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Description  |
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The present invention relates to a coating composition capable of forming
on a steel plate a coating layer excellent in corrosion resistance and
cationic electrodeposition coating properties.
In recent years, surface-treated steel plates having good corrosion
resistance have been widely used as steel plates for various applications
such as for automobile bodies and household electric appliances.
Zinc-plated steel plates may be mentioned as typical examples of such
surface-treated steel plates. However, when applied as interior plates of
automobile bodies, or when applied to envelope structures or hemmed
structures, they are unable to adequately satisfy the required properties,
and it has been common to employ a method wherein an organic coating layer
is applied to such a plated steel plate and a cationic electrodeposition
coating is further applied to improve the corrosion resistance. Therefore,
the surface-treated steel plates are now required to have not only high
corrosion resistance by itself, but also good cation electrodeposition
coating properties.
However, there has been no surface-treated steel plate developed which
practically satisfy these two requirements.
For example, the surface-treated steel plate having a coating containing a
large amount of zinc powder as disclosed in Japanese Examined Patent
Publication No. 24230/1970 or No. 6882/1972, has a problem that the
coating is susceptible to peeling by press working, and the corrosion
resistance is not adequate.
The surface-treated steel plate having an organic and inorganic composite
coating applied to a zinc alloy-plated steel plate as disclosed in U.S.
Pat. No. 4,775,600, European Patent 230,320, Japanese Unexamined Patent
Publication No. 108292/1982, No. 50179/1985, No. 50180/1985, No.
99938/1988, No. 8033/1989 or No. 8034/1989, or Japanese Examined Patent
Publication No. 34406/1979, has a problem that coating defects such as gas
pin holes or craters are likely to form in the cation electrodeposition
coating, since the conductivity of the coating necessary for the cation
electrodeposition coating properties is non-uniform.
Further, the surface-treated steel plate having a coating containing a
large amount of a conductive substance such as zinc, carbon black or
aluminum, applied as disclosed in Japanese Unexamined Patent Publication
No. 60766/1986 or No. 83172/1988, or Japanese Examined Patent Publication
No. 2310/1988, has good conductivity and is excellent in the cation
electrodeposition coating properties, but it is inferior in the flatness
when a thin film is formed and thus has a poor appearance of the coating.
Further, the coating is susceptible to peeling by working, and the
corrosion resistance is not adequate.
The surface-treated steel plate having a coating containing a hydrophilic
polyamide resin for an improvement of the cation electrodeposition coating
properties, applied to a zinc alloy-plated steel plate, as disclosed in
GB2194249, has a problem that the coating is susceptible to peeling by
alkali treatment for electrodeposition, and the corrosion resistance is
not adequate.
Further, a method of forming cracks on a coating film of a surface-treated
steel plate having a thin coating film provided thereon, by e.g. roll skin
pass, in order to improve the cation electrodeposition coating properties,
as disclosed in Japanese Unexamined Patent Publication No. 11733/1987, has
a problem in the corrosion resistance because of the cracks, in addition
to an increase in number of the treating steps.
Under these circumstances, it is an object of the present invention to
provide a coating composition to obtain a surface-treated steel plate
excellent in corrosion resistance and cation electrodeposition coating
properties.
The present invention provides a corrosion resistant coating composition
comprising (i) 100 parts by weight of a bisphenol type epoxy resin
comprising bisphenol skeletons and epichlorohydrin skeletons and having at
least two epoxy groups per molecule, the bisphenol skeletons comprising
bisphenol A skeletons and bisphenol F skeletons in a weight ratio of from
95:5 to 60:40, and (ii) from 5 to 400 parts by weight of silica particles.
Now, the present invention will be described in detail with reference to
the preferred embodiments.
The bisphenol type epoxy resin (i) constituting the coating composition of
the present invention, is a resin comprising bisphenol skeletons and
epichlorohydrin skeletons formed by subjecting bisphenols comprising
bisphenol A and bisphenol F, and epichlorohydrin to a condensation
reaction in accordance with a usual method and having at least two epoxy
groups per molecule. It is preferably a resin having a molecular weight of
from about 500 to 100,000. The condensation reaction of the bisphenols and
epichlorohydrin is preferably conducted by mixing bisphenol A and
bisphenol F and simultaneously reacting them with epichlorohydrin.
