Patent Grant
7979014
The present invention relates to a fusing or transfusing apparatus for a toner based printing, fax or copying system and a method for conditioning a fuser (or transfuse) surface of said fusing apparatus or transfusing apparatus as well as to a printer, fax or copier using the fusing or transfusing apparatus and to a method of printing using the conditioning method. The apparatus and method can integrate the functions of cleaning paper debris and residual toner from the fuser (or transfuse) surface on one hand and the application of a release agent such as silicone oil on the other hand using a single release agent impregnated web.
With a conventional electrophotographic printer, a charging device charges the surface of a photoconductive drum or belt and an exposing unit such as an LED head writes an electrostatic latent image on the charged surface of the photoconductive drum. The electrostatic latent image is developed with toner into a toner image, which is subsequently transferred to a print medium. The toner image on the print medium is then permanently fixed onto the print medium by a fixing unit.
In the electrophotographic art multi-colour printers are known that produce a plurality of colour toner images on a photoconductive drum or endless belt wherefrom the toner images are transferred directly onto printing stock material such as a paper sheet or paper web material. In an alternative embodiment the toner images formed on a photoconductive recording member are transferred subsequently to an intermediate insulating belt from distinct image forming stations and are then transferred simultaneously to a receiving sheet or web. The multicolour toner image on the print medium is then permanently fixed by a fixing unit into a colour copy or colour print.
Different methods and apparatuses are used for fusing toner images. Non-contact fusing relies on convection of a heated gas such as air or exposure to electromagnetic radiation to soften the toner resins to such an extent that the molten toner particles start to flow and adhere to each other and to the print medium. Non-contact fusing systems are popular for printing on an endless web of print medium (30).
Contact fusing methods as in
The internal heating system (12) can be assisted by one or more external heating rollers as described in U.S. Pat. No. 6,411,785 and U.S. Pat. No. 6,890,657.
In an alternative transfuse architecture toner images formed on a photoconductive recording member are transferred subsequently to an intermediate insulating belt from distinct image forming stations and are then transferred simultaneously to a heated belt or drum. In the final transfer the molten toner image is transferred from the transfuse belt or drum to the final medium in a contact area by means of a tacky pressure transfer.
The more common configuration is where a multicolour unfused toner image, transferred to the print medium in a previous step is permanently fixed by a fixing unit into a colour copy or colour print as a separate step.
At least one of the rollers (10), (13) contacts a side of the print medium (30) carrying unfused toner images (31). In
Fuser systems as in
Simultaneous duplex printing systems as in
Fuser rollers and belts, pressure rollers and belts and transfuse rollers or belts typically comprise one or more elastomer or polymer layers bonded on a mechanically stable belt or cylinder by optional bonding agents. Intermediate layers are typically chosen in function of thermal conductivity and conformance. The outer surface of the fusing surface (14) is typically a high release material and selected from material groups such as silicone resins, fluoropolymers, fluoroelastomers and hybrid compositions thereof comprising a number of proprietary additives and fillers to achieve targeted properties. U.S. Pat. No. 6,365,279 describes an example of a silicone based composition used as an outer layer of a fusing roll or belt.
In most applications of both a fusing roller or belt or transfuse roller or belt, a release agent or parting agent, most frequently a silicone oil, is applied to the fusing roller or belt or transfusing roller or belt to prevent offset (i.e. toner particles adhering to the surface of the fuser roller or belt or transfusing roller or belt instead of to the print medium surface) and to enhance the lifetime or the surface (14) of the fusing roller or belt or transfusing roller or belt
Release agent application systems (29) typically comprise a number of release agent transfer rollers represented in
For the removal of debris and toner contaminants from the fuser roller, fuser surface cleaning systems have been proposed.
Systems as in
There remains a need for a fuser surface conditioning system that
The present invention provides an apparatus for fusing or transfusing a toner based image on a print medium comprising
The above arrangement has the advantage that less release agent can be transferred to the printed images or at least the amount of release agent can be better controlled. The use of a release agent improves the lifetime. The slow advancement speed of the web increases the times between replacement, i.e. reduces downtime.
A further cleaning means can be provided to remove toner contaminants and/or paper debris from the cleaning roller. Such means can be a separate web or a scraper system or even it can be the same web as the release agent web. This provides a more optimal use of space, reduction of the number of replaceable components and reduction in the amount of hardware needed
The present invention also provides an apparatus for fusing or transfusing a toner based image on a print medium comprising:
This arrangement provides all the advantages of the previous arrangement and also provides a more optimal use of space, reduction of the number of replaceable components and reduction in the amount of hardware needed
The cleaning roller has a first surface and said release agent application roller has a second surface and preferably the contact angle at room temperature of a silicone fluid droplet on said first surface is more than 2 times bigger than the contact angle on said second surface.
The surface energy of the first surface is preferably less than 30 dyne/cm. The release agent impregnated web is preferably loaded with release agent at a rate of 10-60 gr/m2. The release agent is preferably a silicone or silicone derived release agent. The viscosity of the release agent is preferably between 1000 and 20000 centistokes at room temperature.
