Powder coating

Abstract

To provide a powder coating that can be used to form a conductor coating while maintaining excellent paintability and excellent tracking resistance. [Solution] The powder coating of the present invention is a powder coating used for coating conductors such as coil ends and busbars, and comprises a particulate thermosetting resin composition, wherein the thermosetting resin composition comprises an epoxy resin, a curing agent, and an inorganic filler, wherein the epoxy resin comprises a bisphenol A type epoxy resin and an alicyclic structure-containing epoxy resin having an alicyclic structure in its molecule, and the proportion of the alicyclic structure-containing epoxy resin in the epoxy resin is 25% by mass or more.

Description

Technical Field

[0001] The present invention relates to a powder coating. Background Art

[0002] Due to environmental concerns, many automobiles that obtain driving force from vehicular rotating electric machines (driving motors) have been developed.

[0003] Up to now, 400V has been the mainstream for the system voltage of driving motors, but with the progress of motor miniaturization aimed at space saving and weight reduction, 800V specifications for motors, inverters, and systems including these components have been developed accordingly.

[0004] In addition, the demand for fast charging has also increased, and insulation coating materials in charging stations (power feeding devices) are also required to accommodate higher voltages.

[0005] Meanwhile, powder coatings, which can form an insulating coating on conductor surfaces regardless of shape, are used for coil end connection parts and bus rings of driving motor stators, copper busbar surfaces in inverters, and the like.

[0006] Patent Document 1 describes a method for coating a coil end of a stator coil by immersing the coil end in a powder tank in which air and a powder coating are stirred and mixed.

[0007] Along with the shift to an 800V system voltage, higher tracking resistance has also come to be required for powder coatings that directly insulate and coat copper materials.

[0008] An increase in voltage makes tracking phenomenon more likely to occur in the insulating material coating between conductors, so if the tracking resistance of the insulating coating material is not improved, the creepage distance must be increased, which makes miniaturization difficult.

[0009] For these reasons, there is a need for powder coatings that can be used to form conductor coatings with sufficiently excellent tracking resistance. However, conventionally, it has not been possible to provide powder coatings that can be used to form conductor coatings with sufficiently excellent tracking resistance while maintaining excellent coating properties. [Prior art documents] [Patent Documents]

[0010] [Patent Document 1] Japanese Patent Publication No. 2015-095980 [Overview of the project] [Problems that the invention aims to solve]

[0011] The object of the present invention is to provide a powder coating that can be used to form a conductor coating that has excellent tracking resistance while maintaining excellent paintability. [Means for solving the problem]

[0012] These objectives are achieved by the present invention as described in (1) to (10) below. (1) A powder coating used to cover a conductor, It contains a particulate thermosetting resin composition, The thermosetting resin composition comprises an epoxy resin, a curing agent, and an inorganic filler. The epoxy resin comprises a bisphenol A type epoxy resin and an epoxy resin containing an alicyclic structure having an alicyclic structure within its molecule. A powder coating characterized in that the proportion of the epoxy resin containing the alicyclic structure in the epoxy resin is 25% by mass or more.

[0013] (2) The powder coating as described in (1) above, wherein, in the test method specified in the international standard IEC60112, the comparative tracking index (CTI) of the cured powder coating, which is determined by fixing the electrode so that the angle between the cured powder coating and the electrode is 30° by rotating the electrode 180° with the longitudinal direction of the electrode as the axis of rotation, is 800V or higher.

[0014] (3) The powder coating according to (1) or (2) above, wherein the diameter D [mm] of the sample obtained by pressure molding 0.5 g of the powder coating into a tablet shape with a diameter of 10.0 mm is placed on a horizontal iron plate and immediately after being placed in a heater adjusted to 150°C and left for 30 minutes is determined to be 5% or more and 50% or less when the flow rate of the powder coating, calculated by [(D-10.0) / 10.0] × 100, is 5% or more and 50% or less.

[0015] (4) The powder coating according to any one of (1) to (3) above, wherein the coefficient of linear expansion of the cured product of the powder coating, as determined by measurement in accordance with ISO 11359-2:1999, is 35 ppm or less.

[0016] (5) The powder coating according to any one of (1) to (4) above, wherein the cured product of the powder coating has a bending strength of 100 MPa or more.

[0017] (6) The powder coating according to any one of (1) to (5) above, wherein the dielectric breakdown voltage of the cured product of the powder coating is 35 kV / mm or more.

[0018] (7) The powder coating according to any one of (1) to (6) above, wherein the alicyclic structure-containing epoxy resin has epoxy groups at both ends of the molecule.

[0019] (8) The powder coating according to any one of (1) to (7) above, wherein the epoxy resin containing the alicyclic structure has a chemical structure obtained by hydrogenating a bisphenol epoxy resin.

[0020] (9) The powder coating according to any one of the above (1) to (8), wherein for all types of said epoxy resin and said curing agent contained in said powder coating, when the weight average molecular weight is defined as Mw, the total molecular weight of aromatic ring structure moieties in the molecule is defined as Ma, and the ratio of content by mass ratio relative to the total of all types of said epoxy resin and said curing agent contained in said powder coating is defined as X, the total value of (Ma / Mw)×X for each of these components (Σ((Ma / Mw)×X)) is 0.18 or less.

