Resin composition, insulated wire, and method for producing insulated wire

Abstract

A resin composition containing: a polyimide precursor that is a reaction product of an aromatic tetracarboxylic dianhydride and an aromatic diamine; an organic solvent; and a phthalic acid alkyl ester having a boiling point of 290°C or higher.

Description

Resin composition, insulated wire, and method for producing insulated wire

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

[0002] Patent Document 1 describes an insulating varnish containing a coating film-constituting resin and a thermally decomposable resin that decomposes at a temperature lower than the baking temperature of the coating film-constituting resin.

[0003] JP 2012-224714 A

[0004] A resin composition according to one embodiment 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 an alkyl phthalate ester having a boiling point of 290°C or higher.

[0005] [Problem to be Solved by the Present Disclosure] The problem to be solved by the present disclosure is to provide a resin composition capable of forming an insulating layer having pores.

[0006] Effect of the Present Disclosure According to the resin composition according to one aspect of the present disclosure, an insulating layer having pores can be formed.

[0007] [Explanation of Embodiments of the Present Disclosure] First, embodiments of the present disclosure will be listed and described. Item 1. A resin composition containing a polyimide precursor that is a reaction product of an aromatic tetracarboxylic dianhydride and an aromatic diamine, an organic solvent, and an alkyl phthalate ester having a boiling point of 290°C or higher. Item 2. The resin composition according to Item 1, wherein the alkyl phthalate ester has a boiling point of 380°C or lower. Item 3. The resin composition according to Item 1 or 2, wherein the alkyl phthalate ester is diisopropyl phthalate or diisobutyl phthalate. Item 4. The resin composition according to any one of Items 1 to 3, wherein the alkyl phthalate ester is present in an amount of 1 part by mass or more and 12 parts by mass or less per 100 parts by mass of the polyimide precursor and the organic solvent combined. Item 5. The resin composition according to any one of Items 1 to 4, wherein the organic solvent has a boiling point of 150°C or higher. Item 6. The resin composition according to any one of Items 1 to 5, further containing thermally decomposable resin-containing particles. Item 7. Item 8. The resin composition according to any one of items 1 to 6, which is used to form an insulating layer of an insulated wire. Item 9. An insulated wire comprising: a conductor; and an insulating layer covering the conductor, the insulating layer having a plurality of pores, the insulating layer being formed from the resin composition according to any one of items 1 to 7. Item 10. A method for producing an insulated wire according to item 8, comprising the steps of: applying the resin composition to an outer peripheral surface of the conductor; and heating the resin composition applied in the applying step.

[0008] [Details of Embodiment of Present Disclosure] Hereinafter, a resin composition, an insulated wire, and a method for producing an insulated wire according to one aspect of the present disclosure will be described.

[0009] <Resin Composition> The resin composition contains a polyimide precursor which is a reaction product of an aromatic tetracarboxylic dianhydride and an aromatic diamine, an organic solvent, and an alkyl phthalate ester having a boiling point of 290°C or higher.

[0010] The resin composition can form an insulating layer having pores by containing an alkyl phthalate ester having a boiling point of 290° C. or higher. Although a restrictive interpretation is not desired, when an insulating layer is formed using the resin composition, pores can be formed by phase separation between the polyimide precursor and the alkyl phthalate ester, and it is presumed that the boiling point of the alkyl phthalate ester is involved in whether or not pores are formed by the phase separation.

[0011] The resin composition can be suitably used as a resin composition (resin varnish) for forming an insulating layer of an insulated wire.

[0012] Each component contained in the resin composition will be described below.

[0013] (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 called a polyamic acid (polyamic acid). The polyimide precursor undergoes a dehydration cyclization reaction to form a cyclic imide, resulting in a polyimide.

[0014] The aromatic tetracarboxylic dianhydride containing pyromellitic dianhydride (PMDA) can improve the heat resistance of the insulating layer. This is because PMDA has a rigid and linear molecular structure. The aromatic tetracarboxylic dianhydride may contain an aromatic tetracarboxylic dianhydride other than PMDA (hereinafter, also referred to as "another aromatic tetracarboxylic dianhydride").

