WO2023234961A1

WO2023234961A1 - Heat generating layer for fixing belt having graphite particles dispersed

Info

Publication number: WO2023234961A1
Application number: PCT/US2022/049075
Authority: WO
Inventors: Keiji Komoto
Original assignee: Hewlett-Packard Development Company, L.P.
Priority date: 2022-06-03
Filing date: 2022-11-07
Publication date: 2023-12-07
Also published as: JP2023178025A

Abstract

An example fixing belt includes a heat generating layer. The heat generating layer contains a resin component and spherical graphite particles dispersed in the resin component.

Description

HEAT GENERATING LAYER FOR FIXING BELT HAVING GRAPHITE PARTICLES DISPERSED

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority from Japanese Patent Application No. 2022-091054, filed on June 03, 2022, in the Japan Patent Office, the disclosure of which is incorporated herein by reference in its entirety.

BACKGROUND

[0002] An image forming apparatus may include a fixing device to heat and press a sheet on to which a toner image is transferred, to fix the toner image to the sheet. The fixing device may include a fixing belt, and the sheet on to which the toner image is transferred may be heated by heat of the fixing belt. The fixing belt may be provided with a heat generating layer that generates heat by supplying electric power to the heat generating layer.

BRIEF DESCRIPTION OF DRAWINGS

[0003] Various examples will be described below by referring to the following figures.

[0004] FIG. 1 is a perspective view illustrating an imaging forming apparatus according to an example.

[0005] FIG. 2 is a perspective view illustrating a fixing device according to an example.

[0006] FIG. 3 is a perspective view illustrating a layer of a fixing belt according to an example.

[0007] FIG. 4 is a perspective view illustrating a layer of a fixing belt according to an example.

[0008] FIG. 5 is a perspective view illustrating evaluation of a laminate manufactured according to an example.

[0009] FIG. 6 is a graph illustrating a relationship between temperature and resistivity in a heat generating layer according to an example.

[0010] FIG. 7 includes graphs illustrating relationships between temperature and resistivity in heat generating layers according to various examples.

[0011] FIG. 8 includes graphs illustrating relationships between temperature and resistivity in heat generating layers according to various examples.

[0012] FIG. 9 includes graphs illustrating relationships between temperature and resistivity in heat generating layers of comparative examples 1 to 3.

DETAILED DESCRIPTION

[0013] Hereinafter, examples of an imaging forming apparatus, a fixing device, and a fixing belt will be described with reference to the drawings.

[0014] FIG. 1 is a perspective view illustrating an imaging forming apparatus according to an example. An image forming apparatus 1 illustrated in FIG. 1 includes a recording medium conveying device 10, a transfer device 20, photosensitive drums 30, a fixing device 40, discharge rollers 52 and 54, and four developing devices 100.

[0015] The recording medium conveying device 10 is to contain a sheet P as a recording medium on which an image is to be finally formed, and is to convey the sheet P to a recording medium conveyance path. In an example, an overhead projector (OHP) film or the like other than the sheet P may be used as a recording medium.

[0016] The transfer device 20 is to convey a toner image formed by the four developing devices 100, to a secondary transfer region R in which the toner image is to be secondarily transferred on to the sheet P. The transfer device 20 includes a transfer belt 21 , suspension rollers 21 a, 21 b, 21 c, and 21 d to suspend the transfer belt 21 , primary transfer rollers 22 to pinch the transfer belt 21 together with the photosensitive drums 30, and a secondary transfer roller 24 to pinch the transfer belt 21 together with the suspension roller 21 d.

[0017] The photosensitive drum 30 may be an electrostatic latent image carrier on a peripheral surface of which an image is to be formed. The photosensitive drum 30 may include, for example, an organic photoconductor (OPC). The image forming apparatus 1 may form a color image and, for example, four photosensitive drums 30 may be provided along a movement direction of the transfer belt 21 to correspond to different colors such as magenta, yellow, cyan, and black. As illustrated in FIG. 1 , a charging roller 32, an exposure device 34, the developing devices 100, and a cleaning device 38 may be provided around each of the photosensitive drums 30.

