Stock material or miscellaneous articles – Composite – Of silicon containing
Reexamination Certificate
2000-09-05
2002-12-31
Pianalto, Bernard (Department: 1762)
Stock material or miscellaneous articles
Composite
Of silicon containing
C427S058000, C427S385500, C427S387000, C427S407100, C427S489000, C427S496000, C427S503000, C427S508000, C427S515000, C427S532000, C427S535000, C427S551000, C427S553000, C427S554000, C427S557000, C427S558000, C427S559000, C427S595000, C427S596000
Reexamination Certificate
active
06500552
ABSTRACT:
CLAIM OF PRIORITY
This application claims foreign priority from German application no. 199 42 423.3 filed Sep. 6, 1999 having the same title as indicated above.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a coating, in particular for toner transfer drums, that is producible by hydrolytic condensation of a mixture comprising at least one hydrolyzable silicon compound of the general formula
SiX
n
R
(4−n)
(I).
2. The Prior Art
EP 0 450 625 B1 describes a coating of the aforementioned art and a method for coating a plastic substrate with such a coating. It is proposed there to produce a particularly scratch-resistant coating, proceeding from silane hydrolysate lacquers based on vinyl mercapto addition, that is rapidly curable under UV radiation. Such a coating for use as a layer on a toner transfer drum, however, is suitable only if said layer, in addition to abrasion resistance (scratch resistance), also has the requisite electrical conductivity. This is not provided in the known coating from the cited document.
Toner transfer drums for laser printers, copiers, and fax machines are especially favorably produced in various dimensions and unit quantities by using organic photoconductors, whereby, by the incorporation of photosensitive pigments in specially purified polymers in the form of a so-called generator layer on an aluminum support and a transport layer thereon that is composed of a polymer doped with said photoconductor, the electrophotographic function is achieved. Generator layers as well as transport layers (also known as OPC layers) are relatively soft and have only slight scratch resistance, whereby said OPC layer is even considerably softer than unmodified polycarbonate, for example. Although a number of different technical solutions have claimed to create improved abrasion resistance of such systems, no long-term abrasion-resistant coatings have been achieved at present in a marketable product. Of the currently existing proposals for improving the hardness and abrasion resistance of such systems for this technical use, only the most significant of these will be discussed here.
It is hereby apparent that a combination of high abrasion resistance with the required conductivity has heretofore been associated with a reduction of one of said properties. For example, Patent DE 30 32 773 (Hoechst) describes an image carrier having a hard, crosslinked surface layer, which however exhibits too high a surface resistance. An image carrier having a surface layer based on metal alkoxide and alkyl/aryltrialkoxysilane, described in Patent DE 40 10 328 (Fuji Xerox), has the same properties, whereby it becomes clear that, based on their extraordinarly dense network structure, silane hydrolysate lacquers or those hybrid polymers formed partially from inorganic consitituents are particularly significant for the coating of image carriers or toner transfer drums.
Both U.S. Pat. No. 4,923,775 and U.S. Pat. No. 5,116,703 (both Xerox) describe image carriers having surface layers based on crosslinked polysiloxanes which, by the incorporation of photoconductors, claim to achieve the electrophotographic properties, whereby in U.S. Pat. No. 5,116,703, the layer is also organically crosslinked. Here, on the basis of the high photoconductor content, the surface resistance is markedly lower than for an unmodified silane hydrolysate lacquer. U.S. Pat. No. 4,595,602 (Xerox) also describes surface layers based on crosslinked polysiloxane that claim to impart abrasion-inhibiting properties by means of thermal crosslinking of linear siloxanes with silicic acid.
A further improvable property of the known coating materials is the curing regime of same. Curing is generally carried out by thermal means. For toner transfer drums, said thermal curing is possible only below 100° C. due to the high expansion coefficients of the generator layer.
The object of the present invention is to provide, after curing at low temperatures, an electrically conductive lacquer, in particular for the coating of toner transfer drums, whereby the resulting coating has high scratch resistance and good adhesion to the substrate.
The solution of this object provides an electrically conductive coating, in particular for toner transfer drums, having the features of claim 1. The features cited in Subclaims 2 through 10 concern preferred developments of the solution according to the invention. Preferred variants of the coating according to the invention are described in said subclaims.
The invention further relates to a method for producing an electrically conductive coating, preferably on a toner transfer drum, having the features of claim 11. Subclaims 12 through 17 concern preferred variants of the coating production method described in claim 11.
The invention further relates to a method for producing an electrically conductive coating on a toner transfer drum, having the features of claim 18.
A further requirement of the coating according to the invention is that said coating should be satisfactorily curable in the shortest possible time at relatively low temperatures. In addition, the conductive coating material should have sufficient storage stability. Furthermore, considerable insensitivity to tropical climates (high humidity) should be present, in particular to assure unlimited use of the toner transfer drums provided with a coating according to the invention, and of devices equipped with said toner transfer drums, such as copiers, printers, and the like.
Within the scope of the invention, the following embodiments concern particularly suited preferred variants of the coating, the properties of said coating, and preferred methods for production of such a coating according to the invention.
SUMMARY OF THE INVENTION
A preferred solution consists in the use of vinyl mercapto addition to produce an abrasion-resistant overlayer by UV curing of a suitable lacquer, and incorporation of an electrolytically active compound, for example a quaternary ammonium salt, to divert charge to the exposed sites. Surprisingly, the interaction of such electrolytically active compounds with said incorporated mercapto groups achieves a particularly high conductivity of the material, whereby only small quantities of said quaternary ammonium compounds are required. A particular advantage of the solution according to the invention lies in the option for catalyst-free production of said vinyl mercapto lacquer by use of quaternary ammonium compounds.
Achievement of a three-layer construction allows the technically advantageous production of an image carrier, whereby high productivity is achieved by UV curing. Creation of a higly crosslinked surface layer results in exceptional resistance of said image carrier in the long-term pressure test, whereby an adjusted surface resistance assures the function of said image carrier.
SUMMARY OF THE INVENTION
The lacquer according to the invention for coating of a plastic substrate is produced by hydrolytic condensation of a plurality of silicon compounds and, optionally, one or several hydrolyzable compounds of zirconium and/or aluminum in a maximum quantity of 30 mol % relative to the total quantity of silicon and zirconium/aluminum compounds, whereby 1 to 40 mol % of all groups bound to the aforementioned elements are non-hydrolyzable groups having an ethylenically unsaturated bond, and in addition said non-hydrolyzable groups bound to said aforementioned elements, having a mercapto group, are present in such quantities that the ratio of ethylenically unsaturated bonds to mercapto groups in or on non-hydrolyzable groups is 25:1 to 1:1; said lacquer is optionally cured by radiation in the absence of a photoinitiator; and/or thermal curing of the overlayer is carried out. A significant feature of the solution according to the invention is the option for separate hydrolysis of the hydrolyzable silicon compounds, so that organic crosslinking, proceeding according to the invention without additional catalyst, cannot initially take place during separate stora
Dreihofer Sabine
Geiss Alexandra
Neumann Gert
Rose Klaus
AEG Elektrofotografie GmbH
Hoffman Wasson & Gitler PC
Pianalto Bernard
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