U.S. patent application number 16/496682 was filed with the patent office on 2020-04-30 for coated pigment.
The applicant listed for this patent is Toyo Aluminium Kabushiki Kaisha. Invention is credited to Futa Hayashi, Katsura Kawashima, Masami Sato.
Application Number | 20200131374 16/496682 |
Document ID | / |
Family ID | 63676045 |
Filed Date | 2020-04-30 |
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United States Patent
Application |
20200131374 |
Kind Code |
A1 |
Hayashi; Futa ; et
al. |
April 30, 2020 |
COATED PIGMENT
Abstract
A main object of the present invention to provide a coated
pigment that is composed of a composite particle comprising a
silicon compound coated on the surface of a metal particle, and
that can be dispersed with relatively few aggregates. The present
invention relates to a coated pigment comprising a composite
particle containing a metal particle and one or two or more coating
layers on the surface of the metal particle, wherein (1) at least
one of the coating layers is a silicon compound-containing layer,
and (2) the proportion of aggregates formed by adhesion of at least
four of the composite particles with each other is not more than
35% by number.
Inventors: |
Hayashi; Futa; (Osaka-shi,
JP) ; Sato; Masami; (Osaka-shi, JP) ;
Kawashima; Katsura; (Osaka-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Toyo Aluminium Kabushiki Kaisha |
Osaka-shi |
|
JP |
|
|
Family ID: |
63676045 |
Appl. No.: |
16/496682 |
Filed: |
March 22, 2018 |
PCT Filed: |
March 22, 2018 |
PCT NO: |
PCT/JP2018/011546 |
371 Date: |
November 6, 2019 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C09C 1/648 20130101;
C01P 2004/03 20130101; C08K 3/08 20130101; C08L 87/00 20130101;
C09D 5/028 20130101; C01P 2004/61 20130101; C08K 3/22 20130101;
C09C 1/64 20130101; C09C 3/12 20130101; C08K 9/08 20130101; C08K
3/10 20130101; C01P 2004/62 20130101; C08L 57/00 20130101; C09C
3/08 20130101; C09D 17/00 20130101; C08K 9/02 20130101; C09C 1/62
20130101; B22F 1/00 20130101; B22F 1/02 20130101 |
International
Class: |
C09C 1/64 20060101
C09C001/64; C08L 57/00 20060101 C08L057/00; C08L 87/00 20060101
C08L087/00; C08K 9/02 20060101 C08K009/02; C08K 9/08 20060101
C08K009/08; C08K 3/08 20060101 C08K003/08; C08K 3/10 20060101
C08K003/10; C08K 3/22 20060101 C08K003/22; C09D 5/02 20060101
C09D005/02 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 31, 2017 |
JP |
2017-073272 |
Claims
1. A coated pigment comprising a composite particle containing a
metal particle and one or two or more coating layers on the surface
of the metal particle, wherein (1) at least one of the coating
layers is a silicon compound-containing layer, and (2) the
proportion of the number of aggregates formed by adhesion of at
least four of the composite particles to each other is not more
than 35%.
2. The coated pigment according to claim 1, wherein the shape of
the composite particle is a flake shape, and the volume-based D50
obtained by measuring the particle size distribution with a laser
diffraction particle size distribution analyzer is 0.1 to 50
.mu.m.
3. The coated pigment according to claim 1, comprising at least two
coating layers on the composite particle, and also comprising a
coating layer containing at least one kind selected from metals,
metal oxides, metal hydrates and resins.
4. The coated pigment according to claim 1, wherein at least the
silicon compound-containing layer is disposed as the outermost
layer.
5. The coated pigment according to claim 1, wherein the metal
particle comprises aluminum or an aluminum alloy.
6. A resin composition comprising a coated particle according to
claim 1 and a resin component.
7. A resin composition comprising a coated particle according to
claim 2 and a resin component.
8. A resin composition comprising a coated particle according to
claim 3 and a resin component.
9. A resin composition comprising a coated particle according to
claim 4 and a resin component.
10. A resin composition comprising a coated particle according to
claim 5 and a resin component.
Description
TECHNICAL FIELD
[0001] The present invention relates to a novel coated pigment.
More specifically, it relates to a pigment that can provide
superior hiding power and the like because the individual particles
are highly dispersed.
BACKGROUND ART
[0002] Attention in the paint industry has recently focused on
low-emission paints in an effort to reduce environmental impacts.
Low-emission paints are paints in which the content of hydrocarbons
in the solvent or the like is either 0% or very low, such as
water-based paints, solvent-free paints (powder paints) and the
like. As in the case of conventional organic solvent-based paints,
the use of metal pigments is essential in such low-emission paints
because a metallic appearance is required for a broad range of
applications. However, taking the example of paints using aluminum
pigments, which are especially common as metal pigments, the
problem in the case of water-based paints is that the aluminum
pigments may turn black or emit hydrogen gas when they react with
water in the paint.
[0003] Therefore, to improve the stability of metal pigments in
water-based paints, for example, pigments comprising aluminum
particles coated with amorphous silica or the like have been
proposed (Patent Document 1, (Patent Document 2, etc.).
[0004] For purposes other than improving the stability of metal
pigments in water-based paints, interference pigments comprising
low refractive index layers and high refractive index layers or
transparent layers and metal layers deposited on aluminum pigment
base materials have been proposed in the fields of paints,
coatings, printing, cosmetics and the like in addition to
conventional silver metal pigments. For example, a colored metal
pigment has been proposed (Patent Document 3) comprising at least a
metal pigment, an amorphous silicon oxide film layer formed on the
surface of the metal pigment, a metal layer formed on the surface
of the amorphous silicon oxide film layer, and metal particles
formed on the surface of the metal layer, wherein the metal
particles are provided so as to directly cover a part of the metal
layer.
CITATION LIST
Patent Document
[Patent Document 1] WO2004/096921
[Patent Document 2] Japanese Patent Application Publication No.
2003-147226
[Patent Document 3] Japanese Patent No. 4216903
SUMMARY OF INVENTION
Technical Problem
[0005] When the surface of a metal pigment is coated with amorphous
silica or the like, however, the hiding power after coating is less
than before coating, and brightness declines as a result.
[0006] To investigate the causes of this, we analyzed and
researched the existence states and the like of metal pigments in
coated films before and after the metal pigments were coated with
amorphous silica and the like, and confirmed significant
differences in composition. More specifically, we confirmed that
before a metal pigment is coated with amorphous silica or the like
the individual pigment exist relatively independently in the
coating, but after it is coated with amorphous silica or the like
aggregate particles including two or more metal particles become
coated with the amorphous silica or the like, or the amorphous
silica may actually act as an adhesive to produce aggregates
including two or more pigment (particles).
[0007] As mentioned above, pigments that have been coated with
amorphous silica or the like often exist as aggregates. It is
thought that the hiding power per unit mass declines as a result,
and only coatings with poor brightness can be obtained. These
problems also tend to become more serious when the number of
particles constituting the aggregates become greater. Similarly,
the problems also become more serious, the number of the aggregates
themselves increases.
[0008] Thus, it is a main object of the present invention to
provide a coated pigment that is composed of a composite particle
comprising a silicon compound coated on the surface of a metal
particle, and that can be dispersed with relatively few
aggregates.
Problem to be Solved
[0009] As a result of exhaustive research into these problems of
prior art, the inventors found that the above object is achieved
and perfected the present invention based on the knowledge that a
coated pigment having a unique structure can be obtained by
employing a specific preparation method.
