Method for producing prepolymer solution and method for producing insulated wire

Abstract

A method for producing a prepolymer solution according to one embodiment of the present disclosure, the method continuously producing a prepolymer solution wherein a prepolymer, which is a precursor of a thermosetting resin, is dissolved in a solvent, comprises a step in which a first starting material, a second starting material that reacts with the first starting material so as to form the prepolymer, and the solvent are mixed with each other.

Description

[Technical Field]

[0001] The present disclosure relates to a method for producing a prepolymer solution and a method for producing an insulated wire. [Background technology]

[0002] Patent Document 1 describes a polymer production system for producing a first polymer using raw materials, which are a raw material fluid containing a first polymerizable compound having polyaddition properties and a raw material powder containing a second polymerizable compound having polyaddition properties. The polymer production system includes a raw material fluid supply section that continuously supplies the raw material fluid, a raw material powder supply section that continuously supplies the raw material powder, a first mixing section that continuously mixes the raw material fluid and the raw material powder to produce a first mixed fluid, and a first reaction section that is located downstream of the first mixing section and produces a first polymerization fluid by progressing a polymerization reaction of the first mixed fluid. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2021-31610 Summary of the Invention

[0004] A method for producing a prepolymer solution according to one embodiment of the present disclosure is a method for continuously producing a prepolymer solution in which a prepolymer, which is a precursor of a thermosetting resin, is dissolved in a solvent, and includes a step of mixing, using an extruder, a first raw material, a second raw material that reacts with the first raw material to form the prepolymer, and the solvent. [Brief explanation of the drawings]

[0005] [Figure 1] FIG. 1 is a schematic diagram illustrating a method for producing a prepolymer solution according to an embodiment of the present disclosure. [Figure 2] FIG. 2 is a schematic diagram illustrating a method for producing a prepolymer solution according to an embodiment of the present disclosure. [Figure 3]FIG. 3 is a schematic diagram illustrating a method for producing a prepolymer solution according to an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0006] [Problem to be solved by this disclosure] From the viewpoint of improving the productivity of prepolymer solutions and reducing production costs, a method for continuously producing prepolymer solutions is desired.

[0007] Furthermore, when a prepolymer solution is used as a material for forming an insulating layer of an insulated wire, for example, the solvent contained in the prepolymer solution must be removed, and therefore, a method for producing a highly concentrated prepolymer solution is desired in order to reduce the amount of solvent to be removed.

[0008] The present disclosure has been made in light of the above circumstances, and an object of the present disclosure is to provide a method for producing a prepolymer solution that can continuously produce a highly concentrated prepolymer solution.

[0009] [Effects of this disclosure] A method for producing a prepolymer solution according to one embodiment of the present disclosure can continuously produce a highly concentrated prepolymer solution.

[0010] [Description of the embodiments of the present disclosure] First, embodiments of the present disclosure will be listed and described.

[0011] A method for producing a prepolymer solution according to one embodiment of the present disclosure is a method for continuously producing a prepolymer solution in which a prepolymer, which is a precursor of a thermosetting resin, is dissolved in a solvent, and includes a step of mixing, using an extruder, a first raw material, a second raw material that reacts with the first raw material to form the prepolymer, and the solvent.

[0012] The prepolymer solution manufacturing method can continuously manufacture a high-concentration prepolymer solution by mixing the first raw material, the second raw material, and the solvent using an extruder. "High concentration" means that the solids concentration of the prepolymer solution is 25% by mass or more. "Solids concentration" means the ratio of the total mass of all components other than the solvent to the total mass of the prepolymer solution. "Continuous production" means that the prepolymer solution is manufactured continuously for a certain period of time. This is different from "batch production."

[0013] It is preferable to further mix a reaction inhibitor in the mixing step, which can reduce the viscosity of the prepolymer solution, thereby making it possible to produce an insulated wire.

[0014] It is preferable to further include a step of measuring the viscosity of the prepolymer solution obtained in the mixing step, and to determine the amount of the reaction inhibitor to be supplied in the mixing step based on the viscosity measurement value obtained in the measuring step, in which case the viscosity of the prepolymer solution can be easily controlled.

[0015] It is preferable to further include a step of stirring the prepolymer solution obtained in the mixing step, in which case the variation in viscosity of the prepolymer solution can be reduced.

[0016] The solids concentration of the prepolymer solution is preferably 20% by mass or more and 50% by mass or less, which makes it possible to reduce the number of repeated coatings required to form an insulating layer with a target thickness, thereby improving production efficiency.

[0017] It is preferable that the prepolymer has a group capable of forming an imide group by a dehydration reaction, the first raw material is a carboxylic acid anhydride, and the second raw material is a diamine compound, in which case the heat resistance of the thermosetting resin obtained by curing the prepolymer solution can be improved.

[0018] It is preferable that the prepolymer is a polyimide prepolymer and the carboxylic acid anhydride is a tetracarboxylic acid dianhydride, in which case the heat resistance of the thermosetting resin obtained by curing the prepolymer solution can be further improved.

[0019] The extruder is preferably a twin-screw extruder. In this case, a sufficient residence time required for forming the prepolymer can be ensured. By ensuring a sufficient residence time, unreacted prepolymer can be reacted, thereby improving the mechanical strength of the insulated wire.

