KR20080092979A - Acrylic and para-aramid pulp and processes making same - Google Patents

Abstract

The present invention relates to acrylic and para-aramid pulp for use as reinforcement material in products such as seals and friction materials. The pulp comprises (a) irregularly shaped, acrylic fibrous structures, (b) irregularly shaped, para-aramid fibrous structures, and (c) water, whereby acrylic fibrils and/or stalks are substantially entangled with para-aramid fibrils and/or stalks. The invention further relates to processes for making such acrylic and aramid pulp.

Description

Acrylic and para-aramid pulp and its manufacturing method {ACRYLIC AND PARA-ARAMID PULP AND PROCESSES MAKING SAME}

The present invention relates to acrylic and para-aramid pulp for use as reinforcement in products such as seals and friction materials. The invention further relates to a process for producing said 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 traditionally been used as reinforcements, but alternatives have been made or proposed due to health risks. However, many alternatives do not perform as well as asbestos in various ways.

Research publications 74-75, published in February 1980, disclose the use of the pulp as a reinforcement in the manufacture of pulp made from fibrillated Kevlar brand para-aramid fibers of various lengths and in various applications. do. The publication discloses that pulp made from Kevlar brand para-aramid fibers alone or in other materials, such as fibers of NOMEX® brand meta-aramid, wood pulp, cotton and other natural cellulose, rayon, Disclosed can be used in sheet products in combination with polyesters, polyolefins, nylons, polytetrafluoroethylene, asbestos and other minerals, glass fibers and other fibers, ceramics, steel and other metals, and carbon. The publication also discloses the use of pulp made of Kevlar brand para-aramid fibers alone or in combination with Kevlar brand para-aramid short fibers in friction material to replace a portion of the asbestos volume, the remainder of the asbestos volume being filled with filler or Replaced with another fiber.

US Pat. No. 5,811,042 (Hoiness) discloses a composite friction material or gasket material made of thermoset or thermoplastic matrix resin, fiber reinforcement, and substantially fibrillated aramid particles. Poly (p-phenylene terephthalamide) and poly (m-phenylene isophthalamide) are preferred fiber reinforcements, and the fibers may be in the form of flocs or pulp.

U.S. Patent Application 2003/0022961 (Kusaka et al.) Discloses a friction material made of a friction modifier, a binder and a fibrous reinforcement made from a mixture of (a) dry aramid pulp and (b) wet aramid pulp, wood pulp or acrylic pulp. It starts. Dry aramid pulp is defined as aramid pulp obtained by the "dry fibrillation process". The dry fibrillation method produces pulp by dry milling aramid fibers between a rotary cutter and a screen. Wet aramid pulp is defined as aramid pulp obtained by the "wet fibrillation process". The wet fibrillation method mills short aramid fibers in water between two rotating disks to form fibrillated fibers and then dehydrates the fibrillated fibers, ie pulp. Kusaka et al. Further disclose a fiber mixed-fibrillation process in which a plurality of types of organic fibers fibrillated in a defined ratio are first mixed and then the mixture is fibrillated to produce pulp.

In products such as seal and friction applications, there is a need to provide a superior and low cost alternative reinforcement. Despite the numerous disclosures suggesting cheaper alternative reinforcements, many of the proposed products do not perform adequately in use or have much more expensive or other negative attributes than current commercial products. Thus, there is still a need for a reinforcement that exhibits high wear resistance and heat resistance and is below the price of other commercial reinforcements.

The present invention

(a) (1) acrylic fibers comprising acrylonitrile units of at least 85% by weight of the total acrylic fibers and having from 10 to 90% by weight of the total solids in the components and having an average length of 10 cm or less;

(2) para-aramid fibers having from 10 to 90% by weight of total solids in the component and having an average length of 10 cm or less; And

(3) 95 to 99% by weight of the total components of water

Combining the pulp components comprising;

(b) mixing the components into a substantially homogeneous slurry;

(c) simultaneously (1) fibrillating, cutting and musticating acrylic fibers and para-aramid fibers into irregularly shaped fibrillated fibrous structures with stalk and fibrils;

(2) substantially homogeneously disperse all solids in the refined slurry

Co-refining the slurry;

(d) water is removed from the refined slurry up to a total of 60% by weight of water,

Acrylic and para-arabic fibrous structures having an average maximum dimension of 5 mm or less and a length weighted average of 1.3 mm or less and acrylic fibrils and / or stocks substantially entangled with para-aramid fibrils and / or stocks Preparing aramid pulp

A first embodiment of a process for producing acrylic and para-aramid pulp for use as a reinforcement comprising a.

