JP5171480B2 - Image heating and pressing apparatus and image forming apparatus - Google Patents

Description

  The present invention relates to an image heating and pressing apparatus that heats and presses a recording medium carrying a toner image while nipping and conveying the recording medium, and an image forming apparatus including the image heating and pressing apparatus.

  Examples of the image heating and pressing device include a fixing device that fixes a toner image on a recording medium, and a gloss increasing device that increases the gloss of an image by heating the toner image fixed on the recording medium. it can.

  A fixing device used in a conventional image forming apparatus is a toner formed on a recording medium while the recording medium is nipped and conveyed by a pressure contact portion (nip portion) of a fixing roller and a pressure roller that are pressed against each other. A configuration in which an image is heated and pressurized is common.

  In the nip portion, recording is performed by applying pressure while the toner is heated to a glass transition temperature or higher to become a viscoelastic body, that is, by applying appropriate pressure when the toner has an appropriate melt viscosity. The fixing process is performed by spreading the toner on the medium. At this time, deformation of the toner particles and coalescence of the toner particles occur on the recording medium, and the toner medium wets and spreads to form a thin toner layer. At the same time, when the toner layer is pressed against the recording medium, the toner layer enters the fibers of the recording medium, is anchored (throwed), and is fixed on the recording medium. As described above, the fixing process by heating and pressurization is a process of toner melting → deformation → wet spreading → fiber fixing, and among them, melting and deformation of the toner are important factors.

  The melting state and deformation of the toner have a significant influence on the type of recording medium. For example, when thick paper thicker than plain paper is used, the heat capacity of the recording medium increases, so the amount of heat given to the toner decreases and the toner becomes insufficiently melted. As a result, the toner has a high melt viscosity, and even when a pressure is applied, the toner does not sufficiently wet and spread, and a “pode” occurs in which the toner remains isolated while maintaining the particle form. On the other hand, when thin paper that is thinner than plain paper is used, the heat capacity of the recording medium becomes small, so the amount of heat given to the toner increases and the toner becomes excessively melted. As a result, the melt viscosity of the toner becomes low, and even when a pressure is applied, the layer formed by the toner flows, and “through” occurs where the fibers on the recording medium are exposed. As described above, there is a problem that the properties related to the fixing of the toner to the recording medium change depending on the type of the recording medium.

  Even when the melt viscosity of the toner is good for fixing, if the applied pressure is small, the toner does not spread sufficiently and the anchoring effect is small. Such a problem is mentioned regarding the melt viscosity of the toner and the pressure to be applied.

  A technique for dealing with these problems by switching the fixing conditions (fixing temperature, pressure) according to the type of the recording medium is disclosed. For example, a technique (Patent Document 1) is disclosed that controls the fixing temperature of the fixing roller according to the thickness and type of the recording medium and adjusts the pressing force of the pressure roller. Also disclosed is a technique for switching a plurality of pressure members having different lengths in the direction orthogonal to the conveyance direction of the recording medium in accordance with the length in the direction orthogonal to the conveyance direction of the conveyed recording medium (Patent Document 2). Has been. Furthermore, a technique (Patent Document 3) that includes a plurality of pressure members and switches between the pressure members and the pressure depending on the type of the recording medium and the use environment is disclosed.

JP-A-5-297863 JP 2001-5312 A JP 2005-241954 A

  However, when the heating condition (fixing temperature) of the fixing roller is controlled in accordance with the type of the recording medium, it takes time to cool the fixing roller having a heat quantity, and it is very difficult to control the heating condition to an appropriate heating condition. It takes a lot of time. Moreover, when switching and using a several pressurization member, the structure and operation | movement are complicated, and will enlarge the apparatus and will cost up. Furthermore, in order to cope with the type of recording medium, the temperature of each pressing member must be maintained, and power consumption increases.

  The present invention is a further development of the above-described conventional technology. The object of the present invention is to overcome the above-described conventional problems with a simple configuration and operation, and to sufficiently provide a toner resin while suppressing image defects such as transparency and voids. To improve the anchoring effect.

In order to achieve the above object, the present invention provides a toner image formed on a recording medium while nipping and conveying the recording medium between the first rotating body and the second rotating body that are pressed against each other. An image heating and pressing apparatus that heats and pressurizes, and is provided on one rotating body, forms the pressure contact portion with the other rotating body, and switches the pressure distribution in the conveyance direction of the recording medium at the pressure contacting portion. The pressure member has a maximum pressure of 0.00 in a temperature range where the melt viscosity of the toner on the recording medium is 1.0 × 10 ⁵ Pa · s or less, depending on the type of the recording medium. Conveyance of the recording medium at the press contact portion so as to satisfy the condition that the pressure is 0.15 MPa or less at a temperature at which the melt viscosity of the toner on the recording medium is 1.0 × 10 ³ Pa · s. Cut the pressure distribution in the direction Characterized in that it obtain.