[0015] Examples of the other aromatic tetracarboxylic dianhydrides include 3,3',4,4'-biphenyltetracarboxylic dianhydride (s-BDPA), 2,3,3',4'-biphenyltetracarboxylic dianhydride (a-BDPA), 2,2',3,3'-biphenyltetracarboxylic dianhydride (i-BDPA), 3,3',4,4'-benzophenonetetracarboxylic dianhydride, 4,4'-oxydiphthalic dianhydride, 2,2',3,3'-benzophenonetetracarboxylic dianhydride, 2,2-bis(3,4-dicarboxyphenyl)propane dianhydride, 2,2-bis(3,4-dicarboxyphenyl)propane dianhydride, and 2,2-bis(3,4-dicarboxyphenyl)propane dianhydride. Examples of the other aromatic tetracarboxylic dianhydrides 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. These other aromatic tetracarboxylic dianhydrides may be used alone or in combination of two or more.

[0016] The lower limit of the content of PMDA relative to 100 mol% of the aromatic tetracarboxylic dianhydride may be 0 mol%, 10 mol%, 20 mol%, or 30 mol%, and the upper limit of the content of PMDA relative to 100 mol% of the aromatic tetracarboxylic dianhydride may be 100 mol%, 90 mol%, 80 mol%, or 70 mol%.

[0017] 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 30 mol% or 20 mol%, and the lower limit of the content may be 0 mol% or 10 mol%.

[0018] When the aromatic diamine contains diaminodiphenyl ether (ODA), the heat resistance of the insulating layer can be improved. 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 film elongation of the insulating layer.

[0019] The lower limit of the ODA content relative to 100 mol% of the aromatic diamine may be 50 mol%, 60 mol%, or 70 mol%, and the upper limit of the ODA content relative to 100 mol% of the aromatic diamine may be 100 mol% or 90 mol%.

[0020] 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, 4,4'-benzophenonediamine, 2,2'-dimethyl-4,4'-diaminodiphenylmethane ...

[0021] 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 40 mol% or 30 mol%. The lower limit of the content may be 0 mol% or 10 mol%.

[0022] The polyimide precursor preferably has a glass transition temperature of 250°C or higher, as measured by the method described below. The lower limit of the glass transition temperature may be 280°C or 300°C. While not intended to be restrictive, a glass transition temperature of more than 280°C can suppress softening of the polyimide during pore formation, which tends to facilitate improved porosity. The upper limit of the glass transition temperature is not particularly limited and may be, for example, 400°C. The glass transition temperature is measured using a dynamic viscoelasticity measuring device under conditions of 1 Hz and a temperature increase rate of 10°C / min, after preparing a film-like test specimen by coating a thin film of the resin composition on a glass plate and heating it at 350°C for 1 hour. The glass transition temperature can be adjusted by, for example, changing the type of monomer constituting the polyimide precursor.

[0023] The lower limit of the concentration of the polyimide precursor in the resin composition may be 25% by mass or 27% by mass. The upper limit of the concentration may be 40% by mass or 35% by mass. By setting the concentration at or above the lower limit, the amount of resin composition required in the entire manufacturing process to obtain an insulating layer of the desired thickness when forming an insulating layer using the resin composition can be reduced, and the number of coating and heating steps can be reduced. By setting the concentration at or below the upper limit, the viscosity of the resin composition can be appropriately adjusted while maintaining good film properties, thereby improving coatability.

[0024] 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 amounts. In this case, the molecular weight of the polyimide precursor can be easily increased. The term "substantially equimolar amount" 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.

[0025] (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 described above. The polymerization condensation reaction can be carried out in the same manner as in conventional synthesis of polyimide precursors. Specific methods for the polymerization condensation reaction include, for example, mixing the aromatic tetracarboxylic dianhydride and the aromatic diamine in an organic solvent. This method polymerizes the aromatic tetracarboxylic dianhydride and the aromatic diamine, thereby obtaining a solution in which the polyimide precursor is dissolved in the organic solvent. For example, the degree of polymerization (weight average molecular weight) can be controlled by carrying out the polymerization condensation reaction in the presence of a reaction inhibitor.

