Patent Description:
In a fixing apparatus utilized in an electrophotographic image forming apparatus (hereafter also referred to as "image forming apparatus") such as a copier or a laser printer, rotating members in the form of a pair of heated rollers, a film and a roller, a belt and a roller, or a belt and a belt, are in pressure contact against each other. A recording medium such as paper, holding thereon an image formed by unfixed toner, is introduced into a pressure-contact portion (hereafter referred to as "fixing nip portion") formed between the rotating members, and the unfixed toner is melted through heating, to fix an image on the recording medium. The fixing rotating member with which the unfixed toner image on the recording medium comes into contact may be referred to as a fixing roller, a fixing film or a fixing belt, depending on the form in which the member is embodied.

Paper media used for forming electrophotographic images have become growingly diverse in recent years, and for instance there is a demand for accommodating thin paper, for instance paper having a basis weight of <NUM>/m<NUM>. In a conventional fixing member such as a fixing rotating member, however, molten toner at the time of heat fixing might in some instances adhere to the surface of the fixing rotating member, as a result the thin paper wraps around the fixing rotating member, on account of the low rigidity of such thin paper. In order to stably form electrophotographic images on thin paper it is thus necessary to impart higher toner releasability to the surface of the fixing rotating member. <CIT> discloses a fixing member whose a surface layer contains a fluororesin and a perfluoropolyether (hereafter also referred to as "PFPE"), such that the fixing member can maintain high toner releasability over long periods of time.

Studies by the inventors reveal that the fixing member according to <CIT> exhibits excellent toner releasability over long periods of time. However, <CIT> (paragraph [<NUM>]) indicates that fluorine oil is present, without phase separation from the fluororesin, in the surface layer of the disclosed fixing member. In such a case there is a limit to the amount of fluorine oil that can be incorporated into the surface layer. It was therefore found that in order to impart excellent toner releasability over longer periods of time to the fixing rotating member, a technique needs to be developed that aims at providing a fixing rotating member capable of holding a larger amount of PFPE and the PFPE can be supplied stably to the outer surface of the fixing rotating member.

<CIT> relates to a fixing member for electrophotography comprising: a base layer; an elastic layer that contains fluorine oil having a perfluoropolyether structure and fluororubber; and a surface layer that contains fluorine resin and fluorine oil having a perfluoropolyether structure, and has a porous structure having a plurality of pores.

<CIT> relates to a fixing member comprising a base layer, and a surface layer disposed directly or via a primer layer on the outer surface of the base layer, wherein the surface layer consists of a single layer, and contains a fluoro resin and a fluoro oil having a perfluoropolyether structure, wherein, when treatment (i) is performed on a measurement sample taken from the surface layer, the mass P11 of a deposit containing the fluoro oil and attached to a detection surface of a QCM sensor is <NUM>×<NUM><NUM> to <NUM>×<NUM><NUM> ng per unit area of the detection surface, and when treatment (ii) is performed on said measurement sample, the mass P12 of a deposit containing the fluoro oil and attached to the detection surface of the QCM sensor is <NUM>×P11 to <NUM>×P11 per unit area of the detection surface.

<CIT> relates to a method of forming a hydrophobic composite coating can include providing a substrate, wherein the substrate can include at least one region, the method can also include providing a dispersion including a plurality of carbon nanotubes, a stabilizer, a hydrophobic polymer, and a solvent, wherein the plurality of carbon nanotubes can be selected from the group consisting of single wall carbon nanotubes and multiple wall carbon nanotubes, and wherein each of the plurality of carbon nanotubes has an aspect ratio of at least about <NUM>, and the method can further include applying the dispersion to the one region to form a coated substrate and heating the coated substrate to form a hydrophobic composite coating such that the hydrophobic composite coating has a water contact angle of at least about <NUM>°.

At least one of aspects of the present disclosure is directed to providing a fixing rotating member capable of maintaining high toner releasability over longer periods of time than in conventional instances, and at providing a method for producing the fixing rotating member. Another aspect of the present disclosure is directed to providing a fixing apparatus and an electrophotographic image forming apparatus capable of stably forming high-quality electrophotographic images over long periods of time.

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

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

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

According to still another aspect of the present disclosure, there is provided a method as specified in claims <NUM> to <NUM>.

Further, in the present disclosure, the expression of "from XX to YY" or "XX to YY" indicating a numerical range means a numerical range including a lower limit and an upper limit which are end points, unless otherwise specified. When numerical value ranges are provided in stages, the upper limits and lower limits of the respective numerical values can be combined in any combination.

The inventors have conducted repeated studies with a view to obtaining a fixing rotating member capable of maintaining excellent toner releasability even upon prolonged use. As a result, the inventors found that the above goal can be attained by prescribing that a surface layer contains a tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA); the surface layer has pores having openings in a first surface that constitutes an outer surface of the fixing rotating member; at least part of the pores contains a perfluoropolyether; and an opening ratio P1 of the pores in the outer surface and a porosity P2 of the openings in a cross section are set to lie in the ranges set forth above.

Since the surface layer has pores, the surface layer can contain PFPE in the pores. As a result, a greater amount of PFPE can be held in the surface layer of the above fixing rotating member than in the surface layer disclosed in <CIT> in which PFPE is held within a fluororesin in a state without phase separation.

The openings of the pores are at the first surface of the surface layer, which constitutes an outer surface of the fixing rotating member, and hence the PFPE within the pores can migrate to the first surface. Further, the amount of PFPE that migrates from within the pores to the outer surface can be controlled by setting a relationship between a proportion P1 of opening area per unit area of the outer surface of the surface layer, and a proportion P2 of pore area per unit area of a cross section of the surface layer, to obey P2/P1≥<NUM>. It is considered that, as a result, the fixing rotating member according to the present aspect can maintain excellent toner releasability for longer periods of time than the fixing member according to <CIT>.

The reference symbols in the figures are as follows. <NUM>: resin portion containing PFA, <NUM>: openings, <NUM>: pores, <NUM>, PFPE, <NUM>: first surface.

The fixing rotating member will be described in detail below.

The fixing rotating member is for instance a fixing roller, a fixing film, a fixing belt or the like. The fixing rotating member has a base layer, an elastic layer and a surface layer, in this order.

<FIG> are cross-sectional diagrams illustrating different forms of fixing rotating members. <FIG> illustrates a fixing rotating member having an endless belt shape (hereafter also referred to as "fixing belt <NUM>"), and <FIG> illustrates a fixing rotating member having a roller shape (hereafter also referred to as "fixing roller <NUM>").

The fixing rotating members in <FIG> each have a base layer <NUM>, an elastic layer <NUM> that covers the outer surface of the base layer <NUM>, and a surface layer <NUM> that covers the surface, of the elastic layer, on the reverse side from that of the face opposing the base layer. The surface layer <NUM> may be bonded, by way of an adhesive not shown, to the surface of the elastic layer <NUM> on the reverse side from that opposing the base layer.

A known material used as a base layer of fixing members such as fixing rotating members can be utilized, without particular limitations, as the material of the base layer <NUM>. For instance, a metal or alloy such as aluminum, iron, stainless steel or nickel, or a heat-resistant resin such as polyimide, is used herein.

A base material having an endless belt shape may be used as the base layer <NUM> in the fixing belt <NUM>. Examples of the material of the base layer <NUM> in this case include materials exhibiting excellent heat resistance, such as nickel, stainless steel and polyimide. The thickness of the base layer <NUM> is not particularly limited, but is preferably from <NUM> to <NUM>, for instance from the viewpoint of strength, flexibility and heat capacity.

For instance a solid or hollow core metal is used as the base layer <NUM> in the fixing roller <NUM>. Examples of the material of the core metal include metals and alloys such as aluminum, iron and stainless steel. In a case where a hollow core metal is used, a heat source can be provided in the interior thereof.