  According to the present invention, the toner resin is sufficiently wetted and spread while suppressing image defects such as sheer and voids by simply switching the pressure distribution in the conveyance direction of the recording medium in the pressure contact portion according to the type of the recording medium. Anchoring effect can be improved.

  Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the drawings. However, the dimensions, materials, shapes, and relative arrangements of the components described in the following embodiments should be appropriately changed according to the configuration of the apparatus to which the present invention is applied and various conditions. Therefore, unless specifically stated otherwise, the scope of the present invention is not intended to be limited thereto.

  An image forming apparatus provided with an image heating and pressing apparatus will be described with reference to FIGS. First, the configuration of the image forming apparatus will be described, and then the image heating and pressing apparatus will be described.

(Image forming device)
FIG. 1 is a configuration diagram of an image forming apparatus according to the present embodiment. As shown in FIG. 1, a color electrophotographic recording apparatus, which is an image forming apparatus, has developing devices 1a, 1b, 1c, 1d, and transfer chargers 24a, 24b, 24c on the outer periphery of photosensitive drums 3a, 3b, 3c, 3d. 24d and cleaners 4a, 4b, 4c, 4d. A light source device and a polygon mirror (not shown) are installed in the upper part of the device. The photosensitive drum 3 and the transfer charger 24 constitute an image forming unit.

  The laser light emitted from the light source device is scanned by rotating the polygon mirror, and the light beam of the scanning light is deflected by the reflection mirror. The deflected light beam is condensed on the buses of the photosensitive drums 3a to 3d by the fθ lens and exposed to form latent images corresponding to the image signals on the photosensitive drums 3a to 3d.

  The developing devices 1a, 1b, 1c, and 1d are filled with a predetermined amount of cyan, magenta, yellow, and black toners as developers, respectively, by a supply device (not shown). The developing devices 1a, 1b, 1c, and 1d develop the latent images on the photosensitive drums 3a, 3b, 3c, and 3d, respectively, and visualize them as cyan toner images, magenta toner images, yellow toner images, and black toner images.

  The recording medium P is accommodated in the recording medium cassette 10, and is then supplied onto the transfer belt 130 through a plurality of conveyance rollers and registration rollers 12, and is opposed to the photosensitive drums 3 a, 3 b, 3 c, 3 d by conveyance by the transfer belt 130. Sequentially sent to the transfer section.

  When the transfer belt 130 is rotated by the driving roller 13 and is confirmed to be in a predetermined position, the recording medium P is sent out from the registration roller 12 to the transfer belt 130, and the recording medium P is moved to the first image forming unit. It is conveyed toward the transfer part. At the same time, the image writing signal is turned on, and image formation is performed on the photosensitive drum 3a of the first image forming unit at a certain timing based on the signal. Then, the transfer charger 24a applies an electric field or electric charge at the lower transfer portion of the photosensitive drum 3a, whereby the first color toner image formed on the photosensitive drum 3a is transferred onto the recording medium P. By this transfer, the recording medium P is held on the transfer belt 130 with an electrostatic attraction force and is conveyed to the second image forming unit. The transfer charger 24 was a contact charger. Further, it is known that the transfer charging means stabilizes the image when the current contributing to the transfer is kept constant at an appropriate current. Therefore, it is common to perform constant current control so that a constant current can be obtained even when the volume resistance value changes depending on the type (thickness, material, etc.) of the recording medium and moisture absorption conditions.

  Image formation and transfer in the second to fourth image forming units are performed in the same manner as in the first image forming unit. The recording medium P onto which the four color toner images have been transferred is separated from the end of the transfer belt 130 by removing electricity by the separation charger 32 at the downstream portion in the transport direction of the transfer belt 130 to attenuate the electrostatic adsorption force. In particular, in a low humidity environment, the recording medium P is also dried to increase the electrical resistance, so that the electrostatic adsorption force with the transfer belt 130 is increased and the effect of the separation charger 32 is increased. Normally, the separation charger 32 is a non-contact charger because the recording medium P is charged with the toner image unfixed. The separated recording medium P is transported to the fixing device F by the transport unit 33.

(Fixing device)
Here, the fixing device F as an image heating and pressing device will be described. FIG. 2 is a configuration diagram of the fixing device F used in the present embodiment. As shown in FIG. 2, the fixing device F is a film fixing device. The fixing device F includes a fixing film 50, an IH coil 51, a pressure pad 52, a pressure roller 53, a side core 54, a center core 55, and a pressure pad support member 56. In this embodiment, a film heating and fixing method using an IH coil as a heat source is used, but a film heating and fixing method in which the heat source is a halogen heater may be used.

