JP2003098871A - Fixing belt - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixing belt for characterizing its surface hardness, meeting image uniformity and a fixing characteristic and achieving energy saving by shortening the startup time. SOLUTION: The relation, between a universal hardness HU1 at a thrust depth of 4 μm and a universal hardness HU2 at a thrust depth of 20 μm from a surface of the fixing belt 113, is set so as to satisfy equations (1), (2). The universal hardness HU1 is 15 N/mm<2> or less ...(1); a ratio HU1/HU2 is 10 or less ...(2). A material of an elastic layer 202 is silicone rubber. The material of a mold releasing layer 203 contains at least one fluoroplastic as a component. A film thickness of the mold releasing layer is 30 μm or less.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing belt of a fixing device used in an image forming apparatus such as a copying machine, a printer and a facsimile.

[0002]

2. Description of the Related Art FIG. 1 is a schematic view showing an image forming process of an image forming apparatus. The image forming apparatus has a rotating photosensitive drum 101, and a photosensitive layer on the surface of the photosensitive drum 101 is uniformly charged by a charging device 102, and then a laser beam from a laser scanning unit (not shown) is used. The exposure 103 is applied to the photosensitive drum 101 to form an electrostatic image. The electrostatic latent image is developed by the developing device 104 into a toner image, the toner image is transferred onto the recording paper 107 by the transfer device 106, and the recording paper is further fixed by the fixing device 11.
2 and the toner image is thermally fixed on the recording paper 107.

The fixing device 112 shown in FIG. 1 is composed of a heating roller 110 and a pressure roller 111 which use rollers for the heating section and the pressing section, respectively. Conventional heating roller 110
For example, a cored bar made of a hollow cylindrical body of aluminum or the like having a sticking prevention layer such as a fluororesin layer for preventing sticking of toner is provided on the outer peripheral surface. In such a heating roller 110, a heater such as a halogen lamp is arranged in the hollow portion of the core along the rotation center line,
The radiant heat heats the heating roller 110 from the inside. Further, a pressure roller 111 that is in pressure contact with the heating roller 110 is provided in parallel with the heating roller 110, and the recording paper 107 passes between the pressure roller and the heating roller.
The toner adhered on the recording paper 107 is heated by the heating roller 11
While being softened by the heat of 0, it is fixed on the recording paper 107 by the pressure of the pressure roller 111.

The heating roller 110 having the fluororesin layer provided on the core metal as described above has excellent releasability but is inferior in flexibility and elasticity. It is difficult to support an electrophotographic image forming apparatus such as a full-color laser printer. In these electrophotographic image forming apparatuses, four color toners of red (magenta), blue (cyan), yellow (yellow), and black (black) are used. When fixing a color image,
It is necessary to mix these color toners in a melted state, and to lower the melting point of the toners to facilitate the melting, and to wrap the plural kinds of color toners on the surface of the heating roller 110 to uniformly mix them in the melted state. Will be required. For this reason, the surface of the fixing portion of the fixing device needs to be flexible.

In order to give the surface flexibility, a fixing device used in a conventional electrophotographic image forming apparatus has a heating roller in which a rubber layer such as silicone rubber or fluororubber is provided on a silicone rubber roller. There is 110. This uses a rubber material in consideration of releasability and durability rather than the underlying silicone rubber.

However, the fixing method using the heating roller is
It is suitable for increasing the printing speed because it keeps the entire heating roller at a predetermined temperature and has a large heat capacity, but it requires a considerable amount of time to heat the heating roller to a predetermined temperature. Further, from this, power consumption becomes large to heat the entire heating roller.

In recent years, activities for energy saving have become active, and reduction of start-up time has been studied. As one of them, a belt fixing method has been proposed in which toner on recording paper is heated through a film-shaped endless belt heated by a heater. In this fixing method, the thin film-shaped fixing belt is directly heated, and since the heating unit reaches a predetermined temperature in a short time after the power is turned on, the waiting time after the power is turned on can be considerably reduced. Further, since only the necessary portion is heated, there is an advantage that power consumption is small.

FIG. 2 is a schematic view of the image forming process of the image forming apparatus using the belt fixing method. Fixing belt 11
3 is stretched between the heating roller 110 and the fixing roller 115. The toner is heated by the heat of the heating roller 110 and is fixed by the pressure of the fixing roller 115 and the pressure roller 111. In the case of the fixing belt 113, the above-mentioned rubber material in consideration of releasability and durability is directly formed on the substrate. However, it has the same problems as described below. Although the fixing roller 115 and the belt surface (silicone rubber, fluororubber, etc.) described above have excellent flexibility, the toner releasability is insufficient, so that the toner offset phenomenon easily occurs. Further, since these rubber elastic layers have low wear resistance, the surface is greatly worn and deteriorated.

