[Technical Field]
[0001]
The present invention relates to a coating composition for an electrical steel
sheet, an electrical steel sheet, a laminated core, and a rotary electric machine. Priority
is claimed on Japanese Patent Application No. 2020-104254, filed June 17, 2020, the
10 content of which is incorporated herein by reference.
[Background Art]
[0002]
A laminated core in which a plurality of electrical steel sheets are joined to each
other and laminated is known as a core (iron core) used in a rotary electric machine.
15 Caulking or welding is known as a method for joining electrical steel sheets to each
other. However, in caulking or welding, the magnetic property (core iron loss) of
electrical steel sheets is likely to deteriorate due to thermal strains or mechanical strains
during processing.
20
[0003]
A method for adhesion electrical steel sheets to each other on which insulation
coatings having an adhesive capability are formed on their surfaces (Patent Document 1)
is known as a joining method other than caulking and welding, for example. Since the
adhesion using the insulation coating does not impart mechanical strains or thermal
strains, it is superior in core iron loss compared with in caulking or welding. Epoxy
25 resins have little volume change and have excellent heat resistance, oil resistance, and
1
chemical resistance and are excellent as adhesives that bond electrical steel sheets to each
other (Patent Documents 2 and 3).
[Citation List]
[Patent Documents]
5 [0004]
[Patent Document 1]
Japanese Unexamined Patent Application, First Publication No. 2017-011863
[Patent Document 2]
Japanese Unexamined Patent Application, First Publication No. 2000-173816
10 [Patent Document 3]
15
PCT International Publication No. W02004/070080
[Summary of the Invention]
[Problems to be Solved by the Invention]
[0005]
In recent years, in response to a request for further improvement in motor
efficiency, further reduction in core iron loss has been required. Thinning of electrical
steel sheets is effective for reducing core iron loss. However, since the Young's
modulus of a steel sheet decreases as the film thickness decreases, it is required for stress
strain causing deterioration in iron loss not to be applied to the steel sheet. Since an
20 epoxy resin has excellent heat resistance but is hard and has low toughness, stress strain
is applied to a steel sheet due to hardening of the epoxy resin during adhesion.
Therefore, thinning of the steel sheet causes deterioration in iron loss.
In addition, in drive motors or the like of electric vehicles, the temperature
increases during driving, so that more heat resistance is required.
25 [0006]
2
As techniques for improving heat resistance, there is a method for incorporating
phenol resins. However, resins having excellent heat resistance are hard at normal
temperature and a large stress is applied to a laminated core, so that the magnetic
property deteriorates. On the other hand, resins having an appropriate hardness near
5 normal temperature become soft at high temperature, and therefore are inferior in heat
resistance. From these, it is difficult to achieve both excellent magnetic property and
excellent heat resistance that can maintain sufficient adhesion strength even when
exposed to high temperature during driving.
10
[0007]
An object of the present invention is to provide a coating composition for an
electrical steel sheet that can achieve both a magnetic property of a laminated core and
heat resistance that can maintain adhesion strength between electrical steel sheets even at
a high temperature during driving, and an electrical steel sheet, a laminated core, and a
rotary electric machine using the coating composition for an electrical steel sheet.
15 [Means for solving the Problem]
[0008]
The present invention has the following aspects.
[ 1] A coating composition for an electrical steel sheet according to one aspect of
the present invention includes: an epoxy resin; an epoxy resin curing agent; and an
20 elastomer-modified phenolic resin, in which the amount of the elastomer-modified
phenolic resin is 10 parts by mass to 100 parts by mass with respect to 100 parts by mass
of the epoxy resin.
[2] In the coating composition for an electrical steel sheet according to [ 1]
above, a weight average molecular weight of an elastomer portion of the elastomer-
25 modified phenolic resin may be 2,000 to 200,000.
3
[3] In the coating composition for an electrical steel sheet according to [1] or [2]
above, a curing shrinkage rate may be 15% or less.
[ 4] An electrical steel sheet according to one aspect of the present invention
having an insulating coating containing the coating composition for an electrical steel
5 sheet according to any one of [1] to [3] above on a surface.
[5] A laminated core according to one aspect of the present invention, in which a
plurality of the electrical steel sheets according to [ 4] above are laminated and caused to
adhere together.
[ 6] A rotary electric machine according to one aspect of the present invention
10 includes: the laminated core according to [5] above.
[Effects of the Invention]
[0009]
According to the above-described aspects of the present invention, it is possible
to provide a coating composition for an electrical steel sheet that can achieve both a
15 magnetic property of a laminated core and heat resistance that can maintain adhesion
strength between electrical steel sheets even at a high temperature during driving, and an
electrical steel sheet, a laminated core, and a rotary electric machine using the coating
composition for an electrical steel sheet.