[0026] The reaction inhibitor may be, for example, water (H ２ and alcohols having 1 to 15 carbon atoms. Examples of the 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.

[0027] 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.

[0028] Examples of the organic solvent used in the above polymerization condensation reaction include the same organic solvents as those described below.

[0029] (Organic Solvent) Examples of the organic solvent include aprotic polar organic solvents such as N-methyl-2-pyrrolidone (NMP, boiling point: 202°C), N,N-dimethylacetamide (DMAc, boiling point: 165°C), N,N-dimethylformamide (boiling point: 153°C), dimethyl sulfoxide (boiling point: 189°C), and γ-butyrolactone (boiling point: 204°C). One type of organic solvent may be used alone, or two or more types may be used in combination. The term "aprotic polar organic solvent" refers to a polar organic solvent that does not have a group that releases a proton.

[0030] When the boiling point of the organic solvent is 150°C or higher, unintended drying before baking can be suppressed during the insulating layer formation process. If the difference (boiling point difference) between the boiling point of the organic solvent and the boiling point of the alkyl phthalate ester is large, pores tend to be more likely to form. Note that the boiling point of the alkyl phthalate ester is usually higher than the boiling point of the organic solvent.

[0031] The content of the organic solvent is not particularly limited as long as it is an amount that can uniformly dissolve or disperse the aromatic tetracarboxylic dianhydride and the aromatic diamine, but if the amount is too large, a large amount of organic solvent needs to be volatilized when forming the insulating layer of the insulated wire, which may require a long time to form the insulating layer. Therefore, the content of the organic solvent can be, for example, 100 parts by mass or more and 1,000 parts by mass or less per 100 parts by mass of the total of the aromatic tetracarboxylic dianhydride and the aromatic diamine.

[0032] (Phthalic acid alkyl ester) The above-mentioned phthalic acid alkyl ester is an alkyl phthalate ester having a boiling point of 290°C or higher. "Alkyl ester" means an ester containing a linear or branched alkyl group. "Phthalic acid" means phthalic acid in the narrow sense, i.e., the ortho-isomer of benzenedicarboxylic acid. Phthalic acid is clearly distinguished from isophthalic acid, which is the meta-isomer, and terephthalic acid, which is the para-isomer.

[0033] The boiling point of the alkyl phthalate ester is 290° C. or higher. By using an alkyl phthalate ester having a boiling point of 290° C. or higher, an insulating layer having pores can be formed. Although a restrictive interpretation is not desired, it is presumed that if the boiling point is lower than 290° C., the alkyl phthalate ester volatilizes before phase separation between the polyimide precursor and the alkyl phthalate ester occurs during the heating step in forming the insulating layer, making it impossible to form pores.

[0034] The lower limit of the boiling point of the alkyl phthalate ester may be 300°C, 310°C, or 320°C. When the boiling point is 300°C or higher, an insulating layer with high porosity can be formed. The upper limit of the boiling point may be 410°C, 400°C, 390°C, 380°C, 340°C, 330°C, or 320°C. When the boiling point is 380°C or lower, the residue of the alkyl phthalate ester in the insulating layer can be suppressed. When the boiling point is 330°C or lower, the dielectric breakdown voltage and film elongation of the insulating layer can be improved. When the boiling point is 320°C or lower, the dielectric breakdown voltage and film elongation of the insulating layer can be further improved.

[0035] Examples of the alkyl phthalate esters include diethyl phthalate (boiling point: 298°C), diisopropyl phthalate (boiling point: 313°C), dipropyl phthalate (boiling point: 317°C), diisobutyl phthalate (boiling point: 327°C), dibutyl phthalate (boiling point: 340°C), dioctyl phthalate (boiling point: 385°C), bis(2-ethylhexyl) phthalate (boiling point: 384°C), and diisononyl phthalate (boiling point: 403°C). Note that dimethyl phthalate (boiling point: 282°C) does not fall under the category of alkyl phthalate esters.

