Laminated insulation film, and method for producing laminated insulation film

Abstract

To provide a laminated insulation film which has low relative dielectric constant, is made to be thick, has a sufficiently high partial discharge start voltage and is excellent in insulation property, and a method for producing a laminated insulation film.SOLUTION: A laminated insulation film 10 formed on the surface of a conductive base material 1 is constituted by laminating a first insulation layer 11 composed of a mixed resin containing a fluorine resin and a polyimide resin and a second insulation layer 12 composed of a polyimide resin, wherein the outermost layer is composed of the second insulation layer 12.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a laminated insulating film formed on the surface of a conductive substrate, and a method for manufacturing the laminated insulating film. [Background technology]

[0002] BACKGROUND ART Insulated conductors, which are made by covering a conductive substrate with an insulating coating made of insulating resin, are widely used as conductive materials and heat sink materials for various electrical devices that require insulation. Various resins are used as constituent materials for the insulating coating. For example, Patent Document 1 discloses a coating using a polyimide resin such as polyamide-imide resin, and Patent Document 2 proposes a coating using a mixed resin of a polyimide resin and a fluorine-based resin.

[0003] Electrodeposition is known as a method for forming an insulating film made of such an insulating resin on the surface of a conductive substrate. The electrodeposition method is a method of forming an electrodeposited film by immersing a substrate on which an insulating film is to be formed and a counter electrode in an electrodeposition solution in which the insulating film material is dispersed, and applying a voltage between the substrate and the counter electrode to deposit the insulating film material on the surface of the substrate.The formed electrodeposited film is then heated and baked onto the substrate, thereby forming the insulating film. The electrodeposition method includes an anionic electrodeposition method in which a voltage is applied to the substrate as the anode to form an insulating coating on the surface of the substrate, and a cationic electrodeposition method in which a voltage is applied to the substrate as the cathode to form an insulating coating on the surface of the substrate. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-115120 [Patent Document 2] Japanese Patent Application Publication No. 2018-131562 Summary of the Invention [Problem to be solved by the invention]

[0005] The above-mentioned insulating coating is required to have a high partial discharge inception voltage and excellent insulating properties. In order to increase the partial discharge inception voltage of the insulating coating, the dielectric constant must be low and the thickness must be large.

[0006] Electrodeposited films made of fluorine-free polyimide resins are prone to blister defects during firing, making them difficult to thicken. Furthermore, it has been difficult to achieve a sufficiently low dielectric constant. On the other hand, an insulating film made of a mixed resin of polyimide resin and fluororesin has a low dielectric constant, but has low film strength, and there is a risk that the insulating film will peel off when it comes into contact with other insulating films during bending, etc.

[0007] The present invention has been made in view of the above-mentioned circumstances, and has an object to provide a laminated insulating coating that has a low relative dielectric constant, can be made thicker, has a sufficiently high partial discharge inception voltage, and has excellent insulating properties, and a method for manufacturing the laminated insulating coating. [Means for solving the problem]

[0008] In order to solve the above problems, the laminated insulating coating of aspect 1 of the present invention is a laminated insulating coating formed on the surface of a conductive substrate, and is characterized in that it has a structure in which a first insulating layer made of a mixed resin containing a fluorine-based resin and a polyimide-based resin and a second insulating layer made of a polyimide-based resin are laminated together, and the outermost layer is made of the second insulating layer.

[0009] The laminated insulating film of aspect 1 of the present invention has a structure in which a first insulating layer made of a mixed resin containing a fluorine-based resin and a polyimide-based resin and a second insulating layer made of a polyimide-based resin are laminated together, so that it is possible to ensure the thickness of the insulating film without forming a thick second insulating layer made of polyimide-based resin. Furthermore, since the first insulating layer is made of a mixed resin containing a fluorine-based resin and a polyimide-based resin, the relative dielectric constant of the entire insulating coating can be reduced. Furthermore, since the outermost layer is the second insulating layer made of polyimide resin, peeling of the laminated insulating film can be prevented even when the laminated insulating film comes into contact with each other. Therefore, it is possible to provide a laminated insulating film having a sufficiently high partial discharge inception voltage and excellent insulating properties.

