Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
2~597~2
TITLE OF THE INVENTIO
ULTRAVIOLET SCREENI~G COMPOSITE OXIDE
AND PROCESS FOR PRODUCING THE SAME
BACKGROUND OF THE INVENTION
[Field of the Invention]
The present invention relates to an ultraviolet
screening composite oxide and a process for producing
the same. More particularly, the present invention is
concerned with a white ultraviolet screening composite
oxide which is incorporated in paints, inks,
cosmetics, etc., excellent in the capability of
screening ultraviolet rays and has a high visible
light transmittance.
[Prior Art]
Ultraviolet rays having a wavelength of 320 to
400 nm bring about a sunburn of the skin and are
causative of melanism, inflammation, etc. Further,
the ultraviolet rays often decompose a matrix resin
contained in paints and cosmetics, decompose or fade a
pigment, or oxidize fats and oils and a perfume to
bring about the deterioration and change of flavor
thereof.
For this reason, an attempt to solve these
problems has been made through the use of an
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ultraviolet screening material. An ultraviolet
screening material of this type ~nown in the art is
ultrafine titanium oxide. Although titanium oxide
exhibits an excellent screening effect in the
ultraviolet region, the transmittance is poor in the
visible region, because the refractive index of
titanium oxide (2.61 to 2.90 in the rutile form) is
larger than that of zinc oxide (2.00 to 2.02). For
this reason, the incorporation of titanium oxide in
transparent materials, such as paints and cosmetics,
causes them material to turn opaque white. Further,
titanium oxide is disadvantageous because it is liable
to deteriorate the matrix upon being exposed to
ultraviolet rays as compared with zinc oxide.
It was reported that ultrafine zinc oxide might
be used as other screening material. Specifically,
Japanese Patent Appln. ~aid-Open Gazette No. Hei.2-
208369 (208369/90) proposed the use of ultrafine zinc
oxide having a specific surface area of 20 m2/g or
more as the ultraviolet screening material, and made
mention of the screening effect in the ultraviolet
region and the transmittance in the visible region.
Even when such an ultrafine zinc oxide having a large
surface area was used, the transmittance in the
visible region was unsatisfactory.
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SUMMARY OF THE INVENTION
The present invention has been made with a view
to solving the above-described problems of the prior
art,- and an object of the present invention is to
provide a white ultraviolet screening material which
o~fers a good balance between excellent capability of
screening ultraviolet rays and high visible light
transmittance, and a process for producing the same.
The above-described object can be attained by
incorporating a predetermined amount of an oxide of a
particular element as a dopant in zinc oxide.
Specifically, the ultraviolet screening
composite material of the present invention comprises
100 parts by weight of zinc oxide and, incorporated
therein, at least one member selected from among the
following oxides (1) to (7):
(1) 0.001 to 5.0 parts by weight of lanthanum
oxide,
(2) 0.001 to 5.0 parts by weitht of cerium
oxide,
(3) 1.0 to 10.0 parts by weight of iron oxide,
(4) 1.0 to 10.0 parts by weight of cobalt oxide,
(5) 1.0 to 10.0 parts by weight of nickel oxide,
(6) 0.1 to 30.0 parts by weight of titanium
oxide,
and
(7) 0.1 to 30.0 parts by weight of aluminum
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oxide.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIME~ITS
In the present invention, the ultraviolet
screening composite material comprises 100 parts by
weitht of zinc oxide and, incorporated therein, at
least one member selected from among the
above-described oxides (1) to (7). The content of the
oxide of each of the doping elements based on zinc
oxide varies from element to element. When the
content of the oxide of each doping element is below
the above-described lower limit, the ultraviolet
screening effect is small. On the other hand, when the
content exceeds the upper limit, the ultraviolet
screening effect is saturated and unfavorably there
occurs a problem of transparency in the visible
region. In the present invention, it is a matter of
course that two or more oxides selected from among the
oxides (1) to (7) may be incorporated. In this case,
it will suffice when the content of at least one oxide
is included within the above-described range and the
content of the other oxides is below this range. For
example, in the ca~e of the incorporation of lanthanum
oxide and iron oxide in zinc oxide, when the amount of
25 incorporation of lanthanum oxide is 0.001 to 5.0 parts
by weight based on 100 parts by weight of zinc oxide,
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the content of the iron oxide may be less than 1.0
part by ~Yeight.