[0036] The content of the alkyl phthalate ester in the resin composition can be appropriately set within a range that achieves the effects of the present disclosure. Since an increase in the content of the alkyl phthalate ester improves the porosity of the insulating layer formed, the porosity of the insulating layer can be adjusted by adjusting the content of the alkyl phthalate ester. The upper limit of the content of the alkyl phthalate ester may be 12 parts by mass, 10 parts by mass, 9 parts by mass, 8 parts by mass, or 7 parts by mass, relative to 100 parts by mass of the polyimide precursor and the organic solvent combined. When the content is 12 parts by mass or less, the insulating layer formed has a good shape with no foaming in appearance. While not intended to be limiting, it is presumed that when the content is 12 parts by mass or less, the balance between the island and sea portions of the sea-island structure formed by phase separation between the polyimide precursor and the alkyl phthalate ester is appropriately adjusted, thereby suppressing the occurrence of poor appearance of the insulating layer, such as foaming, swelling, or peeling. When the content is 10 parts by mass or less, the breakdown voltage and film elongation can be further improved. When the content is 8 parts by mass or less, the breakdown voltage and film elongation can be further improved. The lower limit of the content of the alkyl phthalate may be 1 part by mass, 2 parts by mass, 4 parts by mass, or 6 parts by mass, relative to 100 parts by mass of the polyimide precursor and the organic solvent combined.

[0037] (Thermal Decomposable Resin-Containing Particles) When the resin composition further contains thermally decomposable resin-containing particles, an insulating layer with a good appearance can be formed even when the porosity is high. The thermally decomposable resin-containing particles are gasified by thermal decomposition, and pores are formed in the insulating layer in the areas where the thermally decomposable resin-containing particles were present. In this case, the fine particles can be uniformly distributed as an island phase in the sea phase of the resin matrix that forms the insulating layer, forming independent pores.

[0038] The thermally decomposable resin contained in the thermally decomposable resin-containing particles is preferably a resin that thermally decomposes at a temperature lower than the baking temperature of the polyimide that is the main component of the resin matrix of the insulating layer. The baking temperature is set appropriately depending on the type of polyimide, but is usually about 200°C or higher and 600°C or lower. The "thermal decomposition temperature" refers to the temperature at which the mass loss rate reaches 50% when the temperature is increased from room temperature at a rate of 10°C / min in an air atmosphere. The thermal decomposition temperature can be measured by measuring the thermogravimetry using a thermogravimetry-differential thermal analyzer ("TG / DTA" from SII NanoTechnology, Inc.).

[0039] Examples of thermally decomposable resins include compounds such as polyethylene glycol and polypropylene glycol in which one or both ends or a portion thereof are alkylated, (meth)acrylated, or epoxidized; polymers of (meth)acrylic acid esters having an alkyl group of 1 to 6 carbon atoms, such as polymethyl(meth)acrylate, polyethyl(meth)acrylate, polypropyl(meth)acrylate, and polybutyl(meth)acrylate; urethane oligomers, urethane polymers, polymers of modified (meth)acrylates such as urethane(meth)acrylate, epoxy(meth)acrylate, and ε-caprolactone(meth)acrylate; poly(meth)acrylic acid; crosslinked products thereof; polystyrene; and crosslinked polystyrene. Polymers of (meth)acrylic acid esters having an alkyl group of 1 to 6 carbon atoms are prone to thermal decomposition at the baking temperature, easily forming pores in the insulating layer. An example of such a polymer of (meth)acrylic acid ester is polymethyl methacrylate (PMMA). The term "(meth)acrylic acid" encompasses both "acrylic acid" and "methacrylic acid."

[0040] The thermally decomposable resin-containing particles may be particles consisting solely of the thermally decomposable resin, or may be particles having a core-shell structure having a core mainly composed of the thermally decomposable resin and a shell mainly composed of a resin having a thermal decomposition temperature higher than that of the thermally decomposable resin. In this case, interconnection of pores can be suppressed, and variation in pore size can be reduced.

