Patent Publication Number: US-2010129125-A1

Title: Light-absorptive device, fixing unit using the light-absorptive device, and image forming apparatus

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATIONS 
     This application claims the benefit of Korean Patent Application No. 10-2008-0118812, filed on Nov. 27, 2008, in the Korean Intellectual Property Office, the disclosure of which in its entirety is incorporated herein by reference. 
     TECHNICAL FIELD 
     The present disclosure relates generally to a light-absorptive device having an improved thermal efficiency, a fixing unit using the light-absorptive device, and an image forming apparatus incorporating such fixing unit. 
     BACKGROUND OF RELATED ART 
     Light-absorptive devices for absorbing light emitted from a light source may be used as a heating device utilizing the absorbed light energy as the source of heat. A light-absorptive device may be used for, for example, a fixing unit in an electrophotographic image forming apparatus. 
     In an electrophotographic image forming apparatus, after a photosensitive drum is uniformly charged, the photosensitive drum is exposed to light using a laser scanning unit (LSU) to form an electrostatic latent image according to an image signal. Toner that is charged by a developing unit is supplied to the photosensitive drum to form a toner image. The toner image is transferred to a recording medium. The toner image transferred to the recording medium is not fixed at this point, but is merely carried on the recording medium. By heating and pressing the toner image using a fixing unit, the toner image is thermally used or otherwise fixed on the recording medium so that a fixed image may be formed on the recording medium. For example, in a roller type fixing unit, as the recording medium holding the toner image passes through a nip portion that is formed between a heating roller and a press roller which are in a pressing contact with each other, the toner image on the recording medium is heated by the heat from the heating roller and simultaneously pressed by the heating roller and the press roller, thereby being fixed on the recording medium. The heating roller may generally have the form of a metal roller having a cylindrical shape and may be heated by a heat source, such as, for example, a halogen lamp, and is an example of a light-absorptive device. 
     SUMMARY OF THE DISCLOSURE 
     According to an embodiment, a light-absorptive device with an improved thermal efficiency configured to absorb light emitted from a light source may include a light-absorptive element having a light-absorptive layer in which a nano-component, obtained by coating a nano particle with a shape keeping agent, is dispersed. 
     According to another embodiment, a fixing unit may include a light source, a heating member configured to absorb light emitted from the light source and including a light-absorptive layer in which a nano-component obtained by coating a nano particle with a shape keeping agent is dispersed, and a press member configured to form a fixing nip by facing and pressing against the heating member. 
     The shape keeping agent may be, for example, silica or carbon. 
     The nano particle may be, for example, a nano-sphere or a nano-rod. The nano particle may be formed of at least one metal selected from the group including Ag, Au, Pt, Pd, Fe, Ni, Al, Sb, W, Tb, Dy, Gd, Eu, Nd, Pr, Sr, Mg, Cu, Zn, Co, Mn, Cr, V, Mo, Zr and Ba. 
     A medium of the light-absorptive layer may be polymer. The polymer may be a fluorine based resin such as PFA (Perfluoroalkoxy) or PTFE (Polytetrafluoroethylene), for example. 
     The light source may be configured to emit light of a single wavelength, and the nano particle may have an aspect ratio at which a peak wavelength of absorption spectrum of the nano particle is a wavelength of the light emitted from the light source. 
     The light source may be configured to emit light of multiple wavelengths, and the nano particle may have a plurality of aspect ratios, the plurality of aspect ratios of the nano particle being set to allow a peak wavelength of absorption spectrum of the nano particle to belong to a wavelength of the light emitted from the light source. 
     The light-absorptive layer may include a plurality of dielectric layers having different dielectric constants. The dielectric constant of each of the plurality of dielectric layers may be set to allow a peak wavelength of absorption spectrum of the nano particle to belong to a wavelength of the light emitted from the light source. 
