JP2014174535A - Pressure roller, fixing device, and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pressure roller capable of suppressing deformation of a sheet material without providing a difference in outer diameter in an axial direction, a fixing device including the pressure roller, and an image forming apparatus including the fixing device.SOLUTION: A pressure roller 50 is pressed against a fixing belt 41, and a sheet S is inserted through between the pressure roller 50 and the fixing belt 41. The pressure roller 50 comprises: a core bar 51; an elastic layer 52 that is provided around the core bar 51 and has a porous structure; and a surface release layer 53 that is provided overlapped on an outer peripheral surface of the elastic layer 52. The elastic layer 52 has a porosity at both ends larger than a porosity in a central part in a width direction of a paper feeding area Wt of the sheet S.

Description

  The present invention relates to a pressure roller that is pressed against a rotating body and a sheet material is inserted between the rotating body, a fixing device including the pressure roller, and an image forming apparatus including the fixing device. .

  For example, an image forming apparatus such as a copying machine, a printer, or a facsimile using an electrophotographic method fixes a non-fixed toner image formed on a sheet material such as a sheet as a sheet-like recording medium on the sheet material. Equipped with equipment. The fixing device includes a heating rotator such as a roller and a belt for heating the sheet material, and a pressure roller in which the outer peripheral surface is pressed against the rotating surface of the heating rotator and the sheet material is inserted between the heating rotator And. The fixing device sandwiches the sheet material between the heating rotator and the pressure roller, and presses the sheet material with a pressure necessary for fixing the toner while conveying the sheet material by these rotations.

  In such a fixing device, when the sheet material passes between the heating rotator and the pressure roller, mechanical stress is applied to the sheet material, which causes wrinkles in the sheet material. May end up. Therefore, in order to suppress the occurrence of such wrinkles, the pressure roller has a shape in which the outer diameter gradually increases from the center portion in the axial direction to both end portions (also referred to as a pinch shape or an inverted crown shape). Is known (see, for example, Patent Document 1). By forming the pressure roller in such a shape, a tensile force is generated in the direction perpendicular to the sheet material conveyance direction (that is, the axial direction of the pressure roller) from the center portion of the sheet material to both ends, thereby causing wrinkles. Can be suppressed.

  However, in the shape of the pressure roller, if the difference in the outer diameter between the central portion and both ends in the axial direction is small, the generation of wrinkles cannot be suppressed. May occur. Therefore, even if the outer diameter difference of the pressure roller is too small or excessive, deformation of the sheet material such as wrinkles and curls occurs, and it is difficult to adjust the outer diameter difference of the pressure roller. There was a problem.

  The present invention aims to solve this problem. That is, the present invention relates to a pressure roller capable of suppressing deformation of a sheet material without providing an outer diameter difference in the axial direction, a fixing device including the pressure roller, and an image forming including the fixing device. The object is to provide a device.

  In order to achieve the above object, the invention described in claim 1 is a pressure roller that is pressed against a rotating body and a sheet material is inserted between the rotating body, the cored bar, and the core A porous structure elastic layer provided around gold, and a surface release layer provided so as to overlap the outer peripheral surface of the elastic layer, the width direction of the insertion region of the sheet material in the elastic layer The pressure roller is characterized in that the porosity of the both end portions is larger than the porosity of the central portion.

  According to the invention described in claim 1, the porosity of both end portions in the width direction of the insertion region of the sheet material in the elastic layer is larger than the porosity of the central portion. Since it did in this way, the hardness of the both ends of the insertion area | region of the sheet | seat material in a pressure roller is smaller than the hardness of the center part. For this reason, even in a configuration in which the outer diameter of the pressure roller is made uniform in the axial direction (coincidence with the width direction of the insertion region) due to the hardness difference between both ends and the center of the insertion region of the sheet material in the pressure roller. Sometimes, as in the case where there is a difference in outer diameter, a tensile force is generated from the central portion of the sheet material toward both ends. Thereby, since generation | occurrence | production of a wrinkle can be suppressed, a deformation | transformation of a sheet | seat material can be suppressed, without providing the outer diameter difference of the center part and both ends of the axial direction of a pressure roller.

1 is a diagram illustrating a schematic configuration of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a diagram illustrating a schematic configuration of a fixing device according to an embodiment of the present invention provided in the image forming apparatus of FIG. 1. FIG. 3 is an enlarged cross-sectional view schematically showing a configuration of a fixing belt provided in the fixing device of FIG. 2. FIG. 3 is a cross-sectional view in a direction orthogonal to an axial direction schematically showing a configuration of a pressure roller according to an embodiment of the present invention provided in the fixing device of FIG. 2. 2A is an axial cross-sectional view schematically showing a configuration of a pressure roller included in the fixing device of FIG. 2, and FIG. 3B is a cross-sectional view in a width direction of a sheet passing region of the pressure roller in FIG. It is a graph which shows typically the relation between a position and the porosity and hardness in the position concerned. (A) is an axial sectional view schematically showing a configuration of a first modification of the pressure roller provided in the fixing device of FIG. 2, and (b) is a schematic view of the passage of the pressure roller of (a). It is a graph which shows typically the relationship between the position of the width direction of a paper area | region, and the porosity and hardness in the said position. (A) is an axial sectional view schematically showing a configuration of a second modification of the pressure roller provided in the fixing device of FIG. 2, and (b) is a schematic view of the passage of the pressure roller of (a). It is a graph which shows typically the relationship between the position of the width direction of a paper area | region, and the porosity and hardness in the said position. (A) is an enlarged view showing a part of the rear end of the paper before being pressed by the pressure roller, and (b) is a part of the rear end of the paper after being pressed by the pressure roller. It is an enlarged view shown.

(Embodiment)
An image forming apparatus according to an embodiment of the present invention will be described with reference to FIG.

