Method of manufacturing a poly(etherimide) polymer

Abstract

Method of manufacturing a poly(etherimide) polymer A method of manufacturing a poly(etherimide) polymer comprises heating a solution comprising an aromatic bis(ether anhydride) and / or its carboxylic acid precursor, a 5 diisocyanate and a first solvent. In a first heating step the solution is heated to a temperature in a first temperature range of 50 °C to 120 °C with a first heating rate of 5 °C / h to 30 °C / h and subsequently held within the first temperature range for 1 h to 8 h. In a second heating step the solution is heated to a temperature in a second temperature range of 145 °C to 165 °C with a second heating rate of 10° C / h to 10 30 °C / h and subsequently held within the second temperature range for 3 h to 6 h.

Description

[0001] Method of manufacturing a poly(etherimide) polymer

[0002] The invention relates to a method of manufacturing a poly(etherimide) polymer comprising heating a solution comprising an aromatic bis(ether anhydride) and / or its carboxylic acid precursor, a diisocyanate and a first solvent. The invention also relates to a method of manufacturing an enamel coated wire, a wire obtained by such a method and an electrical device comprising such a wire.

[0003] Poly(etherimides) (PEIs) are amorphous, transparent, high performance polymers having a high strength, heat resistance, and modulus, and broad chemical resistance, and so are widely used in applications as diverse as automotive, telecommunication, aerospace, electrical / electronics, transportation, and healthcare. A number of processes for making PEIs have been disclosed. Two processes which have been of particular interest are the so-called melt polymerization and solution polymerization processes. Solution polymerization is generally conducted by reacting an aromatic bis(ether anhydride) and an organic diamine in an inert solvent at elevated temperatures to form an amide-acid polymer via ring opening of the anhydride by nucleophilic attack of the diamine. The polyamide acid is then formed into a polyetherimide by removal of water. With this procedure, water of reaction is typically removed by azeotropic distillation.

[0004] US 4,417,044 relates to a process for making poly(etherimides) involving reacting an aromatic bis(ether anhydride) with an organic diamine in an inert solvent to form a prepolymer solvent mixture, effecting solvent removal by thin-film evaporation, and heating the resulting prepolymer to a temperature above the glass transition temperature of the final poly(etherimide) product and less than 450 °C to form the polyetherimide.

[0005] US 9,181 ,396 discloses poly(etherimide) compositions wherein the poly(etherimide) composition comprises a poly(etherimide) comprising a reacted combination of alkali metal salts comprising an alkali metal salt of a dihydroxy aromatic compound and an alkali metal salt of a monohydroxy aromatic compound with a bis(halophthalimide), wherein the alkali metal salt of the monohydroxy aromatic compound is included in an amount of greater or equal to 5 mole percent based on the total moles of the alkali metal salts, and the poly(etherimide) has a weight average molecular weight less than 43,000 Daltons. The poly(etherimide) is reported to exhibit lower levels of chlorine and chlorine end groups, lower levels of bis(halophthalimide) and bis(phthalimide), and low plate-out during manufacturing.

[0006] US 2014 / 171613 A1 describes a process for preparing a poly(etherimide) resin comprising charging a reactor with a liquid reaction solvent, bisphenol A dianhydride, meta-phenylene diamine and a chain stopper selected from phthalic anhydride and aniline, introducing a stream of dry inert gas below the surface of the liquid reactor contents and selectively removing water from the reactor by dispersing the inert gas within the liquid reactor contents and drawing off the inert gas and water from the headspace of the reactor, thereby preparing the poly(etherimide) resin.

