JP2018116850A - Insulation wire and manufacturing method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an insulation wire excellent in appearance, flexure processability and moisture heat degradation resistance of an insulation layer.SOLUTION: An insulation wire has a conductor and one or a plurality of insulation layers laminated on an outer peripheral side of the conductor, in which at least one layer of the insulation layers mainly contains polyimide derived from a polyimide precursor, which is a reaction product of aromatic tetracarboxylic acid dianhydride and aromatic diamine, and having calorie of crystal melting peak measured under a temperature rise condition at 20°C/min. by a differential scanning calorimeter of 5 J/g or less, the aromatic tetracarboxylic acid dianhydride contains biphenyltetracarboxylic acid dianhydride, and content of the biphenyltetracarboxylic acid dianhydride is 25 mol% to 95 mol% based on 100 mol% of the aromatic tetracarboxylic acid dianhydride. The aromatic tetracarboxylic acid dianhydride may further contain pyromellitic acid dianhydride.SELECTED DRAWING: None

Description

  The present invention relates to an insulated wire and a method for manufacturing the same.

  In an insulated wire used for a coil of a motor or the like, an insulating layer covering a conductor is required to have excellent insulation, adhesion to the conductor, heat resistance, mechanical strength, appearance, and the like. Examples of the synthetic resin used for forming the insulating layer include polyimide, polyamideimide, and polyesterimide.

  In addition, in an electric device having a high applied voltage, for example, a motor used at a high voltage, a high voltage is applied to an insulated wire constituting the electric device, and partial discharge (corona discharge) is likely to occur on the surface of the insulating layer. . When corona discharge occurs, local temperature rise and generation of ozone and the like are likely to be caused. As a result, the insulation layer of the insulated wire is deteriorated, thereby causing early dielectric breakdown and shortening the life of the electric device. Insulated wires to which a high voltage is applied are required to improve the corona discharge starting voltage for the above reasons, and for this purpose, it is known that reducing the dielectric constant of the insulating layer is effective.

  Furthermore, the insulated wire may be exposed to a humid heat environment. Under such an environment, the synthetic resin forming the insulating layer is hydrolyzed and its molecular weight is remarkably reduced. As a result, cracks or the like are generated, and the function as the insulating layer may be reduced. Therefore, the insulating layer of the insulated wire may be required to have a performance (moisture and heat resistance) that suppresses functional degradation in the wet heat environment.

  Furthermore, when using an insulated wire as a coil, the insulated wire is bent to increase the space factor of the coil. Specifically, for example, after forming the coil by winding the insulated wire, the coil is inserted into the slot, or the insulated wire deformed in advance is welded to form the coil. The insulating layer of an insulated wire used in such applications is required to have bending workability that suppresses the occurrence of cracks, pinholes, voids, and the like that cause electrical characteristics to be lowered when bent.

  Polyimide is particularly excellent in heat resistance, low dielectric constant and mechanical strength among the synthetic resins used in the insulation layer of insulated wires, and good when certain raw materials and manufacturing conditions are applied. Therefore, it is used for an insulating layer of an insulated wire used at a high voltage. For example, JP2013-253124A discloses a resin containing a polyimide precursor which is a reaction product of an aromatic diamine and an aromatic tetracarboxylic dianhydride and has a specific range of imide groups after imidization. It is described that by forming an insulating layer using a varnish, an insulated wire that is excellent in heat resistance and crazing resistance and hardly corona discharge can be obtained.

JP 2013-253124 A

  However, since polyimide is a material that may be hydrolyzed when exposed to a humid heat environment for a long time, the insulating layer provided in the conventional insulated wire has room for improvement in resistance to heat and moisture degradation.

  This invention is made | formed based on the above situations, and it aims at providing the insulated wire which is excellent in the external appearance property of an insulating layer, bending workability, and heat-and-moisture resistance, and its manufacturing method.

  An insulated wire according to an aspect of the present invention made to solve the above problems is an insulated wire comprising a conductor and one or a plurality of insulating layers laminated on the outer peripheral side of the conductor, wherein the insulating layer At least one layer is derived from a polyimide precursor which is a reaction product of an aromatic tetracarboxylic dianhydride and an aromatic diamine, and is measured with a differential scanning calorimeter at a temperature rising condition of 20 ° C./min. The main component is a polyimide having a crystal melting peak calorie of 5 J / g or less, and the aromatic tetracarboxylic dianhydride contains biphenyltetracarboxylic dianhydride, and the aromatic tetracarboxylic dianhydride is 100 mol%. The content of biphenyltetracarboxylic dianhydride is 25 mol% or more and 95 mol% or less.

  An insulated wire manufacturing method according to another aspect of the present invention, which has been made to solve the above problems, includes a conductor and one or a plurality of insulating layers laminated on the outer peripheral side of the conductor. A coating step of coating a resin varnish on the outer peripheral side of the conductor, and a heating step of heating the coated resin varnish, wherein the resin varnish is an aromatic tetracarboxylic dianhydride and Containing a polyimide precursor which is a reaction product of an aromatic diamine, wherein the aromatic tetracarboxylic dianhydride includes biphenyltetracarboxylic dianhydride, and biphenyl with respect to 100 mol% of the aromatic tetracarboxylic dianhydride. The tetracarboxylic dianhydride content is 25 mol% or more and 95 mol% or less, and the heating step is performed at a temperature increase of 20 ° C./min from the polyimide precursor by a differential scanning calorimeter. Heat of crystal melting peak measured in matter to form a polyimide or less 5 J / g.

