Continuous process for producing poly(amide-imide) polymer

Abstract

The present invention relates to a continuous, solvent free, process for producing poly(amide-imide) polymer, the process comprising the steps of a. Feeding a polycarboxylic acid anhydride, and a compound having at least two isocyanate functional groups through one or more feeding ports into an extruder; b. Mixing and melting the composition inside the extruder; c. Reacting the composition inside the extruder at a temperature in the range of 260 – 400°C; d. Collecting the reacting mixture at the exit of the extruder; and e. Cooling the reacting mixture.

Description

[0001] CONTINUOUS PROCESS FOR PRODUCING POLY(AMIDE-IMIDE) POLYMER

[0002] The present invention relates to a continuous, solventless process for producing poly(amide-imide) polymer.

[0003] A poly(amide-imide) polymer (PAI) can be used as a magnet wire for coatings. Currently such polymers are synthesized in a batch process using N-methylpyrrolidone (NMP) in combination with hydrocarbon solvents.

[0004] US 3,673,160 discloses a process for producing thermostable polyamide-imide fibers and such fibers so produced, such process comprising extruding an N- methylpyrrolidone solution of a polymer having amide-imide linkages and amide linkages as described therein. The process of this disclosure is reported to allow for the production of very brilliant filaments, fibers and yarns not previously obtainable by the wet spinning of polyamide-imides. In this regard, such process is reported to be dependent upon the introduction into a polyamide-imide of linkages derived from an alkali or alkaline earth salt of dicarboxy-3,5 benzene sulfonic acid in an amount of at least 3 mole percent, based upon the polyamide-imide; extruding the polymer into a coagulating bath containing 30 to 75 percent by weight of N-methylpyrrolidone; drawing the filaments in air at a rate of at least 1 .5 x; washing the drawn filaments to eliminate the N-methylpyrrolidone; drying the washed filaments by any known conventional means; and, optionally, again drawing the filaments at a rate of at least 1 .5 x. It is reported that in accordance with this disclosure the brilliant filaments and yarns obtained through the foregoing procedure cannot be obtained utilizing a polyamide-imide without the aforementioned linkages and cannot be obtained by utilizing different coagulating baths or rates of drawings. All of these variations in the process of this disclosure are reported to produce very porous and dull filaments having characteristics far inferior to the very brilliant filaments produced in accordance with this disclosure. By way of example, a 21.3 percent solution of a sulfonated polyamide-imide is prepared in N-methylpyrrolidone by the reaction of 25 molar parts diisocyanato diphenylmethane, 24.25 molar parts trimellitic anhydride and 0.75 molar parts sodium dicarboxy-3,5 benzene sulfonate in dehydrated N-methylpyrrolidone. The solution is extruded at a speed of 10 m / min through a spinneret having 600 orifices of 0.06 mm in diameter, into a coagulating bath containing 60 percent N- methylpyrrolidone and 40 percent water. After a travel of 20 cm in the coagulating bath, the yarn exits in a gel state, and is drawn in air at ambient temperature at a rate of 1 .5 x. Then the drawn yarn is washed with water to remove the solvent and dried on two drying rollers at 40 °C and 150 °C, respectively.

[0005] US 201 1 / 048766 A1 relates to an insulated wire including: a conductor wire; and a polyamide-imide insulation coating formed around the conductor wire, the polyamideimide insulation coating being made from a polyamide-imide resin based insulating varnish, the varnish being synthesized by reaction of an isocyanate constituent and an acid constituent in a solvent, the isocyanate constituent including 5 to 50 mol % of 2,4‘- diphenylmethane-diisocyanate having a flexible molecular structure. By way of example, 12.5 g (0.05 mol) of 2,4’-diphenylmethane-diisocyanate (MDI) plus 237.5 g (0.95 mol) of 4,4‘-MDI (as an isocyanate constituent) and 192.0 g (1 .0 mol) of TMA (as an acid constituent) were reacted in an N-methylpyrrolidone (NMP) solvent (1000 g) for synthesis. Then, the solution was further diluted with 300 g of N,N- dimethylformamide (DMF). Thus, a polyamide-imide resin based insulating varnish (used for highly flexible insulation coatings) having a resin constituent concentration of approximately 25 mass-% was prepared. After that, the thus prepared polyamide-imide resin based insulating varnish was applied around a 0.8 mm diameter copper wire and baked. Thus, a copper wire covered with a 31 pm thick enamel coating was formed.