Since the surface of the ultraviolet screening
composite oxide of the present invention is very
active, it is desirable to conduct a surface treatment
with a silicone oil or a fatty acid for the purpose of
preventing the reaction with the matrix or other
additives. Examples of the silicone oil used for this
purpose include dimethylsilicone oil, methylphenyl-
silicone oil, cyclic silicone oil, polyether siliconeoil, modified silicone oil and methylhydrogensilicone
oil. Examples of the fatty acid include saturated
fatty acids such as n-decanoic acid, caprilic acid,
lauric acid, stearic acid, behenic acid and palmitic
acid, linolic acid, linolenic acid and oleic acid.
The amount of use of the silicone oil or fatty acid
for the treatment (coating) is preferably 0.05 to 10%
by weight based on the composite oxide.
The process for producing an ultraviolet
screening composite oxide according to the present
invention comprises separately and simultaneously
feeding an acid solution containing zinc and at least
one member selected~from among lanthanum, cerium,
iron, cobalt, nickel, titanium and aluminum and an
alkaline solution to a reaction tank and agitating the
mixture.
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The process of the present invention ~ill now
described in more detail.
At the outset, the above-described doping
element is added in a predetermined amount to an
aqueous solution of an acid salt having a zinc
concentration of 1 to 5 mol/Q to prepare an acid
solution. Se~parately, a precipitant solution is
prepared. A solution of an alkali metal carbonate, a
solution of an alkali metal hydroxide and an oxalate
compound solution are preferably used as the
precipitant solution. The concentration of the
precipitant solution is in the range of from 0.1 to 10
mol/~ .
The acid solution and the precipitant solution
are continuously fed separately from each other to a
reaction tank through the use of a varial flow-rate
pump while maintaining the reaction temperature and pH
each at a constant value. In the reaction tank, a
coprecipitate comprising zinc and the doping element
is formed by neutralization. In the reaction, the
flow rate is adjusted so that the equivalent ratio of
zinc to the precipitant is 1 : 1 to 1 : 3. In this
case, it is necessary to conduct agitation
homogeneously at a high rate of 2000 to 20000 rpm.
The coprecipitation of the reaction product under the
above-described condition makes it possible to stably
conduct the operation and prepare a coprecipitate
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having a stable quality even in mass production.
Further, the high-speed agitation serves to
instantaneously diffuse the resultant coprecipitate
and prevent particles from coarsening, thus promoting
the formation of ultrafine particles. In the above-
described continuous treatment, a slurry containing a
coprecipitate suspended therein is gradually
withdrawn, for example, through the bottom of the
reaction tank.
The withdrawn slurry containing a coprecipitate
suspended therein is subjected to solid-liquid
separation, filtration, washing and drying, and then
fired for 2 to 3 hrs at a temperature in the range of
from 300 to 1000C, preferably from 350 to 700C under
atmospheric or reduced pressure (10 mmHg or less).
The resultant composite oxide, as such, may be
used for screening ultraviolet rays. As described
above, however, it is desired to subject the resultant
composite oxide to a surface treatment with a silicone
oil or a fatty acid, for the purpose of maintaining
the storage stability. This treatment is conducted by
dissolving the silicone oil or fatty acid in an
alcohol, such as mèthanol or ethanol, or a ketone,
such as acetone or MEK, and either directly immersing
the composite oxide in the solution or spraying the
solution on the composite oxide. Thereafter the
composite oxide is dried again at 80 to 150C.
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The present invention exhibits the following
operations.
(1) An ultraviolet screening effect superior to
that of the conventional zinc oxide can be attained in
an ultraviolet region from 320 to 400 nm.
(2) The composite oxide has an ultraviolet
absorption peak at a wavelength in the range of from
350 to 400 nm and the ultraviolet screening effect in
this region is particularly superior to that of the
conventional titanium oxide.
(3) The transmittance in the visible region is
higher than that of the conventional titanium oxide.
(4) In the case of the incorporation of the
composite oxide in paints and cosmetics, the surface
lS treatment of the composite oxide prevents the
composite oxide from reacting with the matrix or
additive and contributes to an improvement in the
storage stability.
As described above, the ultraviolet screening
composite oxide of the present invention has an
excellent capability of screening ultraviolet rays and
a high visible light transmittance in a good balance.
Further, the surface treatment of this composite oxide
can impart an excellent storage stability to the
composite oxide and prevents the composite oxide from
reacting with a matrix, etc., in the case of the
incorporation in paints, cosmetics, etc. Further,
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according to the process of the present invention, the
composite oxide can be stably and homogeneously
produced on a commercial scale.
Therefore, the ultraviolet screening composite
oxide of the present invention is suitable for use as
an ultraviolet screening material in applications such
as paints and cosmetics.
