U.S. patent application number 11/042067 was filed with the patent office on 2005-07-28 for process for forming multi layered coated film and multi layered coated film.
Invention is credited to Mihara, Yasuo, Toi, Teruzo.
Application Number | 20050161330 11/042067 |
Document ID | / |
Family ID | 34797795 |
Filed Date | 2005-07-28 |
United States Patent
Application |
20050161330 |
Kind Code |
A1 |
Toi, Teruzo ; et
al. |
July 28, 2005 |
Process for forming multi layered coated film and multi layered
coated film
Abstract
The present invention provides a process for forming a multi
layered coated film having good finished appearance. The present
invention relates to a process for forming a multi layered coated
film comprising the steps of conducting electrodeposition coating
with a cationic electrodeposition coating composition on a
substrate, and then heating and curing it to form an cured
electrodeposition coated film on the substrate, applying an
intermediate coating composition on the cured coated film to form
an uncured intermediate coated film, applying a base top coating
composition on the uncured intermediate coated film to form an
uncured base coated film, applying a clear top coating composition
on the uncured base coated film to form an uncured clear coated
film, and simultaneously heating and curing the three uncured
coated films, wherein the cured electrodeposition coated film has
specified ranges of Ra and Pa; or has specified ranges of Tg and
crosslinking density.
Inventors: |
Toi, Teruzo; (Osaka-shi,
JP) ; Mihara, Yasuo; (Souraku-gun, JP) |
Correspondence
Address: |
WENDEROTH, LIND & PONACK, L.L.P.
2033 K STREET N. W.
SUITE 800
WASHINGTON
DC
20006-1021
US
|
Family ID: |
34797795 |
Appl. No.: |
11/042067 |
Filed: |
January 26, 2005 |
Current U.S.
Class: |
204/484 ;
204/487 |
Current CPC
Class: |
B05D 7/572 20130101;
C09D 5/4488 20130101; C23C 26/00 20130101; C23C 28/00 20130101;
B05D 7/577 20130101 |
Class at
Publication: |
204/484 ;
204/487 |
International
Class: |
C23C 028/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 26, 2004 |
JP |
2004-17107 |
Jan 26, 2004 |
JP |
2004-17109 |
Claims
1. A process for forming a multi layered coated film comprising the
steps of: conducting electrodeposition coating with a cationic
electrodeposition coating composition on a substrate, and then
heating and curing it to form an cured electrodeposition coated
film on the substrate, applying an intermediate coating composition
on the cured electrodeposition coated film to form an uncured
intermediate coated film, applying a base top coating composition
on the uncured intermediate coated film to form an uncured base
coated film applying a clear top coating composition on the uncured
base coated film to form an uncured clear coated film, and
simultaneously heating and curing the uncured intermediate coated
film, the uncured base top coated film and the uncured clear coated
film; wherein the cured electrodeposition coated film has a
centerline average roughness (Ra) of 0.05 to 0.25 .mu.m obtained
from a roughness curve and a centerline average roughness (Pa) of
0.05 to 0.30 .mu.m obtained from a profile curve.
2. A process for forming a multi layered coated film comprising the
steps of: conducting electrodeposition coating with a cationic
electrodeposition coating composition on a substrate, and then
heating and curing it to form an cured electrodeposition coated
film on the substrate, applying an intermediate coating composition
on the cured electrodeposition coated film to form an uncured
intermediate coated film, applying a base top coating composition
on the uncured intermediate coated film to form an uncured base
coated film applying a clear top coating composition on the uncured
base coated film to form an uncured clear coated film, and
simultaneously heating and curing the uncured intermediate coated
film, the uncured base top coated film and the uncured clear coated
film; wherein the cured electrodeposition coated film has a surface
energy of 37 to 43 mJ/m.sup.2, and the intermediate coating
composition has a contact angle of 10 to 30 degrees on the cured
electrodeposition coated film.
3. A process for forming a multi layered coated film comprising the
steps of: conducting electrodeposition coating with a cationic
electrodeposition coating composition on a substrate, and then
heating and curing it to form an cured electrodeposition coated
film on the substrate, applying an intermediate coating composition
on the cured electrodeposition coated film to form an uncured
intermediate coated film, applying a base top coating composition
on the uncured intermediate coated film to form an uncured base
coated film applying a clear top coating composition on the uncured
base coated film to form an uncured clear coated film, and
simultaneously heating and curing the uncured intermediate coated
film, the uncured base top coated film and the uncured clear coated
film; wherein the cured electrodeposition coated film has a
centerline average roughness (Ra) of 0.05 to 0.25 .mu.m obtained
from a roughness curve, a centerline average roughness (Pa) of 0.05
to 0.30 .mu.m obtained from a profile curve and a surface energy of
37 to 43 mJ/m.sup.2, and the intermediate coating composition has a
contact angle of 10 to 30 degrees on the cured electrodeposition
coated film.
4. A process for forming a multi layered coated film comprising the
steps of: conducting electrodeposition coating with a cationic
electrodeposition coating composition on a substrate, and then
heating and curing it to form an cured electrodeposition coated
film on the substrate, applying an intermediate coating composition
on the cured electrodeposition coated film to form an uncured
intermediate coated film, applying a base top coating composition
on the uncured intermediate coated film to form an uncured base
coated film applying a clear top coating composition on the uncured
base coated film to form an uncured clear coated film, and
simultaneously heating and curing the uncured intermediate coated
film, the uncured base top coated film and the uncured clear coated
film; wherein the cured electrodeposition coated film has a glass
transition temperature Tg of 100 to 130.degree. C. and a
crosslinking density of 1.2 to 2.6 mmol/cc, obtained by dynamic
viscoelastic measurement.
5. The process for forming a multi layered coated film according to
claim 1, wherein the intermediate coating composition comprises an
intermediate coating resin comprising at least one selected from
the group comprising of acrylic resin, polyester resin and
polyurethane resin an intermediate coating curing agent comprising
at least one selected from the group consisting of blocked
isocyanate compound, oxazoline compound, carbodiimide compound and
melamine compound, and a pigment.
6. The process for forming a multi layered coated film according to
claim 2, wherein the intermediate coating composition comprises an
intermediate coating resin comprising at least one selected from
the group comprising of acrylic resin, polyester resin and
polyurethane resin an intermediate coating curing agent comprising
at least one selected from the group consisting of blocked
isocyanate compound, oxazoline compound, carbodiimide compound and
melamine compound, and a pigment.
7. The process for forming a multi layered coated film according to
claim 3, wherein the intermediate coating composition comprises an
intermediate coating resin comprising at least one selected from
the group comprising of acrylic resin, polyester resin and
polyurethane resin an intermediate coating curing agent comprising
at least one selected from the group consisting of blocked
isocyanate compound, oxazoline compound, carbodiimide compound and
melamine compound, and a pigment.
8. The process for forming a multi layered coated film according to
claim 4, wherein the intermediate coating composition comprises an
intermediate coating resin comprising at least one selected from
the group comprising of acrylic resin, polyester resin and
polyurethane resin an intermediate coating curing agent comprising
at least one selected from the group consisting of blocked
isocyanate compound, oxazoline compound, carbodiimide compound and
melamine compound, and a pigment.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a process for forming a
multi layered coated film having good finished appearance.
BACKGROUND OF THE INVENTION
[0002] Multi layers of coated films having various functions are
formed on the surface of a substrate of automobile body to protect
the substrate and impart the substrate into good appearance.
However, in recent years, a process for forming a multi layered
coated film comprising the steps of: applying the next coated film
on an uncured coated film by so-called wet on wet coating; and
simultaneously baking the multi layers; without the step of baking
the uncured coated film after applying every layer has been used
because of a requirement of saving energy and reducing cost.
[0003] As an example of the process, a three coat one bake coating
process (three wet coating) comprising the steps of: applying an
intermediate coating, a base top coating and a clear top coating on
an cured electrodeposition coated film by wet on wet coating; and
simultaneously baking and curing the three layers of uncured coated
films; is considered to be the most practical process. A schematic
flow chart of the coating process is shown in FIG. 1.
[0004] In Japanese Patent Kokai Publication No. 277474/1998, a
process for forming a multi layered coated film comprising the
steps of: applying an intermediate coating, a metallic coating and
a clear top coating on a substrate to be coated in the order; and
simultaneously baking the three layers of the coated films; is
disclosed. It is described therein that the process provides the
coated film having excellent vividness and excellent
lustrousness.
[0005] In the three coat one bake coating process shown in FIG. 1,
it has been found that the surface condition of the cured
electrodeposition coated film has a great effect on an appearance
of the multi layered coated film. The reason is considered that the
three coat one bake coating process has smaller number of baking
step as described above. In the above process for forming a multi
layered coated film (Japanese Patent Kokai Publication No.
277474/1998), the surface condition of the electrodeposition coated
film for improving the appearance of the multi layered coated film
is not described.
[0006] In Japanese Patent Kokai Publication No. 224613/2002, a
process for forming a multi layered coated film comprising the
steps of: forming a cured electrodeposition coated film on a
substrate from a cationic electrodeposition coating composition;
applying three layers of coatings on the cured electrodeposition
coated film by a three coat one bake coating process; and
simultaneously baking and curing the three layers of uncured coated
films; wherein the cured electrodeposition coated film has a glass
transition temperature of not less than 110.degree. C. and a
surface roughness (Ra: centerline average roughness) of not more
than 0.3 .mu.m; is disclosed. In this process, only the centerline
average roughness (Ra) is used as a parameter for evaluating the
appearance of the coated film, but the other parameters are not
used.
[0007] Moreover, in the three coat one bake coating process shown
in FIG. 1, a composition for the intermediate coating are applied
on the cured electrodeposition coated film. There is a case that a
solvent contained in the composition for the intermediate coating
is absorbed in the cured electrodeposition coated film during
applying the composition. The solvent absorbed in the cured
electrodeposition coated film is volatilized during baking the
laminated coated film to affect the intermediate coated film and
the like, which degrades the finished appearance of the laminated
coated film. It has been found that the solvent contained in the
uncured intermediate coated film applied on the cured
electrodeposition coated film has a great effect on the cured
electrodeposition coated film, because the number of baking step is
small and the uncured coated films laminated to two or more layer
are simultaneously baked in the three coat one bake coating
process. In the above process for forming a multi layered coated
film (Japanese Patent Kokai Publication No. 277474/1998), physical
properties of the electrodeposition coated film are not described
for improving the appearance of the multi layered coated film.
OBJECTS OF THE INVENTION
[0008] A main object of the present invention is to provide a
process for forming a multi layered coated film having good
finished appearance in a three coat one bake coating process which
can save energy and reduce cost.
[0009] In the present invention, a process for obtaining a coated
film having good finished appearance has been found. In according
to the process of the present invention, a multi layered coated
film having good appearance can be obtained even in the three coat
one bake coating process having smaller number of baking step. The
multi layered coated film contains an electrodeposition coated
film, an intermediate coated film, a base top coated film and a
clear top coated film. In according to the process of the present
invention, energy required for baking and curing in the coating
step can be saved, and production cost can be reduced. The process
of the present invention can be suitably used in the art that
energy saving during the application and good appearance are
required.
[0010] This object as well as other objects and advantages of the
present invention will become apparent to those skilled in the art
from the following description with reference to the accompanying
drawing.
BRIEF EXPLANATION OF DRAWINGS
[0011] The present invention will become more fully understood from
the detailed description given hereinbelow and the accompanying
drawing which is given by way of illustration only, and thus are
not limitative of the present invention, and wherein:
[0012] FIG. 1 is a flow chart illustrating one embodiment of the
process of the present invention.
SUMMARY OF THE INVENTION
[0013] The present invention provides a process for forming a multi
layered coated film comprising the steps of:
[0014] conducting electrodeposition coating with a cationic
electrodeposition coating composition on a substrate, and then
heating and curing it to form an cured electrodeposition coated
film on the substrate, applying an intermediate coating composition
on the cured electrodeposition coated film to form an uncured
intermediate coated film,
[0015] applying a base top coating composition on the uncured
intermediate coated film to form an uncured base coated film
[0016] applying a clear top coating composition on the uncured base
coated film to form an uncured clear coated film, and
[0017] simultaneously heating and curing the uncured intermediate
coated film, the uncured base top coated film and the uncured clear
coated film; wherein
[0018] the cured electrodeposition coated film has a centerline
average roughness (Ra) of 0.05 to 0.25 .mu.m obtained from a
roughness curve and a centerline average roughness (Pa) of 0.05 to
0.30 .mu.m obtained from a profile curve, thereby accomplishing the
object described above.
