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Description  |
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FIELD OF THE INVENTION
The present invention relates to an epoxy resin powder coating composition.
More particularly, it is concerned with an epoxy resin powder coating
composition which can form a coating having an excellent impact resistance
not only at room temperature but also at low temperatures.
BACKGROUND OF THE INVENTION
An epoxy resin powder coating composition usually comprises an epoxy resin
with a hardener and a granular inorganic filler compounded thereto. This
coating composition has been widely used as an anticorrosive paint for
ships, vehicles, large-sized structures, and so forth because it exhibits
excellent adhesion to members to be coated and also excellent
anticorrosion properties.
The epoxy resin coating composition, however, has a disadvantage in that
although a coating formed using the coating composition generally exhibits
good impact resistance at room temperature, its impact resistance at low
temperatures is unsatisfactorily low. In order to overcome the above
defect, several methods have been proposed: a method in which the
thickness of the coating is increased, a method in which the amount of the
granular inorganic filler is increased, and a method in which a flaky
inorganic filler is used in place of the granular inorganic filler.
The above methods, however, undesirably lower the flexibility of the
coating. If the coating has a poor flexibility, cracks tend to develop
therein during handling of members with the coating.
SUMMARY OF THE INVENTION
As a result of extensive investigations to provide an epoxy resin coating
composition which can form a coating having good flexibility and also
exhibiting excellent impact resistance not only at room temperature but
also at low temperatures, it has been found that the object can be
attained by employing specified amounts of a granular inorganic filler and
a specific needle-like glass powder as fillers which are compounded to an
epoxy resin.
Accordingly, an object of the present invention is to provide an epoxy
resin coating composition comprising an epoxy resin with at least a
hardener and a filler compounded thereto, wherein the filler is a mixture
of from 30 to 180 parts by weight per 100 parts by weight of the epoxy
resin of a needle-like glass powder having an average length of at least
40 .mu.m and an aspect ratio of at least 4, and at least 30 parts by
weight per 100 parts by weight of the epoxy resin of a granular inorganic
filler having an average particle diameter of 1.0 .mu.m or less.
DETAILED DESCRIPTION OF THE INVENTION
It is known that the needle-like glass powder is a filler having a great
reinforcing effect. When, however, the needle-like glass powder is used as
a filler for an epoxy resin coating composition, a coating formed using
the resulting composition is markedly decreased in flexibility. For this
reason, in the preparation of conventional epoxy resin coating
composition, such a needle-like glass powder has been rarely compounded.
According to the present invention, however, it has been found that if a
mixture of the needle-like glass powder and granular inorganic filler is
used as a filler for the epoxy resin powder coating composition and,
furthermore, those are added in the specified amounts, the resulting epoxy
resin powder coating composition can provide a coating having good
flexibility and further exhibiting excellent impact resistance not only at
room temperature but also at low temperatures.
Epoxy resins which can be used in the present invention are glycidyl
ether-type epoxy resins such as bisphenol A-type epoxy resins and
novolak-type epoxy resins. Bisphenol A-type epoxy resins are particularly
preferred. When these bisphenol A-type epoxy resins are used, suitable
amounts of other epoxy resins such as bisphenol F-type epoxy resins can be
used in combination therewith to increase the heat resistance and the like
of the coating composition. In this case, it is preferred that the amount
of the bisphenol A-type epoxy resin used is at least 70% by weight based
on the total weight of all the epoxy resins used.
The epoxy resins having a molecular weight of from 900 to 3,600 and an
epoxy equivalent of from 450 to 1,800 are generally preferably used in the
present invention. If the epoxy equivalent is too small, the resulting
epoxy resin powder coating composition tends to cause blocking and the
coating workability is undesirably reduced. On the other hand, if the
epoxy equivalent is too large, the melt viscosity of the coating
composition is excessively increased and a uniform coating cannot be
obtained.
The preferred epoxy resins are ones that the ratio of the number of
unreactive terminal groups, i.e., terminal groups other than the epoxy
group (e.g., glycol and chlorohydrin resulting from ring opening of the
epoxy group) to the total number of groups is less than 5:100. If this
ratio is too large, the flexibility and impact resistance of the coating
are adversely influenced.
The hardener which can be used in the present invention is appropriately
selected from hardeners which are commonly used in the conventional epoxy
resin powder coating composition. Examples of such hardeners are
amine-based hardeners such as aromatic diamines (e.g.,
diaminodiphenylamine), aliphatic amine/aliphatic dicarboxylic acid
condensates, dicyandiamide, and imidazoles; organic acid anhydride-based
hardeners such as tetrahydrophthalic anhydride,
benzophenonetetracarboxylic anhydride, and trimellitic anhydride; and
phenol-based hardeners such as a phenol resin and bisphenol A. The
hardener is generally used in an amount of from 0.5 to 1.5 equivalents per
epoxy equivalent of the epoxy resin.