[0010] A laminated insulating coating according to a second aspect of the present invention is the laminated insulating coating according to the first aspect of the present invention, characterized in that the thickness of the laminated insulating coating is 40 μm or more. According to the laminated insulating coating of aspect 2 of the present invention, the thickness of the laminated insulating coating is set to 40 μm or more, so that the thickness of the laminated insulating coating is sufficiently ensured, and it is possible to reliably increase the partial discharge inception voltage.

[0011] The laminated insulating coating of aspect 3 of the present invention is characterized in that, in the laminated insulating coating of aspect 1 or aspect 2 of the present invention, the fluorine-based resin contains one or both of polytetrafluoroethylene and perfluoroalkoxyalkane. According to the laminated insulation coating of aspect 3 of the present invention, the fluorine-based resin contains one or both of polytetrafluoroethylene and perfluoroalkoxyalkane, so that the relative dielectric constant of the entire insulation coating can be reliably reduced and the partial discharge inception voltage can be reliably increased.

[0012] A fourth aspect of the present invention provides a method for manufacturing a laminated insulating film, which forms a laminated insulating film on the surface of a conductive substrate, and is characterized by comprising: a first electrodeposition film formation step of forming a first electrodeposition film on the surface of the substrate by anionic electrodeposition using a mixed resin electrodeposition liquid containing a fluorine-based resin and a polyimide-based resin; a second electrodeposition film formation step of forming a second electrodeposition film by anionic electrodeposition using a polyimide-based resin electrodeposition liquid; and a baking step of heating the laminated electrodeposition film formed by stacking the first electrodeposition film and the second electrodeposition film to form a laminated insulating film.

[0013] The method for producing a laminated insulating coating according to the fourth aspect of the present invention includes a first electrodeposited film formation step of forming a first electrodeposited film by anionic electrodeposition using a mixed resin electrodeposition liquid containing a fluorine-based resin and a polyimide-based resin, a second electrodeposited film formation step of forming a second electrodeposited film by anionic electrodeposition using a polyimide-based resin electrodeposition liquid, and a baking step of heating the laminated electrodeposited film formed by stacking the first electrodeposited film and the second electrodeposited film to form a laminated insulating coating. This makes it possible to produce a laminated insulating coating that has a sufficiently high partial discharge inception voltage and excellent insulating properties. [Effects of the Invention]

[0014] According to the present invention, it is possible to provide a laminated insulating coating that has a low dielectric constant, can be made thick, has a sufficiently high partial discharge inception voltage, and has excellent insulating properties, and a method for manufacturing the laminated insulating coating. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a cross-sectional view illustrating an example of a laminated insulating film according to an embodiment of the present invention. [Figure 2] FIG. 1 is a flow diagram showing a method for manufacturing a laminated insulating film according to an embodiment of the present invention. [Figure 3] FIG. 2 is a schematic diagram of a tester for measuring partial discharge inception voltage in the examples. DETAILED DESCRIPTION OF THE INVENTION

[0016] A laminated insulating film according to one embodiment of the present invention and a method for manufacturing the laminated insulating film will be described below.

[0017] As shown in FIG. 1, the laminated insulating film 10 of this embodiment is formed on the surface of a conductive substrate 1, and has a structure in which a first insulating layer 11 made of a mixed resin containing a fluorine-based resin and a polyimide-based resin and a second insulating layer 12 made of a polyimide-based resin are laminated together, and the second insulating layer 12 is positioned as the outermost layer of the laminated insulating film 10. In this embodiment, as shown in FIG. 1, a first insulating layer 11 is formed so as to contact the substrate 1, and a second insulating layer 12 is formed so as to be laminated on this first insulating layer 11, thereby forming a laminated insulating coating 10 with a two-layer structure.

