Stock material or miscellaneous articles – Structurally defined web or sheet – Discontinuous or differential coating – impregnation or bond
Reexamination Certificate
1998-09-30
2001-07-24
Lam, Cathy (Department: 1775)
Stock material or miscellaneous articles
Structurally defined web or sheet
Discontinuous or differential coating, impregnation or bond
C428S344000, C428S3550RA, C174S251000, C174S258000
Reexamination Certificate
active
06265050
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
The present invention is related to U.S. patent application Ser. Nos. 09/163,893, 09/164,124, 09/163,308, 09/163,765, 09/163,839, 09/163,954, 09/163,924, 09/163,904, now U.S. Pat. No. 6,116,718, Ser. Nos. 09/163,799, 09/163,518, 09/164,104, 09/163,825, now U.S. Pat. No. 6,136,442, U.S. Pat. Nos. 5,717,986, 5,893,015, 5,968,674, and 5,853,906, and U.S. patent application Ser. No. 09/128,160, each of the above being incorporated herein by reference.
BACKGROUND
The present invention relates to the field of overcoat materials, and more specifically relates to overcoat materials functioning as relaxation coatings applied of electrode grids.
There are known or proposed systems for electrostatically agitating or moving fine particulate materials, such as marking material (e.g., toner) and the like. One such system is described in U.S. patent application Ser. No. 09/163,839, in which a grid of small and closely spaced electrodes are connected to a driver circuit such that a phased d.c. travelling electrostatic wave is established along the grid. Charged particulate material is transported by the electrostatic wave in a desired direction, at a desired velocity. Other such systems cause marking material particles to be agitated from a surface so as to be proximate a receiving surface such as a photoreceptor.
It is known to encapsulate electronic devices, such as integrated circuits, in protective coatings. Such coatings may provide physical protection from scratches, and a moisture barrier between the devices and the ambient environment. However, such materials are generally not used as top-surface dielectrics. Furthermore, such insulation and passivation layers typically have very high resistivities to avoid possible electrical shorts between covered leads.
We have discovered that there are a variety of criteria which overcoats for virtually all electrode grids of the type described above should address. First, it is desirable to provide a planarized surface over which the particulate material may reside or travel. Such a surface eliminates the problem of particulate material becoming trapped between the electrodes. Second, it is desirable to provide a material over the electrodes to provide rapid charge dissipation at a selected time constant. Third, arcing between electrodes must be prevented. Fourth, it is desirable that the overcoat provide a degree of wear resistance, especially in the case of marking material transport. Finally, it is important that such a layer be chemically stable. That is, the layer material must not react with the particulate material nor change characteristics in the presence of the operating environment. However, no known material to date has been able optimize each of these desired attributes.
SUMMARY
The present invention is a novel coating, for application over e.g. an electrode grid. The coating is an organic polymer layer, deposited over the metal electrodes of an electrode grid, protecting the metal electrodes from being affected by chemical, mechanical, and electrical environments. Arcing between electrodes is eliminated by the coating, which does not break down in the high voltage regime typically employed by particulate material moving grids (e.g., in the range of 400 volts or more). Forming the coating sufficiently thick to allow establishing a planar surface eliminates the accumulation of particulate material interstitially between electrodes.
The coating is a top-surface (that is, not sandwiched between layers) semiconducting dielectric, having a selected time constant to permit electric field charge and dissipation at a selected rate to permit particulate material agitation or movement over an underlying electrode grid.
In general, the coating is comprised of a polymeric binder (e.g., a polycarbonate such as MAKROLON 3108, a bisphenol A polycarbonate available from Bayer Polymers Division), a charge transport molecule (e.g., N,N′-bis(3-methylphenyl)-N,N′-diphenyl-(1,1′-biphenyl)-4,4″-diamine, also known as m-TBD), and solvents (e.g., methylene chloride, 1,1,2-trichloroethane) to dissolve the aforesaid chemicals. Alternatively, a chemical dopant (e.g., oxidant) may also be included to assist in the production of the conductive species in-situ.
According to one embodiment, the coating is a combination of Makrolon 3108, m-TBD, and the solvents methylene chloride and 1,1,2-trchloroethane. According to another embodiment, the coating is a combination of Makrolon 3108, m-TBD, the solvents methylene chloride and 1,1,2-trichloroethane, and (di-tert-butylphenyl)iodonium hexafluoroarsenate. Still another embodiment, the coating is a combination of MAKROLON 3108 a bisphenol A polycarbonate m-TBD, the solvents methylene chloride and 1,1,2-trichloroethane, and a cation salt of TM-TBD together with trifluoroacetate. One method of application is use of a low pressure, high volume spray gun to spray coat to a desired thickness, for example about 37 &mgr;m ±2 &mgr;m. The thickness is a function of the electrode thickness, and should be sufficient to provide a planar surface.
However, since one application of the present invention may be a coating overlying a flexible substrate, an excessively thick (e.g., 50 &mgr;m) coating may crack when the electrode substrate is bent to conform to a particular shape. Thus, the thinner the electrode, the thinner the required coating, and the easier the polishing procedure. And, the thinner the electrode, the easier it is to achieve planarization.
Following drying, the spray coated electrode grid is polished to produce a smooth, planar surface. One of many known polishing techniques is employed, such as polishing with successively finer abrasives.
The time constant of the coating, as determined by the product of the dielectric constant and the resistivity of the material, is preferably between 1-200 microseconds (ms). Within this range of time constant, particulate material may be either agitated to a desired height or moved from electrode to electrode, across a grid of electrodes at a speed about 1 to 2 meters per second (m/s). However, in the case of a particle moving grid, the larger the time constant, the slower the speed of movement of the particulate material across the electrode grid. The bulk resistivity of the coating is preferably between 1×10
9
and 1×10
12
ohm·centimeters (&OHgr;·cm). The dielectric constant of the coating should be in the range of 4 to 12.
Thus, the present invention and its various embodiments provide numerous advantages discussed above, as well as additional advantages which will be described in further detail below.
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Hsieh Bing R.
Vo Tuan Anh
Wong Kaiser H.
Lam Cathy
Robb Linda M.
Small Jonathan A.
Xerox Corporation
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