Patent Application
20110274458
1. Field of the Invention
The present invention relates an image forming apparatus including a fixing unit.
2. Description of the Related Art
Conventionally, a toner image formed on a recording sheet (hereinafter referred to as “recording material”) using an electrophotographic process is subjected to heat-fixing processing by a fixing unit. A majority of the recent electrophotographic toners contain a release wax as a constituent material. A release wax is added in order to provide effects such as adjustment of a glossiness of a printed image and dispersibility of pigments as well as prevention of fixing offsets.
Here, there are some types of fixing offset phenomena as described below. In a process of fixing onto a recording material, if the fixing roller or the fixing film is not sufficiently heated (has a low temperature), the toner is not sufficiently fused, and the strength of fixing on the recording material is decreased. Such state may result in a part of the toner adhering to the fixing roller. Such phenomenon is called “cold offset”, and the part of the recording material in which the toner adheres to the fixing roller appears as a missing part of the image on the recording material. In addition, the fixed toner may fall out of the recording material due to, e.g., friction because of its weak fixing strength.
On the contrary, if the temperatures of the fixing roller and/or the fixing film are excessively high, the toner is sufficiently fused, but the viscosity is lowered and the fused toner partially falls out of the recording material, contaminating the fixing roller surface. This phenomenon is called “hot offset”, which results in a missing part of the image appearing on the recording material as in cold offset.
Therefore, in order to prevent the above-described fixing offsets, Japanese Patent Application Laid-Open No. H08-184992 proposes addition of wax components to toner as a release agent. Inclusion of release wax in toner causes the release wax to move to the interface between the fused toner and the fixing roller when heat-fixing is performed, enhancing the withstanding offset. Furthermore, Japanese Patent Application Laid-Open No. 2000-003070 proposes a technique in which two or more types of release waxes are added to toner for offset resistibility enhancement.
A recording material is simultaneously heated and pressured by a fixing roller and a pressure roller, and then pinched and conveyed by the rollers, so that a release wax included in toner is liquefied. A majority of the release wax is fixed to the recording material together with the fused toner, while a part of the release wax vaporizes and enters a gaseous state.
Components of the evaporated release wax float in a liquid or fine solid particle state within the fixing unit depending on the temperature of the surroundings. In some cases, the floating release wax components may adhere to various parts within the image forming apparatus.
Accumulation of such components on, for example, a recording material conveyance roller adversely affects the conveyance performance, causing, e.g., jamming of a recording material during conveyance or a decrease in the friction coefficient of the roller, and thus, is a significant problem to be solved for ensuring the reliability of the apparatus as well as extending the life of the apparatus. Accordingly, it is necessary to take special measures, such as controlling the direction of the air flowing in the apparatus, in order to prevent adherence of the release wax components to the conveyance part.
Meanwhile, in recent years, there are very high demands for speed-up and downsizing of laser beam printers. An increase in the speed for performing heat-fixing processing in an image forming apparatus requires higher thermal energy and pressure than ever before. As thermal energy provided to toner increases, the amount of evaporation of the release wax increases, and thus, it can be anticipated that the aforementioned problems related to adherence of evaporated release wax components occur more frequently. Accordingly, it is important to develop a technique to collect evaporated components of a release wax included in toner in a heating and pressure-applying fixing unit.
The present invention has been made in order to solve the aforementioned problems, and a purpose of the present invention is to provide an image forming apparatus that can prevent conveyance failures resulting from evaporated components of a release wax adhering to parts within the image forming apparatus.
Another purpose of the present invention is to provide an image forming apparatus including: a fixing part that heats and fixes an unfixed toner image formed on a recording material to the recording material; an electric field generation member that forms an electric field in a space in which a component evaporated from a wax flows, the component being generated during the heating and fixing; and a collection member to which a voltage is applied, the collection member electrostatically collecting the component passing through the space in which the electric field has been formed.
A further purpose of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
Preferred embodiments of the present invention will now be described in detail in accordance with the accompanying drawings.
