Patent Application
20130051824
This invention generally relates to electrostatographic devices and methods that use a heated fuser roller to permanently fix dry toner images to a receiver.
In a typical electrophotographic print engine that uses dry toner to print images on receiver sheets such as paper, the dry toner image is permanently fixed to a receiver sheet by subjecting the dry toner-bearing receiver sheet to include heat and pressure. This is generally accomplished by feeding the dry toner image bearing receiver sheet into a nip formed between a heated rotatable fuser roller and a second rotatable fuser roller. Then, subjecting the dry toner image to sufficient heat and pressure so as to raise the toner to a temperature above the glass transition temperature Tg of the toner while subjecting the dry toner to sufficient pressure to permit the individual toner particles to flow into a coherent mass and bond to the receiver. Typically, dry toner contains a polymer binder such as polyester or polystyrene. In addition, dry toner can contain other components such as charge control agents, waxes or semicrystalline materials such as polyethylene or polypropylene to facilitate release of the image-bearing receiver sheets from the fuser rollers, particulate addenda such as silica to control toner flow and adhesion. In many applications, the fuser rollers are coated with a thin layer of a release aid such as a silicone oil to facilitate release of the receiver sheet from the fuser rollers.
The surface (or the topcoat) for both rotatable fuser rollers requires ultra low surface energy to release the substrate. An effective topcoat material for oil-less fusing is high-temperature tolerant thermoplastic, such as FEP (polyfluorinated ethylene-propylene), PFA (perfluoroalkoxy-tetrafluoroethylene), or PTFE (polytetrafluoroethylene) as described in US Published Applications 20070298252, 20070298251, 20070298217, and 20070296122 each of which were published on Dec. 27, 2007.
It has been observed that receiver sheet lead and trail edges can also leave wear marks on the topcoat of the fuser roller surface, and that foreign materials from the receiver sheet can also periodically accumulate on that surface and can cause damage to the fuser roller and particularly its top coat.
The present invention provides a method that reduces or limits damage to a fuser rollers used in a dry electrophotographic print engine when feeding receiver sheets.
The present invention provides an electrophotographic method for reducing damage to a fusing roller, comprising:
a) providing a fusing system having first and second rotatable fusing rollers that engage each other to form a fuser nip, the first roller having a surface that engages a toned receiver sheet having a top surface that engages and the second roller having a surface that engages the opposite surface of the receiver sheet;
b) using a sheet feeding transport member in the form of a moveable web to feed a toned receiver sheet into the fuser nip;
c) detecting the lead edge of the receiver sheet to produce a signal indicating the receiver sheet is about to enter the fuser nip;
d) determining the thickness of the receiver sheet that is a function of the relative spacing between the rotatable fusing rollers; and
e) moving the first or second rotatable fusing rollers or both from an unloaded or partially loaded state to a closed or fully loaded state in response to the signal and the thickness of the receiver sheet and then using the rotatable rollers forming the fuser nip to transport the receiver sheet through the fuser nip.
The present invention recognizes that the thickness of a receiver sheet is used to determine the fully loaded state of the fusing system. This feature reduces damage to the fusing rollers by taking into account the thickness of the receiver sheet.
Rotatable fusing rollers 100 and 105 are used in a fusing system in an electrophotographic print engine to permanently fix images made with dry toner 75 to a receiver sheet 140. Both of these rollers include a rigid cylindrical core 175 and an elastomeric blanket 180 coaxial with the core. A heating element 110 provides enough heat to raise the temperature of the dry toner 75 above its glass transition temperature to melt the dry toner 75 and fix it to the receiver sheet 140. A fuser drive controller 85 rotates the rotatable fusing rollers 100 and 105. Receiver sheet skiving devices 115 guide the receiver sheet 140 out of the fuser nip 170. To facilitate release of the fused image bearing receiver sheet 140 from the fusing system, the rotatable fusing rollers 100 and 105 are often coated with low surface energy, semicrystalline thermoplastic topcoat materials, such as FEP (polyfluorinated ethylene-propylene), PFA (perfluoroalkoxy-tetrafluoroethylene), or PTFE (polytetrafluoroethylene). Low surface energy refers to materials having a surface energy of less than 30 ergs/cm2, preferably less than 25 ergs/cm2, and more preferably less than 20 ergs/cm2, as determined from the contact angle with a non-polar and a polar liquid such as distilled water and diiodomethane and using the Good-Girafalco approximation to approximate the interfacial energy. Other forms of low surface energy materials can also be used to overcoat the rollers. These include various elastomeric silicones as well as certain low surface energy ceramics such as fluorinated creamers.
The present invention is not dependent on how the rotatable fusing roller is manufactured, i.e., not affected by whether the topcoat is sleeve molded, sintered with dispersion, sprayed or transfer-coated. The method of the present invention will increase the usable life of the rotatable fusing roller owing to its ability to prevent surface irregularities by taking into account the thickness of the toned receiver sheet.