[0018] The fixing device 40 is to attach and fix a toner image that is secondarily transferred from the transfer belt 21 on to the sheet P, to the sheet P. The fixing device 40 may be, for example, a belt nip-type fixing device. The fixing device 40 may include, for example, a fixing belt 41 and a pressure roller 42. The pressure roller 42 may be disposed to be in pressure contact with the fixing belt 41.

[0019] Each of the four developing devices 100 is to develop an electrostatic latent image formed on the peripheral surface of the photosensitive drum 30, and generate a toner image by causing a developing roller 110 to carry a developer using a toner supplied from a toner tank 36 provided to correspond to each of the developing devices 100, and by moving the toner of the developer carried on the developing roller 110, to the electrostatic latent image formed on the peripheral surface of the photosensitive drum 30. Four toner tanks 36 are respectively filled with magenta, yellow, cyan, and black toners.

[0020] The discharge rollers 52 and 54 are to discharge the sheet P to which the toner image is fixed by the fixing device 40, to the outside of the apparatus.

[0021] FIG. 2 is a perspective view illustrating a fixing device according to an example. The fixing device 40 illustrated in FIG. 2 includes the fixing belt 41 and the pressure roller 42. The fixing belt 41 may be, for example, a belt having an endless shape (endless belt). The fixing belt 41 may be formed in a cylindrical shape (for example, a circular cylindrical shape) that is rotatable around a rotation axis. The pressure roller 42 may include a shaft portion 42a and an outer peripheral portion 42b that is elastically deformable. The outer peripheral portion 42b may be attached around the shaft portion 42a and be rotatable around a rotation axis. The pressure roller 42 is to press the sheet P against the fixing belt 41 . Accordingly, a nip region, in which the toner image on the sheet P is to be fixed to the sheet P, may be formed between the fixing belt 41 and the pressure roller 42.

[0022] FIG. 3 is a perspective view illustrating a layer of a fixing belt according to an example. A fixing belt 41 A may include a heat generating layer

411 , a support layer 412 provided on an outer peripheral surface of the heat generating layer 411 , an elastic layer 413 provided on an outer peripheral surface of the support layer 412, and a surface layer 414 provided on an outer peripheral surface of the elastic layer 413.

[0023] FIG. 4 is a perspective view illustrating a layer a fixing belt according to an example. A fixing belt 41 B of may include the support layer 412, the heat generating layer 411 provided on the outer peripheral surface of the support layer

412, the elastic layer 413 provided on an outer peripheral surface of the heat generating layer 411 , and the surface layer 414 provided on the outer peripheral surface of the elastic layer 413.

[0024] The heat generating layer 411 may include a heat generating element and contain a resin component and spherical graphite particles 45 dispersed in the resin component. The heat generating layer 411 can also be referred to as a layered heat generating element. A thickness of the heat generating layer 411 may be 10 pm or more, 50 pm or more, 1000 pm or less, or 500 pm or less.

[0025] The support layer 412 may include, for example, a resin. Examples of the resin include polyimide resin, polyether ether ketone resin, polyamide-imide resin, polyphenylene sulfide resin, and the like. A thickness of the support layer 412 may be 20 pm or more, 50 pm or more, 300 pm or less, or 200 pm or less. [0026] The elastic layer 413 may include, for example, a rubber. Examples of the rubber include fluorine rubber, silicone rubber, and the like. A thickness of the elastic layer 413 may be 100 m or more and may be 300 pm or less. In other examples, the fixing belt may not include an elastic layer.

[0027] The surface layer 414 can also be referred to as a release layer having releasability. The surface layer 414 may include, for example, fluororesin. Examples of the fluororesin include polytetrafluoroethylene (PTFE), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), tetrafluoroethylene-hexafluoroethylene copolymer (FEP), and the like. In an example, the surface layer 414 may contain a PFA tube. A thickness of the surface layer 414 may be 5 pm or more and may be 30 pm or less.

