Resin composition for insulation layer, insulated wire, and method for manufacturing insulated wire

Abstract

To provide a resin composition for an insulation layer which enables formation of an insulation layer that is excellent in surge resistance and elongation.SOLUTION: A resin composition for an insulation layer contains a polyimide precursor which is a reaction product of an aromatic tetracarboxylic dianhydride and an aromatic diamine, an organic solvent, and surface-treated silica, wherein the surface-treated silica is trimethylsilane surface-treated silica, dimethylsilane surface-treated silica or a combination thereof, and an average particle diameter of primary particles of the surface-treated silica is 0.01 μm or more and 0.05 μm or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a resin composition for an insulating layer, an insulated wire, and a method for producing an insulated wire. [Background technology]

[0002] Insulated wires having a conductor and an insulating layer covering the conductor are used in motors, transformers, etc. In the prior art, a three-layer structure has been proposed for such insulated wires, which has an inner insulating layer that does not contain inorganic compound particles, a middle insulating layer that contains inorganic compound particles, and an outer insulating layer made of polyamideimide that does not contain inorganic compound particles, with the thicknesses of the middle insulating layer and the outer insulating layer adjusted to a predetermined ratio (see Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 11-191325 Summary of the Invention

[0004] The resin composition for an insulating layer of the present disclosure contains a polyimide precursor that is a reaction product of an aromatic tetracarboxylic dianhydride and an aromatic diamine, an organic solvent, and surface-treated silica, wherein the surface-treated silica is trimethylsilane-surface-treated silica, dimethylsilane-surface-treated silica, or a combination thereof, and the average particle size of primary particles of the surface-treated silica is 0.01 μm or more and 0.05 μm or less. [Brief explanation of the drawings]

[0005] [Figure 1] FIG. 1 is a schematic cross-sectional view showing an insulated wire according to one embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0006] [Problem to be solved by this disclosure] In electrical equipment with high operating voltages, such as motors operated at high voltages, a sudden voltage application to an insulated wire included in the electrical equipment causes a small discharge (surge) between the insulated wires. This surge can cause early dielectric breakdown, shortening the life of the insulated wire and ultimately the electrical equipment. Therefore, further improvements are needed in the property of reducing dielectric breakdown caused by surges (hereinafter also referred to as "surge resistance"). Furthermore, insulated wires are required to have good elongation of the insulating layer from the viewpoint of bending workability.

[0007] An object of the present disclosure is to provide a resin composition for an insulating layer that can form an insulating layer that is excellent in surge resistance and elongation.

[0008] [Effects of this disclosure] According to the present disclosure, it is possible to provide a resin composition for an insulating layer that can form an insulating layer that is excellent in surge resistance and elongation.

[0009] [Description of the embodiments of the present disclosure] First, embodiments of the present disclosure will be listed and described.

[0010] (1) The resin composition for an insulating layer of the present disclosure contains a polyimide precursor that is a reaction product of an aromatic tetracarboxylic dianhydride and an aromatic diamine, an organic solvent, and surface-treated silica, wherein the surface-treated silica is trimethylsilane-surface-treated silica, dimethylsilane-surface-treated silica, or a combination thereof, and the average particle size of primary particles of the surface-treated silica is 0.01 μm or more and 0.05 μm or less.

[0011] The resin composition for an insulating layer contains a polyimide precursor, which is a reaction product of an aromatic tetracarboxylic dianhydride and an aromatic diamine, thereby improving the toughness, insulating properties, and heat resistance of the insulating layer. Furthermore, the resin composition for an insulating layer contains surface-treated silica, and the surface-treated silica is trimethylsilane-surface-treated silica, dimethylsilane-surface-treated silica, or a combination thereof, thereby improving the compatibility between the polyimide precursor and silica, thereby improving the elongation of the insulating layer. The average particle diameter of the primary particles of the surface-treated silica is 0.01 μm or more and 0.05 μm or less, thereby improving the surge resistance and elongation of the insulating layer. Therefore, the resin composition for an insulating layer can form an insulating layer with excellent surge resistance and elongation.

[0012] The term "primary particles" refers to particles that do not have visible grain boundaries when observed using a scanning electron microscope (SEM). The term "average particle size of primary particles" can be determined by observing a resin composition for an insulating layer frozen with liquid nitrogen using a cryo-FIB-SEM while the resin composition is still frozen, measuring the particle sizes of 50 random primary particles on the SEM image, and then calculating the average particle size of the 50 primary particles (average particle size). The term "surface-treated silica" refers to silica in which some or all of the silanol groups on the surface of the silica particles have been chemically reacted.

[0013] The surface treatment state of the surface-treated silica can be identified by heating the resin composition for insulating layer at 250° C. to remove the organic solvent, and then subjecting the sample to solid-state Si-NMR measurement.