[0041] The main component of the shell is not particularly limited as long as it has a thermal decomposition temperature higher than that of the core, and is preferably a synthetic resin with a low dielectric constant and high heat resistance. Examples include polystyrene, silicone, fluororesin, and polyimide. Silicone tends to increase elasticity, which in turn tends to improve the dispersion of pores in the insulating layer, resulting in excellent insulating properties and heat resistance.

[0042] (Other Components) The resin composition may contain other components in addition to the above-described 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 layer of an insulated wire, and examples thereof include a filler, an antioxidant, a leveling agent, a curing agent, and an adhesion aid.

[0043] <Insulated Wire> The insulated wire includes a conductor and an insulating layer covering the conductor. The insulated wire can be suitably used as a winding wire for a coil (magnet wire).

[0044] (Conductor) The conductor is usually composed mainly of a metal. The metal is not particularly limited, but if copper, a copper alloy, aluminum, or an aluminum alloy is used, an insulated electric wire having good processability, electrical conductivity, etc. can be obtained. The conductor may contain other components such as known additives in addition to the metal as the main component.

[0045] 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 the diameter (short side width) can be, for example, 0.2 mm or more and 8.0 mm or less.

[0046] (Insulating Layer) The insulating layer is laminated on the peripheral surface of the conductor so as to cover the conductor. The insulating layer may cover the conductor directly or indirectly. In the case of indirect coverage, for example, a multilayer structure in which the covering layer of the conductor includes a layer other than the insulating layer can be mentioned.

[0047] The insulating layer is formed from the resin composition described above, and therefore has a plurality of pores.

[0048] The average thickness of the insulating layer is not particularly limited, but is usually 2 μm or more and 200 μm or less.

[0049] The insulated wire may further have another layer laminated on the outer peripheral surface of the insulating layer, such as a surface lubricating layer.

[0050] The lower limit of the porosity of the insulating layer may be 20 vol%, 25 vol%, or 30 vol%. The upper limit of the porosity may be 70 vol%, 60 vol%, or 50 vol%. "Porosity" refers to the percentage of the volume of pores relative to the volume of the insulating layer including the pores.

[0051] When the thermally decomposable resin-containing particles are particles with the core-shell structure, the pores have an outer shell at their periphery that originates from the shell of the particle with the core-shell structure.

[0052] The 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 incorporated into the insulating layer of an insulated wire, and examples thereof include fillers, antioxidants, leveling agents, curing agents, and adhesion aids.

[0053] <Method for manufacturing insulated wire> The insulated wire can be manufactured by a method including, for example, a step of applying the resin composition to the outer peripheral surface of a conductor (hereinafter referred to as a “coating step”) and a step of heating the resin composition applied to the conductor (hereinafter referred to as a “heating step”).

[0054] In the coating step, the resin composition is applied to the outer peripheral surface of the conductor. For example, a method for applying the resin composition to the outer peripheral surface of the conductor may use a coating device equipped with a liquid composition tank containing the resin composition and a coating die. With this coating device, the conductor passes through the liquid composition tank, causing the resin composition to adhere to the outer peripheral surface of the conductor. The conductor then passes through the coating die, coating the resin composition to a uniform thickness.

[0055] In the heating step, the resin composition applied to the conductor in the application step is heated, which volatilizes the solvent in the resin composition and cures the polyimide precursor to form polyimide.

[0056] 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.

[0057] The heating temperature can be, for example, 300° C. to 800° C. The heating time can be, for example, 5 seconds to 1 minute.

[0058] 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.

[0059] [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.

[0060] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0061] The abbreviations for the various components used in the examples are shown below. (Aromatic tetracarboxylic dianhydrides) PMDA: Pyromellitic dianhydride BPDA: 3,3',4,4'-biphenyltetracarboxylic dianhydride (Aromatic diamines) ODA: 4,4'-diaminodiphenyl ether (Organic solvents) NMP: N-methyl-2-pyrrolidone (boiling point: 202°C) DMAc: N,N-dimethylacetamide (boiling point: 165°C) (Phthalic acid alkyl esters) DIBP: Diisobutyl phthalate (boiling point: 327°C) DPP: Dipropyl phthalate (boiling point: 317°C) DIPP: Diisopropyl phthalate (boiling point: 313°C) DBP: Dibutyl phthalate (boiling point: 340°C) DEP: Diethyl phthalate (boiling point: 298°C) DMP: Dimethyl phthalate (boiling point: 282°C)

[0062] Test Example 1 In Test Example 1, the influence of differences in boiling points of alkyl phthalates on pore formation was tested.