  The fixing film 50 is a first rotating body and has a three-layer composite structure of a base layer, an elastic layer, and a release layer in order from the inner surface side to the outer surface side. The base layer is a metal heating layer that generates an eddy current inside by an alternating magnetic field generated by the IH coil 51, and is made of a material such as iron, stainless steel, or nickel. The thickness is preferably 10 μm or more and 100 μm or less. When the thickness is 10 μm or less, the durability as a fixing film is inferior, and most electromagnetic energy cannot be absorbed, resulting in poor efficiency. When the thickness is 100 μm or more, the rigidity of the film becomes high, the flexibility becomes poor, and it is not practical to use as a rotating body. The elastic layer is made of silicone rubber, fluorine rubber, fluorosilicone rubber or the like, which has good heat resistance, good heat conduction, and low hardness. The thickness of the elastic layer is preferably 10 to 500 μm. For the release layer, it is preferable to select a material having excellent releasability and heat resistance such as fluororesin (PTFE, PFA, FEP, etc.), silicone resin, fluororubber, and silicone rubber. The thickness is preferably 1 μm or more and 100 μm or less. If it is 1 μm or less, a toner offset phenomenon occurs due to abrasion of the release layer, and if it is 100 μm or more, heat generated in the heat generating layer cannot be sufficiently transmitted to the recording medium and the toner, resulting in a fixing failure. .

  The pressure roller 53 is a second rotating body and has a core metal provided with an elastic layer such as silicone rubber to reduce the hardness. In order to improve surface properties, a fluororesin layer such as PTFE, PFA, FEP or the like may be provided on the outer periphery. The pressure roller 53 is disposed as a pressure rotator by rotatably supporting both ends of a core metal between left and right side plates of an apparatus chassis (not shown) via a bearing member.

  A toner image (unfixed toner T in FIG. 3) is formed on the recording medium while the recording medium is nipped and conveyed by a fixing nip portion (pressing portion) N formed by a pressure roller 53 and a fixing film 50 that are in pressure contact with each other. ) Is fixed by heating and pressing.

  The pressure pad 52 is provided on the fixing film 50 and forms the fixing nip portion N with the pressure roller 53. The pressure pad 52 is made of a heat-resistant engineering plastic, and a sliding cover treatment is applied to the surface in order to improve the slidability with the base metal of the fixing film 50.

  The pressure pad 52 is a pressure member that switches the pressure distribution in the conveyance direction of the recording medium in the fixing nip portion N according to the type of the recording medium. Specifically, as will be described later with reference to FIG. 5, the pressure pad 52 inclines in the fixing nip portion N toward the upstream side, the center, and the downstream side in the conveyance direction of the recording medium and comes into contact with the pressure roller 53. The pressure distribution in the conveyance direction of the fixing nip portion N can be switched. The pressure pad 52 is switched when the switching motor 103 shown in FIG. 1 is driven. As shown in FIG. 1, the user selects the type of recording medium with the operation unit 101 of the image forming apparatus, and information (thickness, basis weight) of the recording medium is transmitted to the CPU (control unit) 102. Accordingly, the switching motor 103 is driven. As a result, the pressure pad 52 operates and the pressure distribution in the conveyance direction of the fixing nip portion N is automatically switched.

  The pressure pad support member 56 is made of a metal such as stainless steel or aluminum, and operates to press the pressure pad 52 against the pressure roller 53 through the fixing film 50.

  An excitation circuit (not shown) is connected to the IH coil 51, and this circuit can generate a high frequency of 20 kHz to 500 kHz by a switching power supply.

  The side core 54 and the center core 55 are made of a ferromagnetic material such as ferrite, and perform magnetic coupling by a magnetic field generated by the IH coil 51. In particular, magnetic coupling is strengthened by arranging a center core at the winding center of the coil and a side core on the side surface.

  In this embodiment, film heating means using an IH coil is used, but a method of heating a film by pressing a heating member from the outside of the film may be used.

(Fixing device operation)
First, an image with toner T is formed on the recording medium P by the image forming apparatus. The toner T at this time is in a powder state, and passes through the fixing nip portion N of the fixing device F and is permanently fixed on the recording medium by being heated and pressurized.

  When the recording medium P approaches the fixing device F, an alternating magnetic field is generated by applying a current to the IH coil 51, an eddy current is generated in the metal base layer in the fixing film 50, and the fixing film 50 is heated. When the fixing film 50 is sufficiently heated, the pressure pad 52 is pressed against the pressure roller 53 to form the fixing nip portion N. Then, when the recording medium P passes through the fixing nip portion N, the toner T is permanently fixed to the recording medium P by applying heat and pressure to the toner T.

(Experiment 1)
Here, an experiment was conducted on the relationship between toner temperature, applied pressure, and toner wetting and spreading. FIG. 3 shows a schematic diagram of the fixing experiment apparatus used in this experiment.

