Patent Description:
An electrophotographic image forming apparatus includes a fixing apparatus for heating and pressurizing a toner image formed on a recording material such as paper (which may be hereinafter described as a "sheet"), and thereby fixing the toner image on the sheet. The fixing apparatus includes fixing members such as a heat roller (heating film) and a pressure roller (pressure film), and performs a fixing treatment of the unfixed toner image on the sheet at a position (fixing nip part) at which the heat roller and the pressure roller are in pressure contact with each other.

Examples of the fixing apparatus include a film heating type apparatus. The apparatus has a heater as a heating member (heating source) having a resistive heat generator on a substrate made of ceramics. The apparatus has an endless fixing film as a heating member travelling rotatively while including a heater therein and being in contact with the heater. The apparatus has a pressure roller (pressurizing rotating member) as a nip part forming member for forming a nip part by coming in pressure contact with the fixing film, and rotatively driving the fixing film.

The film heating system enables a lower heat capacity and a smaller size of the fixing film, and hence can implement energy saving of the fixing apparatus. Further, it becomes possible to shorten the time (warm-up time) taken until the temperature of the fixing film reaches a prescribed temperature enough to heat and fix a toner image.

For the film-shaped base material, a resin such as polyimide or a metal such as nickel or a stainless steel is used. On such a base material, an elastic layer including rubber excellent in heat resistance such as silicone rubber is provided. Due to the presence of the elastic layer, when a sheet onto which a toner has been transferred passes through the nip part, the flexibility of the elastic layer deforms the surface of the fixing member, which well follows the unfixed toner image on the sheet, resulting in an increase in contact area between the fixing member and the unfixed toner image on the sheet. For this reason, the unfixed toner image can be more uniformly molten, and can be fixed on the sheet. As a result, a high quality electrophotographic image can be obtained.

Then, on the elastic layer, a release layer is provided for imparting the releasability with respect to the toner of the fixing member. As the materials forming the release layer, fluorine resins such as polytetrafluoroethylene (PTFE), tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer (PFA), and tetrafluoroethylene / hexafluoropropylene copolymer (FEP) are used.

As the method for forming the release layer on the elastic layer, the following method is known: the surface of the elastic layer is covered with a tube including a fluorine resin previously manufactured by extrusion (which will be also hereinafter referred to as a "fluorine resin tube"). Incidentally, for the fluorine resin tube, molecules of the fluorine resin are oriented along the extrusion direction. As a result, the fluorine resin tube tends to be torn in the orientation direction of the molecular chain, namely, in the direction in parallel with the extrusion direction.

<CIT> discloses as follows: a thermally contractible tube obtained by extending the diameter of a PFA tube is heated and contracted to be allowed to melt-adhere to and integrated with a rubber roller, thereby forming a PFA layer on the outer circumferential surface of the rubber roller; then, the PFA is reheated to a temperature equal to, or higher than the melting point of the PFA contained in the PFA tube, thereby relaxing and removing the internal stress of the PFA layer formed from the PFA tube after thermal contraction; as a result, breakage of the PFA layer in the direction along the rotational axis of a roller or a belt is prevented.

At least one aspect of the present disclosure is directed to providing a fixing film which includes a surface layer exhibiting the tear resistance in the direction along the rotational axis, and the wear resistance of the edge region on each opposite side in the direction along the rotational axis at a higher level even by long-term use. Further, at least one aspect of the present disclosure is directed to providing a heat fixing apparatus which contributes to the stable formation of a high quality electrophotographic image. Still further, at least one aspect of the present disclosure is directed to providing an electrophotographic image forming apparatus which can form a high quality electrophotographic image with stability. Furthermore, at least one aspect of the present disclosure is directed to providing a manufacturing method of a fixing film including a surface layer exhibiting the tear resistance in the direction along the rotational axis, and the wear resistance of the edge region on each opposite side in the direction along the rotational axis at a higher level even by long-term use.

According to at least one aspect of the present disclosure, there is provided a fixing film as specified in claims <NUM> to <NUM>.

According to at least one aspect of the present disclosure, there is provided a heat fixing apparatus as specified in claims <NUM> to <NUM>.

According to at least one aspect of the present disclosure, there is provided an electrophotographic image forming apparatus as specified in claim <NUM>.

According to at least one aspect of the present disclosure, there is provided a method for manufacturing the fixing film as specified in claims <NUM> to <NUM>.

Unless otherwise specified, descriptions of numerical ranges such as "from XX to YY" or "XX to YY" in the present disclosure include the numbers at the upper and lower limits of the range. When numerical ranges are described in stages, the upper and lower limits of each of each numerical range may be combined arbitrarily.

According to a study by the present inventors, it has been indicated as follows: the PFA layer whose internal stress has been released by the method disclosed in <CIT> is relaxed in molecular orientation in the extrusion direction (the direction along the rotational axis) included by the PFA tube, and becomes less likely to be torn in the direction along the rotational axis. Herein, as disclosed in <CIT>, the degree of orientation and the degree of crystallinity of a fluorine resin are correlated with each other. For this reason, a fluorine resin tube with a high degree of orientation of the molecules in the direction along the rotational axis is also high in crystallinity, and has an excellent wear resistance. Therefore, the fluorine resin tube relaxed in molecular orientation of a fluorine resin in the direction along the rotational axis by the method disclosed in <CIT> is also reduced in wear resistance.

To meet a recent demand for a still longer life for an electrophotographic image forming apparatus, a fixing film has also been demanded to be improved in durability. Then, the edge region on each opposite side in the direction along the rotational axis of the fixing film is the segment with which the edge of paper repeatedly comes in contact, and hence is required to have a particularly high wear resistance.

The present inventors conducted a close study thereon, and as a result, they found the following: the orientation state of the molecules of the fluorine resin in the release layer is varied between in the central region in the direction along the rotational axis of the fixing film roughly corresponding to the image formation region of a recording material (which will be also hereinafter referred to as a "longitudinal direction"), and in the edge region on each opposite side in the direction along the axis roughly corresponding to the region with which the edge of the recording material comes in contact; as a result, the tear resistance and the wear resistance can be made compatible with each other at a higher level.

