Note: Descriptions are shown in the official language in which they were submitted.
13276~
1 EPOXY RESIN POWDER COATING COMPOSITION
FIELD OF THE INVENTION
The present invention relates to an epoxy resin
powder coating composition suitably used for the
insulation of slots of motor rotors.
BACKGROUND OF THE INVENTION
~ poxy resin powder coating compositions are widely
used for the insulation of electric and electronic
equipments and parts. Examples are in JP-A-55-84371 and
~ 10
57-42760 (the term "JP-A" as used herein means an
unexamined published Japanese patent application) which
disclose powder coating compositions comprising a rubber
modified epoxy resin, a hardener, and a filler. Those
powder coating compositions are effective to form
insulating films on smooth surfaces, however, are not
satisfactory as insulating powder coating compositions for
slots having edges such as in motor rotors and stators of
ele~tric and electronic equipments and parts.
A temperature of 180C or higher is required to
rapidly harden the epoxy resin to form insulating films on
slots having edges. However, the aforesaid conventional
epoxy resins, when heated under such a temperature
condition, fail to form films with sufficient thickness on
the edge parts, and, moreover, lack the necessary physical
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1 properties such as thermal resistance, adhesiv~ness, and
impact resistance. In addition, surface smoothness is not
attained.
SUMMARY OF THE INVENTION
The present invention aims to provide an epoxy
resin powder coating composition which overcomes the
aforesaid shortcomings of the conventional epoxy resin
- powder coating compositions.
That is, the present invention provides an epoxy
resin powder coating composition which comprises:
(A~ an epoxy resin comprising mainly of a
bisphenol A type epoxy resin mixture of (a) a bi~phenol
A type ,epoxy resin having a number average molecular weight
of from 2, 500 to 8, 000 and ~b) a bisp~enol A type epoxy resin
~ 15 ~aving 8 number average molecular weight of from 350 eo
1 1,700, said ~ixeure baving a number average molecular weight of from 1~700 to 4,500;
(B~ rubber powder ~n an amount of 2 to 30 part~ -
by weight per lOO parts by weiqht of said epoxy resin (A); ~'
(C) at least one hardener; and
(D) a filler. ' , ,
DETAILED EXPL~NATION OF THE INVENTION '~
The epoxy resin used in the present invention is
j based on bisphenol A type epoxy resin. The bisphenol A ,~
1 25 type epoxy resin is pr.epared by blending a bisphenol A
! q~ epoxy ~#~n having a nu~ average leQ~ar weight of from 2,500 ~,','''',',
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,
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to 8,000 with that having a nu~r average m~lecular weight of from 350
to 1,700.
` The mixture has a n~r average molecular weight of
from 1,700 to 4,500, preferably from 1,800 to 4,000, and
more preferably from 2,000 to 3,000- When the n~r average
molecular weight is less than 1,700, the edge coverage
' decreases, and when it exceeds 4,500, it is not
appropriate since adhesiveness or surface smoothness of
film is damaged and is apt to form pinholes.
` 10The bisphenol A type epoxy resin is a synthetic
resin obtained by condensation polymerization of bisphenol
A and epichlorohydrin, and is represented by general
formula ~
. ..-
15 ` O - C~13 ~ o~ C~3 0
CH2-CB-C~2 o~ CH2-1B-CB2 ~ ~ -CH2-CH-C~2
CH~ CB3
n
wherein n is a degree of polymerization.
ffle bispx~ol A type ep~y resin a having a number average
molecular weight of from 2,500 to 8,000 suitably used in
the present invention has a melting point of from 120 to
160C, and pr~ably ~rom 130 to 150C. ffle nu~r average mol~ar
weight of (a) is preferably from 2,700 to 6,S00.
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The other bisperx)l A type epoxy resin b ~ving a nuT~er average
molecular weight of from 350 to 1,700 has a melting point
- of 100C or lower, preferably having a liquid phase at
'3 ordinary temperature. The molecular weight of (b) is
preferably from 30Q to 50Q.
A mixture of (a! and (b) is used for the present
invention.
Also, a third different bisphenol A type epoxy
resin with a nu~x~ average mole~i~r weight of ~mm 1,700 to 2,500 may
be added in a small amount (generally, of from 5 to 40~ by
weight, preferably from 5 to 35% by weight, and more
preferably from 10 to 3Q~ by weight of the total amount of
the epoxy resins) such that the nu~r average mole~ar weight
~ of the resulting mixture is in the range of from 1,700 to
¦ 15 4,500. Further, an epoxy resin of a different type may be
~ added in ~n amount of, generally from 5 to 40~ by weight,
i preflerably from 5 to 35~ by weight, and more preferably
from 10 to 30~ by weight of the totàl amount of the epoxy
~ resins.
