JP2020118765A - Image formation device - Google Patents

Abstract

To provide an image formation device that can alleviate a degree to which thermal energy given to a belt of a fixing device is wasted.SOLUTION: An image formation device comprises: an endless belt circulatable to transport a recording medium from an upstream to a downstream; a fixing pad 52 for pressing the belt from the inner side of the belt toward at least a first side; a sliding sheet arranged between the belt and the fixing pad; a support member 54 for supporting the fixing pad 52 from the opposite side of the belt; and a roller. The roller and the fixing pad 52 sandwich the sliding sheet and the belt. The fixing pad 52 has a plurality of recessed portions 5 on a surface near the roller.SELECTED DRAWING: Figure 6

Description

The present invention relates to an image forming apparatus.

An image forming apparatus including a fixing device is known. In recent years, a fixing device may employ a method using a fixing pad from the viewpoint of energy saving and cost reduction.

Such a fixing device is described, for example, in JP-A-2006-47769 (Patent Document 1) and JP-A-2013-68724 (Patent Document 2).

JP, 2006-47769, A JP, 2013-68724, A

In a fixing device using a fixing pad, the fixing pad is fixed while being pressed against a belt. In the fixing device, the fixing pad and the roller are arranged so as to sandwich the belt, and the roller presses the fixing belt toward the fixing pad. Since the fixing pad is generally made of resin and has low rigidity, it is easily bent if the pad is used alone when pressure is applied from the roller. In order to suppress bending when pressure is applied, a support member formed of a metal plate material is installed on the back surface of the pad.

To increase the rigidity of the support member, a certain amount of wall thickness is required. However, when the support member is formed of a thick plate material, the heat capacity of the support member increases. Since the heat from the heat source is applied to the belt in the fixing device, the belt reaches the fixing nip portion in a high temperature state. This heat is transferred to the paper as a recording medium to melt the toner on the paper and fix it on the paper.

However, the heat carried from the belt to the fixing nip portion is not only transferred from the surface of the belt to the paper but also to the fixing pad on the back side of the belt. This heat is further transferred from the fixing pad to the support member and warms the support member. It means that the support member is warmed, and the heat energy given to the belt from the heat source is wasted in a wasteful manner. Since the heat energy is originally generated by the electric energy for causing the heat source to generate heat, wasting this is a waste of the electric energy.

Therefore, it is an object of the present invention to provide an image forming apparatus that can reduce the degree to which the thermal energy applied to the belt in the fixing device is wasted in a wasteful manner.

To achieve the above object, an image forming apparatus according to the present invention includes an endless belt that can be circulated to convey a recording medium from upstream to downstream, and the belt from the inside of the belt to at least the first side. The roller includes: a fixing pad that is pressed toward the sliding sheet; a sliding sheet that is arranged between the belt and the fixing pad; a supporting member that supports the fixing pad from the side opposite to the belt; and a roller. And the fixing pad sandwiches the sliding sheet and the belt, and the fixing pad has a plurality of recesses on the roller side surface.

According to the present invention, the heat insulating property in the vicinity of the surface of the fixing pad is enhanced by interposing the recessed portion which is a closed space, and as a result, heat transfer from the belt to the support member is suppressed. As a result, it is possible to provide an image forming apparatus that can reduce the degree to which the thermal energy applied to the belt in the fixing device is wasted in a wasteful manner.