Namely, a fixing film in accordance with at least one aspect of the present disclosure has at least a base material, an elastic layer, and a release layer in this order.

The release layer includes a tube including a fluorine resin (which will be also hereinafter referred to as a "fluorine resin tube").

Then, a value (Xe/Xm) of a ratio of Xe to Xm is <NUM> or more, where.

The maximum peak observed in the region of 2θ = <NUM> to <NUM>° in the chart of the X-ray diffraction peaks obtained by measuring the fluorine resin tube with the reflection X-ray diffraction method is considered to be the diffraction peak of the α type crystal (<NUM>) plane by the fluorine resin in the fluorine resin tube. Further, in the chart, the halo pattern observed in the region of 2θ = <NUM> to <NUM>° is considered to be derived from the amorphous component of the fluorine resin in the fluorine resin tube.

Thus, in the present disclosure, Ia represents the maximum X-ray diffraction strength at 2θ = <NUM> to <NUM>° of the amorphous halo peaks in the chart. Whereas, Ic represents the maximum X-ray diffraction strength of the diffraction peaks derived from the α type crystal (<NUM>) plane of the fluorine resin at 2θ = <NUM> to <NUM>° in the chart. Then, as the parameter indicative of the degree of development of crystallization in the fluorine resin tube, a value (X) of the ratio (Ic/Ia) of Ic to Ia is set.

Incidentally, for Ic and Ia, the values obtained by deducting the X-ray diffraction strength at 2θ = <NUM> to <NUM>° as the reference is assumed to be used in order to eliminate the influence of the base line.

For the fluorine resin tube in accordance with one aspect of the present disclosure, the ratio (Xe/Xm) of X in the edge region, namely, Xe, to X in the central region, namely, Xm is <NUM> or more. In other words, for the fluorine resin tube, the degree of development of crystallization of the fluorine resin in the edge region is higher than the degree of development of crystallization of the fluorine resin in the central region. This indicates that the fluorine resin tube in accordance with the present disclosure is less likely to be torn in the direction along the rotational axis even by long-term use in the central region. Further, the fluorine resin tube has a high wear resistance in the edge region that tends to come in contact with the edge portion of paper. As a result, the fixing film in accordance with at least one aspect of the present disclosure combines the tear resistance in the direction along the rotational axis and the wear resistance of the edge region on each opposite side in the direction along the rotational axis at a higher level even by long-term use.

Below, embodiments of the present disclosure will be described in details by reference to the accompanying drawings.

<FIG> is a schematic block view of one example of an electrophotographic image forming apparatus (which will be also hereinafter referred to as an image forming apparatus). The image forming apparatus is an image forming apparatus of an electrophotographic system, and has a rotating electrophotographic photosensitive body <NUM>. The image forming apparatus has a charging device <NUM>, and an image exposure means <NUM> as electrostatic latent image forming means with respect to the photosensitive body <NUM>, and a developing means <NUM> for developing the electrostatic latent image on the photosensitive body <NUM> as a toner image (developer image). Further, the image forming apparatus has a transfer means <NUM> for transferring the toner image on the photosensitive body <NUM> onto a sheet-shaped recording material (which will be hereinafter described as paper or sheet) P. The image forming apparatus has a cleaning means <NUM> for cleaning the photosensitive body <NUM> surface after toner image transfer, a heat fixing apparatus (fixing apparatus) <NUM> (<FIG>) as a fixing means for fixing a toner image T on the sheet P, and the like.

<FIG> is a transverse cross sectional schematic view showing a schematic configuration of a fixing apparatus <NUM> in the present embodiment. In the following description, regarding a fixing apparatus and the members configuring the fixing apparatus, the direction along the rotational axis is the direction orthogonal to the transport direction of paper on the plane of paper. The length is the dimension in the direction along the rotational axis. The direction along the rotational axis of the fixing film is also similarly the direction orthogonal to the paper transport direction, and is the direction perpendicular with respect to the surface on which a fixing film <NUM> is drawn in <FIG> (the direction perpendicular to the drawing).

The fixing apparatus <NUM> is a fixing apparatus of a belt (film) heating system. The fixing apparatus <NUM> includes a ceramics heater (which will be hereinafter described as a heater) as a heating body, and a film guide <NUM> also serving as a heating body support member. Further, the fixing apparatus <NUM> includes a fixing film <NUM> which is in an endless shape (cylindrical shape), and flexible and heat resistant as a heating member (fixing member). Further, the fixing apparatus <NUM> includes a pressure roller <NUM> as a nip part forming member for forming a nip part (fixing nip part) N by coming in pressure contact with the fixing film <NUM>.

The heater <NUM> is a sheet-shaped member elongated along the longitudinal direction of the fixing film <NUM> (the direction perpendicular to the drawing), and has a heat source such as a resistive heat generator for generating heat by passage of an electric current by a feeding means not shown, and is rapidly increased in temperature by feeding. The temperature of the heater <NUM> is detected by a temperature detecting means not shown. The detected temperature information is inputted to a control means not shown. The control means controls the power supply from the feeding means to the heat source so that the detected temperature inputted from the temperature detecting means may be kept at a prescribed fixation temperature, and adjusts the temperature of the heater <NUM> at a prescribed temperature.

The heater <NUM> is supported by a film guide <NUM> formed in a substantially semicircular arc-shaped gutter type in transverse cross section with a heat resistant material having a rigidity. More specifically, the outer surface of the film guide <NUM> is provided with a groove part 2a along the guide longitudinal direction, and the heater <NUM> is fitted into the groove part 2a.

As described later, the fixing film <NUM> includes at least a ring-shaped (tubular) base material <NUM>, elastic layer <NUM>, release layer <NUM>, and the like in this order from inward to outward (<FIG>). As shown in <FIG>, the fixing film <NUM> may further have other layers such as an inner surface sliding layer <NUM> and a primer layer <NUM>. The fixing film <NUM> is an endless film whose inner circumferential surface is rubbed by the heater <NUM> and the film guide <NUM> in use, and is fitted around the outer circumference of the film guide <NUM> supporting the heater <NUM> with a margin allowed for the circumference.