[0019] The present invention also provides a process for forming a
multi layered coated film comprising the steps, wherein the cured
electrodeposition coated film has a surface energy of 37 to 43
mJ/m.sup.2, and the intermediate coating composition has a contact
angle of 10 to 30 degrees on the cured electrodeposition coated
film, thereby accomplishing the object described above.
[0020] The present invention also provides a process for forming a
multi layered coated film comprising the steps, wherein the cured
electrodeposition coated film has a centerline average roughness
(Ra) of 0.05 to 0.25 .mu.m obtained from a roughness curve, a
centerline average roughness (Pa) of 0.05 to 0.30 .mu.m obtained
from a profile curve and a surface energy of 37 to 43 mJ/m.sup.2,
and the intermediate coating composition has a contact angle of 10
to 30 degrees on the cured electrodeposition coated film, thereby
accomplishing the object described above.
[0021] The present invention also provides a process for forming a
multi layered coated film comprising the steps, wherein the cured
electrodeposition coated film has a glass transition temperature Tg
of 100 to 130.degree. C. and a crosslinking density of 1.2 to 2.6
mmol/cc, obtained by dynamic viscoelastic measurement, thereby
accomplishing the object described above.
[0022] The process to accomplish the present invention will be
explained in detail. The present inventors have suggested a method
of evaluating the cured electrodeposition coated film by the
surface roughness (Ra: centerline average roughness) in Japanese
Patent Kokai Publication No. 224613/2002.
[0023] It is difficult to evaluate the appearance of the coated
film by a single method, because surface morphology, optical
properties and color complexly visually affect the appearance. In
an evaluation of the appearance by wavelength as a method of
evaluating the appearance of the coated film, for example,
roughness related to gloss and vividness can be evaluated by short
wavelength and roughness related to winding can be evaluated by
long wavelength. In JIS related to the surface roughness, it is
described that a contour curve can be divided into a profile curve
(P), roughness curve (R) and winding curve (W).
[0024] The appearance of the coated film can be evaluated by
classifying it into items of smoothness, orange peel and luster. In
the present invention, it has been found for the Ra value
(centerline average roughness in the roughness curve) of the cured
electrodeposition coated film used in the conventional evaluating
method to have a correlation to the item of orange peel. It has
been found for the Wa value (centerline average roughness in the
winding curve) of the cured electrodeposition coated film as a
parameter related to the winding curve (W) to have a correlation to
the item of smoothness in the appearance of the multi layered
coated film. In addition, it has been found for the winding
measured by long wavelength to have great effect on the appearance
of the resulting multi layered coated film. Moreover; it has been
found to improve the finished appearance of the resulting multi
layered coated film by evaluating the cured electrodeposition
coated film using the Ra value and the Pa value (centerline average
roughness in the profile curve) containing both the Ra value and Wa
value as parameters to control the surface condition, thereby
accomplishing one embodiment of the present invention.
[0025] It is considered that the multi layered coated film having
good appearance is not occasionally obtained when the intermediate
coating composition has low wettability with the cured
electrodeposition coated film, even if controlling the surface
condition of the cured electrodeposition coated film as described
above during the formation of the multi layered coated film in the
three coat one bake coating process as described in the present
invention. Such defect has great effect on the appearance of the
resulting multi layered coated film, because the three coat one
bake coating process has smaller number of baking step.
[0026] In the present invention, it has been found that the
wettability of the intermediate coated film can be controlled by
adjusting the surface energy of the cured electrodeposition coated
film to a specified range, and the finished appearance of the
resulting multi layered coated film can be improved, thereby
accomplishing another embodiment of the present invention.
[0027] In the present invention, it has been found that the solvent
resistance of the cured electrodeposition coated film can be
improved by adjusting the glass transition temperature Tg and
crosslinking density from dynamic viscoelastic measurement of the
cured electrodeposition coated film to specified ranges, and the
finished appearance of the resulting multi layered coated film can
be improved, thereby accomplishing further another embodiment of
the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0028] In one embodiment of the present invention, components
contained in a cationic electrodeposition coating composition and
the content thereof are selected such that the cured
electrodeposition coated film formed by electrodeposition coating
has a centerline average roughness (Ra) of 0.05 to 0.25 .mu.m
obtained from a roughness curve and a centerline average roughness
(Pa) of 0.05 to 0.30 .mu.m obtained from a profile curve. The upper
limit of the centerline average roughness (Ra) is preferably 0.20
.mu.m. The upper limit of the centerline average roughness (Pa) is
preferably 0.25 .mu.m. It is difficult to obtain the cured
electrodeposition coated film having a centerline average roughness
(Ra) and centerline average roughness (Pa) of smaller than the
lower limit of 0.05 .mu.m in the level of the current
technology.
[0029] The centerline average roughness (Ra) obtained from a
roughness curve and the centerline average roughness (Pa) obtained
from a profile curve as used herein are parameters defined in JIS B
0601. The centerline average roughness (Ra) obtained from the
roughness curve and the centerline average roughness (Pa) obtained
from the profile curve of the cured electrodeposition coated film
can be measured, for example, by using an evaluation type surface
roughness tester manufactured by Mitutoyo Corporation according to
JIS B 0601.
[0030] When the Ra value is larger than 0.25 .mu.m, the appearance
of the multi layered coated film, particularly orange peel, is
degraded. When the Pa value is larger than 0.30 .mu.m, the
appearance of the multi layered coated film, particularly
smoothness, is degraded.
[0031] A method of preparing the cationic electrodeposition coating
composition for obtaining the cured electrodeposition coated film
having the centerline average roughness (Ra) obtained from the
roughness curve and the centerline average roughness (Pa) obtained
from the profile curve within the above ranges, includes a method
of adjusting the type and content of the cationic epoxy resin,
blocked isocyanate curing agent and catalyst in the cationic
electrodeposition coating composition. Particularly, the type and
content of the blocked isocyanate curing agent has a great effect
on the Ra and Pa values. The flowability and curing rate of the
coated film during forming the film (deposited film) are improved
to improve the smoothness of the coated film by adjusting the solid
content ratio between the cationic epoxy resin and blocked
isocyanate curing agent. The smoothness of the electrodeposition
coated film can be further improved by using the surface treated
steel plate having smaller surface roughness.
[0032] In another embodiment of the present invention, the cationic
electrodeposition coating composition and intermediate coating
composition are used such that the cured electrodeposition coated
film formed has a surface energy of 37 to 43 mJ/m.sup.2, and the
intermediate coating composition coated has a contact angle of 10
to 30 degrees on the cured electrodeposition coated film. When the
surface energy of the cured electrodeposition coated film is within
the above range and the contact angle between the cured
electrodeposition coated film and intermediate coating composition
is within the range of 10 to 30 degrees, the wettability of the
intermediate coating composition to the cured electrodeposition
coated film is high, and the finished appearance of the resulting
multi layered coated film.
[0033] The surface energy of the cured electrodeposition coated
film has the lower limit of preferably 38 mJ/m.sup.2, more
preferably 39 mJ/m.sup.2, and has the upper limit of preferably 42
mJ/m.sup.2, more preferably 41 mJ/m.sup.2. The contact angle
between the cured electrodeposition coated film and intermediate
coating composition has the lower limit of preferably 10 degrees
and has the upper limit of preferably 25 degrees.
[0034] When the surface energy is lower than 37 mJ/m.sup.2, the
adhesion between the cured electrodeposition coated film and
intermediate coated film is degraded. On the other hand, when the
surface energy is higher than 43 mJ/m.sup.2, the wettability of the
intermediate coating composition to the cured electrodeposition
coated film is degraded. In addition, when the contact angle
between the cured electrodeposition coated film and intermediate
coating composition is larger than 30 degrees, the wettability of
the intermediate coating composition to the cured electrodeposition
coated film is degraded.
[0035] The surface energy of the coated film is force applied in
the perpendicular direction to free length. The surface energy is
determined by measuring a contact angle between the coated film and
three kinds of liquids (such as water, methylene iodide and
ethylene glycol) having known .gamma..sup.LW value based on the
Lifshitz-van der Waals forces, an acidic component .gamma..sup.+
based on acid-base force and an basic component .gamma..sup.- based
on acid-base force in a contact angle process; obtaining
.gamma..sup.LW, .gamma..sup.+ and .gamma..sup.- values of the
coated film from the following equation 1 led from Young-Dupre
Equation; and calculating from the values using the following
equation 2 (See C. J. Van Oss, "J. Protein Chem", Vol. 4, 245, 1985
and C. J. Van Oss, "J. Colloid Interface Sci", Vol. 111, 378,
1986). 1 2 { ( i LW j LW ) 1 / 2 + ( i + j - ) 1 / 2 + ( i - j + )
1 / 2 } = ( 1 + cos ) { i LW + 2 ( i + j - ) 1 / 2 } Equation 1 )
Surface free energy ( ) = j LW + ( j + j - ) 1 / 2 Equation 2 )
[0036] .gamma..sub.i.sup.LW a term based on the Lifshitz-van der
Waals forces of the liquid
[0037] .gamma..sub.i.sup.+: an acidic component based on acid-base
force of the liquid
[0038] .gamma..sub.i.sup.-: an basic component based on acid-base
force of the liquid
[0039] .THETA.: contact angle
[0040] A method of preparing the cationic electrodeposition coating
composition and intermediate coating composition, from which the
surface energy of the cured electrodeposition coated film and the
contact angle between the cured electrodeposition coated film and
the intermediate coating composition within the above ranges can be
obtained, includes a method of adjusting the type and the content
of the cationic epoxy resin, blocked isocyanate curing agent,
catalyst and surface conditioner contained in the cationic
electrodeposition coating composition. Particularly, the type and
the content of the surface conditioner have a great effect on the
surface energy and the contact angle between the cured
electrodeposition coated film and the intermediate coating
composition. The types of the surface conditioner used in the
present invention include acryl-based type, silicone-based type and
vinyl-based type.
[0041] In the process for forming a multi layered coated film of
the present invention, it is more preferable that the cured
electrodeposition coated film have a centerline average roughness
(Ra) of 0.05 to 0.25 .mu.m obtained from a roughness curve and a
centerline average roughness (Pa) of 0.05 to 0.30 .mu.m obtained
from a profile curve and the contact angle between the cured
electrodeposition coated film and intermediate coating composition
is within the range of 10 to 30 degrees. This is because the multi
layered coated film having more excellent finished appearance can
be obtained.
[0042] In the present invention, components contained in a cationic
electrodeposition coating composition and the content thereof are
selected such that the cured electrodeposition coated film formed
by electrodeposition coating has a specified range of glass
transition temperature Tg (which is also represented by "dynamic
Tg" herein) and a specified range of crosslinking density, obtained
by dynamic viscoelastic measurement.
[0043] The dynamic Tg as used herein is determined by measuring a
dynamic glass transition temperature Tg using a sample in the same
way as a general measuring method of Tg by dynamic viscoelastic
measurement. Examples of the measuring methods used in the present
invention include a method of performing dynamic viscoelastic
measurement using the sample prepared by forming a cured
electrodeposition coated film on a substrate, separating the coated
film using mercury and cutting it. In the method, the sample was
heated from room temperature to 200.degree. C. at a raising rate of
temperature of 2.degree. C. per one minute and vibrated at a
frequency of 11 Hz to determine viscoelasticity thereof. A ratio
(tan .delta.) of storage elasticity (E')/loss elasticity (E") was
calculated and its inflexion point (a temperature at a peak of tan
.delta.) was determined to obtain a dynamic Tg. Example of a
measuring apparatus of dynamic viscoelastic includes, for example,
Rheovibron model RHEO 2000, 3000 (trade name), manufactured by
Orientec Co., Ltd.
[0044] In the present invention, it is preferable for the cured
electrodeposition coated film formed by electrodeposition coating
to have a dynamic Tg of 100 to 130.degree. C. The lower limit of
the dynamic Tg is preferably 110.degree. C. and the upper limit of
the dynamic Tg is preferably 125.degree. C. When the dynamic Tg of
the cured electrodeposition coated film is lower than 100.degree.
