Patent Application
20230058033
The present disclosure relates generally to electrophotographic image forming devices, and more particularly to a formulation for an overcoat layer used in an organic photoconductor drum The overcoat layer is prepared from a curable composition including nano metal oxide particles, a urethane resin having at least six radical polymerizable functional groups and a crosslinkable siloxane, in particular a polyether modified acryl functional polymethylsiloxane in combination with a structured acrylic copolymer with pigment affinic groups. No component of the overcoat layer contains any charge transport structure. The addition of the crosslinkable siloxanes greatly improves the stability of the overcoat formulation containing nano metal oxide particles. Importantly, the organic photoconductor overcoated with this formulation has excellent photo-induced-discharge characteristics and reduced residual image.
Organic photoconductor drums have generally replaced inorganic photoconductor drums in electrophotographic image forming device including copiers, and laser printers due to their superior performance and numerous advantages compared to inorganic photoconductors. These advantages include improved optical properties such as having a wide range of light absorbing wavelengths, improved electrical properties such as having high sensitivity and stable chargeability, availability of materials, good manufacturability, low cost, and low toxicity.
While the above enumerated performance and advantages exhibited by an organic photoconductor drum are significant, inorganic photoconductor drums traditionally exhibit much higher durability—thereby resulting in a photoconductor having a desirable longer life. Inorganic photoconductor drums (e.g., amorphous silicon photoconductor drums) are ceramic-based, thus are extremely hard and abrasion resistant. Conversely, the surface of an organic photoconductor drum is typically comprised of a low molecular weight charge transport material and an inert polymeric binder and are susceptible to scratches and abrasions. Therefore, the drawback of using organic photoconductor drums typically arises from mechanical abrasion of the surface layer of the photoconductor drum due to repeated use. Abrasion of photoconductor drum surface may arise from its interaction with print media (e.g. paper), paper dust, or other components of the electrophotographic image forming device such as the cleaner blade or charge roll.
The abrasion of photoconductor drum surface degrades its electrical properties, such as sensitivity and charging properties. Electrical degradation results in poor image quality, such as lower optical density, and background fouling. When a photoconductor drum is locally abraded, images often have black toner bands due to the inability to hold charge in the thinner regions. This black banding on the print media often marks the end of the life of the photoconductor drum, thereby causing the owner of the printer with no choice but to purchase another expensive photoconductor drum, or a new image unit, or in some cases, the whole cartridge altogether.
Increasing the life of the photoconductor drum will allow the photoconductor drum to become a permanent part of the electrophotographic image forming device. The photoconductor drum will no longer be a replaceable unit nor be viewed as a consumable item that has to be purchased multiple times by the owner of the electrophotographic printer. Photoconductor drums having a long life allow the printer to operate with a lower cost-per-page, more stable image quality, and less waste leading to a greater customer satisfaction with his or her printing experience.
To achieve a long-life photoconductor drum, especially with organic photoconductor drum, a protective overcoat layer may be coated onto the surface of the photoconductor drum. The protective overcoat may be polymeric and/or crosslinkable. However, many overcoat layers do not have the robustness for edge wear of photoconductor drums used in direct-to-paper printing applications.
Another drawback of these overcoats is that they significantly alter the electrophotographic properties of the photoconductor drum in a negative way. If the overcoat layer is too electrically insulating, the photoconductor drum will not discharge and will result in a poor latent image. On the other hand, if the overcoat layer is too electrically conducting, then the electrostatic latent image will spread resulting in a blurred image. Thus, a protective overcoat layer that extends the life of the photoconductor drum must not negatively alter the electrophotographic properties of the photoconductor drum, thereby allowing sufficient charge migration through the overcoat layer to the photoconductor surface for adequate development of the latent image with toner.
Many protective overcoat formulations include cross-linkable charge transport materials. Photoconductors having a protective layer with no cross-linkable charge transport materials usually show image defects and higher wear rates when compared to photoconductors having an overcoat with these cross-linkable charge transport materials. However, there are some drawbacks to including charge transport materials into a protective overcoat. Multiple synthesis steps and lengthy purification processes are involved in preparing these cross linkable charge transport materials. Therefore, the cost to manufacture charge transport materials is extremely high, ultimately increasing the price of the photoconductor.
