U.S. patent application number 12/312078 was filed with the patent office on 2010-05-13 for cationic electrodeposition coating and application thereof.
Invention is credited to Teruzo Toi.
Application Number | 20100116673 12/312078 |
Document ID | / |
Family ID | 39324591 |
Filed Date | 2010-05-13 |
United States Patent
Application |
20100116673 |
Kind Code |
A1 |
Toi; Teruzo |
May 13, 2010 |
CATIONIC ELECTRODEPOSITION COATING AND APPLICATION THEREOF
Abstract
The present invention relates to a cationic electrodeposition
coating composition, which provides an uncured electrodeposited
film having storage elasticity modulus (G') at 140.degree. C.
within a range of from 80 to 500 dyn/cm.sup.2 and loss elasticity
modulus (G'') at 80.degree. C. within a range of from 10 to 150
dyn/cm.sup.2, and which is superior in smoothness and edge
coatability; and a method for establishing both of smoothness and
edge coatability therewith; as well as; a cationic
electrodeposition coating composition comprising crosslinked resin
particles having an average particle size within a range of from
1.0 to 3.0 .mu.m and thermal softening temperature within a range
of from 120 to 180.degree. C.; and a method for producing a
cationic electrodeposition film having established smoothness and
edge coatability, wherein the cationic electrodeposition film is
prepared by applying a voltage to an article immersed in a cationic
electrodeposition coating composition, and wherein the cationic
electrodeposition coating composition comprises crosslinked resin
particles having an average particle size within a range of from
1.0 to 3.0 .mu.m and thermal softening temperature within a range
of from 120 to 180.degree. C. The present invention can provide a
method for establishing both of surface smoothness and edge
coatability of the cationic electrodeposition coating composition,
and cationic electrodeposition coating composition which can
provide an electrodeposition film having excellent surface
conditions.
Inventors: |
Toi; Teruzo; (Osaka,
JP) |
Correspondence
Address: |
WENDEROTH, LIND & PONACK, L.L.P.
1030 15th Street, N.W.,, Suite 400 East
Washington
DC
20005-1503
US
|
Family ID: |
39324591 |
Appl. No.: |
12/312078 |
Filed: |
October 24, 2007 |
PCT Filed: |
October 24, 2007 |
PCT NO: |
PCT/JP2007/070723 |
371 Date: |
January 8, 2010 |
Current U.S.
Class: |
205/98 |
Current CPC
Class: |
C09D 163/00 20130101;
C08G 59/4028 20130101; C09D 5/4438 20130101; C25D 13/04 20130101;
C08G 18/8077 20130101; C08G 18/643 20130101; C09D 5/4492 20130101;
C09D 175/04 20130101; C08G 18/8064 20130101 |
Class at
Publication: |
205/98 |
International
Class: |
C25D 21/00 20060101
C25D021/00 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 25, 2006 |
JP |
2006-290003 |
Oct 25, 2006 |
JP |
2006-290007 |
Claims
1. A cationic electrodeposition coating composition, which provides
an uncured electrodeposited film having storage elasticity modulus
(G') at 140.degree. C. within a range of from 80 to 500
dyn/cm.sup.2 and loss elasticity modulus (G'') at 80.degree. C.
within a range of from 10 to 150 dyn/cm.sup.2, and which is
superior in smoothness and edge coatability.
2. The cationic electrodeposition coating composition according to
claim 1, which comprises a cationic epoxy resin, a blocked
isocyanate curing agent, and if necessary, a crosslinked resin
particle and/or an inorganic pigment.
3. A method for producing a cationic electrodeposition film having
established smoothness and edge coatability, wherein the cationic
electrodeposition film is prepared by applying a voltage to an
article immersed in a cationic electrodeposition coating
composition, which includes steps of: adjusting storage elasticity
modulus of an uncured electrodeposited film of the cationic
electrodeposition coating composition (G') at 140.degree. C. within
a range of from 80 to 500 dyn/cm.sup.2, and adjusting loss
elasticity modulus of an uncured electrodeposited film of the
cationic electrodeposition coating composition (G'') at 80.degree.
C. within a range of from 10 to 150 dyn/cm.sup.2.
4. The method according to claim 3, wherein crosslinked resin
particles having an average particle size within a range of from
1.0 to 3.0 .mu.m are added to the cationic electrodeposition
coating composition in order to adjust storage elasticity modulus
and loss elasticity modulus.
5. The method according to claim 4, wherein content of the
crosslinked resin particles is 3 to 15% by weight relative to
weight of resin solid contents in the cationic electrodeposition
coating composition.
6. The method according to claim 3, wherein an inorganic pigment is
added to the cationic electrodeposition coating composition,
wherein content of the inorganic pigment is 10 to 20% by weight
relative to weight of solid contents in the cationic
electrodeposition coating composition, in order to adjust storage
elasticity modulus and loss elasticity modulus.
7. The method according to claim 3, wherein crosslinked resin
particles having an average particle size within a range of from
1.0 to 3.0 .mu.m and an inorganic pigment are added to the cationic
electrodeposition coating composition, wherein content of the
inorganic pigment is 0.5 to 10% by weight relative to weight of
solid contents in the cationic electrodeposition coating
composition, in order to adjust storage elasticity modulus and loss
elasticity modulus.
8. The method according to claim 7, wherein content of the
crosslinked resin particles is 3 to 15% by weight relative to
weight of resin solid contents in the cationic electrodeposition
coating composition.
Description
TECHNICAL FIELD
[0001] The present invention relates to a cationic
electrodeposition coating composition superior in smoothness and
edge coatability and a method for satisfying both of the smoothness
and the edge coatability of a cationic electrodeposition film using
the same.
[0002] Further, the present invention relates to a cationic
electrodeposition coating composition superior in smoothness and
edge coatability, specifically a cationic electrodeposition coating
composition superior in smoothness and edge coatability which
comprises a specific crosslinked resin particle, and a method for
satisfying both of the smoothness and edge coatability of a
cationic electrodeposition film using the same.
BACKGROUND OF THE INVENTION
[0003] Electrodeposition coating is a coating process carried out
by immersing an article to be coated in an electrodeposition
coating composition and applying a voltage. Since the
electrodeposition coating process can automatically and
continuously coat an article to be coated having a complicate shape
to a nicety, it has been widely and practically used as a process
for primarily coating a large size article having complicate shape
such as, in particular, an automobile body.
[0004] Since the electrodeposition coating is a coating on an
article, it is naturally desirable that coated surface is smooth.
Further, the perforation portion of metal and the like have sharp
edge and unless a coated film is adequately coated on the edge
portion, anticorrosive performance is deteriorated. Consequently,
both of surface smoothness and edge coatability are performances
required for the electrodeposition coating. On the other hand, the
surface smoothness is obtained by lowering the viscosity of the
uncured coating film at curing by baking to be fluidized, but the
edge coatability is obtained by keeping so as not lowering the
viscosity of the uncured coating film. Namely, the edge coatability
requires the suppression of sagging of coating film at curing the
coating film and the coating film remains also at sharp edge.
Namely, the surface smoothness and the edge coatability are
conflicting performances.
[0005] Technology relating to the coating film viscosity of the
electrodeposition film is described in Japanese Patent Application
Publication No. 2002-285077 (Patent document 1) and it describes an
electrodeposition coating composition for an electric wire wherein
the minimum coating film viscosity at the curing process of coating
film is between 30 to 150 PaS (claim 3). The patent document 1
describes edge coatability and the like can be improved without
sagging at melt by adjusting the minimum coating film viscosity at
the curing process of coating film.
[0006] Japanese Patent Application Publication No. 6-65791 (Patent
document 2) discloses a process for coating an anti-chipping primer
on an uncured coating film surface formed by coating a cationic
electrodeposition coating composition, further carrying out an
intermediate coating and a top coating, and curing the three layers
simultaneously, wherein the minimum melt viscosity during curing
the coating film of the cationic electrodeposition coating
composition is 10.sup.4 to 10.sup.8 cps. It discloses that since
the three layers of the coating films are baked only at once,
coating steps are shortened, it is superior in edge covering
property and the resulting coating film consisting of a plurality
of layers is superior in finishing property and anti-chipping
property. The publication discloses the finishing property and edge
covering property in the coating film consisting of a plurality of
layers, but does not study the finishing property and the edge
covering property on an electrodeposition film itself. On the other
hand, it has been conventionally carried out in general coating
compositions including the cationic electrodeposition coating
composition of the present invention that the viscosity of the
coating film is controlled using a particle described later.
[0007] By the way, the reduction of ash contents in the
electrodeposition coating composition has been recently promoted.
The reduction of ash contents is that the amount of solid
components with a high specific gravity such as an inorganic
pigment is reduced and that sedimentation is designed not to occur
in the solid contents of the electrodeposition coating composition.
The reduction of ash contents reduces energy and labor for stirring
an electrodeposition bath hitherto for prevention of sedimentation.
Accordingly, when the content of an inorganic pigment is reduced in
order to correspond the request of the above-mentioned reduction of
ash contents, the quantity of resin contents in the coating
composition is relatively enhanced, the viscosity of the uncured
coating film obtained by the electrodeposition coating cannot be
appropriately increased, and as a result, the control of sagging at
an edge portion cannot be suitably adjusted to the lower edge
coatability.
[0008] On the other hand, since solid concentration of about 20% by
weight is used in the current cationic electrodeposition coating
composition, rinsing with water is carried out at several steps
separately after the electrodeposition coating, and a baking step
is carried out after completely removing the electrodeposition
coating composition adhered on the article unnecessarily, in
particular, its solid contents. Accordingly, a large quantity of
rinsing water is used, the rinsing step with water is elongated and
the reduction of rinsing water and the shortening of the rinsing
steps with water has been recently desired. As the means for
shortening the rinsing step with water, the further lowering of
solid concentration in the coating composition of 20% by weight,
so-called low solid content is required. However, when such low
solid content is simply carried out, the sedimentation of solid
contents in the electrodeposition coating composition occurs easily
because of the lowering of the coating composition viscosity, and
the like. When the content of an inorganic pigment is further
reduced as described above, the sedimentation of solid contents
occur further easily. Consequently, the stirring in an
electrodeposition bath must be carried out in order to prevent the
sedimentation, and the reduction of energy load is difficult.
Namely, a cationic electrodeposition coating composition capable of
controlling viscoelasticity so as to easily carry out the edge
coatability, and superior in surface smoothness and prevent the
sedimentation, has been desired, even if low solid content is
realized for energy saving and the shortening of steps.
[0009] In relation to a means for obtaining such coating
composition, namely a coating composition improved in thixotropy,
there exist several technologies adding crosslinked resin particles
to the cationic electrodeposition coating composition. Japanese
Patent Application Publication No. 2005-23232 (Patent document 3)
discloses that minute resin particles with a particle size of 0.01
to 0.2 .mu.m whose inside was crosslinked are added to a cationic
electrodeposition coating composition (Patent document 3, claim 6).
It has been conventionally existed as improving thixotropy that
resin particles with such small sizes are added in the
electrodeposition coating composition.
[0010] Japanese Patent Application Publication No. 2002-212488
(Patent document 4) discloses a cationic electrodeposition coating
composition that comprises crosslinked resin particles obtained by
carrying out the emulsion polymerization of
.alpha.,.beta.-ethylenically unsaturated monomer mixture using an
acryl resin having an ammonium group as an emulsifier, in order to
improve the anticorrosive property of an edge portion of an
article. The resin particles obtained herein is small with a
particle size of 0.05 to 0.3 .mu.m. However, when a crosslinked
resin particles with an average particle size of 1.0 .mu.m or less
are added in an electrodeposition coating composition, the
smoothness of the resulting coating film is lowered.
Patent document 1: Japanese Patent Application Publication No.
2002-285077 Patent document 2: Japanese Patent Application
Publication No. 6-65791 Patent document 3: Japanese Patent
Application Publication No. 2005-23232 Patent document 4: Japanese
Patent Application Publication No. 2002-212488
SUMMARY OF THE INVENTION
Disclosure of the Invention
Problem to be Solved by the Invention
[0011] It is the object of the present invention to provide a
method for satisfying both of the conflicting performances of the
surface smoothness and edge coatability in a cationic
electrodeposition coating composition, as described above.
[0012] Further, it is the object of the present invention to
provide a method for lowering the solid concentration in a cationic
electrodeposition coating composition, preventing the sedimentation
of the coating composition for reduction of ash contents, and
satisfying both of the conflicting performances of the surface
smoothness and edge coatability in a cationic electrodeposition
coating composition, as described above.
Means for Solving Problem
[0013] Accordingly, the present invention provides a cationic
electrodeposition coating composition, which provides an uncured
electrodeposited film having storage elasticity modulus (G') at
140.degree. C. within a range of from 80 to 500 dyn/cm.sup.2 and
loss elasticity modulus (G'') at 80.degree. C. within a range of
from 10 to 150 dyn/cm.sup.2, and which is superior in smoothness
and edge coatability.
[0014] The cationic electrodeposition coating composition
preferably comprises a cationic epoxy resin, a blocked isocyanate
curing agent, and if necessary, a resin particle (preferably a
crosslinked resin particle) and/or a pigment (preferably an
inorganic pigment).
[0015] The present invention further provides a method for
producing a cationic electrodeposition film having established
smoothness and edge coatability, wherein the cationic
electrodeposition film is prepared by applying a voltage to an
article immersed in a cationic electrodeposition coating
composition, which includes steps of:
[0016] adjusting storage elasticity modulus of an uncured
electrodeposited film of the cationic electrodeposition coating
composition (G') at 140.degree. C. within a range of from 80 to 500
dyn/cm.sup.2, and
[0017] adjusting loss elasticity modulus of an uncured
electrodeposited film of the cationic electrodeposition coating
composition (G'') at 80.degree. C. within a range of from 10 to 150
dyn/cm.sup.2.
[0018] In order to adjust storage elasticity modulus and loss
elasticity modulus, addition of a crosslinked resin particle or an
inorganic pigment is preferable. The crosslinked resin particles
preferably have an average particle size within a range of from 1.0
to 3.0 .mu.m. The content of the crosslinked resin particles is
preferably 3 to 15% by weight relative to weight of resin solid
contents in the cationic electrodeposition coating composition.
[0019] The inorganic pigment is added to the cationic
electrodeposition coating composition, wherein content of the
inorganic pigment is preferably 10 to 20% by weight relative to
weight of solid contents in the cationic electrodeposition coating
composition, in order to adjust storage elasticity modulus and loss
elasticity modulus.
[0020] In order to adjust storage elasticity modulus and loss
elasticity modulus, both of an inorganic pigment and crosslinked
resin particles having an average particle size within a range of
from preferably 1.0 to 3.0 .mu.l can be added to the cationic
electrodeposition coating composition, wherein content of the
inorganic pigment is preferably 0.5 to 10% by weight relative to
weight of solid contents in the cationic electrodeposition coating
composition,
[0021] In the case that both of an inorganic pigment and
crosslinked resin particles are added to the cationic
electrodeposition coating composition in order to adjust storage
elasticity modulus and loss elasticity modulus, it is preferable
that the content of the crosslinked resin particles is 3 to 15% by
weight relative to weight of resin solid contents in the cationic
electrodeposition coating composition.
[0022] The present inventors have investigated a method for
establishing both of surface smoothness and edge coatability in a
cationic electrodeposition coating composition with low solid and
low ash content. The present inventors found that addition of a
certain crosslinked resin particle to a cationic electrodeposition
coating composition easily and facilely could solve the problem and
reached to the present invention.