[0010] That is, the present invention relates to the following
coated pigment.
[0011] 1. A coated pigment comprising a composite particle
comprising a metal particle and one or two or more coating layers
on the surface of the metal particle, wherein
[0012] (1) at least one of the coating layers is a silicon
compound-containing layer, and
[0013] (2) the proportion of aggregates constituted by adhesion of
at least four of the composite particles with each other is not
more than 35% by number.
[0014] 2. The coated pigment according to 1 above, wherein the
shape of the composite particle is a flake shape, and the
volume-based D50 obtained by measuring the particle size
distribution with a laser diffraction particle size distribution
analyzer is 0.1 to 50 .mu.m.
[0015] 3. A coated pigment according to 1 or 2 above, comprising at
least two coating layers on the particle, and also comprising a
coating layer including at least one kind selected from metals,
metal oxides, metal hydrates and resins.
[0016] 4. A coated pigment according to any one of 1 to 3 above,
wherein at least the silicon compound-containing layer is disposed
as the outermost layer.
[0017] 5. A coated pigment according to any one of 1 to 4 above,
wherein the metal particle is aluminum or an aluminum alloy.
Advantageous Effects of Invention
[0018] With the present invention, it is possible to provide a
coated pigment that is composed of a composite particle comprising
a silicon compound coated on the surface of a metal particle, and
that can be dispersed with relatively few aggregates.
[0019] In particular, in the present invention the composite
particle can be produced and maintained in a highly dispersed state
because the composite particle is manufactured by subjecting a
metal particle to a coating process under stirring under specific
conditions. As a result, aggregates (aggregated particles)
constituted by adhesion of composite particles with each other can
be greatly reduced. More specifically, it is possible to achieve a
low value of not more than 35% on the number basis as the
proportion of aggregates formed by adhesion of at least four of the
composite particles with each other. By thus effectively reducing
the number of aggregates of many composite particles, it is
possible to provide a pigment with a strong hiding force per unit
mass.
[0020] Thus, the highly dispersible coated pigment of the present
invention can be used in a wide range of applications including
various paints, inks, writing implements, electronic materials and
parts, automobile parts, household electrical goods, cosmetics and
the like for example.
BRIEF DESCRIPTION OF DRAWINGS
[0021] FIG. 1 is a cross-sectional SEM image of a coating formed
using a coated pigment (Comparative Example 1) manufactured by a
conventional technology.
[0022] FIG. 2 is a cross-sectional SEM image of a coating formed
using a coated pigment (Example 1) of the present invention.
DESCRIPTION OF EMBODIMENTS
[0023] 1. Coated Pigment
[0024] The coated pigment of the present invention (pigment of the
invention) is a pigment comprising a composite particle comprising
a metal particle and one or two or more coating layers on the
surface of the metal particle, wherein
[0025] (1) at least one of the coating layers is a silicon
compound-containing layer, and
[0026] (2) the proportion of the number of aggregates constituted
by adhesion of at least four of the composite particles with each
other is not more than 35%.
[0027] Metal Particle
[0028] The composite particle constituting the pigment of the
invention comprises a metal particle and one or two or more coating
layers formed on the surface of the metal particle. That is, the
composite particle has one or two or more coating layers formed on
the surface of a metal particle that serves as a core. A group of
such composite particles constitutes the pigment (powder) of the
invention.
[0029] The material of the metal particle (core particle)
constituting the composite particle is not particularly limited,
and any metal used as a known or commercial metal pigment may be
used, such as aluminum, aluminum alloy, copper, silver, tin,
chromium, stainless steel or the like. In the present invention,
the term "metal" encompasses not only metals by themselves but also
alloys and intermetallic compounds.
[0030] Moreover, the metal particle need not necessarily be
composed only of a metal, and a particle obtained by coating a
metal on the surface of a synthetic resin particle or an inorganic
particle of mica, glass or the like for example may also be used as
long as the advantages of the present invention are obtained. An
aluminum or aluminum alloy particle is especially desirable in the
present invention for reasons of weather resistance, low specific
gravity, availability and the like.
[0031] The average particle diameter of the metal particle is not
particularly limited, and the metal particle may be any that
produces the average particle diameter described below. In other
words, the volume-average particle diameter (D50) of the metal
particle may be set so that the D50 of the pigment of the invention
is 0.1 to 50 .mu.m when the volume distribution of the pigment is
measured with a laser diffraction particle size distribution
analyzer.
[0032] The shape of the metal particle is not particularly limited,
but a flake shape is particularly desirable. This allows the
composite particle constituting the pigment of the invention to
also assume a flake shape, so that a high level of hiding power can
be obtained more reliably. From this perspective, the aspect ratio
of the flake-shaped metal particle (shape factor obtained by
dividing average particle diameter by average thickness) is
preferably 5 to 1,000, or especially 15 to 500. If the aspect ratio
is less than 5, brilliance is likely to be insufficient. If the
aspect ratio exceeds 1,000, on the other hand, the color tone may
be unstable because the mechanical strength of the flakes is
reduced. The average thickness of the metal particle used in the
present invention is calculated here from the water covering area
and density of the metal particle.
[0033] Coating Layer (Silicon Compound-Containing Layer)
[0034] In the composite particle constituting the pigment of the
invention, one or two or more coating layers are formed on the
surface of a metal particle, and at least one of the coating layers
is a silicon compound-containing layer. The composite particle of
the invention encompasses those having other layers as coating
layers instead of the silicon compound-containing layer or in
addition to the silicon compound-containing layer. Examples include
coating layers comprised of metal oxides such as titanium oxide,
zirconium oxide and iron oxide. The explanation below focuses on a
silicon compound-containing layer as a typical example of a coating
layer.
[0035] The silicon compound-containing layer is preferably a layer
composed of a compound containing Si--O bonds in particular
(hereunder also called an "Si--O coating layer"). Examples of such
layers include layers containing at least one kind of silane
compound or silicon oxide. Examples include silane compounds
[H.sub.3SiO(H.sub.2SiO)nSiH.sub.3] (in which n is any positive
integer) and silicon oxides represented by SiO.sub.2,
SiO.sub.2nH.sub.2O (in which n is any positive integer) and the
like. These compounds may be either crystalline or amorphous, but
amorphous compounds are especially desirable. Accordingly, a layer
containing amorphous silica can be employed by preference as a
layer containing a silicon oxide (silica, etc.).
[0036] Layers formed using organic silicon compounds (including
silane coupling agents) as starting materials for example may also
be used as the Si--O coating layer.
Consequently, the silicon compound-containing layer may also
contain an organic silicon compound or a component derived
therefrom as long as they do not substantially adversely affect the
advantages of the present invention.
[0037] In addition, the silicon compound-containing layer need not
be a coating consisting solely of a silicon compound, and may also
contain additives, impurities and the like other than the silicon
compound to the extent that the characteristics required in the
present invention are not adversely affected.
[0038] The silicon content of the silicon compound-containing layer
here is not particularly limited, but is preferably 1 to 20 parts
by mass, or more preferably 2 to 15 parts by mass per 100 parts by
mass of the metal particle. If the silicon content is less than 1
part by mass, corrosion resistance, water dispersibility, stability
and the like tend to decline. If the silicon content exceeds 20
parts by mass, the aluminum pigment may aggregate, the hiding power
may decline, and color tone such as metallic luster may be
adversely affected.
[0039] In the present invention, it is especially desirable for a
coating layer to be hydrophilic. If a coating layer has a
hydrophilic surface, the composite particle can be highly dispersed
in an aqueous solvent (water or a mixed solvent containing water
and an organic solvent).