However, an epoxy resin obtained by reacting bisphenol A with
epichlorohydrin and further adding and reacting bisphenol F thereto, or an
epoxy resin obtained by reacting bisphenol F with epichlorohydrin and
further adding and reacting bisphenol A thereto, is also included in the
present invention.
A bisphenol A type epoxy resin obtained from bisphenol A provides a coating
layer which is excellent in the water resistance and chemical resistance,
and it is also excellent in the adhesion to a steel plate and in the
adhesion to a overcoating layer. On the other hand, the coating layer is
hard and poor in the flexibility, and it has electrical insulating
properties and thus is rather poor in the cation electrodeposition coating
properties.
Therefore, the present inventors blended a bisphenol F type epoxy resin to
the bisphenol A type epoxy resin, but it was found that the corrosion
resistance decreased and no improvement in the cation electrodeposition
coating properties was observed. On the other hand, when a bisphenol type
resin comprising bisphenol skeletons and epichlorohydrin skeletons and
having at least two epoxy groups per molecule, is used wherein said
bisphenol skeletons comprise bisphenol A skeletons and bisphenol F
skeletons in a certain specific weight ratio, it has been unexpectedly
found that not only the corrosion resistance but also the cation
electrodeposition coating properties can be improved to a substantial
extent. Thus, the present invention is based on these discoveries.
Namely, the bisphenol A type epoxy resin is a resin represented by the
formula:
##STR1##
By substituting and/or introducing bisphenol F skeletons for a part of
bisphenol A skeletons in the formula, the resulting resin shows a better
hydrophilic nature than the bisphenol A type epoxy resin, whereby the
electrical resistance of the coating layer during the cation
electrodeposition coating decreases, and the entire layer will be
electrically uniform. This is believed to be the reason for the excellent
cation electrodeposition coating properties. Further, the bisphenol A type
epoxy resin is known to be a resin having good corrosion resistance.
However, when applied as a thin coating film, it is unable to completely
cover the surface roughness of the steel plate, whereby moisture or oxygen
is likely to penetrate, and corrosion resistance tends to be poor. By
substituting and introducing bisphenol F skeletons for a part of bisphenol
A skeletons, the glass transition point will be lowered, and the resulting
coating layer tends to have flexibility, whereby the moisture or oxygen
penetrated in the coating layer will readily be dissipated out of the
system. It is believed that the corrosion resistance is thereby improved.
In order to obtain such effects, the weight ratio of the bisphenol A
skeletons to the bisphenol F skeleton is preferably within a range of from
95:5 to 60:40. If the proportion of the bisphenol A skeletons is larger
than the above range, no adequate effects by the substitution with the
bisphenol F skeletons will be observed. On the other hand, if the
proportion of the bisphenol A skeletons is less than the above range, the
coating layer tends to be so soft that the corrosion resistance and water
resistance tend to be low, such being undesirable.
The above bisphenol type epoxy resin (i) may be the one wherein the epoxy
groups in the resin are modified with a primary and/or secondary amine
compound (hereinafter referred to simply as an amine compound) or with a
polybasic acid compound. By using such a modified epoxy resin, the alkali
resistance and water resistant secondary bond strength of the resulting
coating layer will be improved over the case where the corresponding
non-modified epoxy resin is used.
Such a modified epoxy resin (i) is preferably modified to such an extent
that from 30 to 100% of epoxy groups in the bisphenol type epoxy resin is
modified with the amine compound or the polybasic acid compound. If the
modification is less than this range, the effects for the improvement of
alkali resistance tends to be low.
Typical examples of the amine compound include n-propylamine,
iso-propylamine, n-butylamine, sec-butylamine, tert-butylamine,
diethylamine, ethylenediamine, diethylenetriamine, triethylenediamine,
tetraethylenediamine, propylenediamine, N-methylpiperazine, ethanolamine,
diethanolamine, N-methylethanolamine, iso-propanolamine,
diisopropanolamine, n-propanolamine, ethylethanolamine, and
3-methanolpiperidine.
Typical examples of the polybasic acid compound include isophthalic acid,
terephthalic acid, succinic acid, adipic acid, fumaric acid, itaconic
acid, citraconic acid, maleic anhydride, phthalic anhydride, succinic
anhydride, citric acid, tartaric acid, rosin maleic anhydride and benzene
tricarboxylic anhydride.
