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Description  |
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FIELD OF THE INVENTION
The present invention relates to a method for coating steel structures in
water. More particularly, it is concerned with a method for coating in
water, whereby corrosion and stain of steel structures placed in water or
under humid conditions can be effectively prevented.
BACKGROUND OF THE INVENTION
In recent years, with development of the ocean, oil digging rig or steel
structures such as oil storage purge and sea plant ships, piers of long
bridges constructed in the sea, and steel structures in water of sea air
ports have been increasingly constructed. These steel structures are
substantially impossible to transmit to another place for the maintenance
or corrosion repairing thereof, and such operations must be carried out
under bad conditions such as in the sea or at a location where water is
splashed. For this reason, it has been desired to develop a corrosion
repairing method which can be easily carried out on or in the sea.
Japanese Patent Application (OPI) No. 137034/79, for example, discloses a
coating method which can form a coating having excellent corrosion
resistance on portions in water or splash zones of underwater structures
in a simple and easy manner as on the ground (the term "OPI" as used
herein refers to a "published unexamined Japanese patent application").
Conventional compositions for use in such underwater coating include a
composition comprising an epoxy resin as a base resin, polyamide or
polyamine as a curing agent and a filler as described in Japanese Patent
Application (OPI) No. 67400/76. However, these conventional compositions
have disadvantages that underwater coating properties are poor and
coatings are quite easily lost by waves during hardening because of their
poor adhesion force. Even if the coatings harden, the hardened coatings
have poor adhesion properties and therefore anticorrosion over a long
period of time cannot be expected.
SUMMARY OF THE INVENTION
As a result of extensive investigations to overcome the above problems, it
has been found that in underwater coating of steel structures, if a paint
containing a specific metal powder is coated as the first layer and a
paint not containing the metal powder is then coated thereon as the second
layer, a coating operation can be carried out in the sea in a simple
manner as on the ground and a coating having excellent anticorrosion
properties can be formed. Based on these findings, the present invention
has been accomplished. In particular, it is a novel discovery that the
adhesion properties of an epoxy resin to iron in water are greatly
improved by using a metal powder in combination in the first layer-forming
paint.
Accordingly, an object of the present invention is to provide a method for
coating steel structures in water which comprising
coating as a first layer an underwater-curable composition comprising
(1) a two-pack resin blend system comprising
(a) a blend system comprising an epoxy-based resin, and
(b) a blend system comprising an underwater-curable curing agent capable of
hardening the epoxy-based resin blend systen, and
(2) from 5 to 75% by weight, based on the total weight of the
underwater-curable composition, of a metal powder having an ionization
tendency greater than that of iron,
on the steel structures, and
coating an underwater-curable composition comprising the two-pack resin
blend systen and a coloring pigment on the first layer as a second layer.
DETAILED DESCRIPTION OF THE INVENTION
The term "epoxy-based resin" as used herein means both an epoxy resin and a
mixed resin of an epoxy resin and other resin compatible therewith.
Of two blend systems which constitute the two-pack epoxy resin composition
of the present invention, one blend system comprises an epoxy resin or a
mixed resin of the epoxy resin and other resin compatible therewith. This
blend system can contain additives such as a filler such as calcium
carbonate, silica, talc and baryta; a flowability adjusting agent such as
finely powdered silica and montmorillonite; and the like depending on the
purpose of use. These additives are compounded in an amount up to 1,000
parts by weight, preferably 1 to 500 parts by weight, per 100 parts by
weight of the epoxy resin or the mixed resin. In particular, a blend
system having a relatively high viscosity can be formed by increasing the
amount of the filler added.
The epoxy resin is preferably a bisphenol type epoxy resin. In addition, a
cyclic aliphatic epoxy resin, a phenol or cresol novolak type epoxy resin,
a glycidyl phthalate type epoxy resin, a .beta.-methylepichlorohydrin type
epoxy resin, a polyepoxy resin, a dimer acid type epoxy resin, a
polyglycol type epoxy resin and the like can be used. These epoxy resins
can be used alone or as mixtures comprising two or more thereof.
