KR20110120986A - Co-polymer based polyimide articles and their uses in high temperature applications - Google Patents

Abstract

Disclosed herein are methods of making polyimide articles suitable for high temperature applications. The articles disclosed herein are rigid, oxidatively stable, wear resistant, permeable to heated moisture and gases, comprise copolymer-based polyimides, and at least one additive or filler, and are from 138 to 345 MPa (20,000 to And a compression pressure of 50,000 psi).

Description

Copolymer-Based Polyimide Articles and Their Uses in High Temperature Applications {CO-POLYMER BASED POLYIMIDE ARTICLES AND THEIR USES IN HIGH TEMPERATURE APPLICATIONS}

Plastic materials have a wide range of industrial applications, including some high temperature applications. Polyimides may be used in some high temperature applications, but may also need to have some other physical properties. Disclosed herein are copolymer based polyimide articles suitable for use in high temperature applications, and which also have increased permeability, durability, oxidative stability, desirable wear life and resistance to defects upon thermal exposure.

High temperature operating conditions and industrial manufacturing require the use of materials that withstand such conditions. Currently, as is conventional, metals, ceramics, graphite, asbestos and other materials are used for high temperature applications. Plastics have been useful to replace some of these materials for high temperature applications. However, some applications also require materials with additional properties such as, for example, wear resistance, chemical resistance, low friction, reduced wear, and other properties that impart compatibility to their applications.

Some applications require suitable materials that can withstand temperatures well above 400 ° C. For example, glass making operations are performed at about 1400 ° C. to 1600 ° C. Other systems, for example internal combustion engines, require the use of materials that withstand high temperatures and do not quickly weaken or wear out due to such high temperatures.

Materials used to make articles or mechanical parts suitable for high temperatures can be made. However, as the cross-sectional area of a mechanical part increases, the surface area of the part becomes less accessible to the trapped heated water and gas, thereby suppressing their release. In such cases, mechanical parts are vulnerable to defects such as blistering due to the thermal exposure of rapid thermal cycling. The gradual decrease in the mechanical properties of the part can also be caused by repeated cycles of moisture exposure and heat exposure, which is sometimes referred to as "wet Tg knockdown" of the measured glass transition temperature (tg) of the plastic. Evidenced by a decrease.

Although graphite has been used for high temperature applications, it is brittle and therefore lacks durability, cannot withstand the load applied in some applications, and lacks the wear life required for many applications.

Other materials made from plastics, such as thermoset materials, have been used. However, many of these materials are not suitable for high temperature applications and lack strength, durability and the necessary mechanical properties, which degrade faster than graphite.

Some polyimide materials have also been used, but due to the temperature range in certain applications, or polyimide parts having significant or larger cross-sectional areas relative to the surface area of the part, they cannot release heated moisture or gas upon thermal exposure. May have limitations and are not suitable for high temperature applications.

It is an object of the present invention to be made from a polyimide composition, to be suitable for high temperature applications and to have rigidity, oxidation stability, permeability to heated moisture and gases to prevent defects caused by rapid thermal cycling or heat exposure. It is to provide a method for producing an article.

In addition, the polyimide parts produced by the process of the invention are not sensitive to the accumulation of deteriorated oil residues, as is the case with graphite based materials used in the same or different applications.

<Figure 1>
1 is a graph showing tensile strength versus compaction pressure for an article comprising a copolymer based polyimide prepared according to the present invention.
<FIG. 2>
FIG. 2 is a graph showing elongation versus compression pressure for articles comprising copolymer based polyimide prepared according to the present invention. FIG.
[Content of invention]
A method of making an article suitable for use in a high temperature system, the system consisting of an instrumentation and an equipment, the article comprising a copolymer based polyimide composition, the composition comprising
a) aromatic tetracarboxylic dianhydride component; And
b) a diamine component further comprising (i) greater than 60 mol% to about 85 mol% p-phenylene diamine and (ii) 15 mol% to less than 40 mol% m-phenylene diamine Includes;
a) and b) are present in a ratio of 1: 1;
The method comprises using compression to form a part of a predetermined shape; The amount of pressure used for compression is from about 137.9 MPa (20,000 psi) to about 344.7 MPa (50,000 psi) such that a method of achieving a porous article having permeability to moisture and resistance to defects caused by heat exposure is disclosed herein. Is initiated.
An article suitable for use in a high temperature system, the system consisting of appliances and equipment, the article comprising a copolymer based polyimide composition, the composition comprising
a) aromatic tetracarboxylic dianhydride component; And
b) a diamine component further comprising i) greater than 60 mol% to about 85 mol% p-phenylene diamine, and ii) 15 mol% to less than 40 mol% m-phenylene diamine; ;
a) and b) are present in a ratio of 1: 1;
Also disclosed herein is an article that is porous and permeable to moisture and resistant to defects caused by thermal exposure.