The outer surface of the base layer <NUM> may be subjected to a surface treatment in order to impart adhesiveness towards the elastic layer <NUM>. The surface treatment that is resorted to may be a physical treatment such as blasting, lapping or polishing, or a chemical treatment such as an oxidation treatment, a coupling agent treatment or a primer treatment, singly or in the form of a combination of a plurality of treatments.

In a case where an elastic layer <NUM> containing silicone rubber is provided on the surface of the base layer <NUM>, it is preferable to perform a primer treatment on the surface of the base layer <NUM>, in order to improve adhesiveness between the base layer <NUM> and the elastic layer <NUM>.

Examples of primers used in primer treatments include coating materials in which a silane coupling agent, a silicone polymer, a hydrogenated methylsiloxane, an alkoxysilane, a reaction promoting catalyst and/or a colorant such as red iron oxide, are mixed and dispersed as appropriate in an organic solvent.

The primer can be selected as appropriate depending on the material of the base layer <NUM>, the type of the elastic layer <NUM>, and the form of crosslinking reactions. A primer containing hydrosilyl groups is preferably used in a case in particular where the elastic layer <NUM> contains a large amount of unsaturated aliphatic groups, in order to impart adhesiveness derived from a reaction with the unsaturated aliphatic groups. A primer containing unsaturated aliphatic groups is preferably used in a case where the elastic layer <NUM> contains a large amount of hydrosilyl groups,.

Other primers include primers containing alkoxy groups. A commercially available product can be used as the primer. The primer treatment includes a step of applying the primer onto the outer surface of the base layer <NUM> (surface bonded to the elastic layer <NUM>), with drying or baking.

The material of the elastic layer <NUM> is not particularly limited, and there can be used a known material utilized as an elastic layer in fixing rotating members. Preferably, the elastic layer <NUM> contains a silicone rubber having excellent heat resistance. An addition-curable liquid silicone rubber is preferably used as the starting material of the silicone rubber.

The thickness of the elastic layer <NUM> can be designed as appropriate taking into consideration the surface hardness of the fixing rotating member and the width of the fixing nip portion that is to be formed. In a case where the fixing rotating member is the fixing belt <NUM>, the thickness of the elastic layer <NUM> is preferably from <NUM> to <NUM>, more preferably from <NUM> to <NUM>.

In a case where the fixing rotating member is the fixing roller <NUM>, the thickness of the elastic layer <NUM> is preferably from <NUM> (<NUM>) to <NUM>, more preferably from <NUM> (<NUM>) to <NUM>.

By setting the thickness of the elastic layer <NUM> to lie within this range it becomes possible to secure a sufficient width of the fixing nip portion at a time where the fixing rotating member is built into the fixing apparatus.

By virtue of the fact that the elastic layer contains silicone rubber of poor chemical affinity with fluorine oils, the fluorine oil contained in the surface layer does not easily migrate to the elastic layer, even after prolonged use, and is solely supplied to the surface of the fixing rotating member.

The elastic layer <NUM> may contain a filler. The filler is added in order to control thermal conductivity, heat resistance and elastic modulus.

Specific examples include silicon carbide (SiC), silicon nitride (Si<NUM>N4), silica (SiO<NUM>), boron nitride (BN), aluminum nitride (AlN), alumina (Al<NUM>O<NUM>), iron oxide (Fe<NUM>O<NUM>), zinc oxide (ZnO), magnesium oxide (MgO), titanium oxide (TiO<NUM>), copper (Cu), aluminum (Al), silver (Ag), iron (Fe), nickel (Ni), carbon black (C), carbon fibers (C) and carbon nanotubes (C).

A surface layer <NUM> contains a tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA) and a perfluoropolyether (PFPE). As illustrated in <FIG>, the surface layer has pores <NUM> with openings at a first surface <NUM> that constitutes the outer surface of the fixing rotating member. The outer surface of the fixing rotating member is defined as the surface that comes in contact with unfixed toner on the material to be recorded at the time of fixing. Preferably, the pores <NUM> do not have a shell.

That is, the wall of the pores <NUM> is preferably made up of a solid portion of the surface layer, specifically, of a resin portion <NUM> that contains PFA.

At least part of the pores contains a perfluoropolyether (PFPE) <NUM>. For example, the pores are filled with PFPE.

The surface layer further satisfies the following requirement.

(Requirement) When a first observation region having <NUM> long × <NUM> wide is placed on the first surface of the surface layer after removing the PFPE in the pores with a solvent from the side of the first surface, and a ratio (hereafter also referred to as "opening ratio") of the total sum of the areas of the openings observed in the first observation region relative to the area of the first observation region is defined as P1. When a second observation region having <NUM> long × <NUM> wide is placed at a predetermined position in a cross section of the surface layer after removing the PFPE in the pores with a solvent from a side of the first surface, the cross section including an entire thickness portion of the surface layer along a circumferential direction of the fixing rotating member, and a ratio (porosity) of the total sum of the areas of the pores observed in the second observation region relative to the surface area of the second observation region is defined as P2. P1 and P2 satisfy the following relationship:
P2/P1 is <NUM> or higher.

By prescribing P1 and P2 to obey the above relationship, the surface layer can hold a sufficient amount of PFPE, and PFPE can be stably transferred to the first surface. Herein P2/P1 is preferably <NUM> or higher, more preferably <NUM> or higher. From the viewpoint of striking a balance between the amount of PFPE that the surface layer can hold and migration of PFPE to the first surface, the upper limit of P2/P1 is preferably <NUM> or lower, more preferably <NUM> or lower. That is, for example, preferable range of P2/P1 is <NUM> or higher, and <NUM> or lower.

Herein P1 is calculated in accordance with following method. The first surface of the surface layer constituting the outer surface of the fixing rotating member is observed with a scanning electron microscope, to obtain a SEM image (<NUM> magnifications) of an observation region <NUM> long × <NUM> wide of the first surface. The resolution (for instance <NUM> pixels longitudinally and <NUM> pixels transversally) is set herein so that individual openings can be recognized.

The SEM image is converted into an <NUM>-bit gray scale image using image processing software (product name: ImageJ, by the National Institutes of Health (NIH)). A median filter is applied to the obtained gray scale image, and thereafter a binarization process is further carried out using the above image processing software, to obtain a binarized image. The binarization process relies herein on the YEN method as disclosed in "<NPL>" in order to discriminate between portions corresponding to the openings, in the SEM image, and portions corresponding to PFA.

A ratio of the number of pixels of the portions corresponding to the openings in the obtained binarized image, relative to the number of pixels of the entire image, is then calculated. In the present disclosure observation regions are disposed at <NUM> arbitrary locations on the first surface of the surface layer, and the arithmetic mean value of the ratio calculated from each observation region is taken as P1. The <NUM> locations at which the observation regions are placed are set to positions such that the respective observation regions do not overlap each other. A concrete method involved will be described in examples described below.

Further, P2 is calculated in accordance with the following method. A sample of the surface layer is cut out such that on the sample there appears a cross section in a direction along the circumferential direction of the fixing rotating member, from the surface layer. The cross section includes the entire thickness portion of the surface layer. A predetermined position of the cross section of the sample thus cut out is observed using a scanning electron microscope, to yield a SEM image of a rectangular observation region <NUM> long × <NUM> wide of the cross section. The resolution (for instance <NUM> pixels longitudinally and <NUM> pixels transversally) is set so that the pores appearing in the cross section can be discerned.

The SEM image is binarized using numerical calculation software (product name: MATLAB; by The MathWorks, Inc. ) to obtain a binarized image. The binarization process relies on Otsu's method as disclosed in "<NPL>", in order to discriminate between portions corresponding to the pores and portions corresponding to PFA in the SEM image. A ratio of the number of pixels of the portions corresponding to the pores in the binarized image relative to the number of pixels of the entire image is then calculated. In the present disclosure, the following applies to the thickness direction of the surface layer in the cross section:.

