webs.This creates continuous openings in the paper structure that are approximately as large as the surface area of ​​the webs. The inserts for creating continuous openings in the paper structure are preferably made of plastic or metal. Furthermore, the inserts for creating continuous openings in the paper structure are expediently each formed in the shape of a motif, in particular in a (circular) round shape or in the shape of a polygon, in particular in the shape of a square or a rectangle. Round, continuous openings are preferred due to their mechanical stability. According to a particular variant, the continuous openings can be in the form of information, in particular in the form of numbers, letters, or the like, in order to represent a product identifier, a code, or processing instructions such as the terms "top" or "bottom."

[0011] During the production of the paper structure, unwanted paper residues, e.g. thin paper layers, can under certain circumstances form within the areas of the through openings to be created. The thin paper layers can be removed, for example, by vacuuming or by a suitable mechanical measure. Suitable mechanical measures include, for example, a brush or the use of a textile fabric, in particular a web-shaped felt, with a suitable roughness. The paper structure formed during paper production can, for example, be brought into contact with the web-shaped felt by means of a roll nip, so that unwanted paper residues, such as thin paper layers, adhere to the felt and are thus removed.

[0012] The frequency of through openings is determined by the stability of the material and is generally not subject to any particular restrictions. In the electrically conductive paper structure according to the invention, the frequency of through openings is, for example, in a range from 4% to 60%, whereby this refers to the total area of ​​all through openings relative to the total paper area.

[0013] The diameter of the through-holes is determined by the stability of the material and is generally not subject to any particular restrictions. For example, the through-holes have a diameter in the range of 3 mm to 20 mm.

[0014] To achieve optimal plasterability of the electrically conductive paper structure, it is preferable to distribute the through openings evenly, i.e., homogeneously, throughout the electrically conductive paper structure. This also enables advantageous sound insulation of the paper structure installed in the wall, floor, or ceiling.

[0015] The method according to the invention for producing an electrically conductive paper structure provided with through openings, containing cellulose-containing fibers and electrically conductive fibers comprises the following steps: a) providing a paper machine having a dewatering screen for producing a paper structure, the dewatering screen having inserts for creating through-openings in the paper structure; b) providing a stock suspension containing cellulose-containing fibrous materials, electrically conductive fibers, and water; c) conveying the stock suspension to the dewatering screen in order to deposit cellulose-containing fibrous materials and electrically conductive fibers on the dewatering screen and thus form a paper web; d) dewatering the paper web.

[0016] The provision of the stock suspension in step b) is preferably carried out in such a way that first a stock suspension containing cellulose-containing fibers and water is provided, optionally at least one chemical additive is added, and then electrically conductive fibers are added.

[0017] The paper machine is preferably a cylinder-shaped paper machine. According to a preferred embodiment, at least one continuous, electrically conductive thread (hereinafter also referred to as "contact thread") is additionally introduced into the stock suspension in the cylinder-shaped paper machine. The thread is guided to the dewatering wire, namely a cylinder-shaped wire, in such a way that the thread is embedded in the fiber structure during the formation of the paper web. Analogous to a security thread incorporated into banknote paper, an electrically conductive paper structure with improved contacting can be provided in this way. The electrically conductive paper structure is preferably traversed from one end to the opposite end by continuous, conductive contact threads.This enables easy contacting of the electrically conductive paper structure at the ends of the contact threads and, by introducing the contact threads over the entire surface of the paper structure, provides a local power supply to all areas of the paper structure.

[0018] Advantageously, the electrically conductive paper structure contains a plurality of continuous, electrically conductive threads for contacting the electrically conductive paper structure, each of which is embedded from one end to the opposite end of the paper structure, wherein the plurality preferably assumes a value in the range from two to eight, more preferably a value in the range from two to six, and particularly preferably the value two.