[0023] Accordingly, the present invention provides a cationic
electrodeposition coating composition comprising crosslinked resin
particles having an average particle size within a range of from
1.0 to 3.0 .mu.m and thermal softening temperature within a range
of from 120 to 180.degree. C., which is superior in smoothness and
edge coatability.
[0024] The content of the crosslinked resin particles is preferably
3 to 15% by weight relative to weight of resin solid contents in
the cationic electrodeposition coating composition.
[0025] The present cationic electrodeposition coating composition
is preferably a cationic electrodeposition coating composition with
low solid and low ash content comprising no inorganic pigment or a
inorganic pigment no more than 7% by weight relative to weight of
the solid contents in the cationic electrodeposition coating
composition.
[0026] The present cationic electrodeposition coating composition
has a solid concentration within a range of from preferably 0.5 to
9% by weight.
[0027] In the present invention, the crosslinked resin particles
may be prepared from (a) a compound preferably having two or more
unsaturated double bonds in the molecule and (b) a (meth)acrylate
by a known method such as a suspension polymerization, emulsion
polymerization, etc.
[0028] The present invention further provides an uncured
electrodeposited film of a cationic electrodeposition coating
composition, which has storage elasticity modulus (G') at
140.degree. C. within a range of from 80 to 500 dyn/cm.sup.2 and
loss elasticity modulus (G'') at 80.degree. C. within a range of
from 10 to 150 dyn/cm.sup.2.
[0029] The present invention further provides a cured cationic
electrodeposition film having no more than 0.25 .mu.m of Ra value
(as an index of smoothness of a coating film), which is obtained by
curing the cationic electrodeposition coating composition.
[0030] The present invention further provides a method for
producing a cationic electrodeposition film having established
smoothness and edge coatability, wherein the cationic
electrodeposition film is prepared by applying a voltage to an
article immersed in a cationic electrodeposition coating
composition, and wherein the cationic electrodeposition coating
composition comprises crosslinked resin particles having an average
particle size within a range of from 1.0 to 3.0 .mu.m and thermal
softening temperature within a range of from 120 to 180.degree.
C.
[0031] The present invention further provides a method for
producing a cationic electrodeposition film having improved
smoothness and edge coatability from a cationic electrodeposition
coating composition with low ash and low solid content, which
includes steps of:
[0032] adjusting storage elasticity modulus of an uncured
electrodeposited film (G') at 140.degree. C. within a range of from
80 to 500 dyn/cm.sup.2, and
[0033] adjusting loss elasticity modulus of an uncured
electrodeposited film (G'') at 80.degree. C. within a range of from
10 to 150 dyn/cm.sup.2,
wherein the cationic electrodeposition coating composition
comprises crosslinked resin particles having an average particle
size within a range of from 1.0 to 3.0 .mu.M and thermal softening
temperature within a range of from 120 to 180.degree. C. and
content of the crosslinked resin particles is 3 to 15% by weight
relative to weight of resin solid contents in the cationic
electrodeposition coating composition.
EFFECT OF THE INVENTION
[0034] According to the present invention, both of the smoothness
and edge coatability can be established by simultaneously adjusting
loss elasticity modulus G'' and storage elasticity modulus G' among
the dynamic viscoelasticities of an uncured electrodeposited
coating film during the electrodeposition coating. In a
conventional technology, smoothness has been secured only by
managing the lowest melt viscosity by controlling complex viscosity
coefficient .eta.* in the measurement of dynamic viscoelasticity,
but it was grasped that the compatibility of the above-mentioned
smoothness and the edge coatability was impossible by only
viscosity merely. In the present invention, it has been found that
it is important to control loss elasticity modulus: G'' (viscosity
item) within a specified range at controlling the smoothness, in
dynamic viscoelasticities of an uncured coating film of a cationic
electrodeposition coating composition.
[0035] Further, it has been found that it is important to control
the storage elasticity modulus G' (elastic item) in a specified
range at controlling the edge coatability. Further, in the present
invention, it has been found that it is important to control the
loss elasticity modulus G'' in a specific range and to
simultaneously control the storage elasticity modulus G' in a
specific range in order to secure the both of the smoothness and
edge coatability of the electrodeposition film, that has been
conventionally considered as a contradictable event. The both of
the established smoothness and the edge coatability of the
resulting electrodeposition film have been achieved by considering
these G'' and G' as independent parameters and controlling these
parameters within respective specific ranges.
[0036] According to the present invention, both of the established
surface smoothness and edge coatability can be evaluated only by
controlling both of the loss elasticity modulus and storage
elasticity modulus of an uncured electrodeposited film by an
electrodeposition coating. A method for performance test or
performance management useful for a cationic electrodeposition
coating composition can be provided.
[0037] Further, according to the present invention, both of the
established surface smoothness and edge coatability are possible by
adding crosslinked resin particles with an average particle size
within a range of from 1.0 to 3.0 .mu.m and thermal softening
temperature within a range of from 120 to 180.degree. C. to a
cationic electrodeposition coating composition. Since increase of
the viscosity in a coating film cannot be achieved by an inorganic
pigment in case of a low ash type cationic electrodeposition
coating composition, it is anticipated that the edge coatability is
deteriorated, but the edge coatability is also improved by adding
the specific crosslinked resin particles to the cationic
electrodeposition coating composition according to the present
invention and it is effective as a means for keeping or improving
the coating film performance in the low ash type cationic
electrodeposition coating composition. Herein, the low ash type
cationic electrodeposition coating composition means that an
inorganic pigment is not contained at all in the solid contents in
the cationic electrodeposition coating composition or even if it is
contained, it is up to 7% by weight relative to the weight of the
solid contents in the composition (i.e., a cationic
electrodeposition coating composition with low ash content).
Further, in the present invention, there is provided the low solid
type cationic electrodeposition coating composition that is
superior in an ability of preventing sedimentation than the
conventional one and enables the establishment of the surface
smoothness and the edge coatability as described above. Herein, the
low solid type cationic electrodeposition coating composition means
that the solid content concentration of the cationic
electrodeposition coating composition is lower than the
conventional 20% by weight, and within a range of from specifically
0.5 to 9% by weight (i.e., a cationic electrodeposition coating
composition with low solid content).
[0038] In the study by the present inventors, the establishment of
both of the surface smoothness and edge coatability can be
correlated with measurement of dynamic viscoelasticities of the
resulting electrodeposited film by the electrodeposition coating.
In particular, when the loss elasticity modulus G'' at 80.degree.
C. and the storage elasticity modulus G' at 140.degree. C. are
within specific ranges, namely, the loss elasticity modulus G'' at
80.degree. C. is 10 to 150 dyn/cm.sup.2, and the storage elasticity
modulus G' at 140.degree. C. is 80 to 500 dyn/cm.sup.2, both of the
surface smoothness and the edge coatability are established, but in
the present invention, it has been found, as an solving means, that
crosslinked resin particles with an average particle size within a
range of from 1.0 to 3.0 .mu.m and thermal softening temperature of
120.degree. C. or more are added to the cationic electrodeposition
coating composition.
BRIEF DESCRIPTION OF DRAWINGS
[0039] FIG. 1 is a graph showing the behaviors of the loss
elasticity modulus (G'') values in the dynamic viscoelasticities in
five coating compositions.
[0040] FIG. 2 is a graph showing the behaviors of the storage
elasticity modulus (G') values in the dynamic viscoelasticities in
five coating compositions.
[0041] FIG. 3 is a graph showing the behaviors of the complex
viscosity coefficient (.eta.*) values in the dynamic
viscoelasticities in five coating compositions.
[0042] FIG. 4A is a graph showing a relation between the storage
elasticity modulus (G') at 80.degree. C. and electrodeposition
texture in several coating compositions.
[0043] FIG. 4B is a graph showing a relation between the complex
viscosity coefficient (.eta.*) at 80.degree. C. and
electrodeposition texture in several coating compositions.
[0044] FIG. 4C is a graph showing a relation between the loss
elasticity modulus (G'') at 80.degree. C. and electrodeposition
texture in several coating compositions.
[0045] FIG. 5A is a graph showing a relation between the storage
elasticity modulus (G') at 140.degree. C. and electrodeposition
texture in several coating compositions.
[0046] FIG. 5B is a graph showing a relation between the complex
viscosity coefficient (.eta.*) at 140.degree. C. and
electrodeposition texture in several coating compositions.
[0047] FIG. 5C is a graph showing a relation between the loss
elasticity modulus (G'') at 140.degree. C. and electrodeposition
texture in several coating compositions.
[0048] FIG. 6A is a graph showing a relation between the storage
elasticity modulus (G') at 80.degree. C. and edge coatability in
several coating compositions.
[0049] FIG. 6B is a graph showing a relation between the complex
viscosity coefficient (.eta.*) at 80.degree. C. and edge
coatability in several coating compositions.
[0050] FIG. 6C is a graph showing a relation between the loss
elasticity modulus (G'') at 80.degree. C. and edge coatability in
several coating compositions.
[0051] FIG. 7A is a graph showing a relation between the storage
elasticity modulus (G') at 140.degree. C. and edge coatability in
several coating compositions.
[0052] FIG. 7B is a graph showing a relation between the complex
viscosity coefficient (.eta.*) at 140.degree. C. and edge
coatability in several coating compositions.
[0053] FIG. 7C is a graph showing a relation between the loss
elasticity modulus (G'') at 140.degree. C. and edge coatability in
several coating compositions.
[0054] FIG. 8 is a graph showing a relation between temperature and
storage elasticity modulus G' for illustrating the thermal
softening temperature.
[0055] FIG. 9 is a view schematically showing a part in a distance
of 30 microns from an edge of a cutter knife blade.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0056] The dynamic viscoelasticity is an elasticity modulus
observed when vibrational (periodical) strain or force (stress) is
applied to a linear viscoelastic body, and depends on a vibrational
number and temperature. The description related to the dynamic
viscoelasticity below refers to contents described in Rheology
(edited by Japan Rheology Academy), the second section: Polymer
liquid rheology, pages 31 to 39; and Polymer Chemistry,
Introduction (edited by Seizo Okamura, Akio Nakajima, Shigeharu
Onogi, Yasunori Nishijima, Toshinobu Higashimura and Norio Ise),
the fourth section: Various performances of polymer substances,
Viscoelasticities, pages 149 to 155.
[0057] Stress and strain at an angular velocity
[.omega.(2.pi..times.frequency F)] are provided by the following
formulae.
Strain .gamma.(t)=.gamma..sub.0e.sup.i.omega.t(dyn/cm.sup.2)
Stress
.sigma.(t)=.sigma..sub.0e.sup.i(.omega.t+.delta.)(dyn/cm.sup.2)
wherein .gamma.(t) is a strain at a time (t), .sigma.(t) is a
stress at a time (t), .gamma..sub.0 is a strain at t=0,
.sigma..sub.0 is a stress at t=0, and .delta. represents phase
contrast.
[0058] The complex elasticity modulus G* is represented by the
equation:
G*=(.sigma..sub.0/.gamma..sub.0)e.sup.i.delta.=(.sigma..sub.0/.gamma..su-
b.0)(cos .delta.-i sin .delta.)
The complex viscosity coefficient [.eta.*=G*/.omega.(poise)]
generally used as a viscosity control factor of a coating
composition is obtained by quantifying viscoelasticity having
properties in combination of both of viscosity and elasticity of
the coating composition.
[0059] Namely, in the present invention, viscosity and elasticity
are grasped separately, and the establishment of both of the
smoothness and edge coatability was enabled by controlling them
respectively. It is necessary for securing smoothness to control
the flowability of the coating composition at the baking process.
Viscous properties are related to the flowability, and this is
represented by the following formula according to a relation
between stress and strain.
Loss elasticity modulus (viscosity) G''=G*
sin.delta.(dyn/cm.sup.2)
[0060] On the other hand, it is necessary for the securing the edge
coatability to control a force going to remain at the site at the
baking process, and the force is related with elastic properties.
This is represented by the following formula according to a
relation between stress and strain.
Storage elasticity modulus (elasticity) G'=G* cos
.delta.(dyn/cm.sup.2)
[0061] In case of a general coating composition including a
cationic electrodeposition coating composition, the viscosity item
dominates an uncured coating film at the initial stage of a baking
process, and the composition is greatly subjected to an influence
of the loss elasticity modulus G''. At the posterior stage, the
uncured coating film is reached to a gelation point (apparently, in
a continuous state in both ends) by a fusing and a
pseudo-crosslinking. The elastic item dominates thereafter, and the
film is greatly subjected to an influence of the storage elasticity
modulus G'. The gelation point is a temperature at which a relation
between the loss elasticity modulus G'' (the viscosity item) and
the storage elasticity modulus G' (the elastic item) as
viscoelasticity-behaviors during the baking process is (Loss
elasticity modulus G'')<(Storage elasticity modulus G'). Namely,
it means a point at which the domination by the viscosity item is
changed to a domination by the elastic item.
[0062] In the present invention, it has been found that the
establishment of both of the smoothness and edge coatability is
enabled by the control of the loss elasticity modulus G'' at
temperature (80.degree. C.) no more than the gelation point and the
control of the storage elasticity modulus G' at temperature
(140.degree. C.) no less than the gelation point, and the present
invention was achieved thereby.
[0063] Herein, the present invention is described by an explanation
of the process by which the present invention has been achieved.
Firstly, the followings were carried out as preliminary
experiments.
[0064] Viscoelastic behaviors were observed for several coating
compositions, specifically, a conventional coating composition to
which components such as a pigment were added, a coating
composition without them, and a coating composition comprising a
crosslinked resin particle. The viscosity of the coating
compositions begins to be lowered at 40 to 80.degree. C. in
accordance with the rising of the temperature, the viscosity is
slightly raised between about 80 and about 100.degree. C., and when
it exceeds 100.degree. C., the viscosity is greatly decreased to be
flown. After the flowing, the curing reaction starts to raise the
viscosity again, to raise it gradually till nearby 150.degree. C.
and then, the viscosity is abruptly raised to complete the curing.
In order to investigate the dynamic viscoelasticities of the
coating composition while confirming it, five coating compositions
were measured using Rheosol-G3000 by UBM Corporation, and strain
values .gamma.(t) for stress values .rho.(t) applied and phase
contrast .delta. between stress and strain were measured under
conditions of a strain of 0.5 degree, a frequency of 0.02 Hz and a
temperature rising rate of 2.degree. C./min. The storage elasticity
modulus (G'), the loss elasticity modulus (G'') and the complex
viscosity coefficient (.eta.*) are calculated according to the
above formulae from the relations between the resulting stress
values .sigma.(t), strain values .gamma.(t) and phase contrast
.delta., and are respectively shown in FIG. 1 to FIG. 3. The
coating compositions used in FIGS. 1 to 3 are as followings: "STD"
is PN-310 (a cationic electrodeposition coating composition:
manufactured by Nippon Paint Co., Ltd.); "Pigment free" is a
coating composition without any pigment components in the PN-310
(PWC=0%); "Resin particle 1" is a coating composition in which 15%
by weight of crosslinked resin particles (with average particle
size of 1 to 3 .mu.m) were added to the "Pigment free"; "Resin
particle 2" is a coating composition in which 5% by weight of
crosslinked resin particles (with average particle size of 100 nm)
were added to the "Pigment free"; and "Resin particle 3" is a
coating composition in which 10% by weight of crosslinked resin
particles (with average particle size of 100 nm) were added to the
"Pigment free", which particles are different from those in the
"Resin particle 2".