The heater <NUM> and the pressure roller <NUM> are in pressure contact with each other with the fixing film <NUM> interposed therebetween, and the nip part N is formed between the fixing film <NUM> and the pressure roller <NUM>. The pressure roller <NUM> is rotatively driven in the counterclockwise direction indicated with an arrow R30 at a prescribed peripheral velocity by a rotatively driving device M such as a motor. Following the rotational driving of the pressure roller <NUM>, the fixing film <NUM> rotates in the clockwise direction of an arrow R20 around the outer circumference of the film guide <NUM> with its inner surface sliding in intimate contact with the surface of the heater <NUM>. The edge on each opposite side in the direction along the rotational axis of the fixing film <NUM> is rotatably supported by a flange (not shown) of a regulating member fixed to the fixing apparatus <NUM>.

The film guide <NUM> functions as the support member of the heater <NUM>, and also functions as the rotation guide member of the fixing film <NUM>. A lubricant (grease) is coated on the inner circumferential surface of the fixing film <NUM> in order to ensure the slidability with the heater <NUM> and the film guide <NUM>.

The pressure roller <NUM> includes a substrate <NUM> in a solid round bar shape, a cylindrical shape (pipe shape), or another shape, an elastic layer <NUM>, and a release layer <NUM> from inward to outward. The pressure roller <NUM> is rotatively driven in use by a rotatively driving device M such as a motor. For this reason, the edge on each opposite side in the direction along the rotational axis of the substrate <NUM> is rotatably supported at a fixing part not shown of the frame of the fixing apparatus <NUM>, or the like via a bearing member.

Further, the pressure roller <NUM> is arranged at a position opposed to the heater <NUM> supported by the film guide <NUM> across the fixing film <NUM>. Then, a pressurizing mechanism (not shown) applies a prescribed pressure to the pressure roller <NUM> and the fixing film <NUM>. As a result, the pressure roller <NUM> and the fixing film <NUM> are in pressure contact with each other, so that respective elastic layers (<NUM>, <NUM>) are elastically deformed. As a result of this, the nip part N with a prescribed width in the sheet transport direction is formed between the pressure roller <NUM> and the fixing film <NUM>.

Pressure contact between both of the fixing film <NUM> as a heating member and the pressure roller <NUM> as a nip forming member may be accomplished by a configuration in which the pressure roller <NUM> is brought into pressure contact with the fixing film <NUM> under a prescribed pressure, or a configuration in which the fixing film <NUM> side is brought into pressure contact with the pressure roller <NUM>. Alternatively, a still other configuration is also acceptable in which both of the fixing film <NUM> side and the pressure roller <NUM> are brought into pressure contact with each other under a prescribed pressure.

When the pressure roller <NUM> is rotatively driven by the rotatively driving device M, the pressure roller <NUM> transports the sheet P while sandwiching the sheet P at the nip part N between it and the drivenly rotating fixing film <NUM>. Further, the fixing film <NUM> is heated by the heater <NUM> until the temperature of the surface thereof reaches a prescribed temperature (e.g., <NUM>). In this state, the sheet P carrying an unfixed toner image T is introduced to the nip part N, and is sandwiched and transported. As a result, the unfixed toner T on the sheet P is heated and pressurized. Then, the unfixed toner T is molten / color mixed. For this reason, subsequently, by cooling this, the toner image is fixed on the sheet P as a fixed image.

Then, the fixing film <NUM> in the present Example will be described in details.

<FIG> is a cross sectional schematic view showing the layer configuration of the fixing film <NUM>. A reference No. <NUM> represents the base material (cylindrical substrate) of the fixing film <NUM>, a reference No. <NUM> represents an inner surface sliding layer arranged on the inner circumferential surface of the base material <NUM>, a reference No. <NUM> represents a primer layer covering the outer circumferential surface of the base material <NUM>, and a reference No. <NUM> represents an elastic layer arranged on the primer layer <NUM>. A reference No. <NUM> represents a fluorine resin tube as a release layer, and a reference No. <NUM> represents an adhesive layer for fixing the release layer <NUM> on the elastic layer <NUM>.

Below, respective constituent layers will be specifically described.

The base material <NUM> of the fixing film <NUM> has an endless shape. Then, in view of the fact that the base material <NUM> is required to have a heat resistance and a flex resistance, also in consideration of the heat resistant resins such as polyimide, polyamideimide, and polyether ether ketone (PEEK), and the thermal conductivity, a metal such as a stainless steel (SUS), nickel, or a nickel alloy having a higher thermal conductivity than that of the heat resistance resin is preferably used. The base material <NUM> is required to be increased in mechanical strength while being reduced in heat capacity. For this reason, the thickness is desirably set at <NUM> to <NUM>, and preferably set at <NUM> to <NUM>.

The fixing film <NUM> may include the inner surface sliding layer <NUM> on the inner circumferential surface side of the base material <NUM>.

As the inner surface sliding layer <NUM>, a resin having both high durability and high heat resistance such as a polyimide resin is suitable. In the present Example, a polyimide precursor solution obtained by effecting the reaction between aromatic tetracarboxylic acid dianhydride or a derivative thereof and aromatic diamine in substantially equal moles in an organic polar solvent is coated on the inner circumferential surface of the base material <NUM>, and the solvent is dried, followed by heating, thereby effecting the dehydration ring closure reaction (imidization reaction). As a result, the inner surface sliding layer <NUM> is formed. The inner surface sliding layer <NUM> is gradually worn away by rubbing with the heater <NUM>. Accordingly, the inner surface sliding layer <NUM> is preferably provided with a thickness enough to allow action as the sliding layer through endurable use. On the other hand, when the thickness is set too large, the inner surface sliding layer <NUM> acts as a heat resistant layer for hindering heat supply from the heater <NUM>. For this reason, the thickness is preferably <NUM> to <NUM>, and more preferably <NUM> to <NUM>.