C., the electrodeposition coated film swells with a solvent
contained in the intermediate coating composition, and the finished
appearance of the resulting multi layered coated film is degraded.
On the other hand, when the dynamic Tg is higher than 130.degree.
C., the elastic modulus of the resulting multi layered coated film
is low, and the impact resistance the coated film is degraded.
[0045] The crosslinking density is determined by measuring dynamic
viscoelasticity of the cured electrodeposition coated film formed
by electrodeposition coating in the same way as the measuring
method of the dynamic Tg, and calculating with the resulting
storage elasticity (E') in rubbery region from the following
equation:
E'=3nRT
[0046] wherein E' is storage elasticity; n is crosslinking density;
R is gas constant; and T is absolute temperature.
[0047] In the present invention, the crosslinking density of the
cured electrodeposition coated film formed by electrodeposition
coating is within the range of preferably 1.2 to 2.6 mmol/cc. The
lower limit of the crosslinking density is more preferably 1.4
mmol/cc and the upper limit is more preferably 2.3 mmol/cc. When
the crosslinking density of the cured electrodeposition coated film
is lower than 1.2 mmol/cc, the electrodeposition coated film swells
with a solvent contained in the intermediate coating composition,
and the finished appearance of the resulting multi layered coated
film is degraded. On the other hand, when the crosslinking density
is higher than 2.6 mmol/cc, blisters easily occur by containing
water, and the corrosion resistance is degraded.
[0048] A method of preparing the cationic electrodeposition coating
composition for obtaining the cured electrodeposition coated film
having the dynamic Tg and the crosslinking density within the above
ranges includes a method of adjusting the type and content of the
cationic epoxy resin, blocked isocyanate curing agent and catalyst
in the cationic electrodeposition coating composition.
Particularly, the type and content of the cationic epoxy resin and
the blocked isocyanate curing agent have a great effect on the
dynamic Tg and crosslinking density. Examples of the cationic epoxy
resins include resins obtained by opening the epoxy ring of
bisphenol A type epoxy resin or bisphenol F type epoxy resin with
activated hydrogen compound, into which a cationic group can be
introduced. Examples of the blocked isocyanate curing agents
include hexamethylene diisocyanate (comprising trimer),
tetramethylene diisocyanate and trimethylhexamethylene
diisocyanate; cycloaliphatic diisocyanates, such as and
4,4'-methylene bis(cyclohexylisocyanate); aromatic diisocyanates
such as tolylene diisocyanate (TDI), diphenylmethane diisocyanate
(MDI), isophorone diisocyanate (IPDI) and hexamethylene
diisocyanate (HDI) blocked with a suitable block agent. In
addition, the dynamic Tg and crosslinking density can be also
adjusted by selecting the ratio of the blocked isocyanate curing
agent to the cationic epoxy resin or the baking temperature of the
electrodeposition coated film.
[0049] The materials to be coated, cationic electrodeposition
coating composition, intermediate coating composition, base top
coating composition and clear top coating composition used in the
process for forming a multi layered coated film of the present
invention, and applying methods thereof will be explained
hereinafter.
[0050] Substrates to be Coated
[0051] The substrates to be coated used in the process for forming
a multi layered coated film of the present invention may be any
substrates, which can be electrodeposition coated. Examples of the
substrates include metals such as iron, steel, aluminum, tin, zinc
and the like, and alloys thereof, and plated articles thereof or
deposited articles thereof. The concrete examples thereof include
passenger car, motor truck, motorcycle, bus and the like,
manufactured by using the metallic components. Moreover, plastic
materials obtained by conductive treating resins such as
polyethylene resin, polypropylene resin, ethylene-vinyl acetate
copolymer resin, polyamide resin, acrylic resin, vinylidene
chloride, polycarbonate resin, polyurethane resin, epoxy resin, and
various FRP, may be used as the substrate.
[0052] In the process for forming a multi layered coated film of
the present invention, the substrate may be used as-received
condition or after pre-treatment such as degreasing treatment or
chemical conversion treatment prior to electrodeposition
coating.
[0053] Cationic Electrodeposition Coating Composition
[0054] The cationic electrodeposition coating composition used in
the present invention comprises binder resin containing aqueous
solvent, cationic epoxy resin and blocked isocyanate curing agent
dispersed or dissolved in the aqueous solvent; acid for
neutralization; and organic solvent. The cationic electrodeposition
coating composition may further contain pigment.
[0055] Cationic Epoxy Resin
[0056] The cationic epoxy resins used in the present invention
include amine-modified epoxy resins. The cationic epoxy resins may
be well known resins described in Japanese Patent Kokai Publication
Nos. 4978/1979, 34186/1981 and the like.
[0057] The cationic epoxy resins are typically made by opening the
all epoxy rings of bisphenol type epoxy resin with activated
hydrogen compound, into which a cationic group can be introduced;
or by opening a part of the epoxy rings with the other activated
hydrogen compound and opening the residual epoxy rings with
activated hydrogen compound, into which a cationic group can be
introduced.
[0058] The concrete examples of the bisphenol type epoxy resins
include bisphenol A type epoxy resins and bisphenol F type epoxy
resins. Examples of the bisphenol A type epoxy resins, which are
commercially available from Yuka Shell Epoxy Co., Ltd., include
Epikote 828 (epoxy equivalent value: 180 to 190), Epikote 1001
(epoxy equivalent value: 450 to 500), Epikote 1010 (epoxy
equivalent value: 3000 to 4000) and the like. Examples of the
bisphenol F type epoxy resins, which are commercially available
from Yuka Shell Epoxy Co., Ltd., include Epikote 807 (epoxy
equivalent value: 170) and the like.
[0059] Oxazolidone ring containing epoxy resins having the
following formula: 1
[0060] wherein R represents a residual group obtained by removing
glycydyl group from diglycidyl epoxy compound, R' represents a
residual group obtained by removing isocyanate group from
diisocyanate compound and n represents a positive integer,
[0061] may be used in the cationic epoxy resin because of obtaining
a coated film having excellent heat resistance and corrosion
resistance. This is because the coated film having excellent
solvent resistance (solvent swelling resistance) can be
obtained.
[0062] A method of introducing the oxazolidone ring into the epoxy
resin includes a method comprising the steps of heating the blocked
isocyanate curing agent blocked with lower alcohol such as methanol
and polyepoxide under basic catalyst and keeping the temperature
constant, and distilling the lower alcohol as a by-product off the
system.
[0063] The particularly preferred epoxy resin is oxazolidone ring
containing resin. This is because the coated film, which is
superior in solvent resistance (solvent swelling resistance), heat
resistance, corrosion resistance and impact resistance, can be
obtained.
[0064] It is well known to obtain epoxy resins containing
oxazolidone ring by reaction of bifunctional epoxy resin with
diisocyanate blocked with monoalcohol (that is, bisurethane). The
concrete examples of the oxazolidone ring containing epoxy resins
and the preparing method thereof are disclosed in paragraphs [0012]
to [0047] of Japanese Patent Kokai Publication No. 128959/2000,
which are well known.
[0065] The epoxy resin may be modified with suitable resins, such
as polyesterpolyol, polyetherpolyol, and monofuctional alkylphenol.
In addition, the epoxy resins can be chain-extended by the reaction
of epoxy group with diol or dicarboxylic acid.
[0066] It is desired for the epoxy resins to be ring-opened with
activated hydrogen compound such that they have an amine equivalent
value of 0.3 to 4.0 meq/g after ring opening, and particularly 5 to
50% thereof is primary amine group.
[0067] Examples of the activated hydrogen compounds, into which a
cationic group can be introduced, include primary amine, secondary
amine, and an acid salt of tertiary amine, sulfide and acid
mixture. In order to prepare primary amine, secondary amine and/or
tertiary amine containing epoxy resin, primary amine, secondary
amine, and an acid salt of tertiary amine are used as the activated
hydrogen compound, into which a cationic group can be
introduced.
[0068] The concrete examples thereof include butylamine,
octylamine, diethylamine, dibutylamine, methylbutylamine, an acid
salt of triethylamine, an acid salt of N,N-dimethylethanolamine,
diethyldisulfide-acetic acid mixture, and secondary amines obtained
by blocking primary amines, such as ketimine of
aminoethylethanolamine, ketimine of diethylenetriamine. The amines
may be used in combination.
[0069] Blocked Isocyanate Curing Agent
[0070] Polyisocyanate used for preparing the blocked isocyanate
curing agent of the present invention is a compound having at least
two isocyanate groups in the molecular. The polyisocyanates may be
aliphatic, cycloaliphatic, aromatic or aromatic-aliphatic.
[0071] Examples of the polyisocyanates include aromatic
diisocyanates, such as tolylene diisocyanate (TDI), diphenylmethane
diisocyanate (MDI), p-phenylene diisocyanate and naphthalene
diisocyanate; aliphatic diisocyanates having 3 to 12 carbon atoms,
such as hexamethylene diisocyanate (HDI), 2,2,4-trimethylhexane
diisocyanate and lysine diisocyanate; cycloaliphatic diisocyanates
having 5 to 18 carbon atoms, such as 1,4-cyclohexane diisocyanate,
isophorone diisocyanate (IPDI), 4,4'-dicyclohexylmethane
diisocyanate (hydrogenated MDI), methylcyclohexane diisocyanate,
isopropylidenedicyclohexyl-4,4'-diisocyan- ate and
1,3-diisocyanatomethylcyclohexane (hydrogenated XDI), hydrogenated
TDI, 2,5- or 2,6-bis(isocyanate methyl)-bicyclo[2.2.1]heptane
(=norbornane diisocyanate); aliphatic diisocyanates having aromatic
ring, such as xylylene diisocyanate (XDI) and tetramethylxylylene
diisocyanate (TMXDI); modified compounds thereof (urethane
compound, carbodiimide, urethodion, urethonimine, biuret and/or
isocyanurate modified compound); and the like. The polyisocyanate
may be used alone or in combination of two or more.
[0072] Adducts or prepolymers obtained by reacting the
polyisocyanate with polyalcohols such as ethylene glycol, propylene
glycol, trimethylolpropane and hexanetriol at a NCO/OH ratio of not
less than 2 may be used as the blocked isocyanate curing agent.
[0073] The block agent is adducted to polyisocyanate group and
stable at room temperature, but free isocyanate group can be
regenerated when heating it at the temperature not less than the
dissociation temperature.
[0074] Pigment
[0075] The cationic electrodeposition coating composition used in
the process of the present invention may contain pigment, which has
been conventionally used for a coating. Examples of the pigments
include inorganic pigments, for example, a coloring pigment, such
as titanium dioxide, carbon black and colcothar; an extender
pigment, such as kaolin, talc, aluminum silicate, calcium
carbonate, mica and clay; a rust preventive pigment, such as zinc
phosphorate, iron phosphorate, aluminum phosphorate, calcium
phosphorate, zinc phosphite, zinc cyanide, zinc oxide, aluminum
tripolyphosphorate, zinc molybdate, aluminum molybdate, calcium
molybdate, aluminum phosphomolybdate and aluminum zinc
phosphomolybdate.
[0076] When the pigment is used as a component of the
electrodeposition coating, the pigment is generally pre-dispersed
in an aqueous solvent at high concentration in the form of a paste
(pigment dispersed paste). This is because it is difficult to
uniformly disperse the pigment, which is powdery, at low
concentration in one step. The paste is generally called as pigment
dispersed paste.
[0077] The pigment dispersing paste is prepared by dispersing the
pigment together with pigment dispersing resin varnish in an
aqueous medium. As the pigment dispersing resin, cationic or
non-ionic low molecular weight surfactant, or cationic polymer such
as modified epoxy resin having quaternary ammonium group and/or
tertiary sulfonium group can be used. As the aqueous medium,
deionized water or water containing a small amount of alcohol can
be used. The pigment dispersing resin is generally used at the
solid content of 20 to 100 parts by mass based on 100 parts by mass
of the coating. The pigment dispersing paste can be obtained by
mixing the pigment dispersing resin varnish with the pigment, and
dispersing the pigment using a suitable dispersing apparatus, such
as a ball mill or sand grind mill.
