U.S. patent application number 09/562075 was filed with the patent office on 2002-07-04 for method of forming coating films.
Invention is credited to Harakawa, Tsuyoshi, Kuwajima, Teruaki, Masuda, Kazuaki, Takeuchi, Yutaka.
Application Number | 20020086162 09/562075 |
Document ID | / |
Family ID | 26460783 |
Filed Date | 2002-07-04 |
United States Patent
Application |
20020086162 |
Kind Code |
A1 |
Masuda, Kazuaki ; et
al. |
July 4, 2002 |
Method of forming coating films
Abstract
A method is provided of forming multilayer coating films having
a high quality appearance while controlling interfacial bleeding or
inversion between coating film layers otherwise found when a
water-borne intermediate coating film and a water-borne metallic
coating film are formed in that order. The method comprising
forming coating films one after another on a substrate, namely
forming an intermediate coating film using a water-borne
intermediate coating, a metallic base coating film using a
water-borne metallic base coat and a clear coating film using a
clear coat, wherein said water-borne intermediate coating and/or
said water-borne metallic base coat contains a polycarbodiimide
compound and a carboxyl-containing aqueous resin.
Inventors: |
Masuda, Kazuaki; (Osaka,
JP) ; Harakawa, Tsuyoshi; (Kyoto, JP) ;
Kuwajima, Teruaki; (Osaka, JP) ; Takeuchi,
Yutaka; (Osaka, JP) |
Correspondence
Address: |
Sughrue Mion Zinn Macpeak Seas PLLC
2100 Pennsylvania Avenue N W
Washington
DC
20037-3213
US
|
Family ID: |
26460783 |
Appl. No.: |
09/562075 |
Filed: |
May 1, 2000 |
Current U.S.
Class: |
428/423.3 ;
427/402 |
Current CPC
Class: |
C08G 18/4825 20130101;
C08G 18/6254 20130101; C08G 18/797 20130101; C09D 175/04 20130101;
Y10T 428/31551 20150401; Y10T 428/31554 20150401; C08G 18/0828
20130101; B05D 7/574 20130101; C08G 18/44 20130101; C08G 18/283
20130101; C08L 2666/16 20130101; C09D 175/04 20130101; C08G 18/025
20130101; Y10T 428/31609 20150401; B05D 5/068 20130101 |
Class at
Publication: |
428/423.3 ;
427/402 |
International
Class: |
B32B 027/40 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 30, 1999 |
JP |
11-124008 |
Feb 25, 2000 |
JP |
2000-49807 |
Claims
1. A method of forming coating films one after another on a
substrate, namely forming an intermediate coating film using a
water-borne intermediate coating, a metallic base coating film
using a water-borne metallic base coating and a clear coating film
using a clear coating, wherein said water-borne intermediate
coating and/or said water-borne metallic base coating contains a
polycarbodiimide compound and a carboxyl-containing aqueous
resin.
2. The method of forming coating films according to claim 1,
wherein said polycarbodiimide compound is a carbodiimide compound
modified for hydrophilicity obtainable by the step of reacting a
polycarbodiimide compound (a) having at least two isocyanato groups
within each molecule with a hydroxy-terminated polyol (b) in a mole
ratio such that the number of moles of the isocyanato groups of (a)
the polycarbodiimide compound is in excess of the number of moles
of the hydroxy groups of (b) the polyol and the step of reacting
the reaction product obtainable in the preceding step with a
modifier for hydrophilicity (c) having an active hydrogen atom and
a hydrophilic moiety.
3. The method of forming coating films according to claim 2,
wherein said polyol (b) has a number average molecular weight of
300 to 5,000 and said modifier for hydrophilicity (c) is a
monoalkoxypolyalkylene glycol with a monoalkoxy group containing 4
to 20 carbon atoms.
4. The method of forming coating films according to any of claims 1
to 3, wherein said clear coating film formation with the clear
coating is carried out without curing of said intermediate coating
film and metallic base coating film.
5. A multilayer coating film obtainable by the method according to
one of claims 1 to 4.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a method of a metallic
coating film to be formed on an automotive body or automotive part
and to a multilayer coating film obtained by the method.
PRIOR ART
[0002] The amount of an organic volatile solvent(s) in the step of
application and curing by baking of coatings for automobiles is
generally large and, for reducing the number of steps, attempts
have been made to convert the coating form to a water-borne
ones.
[0003] For example, Japanese Kokai Publication Sho-62-216671
proposes applying a resin particle-containing water-borne
intermediate coating, applying a water-borne metallic coating,
without curing the intermediate coating, and, after drying or
curing, applying a clear coating. This technology, however, is not
sufficient to obtain coating films capable of meeting the current
high quality appearance requirement.
[0004] On the other hand, Japanese Kokai Publication Hei-09-235508
discloses a water-borne coating for a precoated metal as prepared
by incorporating a mono- and/or polycarbodiimide compound in a
water-borne coating containing, as a binder, an aqueous resin
selected from among acrylic copolymer resins, polyester resins,
polyurethane resins and modifications of these resins, each having
carboxyl groups within the molecule and capable of being
neutralized with a basic substance. This, however, is not
satisfactory, from the appearance and performance characteristics
viewpoint, in using for forming metallic coating films for
automobiles.
SUMMARY OF THE INVENTION
[0005] Accordingly, the present invention has it for its object to
provide a method of forming multilayer coating films having a high
quality appearance while controlling the bleeding and inversion at
the interface between the neighboring coating layers in applying a
water-borne intermediate coating and a topcoat in that order to a
substrate.
[0006] The present invention provides a method of forming coating
films one after another on a substrate, namely forming an
intermediate coating film using a water-borne intermediate coating,
a metallic base coating film using a water-borne metallic base
coating and a clear coating film using a clear coating,
[0007] wherein said water-borne intermediate coating and/or said
water-borne metallic base coating contains a polycarbodiimide
compound and a carboxyl-containing aqueous resin.
[0008] The invention also provides a method of forming coating
films
[0009] wherein said polycarbodiimide compound is a carbodiimide
compound modified for hydrophilicity obtainable by the step of
reacting a polycarbodiimide compound (a) having at least two
isocyanato groups within each molecule with a hydroxy-terminated
polyol (b) in a mole ratio such that the number of moles of the
isocyanato groups of the polycarbodiimide compound (a) is in excess
of the number of moles of the hydroxy groups of the polyol (b)
and
[0010] the step of reacting the reaction product obtainable in the
preceding step with a modifier for hydrophilicity (c) having an
active hydrogen atom and a hydrophilic moiety.
[0011] The invention further provides a method of forming coating
films
[0012] wherein said polyol (b) has a number average molecular
weight of 300 to 5,000 and
[0013] the modifier for hydrophilicity (c) is a
monoalkoxypolyalkylene glycol with a monoalkoxy group containing 4
to 20 carbon atoms.
[0014] The invention still further provides a method of forming
coating films
[0015] wherein the clear coating film formation with the clear
coating is carried out without curing of the intermediate coating
film and metallic base coating film.
[0016] Furthermore, the invention provides a multilayer coating
film obtainable by any of the methods mentioned above. In the
following, the present invention is described in further
detail.