1 is a conceptual diagram of an image forming apparatus according to a first embodiment of the present invention. FIG. 3 is a conceptual diagram of a fixing device included in the image forming apparatus according to Embodiment 1 of the present invention. FIG. 3 is a partially enlarged view of the fixing device shown in FIG. 2. FIG. 6 is a first explanatory diagram of a method of attaching a fixing pad to a support member. FIG. 9 is a second explanatory diagram of a method of attaching the fixing pad to the support member. FIG. 6 is a perspective view of a fixing pad attached to a support member. FIG. 3 is a cross-sectional view of a structure included in a fixing device included in the image forming apparatus according to Embodiment 1 of the present invention. FIG. 3 is a front view of a fixing pad included in the image forming apparatus according to the first embodiment of the present invention. FIG. 3 is a partial perspective view of a fixing pad included in the image forming apparatus according to the first embodiment of the present invention. FIG. 3 is a conceptual diagram of a structure near a fixing pad included in the image forming apparatus according to Embodiment 1 of the present invention. FIG. 9 is a partial perspective view of a modified example of the fixing pad included in the image forming apparatus according to the first embodiment of the present invention. FIG. 4 is a first explanatory diagram of the shape of the unevenness of the fixing pad and the way the belt hits. FIG. 8 is a second explanatory diagram of the shape of the unevenness of the fixing pad and the way of hitting the belt. FIG. 7 is a front view of a first example of how to arrange a plurality of recesses in the fixing pad. FIG. 9 is a front view of a second example of how to arrange a plurality of recesses in the fixing pad. It is a front view of the 3rd example of how to arrange a plurality of crevices in a fixing pad. It is a front view of the 4th example of how to arrange a plurality of crevices in a fixing pad. It is a front view of the 5th example of how to arrange a some recessed part in a fixing pad. It is a front view of the 6th example of a method of arrangement of a plurality of crevices in a fixing pad. FIG. 7 is an explanatory diagram of a first example in which a fixing nip portion is configured using a fixing pad. It is a front view of the 7th example of how to arrange a some recessed part in a fixing pad. It is explanatory drawing of the 2nd example which comprises a fixing nip part using a fixing pad. It is a front view of the 8th example of how to arrange a plurality of crevices in a fixing pad. It is sectional drawing of a sliding sheet. FIG. 6 is an explanatory diagram when the width of the concave portion of the fixing pad is large to some extent. FIG. 6 is an explanatory diagram when the width of the concave portion of the fixing pad is small to some extent. It is a graph which shows an experimental result. FIG. 6 is an explanatory diagram of a model in which a sliding sheet and a recording medium are stacked and pressed on a fixing pad. It is explanatory drawing of the bending amount which arises in a sliding sheet. It is explanatory drawing of the second moment of area.

(Embodiment 1)
(Constitution)
An image forming apparatus according to the first embodiment of the present invention will be described with reference to FIGS.

FIG. 1 shows a conceptual diagram of the image forming apparatus 801 according to the present embodiment. The image forming apparatus 801 includes a housing 1 and a cassette 40 arranged below the housing 1. Inside the housing 1, a photosensitive member 44, a charger 46, a transfer belt 47, an image exposure device 48, a developing roller 45, a primary transfer roller 42, a secondary transfer roller 43, a fixing device 101, etc. are arranged. .. One or more recording media 2 are stored in the cassette 40. The recording medium 2 may be paper, for example, but may be other than paper. The transfer belt 47 is endless and is arranged so as to circulate and travel.

In the image forming apparatus 801, the surface of the photoconductor 44 is uniformly charged by the charger 46 so as to have a predetermined potential. Image exposure according to the original image is performed from the image exposure device 48 to this charged area. As a result, an electrostatic latent image is formed on the surface of the photoconductor 44. This electrostatic latent image is developed by the developing roller 45 to which a developing bias is applied to form a visible toner image. A bias for attracting toner is applied to the primary transfer roller 42, and the visible toner image on the surface of the photoconductor 44 is transferred to the transfer belt 47.

On the other hand, the recording medium 2 is taken out one by one from the cassette 40 by the paper feed roller 41 and conveyed to the secondary transfer roller 43. A voltage is applied to the secondary transfer roller 43 as well as the primary transfer roller 42. The transfer belt 47 is sandwiched between the secondary transfer roller 43 and the pressing roller 49, and this portion serves as a secondary transfer nip portion 38. When the recording medium 2 passes through the secondary transfer nip portion 38, the recording medium 2 and the transfer belt 47 are sandwiched and pressed by the secondary transfer roller 43 and the pressing roller 49. The visible toner image conveyed by the transfer belt 47 is transferred to the recording medium 2 at the secondary transfer nip portion 38. The recording medium 2 carrying the visible toner image is sent to the fixing device 101. The detailed structure of the fixing device 101 will be described later. In the fixing device 101, heating and pressurization are performed, and the toner is fixed on the recording medium 2. The recording medium 2 on which image formation is completed in this way is ejected from the outlet 39.