[0021] (10) The powder coating according to any one of the above (1) to (9), comprising as a flame retardant at least one selected from the group consisting of aluminum hydroxide, brominated epoxy resins and phosphorus compounds. Effects of the Invention

[0022] According to the present invention, there can be provided a powder coating that can be used for forming a conductor covering portion having excellent tracking resistance while maintaining excellent coatability. Brief Description of Drawings

[0023] [Figure 1] FIG. 1 is a perspective view showing a configuration example of a stator to which the powder coating of the present invention is applied. [Figure 2] FIG. 2 is a plan view showing a configuration example of a coil end of a stator coil in the stator shown in FIG. 1. [Figure 3] FIG. 3 is an explanatory view showing an example of coating a coil end as an example of a coating method. Mode for Carrying Out the Invention

[0024] Hereinafter, preferred embodiments of the present invention will be described in detail.

[0025] [1] Powder coating First, the powder coating of the present invention will be described.

[0026] The powder coating of the present invention is a powder coating used for coating a conductor, and comprises a particulate thermosetting resin composition, wherein the thermosetting resin composition comprises an epoxy resin, a curing agent, and an inorganic filler, and the epoxy resin comprises a bisphenol A type epoxy resin and an alicyclic structure-containing epoxy resin having an alicyclic structure in its molecule, and the proportion of the alicyclic structure-containing epoxy resin in the epoxy resin is 25% by mass or more.

[0027] By meeting these conditions, it is possible to provide a powder coating that can be used to form coated parts such as coil ends, bus rings, and bus bars with excellent tracking resistance and excellent paintability. Furthermore, the curing speed of the powder coating, the cured product of the powder coating, and more specifically, the adhesive strength and appearance quality of the coated part formed by the powder coating can also be improved.

[0028] Conversely, if the above conditions are not met, satisfactory results cannot be obtained.

[0029] For example, if bisphenol A type epoxy resin is not included, the paintability will be inferior.

[0030] Furthermore, if the epoxy resin containing an alicyclic structure is not included, the tracking resistance of the conductor coating formed using powder coating will be inferior.

[0031] Furthermore, even if the epoxy resin contains bisphenol A type epoxy resin and alicyclic structure-containing epoxy resin, if the content of alicyclic structure-containing epoxy resin in the epoxy resin is less than 25% by mass, it becomes difficult to achieve sufficiently excellent tracking resistance in the coated portion of the coil end formed using powder coating.

[0032] Furthermore, paintability can be evaluated, for example, by the melt flowability (flow rate) of the powder coating as described later, and tracking resistance can be evaluated, for example, by the comparative tracking index (CTI) of the cured powder coating, which is obtained by fixing the electrode so that the angle between the cured powder coating and the electrode is 30°, by rotating the electrode 180° around the longitudinal direction of the electrode as the axis of rotation, as specified in the test method of the international standard IEC60112.

[0033] [1-1] Thermosetting resin composition The powder coating of the present invention contains a particulate thermosetting resin composition. The thermosetting resin composition comprises an epoxy resin, a curing agent, and an inorganic filler.

[0034] [1-1-1] Epoxy resin Epoxy resin is a thermosetting resin containing epoxy groups, and it has excellent adhesive properties, heat resistance, chemical resistance, and electrical insulation properties.

[0035] The epoxy resin constituting the thermosetting resin composition includes a bisphenol A type epoxy resin and an alicyclic structure-containing epoxy resin having an alicyclic structure within its molecule.

[0036] Thus, by including an alicyclic structure-containing epoxy resin along with bisphenol A type epoxy resin, it is possible to improve the tracking resistance of the coated portion of the coil end formed using powder coating while maintaining excellent paintability.

[0037] The epoxy resin content in the thermosetting resin composition is preferably 25.0% by mass or more and 80.0% by mass or less, more preferably 27.0% by mass or more and 75.0% by mass or less, and even more preferably 27.0% by mass or more and 70.0% by mass or less.

[0038] This allows the conductor to be more stably covered by the coating formed by the powder coating.

[0039] In particular, when the thermosetting resin composition is used to coat a busbar and flexibility is required, the epoxy resin content in the thermosetting resin composition is preferably 60.0% by mass or more and 90.0% by mass or less, more preferably 65.0% by mass or more and 87.5% by mass or less, and even more preferably 70.0% by mass or more and 85.0% by mass or less.

[0040] This allows the busbar to be more stably coated with the powder coating, and also enables bending after coating.

[0041] Furthermore, when the thermosetting resin composition is used for covering coil ends or busbars where flexibility is not required, the epoxy resin content in the thermosetting resin composition is preferably 25.0% by mass or more and 60.0% by mass or less, more preferably 30.0% by mass or more and 55.0% by mass or less, and even more preferably 35.0% by mass or more and 50.0% by mass or less.

[0042] This allows for more stable coating of coil ends and busbars without bending processes with the coating formed by powder coating.

[0043] [1-1-1-1] Bisphenol A type epoxy resin The epoxy resin constituting the thermosetting resin composition includes a bisphenol A type epoxy resin.

[0044] Bisphenol A type epoxy resin has the function of improving the coating properties of powder coatings, for example.

[0045] The softening point of the bisphenol A type epoxy resin is preferably between 50°C and 100°C, and more preferably between 55°C and 90°C.

[0046] This makes it possible to more effectively suppress the solidification of the powder coating in the fluidized bed, and to make the appearance of the coating formed by the powder coating more favorable.

[0047] The proportion of bisphenol A type epoxy resin in the epoxy resin constituting the thermosetting resin composition is preferably 20% by mass or more and 75% by mass or less, more preferably 22% by mass or more and 73% by mass or less, and even more preferably 25% by mass or more and 70% by mass or less. This makes it possible to improve the coating properties of powder coatings.

[0048] [1-1-1-2] Epoxy resin containing alicyclic structure The epoxy resin constituting the thermosetting resin composition includes an epoxy resin containing an alicyclic structure.

