Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Post imaging process – finishing – or perfecting composition...
Reexamination Certificate
2001-11-07
2004-01-27
Chapman, Mark A. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Post imaging process, finishing, or perfecting composition...
C430S108800, C430S109400
Reexamination Certificate
active
06682866
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a dry toner for developing electrostatic images in electrophotography, electrostatic recording and electrostatic printing. More specifically, the present invention is directed to a dry toner used in full color or monochromatic copying machines, full color or monochromatic laser printers, full color or monochromatic facsimile machines and the like image forming machines.
Dry toner for use in the above image forming machines are desired to have the following characteristics:
(1) Freedom of Hot Offset
“Hot offset” is a phenomenon occurring in fixation of toner image on paper with a heated roll and refers to deposition of fused toner onto the heated roll. Conventionally, an oil is applied to a heated roll to improve releasability. This requires an oil tank and hinders compactness of the apparatus. Recent trend is toward incorporation of a wax into the toner.
(2) Capability of Fixing at Low Temperature
For reasons of energy saving, it is desired that the toner image be sufficiently fixed at a low temperature.
(3) Freedom of Toner Filming
“Filming” is a phenomenon occurring when a wax is incorporated into dry toner to improve releasability thereof from a heated roll and refers to transference of the wax to a photoconductor or carrier particles to form a film thereon.
(3) Good Fluidity
Toner is desired to have a small particle size for obtaining high grade toner images. However, fine toner particles generally have random shapes and fail to exhibit good fluidity. Good fluidity of toner is desired to increase the amount thereof chargeable in a toner bottle and to reduce the amount of a fluidizing agent.
(4) Good Transferability
Toner image on a photoconductor must be transferred to a transfer medium with high efficiency to obtain high quality image.
Known toner, however, fails to simultaneously attain the above characteristics. For example, to attain low temperature fixation and anti-hot offset, JP-A-S57-109825 proposes the use of a polyester partially crosslinked with a polyfunctional monomer as a toner binder and JP-B-H07-101318 proposes the use of an urethane-modified polyester as a toner binder. These toners, however, do not exhibit satisfactory fluidity and transferability.
JP-A-H07-56390 proposes a toner containing polyester particles and wax particles to reduce the amount of a silicone oil which is applied to a heated fixing roll to prevent hot offset. The proposed toner, however, fails to attain satisfactory fluidity, transferability and low temperature fixation.
To improve fluidity and transferability, JP-A-H09-43909 proposes a toner obtained by a method in which an aqueous dispersion containing a colorant, a polar resin and a releasing agent is subjected to suspension polymerization; and JP-A-H09-34167 proposes a toner obtained by treating toner particles containing a polyester resin with an organic solvent in water. The former proposal, however, fails to attain low temperature fixation, while the latter proposal fails to improve anti-hot offset.
JP-A-H11-133666 proposes a dry toner using a urea-modified polyester resin as a toner binder. While the proposed toner gives good releasability and suitable gloss, anti-hot offset is not satisfactory.
JP-H10-207116 proposes a toner having a controlled amount of a wax exposed to the external surfaces thereof and a specific particle diameter. The proposed toner, however, causes filming of spent toner.
SUMMARY OF THE INVENTION
It is, therefore, an object of the present invention to provide a dry toner which is devoid of the drawbacks of conventional toners.
Another object of the present invention is to provide a toner which exhibits sufficient anti-hot offset, which permit low temperature fixation, which is free of toner filming problems and which has good fluidity and good transferability.
In accordance with the present invention, there is provided a toner for dry developing, comprising a colorant, a binder including a modified polyester, and wax particles dispersed in said binder, wherein that portion of said wax particles having a dispersion diameter of 0.1-3 &mgr;m accounts for at least 70% by number of said wax particles.
The “dispersion diameter of wax particle” as used herein refers to the maximum length of a line extending between two points on the peripheral line of the TEM pattern of the particle. TEM pattern is obtained as follows. A sample toner is embedded in an epoxy resin and the embedded body is cut into a slice having a thickness of about 100 nm. The slice is dyed with ruthenium tetraoxide and a cross-sectional photograph (magnification: 10,000) is taken using a transmission electron microscope.
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 according to the present invention comprises wax particles, a colorant, and a binder including a modified polyester.
It is important that the wax particles have such a particle size distribution that portion of the wax particles having a dispersion diameter of 0.1-3 &mgr;m accounts for at least 70% by number of the wax particles. Preferably, that portion of the wax particles having a dispersion diameter of 1-2 &mgr;m accounts for at least 70% by number of the wax particles. When wax particles having a dispersion diameter of less than 0.1 &mgr;m are present in excess of 30% by number of the whole wax particles, satisfactory releasability cannot be attained. On the other hand, when wax particles having a dispersion diameter of more than 3 &mgr;m are present in excess of 30% by number of the whole wax particles, fluidity of the resulting toner becomes poor and filming is apt to occur and, further, color reproducibility and gloss of the color images are not satisfactory.
Any wax may be suitably used for the purpose of the present invention. Examples of such waxes include polyolefin wax such as polyethylene wax and polypropylene wax; long chain hydrocarbon wax such as paraffin wax and sazole wax; and carbonyl group-containing wax. The carbonyl group-containing wax is particularly preferably used for the purpose of the present invention.
Illustrative of suitable carbonyl group-containing waxes are polyalkanoic acid ester waxes such as carnauba wax, montan wax, trimethylolpropane tribehenate, pentaerythritol tetrabehenate, pentaerythritol diacetate dibehenate, glycerin tribehenate and 1,18-octadecanediol distearate; polyalkanol ester waxes such as tristearyl trimellitate and distearyl maleate; polyalkanoic acid amide waxes such as ethylenediamine dibehenyl amide; polyalkylamide waxes such as trimellitic acid tristearyl amide; and dialkyl ketone waxes such as distearyl ketone. Above all, the use of a polyalkanoic acid ester wax is preferred.
The wax used in the present invention generally has a melting point of 40-160° C., preferably 50-120° C., more preferably 60-90° C. A melting point of wax below 40° C. may adversely affect the heat resistance and preservability of the toner, while too high a melting point in excess of 160° C. is apt to cause cold offset of toner when the fixation is performed at a low temperature. Preferably, the wax has a melt viscosity of 5-1000 cps, more preferably 10-100 cps, at a temperature higher by 20° C. than the melting point thereof. When the viscosity is greater than 1000 cps, the anti-hot offset properties and low fixation properties of the toner are adversely affected. The amount of the wax in the toner is generally 1-40% by weight, preferably 3-30% by weight, based on the weight of the toner.
It has been found that the wax particles having suitable particle diameters can be dispersed in a modified ester-containing binder resin in a stable manner. Probably, the polar regions of the modified polyester provide negative adsorption in the interface between the wax and the polar regions so that non polar wax particles can be stably dispersed in the polyester.
The modified polyester used as a binder is (A) a pol
Emoto Shigeru
Sugiyama Tsunemi
Tomita Masami
Yamashita Hiroshi
Chapman Mark A.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Ricoh & Company, Ltd.
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