Samples for the above operation are acquired from three locations at every <NUM>° in the circumferential direction of the fixing rotating member. Therefore, P2 is the arithmetic mean value of nine ratios above calculated from a total of nine SEM images.

Herein P1 is preferably <NUM>% or higher, more preferably <NUM>% or higher, and further <NUM>% or higher. The upper limit of P1 is preferably <NUM>% or lower, and more preferably <NUM>% or lower.

By virtue of the fact that P <NUM> is <NUM>% or higher, migration of PFPE in the pores towards the first surface of surface layer is hindered less readily, and stable toner releasability can be imparted to the first surface. When P1 is <NUM>% or lower, excessive migration of PFPE in the pores to the first surface can be suppressed, which contributes to maintaining stable toner releasability over long periods of time. Thus, for example, the preferable range of P1 is <NUM> % or higher and <NUM> % or lower, and more preferable range of P1 is <NUM>% or more and <NUM>% or lower.

Herein P2 is preferably <NUM>% or higher, more preferably <NUM>% or higher. The upper limit of P2 is not particularly restricted, but is preferably <NUM>% or lower, more preferably <NUM>% or lower.

When P2 is <NUM>% or higher, the surface layer can hold more PFPE and can impart stable toner releasability to the first surface over longer periods of time. On the other hand, wear of the surface layer can be better prevented by setting P2 to be <NUM>% or lower. Thus, for example, preferable range of P2 is <NUM>% or higher and <NUM>% or lower, and more preferable range of P2 is <NUM>% or higher and <NUM>% or lower.

The average opening diameter of the openings in the outer surface of the surface layer is preferably from <NUM> to <NUM>, more preferably from <NUM> to <NUM>. Keeping the average opening diameter within the above ranges contributes to maintaining superior toner releasability stably. The average opening diameter of the openings in the first surface is herein the average value of the diameters of circles having the same surface area as the surface area of portions corresponding to the openings, from the binarized image used for the calculation of P1 described above. The concrete method involved will be described further on.

The thickness of the surface layer is preferably from <NUM> to <NUM>, more preferably from <NUM> to <NUM>.

The PFA contained in the surface layer will be described in detail next.

Herein PFA is a copolymer of perfluoroalkyl vinyl ether (hereafter "PAVE") and tetrafluoroethylene (hereafter "TFE"). The number of carbon atoms of the perfluoroalkyl chain of PAVE is preferably <NUM> to <NUM>, more preferably <NUM> to <NUM>, and yet more preferably <NUM> to <NUM>.

Further, PAVE is preferably selected from among perfluoromethyl vinyl ether (CF<NUM>=CF-O-CF<NUM>), perfluoroethyl vinyl ether (CF<NUM>=CF-O-CF<NUM>CF<NUM>) and perfluoropropyl vinyl ether (CF<NUM>=CF-O-CF<NUM>CF<NUM>CF<NUM>).

The melting point of PFA is preferably <NUM> to <NUM>, more preferably <NUM> to <NUM>.

A commercially available product can be used as the PFA; concrete examples are given below.

The PFPE contained in at least part of the pores will be described in detail next. The PFPE in the pores may be referred to as a "second" PFPE in order to distinguish it from the below-described PFPE (first PFPE) used for forming the pores. However, this does not rule out the second PFPE being the same PFPE as the first PFPE.

The second PFPE is not particularly limited, and known instances of PFPE can be used.

As the second PFPE, PFPE having the structure represented by Formula (<NUM>) below may preferably be employed. The PFPE is preferably oily at the melting point of PFA.

In Formula (<NUM>), a, b, c, d, e and f are each independently <NUM> or a positive integer, satisfy <NUM>≤a+b+c+d+e+f≤<NUM>, and at least one from among a, b, c and d represents a positive integer.

Further, the order in which each repeating unit is present in Formula (<NUM>) is not limited to the order described above. Further, each repeating unit in Formula (<NUM>) may be present at a plurality of sites in the PFPE. That is, the PFPE represented by Formula (<NUM>) may be a block copolymer or a random copolymer.

Examples of commercially available PFPE include for instance a PFPE having the structure represented by Formula (<NUM>) below (for instance Demnum S-<NUM> and Demnum S-<NUM> (both product names); by Daikin Industries, Ltd. ), PFPE having the structure represented by Formula (<NUM>) below (for instance Krytox XHT-<NUM>, Krytox VPF16256, Krytox GPL-<NUM>, Krytox GPL-<NUM>, Krytox GPL-<NUM>, Krytox GPL-<NUM>, Krytox GPL-<NUM>, Krytox GPL-<NUM> and Krytox GPL-<NUM> (all product names); by The Chemours Company), PFPE having the structure represented by Formula (<NUM>) below (for instance Fomblin M60, Fomblin M100 and Fomblin Z25 (all product names); by Solvay Specialty Polymers Co. ), and PFPE represented by Formula (<NUM>) below (for instance Fomblin Y45 and Fomblin Y25 (both product names); by Solvay Specialty Polymers Co.

Preferably, the perfluoropolyether has at least one structure selected from the group consisting of Formulas (<NUM>) to (<NUM>) below.

In Formula (<NUM>), n is a positive number, n lying in a range such that PFPE viscosity at a temperature of <NUM> ranges <NUM> to <NUM> mPa s.

In Formula (<NUM>), n' is a positive number, n' lying in a range such that PFPE viscosity at a temperature of <NUM> ranges <NUM> to <NUM> mPa s.

In Formula (<NUM>), n" and m are each independently a positive number, m/n" is a number from <NUM> to <NUM>, and n"+m is a number lying in a range such that PFPE viscosity at a temperature of <NUM> ranges <NUM> to <NUM> mPa s.

In Formula (<NUM>), n‴ and m' are each independently a positive number, m'/n‴ is a number from <NUM> to <NUM>, and n‴+m' is a number lying in a range such that PFPE viscosity at a temperature of <NUM> ranges <NUM> to <NUM> mPa·s.

The viscosity of the second PFPE is preferably <NUM> mPa s to <NUM> mPa s, more preferably <NUM> mPa s to <NUM> mPa s. Herein a PFPE within such a viscosity range contributes to a stable migration thereof from the pores to the first surface of the surface layer.

The term viscosity as used herein denotes a value of viscosity obtained after <NUM> seconds of rotation at a shear velocity of <NUM>-<NUM> and at a measurement temperature of <NUM> using a rheometer (by TA Instruments Inc. : DHR-<NUM>) having attached thereto a cone plate having a cone angle of <NUM>° and a cone radius of <NUM>.

Examples of commercially available PFPE within the above viscosity range include for instance "Krytox GPL-<NUM>" (viscosity <NUM> mPa·s), "Krytox GPL-<NUM>" (viscosity <NUM> mPa s), "Krytox GPL-<NUM>" (viscosity <NUM> mPa s), "Krytox VPF16256" (viscosity <NUM> mPa s), "Krytox XHT-<NUM>" (viscosity <NUM> mPa s), "Fomblin M60" (viscosity <NUM> mPa·s) and "Fomblin M100" (viscosity <NUM> mPa·s).

The content of perfluoropolyether in the surface layer is preferably from <NUM> mass% to <NUM> mass%, more preferably from <NUM> mass% to <NUM> mass%. When the content is <NUM> mass% or higher, toner releasability is yet better preserved over long periods of time. When the content is <NUM> mass% or lower, wear arising from the use of the surface layer can be more reliably prevented.

A non-limiting exemplary method for producing the above-described fixing rotating member according to one aspect of the present disclosure includes steps (i) through (v) below.

Step (i): step of providing a layered body comprising a base layer having an endless belt shape or a roller shape, an elastic layer on an outer peripheral surface of the base layer, and a resin layer comprising PFA, on an outer peripheral surface of the elastic layer.

Step (ii): a step of bringing the first PFPE, at a temperature near the melting point of PFA, into contact with the surface, of the resin layer, on the reverse side from that facing the elastic layer, to thereby impregnate the resin layer with the first PFPE;.

