JP5209303B2 - Acrylic and para-aramid pulp and method for producing the same - Google Patents

Description

  The present invention relates to acrylic and para-aramid pulps for use as reinforcements in products such as seals and friction materials. The invention further relates to a method for producing such pulp.

  Fibrous and non-fibrous reinforcements have been used for many years in friction products, sealing products and other plastic or rubber products. Such reinforcements typically must exhibit high wear and heat resistance.

  Asbestos fibers have historically been used as reinforcements, but alternatives have been manufactured or proposed due to their health risks. However, many of these alternatives do not function as well as asbestos in various ways.

  Non-Patent Document 1 discloses the manufacture of pulp made from variable length fibrillated Kevlar (R) brand para-aramid fibers and the use of such pulp as a reinforcement in various applications. ing. This publication describes a pulp made from Kevlar (R) brand para-aramid fibers alone or NOMEX (R) brand meta-aramid, wood pulp, cotton and other natural cellulose derivatives, rayon. Disclosure that can be used in sheet products in combination with fibers of polyester, polyolefin, nylon, polytetrafluoroethylene, asbestos and other minerals, glass fibers and other ceramics, steel and other metals, and other materials such as carbon doing. The publication also describes from a Kevlar® brand para-aramid fiber alone with a friction material to replace a portion of the asbestos volume, with the remainder of the asbestos volume replaced with fillers or other fibers. , Or the use of pulp with Kevlar® brand para-aramid staple fibers.

  U.S. Patent No. 6,099,056 (given to Hoines) discloses a composite friction material or gasket material made of thermosetting or thermoplastic matrix resin, fiber reinforcement, and substantially fibril-free aramid particles. Yes. Poly (p-phenylene terephthalamide) and poly (m-phenylene isophthalamide) are preferred fiber reinforcements, and the fibers may be in the form of floc or pulp.

  U.S. Patent No. 6,099,096 (Kusaka et al.) Is made from a friction modifier, a binder and a fibrous reinforcement made of a mixture of (a) dry aramid pulp and (b) wet aramid pulp, wood pulp or acrylic pulp. A friction material is disclosed. Dry aramid pulp is defined as aramid pulp obtained by the “dry fibrillation method”. The dry fibrillation method is dry milling of aramid fibers between a rotary cutter and a screen to produce pulp. Wet aramid pulp is defined as aramid pulp obtained by “wet fibrillation method”. The dry fibrillation method is to grind short aramid fibers in water between two rotating disks to form fibrillated fibers and then dehydrate the fibrillated fibers, ie pulp. Patent document 2 further discloses a mixed fibrillation method of fibers by first mixing a plurality of types of organic fibers to be fibrillated at a certain ratio, and then fibrillating the mixture to produce pulp. .

US Pat. No. 5,811,042 US Patent Application Publication No. 2003/0022961 Research Disclosure 74-75 published in February 1980

  There is a continuing need to provide alternative stiffeners that work well in products such as seal and friction applications and that are also low cost. Despite numerous disclosures suggesting lower cost alternative stiffeners, many of these proposed products do not function well in terms of use and cost significantly over currently marketed products. Or have other negative characteristics. Thus, there remains a need for reinforcements that exhibit high wear and heat resistance and that are comparable to or cheaper than other commercially available reinforcements.

The present invention
(A) (1) An acrylic fiber comprising acrylonitrile units that is at least 85% by weight of the total acrylic fiber, which is 10 to 90% by weight of the total solids in the raw material, and has an average length of 10 cm or less Having fibers,
(2) A pulp containing 10-90% by weight of total solids in the raw material and having an average length of 10 cm or less, and (3) water, which is 95-99% by weight of the total raw material Combining raw materials,
(B) mixing the raw material into a substantially uniform slurry;
(C) at the same time (1) fibrillating, cutting and masticating acrylic and para-aramid fibers to form irregularly shaped fibrillated fibrous structures with stalks and fibrils; and (2) co-refining the slurry by substantially uniformly dispersing all solids in the purified slurry;
(D) removing water from the purified slurry to make water 60% by weight or less,
Thereby producing acrylic and para-aramid pulp with acrylic and para-aramid fibrous structures having an average maximum dimension of 5 mm or less, a length-weighted average of 1.3 mm or less, and The invention relates to a first embodiment of a method for producing acrylic and para-aramid pulp for use as a reinforcement, wherein the fibrils and / or starks are substantially intertwined with para-aramid fibrils and / or starks.

The present invention further includes
(A) water and (1) an acrylic fiber comprising acrylonitrile units that is at least 85% by weight of the total acrylic fiber, the fiber being 10-90% by weight of the total solids in the raw material, and (2) Combining a raw material comprising a first fiber from the group consisting of para-aramid fibers that is 10-90% by weight of the total solids in the raw material;
(B) mixing the raw material into a substantially uniform suspension;
(C) purifying the suspension with a disc refiner, cutting the fibers to have an average length of 10 cm or less, and fibrillating and masticating at least some of the fibers to form irregular shapes A process of making a fibrillated fibrous structure of
(D) combining the purified suspension, the second fibers of group (1) (1) and (2) and, if necessary, the raw material containing water to raise the water concentration to 95-99% by weight of the total raw material Process,
(E) if necessary, mixing the raw materials to form a substantially uniform suspension;
(D) (1) in suspension such that all or substantially all of the acrylic and para-aramid fibers are converted to irregularly shaped fibrillated acrylic and para-aramid fibrous structures with starks and fibrils. Co-purifying the mixed suspension by fibrillating, cutting and masticating the solids of the mixture, and (2) substantially uniformly dispersing the total solids in the refined slurry;
(H) removing water from the refined slurry to reduce water to 60% by weight or less (60 total wt%),
Thereby producing acrylic and para-aramid pulps with acrylic and para-aramid fibrous structures having an average maximum dimension of 5 mm or less, a length-weighted average of 1.3 mm or less, and acrylic fibrils and / or starches It relates to a second embodiment of a method for producing acrylic and para-aramid pulps for use as reinforcement, substantially intertwined with para-aramid fibrils and / or stark.

The present invention further includes
(A) an irregular acrylic fibrous structure comprising at least 85% by weight of acrylonitrile units of the total acrylic fibrous structure and having a total solid content of 10 to 90% by weight;
(B) an irregularly shaped para-aramid fibrous structure that is 10 to 90% by weight of the total solids, and (c) water that is 4 to 60% by weight of the total pulp,
Thereby acrylic and para-aramid fibrous structures have an average maximum dimension of 5 mm or less, a length weighted average of 1.3 mm or less, and stark and fibrils, where the acrylic fibrils and / or stark are para-aramids Substantially entangled with fibrils and / or starks,
It relates to acrylic and para-aramid pulps for use as reinforcement.

