Compositions: coating or plastic – Materials or ingredients – Pigment – filler – or aggregate compositions – e.g. – stone,...
Reexamination Certificate
2002-06-13
2003-09-09
Koslow, C. Melissa (Department: 1755)
Compositions: coating or plastic
Materials or ingredients
Pigment, filler, or aggregate compositions, e.g., stone,...
C106S426000, C106S428000, C106S430000, C106S431000, C106S443000, C106S447000
Reexamination Certificate
active
06616746
ABSTRACT:
TECHNICAL FIELD
This invention relates to a titanium dioxide pigment which exhibits an excellent dispersibility and a high hiding power in plastics, particularly in polyolefin resins and to a process for producing the pigment.
BACKGROUND ART
Since titanium dioxide pigments are hydrophilic, they have low affinity for organic resins and, when compounded into plastics, they are apt to cause defective processing, such as so-called lacing (void formation) and pinholes, due to poor dispersion of titanium dioxide pigments. For ameliorating the situation, some methods have been proposed in which the particle surface of titanium dioxide is coated with various organic compounds to improve its affinity for plastic resins. These methods, however, are not sufficiently effective and, particularly when thin film is processed with polyolefin resins such as polyethylene and polypropylene, a high degree of hiding effect is difficult to obtain.
DISCLOSURE OF THE INVENTION
The object of this invention is, overcoming the above-mentioned problems of the prior art, to provide a titanium dioxide pigment which is excellent in affinity and dispersibility, hardly produces defective results in plastics processing including thin film processing and has a high hiding power, and a process for producing the pigment.
The present inventors have made extensive study to solve the above-mentioned problems. As a result, the inventors have found that (1) when a hydrolysis product of aminosilane compounds is coated on the particle surface of titanium dioxide, the affinity of the titanium dioxide for plastic resins, particularly polyolefin resins, is enhanced and that (2) when a polyhydric alcohol is additionally coated, the dispersibility is further improved. The present invention has been accomplished on the basis of the above finding.
Thus, this invention provides a titanium dioxide pigment which comprises titanium dioxide particles having a coating layer comprising a polyhydric alcohol and a hydrolysis product of an aminosilane compound, wherein the dispersibility of the pigment, as judged in terms of resin pressure increase, is not more than 20 kg/cm
2
, and a process for producing the pigment.
BEST MODE FOR CARRYING OUT THE INVENTION
The titanium dioxide which constitutes the base substance of the titanium dioxide pigment of this invention preferably has an average particle diameter of 0.1-0.4 &mgr;m as measured by electron microphotography, and its crystal form may be either of the anatase type or of the rutile type or a mixture of the two types. The titanium dioxide may be either a product obtained by the so-called sulfate process in which a titanium sulfate solution is hydrolyzed or a product obtained by the so-called chloride process wherein a titanium halide is oxidized in gas phase.
Since titanium dioxide pigments in general are poor in resistance to light, plastic resins incorporated with the pigment, under ultraviolet light, are apt to undergo discoloration or fading or to undergo acceleration of decomposition. Therefore, the titanium dioxide pigment in this invention preferably has on its surface a coating layer comprising the hydrated oxide of aluminum. Moreover, the coating of hydrated oxide of aluminum facilitates the operations of dehydration, drying, grinding, etc. in the process of producing the titanium dioxide pigment, so that said coating is also favorable from the industrial aspect. The coating amount of the hydrated oxide of aluminum is preferably 0.01-0.5% by weight in terms of Al
2
O
3
relative to titanium dioxide constituting the base substance. When the amount is smaller than the above-mentioned range, the intended light resistance tends to be difficult to obtain, whereas when it is larger than the range, owing to bound water contained in the hydrated oxide, when the titanium dioxide pigment is compounded into a plastic resin and the resin is subjected, for example, to thin film processing, defective processing due to contained water is apt to occur in the plastic processing. The above-mentioned coating layer need not coat the whole surface of titanium dioxide but may partly contain uncoated portion within limits wherein the intended light resistance can be obtained. Furthermore, other coating layers suited to titanium dioxide pigment which are known to the art, for example, layers of hydrated oxides of silicon, tin, zirconium, etc., may be provided within ranges not deleterious to the object of this invention.
