Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Post imaging process – finishing – or perfecting composition...
Reexamination Certificate
2002-05-07
2004-05-11
Goodrow, John (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Post imaging process, finishing, or perfecting composition...
C430S137100
Reexamination Certificate
active
06733942
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a toner composition for electrophotography, used for development of electrostatic image in electrophotography, electrostatic printing, etc.
BACKGROUND ART
With the progress of office automation, the demand for electrophotography-based copying machines and laser printers has increased rapidly and the performance requirements for such equipment have become higher.
In order to obtain a visible image using electrophotography, there is a generally used method which comprises electrifying a photo-sensitive material such as selenium, amorphous silicon, organic semiconductor or the like, then applying a light thereto, subjecting the resulting photo-sensitive material to development using a developing agent containing a toner, to form a toner image on the photo-sensitive material, transferring the toner image onto a transfer paper, and fixing the transferred toner image using a hot roll or the like.
At this time, it is natural that the image after development needs to be a clear image free from fogging and having a sufficient image density. Further, in recent years, higher speed, energy saving and high development durability have come to be required. Further more, in particular, from the standpoints of higher safety, maintenance-free operation has come to be required strongly; and a toner superior in low-temperature fixing properties is needed. In order to improve the fixing properties of toner, it is generally necessary to lower the viscosity of toner when melted, to enlarge the adhesion area between toner and substrate for toner; therefore, it has heretofore been conducted to lower the glass transition temperature (Tg) of the binder resin used or make smaller its molecular weight.
A resin of low glass transition temperature, however, is generally inferior in blocking resistance and, therefore, hardly stays as a stable powder during the use or storage of toner. Also, when a resin of small molecular weight and high fluidity is used and when a toner image is fixed using a hot roll, direct contact occurs between the hot roll and the molten toner during the fixing.
At this time, there has been a problem that the toner transferred on the hot roll tends to stain the transfer paper, etc. fed thereon after the toner (this is called an offset phenomenon).
In order to solve the above problem, it is being conducted generally to use a widened molecular weight distribution, whereby the high fluidity of resin when melted and the high viscosity of resin at high temperatures are satisfied simultaneously and low-temperature fixing properties and high-temperature offset resistance are achieved simultaneously.
When the proportion of low-molecular resin is increased or the molecular weight of low-molecular polymer is reduced, high fluidity is secured and improved low-temperature fixing properties is obtained; however, there have been problems of deterioration in offset resistance, reduction in resin strength owing to molecular weight reduction, deterioration of toner in long-period operation, and deterioration of image quality.
Meanwhile, when the proportion of low-molecular weight resin is decreased, or when molecular weight of resin is increased, improved offset resistance is obtained; however, fluidity is impaired and accordingly low-temperature fixing properties is deteriorated.
Thus, according to conventional techniques, it has been impossible to achieve excellent low-temperature fixing properties and excellent offset resistance (these two properties are antinomic) simultaneously.
In general, the polyester resin used as a binder resin of toner needs to have a wide molecular weight distribution in order to achieve satisfactory fixing properties and satisfactory offset resistance; therefore, tri-functional monomers are used.
When, in subjecting a polyhydric alcohol and a polycarboxylic acid to dehydration and polycondensation to produce a polyester, trifunctional monomers are fed into a polymerization reactor to allow a dehydration and polycondensation reaction and a crosslinking reaction to proceed simultaneously, excessive proceeding of crosslinking reaction generally incurs the winding of resin round the agitating rod used, owing to the Weissenberg effect and makes the agitation impossible. Therefore, it has been necessary to complete a polycondensation reaction before such trouble occurs and allow a crosslinking reaction to proceed in a separate reactor such as twin screw extruder or the like.
The present inventors already disclosed, in JP-B-7-101319, a technique of increasing the molecular weight of a polyester resin and widening its molecular weight distribution by means of a particular urethane crosslinkage. In this technique, a polyester resin to be crosslinked and a linear low-molecular polyester resin are produced separately, the two resins are combined, the resulting mixture and a polyisocyanate are kneaded using a twin-screw extruder or the like to give rise to a crosslinking reaction. This technique is very meaningful in that it could respond to the needs of the time. Since then, copiers and printers have come to employ a higher speed, and digital and color technologies have made significant progresses; therefore, even with the above technique, increasing the proportion of low-molecular resin for higher fluidity in order to achieve satisfactory low-temperature fixing properties has resulted in inferior offset resistance in some cases, and increasing the proportion of high-molecular resin for higher viscosity in order to achieve satisfactory offset resistance has resulted in inferior fixing properties in some cases.
Also in JP-B-08-5947 is disclosed a technique regarding a toner containing a modified polyester resin. That is, a polyester, a particular hydroxycarboxylic acid, a particular diol, a particular dicarboxylic acid and a particular crosslinking agent are reacted in given proportions to produce the above-mentioned resin superior in physical and chemical properties, useful as a construction material, etc. More specifically, (A) a polyester or a polyester mixture (1 to 99% by weight) is reacted with (B) a C2 to C21 hydroxycarboxylic acid or its derivative (0 to 60%), a mixture of (C) a C2 to C25 diol (40 to 60 mole %) and (D) a C3 to C22 carboxylic acid (40 to 60 mole %) or its derivative (1 to 99%), and (E) a crosslinking agent (e.g. trimellitic acid anhydride) (0 to 10%), at 130 to 350° C. in the presence of an ester transfer catalyst to produce an intended resin. Here, the components (A) to (E) are preferably 100% in total, and the components (C) and (D) are preferably 100 mole % in total.
However, only with the technique disclosed in JP-B-08-5947, it was unable to achieve the following properties simultaneously:
(1) superior blocking resistance,
(2) superior offset resistance,
(3) superior grindability,
(4) superior mechanical durability,
(5) superior wax dispersibility, and
(6) superior balance between post-development fixing properties and development durability.
In recent years, for image formation in electrophotography, a digital method capable of taking out information from computers or facsimile equipment has drawn attention. In the light application using this digital method, a laser is used as a means for light application; therefore, a fine line image can be outputted as compared with the conventional analog method and, in order to obtain a finer image, a toner small in particle diameter (average particle diameter) is required.
When a toner has a small particle diameter and when the resin used therein has a small strength, i.e. a small mechanical strength, however, there have been problems that an undesirable fine powder is formed in a large amount in the production process of the toner, resulting in a significant decrease in production yield and an increase in cost.
Also when a toner has a small diameter, a fine powder is formed easily in a copier during its stirring with a carrier, the carrier is stained thereby, and, in some cases, the amount of triboelectric charge becomes unstable and fogging appears; these matters h
Emura Yuji
Kawasaki Shoji
Matsuoka Hiroshi
Shin Masaaki
Burns Doane , Swecker, Mathis LLP
Goodrow John
Mitsui Chemicals Inc.
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