[0018] Examples of polyimide resins include polyimide, polyetherimide, and polyamideimide. Examples of the fluorine-based resin include polytetrafluoroethylene and perfluoroalkoxyalkane.

[0019] In this embodiment, the thickness t of the laminated insulating coating 10 is preferably 40 μm or more. The thickness t of the laminated insulating coating 10 is more preferably 60 μm or more, and even more preferably 80 μm or more. There is no particular upper limit to the thickness t of the laminated insulating coating 10, but it is substantially 150 μm or less.

[0020] In this embodiment, the thickness t1 of the first insulating layer 11 is preferably 40 μm or more, and more preferably 60 μm or more. Furthermore, in this embodiment, the thickness t2 of the second insulating layer 12 is preferably 10 μm or more, and more preferably 20 μm or more, and is preferably 40 μm or less, and more preferably 30 μm or less. Furthermore, it is preferable that the ratio t2 / t1 of the thickness t1 of the first insulating layer 11 to the thickness t2 of the second insulating layer 12 is within the range of 0.1 to 0.75.

[0021] Next, a method for manufacturing the laminated insulating coating 10 according to this embodiment will be described with reference to the flow chart of FIG. As shown in FIG. 1, the method for producing an insulating film in this embodiment includes a surface pretreatment step S01, a first electrodeposited film forming step S02, a second electrodeposited film forming step S03, and a baking step S04. That is, this embodiment includes a first electrodeposited film forming step S02 and a second electrodeposited film forming step S03, in which a laminated electrodeposited film is formed by stacking the first electrodeposited film and the second electrodeposited film, and this is baked to form the laminated insulating coating 10.

[0022] (electrodeposition liquid) Here, the mixed resin electrodeposition solution used in the first electrodeposition film forming step S02 and the polyimide-based resin electrodeposition solution used in the second electrodeposition film forming step S03 will be described. The mixed resin electrodeposition liquid and the polyimide-based resin electrodeposition liquid contain water, an organic solvent, a solid component, and a neutralizer. Here, the solid component in the mixed resin electrodeposition liquid used in the first electrodeposition film formation step S02 is a mixed resin containing a fluorine-based resin and a polyimide-based resin, and the solid component in the polyimide-based resin electrodeposition liquid used in the second electrodeposition film formation step S03 is a polyimide-based resin.

[0023] The mixed resin electrodeposition liquid and the polyimide resin electrodeposition liquid preferably have a solid content of 1% by mass or more and 20% by mass or less, a water content of 15% by mass or more and 85% by mass or less, an organic solvent content of 15% by mass or more and 85% by mass or less, and a neutralizing agent content of 0% by mass or more and 3% by mass or less. In this embodiment, since the first electrodeposition film and the second electrodeposition film are formed by anionic electrodeposition, amines are used as neutralizing agents.

[0024] The average particle size of the solid component may be 50 nm or more and 500 nm or less, more preferably 50 nm or more and 450 nm or less, and even more preferably 50 nm or more and 300 nm or less, and the standard deviation of the particle size of the solid component may be 250 nm or less, more preferably 150 nm or less, and even more preferably 100 nm or less.

[0025] The water and organic solvent are used to disperse the solid component (a mixed resin containing a fluorine-based resin and a polyimide-based resin, or a polyimide-based resin). Examples of the organic solvent include N,N-dimethylacetamide, propylene carbonate, dimethyl sulfoxide, N,N-dimethylformamide, 4-butyrolactone, N-methyl-2-pyrrolidone, and N-methyl-2-pyrrolidone.

[0026] (Surface pretreatment process S01) First, a substrate is prepared on which the laminated electrodeposited film (laminated insulating film 10) is to be formed. This substrate is electrically conductive and is made of a metal material such as copper or a copper alloy, aluminum or an aluminum alloy, etc. Then, a surface treatment liquid such as an organic solvent or a surfactant is used to remove oils and grease and oxide films adhering to the surface of the above-mentioned base material.