  FIG. 1 is a diagram showing a schematic configuration of an image forming apparatus according to an embodiment of the present invention.

  As shown in FIG. 1, an electrophotographic image forming apparatus (indicated by reference numeral 100 in the figure) includes image forming units 10Y, 10M, 10C, and 10Bk, which are examples of four sets of image forming units, and a fixing unit. A fixing device 40 as an example.

  The image forming units 10Y, 10M, 10C, and 10Bk include photosensitive drums 1Y, 1M, 1C, and 1Bk, which are examples of image carriers. The image forming units 10Y, 10M, 10C, and 10Bk form toner images of four colors, yellow, magenta, cyan, and black, on the surfaces of the corresponding photosensitive drums 1Y, 1M, 1C, and 1Bk, respectively.

  Below these image forming units 10Y, 10M, 10C, and 10Bk in the drawing, a conveying belt 20 for conveying a sheet S that is an example of a sheet-like recording medium through each image forming unit is stretched. The sheet S is electrostatically attracted to the surface of the conveyance belt 20. The photosensitive drums 1Y, 1M, 1C, and 1Bk of the image forming units 10Y, 10M, 10C, and 10Bk are rotatably disposed with their outer peripheral surfaces in contact with the conveyance belt 20. The toner images formed on the surfaces of the photoconductive drums 1Y, 1M, 1C, and 1Bk are sequentially transferred onto the paper S that is transported by the transport belt 20. The paper S corresponds to an example of a sheet material.

  The four sets of image forming units 10Y, 10M, 10C, and 10Bk have substantially the same structure. Therefore, here, the yellow image forming unit 10Y disposed on the most upstream side in the transport direction of the sheet S will be described as a representative. The other color image forming units 10M, 10C, and 10Bk are denoted by the same reference numerals, and detailed description thereof is omitted.

  The image forming unit 10Y includes a photosensitive drum 1Y that is in rolling contact with the conveyance belt 20 at a substantially central position thereof, and around the photosensitive drum 1Y, a charging device 2Y, an exposure device 3Y, a developing device 4Y, and a transfer roller. 5Y, cleaner 6Y, and a static elimination lamp (not shown) are provided. The charging device 2Y, the exposure device 3Y, the developing device 4Y, the transfer roller 5Y (transfer device), the cleaner 6Y, and the charge eliminating lamp are sequentially arranged along the rotation direction of the photosensitive drum 1Y.

  The charging device 2Y charges the surface of the photosensitive drum 1Y to a predetermined potential. The exposure device 3Y exposes the charged drum surface based on the color-separated image signal to form an electrostatic latent image on the drum surface. The developing device 4Y supplies yellow toner to the electrostatic latent image formed on the drum surface and develops it. The transfer roller 5 </ b> Y (transfer device) transfers the developed toner image onto the sheet S conveyed via the conveyance belt 20. The cleaner 6Y removes residual toner remaining on the drum surface without being transferred. The static elimination lamp removes electric charges remaining on the drum surface (not shown).

  A paper feed mechanism 30 for feeding the paper S onto the transport belt 20 is disposed on the lower right side of the transport belt 20 in the drawing.

  A fixing device 40 described later is disposed on the left side of the transport belt 20 in the drawing. The sheet S transported by the transport belt 20 is transported through a transport path continuously extending from the transport belt 20 through the fixing device 40 and passes through the fixing device 40.

  The fixing device 40 heats and pressurizes the transported paper S, that is, the paper S on which the toner images of the respective colors are transferred. Then, the toner images of the respective colors are melted and permeated into the paper S to be fixed. Then, the fixing device 40 discharges paper to the downstream side of the conveyance path via a paper discharge roller.

  Next, a fixing device 40 according to an embodiment of the present invention will be described with reference to FIGS.

  FIG. 2 is a diagram showing a schematic configuration of a fixing device according to an embodiment of the present invention provided in the image forming apparatus of FIG. FIG. 3 is an enlarged cross-sectional view schematically showing a configuration of a fixing belt provided in the fixing device of FIG.

  As shown in FIG. 2, the fixing device 40 is an example of a fixing belt 41 that is an example of a heating rotator that is rotatably provided, and a pressure rotator that is rotatably provided to face the fixing belt 41. And a certain pressure roller 50. The fixing device 40 includes a halogen heater 42 that is an example of a heating source that heats the fixing belt 41. Instead of the halogen heater 42, a carbon heater or the like may be provided. Further, the fixing device 40 transmits the light emitted from the nip forming member 43 disposed inside the fixing belt 41, the stay 44 as a support member that supports the nip forming member 43, and the halogen heater 42 to the fixing belt 41. A reflection member 45 that reflects toward the surface is provided. The pressure roller 50 has an outer peripheral surface pressed against the rotating surface of the fixing belt 41, and the sheet S on which the toner image T is formed is inserted between the pressure roller 50 and the fixing belt 41.

  The fixing belt 41 is composed of an endless belt member (including a film) that is thin and flexible. As shown in FIG. 3, the fixing belt 41 is configured by a base material 41 a, an elastic layer 41 b, and a release layer 41 c that are stacked in order from the inside to the outside. FIG. 3 is an enlarged cross-sectional view schematically showing a configuration of a fixing belt provided in the fixing device of FIG. The base material 41a is formed of a metal material such as nickel or SUS or a resin material such as polyimide (PI). The elastic layer 41b is provided between the base material 41a and the release layer 41c, and is formed of a rubber material such as silicone rubber, foamable silicone rubber, or fluorine rubber. The release layer 41c is made of tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), polytetrafluoroethylene (PTFE) or tetrafluoroethylene-hexafluoropropylene copolymer (FEP), or a mixture of these resins. It is made of a heat-resistant resin in which these fluororesins are dispersed. The fixing belt 41 may have a configuration in which the elastic layer 41b is omitted.

