Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Particulate matter
Reexamination Certificate
1999-03-31
2001-05-01
Le, Hoa T. (Department: 1773)
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Particulate matter
C106S446000, C427S219000, C428S407000
Reexamination Certificate
active
06224980
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to fine powder of hydrophobic titanium oxide and to a method for producing it. In particular, it relates to fine powder of hydrophobic titanium oxide which is added as an additional agent to powder coating compositions, toners for electrophotography and other compositions for the purpose of, for example, improving their powdery flowability, preventing them from becoming caked, and controlling the electrification thereof.
2. Description of the Related Art
Many patents have heretofore been issued relating to fine powders of hydrophobic titanium oxide that are used, for example, as additional agents in toners for electrostatic development.
JP-A 5-72797 discloses ultra-fine grains of amorphous and hydrophobic titanium oxide that are produced through vapor-phase pyrolysis or hydrolysis of a volatile titanium compound to give fine grains of amorphous titanium oxide followed by treatment of the grains with an organosilane compound.
JP-A 60-136755 describes a technique of adding both hydrophobic titanium oxide and hydrophobic silica to a negatively charged toner. The hydrophobic titanium oxide used therein is prepared from titanium oxide having a mean grain size of 30 nm and a BET specific surface area of 50 m
2
/g.
JP-A 8-220791, 8-220795 and 8-220796, disclose a technique of using, as an additional agent for toners, hydrophobic titanium oxide as prepared in a wet method and processed in an aqueous system for hydrophobication.
However, among these conventional fine powders of hydrophobic titanium oxide, the ultra-fine grains of hydrophobic amorphous titanium oxide described in JP-A 5-72797 contain a large amount of water which is adsorbed inside the grains and is therefore problematic because their electrification properties often fluctuate depending on changes in the surroundings including temperature and humidity, and they exhibit a weak electrification.
The hydrophobic titanium oxide described in JP-A 60-1367 55, which is prepared from titanium oxide having a mean grain size of 30 nm and a BET specific surface area of 50 m
2
/g, is problematic in that, when it is added to toners by itself, it does not ensure good flowability of toners containing it.
The fine powder of hydrophobic titanium oxide described in JP-A 8-220791, which is prepared in a wet method and is processed in an aqueous system for hydrophobication, is problematic in that it requires a drying step, and that an additional step of pulverizing the aggregates of the powder having a large bulk density is indispensable. In addition, the fine titanium oxide powder produced according to the disclosed method contains a large amount of water adsorbed thereto. Therefore, like that in JP-A 60-136755, the powder is still problematic in that its electrification property often fluctuates depending on changes in the surroundings including temperature and humidity.
Moreover, an additional problem with all of these conventional fine powders of hydrophobic titanium oxide is that they are expensive to produce.
As mentioned above, the conventional fine powders of hydrophobic titanium oxide all face, in no small way, the above-mentioned problems in electrification properties, flowability, and production costs.
On the other hand, a recent tendency in the field of electrophotography is toward producing images of much higher quality, for which the grains to be used are much smaller. The same applies to various powder coating materials. Under these circumstances, the necessity of enhancing the flowability of various powders, such as toners and others, is increasing greatly.
SUMMARY OF THE INVENTION
An object of the invention is to provide relatively inexpensive, fine powder of hydrophobic titanium oxide which is excellent in its flowability improving effect and electrification-stabilizing effect, and also to provide a method for producing it.
The fine powder of hydrophobic titanium oxide of the present invention is obtained through surface modification of titanium oxide with a silane coupling agent and/or a silicone compound, and the titanium oxide is prepared by hydrolyzing a volatile titanium compound while in a high-temperature vapor-phase condition, in the presence of a combustible or incombustible gas. It has a BET specific surface area of from 55 to 150 m
2
/g while having an anatase/rutile crystal structure in a ratio of anatase falling between 0.3 and 0.98.
The fine powder of hydrophobic titanium oxide of the invention is obtained through surface modification of titanium oxide having a BET specific surface area of from 55 to 150 m
2
/g and having an anatase/rutile crystal structure with a ratio of anatase falling between 0.3 and 0.98, using a silane coupling agent and/or a silicone compound. The product has an extremely high degree of hydrophobicity, and, therefore, its electrification property fluctuates little. Accordingly, when the fine powder of hydrophobic titanium oxide of the invention is used in toners for electrophotography, it ensures good electrification stability and high flowability for a long period of time. In addition, the fine powder of hydrophobic titanium oxide of the invention is produced by a relatively simple method comprising only a few steps, without causing any problems of environmental pollution, and the production costs for it are low.
The preferred silane coupling agent to be used is represented by the following general formulas (I) or (II). The preferred silicone compound is represented by formula (III);
X
4−n
SiR
n
(I)
wherein X represents a hydroxyl group, an alkoxy group or a halogen atom; R represents an alkyl group having from 1 to 18 carbon atoms; and n represents an integer of from 0 to 3;
R′
3
SiNHSiR′
3
(II)
wherein each R′ represents an alkyl group having from 1 to 3 carbon atoms, optionally substituted with any other substituent including hydrogen atoms, vinyl groups and others;
wherein R
1
represents a methyl group or an ethyl group; R
2
represents a hydrogen atom, a methyl group, an ethyl group, or an alkyl group optionally substituted by a vinyl group, a phenyl group or an amino group; X′ represents a hydroxyl group, an alkoxy group, a halogen atom or an alkyl group; and m represents an integer of from 1 to 500.
Desirably, the fine powder of hydrophobic titanium oxide of the invention has a degree of hydrophobicity of at least 70% as measured according to a transmittance method.
The fine powder of hydrophobic titanium oxide of the invention can be readily produced by hydrolyzing a volatile titanium compound while it is in a high-temperature vapor-phase condition, in the presence of a combustible or incombustible gas to prepare titanium oxide having a BET specific surface area of from 55 to 150 m
2
/g and having an anatase/rutile crystal structure with a ratio of anatase falling between 0.3 and 0.98, followed by mixing the resulting titanium oxide with from 0.1 to 50% by weight, relative to the titanium oxide, of a silane coupling agent and/or from 0.1 to 50% by weight, relative to the same, of a silicone compound and heating the resulting mixture.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
In the invention, titanium oxide which is prepared by hydrolyzing a volatile titanium compound, such as TiCl
4
, in the presence of a combustible or incombustible gas while the compound is in a high-temperature vapor-phase condition, and which has a BET specific surface area of from 55 to 150 m
2
/g and has an anatase/rutile crystal structure with a ratio of anatase (hereinafter referred to as the “anatase ratio”) falling between 0.3 and 0.98, is processed with a silane coupling agent and/or a silicone compound for surface modification.
Many commercially-available products of so-called wet titanium oxide, which are produced according to a sulfuric acid method or the like, have surface area sites to increase their specific surface area even inside the titanium oxide grains. Therefore, their drying loss is large and their electrification property is poor. In addition, th
Komai Eiji
Murota Masamichi
Shirono Hirokuni
Le Hoa T.
Nippon Aerosil Co., Ltd.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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