[0078] The cationic electrodeposition coating composition may
optionally contains dissociation catalyst, organic tin compounds,
such as dibutyltin dilaurate, dibutyltin oxide, dioctyltin oxide;
amines, such as N-methyl morpholine; lead acetate; metal salts of
strontium, cobalt and cupper; in order to dissociate the block
agent in addition to the above components. The amount of the
dissociation catalyst is from 0.1 to 6 parts by mass based on 100
parts by mass of the total solid content of the cationic epoxy
resin and blocked isocyanate curing agent in the cationic
electrodeposition coating composition.
[0079] Preparation and Application of Cationic Electrodeposition
Coating Composition
[0080] The cationic electrodeposition coating composition of the
present invention is prepared by dispersing the above catalyst,
cationic epoxy resin, blocked isocyanate curing agent, and pigment
dispersed paste in an aqueous solvent. In addition, the aqueous
medium may contain a neutralizing acid in order to neutralize the
cationic epoxy resin to improve the dispersibility of binder resin
emulsion. Examples of the neutralizing acid include inorganic acids
or organic acids, such as hydrochloric acid, nitric acid,
phosphoric acid, formic acid, acetic acid, lactic acid.
[0081] The amount of the neutralizing acid is preferably from 10 mg
equivalent to 25 mg equivalent, based on 100 g of the binder resin
containing the cationic epoxy resin and blocked isocyanate curing
agent. The lower limit of the amount of the neutralizing acid is
more preferably 15 mg equivalent and the upper limit is more
preferably 20 mg equivalent. When the amount of the neutralizing
acid is smaller than 10 mg equivalent, the miscibility with water
is not sufficiently obtained, and it is difficult to disperse in
water, or the stability is greatly degraded. On the other hand,
when the amount of the neutralizing acid is larger than 25 mg
equivalent, the electric power necessary to deposition increases,
and the deposition of the solid content of the coating is degraded,
which degrades the throwing power.
[0082] The cationic electrodeposition coating composition can be
prepared by dispersing the cationic epoxy resin and blocked
isocyanate curing agent in an aqueous solvent. It is desired for
the amount of the blocked isocyanate curing agent to be sufficient
to react with activated hydrogen containing functional group, such
as primary amino group, secondary amino group, and hydroxyl group
during curing to provide good cured coated film. The amount of the
blocked isocyanate curing agent, which is represented by a solid
content ratio of the cationic epoxy resin to the blocked isocyanate
curing agent (cationic epoxy resin/curing agent), is within the
range of preferably 90/10 to 50/50, more preferably 80/20 to 60/40,
most preferably 80/20 to 65/35. The flowability and curing rate of
the coated film at the time of film forming (deposited film) are
improved by adjusting the ratio, and the smoothness of the coated
film is improved. The smoothness of the electrodeposition coated
film is further improved by using surface treated steel plate
having smaller roughness. In addition, it is easy to impart the
cured electrodeposition coated film to the desired dynamic Tg and
crosslinking density by adjusting the amount of the blocked
isocyanate curing agent to the above range or selecting the baking
temperature.
[0083] The organic solvent is used as a solvent when synthesizing
resin components, such as the cationic epoxy resin, blocked
isocyanate curing agent, pigment dispersing resin. The complicated
procedure is necessary for completely removing the solvent. The
flowability of the coated film at the time of film forming is
improved by containing the organic solvent in the binder resin, and
the smoothness of the coated film is improved.
[0084] Examples of the organic solvents used in the cationic
electrodeposition coating composition include ethylene glycol
monobutyl ether, ethylene glycol monohexyl ether, ethylene glycol
monoethylhexyl ether, propylene glycol monobutyl ether, dipropylene
glycol monobutyl ether, propylene glycol monophenyl ether and the
like.
[0085] The cationic electrodeposition coating composition can
contain additives for a coating, such as a plasticizer, surfactant,
antioxidant and ultraviolet absorber, in addition to the above
components. The cationic electrodeposition coating composition may
contain amino group containing acrylic resin, amino group
containing polyester resin and the like.
[0086] Electrodeposition coating is carried out by applying a
voltage of usually 50 to 450 V between the substrate serving as
cathode and anode. When the applied voltage is lower than 50 V, the
electrodeposition becomes insufficient. On the other hand, when the
applied voltage is higher than 450 V, the coated film may be broken
and appearance thereof becomes unusual. The electrodeposition bath
temperature is usually controlled at 10 to 45.degree. C.
[0087] The electrodeposition process comprises the steps of
immersing a substrate to be coated in an electrodeposition coating
composition, and applying a voltage between the substrate as
cathode and anode to cause deposition of coated film. Also, the
period of time for applying the voltage can be generally 2 to 4
minutes, though it varies with the electrodeposition condition.
[0088] The thickness of the electrodeposition coated film is
preferably 5 to 25 .mu.m, more preferably 20 .mu.m. When the
thickness is smaller than 5 .mu.m, rust resistance is not
sufficiently obtained. On the other hand, when the thickness is
larger than 25 .mu.m, it leads waste of the coating
composition.
[0089] The electrodeposition coated film obtained in the manner as
described above is baked at a temperature of 120 to 260.degree. C.,
preferably 140 to 220.degree. C. for 10 to 30 minutes to be cured
directly or after being washed with water after completion of the
electrodeposition process, thereby the cured electrodeposition
coated film is formed.
[0090] Intermediate Coating Composition
[0091] The intermediate coating composition used in the present
invention contains an intermediate coating resin component,
pigment, aqueous medium and/or organic solvent. The intermediate
coating resin component comprises an intermediate coating resin and
optionally an intermediate coating curing agent. The aqueous medium
and organic solvent can be the same as used in the cationic
electrodeposition coating composition.
[0092] Examples of the intermediate coating resins include acrylic
resin, polyester resin, polyurethane resin, alkyd resin, fluorine
resin, epoxy resin, polyether resin and the like. Preferred are
acrylic resin, polyester resin and polyurethane resin. The
intermediate coating resin may be used alone or in combination with
two or more.
[0093] Examples of the acrylic resins include copolymer of acrylic
monomer and the other ethylenically unsaturated monomer. Examples
of the acrylic monomers, which can be used in the copolymer,
include methyl ester, ethyl ester, propyl ester, n-butyl ester
i-butyl ester, t-butyl ester, 2-ethylhexyl ester, lauryl ester,
phenyl ester, benzyl ester and 2-hydroxypropyl ester of acrylic
acid or methacrylic acid; ring opening addition product of
caprolactone of 2-hydroxyethyl acrylate or methacrylate; glycidyl
acrylate, glycidyl methacrylate, acrylamide, methacrylamide and
N-methylol acrylamide, (meth)acrylic ester of polyalcohol and the
like. Examples of the other ethylenically unsaturated monomers,
which can copolymerize with the above monomer, include styrene,
.alpha.-methylstyrene, itaconic acid, maleic acid, vinyl acetate
and the like.
[0094] Example of the polyester resins include saturated polyester
resins or unsaturated polyester resins, for examples, condensates
obtained by condensing polybasic acid and polyalcohol with applied
heat. Examples of the polybasic acids include saturated polybasic
acids and unsaturated polybasic acids. Examples of the saturated
polybasic acids include succinic acid, adipic acid, azelaic acid,
sebacic acid, hexahydrophthalic acid and 1,4-cyclohexane
dicarboxylic acid. Examples of the unsaturated polybasic acids
include maleic acid, maleic anhydride, fumaric acid, phthalic
anhydride, terephthalic acid and isophthalic acid. Examples of
polyalcohols include divalent alcohols and trivalent alcohols.
Examples of the divalent alcohols include ethylene glycol,
diethylene glycol, neopentyl glycol, 1,5-pentanediol and
1,6-hexanediol. Examples of the trivalent alcohols include glycerin
and trimethylolpropane.
[0095] Examples of the polyurethane resins include resins having
urethane bond obtained from polyols components of acrylic,
polyester, polyether, polycarbonate and the like and polyisocyanate
compounds. Examples of the polyisocyanate compounds include
2,4-tolylene diisocyanate (2,4-TDI), 2,6-tolylene diisocyanate
(2,6-TDI) and the mixture thereof (TDI),
diphenylmethane-4,4'-diisocyanate (4,4'-MDI),
diphenylmethane-2,4'-diisoc- yanate (2,4'-MDI) and the mixture
thereof (MDI), naphthalene-1,5-diisocyan- ate (NDI),
3,3'-dimethyl-4,4'-biphenylene diisocyanate (TODI), xylylene
diisocyanate (XDI), dicyclohexylmethane diisocyanate (hydrogenated
MDI), isophorone diisocyanate (IPDI), hexamethylene diisocyanate
(HDI), hydrogenated xylylene diisocyanate (HXDI) and the like.
[0096] Examples of the alkyd resins include alkyd resins obtained
by reacting the polybasic acid and polyalcohol with modifiers, such
as fats and oils or fatty acid thereof (such as soybean oil,
linseed oil, coconut oil, stearic acid and the like), natural resin
(such as rosin, amber and the like).
[0097] Examples of the fluorine resins include vinylidene fluoride
resin, tetrafluoroethylene resin, or the mixture thereof,
fluorine-based copolymer obtained by copolymerizing fluoroolefin
and monomers comprising hydroxyl group containing compound and the
other copolymerizable vinyl-based compound.
[0098] Examples of the epoxy resins include resins obtained by the
reaction of bisphenol with epichlorohydrin and the like. Examples
of the bisphenols include bisphenol A and bisphenol F. Examples of
the bisphenol type epoxy resins include Epikote 828, Epikote 1001,
Epikote 1004, Epikote 1007, Epikote 1009 (which are commercially
available from Shell Chemical Co.). In addition, the resins may be
chain-lengthened by a suitable chain extender.
[0099] Examples of the polyether resins, which are polymer or
copolymers having ether bond, include polyoxyethylene-based
polyether, polyoxypropylene-based polyether or polyoxybutylene
polyether, or polyether resin having at least two hydroxyl groups
in one molecular, such as polyethers derived from aromatic
polyhydroxy compounds, such as bisphenol A or bisphenol F. In
addition, the examples also include carboxyl group containing
polyether resins obtained by the reaction of the polyether resins
and reactive derivatives, such as polyvalent carboxylic acid
including succinic acid, adipic acid, sebacic acid, phthalic acid,
isophthalic acid, terephthalic acid and trimellitic acid or
anhydrides thereof.
[0100] It is desired for the intermediate coating resin to have an
acid value of 3 to 200, a hydroxyl number of 30 to 200 and a number
average molecular weight of 500 to 50,000. The preferred resins are
particularly acrylic resin having an acid value of 3 to 200, a
hydroxyl number of 30 to 200 and a number average molecular weight
of 2,000 to 50,000 and polyester resin having an acid value of 3 to
200, a hydroxyl number of 30 to 200 and a number average molecular
weight of 500 to 20,000. In the case of preparing the intermediate
coating composition as an aqueous solution or aqueous dispersion,
it is desired for the intermediate coating resin to have an acid
value of 10 to 200 and a hydroxyl number of 30 to 200.
[0101] In the intermediate coating resins, there is generally a
curable type and lacquer type resins. Preferred is the curable
type. If using the curable type, an intermediate coating curing
agent, such as a blocked isocyanate compound, oxazolidone compound,
carbodiimide compound and melamine compound is used in combination
with the intermediate coating resin. The curing reaction of the
intermediate coating resin component containing the intermediate
coating curing agent can be advanced under heating or at room
temperature. In addition, the combination of the curable type and
non-curable type intermediate coating resins can be used.
[0102] If containing the intermediate coating curing agent, a
weight ratio of the intermediate coating resin to the intermediate
coating curing agent in the coating solid content is preferably
90/10 to 50/50, more preferably 85/15 to 60/40. When the ratio is
larger than 90/10 and the amount of the intermediate coating curing
agent is smaller than 10% by weight, the crosslinking in the coated
film is not sufficiently obtained. On the other hand, when the
ratio is smaller than 50/50 and the amount of the intermediate
coating curing agent is larger than 50% by weight, the storage
stability of the coating composition is degraded and the curing
rate is large, and the appearance of the coated film is
degraded.