The filler which is added to the coating composition of the present
invention comprises a specified needle-like glass powder and a specified
granular inorganic filler.
The needle-like glass powder has an average length of at least 40 .mu.m,
preferably at least 50 .mu.m, and particularly preferably from 50 to 350
.mu.m, an aspect ratio (average length/average diameter) of at least 4:1,
preferably at least 5:1, and particularly preferably from 5:1 to 100:1,
and an average diameter of from 1 to 30 .mu.m.
If the average length of the needle-like glass powder is less than 40
.mu.m, or the aspect ratio is less than 4:1, the resulting coating
composition can provide only a coating having poor impact resistance
particularly at low temperatures (0.degree. C. or less). On the other
hand, if the average length is too large, it becomes sometimes difficult
to prepare a powder coating composition and the smoothness of the coating
is undesirably reduced.
The needle-like glass powder used in the present invention is a rod-shaped
piece, the diameter of which is substantially constant (within the
tolerance of about .+-.10%) along the whole lengthwise direction thereof.
Such a needle-like glass powder can be obtained by pulverizing
conventional glass fibers. Of course, needle-like glass powders having
forms other than the rod-like form can be used so long as their aspect
ratio (long axis/short axis) and so forth are within the above-specified
ranges.
The term "aspect ratio" is the art-recognized term in the sence of a shape
coefficient of an article, and the term is used in the present invention
to indicate the shape of a particle. That is, the aspect ratio is used to
indicate the long axis/short axis ratio of the particle. For example, in
the case or rod-shaped particles, the aspect ratio indicates (length of
the rod/diameter of the rod) ratio. In the case of particles having a form
other than the rod-like form, the aspect ratio indicates (maximum
length/maximum length in a direction at right angles to the maximum
length) ratio.
The above aspect ratio is generally determined by a method in which the
images of particles are obtained by, for example, a microscopic
photograph, and the long axis/short axis ratio is measured. In this case,
it is preferred that the average value of at least 500 particles be
employed.
It is preferred to use a needle-like glass powder the surface of which has
been treated with a silane coupling agent, because of this surface
treatment increases the wettability between the glass and the epoxy resin,
thereby increasing the adhesion therebetween, and makes it possible to
prevent penetration of water in the interface between the glass and the
epoxy resin. Thus, the anticorrosion properties of the coating are
increased, and the corrosion of a coated member due to the swelling of the
coating caused by the penetration of water and also due to the reduction
in the insulation properties of the coating can be sufficiently prevented.
Silane coupling agents which are preferably used for this purpose include
aminosilanes such as N-phenyl-.gamma.-aminopropyltrimethoxysilane.
n-.beta.-(aminoethyl)-.gamma.-aminopropyltrimethoxysilane, and
.gamma.-aminopropyltriethoxysilane; epoxy-silanes such as
.gamma.-glycidoxypropylmethyldiethoxysilane and
.beta.-(3,4-epoxycyclohexyl)ethyltrimethoxysilane; and mercaptosilanes
such as .gamma.-mercaptopropyltrimethoxysilane.
The amount of the needle-like glass powder used is from 30 to 180 parts by
weight, preferably from 50 to 160 parts by weight, and particularly
preferably from 60 to 150 parts by weight, per 100 parts by weight of the
epoxy resin. If the amount of the needle-like glass powder used is less
than 30 parts by weight, the resulting powder coating composition can
provide only a coating having poor impact resistance particularly at low
temperatures. On the other hand, if the amount thereof is more than 180
parts by weight, the smoothness and flexibility of the coating are
reduced.
The granular inorganic filler which is used in combination with the
needle-like glass powder has an average particle diameter of 1.0 .mu.m or
less and preferably from about 0.1 to 0.7 .mu.m. If the average particle
diameter is more than 1.0 .mu.m, the coating formed has a poor
flexibility. It is preferred that the aspect ratio as defined before be
2:1 or less.
Examples of the granular inorganic filler are titanium dioxide, barium
sulfate, fused silica, alumina, and calcium carbonate, each having an
average particle diameter of 1.0 .mu.m or less and an aspect ratio of 2:1
or less.
It is preferred for the granular inorganic filler to be subjected to the
surface treatment to increase its wetting properties to the epoxy resin.