Polyimide materials readily absorb moisture in the atmosphere. Depending on the environment, the equilibrium point may be greater than 1 weight percent. When the polyimide material is heated, this moisture will be released. However, if the material is heated at a faster rate than this moisture can escape, blistering may occur.

The present invention provides a method of making an article suitable for use in a high temperature system, the system consisting of appliances and equipment. Articles made in accordance with the method of the present invention are articles that are durable, wear-resistant, rigid, oxidatively stable, and resistant to defects caused by rapid thermal cycling in high temperature applications.

In the process of the invention, the article comprises a copolymer based polyimide composition, wherein the composition

a) aromatic tetracarboxylic dianhydride component; And

b) a diamine component further comprising i) greater than 60 mol% to about 85 mol% p-phenylene diamine, and ii) 15 mol% to less than 40 mol% m-phenylene diamine; ;

a) and b) are present in a ratio of 1: 1;

The method comprises using compression to form a part of a predetermined shape; The amount of pressure used for compression is from about 137.9 MPa (20,000 psi) to about 344.7 MPa (50,000 psi) to achieve a porous article having permeability to water and resistance to defects caused by heat exposure.

In one embodiment of the present invention, the compression pressure can be predetermined to produce an article having a desired desired density.

In one embodiment of the method of the present invention, the article may have a larger cross-sectional area relative to the surface area of the article, and the article may release moisture and gas present in the cross-sectional area of the article through the surface area of the article.

In another embodiment of the methods disclosed herein, the polyimide composition may comprise at least one filler. Fillers used in the present invention include carbonaceous fillers selected from the group consisting of natural graphite, synthetic graphite, and carbon fibers; Fluoropolymers including but not limited to polytetrafluoroethylene; And an inorganic filler selected from the group consisting of kaolinite, sepiolite and mixtures thereof.

The present invention is useful in a variety of high temperature systems, the system consisting of appliances and equipment. Articles made as disclosed herein can be used to replace conventional materials used at high temperatures. For example, articles made as disclosed herein can be used to replace mechanical elements, components primarily composed of graphite, metal, ceramic, or asbestos.

Uses of the articles of the present invention include convection ovens, diffraction, including emission system components, internal combustion engine components, bushings, bearings, washers, seal rings, wear pads, and slide blocks. Scientific instruments, such as for separating defracting chambers, as components in automotive systems. Further uses of the components disclosed herein include recycling systems; Clutch system; Pump; Turbochargers; A thrust reverser, a nacelle, a flaps system; Injection molding machine; conveyor; And a tenter frame.

The present invention provides a method of making a part formed from a polyimide composition, the part having improved oxidative stability and excellent tensile properties. Such formed parts are useful for high temperature applications, or applications operating above about 400 ° C. Other uses of articles produced by the method of the present invention include scientific instruments, convection ovens, heated conveyors, automotive applications and aerospace engines. Parts and other articles made using the method of the present invention may also include automotive engines; Other vehicle subsystems such as exhaust gas recirculation systems and clutch systems; Pump; Non-aircraft jet engines; Turbocharger; Material processing equipment such as injection molding machines; Material handling equipment such as conveyors, belt presses and tenter frames; And films, seals, washers, bearings, bushings, gaskets, wear pads, seal rings, slide blocks and push pins, and other applications where low wear is desirable. In some applications, a part or other article made in accordance with the methods disclosed herein is in contact with the metal for at least a portion of the time it is assembled and normally used.

The term "rigid polyimide" means that there are no flexible linkers in the polyimide unit.

