KR100895185B1 - Cellulosic and para-aramid pulp and processes making same - Google Patents

Abstract

The present invention relates to cellulose and para-aramid pulp for use as reinforcement in products such as seals and friction materials. The pulp may comprise (a) an irregularly shaped cellulose fibrous structure in which cellulose fibrils and / or stocks are substantially entangled with para-aramid fibrils and / or stocks; (b) irregularly shaped para-aramid fibrous structures; And (c) water. The present invention further relates to a process for producing said cellulose and aramid pulp.

Cellulose pulp, aramid pulp, sealant, friction material, reinforcement

Description

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

The present invention relates to cellulose 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 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 seals and friction materials, there is a need to provide alternative reinforcements that provide good performance and low cost. 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 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.

Summary of the Invention

The present invention

(a) (1) cellulose fibers having at least 10% of the weight and 10 to 90% by weight of the total solids in the components and an average length of 10 cm or less when heated to 700 ° C. at a rate of 20 ° C./min in air; ;

(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 musifying cellulose fibers and para-aramid fibers into irregularly shaped fibrillated fibrous structures with stalk and fibrils;

(2) disperse all solids so that the refined slurry is substantially homogeneous

Co-refining the slurry;

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

Preparing cellulose and para-aramid pulp in which cellulose fibrils and / or stocks are substantially entangled with para-aramid fibrils and / or stocks

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

The present invention further

(a) cellulose fibers which maintain at least 10% of the weight and are 10 to 90% by weight of the total solids in the pulp when heated to 700 ° C at a rate of 20 ° C / min in water and (1) air;

(2) 10-90% by weight of para-aramid fibers in total solids in pulp

First fiber selected from the group consisting of

Combining the components comprising a;

(b) mixing the combined 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 cellulose and para-aramid fibers into irregularly shaped fibrillated fibrous structures with stocks and fibrils;

(2) disperse all solids so that the refined slurry is substantially homogeneous

Co-refining the mixed suspension; And

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

Preparing cellulose and para-aramid pulp in which cellulose fibrils and / or stocks are substantially entangled with para-aramid fibrils and / or stocks

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

The present invention further

(a) an irregularly shaped cellulose fibrous structure that maintains at least 10% of the weight and is 10 to 90% by weight of total solids when heated to 700 ° C. at 20 ° C./min in air;

(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 cellulose and para-aramid fibrous structure has an average maximum dimension of 5 mm or less, a length weighted average of 1.3 mm or less, and cellulose fibrils and / or stocks substantially entangled with para-aramid fibrils and / or stocks And having fibrils

Cellulose 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.

The invention can be more fully understood from the accompanying drawings and the detailed description thereof described below.

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.

Term Definition

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. The cellulose fibers of the present invention are also fibrillated.

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 having a diameter of a few or a few micrometers below and a length of about 10 to 100 micrometers.

"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 cellulose and para-aramid pulp for use as reinforcement. The invention also relates to cellulose 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 producing cellulose 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) cellulose 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.

Cellulose fiber

Cellulose 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.

Cellulose fibers useful in the present invention are ash-forming cellulose fibers. "Ash-forming" means that the cellulose fiber maintains at least 10% of its weight when heated in air at 700 ° C at a rate of 20 ° C / min. The cellulose fiber preferably has 10% inorganic compound incorporated into the fiber. Such fibers and methods of making them are generally disclosed in US Pat. No. 3,565,749 and UK Patent GB 1,064,271.

Preferred ash-forming cellulosic fibers for the present invention are fibers containing silicon dioxide in the form of polysilicates containing aluminum silicate sites, or salts thereof, in the cellulose support structure. The fibers are made by spinning viscose with evenly dispersed amounts of a silicon dioxide alkali solution into the fibers and treating the fibers with an aluminum solution in a subsequent step. The silicon dioxide alkali solution is preferably an aqueous solution of silicon dioxide and sodium hydroxide, and is preferably prepared by dissolving essentially soluble silicon dioxide at a level of 0.5 to 25% by weight in an aqueous solution of sodium hydroxide at a concentration of 10 to 25% by weight. The viscose containing the silicon dioxide alkali solution is spun in an acid spinning bath where the viscose is regenerated into cellulose fibers and the silicon dioxide alkali solution precipitates into polysilicate, a water-containing form of silicon dioxide, and evenly dispersed in cellulose. Polysilicic acid is precipitated in such a way that its primary particles, regularly dispersed in cellulose, form larger aggregates with diameters measurable in nanometers. After the fiber is formed, it is preferably drawn and washed and then treated with an aqueous aluminum solution, for example sodium aluminate at a concentration of 0.1 to 10% by weight, at a temperature of 0 ° C to 100 ° C, preferably 20 ° C to 60 ° C. When modified with an aluminum solution, the surface of the polysilicate aggregate in the cellulose support structure is converted to aluminum silicate. Aluminate anions in sodium aluminate react with silanol groups on the surface of the polysilic acid to form a fiber surface that accepts charges neutralized with aluminum silicate sites and sodium cations. Other salts of aluminum may be used for the modification, in which case an aqueous solution prepared therefrom with aluminum in a suitable reactive form is used in the same manner as the aluminum solution after spinning the fibers. Such preferred fibers, and methods of making such fibers, are disclosed in US Pat. No. 5,417,752 and International Patent Application WO9217629. Representative fibers also preferably have about 31 (± 3)% of an inorganic material, such as, for example, those sold under the trade name VISIL ^® by the Sateri Oy Company, Finland. The ash-forming fibers of the present invention, when incorporated into the pulp of the present invention, provide improved heat resistance over cellulose without the addition of inorganic components.

