HK1159150A - Polyimide resins for high temperature wear applications - Google Patents

Description

Polyimide resins for high temperature wear applications

This patent application claims priority and benefit from U.S. patent application 12/182,435 filed on 30.7.2008, which is incorporated by reference herein in its entirety for all purposes.

Technical Field

The present disclosure relates to filled polyimide resin compositions for high temperature wear applications such as aircraft engine parts.

Background

The unique properties of polyimide compositions under stress and high temperature make them useful in applications requiring high abrasion resistance, especially under high pressure and high speed conditions. Some examples of such applications are aircraft engine parts, aircraft wear pads, automatic transfer bushings and seal rings, tenter frame pads and bushings, material processing equipment parts, and pump bushings and seals.

Typically, polyimide components in applications such as those described above are intended to be used as protective or consumable components, thereby preventing or reducing wear or damage that may be experienced if a more expensive mating or adjoining component is mated with some other component. However, as the polyimide component wears, the resulting increased clearance can cause other adverse effects, such as increased leakage (of gas pressure or fluid) or increased noise, thereby reducing the operating efficiency of the overall system in which the polyimide component is included. Restoring the system to its original operating efficiency would require replacing worn polyimide components with new unused polyimide components. Replacement may require disassembly, reassembly, testing, and recalibration ("troubleshooting") of the system, resulting in considerable expense in repair time and labor. Accordingly, polyimide components exhibiting lower wear rates are desired to reduce the frequency of replacement and service, thereby reducing costs.

Despite the availability of a variety of polyimide compositions and additives for those compositions, such as graphite, there remains a need for polyimide compositions that exhibit the desired high degree of wear resistance as molded parts at the high temperatures required for applications such as aircraft engine parts, while maintaining the other advantageous properties of polyimide materials.

Disclosure of Invention

In one embodiment, the present invention provides a composition comprising an aromatic polyimide, graphite and a sepiolite filler or a mixture of a sepiolite filler and a kaolin filler.

In another embodiment, the present invention provides a composition comprising (a) about 40 parts by weight or more but about 54 parts by weight or less of an aromatic polyimide, (b) about 46 parts by weight or more but about 60 parts by weight or less of graphite, and (c) about 0.5 parts by weight or more but about 3.0 parts by weight or less of sepiolite filler; wherein all parts by weight add up to 100 parts by weight.

Another embodiment of the invention is a combination of substances substantially as shown or described in any one or more of figures 1-4.

Articles made from the above compositions are also provided.

Brief Description of Drawings

Various features and/or embodiments of the invention are illustrated in the accompanying drawings as described below. Such features and/or embodiments are merely representative, and the inclusion of such features and/or embodiments in the drawings should not be taken to imply that the subject matter not included in the drawings is not suitable for practicing the invention, or that the subject matter not included in the drawings is excluded from the scope of the appended claims and their equivalents.

FIG. 1 is a schematic diagram of the experimental design space used in the examples.

FIG. 2 is a response surface diagram of the thermal oxidation stability model derived in the example.

Fig. 3 is a response surface diagram of the resin abrasion degree model derived in the example.

FIG. 4 is a superposition of the resin wear response surface plot and the thermal oxidation stability response surface plot derived in the examples.

Detailed Description

Disclosed herein are compositions comprising (a) an aromatic polyimide, (b) graphite, and (c) a sepiolite filler or a mixture of sepiolite filler and kaolin filler.

The polyimides useful in the compositions herein as component "(a)" are polymers in which at least about 80%, preferably at least about 90%, and more preferably substantially all (e.g., at least about 98%) of the linking groups between repeat units are imine groups. Aromatic polyimides as used herein include organic polymers in which about 60 to about 100 mol%, preferably about 70 mol% or more, and more preferably about 80 mol% or more of the repeating units in the polymer chain have the structure shown in the following formula (I):

wherein R is¹Is a tetravalent aromatic radical, and R²Is a divalent aromatic radicalThe bolus, as described below.

Polyimide polymers suitable for use herein can be synthesized by reacting, for example, aromatic diamine compound monomers (including derivatives thereof) with aromatic tetracarboxylic acid compound monomers (including derivatives thereof), which can be tetracarboxylic acid itself or the corresponding dianhydride, or a tetracarboxylic acid derivative such as a diester diacid or diester diacid chloride. Depending on the choice of starting materials, the reaction of an aromatic diamine compound with an aromatic tetracarboxylic acid compound produces the corresponding polyamic acid ("PAA"), amide ester, amide acid ester, or other reaction product. Aromatic diamines are usually reacted with dianhydrides in preference to tetracarboxylic acids, and in this reaction, catalysts are used in many cases in addition to solvents. Nitrogen-containing bases, phenols or amphoteric substances can be used as such catalysts.