Furthermore, because silicon oxides (amorphous silica and the like)
are extremely stable in aqueous solvents, it is possible to provide
a pigment that is extremely stable in aqueous solvents. From this
perspective, at least the outermost layer is preferably a layer
containing a silicon-containing compound (especially an Si--O
coating layer) in the pigment of the invention. In this case, if
the coating layer is composed of multiple layers, a layer
containing a silicon-containing compound (especially an Si--O
coating layer) may also be formed separately as a layer other than
the outermost layer to the extent that this does not detract from
the advantages of the present invention.
[0040] The thickness of the coating layer is not particularly
limited, but normally is preferably in the range of about 1 to
2,500 nm (especially 1 to 2,000 nm, or more preferably 1 to 1,500
nm). If the thickness is too small, water resistance will be
insufficient, potentially causing corrosion or discoloration of the
metal particle in a water-based paint. If the coating layer is too
thick, on the other hand, the composite particle will be too thick,
and brightness may decline because the composite particles overlap
one another, disturbing the orientation of the composite particles
in the coated film. Even if the individual composite particles can
be highly dispersed, the distinctness of image of the coated film
may decline because the surface roughness of the coated film is
increased. Moreover, hiding power may also decline because the
proportion of composite particles in the coated pigment per unit
mass decreases.
[0041] The thickness of the silicon compound-containing layer is
also not particularly limited, but in order to more reliably obtain
the functions of the silicon compound-containing layer, the
thickness is preferably in the range of 1 to 1,500 nm, or
especially in the range of 10 to 1,000 nm.
[0042] Coating Layer (Other Layer)
[0043] A coating layer (hereunder called the "second coating
layer") other than the silicon compound-containing layer may also
be formed as necessary as a coating layer of the pigment of the
invention. For example, a molybdenum-containing coating or a
phosphate compound coating or the like may be formed. It is
especially desirable to form the second coating layer between the
metal particle and the silicon compound-containing layer.
Accordingly, for example a layer configuration of "metal
particle/second coating layer/silicon compound-containing layer"
can be adopted by preference.
[0044] To further improve the corrosion resistance of the core
metal particle (preferably aluminum particle or aluminum alloy
particle) in particular, the second coating layer may also be a
layer containing another corrosion inhibitor. There are no
particular limits on the corrosion inhibitor added, and a known
corrosion inhibitor can be used in an amount that does not detract
from the advantageous effects of the invention. Examples include
acidic phosphoric acid esters, dimer acids, organic phosphorus
compounds, metal salts of molybdic acid and the like.
[0045] Coated Pigment (Composite Particle)
[0046] In the coated pigment of the present invention the
proportion of the number of aggregates (aggregate particles)
constituted by adhesion of at least four composite particles with
each other is not more than 35%, or preferably not more than 30%,
or more preferably not more than 20%, or yet more preferably not
more than 10% on the basis of the total number of particles.
The lower limit of the proportion is not particularly limited, but
can be about 5% for example.
[0047] In aggregates formed by adhesion of at least four composite
particles with each other, four or more composite particles
aggregate and interlock to function as a single particle, and is
not separated into individual particles again by ordinary
dispersion operations. Aggregates here also include those
constituted by aggregation of at least four metal particles. For
example, they include those in which a coating layer is formed
after aggregation of at least four metal particles.
[0048] In the present invention, the proportion of aggregates
represents the results of observation of all of coated pigment
composed of 500 to 600 particles obtained by random sampling.
Observation is performed in multiple fields so that the total
number of observed particles is at least 500. More specifically,
observation may be performed by the methods described below under
Test Example 1, "(2) Evaluating degree of overlapping by composite
particles".
[0049] Thus, because the proportion of aggregates constituted by at
least four composite particles, which are relatively large numbers
of composite particles, is minimized in the pigment of the
invention, the hiding power per unit mass of the pigment of the
invention is increased, and even greater brightness and the like
can be achieved. In other words, this excellent hiding power and
brightness of the pigment of the invention can be achieved because
most of the individual composite particles do not aggregate in
large quantities, and effectively exist independently at a level
that does not detract from their hiding power.
[0050] If the proportion A is over 35%, the hiding power of a
coating film formed by the pigment of the invention decreases due
to the presence of large numbers of composite particle in an
aggregated state in the coating film, and good brightness is also
not obtained because the orientation of the composite particles in
the coating film is disturbed (fewer of the composite particles are
arranged parallel to the coating surface). Furthermore, when
relatively large numbers of individual composite particles
aggregate together, because the apparent thickness of the composite
particles increases it increases the surface roughness of the
coating film and causes a decline in the distinctness of image
(DOI) of the coating film. In contrast, in the present invention,
by controlling the proportion A within a specific range, the hiding
power and brightness of the pigment of the invention can be
improved and design properties such as distinctness can also be
improved.
[0051] The particle diameter of the pigment of the invention
(composite particle) is not particularly limited, but preferably
the volume-based median diameter D50 is 1 to 50 m as measured by
laser diffraction. It can thus be set to about 10 to 40 .mu.m for
example. If the D50 is less than 1 .mu.m, the core metal particle
must therefore be a correspondingly fine particle, and in this case
the percentage of metal particles that adhere to one another
increases in the step of coating the surface of the metal particle
with the silicon compound-containing layer, potentially detracting
from the hiding power and brightness. If the D50 is over 50 .mu.m,
on the other hand, it is easy to obtain a highly independent coated
particle without using the method of the invention.
[0052] The D50 here is the 50% cumulative particle diameter
(D.sub.50) in a volume cumulative particle size distribution
obtained by laser diffraction. Because the particle diameter of a
coated pigment in a resin composition as discussed below cannot be
measured by such a method, a method can be substituted in which the
coated pigment in the resin composition is observed from the
coating surface with an optical microscope, laser microscope or the
like, and the distribution of the major axes (distance between the
two most distant points on the outline of the coated pigment in
two-dimensional analysis) is then obtained using commercial image
processing software to determine the particle diameter for
example.
[0053] The shape of the composite particle is not particularly
limited, but a flake shape is particularly desirable as in the case
of the metal particle. A coating film of the pigment of the
invention can thus achieve strong hiding power and the like. From
this perspective, the aspect ratio of the flake-shaped composite
particle (shape factor obtained by dividing average particle
diameter by average thickness) is preferably 5 to 1,000, or
especially 15 to 500. If the aspect ratio is less than 5,
brilliance is likely to be insufficient. If the aspect ratio
exceeds 1,000, on the other hand, the color tone may be unstable
because the mechanical strength of the flakes is reduced. The
average thickness is calculated here from the covering diffusion
area and density of the composite particle.
[0054] 2. Coated Pigment Manufacturing Method
[0055] The pigment of the invention can be manufactured favorably
by a manufacturing method that includes a step of coating a silicon
compound-containing layer onto a metal particle under stirring for
example. More specifically, the method may be the following.
[0056] Namely, the pigment of the invention can be manufactured
favorably by a manufacturing method comprising a step (silicon
compound-containing layer-forming step) in which an organic silicon
compound is hydrolyzed in a liquid mixture containing (a) a metal
particle, (b) a silicon-containing raw material including at least
one kind of the organic silicon compound and (c) a solvent to
thereby form a silicon compound-containing layer on the surface of
the metal particle, wherein at least this step is performed under
stirring.