[0049] Epoxy resins containing alicyclic structures have the function of improving the tracking resistance of the coating portion of a conductor formed using powder coatings, for example.

[0050] The proportion of epoxy resin containing an alicyclic structure in the epoxy resin constituting the thermosetting resin composition is 25% by mass or more.

[0051] By satisfying these conditions, the tracking resistance of the conductive coating formed using powder coating can be made sufficiently excellent.

[0052] The proportion of epoxy resin containing an alicyclic structure in the epoxy resin constituting the thermosetting resin composition may be 25% by mass or more, but is preferably 25% by mass or more and 80% by mass or less, more preferably 27% by mass or more and 78% by mass or less, and even more preferably 30% by mass or more and 75% by mass or less. This makes the aforementioned effects even more pronounced.

[0053] The alicyclic structure-containing epoxy resin preferably has epoxy groups at both ends of the molecule, and more preferably has epoxy groups present only at both ends. This makes the aforementioned effects even more pronounced.

[0054] Examples of epoxy resins containing alicyclic structures include epoxy resins having a chemical structure obtained by reducing (hydrogenating) at least a portion of the aromatic rings in epoxy resins such as bisphenol A type, bisphenol F type, bisphenol S type, novolac type, phenol novolac type, cresol novolac type, biphenyl type, naphthalene type, biphenyl aralkyl type, and aromatic amine type.

[0055] In particular, the epoxy resin containing an alicyclic structure is preferably one that has a chemical structure obtained by hydrogenating a bisphenol A type epoxy resin. This makes the aforementioned effects even more pronounced.

[0056] The softening point of the epoxy resin containing the alicyclic structure is preferably 50°C to 120°C, and more preferably 55°C to 110°C.

[0057] This makes it possible to more effectively suppress the solidification of the powder coating in the fluidized bed, and to make the appearance of the coating formed by the powder coating more favorable.

[0058] [1-1-1-3] Other epoxy resin components

[0059] The epoxy resin constituting the thermosetting resin composition may contain epoxy resin components other than the bisphenol A type epoxy resin and alicyclic structure-containing epoxy resin described above. Hereinafter, in this section, such epoxy resin components will also be referred to as other epoxy resin components.

[0060] Other specific examples of epoxy resin components include those having two or more epoxy groups in their molecule and being solid at room temperature. Examples of such epoxy resins include bisphenol F type, bisphenol S type, novolac type, phenol novolac type, cresol novolac type, biphenyl type, naphthalene type, biphenyl aralkyl type, and aromatic amine type epoxy resins.

[0061] In addition, other epoxy resin components may include, for example, brominated epoxy resin.

[0062] By using brominated epoxy resin, the cured product of the powder coating, more specifically the coating formed by the powder coating, can be made to have excellent adhesion, heat resistance, chemical resistance, electrical insulation, etc., and its flame retardancy can be made more favorable.

[0063] When the powder coating of the present invention contains a brominated epoxy resin, the proportion of the brominated epoxy resin in the epoxy resin is preferably 10% by mass or more and 30% by mass or less, more preferably 12% by mass or more and 28% by mass or less, and even more preferably 15% by mass or more and 25% by mass or less. This makes the aforementioned effects even more pronounced.

[0064] [1-1-2] Hardener A thermosetting resin composition and a curing agent are included.

[0065] The curing agent has the function of curing epoxy resin, thereby improving the curability of the powder coating.

[0066] Specific examples of curing agents include, for example, aromatic amines such as diaminodiphenylmethane and aniline resins, condensates of aliphatic amines and aliphatic dicarboxylic acids, dicyandiamides and their derivatives; various imidazole and imidazoline compounds; polydicarboxylic acids or acid anhydrides such as adipic acid, sebatic acid, phthalic acid, maleic acid, trimellitic acid, benzophenone dicarboxylic acid, benzophenone tetracarboxylic acid, and pyromellitic acid; phenolic resins such as novolac-type phenolic resins, biphenylaralkyl-type phenolic resins, and naphtholaralkyl-type phenolic resins; novolacs, which are condensates of dihydrazides such as adipic acid and phthalic acid, phenol, cresol, xylenol, bisphenol A, etc., with aldehydes; carboxylic acid amides; methylolated melamines; and block-type isocyanurates. In particular, the curing agent is preferably an acid anhydride.

[0067] This makes it possible to more effectively suppress unintended dripping of the powder coating during the formation of the coating, and also improves the filling properties of the powder coating.

[0068] The ratio of curing agent to epoxy resin can be adjusted, for example, depending on the type of epoxy resin and curing agent used. However, it is preferable that the number of moles of functional groups of the curing agent contained in the thermosetting resin composition is 0.3 molar equivalents or more and 2.0 molar equivalents or less, more preferably 0.3 molar equivalents or more and 1.8 molar equivalents or less, and even more preferably 0.4 molar equivalents or more and 1.7 molar equivalents or less, relative to the number of moles of epoxy groups in the epoxy resin.

[0069] This makes it possible to improve the curability of the powder coating. Furthermore, it is possible to improve the flexural strength and shear tensile strength of the cured powder coating, more specifically, the coating formed by the powder coating.

[0070] In powder coatings, the content of the curing agent per 100 parts by mass of epoxy resin is preferably 7 parts by mass or more and 20 parts by mass or less, more preferably 8 parts by mass or more and 18 parts by mass or less, and even more preferably 9 parts by mass or more and 16 parts by mass or less.

[0071] This makes it possible to improve the curability of the powder coating. Furthermore, it is possible to improve the flexural strength and shear tensile strength of the cured powder coating, more specifically, the coating formed by the powder coating.