[0014] (2) In the above (1), the weight-average molecular weight of the polyimide precursor may be 25,000 or more and 80,000 or less. When the weight-average molecular weight of the polyimide precursor is within the above range, deterioration of the polyimide due to molecular chain scission caused by partial discharge in the insulating layer of the insulated electric wire is reduced, thereby improving the surge resistance of the insulating layer. The "weight-average molecular weight" refers to the weight-average molecular weight in terms of polystyrene measured by gel permeation chromatography (GPC).

[0015] (3) In the above (1) or (2), the content of the surface-treated silica may be 15 parts by mass or more and 30 parts by mass or less per 100 parts by mass of the polyimide precursor. By having the content of the surface-treated silica in this range, the surge resistance and elongation of the insulating layer can be improved.

[0016] (4) In any of the above (1) to (3), the ratio of the shear viscosity at 30°C and a shear rate of 1 / s to the shear viscosity at 30°C and a shear rate of 100 / s may be 3.0 or more and 23.0 or less. When the ratio of the shear viscosity at 30°C and a shear rate of 1 / s to the shear viscosity at 30°C and a shear rate of 100 / s in the resin composition for an insulating layer is within the above range, the viscosity after being sheared by a coating die can be increased while maintaining good coatability of the resin composition for an insulating layer to a conductor, and therefore the thickness uniformity of the insulating layer can be improved.

[0017] (5) The insulated wire of the present disclosure includes a conductor and an insulating layer covering the conductor, the insulating layer being formed from the resin composition for an insulating layer described above in any one of (1) to (4). Because the insulating layer is formed from the resin composition for an insulating layer, the insulated wire has an insulating layer that is excellent in surge resistance and elongation.

[0018] (6) The present disclosure also provides a method for producing an insulated wire including a conductor and an insulating layer covering the conductor, the method comprising the steps of: applying the resin composition for an insulating layer according to any one of (1) to (4) to the outer peripheral surface of the conductor; and heating the resin composition for an insulating layer applied in the applying step. Since the method for producing an insulated wire uses the resin composition for an insulating layer to form the insulating layer, the method can produce an insulated wire having an insulating layer that is excellent in surge resistance and elongation.

[0019] [Details of the embodiments of the present disclosure] A resin composition for an insulating layer, an insulated wire, and a method for producing an insulated wire according to embodiments of the present disclosure will be described below with reference to the drawings.

[0020] <Resin composition for insulating layer> The resin composition for an insulating layer contains a polyimide precursor, which is a reaction product of an aromatic tetracarboxylic dianhydride and an aromatic diamine, an organic solvent, and surface-treated silica, the surface-treated silica being trimethylsilane-surface-treated silica, dimethylsilane-surface-treated silica, or a combination thereof, and the average particle size of primary particles of the surface-treated silica is 0.01 μm or more and 0.05 μm or less.

[0021] The lower limit of the ratio of the shear viscosity at 30°C and a shear rate of 1 / s to the shear viscosity at 30°C and a shear rate of 100 / s in the resin composition for an insulating layer may be 3.0 or 4.0. When the ratio of the shear viscosity at 30°C and a shear rate of 1 / s to the shear viscosity at 30°C and a shear rate of 100 / s in the resin composition for an insulating layer is 3.0 or more, the viscosity after being sheared by the coating die can be increased, thereby improving the thickness uniformity of the insulating layer. On the other hand, the upper limit of the ratio of the shear viscosity at 30°C and a shear rate of 1 / s to the shear viscosity at 30°C and a shear rate of 100 / s in the resin composition for an insulating layer may be 23.0 or 13.0. When the ratio of the shear viscosity of the resin composition for an insulating layer at 30°C and a shear rate of 1 / s to the shear viscosity at 30°C and a shear rate of 100 / s is 23.0 or less, the resin composition for an insulating layer can be well maintained in its applicability to a conductor, thereby improving the thickness uniformity of the insulating layer.

[0022] [Polyimide precursor] A polyimide precursor is a reaction product obtained by a polymerization condensation reaction between an aromatic tetracarboxylic dianhydride and an aromatic diamine. The polyimide precursor is a compound also known as a polyamic acid (polyamic acid). The polyimide precursor undergoes a dehydration cyclization reaction to form a cyclic imide, resulting in a polyimide.

[0023] The lower limit of the weight-average molecular weight of the polyimide precursor may be 25,000, 30,000, or 35,000. The upper limit of the weight-average molecular weight may be 80,000 or 70,000. When the weight-average molecular weight of the polyimide precursor is 25,000 or more, deterioration of the polyimide due to molecular chain scission associated with partial discharge in the insulating layer of the insulated wire is reduced, thereby improving surge resistance. Furthermore, when the weight-average molecular weight of the polyimide precursor is 80,000 or less, the viscosity of the resin composition for the insulating layer can be prevented from becoming too high.