DETAILED DESCRIPTION OF THE INVENTION
[0017] Intermediate Coating Film
[0018] In the above coating film forming method of the invention, a
water-borne intermediate coating is used for the formation of the
intermediate coating film. This water-borne intermediate coating
may contain a polycarbodiimide compound and a carboxyl-containing
aqueous resin. For obtaining multilayer coating films having a good
appearance, this water-borne intermediate coating should preferably
contain a polycarbodiimide compound and a carboxyl-containing
aqueous resin. In the following, the case of its containing a
polycarbodiimide compound and a carboxyl-containing aqueous resin
is mentioned.
[0019] The polycarbodiimide compound may be the product of any of
various methods. Fundamentally, an isocyanato-terminated
polycarbodiimide synthesized by the condensation reaction,
accompanying carbon dioxide elimination, of an organic
diisocyanate.
[0020] More specifically, there can be mentioned those
polycarbodiimide compounds modified for hydrophilicity which are
obtained, in the production of polycarbodiimide compounds, by the
step of reacting a polycarbodiimide compound (a) having at least
two isocyanato groups within each molecule with a
hydroxy-terminated polyol (b) in a mole ratio such that the number
of moles of the isocyanato groups of the polycarbodiimide compound
(a) is in excess of the number of moles of the hydroxy groups of
the polyol (b) and the step of reacting the reaction product
obtained in the preceding step with a modifier for hydrophilicity
(c) having an active hydrogen atom and a hydrophilic moiety.
[0021] In the above step of reacting a polycarbodiimide compound
(a) having at least two isocyanato groups within each molecule with
a hydroxy-terminated polyol (b), the polycarbodiimide compound (a)
having at least two isocyanato groups within the molecule is not
particularly restricted but, from the reactivity viewpoint, it is
preferably a carbodiimide compound having an isocyanato group at
both termini. The method of producing carbodiimide compounds having
an isocyanato group at both termini is well known in the art and
the condensation reaction of an organic diisocyanate under
elimination of carbon dioxide can be utilized.
[0022] As the organic diisocyanate, there can be mentioned an
aromatic diisocyanate, an aliphatic diisocyanate, an alicyclic
diisocyanate, or a mixture of these. As specific examples, there
may be mentioned 1,5-naphthylene diisocyanate,
4,4'-diphenylmethanediisocyanate,
4,4'-diphenyldimethylmethanediisocyanate, 1,3-phenylene
diisocyanate, 1,4-phenylene diisocyanate, 2,4-tolylene
diisocyanate, 2,6-tolylene diisocyanate, a mixture of 2,4tolylene
diisocyanate and 2,6-tolylene diisocyanate, hexamethylene
diisocyanate, cyclohexane-1,4-diisocyanate, xylylene diisocyanate,
isophoronediisocyanate, dicyclohexylmethane-4,4'-d- iisocyanate,
methylcyclohexanediisocyanate, tetramethylxylylene diisocyanate and
the like.
[0023] The above-mentioned condensation reaction is generally
carried out in the presence of a carbodiimidation catalyst. As
specific examples of the carbodiimidation catalyst, there may be
mentioned phospholene oxides such as 1-phenyl-2-phospholene
1-oxide, 3-methyl-2-phospholene 1-oxide, 1-ethyl-2-phospholene
1-oxide, 3-methyl-1-phenyl-2-phospholene 1-oxide and 3-phospholene
isomers of these, among others. From the reactivity viewpoint,
however, 3-methyl-1-phenyl-2-phospholene 1-oxide is preferred.
[0024] The hydroxy-terminated polyol (b) to be used in the process
for producing polycarbodiimide compounds modified for
hydrophilicity is not particularly restricted but, from the
reaction efficiency viewpoint, it is preferred that its number
average molecular weight be 300 to 5,000. Specifically, such polyol
(b) includes polyether diols, polyester diols and polycarbonate
diols. Typical examples are polyalkylene glycols such as
polyethylene glycol, polypropylene glycol, polyethylene-propylene
glycol, polytetramethylene ether glycol, polyhexamethylene ether
glycol and polyoctamethylene ether glycol, polyester diols such as
polyethylene adipate, polybutylene adipate, polyhexamethylene
adipate, polyneopentyl adipate, poly-3-methylpentyl adipate,
polyethylene/butylene adipate and polyneopentyl/hexyl adipate,
polylactone diols such as polycaprolactone diol,
poly-3methylvalerolactone diol, polycarbonate diols such as
polyhexamethylene carbonate diol, and mixtures of these.
[0025] In the first step of the above process for producing
polycarbodiimide compounds modified for hydrophilicity, the
polycarbodiimide compound (a) having at least two isocyanato groups
within each molecule is reacted with a hydroxy-terminated polyol
(b) in a mole ratio such that the number of moles of the isocyanato
groups of the polycarbodiimide compound (a) is in excess of the
number of moles of the hydroxy groups of the polyol (b). When the
number of moles of the isocyanato groups is equal to or smaller
than the number of moles of the hydroxy groups, the reaction of the
reaction product obtained in the first step with a modifier for
hydrophilicity in the second step, which is to be mentioned below
cannot be carried out to a sufficient extent. From the viewpoint of
reaction efficiency and economy, the ratio between the number of
moles of the isocyanato groups of the above polycarbodiimide
compound (a) and that of the hydroxy groups of the polyol (b) is
preferably 1.0:1.1 to 1.0:2.0. From the reaction efficiency
viewpoint, the degree of polymerization of the polycarbodiimide
compound (a) and polyol (b) in the reaction product obtained in
this step is preferably 1 to 10.
[0026] The second step of the above process for producing
polycarbodiimide compounds modified for hydrophilicity is a step of
reacting the reaction product obtained in the above first step with
a modifier for hydrophilicity (c) having an active hydrogen atom
and a hydrophilic moiety.
[0027] As the modifier for hydrophilicity (c) having an active
hydrogen atom and a hydrophilic moiety, there may be mentioned
quaternary salts of dialkylamino alcohols represented by
(R.sub.1).sub.2--N--R.sub.2--O--H (in which R.sub.1 is a lower
alkyl group and R.sub.2 is an alkylene, polyalkylene or oxyalkylene
group each having 1 to 10 carbon atoms), quaternary salts of
dialkylaminoalkylamines represented by
(R.sub.1).sub.2--N--R.sub.2--NH.sub.2 (in which R.sub.1 and R.sub.2
are as defined above), alkylsulfonic acid salts containing at least
one reactive hydroxy group and represented by
H--O--R.sub.3--SO.sub.3--R.sub.- 4 (in which R.sub.3 is an alkylene
group having 1 to 10 carbon atoms and R.sub.4 is an alkali metal
atom), monoalkoxy-polyalkylene glycols such as poly(ethylene oxide)
or poly(propylene oxide) terminally blocked with a monoalkoxy group
as represented by a R.sub.5--O--(CH.sub.2--CHR.sub.6--O--
-).sub.m--H (in which R.sub.5 is an alkyl group having 1 to 20
carbon atoms, R.sub.6 is a hydrogen atom or a methyl group and m is
an integer of 4 to 30), and mixtures thereof, and the like.
[0028] From the viewpoint of water resistance of coating films
obtained, monoalkoxy-polyalkylene glycols are preferred as the
modifier for hydrophilicity (c). From the storage stability
viewpoint, the number of carbon atoms contained in R.sub.5 in the
monoalkoxy-polyalkylene glycols is preferably 4 to 20, more
preferably 8 to 12. From the viewpoint of water dispersibility, it
is preferred that R.sub.6 be a hydrogen atom. Furthermore, from the
viewpoint of water dispersibility and reactivity after evaporation
of water, the integer m is preferably 4 to 20, more preferably 6 to
12. The number of carbon atoms in R.sub.5 and the value of m in the
above unit can adequately be selected within the above respective
ranges while taking into consideration the storage stability and
water dispersibility and the reactivity after evaporation of
water.
