Title of Invention	METHODS OF IMPROVING POLYIMIDE FILMS
Abstract	Polyimide oligomers and polymers are cured with the assistance of a phosphorus based catalyst, such as an aryl, alkyl or arylalkyl phosphite. The resulting material has the desirable high thermal properties of condensation polyimides, but with minimal outgassing of water during cure. Novel properties obtained include an increase in glass transition, crosslink density, lower temperature cure, and improved film formation. These properties are important in applications including solvent based coatings, films, powder coatings, pre¬impregnated (prepreg) coatings, laminates, compression molding, and thermosetting resin extrusions.

Title of Invention

METHODS OF IMPROVING POLYIMIDE FILMS

Abstract

Polyimide oligomers and polymers are cured with the assistance of a phosphorus based catalyst, such as an aryl, alkyl or arylalkyl phosphite. The resulting material has the desirable high thermal properties of condensation polyimides, but with minimal outgassing of water during cure. Novel properties obtained include an increase in glass transition, crosslink density, lower temperature cure, and improved film formation. These properties are important in applications including solvent based coatings, films, powder coatings, pre¬impregnated (prepreg) coatings, laminates, compression molding, and thermosetting resin extrusions.

Full Text	CATALYSIS OF POLYIMIDE CURING BACKGROUND OF THE INVENTION [001] This invention relates to polyimide resin compositions; and, more particularly, to a composition of polyimide materials used in solvent based coatings, films, powder coatings, pre¬impregnated coatings (commonly referred to as "prepreg" coatings), compression molding, and thermosetting resin extrusions. The composition includes a polyimide oligomer/polymer~and a phosphorus based catalyst. [002] Polyimide resins are high-temperature resistant polymers that retain their physical properties during short-term exposures at temperatures of up to 5550C (1 0300F), and can be used for prolonged periods of time at temperatures ranging up to approximately 3330C (6300F). Polyimide resins include condensation polyimide resins, addition polyimide resins, thermoplastic polyimides (e.g., polyamideimide and polyetherimide resins) and polyesterimide resins. All of these polymers have excellent electrical and physical properties, as well as high thermal and oxidative stability. Because of this combination of properties, these polyimides are used in aerospace, electronics and various other industrial applications. In these applications, molecular weights of the condensation polyimides (polyamideimides and polyesterimides) are kept low so they can be applied onto a substrate in solution, and to permit thermoplastic processing. [003] Subsequent heating (in the case of a laminate or a molded article under pressure) carries the polymerization reaction further, increasing molecular weight, and developing the product's final properties. However, evolution of a water by-product during this second reaction step causes some porosity which is undesirable for applications involving laminates, moldings, and films. This drawback is partially eliminated by the addition of polyimides to the solution which cross-link through an addition reaction. Fully imidized polyimides are capable of producing low-void laminates, since ring closure prevents the water by-product from being released during curing. However, these addition polyimides are poor for film formation, are difficult to synthesize, result in lower thermal properties, and are expensive to use. [004] Due to the limitations of both condensation and addition polyimides, a new polyimide material is desired which can achieve the desirable high thermal properties of condensation polyimides; while, minimizing the outgassing of water upon final cure. Phosphorus based catalysis of polyamideimide resin synthesis has been known and reported in the literature since the I 980's. In these applications, triphenylphosphite (TPP) is added in stoichiometric amounts to trimellitic anhydride and a diamine, and the resulting reaction is further facilitated by the addition of excess pyridine in solution. The TPP activates the carboxylic acid group to achieve amide formation with the diamine. However, this process has not been widely used commercially; due to the high cost of the catalysts and the large amounts of them needed to synthesize the polymer backbone. [005] TPP has been post-added in the extrusion of polyester and polyamide resins. In their article, H,ph- Temperature Reactions of Hydroxyl and Carboxyl PET Chaib End Groups lb the Presence of Aromatic Phospli/te, Aharon, S.M. et al, Journal of Polymer Science: Part A, Polymer Chemistry Vol. 24, pp. 1281-1296 (1986), the authors added varying levels of TPP to polyethyleneterephthalate (PET) and found an increase in molecular weight compared to a degradation in molecular weight without the catalyst. Similar findings were reported for polyamide resins such as nylon 6,6. [006] U.S. Pat. No. 4,749,768 describes a process for producing thermoplastic processable aromatic polyamides with phosphorus catalysis. In this patent, a diamine is condensed with a dicarboxylic acid with catalysis by either triphenylphosphite or H3POn acid. [007] Japanese Pat. No. 2005213387, describes a method in which thermosetting resins in the presence of 0.01-10 phr phosphite esters show low emission of volatile organic compounds. The thermosetting resin system is an unsaturated polyester with a styrene monomer. BRIEF SUMMARY OF THE INVENTION [008] In accordance with the invention, there is described the use of a phosphorus based catalyst to promote the cure of polyimide resins. Use of the catalyst dramatically increases glass transition temperature. A second aspect of the invention is that the catalyst minimizes the amount of water generated, thereby possibly minimizing void formation in a cured substrate. A third aspect of the invention is that the catalyst accelerates cure thereby minimizing the long curing procedures needed with polyimides such as a polyamideimide resin. Additionally, the catalyst allows for temperature at which the curing procedure is carried out to be substantially reduced than is required when a catalyst is absent. The result is a new polyimide material having the desired high thermal properties of condensation polyimides with minimal outgassing of water during cure. [009] Other objects and features will be in part apparent and in part pointed out hereinafter. DETAILED DESCRIPTION OF INVENTION [0010] The following detailed description illustrates the invention by way of example and not by way of limitation. This description will clearly enable one skilled in the art to make and use the invention, and describes several embodiments, adaptations, variations, alternatives and uses of the invention, including what we presently believe is the best mode of carrying out the invention. As various changes could be made in the above constructions without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense. [0011] Polyimide resins useful in the present invention are commonly used in solvent based coatings, films, prepreg coatings, laminates, compression molding, and thermosetting resin extrusion. These resins include condensation polyimides, addition polyimides and thermoplastic polyimides. Useful polyimide resins are obtained by condensation polymerization between a diamine and a dianhydride. Non-limiting examples of diamines include: [0012] X-R"-(-NH2)n [0013] where R" is an organic radical, n is at least 2, and X is hydrogen, an amino group or an organic group including those having at least one amino group. [0014] Diamines useful for this purpose are expressed by the formula: [0015] R"-(-NH2)n [0016] where R"' is a member selected from a class consisting of organic radicals of at least two carbon atoms (both halogenated and unhalogenated) including but not limited to, e.g., hydrocarbon radicals of up to 40 carbon atoms, and groups consisting of at least two aryl residues attached to each other through the medium of a member selected from the class consisting of an alkylene radical of from 1 to 10 carbon atoms, --S--, 0 II [0017]--S02--,'C",and --0--etc., and n is again at least 2. [0018] Among specific useful amines, alone or in admixture, are the following: [0019] p-xylene diamine [0020] bis(4-amino-cyclohexyl)methane [0021] hexamethylene diamine [0022] heptamethylene diamine [0023] octamethylene diamine [0024] nonamethylene diamine [0025] decamethylene diamine [0026] 3-methyl-heptamethylene diamine [0027] 4,4'-dimethylheptamethylene diamine [0028] 2,1 1-diamino-dodecane [0029] 1 ,2-bis-(3-amino-propoxy)ethane [0030] 2,2-dimethyl propylene diamine [0031] 3-methoxy-hexamethylene diamine [0032] 2 ,5-dimethylhexamethylene diamine [0033] 2, 5-dimethylheptamethylene diamine [0034] 5-methylnonamethylene diamine [0035] 1 ,4-diamino-cyclo-hexane [0036] 1,1 2-diamino-octadecane [0037] 