[0028] The fixing belts 41 A and 41 B may each further include an electrode (not illustrated) to supply electric power to the heat generating layer 411. The electrode may be electrically connectable to the heat generating layer 411 and may be exposed to be electrically connectable to an external power source. The electrode may be made of, for example, Cu, Ni, Ag, Al, Au, Mg, or the like. A thickness of the electrode may be 1 pm or more and may be 50 pm or less.

[0029] An example of a heat generating element to form the heat generating layer 411 will be described. In the following description, the heat generating element may be described as a heat generating layer (i.e., a layered heat generating element).

[0030] The heat generating element may contain a resin component and spherical graphite particles dispersed in the resin component.

[0031] The heat generating element has an inherent resistance and is a resistance heat generating element that generates heat based on a voltage being applied thereto and a current flowing therethrough. The heat generating element has a characteristic in which the electrical resistance rises with a rise in temperature (e.g., a positive temperature characteristic (PTC)), and maintains temperature in a low temperature region (for example, 20 to 50°C).

[0032] The heat generating element having the PTC characteristic has a trip temperature Tt. Here, the trip temperature Tt is a lowest temperature in a temperature range of 30°C or higher among temperatures showing a resistivity that is three times a resistivity at a 10°C lower temperature (i.e., a temperature at which a ratio of resistivity based on the surface temperature of the heat generating element having risen by 10°C is 3), and can be confirmed by measuring a surface temperature and a resistivity of the heat generating element. In an example, the resistivity of the heat generating element is measured each time the surface temperature of the heat generating element rises by 10 to 15°C by heating the heat generating element from the outside. An increase factor fo of the resistivity from a previous measurement temperature for each measurement temperature is obtained. Based on a measurement temperature on a high temperature side of two measurement temperatures being T_x and a measurement temperature on a low temperature side being T_x-i, the increase factor fo is a value calculated by an equation: resistivity at the measurement temperature T_x/resistivity at the measurement temperature T_x-i

[0033] The increase factor fo is converted into an increase factor fi of the resistivity based on the surface temperature rising by 10°C by being divided by a difference between the two measurement temperatures (T_x - T_x-i) and being multiplied by 10. The trip temperature Tt is determined by plotting the increase factor fi obtained in such a manner with respect to an average value of two measurement temperatures ([T_x + -1/2]), by connecting each plot with a straight line, and by reading a lowest temperature based on the increase factor fi being 3, from the straight line. As described above, in various examples, the trip temperature is calculated from a change in temperature rise.

[0034] The trip temperature Tt of the heat generating element may be, for example, 60 to 200°C or may be 70 to 200°C. In various examples, the larger a ratio r between a resistivity at a temperature 10°C lower than the trip temperature Tt and a resistivity at a temperature 10°C higher than the trip temperature Tt (i.e. , [resistivity at the temperature 10°C higher than the trip temperature Tt]/[resistivity at the temperature 10°C lower than the trip temperature Tt]), the better PTC characteristic the heat generating element has. The ratio r may be, for example, 2.0 to 20.0 or may be 3.0 to 18.0 or 5.0 to 18.0.

[0035] As the resin component, a resin can be used which has heat resistance so as not to decompose at a temperature lower than a reach temperature of the heat generating element in use. Based on the reach temperature of the heat generating element in use being T°C, a weight loss rate based on the resin component being heated from 25°C to (T + 10) °C can be, for example, 5% by mass or less. The weight loss rate is a weight loss rate based on a weight of the resin component at 25°C and is obtained by thermogravimetrydifferential thermal measurement. The reach temperature (T) of the heat generating element in use varies depending on the application and may be 80 to 200°C based on the heat generating element being used in the fixing belt.

[0036] A temperature at which the weight loss rate based on the resin component being heated to 25°C is larger than 5% by mass (i.e. , 5% weight loss temperature) may be 90°C or higher, 180°C or higher, 210°C or higher, or 250°C or lower.

[0037] The resin component may be a rubber-like component. Examples of the resin component include silicone resin (including silicone rubber), polyimide resin, polyphenylene sulfide resin, and the like. These resin components may be used alone or may be used in combination of two or more.