[0029] As the above monoalkoxy-polyalkylene glycols, there may
specifically be mentioned, among others, poly(oxyethylene)
monomethyl ether, poly(oxyethylene) mono-2-ethylhexyl ether and
poly(oxyethylene) monolauryl ether.
[0030] In the second step of said process for producing
polycarbodiimide compounds modified for hydrophilicity, the above
reaction product is reacted with the above modifier for
hydrophilicity (c) in a mole ratio such that the number of moles of
the isocyanato groups of the above reaction product is equal to or
in excess of the number of moles of the hydroxy groups of the
modifier for hydrophilicity. When the number of moles of the
isocyanato groups is smaller than the number of the hydroxy groups,
the reaction of the above reaction product with the modifier for
hydrophilicity cannot be carried out to a sufficient extent. The
number of moles of the isocyanato groups in the above reaction
product can be directly determined by assaying, or the calculated
value based on the formulation in the first step may be
employed.
[0031] In the first and/or second step, a catalyst may be used. The
temperature in the above-mentioned reactions is not restricted but,
from the viewpoint of reaction system control and reaction
efficiency, a temperature of 60 to 120.degree. C. is preferred. In
the above reactions, an active hydrogen-free organic solvent is
preferably used.
[0032] By the above first step and second step, it is possible to
obtain polycarbodiimide compounds modified for hydrophilicity.
[0033] In a preferred embodiment of the invention, the
polycarbodiimide compound modified for hydrophilicity, which is
preferably contained in the water-borne intermediate coating to be
used in the practice of the present invention, is a product in
which a carbodiimide unit and a polyol unit occur alternately via a
urethane bond and repeatedly and a monoalkoxypolyalkylene oxide
unit occurs as both molecular termini and is bound to a
carbodiimide unit via a urethane bond.
[0034] The carbodiimide unit mentioned above is obtained from a
polycarbodiimide compound (a) having at least two isocyanato groups
within each molecule by removal of the isocyanato groups and is a
unit represented by (--N.dbd.C.dbd.N--R.sub.7--).sub.n-- (in which
R.sub.7 is a saturated or unsaturated hydrocarbon group, which may
optionally contain a nitrogen atom and/or an oxygen atom and n
means the degree of polymerization and is a natural number of 1 to
20).
[0035] Said polycarbodiimide compound (a) is the same as that
mentioned hereinabove with respect to the method of producing the
polycarbodiimide modified for hydrophilicity.
[0036] The polyol unit mentioned above is obtained from (b) the
hydroxy-terminated polyol by removal of the active hydrogen
atoms.
[0037] The polyol (b) is the same as that mentioned above with
respect to the process for producing the polycarbodiimide compound
modified for hydrophilicity.
[0038] In the polycarbodiimide compound modified for hydrophilicity
according to the invention, the above carbodiimide unit and polyol
unit occur alternately via a urethane bond represented by
--NH--CO-- and repeatedly. The number of the repetitions is not
restricted but, from the reaction efficiency viewpoint, it is
preferably 1 to 10.
[0039] In a preferred embodiment of the invention, the
polycarbodiimide compound modified for hydrophilicity according to
the invention has a monoalkoxy polyalkylene oxide unit at both
molecular termini thereof, and the monoalkoxy polyalkylene oxide
unit is bound to the above carbodiimide unit via the above urethane
bond.
[0040] The monoalkoxy polyalkylene oxide unit mentioned above is
obtained from the above monoalkoxy polyalkylene glycol by removal
of the active hydrogen atoms and represented by
R.sub.5--O--(CH.sub.2--CHR.sub.6--O--).- sub.m-- (in which R.sub.5,
R.sub.6 and m are as defined above).
[0041] The monoalkoxypolyalkylene glycol is specifically the same
as that mentioned above with respect to the process for producing
the polycarbodiimide compound modified for hydrophilicity.
[0042] The carboxyl-containing aqueous resin to be contained in the
intermediate coating is one generally used as a binder component
for aqueous resins but is not particularly restricted. Such resin
may be water-soluble or water-dispersible and includes, for
example, carboxyl-containing acrylic resins, carboxyl-containing
polyester resins, carboxyl-containing alkyd resins and
carboxyl-containing polyurethane resins. These aqueous resins are
commercially available or can be produced by the methods well known
in the art. The carboxyl-containing aqueous resin to be contained
in the above intermediate coating may comprise a combination of two
or more species.
[0043] The carboxyl-containing aqueous resin, when it is
water-soluble, generally has a carboxyl group-due resin solid acid
value of 20 to 200 and, when it is water-dispersible, a carboxyl
group-due resin solid acid value of 3 to 30 although 1 these
factors vary depending on the resin species and molecular weight.
In the present specification, the term "aqueous" means both
water-soluble and water-dispersible.
[0044] The mole ratio between the total number of carboxyl groups
contained in the water-borne intermediate coating to be used in the
practice of the invention and the total number of carbodiimide
groups in the above polycarbodiimide compound is 1:0.05 to 1:3,
preferably 1:0.1 to 1:2. When the mole ratio of the carboxyl groups
is less than 0.05, the reaction cannot proceed to a sufficient
extent, so that the physical properties of the coating film
obtained will be poor. When it is in excess of 3, any extra effect
proportional to the amount used will not be obtained.
[0045] On the other hand, in cases where said water-borne
intermediate coating does not contain any polycarbodiimide compound
or any carboxyl-containing aqueous resin, the composition may
contain some other curing agent, which is to be mentioned later
herein, in lieu of the polycarbodiimide compound and a coating
film-forming resin, such as an acrylic resin, polyester resin,
alkyd rein, epoxy resin or urethane resin, in lieu of the
carboxyl-containing aqueous resin.
[0046] The water-borne intermediate coating may contain, if
necessary, in addition to the carboxyl-containing aqueous resin and
polycarbodiimide compound, one or more additives selected from
among color pigments, other curing agents, viscosity modifiers,
curing catalysts, surface modifiers, antifoaming agents, pigment
dispersants, plasticizers, film forming aids, ultraviolet
absorbers, antioxidants and so forth.
[0047] As the color pigments, there may be mentioned, for example,
organic ones such as azo chelate pigments, insoluble azo pigments,
condensed azo pigments, phthalocyanine pigments, indigopigments,
perinonepigments, perylenepigments, dioxane pigments, quinacridone
pigments, isoindolinone pigments and metal chelate pigments, and
inorganic ones such as chrome yellow, yellow iron oxide, red iron
oxide, carbon black and titanium dioxide. As extender pigments,
there may be mentioned calcium carbonate, barium sulfate, clay,
talc and the like. Flat pigments such as aluminum powder and mica
powder may also be added.
[0048] As a standard formulation, a gray intermediate coating
containing carbon black and titanium dioxide as main pigments is
used. Furthermore, the so-called color intermediate coating in
which the hue for the top coat is matched with set gray or various
color pigments are used combinedly.