  The nip forming member 43 is disposed so as to contact a part of the inner peripheral surface of the fixing belt 41, and the pressure roller 50 sandwiches the fixing belt between the outer peripheral surface and the nip forming member 43 and fixes the fixing nip. It is pressed toward the nip forming member 43 so as to form the portion N. That is, the pressure roller 50 is disposed so that the outer peripheral surface is pressed against the outer peripheral surface (rotating surface) of the fixing belt 41. When the pressure roller 50 is rotated by a rotation driving unit (not shown), the fixing belt 41 is rotated along with the rotation of the pressure roller 50. Then, the portion of the fixing belt 41 heated by the halogen heater 42 moves to the fixing nip portion N, and at this time, the sheet S inserted between the fixing belt 41 and the pressure roller 50 is heated and pressed. Thus, the toner image T is fixed. In addition to the configuration in which the pressure roller 50 is rotationally driven, the fixing belt 41 may be rotationally driven, or the pressure roller 50 and the fixing belt 41 may be rotationally driven together.

  Next, a pressure roller 50 according to an embodiment of the present invention will be described with reference to FIGS. 4 and 5.

  4 is a cross-sectional view in a direction orthogonal to the axial direction schematically showing the configuration of the pressure roller according to the embodiment of the present invention provided in the fixing device of FIG. FIG. 5A is an axial sectional view schematically showing the configuration of the pressure roller provided in the fixing device of FIG. 2, and FIG. 5B is the width of the sheet passing area of the pressure roller in FIG. It is a graph which shows typically the relation between the position of a direction and the porosity and hardness in the position concerned.

  As shown in FIGS. 4 and 5A, the pressure roller 50 includes a cored bar 51, an elastic layer 52, a surface release layer 53, and a pair of grip layers 54.

  The metal core 51 is a cylindrical or columnar (that is, hollow or solid) member made of a metal having relatively high rigidity, such as stainless steel or carbon steel.

  The elastic layer 52 is made of, for example, a porous structure material (porous body) such as foamed silicone rubber, and circumferential and axial directions (left and right in FIG. 5A) on the outer peripheral surface of the cored bar 51. So as to have a uniform thickness. Details of the elastic layer 52 will be described later.

  The surface release layer 53 is, for example, a fluororesin such as tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), polytetrafluoroethylene (PTFE), or tetrafluoroethylene-hexafluoropropylene copolymer (FEP). It is configured as a material. The surface release layer 53 is a layer formed with a uniform thickness in a sheet passing region Wt (an example of a sheet material inserting region) through which the sheet S is inserted on the outer peripheral surface of the elastic layer 52. In the present embodiment, the length in the width direction of the sheet passing area Wt is a length including a margin of about several tens of mm in the width direction of the sheet S.

  In the present embodiment, the sheet passing area Wt provided with the surface release layer 53 in the pressure roller 50 has an outer diameter of about 20 mm to 40 mm over the entire width direction (that is, the axial direction of the pressure roller 50). It is formed uniformly.

  The pair of grip layers 54 are provided at both ends of the outer peripheral surface of the elastic layer 52 so as to sandwich the surface release layer 53 therebetween. As a material constituting the grip layer 54, a material having a higher surface friction coefficient than the surface release layer 53 is used. As a result, when the grip layer 54 comes into contact with the rotating outer peripheral surface of the fixing belt 41, the occurrence of slippage between the pressure roller 50 and the fixing belt 41 is suppressed. Examples of the material constituting the grip layer 54 include rubber materials such as silicone rubber and fluorine rubber.

  In the present embodiment, members other than the cored bar 51 in the pressure roller 50 are formed symmetrically with respect to the axial center. At one end of the cored bar 51, the amount of protrusion from the end surface of the elastic layer 52 is larger than that at the other end.

  The pressure roller 50 is disposed to face the nip forming member 43 so as to sandwich a part of the fixing belt 41 between the pressure roller 50 and the nip forming member 43. In the pressure roller 50, the cored bar 51 is pressed toward the nip forming member 43 by a pressing member such as a spring (not shown), and the outer peripheral surface of the pressure roller 50 is pressed against the outer peripheral surface (rotating surface) of the fixing belt 41. It has been.

  Here, the elastic layer 52 will be described.

  The elastic layer 52 is composed of a porous body having a porous structure. In this embodiment, foamed silicone rubber in which a large number of bubbles (holes) are formed is used as an example. Of course, as long as it has a porous structure, elastic materials other than foamed silicone rubber, such as other types of foamed elastomers, may be used. Methods for obtaining foamed silicone rubber include (1) chemical foaming in which a foaming agent is added to silicone rubber to form a foamed structure, and (2) water is emulsified in liquid silicone rubber and water is volatilized by heating. Water foaming, which forms a foamed structure, is generally known. Since a heat insulating property can be obtained by using a porous body such as foamed silicone rubber for the elastic layer 52, heat transfer to the pressure roller can be reduced. Therefore, warm-up time (time required from normal temperature state such as when the power is turned on to the printable temperature (reload temperature)) and first print time (after receiving a print request, printing operation is performed through print preparation. (Time until paper discharge is completed) can be shortened. Thereby, the start-up time of an apparatus can be shortened and energy saving (TEC value reduction) is attained.

  As shown in FIG. 5 (a), the elastic layer 52 includes a first elastic layer portion 521 disposed in the center portion in the axial direction and both end portions in the axial direction so as to sandwich the first elastic layer portion 521 from both sides. And two second elastic layer portions 522 disposed on each other. That is, one second elastic layer portion 522, the first elastic layer portion 521, and the other second elastic layer portion 522 are arranged side by side in the axial direction. The first elastic layer portion 521 is disposed so as to be positioned at the center in the width direction of the sheet passing region Wt, and at least a part of each of the two second elastic layer portions 522 is at both ends of the sheet passing region Wt. It is arranged to be located. In the present embodiment, the central portion in the width direction of the paper passing area Wt is a portion up to 10% from the center in the width direction to both ends of the paper passing area Wt (that is, the center in the width direction of the paper passing area Wt) Of 20%). Further, the both end portions in the width direction of the paper passing area Wt refer to portions up to 20% from the both ends of the paper passing area Wt toward the center.