The particularly preferred surface treatment is a Zn-Al-Si treatment. In
addition, surface treatments using Al alone, or together with a resin
acid, a fatty acid, a silane coupling agent, and/or a titanium coupling
agent can be employed depending on the type of the filler.
The above Zn-Al-Si treatment comprises coating the hydrates of silicic
acid, aluminum oxide and zinc oxide on the surface of the filler, thereby
improving the affinity of the epoxy resin to the filler and the
hydrophilic properties of the filler.
This surface treatment increases the adhesion between the granular
inorganic filler and the epoxy resin in the coating and, therefore, as in
the case of the surface treatment of the needle-like glass powder, can
increase the anticorrosion and insulation properties of the coating.
The amount of the granular inorganic filler used is at least 30 parts by
weight, preferably from 30 to 150 parts by weight, and particularly
preferably from 40 to 140 parts by weight, per 100 parts by weight of the
epoxy resin. If the amount of the granular inorganic filler used is less
than 30 parts by weight, the resulting epoxy resin powder coating
composition can provide only a coating having a poor flexibility. On the
other hand, if the amount thereof is too large, the smoothness of the
coating is reduced.
The epoxy resin powder coating composition of the present invention
comprises the above-described epoxy resin, hardener, needle-like glass
powder, and granular inorganic filler as essential constituents. In
addition to these constituents, the composition may further contain, if
desired and necessary, additives such as pigment, a leveling agent, a
hardening accelerator and a flow-adjusting agent. The amount of the
additive used is usually 5 parts by weight or less per 100 parts by weight
of the epoxy resin.
The epoxy resin powder coating composition according to the present
invention can be prepared by either a melt mixing method or a dry mixing
method. It is preferred to employ the melt mixing method. This melt mixing
method includes a step where the constituents are melt mixed and then
pulverized to a predetermined particle size. At this pulverization step,
therefore, the size of the filler, i.e., the average length and aspect
ratio of the needle-like glass powder or the average particle diameter of
the granular inorganic filler, may change during pulverization.
In preparing the powder coating composition of the present invention, the
following procedure is preferably employed particularly when it is desired
to more increase the flexibility of the hardened coating.
At least 80 wt% of the needle-like glass powder+granular inorganic filler
and at least 50 wt%, preferably at least 80 wt%, of the epoxy resin are
preliminarily melt mixed and pulverized to form a powder and, thereafter,
the resulting powder and the remainder ar melt mixed and pulverized to
form the desired powder coating composition.
This method is particularly effective when the needle-like glass powder is
used in an amount of at least 100 parts by weight per 100 parts by weight
of the epoxy resin.
It is important in the present invention that the size of the filler after
pulverization falls within the above-specified range, and the above
effects of the present invention can be obtained even using needle-like
glass powders and granular inorganic fillers which do not satisfy the
above-specified size requirements so long as the size of the filler after
pulverization can satisfy the requirements. For example, under the
conditions of preparation of the powder coating composition shown in the
example as described hereinafter, the average length of the needle-like
glass powder after pulverization changed to 90 to 95% of the length before
compounding, whereas the average diameter of the needle-like glass powder
and the average particle diameter of the granular inorganic filler
remained unchanged.
The particle size of the epoxy resin powder coating composition of the
present invention prepared by either the melt mixing method or the dry
mixing method varies depending on the purpose of use of the powder coating
composition. The maximum particle size thereof if generally from about 200
to 40 mesh.
The epoxy resin powder coating composition of the present invention can be
coated by conventional coating techniques such as an electrostatic spray
method, an electrostatic dipping method, and a fluid dipping method. When
coated, the composition adheres to a member to be coated and hardens,
thereby forming a coating. The thickness of the coating is determined
depending on the purpose of use of the final coated member. If the
thickness is too small, defects tend to develop in the coating. On the
other hand, if the thickness is too large, the flexibility drops.
Therefore, the thickness of the coating is usually within the range of
from about 0.1 to 1.0 mm.
The coating thus formed has an excellent impact resistance, of course, at
room temperature and also at temperatures as low as about -50.degree. C.,
and further exhibits a good flexibility.
The epoxy resin powder coating composition of the present invention can
provide a coating having the above-described excellent characteristics,
and is therefore very useful as a powder coating composition for
anticorrosive coating of ships, vehicles, large-sized structures, and so
forth, and also for decoration, anticorrosive coating, electrical
insulation, or fixation of electric appliances and so forth.
When the powder coating composition of the present invention is coated on
the surface of a steel member, for example, by coating techniques as
described above and then hardened by heating, a protective coating
exhibiting good adhesion to the steel surface and also excellent impact
resistance and flexibility is formed.
