JP6918627B2 - Fixing device and fixing member used for it - Google Patents

Description

The present invention relates to a fixing device for fixing a toner image carried on a recording material to a recording material and a fixing member used therein.

In recent years, users of printers and the like sometimes use plain paper having a coarser surface than conventional plain paper as a recording material. Therefore, there is an increasing need to achieve the same image quality as conventional plain paper even on coarse plain paper. In addition, improvement in image quality is also required for paper such as embossed paper that is intentionally provided with irregularities in design.

In response to these demands, it has been proposed to set the fixing member configuration and the pressurizing conditions of the fixing device in order to improve the image quality (Patent Documents 1 and 2).

In Patent Document 1, in order to improve the image quality of plain paper, a range of universal hardness and a range of pressing force (the average pressure of the nip portion is 0.2 to 1 MPa) are defined.

Further, Patent Document 2 describes that the following is defined in order to improve the fixability of a member having large irregularities such as embossed paper. That is, the thickness of the release layer of the fixing belt is defined as 10 μm or more and 15 μm or less, and the JIS-A hardness of the elastic layer is defined as 20 degrees or less. The average surface pressure at the nip portion is defined as 1.2 kgf / cm ² or more and 3.0 kgf / cm ² or less (corresponding to 0.12 MPa or more and 0.29 MPa or less).

Japanese Unexamined Patent Publication No. 2006-47960 Japanese Unexamined Patent Publication No. 2013-130731

However, what is shown in these documents is the characteristics of the fixing member in the fixing device in which the average surface pressure of the nip portion is 0.12 MPa or more (that is, the maximum surface pressure is larger than 0.12 MPa). In providing a fixing device in which the load applied to the nip portion is small, if the conventional fixing member is used as it is, the load becomes small, which may reduce the followability of the recording material to the unevenness or deteriorate the gloss (glossiness). There is. That is, there is a risk of degrading the image quality.

An object of the present invention is to provide a fixing device capable of suppressing deterioration of image quality even when the maximum surface pressure of the nip portion is smaller than that of the conventional one, and a fixing member used therein.

In order to achieve the above object, the fixing device according to the present invention has a nip portion that sandwiches and conveys a rotatable fixing member and a recording material that faces the fixing member and carries a toner image between the fixing member. It has a rotating body to be formed and a heating member for heating the fixing member, and the maximum surface pressure in the recording material transport direction at the nip portion is 0.09 MPa or more and 0.12 MPa or less, and the fixing member is fixed. When the transparent plate is pressurized to the maximum surface pressure of the transparent plate via a sphere having a diameter of 20 μm instead of the rotating body, the transparent plate and the fixing member are viewed from the pressing direction. The diameter of the region that does not come into contact is 40 μm or more and 227 μm or less, the body is heated to the heating temperature at the time of fixing, and the crown is pressurized at the maximum surface pressure by a hemispherical probe having a diameter of 1 mm instead of the rotating body. The pressure applied to the crown is 0.39 MPa or more and 1 MPa or less, and the amount of displacement by the probe is 35 μm or more and 90 μm or less.

Further, the fixing member according to the present invention is a rotatable fixing member that forms a nip portion that is heated at the time of fixing and that sandwiches and conveys a recording material carrying a toner image between the rotating body and the opposing rotating body. The maximum surface pressure of the nip portion in the recording material transport direction at the time is 0.09 MPa or more and 0.12 MPa or less, and the transparent plate is heated to the heating temperature at the time of fixing and replaced with the rotating body through a sphere having a diameter of 20 μm. When pressurized at the maximum surface pressure, the diameter of the region that does not contact the transparent plate when viewed from the pressurizing direction is 40 μm or more and 227 μm or less, and is heated to the heating temperature at the time of fixing and replaced with the rotating body. When the crown is pressurized with the maximum surface pressure by a hemispherical probe having a diameter of 1 mm, the pressure applied to the crown is 0.39 MPa or more and 1 MPa or less, and the amount of displacement by the probe is 35 μm or more and 90 μm or less. It is characterized by being.

According to the present invention, it is an object of the present invention to provide a fixing device capable of suppressing deterioration of image quality even when the maximum surface pressure of the nip portion is smaller than that of the conventional one, and a fixing member used therefor.