[0072] [1-1-3]Inorganic filler The thermosetting resin composition contains an inorganic filler.

[0073] Inorganic fillers, for example, have the function of improving the strength, heat resistance, electrical insulation, and flame retardancy of coatings formed by powder coatings.

[0074] Examples of inorganic fillers include silica such as crystalline silica, fused silica such as molten crushed silica, spherical silica, surface-treated silica, and amorphous silica; calcium compounds such as calcium carbonate and calcium sulfate; barium sulfate, aluminum oxide (specifically alumina), aluminum hydroxide, magnesium hydroxide, talc, kaolin, clay, mica, dolomite, wollastonite, glass fibers, glass beads, zircon, and molybdenum compounds. One or more of these can be used in combination, but it is preferable to use silica, and more preferable to use amorphous silica.

[0075] This makes it possible to improve the tracking resistance of the cured powder coating, more specifically, the coating portion of the coil end formed using the powder coating, and to make the bending strength more suitable. In addition, it is possible to effectively prevent the thermal expansion coefficient of the coating portion from becoming too large, and to improve the adhesion between the conductor and the coating portion.

[0076] When silica is included as an inorganic filler, the average particle size D50 of the silica is preferably 1 μm or more and 50 μm or less, more preferably 1 μm or more and 40 μm or less, and even more preferably 5 μm or more and 37 μm or less.

[0077] This makes it possible to further improve the tracking resistance of the cured powder coating, more specifically, the coating portion of a conductor formed using the powder coating, and to further improve its bending strength. In addition, it is possible to effectively prevent the coefficient of thermal expansion of the coating portion from becoming too large, and to further improve the adhesion between the conductor and the coating portion. Furthermore, the paintability of the powder coating can be further improved.

[0078] In this specification, D50 is the particle size at which the cumulative value of the volume frequency particle size distribution of the inorganic filler, as measured by laser diffraction scattering, reaches 50%.

[0079] When silica is included as an inorganic filler, the silica content per 100 parts by mass of epoxy resin is preferably 30 parts by mass or more and 230 parts by mass or less, more preferably 40 parts by mass or more and 200 parts by mass or less, and even more preferably 45 parts by mass or more and 180 parts by mass or less.

[0080] This makes it possible to further improve the tracking resistance of the cured powder coating, more specifically, the coating portion of a conductor formed using the powder coating, and to further improve its bending strength. In addition, it is possible to effectively prevent the coefficient of thermal expansion of the coating portion from becoming too large, and to further improve the adhesion between the conductor and the coating portion. Furthermore, the paintability of the powder coating can be further improved.

[0081] Furthermore, by including aluminum hydroxide as an inorganic filler, the flexural strength, insulation, and flame retardancy of the cured powder coating, more specifically, the coating formed by the powder coating, can be improved. In addition, it is possible to effectively prevent the thermal expansion coefficient of the coating from becoming too large, and the adhesion between the conductor and the coating can be improved.

[0082] When aluminum hydroxide is included as an inorganic filler, the average particle size D50 of the aluminum hydroxide is preferably 1 μm or more and 50 μm or less, more preferably 1 μm or more and 40 μm or less, and even more preferably 5 μm or more and 30 μm or less.

[0083] This makes it possible to further improve the flexural strength, insulation properties, and flame retardancy of the cured powder coating, and more specifically, the coating formed by the powder coating. In addition, it is possible to effectively prevent the coefficient of thermal expansion of the coating from becoming too large, and to further improve the adhesion between the conductor and the coating.

[0084] In powder coatings, the content of inorganic filler per 100 parts by mass of epoxy resin is preferably 30 parts by mass or more and 230 parts by mass or less, more preferably 40 parts by mass or more and 200 parts by mass or less, and even more preferably 45 parts by mass or more and 180 parts by mass or less.

[0085] This improves the mechanical strength of the cured powder coating, more specifically, the coating formed by the powder coating, and also improves the smoothness of the surface of the coating.

[0086] The content of inorganic fillers in the thermosetting resin composition is preferably 15.0% by mass or more and 70.0% by mass or less, more preferably 20.0% by mass or more and 66.0% by mass or less, and even more preferably 25.0% by mass or more and 62.0% by mass or less.

[0087] This improves the mechanical strength of the cured powder coating, more specifically, the coating formed by the powder coating, and also improves the smoothness of the surface of the coating.

[0088] [1-1-4] Curing accelerator The thermosetting resin composition may further contain a curing accelerator (curing catalyst). Curing accelerators have the function of accelerating the reaction between epoxy resin and hardener, thereby improving the curing speed.

[0089] This makes it possible to more effectively suppress unintended dripping of the powder coating during the formation of the coating, and also improves the curability of the powder coating.

[0090] Examples of curing accelerators include organophosphines such as triphenylphosphine; imidazole compounds such as 2-phenylimidazole; and amine compounds such as tertiary amines.

[0091] The content of the curing catalyst per 100 parts by mass of epoxy resin is preferably 0.01% by mass or more and 1.0% by mass or less, more preferably 0.03% by mass or more and 0.5% by mass or less, and even more preferably 0.05% by mass or more and 0.3% by mass or less. This allows for obtaining better curing properties.

[0092] [1-1-5] Flame retardant The thermosetting resin composition preferably contains a flame retardant. This makes it possible to improve the flame retardancy of the coating formed by the powder coating.

[0093] Examples of flame retardants include phosphorus compounds, nitrogen compounds, and boron compounds, and one or more of these can be used in combination.

[0094] Furthermore, by using aluminum hydroxide or magnesium hydroxide as part of the filler, or by using brominated epoxy resin as part of the resin, it can function as a flame retardant.