[Brief Description of Drawings]
20 [0010]
25
Fig. 1 is a cross-sectional view of a rotary electric machine including a
laminated core according to a first embodiment of the present invention.
Fig. 2 is a side view of the laminated core shown in Fig. 1.
Fig. 3 is a cross-sectional view taken along line A-A of Fig. 2.
Fig. 4 is a plan view of a material for forming the laminated core shown in Fig.
4
1.
Fig. 5 is a cross-sectional view taken along line B-B of Fig. 4.
Fig. 6 is an enlarged view of a portion C of Fig. 5.
Fig. 7 is a side view of a manufacturing device used for manufacturing the
5 laminated core shown in Fig. 1.
[Embodiments for Implementing the Invention]
[0011]
Hereinafter, a laminated core according to one embodiment of the present
invention, a rotary electric machine including this laminated core, and a material forming
10 this laminated core will be described with reference to the drawings. In the present
embodiment, an electric motor, specifically an AC electric motor, more specifically a
synchronous electric motor, and still more specifically a permanent-magnet field electric
motor will be described as an example of a rotary electric machine. This type of electric
motor is suitably adopted for electric vehicles, for example.
15 [0012]
In addition, a lower limit value and an upper limit value are included in a
numerical limit range described below with "to" in between. A numerical value
represented by "less than" or "greater than" is not included in the numerical range.
[0013]
20 (Rotary Electric Machine 1 0)
25
As shown in Fig. 1, a rotary electric machine 10 includes a stator 20, a rotor 30,
a case 50, and a rotation shaft 60. The stator 20 and the rotor 30 are housed in the case
50.
The stator 20 is fixed in the case 50.
In the present embodiment, an inner rotor type is adopted for the rotary electric
5
machine 10 in which the rotor 30 is located inside in the radial direction of the stator 20.
However, an outer rotor type may be adopted for the rotary electric machine 10 in which
the rotor 30 is located outside the stator 20. In addition, in the present embodiment, the
rotary electric machine 10 is a 12-pole 18-slot three-phase AC motor. However, the
5 number of poles, the number of slots, the number of phases, and the like can be
appropriate! y changed.
The rotary electric machine 10 can rotate at a rotational speed of 1,000 rpm by
applying an excitation current having an effective value of 10 A and a frequency of 100
Hz to each phase, for example.
10 [0014]
The stator 20 includes an adhesive laminated core for a stator (hereinafter, stator
core) 21 and a winding not shown in the drawing.
The stator core 21 includes a circular core back portion 22 and a plurality of
teeth portions 23. Hereinafter, a direction of a central axis 0 of the stator core 21 (or
15 the core back portion 22) is referred to as an axial direction, a radial direction (a direction
orthogonal to the central axis 0) of the stator core 21 (or the core back portion 22) is
referred to as a radial direction, and a circumferential direction (a direction of revolving
around the central axis 0) of the stator core 21 (or the core back portion 22) is referred to
as a circumferential direction.
20 [0015]
The core back portion 22 is formed in an annular shape in a plan view of the
stator 20 when viewed from the axial direction.
The plurality of teeth portions 23 protrude from the inner circumference of the
core back portion 22 toward the inside in the radial direction (toward the central axis 0
25 of the core back portion 22 along the radial direction). The plurality of teeth portions 23
6
are arranged at equal angular intervals in the circumferential direction. In the present
embodiment, 18 teeth portions 23 are provided at every 20 degrees of the central angle
around the central axis 0. The plurality of teeth portions 23 are formed to have the
same shape and the same size as each other. Accordingly, the plurality of teeth portions
5 23 have the same thickness dimension as each other.
The winding is wound around the teeth portions 23. The winding may be
concentrically or distributedly wound.
[0016]
The rotor 30 is placed inside in the radial direction of the stator 20 (stator core
10 21). The rotor 30 includes a rotor core 31 and a plurality of permanent magnets 32.
The rotor core 31 is formed in a circular shape (annular shape) placed coaxially
with the stator 20. The rotation shaft 60 is placed in the rotor core 31. The rotation
shaft 60 is fixed to the rotor core 31.
The plurality of permanent magnets 32 are fixed to the rotor core 31. In the
15 present embodiment, a set of two permanent magnets 32 forms one magnetic pole. The
plurality of sets of permanent magnets 32 are arranged at equal angular intervals in the
circumferential direction. In the present embodiment, 12 sets (24 in total) of the
permanent magnets 32 are provided at every 30 degrees of the central angle around the
central axis 0.
20 [0017]
In the present embodiment, an embedded magnet motor is adopted as a
permanent-magnet field electric motor.
