JP2007163902A - Fixing belt and fixing device using the same, and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain satisfactory smoothness and uniform gloss regardless of an image density or the like in a system in which a toner image carried on a recording sheet is fixed by being heated and pressed while being put beneath a belt member. <P>SOLUTION: An endless fixing belt 2 for use in a fixing device has a surface brought into contact with an unfixed toner image on a recording sheet 1 having the unfixed toner image carried thereon and fixes the unfixed toner image by heat and pressure. The surface to be brought into contact with the unfixed toner image has a microhardness of 5 to 30 and a glossiness Gs (20°) of 50 or more. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a fixing belt for transferring or fixing a toner image formed on an image forming apparatus using an electrophotographic system, an electrostatic recording system, or the like to a recording sheet, a fixing apparatus using the same, and an improvement of the image forming apparatus. .

2. Description of the Related Art Conventionally, image forming apparatuses such as electrophotographic copying machines and printers are well known. In recent years, photographic images taken with a digital still camera have been actively printed out by an electrophotographic image forming apparatus.
In such applications, since the image to be formed preferably has a high gloss finish, many examples of application in an electrophotographic image forming apparatus have been presented.

  For example, by using a recording sheet having an image-receiving layer made of a thermoplastic resin on the surface, a toner image is embedded in the image-receiving layer softened by heating and pressing the recording sheet using a fixing belt at the time of fixing. In addition, a method is described in which the surface level difference of the image is reduced and the surface property of the fixing belt is copied as it is to increase the gloss of the image surface (see, for example, Patent Documents 1 to 4).

On the other hand, a suitable example is also presented for such a fixing belt itself. For example, in Patent Document 5, it is possible to obtain a stable and highly glossy image over a long period of time by forming a surface layer mainly composed of fluorocarbon siloxane rubber in which fluorine-based particles are dispersed on the surface of a belt base material. Are listed.
Further, the hardness of the surface of the fixing belt, particularly the microhardness, is also presented. In Patent Document 6, the microhardness is set to 0.1 to 5 and the surface glossiness is set to 75 or more (at an incident angle of 75 °). It is noted that a high gloss image can be obtained.

JP-A-64-35452 (Example, FIG. 1) Japanese Patent Laid-Open No. 5-216322 (Means for Solving the Problems, FIG. 2) JP 2001-83834 A (Example 1, FIG. 2) JP 2004-191678 A (Embodiment of the Invention, FIG. 1) Japanese Patent Laying-Open No. 2005-43657 (Example) JP 2002-91212 A (Example, Table 1)

  As described above, in the method of fixing by heating and pressing in a state where the recording sheet carrying the toner and the fixing belt are overlapped, in order to secure the gloss of the image, the toner is heated on the surface of the recording sheet. It is necessary to be sufficiently embedded in the plastic resin layer.

However, if the surface of the fixing belt is too soft, there is a problem that gloss reduction occurs in the halftone portion (halftone portion) of the toner image.
For example, the height of the toner image carried on the recording sheet is scattered in the range of several μm to several tens of μm depending on the image density. Further, the toner accumulation density varies depending on the toner density, the image resolution, and the number of screen lines. For this reason, the adhesion between the fixing belt and the recording sheet is improved particularly in a portion where there is no toner image, and high gloss can be obtained. On the other hand, a solid image (for example, process black) where toner is carried at a height of several tens of μm In this case, the adhesion between the fixing belt and the toner image is improved and the toner image is in a high pressure state, so that the solid image is well embedded in the thermoplastic resin layer of the recording sheet, and the smoothness and uniformity are excellent. You can get a good gloss. However, since the surface of the fixing belt itself is soft at the halftone part (halftone image) of the toner density, it can be deformed according to the surface shape of the toner, so that some gloss can be obtained, but the pressure on the toner image is The toner image is dispersed more than the solid image, and the toner image cannot be sufficiently embedded in the thermoplastic resin layer of the recording sheet. Further, the distortion caused when the toner image is embedded at the fixing nip is released after the fixing nip is discharged. Since the minute unevenness is restored, the gloss is relatively lowered as compared with the non-image portion and the solid image portion.

  If the surface of the fixing belt is too hard, the followability of the surface of the fixing belt with respect to the toner image on the recording sheet is deteriorated, and occurs at the image density boundary portion (particularly upstream of the intersecting portion of intersecting line images). Easily), a bubble accumulation called an edge void occurs, thereby causing a slight decrease in gloss at the boundary between the high density portion and the low density portion. Further, depending on the image density, the adhesion between the recording sheet and the surface of the fixing belt is lowered, and uneven glossiness may occur in the image. Furthermore, when using thick paper as a recording sheet, a large stress acts on the belt surface contacting the leading end portion or both end portions of the thick paper, and the belt surface is damaged.

  The present invention has been made in order to solve the above technical problem, and is in a system in which a toner image carried on a recording sheet is fixed by heating and pressing in a state of being superimposed on a belt member. The present invention provides a fixing belt capable of obtaining good smoothness and uniform glossiness regardless of image density and the like, a fixing device using the same, and an image forming apparatus.

  In order to solve such a technical problem, the present inventor pays attention to the effect of the image receiving layer on the surface of the recording sheet with respect to the glossiness of the image, and studies by reducing the difference in glossiness in the halftone image. As a result of overlapping, a more appropriate range of the hardness and smoothness of the surface of the fixing belt was found. In addition, when evaluating the smoothness of the fixing belt with the specular gloss, it is difficult to directly measure the minute unevenness on the surface at the conventional incident angle of 75 °, and the smoothness can be appropriately adjusted by reducing the incident angle. Obtaining knowledge that evaluation is possible, the present invention has been devised.