The silica particles (ii) constituting the coating composition of the
present invention are incorporated to further impart high corrosion
resistance. Typical examples include colloidal silica dispersed in an
organic solvent and having a particle size of from 1 to 500 m.mu.m or
powdery fumed silica having a particle size of from 1 to 500 m.mu.m. The
colloidal silica dispersed in an organic solvent is a colloidal silica
dispersed in an organic solvent such as methyl alcohol, ethyl alcohol,
propyl alcohol, butyl alcohol, ethyl cellosolve, ethylene glycol,
dimethylacetamide or dimethylformamide. Commercial products include, for
example, OSCAL 1132, 1232, 1332, 1432, 1532, 1622, 1722 and 1724
(tradenames, manufactured by Catalysts & Chemicals Industries Co., Ltd.);
and MA-ST, IPA-ST, NBA-ST, IBA-ST, EG-ST, ETC-ST, DMAC-ST, AND DMF-ST
(tradenames, manufactured by Nissan Chemical Industries Ltd.).
Commercial products of the powdery fumed silica include, for example, R974,
R811, R812, R972, R805, T805, R202, RX200, RY200, RY300, RY380, RY180 and
OX50 (tradenames, manufactured by Nippon Aerosil Company Ltd.). By
incorporation of such silica particles, when a coating layer is formed,
hydrogen bonding will be formed between silanol groups on the surface of
the silica particles and the steel plate surface and between such silanol
groups and the topcoating layer. Further, when such a coating layer is
baked, the silanol groups undergo a dehydration condensation reaction, and
integration of the topcoating layer-silica-steel plate will thereby be
promoted, whereby the corrosion resistance will be substantially improved.
The silica particles (ii) are preferably incorporated in an amount of from
5 to 400 parts by weight (as solid) per 100 parts by weight of the
bisphenol type epoxy resin (i). If the amount is less than this range, the
corrosion resistance tends to be low. On the other hand, if the amount is
excessive, the processability, alkali resistance and adhesion to the
topcoating layer tend to decrease.
The coating composition of the present invention is a coating material
comprising the above described bisphenol type epoxy resin (i) and silica
particles (ii) as essential components, which preferably has a solid
content of from 10 to 60% by weight.
The steel plate treated by the coating composition of the present invention
is likely to be subjected to welding. Therefore, it is preferred to
incorporate graphite particles (iii) to the coating composition, so that a
coating layer having excellent weldability will be obtained. The graphite
particles (iii) are incorporated to improve the weldability. For this
purpose, the particle size thereof is preferably at most 1 .mu.m. Typical
commercial products of such graphite particles include, for example,
Hitasol GO-102, Hitasol GP-60 and Hitasol GP-82 (tradenames, manufactured
by Hitachi Funmatsu Yakin K. K.), and Supercorophite #15, Supercorophite
#15Z, Supercorophite #15B, Prophite AS, Prophite W-300D, Baneyphite P-602,
Baneyphite BP-4, Baneyphite BP-112, Baneyphite C-812 and Baneyphite C-9A
(tradenames, manufactured by Nippon Kokuen Shoji K. K.).
The graphite particles (iii) are preferably incorporated in an amount of
from 0.1 to 30 parts by weight (as solid) per 100 parts by weight of the
bisphenol type epoxy resin (i). If the amount is less than this range, no
adequate effects for improvement of the weldability will be obtained. On
the other hand, if an excess amount is incorporated, processability during
press processing and the corrosion resistance tend to be low.
In the present invention, a bisphenol type epoxy resin containing bisphenol
F skeletons is used, whereby adequate effects are obtainable even with
such a small amount of graphite particles as mentioned above. However,
when a bisphenol type epoxy resin composed solely of bisphenol A skeletons
without containing bisphenol F skeletons, is used, a large amount of
graphite particles is required to be incorporated in order to improve the
weldability.