The inventors conjectured the following concerning the mechanism whereby the fixing rotating member according to one aspect of the present disclosure is formed by resorting to the above method.

In step (ii), the first surface of the resin layer is brought into contact with the first PFPE at a temperature near the melting point of the PFA contained in the resin layer (temperature of <NUM>± <NUM> (preferably of <NUM> to <NUM>)), as a result of which the resin layer becomes impregnated with the first PFPE.

The resin layer impregnated with the first PFPE in step (ii) is in a high-temperature state, and accordingly the resin layer is cooled down to room temperature of, for instance about <NUM>, in step (iii) subsequent to into step (ii). In step (iv), next, the first PFPE in the resin layer is removed using a solvent, as a result of which there are formed pores having openings in the first surface of the resin layer at sites where the first PFPE in the resin layer was present.

The surface area proportion P2 of the pores per unit area in a cross section parallel to the circumferential direction of the surface layer having undergone step (iii) and step (iv) above is higher than a surface area proportion P1 of the openings per unit area in the first surface. It is considered that the reason is as follows.

When the PFA tube having thermally expanded on account of the heating in step (ii) shrinks in the cooling process of step (iii), cooling progresses more quickly at the first surface of the resin layer, and accordingly the extent of shrinkage is larger, than at the elastic layer-side surface of the resin layer. The first PFPE present in the vicinity of the first surface of the resin layer is pushed out of the resin layer from the first surface accompanying shrinkage of the first surface side. The diameter of the openings in the first surface of the resin layer shrinks as a result. On the other hand, the first PFPE having permeated deep into the resin layer, in the thickness direction thereof, for instance down to a position in the vicinity of the surface on the elastic layer side, is not released to the exterior of the resin layer even upon shrinkage of the resin layer, but remains within the resin layer. The aggregate portions of the first PFPE, which constitute voids after removal of the first PFPE exhibit therefore virtually no reduction in size. The proportion (P2/P1) of the porosity P2 relative to the opening ratio P1 of the first surface of the surface layer formed in step (iv) increases as a result.

Herein the value of P2/P1 can be adjusted on the basis of the impregnation amount of the first PFPE into the resin layer in step (ii). Specifically, increasing the impregnation amount of the PFPE into the resin layer allows increasing the voids formed in the interior of the resin layer, such that the value of P2 increases. Increasing the amount of impregnation into the resin layer translates into a greater number of openings in the first surface of the resin layer as well, and therefore likewise in an increased value of P1. Although the underlying reasons are unclear, the degree of increase in P1 derived from the increase in the amount of impregnation in the resin layer is larger than the degree of increase in P2. Accordingly, P2/P1 can be adjusted to be smaller by increasing the amount of first PFPE impregnated into the PFA tube.

To achieve the above preferable range of P2, the resin layer is preferably impregnated with the first PFPE so that the impregnation amount of the first PFPE into the resin layer in step (ii), in the form of the content ratio for the first PFPE relative to the mass of the resin layer that contains the first PFPE, is preferably <NUM> mass% to <NUM> mass%, and particularly preferably <NUM> mass% to <NUM> mass%.

The impregnation amount of the first PFPE into the resin layer can be adjusted for instance on the basis of the temperature of the first PFPE, the viscosity of the first PFPE and the contact time between the resin layer and the first PFPE at the time of impregnation. Specifically, the higher the temperature within a temperature range near the melting point of PFA (temperature of <NUM> to <NUM>), the lower is the viscosity of the first PFPE, the longer is the contact time, and the greater can be made the impregnation amount of the first PFPE into the resin layer.

A preferable viscosity of the first PFPE is <NUM> mPa s to <NUM> mPa s, more preferably <NUM> mPa s to <NUM> mPa s.

Examples of commercially available PFPE in such viscosity ranges include "Krytox GPL-<NUM>" (viscosity <NUM> mPa s), "Krytox GPL-<NUM>" (viscosity <NUM> mPa s), "Krytox GPL-<NUM>" (viscosity <NUM> mPa·s), "Krytox GPL-<NUM>" (viscosity <NUM> mPa·s), "Fomblin M03" (viscosity <NUM> mPa·s) and "Krytox GPL-<NUM>" (viscosity <NUM> mPa·s).

Herein a PFPE-impregnated resin layer having a content of the first PFPE of <NUM> mass% can be produced over a contact time of <NUM> minute in a case for instance where the viscosity of the first PFPE is <NUM> mPa·s, the thickness of the resin layer containing the PFA is <NUM>, the melting point of the resin layer is <NUM>, and the temperature at the time of contact between the resin layer and the first PFPE is <NUM>.

The term content is herein defined as the percentage (%) of the mass of the PFPE impregnated into the resin layer with respect to the sum of the mass of the resin layer itself plus the mass of the PFPE impregnated into the resin layer.

In a case where in the above example PFPE having a viscosity of <NUM> mPa·s is used as the first PFPE while other conditions remain the same, a PFPE-impregnated resin layer can be produced in which the content of the first PFPE is <NUM> mass%. In a case where in the above example the temperature at the time of contact is set to <NUM> while other conditions remain the same, a PFPE-impregnated resin layer can be produced in which the content of the first PFPE is <NUM> mass%.

The viscosity of "Krytox GPL106" as the PFPE used in the examples of <CIT> is <NUM> mPa·s. Upon contact of such PFPE with a resin layer containing PFA, at a temperature of <NUM> for <NUM> minutes, a PFPE-impregnated resin layer was obtained that had a PFPE content of <NUM> mass%. When the content of PFPE stands at that level, however, there is no PFPE aggregation within the resin layer. Accordingly, pores did not form in the resin layer, even upon subsequent elution of the PFPE using a fluorine-based solvent.

Any method can be used as the contact method of the resin layer and the first PFPE in the production of the fixing rotating member, so long as the PFPE can be brought into contact with the resin layer at a temperature near the melting point of the PFA resin contained in the resin layer.

Further, the resin layer that is brought into contact with the first PFPE may be a resin layer in a layered body in which a base layer, an elastic layer, and a resin layer are laid up on each other beforehand; alternatively, there may be prepared a PFA sheet or PFA tube for the resin layer, in a state where the surface to be bonded to the elastic layer is masked. For instance, a dipping method is a further example of the contact method.

In order to remove the first PFPE impregnated into the resin layer in step (iv) the first surface of the resin layer is immersed in a solvent capable of dissolving the first PFPE but which does not dissolve PFA, so that the first surface of the resin layer is wetted. The "solvent that dissolves PFPE" may be for instance a solvent such that the dissolution amount of PFPE in <NUM> of the solvent at <NUM> is <NUM> or greater. Meanwhile, the term "solvent which does not dissolve PFA" includes solvents such that the dissolution amount of PFA in <NUM> of the solvent at <NUM> is <NUM> or smaller. Examples of such a solvent include a hydrofluoroether (product name: Novec <NUM>; by The <NUM> Company).

To remove the first PFPE from the resin layer in step (iii) it is preferable to apply ultrasounds to the resin layer so as to promote removal of the first PFPE from the resin layer.

A method for producing a fixing rotating member according to one aspect of the present disclosure will be described more specifically next.

Step (i): A layered body being a stack of a base layer, an elastic layer containing silicone rubber, and a resin layer containing PFA, in this order, is mounted on a dipping device.

Step (ii): the layered body is immersed in a bath of PFPE heated to near the melting point of PFA (<NUM>±<NUM> (preferably <NUM> to <NUM>)), and is allowed to stand preferably for <NUM> seconds to <NUM> minutes, more preferably for <NUM> seconds to <NUM> minutes (for instance for <NUM> minute) (impregnation step -<NUM>).

It was found that in (impregnation step - <NUM>) the impregnation amount increases as the contact temperature between the resin layer and the first PFPE increases and as the viscosity of PFPE decreases. The contact temperature and the viscosity of PFPE can be selected as appropriate, so long as an impregnation amount is achieved which is equal to or greater than a given amount that allows forming the above specific pores.