  That is, as shown in FIG. 1, the present invention is an endless shape used in a fixing device that is fixed by heating and pressing the surface of the recording sheet 1 on which the unfixed toner image is carried while being in contact with the surface. The surface of the fixing belt 2 that is in contact with the unfixed toner image has a microhardness of 5 to 30 and a glossiness Gs (20 °) of 50 or more. is there.

  In such a technical means, when the microhardness of the fixing belt 2 is less than 5, the surface of the fixing belt 2 is too soft. In particular, in the case of a halftone image (a halftone portion of toner density), fixing is performed in the fixing nip region. The belt 2 is deformed according to the unevenness of the toner image, and the surface of the toner image cannot be pressed sufficiently uniformly, making it difficult to obtain a glossy image. On the other hand, when the microhardness exceeds 30, the toner image is crushed in the fixing nip region, and edge voids are generated and a sharp image cannot be obtained. The micro hardness is a value measured using a dynamic ultra micro hardness meter DUH-201 (manufactured by Shimadzu Corporation), and can measure the surface hardness of the thin fixing belt 2.

  Even if the microhardness of the fixing belt 2 is selected to be a predetermined value, in the method using the fixing belt 2, the surface of the belt is copied to a toner image. It becomes difficult to obtain images. In the present invention, the glossiness Gs (20 °) with an incident angle of 20 ° is defined from the judgment that it is necessary to evaluate more minute unevenness as the specular glossiness of the fixing belt 2. When this Gs (20 °) is set to 50 or more, the gloss of the image surface is high and the difference in glossiness can be kept small. If Gs (20 °) is less than 50, the glossiness of the image is lowered, and in particular, it cannot be applied as a photographic print.

  In the present invention, it is preferable that the microhardness of the fixing belt 2 is 6 or more and 30 or less. According to this, the friction resistance of the fixing belt 2 itself can be further improved, and the fixing belt 2 can be used for a long time. And maintain a stable image.

Further, the fixing belt 2 of the present invention preferably has an elastic layer or further a release layer laminated on the surface of the heat-resistant belt base material, and an elastic layer is laminated on the surface of the belt base material as the fixing belt 2. As a result, the mechanical strength of the fixing belt 2 can be improved and a stable micro hardness can be realized. Further, a release layer may be further provided on the elastic layer, and further, a release layer may be provided on the surface of the belt base material. In particular, in the release layer, toner adhesion to the fixing belt 2 can be suppressed, and the cleaning action on the surface of the fixing belt 2 can be maintained over a long period of time.
The elastic layer and the release layer are preferably composed mainly of fluorocarbon siloxane rubber. According to this, the toner and the like are prevented from being adhered to the fixing belt 2 and stable for a long period of time. The surface can be maintained. Furthermore, it becomes more effective if the main component is a fluorocarbon siloxane rubber in which fluorine fine particles are dispersed as the elastic layer and the release layer.

  The present invention is intended not only for the fixing belt 2 but also for a fixing device. In this case, the surface of the fixing belt 2 is added to the unfixed toner image of the recording sheet 1 carrying the unfixed toner image. The fixing belt 2 described above may be used as the fixing belt 2 in the fixing device that is fixed by contact and heating and pressing.

  Further, as the recording sheet 1 suitable for such a fixing device, it is preferable that a thermoplastic resin layer is provided at least on the toner image carrying surface side, and the toner image is fixed on the thermoplastic resin layer. According to this, the toner image can be embedded in the thermoplastic resin layer, and the glossiness of the image is improved. Furthermore, if a transparent toner is used as the uppermost layer of the toner image, the transparent toner can be formed over the entire image surface, further improving the glossiness of the image and achieving a finish closer to a photographic image. Be able to get.

Further, from the viewpoint of effectively embedding the toner image in the thermoplastic resin layer, the melt viscosity of the thermoplastic resin layer in the fixing nip is set to be 10 ⁴ Pa · s or less under the condition of 110 ° C. Preferably it is.
From the viewpoint of reducing uneven glossiness of the image, the toner image on the recording sheet 1 after being fixed has a difference in glossiness ΔGs (20 °) of 10 at different image area ratios in the recording sheet 1. It is preferable to set as follows. Here, ΔGs (20 °) means the difference between the maximum value and the minimum value when Gs (20 °) is measured when the area ratio of process black is output at 10% intervals.

  Furthermore, the present invention is also intended for an image forming apparatus. In this case, the image forming engine for forming an unfixed toner image on the recording sheet 1 and the above-described fixing device may be provided. In such an image forming apparatus in which the image forming engine uses an intermediate transfer belt, the fixing belt 2 may also serve as the intermediate transfer belt.

According to the present invention, as an endless fixing belt used in a fixing device that fixes an unfixed toner image of a recording sheet carrying an unfixed toner image by contacting the surface and heating and pressurizing the fixing belt, Since the microhardness of the surface is set to 5 or more and 30 or less and the glossiness Gs (20 °) is set to 50 or more, a high-gloss image that is stable over a long period of time can be obtained. In particular, even when the image density is different, such as a halftone image, good smoothness and uniform gloss can be obtained, and an image free from an edge void generated at the image step feeling and the image boundary portion can be obtained.
Further, by using such a fixing belt, it is possible to provide a fixing device and an image forming apparatus capable of forming good smoothness and uniform gloss over a long period of time.

