JP7620211B2 - Coating composition for electromagnetic steel sheet, electromagnetic steel sheet, laminated core and rotating electric machine - Google Patents

Description

The present invention relates to a coating composition for electromagnetic steel sheets, electromagnetic steel sheets, laminated cores, and rotating electrical machines.

Laminated cores, in which multiple electromagnetic steel sheets are joined together and laminated, are known as cores (iron cores) used in rotating electric machines. Crimping and welding are known methods for joining electromagnetic steel sheets together. Joining methods such as crimping and welding tend to degrade core iron loss because they impart mechanical and thermal strain to the steel sheets. Another joining method known other than crimping and welding is adhesive. Adhesive adhesives are superior in terms of core iron loss compared to crimping and welding because they do not impart mechanical or thermal strain to the steel sheets.

On the other hand, when joining electromagnetic steel sheets by adhesive bonding, the hardening of the adhesive imparts stress strain to the steel sheets. In recent years, there has been a demand for further improvements in motor efficiency, and so there is a need to further reduce core iron loss. Reducing the thickness of electromagnetic steel sheets is an effective way to reduce core iron loss, but the Young's modulus of the steel sheet decreases as the sheet thickness decreases. For this reason, there is a need to further reduce the stress strain that causes iron loss deterioration.

Epoxy resins have little volume change and are excellent in heat resistance, oil resistance, and chemical resistance, making them excellent adhesives for bonding electromagnetic steel sheets together. However, epoxy resins require relatively high temperatures to harden, which can cause stress to be applied to the steel sheets during bonding, which can lead to deterioration of iron loss. Adhesives that can bond at lower temperatures than epoxy resins are known, such as those that use urethane resins (see, for example, Patent Documents 1 to 6). It is also known to form a polymer adhesive layer made of baked enamel such as polyvinyl butyral or polyamide on the surface of the steel sheets, and to further place a binder layer made of polyvinyl alcohol, amine, or the like between the polymer adhesive layers that bond the steel sheets together (Patent Document 7). However, it is difficult to obtain sufficient heat resistance with these adhesives and binders to be applicable to applications that are exposed to high temperatures during use, such as electric vehicle motors.

JP 2017-179233 A JP 2017-186542 A Japanese Patent Application Publication No. 6-182929 Japanese Patent Application Publication No. 6-271834 Japanese Patent Application Publication No. 7-268051 JP 2002-293864 A Patent No. 6548081

The present invention aims to provide a coating composition for electromagnetic steel sheets that can reduce the stress distortion caused by adhesive components even when the electromagnetic steel sheets are thin, and that can provide heat resistance that ensures adhesive strength even when the motor heats up, as well as electromagnetic steel sheets, laminated cores, and rotating electric machines that use the same.

The present invention has the following configuration.
[1] A coating composition for electrical steel sheets, comprising: a cross-linked hot melt adhesive consisting of a polyester-based urethane resin, which is a reaction product of a polyester polyol and a polyisocyanate, and a curing agent; and a room-temperature solidifying resin, wherein the softening point of the room-temperature solidifying resin is 100°C or higher and 200°C or lower, and the content of the room-temperature solidifying resin is 50 parts by mass or higher and 300 parts by mass or lower relative to 100 parts by mass of the cross-linked hot melt adhesive.
[2] The coating composition for electrical steel sheets according to [1], wherein the curing agent is an aromatic amine having a melting point of 50° C. or more and 200° C. or less.
[3] An electrical steel sheet having an insulating coating on its surface, the insulating coating being formed by applying the coating composition for electrical steel sheet according to [1] or [2].
[4] The electrical steel sheet according to [3], having a sheet thickness of 0.50 mm or less.
[5] A laminated core in which a plurality of the electromagnetic steel sheets according to [3] or [4] are laminated and bonded to each other.
[6] A rotating electrical machine comprising the laminated core according to [5].

The present invention provides a coating composition for electromagnetic steel sheets that can reduce the stress distortion caused by adhesive components even when the electromagnetic steel sheets are thin, and can provide heat resistance that can ensure adhesive strength even when the motor heats up, as well as electromagnetic steel sheets, laminated cores, and rotating electrical machines that use the same.

1 is a cross-sectional view of a rotating electrical machine including a laminated core according to a first embodiment of the present invention. FIG. This is a cross-sectional view taken along line AA in FIG. FIG. 2 is a plan view of a material forming the laminated core. This is a cross-sectional view taken along line B-B of FIG. FIG. 6 is an enlarged view of part C in FIG. 5 . FIG. 2 is a side view of a manufacturing apparatus used to manufacture the laminated core.

The following describes a laminated core according to one embodiment of the present invention, a rotating electric machine equipped with this laminated core, and the material from which this laminated core is formed, with reference to the drawings. Note that in this embodiment, the rotating electric machine will be described using an electric motor, specifically an AC electric motor, more specifically a synchronous electric motor, and even more specifically a permanent magnet field type electric motor, as an example. This type of electric motor is suitable for use in, for example, electric vehicles.