The polyamic acid as a polyimide precursor can be obtained by polymerizing preferably substantially equimolar amounts of an aromatic diamine compound and an aromatic tetracarboxylic acid compound in an organic polar solvent, which is generally a high boiling point solvent such as pyridine, N-methylpyrrolidone, dimethylacetamide, dimethylformamide, or a mixture thereof. The amount of all monomers in the solvent can range from about 5 to about 40 weight percent, from about 6 to about 35 weight percent, or from about 8 to about 30 weight percent, based on the combined weight of the monomers and the solvent. The temperature of the reaction is generally no greater than about 100 ℃ and may range from about 10 ℃ to 80 ℃. The polymerization time is generally within about 0.2 to 60 hours.

Imidization is then achieved via heat treatment, chemical dehydration, or both, to produce a polyimide, i.e., ring closure of the polyamic acid, followed by removal of the condensate (typically water or alcohol). For example, ring closure can be achieved via a ring forming agent such as pyridine and acetic anhydride, picoline and acetic anhydride, 2, 6-lutidine and acetic anhydride, and the like.

In various embodiments of the polyimide thus obtained, about 60 to 100 mol%, preferably about 70 mol% or more, and more preferably about 80 mol% or more of the repeating units in the polymer chain have a polyimide structure represented by the following formula (I):

wherein R is¹A tetravalent aromatic radical derived from a tetracarboxylic acid compound; and R is²Is a divalent aromatic radical derived from a diamine compound, which may be generally represented by H₂N-R²-NH₂。

The diamine compound used to prepare the polyimides in the compositions herein can be one or more compounds represented by the structure H₂N-R²-NH₂An aromatic diamine of wherein R²Is a divalent aromatic radical containing up to 16 carbon atoms and optionally containing in the aromatic ring one or more (but usually only one) heteroatom (S) selected, for example, from the group consisting of-N-, -O-, or-S-. Also included herein are those R²Group, wherein R²Is biphenylene. Examples of aromatic diamines suitable for use in preparing the polyimides in the compositions herein include, without limitation, 2, 6-diaminopyridine, 3, 5-diaminopyridine, 1, 2-diaminobenzene, 1, 3-diaminobenzene (also known as m-phenylenediamine or "MPD"), 1, 4-diaminobenzene (also known as p-phenylenediamine or "PPD"), 2, 6-diaminotoluene, 2, 4-diaminotoluene, and p-diaminobiphenyls such as p-diaminobiphenyl and 3, 3' -dimethyl-p-diaminobiphenyl. The aromatic diamines may be used alone or in combination. In one embodiment, the aromatic diamine compound is 1, 4-diaminobenzene (also known as p-phenylenediamine or "PPD"), 1, 3-diaminobenzene (also known as m-phenylenediamine or "MPD"), or mixtures thereof.

Aromatic tetracarboxylic acid compounds suitable for use in preparing the polyimides in the compositions herein can include, without limitation, aromatic tetracarboxylic acids, anhydrides thereof, salts thereof, and esters thereof. The aromatic tetracarboxylic acid compound can be represented by the general formula (II):

wherein R is¹Is a tetravalent aromatic radical, and each R³Independently hydrogen or lower alkyl (e.g. normal chain or branched C)₁～C₁₀、C₁～C₈、C₁～C₆Or C₁～C₄) A group. In various embodiments, alkyl is C₁-C₃An alkyl group. In various embodiments, a tetravalent organic group R¹May have a structure represented by one of the following formulae:

examples of suitable aromatic tetracarboxylic acids include, without limitation, 3, 3 ', 4, 4' -biphenyltetracarboxylic acid, 2, 3, 3 ', 4' -biphenyltetracarboxylic acid, pyromellitic acid, and 3, 3 ', 4, 4' -benzophenonetetracarboxylic acid. The aromatic tetracarboxylic acids may be used alone or in combination. In one embodiment, the aromatic tetracarboxylic acid compound is an aromatic tetracarboxylic dianhydride, particularly 3, 3 ', 4, 4 ' -biphenyl tetracarboxylic dianhydride ("BPDA"), pyromellitic dianhydride ("PMDA"), 3, 4, 4 ' -benzophenone tetracarboxylic dianhydride, or a mixture thereof.