FIG. 2 shows the fixing device 101 taken out independently. The fixing device 101 includes an endless belt 51, a roller 58 for pressurizing, and a fixing pad 52 fixedly arranged inside the belt 51. The fixing pad 52 and the roller 58 are positioned so as to sandwich the belt 51, and these form a fixing nip portion 50. The fixing pad 52 defines the path of the belt 51. The belt 51 is fed along the shape of the fixing pad 52.

The fixing pad 52 is supported by the support member 54. The heat source 56 is arranged inside the heating member 57. The belt 51 is stretched around a heating member 57 and a fixing pad 52. The roller 58 is rotated at a predetermined rotation speed by a motor (not shown). As a result, the belt 51 is sent.

The fixing pad 52 may be formed of a resin such as polyphenylene sulfide, polyimide, or liquid crystal polymer. The fixing pad 52 may be formed of a metal such as aluminum or iron, or a ceramic instead of the resin. .. The fixing pad 52 may include a fixing member made of silicone rubber, fluororubber, or the like. The fixing pad 52 may be composed of a combination of two or more parts.

The heating member 57 is a member formed of a metal such as aluminum or SUS, and has a substantially cylindrical shape. The roller 58 has a three-layer structure of a cored bar/elastic layer/release layer. The elastic layer is preferably formed of a material having high heat resistance such as silicone rubber and fluororubber. The core metal is preferably made of a metal such as aluminum or iron. The core metal may have a pipe shape or a solid shape. The release layer is preferably formed of a fluorine tube or has a configuration in which release properties such as fluorine coating are imparted.

The heat source 56 may be a halogen heater. Alternatively, the heat source 56 may be a system that heats the heating member 57 and/or the belt 51 with IH. A method may be adopted in which the heating member 57 and/or the belt 51 is formed of a resistance heating element and heats itself.

The recording medium 2 on which the toner image is transferred is conveyed to the fixing nip portion 50 with the surface on which the toner image is transferred facing the heated belt 51, and passes through the fixing nip portion 50. The recording medium 2 passing through the fixing nip portion 50 is pressed and heated by being sandwiched between the belt 51 and the roller 58. As a result, the toner image is fixed on the recording medium 2.

An enlarged view of the vicinity of the fixing pad 52 is shown in FIG. In this figure, the recording medium 2 is fed from the bottom to the top as shown by arrows 91 and 92, so the lower side is the upstream side and the upper side is the downstream side. The roller 58 presses to the left in FIG.

The recording medium 2 sent to the fixing nip portion 50 is correctly guided to the fixing nip portion 50 as indicated by an arrow 91. The recording medium 2 that has passed through the fixing nip portion 50 is discharged from the fixing nip portion 50 as indicated by an arrow 92.

The attachment of the fixing pad 52 to the support member 54 will be described with reference to FIGS. 4 to 6. The fixing pad 52 has a surface 6. The surface 6 is provided with a plurality of recesses 5. The support member 54 may be formed of sheet metal. As shown in FIGS. 4 and 5, the support member 54 is provided with a hole 54 a for mounting the fixing pad 52. As shown in FIG. 5, a pin 52b is provided on the surface of the fixing pad 52 on the side of the support member 54 so as to be attached to the support member 54. The fixing pad 52 can be attached to the support member 54 by fitting the pin 52b into the hole 54a. FIG. 6 is a perspective view showing a state in which the mounting is completed. The fixing pad 52 and the supporting member 54 are combined, and the sliding sheet 53 is further wound. Thus, the fixing pad structure 60 as shown in FIG. 7 is completed. The edge of the sliding sheet 53 may be inserted between the fixing pad 52 and the support member 54.

A front view of the fixing pad 52 is shown in FIG. In the example shown here, the recess 5 is rectangular when viewed from the front. The plurality of recesses 5 are arranged in parallel. FIG. 9 shows a part of the fixing pad 52 taken out. As shown in FIG. 10, the sliding sheet 53 is arranged so as to cover the surface 6 of the fixing pad 52. The belt 51 is conveyed in the direction of arrow 90 while contacting the sliding sheet 53. Although the conveyance direction of the belt 51 and the longitudinal direction of the recess 5 are not necessarily perpendicular, they are schematically shown in FIG. 10 for convenience of description. In FIG. 10, a cross section of the fixing pad 52 and the sliding sheet 53 taken along a plane perpendicular to the longitudinal direction of the recess 5 and the belt 51 are shown at the same time. Since the entrance of the recess 5 is closed by the sliding sheet 53, the interior of the recess 5 is a space isolated from the outside. That is, a void is formed in the recess 5.