[0020] In the measuring step, it is preferable to measure the viscosity using a vibration viscometer, which allows the prepolymer to be produced without impairing the continuous productivity of the prepolymer solution.

[0021] The stirring step is preferably carried out under conditions of 20° C. to 200° C. In this case, the viscosity variation can be reduced by stirring for a short time without causing the solvent to volatilize.

[0022] The method for manufacturing an insulated wire includes a conductor and an insulating layer covering the conductor, and includes the steps of applying a prepolymer solution obtained by the above-described method for manufacturing a prepolymer solution to the outer periphery of the conductor, and heating the prepolymer solution applied to the conductor.

[0023] The method for producing an insulated wire uses the prepolymer solution obtained by the above-described method for producing a prepolymer solution as a material for forming an insulating layer, thereby making it possible to continuously produce insulated wires having appropriate properties.

[0024] [Details of the embodiments of the present disclosure] Hereinafter, a method for producing a prepolymer solution and a method for producing an insulated wire according to an embodiment of the present disclosure will be described in detail.

[0025] <Method of manufacturing prepolymer solution> The method for producing the prepolymer solution is a method for continuously producing a prepolymer solution in which a prepolymer, which is a precursor of a thermosetting resin, is dissolved in a solvent, and includes a step of mixing a first raw material, a second raw material that reacts with the first raw material to form the prepolymer, and the solvent using an extruder (hereinafter also referred to as the "mixing step").

[0026] The method for producing a prepolymer solution preferably further comprises a step of measuring the viscosity of the prepolymer solution obtained in the mixing step (hereinafter also referred to as a "viscosity measurement step").

[0027] The method for producing a prepolymer solution preferably further comprises a step of stirring the prepolymer solution obtained in the mixing step (hereinafter also referred to as a "stirring step").

[0028] The method for producing a prepolymer solution may include other steps in addition to the mixing step, the viscosity measuring step, and the stirring step, such as a supply amount measuring step, a pressure measuring step, a refractive index measuring step, a density measuring step, a temperature measuring step, a flow rate measuring step, a chromaticity measuring step, an absorbance measuring step, a conductivity measuring step, a turbidity measuring step, and an infrared spectroscopy measuring step.

[0029] The prepolymer solution is a solution in which a prepolymer, which is a precursor of a thermosetting resin, is dissolved in a solvent. Examples of the thermosetting resin include polyimide, polyamideimide, polyetherimide, polyester, etc. Among these, a thermosetting resin having an imide group is preferred, and polyimide is more preferred.

[0030] The prepolymer is a precursor of the thermosetting resin. For example, when the thermosetting resin is a polyimide, the prepolymer is its precursor, a polyamic acid. The polyamic acid undergoes a dehydration cyclization reaction by heating or the like to form a cyclic imide group, thereby becoming a polyimide.

[0031] The lower limit of the solids concentration of the prepolymer solution obtained by this prepolymer solution production method is preferably 20% by mass, more preferably 24% by mass, and even more preferably 28% by mass. This prepolymer solution production method makes it possible to produce a prepolymer solution with a high solids concentration of 20% by mass or more. Furthermore, the amount of solvent can be relatively reduced. The upper limit of the solids concentration is preferably 50% by mass, more preferably 45% by mass, even more preferably 40% by mass, and even more preferably 36% by mass. The solids concentration of the prepolymer solution can be adjusted by the amounts of the first raw material, the second raw material, and the solvent supplied, etc.

[0032] The lower limit of the viscosity of the prepolymer solution at 30°C is preferably 5 Pa·s. The upper limit of the viscosity of the prepolymer solution at 30°C is preferably 450 Pa·s. If the viscosity of the prepolymer solution at 30°C is below the lower limit, it becomes difficult to apply the prepolymer solution uniformly, which may result in insulated wires being insufficiently coated. On the other hand, if the viscosity of the prepolymer solution at 30°C exceeds the upper limit, it may become difficult to apply the prepolymer solution. The viscosity of the prepolymer solution is measured using an E-type viscometer (Toki Sangyo Co., Ltd.'s "TV-25").

[0033] The lower limit of the polystyrene-equivalent weight average molecular weight (Mw) of the prepolymer is preferably 10,000, more preferably 15,000. The upper limit of the polystyrene-equivalent Mw of the prepolymer is preferably 100,000, more preferably 80,000. If the polystyrene-equivalent Mw of the prepolymer is below the lower limit, the coating may not elongate sufficiently when forming the insulating layer of the insulated wire. On the other hand, if the polystyrene-equivalent Mw of the prepolymer exceeds the upper limit, the viscosity of the prepolymer solution may become too high.

[0034] The polystyrene-equivalent number average molecular weight (Mn) of the prepolymer is preferably 5,000 or more and 50,000 or less.

[0035] The ratio of Mw to Mn of the prepolymer (Mw / Mn) is preferably 1.5 or more and 4.0 or less.

[0036] The Mw, Mn, and Mw / Mn of the prepolymer solution are polystyrene-equivalent values ​​measured by gel permeation chromatography in accordance with JIS-K7252-1:2008 "Plastics - Determination of average molecular weight and molecular weight distribution of polymers by size exclusion chromatography - Part 1: General rules."