  The fixing experiment apparatus includes a pressure head composed of a pressure support member 60, a pressure member rubber layer 61, and a pressure member surface layer 62, and a fixing head composed of a fixing member surface layer 63, a fixing member rubber layer 64, and a fixing support member 65. Have. Further, the fixing experiment apparatus has a heating device (not shown) for heating both the pressure head and the fixing head to a predetermined temperature, and a driving means (not shown) for pressing the fixing head against the pressure head with a predetermined pressure. . The pressure support member 60 and the fixing support member 65 are made of stainless steel and have a mechanism that is heated to a predetermined temperature by a heating means (not shown). Further, a pressure member rubber layer 61 and a fixing member rubber layer 64 made of silicone rubber having a thickness of 500 μm are provided on each support member, and a PFA tube having a thickness of 50 μm is formed on each rubber layer. A pressure member surface layer 62 and a fixing member surface layer 63 are provided.

  The operation of the fixing experiment apparatus will be described. First, the pressure head and the fixing head are heated to a set temperature by a heating means (not shown) to be in a standby state. Then, the fixing head is pressed against the pressure head by a driving means (not shown) through the recording medium P on which the unfixed toner T is placed, and the unfixed toner T is fixed to the recording medium P by applying heat and pressure. Let By using this experimental apparatus, it is possible to apply a desired pressure while accurately controlling the temperature of the unfixed toner T on the recording medium P.

The experimental conditions were five toner temperatures of 100 ° C., 110 ° C., 120 ° C., 130 ° C., and 140 ° C., and the applied pressure was 0.1 MPa, 0.15 MPa, 0.2 MPa, 0.3 MPa, and 0.4 MPa. Standard level. Further, CLC paper (manufactured by Nippon Paper Industries Co., Ltd., basis weight 80 g / m ² ) was used as a recording medium, an unfixed toner T image was created by an image forming apparatus, and fixing processing was performed by this experimental apparatus. The amount of unfixed toner on the recording medium was 0.6 mg / cm ² .

  This time, the fixability was evaluated by the wetting and spreading of the toner layer onto the recording medium, and a comparison was made with the index “surface layer coverage”. The calculation method of the surface layer coverage is as follows.

  First, an image after the fixing process is captured by a scanner and converted into a monochrome gradation of 255 gradations using image processing software. The converted image is binarized with a black portion and a white portion with a threshold value of 120. The area ratio of the black part / white part of the obtained binarized image was calculated, and the area ratio of the black part was defined as the surface layer coverage. This is because the portion where the base of the recording medium is exposed is a portion not covered with the toner layer, and the difference in wetting and spreading can be quantitatively evaluated. The surface coverage ratio of 75% or less is a level where the image after the fixing process is light in color and the entire image looks whitish and can be visually recognized as an image defect.

  FIG. 4 shows the change in the surface layer coverage with respect to the pressure under each temperature condition in this experiment. From this figure, the surface layer coverage increases as the applied pressure increases at 100 to 110 ° C., and the surface layer coverage increases up to a pressure of 0.15 MPa at 120 ° C. or higher, but at a pressure of 0.2 MPa or higher. , Surface layer coverage decreased.

  Further, the fine structure of the surface layer of the image subjected to the fixing treatment under the above-described conditions was observed using an optical microscope (Keyence Corporation, VHX-500 digital microscope).

  First, the surface layer of an image subjected to fixing treatment by applying pressures of 0.1 MPa and 0.15 MPa was observed using the optical microscope. In the image subjected to the fixing process by applying a pressure of 0.15 MPa, it was observed that the recording medium was covered with the toner. On the other hand, in the image subjected to the fixing process by applying a pressure of 0.1 MPa, it was observed that the toner particles remained in the form of particles and did not spread on the recording medium. This indicates that 0.1 MPa is not sufficient as the pressure for deforming the toner resin and spreading it onto the recording medium. Therefore, it can be said that the applied pressure needs to be at least 0.15 MPa.

  Next, the surface layer of the image subjected to the fixing process by applying a pressure of 0.2 MPa or more was observed. First, in an image that has been fixed at a temperature of 100 ° C. and a pressure of 0.15 MPa, wetting and spreading of the toner thin layer is observed on the surface of the recording medium, and when the pressure increases to 0.2 MPa or more, It was observed that wetting spread was even greater and covered the recording medium. In addition, in the image subjected to the fixing process at a temperature of 130 ° C. and a pressure of 0.15 MPa, wetting and spreading of the toner thin layer was observed on the surface of the recording medium, but when the pressure increased to 0.2 MPa or more, the recording medium Generation | occurrence | production of "sheering" which the fiber of this was exposed and the surface layer coverage fell was observed. Through-through is a phenomenon in which when a large pressure is applied in a state where the toner has a low melt viscosity, the toner layer is interrupted and the fibers are exposed.