  The present invention further relates to a friction material comprising a friction modifier, optionally at least one filler, a binder, and a fibrous reinforcement comprising the pulp of the present invention.

  The invention further relates to a sealing material comprising a fibrous reinforcing material comprising a binder, optionally at least one filler, and the pulp of the invention.

  The present invention can be more fully understood from the following detailed description thereof in addition to the accompanying drawings described as follows.

Glossary Before describing the present invention, it is useful to define in the following glossary several terms that have the same meaning throughout this disclosure unless otherwise stated.

  “Fiber” means a relatively flexible unit of material having a high ratio of length to width across its cross-sectional area perpendicular to its length. As used herein, the term “fiber” is used interchangeably with the term “filament” or “warp”. The cross-sections of the filaments described herein can be any shape, but are typically round or bean-shaped. The fiber spun in the package on the bobbin is called continuous fiber. The fibers can be cut into short lengths called staple fibers. The fibers can be cut into even shorter lengths called flocs. Yarn, multifilament yarn or tow comprises a plurality of fibers. The yarn can be entangled and / or twisted.

  “Fibril” means a small fiber having a diameter as small as a fraction of a micrometer to a few micrometers and having a length of about 10-100 micrometers. Fibrils generally extend from a larger fiber backbone having a diameter of 4-50 micrometers. Fibrils act as hooks or fasteners to entrain and catch adjacent material. Some fibers fibrillate, others do not fibrillate or effectively fibrillate, and for purposes of this definition such fibers do not fibrillate. Poly (para-phenylene terephthalamide) fibers easily fibrillate when worn, creating fibrils. The acrylic fibers of the present invention are also fibrillated.

  A “fibrillated fibrous structure” is a particle of material having a stark and fibrils extending therefrom, where the stark is substantially cylindrical and is about 10-50 microns in diameter, with only one fibril attached to the stark. By means of a particle that is a hair-like component about 10 to 100 microns long with a diameter of a fraction of a micron to a few microns.

  "Flock" means a short length of fiber that is shorter than staple fibers. The length of the floc is about 0.5 to about 15 mm and has a diameter of 4 to 50 micrometers, preferably a length of 1 to 12 mm and a diameter of 8 to 40 micrometers. A floc that is less than about 1 mm does not significantly increase the strength of the material in which it is used. Flocks or fibers greater than about 15 mm often do not function well because individual fibers may become entangled and cannot be distributed sufficiently and uniformly throughout the material or slurry. Aramid floc is disclosed in US Pat. No. 3,063,966, US Pat. No. 3,133,138, US Pat. No. 3,767,756, and US Pat. No. 3,869,430. Manufactured by cutting aramid fibers to short lengths without significant or any fibrillation, such as those produced by the methods described in the specification.

  “Length-weighted average” means a length calculated from the following equation.

  The “maximum dimension” of an object refers to the linear distance between each other between the two extreme points of the object.

  “Staple fibers” can be produced by cutting filaments to a length of 15 cm or less, preferably 3-15 cm, most preferably 3-8 cm. The staple fibers can be straight (ie, non-crimped), or can be crimped and have a sawtooth-shaped crimp along its length at any crimp (or repeated bend) frequency. . The fibers can be present in an uncoated or coated or otherwise pretreated (eg, predrawn or heat treated) form.

  The present invention relates to a process for producing acrylic and para-aramid pulps for use as reinforcement. The invention also relates to acrylic and para-aramid pulps that can be produced by the method of the invention for use as reinforcement. The present invention further relates to products such as sealants and friction materials incorporating the pulp of the present invention, and methods for their production.

I. First Embodiment of the Method of the Invention In the first embodiment, the method for producing acrylic and para-aramid pulp comprises the following steps. First, the pulp ingredients are combined, added or contacted together. Second, the combined pulp stock is mixed into a substantially uniform slurry. Third, the slurry is simultaneously purified or co-purified. Fourth, water is removed from the refined slurry.

Combining step In the combining step, the pulp ingredients are preferably added together in a container. Pulp raw materials include (1) acrylic fibers, (2) para-aramid fibers, (3) granular para-aramid particles, which are optionally substantially or completely free of fibrils, (4) optionally, other small additives, And (5) water is included.

Acrylic fiber The acrylic fiber is 10 to 90% by weight of the total solid content in the raw material, preferably 25 to 60% by weight of the total solid content in the raw material, most preferably 25 to 55% by weight of the total solid content in the raw material. Added to the concentration.

  The acrylic fibers preferably have an average length of 10 cm or less, more preferably 0.5 to 5 cm, and most preferably 0.6 to 2 cm. Any acrylic fibers in the form of continuous filaments can be cut into shorter fibers such as staple fibers or flocks before combining the pulp ingredients together.

Acrylic Polymer The acrylic fiber useful in the present invention comprises acrylonitrile units that are at least 85% by weight of the total acrylic fiber. Acrylonitrile unit is _- (CH 2 -CHCN) _- a. Acrylic fibers are made from an acrylic polymer composed of 85% by weight or more acrylonitrile and 15% by weight or less of an ethylene monomer copolymerizable with acrylonitrile and a mixture of two or more of these acrylic polymers. Can do. Examples of ethylene monomers that can be copolymerized with acrylonitrile include acrylic acid, methacrylic acid and their esters (such as methyl acrylate, ethyl acrylate, methyl methacrylate, ethyl methacrylate), vinyl acetate, vinyl chloride, vinylidene chloride, Examples include acrylamide, methacrylamide, methacrylonitrile, allyl sulfonic acid, methane sulfonic acid and styrene sulfonic acid.

