U.S. patent application number 11/992977 was filed with the patent office on 2009-10-15 for pearlescent pigment, process for producing the same, coating composition and multilayered coat.
This patent application is currently assigned to DAINICHISEIKA COLOR & CHEMICALS MFG. CO., LTD.. Invention is credited to Takashi Abe, Satoru Matsuzaki, Shotoku Takami.
Application Number | 20090258251 11/992977 |
Document ID | / |
Family ID | 37906247 |
Filed Date | 2009-10-15 |
United States Patent
Application |
20090258251 |
Kind Code |
A1 |
Abe; Takashi ; et
al. |
October 15, 2009 |
Pearlescent Pigment, Process for Producing the Same, Coating
Composition and Multilayered Coat
Abstract
This invention relates to a pearlescent pigment, which is
composed of flaky alumina substrate particles produced by a
hydrothermal process and coat layers formed on the flaky substrate
particles and composed of at least one metal oxide including at
least a titanium oxide. The metal oxide has an average particle
size of from 1 to 500 nm. According to this invention, it is
possible to provide a pearlescent pigment, which has wholly uniform
photoluminescence and an elegant and silky feel in combination and
can fully satisfy artistry as desired.
Inventors: |
Abe; Takashi; (Tokyo,
JP) ; Matsuzaki; Satoru; (Tokyo, JP) ; Takami;
Shotoku; (Tokyo, JP) |
Correspondence
Address: |
CHAPMAN AND CUTLER
111 WEST MONROE STREET
CHICAGO
IL
60603
US
|
Assignee: |
DAINICHISEIKA COLOR & CHEMICALS
MFG. CO., LTD.
Chuo-ku
JP
|
Family ID: |
37906247 |
Appl. No.: |
11/992977 |
Filed: |
October 2, 2006 |
PCT Filed: |
October 2, 2006 |
PCT NO: |
PCT/JP2006/319713 |
371 Date: |
April 2, 2008 |
Current U.S.
Class: |
428/702 ;
106/442; 524/430 |
Current CPC
Class: |
A61Q 1/02 20130101; B82Y
30/00 20130101; C09C 2200/505 20130101; A61K 2800/434 20130101;
A61K 2800/436 20130101; A61K 8/26 20130101; C01P 2004/54 20130101;
A61K 2800/621 20130101; C09D 5/29 20130101; C01P 2004/62 20130101;
A61K 2800/651 20130101; C09D 5/36 20130101; C09D 11/037 20130101;
C09C 1/0021 20130101; C09C 2200/1004 20130101; A61K 8/0262
20130101; C09C 1/0015 20130101; C09D 11/322 20130101; C01P 2004/64
20130101 |
Class at
Publication: |
428/702 ;
106/442; 524/430 |
International
Class: |
B32B 27/06 20060101
B32B027/06; C09D 1/00 20060101 C09D001/00; C08K 3/22 20060101
C08K003/22 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 3, 2005 |
JP |
2005-290148 |
Claims
1. A pearlescent pigment comprising flaky alumina substrate
particles produced by a hydrothermal process and coat layers formed
on said flaky substrate particles and composed of at least one
metal oxide comprising at least a salt of titanium, wherein said
metal oxide has an average particle size of from 1 to 500 nm.
2. The pearlescent pigment according to claim 1, wherein said coat
layers of said metal oxide are at least one of mixed layers and
stacked layers of two or more metal oxides comprising at least
titanium oxide.
3. The pearlescent pigment according to claim 1, wherein said flaky
substrate particles have an average particle size of from 0.1 to 50
.mu.m.
4. The pearlescent pigment according to claim 1, wherein said flaky
alumina substrate particles have an aspect ratio (particle
size/thickness) of from 5 to 500.
5. The pearlescent pigment according to claim 1, wherein said flaky
alumina substrate particles have an average particle size a
statistical variation coefficient of which is from 20 to 90.
6. The pearlescent pigment according to claim 1, which has an
average particle size a statistical variation coefficient of which
is from 20 to 90.
7. A process for the production of a pearlescent pigment, which
comprises the steps of: dispersing in water flaky alumina substrate
particles produced by a hydrothermal process and activated at
surfaces thereof by at least one method selected from plasma
treatment, ultrasonic treatment, acid treatment, alkali treatment
shock treatment and chemical etching treatment, hydrolyzing in the
resulting dispersion a metal salt comprising at least a salt of
titanium, allowing the resulting metal hydroxide or metal oxide to
deposit on surfaces of said alumina substrate particles, and then
subjecting the resulting deposit to heat treatment to form, on said
surfaces of said alumina substrate particles, metal oxide coat
layers having an average particle size of from 1 to 500 nm.
8. (canceled)
9. A coating composition comprising a pearlescent pigment according
to claim 1 and a film-forming resin.
10. The coating composition according to claim 9, further
comprising a liquid medium.
11. A multilayered coat comprising a base coat layer formed from a
coating composition according to claim 9 and a clear coat layer
formed on said base coat layer.
12. The multilayered coat according to claim 11, which has
reflected light intensities having a statistical variation
coefficient of not greater than 5 when measured by a
photometer.
13. The multilayered coat according to claim 11, which has a
45.degree./0.degree. reflection intensity ratio of not greater than
100 when measured at an elevation angle of not smaller than
0.degree. by a goniophotometer.
14. A multilayered coat comprising a colored first base coat layer
formed on a surface of a substrate, a second base coat layer formed
from a coating composition according to claim 9 on said colored
first base coat layer, and a clear coat layer formed on said second
base coat layer.
15. A multilayered coat comprising a first coat layer formed on a
surface of a substrate and at least one second coat layer formed
from a coating composition according to claim 9 on said first coat
layer.
16. A multilayered coat comprising at least two first coat layers
formed one over the other on a surface of a substrate and at least
one second coat layer formed from a coating composition according
to claim 9 between said at least two first coat layers.
Description
TECHNICAL FIELD
[0001] This invention relates to a pearlescent pigment obtained by
coating surfaces of specific flaky substrate particles (which may
herein after be called simply "substrate particles") with a metal
oxide, its production process, and its use.
BACKGROUND ART
[0002] Known pearlescent pigments include those obtained by coating
surfaces of substrate particles, such as mica flakes, with a metal
oxide of large refractive index like titanium dioxide. In recent
years, pearlescent pigments making use of thin alumina flakes as
substrate particles improved in smoothness, heat resistance and
transparency, in which mica flakes are deficient as substrate
particles, have been proposed (Patent Document 1). However, when
plate alumina produced by a hydrothermal process is used as
substrate particles in the process described in the above patent
document, adsorbability of particles of a metal oxide on the
alumina is very low, and hence, the particles of the metal oxide
are bound into large aggregates, thereby failing to provide a
pigment equipped with satisfactory photoluminescence. Even if the
metal oxide particles are adsorbed on the plate alumina, the
particles of the metal oxide which cover the substrate particles
are so large that wholly uniform photoluminescence, from which no
graininess is felt, or smooth and elegant photoluminescence, that
is, silky pearlescence is hardly available. It has, therefore, been
unable to fully satisfy artistry required for various
applications.
Patent Document 1: JP-A-09-255891
DISCLOSURE OF THE INVENTION
Problem to Be Solved by the Invention
[0003] When the metal oxide coating is conducted using ordinary
substrate particles, the pearlescence of the conventional
pearlescent pigments is not uniform and is deficient in smoothness
as a whole due to the inclusion of large substrate particles having
a large average particle size and wide reflection areas as
mentioned above, although it has discontinuous strong
photoluminescence. In an attempt to overcome this problem,
substrate particles of small average particle size were used. The
above-described grainy feel was reduced, but it was still unable to
derive any pearlescence having a smooth, elegant, photoluminescent
and silky feel.