[0049] The other curing agent mentioned above can be selected,
according to the functional group(s) contained in the above
carboxyl-containing resin, from among various ones well known in
the art. For example, when the above carboxyl-containing resin has
a hydroxy group(s), amino resins such as melamine resins and
benzoguanamine resins, isocyanate compounds such as trimethylene
diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate and
isophoronediisocyanate, and blocked isocyanates which are blocked
nurate forms, and, further, aliphatic polybasic carboxylic acids
and epoxy resins, among others. These may be used singly or two ore
more of them may be used combinedly. From the viewpoint of
performance characteristics cost of product coating films, amino
resins and/or blocked isocyanates are generally used.
[0050] The mixing ratio between the carboxyl-containing resin and
curing agent in the water-borne intermediate coating composition
can be arbitrarily selected by a skilled person in the art
according to the coating storage stability and coating film
performance characteristics.
[0051] In said water-borne intermediate coating, there may be
incorporated some other viscosity modifier for preventing bleeding
with the top coat film and securing the workability in coating
application. Substances showing thixotropy can generally be used as
the viscosity modifier, for example crosslinked or uncrosslinked
resin particle, swollen and dispersed fatty acid amides, fatty acid
amides, long-chain polyaminoamide phosphate salts and like
polyamides, colloidal swollen and dispersed polyethylene oxide and
like polyethylene type ones, organic acid smectite clay,
montmorillonite and like organic bentonites, inorganic pigments
such as aluminum silicate and barium sulfate, and flat pigments
causing viscosity owing to their shape.
[0052] Said water-borne intermediate coating includes those
generally called water base primers (sealers).
[0053] The method of producing the coating composition to be used
according to the invention, inclusive of those to be mentioned
later, is not particularly restricted but all methods well known in
the art, for example the method comprising dispersing a pigment
and/or like ingredient by kneading on a kneader, roll or the like,
can be employed.
[0054] Metallic Coating Film
[0055] In the coating film forming method of the invention, the
metallic coating film is composed of a metallic base coating film
formed from a water-borne metallic base coating and a clear coating
film formed from a clear coating.
[0056] Metallic Base Coating Film
[0057] The water-borne metallic base coating for forming the above
metallic base coating film may contain a polycarbodiimide compound
and a carboxyl-containing aqueous resin. For obtaining multilayer
coating films having a good appearance, it is preferred that this
water-borne metallic base coating contain a polycarbodiimide
compound and a carboxyl-containing aqueous resin. In addition, it
contains a color pigment and a luster color pigment, among others,
which are contained in metallic base coatings in general.
[0058] The polycarbodiimide compound, carboxyl-containing aqueous
resin and color pigment may be the same as those mentioned above in
relation to said water-borne intermediate coating. In cases where
the water-borne metallic base coating does not contain any
polycarbodiimide compound or carboxyl-containing aqueous resin, it
contains the other curing agent and film forming resin respectively
mentioned hereinabove in the description of the water-borne
intermediate coating.
[0059] The mole ratio between the total number of the carboxyl
groups of the resin and the total number of the carbodiimide groups
of the polycarbodiimide compound both contained in the water-borne
metallic base coating is 1:0.05 to 1:1.5, preferably 1: 0.1 to 1:
1.3. When the mole ratio of the carboxyl groups is smaller than
0.05, the reaction does not proceed to a sufficient extent, so that
the physical properties of the coating film obtained will be
lowered. When it is in excess of 1.5, any extra effect cannot be
obtained in proportion to the amount used.
[0060] The luster color pigment to be contained in the above
metallic base coating is not particularly restricted in shape but
may be a colored one. Preferably, it has a mean particle size
(D.sub.50) of 2 to 50 .mu.m and a thickness of 0.1 to 5 .mu.m.
Those whose mean particle size is within the range of 10 to 35
.mu.m are excellent in feel of glitter, hence are more
preferred.
[0061] Generally, the luster color pigment concentration (PWC) in
the above coating is preferably not more than 18.0%. When the upper
limit is exceeded, the coating appearance becomes poor. A more
preferred range is 0.01% to 15.0%, still more preferably 0.01% to
13.0%.
[0062] As the luster color pigment, there may be mentioned
colorless or colored metallic luster color pigments, such as
aluminum, copper, zinc, iron, nickel, tin, aluminum oxide and like
metals and alloys of these, and mixtures thereof. Further,
interfering mica pigments, white mica pigments, graphite pigments,
other colored or color flat pigments and so on may be used
combinedly.
[0063] The total pigment concentration (PWC), inclusive of the
above luster color pigment and other all pigments, in the coating
is preferably 0.1% to 50%, more preferably 0.5% to 40%, still more
preferably 1.0% to 30%. When the upper limit is exceed, the coating
film appearance may deteriorate.
[0064] The total solid content in the above water-borne metallic
base coating is preferably 15 to 50% by weight, more preferably 18
to 45%. When it is above the upper limit or below the lower limit,
the coating stability decreases. When it is in excess of the upper
limit, the viscosity is too high, and the coating film appearance
may deteriorate. When it is below the lower limit, the viscosity is
too low and defects in appearance such as bleeding and mottle may
readily appear.
[0065] For securing the workability in application, a viscosity
modifier is preferably added to the above metallic base coating.
The viscosity modifier is used to form good coating films without
mottle or sagging and may be a substance generally showing
thixotropy. As such substance, use may be made, for example, of
those mentioned above in the description of the water-borne
intermediate coating.
[0066] The above water-borne metallic base coating may containing a
phosphate ester containing a long-chain alkyl group having 8 to 18
carbon atoms and having an HLB value of 3 to 12 as a corrosion
inhibitor for the metallic luster color pigment, when used, or for
improving the wettability with the coating film and improving the
adhesion thereto. When the number of carbon atoms is less than 8,
the wettability with the coating film may deteriorate and, when it
is in excess of 18, the compound may crystallize in the coating,
causing troubles. A more preferred number of carbon atoms is 10 to
14 and, in that case, the wettability becomes still better and the
adhesion is improved. The above compound preferably has an HLB
value of 4 to8. The HLB value can be calculated using Griffin's
equation based on the weight fraction: HLB=20.times.(MH/M) [wherein
MH means the molecular weight of the hydrophilic group moiety and M
means the molecular weight of the active agent]. As the molecular
weight of the hydrophilic group moiety, the molecular weights of
phosphate esters, sulfonic acids and carboxylic acids were used.
Outside the above range, a decrease in wettability unfavorably
results.
[0067] As preferred compounds, there may be mentioned 2-ethylhexyl
acid phosphate, mono- or di-diisodecyl acid phosphate, mono- or
di-tridecyl acid phosphate, mono- or di-lauryl acid phosphate,
mono- or di-nonylphenyl acid phosphate and the like.
[0068] The addition amount of the above component is preferably 0.1
to 5% by weight, more preferably 0.2 to 2% by weight, relative to
the total amount of resin solids. When it is less than the lower
limit, the adhesion decreases. When it is in excess of the upper
limit, the water resistance decreases to the contrary.
[0069] In the water-borne metallic base coating to be used
according to the invention, there may be incorporated, in addition
to the above ingredients, one or more of additives added to
coatings in general, for example surface modifiers, viscosity
modifiers, antioxidants, ultraviolet absorbers, antifoaming agents
and so on. The addition amount of these are publicly known in the
art.
[0070] Clear Coating Film
[0071] The clear coating for forming the clear coating film is not
particularly restricted but may be a clear coating containing a
film forming resin and a curing agent, among others. The form of
the clear coating which can adequately be used includes the
solvent-borne type, water-borne type and powder type.