¦ 20 Example of epoxy resins other than bisphenol A
type include polyfunctional epoxy resins having three or
I more epoxy groups in the molecule. Such epo~y resinsinclude novolak type (o-cresol novolak type, phenol
novolak type, etc.) e]poxy resins, triglicydyl ether epoxy
type reslns ~epoxy co~npounds of cyanuric acid or
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`` 13~7~
1 triphenylpropane) and tetraglycidyl ether type epoxy
resins (epoxy compounds of bisresorcinol F or tetraoxy
tetraphenylethane, etc.).
, When the polyfunctional epoxy resin is used in the
j 5 coating composition of the present invention, the
proportion of the polyfunctional epoxy resin is generally
from 5 to 40~ by wei~ht, preferably from 5 to 35% by
w~ight, and more preferably from 10 to 30% by wei~ht of
the total amount of the epoxy resins.
Other types of epoxy resins may be used in the
present invention, provided that the epoxy resin other
~ than bisphenol A type should not be incorporated in an
¦ amount of more than 40% by weight of the total epoxy
resin~ -
3 15 In the powder coating composition of the present
invention, rubber powder is blended. The content of the
rubber powder in the coating composition is from 2 to 30
parts, preferably from 5 to 15 parts by weight per 100
parts by weight of the total amount of epoxy resin. This
¦ 20 relative content provides for a powder coating composition
having a coating property especially improved in edge
coverage and thermal resistance.
The rubber powder used in the present invention is
essentially chemically inert to epoxy resin. Further, it
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1 substantially disperses in the solid state when mixed with
; molten epoxy resin.
Examples of rubber powders are nitrile/butadiene
t, based rubber (NBR), a chloroprene rubber, butadiene
rubber, isoprene rubber, etc. The particle size of the
rubber should be in the range of from about 100 to 500 ~m,
~ preferably from 130 to 250 ~m.
~~ When it is mixed with molten epoxy resin, it is
preferable to use the rubber powder in a mixture with a
filler, especially with calcium carbonate. The rubber
powder is better dispersed in molten epoxy resin when used `
as a mixture. Moreover, rubber powder is more readily
~ ground to fine powder and the filler incorporated in the
`2~ mixture avoids blocking of the finely ground rubber
.,.
po~der.
The amount of filler added is preferably from 5 to `
25 parts, and more pre$erably from 10 to 20 parts, by
weight, per 100 parts by weight of rùbber powder. `
The hardener to be blended with the powder coating
composition of the present invention includes those
conventiona~ly usedr such as aromatic amines, acid
anhydrides, guanidines (dicyandiamide, etc.), and
imidazoles. To achieve optimal gloss, adhesiveness and
I edge coverage, two or more hardeners having different
hardening speed can be appropriately blended to give a - ;
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1327664
1 mixture of hardeners with controlled hardening speed. Too
high a hardening speed results in a hardener which gives a
dull coatin~ with poor adhesiveness, and too low a speed
results in poor edge coverage. The amount of hardener
added differs according to the type. An example is an
s imidazole type hardener which is added in an amount of
from O.l to 5 parts, preferably from 0.2 to 4 parts by
weight per lO0 parts by weight of the total amount of the
epoxy resins.
~ lO In the case of using a combination of hardeners
havinq different hardening speed, the high speed hardener
can function as a hardening promoter to the low speed
hardener.
Specific examples of the low speed hardeners
include 2-methyl imidazole, diaminodiphenylsulfone,
¦ diaminodiphenylether, etc.
Specfic examples of the high speed hardeners
include 2,4-diamino-6-12'-methylimidazolyl (l)]ethyl-s-
triazine, 2-phenyl imida20le, 2-ethyl-4-methyl imidazole,
etc~
When a mixture of two or more hardeners having
different hardening speed is employed, the combination of
¦ an imidazole type high speed hardener with a low speed
! hardener chosen from ~elow is preferred.
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1 Examples of imidazole compounds that are high
speed hardeners can be expressed in accordance with
general formula (II);
Rl-N ~ (II)
R
,
wherein Rl represents a hydro~en atom or an alkyl group - -
substituted with an aryl group (e.g., -CH2- ~ ),
and R2 represents a substituted or unsubstituted alkyl
group (e.g., CH3, C~Hs, CH(CH3)2, CllH23, C~H35) or an aryl
group te.g... phenyl, tolyl, xylyl). Preferably, the alkyl `
group has 1 to 20 carbon atoms and the aryl group has 6 to
20 carbon atoms.