In one embodiment of the compositions herein, a suitable polyimide polymer may be prepared from 3, 3 ', 4, 4' -biphenyltetracarboxylic dianhydride ("BPDA") as the aromatic tetracarboxylic acid compound and greater than 60 to about 85 mole percent p-phenylenediamine ("PPD") and 15 to less than 40 mole percent m-phenylenediamine ("MPD") as the aromatic diamine compound. Such polyimides are described in U.S. Pat. No. 5,886,129, which is incorporated herein by reference as part thereof for all purposes, and the repeat units of such polyimides can also be represented by the structure shown in the following general formula (III):

wherein greater than 60 to about 85 mol% R²The group is p-phenylene:

and 15 to less than 40 mol% is m-phenylene:

in an alternative embodiment, a suitable polyimide polymer can be prepared from 3, 3 ', 4, 4' -biphenyltetracarboxylic dianhydride ("BPDA") as the dianhydride derivative of the tetracarboxylic acid compound and 70 mole% p-phenylenediamine and 30 mole% m-phenylenediamine as the diamine compound.

The polyimide as used herein is preferably a rigid polymer. A polyimide polymer is considered rigid when there are no or trace amounts (e.g., less than 10 mol%, less than 5 mol%, less than 1 mol%, or less than 0.5 mol%) of flexible linkages in the polyimide repeat unit. A flexible linker is a moiety that consists primarily of a small number of atoms and has a simple structure (e.g., linear rather than branched or cyclic) and thus is relatively susceptible to allowing polymer chains to bend or twist at the linker site. Examples of flexible linkers include, without limitation: -O-, -N (H) -C (O) -, -S-, -SO₂-、-C(O)-、-C(O)-O-、-C(CH₃)₂-、-C(CF₃)₂-、-(CH₂) -, and-NH (CH)₃) -. Although disadvantageous, these or other flexible linking groups, when present, are sometimes present in the R of the aromatic diamine compound²In part (a).

The polyimide as used herein is preferably an infusible polymer, which is a polymer that does not melt (i.e., liquefy or flow) below its decomposition temperature. Typically, parts made from infusible polyimide compositions are made under heat and pressure much like powdered metal forming parts (as described in U.S.4,360,626, which is incorporated by reference herein as part thereof for all purposes).

The polyimide as used herein is preferably highly stable to thermal oxidation. Thus at high temperatures, the polymer will generally not undergo combustion throughout the reaction with an oxidant such as air, but will become vaporized in a pyrolysis reaction.

Graphite is used as component ("b") in the compositions herein. Graphite is commonly added to polyimide compositions to improve wear and friction characteristics and to adjust the Coefficient of Thermal Expansion (CTE). Thus, for this purpose, it is sometimes advantageous to select the amount of graphite used in the polyimide composition to match the CTE of the mating components.

Graphite is commercially available in a variety of forms such as fine powders and may have widely varying average particle sizes, however the average particle size is generally in the range of about 5 to about 75 microns. In one embodiment, the average particle size is in the range of about 5 to about 25 microns. In another embodiment, graphite as used herein comprises less than about 0.15 wt.% reactive impurities, such as those selected from the group consisting of: iron sulfide, barium sulfide, calcium sulfide, copper sulfide, barium oxide, calcium oxide, and copper oxide.

The graphite suitable for use herein may be naturally occurring graphite or artificial graphite. Natural graphite generally has a wide range of impurities, while synthetically produced graphite is commercially available with low concentrations of reactive impurities. Graphite containing unacceptably high concentrations of impurities may be purified by any of a variety of known treatments, including, for example, chemical treatment with mineral acids. Treatment of impure graphite with sulfuric, nitric or hydrochloric acid, for example at elevated or reflux temperatures, can be used to reduce impurities to a desired level.

Sepiolite fillers or sepioliteMixtures of fillers with kaolin fillers are used as component ("c") in the compositions herein. Sepiolite fillers suitable for use herein include sepiolite itself [ Mg₄Si₆O₁₅(OH)₂·6(H₂O)]It is a hydrous magnesium silicate filler that exhibits a high aspect ratio due to its fibrous structure. Sepiolite consists of elongated crystallites, which is the only one in silicates, where the silica chains extend parallel to the fiber axis. The material has been shown to include two forms, the alpha and beta forms. The alpha form is known as long strand fibers, while the beta form appears as an amorphous aggregate.

Sepiolite fillers suitable for use herein also include attapulgite (also known as magnalite), which is structurally and chemically nearly identical to sepiolite, except that the attapulgite has a slightly smaller unit cell.