It is a schematic diagram of the image forming apparatus equipped with the fixing apparatus which concerns on embodiment of this invention. It is a schematic diagram of the fixing member and the fixing device which concerns on embodiment of this invention. It is a schematic diagram of the fixing film as a fixing member which concerns on embodiment of this invention. It is a schematic diagram which showed the followability to the recording paper of the fixing film when the deformation amount of the fixing film is small. It is a schematic diagram which showed the followability to the recording paper of the fixing film when the amount of deformation of the fixing film is large. It is a schematic diagram of the method of measuring the non-contact diameter in embodiment of this invention. It is a graph which shows the relationship between the non-contact diameter and the density (reflection density) of a toner image. It is a graph which shows the relationship between the contact pressure and the gloss of a toner image. It is a graph which shows the relationship between the displacement amount (deformation amount), and the rank about the gloss unevenness of a toner image. It is a graph which shows the relationship (trade-off relationship) of the displacement amount and contact pressure.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

<< First Embodiment >>
(Image forming device)
FIG. 1 is a cross-sectional view of a color electrophotographic printer 1 which is an example of an image forming apparatus equipped with a fixing device according to an embodiment of the present invention, and is a cross-sectional view of a sheet P which is a recording material (recording paper). It is a cross-sectional view. In this embodiment, the color electrophotographic printer is simply referred to as a "printer".

The printer shown in FIG. 1 includes an image forming unit 10 of each color of Y (yellow), M (magenta), C (cyan), and Bk (black) in the image forming apparatus main body 4. The photosensitive drum 11 is precharged by the charger 12. After that, a latent image is formed on the photosensitive drum 11 by the laser scanner 13.

Then, the latent image becomes a toner image by the developer 14. The toner image of the photosensitive drum 11 is sequentially transferred by the primary transfer blade 17 to, for example, an intermediate transfer belt 31 (suspended by a plurality of rollers including a roller 34) which is an image carrier. After the transfer, the toner remaining on the photosensitive drum 11 is removed by the cleaner 15. As a result, the surface of the photosensitive drum 11 becomes clean and ready for the next image formation.

On the other hand, the sheet P is sent out one by one from the paper feed cassette 20 or the multi-paper feed tray 25 and is sent to the resist roller pair 23. The resist roller pair 23 once receives the sheet P, and if the sheet is skewed, straightens it. Then, the resist roller pair 23 feeds the sheet between the intermediate transfer belt 31 and the secondary transfer roller 35 in synchronization with the toner image on the intermediate transfer belt 31. The color toner image on the intermediate transfer belt is transferred to the sheet P by a transfer body such as the secondary transfer roller 35.

After that, the toner image of the sheet is fixed to the sheet P by heating and pressurizing the sheet by the fixing device 40 which is a fixing device. After fixing, the sheet P is discharged to the output tray 65.

(Fixing device)
Next, the fixing device according to the embodiment of the present invention will be described with reference to FIG. The fixing device 40 of the present embodiment is a method (tensionless type) in which an endless belt (hereinafter, belt) 41, which is a fixing film that can rotate as a fixing member, is heated. Then, the pressure roller 44 is used as a rotating body that faces the belt 41 and forms the fixing nip portion (hereinafter, nip portion) N with the belt 41. However, in addition to the method of this embodiment in which a film forming a nip portion N for fixing the unfixed toner image T and a roller are combined, a roller pair type fixing device for forming the nip portion N can also be used.

In the fixing device according to the present embodiment, the longitudinal direction is a direction orthogonal to the transport direction of the recording material (recording paper) and the thickness direction of the recording material. The short side is the transport direction of the recording material. Further, with respect to the recording material, the width direction is a direction parallel to the longitudinal direction.

In FIG. 2, reference numeral 43 denotes a ceramic heater (hereinafter referred to as a heater) as a heating body. The heater 43 is basically composed of an elongated thin plate-shaped ceramic substrate long in the longitudinal direction and an energization heat generation resistor layer provided on the substrate surface, and has a steep rise characteristic as a whole due to energization of the heat generation resistor layer. It is a heater with a low heat capacity that raises the temperature with. Further, the heater 43 is configured to switch the energization region according to the size of the recording material in the width direction. In the present embodiment, the ceramic heater is exemplified as the heating body, but other heating means such as a halogen heater and an IH heater may be used.

The belt 41 has a cylindrical (endless) heat resistance as a heating member for transmitting heat, and is loosely fitted to a heater holder 46 which is a holding member for holding a heater 43 that has generated heat at a high temperature. Reference numeral 45 denotes a contact type thermometer (thermistor). As shown in FIG. 3, the belt 41 in the present embodiment has a three-layer composite structure of a surface layer (release layer) 41a, an elastic layer 41b, and a base layer (base metal layer) 41c. An adhesive layer for adhering the layers may be provided between the surface layer 41a and the elastic layer 41b, or between the elastic layer 41b and the base layer 41c. In this case, it is assumed that the adhesive layer is not included in the thickness and Young's modulus of the elastic layer described later shown in Table 1.