  Therefore, the melt viscosity of the toner at each toner temperature and the surface layer coverage of the image fixed at pressures of 0.15 MPa and 0.2 MPa are summarized in Table 1 below. The melt viscosity of the toner in this experiment was measured using an elevated flow tester (Shimadzu flow tester CFT-100 type). A sample having a weight of 1.0 g molded using a pressure molding machine was extruded from a nozzle having a diameter of 1 mm and a length of 1 mm by applying a load of 196 N (20 kgf) with a plunger at a heating rate of 5.0 ° C./min. Thereby, the plunger lowering amount of the flow tester was measured. At this time, the temperature at the sample outflow start point of the plunger descent amount-temperature curve of the flow tester is defined as the flow start temperature.

As described above, when the toner temperature is 120 ° C. or more, the melt viscosity of the toner is 1.0 × 10 ³ Pa · s or less, and the toner is very easy to flow. Therefore, it can be said that the toner thin layer is transparent when a high pressure exceeding 0.15 MPa is applied under a temperature condition where the melt viscosity of the toner is 1.0 × 10 ³ Pa · s or less.

Therefore, the fixing treatment is performed by applying pressure so that the melt viscosity of the toner T used in this experiment is 0.15 MPa or less at a temperature (120 ° C.) of 1.0 × 10 ³ Pa · s or less. Thus, it was possible to reduce the see-through and obtain a high surface layer coverage.

(Experiment 2)
Next, using the fixing device F, an experiment was performed on the applied pressure and toner wetting and spreading. This will be described with reference to FIGS.

  In this experiment, the heating conditions of the fixing film 50 were made the same, the pressing angle of the pressure pad 52 was changed, and the relationship between the pressure distribution in the conveyance direction of the fixing nip portion N and the toner wetting spread state was examined.

  First, the pressure pad 52 is pressed against the pressure roller 53 through the fixing film 50 to form the fixing nip portion N, and the IH coil is rotated so that the surface temperature becomes 200 ° C. while the fixing film 50 is rotated. The temperature was adjusted using the and a standby state was set. In the present embodiment, the pressure distribution in the conveyance direction of the fixing nip portion N is changed by using the pressure pad 52 shown in FIG. FIG. 6C shows the pressure distribution when the pressing angle of the pressure pad 52 is changed.

  Condition (4) is a pressure distribution (FIG. 5A) in which the pressure pad 52 is pressed in a direction perpendicular to the tangent to the pressure roller 53, and in the center of the fixing nip portion N in the conveyance direction of the recording medium. Maximum surface pressure (maximum pressure) is applied. Conditions (1), (2), and (3) are pressure distributions in which the pressure pad 52 is pressed in a state where the pressure pad 52 is inclined to the downstream side of the fixing nip portion N with respect to the tangent to the pressure roller 53 (FIG. 5B The maximum surface pressure (maximum pressure) is applied downstream of the condition (4) in the fixing nip N in the recording medium conveyance direction. Conditions (5) and (6) are pressure distributions (FIG. 5C) in which the pressure pad 52 is pressed in a state where the pressure pad 52 is inclined to the upstream side of the fixing nip N with respect to the tangent to the pressure roller 53. The maximum surface pressure (maximum pressure) is applied to the upstream side in the conveyance direction of the recording medium in the fixing nip portion N relative to the condition (4).

The fixing nip N formed under such pressing conditions was passed through a recording medium on which unfixed toner was placed, and a fixing process was performed. Incidentally, CLC paper (Nippon Paper Industries Co., basis weight 80 g / ^{m 2)} as a recording medium using, create an image of the unfixed toner T was put 0.6 mg / cm ² by an image forming apparatus, a fixing nip Part N was passed.

  FIG. 6 shows the position in the transport direction in the fixing nip N, the toner temperature at that position (FIG. 6A), the melt viscosity of the toner at that toner temperature (FIG. 6B), and the pressure applied to the toner. The relationship of (FIG.6 (c)) is shown. In this experiment, the toner temperature is measured by sticking a thermocouple (Ambess EMT Co., Ltd., ultra-thin thermocouple KFST-10-100-200) on the recording medium, and the pressure distribution is measured by a tactile sensor (NITTA ( Co., Ltd., sealer). Further, the melt viscosity of the toner is measured using the method shown in Experiment 1, and is not a value obtained by directly measuring the toner melt viscosity in the fixing nip N.

From FIG. 6, under any condition, at a temperature (120 ° C.) at which the toner has a melt viscosity of 1.0 × 10 ³ Pa · s, the pressure is 0.15 MPa or less, and the surface coverage is reduced due to see-through. Is not seen. Table 2 below compares the surface layer coverage under these fixing conditions.

  In conditions (1) to (4), a high surface layer coverage was shown, but in condition (5), a low surface layer coverage was shown. Further, under condition (6), the toner was not sufficiently melted, and an offset was generated and could not be fixed.

  Observation of the surface layer of these images with an optical microscope confirmed the following.