It should also be mentioned that to improve the weldability, it is known to
improve the conductivity. As a conductive substance to be incorporated in
a coating material in order to improve the conductivity, it is known to
employ a powder of Zn, Al, Mg, Fe, Ni, Co, Sn, Cu, Cr, Mn or an alloy
thereof; a powder of Ti, Zr, V, Nb, W, Mo or an alloy thereof; a carbide
powder; as well as iron phosphide powder, aluminum-doped zinc oxide
powder, or a semiconductor oxide powder such as tin oxide-titanium oxide,
tin oxide-barium sulfate or nickel oxide-alumina. However, with such a
conductive material, white rust is likely to form, and it has a corrosion
problem. Further, the specific gravity is high, whereby there is a problem
from the viewpoint of the stability of the coating material due to the
precipitation or coagulation. Further, conductive carbon black is also
widely used. Primary particles are small in size but are likely to
coagulate. Therefore, when the coating material is applied in a coated
amount of from 0.5 to 4 g/m.sup.2, they tend to protrude from the coating
layer, and they have a problem in the processability. Whereas, graphite
particles have a feature that they do not adversely affect the corrosion
resistance, the stability of the coating material and the processability,
as a conductive material.
To the coating composition of the present invention, other components which
are commonly employed in conventional coating materials, may optionally be
incorporated. Specifically, various organic solvents of hydrocarbon type,
ester type, ketone type, alcohol type and amide type; cross linking agents
such as a melamine resin, a benzoguanamine resin and a polyblocked
isocyanate compound; organic or inorganic pigments; additives such as a
dispersing agent, a precipitation-preventing agent and a leveling agent,
of various resins for modification, may be incorporated.
The coating composition of the present invention is preferably employed as
an undercoating material for various steel plates such as a hot dip
zinc-plated steel plate, a hot dip zinc-aluminum alloy-plated steel plate,
an electrolytic zinc-plated steel, an electrolytic zinc-nickel
alloy-plated steel plate, an electrolytic zinc-iron alloy-plated steel
plate, an electrolytic zinc-iron double layer-plated steel plate and a
cold-rolled steel plated, or steel plates pre-treated by e.g. chromate
treatment or phosphate treatment, which are used for automobiles,
household electrical appliances, building materials, etc. However, the
objects to be treated by the composition of the present invention are not
restricted to such specific examples.
The coating composition of the present invention may be coated on such a
steel plate by a method such as spraying, roll coating or shower coating
and can be cured at a temperature of from 15.degree. to 300.degree. C.,
preferably from 100.degree. to 250.degree. C. Adequate performance will be
obtained even with a thin layer having a thickness of about a few .mu.m.
However, the thickness may be greater.
With the surface treated-steel plate having the coating composition of the
present invention applied, the resulting coating layer imparts high
corrosion resistance and has flexibility for processing. Further, it
provides excellent cation electrocoating properties. Thus, it is a coating
material having a high practical value.
Now, the present invention will be described in further detail with
reference to Examples. However, it should be understood that the present
invention is by no means restricted by such specific Examples. In the
Examples, "parts" and "%" mean "parts by weight" and "% by weight",
respectively.
Preparation of Epoxy Resin Solution (I)
Into a three-necked flask equipped with a reflux condenser, a thermometer
and a stirrer, 109.4 parts of bisphenol A, 64.0 parts of bisphenol F and
an aqueous sodium hydroxide solution having 60 parts of sodium hydroxide
dissolved in 600 parts of water, were added, and the mixture was heated at
50.degree. C. for 13 minutes under stirring. Then, 116 parts of
epichlorohydrin was added thereto, and the temperature was gradually
raised and brought to 100.degree. C. in 20 minutes. The mixture was
maintained at this temperature for 40 minutes under stirring. Then, after
cooling, the supernatant aqueous layer was removed by decantation, and 600
parts of water was further added. The mixture was heated to 90.degree. C.
and vigorously stirred and then cooled again. Then, the supernatant
aqueous layer was removed in the same manner. Such an operation was
repeated until the aqueous layer no longer showed alkaline nature, and
finally water was thoroughly separated. The residue was heated for removal
of water at 150.degree. C. for 30 minutes under stirring to obtain an
epoxy resin having a molecular weight of about 900.
200 parts of the epoxy resin thus obtained was dissolved in 200 parts of
ethylene glycol monoethyl ether heated to 80.degree. C. to obtain an epoxy
resin solution (I) having a solid content of 50%.
Preparation of Epoxy Resin Solution (II)
Into a flask equipped with a stirrer, a thermometer and dropping funnel,
729.6 parts of bisphenol A, 160 parts of bisphenol F and 2,572 parts of a
10% sodium hydroxide aqueous solution were added, and the mixture was
heated at 50.degree. C. for 10 minutes under stirring. Then, 463 parts of
epichlorohydrin was added thereto, and the mixture was heated to
100.degree. C. under stirring and maintained at that temperature for 30
minutes.