Sepiolite fillers suitable for use herein also include clays, which are layered fibrous materials in which each layer is composed of two sheets of tetrahedral silica units bonded to a central octahedral unit sheet containing magnesium ions [ see, e.g., "Polymer International" by L.Bokobza et al "531060-1065(2004) FIGS. 1 and 2]. The fibers stick together to form fiber bundles, which in turn can form agglomerates. These agglomerates can be broken up by industrial processes such as micronization or chemical modification (see for example european patent 170,299 to Tolsa s.a.).

In one embodiment, sepiolite fillers suitable for use herein include rheological grade sepiolite clays such as those described in EP-A-454,222 and/or EP-A-170,299 and are available under the trade mark PangelSold by Tolsa s.a. (Madrid, Spain). In this context, the term "rheological grade" means sepiolite clays typically having a particle size of greater than 120m²Average surface area in g [ according to the Brunauer/Emmett/Teller method, in N₂Measured (e.g., "Adsorption of Gases in Multimolecular Layers" by Brunauer et al, Journal of the American Chemical Society, 60: 309-19,1938) as described in]And typically have an average fiber size of about 200 to 2000nm long, 10-30nm wide and 5-10nm thick. Rheological grade sepiolite is derived from natural sepiolite via a micronization process which substantially prevents breakage of sepiolite fibres, makes it readily dispersible in water and other polar liquids, and has a highly irregular outer surface, greater than 300m²A high specific surface area per gram, and a high density of active centers for adsorption, which provides very high water retention capacity to the active centers while being able to form hydrogen bridges with relative ease. The microfibre characteristics of the rheological grade sepiolite granules make sepiolite a material with high porosity and low apparent density.

Furthermore, the rheological grade sepiolite has a very low cation exchange capacity (10-20meq/100g) and very weak interaction with the electrolyte, which in turn results in a rheological grade sepiolite which is hardly affected by the presence of salts in the medium in which it is present and therefore remains stable over a wide pH range. Rheological grade sepiolite of the above qualities may also be present in rheological grade attapulgite, which typically has a particle size of less than 40 microns, such as ATTAGEL manufactured and sold by Engelhard Corporation (United States)Clay (e.g., ATTAGEL 40 and ATTAGEL 50) series; and MIN-U-GEL product series available from Floridin Company.

Kaolin fillers suitable for use herein include kaolinite itself, which is a sheet silicate whose molecules are arranged in two layers or two plate layers of a sheet of silica and a sheet of alumina. The kaolin is of Al₂Si₂O₅(OH)₄A chemically composed clay mineral. It is a layered silicate mineral with one tetrahedral sheet connected by oxygen atoms to one octahedral sheet of alumina octahedra. Rock masses rich in kaolinite are known as china clay or kaolin. In contrast, smectite clays such as montmorillonite clay minerals are arranged in two silica platelets and one alumina platelet. Those phases of the kaolinite classIn contrast, the smectite molecules are loosely linked together and therefore more spaced. It is desirable to maintain the phase stability of the crystalline structure of the sheet silicate, as well as the thermal stability of water in the sheet silicate structure at higher temperatures, e.g., up to about 450 ℃ [ as shown, for example, by thermogravimetric analysis (TGA) ]]. Loss of structural water during processing of the polyimide composition may cause damage to the polyimide integrity and may alter the crystal structure of the sheet silicate, resulting in a harder, more abrasive compound. Examples of sheet silicates that are not sufficiently stable to be included in the compositions described herein are montmorillonite, vermiculite and pyrophyllite.

Sepiolite fillers and kaolin fillers suitable for use herein are further discussed in Murray, Applied Clay Science 17(2000) 207-. When a mixture of sepiolite filler and kaolin filler is used as component (c) in the composition of the present invention, the amount of each type of filler in the mixture ranges from about 10% to about 90% by weight, based on the total weight of all fillers in the mixture taken together.

In many cases, the graphite and sepiolite fillers (or mixtures of sepiolite fillers and kaolin fillers) used in the compositions and articles herein are incorporated into a hot solvent prior to transfer of the PAA polymer solution (or other solution of other types of monomers) as described above, such that the resulting polyimide precipitates in the presence of components (b) and (c) and is thereby incorporated into the composition.