Defining X°C as the heating temperature of the first PFPE in impregnation step -<NUM> and Y°C as the melting point of PFA, preferably X-Y is <NUM> to <NUM>, more preferably <NUM> to <NUM>.

Step (iii): the layered body is removed from the bath of the first PFPE bath, and is cooled down to room temperature.

Step (iv): after cooling, the layered body is impregnated with the solvent capable of dissolving the first PFPE, to elute the first PFPE impregnated into the resin layer, from the openings of the first surface of the resin layer (pore formation step). Pores having openings in the first surface become formed in the resin layer as a result of this step.

Step (v-<NUM>): the layered body provided with the resin layer having pores and obtained as a result of the above steps is then immersed in a bath of the second PFPE, and is allowed to stand, preferably for <NUM> to <NUM> minutes, more preferably for <NUM> minutes to <NUM> minutes (for instance <NUM> minutes). As a result the second PFPE becomes incorporated into the pores in the resin layer (impregnation step - <NUM>).

The temperature of the second PFPE at this time is preferably a temperature that allows promoting impregnation of the second PFPE into the pores but such that the openings in the first surface of the resin layer do not disappear. As a non-limiting example, the lower limit of the temperature of the second PFPE in this step is preferably <NUM> or higher, and the upper limit is preferably <NUM> or lower, more preferably <NUM> or lower.

Step (v-<NUM>): the layered body obtained as a result of the above steps is retrieved from the bath of the second PFPE, and the second PFPE adhered to the outer surface is removed, to thereby yield a fixing rotating member according to one aspect of the present disclosure.

In the present step, the method for removing the excess amount of the second PFPE adhered to the surface is not particularly limited, and examples thereof include washing with a fluorosolvent, removal with air, and wipe-off using a nonwoven fabric. Examples of methods for washing with a fluorosolvent include a removal method using fibers such as a nonwoven fabric, impregnated with a fluorosolvent.

The fixing apparatus includes a fixing rotating member and a heating means for heating the fixing rotating member. The fixing apparatus includes for instance a heating rotating member, and a pressing rotating member disposed so as to form a fixing nip portion with the heating rotating member.

Examples of a combination of a heating rotating member and a pressing rotating member include for instance a heat roller and an elastic pressure roller disposed opposing the heat roller, and a heating film and an elastic pressure roller disposed in contact with the heating film. Other examples of a combination of a heating rotating member and a pressing rotating member include a heating belt and an elastic pressure roller disposed in contact with the heating belt, and a heating belt and an elastic pressure belt disposed in contact with the heating belt.

<FIG> is a cross-sectional diagram of a fixing apparatus having the fixing belt <NUM> for heating and an elastic pressure roller <NUM>, along the circumferential direction of a fixing belt.

The fixing belt <NUM> is the fixing belt described as the above fixing rotating member. The fixing belt <NUM> is loosely fitted from outside a belt guide member <NUM>. A pressing rigid stay <NUM> is inserted inward of the belt guide member <NUM>. The belt guide member <NUM> is formed of for instance a heat-resistant / heat-insulating resin.

The heating means is for instance a heater disposed in contact with the inner peripheral surface of the fixing belt. A ceramic heater <NUM> as a heat source is provided at a position at which the belt guide member <NUM> and the inner surface of the fixing belt <NUM> are in contact with each other. The ceramic heater <NUM> is fitted to and fixed in a groove provided along the longitudinal direction of the belt guide member <NUM>. The ceramic heater <NUM> generates heat through energization by a means not shown.

The elastic pressure roller <NUM> is provided for instance with an elastic layer 19b containing a cured silicone rubber, on the peripheral surface of a core metal 19a made of stainless steel. A surface layer 19c containing a fluororesin is provided on the peripheral surface of the elastic layer 19b. The thickness of the surface layer 19c is for instance <NUM>.

A push-down force is exerted on the pressing rigid stay <NUM> by arranging pressure springs (not shown) between both ends of the pressing rigid stay <NUM> and spring receiving members (not shown) on the device chassis side. As a result, the lower face of the ceramic heater <NUM> disposed on the lower face of the belt guide member <NUM> and the top face of the elastic pressure roller <NUM> are pressed against each other, with the fixing belt <NUM> nipped in between, to form a predetermined fixing nip portion N. That is, the lower face of the ceramic heater <NUM> is disposed in contact with the inner peripheral surface of the fixing belt <NUM>.

A recording medium P as a body to be heated having formed thereon an image by unfixed toner G is nipped and transported in the fixing nip portion N at a transport speed V. The toner image is heated and pressed as a result. In consequence the toner image melts, with color mixing, after which the toner image is cooled, whereby a toner image becomes fixed as a result on the recording medium P.

<FIG> is a cross-sectional diagram along the circumferential direction of a fixing roller in a heat fixing apparatus that is provided with the fixing roller <NUM> for heating, the elastic pressure roller <NUM> disposed opposing the fixing roller <NUM>, and a heater <NUM> which is a heating means of the fixing roller <NUM>.

The fixing roller <NUM> is the fixing roller described as the above fixing rotating member. In the fixing roller <NUM> there are formed the elastic layer <NUM> on the outer peripheral surface of a hollow core metal as the base layer <NUM>, and the release surface layer <NUM> on the outer side of the elastic layer <NUM>.

The fixing roller <NUM> and the elastic pressure roller <NUM> are rotatably pressed against each other, by a pressure means not shown, so that the fixing nip portion N is formed as a result.

The heater <NUM> as a heat source for supplying heat necessary for melting the unfixed toner G is installed inside the fixing roller <NUM> and inside the elastic pressure roller <NUM>. A halogen heater is generally used as the heater <NUM>. A plurality of halogen heaters may be installed in the interior of the rollers depending on the size of the recording medium P to be transported.

Respective rotational forces are applied to the fixing roller <NUM> and the elastic pressure roller <NUM> through the ends of the base layer (core metal) <NUM> and the core metal 19a, by a means not shown, the rotation being controlled herein so that the moving speed of the surface of the fixing roller <NUM> is substantially equal to the transport speed V of the recording medium P. At this time, the rotational force may be applied to either one of the fixing roller <NUM> and the elastic pressure roller <NUM> having elasticity, so that the other roller rotates by being driven; alternatively, the rotational force may be applied to both rollers.

The recording medium P that is a body to be heated having formed thereon an image by the unfixed toner G is nipped and transported at the fixing nip portion N of the fixing apparatus formed as described above. The toner image is heated and pressed as a result. In consequence the toner image melts, with color mixing, after which the toner image is cooled, and a toner image becomes fixed as a result on the recording medium P.

A known configuration can be adopted as the electrophotographic image forming apparatus. Such apparatuses include multifunction devices, copiers, fax machines and printers that utilize an electrophotographic system. The overall structure of an electrophotographic image forming apparatus will be explained schematically herein using a color laser printer as an example.

<FIG> is a schematic cross-sectional diagram of a laser printer <NUM>. The laser printer <NUM> illustrated in FIG. <NUM> has respective "electrophotographic photosensitive member drums <NUM> (hereafter referred to as "photosensitive member drums <NUM>") that rotate at a constant speed for each respective color including yellow (Y), magenta (M), cyan (C) and black (K). The laser printer <NUM> further has an intermediate transfer member <NUM> which holds a color image, developed at an image forming section and resulting from multiple transfer, and which transfers the color image to the recording medium P that is fed from a feeding unit.

Each photosensitive member drum <NUM> (39Y, <NUM>, 39C, <NUM>) is rotationally driven counterclockwise, as illustrated in <FIG>, by a driving means (not shown).