[0019] The production of the electrically conductive paper structure according to the invention using cylinder screen technology makes it possible to process varying fiber compositions. It is expedient to admix carbon fibers as conductive fibers with the cellulose-containing fibers. Alternatively or additionally, metallic short-cut fibers can also be used. The carbon fibers or metallic short-cut fibers have, for example, a fiber length in the range of 3 to 12 mm. The amount in which the carbon fibers and / or metallic short-cut fibers are admixed is expediently selected such that sufficient fiber-to-fiber contact is provided, thus ensuring a suitable electrical current flow. The electrically conductive paper structure can contain other natural and / or synthetic fibers, optionally chemical additives, and optionally residual moisture.Furthermore, electrical conductivity can be achieved not only by conductive metallic fibers, in particular metallic short-cut fibers, or by carbon fibers, but also by adding carbon particles or carbon nanotubes.

[0020] The cellulose-containing fibers usable for the electrically conductive paper structure according to the invention can be selected, for example, from fibers of natural origin or from synthetic fibers. Cellulosic fibers of natural origin include, for example, wood fibers, semi-chemical pulps, thermomechanical pulp, cotton fibers, chemically digested cellulose such as sulfate or sulfite pulp, mechanical pulp, chemically modified mechanical pulp, recycled fibers, and combinations of two or more of the aforementioned elements.

[0021] The proportion of carbon fibers and / or metallic short-cut fibers added to the cellulose-containing fibers can vary depending on the application, particularly within a range from a few percent by weight (wt.%) to 35 wt. Ideally, sufficient conductive fibers are added to exceed the so-called percolation threshold to ensure sufficient conductivity. Consequently, a sufficient network of conductive fibers is required to ensure the flow of electrical current.

[0022] Chemical additives can optionally be added to the electrically conductive paper structure according to the invention, which are selected, for example, from a group comprising, in particular, retention aids, drainage aids, retention aid dual systems or microparticle systems, wet and dry strength agents, sizing agents, fillers and / or pigments, in particular selected from a group comprising talc, titanium dioxide, aluminum hydroxide, bentonite, barium sulfate, calcium carbonate, kaolin, defoamers, deaerators, biocides, enzymes, bleaching aids, optical brighteners, dyes, shading dyes, impurity scavengers, precipitants (fixing agents), wetting agents, pH regulators. Alternatively or in combination, the chemical additive can also be selected from a group of preferably water-soluble polymers, which in particular comprise amine-containing polymers, polyethyleneimine, pyrolidine, polyamides, polyacrylamide, aridine, proteins, peptides, polyether-containing polymers,in particular polyethylene oxide, polyethers, hydroxyl-containing polymers, in particular starch, carboxymethylcellulose, polyvinyl alcohol, charged polymers, in particular cationic polymers, in particular cationic starch, corn starch, potato starch, wheat starch, rice starch, ammonium-containing polymers, anionic polymers, in particular anionically modified polyacrylamides, sulfonated polymers, inorganic salts with high charge density, in particular aluminum salts, aluminum(III) chlorides, aluminum sulfate, sodium aluminate, inorganic, charged particles / pigments, in particular bentonite, montmorillonite, sodium silicate, wet strength agents, in particular epichlorohydrin resins, glyoxal, zirconium salts, zirconium carbonate, combinations of anionic polymers and cationically modified pigments, flash point reducing agents, combinations thereof, and the like.

[0023] According to a further particularly preferred embodiment, the paper structure according to the invention has a basis weight according to DIN EN ISO 536 which is in a range from 15 g / m 2< to 1000 g / m 2< , preferably in a range from 20 g / m 2< to 300 g / m 2< .

[0024] The paper structure according to the invention further exhibits, for example, a power consumption in the range of 20 W / m 2 to 5000 W / m 2 . A temperature in the range of 15 °C to 130 °C can be achieved on the surface of the paper structure.

[0025] The electrically conductive paper structure according to the invention can be provided with additional reinforcing fibers to control the desired properties. Surface sizing or surface impregnation is also possible.

