Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Post imaging process – finishing – or perfecting composition...
Reexamination Certificate
2001-10-09
2003-05-13
Goodrow, John (Department: 1753)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Post imaging process, finishing, or perfecting composition...
C430S109100, C430S124300
Reexamination Certificate
active
06562534
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a toner composition, especially to toner particles useful in eletrostatographic or magnetographic imaging methods wherein the toner particles are fixed to the final image-receiving member by application of heat or heat and pressure.
BACKGROUND OF THE INVENTION
In imaging methods such as electro(photo)graphy, magnetography, ionography, a latent image is formed that is developed by attraction of toner particles. In direct electrostatic printing, the toner particles are image-wise deposited on a substrate.
Toner particles are basically polymeric particles comprising a polymeric resin as main component and various ingredients mixed with the toner resin. Apart from colourless toners, which are used e.g. for finishing functions, the toner particles comprise at least one black and/or coloured substance, i.e. pigment.
In the different imaging methods, described above, the toner particles can be present in a liquid or in a dry developer composition. An advantage of using a dry developer composition instead of a liquid one resides in the absence of the need to eliminate the liquid phase after development. The avoidance of the need to evacuate (mainly organic) liquids may be desirable both from an economical standpoint and from an ecological standpoint.
After development of the latent image the developed image is transferred to a substrate directly or via one or more intermediate image-carrying members. In direct electrostatic printing the toner image may be deposited directly on the substrate or alternately on an intermediate image-carrying member and subsequently transferred to the substrate directly or via one or more intermediate image-carrying members.
The visible image, on this substrate, of electrostatically or magnetically attracted toner particles is not permanent and has to be fixed by causing the toner particles to adhere to each other and the substrate by softening or fusing them followed by cooling. Normally fixing proceeds on more or less porous paper by causing or forcing the softened or fused toner mass to penetrate into the surface irregularities of the paper.
There are different types of fixing processes used for fixing a toner powder image to a substrate. Some are based upon fixing primarily on fusing by heat, others are based on softening by solvent vapours, or by the application of cold flow using high pressure at ambient temperature.
In the fixing processes based on heat, two major types should be considered, the “noncontact” fixing process and the “contact” fixing process. In the non-contact fixing process, there is no direct contact of the toner image with a solid heating body. In a “contact” fixing process the substrate carrying the non-fixed toner image is conveyed through the contact zone formed by establishing pressure contact between a heated fixing member and a backing member while the substrate carrying the toner images passes in-between. Both the heated fixing member as well as the backing member may be in the form of a belt or a roller. The backing member may be heated too to avoid strong loss of heat within a copying cycle or to enable duplex fusing. This process has been employed widely in low-speed as well as high-speed fusing systems, since a remarkably high thermal efficiency is obtained because the surface of the heated fusing member is pressed against the surface of the substrate carrying the toner images to be fixed.
Another “contact” fixing process is the transfuse process where the toner image is not formed or transferred directly to the substrate and fixed there, but is first transferred, optionally via one ore more intermediate image-carrying members to a transfusing member, from where it is further, in one step, transferred and fixed to the substrate. As the transfuse process is usually executed at temperatures of 140 degrees Centigrade or below, low temperature feasibility of the toner is also a requirement.
Both contact fixing processes have to be monitored carefully in that when the fusing or transfuse member provide too much thermal energy to the toner and substrate, the toner will melt to a point where its melt cohesion and melt viscosity is so low that “splitting” will occur, and some of the toner is transferred to the fusing member. The toner present on the fusing member may be transferred back in a subsequent cycle of the fusing member to the substrate where it may disturb other images. Such a phenomenon is called “hot-offset”. In order to avoid this phenomenon the toner particles have to be designed for a contact fusing process.
Both non-contact and contact fusing toners may be exposed to severe mechanical stress, e.g. during mixing, transport through the devices, by doctor blades, etc. Moreover as the transfer efficiency is usually not 100% but somewhat below, any residual toner image present on an image-delivering member, being an image-forming member such as e.g. a photoconductor, or an intermediate image-carrying member, has to be removed because otherwise the image quality of any subsequently formed or transferred images may be seriously disturbed. This residual image has to be removed within each cycle of the image-delivering member, being before re-entering into the development zone in case of an image forming member or before re-entering into the transfer zone in case of an intermediate image transfer member. Otherwise, this could lead to serious image defects because of mixing up of the new developed or transferred image with the residual image. This cleaning action is executed by a cleaning station positioned downstream the transfer zone. A cleaning station usually comprises a revolving brush and/or a scraper blade and/or other cleaning means, which can be engaged against the image-delivering member for removing residual toner therefrom. It is known that any cleaning means relying at least partly on mechanical forces to perform the cleaning, may result in filming on the image-delivering member due to smeared out toner particles. In case of an image-delivering member such as e.g. a photosensitive belt or drum, this filming may influence the level of chargeability amongst others resulting in a decreased image density of the final printed image. In case the image delivering member is an intermediate image transfer member this filming may negatively influence the surface properties of the image transfer member which directly affect the transfer properties leading to transfer efficiency degradation and deterioration of the overall image quality. Filming may be one of the failure mechanisms limiting lifetime of such an image-delivering member. Another failure mechanism may be the formation of defects such as micro-cracks and/or scratches on the surface of the image-delivering member during handling, introduction in the printing system, or after extended use. Compressed toner particles and other extraneous matter may accumulate on these defects. Both filming as well as accumulated toner/extraneous matter is further referred to in this disclosure as fused-on-toner (FOT). Therefore, regardless of the type of fixing process, the toner particles have to be strong enough to withstand the mechanical stresses and avoid FOT.
Some further specifications a toner has to meet are a good adhesion to the substrate and a high gloss capability. To improve the feasibility of a toner, and more particularly the binder resin(s), it is beneficial to lower the viscosity of the resin(s) at softening/melting temperature in order to provide a larger contact area between the softened/melted toner and the substrate to thereby improve adhesion. A possible approach to accomplish this could be by lowering the glass transition temperature (Tg) and the molecular weight of the binder resin(s) of the toner. However, if the Tg and molecular weight of the binder resin are simply lowered, the above mentioned hot-offset is liable to occur. Moreover, the obtained binder resins are not strong enough to avoid or limit FOT and to withstand the mechanical stresses.
Several propositions have been made in the art. Thus
De Meutter Stefaan
Deprez Lode
Gijsbrechts Dirk
Goodrow John
Xeikon N.V.
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