Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Post imaging process – finishing – or perfecting composition...
Reexamination Certificate
1999-12-22
2001-05-08
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...
C430S111400
Reexamination Certificate
active
06228551
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a toner for developing an electrostatic image, particularly relates to a toner comprising particles of low molecular weight polypropylene.
BACKGROUND OF THE INVENTION
In an example of image formation process in the electrophotographic method, an electrostatic image is formed on a photoreceptor by giving uniformly charge and imagewise exposure thereto. The electrostatic image is developed by a developer containing a toner to form a toner image, and the toner image is transferred to a paper and fixed to form a visual image. On the other hand, a cleaning member arranged on the surface of photoreceptor so as to be contacted with pressure to the surface removes the toner which is not transferred to the paper and remained on the photoreceptor.
In the fixing process of such the image forming procedure, the fixing image is usually formed by the use of a heat-roller fixing device.
There is a drawback in the fixing by the heat-roller device that an offset problem tends to raise. The offset problem is caused by transferring a part of the molten toner to the surface of the heat-roller, the transferred toner is transferred back to the next paper so as to contaminate the image.
A technique has been known to prevent the offset problem, in which a particle of low molecular weight polypropylene is contained in the colored particle for giving a mold-releasing ability of the toner.
The low molecular weight polypropylene particle has a high mole-releasing ability itself and is able to be sharply fused when the particle is heated. Therefore, when the toner comprising such the colored particle is used, the low molecular weight polypropylene particle is rapidly fused at the fixing treatment by the heat-roller and the surface of the toner particle is covered by the fused low molecular weight polypropylene. As a result of that, the interface energy between the toner particle and the surface of heat-roller is lowered and the mold releasing ability of the toner is made higher.
However, a part of the low molecular weight polypropylene particles can not be included in the colored particles since the miscibility of the low molecular weight polypropylene particle with the binder resin of the colored particle is not so high. Accordingly, low molecular weight polypropylene particles freely existing outside the colored particles, hereinafter referred to free polypropylene particle, are formed.
When the toner containing the free polypropylene particles is used in the image forming process, problems are raised such as that the charging ability of the toner is made unstable and toner filming on the photoreceptor tends to be formed.
Moreover, a problem that a black spot like contamination is formed on the image when the diameter of the free polypropylene particle is large.
Furthermore, a problem is raised that the presence of the free polypropylene particles causes lowering in the flowing ability of the toner and the life of the developer is shortened.
On the other hand, when a toner with no free polypropylene particle or a wax-free toner is used in the image forming process, a sufficient transferring ability cannot be obtained since the particles are not present which fill the role of spacer for lowering the adhesive force between the toner particle and the photoreceptor.
SUMMARY OF THE INVENTION
The object of the invention is to provide a toner by which the offset problem and the toner film formation on the photoreceptor can be inhibited while maintaining a high transferring ability in the image forming process.
The toner of the invention comprises a colored particle containing at least a binder resin, a colorant, and a low molecular weight polypropylene particle, which has a content of the low molecular weight polypropylene particle of from 0.3 to 8.0 percent by weight based on the toner, a free polypropylene index measured by a centrifugal method of from 0.1 to 0.7 and a free polypropylene index measured by a natural sedimentation method of not more than 0.1.
It is preferable in the toner that the shape of the polypropylene particle separated by the centrifugal method is substantially ellipsoid. It is also preferable a number ratio of ellipsoid polypropylene particles each having an elliptical axis ratio of projection image of not more than 0.8 to the whole number of the separated polypropylene particles is not less than 50 percent.
It is preferable in the toner that the ratio of the number of the particles each having a particle diameter of not more than 4 &mgr;m present in the polypropylene particles separated by the centrifugal method to the whole number of the polypropylene particles separated by the centrifugal method is not less than 50%, more preferably not less than 60%.
DETAILED DESCRIPTION OF THE INVENTION
The invention is described in detail bellow.
Toner
The toner of the invention comprises colored particles and an external additive added according to necessity, and the colored particle comprises a binder resin, a colorant and a mold releasing agent, or low molecular weight polypropylene particle, in which an internal additive may be added according to necessity.
(1) Binder resin
A binder resin usually used in toner, such as a styrene resin, an acryl resin, a styrene/acryl resin and a polyester resin, is usable for the binder resin of the toner of the invention.
(2) Colorant
A colorant usually used in toner, such as carbon black, a magnetic material, a dye and a pigment, is usable for the colorant of the toner.
Examples of the carbon black usable as the colorant include channel black, furnace black, acetylene black, thermal black and lump black.
Examples of the magnetic substance include a ferromagnetic metal such as iron, nickel and cobalt, an alloy containing such the metal, a compound of a ferromagnetic metal such as ferrite and magnetite, a ferromagnetic alloy by a heat treatment even though containing no ferromagnetic metal such as a kind of alloy called Heuslar alloy such as manganese-copper-aluminum and manganese-copper-tin, and chromium dioxide.
As the dye, for example, C.I. Solvent Red series of 1, 49, 52, 58, 63, 111, and 122, C.I. Solvent Yellow series of 19, 44, 77, 79, 81, 82, 93, 98, 103, 104, 112 and 162, and C.I. Solvent Blue series of 25, 36, 60, 70, 93 and 95, are usable. A mixture of them may also be used.
Examples of the pigment include C.I. Pigment Red series of 5, 48:1, 53:1, 57:1, 122, 139, 144, 149, 166, 177, 178 and 222, C.I. Pigment Orange series of 31 and 43, C.I. Pigment Yellow series of 14, 17, 93, 94 and 138, C.I. Pigment Green 7, C.I. Pigment Blue series of 15:3 and 60. These pigments may be used singly or in combination.
Examples of preferred colorant include carbon black, Nigrosine dye, aniline blue, chalcoil blue, chrome yellow, ultramarine blue, du Pont oil red, quinoline yellow, methylene blue chloride, phthalocyanine blue, malachite green oxalate and rose bengal.
(3) Mold releasing agent
A low molecular weight polypropylene particle is used as the mold-releasing agent for the toner. A low molecular weight polypropylene particle synthesized by using a metallocene catalyst may be used as such the low molecular weight polypropylene particle.
The molecular weight of the low molecular weight polypropylene particle is preferably from 1,500 to 10,000, particularly from 1,800 to 4,000, in number average molecular weight Mn.
The number average molecular weight Mn is a number average molecular weight Mn measured by a high temperature GPC method. In concrete, the number average molecular weight is determined by a procedure in which a sample is flowed out at 135° C. using o-dichlorobenzene containing 0.1% of ionol and the refractive index thereof is measured by a difference refractive index meter and converted by polypropylene absolute molecular weight conversion according to the universal compensation method.
Heat energy necessary for fusing the toner can be lowered when the number average molecular weight Mn of the low molecular weight polypropylene particle is within the range of from 1,500 to 10,000, with the result that
Ohmura Ken
Oshiba Tomomi
Cantor & Colburn LLP
Goodrow John
Konica Corporation
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