The titanium dioxide pigment of this invention has on its surface, preferably via an above-mentioned coating layer comprising the hydrated oxide of aluminum, a coating layer comprising a polyhydric alcohol and a hydrolysis product of an aminosilane compound. The hydrolysis product of an aminosilane compound and hydroxyl groups which titanium dioxide has on its surface chemically react and bond with each other thereby to coat the surface of titanium dioxide with amino-containing hydrocarbon groups, so that the affinity of the surface for olefin resins is enhanced. Consequently, when the titanium dioxide pigment of this invention is compounded into plastic resins, particularly olefin resins, and the resin is formed into thin film or the like, a high hiding effect can be obtained. Though the hydrolysis product of an aminosilane compound in some cases liberates a part of the compound as an unreacted substance, even in such cases the adhesion and aggregation of titanium dioxide particles via an unreacted free substance can be prevented by the polyhydric alcohol-type compound in this invention, so that the titanium dioxide pigment is excellent also in dispersibility.
The aminosilane compound used in this invention is preferably a compound represented by the following formula (1)
Rn—Si—(OR′)
4−n
(1)
wherein R is an amino group-containing hydrocarbon group having 1-10 carbon atoms selected from the group consisting of aminoalkyl groups, diaminoalkyl groups and triaminoalkyl groups, R′ is the methyl group or ethyl group, and n is an integer of 1-3; provided that when n is 2 or 3, R may be either the same kind of amino group-containing hydrocarbon groups or different kinds of amino group-containing hydrocarbon groups and that so long as at least one R is an amino group-containing hydrocarbon group, the remaining R(s) may be an alkyl group, preferably an alkyl group having 1-10 carbon atoms, vinyl group or methacryl group. When the hydrocarbon group of R has 11 or more carbon atoms, not only the aminosilane compound tends to be difficult to hdyrolyze but the titanium dioxdie pigment coated therewith tends to be poor in heat resistance and, as the result of heating at the drying and/or grinding step conducted after the coating, the titanium dioxide powder tends to become yellowish and resultantly processed plastic products also tend to become yellowish.
Specific examples of the aminosilane compound include N-&bgr;(aminoethyl)&ggr;-aminopropyltrimethoxysilane, N-&bgr;(aminoethyl)&ggr;-aminopropyltriethoxysilane, &ggr;-aminopropyltrimethoxysilane, &ggr;-aminopropyltriethoxysilane, N-&bgr;(aminoethyl)&ggr;-aminopropylmethyldimethoxysilane and &ggr;-aminopropylmethyldimethoxysilane, used each alone or in a combination of two or more thereof.
The hydrolysis product in this invention refers to a product wherein the alkoxy group of the aminosilane compound represented by the above-mentioned formula has been hydrolyzed to form a silanol and a product wherein the silanols have undergone polycondensation with each other to form an oligomer or polymer having a siloxane linkage. The hydrolysis product may partly contain an unreacted aminosilane compound within limits not deleterious to the object of this invention.
The coating amount of the hydrolysis product of aminosilane compound in this invention is preferably 0.01-3.0% by weight, more preferably 0.02-1.0% by weight, in terms of the aminosilane compound relative to titanium dioxide constituting the base substance. When the amount is less than the above-mentioned range, the intended effect tends to be difficult to obtai
Akamatsu Toshihiko
Fujimura Takeshi
Takahashi Hideo
Yamada Eiji
Ishihara Sangyo Kaisha Ltd.
Koslow C. Melissa
Manelli Denison & Selter PLLC
Manlove Shalie
White, Jr. Paul E.
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