Modified aramid pulp and friction material comprising modified aramid pulp

Abstract

The present invention relates to an aromatic polyamide pulp comprising polyoxazoline. The present invention further relates to a method of manufacturing an aromatic polyamide pulp comprising polyoxazoline, the method comprising - mixing aromatic polyamide cut fibers, partially fibrillated aromatic polyamide cut fibers or an aromatic polyamide pulp with polyoxazoline in an aqueous solution to form a mixture, - subjecting the mixture to a defibrating step to form an aqueous slurry of an aromatic polyamide pulp. Furthermore, the present invention relates to a paper comprising an aromatic polyamide pulp comprising polyoxazoline, and to a friction material comprising said paper and / or said aromatic polyamide pulp comprising polyoxazoline.

Description

[0001] The present invention relates to a pulp comprising poly oxadiazole, a paper comprising said pulp, a friction material comprising said pulp or said paper and a method of manufacturing a pulp comprising poly oxadiazole.

[0002] It is known that aromatic polyamide pulp can be used in various fields of application, including for example paper, friction materials, in particular friction paper. It is well known in the art that aromatic polyamides have high strength and high temperature resistance properties.

[0003] Friction paper or paper-based friction materials can be used in wet friction applications, such as clutch facings in automatic transmissions. These paper-based materials are usually bonded to a support for mechanical energy transfer applications. Friction paper is manufactured with traditional papermaking processes, but these materials are in fact carefully engineered composite structures comprising pulp, fillers and a binder, usually a thermoset resin, and optionally other components such as fibers and friction additives.

[0004] Friction paper is a composite material whose formulation can provide appropriate friction, noise control, temperature and wear resistance properties in various specific applications.

[0005] Pulp material can increase the mechanical strength of the paper, adjust the porosity of the paper and ensure the retention of fillers during the papermaking process. Since aromatic polyamide pulp has very good mechanical and thermal properties, it is often used as a pulp. In particular, para-aramid pulp has good heat resistance, friction properties and durability. It also exhibits good performance in terms of noise and vibration performance (NVH) and does not chemically interact with automatic transmission fluid (ATF). It also has good compressibility and shear strength properties and good flexibility compared to metal fibers.

[0006] WO2006 / 012040 describes an acrylic and para-aramid pulp used as a reinforcing material for products such as seals and friction materials.

[0007] A modified aromatic polyamide pulp for friction paper is described in WO2018 / 037015. PVP (polyvinylpyrrolidone) is added to the aromatic polyamide pulp for friction paper. The PVP modified aromatic polyamide pulp can improve the friction properties.

[0008] Despite this, it was found that there is still room for improvement in the performance of aromatic polyamide pulp in paper, in particular friction paper. In particular, there is a need for an aromatic polyamide pulp that provides high shear strength and high tensile strength as well as high porosity to the paper and material, in particular friction paper. In addition, there is also a need for high filler retention to improve the uniform distribution of fillers in the paper, resulting in a uniform paper.

[0009] The present invention provides a solution to this problem.

[0010] The present invention relates to a pulp comprising a poly oxadiazole-modified aramid paper pulp (herein also referred to as "modified aramid paper pulp").

[0011] Modified continuous aramid yarn has been described for use in ballistic fabrics and thermoplastic composites.

[0012] US 5266076 describes continuous aramid fibers coated with a finish such as a fluorinated poly oxadiazole polymer. The continuous fibers are used in fabrics for ballistic applications. US 5266076 does not mention aramid paper pulp, paper and friction materials, in particular friction paper. WO 01 / 34385 Al discloses a thermoplastic composite comprising fibers coated with a poly-2- oxadiazole polymer and a polymeric resin. WO 01 / 34385 Al does not mention paper pulp and paper. The fibers in WO 01 / 34385 Al are continuous fibers (i.e. fibers that are essentially endless) and are selected from fibers such as glass fibers, carbon fibers, nickel-coated carbon fibers and aramid fibers, which are cut into short fibers after coating with the poly-2- oxadiazole and coated with a thermoplastic resin. Continuous fibers and short fibers are different from paper pulp.

[0013] It was found that poly oxadiazole-modified aramid paper pulp can combine high strength and high porosity when used in, for example, paper and friction materials such as friction paper. Generally, when the porosity of paper increases, the mechanical properties (tensile strength, tear strength) decrease. Therefore, a friction paper that improves the mechanical properties without negatively affecting the level of porosity, or a friction paper that improves the porosity without negatively affecting the level of mechanical properties or maintains the level of mechanical properties is of interest. Surprisingly, aramid paper pulp comprising poly oxadiazole provides such properties for paper, in particular for friction paper. In addition, the modification with poly oxadiazole improves the filler retention of the paper.

[0014] Pulp is a structure of irregularly shaped fibers. Pulp is composed of short fibers that fibrillate upon exposure to shear forces, with the fibrils mostly remaining attached to the "stem" of the original fiber, and with the finer fibrils peeling off the thicker ones. The fibers are curly, sometimes ribbon-like, and vary in length and thickness. Pulp is obtained by fibrillating short fibers (also referred to as chopped fibers), for example in a refiner. Thus, pulp comprises fiber stems and fibrils. As a result of fibrillation, pulp has different morphology and properties compared to continuous fibers or chopped fibers. In particular, pulp is shorter in length and has a larger specific surface area.

[0015] In the present specification, aromatic polyamide means an aromatic polyamide comprising or consisting of aromatic fragments directly linked to each other by amide fragments. Methods for the synthesis of aromatic polyamides are well known to the person skilled in the art and generally involve the polycondensation of aromatic diamines with aromatic diacid halides. Both the ortho and para forms of aromatic polyamides can be used, both forms can be used. The aromatic polyamide pulp of the present application is preferably para-aramid pulp.