The main use of the powder coating composition of the present invention is
a protective coating of a steel member. In another embodiment, the present
invention provides a steel member with a coating as described above, i.e.,
a coated steel member. This coated steel member will hereinafter be
explained in detail.
In producing the coated steel member, the powder coating composition may be
coated directly on the surface of the steel member. It is preferred,
however, that the steel surface be subjected to chemical treatment using a
phosphate solution, a chromate solution, or a chromium/phosphoric acid
solution to thereby form a layer (hereinafter referred to as a "chemically
treated layer") and, thereafter, the powder coating composition to form a
coating on the chemically treated layer. The coating of the powder coating
composition provided on the steel surface through the chemically treated
layer exhibits more increased impact resistance over a wide temperature
range of from low temperature to high temperature and also excellent
flexibility as a result of the synergistic effect of the two layers.
Furthermore, the inherent advantages of the chemically treated layer are
not deteriorated.
In the production of the coated steel member of the present invention, the
chemically treated layer is first formed. Prior to the formation of the
chemically treated layer, the steel surface is subjected to preliminary
treatment. This preliminary surface treatment roughens the surface of the
steel member. This roughening is usually carried out by suitable
techniques such as shot blasting and sand blasting so that the surface
roughness (the maximum roughness as determined by JIS B0601) is from 10 to
120 .mu.m, preferably the surface roughness is within the above-specified
range and is 1/4 or less of the thickness of the coating of the powder
coating composition. If the maximum roughness is less than 10 .mu.m, the
anchor effect becomes insufficiently, and the adhesion force of the
coating drops. This also leads to reduction in the impact resistance of
the coating. On the other hand, if the maximum roughness is more than 120
.mu.m, cracks tend to develop in the coating when an impact is applied
thereon. In particular, when the thickness of the coating is too small,
e.g., less than 300 .mu.m, this tendency becomes marked, and the impact
resistance is decreased.
The chemically treated layer is a layer formed on the steel surface by
treating it with a phosphate solution, a chromate solution, or a
chromium/phosphoric acid solution. Either a single layer or two or more
layers are formed. These treating solutions are known in the art, and
solutions conventionally used can be used as they are. The chemical
treatment can be carried out by conventional techniques. The solutions are
described in detail below.
(A) PHOSPHATE SOLUTION
The phosphate solution is an aqueous solution composed mainly of phosphoric
acid, phosphate and an axidizing agent such as nitric acid, which may
further contain, depending on the purpose, heavy metals (e.g., Fe, Ni, Co,
Ca, Mg, and Cu), anions (e.g., BO.sub.3, F, SiF.sub.6, BF.sub.4,
ClO.sub.3, and P.sub.3 O.sub.10), and organic acids (e.g., oxalic acid,
tartaric acid, citric acid, glyceric acid, tannic acid, and ascorbic
acid). When the phosphate solution is coated on the steel member by
techniques such as dipping, spraying, and coating, a phosphate layer is
formed, which contains as a major component the following compounds.
(1) Iron phosphate-based layer
FePO.sub.4.2H.sub.2 O and .gamma.-Fe.sub.2 O.sub.3
(2) Zinc phosphate-based layer
Zn.sub.3 (PO.sub.4).sub.2.4H.sub.2 O, and ZnFe.sub.2
(PO.sub.4).sub.2.4H.sub.2 O
(3) Manganese phosphate-based layer
Mn(PO.sub.4).sub.2.3H.sub.2 O, and 2MnHPO.sub.4.5/2H.sub.2 O.FeHPO.sub.4
(4) Calcium phosphate-based layer
CaHPO.sub.4.2H.sub.2 O, and CaHPO.sub.4
(5) Zinc/calcium phosphate-based layer
Zn.sub.2 Fe(PO.sub.4).sub.2.4H.sub.2 O, Zn.sub.2
Ca(PO.sub.4).sub.2.2H.sub.2 O, and Zn.sub.3 (PO.sub.4).sub.2.4H.sub.2 O
(6) Alkali phosphate-based layer
Fe.sub.3 (PO.sub.4).sub.2.8H.sub.2 O
(7) Alkali phosphate+Fe.sup.++ +H.sub.3 PO.sub.4 -based layer
Fe.sub.5 H.sub.2 (PO.sub.4).sub.4.4H.sub.2 O
(B) CHROMATE SOLUTION
The chromate solution is basically an aqueous solution containing Cr.sup.6+
(e.g., CrO.sub.3 and Na.sub.2 Cr.sub.2 O.sub.7) as a major component and
an anion (e.g., SO.sub.4, SiF.sub.6, Cl, NO.sub.3, and F) as a
layer-forming accelerator, which may further contain a pH controller, a
water-soluble resin, and so forth, depending on the purpose. It is
believed that the layer formed on the steel manner by coating, dipping,
electrolysis, and so forth is composed mainly of xCrO.sub.3.yCr.sub.2
O.sub.3.zH.sub.2 O and further contains other additives.