[0037] (Mixing process) In this process, a first raw material, a second raw material that reacts with the first raw material to form the prepolymer, and the solvent are mixed using an extruder, and by using the extruder, a highly concentrated prepolymer solution can be continuously produced.

[0038] In this step, the first raw material and the second raw material react with each other to form a prepolymer.

[0039] The mixing time is preferably 30 seconds to 60 minutes. In this case, sufficient time can be ensured to form a polymer without the prepolymer solution curing too much and gelling. The mixing temperature is preferably 20°C to 200°C. In this case, sufficient temperature can be ensured to form a polymer without the prepolymer solution curing too much and gelling.

[0040] The prepolymer is not particularly limited as long as it is a precursor of the above-mentioned thermosetting resin. Among them, a prepolymer having a group capable of forming an imide group by a dehydration reaction is preferred, and a polyimide prepolymer is more preferred.

[0041] When the prepolymer has a group capable of forming an imide group by a dehydration reaction, the first raw material is a carboxylic acid anhydride and the second raw material is a diamine compound. By using the first raw material and the second raw material as described above, a prepolymer having a group capable of forming an imide group by a dehydration reaction is formed in this process. In this case, the heat resistance of the thermosetting resin obtained by curing the prepolymer solution can be improved.

[0042] The carboxylic acid anhydride may, for example, be a tetracarboxylic acid dianhydride.

[0043] Examples of the diamine compound include aliphatic diamines such as hexamethylenediamine, 1,2-diaminotetradecane, 1,2-diaminoheptadecane, 1,2-diaminooctadecane, 1,9-diaminononane, 2,2-dimethyl-1,3-propanediamine, and 1,11-diaminoundecane; m-phenylenediamine, p-phenylenediamine, 2,4-diaminotoluene, 4,4'-diamino-3,3'-dimethyl-1,1'-biphenyl, 4,4'-diamino-3,3'-dihydroxy-1,1'-biphenyl, 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl ether, 3,3'-diaminodiphenyl sulfone, 4,4'-diaminodiphenyl sulfone, 4,4'-diaminodiphenyl sulfide, and 2,2-bis(4-amino)-2,2-diphenylpropanediamine. and aromatic diamines such as 2,6-diamino-4-methylpyridine, 4,4'-(9-fluorenylidene)dianiline, 2,6-diamino-4-methylpyridine, 4,4'-(9-fluorenylidene)dianiline, 2,6-diamino-4-methylpyridine, 2,6-diamino-4-methylpyridine, 2,6-diamino-4-methylpyridine, 2,6-diamino-4-methylpyridine, 4,4'-(9-fluorenylidene)dianiline, and 2,6-diamino-4-methylpyridine.

[0044] The diamine compound is preferably an aromatic diamine, which can improve the mechanical strength of the thermosetting resin obtained by curing the prepolymer solution.

[0045] When the prepolymer is a polyimide prepolymer, the carboxylic acid anhydride is preferably a tetracarboxylic acid dianhydride, which can further improve the heat resistance of the thermosetting resin obtained by curing the prepolymer solution.

[0046] Examples of the tetracarboxylic acid dianhydride include aliphatic tetracarboxylic acid dianhydrides such as 1,1,2,2-ethanetetracarboxylic acid dianhydride, 1,2,3,4-butanetetracarboxylic acid dianhydride, 1,2,3,4-cyclobutanetetracarboxylic acid dianhydride, and bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic acid dianhydride; and aromatic tetracarboxylic acid dianhydrides such as pyromellitic acid dianhydride, 3,3',4,4'-biphenyltetracarboxylic acid dianhydride, bis(3,4-dicarboxyphenyl)ether dianhydride, 3,3',4,4'-benzophenonetetracarboxylic acid dianhydride, 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride, and 3,3',4,4'-biphenylsulfonetetracarboxylic acid dianhydride.

[0047] The tetracarboxylic dianhydride is preferably an aromatic tetracarboxylic dianhydride, which can improve the mechanical strength of the thermosetting resin obtained by curing the prepolymer solution.

[0048] The amounts of the first and second raw materials supplied can be determined appropriately depending on factors such as the target solids concentration of the prepolymer solution. The molar ratio of the first raw material to the second raw material (first raw material:second raw material) can be, for example, 95:105 or more and 105:95 or less, more preferably 97:103 or more and 103:97 or less, and even more preferably 99:101 or more and 101:99 or less. It is also preferable that the first raw material and the second raw material are substantially equimolar. When the prepolymer solution is used as a material for forming the insulating layer of an insulated electric wire, an insulated electric wire having excellent coating elongation, breakdown voltage, and relative dielectric constant can be formed. "Substantially equimolar amounts" refers to a molar ratio of the first raw material to the second raw material (first raw material:second raw material) in the range of 99:101 or more and 101:99 or less.

[0049] In this step, raw materials other than the first raw material and the second raw material can be supplied within a range that does not impair the effects of the present disclosure.