(Rotating electric machine 10)
1 , the rotating electric machine 10 includes a stator 20, a rotor 30, a case 50, and a rotating shaft 60. The stator 20 and the rotor 30 are housed in the case 50. The stator 20 is fixed within the case 50.
In this embodiment, an inner rotor type rotating electric machine 10 is used in which the rotor 30 is located radially inside the stator 20. However, an outer rotor type rotating electric machine 10 in which the rotor 30 is located outside the stator 20 may also be used. Also, in this embodiment, the rotating electric machine 10 is a three-phase AC motor with 12 poles and 18 slots. However, the number of poles, the number of slots, the number of phases, etc. can be changed as appropriate.
The rotating electric machine 10 can rotate at a rotation speed of 1000 rpm by applying an excitation current of, for example, 10 A effective value and a frequency of 100 Hz to each phase.

The stator 20 includes a stator adhesive laminated core (hereinafter, stator core) 21 and a winding (not shown).
The stator core 21 includes an annular core back portion 22 and a plurality of teeth portions 23. Hereinafter, the direction of the central axis O of the stator core 21 (or the core back portion 22) will be referred to as the axial direction, the radial direction of the stator core 21 (or the core back portion 22) (the direction perpendicular to the central axis O) will be referred to as the radial direction, and the circumferential direction of the stator core 21 (or the core back portion 22) (the direction going around the central axis O) will be referred to as the circumferential direction.

The core back portion 22 is formed in an annular shape when viewed in a plan view of the stator 20 in the axial direction.
The multiple teeth portions 23 protrude radially inward from the inner circumference of the core back portion 22 (toward the central axis O of the core back portion 22 along the radial direction). The multiple teeth portions 23 are arranged at equal angular intervals in the circumferential direction. In this embodiment, 18 teeth portions 23 are provided at central angle intervals of 20 degrees centered on the central axis O. The multiple teeth portions 23 are formed to have the same shape and size as one another. Therefore, the multiple teeth portions 23 have the same thickness dimension as one another.
The winding is wound around the teeth portion 23. The winding may be a concentrated winding or a distributed winding.

The rotor 30 is disposed radially inward of the stator 20 (the stator core 21). The rotor 30 includes a rotor core 31 and a plurality of permanent magnets 32.
The rotor core 31 is formed in an annular (circular) shape and is disposed coaxially with the stator 20. The rotating shaft 60 is disposed within the rotor core 31. The rotating shaft 60 is fixed to the rotor core 31.
The permanent magnets 32 are fixed to the rotor core 31. In this embodiment, a pair of the permanent magnets 32 form one magnetic pole. The pairs of the permanent magnets 32 are arranged at equal angular intervals in the circumferential direction. In this embodiment, 12 pairs of the permanent magnets 32 (total of 24 magnets) are provided at central angle intervals of 30 degrees around the central axis O.

In this embodiment, an embedded magnet type motor is used as the permanent magnet field type motor. The rotor core 31 is formed with a plurality of through holes 33 that pass through the rotor core 31 in the axial direction. The plurality of through holes 33 are provided corresponding to the arrangement of the plurality of permanent magnets 32. Each permanent magnet 32 is fixed to the rotor core 31 while being arranged in the corresponding through hole 33. Each permanent magnet 32 can be fixed to the rotor core 31, for example, by bonding the outer surface of the permanent magnet 32 to the inner surface of the through hole 33 with an adhesive. Note that a surface magnet type motor may be used as the permanent magnet field type motor instead of the embedded magnet type.

Both the stator core 21 and the rotor core 31 are laminated cores. For example, as shown in FIG 2, the stator core 21 is formed by laminating a plurality of electromagnetic steel sheets 40 in a lamination direction.
The lamination thickness (total length along the central axis O) of each of the stator core 21 and the rotor core 31 is, for example, 50.0 mm. The outer diameter of the stator core 21 is, for example, 250.0 mm. The inner diameter of the stator core 21 is, for example, 165.0 mm. The outer diameter of the rotor core 31 is, for example, 163.0 mm. The inner diameter of the rotor core 31 is, for example, 30.0 mm. However, these values are merely examples, and the lamination thickness, outer diameter, and inner diameter of the stator core 21 and the lamination thickness, outer diameter, and inner diameter of the rotor core 31 are not limited to these values. Here, the inner diameter of the stator core 21 is based on the tip end of the teeth portion 23 of the stator core 21. In other words, the inner diameter of the stator core 21 is the diameter of a virtual circle inscribed in the tip end of all the teeth portion 23.

Each of the electromagnetic steel sheets 40 forming the stator core 21 and the rotor core 31 is formed, for example, by punching a blank 1 as shown in Fig. 4 to Fig. 6. The blank 1 is a steel sheet (electromagnetic steel sheet) that serves as a base material for the electromagnetic steel sheets 40. Examples of the blank 1 include a strip-shaped steel sheet and a cut sheet.
Although we are still in the middle of explaining the laminated core, the following will explain this material 1. In this specification, the strip-shaped steel sheet that is the base material of the electromagnetic steel sheet 40 may be referred to as material 1. The steel sheet that is punched from material 1 into a shape used for the laminated core may be referred to as electromagnetic steel sheet 40.

(Material 1)
The material 1 is handled in a state in which it is wound around a coil 1A shown in FIG. 7, for example. In this embodiment, a non-oriented electromagnetic steel sheet is used as the material 1. As the non-oriented electromagnetic steel sheet, a non-oriented electromagnetic steel strip according to JIS C 2552:2014 can be used. However, as the material 1, a directional electromagnetic steel sheet may be used instead of the non-oriented electromagnetic steel sheet. As the directional electromagnetic steel sheet in this case, a directional electromagnetic steel strip according to JIS C 2553:2019 can be used. In addition, a non-oriented thin electromagnetic steel strip or a directional thin electromagnetic steel strip according to JIS C 2558:2015 can be used.