The present disclosure provides an overcoat layer for an organic photoconductor drum of an electrophotographic image forming device. The organic photoconductor contains an electroconductive support, a charge generation layer deposited over the support, a charge transport layer deposited over the charge generation layer, and a cross linked overcoat deposited over the charge transport layer. The overcoat layer is prepared from a curable composition including nano metal oxide particles, a urethane resin having at least six radical polymerizable functional groups, a crosslinkable siloxane, in particular a polyether modified acryl functional polymethylsiloxane and an acrylic copolymer with pigment affinic groups. A useful nano metal oxide particle is indium tin oxide (“ITO”). Other nano metal oxide particles may include aluminum oxide, zirconium oxide, zinc oxide, indium oxide, lanthanum oxide, antimony tin oxide or a combination of two or more. The inventive overcoat formulation does not include charge transport materials. Surprisingly, the resulting cured overcoated organic photoconductor shows excellent abrasion resistance and electrical stability without the use of costly cross-linkable charge transport materials. The addition of the structured acrylic copolymer with pigment affinic groups to the overcoat formulation mitigates the agglomeration of the ITO, thereby improving the formulation stability. The addition of the crosslinkable siloxane reduces of the surface energy of the photoconductor. The amount of the nano metal oxide particles in the curable overcoat composition is about 5 percent to about 30 percent by weight. The amount of the urethane resin having at least six radical polymerizable functional groups in the curable overcoat composition is about 20 percent to about 95 percent by weight. The amount of the crosslinkable siloxane in the curable overcoat composition is about 0.05 percent to about 3.0 percent. The amount of the structured acrylic copolymer with pigment affinic groups in the curable overcoat composition is about 0.05 percent to about 6.0 percent. Curing of the overcoat formulation creates a three-dimensional crosslinked structure with a high degree of optical transparency and excellent abrasion resistance. The overcoat is free of cracks or other defects arising from internal stress. A photoconductor drum overcoated with the inventive overcoat formulation has excellent wear resistance while simultaneously having excellent electrical properties.
The accompanying drawings incorporated in and forming a part of the specification, illustrate several aspects of the present disclosure, and together with the description serve to explain the principles of the present disclosure.
It is to be understood that the disclosure is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the drawings. The disclosure is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Further, the terms “a” and “an” herein do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced item.
Developer unit 120 includes a toner sump 122 having toner particles stored therein and a developer roll 124 that supplies toner from toner sump 122 to photoconductor drum 101. Developer roll 124 is electrically charged and electrostatically attracts the toner particles from toner sump 122. A doctor blade 126 disposed along developer roll 124 provides a substantially uniform layer of toner on developer roll 124 for subsequent transfer to photoconductor drum 101. As developer roll 124 and photoconductor drum 101 rotate, toner particles are electrostatically transferred from developer roll 124 to the latent image on photoconductor drum 101 forming a toned image on the surface of photoconductor drum 101. In one embodiment, developer roll 124 and photoconductor drum 101 rotate in the same rotational direction such that their adjacent surfaces move in opposite directions to facilitate the transfer of toner from developer roll 124 to photoconductor drum 101. A toner adder roll (not shown) may also be provided to supply toner from toner sump 122 to developer roll 124. Further, one or more agitators (not shown) may be provided in toner sump 122 to distribute the toner therein and to break up any clumped toner.
The toned image is then transferred from photoconductor drum 101 to print media 150 (e.g., paper) either directly by photoconductor drum 101 or indirectly by an intermediate transfer member. A fusing unit (not shown) fuses the toner to print media 150. A cleaning blade 132 (or cleaning roll) of cleaner unit 130 removes any residual toner adhering to photoconductor drum 101 after the toner is transferred to print media 150. Waste toner from cleaning blade 132 is held in a waste toner sump 134 in cleaning unit 130. The cleaned surface of photoconductor drum 101 is then ready to be charged again and exposed to laser light source 140 to continue the printing cycle.