To solve these problems, there is a method of applying a lubricating oil of silicone type to the surface of the fixing portion. However, although this oil application method is initially effective, it is not sufficiently stable over a long period of time, and this oil causes a new problem of swelling of the rubber material. Further, the mechanism for applying the oil (including the coating amount control mechanism) and the replenishment of the oil also have the disadvantages of user maintenance load and high cost, so that a fixing device that does not use oil is required.

Recently, a structure has been proposed in which a rubber elastic layer is provided on a roller and a belt base, and a release material such as fluororesin is coated on the elastic layer. However, when the release material is coated, the flexibility, which is an important characteristic of the surface described above, tends to decrease. Problems in this case include non-uniformity of the image and poor transparency of the image on the OHP sheet. Therefore, it is important to take measures to avoid these problems, that is, to consider a coating method and a coating material that do not impair the flexibility of the elastic layer as much as possible, and a surface hardness characteristic value at the time of coating.

In Japanese Unexamined Patent Publication No. 10-198201, a soft index S representing flexibility is defined to define the thickness of the substrate, the thickness of the outer layer and the allowable range of the soft index S. There is no description about the hardness of the (outer surface layer).
Further, in Japanese Patent No. 3000516, the flexural modulus of elasticity of the toner, the polyimide substrate, the heat resistant elastic layer, and the surface layer resin is defined and defined by the linear pressure. There is no description.

The surface of the fixing belt 113 is brought into contact with an unfixed toner image, and the toner is heated and pressed to fix the toner on the recording paper 107. The contact state with respect to the toner is different between the portion and the valley portion. The difference in this contact state is
Naturally, it appears due to the difference in heat transfer and the pressure on the toner, and as a result, it appears as image unevenness (uneven gloss). The elastic layer described above has the effect of reducing this difference in contact state by elasticity. Hereinafter, the influence of the surface condition on the image uniformity and the fixing property will be described.

First, the image uniformity will be described. As described above, it is considered that the image unevenness is caused by the difference in the contact state of the unevenness (peaks and valleys) on the belt surface. When pressed against the toner and recording paper, due to the elasticity of the belt surface,
The ridges are crushed and tend to be flat, but the contact state differs depending on the size and shape of the elasticity. When the material of the belt surface is the same, the effect is only due to the shape. Therefore, the smaller the mountain portion is, the smaller the variation in the contact state due to the unevenness is. In addition, a state in which the image is not uniform (uneven gloss) looks like the surface of a pear, and is also called pear-skin.

Next, the fixing characteristic will be described. The fixing characteristic here means releasability. That is, how the fixing temperature range changes depending on the surface condition of the fixing belt. The fixing temperature range means a temperature range obtained by subtracting the cold offset temperature from the hot offset temperature. Cold offset is generally a state in which toner is not sufficiently fixed on recording paper, and is caused by insufficient melting of toner (low fixing temperature) and insufficient pressure between the belt and recording paper. If the belt surface is rough, the heat transfer to the toner and the pressure applied to the toner at the valleys are low, and the possibility of causing cold offset is high. Hot offset is a phenomenon in which molten toner adheres to and remains on the belt surface, and occurs when the adhesive force between the belt and the toner becomes larger than the cohesive force of the toner. A schematic diagram is shown in FIG. When the material of the belt surface is the same, the larger the contact area with the toner, the greater the adhesive force between the belt and the toner.
However, recently, the releasability of many fluorine materials used for the release layer has been improved, and in many cases, there is not much difference in the material such as the simple hot offset property.

Rather, the following paper separability is more problematic. When both the adhesion force between the fixing belt / toner and the adhesion force between the toner / paper are strong, the phenomenon that the recording paper is wound around the fixing belt side and is not discharged occurs. This phenomenon is a phenomenon caused by the thickness and stiffness of the paper. The thinner the paper, the more remarkable this wrapping phenomenon occurs. Of course, the unit configuration, especially the diameter of the fixing roller, and the viscoelasticity of the toner have a great influence. However, when such a phenomenon cannot be solved, members (separation claws, separation plates) for separating the paper from the fixing belt have to be installed in contact or non-contact. However, the separating member is only a final avoidance means, and it is basically desirable that the paper can be separated without using the separating member in consideration of reliability. As described above, the surface roughness and hardness have a great influence on the image uniformity and the releasability, and it is necessary to make these characteristic values in order to realize a stable fixing system.