The configuration of image forming apparatus 801 in the present embodiment can be expressed as follows. The image forming apparatus 801 includes an endless belt 51 that can be circulated to convey the recording medium 2 from upstream to downstream, and a fixing pad 52 that presses the belt from the inside of the belt 51 toward at least the first side 95. , A sliding sheet 53 arranged between the belt 51 and the fixing pad 52, a support member 54 for supporting the fixing pad 52 from the side opposite to the belt 51, and a roller 58. The roller 58 and the fixing pad 52 are provided. Sandwiches the sliding sheet 53 and the belt 51, and the fixing pad 52 has a plurality of recesses 5 on the surface on the roller 58 side.

(Action/effect)
In the present embodiment, as shown in FIG. 10, the fixing pad 52 is covered with the sliding sheet 53 so that the recess 5 becomes a closed space, and the heat insulating property can be improved. Conventionally, there is a problem that heat is transferred from the belt 51 to the fixing pad 52 via the sliding sheet 53 and further to the support member 54, but the recess 5 that becomes a closed space is formed. Is interposed, heat insulation near the surface of the fixing pad 52 is enhanced, and as a result, heat transfer from the belt 51 to the support member 54 is suppressed. This can improve energy saving performance. That is, the image forming apparatus can reduce the degree to which the thermal energy applied to the belt in the fixing device is wasted in a wasteful manner.

Since the concave portion 5 of the fixing pad 52 is closed by the sliding sheet 53, it is possible to prevent grease, abrasion dust and the like from entering the concave portion 5, and it is also excellent in durability.

In the example shown in FIG. 10, the bottom of the recess 5 is a plane parallel to the surface 6, but the shape of the inside of the recess 5 is not limited to such a shape. For example, as shown in FIG. 11, the bottom of the recess 5 may be a curved surface.

Here is a different example. For example, in the example shown in FIG. 12, the concave portion is V-shaped and the convex portion is also sharp. Even if the fixing pad 52 has such a shape, a certain effect can be obtained, but it is not preferable. In this case, since the sliding sheet 53 makes point contact with the fixing pad 52, the sliding sheet 53 itself has a shape in which irregularities are repeated along the shape of the fixing pad 52. In this case, the belt 51 has a shape in which the unevenness is repeated due to the effect of the unevenness of the sliding sheet 53. If this happens, the pressure distribution in the fixing nip portion 50 becomes non-uniform. In that case, fixing noise may occur. The “fixing noise” here includes, for example, a defect in which an area where toner is not yet fixed partially remains in an image, or uneven gloss appears due to insufficient toner fixing.

In order to prevent such defects from occurring, it is preferable that the upper surface of the convex portion, that is, the surface 6 is left as a flat surface, as shown in FIG. With such a configuration, the sliding sheet 53 comes into contact with the surface 6 so that the sliding sheet 53 has a relatively flat shape, and the belt 51 that comes into contact with the sliding sheet 53 also has a relatively flat state. By being conveyed, the pressure distribution in the fixing nip portion 50 can be made as uniform as possible.

Assuming an arbitrary straight line extending from the upstream side to the downstream side on the surface of the fixing pad 52 on the roller 58 side, the plurality of concave portions 5 pass through a portion which is not the concave portion at least once even if the arbitrary straight line is set anywhere. Are preferably arranged as follows. This will be described with reference to FIGS. 14 to 16. 14 to 16 are front views of the surface of the fixing pad 52 on the roller 58 side.

For example, in the fixing pad 52z shown in FIG. 14, each of the plurality of recesses 5 is arranged such that the direction parallel to the sheet passing direction is the longitudinal direction. In the case where the plurality of recesses 5 are arranged in this way, the number of times and the length of passing through the portion other than the recesses in the fixing nip portion 50 are greatly different between the arrow 81 and the arrow 82. The arrow 81 passes through the concave portion 5 while passing through the fixing nip portion 50, and does not pass through a portion other than the concave portion even once. On the other hand, as indicated by an arrow 82, while passing through the fixing nip portion 50, it always passes through a portion that is not a recess. As described above, a great difference in the number of times or lengths of passing through the portions other than the concave portions in the arrows 81 and 82 causes nonuniformity of the fixing degree, and thus fixing noise is likely to occur, which is not preferable.