[0006] WO 2007 / 054543 A1 discusses a process for extruding a film (F) having a thickness of below 1000 pm from a polymer composition (C), wherein the polymer composition (C) comprises at least 40 wt.-%, based on the total weight of the polymer composition (C), of at least one aromatic polyamide-imide manufactured by a process including the polycondensation reaction of : (i) trimellitic anhydride monoacid halide; (ii) at least one comonomer chosen from diamines and diisocyanates, and (iii) at least one substance (S) comprising on e and only one functional group capable of reacting with either an anhydride group and an acid halide group on one hand, or an amine group and an isocyanate group on the other hand, or one and only one precursor of said functional group, wherein the amount of substance (S) is of above 1 mol. %, based on the total number of moles of trimellitic anhydride monoacid halide and substance (S). As substances (S) comprising one and only one functional group capable of reacting with an anhydride group and an acid halide group, it can be cited aniline, napthylamine, anisidine and phenyl isocyanate. As substances (S) comprising one and only one functional group capable of reacting with an amine group and an isocyanate group, it can be cited phthalic anhydride, 1 ,8-naphthalic anhydride, 1 ,2- cyclohexenedicarboxylic anhydride (cis or trans), succinic anhydride, maleic anhydride, benzoic anhydride, benzoyl chloride and naphthoyl chloride. As substances (S) comprising one and only one precursor of a functional group capable of reacting with an amine group and an isocyanate group, it can be cited any substance comprising two vicinal carboxylic acids, in particular trimellitic acid and maleic acid. The PAI powders used in the working examples were manufactured by a process including the polycondensation reaction of trimellitic acid chloride, 4,4'-diaminodiphenylether and m- phenylenediamine, and trimellitic acid. Three grades (PAI 1 , PAI 2 and PAI 3) were prepared, differing only by the amount of trimellitic acid. It is reported that films obtained according to this disclosure featured some anisotropic properties. Properties such as tensile strength, tensile elongation and tensile modulus along the machine direction (MD) were described as better than those in the transverse direction (TD).

[0007] US 4,581 ,264 discloses a process for the manufacture of extruded articles by extruding polyamide-imide polymers and copolymers through melt flow channels and extrusion dies at ever increasing shear rates ranging from 0.1 / s to about 2000 / s. The extruder barrel and melt flow channel temperatures range from about 480 °F (249 °C) to about 600 °F (316 °C) and the extrusion die temperatures range from about 575 °F (302 °C) to about 680 °F (360 °C). Also, the addition of polyetherimides and polysulfones is disclosed. Thin films, thin sheets and hollow tubes are disclosed. All these articles are described to be useful in engineering applications requiring high temperature resistant plastics. Useful applications according to this disclosure include use in the aerospace and automobile industry.

[0008] Solvent-based processes, especially industrial-scale processes, for the production of PAI polymers suffer from the inherent limitation of the maximum reaction temperature being tied to the boiling point of the solvent that is used. For example, NMP has a boiling point of 202 °C. Another drawback in solvent-based processes is that the viscosity increase during the reaction in conjunction with the liberation of carbon dioxide leads to the formation of a PAI foam which must be controlled. This may require specially designed reaction vessels with a higher than usual surface area to volume ratio.

[0009] From a structural perspective it is believed that a certain number of iso-imide groups will be formed in polymers obtained via solvent-based processes.