[0004] With the foregoing circumstances of the conventional art in
view, an object of the present invention is, therefore, to provide
a pearlescent pigment, which has, as a whole, both uniform
photoluminescence and an elegant and silky feel and can fully
satisfy artistry as required.
[0005] An other object of the present invention is to provide a
coating composition capable of forming a coat having characteristic
photoluminescence in a single-apply coating process, a 2-coat
1-bake coating process, a 3-coat 2-bake coating process or a
coating process that forms at least one pearlescent coat layer
between stacked at least one desired coat layers or on a coat
layer.
Means for Solving the Problem
[0006] The above-described objects can be achieved by the present
invention to be described herein after.
[0007] Described specifically, the present invention provides a
pearlescent pigment comprising flaky alumina substrate particles
produced by a hydrothermal process and coat layers formed on the
substrate particles and composed of at least one metal oxide
comprising at least a titanium oxide, wherein the metal oxide has
an average particle size of from 1 to 500 nm.
[0008] In the above-described pearlescent pigment according to the
present invention, it can be preferred that the coat layers of the
metal oxide are mixed layers and/or stacked layers of two or more
metal oxides comprising at least the titanium oxide; that the flaky
alumina substrate particles have an average particle size of from
0.1 to 50 .mu.m; that the alumina substrate particles have an
aspect ratio (particle size/thickness) of from 5 to 500; that the
alumina substrate particles have an average particle size a
statistical variation coefficient of which is from 20 to 90; and
that the pearlescent pigment has an average particle size a
statistical variation coefficient of which is from 20 to 90.
[0009] The present invention also provides a process for the
production of a pearlescent pigment, which comprises dispersing in
water flaky alumina substrate particles produced by a hydrothermal
process and activated at surfaces thereof by at least one method
selected from plasma treatment, ultrasonic treatment, acid
treatment, alkali treatment, shock treatment or chemical etching
treatment, hydrolyzing in the resulting dispersion a metal salt
comprising at least a salt of titanium, allowing the resulting
metal hydroxide or metal oxide to deposit on surfaces of the
alumina substrate particles, and then subjecting the resulting
deposit to heat treatment to form, on the surfaces of the substrate
particles, metal oxide coat layers having an average particle size
of from 1 to 500 nm.
[0010] Further, the present invention also provides a coating
composition comprising the above-described pearlescent pigment of
the present invention and a film-forming resin. Preferably, the
coating composition can further contain a liquid medium.
[0011] Still further, the present invention also provides a
multilayered coat comprising a base coat layer formed from the
above-described coating composition of the present invention and a
clear coat layer formed on the base coat layer.
[0012] Preferably, the above-described multilayered coat can have
reflected light intensities having a statistical variation
coefficient of not greater than 5 when measured by a photometer; or
a 45.degree./0.degree. reflection intensity ratio of not greater
than 100 when measured at an elevation angle of not smaller than
0.degree. by a goniophotometer.
[0013] Moreover, the present invention provides a multilayered coat
comprising a colored first base coat layer formed on a surface of a
substrate, a second base coat layer formed from the above-described
coating composition of the present invention on the colored first
base coat layer, and a clear coat layer formed on the second base
coat layer; a multilayered coat comprising a first coat layer
formed on a surface of a substrate and at least one second coat
layer formed from the above-described coating composition of the
present invention on the first coat layer; and also a multilayered
coat comprising at least two first coat layers formed one over the
other on a surface of a substrate and at least one second coat
layer formed from a coating composition according to claim 8
between the at least two first coat layers.
ADVANTAGEOUS EFFECTS OF THE PRESENT INVENTION
[0014] The present inventors have proceeded with extensive research
to achieve the above-described objects of the present invention. As
a result, it has been found that color visions of a pearlescent
pigment, which was obtained by activating surfaces of substrate
particles obtained by a hydrothermal process and then by coating
the substrate particles with at least one metal oxide of a particle
size in a range of from 1 to 500 nm, and colored articles making
use of the pigment have such artistry as giving a graininess-free,
smooth, elegant, photoluminescent and silky color tone. In
addition, it has also been found that, when the above-described
various coats are formed on substrates by using coating
compositions containing the above-described pearlescent pigment,
the coats fully show good artistry.
BEST MODES FOR CARRYING OUT THE INVENTION
[0015] The present invention will next be described in further
detail based on certain preferred embodiments.
[0016] The term "hydrothermal process" as used herein means a
process that allows crystals of a substrate material such as
alumina to grow in a solvent of high temperature and high pressure.
Conditions for the crystal growth are specific to the chemical
structure of the substrate material, the solvent, temperature and
pressure used, and the like. It is, therefore, possible to
synthesize desired substrate particles in accordance with an
average particle size, an aspect ratio and the like, which are
required for the substrate particles. The chemical and physical
properties of the substrate particles produced by the hydrothermal
process are unique properties not available from any process other
than the hydrothermal process.
[0017] Substrate particles which can be obtained by the
hydrothermal process can include alumina, boehmite, iron oxide,
hydroapatite, zirconia, titanates, titanium oxide, cobalt hydroxide
oxide, calcium silicate and the like. Any substrate particles may
be used insofar as they have uniformity, smoothness, heat
resistance, transparency and the like and provide artistry as
required. However, preferred is alumina which satisfies the
above-described conditions with a good balance. Flaky alumina
substrate particles which are preferred as mentioned above are
known by themselves, and are available for use in the present
invention, for example, from Kinsei Matec Co., Ltd., for example,
under the trade names of "YFA-02050" (average particle size: 2.0
.mu.m, aspect ratio: 50), "YFA-07070" (average particle size: 7.0
.mu.m, aspect ratio: 70), "YFA-05070" (average particle size: 5.0
.mu.m, aspect ratio: 70), "YFA-10030" (average particle size: 10.0
.mu.m, aspect ratio: 27), etc.
[0018] The average particle size of the substrate particles may be
from 0.1 to 50 .mu.m, preferably from 0.3 to 30 .mu.m, more
preferably from 0.5 to 20 .mu.m. An average particle size greater
than 50 .mu.m is not preferred in that the resulting pearlescent
pigment strongly reflects light to impair a silky color tone. On
the other hand, an average particle size smaller than 0.1 .mu.m is
not preferred in that the resulting pearlescent pigment strongly
scatters light to impair a silky color tone. The aspect ratio of
the substrate particles may be from 5 to 500, preferably from 7 to
300, more preferably from 10 to 200. An aspect ratio smaller than 5
is not preferred in that the substrate particles is poor in
orientation and interference light (pearlescence) is hardly
available from the resulting pearlescent pigment. On the other
hand, an aspect ratio greater than 500 is not preferred in that the
substrate particles are prone to breakage during handling such as
circulation, mixing and dispersion.
[0019] Further, the particle size distribution of the substrate
particles may be from 20 to 90, preferably from 25 to 80, more
preferably from 30 to 70 in terms of statistical variation
coefficient (CV value). This CV value means the percentage of a
standard deviation based on an average particle size in a particle
size distribution, and indicates the degree of scattering of the
particle size distribution. It is to be noted that each particle
size distribution was measured by "MULTISIZER3 COULER COUNTER"
(trade name; manufacture by Beckman Coulter, Inc.) and its
statistical variation coefficient was also calculated.