  First, in the conditions (1) to (4), it was observed that the toner thin layer was wet spread on the recording medium and was entirely covered. On the other hand, in the condition (5), it was observed that the toner T was isolated while maintaining the particle form. Pore is generated when the toner is melted and the coalescence of particles does not proceed when fixing is performed by applying pressure when the toner is not sufficiently heated. As described above, in a state where the toner is not sufficiently melted, voids occur because the deformation amount of the toner is small even when a large pressure is applied. Under the condition (6) where the melt viscosity of the toner is even larger, the toner does not anchor to the recording medium, and an offset occurs.

  As described above, the melt viscosity of the toner at the stage where the maximum pressure is applied is greatly related to the surface layer coverage and anchoring.

  Therefore, the pressure distribution in the conveyance direction of the recording medium at the fixing nip N of the fixing device F is switched, and the relationship between the melt viscosity of the toner, the surface layer coverage, and the image state at the stage of applying the maximum pressure and the maximum pressure is investigated. It was. FIG. 7 shows a summary of the results.

As shown in FIG. 7, when a pressure greater than 0.15 MPa is applied when the toner has a melt viscosity of 1 × 10 ⁵ Pa · s or less, the decrease in the surface layer coverage due to the occurrence of voids is reduced, and the surface layer coverage is reduced. 75% or more could be obtained. In addition, even when the melt viscosity of the toner is greater than 1 × 10 ⁵ Pa · s, by applying a pressure greater than 0.15 MPa, the amount of deformation of the toner increases and a surface layer coverage of 75% or more can be obtained. It was. However, in this case, since the toner is not sufficiently melted, a large pressure is applied while the toner is hard, so that the upper surface of the fixing toner does not become flat, and other image defects such as reduced gloss occur. have done. Similarly, by applying a maximum pressure of 0.15 MPa or less in a region where the melt viscosity of the toner is greater than 1 × 10 ⁵ Pa · s, it was possible to obtain a surface layer coverage of 75% or more. However, in this case, although the toner is in a soft state, since the pressure is insufficient, the gloss is lowered and a good image quality cannot be obtained.

Therefore, it is preferable to apply a maximum pressure of more than 0.15 MPa in a temperature range where the melt viscosity of the toner is 1.0 × 10 ⁵ Pa · s or less in order to eliminate voids and spread the toner layer. It was confirmed.

Therefore, when the toner temperature rises to a temperature (90 ° C.) or higher at which the melt viscosity of the toner T used in this experiment is 1.0 × 10 ⁵ Pa · s or less, a maximum pressure of greater than 0.15 MPa is applied. To fix. Further, at a temperature (120 ° C.) at which the melt viscosity of the toner T is 1.0 × 10 ³ Pa · s, a fixing process is performed by applying a pressure so as to be 0.15 MPa or less. As a result, the see-through was reduced, and a high surface coverage was obtained.

  However, the melting temperature of the toner T has a significant influence on the type of recording medium. For example, when thick paper thicker than plain paper is used, the heat capacity of the recording medium increases, so the amount of heat given to the toner decreases and the toner becomes insufficiently melted. As a result, the toner has a high melt viscosity, and even when a pressure is applied, the toner does not sufficiently wet and spread, and a “pode” occurs in which the toner remains isolated while maintaining the particle form. On the other hand, when thin paper that is thinner than plain paper is used, the heat capacity of the recording medium becomes small, so the amount of heat given to the toner increases and the toner becomes excessively melted. As a result, the melt viscosity of the toner becomes low, and even when a pressure is applied, the layer formed by the toner flows, and “through” occurs where the fibers on the recording medium are exposed.

(Experiment 3)
Therefore, the fixing device F was used, and a comparison experiment of the surface layer coverage was performed under the condition that the thickness (basis weight) of the recording medium was different. As the recording medium, View Corona S (Oji Paper Co., Ltd., 37 g / m ² ), which has a smaller basis weight than the CLC paper (80 g / m ² , hereinafter referred to as plain paper) used in Experiment 1, And CLC cardboard paper (Nippon Paper Industries Co., Ltd., 207 g / m ² , hereinafter referred to as cardboard) having a large basis weight was used.

  FIG. 8 shows the toner temperature (FIG. 8A) at the position in the conveying direction in the fixing nip N for each recording medium, the melt viscosity of the toner at that toner temperature (FIG. 8B), and the fixing nip N. The relationship of the pressure (FIG.8 (c)) in a conveyance direction is shown.

From the graph of toner temperature change, depending on the thickness of the recording medium, the toner temperature (90 ° C.) at which the melt viscosity of the toner becomes 1.0 × 10 ⁵ Pa · s or the toner at which the toner viscosity becomes 1.0 × 10 ³ Pa · s. It can be seen that the position of the fixing nip N that reaches the temperature (120 ° C.) changes. This is because the heat capacity varies depending on the thickness of the recording medium.