Para-aramid fiber The para-aramid fiber is 10 to 90% by weight of the total solid content in the raw material, preferably 40 to 75% by weight of the total solid content in the raw material, most preferably 40 to 70% of the total solid content in the raw material. Added to a concentration of 55% by weight. The para-aramid fibers preferably have a linear density of 10 dtex or less, more preferably 0.5 to 10 dtex, and most preferably 0.8 to 2.5 dtex. The para-aramid fibers also preferably have an average length of 10 cm or less along their longitudinal axis, more preferably an average length of 0.65 to 2.5 cm, most preferably an average length of 0.65 to 1.25 cm. Have

Para-aramid particles Optionally, in one embodiment, the pulp feedstock further includes particulate para-aramid particles that are substantially or completely fibril free. When these particles are added, they are not more than 50% by weight of the total solids in the raw material, preferably 20 to 50% by weight of the total solids in the raw material, most preferably 25 to 25% of the total solids in the raw material. Added to a concentration of 35% by weight. Because they are made of para-aramid, they contribute to excellent abrasion resistance and dispersibility in the pulp being produced. Since the particles are substantially free of fibrils, they also serve as a compounding agent to assist in the dispersion of the other ingredients in the mixture and slurry. Particles that perform this function are often known as processing agents or processing aids. The particulate para-aramid particles substantially or completely free of fibrils have an average maximum dimension of 50-2000 microns (0.05-2 mm), preferably 50-1500 microns, most preferably 75-1000 microns. However, particles below about 50 microns lose efficacy in friction and sealing applications. Particles above about 2000 microns do not remain well dispersed in water with other ingredients when mixed. FIG. 5 is a photomicrograph of para-aramid particles that can be used as a raw material for the method of the present invention.

Aramid polymers Polymers suitable for use in the manufacture of the aramid fibers and aramid particles of the present invention are synthetic aromatic polyamides. The polymer must be of fiber-forming molecular weight in order to be shaped into fibers. The polymer may include polyamide homopolymers, copolymers, and mixtures thereof that are predominantly aromatic in which at least 85% of the amide (—CONH—) linkages are directly attached to two aromatic rings. The ring can be unsubstituted or substituted. A polymer is para-aramid when the two rings are para to each other along the molecular chain. Preferably, the copolymer is replaced by 10% or less of other diamines in place of the primary diamine used in the formation of the polymer, or 10% or less of other diacid chlorides are used in the formation of the polymer. It is replaced by a new diacid chloride. It has been found that additives can be used with aramid and as many as 13 weight percent or less of other polymeric materials can be blended or combined with aramid. The preferred para-aramid is poly (para-phenylene terephthalamide) (PPD-T) and copolymers thereof.

Optional other additives Other additives, unless they remain suspended in solution during the mixing process and significantly change the effect of the purification process on the essential solid ingredients listed above Optionally, it can be added. Suitable additives include pigments, dyes, antioxidants, flame retardant compounds, and other processing and dispersion aids. Preferably, the pulp raw material does not include asbestos. In other words, the resulting pulp is asbestos free, i.e. free of asbestos.

Water Water is added to a concentration of 95 to 99% by weight of the total raw material, preferably 97 to 99% by weight of the total raw material. In addition, water can be added first. Other ingredients can then be added at a rate to optimize the underwater dispersion while simultaneously mixing the combined ingredients.

Mixing Step In the mixing step, the raw materials are mixed into a substantially uniform slurry. “Substantially uniform” means that a random sample of the slurry has the same weight% concentration ± 10 wt%, preferably ± 5 wt%, most preferably ± 2 wt% starting material as in all ingredients in the combination process. It means that each of these is contained. For example, if the solids concentration in the total mixture is 50 wt% acrylic fiber plus 50 wt% para-aramid fiber, the substantially uniform mixture in the mixing process is (1) 50% by weight ± 10% by weight, preferably ± 5% by weight, most preferably ± 2% by weight acrylic fiber concentration and (2) 50% by weight ± 10% by weight, preferably ± 5% by weight, most preferably ± It means having a concentration of 2% by weight of para-aramid fiber. Mixing can be accomplished in any vessel containing rotating blades or some other stirrer. Mixing can occur after the ingredients are added or while the ingredients are being added or combined.

Refining process In the refining process, the pulp stock is co-refined, converted or modified simultaneously as follows. Acrylic fibers and para-aramid fibers are fibrillated, cut and masticated into irregularly shaped fibrous structures with starks and fibrils. When para-aramid particles are added with other ingredients, at least some of the para-aramid particles are masticated into smaller, rounder, substantially fibril free particles. The total solids are dispersed so that the refined slurry is substantially uniform. “Substantially uniform” is as defined above. The purification step preferably comprises passing the mixed slurry through one or more disk refiners, or back recycling the slurry to a single refiner. The term “disc refiner” refers to a refiner that contains one or more pairs of discs that rotate relative to each other and thereby purify the raw material by shearing between the discs. In one preferred type of disk refiner, the slurry to be refined is pumped between closely spaced circular rotor disks and stator disks that can rotate relative to each other. Each disc has a surface facing the other disc with surface grooves extending at least partially radially. A preferred disc refiner that can be used is disclosed in US Pat. No. 4,472,241. If necessary for uniform dispersion and sufficient purification, the mixed slurry can be passed through the disc refiner more than once or through a series of at least two disc refiners. When the mixed slurry is purified with only one refiner, the resulting slurry tends to be poorly purified and unevenly distributed. Aggregates or agglomerates that consist of, or consist essentially of, only one solid source, or the other, or both, or three, are substantially uniform rather than dispersed. A dispersion system can be formed. Such aggregates or agglomerates have a greater tendency to fall apart when the mixed slurry is passed through the refiner more than once or through more than one refiner and dispersed in the slurry.

  Since a substantially uniform slurry containing a number of raw materials is co-refined in this step of the process, any other type of non-pulp raw material (eg, para-aramid fiber) can be used while the other raw materials are also purified. ) Is also refined to pulp in the presence of all other types of non-pulp raw materials (eg, aramid material pieces and optionally para-aramid particles). This co-refining of the non-pulp raw material forms a pulp that is superior to the pulp blend produced by simply mixing the two pulps together. Adding two pulps and then simply mixing them together does not form a substantially uniform, closely bound fibrous component of the pulp produced by co-refining non-pulp raw material into pulp according to the present invention.

Removal Step Next, water is removed from the refined slurry to 60 wt% or less of water, preferably 4 to 60 wt% of water, most preferably 5 to 58 wt% of water. The water can be removed by collecting the pulp in a dewatering device such as a horizontal filter, and if necessary, additional water can be removed by applying pressure or pressing the pulp filter cake. The dewatered pulp can then optionally be dried to the desired moisture content and / or packaged or wound up on a roll.

1 and 2
The method will now be described with reference to FIGS. Throughout this detailed description, similar reference symbols refer to similar elements in all figures of the drawings.