[0020] When the CV value of the substrate particles is 20 or
greater, small particle-size particles, which produce scattered
light, and particles, which produce rather strong reflected light,
are well-balanced so that the resulting pearlescent pigment can be
provided with a silky color tone. When the CV value of the
substrate particles is smaller than 20, on the other hand, the
particle size distribution of the substrate particles is extremely
narrow, but small particle-size particles, which produce scattered
light, and large particle-size particles, which produce rather
strong reflected light, both decrease, resulting in the lack of a
balance between scattered light and reflected light so that the
resulting pearlescent pigment is deprived of a silky color tone. On
the other hand, a CV value of the substrate particles, which is
greater than 90, is not preferred in that scattered light and
reflected light are poorly balanced and the resulting pearlescent
pigment is also provided with an impaired silky color tone.
[0021] The pearlescent pigment according to the present invention
can be obtained by activating the surfaces of the substrate
particles and then coating the surfaces with at least one metal
oxide. In the pearlescent pigment according to the present
invention, the metal oxide is required to have a particle size of
from 1 to 500 nm, preferably from 3 to 300 nm, more preferably from
5 to 200 nm. When the particles size of the metal oxide with which
the substrate particles are coated fall within the range of from 1
to 500 nm, the metal oxide has high crystallinity so that the
refractive index inherent to the metal oxide is fully exhibited.
Moreover, the top surfaces of the coats of the pearlescent pigment
are smooth and produce sufficient reflected light. As a result, a
satisfactory interference color is produced, so that
graininess-free, smooth and elegant photoluminescence, that is, a
silky feel is higher, thereby making it possible to fully satisfy
artistry as desired.
[0022] It is to be noted that the above-described particle size
indicates the particle size of metal oxide particles or aggregates
of metal oxide particles after hydrolysis or sintering. The average
particle size of each metal oxide was calculated from 50 particles
chosen at random from a micrograph obtained by a scanning electron
microscope, "FE-SEMS-4800" (tradename; manufactured by Hitachi,
Ltd.)
[0023] When the particle size of the metal oxide exceed 500 nm, the
metal oxide layers have substantial surface roughness so that
reflected light from the pearlescent pigment is considerably
weakened and no sufficient interference color is produced. When the
particle size of the metal oxide is smaller than 1 nm, on the other
hand, the metal oxide is provided with substantially reduced
crystallinity so that the refractive index inherent to the metal
oxide is not available. As a result, the pearlescent pigment does
not produce any sufficient interference color. Even if the coats of
the metal oxide are specified in thickness, a sufficient
interference color cannot be obtained unless the metal oxide
forming the coat layers is controlled in particle size.
[0024] By the coats of the metal oxide, the resulting pearlescent
pigment is provided with a silver tone color or, when the coats is
increased in thickness, with an interference color. Further, the
surfaces of the substrate particles may be coated with a colored
metal oxide, for example, with an iron oxide to obtain a reddish or
blackish, pearlescent pigment. Furthermore, the pearlescent pigment
may be provided with still higher saturation by adsorbing fine
particles of a coloring pigment, which will be described
subsequently herein, on the surfaces of the pearlescent
pigment.
[0025] The pearlescent pigment according to the present invention
can also be obtained by coating the surfaces of the above-described
substrate particles with a mixture of two or more metal oxides or
by stacking and coating two or more metal oxide layers stepwise on
the surfaces of the above-described substrate particles. By coating
with such a mixture or by conducting such stacking and coating,
physical properties not available from a single metal oxide alone
can be obtained, for example, light resistance, water resistance
and the like can be improved. Especially by successively stacking
two or more metal oxides into an increased number of layers, a
pearlescent pigment of still higher photoluminescence can be
obtained.
[0026] Furthermore, the pearlescent pigment according to the
present invention may preferably have a particle size distribution
the statistical variation coefficient (CV value) ranges from 20 to
90. Its reasons are similar to those mentioned above in connection
with the substrate particles.
[0027] A description will next be made of the process of the
present invention for the production of the pearlescent pigment.
The pearlescent pigment can be obtained by coating the surfaces of
the substrate particles with the metal oxide having the particle
size of from 1 to 500 nm.
[0028] For a general pearlescent pigment, it is necessary to
control the particle size of a metal oxide to be deposited on
substrate particles after hydrolysis or sintering and the
aggregation property of the particles such that the particles of
the metal oxide are arrayed on the surfaces of the substrate
surfaces. The process described in Patent Document 1 referred to in
the above, however, is practically impossible to control the
particle size, aggregation and arraying of the metal oxide, and
therefore, cannot obtain a pearlescent pigment capable of producing
sufficient interference light, because substrate particles produced
by a hydrothermal process are extremely high in surface smoothness
and have low adsorbing ability for the metal oxide on their
surfaces, and the aggregation of the metal oxide itself tends to
proceed easily. As a result, the metal oxide exists as large
aggregates and has low adsorbability on the surfaces of the
substrate particles. Even when adsorbed, the resulting coats of the
metal oxide are not uniform in thickness and the top surfaces of
the coats become rough. Accordingly, reflected light is
considerably weakened so that no sufficient interference color is
produced.
[0029] Even if the substrate particles produced by the hydrothermal
process are coated with the metal oxide by a known technique and
moreover, the resulting coats are specified in thickness, it is
still impossible to control the particle size and aggregation
property of the metal oxide forming the coat layers and to obtain a
pearlescent pigment having a sufficient interference color unless
the adsorbing ability of the surfaces of the substrate particles is
improved.
[0030] In the present invention, it was found that by activating
beforehand the surfaces of the substrate particles produced by the
hydrothermal process, the particles of the metal oxide can be
evenly adsorbed as fine particles on the surfaces of the substrate
particles. For the above-described surface activation, usable
examples include plasma treatments such as thermal plasma treatment
and low-temperature plasma treatment, ultrasonic treatment, acid
treatment, alkali treatment, tumbling-medium-assisted dispersion
treatment, shock treatments such as high-pressure shock treatment
and sand blasting treatment, ozone treatment, and chemical etching
treatments such as electrochemical treatment. These treatments can
be applied either singly or in combination.
[0031] Treatment gas usable in plasma treatment can be one of or a
combination of two or more of nitrogen, ammonia, a mixed
nitrogen-hydrogen gas, oxygen-containing gases such as oxygen,
ozone, water vapor, carbon monoxide, carbon dioxide, nitrogen
monoxide and nitrogen dioxide, rare gases such as helium, argon,
neon and xenon, halogen gases such as fluorine, chlorine and
iodine, and mixed gases obtained by mixing fluorocarbon gases, such
as tetra fluorocarbon, hexa fluorocarbon and hexa fluoropropylene,
in oxygen-containing gases at volume ratios not greater than
1/2.
[0032] Examples of a method for generating the above-described
plasma include the method that a direct current is applied to a gas
to effect plasma decomposition, the method that a radiofrequency
voltage is applied to a gas to effect plasma decomposition, the
method that a gas is subjected to plasma decomposition by electron
cyclotron resonance, and the method that a gas is thermally
decomposed by a hot filament.
[0033] As the pressure of the treatment gas upon the
above-described plasma treatment, 1.times.10.sup.-4 to 100 Torr is
preferred because a low pressure requires a costly vacuum chamber
and vacuum pumping system. The actual treatment gas pressure is
appropriately determined depending on the excitation means within
the above-described pressure range. However, 1.times.10.sup.-2 to
100 Torr is more preferred because it is possible to apply a direct
current or radiofrequency current capable of generating a plasma
even when the system is simple and the treatment gas pressure is
relatively high.
[0034] The inputted electric power required for the above-described
plasma treatment differs depending on the area and shape of
electrodes. Lower electric power results in a low plasma density so
that more time is required for the treatment. On the other hand,
higher electric power induces uneven treatment. The electric power
may, therefore, be from 20 to 200 W preferably.