BRIEF DESCRIPTION OF T~E DRAWINGS
10 Fig. 1 is a graph showing an ultraviolet
transmittance over the whole ultraviolet region in the
Examples and Comparative Examples; and
Fig. 2 is a graph showing the results of X-ray
diffractometry of a composite oxide produced in
Example 1, an ASTM standard sample (ZnO) and an ASTM
standard sample (Zn2TiO4).
PREFERRED EMBODIMENTS OF T~E PRESENT INVENTION
The present invention will now be described in
more detail with reference to the following Examples
and Comparative Examples.
Example 1
5075 g (3 kg in terms of zinc oxide) of 99/O zinc
chloride was dissolved in 9Q of pure water, and 3.13
kg (5/O by weight in terms of titanium based on zinc
oxide) of 24% titanium sulfate was dissolved in the
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resultant solution to prepare an acid mixed solution.
The zinc oxi~e concentration was 4.1 mol/Q.
Separately, 6.4 kg of 99% sodium carbonate and 6.4 kg
of pure water were dissolved in 60 ~ of pure water to
prepare a 1 mol/Q alkaline solution.
The acid solution and the alkaline solution were
fed separately from each other and simultaneously to a
reaction tank by means of a variable f'low-rate pump in
such a manner that the molar ratio of zinc oxide to
the alkaline solution is 1 : 2 to form a coprecipitate
by neutralization. During this period, a continuous
reaction was conducted through agitation at a high
speed without particular heating while ad~usting the
pH value to 6 to 8.
The slurry after the reaction was subjected to
repetition of filtration and washing until the
electrical conductivity reached 200 l~s/cm or less.
The resultant cake was dried at 150C and fired in the
air at 400C for 3 hrs to give an ultrafine composite
oxide. The content of titanium oxide in the composite
oxide was 8.34 parts by weight based on 100 parts by
weight of zinc oxide.
The composite oxide powder was incorporated in
an amount of 30 to 40% by weight in a polyester resin.
and the mixture was subjected to dispersion together
with glass beads for 1.5 hrs in a paint shaker,
applied to an OHP sheet by means of a bar coater and
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dried at 70 to 80C to prePare a ~ransparen~ coating
film.
The transparent coating film was subjected to
the measurement of transmittance in a visible region
(400 to 700 nm) by means of a turbidimeter
manufactured by ~ippon Denshoku Kogyo Co., Ltd.
Further, the transmittance in an ultraviolet region
(380 nm) was measured by means of a spectrophotometer
manufactured by Hitachi Seisakusho Co., Ltd. The
. results are given in Table 1.
Further, the transmittance in an ultraviolet
region of from 320 to 400 nm was measured, and the
results are given in Fig. 1.
Further, the results of X-ray diffractometry of
this composite oxide are shown in Fig. 2 (a), while
the results of X-ray diffractometry of an ASTM
standard sample (ZnO) and an ASTM standard sample
(Zn2TiO4) are shown in Figs. 2 (b) and (c).
ExamDles 2 to 19 and ComParative Examples 1 to 10
Ultrafine composite oxides were prepared in the
same manner as that of the Example 1, except that the
doping element and lts amount were varied to prepare
compositions listed in the Table l. Transparent
coating films were prepared from the ultrafine
composite oxides in the same manner as that of the
Example l.
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The coating film was subjected to measurement of
the ~ransmittance in the visible region and
ultraviolet region in the same manner as that of the
Example 1. The results are given in the Tabie 1. In
Example 14, the transmittance in an ultra~iolet re~rion
(320 to 400 nm) was measured, and the results are
shown in the Fig. 1.
Comparative Example 11
Use was made of a high-purity ultrafine zinc
oxide having a specific surface area of 20 m2/g
prepared by an indirect process (French process), and
a transparent coating film was prepared from this zinc
oxide in the same manner as that of the Example 1.
The coating film was subjected to measurement of
the transmittance in a visible region and an
ultraviolet region in the same manner as that of the
Example 1, and the results are given in the Table 1.
Further, the transmittance in an ultraviolet region
(320 to 400 nm) was measured, and the results are
shown in the Fig. 1.
Comparative Example 12
An ultrafine composite oxide was prepared in the
same manner as that of the Example 1 without using any
doping element. A transparent coating film was
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prepared from the composite oxide in the same manner
as that of the Example 1.
The coating film was subjected to the
measurement of the transmittance in a visiblè region
and an ultraviolet region in the same manner as that
of the Example 1, and the results are given in the
Table 1. Further, the transmittance in an ultraviolet
region (320 to 400 nm) was measured, and the results
are shown in the Fig. 1.