For the surface layer 41a provided on the outside of the elastic layer 41b, a fluororesin material having a thickness of 100 μm or less, preferably 10 to 70 μm can be used. Examples of the fluororesin layer include PTFE, FEP, PFA and the like. In this embodiment, a PFA tube having a thickness of 10 to 20 μm was used.

The elastic layer 41b provided on the outside of the base layer 41c is provided with a filler for increasing thermal conductivity in order to reduce the heat capacity and improve the quick start product. In this embodiment, a silicone rubber having a rubber hardness of 5 to 30 degrees (JIS-A), a thermal conductivity of 1.3 W / m · K, and a thickness of 100 to 300 μm was used.

Similar to the elastic layer 41b, the base layer 41c can also use a heat-resistant material having a thickness of 100 μm or less, preferably 50 μm or less and 20 μm or more, in order to improve the quick start property. For example, a metal film such as SUS or nickel can be used. In this embodiment, a cylindrical stainless metal film having a thickness of 30 μm and a diameter of 25 mm was used.

Reference numeral 44 denotes a rotating body, which is a heat-resistant elastic pressure roller as a pressure member, and is an elastic layer made of a core metal, heat-resistant rubber such as silicone rubber or fluororubber, or a foam of silicone rubber. Both ends of the core metal are rotatably supported by bearings. The belt 41 and the heater 43 are arranged in parallel with the pressure roller 44 on the upper side of the pressure roller 44, and are pressed by a pressing member (not shown). As a result, a nip portion N having a predetermined width as a heating portion that is pressure-welded against the elasticity of the roller elastic layer is formed on the lower surface of the heater 43 and the upper surface of the pressurizing roller 44 via the belt 41.

The pressurizing roller 44 is rotationally driven at a predetermined rotational peripheral speed in the counterclockwise direction of the arrow (FIG. 2) by a driving means (not shown). The rotational force acts on the cylindrical belt 41 due to the pressure contact friction force between the pressure roller 44 and the belt 41 due to the rotational drive of the pressure roller 44 at the nip portion N. Then, the belt 41 is brought into a driven rotation state in the clockwise direction of the arrow (FIG. 2) while sliding in close contact with the downward surface of the heater 43 (the surface of the heater 43 on the pressure roller 44 side). The heater holder 46 is also a rotation guide member for the cylindrical belt 41.

The pressure roller 44 is rotationally driven, and the cylindrical belt 41 is brought into a driven rotational state accordingly. Further, in a state where the heater 43 is energized, the heater rapidly rises to a predetermined temperature, and the temperature is adjusted, the unfixed toner image T is between the belt 41 of the nip portion N and the pressure roller 44. The recording material P carrying the above is introduced. Then, in the nip portion N, the toner image-supporting side surface of the recording material P comes into close contact with the outer surface of the belt 41, and the nip portion N is sandwiched and conveyed together with the belt 41.

In this sandwiching and transporting process, the recording material P is heated by the heat of the belt 41 heated by the heater 43, and the unfixed toner image T on the recording material P is heated and pressurized on the recording material P to be melt-fixed. .. The recording material P that has passed through the nip portion N is discharged and conveyed with the curvature separated from the surface of the belt 41.

The contact thermometer (thermistor) 45 measures the temperature of the belt 41 heated by the heater 43, and passes the detection result to a temperature control means (not shown).

(Evaluation method of image quality)
In this embodiment, attention was paid to the density (image density), gloss (glossiness), and gloss unevenness of the toner image as items of the image quality of plain paper.

The image density is a measurement of the reflection density of the toner image after fixing, and in the present embodiment, a color difference measuring device (spectral densitometer, manufactured by X-RITE Co., Ltd.) is used for the measurement. In the comparison, the reflection density of the toner image with the same amount of toner is measured and compared.

The gloss (gloss) of the toner image is a measurement of the amount of specular reflected light of the toner image after fixing. In this embodiment, the handy gloss meter (PG-1M type, Nippon Denshoku Kogyo Co., Ltd.) is used for the measurement. Was measured at an incident angle of 60 degrees. In the comparison, the amount of specularly reflected light with the same amount of toner is measured and compared.

In the present embodiment, CS-680 (manufactured by Nippon Paper Industries, Ltd., 70 g paper) was used as plain paper for measuring the density (image density) and gloss (glossiness) of the toner image.