First, a full-color laser beam printer, which is an image forming apparatus according to an embodiment of the present invention, will be described. Although a full-color laser beam printer including a plurality of photosensitive drums will be described as an embodiment of the present invention, the present invention is also applicable to a monochrome copier or printer including a single photosensitive drum. Accordingly, the image forming apparatus according to the present invention is not limited to full-color laser beam printers.
A cassette 2 is housed in a lower portion of the printer 1 in such a manner that the cassette 2 can be drawn out of the printer 1. A manual feed part 3 is provided on the right side of the printer 1. Sheets, which are recording materials, are loaded in a stacked state in each of the cassette 2 and the manual feed part 3. Sheets from the cassette 2 and the manual feed part 3 are separated one by one, and fed to registration rollers 4.
The printer 1 includes an image forming part 5, which is an image forming unit in which image forming stations 5Y, 5M, 5C and 5K for respective colors, i.e., yellow, magenta, cyan and black, are transversely aligned. The image forming part 5 includes photosensitive drums 6Y, 6M, 6C and 6K (hereinafter uniformly referred to as “photosensitive drums 6”), which are image bearing members, and charging units 7Y, 7M, 7C and 7K that evenly charge the surfaces of the photosensitive drums 6. Furthermore, at a lower portion of the image forming part 5, scanner units 8 that form electrostatic latent images on the photosensitive drums 6 by means of irradiation with a laser beam based on image information. Furthermore, developing units 9Y, 9M, 9C and 9K that make toners adhere to electrostatic latent images to develop toner images, and primary transfer parts 11Y, 11M, 11C and 11K (hereinafter uniformly referred to as “primary transfer parts 11”) that transfer the toner images on the photosensitive drums 6 to an electrostatic transfer belt 10 are provided. The toner images on the electrostatic transfer belt 10, which have been transferred in the primary transfer parts 11, are transferred to a sheet in a secondary transfer part 12.
Subsequently, the unfixed toner images formed on the sheet are heated and fixed on the sheet when passing through a fixing nip portion N including a heating unit 101 and a pressure roller 102 that is in pressure contact with the heating unit 101. Furthermore, the sheet passes through an output conveyance part 150 is conveyed to any one of an output roller pair 14 and a switchback roller pair 15, which is determined by switching of the conveyance path via a double-side print flapper 13. The sheet conveyed to the switchback roller pair 15 side is reversed and conveyed by the switchback roller pair 15 part, passes through the registration rollers 4, the secondary transfer part 12 and a fixing unit 100 again, and then passes through the output conveyance part 150. The sheet is then conveyed to the output roller 14 side. The sheet passes through the output roller pair 14 and then is output to a sheet stacking part 16.
Next, a detailed configuration of the fixing unit (fixing part) 100 of the printer 1 will be described with reference to
The heating unit 101 includes a heater 103, which is a heating unit. The heater 103 is supported by a heater holder 104, which is a support member. The heater holder 104 is formed in a substantially semicircular gutter shape in cross section using a heat resistant resin having heat resistance and slidability, such as a liquid crystal polymer. The heater holder 104 is sheathed with a fixing sleeve 105, which is a heating rotating body. The fixing sleeve 105 is resistant to thermal and mechanical stress, and includes a base layer of a metal with good heat conductivity, for example, SUS, coated with, for example, a PFA resin with good releasability, in order to ensure the capability of separation of the sheet P.
The pressure roller 102 includes an elastic layer formed by, e.g., silicone rubber in its metal core bar, and a surface layer coated with a fluorine-contained resin such as PFA having good releasability as with the fixing sleeve. The pressure roller 102 is pressed against the fixing sleeve 105 so as to face the heater 103 supported by the heater holder 104, thereby forming the fixing nip portion N between the fixing sleeve 105 and the pressure roller 102.