[0007] EP 2519561 A1 relates to a method for preparing poly(etherimides) which comprises contacting, in o-dichlorobenzene or anisole as diluent, substantially equimolar amounts of a disodium salt of a dihydroxy compound of formula HO-R'- OH, and a slurry of a bisimide, in the presence of a catalytically active amount of a phase transfer catalyst, thereby polymerizing the bisimide and the disodium salt; wherein the bisimide and the disodium salt are polymerized in the presence of a base selected from the group consisting of alkali metal carbonates, alkyl hydrides, alkali metal hydroxides, alkali metal phosphates, alkali metal bicarbonates, alkali metal acetates, and combinations thereof; wherein said slurry of bisimide comprises the reaction product of a mixture comprising a diamine of formula H2N-R-NH2; chlorophthalic anhydride; and o-dichlorobenzene or anisole; and an optional imidization catalyst, said mixture having a solids content of greater than or equal to about 5% by weight; wherein the base is added in an amount that is sufficient to produce the polyetherimide.

[0008] US 3,917,643 discusses a method for making poly(etherimides) involving the reaction of aromatic bis(ether anhydride)s and organic diamines in the presence of a phenolic solvent. The resulting polyetherimide-phenolic solvent mixture can be employed as a wire coating enamel.

[0009] Given the above-mentioned drawbacks associated with diamines in the synthesis of PEIs attempts have been made to create reaction routes which lead to byproducts that are inert and gaseous under standard conditions, hence greatly simplifying any separation processes.

[0010] US 4,423,111 discloses high molecular weight resins, useful for electrically insulating conductors, which are prepared by polycondensation of a dianhydride, or a mixture of two or more dianhydrides, and a diisocyanate in an inert organic solvent, preferably in the presence of a catalytic amount of 2-methylimidazole. The three working examples in this publication use NMP as solvent and employ a heating scheme of heating from room temperature to 135 °C in approximately two hours and holding at 135 °C for 18 to 22 hours until a viscosity of Z1 to Z21 / 2 is obtained. Reported cut-through temperatures at 2000 g for wire enamels with the PEIs of the examples as sole coats range from 321 °C to 383 °C.

[0011] US 4,354,965 relates to polyetheramideimide resins and to electrical conductors coated therewith. More particularly it relates to polyetheramideimides derived from a combination of a dianhydride of a diphenolic compound and a tribasic acid anhydride and a diisocyanate and / or a diamine.

[0012] GB 2 079761 A relates to polyetherimide resins and to electrical conductors coated therewith. More particularly it relates to polyetherimides derived from a dianhydride of a diphenolic compound and a diisocyanate.

[0013] The invention has the object of improving the diisocyanate-based solution polymerization processes for the manufacture of PEIs of the prior art in such a way that reaction times are shortened while at the same time resulting in a storagestable material which is useful as a wire enamel. This object has been achieved by a method according to claim 1. Further aspects of the invention are a method of coating a wire, a wire obtained from such a method and an electrical device comprising such a wire. Advantageous embodiments are the subject of the dependent claims. They can be combined freely unless the context clearly indicates otherwise.

[0014] Accordingly, a method of manufacturing a poly(etherimide) polymer comprises heating a solution comprising an aromatic bis(ether anhydride) and / or its carboxylic acid precursor, a diisocyanate and a first solvent, wherein in a first heating step the solution is heated to a temperature in a first temperature range of 50 °C to 120 °C (preferred 70 °C to 100 °C, more preferred 80 °C to 90 °C) with a first heating rate of 5 °C / h to 30 °C / h (preferred 10 °C / h to 20 °C / h, more preferred 14 °C / h to 16 °C / h) and subsequently held within the first temperature range for 1 h to 8 h (preferred 2 h to 3 h) and wherein in a second heating step the solution is heated to a temperature in a second temperature range of 145 °C to 165 °C (preferred 150 °C to 160 °C, more preferred 153 °C to 157 °C) with a second heating rate of 10 °C / h to 30 °C / h (preferred 15 °C / h to 25 °C / h, more preferred 19 °C / h to 21 °C / h) and subsequently held within the second temperature range for 3 h to 6 h (preferred 4 h to 5 h).

[0015] In the first heating step the solution can be heated starting from any temperature which is below the target temperature within the first temperature range, although in practice starting from room temperature will be preferred. Likewise, it will also be preferred that the second heating step follows immediately after the second step which encompasses a starting temperature for the second heating within the first temperature range.