[0103] The intermediate coating composition of the present
invention contains a pigment. Examples of the pigments include
extender pigments, such as baryta powder, precipitated sulfate,
barium carbonate, gypsum, clay, silica, talc, magnesium carbonate,
alumina white and the like, and coloring pigments. Examples of the
coloring pigments include organic pigments, such as azo lake-based
pigment, phthalocyanine-based pigment, indigo-based pigment,
perylene-based pigment, quinophtharone-based pigment,
dioxazine-based pigment, quinacridone-based pigment,
isoindorinone-based pigment, metal complex pigment, carbon black;
or inorganic pigments, such as yellow lead, yellow iron oxide,
colcothar, titanium dioxide. The amount of the pigment can be
optionally selected depending on the desired performance and hue.
The pigment may be used alone or in combination with two or
more.
[0104] The concentration of the pigment (PWC) based on the coating
solid content of the intermediate coating composition is within the
range of preferably 10 to 50% by weight. The upper limit of the
concentration is more preferably 30% by weight.
[0105] The solid content of the intermediate coating composition is
within the range of preferably 35 to 65% by weight. The lower limit
is more preferably 40% by weight and the upper limit is more
preferably 60% by weight. When the lower limit of the solid content
is smaller than 35% by weight, sag occurs during the application of
the coating, and the finished appearance is degraded. On the other
hand, when the upper limit is larger than 65% by weight, the
flowability during the application of the coating is reduces, and
the finished appearance is degraded.
[0106] The intermediate coating composition can contain polyamide
wax, which is lubricant dispersion of aliphatic amide, polyethylene
wax, which is colloidal dispersion based on polyethylene oxide,
curing catalyst, ultraviolet absorber, antioxidant, leveling agent,
surface conditioner such as silicone and organic polymer, anti-sag
agent, thickening agent, defoaming agent, lubricant, crosslinkable
polymer powder (micro gel) and the like in addition to the above
components. The performance of the coating composition and coated
film can be improved by compounding the above additive in amount of
not more than 15 parts by mass (based on solid content), based on
100 parts by mass of the intermediate coating resin.
[0107] Preparation and Application of Intermediate Coating
Composition
[0108] The intermediate coating composition can be prepared by
dissolving or dispersing the above components in a solvent. The
solvent is not limited as long as it can dissolve and disperse the
intermediate coating resin component, but may be organic solvent
and/or water. The organic solvent may be one, which has been
conventionally used in the art of the coating composition. Examples
of the organic solvents include hydrocarbons such as toluene and
xylene, ketones such as acetone and methyl ethyl ketone, esters
such as ethyl acetate, butyl acetate, cellosolve acetate and butyl
cellosolve, alcohols and the like. If it is restrained to use the
organic solvent in view of circumstance, it is desire to use water.
If so, a proper amount of hydrophilic organic solvent may be
contained therein.
[0109] The viscosity of the intermediate coating composition during
the application thereof is adjusted to preferably 10 to 30 seconds
(ford cup #4/20.degree. C.) using the organic solvent and/or water,
and the mixture thereof. When the viscosity is lower than the above
range, the intermediate coated film is miscible with the base top
coated film formed in the subsequent applying step. On the other
hand, when the viscosity is higher than the above range, it is
difficult to handle the coating composition and the coated film is
early solidified, and the surface evenness occurs in such a level
that it can not be coated and repaired by the coated film in the
subsequent coating step.
[0110] The intermediate coated film is obtained by applying the
intermediate coating composition on the cured electrodeposition
coated film. The opacifying properties of the electrodeposition
coated film by forming the intermediate coated film, the chipping
resistance are imparted. In addition, the adhesion to the base top
coated film applied on the intermediate coated film in the
subsequent step is also improved.
[0111] A method of applying the intermediate coating is not
limited, but it is conducted by using an air electrostatic spray
coater, which is so-called "react gun"; a rotary spray
electrostatic coater, which is so-called "micro micro (.mu..mu.)
bell", "micro (.mu.) bell", and "meta bell"; and the like.
Preferred is the method by the rotary spray electrostatic
coater.
[0112] It is desired for the intermediate coated film to have a dry
thickness of 5 to 80 .mu.m, preferably 10 to 50 .mu.m. After the
formation of the intermediate coated film, the step of forming the
base top coated film is conducted without heating and curing. The
intermediate coated film may be preheated at a temperature lower
than that of heating and curing (baking) treatment before forming
the base top coated film.
[0113] Base Top Coating Composition
[0114] The base top coating composition used in the present
invention is brilliant coating composition or solid coating
composition containing a base top coating resin component,
brilliant pigment and/or coloring pigment, extender pigment and
solvent. The base top coating composition is water-based or organic
solvent-based including water-dispersed or organic
solvent-dispersed.
[0115] The base top coating resin component contained in the base
top coating composition comprises a base top coating resin and
optionally a base top coating curing agent. The base top coating
resin component (the base top coating resin and base top coating
curing agent), coloring pigment, extender pigment, various
additives and solvents contained in the base top coating
composition may be the same as described in the intermediate
coating. By using the base top coating resin component, the
brilliant pigment and optionally the coloring pigment are dispersed
in the brilliant base top coating composition and the coloring
pigment are dispersed in the solid base top coating
composition.
[0116] Examples of the base top coating resin used may include at
least one of coated film forming resin selected from the group
consisting of acrylic resin, polyester resin, fluorine resin, epoxy
resin, polyurethane resin, polyether resin and the modified resins
thereof. Examples of the base top coating curing agents include the
intermediate coating curing agents as described above. Preferred is
melamine compound, particularly etherified melamine resin. The
etherified melamine resin is obtained by etherifying a melamine by
alcohols, such as methanol and butanol. The preferred combination
of the base top coating resin and base top coating curing agent as
the base top coating resin component includes acrylic
resin-melamine resin system. In the system, it is desired for the
acrylic resin to have an acid value of 10 to 200, a hydroxyl number
of 30 to 200 and a number average molecular weight of 2,000 to
50,000.
[0117] Examples of the brilliant pigments as the pigment contained
in the base top coating composition include aluminum flake pigment,
colored aluminum flake pigment, interference mica pigment, colored
mica pigment, metal oxide coated glass flake pigment, metal plated
glass flake pigment, metal oxide coated silica flake pigment,
metallic titanium flake pigment, graphite pigment, stainless steel
flake pigment, platy iron oxide pigment, phthalocyanine flake
pigment and hologram pigment. If using the brilliant pigment and/or
coloring pigment, a weight content of the all pigments (PWC) is
within the range of preferably 1 to 50%, more preferably 5 to 30%.
When the PWC is smaller than 1%, it is not sufficient to add design
to the coated film. On the other hand, the PWC is larger than 50%,
the appearance of the coated film is degraded.
[0118] Preparation and Application of Base Top Coating
Composition
[0119] The base top coating composition is prepared by dissolving
or dispersing the above components in a solvent. The solvent is not
limited as long as it can dissolve and disperse the base top
coating resin component, but may be organic solvent and/or water.
Examples of the organic solvents include hydrocarbons such as
toluene and xylene, ketones such as acetone and methyl ethyl
ketone, esters such as ethyl acetate, butyl acetate, cellosolve
acetate and butyl cellosolve, alcohols and the like.
[0120] The viscosity of the base top coating composition is
preferably adjusted to the range of 10 to 30 seconds (ford cup
#4/20.degree. C.) using a suitable diluent. When the viscosity is
lower than the above range, the base top coated film is miscible
with the clear top coated film formed in the subsequent applying
step. On the other hand, when the viscosity is higher than the
above range, it is difficult to handle the coating composition and
the coated film is early solidified, and the surface evenness
occurs in such a level that it can not be coated and repaired by
the coated film in the subsequent coating step.
[0121] The base top coated film is obtained by applying the base
top coating composition on the intermediate coated film. The base
top coating composition is applied on the uncured intermediate
coated film by wet on wet coating. The method of applying the base
top coating composition is not limited, but includes the method
described as the method of applying the intermediate coating
composition. When the base top coating composition is applied on an
automobile body, it is conducted by multi-stage coating, preferably
two-stage coating with an air electrostatic spray coater in order
to impart the coated film to high elegance. The applying method may
be also the combination of an air electrostatic spray coater and
rotary spray type electrostatic coater.
[0122] The formation of the base top coated film allows to add
design to the coated film, assures the adhesion to the intermediate
coated film formed in the previous step and assures the adhesion to
the base top coated film coated in the subsequent step.
[0123] It is desired for the base top coated film to have a dry
thickness of 5 to 50 .mu.m, preferably 10 to 30 .mu.m, per one
coating. After the formation of the base top coated film, the
subsequent step of forming the clear top coated film is conducted
without heating and curing. The base top coated film may be
preheated at a temperature lower than that of heating and curing
(baking) treatment before forming the clear top coated film.
[0124] Clear Top Coating Composition
[0125] The clear top coating composition is formed from a clear
coating composition containing a clear top coating resin component,
various additives and solvents. The clear top coating composition
is water-based or organic solvent-based including water-dispersed
or organic solvent-dispersed.
[0126] The clear top coating resin component contained in the clear
top coating composition comprises a clear top coating resin and
optionally a clear top coating curing agent. The clear top coating
resin component (the clear top coating resin and clear top coating
curing agent), various additives and solvents contained in the
clear top coating composition may be the same as described in the
intermediate coating.
[0127] The preferred combination of the clear top coating resin and
clear top coating curing agent as the clear top coating resin
component includes acrylic resin-melamine resin system. In the
system, it is desired for the acrylic resin to have an acid value
of 10 to 200, a hydroxyl number of 30 to 200 and a number average
molecular weight of 2,000 to 50,000.
[0128] As the clear top coating composition, a clear coating
composition comprising carboxyl group containing polymer and epoxy
group containing polymer disclosed in Japanese Patent Kokoku
Publication No. 19315/1996 can be suitably used in order to assure
the acid rain resistance and maintain the orientation of the
brilliant pigment in the base top coated film by increasing the
solubility difference from the base top coated film in wet on wet
coating. The clear top coating composition can optionally contain
additives, such as coloring pigment, extender pigment, modifier,
ultraviolet absorber, leveling agent, dispersant and defoaming
agent.
[0129] Preparation and Application of Clear Top Coating
Composition
[0130] The clear top coating composition is prepared by dissolving
or dispersing the above components in a solvent. The optional
solvent described above can be used. The clear top coated film is
obtained by applying the clear top coating composition on the base
top coated film. The clear top coating composition is applied on
the uncured base top coated film by wet on wet coating.
[0131] The method of forming the clear top coated film is not
limited, but preferably includes spraying method, roll coater
method and the like. It is desired for the clear top coated film to
have a dry thickness of 20 to 50 .mu.m, preferably 25 to 40 .mu.m,
per one coating.
[0132] The formation of the clear top coated film allows to protect
the base top coated film and add depth feeling to the resulting
multi layered coated film.
[0133] Baking
[0134] After the formation of the clear top coated film, the three
layers of coated films of the uncured intermediate coated film,
base top coated film and clear top coated film are baked and cured
at 120 to 160.degree. C. for a given time to obtain the multi
layered coated film. In the method of the present invention, the
intermediate coating composition, base top coating composition and
clear top coating composition are applied in the order respectively
by wet and wet coating. That is, uncured coated films are formed in
order of precedence. The term "uncured" as used herein refers to
the state that the coated film does not completely cured, and
includes the state of preheated coated film. The term "preheat" as
used herein refers to leaving or heating the coated film at a
temperature of room temperature to 100.degree. C. as the
temperature lower than that of heating and curing (baking)
treatment for 1 to 10 minutes. The coated film having better
finished appearance can be obtained by preheating the coated film
after the formation of the intermediate coated film and the
formation of the base top coated film respectively.
EXAMPLES
[0135] The present invention will be further explained in detail in
accordance with the following examples, however, the present
invention is not limited to these examples. In the examples, "part"
is based on weight unless otherwise specified.
Preparation Example 1
[0136] Preparation of Amine Modified Epoxy Resin
[0137] 92 parts of 2,4-/2,6-tolylenediisocyanate (weight
ratio=8/2), 95 parts of methyl isobutyl ketone (hereinafter,
referred to as MIBK) and 0.5 part of dibutyltin dilaurate were
loaded to a flask equipped with a stirrer, a cooling tube, a
nitrogen introducing tube, a thermometer and a dropping funnel. 21
parts of methanol was added while stirring the reaction mixture.