Further, the gloss unevenness of the toner image indicates the unevenness of the reflected light amount due to the paper fiber in the plain paper having a rougher surface, and in this embodiment, the ranking is performed visually.

In the present embodiment, GFC-104 (Nippon Paper Industries, Ltd., 104 g paper) was used as the coarser plain paper in the measurement of the gloss unevenness of the toner image.

(Relationship between the characteristic parameters of the fixing film and the image quality)
Next, the relationship between the characteristic parameters of the fixing film (belt 41) as the fixing member in the present embodiment and the image quality of plain paper as the recording material will be described. In the present embodiment, the fixing film alone was taken out, and the characteristics of the fixing film were evaluated by applying pressure in the following two measurement methods instead of the pressure roller, and the relationship with the image quality of plain paper was confirmed.

(First measurement method)
First, the first measurement method will be described.

The toner on the paper melts and spreads due to the pressure and heat of the fixing process, and develops a high-concentration and vivid color. When the fixing film has low followability to small irregularities at the paper fiber level in recording paper such as plain paper, as shown in FIG. 4, the toner in the gap between the paper fibers of the sheet P which is the recording material (recording paper) and the toner are used. The heated fixing film (belt 41) cannot be contacted well. Then, since the toner cannot be melted and spread, the density of the toner image on the recording paper cannot be increased. On the other hand, when the fixing film has a high followability to the paper fibers as shown in FIG. 5, the force for melting and spreading the toner is large, so that the density of the toner image on the recording paper is improved.

In the present embodiment, the fixing film heated to the heating temperature at the time of fixing (150 ° C. near the fixing temperature) is pressed by a transparent plate via a small ball shown below instead of the pressure roller. .. Then, it is confirmed whether or not the characteristic parameters of the fixing film satisfy the predetermined image quality evaluation (density).

The present inventors performed measurement using the first measurement method for the purpose of deeply understanding the followability of the fixing film, and evaluated the followability of the fixing film to the unevenness of the paper fiber scale. The method for measuring the non-contact diameter is as follows (1-1) to (1-3).
(1-1) As shown in FIG. 6, spherical alumina particles 102 having a diameter of 20 μm (spheres simulating a scale equivalent to that of paper fibers) are not aggregated on a glass plate 104 which is a transparent plate. Spray on.
(1-2) The fixing film (belt 41) is heated to 150 ° C., which is close to the fixing temperature, by the heating core 101. The fixing film (belt 41) on which the alumina particles 102 are sprayed and heated to 150 ° C. by the heating core 101 is sandwiched between the glass plate 104 and the heating core 101 for measurement. As the heating core 101, a core having a uniform diameter is used in the region where it comes into contact with the fixing film.

FIG. 7 is a graph showing the relationship between the non-contact diameter and the density of the toner image (coverage after fixing the toner on the recording paper). The horizontal axis of FIG. 7 shows that the non-contact diameter is changed by changing the thickness and material of the release layer constituting the fixing film and the thickness and material of the elastic layer. As a measurement condition, a contact pressure is applied so as to be a predetermined pressure (for example, 0.12 MPa), and the non-contact diameter at that time is measured. The vertical axis of FIG. 7 shows the toner coverage after fixing with the fixing film used for each measurement on the horizontal axis. The toner coverage can be measured by image analysis of the observation result of a microscope.

Here, the toner on the paper melts and spreads due to the pressure and heat of the fixing process, thereby developing a bright color with high density. The toner coverage is the ratio of the toner (toner image) on the paper covering the white background of the paper, and the high coverage means that the toner sufficiently covers the paper to obtain a high-density color image. Can be done. In an actual toner image, it is known that when the toner coverage is less than 76%, the white background of the paper is transparent and the color development of the toner is insufficient, so that the image quality is deteriorated. Therefore, it can be said that the toner coverage is preferably 76% or more.

The toner coverage rate referred to here does not mean the printing rate on the recording material. In the unfixed state, the toner particles are overlapped because they are not crushed. As a result, the white background of the paper is transparent, and the toner coverage is lower than after fixing. On the other hand, after fixing, the toner particles are crushed and spread by pressurization and heating, so that the toner coverage is higher than in the unfixed state.

In this experiment, it was confirmed that when the toner coverage in the unfixed state was 68% and the toner coverage was 76% or more after fixing, an image with good image quality could be obtained.

In addition, the non-contact diameter in this experiment has a strong correlation with the toner coverage, and it was confirmed that an image with a high density as targeted can be obtained when the non-contact diameter at which the toner coverage is 76% or more is 227 μm or less. .. In the present embodiment, as shown in FIG. 7, a toner coverage ratio of 76% or more was obtained with a non-contact diameter of 40 μm or more and 227 μm or less, so the lower limit value is set to 40 μm.