[0095] In particular, the powder coating of the present invention preferably contains at least one selected from the group consisting of aluminum hydroxide, brominated epoxy resin, and phosphorus compounds as a flame retardant.

[0096] This makes it possible to improve the flame retardancy of the coating formed by the powder coating, as well as the paintability of the powder coating.

[0097] If the thermosetting resin composition contains a flame retardant, the content of the flame retardant in the thermosetting resin composition is preferably 10% by mass or more and 30% by mass or less, more preferably 12% by mass or more and 28% by mass or less, and even more preferably 15% by mass or more and 25% by mass or less. This makes the aforementioned effects even more pronounced.

[0098] [1-1-7] Other ingredients The thermosetting resin composition may contain components other than those described above. Hereinafter, in this section, such components will be referred to as "other components."

[0099] Other components include, for example, thermosetting resins other than epoxy resins, colorants, leveling agents, coupling agents, and so on.

[0100] Examples of thermosetting resins other than epoxy resins include phenolic resins, melamine resins, unsaturated polyester resins, and polyurethane resins.

[0101] Various inorganic and organic pigments can be used as pigments, but organic pigments are preferred.

[0102] This makes it possible to improve the opacity due to coloring, the cured product of the powder coating, and more specifically, the durability of the coating formed by the powder coating.

[0103] Examples of organic pigments include azo pigments, phthalocyanine pigments, quinacridone pigments, anthraquinone pigments, berine pigments, thioindigo pigments, dioxane pigments, isoindoline pigments, imidazolon pigments, and perinone pigments.

[0104] Examples of inorganic pigments include titanium dioxide, iron oxide, zinc oxide, and carbon black.

[0105] However, the content of other components in the thermosetting resin composition is preferably 10.0% by mass or less, more preferably 7.0% by mass or less, and even more preferably 5.0% by mass or less.

[0106] [1-1-8] Other conditions

[0107] The thermosetting resin composition is in granular form.

[0108] The average particle size D50 of the thermosetting resin composition is preferably 20 μm or more and 100 μm or less, more preferably 40 μm or more and 80 μm or less, and even more preferably 50 μm or more and 70 μm or less. This allows for improved paint finish and continuous coating stability. Furthermore, it improves the mechanical strength and tracking resistance of the coating formed by the powder coating.

[0109] [1-2] Components other than granular thermosetting resin composition The powder coating may consist solely of a particulate thermosetting resin composition, or it may further contain components other than the particulate thermosetting resin composition. Examples of such components include fluidity enhancers.

[0110] Specific examples of fluidity-imparting materials include, for instance, inorganic particles such as silica and alumina.

[0111] However, the content of components other than the thermosetting resin composition in the powder coating is preferably 2.0% by mass or less, more preferably 1.5% by mass or less, and even more preferably 1.0% by mass or less.

[0112] [1-3] Other conditions The powder coating or its cured product preferably satisfies the following conditions:

[0113] The flow rate of the powder coating is preferably 5% to 50%, more preferably 10% to 45%, and even more preferably 13% to 40%.

[0114] This improves the fluidity of the powder coating in the fluidized bed, for example, making it easier to apply to conductors, and also more effectively suppresses sagging of the coating film.

[0115] In this specification, the flow rate refers to the value obtained by [(D-10.0) / 10.0] × 100, where the diameter D [mm] of the sample obtained immediately after placing a sample, which has been pressure-molded (5 MPa × 1 minute) of 0.5 g of the powder coating into a tablet shape with a diameter of 10.0 mm, on a horizontal iron plate and being placed in a heater adjusted to 150°C for 30 minutes.

[0116] For all types of epoxy resins and curing agents contained in the powder coating, when the weight-average molecular weight is Mw, the total molecular weight of the aromatic ring structure portion in the molecule is Ma, and the mass ratio of the content of each component to the total amount of all types of epoxy resins and curing agents contained in the powder coating is X, the sum of the values ​​of (Ma / Mw) × X for each of these components (Σ((Ma / Mw) × X)) is preferably 0.18 or less, more preferably 0.01 to 0.16, and even more preferably 0.02 to 0.15.

[0117] By satisfying these conditions, the tracking resistance of the cured powder coating, or more specifically, the coating portion of a conductor formed using the powder coating, can be improved. The comparative tracking index (CTI) of the cured powder coating is preferably 800V or higher.

[0118] This makes it possible to improve the tracking resistance of the cured powder coating, or more specifically, the coating portion of a conductor formed using the powder coating.

[0119] In this specification, the comparative tracking index (CTI) refers to the value obtained by fixing the electrode so that the angle between the cured powder coating and the electrode is 30°, by rotating the electrode 180° around the longitudinal direction of the electrode as the axis of rotation, as specified in the test method of the international standard IEC60112.

[0120] The coefficient of linear expansion of the cured powder coating below the glass transition temperature, as determined by measurement in accordance with ISO 11359-2:1999, is preferably 35 ppm or less, more preferably 10 ppm to 30 ppm, and even more preferably 15 ppm to 25 ppm.

[0121] This improves the adhesion between the conductor and the coating, and more effectively prevents unintended peeling of the coating during heat generation or other events.

[0122] In this specification, the coefficient of linear expansion below the glass transition temperature refers to the average coefficient of linear expansion from 60°C to 80°C.

[0123] The glass transition temperature of the cured powder coating is preferably 100°C or higher, more preferably 110°C or higher, and even more preferably 120°C or higher.

[0124] This increases the crosslinking density of the coating formed by the powder coating, resulting in improved strength and resistance to thermal cycling of the coating.