[0024] The lower limit of the content of the polyimide precursor in the resin composition for an insulating layer may be 10% by mass or 20% by mass. The upper limit of the content may be 50% by mass or 40% by mass. By setting the content at or above the lower limit, it is possible to reduce the amount of resin composition for an insulating layer required in the entire manufacturing process to obtain an insulating layer of the desired thickness when forming an insulating layer using the resin composition for an insulating layer, and it is possible to reduce the number of steps of applying and heating the resin composition for an insulating layer. By setting the content at or below the upper limit, it is possible to appropriately adjust the viscosity of the resin composition for an insulating layer while maintaining good film properties, thereby improving coatability.

[0025] When the aromatic tetracarboxylic dianhydride contains pyromellitic dianhydride (PMDA), the heat resistance of the insulating layer can be improved because PMDA has a rigid and linear molecular structure.

[0026] The aromatic tetracarboxylic dianhydride may further contain an aromatic tetracarboxylic dianhydride other than PMDA (hereinafter also referred to as "other aromatic tetracarboxylic dianhydrides"). Examples of the other aromatic tetracarboxylic dianhydrides include 3,3',4,4'-biphenyltetracarboxylic dianhydride (s-BPDA), 2,3,3',4'-biphenyltetracarboxylic dianhydride (a-BPDA), 2,2',3,3'-biphenyltetracarboxylic dianhydride (i-BPDA), 3,3',4,4'-benzophenonetetracarboxylic dianhydride, 4,4'-oxydiphthalic dianhydride, 2,2',3,3'-benzophenonetetracarboxylic dianhydride, 2,2-bis(3,4-dicarboxyphenyl)propane dianhydride, and 2,2-bis(3,4-dicarboxyphenyl)propane dianhydride. Examples of the aromatic tetracarboxylic dianhydride include bis(2,3-dicarboxyphenyl)propane dianhydride, 1,1-bis(3,4-dicarboxyphenyl)ethane dianhydride, 1,1-bis(2,3-dicarboxyphenyl)ethane dianhydride, bis(3,4-dicarboxyphenyl)methane dianhydride, bis(2,3-dicarboxyphenyl)methane dianhydride, bis(3,4-dicarboxyphenyl)sulfone dianhydride, bis(3,4-dicarboxyphenyl)ether dianhydride, 1,2,5,6-naphthalenetetracarboxylic dianhydride, and 2,3,6,7-naphthalenetetracarboxylic dianhydride. The aromatic tetracarboxylic dianhydrides may be used alone or in combination of two or more.

[0027] When the other aromatic tetracarboxylic dianhydride is biphenyltetracarboxylic dianhydride (BPDA), the hydrolysis resistance of the polyimide can be improved.

[0028] The lower limit of the PMDA content in 100 mol% of the aromatic tetracarboxylic dianhydride may be 60 mol% or 70 mol%, and the upper limit of the PMDA content in 100 mol% of the aromatic tetracarboxylic dianhydride may be 100 mol%, 90 mol%, or 80 mol%.

[0029] The content of the other aromatic tetracarboxylic dianhydride relative to 100 mol% of the aromatic tetracarboxylic dianhydride can be appropriately determined within a range that does not impair the effects of the present disclosure. The upper limit of the content may be 40 mol% or 30 mol%. The lower limit of the content may be 0 mol%, 10 mol%, or 20 mol%.

[0030] The above aromatic diamines can improve the heat resistance of the insulating layer by including diaminodiphenyl ether (ODA). This is because ODA has a rigid and linear molecular structure. Examples of diaminodiphenyl ethers include 4,4'-diaminodiphenyl ether (4,4'-ODA), 3,4'-diaminodiphenyl ether (3,4'-ODA), 3,3'-diaminodiphenyl ether (3,3'-ODA), 2,4'-diaminodiphenyl ether (2,4'-ODA), and 2,2'-diaminodiphenyl ether (2,2'-ODA). 4,4'-diaminodiphenyl ether (4,4'-ODA) can improve the elongation of the insulating layer.

[0031] The aromatic diamine may further contain an aromatic diamine other than ODA (hereinafter also referred to as "other aromatic diamine"). Examples of the other aromatic diamine include 2,2-bis[4-(4-aminophenoxy)phenyl]propane (BAPP), 4,4'-bis(4-aminophenoxy)biphenyl (BAPB), 4,4'-diaminodiphenylmethane, 3,4'-diaminodiphenylmethane, 3,3'-diaminodiphenylmethane, 2,4'-diaminodiphenylmethane, 2,2'-diaminodiphenylmethane, 4,4'-diaminodiphenylsulfone, 3,4'-diaminodiphenylsulfone, 3,3'-diaminodiphenylsulfone, 2,4'-diaminodiphenylsulfone, 2,2'-diaminodiphenylsulfone, 4,4' Examples of the aromatic diamines include 4,4'-dimethyl-4,4'-diaminodiphenylmethane, 3,3'-dimethyl-4,4'-diaminodiphenylmethane, and 3,3',5,5'-tetramethyl-4,4'-diaminodiphenylmethane. The aromatic diamines may be used alone or in combination of two or more.