That is, as a result of measuring the belt (fixing member) 41 used in the fixing device 40 by the above-mentioned first measurement method ((1-1) to (1-3)), the non-contact diameter is 40 μm or more and 227 μm or less. In this case, the belt 41 is a belt that can obtain an image having a high density as targeted.

However, in the above (1-2), the fixing film and the glass plate are pressurized at the maximum surface pressure Pmax (unit: Pa) of the nip portion N in the recording material transport direction at the time of fixing.

Here, the maximum surface pressure Pmax of the nip portion N in the recording material transport direction is the maximum value in the pressure distribution in the transport direction passing through the center A in the paper passing region of the nip portion N. Here, the center A is the center in the longitudinal direction in the paper passing region of the nip portion N. The paper passing area of the nip portion N is an area of the nip portion N through which the recording material fixed by the fixing device 40 can pass. In the fixing device 40 of the present embodiment, the center of the recording material to be passed in the width direction is conveyed with reference to the center in the longitudinal direction of the nip portion N (center reference paper passing).

When the fixing device 40 has a plurality of stages of loads that can be pressurized at the time of fixing, the maximum surface pressure at the load that maximizes the maximum surface pressure among them is defined as the maximum surface pressure Pmax used in this measurement method. .. That is, in the case of a load having a maximum surface pressure among a load having a plurality of stages, the maximum value in the pressure distribution in the transport direction passing through the center A is used in the paper passing region of the nip portion N.

Further, the pressure applied to the nip portion N is measured using a tactile sensor (manufactured by Nitta Corporation). As the measurement conditions, measurement is performed at intervals of 0.5 mm in the transport direction and at intervals of 2 mm in the direction perpendicular to the transport direction.

In addition, pressurizing the fixing film and the glass plate with the maximum surface pressure refers to the following. That is, when the load applied to the glass plate in (1-2) above is N (unit: N), and the nip area generated when the glass plate and the fixing film are pressed against each other with the load N is S (unit: m ² ). It means that a load is applied to the glass plate so that N / S = Pmax.

The pressing force of the fixing device 40 is 150 to 250 N in total pressure (total load), and the maximum surface pressure Pmax of the nip portion N in the recording material transport direction at the time of fixing is 0.09 MPa or more and 0.12 MPa or less.

(Second measurement method)
Next, the second measurement method will be described. On the surface of plain paper as a recording paper, fiber unevenness (formation unevenness) having a period larger than that of paper fibers is observed, which is caused by aggregation of paper fibers. For such relatively large irregularities, the fixing member (fixing film) is required to have a followability at a level larger than the non-contact diameter shown in the first measurement method. Therefore, it is important to capture the followability of the fixing film at the sub mm level.

Therefore, in the present embodiment, the fixing film heated to the heating temperature at the time of fixing (150 ° C. near the fixing temperature) is pressurized with the probe shown below instead of the pressure roller. Then, it is confirmed whether or not the characteristic parameters of the fixing film satisfy the predetermined image quality evaluation items (gloss and gloss unevenness).

That is, in the present embodiment, a micro rubber hardness tester (trade name: MD-1 capa type C, manufactured by Polymer Meter Co., Ltd.) is used as a hemispherical probe having a crown height of 0.50 mm and a diameter of 1.0 mm. board. When a predetermined load is applied to this probe, the pressure (stress) applied to the hemispherical crown of the probe having a diameter of 1 mm is measured as the contact pressure. In addition, the amount of penetration of the probe is measured as the amount of displacement (deformation amount).

FIG. 8 is a graph showing the relationship between the contact pressure and the gloss, and FIG. 9 is a graph showing the relationship between the displacement amount and the rank of the gloss unevenness of the image. In each case, the thickness and material of the release layer constituting the fixing film, the thickness and material of the elastic layer, and the pressing force are changed to some levels.

Here, the gloss shown on the vertical axis of FIG. 8 is a value at 60 degrees using a handy gloss meter (PG-1M type, manufactured by Nippon Denshoku Industries Co., Ltd.). Further, the rank of the gloss unevenness of the image shown on the vertical axis of FIG. 9 is numerically evaluated on a scale of 10 by visually confirming the target sample and the comparison sample. Rank 10 is the best, rank 1 is the lowest, and rank 3 or higher is an acceptable level.

In this way, it was found that the contact pressure strongly correlates with the gloss and the displacement amount strongly correlates with the uneven gloss of the image.