[0038] A content of the resin component may be 30% by volume or more, 35% by volume or more, 40% by volume or more, 75% by volume or less, 70% by volume or less, 65% by volume or less, 30 to 75% by volume, 35% to 70% by volume, or 40 to 65% by volume, based on a total volume of the heat generating element.

[0039] The spherical graphite particles may have, for example, an average circularity of 0.90 or more. In this description, graphite particles having an average circularity of 0.90 or more are defined as spherical graphite particles. The average circularity of the graphite particles may be 0.90 or more or 0.91 or more. The larger the average circularity of the graphite particles, the closer the shape of the graphite particles to a true spherical shape. In that case, the particles may be dissociated from each other based on the resin expanding. A maximum value of the average circularity of the graphite particles is 1.00. As described above, the average circularity of the graphite particles may be 0.90 to 1 .00 or 0.91 to 1 .00.

[0040] In this description, the average circularity is an average value of circularities measured using, for example, an image analysis device (for example, a flow-type particle analysis device manufactured by Malvern Panalytical Ltd (FPIA-3000), or the like), and is defined as an average value of circularities obtained for 3000 particles randomly selected. The "circularity" is an index indicating how close a particle is to a perfect sphere, and can be calculated by an equation: circularity = 2A/( S)/L

[0041] The circularity may be calculated using a projected area (S) and a peripheral length (L) obtained by image analysis of the graphite particle. In the image analysis, for example, measurement may be performed in an HPF mode using a lens having a high magnification (e.g., 20 times). In an example, a resolution is approximately 0.185 pm as a calculated value obtained from a pixel size and a lens magnification. A plurality of equations for calculating a circularity may be used in addition to the above equation. However, even based on a circularity being obtained by another calculation equation obtained by another device, the circularity can be converted into and compared to the circularity obtained in this description. For example, a circularity defined as 4KS/L² can be converted into the circularity of the present disclosure by calculating a square root of the circularity calculated by the equation.

[0042] A coefficient of variation of the circularities of the graphite particles may be 0.10 or less, 0.09 or less, or 0.08 or less. A lower limit value of the coefficient of variation of the circularities of the graphite particles is 0 and may be 0.01 or more. As described above, the coefficient of variation of the circularities of the graphite particles may be 0.01 to 0.10, 0.01 to 0.09, or 0.01 to 0.08.

[0043] A standard deviation of the circularities of the graphite particles may be 0.10 or less, 0.09 or less, or 0.08 or less. A lower limit value of the standard deviation of the circularities of the graphite particles is 0 and may be 0.02 or more. As described above, the standard deviation of the circularities of the graphite particles may be 0 to 0.10, 0 to 0.09, or 0.02 to 0.08.

[0044] A 10th percentile circularity of the graphite particles may be 0.78 or more, 0.79 or more, or 0.80 or more. The 10th percentile circularity of the graphite particles may be 0.99 or less, 0.98 or less, or 0.97 or less. As described above, the 10th percentile circularity of the graphite particles may be 0.78 to 0.99, 0.79 to 0.98, or 0.80 to 0.97. [0045] A 50th percentile circularity of the graphite particles may be 0.91 or more, 0.92 or more, or 0.93 or more. The 50th percentile circularity of the graphite particles may be 1.00 or less or 0.99 or less. As described above, the 50th percentile circularity of the graphite particles may be 0.91 to 1 .00, 0.92 to 1 .00, or 0.93 to 0.99.

[0046] A 90th percentile circularity of the graphite particles may be 0.96 or more, 0.97 or more, or 0.98 or more. The 90th percentile circularity of the graphite particles may be 1 .00 or less. As described above, the 90th percentile circularity of the graphite particles may be 0.96 to 1 .00, 0.97 to 1 .00, or 0.98 to 1 .00.