For example, in the fixing pad 52 shown in FIG. 15, each of the plurality of recesses 5 is arranged so that the direction intersecting the sheet passing direction at an angle of 45° is the longitudinal direction. If the plurality of recesses 5 are arranged in this manner, as shown by an arrow 81, the recesses 5 pass through the recesses 5 while passing through the fixing nip portion 50, and the non-recessed portions also pass through. Even if the position of the arrow 81 is appropriately shifted to the left and right, it always passes through the recess 5 one or more times. With this configuration, the degree of fixing is substantially uniform at any position in the longitudinal direction of the fixing pad, and the occurrence of fixing noise can be prevented.

For example, in the fixing pad 52i shown in FIG. 16, each of the plurality of concave portions 5 is arranged such that the direction intersecting the sheet passing direction at an angle of about 20° is the longitudinal direction. In the fixing pad 52i, the shape of each of the plurality of recesses 5 is an S shape, not a rectangle. The recess 5 may have such a shape. In such a case as well, as shown by the arrow 81, it passes through the concave portion 5 while passing through the fixing nip portion 50, and also passes through a portion which is not the concave portion. Even if the position of the arrow 81 is appropriately shifted to the left and right, it always passes through the recess 5 one or more times. Also in this case, similarly to the example of FIG. 15, it is possible to prevent the occurrence of fixing noise.

In FIGS. 15 to 16, each of the plurality of concave portions 5 has a groove shape, but the shape is not limited to the groove shape and may be a dot shape. For example, in the fixing pad 52j shown in FIG. 17, each of the plurality of recesses 5 has a rectangular dot shape. The quadrangle here may be, for example, a rhombus. In this case, paying attention to the arrow 81, it passes through the concave portion 5 while passing through the fixing nip portion 50, and also passes through a portion which is not the concave portion. Even if the position of the arrow 81 is appropriately shifted to the left or right, even if the arrows 82, 83, 84 and 85 are assumed, the concave portion 5 always passes through the recess 5 one or more times. Also in this case, the occurrence of fixing noise can be prevented.

In the fixing pad 52k shown in FIG. 18, each of the plurality of recesses 5 is circular. Also in this case, paying attention to the arrow 81, it passes through the concave portion 5 while passing through the fixing nip portion 50, and also passes through a portion which is not the concave portion. Also in this case, the occurrence of fixing noise can be prevented.

However, in the example shown in FIGS. 17 and 18, the arrows 81 and 85 of the arrows 81 to 85 pass through the three recesses 5, so the distance passing through the recesses 5 is long, and the arrow 83 indicates 2 Since it passes through the individual concave portions 5, the distance passing through the concave portions 5 is short. In the arrows 82 and 84, there is no portion that crosses the recess 5, so there is almost no distance through the recess 5. On the contrary, it can be said that the distance passing through the portion other than the concave portion 5, that is, the surface 6, is long in the arrows 82 and 84, short in the arrow 83, and shorter in the arrows 82 and 84. If there is such a difference, the degree of fixing may differ depending on the place. When provided in a dot shape, it is preferable that the plurality of recesses 5 be arranged such that the difference in distance passing through the surface 6 is as small as possible. For example, a fixing pad 52m shown in FIG. 19 is preferable. In the fixing pad 52m, each of the plurality of recesses 5 is circular, and the number of recesses 5 arranged in the sheet passing direction is the same at any place. In the fixing pad 52k shown in FIG. 18, three recessed portions 5 and two recessed portions 5 are alternately arranged. However, in the fixing pad 52m shown in FIG. 19, the recessed portions 5 pass through at any place. Three are lined up in each direction. With this configuration, at least the arrows 81, 83, and 85 pass through the three recesses 5 in any of them, so that the difference in the distance passing through the surface 6 can be reduced.