In the compositions of the present invention, the content of the various components includes all possible ranges formed by the following amounts:

the aromatic polyimide of component (a) is present in an amount of about 40 parts by weight or greater, about 42 parts by weight or greater, about 44 parts by weight or greater, or about 46 parts by weight or greater but said amount is about 54 parts by weight or less, about 52 parts by weight or less, about 50 parts by weight or less, or about 48 parts by weight or less;

the graphite, component (b), is present in an amount of about 46 parts by weight or greater, about 48 parts by weight or greater, about 50 parts by weight or greater, or about 52 parts by weight or greater but said amount is about 60 parts by weight or less, about 58 parts by weight or less, about 56 parts by weight or less, or about 54 parts by weight or less; and is

The sepiolite filler or mixture of sepiolite filler and kaolin filler, component (c), is present in an amount of about 0.5 parts by weight or greater, about 0.75 parts by weight or greater, about 1.0 parts by weight or greater, about 1.25 parts by weight or greater, or about 1.5 parts by weight or greater but said amount is about 3.0 parts by weight or less, about 2.75 parts by weight or less, about 2.5 parts by weight or less, about 2.25 parts by weight or less, or about 2.0 parts by weight or less.

In the compositions herein, the amounts of the respective parts by weight of the three components, taken from the ranges as described above, total 100 parts by weight when the three components are mixed together in any particular formulation.

The compositions of the present invention include all formulations wherein the compositional content may be expressed as any combination of the individual maxima and minima of any one component of the composition described above, as well as any such combination of maxima and minima of one or both of the other two components.

One or more additives may be used as optional component "(d)" in the compositions herein. When used, the one or more additives may be present in an amount ranging from about 5 to about 70 weight percent based on the total weight of all four components taken together in the 4-component [ (a) + (b) + (c) + (d) ] composition, and 3 to the total weight of all three components taken together in the 3-component [ (a) + (b) + (c) ] composition in an amount ranging from about 30 to about 95 weight percent based on the total weight of all four components taken together in the 4-component [ (a) + (b) + (c) + (d) ] composition.

Suitable additives optionally used in the compositions herein may include, without limitation, one or more of the following: a pigment; an antioxidant; substances imparting a low coefficient of thermal expansion, such as carbon fibers; substances imparting high strength characteristics, such as glass fibers, ceramic fibers, boron fibers, glass beads, whiskers, graphite whiskers, or diamond powder; a substance imparting heat dissipation or heat resistance properties, such as aramid fibers, metal fibers, ceramic fibers, whiskers, silica, silicon carbide, silica, alumina, magnesium powder, or titanium powder; substances imparting corona resistance, such as natural mica, synthetic mica, or alumina; a substance imparting conductivity, such as carbon black, silver powder, copper powder, aluminum powder, or nickel powder; substances which further reduce the wear or coefficient of friction, such as boron nitride or poly (tetrafluoroethylene) homopolymers and copolymers. The filler may be added to the final resin in dry powder form prior to part manufacture.

Materials suitable for use in or for preparing the compositions herein may themselves be prepared by methods known in the art, or may be obtained commercially from suppliers such as Alfa Aesar (Ward Hill, Massachusetts), City Chemical (West Haven, Connecticut), Fisher Scientific (Fairlawn, New Jersey), Sigma-Aldrich (st. louis, Missouri), or Stanford Materials (alio Viejo, California).

As with products made from other non-meltable polymeric materials, parts made from the compositions herein can be made by techniques involving the application of heat and pressure (see, e.g., U.S. patent No.4,360,626). Suitable conditions may include, for example, pressures in the range of about 50,000 to 100,000psi (345 to 690MPa) at ambient temperature. The physical properties of articles molded from the compositions herein may be further improved by sintering, which is typically carried out at temperatures in the range of about 300 ℃ to about 450 ℃.

Parts and other articles made from the compositions herein are useful as aircraft engine parts, such as bushings, bearings, gaskets, seal rings, gaskets, wear pads, and sliders. These components can be used in all types of aircraft engines, such as reciprocating piston engines, in particular jet engines. Parts and other articles made from the compositions of the present invention may also be used in the following: automotive and other types of internal combustion engines; other vehicle subsystems such as exhaust gas recirculation systems and clutch systems; a pump; jet engines for non-aircraft use; a turbocharger; aircraft subsystems such as thrust reversers, nacelles, flap systems and valves; material processing equipment such as injection molding machines; material handling equipment such as conveyors, belt presses, and tenter frames; as well as membranes, seals, gaskets, bearings, bushings, washers, wear pads, seal rings, sliders, and push pins and other applications where low wear is desired. In some applications, a part or other article made from the composition herein is contacted with metal for at least a portion of the time when the device in which it is present is assembled and in normal use.