Starting at room temperature, the reaction mixture was allowed to
rise to 60.degree. C. by exothermic, the reaction was retained for
30 minutes, and 50 parts of ethylene glycol mono-2-ethylhexyl ether
was dropped from the dropping funnel. Furthermore, 53 parts of
bisphenol A-propylene oxide 5 mol adduct was added. The reaction
was carried out mainly in the temperature range of 60 to 65.degree.
C., and continued until absorption based on an isocyanate group
disappeared in IR spectrum measurement.
[0138] Next, 365 parts of epoxy resin of epoxy equivalent 188
synthesized from bisphenol A and epichlorohydrin in accordance with
a known method was added to the reaction mixture and heated to
125.degree. C. After that, 1.0 part of benzyldimetylamine was added
and allowed to react at 130.degree. C. until epoxy equivalent
became 410.
[0139] Subsequently, 61 parts of bisphenol A and 33 parts of
octylic acid were added and allowed to react at 120.degree. C. to
achieve epoxy equivalent of 1190. Thereafter, the reaction mixture
was cooled, and 11 parts of diethanolamine, 24 parts of
N-ethylethanolamine and 25 parts of 79% by weight solution in MIBK
of ketimined aminoethyl ethanolamine were added, and was allowed to
react for 2 hours at 110.degree. C. Then, the reaction mixture was
diluted with MIBK until nonvolatile solid content became 80%, and
an amine modified epoxy resin having a glass transition temperature
of 2.degree. C. (resin solid content: 80%) was obtained.
Preparation example 2
[0140] Preparation of Block Polyisocyanate Curing Agent (1)
[0141] 1250 parts of diphenylmethane diisocyanate, 266.4 parts of
MIBK were loaded to a reaction vessel, and 2.5 parts of dibutyltin
dilaurate were added thereto after heating to 80.degree. C. A
solution of 226 parts of .epsilon.-caprolactam dissolved in 944
parts of butylcellsolve was dropped thereto at 80.degree. C. over 2
hours. The reaction was retained at 100.degree. C. for 4 hours, it
was confirmed that absorption based on an isocyanate group
disappeared in IR spectrum measurement, and left to be cooled.
336.1 parts of MIBK were added and thereby, a blocked isocyanate
curing agent having a glass transition temperature of 0.degree. C.
was obtained.
Preparation Example 3
[0142] Preparation of Pigment Dispersing Resin
[0143] 222.0 parts of isophorone diisocyanate (hereinafter,
referred to as IPDI) was loaded in a reaction vessel equipped with
a stirrer, a cooling tube, a nitrogen introducing tube and a
thermometer, and after diluted with 39.1 parts of MIBK, 0.2 part of
dibutyltin dilaurate was added. Then, the reaction mixture was
heated to 50.degree. C., and 131.5 parts of 2-ethyl hexanol was
dropped under dry nitrogen atmosphere over 2 hours with stirring.
Reaction temperature was kept at 50.degree. C. by cooling as
necessary. As the result, 2-ethyl hexanol half blocked IPDI (resin
solid content: 90.0%) was obtained.
[0144] 87.2 parts of dimethylethanolamine, 117.6 parts of 75%
aqueous solution of lactic acid, and 39.2 parts of ethylene glycol
monobutyl ether were added to a suitable reaction vessel, the
reaction mixture was stirred at 65.degree. C. for half an hour to
prepare a quaternarizing agent.
[0145] Subsequently 710.0 parts of EPON 829 (bisphenol A type epoxy
resin manufactured by Shell Chemical Company, epoxy equivalent 193
to 203), and 289.6 parts of bisphenol A were loaded to a reaction
vessel. The reaction mixture was heated to 150 to 160.degree. C.
under nitrogen atmosphere, initial exothermic reaction was
occurred. Heating was continued at 150 to 160.degree. C. for about
1 hour, the reaction mixture was then cooled to 120.degree. C.,
498.8 parts of the prepared 2-ethyl hexanol half-blocked IPDI (MIBK
solution) was added.
[0146] The reaction mixture was held at 110 to 120.degree. C. for
about 1 hour, 463.4 parts of ethylene glycol monobutyl ether were
added, the mixture was cooled to 85 to 95.degree. C., homogenized,
and 196.7 parts of the prepared quaternarizing agent was added
thereto. The reaction mixture was held at 85 to 95.degree. C. until
the acid value became 1, 964 parts of deionized water were added to
finalize quaternarization of an epoxy-bisphenol A resin and to
obtain a pigment dispersing resin having quaternary ammonium salt
moiety (resin Tg=5.degree. C., resin solid content: 50%).
Preparation Example 4
[0147] Preparation of Pigment Dispersion Paste
[0148] 120 parts of the pigment dispersing resin obtained in
Preparation example 3, 2.0 parts of carbon black, 100.0 parts of
kaolin, 80.0 parts of titanium dioxide, 18.0 parts of aluminum
phosphomolibudate and 221.7 parts of ion-exchange water were loaded
into a sand grinding mill, and they were dispersed until particle
size was not more than 10 .mu.m, to obtain a pigment dispersion
paste (solid content: 48%).
Example 1
Preparation of Cationic Electrodeposition Coating Composition and
Formation of Electrodeposition Coated Film
[0149] The amine-modified epoxy resin obtained in Preparation
example 1 and the blocked isocyanate curing agent obtained in
Preparation example 2 were uniformly mixed in solid content ratio
of 80/20. To the mixture glacial acetic acid was added so that
milligram equivalent value of acid based on 100 g of the binder
resin solid content MEQ(A) was 30, and ion-exchanged water was
slowly added for dilution. MIBK was removed under reduced pressure
to obtain an emulsion having a solid content of 36%.
[0150] 1500 parts of this emulsion, 540 parts of the pigment
dispersing resin obtained in Preparation example 4, 1920 parts of
ion-exchanged water, 40 parts of 10% cerium acetate aqueous
solution, and 10 parts of dibutyltin oxide were mixed, and a
cationic electrodeposition coating composition having a solid
content of 20.0% by weight was obtained. Tg of the
electrodeposition coated film (deposited film) determined by the
calculation from each resin Tg of all resin components in this
electrodeposition coating composition was 15.degree. C. The
electrodeposition coating composition had a volatile organic
content in the coating (VOC) of 0.5%, and a milligram equivalent
value of acid based on 100 g of the resin solid content (MEQ(A)) of
24.2. Electrodeposition coating was conducted using the coating
composition on a surface-treated steel plate having a surface
roughness Ra=0.90 .mu.m (cutoff value: 2.5 mm) at the
electrodeposition bath temperature of 30.degree. C. so that the
electrodeposition coated film after baking had a dry thickness of
15 .mu.m to obtain a cationic electrodeposition coated film
(A-1).
[0151] Formation of Cured Electrodeposition Coated Film
[0152] The resulting cationic electrodeposition coated film (A-1)
was baked at 170.degree. C. for 20 minutes to obtain a cured
electrodeposition coated film as a substrate.
[0153] Formation of Intermediate Coated Film
[0154] Polyester-melamine cured type intermediate coating
composition ("OTO H-880", commercially available from Nippon Paint
Co., Ltd.) was applied on the substrate using rotary aerification
type electrostatic coating apparatus so that a dry thickness was 20
.mu.m, preheated at room temperature for 8 minutes after applying
to form an uncured intermediate coated film.
[0155] Formation of Base Top Coated Film and Clear Top Coated
Film
[0156] Acryl-melamine cured type base top coating composition ("OTO
H-600", commercially available from Nippon Paint Co., Ltd.) was
applied on the intermediate coated film so that a dry thickness was
10 .mu.m, and preheated at room temperature for 7 minutes after
applying to form an uncured base top coated film. Then, Acrylic
acid-epoxy cured type clear top coating composition ("MAC 0-1600",
commercially available from Nippon Paint Co., Ltd.) was applied on
the base top coated film so that a dry thickness was 35 .mu.m. The
intermediate coated film, the base top coated film and the clear
top coated film applied were baked at 140.degree. C. for 30 minutes
to obtain a multi layered coated film.
[0157] Measurement of Centerline Average Roughness of Roughness
Curve (Ra) and Centerline Average Roughness of Profile Curve
(Pa)
[0158] The Ra value and Pa value of the cured electrodeposition
coated film obtained from the electrodeposition coating composition
were measured using an evaluation type surface roughness tester
manufactured by Mitutoyo Corporation according to JIS-B 0601. The
measurement was conducted seven times using a sample comprising
cutoff of 2.5 mm width, and Ra value and Pa value determined from
an average obtained by removing the upper and lower values. The
results are shown in Table 1.
[0159] Measurement of Surface Energy
[0160] The contact angle between the cured electrodeposition coated
film of Examples and Comparative Examples, and DIW (deionized
water), ethylene glycol and methylene iodide using an auto contact
angle meter (PD-X type, manufactured by Kyowa Interface Science
Co., Ltd.) after 30 seconds from dropping the droplet of the
solvents. The surface energy of the cured electrodeposition coated
film determined by the calculation from the resulting measurement
values with the above equation.
[0161] Measurement of Contact Angle
[0162] The contact angle between the cured electrodeposition coated
film of Examples and Comparative Examples, and the intermediate
coating composition ("OTO H-880") using an auto contact angle meter
(PD-X type, manufactured by Kyowa Interface Science Co., Ltd.)
after 30 seconds from dropping the droplet of the intermediate
coating composition.
[0163] Appearance Evaluation of Multi Layered Coated Film
[0164] The finished appearance of multi layered coated film after
baking and curing was measured using a Wave-scan DOI (BYK-Gardner
Co.). Among measurement values, "Wa" value has a correlation to the
item of luster, "Wc" value has a correlation to the item of orange
peel and "Wd" value has a correlation to the item of smoothness in
the appearance of the multi layered coated film. The evaluation was
conducted from the Wa, Wc and Wd values. The smaller the value is,
the better the appearance is.
Example 2
[0165] The amine-modified epoxy resin obtained in Preparation
example 1 and the blocked isocyanate curing agent obtained in
Preparation example 3 were uniformly mixed in solid content ratio
of 70/30. To the mixture glacial acetic acid was added so that
milligram equivalent value of acid based on 100 g of the binder
resin solid content MEQ(A) was 35, and ion-exchanged water was
slowly added for dilution. MIBK was removed under reduced pressure
to obtain an emulsion having a solid content of 36%.
[0166] 1500 parts of this emulsion, 280 parts of the pigment
dispersing resin obtained in Preparation example 4, 1560 parts of
ion-exchanged water, 20 parts of 10% cerium acetate aqueous
solution, and 10 parts of dibutyltin oxide were mixed, and a
cationic electrodeposition coating composition having a solid
content of 20% by weight was obtained. Tg of the electrodeposition
coated film (deposited film) determined by the calculation from
each resin Tg of all resin components in this electrodeposition
coating composition was 14.degree. C. The electrodeposition coating
composition had a volatile organic content in the coating (VOC) of
0.5%, and a milligram equivalent value of acid based on 100 g of
the resin solid content (MEQ(A)) of 25.5. Electrodeposition coating
was conducted using the coating composition on a surface-treated
steel plate having a surface roughness Ra=0.90 .mu.m (cutoff value:
2.5 mm) at the electrodeposition bath temperature of 30.degree. C.
to obtain a cationic electrodeposition coated film (A-2).
[0167] A multi layered coated film was obtained as described in
Example 1 except for the preparation of cationic electrodeposition
coating composition and formation of electrodeposition coated film
described above. The resulting multi layered coated film was
evaluated as described in Example 1. The results are shown in Table
1.
Example 3
[0168] The amine-modified epoxy resin obtained in Preparation
example 1 and the blocked isocyanate curing agent obtained in
Preparation example 2 were uniformly mixed in solid content ratio
of 70/30. To the mixture glacial acetic acid was added so that
milligram equivalent value of acid based on 100 g of the binder
resin solid content MEQ(A) was 30, and ion-exchanged water was
slowly added for dilution. MIBK was removed under reduced pressure
to obtain an emulsion having a solid content of 36%.