[0065] As seen from FIGS. 1 to 3, it is grasped that the behaviors
are considerably different depending on the respective coating
compositions. Almostly, it is divided into 3 modes (40 to
80.degree. C., 80 to 100.degree. C. and 100.degree. C. or more),
but it can be grasped that the behaviors of the dynamic
viscoelasticities are greatly changed depending on the formulations
of the coating compositions, in particular, in the presence of the
components such as the particles, and that these graphs depicted by
five coating compositions are different. Accordingly, it is also
grasped that the behaviors of the dynamic viscoelasticities can be
optimally controlled by changing the formulation.
[0066] In particular, viewing FIGS. 1 to 3, it can be understood
that great differences between respective coating compositions are
based on the behavior of the viscoelasticity nearby 80.degree. C.
and the behavior of the viscoelasticity nearby 140.degree. C.
[0067] Further, the following experiments were carried out based on
these bases. Several coating compositions, such as PN-310 (a
cationic electrodeposition coating composition: manufactured by
Nippon Paint Co., Ltd.); a coating composition in which the amount
of the inorganic pigment component in the PN-310 coating
composition was changed; a coating composition in which an
inorganic pigment component was removed from the PN-310; and a
coating compositions in which the kind and amount of the
crosslinked resin particles to be added in the last composition
were changed, were prepared, and viscosity behavior for each of
them was measured. From the results of their viscoelasticities,
three viscoelasticity behaviors at 80.degree. C., namely, all of G'
values and electrodeposition texture (FIG. 4A), .eta.* values and
electrodeposition texture (FIG. 4B) and G'' values and
electrodeposition texture (FIG. 4C) were displayed in FIG. 4 so
that changes at the respective temperatures are easily grasped from
the result of those viscoelasticities. Similarly, three
viscoelasticity behaviors at 140.degree. C., namely, all of G'
values and electrodeposition texture (FIG. 5A), values and
electrodeposition texture (FIG. 5B) and G'' values and
electrodeposition texture (FIG. 5C) were displayed in FIG. 5.
Further, the electrodeposition texture is represented by a surface
roughness (Ra). The electrodeposition texture evaluated herein
means the appearance of electrodeposition film described later,
namely smoothness, and that represented by the measurement value of
the arithmetic average roughness (Ra) of a roughness carve. Namely,
the relation between the electrodeposition texture and the
viscoelasticity behavior is observed by evaluating the
above-mentioned smoothness by the electrodeposition texture.
[0068] As seen from the behaviors of FIGS. 4 and 5, there is a
correlation with the electrodeposition texture at 80.degree. C. in
the relation between the viscoelasticity change and
electrodeposition texture at the respective measurement points and
in the measured coating compositions (see FIG. 4C). Further,
similarly, the measuring results of the behaviors of the edge
coatabilities and three viscoelasticity behaviors are described in
FIGS. 6A to 6C and FIGS. 7A to 7C. As seen from FIGS. 6 and 7, it
is grasped that the relation between the storage elasticity modulus
(G') at 140.degree. C. and the edge coatability exhibits a
correlation (see FIG. 7A). Namely, it means that the change of the
viscosity value and the electrodeposition texture (smoothness) or
the edge coatability have a correlation. Herein, the
above-mentioned edge coatability can be determined by an evaluation
method described later. Further, the "coatability" represented in
FIGS. 6 and 7 is the same meaning as the "edge coatability"
mentioned here.
[0069] From these measuring results, it is found that, as an
evaluation basis, the present invention can employ the loss
elasticity modulus (G'') at 80.degree. C. for the electrodeposition
texture (smoothness) and the storage elasticity modulus (G') at
140.degree. C. for the edge coatability. The present invention has
been completed thereby. Further, the preferable ranges of the
storage elasticity modulus (G') and the loss elasticity modulus
(G'') can be selected referring to the appended FIGS. 4 and 7.
Namely, G' at 140.degree. C. is within a range of from preferably
80 to 500 dyn/cm.sup.2 referring to FIG. 7A, and G'' at 80.degree.
C. can be selected within a range of from 10 to 150 dyn/cm.sup.2
referring to FIG. 4C (the smaller electrodeposition texture Ra
means the better smoothness). The storage elasticity modulus (G')
is within a range of from preferably 90 to 500 dyn/cm.sup.2 and
more preferably from 100 to 500 dyn/cm.sup.2. Further, the loss
elasticity modulus (G'') at 80.degree. C. is within a range of from
preferably 10 to 120 dyn/cm.sup.2 and more preferably from 10 to
100 dyn/cm.sup.2.
[0070] When the storage elasticity modulus (G') is lowered than the
desirable lower limit of the storage elasticity modulus (G'), there
is a fear that the edge coatability of the electrodeposition film
obtained is deteriorated, and when the storage elasticity modulus
(G') exceeds the desirable upper limit, there is a fear that
smoothness is lowered. When the loss elasticity modulus G'' is
lowered than the desirable lower limit of the loss elasticity
modulus G'', there is a fear that although the smoothness is
improved, the edge coatability of the electrodeposition film
obtained is deteriorated, and when the loss elasticity modulus G''
exceeds a desirable upper limit, there is a fear that smoothness is
lowered.
[0071] Herein, the storage elasticity modulus G' and the loss
elasticity modulus G'' are relate to the elasticity modulus of
uncured electrodeposited film. The "uncured" means a state in which
an electrodeposited coating film obtained by carrying an
electrodeposition coating of a cationic electrodeposition coating
composition is not cured yet by baking.
[0072] The cationic electrodeposition coating composition, as
described above, contains or comprises a crosslinked resin particle
and/or an inorganic pigment, but further contains an aqueous
medium; a binder resin containing a cationic epoxy resin and a
blocked isocyanate curing agent dispersed or dissolved in an
aqueous medium; a neutralizing acid; and an organic solvent.
[0073] In order to adjust the above-mentioned viscoelasticity
behaviors, there is a process of adding a crosslinked resin
particle, as a first process. The average particle size of the
crosslinked resin particles is within a range of from preferably
1.0 to 3.0 .mu.m. When the average particle size is smaller than
1.0 .mu.m, the proportion of the surface area is increased, and
interaction with a cationic epoxy resin or the like, as binder
resin components, contained in the cationic electrodeposition
coating composition is increased, and the viscosity of the
deposited coating film is abruptly raised; therefore the
above-mentioned adjustments of viscoelasticity behaviors become
difficult. On the other hand, when the particle size is larger than
3.0 .mu.m, the lowering of smoothness caused by the sedimentation
of the electrodeposition coating composition at no stirring and by
the accumulation of particles applied on a horizontal plane upon
coating occurs.
[0074] Further, the crosslinked resin particles used in the present
invention have preferably an average particle size within a range
of from 1.0 to 3.0 .mu.m and a thermal softening temperature of
120.degree. C. or more and within a range of from preferably 120 to
180.degree. C. for establishing both of the surface smoothness and
the edge coatability of a cationic electrodeposition coating
composition with low ash and low solid content. Although a proposal
of an addition of crosslinked resin particles in cationic
electrodeposition coating composition is carried out also in a.
conventional technology, the resin particles are almost those
having an average particle size of less than 1.0 .mu.m. Since resin
particles are added for merely controlling the viscosity in a
conventional technology, the resin particles with an average
particle size of less than 1.0 .mu.m are required, but in the
present invention, the crosslinked resin particles having a larger
average particle size than that in the conventional technology and
a thermal softening temperature of 120.degree. C. or more and
within a range of from preferably 120 to 180.degree. C. are
preferably added for the achievement of establishing both of the
surface smoothness and the edge coatability, from the view point of
the dynamic viscoelasticities, in particular, from the view points
of the loss elasticity modulus (G'') at 80.degree. C. and the
storage elasticity modulus (G') at 140.degree. C.
[0075] The average particle size of the crosslinked resin particles
used in the present invention is within a range of from 1.0 to 3.0
.mu.m, as described above, but the lower limit is preferably 1.2
.mu.m and further preferably 1.5 .mu.m. On the other hand, the
upper limit is preferably 2.5 .mu.m and further preferably 2.2
.mu.m. As described above, when it is less than 1.0 .mu.m, it is
within the range of the average particle size of resin particles in
a conventional technology, and it is not preferable because the
surface smoothness is deteriorated. The crosslinked resin particles
having an average particle size of more than 3.0 .mu.m provide the
lowering of smoothness caused by the sedimentation in an
electrodeposition coating composition at no stirring and by the
accumulation of particles on a horizontal plane at an
electrodeposition coating caused by dropping. The average particle
size herein can be measured by the method below.
[0076] The average particle size of the resin particles is measured
by a granular particle transmission measurement method using
MICROTRAC9340UPA manufactured by Nikkiso Co., Ltd. Further, the
particle size distribution of the resin particles is measured in a
measurement device, and the average particle size at cumulative
relative frequency F(x)=0 is calculated from the measurement
values. These measurements and calculations employ the refractive
index of 1.33 of solvent (water) and the refractive index of 1.59
of the resin content.
[0077] The crosslinked resin particle used for the present
invention have a thermal softening temperature within a range of
from 120 to 180.degree. C., as described above, for establishing
both of the surface smoothness and the edge coatability in a
cationic electrodeposition coating composition with low ash and low
solid content, but the upper limit value is preferably 140.degree.
C. and more preferably 160.degree. C.
[0078] When the thermal softening temperature is lower than
120.degree. C., the storage elasticity modulus G' is not a given
value at baking the uncured electrodeposition film, and the edge
coatability cannot be secured. On the other hand, a material in
which the thermal softening temperature of the crosslinked resin
particle exceeds 180.degree. C. cannot substantially be
synthesized.
[0079] The thermal softening temperature is a temperature at which
the crosslinked resin particle starts to be softened. Namely, G'
values at the respective temperatures of the objective crosslinked
resin particles are determined. The temperature at a point at which
the changes of G' values for the temperature changes are abruptly
changed is called as a thermal softening temperature. It can be
determined according to the followings. The storage elasticity
modulus G' of a sample obtained by adjusting the concentration of
the crosslinked resin particles to 30% by weight (as a solid
content) is measured from 90.degree. C. under conditions of a
strain of 0.5 degree, a frequency of 0.02 Hz and a rising
temperature rate of 4.0.degree. C./min in a temperature dependent
measurement with Rheosol-G3000 (manufactured by UBM Corporation)
that is a rotational type dynamic viscoelasticity measurement
device. The measurement results are shown in a graph in FIG. 8. As
seen in FIG. 8, although the storage elasticity modulus G' of the
crosslinked resin particle keeps a constant viscosity at an initial
temperature region (about 90 to 140.degree. C. in FIG. 8), the
lowering of the storage elasticity modulus G' begins to occur at a
temperature (temperature exceeding 140.degree. C. in FIG. 8). The
tangential line in an area at which viscosity is a constant and the
tangential line in an area at which the lowering of viscosity
occurs are drawn, and the temperature at the cross point is defined
as a thermal softening temperature.
[0080] In order to increase the thermal softening temperature of
the resin particle, the crosslinking degree of the resin particle
is required to be increased. It is necessary for securing the
thermal softening temperature area in the present invention that
the resin particle is a crosslinked resin particle. Glass
transition temperature is also an index of softening of a resin,
but when the glass transition temperature (Tg) is measured in the
crosslinked resin particle, it reaches at a level of several
hundred order (.degree. C.); therefore the thermal decomposition of
the resin is frequent at the temperature, and the softening
property of particle itself cannot be observed. Accordingly, the
thermal softening temperature is employed in the present
invention.
[0081] Further, the crosslinked resin particle is required to have
a crosslinking structure. In case of no crosslinking structure, the
value of the above-mentioned storage elasticity modulus G' at
140.degree. C. is less than 80 dyn/cm.sup.2, and it is not
preferable because the edge coatability cannot be secured. The
crosslinked resin particle is preferably used in an amount of 3 to
15% by weight relative to the weight of the solid resin contents of
the cationic electrodeposition coating composition. When the
content of the crosslinked resin particles is less than 3% by
weight, the establishment of both of the surface smoothness and the
edge coatability is difficult, and when it exceeds 15% by weight,
there is a fear that the lowering of a coating film performance
such as anticorrosion property is provided. Herein, the "solid
resin content(s)" mean(s) all of the solid content(s) weight of the
resin components (including the crosslinked resin particles)
contained in the cationic electrodeposition coating
composition.
[0082] The content of the crosslinked resin particles in the
present invention is within a range of from preferably 3 to 15% by
weight relative to the weight of the solid resin contents in the
cationic electrodeposition coating composition with low ash and low
solid content for establishment of both of the surface smoothness
and the edge coatability, but its lower limit is preferably 4% by
weight and further preferably 5% by weight. On the other hand, its
upper limit is preferably 10% by weight and further preferably 8%
by weight.
[0083] Considering that the average particle size of the
crosslinked resin particles is within a range of from 1.0 to 3.0
.mu.m, they are preferably produced by a suspension polymerization.
Although it is also possible to produce them by other process such
as an emulsion polymerization if their particle size and the
thermal softening temperature satisfy the above-mentioned range,
but the suspension polymerization is preferable from the aspect of
arranging the particle size within a desired range.
[0084] The crosslinked resin particles include, but are not
specifically limited to, for example, resin particles containing a
resin having a crosslinking structure obtained by mainly using an
ethylenically unsaturated monomer, resin particles containing a
urethane resin internally crosslinked, fine resin particles
containing a melamine resin internally crosslinked, and the
like.
[0085] The above-mentioned resin having a crosslinking structure
obtained by mainly using an ethylenically unsaturated monomer
includes, but is not specifically limited to, for example, resin
particles internally crosslinked that are obtained by carrying out
a suspension polymerization of a monomer composition containing a
crosslinking monomer as an essential component and an ethylenically
unsaturated monomer, in an aqueous medium, to prepare an aqueous
dispersion, and substituting the above-mentioned aqueous dispersion
with a solvent; resin particles internally crosslinked obtained by
a NAD method of dispersing resin particles internally crosslinked
that are obtained by carrying out the copolymerization of a monomer
composition containing a crosslinking monomer as an essential
component and an ethylenically unsaturated monomer, in a
non-aqueous organic solvent that dissolves a monomer but does not
dissolve a polymer such as a low SP organic solvent such as an
aliphatic hydrocarbon, a high SP organic solvent such as an ester,
a ketone and an alcohol, or by a sedimentation-precipitation
method, or the like.
[0086] The above-mentioned ethylenically unsaturated monomer
includes, but is not specifically limited to, for example, the
alkyl esters of acrylic acid or methacrylic acid such as methyl
(meth)acrylate, ethyl (meth)acrylate, n-butyl(meth)acrylate,
isobutyl (meth)acrylate and 2-ethylhexyl (meth)acrylate; styrene,
.alpha.-methylstyrene, vinyl toluene, t-butylstyrene, ethylene,
propylene, vinyl acetate, vinyl propionate, acrylonitrile,
methacrylonitrile, dimethylaminoethyl (meth)acrylate, and the like.
Two or more of the above-mentioned ethylenically unsaturated
monomers may be used in combination.
[0087] The above-mentioned crosslinking monomer includes, but is
not specifically limited to, for example, a monomer having 2 or
more of ethylenically unsaturated bonds, that are radically
polymerizable, in the molecule, a monomer having 2 or more of
ethylenically unsaturated groups respectively supporting mutually
reactive groups, etc.