The main controller 80 sends a signal to the transport member drive controller 90 which actuates the sheet feeding transport member in the form of a moveable web 135 to feed the receiver sheet 140 into the fuser nip 170.
Methods of actuating the nip between the first rotatable fusing roller 100 and the second rotatable fusing roller 105 are not limited to the rotatable fusing member nip engagement mechanism 70 shown and can include other actuation devices such as air cylinders, electrical solenoids or a worm gear mechanism (not shown) to change the displacement between the first rotatable fusing roller 100 and the second rotatable fusing roller 105. The air cylinder would use pneumatic pressure to actuate. The solenoid would use electric current to actuate and the worm gear would actuate along a line.
One method of detecting the thickness of the receiver sheet 140 is shown. A receiver sheet thickness detector roller 145 is attached to a receiver sheet thickness detector mounting frame 150 and engaged with the sheet feeding transport member in the form of a moveable web 135 by a rotatable thickness detector pivot point 155. The receiver sheet thickness detector roller 145 position is sensed by a thickness detector transducer 160 such as a strain gage that measures the deflection of the receiver sheet thickness detector roller 145 from the sheet feeding transport member in the form of a moveable web 135. Upon entry into the thickness detector nip 190 formed between the receiver sheet thickness detector roller 145 and the sheet feeding transport member in the form of a moveable web 135 by the receiver sheet 140, the receiver sheet thickness determination roller 145 is deflected by the thickness of the receiver sheet 140. This deflection is registered by the thickness detector transducer 160 which feeds the deflection signal into the main controller 80 that controls the rotatable fusing member nip engagement mechanism 70. The rotatable fusing member nip engagement mechanism 70 then separates the first rotatable fusing roller 100 from the second rotatable fuser roller 105 by an amount at least as great as the thickness of the receiver sheet 140. The reengagement time for reengaging the first and second rotatable fusing rollers 100 and 105 is determined by the process speed of the electrophotographic apparatus and the distance between the contact point of the receiver sheet thickness detector roller 145 and the sheet feeding transport member in the form of a moveable web 135 and the fuser nip 170 between the first rotatable fusing roller 100 and second rotatable fusing roller 105. After disengaging for the period sufficient to permit the receiver lead edge of the receiver sheet 140 to enter the fuser nip 170, but preferably prior to the time needed for the dry toner 75 bearing portion of the receiver sheet 140 to enter the fusing nip 170, the main controller 80 reengages the first rotatable fusing roller 100 and second rotatable fuser roller 105.
The rotatable fusing member nip engagement mechanism 70 permits adjustable displacement between the first rotatable fusing roller 100 and the second rotatable fusing roller 105 can apply fully loaded pressure to the receiver sheet 140 while the receiver sheet 140 is in the fuser nip 170 to raise the dry toner 75 to a temperature above the glass transition temperature Tg of the dry toner 75 while subjecting the dry toner 75 to sufficient pressure to permit the individual dry toner particles 75 to flow into a coherent mass and bond to the receiver sheet 140 for the receiver sheet type and desired surface finish. During the time the receiver sheet 140 is not in the fuser nip 170, the rotatable fusing member nip engagement mechanism 70 can cause the displacement between the first rotatable fusing roller 100 and the second rotatable fusing roller 105 to be in an open or unloaded state where the distance between the first rotatable fusing roller 100 and the second rotatable fusing roller 105 is greater than the thickness of the receiver 140 or it can be in a partially loaded state where the displacement is less than the thickness of the receiver sheet 140. Thereafter, the distance between the fusing rollers is reduced and they are in a fully loaded state where they engage and fix the toned image to the receiver.
As shown in
Other ways (not shown) of determining the thickness of the receiver sheet 140 can also be employed. These include measuring the transit times of ultrasonic waves to the transport member in the form of a moveable web 135. This time is determined by the size of the gap between the ultrasonic transmitter/receiver assembly (not shown) and the surface against which the ultrasonic waves are reflected. The presence of a receiver sheet 140 will decrease this distance, thereby shortening the transit time of the ultrasonic wave.
In another method of practicing this invention, the characteristics of the receiver sheet 140 is entered into the main controller 80. This is done either using a bar code on the receiver sheet 140 or the packaging of the receiver sheets 140 that contains the appropriate information. Alternatively, the operator can input the thickness of the receiver sheet 140 directly into the main controller 80 in a well known manner. The main controller 80 then uses a look up table to determine the thickness of the receiver sheet 140.
In yet another embodiment of this invention, the impact force of the receiver sheet 140 entering the fuser nip 170 between the rotatable fusing rollers 100 and 105 is measured and the nip drive controller 95 can increase the separation or pressure until the impact force decreases to a sufficiently low level, preferably no impact force, indicating that sufficient separation has been achieved.
It will be understood that the receiver sheet 140 in
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
Reference is made to commonly-assigned U.S. patent application Ser. No. 12/915,364 filed Oct. 29, 2010 (D96483), entitled “CONTROLLING SPEED TO REDUCE IMAGE QUALITY ARTIFACTS” to Dobbertin, et al., the disclosure of which is incorporated herein.
