Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Post imaging process – finishing – or perfecting composition...
Reexamination Certificate
2003-02-25
2004-11-30
Rodee, Christopher (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Post imaging process, finishing, or perfecting composition...
C430S108200, C430S108300
Reexamination Certificate
active
06824943
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a black toner for electrostatic image development which can provide high-quality images with less surface contamination in an electrostatic image developing apparatus operated at a speed ranging from low to high speed, and which is also free from toxic substances.
2. Description of the Related Art
As a black pigment in a toner for electrostatic image development, carbon black and black iron oxide (magnetite) have exclusively been employed heretofore. Carbon black is a pigment which is generally cheap and is in the form of a powder having a fine particle diameter, and is also superior in colorability. However, carbon black is inferior in handling properties and operability because it is a bulky powder having a bulk density of 0.1 g/cm
3
. Also carbon black is classified into Group 2B (possibly carcinogenic to human) by the International Agency for Research on Cancer and a problem related to safety and health has been pointed out.
On the other hand, black iron oxide (magnetite) powders have aggregation properties because Fe
3
O
4
is magnetic and it is difficult for them to mix with other toner materials. They are also converted into brown Fe
2
O
3
at about 150° C. and are inferior in heat resistance.
The characteristics required for a black colorant employed in a toner for electrostatic image development include, for example, colorability, safety, handling properties during manufacture, heat resistance, and electrical characteristics which exert an influence on developing properties. Electrical characteristics are important among the characteristics required for the colorant. The electrical characteristics can be subdivided into charging characteristics, being able to retain charges for a long period, charge uniformity (charge amount distribution), and charge environmental stability. Various factors exert an influence on these electrical characteristics and examples thereof include dispersibility, electrical resistivity, and surface physical properties of the colorant. If the colorant has poor electrical characteristics, the charge amount of each of the toner particles becomes non-uniform and the charge amount distribution is widened. Also the proportion of the number of particles having charges in the opposite polarity and the number of insufficiently charged particles increases causing dispersion of the toner in the apparatus during development and fogging wherein the toner adheres onto the non-image portion of a print. Furthermore, the resulting toner is likely to have poor durability, that is, the image density and resolution vary after extended use or printing of a large number of sheets.
Various materials have hitherto been studied to overcome the drawbacks of carbon black and black iron oxide (magnetite) and to develop a novel material to replace them. Among these materials, Japanese Unexamined Patent Application, First Publication No. Hei 3-2276 proposes a black particle powder made of polycrystalline particles comprising Fe
2
TiO
5
and a Fe
2
O
3
—FeTiO
3
solid solution and also discloses a technique relating to a toner employing the same. An object of this publication is to provide a black colorant which is safe and innoxious and which is also superior in operability and heat resistance. However, the black colorant does not provide the electrical characteristics of the toner employing the black particle powder. Also the black colorant does not have sufficient blackness suited for use as the black colorant, and therefore a large amount of the black particle powder must be employed to provide sufficient blackness of the toner. Such a toner has an increased specific gravity and is likely to cause dispersion of the toner in the developing apparatus due to stirring together with a carrier in the developing apparatus, or due to a centrifugal force applied during the rotation of a development sleeve.
Japanese Unexamined Patent Application, First Publication No. 2000-319021 proposes a black particle powder comprising iron oxide (magnetite) particles and a titanium component in an amount of 0.3 to 3.5% by weight in terms of titanium atoms, and a toner employing the same. Furthermore, Japanese Unexamined Patent Application, First Publication No. Hei 8-34617 proposes a black magnetic iron oxide particle powder comprising iron oxide (magnetite) particles and a titanium component in an amount of 0.5 to 10.0% by weight in terms of titanium atoms, and a toner employing the same. However, iron oxide (magnetite) cannot sufficiently maintain charges on the toner because it has conductivity, and is likely to cause aggregation between particles because it has magnetism, and thus it is difficult to obtain a black toner having sufficient coloring strength.
As described above, the prior art does not disclose a technique which overcomes the drawbacks of carbon black and black iron oxide (magnetite) and does not disclose a toner employing a novel black colorant capable of sufficiently providing the electrical characteristics of the toner.
BRIEF SUMMARY OF THE INVENTION
In consideratin of the above, the present invention has been completed and an object thereof is to provide a toner for electrostatic image development which employs a black colorant free from toxic substances and which exhibits stable charge behavior even after extended use or printing of a large number of sheets, thus making it possible to provide printed images having sufficient image density without causing toner dispersion, fogging, and variation in image density.
The present inventors have made intensive studies and found that the above object can be achieved by employing a toner using black fine particles obtained by coating the surface of titanium dioxide particles with a complex oxide of titanium and iron, and thus the present invention has been completed.
The present invention provides a toner for electrostatic image development comprising a binder resin and a colorant, wherein the colorant is made of black fine particles obtained by coating the surface of titanium dioxide particles with a complex oxide of titanium and iron.
The black fine particles employed in the toner for electrostatic image development of the present invention are fine particles obtained by coating the surface of titanium dioxide particles with a layer containing a complex oxide of titanium and iron, and therefore, unlike magnetite, they are low-magnetism fine particles. Therefore, they can be uniformly dispersed in a binder resin because of poor aggregation properties between the particles. Also the complex oxide of titanium and iron is a black oxide and black fine particles are particles having good dispersibility. Therefore, the toner employing the same is a toner having an excellent degree of blackness. Due to excellent dispersibility, black fine particles are uniformly included in the respective toner particles. Therefore, non-uniformity of the charge amount between toner particles disappears, thereby making it possible to reduce the number of insufficiently charged particles. Furthermore, black fine particles employed in the toner for electrostatic image development of the present invention contain, as the core, titanium oxide having a specific gravity smaller than that of the complex oxide of titanium and iron and magnetite. Therefore, the true specific gravity of the toner of the present invention becomes smaller than that of the toner employing magnetite or a complex oxide of titanium and iron in the form of a simple substance. Therefore, even if the toner is transferred to a rotating body, such as a stirring member or development sleeve in a developing apparatus, toner dispersion resulting from centrifugal force can be remarkably reduced.
The toner for electrostatic image development of the present invention, which employs black fine particles obtained by coating the surface of titanium dioxide particles with a complex oxide of titanium and iron, exhibits stable charge behavior even after extended use or printing of a large number of sheets, thus ma
Armstrong Kratz Quintos Hanson & Brooks, LLP
Dainippon Ink and Chemicals Inc.
Rodee Christopher
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