The components of image forming device 100 are replaceable as desired. For example, in one embodiment, developer unit 120 is housed in a replaceable unit with photoconductor drum 101, cleaner unit 130 and the main toner supply of image forming device 100. In another embodiment, developer unit 120 is provided with photoconductor drum 101 and cleaner unit 130 in a first replaceable unit while the main toner supply of image forming device 100 is housed in a second replaceable unit. In another embodiment, developer unit 120 is provided with the main toner supply of image forming device 100 in a first replaceable unit and photoconductor drum 101 and cleaner unit 130 are provided in a second replaceable unit. Further, any other combination of replaceable units may be used as desired. In some example embodiment, the photoconductor drum 101 may not be replaced and is a permanent component of the image forming device 100.
The support element 210 as illustrated in
The charge generation layer 220 is designed for the photogeneration of charge carriers. The charge generation layer 220 may include a binder and a charge generation compound. The charge generation compound may be understood as any compound that may generate a charge carrier in response to light. In one example embodiment, the charge generation compound may comprise a pigment being dispersed evenly in one or more types of binders.
The charge transport layer 230 is designed to transport the generated charges. The charge transport layer 230 may include a binder and a charge transport compound. The charge transport compound may be understood as any compound that may contribute to surface charge retention in the dark and to charge transport under light exposure. In one example embodiment, the charge transport compounds may include organic materials capable of accepting and transporting charges.
In an example embodiment, the charge generation layer 220 and the charge transport layer 230 are configured to combine in a single layer. In such configuration, the charge generation compound and charge transport compound are mixed in a single layer.
The overcoat layer 240 is designed to protect the photoconductor drum 101 from wear and abrasion without altering the electrophotographic properties, thus extending the service life of the photoconductor drum 101. The overcoat layer 240 has a thickness of about 0.1 μm to about 10 μm. Specifically, the overcoat layer 240 has a thickness of about 1 μm to about 6 μm, and more specifically a thickness of about 1-2 μm. The thickness of the overcoat layer 240 is kept at a range that will not provide adverse effect to the electrophotographic properties of the photoconductor drum 101.
In an example embodiment, the overcoat layer 240 includes a three-dimensional crosslinked structure formed from a curable composition. The overcoat layer is prepared from a curable composition including nano metal oxide particles, a urethane resin having at least six radical polymerizable functional groups, a crosslinkable siloxane, in particular a polyether modified acryl functional polymethylsiloxane and an acrylic copolymer with pigment affinic groups. The curable composition includes about 20 percent to about 95 percent by weight of the urethane resin having at least six crosslinkable functional groups, about 5 percent to about 30 percent by weight of the nano metal oxide particles, about 0.05 percent to about 3.0 percent of the crosslinkable siloxane, and about 0.05 percent to about 6.0 percent of the structured acrylic copolymer with pigment affinic groups. Importantly, the overcoat does not have any component having charge transporting materials. In an example embodiment, the curable composition includes about 20 percent to about 95 percent by weight of the urethane acrylate resin having at least six radical polymerizable functional groups, 5 percent to about 30 percent by weight of the nano metal oxide particles, and 0.1 percent to about 2 percent by weight of the crosslinkable siloxane, and 0.1 percent to about 5 percent by weight of the structured acrylic copolymer with pigment affinic groups.
Usable nano metal oxide particles are sized less than 400 nm. Nano metal oxides can be aluminum oxide, zirconium oxide, zinc oxide, indium oxide, lanthanum oxide, antimony tin oxide or a combination of two or more. A useful nano metal oxide particle is indium tin oxide sized 30 nm to 300 nm. In particular, an indium tin oxide particle is sized less than 200 nm sold by Sigma-Aldrich.
The at least six radical polymerizable functional groups of the urethane resin may be the same or different and may be selected from the group consisting of acrylate, methacrylate, styrenic, allylic, vinylic, glycidyl ether, epoxy, or combinations thereof. A particularly useful urethane resin having at least six radical polymerizable functional groups includes a hexa-functional aromatic urethane acrylate resin, a hexa-functional aliphatic urethane acrylate resin, or combinations thereof.
In an example embodiment, the hexa-functional aromatic urethane acrylate resin has the following structure:
and is commercially available under the trade name CN975 manufactured by Sartomer Corporation, Exton, Pa.