[0035] When the construction of the electrodes employed in the
above-described plasma treatment is the parallel plate type, the
coaxial cylinder type, the curved counter plate type or the
hyperbolic counter plate type, a voltage is applied by the capacity
coupling method. When a radiofrequency voltage is applied, it can
be applied in an induction manner by using external electrodes. The
distance between the electrodes is appropriately determined
depending on the treatment pressure and the substrate particles,
and can be set desirably at a possible shortest distance for plasma
treatment because a longer distance leads to a lower plasma density
and requires higher electric power.
[0036] The time of the plasma treatment is determined depending on
the inputted electric power. In general, however, 1 to 60 minutes
are preferred because a shorter plasma treatment time cannot
achieve a sufficient degree of activation of the substrate
particles while no significant improvement can be expected in the
degree of activation of the substrate particles even when the
plasma treatment time is made excessively long. Concerning the
temperature during the plasma treatment, neither heating nor
cooling is absolutely needed.
[0037] The above-described plasma treatment is required to be
evenly applied over the entire surfaces of the flaky substrate
particles. It is, therefore, preferred to conduct the plasma
treatment while rolling the flaky substrate particles. Such mixing
methods can include the method that the flaky substrate particles
are sealed in a vessel and are tumbled together with the vessel and
the method that the flaky substrate particles are mixed by
vibrations. An appropriate mixing method can be determined
depending on the particle size and amount of the flaky substrate
particles to be treated.
[0038] Any ultrasonic oscillator can be used in the ultrasonic
treatment insofar as its oscillating frequency is in a range of
from 50 Hz to 100 KHz and its output power is in a range of from 20
to 1,000 W. An oscillating frequency lower than 50 Hz leads to a
substantial reduction in the surface uniformity of the energy
distribution of ultrasonic waves striking the flaky substrate
particles, and hence to insufficient activation. An oscillating
frequency higher than 100 KHz, on the other hand, leads to a
substantial reduction in the overall energy density, and also to
insufficient activation of the substrate particles. Even within the
above-described range, cavitations may still occur depending on the
structure and material of a tank to be used and on the kind of a
dispersing medium to be used. In such a case, it is desired to
increase the oscillation frequency or to lower the output power
such that the treatment system can be kept under conditions which
do not cause cavitations.
[0039] In the present invention, ultrasonic vibrations can be
applied either continuously or intermittently. It is, however,
preferred to apply ultrasonic vibrations by controlling them to
appropriate conditions within the above-described frequency range
of from 50 Hz to 100 KHz and the above-described power output range
of from 20 to 1,000 W.
[0040] An acid usable in the acid treatment can be one of or a
combination of two or more of inorganic acids such as hydrochloric
acid, nitric acid, sulfuric acid, phosphoric acid and carbonic
acid, organic acids such as acetic acid, citric acid and benzoic
acid, and resin acids such as acrylic resins and rosin. An alkali
usable in the alkali treatment can be one of or a combination of
two or more of alkali metal salts such as caustic soda and caustic
potash, alkaline earth metal salts such as calcium hydroxide, and
weak bases such as ammonia, sodium carbonate, aniline and
phenol.
[0041] The concentration and temperature of an acid or alkali
solution in the acid treatment or alkali treatment may be in a
range of from 0.1 to 99 wt % and a range of from 5 to 95.degree.
C., respectively, although an efficient treatment temperature may
be more preferably from 15 to 70.degree. C. The treatment time is
suitably determined depending on the concentration and temperature,
with a range of from 5 minutes to 6 hours being preferred. The acid
or alkali treatment may be repeated twice or more, or the acid and
alkali treatments may be alternately conducted at least once. The
acid treatment or alkali treatment also effects a pH adjustment, so
that a pH buffer may be used. Further, a surfactant, organic
solvent and/or the like may also be used as aid(s) in
combination.
[0042] The shock treatment is a method for physically activating
the substrate particles. Specific methods include partial grinding
of the surfaces of the substrate particles by shaking or collision,
and also, polishing by tumbling. Treatment methods which can
achieve such partial grinding or polishing include dispersing shock
treatment by a homogenizer, dissolver, sand mill, high-speed mixer
or paint conditioner, high-pressure shock treatment by a
high-pressure homogenizer, sand blasting treatment, jet mill
treatment, and the like.
[0043] The concentration of the substrate particles in the liquid
medium in the shock treatment may be from 1 to 200 wt %, with from
5 to 150 wt % being preferred. A concentration lower than 1 wt %
results in a poor shock efficiency, while a concentration higher
than 200 wt % results in thickening so that the shock treatment is
rendered difficult. For the shock treatment that needs a medium
upon effecting the same, glass beads, steel balls, zirconia beads
and the like can be used, and the weight ratio of the medium to the
substrate particles may be from 0 to 1,000 wt %, preferably from 0
to 500 wt %. It is not particularly needed to use a medium when the
activation of the surfaces of the substrate particles can be
sufficiently achieved by the collision of the substrate particles
themselves.
[0044] In the shock treatment, a pH buffer may be used. Further, a
surfactant, organic solvent and/or the like may also be used as
aid(s) in combination. The time of the shock treatment is
determined depending on the concentration of the substrate
particles and the type and amount of the medium. However, the
substrate particles cannot be provided with a sufficient degree of
activation when the time of the shock treatment becomes short, and
no substantial improvement can be expected in the activation degree
of the substrate particles even when the time of the shock
treatment is made excessively long. Therefore, 1 to 60 minutes are
preferred in general. It is to be noted that the above-described
physical activation treatment requires the payment of an attention
to substantial changes in particle size distribution and CV value
because, when the intensity of shock on the substrate particles is
increased, the treatment is not limited to the surface activation
of the substrate particles and may also break the substrate
particles.
[0045] In addition, other conventional treatments, including
chemical etching treatments such as ozone treatment, UV treatment
and electrochemical treatment, can also be used widely.
[0046] The pearlescent pigment according to the present invention
can also be obtained by adsorbing a hydrated oxide of a metal such
as titanium, zirconium, tin or iron with a particle size of from 1
to 500 nm on the surface-treated substrate particles by a known
method, for example, by a method that thermally hydrolyzes a salt
of the metal in water in which the substrate particles have been
dispersed or by a method that subjects the salt of the metal to
neutralization hydrolysis with an alkali in the water; and then by
calcining the hydrated oxide. By conducting this calcination step
in a reducing atmosphere, the metal oxide is converted into a
low-valence titanium oxide or a low-valence iron oxide, so that a
pearlescent pigment tinged in a black color can be obtained.
Additional artistry can be also imparted by a known method in
addition to the use of the metal oxide.
[0047] The atomic weight of the metal in the water-soluble metal
salt required to obtain pearlescence (interference color) may be
from 2.0.times.10.sup.-5 mol to 2.0.times.10.sup.-1 mol, more
preferably from 4.0.times.10.sup.-5 mol to 1.0.times.10.sup.-1 mol.
If the atomic weight of the metal is lower than 2.0.times.10.sup.-5
mol, the flaky substrate particles cannot be coated so that no
interference light is produced. If the atomic weight of the metal
exceeds 1.0.times.10.sup.-1 mol, inconveniences arise in that, even
if the flaky substrate particles can be coated, cracks tend to
occur in the coat layers after calcinations, and as a result, the
intensity of interference light is lowered.
[0048] A description will next be made about the coating
composition according to the present invention. The coating
composition according to the present invention contains the
above-described pearlescent pigment of the present invention and a
film-forming resin, and preferably, may contain the pearlescent
pigment and film-forming resin in a liquid medium. Usable examples
of the film-forming resin include, but are not limited to,
film-forming resins employed in the field of conventionally-known
coating compositions, such as acrylic resins, acrylic melamine
resins, vinyl chloride-vinyl acetate copolymer resins, alkyd
resins, polyester resins, polyurethane resins and amino resins.