[0016]

SUMMARY OF THE INVENTION In order to eliminate these disadvantages, the present invention provides a fixing belt and a belt component having a three-layer structure of a belt base, an elastic layer and a surface layer, which are required to have the required characteristics of the component. It is a clarification. An object of the present invention is to provide a fixing belt which has a surface hardness as a characteristic value and thereby satisfies an image and a fixing characteristic and which achieves energy saving by shortening a rising time.

[0017]

In order to solve the above-mentioned problems, the present invention according to claim 1 is such that an elastic layer is formed on a belt substrate, and a release layer is further formed on the elastic layer. A belt, which is a fixing belt for fixing an unfixed toner image on a recording medium by a heat fixing method, has a universal hardness at a pressing depth of 4 μm from the surface side of the fixing belt: HU1, and a universal hardness at a pressing depth of 20 μm. Hardness: The relationship with HU2 is the following (1),
The fixing belt is characterized by satisfying the expression (2). HU1 ≤ 15 N / mm ² (1) HU1 / HU2 ≤ 10 (2)

According to a second aspect of the present invention, the fixing belt according to the first aspect is characterized in that the material of the elastic layer is silicone rubber. In the invention according to claim 3, the material of the release layer is tetrafluoroethylene resin (PTFE), tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer resin (PFA), and tetrafluoroethylene / hexafluoride. The fixing belt according to claim 1 or 2, wherein at least one of fluorinated propylene copolymer resin (FEP) is contained as a component. The present invention according to claim 4 provides the fixing belt according to any one of claims 1 to 3, wherein the release layer has a film thickness of 30 μm or less.

According to a fifth aspect of the present invention, there is provided an image forming apparatus characterized in that the fixing belt according to any one of the first to fourth aspects and the wax-containing toner are used in combination.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. The image forming process of the image forming apparatus relating to the fixing belt of the present invention is the same as in FIG. FIG. 4 is a sectional view of the fixing belt 113 according to the present invention. The configuration of the fixing belt 113 includes a belt base 201,
The elastic layer 202 and the release layer 203 are included. The belt base 201 is made of a heat resistant material, and as the heat resistant material,
Metal materials such as SUS and nickel, or polyimide,
A heat resistant resin such as polyamide-imide or fluororesin is used. When a metal material is used, it is desirable that the film thickness is 100 μm or less in consideration of the bending of the belt. In the case of a heat resistant resin, it is 30 to 20 in terms of heat capacity and strength.
A film thickness of 0 μm is desirable. Thinning is advantageous for shortening the rise time, but if it is too thin, the strength cannot be maintained.

For the elastic layer 202, silicone rubber, fluorosilicone rubber or the like is used as a material having flexibility required for the belt surface and heat resistance capable of withstanding the temperature at fixing (up to 200 ° C.).

As the material used for the release layer 203,
Tetrafluoroethylene resin (PTFE), tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer resin (P
FA), and fluororesins such as tetrafluoroethylene / hexafluoropropylene copolymer resin (FEP), a mixture of these resins, or a dispersion of these fluororesins in a heat resistant resin. .

When the elastic layer 202 is covered with the release layer 203, the toner releasability and the prevention of paper dust adhesion can be achieved without applying the lubricating oil. However, since these releasable resins generally do not have elasticity like rubber materials, when the release layer 203 is formed thick on the elastic layer 202, uneven gloss of an image occurs. I will end up. That is, in order to prevent the uneven glossiness and ensure the releasability of the toner and the paper powder, it is necessary to form the release layer 203 that does not impair the flexibility of the elastic layer 202. For this purpose, it is necessary that the material of the release layer 203 is as flexible as possible and the film thickness thereof is thin.

Like the constitution of the present invention, the material of the elastic layer 202 is silicone rubber, and the material of the release layer 203 on the surface thereof is tetrafluoroethylene resin (PTFE), tetrafluoroethylene / perfluoroalkyl. At least one of a vinyl ether copolymer resin (PFA) and a tetrafluoroethylene / hexafluoropropylene copolymer resin (FEP) is contained as a component, and the release layer 203 has a thickness of 30 μm.
When the thickness is m or less, the fixing belt 113 can have flexibility and releasability.