[0088] The monomer having 2 or more of ethylenically unsaturated
bonds, that are radically polymerizable, in the molecule, that can
be used for the production of the above-mentioned internally
crosslinked fine resin particles includes, but is not specifically
limited to, for example, the polymerizable unsaturated
monocarboxylic acid esters of polyalcohols such as ethylene glycol
diacrylate, ethylene glycol dimethacrylate, triethylene glycol
dimethacrylate, tetraethylene glycol dimethacrylate, 1,3-butylene
glycol dimethacrylate, trimethylolpropane triacrylate,
trimethylolpropane trimethacrylate, 1,4-butanediol diacrylate,
neopentyl glycol diacrylate, neopentyl glycol dimethacrylate,
1,6-hexanediol diacrylate, pentaerythritol diacrylate,
pentaerythritol triacrylate, pentaerythritol tetraacrylate,
pentaerythritol dimethacrylate, pentaerythritol trimethacrylate,
pentaerythritol tetramethacrylate, glycerol dimethacrylate,
glycerol diacrylate, glycerolaryloxy dimethacrylate,
1,1,1-trishydroxymethylethane diacrylate,
1,1,1-trishydroxymethylethane triacrylate,
1,1,1-trishydroxymethylethane dimethacrylate,
1,1,1-trishydroxymethylethane trimethacrylate,
1,1,1-trishydroxymethylpropane diacrylate and
1,1,1-trishydroxymethylpropane dimethacrylate; polymerizable
unsaturated alcohol esters of polybasic acids such as triallyl
cyanurate, triallyl isocyanurate, triallyl trimellitate, diallyl
terephthalate and diallyl phthalate; aromatic compounds substituted
with 2 or more of vinyl groups such as divinyl benzene, etc.
[0089] The combination of mutually reactive functional groups
existing in the above-mentioned monomer having 2 or more of
ethylenically unsaturated groups respectively supporting mutually
reactive groups includes, but is not specifically limited to, for
example, the combinations of an epoxy group and a carboxyl group,
an amino group and a carbonyl group, an epoxy group and a
carboxylic anhydride group, an amino group and a carboxylic acid
chloride group, an alkyleneimino group and a carbonyl group, an
organoalkoxysilane group and a carboxyl group, a hydroxyl group and
isocyanate glycidyl acrylate group, and the like. Among others, the
combination of an epoxy group and a carboxyl, group is more
preferable.
[0090] The above-mentioned resin particles containing a urethane
resin internally crosslinked are fine resin particles composed of
polyurethane polymer that is obtained by reacting a polyisocyanate
component with an active hydrogen containing component having diol
having a hydroxy group at a terminal and diol or triol having a
carboxyl group to form a polyurethane prepolymer containing an
isocyanate terminal group having a carboxylic acid salt at a side
chain, and successively reacting the prepolymer with a chain
elongating agent containing an active hydrogen.
[0091] The polyisocyanate component used for the above-mentioned
prepolymer includes aromatic diisocyanates such as
diphenylmethane-4,4'-diisocyanate, tolylene diisocyanate and
xylylene diisocyanate; aliphatic diisocyanates such as
hexamethylene diisocyanate and 2,2,4-trimethylhexane diisocyanate;
alicyclic diisocyanates such as 1-cyclohexane diisocyanate,
1-isocyanato-3-isocyanatomethyl-3,5-trimethylcyclohexane
(isophorone diisocyanate), 4,4'-dicyclohexylmethane diisocyanate
and methylcyclohexylene diisocyanate; and the like. The
above-mentioned polyisocyanate component is more preferably
hexamethylene diisocyanate and isophorone diisocyanate.
[0092] The above-mentioned diol having a hydroxy group at a
terminal includes, but is not specifically limited to, for example,
polyether diol, polyester diol or polycarbonate diol having a
molecular weight of 100 to 5000 and the like. The diol having a
hydroxy group at a terminal includes, but is not specifically
limited to, for example, polyethylene glycol, polypropylene glycol,
polytetramethylene glycol, polybutyrene adipate, polyhexamethylene
adipate, polyneopentyl adipate, polycaprolactone diol,
poly-3-methylvalerolactone diol, polyhexamethylene carbonate, and
the like.
[0093] The above-mentioned diol containing a carboxyl group
includes, but is not specifically limited to, for example,
dimethylol acetate, dimethylol propionate, dimethylol lactate, and
the like. Among others, dimethylol propionate is preferable.
[0094] The above-mentioned triol includes, but is not specifically
limited to, for example, trimethylol propane, trimethylol ethane,
glycerine polycaprolactone triol, and the like. The inside of
urethane resin particles has a crosslinking structure by using a
triol.
[0095] The above-mentioned fine resin particles containing a
melamine resin internally crosslinked include, but is not
specifically limited to, for example, melamine resin particles
internally crosslinked that are obtained by dispersing a melamine
resin and a polyol, in the presence of an emulsifier, in water, and
then, carrying out the crosslinking reaction of the melamine resin
and the polyol in the particles formed by dispersing; and the
like.
[0096] The above-mentioned melamine resin includes, but is not
specifically limited to, for example, di-; tri-, tetra-, penta- and
hexa-methylol melamines and alkyl ethers thereof (alkyl is methyl,
ethyl, propyl, isopropyl, butyl or isobutyl), and the like. As the
above-mentioned melamine resin that is commercially available, for
example, resins such as CYMEL 303, CYMEL 325, CYMEL 1156
(manufactured by Mitsui Cytec Industries Inc.) can be
mentioned.
[0097] The above-mentioned polyol includes, but is not specifically
limited to, for example, triol or tetrol having a molecular weight
of 500 to 3000, and the like. The above-mentioned polyol is more
preferably polypropylene ether triol and polyethylene ether
triol.
[0098] The above-mentioned crosslinked resin particles may be those
obtained by isolating the internally crosslinked fine resin
particles by methods such as filtration, spray drying and freeze
drying, and pulverizing them to an appropriate particle size, as
they are or using a mill, to be used in a state of powder; an
aqueous dispersion obtained as they are; or those in which medium
is replaced with solvent replacement to be used.
[0099] As the second process adjusting the above-mentioned
viscoelasticity behaviors, there is a process by which an inorganic
pigment is used at an amount within a range of from 10 to 20% by
weight (hereinafter, occasionally called as "PWC") relative to the
weight of the solid contents of a cationic electrodeposition
coating composition. In a conventional cationic electrodeposition
coating composition, the above-mentioned PWC exceeds 20% by weight,
and is set as 25% by weight or less; therefore both of the
smoothness and edge coatability could not be established, but both
of the smoothness and edge coatability can be established by using
the PWC within a range of from 10 to 20% by weight. Herein, the PWC
means a proportion for all of the solid contents of the resin
components and pigment components contained in the cationic
electrodeposition coating composition. When the PWC of the
inorganic pigment is less than 10% by weight, the content of a
resin is much, and the resin is softened by the rising of
temperature; therefore objective high viscosity cannot be obtained,
and the above-mentioned viscosity behaviors cannot be adjusted. On
the other hand, when the PWC exceeds 20% by weight, pigments become
adversely much, fusing effects by the resin cannot be obtained, and
as a result, high viscosity is not expressed; therefore the control
of viscoelasticity is difficult. Further, as described above, the
PWC for the inorganic pigment affects the viscosity behaviors, but
the particle size does not affect the viscosity behaviors so
much.
[0100] The inorganic pigment, as used herein, is not specifically
limited so far as it is a pigment usually used for an
electrodeposition coating composition. The example of the pigment
includes inorganic pigments usually used, for example, coloring
pigments such as titanium white and colcothar; filler pigments such
as kaolin, talc, aluminum silicate, calcium carbonate, mica and
clay; anticorrosive pigments such as zinc phosphate, iron
phosphate, aluminum phosphate, calcium phosphate, zinc phosphite,
zinc cyanide, zinc oxide, aluminum tripolyphosphate, zinc
molybdate, aluminum molybdate, calcium molybdate, aluminum
phosphomolybdate, aluminum zinc phosphomolybdate, bismuth compounds
and cerium compounds, etc.
[0101] The third process adjusting the above-mentioned
viscoelasticity behaviors is a process of using the above-mentioned
crosslinked resin particle and inorganic pigment in a combination.
In this case, the average particle size of the above-mentioned
crosslinked resin particles is within a range of from 1.0 to 3.0
.mu.m, and its amount to be used is within a range of from 3 to 15%
by weight relative to the weight of the solid contents in a coating
composition. On the other hand, the amount of inorganic pigment to
be used (PWC) can be reduced to within a range of from 0.5 to 10%
by weight relative to the weight of the solid contents in the
cationic electrodeposition coating composition. Its lower limit is
preferably 1% by weight, and further preferably 2% by weight. On
the other hand, its upper limit is preferably 7% by weight, and
further preferably 5% by weight. When it is used in an amount
exceeding 10% by weight, the pigment amount is much more than the
necessary amount, and there is a fear of the deterioration of the
planar appearance caused by the sedimentation of the pigment.
Further, when it is less than 0.5% by weight, there is a fear of
lowering color-hiding property.
[0102] The amount of the inorganic pigments can be further reduced
by using both of the inorganic pigment and the crosslinked resin
particle, and as a result, the reduction of energy and labor for
preventing the sedimentation of the solid contents in the
electrodeposition coating composition can be expected. Further,
when the viscoelasticity behaviors are adjusted only by using the
crosslinked resin particle without using the inorganic pigment, the
above-mentioned energy and labor for preventing the above-mentioned
sedimentation of the solid contents can be greatly reduced.
Further, when the inorganic pigment is not contained or when an
extremely small amount of the inorganic pigment is contained even
if the inorganic pigment is contained, the water rinsing step is
greatly shortened although the rinsing of a coated article with
water is carried out after the electrodeposition coating; therefore
great effects for the simplification of the facilities and the
reduction of using resources are provided.
[0103] Then, components used for a general cationic
electrodeposition coating composition are described.
[0104] Cationic Electrodeposition Coating Composition
[0105] The cationic electrodeposition coating composition comprises
an aqueous media; a binder resin comprising a cationic epoxy resin
dispersed or dissolved in an aqueous media and a blocked isocyanate
curing agent; a neutralizing acid; and an organic solvent. The
cationic electrodeposition coating composition may further comprise
an inorganic pigment. Content of the inorganic pigment is
preferably no more than 7% by weight relative to weight of the
solid contents of the cationic electrodeposition coating
composition. As stated above, in order to realize the low ash
content, the composition may comprise no inorganic pigments. As
stated above, in the present invention, in order to provide a low
ash and/or low solid type cationic electrodeposition coating
composition having both of the surface smoothness and edge
cotability, the cationic electrodeposition coating composition may
comprise the particular crosslinked resin particles.
[0106] Cationic Epoxy Resin
[0107] The cationic epoxy resin which may be employed in the
present invention includes an epoxy resin modified with an amine.
The cationic epoxy resin is typically produced by opening all of
the epoxy rings of a bisphenol type epoxy resin with an active
hydrogen compound which can introduce a cationic group, or by
opening a portion of epoxy rings with other active hydrogen
compound and then opening the residual epoxy rings with an active
hydrogen compound which can introduce a cationic group.
[0108] A typical example of the bisphenol type epoxy resin includes
a bisphenol A type epoxy resin and a bisphenol F type epoxy resin.
The commercially available product of the former includes YD-7011R
(manufactured by Tohto Kasei Co., Ltd., epoxy equivalent: 460 to
490), Epikote 828 (manufactured by Yuka-Shell Epoxy Co., Ltd.,
epoxy equivalent: 180 to 190), Epikote 1001 (the same manufacturer,
epoxy equivalent: 450 to 500), Epikote 1010 (the same manufacturer,
epoxy equivalent: 3000 to 4000) and the like, and the commercially
available product of the latter includes Epikote 807 (the same
manufacturer, epoxy equivalent: 170) and the like.
[0109] An oxazolidone ring-containing epoxy resin which is
represented by the following formula and disclosed in
JP-A-5-306327:
##STR00001##
wherein R means a residual group formed by removing a glycidyloxy
group of a diglycidylepoxy compound, R' means a residual group
formed by removing an isocyanate group of a diisocyanate compound,
and n means a positive integer, may be used as the cationic epoxy
resin. This is because the resulting coating film is superior in
heat resistance and corrosion resistance.
[0110] An example of the method for introducing an oxazolidone ring
into an epoxy resin includes reacting a polyepoxide with a blocked
isocyanate curing agent which has been blocked with a lower alcohol
such as methanol, in the presence of a basic catalyst, with heating
and keeping its temperature, and distilling off a lower alcohol as
a resulting by-product from the system to give the product.
[0111] It is known that a reaction of a bifunctional epoxy resin
with a monoalcohol-blocked diisocyanate (i.e., bisurethane) gives
an oxazolidone ring-containing epoxy resin. Examples of the
oxazolidone ring-containing epoxy resin and preparation thereof are
known and disclosed in JP-A-2000-128959, paragraphs 0012 to
0047.
[0112] Such epoxy resin may be modified with an appropriate resin
such as polyester polyol, polyether polyol and monofunctional
alkylphenol. Furthermore, the epoxy resin can extend its chain by
utilizing the reaction of an epoxy group with a diol or a
dicarboxylic acid.
[0113] It is desirable that the ring of the epoxy resin is opened
with an active hydrogen compound so that an amine equivalent is 0.3
to 4.0 meq/g, after ring opening, and the primary amino group
occupies more preferably 5 to 50% therein.
[0114] The active hydrogen compound which can introduce a cationic
group includes the acid salts of primary amine, secondary amine and
tertiary amine, sulfide and an acid mixture. The acid salts of
primary amine, secondary amine or/and tertiary amine(s) are used as
the active hydrogen compound which can introduce a cationic group
in order to prepare an epoxy resin containing primary amino,
secondary amino or/and tertiary amino group(s).
[0115] Specific examples include butylamine, octylamine,
diethylamine, dibutylamine, methylbutylamine, monoethanolamine,
diethanolamine, N-methyl-ethanolamine, triethylamine hydrochloride,
N,N-dimethyl-ethanolamine acetate, a mixture of diethyldisulfide
and acetic acid, and secondary amine, which is a blocked primary
amine, such as ketimine of aminoethylethanolamine and diketimine of
diethylenetriamine, etc. One or more amines are available in a
combination.
[0116] Blocked Isocyanate Curing Agent
[0117] As a polyisocyanate for a blocked isocyanate curing agent to
be employed in the present invention means a compound having 2 or
more of isocyanate groups in a molecule. An example of the
polyisocyanate includes any type of polyisocyanates, such as an
aliphatic type, an alicyclic type, an aromatic type, an
aromatic-aliphatic type, etc.
[0118] Specific example of the polyisocyanate includes 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; alicyclic diisocyanates
having 5 to 18 carbon atoms, such as 1,4-cyclohexane diisocyanate
(CDI), isophorone diisocyanate (IPDI), 4,4'-dicyclohexylmethane
diisocyanate (hydrogenated MDI), methylcyclohexane diisocyanate,
isopropylidene dicyclohexyl-4,4'-diisocyanate and
1,3-diisocyanatomethylcyclohexane (hydrogenated XDI), hydrogenated
TDI and 2,5- or 2,6-bis(isocyanatomethyl)-bicyclo[2.2.1]heptane
(also called as norbornane diisocyanate); aliphatic diisocyanates
having an aromatic ring, such as xylylene diisocyanate (XDI) and
tetramethylxylylene diisocyanate (TMXDI); the modified products of
these diisocyanates (e.g., urethanated product, carbodiimides,
urethodione, urethoimine, biuret and/or isocyanurate modified
product), etc. These can be used alone or 2 or more thereof can be
used in combination.