The present invention further

(a) water and

(1) acrylic fibers comprising at least 85% by weight of acrylonitrile units of the total acrylic fibers and from 10 to 90% by weight of the total solids in the components; And

(2) para-aramid fiber, which is 10 to 90% by weight of total solids in the component

First fiber selected from the group consisting of

Combining the components comprising a;

(b) mixing the components into a substantially homogeneous suspension;

(c) refining the suspension in a disk refiner to cut the fibers to have an average length of 10 cm or less and to fibrillate and masticate at least some of the fibers into an irregularly shaped fibrillated fibrous structure;

(d) combining the refined suspension, (a) the second fiber of groups (1 and 2) and, if necessary, water to increase the water concentration in the total component to 95 to 99% by weight;

(e) mixing the ingredients as necessary to form a substantially homogeneous suspension;

(f) (1) fibrillating, cutting and masticating solids in suspension to convert all or substantially all acrylic and para-aramid fibers into irregularly shaped fibrillated fibrous structures with stocks and fibrils;

(2) substantially homogeneously disperse all solids in the refined slurry

Co-refining the mixed suspension; And

(g) water is removed from the refined slurry up to a total of 60% by weight of water,

Acrylic and para-arabic fibrous structures having an average maximum dimension of 5 mm or less and a length weighted average of 1.3 mm or less and acrylic fibrils and / or stocks substantially entangled with para-aramid fibrils and / or stocks Preparing aramid pulp

A second embodiment of a process for producing acrylic and para-aramid pulp for use as a reinforcement comprising a.

The present invention further

(a) an irregularly shaped acrylic fibrous structure comprising at least 85% by weight of acrylonitrile units of the total acrylic fibrous structure and from 10 to 90% by weight of the total solids;

(b) irregularly shaped para-aramid fibrous structure of 10 to 90% by weight of total solids; And

(c) 4 to 60% by weight of the total pulp

Wherein the 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 acrylic fibrils and / or stocks substantially entangled with para-aramid fibrils and / or stocks And having fibrils

It relates to acrylic and para-aramid pulp for use as reinforcement.

The present invention further provides a friction modifier; Optionally at least one filler; Binders; And a fibrous reinforcement material comprising the pulp of the present invention.

In addition, the present invention is a binder; Optionally at least one filler; A sealant comprising a fibrous reinforcement comprising the pulp of the present invention.

Before describing the present invention, it is useful to define the following term definitions that will have the same meaning throughout the present disclosure unless a specific term is indicated otherwise.

"Fiber" means a unit of relatively flexible material with a high length to width ratio across the cross-sectional area perpendicular to the length. As used herein, the term "fiber" is used interchangeably with the terms "filament" or "end". The cross section of the filaments described herein may be of any shape, but is typically circular or bean shaped. Fibers spun into a package on bobbins are called continuous fibers. The fibers can be cut into short lengths called staple fibers. The fibers can be cut into shorter lengths called flocs. Yarns, multifilament yarns or tows comprise a plurality of fibers. Yarn can be entangled and / or entangled.

"Fibrils" means small fibers having a small diameter of less than one micrometer to several micrometers and a length of about 10 to 100 micrometers. Fibrils generally extend from the main trunk of larger fibers with a diameter of 4 to 50 micrometers. Fibrils act as hooks or fasteners to trap and capture adjacent materials. Some fibers are fibrillated, while others are not fibrillated or effectively fibrillated and in this case the fibers are not fibrillated. Poly (para-phenylene terephthalamide) fibers are readily fibrillated upon polishing to produce fibrils.

A “fibrillated fibrous structure” is a particle of a material having a stock and fibrils extending therefrom, wherein the stock is generally cylindrical and has a diameter of about 10 to 50 micrometers, and fibrils are 1 micrometer attached to the stock It is meant a hair-like component of diameters of a few or a few micrometers below and about 10 to 100 micrometers long.

"Flock" means shorter fibers than staple fibers. The floc has a length of about 0.5 to about 15 mm and a diameter of 4 to 50 micrometers, preferably a length of 1 to 12 mm and a diameter of 8 to 40 micrometers. Flock less than about 1 mm does not significantly affect the strength of the material in which it is to be used. Flocks or fibers larger than about 15 mm generally do not function because individual fibers can be entangled and cannot be appropriately and homogeneously dispersed throughout the material or slurry. Aramid flocs can be cut into short lengths of aramid fibers without significant or any fibrillation, such as, for example, by the methods described in US Pat. Nos. 3,063,966, 3,133,138, 3,767,756, and 3,869,430. Are manufactured.

"Length weighted average" means the length calculated from the following equation.

Length weighted average = Σ [(each individual pulp length) ² ] / Σ [each individual pulp length]

The "maximum dimension" of an object means the straight line distance between the farthest points in the object.

"Staple fibers" means filaments of up to 15 cm, preferably from 3 to 15 cm; And most preferably by cutting to a length of 3 to 8 cm. The staple fibers are straight (ie, non-crimped) or crimped to have serrated crimps along their length at any crimp (or repeat bend) frequency. The fibers may be present in uncoated or coated, or pretreated (eg, pre-stretched or heat-treated) form.

The present invention relates to a process for producing acrylic and para-aramid pulp for use as reinforcement. The invention also relates to acrylic and para-aramid pulp that can be prepared by the process of the invention for use as reinforcement. The present invention further relates to articles such as sealing materials and friction materials incorporating the pulp of the present invention and methods of making the same.