[0169] 1500 parts of this emulsion, 540 parts of the pigment
dispersing resin obtained in Preparation example 4, 1920 parts of
ion-exchanged water, 40 parts of 10% cerium acetate aqueous
solution, and 10 parts of dibutyltin oxide were mixed, and a
cationic electrodeposition coating composition having a solid
content of 20% by weight was obtained. Tg of the electrodeposition
coated film (deposited film) determined by the calculation from
each resin Tg of all resin components in this electrodeposition
coating composition was 10.degree. C. The electrodeposition coating
composition had a volatile organic content in the coating (VOC) of
0.5%, and a milligram equivalent value of acid based on 100 g of
the resin solid content (MEQ(A)) of 24.2. Electrodeposition coating
was conducted using the coating composition on a surface-treated
steel plate having a surface roughness Ra=0.60 .mu.m (cutoff value:
2.5 mm) at the electrodeposition bath temperature of 30.degree. C.
to obtain a cationic electrodeposition coated film (A-3).
[0170] A multi layered coated film was obtained as described in
Example 1 except for the preparation of cationic electrodeposition
coating composition and formation of electrodeposition coated film
described above. The resulting multi layered coated film was
evaluated as described in Example 1. The results are shown in Table
1.
Example 4
[0171] The amine-modified epoxy resin obtained in Preparation
example 1 and the blocked isocyanate curing agent obtained in
Preparation example 2 were uniformly mixed in solid content ratio
of 80/20. To the mixture glacial acetic acid was added so that
milligram equivalent value of acid based on 100 g of the binder
resin solid content MEQ(A) was 30, and ion-exchanged water was
slowly added for dilution. MIBK was removed under reduced pressure
to obtain an emulsion having a solid content of 36%.
[0172] 1500 parts of this emulsion, 280 parts of the pigment
dispersing resin obtained in Preparation example 4, 1560 parts of
ion-exchanged water, 40 parts of 10% cerium acetate aqueous
solution, and 10 parts of dibutyltin oxide were mixed, and a
cationic electrodeposition coating composition having a solid
content of 20% by weight was obtained. Tg of the electrodeposition
coated film (deposited film) determined by the calculation from
each resin Tg of all resin components in this electrodeposition
coating composition was 15.degree. C. The electrodeposition coating
composition had a volatile organic content in the coating (VOC) of
0.5%, and a milligram equivalent value of acid based on 100 g of
the resin solid content (MEQ(A)) of 24.2. Electrodeposition coating
was conducted using the coating composition on a surface-treated
steel plate having a surface roughness Ra=0.20 .mu.m (cutoff value:
2.5 mm) at the electrodeposition bath temperature of 30.degree. C.
to obtain a cationic electrodeposition coated film (A-4).
[0173] A multi layered coated film was obtained as described in
Example 1 except for the preparation of cationic electrodeposition
coating composition and formation of electrodeposition coated film
described above. The resulting multi layered coated film was
evaluated as described in Example 1. The results are shown in Table
1.
Example 5
[0174] The amine-modified epoxy resin obtained in Preparation
example 1 and the blocked isocyanate curing agent obtained in
Preparation example 2 were uniformly mixed in solid content ratio
of 60/40. To the mixture glacial acetic acid was added so that
milligram equivalent value of acid based on 100 g of the binder
resin solid content MEQ(A) was 30, and ion-exchanged water was
slowly added for dilution. MIBK was removed under reduced pressure
to obtain an emulsion having a solid content of 36%.
[0175] 1500 parts of this emulsion, 540 parts of the pigment
dispersing resin obtained in Preparation example 4, 1920 parts of
ion-exchanged water, 40 parts of 10% cerium acetate aqueous
solution, and 10 parts of dibutyltin oxide were mixed, and a
cationic electrodeposition coating composition having a solid
content of 20% by weight was obtained. Tg of the electrodeposition
coated film (deposited film) determined by the calculation from
each resin Tg of all resin components in this electrodeposition
coating composition was 4.degree. C. The electrodeposition coating
composition had a volatile organic content in the coating (VOC) of
0.5%, and a milligram equivalent value of acid based on 100 g of
the resin solid content (MEQ(A)) of 24.2. Electrodeposition coating
was conducted using the coating composition on a surface-treated
steel plate having a surface roughness Ra=0.60 .mu.m (cutoff value:
2.5 mm) at the electrodeposition bath temperature of 30.degree. C.
to obtain a cationic electrodeposition coated film (A-5).
[0176] A multi layered coated film was obtained as described in
Example 1 except for the preparation of cationic electrodeposition
coating composition and formation of electrodeposition coated film
described above. The resulting multi layered coated film was
evaluated as described in Example 1. The results are shown in Table
1.
Comparative Example 1
[0177] The amine-modified epoxy resin obtained in Preparation
example 1 and the blocked isocyanate curing agent obtained in
Preparation example 2 were uniformly mixed in solid content ratio
of 70/30. To the mixture glacial acetic acid was added so that
milligram equivalent value of acid based on 100 g of the binder
resin solid content MEQ(A) was 30, and ion-exchanged water was
slowly added for dilution. MIBK was removed under reduced pressure
to obtain an emulsion having a solid content of 36%.
[0178] 1500 parts of this emulsion, 540 parts of the pigment
dispersing resin obtained in Preparation example 4, parts of
ion-exchanged water, 40 parts of 10% cerium acetate aqueous
solution, and 10 parts of dibutyltin oxide were mixed, and a
cationic electrodeposition coating composition having a solid
content of 20% by weight was obtained. Tg of the electrodeposition
coated film (deposited film) determined by the calculation from
each resin Tg of all resin components in this electrodeposition
coating composition was 10.degree. C. The electrodeposition coating
composition had a volatile organic content in the coating (VOC) of
0.5%, and a milligram equivalent value of acid based on 100 g of
the resin solid content (MEQ(A)) of 24.2. Electrodeposition coating
was conducted using the coating composition on a surface-treated
steel plate having a surface roughness Ra=0.90 .mu.m (cutoff value:
2.5 mm) at the electrodeposition bath temperature of 30.degree. C.
to obtain a cationic electrodeposition coated film (B-1).
[0179] A multi layered coated film was obtained as described in
Example 1 except for the preparation of cationic electrodeposition
coating composition and formation of electrodeposition coated film
described above. The resulting multi layered coated film was
evaluated as described in Example 1. The results are shown in Table
1.
Comparative Example 2
[0180] The amine-modified epoxy resin obtained in Preparation
example 1 and the blocked isocyanate curing agent obtained in
Preparation example 2 were uniformly mixed in solid content ratio
of 70/30. To the mixture glacial acetic acid was added so that
milligram equivalent value of acid based on 100 g of the binder
resin solid content MEQ(A) was 30, and ion-exchanged water was
slowly added for dilution. MIBK was removed under reduced pressure
to obtain an emulsion having a solid content of 36%.
[0181] 1500 parts of this emulsion, 540 parts of the pigment
dispersing resin obtained in Preparation example 4, 1920 parts of
ion-exchanged water, 40 parts of 10% cerium acetate aqueous
solution, and 10 parts of dibutyltin oxide were mixed, and a
cationic electrodeposition coating composition having a solid
content of 20% by weight was obtained. Tg of the electrodeposition
coated film (deposited film) determined by the calculation from
each resin Tg of all resin components in this electrodeposition
coating composition was 10.degree. C. The electrodeposition coating
composition had a volatile organic content in the coating (VOC) of
0.5%, and a milligram equivalent value of acid based on 100 g of
the resin solid content (MEQ(A)) of 24.2. Electrodeposition coating
was conducted using the coating composition on a surface-treated
steel plate having a surface roughness Ra=1.20 .mu.m (cutoff value:
2.5 mm) at the electrodeposition bath temperature of 30.degree. C.
to obtain a cationic electrodeposition coated film (B-2).
[0182] A multi layered coated film was obtained as described in
Example 1 except for the preparation of cationic electrodeposition
coating composition and formation of electrodeposition coated film
described above. The resulting multi layered coated film was
evaluated as described in Example 1. The results are shown in Table
1.
Example 6
[0183] Preparation of Cationic Electrodeposition Coating
Composition and Formation of Electrodeposition Coated Film
[0184] The amine-modified epoxy resin obtained in Preparation
example 1 and the blocked isocyanate curing agent obtained in
Preparation example 2 were uniformly mixed in solid content ratio
of 70/30. To the mixture glacial acetic acid was added so that
milligram equivalent value of acid based on 100 g of the binder
resin solid content MEQ(A) was 30, and ion-exchanged water was
slowly added for dilution. MIBK was removed under reduced pressure
to obtain an emulsion having a solid content of 36%.
[0185] 1500 parts of this emulsion, 540 parts of the pigment
dispersing resin obtained in Preparation example 4, 1920 parts of
ion-exchanged water, 40 parts of 10% cerium acetate aqueous
solution, and 10 parts of dibutyltin oxide were mixed, and a
cationic electrodeposition coating composition having a solid
content of 20.0% by weight was obtained. The electrodeposition
coating composition had a volatile organic content in the coating
(VOC) of 0.5%, and a milligram equivalent value of acid based on
100 g of the resin solid content (MEQ(A)) of 24.2.
Electrodeposition coating was conducted using the resulting
cationic electrodeposition coating composition at the
electrodeposition bath temperature of 30.degree. C. to obtain a
cationic electrodeposition coated film. The resulting deposited
coated film was baked at 160.degree. C. for 20 minutes to obtain a
cured electrodeposition coated film (A-6) as a substrate.
[0186] Formation of Intermediate Coated Film
[0187] Polyester-melamine cured type intermediate coating
composition ("OTO H-880", commercially available from Nippon Paint
Co., Ltd.) was applied on the substrate using rotary aerification
type electrostatic coating apparatus so that a dry thickness was 20
.mu.m, preheated at room temperature for 8 minutes after applying
to form an uncured intermediate coated film.
[0188] Formation of Base Top Coated Film and Clear Top Coated
Film
[0189] Acryl-melamine cured type base top coating composition ("OTO
H-600", commercially available from Nippon Paint Co., Ltd.) was
applied on the intermediate coated film so that a dry thickness was
10 .mu.m, and preheated at room temperature for 7 minutes after
applying to form an uncured base top coated film. Then, Acrylic
acid-epoxy cured type clear top coating composition ("MAC 0-1600",
commercially available from Nippon Paint Co., Ltd.) was applied on
the base top coated film so that a dry thickness was 35 .mu.m. The
intermediate coated film, the base top coated film and the clear
top coated film applied were baked at 140.degree. C. for 30 minutes
to obtain a multi layered coated film.
[0190] Measurement of Dynamic Tg of Cured Electrodeposition Coated
Film
[0191] The electrodeposition coating composition prepared in
Examples and Comparative Examples was electrodeposition coated on a
tinplate for dynamic viscoelastic measurement to obtain an
electrodeposition coated film. The electrodeposition coated film
was then baked at 170.degree. C. for 20 minutes to obtain a cured
electrodeposition coated film. The resulting coated film was
separated from the tinplate using mercury and cut it to prepare a
sample for the measurement. The sample was heated from room
temperature to 200.degree. C. at a raising rate of temperature of
2.degree. C. per one minute and vibrated at a frequency of 10 Hz to
measure viscoelasticity by using Rheovibron model RHEO 2000, 3000
(trade name), manufactured by Orientec Co., Ltd. A ratio (tan
.delta.) of storage elasticity (E') to loss elasticity (E") was
calculated and its inflexion point (a temperature at a peak of tan
.delta.) was determined to obtain a dynamic Tg.
[0192] Measurement of Crosslinking Density of Cured
Electrodeposition Coated Film
[0193] The crosslinking density was determined by calculating with
the resulting storage elasticity (E') obtained in the measurement
of the dynamic Tg from the equation described above.
[0194] Appearance Evaluation of Multi Layered Coated Film
[0195] The finished appearance of multi layered coated film after
baking and curing was measured using a Wave-scan DOI (BYK-Gardner
Co.). Among measurement values, "Wa" value has a correlation to the
item of luster, "Wc" value has a correlation to the item of orange
peel and "Wd" value has a correlation to the item of smoothness in
the appearance of the multi layered coated film. The evaluation was
conducted from the Wa, Wc and Wd values. The smaller the value is,
the better the appearance is.