[0119] An adduct or a prepolymer which is obtained by reacting a
polyisocyanate with a polyalcohol such as ethylene glycol,
propylene glycol, trimethylolpropane or hexanetriol at a ratio
NCO/OH of 2 or more may be also used as a blocked isocyanate curing
agent.
[0120] The blocking agent is added to a polyisocyanate group,
stable at ambient temperature, but can regenerate a free isocyanate
group when it is heated to the dissociation temperature or
more.
[0121] The blocking agent includes conventional blocking agents,
such as .epsilon.-caprolactam, butyl cellosolve, etc.
[0122] The cationic electrodeposition coating composition comprises
crosslinked resin particles as an component, the crosslinked resin
particles may be added to the electrodeposition coating composition
at any stage of the preparing process. Preferably, the crosslinked
resin particles may be directly added to the previously prepared
cationic electrodeposition coating composition.
[0123] Inorganic Pigment
[0124] The electrodeposition coating composition used in the
present invention may contain a conventional inorganic pigment.
When it is used in a low ash type, the content of the pigment, in
particular, inorganic pigment may be reduced or the pigment may not
be added. The example of the inorganic pigment includes
conventional inorganic pigments, for example, coloring pigments
such as titanium white and colcothar; filler pigments such as
kaolin, talc, aluminum silicate, calcium carbonate, mica and clay;
anticorrosive pigments such as zinc phosphate, iron phosphate,
aluminum phosphate, calcium phosphate, zinc phosphite, zinc
cyanide, zinc oxide, aluminum tripolyphosphate, zinc molybdate,
aluminum molybdate, calcium molybdate, aluminum phosphomolybdate,
aluminum zinc phosphomolybdate, bismuth oxide, bismuth hydroxide,
basic bismuth carbonate, bismuth nitrate and bismuth sulfate, and
the like.
[0125] The content of the inorganic pigment is 7% by weight or
less, and preferably 5% by weight or less and more preferably 3% by
weight or less, relative to the weight of the solid resin contents
in the cationic electrodeposition coating composition. Further, the
"percent weight" relative to the weight of the solid resin contents
is called as PWC. When the concentration of the inorganic pigment
exceeds 7% by weight, low ash cannot be adequately attained;
therefore energy load for the prevention of the sedimentation is
increased.
[0126] When the pigment is used as a component of the
electrodeposition coating composition, these pigments are generally
dispersed in an aqueous medium at a high concentration
preliminarily to be a paste (i.e., pigment dispersed paste). Since
the pigment is a powder, it is difficult to disperse the powder at
one step in an uniform state at a low concentration to be used for
the electrodeposition coating composition. Such paste is generally
called as a pigment dispersed paste.
[0127] The pigment dispersed paste is prepared by dispersing the
pigments together with a pigment dispersing resin in an aqueous
medium. As the pigment dispersing resin, a cationic or nonionic low
molecular weight surfactant, or a cationic polymer such as a
modified epoxy resin having a quaternary ammonium group and/or a
tert-sulfonium group is generally used. As the aqueous medium, ion
exchanged water, water containing a small amount of an alcohol, and
the like are employed.
[0128] In general, the pigment dispersing resin is used in an
amount of 20 to 100 parts by weight based on 100 parts by weight of
the pigments (as a basis of the solid content). After the pigment
dispersing resin is mixed with a pigment, the pigment is dispersed
using a usual dispersion device such as a ball mill or a sand grind
mill until the particle size of the pigment in the mixture becomes
a certain uniform particle size to give a pigment dispersed
paste.
[0129] The cationic electrodeposition coating composition used in
the present invention may contain an organotin compound such as
dibutyltin laurate, dibutyltin oxide and dioctyltin oxide; amines
such as N-methylmorpholine; and metal salts such as strontium
salts, cobalt salts and copper salts, as a catalyst, in addition to
the above-mentioned components. These can act as a catalyst for
dissociation of the blocking agent from the curing agent. The
concentration of the catalyst is preferably 0.1 to 6 parts by
weight based on 100 parts by weight of the solid contents in the
total of the cationic epoxy resin and the curing agent in the
electrodeposition coating composition.
[0130] Preparation of Cationic Electrodeposition Coating
Composition
[0131] The cationic electrodeposition coating composition of the
present invention can be prepared by dispersing the above-mentioned
cationic epoxy resin and a blocked isocyanate curing agent, and if
necessary, the crosslinked resin particles and/or a
pigment-dispersed paste and a catalyst, in aqueous medium. Further,
the aqueous medium usually contains a neutralizing acid for
neutralizing the cationic epoxy resin to improve the
dispersibility. The neutralizing acid includes inorganic acids or
organic acids, such as hydrochloric acid, nitric acid, phosphoric
acid, formic acid, acetic acid, lactic acid, sulfamic acid and
acetylglycine. The aqueous medium, as used herein, is water or a
mixture of water with an organic solvent. Ion exchanged water is
preferably used as water. The example of the usable organic solvent
includes hydrocarbons (for example, xylene or toluene), alcohols
(for example, methyl alcohol, n-butyl alcohol, isopropyl alcohol,
2-ethylhexyl alcohol, ethylene glycol and propylene glycol), ethers
(for example, ethyleneglycol monoethyl ether, ethyleneglycol
monobutyl ether, ethyleneglycol monohexyl ether, propyleneglycol
monoethyl ether, 3-methyl-3-methoxybutanol, diethyleneglycol
monoethyl ether and diethyleneglycol monobutyl ether), ketones (for
example, methyl isobutyl ketone, cyclohexanone, isophorone and
acetylacetone), esters (for example, ethyleneglycol monoethyl ether
acetate and ethyleneglycol monobutyl ether acetate), and a mixture
thereof.
[0132] The cationic electrodeposition coating composition of the
present invention may contain the crosslinked resin particle. As a
method for the addition, the crosslinked resin particle may be
added at any stage during the production stages of the
electrodeposition coating composition, and it is preferable to
directly add the crosslinked resin particle to the previously
produced cationic electrodeposition coating composition.
[0133] The amount of the blocked isocyanate curing agent must be
adequate for the curing reaction with a functional group containing
an active hydrogen, such as the primary amino group, secondary
amino group or a hydroxyl group in the cationic epoxy resin, to
provide a good cured coating. In general, the weight ratio of the
solid contents in the cationic epoxy resin to the solid contents in
the blocked isocyanate curing agent is generally within a range of
from 90/10 to 50/50 and preferably 80/20 to 65/35 (epoxy
resin/curing agent). The amount of neutralizing acid is an amount
adequate for neutralizing at least 20% and preferably 30 to 60% of
the cationic group of the cationic epoxy resin.
[0134] The organic solvent is an essential as a solvent for
preparing the resin components such as the cationic epoxy resin and
the blocked isocyanate curing agent. The complex operations are
necessary for completely removing the solvent.
[0135] Further, when an organic solvent is contained in the
cationic epoxy resin as a binder resin component, the fluidity of a
coating film during the film formation is improved, and the
smoothness of the coating film is improved.
[0136] The organic solvent usually contained in the coating
composition includes ethyleneglycol monobutyl ether, ethyleneglycol
monohexyl ether, ethyleneglycol monoethylhexyl ether,
propyleneglycol monobutyl ether, dipropyleneglycol monobutyl ether,
propyleneglycol monophenyl ether, and the like.
[0137] The cationic electrodeposition coating composition can
contain a conventional additive for a coating composition, such as
a plasticizer, a surfactant, an antioxidant and an ultraviolet
absorbent, in addition to the above-mentioned components.
[0138] According to the present invention, in the case of the
cationic electrodeposition coating composition with low solid
content, the solid content concentration is set at 20% by weight or
less. The conventional content is 20% by weight. Specifically, the
solid content concentration of the coating composition is within a
range of from preferably 0.5 to 9% by weight, and its lower limit
value is preferably 2% by weight and more preferably 4% by weight.
On the other hand, its upper limit value is preferably 7% by weight
and more preferably 6% by weight. When the solid content
concentration is less than 0.5% by weight, the appropriate coating
film cannot be formed, and when it is higher than 9% by weight,
effects such as the removal of a rinsing step with water and the
simplification of the facilities, these are effects caused by low
solid content, cannot be obtained in the cationic electrodeposition
coating process. Herein, the solid content concentration means a
concentration relative to the total weight of the pigment(s)
component and the resin component(s) (also including the
crosslinked resin particle component) (as a basis of the solid
content) in a cationic electrodeposition coating composition. Thus,
the low solid content has fear of lowering the electric
conductivity of the cationic electrodeposition coating composition.
Accordingly, it is preferable to separately add an
electroconductivity controlling agent.
[0139] The electroconductivity controlling agent used for the
present invention is not specifically limited so far as it is a
material adjusting the electroconductivity of the cationic
electrodeposition coating composition within a desired range, but
the electroconductivity controlling agent composed of an amino
group-containing containing compound having an amine value of 200
to 500 mmol/100 g is preferable. When the amine value is adjusted
for the electroconductivity controlling agent for the cationic
electrodeposition coating composition of the present invention
within the above-mentioned range, it may be any compound containing
an amino group, but generally, the electroconductivity controlling
agent is preferably an amine modified epoxy resin or an amine
modified acryl resin. Further, the electroconductivity controlling
agent for the cationic electrodeposition coating composition of the
present invention may be neutralized by an acid, if necessary. The
amine value is preferably 250 to 450 mmol/100 g and most preferably
300 to 400 mmol/100 g. When the amine value is less than 200
mmol/100 g, addition amount necessary for adjusting the
electroconductivity of the cationic electrodeposition coating
composition with low solid content concentration to an optimum
value is increased, and there is a fear of loosing anticorrosive
property. Further, when it exceeds 500 mmol/100 g, it has defects
that depositability is lowered and the desired throwing power is
not obtained. Further, the adaptability to a zinc steel plate is
also lowered.
[0140] The above-mentioned electroconductivity controlling agent
includes an amino-group containing compound having from a low
molecular weight to a high molecular weight, such as a conventional
high molecular weight resin such as amine modified epoxy resins and
amine modified acryl resins. The example of the low molecular
weight compound containing an amino group includes
monoethanolamine, diethanolamine, dimethylbutylamine, and the
like.
[0141] The high molecular weight compound containing an amino group
is preferable, and in particular, the amine modified epoxy resins
and the amine modified acryl resins are preferable. The amine
modified epoxy resin is obtained by modifying an epoxy group of an
epoxy resin with an amine compound. As the epoxy resin, general
epoxy resins can be used, and a bisphenol type epoxy resin, a
t-butylcathecol type epoxy resin, a phenolnovolak type epoxy resin
and a cresolnovolac type epoxy resin, that have a molecular weight
of 500 to 20000, are preferable. Among these epoxy resins, a
phenolnovolak type epoxy resin and a cresolnovolac type epoxy resin
are most desirable. In particular, these epoxy resins are
commercially available. Example of the epoxy resin includes a
phenolnovolak type epoxy resin DEN-438 manufactured by Dow Chemical
Japan Co., Ltd.; a cresolnovolac type epoxy resin YDCN-703
manufactured by Tohto Kasei Co., Ltd., etc.
[0142] These epoxy resins may be modified with resins such as
polyester polyol, polyether polyol and monofunctional alkylphenol.
Further, the epoxy resin can extend its chain utilizing a reaction
of an epoxy group with a diol or a dicarboxylic acid.
[0143] As the amine modified acryl resin, for example, the
homopolymer of dimethylaminoethyl methacrylate that is a monomer
containing an amino group, or a copolymer of dimethylaminoethyl
methacrylate with other polymerizable monomer may be used as it is,
and it can be obtained by modifying the glycidyl group of the
homopolymer of glycidyl methacrylate or the glycidyl group of a
copolymer of glycidyl methacrylate with other polymerizable
monomer, with an amine compound.
[0144] The compound introducing an amino group to the epoxy resin
or the acryl resin containing an epoxy group includes primary
amines, secondary amines, tertiary amines, and the like. Their
specific example includes butylamine, octylamine, diethylamine,
butylamine, dimethylbutylamine, monoethanolamine, diethanolamine,
N-methylethanolamine, triethylamine hydrochloride,
N,N-dimethylethanolamine hydrochloride, a mixture of
diethyldisulfide and acetic acid, and additionally, secondary
amines that are blocked primary amines such as the diketimine of
aminoethylethanolamine and the diketimine of diethylhydroamine. A
plurality of the amines may be used.
[0145] As described above, the number average molecular weight of
the amine modified epoxy resin or the amine modified acryl resin is
within a range of from preferably 500 to 20000. When the number
average molecular weight is smaller than 500, there is a fear of
losing anticorrosive property, and although the reason is not
clear, the throwing power is lowered and the adaptability to a zinc
steel plate is lowered. When the number average molecular weight is
larger than 20000, there is a fear of providing the deterioration
of the finishing appearance.
[0146] The amine modified epoxy resin and/or the amine modified
acryl resin can be also used by being preliminarily neutralized by
a neutralizing acid. Acid used for neutralization includes
inorganic and organic acids such as hydrochloric acid, nitric acid,
phosphoric acid, sulfamic acid, formic acid, acetic acid and lactic
acid.
[0147] Application of Cationic Electrodeposition Coating
Composition
[0148] The above-mentioned cationic electrodeposition coating
composition is applied on an article by an electrodeposition to
form an electrodeposition film. The article includes, but is not
specifically limited to, so far as it is electroconductive, for
example, an iron plate, a steel plate, an aluminum plate and a
surface treated article thereof, and a molded article thereof,
etc.
[0149] The electrodeposition coating with the cationic
electrodeposition coating composition is usually carried out by
applying a voltage within a range of from 50 to 450 V between an
anode and a cathode which is an article to be coated. When the
applied voltage is less than 50 V, the electrodeposition is
inadequate, and when it exceeds 450 V, the coating film is broken
and the appearance is abnormal. During the electrodeposition
coating, the temperature of the liquid coating composition in a
bath is usually adjusted within a range of from 10 to 45.degree.
C.
[0150] The electrodeposition coating includes a step of immersing
an article in a cationic electrodeposition coating composition, and
a step of applying a voltage between an anode and a cathode, which
is an article to be coated, to form an electrodeposited film.
Further, the time for applying a voltage can be varied depending on
the electrodeposition conditions and generally 2 to 4 min.
[0151] The thickness of the resulting electrodeposition film can be
generally within a range of from 5 to 25 .mu.m. When the film
thickness is less than 5 .mu.m, there is a fear of inadequate
anticorrosive property, and when the film thickness exceeds 25
.mu.m, the thickness is sufficient to provide the required coating
film performances. Further, the film resistance of the
electrodeposition film is within a range of from preferably 1000 to
1600 k.OMEGA./cm.sup.2 at a film thickness of 15 p.m. When the film
resistance of the coating film is less than 1000 k.OMEGA./cm.sup.2,
it is a state in which adequate electric resistance is not
obtained, and there is a fear of inferior throwing power. Further,
when it exceeds 1600 k.OMEGA./cm.sup.2, there is a fear of inferior
coating film appearance. The film resistance of the coating film is
within a range of from more preferably 1100 to 1500
k.OMEGA./cm.sup.2.