[0016] For the purposes of the present application, the term para-aramid means a class of wholly aromatic polymeric and copolymeric polymers in which at least 60%, preferably at least 80%, more preferably at least 90% of the linkages between the aromatic moieties are para linkages. In one embodiment, at least 95% or all (i.e. 100%) of the linkages are para linkages.

[0017] Typical para-aramids are poly(para-phenyleneterephthalamide) (PPTA), poly(4,4'-benzanilide terephthalamide), poly(para-phenylene-4,4'-biphenylene dicarboxamide) and poly(para-phenylene-2,6-naphtalene diamide), 5,4'-diamino-2-phenylbenzimidazole or poly(para-phenylene-co-3,4'-oxidiphenylene terephthalamide) or copolymers thereof.

[0018] Preferably, the aromatic polyamide pulp comprises 0.1 to 10 wt.% of poly oxadiazole, preferably 0.25 to 7.5 wt.% of poly oxadiazole, more preferably 0.5 to 5 wt.% of poly oxadiazole (based on the weight of the dry pulp). In one embodiment, the aromatic polyamide pulp comprises less than 6 wt.% of poly Azoline, preferably up to 4% by weight of polyoxoline Azoline (based on the weight of dried pulp). The dried pulp has a balance water content ranging from 3% to 8% by weight. Poly The dosage of zozoline is relative to the amount of poly(oxophylline) used. The total weight of the dried pulp, including azazoline and equilibrium moisture.

[0019] In this invention, poly Azoline refers to... Polymers with a zoline structure can also be called... Azoline polymers.

[0020] Gather Azoline polymers differ from non-polymerized ones. Azoline compounds can be used as curing agents for, for example, epoxy resins. Poly azoline The zoline structure is based on this. Azoline is a five-membered heterocyclic ring (3xC, O, N), and has three different structural isomers depending on the position of the double bonds within the ring. 2- Azoline can be used to prepare poly Azoline.

[0021] Gather Azoline is preferably based on (possibly substituted) N-acylethyleneimine units (linear, in 2- (obtained by ring-opening of azoline monomer), wherein the main chain carbon is preferably substituted with hydrogen, and the acyl group is substituted with hydrogen or C1-C4 alkyl (R in the following formula is H or C1-C4 alkyl), preferably substituted with ethyl (R is C2 alkyl):

[0022]

[0023] Therefore, gathering Azazoline is preferably a polyalkyl-2- Azazoline, preferably poly-2-ethyl-2- Azoline (PEOX). Alkyl groups refer to monovalent saturated straight-chain or branched hydrocarbon groups having 1 to 4 carbon atoms.

[0024] Preferably, poly Azoline is essentially free of halogen groups, especially fluorine groups. "Essentially free of halogen groups" means that the polyoxometalate... The azoline polymer has a halogen group content of less than 5 mol%, preferably less than 1 mol%, especially fluorine groups.

[0025] Preferably, poly The oxazoline has a molecular weight in the range of 1000-1000000 g / mol, preferably 5000-750000 g / mol, more preferably 10000-600000 g / mol, even more preferably 200000-500000 g / mol. In some embodiments, the poly An increase in the molecular weight of the oxazoline can increase the strength of paper comprising the poly The oxazoline modified pulp increases the strength of paper.

[0026] The poly The length (LL0.25) of the oxazoline containing aramid pulp is typically in the range of 0.5 to 1.5 mm, in particular in the range of 0.60 to 1.4 mm, in some embodiments in the range of 0.7 to 1.3 mm. This parameter is determined by a Valmet Fiber Image Analyzer, i.e. Valmet FS5, which is calibrated using pulp samples of known length. The length weighted length LL0.25 [mm] is the length weighted average length determined according to ISO 16065-2, wherein particles with a length of more than 250 pm, i.e. more than 0.25 mm, are included.

[0027] The poly The Schopper Riegler (SR) of the oxazoline containing aramid pulp is typically in the range of 15 to 80 °SR, in particular in the range of 16 to 60 °SR, more in particular in the range of 17 to 40 °SR. SR is a parameter often used in pulp and paper technology. It is an indicator to measure the drainage of a pulp suspension in water. According to the ISO 5267 / 1 standard, SR can be determined by dispersing 2 grams (dry weight) of pulp in 1 liter of water in a Lorentzen and Wettre pulper during 600 counts.

[0028] The poly The Canadian Standard Freeness (CSF) of the oxazoline containing aramid pulp is typically in the range of 15 to 700 mL, in particular in the range of 100 to 670 mL, more in particular in the range of 200 to 650 mL. CSF is a parameter often used in pulp and paper technology. Like SR, it is an indicator to measure the drainage of a pulp suspension in water. CSF can be determined according to TAPPI T227.

[0029] The poly The specific surface area (SSA) of the oxazoline containing aramid pulp can be in the range of 2 to 20 m 2 / g, preferably in the range of 3 to 15 m 2 / g, more preferably in the range of 4 to 10 m 2 / g or in the range of 5 to 8 m 2 / g.

[0030] The specific surface area (m 2 The specific surface area (m

[0031] Non-fibrillated fibres (such as continuous fibres or chopped fibres) have a much smaller specific surface area, and are in the range of 0.1 to 0.2 m 2 / g.

[0032] Poly The azolines are preferably (only) present on the surface of the pulp. The azolines are preferably present on the surface of the pulp. The azolines are preferably present on at least part of the surface of the aramid pulp or on the entire surface of the aramid pulp. The azolines are preferably present on the surface of the aramid pulp. The azolines are preferably not used for the manufacture of chopped fibres, wherein the pulp is manufactured from chopped fibres, but are applied on the surface of the pulp. During the process of manufacturing the modified pulp, the azolines are provided to the surface of the aramid pulp, as described below. The azolines are preferably present on at least part of the surface of the aramid pulp or on the entire surface of the aramid pulp. The azolines are preferably present on the surface of the aramid pulp.