The contact region of the release agent impregnated web and the cleaning roller is preferably a pressure contact provided by a conformable sponge rubber type pressing roller engaged against said cleaning roller.
The present invention also provides a method for fusing or transfusing a toner based image on a print medium using a fusing or transfusing apparatus comprising
The present invention also provides a method for fusing or transfusing a toner based image on a print medium using a fusing or transfusing apparatus comprising
The second surface speed is preferably adjusted in relation to said first surface speed to result in an amount of release agent per printed A4 sheet in the range of 0.6-5 mg per A4 sheet.
The present invention will be described with respect to particular embodiments and with reference to certain drawings but the invention is not limited thereto but only by the claims. The drawings described are only schematic and are non-limiting. In the drawings, the size of some of the elements may be exaggerated and not drawn on scale for illustrative purposes. The dimensions and the relative dimensions do not correspond to actual reductions to practice of the invention.
Furthermore, the terms first, second, third and the like in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a sequence, either temporally, spatially, in ranking or in any other manner. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other sequences than described or illustrated herein.
Moreover, the terms top, bottom, over, under and the like in the description and the claims are used for descriptive purposes and not necessarily for describing relative positions. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other orientations than described or illustrated herein.
It is to be noticed that the term “comprising”, used in the claims, should not be interpreted as being restricted to the means listed thereafter; it does not exclude other elements or steps. It is thus to be interpreted as specifying the presence of the stated features, integers, steps or components as referred to, but does not preclude the presence or addition of one or more other features, integers, steps or components, or groups thereof. Thus, the scope of the expression “a device comprising means A and B” should not be limited to devices consisting only of components A and B. It means that with respect to the present invention, the only relevant components of the device are A and B.
Similarly, it is to be noticed that the term “coupled”, also used in the claims, should not be interpreted as being restricted to direct connections only. The terms “coupled” and “connected”, along with their derivatives, may be used. It should be understood that these terms are not intended as synonyms for each other. Thus, the scope of the expression “a device A coupled to a device B” should not be limited to devices or systems wherein an output of device A is directly connected to an input of device B. It means that there exists a path between an output of A and an input of B which may be a path including other devices or means. “Coupled” may mean that two or more elements are either in direct physical or electrical contact, or that two or more elements are not in direct contact with each other but yet still co-operate or interact with each other.
The present invention will mainly be described with reference to a multicolour unfused toner image, that has been transferred to a print medium in a previous step, is permanently fixed by a fixing unit into a colour copy or colour print as a separate step. However, the present invention is not limited thereto and includes within its scope devices that use transfer of images, i.e. the present invention also relates to the conditioning of transfuse surfaces.
A drive mechanism such as a motor (not shown) is connected to the shaft of take-up spool (22) and provides a continuous renewal of the web. The web may be provided in a speed range of 0.2 mm/s to 2 mm/s. Tension of the web is preferably controlled by providing a brake on the shaft of the supply spool (20). Preferably web velocity measuring means are provided. For example, a pressing roller (25) can be equipped with an encoder disc on its axis for use in measuring and for use in a feedback loop for a control system for controlling the velocity of the web (21).
The web is typically made of a textile material such as a non-woven textile and has the function to hold an amount of release agent as well as having the function to deliver it to a release agent delivery roller (24). A common choice for the textile web is known as thermal bonded non-woven textile. Other examples of textiles include those known as spun bound non-woven webs and hydro-entangled non-woven webs. For use in electrophotography these webs typically comprise polyester fibres and Aramid fibres such as Nomex® from Dupont de Nemours but fibres of Imide, polyphenylene sulphide, PTFE or viscose rayon fibres can also be used. Release agent impregnated webs are manufactured at BMP Europe limited located in Accrington, Lancashire. United Kingdom and BMP America Incorporated located in Medina, N.Y. and Portland, Oreg., both in the United States of America. Suitable webs are discussed, for example, in U.S. Pat. No. 6,449,455 which is incorporated herein by reference.
Silicone fluids such as polydimethylsiloxane are the standard choice for release agents in hot roller toner fusing for fuser surfaces (14) with a silicone based outer layer. Functionalized oils such as those with phenyl-groups, amino groups or mercapto groups will be further referred to as silicone derived release agents. These silicon derived release agents can be selected for more optimal performance with high durability fuser surface surfaces with a fluorelastomer or fluoropolymer outer layers on an elastic cushion layer for which wetting by standard silicone oil is poor. Very good results were obtained with a polyester/aramid fibre web impregnated with 30 grams per square meter of web of a PDMS silicone oil of 10000 centistokes on the chosen fusing surface (14).