     According to another embodiment, an image forming apparatus may include a printing unit configured to transfer a toner image to a recording medium using an electrophotographic method; a fixing unit which includes a light source; a heating member configured to absorb light emitted from the light source and including a light-absorptive layer in which a nano-component obtained by coating a nano particle with a shape keeping agent is dispersed; and a press member forming a fixing nip by facing and pressing against the heating member. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Various features and advantages of the disclosure will become more apparent by the following detailed description of several embodiments thereof with reference to the attached drawings, of which: 
         FIG. 1  schematically illustrates the structure of a light-absorptive device according to an embodiment; 
         FIG. 2  illustrates an example of a nano-composite; 
         FIG. 3  is a graph qualitatively showing that a wavelength for maximizing a light energy absorption rate varies as the aspect ratio of nano-rod changes; 
         FIG. 4  schematically illustrates the structure of a light-absorptive device according to another embodiment; 
         FIG. 5  schematically illustrates the structure of a light-absorptive device according to yet another embodiment; 
         FIG. 6  is a graph showing that a wavelength for maximizing a light energy absorption rate of a nano-composite varies as the dielectric constant of a dielectric layer in which the nano-composite is dispersed changes; 
         FIG. 7  schematically illustrates the structure of a fixing unit according to an embodiment; and 
         FIG. 8  schematically illustrates the structure of an image forming apparatus according to an embodiment. 
     
    
    
     DETAILED DESCRIPTION OF SEVERAL EMBODIMENTS 
     Reference will now be made in detail to the embodiment, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout. While the embodiments are described with detailed construction and elements to assist in a comprehensive understanding of the various applications and advantages of the embodiments, it should be apparent however that the embodiments can be carried out without those specifically detailed particulars. Also, well-known functions or constructions will not be described in detail so as to avoid obscuring the description with unnecessary detail. It should be also noted that in the drawings, the dimensions of the features are not intended to be to true scale and may be exaggerated for the sake of allowing greater understanding. 
       FIG. 1  schematically illustrates the structure of a light-absorptive device according to an embodiment. Referring to  FIG. 1 , the light-absorptive device may include a light-absorptive element  100  and a light source  180 . The light source  180  may be configured to emit light L to a light-absorptive layer  110  of the light-absorptive element  100 . A halogen lamp or a semiconductor laser diode, for example, may be employed as the light source  180 . Other types of light sources may alternatively or additionally be employed as the light source  180 . A reflection member (not shown) for guiding light to the light-absorptive element  100  may be further provided around the light source  180 . Although the present embodiment the light-absorptive device is described as including the light source  180 , an external light source, such as sun light, may be used as the light source  180  so that the light source  180  need not be separately provided. 
     The light-absorptive element  100  is configured to absorb the light L emitted from the light source  180 , and may include the light-absorptive layer  110 , in which a nano-composite  140  is dispersed, and a substrate  150  configured to support the light-absorptive layer  110 . The substrate  150  may be a layer coated with the light-absorptive layer  110 . The substrate  150  may be heated, and may be a heat transfer medium that transfers heat. 
     The light-absorptive layer  110  is a layer configured to absorb energy of the incident light L, and to convert the absorbed energy to thermal energy. When the light-absorptive device according to an embodiment is applied to a heating member of a fixing unit, fluorine based resin, such as perfluoroalkoxy (PFA) or polytetrafluoroethylene (PTFE), for example, may be used as the medium of the light-absorptive layer  110 . 
     The nano-composite  140  may comprise a plurality of nano particles on which a shape keeping agent is coated thereon to improve thermal stability of the nano particles. Each nano particle may be, for example, a nano-rod or a nano-sphere having a size of several nanometers through hundreds of nanometers. 
     A surface plasmon resonance phenomenon may be generated at a boundary surface between a typical dielectric material having a positive dielectric characteristic and a material having a negative dielectric characteristic when the typical dielectric material having a positive dielectric characteristic and the material having a negative dielectric characteristic contact each other. In particular, the surface plasmon resonance phenomenon may be easily generated in metal having a high negative dielectric characteristic. The nano particle used for the nano-composite  140 , according to an embodiment, may be formed of metal having the surface plasmon resonance phenomenon. For example, a nano-rod formed of metal selected from a group of Ag, Au, Pt, Pd, Fe, Ni, Al, Sb, W, Tb, Dy, Gd, Eu, Nd, Pr, Sr, Mg, Cu, Zn, Co, Mn, Cr, V, Mo, Zr, and Ba may be used as the nano particle. When the surface plasmon resonance phenomenon is generated in the nano particle, the reflection or dispersion of light incident on the nano particle may be restricted and the light energy absorption rate of the nano particle may accordingly be at or near a peak. Accordingly, photo-thermal energy conversion may efficiently be achieved. 