I. First Embodiment of the Method of the Invention

In a first embodiment, the process for preparing acrylic and para-aramid pulp comprises the following steps. First, the pulp components are combined, added or contacted with each other. Secondly, the combined pulp components are mixed into a substantially homogeneous slurry. Third, the slurry is simultaneously refined or co-refined. Fourth, water is removed from the refined slurry.

Step of sum

In the combining step, the pulp components are preferably added together into the vessel. The pulp component may comprise (1) acrylic fibers, (2) para-aramid fibers, (3) optionally substantially or completely fibril free, granular, para-aramid particles, (4) optionally other trace additives, and (5 ) Contains water.

Acrylic fiber

Acrylic fibers are added at a concentration of 10 to 90% by weight of the total solids in the components, preferably 25 to 60% by weight of the total solids in the components, and most preferably 25 to 55% by weight of the total solids in the components.

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. Prior to combining the pulp components with each other, any acrylic fibers in the form of continuous filaments can be cut into shorter fibers, such as staple fibers or flocs.

Acrylic polymer

Acrylic fibers useful in the present invention include acrylonitrile units that are at least 85% by weight of the total acrylic fibers. The acrylonitrile unit is-(CH ₂ -CHCN)-. Acrylic fibers may be prepared from acrylic polymers made from at least 85% by weight of acrylonitrile and 15% by weight or less of ethylene-based monomers copolymerizable with acrylonitrile and mixtures of two or more of the acrylic polymers. Examples of ethylenic monomers copolymerizable with acrylonitrile include acrylic acid, methacrylic acid and esters thereof (methyl acrylate, ethyl acrylate, methyl methacrylate, ethyl methacrylate, etc.), vinyl acetate, vinyl chloride, vinylidene chloride , Acrylamide, methacrylamide, methacrylonitrile, allylsulfonic acid, methanesulfonic acid and styrenesulfonic acid.

Para- Aramid  fiber

Para-aramid fibers are added at a concentration of 10 to 90% by weight of the total solids in the components, preferably 40 to 75% by weight of the total solids in the components, and most preferably 40 to 55% by weight of the total solids in the components. . Para-aramid fibers preferably have a line density of 10 dtex or less, more preferably 0.5 to 10 dtex, and most preferably 0.8 to 2.5 dtex. Para-aramid fibers also have an average length of less than 10 cm, more preferably 0.65 to 2.5 cm, and most preferably 0.65 to 1.25 cm along their longitudinal axis.

Para- Aramid  particle

Optionally, in one embodiment, the pulp component further comprises substantially or completely fibril free, granular, para-aramid particles. When the particles are added, they are at a concentration of up to 50% by weight of the total solids in the components, preferably from 20 to 50% by weight of the total solids in the components, and most preferably from 25 to 35% by weight of the total solids in the components. Is added. When made from para-aramid, they contribute to better wear resistance and dispersibility of the pulp to be produced. Since the particles are substantially fibrill free, they also act as compounding agents to assist in the dispersion of other components in the mixture and slurry. Particles that perform this function are often known as processing agents or preparations. Substantially or completely fibril-free, granular, para-aramid particles may have a diameter of 50 to 2000 micrometers (0.05 to 2 mm), preferably 50 to 1500 micrometers, and most preferably 75 to 1000 micrometers. Have an average maximum dimension. However, particles up to about 50 micrometers lose efficiency in friction and sealing products. Particles larger than about 2000 micrometers do not disperse properly in other components and water when mixed. 5 is a microscopic image of para-aramid particles that may be used as a component in the method of the present invention.

Aramid  polymer

Suitable polymers for use in making the aramid fibers and aramid particles of the present invention are synthetic aromatic polyamides. The polymer must be fiber-forming molecular weight to be shaped into fibers. The polymer may comprise polyamide homopolymers, copolymers, and mixtures thereof, which are mainly aromatic and at least 85% of the amide (-CONH-) bonds are directly attached to the two aromatic rings. The ring may be unsubstituted or substituted. The polymer is para-aramid when the two rings are para-oriented relative to one another along the molecular chain. Preferably the copolymer has up to 10% of other diamines in place of the primary diamine used to form the polymer or up to 10% of other dichloride chlorides instead of the primary dichloride used to form the polymer. Additives can be used with aramids; It has been found that up to 13% by weight of other polymeric materials can be blended or combined with aramid. Preferred para-aramids are poly (para-phenylene terephthalamide) (PPD-T) and copolymers thereof.

Any other additives

Other additives may optionally be added as long as the additive is suspended in solution in the mixing step and does not significantly change the effect of the refining step on the essential solid components listed above. Suitable additives include pigments, dyes, antioxidants, flame retardant compounds, and other processing and dispersing aids. The pulp component preferably does not include asbestos. In other words, the resulting pulp is asbestos-free.

water

Water is added at a concentration of 95 to 99% by weight of the total component, and preferably 97 to 99% by weight of the total component. In addition, water may be added initially. The other ingredients can then be added at a rate that optimizes dispersion in water while simultaneously mixing the combined ingredients.