[0049] As a solvent for dissolving or dispersing the pearlescent
pigment and film-forming resin, one conventionally and commonly
known to be useful in coating compositions can be used. Specific
examples include water, toluene, xylene, butyl acetate, methyl
acetate, acetone, methyl ethyl ketone, methyl isobutyl ketone,
methanol, ethanol, butanol, cyclohexane, and the like. These
solvents may also be used as mixed solvents.
[0050] In the coating composition according to the present
invention, the pearlescent pigment of the present invention may be
used in a proportion of from 0.005 to 50 parts by weight,
preferably from 0.1 to 30 parts by weight per 100 parts by weight
of the film-forming resin. Use of the pearlescent pigment in a
proportion of smaller than 0.005 parts by weight cannot obtain a
coating composition the provision of which is one of the objects of
the present invention. On the other hand, use of the pearlescent
pigment in a proportion of greater than 50 parts by weight can
obtain a coating composition the provision of which is one of the
objects of the present invention, but is not preferred because the
resulting coats are provided with reduced physical properties.
[0051] In the present invention, the above-described pearlescent
pigment can be used singly or in combination with one or more other
pigments. As coloring pigments usable in combination, pigments
employed in ordinary coating compositions and the like can be used.
Specific examples include phthalocyanine pigments, quinacridone
pigments, perylene pigments, anthraquinone pigments, DPP pigments,
metal complex pigments, transparent iron oxide pigments, carbon
black, titanium oxide, and zinc oxide. Further, as metal powder
pigments, aluminum powder, copper powder, stainless steel powder,
and the like can be mentioned. Among these, aluminum powder is used
most commonly. As special metal pigments, metal colloids and the
like can be used. As mica pigments usable in combination in the
present invention, conventionally-known mica pigments can be widely
used in combination, and illustrative are transparent pearl mica
and colored mica. As light interference pigments, interference
mica, interference alumina, interference mica (interference glass)
and the like can be mentioned. In addition, one or more of fillers,
antistatic agents, stabilizers, antioxidants, UV absorbers and the
like can also be added as needed in the coating composition
according to the present invention.
[0052] When the coating composition according to the present
invention contains the pearlescent pigment of the present invention
and another pigment, a base coating composition containing the
pearlescent pigment of the present invention and another base
coating composition containing the another pigment can be prepared
beforehand and these two types of base coating compositions can
then be blended together into the coating composition as desired,
or as an alternative, the pearlescent pigment and the another
pigment can be mixed together at the beginning and can then be
formulated into the coating composition.
[0053] The coating composition obtained as described above is
applied onto a substrate such as a metal plate, glass plate,
ceramic plate or plastic plate, to which surface preparation may
have been applied as needed, by spray coating, electrostatic
coating, flow coating, roll coating or the like, dried and then
crosslinked and cured to form a colored coat layer.
[0054] The coat formed by applying the coating composition of the
present invention onto a substrate has a color tone of a
graininess-free, smooth, elegant and silky feel, compared with
conventional TiO.sub.2-based pearlescent pigments for coatings.
Owing to the possession of the above-described properties, coats
having excellent characteristic photoluminescence, which are not
seen on coats available from conventional coating compositions, can
be formed in a single-apply coating process, a 2-coat 1-bake
coating process, a 3-coat 2-bake coating process or a coating
process that forms, with a coating composition containing the
pearlescent pigment of the present invention, at least one coat
layer between stacked at least one desired coat layers or on a coat
layer.
[0055] A coat can also be formed by using the above-described
colored coat layer as a base coat layer; applying a clear coating
composition, which has been prepared by dissolving or dispersing a
resin having low compatibility with the above-described
film-forming resin in an organic solvent, on the base coat layer;
drying the clear coating composition; and then subjecting it to
heat treatment. The coat formed by applying the coating composition
of the present invention onto the substrate has graininess-free,
smooth, elegant, silky photoluminescence. Namely, the pearlescent
pigment according to the present invention is formed of uniform
particles, and therefore, is free of a localized strong
photoluminescent feel associated with large particles and has
continuous uniform photoluminescence. Moreover, reflected light and
scattered light are well-balanced, thereby presenting a smooth,
elegant and silky feel.
[0056] A localized strong photoluminescent feel occurs as a result
of discontinuous specular reflection of light, which has entered
into the coat, by the pearlescent pigment. A difference between a
localized strong photoluminescent feel and a uniform
photoluminescent feel can be quantitated by measuring specular
light intensities of a continuous surface of a coat, statistically
calculating the degrees of scattering, that is, the dissemination
of the specular light intensities, and comparing their variances
with each other. No particular limitation is imposed on a
photometer insofar as it can measure the specular light intensities
of the continuous surface of the coat, but preferred is a
photometer which can measure specular light intensities while
moving a surface of a specimen in the direction of an X-axis on the
system. As a specific example, a three-dimensional goniophotometer,
"GP-200" (trade name; manufactured by Murakami Color Research
Laboratory Co., Ltd.), or the like can satisfy the above-mentioned
measurement conditions.
[0057] A coat obtained from the coating composition according to
the present invention is provided with uniform, graininess-free,
smooth photoluminescence in visual perception when its quantitated
variance is 5 or smaller. When its quantitated variance is greater
than 5, on the other hand, the coat is provided with glaring,
grainy photoluminescence in visual perception and cannot be
provided with uniform, graininess-free, smooth photoluminescence in
visual perception.
[0058] Light, which has entered into a coat, is separated into
specular light and scattered light, and is reflected out of the
coat. By balancing the specular light and the scattered light with
each other, a smooth, elegant, silky color tone is obtained as
visual perception. Light other than specular light scatters in all
directions, and exists as three-dimensional scattered light. By
three-dimensionally capturing the specular light and the
three-dimensional scattered light, a perception close to a state
that they are viewed by the human can be reproduced. The
above-mentioned specular light can be measured by a photometer
shown in the system. No particular limitation is imposed on the
photometer insofar as it can measure the reflection intensity at a
desired elevation angle while changing the receiving angle.
Preferred is, however, a three-dimensional goniophotometer which
can continuously measure reflected light. As a specific example, a
three-dimensional goniophotometer, "GP-200", or the like can
satisfy the above-mentioned measurement conditions.
[0059] A silky feel of a coat can be quantitated by measuring the
intensities of reflected light and scattered light at a desired
elevation angle with a three-dimensional goniophotometer; measuring
the reflection intensity at 45.degree. receiving angle, which is in
the neighborhood of specular light, and the reflection intensity at
0.degree. receiving angle, which corresponds to representative
scattered angle; and then determining the intensity ratio
(45.degree./0.degree.) of the intensity at 45.degree. to that at
0.degree.. A coat obtained from the coating composition according
to the present invention is provided with a smooth, elegant, silky
photoluminescent feel in visual perception when the
(45.degree./0.degree.) reflection intensity ratio of the intensity
at 45.degree. receiving angle to that at 0.degree. receiving angle
is 100 or smaller. When the (45.degree./0.degree.) reflection
intensity ratio of the intensity at 45.degree. receiving angle to
that at 0.degree. receiving angle is greater than 100, on the other
hand, no silky photoluminescent feel can be obtained in visual
perception.
[0060] The pearlescent pigment according to the present invention
has a small particle size and a large aspect ratio so that, even
when its content is high in a coat, it is oriented and the surface
smoothness is not lost. Because the pearlescent pigment according
to the present invention is a pearlescent pigment making use of
chemically-uniform plate particles produced by a hydrothermal
process, it is also unique in optical characteristics, is excellent
in the balance between reflected light and scattered light,
presents photoluminescence of a graininess-free, smooth, elegant
and silky feel, and can provide a coat of excellent finish. In a
coated color making use of a general pearlescent pigment, on the
other hand, the adoption of a small average particle size results
in non-uniform plate particles having a small aspect ratio and the
fine pigment is not oriented in the resulting coat, leading to a
drawback that the coat is provided with significantly-reduced
photoluminescence or the smoothness of a clear finish is impaired.