[0050] The solvent is selected from those that have high solubility for the prepolymer, which is the reaction product of the first and second raw materials, and that do not react with the first and second raw materials and the prepolymer. A polar aprotic organic solvent is preferred as such a solvent. By using a solvent that does not have a proton that can react with the prepolymer, side reactions between the solvent and the raw materials or the prepolymer can be avoided. Furthermore, polar organic solvents can sufficiently dissolve the prepolymer, which also has polarity.

[0051] Examples of the aprotic polar organic solvent include N-methyl-2-pyrrolidone (NMP), N,N-dimethylacetamide (DMAc), N,N-dimethylformamide, and dimethyl sulfoxide.

[0052] The amount of solvent supplied can be appropriately determined depending on the target solids concentration of the prepolymer solution.

[0053] The extruder is not particularly limited as long as it is a device having an extrusion mechanism, and examples thereof include a single-screw extruder, a twin-screw extruder, a four-screw extruder, and an eight-screw extruder. Among these, a twin-screw extruder is preferred. In this case, the residence time required for forming the prepolymer can be sufficiently secured while suppressing equipment costs.

[0054] In this step, it is preferable to further mix a reaction inhibitor in addition to the first raw material, the second raw material, and the solvent. The reaction inhibitor reacts with a portion of the carboxylic acid anhydride groups located at the terminals of the prepolymer to cap the ends of the polymer chain. By using the reaction inhibitor, it is possible to control the polymerizability of the first raw material, and as a result, it is possible to reduce the viscosity of the prepolymer solution.

[0055] Examples of reaction inhibitors include water (HO) and alcohols having 1 to 15 carbon atoms. Examples of alcohols having 1 to 15 carbon atoms include monohydric alcohols such as ethanol, methanol, propanol, butanol, and pentanol; and polyhydric alcohols such as ethylene glycol, propylene glycol, and glycerin. Among these, water or methanol is preferred from the viewpoints of reactivity and cost.

[0056] The amount of the reaction inhibitor to be supplied can be appropriately determined based on the molar amount of the carboxylic acid anhydride, and can be, for example, 0.01 to 3 moles per mole of the carboxylic acid anhydride.

[0057] In this process, components other than the first raw material, second raw material, solvent, and reaction inhibitor may be included to improve the performance of the thermosetting resin. For example, functional materials may be included to improve the mechanical strength, electrical properties, thermal conductivity, heat resistance, cold resistance, abrasion resistance, water absorption resistance, chemical resistance, radiation resistance, and surge resistance of the thermosetting resin. More specifically, examples of such functional materials include chemical foaming agents, thermally expandable microcapsules, hollow-forming particles with a core-shell structure, and pore-forming agents such as high-boiling-point solvents.

[0058] An example of this process will be described with reference to Fig. 1. As shown in Fig. 1, a twin-screw extruder 1 is equipped with a second raw material supply section 11 that supplies a second raw material, a solvent supply section 13 that supplies a solvent, a first raw material supply section 12 that supplies a first raw material, and a mixing section 14 that mixes the first raw material, the second raw material, and the solvent to cause a polymerization reaction. Note that in Fig. 1, the second raw material supply section 11, the solvent supply section 13, and the first raw material supply section 12 are arranged in this order from upstream, but continuous productivity can be ensured even if this order is changed as appropriate.

[0059] The first raw material is supplied in fixed amounts from a first raw material supply unit 12, and the second raw material is supplied in fixed amounts from a second raw material supply unit 11. The first raw material supply unit 12 and the second raw material supply unit 11 may each be equipped with a feeder.

[0060] The first raw material supply unit 12 and the second raw material supply unit 11 may further include a side feeder.

[0061] The solvent is supplied at a constant rate from the solvent supply unit 13. The solvent supply unit 13 may be equipped with a pump. When a reaction inhibitor is used, it is preferable to supply it from the solvent supply unit 13.

[0062] The prepolymer solution obtained in the mixing section 14 is recovered from a discharge port (not shown) disposed downstream of the mixing section 14 .

[0063] (Viscosity measurement process) In this step, the viscosity of the prepolymer solution obtained in the mixing step is measured, and the amount of the reaction inhibitor to be supplied in the mixing step is determined based on the viscosity measurement value thus obtained. By including this step in the method for producing a prepolymer solution, the viscosity of the prepolymer solution can be easily controlled.

[0064] The viscosity measurement in this step is preferably carried out using a vibration viscometer. Since a vibration viscometer can measure viscosity in-line, it is possible to produce a prepolymer without impairing the continuous productivity of the prepolymer solution. Furthermore, by automatically measuring the viscosity using a vibration viscometer, it is possible to automate the control of the supply amount of the reaction inhibitor based on the measured viscosity information, and thus to automate the control of the viscosity of the prepolymer solution.

[0065] An example of this step will be described with reference to Fig. 2. As shown in Fig. 2, the viscosity of the prepolymer solution discharged from a twin-screw extruder 1 is measured by an oscillating viscometer 2 disposed in a flow path. The oscillating viscometer 2 may be disposed not only in the flow path but also in a stirring tank described below.

[0066] (stirring process) In this step, the prepolymer solution obtained in the mixing step is stirred. By including this step in the method for producing the prepolymer solution, it is possible to reduce variation in viscosity of the prepolymer solution.

[0067] The stirring in this step is preferably carried out using a stirrer. The stirring conditions are not particularly limited and can be determined appropriately.