[0032] Other aromatic diamines such as 2,2-bis[4-(4-aminophenoxy)phenyl]propane (BAPP) or 4,4'-bis(4-aminophenoxy)biphenyl (BAPB) can reduce the dielectric constant of the insulating layer.

[0033] The lower limit of the ODA content in 100 mol % of the aromatic diamine may be 50 mol %, 60 mol %, or 70 mol %, and the upper limit of the ODA content in 100 mol % of the aromatic diamine may be 100 mol % or 90 mol %.

[0034] The content of the other aromatic diamine relative to 100 mol% of the aromatic diamine can be appropriately determined within a range that does not impair the effects of the present disclosure. The upper limit of the content may be 50 mol%, 40 mol%, or 30 mol%. The lower limit of the content may be 0 mol% or 10 mol%.

[0035] The molar ratio of the aromatic tetracarboxylic dianhydride to the aromatic diamine used as raw materials for the polyimide precursor (aromatic tetracarboxylic dianhydride:aromatic diamine) may be, for example, 95:105 or more and 105:95 or less, 97:103 or more and 103:97 or less, or 99:101 or more and 101:99 or less, from the viewpoint of ease of synthesis of the polyimide precursor. The aromatic tetracarboxylic dianhydride and the aromatic diamine may be substantially equimolar. In this case, the molecular weight of the polyimide precursor can be easily increased. "Substantially equimolar" refers to a molar ratio of the aromatic tetracarboxylic dianhydride to the aromatic diamine (aromatic tetracarboxylic dianhydride:aromatic diamine) in the range of 99:101 or more and 101:99 or less.

[0036] (Method for synthesizing polyimide precursor) The polyimide precursor can be obtained by a polymerization condensation reaction between the aromatic tetracarboxylic dianhydride and the aromatic diamine. The polymerization condensation reaction can be carried out in the same manner as in conventional synthesis of polyimide precursors. A specific example of the polymerization condensation reaction is mixing the aromatic tetracarboxylic dianhydride and the aromatic diamine in an organic solvent. This method allows the aromatic tetracarboxylic dianhydride and the aromatic diamine to polymerize, resulting in a solution of the polyimide precursor dissolved in the organic solvent. For example, the polymerization condensation reaction can be carried out in the presence of a reaction inhibitor to control the degree of polymerization (weight-average molecular weight).

[0037] 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.

[0038] The reaction conditions for the polymerization can be appropriately set depending on the raw materials used, etc. For example, the reaction temperature can be set to 10° C. or higher and 100° C. or lower, and the reaction time can be set to 0.5 hours or higher and 24 hours or lower.

[0039] Examples of organic solvents that can be used in the polymerization condensation reaction include aprotic polar organic solvents such as N-methyl-2-pyrrolidone (NMP), N,N-dimethylacetamide (DMAc), N,N-dimethylformamide, dimethyl sulfoxide, and γ-butyrolactone. These organic solvents may be used alone or in combination of two or more. "Aprotic polar organic solvent" refers to a polar organic solvent that does not have a group that releases a proton.

[0040] The amount of organic solvent used in synthesizing the polyimide precursor is not particularly limited as long as it is an amount that can uniformly dissolve and disperse the aromatic tetracarboxylic dianhydride and aromatic diamine. If the amount is too large, a large amount of organic solvent must be volatilized when forming the insulating layer, which may require a long time to form the insulating layer. Therefore, the organic solvent can be used in an amount of, for example, 100 to 1,000 parts by mass per 100 parts by mass of the aromatic tetracarboxylic dianhydride and aromatic diamine combined.

[0041] [Organic solvents] The organic solvent in the resin composition for an insulating layer is the same as the organic solvent used in the above-mentioned polymerization condensation reaction.

[0042] [Surface-treated silica] The insulating layer resin composition contains surface-treated silica, and the surface-treated silica is trimethylsilane-surface-treated silica, dimethylsilane-surface-treated silica, or a combination thereof, which improves the compatibility between the polyimide precursor and the surface-treated silica, thereby improving the elongation of the insulating layer. The method for producing the surface-treated silica is not particularly limited, but it can be obtained by a method in which hydroxyl groups on the surface of silica particles are reacted with hexamethyldisilazane or dimethyldichlorosilane to introduce trimethylsilyl groups or dimethylsilyl groups.