Since the fixing strength is determined at the portion where the nip pressure is maximized during the nip work, it is preferable that no recess is provided at this portion. In other words, it is preferable that the plurality of recesses 5 are arranged so as to avoid the position where the pressure distribution is maximum in the region where the roller 58 and the belt are in close contact with each other. For example, as shown in FIG. 20, when the roller 58 is pressed against the fixing pad 52n having a simple shape to pass the paper along the arrow 97, as shown in FIG. In, the recess 5 is arranged so as to avoid the maximum pressure position 9. In this example, since the fixing pad 52n has a substantially symmetrical shape on both the inlet side and the outlet side, the maximum pressure position 9 is also near the center. At the maximum pressure position 9, the surface 6 is arranged instead of the recess 5. At the maximum pressure position 9, the surface 6 is horizontally aligned.

As shown in FIG. 22, when the fixing pad 52r has a shape in which the outlet side protrudes from the inlet side, the maximum pressure position 9 is near the outlet. In this case, as shown in FIG. 23, the pad member 52r is provided with the recess 5 while avoiding the maximum pressure position 9 located near the outlet.

FIG. 24 shows an enlarged cross section of the sliding sheet 53. The sliding sheet 53 has a surface 53a and a surface 53b. The surface 53b has unevenness. The surface 53a is a surface against which the belt 51 rubs. The surface 53b is a surface that contacts the fixing pad 52. The surface 53b of the sliding sheet 53 on the fixing pad 52 side has irregularities, and the width of each of the plurality of concave portions 5 provided on the fixing pad 52 is larger than the width of the convex portion included in the irregularities of the sliding sheet 53. It is preferably small. This will be described with reference to FIGS. 25 to 26. The width of each of the plurality of recesses 5 provided on the fixing pad 52 is L1. The width of the convex portion included in the irregularities of the sliding sheet 53 is L2. In the example shown in FIG. 25, L1>L2. In this example, the convex portions of the sliding sheet 53 enter the concave portions 5 of the sliding sheet 53 at the portions G1, G2, G3, G4. In such a case, the pressure required for fixing cannot be applied, and fixing failure locally occurs. Poor fixing causes a decrease in glossiness, for example.

In the example shown in FIG. 26, L1<L2. In this example, the convex portion of the sliding sheet 53 does not enter the concave portion 5 of the sliding sheet 53 at any part.

The sliding sheet 53 may be a cloth-like sheet member in which glass fiber is coated with fluorine. The thickness of the sliding sheet 53 may be 120 μm, for example.

For example, if the weaving cycle of the sliding sheet 53 is 1.2 mm pitch, the width of the convex portion is 0.6 mm. In this case, if the width of the recess 5 of the fixing pad 52 is 0.9 mm, the fixing pad 52 may enter the recess 5.

Even if the weaving cycle of the sliding sheet 53 is 1.2 mm pitch, if the width of the concave portion 5 of the fixing pad 52 is 0.4 mm, the width of the convex portion is smaller than 0.6 mm. Does not occur.

(Experiment)
Regardless of whether the surface of the sliding sheet 53 is uneven or not, if the width of the recess 5 of the fixing pad 52 is too wide, the sliding sheet 53 may locally sink. An experiment for verifying the relationship between the width of the recess 5 and the thickness of the sliding sheet 53 will be described.

A fixing pad 52 provided with a plurality of concave portions 5 on its surface was prepared. Each of the plurality of recesses 5 was arranged such that the direction inclined by 45° with respect to the sheet passing direction was the longitudinal direction.

As the sliding sheet 53, those under the conditions shown in Table 1 were used.

An image forming apparatus including a fixing device including the fixing pad 52 and the sliding sheet 53 described above was used to print a solid color image of three colors superimposed on plain paper, and the glossiness of this fixed image was measured and evaluated.

As shown in Table 2, the experiment was performed by changing the width of the recess 5 from 0.4 mm to 1.4 mm in steps of 0.2 mm.

The experimental results are shown in FIG. As shown in this graph, it was found that when the width of the recess 5 is less than 1.0 mm, the glossiness is not extremely lowered. The arrow 88 is almost horizontal, indicating that the glossiness has not changed much. However, when the width of the recess 5 becomes 1.0 mm or more, the glossiness sharply decreases as shown by an arrow 89. That is, a fixing failure has occurred. In this experiment, the thickness of the sliding sheet 53 is 200 μm, and the upper limit of 1.0 mm under which the glossiness is not extremely lowered is 5 times the thickness of the sliding sheet 53.