Hereinafter, the present invention will be described in detail based on embodiments shown in the accompanying drawings.
Embodiment 1
FIG. 2 shows Embodiment 1 of a color image forming apparatus to which the present invention is applied. In the figure, the image forming apparatus according to the present embodiment employs, for example, an electrophotographic system, and includes yellow (Y color), magenta (M color), cyan (C color), and black (K color). An image forming engine 20 that forms a four-color toner image, and a multi-stage sheet feeding cassette 11 to 13 that supplies a sheet as a recording material to the image forming engine 20 are detachably accommodated, and the image forming engine 20 downstream in the sheet conveying direction. The fixing device 40 is disposed on the side.

The image forming engine 20 of the present embodiment is a so-called rotary type, and is configured to multiplex-transfer the respective color toner images formed on the photosensitive drum 21 onto the intermediate transfer belt 30.
Around the photosensitive drum 21, there are a charger 22 such as a charging roll for charging the photosensitive drum 21, an exposure unit 23 such as a laser scanner for forming a latent image on the photosensitive drum 21, and a latent on the photosensitive drum 21. Developing unit 24 that visualizes an image, each color toner image on photosensitive drum 21 is primarily transferred onto intermediate transfer belt 30, for example, primary transfer unit 25 including a primary transfer roll, and residual toner remaining on photosensitive drum 21. A photoreceptor cleaner 26 for cleaning the toner is disposed.

The intermediate transfer belt 30 is stretched around a plurality of stretching rolls, and circulates and transports, for example, using the stretching roll 31 as a driving roll and the stretching roll 32 as a tension roll. The next transfer unit 34 is disposed opposite to the tension roll 33 as a backup roll. Further, a belt cleaner 35 for cleaning residual toner on the intermediate transfer belt 30 is provided at a position facing the stretch roll 31 of the intermediate transfer belt 30.
Further, a four-color toner box 36 for replenishing each color toner to the developing device 24 is provided above the image forming engine 20, and positions corresponding to the respective colors in the developing device 24 through a conveyance path (not shown). Toner is supplied to the printer.

  The paper transport system in the present embodiment is as follows. The sheets sent out from the respective sheet feeding cassettes are conveyed to the sheet conveying path 14, and an unfixed toner image is formed by the registration roll 15 and the secondary transfer unit 34 that regulate the positioning of the sheet before entering the secondary transfer unit 34. A transport belt 16 for transporting the transferred paper, a fixing device 40 for fixing an unfixed toner image, a discharge roll 17 for sending the fixed paper to the discharge tray 18 and the like are provided. In this embodiment, in addition to the paper feed cassettes 11 to 13, a manual feed tray 19 capable of manually supplying paper is provided, and paper can be supplied to the paper transport path 14.

  In particular, the fixing device 40 of the present embodiment is configured as shown in FIG. In the figure, a fixing device 40 includes a fixing roll 41 having a heating source 42 such as a halogen lamp inside, a pressure roll 43 disposed opposite to the fixing roll 41 and having a heating source 44 therein, and fixing. A fixing belt 45 that is nipped and conveyed between the roll 41 and the pressure roll 43 and stretched around the fixing roll 41 and a plurality of roll members (a peeling roll 46 and a steering roll 47), and the downstream side of the fixing roll 41 And a cooler 48 that cools the fixing belt 45 in contact with the back surface of the fixing belt 45.

The fixing roll 41 has a configuration in which a release layer (not shown) made of a PFA tube having a thickness of about 10 to 200 μm is formed around a metal core 41a such as aluminum or stainless steel having high thermal conductivity. In addition, a heating source 42 is provided inside the core 41a, and the heating source 42 is controlled to be heated so that the surface of the fixing roll 41 has a predetermined temperature.
On the other hand, the pressure roll 43 has an elastic layer 43b such as silicone rubber having a rubber hardness (JIS-A hardness) of about 30 to 70 degrees around a core 43a made of metal such as aluminum or stainless steel having high thermal conductivity. A uniform release layer (not shown) similar to the release layer of the fixing roll 41 is formed on the surface of the elastic layer 43b. In the present embodiment, a heating source 44 is also provided inside the core 43a of the pressure roll 43, and the surface of the pressure roll 43 is the same as the surface of the fixing roll 41 or is lower by about 0 to 30 ° C. The heating is controlled so that the temperature becomes.
Therefore, the sheet conveyed to the fixing device 40 is sufficiently heated and pressed in the fixing nip region N between the fixing roll 41 and the pressure roll 43 with the toner image surface in contact with the fixing belt 45. It becomes like this. The pressure roll 43 is supported by a support frame (not shown), and is used to apply a predetermined load between the fixing roll 41 and the pressure roll 43 when the paper passes through the fixing nip area N. A mechanism is provided so that the pressure roll 43 retracts in accordance with the presence or absence of paper.

As shown in FIG. 4A, the fixing belt 45 has a three-layer structure in which an elastic layer 45b and a release layer 45c are provided on a heat-resistant base material layer 45a.
As the base material layer 45a, PET, PBT, polyimide, polyamide, polyamideimide, polybenzimidazole, thermotropic liquid crystal polymer, etc. from the viewpoint of heat resistance, mechanical strength and thermal characteristics (thermal conductivity, expansion coefficient, etc.) However, in consideration of thermal characteristics, a heat resistant resin sheet made of polyimide or polybenzimidazole is preferable. In addition, as the base material layer 45a, in consideration of charging characteristics, the volume resistivity may be adjusted by adding conductive powder, carbon black or the like to the above-mentioned heat resistant resin. If it is a well-known method, it will not restrict | limit in particular.

  Furthermore, the thickness of the base material layer 45a is preferably in the range of 20 to 200 μm from the viewpoints of mechanical strength, heat capacity, thermal conductivity, etc. as the fixing belt 45. If the thickness is less than 20 μm, the mechanical strength is insufficient and the handling property as the fixing belt 45 is deteriorated, and if the thickness exceeds 200 μm, the heat capacity of the fixing belt 45 itself becomes too large and warm-up is performed. It will be necessary to lengthen the time, resulting in an increase in power consumption.