Around each photosensitive member drum <NUM> there are sequentially disposed, according to the rotation direction thereof, a respective charging device <NUM> (21Y, <NUM>, 21C, <NUM>) that charges uniformly the surface of the photosensitive member drum <NUM>, a respective scanner unit <NUM> (22Y, <NUM>, 22C, <NUM>) that projects a laser beam, on the basis of image information, to form an electrostatic latent image on the photosensitive member drum <NUM>, a respective developing unit <NUM> (23Y, <NUM>, 23C, <NUM>) that causes toner to adhere onto the electrostatic latent image, to thereby develop the toner in the form of a toner image, a respective primary transfer roller <NUM> (24Y, <NUM>, 24C, <NUM>) that transfers the toner image on the photosensitive member drum <NUM> to the intermediate transfer member <NUM>, at a primary transfer section T1, and a respective cleaning unit <NUM> (25Y, <NUM>, 25C, <NUM>) having a cleaning blade that removes untransferred toner remaining on the surface of the photosensitive member drum <NUM> after transfer.

At the time of image formation, the belt-shaped intermediate transfer member <NUM> spanned around rollers <NUM>, <NUM> and <NUM> rotates and the color toner images formed on respective photosensitive member drums <NUM> undergo primary transfer, superimposed on each other, onto the intermediate transfer member <NUM>, so that a color image is formed as a result.

The recording medium P is then transported to a secondary transfer section T2 by a transport means, in synchrony with primary transfer to the intermediate transfer member <NUM>. The transport means includes a feed cassette <NUM> that accommodates a plurality of sheets of the recording medium P, a feed roller <NUM>, a separation pad <NUM>, and a resist roller pair <NUM>. At the time of image formation, the feed roller <NUM> is rotationally driven in accordance with the image forming operation, the recording medium P in the feed cassette <NUM> is separated sheet by sheet, and is transferred by the resist roller pair <NUM> to the secondary transfer section T2 at a timing synchronized with the image formation operation.

A movable secondary transfer roller <NUM> is disposed in the secondary transfer section T2. The secondary transfer roller <NUM> can move substantially in the vertical direction. At the time of image transfer, the secondary transfer roller <NUM> is pressed against the intermediate transfer member <NUM> with a predetermined pressure, via the recording medium P. Simultaneously therewith, bias is applied to the secondary transfer roller <NUM>, and the toner image on the intermediate transfer member <NUM> becomes transferred to the recording medium P.

The intermediate transfer member <NUM> and the secondary transfer roller <NUM> are each driven, and accordingly the recording medium P nipped between the intermediate transfer member <NUM> and the secondary transfer roller <NUM> is transported in the direction of the left arrow in <FIG> at a predetermined transport speed V; the recording medium P is then further transported, by the transport belt <NUM>, to the fixing unit <NUM> which is a subsequent process. In the fixing unit <NUM> the transferred toner image is fixed on the recording medium P through application of heat and pressure. The recording medium P is then discharged onto a discharge tray <NUM>, on the top face of the apparatus, by discharge roller pairs <NUM>.

An image forming apparatus capable of delivering a high-quality image of excellent image uniformity can be thus achieved by utilizing the fixing apparatus illustrated in <FIG> in the fixing unit <NUM> of the electrophotographic image forming apparatus illustrated in <FIG>.

The present disclosure will be specifically described next with reference to examples. The present disclosure is not limited to the following examples.

In the present example a fixing member being a fixing rotating member was produced using the PFA resin and the perfluoropolyether below.

As a base layer there was prepared base material obtained through nickel electroforming and having an endless belt shape with an inner diameter of <NUM>, a width of <NUM>, and a thickness of <NUM>. The outer peripheral surface of this base material was subjected to a primer treatment.

As a starting material for forming the elastic layer there was prepared an addition-curable liquid silicone rubber (product name: SE1886, by Dow Corning Toray Co. ) containing no filler. To <NUM> parts by volume of this liquid silicone rubber there were added <NUM> parts by volume of spherical alumina (product name: Alunabeads CB-A30S, by Showa Denko KK) as a spherical filler, and <NUM> part by volume of gas-phase carbon fibers (product name: VGCF-S, by Showa Denko KK, aspect ratio=<NUM>, average fiber length =<NUM>).

An addition-curable silicone rubber composition for forming an elastic layer was thus prepared in this manner. The above composition was applied by ring coating onto the outer peripheral surface of the above base material, followed by heating for <NUM> hours at a temperature of <NUM>, to elicit crosslinking of the layer of the addition-curable silicone rubber composition, and form thereby an elastic layer having a thickness of <NUM>.

The elastic layer surface was irradiated with ultraviolet rays in an ambient atmosphere, using an ultraviolet lamp disposed at a position spaced by <NUM> from the surface of the elastic layer, while the base material having the elastic layer formed thereon was caused to rotate at a moving speed of <NUM>/second. The ultraviolet lamp used herein was a low-pressure mercury ultraviolet lamp (product name: GLQ500US / <NUM>, by Toshiba Lighting & Technology Corporation), and irradiation was performed so that the integrated light intensity on the irradiated surface, at a wavelength of <NUM>, was <NUM> mJ/cm<NUM>.

The surface of the elastic layer was then coated substantially uniformly, to a thickness of about <NUM>, with an addition-curable silicone rubber adhesive (product name: SE1819CV, equal mixture of "liquid A" and "liquid B", by Dow Corning Toray Co.

The inner surface was covered next with a hydrophilized fluororesin tube (PFA-<NUM>, <NUM> thick, melting point <NUM>), and the belt surface was uniformly squeezed from above the fluororesin tube to thereby remove excess adhesive from between the elastic layer and the fluororesin tube.

The base layer coated with the elastic layer and the fluororesin tube was placed then in an electric furnace set to at a temperature of <NUM>, and the whole was heated for <NUM> hour, to cure the adhesive and bond the fluororesin tube onto the elastic layer, after which both ends were cut off, to yield a <NUM>-wide layered body for a fixing belt.

The first PFPE (PFPE-<NUM>) was placed in a graduated cylinder made of borosilicate glass. A heating wire covered with a thermal insulation material was wound around the whole graduated cylinder, and the graduated cylinder was heated up to a temperature of <NUM> of the PFPE. This preliminary fixing belt thus produced was mounted on a dipping device, and the layered body was immersed in the heated PFPE for <NUM> minute, and was then retrieved.

The content of the first PFPE in the obtained resin layer impregnated with the first PFPE was measured in accordance with the following method. Specifically, a multilayer sample of the elastic layer and the resin layer was cut out from the layered body. Next, the elastic layer was removed from the multilayer sample through dissolution of the silicone rubber in the elastic layer from the multilayer sample, by immersing the multilayer sample in a silicone resin dissolving agent (product name: e-Solve 21RS, by Kaneko Chemical Co. A measurement sample made up of only the entire thickness portion of the resin layer was prepared in this manner. This measurement sample was measured using a thermogravimetric analyzer (TGA) under the conditions below, and the content (mass%) of the first PFPE with respect to the resin layer containing the first PFPE was calculated.

In a profile of measurement time-weight loss rate obtained on the basis of the above thermogravimetric analysis, a linear least squares approximation expression was worked out from the region at which the slope was constant and at which only PFA decreased. The intercept of the linear least squares approximation expression was taken as the PFA content (mass%), and the first PFPE content was calculated as first PFPE content (mass%)=<NUM>-PFA content).

After cooling of the layered body obtained in the impregnation step -<NUM> down to room temperature (<NUM>), the layered body was immersed in a graduated cylinder containing a separately prepared fluorosolvent (product name: Novec <NUM>, by The <NUM> Company) for <NUM> minutes. Next, the graduated cylinder was placed in a water tank of an ultrasonic cleaning device (product name: Bransonic (model 2510J-DTH); by Emerson Japan, Ltd. ), and was irradiated with ultrasounds for <NUM> minutes. After the treatment, the layered body was retrieved from the graduated cylinder and was dried by being allowed to stand in an environment at a temperature of <NUM> for <NUM> minutes. A layered body was thus obtained from which there was removed PFPE present on the surface and in the interior of the of the resin layer. The visual appearance of the obtained layered body was white, and pores were observed to have formed in the resin layer.