Mixing step

In the mixing step, the components are mixed into a substantially homogeneous slurry. "Substantially homogeneous" means that the random slurry samples contain each starting component at a concentration by weight equal to the total component ± 10% by weight, preferably ± 5% by weight and most preferably ± 2% by weight in the step of combining do. For example, if the concentration of solids in the total mixture is 50% by weight acrylic fiber + 50% by weight para-aramid fiber, the substantially homogeneous mixture in the mixing step is a random slurry sample of (1) 50% by weight ± 10% by weight acrylic fiber. At a concentration of preferably ± 5% by weight and most preferably ± 2% by weight and (2) 50% by weight of para-aramid fibers ± 10% by weight, preferably ± 5% by weight and most preferably ± 2% by weight. It means having a concentration of%. Mixing can be performed in a vessel equipped with a rotary blade or some other stirrer. Mixing may proceed after the ingredients are added, or while the ingredients are being mixed or combined.

Refining stage

In the refining step, the pulp component 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 stocks and fibrils. If para-aramid particles are added together with the other components, at least some of the para-aramid particles are masticated into smaller, more circular substantially fibril-free particles. All solids are dispersed such that the refined slurry is substantially homogeneous. "Substantially homogeneous" is as defined above. The refining step preferably involves passing the mixed slurry through one or more disk refiners or recycling the slurry through a single refiner. The term "disk refiner" means a refiner that contains one or more disk pairs that rotate about each other to refine the component by shear action between the disks. In one suitable type of disc refiner, the slurries to be refined are pumped between closely spaced circular rotors and stator discs that are rotatable relative to one another. Each disk has a surface facing another disk, with at least partially radially extending surface grooves. Preferred disc refiners that can be used are disclosed in US Pat. No. 4,472,241. If homogeneous dispersion and proper refining are required, the mixed slurry may be passed through the disc refiner one or more times or in a series of two or more disc refiners. If the mixed slurry is refined in only one refiner, the resulting slurry tends to be improperly refined and heterogeneously dispersed. Rather than being dispersed to form a substantially homogeneous dispersion, a total or substantially one solid component or other component, or both, or in the presence of a three component, may form a three component conglomerate or aggregate. If the mixed slurry passes through the refinery one or more times or through the one or more refiners, the mass or aggregate is more likely to break up and disperse in the slurry.

Since a substantially homogeneous slurry containing multiple components is co-refined in this process step, any one type of non-pulp component (eg para-aramid fiber) may be used for all other types of non-pulp components (eg For example, in the presence of aramid piece of material and optionally para-aramid particles) it is refined in the pulp and other components are also refined. The co-refining of the non-pulp component merely mixes the two pulp to form a pulp superior to the resulting pulp blend. Adding only two pulp and then mixing them does not form a substantially homogeneous, intimately connected fibrous component of the pulp produced by co-refining the non-pulp component in the pulp according to the present invention.

Removal steps

The water is then removed from the slurry refined to up to 60% by weight in total, preferably 4 to 60% by weight in total and most preferably 5 to 58% by weight in total. The water may be removed by collecting pulp on a dewatering device, for example a horizontal filter, and additional water may be removed if necessary by applying pressure or pressing the pulp filter cake. The dewatered pulp may then be dried and / or wrapped or rolled to a desired moisture content.

1 and 2

The method is now described with reference to FIGS. 1 and 2. Like numbers refer to like elements throughout the drawings.

1 shows a block diagram of one embodiment of a wet process for producing “wet” pulp in accordance with the present invention. The pulp component 1 is added to the vessel 2. The container 2 is equipped with an internal mixer similar to the mixer in the washing machine. The mixer disperses the components in water to produce a substantially homogeneous slurry. The mixed slurry is passed to the first refiner 3 to refine the slurry. Then, optionally, the refined slurry is transferred to the second refiner 4 and then optionally to the third refiner 5. Although three refiners are illustrated, any number of refiners can be used depending on the degree of homogenization and degree of refinement desired. After the last refiner in the series of refiners, the refined slurry passes through a slurry with solids dispersed arbitrarily below the selected mesh or screen size and the dispersed solids exceeding the selected mesh or screen size are at least one refiner, e.g. For example, it is passed to a filter or sorter 6 for recycling to line 7 or a dedicated refiner 8 for refining the recycled slurry, from which the refined slurry passes back through a filter or sorter 6. The suitably refined slurry is passed through a horizontal water vacuum filter 9 which removes water from the filter or fractionator 6 such that the pulp has a water concentration of 75% by weight or less of the total components. The slurry can be delivered from one point to another by any conventional method and apparatus, such as one or more pumps 10. The pulp is then sent to a dryer 11 which further removes water until the pulp has a water concentration of up to 60% by weight of the total components. The refined pulp is then packaged in a baler 12.

2 shows a block diagram of one embodiment of a dry process for producing “dry” pulp in accordance with the present invention. The dry process is the same as the wet process except after the horizontal water vacuum filter 9. After the filter, the pulp is passed through a press 13 which further removes water until the pulp has a water concentration of 20% by weight or less of the total components. The pulp is then passed through the fluff 14 to inflate the pulp and then through the rotor 15 to further remove water. Then, like the wet process, the pulp is passed through a dryer 11 and packed in a baler 12.