Examples

The advantageous properties and efficacy of the compositions herein can be seen in a series of examples (examples 1-14) as described below. The embodiments of these compositions on which the examples are based are representative only, and the selection of those embodiments to illustrate the invention does not indicate that materials, components, reactants, ingredients, formulations or specifications not described in these examples are not suitable for the practice of the invention, or that subject matter not described in these examples is excluded from the scope of the appended claims and equivalents thereof. The significance of the examples can be better understood by comparing the results thus obtained with the results obtained from certain tests designed to serve as control experiments (controls a-D) and to provide a benchmark for this comparison, since the compositions therein do not contain any sepiolite (or sepiolite/kaolin mixtures) filler.

In the examples, the following abbreviations are used: "BPDA" is defined as 3, 3 ', 4, 4' -biphenyltetracarboxylic anhydride, "MPD" is defined as m-phenylenediamine, "PPD" is defined as p-phenylenediamine, "COF" is defined as coefficient of friction, "TOS" is defined as thermal oxidative stability, "avg" is defined as average or equilibrium, "h" is defined as hour, "mL" is defined as milliliter, "m" is defined as meter, "cm" is defined as centimeter, "mm" is defined as millimeter, "in" is defined as inch, "g" is defined as gram, "kg" is defined as kilogram, "oz" is defined as ounce, "psia" is defined as pounds per square inch (absolute pressure), "rpm" is defined as revolutions per minute, and "wt%" is defined as weight percent.

Raw materials。

3, 3 ', 4, 4' -Biphenyltetracarboxylic anhydride was obtained from Mitsubishi Gas Chemical Co., Inc. (Tokyo, Japan). M-phenylenediamine and P-phenylenediamine are available from DuPont (Wilmington, Delaware, USA). The graphite used was synthetic graphite, up to 0.05% ash, with a median particle size of about 8 microns. PangelS-9 sepiolite was purchased from EM sublivan Associates, Inc (Paoli, Pennsylvania, USA), a distributor of the manufacturer Tolsa s.a. (Madrid 28001, Spain). PangelS-9 sepiolite is a rheological grade sepiolite, the particles of which have an unmodified or uncoated surface.

Method。

The dried polyimide resin was formed into Tensile bars by direct molding at room temperature and 100,000psi (690MPa) molding pressure according to ASTM E8(2006), "Standard Test Specification for Powdered Metal Products-Flat inorganic Tensile Test Bar". The tensile bar was sintered at 405 ℃ for 3 hours using a nitrogen purge.

The high temperature wear on the tensile bar was measured at 800 ° f (427 ℃). In these tests, a steel ball bearing was rubbed on the test specimen surface for 3 hours under a 2 pound load. At the end of the experiment, the volume of the resulting wear scar on the test specimen ("resin wear") was determined, and the wear experienced by the steel ball ("steel ball wear") and the coefficient of friction between the test specimen and the steel ball ("COF") were determined. The resin wear was determined by optical profilometry, from which the volume of the wear scar could be determined. The results for resin and steel ball attrition are reported as the volume of weight loss in³Or cm³Is expressed in units. COF results reported were noneDimensional value, since it is the relative coefficient of friction of each sheet with respect to the other. All measurements were made using the Test Method described in ASTM G133-05 (2005) "Standard Test Method for Linear reporting Ball-on-Flat slipping Wear", modified by using a temperature controlled oven while collecting the frictional force data on a computer.

Thermo-oxidative stability ("TOS") was determined as follows: tensile bars were first weighed and then two of the tensile bars ("TOS-1" and "TOS-2") were exposed to a temperature of 800 ° F (427 ℃) for 25 hours at a pressure of 88psia (0.61MPa) in air for each tensile bar. Final weight measurements were then made and the weight loss percentage for each tensile bar was calculated according to the following formula:

and the calculated and reported percentage is the percent weight loss. The weight loss percentages for TOS-1 and TOS-2 were then averaged.

Examples 1 and 2, control A

Polyimide resin particles comprising 50 weight percent graphite and 0, 5, or 10 weight percent sepiolite filler based on 3, 3 ', 4, 4' -biphenyltetracarboxylic dianhydride (BPDA), m-phenylenediamine (MPD), and p-phenylenediamine (PPD) were prepared according to the method described in U.S. patent 5,886,129, which is incorporated by reference herein in its entirety for all purposes. After drying, the resin was ground through a 20 mesh screen using Wiley milling. Test sample tensile bars were then prepared as described above and the resin abrasion, steel ball abrasion and COF were determined according to the methods described above. The results are shown in Table 1.