[0063] [No. 1-1] (Preparation of Resin Composition) ODA as an aromatic diamine was dissolved in NMP. PMDA 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, and a polyimide precursor solution containing NMP as a solvent (solids concentration: 28% by mass) was obtained. 8.2 parts by mass of DIBP was added to 100 parts by mass of the polyimide precursor solution to prepare Resin Composition No. 1-1.

[0064] (Preparation of Insulated Wire) A round copper wire having an average diameter of 1 mm was used as the conductor. Resin composition No. 1-1 was applied to the surface of the conductor, and the conductor coated with resin composition No. 1-1 was heated in a heating furnace at an inlet temperature of 400°C, an outlet temperature of 450°C, and a linear speed of 3 m / min. This process was repeated 10 times to form an insulating layer having an average thickness of 35 μm, thereby producing insulated wire No. 1-1.

[0065] [No. 1-2 to No. 1-6] Resin compositions No. 1-2 to No. 1-6 were prepared in the same manner as in No. 1-1, except that the types and amounts of each component shown in Table 1 below were used, and insulated wires No. 1-2 to No. 1-6 were fabricated.

[0066] <Evaluation> For the insulated wires No. 1-1 to No. 1-6 prepared above, the porosity was calculated, and the relative dielectric constant, the dielectric breakdown voltage, and the coating elongation were measured according to the following methods. The results are shown in Table 1 below.

[0067] [Calculation of Porosity] For the insulated wires No. 1-1 to No. 1-5 prepared above, the insulating layer was peeled off from the conductor into a tube shape, and the mass W2 of the cylindrical insulating layer was measured. The apparent volume V1 was determined from the outer shape of the cylindrical insulating layer, and the mass W1 without pores was calculated by multiplying the volume V1 by the density ρ1 of the material of the insulating layer. From these values ​​of W1 and W2, the porosity (unit: volume %) was calculated using the following formula 1. Formula 1: Porosity = (W1 - W2) × 100 / W1

[0068] [Measurement of Relative Dielectric Constant] The relative dielectric constant of the insulating layer was measured for the insulated wires No. 1-1 to No. 1-6 prepared above. 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 insulated wire to expose the conductor. The lengths of the silver paste applied to the three locations on the surface of the insulated wire in the longitudinal direction of the insulated wire were 10 mm, 100 mm, and 10 mm, respectively. The two 10-mm-long silver paste applications were grounded, and the capacitance between the 100-mm-long silver paste applied between these two silver paste applications and the exposed conductor was measured using an LCR meter. The relative dielectric constant of the insulating layer was calculated from the measured capacitance and the average thickness of the insulating layer. The relative dielectric constant was measured three times after heating at 105°C for 1 hour, and the average value was calculated.

[0069] [Measurement of Breakdown Voltage] For the insulated wires No. 1-1 to No. 1-6 prepared above, an AC voltage was applied between two twisted wires, and the voltage was increased at 500 V / sec, and the voltage (unit: kV) at the time of breakdown was measured in accordance with JIS C3216-5:2011. The breakdown voltage was measured five times, and the average value was calculated.

[0070] [Measurement of Coating Elongation] For each of the insulated wires No. 1-1 to No. 1-6 prepared above, the conductor was removed from the insulated wire to form a tubular insulating layer. The elongation at break (unit: %) was measured when the tubular insulating layer was pulled in the longitudinal direction at a pulling rate of 50 mm / min in an environment of 25° C. using a tensile tester (Shimadzu Corporation's "Autograph AGS-X") The coating elongation was measured five times, and the average value was calculated.