The elastic layer 45b is not particularly limited as long as it has heat resistance. Typically, silicone rubber, fluorine rubber, or a hybrid rubber thereof is applied, and a method for forming the elastic layer 45b is also described. If it is a well-known method, it will not restrict | limit in particular.
Furthermore, the thickness of the elastic layer 45b is preferably in the range of 10 to 200 μm from the viewpoint of the mechanical strength, heat capacity, and thermal conductivity of the elastic layer 45b, and when the thickness is less than 10 μm. Not only does not function as an elastic body, but also loses rubber elasticity or breaks due to elastic deformation in the fixing nip region N or strain due to stress. On the other hand, if it exceeds 200 μm, the heat capacity of the elastic layer 45b itself becomes too large, and it is necessary to lengthen the warm-up time, thereby increasing the power consumption.

The release layer 45c is not particularly limited as long as it is a material having releasability with respect to the toner, and a known material can be used. For example, PFA (ethylene tetrafluoride / perfluoroalkoxyethylene copolymer resin) or FEP (ethylene tetrafluoride / hexafluoropropylene copolymer resin) are used in consideration of releasability from the toner image and heat resistance. And PTFE (tetrafluoroethylene resin).
Furthermore, if the release layer 45c is composed mainly of a fluorocarbon siloxane rubber in which fluorine particles are dispersed, the stability of the release layer 45c surface can be ensured over a long period of time. A high image can be obtained.
In the release layer 45c described above, the optimum hardness can be selected by controlling the blending ratio and molecular weight of various additives, and the method for forming the release layer 45c may be a known method. There is no particular limitation.
The thickness of the release layer 45c is preferably about 3 to 50 [mu] m from the viewpoint of wear due to wear of the release layer 45c and a release function with the toner.

Further, the fixing belt 45 of the present embodiment has a micro hardness of 5 to 30 on the surface of the belt in contact with the toner image of the paper and a glossiness Gs (20 °) regardless of the structure as described above. ) Is set to 50 or more. More preferably, the frictional resistance of the fixing belt 45 can be improved by setting the microhardness to 6 to 30.
The micro hardness (DH: Dynamic Hardness) is measured using a dynamic micro hardness tester DUH-201 (manufactured by Shimadzu Corporation), and the measurement load P (the load when the indenter reaches the indentation depth D) is measured. In addition, based on the measured load P and the indentation depth D at that time, the following is obtained. That is, the tip of the indenter of the hardness meter is pushed perpendicularly to the belt surface at a constant speed, and the pushing depth D and the necessary load P at that time are measured. For this reason, the characteristic in a state including not only elastic deformation but also plastic deformation of the measurement sample comes to be measured.

The measurement conditions are as follows.
・ Indenter: Triangular pyramid (115 °), Belkovic type ・ Load speed: 0.14219 mN / sec
・ Test load: 3mN
・ Measurement environment: 22 ℃ 55% RH
Calculation formula: micro hardness (DH) = α × P / D ² (where α = 3.8854)

  Further, the glossiness Gs (20 °) is a numerical value obtained when an incident angle and a reflection angle are set to 20 ° using a gloss measuring device GB-4512 (manufactured by BYK-Gardner) based on JIS Z8741. In this embodiment, the glossiness of the surface of the fixing belt 45 is 50 or more.

  Note that the fixing belt 45 in the present embodiment is not limited to the above-described three-layer configuration, and for example, a configuration as shown in FIGS. 4B and 4C can be used. That is, as shown in FIG. 4 (b), the base layer 45a may be provided with only the release layer 45c, or as shown in FIG. 4 (c), only the base layer 45a may be used. In any case, the microhardness and the glossiness Gs (20 °) may be satisfied.

  A method for obtaining such glossiness is not particularly limited, but it can be said that it is necessary to select appropriately according to the layer configuration of the belt described above. For example, in the case of a belt having a release layer 45c as an upper layer of the base material layer 45a, the belt can be obtained by appropriately selecting the application process of the release layer 45c and parameters during primary vulcanization. In the case of using a belt formed only of the base material layer 45a, for example, it is performed by a method of polishing the surface with a polishing tape or the like by a wet or dry method, and in particular, a polishing tape of No. 5000 or more is selected. It is important to select appropriate polishing conditions.

  As shown in FIG. 3, the peeling roll 46 used in the fixing device 40 in the present embodiment rotates following the movement of the fixing belt 45, and the peeling roll 46 is stretched while winding the fixing belt 45. As a result, the moving direction of the fixing belt 45 is rapidly changed, and the sheet on the fixing belt 45 is naturally peeled from the fixing belt 45 by the rigidity of the sheet itself at the position of the peeling roll 46. Further, the steering roll 47 is configured so that the fixing belt 45 itself is always tensioned, the tension is maintained by pressing the fixing belt 45 outward, and the bias generated when the fixing belt 45 is circulated and moved. Provided to correct.

  Further, the cooler 48 in the present embodiment is provided between the fixing roll 41 and the peeling roll 46 in contact with the back surface of the fixing belt 45, and cools the fixing belt 45 by absorbing the heat of the fixing belt 45. It is supposed to be. For this reason, the sheet that is conveyed in close contact with the fixing belt 45 is cooled. The cooler 48 in the present embodiment includes a fin member 48a provided with a large number of heat dissipating fins extending in a direction substantially orthogonal from the surface along the fixing belt 45, and a cover 48b provided so as to cover the fin member 48a. In this configuration, the heat of the fin member 48a is forcibly radiated by flowing air through a blower blower (not shown).