<FIG> illustrate schematic diagrams of observation images, by scanning electron microscopy, of the first surface of the resin layer of the obtained layered body, and of a cross section of the layered body in a direction along the circumferential direction.

<FIG> is a schematic diagram of an SEM image of the first surface. A resin portion <NUM> containing PFA and openings <NUM> were observed. <FIG> is a schematic diagram of an SEM image of a cross section of the resin layer in a direction along the circumferential direction of the layered body. The resin portion <NUM> containing PFA and the pores <NUM> were observed herein. It was found that the pores <NUM> had openings in the first surface <NUM> and had thus openings in the first surface.

The opening ratio P1 and the average opening diameter of the first surface of the surface layer (resin layer) were calculated as follows.

The surface of the layered body having had the first PFPE removed therefrom and obtained in the above pore formation step, i.e. the surface of the resin layer on the reverse side from that opposing the elastic layer, was observed using a scanning electron microscope, and a SEM image (<NUM> magnifications) of a rectangular <NUM> long ×<NUM> wide observation region was acquired. The resolution was set to <NUM> pixels longitudinally and <NUM> pixels transversally so that the openings could be recognized. The acquired SEM image was converted into an <NUM>-bit gray scale image using image processing software (product name: ImageJ, by the National Institutes of Health (NIH)). After application of a median filter to the obtained gray scale image, a binarization process was further carried out using the above image processing software, to obtain a binarized image. The binarization process relied on the YEN method, to discriminate between portions corresponding to the openings and portions corresponding to PFA in the SEM image. A ratio of the number of pixels of the portions corresponding to the openings in the obtained binarized image relative to the number of pixels of the entire image was then calculated. The observation regions were disposed at <NUM> arbitrary locations on the surface of the resin layer having openings, and the arithmetic mean value of the ratios calculated from respective observation regions was taken as P1. The observation regions were set to positions such that the observation regions did not overlap each other.

The surface areas of the portions corresponding to the openings in each binarized image were approximated to respective true circles of surface area identical thereto, and the arithmetic mean value of the diameters of the true circles (hereafter circle-equivalent diameters) was taken as the average opening diameter.

The porosity P2 was calculated as follows.

From the resin layer of the layered body having had the first PFPE removed therefrom a cross-sectional sample was cut out using a Cryo-Ultra-microtome (by Leica Microsystems GmbH), so that a cross section of the resin layer in a direction along the circumferential direction of the layered body appeared on the sample. The cross section was set to include the entire thickness portion of the resin layer. Next, the cross section was observed under a scanning electron microscope, and an SEM image of an observation region <NUM> long ×<NUM> wide was acquired. The resolution was set to <NUM> pixels longitudinally and <NUM> pixels transversally so that the pores appearing in the cross section could be discerned. The SEM image was binarized using numerical calculation software (product name: MATLAB; by The MathWorks, Inc. ) to obtain a binarized image. The binarization process relied on Otsu's method to discriminate between portions corresponding to the pores and portions corresponding to PFA, in the SEM image. A ratio of the number of pixels of the portions corresponding to the pores in the binarized image relative to the number of pixels of the entire image was then calculated. The thickness-direction acquisition positions of the SEM images in the cross section of each cross-sectional sample were set to three locations as prescribed in (i) to (iii) below.

Samples for the above operation were acquired from three locations at every <NUM>° in the circumferential direction of the layered body. Therefore, a total of nine SEM images were obtained in accordance with the above operation, and nine ratios were calculated on the basis of the binarized images created from the SEM images. The arithmetic mean value of these nine ratios was taken as the porosity P2.

The following operations were performed then on the layered body provided with the resin layer having pores and obtained as a result of the above pore formation step. Specifically, the second PFPE (PFPE-<NUM>) was placed in a graduated cylinder made of borosilicate glass.

A heating wire covered with a thermal insulation material was wound around the whole graduated cylinder, and the graduated cylinder and heated up so that the PFPE temperature became <NUM>. Next, the layered body was attached to a dipping device, and the entire layered body was immersed in the heated second PFPE for <NUM> minutes, and was then retrieved.

Next, the second PFPE adhered to the outer surface of the retrieved layered body was removed using a nonwoven fabric impregnated with a fluorine-based solvent (product name: Novec <NUM>; by The <NUM> Company). The fixing belt according to the present embodiment was obtained in this manner. <FIG> illustrates a schematic diagram of an observation image, by scanning electron microscopy, of a cross section of a surface layer in a direction along the circumferential direction of the obtained fixing belt. It was found that the pores <NUM> observed in <FIG> became filled with the second PFPE <NUM> as a result of the impregnation step -<NUM>.

Similarly to Evaluation A-<NUM>, a measurement sample of an obtained fixing belt was prepared which was made up of only the entire thickness portion of the surface layer. This measurement sample was measured using a thermogravimetric analyzer (TGA) under the under the conditions below, and there was calculated the content ratio (mass%) of the second PFPE in the surface layer, with respect to the total mass of the surface layer including the mass of the second PFPE in the pores.

In a profile of measurement time-weight loss rate obtained as a result of the above thermogravimetric analysis, a linear least squares approximation expression was worked out from the region at which the slope was constant and only PFA decreased. The intercept of the linear least squares approximation expression was taken as the PFA content (mass%), and the second PFPE content was calculated as second PFPE content (mass%)=<NUM>-PFA content.

The obtained fixing belt was subjected to the following Evaluations B-<NUM> and B-<NUM>.

The fixing belt was attached to an electrophotographic image forming apparatus (product name: imageRUNNER-ADVANCE C5051; by Canon Inc. ) in which the angle of a paper separation claw had been adjusted.

An image forming process was carried out then of forming a <NUM>×<NUM> cyan solid image on A4-size paper (by International Paper Co. , basis weight <NUM>/m<NUM>). The fixing temperature was set to <NUM>, and the paper transport speed was set to <NUM>/sec.

Once the numbers of formed solid cyan images respectively reached <NUM> print, <NUM>,<NUM> prints, and <NUM>,<NUM> prints, one sheet A4-size plain thin paper (product name: CS-<NUM>, basis weight <NUM>/m<NUM>, by Canon Inc. ) was run, to form a <NUM>×<NUM> cyan solid image. The solid image formed on this plain thin paper was observed visually and under a microscope, and was evaluated according to the criteria below.

In Evaluation <NUM>, the surface free energy of the outer surface of the fixing belt immediately prior to the formation of a solid image on the plain thin paper was calculated in accordance with the "Kitazaki-Hata method" described in the literature "<NPL>. Specifically, there were measured the contact angles of the outer surface of the fixing belt with water, n-hexadecane and diiodomethane (measurement environment: temperature <NUM>, relative humidity <NUM>%).

The surface free energy was then worked out, using the measurement results of each contact angle, on the basis of the "extended Fowkes equation" according to the "Kitazaki-Hata theory" set forth in the above literature.

A contact angle meter (product name: DM-<NUM>, by Kyowa Interface Science Co. ) was used for the measurement, and analysis software (product name: FAMAS, by Kyowa Interface Science Co. ) was utilized for analyzing the surface free energy.

A layered body provided with a resin layer having pores was produced in the same way as in Example <NUM>, but herein the contact temperature between the resin layer and the first PFPE in the impregnation step -<NUM> was set to the temperature given in Table <NUM>. From the impregnation step -<NUM> onwards, Fixing belt No. <NUM> was produced in the same way as in Example <NUM>. The results of Evaluations A-<NUM> to A-<NUM> and Evaluations B-<NUM> and B-<NUM> for the obtained Fixing belt No. <NUM> are given in Table <NUM> and Table <NUM>.