[0057] Silicon Compound-Containing Layer-Forming Step
[0058] The liquid mixture can be prepared by mixing (a) a metal
particle, (b) a silicon-containing raw material including at least
one kind of organic silicon compound, and (c) a solvent.
[0059] A metal particle described under the above 1. can be used as
the metal particle. In particular, a particle of aluminum or an
aluminum alloy can be favorably used as a metal particle in the
present invention. As explained under the above 1, moreover, a
flake-shaped metal particle can be used by preference. Known or
commercial metal particles can be used as these metal
particles.
[0060] The content (solids content) of the metal particle in the
liquid mixture is not particularly limited, and can be set
appropriately according to the type and particle diameter of the
metal particle used.
[0061] An organic silicon compound is used as a silicon-containing
raw material. The organic silicon compound is not particularly
limited, but for example at least one kind selected from 1) a
tetraalkoxysilane, 2) a tetraalkoxysilane condensate and 3) a
silane coupling agent may be used by preference. The above 1) and
2) here are together called "tetraalkoxysilane" unless otherwise
specified.
[0062] In particular, when a tetraalkoxysilane and a silane
coupling agent are used together, it is possible to use a method
using a mixture of the two (first method), or a method including a
step of treating with one to form a first silicon
compound-containing layer, and then treating with the other to form
a second silicon compound-containing layer (second method).
[0063] An example of the first method is a method including a step
in which the pH of a liquid mixture containing a metal particle, a
tetraalkoxysilane and a silane coupling agent is adjusted to
thereby hydrolyze the tetraalkoxysilane and the silane coupling
agent and form a silicon compound-containing layer.
[0064] An example of the second method is a method including a step
in which the pH of a liquid mixture containing a metal particle and
a tetraalkoxysilane is adjusted to thereby hydrolyze the
tetraalkoxysilane and form a first silicon compound-containing
layer (silica coating including amorphous silica for example) on
the surface of the metal particle, and a step in which the pH of a
liquid mixture containing the particle obtained above and a silane
coupling agent is adjusted to thereby hydrolyze the silane coupling
agent and form a second silicon compound-containing layer on the
surface of the first silicon compound-containing layer.
[0065] The tetraalkoxysilane that is one silicon-containing raw
material is not particularly limited as long as it can serve as a
precursor for forming an Si--O coating layer such as an amorphous
silica layer, and tetraethoxysilane, tetramethoxysilane,
tetraisopropoxysilane or the like or a condensate of these may be
used. These tetraalkoxysilanes can be used independently, or two or
more may be combined.
[0066] The amount of the tetraalkoxysilane or condensate thereof
that is used can be set appropriately according to the type of
tetraalkoxysilane and the like, but normally is preferably 2 to 200
parts by mass, or more preferably 5 to 100 parts by mass per 100
parts by mass of the metal particle. If the content is less than 2
parts by mass, the merit of treatment tends to be insufficient. If
the content exceeds 200 parts by mass, on the other hand, there may
be more aggregation of metal particles or a conspicuous decrease in
brilliance.
[0067] The silane coupling agent that is one silicon-containing raw
material is not particularly limited as long as it can serve as a
precursor for forming an Si--O coating layer, and a known or
commercial silane coupling agent may be used. More specific
examples include organic silane compounds other than
tetraalkoxysilanes. Examples include methyl triethoxysilane, methyl
trimethoxysilane, dimethyl dimethoxysilane, trimethyl
methoxysilane, dimethyl diethoxysilane, trimethyl ethoxysilane,
3-aminopropyl-trimethoxysilane,
n-methyl-3-aminopropyl-trimethoxysilane,
3-aminopropyl-triethoxysilane,
3-aminopropyl-tris(2-methoxy-epoxysilane),
n-aminoethyl-3-aminopropyl trimethoxysilane,
n-aminoethyl-3-aminopropyl-methyl-dimethoxysilane,
3-methacryloxypropyl-trimethoxysilane,
3-methacryloxypropyl-methyl-dimethoxysilane,
3-acryloxypropyl-trimethoxysilane,
3-glycidyloxypropyl-trimethoxysilane,
3-glycidyloxypropyl-methyl-dimethoxysilane,
3-mercaptopropyl-trimethoxysilane,
3-mercaptopropyl-triethoxysilane,
3-mercaptopropyl-methyl-dimethoxysilane, vinyl trichlorosilane,
vinyl trimethoxysilane, vinyl triethoxysilane,
vinyl-tris(2-methoxyethoxy) silane, vinyl triacetoxysilane,
3-(3,4-epoxycyclohexylethyltrimethoxy) silane, .gamma.-aminopropyl
triethoxysilane, N-.beta.-(aminoethyl)-.gamma.-aminopropyl
trimethoxysilane, 3-ureidopropyl triethoxysilane, 3-chlorpropyl
trimethoxysilane, 3-anilidopropyl trimethoxysilane,
3-(4,5-dihydroimidazolpropyltriethoxy) silane,
n-phenyl-3-aminopropyl trimethoxysilane, heptadecafluorodecyl
trimethoxysilane, tridecafluorooctyl trimethoxysilane,
trifluoropropyl trimethoxysilane, 3-isocyanatopropyl
triethoxysilane, p-styryl trimethoxysilane and the like. One or two
or more kinds of these may be used.
[0068] In the present invention, the following compounds are
examples of especially desirable silane coupling agents:
R.sub.A--Si(OR.sub.B).sub.3 or
R.sub.A--SiR.sub.B(OR.sub.B).sub.2
(in which R.sub.A represents a C.sub.2-18 alkyl group, C.sub.2-18
aryl group or C.sub.2-18 alkenyl group, and R.sub.B represents a
C.sub.1-3 alkyl group).
[0069] Examples of such compounds include at least one of n-propyl
trimethoxysilane, isobutyl trimethoxysilane, octyl triethoxysilane,
decyl trimethoxysilane, octadecyl triethoxysilane, phenyl
trimethoxysilane, phenyl triethoxysilane, diphenyl diethoxysilane
and the like.
[0070] The amount of the silane coupling agent used is not
particular limited, but is normally about 0.1 to 20 parts by mass
or especially 1 to 10 parts by mass per 100 parts by mass of the
metal particle. If this amount is less than 0.1 part by mass, the
desired effects may not be obtained. If this amount exceeds 10
parts by mass, on the other hand, the physical coating properties
and the like may decline because there is too much unreacted silane
coupling agent.
[0071] The solvent in the liquid mixture can be selected
appropriately according to the type of silicon-containing raw
material and the like, and may normally be 1) water, 2) a
hydrophilic organic solvent, or (3) a mixed solvent of these. Of
these, it is desirable to include a hydrophilic organic solvent in
order to avoid abnormal reactions between the metal particles and
water as much as possible. Accordingly, a mixed solvent of water
and a hydrophilic organic solvent can be used by preference in the
present invention.
[0072] Examples of hydrophilic organic solvents include methyl
alcohol, ethyl alcohol, isopropyl alcohol, n-propyl alcohol,
t-butyl alcohol, n-butyl alcohol, isobutyl alcohol, ethyl
cellosolve, butyl cellosolve, propylene glycol monobutyl ether,
dipropylene glycol monomethyl ether, propylene glycol monopropyl
ether, acetone and the like. One or two or more kinds of these can
be used.
[0073] When using a mixed solvent of water and a hydrophilic
organic solvent as the solvent above, the ratios of each are not
particularly limited, but from the perspective of preventing
abnormal reactions between the metal particles and water, the
content of water is preferably not more than 20 mass % given 100
mass % as the total of the two. In this case there is no particular
lower limit on the water content, which may normally be about 1
mass %.