The aromatic tetracarboxylic dianhydride component used to prepare the copolymer polyimide of the present invention includes pyromellitic dianhydride (PMDA), 3,3'4,4'-biphenyltetracarboxylic dianhydride ( BPDA), and any other rigid aromatic dianhydrides. Best results are seen when BPDA is used as a dianhydride component. In a preferred embodiment of the invention, a solution imidization method is used to provide a rigid, aromatic polyimide composition having the following repeating units.

R is greater than 60 mol% to 85 mol% PPD units and 15 mol% to less than 40 mol% MPD units. Preference is given to polyimide compositions having 70% PPD and 30% MPD.

In the preparation of the polyimide composition of the present invention, the solution imidization method is used as follows. Diamines (PPD and MPD) are generally first dissolved in a solvent to form the diamine component. Generally, after dissolving the diamine component in a solvent of the required concentration, the dianhydride is added to the reaction solution in substantially equimolar amounts to form a polyamic acid (PAA) polymer solution. It is possible that either the dianhydride or diamine component is slightly molar excess. It was found that 0.5 to 1.0% molar excess of diamine component gave the best results. Usually, the closer to equimolar stoichiometry, the better the tensile properties are obtained, but this must be comparable to the higher viscosity that appears as it approaches the equimolar point, as is known to those skilled in the art.

The resulting PAA polymer solution is delivered to a heated solution of solvent over time. The delivered PAA polymer solution is continuously heated and stirred to complete the reaction of the soluble PAA into an insoluble polyimide slurry.

The resulting polyimide slurry is washed with a solvent and dried at 100-230 ° C., preferably 140-190 ° C., more preferably 180 ° C. to convert the polyimide slurry into a polyimide resin in powder form having a large surface area. . Optimal temperatures of 180 ° C. result in greater processing efficiency and better physical properties. Depending on the particle size caused by precipitation of the polyamic acid from the reaction solution, the particles of the polyimide can be further modified, for example by suitable grinding techniques, to provide the desired particle size for handling and subsequent molding. have.

Solvents useful in the solution polymerization process for synthesizing PAA polymer solutions are organic solvents having functional groups that do not react to any detectable degree with any of the reactants (BPDA or diamine). The solvent exhibits a pH of about 8 to 10, and the pH can be measured by mixing the solvent with a small amount of water and then using a pH test paper or a probe. Such solvents include, for example, pyridine and β-picolin. Of the solvents described in US Pat. No. 3,179,614 to Gall and Edwards, pyridine (KB = 1.4 × 10-9) is not only a preferred solvent for this reactant in the polymerization but also acts as a catalyst. In order for the dianhydride and the diamine to react to form a PAA polymer solution, a basic catalyst is required. Since pyridine is a basic compound, it serves here as both a catalyst and a solvent.

The amount of solvent is important in obtaining a product having a large surface area. In particular, the solvent should be present in an amount such that the concentration of the PAA polymer solution is about 1 to 15 wt% solids, preferably about 8 to 12 wt% solids.

The surface area of the polyimide resin produced from the polyimide composition of the present invention should be at least 20 m 2 / g. In order to achieve acceptable physical properties and for ease of processing, the surface area is preferably at least 75 m 2 / g.

In the preparation of PAA, it is essential that the molecular weight is such that the inherent viscosity (IV) of the PAA polymer solution is at least 0.2 dl / g, preferably 0.5 to 2.0 dl / g. Methods for measuring and calculating IV are described below.

Polyimide compositions often include at least one filler or one type of filler. Fillers in the polyimide compositions of the invention include clays such as kaolinite or sepiolite; Fluoropolymers or copolymers such as polytetrafluoroethylene; Molybdenum disulfide; And / or carbonaceous fillers such as graphite, carbon fibers. Fillers can be used to improve wear and friction properties while maintaining excellent tensile and oxidative stability of polyimide compositions and components made therefrom.

Graphite suitable for use herein may be naturally occurring graphite or synthetic graphite. Natural graphites generally have a wide range of impurity concentrations, while synthetically produced graphites with low concentrations of reactive impurities are commercially available. Graphite containing an unacceptably high concentration of impurities can be purified by any of a variety of known treatments, including, for example, chemical treatment with mineral acid. For example, treatment of non-pure graphite with sulfuric acid, nitric acid or hydrochloric acid at elevated or reflux temperatures can be used to reduce impurities to a desired level.

