Electrophotography – Image formation – Fixing
Reexamination Certificate
2002-09-23
2004-02-17
Ngo, Hoang (Department: 2852)
Electrophotography
Image formation
Fixing
C399S328000, C399S331000, C399S333000, C219S216000
Reexamination Certificate
active
06694121
ABSTRACT:
BACKGROUND OF THE INVENTION
1) Field of the Invention
The present invention relates to a fixing unit which fixes a developed image, and an image formation apparatus represented by a copying machine, a facsimile, a printer, a scanner, and a composite machine thereof.
2) Description of the Related Art
In an image formation apparatus such as a copying machine, a printer and a facsimile apparatus, a fixing unit is provided for fixing a visible image transferred from an image supporting member such as a photosensitive material to a recording material. For the fixing unit, when the visible image is a toner image, a configuration comprising a fixing rotating member to be heated to a temperature capable of melting the toner, and a pressuring rotating member for contacting the toner image with the fixing rotating member is provided.
As to the toner image transferred on a recording material, the toner adhesion amount irregularity is generated in the direction perpendicular to the image formation surface of the recording material, that is, in the toner adhesion height direction due to factors such as the toner particle size, the charge amount irregularity on the image supporting member surface, the edge effect with a toner adhesion amount increase at the rim of the image and the image density.
As a method for fixing a toner image on a recording material, a roller fixing method of providing a fixing rotating member and a pressuring rotating member as a roller for forming a forcing section as a fixing nip section by forcing them with each other and providing the fixing rotating member as a heating roller, and a belt fixing method of providing a fixing rotating member as an endless belt placed around roller members and a pressuring rotating member as a roller for forming a forcing section as a fixing nip section by forcing the roller and the endless belt and heating the endless belt directly or indirectly, can be presented. In particular, according to the roller fixing method, since the toner image and the heating roller are contacted directly with a relatively high pressure so as to provide heat to the toner evenly, it is a fixing method with a good thermal efficiency, and thus it is used widely.
Among the heating rollers as the fixing rotating member used in the roller fixing method, there are those referred to as the hard type with a mold releasing layer by about 10 to 30 &mgr;m on the surface of a mandrel of an aluminum based or iron based metal material. For the mold releasing layer of the hard type heating roller, a fluorine resin material, or the like such as a PFA and a PTFE is used. Therefore, the surface hardness of the hard type heating roller is substantially equal to the hardness of the surface of the mandrel so that the toner image transferred on the recording material can be crushed to an even height by the fixing nip section. However, since the toner image has the adhesion amount irregularity in the toner adhesion height direction, degree of crushing the image differs between the part with a low toner adhesion height and the part with a high toner adhesion height. Specifically, the image in the high part is spread in the paper surface direction compared with the low part.
Therefore, in order to prevent the image spread irregularity in the paper surface direction derived from crushing the toner to the even height, a heating roller called soft type with an elastic layer provided on the surface of an aluminum based or an iron based metal material for facilitating deformation of the roller surface is proposed. As the material of the elastic layer used for the soft type heating roller, a fluorine rubber, a silicone rubber or a mixture of a resin and a rubber is used. As the soft type heating roller, there is one with the elastic layer surface covered with a PFA tube in consideration of the wear resistance of the roller surface.
In the field of the image formation, with propagation to a wide range of users of an image inputting apparatus such as a scanner and a digital camera, an apparatus having an image recording/editing function such as a computer, and an image outputting apparatus such as a printer and an MFP, a high image quality of the outputted image, a high quality and a high productivity (high speed printing) are highly requested. In particular, needs of the high image quality are highly required so that the reproductivity of the image details attracts the attention. In order to accurately reproduce the details, it is apparent that influence of the toner particle size used for the image formation is significant, that is, with a smaller particle, more detailed reproduction can be enabled. For example, the Japanese Patent Application Laid Open (JP-A) No. 8-82951 proposes an image formation apparatus a small size toner having 6 to 9 &mgr;m volume average particle size, 10 to 40 numerical % of particles of 5 &mgr;m or less, and 0 to 20 numerical % of particles of 4 &mgr;m or less compared with the conventional toner having 9.5 &mgr;m volume average particle size, and 30 numerical % of particles of 5 &mgr;m or less, and an image formation apparatus using the same.
In the case of an image developed with a toner having a relatively large particle size of 9.5 &mgr;m volume average particle size, and 30 numerical % of particles of 5 &mgr;m or less, the image ruggedness on the recording material, that is irregularity of the adhesion amount in the toner height direction is drastic so that the image tends to be swelled after the fixation. This tendency is conspicuous in the case of fixing with a soft type heating roller rather than the case of fixing with a hard type heating roller. Therefore, when a soft type heating roller is used, the image fixed on the recording material can easily be peeled off. In order to fulfill the demand for the high image quality with such a toner with a relatively large particle size, the elastic layer thickness needs to be about 0.5 mm to several mm. However, when the elastic layer is thick, heat supply from the roller inside to the roller surface is delayed so that the demand for the high speed printing cannot be achieved.
With a small size toner, since the charge amount per one toner is high, when a recording material with an image formed by such a toner is conveyed to the fixing nip section charged by friction by rotation in a state forced with each other, the toner may be scattered due to generation of discharge by nipping, or the toner may be repelled from the recording material by the repulsion force by the same pole so as to be adhered on the heating roller side depending on the polarity of the toner and the polarity of the heating roller or the pressuring roller comprising the fixing nip section.
In such a small size toner, in order to reduce the ratio of particles having 5 &mgr;m or less particle size to 10 to 40 numerical %, the toner of 5 &mgr;m or less particle size is eliminated. Thereby, the production step is complicated so as to provide a cause of the cost increase.
From this point of view, a toner with elimination of the toner having 5 &mgr;m or less particle size executed as little as possible, for example, a toner “having 4 to 7 &mgr;m volume average particle size and containing 60 to 80 numerical % of toner particles having 5 &mgr;m or less particle size” as disclosed in the Japanese Patent Application Laid-Open (JP-A) No. 2000-267340 has been developed.
However, as mentioned above, when a small size toner having 5 &mgr;m particle size accounts for more than half or the entire developer, since the flowability tends to be lowered according to the fineness of the toner, a silica, a titanium oxide, or the like is added by a certain amount for ensuring the flowability sometimes. However, with the improvement of the flowability, the toner can easily be scattered by the external force such as the static electricity so that the image scattering is generated so as to prevent achievement of the high image quality effect by the small size toner.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a developer capable of
Ngo Hoang
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Ricoh & Company, Ltd.
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