2,5-diamino-1 ,3,4-oxadiazole [0038] H2N(CH2)30(CH2)20(CH2)3NH2 [0039] H2N(CH2)35(CH2)3NH2 [0040] H2N(0H2)3N(CH3)(CH2)3NH2 [0041] meta-phenylene diamine [0042] para-phenylene diamine [0043] 4,4'-diamino-diphenyl propane [0044] 4,4'-diamino-diphenyl methane benzidine [0045] 4,4'-diamino-diphenyl sulfide [0046] 4,4'-diamino-diphenyl sulfone [0047] 3,3'-diamino-diphenyl sulfone [0048] 4,4'-diamino-diphenyl ether [0049] 2,6-diamino-pyridine [0050] bis(4-amino-phenyl)diethyl silane [0051] bis(4-amino-phenyl)diphenyl silane [0052] bis(4-amino-phenyl)phosphine oxide [0053] 4,4'-diaminobenzophenone [0054] bis(4-amino-phenyl)-N-methylamine [0055] bis(4-aminobutyl)tetramethyldisiloxane [0056] 1 ,5-diaminonaphthalene [0057] 3, 3'-dimethyl-4,4'-diamino-biphenyl [0058] 3,3'-dimethoxy benzidine [0059] 2 ,4-bis(beta-amino-t-butyl)toluene toluene diamine [0060] bi(para-beta-amino-t-butyl-phenyl)ether [0061] para-bis(2-methyl-4-amino-pentyl)benzene [0062] para-bis(1 ,1 -dimethyl-5-amino-pentyl)benzene [0063] m-xylylene diamine [0064] poly(methylene) polyaniline [0065] The dianhydride can be expressed by the following structure [0066] [0067] where Y is an organic group, and Z' and Z" are hydrogen or an organic group. Y' can be 0, NR, S02, S, 0=0, alkyl, alkyliluoro, or an aromatic group. Non-limiting examples of dianhydrides include: Benzophenonetetracarboxylic acid anhydride, Pyromellitic dianhydride and 3,3',4,4'-biphenyltetracarboxylic dianhydride (s-, a-, and i- versions). [0068] A subset of polyimide polymers are polyamideimide resins which are mainly produced in one of three ways. One way utilizes a polyisocyanate with a carboxylic anhydride. Any polyisocyanate, that is, any isocyanate having two or more isocyanate groups, whether blocked or unblocked, can be used in making polyamideimides. Blocked isocyanates using, for example, phenols or alcohols as the blocking constituent, can also be used. In general, they provide a higher molecular weight of the final material and this is advantageous, for example, in varnishes. Conversely, unblocked isocyanates provide more flexible final materials. Regardless of which is used, as much of the blocking material must be evaporated off as possible, and there is no advantage, from a purely reaction point of view, as to which material is used. A typical blocked polyisocyanate is Mondur 5TM in which mixtures of 2,4- and 2,6-tolylene diisocyanate are reacted with trimethylol propane, and blocked by esterification with phenol in the proportions of three moles of isocyanate, one mole of trimethylol propane, and three moles of phenol. Another blocked polyisocyanate is Mondur SHTM, in which isocyanate groups of mixed 2,4- and 2,6-tolylene diisocyanate are blocked by esterification with cresol. Polyisocyanates which are useful alone, or in admixture, include: [0069] tetramethylenediisocyanate [0070] hexamethylenediisocyanate [0071] 1 ,4-phenylenediisocyanate [0072] 1 ,3-phenylenediisocyanate [0073] 1 ,4-cyclohexylenediisocyanate [0074] 2,4-tolylenediisocyanate [0075] 2,5-tolylenediisocyanate [0076] 2,6-tolylenediisocyanate [0077] 3,5-tolylenediisocyanate [0078] 4-chloro-1 ,3-phenylenediisocyanate [0079] 1 -methoxy-2,4-phenylenediisocyanate [0080] 1 -methyl-3,5-diethyl-2,6-phenylenediisocyanate [0081] 1, 3,5-triethyl-2,4-phenylenediisocyanate [0082] 1 -methyl-3, 5-diethyl-2 ,4-phenylenediisocyanate [0083] 1 -methyl-3,5-diethyl-6-chloro-2,4-phenylenediisocyanate [0084] 6-methyl-2,4-diethyl-5-nitro-1 ,3-phenylenediisocyanate [0085] p-xylylenediisocyanate [0086] m-xylylenediisocyanate [0087] 4,6-dimethyl- 1 ,3-xylylenediisocyanate [0088] 1, 3-dimethyl-4,6-bis-(b-isocyanatoethyl)-benzene [0089] 3-(a-isocyanatoethyl)-phenylisocyanate [0090] 1 -methyl-2,4-cyclohexylenediisocyanate [0091] 4,4'-biphenylenediisocyanate [0092] 3,3'-dimethyl-4,4'-biphenylenediisocyanate [0093] 3, 3'-dimethoxy-4,4'-biphenylenediisocyanate [0094] 3,3'-diethoxy-4,4-biphenylenediisocyanate [0095] 1,1 -bis-(4-isocyanatophenyl)cyclohexane [0096] 4,4'-diisocyanato-diphenylether [0097] 4,4'-diisocyanato-dicyclohexylmethane [0098] 4,4'-diisocyanato-diphenylmethane [0099] 4,4-diisocyanato-3, 3-dimethyldiphenylmethane [0100] 4,4'-diisocyanato-3,3'-dichlorodiphenylmethane [0101] 4,4'-diisocyanato-diphenyldimethylmethane [0102] 1 ,5-naphthylenediisocyanate [0103] 1 ,4-naphthylenediisocyanate [0104] 4,4',4"-triisocyanato-triphenylmethane [0105] 2,4,4'-triisocyanato-diphenylether [0106] 2,4, 6-triisocyanato- 1 -methyl-3,5-diethylbenzene [0107] o-tolidine-4,4'-diisocyanate [0108] m-tolidine-4,4'-diisocyanate [0109] benzophenone-4,4'-diisocyanate [0110] biuret triisocyanates [0111] polymethylene polyphenylene isocyanate [0112] The carboxylic anhydride mainly includes trimellitic anhydride. Other potential materials include trimellitic acid and a dehydrating material. [0113] A second way of producing polyamideimide resins involves the use of a diamine and a carboxylic anhydride acid chloride. This is the preferred route to synthesis of polyamideimide polymers sold by Solvay Advanced Polymers, L.L.C. under the name TORLON®. The carboxylic anhydride acid chloride is preferably trimellitic anhydride acid chloride. The diamines include ODA (oxydianiline) and MDA (methylenediphenyldiamine). [0114] A third and less common way of producing polyamideimide resins involves the condensation of an organic diamine with two equivalents of carboxylic anhydride. In general, a slight molar excess of carboxylic acid anhydride and organic polyamine is heated from about 2000C (3920F) to about 2450C (4730F) in an inert atmosphere and with a solvent. This drives off any water formed, and forms an amideimide group containing a prepolymer. A polyisocyanate is then added and the mixture reacted to form a block amide-imide prepolymer having a relatively high molecular weight. This is then cured (as by heating) to form a flexible film or coating. [0115] As taught, for example, in United States patent 3,817,926, up to 75 mole percent of the carboxylic anhydride can be replaced by a substituted or unsubstituted aliphatic anhydride or diacid such as oxalic, maleic, succinic, glutaric, adipic, pimelic, suberic, azelaic, sebacic and dodecanedioic, as well as unsaturated materials including maleic and fumaric materials, among others. Such acids are expressed by the formula: [0116] HOOC--R'--COOH [0117] where R' is a divalent saturated or unsaturated aliphatic group, or one containing a carbon-to-carbon double bond and having from about one to 40 carbon atoms. The anhydrides can be expressed by the formula: [0118] (Formula Removed) L0119] A phosphite catalyst can be added to the resin in the range of 0.01% to 10% by weight of the resin. The catalyst can be an aryl, arylalkyl or alkyl phosphorus based catalyst. Arylphosphites, 'such as a diaryl- or triaryl-phosphite, work well. Alkyldiarylphosphites and dialkylarylphosphites should also work. Triphenylphosphite (TPP) can be produced, in-situ, by the addition of a phenol- or a phenolic-like substance to an activated phosphorus compound. Such activated phosphorus compounds include, for example, species such as phosphorus trichloride or phosphorus tribromide. [0120] Fillers and additives can also be incorporated into the polymer matrix. Non-limiting examples of fillers include titanium dioxide, alumina, silica, graphite, carbon black, and fiberglass. Other additives include thickeners, plasticizers, flow agents, antiblocking agents, antistatic agents, antioxidants, hindered amine light stabilizers, and ultraviolet light stabilizers. [0121] In a coating application, the polyimide solution is mixed with the phosphorus catalyst. The solution is either directly coated onto a substrate, web, or composite material. The solvent is then evaporated by thermal or vacuum means and the remaining resin cured by thermal means including oven heat, inductive heating, or infrared sources. [0122] A polyimide coating solution, such as Ultratherm® A 828 (available from The P.D. George Co.), requires temperatures of greater than 1 500C (z3000F) to achieve enough cure so that a chemically resistant film can be obtained. The same polyimide material can be cured at less than 1 250C (2570F) with phosphorus catalyst. Catalyst concentration also impacts the rate at which cure is achieved. [0123] A polyamideimide coating solution, such as Tritherm® A 981 (available from The P.D. George Co.), requires temperatures of greater than 2400C (~4650F) to achieve enough cure so that a chemically resistant film is obtained. The same polyamideimide material can be cured at 2000C (3020F) with a phosphorus catalyst. Again, catalyst concentration also impacts the rate at which cure is achieved. [01241 Glass transition temperature is also dramatically impacted by phosphorus based catalysis. A polyamideimide resin, such as Tritherm® A 981 (available from The P.D. George Co.), typically has a glass transition temperature of approximately 270-3000C (~52O-57O0F). Multiple reheats will still demonstrate a similar glass transition temperature. Phosphorus