Sepiolite fillers, kaolin fillers, or mixtures thereof are also suitable for use in the present invention. Sepiolite fillers suitable for use in the present invention include sepiolite itself [Mg ₄ Si ₆ O ₁₅ (OH) ₂ .6 (H ₂ O)], which has a high aspect ratio due to its fibrous structure. hydrated magnesium silicate filler. Unique among silicates, sepiolite is composed of long lath microcrystalline with silica chains running parallel to the axis of the fiber. This material appeared to be composed of two forms, α form and β form. The α form is known as a long fiber bundle, and the form exists as an amorphous aggregate.

Sepiolite fillers suitable for use in the present invention also include attapulgite (also known as paligosky), which is structurally and chemically related to sepiolite except that attapulgite has slightly smaller unit cells. Is almost the same.

Sepiolite fillers suitable for use in the present invention also include clay, which is a layered fibrous material, wherein each layer consists of two sheets of tetrahedral silica units bonded to a central sheet of octahedral units containing magnesium ions. [See, eg, L. Bokobza et al, Polymer International, 53, 1060-1065 (2004)]. The fibers stick together to form a fiber bundle, which in turn can form aggregates. These aggregates can be separated by industrial processes such as micronization or chemical modification (see, e.g., European Patent No. 170,299 to Tolsa S.A.).

In one embodiment, sepiolite fillers suitable for use in the present invention are disclosed in European Patent EP-A-454,222 and / or EP-A-170,299 and are trademarked by Tolsa S.A., Madrid, Spain. Rheological grade sepiolite clay such as sold under Pangel®. In this regard, the term "rheological grade" typically refers to an average surface area of 120 m 2 / g [Brunauer et al, "Adsorption of Gases in Multimolecular Layers", Journal of the American Chemical Society, 60: 309-19. , Measured at N ₂ by the Brunauer / Emmett / Teller method), typically having an average fiber dimension of about 200-2000 nm in length, 10 Sepiolite clay with an area of from 30 nm and a thickness of from 5 to 10 nm. Rheological grade sepiolites are obtained from natural sepiolites by a micronization process that substantially prevents the breakage of sepiolite fibers, resulting in sepiolites that are readily dispersed in water and other polar liquids and have a high degree of irregularity. It has a high specific surface, greater than 300 m2 / g, and an outer surface with a high density of active centers for adsorption, and provides very high water retention when it is relatively easy to form hydrogen bridges with active centers. Done. The microfiber properties of rheological grade sepiolite particles make the sepiolite a material with high porosity and low apparent density.

In addition, rheological grade sepiolites have very low cation exchange capacity (10-20 meq / 100 g) and the interaction with the electrolyte is very weak, which in turn leads to the formation of rheological grade sepiolites The sepiolite is therefore stable over a wide pH range so that it is not substantially affected by the presence of salts in the medium. The quality of the above mentioned rheological grade sepiolite can also be found in rheology grade attapulgite, which is typically a series of ATTAGELs manufactured and marketed by Angelhard Corporation, USA. (Trademark) clay (eg, Atazel 40 and Atazel 50); And particle sizes smaller than 40 micrometers, such as a series of MIN-U-GEL products from Floridin Company.

Kaolin fillers suitable for use in the present invention include kaolinite itself, which is a sheet-like silicate arranged in two sheets or plates whose molecules are one silica and one alumina. Kaolinite is a clay mineral with a chemical composition of Al ₂ Si ₂ O ₅ (OH) ₄ . It is a layered silicate mineral in which one tetrahedral sheet is connected to an octahedral sheet of one alumina octahedron via an oxygen atom. Kaolinite-rich rocks are known as china clay or kaolin. In contrast, smectite, such as montmorillonite clay mineral, is arranged in two silica sheets and one alumina sheet. The molecules of smectite are linked together less firmly than the molecules of the kaolinite group and are therefore farther apart. Of the crystal structure of the sheet silicate as desired to maintain the thermal stability of the structural water of the sheet silicate at a high temperature such as up to about 450 ° C. (eg, as shown by thermal gravity analysis (TGA)). It is desirable to maintain phase stability. Loss of structural water during processing of the polyimide composition can lead to damage to polyimide integrity, possibly altering the crystal structure of the sheet silicate, providing a harder and more abrasive compound. Examples of sheet silicates that are not sufficiently stable to be included in the compositions disclosed herein are montmorillonite, vermiculite and pyrophyllite. Kaolin fillers suitable for use in the present invention are further discussed in Murray, Applied Clay Science 17 (2000) 207-221.