A plurality of through-holes 33 penetrating the rotor core 31 in the axial
direction are formed in the rotor core 31. The plurality of through-holes 33 are
25 provided corresponding to the arrangement of the plurality of the permanent magnets 32.
7
Each permanent magnet 32 is fixed to the rotor core 31 in a state where it is placed in a
corresponding through-hole 33. The fixation of each permanent magnet 32 to the rotor
core 31 can be realized, for example, by adhesion the outer surface of the permanent
magnet 32 to the inner surface of a through-hole 33 with an adhesive. A surface magnet
5 motor may be adopted as a permanent-magnet field electric motor instead of the
embedded magnet motor.
[0018]
Both the stator core 21 and the rotor core 31 are laminated cores. For example,
the stator core 21 is formed by laminating a plurality of electrical steel sheets 40 in the
10 lamination direction as shown in Fig. 2.
The lamination thickness (the total length along the central axis 0) 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,
15 163.0 mm. The inner diameter of the rotor core 31 is, for example, 30.0 mm.
However, these values are merely an example, and the lamination thickness, the outer
diameter, or the inner diameter of the stator core 21 and the lamination thickness, the
outer diameter, and the 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 distal portions of the teeth
20 portions 23 in the stator core 21. That is, the inner diameter of the stator core 21 is a
diameter of a virtual circle inscribed in the distal portions of all the teeth portions 23.
[0019]
Each electrical steel sheet 40 forming the stator core 21 and the rotor core 31 is
formed, for example, through punching a material I as shown in Figs. 4 to 6. The
25 material 1 is an electrical steel sheet that is a base material of the electrical steel sheets
8
40. Examples of the material I include a strip-like steel sheet or a cut sheet.
[0020]
Although it is in the middle of explanation of the laminated core, the material 1
will be described below. In the present specification, a strip-like steel sheet that is a
5 base material of the electrical steel sheets 40 is sometimes referred to as the material 1.
10
Steel sheets having a shape used for a laminated core by punching the material 1 are
sometimes referred to as the electrical steel sheets 40.
[0021]
(Material 1)
The material I is handled in a state where it is wound around a coillA shown in
Fig. 7, for example. In the present embodiment, a non-oriented electrical steel sheet is
adopted as the material I. As the non-oriented electrical steel sheet, a non-oriented
electrical steel sheet of JIS C 2552:2014 can be adopted. However, a grain-oriented
electrical steel sheet may be adopted as the material I instead of the non-oriented
15 electrical steel sheet. As the grain-oriented electrical steel sheet in this case, a grain-
20
oriented electrical steel sheet of JIS C 2553:2019 can be adopted. In addition, a nonoriented
thin electrical steel strip or a grain-oriented thin electrical steel strip of JIS C
2558:2015 can be adopted.
[0022]
For example, upper and lower limit values of an average sheet thickness tO of
the material 1 are set as follows in consideration of a case where the material 1 is used as
the electrical steel sheet 40.
As the material 1 becomes thinner, the production cost of the material 1
Increases. For this reason, when considering the production cost, the lower limit value
25 of the average sheet thickness tO of the material I is 0.10 mm, preferably 0.15 mm, and
9
more preferably 0.18 mm.
On the other hand, if the material 1 is too thick, the production cost becomes
favorable. However, in a case where the material 1 is used as the electrical steel sheet
40, eddy current loss increases and core iron loss deteriorates. For this reason, when
5 considering the core iron loss and the production cost, the upper limit value of the
average sheet thickness tO of the material 1 is 0.65 mm, preferably 0.35 mm, and more
preferably 0.30 mm.
For example, 0.20 mm may satisfy the above-described range of the average
sheet thickness tO of the material 1.
10 [0023]
The average sheet thickness tO of the material I includes not only the thickness
of the base steel sheet 2 to be described below but also the thickness of an insulation
coating 3. In addition, a method for measuring the average sheet thickness tO of the
material 1 is, for example, a measurement method below. For example, in a case where
15 the material 1 is wound into a shape of the coil 1 A, at least a part of the material 1 is
unwound into a flat sheet shape. In the material 1 unwound into a flat plate shape, a
predetermined position in the longitudinal direction of the material I (for example, a
position separated from an edge of the material 1 in the longitudinal direction by 10% of
the total length of the material 1) is selected. At this selected position, the material 1 is
20 divided into five regions along the width direction thereof. The sheet thickness of the
material I is measured at four locations that become boundaries of these five regions.
The average value of the sheet thickness at four locations can be set to the average sheet
thickness tO of the material 1.
[0024]
25 The upper and lower limit values of the average sheet thickness tO of this
10
material 1 can be naturally adopted as upper and lower limit values of the average sheet
thickness tO of the electrical steel sheet 40. A method for measuring the average sheet
thickness tO of the electrical steel sheet 40 is, for example, a measurement method below.