based catalysis dramatically changes the thermoplastic properties. Multiple reheats of up to 4000C (~75O0F) increases the glass transition from roughly 27000 (z52O0F) to greater than 35000 (~6600F). This dramatic increase is also observed using Solvay based Torlon® Al-i 0. [0125] In an extrudable material such as Torlon® 4203, an un-reinforced polyamideimide containing 3% titanium and 0.5% fluoropolymer available from Solvay Advanced Polymers, LLC, TPP (triphenylphosphite) can be added prior to solvent stripping to make a powdered resin. It should also possible to compound the resin powder with TPP after solvent removal. We have also found that extruded Torlon® 4203 (fully imidized) can be post-treated with TPP and further cured upon heat treatment. Either method should allow for post-heat treatment to obtain a final cured part with improved glass transition and physical properties. [0126] EXAMPLES [0127] Example 1: [0128] Glass panels were coated with a Tritherm®A 981-H (The P.D. George Co.) using a #80 Meier bar. The panels were cured for 15 and 30 minutes in a Thermotron forced air oven at temperatures of 15000 (3020F), 17500 (3470F), and 200CC (3920F). The cured films had an average thickness of 15 microns. A small portion of the resulting film was placed in dimethyl formamide(DMF) to determine solubility. The results are included in Table I below. [0129] Example 2: [0130] To I OOg of Tritherm®A 981-H, add 2g of triphenyl phosphite (TPP). Stir the mixture, using a stir bar, until the sample is uniform. Glass panels were coated with the sample using a #80 Meier bar. The panels were then cured for 15 and 30 minutes in a Thermotron forced air oven at temperatures of 15000, 175"C, and 20000. The cured films had an average thickness of 15 microns. A small portion of the resulting film was placed in dimethyl formamide (DMF) to determine solubility. The results are also included in Table I. Table I (Table Removed) [0131] As seen from Table I, the polyamideimide film made from Tritherm A 981-H was soluble in DMF irrespective of the cure time and cure temperature. However, the polyamideimide film made from Tritherm A 981-H when mixed with 2% TPP, the resulting film was not soluble in DMF when cured 20000 and was only partially soluble in DMF when cured at 17500. The film was soluble in DMF when cured at 15000. These results show that the addition of TPP in a small amount (i.e., 2%) produces a chemically resistant film when cured at 20000, and a partially chemically resistant film when cured at 1750C. However, without the addition of the TPP, the Tritherm would have to be cured at higher temperatures and/or for longer periods of time to produce a chemically resistant film. [0132] Example 3: [0133] Glass panels were coated with Tritherm®A 981-H using a #80 Meier bar. The panels were cured for 30 minutes in a Thermotron forced air oven at temperatures of 20000 (3920F) and 26000 (5000F). The cured films had an average thickness of 15 microns. The glass transition temperature of the film was determined by differential scanning calorimetry (DSO). Each sample was heated to 40000 (7520F), cooled to room temperature (2500, or 770F), reheated to 40000, cooled to room temperature again, then reheated to 40000 again. The glass transition temperature was determined after each heating cycle. The results are included in Table II. [0134] Example 4: [0135] To bOg of Tritherm®A 981-H, add 2g of TPP. Stirthe mixture, using a stir bar, until the sample is uniform. Glass panels were coated with the sample using a #80 Meier bar. The panels were cured 30 minutes in a Thermotron forced air oven at temperatures of 20000 and 26000. The cured films had an average thickness of 15 microns. The glass transition temperature of the film was determined by DSC. Each sample was heated to 40000, cooled to room temperature (2500), reheated to 40000, cooled to room temperature again, then reheated to 40000 again. The glass transition temperature was determined after each heating cycle. The results are also included in Table II. [0136] Example 5: [0137] To 1 OOg of Tritherm®A 981-H, add I g of TPP. Stir the mixture, using a stir bar, until the sample is uniform. A glass panel was coated with the sample using a #80 Meier bar. The panel was cured 30 minutes in a Thermotron forced air oven at a temperature of 26000. The cured film had an average thickness of 15 microns. The glass transition temperature of the film was determined by DSC. Each sample was heated to 40000, cooled to room temperature (2500), reheated to 40000, cooled to room temperature again, then reheated to 40000 again. The glass transition temperature was determined after each heating cycle. The results are included in Table II. [0138] Example 6: [0139] To bOg of Tritherm®A 981-H, add 0.Sg of TPP. Stir the mixture, using a stir bar, until the sample is uniform. A glass panel was coated with the sample using a #80 Meier bar. The panel was cured 30 minutes in a Thermotron forced air oven at a temperature of 2600C. The cured film had an average thickness of 15 microns. The glass transition temperature of the film was determined by DSO. Each sample was heated to 40000, cooled to room temperature (2500), reheated to 400"C, cooled to room temperature again, then reheated to 40000 again. The glass transition temperature was determined after each heating cycle. The results are included in Table II. [0140] Example 7: [0141] To bOg of Tritherm®A 981-H, add 0.2g of TPP. Stir the mixture, using a stir bar, until the sample is uniform. A glass panel was coated with the sample using a #80 Meier bar. The panel was cured 30 minutes in a Thermotron forced air oven at a temperature of 26000. The cured film had an average thickness of 15 microns. The glass transition temperature of the film was determined by DSC. Each sample was heated to 40000 cooled to room temperature (2500), reheated to 40000, cooled to room temperature again, then reheated to 40000 again. The glass transition temperature was determined after each heating cycle. The results are included in Table II. [0142] Example 8: [0143] To lOOg of Tritherm®A 981-H, add 2g of diphenyl phosphite (DPP). Stir the mixture, using a stir bar, until the sample is uniform. Glass panels were coated with the sample using a #80 Meier bar. The panels were cured 30 minutes in a Thermotron forced air oven at temperatures of 20000 and 26000. The cured films had an average thickness of 15 microns. The glass transition temperature of the film was determined by DSC. Each sample was heated to 40000, cooled to room temperature (2500), reheated to 40000, cooled to room temperature again, then reheated to 40000 again. The glass transition temperature was determined after each heating cycle. The results are included in Table II. [0144] Example 9: [0145] To lOOg of Tritherm®A 981-H, add ig of DPP. Stir the mixture, using a stir bar, until the sample is uniform. A glass panel was coated with the sample using a #80 Meier bar. The panel was cured 30 minutes in a Thermotron forced air oven at a temperature of 26000. The cured film had an average thickness of 15 microns. The glass transition temperature of the film was determined by DSO. Each sample was heated to 40000, cooled to room temperature (2500), reheated to 40000, cooled to room temperature, then reheated to 40000 again. The glass transition temperature was determined after each heating cycle. The results are included in Table II. [0146] Example 10: [0147] To lOOg of Tritherm®A 981-H, add 0.Sg of DPP. Stir the mixture, using a stir bar, until the sample is uniform. A glass panel was coated with the sample using a #80 Meier bar. The panel was cured 30 minutes in a Thermotron forced air oven at a temperature of 2600C. The cured film had an average thickness of 15 microns. The glass transition temperature of the film was determined by DSC. Each sample was heated to 40000, cooled to room temperature (2500), reheated to 4000C, cooled to room temperature again, then reheated to 40000 again. The glass transition temperature was determined after each heating cycle. The results are included in Table II. [0148] Example 11: [0149] A glass panel was coated with Torlon® AI-lO (Solvay) using a #80 Meier bar. The panel was cured for 30 minutes in a Thermotron forced air oven at a temperature of 26000. The cured film had an average thickness of 15 microns. The glass transition temperature of the film was determined by differential scanning calorimetry (DSO). Each sample was heated to 40000, cooled to room temperature (2500), reheated to 40000, cooled to room temperature again, then reheated to 40000 again. The glass transition temperature was determined after each heating cycle. The results are included in Table II. [0150] Example 12: [0151] To bOg of Torlon®AI-10, add 2g of TPP., Stir the mixture, using a stir bar, until the sample is uniform. A glass panel was coated with the sample using a #80 Meier bar. The panel was cured 30 minutes in a Thermotron forced air oven at a temperature of 