(C) CHROMIUM/PHOSPHORIC ACID SOLUTION CONTAINING Cr.sup.6+ AND PHOSPHORIC
ACID
This solution is a solution prepared by adding the soluble salts of heavy
metals such as Zn and Ni to an aqueous solution containing Cr.sup.6+ and
phosphoric acid. The layer formed on the steel member by dipping, coating,
electrolysis, and so forth is considered to be a layer in which iron
phosphate, a chromate coating, and the added heavy metal are present as a
mixture, although the exact composition is not known.
The thickness of the chemically treated layer is, as expressed in terms of
dry weight, from 0.1 to 10 g/m.sup.2 and preferably from 0.2 to 5
g/m.sup.2. If the thickness is less than the lower limit, the
anticorrosion properties are reduced. On the other hand, if the thickness
exceeds the upper limit, the adhesion of the chemically treated layer to
the coating of the powder coating composition is reduced, resulting in
reduction of the impact resistance.
The present invention is described in greater detail by reference to the
following examples. All parts are by weight.
EXAMPLE 1
A composition consisting of 100 parts by weight of a bisphenol A-type epoxy
resin (epoxy equivalent: 750; ratio of the number of unreactive terminal
groups to the total number of groups: 3.5:100), 70 parts of a needle-like
glass powder (averge length: 100 .mu.m; average diameter: 10 .mu.m; aspect
ratio: 10:1) which had been subjected to surface treatment using
N-phenyl-.gamma.-aminopropyltrimethoxysilane, 80 parts of granular
titanium dioxide which had been subjected to Zn-Al-Si treatment (average
particle diameter: 0.35 .mu.m), 24 parts of a resin (hardener) (hydroxyl
group equivalent: 250) prepared by addition reaction of 1 mole of
epichlorohydrin and 2 moles of bisphenol, 1.0 part of 2-methylimidazole,
0.6 part of a pigment, and 0.5 part of a leveling agent was melt kneaded
in a twin-screw extruder (trade name: TEM-50, manufactured by Toshiba
Kikai Co., Ltd.).
The above-kneaded mass was pulverized to a particle size of 120 mesh or
less using a hammer mill to obtain an epoxy resin powder coating
composition of the present invention. The needle-like glass powder
containing in the coating composition had the average length of 95 .mu.m,
the average diameter of 10 .mu.m, and the aspect ratio of 10.5:1. The
average particle diameter of the granular titanium dioxide was 0.35 .mu.m.
The average length and average diameter of the needle-like glass powder,
and the average particle diameter of the granular inorganic filler were
measured using a microscope. In measuring the above physical values of the
needle-like glass power and granular inorganic filler in the coating
composition, the coating composition was dissolved in an organic solvent,
diluted, and dried and, thereafter, the values were measured using a
microscope.
EXAMPLES 2 TO 5
In each example, an epoxy resin powder coating composition of the present
invention was prepared in the same manner as in Example 1 except that the
amounts of the needle-like glass powder and titanium dioxide added were
changed as shown in Table 1. The sizes of the needle-like glass powder and
granular titanium dioxide after pulverization were substantially the same
as those in Example 1 and within the ranges of the present invention.
COMPARATIVE EXAMPLES 1 TO 7
In each example, an epoxy resin powder coating composition was prepared in
the same manner as in Example 1 except that the amounts of the needle-like
glass powder and titanium dioxide added were changed as shown in Table 1.
The epoxy resin powder coating compositions prepared in Examples 1 to 5 and
Comparative Examples 1 to 7 were evaluated, and the results obtained are
shown in Table 1.
IMPACT RESISTANCE
A hot rolled steel plate (100 mm.times.100 mm.times.12 mm) which had been
degreased and roughened to a maximum roughness of 50 .mu.m by shot
blasting was first heated to 240.degree. C. The epoxy resin powder coating
composition was coated on the hot steel plate by electrostatic spraying
and then hardened by heating at 200.degree. C. for 10 minutes to form a
coating having a thickness of 0.3 to 0.4 mm. This steel plate with the
coating was used as a test piece.