Then, the supernatant aqueous layer was removed by decantation, and washing
with boiling water was repeated until the aqueous layer no longer showed
alkaline nature. Then, the residue was heated to 150.degree. C. for
removal of water to obtain an epoxy resin having a molecular weight of
about 1,400.
300 parts of the epoxy resin thus obtained was dissolved in 300 parts of
ethylene glycol monobutyl ether heated to 80.degree. C. to obtain an epoxy
resin solution (II) having a solid content of 50%.
Preparation of Epoxy Resin Solution (III)
Into a three-necked flask equipped with a reflux condenser, a thermometer
and a stirrer, 680 parts of ethylene glycol monoethyl ether acetate was
added and heated to 100.degree. C. Then, 1,000 parts of an epoxy resin
having an epoxy equivalent of from 2,800 to 3,300 obtained by reacting
bisphenol A with epichlorohydrin, was gradually added and dissolved
therein. Then, 25 parts of bisphenol F and 1 part of lithium chloride were
added thereto, and the mixture was reacted at 200.degree. C. for 60
minutes to obtain an epoxy resin solution (III) having a solid content of
60% and a molecular weight of about 7,000.
Preparation of Epoxy Resin Solution (IV)
An epoxy resin having a molecular weight of about 900 was prepared in the
same manner as the Preparation of the epoxy resin solution (I) except that
bisphenol A was changed to 72.9 parts, and bisphenol F was changed to 96
parts. Then, 200 parts of this epoxy resin was dissolved in 200 parts of
ethylene glycol monoethyl ether heated to 100.degree. C. to obtain an
epoxy resin solution IV) having a solid content of 50%.
Preparation of Epoxy Resin Solution (V)
300 parts of bisphenol A type epoxy resin ("Epicoat 1001", tradename,
manufactured by Shell Chemical Company, epoxy equivalent: 450-500) was
dissolved in 300 parts of ethylene glycol monoethyl ether to obtain an
epoxy resin solution (V) having a solid content of 50%.
Preparation of Epoxy Resin Solution (VI)
300 parts of a bisphenol F type epoxy resin ("Epichron 830", tradename,
manufactured by Dainippon Ink & Chemicals Inc, epoxy equivalent: about
175) was dissolved in 300 parts of ethylene glycol monoethyl ether to
obtain an epoxy resin solution (VI) having a solid content of 50%.
Preparation of Epoxy Resin Solution (VII)
The epoxy resin solution (V) and the epoxy resin solution (VI) were mixed
in a ratio of 2 1 to obtain an epoxy resin solution (VII) having a solid
content of 50%.
Preparation of Amine-Modified Epoxy Resin Solution (A-I)
180 parts of the epoxy resin solution (I) was heated to 60.degree. C., and
then 17.7 parts of diethanol amine was dropwise added over a period of 2
hours, and the mixture was further reacted at 70.degree. C. for 3 hours to
obtain a modified epoxy resin solution (A-I) having a solid content of
55%.
Preparation of Amine-Modified Epoxy Resin Solution (A-II)
To 280 parts of the above epoxy resin solution (II), 7.1 parts of diethanol
amine was added, and the mixture was reacted in the same manner as the
above solution (A-I) to obtain a modified epoxy resin solution (A-II)
having a solid content of 51%.
Preparation of Amine-Modified Epoxy Resin Solution (A-III)
To 1,167 parts of the above epoxy resin solution (III), 7.5 parts of
N-methylethanol amine was added, and the mixture was reacted in the same
manner as the above solution (A-I) to obtain a modified epoxy resin
solution (A-III) having a solid content of 60.2%.
Preparation of Amine-Modified Epoxy Resin Solution (A-IV)
To 450 parts of the above epoxy resin solution (I), 29.5 parts of
n-propylamine was added, and the mixture was reacted in the same manner as
the above solution (A-I) to obtain a modified epoxy resin solution (A-IV)
having a solid content of 53%.
Preparation of Amine-Modified Epoxy Resin Solution (A-V)
To 450 parts of the above epoxy resin solution (I), 30.0 parts of
ethylenediamine was added, and the mixture was reacted in the same manner
as the above solution (A-I) to obtain a modified epoxy resin solution
(A-V) having a solid content of 53%.