TABLE 1：

Examples 3-14, controls B-D

These experiments were conducted to investigate the effect of compositional content (relative amounts of polymer, graphite, and sepiolite filler) on the characteristics of parts molded from the compositions, including thermo-oxidative stability ("TOS") and resin abrasion.

The content and performance relationships for twelve formulations with different compositional contents of three components (polyimide, graphite, and sepiolite filler) are represented using a binary extreme apex design. The design space is summarized as follows, and is illustrated in fig. 1:

0.30 to 0.50 parts by weight of polyimide

0.50 to 0.70 parts by weight of graphite

Sepiolite 0.00 to 0.10 part by weight

Control compositions B-D represent the condition of 0.00 parts by weight sepiolite, since this component was not included therein.

Each composition was synthesized and test specimens were prepared as described in examples 1-2. TOS and resin abrasion were determined in the manner as described above. The results are summarized in table 2.

TABLE 2：

In FIG. 2, a constant line representing a range of 4 to 9 average TOS values is superimposed on the design space diagram to obtain a surface diagram indicating the approximate compositional content to obtain a particular average TOS in the molded part. As can be seen from fig. 2, the effect of the polyimide content is less than the effect of the other component content in the investigated composition range. Higher levels of graphite slightly improve (i.e., lower) TOS, while higher levels of sepiolite filler slightly worsen (i.e., increase) TOS. In fig. 2, the lowest TOS is generally within the vicinity of the line representing a TOS of 4, which represents compositions each having different amounts of polyimide and graphite.

In fig. 3, will represent 1750 to 6000 × 10^-8in³A constant line of the resin abrasiveness range is superimposed on the design space map to obtain a surface map indicating the approximate compositional content that produces a particular resin abrasiveness in the molded part. Figure 3 shows that there is minimal resin abrasion near the mid-point of the sepiolite filler weight parts under study. For higher content values of polyimide, the resin abrasion was slightly improved (decreased), while for higher content values of graphite, the resin abrasion was slightly deteriorated (increased). In figure 3, the lowest abrasion is generally in the region about the centre of the line with a sepiolite filler content of 0.05 parts by weight.

Figure 4 is a superposition of the TOS response surface plot of figure 2 and the resin wear response surface plot of figure 3. The line with the middle broken line represents the approximate position of the constant line indicating a TOS of 3.5 or less, and the line with the small broken line represents the approximate position of the constant line indicating a resin abrasion degree of 2000 or less. The hatched area represents the overlap of those two regions.

Where a range of numerical values is recited herein, the range includes the endpoints thereof, and all the individual integers and fractions within the range, and also includes each of the narrower ranges therein formed by all the various possible combinations of those endpoints and internal integers and fractions to form subgroups of the larger group of values within the stated range to the same extent as if each of those narrower ranges were explicitly recited. Where a range of numerical values is described herein as being greater than a stated value, the range is nevertheless limited and its upper limit is defined by values operable in the context of the invention as described herein. When a range of values is described herein as being less than a stated value, the range is still bounded on its lower limit by non-zero values.

In this specification, unless explicitly stated otherwise or indicated to the contrary by the context of usage, where an embodiment of the subject matter hereof is stated or described as comprising, including, containing, having, being composed of or being constituted by or of certain features or elements, one or more features or elements other than those explicitly stated or described may be present in the embodiment. However, an alternative embodiment of the inventive subject matter may be discussed or described as consisting essentially of certain features or elements, in which embodiment features or elements that would materially alter the principle of operation or the distinguishing characteristics of the embodiment are not present. Another alternative embodiment of the inventive subject matter may be discussed or described as consisting essentially of certain features or elements, in which embodiment, or in insubstantial variations thereof, only the features or elements specifically discussed or described are present.

In the present specification, unless explicitly stated otherwise or indicated to the contrary by the context of usage

(a) The amounts, dimensions, ranges, formulations, parameters, and other quantities and characteristics recited herein, particularly when modified by the term "about," may but need not be exact, and may also be approximate and/or greater or less than that recited (as desired), within the context of the present invention, expressing tolerances, conversion factors, numerical reductions, measurement error and the like, and including within those values outside thereof, having a utility and/or operability comparable to that recited;

(b) all numbers of parts, percentages or ratios given are parts, percentages or ratios by weight.