This test piece was mounted on a Gardner impact tester, and a tup of fixed
weight (weight: 1 kg) with a steel ball (diameter: 5/8 inch) fitted to the
top of a rod-shaped iron was dropped on the coating of the test piece. The
maximum height at which the coating was not broken was measured. This
measurement was carried out at 20.degree. C. and -30.degree. C.
FLEXIBILITY
A coating was prepared in the same manner as in the preparation of the test
piece for the measurement of the impact resistance except that a steel
plate which had been subjected to release treatment was used as the hot
rolled steel plate. This coating was then separated from the steel plate
to obtain a film. This film was punched with No. 2 Dumbbell defined in
JIS-K-7113. The dumbbell-shaped film thus obtained was subjected to a
tensile testing at a tensile speed of 50 mm/min using Tensilon Model
UTM-III (manufactured by Toyo Bowldwin Co., Ltd.). The rate of elongation
when the film was broken was measured. This measurement was carried out at
20.degree. C. and at -30.degree. C.
SMOOTHNESS
The appearance of the test piece prepared for the measurement of the impact
resistance was visually judged.
ANTICORROSION PROPERTIES
A test piece was prepared in the same manner as in the preparation of the
test piece for the measurement of the impact resistance. This test piece
was immersed in boiling water for 10 days. At the end of the time, the
formation of blister in the coating was examined and at the same time, the
volume resistivity of the coating was measured.
TABLE 1
__________________________________________________________________________
Amount (parts) Anticorrosion
Needle- Impact Properties
Like Resistance
Flexibility Formation
Volume
Glass
Titanium
(cm) (%) of Resistivity
Powder
Dioxide
20.degree. C.
-30.degree. C.
20.degree. C.
-30.degree. C.
Smoothness
Blister
(.OMEGA. .multidot.
__________________________________________________________________________
cm)
Example 1
70 80 120 110 11.0
8.5 Good No 5 .times. 10.sup.13
Example 2
40 130 120 100 14.0
10.5 " " 4 .times. 10.sup.13
Example 3
40 40 100 100 13.0
11.0 " " 4 .times. 10.sup.13
Example 4
90 40 110 110 10.5
9.0 " " 5 .times. 10.sup.13
Example 5
90 130 140 120 10.0
8.5 " " 6 .times. 10.sup.13
Comparative
20 20 40 20 18.0
15.0 " " 5 .times. 10.sup.13
Example 1
Comparative
70 0 80 70 5.0 3.5 " " 5 .times. 10.sup.13
Example 2
Comparative
100 10 90 70 4.5 3.5 " " 5 .times. 10.sup.13
Example 3
Comparative
150 20 100 110 4.0 3.2 Slightly
" 4 .times. 10.sup.13
Example 4 bad
Comparative
20 80 70 35 14.0
12.5 Good " 5 .times. 10.sup.13
Example 5
Comparative
0 200 120 40 13.5
10.5 Slightly
" 3 .times. 10.sup.13
Example 6 bad
Comparative
20 200 100 50 10.0
9.0 Slightly
" 3 .times. 10.sup.13
Example 7 bad
__________________________________________________________________________
EXAMPLE 6
A composition consisting of 100 parts of a bisphenol A-type epoxy resin
(epoxy equivalent: 850; ratio of the number of unreactive terminal groups
to the total number of groups: 3.0:100), 60 parts of a needle-like glass
powder (average length: 80 .mu.m; average diameter: 9 .mu.m; aspect ratio:
8.9:1) which had been subjected to surface treatment using
.gamma.-glycidoxypropylmethyldiethoxy silane, 80 parts of granular barium
sulfate (average particle diameter: 0.25 .mu.m) which had been subjected
to Zn-Al-Si treatment, 10 parts of diaminodiphenylmethane, 0.2 part of
2-methylimidazole, 0.5 part of a pigment, and 0.5 part of a leveling agent
was melt kneaded in a twin-screw extruder in the same manner as in Example
1.
The above-kneaded mass was then pulverized to a size of 120 mesh or less to
obtain an epoxy resin powder coating composition of the present invention.
The needle-like glass powder contained in the coating composition thus
prepared had the average length of 75 .mu.m, the average diameter of 9
.mu.m, and the aspect ratio of 8.3:1. The average particle diameter of the
granular barium sulfate was 0.25 .mu.m.
EXAMPLES 7 AND 8
In each example, an epoxy resin powder coating composition of the present
invention are prepared in the same manner as in Example 6 except that the
amounts of the needle-like glass powder and barium sulfate added were
changed as shown in Table 2.