The outer circumferential surface of the base material <NUM> is provided with the elastic layer <NUM> via the primer layer <NUM>. The elastic layer <NUM> uniformly gives a heat to the unfixed toner T in such a manner as to encompass the unfixed toner T on the sheet P when the sheet P passes through the nip part N. The elastic layer <NUM> functions in this manner, resulting in a good-quality image with a high gloss and without uneven fixing.

The materials for the primer layer <NUM> have no particular restriction, and known ones can be used. Examples thereof may include "DY39-<NUM> A/B" (tradename) manufactured by DOW and TORAY Co. The thickness of the primer layer <NUM> has no particular restriction, and is, for example, <NUM> to <NUM>. The method for forming the primer layer <NUM> also has no particular restriction. Examples thereof may include spray coating and immersion coating.

The materials for the elastic layer <NUM> have no particular restriction, and known ones can be used. Because of the reasons that processing is easy, processing can be performed with a high dimensional precision, and a reaction by-product is not generated at the time of heating and curing and other reasons, a cured product of an addition reaction crosslinking type liquid silicone rubber is preferable. The addition reaction crosslinking type liquid silicone rubber may include, for example, organopolysiloxane and organohydrogen polysiloxane, and may further include a catalyst and other additives. Organopolysiloxane is a base polymer including silicone rubber as the raw material, and the one having a number average molecular weight of <NUM>,<NUM> to <NUM>,<NUM>, and a weight-average molecular weight of <NUM>,<NUM> to <NUM>,<NUM> may be desirably used.

Liquid silicone rubber is a polymer having flowability at room temperature, and is cured by heating, has an appropriately low hardness after curing, and has sufficient heat resistance and deformation recovery force. For this reason, the liquid silicone rubber is preferably used not only for a belt elastic layer <NUM> but also for an elastic layer <NUM> of the pressure roller <NUM> described later.

Incidentally, when the elastic layer <NUM> is formed of a silicone rubber simple substance, the thermal conductivity of the elastic layer <NUM> is reduced. Preferably, the thermal conductivity of the elastic layer <NUM> is increased, which makes the heat generated at the heater <NUM> more likely to be transferred to the sheet P via the fixing film <NUM>, and heating is sufficiently performed for fixing the toner on the sheet P, thereby suppressing an image defect such as uneven fixing. Thus, in order to increase the thermal conductivity of the elastic layer <NUM>, for example, a granular highly thermally conductive filler having a high thermal conductivity is preferably mixed and dispersed in the elastic layer <NUM>.

As the granular highly thermally conductive filler, at least one selected from the group consisting of silicon carbide (SiC), zinc oxide (ZnO), alumina (Al<NUM>O<NUM>), aluminum nitride (AlN), magnesium oxide (MgO), carbon, and the like is used. These can be used alone, or in mixture of two or more thereof.

The average particle diameter of the highly thermally conductive filler is preferably from <NUM> to <NUM> for handling, and from the viewpoint of the dispersibility. Further, for the shape, a spherical shape, a pulverized shape, a needle-shape, a sheet shape, a whisker shape, or the like is used. From the viewpoint of the dispersibility, a spherical shape is preferable. The thickness of the elastic layer <NUM> is preferably <NUM> to <NUM>, and more preferably <NUM> to <NUM> in order to obtain a good quality image due to sufficient elasticity, and in order to make favorable the time required for the temperature to reach a prescribed temperature by heating due to the heat capacity.

On a cured silicone rubber of the elastic layer <NUM>, the adhesive layer <NUM> for fixing the fluorine resin tube of the release layer <NUM> is formed. The adhesive layer <NUM> can be formed by, for example, coating an adhesive with a thickness of <NUM> to <NUM> on the surface of the elastic layer <NUM>, or other processes (an adhesive coating step of coating an adhesive on the outer circumferential surface of the cylindrical elastic layer).

Examples of the adhesive layer <NUM> may include a cured product of an addition curable silicone rubber adhesive. The addition curable silicone rubber adhesive <NUM> includes an addition curable silicone rubber mixed with a self-adhesive component. Specifically, the addition curable silicone rubber adhesive <NUM> includes organopolysiloxane having an unsaturated hydrocarbon group represented by a vinyl group, hydrogen organopolysiloxane, and a platinum compound as a crosslinkable catalyst. Then, curing is effected by the addition reaction.

The adhesive for use in the adhesive layer <NUM> has no particular restriction, and may only be selected in consideration of the materials for the elastic layer and the release layer. Known ones can be used.

The release layer includes a fluorine resin tube. The fluorine resin tube is preferably, for example, a cylindrically extruded product. For the release layer of the surface layer of a fixing member, for example, a fluorine resin tube by extrusion is used from the viewpoint of the moldability and the toner releasability. As the fluorine resin, a tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer (PFA) excellent in heat resistance is preferably used. For example, the release layer is preferably an extruded tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer (PFA tube).

The form of copolymerization of PFA serving as the raw material has no particular restriction. Examples thereof may include random copolymerization, block copolymerization, and graft copolymerization. Further, the content molar ratios of tetrafluoroethylene (TFE) and perfluoroalkyl vinyl ether (PAVE) in PFA serving as the raw materials have no particular restriction. For example, the one with a content molar ratio of TFE/PAVE of <NUM>/<NUM> to <NUM>/<NUM> can be preferably used.

Other than PFA, as a fluorine resin, mention may be made of a tetrafluoroethylene /hexafluoropropylene copolymer (FEP), polytetrafluoroethylene (PTFE), or an ethylene /tetrafluoroethylene copolymer (ETFE). Further, mention may be made of polyclorotrifluoroethylene (PCTFE), an ethylene / chlorotrifluoroethylene copolymer (ECTFE), polyvinylidene fluoride (PVDF), and the like. Then, the fluorine resins can be used alone singly, or in combination of a plurality thereof.

The thickness of the release layer <NUM> is preferably set at <NUM> or more in order to keep the function as the release layer through endurance in consideration of the wear by rubbing with the sheet. On the other hand, when the thickness is set too large, the reduction of the thermal efficiency arising from an increase in thermal resistance, and an increase in contact thermal resistance with the sheet arising from the lack of the flexibility cause the reduction of the energy saving performance and the image quality. Accordingly, the thickness is desirably <NUM> or less. For example, the thickness of the release layer is preferably <NUM> to <NUM>, <NUM> to <NUM>, or <NUM> to <NUM>.