[0125] In this specification, the glass transition temperature refers to the value obtained by the method in accordance with ISO 11359-2:1999.

[0126] The flexural strength of the cured powder coating is preferably 100 MPa or more, more preferably 110 MPa or more, and even more preferably 115 MPa or more.

[0127] This increases the strength of the coating formed by the powder coating, resulting in improved durability of the coating.

[0128] In this specification, bending strength refers to the value obtained by the method conforming to JIS K 6911 (2006).

[0129] The dielectric breakdown voltage of the cured powder coating at 25°C is preferably 35kV / mm or higher.

[0130] This makes it possible to improve the high voltage resistance of the cured powder coating, or more specifically, the coating portion of a conductor formed using the powder coating.

[0131] The dielectric breakdown voltage is a value measured using a method compliant with JIS C2110-1.

[0132] Furthermore, the shear tensile strength of the cured powder coating is preferably 7 MPa or higher, more preferably 8 MPa or higher, and even more preferably 9 MPa or higher.

[0133] This allows for better adhesion between the conductor and the coating formed by the powder coating, especially when the conductor is made of copper.

[0134] The shear tensile strength was measured according to the method specified in JIS K 6850.

[0135] Furthermore, the physical properties of the cured powder coatings mentioned above can be based on measurements taken from cured products obtained by curing the powder coatings at 190°C for 20 minutes.

[0136] [2] Method for manufacturing powder coatings Next, we will explain the manufacturing method of powder coatings.

[0137] The method for manufacturing powder coatings according to this embodiment includes a preparation step for preparing a thermosetting resin composition. Furthermore, if the powder coating contains components other than the thermosetting resin composition (for example, a fluidity imparter), the method for manufacturing the powder coating may further include a mixing step for mixing the thermosetting resin composition with the other components. For example, in the preparation step for a particulate thermosetting resin composition, epoxy resin, inorganic filler, curing agent, and optional components are blended in a predetermined order, mixed, and then melt-kneaded while heating to obtain a mixture of all raw materials.

[0138] Next, the resulting mixture of raw materials is pulverized using an impact-type pulverizer to obtain epoxy resin powder coating. Alternatively, after pulverization, the powder may be sieved to separate fine and coarse particles, thereby adjusting the particle size of the powder coating.

[0139] [3] Coil end Next, we will describe one example of an application of the powder coating of the present invention: a coil end. In other words, we will describe below a coil end as an example of a conductor whose coating is formed by the powder coating of the present invention. Figure 1 is a perspective view showing an example of the configuration of a stator to which the powder coating of the present invention is applied. Figure 2 is a plan view showing an example of the configuration of the coil end of the stator coil in the stator shown in Figure 1.

[0140] The coil according to the present invention has coil ends whose exposed portions are sealed with the powder coating of the present invention.

[0141] The coil end may be made of any conductive material, but it is preferably made of copper. Copper has advantages in that it is a relatively inexpensive material with high electrical conductivity.

[0142] Specific examples of coils include motor coils, such as drive motor coils. The following provides a more detailed explanation using a motor stator coil as an example.

[0143] The stator 100 shown in Figure 1 has a stator core 101 and a stator coil 103. The stator coil 103 is arranged in a groove (slot) (not shown) provided in the inner wall of the stator core 101.

[0144] As shown in Figure 2, the coil end 105 is provided with an enamel-coated portion 107 in which the conductor portion is covered with an insulating coating, such as enamel, and an exposed portion 109 in which the conductor portion is exposed from the enamel coating. The exposed portion 109 is sealed with the powder coating of the present invention. In Figure 2, a coating portion 111 is provided extending from the exposed portion 109 to the enamel-coated portion 107. The coating portion 111 is made of a cured product of the powder coating of the present invention. As a result, the coating portion 111 has excellent tracking resistance.

[0145] [4] Painting method Next, a painting method using the powder coating of the present invention, or in other words, a method for forming a coating portion of a conductor, will be described. Figure 3 is an explanatory diagram illustrating an example of a painting method, specifically the painting of a coil end.

[0146] The coating method of this embodiment specifically includes an adhesion step (first step) in which the coil end 105 of a coil (stator coil 103) having a coil end 105 in which the conductor portion is covered with an insulating coating and an exposed portion 109 is provided where the conductor portion is exposed from the insulating coating is immersed in a fluidized tank 20 in which powder coating 10 flows, and the molten powder coating 10 is attached to the outside of the exposed portion 109, and a curing step (second step) in which the powder coating 10 attached to the coil end 105 is cured.

[0147] The adhesion process may include, for example, a fluidization step in which gas G is introduced into a fluidized tank 20 containing the powder coating 10 to fluidize the powder coating 10, and an immersion step in which the coil end 105 is immersed in the fluidized tank 20 in which the powder coating 10 is flowing.

[0148] The fluidization process can be carried out, for example, by introducing gas G into the fluidization tank 20 via the perforated plate 21, using a fluidization tank 20 equipped with a perforated plate 21 at the bottom, with the powder coating 10 filled on top of the perforated plate 21.

[0149] In the immersion process, the stator core 101 is positioned so that the coil end 105 is located vertically downward, and the stator core 101 is lowered. Then, the coil end 105 is immersed in the powder coating 10 in the fluidized bed 20.

[0150] In the immersion process, immersing the coil end 105 in the fluidized bath 20 and adhering the molten powder coating 10 to the outside of the exposed portion 109 may be performed as a single step or as separate steps, but it is preferable to perform it as a single step. In other words, it is preferable that the adhesion of the molten powder coating 10 to the outside of the exposed portion 109 occurs while the coil end 105 is immersed in the fluidized bath 20.