Here, the paper used in the present embodiment will be described.
The image forming apparatus according to the present embodiment can be applied to various types of paper (for example, plain paper, coated paper, art paper, etc.) used in a normal image forming apparatus. In particular, the configuration shown in FIG. The most effective effect can be obtained by using this paper.
In FIG. 5, the paper is coated on a base material layer L1 made of the same component as that of so-called plain paper (cellulose or the like), a moisture-proof layer L2 coated on both surfaces of the base material layer L1, and further on the moisture-proof layer L2. Image receiving layer L3.

As the base material layer L1, in particular, when a high gloss image such as a photographic image is formed, it is desirable that the white layer has a high whiteness and an appropriate thickness (150 to 230 μm).
Further, the moisture-proof layer L2 is made of a resin having low air permeability such as polyethylene and may be about several μm. The moisture-proof layer L2 prevents moisture from entering the base material layer L1, and prevents the base material layer L1 from absorbing and curling even in a high humidity environment.
Further, the image receiving layer L3 is a layer mainly composed of a thermoplastic resin such as polyester, and is formed on a surface (recording surface) on which a toner image is formed. The thickness of the image receiving layer L3 is preferably about 5 to 30 μm. If the thickness of the image receiving layer L3 is less than this range, the toner cannot be sufficiently embedded in the image receiving layer L3 at the time of fixing, resulting in unevenness on the image surface. On the other hand, when the glossiness is lowered, exceeding this range, cracks are likely to occur on the image surface when the paper is curved at the peeling site (by the peeling roll), for example. The image-receiving layer L3 is not limited to polyester, and synthetic resins such as styrene- (meth) acrylic copolymer, styrene-butadiene copolymer, epoxy resin, and polyurethane can be used.

Next, the operation of the image forming apparatus in the present embodiment will be described focusing on the operation of the fixing device 40 in particular.
FIGS. 6A and 6B show the embedding state of the toner image in the fixing nip area N at the time of fixing. FIG. 6A shows the fixing belt 45 before fixing and the sheet on which the unfixed toner image is transferred. Shows a state where contact has started, and (b) shows a state after the completion of fixing. In this example, the fixing belt 45 is shown as a substrate layer 45a covered with a release layer 45c.

  In the present embodiment, the toner image is pushed into the image receiving layer L3 (thermoplastic resin layer) of the paper in the fixing nip area N, although the state as shown in FIG. In particular, in this embodiment, since the microhardness and glossiness Gs (20 °) of the fixing belt 45 are set to desired values, sufficiently uniform pressure can be applied to the toner image in the fixing nip region N. Thus, the unfixed toner image is embedded in the image receiving layer L3 of the paper.

FIGS. 7A and 7B show the embedding state of the toner image in the fixing nip area N at the time of fixing when the image density is different. FIG. 7A shows that the fixing belt 45 and the fixing belt 45 are not fixed before fixing. This is the state immediately before the toner image comes into contact, and (b) shows the pressurized state in the fixing nip area N.
Here, as shown in (c), the unfixed toner image has different image densities, and has three types of solid part T100 (100%), 10% density part (T10), and 50% density part (T50). Although the case is illustrated, the toner is the thickest at T100, and then becomes thinner in the order of T50 and T10.
Therefore, when pressed by the fixing belt 45, if the thickness of the toner changes if the hardness of the fixing belt 45 is too soft, the belt surface also changes accordingly, and each toner (T100, T10, T50). For example, at T100, the paper is not sufficiently embedded in the image receiving layer L3, and the glossiness of the image surface after fixing is lowered. On the other hand, if the fixing belt is too hard, a large pressure is applied to the thickest T100 to cause image collapse or to embed each toner (T100, T10, T50) sufficiently uniformly in the image receiving layer L3. On the other hand, it may cause uneven luster.

  In the present embodiment, the microhardness and surface glossiness Gs (20 °) of the fixing belt 45 are adjusted to desired values. Since uniform pressurization is possible and the smoothness of the image surface after fixing can be improved, a high-gloss image such as a photographic image can be realized.

  In the present embodiment, full-color four-color image formation has been described. However, the present invention can also be applied to, for example, a five-color image forming apparatus to which transparent toner is added. In this case, by using the uppermost layer of the toner image as a transparent toner, If this transparent toner is formed over the entire area of the image, the glossiness of the portion where the color toner is not formed (the surface of the paper itself) can be improved. In addition, the entire surface can be averaged with the transparent toner, and the glossiness of the image can be further improved.

Furthermore, in the present embodiment, a so-called rotary type image forming apparatus is shown. However, for example, a similar fixing device is also used in a so-called tandem type in which image forming units for each color are arranged in parallel facing an intermediate transfer belt. If provided, a high gloss image such as a photographic image can be obtained.
Furthermore, in addition to the fixing device using a fixing belt as a fixing device, for example, a normal heating / pressing type fixing device is additionally arranged on the upstream side of the fixing device, and a low-gloss print that outputs to normal plain paper, and a photograph A high gloss print such as an image may be performed by switching the fixing device.

Embodiment 2
FIG. 8 shows Embodiment 2 of the image forming apparatus to which the present invention is applied. Although the present embodiment is configured in substantially the same manner as the first embodiment, the fixing device 40 is arranged on the side of the option unit 60 that can be attached to the image forming unit 10. Therefore, on the image forming unit 10 side, a normal heating and pressing type fixing unit 50 is mounted in the sheet conveyance path. Components similar to those in the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted here.