  Referring to FIG. 1, there is a block diagram of an embodiment of a “wet” pulp wet manufacturing method according to the present invention. The pulp raw material 1 is added to the container 2. The container 2 has an internal mixer similar to the mixer of a washing machine. The mixer disperses the raw material into water to produce a substantially uniform slurry. The mixed slurry is transferred to a first refiner 3 that purifies the slurry. Then, optionally, the refined slurry can be transferred to the second refiner 4 and optionally to the third refiner 5 next. Although three refiners are illustrated, any number of refiners can be used depending on the desired homogeneity and degree of purification. After the last refiner in a series of refiners, the refined slurry is optionally transferred to a filter or sorter 6 which passes the selected solids or slurry with dispersed solids below the screen size and passes the selected mesh. Alternatively, the dispersed solids larger than the screen size are recycled back to one or more of the refiners, such as by line 7, or to a dedicated refiner 8 for purifying the recirculated slurry, and purified from the recirculated slurry. The slurry is again passed through the filter or sorter 6. Properly refined slurry passes from a filter or sorter 6 to a horizontal water vacuum filter 9, which removes water so that the pulp has a water concentration of 75% or less by weight of the total feed. The slurry can be transferred from one to the next by any conventional method and equipment such as using one or more pumps 10. The pulp is then conveyed to the dryer 11, which removes more water until the pulp has a water concentration of 60% by weight or less of the total raw material. The refined pulp is then packaged in a baler 12.

  Referring to FIG. 2, there is a block diagram of an embodiment of a method for dry production of “dry” pulp according to the present invention. This dry method is the same as the wet method except after the horizontal water vacuum filter 9. After the filter, the pulp passes through the press 13, which removes more water until the pulp has a water concentration of 20% by weight or less of the total feed. The pulp then passes through a fluffing machine 14 for fluffing the pulp and then a rotor 15 for removing more water. Next, the pulp passes through the dryer 11 and is packed by the baler 12 as in the wet method.

II. Second Embodiment of Method of the Present Invention In the second embodiment, the method for producing acrylic fiber and para-aramid pulp is the same as the first embodiment of the present method described above with the following differences.

  Before combining all raw materials together, either acrylic fibers or para-aramid fibers, or both acrylic and para-aramid fibers may need to be shortened. This is done by combining water with the fiber raw material. Next, water and fibers are mixed to form a first suspension and processed by a first disc refiner to shorten the fibers. The disc refiner cuts the fibers to an average length of 10 cm or less. The disc refiner will also partially fibrillate and partially masticate the fibers. Other fibers not previously added can be shortened in this manner, also forming a second treated suspension. Next, other fibers (or second suspension if treated in water) are combined with the first suspension.

  If necessary, more water is added to raise the water concentration to 95-99% by weight of the total ingredients before or after other ingredients are added or when they are added. After all the ingredients have been combined, they can be mixed, if necessary, to achieve a substantially uniform slurry.

  The raw materials in the slurry are then co-purified together, ie simultaneously. This purification step fibrillates and cuts the solids in the suspension so that all or substantially all of the acrylic and para-aramid fibers are converted to irregularly shaped fibrillated fibrous structures. And masticating. This purification step also disperses all solids so that the refined slurry is substantially uniform. The water is then removed as in the first embodiment of the method. Both processes produce the same or substantially the same acrylic and para-aramid pulp.

Pulp of the Invention The product produced by the method of the invention is an acrylic and para-aramid pulp for use as a reinforcement in the product. The pulp comprises (a) an irregularly shaped acrylic fibrous structure, (b) an irregularly shaped para-aramid fibrous structure, (c) optionally, substantially fibril-free granular para-aramid particles, (d ) Optionally comprising other minor additives, and (e) water.

  The concentration of the individual raw material components in the pulp, of course, corresponds to the aforementioned concentration of the corresponding raw material used for the manufacture of the pulp.

  Irregularly shaped acrylic and para-aramid fibrillated fibrous structures have stark and fibrils. Acrylic fibrils and / or starks are substantially entangled with para-aramid fibrils and / or starks. Fibrils are important and act as hooks or fasteners or tentacles that adhere to and hold adjacent particles in the pulp and final product, thereby providing integrity to the final product.

  Acrylic and para-aramid fibrillated fibrous structures preferably have an average maximum dimension of 5 mm or less, more preferably 0.1 to 4 mm, and most preferably 0.1 to 3 mm. The acrylic and para-aramid fibrillated fibrous structure preferably has a length weighted average of 1.3 mm or less, more preferably 0.7 to 1.2 mm, and most preferably 0.75 to 1.1 mm.

  If para-aramid particles are included in the pulp, the acrylic and para-aramid fibrous structures will also contact and surround at least some of these rounder, substantially fibril-free para-aramid particles. Partly wrapped. These para-aramid particles also preferably have a size of at least 50 microns, more preferably 50-100 microns, and most preferably 50-75 microns. The fibrils on and along the acrylic and para-aramid fibrous structures can contact and form a partial cocoon around the rounder, substantially fibril-free para-aramid particles.

  Acrylic and para-aramid pulps do not contain substantial aggregates or aggregates of the same material. In addition, the pulp is Canadian standard freeness as measured by TAPPI (Pulp Paper Industry Technology Association) test T 227 om-92, which is a measure of its drainage properties, of 100-700 ml, preferably 250-450 ml. CSF).

  The surface area of the pulp is a measure of the degree of fibrillation and affects the porosity of products made from the pulp. Preferably, the surface area of the pulp of the present invention is 7-11 square meters per gram.

  FIG. 4 is a photomicrograph image of acrylic and para-aramid pulp produced by the method of the present invention.

  Aramid particles and fibrous structures that are substantially uniformly dispersed throughout the reinforcing material, as well as the friction material and sealant, are reinforced by the high temperature properties of the para-aramid polymer and the fibrillation tendency of the para-aramid fibers. Many sites and thought to provide improved wear resistance. When co-purified, the blending of acrylic and para-aramid materials is so dense that with friction material or sealant, some para-aramid fibrous structures are always near the acrylic structure, so Service stresses and wear are always shared.

The present invention further relates to a sealing material and a method for producing the sealing material. The sealant is used in or as a barrier to prevent the discharge of fluids and / or gases, and is used to prevent entry of contaminants where the two items meet. An exemplary application for the sealant is in gaskets. The sealant comprises a binder, optionally at least one filler, and a fibrous reinforcement comprising the acrylic and para-aramid pulps of the present invention. Suitable binders include nitrile rubber, butadiene rubber, neoprene, styrene-butadiene rubber, nitrile-butadiene rubber, and mixtures thereof. The binder can be added with all other starting materials. The binder is typically added in the first step of the gasket manufacturing method where the dry ingredients are mixed together. Other raw materials optionally include uncured rubber particles and a rubber solvent, or a solution of rubber in a solvent, to cause the binder to coat the filler and pulp surface. Suitable fillers include barium sulfate, clay, talc, and mixtures thereof.