[0072] As preferred examples of the solvent-borne clear coating,
there may be mentioned, from the viewpoint of transparency or
resistance to acid etching, for instance, combinations of an
acrylic resin and/or polyester resin and an amino resin and/or
isocyanate, and an acrylic resin and/or polyester resin having a
carboxylic acid-epoxy curing system.
[0073] As examples of the water-borne clear coating, there may be
mentioned those containing a resin obtained from a film forming
resins, which is included among the ones mentioned above as
examples of the solvent-borne clear coating, by neutralization with
a base for rendering it aqueous. This neutralization may be
conducted, before or after polymerization, by adding a tertiary
amine such as dimethylethanolamine or triethylamine.
[0074] On the other hand, the power type clear coating can be
obtained by using an ordinary powder coating such as a
thermoplastic or thermosetting powder coating. For obtaining
coating films with good physical properties, a thermosetting powder
coating is preferred. As typical examples of the thermosetting
powder coating, there may be mentioned epoxy, acrylic and
polyester-based powder clear coatings. Acrylic powder clear
coatings are much more preferred because of their good weathering
resistance.
[0075] In the above clear coating, there may be incorporated a
viscosity modifier for securing the workability in application, as
in the case of the above intermediate coating. The clear coating
may further contain a curing catalyst or surface modifier, among
others, if necessary.
[0076] The thickness of the clear coating film may vary according
to the intended use but, in many cases, a thickness of 10 to 80
.mu.m is useful. When it is in excess of the upper limit, the image
sharpness may deteriorate or such a trouble as mottle, pinhole
formation or running may arise. When it is below the lower limit,
the substrate cannot be hidden, and the coating film appearance may
deteriorate.
[0077] Substrate
[0078] The coating film forming method of the invention can
advantageously be applied to various substrates such as metals,
plastics and foamed bodies.
[0079] As the metal products, there may be mentioned, among others,
iron, copper, aluminum, tin, zinc and the like and alloys
containing these metals. Specifically, mention may be made of
bodies and parts of automobiles such as passenger cars, trucks,
motorcycles and buses. In the case of these metal substrates, it is
particularly preferred that they be preliminarily subjected to
chemical conversion treatment with a phosphate salt, a chromate
salt or the like. Further, it is possible to form an
electrodeposited coating film on steel panels after chemical
conversion treatment using a cationic or anionic electrodeposition
coating. A cationic electrodeposition coating is preferred,
however, since it gives multilayer coating film excellent in
corrosion resistance.
[0080] As the above plastics products, there may be mentioned
polypropylene resins, polycarbonate resins, urethane resins,
polyester resins, polystyrene resins, ABS resins, vinyl chloride
resins, polyamide resins and the like. Specifically, mention may be
made of automotive parts such as spoilers, bumpers, mirror covers,
grilles and doorknobs, and the like. Further, these plastic
products are preferably ones washed by vapor cleaning with
trichloroethane or by using a neutral detergent. They may further
be coated with a primer for enabling electrostatic coating.
[0081] Method of Forming Coating Films
[0082] According to the coating film forming method of the
invention, an intermediate coating film is formed on the substrate
using a water-borne intermediate coating, then a metallic base
coating film is formed using a water-borne metallic base coating
and a clear coating film is formed using a clear coating in that
order. It is preferred that both the water-borne intermediate
coating and water-borne metallic base coating contain a
polycarbodiimide compound and a carboxyl-containing aqueous
resin.
[0083] In cases where the water-borne intermediate coating is
applied to automotive bodies according to the coating film forming
method of the invention, techniques comprising multistage,
preferably two-stage, application by air-electrostatic spray
coating, or techniques using a combination of air-electrostatic
spray coating and a rotatry spraying type electrostatic coating
machine popularly called ".mu..mu. (micromicro) bell", ".mu.
(micro) bell" or "metabell", for instance, may be mentioned as
coating film forming techniques a for attaining high quality
appearance.
[0084] In the coating film forming method of the invention, the
thickness of the coating film in the step of application of the
water-borne intermediate coating varies according to the intended
use. In many cases, however, a thickness of 10 to 60 .mu.m is
useful. When it is above the upper limit, the image sharpness may
deteriorate or a trouble such as mottle or running may occur at the
time of application. When it is below the lower limit, the
substrate cannot be masked, and the coating film appearance may
deteriorate.
[0085] According to the coating film forming method of the
invention, a water-borne metallic base coating is further applied
to the intermediate coating film to form a metallic base coating
film thereon.
[0086] The formation of a metallic base coating film according to
the invention is carried out by applying the water-borne metallic
base coating by air-electrostatic spray coating or using a rotary
spraying type electrostatic coating machine such as a .mu..mu. bell
or .mu. bell, in the same manner as in the intermediate coating.
The dry coating film thickness can be selected within the range of
10 to 30 .mu.m.
[0087] Further, in the coating film forming method of the
invention, a clear coating film applied after the formation of said
metallic base coating film is formed for the purpose of smoothing
the unevenness or glittering due to the luster color pigment
contained in the metallic base coating film and protecting the
film. As the specific technique of application, the one comprising
forming coating films using a rotary spraying type electrostatic
coating machine such as mentioned above, for example a .mu..mu.
bell or .mu. bell is preferred.
[0088] The dry film thickness of the clear coating film formed by
said clear coating is in general preferably about 10 to 80 .mu.m,
more preferably about 20 to 60 .mu.m. When it is in excess of the
upper limit, such a trouble as foaming or sagging may occur. When
it is below the lower limit, the unevenness of the substrate cannot
be masked.
[0089] The coating films obtained in the above manner may be cured
following the formation of each coating film layer. It is
preferred, however, that the consecutive two layers be formed in
the so-called wet-on-wet manner. Furthermore, it is particularly
preferred that the coating film formation is carried out by the
so-called three-coat one-bake technique comprising forming the
clear coating film without curing the intermediate coating film and
metallic base coating film and curing the thus-multilayer coating
films simultaneously. In this case, the stoves can partly be
omitted, which is favorable from the economy and environmental
viewpoint as well. For obtaining well finished coating films, it is
desirable that the above intermediate coating film and metallic
base coating film be preheated at 40 to 100.degree. C. for 2 to 10
minutes after formation of each coating film.
[0090] By selecting the curing, temperature for curing coating
films after application of the above clear coating within the range
of 80 to 180.degree. C., preferably 120 to 160.degree. C., it is
possible to obtained cured coating films with a high crosslink
density. When the curing temperature is higher than the upper
limit, the coating films become hard and brittle. When it is lower
than the lower limit, the degree of curing is insufficient. While
the curing time varies depending on the curing temperature, a
curing time of 10 to 30 minutes is adequate when the curing
temperature is 120.degree. C. to 160.degree. C.
[0091] The thickness of the multilayer coating film formed
according to the invention is, in many instances, 30 to 300 .mu.m,
preferably 50 to 250 .mu.m. When it is in excess of the upper
limit, the physical properties of the film, such as those found in
a thermal shock cycle test, deteriorate. When it is below the lower
limit, the strength of the film itself decreases.
[0092] By the method of the invention, it is now possible to
provide, on a commercial scale, multilayer coating films having a
high quality appearance while controlling interfacial bleeding or
inversion between coating film layers otherwise found when a
water-borne intermediate coating film and a water-borne metallic
coating film are formed in that order. This is probably due to the
use of those polycarbodiimide compound and carboxyl-containing
aqueous resin in the water-borne intermediate coating and/or
water-borne metallic base coating which readily react upon heating
at low temperatures, for example under preheating conditions,
leading to an increased coating film surface hardness and
facilitating the interfacial control with the coating film formed
thereon.