Preparation of Amine-Modified Epoxy Resin Solution (A-VI)
To 600 parts of the above epoxy resin solution (V), 55.4 parts of
diethanolamine was added, and the mixture was reacted in the same manner
as the above solution (A-I) to obtain a modified epoxy resin solution
(A-VI) having a solid content of 54.2%.
Preparation of Amine-Modified Epoxy Resin Solution (A-VII)
To 600 parts of the above epoxy resin solution (VI), 143.9 parts of
diethanol amine was added, and the mixture was reacted in the same manner
as the above solution (A-I) to obtain a modified epoxy resin solution
(A-VII) having a solid content of 59.7%.
Preparation of Amine-Modified Epoxy Resin Solution (A-VIII)
The above amine-modified epoxy resin solution (A-VI) and the amine-modified
epoxy resin solution (A VII) were mixed in a ratio of 2:1 to obtain a
modified epoxy resin solution (A-VIII) having a solid content of 57%.
Preparation of Polybasic Acid-Modified Epoxy Resin Solution (C-I)
180 parts of the above epoxy resin solution (I) was heated to 150.degree.
C., and 2 parts of hydroquinone, 1 part of dimethylbenzylamine and 26.6
parts of phthalic anhydride were added, and the mixture was reacted for 5
hours to obtain a modified epoxy resin solution (C-I) having a solid
content of 56%.
Preparation of Polybasic Acid-Modified Epoxy Resin Solution (C-II)
To 280 parts of the above epoxy resin solution (II), 2.8 parts of
hydroquinone, 1.5 parts of dimethylbenzylamine and 6.9 parts of maleic
anhydride were added, and the mixture was reacted in the same manner as
the above solution (C-I) to obtain a modified epoxy resin solution (C-II)
having a solid content of 51%.
Preparation of Polybasic Acid-Modified Epoxy Resin Solution (C-III)
To 1,167 parts of the above epoxy resin solution (III), 4.5 parts of
hydroquinone, 3.8 parts of dimethylbenzylamine and 14.6 parts of adipic
acid were added, and the mixture was reacted in the same manner as above
solution (C-I) to obtain a modified epoxy resin solution (C-III) having a
solid content of 60.5%.
Preparation of Polybasic Acid-Modified Epoxy Resin Solution (C-IV)
To 600 parts of the above epoxy resin solution (V), 3 parts of
hydroquinone, 2.5 parts of dimethylbenzylamine and 78.1 parts of phthalic
anhydride were added, and the mixture was reacted in the same manner as
the above solution (C-I) to obtain a modified epoxy resin solution (C-IV)
having a solid content of 55.8%.
Preparation of Polybasic Acid-Modified Epoxy Resin Solution (C-V)
To 600 parts of the above epoxy resin solution (VI), 3 parts of
hydroquinone, 2.5 parts of dimethylbenzylamine and 202.8 parts of phthalic
anhydride were added, and the mixture was reacted in the same manner as
the above solution (C-I) to obtain a modified epoxy resin solution (C-V)
having a solid content of 62.6%.
Preparation of Polybasic Acid-Modified Epoxy Resin Solution (C-VI)
The above modified epoxy resin solution (C-IV) and the modified epoxy resin
solution (C-V) were mixed in a ratio of 2:1 to obtain a modified epoxy
resin solution (C-VI) having a solid content of 59.2%.
EXAMPLE 1
200 parts of the epoxy resin solution (I), 400 parts of colloidal silica
("ETC-ST", tradename, manufactured by Nissan Chemical Industries Ltd.,
dispersion in ethylene glycol monoethyl ether, solid content: 20%) and 418
parts of ethylene glycol monoethyl ether were mixed and dissolved to
obtain a coating material.
The coating material thus obtained was coated by roll coating on various
steel plates as identified in Table 2 so that the dried layer thickness
would be 3 .mu.m and baked under such condition that the peak metal
temperature would be 150.degree. C. in 30 seconds. Then, tests for
corrosion resistance, cation electrodeposition coating properties, topcoat
adhesion and water resistance were conducted, and the results are shown in
Table 2.
EXAMPLES 2 TO 6 AND COMPARATIVE EXAMPLES 1 TO 4
The epoxy resin solution and silica particles were mixed in the proportions
as identified in Table 1, and the mixture was dissolved in an ethylene
glycol monoethyl ether in an amount to bring the solid content to a level
of 20%, to obtain a coating material.