[0152] The film resistance value of the coating film can be
determined by the following formula according to the residual
electric current value (A) of the coating film at the final coating
voltage (V).
Film resistance value (FR)=V/A
[0153] After the electrodeposition coating, thus obtained
electrodeposition film as it is or rinsed with water, baked at 120
to 260.degree. C. and preferably 140 to 220.degree. C. for 10 to 30
min to give a cured electrodeposition film.
[0154] The cured electrodeposition film of the present invention
has an excellent surface smoothness or Ra value as an evaluation
index of the surface smoothness, preferably 0.25 .mu.m or less and
more preferably 0.20 .mu.m or less. Further, its lower limit value
is preferably zero. Ra value is measured with an evaluation type
surface roughness measuring machine (SURFTEST SJ-201P manufactured
by Mitsutoyo Corporation) according to JIS-B0601. The smaller Ra
value provides the better coating film appearance having a
suppressed concavo-convex.
[0155] Further, in the present invention, there is provided a
method for establishing both of the smoothness and the edge
coatability of the cationic electrodeposition coating composition
characterized in that the cationic electrodeposition coating
composition comprises the crosslinked resin particles having an
average particle size within a range of from 1.0 to 3.0 .mu.m and a
thermal softening temperature within a range of from 120 to
180.degree. C. in a process of forming a cationic electrodeposition
film by immersing an article in the cationic electrodeposition
coating composition and applying a voltage. Further, in the present
invention, even if the cationic electrodeposition coating
composition is low solid type and low ash type, the ability of
preventing the sedimentation of the solid contents in the
electrodeposition coating composition can be improved by adding the
specific crosslinked resin particle in the cationic
electrodeposition coating composition as an additive, and both of
the surface smoothness and edge coatability can be established. The
amount in that case is within a range of from 3 to 15% by weight
relative to the weight of the solid contents in the cationic
electrodeposition coating composition.
EXAMPLES
[0156] The present invention is further specifically described
below according to the Examples, but the present invention is not
limited to these Examples. Further, the term "part(s)" represent(s)
part(s) by weight unless otherwise noticed.
Production Example 1A
Production of Blocked Isocyanate Curing Agent
[0157] In a flask equipped with a stirrer, a cooler, a nitrogen
charging tube, a thermometer and a dropping funnel, 199 parts of
the trimer of hexamethylene diisocyanate (CORONATE HX: manufactured
by Nippon Polyurethane Industry Co., Ltd.), 32 parts of methyl
isobutyl ketone and 0.03 part of dibutyltin dilaurate were weighed,
and 87.0 parts of methyl ethyl ketone oxime was added dropwise
thereto from the dropping funnel over 1 hr, while stirring and
bubbling nitrogen. Temperature was raised from 50.degree. C. to
70.degree. C. Thereafter, the reaction was continued for 1 hr, and
the reaction was continued until the absorption of NCO group was
extinguished by an infrared spectrometer. Then, 0.74 part of
n-butanol and 39.93 parts of methyl isobutyl ketone were added to
prepare a mixture with a non-volatile content of 80%.
Production Example 2A
Production of Amine Modified Epoxy Resin Emulsion
[0158] In a flask equipped with a stirrer, a cooler, a nitrogen
charging tube and a dropping funnel, 71.34 parts of
2,4-/2,6-tolylene diisocyanate (80/20% by weight), 111.98 parts of
methyl isobutyl ketone and 0.02 part of dibutyltin dilaurate were
weighed, and 14.24 parts of methanol was added dropwise from the
dropping funnel over 30 min while stirring and bubbling nitrogen.
The temperature was raised from room temperature to 60.degree. C.
by exothermic heat. Then, after the reaction was continued for 30
minutes, 46.98 parts of ethyleneglycol mono-2-ethylhexyl ether was
added dropwise from the dropping funnel over 30 min. Temperature
was raised to 70 to 75.degree. C. by exothermic heat. After the
reaction was continued for 30 min, 41.25 parts of the adduct of
bisphenol A with propylene oxide (5 mol) (BP-5P manufactured by
Sanyo Kasei Co., Ltd.) was added to the mixture, temperature was
raised to 90.degree. C., and the reaction was continued while
measuring IR spectrum until NCO group was extinguished.
[0159] Successively, 475.0 parts of a bisphenol A type epoxy resin
having an epoxy equivalent of 475 (YD-7011R manufactured by Tohto
Kasei Co., Ltd.) was added to be homogeneously dissolved, and then
temperature was raised from 130.degree. C. to 142.degree. C., and
water was removed from the reaction system by azeotrope with MIBK.
After the reaction mixture was cooled to 125.degree. C., 1.107
parts of benzyldimethylamine was added, and reaction of forming an
oxazolidone ring by demethanolation was carried out. The reaction
was continued until the epoxy equivalent was 1140.
[0160] Then, the mixture was cooled to 100.degree. C., and 24.56
parts of N-methylethanolamine, 11.46 parts of diethanolamine and
26.08 parts of ketimine of aminoethylethanolamine (78.8% methyl
isobutyl ketone solution) were added thereto to be reacted at
110.degree. C. for 2 hrs. Then, 20.74 parts of ethyleneglycol
mono-2-ethylhexyl ether and 12.85 parts of methyl isobutyl ketone
were added to the mixture to be diluted, and non-volatile content
was adjusted to 82%. Number average molecular weight (by GPC
method) was 1380 and amine equivalent was 94.5 meq/100 g.
[0161] 145.11 Parts of ion exchanged water and 5.04 parts of acetic
acid were weighed in another container, a mixture of 320.11 parts
(75.0 parts as solid content) of the above-mentioned amine modified
epoxy resin and 190.38 parts (25.0 parts as solid content) of the
blocked isocyanate curing agent of Production Example 1A, which was
heated to 70.degree. C., was added thereto dropwise gradually, and
the mixture was stirred to be homogeneously dispersed. Then, ion
exchanged water was added thereto to adjust the solid content to
36%.
Production Example 3A
Production of Pigment Dispersing Resin
[0162] In a flask equipped with a stirrer, a cooler, a nitrogen
charging tube, a thermometer and a dropping funnel, 382.20 parts of
a bisphenol A type epoxy resin having an epoxy equivalent of 188
(under product name: DER-331J) and 111.98 parts of bisphenol A were
weighed, temperature was raised to 80.degree. C. to dissolve the
mixture homogeneously, then 1.53 parts of 1% solution of
2-ethyl-4-methylimidazole was added, and reaction was carried out
at 170.degree. C. for 2 hrs. After cooling the mixture to
140.degree. C., 196.50 parts of 2-ethylhexanol-half blocked
isophorone diisocyanate (non-volatile content: 90%) was added to
the mixture, and the reaction was carried out until NCO group was
extinguished. Thereto, 205.00 parts of dipropylene glycol monobutyl
ether was added, successively, 408.00 parts of
1-(2-hydroxyethylthio)-2-propanol and 134.00 parts of dimethylol
propionate were added, 144.00 parts of ion exchanged water was
added, and the mixture was reacted at 70.degree. C. The reaction
was continued until acid value was 5 or less. The obtained resin
varnish obtained was diluted to a non-volatile content of 35% with
1150.50 parts of ion exchanged water.
Production Example 4A
Production of Pigment Dispersed Paste
[0163] In a sand grind mill, 120 parts of the pigment dispersing
resin varnish obtained in Production Example 3A, 100.0 parts of
kaolin, 92 parts of titanium dioxide, 8.0 parts of dibutyltin oxide
and 184 parts of ion exchanged water were charged, and dispersed
until particle size was 10 .mu.m or less to obtain a pigment
dispersed paste (solid content: 48%).
Production Example 5A
Production of Crosslinked Resin Particles
[0164] In a reaction container, 120 parts of butylcellosolve was
charged, and it was heated to 120.degree. C. with stirring.
Thereto, a solution which was a mixture of 2 parts of
t-butylperoxy-2-ethylhexanoate and 10 parts of butylcellosolve, and
a monomer mixture containing 15 parts of glycidyl methacrylate, 50
parts of 2-ethylhexyl methacrylate, 20 parts of 2-hydroxyethyl
methacrylate and 15 parts of n-butyl methacrylate whose SP value
was 10.1 were added dropwise over 3 hrs. After aging for 30 min, a
solution which was a mixture of 0.5 part of
t-butylperoxy-2-ethylhexanoate and 5 parts of butylcellosolve was
added dropwise for 30 min, and after aging for 2 hrs, the mixture
was cooled. Quartenization was carried out by adding 7 parts of
N,N-dimethylaminoethanol and 15 parts of 50% aqueous lactic acid
solution to the mixture with heating at 80.degree. C. and stirring.
When acid value was 1 or less and the rising of viscosity was
stopped, heating was terminated to obtain an acryl resin having an
ammonium group. The number of the ammonium group per one molecule
of the acryl resin having an ammonium group was 6.0.
[0165] To the reaction container, 120 parts of the acryl resin
having an ammonium group and 270 parts of deionized water were
added, and the mixture was stirred with heating at 75.degree. C.
Thereto, the 100% neutralized aqueous solution of 1.5 parts of
2,2'-azobis(2-(2-imidazolin-2-yl)propane) with acetic acid was
added dropwise over 5 min. After aging for 5 min, 30 parts of
methyl methacrylate was added dropwise over 5 min. After aging
further 5 min, an .alpha.,.beta.-ethylenically unsaturated monomer
mixture containing 170 parts of methyl methacrylate, 40 parts of
styrene, 30 parts of n-butyl methacrylate, 5 parts of glycidyl
methacrylate and 30 parts of neopentylglycol dimethacrylate was
added to a solution which was a mixture of 170 parts of the acryl
resin having an ammonium group and 250 parts of deionized water
with stirring to give a pre-emulsion, and the pre-emulsion was
added dropwise over 40 min. After aging for 60 min, it was cooled
to give a dispersion of crosslinked resin particles 1. The
non-volatile content in the dispersion of the crosslinked resin
particles was 35%, pH was 5.0 and an average particle size was 100
nm.
Production Example 6A
Production of Non-Crosslinked Resin Particles
[0166] 2 Parts of lauroyl peroxide was dissolved in a solution
which was a mixture of 104 parts of styrene, 20 parts of
2-ethylhexyl methacrylate and 76 parts of lauryl methacrylate. This
was added in 497 parts of aqueous solution in which 8 parts of
polyvinyl alcohol (GOUSENOL GH-17, manufactured by Nippon Synthetic
Chemical Industry Co., Ltd.) was dissolved in deionized water,
while stirring, and a dispersion was produced at 3500 rpm with a
HOMOMIC LINE FLOW 30 type machine (high speed dispersing machine
manufactured by TOKUSYU KIKA KOUGYOU Co., Ltd.).
[0167] The suspension polymerization of the suspension was carried
out at a stirring speed of 150 rpm and a reaction temperature of 81
to 83.degree. C. over 5 hrs using a usual batch wise reaction
container, and after cooling, the resulted dispersion was filtered
with a 200 mesh net to give non-crosslinked resin particles. The
non-volatile content in the dispersion of the non-crosslinked resin
particles was 30% and an average particle size was 3 .mu.m.
Example 1A
[0168] 2222 Parts of the emulsion obtained in Production Example
2A, 417 parts of the pigment dispersed paste obtained in Production
Example 4A and 2361 parts of ion exchanged water were mixed to give
a cationic electrodeposition coating composition in which PWC was
16.5%, the content of the crosslinked resin particles was zero % by
weight, and the solid content was 20% by weight.
Comparative Example 1A
[0169] 738 Parts of the emulsion obtained in Production Example 2A,
4 parts of dibutyltin oxide and 4598 parts of ion exchanged water
were mixed to give a cationic electrodeposition coating composition
in which PWC was 0%, the content of the crosslinked resin particles
was zero % by weight, and the solid content was 5% by weight.
Comparative Example 2A
[0170] 702 Parts of the emulsion obtained in Production Example 2A,
38 parts of the crosslinked resin particles obtained in Production
Example 5A, 4 parts of dibutyltin oxide and 4596 parts of ion
exchanged water were mixed to give a cationic electrodeposition
coating composition in which PWC was 0%, the content of the
crosslinked resin particles was 5% by weight, and the solid content
was 5% by weight.
Comparative Example 3A
[0171] 665 Parts of the emulsion obtained in Production Example 2A,
76 parts of the crosslinked resin particles obtained in Production
Example 5A, 4 parts of dibutyltin oxide and 4596 parts of ion
exchanged water were mixed to give a cationic electrodeposition
coating composition in which PWC was 0%, the content of the
crosslinked resin particles was 10% by weight, and the solid
content was 5% by weight.
Comparative Example 4A
[0172] 665 Parts of the emulsion obtained in Production Example 2A,
89 parts of the non-crosslinked resin particles obtained in
Production Example 6A, 4 parts of dibutyltin oxide and 4582 parts
of ion exchanged water were mixed to give a cationic
electrodeposition coating composition in which PWC was 0%, the
content of the non-crosslinked resin particles was 10% by weight,
and the solid content was 5% by weight.
Comparative Example 5A
[0173] 389 Parts of the emulsion obtained in Production Example 2A,
125 parts of the pigment dispersed paste obtained in Production
Example 4A and 3486 parts of ion exchanged water were mixed to give
a cationic electrodeposition coating composition in which PWC was
25%, the content of the crosslinked resin particles was 0% by
weight, and the solid content was 5% by weight.
Example 2A
[0174] 702 Parts of the emulsion obtained in Production Example 2A,
42 parts of the crosslinked resin particles (crosslinked resin
particles in which methyl methacrylate was a main component;
TAFTIC.RTM. F-200: manufactured by Toyobo Co., Ltd.), 4 parts of
dibutyltin oxide and 4592 parts of ion exchanged water were mixed
to give a cationic electrodeposition coating composition in which
PWC was 0%, the content of the crosslinked resin particles was 5%
by weight, and the solid content was 5% by weight.
Example 3A
[0175] 665 Parts of the emulsion obtained in Production Example 2A,
84 parts of the crosslinked resin particles (crosslinked resin
particles in which methyl methacrylate was a main component;
TAFTIC.RTM. F-200: manufactured by Toyobo Co., Ltd.), 4 parts of
dibutyltin oxide and 4587 parts of ion exchanged water were mixed
to give a cationic electrodeposition coating composition in which
PWC was 0%, the content of the crosslinked resin particles was 10%
by weight, and the solid content was 5% by weight.
Example 4A
[0176] 628 Parts of the emulsion obtained in Production Example 2A,
127 parts of the crosslinked resin particles (crosslinked resin
particles in which methyl methacrylate was a main component;
TAFTIC.RTM. F-200: manufactured by Toyobo Co., Ltd.), 4 parts of
dibutyltin oxide and 4581 parts of ion exchanged water were mixed
to give a cationic electrodeposition coating composition in which
PWC was 0%, the content of the crosslinked resin particles was 15%
by weight, and the solid content was 5% by weight.
Example 5A
[0177] 628 Parts of the emulsion obtained in Production Example 2A,
40 parts of the crosslinked resin particles (crosslinked resin
particles in which Styrene monomer was a main component; CHEMISNOW
SX500H: manufactured by Soken Chemical & Engineering Co., Ltd.,
which had an average particle size of 3 .mu.m), 4 parts of
dibutyltin oxide and 4668 parts of ion exchanged water were mixed
to give a cationic electrodeposition coating composition in which
PWC was 0%, the content of the crosslinked resin particles was. 15%
by weight, and the solid content was 5% by weight.