  A suitable method for producing the sealant is, for example, what is called a beater addition method or a wet method in which the gasket is produced from a slurry of the material, or a calendering method or dry method in which the raw materials are combined in an elastomer or rubber solution.

Friction material The pulp of the present invention is a friction material and can be used as a reinforcement. “Friction materials” are materials used for their friction properties, such as coefficient of friction to stop or move kinetic energy, stability at high temperatures, wear resistance, noise and vibration damping properties, etc. means. Exemplary applications for friction materials include brake pads, brake blocks, dry clutch overlays, clutch face segments, brake pad backing / insulation layers, automotive transmission paper, and friction paper.

  In view of this new application, the present invention further relates to a friction material and a method of manufacturing the friction material. Specifically, the friction material comprises a friction modifier, optionally at least one filler, a binder, and a fibrous reinforcement comprising the acrylic and para-aramid pulps of the present invention. Suitable friction modifiers include metal powders such as iron, copper and zinc; abrasives such as magnesium and aluminum oxides; lubricants such as synthetic and natural graphite, and molybdenum and zirconium sulfides; and synthetic rubber and cashew nut shells Organic friction modifier such as resin particles. Suitable binders are thermosetting resins such as phenolic resins (ie, straight (100%) phenolic resins and various phenolic resins modified with rubber or epoxy), melamine resins, epoxy resins and polyimide resins, and mixtures thereof. It is. Suitable fillers include barite, calcium carbonate, wollastonite, talc, various clays, and mixtures thereof.

  The actual manufacturing process of the friction material can vary depending on the type of friction material desired. For example, a method for producing a molded friction part generally includes combining desired ingredients in a mold, curing the part, shaping, heat treating, and optionally grinding the part. Automobile transmission paper and friction paper can generally be produced by combining desired raw materials in a slurry and producing the paper on a paper machine using conventional papermaking methods.

Test Methods The following test methods were used in the following examples.

  Canadian Standard Freeness (CSF) is a well-known measure of the ease with which water can escape from a slurry or dispersion of particles. Freeness is measured by TAPPI test T227. Data obtained from the performance of the test is expressed as Canadian freeness, which represents milliliters of water flowing out of the aqueous slurry under specified conditions. A large number suggests a high freeness and a high tendency for water to escape. A low number indicates a tendency for the dispersion to drain slowly. Since a higher number of fibrils reduces the rate at which water flows out through the paper-forming mat, freeness is inversely proportional to the degree of pulp fibrillation.

  The length-weighted average is a “FiberExpert” tabletop analyzer (available from Metso Automation of Helsinki, Finland, now known as PulpExpert FS, Helsinki, Finland). Use to measure. This analyzer takes a photographic image of the pulp with a digital CCD camera as the pulp slurry flows through the analyzer, then the embedded computer analyzes the fibers in these images and calculates their length-weighted average To do.

temperature:
All temperatures are measured in degrees Celsius (° C).

  Denier is the linear density of a fiber as measured according to ASTM D 1577 and expressed as a weight in grams of 9000 meters of fiber. Denier is measured with a Vibroscope manufactured by Texttechno of Munich, Germany. Denier multiplication (10/9) is equal to decitex (dtex).

  The invention will now be illustrated by the following specific examples. All parts and percentages are by weight unless otherwise specified. Examples prepared according to the method of the present invention are indicated numerically.

Example 1
In this example of the present invention, the pulp of the present invention was produced from para-aramid fiber and acrylic staple feedstock. Acrylic staples having a cut length of 2 inches and a filament linear density of 3 dpf (3.3 dtex per filament) were obtained from Solutia, Inc. with offices in St. Louis, MO. ). Commercially available KEVLAR® brand frock with a 1/4 inch cut length, Para-aramid fiber in the form of Style 1F178, located in Wilmington, Delaware Obtained from EI du Pont de Nemours and Company.

  Acrylic staples and water are fed together directly into a Sprout-Walderon 12 "Single Disc Refiner using a 10 mil plate clearance setting and acceptable processing lengths in the range of 13 mm Pre-pulpation to reach

  The prepulped acrylic fibers and the cut para-aramid fibers plus water are then combined into a highly stirred mixing tank at a solids concentration of 50 wt% para-aramid fibers and 50 wt% acrylic staples, about 2 to Mixing to form a uniform pumpable slurry with a total feed concentration of 3% by weight. The slurry was then recirculated through a Sprout-Walderon 12 inch single disk refiner and co-purified.

At the same time, the refiner
(1) Para-aramid fibers and acrylic staples were fibrillated, cut and masticated to form irregularly shaped fibrous structures having stark and fibrils.
(2) All solids were dispersed so that the refined slurry was substantially uniform as defined previously.

  This purified slurry was then filtered using a filter bag, dehydrated by pressure, and placed in a large ZIPLOC® type storage bag. The fibrous structure had an average maximum dimension of 5 mm or less, and a length-weighted average of 1.3 mm or less as measured by Fiber Expert®.

Example 2
This example illustrates another method by which co-refined pulp can be produced from para-aramid fiber and acrylic fiber feedstocks. Acrylic staples with a cut length of 2 inches available from Soluchia and a filament linear density of 3 dpf (3.3 dtex per filament) most fibers are shorter than 3/4 inch (1.91 cm) Cut with a guillotine cutter 2-3 times at right angles to produce a random length fiber that averages about 1/2 inch (1.27 cm) in length.

  Para-aramid fibers in the form of commercially available Kevlar® brand multifilament yarns available on the bobbin from EI Dupont de Nemours and Company are para-aramid yarns Cut to a nominal 1/2 inch (1.27 cm) cut length with a Lummus Cutter (available from Lummus Industries, with offices in Columbus, Georgia) To make. Other Kevlar® brand para-aramid fibers, which are not initially on the bobbin and are of various lengths, are less than 3/4 inch (1.91 cm) of most fibers, averaging about 1 Cut with a guillotine cutter 2-3 times at right angles to produce random length fibers that are 2 inches (1.27 cm) long.

The two raw materials plus water produced as described above are then combined into a highly stirred mixing tank called a hydropulper at a solids concentration of 50 wt% para-aramid fiber and 50 wt% acrylic fiber. , To form a substantially uniform pumpable slurry having a total solids concentration of about 2-3 wt% total feed. The slurry is pumped through a series of three refiners as described in US Pat. No. 4,472,241. At the same time, the refiner
(1) fibrillated, cut and masticated acrylic and para-aramid fibers to form irregularly shaped fibrous structures with stark and fibrils, and (2) a refined slurry was defined previously Disperse all solids so that they are substantially uniform.