[0071] In Table 1 below, the units of values ​​in the rows for "Polyimide precursor solution" and "Phthalic acid alkyl ester" are parts by mass. A "-" in the row for "Phthalic acid alkyl ester (boiling point)" indicates that the corresponding component is not used. A "-" in the row for "Porosity [volume %]" indicates that the insulating layer of the corresponding insulated wire does not have multiple pores.

[0072]

[0073] It can be seen from Table 1 that when resin compositions No. 1-1 to No. 1-5 were used, pores were able to be formed in the insulating layer, whereas when resin composition No. 1-6 was used, pores were not able to be formed. This shows that the boiling point of the alkyl phthalate ester affects whether or not pores are formed.

[0074] Test Example 2 In Test Example 2, the influence of different contents of alkyl phthalate on the characteristics of the insulated wire was tested.

[0075] [No. 2-1 to No. 2-5] Resin compositions No. 2-1 to No. 2-5 were prepared in the same manner as in No. 1-1, except that the types and amounts of each component shown in Table 2 below were used, and insulated wires No. 2-1 to No. 2-5 were produced.

[0076] <Evaluation> For the insulated wires No. 2-1 to No. 2-5 prepared above, the porosity was calculated, and the relative dielectric constant, breakdown voltage, and coating elongation were measured using the same methods as in Test Example 1 above. Furthermore, for the insulated wires No. 1-1 and No. 2-1 to No. 2-5 prepared above, the appearance of the insulating layer was observed using the following method. The results are shown in Table 2 below.

[0077] [Appearance of Insulating Layer] The appearance of the insulating layer of each of the insulated wires No. 1-1 and No. 2-1 to No. 2-5 prepared above was visually observed. The evaluation criteria for the appearance of the insulating layer were as follows: A: No foaming was observed on the surface of the insulating layer. B: Foaming was observed on the surface of the insulating layer.

[0078] In Table 2 below, the units of the values ​​in the rows of "Polyimide precursor solution" and "DIBP" are parts by mass. The data in the column No. 1-1 is listed for comparison, and the data in the column No. 1-1 in Table 1 above is listed except for the item "Appearance of insulating layer."

[0079]

[0080] It can be seen from Table 2 that the appearance of the insulating layer was good when resin compositions No. 1-1 and No. 2-1 to No. 2-3 were used, whereas the appearance of the insulating layer was poor when resin compositions No. 2-4 and No. 2-5 were used. This shows that the content of alkyl phthalate affects the appearance of the insulating layer.

[0081] Test Example 3 In Test Example 3, the influence of the difference in boiling point between the alkyl phthalate ester and the organic solvent and the difference in glass transition temperature of the polyimide precursor on the characteristics of the insulated wire was examined.

[0082] [No. 3-1 to No. 3-5] Resin compositions No. 3-1 to No. 3-5 were prepared in the same manner as No. 1-1, except that the types and amounts of each component were used as shown in Table 3 below. Then, insulated wires No. 3-1 to No. 3-5 were produced in the same manner as No. 1-1, except that the inlet temperatures of the heating furnaces were set as shown in Table 3 below.

[0083] <Evaluation> For the insulated wires No. 3-1 to No. 3-5 prepared above, the porosity was calculated, and the relative dielectric constant, breakdown voltage, and coating elongation were measured in the same manner as in <Test Example 1> above. Furthermore, the glass transition temperature of the polyimide was measured according to the following method. The results are shown in Table 3 below.

[0084] [Glass transition temperature] Each of the resin compositions No. 3-1 to No. 3-3 prepared above was applied to a glass plate as a thin film, and heated at 350°C for 1 hour to obtain a film-like test specimen. The glass transition temperature of the obtained test specimen was measured using a dynamic viscoelasticity measuring device (Seiko Instruments Inc.'s "DMS6100") under conditions of 1 Hz and a temperature increase rate of 10°C / min.

[0085] In Table 3 below, "acid anhydride" means "aromatic tetracarboxylic dianhydride." "Diamine" means "aromatic diamine." The units of values ​​in the "acid anhydride" and "diamine" rows are mol%, and "-" indicates that the corresponding component was not used. The units of values ​​in the "polyimide precursor solution," "DIBP," and "DEP" rows are parts by mass. The "-" in the "glass transition temperature [°C]" row indicates that no measurement was performed.