The fixing unit 50 in the present embodiment has a normal configuration, and fixing is performed by a nip between the heating roll 51 and the pressure roll 52. In the present embodiment, both the heating roll 51 and the pressure roll 52 are provided with a heating source such as a halogen lamp.
Therefore, in the present embodiment, the unfixed toner image on the paper is once fixed by the fixing unit 50 provided in the image forming unit 10, and then a high gloss image is obtained by the fixing device 40 of the option unit 60. Be able to. The sheet on which the high gloss image is formed by the fixing device 40 is discharged from the discharge roll 61 on the option unit 60 side to the discharge tray 18. In the figure, reference numeral 53 denotes a transport roll provided immediately after the fixing unit 50.

  In such a configuration, since the fixing device 40 is the same as that of the first embodiment, the same effect as that of the first embodiment is obtained in this embodiment.

Embodiment 3
FIG. 9 shows Embodiment 3 of the image forming apparatus to which the present invention is applied. Although the present embodiment is configured in substantially the same manner as the second embodiment, the configuration of the option unit 70 that can be attached to the image forming unit 10 is different from the configuration of the second embodiment. Further, the image forming unit 10 includes four paper feed cassettes (reference numerals 11, 12, 13a, and 13b), and does not include a toner box above the image forming engine 20. In addition, the same code | symbol is attached | subjected to the component similar to Embodiment 2, and the detailed description is abbreviate | omitted here.

  The option unit 70 according to the present exemplary embodiment is configured to switch the downstream sheet conveyance path by the switching member 71 for the sheet that is temporarily fixed by the fixing unit 50 in the image forming unit 10 and discharged from the discharge roll 17. It has become. That is, the fixing unit 40 is the same as that in the first embodiment through the path for discharging from the first discharge roll 72 of the option unit 70 to the first discharge tray 73 formed in the upper casing of the option unit 70 and the conveyance belt 74. And after the fixing, the path is switched from the second discharge roll 75 to the second discharge tray 76.

Therefore, for example, when text is printed on plain paper, low-gloss print is realized in which the image fixed by the fixing unit 50 is discharged as it is to the first discharge tray 73, while a photographic image is printed on dedicated paper. When printing is performed, it is possible to realize high-gloss printing in which the fixing unit 50 temporarily performs temporary fixing and then the fixing device 40 discharges the image as a high-gloss image to the second discharge tray 76.
In this embodiment, fixing according to the image can be selected as described above, and accordingly, visibility matching the image can be secured, and power consumption can be reduced. It becomes possible.

  Further, in the present embodiment, since the fixing device 40 is configured in the same manner as in the first embodiment, a high-gloss image can be realized.

Embodiment 4
FIG. 10 shows Embodiment 4 of an image forming apparatus to which the present invention is applied. Although the present embodiment is configured in substantially the same manner as the first embodiment, the fixing device 40 is not dedicated, and the fixing belt of the fixing device 40 serves as an intermediate transfer belt of the image forming engine 20. It has become. Components similar to those in the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted here.

  In this embodiment, the intermediate transfer belt and the fixing belt of the image forming engine 20 are used as a single belt member 80, and the belt member 80 includes a plurality of stretching rolls (for example, driving rolls). 82, a fixing roll 41, a peeling roll 46, a steering roll 47, etc.) and circulates. Reference numeral 81 denotes a backup roll disposed to face the secondary transfer device 34, and reference numeral 83 denotes a transport belt for transporting the paper after the secondary transfer.

  In the present embodiment, the secondary transfer unit 34 and the pressure roll 43 are retracted until a four-color toner image is formed on the belt member 80, and the heating source of the fixing roll 41 is the belt member 80. The temperature has fallen within a range that does not affect the toner image conveyed. Under these circumstances, after the four color toner images are transferred onto the belt member 80 in a multiple manner, the multiplexed toner image on the belt member 80 is transferred to the paper by the transfer bias between the secondary transfer unit 34 and the backup roll 81. Are collectively transferred. The batch-transferred paper is fixed in a fixing nip area formed by the fixing roll 41 and the pressure roll 43 via the conveyance belt.

The present embodiment is an image forming apparatus of such a simultaneous transfer and fixing system, and the belt member 80 has the same configuration as that of the first embodiment even in such a system. 1 has the same effect.
In the present embodiment, a so-called rotary type image forming apparatus is used. However, if a so-called tandem type is adopted, the retracting of the secondary transfer unit 34 and the pressure roll 43 is unnecessary, and the control of the heating source is also performed. It is clear that it is simplified.

In this embodiment, image evaluation tests using various fixing belts are performed.
The evaluated fixing belt is a polyimide base material having an endless shape with a peripheral length of 527.8 mm, a width of 330 mm, and a thickness of 75 μm as a belt base material, and having a volume resistivity adjusted to Rv = 10 ¹² Ω · cm by adding carbon black. It was used.