Example 7
[0196] The amine-modified epoxy resin obtained in Preparation
example 1 and the blocked isocyanate curing agent obtained in
Preparation example 3 were uniformly mixed in solid content ratio
of 80/20. To the mixture glacial acetic acid was added so that
milligram equivalent value of acid based on 100 g of the binder
resin solid content MEQ(A) was 35, and ion-exchanged water was
slowly added for dilution. MIBK was removed under reduced pressure
to obtain an emulsion having a solid content of 36%.
[0197] 1500 parts of this emulsion, 540 parts of the pigment
dispersing resin obtained in Preparation example 4, 1920 parts of
ion-exchanged water, 20 parts of 10% cerium acetate aqueous
solution, and 10 parts of dibutyltin oxide were mixed, and a
cationic electrodeposition coating composition having a solid
content of 20% by weight was obtained. The electrodeposition
coating composition had a volatile organic content in the coating
(VOC) of 0.5%, and a milligram equivalent value of acid based on
100 g of the resin solid content (MEQ(A)) of 25.5.
Electrodeposition coating was conducted using the resulting
cationic electrodeposition coating composition at the
electrodeposition bath temperature of 30.degree. C. to obtain a
cationic electrodeposition coated film. The resulting deposited
coated film was baked at 160.degree. C. for 20 minutes to obtain a
cured electrodeposition coated film (A-7) as a substrate.
[0198] A multi layered coated film was obtained as described in
Example 6 except for the preparation of cationic electrodeposition
coating composition and formation of electrodeposition coated film
described above. The resulting multi layered coated film was
evaluated as described in Example 6. The results are shown in Table
2.
Example 8
[0199] The amine-modified epoxy resin obtained in Preparation
example 1 and the blocked isocyanate curing agent obtained in
Preparation example 2 were uniformly mixed in solid content ratio
of 80/20. To the mixture glacial acetic acid was added so that
milligram equivalent value of acid based on 100 g of the binder
resin solid content MEQ(A) was 30, and ion-exchanged water was
slowly added for dilution. MIBK was removed under reduced pressure
to obtain an emulsion having a solid content of 36%.
[0200] 1500 parts of this emulsion, 540 parts of the pigment
dispersing resin obtained in Preparation example 4, 1920 parts of
ion-exchanged water, 40 parts of 10% cerium acetate aqueous
solution, and 10 parts of dibutyltin oxide were mixed, and a
cationic electrodeposition coating composition having a solid
content of 20% by weight was obtained. The electrodeposition
coating composition had a volatile organic content in the coating
(VOC) of 0.5%, and a milligram equivalent value of acid based on
100 g of the resin solid content (MEQ(A)) of 24.2.
Electrodeposition coating was conducted using the resulting
cationic electrodeposition coating composition at the
electrodeposition bath temperature of 30.degree. C. to obtain a
cationic electrodeposition coated film. The resulting deposited
coated film was baked at 180.degree. C. for 20 minutes to obtain a
cured electrodeposition coated film (A-8) as a substrate.
[0201] A multi layered coated film was obtained as described in
Example 6 except for the preparation of cationic electrodeposition
coating composition and formation of electrodeposition coated film
described above. The resulting multi layered coated film was
evaluated as described in Example 6. The results are shown in Table
2.
Example 9
[0202] The amine-modified epoxy resin obtained in Preparation
example 1 and the blocked isocyanate curing agent obtained in
Preparation example 2 were uniformly mixed in solid content ratio
of 60/40. To the mixture glacial acetic acid was added so that
milligram equivalent value of acid based on 100 g of the binder
resin solid content MEQ(A) was 30, and ion-exchanged water was
slowly added for dilution. MIBK was removed under reduced pressure
to obtain an emulsion having a solid content of 36%.
[0203] 1500 parts of this emulsion, 540 parts of the pigment
dispersing resin obtained in Preparation example 4, 1920 parts of
ion-exchanged water, 40 parts of 10% cerium acetate aqueous
solution, and 10 parts of dibutyltin oxide were mixed, and a
cationic electrodeposition coating composition having a solid
content of 20% by weight was obtained. The electrodeposition
coating composition had a volatile organic content in the coating
(VOC) of 0.5%, and a milligram equivalent value of acid based on
100 g of the resin solid content (MEQ(A)) of 24.2.
Electrodeposition coating was conducted using the resulting
cationic electrodeposition coating composition at the
electrodeposition bath temperature of 30.degree. C. to obtain a
cationic electrodeposition coated film. The resulting deposited
coated film was baked at 180.degree. C. for 20 minutes to obtain a
cured electrodeposition coated film (A-9) as a substrate.
[0204] A multi layered coated film was obtained as described in
Example 6 except for the preparation of cationic electrodeposition
coating composition and formation of electrodeposition coated film
described above. The resulting multi layered coated film was
evaluated as described in Example 6. The results are shown in Table
2.
Comparative Example 3
[0205] The amine-modified epoxy resin obtained in Preparation
example 1 and the blocked isocyanate curing agent obtained in
Preparation example 2 were uniformly mixed in solid content ratio
of 90/10. To the mixture glacial acetic acid was added so that
milligram equivalent value of acid based on 100 g of the binder
resin solid content MEQ(A) was 30, and ion-exchanged water was
slowly added for dilution. MIBK was removed under reduced pressure
to obtain an emulsion having a solid content of 36%.
[0206] 1500 parts of this emulsion, 540 parts of the pigment
dispersing resin obtained in Preparation example 4, 1920 parts of
ion-exchanged water, 40 parts of 10% cerium acetate aqueous
solution, and 10 parts of dibutyltin oxide were mixed, and a
cationic electrodeposition coating composition having a solid
content of 20% by weight was obtained. The electrodeposition
coating composition had a volatile organic content in the coating
(VOC) of 0.5%, and a milligram equivalent value of acid based on
100 g of the resin solid content (MEQ(A)) of 24.2.
Electrodeposition coating was conducted using the resulting
cationic electrodeposition coating composition at the
electrodeposition bath temperature of 30.degree. C. to obtain a
cationic electrodeposition coated film. The resulting deposited
coated film was baked at 160.degree. C. for 20 minutes to obtain a
cured electrodeposition coated film (B-3) as a substrate.
[0207] A multi layered coated film was obtained as described in
Example 6 except for the preparation of cationic electrodeposition
coating composition and formation of electrodeposition coated film
described above. The resulting multi layered coated film was
evaluated as described in Example 6. The results are shown in Table
2.
Comparative Example 4
[0208] The amine-modified epoxy resin obtained in Preparation
example 1 and the blocked isocyanate curing agent obtained in
Preparation example 2 were uniformly mixed in solid content ratio
of 80/20. To the mixture glacial acetic acid was added so that
milligram equivalent value of acid based on 100 g of the binder
resin solid content MEQ(A) was 30, and ion-exchanged water was
slowly added for dilution. MIBK was removed under reduced pressure
to obtain an emulsion having a solid content of 36%.
[0209] 1500 parts of this emulsion, 540 parts of the pigment
dispersing resin obtained in Preparation example 4, 1920 parts of
ion-exchanged water, 40 parts of 10% cerium acetate aqueous
solution, and 10 parts of dibutyltin oxide were mixed, and a
cationic electrodeposition coating composition having a solid
content of 20% by weight was obtained. The electrodeposition
coating composition had a volatile organic content in the coating
(VOC) of 0.5%, and a milligram equivalent value of acid based on
100 g of the resin solid content (MEQ(A)) of 24.2.
Electrodeposition coating was conducted using the resulting
cationic electrodeposition coating composition at the
electrodeposition bath temperature of 30.degree. C. to obtain a
cationic electrodeposition coated film. The resulting deposited
coated film was baked at 150.degree. C. for 20 minutes to obtain a
cured electrodeposition coated film (B-4) as a substrate.
[0210] A multi layered coated film was obtained as described in
Example 6 except for the preparation of cationic electrodeposition
coating composition and formation of electrodeposition coated film
described above. The resulting multi layered coated film was
evaluated as described in Example 6. The results are shown in Table
2.
Comparative Example 5
[0211] The amine-modified epoxy resin obtained in Preparation
example 1 and the blocked isocyanate curing agent obtained in
Preparation example 2 were uniformly mixed in solid content ratio
of 70/30. To the mixture glacial acetic acid was added so that
milligram equivalent value of acid based on 100 g of the binder
resin solid content MEQ(A) was 30, and ion-exchanged water was
slowly added for dilution. MIBK was removed under reduced pressure
to obtain an emulsion having a solid content of 36%.
[0212] 1500 parts of this emulsion, 280 parts of the pigment
dispersing resin obtained in Preparation example 4, 1560 parts of
ion-exchanged water, 40 parts of 10% cerium acetate aqueous
solution, and 10 parts of dibutyltin oxide were mixed, and a
cationic electrodeposition coating composition having a solid
content of 20% by weight was obtained. The electrodeposition
coating composition had a volatile organic content in the coating
(VOC) of 0.5%, and a milligram equivalent value of acid based on
100 g of the resin solid content (MEQ(A)) of 24.2.
Electrodeposition coating was conducted using the resulting
cationic electrodeposition coating composition at the
electrodeposition bath temperature of 30.degree. C. to obtain a
cationic electrodeposition coated film. The resulting deposited
coated film was baked at 180.degree. C. for 20 minutes to obtain a
cured electrodeposition coated film (B-S) as a substrate.
[0213] A multi layered coated film was obtained as described in
Example 6 except for the preparation of cationic electrodeposition
coating composition and formation of electrodeposition coated film
described above. The resulting multi layered coated film was
evaluated as described in Example 6. The results are shown in Table
2.
[0214] Test Results
1 TABLE 1 Comparative Example No. Example No. 1 2 3 4 5 1 2 A-1 A-2
A-3 A-4 A-5 B-1 B-1 Evaluation of cured electrodeposition coated
film Ra(.mu.m) (Cutoff 2.5) 0.25 0.23 0.23 0.05 0.19 0.25 0.3
Pa(.mu.m) (Cutoff 2.5) 0.3 0.24 0.28 0.05 0.21 0.34 0.44 Surface
energy 37 39 41 37 44 41 42 (mJ/m.sup.2) Contact angle to 17 20 25
17 36 32 33 intermediate coating composition (degree) Evaluation of
appearance of multi layered coated film Wa 8 9 8 7 10 12 15 Wc 14
16 16 12 20 23 27 Wd 14 16 17 11 17 20 23
[0215]
2 TABLE 2 Comparative Example Example No. No. 6 7 8 9 3 4 5 A-6 A-7
A-8 A-9 B-3 B-4 B-5 Evaluation of cured electrodeposition coated
film Cross- 1.42 1.20 1.62 2.51 0.91 1.10 1.99 linking density
(mmol/ cc) Dynam- 108 100 110 130 110 101 90 ic Tg (.degree. C.)
Evaluation of appearance of multi layered coated film Wa
.smallcircle.(8) .smallcircle.(9) .smallcircle.(8) .smallcircle.(8)
x(12) x(12) x(15) Wc .smallcircle.(18) .smallcircle.(17)
.smallcircle.(17) .smallcircle.(17) x(21) x(21) x(24) Wd
.smallcircle.(16) .smallcircle.(16) .smallcircle.(16)
.smallcircle.(17) x(22) x(21) x(22) Wa .smallcircle.: not more than
10, x: not less than 11 Wc .smallcircle.: not more than 20, x: not
less than 21 Wd .smallcircle.: not more than 20, x: not less than
21
[0216] As is apparent from the results shown in Table 1, the cured
electrodeposition coated films of the present invention of Examples
1 to 5 had good surface condition. The multi layered coated films
having good appearance without appearance defects from the
electrodeposition coated films were obtained by three coat one bake
coating on the cured electrodeposition coated films. On the other
hand, in Comparative Examples 1 to 2, since the electrodeposition
coated films had appearance defects therefrom, the multi layered
coated films having good appearance were not obtained.
[0217] As is apparent from the results shown in Table 2, the multi
layered coated films obtained by three coat one bake coating on the
cured electrodeposition coated films of the present invention of
Examples 6 to 9 had good appearance. On the other hand, in
Comparative Examples 3 to 5, the multi layered coated films having
good appearance were not obtained.
* * * * *