In the present Example described later, as a fluorine resin tube, a tube including PFA with a thickness of <NUM> to <NUM> manufactured by extrusion (which will be hereinafter also referred to as a "PFA tube") was used. The inner surface of the PFA tube is preferably previously subjected to a sodium treatment, an excimer laser treatment, an ammonia treatment, or the like. This is because the wettability with the addition curable silicone rubber adhesive and the adhesion after curing can be improved.

The release layer <NUM> is formed by covering the top of the outer circumferential surface of the elastic layer <NUM> coated with the addition curable silicone rubber adhesive <NUM> with a PFA tube by a known technology. In Example described later, the method in which the PFA tube is vacuum extended externally for covering (vacuum extension covering method) was used.

The excess addition curable silicone rubber adhesive <NUM> not contributing to adhesion, and air sucked upon tube covering are present between the PFA tube after covering and the elastic layer <NUM>. In order to squeeze out the excess adhesive <NUM> and the air, using the method in which a ring-shaped nozzle slightly larger than the outer diameter of the fixing film is moved in the longitudinal direction of the fixing film while emitting an air from the nozzle, thereby squeezing out them, the method for squeezing out them using an O ring smaller than the outer diameter of the fixing film, or another method, the excess adhesive <NUM> and the air are removed.

Then, heating is performed for a prescribed time by a heating means such as an electric furnace, thereby curing / bonding the addition curable silicone rubber adhesive <NUM>, and cutting both edges to a desirable length. As a result, a fixing film can be obtained.

For the fixing film in accordance with one aspect of the present disclosure, the crystal orientation state of the release layer <NUM> is varied according to the position in the direction along the rotational axis. One example of a specific manufacturing method of such a fixing film will be described. For the heat treatment of the release layer (fluorine resin tube), an erect type and cylindrical heating cylinder capable of heating to a temperature of <NUM> or more is used for heating the entire region of the fixing film. In Example described later, a heating cylinder with an inner diameter of <NUM> was used according to the outer diameter of the fixing film of <NUM>. The inner surface of the heating cylinder has been subjected to heat resistant black coating.

Further, band heaters are set dividedly at at least <NUM> sites of upper, middle, and lower parts of the heating cylinder so as to perform control by changing the heating temperature according to the position in the direction along the axis of the fixing film. A thermocouple capable of independently controlling the temperature is mounted at each band heater. As a result of this, a heat treatment is performed by controlling the heating temperature to a different temperature according to the direction along the axis of the fixing film, thereby varying the crystal orientation state of the release layer <NUM> between in the regions corresponding to the edge regions on both sides in the direction along the axis, and in the region corresponding to the central region. For the fluorine resin tube of the cylindrically extruded product of a resin mixture including a fluorine resin, the molecules of the fluorine resin are oriented in the extrusion direction. Therefore, regarding the fixing film obtained by covering the elastic layer with the fluorine resin tube, in the release layer including the fluorine resin tube, the molecules of the fluorine resin are oriented in the direction along the rotational axis of the fixing film.

Such a fluorine resin tube is preferably heated at a temperature of not exceeding the melting temperature of a fluorine resin, for example, for the regions corresponding to the edge regions each up to <NUM> from the edges on both the sides in the direction along the rotational axis of the fixing film. For example, when the fluorine resin is PFA, the temperature of the heat treatment of the region corresponding to the edge region is preferably <NUM> to <NUM>, more preferably <NUM> to <NUM>, and further preferably <NUM> to <NUM>.

Further, the central region with a length of <NUM> of the central part in the direction along the rotational axis present between the regions each up to <NUM> from both the edges of the fixing film is preferably heated to a temperature equal to or higher than the melting temperature of the fluorine resin, to be heat treated. For example, when the fluorine resin is PFA, the temperature of the heat treatment is preferably <NUM> to <NUM>, more preferably <NUM> to <NUM>, and further preferably <NUM> to <NUM>.

The heating time may only be a time such that the temperature of the release layer can sufficiently reach a desirable temperature. Mention may be made of, for example, <NUM> to <NUM> minutes, <NUM> to <NUM> minutes, and <NUM> to <NUM> minutes.

In the present disclosure, X represents the value (Ic/Ia) of the ratio of the maximum X-ray diffraction strength Ic at 2θ = <NUM> to <NUM>° to the maximum X-ray diffraction strength Ia at 2θ = <NUM> to <NUM>° by the reflection X-ray diffraction method of the release layer.

Further, L represents the length in the direction along the rotational axis of the fixing film, Xe represents the average value of the values of X in the edge region with a length of up to <NUM> from the edge on each opposite side in the direction <NUM> along the rotational axis of the fixing film, and Xm represents the average value of the values of X in the central region with a length of <NUM> of the central part in the direction along the rotational axis present between the edge regions each with a length of up to <NUM> from the edge on each opposite side of the fixing film (<FIG>). At this step, the value (Xe /Xm) of the ratio of Xe to Xm is <NUM> or more.

As described previously, a value of Xe /Xm being <NUM> or more indicates that the crystallinity associated with the molecular orientation upon extrusion is higher in the edge regions than in the central region of the release layer. A value of Xe /Xm being <NUM> or more means that the orientation crystallinity of each edge region is higher than that of the central region. Namely, in the edge region, the orientation of the molecules of a fluorine resin in the direction along the rotational axis due to cylindrical extrusion is kept better. For this reason, the edge region is considered to be less likely to be worn even when coming in contact with the edge (edge part) of the sheet. Further, by setting the value of Xe /Xm at <NUM> or more, the orientation of the central part, namely, the region through which the sheet carrying a toner passes is relatively lower. Namely, in the central region in one fluorine resin tube, the molecular orientation of the fluorine resin in the direction along the rotational axis due to cylindrical extrusion is relaxed or eliminated. The heat transmitted from the heater in contact with the inner circumferential surface of the fixing film tends to be transmitted in the orientation direction of the molecules of the fluorine resin. For this reason, in the central region where the orientation in the direction along the rotational axis of the fluorine resin is relaxed or eliminated, the heat is less likely to be transmitted in the direction of the rotational axis, and tends to be transmitted in the thickness direction. As a result, in the central region, the heating efficiency of the unfixed toner on paper is improved, and the energy saving performance is improved. Furthermore, the crystallinity of the fluorine resin is low, and hence the flexibility is also improved, so that the occurrence of cracks can be suppressed.