The upper and lower limits of the average sheet thickness t0 of the raw material 1 are set, for example, as follows, taking into consideration the case where the raw material 1 is used as the electromagnetic steel sheet 40.
As the material 1 becomes thinner, the manufacturing cost of the material 1 increases. Therefore, taking the manufacturing cost into consideration, the lower limit of the average plate thickness t0 of the material 1 is 0.10 mm, preferably 0.15 mm, and more preferably 0.18 mm.
On the other hand, if the material 1 is too thick, the manufacturing cost is favorable, but when the material 1 is used as the electromagnetic steel sheet 40, eddy current loss increases and core iron loss deteriorates. In addition, since the occurrence of stress strain due to hardening is suppressed in the insulating coating according to this embodiment, the adverse effect of the stress strain (increased iron loss) can be effectively suppressed, particularly when the material 1 is thin. Therefore, taking into account the core iron loss and manufacturing cost, the upper limit of the average sheet thickness t0 of the material 1 is 0.65 mm, preferably 0.35 mm. Furthermore, if the effect of suppressing stress strain is to be sufficiently obtained, the upper limit is preferably 0.30 mm, more preferably 0.26 mm.
An example of the average sheet thickness t0 of the raw material 1 that satisfies the above range is 0.20 mm.

The average thickness t0 of the material 1 includes not only the thickness of the base steel plate 2, which will be described later, but also the thickness of the insulating coating 3. The average thickness t0 of the material 1 is measured, for example, by the following measurement method. For example, when the material 1 is wound in the shape of a coil 1A, at least a part of the material 1 is unwound into a flat plate shape. In the material 1 unwound into a flat plate shape, a predetermined position in the longitudinal direction of the material 1 (for example, a position away from the longitudinal edge of the material 1 by a length of 10% of the total length of the material 1) is selected. At this selected position, the material 1 is divided into five regions along its width direction. The thickness of the material 1 is measured at four points that are the boundaries between these five regions. The average value of the thicknesses at the four points can be set as the average thickness t0 of the material 1.

The upper and lower limits for the average sheet thickness t0 of this material 1 can naturally also be adopted as the upper and lower limits for the average sheet thickness t0 of the electromagnetic steel sheets 40. The average sheet thickness t0 of the electromagnetic steel sheets 40 can be measured, for example, by the following measurement method. For example, the lamination thickness of the laminated core is measured at four locations equally spaced apart in the circumferential direction (i.e., at 90 degree intervals around the central axis O). Each of the measured lamination thicknesses at the four locations is divided by the number of laminated electromagnetic steel sheets 40 to calculate the sheet thickness per sheet. The average value of the sheet thicknesses at the four locations can be taken as the average sheet thickness t0 of the electromagnetic steel sheets 40.

As shown in Figures 5 and 6, the material 1 includes a base steel plate 2 and an insulating coating 3. The material 1 is formed by covering both sides of a strip-shaped base steel plate 2 with an insulating coating 3. In this embodiment, the majority of the material 1 is formed of the base steel plate 2, and an insulating coating 3 that is thinner than the base steel plate 2 is laminated on the surface of the base steel plate 2.

The chemical composition of the base steel sheet 2 contains 2.5% to 4.5% Si by mass, as shown below in mass % units. By setting the chemical composition within this range, the yield strength of the material 1 (electromagnetic steel sheet 40) can be set to, for example, 380 MPa or more and 540 MPa or less.

Si: 2.5% to 4.5%
Al: 0.001% to 3.0%
Mn: 0.05% to 5.0%

When the material 1 is used as an electromagnetic steel sheet 40, the insulating coating 3 exerts insulating properties between adjacent electromagnetic steel sheets 40 in the stacking direction. In this embodiment, the insulating coating 3 has adhesive properties and bonds adjacent electromagnetic steel sheets 40 in the stacking direction. The insulating coating 3 may have a single layer structure or a multi-layer structure. More specifically, for example, the insulating coating 3 may have a single layer structure that combines insulating properties and adhesive properties, or may have a multi-layer structure that includes a base insulating coating with excellent insulating properties and a top insulating coating with excellent adhesive properties.

In this embodiment, the insulating coating 3 covers both sides of the base steel plate 2 without any gaps. However, as long as the above-mentioned insulating performance and adhesive performance are ensured, some layers of the insulating coating 3 do not need to cover both sides of the base steel plate 2 without any gaps. In other words, some layers of the insulating coating 3 may be intermittently provided on the surface of the base steel plate 2. However, in order to ensure the insulating performance, both sides of the base steel plate 2 must be covered by the insulating coating 3 so that the entire surface is not exposed. Specifically, when the insulating coating 3 does not have an underlying insulating coating with excellent insulating performance and has a single-layer structure that combines insulating performance and adhesive performance, the insulating coating 3 must be formed without any gaps over the entire surface of the base steel plate 2. In contrast, when the insulating coating 3 has a multi-layer structure including a base insulating coating with excellent insulating performance and a top insulating coating with excellent adhesive performance, it is possible to achieve both insulating performance and adhesive performance by forming both the base insulating coating and the top insulating coating without gaps over the entire surface of the base steel sheet 2, or by forming the base insulating coating without gaps over the entire surface of the base steel sheet and providing the top insulating coating intermittently.