Although not illustrated, a heater drive control circuit, which is a control unit for the heater 103, includes a power feeding unit such as a triac, and, e.g., a CPU for controlling the same. Upon a print signal being input to the heater drive control circuit, the CPU controls the power feeding unit to start power supply to the heater 103. Consequently, the temperature of the heater 103 rapidly increases. The temperature of the heater 103 is detected by a thermistor (not illustrated), which is a temperature detection unit provided on a back surface (a surface opposite to the fixing nip portion N) of the heater 103. Based on the detected temperature, the heater 103 is controlled to adjust the temperature thereof to a predetermined target set temperature to heat the fixing sleeve 105 to such temperature. In the embodiment of the present invention, the set temperature is, for example, 180° C.
In such state, the sheet P bearing unfixed toner (S in
A release wax is included in the toner and comes out of the inside of the toner punctured by the pressure of the fixing nip portion N as the sheet P is pinched and conveyed by the fixing nip portion N. Furthermore, the temperature of the release wax is brought to its melting point or higher by the heat of the fixing nip portion N, and the release wax enters a liquid or gaseous state. The melting point of the release wax used in the embodiment of the present invention is, for example, 76° C.
Components evaporated from the liquid or gaseous release wax are generated from the print surface side of the sheet P, and moves according to air flows in the fixing unit 100. The air flows in the fixing unit 100 are generated by thermal convection according to the temperatures in the fixing unit 100, air flows according to rotation of the fixing sleeve 105 and the pressure roller 102 and an air flow generated as a result of conveyance of the sheet P. Among such air flows, the air flows according to rotation of the fixing sleeve 105 and the pressure roller 102 are larger than the others, that is, the heat convention and the air current generated as a result of conveyance of the sheet P, constitute a major part of the air flows in the fixing unit 100. Furthermore, the components evaporated from the release wax are generated on the print surface side in the fixing nip portion N provided by the fixing sleeve 105 and the pressure roller 102, and thus, move mainly along the air flow according to rotation of the fixing sleeve 105.
In
However, when an external force, such as an electric field, is exerted on the release wax particle 401, the electric field make the negative pole sides of the release wax molecules 402 be attracted by the positive pole side of the electric field generation unit 201 and the positive pole sides of the release wax molecules 402 be attracted by the negative pole side of the electric field generation unit 201. Consequently, as illustrated in
Furthermore, in the embodiment of the present invention, voltages required for the electric field generation unit 201 and the collection unit 301 are supplied through supply paths branching from the above-described supply path of the transfer bias from the power supply unit 17a to the transfer roller 12a. It should be noted that a voltage may be applied to at least one of the electric field generation member and the collection member using a power supply used for the image forming part.
It is also common to apply a bias voltage to the fixing sleeve and the pressure roller as a countermeasure for a fixing offset causing toner to adhere to the fixing sleeve side in the fixing unit. Accordingly, a voltage may be applied to the electric field generation unit 201 and/or the collection unit 301 through a power supply path branching from the supply path of the bias.
As described above, power is supplied to the electric field generation unit 201 and the collection unit 301 through voltage supply paths branching from a voltage supply path for the existing image forming process, eliminating the need to separately provide a dedicated power supply, enabling provision of the configuration according to the present proposal at minimum costs.
In
Also, in the case of
Where the release wax and the collection plate surface 304a have a temperature equal to or higher than the melting point of the release wax, the release wax is liquefied, and thus, the release wax particles are not strung together, but exhibits the same electrical effect.
As described above, when an electric field is applied to components evaporated from a release wax, which are generated as a result of the release wax being heated by the fixing unit, by means of the electric field generation unit, the release wax particles can be electrically biased, enabling the components evaporated from the release wax to be electrostatically collected. Accordingly, an image forming apparatus that can prevent conveyance failures resulting from evaporated components of a release wax adhering to parts within the image forming apparatus, such as a sheet guide and/or a conveyance roller, can be provided.
Next, a second embodiment of the present invention will be described. In the second embodiment, components that are the same as those in the above-described first embodiment are provided with same reference numerals, and a description of such same components is omitted to avoid overlap.