II. Second Embodiment of the Method of the Invention

In a second embodiment, the process for producing acrylic fibers and para-aramid pulp is similar to the first embodiment described above except for the following differences.

Before combining all the components together, either acrylic fibers or para-aramid fibers, or both acrylic fibers and para-aramid fibers need to be shortened. This is done by combining water with the fiber component. Water and fibers are then mixed to form a first suspension and processed through a first disk refiner to shorten the fibers. Disk refiners cut the fibers to an average length of 10 cm or less. Disk refiners also partially fibrillate and partially chew the fibers. Other fibers not added in advance are shortened in this manner to form a second treatment suspension. The other fiber (or second suspension when treated in water) is then combined with the first suspension.

If necessary, additional water is added before, after or during the addition of other ingredients to increase the water concentration to a concentration of 95 to 99% by weight of the total ingredients. After all the components have been combined, they can be mixed if necessary to achieve a substantially homogeneous slurry.

The components in the slurry are then co-refined together, ie simultaneously. The refining step fibrillates, cuts and masticates the solids in the suspension so that all or substantially all of the acrylic and para-aramid fibers are converted into irregularly shaped fibrillated fibrous structures. The refining step also disperses all solids such that the refined slurry is substantially homogeneous. The water is then removed as in the first embodiment of the process. All of the above methods produce identical or substantially identical acrylic and para-aramid pulp.

Pulp of the Invention

The products produced by the process of the invention are acrylic and para-aramid pulp for use as reinforcements in the product. The pulp may comprise (a) irregularly shaped acrylic fibrous structures, (b) irregularly shaped para-aramid fibrous structures, (c) optionally substantially fibrillated, granular, para-aramid particles, and (d) optionally other small amounts of additives. And (e) water. The concentration of each component in the pulp, of course, corresponds to the concentration previously described for the corresponding component used to make the pulp.

Irregular shapes, acrylic and para-aramid fibrillated fibrous structures have stocks and fibrils. Acrylic fibrils and / or stocks are substantially entangled with para-aramid fibrils and / or stocks. Fibrils are important and act as hooks or fasteners or tentacles that attach and secure to adjacent particles in the pulp and final product to provide completeness to the final product.

The 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 structures preferably have 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 also further contact and partially wrap around at least some of the more circular substantially fibril-free, para-aramid particles. The para-aramid particles also preferably have an average maximum dimension of at least 50 micrometers, more preferably 50 to 100 micrometers, and most preferably 50 to 75 micrometers. Fibrils on acrylic and para-aramid fibrous structures can contact and form partial cocoons around the more circular substantially fibrill free, para-aramid particles.

Acrylic and para-aramid pulp are free of substantial aggregates or lumps of the same material. In addition, the pulp has a Canadian standard freeness (CSF) of 100 to 700 ml, and preferably 250 to 450 ml, measured according to TAPPI test T 227 om-92, which is a measure of drainage properties.

The surface area of the pulp is a measure of the degree of fibrillation that affects the porosity of products made from the pulp. The surface area of the pulp of the present invention is preferably 7 to 11 m ² / g.

4 is a microscopic image of acrylic and para-aramid pulp prepared according to the method of the present invention.

It is believed that the aramid particles and the fibrous structure substantially homogeneously dispersed throughout the reinforcement and friction material and sealant provide a number of reinforcement sites and increased wear resistance due to the high temperature properties of the para-aramid polymer and the tendency of fibrillation of the para-aramid fibers. . When co-refined, the blending of acrylic and para-aramid materials is so intimate that there is always some para-aramid fibrous structure close to the acrylic structure in the friction material or sealant, so that service stress and polishing are always shared.

Sealant

The present invention further relates to a sealant and a method for producing the sealant. The sealant is used as a barrier to prevent the release of fluids and / or gases and to prevent the ingress of impurities where the two articles are connected to each other. An exemplary use of the sealant is a gasket. The sealant is a binder; Optionally at least one filler; And fibrous reinforcements comprising the acrylic and para-aramid pulp 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 stage where the dry ingredients are mixed together during the gasket making process. Other components optionally include uncured rubber particles and a rubber solvent, or a solution of rubber in the solvent to allow the binder to coat the surface of the filler and pulp. Suitable fillers include barium sulfate, clays, talc and mixtures thereof.

Suitable processes for producing the sealant are, for example, a beater-adding process or a wet process in which a gasket is made from a slurry of material, or a process or component called calendering, in which an elastomer or rubber solution is combined in an elastomeric or rubber solution.

Friction material

The pulp of the present invention can be used as a reinforcement in friction materials. By “friction material” is meant a material used for its friction properties, for example, the coefficient of friction to stop or transmit kinetic energy, stability at high temperatures, wear resistance, noise and vibration damping properties, and the like. Exemplary uses of friction materials include brake pads, brake blocks, dry clutch facings, clutch face segments, brake pad backing / insulating layers, automotive transmission paper, and friction paper.