A layered body provided with a resin layer having pores was produced in the same way as in Example <NUM>, but herein the first PFPE in the impregnation step -<NUM> was modified to the first PFPE given in Table <NUM>. From the impregnation step -<NUM> onwards, Fixing belt No. <NUM> was produced in the same way as in Example <NUM>. The results of Evaluations A-<NUM> to A-<NUM> and Evaluations B-<NUM> and B-<NUM> for the obtained Fixing belt No. <NUM> are given in Table <NUM> and Table <NUM>.

The type of the second PFPE used in the impregnation step -<NUM> was modified as given in Table <NUM>. Otherwise, Fixing belts No. <NUM> and <NUM> were produced in the same way as in Example <NUM>. The results of Evaluations A-<NUM> to A-<NUM> and Evaluations B-<NUM> and B-<NUM> for the obtained Fixing belts No. <NUM> and <NUM> are given in Table <NUM> and Table <NUM>.

A layered body provided with a resin layer having pores was produced in the same way as in Example <NUM>, but herein the thickness of the resin layer was modified as given in Table <NUM>. From the impregnation step -<NUM> onwards, Fixing belts No. <NUM> and <NUM> were produced in the same way as in Example <NUM>. The results of Evaluations A-<NUM> to A-<NUM> and Evaluations B-<NUM> and B-<NUM> for the obtained Fixing belts No. <NUM> and <NUM> are given in Table <NUM> and Table <NUM>.

A layered body provided with a resin layer having pores was produced in the same way as in Example <NUM>, but herein the material type of the resin layer in the impregnation step -<NUM> and the contact temperature with the first PFPE were modified as given in Table <NUM>. From the impregnation step -<NUM> onwards, Fixing belt No. <NUM> was produced in the same way as in Example <NUM>. The results of Evaluations A-<NUM> to A-<NUM> and Evaluations B-<NUM> and B-<NUM> for the obtained Fixing belt No. <NUM> are given in Table <NUM> and Table <NUM>.

A layered body having a base layer, an elastic layer and a resin layer containing PFA was produced in the same way as in Example <NUM>, and was used as Fixing belt No. C-<NUM> according to the present comparative example. Table <NUM> sets out the results of Evaluations B-<NUM> and B-<NUM> for this Fixing belt No. C-<NUM>. The Fixing belt No. C-<NUM> did not undergo the impregnation step -<NUM>, the pore formation step, or the second impregnation step, and accordingly Evaluations A-<NUM> to A-<NUM> were not carried out.

A layered body having a resin layer that had pores was produced in the same way as in Example <NUM>, but herein the material of the first PFPE in the method described in Example <NUM> was modified to the material given in Table <NUM>. This layered body was used as Fixing belt No. C-<NUM> according to the present comparative example. Table <NUM> and Table <NUM> set out the results of Evaluations A-<NUM> and A-<NUM> and Evaluations B-<NUM> and B-<NUM> performed on the obtained Fixing belt No. C-<NUM>. The Fixing belt No. C-<NUM> according to the present comparative example did not undergo the impregnation step -<NUM>, and accordingly Evaluation A-<NUM> was not performed.

The material type of the first PFPE and the temperature at the time of contact in the impregnation step -<NUM> of the method described in Example <NUM> were modified herein as given in Table <NUM>. The result of Evaluation A-<NUM> for the obtained layered body, i.e. the content ratio of PFPE in the resin layer containing the first PFPE obtained in the impregnation step -<NUM> was herein <NUM> mass%.

The first PFPE in the resin layer could not be removed when this layered body was subjected to the pore formation step described in Example <NUM>. Although the underlying reasons are unclear, it is deemed that due to the small amount of impregnation the first PFPE fail to aggregate and connect in the resin layer, and first PFPE intruded thus in between molecules of PFA; as a result, the first PFPE could not be eluted with the solvent. Accordingly, the impregnation step -<NUM> was not performed, and the layered body obtained up to the impregnation step -<NUM> was used as Fixing belt No. C-<NUM> of the present comparative example. Table <NUM> and Table <NUM> set out the results of Evaluation A-<NUM> and Evaluations B-<NUM> and B-<NUM> performed on the obtained Fixing belt No. C-<NUM>. As expounded above, pores could not be formed in the resin layer even in the pore formation step, and hence the impregnation step -<NUM> was not performed; accordingly, neither Evaluation A-<NUM> nor Evaluation A-<NUM> was performed.

A base material was prepared the outer peripheral surface of which had undergone a primer treatment in the same way as in Example <NUM>. The primer-treated surface of the base material was coated with a stretched porous PTFE tube (product name: Poreflon HP-<NUM>-<NUM>; by Sumitomo Electric Fine Polymer Inc. ) to obtain a layered body having a porous resin layer. The second PFPE was introduced into the pores of the resin layer in the same way as in the impregnation step -<NUM> of Example <NUM>, but using herein this layered body. The contact time with the second PFPE was <NUM> minutes in Comparative example <NUM>, and <NUM> minutes in Comparative example <NUM>. The layered bodies resulting from impregnation of the resin layer with the second PFPE were used as Fixing belt Nos. C-<NUM> and C-<NUM>. Table <NUM> and Table <NUM> set out the results of Evaluations A-<NUM> and A-<NUM>, and Evaluations B-<NUM> and B-<NUM> for Fixing belts No. C-<NUM> and C-<NUM>.

A base material with a primer-treated outer peripheral surface was prepared in the same way as in Example <NUM>. Next, an amorphous fluoropolymer (product name: Teflon AF2400, by The Chemours Company) was dissolved in a fluorosolvent (product name: Novec <NUM>, by The <NUM> Company), to prepare a <NUM> mass% solution. The base material was immersed in the above solution, was then applied, in accordance with a dipping method, so that film thickness was <NUM>. The immersion time was <NUM> sec, and the pull-up speed was <NUM>/sec. The base material having a coating film of the solution formed on the outer peripheral surface was then dried in an oven at a temperature of <NUM> for <NUM> minutes, to yield a layered body having a porous polytetrafluoroethylene (PTFE) film on the surface. Other than by using this layered body, the pores of the porous PTFE film were impregnated with PFPE-<NUM> in the same manner as in the impregnation step -<NUM> of Example <NUM>, to yield a fixing belt according to the present comparative example. Table <NUM> and Table <NUM> set out the results of Evaluations A-<NUM> and A-<NUM> and Evaluations B-<NUM> and B-<NUM> of the obtained fixing belt.

Table <NUM> sets out the formulations of the fixing belts produced in Examples <NUM> to <NUM> and Comparative examples <NUM> to <NUM>.

Table <NUM> sets out the evaluation results of the fixing rotating members produced in Examples <NUM> to <NUM> and Comparative examples <NUM> to <NUM>.

Table <NUM> reveals that excellent toner releasability even after prolonged use can be maintained in the fixing rotating members of the examples, and that a high-quality electrophotographic image can be formed as a result.

One aspect of the present disclosure makes it possible to obtain a fixing rotating member in which high toner releasability can be maintained over longer periods of time. Other aspects of the present disclosure make it possible to achieve a fixing apparatus and an electrophotographic image forming apparatus in which a high-quality electrophotographic image can be formed stably over long periods of time.

Claim 1:
A fixing rotating member comprising a base layer, an elastic layer and a surface layer, in this order,
the surface layer containing a tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer and a perfluoropolyether;
the surface layer having pores with openings at a first surface thereof constituting an outer surface of the fixing rotating member;
at least part of the pores containing the perfluoropolyether, characterized in that
when a first observation region <NUM> long ×<NUM> wide is placed on the first surface of the surface layer after removing the perfluoropolyether in the pores, and a ratio of a total sum of areas of the openings observed in the first observation region relative to an area of the first observation region is defined as P1; and
when a second observation region <NUM> long × <NUM> wide is placed in a cross section of the surface layer after removing the perfluoropolyether in the pores, the cross section including an entire thickness portion of the surface layer along a circumferential direction of the fixing rotating member, and a ratio of a total sum of areas of the pores observed in the second observation region relative to an area of the second observation region is defined as P2,
P2/P1, as determined according to the description, is <NUM> or higher.