Patent Application
20080267651
The invention relates generally to the field of print finishing, and more particularly to a device and method for a cooling roller with varying heat transfer characteristics.
In an electrophotographic modular printing machine of known type for example, the 2100 printer manufactured by Eastman Kodak of Rochester, N.Y., color toner images are made sequentially in a plurality of color imaging modules arranged in tandem, and the toner images are successively electrostatically transferred to a receiver member adhered to a transport web moving through the modules. Commercial machines of this type typically employ intermediate transfer members in the respective modules for the transfer to the receiver member of individual color separation toner images. Of course, in other electrostatographic printers, each color separation toner image is directly transferred to a receiver member.
Electrostatographic printers having multicolor capability are known to also provide an additional toner depositing assembly for depositing clear toner. The provision of a clear toner overcoat to a color print is desirable for providing protection of the print from fingerprints and reducing certain visual artifacts. However, a clear toner overcoat will add cost and may reduce color gamut of the print, thus, it is desirable to provide for operator/user selection to determine whether or not a clear toner overcoat will be applied to the entire print. In U.S. Pat. No. 5,234,783, issued on Aug. 10, 1993 it is noted that in lieu of providing a uniform layer of clear toner, a layer that varies inversely according to heights of the toner stacks may be used instead as a compromise approach to establishing even toner stack heights. As is known, the respective color toners are deposited one upon the other at respective locations on the receiver member and the height of a respective color toner stack is the sum of the toner contributions of each respective color and provides the print with a more even or uniform gloss.
Many electrographic printers/copiers use rollers to feed material to a nip near a web and a fusing system. In many the fusing subsystem is composed of one to two heated rollers, which are pressed together forming the nip. When a pressure sensitive roller and a heated roller form a nip. The pressure sensitive roller and heated roller are in pressure contact with one another in what is referred to as contact fusing during fusing.
In electrostatographic controlling heat transfer after fusing is crucial since when a receiver, such as paper, passes through this nip and the temperature is too high then the toner can stick to the paper and/or the receiver can stick to one or more rollers causing multiple problems and poor prints and possible maintenance problems such as paper jams. Using the roller cooling system is very important in a situation where the receiver will pass through the fuser two or more times since it is important to maintain a low temperature of the pressure roller (using the roller cooler) the 2nd pass through the fuser (when running perfected or duplex images) will not increase the gloss or over-gloss the image. In addition during long runs of lightweight paper result in heat from the fuser roller heating the pressure roller beyond its set point. This leads to pressure roller over-temperature alarms and over-glossing on the 2nd pass through the fuser. The pressure roller cooler enables control of the pressure roller at the desired temperature and thus minimizes over-temperature alarms and over-glossing. Minimizing contact skive marks is also achieved by controlling the temperature of the pressure roller to the desired temperature.
There is a need for a printer with a cooling roller that wears well and does not have associated maintenance problems but also works well with the fuser to provide increased throughput while maintaining a high level of image quality with a wide range of paper weights while minimizing skive marks on the prints and not changing any properties that are not desired, such as changing the gloss level when it is not desired.
In one embodiment, the present invention provides an electrostatic printer including a fuser and a cooling system a roller cooling device including one or more cooling rollers in thermal communication with the pressure roller to cool the pressure roller from the fusing temperature to a desired temperature. The cooling roller includes a housing with one or more internal spaces and a fluid supply system configured to provide fluid flow at a desired temperature through the internal space to vary the heat transfer rate from the pressure roller.
Embodiments of the invention are better understood with reference to the following drawings. The elements of the drawings are not necessarily to scale relative to each other. Like reference numerals designate corresponding similar parts.
a-11c are schematics of a portion of the embodiment shown in
The receiver 12 is advanced in the direction indicated by arrow P by a motor and/or web. Note that the substrate or receiver 12 may be any medium to be imaged and or coated such as a substrate, receiver or web. The receiver normally has a first and second opposite side such that the first side has an outside heat softenable layer upon which the toner image is formed said first pressure member contacting the image and being heated to a temperature sufficient to soften said heat softenable layer and to fix a toner image by at least partially embedding the toner image in the heat softenable layer as a result of the pressure in the nip. One skilled in the art understands that the receiver could be paper that is printed or non-printed or a non-paper, such as metal, ceramics, photoconductor, textile, glass, plastic sheet, metal sheet paper sheet and other bases that are capable of receiving a toner or toner related material. It will be understood that an optional supplementary source of heat for fusing, either external or internal, may be provided, directly or indirectly, to any roller included in a fusing station of the invention.
Each receiver 12, during a single pass by the modules, can have transferred in registration thereto, for a plurality of single-color toner images to form a multicolor image with a clear toner overcoat or other desired application. As used herein, the term multicolor implies that in an image formed on the receiver member has combinations of subsets of primary colors combined to form other colors on the receiver member, at various locations on the receiver member. The primary colors participate to form process colors in at least some of the subsets wherein each of the primary colors may be combined with one more of the other primary colors at a particular location on the receiver member to form a color different than the specific color toners combined at that location.
