JP2006078555A - Electrophotographic recording apparatus and fixing device therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To eliminate the need to change a nipping time regardless of paper thickness in a fixing device that requires a long nipping time, thus providing high reliability and usability. <P>SOLUTION: The electrophotographic recording apparatus is composed of at least an image forming device for forming a toner image on a recording medium, and the fixing device having at least a fixing member and adapted to fix the unfixed toner image formed on the recording medium. In the electrophotographic recording device, the temperature of the fixing member is changed before the thickness of the recording medium is switched. The temperature of the fixing member is then set to a nonvisual offset area before the first recording medium immediately after the switching of the thickness is set to a nonvisual offset area. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an electrophotographic recording apparatus that visualizes an image using colored particles of a toner such as a printer, a facsimile machine, and a copying machine, and a fixing that fixes a toner image formed on the surface of the recording body to the recording body. Relates to the device.

  A recording apparatus using an electrophotographic method includes a developing process for visualizing colored particles as an image on the surface of a recording medium, and a fixing process for fixing the visualized colored particle images to the recording medium. As the colored particles, a powder called toner exclusively for electrophotography is used. The toner melts by heating and solidifies by cooling. In the fixing step, utilizing the properties of the toner, the toner is melted by heating and fixed on the recording medium.

  Hereinafter, a conventional fixing device will be described. In the fixing process, a heating method that is often performed is to press a pair of fixing rollers including one roller and one support roller, and heat at least one of the fixing rollers. In this method, a fusing portion where the two fixing rollers are in contact with each other is formed, and a recording medium on which a toner image is formed is inserted into the fusing portion. There is also a method of forming a melt sandwiching part by pressing a belt so as to support one heating roller and the heating roller. Conversely, there are a method in which a roller is supported by a heating belt to form a melt sandwiched portion, and a method in which a melt sandwiched portion is formed by a belt and a belt. In the following description, these rollers and belts are called fixing members. In the following, description will be made by taking as an example a method of forming the fusion sandwiching portion by pressing two fixing rollers. The toner arranged as an image on the surface of the recording medium by inserting the recording medium through the fusion sandwiching portion is pressurized simultaneously with the heating. The toner is melted and deformed by receiving two types of energy supply, that is, heat energy and work by pressure in the melt sandwiching portion. As a result, the toner is fixed on the recording medium. Here, at least one of the fixing rollers is heated. Further, when the toner image formed on the recording medium is inserted into the fixing roller, the toner image carrying surface and the heated fixing roller are inserted into contact with each other. The heating roller is called a heat roller. The support roller is called a back up roller. In the following description, the heat roller is called HR and the backup roller is called BR for simplicity. Both the HR and BR rollers are called a fixing roller pair. Also, any one of HR and BR may be called a fixing roller. The method of heating and melting the toner using HR and BR is called HR fixing. On the other hand, BR as a support roller is provided with an elastic layer on the outer side of a metal rotating shaft, and this elastic layer is deformed when pressed against HR to form a fusion sandwiching portion. The melt sandwiching part is called a nip part. Further, the length of the nip portion in the sheet passing direction is called a nip width. The time for one point on the recording medium to pass through the nip is called the nip time. The elastic layer may also be provided on the HR. In this case, the nip portion is formed by deformation of both the BR and HR elastic layers.

  The HR is made of a hollow cylinder made of a high thermal conductivity material such as aluminum, and a heater is provided at the center thereof. The hollow cylinder is called a cored bar. Further, a halogen lamp is often used for the heater. In this fixing device, when the toner image is heated, a phenomenon that the melted toner adheres to the fixing roller may occur. This development is called offset, and the toner attached to the fixing roller is called offset toner. When a large amount of offset toner is generated, the offset toner is re-transferred to the recording medium, and it becomes impossible to distinguish from the recorded information, causing a problem of erroneous printing.

  FIG. 1 is a diagram showing the generation characteristics of offset toner. Reference numeral 19 denotes a low temperature region, 20 denotes a high temperature region, and 21 denotes a non-offset band. The horizontal axis shows the temperature of the fixing roller, and the vertical axis shows the amount of offset toner. The amount of offset toner is large in the low temperature region 19 and the high temperature region 20, and the offset generated in the low temperature region 19 is referred to as a low temperature offset, and the offset generated in the high temperature region 20 is referred to as a high temperature offset. The area narrowed by the low temperature area 19 and the high temperature area 20 is called a non-offset band 21 and the amount of offset toner is small. Further, the boundary region between the low-temperature region and the non-offset band 21 in the high-temperature region is referred to as a non-visual offset region 191, 201. In the non-visual offset areas 191, 201, the amount of offset toner is so small that the offset toner is not visible. When the offset occurs, the most serious problem is that the offset toner attached to the fixing roller is retransferred to the recording medium to cause erroneous printing. Therefore, this problem cannot occur unless the offset toner re-transferred to the recording medium is recognized as an image. Such a problem of erroneous printing does not occur in the non-visual offset areas 191 and 201. In order to prevent offset, silicon rubber, fluororubber, or fluororesin having high releasability is used as a release layer for the outer layer in contact with the HR toner. In particular, fluororesins are well known for their high releasability, and PFA (perfluoroalkoxy), PTFE (polytetrafluoroethylene), and the like are often used as coating layer materials. In addition, in the fixing device, the temperature of the fixing roller is usually set in the non-offset band 21 in order to minimize the amount of offset toner. Even if the temperature of the fixing roller is set in the non-offset band 21, a slight offset smaller than that in the non-visual offset areas 191 and 201 is generated. Therefore, the offset toner is wiped by bringing a nonwoven fabric or a porous material into contact with the fixing roller. There are fixing devices with cleaners to take. In this case, when the offset toner exceeding the amount capable of collecting the nonwoven fabric or the porous material is collected, the offset toner once collected by the nonwoven fabric or the porous material is transferred again to the fixing roller. Furthermore, there is a problem that this is transferred to the recording medium. This problem is called accumulated toner contamination. In order to prevent this, the cleaner made of the nonwoven fabric or porous material must be replaced before the offset toner wiped by the nonwoven fabric or porous material is accumulated up to the amount that can be collected. In the non-visual offset areas 191 and 201 described above, erroneous printing does not occur, but there is a problem that a large amount of offset toner needs to be collected and the cleaner must be replaced in a very short period.