  The insulated wire and the method for manufacturing the insulated wire according to one embodiment of the present invention can provide an insulated wire that is excellent in appearance, bending workability, and wet heat resistance.

[Description of Embodiment of the Present Invention]
An insulated wire according to an aspect of the present invention is an insulated wire including a conductor and one or more insulating layers stacked on the outer peripheral side of the conductor, and at least one of the insulating layers is aromatic. The calorific value of the crystal melting peak derived from a polyimide precursor which is a reaction product of tetracarboxylic dianhydride and aromatic diamine and measured with a differential scanning calorimeter at 20 ° C./min is 5 J / g. The following polyimide is a main component, and the aromatic tetracarboxylic dianhydride includes biphenyltetracarboxylic dianhydride (BPDA), and biphenyltetracarboxylic dianhydride with respect to 100 mol% of the aromatic tetracarboxylic dianhydride. The anhydride content is 25 mol% or more and 95 mol% or less.

  The said insulated wire is excellent in the external appearance property of an insulating layer, bending workability, and heat-and-moisture-proof deterioration property by having the said structure. The reason why the insulated wire has the above-described configuration provides the above-mentioned effect is not clear, but is presumed as follows, for example. That is, at least one of the one or more insulating layers of the insulated wire includes, as a main component, polyimide derived from a polyimide precursor using a specific amount of BPDA that is difficult to be hydrolyzed as a raw material. Since this polyimide contains a specific amount of a structure that is difficult to be hydrolyzed derived from BPDA, it is difficult to hydrolyze even in a moist heat environment. Therefore, it is considered that the heat resistance of the insulating layer is improved. Moreover, the said insulated wire is excellent in the bending workability and external appearance property of an insulating layer for the reason mentioned later by making the calorie | heat amount of the crystal melting peak of the said polyimide below the said upper limit, ie, suppressing the crystallization of a polyimide. Here, although the amount of heat at the crystal melting peak of the polyimide is determined by the structure of the polyimide and the formation conditions of the insulating layer, the polyimide containing an excessive structure derived from BPDA promotes packing between molecules due to the biphenyl structure of BPDA. Therefore, it is easy to crystallize, and it is difficult to make the heat quantity of the crystal melting peak below the upper limit only by controlling the formation conditions of the insulating layer. Therefore, the insulated wire easily and surely has a crystal melting peak by making the content of BPDA in the raw material of the polyimide precursor not more than the above upper limit, that is, making the structure derived from BPDA contained in the polyimide not more than a certain value. The amount of heat can be made below the above upper limit.

  It is considered that the reason why the insulated wire is excellent in the bending workability and appearance of the insulating layer by setting the heat amount of the crystal melting peak to the upper limit or less is as follows. That is, as a method of forming an insulating layer containing polyimide as a main component, a coating step of coating a resin varnish containing a polyimide precursor (polyamic acid) on the outer peripheral side of a conductor, and heating the obtained coating film A heating method is generally provided. In the above method, only a relatively thin insulating layer of about several μm can be formed in a single coating step and heating step, so that the normal coating step and heating step are repeated until a predetermined thickness (about several tens of μm) is reached. A plurality of insulating layers are sequentially stacked. In the second and subsequent coating steps, when the solvent contained in the resin varnish slightly dissolves the polyimide contained in the base layer (insulating layer formed in the previous coating step and heating step), It is considered that the adhesion between each layer is improved because the base layer and the newly laminated insulating layer are easily adapted. Here, it is considered that the polyimide having a high degree of crystallinity tends to have excessively high solvent resistance because the solvent hardly penetrates into the crystal part.

  The insulated wire can moderately reduce its solvent resistance by setting the amount of heat of the crystal melting peak of the polyimide to the upper limit or less, and as a result, adhesion between the layers of the insulating layer due to dissolution of the polyimide described above. The power improvement effect can be demonstrated. As a result, when the insulated wire is subjected to a large deformation in the insulating layer by bending or the like, it can be suppressed that each layer of the insulating layer is peeled off and the insulating property is deteriorated. It is considered excellent. In addition, a polyimide having a high degree of crystallinity may become cloudy due to light scattering generated at the interface between the crystal part and the amorphous part. The said insulated wire can suppress the said cloudiness by making the calorie | heat amount of the crystal melting peak of the said polyimide below the said upper limit, As a result, it is thought that it is excellent in the external appearance of an insulating layer. Furthermore, the said insulated wire can improve familiarity with a solvent by moderately reducing the imide group density | concentration of the said polyimide, and suppressing the polarity by making content of the said BPDA more than the said minimum. Thereby, the said insulated wire can improve the adhesive force between each layer of the insulating layer resulting from melt | dissolution of the above-mentioned polyimide, As a result, can exhibit the more excellent bending workability. Here, the “main component” is a component having the largest content, for example, a component having a content of 50% by mass or more.

  “The amount of heat of crystal melting peak [J / g]” is a value calculated by the following method. First, DSC measurement (differential scanning calorimetry) is performed at a heating rate of 20 ° C./min using an insulating layer collected from an insulated wire as a sample. Based on the DSC measurement result, the amount of heat of crystal melting [J / g] is determined from the endothermic peak area accompanying the crystal melting of polyimide. In addition, when the endothermic peak accompanying crystal melting is not observed, the heat of crystal melting shall be 0 J / g. Even when the insulating layer contains a synthetic resin other than polyimide, the temperature at which the endothermic peak is detected is unique to each synthetic resin type, and therefore the amount of heat of the crystal melting peak is determined by the method described above. It can be measured.

  The aromatic tetracarboxylic dianhydride preferably further contains pyromellitic dianhydride. In this case, the content of pyromellitic dianhydride with respect to 100 mol% of the aromatic tetracarboxylic dianhydride is as follows: 5 mol% or more and 75 mol% or less are preferable. Thus, since the aromatic tetracarboxylic dianhydride contains a specific amount of pyromellitic dianhydride, a rigid structure can be introduced into the polyimide, so that the heat resistance of the insulating layer can be improved.

  The aromatic diamine may contain diaminodiphenyl ether. Thus, the toughness of an insulating layer can be improved because the aromatic diamine contains diaminodiphenyl ether.

  The manufacturing method of the insulated wire which concerns on another aspect of this invention is a manufacturing method of the insulated wire provided with a conductor and the 1 or several insulating layer laminated | stacked on the outer peripheral side of this conductor, Comprising: The outer peripheral side of the said conductor A coating step of coating the resin varnish and a heating step of heating the coated resin varnish, wherein the resin varnish is a reaction product of an aromatic tetracarboxylic dianhydride and an aromatic diamine. A polyimide precursor is contained, the aromatic tetracarboxylic dianhydride contains biphenyltetracarboxylic dianhydride, and the content of biphenyltetracarboxylic dianhydride with respect to 100 mol% of the aromatic tetracarboxylic dianhydride Is 25 mol% or more and 95 mol% or less, and the crystal melting peak measured at 20 ° C./min with a differential scanning calorimeter from the polyimide precursor in the heating step. Heat of forming a polyimide or less 5 J / g.

  The method for producing the insulated wire uses a resin varnish containing a polyimide precursor made of BPDA as a raw material in the coating step, so that hydrolyzability derived from BPDA is used as the main component of the insulating layer to be formed. Can be introduced in a specific amount, and as a result, the wet heat resistance of the insulating layer can be improved. Moreover, the manufacturing method of the said insulated wire originates in the high crystallinity degree of a polyimide by forming the heat quantity of the said crystal melting peak below the said upper limit by the imidation of the said polyimide precursor at the said heating process. The appearance of the insulating layer can be improved by suppressing white turbidity. Furthermore, the interlayer adhesion of the insulating layer is improved by appropriately reducing the solvent resistance of polyimide, and as a result, the bending workability of the insulating layer can be improved. Furthermore, in the method for producing the insulated wire, the content of BPDA used as a raw material of the polyimide precursor is set to the upper limit or less, and the structure derived from BPDA is not introduced into the polyimide more than necessary, whereby the crystal of the polyimide is crystallized. The amount of heat at the melting peak can be easily and reliably made not more than the above upper limit.

[Details of the embodiment of the present invention]
Hereinafter, an insulated wire and a manufacturing method thereof according to one embodiment of the present invention will be described.

<Insulated wire>
The insulated wire includes a conductor and one or a plurality of insulating layers stacked on the outer peripheral side of the conductor. The said insulated wire is excellent in the external appearance property of an insulating layer, bending workability, and heat-and-moisture resistance.

[conductor]
As a material for the conductor of the insulated wire, a metal having high conductivity and high mechanical strength is preferable. Examples of such metals include copper, copper alloys, aluminum, nickel, silver, soft iron, steel, and stainless steel. The conductor of the insulated wire is a material in which these metals are formed in a linear shape, or a multilayer structure in which such a linear material is coated with another metal, such as a nickel-coated copper wire, a silver-coated copper wire, A copper covering aluminum wire, a copper covering steel wire, etc. can be used.

The lower limit of the average cross-sectional area of the conductor of the insulated wire, preferably 0.01 mm ^2, 0.1 mm ² is more preferable. In contrast, the upper limit of the average cross-sectional area of the conductor is preferably 10 mm ^2, 5 mm ² is more preferable. When the average cross-sectional area of the conductor is smaller than the lower limit, the resistance value may increase. Conversely, if the average cross-sectional area of the conductor exceeds the upper limit, the insulating layer must be formed thick in order to sufficiently reduce the dielectric constant, which may unnecessarily increase the diameter of the insulated wire. .

[Insulation layer]
One or a plurality of insulating layers of the insulated wire are laminated on the outer peripheral side of the conductor. When the insulated wire includes a plurality of insulating layers, the insulating layers are sequentially stacked concentrically on the outer peripheral side of the conductor in a sectional view. In this case, the average thickness of each insulating layer can be, for example, 1 μm or more and 5 μm or less. The average total thickness of the plurality of insulating layers can be, for example, 10 μm or more and 200 μm or less. Furthermore, the total number of insulating layers can be, for example, 2 or more and 200 or less.

  At least one of the plurality of insulating layers is derived from a polyimide precursor (polyamic acid) which is a reaction product of an aromatic tetracarboxylic dianhydride and an aromatic diamine, and the calorific value of the crystal melting peak is 5 J. The main component is polyimide which is not more than / g.

  The upper limit of the calorific value of the crystal melting peak of the polyimide is preferably 3 J / g. When the heat amount of the crystal melting peak of the polyimide exceeds the upper limit, the appearance and bending workability of the insulating layer of the insulated wire may be deteriorated. The amount of heat at the crystal melting peak of the polyimide is most preferably 0 J / g.

(Polyimide precursor)
The polyimide precursor used as the raw material of the polyimide is a polymer that forms a polyimide by imidization, and is a reaction product obtained by polymerization of an aromatic tetracarboxylic dianhydride and an aromatic diamine. That is, the polyimide precursor is made from aromatic tetracarboxylic dianhydride and aromatic diamine as raw materials.

  The lower limit of the weight average molecular weight of the polyimide precursor is preferably 10,000, and more preferably 15,000. On the other hand, the upper limit of the weight average molecular weight is preferably 180,000, and more preferably 130,000. By setting the weight average molecular weight of the polyimide precursor to the above lower limit or more, it is possible to form a polyimide that has excellent extensibility and can easily maintain a constant molecular weight even if hydrolysis occurs. It is considered that the heat resistance and wet heat resistance can be further improved. Moreover, the extreme viscosity increase of the resin varnish used for manufacture of the said insulated wire can be suppressed, and applicability | paintability can be improved by making the weight average molecular weight of the said polyimide precursor below the said upper limit. Moreover, in the said resin varnish, it becomes easy to improve the density | concentration of a polyimide precursor, maintaining the outstanding applicability | paintability. Here, “weight average molecular weight” refers to gel permeation in accordance with JIS-K7252-1: 2008 “Plastics—How to determine the average molecular weight and molecular weight distribution of polymers by size exclusion chromatography—Part 1: General rules”. Refers to a value measured using chromatography (GPC).

  As the molar ratio of aromatic tetracarboxylic dianhydride and aromatic diamine used as the raw material of the polyimide precursor (aromatic tetracarboxylic dianhydride / aromatic diamine), from the viewpoint of easy synthesis of the polyimide precursor For example, it can be set to 95/105 or more and 105/95 or less.

(Aromatic tetracarboxylic dianhydride)
The aromatic tetracarboxylic dianhydride used as a raw material for the polyimide precursor contains BPDA. Examples of BPDA include 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride (3,3 ′, 4,4′-BDPA), 2,3,3 ′, 4′-biphenyltetracarboxylic acid Anhydrides (2,3,3 ′, 4′-BDPA), 2,2 ′, 3,3′-biphenyltetracarboxylic dianhydrides (2,2 ′, 3,3′-BDPA) and the like Of these, 3,3 ′, 4,4′-BDPA is preferred.

  The lower limit of the BPDA content relative to 100 mol% of the aromatic tetracarboxylic dianhydride is 25 mol%, preferably 35 mol%, and more preferably 55 mol%. On the other hand, the upper limit of the BPDA content is 95 mol%, preferably 92 mol%. By setting the content of the BPDA within the above range, a structure derived from BPDA can be appropriately introduced into the polyimide that is the main component of the insulating layer, and as a result, appearance, bending workability, and resistance to moist heat degradation. Can be improved in a well-balanced manner.

  Of the aromatic tetracarboxylic dianhydrides used as raw materials for the polyimide precursor, examples of aromatic tetracarboxylic dianhydrides other than BPDA include pyromellitic dianhydride (PMDA), 3, 3 ′, 4 , 4′-benzophenone tetracarboxylic dianhydride (BTDA), 4,4′-oxydiphthalic dianhydride, 2,2 ′, 3,3′-benzophenone tetracarboxylic dianhydride, 2,2-bis ( 3,4-dicarboxyphenyl) propane dianhydride, 2,2-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-dicarboxyphene) ) Methane dianhydride, bis (3,4-dicarboxyphenyl) sulfone dianhydride, bis (3,4-dicarboxyphenyl) ether dianhydride, 1,2,5,6-naphthalene tetracarboxylic acid Anhydrides, 2,3,6,7-naphthalenetetracarboxylic dianhydride and the like can be mentioned. The other aromatic tetracarboxylic dianhydrides may be used alone or in combination of two or more.

  The aromatic tetracarboxylic dianhydride used as a raw material for the polyimide precursor preferably further includes PMDA, BTDA, or a combination thereof. In particular, by using PMDA having a rigid structure as a raw material for the polyimide precursor, a rigid structure can be introduced into the polyimide after imidization, so that the heat resistance of the insulating layer can be improved.

  As a minimum of content of PMDA with respect to 100 mol% of aromatic tetracarboxylic dianhydrides used as a raw material of the above-mentioned polyimide precursor, 5 mol% is preferred and 8 mol% is more preferred. On the other hand, the upper limit of the PMDA content is preferably 75 mol%, more preferably 65 mol%, still more preferably 45 mol%, and particularly preferably 20 mol%. When the content of PMDA is smaller than the lower limit, the heat resistance of the insulating layer may be insufficient. On the other hand, when the content of the PMDA exceeds the upper limit, a structure derived from BPDA cannot be sufficiently introduced into the polyimide which is the main component of the insulating layer, and as a result, the heat and heat resistance of the insulating layer is deteriorated. May decrease.

  Although content of BTDA with respect to 100 mol% of aromatic tetracarboxylic dianhydride used as a raw material of the said polyimide precursor is not specifically limited, For example, it can be 5 mol% or more and 20 mol% or less.

(Aromatic diamine)
Examples of the aromatic diamine used as a raw material for the polyimide precursor include 4,4'-diaminodiphenyl ether (4,4'-ODA), 3,4'-diaminodiphenyl ether (3,4'-ODA), and 3,3. Diaminodiphenyl ether (ODA) such as' -diaminodiphenyl ether (3,3'-ODA), 2,4'-diaminodiphenyl ether (2,4'-ODA), 2,2'-diaminodiphenyl ether (2,2'-ODA) ), 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'-diaminodiphenyl sulfide, 3,4'-diaminodiphenyl sulfide, 3,3'-diaminodiphenyl sulfide, 2,4'-diaminodiphenyl sulfide, 2,2'-diaminodiphenyl sulfide, paraphenylenediamine (PPD), Metaphenylenediamine, p-xylylenediamine, m-xylylenediamine, 2,2′-dimethyl-4,4′-diaminobiphenyl, 1,5-diaminonaphthalene, 4,4′-benzophenonediamine, 3,3 ′ -Dimethyl-4,4'-diaminodiphenylmeta , 3,3 ', 5,5'-tetramethyl-4,4'-diaminodiphenylmethane and the like. These aromatic diamines may be used alone or in combination of two or more.

  The aromatic diamine used as the raw material for the polyimide precursor preferably contains ODA, BAPP, or a combination thereof. In particular, the toughness of the insulating layer can be improved by using ODA as a raw material for the polyimide precursor. As the ODA, 4,4′-ODA is preferable.

  As a minimum of content of ODA with respect to 100 mol% of said aromatic diamine, 50 mol% is preferable, 90 mol% is more preferable, 99 mol% is further more preferable. Thus, the toughness of an insulating layer can be improved more by making content of the said ODA more than the said minimum. Moreover, as content of the said ODA, 100 mol% is especially preferable. Moreover, as content of BAPP with respect to 100 mol% of said aromatic diamine, it can be 0 mol% or more and 50 mol% or less, for example.

  The polyimide precursor may be a reaction product obtained by polymerization of aromatic tetracarboxylic dianhydride and aromatic diamine and other raw materials. Examples of the other raw materials include aliphatic tetracarboxylic dianhydrides such as 1,2,4,5-cyclohexanetetracarboxylic dianhydride, and aliphatic diamines such as hexamethylenediamine.

  The polyimide precursor is preferably a reaction product obtained using substantially only BPDA, PMDA and ODA as raw materials. That is, it is preferable that the polyimide which is the main component of the insulating layer of the insulated wire is formed only by a structure substantially derived from BPDA, PMDA, and ODA. Specifically, the lower limit of the total ratio of BPDA, PMDA and ODA in all raw materials of the polyimide precursor is preferably 95 mol%, more preferably 99 mol%. The total ratio is most preferably 100 mol%.

  In addition, although it is preferable that all the insulating layers have the above-mentioned polyimide as a main component in the plurality of insulating layers, the main component of some of the insulating layers is a polyimide other than the above-described polyimide or other synthetic resin. Also good. As said other synthetic resin, a polyamideimide, a polyesterimide, a polyurethane, a polyetherimide etc. can be used, for example.

(Method for synthesizing polyimide precursor)
The polyimide precursor can be obtained by the polymerization reaction of the aromatic tetracarboxylic dianhydride and the aromatic diamine. The method for the polymerization reaction can be the same as the synthesis of a conventional polyimide precursor. Specific examples of the polymerization reaction include a method in which an aromatic tetracarboxylic dianhydride and an aromatic diamine are mixed in an organic solvent and the mixture is heated. By this method, an aromatic tetracarboxylic dianhydride and an aromatic diamine are polymerized, and a solution in which a polyimide precursor is dissolved in an organic solvent can be obtained.

  The reaction conditions for the above polymerization may be appropriately set depending on the raw materials used. For example, the reaction temperature may be 10 ° C. or more and 100 ° C. or less, and the reaction time may be 0.5 hours or more and 24 hours or less.