  The first elastic layer portion 521 and the second elastic layer portion 522 are made of foamed silicone rubber and have different porosity. In this specification, the “porosity” is the ratio of the space volume due to holes or the like per unit volume. Specifically, the porosity of the second elastic layer portion 522 disposed at both ends in the axial direction is larger than the porosity of the first elastic layer portion 521 disposed at the central portion in the axial direction. . As a result, the porosity of both end portions in the width direction of the sheet passing area Wt of the paper S in the elastic layer 52 is larger than the porosity of the central portion.

  The first elastic layer portion 521 and the second elastic layer portion 522 are changed, for example, by changing the amount of a foaming agent when made by chemical foaming, or by changing the amount of water when made by water foaming. Thus, the porosity of each other is made different. And in porous bodies, such as foaming silicone rubber, hardness changes with the porosity. Therefore, the second elastic layer portion 522 having a large porosity arranged at both ends in the axial direction has a smaller hardness (softer) than the first elastic layer portion 521 having a small porosity arranged in the central portion in the axial direction. )Become. FIG. 5B schematically shows the relationship between the position in the width direction of the paper passing area Wt of the pressure roller 50, the porosity, and the hardness. In the present embodiment, the porous body constituting the first elastic layer portion 521 and the second elastic layer portion 522 has a thermal conductivity of 0.1 to 0.2 W / (m · K), a hardness of 20 to 60 ° (Asker) C).

  In this embodiment, when the length in the width direction (that is, the axial direction) of the sheet passing area Wt of the pressure roller 50 is 100, the length in the width direction of the first elastic layer portion 521 is 60, the second length. The lengths in the width direction of the portions included in the paper passing area Wt in the elastic layer portion 522 are 20 respectively. This ratio is an example, and in addition to this, the length in the width direction of the first elastic layer portion 521 is 40, and the length in the width direction of the portion included in the paper passing region Wt in the second elastic layer portion 522 is set. Each may be 30, etc. Regarding the length of each elastic layer portion in the width direction, when the paper S is passed, the central portion of the paper S in the width direction (direction perpendicular to the insertion direction) overlaps the first elastic layer portion 521, and the paper Both end portions in the width direction of S are set to overlap the second elastic layer portion 522, respectively.

The porous body constituting the elastic layer 52 preferably satisfies the following conditions (i) to (iii).
(I) For a square area 100 in which the size of bubbles in the cross section obtained when the porous body is cut is in the range of 0.1 μm to 50 μm, and one side of the cross section is 200 μm The area occupied by the composite bubbles formed by overlapping the spherical bubbles partially in the square is 60 or more and 70 or less.
(Ii) The bubbles present in the cross section obtained when the porous body is cut have a size in the range of 0.1 μm to 50 μm, and the bubbles having a size of 5 μm to 50 μm are separated every 5 μm. When drawn, there are the most bubbles with a size of 5 μm or more and 10 μm or less.
(Iii) When the number of bubbles having a size of 5 μm or more and 10 μm or less is defined as 100, the number ratio of the bubbles having a size of 10 μm or more and 20 μm or less is 45 or more.

  By satisfying the above condition (i), a wide nip width in the circumferential direction can be obtained even if the pressure roller 50 has a small diameter, and the warming-up time can be shortened, and the pressure roller 50 has excellent durability. It becomes. In addition, since the composite bubbles are different from the spherical shape of the single bubbles, the spherical shapes partially overlap each other, so that they can be easily distinguished from the single bubbles by observing the cross section of the porous body with a microscope or the like.

  By satisfying the above condition (ii), the pressure stress can be evenly distributed, so that a wide nip width can be obtained in the circumferential direction even if the pressure roller 50 has a small diameter, and the warm-up time can be shortened. However, the pressure roller is excellent in durability.

  By satisfying the above condition (iii), the pressure stress can be more evenly distributed, so that higher durability can be obtained.

  As described above, chemical foaming and water foaming are generally known as methods for producing a porous body. Among these, bubbles (cells) are large in chemical foaming, so when used as a rotating body for fixing a copying machine, a uniform pressure load cannot be applied to the toner, resulting in image unevenness and insufficient durability (decrease in hardness, breakage) Etc.) may occur. On the other hand, since the water-foamed silicone method can form fine bubbles uniformly, a uniform pressure load can be applied to the toner and the pressure load can be evenly received, so that insufficient durability is unlikely to occur. And the foaming silicone rubber which satisfy | fills the conditions of said (i)-(iii) can be obtained by applying the technique of water foaming.

  Next, an example of a method for manufacturing the pressure roller 50 described above will be described.

  The pressure roller 50 is formed by sequentially superposing the elastic layer 52 and the surface release layer 53 and forming the grip layer 54 so as to sandwich the surface release layer 53 at both ends of the outer peripheral surface of the elastic layer 52. can get.

  First, a porous body constituting the elastic layer 52 is formed. In order to obtain a porous body that becomes the elastic layer 52 (specifically, the first elastic layer portion 521 and the second elastic layer portion 522), an emulsion composition is prepared. The emulsion composition is a two-part liquid silicone that is mixed with a catalyst, a surfactant, and a cross-linking agent, and an additive, a filler, a dispersing agent, etc., added to water (adding alcohol if necessary). A mixed solution having a viscosity equal to that of liquid silicone rubber is mixed and stirred. That is, an emulsion composition comprising a liquid silicone rubber and a predetermined liquid is prepared.