The epoxy resin used is not particularly limited, but generally has epoxy
equivalents of from 70 to 1,000, preferably from 100 to 700.
Other resins which are compatible with the above epoxy resins include
thermosetting and thermoplastic resins. Representative examples of the
thermosetting resins are a phenoxy resin, a phenol resin, a xylene resin,
an acrylic resin and an unsaturated polyester resin. Examples of the
thermoplastic resins are a polyester resin, an ethylene-vinyl acetate
copolymer, a thiocol resin, an ionomer resin, a modified
butadiene-acrylonitrile resin, a vinyl acetate resin, coal such as coal
tar and asphalt pitch, and a petroleum residue resin. One or more of those
other resins can be used in combination with the above epoxy resin. Those
other resins compatible with the epoxy resin can be used by replacing up
to 50% by weight, preferably up to 30% by weight, of the epoxy resin.
The other blend system in the two-pack epoxy resin composition used in the
present invention comprises a curing agent containing an
underwater-curable curing agent capable of curing the epoxy resin even in
water. In addition, additives such as a filler and a flowability adjusting
agent as described above are compounded thereto depending on the purpose
of use.
These additives are compounded in an amount up to 1,000 parts by weight,
preferably from 1 to 500 parts by weight, per 100 parts by weight of the
curing agent. A composition having a relatively high viscosity can be
formed by increasing the amount of the filler added.
Curing agents for the epoxy resin which are sparingly soluble in water are
replaceable with a water molecule, and active hydrogen can be used as the
underwater-curable curing agent. Examples of the curing agent are
amine-based curing agent such as aromatic amines, polyalkylenepolyamines,
cyclic aliphatic polyamines, polyamideamines, modified polyamines, and
ketemines; polymercaptans; and the like. Those are used alone or in
combination with each other. In combination with the underwater-curable
curing agent, cold-curable curing agents which are conventionally used in
the atmosphere can be used. Examples of such cold-curable curing agents
are aliphatic polyamines, polyamideamines, amine-containing adducts and
separated adducts. The cold-curable curing agent is used by replacing up
to 40% by weight, preferably up to 30% by weight, of the
underwater-curable curing agent.
A metal powder which is contained in the composition for the formation of
the first layer and having the ionization tendency larger than that of
iron includes a zinc powder, an aluminum powder, a magnesium powder, a
chromium powder, a zirconium powder, etc., powders of alloys of the above
metals, and composite powders resulting from plating or vacuum deposition
of the above metals. These metal powders can be used alone or in
combination with each other. The composite powder is a powder wherein the
surface of particles is composed of the above described metals. For
example, the composite powder is obtained by coating the metals on the
surface of metal powder (including iron) having the ionization tendency
smaller than that of iron or the surface of synthetic resin powder by
means of, for example, deposition. Use of such metal powders in
combination greatly increases the adhesion of the epoxy-based resin to
iron in water. Of those powders, a zinc powder and an aluminum powder are
particularly preferred.
The metal powder of the present invention preferably has the average
particle size of from 1 to 300 .mu.m. If the average particle size is less
than 1 .mu.m, the effect of increasing underwater adhesion properties is
insufficient. On the other hand, if the average particle size is more than
300 .mu.m, a coating having a poor appearance is undesirably obtained. The
shape of the particle may be any of shapes such as flat, spherical and
needle-like and the effect of increasing underwater adhesion properties
can be obtained regardless of the particle shape. The metal powder must be
added in an amount of from 5 to 75 wt % based on the total weight of the
two-pack resin blend system (including additives) and the metal powder. If
the amount of the metal powder added is less than 5 wt %, the effect of
increasing underwater adhesion properties cannot be obtained. On the other
hand, if the amount of the metal powder added is more than 75 wt %, the
cohesive force of the resulting composition and the adhesion force of the
composition to a steel material are undesirably decreased.
The mixing proportion of the blend system comprising the epoxy resin and
the blend system comprising the underwater-curable curing agent is
generally such that the active hydrogen equivalent in the underwater
curing agent component is from 0.2 to 2.0, preferably from 0.5 to 1.5, per
equivalent of the epoxy group in the epoxy resin. If the proportion is too
small, the curing rate becomes slow, and if the proportion is too large,
the properties of the cured product deteriorate.