[0043] The lower limit of the average particle size of the primary particles of the surface-treated silica is 0.01 μm, and may be 0.02 μm. The upper limit of the average particle size of the primary particles of the surface-treated silica is 0.05 μm, and may be 0.04 μm. If the average particle size of the primary particles of the surface-treated silica is less than 0.01 μm, aggregation of the surface-treated silica particles may occur, which may result in a decrease in the surge resistance and elongation of the insulating layer. By ensuring that the average particle size of the primary particles of the surface-treated silica is 0.01 μm or more, the surge resistance and elongation of the insulating layer can be improved. On the other hand, by ensuring that the average particle size of the primary particles of the surface-treated silica is 0.05 μm or less, the thickness uniformity and surge resistance of the insulating layer can be maintained well. The shape of the surface-treated silica is not particularly limited, and examples thereof include granular, spherical, scaly, acicular, and tabular shapes.

[0044] The lower limit of the content of the surface-treated silica in the resin composition for an insulating layer may be 10 parts by mass, 15 parts by mass, or 17 parts by mass per 100 parts by mass of the polyimide precursor. Meanwhile, the upper limit of the content of the surface-treated silica may be 35 parts by mass, 30 parts by mass, or 25 parts by mass per 100 parts by mass of the polyimide precursor. By having the content of the surface-treated silica equal to or greater than the lower limit, the surge resistance of the insulating layer can be further improved. Furthermore, by having the content of the surface-treated silica equal to or less than the upper limit, the elongation of the insulating layer can be further improved.

[0045] [Other ingredients] The resin composition for an insulating layer may contain other components in addition to the above components. The other components are not particularly limited as long as they are additives that can be blended into a resin varnish for forming an insulating coating for an insulated electric wire, and examples thereof include antioxidants, radical scavengers, ultraviolet inhibitors, surface lubricants, leveling agents, curing agents, and adhesion promoters.

[0046] [Method of manufacturing resin composition for insulating layer] The method for producing the resin composition for an insulating layer includes, for example, a step of synthesizing a polyimide precursor and a step of adding surface-treated silica and other optional components to a polyimide precursor solution obtained after the step of synthesizing the polyimide precursor.

[0047] The resin composition for an insulating layer can form an insulating layer that is excellent in surge resistance and elongation.

[0048] <Insulated wire> 1 includes a conductor 2 and an insulating layer 3 that covers the conductor 2. In the insulated wire 1, the insulating layer 3 contains surface-treated silica 4.

[0049] The cross-sectional shape of the insulated wire 1 is not particularly limited, and examples thereof include a circle (round wire), an oval, a square (rectangular wire), and a rectangle (flat wire). The cross-sectional shape of the insulated wire 1 is preferably a rectangle, in other words, a flat wire. In this case, the insulated wire 1 can be wound at a high density during coil processing. Furthermore, the cross-sectional shape of the insulated wire 1 and the cross-sectional shape of the conductor 2, which will be described later, are preferably the same type of shape.

[0050] The insulated wire 1 can be suitably used as a winding wire for a coil (magnet wire).

[0051] [conductor] The cross-sectional shape of the conductor 2 may be, for example, a circle, an oval, a square, or a rectangle. When the insulated wire 1 is a rectangular wire, the cross-sectional shape of the conductor 2 is preferably a rectangle.

[0052] The conductor 2 is preferably made of a metal with high electrical conductivity and high mechanical strength. Examples of such metals include copper, copper alloys, aluminum, nickel, silver, mild steel, steel, and stainless steel. The conductor 2 can be made of a wire-shaped material made of any of the above metals, or a multilayer structure made by coating a wire-shaped material with another metal, such as a nickel-coated copper wire, a silver-coated copper wire, a copper-coated aluminum wire, or a copper-coated steel wire.

[0053] The lower limit of the average cross-sectional area of ​​the conductor 2 is 0.01 mm 2 may be 0.1 mm 2 In this case, the volume of the insulating layer 3 relative to the conductor 2 in the insulated wire 1 can be made appropriate, and the volume efficiency of a coil or the like formed using the insulated wire 1 can be improved. The upper limit of the average cross-sectional area of ​​the conductor 2 is 40 mm 2 may be 30mm 2 In this case, it is possible to avoid a decrease in the output efficiency of the coil or the like due to an increase in copper loss caused by eddy currents.

[0054] [Insulating layer] The insulating layer 3 is laminated on the outer peripheral surface of the conductor 2 so as to cover the conductor 2 .