The sizes of the needle-like glass powder and granular barium sulfate after
pulverization were substantially the same as those in Example 6 and fallen
within the ranges of the present invention.
COMPARATIVE EXAMPLE 8
An epoxy resin powder coating composition was prepared in the same manner
as in Example 6 except that a needle-like glass powder which had been
subjected to surface treatment using
.gamma.-glycidoxypropylmethyldiethoxysilane, and having an average length
of 30 .mu.m, an average diameter of 13 .mu.m, and an aspect ratio of 2.3:1
was used.
COMPARATIVE EXAMPLE 9
An epoxy resin powder coating composition was prepared in the same manner
as in Example 6 except that barium sulfate which had been subjected to
Zn-Al-Si treatment and having an average particle diameter of 3.0 .mu.m
was used.
The characteristics of coating prepared using the epoxy resin powder
coating compositions prepared in Examples 6 to 8 and Comparative Examples
8 and 9 were evaluated in the same manner as described above. The results
obtained are shown in Table 2.
TABLE 2
__________________________________________________________________________
Amount (parts) Anticorrosion
Needle- Impact Properties
Like Resistance
Flexibility Formation
Volume
Glass
Barium
(cm) (%) of Resistivity
Powder
Sulfate
20.degree. C.
-30.degree. C.
20.degree. C.
-30.degree. C.
Smoothness
Blister
(.OMEGA. .multidot.
__________________________________________________________________________
cm)
Example 6
60 80 125 115 12.0
9.5 Good No 4 .times. 10.sup.13
Example 7
60 40 110 105 11.5
9.5 " " 4 .times. 10.sup.13
Example 8
60 130 130 120 12.5
9.5 " " 4 .times. 10.sup.13
Comparative
60 80 95 50 11.5
8.5 " " 4 .times. 10.sup.13
Example 8
Comparative
60 80 100 90 4.0 3.0 Slightly
" 4 .times. 10.sup.13
Example 9 bad
__________________________________________________________________________
EXAMPLE 9
100 parts of a bisphenol A-type epoxy resin (epoxy equivalent: 750; ratio
of the number of unreactive terminal groups to the total number of groups:
3.5:100), 110 parts of a needle-like powder (average length: 100 .mu.m;
average diameter: 9 .mu.m; aspect ratio: 10:1) which had been subjected to
surface treatment using N-phenyl-.gamma.-aminopropyltrimethoxysilane, and
50 parts of granular titanium dioxide which had been subjected to Zn-Al-Si
treatment (average particle diameter: 0.35 .mu.m) were melt mixed in a
planetary mixer at 130.degree. C. for 2 hours, taken out from the mixer,
cooled, and then pulverized using a hammer mill.
To 270 parts of the pulverized product as obtained above were added 24
parts of a resin (hardener) (hydroxyl group equivalent: 250) prepared by
addition reaction of 1 mole of epichlorohydrin and 2 moles of bisphenol,
1.0 part of 2-methylimidazole, 0.5 part of a pigment, and 0.5 part of a
leveling agent. The composition thus prepared was melt kneaded in a
twin-screw extruder.
The above-kneaded mass was pulverized to a particle size of 120 mesh or
less using a manner mill to obtain an epoxy resin powder coating
composition of the present invention. The needle-like glass powder
contained in the coating composition had the average length of 80 .mu.m,
the average diameter of 10 .mu.m, and the aspect ratio of 8.0:1. The
average particle diameter of the granular titanium dioxide was 0.35 .mu.m.
EXAMPLES 10 TO 12
In each example, an epoxy resin powder coating composition of the present
invention was prepared in the same manner as in Example 9 except that the
amounts of the needle-like glass powder and titanium dioxide added were
changed as shown in Table 3.
The sizes of the needle-like glass powder and granular titanium dioxides
after pulverization were substantially the same as those in Example 9 and
fallen within the ranges of the present invention.
COMPARATIVE EXAMPLES 10 TO 16
In each example, an epoxy resin powder coating composition was prepared in
the same manner as in Example 9 except that the amount of the needle-like
glass powder and titanium dioxide added were changed as shown in Table 3.
The characteristics of coating prepared using the epoxy resin powder
coating composition prepared in Examples 9 to 12 and Comparative Examples
10 to 16 were evaluated in the same manner as described above. The results
obtained are shown in Table 3.
TABLE 3
__________________________________________________________________________
Amount (parts) Anticorrosion
Needle- Impact Properties
Like Resistance
Flexibility Formation
Volume
Glass
Titanium
(cm) (%) of Resistivity
Powder
Dioxide
20.degree. C.
-30.degree. C.
20.degree. C.