[0010] PAI polymers are applied to a conductor typically at 30-50% solids content. The solvents are then traditionally burned as a source of high-cost fuel which adds to additional environmental emissions. Also due to the low solids content, it is costly to ship a hazardous material around the world where 50-70% of the material is not adding value to the final product. What is desired is a coating that can be applied without solvent yet duplicate the performance of the solvent based coating. This would eliminate the hazardous solvent component and reduce shipping volume by potentially 50-70%.

[0011] The process according to the present invention allows for the manufacture of PAI polymers without the use of any toxic or hazardous solvents and allows for the direct application of the fresh prepared PAI on a conductor wire.

[0012] The present invention therefore relates to a continuous, solvent free, process for producing poly(amide-imide) polymer, the process comprising the steps of a. Feeding a polycarboxylic acid anhydride, and a compound having at least two isocyanate functional groups through one or more feeding ports into an extruder; wherein the polycarboxylic acid anhydride is trimellitic anhydride, naphthalene tricarboxylic anhydrides or bisphenyl tricarboxylic anhydride; and wherein the compound having at least two isocyanate groups is 4,4'- diphenylmethane diisocyanate, 2,4- and 2,6-toluylene diisocyanate or hexamethylene diisocyanate; b. Mixing and melting the composition inside the extruder; c. Reacting the composition inside the extruder at a temperature in the range of 260 - 400°C; d. Collecting the reacting mixture at the exit of the extruder; and e. Cooling the reacting mixture.

[0013] Without wishing to be bound by theory it is believed that the higher reaction temperatures possible by the reactive extrusion process according to the invention also has an influence on the structure of the polymer product. In particular it is believed that substantially no iso-imide groups will be present in the product as the higher temperatures of the process according to the invention will effect their rearrangement to imide groups.

[0014] For this process it is important that all ingredients of the composition are properly mixed before the reaction takes place. Therefore, prior to reacting the components, they are thoroughly mixed at a temperature where all components that take part in the reaction are in a molten state. By applying shear in the extruder through the extruder elements, the temperature of the mixture inside the extruder can be raised.

[0015] In one embodiment of the process according to the present invention the compound having at least two isocyanate functional groups is fed into the extruder as a liquid material. A liquid material being defined as a material having a viscosity between 1 and 5000 mPa.s, as measured in accordance with ASTM D445 at the relevant temperature. For example, if the material is fed into the extruder at a temperature of 60°C, the viscosity should be measured at the same temperature.

[0016] In a further embodiment of the process according to the present invention the extruder is a twin-screw extruder or a planetary extruder.

[0017] In a further embodiment of the process according to the present invention the extruder is equipped with vents to remove an excess of gas from the inside of the extruder.

[0018] In a further embodiment of the process according to the present invention a catalyst is added to the feeding mixture. In a further embodiment of the process according to the present invention a titanate is added to the feeding mixture as a catalyst.

[0019] In a further embodiment of the process according to the present invention a Schiff base is added to the feeding mixture as a catalyst.

[0020] In a further embodiment of the process according to the present invention the poly(amide-imide) that is obtained by the processing in the extruder is applied to a wire.

[0021] In the process according to the present invention trimellitic anhydride, naphthalene tricarboxylic anhydrides or bisphenyl tricarboxylic anhydrides are used Very particular preference is given to the employment of trimellitic anhydride.

[0022] A compound having at least two isocyanate functional groups can be schematically represented as R - (N=C=O)x, wherein R is an organic group and x > 2. A compound having two isocyanate functional groups is often referred to as a diisocyanate compound. Diisocyanates suitable for use in the process according to the present invention are of 4,4'- diphenylmethane diisocyanate and 2,4- and 2,6-toluylene diisocyanate.

[0023] A polymerization catalyst can be added to the ingredients inside the extruder. However, this is not necessary. Examples of a suitable catalysts include titanates and aldimides, which are known to the person skilled in the art. Particular preferred for use in the process according to the present are aldimide compounds with the general structure R1R2C=R3, wherein R1and R3are organic groups (aliphatic or aromatic) and R2is an organic group or hydrogen. One example of a suitable catalyst is Vulkacit®576.