[0047] The 10th percentile circularity, the 50th percentile circularity, and the 90th percentile circularity of the graphite particles may be obtained from a cumulative distribution curve of the circularities of the graphite particles. The cumulative distribution curve of the circularities of the graphite particles may be created by obtaining a cumulative distribution based on a frequency distribution at each representative value of the circularity. As an example, in a frequency distribution chart in which circularity is on the horizontal axis and frequency (i.e., ratio of particles per each circularity based on the total number of particles being 100) is on the vertical axis, a curve showing cumulative values from a side where the circularity is small is referred to as a cumulative distribution curve, and circularities based on cumulative values of the number of particles from the side where the circularity is small being 10%, 50%, and 90% of the total are referred to as a "10th percentile circularity", a "50th percentile circularity", and a "90th percentile circularity", respectively.

[0048] A 10th percentile particle diameter based on a volume of the graphite particles (hereinafter, also referred to as "D10") may be 2.0 pm or more,

2.5 pm or more, or 3.0 pm or more. The D10 may be 15.0 pm or less, 13.0 pm or less, or 11 .0 pm or less. As described above, the D10 may be 2.0 to 15.0 pm, 2.5 to 13.0 pm, or 3.0 to 11.0 pm.

[0049] A 50th percentile particle diameter based on the volume of the graphite particles (hereinafter, also referred to as "D50") may be 3.0 pm or more,

3.5 pm or more, or 4.0 pm or more. The D50 may be 50.0 pm or less, 45.0 pm or less, or 40.0 pm or less. As described above, the D50 may be 3.0 to 50.0 pm, 3.5 to 45.0 pm, or 4.0 to 40.0 pm.

[0050] A 90th percentile particle diameter based on the volume of the graphite particles (hereinafter, also referred to as "D90") may be 3.5 pm or more, 4.0 pm or more, or 4.5 pm or more. The D90 may be 60.0 pm or less, 55.0 pm or less, or 50.0 pm or less. As described above, the D90 may be 3.5 to 60.0 pm, 4.0 to 55.0 pm, or 4.5 to 50.0 pm.

[0051] The D10, the D50, and the D90 may be obtained from a cumulative particle size distribution curve based on the volume of the graphite particles. The cumulative particle size distribution curve based on the volume of the graphite particles may be obtained by measurement using a Coulter counter-type measurement device (for example, a Coulter counter (manufactured by Beckman Coulter, Inc.).

[0052] A ratio of the D10 (10th percentile particle diameter based on the volume of the graphite particles) to the D50 (50th percentile particle diameter based on the volume of the graphite particles) may be 0.40 or more, 0.45 or more, or 0.50 or more. The ratio of the D10 to the D50 may be 0.95 or less, 0.90 or less, or 0.85 or less. As described above, the ratio of the D10 to the D50 may be 0.40 to 0.95, 0.45 to 0.90, or 0.50 to 0.85.

[0053] A ratio of the D10 (10th percentile particle diameter based on the volume of the graphite particles) to the D90 (90th percentile particle diameter based on the volume of the graphite particles) may be 0.15 or more, 0.20 or more, or 0.25 or more. The ratio of the D10 to the D90 may be 0.90 or less, 0.85 or less, or 0.80 or less. As described above, the ratio of the D10 to the D90 may be 0.15 to 0.90, 0.20 to 0.85, or 0.25 to 0.80.

[0054] A content of the graphite particles may be 25% by volume or more, 30% by volume or more, 35% by volume or more, 70% by volume or less, 65% by volume or less, or 60% by volume or less or may be 25 to 70% by volume, 30% to 65% by volume, or 35 to 60% by volume, based on the total volume of the heat generating element.

[0055] The heat generating element may contain the resin component and the graphite particles and may further contain another component. The other components may be selected from materials having heat resistance at a temperature at which the heat generating element is used. Examples of the other component include conductive materials such as carbon black, carbon nanotubes, metal powder, and the like.

[0056] The heat generating element can be manufactured using, for example, a dispersion liquid containing the resin component or a material of the resin component, the graphite particles, and a dispersion medium (for example, toluene). For example, the layered heat generating element may be obtained by preparing the dispersion liquid, by applying the dispersion liquid to form a coating film, and by heating the coating film to remove the dispersion medium. The material of the resin component may be, for example, two or more types of materials that react with each other based on being mixed or due to an external stimulus (i.e. , heating or the like) after mixing, to form the resin component.