The coating composition that forms the base insulating coating is not particularly limited, and general treatment agents such as chromate-containing treatment agents and phosphate-containing treatment agents can be used.

The insulating coating with adhesive properties is formed by applying the coating composition for electromagnetic steel sheets, which will be described below, onto a base steel sheet. The insulating coating made of the coating composition for electromagnetic steel sheets is in an uncured or semi-cured state (B stage) before the heat-pressing process during the manufacture of the laminated core, and the heat applied during the heat-pressing process causes a curing reaction to progress, resulting in the development of adhesive properties.

The coating composition for electrical steel sheets contains a cross-linked hot melt adhesive made of a polyester-based urethane resin and a curing agent, and a room temperature hardening resin.

Polyester-based urethane resin is a reaction product (urethane resin) obtained by reacting polyester polyol with polyisocyanate. In general, the viscoelastic properties of urethane resin can be adjusted by changing the length of the carbon chain of the polyol, and a wide range of products are available on the market, from hard glass-like to rubber-elastic.

Polyester polyols have superior mechanical strength compared to polyether polyols. There are no particular limitations on the polyester polyols, and examples include polyester-polyether type copolymers (such as copolymers of butylene terephthalate and tetramethylene oxide glycol) and polyester-polyester type copolymers (such as copolymers of butylene terephthalate and butylene adipate). One type of polyester polyol may be used alone, or two or more types may be used in combination.

The polyisocyanate is not particularly limited, and examples thereof include tolylene diisocyanate (TDI), 4,4'-diphenylmethane diisocyanate, 3,3'-dimethyl-4,4'-biphenylene diisocyanate, 1,4-phenylene diisocyanate, xylylene diisocyanate, tetramethylxylylene diisocyanate, naphthylene diisocyanate, dicyclohexylmethane-4,4'-diisocyanate, crude TDI, polymethylene polyphenylisocyanate, isophorone diisocyanate, hexamethylene diisocyanate, hydrogenated xylylene diisocyanate, their isocyanurates, carbodiimides, and biuret derivatives. One type of polyisocyanate may be used alone, or two or more types may be used in combination.

In order to heat-harden the insulating coating during the manufacture of the laminated core, the hardener must have latency. Here, "the hardener has latency" means that the hardening reaction is inhibited from progressing until hardening is started by heating. In this embodiment, an aromatic amine having a melting point (MP) of 50°C or more and 200°C or less is used as the hardener having latency. If the MP of the aromatic amine is within the above range, both latency and an appropriate bonding temperature range can be achieved, and the adhesive strength between the magnetic steel sheets is increased. The MP of the aromatic amine is preferably 60°C or more and 180°C or less.
The "melting point" is a value measured visually at a temperature rise rate of 1°C/min in accordance with JIS K0064 (1992).

Specific examples of aromatic amines include metaphenylenediamine (MP: 62°C), diaminodiethyldimethyldiphenylmethane (MP: 76°C), diaminodiphenylmethane (MP: 89°C), dichlorodiaminodiphenylmethane (MP: 98°C), trimethylenebis(4-aminobenzoate) (MP: 122-128°C), etc. Aromatic amines may be used alone or in combination of two or more.

The content of the curing agent is preferably 3 parts by mass or more and 100 parts by mass or less, and more preferably 5 parts by mass or more and 20 parts by mass or less, per 100 parts by mass of the polyester-based urethane resin. If the content of the curing agent is equal to or more than the lower limit of the above range, the adhesive strength between the magnetic steel sheets is increased. If the content of the curing agent is equal to or less than the upper limit of the above range, the pot life is extended.

Room temperature solidifying resins have a softening point of 100°C or higher and 200°C or lower, and can be solidified by cooling to room temperature (e.g., 25°C). Note that "softening point" refers to the melting point if the resin is a crystalline polymer, and the glass transition temperature if the resin is an amorphous polymer, and is a value measured using a differential scanning calorimeter (DSC) at a heating rate of 5°C/min in accordance with JIS K6863 (1994).

Specific examples of room temperature solidifying resins include rosin, rosin derivatives (hydrogenated rosin, polymerized rosin, hydrogenated polymerized rosin, rosin glycerin ester, hydrogenated rosin glycerin ester, rosin pentaerythritol ester, hydrogenated rosin pentaerythritol ester, disproportionated rosin glycerin ester, water-proportionated rosin pentaerythritol ester, etc.), terpene phenol resin, hydrogenated terpene phenol resin, ketone resin, petroleum resin (aliphatic, aromatic, copolymers thereof, alicyclic, and hydrogenated petroleum resins thereof), terpene resin, hydrogenated terpene resin, coumarone-indene resin, phenol resin, xylene resin, etc. One type of room temperature solidifying resin may be used alone, or two or more types may be used in combination.

The softening point of the room-temperature solidifying resin is preferably 80°C or higher and 230°C or lower, and more preferably 100°C or higher and 200°C or lower. If the softening point of the room-temperature solidifying resin is equal to or higher than the lower limit of the above range, the coating composition for magnetic steel sheets will have excellent coating properties, and will have heat resistance that can ensure adhesive strength even when the motor heats up. If the softening point of the room-temperature solidifying resin is equal to or lower than the upper limit of the above range, a laminated core with excellent magnetic properties can be formed.