[0024] In another embodiment the molar ratio of the polycarboxylic acid anhydride and the compound having at least two isocyanate functional groups is 1 .01 :1 to 1.1 :1. Smaller ratios will lead to a higher molecular weight of the PAI polymer and vice versa. The molten material that is collected at the exit of the extruder can be used in various ways. Either it is left to solidify for later use, or it is kept in a molten state and directly used, for example to coat a wire, for example through a wire coating technique, as disclosed in WO 2016 / 038335. However, it is also possible to dissolve the solidified material in a suitable solvent, for example a strong aprotic solvent like NMP, dimethylacetamide (DMAc), dimethylformamide (DMF), tetrahydrofuran (THF), methylethyl ketone (MEK), gamma butyrolactone (GBL), dimethyl sulfoxide (DMSO) or N-(n-butyl)-pyrrolidone (NBP).

[0025] Using techniques known to the person skilled in the art, such solution can also be used to coat a wire in a more traditional process.

[0026] To enhance the cut through resistance of a wire coated with the composition of the current invention, nano particles may also be included in the composition according to the present invention.

[0027] These nanoparticles can be added during the synthesis of the polyamideimide inside the extruder or added to the material after the synthesis has been completed, for example once the polyamideimide is in a solution.

[0028] The nanoparticles which can be used in the composition according to the invention are particles whose average radius is in the range from 1 to 300 nm, preferably in a range from 2 to 100 nm, particularly preferably in a range from 5 to 65 nm. Examples of preferred nanoparticles are nano-oxides, nano-metal oxides, colloidal oxides, colloidal metal oxides, metal oxides or hydrated oxides of aluminum, tin, boron, germanium, gallium, lead, transition metals and lanthanides and actinides, particularly of the series comprising aluminum, silicon, titanium, zinc, yttrium, vanadium, zirconium and / or nickel, preferably aluminum, silicon, titanium and / or zirconium, which are nanosized in the dispersed phase, which can be employed alone or in combination. Among nanometal oxides, nanoaluminas are the most preferred. Examples of nanoaluminas are: BYK- LP X 20693 and NanoBYK 3610 by BYK-Chemie GmbH Nycol AI20OSD by Nycol Nano Technologies Inc., Dispal X-25 SR and SRL, Disperal P2, P3, OS1 and OS2 by Sasol Germany GmbH. Among nanoaluminas, ceramic particles of aluminum oxide pre-dispersed in a polar solvent, such as BYK-LP X 20693 and NanoBYK 3610 by BYK-Chemie GmbH are preferred.

[0029] The nanoparticles can be used together with coupling agents. As coupling agents, any commonly known functional alkoxy- or aryloxy-silanes may be used. Among functional silanes, (isocyanatoalkyl)-trialkoxy silanes, (aminoalkyl)- trialkoxy silanes, (trialkoxysilyl)-alkyl anhydrides, oligomeric diamino-silane-systems are preferred. The alkyl radical and the alkoxy group of the functional silane having 1 to 6 carbon atoms and more preferably 1 to 4. The aforementioned alkyl and alkoxy groups may further have a substituent thereon. Also useful as coupling agents are titanates and / or zirconates. Any common ortho-titanic or zirconic acid ester may be used such as, for example, tetraisopropyl, tetrabutyl, acetylacetone, acetonacetic acid esters, diethanolamine, triethanolamine, cresyl titanate or zirconate.

[0030] To enhance the dispersion of nanoparticles in the polymer solution matrix, coupling agents such as functional silanes, titanates or zirconates may be added directly to the nanoparticle dispersion and herein mixed before it is loaded to the polymer resin solution or may be added directly to the polymer solution before adding the nanoparticles dispersion. Coupling agents may alternatively be mixed to the polymer solution prior to the nanoparticle dispersion loading, for a better linkage of the inorganic moiety to the organic one. The mixture of polymer solution and coupling agent may be stirred at room temperature or at temperatures relatively low for a few hours, before nanometal oxide solution is added.