Sepiolite fillers and kaolin fillers suitable for use in the present invention are further discussed in Murray, Applied Clay Science 17 (2000) 207-221.

In embodiments of the invention, graphite, sepiolite and / or kaolin used as fillers are typically incorporated into a heated solvent prior to delivery of the PAA polymer solution (or other solution for other types of monomers), thereby In the presence of component (b) and component (c) which have been incorporated into the composition, the resulting polyimide is allowed to precipitate.

Additives suitable for use selectively in the present compositions may include, without limitation, one or more of the following: pigments; Antioxidants; Materials for imparting a lower coefficient of thermal expansion, such as carbon fibers; Materials for providing high strength properties such as, for example, glass fibers, ceramic fibers, boron fibers, glass beads, whiskers, graphite whiskers or diamond powders; Materials for providing heat or heat resistant properties such as, for example, aramid fibers, metal fibers, ceramic fibers, whiskers, silica, silicon carbide, silicon oxide, alumina, magnesium powder or titanium powder; Substances for providing corona resistance, such as, for example, natural mica, synthetic mica or alumina; Materials for providing electrical conductivity such as, for example, carbon black, silver powder, copper powder, aluminum powder or nickel powder; Materials to further reduce wear or coefficient of friction, such as boron nitride or poly (tetrafluoroethylene) homopolymers and copolymers. The filler may be added to the final resin as a dry powder prior to the manufacture of the parts.

Any one or combination of additives and / or fillers may be present in amounts ranging from 0.1 to 80% by weight. The particular filler or fillers selected, as well as the amount of use, will, of course, depend on the effect required in the final composition, as will be apparent to those skilled in the art.

Such additives or fillers are typically incorporated into heated solvents prior to delivery of the PAA polymer solution, thereby precipitating the polyimide in the presence of the fillers incorporated therein, but this is not always the case. In some cases, the filler (s) or additive (s), or both, are dry blended with the polyimide particulates. The form of the filler will depend on the function of the filler in the final product. For example, the filler may be in particulate or fibrous form.

As mentioned above, the polyimide compositions of the present invention are oxidatively stable. To test oxidative stability, tension bars are formed as described below and then exposed to extreme temperatures for a defined length of time. Weigh the tension bar both before and after the test and calculate the percent weight loss. When the percent weight loss is less than 5%, preferably less than 3%, the rigid, aromatic polyimide compositions of the present invention are considered to be oxidatively stable, such that the weight loss is a tension bar, or more specifically, herein This is because the completeness of the parts produced by the method of the present invention as disclosed is not impaired.

The polyimide articles of the present invention are not only due to excellent oxidative stability, or only by any one property, but also durability, wear resistance and wear life, stiffness, permeability to heated moisture and gases, and defects upon thermal exposure. Characterized by exceptional tensile properties, along with other properties important in high temperature applications, such as resistance to. Tensile strength and elongation are particularly important properties for such applications as described above. As is generally known to those skilled in the art, products with low elongation tend to be brittle, causing cracking during machining or in load bearing applications.

Polyimide compositions prepared as disclosed herein can be molded into a wide variety of forms under elevated pressure. In many applications, the polyimide composition is molded at a pressure of about 50,000 to 100,000 psi at ambient temperature of about 345 to 690 MPa (50,000 to 100,000 psi).

The method of making an article for high temperature applications, including permeability to heated moisture and gas, is a direct forming method, the polyimide composition is introduced into a mold and the polyimide composition is at an elevated temperature of about 300 ° C. to about 450 ° C. Pressure from about 138 MPa (20,000 psi) to about 345 MPa (50,000 psi), preferably about 241 MPa (35,000 psi) to about 310 MPa (45,000 psi), most preferably about 276 MPa (40,000 psi) By compressing the parts using the formed article or part.