[0033] The present invention also relates to a paper comprising the aramid pulp comprising azolines according to the above-mentioned embodiments. The present invention also relates to a paper comprising the aramid pulp comprising azolines according to the above-mentioned embodiments.

[0034] Such a paper can for example be a friction paper, an isolation paper or a honeycomb paper.

[0035] In particular, the present invention relates to a friction paper comprising the aramid pulp comprising azolines according to the above-mentioned embodiments. The present invention also relates to a paper comprising the aramid pulp comprising azolines according to the above-mentioned embodiments.

[0036] A friction paper is a composite material, which typically comprises a number of different materials, each contributing to the performance of the paper.

[0037] Reinforcing fibres are typically used to increase the mechanical strength and durability of the system. They also help to provide a porous structure, which helps to ensure proper resin uptake.

[0038] Fillers are added to achieve various functions, such as helping resin uptake, promoting oil flow through the paper to control temperature decay in use, ensuring adequate friction performance and / or reducing noise.

[0039] The addition of resin ensures that the paper has good dimensional stability, good tribological properties and good heat resistance.

[0040] Preferably, the paper of the present application comprises 2-70 wt% of the modified aromatic polyamide pulp, more preferably 5-55 wt% of the modified aromatic polyamide pulp, even more preferably 10-35 wt% of the modified aromatic polyamide pulp, based on the weight of the paper.

[0041] In one embodiment, the paper of the present application comprises a pulp comprising a poly oxadiazole, a filler and a resin.

[0042] Preferably, the paper of the present application comprises 5-55 wt% of the filler, more preferably 20-40 wt% of the filler and 5-50% of the resin, more preferably 15-40 wt% of the resin, based on the weight of the paper.

[0043] In the present specification, the term "filler" is intended to include all particulate materials other than fibres or resin, which preferably affect the friction properties of the paper. Suitable fillers for friction paper are known in the art. Examples of suitable fillers include refractory organic and inorganic particles such as calcium carbonate, magnesium carbonate, silicon carbide, titanium carbide, activated carbon, clay, kaolin, zeolite, alumina, silica, barium sulphate, barite powder, and particles extracted from renewable resources such as cocoa husk powder and cashew nut powder. Other suitable filler particles also include diatomite, graphite particles and copper particles, although copper particles have generally been discontinued in view of health, safety and environmental factors (HSE).

[0044] The (friction) paper preferably comprises diatomite and / or graphite particles.

[0045] The content of the filler is preferably 5 to 55 wt%. If the percentage of the filler is too low, its effect on the friction properties of the paper cannot be achieved. If the content of the filler is too high, the content of the other components will be too low. The content of the filler is preferably in the range of 10 to 50 wt%, in particular in the range of 20 to 40 wt% (based on the weight of the paper).

[0046] The paper of the present application comprises a resin as a binder. Suitable resins are known in the art. The content of the resin is generally 5 to 50 wt%, in particular 15 to 40 wt% (based on the weight of the paper). If the content of the resin is too low, the structural integrity of the paper will be affected. If the content of the resin is too high, the content of the other components will be too low. The resin is preferably a thermosetting resin. The resin is preferably selected from the group consisting of phenolic resins, vitrimer resins (so-called plastic thermosetting resins), polythiourethane resins, melamine resins, silicone resins and epoxy resins.

[0047] It is preferred to use resins that can be removed or reprocessed to separate the components of the paper for recycling. Suitable glassy resins are described for example in WO 2020 / 051506 A1. EP 3149065 A1 describes thermomechanically reprocessable epoxy resins, WO 2019 / 063787 A1 describes reprocessable polythiourethane resins.

[0048] Suitable silicone resins are for example the organopolysiloxane resins described in EP 3473883 A1.

[0049] The phenolic resin can optionally be modified with for example polysiloxane, melamine, epoxy resin, cresol or cashew nut oil. The resin is present to improve the heat resistance, dimensional stability and friction and wear properties of the paper.

[0050] The paper of the present application can also comprise further components.

[0051] In one embodiment, the paper comprises additional reinforcing fibers, such as carbon fibers, mineral fibers, ceramic fibers, glass fibers, basalt fibers and rock wool, or polymeric fibers, such as acrylic fibers, polyimide fibers and polyamide fibers. Organic fibers such as cotton and cellulose are also often used as (chopped) fibers or pulp. The paper can also comprise unmodified aramid pulp, i.e. aramid pulp that does not comprise poly azide. Thus, the paper can comprise unmodified aramid pulp and poly azide modified pulp. According to the present application, the friction paper preferably comprises one or more of cellulose, cotton or carbon fibers. Reinforcing fibers are generally used to improve the durability and mechanical strength of the paper. If used, their amount is typically 2 to 40 wt.%, in particular 5 to 35 wt.%. Reinforcing fibers and their use are well known in the art.

[0052] Preferably, in the resin-impregnated paper, the sum of all reinforcing fibers and pulp (referred to as the fiber amount of the friction paper), including aramid pulp comprising poly azide, amounts to 25-45 wt.%, preferably 30-40 wt.% of the paper weight. In one embodiment, the paper comprises 25-45 wt.% fibers and comprises 25-45 wt.% filler and 25-45 wt.% resin. The fiber amount, filler and resin preferably each amount to (about) 1 / 3 of the paper weight. The content of aramid pulp comprising poly azide can be 20 wt.% to 100 wt.%, preferably 30 wt.% to 80 wt.% of the fiber weight.

[0053] The grammage of the paper of the present application is preferably in the range of 100-800 g / m 2 , in particular 200-600 g / m 2 .

[0054] The paper comprises aramid pulp, which is preferably at least partially polymerized. Azoline coating. Preferably, it contains poly([unclear]). Azoline-modified pulp and filler paper were not polymerized before or after the addition of resin. Azoline coating or covering. Preferably, only the aromatic polyamide pulp contained in the friction paper is at least partially coated with azoline. The azoline coating prevented other paper components from being polymerized. Azoline coating or covering.