For example, the lamination thickness of the laminated core is measured at four locations
5 at equal intervals in the circumferential direction (that is, every 90 degrees around the
central axis 0).
Each lamination thickness measured at the four locations is divided by the
number of sheets of the electrical steel sheets 40 laminated to calculate the sheet
thickness per sheet. The average value of the sheet thickness at four locations can be set
10 to the average sheet thickness tO of the electrical steel sheet 40.
[0025]
As shown in Figs. 5 and 6, the material 1 includes the base steel sheet 2 and the
insulation coating 3.
The material 1 is formed by covering both surfaces of the strip-like base steel
15 sheet 2 with the insulation coating 3. In the present embodiment, the majority of the
material 1 is formed of the base steel sheet 2, and insulation coatings 3 thinner than the
base steel sheet 2 are laminated on the surfaces of the base steel sheet 2.
[0026]
The chemical composition of the base steel sheet 2 contains 2.5% to 4.5% of Si
20 by mass% as shown below. By setting the chemical composition to be within this
range, the yield strength of the material 1 (electrical steel sheet 40) can be set to, for
example, 380 MPa to 540 MPa.
[0027]
25
Si: 2.5% to 4.5%
Al: 0.001% to 3.0%
11
Mn: 0.05% to 5.0%
Remainder: Fe and Impurities
[0028]
When the material 1 is used as the electrical steel sheet 40, the insulation coating
5 3 exhibits insulation performance between electrical steel sheets 40 adjacent to each
other in the lamination direction. In addition, in the present embodiment, the insulation
coating 3 has an adhesive capability and causes the electrical steel sheets 40 adjacent to
each other in the lamination direction to adhere to each other. The insulation coating 3
may have a single-layer structure or a multi-layer structure. More specifically, for
10 example, the insulation coating 3 may have a single-layer structure having both the
insulation performance and an adhesive capability or may have a multi-layer structure
including a lower base insulation coating having excellent insulation performance and an
upper base insulation coating having an excellent adhesion performance. The "adhesive
capability of the insulation coating 3" in the present embodiment means a capability of
15 expressing an adhesion strength of greater than or equal to a predetermined value under a
predetermined temperature condition in a laminate including a plurality of the electrical
steel sheets 40 laminated with insulation coatings 3 sandwiched therebetween.
[0029]
In the present embodiment, the insulation coating 3 covers both surfaces of the
20 base steel sheet 2 without any gap over the entire surfaces. However, a partial layer of
the insulation coating 3 may not cover both surfaces of the base steel sheet 2 without any
gap as long as the above-described insulation performance or adhesive capability can be
ensured. In other words, a partial layer of the insulation coating 3 may be intermittently
provided on the surfaces of the base steel sheet 2. However, in order to ensure
25 insulation performance, it is necessary for both surfaces of the base steel sheet 2 to be
12
covered with the insulation coating 3 so that the entire surfaces of the base steel sheet 2
are not exposed. Specifically, in a case where the insulation coating 3 has a single-layer
structure having both insulation performance and adhesive capability without having a
lower base insulation coating having excellent insulation performance, it is necessary for
5 the insulation coating 3 to be formed over the entire surfaces of the base steel sheet 2
without any gap. On the other hand, in a case where the insulation coating 3 has a
multi-layer structure including a lower base insulation coating having excellent insulation
performance and an upper base insulation coating having an excellent adhesive
capability, both the insulation performance and the adhesive capability can be obtained
10 not only by forming both the lower base insulation coating and the upper base insulation
coating over the entire surfaces of the base steel sheet 2 without any gap but also by
forming the lower base insulation coating over the entire surfaces of the base steel sheet
without any gap and intermittently providing the upper base insulation coating.
15

What is claimed is:
1. A coating composition for an electrical steel sheet comprising:
an epoxy res1n;
an epoxy resin curing agent; and
an elastomer-modified phenolic resin,
wherein an amount of the elastomer-modified phenolic resin is 10 parts by mass
to 100 parts by mass with respect to 100 parts by mass of the epoxy resin.
10 2. The coating composition for an electrical steel sheet according to claim 1,
wherein a weight average molecular weight of an elastomer portion of the
elastomer-modified phenolic resin is 2,000 to 200,000.
3. The coating composition for an electrical steel sheet according to claim 1 or 2,
15 wherein a curing shrinkage rate is 15% or less.
20
4. An electrical steel sheet comprising:
an insulation coating containing the coating composition for an electrical steel
sheet according to any one of claims 1 to 3 on a surface.
5. A laminated core,
wherein a plurality of the electrical steel sheets according to claim 4 are
laminated and caused to adhere together.
25 6. A rotary electric machine comprising:
37
the laminated core according to claim 5.
38