The value of Xe / Xm is preferably <NUM> to <NUM>, and more preferably <NUM> to <NUM>. Alternatively, the value of Xe / Xm may be <NUM> to <NUM>.

The value of Xe /Xm can be increased by heat treating the central part of the fixing film covered with a PFA tube with a high orientation crystallinity upon extrusion to a temperature equal to, or higher than the melting point of PFA.

Further, the value of Xe /Xm can be reduced by not performing a heat treatment, reducing the difference in heating temperature between at the central part and at each edge for the heat treatment, or other procedures.

Xe preferably falls within the range of, for example, <NUM> to <NUM>, in particular preferably falls within the range of <NUM> to <NUM>, and further preferably falls within the range of <NUM> or more and less than <NUM>.

Xm preferably falls within the range of <NUM> to <NUM>, in particular preferably falls within the range of <NUM> to <NUM>, and is further preferably <NUM> or more and less than <NUM>.

Each value of Xe and Xm falling within the foregoing ranges can control the in-plane orientation of the crystal small, and facilitates control of tearing of the release layer in endurable use.

Xe can be made larger by raising the orientation at the time of extrusion of the PFA tube. Whereas, Xe can be made smaller by reducing the orientation at the time of extrusion.

Xm can be made larger by raising the orientation at the time of extrusion of the PFA tube as with Xe. Further, Xm can be made smaller by heat treating the central part of the fixing film to a temperature equal to or higher than the melting point of the PFA.

In accordance with at least one aspect of the present disclosure, it is possible to obtain a fixing film including a surface layer exhibiting the tear resistance in the direction along the rotational axis, and the wear resistance of the edge region on each opposite side in the direction along the rotational axis at a higher level even by long-term use. Further, in accordance with at least one aspect of the present disclosure, it is possible to obtain a heat fixing apparatus contributing to the stable formation of a high quality electrophotographic image. Still further, in accordance with at least one aspect of the present disclosure, it is possible to obtain an electrophotographic image forming apparatus capable of stably forming a high quality electrophotographic image. Furthermore, in accordance with at least one aspect of the present disclosure, it is possible to obtain a manufacturing method of a fixing film including a surface layer exhibiting the tear resistance in the direction along the rotational axis, and the wear resistance of the edge region on each opposite side in the direction along the rotational axis at a higher level even by long-term use.

Below, the present disclosure will be described by reference to Examples and Comparative Examples described later. However, the present disclosure should not be construed as being limited by the Examples.

First, the physical property evaluation method will be described. Measurement of Crystallinity of Release Layer: Reflection X-Ray Diffraction Method.

<FIG> is one example of the X-ray diffraction pattern obtained by the measurement. Ic represents the maximum X-ray diffraction strength of the diffraction peaks of the α type crystal (<NUM>) plane appearing at 2θ=<NUM> to <NUM>°. Further, Ia represents the maximum strength of the broad amorphous halo peak appearing at 2θ = <NUM> to <NUM>° (the maximum X-ray diffraction strength at 2θ = <NUM> to <NUM>°). Then, X = Ic/Ia of the ratio thereof was assumed to be the index for the crystallinity and the orientation. Incidentally, for Ic and Ia, the value obtained by deducting the X-ray diffraction strength at 2θ = <NUM> to <NUM>° as the reference was used in order to eliminate the influence from the base line.

Further, the X-ray diffraction measurement of the release layer <NUM> was performed every <NUM> in length in the direction along the rotational axis of the fixing film, thereby calculating X at each measurement position. Incidentally, <NUM>-point measurement positions were evenly provided in the circumferential direction at respective positions every <NUM> in the length in the direction along the rotational axis.

As shown in <FIG>, Xe represents the average value of the values of X in the region (edge region) with a length of <NUM> from each opposite end in the direction along the rotational axis where L represents the length in the direction along the rotational axis of the fixing film <NUM>. Whereas, Xm represents the average value of the values of X in the central region with a length of <NUM> at the central part in the direction along the rotational axis sandwiched between the edge regions with a length of <NUM> from the edges on both sides in the direction of the rotational axis.

Then, the evaluation method of the fixing film will be described.

The durability evaluation of the fixing film <NUM> was performed using the film heating system fixing apparatus <NUM> shown in <FIG> including each fixing film of Examples and Comparative Examples mounted therein. With the pressurizing force set at <NUM> N on one end side, and the total pressurizing force set at <NUM> N (<NUM> kgf), rotational driving was caused so that the moving speed (peripheral speed) of the pressure roller surface may become <NUM> /sec. Thus, with the paper feeding part surface temperature of the fixing film being temperature-controlled to <NUM>, <NUM>,<NUM> A4-sized paper sheets (trade name: GF-C068; manufactured by CANON Corporation) was fed continuously in the transverse direction at a speed of <NUM> sheets per minute. The portions of the edge regions of the fixing film after feeding <NUM>,<NUM> paper sheets with which the edge part of the paper came in contact were visually observed, and the wear resistance of each edge region was evaluated on the basis of the following criteria.

The same fixing apparatus as the fixing apparatus used for the evaluation of the wear resistance of the edge region was separately prepared. Then, the fixing apparatus was mounted on an electrophotographic image forming apparatus (trade name: imageRUNNER ADVANCE DX C5870F; manufactured by CANON Corporation). Then, <NUM>,<NUM> A4-sized paper sheets (trade name: GF-C068; manufactured by CANON Corporation) were fed continuously in the transverse direction at a speed of <NUM> sheets per minute. Then, one coated paper (trade name: OK Top Coat <NUM>/m<NUM>; manufactured by Oji Paper Co. , SRA3 size (<NUM> x <NUM>) was fed every time <NUM>,<NUM> A4-sized paper sheets had been fed, thereby forming a black lattice image on the entire surface of the coated paper. Then, the resulting five black lattice images were visually observed, and were evaluated on the basis of the following criteria.