Further, problems of the fixing belt 113 of the present invention include optimization of the surface condition and conversion of characteristic values. Next, a method of characteristic value conversion in the present invention will be described. There are surface roughness and surface hardness as methods for evaluating the surface state (shape). Commonly used characteristic values for surface roughness include center line average roughness Ra and ten-point average roughness Rz. FIG. 5 is a diagram showing the relationship between the ten-point average roughness Rz and the fixing temperature range. As for the surface hardness, as described in the related art, it is difficult to find characteristics that are highly correlated with the image uniformity and the OHP sheet image transparency, which are the main image quality characteristics of the fixing device 112, and stable image quality is obtained. It was difficult to reproduce. Therefore, in the present invention, in consideration of fixing the developed toner image on paper or OHP film, the optimum characteristics as the surface hardness of the fixing belt 113 and the universal hardness defined in DIN 50359-1 are considered. S: The correlation with HU was examined. Specifically, it was examined whether the characteristics of the fixing belt 113 can be expressed by obtaining the relationship between the indentation depth and the universal hardness: HU.

As a result of the examination, the indentation depth from the surface is 4 μm.
The relationship that the HU of m and the image uniformity are highly correlated was obtained. Similarly, the indentation depth from the surface is 4 μm and 2
Universal hardness of 0 μm: HU is assumed to be HU1 and HU2, respectively, and as a result of studying the relationship with releasability (paper releasability), the surface hardness that satisfies the following expressions (1) and (2) is optimal. I understood it. HU1 ≤ 15 N / mm ² (1) HU1 / HU2 ≤ 10 (2) Universal hardness: HU is DIN 50359-1.
Although it is a new standard standardized in (1997), it has a feature that material characteristics can be described in more detail than Vickers hardness: Hv.

Further, by using a wax-containing toner as the toner to be fixed on the recording paper by the fixing belt 113 of the present invention, the releasability can be further improved.

[0028]

EXAMPLES The influence of the surface condition of the fixing belt 113 on the image characteristics and the fixing characteristics will be described with reference to Examples. Using the fixing device 112 whose schematic diagram is shown in FIG. 4, the conditions of image gloss unevenness and releasability were investigated. The fixing temperature range was changed from cold offset to hot offset, and the releasability was paper separability. The load between the fixing roller 115 and the pressure roller 111 is 20 kg, the fixing roller 115 has a diameter of 38 mm,
A rubber having a hardness of 30 ° (JISA) was used.

Prototypes and evaluations were performed by shaking the constitution of the fixing belt 113 with the combinations shown in Table 1 below. The belt base 201 is made of polyimide resin with a diameter of 60 mm and a face length of 31.
5 mm and 50 μm are formed, and two kinds of silicone rubber (hardness (JIS K6301) are formed on the elastic layer 202.
Coating at 20 and 30 ° has 4 levels of film thickness (100 to 50)
To 0 μm). Although the blade coating method was used as the film forming method, a spray coating method, a dipping coating method, or the like may be used. After that, the release layer 20 is applied via a primer.
Formed 3. As a material of the release layer 203, a typical PFA among fluororesins was used, and three types were used (PFA).
1, PFA2, PFA3). A spray coating method was used as the film forming method. In addition, what is described as a tube in Table 1 is a PFA tube covered after the elastic layer 202 is formed.

Example of tester Fisherscope H-100 test load 0.4 mN to 1000 mN (3 times this time)
(Measurement at 00 mN) Since the fixing belt has a weak stiffness, it was measured after being cut into a sheet shape and then adhered and cured on BK7 glass for reinforcement. Further, the fixing property was evaluated by using the fixing device shown in FIG. 4, and toner for oilless fixing (wax-containing toner)
Was fixed on a recording paper. Also, the belt fixing method is shown in FIG.
There are two installation methods, as shown in. In this example, the evaluation was performed by the method of FIG. 6B, but there is no significant difference in the tendency with either installation method. It is selected according to the required degree of energy saving and high-speed compatibility. Table 1 shows the relationship between the belt structure and its universal hardness HU and the image uniformity and the paper separability. Further, graphs showing each relationship are shown in FIGS.

[Table 1]

To summarize the above, the depth from the surface is 4 μm.
Hardness in HU: Good image uniformity (rank 4 or higher) when HU1 is in the range of HU1 ≤ 15 N / mm ² (1)
It was possible to obtain the image quality of. A fixing belt with a hardness of HU1 of 15 or more causes image unevenness, and the target rank 4
The above image quality was not obtained. As described above, when the surface hardness is high, it is impossible to follow the minute irregularities of the paper, and uneven gloss occurs in the image. Further, when the relationship with the universal hardness: HU2 at a depth of 20 μm from the surface is in the range of HU1 / HU2 ≦ 10 (2), good paper separation at a temperature of 170 ° C. or higher, which is the standard (paper wrapping) It was possible to achieve paper transportability (paper jam is less likely to occur). Further, with a fixing belt of 10 or more, the paper separation temperature is lowered, and stable paper transportability cannot be achieved.