[0068] The stirring temperature is preferably 20° C. or higher and 200° C. or lower, and more preferably 40° C. or higher and 110° C. or lower. In this case, a temperature sufficient for forming a polymer can be ensured without excessive curing of the prepolymer solution causing gelation.

[0069] An example of this process will be described with reference to Fig. 3. As shown in Fig. 3, a prepolymer solution discharged from a twin-screw extruder 1 is supplied to a stirring tank 3. The prepolymer solution stirred in the stirring tank 3 is discharged into a flow path by a pump (not shown) or the like.

[0070] <Insulated wire manufacturing method> The method for manufacturing an insulated wire is a method for manufacturing an insulated wire comprising a conductor and an insulating layer covering the conductor, and comprises a step of applying a prepolymer solution obtained by the above-mentioned method for manufacturing a prepolymer solution to the outer periphery of the conductor (hereinafter also referred to as the "applying step"), and a step of heating the prepolymer solution applied to the conductor (hereinafter also referred to as the "heating step").

[0071] The method for producing an insulated wire uses the prepolymer solution obtained by the method for producing a prepolymer solution as described above as a material for forming an insulating layer, and therefore can produce an insulated wire having appropriate properties. More specifically, the method for producing an insulated wire can produce an insulated wire having excellent coating elongation, a high breakdown voltage, and a low dielectric constant.

[0072] The conductor generally contains a metal as its main component. While the metal is not particularly limited, copper, copper alloys, aluminum, or aluminum alloys are preferred. By using such a metal for the conductor, an insulated wire having excellent processability and electrical conductivity can be obtained. The conductor may contain other components, such as known additives, in addition to the metal as its main component.

[0073] The cross-sectional shape of the conductor is not particularly limited, and various shapes such as a circle, a square, a rectangle, etc. The size of the cross section of the conductor is also not particularly limited, and can be determined appropriately depending on the application of the insulated wire, etc.

[0074] (Coating process) In the coating process, the prepolymer solution is applied to the outer peripheral side of the conductor. For example, a method of applying the prepolymer solution to the outer peripheral side of the conductor can be implemented using a coating device equipped with a storage tank for storing the prepolymer solution and a coating die. With this coating device, the conductor passes through the storage tank, causing the prepolymer solution to adhere to the outer peripheral side of the conductor. The conductor then passes through the coating die, causing the prepolymer solution to be applied to a uniform thickness.

[0075] (Heating process) In the heating step, the prepolymer solution applied to the conductor in the application step is heated. This heating volatilizes the solvent in the prepolymer solution, hardens the prepolymer, and forms a thermosetting resin. In this way, an insulating layer is formed. The prepolymer solution is obtained by the above-mentioned method for producing the prepolymer solution, and therefore has a high concentration. Therefore, the amount of solvent to be volatilized in the heating step is relatively small, which is advantageous in terms of production costs.

[0076] The heating step may be performed using a cylindrical baking oven that is long in the direction of travel of the conductor, but is not limited to this. The heating method may be any conventional method, such as hot air heating, infrared heating, or high-frequency heating.

[0077] The heating temperature can be, for example, 300°C or higher and 800°C or lower, and the heating time can be 5 seconds or higher and 1 minute or lower. If the heating temperature or heating time is below the lower limit, the solvent may not volatilize sufficiently, or the insulating layer may not be formed sufficiently, which may result in poor appearance, electrical properties, mechanical properties, thermal properties, etc. of the insulated wire. Conversely, if the heating temperature exceeds the upper limit, excessive rapid heating may cause foaming of the insulating layer or a deterioration in mechanical properties. Furthermore, if the heating time exceeds the upper limit, the productivity of the insulated wire may decrease.

[0078] The coating step and the heating step are usually repeated multiple times. In this way, the thickness of the insulating layer can be increased. At this time, the hole diameter of the coating die is appropriately adjusted according to the number of repetitions.

[0079] [Other embodiments] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of the present invention is not limited to the configurations of the above-described embodiments, but is defined by the claims, and is intended to include all modifications within the meaning and scope of the claims. [Example]

[0080] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0081] <Test Example 1> In this test example, the influence of different mixing methods on the prepolymer solution was tested according to the following method.

[0082] The abbreviations for the components used in preparing the prepolymer solutions are shown below. PMDA: Pyromellitic dianhydride ODA: 4,4'-diaminodiphenyl ether DMAc: N,N-dimethylacetamide

[0083] [No.1-1] (Preparation of prepolymer solution) PMDA powder as the first raw material, ODA powder as the second raw material, and DMAc as the solvent were continuously fed into a twin-screw extruder (Kobe Steel, Ltd., "HYPER KTX30," screw diameter: 32 mm, L / D: 56) in amounts such that the target solids concentration of the resulting prepolymer solution would be 28% by mass. The PMDA / ODA mixture ratio (molar ratio) was 97:103. The first and second raw materials were reacted in the twin-screw extruder at a temperature of 80°C, a rotation speed of 200 rpm, and a raw material residence time of 3 minutes to obtain prepolymer solution No. 1-1, a polyimide precursor. The device was then operated for 2 hours, confirming the continuous production of prepolymer solution. The solids concentration of the resulting prepolymer solution was 28.1% by mass and the viscosity was 29.4 Pa·s. The polyimide precursor obtained had an Mw of 45,900, an Mn of 15,300, and an Mw / Mn ratio of 3.0.