The coating material thus obtained was applied and subjected to various
tests as in Example 1, and the results are shown in Table 2.
As shown in Table 2, in each of Examples 1 to 6 wherein the coating
compositions of the present invention were employed, the corrosion
resistance, the cation electrodeposition coating properties and the
adhesion are all excellent.
On the other hand, in each of Comparative Example 1 wherein the coating
material used was a bisphenol A type epoxy resin, Comparative Example 2
wherein the coating material used was an epoxy resin having a low
proportion of bisphenol A, Comparative Example 3 wherein a bisphenol F
type epoxy resin was used, but the coating material used contained no
silica particles and Comparative Example 4 wherein the coating material
used was a mixture of a bisphenol A type epoxy resin and a bisphenol F
type epoxy resin, the corrosion resistance, the cation electrodeposition
coating properties and the adhesion were all inferior as compared with
those of the present invention.
TABLE 1
__________________________________________________________________________
Examples Comparative Examples
1 2 3 4 5 6 1 2 3 4
__________________________________________________________________________
Epoxy I I II II III III V IV VI VII
resin solution
200 200 200 200 167 167 200 200 200 200
Silica particles
Colloidal
Fumed
Fumed
Colloidal
Colloidal
Fumed
Colloidal
Fumed
-- Colloidal
silica*1
silica*2
silica*2
silica*3
silica*3
silica*4
silica*1
silica*2
silica*1
400 7 350 120 100 40 400 2 -- 400
Bis-phenol
63/37
63/37
82/18
82/18
93/7 93/7
100/0
43/57
0/100
--
A/Bis-phenol F
__________________________________________________________________________
*1) "ETCST", tradename, manufactured by Nissan Chemical Industries Ltd.,
dispersion in ethylene glycol monoethyl ether, solid content: 20%
*2) "R972", tradename, manufactured by Nippon Aerosil K.K.
*3) "OSCAL 1632", tradename, manufactured by Catalysts & Chemicals
Industries Co., Ltd., dispersion in ethylene glycol monoethyl ether, soli
content: 20%
*4) "RX200", tradename, manufactured by Nippon Aerosil K.K.
TABLE 2
__________________________________________________________________________
Examples
1 2 3 4 5 6
__________________________________________________________________________
Type of steel plate
Hot dip
Electrolytic
Electrolytic
Electrolytic
Electrolytic
Cold rolled
zinc-plated
zinc-plated
zinc-nickel
zinc-plated
zinc-nickel
steel plate
steel plate
steel plate
alloy-plated
steel plate
alloy-plated
steel plate steel plate
Tested items
Corrosion resistance*5)
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Cation electrodeposition
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coating properties*6)
Topcoat adhesion*7)
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Water resistance*8)
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__________________________________________________________________________
Comparative Examples
1 2 3 4
__________________________________________________________________________
Type of steel plate
Hot dip
Electrolytic Electrolytic
Hot dip
zinc-plated
zinc-plated zinc-nickel
zinc-plated
steel plate
steel plate alloy-plated
steel plate
steel plate
Tested items
Corrosion resistance*5)
.DELTA.
.DELTA. X .DELTA.
Cation electrodeposition
X .DELTA. X .DELTA.
coating properties*6)
Topcoat adhesion*7)
X X X .DELTA.
Water resistance*8)
X X X .DELTA.
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*5) Cross cut lines were imparted to the coated surface of the test sheet
and salt spray test was conducted for 500 hours in accordance with JIS
Z2371, whereupon formation of red rust was observed. .largecircle.: No
formation of red rust, .DELTA.: less than 5% of red rust, X: at least 5%
of red rust.
*6) On the coated surface of the test sheet, an amineadded epoxy
resinblock isocyanate type cationic electrodeposition coating material wa
coated by cation electrodeposition under a condition of 100 V for 3
minutes at a bath temperature of 28.degree. C. and baked at 165.degree. C
for 20 minutes, whereupon the appearance of the coated layer (area: 100
cm.sup.2) was observed. .largecircle.: Formation of gas pin holes and
craters: from 0 to 5 points, .DELTA.: Formation of gas pin holes and
craters: 6-20 points, X: Formation of gas pin holes and craters: at least
20 points.