[0086]

[0087] Table 3 shows that when resin compositions No. 3-2 and No. 3-5 are used, insulating layers with higher porosity and lower dielectric constants can be formed compared to when resin compositions No. 3-1 and No. 3-4 are used, respectively. This shows that the difference in boiling point between the phthalic acid alkyl ester and the organic solvent affects porosity.

[0088] Furthermore, Table 3 shows that when resin composition No. 3-1 is used, an insulating layer having a higher porosity and a lower dielectric constant can be formed compared to when resin composition No. 3-3 is used. This shows that the glass transition temperature of the polyimide precursor affects the porosity.

[0089] Test Example 4 In Test Example 4, the influence on pore formation when an alkyl phthalate ester and particles containing a thermally decomposable resin were used in combination was tested.

[0090] [No. 4-1] (Preparation of Resin Composition) ODA as an aromatic diamine was dissolved in NMP. PMDA 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, obtaining a polyimide precursor solution containing NMP as the solvent (solids concentration: 28% by mass). To 100 parts by mass of the polyimide precursor solution, 6.2 parts by mass of DIBP and 4.8 parts by mass of thermally decomposable resin-containing particles were added to prepare Resin Composition No. 4-1. Core-shell particles with an average particle diameter of 3 μm, each having a core made of polymethyl methacrylate particles and a shell made of silicone, were used as the thermally decomposable resin-containing particles.

[0091] (Preparation of Insulated Wire) Insulated wire No. 4-1 was prepared in the same manner as insulated wire No. 1-1 described above.

[0092] [No. 4-2 to No. 4-8] Resin compositions No. 4-2 to No. 4-8 were prepared in the same manner as No. 4-1, except that the types and amounts of each component shown in Table 4 below were used, and insulated wires No. 4-2 to No. 4-8 were produced.

[0093] In Table 4 below, the units of the values ​​in the rows of "Polyimide precursor solution," "Phthalic acid alkyl ester," and "Thermal decomposable resin-containing particles" are parts by mass, and "-" in the row of "Phthalic acid alkyl ester" indicates that the corresponding component was not used.

[0094]

[0095] Table 4 shows that when resin compositions No. 4-1 to No. 4-7 are used, insulating layers with good appearance can be formed even when the porosity is as high as 20% by volume or more. Furthermore, it can be seen that similar porosity and performance can be achieved as when resin composition No. 4-8 is used. These results suggest that increasing the amount of alkyl phthalate, which is less expensive than the thermally decomposable resin-containing particles, and decreasing the amount of thermally decomposable resin-containing particles used will enable the cost of insulating layers with pores to be reduced.

Claims

1. a polyimide precursor which is a reaction product of an aromatic tetracarboxylic dianhydride and an aromatic diamine; an organic solvent; Alkyl phthalate esters with a boiling point of 290°C or higher A resin composition comprising:

2. 2. The resin composition according to claim 1, wherein the boiling point of the alkyl phthalate ester is 380°C or lower.

3. 2. The resin composition according to claim 1, wherein the alkyl phthalate is dipropyl phthalate, diisopropyl phthalate, or diisobutyl phthalate.

4. 2. The resin composition according to claim 1, wherein the content of the alkyl phthalate is 1 part by mass or more and 12 parts by mass or less per 100 parts by mass of the polyimide precursor and the organic solvent combined.

5. 2. The resin composition according to claim 1, wherein the organic solvent has a boiling point of 150°C or higher.

6. The resin composition according to claim 1, further comprising thermally decomposable resin-containing particles.

7. The resin composition according to claim 1 , which is used to form an insulating layer for an insulated wire.

8. A conductor; an insulating layer covering the conductor; Equipped with the insulating layer has a plurality of pores, An insulated wire, wherein the insulating layer is formed from the resin composition according to any one of claims 1 to 6.

9. The method for producing an insulated wire according to claim 8, applying the resin composition to an outer peripheral surface of the conductor; a step of heating the resin composition applied in the application step; A method for manufacturing an insulated wire comprising: