CN110933949A - Resin varnish, insulated wire, and method for producing insulated wire - Google Patents
Resin varnish, insulated wire, and method for producing insulated wire Download PDFInfo
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- CN110933949A CN110933949A CN201880003677.7A CN201880003677A CN110933949A CN 110933949 A CN110933949 A CN 110933949A CN 201880003677 A CN201880003677 A CN 201880003677A CN 110933949 A CN110933949 A CN 110933949A
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- resin varnish
- polyimide precursor
- insulated wire
- insulating layer
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
- C08G73/00—Macromolecular compounds obtained by reactions forming a linkage containing nitrogen with or without oxygen or carbon in the main chain of the macromolecule, not provided for in groups C08G12/00 - C08G71/00
- C08G73/06—Polycondensates having nitrogen-containing heterocyclic rings in the main chain of the macromolecule
- C08G73/10—Polyimides; Polyester-imides; Polyamide-imides; Polyamide acids or similar polyimide precursors
- C08G73/12—Unsaturated polyimide precursors
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
- C08L79/00—Compositions of macromolecular compounds obtained by reactions forming in the main chain of the macromolecule a linkage containing nitrogen with or without oxygen or carbon only, not provided for in groups C08L61/00 - C08L77/00
- C08L79/04—Polycondensates having nitrogen-containing heterocyclic rings in the main chain; Polyhydrazides; Polyamide acids or similar polyimide precursors
- C08L79/08—Polyimides; Polyester-imides; Polyamide-imides; Polyamide acids or similar polyimide precursors
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- C—CHEMISTRY; METALLURGY
- C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
- C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
- C09D179/00—Coating compositions based on macromolecular compounds obtained by reactions forming in the main chain of the macromolecule a linkage containing nitrogen, with or without oxygen, or carbon only, not provided for in groups C09D161/00 - C09D177/00
- C09D179/04—Polycondensates having nitrogen-containing heterocyclic rings in the main chain; Polyhydrazides; Polyamide acids or similar polyimide precursors
- C09D179/08—Polyimides; Polyester-imides; Polyamide-imides; Polyamide acids or similar polyimide precursors
Abstract
A resin varnish according to one aspect of the present disclosure contains a polyimide precursor as a reaction product of an aromatic tetracarboxylic dianhydride and an aromatic diamine, the polyimide precursor having a weight average molecular weight of 10,000 or more and 180,000 or less, the aromatic tetracarboxylic dianhydride including a biphenyltetracarboxylic dianhydride in an amount of 25 mol% or more and 95 mol% or less with respect to 100 mol% of the aromatic tetracarboxylic dianhydride.
Description
Technical Field
The present disclosure relates to a resin varnish, an insulated wire, and a method for manufacturing an insulated wire.
Background
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 properties, adhesion to the conductor, heat resistance, mechanical strength, flexibility, and the like. Examples of the synthetic resin used for forming the insulating layer include: polyimide, polyamideimide, polyesterimide, and the like.
In addition, in an electric device to which a high voltage is applied (for example, a motor used at a high voltage), a high voltage is applied to an insulated wire constituting the electric device, and a partial discharge (corona discharge) is likely to occur on the surface of the insulated wire. When corona discharge occurs, local temperature rise or generation of ozone or the like is easily caused, and as a result, insulation breakdown is caused at an initial stage due to deterioration of the insulation layer of the insulated wire, and the life of the electric device becomes short. In an insulated wire to which a high voltage is applied, it is necessary to increase a corona discharge inception voltage for the above-described reasons, and therefore, it is known that it is effective to reduce the dielectric constant of an insulating layer.
In addition, the insulated wire is sometimes exposed to a damp heat environment. In such an environment, the synthetic resin forming the insulating layer is hydrolyzed, and the molecular weight thereof is significantly reduced, and 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 is sometimes required to have performance (resistance to wet heat deterioration) of suppressing the deterioration of the function under the above-described wet heat environment.
Among synthetic resins used for an insulating layer of an insulated wire, in particular, polyimide is excellent in heat resistance, low in dielectric constant, and also excellent in mechanical strength, and thus is used for an insulating layer of an insulated wire used under high voltage. For example, japanese patent application laid-open No. 2013-253124 describes: an insulated wire which is excellent in heat resistance and crack resistance and in which corona discharge is less likely to occur is obtained by forming an insulating layer using a resin varnish containing a polyimide precursor which is a reaction product of an aromatic diamine and an aromatic tetracarboxylic dianhydride and in which the imide group concentration after imidization is in a specific range.
As a method for forming an insulating layer of an insulated wire from polyimide, a method including the steps of: a coating step of coating the outer peripheral side of the conductor with a resin varnish containing a polyimide precursor (polyamic acid), and a heating step of heating the obtained coating film. By this heating step, the polyimide precursor is imidized to form polyimide. In the above method, since only a thin film of about several μm can be formed in one coating step and heating step, the coating step and heating are usually repeated to form a film of a predetermined thickness (about 10 μm). The resin varnish is required to have excellent coatability, and particularly, it is required to maintain excellent coatability even when the concentration of the polyimide precursor contained therein is increased in order to thicken the coating film that can be formed in the primary coating step and the heating step.
Documents of the prior art
Patent document
Patent document 1: japanese patent laid-open publication No. 2013-253124
Disclosure of Invention
A resin varnish according to one aspect of the present disclosure is a resin varnish containing a polyimide precursor that is a reaction product of an aromatic tetracarboxylic dianhydride and an aromatic diamine, wherein the polyimide precursor has a weight average molecular weight of 10,000 or more and 180,000 or less, the aromatic tetracarboxylic dianhydride includes a biphenyltetracarboxylic dianhydride, and the content of the biphenyltetracarboxylic dianhydride is 25 mol% or more and 95 mol% or less with respect to 100 mol% of the aromatic tetracarboxylic dianhydride.
An insulated wire according to another aspect of the present disclosure is an insulated wire including a conductor and 1 or more insulating layers laminated on an outer peripheral side of the conductor, wherein at least 1 of the 1 or more insulating layers is a cured product of the above resin varnish.
A method for manufacturing an insulated wire according to still another aspect of the present disclosure is a method for manufacturing an insulated wire including a conductor and 1 or more insulating layers laminated on an outer peripheral side of the conductor, the method including: a coating step of coating the resin varnish on the outer peripheral side of the conductor, and a heating step of heating the coated resin varnish.
Detailed Description
[ problems to be solved by the present disclosure ]
In order to provide the insulating layer of the insulated wire with good flexibility, it is necessary to use a material having excellent stretchability as a main component of the insulating layer. Among materials used for the insulating layer, polyimide is a material having high stretchability, but has inferior stretchability as compared with an elastomer or the like. In addition, polyimide is a material that may undergo hydrolysis when exposed to a moist heat environment for a long period of time. Therefore, there is room for improvement in the flexibility and resistance to wet heat deterioration of the insulating layer formed from the above-described conventional resin varnish.
As a method for improving the flexibility and the resistance to wet heat deterioration of the insulating layer, for example, it is conceivable to increase the molecular weight of polyimide as a main component to thereby improve the elongation of polyimide and to easily maintain a constant molecular weight even after hydrolysis. However, although this method is effective in improving the flexibility of the insulating layer, in order to sufficiently improve the resistance to wet heat deterioration of the insulating layer, it is necessary to make the molecular weight of the polyimide extremely high, and therefore, it is necessary to make the resin varnish contain a polyimide precursor having an extremely high molecular weight (for example, a weight average molecular weight exceeding 180,000). Since the viscosity becomes extremely high, the coatability of such a resin varnish may be lowered, and it is difficult to improve the wet heat deterioration resistance of the insulating layer only by the above method.
The present disclosure has been made in view of the above circumstances, and an object thereof is to provide a resin varnish which is excellent in coatability and in which an insulating layer formed is excellent in resistance to wet heat deterioration and flexibility, and an insulated wire using the resin varnish and a method for manufacturing the insulated wire.
[ Effect of the present disclosure ]
According to the resin varnish of one aspect of the present disclosure, an insulating layer having excellent coatability and excellent resistance to wet heat deterioration and flexibility can be formed. According to another aspect of the present disclosure, an insulated wire including an insulating layer having excellent resistance to deterioration by heat and humidity and excellent flexibility can be provided.
[ description of embodiments of the present disclosure ]
A resin varnish according to one aspect of the present disclosure is a resin varnish containing a polyimide precursor that is a reaction product of an aromatic tetracarboxylic dianhydride and an aromatic diamine, wherein the polyimide precursor has a weight average molecular weight of 10,000 or more and 180,000 or less, the aromatic tetracarboxylic dianhydride includes biphenyltetracarboxylic dianhydride (BPDA) in an amount of 25 mol% or more and 95 mol% or less relative to 100 mol% of the aromatic tetracarboxylic dianhydride.
The resin varnish having the above-described structure can form an insulating layer having excellent coatability and excellent resistance to wet heat deterioration and flexibility. The reason why the resin varnish having the above-described structure achieves the above-described effects is not clear, but it is presumed that the resin varnish has the following structure (for example). That is, since the resin varnish contains a polyimide precursor having a relatively high molecular weight with a weight average molecular weight of not less than the lower limit, an insulating layer containing a polyimide having a relatively high molecular weight as a main component can be formed by coating and heating on the outer peripheral side of the conductor. It is considered that such a polyimide having a high molecular weight is excellent in extensibility and easily maintains a constant molecular weight even if hydrolysis occurs, and thus the flexibility and resistance to wet heat deterioration of the insulating layer are improved. In addition, in the resin varnish, a specific amount of BPDA having low hydrolyzability is used as a raw material of the polyimide precursor, whereby a structure having low hydrolyzability can be introduced into polyimide, which is a main component of the insulating layer to be formed. As a result, it is considered that the resin varnish does not extremely increase the molecular weight of the polyimide precursor, and the resistance to wet heat deterioration of the insulating layer can be sufficiently improved even if the weight average molecular weight is not more than the upper limit. Further, in the resin varnish, by setting the weight average molecular weight of the polyimide precursor to the upper limit or less, an extreme increase in viscosity can be suppressed, and coatability can be improved, and particularly, even when the concentration of the polyimide precursor is increased, excellent coatability can be maintained. In addition, in the resin varnish, by setting the content of BPDA to the content of the aromatic tetracarboxylic dianhydride which is the raw material of the polyimide precursor to the upper limit or less, the occurrence of coating defects due to the crystallization of BPDA can be suppressed. Thus, it is considered that the resin varnish is excellent in coatability and can form an insulating layer excellent in resistance to wet heat deterioration and flexibility. Here, "weight average molecular weight" means a molecular weight in accordance with JIS-K7252-1: 2008 "plastic: method for calculating average molecular weight and molecular weight distribution of macromolecules from size exclusion chromatography-section 1: general "is a value measured by Gel Permeation Chromatography (GPC) using monodisperse polystyrene as a standard substance. That is, the weight average molecular weight of the polyimide precursor is a weight average molecular weight in terms of polystyrene.
The aromatic tetracarboxylic dianhydride may further include pyromellitic dianhydride, and in this case, the content of pyromellitic dianhydride is preferably 5 mol% or more and 75 mol% or less with respect to 100 mol% of the aromatic tetracarboxylic dianhydride. Therefore, the aromatic tetracarboxylic dianhydride contains a specific amount of pyromellitic dianhydride, whereby a rigid structure is introduced into the polyimide which is the main component of the insulating layer to be formed, and the heat resistance of the insulating layer can be improved.
The aromatic diamine may include diaminodiphenyl ether. In this way, the toughness of the insulating layer formed can be improved by including diaminodiphenyl ether as the aromatic diamine.
The concentration of the polyimide precursor in the resin varnish is preferably 25 wt% to 50 wt%. As described above, by setting the concentration of the polyimide precursor in the resin varnish to the above range, that is, to a high concentration, the coating film formed in one coating step and heating step can be thickened, and therefore, the number of times of repeating the coating step and heating step can be reduced, and the total amount of the resin varnish used in the entire production step can be reduced, which results in reduction of the production cost of the insulated wire.
The weight average molecular weight of the polyimide precursor is preferably 130,000 or less. In this way, the coatability can be further improved by setting the weight average molecular weight of the polyimide precursor to the upper limit or less.
An insulated wire according to another aspect of the present disclosure is an insulated wire including a conductor and 1 or more insulating layers laminated on an outer peripheral side of the conductor, wherein at least 1 of the 1 or more insulating layers is a cured product of the resin varnish.
The insulated wire is provided with an insulating layer having excellent resistance to deterioration by moist heat and excellent flexibility, because the insulating layer is formed using the resin varnish.
A method for manufacturing an insulated wire according to still another aspect of the present disclosure is a method for manufacturing an insulated wire including a conductor and 1 or more insulating layers laminated on an outer peripheral side of the conductor, the method including: a coating step of coating the resin varnish on the outer peripheral side of the conductor, and a heating step of heating the coated resin varnish.
In the method for producing an insulated wire, since the insulating layer is formed using the resin varnish, an insulated wire having an insulating layer excellent in resistance to deterioration by moist heat and flexibility can be easily and reliably produced.
[ details of embodiments of the present disclosure ]
The resin varnish according to one aspect of the present disclosure, the insulated wire according to another aspect of the present disclosure, and the method for manufacturing the same are explained in order below.
< resin varnish >
The resin varnish contains a polyimide precursor (polyamic acid). In addition, the resin varnish usually further contains an organic solvent. Hereinafter, each component will be described.
[ polyimide precursor ]
The polyimide precursor contained in the resin varnish is a reaction product obtained by polymerizing aromatic tetracarboxylic dianhydride and aromatic diamine. That is, the polyimide precursor is prepared from an aromatic tetracarboxylic dianhydride and an aromatic diamine.
The lower limit of the weight average molecular weight of the polyimide precursor is 10,000, preferably 15,000. On the other hand, the upper limit of the weight average molecular weight is 180,000, preferably 130,000. When the weight average molecular weight is less than the lower limit, the insulating layer formed of the resin varnish may have insufficient resistance to wet heat deterioration and flexibility. Conversely, when the weight average molecular weight exceeds the upper limit, the viscosity of the resin varnish may increase significantly, and the coatability may become insufficient.
From the viewpoint of easy synthesis of the polyimide precursor, the molar ratio of the aromatic tetracarboxylic dianhydride to the aromatic diamine (aromatic tetracarboxylic dianhydride/aromatic diamine) used as a raw material of the polyimide precursor can be, for example, from 95/105 to 105/95.
(aromatic tetracarboxylic acid dianhydride)
The aromatic tetracarboxylic dianhydride used as a raw material for the above polyimide precursor includes BPDA. Examples of BPDA include: 3,3 ', 4, 4' -biphenyltetracarboxylic dianhydride (3,3 ', 4, 4' -BPDA), 2,3,3 ', 4' -biphenyltetracarboxylic dianhydride (2,3,3 ', 4' -BPDA), 2 ', 3, 3' -biphenyltetracarboxylic dianhydride (2,2 ', 3, 3' -BPDA), and the like. Of these, 3,3 ', 4, 4' -BPDA is preferred.
The lower limit of the content of BPDA is 25 mol%, preferably 35 mol%, and more preferably 60 mol% with respect to 100 mol% of the aromatic tetracarboxylic dianhydride. On the other hand, the upper limit of the content of the BPDA is 95 mol%, preferably 80 mol%. By setting the content of BPDA to the above range, the resistance to wet heat deterioration of the insulating layer formed of the resin varnish can be further improved. When the content of BPDA is less than the lower limit, the insulating layer formed of the resin varnish may have insufficient wet heat deterioration resistance. Conversely, when the content of BPDA exceeds the upper limit, the polyimide, which is the main component of the insulating layer formed from the resin varnish, tends to have a crystal structure, and thus coating defects such as color unevenness due to the opacification caused by crystallization or the unevenness of crystallization in each portion may occur.
Among the aromatic tetracarboxylic dianhydrides used as the raw material of the polyimide precursor, examples of the aromatic tetracarboxylic dianhydrides other than BPDA include: pyromellitic dianhydride (PMDA), 3,3 ', 4,4 ' -benzophenonetetracarboxylic dianhydride, 4,4 ' -oxydiphthalic anhydride, 2 ', 3,3 ' -benzophenonetetracarboxylic dianhydride, 2-bis (3, 4-dicarboxyphenyl) propane dianhydride, 2-bis (2, 3-dicarboxyphenyl) propane dianhydride, 1-bis (3, 4-dicarboxyphenyl) ethane dianhydride, 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-carboxyphenyl) ether dianhydride, 1,2,5, 6-naphthalenetetracarboxylic dianhydride, 2,3,6, 7-naphthalenetetracarboxylic dianhydride, and the like. These other aromatic tetracarboxylic dianhydrides may be used alone or in combination of 2 or more.
The aromatic tetracarboxylic dianhydride used as the raw material of the polyimide precursor preferably further includes PMDA. By using PMDA having a rigid structure as a raw material of the polyimide precursor, the rigid structure is introduced into the imidized polyimide, and therefore, the heat resistance of the insulating layer formed of the resin varnish can be improved.
The lower limit of the PMDA content is preferably 5 mol%, and more preferably 20 mol% with respect to 100 mol% of the aromatic tetracarboxylic dianhydride used as the raw material of the polyimide precursor. On the other hand, the upper limit of the PMDA content is preferably 75 mol%, more preferably 65 mol%, and still more preferably 40 mol%. If the PMDA content is less than the lower limit, the heat resistance of the insulating layer formed from the resin varnish may become insufficient. Conversely, when the PMDA content exceeds the upper limit, the structure derived from BPDA cannot be sufficiently introduced into the polyimide that is the main component of the insulating layer formed of the resin varnish, and as a result, the moisture-heat deterioration resistance of the insulating layer may be lowered.
(aromatic diamine)
Examples of the aromatic diamine used as a raw material of the polyimide precursor include: diaminodiphenyl ethers (ODA) such as 4,4 '-diaminodiphenyl ether (4, 4' -ODA), 3,4 '-diaminodiphenyl ether (3, 4' -ODA), 3 '-diaminodiphenyl ether (3, 3' -ODA), 2,4 '-diaminodiphenyl ether (2, 4' -ODA), and 2,2 '-diaminodiphenyl ether (2, 2' -ODA); 2, 2-bis [4- (4-aminophenoxy) phenyl ] propane (BAPP), 4 ' -diaminodiphenylmethane, 3 ' -diaminodiphenylmethane, 2,4 ' -diaminodiphenylmethane, 2 ' -diaminodiphenylmethane, 4 ' -diaminodiphenylsulfone, 3 ' -diaminodiphenylsulfone, 2,4 ' -diaminodiphenylsulfone, 2 ' -diaminodiphenylsulfone, 4 ' -diaminodiphenylsulfide, 3 ' -diaminodiphenylsulfide, 2,4 ' -diaminodiphenylsulfide, 2 ' -diaminodiphenylsulfide, 2 ' -, P-phenylenediamine, m-phenylenediamine, p-xylylenediamine, m-xylylenediamine, 2 '-dimethyl-4, 4' -diaminobiphenyl, 1, 5-diaminonaphthalene, 4 '-benzophenone diamine, 3' -dimethyl-4, 4 '-diaminodiphenylmethane, 3', 5,5 '-tetramethyl-4, 4' -diaminodiphenylmethane, and the like. These aromatic diamines may be used alone or in combination of 2 or more.
The aromatic diamine used as a raw material of the above polyimide precursor preferably includes ODA. By using ODA as a raw material of the polyimide precursor, the toughness of the insulating layer formed from the resin varnish can be improved. The ODA is preferably 4, 4' -ODA.
The lower limit of the ODA content is preferably 50 mol%, more preferably 90 mol%, and still more preferably 99 mol% with respect to 100 mol% of the aromatic diamine. In this way, by setting the ODA content to be not less than the lower limit, the toughness of the insulating layer formed of the resin varnish can be further improved. The ODA content is particularly preferably 100 mol%.
The polyimide precursor may be a reaction product obtained by polymerizing an aromatic tetracarboxylic dianhydride with an aromatic diamine, and other raw materials. Examples of the other raw materials include: aliphatic tetracarboxylic acid dianhydrides such as 1,2,4, 5-cyclohexanetetracarboxylic acid dianhydride, and aliphatic diamines such as hexamethylenediamine.
The polyimide precursor is preferably a reaction product obtained by using substantially only BPDA, PMDA, and ODA as raw materials. Specifically, the lower limit of the total proportion of BPDA, PMDA, and ODA in the total raw materials of the polyimide precursor is preferably 95 mol%, and more preferably 99 mol%. The total proportion is most preferably 100 mol%.
The lower limit of the concentration of the polyimide precursor in the resin varnish is preferably 25% by mass, and more preferably 30% by mass. On the other hand, the upper limit of the concentration is preferably 50% by mass, and more preferably 40% by mass. When the concentration is less than the lower limit, the amount of the resin varnish required in the entire production process to obtain an insulating layer having a desired thickness may increase or the number of coating steps and heating steps may increase when the resin varnish is used to form the insulating layer. Conversely, when the concentration exceeds the upper limit, the viscosity of the resin varnish may increase, thereby reducing the coatability.
(method for synthesizing polyimide precursor)
The polyimide precursor can be obtained by a polymerization reaction of the aromatic tetracarboxylic dianhydride and the aromatic diamine. The polymerization reaction can be carried out in the same manner as in the synthesis of a conventional polyimide precursor. Specific examples of the polymerization reaction include the following methods: mixing an aromatic tetracarboxylic dianhydride and an aromatic diamine in an organic solvent, and heating the mixed solution. By this method, an aromatic tetracarboxylic dianhydride and an aromatic diamine are polymerized to obtain a solution in which a polyimide precursor is dissolved in an organic solvent.
The reaction conditions in the above polymerization may be appropriately set depending on the raw materials used, and for example, the reaction temperature may be set to 10 ℃ to 100 ℃ inclusive, and the reaction time may be set to 0.5 hour to 24 hours inclusive.
From the viewpoint of efficiently carrying out the polymerization reaction, the molar ratio of the aromatic tetracarboxylic dianhydride to the aromatic diamine (aromatic tetracarboxylic dianhydride/aromatic diamine) used in the above polymerization is preferably as close as 100/100. The molar ratio may be, for example, 95/105 or more and 105/95 or less. In this manner, the weight average molecular weight of the polyimide precursor to be obtained can be easily increased by setting the molar ratio to the above range.
As the organic solvent used in the above polymerization, for example, there can be used: aprotic polar organic solvents such as N-methyl-2-pyrrolidone (NMP), N-dimethylformamide, N-dimethylacetamide, dimethylsulfoxide, and γ -butyrolactone. These organic solvents may be used alone, or 2 or more of them may be used in combination. Here, the "aprotic polar organic solvent" refers to a polar organic solvent having no group which releases a proton.
The amount of the organic solvent used is not particularly limited as long as it can uniformly dissolve and disperse the aromatic tetracarboxylic dianhydride and the aromatic diamine. For example, the amount of the organic solvent used may be 100 parts by mass or more and 1,000 parts by mass or less with respect to 100 parts by mass of the total of the aromatic tetracarboxylic dianhydride and the aromatic diamine.
In the above polymerization, a molecular weight modifier may be added to the reaction system. In this manner, the weight average molecular weight of the polyimide precursor to be obtained can be appropriately reduced by adding a molecular weight modifier to the reaction system during the polymerization. Examples of the molecular weight controlling agent include monoamines, dicarboxylic anhydrides, and the like, and specifically, aromatic monoamines such as aniline, toluidine, chloroaniline, and the like, and aromatic dicarboxylic anhydrides such as phthalic anhydride, and the like. For example, the amount of the molecular weight modifier added in the polymerization may be 1 mol% or more and 100 mol% or less based on 100 mol% of the total amount of the aromatic tetracarboxylic dianhydride and the aromatic diamine used.
[ organic solvent ]
The organic solvent used for the resin varnish improves the coatability of the resin varnish. In addition, when the coating step and the heating step are repeated on the outer peripheral surface of the conductor to form the plurality of insulating layers in the resin varnish containing the organic solvent, the organic solvent in the resin varnish slightly dissolves polyimide in the insulating layer formed in the previous step in the 2 nd and subsequent coating steps, and thus the adhesion force between the layers of the plurality of insulating layers formed can be improved.
The organic solvent is preferably an aprotic polar organic solvent. Since the polyimide precursor has high solubility in an aprotic polar organic solvent, the use of an aprotic polar organic solvent as the organic solvent can reliably dissolve the polyimide precursor even when the concentration of the polyimide precursor in the resin varnish is increased. Further, by using an aprotic polar organic solvent as the organic solvent, the organic solvent in the resin varnish in the 2 nd or subsequent coating step can easily dissolve the polyimide in the insulating layer formed in the previous step, and thus the adhesion strength between the insulating layers can be further improved.
The aprotic polar organic solvent is preferably N-methyl-2-pyrrolidone (NMP), N-dimethylformamide, N-dimethylacetamide, dimethylsulfoxide, γ -butyrolactone, or a combination thereof, and more preferably NMP, from the viewpoint of improving the solubility of the polyimide precursor and improving the adhesion force between insulating layers.
The organic solvent used in the polymerization reaction of the polyimide precursor may be used as it is, or may be added separately after the polyimide precursor is obtained. For example, the content of the organic solvent in the resin varnish may be in a range of 100 parts by mass or more and 300 parts by mass or less with respect to 100 parts by mass of the polyimide precursor.
In addition to the above components, the resin varnish may contain various additives such as pigments, dyes, inorganic or organic fillers, lubricants, adhesion improvers, and reactive low molecules. Among them, the inclusion of a melamine compound as an adhesion improver can improve the adhesion between the formed insulating layer and the conductor. Further, the resin varnish may contain other resins within a range not to impair the gist of the present disclosure. When the resin varnish contains the above components, the content of the above components in the resin varnish may be, for example, 0.5 to 30 parts by mass with respect to 100 parts by mass of the polyimide precursor.
< method for producing resin varnish >
As a method for producing the resin varnish, for example, a method in which a solution obtained by dissolving a polyimide precursor described in the method for synthesizing a polyimide precursor in an organic solvent is directly used as the resin varnish can be cited. Further, examples of the method for producing the resin varnish include the following methods: a polyimide precursor is purified from a solution obtained by dissolving the polyimide precursor in an organic solvent, and the obtained purified polyimide precursor is mixed with other components such as an organic solvent.
< insulated wire >
Next, the insulated wire obtained by forming an insulating layer using the resin varnish will be described. The insulated wire is provided with a conductor and 1 or more insulating layers laminated on the outer peripheral side of the conductor, wherein at least 1 layer of the insulating layers of the plurality of layers is a cured product of the resin varnish. The insulated wire has excellent resistance to deterioration by moist heat and flexibility because of the insulating layer formed of the resin varnish.
The insulating layer, which is a cured product of the resin varnish, contains polyimide as a main component. The upper limit of the amount of heat of the crystal melting peak of the polyimide as determined by differential scanning calorimetry is preferably 5J/g, more preferably 3J/g. The heat quantity of the crystal melting peak of the polyimide is most preferably 0J/g. The "heat amount of the crystal melting peak of the polyimide" is a value obtained by the following procedure. About 8mg to 10mg of a sample was taken out from the insulating layer, and the sample was supplied to a differential scanning calorimeter. The heat measurement was performed by raising the temperature from room temperature (about 25 ℃) to 420 ℃ at 20 ℃/min under a nitrogen gas (flow rate 60 ml/min).
In this insulated wire, the amount of heat in the crystal melting peak of the polyimide is set to the upper limit or less, that is, the crystallization of the polyimide is suppressed, whereby the bending workability and the appearance of the insulating layer can be improved for the reasons described later. Here, the amount of heat of the crystal melting peak of the polyimide is determined by the structure of the polyimide and the formation condition of the insulating layer, and since the biphenyl structure of BPDA promotes the deposition (packing) of molecules, the polyimide containing a structure derived from BPDA in an excessive amount is likely to be crystallized, and it is difficult to set the amount of heat of the crystal melting peak to the upper limit or less only by controlling the formation condition of the insulating layer. On the other hand, in this insulated wire, the content of BPDA in the polyimide precursor raw material is set to the upper limit or less, and the structure derived from BPDA contained in the polyimide is set to a constant value or less, so that the amount of heat of the crystal melting peak can be easily and reliably set to the upper limit or less.
The reason why the insulating layer is excellent in bending workability and appearance by setting the heat quantity of the crystal melting peak to the upper limit or less is considered as follows. That is, as a method for forming an insulating layer mainly composed of polyimide, a method including the steps of: a coating step of coating a resin varnish containing a polyimide precursor (polyamic acid) on the outer peripheral side of the conductor, and a heating step of heating the obtained coating film. In the above method, since only a thin insulating layer of about several μm can be formed in one coating step and heating step, the coating step and heating step are usually repeated to sequentially laminate a plurality of insulating layers to a predetermined thickness (about 10 μm). It is considered that, in the coating step 2 and subsequent steps, when the solvent contained in the resin varnish slightly dissolves the polyimide contained in the undercoat layer (the insulating layer formed in the previous coating step and the heating step), the undercoat layer and the newly laminated insulating layer are easily fused with each other, and the adhesion force between the layers is improved. Here, it is considered that since the solvent hardly permeates into the crystal portion, the solvent resistance of the polyimide having a high crystallinity tends to be excessively high.
In this insulated wire, the solvent resistance can be appropriately reduced by setting the amount of heat of the crystal melting peak of the polyimide to the upper limit or less, and as a result, the effect of improving the adhesion between the insulating layers due to the dissolution of the polyimide can be exhibited. Thus, when a large deformation is applied to the insulating layer by bending the insulated wire or the like, it is considered that the reduction in the insulating property or the like due to the peeling between the layers of the insulating layer is suppressed, and excellent bending workability is exhibited. In addition, polyimide having high crystallinity may be turbid due to light scattering at the interface between the crystalline portion and the amorphous portion. In this insulated wire, the haze can be suppressed by setting the heat quantity of the crystal melting peak of the polyimide to the upper limit or less, and as a result, it is considered that the appearance of the insulating layer can be improved.
The material of the conductor is preferably a metal having high electrical conductivity and high mechanical strength. Examples of such metals include: copper, copper alloys, aluminum alloys, nickel, silver, soft iron, steel, stainless steel, and the like. The conductor of the insulated electric wire may be formed by shaping these metals into a wire or may be formed by coating such a wire with another metal to form a multilayer structure, for example, a nickel-coated copper wire, a silver-coated copper wire, a copper-coated aluminum wire, a copper-coated steel wire, or the like.
As the insulated wireThe lower limit of the average cross-sectional area of the conductor of (4), preferably 0.01mm2More preferably 0.1mm2. On the other hand, the upper limit of the average cross-sectional area of the conductor is preferably 10mm2More preferably 5mm2. When the average cross-sectional area of the conductor is less than the lower limit, the resistance value may increase. Conversely, when the average cross-sectional area of the conductor exceeds the upper limit, the insulating layer must be formed thick to sufficiently lower the dielectric constant, and the diameter of the insulated wire may be unnecessarily increased.
The insulated wire has 1 or more layers of insulating layers laminated on the outer periphery of the conductor, and at least 1 layer is formed of the above resin varnish. When the insulated wire includes a plurality of insulating layers, the insulating layers are sequentially stacked on the outer peripheral side of the conductor so as to form concentric circles in a cross-sectional view. In this case, the average thickness of the insulating layers may be set to, for example, 1 μm or more and 5 μm or less. The average total thickness of the insulating layers of the plurality of layers may be, for example, 10 μm to 200 μm. Further, the total number of insulating layers of the plurality of layers may be set to, for example, 2 layers or more and 200 layers or less. In the above-described multilayer insulating layer, it is preferable that all the insulating layers are formed of the resin varnish, but some of the insulating layers may be formed of a resin varnish other than the resin varnish. Examples of the synthetic resin used for the other resin varnish include polyamide imide, polyester imide, polyurethane, and polyether imide.
In this insulated wire, another layer may be laminated on the outer periphery side of 1 or more insulating layers. Examples of the other layer include a surface lubricating layer.
< method for producing insulated wire >
Next, a method for manufacturing the insulated wire will be described. The manufacturing method of the insulated wire comprises the following steps: a coating step of coating the outer periphery of the conductor with the resin varnish, and a heating step of heating the resin varnish coated. In the method of manufacturing an insulated wire, it is preferable that the coating step and the heating step are repeatedly performed. According to the method for manufacturing an insulated wire, the insulated wire can be easily and reliably manufactured. Hereinafter, each step of the present embodiment will be described.
[ coating step ]
In this step, the resin varnish is applied to the outer peripheral side of the conductor. The coating method is not particularly limited, and examples thereof include: an application apparatus equipped with a resin varnish tank for storing the resin varnish and an application die was used. According to this coating apparatus, the conductor is inserted into the resin varnish tank so that the resin varnish adheres to the outer peripheral surface of the conductor, and then the resin varnish is coated on the outer peripheral surface of the conductor in a uniform thickness by the coating die. In this step, the resin varnish may be directly applied to the outer peripheral surface of the conductor, or an intermediate layer such as an adhesion improving layer may be provided on the outer peripheral surface of the conductor in advance, and the resin varnish may be applied to the outer peripheral side of the intermediate layer.
In the case where the above-described coating step and heating step are repeated in the method for producing an insulated wire, a resin varnish other than the resin varnish may be used in a part of the coating steps among the plurality of coating steps.
[ heating step ]
In this step, the resin varnish applied to the conductor is heated, for example, by a method of running the conductor coated with the resin varnish in a heating furnace. In this heating step, the polyimide precursor contained in the resin varnish is imidized, and volatile components such as organic solvents are removed, so that an insulating layer as a sintered layer is laminated on the outer peripheral side of the conductor. The heating method is not particularly limited, and may be performed by a conventionally known method such as hot air heating, infrared heating, or high-frequency heating. The heating temperature may be, for example, 350 ℃ to 500 ℃. The heating time may be set to 5 seconds to 100 seconds, in general. When the conductor coated with the resin varnish is heated by being run in a heating furnace, the set temperature in the heating furnace is regarded as the heating temperature.
In the method of manufacturing an insulated wire, when the coating step and the heating step are repeated, the number of times of repeating the coating step and the heating step may be, for example, 2 to 200 times.
[ other embodiments ]
The disclosed embodiments are to be considered in all respects as illustrative and not restrictive. The scope of the present disclosure is not limited to the configuration of the above-described embodiments, but is indicated 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.
Examples
Hereinafter, the present disclosure will be described more specifically by way of examples, but the present disclosure is not limited to the following examples.
In the examples, the weight average molecular weight of the polyimide precursor was measured in accordance with JIS-K7252-1: 2008 "plastic: calculation of the average molecular weight and molecular weight distribution of macromolecules using size exclusion chromatography-section 1: general "is measured by Gel Permeation Chromatography (GPC) using monodisperse polystyrene as a standard.
[ resin varnish No.8]
After dissolving 100 mol% of 4,4 ' -ODA in N-methyl-2-pyrrolidone, 10 mol% of PMDA, 90 mol% of 3,3 ', 4,4 ' -BPDA, and an appropriate amount of dicarboxylic anhydride (phthalic anhydride) as a molecular weight modifier were added to the resulting solution, and stirring was performed under a nitrogen atmosphere. Subsequently, the reaction was carried out at 80 ℃ for 3 hours while stirring, and then the reaction mixture was cooled to room temperature, whereby varnish No.8, in which a polyimide precursor was dissolved in N-methyl-2-pyrrolidone as an organic solvent, was produced. The polyimide precursor concentration in this resin varnish No.8 was 30% by mass. Further, the weight average molecular weight of the polyimide precursor contained in the resin varnish No.8 was 9,000.
[ resin varnish Nos. 1 to 7, and 9 to 35]
Resin varnish nos. 1 to 7 and 9 to 35 were produced in the same manner as resin varnish No.8, except that the amounts of PMDA, 3 ', 4,4 ' -BPDA and 4,4 ' -ODA used and the weight average molecular weights were as shown in table 1. When the weight average molecular weight of the polyimide precursor was increased to more than 9,000, the amount of the molecular weight modifier used was appropriately reduced as compared with the resin varnish No. 8.
< evaluation >
The insulating layers of the insulated wires were formed as described below using resin varnish nos. 1 to 35, and the coatability of each resin varnish and the wet heat deterioration resistance and flexibility of the formed insulating layers were evaluated. The evaluation results are shown in table 1.
[ production of insulated wire ]
A rectangular conductor composed mainly of copper and having an average thickness of 1.5mm and an average width of 3mm was prepared. The following steps were repeated 10 times to obtain an insulated wire including the conductor and an insulating layer having an average thickness of 35 μm laminated on the outer peripheral surface of the conductor: applying varnish nos. 1 to 35 to the outer peripheral surface of the conductor; and heating the conductor coated with the resin varnish at a set temperature of 400 ℃ for 30 seconds in a heating furnace.
[ coatability ]
Regarding the coatability of the resin varnish, the insulating layer formed was visually observed, and it was assumed that defects such as uneven thickness, white spots (かすれ), uneven color, peeling, indentation, and pin holes were not observed as "a (good)". The resin varnish in which the above-described defects were observed was subjected to a measure for improving coatability, and then, the insulated wire was again produced, and the coatability was again evaluated. As a measure for improving the coatability, for example, an operation of lowering the viscosity or the like is performed by raising the temperature of the resin varnish within a temperature range in which denaturation does not occur at the time of coating. The case where the defect is eliminated by the above measures is "B (good under the additional condition)" and the case where the defect cannot be eliminated even if the measures are taken is "C (bad)".
[ Damp-Heat deterioration resistance ]
Regarding the resistance to wet heat deterioration of the insulating layer, the insulated wire was stretched 10% in the longitudinal direction while being subjected to a wet heat treatment under conditions of a temperature of 85 ℃, a relative humidity of 95%, and a relative humidity of 750 hours. The treated insulated wire was visually observed, and the case where no cracks were observed on the surface was referred to as "a (good)", the case where cracks were observed on the surface but the number and size thereof were not significant was referred to as "B (not good)", and the case where cracks were observed on the surface and the number and size thereof were significant was referred to as "C (bad)".
[ tensile elongation ]
The conductor is removed from the insulated wire by electrolytic treatment, and the tubular insulating layer is collected. For this insulating layer, a tensile elongation of the insulating layer was measured using a tensile testing machine ("shimadzu" manufactured by company) under a tensile condition with a tensile rate of 10 mm/minute. The larger the value of tensile elongation (%) is, the more excellent the stretchability is, and therefore, the flexibility of the insulating layer is good, and the case where the tensile elongation is 10% or more is referred to as "a (good)" and the case where the tensile elongation is less than 10% is referred to as "B (poor)".
[ Table 1]
With respect to the resin varnish nos. 9 to 13, 16 to 20, and 23 to 27, good coatability, flexibility, and resistance to wet heat deterioration were exhibited by using BPDA in an amount of 25 mol% or more and 95 mol% or less with respect to 100 mol% of aromatic tetracarboxylic dianhydride in the polymerization of the polyimide precursor and by making the weight average molecular weight of the polyimide precursor 10,000 or more and 180,000 or less. In addition, with respect to the resin varnishes 9 to 12, 16 to 19, and 23 to 26, the coatability can be further improved by making the above-mentioned weight average molecular weight 130,000 or less.
On the other hand, the resin varnish nos. 1 to 7 cannot exhibit sufficient coatability because the content of BPDA exceeds 95 mol% with respect to 100 mol% of the aromatic tetracarboxylic dianhydride. In addition, with respect to the resin varnish nos. 29 to 35, since the content of BPDA is less than 25 mol%, the effect of improving the wet heat deterioration resistance by using BPDA cannot be sufficiently obtained.
With respect to the resin varnish nos. 8, 15 and 22, since the weight average molecular weight of the polyimide precursor is less than 10,000, at least one of the resistance to wet heat deterioration and flexibility is poor. In addition, resin varnish nos. 14, 21 and 28 had poor coatability because the weight average molecular weight of the polyimide precursor exceeded 180,000.
Claims (7)
1. A resin varnish containing a polyimide precursor which is a reaction product of an aromatic tetracarboxylic dianhydride and an aromatic diamine,
the weight average molecular weight of the polyimide precursor is 10,000 or more and 180,000 or less,
the aromatic tetracarboxylic dianhydride comprises biphenyl tetracarboxylic dianhydride,
the content of the biphenyltetracarboxylic dianhydride is 25 to 95 mol% based on 100 mol% of the aromatic tetracarboxylic dianhydride.
2. The resin varnish according to claim 1,
the aromatic tetracarboxylic dianhydride further comprises pyromellitic dianhydride,
the pyromellitic dianhydride is contained in an amount of 5 to 75 mol% based on 100 mol% of the aromatic tetracarboxylic dianhydride.
3. The resin varnish according to claim 1 or 2,
the aromatic diamine includes diaminodiphenyl ether.
4. The resin varnish according to claim 1, claim 2 or claim 3,
the concentration of the polyimide precursor in the resin varnish is 25 mass% or more and 50 mass% or less.
5. The resin varnish according to any one of claim 1 to claim 4,
the weight average molecular weight of the polyimide precursor is 130,000 or less.
6. An insulated wire comprising a conductor and 1 or more insulating layers laminated on the outer periphery of the conductor,
at least 1 of the 1 or more insulating layers is a cured product of the resin varnish recited in any one of claims 1 to 5.
7. A method for manufacturing an insulated wire including a conductor and 1 or more insulating layers laminated on an outer peripheral side of the conductor, the method comprising:
a coating step of applying the resin varnish recited in any one of claims 1 to 5 to an outer peripheral side of a conductor, and
a heating step of heating the above-mentioned coated resin varnish.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| PCT/JP2018/026872 WO2020016954A1 (en) | 2018-07-18 | 2018-07-18 | Resin varnish, insulated electric wire, and method for producing insulated electric wire |
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| Publication Number | Publication Date |
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| CN110933949A true CN110933949A (en) | 2020-03-27 |
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| Application Number | Title | Priority Date | Filing Date |
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| CN201880003677.7A Pending CN110933949A (en) | 2018-07-18 | 2018-07-18 | Resin varnish, insulated wire, and method for producing insulated wire |
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| CN (1) | CN110933949A (en) |
| WO (1) | WO2020016954A1 (en) |
Cited By (1)
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| CN114806396A (en) * | 2022-05-17 | 2022-07-29 | 住井科技(深圳)有限公司 | Method for making polyimide varnish have surge resistance and moist heat resistance, polyimide varnish and insulated wire |
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| WO2020016954A1 (en) | 2020-01-23 |
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