The content of the room temperature solidifying resin is 50 parts by mass or more and 300 parts by mass or less, and preferably 100 parts by mass or more and 180 parts by mass or less, per 100 parts by mass of the cross-linking hot melt adhesive. If the content of the room temperature solidifying resin is equal to or more than the lower limit, a laminated core with excellent magnetic properties can be formed. If the content of the room temperature solidifying resin is equal to or less than the upper limit, heat resistance can be obtained that can ensure adhesive strength even when the motor generates heat.

Hot melt adhesives adhere by heating and melting, and can be made solvent-free, which has the advantage of significantly reducing the amount of volatilized components during adhesion. In addition, various properties can be expressed by molecular design and mixing with various resins. In the crosslinked hot melt adhesive used in this embodiment, the polyester-based urethane resin, which is characterized by its high mechanical strength, is crosslinked, so that heat resistance is obtained even after adhesion and high-temperature strength can be secured, making it usable for motors. Furthermore, by mixing with a room-temperature solidifying resin, core iron loss and heat resistance can be achieved at the same time. In addition, by combining an aromatic amine with latent properties as a curing agent, sufficient coating properties can be secured, and low-temperature baking and low-temperature adhesion are possible.

The insulating coating 3 can be formed, for example, by applying a coating composition for electromagnetic steel sheets to the surface of the base steel sheet, drying it, and baking it.
The lower limit of the temperature to be reached during baking is preferably 90° C., more preferably 110° C. The upper limit of the temperature to be reached during baking is preferably 180° C., more preferably 160° C.
The lower limit of the baking time is preferably 5 seconds, more preferably 10 seconds, and the upper limit of the baking time is preferably 60 seconds, more preferably 45 seconds.

The upper and lower limits of the average thickness t1 of the insulating coating 3 are set, for example, as follows, taking into consideration the case where the material 1 is used as an electromagnetic steel sheet 40.
When the material 1 is used as the electromagnetic steel sheet 40, the average thickness t1 of the insulating coating 3 (the thickness per side of the electromagnetic steel sheet 40 (material 1)) is adjusted so as to ensure the insulating performance and adhesive ability between the electromagnetic steel sheets 40 that are stacked on top of each other.

In the case of a single-layer insulating coating 3, the lower limit of the average thickness t1 of the insulating coating 3 is preferably 2.0 μm, more preferably 2.5 μm. On the other hand, as the insulating coating 3 becomes thicker, the insulating effect becomes saturated. Also, as the insulating coating 3 becomes thicker, the proportion of the base steel sheet 2 in the laminated core decreases, and the performance as a laminated core decreases. Therefore, the upper limit of the average thickness t1 of the insulating coating 3 is preferably 8.0 μm, more preferably 6.0 μm.
In the case of the insulating coating 3 having a multilayer structure, the average thickness of the base insulating coating may be, for example, from 0.3 μm to 2.5 μm, and preferably from 0.5 μm to 1.5 μm. The lower limit of the average thickness of the top insulating coating may be 2.0 μm, and preferably 2.5 μm. The upper limit of the average thickness of the top insulating coating may be 6.0 μm, and preferably 4.5 μm.
The average thickness t1 of the insulating coating 3 on the base material 1 can be measured in the same manner as the average plate thickness t0 of the base material 1, by measuring the thicknesses of the insulating coating 3 at multiple locations and averaging these thicknesses.

The upper and lower limits of the average thickness t1 of the insulating coating 3 of the material 1 can naturally be adopted as the upper and lower limits of the average thickness t1 of the insulating coating 3 of the electromagnetic steel sheet 40. The average thickness t1 of the insulating coating 3 of the electromagnetic steel sheet 40 is measured, for example, by the following measurement method. For example, among the multiple electromagnetic steel sheets forming the laminated core, the electromagnetic steel sheet 40 located at the outermost position in the lamination direction (the electromagnetic steel sheet 40 whose surface is exposed in the lamination direction) is selected. On the surface of the selected electromagnetic steel sheet 40, a predetermined position in the radial direction (for example, a position exactly halfway (center) between the inner peripheral edge and the outer peripheral edge of the electromagnetic steel sheet 40) is selected. At the selected position, the thickness of the insulating coating 3 of the electromagnetic steel sheet 40 is measured at four positions equally spaced apart in the circumferential direction (i.e., at 90° intervals around the central axis O). The average value of the thicknesses measured at the four positions can be set as the average thickness t1 of the insulating coating 3.
The reason why the average thickness t1 of the insulating coating 3 was measured in this manner for the electromagnetic steel sheet 40 located at the outermost side in the stacking direction is that the insulating coating 3 is fabricated so that the thickness of the insulating coating 3 hardly changes depending on the stacking position along the stacking direction of the electromagnetic steel sheet 40.

The above-described material 1 is punched to produce electromagnetic steel sheets 40, which are then used to produce bonded cores (stator core 21 and rotor core 31).

(Lamination method of laminated core)
Returning to the description of the laminated core, the plurality of electromagnetic steel sheets 40 that form the stator core 21 are laminated with insulating coatings 3 interposed therebetween, as shown in FIG.
The electromagnetic steel sheets 40 adjacent to each other in the stacking direction are bonded over their entire surfaces by the insulating coating 3. In other words, the surface of the electromagnetic steel sheet 40 facing the stacking direction (hereinafter referred to as the first surface) is the bonding region 41a over its entire surface. However, the electromagnetic steel sheets 40 adjacent to each other in the stacking direction do not have to be bonded over their entire surfaces. In other words, the first surface of the electromagnetic steel sheet 40 may include a mixture of bonding regions 41a and non-bonding regions (not shown).