[0016] The inventors do not wish to be bound by theory, in particular the literature discussions of a seven-membered ring mechanism versus a urea-dianhydride mechanism (where the urea structure is formed from the intermediary amine hydrolysis product of the isocyanates) for the aromatic isocyanate-anhydride reaction. It is believed that during the first heating step, which is performed at a moderate heating rate, and the approximately isothermal treatment within the first temperature range, in the presence of ubiquitous and catalytic moisture, the NCO groups smoothly react to ultimately yield imine oligomers. The CO2 evolution is mild and the reaction exotherm can be controlled easily.

[0017] During the second heating, the preformed oligomeric mixture can further react in a smooth and controlled manner without sudden exotherm evolution, and it is possible to reach desired high viscosities in a relatively short time. Compared to the process of US 4,423,111 the total reaction time can be almost cut in half under certain conditions.

[0018] The method according to the invention has been shown to work with solvents other than the NMP mentioned in US 4,423,111 such as cresylic acids and 3-methyl-2- oxazolidinone. Especially the latter solvent has a favorable regulatory status.

[0019] The poly(etherimide) polymer solutions obtained by the invention can be applied as an enamel to wires at much higher line speeds as contemplated in US 4,423,111. Furthermore, flexibility and cut-through temperature values compare well to the data reported this US patent publication.

[0020] In one embodiment the second heating step is conducted until a viscosity of the solution as determined with a viscometer equipped with coaxial cylinders according to EN ISO 3219 of 5000 mPas or more is achieved. Preferred are viscosities of 10000 mPas to 70000 mPas, more preferred 11000 mPas to 60000 mPas. Such solid contents have been found to balance the requirements of layer build-up and curing behavior in wire enameling applications.

[0021] In another embodiment the aromatic bis(ether anhydride) comprises a bis(oxyphenyl) moiety. Such moieties can be derived from the corresponding bisphenols such as bisphenol A, AF, AP, B, BP, C, C2, E, F, FL, G, M, P, PH, S, TMC and Z. An example is given in the following structure, wherein R1and R2 independently denote hydrogen, alkyl or aryl. Preference is given to a moiety where R1and R2both are methyl.

[0022] In another embodiment the aromatic bis(ether anhydride) comprises a phthalic anhydride moiety. Examples are given in the following structures.

[0023] A particularly preferred aromatic bis(ether anhydride) is of the type given in the following structure, wherein R1and R2independently denote hydrogen, alkyl or aryl. It is most preferred that R1and R2both are methyl.

[0024] The combination the aforementioned moieties is believed to impart particular flexibility, stability and solubility to the resulting poly(etherimides).

[0025] In another embodiment the diisocyanate is toluene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), polymeric diphenylmethane diisocyanate (pMDI) or a mixture of the aforementioned substances. Particularly preferred is 4,4’- MDI. In another embodiment the first solvent and / or the second solvent independently of each other comprise N-methylpyrrolidone (NMP), 3-methyl-2-oxazolidinone (MeOx), cresylic acids, in particular metaparacresol (MPC), or a mixture of two or more of the aforementioned substances. It has surprisingly been found that MeOx can replace NMP as solvent in at least some applications. Likewise, it is advantageous to use cresylic acids as solvents for wire top coats in processes where a base coat is already applied as a solution in cresylic acids. Not having two different solvents for the base and the top coat saves having to flush lines in order to remove the prior solvent and prevents contamination of any reclaimed solvents.

[0026] In another embodiment the solution further comprises a lactam, a monofunctional alcohol, a monofunctional carboxylic acid or a mixture of two or more of the aforementioned substances. These chain termination agents may be employed to control the polymer growth during the synthesis procedure. Preferably caprolactam, methanol, benzyl alcohol and / or formic acid are used in this context.

[0027] In another embodiment the solution further comprises a cross-linker and / or an imide group formation catalyst. They can be added prior to the first heating step, during the first heating step, prior to the second heating step, during the second heating step or after the second heating step. Preferred is an addition after the second heating step. Preferred cross-linkers are trifunctional amine compounds. A preferred catalyst is triphenyl phosphite (TPP). The presence of these cross-linkers and / or catalysts can facilitate the curing of the coating on a wire.