  This refined slurry is then dewatered using a horizontal filter and dried in an oven to a moisture content of 50% by weight desired for wet pulp. The wet pulp is then packaged into bales by a baler. All of the raw materials in the pulp have a length weighted average of 1.3 mm or less as measured by Fiber Expert®.

Example 3
This example illustrates further process steps of the present invention and another embodiment of the pulp. Follow the procedure of Example 2. However, after dehydrating the pulp with a horizontal filter, the pulp is pressed with a mechanical press to further remove water, and then the pulp is fluffed to better separate the pressed wet pulp. Fluffing is available from Bepex Corporation with offices in Santa Rosa, California. The fluffed wet pulp is then dried in an oven to a moisture content of approximately 8 total weight percent, and then the dried pulp is disclosed in US Pat. No. 5,084,136 for further fluffing and dispersing. Further processing with an ultrarotor (model IIIA available from Altenburger Machinen Jackering GmbH, located in the office of Voisterhauser, Germany). The dried pulp is then packaged into a bale. All of the raw materials in the pulp have a length weighted average of 1.3 mm or less as measured by Fiber Expert®.

Example 4
This example illustrates another embodiment of the pulp of the present invention. The method of Example 2 is followed except that 1/3 weight of para-aramid fiber is replaced with para-aramid particles. Para-aramid resin particles are prepared as generally disclosed in US Pat. No. 3,884,881, but using N-methylpyrrolidone / calcium chloride as a solvent to produce a fragment-like polymer that precipitates from the solvent. It is produced by continuously reacting para-phenylenediamine and terephthaloyl chloride in a screw extruder. The solvent is extracted, the polymer fragments are washed and dried to a mixed granular powder. The para-aramid resin particles are then treated in substantially the same manner as the para-aramid fibers were treated in Example 2. However, the refiner not only purifies the fibers, but also cuts and / or masticates the para-aramid particles into rounder, substantially fibril-free particles. After dehydration, some of the resulting pulp having a moisture content of 50 total weight percent is then packaged into a bale. The resulting pulp residue is further pressed to a moisture content of approximately 8 total weight percent, then fluffed, dispersed, and packaged as in Example 3. All of the raw materials in the pulp have a length weighted average of 1.3 mm or less as measured by Fiber Expert®.

Example 5
A disc brake pad incorporating the pulp of the present invention was produced by the following method. Approximately 20 kilograms of non-asbestos content comprising a mixture of 7% by weight cashew nut shell resin, 17% by weight inorganic filler, 21% by weight graphite, coke and lubricant, 18% by weight inorganic abrasive, and 16% by weight soft metal. The base compound powder was mixed together for 10-20 minutes in a 50 liter Littleford mixer. The mixer had two high speed shredders with “Southern Union Flag” shaped wings and a slower rotating plow.

  5 kilograms of fully blended base compound powder is then added in an amount of 3.8% by weight based on the combined weight of the compound powder and pulp (50% by weight para-aramid). And 50% by weight acrylic fiber co-refined pulp). The pulp was then dispersed in the base compound powder by mixing for an additional 5-10 minutes. Once mixed, the resulting brake pad composition is such that the fibers are well dispersed in the base compound powder with essentially no detectable pulp disruption or any component separation. It had a normal appearance, fully coated.

  The brake pad composition is then poured into a single piece steel mold for the front wheel disc brake pad, cold pressed to a standard thickness of about 5/8 inch (16 mm), and then removed from the mold to 200 A preformed brake pad having an approximate weight of grams was formed. The preform did not have any excessive springback or blistering and was robust enough to withstand normal handling without damage. Twelve replicate preforms were produced. The preform is then placed in two multi-cavity molds, placed in a commercial press, and press cured at 300 ° F. (149 ° C.) for about 15 minutes with periodic pressure relief to escape the phenol reactant gas. (Binder phenolic crosslinking and reaction) followed by lightly constrained oven curing at 340 ° F. (171 ° C.) for 4 hours to complete the phenolic binder crosslinking. The cured molding pad was then ground to the desired thickness of about half an inch (13 mm). The test pad is indistinguishable when compared visually with a commercial brake pad containing equal amounts of all para-aramid pulp or acrylic pulp, has good compound flow into the backing plate hole, I didn't have any.

  A sample of a brake pad incorporating the pulp of the present invention was then tested to determine its friction performance. Cut specimens, typically 1 inch by 1 inch and about 3/16 inch (5 mm) thick, from the test pad are hot during constant pressure and controlled temperature drag tests towards the heated steel drum. And a tracking machine available from Link Engineering, Detroit, MI using the Test Protocol Society of Engineers (SAE) J661 to measure the cold coefficient of friction. Chase Machine). Samples were periodically measured for wear (thickness loss). This was repeated with two test samples after cutting from the other replicated pads. Brake pad samples incorporating the pulp of the present invention exhibited hot and cold friction performance substantially equivalent to commercially available pads containing substantially equal amounts of all para-aramid pulp. The test further suggested that the pad-pad uniformity and average friction rating were also substantially equivalent.

  The pad was then tested using a test protocol J2681 (ISO-SWG4) with a radiometer of 289.0 mm on a dynamometer (Link Testing Laboratories, Inc. in Detroit, MI). A single piston dynamometer was used to test for friction and wear under various braking conditions. The test consisted of 17 scenarios each with 5 to 200 brakes applied, and the coefficient of friction was measured as a function of applied brake pressure, temperature, brake speed and deceleration. This test also had two high temperature fade sections, during which the brake pads were exposed to progressively higher initial temperatures during constant deceleration, reaching temperatures above 600 ° C. Wear was measured as a reduction in pad thickness and weight at the end of the test (608 brake application). The results for the pads made with the compound of this example show that very little fade and fully restored fade (where fade is defined as loss of friction in the highest temperature brake application), non-fade part Showed an acceptable coefficient of friction of 0.25 to 0.4, no pad surface cracks, and acceptable wear rates for both the pad and the rotor.

Example 6
This example illustrates how the pulp of the present invention can be incorporated into a beater-added gasket for sealing applications. To form the slurry, water, rubber, latex, fillers, chemicals, and pulp of the present invention are combined in the desired amounts. In a circulating mesh screen (such as a paper machine screen or wire), the water is largely drained from the slurry, and the slurry is dried in a heated tunnel to form a material having a maximum thickness of about 2.0 mm. Vulcanize with roll. This material is compressed with a hydraulic press or a two-roll calender, which increases density and improves sealability.