[0031] EXAMPLES

[0032] Process description

[0033] In an extruder, type Tex44alll-42BW-3V, having in total 17 barrel sections the raw materials were fed into zone 6 of the extruder. The material was mixed and further conveyed in zones 7 to 9 at a temperature in the range of 100 to 180 °C. In zone 10 the temperature was raised to 200 °C and the mixture was conveyed and kneaded. In this zone the extruder was equipped with a vent to atmospheric pressure. In zones 1 1 to 16 the mixture was further conveyed and reacted at a temperature in the range of 280 to 300°C. In zone 13 and 16 the extruder was equipped with a vent to atmospheric pressure. In zone 17 the content of the extruder was further kneaded and discharged from the extruder.

[0034] Examples 1 - 3

[0035] Trimellitic anhydride (TMA) and methylene diphenyl diisocyanate (MDI) were used in the process as described above. Prior to introduction into the extruder, MDI was heated to 60°C to obtain a molten material and the material was kept at that temperature just before feeding it into the extruder. The feed rates of the different components were:

[0036] The molten reaction mixture (poly(amide-imide)) was collected at the exit of the extruder and left to cool and solidify. Samples (“measured product”) were taken throughout the extrusion experiments and were analyzed by gel permeation chromatography using N,N-dimethylacetamide with 5 g / l LiBr as the eluent against PMMA standards. Molecular weights are given in g / mol. Mpis the molecular weight at the peak maximum. Experiment 1 :

[0037] Experiment 2: Experiment 3:

[0038] Without wishing to be bound by theory the inventors attribute the variations in molecular weight observed over the individual experiments to shortcomings of the dosage equipment used and not to the underlying invention.

Claims

CLAIMS1 . A continuous, solvent free, process for producing poly(amide-imide) polymer, the process comprising the steps of a. Feeding a polycarboxylic acid anhydride, and a compound having at least two isocyanate functional groups through one or more feeding ports into an extruder; wherein the polycarboxylic acid anhydride is trimellitic anhydride, naphthalene tricarboxylic anhydrides or bisphenyl tricarboxylic anhydride; and wherein the compound having at least two isocyanate groups is 4,4'- diphenylmethane diisocyanate, 2,4- and 2,6-toluylene diisocyanate or hexamethylene diisocyanate; b. Mixing and melting the composition inside the extruder; c. Reacting the composition inside the extruder at a temperature in the range of 260 - 400°C; d. Collecting the reacting mixture at the exit of the extruder; and e. Cooling the reacting mixture.

2. The process of claim 1 wherein the compound having at least two isocyanate functional groups is fed into the extruder as a liquid material.

3. The process of claim 1 , wherein the polycarboxylic acid anhydride and the compound having at least two isocyanate functional groups are mixed prior to feeding them into the extruder.

4. The process of claim 1 or 2, wherein the extruder is a twin-screw extruder or a planetary extruder.

5. The process according to any of the preceding claims wherein the extruder is equipped with vents to remove an excess of gas from the inside of the extruder.

6. The process according to any of the preceding claims wherein a catalyst is added to the feeding mixture.

7. The process according to claim 6, wherein the catalyst is an aldimide compound.

8. The process according to any one of the preceding claims wherein the molar ratio of the polycarboxylic acid anhydride and the compound having at least two isocyanate functional groups is 1 .01 :1 to 1 .1 :1 .

9. The process according to any one of the preceding claims wherein nanoparticles are added inside the extruder.

10. Poly(amide-imide) polymer obtainable by the process of claim 1 . 1 1. A process for applying a poly(amide-imide) polymer on a wire wherein the reaction mixture that is obtained at the end of the extruder according to the process of claim 1 , is solved in a strong aprotic solvent prior to application to the wire.

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