[0084] The solids concentration and viscosity of the prepolymer solution, as well as Mw, Mn and Mw / Mn of the polyimide precursor were measured according to the following methods.

[0085] (solid content concentration) The prepolymer solution was dried at 250° C. for 2 hours, and the mass W0 before drying and the mass W1 after drying were measured, and the solid content concentration (unit: mass %) was calculated by W1 / W0×100.

[0086] (viscosity) Measurement was carried out at a temperature of 30°C using an E-type viscometer (Toki Sangyo Co., Ltd.'s "TV-25").

[0087] (Mw, Mn and Mw / Mn) The prepolymer solution was analyzed using a Tosoh Corporation "GPC system" to calculate the Mn, Mw, and Mw / Mn of the prepolymer. The developing solvent used during the analysis was N-methyl-2-pyrrolidone in which 30 mmol of phosphoric acid and 10 mmol of lithium bromide were dissolved. Polystyrene was used as the standard material. The analysis was performed using two Tosoh Corporation "TSKgel GMH HR-H" columns connected in series, with a "TSK Guard Column HHR-H" guard column. The measurement was performed at a flow rate of 0.5 mL / min for 60 minutes.

[0088] (Making insulated wire) A round copper wire with an average conductor diameter of 1 mm was used as the conductor. Prepolymer solution No. 1-1 was applied to the surface of the conductor, and the conductor coated with prepolymer solution No. 1-1 was heated in a heating furnace at a set temperature of 450°C. This process was repeated to form an insulating layer with an average thickness of 30 μm, thereby producing insulated wire No. 1-1.

[0089] [No.1-2~1-4] (Preparation of prepolymer solution) Prepolymer solutions Nos. 1-2 to 1-4 were prepared in the same manner as No. 1-1, except that the target solids concentration of the prepolymer solution and the mixing ratio (molar ratio) of PMDA to ODA were changed as shown in Table 1 below. The equipment was operated for 2 hours to confirm that the prepolymer solutions could be continuously produced. The solids concentration and viscosity of the obtained prepolymer solutions, as well as the Mw, Mn, and Mw / Mn of the obtained polyimide precursors, are shown in Table 1 below.

[0090] (Making insulated wire) Insulated wire No. 1-2 was produced in the same manner as in No. 1-1, except that prepolymer solution No. 1-2 was used. Insulated wire Nos. 1-3 and 1-4 were produced in the same manner as in No. 1-1, except that prepolymer solutions No. 1-3 and 1-4 were used and heated to 80°C before being applied to the surface of the conductor.

[0091] [No.1-5] (Preparation of prepolymer solution) PMDA powder as the first raw material, ODA powder as the second raw material, and DMAc as the solvent were continuously fed into a static mixer (Noritake Co., Ltd., 1.5 / 2-N60-331-1, inner diameter: 41 mm, total length: 400 mm, number of elements: 6) in amounts such that the target solids concentration of the resulting prepolymer solution would be 15% by mass. The PMDA / ODA mixing ratio (molar ratio) was 97:103. The static mixer is a stationary mixer without an extrusion mechanism. The first raw material and the second raw material were reacted in the static mixer at a temperature of 80°C for a residence time of 3 minutes to obtain prepolymer solution No. 1-5, a polyimide precursor. The device was then operated for 2 hours, confirming the continuous production of prepolymer solution. The resulting prepolymer solution had a solids concentration of 15.1% by mass and a viscosity of 0.20 Pa·s. The polyimide precursor obtained had an Mw of 41,200, an Mn of 13,600, and an Mw / Mn ratio of 3.0.

[0092] (Making insulated wire) An insulated wire No. 1-5 was produced in the same manner as in No. 1-1, except that prepolymer solution No. 1-5 was used instead of prepolymer solution No. 1-1.

[0093] [No.1-6] An attempt was made to prepare a prepolymer solution in the same manner as in No. 1-5, except that the first raw material, second raw material, and solvent were supplied in amounts such that the target solids concentration of the resulting prepolymer solution would be 28% by mass. However, one minute after the start of operation, backflow of material occurred in the static mixer, so the operation of the equipment was stopped. As a result, a prepolymer solution with the target solids concentration could not be obtained. The cause of the backflow of material is thought to be a significant increase in the viscosity of the material in the static mixer.

[0094] [evaluation] The coating elongation, dielectric breakdown voltage, and relative dielectric constant of the insulated wires Nos. 1-1 to 1-5 prepared above were measured by the following methods.

[0095] (film elongation) The conductor was removed from the insulated wire to leave a tubular insulating layer, which was then subjected to a tensile test using a tensile testing machine (Shimadzu Corporation's "Autograph AGS-X") at a chuck distance of 20 mm and a speed of 10 mm / min to measure the coating elongation (elongation at break) (unit: %). The results are shown in the "Coating Elongation" row in Table 1 below.