26000. The cured film had an average thickness of 15 microns. The glass transition temperature of the film was determined by DSO. Each sample was heated to 40000, cooled to room temperature (25~0), reheated to 40000, cooled to room temperature again, then reheated to 40000 again. The glass transition temperature was determined after each heating cycle. The results are included in Table II. [0152] Example 13: [0153] The glass transition temperature of Torlon® 4203(Solvay) rod shavings was determined by differential scanning calorimetry (DSC). Each sample was heated to 40000, cooled to room temperature (2500), reheated to 40000, cooled to room temperature again, then reheated to 400-0 again. The glass transition temperature was determined after each heating cycle. The results are included in Table II. [0154] Example 14: [0155] To 100g of Torlon® 4203 rod shavings, add Sg of TPP. The sample was mixed using ceramic milling beads. The glass transition temperature of the powder was determined by DSC. Each sample was heated to 4000C, cooled to room temperature (25"C), reheated to 40000, cooled to room temperature again, then reheated to 40000 again. The glass transition temperature was determined after each heating cycle. The results are included in Table II. A? Table II (Table Removed) [0156] The results as tabulated above show that the addition of DPP and TPP of at least 0.5% by weight, and in the range of 0.5%-2% by weight (for DPP) and 0.5%-5% by weight (for TPP), dramatically increases the glass transition temperature of the cured polyamideimide film. [0157] Example 15: [0158] Glass panels were coated with Ultratherm®A 828 (The PD. George Co.) using a #80 Meier bar. The panels were cured for 15 and 30 minutes at temperatures of 1 000C (21 20F) and 1250C (2570F), and 15 minutes at 1500C (3020F) in a Thermotron forced air oven. The cured films had an average thickness of 15 microns. A small portion of the resulting film was placed in dimethyl formamide (DMF) to determine solubility. The results are included in Table III. [0159] Example 16: [0160] To bOg of Ultratherm®A 828, add 2g of triphenyl phosphite (TPP). Stir the mixture, using a stir bar, until the sample is uniform. Glass panels were coated with the sample using a #80 Meier bar. The panels were cured for 15 and 30 minutes at temperatures of 1000C and 1250C, and 15 minutes at 1500C in a Thermotron forced air oven. The cured films had an average thickness of 15 microns. A small portion of the resulting film was placed in dimethyl formamide (DMF) to determine solubility. The results are included in Table Ill. Table Ill (Table Removed) [0161] As can be seen from the data from Examples 15 and 16, the addition of TPP to the polyimide produced a chemical resistant film by curing the film at a lower temperature than was possible without the TPP. The cured polyimide film that did not include TPP was still partially soluble when cured at 1500C. However, the polyimide film that included TPP was partially soluble when cured for 15 minutes at 1000C and was not soluble (and hence not chemically resistant) when cured for 15 minutes at 1 250C. This reinforces the results of Examples 1 and 2, namely, that the addition of a phosphorous based catalyst to a polyimide allows for a chemically resistant film or coating to be produced which can be cured at lower temperatures and for shorter periods of time than is required if the catalyst is not used. [0162] As noted above, the use of a phosphorous catalyst to produce the film should reduce void formation in the film. Imides are commonly formed from amic acids. Amic acid, which has [0163] (Formula Removed) [0164] when heated forms an imide or a polyimide. As is known, when the amic acid is heated, the hydrogen from the amide group and the hydroxyl from the carboxylic group separate from the amic acid molecule, allowing the amic acid to form an imide cyclic structure. Therefore, imide formation produces water. Hence, the resulting polyimide resin contains water within the polymer matrix. The water tends to form voids in the film as the polyimide is cured. [0165] However, when a phosphorous catalyst, such as TPP or DPP, is added to the polyimide, the hydroxyl group combines with the catalyst to release phenol, thereby avoiding the formation of water molecules. Phenol is not as volatile as water, and is a potential solvent of the polyimide matrix. Thus, during curing, the phenol will slowly migrate through the curing matrix to be released from the film, thereby avoiding formation of voids within the film. [0166] In view of the above, it will be seen that the post adding of phosphorous catalysts, such as TPP and DPP, can reduce the cure time and temperature of polyamide films, increase the glass transition temperature of the cured film, and should reduce void formation in the cured film. [0167] A Meier bar is a coating instrument. It allows one to apply coatings of a known thickness to a substrate such as a Q panel. The #80 refers to the size of the bar. Different sizes allow one to apply different thicknesses of coating. WE CLAIMS: 1. A method of producing a cured polyimide film having an increased glass transition temperature comprising: mixing a phosphorus catalyst with a polyimide, the catalyst being added in an amount of between about 0.1% to about 10% by weight of the polyimide solution; coating a substrate with the polyimide/catalyst mixture; and curing the polyimide by heating the coated substrate to form a polyimide film. 2. The method of claim 1 wherein the phosphrous catalyst is added to the polyimide in an amount of about 0.2% to about 5% by weight of the polyimide solution. 3. The method of claim 1 wherein the phosphorus catalyst is added to the polyimide in an amount of about 0.5% to about 5% by weight of the polyimide solution. 4. The method of claim 1 wherein the phosphorus catalyst is chosen from the group consisting of aryl, arylalkyl, alkyl phosphorus based catalysts, and combinations thereof. 5. The method of claim 4 wherein the arylphosphite catalyst is chosen from the group consisting of diaryl- and triaryl-phosphites and combinations thereof. 6. The method of claim 4 wherein the arylphosphite catalyst is chosen from the group consisting of alkyldiarylphosphites and dialkylarylphosphites and combinations thereof. 7. The method of claim 5 wherein the catalyst is chosen from the group consisting of diphenylphosphite and triphenylphosphite. 8. The method of claim 1 wherein including a step of adding fillers to the polyimide/catalyst mixture. 9. The method of claim 8 wherein the fillers are chosen from the group consisting of include titanium dioxide, alumina, silica, graphite, carbon black, fiberglass and combinations thereof. 10. The method of claim 1 including a step of adding additives to the polyimide/catalyst mixture. 11. The method of claim 10 wherein the additives are chosen from the group consisting of thickeners, plasticizers, flow agents, antiblocking agents, antistatic agents, antioxidants, hindered amine light stabilizers, ultraviolet light stabilizers and combinations thereof. 12. The method of claim 1 wherein the coated substrate is heated for up to about 30 minutes. 13. A method of increasing the glass transition temperature of a polyimide film, the method comprising: mixing a phosphorous catalyst with a polyimide, the catalyst being added in an amount of between about 0.1% to about 10% by weight of the polyimide solution; coating a substrate with the polyimidelcatalyst mixture; and curing the polyimide by heating the coated substrate to form a poryimide film. 14. The method of claim 13 wherein the catalyst is chosen from the group of diaryl- and triaryl- phosphites. 15. The method of claim 14 wherein the curing step is carried out at a temperature of greater than 10000. 16. The method of claim 14 wherein curing step is carried out at a temperature of between about 100CC and about 20000. 17. The method of claim 14 wherein the curing step involves heating the coated substrate for up to about 30 minutes 18. The method of claim 14 wherein the curing step involves heating the coated substrate for up to about 15 minutes. 19. A method of decreasing the temperature and time for curing polyimide films, the method comprising: mixing a phosphorous catalyst with a polyimide, the catalyst being added in an amount of between about 0.1% to about 10% by weight of the polyimide solution; coating a substrate with the polyimide/catalyst mixture; and curing the polyimide by heating the coated substrate at a temperature of greater than 1 000C for up to about 30 minutes. 20. A method of reducing void formation in cured polyimide films, the method comprising: mixing a phosphorous catalyst with a poryimide, the catalyst being added in an amount of between about 0.1% to about 10% by weight of the polyimide solution; coating a substrate with the polyimide/catalyst mixture; and curing the polyimide by heating the coated substrate at a temperature greater than 10000 for up to about 30 minutes.

