[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. 2020-104235, 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 an excellent magnetic property and
excellent heat resistance that can maintain sufficient adhesion strength even in a state
where the drive motors or the like are 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; a first curing agent including an
20 alkylphenol; and a second curing agent including either one or both of a phenol resol
resin and a phenol novolac resin, in which the amount of the first curing agent is 1.0 part
by mass to 20.0 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, the alkyl phenols may include either one or both of a monoalkylphenol having an
25 alkyl group with 2 to 20 carbon atoms and a dialkylphenol having an alkyl group with 2
3
5
10
to 20 carbon atoms.
[3] In the coating composition for an electrical steel sheet according to [1] or [2]
above, the amount of the second curing agent may be 5.0 parts by mass to 150.0 parts by
mass with respect to 100 parts by mass of the epoxy resin.
[ 4] In the coating composition for an electrical steel sheet according to any one
of [1] to [3] above, a curing shrinkage rate may be 15% or less.
[5] In the coating composition for an electrical steel sheet according to any one
of [1] to [ 4] above, a mass ratio represented by (amount of the first curing agent
(A))/( amount of the second curing agent (B)) may be 0.01 to 4.0.
[ 6] An electrical steel sheet according to one aspect of the present invention
having an insulating coating containing the coating composition for an electrical steel
sheet according to any one of [1] to [5] above on a surface.
[7] A laminated core according to one aspect of the present invention, in which a
plurality of the electrical steel sheets according to [6] above are laminated and caused to
15 adhere together.
20
[8] A rotary electric machine according to one aspect of the present invention
includes: the laminated core according to [7] 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
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
25 composition for an electrical steel sheet.
4
5
10
15
[Brief Description of Drawings]
[0010]
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.
1.
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.
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
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
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
20 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.
[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
25 represented by "less than" or "greater than" is not included in the numerical range.
5
[0013]
(Rotary Electric Machine 1 0)
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
5 50.
The stator 20 is fixed in the case 50.
In the present embodiment, an inner rotor type is adopted for the rotary electric
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
10 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
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
15 applying an excitation current having an effective value of 10 A and a frequency of 100
Hz to each phase, for example.
20
[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
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
25 around the central axis 0) of the stator core 21 (or the core back portion 22) is referred to
6
5
as a circumferential direction.
[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
of the core back portion 22 along the radial direction). The plurality of teeth portions 23
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
10 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
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.
15 [0016]
The rotor 30 is placed inside in the radial direction of the stator 20 (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 a circular shape (annular shape) placed coaxially
with the stator 20. The rotation shaft 60 is placed in the rotor core 31. The rotation
20 shaft 60 is fixed to the rotor core 31.
The plurality of permanent magnets 32 are fixed to the rotor core 31. In the
present embodiment, a set of two permanent magnets 32 forms one magnetic pole. The
plurality 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
25 permanent magnets 32 are provided at every 30 degrees of the central angle around the
7
central axis 0.
[0017]
In the present embodiment, an embedded magnet motor is adopted as a
permanent-magnet field electric motor.
5 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
provided corresponding to the arrangement of the plurality of the permanent magnets 32.
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
10 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
motor may be adopted as a permanent-magnet field electric motor instead of the
embedded magnet motor.
15
[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
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
20 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 an example, and the lamination thickness, the outer
diameter, or the inner diameter of the stator core 21 and the lamination thickness, the
25 outer diameter, and the inner diameter of the rotor core 31 are not limited to these values.
8
5
10
Here, the inner diameter of the stator core 21 is based on distal portions of the teeth
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
material 1 is an electrical steel sheet that is a base material of the electrical steel sheets
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
base material of the electrical steel sheets 40 is sometimes referred to as the material 1.
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.
15 [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
20 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
electrical steel sheet. As the grain-oriented electrical steel sheet in this case, a grainoriented
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
25 2558:2015 can be adopted.
9
5
[0022]
For example, upper and lower limits 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
of the average sheet thickness tO of the material I 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 production cost becomes
10 favorable. However, in a case where the material 1 is used as the electrical steel sheet
15
40, eddy current loss increases and core iron loss deteriorates. For this reason, when
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.
[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
20 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
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
25 position separated from an edge of the material 1 in the longitudinal direction by 10% of
10
the total length of the material 1) is selected. At this selected position, the material 1 is
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.
An average value of the sheet thickness at four locations can be set to the average sheet
5 thickness tO of the material 1.