[0028] In another embodiment the method further comprises diluting a poly(etherimide) solution obtained after the second heating step with a second solvent which is identical to or different from the first solvent. Examples for such a second solvent which is different from the first solvent include solvent naphthas such as S100. Here it has been surprisingly found that poly (etherimide) material in the first solvent, particularly in NMP, MeOx and cresylic acids, tolerates the solvent naphthas. It has also been surprisingly found that the solvent naphtha is able to cut the viscosity of the poly (etherimide) solutions. Target viscosities of the resulting mixture may be in a range of 2000 to 4000 mPas at 23 °C. A method of manufacturing an enamel coated wire comprises applying a solution of a poly(etherimide) polymer manufactured by a method according to the invention to a wire and removing the solvent of the solution. This includes manufacturing a poly(etherimide) polymer according to the invention, applying a solution of the poly(etherimide) polymer to a wire and removing the solvent of the solution. Application and removal (for example via evaporation and / or distillation) can be conducted using customary wire enameling machines. The shape or material of the wire is not limited per se. Round and non-round wires as well as copper, aluminum and copper-coated aluminum wires are expressly contemplated. For round wires, suitable diameter ranges include 0.02 mm to 5 mm, preferably 0.1 mm to 5 mm and more preferred 0.2 mm to 3.5 mm. For flat wires, suitable cross-section ranges include 0.1 mm2to 100 mm2, preferably 1 mm2to 50 mm2and more preferred 1 mm2to 10 mm2.

[0029] In one embodiment the solution is applied to the wire at a wire velocity, expressed in m / min, corresponding to a v x d factor of 50 to 200 with v being the numerical value of the wire velocity in m / min and d being the numerical value of the wire diameter in mm. Preferred is a v x d factor of 100 to 200.

[0030] The invention also concerns a wire obtained by a method according to the invention having one or more of the following properties: a tan delta temperature as determined according to CEI EN 60851-5 of 200 °C (lin) or more (preferably 205 °C to 230 °C, more preferred 210 °C to 225 °C); a flexibility as determined according to CEI EN 60851-3 of 20 % or more (preferably 25 % to 30%); a cut-through temperature as determined according to CEI EN 60851-6 of 350 °C or more (preferably 380 °C to 450 °C, more preferred 390 °C to 430 °C) and a relative permittivity Eras determined according to the procedure in the experimental section of 3.05 or less (preferably 2.9 or less, more preferred 2.7 to 3.0).

[0031] It is understood that the flexibility test of CEI EN 60851-3 references CEI EN 60317- 0'-1 (2014-06) "Specifications for particular types of winding wires Part 0-1 General Requirements - Enameled round copper wire", chapter 8. In particular the wire is pre-elongated before winding on the mandrel. The percentage of elongation at which 2 out of 3 specimens pass gives the corresponding value of flexibility reached

[0032] It is also understood that the cut-through temperature test of CEI EN 60851-6 references CEI EN 60317-0-1 (2014-06), chapter 4.

[0033] In one embodiment the wire has a rectangular shape. This includes flat wires having chamfered edges. Suitable cross-section ranges include 0.1 mm2to 100 mm2, preferably 1 mm2to 50 mm2and more preferred 1 mm2to 10 mm2.

[0034] The invention also concerns an electrical device comprising a wire according to the invention. Preferred devices are motors, in particular motors rated for an operating voltage of 800 volts and more.

[0035] EXAMPLES

[0036] The invention will be further described with reference to the following examples without wishing to be limited by them. Abbreviations used are BISDA (4,4-Bisphenol A Dianhydride), MDI (4,4’-diphenylmethane diisocyanate), NMP (N- methylpyrrolidone), MeOx (3-methyl-2-oxazolidinone), S100 (Solvent naphtha I, a C9 aromatic solvent) and MPC (metaparacresol).

[0037] Viscosities reported were measured using a viscometer in coaxial cylinders configuration according to EN ISO 3219. The solids contents were determined using a one gram sample after drying at 180 °C in a 5.1 mm disk for one hour and are stated as weight-%.