In view of the new use, the present invention further relates to a friction material and a method for producing the friction material. Specifically, the friction material includes a friction modifier; Optionally at least one filler; Binders; And fibrous reinforcements comprising the acrylic and para-aramid pulp of the present invention. Suitable friction modifiers include metal powders such as iron, copper and zinc; Abrasives such as oxides of magnesium and aluminum; Lubricants such as synthetic and natural graphite, and sulfides of molybdenum and zirconium; And organic friction modifiers such as synthetic rubber and cashew nut shell 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. Suitable fillers include barite, calcium carbonate, wollastonite, talc, various clays, and mixtures thereof.

The actual steps for producing the friction material may vary depending on the type of friction material desired. For example, methods of making molded friction parts generally include combining the desired components in a mold, curing the parts, and shaping, heat treating, and grinding the parts, if desired. Automotive transmission papers and friction papers can generally be made by combining the desired components in a slurry and making paper in a paper machine using conventional papermaking processes.

Test Methods

The following test method was used in the following examples.

Canadian Standard Filtration (CSF) is a well known measure of drainage of water from slurry or dispersion of particles. Freeness was measured by TAPPI test 1221. Data obtained from the performance of the test is expressed in Canadian Standard Freedom, which represents millimeters of water drained from the aqueous slurry under certain conditions. Larger value means higher drainage and water drainage. Small values indicate a slow drainage of the dispersion. The greater number of fibrils reduces the rate of water draining through the forming paper mat, so the degree of fibrillation of the freeness and pulp is inversely proportional.

The length weighted average was measured using a "FiberExpert" tabletop analyzer (also known as "PulpExpertFS" available from Metoso Automation, Helsinki, Finland). The analyzer takes a photographic image of the pulp with a digital CCD camera as the pulp slurry passes through the analyzer and then an integrated computer analyzes the fibers in the image to calculate its length weighted average.

Temperature: All temperatures were measured in degrees Celsius (° C.).

Denier is the linear density of a fiber, measured according to ASTM D 1577 and expressed in weight (grams) for 9000 meters of fiber. Denier was measured on a vibroscope from Textechno, Munnich, Germany. 10/9 times denier is equal to dtex.

The invention is illustrated by the following specific examples. All parts and percentages are by weight unless otherwise indicated. Examples prepared according to the method of the invention are indicated by numerical values.

Example  One

In this embodiment of the present invention, the pulp of the present invention was prepared from a feed of para-aramid fiber and acrylic staples. Acrylic staples with a cut length of 2 inches and a filament line density of 3 dpf (3.3 dtex per filament) were obtained from Solutia, Inc. with offices in St. Louis, Missouri. Commercial Kevlar brand flocs with a 1/4 "cut length, style 1F178, para-aramid fibers are available from EI de Pont de Nemours and Company with offices in Wilmington, Delaware. Obtained from.

Acrylic staples and water are fed directly to a Sprout-Waldron 12 "single disk refiner using a 10 mil plate gap setting to pre-pulp to reach an acceptable treatment length in the 13 mm range It was.

The pre-pulped acrylic fibers and chopped para-aramid fibers and water are then combined and mixed in a strongly stirred mixing tank at a solids concentration of 50% by weight of para-aramid fibers and 50% by weight of acrylic staples and mixed to a total component concentration of about 2-3 A weight percent pumpable homogeneous slurry was formed. The slurry was then recycled and co-refined through a Sprout-Baldron 12 "single disk refiner.

Refiner at the same time:

(1) fibrillated, cut and masticated para-aramid fibers and acrylic staples into irregularly shaped fibrous structures with stocks and fibrils,

(2) Disperse all solids so that the refined slurry is substantially homogeneous as previously defined.

The refined slurry was then filtered using a filter bag, dewatered through a compressor and placed in a large-capacity ZIPLOC type storage bag. The fibrous structure has an average maximum dimension of 5 mm or less and a length weighted average of 1.3 mm or less, as measured by fiberexpert.

Example  2

This example illustrates another method by which co-refined pulp can be prepared from a feed of para-aramid fibers and acrylic fibers. Most fibers are available from Solutia, Inc. to make random-length fibers shorter than 3/4 inch (1.91 cm) and having an average length of about 1/2 inch (1.27 cm). Acrylic staples with a cut length of 2 inches and a filament line density of 3 dpf (3.3 dtex per filament) were cut at right angles with a guillotine cutter 2-3 times.

Para-aramid yarns were cut to a nominal 1/2 inch (1.27 cm) cutting length on a Lumus cutter (available from Lumus Industries with offices in Columbus, GA). children. Para-aramid fibers were prepared in the form of Kevlar brand multifilament yarns on commercial bobbins available from Dupont Di Nemoa & Company. In order to produce random-length fibers where most fibers are much shorter than 3/4 inch (1.91 cm) and have an average length of about 1/2 inch (1.27 cm), other Kevlars of varying length are not initially present on the bobbin. Brand para-aramid fibers were cut 2-3 times at right angles using a guillotine cutter.

The two components and water prepared as described above are then combined and mixed in a mixing tank called hydrapulper which is strongly stirred to a solid concentration of 50% by weight of para-aramid fiber and 50% by weight of acrylic staples. A pumpable homogeneous slurry was formed having a total solids concentration of about 2 to 3 weight percent of. As described in US Pat. No. 4,472,241, the slurry was pumped into a series of three refiners.