The cellulose 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 cellulose fibers in the form of continuous filaments can be cut into shorter fibers, such as staple fibers or flocs.

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 fibrillated, granular, para-aramid particles have an average of 50 to 2000 micrometers (0.05 to 2 mm), preferably 50 to 1500 micrometers, and most preferably 75 to 1000 micrometers. Has a 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. 3 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 of cellulose fibers + 50% by weight of para-aramid fibers, then the substantially homogeneous mixture in the mixing step is a random slurry sample of (1) 50% by weight ± 10% by weight of cellulose fibers. 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 any vessel equipped with a rotating 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. Cellulose 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 cellulose fiber and para-aramid pulp is similar to the first embodiment described above except for the following differences.

Before combining all the components together, either cellulose fibers or para-aramid fibers, or both cellulose fibers and para-aramid fibers, need to be shortened. This can be done by combining water with cellulose fibers or para-aramid fibers. Water and fibers may then be mixed to form a first suspension and processed through a first disk refiner to shorten the fibers. The refiner cuts the fibers to an average length of 10 cm or less. 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 if suspended in water) with a length of 10 cm or less 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 to convert all or substantially all cellulose and para-aramid fibers into irregularly shaped fibrillated fibrous structures. The refining step also includes dispersing 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 cellulose and para-aramid pulp.

Pulp of the Invention

The products produced by the process of the invention are cellulose and para-aramid pulp for use as reinforcement in the product. The pulp may comprise (a) irregularly shaped cellulose fibrous structures, (b) irregularly shaped para-aramid fibrous structures, (c) optionally substantially fibrillated, granular, para-aramid particles, (d) optionally other trace 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.

Irregularly shaped cellulose and para-aramid fibrillated fibrous structures have stocks and fibrils. Cellulose 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 cellulose and para-aramid fibrillated fibrous structures preferably have an average maximum dimension of 5 mm or less, more preferably 0.1 to 5 mm, and most preferably 0.1 to 3 mm. The cellulose and para-aramid fibrillated fibrous structures preferably have a length weighted average of 1.3 mm or less, more preferably 0.7 to 1.3 mm, and most preferably 0.75 to 1.2 mm.

If para-aramid particles are included in the pulp, the cellulose 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 cellulose and para-aramid fibrous structures can contact and form partial cocoons around the more circular substantially fibrill free, para-aramid particles.

Cellulose and para-aramid pulp are free of substantial aggregates or agglomerates 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 affects the porosity of products made from the pulp as a measure of the degree of fibrillation. The surface area of the pulp of the present invention is preferably 7 to 11 m ² / g.

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

Aramid particles and fibrous structures substantially homogeneously dispersed throughout the reinforcement and friction materials and seals provide a number of reinforcement sites and increased wear resistance, thanks to the high temperature properties of the para-aramid polymer and the tendency of fibrillation of the cellulose and para-aramid polymers. It is considered. When co-refined, the blending of the aramid material is so intimate that there is always some para-aramid fibrous structure close to the cellulosic 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 cellulose 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 cellulose 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 manufacturing the 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 T227. The data obtained from the performance of this test is expressed in Canadian Standard Freedom, which represents milliliters 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.

Thermogravimetric Analysis: Cellulose fibers used in the present invention retain some of their fiber weight when heated to high temperatures at a certain heating rate. The fiber weight was measured using a Model 2950 Thermogravimetric Analyzer, available from TA Instruments, Waters Corporation, a subsidiary of Waters Corporation, Newark, Delaware. Provide a scan of the loss Using the TA Universal Analysis program, the percent weight loss can be determined at any recording temperature The program profile equilibrates the sample at 50 ° C .; 500 microliter ceramic cup (PN 952018.910) Place the sample in the sample vessel and increase the air temperature measured with a thermocouple located directly on the lip of the sample vessel from 50 ° C. to 1000 ° C. at a heating rate of 20 ° C./min; using air supplied at 10 ml / min as gas It includes.