[0027] (First electrodeposited film formation step S02) Next, a first electrodeposited film is formed on the surface of the surface-pretreated substrate by anionic electrodeposition using a mixed resin electrodeposition solution containing a fluorine-based resin and a polyimide-based resin. In the first electrodeposition film forming step S02, the substrate and a counter electrode are immersed in the mixed resin electrodeposition solution described above, and a voltage is applied between the anode (substrate) and the cathode (counter electrode) with the substrate as the anode and the counter electrode as the cathode. This reduces the pH of the electrodeposition solution around the substrate, causing a solid component (in this embodiment, a mixture of polyimide resin and fluororesin) to precipitate on the surface of the substrate. This forms a first electrodeposition film on the surface of the substrate.

[0028] (Second electrodeposition film formation step S03) Next, a second electrodeposited film is formed on the first electrodeposited film by anionic electrodeposition using a polyimide-based resin electrodeposition liquid. In the second electrodeposition film forming step S03, the substrate on which the first electrodeposition film has been formed and a counter electrode are immersed in the polyimide-based resin electrodeposition solution described above, and a voltage is applied between the anode (substrate) and the cathode (counter electrode) with the substrate as the anode and the counter electrode as the cathode. This reduces the pH of the electrodeposition solution around the substrate, causing a solid component (in this embodiment, polyimide-based resin) to precipitate on the surface of the substrate. This results in the formation of a second electrodeposition film on the first electrodeposition film.

[0029] Here, the temperatures (liquid temperatures) of the mixed resin electrodeposition liquid and the polyimide resin electrodeposition liquid in the first electrodeposition film forming step S02 and the second electrodeposition film forming step S03 are preferably adjusted to within a range of 5°C or higher and 35°C or lower. By keeping the liquid temperature at 5°C or higher, it is possible to prevent water from being mixed into the electrodeposition liquid due to condensation. On the other hand, by keeping the liquid temperature at 35°C or lower, the storage stability of the electrodeposition liquid is improved, and an electrodeposition film can be formed stably.

[0030] Furthermore, the voltage applied between the substrate (anode) and the counter electrode (cathode) in the first electrodeposited film forming step S02 and the second electrodeposited film forming step S03 is preferably in the range of 10V or more and 600V or less. By setting the applied voltage to 10 V or higher, the electrodeposition speed can be ensured and productivity can be improved. On the other hand, by setting the applied voltage to 600 V or lower, the generation of many bubbles on the surface of the substrate can be suppressed, and the occurrence of numerous irregularities in the laminated insulating coating due to the bursting of the bubbles in the subsequent baking step S04 can be suppressed.

[0031] (Baking process S04) In the baking step S04, the substrate on which the laminated electrodeposition film (first electrodeposition film and second electrodeposition film) has been formed in the first electrodeposition film forming step S02 and the second electrodeposition film forming step S03 is dried, for example, within a temperature range of 200°C or higher and lower than the melting point of the solid component to remove residual electrodeposition liquid, and then the laminated electrodeposition film is baked onto the substrate to form the laminated insulating coating 10.

[0032] The baking temperature in the baking step S04 may be within a temperature range in which the electrodeposited film of the solid components is formed and an insulating coating is formed on the substrate, for example, within a range of 200° C. to 400° C. The baking time may be within a range of 0.5 minutes to 60 minutes, for example.

[0033] Through the above-described process, a laminated insulating film 10 is formed, which has a structure in which a first insulating layer 11 made of a mixed resin containing a fluorine-based resin and a polyimide-based resin and a second insulating layer 12 made of a polyimide-based resin are stacked on a conductive substrate.