  The molar ratio (aromatic tetracarboxylic dianhydride / aromatic diamine) between the aromatic tetracarboxylic dianhydride and the aromatic diamine used for the polymerization is 100/100 from the viewpoint of allowing the polymerization reaction to proceed efficiently. The closer it is to the better. The molar ratio can be, for example, 95/105 or more and 105/95 or less.

  Examples of the organic solvent used for the polymerization include aprotic polar organic solvents such as N-methyl-2-pyrrolidone (NMP), N, N-dimethylformamide, N, N-dimethylacetamide, dimethyl sulfoxide, and γ-butyrolactone. Can be used. These organic solvents may be used alone or in combination of two or more. Here, the “aprotic polar organic solvent” refers to a polar organic solvent having no proton releasing group.

  The usage-amount of the said organic solvent will not be restrict | limited especially if aromatic tetracarboxylic dianhydride and aromatic diamine can be uniformly disperse | distributed. As the usage-amount of the said organic solvent, it can be 100 mass parts or more and 1,000 mass parts or less with respect to a total of 100 mass parts of aromatic tetracarboxylic dianhydride and aromatic diamine, for example.

[Other layers]
In the insulated wire, another layer may be further laminated on the outer peripheral side of one or a plurality of insulating layers. As said other layer, a surface lubrication layer etc. are mentioned, for example.

<Insulated wire manufacturing method>
Next, a method for manufacturing the insulated wire will be described. The method for manufacturing an insulated wire includes a coating process for coating a resin varnish on the outer peripheral side of a conductor, and a heating process for heating the coated resin varnish. The resin varnish contains a polyimide precursor that is a reaction product of an aromatic tetracarboxylic dianhydride and an aromatic diamine. Moreover, the said heating process forms the polyimide whose calorie | heat amount of the crystal melting peak measured on the temperature rising condition of 20 degrees C / min with a differential scanning calorimeter from the said polyimide precursor is 5 J / g or less. It is preferable that the manufacturing method of the said insulated wire repeats the said coating process and a heating process. According to the method for manufacturing an insulated wire, the insulated wire can be easily and reliably manufactured. Hereinafter, after describing the resin varnish used in the coating step, each step will be described.

[Resin varnish]
The resin varnish contains a polyimide precursor. The resin varnish usually further contains an organic solvent. As the polyimide precursor contained in the resin varnish, since the polyimide precursor described in the insulated wire can be used, description thereof is omitted.

(Organic solvent)
The organic solvent used for the resin varnish improves the applicability of the resin varnish. Moreover, when the resin varnish containing the organic solvent forms a plurality of insulating layers by repeating the coating process and the heating process on the peripheral surface side of the conductor, the resin varnish is used in the second and subsequent coating processes. Since the organic solvent slightly dissolves the polyimide of the base layer (insulating layer formed in the previous coating step and heating step), the adhesion between the layers of the plurality of insulating layers to be formed can be improved.

  As the organic solvent, an aprotic polar organic solvent is preferable. Since the polyimide precursor is highly soluble in an aprotic polar organic solvent, the polyimide precursor is used even when the concentration of the polyimide precursor in the resin varnish is increased by using an aprotic polar organic solvent as the organic solvent. The precursor can be surely dissolved. In addition, by using an aprotic polar organic solvent as the organic solvent, it becomes easier to dissolve the polyimide of the base layer formed by the organic solvent in the resin varnish in the second and subsequent coating steps. The adhesion between each of the plurality of insulating layers can be further improved.

  Examples of the aprotic polar organic solvent include N-methyl-2-pyrrolidone (NMP), N, N-dimethylformamide, N, N-, from the viewpoint of improving solubility of the polyimide precursor and improving adhesion between insulating layers. Dimethylacetamide, dimethylsulfoxide, γ-butyrolactone and combinations thereof are preferred, and NMP is more preferred.

  As the organic solvent, the organic solvent used for the polymerization reaction of the polyimide precursor described above may be used as it is, and after obtaining the polyimide precursor, it may be added separately. From the viewpoint of workability, the polyimide precursor The organic solvent used in the polymerization reaction is preferably used as it is. As content of the organic solvent in the said resin varnish, it can be set as the range of 100 mass parts or more and 1,000 mass parts or less with respect to 100 mass parts of polyimide precursors, for example.

(Other ingredients)
In addition to the components described above, the resin varnish may contain various additives such as pigments, dyes, inorganic or organic fillers, lubricants, adhesion improvers, reactive low molecules, and the like. Among these, by containing a melamine compound as an adhesion improver, the adhesion between the formed insulating layer and the conductor can be improved. Furthermore, the said resin varnish may contain other resin in the range which does not impair the meaning of this invention. When the above-mentioned component is contained in the resin varnish, the content of the above-described component in the resin varnish can be, for example, 0.5 parts by mass or more and 30 parts by mass or less with respect to 100 parts by mass of the polyimide precursor. .