ExamPle 20
An ultrafine composite oxide was prepared in the
same manner as that of the Example 1, except that 18
kg (about 5 kg in terms of zinc oxide) of 98% zinc
sulfate heptahYdrate was dissolved in 30 Q of pure
water, and 5.22 kg (5% by weight based on zinc oxide)
of 24% titanium sulfate was further dissolved in the
solution to use the resultant mixture as an acid mixed
solution. A transparent coating film was prepared-
from the composite oxide in the same manner as that of20
the Example 1.
The resultant coating film was subjected to the
measurement of the transmittance in a visible region
and an ultraviolet region in the same manner as that
of the Example 1, and the results are given in the
Table 1. Further, the transmittance in an ultraviolet
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region (320 to 400 nm) was measured, and the results
are shown i.n the Fi~. 1.
Example 21
An ultrafine composite oxide ~as prepared in the
same manner as that of the Example 1, except that use
was made of an acid mixed solution prepared by adding
3.6 kg (1 kg in terms of zinc oxide) of 98% zinc
sulfate heptahydrate to an oxalic acid solution . .
containing 17 g of lanthanum (1.7% by weight based on
zinc oxide). A transparent coating film was prepared
from the composite oxide in the same manner as that of
the Example 1.
The resultant coating film was subjected to the
measurement of the transmittance in a visible region
and an ultraviolet region in the same manner as that
of the Example 1, and the results are given in the
Table 1. Further, the transmittance in an ultraviolet
region (320 to 400 nm) was measured, and the results
are shown in the Fig. 1.
Example 22
An ultrafine composite oxide was prepared in the
same manner as that of the Example 21, except that
25 1.72 g of cerium (0.17% by weight of cerium based on
zinc oxide) was used instead of 17 g lanthanum. A
transparent coating film was prepared from thè
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composite oxide in the same manner as that Or the
Example 1.
The resultant coating film was subject to the
measurement of the transmittance in a visible region
and an ultraviolet region in the same manner as that
of the Example 1, and the results are given in the
Table 1. Further, the transmittance in an ultraviolet
region (320 to 400 nm) was measured, and the results
are shown in the Fig. 1.
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Table 1
Doping element (pts. wt.)
(proportion of each doping element based Transmittance
E~:. andon 100 pts. wt. of zlnc oxide)
Conlp. EX. _ _ __ _
No . visibleultraviolet
La2O~ CeO, Fe2O, Coo NiO TiO, Al20, reglon region
_ 400 - 700 nm380 nm
Ex. 18 34 92 0 5 0
_
EX . 2 _ _ 30.0 89.0 3.2
E X . 3 1.0 95.0 5.8
Ex . 4 2.0 _ _ _ 88.0 2.3
Ex, 5 0.2 _ 93.0 3.5
Ex. 6 0.02 96.0 5.5
Ex. 7 2.0 = = = = = =90.0 7.0
Ex. 8_ 10.0 _ 80.0 6.0
Ex. 9 5.0 82.0 6.5
Ex 10 _ 1 0 _ 85 0 7 0
.
Ex. 11 5.0 85.0 6.6
Ex. 12 10.0 _ 83.0 5.9
Ex. 13 1.0 87 0 6 9
_
Ex. 14 . _ 5.0 83.0 6.7
Ex. 15 = = = = = i.45 94.0 10.0
Ex. 16 8.34 9.45 92.0 5.0
Ex. 17 0.2 8 34 91 0 3 0
..
Ex. 18 q.2 9.45 93.0 3~5
~Ex. 19 0.28.34 9.SS 90.0 2.9
Ex. 20 = = = = = 8.34 = 92.0 6.0
Ex. 21 2.0 _ 92.0 8.0
Ex. 22 0.2 90.0 3.0
Comp. Ex. 1 6.0 _ = = = = ~ 69.0 10.0
Comp. Ex. 2 6.0 70.0 2.5
Comp. Ex. 3 _ 12.0 _ _ 65 : 5.7
Comp. Ex. 4 _0.5 90.0 20 0
_o_. Ex. S = 12.0 71.0 ` S.S
Comp. Ex. 6 = = = 0.5 = _ 66.0 25.0
Comp. Ex. 7 = = = = 12.0 = 7i 0 7.0
Comp. Ex. 8 _ _ 35.0 80.0 3.3
Comp. Ex. 9 _ 0.05 97.0 26.0
Comp. Ex. 10 _ _ 35.0 7?.0 30.0
; Comp. Ex. 11 ultrafine 2inc oxide prcpared by French 76.0 21.0
ultrafine xinc oxide prspared by the process
Comp. Ex. 12 described ln Example 1, except that no doping 78.0 12.0
element is incorporated
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As is apparent from the Table 1, each of the
composite oxides of the Examples 1 to 22 exhibits a
higher transmittance in the visible region and a lower
transmittance in the ultraviolet region as compared
with those of the Comparative Example l to 12. This
indicates that each of the composite oxides used in
the Examples l to 22 has an excellent screening effect
in the ultraviolet region and a high transparency in
the visible region.