[0151] The painting method of this embodiment preferably further includes a heating step of heating the coil end 105 before immersing the coil end 105 in the fluidized bed 20. This improves the sealing stability of the exposed portion 109.

[0152] At this time, by immersing the heated coil end 105 in the fluidized bed 20 in which the powder coating 10 flows, the powder coating 10 near the coil end 105 in the fluidized bed 20 adheres to the coil end 105 as a molten substance.

[0153] Alternatively, after removing the coil end 105 from the fluidized bed tank 20, the coil end 105 may be subjected to a heat treatment.

[0154] This allows the powder coating 10 adhering to the coil end 105 to be further stably molten.

[0155] The coil end 105 can be heated, for example, by a heater 22 located at the top of the fluidized bed 20.

[0156] The heat curing conditions in the curing process can be appropriately set according to the type and size of the coil end 105, the components of the powder coating 10, etc.

[0157] The curing process may be carried out continuously with the adhesion process. More specifically, for example, if the coil end 105 was heated before being immersed in the fluidized bed 20, the residual heat of the coil end 105 after it is removed from the fluidized bed 20 may promote the curing reaction of the powder coating 10 attached to the coil end 105. Also, as described above, if the coil end 105 is subjected to a heat treatment after being removed from the fluidized bed 20, this heat treatment may be for the purpose of further stabilizing the powder coating 10 attached to the coil end 105 into a molten state and promoting the curing reaction.

[0158] Furthermore, the aforementioned heat treatment may not be intended to further stabilize the powder coating 10 adhering to the coil end 105 into a molten state, but rather solely to promote the curing reaction.

[0159] The cured powder coating 10 becomes integrated with the coil end 105, forming a coated portion 111. The coated portion 111 formed in this manner has excellent tracking resistance. Furthermore, since the powder coating 10 of the present invention has excellent coating properties, it can suitably form the coated portion 111.

[0160] Furthermore, in the coating method of this embodiment, the adhesion step and the curing step may be repeated alternately multiple times in order to increase the thickness of the coating film (covered portion).

[0161] Although preferred embodiments of the present invention have been described above, the present invention is not limited thereto.

[0162] For example, the powder coating of the present invention may be manufactured by any method, and is not limited to those manufactured by the methods described above. Furthermore, the coating method using the powder coating of the present invention is not limited to the method described above.

[0163] Furthermore, although the above description mainly focused on the case where coil ends are used as conductors, the conductors to which the present invention applies are not limited to coil ends, but may also be, for example, bus rings, bus bars, etc. [Examples]

[0164] The present invention will be described in more detail below with reference to specific examples, but the present invention is not limited to these examples. In the following description, processes for which no specific temperature conditions are given were performed at room temperature, specifically 25°C. Similarly, for various measurement conditions for which no specific temperature conditions are given, the values ​​are for room temperature, specifically 25°C.

[0165] [5] Manufacturing of powder coatings (Examples 1-2, Comparative Examples 1-3) The raw materials were mixed in a mixer according to the formulations shown in Table 1, melt-kneaded under 80°C conditions, then pulverized in a pulverizer. A thermosetting resin composition was obtained as the subsieved fraction using air classification and a 90-mesh (180 μm opening) sieve. The obtained thermosetting resin composition was used as a powder coating. The average particle size D50 of the thermosetting resin composition particles constituting the powder coating was within the range of 50 μm to 70 μm.

[0166] The raw materials used to prepare the powder coatings in each of the above examples and comparative examples are summarized below. (A) Epoxy resin (A-1) Bisphenol A type epoxy resin • Epoxy resin 1: Bisphenol A type epoxy resin (epoxy equivalent 650-750 g / eq)

[0167] (A-2) Epoxy resin containing alicyclic structure • Epoxy resin 2: Hydrogenated bisphenol A type epoxy resin (an epoxy resin having an alicyclic structure and epoxy groups only at both ends of the molecule, epoxy equivalent 630-790 g / eq)

[0168] (B) Hardener • Hardener 1: Benzophenone tetracarboxylic dianhydride (BTDA)

[0169] (C) Inorganic filler • Inorganic filler 1: Spherical silica (average particle size 30 μm)

[0170] (D) Curing accelerator • Curing accelerator 1: Triphenylphosphine (TPP)

[0171] Table 1 summarizes the composition of the powder coatings for each of the above examples and comparative examples. Table 2 summarizes the sum of the (Ma / Mw) × X values ​​(Σ((Ma / Mw) × X)) (indicated as "aromatic ring ratio" in the table) for each of the epoxy resins and curing agents contained in the powder coatings for each of the above examples and comparative examples, where Mw is the weight-average molecular weight, Ma is the total molecular weight of the aromatic ring structure portion in the molecule, and X is the mass ratio of the content of each component relative to the total amount of epoxy resins and curing agents contained in the powder coating.

[0172] [Table 1]

[0173] [Table 2]

[0174] [6] Rating The following evaluations were performed on the obtained powder coatings.

[0175] [6-1] Flow rate The flow rate of each of the powder coatings in the above-mentioned examples and comparative examples was measured using the method described above. It can be said that there is an appropriate range for the flow rate of powder coatings in relation to their paintability.

[0176] [6-2] Comparative Tracking Index CTI First, the powder coatings obtained in each of the above examples and comparative examples were melted and cured by heating at 190°C for 20 minutes to prepare test specimens measuring 3 mm × 30 mm × 30 mm.

[0177] For each of the above examples and comparative examples, the test specimens were measured using the test method specified in the international standard IEC60112, by rotating the electrode 180° around its longitudinal direction as the axis of rotation, so that the angle between the test specimen and the electrode was 30°. A higher comparative tracking index (CTI) value indicates superior tracking resistance.