In this embodiment, the multiple electromagnetic steel sheets forming the rotor core 31 are fixed to one another by crimps 42 (dowels) shown in Fig. 1. However, the multiple electromagnetic steel sheets forming the rotor core 31 may also have a laminated structure fixed by an insulating coating 3, similar to the stator core 21.
Furthermore, the laminated cores such as the stator core 21 and the rotor core 31 may be formed by so-called rotational lamination.

(Manufacturing method of laminated core)
The stator core 21 is manufactured, for example, by using a manufacturing apparatus 100 shown in Fig. 7. In the following, before describing the manufacturing method, the laminated core manufacturing apparatus 100 (hereinafter simply referred to as the manufacturing apparatus 100) will first be described.
In the manufacturing apparatus 100, the raw material 1 is fed from the coil 1A (hoop) in the direction of the arrow F, while being punched multiple times by dies arranged at each stage, and gradually formed into the shape of the electromagnetic steel sheets 40. The punched electromagnetic steel sheets 40 are then stacked and pressurized while being heated. As a result, the electromagnetic steel sheets 40 adjacent in the stacking direction are bonded by the insulating coating 3 (i.e., the portion of the insulating coating 3 located in the bonding region 41a is allowed to exert its adhesive ability), and the bonding is completed.

As shown in FIG. 7, the manufacturing apparatus 100 has multiple punching stations 110. The punching stations 110 may have two stages, or three or more stages. Each punching station 110 has a female die 111 arranged below the material 1 and a male die 112 arranged above the material 1.

The manufacturing apparatus 100 further includes a lamination station 140 located downstream of the most downstream punching station 110. The lamination station 140 includes a heating device 141, a peripheral punching female die 142, a heat insulating member 143, a peripheral punching male die 144, and a spring 145.
The heating device 141, the outer periphery punching female die 142, and the heat insulating member 143 are disposed below the material 1. On the other hand, the outer periphery punching male die 144 and the spring 145 are disposed above the material 1. The reference numeral 21 denotes a stator core.

In the manufacturing apparatus 100 having the configuration described above, the material 1 is first sequentially sent out from the coil 1A in the direction of the arrow F in FIG. 7. Then, the material 1 is subjected to a punching process in multiple stages by the punching station 110. Through these punching processes, the material 1 is given the shape of the electromagnetic steel sheet 40 having the core back portion 22 and multiple teeth portions 23 shown in FIG. 3. However, since it is not completely punched out at this point, it proceeds to the next process in the direction of the arrow F.

Finally, the blank 1 is sent to the lamination station 140, where it is punched out by a peripheral punching male die 144 and laminated with high precision. During this lamination, the electromagnetic steel sheets 40 are subjected to a constant pressure by a spring 145. By sequentially repeating the punching and lamination processes as described above, a predetermined number of electromagnetic steel sheets 40 can be stacked. Furthermore, the laminated core formed by stacking the electromagnetic steel sheets 40 in this manner is heated by a heating device 141 to a temperature of, for example, 200° C. This heating bonds the insulating coatings 3 of adjacent electromagnetic steel sheets 40 together.
It should be noted that the heating device 141 does not have to be disposed in the outer periphery punching female die 142. That is, the electromagnetic steel sheets 40 stacked in the outer periphery punching female die 142 may be removed from the outer periphery punching female die 142 before bonding. In this case, the outer periphery punching female die 142 may not have the heat insulating member 143. Furthermore, in this case, the stacked electromagnetic steel sheets 40 before bonding may be held by clamping them from both sides in the stacking direction with a jig (not shown), and then transported or heated.
Through the above steps, the stator core 21 is completed.

As explained above, in the present invention, a specific cross-linking hot melt adhesive and a room temperature solidifying resin are combined in a specific ratio as a coating composition for electromagnetic steel sheets that forms an insulating coating on the electromagnetic steel sheets. This makes it possible to suppress the application of stress distortion due to the adhesive components even if the electromagnetic steel sheets are thin, so that a laminated core with excellent magnetic properties (core iron loss) can be formed. In addition, because the adhesive strength between the electromagnetic steel sheets is high and has excellent heat resistance, a laminated core can be formed that can ensure adhesive strength even when the motor heats up.

The technical scope of the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention.
The shape of the stator core is not limited to the form shown in the above embodiment. Specifically, the outer diameter and inner diameter of the stator core, the lamination thickness, the number of slots, the circumferential and radial dimensional ratio of the teeth portion, and the radial dimensional ratio of the teeth portion and the core back portion can be designed as desired according to the characteristics of the rotating electric machine.

In the rotor of the above embodiment, a pair of permanent magnets 32 form one magnetic pole, but the present invention is not limited to this. For example, one permanent magnet 32 may form one magnetic pole, or three or more permanent magnets 32 may form one magnetic pole.