[0024]
The upper and lower limits of the average sheet thickness tO of this material 1
can be naturally adopted as upper and lower limits of the average sheet thickness tO of
the electrical steel sheet 40. A method for measuring the average sheet thickness tO of
10 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
(that is, every 90 degrees around the central axis 0) at equal intervals in the
circumferential direction.
Each lamination thickness measured at the four locations is divided by the
15 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
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
20 insulation coating 3.
The material 1 is formed by covering both surfaces of the strip-like base steel
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.
25 [0026]
11
5
10
The chemical composition of the base steel sheet 2 contains 2.5% to 4.5% of Si
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]
Si: 2.5% to 4.5%
Al: 0.001% to 3.0%
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
3 exhibit 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
15 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, 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
20 insulation coating having an excellent adhesion performance, for example. The
"adhesive capability of the insulation coating 3" in the present embodiment means an
ability capable of 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
25 sandwiched therebetween.
12
[0029]
In the present embodiment, the insulation coating 3 covers both surfaces of the
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
5 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
insulation performance, it is necessary for both surfaces of the base steel sheet 2 to be
covered with the insulation coating 3 so that the entire surfaces of the base steel sheet 2
10 are not exposed. Specifically, in a case where the insulation coating 3 has a single-layer
structure having both insulation performance and an adhesive capability without having a
lower base insulation coating having excellent insulation performance, it is necessary for
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
15 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
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
20 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.
[0030]
A coating composition constituting the lower base insulation coating is not
particularly limited, but general treatment agents such as a chromic acid-containing
25 treatment agent and a phosphate-containing treatment agent can be used, for example.
13
5
[0031]
The insulation coating 3 having an adhesive capability is obtained such that a
coating composition for an electrical steel sheet containing an epoxy resin, a first curing
agent (A), and a second curing agent (B) is applied thereto.
The insulation coating made of the coating composition for an electrical steel
sheet is in an uncured state or semi-cured state (stage B) before thermocompressionbonding
during production of a laminated core, and exhibits an adhesive capability when
a curing reaction proceeds through heating during the thermocompression-bonding.
The coating composition for an electrical steel sheet may be used for forming an
10 insulation coating with a single-layer structure, or may be used for forming an upper base
insulation coating provided on a lower base insulation coating.
[0032]
As the epoxy resin, a general epoxy resin can be used. Specifically, any epoxy
resin having two or more epoxy groups in a molecule can be used without particular
15 limitation. Examples of such epoxy resins include a bisphenol A-type epoxy resin, a
bisphenol F-type epoxy resin, a phenol novolac-type epoxy resin, a cresol novolac-type
epoxy resin, a triphenylmethane-type epoxy resin, an alicyclic epoxy resin, a glycidyl
ester-type epoxy resin, a glycidyl amine-type epoxy resin, a hydantoin-type epoxy resin,
an isocyanurate-type epoxy resin, an acrylic acid-modified epoxy resin (epoxy acrylate),
20 a phosphorus-containing epoxy resin, and hydrogenated products or halides (such as a
brominated epoxy resin) thereof. The epoxy resins may be used alone or a combination
of two or more thereof may be used.
[0033]
The amount of epoxy resin with respect to the total mass of the coating
25 composition for an electrical steel sheet is, for example, preferably 30 to 90 mass%, more
14
preferably 40 to 80 mass%, and still more preferably 50 to 70 mass%. When the
amount of epoxy resin is greater than or equal to the above-described lower limit value,
the adhesion strength of the electrical steel sheets 40 can be further enhanced. When
the amount of epoxy resin is less than or equal to the above-described upper limit value,
5 stress strain of the electrical steel sheets 40 can be further suppressed.
[0034]
The first curing agent includes an alkylphenol.
The alkyl phenol is not particularly limited, and examples thereof include cresol
(such as o-cresol), ethylphenol (such as o-ethylphenol), propylphenol (such asp-
10 propylphenol and p-isopropylphenol), butylphenol (such as p-butylphenol and p-secbutylphenol),
nonylphenol (such as p-nonylphenol), dodecylphenol (such as pdodecylphenol),
dimethylphenol (such as 2,3-dimethylphenol), diethylphenol (such as
2,3-diethylphenol), dibutylphenol (such as 2,6-di-sec-butylphenol), and trimethylphenol
(such as 2,3,4-trimethylphenol). The alkylphenols may be used alone or a combination
15 of two or more thereof may be used.