[0096] (breakdown voltage) In accordance with JIS-C3216-5:2011, an AC voltage was applied between the two twisted wires, increasing the voltage at 500 V / s, and the voltage (unit: kV / μm) at which breakdown occurred was measured. The breakdown voltage was measured five times, and the average value was used. The results are shown in the "Breakdown Voltage" row in Table 1 below.

[0097] (dielectric constant) The measurement was carried out in accordance with JIS-C2138:2007, and the results are shown in the "relative dielectric constant" row in Table 1 below.

[0098] The results for Nos. 1-1 to 1-6 are shown in Table 1 below. In Table 1 below, "-" indicates that the corresponding item was not measured. In Table 1 below, "twin-screw extrusion" in the "mixing method" row indicates that the prepolymer solution was prepared using a twin-screw extruder, and "static" indicates that the prepolymer solution was prepared using a static mixer. In Table 1 below, "A" in the "continuous productivity" row indicates that the prepolymer solution could be produced continuously, "B" indicates that the prepolymer solution could be produced continuously, but due to its high viscosity, a step was required to heat the prepolymer solution to 80°C to reduce the viscosity to a level that would allow the production of insulated electric wires, and "C" indicates that the prepolymer solution could not be produced continuously.

[0099] [Table 1]

[0100] As described above, insulated wires No. 1-1 to 1-4, which used a twin-screw extruder, a prepolymer solution with a high solid content could be continuously produced. On the other hand, in No. 1-5 and No. 1-6, which used equipment without an extrusion mechanism, only prepolymer solution No. 1-5, which had a low solid content, could be continuously produced, and a prepolymer solution with a high solid content could not be continuously produced. Therefore, the results of Test Example 1 demonstrate that the use of an extruder makes it possible to continuously produce a prepolymer solution with a high solid content. Furthermore, it was found that insulated wires No. 1-1 to 1-3 were superior to insulated wire No. 1-5 in terms of coating elongation, breakdown voltage, and dielectric constant.

[0101] <Test Example 2> In this test example, the influence of the addition of a reaction inhibitor on a prepolymer solution was tested according to the following method.

[0102] [No.2-1] (Preparation of prepolymer solution) Prepolymer solution No. 2-1 was prepared in the same manner as No. 1-1, except that 0.33 moles of HO per mole of PMDA was added to the twin-screw extruder as a reaction inhibitor, and the mixing ratio (molar ratio) of PMDA to ODA was 100:100. The solids concentration of the resulting prepolymer solution was 28.3 mass% and the viscosity was 8.3 Pa s. The Mw of the resulting polyimide precursor was 32,300, Mn was 10,300, and Mw / Mn was 3.1.

[0103] (Making insulated wire) An insulated wire No. 2-1 was produced in the same manner as in No. 1-1, except that prepolymer solution No. 2-1 was used instead of prepolymer solution No. 1-1.

[0104] [No.2-2~2-16] A prepolymer solution was prepared and then an insulated wire was produced in the same manner as in No. 2-1, except that the type and amount of reaction inhibitor were changed to those shown in Table 2. The solids concentration and viscosity of the obtained prepolymer solution, as well as the Mw, Mn, and Mw / Mn of the obtained polyimide precursor, are also shown in Table 2.

[0105] [No.2-17] As an example in which a prepolymer solution was prepared without using a reaction inhibitor and an insulated wire was produced, No. 1-1 in the above <Test Example 1> was designated as No. 2-17.

[0106] [evaluation] The coating elongation, breakdown voltage, and relative dielectric constant of the insulated wires No. 2-1 to 2-16 prepared above were measured in the same manner as in Test Example 1. The results are shown in Table 2 below. In Table 2 below, the data for No. 2-17 all correspond to the data for No. 1-1 in Table 1 above.

[0107] [Table 2]

[0108] As described above, in Nos. 2-1 to 2-16, which used a reaction inhibitor, the viscosity of the prepolymer solution was suitable for the production of insulated electric wires, similar to No. 2-17, while the PMDA and ODA were substantially equimolar. Furthermore, in Nos. 2-4 to 2-6 and Nos. 2-7 to 2-9, the viscosity decreased as the amount of reaction inhibitor supplied increased. Therefore, the results of Test Example 2 demonstrated that the viscosity of the prepolymer solution can be adjusted by using a reaction inhibitor.

[0109] Furthermore, insulated wires No. 2-1 to 2-16 showed better results in all of the items of coating elongation, dielectric breakdown voltage, and relative dielectric constant compared to insulated wire No. 2-17. This result is thought to be due to the fact that the mixing ratio of PMDA and ODA was equimolar.

[0110] <Test Example 3> In this test example, the correlation between the measured values ​​obtained by the E-type viscometer and the measured values ​​obtained by the vibration viscometer was investigated according to the following method.

[0111] Eighteen samples were prepared, with viscosities at 30°C measured using an E-type viscometer (Toki Sangyo Co., Ltd., TV-25) evenly distributed in the logarithmic range of 200 mPa·s to 20,000 mPa·s. The viscosities of these 18 samples at 30°C were measured using a vibration viscometer (Seconic Corporation, FVM72A-VM-200T3). When the measurements from the E-type viscometer and the vibration viscometer were plotted on the x-axis and y-axis of a double logarithmic graph, respectively, a positive correlation (R 2 =0.96).