Full Text

CATALYSIS OF POLYIMIDE CURING

BACKGROUND OF THE INVENTION

[001] This invention relates to polyimide resin compositions; and, more particularly, to a composition of polyimide materials used in solvent based coatings, films, powder coatings, pre¬impregnated coatings (commonly referred to as "prepreg" coatings), compression molding, and thermosetting resin extrusions. The composition includes a polyimide oligomer/polymer~and a phosphorus based catalyst.

[002] Polyimide resins are high-temperature resistant polymers that retain their physical properties during short-term exposures at temperatures of up to 5550C (1 0300F), and can be used for prolonged periods of time at temperatures ranging up to approximately 3330C (6300F). Polyimide resins include condensation polyimide resins, addition polyimide resins, thermoplastic polyimides (e.g., polyamideimide and polyetherimide resins) and polyesterimide resins. All of these polymers have excellent electrical and physical properties, as well as high thermal and oxidative stability. Because of this combination of properties, these polyimides are used in aerospace, electronics and various other industrial applications. In these applications, molecular weights of the condensation polyimides (polyamideimides and polyesterimides) are kept low so they can be applied onto a substrate in solution, and to permit thermoplastic processing.

[003] Subsequent heating (in the case of a laminate or a molded article under pressure) carries the polymerization reaction further, increasing molecular weight, and developing the product's final properties. However, evolution of a water by-product during this second reaction step causes some porosity which is undesirable for applications involving laminates, moldings, and films. This drawback is partially eliminated by the addition of polyimides to the solution which cross-link through an addition reaction. Fully imidized polyimides are capable of producing low-void laminates, since ring closure prevents the water by-product from being released during curing. However, these addition polyimides are poor for film formation, are difficult to synthesize, result in lower thermal properties, and are expensive to use.

[004] Due to the limitations of both condensation and addition polyimides, a new polyimide material is desired which can achieve the desirable high thermal properties of condensation polyimides; while, minimizing the outgassing of water upon final cure. Phosphorus based catalysis of polyamideimide resin synthesis has been known and reported in the literature since the I 980's. In these applications, triphenylphosphite (TPP) is added in stoichiometric amounts to trimellitic anhydride and a diamine, and the resulting reaction is
further facilitated by the addition of excess pyridine in solution. The TPP activates the carboxylic acid group to achieve amide formation with the diamine. However, this process has not been widely used commercially; due to the high cost of the catalysts and the large amounts of them needed to synthesize the polymer backbone.

[005] TPP has been post-added in the extrusion of polyester and polyamide resins. In their article, H,ph- Temperature Reactions of Hydroxyl and Carboxyl PET Chaib End Groups lb the Presence of Aromatic Phospli/te, Aharon, S.M. et al, Journal of Polymer Science: Part A, Polymer Chemistry Vol. 24, pp. 1281-1296 (1986), the authors added varying levels of TPP to polyethyleneterephthalate (PET) and found an increase in molecular weight compared to a degradation in molecular weight without the catalyst. Similar findings were reported for polyamide resins such as nylon 6,6.

[006] U.S. Pat. No. 4,749,768 describes a process for producing thermoplastic processable aromatic polyamides with phosphorus catalysis. In this patent, a diamine is condensed with a dicarboxylic acid with catalysis by either triphenylphosphite or H3POn acid.

[007] Japanese Pat. No. 2005213387, describes a method in which thermosetting resins in the presence of 0.01-10 phr phosphite esters show low emission of volatile organic compounds. The thermosetting resin system is an unsaturated polyester with a styrene monomer.

BRIEF SUMMARY OF THE INVENTION

[008] In accordance with the invention, there is described the use of a phosphorus based catalyst to promote the cure of polyimide resins. Use of the catalyst dramatically increases glass transition temperature. A second aspect of the invention is that the catalyst minimizes the amount of water generated, thereby possibly minimizing void formation in a cured substrate. A third aspect of the invention is that the catalyst accelerates cure thereby minimizing the long curing procedures needed with polyimides such as a polyamideimide resin. Additionally, the catalyst allows for temperature at which the curing procedure is carried out to be substantially reduced than is required when a catalyst is absent. The result is a new polyimide material having the desired high thermal properties of condensation polyimides with minimal outgassing of water during cure.

[009] Other objects and features will be in part apparent and in part pointed out hereinafter.
DETAILED DESCRIPTION OF INVENTION

[0010] The following detailed description illustrates the invention by way of example and not by way of limitation. This description will clearly enable one skilled in the art to make and use the invention, and describes several embodiments, adaptations, variations, alternatives and uses of the invention, including what we presently believe is the best mode of carrying out the invention. As various changes could be made in the above constructions without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

[0011] Polyimide resins useful in the present invention are commonly used in solvent based coatings, films, prepreg coatings, laminates, compression molding, and thermosetting resin extrusion. These resins include condensation polyimides, addition polyimides and thermoplastic polyimides. Useful polyimide resins are obtained by condensation polymerization between a diamine and a dianhydride. Non-limiting examples of diamines include:
[0012] X-R"-(-NH2)n
[0013]
where R" is an organic radical, n is at least 2, and X is hydrogen, an amino group or an organic group including those having at least one amino group.

[0014] Diamines useful for this purpose are expressed by the formula:
[0015] R"-(-NH2)n

[0016] where R"' is a member selected from a class consisting of organic radicals of at least two carbon atoms (both halogenated and unhalogenated) including but not limited to, e.g., hydrocarbon radicals of up to 40 carbon atoms, and groups consisting of at least two aryl residues attached to each other through the medium of a member selected from the class consisting of an alkylene radical of from 1 to 10 carbon atoms, --S--,

0
II
[0017]--S02--,'C",and --0--etc., and n is again at least 2.
[0018] Among specific useful amines, alone or in admixture, are the following:

[0019] p-xylene diamine
[0020] bis(4-amino-cyclohexyl)methane

[0021] hexamethylene diamine

[0022] heptamethylene diamine

[0023] octamethylene diamine

[0024] nonamethylene diamine

[0025] decamethylene diamine
[0026] 3-methyl-heptamethylene diamine [0027] 4,4'-dimethylheptamethylene diamine [0028] 2,1 1-diamino-dodecane [0029] 1 ,2-bis-(3-amino-propoxy)ethane [0030] 2,2-dimethyl propylene diamine [0031] 3-methoxy-hexamethylene diamine [0032] 2 ,5-dimethylhexamethylene diamine [0033] 2, 5-dimethylheptamethylene diamine [0034] 5-methylnonamethylene diamine [0035] 1 ,4-diamino-cyclo-hexane [0036] 1,1 2-diamino-octadecane [0037] 2,5-diamino-1 ,3,4-oxadiazole [0038] H2N(CH2)30(CH2)20(CH2)3NH2 [0039] H2N(CH2)35(CH2)3NH2 [0040] H2N(0H2)3N(CH3)(CH2)3NH2 [0041] meta-phenylene diamine [0042] para-phenylene diamine [0043] 4,4'-diamino-diphenyl propane [0044] 4,4'-diamino-diphenyl methane benzidine [0045] 4,4'-diamino-diphenyl sulfide [0046] 4,4'-diamino-diphenyl sulfone [0047] 3,3'-diamino-diphenyl sulfone [0048] 4,4'-diamino-diphenyl ether [0049] 2,6-diamino-pyridine

[0050] bis(4-amino-phenyl)diethyl silane [0051] bis(4-amino-phenyl)diphenyl silane [0052] bis(4-amino-phenyl)phosphine oxide [0053] 4,4'-diaminobenzophenone [0054] bis(4-amino-phenyl)-N-methylamine [0055] bis(4-aminobutyl)tetramethyldisiloxane [0056] 1 ,5-diaminonaphthalene

[0057] 3, 3'-dimethyl-4,4'-diamino-biphenyl [0058] 3,3'-dimethoxy benzidine [0059] 2 ,4-bis(beta-amino-t-butyl)toluene toluene diamine

[0060] bi(para-beta-amino-t-butyl-phenyl)ether
[0061] para-bis(2-methyl-4-amino-pentyl)benzene
[0062] para-bis(1 ,1 -dimethyl-5-amino-pentyl)benzene
[0063] m-xylylene diamine
[0064] poly(methylene) polyaniline
[0065] The dianhydride can be expressed by the following structure

[0066]
[0067] where Y is an organic group, and Z' and Z" are hydrogen or an organic group. Y' can be 0, NR, S02, S, 0=0, alkyl, alkyliluoro, or an aromatic group. Non-limiting examples of dianhydrides include: Benzophenonetetracarboxylic acid anhydride, Pyromellitic dianhydride and 3,3',4,4'-biphenyltetracarboxylic dianhydride (s-, a-, and i- versions).