  The blending ratio (volume ratio) of the liquid silicone rubber and the mixed solution varies depending on the desired porosity. For example, when the blending ratio of the liquid silicone rubber and the mixed solution is 1: 1, fine particles of water in the emulsion composition evaporate to form bubbles (cells), thereby obtaining a porous body having a porosity of 50%. Can do.

  The emulsion composition uses a homogenizer and, if necessary, a stirrer with ultrasonic treatment, such as stirring means, stirring time, stirring speed (for example, 300-1500 rpm) so as to obtain a bubble distribution that satisfies the above conditions. Adjust various stirring conditions.

  At this time, in the porous body finally formed, bubbles existing in the cross section obtained by cutting the porous body have a size in the range of 0.1 μm or more and 50 μm or less, and the cross section Is mixed and emulsified so that the area occupied by the composite bubbles formed by overlapping the spherical bubbles partially in the square is 60 or more and 70 or less with respect to the square area 100 of 200 μm on one side An emulsion composition may be prepared by:

  Further, in the finally formed porous body, bubbles existing in a cross section obtained by cutting the porous body have a size in the range of 0.1 μm to 50 μm and a size of 5 μm to 50 μm. The emulsion composition may be prepared by stirring and emulsifying so that the bubbles having a size of 5 μm or more and 10 μm or less exist most when the bubbles are fractionated every 5 μm.

  Then, the prepared emulsion composition is poured into a mold and heated to cure the silicone rubber without evaporating moisture in the emulsion composition (primary heating). Here, the heating temperature is in the range of 80 to 130 ° C., and the heating time is in the range of 30 to 120 minutes. A heating temperature of 90 to 110 ° C. and a heating time of 60 to 90 minutes are desirable.

  Then, secondary heating is performed to remove moisture from the porous body after the primary heating. The heating temperature is 150 to 300 ° C., and the heating time is 1 to 24 hours. A heating temperature of 200 to 250 ° C. and a heating time of 3 to 5 hours are desirable. By performing such secondary heating, moisture is removed from the porous body, the bubbles are made into a continuous foam type, and the final curing of the silicone rubber is terminated. In this way, a porous body that becomes the elastic layer 52 is obtained.

  After the porous body constituting the elastic layer 52 is obtained, the porous body is fixed to the cored bar 51 by adhesion or the like. Then, the elastic layer 52 is formed around the cored bar 51 by cutting the porous body into a predetermined outer diameter and forming it into a roller shape.

  After the elastic layer 52 is formed around the metal core 51, a one-component thermosetting adhesive is uniformly applied to the outer peripheral surface of the elastic layer 52, and then the portion corresponding to the paper passing area Wt on the outer peripheral surface. A surface release layer 53 is formed by covering a tube made of a fluororesin such as PFA.

  Subsequently, the grip layer 54 is provided in the vicinity of both end portions of the outer peripheral surface of the elastic layer 52 in the axial direction with the surface release layer 53. The grip layer 54 is provided so as to sandwich the surface release layer 53 having the same width as the paper passing area Wt in the axial direction. Examples of the method for forming the grip layer 54 include a method in which the composition for forming the grip layer 54 is applied by spray coating, dip coating, roll coating, or the like, and then dried. The material of the grip layer 54 needs to have three characteristics: a tack property for obtaining a grip force, an elastic body for forming a nip portion, and a heat resistance against a fixing temperature. As such a material, it is desirable to use a rubber material such as silicone rubber or fluorine rubber.

  In this way, the pressure roller 50 of the present embodiment is obtained.

  Next, an example of a method for measuring the number of bubbles in the pressure roller 50 of the present embodiment will be described.

  First, the porous body constituting the elastic layer 52 is cut with a sharp blade, and the cross section is photographed with a laser microscope (LSM) and a scanning electron microscope (SEM) so that a square region with a side of 200 μm can be clearly seen. To do.

  The obtained image is binarized with a commercially available image processing software so that the silicone rubber portion is white and the bubble portion is black. After the bubble portion is blackened and extracted, the extracted bubbles are sieved to each bubble diameter using an opening process which is one of image processing methods with each bubble diameter as a component. By taking the difference between the results before and after each opening process, the number of pixels of the component (bubble diameter) screened is known. By dividing this number of pixels by the number of pixels of the constituent elements, the number included in each diameter range (the number of bubbles present in each fractionated fraction) can be known, and the distribution can be obtained.

  Here, the porous body formed of the water-foamed silicone rubber as described above has a so-called open-cell shape connected by a fine passage formed when water or the like escapes from the porous body after the primary heating. is there.

  Further, as described above, the porous body constituting the elastic layer 52 in the present invention has an area occupied by a composite bubble formed by overlapping spherical bubbles partially in a square region having a side of 200 μm in the cross section. The ratio is 60% or more and 70% or less. This area ratio is obtained as follows. In the image data obtained by the microscope, a square region having a side of 200 μm is cut out. In the cut-out area, the image related to the bubbles other than the composite bubbles formed so as to overlap each other is erased while visually confirming, and then binarized into black and white. Then, the area ratio (calculated by the image processing software) of the black portion with respect to the entire area of this region is calculated to obtain the area ratio.

  Moreover, the measurement of the porosity was calculated by the following equation.

Porosity = (specific gravity of solid rubber-specific gravity of porous material)
/ (Specific gravity of solid rubber) x 100 (%)
(Solid rubber: Silicone rubber that does not contain pores, Porous material: Water-foamed silicone rubber)

  The specific gravity was measured using a specific gravity meter (Electron specific gravity meter MD-200S manufactured by A & D).