(Production method of resin varnish)
Examples of the method for producing the resin varnish include a method in which a solution in which the polyimide precursor described in the method for synthesizing a polyimide precursor is dissolved in an organic solvent is used as it is as the resin varnish. Moreover, as a manufacturing method of the said resin varnish, after refine | purifying a polyimide precursor from the solution which the said polyimide precursor melt | dissolved in the organic solvent, for example, the obtained purified polyimide precursor and other components, such as an organic solvent, are mixed. The method of doing is also mentioned.

[Coating process]
In this step, a resin varnish described later is applied to the outer peripheral side of the conductor. Although it does not specifically limit as a coating method, For example, the method using the coating apparatus provided with the resin varnish tank which stored the said resin varnish, and the coating die is mentioned. According to this coating apparatus, after the conductor passes through the resin varnish tank, the resin varnish adheres to the outer peripheral surface of the conductor, and then passes through the coating die so that the resin varnish has a uniform thickness on the outer peripheral surface of the conductor. Now it is coated. In this step, the resin varnish may be applied directly to the outer peripheral surface of the conductor, and an intermediate layer such as an adhesion improving layer is provided in advance on the outer peripheral surface of the conductor, and the resin is applied to the outer peripheral side of the intermediate layer. Varnish may be applied.

  In addition, when repeating the said coating process and a heating process with the manufacturing method of the said insulated wire, you may use resin varnishes other than the said resin varnish in some coating processes among several coating processes.

[Heating process]
In this step, the resin varnish coated on the conductor is heated by, for example, a method of running the conductor coated with the resin varnish in a heating furnace. By this heating step, the polyimide precursor contained in the resin varnish is imidized and volatile components such as an organic solvent are removed, and an insulating layer as a baking layer is laminated on the outer peripheral side of the conductor. It does not specifically limit as a heating method, For example, it can carry out by conventionally well-known methods, such as hot air heating, infrared heating, high frequency heating. As heating temperature, it can be 350 degreeC or more and 500 degrees C or less, for example. The heating time can be, for example, 5 seconds or more and 100 seconds or less. When the conductor coated with the resin varnish is heated by running in a heating furnace, the set temperature in the heating furnace is regarded as the heating temperature, and the distance from the inlet to the outlet of the heating furnace is defined as the conductor linear velocity. The value divided by is regarded as the heating time.

  By heating in this step, a polyimide having a crystal melting peak calorific value of 5 J / g or less is measured from the above polyimide precursor with a differential scanning calorimeter at a temperature rising condition of 20 ° C./min. Here, the crystal structure of the polyimide may already be included in a certain proportion when the polyimide is formed by imidation of the polyimide precursor, and is formed when the formed high temperature polyimide is cooled. There is also a case. Therefore, in this step, the following method (A) to method (C) may be employed in order to ensure that the heat amount of the crystal melting peak is 5 J / g or less. That is, in this step, a method (A) in which the heating temperature is relatively high at 400 ° C. or more and 500 ° C. or less in order to melt the crystal structure already contained in a certain proportion at the stage where the polyimide is formed, and the heating time It is preferable to adopt a method (B) or the like in which the time is relatively long as 30 seconds or more and 100 seconds or less. In this step, in order to suppress the formation of a crystal structure when the above-described high-temperature polyimide is cooled, a method (C) for rapidly cooling the insulating layer and the conductor immediately after heating may be employed. Examples of the rapid cooling method include a method of blowing air to the insulating layer and the conductor, and a method of exposing the insulating layer and the conductor to a low temperature (for example, 0 ° C. or more and 15 ° C. or less). However, since the ease of crystallization of polyimide depends on the structure of the polyimide precursor, the above-described method (A) to method (C) are not necessarily required.

  When repeating the said coating process and a heating process with the manufacturing method of the said insulated wire, as a frequency | count of repeating the said coating process and a heating process, it can be 2 times or more and 200 times or less, for example.

[Other Embodiments]
The disclosed embodiments are to be considered in all respects as illustrative and not restrictive. The scope of the present invention is not limited to the configuration of the embodiment described above, but is defined by the scope of the claims, and is intended to include all modifications within the meaning and scope equivalent to the scope of the claims. The

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples.

  In this example, the calorific value of the crystal melting peak of polyimide was measured using a differential scanning calorimeter (“DSC7020” manufactured by Seiko Instruments Inc.).

<Preparation of resin varnish>
[Preparation of resin varnish V1]
After 100 mol% of 4,4′-ODA was dissolved in N-methyl-2-pyrrolidone, 10 mol% of PMDA and 90 mol% of 3,3 ′, 4,4′-BPDA were added to the resulting solution, and a nitrogen atmosphere was added. Stir with. Then, after making it react at 80 degreeC for 3 hours, stirring, the resin varnish V1 in which the polyimide precursor was melt | dissolving in N-methyl-2-pyrrolidone as an organic solvent was prepared. The polyimide precursor concentration in the resin varnish V1 was 30% by mass.

[Preparation of resin varnishes V2 to V8]
Resin varnishes V2 to V5 and V8 were prepared in the same manner as in the preparation of the resin varnish V1, except that the types and amounts used of the raw materials were as shown in Table 1. Moreover, it was the same as that of preparation of resin varnish V1 except having made the kind and usage-amount of a raw material as shown in Table 1, and having made reaction temperature into 50 degreeC for 4 hours in order to suppress the gelation by the usage-amount increase of PMDA. Resin varnishes V6 and V7 were prepared.