The metal powder can be previously incorporated in any one or both of the
blend system comprising the epoxy resin and the blend system comprising
the underwater-curable curing agent for the epoxy resin, or can be added
at the time of mixing the blend system comprising the epoxy resin and the
blend system comprising the underwater-curable curing agent for the epoxy
resin.
The adhesion force to iron is an important factor for the first layer
coating as an undercoating layer. For this reason, the metal
powder-containing composition is essential, while on the other hand,
coloring is limited due to the presence of the metal powder. Accoringly,
the underwater-curable composition comprising the two-pack resin blend
system and the coloring pigment is used as the second layer (overcoating
layer). The underwater-curable composition does not substantially ccntain
the metal powder. On the other hand, the coloring pigment can be added to
the metal powder-containing composition used for the first layer coating,
if desired. Further, the epoxy-based resin and the underwater-curable
curing agent which constitute the metal powder-containing composition for
the first layer coating can be the same as or different from those in the
composition for the second layer coating.
All coloring pigments which are used in the conventional paints can be used
as the coloring pigment for the preparation of the second layer coating
composition. Examples thereof include oxide type coloring pigments such as
chromium oxide, iron oxide and titanium dioxide, pigments such as carbon
black and graphite, and organic coloring pigments such as phthalocyanine
blue and phthalocyanine green. It is particularly preferred to add
sparingly water-soluble pigments.
The coloring pigment can be added to any one or both of the blend system
comprising the epoxy resin and the blend system comprising the
underwater-curable curing agent. Where the coloring pigment is added to
both the blend systems, pigments having different hues can be added to the
respective blend system, so that a measure of extent of stirring when the
two blend systems are mixed and stirred can be obtained.
The two-pack epoxy resin composition is constituted by the combination of
the blend system comprising the epoxy resin (hereinafter referred to as a
"main component") and the blend system comprising the underwater-curable
curing agent (hereinafter referred to as a "curing agent"). The curing
reaction proceeds by mixing the main component and the curing agent,
resulting in the formation of an epoxy resin-based cured product. In
connection with the properties of the two-pack epoxy resin composition,
the main component and the curing agent are prepared in the form of a high
viscosity composition (paste-like) or a low viscosity composition
(paint-like; viscosity: about 3,000 ps or less) so that the composition
can be mixed and coated by the wet hand method. Depending on the
properties, the composition can be coated using, for example, a brush, a
trowel, a spatula and a roller. Although the coating thickness varies
depending on the viscosity and properties, coating is usually carried out
such that the total thickness of the two coatings is from 100 .mu.m to 10
mm. As the thickness of each layer, the first and second layer coating
each generally has a thickness of from 50 .mu.m to 8 mm.
In the practice of coating, rust, sea animals and the like on the steel
surface in water are first removed by techniques such as a disc sander, a
water jet and a sand water jet, the underwater-curable composition
containing the metal powder is coated on the iron surface as the first
layer, and the underwater-curable composition containing the coloring
pigment is then coated thereon as the second layer. The second layer can
be coated either after the first layer is cured or before the first layer
is cured, i.e., the first layer is uncured. In accordance with the present
invention in which an epoxy resin, a curing agent to cure the epoxy resin,
and a metal powder having an ionization tendency greater than that of iron
are used, the excellent coating properties and curing properties inherent
in the epoxy resin can be maintained and, at the same time, due to the
mutual action with the metal powder, underwater coating properties are
excellent and underwater adhesion properties are greatly increased.
Therefore, the composition applied is not lost by waves and the like and
is cured as such, and the cured coating strongly adheres to an underwater
steel structure because of its great adhesion force. Furthermore, since
the cured coating possesses inherent excellent characteristics of the
epoxy resin, the coating exhibits a quite excellent anticorrosion effect
in combination with the above characteristics, and effectively protects
the underwater structure. Furthermore, when the main component of the
overcoating composition for the second layer is the same as or the similar
type to that of the undercoating composition for the first layer, not only
overcoating is extremely easy but also the adhesion properties between the
layers after curing are excellent. In addition, the multilayer coating
provides the advantage that coating defects such as pinholes are markedly
decreased.