[0055] The insulating layer 3 is formed from the resin composition for an insulating layer described above. Therefore, the insulating layer 3 contains polyimide, which is the main component forming the matrix, and surface-treated silica 4. The "main component" refers to the component with the largest content ratio in terms of mass, for example, a component with a content ratio of 70 mass% or more.

[0056] The average thickness of the insulating layer 3 is not particularly limited, and can usually be set to 5 μm or more and 200 μm or less.

[0057] The insulated wire 1 can be suitably used as a winding wire for a coil (magnet wire).

[0058] (Polyimide) The insulating layer 3 contains polyimide as a main component, which can provide good toughness, insulating properties, and heat resistance.

[0059] The lower limit of the polyimide content in the insulating layer 3 may be 70 mass %, 73 mass %, or 75 mass %. When the polyimide content is 70 mass % or more, the insulating layer 3 can obtain sufficient elongation.

[0060] (Surface-treated silica) The surface-treated silica 4 is as described above, and therefore the description thereof will be omitted.

[0061] (Other ingredients) The insulating layer 3 may contain other components in addition to the above components. The other components are not particularly limited as long as they are additives that can be blended into the resin composition for the insulating layer described above, and examples thereof include antioxidants, radical scavengers, ultraviolet inhibitors, surface lubricants, leveling agents, curing agents, and adhesion aids.

[0062] The insulated wire has an insulating layer that is excellent in surge resistance and elongation because the insulating layer is formed from the resin composition for insulating layer described above.

[0063] <Insulated wire manufacturing method> The method for producing an insulated wire includes a conductor and an insulating layer covering the conductor, and includes a step of applying the resin composition for an insulating layer to the outer peripheral surface of the conductor (a coating step), and a step of heating the resin composition for an insulating layer applied in the coating step (a heating step).

[0064] [Coating process] In the coating step, the resin composition for an insulating layer is coated onto the outer peripheral surface of the conductor.

[0065] A method for applying the resin composition for an insulating layer to the outer peripheral surface of a conductor can be, for example, a method using a coating device equipped with a liquid composition tank storing the resin composition for an insulating layer and a coating die. With this coating device, the resin composition for an insulating layer adheres to the outer peripheral surface of the conductor when the conductor passes through the liquid composition tank, and then the resin composition for an insulating layer is applied to a uniform thickness when the conductor passes through the coating die.

[0066] [Heating process] In the heating step, the resin composition for insulating layer that has been applied to the conductor in the application step is heated, and this heating volatilizes the organic solvent in the resin composition for insulating layer, and also cures the polyimide precursor, thereby forming a polyimide.

[0067] The heating step may be performed using any suitable device, such as a cylindrical baking oven that is long in the direction of travel of the conductor. The heating method may be any suitable method, such as hot air heating, infrared heating, or high-frequency heating.

[0068] The heating temperature can be, for example, 300° C. or more and 800° C. or less. The heating time can be, for example, 5 seconds or more and 1 minute or less.

[0069] The coating step and the heating step are usually repeated multiple times. By repeating the steps multiple times, the thickness of the insulating layer can be increased. The hole diameter of the coating die can be adjusted appropriately depending on the number of repetitions.

[0070] According to the method for producing an insulated wire, an insulating layer is formed using the resin composition for an insulating layer described above, so that an insulated wire having an insulating layer excellent in surge resistance and elongation can be produced.

[0071] [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.

[0072] The insulated wire may have a configuration other than those described above. For example, the insulated wire may have an adhesion layer containing an additive such as an adhesion improver between the conductor and the insulating layer. Examples of the adhesion improver include mercaptans such as 2-mercaptoimidazole and 5-amino-1,3,4-thiadiazole-2-thiol, and melamine compounds.

[0073] The insulating layer of the insulated wire may contain multiple voids. The dielectric constant can be reduced by including multiple voids in the insulating layer. The voids can be formed by either air bubbles or hollow portions of hollow fillers having an outer shell. The voids are formed by a void-forming agent. Any known additives for forming voided insulating layers can be used without particular limitation. Examples of the void-forming agent include chemical foaming agents, thermally expandable microcapsules, thermally decomposable resin-containing particles, high-boiling point solvents, and hollow fillers. The void-forming agent may also be thermally decomposable resin-containing particles, since the porosity can be easily controlled. The thermally decomposable resin-containing particles are gasified by thermal decomposition, forming voids in the insulating layer where the thermally decomposable resin-containing particles were previously present. In this case, the particles can be uniformly distributed as islands of fine particles in a sea phase of polyimide, the main component of the insulating layer, forming multiple independent voids. The content of the pore-forming agent in the resin composition for an insulating layer can be appropriately determined depending on, for example, the type of pore-forming agent and the target porosity of the insulating layer.