Then, it was confirmed that an image having a high gloss as targeted can be obtained when the pressure (contact pressure) of the crown (side of the hemisphere of the probe) of the probe in contact with the fixing film is 0.39 MPa or more. From the viewpoint of gloss of the toner image, good image quality can be obtained if the contact pressure is 0.39 MPa or more, but the upper limit is 1 MPa based on the maximum surface pressure that can be taken by the fixing device 40. That is, it is preferably 0.39 MPa or more and 1 MPa or less.

In addition, it was confirmed that when the displacement amount (penetration depth into the fixing film) of the fixing film by the probe with a hemispherical crown is 35 μm or more (35 μm or more and 90 μm or less), an image in which gloss unevenness is suppressed is obtained as a target. did.

That is, as a result of measuring the belt (fixing member) 41 used in the fixing device 40 by the above-mentioned second measuring method, when the contact pressure is 0.39 MPa or more and 1 MPa or less, the belt 41 has a high gloss as targeted. It is a belt that can obtain an image with. Further, as a result of measuring the belt (fixing member) 41 used in the fixing device 40 by the above-mentioned second measurement method, when the displacement amount is 35 μm or more and 90 μm or less, the belt 41 suppresses gloss unevenness as a target. It is a belt from which the image is obtained.

Here, when the belt (fixing member) 41 used in the fixing device 40 is measured by the above-mentioned second measuring method, the probe in contact with the belt 41 is in the recording material transport direction of the nip portion N at the time of fixing. Pressurize with a load corresponding to the maximum surface pressure Pmax. Thereby, it is possible to verify whether the image quality can be satisfied when the belt 41 is used in the actual fixing device 40. The definition of the maximum surface pressure Pmax is as described above.

Here, pressurizing the probe with the maximum surface pressure means the following. The load applied to the probe is M (unit: N). The area formed by the diameter of the probe (probe shaft diameter) that bites into the belt 41 when the probe is pressed against the belt 41 with a load M (the area of the circle because the probe shaft is a circle) is T (unit). : M ² ). In this case, it means that a load is applied to the probe so that M / T = Pmax.

(Trade-off relationship of member parameters)
Next, the relationship between the contact pressure and the displacement amount in this embodiment was confirmed. For example, the amount of displacement increases when the hardness of the elastic layer having a large thickness is low. However, when the displacement amount becomes large, the contact area with the probe becomes large, so that the contact pressure also decreases. Therefore, it is expected that there is a trade-off relationship between the contact pressure and the displacement amount. Therefore, we verified the relationship between the thickness and material of the release layer constituting the fixing film, the thickness and material of the elastic layer, and the pressure applied by changing the contact pressure and the amount of displacement. ..

FIG. 10 is a graph showing the relationship between the contact pressure and the displacement amount under various conditions. As shown in FIG. 10, it was found that if the fixing film was designed to increase the displacement amount, the contact pressure would decrease, and if the fixing film was designed to increase the contact pressure, the displacement amount would decrease.

Therefore, if the image quality level of one item is simply improved with respect to the items of the image quality of the toner image density, gloss, and uneven gloss described with reference to FIGS. 7 to 9, the image quality level of the other items is rather increased. It cannot be satisfied, which may lead to a decrease in the overall image quality level.

Therefore, in the fixing device 40 shown in the present embodiment, as described above, a belt (fixing member) 41 that satisfies each preferable value for these three image quality items is used. As a result, it is possible to achieve a good balance of image quality with respect to the three items of toner image density, gloss, and uneven gloss.

Specifically, it can be realized by using a fixing member for a surface layer and an elastic layer as shown in Table 1 described later.

(Evaluation experiment of fixing member in this embodiment)
Next, an experiment for evaluating the image quality of the fixing device using the fixing film in the present embodiment was carried out.

In this experiment, the hardness and thickness of the surface layer material of the fixing film, the hardness and thickness of the elastic layer material, and the average surface pressure were compared.

The experimental conditions will be described. In this experiment, the fixing device shown in FIG. 2 was used. The total pressure was 150 to 250 N, the size of the contact point between the fixing film and the pressure roller was 10 mm in the transport direction, and 330 mm in the direction orthogonal to the transport direction. Then, the profile of the pressure distribution of the nip portion N in the transport direction was set so that the maximum surface pressure of the nip portion N in the recording material transport direction was 0.09 to 0.12 MPa.

Further, the rotation speed of the pressure roller was set to 200 mm / s, and the outer peripheral temperature of the fixing film in the region in contact with the recording material was controlled to be 150 ° C.