  Such beater-added gasket materials generally do not have as good sealability as comparable compressed fiber materials and are optimal for moderate pressure / high temperature applications. Beater-added gaskets find applicability in the manufacture of auxiliary engine gaskets or cylinder head gaskets after further processing. For this purpose, the semi-finished product is laminated on both sides of the spiked metal sheet and physically fixed in place by the spike.

Example 7
This example illustrates how the pulp of the present invention can be incorporated into a gasket produced by a calendering method. The same ingredients as in Example 6, minus water, are thoroughly dry mixed together and then blended with the rubber solution prepared using a suitable solvent.

  After mixing, the compound is then generally conveyed in batches to a roll calendar. The calendar consists of a small roll that is cooled and a large roll that is heated. The compound is fed and pulled into the calendar nip by the rotational movement of the two rolls. Depending on the pressure, the compound adheres around the hot lower roll, generally in a layer about 0.02 mm thick, and wraps to form a gasket material made from the built-up compound layer. At that time, the solvent evaporates and vulcanization of the elastomer begins.

Once the desired gasket material thickness is achieved, the roll is stopped, the gasket material is cut from the hot roll, cut to the desired size and / or punctured. No additional pressing or heating is required and the material always functions as a gasket. Thus, a gasket having a thickness of about 7 mm or less can be manufactured. However, most gaskets produced in this way are much thinner, usually less than about 3 mm thick.
The main features and aspects of the present invention are as follows.
1. (A) (1) An acrylic fiber comprising acrylonitrile units that is at least 85% by weight of the total acrylic fiber, which is 10 to 90% by weight of the total solids in the raw material, and has an average length of 10 cm or less Having fibers,
(2) A pulp containing 10-90% by weight of total solids in the raw material and having an average length of 10 cm or less, and (3) water, which is 95-99% by weight of the total raw material Combining raw materials,
(B) mixing the raw material into a substantially uniform slurry;
(C) At the same time (1) Acrylic fiber and para-aramid fiber are fibrillated, cut and masticated into an irregularly shaped fibrillated fibrous structure with stark and fibrils, and (2) the refined slurry is Co-purifying the slurry by dispersing all solids to be substantially uniform;
(D) removing water from the purified slurry to make water 60% by weight or less,
Thereby producing acrylic and para-aramid pulps with acrylic and para-aramid fibrous structures having an average maximum dimension of 5 mm or less, a length-weighted average of 1.3 mm or less, and acrylic fibrils and / or starches A process for producing acrylic and para-aramid pulps for use as reinforcement, substantially entangled with para-aramid fibrils and / or stark.
2. The method of claim 1, wherein the acrylic fiber has a linear density of 10 dtex or less and the para-aramid fiber has a linear density of 2.5 dtex or less.
3. The method of claim 1, wherein the pulp does not contain substantial agglomerates of the same material.
4). The raw material is
Further comprising substantially or completely fibril-free particulate para-aramid particles having an average maximum dimension of 50 to 2000 microns and not more than 50% by weight of total solids in the feedstock, and in the purification step, Masticating at least some of the para-aramid particles into smaller, more round, substantially fibril-free particles;
Thereby, in the produced acrylic and para-aramid pulp, the acrylic and para-aramid fibrous structures contact and around at least some of the rounder, substantially fibril-free para-aramid particles. The method of claim 1, wherein the method is partially wrapped.
5. 2. The method according to 1 above, wherein in the combining step, the acrylic fiber comprises 25 to 60% by weight of the total solid content.
6). The method according to 1 above, wherein in the combining step, the para-aramid fiber comprises 40 to 75% by weight of the total solid content.
7). The process of claim 1 wherein after the removal step, the water is 4-60% by weight of the total pulp and the pulp has a Canadian Standard Freeness (CSF) of 100-700 ml.
8). The method of claim 1, wherein the refining step comprises passing the mixed slurry through a series of disc refiners.
9. (A) water,
(1) an acrylic fiber comprising acrylonitrile units that is at least 85% by weight of the total acrylic fiber, the fiber being 10-90% by weight of the total solids in the pulp, and (2) the total solids in the pulp Combining a raw material comprising a first fiber from the group consisting of para-aramid fibers that is 10-90% by weight per minute;
(B) mixing the combined ingredients into a substantially uniform suspension;
(C) purifying the suspension with a disc refiner, cutting the fibers to have an average length of 10 cm or less, and fibrillating and masticating at least some of the fibers to form irregular shapes A process of making a fibrillated fibrous structure of
(D) Refined suspension, second fibers of group (1 and 2) of (a) having an average length of 10 cm or less, and if necessary, increasing the water concentration to 95-99% by weight of the total raw material Combining raw materials containing water for
(E) if necessary, mixing the raw materials to form a substantially uniform suspension;
(D) Simultaneously (1) Suspension so that all or substantially all of the acrylic and para-aramid fibers are converted to irregularly shaped fibrillated acrylic and para-aramid fibrous structures with starks and fibrils. Fibrillating, cutting and masticating solids in the liquid; and (2) co-purifying the mixed suspension by dispersing the total solids so that the purified slurry is substantially uniform;
(H) removing water from the refined slurry to make water 60% by weight or less,
Thereby producing acrylic and para-aramid pulps with acrylic and para-aramid fibrous structures having an average maximum dimension of 5 mm or less, a length-weighted average of 1.3 mm or less, and acrylic fibrils and / or starches A process for producing acrylic and para-aramid pulps for use as reinforcement, substantially entangled with para-aramid fibrils and / or stark.
10. The raw material is
Further comprising substantially or completely fibril-free granular para-aramid particles having an average maximum dimension of 50 to 2000 microns and not more than 50% by weight of total solids in the feedstock, and In either of the two purification steps, at least some of the para-aramid particles are masticated into smaller, more round, substantially fibril-free particles,
Thereby, in the produced acrylic and para-aramid pulp, the acrylic and para-aramid fibrous structures contact and around at least some of the rounder, substantially fibril-free para-aramid particles. 10. A method according to 9 above which is partially wrapped.
11. 10. The method according to 9 above, wherein the irregularly shaped acrylic fibrous structure is 25 to 60% by weight of the total solid content after the removing step.
12 10. The method according to 9 above, wherein the irregularly shaped para-aramid fibrous structure is 40 to 75% by weight of the total solid content after the removing step.
13. 10. The process of claim 9 wherein after the removal step, the water is 4-60% by weight of the total pulp and the pulp has a Canadian Standard Freeness (CSF) of 100-700 ml.
14 (A) an irregularly shaped acrylic fibrous structure comprising acrylonitrile units that is at least 85% by weight of the total acrylic fibrous structure, the structure having a total solid content of 10 to 90% by weight;
(B) an irregularly shaped para-aramid fibrous structure that is 10 to 90% by weight of the total solids, and (c) water that is 4 to 60% by weight of the total pulp,
Thereby acrylic and para-aramid fibrous structures have an average maximum dimension of 5 mm or less, a length weighted average of 1.3 mm or less, and stark and fibrils, where the acrylic fibrils and / or stark are para-aramids Substantially entangled with fibrils and / or starks,
Acrylic and para-aramid pulp for use as reinforcement.
15. 15. The aramid pulp of claim 14, further comprising particulate para-aramid particles substantially or completely free of fibrils that are 50% by weight or less of total solids.
16. 15. The pulp according to 14 above, wherein the irregularly shaped acrylic fibrous structure is 25 to 60% by weight of the total solid content.
17. 15. The pulp as described in 14 above, wherein the irregularly shaped para-aramid fibrous structure is 40 to 75% by weight of the total solid content.
18. The pulp of claim 14, wherein the water is 4-60% by weight of the total pulp and the pulp has a Canadian Standard Freeness (CSF) of 100-700 ml.
19. Friction modifier,
15. A friction material comprising a binder and a fibrous reinforcing material comprising the pulp according to 14 above.
20. The friction modifier is selected from the group consisting of metal powders, abrasives, lubricants, organic friction modifiers, and mixtures thereof, and the binder is from thermosetting resins, melamine resins, epoxy resins and polyimide resins, and mixtures thereof 20. The friction material as described in 19 above, selected from the group consisting of:
21. 15. A sealing material comprising a binder and a fibrous reinforcing material comprising the pulp described in 14 above.
22. 22. The sealing material according to 21 above, wherein the binder is selected from the group consisting of nitrile rubber, butadiene rubber, neoprene, styrene-butadiene rubber, nitrile-butadiene rubber, and mixtures thereof.