  Moreover, the open cell rate was measured by a methanol immersion weight increase rate. This method is described in JP-A-2002-12696. That is, a test piece (cylindrical shape having a diameter of about 29 mm and a thickness of about 12.5 mm) used for measurement of compression set of JIS 6249 is prepared. This is immersed in a metal can having a capacity of about 1 L filled with 500 g of methanol, covered and left in an atmosphere at 25 ° C. From the weight before immersion and 24 hours after immersion, the weight increase rate was measured by the following calculation formula. In addition, about the sample with small specific gravity and floating, the upper part of methanol was covered with the metal mesh.

  As described above, according to the pressure roller 50 of this embodiment, the sheet S is pressed against the fixing belt 41, and the paper S is inserted between the fixing belt 41. The pressure roller 50 includes a metal core 51, a porous elastic layer 52 provided around the metal core 51, and a surface release layer 53 provided on the outer peripheral surface of the elastic layer 52. doing. The porosity of both end portions in the width direction of the sheet passing area Wt of the sheet S in the elastic layer 52 is larger than the porosity of the central portion. Because of this. The hardness of both end portions of the sheet passing area Wt of the paper S in the pressure roller 50 is smaller than the hardness of the central portion. For this reason, even in a configuration in which the outer diameter of the pressure roller 50 is made uniform in the axial direction due to the difference in hardness between both ends and the center of the sheet passing area Wt of the sheet S in the pressure roller 50, both ends from the center of the sheet S are provided. Since the tensile force toward a part arises, generation | occurrence | production of a wrinkle can be suppressed. Thereby, deformation of the sheet S can be suppressed without providing a difference in outer diameter between the central portion and both end portions of the pressure roller 50 in the axial direction.

  In addition, in the pressure roller 50, the elastic layer 52 is made of an emulsion composition. Since the elastic layer 52 is constituted by the porous body formed by water foaming because of this, a uniform pressure load can be applied to the toner compared to the porous body by chemical foaming, It is possible to suppress image unevenness and insufficient durability (decrease in hardness, fracture, etc.).

  Further, the pressure roller 50 has a size of bubbles in a range of 0.1 μm or more and 50 μm or less in a cross section obtained when the elastic layer 52 is cut, and spherical bubbles partially overlap each other. The ratio of the area occupied by the composite bubbles formed in the square region having a side of 200 μm in the cross section is 60% or more and 70% or less. Thus, even if the pressure roller 50 has a small diameter, a wide nip width can be obtained in the circumferential direction, and the pressure roller 50 having excellent durability can be obtained while shortening the warm-up time.

  Further, in the pressure roller 50, the surface release layer 53 is made of a fluorine resin. Since it did in this way, toner adhesion to the pressure roller 50 can be suppressed and paper releasability can be improved.

  In the fixing device 40 of the present embodiment, the fixing belt 41 that heats the paper S and the paper S on which the toner image T is formed are inserted between the fixing belt 41 and the fixing belt 41. Pressure roller 50. Because of this. The hardness of both end portions of the sheet passing area Wt of the paper S in the pressure roller 50 is smaller than the hardness of the central portion. For this reason, even in a configuration in which the outer diameter of the pressure roller 50 is made uniform in the axial direction due to the difference in hardness between both ends and the center of the sheet passing area Wt of the sheet S in the pressure roller 50, both ends from the center of the sheet S are provided. Since the tensile force toward a part arises, generation | occurrence | production of a wrinkle can be suppressed. Thereby, deformation of the sheet S can be suppressed without providing a difference in outer diameter between the central portion and both end portions of the pressure roller 50 in the axial direction.

  The image forming apparatus 100 according to the present embodiment is formed on the paper S by the image forming units 10Y, 10M, 10C, and 10Bk that form the toner image T on the paper S and the image forming units 10Y, 10M, 10C, and 10Bk. And a fixing device 40 for fixing the toner image T to the paper S. As a result, the hardness of both end portions of the paper passing area Wt of the paper S in the pressure roller 50 of the fixing device 40 is smaller than the hardness of the central portion thereof. For this reason, even in a configuration in which the outer diameter of the pressure roller 50 is made uniform in the axial direction due to the difference in hardness between both ends and the center of the sheet passing area Wt of the sheet S in the pressure roller 50, both ends from the center of the sheet S are provided. Since the tensile force toward a part arises, generation | occurrence | production of a wrinkle can be suppressed. Thereby, deformation of the sheet S can be suppressed without providing a difference in outer diameter between the central portion and both end portions of the pressure roller 50 in the axial direction.

  Although the present invention has been described with reference to the preferred embodiment, the pressure roller, the fixing device, and the image forming apparatus of the present invention are not limited to the configuration of the above embodiment.

  For example, in the pressure roller 50 of the above-described embodiment, the elastic layer 52 includes the first elastic layer portion 521 and the two second elastic layer portions 522 that sandwich the first elastic layer portion 521 in the axial direction. However, it is not limited to this. As shown in FIG. 6A, in the pressure roller 50 described above, instead of the elastic layer 52, a pressure roller 50A provided with an elastic layer 52A having elastic layer portions having three or more different porosities may be used. Good. The pressure roller 50A includes one first elastic layer portion 521, two second elastic layer portions 522, a third elastic layer portion 523, a fourth elastic layer portion 524, and a fifth elastic layer portion 525. ,have. And the 1st elastic layer part 521 is arrange | positioned in the center part of the axial direction, and the 2nd elastic layer part 522, the 3rd elastic layer part 523, the 4th elastic layer part 524, and the 5th elastic layer part in order toward both ends. 525 are arranged side by side. The porosity of the first elastic layer portion 521 is the smallest, and the porosity gradually increases in the order of the second elastic layer portion 522, the third elastic layer portion 523, and the fourth elastic layer portion 524, The porosity of the elastic layer portion 525 is the largest. Therefore, the pressure roller 50A is configured such that the hardness gradually decreases from the central portion in the axial direction toward both ends. FIG. 6B schematically shows the relationship between the position in the width direction of the sheet passing area Wt of the pressure roller 50A, the porosity, and the hardness.