As an optical characteristic, reflected light and scattered light
are poorly balanced so that an elegant and silky feel cannot be
obtained.
[0061] The pearlescent pigment according to the present invention
is extremely good, as it is, as a pigment for ceramics, plastics,
inks, toners, inkjet inks and cosmetics. Further, depending on
these applications, treatments are applied the pearlescent pigment
to impart water resistance, weatherability, chemical resistance,
color fastness and high dispersibility as needed, and the
thus-treated pearlescent pigment is used for the respective
applications.
EXAMPLES
[0062] The present invention will next be described in further
detail based on Examples and Comparative Examples, although the
present invention shall not be limited by the following Examples.
It is to be noted that in the following Examples and Comparative
Examples, the designations of "parts" and "%" are on a weight
basis.
[Production Examples of Pearlescent Pigments]
Example 1
[0063] "YFA-02050" (average particle size: 2.0 .mu.m, aspect ratio:
50, CV value: 45), plate alumina produced by a, hydrothermal
process (hydrothermally produced alumina), (20 g) was placed in a
flask having an internal capacity of 1 L. After the interior of the
flask was depressurized to 0.05 Torr, a radiofrequency voltage of
13.56 MHz was applied under an oxygen atmosphere at 0.11 Torr by a
powder plasma treatment system ("PT-500", tradename; manufactured
by Samco International, Inc.) to conduct plasma treatment at room
temperature for 5 minutes (inputted electric power: 40 W).
[0064] In another flask having an internal capacity of 1 L, sodium
sulfate (anhydride, 20 g) was added to desalted water (300 mL) and
was dissolved with stirring. To the resultant solution, the plate
alumina (20 g) which had been subjected to plasma treatment as
described above was added, followed by dispersion with stirring. A
solution (28 g) of titanium chloride, the titanium concentration of
which was 16.5%, was charged into the dispersion. The thus-obtained
mixture was stirred, heated and then refluxed for 4 hours.
Subsequently, insoluble solid matter was collected by filtration,
washed with water, dried, and then subjected to heat treatment at
700.degree. C. for 1 hour. Water was added to the thus-obtained
treated matter, and with stirring, the free salts were caused to
dissolve. Insoluble solid matter was then collected by filtration,
washed with water and dried to obtain TiO.sub.2-coated plate
alumina (Example 1).
Example 2
[0065] "YFA-07070" (average particle size: 7.0 .mu.m, aspect ratio:
70, CV value: 44), hydrothermally produced alumina, (20 g) was
placed in a flask having an internal capacity of 1 L, and desalted
water (300 mL) was added to disperse the alumina with stirring. The
dispersion was subjected to ultrasonic treatment (inputted electric
power: 180 W, frequency: 20 KHz) at room temperature for 15 minutes
by an ultrasonic processor ("UD-200", trade name; manufactured by
Tomy Seiko Co., Ltd.). Subsequently, sodium sulfate (anhydride, 20
g) was added and was dissolved with stirring. A solution (20 g) of
titanium chloride, the titanium concentration of which was 16.5%,
was charged into the dispersion. The thus-obtained mixture was
stirred, heated and then refluxed for 4 hours. Insoluble solid
matter was then collected by filtration, washed with water, dried,
and then subjected to heat treatment at 700.degree. C. for 1 hour.
Water was added to the thus-obtained treated matter, and with
stirring, the free salts were caused to dissolve. Insoluble solid
matter was then collected by filtration, washed with water and
dried to obtain TiO.sub.2-coated plate alumina (Example 2).
Example 3
[0066] "YFA-05070" (average particle size: 5.0 .mu.m, aspect ratio:
70, CV value: 37), hydrothermally produced alumina, (20 g) was
placed in a flask having an internal capacity of 1 L, and desalted
water (300 mL) was added to disperse the alumina with stirring. 35%
hydrochloric acid (20 g) was charged into the dispersion, followed
by acid treatment at room temperature for 15 minutes.
[0067] Sodium sulfate (anhydride, 40 g) was then added and
dissolved with stirring. A 16.5% solution (30 g) of titanium
chloride and a 50% solution (1.9 g) of stannic chloride were
charged into the dispersion. The thus-obtained mixture was stirred,
heated and then refluxed for 4 hours. Further, insoluble solid
matter was collected by filtration, washed with water, dried, and
then subjected to heat treatment at 800.degree. C. for 30 minutes.
Water was added to the thus-obtained treated matter, and with
stirring, the free salts were caused to dissolve. Insoluble solid
matter was then collected by filtration, washed with water and
dried to obtain mixed TiO.sub.2/SnO.sub.2-coated plate alumina
(Example 3).
Example 4
[0068] "YFA-02050", hydrothermally produced alumina, (20 g) was
placed in a flask having an internal capacity of 1 L, and desalted
water (300 mL) was added to disperse the alumina with stirring.
Caustic soda (10 g) was added to the dispersion, followed by alkali
treatment at room temperature for 15 minutes. Using 35%
hydrochloric acid, the pH of the mixture was then adjusted to pH 2,
and sodium sulfate (anhydride, 40 g) was added and then dissolved
with stirring. A solution (28 g) of titanium chloride, the titanium
concentration of which was 16.5%, and a 50% solution (1.0 g) of
stannic chloride were charged into the dispersion. The
thus-obtained mixture was stirred, heated and then refluxed for 4
hours.
[0069] Insoluble solid matter was then collected by filtration,
washed with water, dried, and then subjected to heat treatment at
800.degree. C. for 30 minutes. Water was added to the thus-obtained
treated matter, and with stirring, the free salts were caused to
dissolve. Insoluble solid matter was then collected by filtration,
washed with water and dried to obtain mixed
TiO.sub.2/SnO.sub.2-coated plate alumina (Example 4).
Example 5
[0070] "YFA-07070", hydrothermally produced alumina, (20 g) was
placed in a flask having an internal capacity of 1 L, and desalted
water (300 mL) was added to disperse the alumina with stirring. The
dispersion was subjected to ultrasonic treatment (inputted electric
power: 180 W, frequency: 20 KHz) at room temperature for 15 minutes
by the ultrasonic processor ("UD-200"). Nitric acid (20 g) was then
charged, followed by acid treatment at room temperature for 15
minutes.
[0071] A 50% solution (1.0 g) of stannic chloride was charged into
the dispersion, and the resulting mixture was adjusted to pH 6.0
with a solution of sodium hydroxide. Subsequently, insoluble solid
matter was collected by filtration, washed with water, and then
dried to obtain SnO.sub.2-coated plate alumina. Sodium sulfate
(anhydride, 20 g) was dissolved in desalted water (300 mL). In the
thus-obtained solution, the above-described SnO.sub.2-coated plate
alumina which had been crushed was added and dispersed. A solution
(20 g) of titanium chloride, the titanium concentration of which
was 16.5%, was charged into the dispersion. The thus-obtained
mixture was stirred, heated and then refluxed for 4 hours.
Subsequently, insoluble solid matter was collected by filtration,
washed with water, dried, and then subjected to heat treatment at
800.degree. C. for 1 hour. Water was added to the thus-obtained
treated matter, and with stirring, the free salts were caused to
dissolve. Insoluble solid matter was then collected by filtration,
washed with water and dried to obtain stacked
SnO.sub.2/TiO.sub.2-coated plate alumina (Example 5).