     With reference to  FIG. 2 , the nano-composite  140 , according to an embodiment, is illustrated. Silica or carbon, for example, may be used as the shape keeping agent that is applied to or coated on the nano particle. Referring to  FIG. 2 , the nano-composite  140  may have, according to an embodiment, a structure in which silica (SiO 2 )  146  is coated on a gold (Au) nano particle  141  having a modified surface. A surfactant  143 , such as hexadecyltrimethylammonium bromide (C16TAB), may encompass the gold (Au) nano particle  141 , for example. A silane coupling agent  145  may be for example, HSRSi(OR) 3 . 
     To manufacture the nano-composite  140 , first, the surface of the gold (Au) nano particle  141  may be modified using HSRSi(OR) 3 , such as 3-Mercaptopropyl trimethoxysilane (MPTS, HS(CH 2 ) 3 Si(OCH 3 ) 3 ), as the silane coupling agent. “R” may be CH 3 . Accordingly, the surface modification of the gold (Au) nano particle  141  may allow the gold (Au) nano particle  141  to maintain a stably dispersed state in another solvent as well as in water. Sodium silicate resin may be mixed on the surface-modified gold (Au), and may be magnetically stirred. After several days, a nano-composite in which a gold (Au) nano particle is inserted in a silica shell may be formed. 
     The above method of manufacturing a nano-composite is merely an example, and a variety of other methods known in the field may be employed. For example, a nano-composite may be manufactured by growing silica on anodized aluminum oxide (AAO) having a porous structure to form a thin layer, making a silica-coated AAO pore, and growing a metal particle in the silica-coated AAO pore. As an another example, an amorphous carbon shell may be formed on a nano-rod using a resistive heating evaporation method. In addition, to stabilize and improve the mechanical characteristic of the nano-composite, a variety of nano-composites in which the nano particle is surrounded by a rigid matrix, such as polymer, glass, or ceramic, (i.e., the shape keeping agent) may be used. 
     The light-absorptive device may absorb the light L emitted from the light source  180 , as shown in  FIG. 1 , and may covert the absorbed light to thermal energy to heat the light-absorptive device itself and/or a subject to be heated. A fixing unit of an image forming apparatus, for example, may maintain a temperature of about 180° C. A pure nano particle may be thermally deformed at such high temperature so that the shape of the nano particle may not be stably maintained. The thermal deformation may change the aspect ratio of the nano particle, thereby changing the peak wavelength of an absorption spectrum. In an embodiment, by using a nano-composite in which a shape keeping agent is coated on a nano particle, the thermal deformation of a nano particle at high temperature may be mitigated so that thermal stability may be improved. 
     The wavelength of light generating the surface plasmon resonance phenomenon may vary according to the aspect ratio of the nano particle  141  in the nano-composite. By varying the aspect ratio of the nano particle  141 , the wavelength that maximizes the light energy absorption rate of the nano-composite  140  may be changed. 
       FIG. 3  is a graph qualitatively showing that a wavelength corresponding to the peak of a light energy absorption rate varies by changing the length of a nano-rod (NR) having the same diameter. Referring to  FIG. 3 , it is illustrated that a wavelength corresponding to the peak of a light energy absorption rate gradually increases as the aspect ratio of the nano-rod (NR) increases. The wavelength of light generating the surface plasmon resonance phenomenon and the aspect ratio of the nano-rod (NR) may vary according to the specific material of metal forming the nano-rod (NR). 
     Referring again to  FIG. 1 , when the light source  180  emits the light L in a predetermined wavelength range, such as, for example, with a semiconductor laser diode, a nano-rod having an aspect ratio at which the peak wavelength of the absorption spectrum of the nano-rod matches the wavelength of the light L emitted from the light source  180  may be used. 