[0055] Using paper containing poly Azoline-based aromatic polyamide pulp improves paper properties. In particular, the paper exhibits a combination of high mechanical strength and high porosity, especially high wet strength, shear strength (and related Z-strength), and tensile index, while also possessing high air permeability and good filler retention. Therefore, this paper is particularly suitable for use as friction paper. Due to these properties, friction paper is especially suitable for use in transmission systems.

[0056] The paper can be manufactured using methods known in the art.

[0057] Friction paper can generally be manufactured by a method including the following steps: manufacturing a paper containing polymers Paper is made from azoline-based aromatic polyamide pulp, resin, and filler, and the paper is heated under conditions that cure the resin. In one embodiment, the first step is to combine all components of the paper except the resin in an aqueous medium to form a pulp. This step can be performed in any order, and the compounds can be added simultaneously or sequentially. The formed pulp is spread on a screen and then the water is removed. This is a conventional papermaking method and requires no further explanation. The resulting paper is dried. The dried paper is then brought into contact with resin. Generally, the resin is provided in a solvent (preferably an alcohol such as ethanol or isopropanol), and the paper is impregnated with the resin solution. Depending on the type of resin, the impregnated paper may also require a curing step to cure the resin. Specific method conditions depend on the properties of the resin and generally include a temperature of 100 to 300°C and a pressure of 0.1 to 10 MPa.

[0058] In another embodiment, solid resin particles are added together with other components to an aqueous medium, and the resulting slurry is then processed into paper as described above. The paper is then dried and cured as described above.

[0059] The present invention also relates to a friction or sealing material comprising the polymer-containing... Aromatic polyamide pulp of zozoline and / or paper containing the aforementioned.

[0060] Such friction or sealing materials can take a variety of forms, such as multi-plate wet clutches comprising multiple layers of friction paper or paper-based washers. Multi-plate wet clutches have proven to be desirable torque transfer devices in high energy applications. Multi-plate clutches comprise alternating friction and steel plates that interact in an oil-cooled friction system to transfer the required torque. Multi-plate "wet" clutch applications are widespread, such as clutches in dual clutch transmissions, torque converter lock-up clutches, clutches and brakes in automatic transmissions, wheel and axle brakes, differential locks, all-wheel drive transfer cases, power take-offs, and main clutches.

[0061] The present invention also relates to a method of manufacturing an aromatic polyamide pulp comprising polyoxadiazole, the method comprising: - mixing aromatic polyamide short fibers, partially fibrillated aromatic polyamide short fibers or aromatic polyamide pulp with polyoxadiazole in an aqueous solution to form a mixture,

[0062] - subjecting the mixture to a refining step to form an aqueous slurry of aromatic polyamide pulp.

[0063] - subjecting the mixture to a refining step to form an aqueous slurry of aromatic polyamide pulp.

[0064] It has been found that according to the method of the present invention, an aromatic polyamide pulp comprising polyoxadiazole can be efficiently obtained by using an easy to handle method. Furthermore, it has been found that the above method of having polyoxadiazole present during fibrillation can improve the surface coverage of polyoxadiazole and the pulp properties compared to a method of first obtaining an unmodified pulp by fibrillation and then coating the pulp by placing the pulp in a polyoxadiazole solution.

[0065] As starting material for the method, aromatic polyamide short fibers, partially fibrillated aromatic polyamide short fibers or aromatic polyamide pulp (or a combination thereof) can be used.

[0066] ​​​​​In the present specification, the term aramid staple fibre refers to aramid fibres cut to a length of, for example, at least 0.5 mm, in particular at least 1 mm, more in particular at least 2 mm, in some embodiments at least 3 mm. The length is generally at most 80 mm, in particular at most 10 mm, more in particular at most 8 mm. The staple fibre has a thickness of, for example, in the range of 5-50 microns, preferably in the range of 5-25 microns, most preferably in the range of 6-18 microns. Aramid fibres, in particular para-aramid fibres, which can be used to prepare such staple fibres, are commercially available, such as Teijin Aramid. The length of the staple fibre refers to the LLo.25, i.e. the length weighted average length, wherein particles having a length of more than 250 microns, i.e. more than 0.25 mm, are included.

[0067] Such aramid staple fibres can be obtained by cutting continuous aramid yarns into pieces of equal or random length by means of a cutting device.

[0068] Partially fibrillated aramid staple fibres refer to aramid staple fibres which have been partially fibrillated, for example by cutting and milling, for example in a knife mill, or by cutting and subjecting to a short refiner treatment.

[0069] In the first step of the process according to the present application, aramid staple fibres, partially fibrillated aramid staple fibres or aramid pulp are mixed with polyoxadiazole in an aqueous solution to form a mixture. This can be done in various ways. For example, dry aramid staple fibres, partially fibrillated staple fibres or pulp can be added to a solution or suspension of polyoxadiazole in water; polyoxadiazole can be added to a suspension of staple fibres, partially fibrillated staple fibres or pulp in water; or polyoxadiazole and staple fibres, partially fibrillated staple fibres or pulp can be added together to an aqueous medium. In the present specification, the term aramid staple fibre refers to aramid fibres cut to a length of, for example, at least 0.5 mm, in particular at least 1 mm, more in particular at least 2 mm, in some embodiments at least 3 mm. The length is generally at most 80 mm, in particular at most 10 mm, more in particular at most 8 mm. The staple fibre has a thickness of, for example, in the range of 5-50 microns, preferably in the range of 5-25 microns, most preferably in the range of 6-18 microns. Aramid fibres, in particular para-aramid fibres, which can be used to prepare such staple fibres, are commercially available, such as Teijin Aramid. The length of the staple fibre refers to the LLo.25, i.e. the length weighted average length, wherein particles having a length of more than 250 microns, i.e. more than 0.25 mm, are included. In the present specification, the term aramid staple fibre refers to aramid fibres cut to a length of, for example, at least 0.5 mm, in particular at least 1 mm, more in particular at least 2 mm, in some embodiments at least 3 mm. The length is generally at most 80 mm, in particular at most 10 mm, more in particular at most 8 mm. The staple fibre has a thickness of, for example, in the range of 5-50 microns, preferably in the range of 5-25 microns, most preferably in the range of 6-18 microns. Aramid fibres, in particular para-aramid fibres, which can be used to prepare such staple fibres, are commercially available, such as Teijin Aramid. The length of the staple fibre refers to the LLo.25, i.e. the length weighted average length, wherein particles having a length of more than 250 microns, i.e. more than 0.25 mm, are included.