Example 6
[0072] "YFA-07070", hydrothermally produced alumina, (20 g) was
placed in a plastic bottle having an internal capacity of 250 mL,
and desalted water (100 mL) and 2-mm glass beads (100 g) were
added, followed by shock treatment for 30 minutes on a paint
conditioner. Desalted water (200 mL) was then added to the
dispersion, and the resultant mixture was stirred. A 50% solution
(1.0 g) of stannic chloride was charged into the dispersion, and
the resulting mixture was adjusted to pH 6.0 with a solution of
sodium hydroxide. Subsequently, insoluble solid matter was
collected by filtration, washed with water, and then dried to
obtain SnO.sub.2-coated plate alumina.
[0073] Sodium sulfate (anhydride, 20 g) was dissolved in desalted
water (300 mL). In the thus-obtained solution, the above-described
SnO.sub.2-coated plate alumina which had been crushed was added and
dispersed. A solution (20 g) of titanium chloride, the titanium
concentration of which was 16.5%, was charged into the dispersion.
The thus-obtained mixture was stirred, heated and then refluxed for
4 hours. Subsequently, insoluble solid matter was collected by
filtration, washed with water, dried, and then subjected to heat
treatment at 800.degree. C. for 1 hour. Water was added to the
thus-obtained treated matter, and with stirring, the free salts
were caused to dissolve. Insoluble solid matter was then collected
by filtration, washed with water and dried to obtain stacked
SnO.sub.2/TiO.sub.2-coated plate alumina (Example 6).
Example 7 & Example 8
[0074] "YFA-10030" (average particle size: 10.0 .mu.m, aspect
ratio: 27, CV value: 50), hydrothermally produced alumina, (20 g)
was placed in a flask having an internal capacity of 1 L. After the
interior of the flask was depressurized to 0.05 Torr, a
radiofrequency voltage of 13.56 MHz was applied under a water vapor
atmosphere at 0.11 Torr by the powder plasma treatment system
("PT-500") to conduct plasma treatment at room temperature for 5
minutes (inputted electric power: 40 W). In another flask having an
internal capacity of 1 L, sodium sulfate (anhydride, 20 g) was
added to desalted water (300 mL) and was dissolved with stirring.
To the resultant solution, the plate alumina (20 g) which had been
subjected to plasma treatment as described above was added,
followed by dispersion with stirring.
[0075] On the side, a solution (50 g) of titanium chloride, the
titanium concentration of which was 16.5%, was dissolved in
desalted water (300 mL) to provide a solution A. After the plate
alumina dispersion was adjusted to pH 2.0 with hydrochloric acid
and was heated to 80.degree. C., the solution A was charged at a
constant rate over 4 hours by a metering pump until the substrate
particles were provided with an interference silver color. During
the charging, a 10% solution of sodium hydroxide was added to
maintain the pH of the dispersion at 2.0 and the temperature of the
dispersion was also maintained at 80.degree. C.
[0076] After the solution A was charged until the substrate
particles were provided with the interference silver color, the
dispersion was heated for 1 hour under reflux.
[0077] Subsequently, insoluble solid matter was collected by
filtration, washed with water, dried, and then subjected to heat
treatment at 700.degree. C. for 1 hour. Water was added to the
thus-obtained treated matter, and with stirring, the free salts
were caused to dissolve. Insoluble solid matter was then collected
by filtration, washed with water and dried to obtain
TiO.sub.2-coated plate alumina (Example 7). Further,
TiO.sub.2-coated plate alumina (Example 8) was obtained by
conducting similar processing as in Example 7 except that the
hydrothermally-produced alumina was changed to "YFA-07070".
Comparative Example 1
[0078] Sodium sulfate (anhydride, 20 g) was added to desalted water
(300 mL) and was dissolved with stirring. To the resultant
solution, plate alumina A (average particle size: 55 .mu.m, aspect
ratio: 30, CV value: 95) (20 g) which was not a hydrothermal
product was added, followed by dispersion with stirring. A solution
(30 g) of titanium chloride, the titanium concentration of which
was 16.5%, was charged into the dispersion. The thus-obtained
mixture was stirred, heated and then refluxed for 4 hours.
Subsequently, insoluble solid matter was collected by filtration,
washed with water, dried, and then subjected to heat treatment at
700.degree. C. for 1 hour. Water was added to the thus-obtained
treated matter, and with stirring, the free salts were caused to
dissolve. Insoluble solid matter was then collected by filtration,
washed with water and dried to obtain TiO.sub.2-coated plate
alumina (Comparative Example 1).
Comparative Example 2
[0079] Sodium sulfate (anhydride, 20 g) was added to desalted water
(300 mL) and was dissolved with stirring. To the resultant
solution, plate alumina B (average particle size: 10 .mu.m, aspect
ratio: 4.0, CV value: 60) (20 g) which was not a hydrothermal
product was added, followed by dispersion with stirring. A solution
(30 g) of titanium chloride, the titanium concentration of which
was 16.5%, was charged into the dispersion. The thus-obtained
mixture was stirred, heated and then refluxed for 4 hours.
Subsequently, insoluble solid matter was collected by filtration,
washed with water, dried, and then subjected to heat treatment at
700.degree. C. for 1 hour. Water was added to the thus-obtained
treated matter, and with stirring, the free salts were caused to
dissolve. Insoluble solid matter was then collected by filtration,
washed with water and dried to obtain TiO.sub.2-coated plate
alumina (Comparative Example 2).
Comparative Example 3
[0080] TiO.sub.2-coated plate alumina (Comparative Example 3) was
obtained as in Example 1 except that the plate alumina
("YFA-02050") was used without the plasma treatment.
Comparative Example 4
[0081] TiO.sub.2-coated plate alumina (Comparative Example 4) was
obtained as in Example 2 except that the plate alumina
("YFA-07070") was used without the ultrasonic treatment.
Comparative Example 5
[0082] Mixed TiO.sub.2/SnO.sub.2-coated plate alumina (Comparative
Example 5) was obtained as in Example 3 except that the plate
alumina ("YFA-05070") was used without the acid treatment.
Comparative Example 6
[0083] Mixed TiO.sub.2/SnO.sub.2-coated plate alumina (Comparative
Example 6) was obtained as in Example 4 except that the plate
alumina ("YFA-02050") was used without the alkali treatment.
Comparative Example 7
[0084] A commercial product composed of mica coated with titanium
oxide, "IRIODIN 225 WII" (trade name, product of Merck Ltd.,
Japan), was provided as Comparative Example 7.
[0085] The average particle sizes (.mu.m), aspect ratios and CV
values of the substrate particles used in Examples 1-8 and
Comparative Examples 1-6 and the particle sizes (nm) and CV values
of the metal oxides of the pearlescent pigments obtained in
Examples 1-8 and Comparative Examples 1-7 were determined and
presented together in Table 1. Each average particle size and its
corresponding aspect ratio were calculated from 50 particles chosen
at random from a micrograph obtained by a scanning electron
microscope "ERA-8000" (manufactured by Elionix Inc.). Each CV value
is a value calculated as a statistical variation coefficient based
on a measurement performed by using "MULTISIZER3 COULTER COUNTER".
The average particle size of each metal oxide was calculated from
50 particles chosen at random from a micrograph obtained by "FE-SEM
S-4800".
TABLE-US-00001 TABLE 1 Flaky alumina substrate particles
Pearlescent pigment Average Particle size particle size Aspect of
metal oxide Kind (.mu.m) ratio CV value (nm) CV value Example 1
"YFA-02050" 2.0 50 45 45 47 Example 2 "YFA-07070" 7.0 70 44 40 47
Example 3 "YFA-05070" 5.0 70 37 80 40 Example 4 "YFA-02050" 2.0 50
45 75 47 Example 5 "YFA-07070" 7.0 70 44 40 45 Example 6
"YFA-07070" 7.0 70 44 40 47 Example 7 "YEA-10030" 10.0 27 50 50 53
Example 8 "YFA-07070" 7.0 70 44 50 45 Comp. Ex. 1 Plate alumina A
55 30 95 45 97 Comp. Ex. 2 Plate alumina B 10 4.0 60 45 65 Comp.