[0026] Different designs are conceivable with regard to the contact threads. What is important in all designs is that contact is ensured with the conductive components in the paper structure, in particular metallic fibers and / or carbon fibers. In the simplest case, a metallic thread, e.g. made of rolled metal, a metal strip or a metal wire, can be used as the contact thread, wherein the metal is in particular selected from a highly conductive metal such as silver, copper, gold, aluminum, tungsten, iron or the like or an alloy of one or more of the aforementioned elements. Furthermore, the use of a metallized thread is also possible, e.g. the use of a thread based on a plastic carrier film as the carrier substrate and metallized with a highly conductive metal such as silver, copper, gold, aluminum, tungsten, iron or the like.Polyethylene terephthalate (PET), in particular, can be used as the plastic carrier film. Furthermore, a metallized film or a laminate of film and rolled metal foil can be used as the contact thread. Particularly reliable contacting using crimp contacts or ZIF connectors (ZIF = Zero Insertion Force) is conceivable with purely metallic threads designed as metal strips, e.g., with a width in the range of 2 mm to 7 mm. Increased metal thickness leads to lower resistance and thus to higher power consumption. Metallized threads of this type can additionally be provided, at least on one side, with an adhesive, which is preferably a conductive adhesive, to better fix the contact thread in the electrically conductive paper structure.Furthermore, it is possible that the contact thread embedded in the electrically conductive paper structure is partially exposed in the area of ​​the contact point, as is the case with so-called window threads in banknotes.

[0027] Furthermore, the contact threads can be additionally provided with a protective layer or protective film on the upper side, which is removed as required in the contacting area, ie in the window area.

[0028] The term contact thread is not necessarily restricted to the sole design as a (fairly narrow) thread which, for example, has a width of 2 mm or less, but designs such as (fairly wide) strips or bands are also conceivable, which, for example, have a width of 4 mm to 20 mm, or even a width of up to 30 mm. In principle, it is also conceivable that a simple conductive metal wire or a metal braid is used as the contact thread. Design variants such as flat strands, braided braids, knitted fabrics, lamella bands and the like are also possible. The thickness of the contact thread can, for example, be selected in a range from 10 to 300 µm, preferably in a range from 10 to 200 µm, more preferably in a range from 10 to 100 µm and particularly preferably in a range from 10 to 50 µm.

[0029] The electrically conductive paper structure according to the invention can additionally be printed with a conductive pattern of conductor tracks in order to reduce the distances between two (or a plurality of greater than two) contact threads serving as electrodes. The printing, i.e. the provision of the printed conductor tracks, can be carried out, for example, using a screen printing process. As conductive varnishes that produce the conductive pattern, aqueous screen printing inks based on soot particles, silver particles, or other conductivity-producing particles can be used, for example. The conductive pattern of printed conductor tracks is expediently produced in such a pattern that the distances between the two electrodes are approximately similar in all areas.According to a preferred variant, the conductive pattern can be made to contact the contact threads embedded in the substrate by contacting them at points (so-called thread windows) where the contact threads are partially exposed. The additional printing with a conductive pattern means that the product can be operated as a conductive surface element with relatively low voltages. Due to the reduced distance between two electrodes, the current required for the respective application, e.g. a heater, can be achieved even with a smaller number of conductive fibers in the substrate. Alternatively, with the same number of conductive fibers in the substrate, the desired current can be achieved with a lower voltage. By appropriately adapting the dimensions of the conductive fibers and the printed, conductive pattern, the percolation threshold can even be reduced.The latter describes the minimum proportion of conductive fibers required to achieve a continuous conductive fiber network between two contact threads serving as electrodes, thus achieving a relevant current flow. This results in cost savings regarding the expensive conductive fibers. A lower operating voltage also reduces the complexity, e.g., for the control electronics, and increases work safety.

[0030] The contact thread can be fully embedded in the paper structure if required. However, the contact thread can also be embedded in such a way that it is freely accessible on one side after embedding in the paper structure. This is possible, for example, by mechanically removing, in particular by suction, the paper layer deposited on one side of the contact thread. The formation of freely accessible areas on at least one side of the embedded contact thread can also be achieved by choosing a sufficiently wide contact thread, see, for example, EP 0 625 431 A1. Furthermore, the contact thread can be embedded in the paper structure in such a way that the contact thread is exposed on the surface of the paper structure at least at one point in order to form a so-called window thread. The production of window security threads is known in the field of banknote paper production, see, for example, EP 0 059 056 A1.The contact thread is guided outside the pulp to the paper screen in such a way that the contact thread rests on raised areas (or bumps) applied to the paper screen. At the points where the contact thread rests on the bumps, no paper can form on the side facing the screen, so the contact thread is freely accessible at precisely these points in the finished paper.