BEST MODES FOR CURRYING OUT THE INVENTION
[0093] The following examples illustrate the present invention in
detail. They are, however, by no means limitative of the scope of
the invention. In the following, "part(s)" means "part(s) by
weight".
[0094] Production Example
[0095] Production of a modified carbodiimide compound
[0096] 4,4-Dicyclohexylmethanediisocyanate (700 parts) and 14 parts
of a carbodiimidating catalyst (3-methyl-1-phenyl-2-phospholene
1-oxide) were heated at 180.degree. C. for 16 hours, to give
isocyanato-terminated 4,4-dicyclohexylmethanecarbodiimide
(carbodiimide group content: 4 equivalents). Then, 226.8 parts of
the carbodiimide obtained was dissolved in 106.7 parts of
N-methylpyrrolidone with heating at 90.degree. C. Then, 200 parts
of polypropylene glycol (number average molecular weight: 2,000)
was added and the mixture was stirred at 40.degree. C. for 10
minutes, 0.16 part of dibutyltin dilaurate was added, the 3
temperature was again raised to 90.degree. C. and the reaction was
allowed to proceed at that temperature for 3 hours. Further, 96.4
parts of poly (oxyethylene) mono-2-ethylhexyl ether having 8
oxyethylene units was added, the reaction was allowed to proceed at
100.degree. C. for 5 hours, and 678.1 parts of deionized water was
added at 50.degree. C. to give an aqueous dispersion of a
carbodiimide compound modified for hydrophilicity with a resin
solid content of 40% by weight.
[0097] Production of an Aqueous Dispersion of a Carboxyl-containing
Acrylic Resin
[0098] A reaction vessel was charged with 126.5 parts of deionized
water and the temperature was raised to 80.degree. C. with stirring
in a nitrogen atmosphere. Then, a monomer emulsion composed of
45.21 parts of methyl acrylate, 27.37 parts of ethyl acrylate, 7.42
parts of 2-hydroxyethyl methacrylate, 0.5 part of Aqualon HS-10
(polyoxyethylene alkylpropenylphenyl ether sulfate ester, product
of Daiichi Kogyo Seiyaku), 0.5 part of Adeka Reasoap NE-20
(.alpha.-[1-[(allyloxy)methyl]--
2-(nonylphenoxy)ethyl]-.omega.-hydroxyoxyethylene, product of Asahi
Denka, 80% aqueous solution) and 80 parts of deionized water, as
the first stage monomer mixture, and an initiator solution composed
of 0.24 part of ammonium persulfate and 10 parts of deionized water
were added dropwise in parallel into the reaction vessel over 2
hours. After completion of the dropping, the mixture was matured at
the same temperature for 1 hour.
[0099] Further, a monomer emulsion composed of 15.07 parts of ethyl
acrylate, 1.86 parts of 2-hydroxyethyl methacrylate, 3.07 parts of
methacrylic acid, 0.2 part of Aqualon HS-10 and 10 parts of
deionized water, as the second stage monomer mixture, and an
initiator solution composed of 0.06 part of ammonium persulfate and
10 parts of deionized water were added dropwise in parallel into
the reaction vessel over 0.5 hour. After completion of the
dropping, the mixture was matured at the same temperature for 2
hours.
[0100] Then, the mixture was cooled to 40.degree. C. and passed
through a 400 mesh filter and adjusted to pH 7.0 by adding 167.1
parts of deionized water and 0.32 part of dimethylaminoethanol, to
give an aqueous dispersion of a carboxyl-containing acrylic resin
with a mean particle size of 150 nm, a nonvolatile matter content
of 20%, a solid matter acid value of 20 mg KOH/g and a hydroxyl
value of 40 mg KOH/g.
[0101] Production of a Carboxyl-containing Acrylic Resin
[0102] A one-liter reaction vessel equipped with a nitrogen inlet
tube, stirrer, temperature controller, dropping funnel and
condenser was charged with 76 parts of ethylene glycol monobutyl
ether. A monomer solution was separately prepared by mixing up 15
parts of styrene, 63 parts of methyl methacrylate, 48 parts of
2-hydroxyethyl methacrylate, 117 parts of n-butyl acrylate, 27
parts of methacrylic acid, 30 parts of acrylamide and 3 parts of
azobisisobutyronitrile. A 61-part portion of this monomer solution
was added to the reaction vessel and the temperature was raised to
120.degree. C. with stirring. Then, 242 parts of the monomer
solution was added over 3 hours and thereafter stirring was
continued for 1 hour, to give a carboxyl-containing acrylic resin
with a number average molecular weight of 12,000, a hydroxyl value
of 70 mg KOH/g and an acid value of 58 mg KOH/g. Then, 28 parts of
diethanolamine and 200 parts of deionized water were added to give
a transparent and viscous carboxyl-containing acrylic resin varnish
with a nonvolatile matter content of 50%.
[0103] Production of a Maleic Anhydride-modified Chlorinated
Polypropylene Emulsion
[0104] A one-liter reaction vessel equipped with a nitrogen E inlet
tube, stirrer, temperature controller, dropping funnel and
condenser was charged with 233 parts of Hardlen M128P (maleic
anhydride-modified chlorinated polypropylene, chlorine content:
21%, weight average molecular weight: 40,000, product of Toyo Kasei
Kogyo), 59 parts of Emulgen 920 (nonylphenyl polyoxyethylene ether,
product of Kao Corp.), 62 parts of Solvesso 100 (aromatic
hydrocarbon solvent, product of Exxon) and 27 parts of carbitol
acetate, and after 1 hour of heating at 110.degree. C. for
effecting dissolution, the mixture was cooled to 100.degree. C. and
a solution of 5 parts of dimethylaminoethanol in 619 parts of
deionized water was added dropwise over 1 hour for effecting
emulsification by phase inversion. After cooling, the emulsion was
filtered through a 400 mesh net, to give a maleic
anhydride-modified chlorinated polypropylene emulsion resin with a
nonvolatile matter content of 30.5% by weight and a mean particle
size of 0.1 .mu.m as determined by the laser beam scattering
method.
[0105] Production of a Carboxyl-containing Aqueous Alkyd Resin
[0106] A reaction vessel equipped with a stirrer, nitrogen inlet
tube, temperature controlling device, condenser and fractionating
column was charged with 155 parts of coconut oil, 248 parts of
trimethylolpropane and 1.7 parts of dibutyltin oxide, and heating
was started under dry nitrogen and, after dissolution of the raw
materials, the temperature was raised gradually to 210.degree. C.
for effecting transesterification, followed by cooling. Then, 267
parts of isophthalic acid, 59 parts of adipic acid, 33 parts of
neopentyl glycol and 41 parts of Epol (hydrogenated polyisoprene
diol, molecular weight 1,860, product of Idemitsu Petrochemical)
were added and the temperature was gradually raised to 220.degree.
C. for effecting dehydration esterification. After allowing the
dehydration esterification reaction to proceed until a resin acid
value of 10 mg KOH/g, the reaction mixture was cooled to
150.degree. C., 40 parts of trimellitic anhydride was added and the
reaction was allowed to proceed until a resin acid value of 40 mg
KOH/g, the reaction mixture was cooled to 140.degree. C., 77 parts
of .epsilon.-caprolactone was further added and the reaction was
allowed to proceed for 1 hour. The reaction procedure was thus
finished. To the alkyd resin were added 75 parts of Solvesso 150
(aromatic hydrocarbon solvent, product of Esso Chemical) and 75
parts of butyl cellosolve, to give an alkyd resin with a solid
content of 83% by weight, a solid matter acid value of 37 mg KOH/g
and a number average molecular weight of 2,850.