During fusing controlling heat transfer during and after fusing is critical. Using the roller cooling system is very important in a situation where the receiver will pass through the fuser two or more times since it is important to maintaining a low temperature of the pressure roller (using the roller cooler) the 2nd pass through the fuser (when running perfected or duplex images) will not increase the gloss or over-gloss the image. In addition during long runs of lightweight paper result in heat from the fuser roller heating the pressure roller beyond its set point. This leads to pressure roller over-temperature alarms and over-glossing on the 2nd pass through the fuser. The pressure roller cooler enables control of the pressure roller at the desired temperature and thus minimizes over-temperature alarms and over-glossing. Minimizing contact skive marks is also achieved by controlling the temperature of the pressure roller to the desired temperature while maintaining a high level of image quality with a wide range of paper weights while not changing any properties that are not desired such as changing the gloss level when it is not desired. This is especially important when the paper is light and/or is run through the fuser more then one time, as in duplex operations since the heat can actually melt and gloss already applied to the other side. This is called “over glossing” and is undesirable. The cooling roller system will allow a temperature sensitive material to be used on the pressure roller. A material such as Teflon™ is useful because it aids in paper movement without sticking. The use of a material such as Teflon™ is only possible when there is adequate cooling as supplied by the roller cooling system.
The cooling system 102 shown in
The roller cooling system 102 including the cooling roller 104 can be near or can come in contact with the pressure roller 106 and can be controlled in a number of ways including a feedback algorithm that may be contained in the controller that can vary air flow, the incident angle the air contacts the pressure roller 106, distance from the receiver surface, air flow rate or capacity, number of openings and their size distribution and nozzle if needed, paper type and size as well as other factors that impact the image and printed receiver and that can be sensed or determined.
The air supply system is configured to provide a plurality of flows at the desired temperature levels through the cooling roller 104, including a hollow tube with one or more internal spaces 115 for fluid flow, so that the cooling roller 104 can to vary the heat transfer rate across the transport path so that it impacts the paper in the areas in contact with the pressure roller.
The roller cooling system 102 embodiment shown in
The roller cooling system 102 including the cooling roller 104, can be near or can come in contact with the pressure roller 106. The controller 112 optimizes the relevant factors including airflow and incident angle, which in this embodiment should be above approximately 35 degrees but probably above 50 degrees. The distance to the receiver was near enough to maximize incident angle and flow without casing interference with the receiver and was between 1 to 3 mm in this example. The airflow rate or capacity and number of openings and their size distribution and nozzle were maximized since more flow resulted in better cooling in this embodiment. The holes were about 4 mm diameter and spaced 8 mm apart but other sizes and spacing would be useful as discussed above, for different receiver types and sizes as well as treatments and other factors that impact the image. Some of the results are discussed below in conjunction with
In another embodiment of the roller cooling system 102 the cooler roller 104 contacts the surface of the pressure roller 106 shown in
The advantage of using the cooling roller 126 in the cooling system is that there is a sealed tube or shell 142 that does not release any fluid or gas and results in axial temperature uniformity. Also when a known liquid to gas phase change temperature controls the shell surface temperature for the working fluid the results can be optimized for certain circumstances and receiver types (weight, finish composition etc) as discussed above. This temperature can be adjusted for the design application by selecting the type of fluid used and the pressure the pipe charged at. In addition there is only a need for minimal airflow around the pressure roller surface. The cooling system's cooling airflow is self generated and is concentrated in the back of the machine where it's hot surfaces could not be touched by the customer.
The embodiment of the roller cooling system 102 shown in
The coating on the surface of the cooling roller 126, sometimes referred to as the heat pipe, needs to be wear resistance and easily cleanable. In one embodiment the typical heat pipe diameter for this application would be 50 mm.
b is a sintered metal wick. The use of this type of wick will provide high power handling, low temperature gradients and high capillary forces.
c is a grooved tube wick. This type of wick takes advantage of the small capillary driving force generated by the axial grooves is adequate for low power heat pipes when operated horizontally.
Materials the heat pipe could be made with include:
As described above, the coating or surface on the cooling rollers needs to be wear resistance and easy to clean. In one embodiment the optimum heat pipe diameter would be 50mm. This embodiment results in a number of advantages over existing systems including uniform axial temperature since the heat pipe surface temperature is controlled by the liquid to gas phase change temperature of the working fluid and this temperature can be adjusted for the design application by selecting the type of fluid used and the pressure the pipe is charged at. This embodiment also results in the need for a minimal airflow around the pressure roller surface which is often desired since it is less disruptive of the printing process and creates less environmental impacts. Since the cooling airflow in this embodiment is self-generated and is concentrated in the back of the machine there are no hot surfaces that the customer or even operator will touch making this a safer embodiment.
The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.