[0031] The invention further encompasses the use of the electrically conductive paper structure as a heating element, in particular as a heating element in floors, walls, wallpaper, containers, fabrics, clothing, table tops, heating plates, heating mats, car interior heaters, in particular door, seat or dashboard heaters, the use for electromagnetic shielding and the use as an element for signal detection.

[0032] Further embodiments and advantages of the invention are explained below with reference to the figure, in which a true-to-scale and true-to-proportion reproduction has been omitted in order to increase clarity.

[0033] It shows: Fig. 1 shows a plan view of an embodiment of an electrically conductive paper structure according to the invention.

[0034] The Fig. 1 shows a plan view of an embodiment of an electrically conductive paper structure 1 according to the invention with two separate contact threads 3 completely embedded in the paper structure. The electrically conductive paper layer 2 is based on a mixture containing paper fiber and carbon fibers. The contact threads 3 were completely embedded in the paper layer 2 using a cylinder paper machine. Fig. 1it can be seen that the contact threads 3 run through the electrically conductive paper structure 1 from one end to the opposite end. The electrically conductive paper structure 1 therefore has excellent contact at both its ends. The electrically conductive paper structure 1 is additionally provided with through-openings 4, which in the present example are circular in shape with a diameter of 10 mm. The through-openings 4 are evenly distributed over the paper layer 2 and enable the electrically conductive paper structure 1 to be efficiently applied and permanently fixed to walls, ceilings and floors by plastering. The through-openings 4 advantageously improve the adhesion of the attached paper structure 1. In addition, the through-openings 4 improve sound insulation, but also breathability, i.e. the exchange of air and moisture.

[0035] The through-openings 4 are created during the production of the paper web in a cylinder-shaped paper machine using a dewatering screen. The dewatering screen is provided with inserts suitable for creating through-openings in the paper structure. Sufficiently high webs are used as inserts; see the dewatering screen known from the prior art in Figure 2 of WO 00 / 39391 A1.

Claims

1. A method for producing an electrically conductive paper structure provided with through openings, containing cellulosic fibers and electrically conductive fibers, comprising a) providing a paper machine having a dewatering screen for producing a paper structure, wherein the dewatering screen has inserts for creating through openings in the paper structure; b) providing a stock suspension containing cellulosic fibers, electrically conductive fibers, and water; c) conveying the stock suspension to the dewatering screen in order to deposit cellulosic fibers and electrically conductive fibers on the dewatering screen and in this way form a paper web; d) dewatering the paper web.

2. The method according to claim 1, wherein the provision of the stock suspension in step b) is carried out in such a way that first a stock suspension containing cellulose-containing fibers and water is provided, optionally at least one chemical additive is added, and subsequently electrically conductive fibers are added.

3. Method according to claim 1 or 2, wherein the paper machine is a cylinder wire paper machine and additionally at least one continuous, electrically conductive thread is introduced into the stock suspension in the cylinder wire paper machine, wherein the thread is brought to the dewatering wire, namely a cylinder wire, in such a way that the thread is embedded in the fiber structure during the formation of the paper web.

4. Method according to one of claims 1 to 3, wherein the inserts for producing through openings in the paper structure are each formed in the form of a motif, in particular in a round form or in the form of a polygon.

5. Method according to one of claims 1 to 4, wherein the inserts for creating through openings in the paper structure are based on plastic or metal.

6. Electrically conductive paper structure with cellulose-containing fibers and electrically conductive fibers, characterized in that the electrically conductive paper structure is provided with through openings, wherein the through openings are obtainable during the production of the paper structure in the form of a paper web by means of a paper machine and the paper machine has a dewatering screen provided with inserts for producing through openings in the paper structure.

7. An electrically conductive paper structure according to claim 6, wherein the paper structure is obtainable by the process according to any one of claims 1 to 5.

8. Use of the electrically conductive paper structure according to claim 6 or 7 as a heating element, as an element for electromagnetic shielding or as an element for signal detection.

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