The same fixing apparatus as the fixing apparatus used for the evaluation of the wear resistance of the edge region was separately prepared. The fixing apparatus was mounted on an electrophotographic image forming apparatus (trade name: imageRUNNER ADVANCE DX C5870F; manufactured by CANON Corporation), and under environment of a temperature of <NUM> and a relative humidity of <NUM>%, the paper feeding part surface temperature of the fixing film was temperature-controlled to <NUM>. Using the electrophotographic image forming apparatus, a black lattice image was formed on the entire surface of the A4-sized paper (trade name: GF-C068; manufactured by CANON Corporation). <NUM>,<NUM> A4-sized paper sheets were fed continuously in the transverse direction at a speed of <NUM> sheets per minute. Then, evaluation was performed on the basis of the following criteria. Herein, for comparison of the power reduction rate in the present evaluation, Comparative Example <NUM> was assumed to be the reference for Example <NUM>. Comparative Example <NUM> was assumed to be the reference for Example <NUM>. Comparative Example <NUM> was assumed to be the reference for Example <NUM>. Comparative Example <NUM> was assumed to be the reference for Example <NUM>. Comparative Example <NUM> was assumed to be the reference for Example <NUM>. Further, Comparative Example <NUM> was assumed to be the reference for Comparative Example <NUM>. For this reason, in the item of the energy saving performance evaluation in Table <NUM>, "-" is described for Comparative Examples <NUM> to <NUM>. Also, "-" is described for Comparative Examples <NUM> because the evaluation of the energy saving performance was not conducted on Comparative Example <NUM>.

As the electric power, the power applied to the heater to maintain the surface temperature of the paper feeding part of the fixing film at <NUM>° C was measured.

A SUS with an internal diameter of <NUM> and a thickness of <NUM> was used as the base material.

First, aromatic tetracarboxylic acid dianhydride or a derivative (<NUM>,<NUM>',<NUM>,<NUM>'-biphenyl tetracarboxylic acid dianhydride) and aromatic diamine (paraphenylene diamine) were allowed to react with each other in equimolar amounts in an aprotic polar organic solvent (N-methyl-<NUM>-pyrrolidone), resulting in a polyimide precursor solution. The resulting polyimide precursor solution was coated on the inner circumferential surface of the base material by the ring coating method, and was heated to <NUM> in an electric furnace. Thus, after drying the solvent, heating was performed at <NUM> for <NUM> minutes, and heating was further performed at <NUM> for <NUM> minutes, so that the polyimide precursor was imidized, thereby forming an inner surface sliding layer. The thickness of the inner surface sliding layer was set at <NUM>.

For the base material on which the inner surface sliding layer was formed, the primer layer and the elastic layer were formed in the following procedure.

Onto the base material, a hydrosilyl type silicone primer (DY39-<NUM> A/B (trade name); manufactured by DOW and TORAY Co. ) was coated, and heated and cured at <NUM> for <NUM> minutes. On the primer layer, alumina-containing addition reaction type liquid silicone rubber (DY35-<NUM> A/B) was coated as a thermally conductive filler, and was heated and cured at <NUM> for <NUM> minutes, thereby forming a silicone rubber elastic layer.

The thermal conductivity of the elastic layer <NUM> was <NUM> W/mK, and the thickness thereof was <NUM>.

After forming the elastic layer, on the elastic layer, an adhesive (SE1819CV A/B (trade name); manufactured by DOW and TORAY Co. ) was coated with a thickness of <NUM> using the ring coating method.

After coating the adhesive, as the release layer, a PFA tube was allowed to cover the top of the adhesive by the method of covering by external vacuum extension (vacuum extension covering method). Specifically, a PFA tube was adsorbed in a vacuum state on the inner surface of the outer cylinder having a larger inner diameter than the outer diameter of a work after formation of the elastic layer coated with the adhesive for diameter extension, and the work was inserted thereinto, followed by release of vacuum. As a result, the PFA tube was allowed to cover the top of the adhesive. The extra adhesive and air between the PFA tube and the elastic layer were squeezed out by an O ring, and then, were heated in an electric furnace, thereby curing and bonding the adhesive. Subsequently, both the edges were each cut to a prescribed length, resulting in a fixing film.

Incidentally, for the release layer of the fixing film, a PFA tube with a thickness of <NUM> and an inner diameter of <NUM> manufactured by extruding a PFA (trade name: NEOFLON PFA AP-231SH; manufactured by DAIKIN INDUSTRIES Ltd. ) as a raw material from a cylindrical die was used. Incidentally, the length L in the longitudinal direction of the tube was <NUM>. Further, the average value of the values of X measured at respective positions every <NUM> from one edge toward the other edge in the longitudinal direction of the tube was <NUM>. Further, in the fixing film with this tube attached, the average value of the values of X of the release layer (before heat treatment) measured at respective positions every <NUM> from one edge toward the other edge in the longitudinal direction of the fixing film was <NUM>. The reason why the value of X is larger than that of the tube is thought to be that the crystalline state of the tube (releasing layer) became higher by expanding the diameter of the tube and putting it on the adhesive layer.

The fixing film covered with the PFA tube as the release layer was inserted into a heating cylinder with a larger inner diameter than the outer diameter thereof, and the fixing film was heated. At this step, only the central region with a length in the direction along the rotational axis of the fixing film of <NUM> where L represents the length in the direction along the rotational axis of the fixing film was subjected to a heat treatment by a band heater in the heating cylinder inside corresponding to the length. The heating control temperature was set at <NUM>, and heating was controlled so that the body temperature of the release layer may become equal to, or higher than the melting temperature of PFA of <NUM>.