As the density evaluation of the toner image, CS-680 (manufactured by Nippon Paper Industries, Ltd., 70 g paper) was used, and the evaluation was performed using an image loaded with ^{0.4 g / cm 2 of cyan toner.} The reflection density was measured using a color difference measuring device (spectral densitometer, manufactured by X-RITE Co., Ltd.), and a reflection density of 1.4 or more was marked with ◯, and a reflection density of 1.4 or less was marked with x. There is a correlation between the toner coverage and the reflection density, and when the toner coverage is 76% or more, the reflection density is 1.4 or more.

The gloss was evaluated using CS-680 (70 g paper manufactured by Nippon Paper Industries, Ltd.) and an image loaded with ^{0.4 g / cm 2 of cyan toner.} The gloss was a gloss at 60 degrees using a handy gloss meter (PG-1M type, manufactured by Nippon Denshoku Industries Co., Ltd.), and 6 or more was marked with ◯ and less than 6 was marked with x.

The uneven gloss was evaluated using GFC-104 (Nippon Paper Industries, Ltd., 104 g paper) and an image loaded with ^{0.4 g / cm 2 of black toner.} The uneven gloss was evaluated by the subjective evaluation of 5 people, and when it was judged that 3 or more people were good, it was evaluated as ○, and when 2 or less people, it was evaluated as ×.

The evaluation results are summarized in Table 1 below.

As shown in Table 1, the concentration is high and the displacement is 35 μm or more under the conditions that the non-contact diameter is 227 μm or less, the pressure at the crown of the part where the hemispherical probe contacts is 0.39 MPa or more, and the displacement amount is 35 μm or more. It was possible to obtain an image with high gloss and suppressed gloss unevenness. That is, the conditions 1-2, 1-3, 2-3, 3-4.

Regarding conditions 1-2, 1-3, 2-3, and 3-4, when the heating temperature at the time of fixing is 150 ° C., the Young's modulus of the surface layer at 150 ° C. is 25 MPa or more and 100 MPa or less, and the thickness of the surface layer. The size is 10 μm or more and 20 μm or less. The Young's modulus of the elastic layer at 150 ° C. is 0.17 MPa or more and 0.60 MPa or less, and the thickness of the elastic layer is 150 μm or more and 250 μm or less.

In this way, by optimizing the hardness and thickness of the surface layer material of the fixing film, the hardness and thickness of the elastic layer material, and the average surface pressure as described in the present embodiment, the toner concentration, gloss, and image gloss are optimized. We were able to obtain a configuration that satisfied the unevenness.

(Relationship between the present embodiment and the prior art)
The relationship between the present embodiment and the prior art will be described.

First, in Patent Document 1, the average surface pressure at the fixing nip portion is 0.2 to 1 MPa. In Patent Document 2, the average surface pressure is 1.2 kgf / cm ² or more and 3.0 ^{kgf / cm 2,} and when converted as 1 kgf = 9.8 N, the average surface pressure is 0.12 to 0.29 MPa.

Generally, the pressure distribution shape of the fixing device is an arc (curve shape), and the fact that the average surface pressure is in this range means that the maximum surface pressure is larger than the average surface pressure. It is different from (0.09 MPa or more and 0.12 MPa or less) (the maximum surface pressure is higher than that of the present embodiment).

Next, the second measurement method of the present embodiment, which is a measurement method in which the contact pressure and the displacement amount are related, is compared with the universal hardness measurement method described in Patent Document 1.

Patent Document 1 stipulates that the universal hardness when the displacement amount is 20 μm is 1.8 N / mm ² . Then, this universal hardness measurement is a method of measuring the hardness of a substance by plastically deforming it with an indenter of a quadrangular pyramid.

On the other hand, the hardness measurement in the present embodiment is a method of measuring the displacement amount and the tip pressure (stress received by the crown of the probe) at that time by elastically deforming by an indenter of a hemisphere.

Therefore, the measurement of universal hardness is different from the measurement of hardness in this embodiment.

As described above, according to the present embodiment, in a fixing device in which the maximum surface pressure of the nip portion N is lower than before, even if the surface of the recording material to be fixed is rough, a high density and high gloss can be obtained as a toner image, and Uneven density of toner images can be suppressed. Further, in a fixing device having a low maximum surface pressure, that is, a small load on the nip portion, it is expected that the life of the fixing device will be extended due to a decrease in the sliding frictional force of the fixing member. That is, in such a fixing device, it is possible to realize the same image quality as the conventional one.