1 is a block diagram of an apparatus for performing a wet process for producing “wet” pulp in accordance with the present invention. 1 is a block diagram of an apparatus for performing a dry process for producing “dry” pulp according to the present invention. FIG. Figure 2 is a photomicrograph of para-aramid particles used as an optional raw material for the method of the present invention. It is an image of the micrograph of the pulp manufactured according to the method of this invention.

Claims (5)

(A) (1) An acrylic fiber comprising an acrylonitrile unit, wherein the acrylonitrile unit is contained at least 85% by weight of the total acrylic fiber, is 10 to 90% by weight of the total solid content in the raw material, and is 10 cm or less. Fibers having an average length,
(2) A pulp containing 10-90% by weight of total solids in the raw material and having an average length of 10 cm or less, and (3) water, which is 95-99% by weight of the total raw material Combining raw materials,
(B) mixing the raw material into a substantially uniform slurry;
(C) At the same time (1) Acrylic fiber and para-aramid fiber are fibrillated, cut and masticated into an irregularly shaped fibrillated fibrous structure with stark and fibrils, and (2) the refined slurry is Co-purifying the slurry by dispersing all solids to be substantially uniform;
(D) removing water from the purified slurry to make water 60% by weight or less,
Thereby producing acrylic and para-aramid pulps with acrylic and para-aramid fibrous structures having an average maximum dimension of 5 mm or less, a length-weighted average of 1.3 mm or less, and acrylic fibrils and / or starches A process for producing acrylic and para-aramid pulps for use as reinforcement, substantially entangled with para-aramid fibrils and / or stark. (A) water,
(1) Acrylic fiber comprising acrylonitrile units, wherein the acrylonitrile unit is contained in at least 85% by weight of the total acrylic fiber and is 10 to 90% by weight of the total solid content in the pulp, and (2) Pulp Combining raw materials comprising a first fiber selected from the group consisting of para-aramid fibers that are 10-90% by weight of the total solid content therein;
(B) mixing the combined ingredients into a substantially uniform suspension;
(C) purifying the suspension with a disc refiner, cutting the fibers to have an average length of 10 cm or less, and fibrillating and masticating at least some of the fibers to form irregular shapes A process of making a fibrillated fibrous structure of
(D) a purified suspension, a second fiber that is not selected as the first fiber in groups (1) and (2) in (a) having an average length of 10 cm or less, and if necessary, Combining the raw materials containing water to increase the water concentration to 95-99% by weight of the total raw materials
(E) if necessary, mixing the raw materials to form a substantially uniform suspension;
(D) Simultaneously (1) Suspension so that all or substantially all of the acrylic and para-aramid fibers are converted to irregularly shaped fibrillated acrylic and para-aramid fibrous structures with starks and fibrils. Fibrillating, cutting and masticating solids in the liquid; and (2) co-purifying the mixed suspension by dispersing the total solids so that the purified slurry is substantially uniform;
(H) removing water from the refined slurry to make water 60% by weight or less,
Thereby producing acrylic and para-aramid pulps with acrylic and para-aramid fibrous structures having an average maximum dimension of 5 mm or less, a length-weighted average of 1.3 mm or less, and acrylic fibrils and / or starches A process for producing acrylic and para-aramid pulps for use as reinforcement, substantially entangled with para-aramid fibrils and / or stark. Acrylic and para-aramid pulp produced by the production method according to claim 1 or 2,
(A) An irregularly shaped acrylic fibrous structure comprising acrylonitrile units, wherein the acrylonitrile units are included in at least 85% by weight of the total acrylic fibrous structure, and the total solid content is 10 to 90% by weight. Structure,
(B) an irregularly shaped para-aramid fibrous structure that is 10 to 90% by weight of the total solids, and (c) water that is 4 to 60% by weight of the total pulp,
Thereby acrylic and para-aramid fibrous structures have an average maximum dimension of 5 mm or less, a length weighted average of 1.3 mm or less, and stark and fibrils, where the acrylic fibrils and / or stark are para-aramids Substantially entangled with fibrils and / or starks,
Acrylic and para-aramid pulp for use as reinforcement. Friction modifier,
A friction material comprising a binder, and a fibrous reinforcing material comprising the pulp according to claim 3. A sealing material comprising a binder, and a fibrous reinforcing material comprising the pulp according to claim 3.