[0038] Unless expressly stated, cited norms and regulations throughout the entire disclosure are understood to be those norms and regulations which were in force on November 1 , 2024. A two liter four-necked flask (reactor) equipped with a thermometer, a condenser and a mechanical stirrer was charged with 280.5 g (0.54 mol) of BISDA, 132.0 g (0.53 mol) of MDI and 587.5 g of NMP.

[0039] The reaction mixture was heated to 85 °C over the course of two hours and subsequently held at this temperature for two hours. Then, the reaction mixture was heated to 155 °C over the course of seven hours and held at this temperature until a viscosity of 50000 mPas was reached. This final holding step was completed in two hours.

[0040] The obtained poly(etherimide) solution was diluted with 154.4 g of S100 and 230.0 g of an 80 / 20 (weight / weight) mixture of NMP / S100.

[0041] The reactor content was cooled to room temperature. The final viscosity was 2400 mPas at 23 °C and the solids content was 30.6%. This solution was stored at room temperature for six months, throughout which it remained stable as evidenced by viscosity testing. This is in contrast to a standard polyimide solution which is only stable for ca. three months under storage between zero and ten degrees Celsius.

[0042] Example 2

[0043] A two liter four-necked flask (reactor) equipped with a thermometer, a condenser and a mechanical stirrer was charged with 280.5 g (0.54 mol) of BISDA, 132.0 g (0.53 mol) of MDI and 587.5 g of MeOx.

[0044] The reaction mixture was heated to 85 °C over the course of two hours and subsequently held at this temperature for two hours. Then, the reaction mixture was heated to 155 °C over the course of seven hours and held at this temperature until a viscosity of 47000 mPas was reached. This final holding step was completed in two hours.

[0045] The obtained poly(etherimide) solution was diluted with 300.0 g of MeOx.

[0046] The reactor content was cooled to room temperature. The final viscosity was 3700 mPas at 23 °C and the solids content was 31.5%. This solution was stored at room temperature for six months, throughout which it remained stable as evidenced by viscosity testing. This is in contrast to a standard polyimide solution which is only stable for ca. three months under storage between zero and ten degrees Celsius.

[0047] Example 3

[0048] A two liter four-necked flask (reactor) equipped with a thermometer, a condenser and a mechanical stirrer was charged with 190.0 g (0.37 mol) of BISDA, 132.0 g (0.36 mol) of MDI and 520 g of MPC.

[0049] The reaction mixture was heated to 85 °C over the course of two hours and subsequently held at this temperature for two hours. Then, the reaction mixture was heated to 155 °C over the course of seven hours and held at this temperature until a viscosity of 11000 mPas was reached. This final holding step was completed in four hours.

[0050] The obtained poly(etherimide) solution was diluted with 293.0 g of S100 and 300.0 g of an 70 / 30 (weight / weight) mixture of MPC / S100.

[0051] The reactor content was cooled to room temperature. The final viscosity was 2850 mPas at 23 °C and the solids content was 19.0%. This solution was stored at room temperature for six months, throughout which it remained stable as evidenced by viscosity testing. This is in contrast to a standard polyimide solution which is only stable for ca. three months under storage between zero and ten degrees Celsius.

[0052] Testing

[0053] 70-75 micron coats of the enameling solutions were applied to a 1 mm diameter copper wire using a vertical VET375 enameling machine at a line speed of 55 m / min. 10 passes of the liquid enamel were applied in total. The enameled wires were tested according to CEI EN 60851 , wherein relative permittivity sris based on capacitance measurements during the tan delta temperature determination according to CEI EN 60851-5 and calculated using the formula: with C being the capacitance [pF / m] of the wire sample, dCOating the thickness [mm] of the enamel coating on the wire, Eo the absolute dielectric permittivity of a vacuum [pF / m] , Igraphite the length [m] of the enameled portion of the wire covered in graphite during testing, dbare the diameter [mm] of the bare wire and denameied the diameter [mm] of the enameled wire.