[0070] Aramid staple fibres can be obtained by cutting continuous aramid yarns to a length of at most 80 mm. Such aramid staple fibres can be further shortened in length, for example in a knife mill, prior to use in the instant process. Aramid staple fibres can be suspended in water to form a suspension, which is subjected to a first homogenisation step to further shorten the length of the fibres, without the addition of polyoxadiazole. If the homogenisation step is prolonged or an additional homogenisation step is performed on the suspension, partially fibrillated fibres or pulp can be obtained. Any of the above-mentioned fibre types (aramid staple fibres, partially fibrillated fibres or pulp) or combinations thereof can be used as starting material for the process.

[0071] ​​​The aqueous solution of polyoxazoline is preferably prepared at an elevated temperature, for example in the temperature range of 20 to 60 °C, preferably in the temperature range of 30 to 50 °C. The aqueous solution of polyoxazoline is preferably prepared at an elevated temperature, for example in the temperature range of 20 to 60 °C, preferably in the temperature range of 30 to 50 °C. The concentration of the aqueous solution of polyoxazoline is preferably at most 30 wt.%, preferably 15 to 25 wt.%. The concentration of the aqueous solution of polyoxazoline is preferably at most 30 wt.%, preferably 15 to 25 wt.%.

[0072] The aqueous solution of polyoxazoline is preferably prepared at an elevated temperature, for example in the temperature range of 20 to 60 °C, preferably in the temperature range of 30 to 50 °C. The aqueous solution of polyoxazoline is preferably prepared at an elevated temperature, for example in the temperature range of 20 to 60 °C, preferably in the temperature range of 30 to 50 °C. The aqueous solution of polyoxazoline is preferably prepared at an elevated temperature, for example in the temperature range of 20 to 60 °C, preferably in the temperature range of 30 to 50 °C.

[0073] The content of the short-cut aramid fibres, the partially fibrillated short-cut fibres or the pulp in the mixture is generally in the range of 0.1 to 7 wt.%, in particular 1 to 5 wt.%.

[0074] The concentration of the aqueous solution of polyoxazoline in the mixture depends on the desired content of polyoxazoline in the final product. The higher the concentration, the lower the amount of polyoxazoline remaining in the suspension. The concentration of the aqueous solution of polyoxazoline in the mixture is preferably in the range of 0.1 to 30 wt.%. The concentration of the aqueous solution of polyoxazoline in the mixture depends on the desired content of polyoxazoline in the final product. The higher the concentration, the lower the amount of polyoxazoline remaining in the suspension. The concentration of the aqueous solution of polyoxazoline in the mixture is preferably in the range of 0.1 to 30 wt.%. The concentration of the aqueous solution of polyoxazoline in the mixture depends on the desired content of polyoxazoline in the final product. The higher the concentration, the lower the amount of polyoxazoline remaining in the suspension. The concentration of the aqueous solution of polyoxazoline in the mixture is preferably in the range of 0.1 to 30 wt.%. The concentration of the aqueous solution of polyoxazoline in the mixture depends on the desired content of polyoxazoline in the final product. The higher the concentration, the lower the amount of polyoxazoline remaining in the suspension. The concentration of the aqueous solution of polyoxazoline in the mixture is preferably in the range of 0.1 to 30 wt.%. The concentration of the aqueous solution of polyoxazoline in the mixture depends on the desired content of polyoxazoline in the final product. The higher the concentration, the lower the amount of polyoxazoline remaining in the suspension. The concentration of the aqueous solution of polyoxazoline in the mixture is preferably in the range of 0.1 to 30 wt.%. The concentration of the aqueous solution of polyoxazoline in the mixture depends on the desired content of polyoxazoline in the final product. The higher the concentration, the lower the amount of polyoxazoline remaining in the suspension. The concentration of the aqueous solution of polyoxazoline in the mixture is preferably in the range of 0.1 to 30 wt.%. The concentration of the aqueous solution of polyoxazoline in the mixture depends on the desired content of polyoxazoline in the final product. The higher the concentration, the lower the amount of polyoxazoline remaining in the suspension. The concentration of the aqueous solution of polyoxazoline in the mixture is preferably in the range of 0.1 to 30 wt.%.

[0075] The aqueous mixture is subjected to a homogenization step to form an aramid pulp comprising polyoxazoline. Homogenization methods are well known in the art. Generally, in the homogenization process the pulp is subjected to a high shear environment, for example by passing the pulp between mutually moving discs. The effect of the homogenization step is to reduce the length of the short-cut fibres and to fibrillate the short-cut fibres to form a pulp (or to further fibrillate the partially fibrillated short-cut fibres or pulp). During the fibrillating process, fibres are formed which will result in "stems" attached to fibrils and loose fibrils. In addition, during the homogenization process the stems of the pulp can be kinked. The aqueous mixture is subjected to a homogenization step to form an aramid pulp comprising polyoxazoline. Homogenization methods are well known in the art. Generally, in the homogenization process the pulp is subjected to a high shear environment, for example by passing the pulp between mutually moving discs. The effect of the homogenization step is to reduce the length of the short-cut fibres and to fibrillate the short-cut fibres to form a pulp (or to further fibrillate the partially fibrillated short-cut fibres or pulp). During the fibrillating process, fibres are formed which will result in "stems" attached to fibrils and loose fibrils. In addition, during the homogenization process the stems of the pulp can be kinked.

