METHOD FOR THE PRODUCTION OF WET-RUNNING PAPER

Description

[0001] The invention relates to a method for producing a wet-rubbed rubbing paper comprising at least a fiber component of at least one type of fiber, a component of at least one filler, and a component of a phenol resin-based binder.

[0002] Document GB-A-2 205 592 discloses a friction coating material described as wet-wash paper, consisting of a porous fiber base material, an inert filler, and phenolic resin. The fiber base material is processed in an aqueous slurry, the phenolic resin in the form of an emulsion, and the filler is processed into a stock solution. This stock solution is applied to a Fourdrinier wire, rolled, and dried using a papermaking process. During the drying process, the phenolic resin is cured by the influence of temperature. Document EP-A-0 129 022 discloses wet-wash coatings and a process for producing wet-wash papers.

[0003] The object of the invention is the further development of a method for producing wet-wash rubbing paper. In particular, the object of the invention is to simplify the production of wet-wash rubbing paper and to improve its properties.

[0004] The problem is solved by the subject matter of claim 1. The dependent claims describe advantageous embodiments of the subject matter of claim 1.

[0005] The proposed process is for the production of a wet friction paper or a layered friction material for friction, clutch, and / or braking devices, particularly in a motor vehicle. The wet friction paper contains a fiber component of at least one fiber type, for example, aramid fibers, carbon fibers, cotton fibers such as linter fibers, and / or the like; a component of at least one filler, for example, diatomaceous earth such as Celite, graphite, coke, and / or the like; and a component of a phenolic resin-based binder, for example, phenol-resol, and / or the like. Further components, such as silicone resin, silanes, flocculants, retention agents, friction particles, and / or the like, may be included.

[0006] Wet-wash pulp paper is produced in a papermaking process. This means that a slurry, such as pulp or suspension, is formed from the fibers and at least one filler. The fibers are present in a short, cut form, for example, with a length of just a few millimeters. The highly aqueous pulp also contains the binder, in which a phenolic resin may be present as a phenolate, along with other resin components. This phenolic resin is produced by dissolving it in a strongly alkaline solution, such as sodium or potassium hydroxide.

[0007] The pulp is processed into wet-rubbed paper using a familiar papermaking process. For example, the pulp is placed on a Fourdrinier wire and rolled in a wet press unit to achieve the desired thickness. The pulp is then dried, if necessary, by further rolling. During this drying phase, certain rollers can be heated to higher temperatures than those used in the wet phase to evaporate any remaining solvent, such as water.

[0008] According to the invention, the phenol resin fraction present in the pulp as a dissolved phenolate of the phenolic resin is precipitated. For this purpose, the pH of the alkaline pulp is lowered by adding acid, for example, by neutralizing the pulp, which converts the phenolate into an insoluble phenolic resin and causes it to precipitate. A dilute acid, such as 5% sulfuric acid, can be used as the precipitating agent. The precipitation process preferably takes place in the wet phase at room temperature or the ambient temperature of the papermaking process.

[0009] Through the precipitation process, and preferably with the use of a retention agent, a uniform distribution of precipitated phenolic resin particles can be achieved across the entire area of ​​the pulp lying on the wire mesh. In this way, after the pressing and rolling processes of the papermaking process and drying of the finished wet-rubbed rubbing paper, a lateral and, across its thickness, uniform distribution of the phenolic resin particles between the two surfaces can be achieved, so that the friction quality of a rubbing partner produced from the wet-rubbed rubbing paper exhibits essentially consistent friction properties throughout its service life. Furthermore, the particle size of precipitated binder particles, such as phenolic resin particles, can be adjusted by means of a predetermined addition rate of the precipitating agent.In particular, by adding a corresponding rate of the precipitating agent, for example 0.5 kg / s, particularly small particle diameters of the phenolic resin, especially phenol-resol in the range of 200 to 1600 nanometers, can be achieved, which penetrate the fibers or fiber assemblies of the fiber content and adhere to the fibers in a uniform distribution.

[0010] By adding appropriate flocculants and / or retention agents, a suitable zeta potential can be set, for example at 80 mV ± 8 mV, so that a high flocculation conversion, essentially 100% deposition of the phenolic resin, can be achieved.

[0011] Improved reinforcement properties, for example in the bonding process of wet-running paper to a suitable substrate such as a backing sheet or the like, are achieved by adjusting the rheological properties of the pulp. In this context, a viscosity of less than 3000 Pa*s for a service life of 800 s has proven advantageous. It is understood that the viscosity may change at other service lives, and it may be necessary to recalculate the viscosity for the specified service life to determine its final viscosity.

[0012] The hardness of the binder, such as phenolic resin, and thus its abrasion resistance, elasticity, temperature resistance, and / or similar properties, can be adjusted during a drying phase of the papermaking process. This can be achieved by maintaining a uniform temperature across the rolls or by gradually increasing or decreasing the temperature profile from roll to roll during the drying phase. The positive properties of wet-run paper, particularly its reinforcing effect when bonded to a substrate, depend on adjusting the activation potential of the binder's curing process. For this purpose, the phenolic resin and its reactants are advantageously adjusted such that the activation energy of the curing process is greater than 60 kJ / mol with a frequency factor In20 and a reaction order < 1.5.