The following treatment was performed on this belt base material to prepare a sample.
○ Example 1
On the base material, SIFEL610 (manufactured by Shin-Etsu Chemical Co., Ltd.) which is a fluorocarbon siloxane rubber precursor composition as an elastic layer, and PTFE which is a different kind of fluorine fine particles for changing hardness as a release layer. A coating film having a thickness of approximately 30 to 50 μm was formed by dip coating a coating solution prepared by dispersing in a fluorine-based solvent. Thereafter, through the primary vulcanization process and the secondary vulcanization process, finally, seven types of fixing belts on which a surface layer having a microhardness of 3 to 35 was formed were obtained. The belt surface glossiness Gs (20 °) obtained by the dip coating method was 50 or more by controlling the primary vulcanization parameters.
Of these, two samples having a microhardness of 3 and 35 were designated as Comparative Example 1 and Comparative Example 3.
○ Comparative Example 1
As described above, one with a small micro hardness was selected from Example 1.
○ Comparative Example 2
SIFEL610 (manufactured by Shin-Etsu Chemical Co., Ltd.) which is a fluorocarbonsiloxane rubber precursor composition as an elastic layer and PTFE which is a fluorine fine particle as a release layer are dispersed in a fluorine-based solvent as an elastic layer. A coating film was formed by dip coating the applied coating solution. Thereafter, a belt having a surface layer having a surface layer thickness of approximately 30 μm was formed through a primary vulcanization process and a secondary vulcanization process. At this time, the belt surface gloss of 50 or more was obtained by controlling the primary vulcanization parameters. After this, the belt surface was further subjected to a dry honing treatment (pear blasting using fine particles of about 1 μm). The belt surface glossiness Gs (20 °) was 50 or less to obtain a belt.
○ Comparative Example 3
As described above, one having a high microhardness was selected from Example 1.
○ Comparative Example 4
A single-layer belt having a thickness of 80 μm was obtained using only the base material without performing any treatment on the base material. At this time, the micro hardness was 45, and the glossiness Gs (20 °) of the belt was 90 or more.

The paper and toner used for this evaluation are as follows.
The paper is A4 size (210 x 297 mm) size, and both sides of the base material layer are coated with polyethylene resin to a thickness of about 10 μm. On the image side only, polyester resin is further applied with a thickness of about 20 μm. It was what was crafted.
Further, a toner having an average particle size of 5.6 μm made of styrene-acrylic resin to which a wax component was added was used.

About the evaluation method, it carried out as follows.
First, in order to carry an unfixed toner image on a sheet, a toner image was formed on the sheet using a color image forming apparatus DocuColor 1256GA remodeling machine (Fuji Xerox Co., Ltd.) with the fixing unit removed. After that, the unfixed toner image was subjected to heat and pressure by inserting various modified fixing belts with the configuration of the fixing device of the first embodiment, and an image evaluation of the image on which the unfixed toner image was fixed was performed. .

The evaluation items were as follows.
● Glossiness Gs of image
The images used for the evaluation are toner images in which the area ratio of process black obtained by superimposing three colors of yellow, cyan, and magenta is changed from 0 to 100% at 10% intervals. A rectangular patch image having a region was formed, and the glossiness Gs (20 °) of the image after fixing was measured. Then, a difference ΔGs (20 °) between the average value (Ave), the maximum value, and the minimum value was calculated.
At this time, the smaller the numerical value of ΔGs (20 °), the better the image smoothness, and the larger the numerical value, the less smooth.
Edge void For the purpose of confirming the embedding property of the toner, the edge void of the image is changed by changing the melt viscosity of the thermoplastic resin layer of the paper by using a cross line chart (× mark) of 100% process black shown in FIG. The occurrence state (particularly generated on the upstream side of the x mark) was evaluated by dividing it into six stages from G0 (no edge voids) to G5 (the entire edge voids). The melt viscosity of the thermoplastic resin layer of the paper was changed by changing the fixing temperature, and edge voids were confirmed at viscosities of about 10 ³ Pa · s and about 10 ⁴ Pa · s.
● Patch step The step of the patch image is also evaluated, and an image of 100% process black with a side of 15 mm square is formed. As shown in FIG. 11B, the step h between the paper surface and the patch image is visually observed. Confirmed.
The results at that time were evaluated according to the following criteria.
○: No sense of incongruity, Δ: Some sense of incongruity, ×: Great sense of incongruity ● Smoothness A predetermined photographic chart was output, and the smoothness of the image was visually evaluated.
The results at that time were evaluated according to the following criteria.
○: No sense of incongruity, Δ: Some sense of incongruity, ×: Great sense of incongruity ● Deterioration of belt elastic layer A paper running test (100,000 sheets) was performed, and the deterioration state of the belt elastic layer was visually evaluated.
The results at that time were evaluated according to the following criteria.
○: No cracking occurred, △: Minor cracking occurred, ×: Significant cracking occurred

The evaluation results are shown in FIG.
According to this, as in Examples 1-1 to 1-5, if the microhardness is 5 to 30 and the glossiness Gs (20 °) is 50 or more, the glossiness Gs of the image is also secured to 80 or more. Further, the gloss difference ΔGs was 10 or less, and a good image was obtained, and the surface property was not uncomfortable. Furthermore, since there was no patch level difference and no edge voids, an image having excellent smoothness could be obtained. Furthermore, image defects such as edge voids did not occur even under fixing conditions in which the melt viscosity of the thermoplastic resin of the paper in the fixing nip was 10 ⁴ Pa · s or less.
On the other hand, when the microhardness is as small as 3 (Comparative Example 1) or as large as 35 (Comparative Example 3), even when the glossiness Gs (20 °) of the fixing belt is 50 or more, the glossiness difference ΔGs is When the melt viscosity of the thermoplastic resin was 10 ⁴ Pa · s, some edge voids were generated, and the patch level difference and smoothness were uncomfortable.
In addition, when the surface was intentionally roughened as in Example 1 (Comparative Example 2), the glossiness of the image was greatly reduced reflecting the surface roughness, or a great sense of incongruity was generated due to smoothness. . In this case, it was also confirmed that toner in a portion corresponding to the image edge portion adhered to the surface of the belt.
Further, when the microhardness is increased to 45 and the glossiness Gs (20 °) is greatly increased (Comparative Example 4), the glossiness Gs of the image and the glossiness difference ΔGs are reduced, and the patch level difference and smoothness are reduced. Caused a sense of discomfort (glossy unevenness and edge voids were large). In particular, in this case, although the glossiness is uniform, the image gloss of the entire image on the paper is lowered, and the texture of the high gloss image is impaired.
From this result, the effectiveness of the present invention was confirmed.