[0107] To 100 parts of this alkyd resin were added 0.41 part of
calcium hydroxide and 4.42 parts of triethylamine and, after
mixing, 191.6 parts of deionized water was added, to give a
carboxyl-containing aqueous alkyd resin varnish with a solid
content of 28% by weight.
[0108] Production of a Solvent-borne Clear Coating E-1
[0109] (1) Production of a Varnish
[0110] A reaction vessel equipped with a nitrogen inlet tube,
stirrer, temperature controller, dropping funnel and condenser was
charged with 70 parts of xylene and 20 parts of n-butanol. A
monomer solution was separately prepared by mixing up 1.2 parts of
methacrylic acid, 26.4 parts of styrene, 26.4 parts of methyl
methacrylate, 10.0 parts of 2-hydroxyethyl methacrylate, 36.0 parts
of n-butyl acrylate and 1.0 part of azobisisobutyronitrile. A
20-part portion of this monomer solution was added to the reaction
vessel and the temperature was raised with stirring. The remaining
81 parts of the monomer solution was added dropwise over 2 hours
under reflux and then an initiator solution composed of 0.3 part of
azobisisobutyronitrile and 10 parts of xylene was added dropwise
over 30 minutes. The reaction mixture was further refluxed for 2
hours with stirring. The reaction procedure was thus finished to
give an acrylic resin varnish with a nonvolatile matter content of
50%, a number average resin molecular weight of 8,000, an acid
value of 8 mg KOH/g and a hydroxyl value of 48 mg KOH/g.
[0111] (2) Production of a Polyester Resin
[0112] A two-liter reaction vessel equipped with a nitrogen inlet
tube, stirrer, temperature controller, condenser and A decanter was
charged with 134 parts of bishydroxyethyltaurine, 130 parts of
neopentyl glycol, 236 parts of azelaic acid, 186 parts of phthalic
anhydride and 27 parts of xylene and the temperature was raised.
The water formed by the reaction was removed by azeotropic
distillation with xylene. The temperature was raised to 190.degree.
C. over about 2 hours from the start of refluxing and the stirring
and dehydration were continued until attainment of a carboxylic
acid equivalent acid value of 145 and then the mixture was cooled
to 140.degree. C. While the temperature of 140.degree. C. was
maintained, 314 parts of Cardura E10 (glycidyl versatate, product
of Shell) was added dropwise over 30 minutes and, thereafter, the
reaction was continued for 2 hours with stirring and the reaction
was then finished. The polyester resin obtained had a number
average molecular weight of 1,054, an acid value of 59 mg KOH/g and
a hydroxyl value of 90 mg KOH/g.
[0113] (3) Production of Resin Particles
[0114] A one-liter reaction vessel equipped with a nitrogen inlet
tube, stirrer condenser and temperature controller was charged with
282 parts of deionized water, 10 parts of the polyester produced as
mentioned above under (2) and 0.75 part of diethanolamine, and
dissolution was effected with stirring while maintaining the
temperature at 80.degree. C. Thereto was added an initiator
solution prepared by dissolving 45 parts of azobiscyanovaleric acid
in 45 parts of deionized water plus 4.3 parts of
dimethylethanolamine. Then, a monomer solution composed of 70.7
parts of styrene, 70.7 parts of methyl methacrylate, 94.2 parts of
n-butyl acrylate, 30 parts of 2-hydroxyethyl acrylate and 4.5 parts
of ethylene glycol dimethacrylate was added dropwise to the
reaction vessel over 1 hour. After dropping, an initiator solution
prepared by dissolving 1.5 parts of azobiscyanovaleric acid in 15
parts of deionized water plus 1.4 parts of dimethylethanolamine was
added, and the mixture was stirred at 80.degree. C. for 1 hour. As
a result, an emulsion was obtained which had a nonvolatile matter
content of 45%, a pH of 7.2, a viscosity of 92 cps (25.degree. C.)
and a particle size of 0.156 .mu.m. This emulsion was spray-dried
for removing the water and 200 parts of xylene was added to 100
parts of the resin particles obtained for effecting redispersion,
whereby a xylene dispersion of the resin particles was prepared.
The particle size was 0.3 .mu.m.
[0115] (4) Production of Solvent-borne Clear Coating E-1
[0116] In a stainless steel vessel, there were placed 100 parts l
of the varnish produced as mentioned above under (1), 38 parts of
U-Van 20SE-60 (butylated melamine resin, product of Mitsui Toatsu),
0.5 part of Modaflow (surface modifier, product of Monsanto) and
2.2 parts of the resin particles produced as mentioned above under
(3). The mixture was stirred using an experimental stirrer to give
a solvent-borne clear coating E-1.
[0117] Production of Solvent-borne Clear Coating E-2
[0118] In a stainless steel vessel, there were placed 100 parts of
the varnish produced as mentioned above in the production of
solvent-borne clear coating E-1 (1), 8.3 parts of Sumidur 3500
(isocyanurate resin, product of Sumitomo Bayer), 0.5 part of
Modaflow (surface modifier, product of Monsanto) and 2.2 parts of
the resin particles produced as mentioned above under (3). The
mixture was stirred using an experimental stirrer to give a
solvent-borne clear coating E-2.
[0119] Water-borne Intermediate Coating A-1
[0120] A 1,000-mL stainless steel vessel was charged with 76 parts
of the carboxyl-containing acrylic resin varnish obtained in the
above production example, 190 parts of Titan R-820 (white pigment,
product of Ishihara Sangyo), 0.5 part of Mitsubishi Carbon MA-100
(black pigment, product of Mitsubishi Chemical) and 76 parts of
deionized water, and dispersion was effected by stirring the
mixture at room temperature for 45 minutes using a coating
conditioner, to give a gray pigment paste.
[0121] To this were added 95 parts of the above carboxyl-containing
acrylic resin varnish, 285 parts of the previous aqueous dispersion
of the carboxyl-containing acrylic resin and 177.7 parts of the
modified carbodiimide compound. The mixture was further stirred for
30 minutes using a labo mixer to give a gray water-borne
intermediate coating A-1.
[0122] Water-borne Intermediate Coating A-2
[0123] (1) Production of a Pigment Dispersion Paste in an Aqueous
Alkyd Resin
[0124] A vessel equipped with a stirrer was charged, with stirring,
with 360 parts of the carboxyl-containing aqueous alkyd resin of
the previous production example, 45 parts of Surfynol CT324
(acetylene type pigment wetting agent, product of Air Products), 7
parts of Foamaster S (silicone antifoaming agent, product of
Henkel), 249 parts of deionized water, 25 parts of Ketjen Black
EC60OJD (conductive carbon pigment, product of Lion Corp.) and 314
parts of Ti-Pure R960 (titanium oxide pigment, product of du Pont),
in that order. After 1 hour of stirring, dispersion was effected on
a 1.4-liter Dyno mill for laboratory use until a size of 20 .mu.m.
The gray aqueous alkyd resin pigment dispersion paste had a
nonvolatile matter content of 54% by weight.