In the fixing unit 110 according to the second embodiment, a collection unit 501 enabling evaporated release wax components to be electrically biased and electrostatically collected simultaneously is provided. In other words, the collection unit 501 according to the second embodiment has both an electric field generation function provided by the electric field generation unit 201 in the first embodiment and a collection function provided by the collection unit 301, and thus, can be called an integrated collection unit. The integrated collection unit 501 in which an electric field generation unit and a collection unit are integrated has a configuration that is the same as that of the collection unit 301 in
However, it is necessary that an applied voltage be higher than that of the collection unit 301 in the first embodiment. In the second embodiment, a voltage of, for example, around 5 to 6 kV is applied to the integrated collection unit 501.
In the first embodiment, the evaporated release wax components are electrically biased in the electric field generation unit 201, and thus, in the collection unit 301, the release wax particles can be attracted even with a weak electric field. Meanwhile, in the integrated collection unit 501, it is necessary to electrically bias the release wax particles and attract and collect the electrically biased release wax particles simultaneously. Furthermore, as opposed to the electric field generation unit 201, in the integrated collection unit 501 where a resin member is present on a surface of an electrode, the electric field is weakened by the amount of the thickness of the resin member. Accordingly, it is necessary to apply a voltage higher than that of the electric field generation unit 201 to the collection unit 501 in the second embodiment.
Accordingly, an image forming apparatus that can prevent conveyance failures resulting from evaporated components of a release wax adhering to parts within the image forming apparatus, such as a sheet guide and/or a conveyance roller, can be provided. In particular, in the second embodiment, an integrated collection unit simultaneously providing a function that electrically biases particles of evaporated release wax components and a function that electrostatically collets the evaporated release wax components is provided. Thus, such integrated collection unit can be arranged in a space that is smaller than that required for separately arranging apparatuses having the respective functions, enabling reduction of costs consumed for the members.
Next, a third embodiment of the present invention will be described. In the third embodiment, components that are the same as those in the above-described first or second embodiment are provided with same reference numerals, and a description of the same components will be omitted to avoid overlap.
As described above, basically, evaporated release wax components are electrically collected within a fixing unit in which a source of generation of the components exists. However, a part of the evaporated release wax components may be carried by thermal convection and/or an air flow generated as a result of a sheet P being conveyed and discharged to the outside of the fixing unit.
The second collection system 600 includes a fun 602 and a duct 603, and uses the fun 602 and the duct 603 to forcibly generate an air flow, thereby drawing evaporated release wax components into the duct 603. In the duct 603, a heater 601 is arranged. The heater 601 is a heating unit that can re-heat the release wax discharged to the outside of the fixing unit 100 by the thermal convection or the air flow generated as a result of conveyance of the sheet P to a temperature equal to or higher than a melting point of the release wax. Also, in the duct 603, an electric field generation unit 201 and a collection unit 301, which are illustrated in
The evaporated release wax components discharged to the outside of the fixing unit 100 by the thermal convection or the air flow generated as a result of conveyance of the sheet P are forcibly drawn into the duct 603 by the air flow generated by the fun 602. Concurrently, the evaporated release wax components are heated by the heater 601 to the temperature equal to or higher than the melting point, and thus, enter a liquid or gaseous state. The evaporated release wax components that have been made into such state pass through the electric field generation unit 201, whereby the evaporated release wax components are electrically biased, and pulled and collected by the collection unit 301.
Accordingly, an image forming apparatus that can prevent conveyance failures resulting from evaporated components of a release wax adhering to parts within the image forming apparatus, such as a sheet guide and/or a conveyance roller, can be provided. In particular, in the third embodiment, evaporated release wax components discharged to the outside of the fixing unit because of failure to collect the evaporated release wax components within the fixing unit can also be collected. Accordingly, evaporated release wax components can be prevented more reliably from adhering to parts within the image forming apparatus, enabling prevention of conveyance failures.
Although in the above-described second collection system, an electric field generation unit and a collection unit are separately provided, it should be understood that the electric field generation unit and the collection unit can be provided by an integrated collection unit.
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
This application claims the benefit of Japanese Patent Application No. 2010-107939, filed May 10, 2010, which is hereby incorporated by reference herein in its entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2010-107939 | May 2010 | JP | national |