  Further, as shown in FIG. 7 (a), in the pressure roller 50 described above, instead of the elastic layer 52, a single component is formed, and the porosity gradually increases from the axial center to both ends. The pressure roller 50B including the elastic layer 52B configured as described above may be used. Here, the single component means not one obtained by connecting a plurality of separately produced porous bodies but one produced as a single porous body. With such a configuration, the pressure roller 50B is configured such that the hardness continuously decreases from the central portion in the axial direction toward both ends. FIG. 7B schematically shows the relationship between the position in the width direction of the paper passing area Wt of the pressure roller 50B, the porosity, and the hardness.

  Like these pressure rollers 50A and 50B, by adopting a configuration in which the porosity of the elastic layer is gradually increased from the central portion in the axial direction to both end portions, the paper S is more uniform in the width direction. A tensile force can be applied. Therefore, deformation of the paper S can be further suppressed.

  In addition, as the pressure roller 50B, the elastic layer is composed of a single component, so that a plurality of porous bodies having different porosity constituting each elastic layer portion can be separately manufactured. It becomes unnecessary to fix each of the plurality of porous bodies to the cored bar. That is, since only one work of producing a single porous body and fixing it to the core is required, the number of manufacturing steps can be reduced and the manufacturing cost can be reduced.

  In addition, embodiment mentioned above only showed the typical form of this invention, and this invention is not limited to embodiment. That is, those skilled in the art can implement various modifications in accordance with conventionally known knowledge without departing from the scope of the present invention. Of course, such deformations are included in the scope of the present invention as long as the configurations of the pressure roller, the fixing device, and the image forming apparatus of the present invention are provided.

(Verification)
The inventors produced Examples 1 and 2 and Comparative Examples 1 and 2 of the pressure roller according to the present invention described below, and verified each of them.

Example 1
In the pressure roller 50 of the embodiment described above, (1) a STKM material (carbon steel pipe for machine structure) having a diameter of 24 mm and a thickness of 2 mm was used as the core metal 51. (2) As the first elastic layer portion 521 and the two second elastic layer portions 522 constituting the elastic layer 52, two kinds of foamed silicone rubbers having the same thickness and having different porosity of 3 mm using the same material, respectively. Was used. The first elastic layer portion 521 had an axial length of 198 mm, a porosity of 45% and a hardness of 50 ° (Asker C) over the entire axial direction. The second elastic layer portion 522 had an axial length of 76 mm, a porosity of 51% over the entire axial direction, and a hardness of 47 ° (Asker C). Accordingly, the elastic layer 52 has an axial length of 350 mm. (3) A PFA tube having a uniform thickness of 30 μm was used as the surface release layer 53, and the paper passing region Wt having a width direction length of 330 mm was formed by covering the outer peripheral surface of the elastic layer 52. From the center position in the width direction in the sheet passing area Wt to 30% toward both ends overlaps the first elastic layer portion 521, and the remaining 20% portions to both ends overlap the second elastic layer portion 522. . (4) Silicone rubber having a hardness of 60 ° (Asker C) is used as the grip layer 54, and a layer having a uniform thickness of 50 μm and a width of 10 mm is formed on the outer peripheral surfaces of both ends of the elastic layer 52 so as to sandwich the surface release layer 53. did. A pressure roller having such a configuration was produced. In the pressure roller according to the first embodiment, the outer diameter of the sheet passing area Wt is formed uniformly over the entire width direction (axial direction).

(Example 2)
In Example 1, a pressure roller having the same configuration as that of Example 1 except that the porosity was 55% and the hardness was 45 ° (Asker C) over the entire axial direction of the second elastic layer portion 522 was produced. .

(Comparative Example 1)
In the first embodiment, only the first elastic layer portion 521 is provided without providing the second elastic layer portion 522, and the elastic layer 52 is configured. The first elastic layer portion 521 has an axial length of 350 mm, and the entire axial direction. The porosity was 45% and the hardness was 50 ° (Asker C). Except for these, a pressure roller having the same configuration as in Example 1 was produced.

(Comparative Example 2)
In the first embodiment, only the first elastic layer portion 521 is provided without providing the second elastic layer portion 522, and the elastic layer 52 is configured. The first elastic layer portion 521 has an axial length of 350 mm, and the entire axial direction. The porosity was 45% and the hardness was 50 ° (Asker C) (up to this point, the same as in Comparative Example 1). Further, by adjusting the outer diameter in the roller-shaped cutting of the first elastic layer portion 521, the outer diameter gradually increases from the center in the width direction of the sheet passing area Wt toward both ends, and the sheet passing area Wt. The outer diameter difference (also referred to as the amount of stitching) between the center and both ends was 0.17 mm. Except for these configurations, a pressure roller having the same configuration as that of Example 1 was manufactured.

(Paper wrinkle test)
A predetermined test image is formed and fixed on a plurality of sheets S by using the image forming apparatus 100 including the fixing device 40 in which the pressure rollers of Examples 1 and 2 and Comparative Examples 1 and 2 are incorporated. It was. Then, the occurrence of wrinkles in the paper S was confirmed by visual observation, and a determination was made based on the following criteria.
... Wrinkles are not confirmed on all 10 sheets of images formed.
X: Wrinkles were confirmed on any of the 10 sheets on which images were formed.

(Tensile strength test)
Using the image forming apparatus 100 provided with the fixing device 40 in which the pressure rollers of Examples 1 and 2 and Comparative Examples 1 and 2 were incorporated, a 200 mm long cut was made in the conveyance direction at the rear end in advance. A predetermined test image was formed and fixed on a plurality of sheets S. Then, the spread amount of the cuts in the paper S was measured and judged based on the following criteria. FIG. 8A schematically shows the trailing edge of the paper before image formation, and FIG. 8B schematically shows the trailing edge of the paper after image formation.
A: The average value of the spread of cuts is 10 mm or more and less than 2.0 mm in 10 sheets on which images are formed.
A: The average value of the spread of the cuts is 10 mm or more and less than 1.0 mm in 10 sheets on which images are formed.
X: The average value of the spread of the cuts is less than 0 mm or the average value of the spread of the cuts is 2.0 mm or more in 10 sheets of the image formed.