Articles or parts made by compressing a polyimide composition from about 138 MPa (20,000 psi) to about 345 MPa (50,000 psi) are useful for high temperature applications. More specifically, articles of parts made by the method of the present invention are useful for glass making, and more specifically for glass container making. Such articles or parts include, but are not limited to, glass handling assemblies, and components thereof. These include take-out jaw inserts, dead plates, sweep out devices, stacker bars, stacker bar pads, stacker bar bearings, among which Included is a take-out jaw assembly and components thereof, including any of the components.

Polyimide materials readily absorb moisture in the atmosphere. Depending on the environment, the equilibrium point may be greater than 1 weight percent. When the polyimide material is heated, this moisture will be released. However, if the material is heated at a faster rate than this moisture can escape, blistering may occur. This phenomenon can limit the use of polyimide materials in many applications. To overcome this limitation, the inventors have studied a method for increasing the permeability of polyimide materials. The inventors have demonstrated that pressing or compressing polyimide materials at low pressure can result in a more porous structure with significantly better resistance to blistering during thermal exposure or during exposure to rapid thermal cycling. The inventors have also demonstrated that this can be done without significantly affecting the mechanical properties of the material, which is critical for high temperature wear performance and durability.

Copolymer-based polyimides used in the method (s) and article (s) of the present invention are compared to the use of traditional and commonly used polyimide materials, and carbon graphite materials (eg, without polyimide) And certain advantages in high temperature applications such as high temperature glass handling applications, aircraft engines and components, or analytical scientific instruments.

The methods and uses disclosed herein provide low thermal conductivity, resulting in about 50 to 100 times lower heat transfer coefficients compared to articles made using traditional carbon graphite. Lower thermal conductivity of the articles of the invention, and related uses of the articles of the invention, result in minimization or removal of blisters and microcracks, thereby reducing quality rejection and improving productivity.

The methods and articles of the present invention have also been found to provide a high impact resistance of 70 to 100% greater than carbon graphite parts traditionally used in high temperature glass making applications. Reduced breakage of the article during manufacture, handling and use extends the life of the article, which in turn increases process reliability and reduces operating costs.

Oil absorption is also observed in the methods and articles of the invention. The components produced in the present invention exhibit 30 times less oil absorption to zero oil absorption than carbon graphite parts. Reduced or absent oil absorption provides the advantage of reducing the checking in containers handled by the articles, thereby increasing the yield of the containers and reducing the operating costs.

Another advantage of the methods and articles of the present invention is the reduction of wear. The test results show three times less wear compared to carbon graphite at 315 ° C. (600 ° F.) under oscillatory conditions, indicating a 2 to 11 times longer life than glass handled carbon graphite take-out inserts. . Such an advantage leads to a considerably longer life of consumables, thereby increasing production efficiency.

Example

For the test data listed in the table above, samples of polyimide compositions as disclosed herein were subjected to ASTM E8-"Standard Tension Test Specimen for Flat Metal Articles-Flat, Unmachined Tensile Test Rod" (Standard Tension Test Specimen for Powdered Metal Products-Flat Un-machined Tensile Test Bar) were fabricated with tension bars at room temperature and at pressures ranging from 20,000 to 100,000 psi (138 to 690 MPa). The tension bar was sintered at 405 ° C. for 3 hours with nitrogen purging. Tensile strength and elongation were measured according to ASTM D638.

Specific gravity was measured using Archimedes' theory (ie, the weight of the specimen was measured in water and subtracted from the dry weight of the specimen to determine the volume. Then, this volume was divided by the dry weight to determine specific gravity).

Tensile bars or parts of tension bars were first immersed in alcohol for 15 minutes and dried at 149 ° C. (300 ° F.) for 1 hour to test thermal oxidation stability (TOS). Upon cooling, the specimens were weighed and then exposed to air at a temperature of 371 ° C. (700 ° F.) for 100 hours at a pressure of 483 kPa (70 psia). The final weight was determined and then the percent weight loss of the tension bar was calculated according to the following formula:

% Weight loss = (initial weight-final weight / initial weight) × 100

Tension bars or parts of tension bars are first immersed in 95 ° C. water for 12 days to test resistance to blistering during heat exposure or rapid thermal cycling. Next, the specimen is placed in an oven preheated to a certain temperature. A pass result is obtained if there are no visible cracks or blisters on the specimen after this thermal exposure. Samples compressed at 138 and 276 MPa (20,000 and 40,000 psi) showed no visible defects after exposure to up to 400 ° C. (including 400 ° C.). Samples compressed at 60,000 to 100,000 psi (414 to 689 MPa) showed defects after exposure to temperatures above 325 ° C.