Examples of imidazole compounds that are low speed
hardeners can be expressed in accordance with general
~ormula (III);
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R3-N ~ (III)
R4
1 wherein R3 represents an alkyl group substituted with a
cyano group (e.g., C~2C~2CN) or a group of
NH2
CH2CH2 ~ ~ , and R~ represents a substituted or
NH2
unsubstituted alkyl group (e.g., CH3, C2~5, CH(CH3)2,
~23- Cl7~3s) or an aryl group (e.g~, phenyl, tolyl,
..
xylyl3. Preferably, thle alkyl group has 1 to 20 carbon
atoms and the aryl group has 6 to 20 carbon atoms.
In the case of using a combination of imidazole
type hardeners, preferably O.OS to 0.7 part by weight of a
high speed hardener is used with 0.5 to 3 parts by weight
of a low speed hardener per 100 parts by weight of the
total amount of epoxy resins.
lS Inorganic }illers suitably blended with the
composition of the present invention include silica,
calcium carbonate, alumina, clay, mica, talc, and powdered
glass fibers. ~he amount to be blended is generally from
5~ '
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~3276~4
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1 10 to 80%, and preferably from 20 to 50~, by weight, of
the total weight of the powder coating composition.
Conventional additives such as leveling agents
(e.g., acrylic acid ester oligomers), pigments (e.g.,
Cr203, Fe203), impact resistance improvers (e.g.,
butadiene-acrylonitrile copolymer, butyral resin), and
hardening promoters (e.g~, 2-phenylimidazole, 2-ethyl-4-
methylimidazole) may be appropriately blended with the
powder coating composition of the present invention.
Conventional methods can be used to blend the
components of the epoxy resin powder coating composition
of the present invention. For example, the components can
be dry-mixed with a mixer or the like, melt-mixed using a
kneader or the like, or solidified by cooling after melt-
mixed usinq an extruder or the like, and then ground to :
fine particles.
The present invention is hereinafter described in
qreater detail with reference to the examples, which are
not to be construed as limiting the scope thereof. Unless
otherwise indicated, all parts, percents and ratios are by
weight.
EXAMPLE 1
Epoxy resin powder coating compositions as shown
in Table 1 were prepared. The following are the
explanations for ~he c:omponents in Table 1.
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13276~
Epikote 1007*: a bisp~enol-A type epoxy resin having a n ~ er average
molecular wei~ht of about 2,900, with a
melting point of 128C; from Yuka
Shell Epoxy Co. Ltd.
EOCN 104*: an o-cresol novolak type epoxy resin
having a softening point of 95C; from
Nippon Kayaku Co~ Ltd.
Epikote lQ04*: a bisp~enol-A type epo~cy resin having a n ~ er average
molecular weight of about 1,600, with a
~ 10 melting point of 98C; from Yuka Shell
,~ Epoxy Co. Ltd.
Rubber modified epoxy resin: ~ -
an epoxy resin modified with a liquid
nitrile rubber having a -COOH group at
the end, with a melting point of 100C; ~ -
Epomic SR-35K from Mitsui Petro-
~ chemicals Industries , Ltd.
`~ Rubbçr Powder: a mixture containing 87% by weight of
rubber having a Mooney viscosity of 75
to 85 and 13% by weight of calcium
carbonate; the calcium carbonate
powder is substantially adhered on the
surface of the rubber particles. ~he
particle distribution is as follows:
, 25 0~5% of over 35 ~m mesh, 2.5% of over
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1 3 2 7 ~ 6 4i
.` 1 42 ~m mesh, 22% of over 60 ~ mesh, 43%
~x of over 80 ~m mesh, 18.5~i of over 125
-~ ~m mesh, and 13.5% of under 125 ~m
~? mesh. HI-BLOW HF-21~ from Nippon Zeon
Co., Ltd.
Hycar-CTsN*: a butadiene-acrylonitrile copolymer
with carboxyl groups at both ends,
having a viscosity of l,200 poises at
27C; from ~he B.F. Goodrich Chemical -
Corp.
Leveling agent: an acrylic ester oligomer
Hardener A: 2-methylimidazole
Hardener B: 2~4-diamino-6-[2'-methylimidazolyl
(l,?3ethyl-s-triazine
lS DAM: 4,4'-diaminodiphenylmethane
AD~: Adipic acid dihydrazide `
Then, each of the aforesaid samples were coated on
slots of motor rotors at 180 to 260C usin~ a flow-
imm~rsion method, and the properties ~of each of the
obtained films were investigated using the methods as
follows. Thè results are given in Table 2.