[0074] The amount of the solvent used is not particularly limited,
but may normally be about 500 to 10,000 parts by mass or preferably
1,000 to 5,000 parts by mass per 100 parts by mass of the metal
particle. If this amount is less than 500 parts by mass the
viscosity of the mixture (slurry) may increase, making stirring
difficult. If the amount exceeds 10,000 parts by mass, on the other
hand, the costs of collecting and recycling the treatment liquid
tend to increase.
[0075] Other additives may be added as necessary in the liquid
mixture so as to not adversely affect the advantages of the
invention. Examples include catalysts such as hydrolysis catalysts
and dehydration condensation catalysts, as well as surfactants,
metal corrosion inhibitors and the like.
[0076] Of these, a hydrolysis catalyst can be used by preference in
the present invention. By using a hydrolysis catalyst, it is
possible to not only adjust the pH of the liquid mixture, but also
to efficiently hydrolyze and dehydration condense the organic
silicon compound, allowing a silicon compound-containing layer to
be efficiently and reliably formed on the surface of the metal
particle.
[0077] A known or commercial hydrolysis catalyst may be used,
without any particular limitations. Examples include basic
hydrolysis catalysts such as monoethanolamine, diethanolamine,
triethanolamine, ammonia, ethylenediamine, t-butylamine,
3-aminopropyl triethoxysilane, n-2-aminoethyl-3-aminopropyl
triethoxysilane, n-2-aminoethyl-3-aminopropyl methyl
dimethoxysilane, urea, sodium silicate and sodium hydroxide, and
acidic hydrolysis catalysts such as oxalic acid, acetic acid,
nitric acid, sulfuric acid, phosphoric acid, phosphonic acid and
the like. One or two or more kinds of these may be used.
[0078] The amount of the hydrolysis catalyst is not particularly
limited, but may normally be 0.1 to 20 parts by mass, or preferably
0.5 to 10 parts by mass per 100 parts by mass of the metal
particle. If the amount is less than 0.1 part by mass, the
precipitation amount of the silicon compound-containing layer may
be insufficient. If the amount exceeds 20 parts by mass, on the
other hand, aggregation of metal particles tends to be much
greater.
[0079] When preparing the liquid mixture, mixing may be performed
so that these components can be uniformly mixed in the liquid
mixture, and the order of addition is not particularly limited.
However, as discussed below, it is necessary to prepare the liquid
mixture under stirring in the present invention.
[0080] The temperature of the liquid mixture may be room
temperature or heated. Normally it may be 20.degree. C. to
90.degree. C., and 30.degree. C. to 80.degree. C. is especially
desirable. If the temperature is below 20.degree. C., the rate of
formation of the silicon compound-containing layer is slower, and
the processing time tends to be greater. If it exceeds 90.degree.
C., on the other hand, it becomes difficult to control the
reaction, and the desired composite particle may not be
obtained.
[0081] A silicon compound-containing layer is formed on the surface
of the metal particle in the liquid mixture by hydrolysis of the
silicon-containing raw material. This hydrolysis can be
accomplished in particular by pH adjustment of the liquid mixture
or the like.
[0082] When adjusting the pH, it is desirable to adjust the pH
appropriately so that it can be maintained within a fixed range at
the stage of forming the silicon compound-containing layer on the
surface of the metal particle because the pH of the liquid mixture
fluctuates especially at this stage. It is desirable to adjust the
pH by adding a hydrolysis catalyst at this stage, but the pH may
also be adjusted using another acidic or alkaline compound as long
as the properties of the pigment of the invention are not adversely
affected.
[0083] In the present invention, the pH of the liquid mixture is
preferably controlled as follows when using a hydrolysis
catalyst.
[0084] When using a basic hydrolysis catalyst as the hydrolysis
catalyst, the pH is preferably 7 to 11, or especially 7.5 to 10. If
the pH is less than 7, the silicon compound-containing layer may
form more slowly. If the pH exceeds 11, on the other hand, the
metal particles may aggregate or brilliance may decline. There is
also a risk of hydrogen gas occurring due to corrosion. From the
perspective of quality, using an acidic hydrolysis catalyst is not
much different from using a basic hydrolysis catalyst.
[0085] When using an acidic hydrolysis catalyst, the pH is
preferably 1.5 to 4, or especially 2 to 3. If the pH is less than
1.5, the desired coated particle may not be obtained because the
reaction cannot be controlled. If the pH exceeds 4, on the other
hand, the silicon compound-containing layer tends to be
precipitated more slowly.
[0086] Step of Forming Second Coating Layer
[0087] In the present invention, if necessary, a second coating
layer can be formed on the surface of the metal particle prior to
forming the silicon compound-containing layer with the aim of
improving the corrosion resistance of the metal particle for
example and promoting the formation of the silicon
compound-containing layer and the like.
[0088] As shown above, various kinds of coatings are possible as
the second coating layer. Thus, a molybdenum-containing coating
film may be formed as the second coating layer for example. When a
molybdenum-containing coating film is formed, it serves as a
nucleus or seeds for precipitation to facilitate formation of a
silicon compound-containing layer that covers more of the surface
of the molybdenum-containing coating film. Because a
molybdenum-containing coating film has a certain degree of
corrosion resistance, moreover, it can increase the corrosion
resistance of the coated pigment of the invention. Furthermore, a
molybdenum-containing coating film also has the ability to control
or prevent abnormal reactions by metal particles in the liquid
mixture in the step of forming the silicon compound-containing
layer. Formation of a molybdenum-containing coating film as a
second coating layer is explained below as a typical example.
[0089] Thus, the present invention encompasses a manufacturing
method comprising a step of forming a molybdenum-containing coating
film on the surface of the metal particle by stirring a dispersed
solution containing the metal particle and a molybdenum compound
prior to forming the silicon compound-containing layer.
[0090] The method for forming the molybdenum-containing coating
film on the surface of the metal particle is not particularly
limited, and may be any capable of uniformly stirring a liquid
mixture containing a molybdenum compound and a metal particle in an
aqueous solvent. One example is a method of forming a
molybdenum-containing coating film on the surface of a metal
particle by stirring or kneading a dispersion solution of the
molybdenum compound and the metal particle in a slurry or paste
form. The molybdenum compound may be either dissolved or dispersed
in the dispersion solution. Consequently, it is possible to use a
dispersion solution in which the molybdenum compound is dissolved
for example.
[0091] The stirrer or mixer used in the step of stirring the
dispersion solution containing the molybdenum compound and the
metal particle is not particularly limited, and a known mixer
capable of efficiently and uniformly stirring a dispersion solution
containing a molybdenum compound and an aluminum particle may be
used. Specific examples include kneaders, kneading machines,
rotating container agitators, stirring reaction tanks, V-shaped
mixers, double cone mixers, screw mixers, sigma mixers, flash
mixers, airflow agitators, ball mills, edge runner mixers and the
like.
[0092] The molybdenum compound used as a starting material is not
particularly limited, and may be any that can serve as a precursor
for forming a molybdenum-containing coating film when added and
stirred with a liquid dispersion containing a metal particle.
Examples include peroxo-polymolybdic acid, ammonium molybdate,
phosphomolybdic acid and the like. These molybdenum compounds may
be used individually, or two or more may be combined.