Further, in the second layer of the overcoating according to the present
invention, a glass flake together with a coloring pigment can be added to
the two-pack resin blend system. The glass flake is added to increase the
anticorrosion effect. The glass flake comprises, as a main component, ones
which pass the 32 mesh (500 .mu.m) sieve and do not pass 350 mesh (45
.mu.m) sieve (the sieves are defined according to JIS Z8801). The "main
component" means at least 50% by weight, preferably at least 60% by weight
and more preferably at least 70% by weight, based on the total weight of
the glass flake.
Further, the glass flakes generally used in the present invention must all
pass the 16 mesh (1,000 .mu.m) sieve (as defined above).
The thickness of glass flake is preferably 0.5 to 10 .mu.m.
The amount of glass flake added is 5 to 30% by weight, preferably 10 to 25%
by weight, per the total weight of the composition.
By using the glass flake within the above described specific range, further
excellent anticorrosion effect can be obtained.
Although the method of the present invention is a coating method in water,
as a matter of course, it can be applied to wet surfaces such as splash
zones and high and low tide zones of structures. Moreover, the method of
the present invention can be applied to structures on the ground.
The present invention is described in greater detail by reference to the
following Examples and Comparative Examples. Unless otherwise indicated,
all percents, parts, ratios and the like are by weight.
EXAMPLES 1 TO 3 AND COMPARATIVE EXAMPLES 1 AND 2
90 Parts of a bisphenol A type epoxy resin having an epoxy equivalent of
185 to 192, 10 parts of phenyl glycidyl ether as a reactive diluent, 40
parts of calcium carbonate, and 2 parts of superfinely divided anhydrous
silica (specific surface area: 200 m.sup.2 /g) as a tag-preventing agent
were mixed and stirred at 50.degree. C. to prepare an epoxy resin blend
system. On the other hand, 50 parts of modified aromatic polyamine having
an active hydrogen equivalent of 95, 15 parts of calcium carbonate and 1
part of superfinely divided anhydrous silica (specific surface area: 200
m.sup.2 /g) as a tag-preventing agent were mixed at 50.degree. C. in a
mixing vessel to prepare a curing agent blend.
142 g of the epoxy resin blend system and 66 g of the curing agent blend
were weighed, and a zinc powder (average particle diameter: 50 .mu.m) was
added in the proportions shown in Table 1 below and mixed to prepare
undercoating compositions 1, 2, 3, 4 and 5 used for the formation of the
first layer.
TABLE 1
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Undercoating Composition (parts)
1 2 3 4 5
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Epoxy Resin
Blend System
Bisphenol A Type
90 90 90 90 90
Epoxy Resin
Reactive Diluent
10 10 10 10 10
Calcium Carbonate
40 40 40 40 40
Tag-Preventing Agent
2 2 2 2 2
Curing Agent
Blend System
Modified Aromatic
50 50 50 50 50
Polyamine
Calcium Carbonate
15 15 15 15 15
Tag-Preventing Agent
1 1 1 1 1
Metal Powder
Zinc Powder 23.1 208 485 2.1 832
(10)* (50)* (70)*
(1)* (80)*
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The numerical values in ()* represent weight % of the zinc powder in the
blend system.
The overcoating composition used for the formation of the second layer was
prepared by adding titanium oxide as a coloring pigment to the epoxy resin
blend system and phthalocyanine blue B as a coloring pigment to the curing
agent blend system and then mixing the respective compositions in a mixing
vessel at 50.degree. C. in the same manner as in the preparation of the
undercoating composition. Each mixing proportion (parts) is shown in Table
2.