Refiner at the same time:

(1) fibrillated, cut and masticated para-aramid fibers and acrylic staples into irregularly shaped fibrous structures with stocks and fibrils,

(2) Disperse all solids so that the refined slurry is substantially homogeneous as previously defined.

The refined slurry was then dewatered using a horizontal filter and dried in an oven at a total of 50 wt% of the desired moisture content for the wet pulp. The wet pulp was then packaged into bales by a baler. When measured by fiberexpert, all components in the pulp have a length weighted average of 1.3 mm or less.

Example  3

This example illustrates further processing steps and other embodiments of the pulp of the present invention. The procedure of Example 2 is performed. However, after the pulp is dehydrated on a horizontal filter, the pulp is compressed with a mechanical press to further remove water; The pulp was then inflated using a flopper (available from Bepex Corporationn with office in Santa Rosa, Calif.) To better separate the compressed wet pulp. The swollen wet pulp was then dried in an oven with a total of about 8 wt. Further pulp to further swell and disperse the dried pulp. The dried pulp was then packaged into bales. When measured by fiberexpert, all components in the pulp had a length weighted average of 1.3 mm or less.

Example  4

This example illustrates another embodiment of the pulp of the present invention. The process of Example 2 is carried out except that 1/3 of the para-aramid fiber weight is replaced with para-aramid particles. Para-aramid resin particles were prepared by continuously reacting para-phenylenediamine and tetraphthaloyl chloride in a screw extruder, generally disclosed in US Pat. No. 3,884,881, and from the solvent using N-methyl pyrrolidone / calcium chloride as solvent. A precipitated powdery polymer was produced. The solvent was extracted and the polymer powder was washed and dried to give a particulate powder of mixed particle size. Subsequently, the para-aramid resin particles were treated substantially the same as those treated with the para-aramid fibers in Example 2. However, the refiner not only refines the fibers but also cuts and / or masticates the para-aramid particles into more circular, substantially fibrillated particles. After dehydration, a portion of the resulting pulp having a total water content of 50% by weight was packed with bales. The remainder of the resulting pulp was further compressed to a total water content of about 8% by weight, then inflated, dispersed and packaged as in Example 3. When measured by fiberexpert, all components in the pulp had a length weighted average of 1.3 mm or less.

Example  5

A disc brake pad incorporating the pulp of the present invention was prepared in the following manner. About 20 kilograms of asbestos-free base compound powder comprising a mixture of 7 wt% cashew nut cell resin, 17 wt% inorganic filler, 21 wt% graphite, coke and lubricant, 18 wt% inorganic abrasive, and 16 wt% soft metal Were mixed together for 10-20 minutes in a 50-liter Littleford mixer. The mixer has two high speed choppers with "star and rod" shaped blades and a slower rotating plow.

Five kilograms of the well-blended base compound powder were then co-refined in an amount of 3.8% by weight based on the combined weight of the compound powder and pulp of the inventive pulp (50% by weight of para-aramid and 50% by weight of acrylic fiber). Pulp). The pulp was then dispersed in the base compound by mixing for an additional 5-10 minutes. After mixing, the resulting brake pad composition had a common appearance that the fibers were well dispersed and completely coated with the base compound powder and substantially no separation of any component or balling up of the pulp was virtually detectable.

The brake pad composition is then poured into a single-cavity steel mold for the front disc brake pad, cold pressed to a standard thickness of about 5/8 inch (16 mm) and then removed from the mold to form a pre-formed brake having a weight of about 200 grams. Pads were formed. The preform was free of excessive spring-back or swelling and was strong enough to withstand normal handling without damage. Twelve replicates were made. The pre-form was then placed in two multi-cavity molds, placed in a commercial press with periodic release of pressure to release the phenolic reaction gas, and press-cured (phenolic binder at 300 ° F. (149 ° C.) for about 15 minutes. Crosslinking and reaction) and then cured at 340 ° F. (171 ° C.) for 4 hours in a lightly compressed oven to complete phenolic binder crosslinking. The cured molding pad was then polished to the desired thickness of about 1/2 inch (13 mm). When compared visually with conventional brake pads containing the same amount of para-aramid pulp or 100% acrylic pulp, the test pads were indistinguishable and there was good flowability of the compound with backing plate holes and no edge chipping.

A sample of the brake pad incorporating the pulp of the present invention was then tested to determine its frictional performance. A 1 inch by 1 inch coupon, typically about 3/16 inch (5 mm) thick, from the test pad was used with a test protocol from the Society of Automotive Engineers (SAE) J661 to link engineering (Detroit, MI). Evaluated on a Chase Machine available from Link Engineering, the hot and cold coefficients of friction were measured during the constant pressure and controlled temperature drag tests on the heated steel drum. Samples were measured periodically for wear (thickness reduction). This was repeated for at least two test samples cut from different replicate pads. Samples of brake pads incorporating the pulp of the present invention exhibited substantially the same high and low temperature friction performance as commercial pads containing substantially the same amount of para-aramid pulp 100%. The test further showed pad-to-pad homogeneity and the average friction rating was substantially the same.