[0076] A single homogenisation step can be performed or the homogenised pulp can be subjected to one or more further homogenisation steps, which can be performed under the same or different conditions to the first homogenisation step. In one embodiment, the previously fibrillated aramid short-cut fibre or pulp is subjected to further homogenisation in an aqueous solution comprising poly oxazoline.

[0077] The pulp produced by the homogenisation process, including the poly oxazoline, can be treated as required. For example, a dewatering step can be performed in which the pulp is dewatered, typically by placing the pulp on a screen or other filter material, optionally involving a press section. This results in a dewatered pulp. The dewatered pulp typically has a water content in the range of 40 to 80 wt%, in particular 50 to 70 wt%. The dewatering step can be repeated to further reduce the water content of the pulp. The dewatered pulp can be in the form of a cake, as it comes from the filter, or the cake can be broken up to form individual pieces, also referred to as shreds.

[0078] The dewatered pulp, in the form of a cake, shreds or any other form, can be the final product, which can be further processed as required. The dewatered pulp can also be dried.

[0079] Drying of the dewatered pulp can be performed by conventional means, for example by contact with a drying atmosphere, optionally at elevated temperature, to form a dried pulp. The dried pulp typically has a water content in the range of 2 to 20 wt%, in particular 3 to 10 wt%. Preferably, the dried pulp has a water content in the range of 3 to 8 wt%.

[0080] If desired, the dried pulp can be subjected to a step of opening. Pulp opening is well known in the art. It involves subjecting the dried pulp to mechanical impact, for example using an impact mill, a mill using turbulent air or a high shear / high agitation mixer. The pulp opening step can reduce the bulk density of the pulp material (i.e. make it more "fluffy"). The opened pulp can be more easily dispersed and thus more easily applied. Generally, the pulp opening step does not substantially change the properties of the pulp.

[0081] For further processing into friction paper or friction material, either the wet (i.e. dewatered) pulp (having a water content preferably in the range of 50 to 70 wt%) or the dry pulp (having a water content preferably in the range of 3 to 8 wt%) can be used. Preferably, the poly oxazoline modified pulp is used in the form of a wet (i.e. dewatered) pulp. For use in friction paper and friction material, it can be advantageous to use the dewatered pulp without a drying treatment, for example having a water content in the range of 40 to 80 wt%, preferably 50 to 75 wt%, more preferably 60 to 70 wt%.

[0082] The various preferred embodiments described above can be combined, unless they are mutually exclusive, for the skilled person.

[0083] The application will be further explained by the following non-limiting examples. Examples

[0084] a) Determination of the grammage

[0085] The grammage of the paper (also called basis weight) is measured according to ISO 536:1995, expressed in grams per square meter (g / m 2 ).

[0086] b) Determination of the air permeability

[0087] The air permeability is an indicator of the porosity and oil penetration of the paper.

[0088] The air permeability of the impregnated paper is determined according to the ASTM D737 standard, using a Textest FX3030-LDM meter, expressed in liters per square meter per second (L / m 2 / s).

[0089] c) Determination of the Z-strength

[0090] The Z-strength of the paper (also called internal bond strength) is closely related to the shear strength. The Z-strength of the impregnated paper is determined according to Tappi T541.

[0091] d) Determination of the wet strength

[0092] The paper is immersed in isopropanol for 1 minute. Then, the wet paper is subjected to a tensile test to determine the tensile index. The method of determination is in accordance with ISO 1924-2.

[0093] e) Filler retention

[0094] The filler retention is a measure of the degree of retention of the filler by the pulp during the papermaking process, with a value of 100% indicating that the filler is completely retained, i.e. there is no loss of filler during the papermaking process. The filler retention of the paper is determined using diatomite as filler. The method to determine the filler retention is: the amount of filler in the final paper (calculated on the basis of the actual grammage, the paper surface area [20 cm in diameter] and subtracting the amount of pulp in the paper [5.5 g]) divided by the amount of filler used (corrected for the water content) multiplied by 100.

[0095] f) Determination of the tensile strength

[0096] The tensile index of the dry paper before impregnation and of the paper after impregnation with resin is determined according to the ISO 1924-2 standard.

[0097] Example 1: Pulp manufacturing

[0098] 4 kg of 6 mm long para-aramid short-cut fibers (based on) 1000 6mm chopped aramid fibers (type 1680f1000) were added to 200 liters of PEOX aqueous solution. The molecular weight of PEOX is approximately 500 kg / mol. Depending on the amount of PEOX added to the suspension (weight percentage per volume of suspension), the resulting suspension contained 2 wt% aramid chopped fibers and 0.07 wt% (pulp A) or 0.1 wt% (pulp B) PEOX. The resulting suspension was passed through a Sprout-Bauer 12" laboratory homogenizer to achieve a target fiber length of 0.95 mm ± 0.1 mm. The homogenized suspension was dewatered on a screen to obtain a dewatered filter cake. The PEOX-modified pulp (referred to as pulp A) contained 3.4 wt% PEOX, and the PEOX-modified pulp (referred to as pulp B) contained 4.8 wt% PEOX.

[0099] For reference, the same procedure is used without the addition of PEOX to obtain aramid pulp without any coating or covering. This pulp is called pulp C.

[0100] For another comparison, following the same procedure as pulp B, PVP (molecular weight approximately 50 kg / mol) was added instead of PEOX. This pulp was called pulp D.