(Modification example)
In the above-described embodiment, the preferred embodiment of the present invention has been described, but the present invention is not limited to this, and various modifications can be made within the scope of the present invention.

(Modification example 1)
The elastic layer 41b in the belt 41 described above may be composed of a single layer or a plurality of layers (including a first elastic layer and a second elastic layer). In this case, the values such as Young's modulus shown in Table 1 are understood to indicate the values of the elastic layer composed of a plurality of layers.

(Modification 2)
In the above-described embodiment, the recording paper has been described as the recording material, but in the present invention, the recording material capable of forming an image by the image forming apparatus is not limited to the paper. Generally, a recording material is a sheet-like member on which a toner image is formed by an image forming apparatus. Glossy paper and the like are included. In the above-described embodiment, the handling of the recording material (sheet) P has been described using terms such as paper feeding for convenience, but the recording material in the present invention is not limited to paper.

(Modification example 3)
In the above-described embodiment, the fixing device for fixing the unfixed toner image to the sheet has been described as an example, but the present invention is not limited to this, and the toner image assumed to be attached to the sheet is used in order to improve the gloss of the image. It can also be applied to a device for heating and pressurizing (also referred to as a fixing device in this case).

41 ... Belt (fixing film), 43 ... Heater, 44 ... Pressurized roller (rotating body)

Claims (6)

With a rotatable fixing member,
A rotating body that faces the fixing member and forms a nip portion that sandwiches and conveys a recording material carrying a toner image between the fixing member and the rotating body.
It has a heating member that heats the fixing member, and has
The maximum surface pressure in the recording material transport direction at the nip portion is 0.09 MPa or more and 0.12 MPa or less.
The fixing member is
When heated to the heating temperature at the time of fixing and pressed by the transparent plate at the maximum surface pressure via a sphere having a diameter of 20 μm instead of the rotating body, the transparent plate and the fixing are viewed from the pressurizing direction. The diameter of the region where the members do not contact is 40 μm or more and 227 μm or less.
When the crown is heated to the heating temperature at the time of fixing and the crown is pressurized at the maximum surface pressure by a hemispherical probe having a diameter of 1 mm instead of the rotating body, the pressure applied to the crown is 0.39 MPa or more and 1 MPa. The fixing device as follows, wherein the displacement amount by the probe is 35 μm or more and 90 μm or less. The fixing member has a base layer, an elastic layer provided outside the base layer, and a surface layer provided outside the elastic layer.
The Young's modulus of the elastic layer at 150 ° C. is 0.17 MPa or more and 0.60 MPa or less, and the thickness of the elastic layer is 150 μm or more and 250 μm or less.
The Young's modulus at the surface of 0.99 ° C. is not less 25MPa or more 100MPa or less, and fixing device according to claim 1, the thickness of the surface layer is equal to or is 10μm or more 20μm or less. When the ratio of the toner image on the paper as the recording material covering the white background of the paper is defined as the toner coverage, the toner coverage before fixing is 68%, and the toner after fixing is The fixing device according to claim 1 or 2 , wherein the coverage is 76% or more. The fixing device according to any one of claims 1 to 3, wherein the fixing member is a fixing film, and the heating member is a heater that comes into contact with the fixing film. A rotatable fixing member that forms a nip portion that is heated at the time of fixing and that sandwiches and conveys a recording material carrying a toner image with an opposing rotating body.
The maximum surface pressure of the nip portion in the recording material transport direction at the time of fixing is 0.09 MPa or more and 0.12 MPa or less.
A region that does not come into contact with the transparent plate when viewed from the pressurizing direction when heated to the heating temperature at the time of fixing and pressed by the transparent plate at the maximum surface pressure via a sphere having a diameter of 20 μm instead of the rotating body. The diameter of is 40 μm or more and 227 μm or less.
When heated to the heating temperature at the time of fixing and the crown is pressurized at the maximum surface pressure by a hemispherical probe having a diameter of 1 mm instead of the rotating body, the pressure applied to the crown is 0.39 MPa or more and 1 MPa or less. The fixing member is characterized in that the amount of displacement by the probe is 35 μm or more and 90 μm or less. It has a base layer, an elastic layer provided outside the base layer, and a surface layer provided outside the elastic layer.
The Young's modulus of the elastic layer at 150 ° C. is 0.17 MPa or more and 0.60 MPa or less, and the thickness of the elastic layer is 150 μm or more and 250 μm or less.
The fixing member according to claim 5 , wherein the Young's modulus of the surface layer at 150 ° C. is 25 MPa or more and 100 MPa or less, and the thickness of the surface layer is 10 μm or more and 20 μm or less.

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