 Various braking using a dynamometer using test protocol J2681 (IS0-SWG4) (a single piston dynamometer with a 289.0 mm rolling radius from Link Testing Laboratories, Inc., Detroit, Mich.) The pads were tested for friction and wear under conditions. The test consists of 17 scenarios for 5 to 200 brake applications each and measures the coefficient of friction as a function of applied brake pressure, temperature, braking speed and deceleration speed. The test also has two temperature fade sections, during which the brake pads receive higher and higher initial temperatures during constant deceleration and reach temperatures above 600 ° C. At the end of the test, the wear was measured as a decrease in the thickness and weight of the pad (608 brake applications). The results of the pads made with the compounds of this example showed very little fade and the fade was well recovered (fade was defined as loss of friction in the hottest brake applications), no pad surface cracking and acceptable in non-fade sections It had a coefficient of friction of 0.25 to 0.4 and had an acceptable wear rate for the pad and the rotor.

Example  6

This example illustrates how the pulp of the present invention may be incorporated into a sealing beater-part gasket. Water, rubber, latex, fillers, chemicals, and pulp of the present invention are combined in desired amounts to form a slurry. On a circulating wire sieve (for example a paper machine screen or wire), most of the water in the slurry was drained, dried in a heating tunnel and vulcanized on a heated calender roll to form a material having a maximum thickness of about 2.0 mm. . The material was compressed by hydraulic or two-roll calender to increase density and improve sealability.

The beater-added gasket material generally does not have as good a seal as an equivalent compressed-fiber material and is best suited for mild-pressure high temperature applications. The beater-added gasket can be applied to the auxiliary engine gasket, or to the cylinder head gasket after further processing. For this purpose, the semifinished product is laminated on both sides of the spiked metal sheet and physically held in place by the spikes.

Example  7

This embodiment illustrates how the pulp of the present invention can be incorporated into a gasket made by a calendering process. Except for water, the same ingredients as in Example 6 were thoroughly mixed together and then blended with a rubber solution prepared using a suitable solvent.

After mixing, the compounds were generally transported in batches on a roll calender. The calendar consists of a small roll to be cooled and a large roll to be heated. The compound is fed and enters the calender nip by the rotational movement of the two rolls. The compound was attached to and wrapped around the hot lower roll in a layer generally about 0.02 mm thick, depending on the pressure, to form a gasket material made from the constituent compound layer. The solvent was then evaporated and the vulcanization of the elastomer started.

Once the desired gasket material thickness is reached, the roll is stopped and the gasket material is cut from the hot roll and / or punched to the desired size. No additional pressure or heating is required and the material can be used as a gasket. In this way gaskets of thickness up to about 7 mm can be produced. However, most gaskets produced in this manner are much thinner, typically up to about 3 mm thick.

1 is a block diagram of an apparatus for performing a wet process for producing “wet” pulp in accordance with the present invention.

2 is a block diagram of an apparatus for performing a dry process for producing “dry” pulp in accordance with the present invention.

3 is a microscopic image of para-aramid particles to be used as optional components in the method of the present invention.

4 is a microscopic image of pulp prepared according to the method of the present invention.

Claims (9)

(a) an irregularly shaped fibrillated acrylic fibrous structure comprising at least 85% by weight of acrylonitrile units of the total acrylic fibrous structure and from 10 to 90% by weight of the total solids; (b) irregularly shaped fibrillated para-aramid fibrous structure of 10 to 90% by weight of total solids; And (c) 4 to 60% by weight of the total pulp Wherein the acrylic and para-aramid fibrous structures have an average maximum dimension of 5 mm or less and a length weighted average of 1.3 mm or less, acrylic fibrils, acrylic stocks, or acrylic fibrils and stocks of para-aramid fibrils, Having para-aramid stock, or para-aramid fibrils and stock and fibrils entangled with the stock, Acrylic and para-aramid pulp for use as reinforcement. The pulp of claim 1 further comprising up to 50% by weight of fibril-free, granular, para-aramid particles up to 50% by total solids. The pulp of claim 1 wherein the irregularly shaped fibrillated acrylic fibrous structure is 25 to 60% by weight of the total solids. The pulp of claim 1 wherein the irregularly shaped fibrillated para-aramid fibrous structure is between 40 and 75 weight percent of total solids. The pulp of claim 1 wherein the water is 4 to 60% by weight of the total pulp and has a Canadian standard freeness (CSF) of 100 to 700 ml. Friction modifiers; Binders; And Fibrous reinforcement comprising the pulp of claim 1 Friction material comprising a. The method of claim 6, The friction modifier is selected from the group consisting of metal powders, abrasives, lubricants, organic friction modifiers, and mixtures thereof; The binder is a friction material selected from the group consisting of thermosetting resins, melamine resins, epoxy resins and polyimide resins, and mixtures thereof. Binders; And Fibrous reinforcement comprising the pulp of claim 1 Sealing material comprising a. 9. The sealant of claim 8, wherein the binder is selected from the group consisting of nitrile rubber, butadiene rubber, neoprene, styrene butadiene rubber, nitrile-butadiene rubber, and mixtures thereof.

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