Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Process of making developer composition
Reexamination Certificate
2001-07-02
2003-04-08
Dote, Janis L. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Process of making developer composition
C430S108100, C430S108220, C430S108240, C430S108300, C430S109300, C430S137180
Reexamination Certificate
active
06544710
ABSTRACT:
TECHNICAL FIELD
The present invention relates to toners and developers for electrophotography to be used in developing electrical or magnetic latent images in electrophotography, electrostatic printing, and the like.
BACKGROUND OF THE INVENTION
Toner for developing electrical or magnetic latent images and the like are used in various processes for forming and recording images. One of such image forming processes is electrophotography, which uses a photosensitive member generally formed of a photoconductive material, and wherein an electrical latent image is formed on the photosensitive member by various means. The electrical latent image is developed using a toner. The toner image thus developed transferred to a recording material, such as paper, and then fixed there to by heating and/or pressure, or by using solvent vapor or the like, thus obtaining a copy of the image. Where a process for transferring toner images to a recording material is included, there is usually also provided a process for removing the toner remaining on the photosensitive member.
The following are examples of developers conventionally used in dry development devices for electrophotography:
1) One-component-type magnetic developers comprising a toner containing magnetic powder.
2) One-component-type non-magnetic developers comprising a toner containing no magnetic powder.
3) Two-component-type non-magnetic developers comprising a toner containing no magnetic powder and a magnetic carrier, which is mixed with the toner in a fixed proportion.
4) Two-component-type magnetic developers comprising a toner containing magnetic powder and a magnetic carrier, which is mixed with the toner in a fixed proportion.
Various development methods using such toners have been proposed and put into practical use. The toners used in these development methods are generally manufactured by a pulverizing method in which a coloring agent like a dye or pigment is mixed with, and uniformly dispersed in, a thermoplastic resin serving as the binder. The mixed substance thus obtained is then finely pulverized and classified to provide a desired particle size distribution. Toners typically contain a principal resin or toner resin, colorant and various functional additives such as release agents and charge control additives.
Heterogeneity of the toner particles' composition is believed to be the root cause of numerous problems throughout the serviceable life of toner in a printing device. The print quality black-on-white (BOW) defect involving unwanted toner black spots on the printed product has been a recurring and sometimes serious problem in certain commercial printers over the past few years. The black spots are highly visible in the background region of the print and are non-repeating in nature. They can and do occur anywhere in the background region of the print and usually appear later in the cartridge life. The onset of this print quality defect depends upon many factors including the print job length. As the print job length decreases (e.g., from 4 to single page jobs), the severity of the black spots increases, and the number of prints before the onset of the defect decreases (e.g., from 16,000 to 10,000 prints). Furthermore, it appears that the extent of these spots and the location of their onset with respect to the number of pages printed is also a function of the percent coverage of toner on the page. Another factor which has proven to affect the level of this defect is the number of developer roll revolutions since the beginning of the cartridge life. The higher the number of such revolutions, the quicker the onset of the spots and the greater their extent.
Even though the precise mechanism for the formation of such black-on-white defects is unknown, it has been observed that a number of factors associated with the toner affect the extent of these defects and the time it takes for their onset. Various extra-particulate additives (EPAS) have been found to reduce the number of spots and delay their onset to higher print counts. However, increasing the level of such additives does not totally eliminate the spots, but does contaminate the charge roll and other machine parts, thereby shortening their useful life. A concern with EPAs in general is the increased abrasivity of the resulting toner and the resulting increase in wear on the contacting device components. Nevertheless, to date no EPAs have been found to totally and consistently eliminate these BOW defects without causing premature cartridge failure.
While Applicants do not wish to be bound by any theory of the mechanism of BOW defect formation, it is presently believed that the toner particle compositional uniformity is a major factor in the existence of such defects. Heterogeneity of the toner particles' composition is believed to be the root cause of observed selectivity throughout the life of the cartridge. An experiment was conducted to prove that the compositional make-up of the toner left in the developer station after the onset of BOW defects is the primary factor affecting this phenomenon. After the onset of black spots was observed in a printer with a particular electrophotographic cartridge, “fresh” toner was added to the developer station and the spots disappeared for a few thousand pages. However, they did return. Moreover, when “used” end-of-life toner is added to a new cartridge, the defects begin almost immediately. Despite these observations, it has yet to be analytically determined what differences in the toner from beginning of cartridge life to the onset of BOW defects are contributing to the formation of these print quality defects.
The present invention successfully eliminates the lack of heterogeneity in toners with the addition of two functional additives reactive with each other to form a stable reaction product. The copolymer reaction product apparently acts as a compatibilizer to improve the dispersion of various polymeric components (such as a release agent) with the backbone structure of the toner resin.
Most toner compositions employ release agents such as waxes and/or silicone polymers. Poly(dimethysiloxane) resins or oils (PDMS) are well known to exhibit excellent external release agent characteristics (i.e. when applied to fuser rolls) due to their extremely low surface energy. The property is highly desirable in contact-fusing electrophotography because it is important to be able to release the toner from the hot-oiled fuser roll and thus prevent hot offset from occurring. Several different low molecular weight organic materials have been used in the toner industry to try to eliminate this hot offset phenomenon. Low molecular weight polyolefin waxes are by far the most common type of internal release agent. Each type of release agent has its own advantages and disadvantages. For example, polyolefins tend to crystallize to a significant extent (between 70 and 90 volume percent crystallinity). When these molecules crystallize, they phase segregate from the toner resin and form large wax domains which cause numerous print quality defects, as well as a wax imbalance between the toner fines and the average sized toner particles. Poor homogeneity of these additives in the toner particles tends to cause a number of problems, the most important of which are low toner powder flow and variations in triboelectric charge distribution, which can lead to print quality defects.
Methods have been reported for compatibilization of immiscible blends of polymers by reactive mixing, in which functionalized versions of the polymeric components react in situ to form a block copolymer compatibilizer. The fundamental requirements for such reactive processing include the following: There must be sufficient mixing to achieve the desired fineness of morphological texture. Some of the polymer molecules must contain chemical functional groups which can react to form primary bonds during the mixing/mastication process. The functional groups must be of sufficient reactivity for reactions to occur across melt-phase boundaries. The reactions must occur r
Baird Brian William
Livengood Bryan Patrick
Marshall George Pharris
Brady John A.
Dote Janis L.
Lexmark International Inc.
LandOfFree
Reactive compatibilization of polymeric components such as... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Reactive compatibilization of polymeric components such as..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Reactive compatibilization of polymeric components such as... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3097316