Therefore, according to the thickness (basis weight) of the recording medium, the pressure distribution in the conveying direction of the fixing nip portion N was switched to perform the fixing process, and the surface layer coverage was compared. At this time, as described above, the relationship between the melt viscosity of the toner and the applied pressure is such that the maximum pressure is applied at the position in the transport direction of the fixing nip N where the melt viscosity of the toner is 1.0 × 10 ⁵ Pa · s or less. To do. Further, the surface pressure is set to 0.15 MPa or less at a position in the conveyance direction of the fixing nip N where the melt viscosity of the toner is 1.0 × 10 ³ Pa · s. The relationship between the change in the melt viscosity of the toner according to the thickness of the recording medium and the change in the applied pressure according to the change in the melt viscosity is as shown in FIG.

  Table 3 below summarizes the surface layer coverage under each fixing condition. For comparison, the fixing process is performed under three levels regardless of the type of recording medium, and the surface layer coverage is compared.

  The thin paper showed a high surface layer coverage in the condition (7), and a low surface layer coverage in the conditions (8) and (9). This is because, under conditions (8) and (9), the toner flowed under the fibers of the recording medium by applying a large pressure with the toner having a low melt viscosity, and the see-through of the fibers of the recording medium occurred. I can say that.

  The plain paper showed a high surface layer coverage in condition (8) and low surface layer coverage in conditions (7) and (9). This is because the toner is insufficiently melted under the condition (7) and the melt viscosity is large, so that voids are generated. Under the condition (9), the toner flows under the fibers of the recording medium, and the see-through occurs. It can be said that the rate has declined.

  The cardboard showed a high surface layer coverage in the condition (9), and a low surface layer coverage in the conditions (7) and (8). In condition (9), it can be said that the toner was warmed before the maximum pressure was applied and the maximum pressure was applied at the stage where the melt viscosity of the toner was reduced, and thus the surface coverage was high due to spreading. . On the other hand, in the conditions (7) and (8), since the thick paper was subjected to the fixing process under a condition where the toner melt viscosity was high, the toner temperature was low and the toner was not completely melted. I can say that.

Therefore, when the toner temperature rises to a temperature (90 ° C.) or higher at which the melt viscosity of the toner T used in this experiment becomes 1.0 × 10 ⁵ Pa · s or lower, fixing is performed by applying a pressure higher than 0.15 MPa. Process. Further, at a temperature (120 ° C.) at which the melt viscosity of the toner T is 1.0 × 10 ³ Pa · s or less, a fixing process is performed by applying a pressure so as to be 0.15 MPa or less. Furthermore, the pressure distribution in the conveyance direction of the recording medium at the fixing nip N is switched depending on the thickness of the recording medium so as to satisfy the above-described melting temperature of the toner T and the pressure condition at the melting temperature of the toner T. . Thereby, regardless of the type of the recording medium, it was possible to suppress the occurrence of see-through and voids and obtain a high surface layer coverage.

  From the results of the above-described experiments, in this embodiment, there are three levels of the pressure distribution (pressure profile) patterns in the conveyance direction of the recording medium in the fixing nip N corresponding to the basis weight of the recording medium in advance. Specifically, when the recording medium is thin paper, the thin paper mode using the condition (7) shown in FIG. 8C is used, and when the recording medium is plain paper, the condition (8) shown in FIG. 8C is used. The plain paper mode is set, and in the case of thick paper, the thick paper mode using the condition (9) shown in FIG.

  When the basis weight of the recording medium is selected by the operation unit 101 shown in FIG. 1, the fixing process is performed by automatically switching to the set pressure distribution in the conveyance direction of the fixing nip portion N according to the basis weight. Do. A flowchart of the operation is shown in FIG.

As shown in FIG. 9, when the type of the recording medium is set by the operation unit (step S11), the information is transmitted to the CPU (step S12). Based on the information, the CPU determines whether the recording medium is thick paper, thin paper, or plain paper. First, it is determined whether the recording medium is cardboard. Specifically, in step S13, it is determined whether the basis weight of the recording medium is 150 g / m ² or more. If it is determined in step S13 that the paper is cardboard, the process proceeds to step S14, and the pressure distribution is switched to the cardboard mode. On the other hand, if it is determined in step S13 that the paper is not thick paper, it is next determined whether it is thin paper. Specifically, in step S15, it is determined whether the basis weight of the recording medium is 37 g / m ² or less. If it is determined in step S15 that the paper is thin, the process proceeds to step S16, and the pressure distribution is switched to the thin paper mode. If it is neither thick paper nor thin paper, the process proceeds to step S17, and the pressure distribution is switched to the plain paper mode. Thereafter, an image forming operation is started (step S18), and a fixing process corresponding to the switched mode is performed (step S19).

  Thus, by switching the pressure distribution in the conveyance direction of the recording medium in the fixing nip portion N according to the type of the recording medium, the toner resin can be sufficiently wetted and spread while suppressing image defects such as transparency and voids. Anchoring effect can be improved. That is, the above-described conventional problems can be overcome and the above-described effects can be obtained with a simple configuration and operation compared to the conventional technology.