In an example embodiment, the hexa-functional aliphatic urethane acrylate resin has the following structure:
and is commercially available under the trade name EBECRYL® 8301 manufactured by Cytec Industries, Woodland Park, N.J. or Genomer 4690 manufactured by Rahn AG., Switzerland.
The crosslinkable siloxanes can include polyether modified acryl functional polydimethylsiloxane, polypropyleneoxide modified acryl functional polydimethylsiloxane. A useful crosslinkable siloxane in the inventive overcoat includes a crosslinkable polyether modified acryl functional polymethylsiloxane. The crosslinkable polyether modified acryl functional polymethylsiloxane is commercially available under the tradename BYK®-UV3500 and sold by BYK-Chemie. The structured acrylic copolymer with pigment affinic groups is available under the tradename DISPERBYK®-2025 and sold by BYK-Chemie.
The present invention describes a photoconductor overcoat layer comprising the unique combination of a urethane acrylate resin having at least six functional groups, nano metal oxide particles, in particular indium tin oxide and crosslinkable siloxanes including a crosslinkable polyether modified acryl functional polymethylsiloxane in combination with a structured acrylic copolymer pigment affinic groups. The addition of the crosslinkable siloxane reduces the surface energy of the photoconductor. The addition of the structured acrylic copolymer with pigment affinic groups to the overcoat formulation mitigates the agglomeration of the ITO, thereby improving the overcoat formulation stability. Importantly, the organic photoconductor overcoated with this formulation has excellent photo-induced-discharge characteristics and reduced residual negative image. Additionally, the overcoat of the present invention has (1) excellent adhesion to the photoconductor surface, (2) optical transparency and (3) provides a photoconductor drum that is resistant to cracking and crazing. Moreover, this overcoat is cost effective to make because it does not incorporate costly charge transporting materials.
The curable composition may further consist of an additive including a coating aid such as a surfactant at an amount equal to or less than about 10 percent by weight of the curable composition. More specifically, the amount of additive is about 0.1 to about 5 percent by weight of the curable composition. The additive may improve coating uniformity of the curable composition or modify the coating surface. The additive can be crosslinkable (reactive) or non-crosslinkable.
The curable overcoat composition is prepared by mixing the nano metal oxide particles, the urethane acrylate resin, the crosslinkable siloxane and the structured acrylic copolymer with pigment affinic groups in a solvent. The solvent may include organic solvent. The curable composition may be coated on the outermost surface of the photoconductor drum 101 through dipping or spraying. If the curable composition is applied through dip coating, an alcohol is used as the solvent to minimize dissolution of the components of the charge transport layer 230. The alcohol solvent includes isopropanol, methanol, ethanol, butanol, or combinations thereof. In an example embodiment, the solvent is ethanol.
The coated curable overcoat composition is exposed to an electron beam or UV of sufficient energy to induce formation of free radicals to initiate the crosslinking. The exposed composition is then subjected to thermal cure to remove solvent, anneal and relieve stresses in the coating.
Photoconductor drums were formed using an aluminum substrate, a charge generation layer coated onto the aluminum substrate, and a charge transport layer coated on top of the charge generation layer.
The charge generation layer was prepared from a dispersion including type IV titanyl phthalocyanine, polyvinylbutyral, poly(methyl-phenyl)siloxane and polyhydroxystyrene at a weight ratio of 45:27.5:24.75:2.75 in a mixture of 2-butanone and cyclohexanone solvents. The polyvinylbutyral is available under the trade name BX-1 by Sekisui Chemical Co., Ltd. The charge generation dispersion was coated onto the aluminum substrate through dip coating and dried at 100° C. for 15 minutes to form the charge generation layer having a thickness of less than specifically a thickness of about 0.2 μm to about 0.3 μm.
The charge transport layer was prepared from a formulation including terphenyl diamine derivatives (200 g), polycarbonate A (365.4 g) and polycarbonate Z00 (365.4 g) as well as polysiloxane DC200 (0.06 g) in a mixed solvent of THF and 1,4-dioxane. The charge transport formulation was coated on top of the charge generation layer and cured at 120° C. for 1 hour to form the charge transport layer having a thickness of about 14 μm as measured by an eddy current tester.