[0013] An advantageous composition for the production of wet rubbing paper can be, for example, containing a fiber content of 40 to 60 wt%, in particular a mixture of aramid fibers, linter fibers and carbon fibers, a binder content of 30 to 40 wt%, in particular phenolic resin, present as phenolate in alkaline solution, and a filler content of 20 to 40 wt%, in particular Celite.

[0014] A particularly advantageous composition contains, for example, in weight percent, 26% aramid fiber, 6% linter fiber, 9% carbon fiber, 30% phenolic resin such as phenolresol, present as phenolate in strongly alkaline solution with subsequent precipitation, 29% Celite.

[0015] It is understood that the inventive concept also encompasses the described wet-wash rubbing paper, in particular produced according to the proposed method. The wet-wash rubbing paper exhibits a uniform distribution of resin particles between its two opposing surfaces. The particle size of the binder particles formed from the binder fraction is preferably between 200 and 1600 nm.

[0016] After the papermaking process, the wet-rubbed rubbing paper is available in sheet or roll form. Depending on its intended use as a radially or axially acting rubbing material, this wet-rubbed rubbing paper is used to produce friction linings by die-cutting, cutting, or similar processes in ring or ring segment form with radial or axial friction surfaces. Following the papermaking process or during the drying phase, the surfaces of the friction lining or the wet-rubbed rubbing paper can be profiled at the designated friction surfaces, for example, by applying varying degrees of pressure. Alternatively or additionally, perforations required for specific applications can be incorporated.

[0017] It is understood that, for the purposes of the invention, a friction lining, brake lining and / or the like made from wet rubbing paper is encompassed by the invention and can be claimed as part of the patent application.

[0018] In summary, at least one, and preferably several, of the following setting parameters are advantageous in the manufacturing process of a proposed wet-running paper: The particle size of the precipitated resin particles is adjusted by a combination of the binder properties, particularly a phenol-resol, and the precipitation conditions of the phenolate. This is achieved by adjusting the pH of the acid used, such as sulfuric acid, and the precipitation rate, i.e., the acid addition rate. The rheological properties are adjusted by adding appropriate amounts of water or solvent and, if necessary, a flow agent to ensure sufficient resin flow for effective reinforcement. The zeta potential is determined by the quality of the binder, for example, its polarity and the type and number of functional groups, as well as the pulp properties. Adjusting the described zeta potential is essential for the precipitated particles to bond securely to the fiber.The reaction behavior with the specified activation energy ensures that the wet-run paper, in combination with the adjusted pulp drying, achieves the necessary curing, as well as good final curing during the gluing process when bonded to a substrate. By appropriately adjusting the activation energy, it is achieved, on the one hand, that the wet-run paper does not stick to the drying cylinder during the drying section of the paper machine, and on the other hand, that the gluing time of the wet-run paper to the substrate is preferably significantly less than one minute.

Claims

1. A method for producing a wet-running friction paper containing at least a fibre fraction consisting of at least one type of fibre, a fraction of at least one filler, and a fraction of a phenolic resin-based binder, wherein the fibre fraction, the filler fraction and the binder dissolved as an alkaline phenolate solution are processed together into a pulp in a paper production process, and the binder is then precipitated using diluted sulphuric acid as a precipitating agent, and the pulp applied to a Foudrinier wire is dried and cured by applying heat, characterized in that the zeta potential of the pulp is adjusted to 80 mV ± 8 mV by adding a flocculant and / or a retention agent.

2. The method according to claim 1, characterized in that a phenolic resol is used as the binder.

3. The method according to any one of claims 1 to 2, characterized in that the pulp is adjusted to a viscosity of less than 3000 Pa*s based on a standing time of 800 s.

4. The method according to any one of claims 1 to 3, characterized in that, due to the precipitation process, particles of the binder having a particle size of between 200 and 1600 nm are precipitated.

5. The method according to any one of claims 1 to 4, characterized in that the binder is adjusted to an activation energy greater than 60 kJ / mol with a frequency factor In20 and a reaction order < 1.5 during its curing.

6. The method according to claim 4 or 5, characterized in that a particle size of precipitated binder particles is adjusted by means of a predefined addition rate of the precipitating agent.

7. The method according to any one of claims 1 to 6, characterized in that the binder is brought to a predefined degree of hardness in a drying phase of the paper production process.

8. The method according to any one of claims 1 to 7, characterized in that the degree of hardness of the binder is adjusted during the curing of the pulp by means of a predefined temperature curve.

9. The method according to any one of claims 1 to 8, characterized in that a fibre fraction of 30 to 60 % by weight, in particular a mixture of aramid fibres, linter fibres, and carbon fibres, a binder fraction of 20 to 40 % by weight, in particular phenolic resol, and a filler fraction of 20 to 40 % by weight, in particular celite, are used.