*7) The coated surface of the cation electrodeposition coated plate
obtained in *6) was crosscut by a cutter knife into 100 squares of 1
mm.sup.2, and peel test was conducted by means of an adhesive tape to
measure the remaining rate of the electrodeposition coated layer.
.largecircle.: 95-100%, .DELTA.: 90-94%, X: less than 89%.
*8) The cation electrodeposition coated plate obtained in *6) was immerse
in water of 40.degree. C. for 240 hours and then dried, and subjected to
the peel test in the same manner as in *7) to measure the remaining rate
of the electrodeposition coated layer. .largecircle.: 95-100%, .DELTA.:
90-94%, X: less than 89%.
EXAMPLE 7
200 parts of the epoxy resin solution (I), 400 parts of colloidal silica
("ETC-ST", tradename, manufactured by Nissan Chemical Industries Ltd.,
dispersion in ethylene glycol monoethyl ether, solid content: 20%), 3
parts of graphite powder ("Hitasol GP-60", tradename, manufactured by
Hitachi Funmatsu Yakin K. K., average particle size: 0.5 .mu.m) and 420
parts of ethylene glycol monoethyl ether were mixed and dissolved to
obtain a coating material.
The coating material thus obtained was coated by roll coating on various
steel plates as identified in Table 4 so that the dried layer thickness
would be 3 .mu.m and then baked so that the maximum plate temperature
would be 150.degree. C. in 30 seconds. Then, tests for the corrosion
resistance, cation electrodeposition coating properties, topcoat adhesion,
water resistance and weldability were conducted, and the results are shown
in Table 4.
EXAMPLES 8 TO 12 AND COMPARATIVE EXAMPLES 5 TO 8
An epoxy resin solution, silica particles and graphite particles were
blended in the proportions as identified in Table 3, and the mixture was
dissolved in ethylene glycol monoethyl ether in an amount to bring the
solid content to 20% to obtain a coating material.
The coating material thus obtained was applied and subjected to various
tests in the same manner as in Example 7, and the results are shown in
Table 4.
As shown in Table 4, in Examples 7 to 12 wherein the coating compositions
of the present invention were used, the corrosion resistance, the cation
electrodeposition coating properties, the adhesion and the weldability are
all excellent.
On the other hand, in each of Comparative Example 5 wherein the coating
material used was a bisphenol A type epoxy resin, Comparative Example 6
wherein the coating material used was an epoxy resin having a low
proportion of bisphenol A, Comparative Example 7 wherein a bisphenol F
type epoxy resin was used, but the coating material used contained no
silica particles and graphite particles and Comparative Example 8 wherein
the coating material used was a mixture of a bisphenol A type epoxy resin
and a bisphenol F type epoxy resin, the corrosion resistance, the cation
electrodeposition coating properties, the adhesion and the weldability
were all interior as compared with those of the present invention.
TABLE 3
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Examples Comparative Examples
7 8 9 10 11 12 5 6 7 8
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Epoxy
I I II II III III V IV VI VII
resin
200 200 200 200 167 167 200 200 200 200
solution
Silica
Colloidal
Fumed Fumed Colloidal
Colloidal
Fumed Colloidal
Fumed -- Colloidal
particles
silica*1
silica*2
silica*2
silica*3
silica*3
silica*4
silica*1
silica*2 silica*1
400 7 350 120 100 40 400 2 -- 400
Graphite
Powder*9
Solvent
Powder*9
Solvent
Solvent
Solvent
Powder*9
Powder*9
-- Powder*9
particles dis- dis- dis- dis-
persion*10 persion*10
persion*11
persion*11
3 150 25 5 200 30 3 50 -- 3
Bis- 63/37 63/37 82/18 82/18 93/7 93/7 100/0 43/57 0/100
--
phenol
A/Bis-
phenol F
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*9) "Hitasol GP60", tradename, manufactured by Hitachi Funmatsu Yakin
K.K., average particle size: 0.5 .mu.m
*10) "Baneyphite C9A", tradename, manufactured by Nippon Kokuen Shoji
K.K., average particle size: 0.5 .mu.m, solid content: 8%
*11) "Hitazol GO102", tradename, manufactured by Hitachi Funmatsu Yakin
K.K., average particle size: 1.0 .mu.m, solid content: 10%
TABLE 4
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Examples
7 8 9 10 11 12
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Type of steel plate
Hot dip
Electrolytic
Electrolytic
Electrolytic
Electrolytic
Co | | |