Example 6A
[0178] 567 Parts of the emulsion obtained in Production Example 2A,
54 parts of the pigment dispersed paste obtained in Production
Example 4A, 40 parts of crosslinked resin particles (crosslinked
resin particles in which styrene monomer was a main component;
CHEMISNOW SX500H: manufactured by Soken Chemical & Engineering
Co., Ltd., which had an average particle size of 3 .mu.m) and 4739
parts of ion exchanged water were mixed to give a cationic
electrodeposition coating composition in which PWC was 8%, the
content of the crosslinked resin particles was 15% by weight, and
the solid content was 5% by weight.
[0179] With respect to thus prepared cationic electrodeposition
coating compositions, the loss elasticity modulus at 80.degree. C.
and the storage elasticity modulus at 140.degree. C. in dynamic
viscoelasticities, and the smoothness and the edge coatability were
evaluated by the methods below.
[0180] Measurement of Loss Elasticity Modulus and Storage
Elasticity Modulus of Electrodeposition Film
[0181] A tin plate was immersed in the cationic electrodeposition
coating composition prepared as described above. An
electrodeposition film was formed by applying a voltage so that the
film thickness after baking was 15 .mu.m, and then the plate was
rinsed with water to remove the excessive electrodeposition coating
composition. Then, after removing moisture, without drying, the
plate having the uncured coating film was immediately taken out to
prepare a sample. The dynamic viscoelasticities of the sample were
measured depending on the temperature with Rheosol-G3000
(manufactured by UBM Corporation) that was a rotational type
dynamic viscoelasticity measurement device (under measurement
conditions of a strain of 0.5 deg and a frequency of 0.02 Hz),
wherein the sample was set, and the measurement temperature was
kept at 50.degree. C. After starting the measurement, the
measurement of the viscosity of the coating film was carried out
when the electrodeposition film was uniformly spread in a cone
plate.
[0182] Evaluation of Appearance (Smoothness) of Electrodeposition
Film
[0183] Evaluation of an appearance of an electrodeposition film was
carried out by measuring an arithmetic average roughness (Ra) on a
roughness curve. A cold rolling steel plate treated with zinc
phosphate was immersed in the cationic electrodeposition coating
composition prepared as described above. An uncured
electrodeposition film obtained by applying a voltage, so that the
film thickness after baking was 15 .mu.m, was baked at 160.degree.
C. for 10 min. Then, the Ra value of the cured electrodeposition
film was measured with an evaluation type surface roughness
measuring machine (SURFTEST SJ-201 P manufactured by Mitsutoyo
Corporation) in accordance with JIS-B0601. Measurement was repeated
7 times on the sample with cut-offs in a width of 2.5 mm (partition
number was 5), and the Ra value was an average of the measured
values without the maximum and minimum values. The results are
shown in Table 1. It can be understood that the smaller Ra value
provides the better coating film appearance with a suppressed
concavo-convex.
[0184] Evaluation Method for Edge Coatability
[0185] A cutter knife blade (LB-50K manufactured by OLFA Co.)
treated with zinc phosphate, as an article to be coated, was
immersed into a cationic electrodeposition coating composition. A
voltage was applied between an anode and a cathode, which is the
above-described article, to give an electrodeposition film, wherein
the above-mentioned electrodeposition conditions on the applying
voltage and time were adjusted so that the thickness of the film
electrodeposited on the knife blade was 15 .mu.m. The resulted
electrodeposition film was rinsed with water, and then baked at
160.degree. C. for 10 min to give a cured electrodeposition
film.
[0186] The cutter knife blade coated with the electrodeposition
film was folded off in the center. The thickness of the
electrodeposition film applied on the cutter knife blade was
measured with a digital microscope (VH-8000 manufactured by KEYENCE
Corporation) in a distance (30 microns) from the (sharp) edge of
the cutter knife blade. FIG. 9 schematically shows the point of the
cutter knife blade in the distance, 30 microns, from the edge of
the blade.
TABLE-US-00001 TABLE 1 Comp. Comp. Comp. Comp. Comp. Ex. 1A Ex. 2A
Ex. 3A Ex. 4A Ex. 5A Ex. 1A Resin particle None Production
Production Production None None Ex. 5A: Ex. 5A: Ex. 6A: Crosslinked
Crosslinked Non-crosslinked Average Average Average particle
particle particle size: size: 0.1 .mu.m size: 0.1 .mu.m 1 to 5
.mu.m Resin particle content (%) None 5 10 10 0 None Ash (pigment)
content (%) 0 0 0 0 25 16.5 Melt Loss 23 156 228 50 152 89
viscosity elasticity modulus G'' (dyn/cm.sup.2) Storage 21 73 110
50 136 155 elasticity modulus G' (dyn/cm.sup.2) Evaluation
Smoothness 0.19 0.30 0.37 0.20 0.33 0.18 results Ra (C/O = 2.5)
Edge 3.6 6.0 8.3 5.1 8.0 7.9 coatability (.mu.m) Ex. 2A Ex. 3A Ex.
4A Ex. 5A Ex. 6A Resin particle TAFTIC TAFTIC TAFTIC CHEMISNOW
CHEMISNOW F-200: F-200: F-200: SX500H SX500H Average Average
Average Average Average particle particle particle particle size:
particle size: size: size: size: 3 .mu.m 3 .mu.m 2 .mu.m 2 .mu.m 2
.mu.m Resin particle content (%) 5 10 15 15 15 Ash (pigment)
content (%) 0 0 0 0 12 Melt Loss 88 113 142 121 144 viscosity
elasticity modulus G'' (dyn/cm.sup.2) Storage 85 107 125 116 136
elasticity modulus G' (dyn/cm.sup.2) Evaluation Smoothness 0.21
0.21 0.23 0.24 0.24 results Ra (C/O = 2.5) Edge 7.5 7.8 8.2 8.1 8.3
coatability (.mu.m)
[0187] As seen in the Table 1, it is understood that the
electrodeposition coating compositions having the loss elasticity
modulus (G'') and the storage elasticity modulus (G') within the
defined ranges as dynamic viscoelasticities provide excellent
performances in the smoothness and the edge coatability.
Specifically, in the Comparative Example 1A, the electrodeposition
coating composition having a storage elasticity modulus (G') out of
the defined range in the present invention does not provide a good
edge coatability. In the Comparative Example 2A, the
electrodeposition coating composition comprising the crosslinked
resin particles of the Production Example 5A and having a loss
elasticity modulus (G'') and a storage elasticity modulus (G'),
both of which are out of the defined ranges in the present
invention, does not provide a good smoothness and a good edge
coatability. Similar to the Comparative Example 2A, in the
Comparative Example 3A, the electrodeposition coating composition
comprising the crosslinked resin particles of the Production
Example 5A, wherein the crosslinked resin particles have a small
average particle size of 100 nm, and having a loss elasticity
modulus (G'') out of the defined range in the present invention,
does provide a poor smoothness. In the Comparative Example 4A, the
electrodeposition coating composition comprising the
non-crosslinked resin particles, and having a storage elasticity
modulus (G') out of the defined range in the present invention,
does provide a poor edge coatability. In the Comparative Example
5A, the electrodeposition coating composition comprising the
inorganic pigment without any resin particles, and having a loss
elasticity modulus (G'') out of the defined range in the present
invention, does not provide a good smoothness. In the Example 1A,
the electrodeposition coating composition comprising the pigment of
the Production Example 4A, wherein all the parameters are within
the present defined ranges, provides an excellent smoothness and an
excellent edge coatability. In the Examples 2A to 6A, each of the
electrodeposition coating compositions comprises a certain
particle, wherein the storage elasticity modulus (G') and the loss
elasticity modulus (G'') are controlled within the present defined
ranges, and provides an excellent smoothness and an excellent edge
coatability.
Production Example 1B
Production of Blocked Isocyanate Curing Agent
[0188] In a flask equipped with a stirrer, a cooler, a nitrogen
charging tube, a thermometer and a dropping funnel, 199 parts of
the trimer of hexamethylene diisocyanate (CORONATE HX: manufactured
by Nippon Polyurethane Industry Co., Ltd.), 32 parts of methyl
isobutyl ketone and 0.03 part of dibutyltin dilaurate were weighed,
and 87.0 parts of methyl ethyl ketone oxime was added dropwise
thereto from the dropping funnel over 1 hr while stirring and
bubbling nitrogen. Temperature was raised from 50.degree. C. to
70.degree. C. initially. Thereafter, the reaction was continued for
1 hr, and the reaction was continued until the absorption of NCO
group was extinguished by an infrared spectrometer. Then, 0.74 part
of n-butanol and 39.93 parts of methyl isobutyl ketone were added
to prepare a mixture with a non-volatile content of 80%.
Production Example 2B
Production of Emulsion Containing Amine Modified Epoxy Resin and
Blocked Isocyanate Curing Agent
[0189] In a flask equipped with a stirrer, a cooler, a nitrogen
charging tube and a dropping funnel, 71.34 parts of
2,4-/2,6-tolylene diisocyanate (80/20% by weight), 111.98 parts of
methyl isobutyl ketone and 0.02 part of dibutyltin dilaurate were
weighed, and 14.24 parts of methanol was added dropwise from the
dropping funnel over 30 min while stirring and bubbling nitrogen.
The temperature was raised from room temperature to 60.degree. C.
by exothermic heat. Then, after the reaction was continued for 30
minutes, 46.98 parts of ethyleneglycol mono-2-ethylhexyl ether was
added dropwise from the dropping funnel over 30 min. Temperature
was raised to 70 to 75.degree. C. by exothermic heat. After the
reaction was continued for 30 min, 41.25 parts of the adduct of
bisphenol A with propylene oxide (5 mol) (BP-5P manufactured by
Sanyo Kasei Co., Ltd.) was added to the mixture, temperature was
raised to 90.degree. C., and the reaction was continued while
measuring IR spectrum until NCO group was extinguished.
[0190] Successively, 475.0 parts of a bisphenol A type epoxy resin
having an epoxy equivalent of 475 (YD-7011 R manufactured by Tohto
Kasei Co., Ltd.) was added to be homogeneously dissolved, and then,
temperature was raised from 130.degree. C. to 142.degree. C., and
water was removed from the reaction system by azeotrope with MIBK.
After the reaction mixture was cooled to 125.degree. C., 1.107
parts of benzyldimethylamine was added and reaction of forming an
oxazolidone ring by demethanolation was carried out. The reaction
was continued until the epoxy equivalent was 1140.
[0191] Then, the mixture was cooled to 100.degree. C., and 24.56
parts of N-methylethanolamine, 11.46 parts of diethanolamine and
26.08 parts of ketimine of aminoethylethanolamine (78.8% methyl
isobutyl ketone solution) were added thereto to be reacted at
110.degree. C. for 2 hrs Then, 20.74 parts of ethyleneglycol
mono-2-ethylhexyl ether and 12.85 parts of methyl isobutyl ketone
were added to the mixture to be diluted, and non-volatile content
was adjusted to 82%. An amine modified epoxy resin in which number
average molecular weight (by GPC method) was 1380 and amine
equivalent was 94.5 meq/100 g was obtained.
[0192] 145.11 Parts of ion exchanged water and 5.04 parts of acetic
acid were weighed in another container, a mixture of 320.11 parts
(75.0 parts as solid content) of the above-mentioned amine modified
epoxy resin and 190.38 parts (25.0 parts as solid content) of the
blocked isocyanate curing agent of Production Example 1B, which was
heated to 70.degree. C., was added thereto dropwise gradually, and
the mixture was stirred to be homogeneously dispersed. Then, ion
exchanged water was added thereto to adjust the solid content to
36%.
Production Example 3B
Production of Pigment Dispersing Resin Varnish
[0193] In a flask equipped with a stirrer, a cooler, a nitrogen
charging tube, a thermometer and a dropping funnel, 382.20 parts of
a bisphenol A type epoxy resin having an epoxy equivalent of 188
(under product name: DER-331J) and 111.98 parts of bisphenol A were
weighed, temperature was raised to 80.degree. C. to dissolve the
mixture homogeneously, then 1.53 parts of 1% solution of
2-ethyl-4-methylimidazole was added, and reaction was carried out
at 170.degree. C. for 2 hrs. After cooling the mixture to
140.degree. C., 196.50 parts of 2-ethylhexanol-half blocked
isophorone diisocyanate (non-volatile content: 90%) was added to
the mixture, and the reaction was carried out until NCO group was
extinguished. Thereto, 205.00 parts of dipropylene glycol monobutyl
ether was added, successively, 408.00 parts of
1-(2-hydroxyethylthio)-2-propanol and 134.00 parts of dimethylol
propionate were added, 144.00 parts of ion exchanged water was
added, and the mixture was reacted at 70.degree. C. The reaction
was continued until acid value was 5 or less. The obtained resin
varnish was diluted to a non-volatile content of 35% with 1150.50
parts of ion exchanged water.
Production Example 4B
Production of Pigment Dispersed Paste
[0194] In a sand grind mill, 120 parts of the pigment dispersing
resin varnish obtained in Production Example 3B, 100.0 parts of
kaolin, 92.0 parts of titanium dioxide, 8.0 parts of dibutyltin
oxide and 184 parts of ion exchanged water were charged, and
dispersed until particle size was 10 .mu.m or less to obtain a
pigment dispersed paste (solid content: 48%).
Production Example 5B
Production of Crosslinked Resin Particles for Comparison
[0195] In a reaction container, 120 parts of butylcellosolve was
charged, and it was heated to 120.degree. C. with stirring.
Thereto, a solution which was a mixture of 2 parts of
t-butylperoxy-2-ethylhexanoate, and 10 parts of butylcellosolve,
and a monomer mixture containing 15 parts of glycidyl methacrylate,
50 parts of 2-ethylhexyl methacrylate, 20 parts of 2-hydroxyethyl
methacrylate, and 15 parts of n-butyl methacrylate were added
dropwise over 3 hrs. After aging for 30 min, a solution which was a
mixture of 0.5 part of t-butylperoxy-2-ethyl hexanoate and 5. parts
of butylcellosolve was added dropwise for 30 min, and after aging
for 2 hrs, the mixture was cooled. Thereto, 7 parts of
N,N-dimethylaminoethanol and 15 parts of 50% aqueous lactic acid
solution were added to the mixture with heating at 80.degree. C.
and stirring. When an acid value was 1 or less and the rising of
viscosity was stopped, heating was terminated to obtain an acryl
resin having an ammonium group. The number of the ammonium group
per one molecule of the acryl resin having an ammonium group was
6.0.
[0196] To the reaction container, 120 parts of the acryl resin
having an ammonium group and 270 parts of deionized water were
added, and the mixture was stirred with heating at 75.degree. C.
Thereto, the 100% neutralized aqueous solution of 1.5 parts of
2,2'-azobis(2-(2-imidazolin-2-yl)propane) with acetic acid was
added dropwise over 5 min. After aging for 5 min, 30 parts of
methyl methacrylate was added dropwise over 5 min. After aging
further 5 min, an ethylenically unsaturated monomer mixture
containing 170 parts of methyl methacrylate, 40 parts of styrene,
30 parts of n-butyl methacrylate, 5 parts of glycidyl methacrylate
and 30 parts of neopentylglycol dimethacrylate was added to a
solution which was a mixture of 170 parts of the acryl resin having
an ammonium group and 250 parts of deionized water with stirring to
give a pre-emulsion, and the pre-emulsion was added dropwise over
40 min. After aging for 60 min, it was cooled to give a dispersion
of crosslinked resin particles 1. The non-volatile content in the
dispersion of the crosslinked resin particles was 35%, pH was 5.0
and an average particle size was 0.1 .mu.m. Herein, the average
particle size was measured according to the followings.