     When a multi-wavelength light source, such as a halogen lamp, is used as the light source  180 , the nano-rod may have a variety of aspect ratios. In such an embodiment, the aspect ratio of the nano-rod may be set such that the peak wavelength of the absorption spectrum belongs to the wavelength range of the light L emitted from the light source  180 . 
       FIG. 4  schematically illustrates the structure of a light-absorptive device according to another embodiment. Referring to  FIG. 4 , a light-absorptive device may include a light-absorptive element  101  and a light source  180 . A multi-wavelength light source, such as a halogen lamp, may used as the light source  180 . The light-absorptive element  101  has a structure that includes a multilayered light-absorptive layer  111  provided and positioned on a substrate  150 . A plurality of nano-composites  141 , which may comprise a plurality of nano particles having different aspect ratios with a shape keeping agent coated thereon, are dispersed in the multilayered light-absorptive layer  111 . 
     If the light source  180  emits light of multiple wavelengths, the aspect ratio of the nano particle may have different values at which the peak wavelength of the absorption spectrum belongs to the multiple wavelength range of the light L emitted from the light source  180 . Accordingly, the light-absorptive layer  111  may include first and second layers  121  and  131 , in which first and second nano-composites  141   a  and  141   b  are respectively dispersed. The first and second nano-composites  141   a  and  141   b  each are obtained by coating the shape keeping agent on the nano particles having different aspect ratios at which the peak wavelength of the absorption spectrum belongs to the multiple wavelength range of the light L emitted from the light source  180 . Additionally, the nano particles of the light-absorptive layer  111  may have aspect ratios of three or more different values. Moreover, the light-absorptive layer  111  is not limited to a double layer structure and may be a three or more layer structure. 
       FIG. 5  schematically illustrates the structure of a light-absorptive device according to another embodiment. Referring to  FIG. 5 , a light-absorptive device may includes a light-absorptive element  102  and a light source  180 . A multi-wavelength light source, such as a halogen lamp, may be used as the light source  180 . The light-absorptive element  102  may include a multilayered light-absorptive layer  112  provided and positioned on the substrate  150 . The light-absorptive layer  112  may include first and second dielectric layers  122  and  132  in which a plurality of nano-composites  142  are dispersed. 
     With reference to  FIG. 6 , which illustrates that the wavelength maximizing the light energy absorption rate of a nano-composite varies as the dielectric constant of the dielectric layer in which the nano-composite is dispersed changes. A surface plasmon resonance condition generated in the nano-composite  142  may vary according to the dielectric constant of a medium around the nano-composite  142 . Thus, the wavelength of light generating the surface plasmon resonance can be changed by the dielectric constant of the medium around the nano-composite  142 . 
     Referring back to  FIG. 5 , the first and second dielectric layers  122  and  132  forming the light-absorptive layer  112  may have different dielectric constants. If the light source  180  is a halogen lamp, for example, the wavelength range of light that is emitted may be of a relatively wide range. To allow the peak wavelength of the absorption spectrum of the nano-composite  142  to belong to the wavelength range of the light emitted from the halogen lamp, the dielectric constants of the first and second dielectric layers  122  and  132 , in which the nano-composite  142  is dispersed, may be accordingly adapted so that the light energy absorption rate may be effectively increased. 
     The light-absorptive layer  112  is not limited to the two dielectric layers  122  and  132  and may be formed of three or more dielectric layers. If the light-absorptive layer  112  is formed of three or more dielectric layers, the light absorption rate may be increased by adjusting the dielectric constant of each dielectric layer such that the peak wavelength of the absorbed light energy is located in the wavelength spectrum of the light source  180 . 
     In an embodiment where the wavelength at which the light energy absorption rate becomes maximum is adjusted by changing the dielectric constants of the first and second dielectric layers  122  and  132 , the aspect ratio of the nano particle of the nano-composite  142  dispersed in the first dielectric layer  122  and the aspect ratio of the nano particle of the nano-composite  142  dispersed in the second dielectric layer  132  may be the same or substantially the same (i.e. within a margin of error in a manufacturing process; nano particles manufactured under the same process condition may have substantially the same aspect ratio). 
