Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Post imaging process – finishing – or perfecting composition...
Reexamination Certificate
1996-04-05
2003-02-04
Rodee, Christopher (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Post imaging process, finishing, or perfecting composition...
C430S109300, C430S111400
Reexamination Certificate
active
06514653
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a toner composition suited for development of electrostatic charge images or magnetic patterns.
BACKGROUND OF THE INVENTION
It is well known in the art of electrographic printing and electrophotographic copying to form an electrostatic latent image corresponding to either the original to be copied, or corresponding to digitized data describing an electronically available image.
In electrophotography an electrostatic latent image is formed by the steps of uniformly charging a photoconductive member and imagewise discharging it by an imagewise modulated photo-exposure.
In electrography an electrostatic latent image is formed by imagewise depositing electrically charged particles, e.g. from electron beam or ionized gas (plasma) onto a dielectric substrate.
The obtained latent images are developed, i.e. converted into visible images by selectively depositing thereon light absorbing particles, called toner particles, which usually are triboelectrically charged.
In magnetography a latent magnetic image is formed in a magnetizable substrate by a patternwise modulated magnetic field. The magnetizable substrate must accept and hold the magnetic field pattern required for toner development which proceeds with magnetically attractable toner particles.
In toner development of latent electrostatic images two techniques have been applied: “dry” powder and “liquid” dispersion development of which dry powder development is nowadays most frequently used.
In dry development the application of dry toner powder to the substrate carrying the latent electrostatic image may be carried out by different methods known as, “cascade”, “magnetic brush”, “powder cloud”, “impression” or “transfer” development also known as “touchdown” development described e.g. by Thomas L. Thourson in IEEE Transactions on Electronic Devices, Vol. ED-19, No. 4, April 1972, pp.495-511.
In DEP (Direct Electrostatic Printing) toner particles or are deposited directly in an imagewise way on a receiving member substrate, the latter not bearing any imagewise latent electrostatic image. Preferentially the receiving member substrate is the final receiving member substrate, e.g. plain paper, transparency, etc. so that after this deposition step only a final fusing step is needed to finish the printout.
The visible image of electrostatically or magnetically attracted toner particles is not permanent and has to be fixed by causing the toner particles to adhere to the final 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.
Dry-development toners essentially comprise a thermoplastic binder consisting of a thermoplastic resin or mixture of resins (ref. e.g. U.S. Pat. No. 4,271,249) including colouring matter, e.g. carbon black or finely dispersed dye pigments. The triboelectrically chargeability is defined by said substances and may be modified with a charge controlling agent.
In the low density parts of toner-developed prints the toner particles are deposited at low coverage and do not form a closed or solid deposit of black or coloured material. On the contrary, in the high density portions toner particles are piled on each other and co-fused to form a closed toner-crust which optically has a quite different look as the separately fixed toner particles in the low density portions. Separately deposited and fixed toner particles or small clusters thereof give rise to a light-straying effect. In particular by inspecting the copy with light directed thereto at small grazing angle the small density parts show a mat (dull) appearance. On the contrary, in the high density parts containing smooth coherently co-fused toner particles light is reflected by the glossy surface of the toner crust; whereby light-reflection stands in relation to the kind of binder which normally is a relatively hard thermoplastic transparent resin or mixture of resins.
There are different types of processes used for fusing a toner powder image to its final substrate. Some are based upon fixation primarily on fusing by heat, others are based on softening by solvent vapours, or by the application of cold flow at high pressure in ambient conditions of temperature. In the fusing processes based on heat, two major types should be considered, the “non-contact” fusing process and the “contact” fusing process. In the non-contact fusing process there is no direct contact of the toner image with a solid heating body. Such process includes: (1) an oven heating process in which heat is applied to the toner image by hot air over a wide portion of the support sheet, (2) a radiant heating process in which heat is supplied by infrared and/or visible light absorbed in the toner, the light source being e.g. an infrared lamp or flash lamp. In said “radiant” non-contact fusing embodiment radiation such as infrared radiation may be at least partly absorbed in the final support and therefrom by conduction transferred to the thereon deposited toner image(s).
According to a particular embodiment of “non-contact” fusing the heat reaches the non-fixed toner image through its substrate by contacting the support at its side remote from the toner image with a hot body, e.g. hot metallic roller.
Non-contact fusing has the advantage that the non-fixed toner image does not undergo any mechanical distortion and fine image details will not suffer from transfer to a contacting fixing member, by so-called “offset” phenomena typical for hot pressure roller fusing.
In an embodiment of common “contact” fusing the support carrying the non-fixed toner image is conveyed through the nip formed by a heating roller also called fuser roller and another roller backing the support and functioning as pressure exerting roller, called pressure roller. This roller may be heated to some extent so as to avoid strong loss of heat within the copying cycle.
In producing halftone, i.e. screened images, toner-contacting pressure fuser rollers can distort the dot structure of the screened images. Such will be particularly the case when the pressure-fuser roller has no perfect smooth structure and textures the obtained image.
Whatever the kind of fixing system the above described phenomenon of unequal gloss between low density parts and high density parts will arise, especially when the final print is on a glossy support.
It is desirable to have of a toner available which on fixing will give an equal not very glossy aspect whatsoever the optical density of the image parts will be. Fixed toner images having a satin-look are preferred for they give a better legibility in text parts and provide a nice image aspect.
OBJECTS AND SUMMARY OF THE INVENTION
It is an object of the present invention to provide dry toner particles wherein the composition of the toner particles is such that the fixed toner image, independent of its optical density, has the same or almost the same reflection properties.
It is more particularly an object of the present invention to provide dry toner particles that, after fixing to a final substrate, form a fixed toner image with a satin-look, without use of special covering layers for controlling reflection properties.
It is more particularly an object of the present invention to provide such dry toner particles suited for being fixed to a substrate by non-contact fusing by moderate heating.
Other objects and advantages of the present invention will appear from the further description.
In accordance with the present invention dry toner particles are provided said toner particles comprising a toner resin, wherein:
(i) said toner resin includes a mixture of two polymers (A and B), said polymers A and B being chosen such that an extruded slab with thickness 250 &mgr;m of a 50:50 mixture of both has a transmission density (D
M
) being between 0.10 and 1.00 higher than the sum of half the transmission density of a 250 &mgr;m extruded slab of polymer A alone (D
A
) and half the transmi
Ghekiere Jean-Pierre
Op De Beeck Werner
Tavernier Serge
Vervoort Michel
Knobbe Martens Olson & Bear LLP
Rodee Christopher
Xeikon NV
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