[0074] The insulated wire may have a surface friction adjusting layer as its outermost layer. Examples of the surface friction adjusting layer include a polyamide-imide layer, a self-lubricating amide-imide layer, and a self-lubricating polyimide layer. The "outermost layer" refers to the layer located outermost in the laminate structure constituting the insulated wire, with the conductor side positioned inside.

[0075] The insulated wire may have an outermost adhesive layer containing an additive such as a foaming agent. Examples of the foaming agent include azo-based foaming agents such as azodicarbonamide and azobisisobutyronitrile, nitroso-based foaming agents such as dinitrosopentamethylenetetramine and N,N'-dinitroso-N,N'-dimethylterephthalamide, hydrazide-based foaming agents such as p-toluenesulfonylhydrazide, p,p'-oxybisbenzenesulfonylhydrazide and benzenesulfonylhydrazide, and trihydrazinotriazine. [Example]

[0076] The present disclosure will be described in more detail below with reference to examples, but the present disclosure is not limited to these examples.

[0077] [Insulated Wire No. 1] (Preparation of Resin Composition for Insulating Layer) 4,4'-Diaminodiphenyl ether as an aromatic diamine was dissolved in N,N-dimethylacetamide. Pyromellitic dianhydride as an aromatic tetracarboxylic dianhydride was added so that the mixing ratio (molar ratio) of the aromatic tetracarboxylic dianhydride to the aromatic diamine was 100:100. The mixture was allowed to react at 30°C for 3 hours with stirring under a nitrogen atmosphere to synthesize a polyimide precursor, yielding a polyimide precursor solution using N,N-dimethylacetamide as the solvent. 20 parts by mass of trimethylsilane-surface-treated silica was added to 100 parts by mass of the polyimide precursor to prepare Resin Composition No. 1 for an insulating layer (solid content: 24% by mass).

[0078] (Making insulated wire) A round copper wire with an average diameter of 1.0 mm was used as the conductor. After coating the surface of the conductor with resin composition No. 1 for insulating layer, heating was performed 18 times under the conditions of an inlet temperature of 400°C, an outlet temperature of 500°C, and a wire speed of 11 m / min to form an insulating layer with an average thickness of 71 μm. In this way, insulated wire No. 1 was produced, which had an insulating layer formed from resin composition No. 1 for insulating layer.

[0079] [Insulated wires No. 2 to No. 22] Resin compositions for insulating layer Nos. 2 to 22 were prepared in the same manner as resin composition for insulating layer No. 1, except that the types and amounts of each component were used as shown in Table 1 below. Insulated wires Nos. 2 to 22 were then produced, each having an insulating layer formed from resin compositions for insulating layer Nos. 2 to 22. In Table 1 below, "-" indicates that the corresponding component was not used.

[0080] [evaluation] For the insulated wires No. 1 to No. 22 prepared above, the average particle size of the primary particles of the surface-treated silica, the relative dielectric constant, and the elongation of the insulating layer were measured according to the following methods. The results are shown in Tables 1 and 2 below.

[0081] (Average particle size of primary particles of surface-treated silica) The average particle size of the primary particles of the surface-treated silica was determined by observing the cross section of an insulated electric wire using a scanning electron microscope, measuring the particle sizes of 50 randomly selected primary particles on the SEM image, and then calculating the average particle size of the 50 primary particles.

[0082] (Measurement of relative permittivity) The dielectric constant of the insulating layer was measured for the insulated wires No. 1 to No. 22. Measurement samples were prepared by applying silver paste to three locations on the surface of the insulated wire and peeling off the insulating layer at one end of the wire to expose the conductor. The lengths of the silver paste applied to the three locations along the length of the insulated wire were 10 mm, 100 mm, and 10 mm, respectively. The two 10-mm lengths of silver paste were grounded, and the capacitance between the 100-mm length of silver paste applied between these two locations and the exposed conductor was measured using an LCR meter. The dielectric constant of the insulating layer was calculated from the measured capacitance and the average thickness of the insulating layer. The dielectric constant measurements were performed in triplicate after heating at 105°C for 1 hour, and the average value was calculated.

[0083] (Measurement of insulation layer elongation) For the insulated wires No. 1 to No. 22 prepared above, the conductors were removed from the insulated wires to form tubular insulating layers, which were then pulled using a tensile tester (Shimadzu Corporation's Autograph AGS-X) at 25°C under conditions of a chuck distance of 20 mm and a pulling rate of 10 mm / min, to measure the elongation (unit: %) of the insulating layer at break. The measurement of the elongation of the insulating layer was carried out five times, and the average value was calculated.