       FIG. 7  schematically illustrates the structure of a fixing unit  200  according to an embodiment. Referring to  FIG. 7 , the fixing unit  200  may include a heating roller  210 , a press roller  270  and a light source  280 . 
     The heating roller  210  may have a cylindrical shape and may be capable of rotating axially. The heating roller  210  may include an inner pipe  220 , an elastic layer  230  and a light-absorptive layer  240 . 
     The inner pipe  220  may be configured to support and/or sustain the shape of the heating roller  210 , and may also function as a rotation shaft. The inner pipe  220  may comprise a core pipe formed of, for example, metal, such as iron, steel, stainless steel, aluminum, or copper; an alloy; ceramics; or a fiber reinforced metal (FRM). Other structures may be utilized in place of the inner pipe  220 , such as, for example, a shaft having a rod shape. 
     The elastic layer  230  of the heating roller  210  is, according to an embodiment, provided on the outer circumferential surface of the inner pipe  220 . The elastic layer  230  may be formed of silicon rubber or fluorine rubber, for example. The silicon rubber may be RTV silicon rubber or HTV silicon rubber. Poly dimethyl silicon rubber, metal vinyl silicon rubber, methal phenyl silicon rubber, or fluorine silicon rubber may alternatively or additionally be used. 
     The light-absorptive layer  240  of the heating roller  210  may comprise a layer in which a nano-composite is dispersed, in which a photo-thermal energy conversion is performed by the surface plasmon resonance phenomenon of the nano particles in the nano-composite. 
     The medium of the light-absorptive layer  240 , in which the nano-composite is dispersed, may be formed of polymer that exhibits, a thermal stability. A releasable resin, such as fluorine based rubber, silicon based rubber, or fluorine based resin, may be used as the medium of the light-absorptive layer  240 . For example, fluorine based resin such as PFA or PTFE may be used as the medium of the light-absorptive layer  240 . The releasable resin may function to separate a recording medium P from the heating roller  210  in a fixing process, for example. According to an embodiment, a release layer formed of a releasable resin may be separately provided on the outer circumferential surface of the light-absorptive layer  240 . The fixing unit  200  is not limited to the heating roller  210 . For example, a belt having a heat-absorptive layer may be utilized as the heating member of the fixing unit  200 . 
     In an embodiment, if nano-composite exhibiting thermal stability is dispersed in the light-absorptive layer  240 , the light-absorptive layer  240  may be stably formed on the heating roller  210 . For example, in a conventional process of forming a release layer formed of PFA on the heating roller, a FPA film is inserted in a roller and is thermally contracted through a plastic process at 400° C. In the above-described embodiment, the heating roller  210  may be manufactured without a drastic change in the conventional manufacturing method due to the use of thermally stable nano-composite. 
     The press roller  270  of the fixing unit  200  may have a cylindrical shape and may be capable of rotating axially. The press roller  270  may have a structure in which a heat-resistant elastic layer  273  is wound around a metal core member  271 . The heat-resistant elastic layer  273  may be formed of for example, silicon rubber. 
     With reference to  FIG. 7 , according to an embodiment, a fixing nip portion may be formed between the press roller  270  and the heating roller  210 . The heat provided by the heating roller  210  as well as the pressure between the press roller  270  and the heating roller  210  may allow a toner image T, which is formed on a recording medium P that passes through the fixing nip portion, to be fixed on the recording medium P. 
     The light source  280  may be configured to emit radiation heat, and may include, for example, a halogen lamp, an IR lamp, a light emitting diode, a laser diode, or the like. A reflection member  290  may be configured to guide light emitted from the light source  280  toward the heating roller  210 . 
     The light source  280  may be positioned outside the heating roller  210  to emit radiation heat to the outer circumferential surface of the heating roller  210 . Since the radiation heat may be emitted directly to the outer circumferential surface of the heating roller  210  and furthermore since the light-absorptive layer  240  is provided on the outer circumferential surface of the heating roller  210 , the temperature of the surface of the heating roller  210  may be quickly raised. Accordingly, as the surface temperature of the heating roller  210  can be raised to a fixing temperature of for example, 180° C.-200° C. in a short amount of time, first page out time (FPOT) for outputting the first printing medium may be reduced in a printing process, thereby improving the printing speed. 