As is apparent from the results shown in the
Fig. 1, each of the composite oxides of the Examples
1, 14 and 20 to 22 exhibits a higher screening effect
in an ultraviolet region from 320 to 400 nm than that
of the Comparative Examples 11 and 12, and this
tendency is significant around 380 nm.
Further, as shown in the Fig. 2 (a), in an X-ray
diffraction pattern of the Example 1, onlY peaks
assignable to ZnO shown in the Fig. 2 (b) were
observed, and no peak assignable to Zn2TiO4 shown in
the Fig. 2 (c) was observed. Therefore, it is
conceivable that the oxide prepared in the Example 1
is a composite oxide formed as a result of dissolution
of titanium in a lattice of zinc oxide to form a solid
solution. It has been found that the oxides prepared
in the other Examples are also composite oxides. It
is conceivable that the excellent transmittance in the
visible region attained in the present invention is
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derived f'rom the fact that the doPed element is in the
form of a composite oxide.
ExamPle 23
The surface of the composite oxide powder
prepared in the Example 1 was treated with a silicone
oil. Specifically. 135 g of silicone oil DC-3PA
(purity: 10%) for addition to a paint manufactured by
Toray Dow Corning Co., Ltd. was added as a silicon oil
to 5Q of toluene and the mixture was agitated for 5
minutes. 2.7 kg of zinc oxide was added to the
resulting solution and the mixture was agitated for
additional 30 minutes. The agitated mixture was
filtered and dried (at 120C) to prepare a powder. It
has been found that the powder has water repellency
and is coated with a sufficient amount of the silicone
oil. The coating of the silicone oil was 0.5~O by
weight based on the composite oxide.
A transparent coating film was prepared from the
surface-treated composite oxide in the same manner as
that of the Example 1.
The coating film was subjected to an
environmental resistance acceleration test under the
conditions of a temperature of 40 C and a relative
humidity of 90% for 240 hrs. The transmittance in the
visible region and the ultraviolet region before and
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after the test was measured in the same manner as that
of the Example 1. The results are given in Table 2.
Example 24
A surface-treated composite oxide was prepared
in the same manner as that of the Example 23, except
that 300 g of n-decanoic acid and 30Q of methyl
alcohol were used respectively instead of 135 g of the
silicone oil and 5Q of toluence used therein. A
transparent coating film was prepared from the
composite oxide.
The coating film was subjected to an
environmental resistance acceleration test in the same
manner as that of the Example 23. The transmittance
lS in the visible region and the ultraviolet region
before and after the test was measured in the same
manner as that of the Example 1. The results are
given in the Table 2.
ExamPle 25
A surface-treated composite oxide was prepared
in the same manner as that of the Example 23, except
that 300 g of lauric acid was used instead of 300 g of
decanoic acid used in the Example 24. A transparent
coating film was prepared from the composite oxide.
The coating film was subjected to an
environmental resistance acceleration test in the same
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manner as that of the Example 23. The transmittance
in the visible region and the ultraviolet region
before and after the test was measured in the same
manner as that of the Example 1. The results are
given in the Table 2.
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Table 2
s
IEx. No. ¦Transmlttance immediatelY ¦Transmlttance after ¦ Surface
¦ ¦after coatlng (%) ¦deterioration test (%) ¦ treatment
¦ ¦visible ¦ ultraviolet ¦visible ¦ ultraviolet
¦ ~region I region Iregion I region
1- t I I I I I
¦EX~ 23 1 90 1 5.0 1 90 15.0 ¦ silicone oil
¦EX . 24 1 92 1 5.0 ¦ 88 ¦8.0 ¦ n-decanoic
¦EX . 25 ~ 92 ¦ 5.0 ¦ 88 ilO.o ¦ laurlc acid ¦
.
,
As is apparent from the results given in the
Table 2, the treatment of the surface of the composite
oxide with a silicone oil or a fatty acid reduced a
; lowering in the screening effect in the ultraviolet
region and imparted an excellent storage stability to
the composite oxide.
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