Color toner for flash fixing

Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Post imaging process – finishing – or perfecting composition...

Reexamination Certificate

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C430S111400, C430S124300

Reexamination Certificate

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06555280

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a color toner used for performing image formation using an electrophotographic method, and, in particular, to a color toner to be fixed on a recording medium using optical energy from flash light.
2. Description of the Related Art
The electrophotographic method is a technology currently widely used in image formation apparatuses, such as a copying machine, an electrophotographic facsimile, and an electrophotographic printer. As the electrophotographic method, generally a form using a photoconductive insulator is used, as disclosed by U.S. Pat. No. 2,297,691, etc. In this form, an electrostatic latent image is formed, by applying light, such as that of a laser or an LED, on a photoconductive insulator electrified by corona electric discharge or an electric charge supply roller. Then, the above-mentioned electrostatic latent image is developed by a resin powder called toner (called colorant) colored by a pigment or a paint which adheres thereto, and, thus, a visualized toner image is obtained therefrom. Then, this toner image is transferred onto a recording medium, such as a paper or a film. However, since the toner image at this time is only a powder image which is only put on the recording medium, this should be fixed onto the recording medium. Then, as a last process, after fusing the toner on the recording medium by heat, pressure, light, etc., it is solidified, and the toner image fixed onto the recording medium is finally obtained.
Thus, fixing of toner is such as fusing it by a heat, the toner being a powder generally having a thermoplastic resin (referred to as a binding resin, hereinafter) as a main ingredient, and adhering onto a recording medium as mentioned above. As systems for this purpose, a heat roll system in which a recording medium having had a toner image formed thereon is heated and pressurized directly by a roller, and a flash fixing system in which a toner is fixed onto a recording medium by irradiating it with flash light, such as that from a xenon flash lamp, are well known.
The above-mentioned flash fixing system is a system in which optical energy from a glint of light (flash light) of a discharge tube, such as a xenon flash lamp is converted into thermal energy, and, thereby, a toner is fused, and fixed on a recording medium.
As compared with the above-mentioned heat roll system, this flash fixing system has the following features, when it is used in an image formation apparatus:
(1) Since it is non-contacting fixing, the resolution of a toner powder image formed on a photoconductive insulator layer is not degraded thereby.
(2) No warming up time is needed after beginning of power supply, and, thus, quick starting is possible.
(3) Material or thickness of a recording medium, such as a paper with paste, a pre-printed paper, a paper having a different thickness, has no influence on the fixing performance.
A process in which a toner is fixed onto a recording medium by the flash fixing method is as follows:
Flash light emitted from a discharge tube is absorbed by a toner image on a recording medium (powder image), and is changed into thermal energy. Thereby, the toner increases in temperature, is softening and fused, and is stuck onto the recording medium. The temperature falls after irradiation of flash light is finished, the fused toner then solidifies, and is fixed onto the recording medium.
However, a xenon flash lamp generally used, for example, as a discharge tube for the flash fixing, emits light in a range between 400 nm through 1400 nm in wavelength, and especially, has a remarkably a high light emission intensity in a range between 800 nm through 1400 nm of a near-infrared wavelength region, compared with the light emission intensity in the range between 400 nm through 800 nm of visible region. By this reason, it is required that a toner on which flash fixing is performed should have a high absorbance for the light of the near-infrared wavelength region.
However, generally, the binding resin which is the main ingredient of the toner has a very low absorbance for the visible region and the near-infrared region. Moreover, when the colorant is of black, it has a high absorbance for the visible region and near-infrared region. However, when the colorant is of a color toner, such as yellow, cyan, magenta, red, blue or green, it has a some absorbance for the visible region but has a low absorbance for the near-infrared region.
Therefore, it is difficult to properly fix a color toner containing the binding resin and a colorant for a color other than monochrome one, by such flash light as that used for fixing a black toner. Therefore, in order to fix a color toner, it is necessary to apply strong optical energy thereto.
Then, in order to reduce optical energy needed for fixing a color toner on a recording medium by flash light, a technology has been proposed in which an infrared absorbent having an absorbance for a light emission wavelength region of a xenon flash lamp. For example, Japanese Laid-Open Patent Applications Nos. 61-132959, 6-118694, 7-191492 and 2000-147824 disclose making a toner for the flash fixing contain a compound of a family of aminium, a compound of a family of diimonium, or a compound of a family of naphthalocyanine. Moreover, Japanese Laid-Open Patent Application No. 6-348056 discloses a technology of making resin particles containing an infrared absorbent of a family of anthraquinone, a family of polymethine, or a family of cyanine adhere to a toner surface. Furthermore, Japanese Laid-Open Patent Application No. 10-39535 discloses a technology of improving a fixing performance of a color toner with flash light by making tin oxide or indium oxide contain in the toner.
According to the above-described technology, performance of conversion of optical energy into thermal energy is improved by improving fusion performance of the binding resin which is the main ingredient of a color toner by adding the infrared absorbent thereto.
However, the binding resin cannot yet be fused fully only by addition of the above-mentioned infrared absorbent. Moreover, the above-mentioned compound of a family of aminium, compound of a family of diimonium, or the like, preferably used as the infrared absorbent, is colored by itself. Thereby, it may have a bad influence on the saturation, hue or the like of a color image obtained after being fixed onto a recording medium when this is used in a large amount. Therefore, the amount of the infrared absorbent used preferably should be reduced as possible.
As mentioned above, in the related art, in order to fix a color toner positively by flash light, still high optical energy is needed.
SUMMARY OF THE INVENTION
The present invention has been devised in consideration of the above-mentioned situation, and, an object of the present invention is to provide a color toner for flash fixing by which formation of a superior printed image can be achieved while aiming at reduction of optical energy required therefor.
A color toner according to the present invention includes, at least, a binding resin, a colorant and an infrared absorbent, wherein the color toner is fixed on a recording medium by flash light, and PAS intensity thereof obtained from integration of a infrared PAS spectrum obtained according to photoacoustic spectroscopy (PAS) analytical measurement through a range between 800 and 2000 nm falls within a range between 0.01 and 0.2 assuming that the value of carbon black is 1.
The above-mentioned photoacoustic spectroscopy (PAS) analyzing method is a method for detecting, finally by a pressure change, a periodic heat change occurring due to application of intermittent light (flash light) on a sample. Measurement by in-situ (spot) is possible by this detecting method.
Specifically, the PAS analyzing method used in the present invention is as follows: When a modulated infrared is absorbed by the sample, the heat corresponding to incident light is generated. Since this generated heat causes a pressure change in a surrounding g

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