As a result of examining the micro hardness and the glossiness Gs (20 °) in more detail, the present inventor has found that when the microhardness of the fixing belt surface is less than 5, the glossiness of the intermediate density portion of the image decreases. It was found that ΔGs (20 °) deteriorates. Also, when the microhardness of the fixing belt is greater than 30, edge voids in the image edge portion began to appear, and the image felt uncomfortable with respect to the level difference between the non-image portion and the image portion. If an image with a pattern such as a human figure is fixed under such conditions, the former causes uneven glossiness in the image plane and the image lacks smoothness, and in the latter case, the images of the image portion and the non-image portion. In an image having a large difference between the boundary portion and light and shade, the relief is easily noticeable.
Furthermore, it has been found that for long-term use of the fixing belt, if the micro hardness is 6 or more, the rubbing property of the belt is improved.

  FIG. 13 is a plot of the relationship between the image density and the glossiness measured in Example 1-2. According to this plot, even when the image density is changed to 10 to 100%, the uniform glossiness is obtained. Is understood to be obtained. On the other hand, FIG. 14 is a plot of the relationship between the image density and the glossiness measured in Comparative Example 3. Compared with Example 1-2 described above, a change in the glossiness due to the image density can be seen. Understood.

In this example, when the thermoplastic resin layer was 10 ⁴ Pa · s or less, a good image was obtained. At this time, the result of measuring the viscosity change of the thermoplastic resin layer is shown in FIG. In this viscosity measurement, the flow tester viscosity was measured, and the load was 10 kgf, the diameter was 5 mm, and the temperature raising condition was 1 ° C./min. From this result, the thermoplastic resin layer was 10 ⁴ Pa · s or less at 110 ° C. That is, under such conditions, the toner image can be satisfactorily embedded in the thermoplastic resin layer.

FIG. 2 is an explanatory diagram showing an outline of a fixing device according to the present invention. 1 is an explanatory diagram showing an overview of Embodiment 1 of an image forming apparatus according to the present invention. FIG. 2 is an explanatory diagram illustrating an outline of a fixing device according to the first embodiment. (A)-(c) is explanatory drawing which shows the structure of the fixing belt of Embodiment 1. FIG. 3 is an explanatory diagram illustrating a structure of a sheet used in Embodiment 1. FIG. (A) and (b) are explanatory views showing the fixing state in the fixing nip area, (a) shows a state in which the fixing belt and the paper are in contact, and (b) shows a state after fixing. (A) and (b) are explanatory views showing the fixing state of images having different image densities in the fixing nip area, (a) is a state in which the fixing belt and the paper are in contact, and (b) is a state after fixing. Show. (C) shows patch images having different image densities. FIG. 6 is an explanatory diagram illustrating an overview of an image forming apparatus according to a second embodiment. FIG. 10 is an explanatory diagram illustrating an overview of an image forming apparatus according to a third embodiment. FIG. 10 is an explanatory diagram illustrating an overview of an image forming apparatus according to a fourth embodiment. It is an evaluation item of an Example, (a) is an edge void, (b) is explanatory drawing which shows a patch level | step difference. It is a table | surface which shows the result of an Example. It is a graph which shows the measurement result of Example 1-2. 10 is a graph showing measurement results of Comparative Example 3. It is a graph regarding the viscosity change of the thermoplastic resin layer of paper.

Explanation of symbols

  1 ... recording sheet, 2 ... fixing belt

Claims (12)

An endless fixing belt for use in a fixing device in which a surface contacts an unfixed toner image of a recording sheet carrying an unfixed toner image and is fixed by heating and pressing,
The fixing belt, wherein the surface in contact with the unfixed toner image has a microhardness of 5 to 30 and a glossiness Gs (20 °) of 50 or more. The fixing belt according to claim 1.
The fixing belt having a micro hardness of 6 or more and 30 or less. The fixing belt according to claim 1.
A fixing belt characterized in that an elastic layer or further a release layer is laminated on the surface of a heat-resistant belt substrate. The fixing belt according to claim 3.
The fixing belt, wherein the elastic layer and the release layer are mainly composed of fluorocarbon siloxane rubber. The fixing belt according to claim 3.
The fixing belt, wherein the elastic layer is mainly composed of fluorocarbonsiloxane rubber in which fluorine fine particles are dispersed. A fixing device for fixing an unfixed toner image on a recording sheet carrying an unfixed toner image by bringing the surface of a fixing belt into contact with the unfixed toner image and heating and pressing the recording sheet
A fixing device using the belt member according to claim 1 as the fixing belt. The fixing device according to claim 6.
A fixing device, wherein a recording sheet is provided with a thermoplastic resin layer at least on a toner image carrying surface side, and a toner image is fixed on the thermoplastic resin layer. The fixing device according to claim 7.
The fixing device according to claim 1, wherein the uppermost layer of the toner image is a transparent toner. The fixing device according to claim 7.
The fixing device, wherein the melt viscosity of the thermoplastic resin layer in the fixing nip is set to be 10 ⁴ Pa · s or less under a condition of 110 ° C. The fixing device according to claim 7.
The fixing device, wherein the toner image on the recording sheet after being fixed has a gloss difference ΔGs (20 °) at different image area ratios within the recording sheet set to 10 or less. An image forming engine for forming an unfixed toner image on a recording sheet;
An image forming apparatus comprising the fixing device according to claim 6. The image forming apparatus according to claim 11, wherein the image forming engine uses an intermediate transfer belt.
An image forming apparatus, wherein the fixing belt also serves as an intermediate transfer belt.

Images