[0178] The higher the comparative tracking index (CTI) of the cured powder coating, the better the tracking resistance of the conductor coating formed using the powder coating.

[0179] [6-3] Coefficient of linear thermal expansion, glass transition temperature (Tg) First, the powder coatings obtained in each of the above examples and comparative examples were melted and cured by heating at 190°C for 20 minutes to prepare test specimens measuring 5 mm × 5 mm × 20 mm.

[0180] For each of the above examples and comparative examples, the test specimens were measured using a TMA SS6000 manufactured by Seiko Instruments, at a heating rate of 5°C / min and a load of 10g. The inflection point of the thermal expansion curve was defined as the glass transition temperature (Tg), and the average slope from 60°C to 80°C was calculated as the average linear expansion coefficient below the glass transition temperature.

[0181] [6-4] Bending strength First, the powder coatings obtained in each of the above examples and comparative examples were melted and cured by heat treatment at 190°C for 20 minutes to prepare test specimens measuring 2 mm × 10 mm × 100 mm.

[0182] The bending strength of the test specimens for each of the above examples and comparative examples was measured at 25°C using a method in accordance with JIS K 6911 (2006).

[0183] [6-5] Dielectric breakdown voltage First, the powder coatings obtained in each of the above examples and comparative examples were melted and cured by heat treatment at 190°C for 20 minutes to prepare test specimens measuring 1.0 mm × 100 mm × 100 mm.

[0184] The dielectric breakdown voltage of the test specimens for each of the above examples and comparative examples was measured in accordance with JIS C2110-1. The dielectric breakdown voltage was measured using a high-voltage breakdown device (in accordance with ASTM D149) equipped with an oil bath. A higher dielectric breakdown voltage indicates that the cured powder coating has superior dielectric strength.

[0185] [6-6] Shear tensile strength First, test specimens were prepared using the powder coatings obtained in each of the above examples and comparative examples, as follows. Specifically, two copper plates measuring 1 mm x 15 mm x 100 mm were prepared and placed so that their longitudinal directions coincided, with the region at one end of one plate overlapping the region at the other end of the other plate. In particular, the two copper plates were overlapped in a 15 mm x 10 mm area. Powder coating was then sandwiched between the overlapping areas to secure them. After that, a test specimen was prepared by heat treatment at 190°C for 20 minutes.

[0186] The shear tensile strength of the test specimens of each of the above-mentioned examples and comparative examples obtained as described above was measured in accordance with the method in accordance with JIS K 6850.

[0187] These results are summarized in Table 3.

[0188] [Table 3]

[0189] As is clear from Table 3, the present invention yielded excellent results in all cases, whereas the comparative examples did not yield satisfactory results. [Explanation of Symbols]

[0190] 10: Powder coating 20: Fluidized tank 21: Perforated plate 22: Heater 100: Stator 101: Stator core 103: Stator coil 105: Coil End 107: Enamel coating 109:Exposed part 111: Covering part G: Gas

Claims

1. A powder coating used to cover a conductor, It contains a particulate thermosetting resin composition, The thermosetting resin composition comprises an epoxy resin, a curing agent, and an inorganic filler. The epoxy resin comprises a bisphenol A type epoxy resin and an epoxy resin containing an alicyclic structure having an alicyclic structure within its molecule. A powder coating characterized in that the proportion of the epoxy resin containing the alicyclic structure in the epoxy resin is 25% by mass or more.

2. The powder coating according to claim 1, wherein, in the test method specified in the international standard IEC 60112, the comparative tracking index (CTI) of the cured powder coating, which is obtained by fixing the electrode so that the angle between the cured powder coating and the electrode is 30° by rotating the electrode 180° with the longitudinal direction of the electrode as the axis of rotation, is 800V or more.

3. The powder coating according to claim 1 or 2, wherein the diameter D [mm] of the sample obtained by pressure molding 0.5 g of the powder coating into a tablet shape with a diameter of 10.0 mm is placed on a horizontal iron plate and then placed in a heater adjusted to 150°C and left for 30 minutes, and the flow rate of the powder coating calculated by [(D - 10.0) / 10.0] × 100 is 5% or more and 50% or less.

4. The powder coating according to claim 1 or 2, wherein the coefficient of linear expansion of the cured product of the powder coating, as determined by measurement in accordance with ISO 11359-2:1999, is 35 ppm or less.

5. The powder coating according to claim 1 or 2, wherein the cured product of the powder coating has a bending strength of 100 MPa or more.

6. The powder coating according to claim 1 or 2, wherein the dielectric breakdown voltage of the cured product of the powder coating is 35 kV / mm or more.

7. The powder coating according to claim 1 or 2, wherein the alicyclic structure-containing epoxy resin has epoxy groups at both ends of the molecule.

8. The powder coating according to claim 1 or 2, wherein the alicyclic structure-containing epoxy resin has a chemical structure obtained by hydrogenating a bisphenol epoxy resin.

9. The powder coating according to claim 1 or 2, wherein, for all types of epoxy resins and curing agents contained in the powder coating, Mw is the weight-average molecular weight, Ma is the total molecular weight of the aromatic ring structure portion in the molecule, and X is the mass ratio of the content of each of the epoxy resins and curing agents contained in the powder coating to the total, the sum of the values ​​of (Ma / Mw) × X for each of these components (Σ((Ma / Mw) × X)) is 0.18 or less.

10. The powder coating according to claim 1 or 2, comprising at least one selected from the group consisting of aluminum hydroxide, brominated epoxy resin, and phosphorus compounds as a flame retardant.

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