[0112] The results of Test Example 3 suggest that by using a vibration viscometer as an in-line viscometer during continuous production of a prepolymer solution, it is possible to measure viscosity without having to stop the production line, etc. It is also possible to automate viscosity measurement. Furthermore, the results of Test Examples 2 and 3 suggest that the viscosity of the prepolymer solution can be adjusted by controlling the amount of reaction inhibitor supplied based on the viscosity measured by the vibration viscometer.

[0113] <Test Example 4> In this test example, the influence of the presence or absence of a stirring step on the prepolymer solution was tested according to the following method.

[0114] [No.4-1] (Preparation of prepolymer solution) Prepolymer solution No. 4-1 was continuously prepared in the same manner as No. 2-3, except that the equipment was operated for 5 hours.

[0115] (Making insulated wire) An insulated wire No. 4-1 was produced in the same manner as in No. 1-1, except that prepolymer solution No. 4-1 was used.

[0116] [No.4-2] (Preparation of prepolymer solution) A prepolymer solution was prepared in the same manner as in No. 4-1, and then the resulting prepolymer solution was supplied to a stirring tank and stirred for 30 minutes at a temperature of 80°C and a stirring speed of 20 rpm. The prepolymer solution after stirring was designated prepolymer solution No. 4-2.

[0117] (Making insulated wire) Insulated wire No. 4-2 was prepared in the same manner as in No. 4-1, except that prepolymer solution No. 4-2 was used.

[0118] [evaluation] The viscosity variation of the prepared prepolymer solutions Nos. 4-1 and 4-2 was evaluated by the following method. Furthermore, the coating elongation variation of the prepared insulated wires Nos. 4-1 and 4-2 was evaluated by the following method.

[0119] (Viscosity variation) The viscosity of samples (N=31) taken at 10-minute intervals was measured at 30°C using the E-type viscometer. From the measurement results, the average viscosity (arithmetic mean), standard deviation σ, and coefficient of variation (CV value) were calculated. The coefficient of variation was calculated by dividing the standard deviation σ by the average viscosity. The results, along with the maximum and minimum viscosities, are shown in Table 3 below.

[0120] (Variation in film elongation) For samples (N=9) sampled at 75-minute intervals, film elongation was measured in the same manner as in the section (Film Elongation) of Test Example 1 above. From the measurement results, the average value (arithmetic mean), standard deviation σ, and coefficient of variation (CV value) of film elongation were calculated. The coefficient of variation was calculated by dividing the standard deviation σ by the average value. The results, along with the maximum and minimum film elongations, are shown in Table 3 below.

[0121] [Table 3]

[0122] As described above, in No. 4-2, in which stirring was performed after mixing in the twin-screw extruder, the variation in viscosity of the prepolymer solution was smaller than in No. 4-1, in which stirring was not performed. Furthermore, in No. 4-2, the variation in coating elongation of the insulated wire was also smaller than in No. 4-1. Therefore, the results of Test Example 4 demonstrate that stirring after mixing in the extruder can reduce the variation in both the viscosity of the prepolymer solution and the coating elongation of the insulated wire. [Explanation of symbols]

[0123] 1 Twin-screw extruder 11 2nd raw material supply section 12 1st raw material supply section 13 Solvent supply section 14 Mixing section 2 Vibrating viscometer 3 Stirring tank

Claims

1. A method for continuously producing a prepolymer solution in which a prepolymer, which is a precursor of a thermosetting resin, is dissolved in a solvent, comprising: mixing, using an extruder, a first feedstock, a second feedstock that reacts with the first feedstock to form the prepolymer, and the solvent; a step of stirring the prepolymer solution obtained by the mixing step; Equipped with the prepolymer has a group capable of forming an imide group by a dehydration reaction, the first raw material is a carboxylic acid anhydride, and the second raw material is a diamine compound; A method for producing a prepolymer solution, wherein the prepolymer is a polyimide prepolymer and the carboxylic acid anhydride is a tetracarboxylic acid dianhydride.

2. The method for producing a prepolymer solution according to claim 1 , wherein a reaction inhibitor is further added in the mixing step.

3. further comprising a step of measuring the viscosity of the prepolymer solution obtained by the mixing step; 3. The method for producing a prepolymer solution according to claim 2, wherein the amount of the reaction inhibitor to be supplied in the mixing step is determined based on the viscosity measured in the measuring step.

4. 2. The method for producing a prepolymer solution according to claim 1, wherein the solids concentration of the prepolymer solution is 20% by mass or more and 50% by mass or less.

5. 2. The method for producing a prepolymer solution according to claim 1, wherein the extruder is a twin-screw extruder.

6. 4. The method for producing a prepolymer solution according to claim 3, wherein the viscosity is measured using a vibration viscometer in the measuring step.

7. The method for producing a prepolymer solution according to claim 1, wherein the stirring step is carried out at a temperature of 20°C or higher and 200°C or lower.

8. A method for manufacturing an insulated wire including a conductor and an insulating layer covering the conductor, a step of applying a prepolymer solution obtained by the method for producing a prepolymer solution according to any one of claims 1 to 7 to an outer periphery of the conductor; heating the prepolymer solution applied to the conductor; A method for manufacturing an insulated wire comprising:

Images