From the above, it is preferable that the width of each of the plurality of recesses 5 provided in the fixing pad 52 is less than 5 times the thickness of the sliding sheet 53.

This will be described with reference to FIGS. 28 to 30.
FIG. 28 shows a model of a state in which the sliding sheet 53 and the recording medium 2 are stacked and pressed on the fixing pad 52. It is assumed that the width of the recess 5 is L and that the load W acts on the sliding sheet 53 on the recess 5. As shown in FIG. 29, the amount of deflection of the sliding sheet 53 in the recess 5 at this time is δ. When calculated, the amount of deflection δ=WL ³ /3EI. W is a load, L is a beam length, E is a longitudinal elastic modulus, and I is a moment of inertia of area. The state of the second moment of inertia I can be calculated by assuming the cross-sectional shape of the beam as shown in FIG. The width of the beam when viewed in a cross-sectional view is b, and the height is h. h/2 is set to e. The amount of deflection δ of the sliding sheet 53 is proportional to the cube of the length L of the beam, that is, the cube of the width of the recess 5. On the other hand, the amount of deflection δ of the sliding sheet 53 is inversely proportional to the cube of the thickness h of the sliding sheet 53. Therefore, if L/h is kept constant, the amount of deflection of the sliding sheet 53 becomes a constant value.

From this conclusion, as described above, assuming that the width of each of the plurality of recesses 5 provided in the fixing pad 52 is less than 5 times the thickness of the sliding sheet 53, The amount of deflection should be able to maintain a good value.

It should be noted that a plurality of the above-mentioned embodiments may be appropriately combined and adopted.
It should be noted that the above-described embodiments disclosed this time are exemplifications in all respects, and are not restrictive. The scope of the present invention is defined by the claims, and includes meanings equivalent to the claims and all modifications within the scope.

DESCRIPTION OF SYMBOLS 1 case, 2 recording medium, 5 concave part, 6 surface, 9 maximum pressure position, 38 secondary transfer nip part, 39 exit, 40 cassette, 41 paper feed roller, 42 primary transfer roller, 43 secondary transfer roller, 44 Photoconductor, 45 developing roller, 46 charger, 47 transfer belt, 48 image exposure device, 49 pressing roller, 50 fixing nip portion, 51 belt, 52, 52i, 52j, 52k, 52m, 52n, 52r, 52z fixing pad, 52b pin, 53 sliding sheet, 53a, 53b (of sliding sheet) surface, 54 support member, 54a hole, 56 heat source, 57 heating member, 58 roller (for pressurization), 59 heating roller, 60 fixing pad Structure, 81, 82, 83, 84, 85, 88, 89, 90, 91, 92 Arrow, 95 First direction, 96 (Roller rotation) Arrow, 97 (Paper feeding direction) Arrow, 101 fixing device, 801 image forming apparatus.

Claims (5)

An endless belt that can be circulated to convey the recording medium from upstream to downstream,
A fixing pad that presses the belt from the inside of the belt toward at least the first side;
A sliding sheet arranged between the belt and the fixing pad,
A support member for supporting the fixing pad from the side opposite to the belt,
Equipped with a roller,
The roller and the fixing pad sandwich the sliding sheet and the belt,
The image forming apparatus, wherein the fixing pad has a plurality of recesses on the roller side surface. Assuming an arbitrary straight line extending from the upstream side to the downstream side on the roller-side surface of the fixing pad, the plurality of recesses pass through at least once a portion that is not a recess no matter where the arbitrary straight line is set. The image forming apparatus according to claim 1, wherein the image forming apparatus is arranged as follows. The image forming apparatus according to claim 1, wherein the plurality of concave portions are arranged so as to avoid a position where a pressure distribution is maximum in a region where the roller and the belt are in close contact with each other. The surface of the sliding sheet on the side of the fixing pad has irregularities, and the width of each of the plurality of concave portions provided in the fixing pad is smaller than the width of the convex portion included in the irregularities of the sliding sheet. The image forming apparatus according to any one of claims 1 to 3. The image forming apparatus according to claim 1, wherein the width of each of the plurality of recesses provided in the fixing pad is less than 5 times the thickness of the sliding sheet.

Images