(c) The use of the indefinite article "a" or "an" in reference to a statement or description of an element or feature present in the invention does not limit the number of the element or feature present to one; and

(d) the words "including", "comprising" and "containing" should be read and understood as being equivalent to the phrase "non-limiting", if in fact the phrase "non-limiting" is not followed.

Claims (20)

1. A composition comprising a mixture of: (a) about 40 parts by weight or more but about 54 parts by weight or less of an aromatic polyimide, (b) about 46 parts by weight or more but about 60 parts by weight or less of graphite, and (c) about 0.5 parts by weight or more but about 3.0 parts by weight or less of sepiolite filler; wherein all parts by weight add up to 100 parts by weight.

2. The composition according to claim 1, wherein the polyimide is prepared from an aromatic tetracarboxylic acid compound or a derivative thereof, wherein the aromatic tetracarboxylic acid compound is represented by the formula (II):

wherein R is¹Is a tetravalent aromatic radical, and each R³Independently is hydrogen or C₁～C₁₀Alkyl groups, or mixtures thereof.

3. The composition according to claim 1, wherein the polyimide is prepared from an aromatic tetracarboxylic acid compound selected from the group consisting of 3, 3 ', 4, 4' -biphenyltetracarboxylic acid, 2, 3, 3 ', 4' -biphenyltetracarboxylic acid, pyromellitic acid, and 3, 3 ', 4, 4' -benzophenonetetracarboxylic acid, or derivatives thereof, or mixtures thereof.

4. The composition of claim 1, wherein the polyimide is prepared from a diamine compound having the structure H₂N-R²-NH₂Is represented by the formula (I) in which R²Is a divalent aromatic radical containing up to 16 carbon atoms and optionally containing in the aromatic ring one or more heteroatoms selected from the group consisting of-N-, -O-and-S-.

5. The composition according to claim 1, wherein the polyimide is prepared from a diamine compound selected from the group consisting of 2, 6-diaminopyridine, 3, 5-diaminopyridine, 1, 2-diaminobenzene, 1, 3-diaminobenzene, 1, 4-diaminobenzene, 2, 6-diaminotoluene, 2, 4-diaminotoluene, p-diaminobiphenyl, and 3, 3' -dimethyl-p-diaminobiphenyl.

6. The composition of claim 1, wherein the polyimide comprises the following repeating units

Wherein R is²Selected from p-phenylene,

M-phenylene radical,

And mixtures thereof.

7. The composition according to claim 6 wherein greater than 60 to about 85 mol% of said R²The group contains p-phenylene, and about 15 to less than 40 mol% of said R²The group comprises m-phenylene.

8. The composition according to claim 6 wherein about 70 mol% of said R²The group contains p-phenylene, and about 30 mol% of said R²The group comprises m-phenylene.

9. The composition according to claim 1 comprising (a) about 42 parts by weight or more but about 52 parts by weight or less of an aromatic polyimide, (b) about 48 parts by weight or more but about 58 parts by weight or less of graphite, and (c) about 0.75 parts by weight or more but about 2.75 parts by weight or less of sepiolite filler; wherein all parts by weight add up to 100 parts by weight.

10. A composition according to claim 1 wherein component (c) comprises a sepiolite filler and a kaolin filler.

11. A composition according to claim 1, wherein the sepiolite filler comprises a rheological grade sepiolite clay.

12. A composition according to claim 1, wherein the sepiolite filler comprises particles having an unmodified or uncoated surface.

13. The composition according to claim 1, further comprising as component (d) one or more additives in an amount ranging from about 5 to about 70 weight percent based on the total weight of the (a) + (b) + (c) + (d) composition, the combined weight of the (a) + (b) + (c) components together ranging from about 30 to about 95 weight percent of the total composition.

14. The composition of claim 13, wherein the additive comprises one or more of the following members: a pigment; an antioxidant; a substance imparting a low coefficient of thermal expansion; a substance imparting high strength characteristics; a substance imparting heat dissipation or heat resistance properties; a substance imparting corona resistance; a substance imparting conductivity; and substances that reduce the wear or coefficient of friction.

15. An article made from the composition of claim 1.

16. The article of claim 15, comprising an internal combustion engine component.

17. The article of claim 15, comprising an aircraft component.

18. The article of claim 15, comprising an automotive part.

19. An article according to claim 15, comprising a bushing, bearing, shim, seal ring, wear pad, or slider.

20. The article according to claim 15, comprising components for: a gas circulation system; a clutch system; a pump; a turbocharger; thrust reverser, nacelle, flap system; an injection molding machine; a conveyor, a belt press, and a tenter frame.