  In the above-described embodiment, the pressure member is exemplified as the pressure member that is inclined toward the upstream side, the center, and the downstream side in the conveyance direction of the recording medium in the fixing nip portion, but is not limited thereto. The pressure member may have other configurations as long as it switches the pressure distribution in the conveyance direction of the recording medium at the fixing nip portion. Moreover, although the case where one was a film and the other was a roller was illustrated as a rotary body which mutually press-contacts, it is not limited to this. For example, other configurations such as a configuration in which a belt stretched around a roller is used as a rotating body and the belt and the belt are in pressure contact, and a configuration in which the belt and the roller are in pressure contact may be used.

  Further, in the above-described embodiment, the image heating and pressing apparatus integrally included in the image forming apparatus is exemplified, but the present invention is not limited to this. For example, it may be an image heating and pressing apparatus that can be attached to and detached from the image forming apparatus, and the same effect can be obtained by applying the present invention to the image heating and pressing apparatus.

  In the above-described embodiment, the image forming apparatus has been described by way of example having a single image heating and pressing apparatus. However, even if the image forming apparatus has a plurality of image heating and pressing apparatuses, The same effect can be obtained by applying the present invention to an image heating and pressing apparatus.

  In the above-described embodiment, the configuration using four image forming units has been exemplified. However, the number of used units is not limited to this, and may be set as appropriate.

  In the above-described embodiment, an example of an image forming apparatus that uses a recording medium carrier (transfer belt) and sequentially superimposes and transfers toner images of respective colors onto the recording medium carried on the recording medium carrier. The invention is not limited to this. For example, an image forming apparatus that uses an intermediate transfer member, sequentially transfers toner images of respective colors on the intermediate transfer member, and transfers the toner images carried on the intermediate transfer member to a recording medium in a lump. good. The image forming apparatus may be an image forming apparatus such as a printer, a copier, or a facsimile machine, or another image forming apparatus such as a multi-function machine that combines these functions. The same effect can be obtained by applying the present invention to an image heating and pressing apparatus used in these image forming apparatuses.

1 is a schematic cross-sectional view of an image forming apparatus including a fixing device. FIG. 2 is a schematic cross-sectional view of a fixing device. It is a schematic diagram of a fixing experiment apparatus. FIG. 6 is a table showing a relationship between a pressure for each toner temperature and a surface layer coverage. FIG. 3 is an enlarged view of a main part showing a shape of a pressure pad of the fixing device and a pressing direction thereof. FIG. 4 is a table schematically showing toner temperature, toner melt viscosity, and pressure distribution. FIG. 6 is a table showing the relationship among maximum pressure, toner melt viscosity and surface layer coverage. FIG. 4 is a table schematically showing toner temperature, toner melt viscosity, and pressure distribution. FIG. 5 is a flowchart showing an operation flow according to the type of recording medium.

Explanation of symbols

F: Fixing device N: Fixing nip P: Recording medium T ... Toner 50 ... Fixing film 51 ... IH coil 52 ... Pressure pad 53 ... Pressure roller 54 ... Side core 55 ... Center core 56 ... Pressure pad support member 101 ... Operation unit 102 CPU
103 ... Switching motor 130 ... Transfer belt

Claims (3)

An image heating and pressurizing apparatus that heats and pressurizes a toner image formed on a recording medium while sandwiching and conveying the recording medium at a pressure contact portion between a first rotating body and a second rotating body that are pressed against each other. ,
A pressure member that is provided on one rotary body, forms the pressure contact portion with the other rotary body, and switches the pressure distribution in the conveyance direction of the recording medium in the pressure contact portion;
The pressure member has a maximum pressure of 0.15 MPa or more in a temperature range in which the melt viscosity of the toner on the recording medium is 1.0 × 10 ⁵ Pa · s or less depending on the type of the recording medium. The pressure distribution in the conveyance direction of the recording medium in the press contact portion is switched so as to satisfy the condition that the pressure is 0.15 MPa or less at a temperature at which the toner has a melt viscosity of 1.0 × 10 ³ Pa · s. An image heating and pressurizing apparatus. The pressure member is a recording medium in which the center of the recording medium in the pressure contact portion is the maximum pressure in the temperature range where the melt viscosity of the toner on the recording medium is 1.0 × 10 ⁵ Pa · s or less. Based on thickness,
When the thickness of the recording medium is thinner than the reference thickness, switching is performed so that the upstream side in the conveyance direction of the recording medium at the pressure contact portion is the maximum pressure,
2. The image heating and pressing according to claim 1, wherein when the thickness of the recording medium is thicker than the reference thickness, switching is performed so that the downstream side in the conveyance direction of the recording medium at the press contact portion becomes the maximum pressure. apparatus.   An image forming apparatus for forming a toner image on a recording medium, comprising the image heating and pressing apparatus according to claim 1.

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