TABLE 2
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Epoxy Resin Blend System
Bisphenol A Type Epoxy Resin
90
Reactive Diluent Phenyl Glycidyl Ether
10
Coloring Pigment, Titanium Oxide
5
Calcium Carbonate 40
Tag-Preventing Agent, Superfinely
2
Divided Anhydrous Silica (specific
surface area: 200 m.sup.2 /g)
Curing Agent Blend System
Modified Aromatic Polyamine
50
Coloring Pigment, Phthalocyanine Blue B
1
Calcium Carbonate 15
Tag-Preventing Agent, Superfinely
1
Divided Anhydrous Silica (specific
surface area: 200 m.sup.2 /g)
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An SS 41 steel plate (9.times.100.times.100 mm) which had been ground with
a disc sander was dipped in sea water for 4 hours as a material to be
coated. The compositions 1, 2, 3, 4 and 5 shown in Table 1 each was coated
in the sea with a spatula. After 30 hours, the overcoating composition was
coated with a roller as the second layer. The thickness of the first layer
was about 200 .mu.m and the thickness of the second layer was about 200
.mu.m, and the total thickness was about 400 .mu.m. Coating workability at
the time of coating, the appearance of the coated surface after coating,
and the adhesion force of the coating after curing are shown in Table 3.
TABLE 3
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Coating Adhesion Force of
Workability Coating after
of 1 Month after
Undercoating
Appearance
Curing in Water**
Composition*
of Coating
(kg/cm.sup.2)
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Example 1:
Undercoating Composition 1 +
o Good 17
Overcoating Composition
Example 2:
Undercoating Composition 2 +
o Good 25
Overcoating Composition
Example 3:
Undercoating Composition 3 +
o Good 28
Overcoating Composition
Comparative
Undercoating Composition 4 +
x Poor 3
Example 1:
Overcoating Composition
Comparative
Undercoating Composition 5 +
.DELTA.
Poor 5
Example 2:
Overcoating Composition
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*o: The whole surface can be uniformly coated easily with a spatula
several times.
.DELTA.: When overcoating is carried out, the first coating sometimes
separates, but the whole surface can be coated by repeating coating with
spatula.
x: Separation from the steel surface occurs even if overcoating is
repeated, and the whole surface cannot be coated.
**Adhesion PullOff Test
A coated sample which had been dipped in sea water for 1 month was taken
out in the air and dried over 1 day and night. This coated sample was
measured for adhesion force using an adhesion tester.
EXAMPLE 4
Example 1 was repeated except that an aluminum powder (average particle
diameter: 15 .mu.m) was used in place of the zinc powder.
The results obtained are shown in Table 4 below.
EXAMPLE 5
Example 2 was repeated except that a zirconium powder (average particle
diameter: 20 .mu.m) was used in place of the zinc powder in the
undercoating composition.
The results obtained are shown in Table 4 below.
EXAMPLE 6
Example 3 was repeated except that a chromium powder (average particle
diameter: 60 .mu.m) was used in place of the zinc powder in the
undercoating composition.
The results obtained are shown in Table 4 below.
EXAMPLE 7
Example 1 was repeated except that composite particles prepared by coating
the surface of glass beads (average particle diameter: 60 .mu.m) with
aluminum in an average thickness of 1 .mu.m was used in place of the zinc
powder in the undercoating composition.
The results obtained are shown in Table 4 below.
COMPARATIVE EXAMPLE 3
Example 1 was repeated except that 120 parts of titanium white was used in
place of the zinc powder in the undercoating composition.
The results obtained are shown in Table 4 below.
TABLE 4
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Coating Adhesion Force of
Workability Coating after
of 1 Month after
Undercoating
Appearance Curing in Water**
Composition*
of Coating (kg/cm.sup.2)
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Example 4
o Good 15
Example 5
o Good 20
Example 6
o Good 22
Example 7
o Good 20
Comparative
x Poor 2
Example 3
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* and **The same as defined in Table 3.
EXAMPLE 8
Example 2 was repeated except that 30 parts of a cyclic aliphatic polyamine
(isophoronediamine-modified product) having an active hydrogen equivalent
of 110 was used in place of the modified aromatic polyamine in the
undercoating composition.
The results obtained are shown in Table 5 below.
EXAMPLE 9
Example 2 was repeated except that 100 parts of a cyclic aliphatic
polyamine (isophoronediamine-modified product) having an active hydrogen
equivalent of 110 was used in place of the modified aromatic polyamine in
the undercoating composition.
The results obtained are shown in Table 5 below.