(Easy molding)
For Examples 1 and 2 and Comparative Examples 1 and 2, the ease of molding was determined based on the following criteria.
A: The outer diameter of the elastic layer is uniform in the axial direction, and molding is easy.
X: The outer diameter of the elastic layer changes in the axial direction, and molding is not easy.

(Comprehensive judgment)
The overall judgment was judged based on the following criteria.
◎ ・ ・ ・ Results of paper wrinkle test, tensile force test and moldability determination are ◯ or more, including one or more ◎.
◯: The results of the paper wrinkle test, tensile force test, and moldability determination are all ◯.
X: One or more xs are included in the results of the paper wrinkle test, the tensile force test, and the moldability determination.

  Table 1 shows the configurations and determination results of Examples 1 and 2 and Comparative Examples 1 and 2.

(Discussion)
As is clear from the determination results shown in Table 1, in the paper wrinkle test, wrinkles were confirmed on the paper S only in Comparative Example 1, and wrinkles were confirmed on the paper S in Examples 1, 2 and Comparative Example 2. Good results. As a result, in the first and second embodiments, instead of providing the outer diameter difference between the center and both ends in the width direction of the sheet passing area Wt, the both ends in the width direction of the sheet passing area Wt are changed by changing the porosity of the elastic layer. This is because the hardness of the part is smaller than the hardness of the central part. By doing in this way, in Examples 1 and 2, when pressure is applied to the paper S by the pressure roller, the amount of biting increases from the center of the paper passing area to both ends. As a result, when the sheet S is passed, a tensile force is generated on the sheet S from the center to the end, similarly to the shape having the outer diameter difference. For this reason, it is considered that paper wrinkles did not occur.

  In addition, the tensile force test for checking the margin for paper wrinkles was replaced with the measurement of tensile force by making a predetermined amount of cut into the paper and measuring the opening of the cut when passing through the unit. Also in this tensile force test, as in the paper wrinkle test, only Comparative Example 1 was defective, and Good results were obtained for Examples 1 and 2 and Comparative Example 2. From the results of Examples 1 and 2, it can be confirmed that the larger the difference in hardness is, the larger the opening amount of the paper breaks is, and the margin for paper wrinkles is increased. This is presumably because the force with which the sheet S is pulled from the center in the width direction to the end increases by increasing the hardness difference between the center and both ends of the sheet passing area Wt.

  Further, in Examples 1 and 2, the outer diameter is uniform in the paper passing area Wt, and even if the shape is not provided with the outer diameter difference as in Comparative Example 2, the occurrence of paper wrinkles can be suppressed and the paper wrinkles can be suppressed. There is also a margin for. Therefore, in Examples 1 and 2, compared to Comparative Example 2, the control of the roller shape is easier, that is, the molding is easier. Therefore, it can be said that Examples 1 and 2 are superior to Comparative Example 2 in terms of productivity.

  As shown in Table 1, in any of the examples, the paper wrinkle suppression and the tensile force are equal to or greater than those of the comparative example, and the productivity is superior because it is not necessary to maintain the nail shape. Therefore, the effect of using the pressure roller of the present invention was also confirmed from the verification results described above.

10Y, 10M, 10C, 10Bk Image forming unit 20 Conveying belt 30 Paper feeding mechanism 40 Fixing device (an example of a fixing unit)
41 Fixing belt (an example of a rotating body and a heating rotating body)
50, 50A, 50B Pressure roller 51 Core metal 52, 52A, 52B Elastic layer 521 First elastic layer portion 522 Second elastic layer portion 53 Surface release layer 54 Grip layer 100 Image forming apparatus S Paper (sheet material and sheet-like) Example of recording media)
T toner image Wt Paper passing area (an example of an insertion area)

JP 2005-195856 A

Claims (8)

A pressure roller that is pressed against a rotating body and a sheet material is inserted between the rotating body,
A cored bar, an elastic layer having a porous structure provided around the cored bar, and a surface release layer provided on the outer peripheral surface of the elastic layer,
The pressure roller, wherein a porosity of both end portions in the width direction of the insertion region of the sheet material in the elastic layer is larger than a porosity of a central portion thereof.   2. The pressure roller according to claim 1, wherein a porosity of the elastic layer is gradually increased from the central portion to the both end portions.   The pressure roller according to claim 1 or 2, wherein the elastic layer is made of an emulsion composition.   The pressure roller according to claim 1, wherein the elastic layer is a single component.   The bubbles present in the cross section obtained when the elastic layer is cut have a size in the range of 0.1 μm or more and 50 μm or less, and the composite bubbles formed by partially overlapping the spherical bubbles are 5. The pressure roller according to claim 1, wherein an area ratio of one side in the cross section in a square region of 200 μm is 60% or more and 70% or less.   The pressure roller according to claim 1, wherein the surface release layer is made of a fluororesin. A heating rotator that heats the sheet-like recording medium, and a pressure rotator that is pressed against the heating rotator and into which the recording medium on which a toner image is formed is inserted. In the fixing device
The fixing device according to claim 1, wherein the pressure rotating body is the pressure roller according to claim 1. An image forming apparatus comprising at least an image forming unit that forms a toner image on a sheet-like recording medium, and a fixing unit that fixes the toner image formed on the recording medium by the image forming unit to the recording medium.
The image forming apparatus, wherein the fixing unit is the fixing device according to claim 7.

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