Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Post imaging process – finishing – or perfecting composition...
Reexamination Certificate
2000-09-26
2002-01-15
Goodrow, John (Department: 1753)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Post imaging process, finishing, or perfecting composition...
C430S108600, C430S111400
Reexamination Certificate
active
06338929
ABSTRACT:
This application is based on an application No. 276350/1999 filed in Japan, the contents of which are hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a toner for developing an electrostatic latent image.
2. Description of the Prior Art
It has been well known that particulate inorganic compounds, such as silica, titania and the like are externally added to toner particles used for an electrophotography in order to afford the desirable flowability to said toner particles. In recent years when demands for a digitization and a high image quality in particular have been increased in the electrophotography, a smaller atomization is required of the toner particles. It is necessary to use a large amount of a fluidizing agent in order to afford the desirable flowability to the toner having small particle size. In the case of a full color toner where the aforesaid characteristics in general are most severely required, ultrafine inorganic particles whose average primary particle size is about 10-50 nm are externally added to almost all full color toners in an amount of not less than 1.0%.
However, in the case where a large amount of these ultrafine inorganic particles is externally added to the toner particles, there is a problem that the inorganic particles which are peeled off from the toner particles pass through a space between the photosensitive member and a cleaning blade in a cleaning process to adhere on the photosensitive member, and the adhered inorganic particles cause a black spot (BS) on the copied images. When the inorganic particles are adhered on the photosensitive member, the toner accumulates on the circumferences of the adhered inorganic particles, and BS appears as a noise in unimaged parts on the copied images.
In order to solve the problem, a technique has been proposed wherein inorganic particles having a relatively large particles size are externally added to the toner particles, and the deposit on the surface of photosensitive member is removed by an abrasive action (U.S. Pat. No. 5,776,646). However, although the technique makes it possible to suppress the occurrence of BS, it brings about a new problem that the surface of the photosensitive member is remarkably abraded and a life of the photosensitive member is shortened.
Furthermore, a technique has been proposed wherein particles of a metal salt of fatty acid are externally added to the toner particles from the viewpoint of a prevention against the adhesion on the surface of the photosensitive member (Japanese Patent Publication (KOKAI) No. 297427/1997). However, although the technique makes it possible to suppress the occurrence of BS, it brings about a new problem that a tendency to increase an electrification amount at the time of initial electrification of the toner is strengthened, and a fogging occurs on the initial copied imaged. In addition, although the potential characteristics are stable because the surface of the photosensitive member is abraded and refreshed at all times, there is a problem that the potential characteristics become unstable and a reproducibility of the image becomes worse when an addition of particulate metal salt of fatty acid brings about too small abraded amount of the surface of the photosensitive member.
Furthermore, as regards the toner in general, there are problems that a decrease of an image concentration and a fogging are occurred as the electrification amount of the toner is remarkably changed under various environments, particularly under the environment of low temperature and humidity (an environmental stability) and that even though the toner is subjected to the environment of middle temperature and humidity, the fogging is occurred on the copied image at the time of continuous copying (a durability).
SUMMARY OF THE INVENTION
The present invention has been made in consideration of the aforementioned circumstances. The object of the present invention is to provide a toner for developing an electrostatic latent image which suppresses the adhesion and wearability on the surface of the photosensitive member and exhibits the excellent rising property of the electrification. Another object of the present invention is to provide a toner for developing an electrostatic latent image which suppresses the adhesion and wearability on the surface of the photosensitive member and exhibits the excellent rising property of the electrification, environmental stability and durability.
The present inventors have found that these objects can be achieved by adding four external additives having specified particle sizes to toner particles containing a binder resin and a colorant.
The present invention relates to a toner which comprises (i) toner particles containing a binder resin and a colorant, (ii) a first external additive consisting of first inorganic particles whose number-average particle size is 5-40 nm, (iii) a second external additive consisting of second inorganic particles whose number-average particle size, which is larger than that of the first external additive, is 20-160 nm, (iv) a third external additive consisting of third inorganic particles whose number-average particle size, which is larger than that of the second external additive, is 80-1200 nm, and (v) the fourth external additive consisting of a metal salt of fatty acid whose volume-average particle size is 1.5-12 &mgr;m, said four external additives being externally added to the toner particles.
DETAILED DESCRIPTION OF THE INVENTION
The toner according to the present invention comprises publicly known toner particles and the particulate first, second, third and fourth external additives which are externally added to said toner particles. In the present specification, the wording of “externally add” means to add these additives to the preformed toner particles in such a way that said additives exist on the outer surfaces of said toner particles.
As the first external additive, the first inorganic particles are employed which have the number-average particle size of 5-40 nm, preferably 10-30 nm, more preferably 10-25 nm. It is preferable to use hydrophobic silica or titania particles as the inorganic particles. The hydrophobic silica is more preferable. By externally adding the first external additive to the toner particles, it is possible to afford the desired flowability to the toner. When the toner has not the desired flowability, the rising property of the electrification becomes worse, and a fineness of the copied images at the initial and last stages becomes coarse. When the number-average particle size is less than 5 nm, the flowability of the toner is remarkably decreased because the first external additive is embeded in the toner by an agitating stress of a developing agent. If the number-average particle size is more than 40 nm, the effect of affording the flowability to the toner is remarkably decreased.
The publicly known hydrophobic silica and titania can be employed as the first external additive provided that they have the aforementioned particle size and are hydrophobic. As the hydrophobic silica which is used as the first external additive, for example, TS500 (Cabosil Co.), R972, R974, R976 (Nihon Aerozil Co.), H2000, H2000/4M (Clarient Co.) and the like can suitably be used. As the hydrophobic titania which is used as the first external additive, STT30A (Titan Kogyo Co.), MT-150 (Teika Co.) and the like can suitably be used. Furthermore, the silica and titania having the desired particle size may be employed which are hydrophobicized with hydrophobicizing agent. The publicly known silane coupling agent, silicone oil and the like can be used as the hydrophobicizing agent.
The desirable hydrophobicizing degree of the first external additive is not less than 50%, preferably 60-70%. When the hydrophobicizing degree is less than 50%, it is difficult to put said additive to practical use because the flowability and electrification amount of the toner are remarkably changed by a small environmental change.
An adding amount of the
Aoki Megumi
Arai Takeshi
Hagi Masayuki
Kido Kenichi
Mikuriya Yoshihiro
Burns Doane , Swecker, Mathis LLP
Goodrow John
Minolta Co. , Ltd.
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