(l) Edge coverage :.:
A half-inch square bar was coated with the powder
coating composition at a thickness of about 0.3 mm and
subjected to ASTM D-2916~ standardized measurements. Those
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1 having hisher ratio (%) are evaluated as having excellent
edge coverage.
~2) Thermal resistance
A metal mold having a concave of 12.7 mm width,
170 mm length, and 12.7 mm depth was first heated to 160
!~ to 170C, then, the powder coating composition was applied
} to the heated metal mold for 10 to 15 minutes, then
molded, and thermoset at 170C for 20 minutes. The heat
deformation temperature (~DT) of the hardened body was
;~ 10 obtained according to the ~STM D-648 standard. Those
having higher HDTs have higher thermal resistances.
~t ( 3) Adhesiveness
Two degreased test pieces ~soft steel plates of
100 mmx20 mmx3 mm) were heated to about 200C. The powder
coating co~position was adhered in molten state on the
upper surface (20 mm wide and about 15 mm long) of the tip
of the either test piece, and was applied to the tip ~20
mm wide and 10 mm long) of the other test piece under load
of 1 kg at 200C for 10 minutes to harden by heating.
Then, the test pieces were left at room temperature and
the tensile` stren~th at which the joint broke was
measured. Those having larger strenqth are evaluated as
having excellent adhesiveness.
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1 ~4) Impact resistance
Preparation of the coated test piece:
~ A soft steel plate of 60x60 mm and 3.2 mm thick
- was coated with the powder coating composition and
thermoset to obtain a film of about 0.3 mm in thickness.
-' Measurements:
A DuPont-type impact tester was employed. A
semispherical striker of 1 kg weight having a head with a
-, curvature radius of 1/4 inch was dropped onto the above
s .
~r. 10 coated sample placed on the table having a semispherical
hole with a curvature radic of about 1/4 inch to concavely
deform the plate, and the dropping distance necessary to
break and peel off the coating was measured. Those
samples having the length of 30 cm or longer were
evaluated to have a fair impact resistance.
(5) Specular gloss
The same test piece used for measuring the impact
strength was employed except that the film thickness is
O.2 mm. The 60-degree specular gloss was measured
according to the JIS Z-8741 standardi2ed method. Those
having larger specular gloss are evaluated as having
excellent surface smoothness. The values shown are values
relative to that of the reference plane defined in the JIS
Z-8741 as 100.
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1327~6~
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- 13276~4
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~3276~
1 It is apparent from the results shown in Table 2
that coating composition samples according to the present
invention show well-balanced results.
EXAMPLE 2
Powder coating compositions having the same
composition as that of sample No. 3 in Example 1 were
prepared except that the bisphenol A type epoxy resin
varied molecular weight was substituted for the Epikote
1004*. The edge coverage for the samples was measured and
the results are given with refe~e to the nu~ber average lecular
weight in ~able 3. The epoxy resins used are as follows.
A A S0;10 mixture by weight of Epikote 828*
~` (num~er average le~ar weight of about 380) and Epikote 1007*
(number average molecNlar weight of about 2,900)
lS B A 4-~:17 mixture by ~ei~ht of Epikote 828
~ ~number average molecular weight of akout 380) and Ep~kote 1007
`~ (nu~r average mol~ar weight of about 2,900).
C A 13:47 mixture by wei~ht of Epikote 828
(nuIber average mol~ar weight of about 380~ ikote 1009*
(nu~x~ average le~ar weight of about 3,800).
D A 8:52 mixture by weight of Epi~ote 1001*
(nu~x~ average molecular weight of about 900) and bdsphenol A
type epoxy resin synthesized by a conventional .
~e~x~ (number~verage molecular weight of akout 6,000)~
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1327~64
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~ 1 E sisphenol A type epoxy resin synthesized by a
- con~entional me~od (n~#r average m~lecular weight of about
6,000)
The n~r average molecular weightin Table 3 are given
for the mixture of bisphenol A type epoxy resins.
s Table 3
* 2 3 4 5*
~ ~poxy resin A B C D E
_I~ 10 ~w~r average molecular
weight1,500 1,700 3,000 4,500 5,000
Edge coverage l%)30 56 69 71 84
Adhesiveness (kg~cm2)230 235 240 201 191
~.
It is apparent from the results shown in Tab}e 3
that coating composition samples according to the present
invention show well-balancèd results.
While the invention has been described in detail
and with reference to specific embodiments thereof, it
will be apparent to one skilled in the art that various ~ -
changes and modifications can be made therein without
departing ~rom the splrit and scope thereoF.
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