[0068] A subset of polyimide polymers are polyamideimide resins which are mainly produced in one of three ways. One way utilizes a polyisocyanate with a carboxylic anhydride. Any polyisocyanate, that is, any isocyanate having two or more isocyanate groups, whether blocked or unblocked, can be used in making polyamideimides. Blocked isocyanates using, for example, phenols or alcohols as the blocking constituent, can also be used. In general, they provide a higher molecular weight of the final material and this is advantageous, for example, in varnishes. Conversely, unblocked isocyanates provide more flexible final materials. Regardless of which is used, as much of the blocking material must be evaporated off as possible, and there is no advantage, from a purely reaction point of view, as to which material is used. A typical blocked polyisocyanate is Mondur 5TM in which mixtures of 2,4- and 2,6-tolylene diisocyanate are reacted with trimethylol propane, and blocked by esterification with phenol in the proportions of three moles of isocyanate, one mole of trimethylol propane, and three moles of phenol. Another blocked polyisocyanate is Mondur SHTM, in which isocyanate groups of mixed 2,4- and 2,6-tolylene diisocyanate are blocked by esterification with cresol. Polyisocyanates which are useful alone, or in admixture, include:
[0069] tetramethylenediisocyanate
[0070] hexamethylenediisocyanate
[0071] 1 ,4-phenylenediisocyanate

[0072] 1 ,3-phenylenediisocyanate

[0073] 1 ,4-cyclohexylenediisocyanate [0074] 2,4-tolylenediisocyanate
[0075] 2,5-tolylenediisocyanate [0076] 2,6-tolylenediisocyanate [0077] 3,5-tolylenediisocyanate [0078] 4-chloro-1 ,3-phenylenediisocyanate [0079] 1 -methoxy-2,4-phenylenediisocyanate [0080] 1 -methyl-3,5-diethyl-2,6-phenylenediisocyanate [0081] 1, 3,5-triethyl-2,4-phenylenediisocyanate [0082] 1 -methyl-3, 5-diethyl-2 ,4-phenylenediisocyanate [0083] 1 -methyl-3,5-diethyl-6-chloro-2,4-phenylenediisocyanate [0084] 6-methyl-2,4-diethyl-5-nitro-1 ,3-phenylenediisocyanate [0085] p-xylylenediisocyanate

[0086] m-xylylenediisocyanate [0087] 4,6-dimethyl- 1 ,3-xylylenediisocyanate [0088] 1, 3-dimethyl-4,6-bis-(b-isocyanatoethyl)-benzene [0089] 3-(a-isocyanatoethyl)-phenylisocyanate [0090] 1 -methyl-2,4-cyclohexylenediisocyanate [0091] 4,4'-biphenylenediisocyanate [0092] 3,3'-dimethyl-4,4'-biphenylenediisocyanate [0093] 3, 3'-dimethoxy-4,4'-biphenylenediisocyanate [0094] 3,3'-diethoxy-4,4-biphenylenediisocyanate [0095] 1,1 -bis-(4-isocyanatophenyl)cyclohexane [0096] 4,4'-diisocyanato-diphenylether [0097] 4,4'-diisocyanato-dicyclohexylmethane [0098] 4,4'-diisocyanato-diphenylmethane [0099] 4,4-diisocyanato-3, 3-dimethyldiphenylmethane [0100] 4,4'-diisocyanato-3,3'-dichlorodiphenylmethane [0101] 4,4'-diisocyanato-diphenyldimethylmethane [0102] 1 ,5-naphthylenediisocyanate [0103] 1 ,4-naphthylenediisocyanate [0104] 4,4',4"-triisocyanato-triphenylmethane [0105] 2,4,4'-triisocyanato-diphenylether [0106] 2,4, 6-triisocyanato- 1 -methyl-3,5-diethylbenzene [0107] o-tolidine-4,4'-diisocyanate [0108] m-tolidine-4,4'-diisocyanate
[0109] benzophenone-4,4'-diisocyanate [0110] biuret triisocyanates

[0111] polymethylene polyphenylene isocyanate

[0112] The carboxylic anhydride mainly includes trimellitic anhydride. Other potential materials include trimellitic acid and a dehydrating material.

[0113] A second way of producing polyamideimide resins involves the use of a diamine and a carboxylic anhydride acid chloride. This is the preferred route to synthesis of polyamideimide polymers sold by Solvay Advanced Polymers, L.L.C. under the name TORLON®. The carboxylic anhydride acid chloride is preferably trimellitic anhydride acid chloride. The diamines include ODA (oxydianiline) and MDA (methylenediphenyldiamine).

[0114] A third and less common way of producing polyamideimide resins involves the condensation of an organic diamine with two equivalents of carboxylic anhydride. In general, a slight molar excess of carboxylic acid anhydride and organic polyamine is heated from about 2000C (3920F) to about 2450C (4730F) in an inert atmosphere and with a solvent. This drives off any water formed, and forms an amideimide group containing a prepolymer. A polyisocyanate is then added and the mixture reacted to form a block amide-imide prepolymer having a relatively high molecular weight. This is then cured (as by heating) to form a flexible film or coating.

[0115] As taught, for example, in United States patent 3,817,926, up to 75 mole percent of the carboxylic anhydride can be replaced by a substituted or unsubstituted aliphatic anhydride or diacid such as oxalic, maleic, succinic, glutaric, adipic, pimelic, suberic, azelaic, sebacic and dodecanedioic, as well as unsaturated materials including maleic and fumaric materials, among others. Such acids are expressed by the formula:

[0116] HOOC--R'--COOH

[0117] where R' is a divalent saturated or unsaturated aliphatic group, or one containing a carbon-to-carbon double bond and having from about one to 40 carbon atoms. The anhydrides can be expressed by the formula:

[0118] (Formula Removed)

L0119] A phosphite catalyst can be added to the resin in the range of 0.01% to 10% by weight of the resin. The catalyst can be an aryl, arylalkyl or alkyl phosphorus based catalyst. Arylphosphites, 'such as a diaryl- or triaryl-phosphite, work well. Alkyldiarylphosphites and
dialkylarylphosphites should also work. Triphenylphosphite (TPP) can be produced, in-situ, by the addition of a phenol- or a phenolic-like substance to an activated phosphorus compound. Such activated phosphorus compounds include, for example, species such as phosphorus trichloride or phosphorus tribromide.

[0120] Fillers and additives can also be incorporated into the polymer matrix. Non-limiting examples of fillers include titanium dioxide, alumina, silica, graphite, carbon black, and fiberglass. Other additives include thickeners, plasticizers, flow agents, antiblocking agents, antistatic agents, antioxidants, hindered amine light stabilizers, and ultraviolet light stabilizers.

[0121] In a coating application, the polyimide solution is mixed with the phosphorus catalyst. The solution is either directly coated onto a substrate, web, or composite material. The solvent is then evaporated by thermal or vacuum means and the remaining resin cured by thermal means including oven heat, inductive heating, or infrared sources.

[0122] A polyimide coating solution, such as Ultratherm® A 828 (available from The P.D. George Co.), requires temperatures of greater than 1 500C (z3000F) to achieve enough cure so that a chemically resistant film can be obtained. The same polyimide material can be cured at less than 1 250C (2570F) with phosphorus catalyst. Catalyst concentration also impacts the rate at which cure is achieved.

[0123] A polyamideimide coating solution, such as Tritherm® A 981 (available from The P.D. George Co.), requires temperatures of greater than 2400C (~4650F) to achieve enough cure so that a chemically resistant film is obtained. The same polyamideimide material can be cured at 2000C (3020F) with a phosphorus catalyst. Again, catalyst concentration also impacts the rate at which cure is achieved.

[01241 Glass transition temperature is also dramatically impacted by phosphorus based catalysis. A polyamideimide resin, such as Tritherm® A 981 (available from The P.D. George Co.), typically has a glass transition temperature of approximately 270-3000C (~52O-57O0F). Multiple reheats will still demonstrate a similar glass transition temperature. Phosphorus based catalysis dramatically changes the thermoplastic properties. Multiple reheats of up to 4000C (~75O0F) increases the glass transition from roughly 27000 (z52O0F) to greater than 35000 (~6600F). This dramatic increase is also observed using Solvay based Torlon® Al-i 0.