Peroxo-polymolybdic acid in particular can be used favorably in the
present invention. Peroxo-polymolybdic acid is a compound
ordinarily represented by compositional formula (1) below, and can
be prepared by dissolving metal molybdenum powder, molybdenum oxide
or the like in a in a 5% to 40% aqueous hydrogen peroxide
solution:
MoxOymH.sub.2O.sub.2nH.sub.2O (1)
(wherein x represents 1 or 2, y represents an integer from 2 to 5,
and m and n represent any positive integers).
[0093] The amount of the molybdenum compound used may be set
appropriately according to the type of molybdenum compound used and
the like, but may ordinarily be 0.02 to 20 parts by mass, or
preferably 0.1 to 10 parts by mass per 100 parts by mass of the
metal particle. If the content is less than 0.02 part by mass, the
profitable effect of treatment may be insufficient. If it exceeds
20 parts by mass, on the other hand, the resulting coated pigment
may be insufficiently brilliant.
[0094] Normally 1) water, 2) a hydrophilic organic solvent or 3) a
mixture of these may be used as the solvent for stirring the metal
particle with the molybdenum compound.
[0095] Examples of hydrophilic organic solvents include methyl
alcohol, ethyl alcohol, isopropyl alcohol, n-propyl alcohol,
t-butyl alcohol, n-butyl alcohol, isobutyl alcohol, ethyl
cellosolve, butyl cellosolve, propylene glycol monobutyl ether,
dipropylene glycol monomethyl ether, propylene glycol monopropyl
ether, acetone and the like. One or two or more of these can be
used.
[0096] In the present invention, a mixed solvent of water and a
hydrophilic organic solvent is preferred over a hydrophilic organic
solvent alone. This is because the rate of contact between the
metal particle and the molybdenum compound can be further increased
by using a mixed solvent of water and a hydrophilic organic
solvent.
[0097] The amount of the solvent used is not particularly limited,
but normally is preferably 50 to 5,000 parts by mass, or more
preferably 100 to 2,000 parts by mass per 100 parts by mass of the
metal particle. If the amount of the solvent is less than 50 parts
by mass, the molybdenum compound becomes unevenly distributed, and
the metal particles tend to aggregate conspicuously. If it exceeds
5,000 parts by mass, on the other hand, the treatment effect of the
metal particle by the molybdenum compound may be insufficient.
[0098] In the step of stirring a liquid mixture containing the
metal particle and the molybdenum compound, the temperature of the
liquid mixture during the stirring step may normally be about
10.degree. C. to 100.degree. C., or especially 30.degree. C. to
80.degree. C. If the temperature is below 10.degree. C., the
reaction time required to obtain a sufficient treatment effect
tends to be longer. If it exceeds 100.degree. C., on the other
hand, the reaction may not be controllable, and the desired coated
pigment may not be obtained.
[0099] In the step of stirring the liquid mixture, the stirring
time may be any time sufficient to form the desired
molybdenum-containing coating. In the present invention, it is
preferably 0.5 to 10 hours for example, or more preferably 1 to 5
hours. If the stirring time is less than 0.5 hours, the desired
effect of treatment tends to be insufficient. If it exceeds 10
hours, on the other hand, the treatment costs tend to increase.
[0100] Particles having a formed second coating layer may be
collected after completion of the step of stirring the liquid
mixture containing the metal particle and molybdenum compound. In
this case, known washing and solid-liquid separation steps or the
like may be performed as necessary. For example, the liquid mixture
is preferably washed with a hydrophilic organic solvent and
filtered with a filter or the like, and water and unreacted
material are then removed from the resulting cake containing a
metal particle having a molybdenum-containing coating film. A
molybdenum-containing coating film may thus be formed as the second
coating layer. When another second coating layer is to be formed,
this may be carried out by the methods described above.
[0101] Stirring Step
[0102] In the manufacturing method of the invention, at least the
step of forming the silicon compound-containing layer is performed
under stirring. More specifically, it is necessary that the
reaction system be under stirring at least when the pH is adjusted
or when the catalyst is added. By thus performing the step of
forming the silicon compound-containing layer under stirring, it is
possible to effectively inhibits adhesion of composite particles to
one another via the silicon compound-containing layer, or
deposition of the silicon compound-containing layer on aggregates
particles formed from metal particles. As a result, it is possible
to more reliably obtain a pigment of the invention in which the
proportion of aggregates constituted by adhesion of four or more
composite particles is not more than 35% by number.
[0103] In the present invention, moreover, stirring is preferably
performed not only during the step of forming the silicon
compound-containing layer, but throughout all steps. That is,
stirring is preferably performed at least from the point at which
the metal particle is dispersed in the solvent until the end of the
reaction (the point at which formation of all desired layers on the
surface of the metal particle is complete). When stirring is ended
or interrupted before the reaction is complete, there is a risk
that metal particles or composite particles may aggregate due to
the presence of unreacted components, and the desired coated
particle may not be obtained.
[0104] Stirring itself may be performed with a known or commercial
stirring apparatus. For example, at least one kneader, kneading
machine, rotating container agitator, stirring reaction tank,
V-shaped mixer, double cone mixer, screw mixer, sigma mixer, flash
mixer, airflow agitator, ball mill, edge runner mixer or the like
may be used.
[0105] Of these, an apparatus that mixes with a stirring blade
(impeller) is desirable. In addition to the circulating action that
causes the reaction system composed of a liquid phase as a whole to
flow, an impeller blade also effectively inhibits aggregates
through a pressure shear action.
[0106] The shape of the impeller is not particularly limited, and
for example a propeller shape, turbine shape, fan turbine shape,
paddle shape, inclined paddle shape or gate shape may be used.
Impellers of these shapes can be combined in multiple stages.
[0107] The stirring speed is preferably such that the impeller
blade is not exposed by the vortex created by stirring. A
cylindrical tank or square tank or a tank equipped with a baffle
plate or the like may preferably be used to prevent the vortex
created by stirring.
[0108] The degree of stirring is not particularly limited as long
as a good dispersion can be obtained, but the stirring Reynolds
number (hereunder abbreviated as "stirring Re number") is
preferably at least 6,000, or more preferably at least 10,000. The
maximum stirring Re number may differ according to the type and
scale of the stirring apparatus for example, and may be about
100,000 in the case of an ordinary laboratory scale apparatus for
example, but may also exceed 100,000 in a range that does not
substantially adversely affect the advantages of the present
invention. An Re number of 1,000,000 is also allowable in the
present invention for example.
[0109] In the present invention, the stirring Re number is
calculated by the following formula:
Stirring Re number=(.rho..times.n.times.d.sup.2)/.mu.
(in which .rho. is the density (kg/m.sup.3) of the liquid mixture
at 25.degree. C., n is the stirring rotation (rps), d is the
impeller span (blade diameter) (m), and .mu. is the viscosity (Pas)
of the liquid mixture at 25.degree. C.).
[0110] Thus, in the manufacturing method of the invention the
stirring Re number can be controlled by setting the optimum
stirring rotation and impeller span in relation to the physical
properties of the liquid mixture used for example. In this case,
the ranges of these values are not particularly limited as long as
the stirring Re number is set within the above range. As one
example, the stirring rotation may be set within a range of 1 to
100 rps, the impeller span within a range of 0.1 to 5 .mu.m, the
density within a range of 500 to 1,500 kg/m.sup.3 and the viscosity
within a range of 1,000 to 30,000 Pas according to the type of
apparatus used and the like if necessary.