Example Photoconductor 1 is overcoated with an overcoat layer having nano metal oxide particles, a urethane resin having at least 6 functional groups and polyether modified acryl functional polymethylsiloxane and no added charge transport material. The overcoat layer was prepared as follows:
10% Nano ITO overcoat formulation, 30% indium tin oxide(ITO) dispersion (11.4 g), Ebecryl E8301 (30.8 g) and polyether modified acryl functional polymethylsiloxane (BYK®-UV3500) (0.05 g) were mixed with 129 g of ethanol.
The formulation was coated through dip coating on the outer surface of the Example Base Photoconductor. The coated layer was subjected to an electron beam cure at 86kGy, and then thermally cured at 120° C. for 60 minutes. The cured cross-linked layer forms the overcoat layer having a thickness of about 1.5 μm as measured by an eddy current tester. The overcoat thickness may be adjusted by either varying the amount of solvent or changing the coat speed.
Example 2 Photoconductor 1 is overcoated with an overcoat layer having nano metal oxide particles, a urethane resin having at least 6 functional groups, a polyether modified acryl functional polymethylsiloxane, and an acrylic copolymer with pigment affinic groups and no charge transport material. The overcoat layer was prepared as follows:
10% Nano ITO overcoat formulation, 30% indium tin oxide(ITO) dispersion (11.4 g), Ebecryl E8301 (30.8 g) and polyether modified acryl functional polymethylsiloxane (BYK®-UV3500) (0.05 g) and an acrylic copolymer with pigment affinic groups (DISPERBYK®-2025) (0.6 g) were mixed with 129 g of ethanol.
The formulation was coated through dip coating on the outer surface of the Example Base Photoconductor. The coated layer was subjected to an electron beam cure at 86kGy, and then thermally cured at 120° C. for 60 minutes. The cured cross-linked layer forms the overcoat layer having a thickness of about 1.5 μm as measured by an eddy current tester. The overcoat thickness may be adjusted by either varying the amount of solvent or changing the coat speed.
NanoTrac Wave II particle analyzer made by Microtrac was used to measure particle size of the prepared two overcoat formulations. Samples were taken in various resting days.
Photo-induced-discharge was taken by an in-house tester (780 nm) with DC charging. The expose-to-develop time was set at 50 ms. The drum surface charge is set at −700V. The chart below shows the effect of with the addition of the acrylic copolymer with pigment affinic groups (DISPERBYK®-2025) to the overcoat formulation on discharge at 0.75 uJ/cm2 (residual voltage). The reduction of residual discharge (less negative) of a photoconductor due to the addition to the overcoat can be clearly illustrated in
A positive voltage difference between the first PC rev of discharge and the second or third PC rev of discharge will result in a lighter print, measured by L*. Since the second or third PC rev measures a lighter L* (higher values of L*), the difference is expressed as a negative value, thus a negative ghost. The relationship between the PC surface voltage delta (1st rev to 3rd rev) and change of darkness of the print (Ghost) is shown in
With this relationship established between the PC surface and the measured darkness (L*) of the print sample, we can now remove other variables from the EP system and focus on the contribution from the PC formulation. After running experiments, we were able to measure a consistent improvement on PC surface voltage delta rev-to-rev by introducing DISPERBYK®-2025, see
The foregoing description illustrates various aspects of the present disclosure. It is not intended to be exhaustive. Rather, it is chosen to illustrate the principles of the present disclosure and its practical application to enable one of ordinary skill in the art to utilize the present disclosure, including its various modifications that naturally follow. All modifications and variations are contemplated within the scope of the present disclosure as determined by the appended claims. Relatively apparent modifications include combining one or more features of various embodiments with features of other embodiments.
This application is a continuation application of U.S. patent application Ser. No. 17/399,722 filed Aug. 11, 2022, entitled “Photoconductor Overcoat Consisting of Nano Metal Oxide Particles, Urethane Resin, Crosslinkable Siloxanes, Acrylic Copolymer and no Charge Transport Materials,” the content of which is hereby incorporated by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 17399722 | Aug 2021 | US |
| Child | 17871560 | US |
