Compositions: coating or plastic – Materials or ingredients – Pigment – filler – or aggregate compositions – e.g. – stone,...
Reexamination Certificate
2002-03-12
2003-06-10
Koslow, C. Melissa (Department: 1755)
Compositions: coating or plastic
Materials or ingredients
Pigment, filler, or aggregate compositions, e.g., stone,...
C106S426000, C106S428000, C106S430000, C106S431000, C106S436000, C106S447000
Reexamination Certificate
active
06576052
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a titanium dioxide pigment having excellent light fastness and excellent hydrophobic and dispersible properties, and a method for production thereof. More particularly, the invention relates to a titanium dioxide pigment suited for use in plastics and a method for production thereof.
BACKGROUND ART
Titanium dioxide pigments are generally poor in light fastness. When titanium dioxide pigments are used in plastics, paints, ink, etc, these pigments thus promote color change, fading or deterioration of organic components such as resin, oil and fats, etc., upon exposure to UV rays. For this reason, titanium dioxide pigments are normally coated with hydrated compounds of aluminum, silicon, zirconium, etc. on the surface of pigment particles thereby to improve light fastness.
Further since titanium dioxide pigments have a hydrophilic nature and when these pigments are incorporated into plastics followed by processing especially into a thin layered film of polyolefin type such as polyethylene or polypropylene, the phenomenon of void formation, which is a so-called lacing problem ascribable to moisture contained in titanium dioxide pigments, occurs to cause deterioration in processing properties such as dispersibility or high packing.
JP, 60-3430, B discloses titanium dioxide pigments having excellent hydrophobicity and dispersibility, which are coated with organosilicons such as silane coupling agents, polysiloxanes, etc., polyhydric alcohols and hydrated oxides of aluminum.
According to this technique, titanium dioxide pigments are imparted hydrophobicity to improve processability, but light fastness is yet insufficient. In order to impart light fastness to titanium dioxide pigments, it is necessary to coat the surface of titanium oxide particles with a sufficient amount of the hydrated oxides of aluminum, silicon, zirconium, etc. Then, the moisture content in titanium dioxide pigments increases to reduce processability. That is, known titanium dioxide pigments could not satisfy light fastness and processing properties (lacing resistance, etc.) at the same time. Furthermore, in order to remove bound water from these hydrated oxides and reduce the moisture content in the resulting anhydrides, heating and firing at high temperatures are required. However, heating and firing at high temperatures result in problems that dispersibility decreases and production costs increase.
DISCLOSURE OF INVENTION
In order to overcome the problems of the prior art described above, the present invention has been made to provide titanium dioxide pigments having excellent light fastness, minimized change in color, highly hydrophobic property and excellent processability including dispersibility, high packing, etc., with less lacing, and to provide a method for producing the same.
The present inventors have made extensive studies to solve these problems. As a result, the inventors have found that by using an aluminum phosphate compound in place of the hydrated oxides of aluminum, silicon or zirconium described above, light fastness of titanium dioxide pigments can be improved even by coating with an aluminum phosphate compound in a small amount, and further by coating with the hydrolyzate of an organosilane compound, titanium dioxide pigments can be rendered hydrophobic to reduce the water content in the resulting titanium dioxide pigments so that titanium dioxide pigments having excellent light fastness and processability for plastics can be obtained. Based on the finding, the present invention has been accomplished.
That is, the present invention is directed to a titanium dioxide pigment comprising titanium dioxide particles, a coating layer containing an aluminum phosphate compound and a coating layer containing the hydrolyzate of an organosilane compound, formed on the surface of the particles, and characterized in that a difference in water content between 100° C. and 300° C. as determined by the Karl Fischer method, is not greater than 1500 ppm. The present invention is also directed to a method for producing the titanium dioxide pigments.
BEST MODE FOR CARRYING OUT THE INVENTION
The titanium dioxide particle that is the substrate of the titanium dioxide pigment of the present invention preferably has an average particle diameter of 0.1 to 0.4 &mgr;m determined by electron microscopic photography. The crystal form of the titanium dioxide particle may be anatase structure, rutile structure or mixture of anatase structure and rutile structure. Any method is available for preparing the titanium dioxide particles without any limitation. The titanium dioxide particles may be those obtained by a so-called sulfate process which comprises hydrolyzing a titanium sulfate solution, or by a so-called chloride process which comprises gas phase oxidation of a titanium halide.
The titanium dioxide pigment of the present invention has acquired excellent light fastness by providing the coating layer containing the aluminum phosphate compound.
The aluminum phosphate compound may be any one of aluminum orthophosphate and aluminum metaphosphate. The coating amount of the aluminum phosphate compound ranges preferably from 0.1 to 2.0 wt % in terms of AlPO
4
based on titanium dioxide as its substrate. With the amount smaller than the lower limit, the intended light fastness is not obtained and when the amount exceeds the upper limit, the bound water contained in the aluminum phosphate compound causes foaming in plastic molding such as processing of thin layer films, etc., which results in deterioration in lacing resistance.
The titanium dioxide pigment of the present invention has acquired excellent processability, dispersibility and hydrophobicity by further providing the coating layer containing the hydrolyzate of organosilane compound.
The organosilane compound is desirably represented by general formula (1):
R
n
—Si—(OR′)
4−n
(1)
wherein R is a hydrocarbon group having carbon atoms of not greater than 10 containing at least one of an alkyl, vinyl and methacryl; R′ is methyl or ethyl; and n is an integer of 1 to 3, provided that when n is 2 or 3, R may be the same or different hydrocarbon group. When the carbon atom number of the hydrocarbon group R is 11 or larger, not only it is difficult to cause hydrolysis but heat resistance of such a hydrolyzate-coated titanium dioxide pigment becomes poor, titanium dioxide powders become yellow upon drying after the coating treatment and heating during grinding, which leads to yellowing of plastics molded therefrom.
The hydrolyzate referred to in the present invention is used to mean the silanol products obtained via hydrolysis of the alkoxy group in the organosilane compounds shown by the formula above, the oligomers or polymers containing siloxane bonds by further polycondensation between the silanol compounds, and a mixture of at least two compounds selected from these compounds. The hydrolyzate may contain unreacted silane compounds. In view of efficient hydrophobicity, it is particularly preferred that the coating be finally in the form of a polymer. When the coating treatment is performed in aqueous slurry as described below, however, it is preferred to use a hydrophilic silanol monomer as a treating agent added to an aqueous slurry, the hydrophilic silanol monomer is coated on the titanium dioxide then followed by polycondensation.
Specific examples of the organosilane compound described above are methyltriethoxysilane, trimethylethoxysilane, methyltrimethoxysilane, vinyltriethoxysilane, vinylmethyldiethoxysilane, vinyltrimethoxysilane, n-butyltrimethoxysilane, n-butylmethyldimethoxysilane, n-butyltrimethoxysilane, isobutyltriethoxysilane, isobutyltrimethoxysilane, hexyltriethoxysilane, hexylmethyldimethaxysilane, hexyltrimethoxysilane, octyltriethoxysilane, octyltrimethoxysilane, desyltriethoxysilane, desyltriethyoxysilane, methacryloxypropyltriethoxysilane, methacryloxypropyltrimethoxysilane, methacryloxypropylmethyldimethoxysilane, etc.
The amount of the hydrolyzate of the organosilane compo
Akamatsu Toshihiko
Shimojo Masaki
Takahashi Hideo
Ishihara Sangyo Kaisha Ltd.
Koslow C. Melissa
Manelli Denison & Selter PLLC
Manlove Shalie
White, Jr. Paul E.
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