Ex. 3 "YFA-02050" 2.0 50 45 920 70 Comp. Ex. 4 "YFA-07070" 7.0 70
44 740 55 Comp. Ex. 5 "YFA-05070" 5.0 70 37 870 62 Comp. Ex. 6
"YFA-02050" 2.0 50 45 1,020 70 Comp. Ex. 7 -- -- -- -- 300 50
Production Example of Automotive Paints
[0086] This example illustrates production and evaluation examples
upon using the pearlescent pigments of the present invention as
coating compositions. Evaluated formulation examples are presented
together in Table 2.
TABLE-US-00002 TABLE 2 (Unit: parts) Acrylic varnish Melamine
varnish Formulation Pearlescent (solid content: (solid content:
"SOLVESSO Butyl No. pigment 60%) 60%) #100" acetate Formulation A
Example 1 30 82 34 21 9 Formulation B Example 2 30 82 34 21 9
Formulation C Example 3 30 82 34 21 9 Formulation D Example 4 30 82
34 21 9 Formulation E Example 5 30 82 34 21 9 Formulation F Example
6 30 82 34 21 9 Formulation G Example 7 30 82 34 21 9 Formulation H
Example 8 30 82 34 21 9 Formulation I Comp. Ex. 1 30 82 34 21 9
Formulation J Comp. Ex. 2 30 82 34 21 9 Formulation K Comp. Ex. 3
30 82 34 21 9 Formulation K Comp. Ex. 4 30 82 34 21 9 Formulation M
Comp. Ex. 5 30 82 34 21 9 Formulation N Comp. Ex. 6 30 82 34 21 9
Formulation O Comp. Ex. 7 30 82 34 21 9 Formulation P None 0 82 34
21 9
[0087] Mixtures of the formulations A-H were separately subjected
to simple dispersion processing in a sand mill. Further, the
resulting dispersion (50 parts, each) of the formulations A-H and a
mixture (50 parts) of the formulation P were combined into intimate
mixtures, respectively, to obtain coating compositions A-H (Table
3). Those coating compositions each contained 8.55 parts of the
pearlescent pigment per 100 parts of the coating composition, and
will be referred to as "example paint A-H".
[0088] Mixtures of the formulations I-O were separately subjected
to simple dispersion processing in a sand mill. Further, the
resulting dispersion (50 parts, each) of the formulations I-O and a
mixture (50 parts) of the formulation P were combined into intimate
mixtures, respectively, to obtain coating compositions I-O (Table
3). Those coating compositions each contained 8.55 parts of the
pearlescent pigment per 100 parts of the coating composition, and
will be referred to as "comparative example paint I-O".
[0089] The example paints A-H, which contained the pearlescent
pigments obtained above in Examples 1-8, respectively, and the
comparative example paints I-O, which contained the pearlescent
pigments obtained above in Comparative Examples 1-7, respectively,
were applied on black coat paper sheets by a bar coater (No. 6),
respectively. After dried at room temperature for 30 minutes, the
paints were baked and cured at 120.degree. C. for 30 minutes to
prepare coated specimens.
[0090] With respect to each of those coated specimens, the
uniformity of photoluminescence was evaluated visually and was also
measured by a three-dimensional goniophotometer ("GP-200") under
the following conditions: reflectance measurement, light source: A
light, incident angle: 45.degree., receiving angle: 45.degree.,
receiver slit: 0.4 mm square, moving measurement over 40 mm along
X-axis on specimen surface, data sampling intervals: 0.1 mm; and
the statistic variance of the reflection intensity was calculated.
The measuring instrument is depicted in FIG. 1, one example of
graphs obtained by the measurements is shown in FIG. 2, and the
measurement results are presented in Table 3.
[0091] Further, graininess-free, smooth conditions of each coated
specimen were evaluated visually and were also measured by the
three-dimensional goniophotometer ("GP-200") under the following
conditions: reflectance measurement, light source: A light,
incident angle: 45.degree., receiving angles: 45.degree. and
0.degree., elevation angle: 2.5.degree.; and the reflection
intensity ratio (45.degree./0.degree.) was calculated. One example
of graphs obtained by the measurements is shown in FIG. 3, and the
measurement results are presented in Table 3.
TABLE-US-00003 TABLE 3 Uniformity of Silky feel photoluminescence
Reflection Visual intensity Visual Coating composition Variance
evaluation ratio (45.degree./0.degree.) evaluation Example 1
Example paint A 4.2 A 25.1 A Example 2 Example paint B 4.3 A 40.6 A
Example 3 Example paint C 3.6 A 33.6 A Example 4 Example paint D
3.2 A 30.4 A Example 5 Example paint E 4.9 A 66.7 A Example 6
Example paint F 3.5 A 48.8 A Example 7 Example paint G 4.3 A 71.2 A
Example 8 Example paint H 3.6 A 57.9 A Comp. Ex. 1 Comp. Ex. paint
I 5.9 B 210 B Comp. Ex. 2 Comp. Ex. paint J 6.2 B 141 B Comp. Ex. 3
Comp. Ex. paint K 7.1 B 220 B Comp. Ex. 4 Comp. Ex. paint L 6.2 B
130 B Comp. Ex. 5 Comp. Ex. paint M 6.5 B 180 B Comp. Ex. 6 Comp.
Ex. paint N 6.8 B 215 B Comp. Ex. 7 Comp. Ex. paint O 5.9 B 210 B
A: good, B: poor
[0092] Compared with the comparative example paints, the example
paints were lower in variance that indicates the degree of
scattering of photoluminescence and had uniform photoluminescence
as a whole. In addition, the example paints were lower in
reflection intensity ratio at receiving angles 45.degree. and
0.degree. than the comparative example paints, and also had a
smooth and silky feel well-balanced in specular light and scattered
light.
[0093] Moreover, cosmetics, plastics, ceramics, inks, toners and
inkjet ink compositions which contain pearlescent pigments of the
present invention also have, as a whole, both uniform photo
luminescence and graininess-free, smooth and elegant
photoluminescence, that is, a silky feel, and can fully satisfy
artistry as required.
INDUSTRIAL APPLICABILITY
[0094] The pearlescent pigment according to the present invention
has, as a whole, uniform photoluminescence and a color tone having
a graininess-free, smooth and elegant photoluminescence, that is, a
silky feel, and therefore, is optimal for fields where such a color
tone is required, for example, for fields such as ceramics, resins,
paints, construction materials, inks, toners, inkjet ink
compositions and cosmetics and also for fields where artistry is
required.
BRIEF DESCRIPTION OF THE DRAWINGS
[0095] FIG. 1 A schematic depicting a measuring instrument.
[0096] FIG. 2 A measurement graph of variations in reflection
intensity against the moving distance along an X-axis.
[0097] FIG. 3 A measurement graph of variations in
three-dimensional gonioreflectance (elevation angle:
2.5.degree.).
[0098] 1: Light source [0099] 2: Specimen [0100] 3: Photoreceptor
[0101] 4: X-axis [0102] 5: Y-axis [0103] 6: Z-axis [0104] 7:
Incident angle [0105] 8: Receiving angle [0106] 9: Elevation angle
[0107] 10: Comparative example paint O [0108] 11: Comparative
example paint C [0109] 12: Comparative example paint A
* * * * *