     When a halogen lamp is used as the light source  180 , the range of the wavelengths of the emitted light may be relatively wide. Accordingly, in order to allow the peak wavelength of the absorption spectrum of nano-composite to belong to the wavelength range of the light emitted from the halogen lamp, as described above, the light energy absorption rate of the light-absorptive layer  240  may be effectively improved by either appropriately selecting the aspect ratios of nano particles in the nano-composite, or by changing the dielectric constants of a plurality of dielectric layers in which the nano-composite is dispersed. 
       FIG. 8  schematically illustrates the structure of an image forming apparatus according to an embodiment. Referring to  FIG. 8 , an image forming apparatus may include a light scanning unit  510 , a development unit  520 , a photosensitive drum  530 , a charge roller  531 , an intermediate transfer belt  540 , a transfer roller  545  and a fixing unit  550 . The fixing unit described with reference to  FIG. 7  may be used as the fixing unit  550 , for example. 
     The light scanning unit  510  may be configured to scan a light ray modulated according to image information onto the photosensitive drum  530 . The photosensitive drum  530  may be a type of photosensitive body, in which a photosensitive layer having a predetermined thickness is formed on the outer circumferential surface of a cylindrical metal pipe. The outer circumferential surface of the photosensitive drum  530  may correspond to a scanned surface, upon which the light ray scanned by the light scanning unit  510  is incident, and upon which electrostatic latent image is thereby formed. In an alternative embodiment, a photosensitive body in the form of belt may be used instead. Toner may be accommodated in the development unit  520 . The toner may be moved to the photosensitive drum  530  by a development bias applied between the development unit  520  and the photosensitive drum  530  to develop the electrostatic latent image into a visible toner image. 
     To print a color image, the light scanning unit  510  may scan four light rays respectively to four photosensitive drums, as illustrated in  FIG. 8 . As a result, electrostatic latent images corresponding to black K, magenta M, yellow Y, and cyan C image information may respectively be formed on the four photosensitive drums. The four development units may respectively supply toner of the black K, magenta M, yellow Y and can C colors to the photosensitive drum  530 , thereby forming a toner image of the black K, magenta M, yellow Y, and cyan C colors. 
     The charge roller  531  is a charger that may be configured to rotate in contact with the photosensitive drum  530 , and may be configured to charge the surface of the photosensitive drum  530  to a uniform electric potential. To that end, a charge bias Vc may be applied to the charge roller  531 . According to an alternative embodiment, a corona charger (not shown) may be used instead of the charge roller  531 . Other types of charging units may also be utilized. 
     The toner images of the black K, magenta M, yellow Y, and cyan C colors formed on the four photosensitive drums may be transferred to the intermediate transfer belt  540 . The toner images may be transferred to the recording medium P passing between the transfer roller  545  and the intermediate transfer belt  540  by, for example, a transfer bias applied to the transfer roller  545 . The toner images transferred to the recording medium P may be fixed on the recording medium P due to the heat and pressure received from the fixing unit  550  so that the formation of an image may be completed. 
     In the image forming apparatus configured as above, thermal efficiency may be improved if the light-absorptive devices according to the above-described embodiments are used in the fixing unit  550 . Furthermore, since the fixing temperature can be quickly raised, the FPOT may be reduced and the printing speed may accordingly be improved. 
     Moreover, the light-absorptive device according to various described embodiments may be used for various mechanisms that may use or incorporate a radiation heat as a heat source. For example, the light-absorptive device may be used for a heat apparatus using radiation heat. In addition, the light-absorptive device may be used for an apparatus capable of locally heating by intensively emitting light to a marker including a nano-composite. The local heating apparatus may be applied to a variety of fields, such as an apparatus for mounting electronic parts on a printed circuit board and a medical equipment for destroying a tumor by locally applying heat to a marker planted in a tumor in a human body, for example. 
     While the disclosure has been particularly shown and described with reference to several embodiments thereof with particular details, it will be apparent to one of ordinary skill in the art that various changes may be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the following claims and their equivalents.