[0035]
From the viewpoint of easily achieving both a magnetic property and heat
resistance, the alkylphenol preferably includes either one or both of a monoalkylphenol
having an alkyl group with 2 to 20 carbon atoms and a dialkylphenol having an alkyl
20 group with 2 to 20 carbon atoms.
The number of carbon atoms of an alkyl group of a monoalkylphenol is more
preferably 3 to 16 and still more preferably 4 to 12.
The number of carbon atoms of each of two alkyl groups of a dialkylphenol is
more preferably 3 to 20 and still more preferably 4 to 12.
25 [0036]
15
The amount of first curing agent (A) in the coating composition for an electrical
steel sheet is 1.0 part by mass to 20.0 parts by mass with respect to 100 parts by mass of
the epoxy resin. If the amount of first curing agent (A) is greater than or equal to the
lower limit value, a laminated core with excellent heat resistance can be obtained. If the
5 amount of first curing agent is less than or equal to the upper limit value, a laminated
core with an excellent magnetic property can be obtained.
The lower limit value of the amount of first curing agent (A) is preferably 2.0
parts by mass or more and more preferably 3.0 parts by mass or more. The upper limit
of the amount of first curing agent (A) is preferably 18.0, more preferably 16.0 parts by
10 mass or less, and still more preferably 15.0 parts by mass or less.
[0037]
The second curing agent (B) is one or more selected from a phenol resol resin
and a phenol novolac resin. The phenol resol resin and the phenol novolac resin as the
second curing agents have neither an alkyl group nor an alkoxy group in the phenol
15 skeleton.
20
As the second curing agent (B), the phenol resol resin may be used alone, the
phenol novolac resin may be used alone, and the phenol resol resin and the phenol
novolac resin may be used in combination.
[0038]
The total amount of second curing agent (B) in the coating composition for an
electrical steel sheet is preferably 5.0 part by mass to 150.0 parts by mass with respect to
100 parts by mass of the epoxy resin. If the amount of second curing agent (B) is
greater than or equal to the lower limit value, heat resistance can be ensured. If the
amount of second curing agent (B) is less than or equal to the upper limit value,
25 deterioration in magnetic property can be suppressed.
16
The upper limit of the amount of second curing agent (B) is preferably 5.0 parts
by mass or more, more preferably 10.0 parts by mass or more, and still more preferably
20.0 parts by mass or more. The upper limit of the amount of second curing agent (B)
is preferably 150.0 parts by mass or less, more preferably 100.0 parts by mass or less,
5 and still more preferably 70.0 parts by mass or less.
[0039]
The mass ratio (hereinafter, also referred to as an "A-to-B ratio") represented by
(amount of first curing agent (A))/(amount of second curing agent (B)) is preferably 0.01
to 4.0. The A-to-B ratio is more preferably 0.1 or more and still more preferably 0.25 or
10 more. In addition, the A-to-B ratio is more preferably 3.8 or less and still more
preferably 3.5 or less. When the A-to-B ratio is within the range between the abovedescribed
upper limit and lower limit values, both the heat resistance and the suppression
of stress strain can be favorably achieved.
15
[0040]
The coating composition for an electrical steel sheet may contain components
other than the epoxy resin, the first curing agent (A), and the second curing agent (B).
Examples of the other components include an acrylic resin, curing agents other than the
first curing agent (A) and the second curing agent (B), a curing promoter (curing
catalyst), an emulsifier, and a defoaming agent. From the viewpoint of ensuring the
20 adhesion strength, the coating composition for an electrical steel sheet does not contain
inorganic fillers such as silica, alumina, and glass. The other components may be used
alone or a combination of two or more thereof may be used.
[0041]
The acrylic resin is not particular! y limited. Examples of monomers used for
25 acrylic resins include unsaturated carboxylic acids such as acrylic acid and methacrylic
17
acid, and (meth)acrylates such as methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl
(meth)acrylate, isobutyl (meth)acrylate, cyclohexyl (meth)acrylate, 2-ethylhexyl
(meth)acrylate, 2-hydroxyethyl (meth)acrylate, and hydroxypropyl (meth)acrylate. The
(methacrylate) means an acrylate or a methacrylate. The acrylic resins may be used
5 alone or a combination of two or more thereof may be used.
[0042]
An acrylic resin may have a structural unit derived from monomers other than an
acrylic monomer. Examples of other monomers include ethylene, propylene, and
styrene. The other monomers may be used alone or a combination of two or more
10 thereof may be used.