[0057] The image forming apparatus is not limited to the above example and may be, for example, an inkjet apparatus. The heat generating element can also be suitable as a heat source in a heat generating device that dries inkjet ink discharged on a sheet, inside the inkjet apparatus. The heat generating element can be widely used in other heat generating devices or the like in which temperature control is used.

Examples

[0058] Hereinafter, examples and comparative examples will be described, but the present disclosure is not limited to the following examples.

[0059] Graphite particles (GF) 1 to 13 shown in the following Table 1 were prepared.

SUBSTITUTE SHEET (RULE 26) [0060] In Table 1 , the graphite particles 1 to 10 are spherical graphite particles, and the graphite particles 11 to 13 are flat graphite particles.

[0061] In Table 1 , "average", "10% value", "50% value", and "90% value" represent an average circularity, a 10th percentile circularity, a 50th percentile circularity, and a 90th percentile circularity of the graphite particles, respectively. An average circularity of and a standard deviation of circularities of the graphite particles 1 to 13 were measured using a flow-type particle analysis device manufactured by Malvern Panalytical Ltd (FPIA-3000), and the 10th percentile circularity, the 50th percentile circularity, and the 90th percentile circularity were obtained from a cumulative distribution curve of the circularities of the graphite particles obtained by the measurement. In addition, a coefficient of variation of the circularities was calculated using the average circularity and the standard deviation of the circularities obtained by the measurement. The measurement samples in the measurement were manufactured by adding 5 mL of ion- exchanged water to the graphite particles, adding three drops of a solution containing 30% Contaminon® N, and irradiating the graphite particles with ultrasonic waves for 15 minutes.

[0062] In Table 1 , "D10", "D50", and "D90" represent a 10th percentile particle diameter, a 50th percentile particle diameter, and a 90th percentile particle diameter based on a volume of the graphite particles, respectively. In addition, "D10/D50" represents a ratio of the D10 (10th percentile particle diameter based on the volume of the graphite particles) to the D50 (50th percentile particle diameter based on the volume of the graphite particles), and "D10/D90" represents a ratio of the D10 (10th percentile particle diameter based on the volume of the graphite particles) to the D90 (90th percentile particle diameter based on the volume of the graphite particles). The D10, the D50, and the D90 percentiles of the graphite particles 1 to 13 were obtained from a cumulative particle size distribution based on the volume of the graphite particles obtained by measurement using a Coulter counter-type measurement device (for example, a Coulter counter (manufactured by Beckman Coulter, Inc.)). The measurement samples were manufactured by adding 5 mL of ion-exchanged water to the graphite particles, adding three drops of a solution containing 30% Contaminon® N, and irradiating the graphite particles with ultrasonic waves for 15 minutes.

[0063] KE-106 (manufactured by Shin-Etsu Chemical Co., Ltd.) as a main agent of liquid silicone rubber (LSR), toluene as a solvent, and the graphite particles (GF) 1 were added to 100 mL of Polycup™ in order while performing stirring, and the stirring was continued until the graphite particles were substantially uniformly mixed in the resin. Thereafter, a composition for forming a heat generating layer was obtained by adding CAT-RG (manufactured by Shin- Etsu Chemical Co., Ltd.) as a curing agent of the liquid silicone rubber to the obtained mixture and by further continuing the stirring until the entirety was substantially uniformly mixed. A mixing amount of each component was as shown in Table 2. The total amount of KE-106 and CAT-RG was set such that a volumetric ratio between a content of the resin component (i.e., liquid silicone rubber) generated due to a reaction thereof and a content of the graphite particles was 50 : 50.