-30.degree. C.
Smoothness
Blister
(.OMEGA. .multidot.
__________________________________________________________________________
cm)
Example 9
110 50 250 180 10.0
8.0 Good No 6 .times. 10.sup.13
Example 10
110 80 260 185 9.5 8.0 " " 7 .times. 10.sup.13
Example 11
160 40 280 210 9.0 7.5 " " 6 .times. 10.sup.13
Example 12
160 80 290 210 9.0 7.5 " " 7 .times. 10.sup.13
Comparative
20 20 40 20 18.0
15.0 " " 4 .times. 10.sup.13
Example 10
Comparative
120 0 90 80 5.0 3.0 " " 5 .times. 10.sup.13
Example 11
Comparative
120 10 100 80 6.0 3.5 " " 5 .times. 10.sup.13
Example 12
Comparative
20 80 70 35 14.0
12.5 " " 5 .times. 10.sup.13
Example 13
Comparative
0 200 120 40 13.5
10.5 Slightly
" 7 .times. 10.sup.13
Example 14 bad
Comparative
200 0 150 130 3.5 3.0 Bad " 6 .times. 10.sup.13
Example 15
Comparative
220 200 No coating was formed.
Example 16
__________________________________________________________________________
EXAMPLE 13
100 parts of a bisphenol A-type epoxy resin (epoxy) equivalent: 850; ratio
of the number of unreactive terminal groups to the total number of groups:
3.0:100), 120 parts of a needle-like glass powder (average length: 80
.mu.m; average diameter: 9 .mu.m; aspect ratio: 8.9:1) which had been
subjected to surface treatment using
.gamma.-glycidoxypropylmethyldiethoxysilane, and 80 parts of granular
barium sulfate which had been subjected to Zn-Al-Si treatment (average
grain diameter: 0.25 .mu.m) were melt mixed in a planetary mixer at
130.degree. C. for 2 hours, taken out from the mixer, cooled, and then
pulverized using a hammer mill.
To 300 parts of the pulverized product as obtained above were added 10
parts of diaminodiphenylmethane, 0.2 part of 2-methylimidazole, 0.5 part
of a pigment, and 0.5 part of a leveling agent. The resulting composition
was melt kneaded in a twin-screw extruder in the same manner as in Example
9 and then pulverized to a particle size of 120 mesh or less to obtain an
epoxy resin powder coating composition of the present invention. The
needle-like glass powder contained in the coating composition had the
average length of 70 .mu.m, the average diameter of 9 .mu.m, and the
aspect ratio of 7.8:1. The average particle diameter of granular barium
sulfate was 0.25 .mu.m.
EXAMPLE 14
An epoxy resin powder coating composition of the present invention was
prepared in the same manner as in Example 13 except that the amount of the
needle-like glass powder and barium sulfate added were changed as shown in
Table 4.
The sizes of the needle-like glass powder and granular barium sulfate after
pulverization were substantially the same as those in Example 13 and
fallen within the ranges of the present invention.
COMPARATIVE EXAMPLE 17
An epoxy resin powder coating composition was prepared in the same manner
as in Example 13 except that a needle-like glass powder which had been
subjected to surface treatment using
.gamma.-glycidoxypropylmethyldiethoxysilane and having an average length
of 30 .mu.m, an average diameter of 13 .mu.m, and an aspect ratio of 2.3:1
was used.
COMPARATIVE EXAMPLE 18
An epoxy resin powder coating composition was prepared in the same manner
as in Example 13 except that barium sulfate which had been subjected to
Zn-Al-Si treatment and having an average particle diameter of 3.0 .mu.m
was used.
The characteristics of coating prepared using the epoxy resin powder
coating composition prepared in Examples 13 and 14, and Comparative
Examples 17 and 18 were evaluated. The results obtained are shown in Table
4.
TABLE 4
__________________________________________________________________________
Amount (parts) Anticorrosion
Needle- Impact Properties
Like Resistance
Flexibility Formation
Volume
Glass
Barium
(cm) (%) of Resistivity
Powder
Sulfate
20.degree. C.
-30.degree. C.
20.degree. C.
-30.degree. C.
Smoothness
Blister
(.OMEGA. .multidot.
__________________________________________________________________________
cm)
Example 13
120 80 260 180 9.0 8.0 Good No 7 .times. 10.sup.13
Example 14
120 40 250 180 9.5 8.0 " " 7 .times. 10.sup.13
Comparative
120 80 150 60 10.0
8.0 " " 6 .times. 10.sup.13
Example 17
Comparative
120 80 180 110 3.5 3.0 Slightly
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