[0043]
The glass transition point (Tg point) of an acrylic resin is not particularly
limited, but the lower limit thereof is preferably -40°C and more preferably -20°C. The
upper limit of the Tg point of an acrylic resin is preferably 80°C and more preferably
15 50°C.
[0044]
In a case where the coating composition for an electrical steel sheet contains an
acrylic resin, the amount of acrylic resin is not particular! y limited and can be set to, for
example, 1 mass% to 50 mass% with respect to the total amount of the epoxy resin and
20 the acrylic resin. In a case where an acrylic modified epoxy resin or an acrylic
monomer is contained, the same applies to the amount thereof.
[0045]
In a case where an acrylic resin is used, an acrylic modified epoxy resin obtained
by grafting an acrylic resin onto an epoxy resin may be used. The coating composition
25 for an electrical steel sheet may contain a monomer that forms an acrylic resin.
18
[0046]
Examples of the other curing agents include a latent epoxy resin curing agent
that initiates a curing reaction through heating. Specific examples thereof include
aromatic polyamines, acid anhydrides, dicyandiamide, boron trifluoride-amine
5 complexes, and organic acid hydrazides. The other curing agents may be used alone or
a combination of two or more thereof may be used.
[0047]
The amount of the other curing agents in the coating composition for an
electrical steel sheet is preferably 20 parts by mass or less and more preferably 10 parts
10 by mass or less with respect to 100 parts by mass of the epoxy resin.
[0048]
In general, epoxy resin adhesives with excellent heat resistance have a large
Young's modulus near normal temperature when the adhesion strength at a high
temperature is guaranteed, and stress is applied to a steel sheet to deteriorate the magnetic
15 property (core iron loss). On the other hand, in a case of a resin composition having a
moderate strength near normal temperature, the heat resistance deteriorates.
In the present embodiment, when an alkylphenol of the first curing agent (A) is
used in combination with the second curing agent (B), a cured product has a structure
having an alkyl group as a side chain. For this reason, the elastic modulus of the cured
20 product decreases moderately, and the stress applied to the steel sheet is reduced,
whereby a laminated core with an excellent magnetic property can be obtained. In
addition, since phenol resins have excellent heat resistance, the heat resistance is also
improved by using the first curing agent (A) and the second curing agent (B) in
combination. Therefore, both a magnetic property and heat resistance can be achieved.
25 [0049]
19
The curing shrinkage rate of the coating composition for an electrical steel sheet
is preferably 15% or less, more preferably 12% or less, still more preferably 10% or less,
and particularly preferably 8% or less. If the curing shrinkage rate is less than or equal
to the upper limit value, the application of stress to a steel sheet is likely to be reduced
5 and a laminated core with an excellent magnetic property is likely to be obtained.
6941.
[0050]
The curing shrinkage rate is measured through a method according to JIS K
The insulation coating 3 can be formed, for example, by applying a coating
10 composition for an electrical steel sheet to the surface of a base steel sheet and
performing drying and baking.

[CLAIMS]
What is claimed is:
1. A coating composition for an electrical steel sheet comprising:
an epoxy res1n;
a first curing agent (A) including an alkylphenol; and
a second curing agent (B) including either one or both of a phenol resol resin
and a phenol novolac resin,
wherein an amount of the first curing agent (A) is 1.0 part by mass to 20.0 parts
by mass with respect to 100 parts by mass of the epoxy resin.
2. The coating composition for an electrical steel sheet according to claim 1,
wherein the alkylphenols include either one or both of a
monoalkylphenol having an alkyl group with 2 to 20 carbon atoms and a dialkylphenol
having an alkyl group with 2 to 20 carbon atoms.
3. The coating composition for an electrical steel sheet according to claim 1 or 2,
wherein an amount of the second curing agent (B) is 5.0 parts by mass to 150.0
parts by mass with respect to 100 parts by mass of the epoxy resin.
20 4. The coating composition for an electrical steel sheet according to any one of claims 1
to 3,
wherein a curing shrinkage rate is 15% or less.
5. The coating composition for an electrical steel sheet according to any one of claims 1
25 to 4,
37
wherein a mass ratio represented by (amount of the first curing agent
(A))/(amount of the second curing agent (B)) is 0.01 to 4.0.
6. An electrical steel sheet comprising:
5 an insulating coating containing the coating composition for an electrical steel
sheet according to any one of claims 1 to 5 on a surface.
7. A laminated core,
wherein a plurality of the electrical steel sheets according to claim 6 are
10 laminated and caused to adhere together.