[0111] Composite Particle Collection Step
[0112] After completion of the step of forming the silicon
compound-containing layer on the metal particle, the resulting
composite particle (coated pigment) may be collected. In this case,
known treatments such as washing, solid-liquid separation and the
like can be performed as necessary. For example, it is desirable to
first wash the dispersion solution with an organic solvent, filter
it with a filter, and then remove the water and unreacted material
from the resulting cake containing the composite particle. The cake
containing the composite particle may then also be heated treated
as necessary at a temperature in the range of 100.degree. C. to
500.degree. C. for example.
[0113] 3. Resin Composition
[0114] The present invention encompasses a resin composition
containing the pigment of the invention and a resin component. It
also encompasses a molded body of the resin composition.
[0115] The resin component is not particularly limited, and for
example an acrylic resin, alkyd resin, polyester resin,
polyurethane resin, polyvinyl acetate resin, nitrocellulose resin,
fluorine resin or the like may be used by preference.
[0116] A coloring pigment other than the pigment of the invention
can also be used in the resin composition of the invention as
necessary. Examples include phthalocyanine, quinacridone,
isoindolinone, perylene, azo lake, iron oxide, chrome yellow,
carbon black, titanium oxide, pearl mica and the like.
[0117] Various additives can also be added to the resin composition
as necessary. Examples include surfactants, curing agents, UV
absorbers, antistatic agents, thickeners, extender pigments, dyes,
corrosion inhibitors and the like. Water or an organic solvent
(particularly a hydrophilic organic solvent) or the like may also
be included.
[0118] The content of the pigment of the invention in the resin
composition of the invention is not limited, but may normally be
0.1 to 30 mass %, or preferably 1 to 20 mass %. If the content is
less than 0.1 mass % the decorative effect (metallic appearance)
tends to decline. If it exceeds 30 mass %, the characteristics of
the resin composition (weather resistance, corrosion resistance,
mechanical strength, etc.) may be insufficient.
[0119] The resin composition of the present invention can be used
as is as a paint or ink, or it can be added to commercial available
paints, inks and the like. Such paints and inks can be used as a
water-based paint and water-based ink by preference.
[0120] The resin composition of the invention may also be molded as
is to provide a molded body. The resin composition of the invention
may also be kneaded and molded together with a rubber composition,
plastic composition or the like. A molded body of the resin
composition of the invention can have a good external appearance
with excellent metallic appearance, and can also be excellent in
weather resistance and stability.
[0121] 5. Water-Based Paint and Water-Based Ink Containing Pigment
of Invention
[0122] The present invention also encompasses a water-based paint
and water-based ink (hereunder sometimes called together a
"water-based paint or the like") containing the pigment of the
invention together with at least one of a solvent and a binder. A
water-based paint or the like containing the pigment of the
invention together with a solvent and a binder can be used by
preference.
[0123] The binder used in the water-based paint or the like
containing the pigment of the invention is not particularly
limited, but for example a resin binder such as an acrylic resin,
alkyd resin, polyester resin, polyurethane resin, polyvinyl acetate
resin, nitrocellulose resin, fluorine resin or the like can be
preferably used. One or two or more kinds of these can be used.
[0124] The binder used in the water-based paint or the like may be
any binder commonly used in known water-based paints and the like
that can be coated and cured to form a good coating film, and in
addition to resin binders, organic components such as rubber
compositions, plastic compositions and natural polymer compositions
can also be used as binders.
[0125] The water-based paint or the like may also contain another
coloring pigment other than the pigment of the invention to the
extent that this does not detract from the profitable effects of
the invention. This coloring pigment is not particularly limited,
but examples include phthalocyanine, quinacridone, isoindolinone,
perylene, azo lake, iron oxide, chrome yellow, carbon black,
titanium oxide, pearl mica and the like.
[0126] Additives that are added to know water-based paints and the
like can also be added as necessary. Examples include surfactants,
curing agents, UV absorbers, antistatic agents, thickeners,
extender pigments, dyes or the like.
[0127] The solvent can be any water-based solvent, and for example
water or a mixed solvent of water and a hydrophilic organic solvent
or the like can be used. The hydrophilic organic solvent is not
particularly limited, but examples include methyl alcohol, ethyl
alcohol, isopropyl alcohol, n-propyl alcohol, t-butyl alcohol,
n-butyl alcohol, isobutyl alcohol, ethyl cellosolve, butyl
cellosolve, propylene glycol monobutyl ether, dipropylene glycol
monomethyl ether, propylene glycol monopropyl ether, acetone and
the like.
[0128] The content of the pigment of the invention in the
water-based paint or the like is not particularly limited, but is
preferably 0.1 to 30 mass %, or more preferably 1 to 20 mass % of
the binder content. If the content of the pigment of the invention
is less than 0.1 mass %, the decorative effect (metallic
appearance) of a coating of the water-based paint or the like will
tend to decline, while if the content exceeds 30 mass % the coating
properties (weather resistance, corrosion resistance, mechanical
strength, etc.) of the water-based paint or the like may be
insufficient.
[0129] The content of the solvent may be set appropriately
according to the type of the pigment of the invention used and the
like, but normally is preferably 20 to 200 mass %, or more
preferably 50 to 100 mass % of the binder content. If the solvent
content is less than 20 mass %, the viscosity of the paint or ink
increases, and it may be difficult to handle. If it exceeds 200
mass %, on the other hand, it may be difficult to perform the film
forming because the viscosity of the paint or ink is too low.
[0130] The applications of the pigment of the invention are not
limited to adding in water-based paints and the like, and it can
also be added to paints containing organic solvents, inks
containing organic solvents, powder coatings, rubber compositions,
plastic compositions, natural macromolecular compositions and the
like.
[0131] The method for coating or printing the water-based paint or
the like is not particularly limited, and various coating methods
and printing methods can be adopted appropriately according to the
form of the water-based paint or the like, the surface shape of the
object to be decorated and the like. Examples of coating methods
include spray methods, roll coater methods, brush painting methods,
doctor blade methods and the like. Examples of printing methods
include gravure printing, screen printing and the like.
[0132] A coating film formed with a water-based paint or the like
containing the pigment of the invention can also be formed on an
under coating or intermediate coating formed by electrodeposition
or the like. A top coat layer or the like can also be formed on a
coating formed with the water-based paint or the like if
necessary.
[0133] In this case, each coating layer may be applied and cured or
dried before applying the next coating layer, or the next coating
layer may be applied without curing or drying the previous coating
layer in so-called "wet-on-wet" coating. To obtain a coating with
good mirror brilliance in the present invention, it is desirable to
employ a method including a step in which a coating layer of the
water-based paint is formed after an under coating has been applied
and then cured or dried.
[0134] The method of curing the coating composition of each coating
layer may be a heat curing method or a room-temperature curing
method for example. The method for drying the coating composition
of each coating layer may be a hot air drying method, or a natural
drying method at room temperature.
[0135] In this case, the thickness of the coating layer formed from
the water-based paint or the like is not particularly limited, but
in an ordinary embodiment it may be about 2 to 100 .mu.m, or
preferably 5 to 50 .mu.m. If the coating layer is less than 2 .mu.m
thick, the hiding effect of the substrate by the ink or paint may
be insufficient. If the thickness exceeds 100 .mu.m, drying becomes
difficult, and there may be more defects such as bubbles and
sagging.
EXAMPLES
[0136] Features of the invention are explained in more detail below
using Examples and Comparative Examples.
However, the scope of the invention is not limited to the
Examples.