In the above embodiment, a permanent magnet field type motor has been used as an example of a rotating electric motor, but the structure of the rotating electric motor is not limited to this, as exemplified below, and various known structures not exemplified below can also be adopted.
In the above embodiment, a permanent magnet field type motor is used as an example of a rotating electric machine, but the present invention is not limited to this. For example, the rotating electric machine may be a reluctance type motor or an electromagnetic field type motor (wound field type motor).
In the above embodiment, a synchronous motor is used as an example of an AC motor, but the present invention is not limited to this. For example, the rotating electric machine may be an induction motor.
In the above embodiment, an AC motor is used as an example of the electric motor, but the present invention is not limited to this. For example, the rotating electric machine may be a DC motor.
In the above embodiment, an electric motor is used as an example of a rotating electric machine, but the present invention is not limited to this. For example, the rotating electric machine may be a generator.

In the above embodiment, the laminated core according to the present invention is applied to a stator core, but it can also be applied to a rotor core.
The laminated core may be used in a transformer instead of a rotating electric machine. In this case, it is preferable to use grain-oriented magnetic steel sheets as the magnetic steel sheets instead of non-oriented magnetic steel sheets.

In addition, the components in the above embodiment may be replaced with well-known components as appropriate without departing from the spirit of the present invention, and the above-mentioned modifications may be combined as appropriate.

The present invention will be specifically described below with reference to examples, but the present invention is not limited to the following description.

[Raw materials]
The raw materials used are shown below.
(Polyester-based urethane resin)
PE1: Polyester-based urethane prepolymer (weight average molecular weight (Mw): 5000)
A reaction vessel equipped with a stirrer, a thermometer, a reflux condenser, a dropping device, and a nitrogen inlet tube was charged with 500 parts by mass of a polyester polyol obtained from terephthalic acid, adipic acid, and 3-methyl-1,5-pentanediol ("Kuraray Polyol P-2011" manufactured by Kuraray Co., Ltd., Mn = 2040), 15 parts by mass of dimethylolbutanoic acid, 100 parts by mass of isophorone diisocyanate, and 80 parts by mass of toluene, and reacted for 4 hours at 90°C under a nitrogen atmosphere, to which 350 parts by mass of toluene was added to obtain a solution of a polyester-based urethane prepolymer containing isocyanate groups (Mw = 5000, molar ratio (NCO/OH) = 1:1).

PE2: Polyester-based urethane prepolymer (Mw: 12000)
A solution of a polyester-based urethane prepolymer (Mw=12,000, molar ratio (NCO/OH)=1:1) containing an isocyanate group was obtained in the same manner as in PE1, except that the reaction time was changed.

PE3: Polyester-based urethane prepolymer (Mw: 35,000)
A solution of a polyester-based urethane prepolymer (Mw=35,000, molar ratio (NCO/OH)=1:1) containing an isocyanate group was obtained in the same manner as in PE1, except that the reaction time was changed.

(Polyether-based urethane resin)
PO1: Polyether-based urethane prepolymer (Mw: 5000)
100 parts by mass of an isocyanate mixture of 2,4-tolylene diisocyanate and 2,6-tolylene diisocyanate in a mass ratio of 8:2 was reacted with 600 parts by mass of polypropylene glycol at 80° C. for 2 hours and then at 100° C. for 3 hours to obtain a solution of a polyether-based urethane prepolymer (Mw=5000, molar ratio (NCO/OH)=3:1) containing an isocyanate group.

PO2: Polyether-based urethane prepolymer (Mw: 35,000)
A solution of a polyether-based urethane prepolymer (Mw=35,000, molar ratio (NCO/OH)=3:1) containing an isocyanate group was obtained in the same manner as in PE1, except that the molecular weight of the polypropylene glycol was changed.

(Hardening agent)
H1: Polytetramethylene oxide-di-p-aminobenzoate (MP: 60°C)
H2: 3,3'-dichloro-4,4'-diaminophenylmethane (MP: 98°C)
H3: Trimethylene-bis(4-aminobenzoate) (MP: 125° C.)
G1: Xylylenediamine trimer (viscous liquid, MP: below 0°C)
G2: Polytetramethylene oxide-di-p-aminobenzoate (MP: 15°C)
G3: Blocked isocyanate (MP: 105°C)
G4: Dicyandiamide (MP: 210°C)

(Room temperature hardening resin)
R1: Rosin derivative resin (softening point: 110°C)
R2: Aromatic hydrocarbon resin (softening point: 140°C)
R3: Terpene phenol resin (softening point: 160°C)
R4: Novolak phenolic resin (softening point: 180°C)

(Comparative Resin)
S1: Terpene resin (softening point: 65°C)
S2: Rosin resin (softening point: 82°C)
S3: Novolak phenolic resin (softening point: 230°C)

[Magnetic properties]
A non-oriented electrical steel sheet having a thickness of 0.25 mm and a width of 100 mm and consisting of, by mass%, 3.0% Si, 0.2% Mn, 0.5% Al, and the balance being Fe and impurities was manufactured as an electrical steel strip. The coating composition for electrical steel sheet of each example was applied to both sides of the electrical steel strip and baked under the conditions shown in Table 1 to form an insulating coating with an average sheet thickness t1 of 3 μm.
A rectangular electromagnetic steel sheet of 55 mm x 55 mm size was cut out from the electromagnetic steel strip, and 10 electromagnetic steel sheets were laminated and bonded together under conditions of a steel sheet temperature of 180°C, a pressure of 10 MPa, and a pressing time of 1 hour to produce a laminated core. The single sheet magnetic properties of the obtained laminated core were measured in the rolling direction and in the direction perpendicular to the rolling direction by a single sheet magnetic measurement method in accordance with JIS C2556 (2015), and the average value of these values was calculated as the magnetic properties.