[0125] In an extrudable material such as Torlon® 4203, an un-reinforced polyamideimide containing 3% titanium and 0.5% fluoropolymer available from Solvay Advanced Polymers, LLC, TPP (triphenylphosphite) can be added prior to solvent stripping to make a powdered resin. It should also possible to compound the resin powder with TPP after solvent removal. We have also found that extruded Torlon® 4203 (fully imidized) can be post-treated with TPP
and further cured upon heat treatment. Either method should allow for post-heat treatment to obtain a final cured part with improved glass transition and physical properties.

[0126] EXAMPLES [0127] Example 1:
[0128] Glass panels were coated with a Tritherm®A 981-H (The P.D. George Co.) using a #80 Meier bar. The panels were cured for 15 and 30 minutes in a Thermotron forced air oven at temperatures of 15000 (3020F), 17500 (3470F), and 200CC (3920F). The cured films had an average thickness of 15 microns. A small portion of the resulting film was placed in dimethyl formamide(DMF) to determine solubility. The results are included in Table I below.

[0129] Example 2:
[0130] To I OOg of Tritherm®A 981-H, add 2g of triphenyl phosphite (TPP). Stir the mixture, using a stir bar, until the sample is uniform. Glass panels were coated with the sample using a #80 Meier bar. The panels were then cured for 15 and 30 minutes in a Thermotron forced air oven at temperatures of 15000, 175"C, and 20000. The cured films had an average thickness of 15 microns. A small portion of the resulting film was placed in dimethyl formamide (DMF) to determine solubility. The results are also included in Table I.

Table I
(Table Removed)

[0131] As seen from Table I, the polyamideimide film made from Tritherm A 981-H was soluble in DMF irrespective of the cure time and cure temperature. However, the
polyamideimide film made from Tritherm A 981-H when mixed with 2% TPP, the resulting film was not soluble in DMF when cured 20000 and was only partially soluble in DMF when cured at 17500. The film was soluble in DMF when cured at 15000. These results show that the addition of TPP in a small amount (i.e., 2%) produces a chemically resistant film when cured at 20000, and a partially chemically resistant film when cured at 1750C. However, without the addition of the TPP, the Tritherm would have to be cured at higher temperatures and/or for longer periods of time to produce a chemically resistant film.

[0132] Example 3:
[0133] Glass panels were coated with Tritherm®A 981-H using a #80 Meier bar. The panels were cured for 30 minutes in a Thermotron forced air oven at temperatures of 20000 (3920F) and 26000 (5000F). The cured films had an average thickness of 15 microns. The glass transition temperature of the film was determined by differential scanning calorimetry (DSO). Each sample was heated to 40000 (7520F), cooled to room temperature (2500, or 770F), reheated to 40000, cooled to room temperature again, then reheated to 40000 again. The glass transition temperature was determined after each heating cycle. The results are included in Table II.

[0134] Example 4:
[0135] To bOg of Tritherm®A 981-H, add 2g of TPP. Stirthe mixture, using a stir bar, until the sample is uniform. Glass panels were coated with the sample using a #80 Meier bar. The panels were cured 30 minutes in a Thermotron forced air oven at temperatures of 20000 and 26000. The cured films had an average thickness of 15 microns. The glass transition temperature of the film was determined by DSC. Each sample was heated to 40000, cooled to room temperature (2500), reheated to 40000, cooled to room temperature again, then reheated to 40000 again. The glass transition temperature was determined after each heating cycle. The results are also included in Table II.

[0136] Example 5:
[0137] To 1 OOg of Tritherm®A 981-H, add I g of TPP. Stir the mixture, using a stir bar, until the sample is uniform. A glass panel was coated with the sample using a #80 Meier bar. The panel was cured 30 minutes in a Thermotron forced air oven at a temperature of 26000. The cured film had an average thickness of 15 microns. The glass transition temperature of the film was determined by DSC. Each sample was heated to 40000, cooled to room temperature (2500), reheated to 40000, cooled to room temperature again, then reheated to 40000 again. The glass transition temperature was determined after each heating cycle. The results are included in Table II.
[0138] Example 6:
[0139] To bOg of Tritherm®A 981-H, add 0.Sg of TPP. Stir the mixture, using a stir bar, until the sample is uniform. A glass panel was coated with the sample using a #80 Meier bar. The panel was cured 30 minutes in a Thermotron forced air oven at a temperature of 2600C. The cured film had an average thickness of 15 microns. The glass transition temperature of the film was determined by DSO. Each sample was heated to 40000, cooled to room temperature (2500), reheated to 400"C, cooled to room temperature again, then reheated to 40000 again. The glass transition temperature was determined after each heating cycle. The results are included in Table II.

[0140] Example 7:
[0141] To bOg of Tritherm®A 981-H, add 0.2g of TPP. Stir the mixture, using a stir bar, until the sample is uniform. A glass panel was coated with the sample using a #80 Meier bar. The panel was cured 30 minutes in a Thermotron forced air oven at a temperature of 26000. The cured film had an average thickness of 15 microns. The glass transition temperature of the film was determined by DSC. Each sample was heated to 40000 cooled to room temperature (2500), reheated to 40000, cooled to room temperature again, then reheated to 40000 again. The glass transition temperature was determined after each heating cycle. The results are included in Table II.

[0142] Example 8:
[0143] To lOOg of Tritherm®A 981-H, add 2g of diphenyl phosphite (DPP). Stir the mixture, using a stir bar, until the sample is uniform. Glass panels were coated with the sample using a #80 Meier bar. The panels were cured 30 minutes in a Thermotron forced air oven at temperatures of 20000 and 26000. The cured films had an average thickness of 15 microns. The glass transition temperature of the film was determined by DSC. Each sample was heated to 40000, cooled to room temperature (2500), reheated to 40000, cooled to room temperature again, then reheated to 40000 again. The glass transition temperature was determined after each heating cycle. The results are included in Table II.

[0144] Example 9:
[0145] To lOOg of Tritherm®A 981-H, add ig of DPP. Stir the mixture, using a stir bar, until the sample is uniform. A glass panel was coated with the sample using a #80 Meier bar. The panel was cured 30 minutes in a Thermotron forced air oven at a temperature of 26000. The cured film had an average thickness of 15 microns. The glass transition temperature of the film was determined by DSO. Each sample was heated to 40000, cooled to room temperature (2500), reheated to 40000, cooled to room temperature, then reheated to 40000 again. The
glass transition temperature was determined after each heating cycle. The results are included in Table II.
[0146] Example 10:

[0147] To lOOg of Tritherm®A 981-H, add 0.Sg of DPP. Stir the mixture, using a stir bar, until the sample is uniform. A glass panel was coated with the sample using a #80 Meier bar. The panel was cured 30 minutes in a Thermotron forced air oven at a temperature of 2600C. The cured film had an average thickness of 15 microns. The glass transition temperature of the film was determined by DSC. Each sample was heated to 40000, cooled to room temperature (2500), reheated to 4000C, cooled to room temperature again, then reheated to 40000 again. The glass transition temperature was determined after each heating cycle. The results are included in Table II.

[0148] Example 11:

[0149] A glass panel was coated with Torlon® AI-lO (Solvay) using a #80 Meier bar. The panel was cured for 30 minutes in a Thermotron forced air oven at a temperature of 26000. The cured film had an average thickness of 15 microns. The glass transition temperature of the film was determined by differential scanning calorimetry (DSO). Each sample was heated to 40000, cooled to room temperature (2500), reheated to 40000, cooled to room temperature again, then reheated to 40000 again. The glass transition temperature was determined after each heating cycle. The results are included in Table II.

[0150] Example 12:
[0151] To bOg of Torlon®AI-10, add 2g of TPP., Stir the mixture, using a stir bar, until the sample is uniform. A glass panel was coated with the sample using a #80 Meier bar. The panel was cured 30 minutes in a Thermotron forced air oven at a temperature of 26000. The cured film had an average thickness of 15 microns. The glass transition temperature of the film was determined by DSO. Each sample was heated to 40000, cooled to room temperature (25~0), reheated to 40000, cooled to room temperature again, then reheated to 40000 again. The glass transition temperature was determined after each heating cycle. The results are included in Table II.

