Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Post imaging process – finishing – or perfecting composition...
Reexamination Certificate
2001-03-27
2004-02-24
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...
C430S108600, C430S108700
Reexamination Certificate
active
06696212
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to improved magnetic single component toner compositions for use in generating documents suitable for magnetic image character recognition. In particular, the present invention relates to improved magnetic single component toner compositions preferably containing no charge agents nor heavy metals.
The formation and development of images on the surface of photoconductive materials by electrostatic means is well known. The basic electrophotographic process, as taught by C. F. Carlson in U.S. Pat. No. 2,297,691 (incorporated in its entirety by reference herein), involves forming a uniform electrostatic charge on the surface of a photoconductive layer, exposing the layer to an image to dissipate the charge in light exposed areas, and developing the resulting latent electrostatic charge image by depositing dry toner compositions on the image.
Magnetic ink printing methods with inks containing magnetic particles are also known. For example, U.S. Pat. No. 3,998,160 (incorporated herein in its entirety by reference) relates to various magnetic inks used in printing digits, characters, or designs on checks or bank notes. The magnetic ink used for these processes consists of acicular magnetic particles, such as magnetite in a fluid medium, and a magnetic coating of ferric oxide, chromium dioxide, or similar materials dispersed in a vehicle containing binders and plasticizers.
While magnetic ink or toner can be used only in the MICR characters in some applications, many other applications require the ink or toner to produce acceptable image quality over the rest of the document as well. For example, a refund check may be attached through perforations at the bottom or top of a financial statement to which it pertains. It is often desirable to print the entire statement and check at the same time to avoid possible mismatch between statement and check amount. As a result, image quality specifications such as solid area density, linewidth, and background need to be met at the same time that adequate magnetic properties are maintained.
Single component toner compositions generally contain, for example, magnetic particles, such as magnetite, resin binders, and other additives. There are several types of magnetites ranging from soft to hard. Generally, there are three types of iron oxides used: (1) cubic; (2) octahedral; and (3) acicular. U.S. Pat. No. 4,859,550 (incorporated in its entirety by reference herein) indicates that hard and/or soft magnetites may be incorporated into toner at amounts of from 35-70% by weight.
In applications requiring MICR capabilities, toners must generally contain magnetites having specific properties, the most important of which is a high enough level of remanence or retentivity. Retentivity is a measure of the magnetism left when the magnetite is removed from the magnetic field, i.e., the residual magnetism. In applications requiring MICR capability, it is important for the toner to show a high enough retentivity such that when the characters are read, the magnetites produce a signal. This is the signal strength of the toner composition. The magnetic signal level is of substantial importance in MICR systems. The signal level can vary in proportion to the amount of toner deposited on the document being generated. Signal strength of a toner composition can be measured by using known devices, including the MICR-Mate 1, manufactured by Checkmate Electronics, Inc.
Effective MICR toner compositions must have magnetic characteristics which meet banking industry requirements for character signal strength. Each MICR character has its own unique signal strength pattern due both to character shape and the toner content. In a typical signal strength tester, a MICR-Mate 1 reading device is calibrated against a standard printed “on-us” character known to represent 100% signal strength. Test samples are then read on the calibrated reading device to determine what their signal strength is in relation to the standard. Different banking organizations have different standards for what constitutes an acceptable signal strength in order to avoid excessive document rejects by high speed automated reader-sorters. For example, the U.S. (ANSI) standard is 70-200%, whereas the Canadian standard is 100-200%.
Toner compositions used in single component development applications, i.e., those having 40-50% soft magnetites, typically have a low retentivity and a low signal strength. Soft or cubic magnetites give a low retentivity whereas octahedral and acicular magnetites give a higher retentivity. Therefore, past toner compositions have contained high levels of acicular magnetites to provide the desired retentivity. However, the use of toner compositions with all acicular magnetites is expensive, and often exhibit signal strengths that are too high.
Single component toners generally use soft magnetites, wherein &rgr;
R
at saturation is less than 15 emu/g. Such magnetites, when present in the toner from 30-60%, will provide sufficient magnetic moment to satisfy the electrophotographic development requirements. However, the toner retentivity may be insufficient to satisfy MICR signal strength requirements due to the presence of soft magnetites. Although the problem can be overcome by increasing the loading of soft magnetite beyond 60%, the higher loadings of soft magnetite can result in low optical density and negatively impact other toner properties such as increased fines, increased minimum fusing temperature, and free magnetite on the surface of the toner. Conversely, if only hard magnetite is used, wherein &rgr;
R
is greater than 25 emu/g, the electrophotographic development required to obtain satisfactory line and solid area density without background results in a signal strength that is too high and unacceptable for MICR applications.
A further problem for single component development toner compositions containing high loadings of magnetites for MICR applications is that printed characters exhibit an unacceptable degree of abrasion or rub-off after multiple passes through a reader/sorter. Such wear may result in the document being rejected by the reader. The toner abrasion also results in contamination of the read/write heads, which can result in false readings. It has been found that the wearability of MICR characters can be substantially improved by incorporating a wax in the toner. U.S. Pat. No. 4,859,550 (incorporated in its entirety by reference herein) relates to the addition of certain polymeric waxes to minimize image smearing. A further reason for using waxes in a toner composition is as a fusing release agent.
Accordingly, there is a need to provide a single component toner composition which will obtain sufficiently high retentivity for MICR applications without the high levels of magnetite loadings that could negatively impact the toner rheological properties and contribute to higher toner cost. At the same time, the toner formulation should reduce sorter image abrasion (rub-off), reduce character void frequency and total void area image defects, and/or not contain heavy metal charge control agents.
SUMMARY OF THE PRESENT INVENTION
A feature of the present invention is to provide a single component magnetic toner for MICR applications having solved the above mentioned problems.
Another feature of the present invention is to provide a single component magnetic toner capable of high line and solid area density.
A further feature of the present invention is to provide a single component magnetic toner capable of providing clear images free of background and MICR characters free from a lowering in recognition rate.
An additional feature of the present invention is to provide a single component magnetic toner useful in MICR applications, wherein the composition is free from charge agents containing heavy metals.
Still another feature of the present invention is to provide a single component magnetic toner useful in MICR applications which enables MICR characters free from character void image defects.
An addition
Contois Robert E.
Crichton John F.
Marsh Dana G.
Putnam David D.
Heidelberger Druckmaschinen AG
Rodee Christopher
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