The fuser roll (10) of the first embodiment for a simplex fuser on a printing web as represented in
As shown in
The freely rotating release agent application roller (24) is pressed towards the fusing roller (10) such that its surface (54) rotates at the same surface speed as the fusing surface (14). The release agent impregnated web (21) rotates at a much lower speed and due to the affinity of the surface (54) towards the release agent, the release application roller extracts release agent from the pores of the web (21) as it moves relative to the slowly advancing web (21). As shown in
The path of the release agent from the supply spool to the oil application roller and onto the fusing surface is shown as the release agent trajectory (51) in
The release agent depleted web (21) follows its path along its trajectory over the pressing roll (25) to a contact zone with the cleaning roll (23). The cleaning roll surface (53) is chosen to have a low affinity for the release agent. In our preferred embodiment the surface of the cleaning roller was chosen as a fluoropolymer. The contact angle of an AKF1000 droplet at room temperature on the preferred surface (53) was found to be 34 degrees. A suitable range for the contact angle is less that 80°, e.g. from 15 to 60 degrees—More preferably from 20 to 50 degrees. As indicated in
It has been found that optimal results are obtained when the cleaning roller is provided with a material that has contact angle >20 degrees with silicone oil AKF1000 whereas the solid surface energy <30 dyn/cm.
The cleaning roll of the first embodiment was provided with a spray coated outer surface of a fluoropolymer, e.g. fluorinated ethylene propylene (FEP) with a solid surface energy of 18.23 dyn/cm2. Other tested fluoropolymers were sleeves of PFA with solid surface energy measurements of 18.6 dyn/cm2. Both PFA and PTFE sleeves were found to be suitable alternative materials for the outer surface (53) of the cleaning roller (23).
It was found that especially in combination with a fuser roll or belt (10) that comprises a metallic base coated with a single relatively thin 130 micron silicone based resin layer, it is preferable to have a conformable base for the cleaning roller 23.
It was found that especially in combination with a fuser roll or belt (10) that comprises a metallic base coated with a single relatively thin 130 micron silicone based resin layer, it is preferable to have a conformable base for the cleaning roller 23.
As experiments have indicated, preferably slightly more than 50% of the release agent is depleted from the web (21) for an initial loading of 30 g/m2 when the release agent web (21) speed is set to by 0.3 mm/s for a printing speed of 122.5 mm/sec. In the tested set up, the supply spool was dimensioned to accommodate 60 meters of web. In this case 25 kilometers of print medium could be printed before having to replace the release agent web spool (20).
Application of a uniform film of release agents is known to facilitate the stripping of the printed sheet form the fuser surface (14).
Levels for application of release agent per printed sheet are typically in the range of 10 to 20 mg per A4 size sheet for fuser system designed for sheet based full colour printers. Whereas fusing systems designed for fusing printed sheets can suffer from paper jams when the printed sheet fails to release from the fuser surface, fusing systems that operate on print media in the form of an endless web have a reliability advantage as there is no risk of jams of that nature.
The useful life of a fuser roll (10) consisting of a 140 mm diameter aluminium tube with a wall thickness of 9 mm coated with a single 130 micron thick layer silicone based resin in the absence of a fuser conditioning surface depends on the type of prints made, the print speed and the idle times in between the jobs. In table 1 a useful life of this fuser roller (10) of in between 5000 and 10000 A4 prints is listed and it is assumed that this limited life is due to the presence of silicone oligomers in the silicone network that have a certain mobility and that can migrate to the free surface where they can act as a built-in release agent. Measurement of the depletion of “natural” oil from a silicone belt over the number of copies made is reported in FIG. 7 of EP1072962 in the context of a possible application in a transfuse system. This document suggests that a target for replacing the lost natural oils would be to add 0.1 to 0.2 mg of release agent per A4 sheet. The reference does not report on the results of a similar oil on copy test over the number of copies made in a system with an oil application system.
The reference suggests the use of an release agent application system as in
It has been found, however, that use of levels of release agent in the range of 0.6 to 5 mg of release agent per printed A4 sheet applied with the system (1) as described above increased the useful life of the fusing roller (10) by a factor of up to more than 40 compared to a reference run where the fuser surface conditioning system (1) was removed.
Table 1 summarizes the observations in the test.
It has been found that the combined action of cleaning the fuser surface (10) using a synchronously rotating cleaning roller (23) and applying the release agent through a synchronously rotating release agent application roller (24) allows the use of significantly lower amounts of release agent than the amounts of 10 to 20 mg/A4 of release agent that are typically used in the art to enhance the useful life of the fuser roller or belt or transfuse roller or belt (10).
Especially for industrial applications such as label printing, it is desirable to reduce the amount of release agent that is applied to the printed medium to an absolute minimum. Release agent films of more than a few milligrams per sheet are known to interfere with subsequent production steps such as the application of a protecting and/or gloss enhancing varnish. Use of higher amounts of release agent necessitates a higher release agent loading of the release agent impregnated web (21) or a higher speed of the release agent impregnated web (21). The maximum amount of release agent that can be loaded in a web without problems of oil dripping out is limited however. An increase of the speed of the release agent impregnated web (21) shortens the interval of replacement of the supply spool (20) and take-up spool (22). High amounts of release agent on the printout compromise the possibility to write with a ballpoint pen on the printed copy, which can be a desirable feature for pre-printed labels.
Preferred levels of release agent application to the printed medium are in the range 0.6 to 5 mg/A4 and more preferentially in the range of 0.8 to 2.5 mg/A4.
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