The test procedure is as follows. The TGA was programmed using the TGA screen on the TA system 2900 controller. Sample ID was entered and a temperature ramp program of 20 ° C./min was selected. The empty sample cup was teared using the tare function of the instrument. The fiber sample was cut to about 1/16 mm (0.16 cm) in length and the sample pan was loosely filled. Sample weight should be 10 to 50 mg. The TGA includes a balance, so there is no need to pre-measure the exact weight. None of the samples should leave the pan. The pan into which the sample was introduced was placed on the balance wire while keeping the thermocouple close to but not in contact with the top edge of the pan. The furnace was put on the pan and TGA started. At the end of the program, the TGA automatically lowers the furnace, removes the sample pan, and switches to cooling mode. It is then analyzed using the TA System 2900 Universal Analysis Program and generates a TGA scan for percent weight loss over the temperature range.

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 cellulose staples. VISIL ^® brand staples with a cut length of 2 inches and a filament line density of 3 dpf (3.3 dtex per filament) were obtained from satin cucumber in Finland. Commercial Kevlar brand floc with 1/4 "cut length, style 1F178, Para-Aramid fiber is manufactured by E.I. DuPont de Nemours and Company with offices in Wilmington, Delaware, USA. ).

Cellulose staples, para-aramid fibers and water were simultaneously fed into a strongly stirred tank and then simultaneously pumped into a Sprout-Waldron 12 "single disk refiner for about 5 minutes. Cellulose staples and water were A mil plate gap setting was used to feed directly to the Sprout-Badlon 12 "single disk refiner and pre-pulp to reach an acceptable treatment length in the 13 mm range.

The pre-pulped cellulose 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 cellulose fibers and mixed to a total component concentration of about 2 to 3 wt% of the 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 cellulose fibers into irregularly shaped fibrous structures with stocks and fibrils,

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

Then dehydrated to the above refined slurry was filtered and compressed using a filter bag and placed in a storage bag of a large home lock (ZIPLOC ^®) type. The resulting pulp 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 cellulose fibers. 2 inches cut length and 3 dpf available from sato cucumber to make random-length fibers with most fibers shorter than 3/4 inch (1.91 cm) and having an average length of about 1/2 inch (1.27 cm) Cellulose fibers having a filament line density (3.3 dtex per filament) were cut 2-3 times at right angles with a guillotine cutter.

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. Other Kevlar brands that do not initially exist on bobbins but vary in length to produce random-length fibers, where most fibers are shorter than 3/4 inch (1.91 cm) and have an average length of about 1/2 inch (1.27 cm). 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 vigorously stirred to a solid concentration of 50% by weight of para-aramid fiber and 50% by weight of cellulose fiber. 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 cellulose fibers and para-aramid fibers into irregularly shaped fibrous structures with stocks and fibrils,

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

"Substantially homogeneous" is as defined above.

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, the pulp structure has 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 processing in Model IIIA) available from GmbH) further swelled and dispersed the dried pulp. The dried pulp was then packaged into bales. When measured by fiberexpert, the pulp fibrous structure 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 particles 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, the fibrous structure 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 cellulose fibers). Pulp). The pulp was then dispersed in the base compound powder 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 at 300 ° F. (149 ° C.) for about 15 minutes. Binder 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% cellulose pulp, the test pads were indistinguishable and the backing plate holes had good flowability of the compound 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 hot fade sections, during which the brake pads receive 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 way are much thinner, typically up to about 3 mm thick.

Claims (26)