[0084] (Thickness deviation of insulating layer) The thickness uniformity of the insulating layer was evaluated by the thickness unevenness of the insulating layer. The thickness unevenness of the insulating layer was measured for the insulated electric wires No. 1 to No. 22 prepared above. The thickness unevenness of the insulating layer is expressed as the ratio of the maximum thickness to the minimum thickness of the insulating layer of each insulated electric wire, as shown in the following formula. The smaller the thickness unevenness of the insulating layer, the better the thickness uniformity of the insulating layer. Insulation layer thickness deviation = Maximum insulation layer thickness / Minimum insulation layer thickness

[0085] (breakdown time) The time to breakdown [hours] was measured using the following procedure. In accordance with the methods specified in JIS-C3003:1999 and IEC60851-5, a twisted wire sample was manufactured by twisting two insulated wires together and evaluated under the following test conditions. (1) Waveform: Sine wave (2) Frequency: 50 kHz (3) Voltage: 2,000V (4) Ambient temperature: 155°C In the durability test under the above test conditions, the time elapsed until a short circuit occurred due to insulation breakdown between the two twisted wires was recorded.

[0086] [Table 1]

[0087] [Table 2]

[0088] As shown in Tables 1 and 2, insulated wires No. 1 to No. 15, in which an insulating layer was formed using a resin composition for an insulating layer containing a polyimide precursor that is a reaction product of an aromatic tetracarboxylic dianhydride and an aromatic diamine, an organic solvent, and surface-treated silica, wherein the surface-treated silica was trimethylsilane-surface-treated silica, dimethylsilane-surface-treated silica, or a combination thereof, and the average particle size of the primary particles of the surface-treated silica was 0.01 μm or more and 0.05 μm or less, obtained good results in all of the evaluations of the dielectric constant, elongation of the insulating layer, thickness unevenness of the insulating layer, and time to dielectric breakdown.

[0089] On the other hand, insulated wire No. 16, which contained silica in the insulation layer and had not been surface-treated, had a slightly higher dielectric constant, poor insulation layer elongation and thickness unevenness, and an extremely short time to breakdown. Insulated wire No. 17, which contained silica with a methacrylsilyl surface treatment in the insulation layer, had a slightly high relative dielectric constant and was very poor in insulation layer elongation, insulation layer thickness deviation, and dielectric breakdown time. Insulated wire No. 18, which contained silica treated with dimethylpolysiloxane in the insulation layer, had a slightly high relative dielectric constant and a slightly high degree of thickness deviation in the insulation layer, and was very poor in elongation of the insulation layer and time to dielectric breakdown. Insulated wire No. 19, which contains surface-treated silica with an average primary particle size of more than 0.05 μm, had a very short time to breakdown. Insulated wire No. 20, which contains surface-treated silica with an even larger average primary particle size than No. 19, had a large uneven thickness of the insulation layer and also had a very short time to breakdown. Insulated wire No. 21, which did not contain surface-treated silica, had very good elongation of the insulation layer, but the thickness deviation of the insulation layer was very large and the time to dielectric breakdown was particularly short. Insulated wire No. 22, which contained surface-treated silica with an average primary particle size of less than 0.01 μm, had poor elongation of the insulation layer and an extremely short time to dielectric breakdown.

[0090] From the above, it can be seen that the insulated wire has excellent surge resistance and elongation of the insulating layer. [Explanation of symbols]

[0091] 1. Insulated wire 2 conductors 3. Insulation layer 4. Surface-treated silica

Claims

1. a polyimide precursor which is a reaction product of an aromatic tetracarboxylic dianhydride and an aromatic diamine; an organic solvent; Surface-treated silica and Contains the surface-treated silica is trimethylsilane surface-treated silica, dimethylsilane surface-treated silica, or a combination thereof; The resin composition for an insulating layer, wherein the average particle size of the primary particles of the surface-treated silica is 0.01 μm or more and 0.05 μm or less.

2. 2. The resin composition for an insulating layer according to claim 1, wherein the weight average molecular weight of the polyimide precursor is 25,000 or more and 80,000 or less.

3. 2. The resin composition for an insulating layer according to claim 1, wherein the content of the surface-treated silica is 15 parts by mass or more and 30 parts by mass or less per 100 parts by mass of the polyimide precursor.

4. 2. The resin composition for an insulating layer according to claim 1, wherein the ratio of the shear viscosity at 30°C and a shear rate of 1 / s to the shear viscosity at 30°C and a shear rate of 100 / s is 3.0 or more and 23.0 or less.

5. A conductor; an insulating layer covering the conductor; Equipped with An insulated wire, wherein the insulating layer is formed from the resin composition for an insulating layer according to any one of claims 1 to 4.

6. A method for manufacturing an insulated wire including a conductor and an insulating layer covering the conductor, a step of applying the resin composition for an insulating layer according to any one of claims 1 to 4 to an outer peripheral surface of the conductor; a step of heating the resin composition for insulating layer coated in the coating step; A method for manufacturing an insulated wire comprising:

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