On the other hand, both the edge regions of the fixing film were heated and controlled at a temperature of not exceeding the melting temperature of PFA of <NUM>.

The heating time was set at <NUM> minutes after charging the fixing film into the heating cylinder as the time enough for allowing the body temperature of the release layer to reach the prescribed temperature. After an elapse of <NUM> minutes from charging, the fixing film was taken out from the heating cylinder to under normal temperature atmosphere, and the release layer was cooled, and crystallized.

The release layer was isolated from the fixing film subjected to the heat treatment. Specifically, the surface layer was removed together with the elastic layer from the base material. Thus, the elastic layer bonded with the surface layer was dissolved using a silicone resolvent (trade name: e SOLVE 21RS; manufactured by KANEKO CHEMICAL Co. ), thereby taking out only the release layer having an endless shape.

Using the resulting release layer, for the surface corresponding to the outer surface of the fixing film, X = Ic/Ia was measured with the reflection X-ray diffraction method described previously. Specifically, for the edge region with a length of up to <NUM> from the edge on each opposite side in the direction orthogonal to the circumferential direction (the direction along the axis) of the release layer, the values of X at positions every <NUM> were measured, and the average value Xe thereof was calculated. Further, for the central region situated between the edge regions, the values of X at positions every <NUM> were measured from one end toward the other end, and the average value Xm thereof was calculated. The values of Xe, Xm, and Xe /Xm are described in Table <NUM>.

Using the same raw materials as those for the PFA tube in accordance with Example <NUM>, a PFA tube with a thickness of <NUM> was prepared. The average value of the values of X measured at respective positions every <NUM> from one edge toward the other edge in the longitudinal direction of the tube was <NUM>. A fixing film and a release layer thereof were obtained in the same manner as in Example <NUM>, except for using the PFA tube. The average value of the values of X of the release layer before heat treatment was <NUM>.

As the raw material, PFA (trade name: Teflon PFA 959HPPlus; manufactured by Chemours-Mitsui Co. ) was extruded from a cylindrical die, thereby preparing a PFA tube with a thickness of <NUM>, and an internal diameter of <NUM>. The length L in the direction orthogonal to the circumferential direction of the tube was <NUM>. Further, the average value of the values of X measured at respective positions every <NUM> from one edge toward the other edge in the longitudinal direction of the tube was <NUM>.

A fixing film and a release layer thereof were obtained in the same manner as in Example <NUM>, except for using the PFA tube. The average value of the values of X of the release layer before heat treatment was <NUM>.

A fixing film was manufactured in the same manner as in Example <NUM>, except for not performing a heat treatment. The values of Xe and Xm of the release layer were obtained by the same reflection X-ray diffraction method as that of Example. Further, Xe/Xm was calculated from the values.

A PFA tube with a thickness of <NUM> was prepared in the same manner as in Example <NUM>, except for using "Algoflon PFA: F1520 (trade name: manufactured by Solvay Japan Co. The average value of the values of X measured at respective positions every <NUM> from one edge toward the other edge in the longitudinal direction of the tube was <NUM>.

Then, a fixing film was obtained in the same manner as in Example <NUM>, except for using the PFA tube, and not performing a heat treatment. The values of Xe and Xm of the release layer were obtained by the same reflection X-ray diffraction method as that of Example. Further, Xe/Xm was calculated from the values.

A fixing film was manufactured in the same manner as in Example <NUM>, except for performing the heat treatment of the release layer in the following manner. For the release layer isolated from the resulting fixing film, the values of Xe and Xm were obtained with the same reflection X-ray diffraction method as that in Example. Further, Xe/Xm was calculated from the values.

The heating cylinder used in Example <NUM> was used. However, heating was performed for <NUM> minutes with the heating control temperature set at <NUM> higher than the melting temperature of PFA in the entire region in the direction along the rotational axis of the fixing film. After heating, the fixing film was taken out from the heating cylinder, and was placed under normal temperature atmosphere, thereby crystallizing the PFA of the release layer.

As shown in the Examples <NUM> to <NUM>, with the fixing film in accordance with one aspect of the present disclosure, the average value Xe of the values of X of the release layer in each edge region is made <NUM> times or more as large as the average value Xm of the values of X in the central region. This can provide a fixing film which is favorable in energy saving performance while preventing the edge region to come in contact with the edge part of paper from being worn, and capable of preventing tear in the direction along the axis of the release layer in the central region.

The fixing film in accordance with Comparative Example <NUM> was more favorable in energy saving performance as compared with the fixing film in accordance with Comparative Example <NUM>. However, X was smaller than X of the fixing belt in accordance with Comparative Example <NUM> over the entire region in the direction along the rotational axis of the fixing film. For this reason, in the edge region, wear due to contact with the edge of paper was caused, so that enough durability could not be kept.

Further, each fixing film in accordance with Comparative Example <NUM> and Comparative Example <NUM> has large values of Xe and Xm, namely, is large in in-plane orientation of the crystal. For this reason, tear of the release layer is caused in endurable use.

Up to this point, the embodiments in accordance with the present disclosure were described. However, the present disclosure should not be construed as being limited to the foregoing aspect.

Claim 1:
A fixing film (2θ) having an endless shape, wherein
the fixing film comprises at least a base material (<NUM>), an elastic layer (<NUM>), and a release layer (<NUM>) in this order,
the release layer comprises a tube comprising a fluorine resin, and
a value of Xe/Xm is <NUM> or more, where
when,
in a chart of an X-ray diffraction peaks obtained by measuring the release layer with a reflection X-ray diffraction method, a maximum X-ray diffraction strength at 2θ = <NUM> to <NUM>° is defined as Ic, a maximum X-ray diffraction strength at 2θ = <NUM> to <NUM>° is defined as Ia, and a value of Ic/Ia is defined as X, and
a length in a direction along a rotational axis of the fixing film is defined as L,
Xe represents an average value of the X in an edge region up to <NUM> from each opposite edge in the direction along the rotational axis of the fixing film, and
Xm represents an average value of the X in a central region with a length in the direction along the rotational axis of <NUM> present between the two edge regions, measured according to the method defined in the description.