Image uniformity can be obtained if the hardness at a certain depth is the same, but the paper separability cannot be explained by the hardness at a certain depth. This is the surface hardness (depth 4μ
It is shown that even if m) is the same, there is a difference from the inner hardness (depth 20 μm). For example, in Comparative Examples 2 and 6, since the surface hardness is almost the same, the image uniformity is almost the same. However, since the inner hardness is different and the ratio is different, a great difference occurs in the paper separability. In other words, in order to achieve both the image uniformity and the paper separability, the above (1) and (2)
It is necessary to satisfy the formula.

[0033]

As described above, according to the first aspect of the present invention, since the fixing belt applies appropriate pressure and heat to the toner during fixing, image unevenness does not occur, and the paper is not Since the releasability is excellent by utilizing the difference in hardness between the surface and the inner side at the time of separation, it is possible to provide a fixing belt capable of achieving both high image quality and good paper transportability. Further, according to the present invention as set forth in claim 2, by using the silicone rubber as the elastic layer of the fixing belt, the fixing temperature is up to 200 ° C.
It can withstand the operating temperature of 1, and exhibits sufficient flexibility for image uniformity. This makes it possible to provide a fixing belt that satisfies the image characteristics of a full-color image and the paper transportability. According to the third aspect of the present invention, a fixing belt having good releasability can be provided by using, as the releasing layer of the fixing belt, one containing a fluororesin or a fluororesin component. it can. Also,
According to the present invention as set forth in claim 4, the release layer has a layer thickness of 30.
When the thickness is not more than μm, the elasticity of the elastic layer can be transmitted to the outermost surface, and a fixing belt satisfying the image characteristics of a full-color image can be provided. Further, according to the present invention of claim 5, by using the fixing belt of the present invention and the wax-containing toner in combination, an image forming excellent in image characteristics, fixing characteristics and durability of a full color image is formed. A device can be provided.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing an image forming process of an image forming apparatus using a roller fixing type fixing device.

FIG. 2 is a schematic view showing an image forming process of an image forming apparatus using a belt fixing type fixing device.

FIG. 3 is a schematic diagram showing the cohesive force of toner during hot offset.

FIG. 4 is a sectional view showing a fixing belt of the present invention.

FIG. 5 is a graph showing a relationship between a belt surface roughness Rz and a fixing temperature range.

FIG. 6 is a schematic view showing a method of installing a fixing device of a belt fixing system.

FIG. 7 is a graph showing a relationship between image uniformity and universal hardness of a fixing belt.

FIG. 8 is a graph showing the relationship between the fixing characteristics and the universal hardness of the fixing belt.

[Explanation of symbols]

101 photoconductor drum 102 charging device 103 exposure 104 developing device 105 power pack 106 transfer device 107 recording paper 108 Cleaning device 109 surface electrometer 110 heating roller 111 pressure roller 112 fixing device 113 fixing belt 114 heater 115 fixing roller 201 belt base 202 elastic layer 203 Release layer

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Koji Kamiya             1-3-3 Nakamagome, Ota-ku, Tokyo Stocks             Company Ricoh F-term (reference) 2H033 AA02 BA08 BA11 BA25 BA58                       BB18 BB28

Claims (5)

[Claims] 1. A fixing belt in which an elastic layer is formed on a belt substrate, and a release layer is further formed on the elastic layer, wherein an unfixed toner image on a recording medium is fixed by a heat fixing method. In the belt, from the surface side of the fixing belt,
Universal hardness at an indentation depth of 4 μm: HU1
And the universal hardness at a pressing depth of 20 μm:
A fixing belt characterized in that the relationship with HU2 satisfies the following expressions (1) and (2). HU1 ≤ 15 N / mm ² (1) HU1 / HU2 ≤ 10 (2) 2. The fixing belt according to claim 1, wherein the material of the elastic layer is silicone rubber. 3. The material of the release layer is tetrafluoroethylene resin (PTFE), tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer resin (PFA), and tetrafluoroethylene / hexafluoropropylene copolymer. Combined resin (FEP)
The fixing belt according to claim 1 or 2, which contains at least one of these as a component. 4. The fixing belt according to claim 1, wherein the release layer has a thickness of 30 μm or less. 5. An image forming apparatus using the fixing belt according to claim 1 and a wax-containing toner in combination.