Specimens pressed at 276 MPa (40,000 psi) exhibited positive blistering resistance performance at 400 ° C. while maintaining 88% of tensile strength and 94% of elongation of the specimens compressed at 689 MPa (100,000 psi). It is noteworthy that in the case of specimens pressed at higher pressures only such performance is shown at 325 ° C.

Other methods, such as the addition of sacrificial fillers that deteriorate or polish or grind during thermal, chemical or mechanical processing steps to create a network of pores or paths of water discharge, can be used to obtain parts of low or increased pore density. Care should be taken. However, the methods described herein are economical because no additional fillers and processing steps are required, while achieving parts with mechanical integrity suitable for high temperature applications.

Example  2: comparative analysis

In "Example 2: Comparative Analysis", the results of the column labeled "Traditional Polyimide" were obtained using a sample of 60 weight percent conventional polyimide and 40 weight percent graphite. "Traditional carbon graphite" results were obtained using graphite without polyimide. The "copolymer based polyimide of the present invention" results were obtained using 50% by weight of a polyimide composition as disclosed herein and a sample of 50% by weight of graphite.

Claims (15)

A method of making an article suitable for use in a high temperature system,
The system consists of instrumentation and equipment, the article comprising a copolymer based polyimide composition,
The composition is
a) aromatic tetracarboxylic dianhydride component; And
b) a diamine component further comprising (i) greater than 60 mol% to about 85 mol% p-phenylene diamine and (ii) 15 mol% to less than 40 mol% m-phenylene diamine Includes;
a) and b) are present in a ratio of 1: 1;
The method comprises using compression to form a part of a predetermined shape;
The amount of pressure used for compression is from about 138 MPa (20,000 psi) to about 345 MPa (50,000 psi) to achieve a porous article having permeability to water and resistance to defects caused by heat exposure. The method of claim 1, wherein the compression pressure is about 241 MPa (35,000 psi) to about 310 MPa (45,000 psi). The method of claim 1, wherein the compression pressure is about 276 MPa (40,000 psi). The method of claim 1, wherein the article has a larger cross-sectional area relative to the surface area of the article, and the article can release moisture and gas present in the cross-sectional area of the article through the surface area of the article. The method of claim 1 wherein the polyimide composition comprises at least one filler or additive. 6. The method of claim 5 wherein said filler is a carbonaceous filler and said carbonaceous filler is selected from the group consisting of natural graphite, synthetic graphite and carbon fibers. The method of claim 6, wherein the filler is a fluoropolymer, and the fluoropolymer is selected from the group consisting of polytetrafluoroethylene. 6. The method of claim 5, wherein said filler is selected from the group consisting of kaolinite, sepiolite, and mixtures thereof. An article made by the method of claim 1. The article of claim 9 suitable for use in an analytical scientific instrument for separating a diffracting chamber. 10. The article of claim 9 suitable for use in a convection oven or a heated conveyor. 10. The article of claim 9 suitable for use in an automotive engine or automotive subsystem. The article of claim 12, wherein the vehicle subsystem is selected from the group consisting of an exhaust gas recirculation system, a clutch system, a pump, and a turbocharger. 13. The article of claim 12, which is a seal, washer, bearing, bushing, gasket and seal ring. As an article of manufacture suitable for use in high temperature systems,
The system consists of an appliance and equipment, the article comprising a copolymer based polyimide composition,
The composition is
a) aromatic tetracarboxylic dianhydride component; And
b) a diamine component further comprising i) greater than 60 mol% to about 85 mol% p-phenylene diamine, and ii) 15 mol% to less than 40 mol% m-phenylene diamine; ;
a) and b) are present in a ratio of 1: 1;
The article is porous and has permeability to moisture and resistance to defects caused by thermal exposure.

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