Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Radiation-sensitive composition or product
Utility Patent
1996-09-13
2001-01-02
Dote, Janis L. (Department: 1753)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Radiation-sensitive composition or product
C430S106100, C430S109500, C430S110100, C430S111400, C430S124300
Utility Patent
active
06168894
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to an image forming method and dry toner useful for developing an electrostatic latent image formed by electrophotography, electrostatic recording and electrostatic printing and the like, and more particularly to an image forming method and dry toner therefor in which a developed toner image is fixable at relatively low temperatures and in a wide temperature range, the printed image having excellent printing and preserving property without contaminating an image forming apparatus.
DISCUSSION OF THE BACKGROUND
A variety of methods using electrophotography for obtaining a printed image have been disclosed in, for example, U.S. Pat. No. 2,297,691 and Japanese Pat. Publications Nos. 49-23910 and 43-24748, incorporated herein by reference. Generally, these methods include the following steps:
(a) an electrostatic latent image is formed on a electrophotoconductor by various methods;
(b) the electrostatic latent image is developed with toner;
(c) the developed toner image is transferred to a recording material such as, paper and the like, if desired; and
(d) the transferred toner image (hereinafter referred to as a toner image) is fixed by application of heat, pressure or organic solvent vapor to obtain a printed image.
Developing methods of an electrostatic latent image are broadly classified into two types. The first type of the developing methods is a liquid toner developing method using liquid toner which is made by dispersing a pigment and/or a dye in an insulating organic liquid. The second type of the developing methods is a dry toner developing method such as, for example, cascade developing method, magnetic brush developing method and powder cloud developing method, which uses dry toner made by dispersing a coloring agent such as, carbon black and the like, in a natural resin or a synthetic resin. Recently, the dry toner developing method has been widely used for electrophotography.
As fixing methods used for a developed image with dry toner (hereinafter referred to as toner), a heat roller fixing method is widely used because of the high efficiency of heating. Recently, the heat energy used for fixing has tended to decrease because of high speed fixing (for high speed printing) and relatively low temperature fixing (in order to save energy). In attempting to improve this situation, an improved fixing unit has been developed in which a cylindrical fixing roller to contact a toner image side of a recording material has thickness of not more than 1.0 mm. This improved fixing unit has the advantage of excellent efficiency of heat energy. However, the unit has a disadvantage of uneven fixation of toner image caused by bending generated by application of pressure for fixing. Therefore, toner used for this improved fixing unit is required to be fixable at relatively low temperatures beyond comparison with current toner because the heat rollers of the improved fixing unit must be applied with relatively low fixing pressure to prevent bending. Low temperature fixable toner used for the improved fixing unit is proposed which includes a resin or a wax having a relatively low melting point. However, the low temperature fixable toner tends to be blocked (hereinafter referred to as blocking) even at the inner temperature of an image forming apparatus or the general preserving temperature during a year and has too narrow a fixing temperature range to keep obtaining good printed images even when using a polyester resin which has both low temperature fixing property and good preservability.
In order to solve this problem, a plurality of improved low temperature fixable toners including two polyester resins having different physical properties are disclosed. For example, Japanese Laid-Open Pat. Application No. 60-90344 discloses toner including a mixture of a non-linear polyester resin and a linear polyester resin. Japanese Laid-Open Pat. Application No. 64-15755 discloses toner including a mixture of a crosslinked polyester resin, which has glass transition temperature Tg of at least 50° C. and softening point of not more than 200° C., and a linear polyester resin which has softening point of not more than 150° C. and weight-average molecular weight MW of from 3,000 to 50,000. Japanese Laid-Open Pat. Application No. 2-82267 discloses toner including a non-linear polyester resin which has weight-average molecular weight MW of at least 5,000 and the ratio of weight-average molecular weight Mw to number-average molecular weight Mn, (Mw/Mn), of at least 20 and another non-polyester resin which has MW of from 1,000 to 5,000 and Mw/Mn of not more than 4. Japanese Laid-Open Pat. Application No. 3-229264 discloses toner including a linear polyester resin having acid value of from 5 to 60 mg KOH/g, a non-linear polyester resin having acid value of smaller than 5 mg KOH/g and an organic metal compound. Japanese Laid-Open Pat. Application No. 3-41470 discloses toner including two saturated polyester resins having different acid values in which the ratio of the large acid value to the small acid value is at least 1.5. However, fixing temperature is recently being set lower and lower; therefore, these toners become unavailable for the improved fixing unit having a thin thickness fixing roller with low fixing pressure referred to above, because the toner does not have satisfactory fixing property such as, low temperature fixability and a wide enough fixable temperature range to be used for the improved fixing unit, and does not provide excellent preservability.
In addition, as the demand for high quality printed image continues to grow, the diameter of a toner particle becomes smaller and smaller. However, as the diameter of a toner particle becomes smaller, there occur a variety of problems which include apparatus contamination by toner scattering and fouling on printed images. In an attempt to solve these problems, a developer is proposed in which a magnetizable material is included in a two-component toner to hold the toner to a magnetic developing roller. For example, Japanese Laid-Open Pat. Application No. 58-216256 discloses two-component developer having carrier and toner which includes a magnetizable material and a fine electroconductive material. Japanese Laid-Open Pat. Application No. 3-42675 discloses two-component magnetic developer having carrier and toner which includes a magnetizable particle and a condensation polyester resin. However, these magnetizable particles are too large to be dispersed in a fine toner particle used for the image quality improved image forming apparatus described above.
Because of these reasons, a need exists for a toner useful for improved image forming methods having excellent fixing properties such as low temperature fixability and a wide fixable temperature range and which can be used for high speed and high heat efficient fixing units having a thin fixing roller and using low fixing pressure. Toners providing excellent preservability in addition to these other properties is also needed.
OBJECTS OF THE INVENTION
Accordingly, one object of the present invention is to provide an image forming method and toner for developing electrostatic latent images, in which a toner image is fixed at relatively low temperature for high speed and high efficient fixing, and toner and a fixed image have excellent preservability.
Another object of the present invention is to provide an image forming method and toner therefor in which a toner image is fixable in a wide temperature range for obtaining uniform printing images.
Yet another object of the present invention is to provide an image forming method and a fine particle toner therefor which can print excellent images without apparatus contamination and fouling on printed images.
SUMMARY OF THE INVENTION
The above objects and other objects of the present invention which will become apparent from the following description are achieved by an image forming method and toner therefor.
The image forming method of the present invention is useful for an i
Aoki Mitsuo
Fushimi Hiroyuki
Kotsugai Akihiro
Suzuki Masanori
Tosaka Hachiro
Dote Janis L.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Ricoh & Company, Ltd.
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