[0064] Subsequently, a laminate for evaluation including a heat generating layer containing the resin component (i.e., silicone rubber) and the spherical graphite particles (i.e., graphite particles 1 ) dispersed in the resin component was manufactured using the composition. FIG. 5 is a perspective view illustrating evaluation of a laminate manufactured according to an example. In the manufacturing, a glass plate (201 ) with a size of 50 mm x 50 mm and a thickness of 0.7 mm of which the surface was degreased with isopropyl alcohol was prepared in advance. Two copper tapes (202), each with a size of 5 mm x 50 mm, were prepared and affixed along two opposing sides of four sides forming a peripheral edge of the degreased surface of the glass plate (201 ). The composition was substantially uniformly applied to the degreased surface of the glass plate (201 ) using a bar coater to form a coating film with a size of 50 mm x 45 mm (size of a region under which the copper tape does not exist was 40 mm x 45 mm). The coating film was cured to form heat generating layer (203) by leaving the obtained laminated film under a room temperature environment for 15 minutes, by putting the laminated film in a hot air circulating oven preheated at 150°C, and by heating the laminated film for 30 minutes. Accordingly, a laminate (200) for evaluation illustrated in FIG. 5 was obtained. A thickness of the formed heat generating layer (203) (i.e., a thickness of a region under which the copper tape does not exist) was 73.2 pm. The thickness of the heat generating layer (203) was measured using a thickness meter (Digimatic Indicator ID-S112X manufactured by Mitutoyo Corporation). Incidentally, a 5% weight loss temperature of the resin component (i.e., silicone rubber) contained in the heat generating layer (203), which is obtained by thermogravimetry-differential thermal measurement, is 220°C or higher.

[0065] A resistivity of the laminate (200) for evaluation was measured using a low resistivity meter (main body: Loresta-GX MCP-T700 manufactured by Nittoseiko Analytech Co., Ltd.), an ESP probe (pin spacing: 5 mm and pin tip: 0.37R x 4), and a probe checker (for ASP/ESP/LSP). The size (40 mm x 45 mm) and the film thickness (73.4 pm) of the heat generating layer measured as described above were input to the low resistivity meter, measurement was performed at any five locations in the vicinity of a central portion, and an average value of the measurement was defined as a resistivity rv of the heat generating layer at room temperature.

[0066] The laminate (200) for evaluation was placed on a 6-series hot plate from a glass plate (201 ) side, and a current based on a voltage of 1 V being applied between electrodes at an interval of approximately 12°C was measured while raising temperature from the room temperature. A resistivity at each temperature was calculated from the measured current value, the voltage, and the size (i.e., size of a region under which the electrodes do not exist: 40 mm x 45 mm) of the heat generating layer. In addition, a K-type thermocouple was affixed to a surface of the heat generating layer to also record a surface temperature of the heat generating layer. FIG. 6 is a graph illustrating a relationship between measurement temperature and resistivity in a heat generating layer according to an example. In more detail, FIG. 6 illustrates a relationship between measurement temperature and resistivity based on the temperature rising and the temperature falling. The horizontal axis of the graph of FIG. 6 represents temperature and the vertical axis represents resistivity. Curves in the graph of FIG. 6 are obtained by connecting each plot with a straight line.

[0067] The increase factor fi of the resistivity based on the surface temperature rising by 10°C between measurement temperatures was obtained by obtaining the increase factor fo of the resistivity from a previous measurement temperature (i.e., increase factor of the resistivity every approximately 12°C) for each measurement temperature, by dividing the increase factor fo by a temperature difference (approximately 12°C) between the measurement temperatures, and by multiplying the resultant by 10. The trip temperature Tt was obtained by plotting the increase factor fi of the resistivity based on the temperature rising by 10°C between two measurement temperatures, which was obtained in such a manner, with respect to an average value of the two measurement temperatures, by connecting each plot with a straight line, and by reading a lowest temperature at which the increase factor fi was 3, from the straight line.

[0068] In addition, a resistivity at a temperature 10°C higher than the trip temperature Tt and a resistivity at a temperature 10°C lower than the trip temperature Tt were read from a curve for temperature rise in the graph of FIG. 6, and the ratio r between the resistivity at the temperature 10°C lower than the trip temperature Tt and the resistivity at the temperature 10°C higher than the trip temperature Tt ([resistivity at the temperature 10°C higher than the trip temperature Tt]/[resistivity at the temperature 10°C lower than the trip temperature Tt]). The larger the ratio r, the easier the electrical resistance in the vicinity of the trip temperature rises and the better the PTC characteristic. Results are shown in Table 2.