[0101] Example 2: Manufacturing friction paper containing fillers, resins and aramid pulp

[0102] 24.48 g of PEOX-containing pulp A (equivalent to 5.50 g dry aramid pulp) from Example 1, with a dry solids content of 22.45%, was suspended in 2 liters of water and mixed for 100 counts (3000 rpm, 20 seconds) in a Lorentzen & Wettre shredder. Then, 6.0 g of diatomaceous earth (Transcend ND-1, as a filler) was added to the suspension, and the mixture was mixed for another 500 counts (3000 rpm, 100 seconds). The mixture was then processed according to ISO 5269-2 standards in a Rapid... Paper was prepared using this mixture on a laboratory paper forming apparatus. The resulting paper was dried between two sheets of blotting paper in a flat dryer at 105°C for at least 20 minutes. The final paper had a basis weight of 350 ± 16 g / m² and consisted of 50% pulp and 50% diatomaceous earth.

[0103] The same procedure was used for pulps B, C, and D, but the amounts of pulp and filler used were slightly different to obtain the same final target paper weight (see Table 1 for usage amounts). The pulp amounts were adjusted to correct for the water content of different pulp samples, thus using the same amount of dry pulp (dry solids content).

[0104] The wet and dry strength of the paper was determined.

[0105] The paper prepared in this way based on pulp samples A, B, C and D was also impregnated with phenol formaldehyde resin (Bakelite PF 0229RP). For the paper comprising pulp A and B (according to the application), the resin was diluted to the required concentration using a mixture of 22 mL resin and 78 mL isopropanol. The paper was placed in a tray covered with a plastic liner and the resin mixture was poured over the paper. The tray was moved for 1 minute and then the paper was transferred to a Teflon plate. The paper was passed twice through a specially designed wringing machine (with the paper being turned over in between). The residual solvent (isopropanol) was then evaporated in a ventilated oven at 90°C for 20 minutes. After impregnation, the target paper weight was 500 ± 16 g / m2. The resin dilution was adjusted accordingly to achieve the required paper weight for the paper comprising pulp C and D as shown in Table 1.

[0106] Finally, the paper was cured in an oven at 180°C for 60 minutes.

[0107] Table 1 : Materials used to prepare the impregnated paper based on pulp samples A-D

[0108]

[0109]

[0110] Example 3: Dry and wet strength of the base paper (before impregnation)

[0111] The pulp of the application is very advantageous for increasing the dry strength of the paper. Furthermore, the use of the pulp of the application also increases the wet strength required during the resin impregnation of the base paper (in these examples, the weight ratio of pulp / diatomaceous earth was 50 / 50). This is illustrated by the tensile properties of the wet and dry paper in Example 2 shown in Table 2 below.

[0112] Table 2: Dry and wet strength of the base paper (unimpregnated) comprising pulp A-D

[0113] Paper based on Paper containing pulp modified with Dry strength [Nm / g] Wet strength [Nm / g] Pulp A 3.4 wt% PEOX 1.05±0.07 0.356±0.019 Pulp B 4.8 wt% PEOX 1.43±0.07 0.430±0.013 Pulp C None 0.20±0.03 0.014±0.004 Pulp D 4.8 wt% PVP 1.22±0.02 0.229±0.016

[0114] From these results it is clear that the wet strength of the paper comprising the pulp A and B of the application is greatly increased (by a factor of 25 to 30) compared to the comparative paper comprising pulp C. The paper comprising the comparative pulp D (PVP pulp) is also increased compared to pulp C, but less than the paper comprising pulp A and B.

[0115] Example 4: Comparison of the (impregnated) rubbed papers

[0116] Various properties of the friction paper of Example 2 were determined, including filler (diatomite) retention, air permeability, tensile strength, and Z-strength. Filler retention and air permeability were determined on two sheets of paper (denoted as Paper 1 and Paper 2). Mechanical properties (Z-strength and tensile strength) were each determined on one of those sheets (as the test would destroy the paper). The results are shown in Table 3.

[0117] Table 3: Properties of impregnated friction paper comprising pulp A-D

[0118]

[0119] The data show that the filler retention of paper made with inventive pulps A and B is substantially higher than the filler retention of paper made with comparative pulp C. Clearly, the polyoxazoline-modified pulps according to the present application retain filler and resin particles much better than the unmodified pulp.

[0120] In friction applications, it is important that the friction paper is as open as possible so that oil can penetrate into the friction paper in applications such as clutches. It is an object of the present application to provide a paper, in particular a friction paper, that combines high strength with high porosity. The air permeability of a paper is an indicator of its porosity.

[0121] The air permeability of paper comprising pulp A or B (PEOX-modified pulp) is comparable to comparative pulp C (unmodified aromatic polyamide pulp), whereas the air permeability of pulp D (PVP-modified pulp) is substantially lower.

[0122] For friction applications, paper strength is also an important property. As the paper is subjected to high shear forces during operation, shear strength is the most relevant strength property. Shear strength is closely related to the so-called Z-strength or internal bond strength.

[0123] The results in Table 3 show that the strength of model friction paper using inventive pulps A and B is substantially improved compared to the friction paper strength using comparative pulp C.

[0124] A great advantage of the inventive pulps is that they combine high strength (in particular Z-strength) with high porosity. The comparative papers comprising unmodified pulp (pulp C) or PVP-modified pulp (paper D) do not show this combination of properties and can only achieve comparable or even lower strength or porosity values, but not both.

[0125] Example 5: Comparison of commercial pulp samples with polyoxazoline-modified pulp and corresponding paper

[0126] ​​Polyamide is produced on a production scale by adding PEOX solution to a suspension of partially fibrillated aromatic polyamide short fibers. Azoline-modified pulp, wherein the suspension comprises 2.5 wt% partially fibrillated chopped aromatic polyamide fibers and 0.09 wt% PEOX (weight percentage per volume of suspension). The resulting suspension is circulated through a homogenizer to achieve a target fiber length of 0.98 mm ± 0.2 mm. The molecular weight of PEOX is 500 kg / mol. PEOX-modified pulp (pulp E) contains approximately 3.3 wt% PEOX (based on dry weight) and has a fiber length of approximately 4.8 m... 2 / g of SSA.

