Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Post imaging process – finishing – or perfecting composition...
Reexamination Certificate
2000-11-29
2002-05-28
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...
Reexamination Certificate
active
06395443
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a toner for developing electrostatic latent images and to a process for the preparation thereof.
In an electrophotographic method, latent electrostatic images formed on a photoconductor are developed into visible toner images with a toner by a suitable method such as a magnetic brush method, a cascade method or a powder cloud method. Then, the toner images are transferred to a sheet of copy paper and fixed thereon, for instance, by the application of heat using heat-application means such as a heated roller or solvent vapors.
For the purpose of controlling triboelectricity of the toner, a charge controlling agent is generally incorporated thereinto. Such a toner is generally prepared by a method in which a binder, a coloring agent and a charge controlling agent are mixed in a powder state. The resulting mixture is then melted and kneaded, followed by solidification, grinding and classification.
Since the state of the charge controlling agent on toner particles greatly varies with conditions, such as mixing and grinding conditions, of the toner manufacturing process, it is difficult to properly control the triboelectricity. Thus, one problem of the above ground toner is concerned with the presence of particles which do contain a desired amount of the charge controlling agent. Such particles, which do not have desired triboelectricity, are apt to migrate on non-image portions of an electrostatic image-bearing photoconductor surface to cause background stains.
In this circumstance, a method is proposed in which a charge controlling agent is not kneaded with a binder and a coloring agent but is adhered to surfaces of kneaded and ground particles of the binder and the coloring agent (JP-A-63-2075). The toner obtained by this method, however, does not have satisfactory service life, because the adhered charge controlling agent receives influence of temperature, moisture, etc. Japanese patent No. 2825615 proposes a method in which an additional charge controlling agent is adhered to surfaces of kneaded and ground particles of the charge controlling agent, a binder and a coloring agent. This method, however, has a problem because the manufacturing efficiency is not high and requires high manufacturing costs.
SUMMARY OF THE INVENTION
It is, therefore, an object of the present invention to provide a toner for developing an electrostatic image, which can give a high quality image having no background stains.
Another object of the present invention is to provide a simple process which can produce the above toner.
It has been found that, when a kneaded and solidified mixture containing a binder, a coloring agent and a charge controlling agent is ground into toner particles, the grinding preferentially occurs at the interfaces between the binder and the charge controlling agent which is not compatible with the binder. As a consequence, the charge controlling agent preferentially exposes on the surfaces of the ground particles. It has also been found that the content of the charge controlling agent in smaller toner particles is higher than that in larger toner particles. However, the amount of toner particles which do not contain the charge controlling agent and which will cause background stains is greater in particles having very small diameters. It has now been found that the number percentage of toner particles having a particle diameter of 5.04 &mgr;m or less plays an important role in prevention of background stains in the case of a toner having a weight average particle diameter of 6.0-11.5 &mgr;m.
In accordance with the present invention there is provided a toner for developing an electrostatic image, comprising a binder, a coloring agent and a charge controlling agent and having the following characteristics (a), (b), (c), (d) and (e):
(a) said toner has a weight average particle diameter of 6.0 to 11.5 &mgr;m, a total particle number N and a total weight W;
(b) that portion of said toner which has a particle diameter of 5.04 &mgr;m or less accounts for greater than 15% but not greater than 60% of the total number N of said toner and has a number average particle diameter of 4.0 to 4.5 &mgr;m;
(c) that portion of said toner which has a particle diameter of greater than 5.04 &mgr;m but not greater than 12.7 &mgr;m accounts for 40 to 90% of the total number N of said toner and has a weight average particle diameter of 6.0 to 9.5 &mgr;m;
(d) that portion of said toner which has a particle diameter of 16 &mgr;m or more is not more than 2% based on the total weight W of said toner; and
(e) that portion of said toner which provides a number average particle diameter of 4.0 to 4.5 &mgr;m has such a content C1% by weight of the charge controlling agent that gives a ratio of C1/CT of 1.00 to 1.10, where CT is a total amount, in terms of % by weight, of said charge controlling agent in said toner.
In another aspect, the present invention provides a process for the preparation of the above toner, said process comprising the steps of:
mixing the binder in the form of a powder, the coloring agent in the form of a powder and the charge controlling agent in the form of a powder to obtain a mixture;
kneading said mixture at a temperature higher than the melting point of said binder;
solidifying the kneaded mixture and grinding the solidified mixture; and
sieving said ground mixture,
said kneading being carried out while applying a specific energy of at least 0.15 kW·h/kg to the mixture.
The present invention further provides a toner for developing an electrostatic image, comprising a binder, a coloring agent and a charge controlling agent and having the following characteristics (a), (b′), (c), (d) and (e′):
(a) said toner has a weight average particle diameter of 6.0 to 11.5 &mgr;m, a total particle number N and a total weight W;
(b′) that portion of said toner which has a particle diameter of 5.04 &mgr;m or less accounts for 15% or less of the total number N of said toner and has a number average particle diameter of 4.2 to 4.8 &mgr;m;
(c) that portion of said toner which has a particle diameter of greater than 5.04 &mgr;m but not greater than 12.7 &mgr;m accounts for 40 to 90% of the total number N of said toner and has a weight average particle diameter of 6.0 to 9.5 &mgr;m;
(d) that portion of said toner which has a particle diameter of 16 &mgr;m or more is not more than 2% based on the total weight W of said toner; and
(e) that portion of said toner which provides a number average particle diameter of 4.2 to 4.8 &mgr;m has such a content C2% by weight of the charge controlling agent that gives a ratio of C2/CT of 1.02 to 1.15, where CT is a total amount, in terms of % by weight, of said charge controlling agent in said toner.
The present invention further provides a process for the preparation of a toner described immediately above, said process comprising the steps of:
mixing the binder in the form of a powder, the coloring agent in the form of a powder and the charge controlling agent in the form of a powder to obtain a mixture;
kneading said mixture at a temperature higher than the melting point of said binder;
solidifying the kneaded mixture and grinding the solidified mixture; and
sieving said ground mixture,
said kneading being carried out while applying a specific energy of at least 0.1 kW·h/kg to the mixture.
Other objects, features and advantages of the present invention will become apparent from the detailed description of the preferred embodiments of the invention to follow.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION
A toner for use in image forming according to the present invention comprises a binder, a coloring agent and a charge controlling agent and has a weight average particle diameter of 6.0 to 11.5 &mgr;m, preferably 6-8 &mgr;m, a total particle number N and a total weight W. When the weight average particle diameter is less than 6.0 &mgr;m, there are apt to cause problems such as fouling of inside of the image forming machine by toner dispersion, reduction of image density und
Emoto Shigeru
Kawamoto Masahiro
Kinoshita Nobutaka
Kouzu Osamu
Kuroda Noboru
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