[0054] Unless stated otherwise, tangent delta temperatures throughout this disclosure are reported using the linear method of CEI EN 60851-5 with the x-axis of the diagram (i.e, tan delta = 0,08) being the agreed-upon reference for the intersection of the tangent line. Therefore, they carry the “(lin)” suffix in accordance with this norm.

[0055] The results show that wires enameled with the poly(etherimide) polymers prepared according to the invention are within the specifications for wires enameled with a reference poly(amideimide) for tan delta temperature, flexibility and cut-through temperature. At the same time, the poly(etherimide) polymers prepared according to the invention display a lower (i.e., leading to higher partial discharge inception voltages (PDIV)) relative permittivity which is comparable to the srvalue of a reference poly(imide) polymer.

[0056] The wires of the examples according to the invention satisfy the specifications of CEI EN 60317-57 “Round copper wire enameled with PAI class 220”.

[0057] The storage stability, expressed by the lack of change of the solutions’ viscosities over time after storage at room temperature, is given below:

Claims

Claims1. A method of manufacturing a poly(etherimide) polymer comprising heating a solution comprising an aromatic bis(ether anhydride) and / or its carboxylic acid precursor, a diisocyanate and a first solvent, characterized in that in a first heating step the solution is heated to a temperature in a first temperature range of 50 °C to 120 °C with a first heating rate of 5 °C / h to 30 °C / h and subsequently held within the first temperature range for 1 h to 8 h and in a second heating step the solution is heated to a temperature in a second temperature range of 145 °C to 165 °C with a second heating rate of 10° C / h to 30 °C / h and subsequently held within the second temperature range for 3 h to 6 h.

2. The method according to claim 1 , wherein the second heating step is conducted until a viscosity of the solution as determined with a viscometer in coaxial cylinders configuration according to EN ISO 3219 of 5000 mPas or more is achieved.

3. The method according to any of the preceding claims, wherein the aromatic bis(ether anhydride) comprises a bis(oxyphenyl) moiety.

4. The method according to any of the preceding claims, wherein the aromatic bis(ether anhydride) comprises a phthalic anhydride moiety.

5. The method according to any one of the preceding claims, wherein the diisocyanate is toluene diisocyanate, diphenylmethane diisocyanate, polymeric diphenylmethane diisocyanate or a mixture of the aforementioned substances.

6. The method according to any one of the preceding claims, wherein the first solvent and / or the second solvent independently of each other comprise N- methylpyrrolidone, 3-methyl-2-oxazolidinone, cresylic acids or a mixture of two or more of the aforementioned substances.

7. The method according to any one of the preceding claims, wherein the solution further comprises a lactam, a monofunctional alcohol, a monofunctional carboxylic acid or a mixture of two or more of the aforementioned substances.

8. The method according to any one of the preceding claims, wherein the solution further comprises a cross-linker and / or an imide group formation catalyst.

9. The method according to any one of the preceding claims, further comprising diluting a poly(etherimide) solution obtained after the second heating step with a second solvent which is identical to or different from the first solvent.

10. A method of manufacturing an enamel coated wire comprising applying a solution of a poly(etherimide) polymer manufactured by a method according to any one of claims 1 to 9 to a wire and removing the solvent of the solution.11 . The method according to claim 10, wherein the solution is applied to the wire at a wire velocity, expressed in m / min, corresponding to a v x d factor of 50 to 200 with v being the numerical value of the wire velocity in m / min and d being the numerical value of the wire diameter in mm.

12. A wire obtained by a method according to claim 10 or 11 having one or more of the following properties: a. a tan delta temperature as determined according to CEI EN 60851-5 of 200 °C (lin) or more b. a flexibility as determined according to CEI EN 60851-3 of 20 % or more c. a cut-through temperature as determined according to CEI EN 60851-6 of 350 °C or mored. a relative permittivity Eras determined according to the procedure in the experimental section of 3.05 or less.

13. The wire according to claim 12, having rectangular shape14. An electrical device comprising a wire according to claim 12 or 13.

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