[0069] Except that the types of graphite particles and/or the mixing ratio of each mixing component were changed as shown in Table 2, respective compositions for forming heat generating layers of Examples 2 to 12 and Comparative Examples 1 to 3 were manufactured in the same manner as in Example 1. Except that the composition of each example obtained above was used and coating films were formed such that thicknesses of the heat generating layers had values shown in Table 2, laminates for evaluation were manufactured in the same manner as in Example 1 , and the PTC characteristic of the heat generating layers were evaluated. Results are shown in Table 2 and FIGS. 7 to 9. FIGS. 7 to 9 are graphs illustrating relationships between measurement temperature and resistivity in heat generating layers based on rising temperature.

SUBSTITUTE SHEET (RULE 26) [0070] As demonstrated above, in Examples 1 to 12 using the graphite particles 1 to 10 including spherical graphite particles, it was confirmed that the heat generating layers having the trip temperature Tt were formed. In addition, as illustrated in FIG. 6, it was confirmed that, based on the temperature falling, the resistivity of the heat generating layer also changed similarly to a situation in which the temperature rises.

[0071] While various examples of the heat generating layer and the like have been described above, it will be apparent that various modifications and changes can be made without departing from the concept of the claims. Namely, all changes within the concept described in the claims are intended to be included.

Claims

1 . A fixing belt comprising: a heat generating layer, wherein the heat generating layer contains a resin component and spherical graphite particles dispersed in the resin component.

2. The fixing belt according to claim 1 , wherein an average circularity of the graphite particles is 0.90 to 1 .00.

3. The fixing belt according to claim 1 , wherein a coefficient of variation of circularities of the graphite particles is 0.10 or less.

4. The fixing belt according to claim 1 , wherein a standard deviation of circularities of the graphite particles is 0.10 or less.

5. The fixing belt according to claim 1 , wherein a 10th percentile circularity of the graphite particles is 0.78 to 0.99.

6. The fixing belt according to claim 1 , wherein a 90th percentile circularity of the graphite particles is 0.96 to 1 .00.

7. The fixing belt according to claim 1 , wherein a 50th percentile circularity of the graphite particles is 0.91 to 1 .00.

8. The fixing belt according to claim 1 , wherein a 50th percentile particle diameter based on a volume of the graphite particles is 3.0 to 50.0 pm.

9. The fixing belt according to claim 1 , wherein a ratio of a 10th percentile particle diameter based on a volume of the graphite particles to a 50th percentile particle diameter based on the volume of the graphite particles is 0.40 to 0.95.

10. The fixing belt according to claim 1 , wherein a content of the graphite particles is 25 to 70% by volume based on a total volume of the heat generating layer.

11 . The fixing belt according to claim 1 , wherein a content of the resin component is 30 to 75% by volume based on a total volume of the heat generating layer.

12. The fixing belt according to claim 1 , further comprising: a support layer provided on an outer peripheral surface of the heat generating layer; an elastic layer provided on an outer peripheral surface of the support layer; and a surface layer provided on an outer peripheral surface of the elastic layer.

13. The fixing belt according to claim 1 , further comprising: a support layer; an elastic layer provided on an outer peripheral surface of the heat generating layer; and a surface layer provided on an outer peripheral surface of the elastic layer, wherein the heat generating layer is provided on an outer peripheral surface of the support layer.

14. A fixing device comprising: a fixing belt; and a pressure roller, wherein the fixing belt includes a heat generating layer, and wherein the heat generating layer contains a resin component and spherical graphite particles dispersed in the resin component.

15. An image forming apparatus comprising: a fixing device, wherein the fixing device includes a fixing belt and a pressure roller, wherein the fixing belt includes a heat generating layer, and wherein the heat generating layer contains a resin component and spherical graphite particles dispersed in the resin component.