Example 1
[0137] First, commercial aluminum pigment flakes (product name
"7670NS", manufactured by Toyo Aluminum K.K., average particle
diameter 15 .mu.m, aspect ratio 68) in the amount of 100 g as
solids were added to 1,000 g of isopropyl alcohol, and thoroughly
mixed to prepare an aluminum slurry. At this point the aluminum
slurry had a viscosity of about 10 mPas (25.degree. C.), and a
liquid density of about 830 kg/m.sup.3 (25.degree. C.). This
aluminum slurry was placed in a roughly 4.5 L round-bottomed flask,
and heated to 50.degree. C. under stirring with a three-bladed
propeller stirrer (Tokyo Rikakikai Co., Ltd., marine blade) so that
the stirring Reynolds number was 19,000. In the following steps,
stirring was also performed so as to maintain the same stirring
Reynolds number.
[0138] Next, 0.5 g of metal molybdenum powder was added bit by bit
to 10 g of hydrogen peroxide water containing 30% hydrogen
peroxide, and reacted to prepare a solution. The resulting aqueous
solution containing molybdenum was added gradually to the previous
aluminum slurry, and stirred continuously as is for 60 minutes.
[0139] Monoethanolamine was then added to the above slurry to
adjust the pH of the slurry to the range of 8.0 to 10.
[0140] 40 g of tetraethoxysilane (hereunder abbreviated as "TEOS")
was then added gradually to the pH-adjusted slurry, which was then
further stirred for 5 hours at 50.degree. C. After completion of
this reaction, the slurry was subjected to solid-liquid separation
with a filter, and the concentration was adjusted with isopropyl
alcohol to a solids content of 50% to obtain a coated aluminum
pigment comprising a flake-shaped composite particle.
[0141] The stirring Reynolds number (stirring Re number) here is
calculated by the following formula:
Stirring Re number=(.rho..times.n.times.d.sup.2)/.mu.
.rho.: density (kg/m.sup.3) of liquid dispersion containing metal
particle at 25.degree. C. n: stirring rotation (rps) d: impeller
span (m) .mu.: viscosity (Pas) of liquid dispersion containing
metal particle at 25.degree. C.
Example 2
[0142] A coated aluminum pigment was obtained by the same
operations as in Example 1 except that the stirring Re number was
14,000.
Example 3
[0143] A coated aluminum pigment was obtained by the same
operations as in Example 1 except that the stirring Re number was
10,005.
Example 4
[0144] A coated aluminum pigment was obtained by the same
operations as in Example 1 except that the stirring Re number was
12,000.
Example 5
[0145] A coated aluminum pigment was obtained by the same
operations as in Example 1 except that a flake-shaped aluminum
pigment having an average particle diameter of 6 .mu.m was used,
and the stirring Re number was 19,200.
Example 6
[0146] A coated aluminum pigment was obtained by the same
operations as in Example 1 except that a flake-shaped aluminum
pigment with an average particle diameter of 25 .mu.m was used, and
the stirring Re number was 10,000.
Example 7
[0147] A coated aluminum pigment was obtained by the same
operations as in Example 1 except that a flake-shaped aluminum
pigment with an average particle diameter of 32 .mu.m was used, and
the stirring Re number was 10,000.
Comparative Example 1
[0148] A coated aluminum pigment was obtained by the same
operations as in Example 1 except that the stirring Re number was
5,000.
Test Example 1
[0149] The particle diameters and the like of the coated aluminum
pigments obtained in the examples and comparative examples were
measured. The results are shown in Table 1.
TABLE-US-00001 TABLE 1 Stirring Coated Proportion of Re pigment D50
aggregates of at least L * 15.degree. number (.mu.m) four particles
(%) value Example 1 19011 15 5 128.8 Example 2 14008 15 10 127.2
Example 3 10005 15 35 122.8 Example 4 12000 15 20 125.5 Example 5
19200 8 30 110.0 Example 6 10000 28 5 135.8 Example 7 10000 32 5
130.3 Comparative 5000 15 40 117.3 Example 1
[0150] The particle diameters and the like of the coated pigments
obtained in the Examples and Comparative Examples were measured as
follows.
[0151] (1) Particle Diameter
[0152] A "Microtrac MT3000 II" laser diffraction particle size
analyzer was used as the analysis device. About 0.1 g of coated
pigment was first dispersed in 20 g of isopropyl alcohol. This
dispersion was loaded into the Microtrac, dispersed for 1 minute
with the ultrasound disperser accessory to the device (output 40
W), and measured. The circulating solvent in the device was
isopropyl alcohol that was the same as the dispersion solvent. The
particle size distribution was then measured immediately. The D50
in the present invention is the median diameter in the volume-based
distribution.
[0153] (2) Evaluating Degree of Overlapping by Composite
Particles
[0154] 16.9 g of NIPPONPAINT Co., Ltd. Nax Admila 280 correction
clear was mixed with 2.8 g of Nax Admila 901 binder, and stirred
with a glass rod to prepare a paint. Next, the pigment obtained in
the Examples and Comparative Examples in the amount of 1.2 g as
solids was added to the paint, and stirred with a glass rod. This
was then thoroughly dispersed with a stirring deaerator to prepare
a paint containing a dispersed aluminum pigment.
[0155] The prepared paint with dispersed aluminum pigment was
applied with a 9-mil applicator to a polyethylene terephthalate
film (PET film), left for 20 minutes at room temperature, and then
baked for 20 minutes at 140.degree. C. The resulting coated film
was peeled off the PET film to obtain a test piece for
observation.
[0156] The test piece for observation was worked into a sample
piece for cross-sectional observation with an ion
milling/cross-section polisher (Hitachi High-Technologies
Corporation "E-3500"). The worked test piece was then observed with
an FE-SEM (Hitachi High-Technologies Corporation "SU8200") to
observe the degree of overlapping among particles.
[0157] First, if overlapping was easily detected, the test piece
was observed at a magnification of about 1,000.times. to
3,000.times.. If overlapping was not detected at this
magnification, overlapping was evaluated by changing the
magnification appropriately. In this observation method,
observation was performed up to a maximum magnification of roughly
100,000.times.. Multiple visual fields were observed from a
cross-section of the same sample until the number of observed
particles was at least 500. Examples of such visual field
observation are shown in FIGS. 1 and 2. While numerous aggregates
constituted by at least four composite particles are seen in FIG. 1
(Comparative Example 1), in FIG. 2 (Example 1) the composite
particles are in a roughly independent state.
[0158] When it is difficult to detect aggregates (aggregated
states) by such an observation method, aggregation can further
evaluated according to the following criteria a) and b).
[0159] a) No aggregation exists when the minimum distance "d"
between the substrate metal (metal particle) surfaces of the
measured particles is at least 2 times of the average thickness "t"
of the coating layer.
[0160] b) Aggregation exists if the minimum distance "d" between
the substrate metal (metal particle) surfaces of the measured
particles is less than 2 times of the average thickness "t" of the
coating layer.
[0161] The average coating layer thickness of 100 random particles
was given as the average thickness of the coating layer.
[0162] (3) Color Tone Evaluation
[0163] The L*15.degree. value obtained with an X-Rite Inc. "MA68II"
multi-angle spectrophotometer was adopted for evaluating the color
tone of the test sample. Color was measured 5 times from an
aluminum pigment-containing coating prepared by the methods
described above, and the average value was used. When measuring
color tone, the profitable effect of the present invention can be
evaluated accurately with an integrating sphere spectrophotometer
rather than a multi-angle spectrophotometer, although there will be
some difference in the absolute brightness value.
* * * * *