[0152] Example 13:

[0153] The glass transition temperature of Torlon® 4203(Solvay) rod shavings was determined by differential scanning calorimetry (DSC). Each sample was heated to 40000, cooled to room temperature (2500), reheated to 40000, cooled to room temperature again, then reheated to 400-0 again. The glass transition temperature was determined after each heating cycle. The results are included in Table II.

[0154] Example 14:
[0155] To 100g of Torlon® 4203 rod shavings, add Sg of TPP. The sample was mixed using ceramic milling beads. The glass transition temperature of the powder was determined by DSC. Each sample was heated to 4000C, cooled to room temperature (25"C), reheated to 40000, cooled to room temperature again, then reheated to 40000 again. The glass transition temperature was determined after each heating cycle. The results are included in Table II.

A?

Table II

(Table Removed)

[0156] The results as tabulated above show that the addition of DPP and TPP of at least 0.5% by weight, and in the range of 0.5%-2% by weight (for DPP) and 0.5%-5% by weight (for TPP), dramatically increases the glass transition temperature of the cured polyamideimide film.

[0157] Example 15:
[0158] Glass panels were coated with Ultratherm®A 828 (The PD. George Co.) using a #80 Meier bar. The panels were cured for 15 and 30 minutes at temperatures of 1 000C (21 20F) and 1250C (2570F), and 15 minutes at 1500C (3020F) in a Thermotron forced air oven. The cured films had an average thickness of 15 microns. A small portion of the resulting film was placed in dimethyl formamide (DMF) to determine solubility. The results are included in Table III.

[0159] Example 16:

[0160] To bOg of Ultratherm®A 828, add 2g of triphenyl phosphite (TPP). Stir the mixture, using a stir bar, until the sample is uniform. Glass panels were coated with the sample using a #80 Meier bar. The panels were cured for 15 and 30 minutes at temperatures of 1000C and 1250C, and 15 minutes at 1500C in a Thermotron forced air oven. The cured films had an average thickness of 15 microns. A small portion of the resulting film was placed in dimethyl formamide (DMF) to determine solubility. The results are included in Table Ill.

Table Ill

(Table Removed)

[0161] As can be seen from the data from Examples 15 and 16, the addition of TPP to the polyimide produced a chemical resistant film by curing the film at a lower temperature than was possible without the TPP. The cured polyimide film that did not include TPP was still partially soluble when cured at 1500C. However, the polyimide film that included TPP was partially

soluble when cured for 15 minutes at 1000C and was not soluble (and hence not chemically resistant) when cured for 15 minutes at 1 250C. This reinforces the results of Examples 1 and 2, namely, that the addition of a phosphorous based catalyst to a polyimide allows for a chemically resistant film or coating to be produced which can be cured at lower temperatures and for shorter periods of time than is required if the catalyst is not used.

[0162] As noted above, the use of a phosphorous catalyst to produce the film should reduce void formation in the film. Imides are commonly formed from amic acids. Amic acid, which has
[0163] (Formula Removed)
[0164] when heated forms an imide or a polyimide. As is known, when the amic acid is heated, the hydrogen from the amide group and the hydroxyl from the carboxylic group separate from the amic acid molecule, allowing the amic acid to form an imide cyclic structure. Therefore, imide formation produces water. Hence, the resulting polyimide resin contains water within the polymer matrix. The water tends to form voids in the film as the polyimide is cured.

[0165] However, when a phosphorous catalyst, such as TPP or DPP, is added to the polyimide, the hydroxyl group combines with the catalyst to release phenol, thereby avoiding the formation of water molecules. Phenol is not as volatile as water, and is a potential solvent of the polyimide matrix. Thus, during curing, the phenol will slowly migrate through the curing matrix to be released from the film, thereby avoiding formation of voids within the film.

[0166] In view of the above, it will be seen that the post adding of phosphorous catalysts, such as TPP and DPP, can reduce the cure time and temperature of polyamide films, increase the glass transition temperature of the cured film, and should reduce void formation in the cured film.

[0167] A Meier bar is a coating instrument. It allows one to apply coatings of a known thickness to a substrate such as a Q panel. The #80 refers to the size of the bar. Different sizes allow one to apply different thicknesses of coating.

WE CLAIMS:

1. A method of producing a cured polyimide film having an increased glass transition temperature comprising:

mixing a phosphorus catalyst with a polyimide, the catalyst being added in an amount of between about 0.1% to about 10% by weight of the polyimide solution;

coating a substrate with the polyimide/catalyst mixture; and

curing the polyimide by heating the coated substrate to form a polyimide film.

2. The method of claim 1 wherein the phosphrous catalyst is added to the polyimide in an

amount of about 0.2% to about 5% by weight of the polyimide solution.

3. The method of claim 1 wherein the phosphorus catalyst is added to the polyimide in an

amount of about 0.5% to about 5% by weight of the polyimide solution.

4. The method of claim 1 wherein the phosphorus catalyst is chosen from the group

consisting of aryl, arylalkyl, alkyl phosphorus based catalysts, and combinations thereof.

5. The method of claim 4 wherein the arylphosphite catalyst is chosen from the group

consisting of diaryl- and triaryl-phosphites and combinations thereof.

6. The method of claim 4 wherein the arylphosphite catalyst is chosen from the group

consisting of alkyldiarylphosphites and dialkylarylphosphites and combinations thereof.

7. The method of claim 5 wherein the catalyst is chosen from the group consisting of

diphenylphosphite and triphenylphosphite.

8. The method of claim 1 wherein including a step of adding fillers to the

polyimide/catalyst mixture.

9. The method of claim 8 wherein the fillers are chosen from the group consisting of

include titanium dioxide, alumina, silica, graphite, carbon black, fiberglass and

combinations thereof.

10. The method of claim 1 including a step of adding additives to the polyimide/catalyst

mixture.

11. The method of claim 10 wherein the additives are chosen from the group consisting

of thickeners, plasticizers, flow agents, antiblocking agents, antistatic agents, antioxidants,

hindered amine light stabilizers, ultraviolet light stabilizers and combinations thereof.

12. The method of claim 1 wherein the coated substrate is heated for up to about 30

minutes.

13. A method of increasing the glass transition temperature of a polyimide film, the method

comprising:

mixing a phosphorous catalyst with a polyimide, the catalyst being added in an amount of between about 0.1% to about 10% by weight of the polyimide solution;

coating a substrate with the polyimidelcatalyst mixture; and

curing the polyimide by heating the coated substrate to form a poryimide film.

14. The method of claim 13 wherein the catalyst is chosen from the group of diaryl- and

triaryl- phosphites.

15. The method of claim 14 wherein the curing step is carried out at a temperature of

greater than 10000.

16. The method of claim 14 wherein curing step is carried out at a temperature of between

about 100CC and about 20000.

17. The method of claim 14 wherein the curing step involves heating the coated substrate

for up to about 30 minutes

18. The method of claim 14 wherein the curing step involves heating the coated substrate

for up to about 15 minutes.

19. A method of decreasing the temperature and time for curing polyimide films, the

method comprising:

mixing a phosphorous catalyst with a polyimide, the catalyst being added in an amount of between about 0.1% to about 10% by weight of the polyimide solution;

coating a substrate with the polyimide/catalyst mixture; and

curing the polyimide by heating the coated substrate at a temperature of greater than 1 000C for up to about 30 minutes.

20. A method of reducing void formation in cured polyimide films, the method comprising:

mixing a phosphorous catalyst with a poryimide, the catalyst being added in an amount of between about 0.1% to about 10% by weight of the polyimide solution;

coating a substrate with the polyimide/catalyst mixture; and

curing the polyimide by heating the coated substrate at a temperature greater than 10000 for up to about 30 minutes.

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Patent Number

268975

Indian Patent Application Number

6370/DELNP/2008

PG Journal Number

40/2015

Publication Date

02-Oct-2015

Grant Date

25-Sep-2015

Date of Filing

21-Jul-2008

Name of Patentee

ALTANA ELECTRICAL INSULATION GMBH

Applicant Address

ABELSTR. 45, 46483 WESEL (DE)

Inventors:

#	Inventor's Name	Inventor's Address
1	MURRAY,THOMAS J.	16722 BENTON TAYLOR DRIVE,CHESTERFIELD,MISSOURI 63005(US)
2	MEISTER,PHILIP R.	216 SPRINGDALE DRIVE,BELLEVILLE, LIINOIS,62223(US)

PCT International Classification Number

C08G 73/10

PCT International Application Number

PCT/EP2007/050622

PCT International Filing date

2007-01-23

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	11/377,599	2006-03-16	U.S.A.