EXAMPLE 10
Example 2 was repeated except that a bisphenol F-type epoxy resin (epoxy
equivalent: 175) was used in place of the bisphenol A-type epoxy resin in
the undercoating composition.
The results obtained are shown in Table 5 below.
EXAMPLE 11
Example 2 was repeated except that a glycidyl phthalate-type epoxy resin
(epoxy equivalent: 140) was used in place of the bisphenol A-type epoxy
resin in the undercoating composition.
The results obtained are shown in Table 5 below.
EXAMPLE 12
Example 1 was repeated except that the thickness of the first layer was 100
.mu.m, the thickness of the second layer was 100 .mu.m, and the total
thickness thereof was 200 .mu.m.
The results obtained are shown in Table 5 below.
EXAMPLE 13
Example 3 was repeated except that the thickness of the first layer was 5
mm, the thickness of the second layer was 3 mm, and the total thickness
thereof was 8 mm, and that the second layer coating was conducted using a
spatula.
The results obtained are shown in Table 5 below.
EXAMPLE 14
Example 2 was repeated except that calcium carbonate was not used in the
undercoating composition and the overcoating composition.
The results obtained are shown in Table 5 below.
EXAMPLE 15
Example 1 was repeated except that barium sulfonate was used in place of
calcium carbonate in the undercoating composition, 200 parts of basrium
sulfonate was added to the epoxy resin blend system, 100 parts of barium
sulfonate was added to the curing agent blend system, and the amount of
the zinc powder was 40 parts.
The results obtained are shown in Table 5 below.
EXAMPLE 16
Example 2 was repeated except that diethylene glycol diacrylate (acrylic
resin) was used in place of phenylglycidyl ether (reactive diluent) in the
undercoating composition.
The results obtained are shown in Table 5 below.
EXAMPLE 17
Example 2 was repeated except that 10 parts of coal tar was added to the
undercoating composition.
The results obtained are shown in Table 5 below.
EXAMPLE 18
Example 2 was repeated except that 10 parts of bisphenol A-type epoxy resin
(epoxy equivalent: 500) was added to the undercoating composition.
The results obtained are shown in Table 5 below.
TABLE 5
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Coating Adhesion Force of
Workability Coating after
of 1 Month after
Undercoating Appearance Curing in Water**
Composition* of Coating (kg/cm.sup.2)
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Example 8
o Good 17
Example 9
o " 20
Example 10
o " 25
Example 11
o " 16
Example 12
o " 18
Example 13
o " 25
Example 14
o " 22
Example 15
o " 16
Example 16
o " 15
Example 17
o " 17
Example 18
o " 18
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* and **The same as defined in Table 3.
EXAMPLE 19
Example 1 was repeated except that the total amount of calcium carbonate
used in the overcoating composition was replaced by the same amount
(weight) of a glass flake (thickness: 3 .mu.m, all 16 mesh pass, the
proportion of 32 mesh pass and 350 mesh not pass; 75 wt %).
The adhesion forces after 1 month and 12 months after curing in water were
measured.
The results obtained are shown in Table 6 below.
EXAMPLE 20
Example 1 was repeated except that the total amount of calcium carbonate
used in the curing agent blend system of the overcoating composition was
replaced by the same glass flake as used in Example 19.
The results obtained are shonw in Table 6 below.
EXAMPLE 21
Example 2 was repeated except that the total amount of calcium carbonate
used in the overcoating composition was replaced by the same glass flake
as used in Example 19.
The results obtained are shown in Table 6 below.
EXAMPLE 22
Example 3 was repeated except that the total amount of calcium carbonate
used in the overcoating composition was replaced by the same glass flake
as used in Example 19.
The results obtained are shown in Table 6 below.
TABLE 6
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Coating Adhesion Force after
Workability Curing in Water**
of After 1 After 12
Undercoating Appearance Month Months
Composition* of Coating (kg/cm.sup.2)
(kg/cm.sup.2)
______________________________________
Example 19
o Good 17 17
Example 20
o " 17 17
Example 21
o " 25 25
Example 22
o " 28 28
______________________________________
* and **The same as defined in Table 3.
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 from the spirit and scope thereof.
* * * * *
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