<Manufacture of insulated wires>
[Insulated wire No. Production of 1]
A round wire having an average diameter of 1 mm mainly composed of copper was prepared as a conductor. The step of coating the resin varnish V1 on the outer peripheral surface of the conductor and the step of heating the conductor coated with the resin varnish in a heating furnace at a heating temperature of 400 ° C. for a heating time of 30 seconds are repeated 10 times. Thus, an insulated wire No. provided with the conductor and an insulating layer having an average thickness of 35 μm laminated on the outer peripheral surface of the conductor. 1 was obtained. Insulated wire No. When the insulating layer was sampled from 1 and subjected to DSC measurement, the heat of crystal fusion of the main component polyimide was 0.0 J / g.

[Insulated wire No. Production of 2-9]
Insulated wire No. 1 was used except that the resin varnish used and the set temperature of the heating furnace in the heating step were as shown in Table 1. 1 and the insulated wire No. 2-9 were produced. Table 1 shows the insulated wire No. measured by DSC. The crystal melting heat amount of polyimide which is the main component of 2 to 9 insulating layers is also shown.

<Evaluation>
Insulated wire No. 1-9 were used to evaluate the heat and humidity resistance, bending workability and appearance of the insulating layer. The evaluation results are shown in Table 1.

[Heat and heat resistance]
The wet heat resistance of the insulating layer is determined by performing wet heat treatment under the conditions of a temperature of 85 ° C., a relative of 95% and 750 hours while the insulated wire is stretched 10% in the longitudinal direction, and visually observing the insulated wire after the treatment. The case where no crack was observed on the surface was “A (good)”, and the case where a crack was observed on the surface was “B (not good)”.

[Bending workability]
Bending workability of the insulating layer is determined by “A (good)” when the insulated wire is bent at 90 ° and held in that state for 10 seconds, and then the insulating layer at the bent portion is visually checked and no delamination is confirmed. The case where delamination was confirmed was judged as “B (not good)”.

[Appearance]
The appearance of the insulating layer is determined by visually observing the appearance of the insulating layer of the insulated wire, when white turbidity, color unevenness, etc. occurs, when it is “B (not good)”, when no white turbidity, color unevenness, etc. occurs. It was judged as “A (good)”.

  As is apparent from Table 1, No1 and No.1. The insulation layer of the insulated wires of 3 to 5 is derived from a polyimide precursor in which the main component polyimide is a specific amount of BPDA as a raw material, and the heat amount of the crystal melting peak is below a certain level. Workability and wet heat resistance were excellent. On the other hand, no. 2 and no. The insulation layer of the insulated wires of 6 to 9 has the appearance of the insulation layer formed, the bending workability and the amount of heat of the BPDA is too small, the heat of the crystal melting peak is too high, or both. Any of the resistance to wet heat degradation was insufficient.

The insulated wire and the method for manufacturing the insulated wire according to one embodiment of the present invention can provide an insulated wire that is excellent in appearance, bending workability, and wet heat resistance.

Claims (4)

Conductors,
1 or a plurality of insulating layers laminated on the outer peripheral side of the conductor,
At least one of the insulating layers is derived from a polyimide precursor which is a reaction product of an aromatic tetracarboxylic dianhydride and an aromatic diamine, and at a temperature rising condition of 20 ° C./min with a differential scanning calorimeter. The main component is a polyimide whose calorie of the measured crystal melting peak is 5 J / g or less,
The aromatic tetracarboxylic dianhydride includes biphenyltetracarboxylic dianhydride,
An insulated wire in which the content of biphenyltetracarboxylic dianhydride is 25 mol% or more and 95 mol% or less with respect to 100 mol% of the aromatic tetracarboxylic dianhydride. The aromatic tetracarboxylic dianhydride further comprises pyromellitic dianhydride,
The insulated wire according to claim 1, wherein the content of pyromellitic dianhydride with respect to 100 mol% of the aromatic tetracarboxylic dianhydride is 5 mol% or more and 75 mol% or less.   The insulated wire according to claim 1 or 2, wherein the aromatic diamine contains diaminodiphenyl ether. A method for producing an insulated wire comprising a conductor and one or more insulating layers laminated on the outer peripheral side of the conductor,
A coating step of coating a resin varnish on the outer peripheral side of the conductor;
A heating step of heating the coated resin varnish,
The resin varnish contains a polyimide precursor that is a reaction product of an aromatic tetracarboxylic dianhydride and an aromatic diamine,
The aromatic tetracarboxylic dianhydride includes biphenyltetracarboxylic dianhydride,
The content of biphenyltetracarboxylic dianhydride with respect to 100 mol% of the aromatic tetracarboxylic dianhydride is 25 mol% or more and 95 mol% or less,
The manufacturing method of the insulated wire which forms the polyimide whose calorie | heat amount of the crystal melting peak measured on the temperature rising condition of 20 degree-C / min with the differential scanning calorimeter from the said polyimide precursor at the said heating process is 5 J / g or less.