[0034] The laminated insulating film 10 of this embodiment configured as described above has a structure in which a first insulating layer 11 made of a mixed resin containing a fluorine-based resin and a polyimide-based resin and a second insulating layer 12 made of a polyimide-based resin are laminated together, so that it is possible to ensure the thickness of the laminated insulating film 10 without making the second insulating layer 12 made of polyimide-based resin thick. Furthermore, since the first insulating layer 11 is made of a mixed resin containing a fluorine-based resin and a polyimide-based resin, the dielectric constant of the laminated insulating coating 10 as a whole can be made low. Furthermore, since the outermost layer is the second insulating layer 12 made of polyimide resin, peeling of the laminated insulating coatings 10 can be prevented even when the laminated insulating coatings 10 come into contact with each other.

[0035] In this embodiment, when the thickness of the laminated insulating coating 10 is 40 μm or more, the thickness of the laminated insulating coating 10 is sufficiently ensured, and it is possible to reliably increase the partial discharge inception voltage. Furthermore, in this embodiment, when the fluorine-based resin contains one or both of polytetrafluoroethylene and perfluoroalkoxyalkane, the relative dielectric constant of the laminated insulation coating 10 as a whole can be reliably reduced, and the partial discharge inception voltage can be reliably increased.

[0036] The method for manufacturing the laminated insulating coating 10 of this embodiment includes a first electrodeposited film formation step S02 in which a first electrodeposited film is formed by anionic electrodeposition using a mixed resin electrodeposition liquid containing a fluorine-based resin and a polyimide-based resin, a second electrodeposited film formation step S03 in which a second electrodeposited film is formed by anionic electrodeposition using a polyimide-based resin electrodeposition liquid, and a baking step S04 in which the laminated electrodeposited film formed by stacking the first electrodeposited film and the second electrodeposited film is heated to form the laminated insulating coating 10.Therefore, it is possible to manufacture a laminated insulating coating 10 that has a sufficiently high partial discharge inception voltage and excellent insulating properties.

[0037] Although the embodiment of the present invention has been described above, the present invention is not limited to this and can be modified as appropriate within the scope of the technical idea of ​​the invention. For example, in this embodiment, the laminated insulating coating 10 has been described as having a two-layer structure consisting of a first insulating layer 11 and a second insulating layer 12, but this is not limited to this, and the structure may be one in which three or more layers are laminated, as long as the outermost layer is composed of the second insulating layer 12. [Example]

[0038] The results of confirmation experiments conducted to confirm the effectiveness of the present invention will be described below.

[0039] A rectangular bar of oxygen-free copper (1.47 mm x 2.94 mm x 25 cm in length) was prepared as a conductive substrate, and a cylindrical copper plate was prepared as a counter electrode. The substrate and the counter electrode were immersed in a mixed resin electrodeposition solution containing a mixed resin containing a fluorine-based resin and a polyimide-based resin as solid components shown in Table 1, and a first electrodeposition film was formed by setting the temperature of the mixed resin electrodeposition solution to 20°C, the applied voltage to 300 V, and the holding time to 1 minute. In addition, the substrate and the counter electrode were immersed in a polyimide resin electrodeposition solution containing the polyimide resins shown in Table 1 as solid components, and a second electrodeposition film was formed by setting the temperature of the polyimide resin electrodeposition solution to 20°C, the applied voltage to 50 V, and the holding time to 1 minute.

[0040] The deposited laminated electrodeposited film was then baked using a three-stage heating profile, in which the work temperature during baking was held at 140-170°C for 10 minutes, at 240-260°C for 5 minutes, and at 340-350°C for 90 seconds, followed by rapid cooling, to produce a laminated insulating film. The obtained laminated insulating film was subjected to various evaluations according to the following procedures. The evaluation results are shown in Tables 1 and 2.

[0041] (film thickness) The thickness of the substrate before electrodeposition and the thickness of the substrate on which the laminated insulating coating was formed were each measured with a micrometer, and the thickness of the laminated insulating coating was calculated from the difference between the thicknesses. The thickness of the first insulating layer and the second insulating layer was calculated by mechanically polishing the laminated insulating film to expose a cross section and then examining the film under an optical microscope.