[0125] (2) Production of a Coating
[0126] The previous maleic anhydride-modified chlorinated
polypropylene emulsion resin (243 parts), 320 parts of the previous
aqueous alkyd resin pigment paste dispersion, 63 parts of the
previous modified carbodiimide compound, 3 parts of Polyflow KL245
(silicone surface modifier, product of Kyoei Kagaku), 349 parts of
deionized water, 2 parts of dimethylaminoethanol and 20 parts of
Primal ASE60 (alkali swelling thickening agent, product of Rohm
& Haas) were charged in that order with stirring and the
mixture was stirred for 1 hour to give a water-borne intermediate
coating A-2.
[0127] Water-borne Intermediate Coating B-1
[0128] A water-borne intermediate coating B-1 was prepared in the
same manner as above except that a melamine resin "Cymel 303"
(methoxylated methylolmelamine, product of Mitsui Cytec) was used
in lieu of the modified carbodiimide compound used in the
production of water-borne intermediate coating A-1.
[0129] Water-borne Metallic Base Coating C-1
[0130] Alpaste7160N (15 parts; aluminum pigment paste, aluminum
content 65%, product of Toyo Aluminum) and 2 parts of lauryl acid
phosphate were homogeneously dispersed in 119 parts of the
carboxyl-containing acrylic resin varnish obtained in the previous
production example and 40 parts of the modified carbodiimide
compound and, then, 100 parts of deionized water was added with
stirring, 356 parts of aqueous dispersion of the previous
carboxyl-containing acrylic resin was further added and homogeneous
dispersion was effected, to give a water-borne metallic base
coating C-1.
[0131] Water-borne Metallic Base Coating D-1
[0132] To 112 parts of the carboxyl-containing acrylic resin
varnish obtained in the previous coating film forming resin
production 1 were added 15 parts of Alpaste 7160N (aluminum pigment
paste, aluminum content 65%, product of Toyo Aluminium) and 30
parts of Cymel 303 (methoxylated methylolmelamine, product of
Mitsui Cytec), and uniform mixing was effected. Further, 2 parts of
lauryl acid phosphate was added and, after homogeneous dispersion
was realized, 47 parts of the aqueous dispersion of the previous
carboxyl-containing acrylic resin particle was added and
homogeneous dispersion was further effected to give a water-borne
metallic base coating D-1.
EXAMPLE 1
[0133] A cationic electrodeposition coating "Power-Top U-50,
product of Nippon Paint) was electrodeposited, to a dry film
thickness of 20 .mu.m, on zinc phosphate-treated dull steel panels
(thickness: 0.8 mm, length: 30 cm, width: 40 cm) and baked at
160.degree. C. for 30 minutes. To the thus-prepared substrates was
applied a dilution of the water-borne intermediate coating A-1 of
the previous production example (diluted with deionized water to a
viscosity of 40 seconds (No. 4 Ford cup, 20.degree. C.)) to a dry
film thickness of 35 .mu.m in two stages by an air sprayer. Between
the two applications, there was a one-minute interval for setting.
The second application was followed by a 5-minute interval for
setting. Thereafter, preheating was carried out at 80.degree. C.
for 5 minutes.
[0134] Then, a dilution of the water-borne metallic coating C-1 of
the previous production example (diluted with deionized water to a
viscosity of 30 seconds (No. 4 Ford cup, 20.degree. C.) ) was
applied to a dry film thickness of 20 .mu.m in two stages by air
spraying. Between the two applications, there was a one-minute
interval for setting. The second application was followed by a
5-minute interval for setting. Thereafter, preheating was carried
out at 80.degree. C. for 5 minutes.
[0135] After preheating, the coated sheets were allowed to cool to
room temperature, and the solvent-borne clear coating E-1 of the
previous production example was applied in one stage to a dry film
thickness of 40 .mu.m, followed by 7 minutes of setting. The coated
sheets were then baked in a drier at 140.degree. C. for 30
minutes.
[0136] The coated sheets obtained were measured and evaluated for
appearance using a portable sharpness/gloss meter PGD-IV (surface
shape measuring apparatus, product of Tokyo Koden)
[0137] Separately, the coated sheets obtained were immersed in warm
water at 40.degree. C. for 10 days, then washed and allowed to
stand for 1 hour, and the coating films were evaluated for their
state by the eye.
[0138] Evaluation Criteria
[0139] .circleincircle.: No abnormality
[0140] .smallcircle.: Slight matting
[0141] .DELTA.: Matting and blistering
[0142] .times.: Matting and blistering in a very large number of
places.
[0143] The results obtained in the above evaluations are shown in
Table 1.
EXAMPLE 2
[0144] A dilution of the water-borne intermediate coating A-2 of
the previous production example (diluted with deionized water to a
viscosity of 40 seconds (No. 4 Ford cup, 20.degree. C.)) to
polypropylene substrates (size: 70 mm.times.260 mm.times.3 mm)
degreased with a neutral detergent to a dry film thickness of 10
.mu.m by air spraying. After a 5-minute interval following
application, preheating was carried out at 80.degree. C. for 10
minutes.
[0145] After cooling, a dilution of the water-borne metallic
coating C-1 of the previous production example (diluted with
deionized water to a viscosity of 30 seconds (No. 4 Ford cup,
20.degree. C.)) was applied to a dry film thickness of 15 .mu.m in
two stages by air spraying. Between the two applications, there was
a one-minute interval for setting. The second application was
followed by a 5-minute interval for setting. Thereafter, preheating
was carried out at 80.degree. C. for 5 minutes.
[0146] After preheating, the coated sheets were allowed to cool to
room temperature, and the solvent-borne clear coating E-2 of the
previous production example was applied in one stage to a dry film
thickness of 30 .mu.m, followed by 7 minutes of setting. The coated
sheets were then baked in a drier at 80.degree. C. for 30 minutes.
The coated sheets obtained were evaluated in the same manner as in
Example 1.
EXAMPLES 3 and 4
[0147] According to each combination of water-borne intermediate
coating, water-borne metallic base coating and clear coating shown
in Table 1, multilayer coating films were produced in the same
manner as in Example 1, and the coated sheets were evaluated in the
same manner.
[0148] COMPARATIVE EXAMPLE 1
[0149] Using the combination of water-borne intermediate coating of
melamine curing type, water-borne metallic base coating and clear
coating as shown in Table 1, multilayer coating films were
produced, and the coated sheets obtained were evaluated.
[0150] The evaluation results obtained in the above examples and
comparative example are shown in Table 1.
1 TABLE 1 Compar. Example Ex. 1 2 3 4 1 Water-borne Carbodiimide
A-1 A-2 A-1 intermediate curing system coating Melamine curing B-1
B-1 system Water-borne Carbodiimide C-1 C-1 C-1 metallic base
curing system coating Melamine curing D-1 D-1 system Clear coating
E-1 E-2 E-1 E-1 E-1 Evaluation Water .circleincircle.
.circleincircle. .circleincircle. .circleincircle. .DELTA. results
resistance Appearance 1.0 1.0 1.0 1.0 0.7
[0151] As shown in the examples of this invention, the coating
films formed by the water-borne intermediate coating of the
carbodiimide curing type and the water-borne metallic base coating,
when each coating film formation was followed by 5 minutes of
preheating at 80.degree. C., could provide a good appearance,
without migration or bleeding possibly caused by the solvent
component or the like contained in the coating subsequently
applied. The coating films showed good water resistance.
* * * * *