Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Post imaging process – finishing – or perfecting composition...
Reexamination Certificate
2002-04-03
2003-12-09
Goodrow, John (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Post imaging process, finishing, or perfecting composition...
C430S108600
Reexamination Certificate
active
06660442
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a nonmagnetic black toner for reversal development used for the development of a latent image formed in electrophotography, electrostatic recording method, electrostatic printing method or the like.
2. Discussion of the Related Art
Conventionally, carbon blacks have been used as a black colorant for a toner. However, the carbon blacks have some defects such that the volume specific resistance is low, so that triboelectric charges required for development cannot be maintained, whereby a sufficient degree of blackness cannot be obtained. In addition, there are also pointed out some problems in safety hygiene. Therefore, various composite oxides have been proposed as black colorants used in place of carbon black (Japanese Patent Laid-Open No. 2000-10344 (U.S. Pat. No. 6,130,017) and Japanese Patent Laid-Open No. Hei 9-25126.
On the other hand, recently, similar to the widespread trends in plain paper copy machines (PPC), there has been a remarkable progress in laser beam printers (LBP). In the case of the PPC, the development is carried out by forming an electrostatic latent image carrying electric charges on a photoconductor, and changing its surface potential by the intensity of the light source, thereby changing the image tone (charged area development). By contrast, in the case of LBP, since a latent image not having electric charges is formed by two-step of on-and-off, the area coverage modulation by the number of halftones is carried out (discharged area development, i.e. reversal development). Therefore, in the reversal development, the transferability of fine halftones affects the clearness, so that an improvement in image transferability is especially desired.
Conventionally, proposals for improving the image transferability, including a toner in which its wettability is adjusted by an amount of a wax or the like (Japanese Patent Laid-Open No. Hei 7-104503), a toner in which a silica having a large size is added (Japanese Patent Laid-Open No. Hei 7-271087), and the like, have been made. However, these toners have some defects such that filming of the toner is likely to take place in the former toner, and that the silica is embedded in the toner, so that its durability tends to be lowered in the latter toner.
An object of the present invention is to provide a nonmagnetic black toner for reversal development, comprising a black colorant useful for reversal development, namely a nonmagnetic black toner for reversal development for performing area coverage modulation by halftone, which has a sufficient high degree of blackness, a high volume-specific resistance, and excellent image transferability.
These and other objects of the present invention will be apparent from the following description.
SUMMARY OF THE INVENTION
According to the present invention, there is provided a nonmagnetic black toner for reversal development comprising:
a resin binder; and
a black colorant comprising a composite oxide of two or more metals, the composite oxide having an oil absorption per unit area of 0.07 ml/m
2
or less.
DETAILED DESCRIPTION OF THE INVENTION
One of the greatest features of the toner of the present invention resides in that the toner comprises a black colorant comprising a composite oxide of two or more metals, the composite oxide having a specified oil absorption. By adjusting the oil absorption of the composite oxide, the affinity of the composite oxide with the resin binder is adjusted, whereby the dispersibility of the composite oxide can be increased. By the improvement in the dispersibility of the composite oxide, the toner can be made into a smaller size, and the transferability of the toner is improved together with the uniform chargeability and the stability with the passage of time. Therefore, the composite oxide has an oil absorption per unit area of 0.07 ml/m
2
or less, preferably from 0.0001 to 0.05 ml/m
2
, more preferably from 0.001 to 0.02 ml/m
2
. In the present invention, the above-mentioned oil absorption (ml/m
2
) is calculated by the following equation using the oil absorption (ml/100 g) as determined by the method according to JIS K5101 and the specific surface area (m
2
/100 g):
Oil
Absorption
Per
Unit
Area
(
ml
/
m
2
)
=
Oil
Absorption
(
ml
/
100
g
)
Specific
Surface
Area
(
m
2
/
100
g
)
The oil absorption of the composite oxide, which may be dependent on its composition, is especially greatly dependent on its particle size. When the specific surface area becomes larger by making the particle size smaller, the oil-absorption also becomes larger. On the other hand, when the specific surface area becomes smaller by making the particle size larger, the oil-absorption also becomes smaller. In addition, the oil absorption can be increased by utilizing capillary phenomenon by the secondary aggregation.
The composite oxide has an average particle size of preferably from 5 nm to 1 &mgr;m, more preferably from 5 to 500 nm, especially preferably from 5 to 200 nm, from the viewpoints of the oil absorption and the covering strength.
In the present invention, the composite oxide is constituted by at least 2 metals, preferably at least 3 metals, from the viewpoint of the degree of blackness of the toner. Especially, it is preferable that at least one, preferably at least two, more preferably at least three of the metals of the composite oxide belongs to Group 2 or 13 of the Third Period of the Periodic Table, or to Groups 3 to 11 of the Fourth Period of the Periodic Table. Magnesium (Mg) and aluminum (Al) belong to Group 2 or 13 of the Third Period of the Periodic Table, and scandium (Sc), titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni) and copper (Cu) belong to Groups 3 to 11 of the Fourth Period of the Periodic Table. Among them, Mg, Al, Ti, Mn, Fe and Cu are preferable, and Mg, Al, Mn, Fe and Cu are especially preferable. The compositional ratio of the metals in the composite oxide is not particularly limited.
The content of the composite oxide is preferably from 4 to 30% by weight, more preferably from 4 to 20% by weight, especially preferably from 7 to 15% by weight, of the toner, from the viewpoints of the degree of blackness and the specific gravity of the toner.
The process for preparing a composite oxide includes a process comprising depositing other oxide on a surface of the main oxide used as a core particle (Japanese Patent Laid-Open No. 2000-10344 (U.S. Pat. No. 6,130,017)), a process of making a composite oxide comprising sintering several oxides (Japanese Patent Laid-Open No. Hei 9-25126), and the like, without being particularly limited thereto.
The preferable commercially available composite oxide in the present invention includes “Dye Pyroxide Black No. 1,” “Dye Pyroxide Black No. 2” (hereinabove commercially available from DAINICHISEIKA COLOR & CHEMICALS MFG. CO., LTD.), “HSB-603Rx,” “HSB-605” (hereinabove commercially available from Toda Kogyo Corp.), “ETB-100” (commercially available from Titan Kogyo K.K.), MC Series (commercially available from MITSUI MINING & SMELTING CO., LTD.), and the like.
The toner of the present invention may contain a known colorant other than the above-mentioned composite oxide as a colorant, but it is preferable that carbon black is not contained.
The resin binder in the present invention includes polyesters, hybrid resins which are defined below, styrene-acrylic resins, epoxy resins, polycarbonates, polyurethanes, and the like, without being particularly limited thereto. Among them, from the viewpoints of the dispersibility and the transferability of the colorant, the polyester and the hybrid resin are preferable, and the polyester is more preferable. The content of the polyester or the hybrid resin is preferably from 50 to 100% by weight, more prefer
Eida Akihiro
Sata Shin-ichi
Shimizu Jun
Shimokusa Koji
Birch & Stewart Kolasch & Birch, LLP
Goodrow John
Kao Corporation
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