[Adhesive strength]
Two rectangular electromagnetic steel sheets, 30 mm wide x 60 mm long, were cut out from the electromagnetic steel strip manufactured in the above test for [Magnetic Properties], and the 30 mm wide x 10 mm long tip portions of each sheet were overlapped and bonded at a steel sheet temperature of 180° C., a pressure of 10 MPa, and a pressing time of 1 hour to prepare a sample. The shear tensile strength was measured at an atmospheric temperature of 25° C. or 150° C. and a tensile speed of 2 mm/min, and the value divided by the adhesive area was taken as the adhesive strength (MPa).

[judgement]
Each example was judged according to the following criteria.
◯ (Excellent): The adhesive strength at 25° C. is 5 MPa or more, the adhesive strength at 180° C. is 0.5 MPa or more, and the magnetic properties are less than 12 W/kg.
Δ (Acceptable): The adhesive strength at 25° C. is 4 MPa or more and less than 5 MPa, the adhesive strength at 180° C. is 0.5 MPa or more, and the magnetic properties are less than 12 W/kg.
× (Poor): Does not satisfy one or more of the following: adhesive strength at 25° C. is 4 MPa or more, adhesive strength at 180° C. is 0.5 MPa or more, and magnetic properties are less than 12 W/kg.

[Examples 1 to 10, Comparative Examples 1 to 11]
The components shown in Table 1 were mixed together to prepare coating compositions for electrical steel sheets.

The composition of the coating composition for electrical steel sheets and the baking conditions for each example are shown in Table 1. The evaluation results for each example are shown in Table 2.

As shown in Table 2, in Examples 1 to 10 in which a specific cross-linking hot melt adhesive and a room temperature solidifying resin were combined in a specific ratio, the adhesive strength between the magnetic steel sheets was high at both room temperature (25°C) and 150°C, and the magnetic properties of the laminated core were also excellent.
In Comparative Examples 1 to 11, which do not satisfy the conditions such as the type of urethane resin, the softening point and content of the room-temperature solidifying resin, it was not possible to achieve both adhesive strength at room temperature and 150° C. and magnetic properties.

[Examples 21 to 26, Comparative Examples 21 to 26]
Next, an example will be shown regarding the influence of the insulating coating when the average sheet thickness t0 of the raw material (electromagnetic steel sheet) is changed. The average thickness t1 of the insulating coating is fixed at "3 μm", and the average sheet thickness t0 of the raw material is changed by changing the sheet thickness of the base steel sheet. The raw material of the insulating coating used was the same as that of Example 2 or Comparative Example 3. In addition, the base steel sheet was a non-oriented electromagnetic steel sheet with a width of 100 mm, consisting of, by mass%, 2.95% Si, 0.2% Mn, 0.4% Al, and the balance Fe and impurities.
The various evaluation methods were the same as those for [Magnetic properties], [Adhesive strength], and [Evaluation] described above, and only the thickness of the non-oriented electrical steel sheet serving as the base steel sheet was changed. The coating composition and baking conditions for Examples 21 to 25 were the same as those for Example 2 in Tables 1 and 2, and for Comparative Examples 21 to 25, they were the same as those for Comparative Example 3 in Tables 1 and 2. The evaluation results for each example are shown in Table 3. Note that "base sheet thickness t0" in Table 3 includes the average thickness t1 (3 μm) of the insulating coating.

As shown in Table 3, the iron loss decreases as the material plate thickness t0 becomes thinner in both the steel plates of the examples and the steel plates of the comparative examples, but the electromagnetic steel plate having the insulating coating of the present invention is able to suppress the iron loss lower than that of the electromagnetic steel plate of the comparative example, especially when the material plate thickness t0 is thin. This is thought to be because, as mentioned above, the insulating coating of the present invention suppresses the occurrence of stress distortion associated with hardening.

The present invention makes it possible to achieve both magnetic properties and heat resistance. Therefore, it has great industrial applicability.

1...Material, 2...Base steel plate, 3...Insulating coating, 10...Rotating motor, 20...Stator, 21...Stator core, 40...Electromagnetic steel plate.

Claims (6)

The adhesive contains a crosslinkable hot melt adhesive made of a polyester-based urethane resin, which is a reaction product of a polyester polyol and a polyisocyanate, and a curing agent, and a room temperature solidifying resin.
The softening point of the room temperature solidifying resin is 100° C. or more and 200° C. or less,
A coating composition for electrical steel sheets, wherein the content of the room-temperature-solidifying resin is 50 parts by mass or more and 300 parts by mass or less relative to 100 parts by mass of the crosslinkable hot melt adhesive. The coating composition for electrical steel sheets according to claim 1, wherein the curing agent is an aromatic amine having a melting point of 50°C or more and 200°C or less. An electrical steel sheet having an insulating coating on its surface, the insulating coating being formed by applying the coating composition for electrical steel sheets according to claim 1 or 2. The electromagnetic steel sheet according to claim 3, having a sheet thickness of 0.50 mm or less. A laminated core in which a plurality of electromagnetic steel sheets according to claim 3 or 4 are laminated and bonded together. A rotating electric machine equipped with the laminated core according to claim 5.

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