[0042] (membrane appearance) Ten locations per sample were observed using an optical microscope at 50x magnification, and the laminated insulating film was rated as "good" if no protrusions with a diameter of 50 μm or more were found, and "unacceptable" if any protrusions with a diameter of 50 μm or more were found.

[0043] (breaking load) Using a scratch tester, an iron ball with a radius of 3 mm was swept while applying a load, and the load at which the insulating laminated film broke was taken as the breaking load.

[0044] (dielectric constant) A laminated insulating film was formed on the surface of a 2 mm diameter copper rod using the above procedure, and the capacitance Cp was measured over a 100 mm length using an LCD device. The relative permittivity ε was then calculated using the following formula: ε=100π×Cp×d / ε0 Cp: ​​capacitance (F), d: thickness of insulating laminated film (mm), ε0: dielectric constant in vacuum

[0045] (Partial discharge inception voltage) The distance between the laminated electrodeposited films was 10 cm, and 1 cm wide aluminum foil was wrapped around both ends, and a detector was attached. The voltage when a current of 5 mA flowed was taken as the partial discharge inception voltage.

[0046] [Table 1]

[0047] [Table 2]

[0048] In Comparative Example 1, a single-layer insulating coating (45 μm thick) of polyamideimide was formed, but poor appearance was confirmed. Also, the relative dielectric constant was high. As a result, the partial discharge inception voltage was low at 960 V. In Comparative Example 2, a single layer insulating coating (film thickness 40 μm) made of a mixed resin of polyamideimide and polytetrafluoroethylene was formed, but the breaking load was significantly low at 10 N, and the strength was poor. In Comparative Example 3, a single layer insulating coating (80 μm thick) made of a mixed resin of polyamideimide, polytetrafluoroethylene, and perfluoroalkoxyalkane was formed, but the breaking load was significantly low at 25 N, and the strength was poor.

[0049] In contrast, in Examples 1 to 11 of the present invention, a first insulating layer made of a mixed resin containing a fluorine-based resin and a polyimide-based resin and a second insulating layer made of a polyimide-based resin were laminated together, and the outermost layer was the second insulating layer. The film had a good appearance, a sufficiently high breaking load, and excellent strength. In addition, the relative dielectric constant was sufficiently low, and the partial discharge inception voltage was high.

[0050] As described above, it has been confirmed that the present invention can provide a laminated insulation coating that has a low dielectric constant, can be made thicker, has a sufficiently high partial discharge inception voltage, and is excellent in insulation, as well as a method for manufacturing the laminated insulation coating. [Explanation of symbols]

[0051] 1 Base material 10. Laminated insulating film 11 First insulating layer 12 Second insulating layer

Claims

1. A laminated insulating coating formed on the surface of a conductive substrate, The insulating layer has a laminated structure in which a first insulating layer made of a mixed resin containing a fluorine-based resin and a polyimide-based resin and a second insulating layer made of a polyimide-based resin are laminated together, A laminated insulating film, characterized in that the outermost layer is composed of the second insulating layer.

2. 2. The laminated insulating film according to claim 1, wherein the thickness of the laminated insulating film is 40 μm or more.

3. 2. The laminated insulating film according to claim 1, wherein the fluorine-based resin contains one or two of polytetrafluoroethylene and perfluoroalkoxyalkane.

4. A method for manufacturing a laminated insulating film, which forms a laminated insulating film on a surface of a conductive substrate, comprising: a first electrodeposition film forming step of forming a first electrodeposition film on the surface of the substrate by anionic electrodeposition using a mixed resin electrodeposition solution containing a fluorine-based resin and a polyimide-based resin; a second electrodeposition film forming step of forming a second electrodeposition film by anionic electrodeposition using a polyimide-based resin electrodeposition solution; a baking step of heating the laminated electrodeposited film formed by laminating the first electrodeposited film and the second electrodeposited film to form a laminated insulating film; A method for manufacturing a laminated insulating film, comprising:

Images