[0197] The average particle size of the resin particles was
measured by a granular particle transmission measurement method
with MICROTRAC9340UPA manufactured by Nikkiso Co., Ltd. Further,
the particle size distribution of the resin particles was measured
by the measurement device, and an average particle size at a
cumulative relative frequency [F(x)=0.5] was calculated from the
measurement values. In these measurements and calculations, the
employed refractive index of a solvent (water) was 1.33, and the
employed refractive index of the resin content was 1.59.
Production Example 6B
[0198] In a flask equipped with a reflux cooler and a stirrer, 295
parts of methyl isobutyl ketone (hereinafter, abbreviated as
"MIBK"), 37.5 parts of methylethanolamine and 52.5 parts of
diethanolamine were charged, and the mixture was kept at
100.degree. C. with stirring. Thereto, 205 parts of cresol novolac
epoxy resin (under product name; YDCN-703, manufactured by Tohto
Kasei Co., Ltd.) was gradually added. After complete addition, the
reaction was carried out for 3 hrs. When its molecular weight was
measured, it was 2100. When the amine value (MEQ(B)) of the amino
modified resin was measured, it was 340 mmol/100 g.
[0199] 5.5 Parts of formic acid and 1254.5 parts of deionized water
were added to 140 parts of the amino modified resin solution, and
the mixture was stirred for 30 min while keeping it at 80.degree.
C. The organic solvent was removed under reduced pressure to give
an electroconductivity-controlling agent with a solid content of
5.0%.
Example 1B
[0200] 628 Parts of the emulsion obtained in Production Example 2B,
127 parts of the crosslinked resin particles (crosslinked resin
particles in which methyl methacrylate monomer was a main
component; GM-0105 (under product name): manufactured by GANZ
Chemical Co., Ltd.), 4 parts of dibutyltin oxide and 4581 parts of
ion exchanged water were mixed to give a cationic electrodeposition
coating composition in which PWC was 0%, the content of the resin
particles was 15% by weight, and the solid content was 5% by
weight.
Example 2B
[0201] 628 Parts of the emulsion obtained in Production Example 2B,
127 parts of the crosslinked resin particles (crosslinked resin
particles in which methyl methacrylate was a main component;
TAFTIC.RTM.F-200: manufactured by Toyobo Co., Ltd.), 4 parts of
dibutyltin oxide and 4581 parts of ion exchanged water were mixed
to give a cationic electrodeposition coating composition in which
PWC was 0%, the content of the crosslinked resin particles was 15%
by weight, and the solid content was 5% by weight.
Example 3B
[0202] 561 Parts of the emulsion obtained in Production Example 2B,
19 parts of the pigment dispersed paste obtained in Production
Example 4B, 114 parts of the crosslinked resin particles
(crosslinked resin particles in which methyl methacrylate monomer
was a main component; TAFTIC.RTM. F-200: manufactured by Toyobo
Co., Ltd.), 3 parts of dibutyltin oxide and 4303 parts of ion
exchanged water were mixed to give a cationic electrodeposition
coating composition in which PWC was 3%, the content of the
crosslinked resin particles was 10% by weight, and the solid
content was 5% by weight.
Example 4B
[0203] 578 Parts of the emulsion obtained in Production Example 2B,
360 parts of the electroconductivity-controlling agent (solid
content: 5%) obtained in Production Example 6B, 127 parts of the
crosslinked resin particles (crosslinked resin particles in which
methyl methacrylate monomer was a main component; TAFTIC.RTM.
F-200: manufactured by Toyobo Co., Ltd.), 4 parts of dibutyltin
oxide and 4331 parts of ion exchanged water were mixed to give a
cationic electrodeposition coating composition in which PWC was 0%,
the content of the crosslinked resin particles was 15% by weight,
and the solid content was 5% by weight.
Comparative Example 1B
[0204] 2444 Parts of the emulsion obtained in Production Example
2B, 250 parts of the pigment dispersed paste obtained in Production
Example 4B, 2346 parts of ion exchanged water and 10 parts of
dibutyltin oxide were mixed to give a cationic electrodeposition
coating composition in which the solid content was 20% by
weight.
Comparative Example 2B
[0205] 738 Parts of the emulsion obtained in Production Example 2B,
4 parts of dibutyltin oxide and 4598 parts of ion exchanged water
were mixed to give a cationic electrodeposition coating composition
in which PWC was 0% (ash content was not contained), the content of
the crosslinked resin particles was 0% by weight, and the solid
content was 5% by weight.
Comparative Example 3B
[0206] 702 Parts of the emulsion obtained in Production Example 2B,
38 parts of the crosslinked resin particles obtained in Production
Example 5B, 4 parts of dibutyltin oxide and 4596 parts of ion
exchanged water were mixed to give a cationic electrodeposition
coating composition in which PWC was 0%, the content of the
crosslinked resin particles was 5% by weight, and the solid content
was 5% by weight.
Comparative Example 4B
[0207] 665 Parts of the emulsion obtained in Production Example 2B,
76 parts of the crosslinked resin particles obtained in Production
Example 5B, 4 parts of dibutyltin oxide and 4596 parts of ion
exchanged water were mixed to give a cationic electrodeposition
coating composition in which PWC was 0%, the content of the
crosslinked resin particles was 10% by weight, and the solid
content was 5% by weight.
Comparative Example 5B
[0208] 579 Parts of the emulsion obtained in Production Example 2B,
38-parts of the crosslinked resin particles (crosslinked resin
particles in which styrene monomer was a main component;
CHEMISNOW.RTM. SX130M: manufactured by Soken Chemical &
Engineering Co., Ltd.), 4 parts of dibutyltin oxide and 4388 parts
of ion exchanged water were mixed to give a cationic
electrodeposition coating composition in which PWC was 0%, the
content of the crosslinked resin particles was 15% by weight and
the solid content was 5% by weight.
[0209] With respect to thus prepared cationic electrodeposition
coating compositions, the loss elasticity modulus at 80.degree. C.
and the storage elasticity modulus at 140.degree. C. in dynamic
viscoelasticities, and the smoothness and the edge coatability, and
the like were evaluated by the methods below.
[0210] Measurement of Loss Elasticity Modulus and Storage
Elasticity Modulus of Electrodeposition Film
[0211] A tin plate was immersed in the cationic electrodeposition
coating composition prepared as described above. An
electrodeposition film was formed by applying a voltage so that the
film thickness after baking was 15 .mu.m, and then the plate was
rinsed with water to remove the excessive electrodeposition coating
composition. Then, after removing moisture, without drying, the
plate having the uncured coating film was immediately taken out to
prepare a sample. The dynamic viscoelasticities of the sample,
i.e., storage elasticity modulus (G') and loss elasticity modulus
(G'') were measured depending on the temperature with Rheosol-G3000
(manufactured by UBM Corporation) that was a rotational type
dynamic viscoelasticity measurement device (under measurement
conditions: a strain of 0.5 deg; a frequency of 0.02 Hz, and a
raising rate of 2.0.degree. C./min).
[0212] Evaluation of Appearance (Smoothness) of Electrodeposition
Film
[0213] Evaluation of an appearance of an electrodeposition film was
carried out by measuring an arithmetic average roughness (Ra) on a
roughness curve. A cold rolling steel plate treated with zinc
phosphate was immersed in a cationic electrodeposition coating
composition. An uncured electrodeposition film obtained by applying
a voltage, so that the film thickness after baking was 15 .mu.m,
was baked at 160.degree. C. for 10 min. Then, the Ra value of the
uncured electrodeposition film was measured with an evaluation type
surface roughness measuring machine (SURFTEST SJ-201 P manufactured
by Mitsutoyo Corporation) in accordance with JIS-B0601. Measurement
was repeated 7-times on the sample with cut-offs in a width of 2.5
mm (partition number was 5), and the Ra value was an average of the
measured values without the maximum and minimum values. The results
are shown in Tables 2 and 3. It can be understood that the smaller
Ra value provides the better coating film appearance with a
suppressed concavo-convex. Specifically, an acceptable range of the
Ra value is no more than 0.25 .mu.m.
[0214] Evaluation Method for Sedimentability (Planer
Appearance)
[0215] A cold rolling steel plate treated with zinc phosphate was
immersed into each of the cationic electrodeposition coating
compositions obtained in Production Examples and Comparative
Examples, in a horizontal direction, and an uncured
electrodeposition film was obtained by applying a voltage so that
the film thickness after baking was 15 .mu.m. After baking of the
uncured electrodeposition film at 160.degree. C. for 10 min, the
arithmetic average roughness (Ra) on a roughness curve was measured
in a similar manner to that in the above-mentioned evaluation for
an appearance of an electrodeposition film with a surface roughness
measuring machine.
[0216] If sedimentability of an electrodeposition coating
composition is inferior, a horizontal (planar) appearance
(smoothness in a horizontal direction) of the electrodeposition
film is deteriorated in comparison with a vertical appearance
(smoothness in a vertical direction) of the electrodeposition film,
since the sedimentable components are sedimented on a horizontal
plane upon the electrodeposition coating. The sedimentability can
be evaluated from the Ra values of the horizontal appearance and
the vertical appearance, as follows, if the sedimentability is
acceptable or not acceptable.
[0217] Evaluation Basis for Sedimentability
[0218] Acceptable (O): Horizontal Ra value-Vertical Ra value=less
than 0.05 .mu.m
[0219] Not acceptable (X): Horizontal Ra value-Vertical Ra value=no
less than 0.05 .mu.m
[0220] Measurement of Thermal Softening Temperature
[0221] The storage elasticity modulus G' of a sample obtained by
adjusting the concentration of the crosslinked resin particles to
30% by weight (as a solid content) is measured from 90.degree. C.
under conditions of a strain of 0.5 degree, a frequency of 0.02 Hz
and a rising temperature rate of 4.0.degree. C./min in a
temperature dependent measurement with Rheosol-G3000 (manufactured
by UBM Corporation) that is a rotational type dynamic
viscoelasticity measurement device. The measurement results are
shown in a graph in FIG. 8. The tangential line in an area at which
viscosity is a constant and the tangential line in an area at which
the lowering of viscosity occurs are drawn, and the temperature at
the cross point is the thermal softening temperature.
[0222] Evaluation Method for Edge Coatability
[0223] As described above, the edge coatability was evaluated. FIG.
9 is a view schematically showing a point in a distance of 30
microns from the edge of a cutter knife blade. If the thickness of
the film on this point is no less than 7.8 .mu.m, the edge
coatability is acceptable.
[0224] The Measurement Method of Average Particle Size of
Crosslinked Resin Particles
[0225] The average particle size of the crosslinked resin particles
employed in each of the above-described Examples and Comparative
Examples was measured according to the followings. The average
particle size of the crosslinked resin particles was measured by a
granular particle transmission measurement method with
MICROTRAC9340UPA manufactured by Nikkiso Co., Ltd. Further, the
particle size distribution of the crosslinked resin particles was
measured by the measurement device, and an average particle size at
cumulative relative frequency F(x)=0.5 was calculated from the
measurement values. In these measurements and calculations, the
refractive index of a solvent (water) was 1.33, and the refractive
index of resin component was 1.59.
TABLE-US-00002 TABLE 2 Example 1B Example 2B Example 3B Example 4B
Content of inorganic pigment (%) 0 0 3 0 Crosslinked resin Species
Crosslinked resin Crosslinked resin Crosslinked resin Crosslinked
resin particles particles #3 particles #4 particles #4 particles #4
Content (%) 15 15 10 15 Degree of Middle Large Large Large
crosslinking Thermal 120 140 140 140 softening temperature Particle
size (.mu.m) 2.0 2.0 2.0 2.0 Electroconductivity controlling agent
-- -- -- .largecircle. Melt viscosity 80.degree. C./G'' value 113
107 90 99 140.degree. C./G' value 125 475 222 188 Evaluation of
sedimentability .largecircle. .largecircle. .largecircle.
.largecircle. Smoothness Ra (C/0 = 2.5) 0.21 0.23 0.23 0.22 Edge
coatability (.mu.m) 7.8 8.0 7.9 7.8
TABLE-US-00003 TABLE 3 Comparative Comparative Comparative
Comparative Comparative Example 1B Example 2B Example 3B Example 4B
Example 5B Content of inorganic 23 0 0 0 0 pigment (%) Crosslinked
Species -- -- Crosslinked Crosslinked Crosslinked resin resin
particles resin resin particles particles #1 particles #1 #2
Content (%) -- -- 5 10 15 Degree of -- -- Large Large Small
crosslinking Thermal -- -- 140 140 107 softening temperature
Particle size -- -- 0.1 0.1 1.5 (.mu.m) Electroconductivity -- --
-- -- -- controlling agent Melt 80.degree. C./G'' 89 23 156 228 94
viscosity value 140.degree. C./G' 155 21 73 110 75 value Evaluation
of X .largecircle. .largecircle. .largecircle. .largecircle.
sedimentability Smoothness Ra (C/0 = 2.5) 0.18 0.19 0.30 0.37 0.22
Edge coatability (.mu.m) 7.9 3.6 6.0 8.3 5.6
[0226] The degree of the crosslinking was described idepending on
the thermal softening temperature and according to the measurement
of the thermal softening temperature.
Degree of crosslinking (Large): Thermal softening temperature of
140.degree. C. or more. Degree of crosslinking (Middle): Thermal
softening temperature of 120.degree. C. or more and less than
140.degree. C. Degree of crosslinking (Small): Thermal softening
temperature of 120.degree. C. or less Crosslinked resin particles
#1: Crosslinked resin particles obtained in the Production Example
5B. Crosslinked resin particles #2: CHEMISNOW SX-130M (under
product name) manufactured by Soken Chemical & Engineering Co.,
Ltd. Crosslinked resin particles #3: GM-0105 (under product name)
manufactured by GANZ Chemical Co., Ltd. Crosslinked resin particles
#4: F-200 (under product name) manufactured by Toyobo Co., Ltd.
[0227] As seen from the above Tables 2 and 3, it is understood that
the electrodeposition coating composition with a low ash content
and a low solid content, which comprises the crosslinked resin
particles having an average particle size within a range of from
1.0 to 3.0 .mu.m and a thermal softening temperature within a range
of from 120 to 180.degree. C., could provide excellent performances
superior in both of the smoothness and the edge coatability. The
performances are in a similar extent to that of the Comparative
Example 1B which is a conventional coating composition. In the
Comparative Example 1B, the electrodeposition coating composition
comprises a conventional inorganic pigment without any resin
particles, which can provide a good surface smoothness and a good
edge coatability. The electrodeposition coating composition has a
low sedimentability evaluation degree, since the ash content
therein is high. In the Comparative Example 2B, the
electrodeposition coating composition comprising no inorganic
pigments and no resin particles can provide a good smoothness and a
highly deteriorated edge coatability. With respect to the
Comparative Examples 3B to 5B, the electrodeposition coating
composition comprises resin particles. In the Comparative Examples
3B and 4B, the particle size is small. In the Comparative Example
5B, the thermal softening temperature is low. Therefore, the
Comparative Examples 3B to 5B would provide a poor edge coatability
and a poor surface smoothness.
* * * * *