(a) (1) Cellulose having an average length of 10 cm or less with 10-90% by weight of total solids in the pulp component when heated to 700 ° C. at 20 ° C./min in air fiber; (2) para-aramid fibers having from 10 to 90% by weight of total solids in the pulp component and having an average length of 10 cm or less; And (3) 95 to 99% by weight of the total pulp component Combining the pulp components comprising; (b) mixing the pulp component into a substantially homogeneous slurry; (c) (1) fibrillating, cutting and musting cellulose fibers and para-aramid fibers into irregularly shaped fibrillated fibrous structures with stalk and fibrils, (2) disperse all solids so that the refined slurry is substantially homogeneous Co-refining the slurry; (d) water is removed from the refined slurry up to a total of 60% by weight of water, Preparing cellulose and para-aramid pulp in which cellulose fibrils, cellulose stocks, or cellulose fibrils and stocks are entangled with para-aramid fibrils, para-aramid stocks, or para-aramid fibrils and stocks Method for producing cellulose and para-aramid pulp for use as a reinforcement comprising a. The method of claim 1, In the combining step, the cellulose fibers have a line density of 10 dtex or less Para-aramid fibers have a line density of 2.5 dtex or less. The method of claim 1 wherein there is no aggregate of the same material in the pulp. The method of claim 1, wherein the cellulose fiber contains silicon dioxide in the form of polysilicic acid, or a salt thereof. 5. The method of claim 4, wherein the cellulose fiber further contains aluminum silicate sites. The method of claim 1, In the combining step, the pulp component further comprises fibril-free, granular, para-aramid particles having up to 50% by weight of total solids in the pulp component and having an average maximum dimension of 50 to 2000 micrometers, In the refining step, at least a portion of the para-aramid particles are triturated into smaller, more circular fibril free particles, The prepared cellulose and para-aramid pulp wherein the cellulose and para-aramid fibrous structures contact at least a portion of the more circular fibril-free, para-aramid particles and partially wrap around them. The method of claim 1, wherein in the combining step, the cellulose fibers make up 25 to 60 weight percent of the total solids. The process of claim 1, wherein in the combining step, the para-aramid fibers comprise 40 to 75 weight percent of the total solids. The method of claim 1, wherein after the removal step, water is 4 to 60% by weight of the total pulp, and the pulp has a Canadian standard freeness (CSF) of 100 to 700 ml. The method of claim 1 wherein the refining step comprises passing the mixed slurry through a series of disk refiners. (a) cellulose fibers which maintain at least 10% of the weight and are 10 to 90% by weight of the total solids in the pulp when heated to 700 ° C at a rate of 20 ° C / min in water and (1) air; And (2) 10-90% by weight of para-aramid fibers in total solids in pulp First fiber selected from the group consisting of Combining the components comprising a; (b) mixing the combined 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 a portion of the fibers into an irregularly shaped fibrillated fibrous structure; (d) the water concentration in the total components of 95-99% by weight of the refined suspension, the second fiber of groups (1) and (2) having an average length of 10 cm or less, and water if necessary; Increasing to; (e) mixing the ingredients as necessary to form a substantially homogeneous suspension; (f) (1) fibrillating, cutting and masticating solids in suspension to convert cellulose and para-aramid fibers into irregularly shaped fibrillated fibrous structures with stock and fibrils, (2) disperse all solids so that the refined slurry is substantially homogeneous Co-refining the mixed suspension; And (g) water is removed from the refined slurry up to a total of 60% by weight of water, Preparing cellulose and para-aramid pulp in which cellulose fibrils, cellulose stocks, or cellulose fibrils and stocks are entangled with para-aramid fibrils, para-aramid stocks, or para-aramid fibrils and stocks Method for producing cellulose and para-aramid pulp for use as a reinforcement comprising a. The method of claim 11, In the combining step, the component further comprises up to 50% by weight of the total solids in the component and comprises fibril-free, granular, para-aramid particles having an average maximum length of 50 to 2000 micrometers, In the first or second refining step, at least a portion of the para-aramid particles are triturated into smaller, more circular fibril-free particles, Wherein the cellulose and para-aramid fibrous structures in the prepared cellulose and para-aramid pulp are in contact with at least a portion of the more circular fibril-free, para-aramid particles and partially wrap around them. 12. The method of claim 11, wherein after the removing step, the irregularly shaped cellulose fibrous structure is 25 to 65 weight percent of total solids. 12. The method of claim 11, wherein after the removing step, the irregularly shaped para-aramid fibrous structure is 40 to 75 weight percent of total solids. The method of claim 11, wherein after the removal step, water is 4 to 60% by weight of the total pulp, and the pulp has a Canadian standard freeness (CSF) of 100 to 700 ml. (a) an irregularly shaped fibrillated cellulose fibrous structure that maintains at least 10% of the weight and is 10 to 90% by weight of total solids when heated to 700 ° C at 20 ° C / min in air; (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 cellulose 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, cellulose fibrils, cellulose stocks, or cellulose fibrils and stocks of para-aramid fibrils, Having para-aramid stock, or para-aramid fibrils and stock and fibrils entangled with the stock, Cellulose and para-aramid pulp for use as reinforcement. 17. The pulp of claim 16 further comprising up to 50% by weight of fibril-free, granular, para-aramid particles up to 50% by total solids. 17. The pulp of claim 16 wherein the irregularly shaped fibrillated cellulose fibrous structure is 25 to 60 weight percent of total solids. 17. The pulp of claim 16 wherein the irregularly shaped fibrillated para-aramid fibrous structure is between 40 and 75 weight percent of total solids. The pulp of claim 16 wherein the cellulose fibrous structure contains silicon dioxide in the form of polysilicic acid, or a salt thereof. 21. The pulp of claim 20 wherein the cellulose fibrous structure further contains aluminum silicate sites. The pulp of claim 16 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 16 Friction material comprising a. The method of claim 23, wherein 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 16 Sealing material comprising a. 26. The sealant of claim 25, 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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