[0127] As a comparison sample, commercially available products were used. Pulp 1092 (abbreviated as 1092) is a type of pulp with a low degree of fibrillation, having a molecular weight of approximately 6.6 m. 2 / g of SSA) and Pulp 1094 (abbreviated as 1094) is a type of pulp with a high degree of fibrillation, having a molecular weight of 12-15m. 2 / g SSA). Generally, pulp with a higher degree of fibrillation increases paper strength but reduces paper air permeability.

[0128] As described in Example 2, paper was prepared based on 1092, 1094 and pulp E.

[0129] Subsequently, the wet strength of the paper was measured.

[0130] Paper prepared using this method based on pulp samples 1092, 1094, and pulp E was impregnated with phenolic resin as described in Example 2. The air permeability, Z-strength, filler retention, and tensile strength of the impregnated paper were determined according to the method described in Example 4.

[0131] The properties (average values) of the base paper and impregnated paper are shown in Table 4.

[0132] Table 4: Properties of base paper and impregnated friction paper containing pulps 1092, 1094 and pulp E

[0133]

[0134] Table 4 shows that, compared to those without polymers Compared to commercially available pulp types containing azazoline, the use of polyoxo-based pulps... Azazoline-modified pulp can improve the mechanical properties of base paper and impregnated paper. Paper based on type 1092 pulp has high air permeability, while paper based on type 1094 pulp has high filler retention. Paper based on the pulp of this invention combines high filler retention and high air permeability. Furthermore, paper based on the pulp of this invention has the highest wet strength as base paper and the highest Z-strength and tensile strength as impregnated paper.

Claims

1. An aromatic polyamide pulp comprising polyamide... Azoline.

2. The aramid pulp according to claim 1, comprising 0.1 to 10% by weight of polyamide. Azoline, based on the weight of dried pulp.

3. The aramid pulp according to claim 1, comprising 0.25 to 7.5% by weight of polyamide. Azoline, based on the weight of dried pulp.

4. The aramid pulp according to claim 1, comprising 0.5 to 5% by weight of polyamide. Azoline, based on the weight of dried pulp.

5. The aromatic polyamide pulp according to any one of claims 1 to 4, wherein the polyamide... Azoline is a polyalkyl-2- Azoline.

6. The aromatic polyamide pulp according to any one of claims 1 to 4, wherein the polyamide... Azazoline is a poly-2-ethyl-2- Azoline.

7. The aromatic polyamide pulp according to any one of claims 1 to 4, wherein the polyamide... The azoline covers at least a portion of the surface of the aromatic polyamide pulp.

8. The aramid pulp according to any one of claims 1 to 4, comprising fiber stems and fibrils.

9. The aramid pulp according to any one of claims 1 to 4, having a content of 2 to 20 m... 2 Specific surface area in the range of / g, and / or length LL in the range of 0.5 to 1.5mm. 0.25 .

10. The aramid pulp according to claim 9, having a content of 3 to 15 m... 2 Specific surface area within the range of / g.

11. The aramid pulp according to claim 9, having a content of 4 to 10 m... 2 Specific surface area within the range of / g.

12. The aramid pulp according to claim 9, having a length LL in the range of 0.6 to 1.4 mm. 0.25 .

13. A paper comprising aramid pulp according to any one of claims 1 to 12.

14. The paper of claim 13, comprising 2-70% by weight of aramid pulp, based on the weight of the paper.

15. The paper of claim 13, comprising 5-55% by weight of aramid pulp, based on the weight of the paper.

16. The paper of claim 13, comprising 10-35% by weight of aramid pulp, based on the weight of the paper.

17. The paper according to claim 13 or 14, comprising filler and resin.

18. The paper of claim 17, comprising 5-55% by weight of filler, based on the weight of the paper.

19. The paper of claim 17, comprising 20-40% by weight of filler, based on the weight of the paper.

20. The paper of claim 17, comprising 5-50% by weight of resin, based on the weight of the paper.

21. The paper of claim 17, comprising 15-40% by weight of resin, based on the weight of the paper.

22. The paper according to claim 17, wherein the resin is a thermosetting resin.

23. The paper according to claim 17, wherein the resin is a thermosetting resin selected from phenolic resin, glass-like resin, polythiourethane resin, melamine resin, silicone resin and epoxy resin.

24. The paper according to any one of claims 13 to 16, wherein it is friction paper, release paper, or honeycomb paper.

25. A friction material comprising aramid pulp according to any one of claims 1 to 12 or paper according to any one of claims 13 to 24.

26. A method for manufacturing aramid pulp according to any one of claims 1 to 12, comprising: - Combine aramid chopped fibers, partially fibrillated aramid chopped fibers, or aramid pulp with polyamide... Azazoline forms a mixture when mixed in aqueous solution. - The mixture is subjected to a homogenization step to form an aqueous pulp of aramid pulp.

27. The method of claim 26, wherein the aqueous pulp of the aramid pulp is dewatered to form dewatered pulp, the water content of the dewatered pulp being in the range of 40-80% by weight, based on the weight of the dewatered pulp.

28. The method of claim 26, wherein the aqueous pulp of the aramid pulp is dewatered to form dewatered pulp, the water content of the dewatered pulp being in the range of 50-70% by weight, based on the weight of the dewatered pulp.

29. The method of claim 27, wherein the dewatered pulp is subjected to a drying step to form a dried pulp having a water content in the range of 2-20% by weight, based on the weight of the dried pulp.

30. The method of claim 27, wherein the dewatered pulp is subjected to a drying step to form a dried pulp having a water content in the range of 3-10% by weight, based on the weight of the dried pulp.

31. The method according to claim 29 or 30, wherein the dried pulp is subsequently subjected to an opening step.

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