  Further, in order to reduce the amount of offset toner in the non-offset band 21, a release agent such as silicon oil may be applied to the fixing roller. In this case, the amount of offset toner may become zero by applying an appropriate amount of silicone oil to the fixing roller. However, the amount of offset toner is not only the amount of the release agent, but also the toner composition and additives, the thickness of the toner layer of the toner image, the printing pattern and density, the amount of heat supplied to the toner during fixing, Since it is defined in relation to various factors such as the supply time, the amount of offset toner can be made zero by applying the release agent only under extremely limited conditions. Therefore, it is possible to reduce the amount of offset toner by applying a release agent, but it is often not zero.

  When a plurality of color toner layers are overlapped and fixed as in a color image, the toner layer becomes thicker and offset is likely to occur. In order to prevent this, a method is used in which the HR temperature is lowered, the nip time is extended, and the temperature distribution in the toner layer at the time of fixing is made as uniform as possible. In that case, a method of supporting the heating roller with a belt is often used. When the nip time is lengthened, a considerable amount of heat flows to the back side of the paper (opposite side where the toner to be fixed is present) during the nip time, so that the amount of heat input to the toner varies depending on the paper thickness. In other words, when the nip time is short, the effective heat propagation distance reached during the nip time is shorter than the paper thickness, in which case the paper thickness can be regarded as thermally infinitely constant no matter what paper thickness is used. The amount of heat input is constant regardless of the paper thickness.

  However, if the nip time is long, the effective heat propagation distance is longer than the paper thickness, and the input heat amount changes depending on the paper thickness. Therefore, in order to keep the input heat amount constant, it is necessary to change the nip time according to the paper thickness. The only way to change the nip time depending on the paper thickness is to change the speed of the entire process including development, or change the speed of only the fixing portion. In the former case, not only paper conveyance but also development and transfer conditions are distorted, leading to a decrease in the reliability of the entire process, and a large loss in usability that the printing speed is not constant depending on the paper thickness. In the latter case, the paper gap is used as a buffer. However, since the conveyance speed is changed between the transfer and the fixing, the conveyance path to the fixing after the transfer is at least longer than the paper length, resulting in an increase in the size of the apparatus. This causes a problem of impairing the reliability of paper conveyance.

  Next, a conventional method will be specifically described with reference to FIGS.

  FIG. 2 is a diagram schematically showing a heat penetration state in fixing when the nip time is short. Reference numeral 1 denotes a heat roller, 2 a paper, and 3 a range in which the temperature is higher than the paper temperature before entering the fixing machine, that is, an effective heat penetration portion. The depth at which heat permeates within a certain period of time is called the heat penetration thickness, and is strictly given by the square root of a value obtained by multiplying the product of thermal diffusivity and time by twelve. Considering this in relation to the paper thickness which is a problem of the present invention, the square root is 12 times the product of the thermal diffusivity of the paper and the nip time. The thickness in this case is defined by a slight increase in temperature at the point of the thickness. Practically, the heat penetration thickness in fixing electrophotography may be considered as the square root of the product of the thermal diffusivity of paper and the nip time. When the nip time is about 10 ms, the heat supplied from the hot roll during the nip time does not reach the back surface of the paper at any paper thickness as shown in FIG. The heat penetration part is the same regardless of the paper thickness. That is, any paper thickness can be regarded as the same thickness with an infinite thickness thermally. In this case, the amount of heat supplied to the toner is the same regardless of the paper thickness.

  FIG. 3 is a diagram schematically showing a heat penetration state in fixing when the nip time is long. Reference numeral 31 denotes a profile showing the range of the heat-permeable portion 3 of thin paper. In the thin paper, the heat reaches the back surface, the profile of the heat penetration portion is different from that of the thick paper, and the heat penetration range near the interface with the heat roller 1 where the toner is present is particularly narrow. It can be seen that the amount of heat input to the toner is reduced. Therefore, in order to put the same amount of heat in the thick paper as in the thin paper, it is necessary to put more heat in the paper.

FIG. 4 is a diagram showing a state of heat penetration when the nip time is extended to a thicker paper thickness. Extending the nip time means that more heat is input to the paper. Reference numeral 32 denotes a profile showing the range of the heat-permeable portion 3 of the cardboard of FIG.
As shown in FIG. 4, by extending the nip time, the same heat penetration portion profile as that of the thin paper is obtained in the vicinity of the interface with the heat roller 1. As described above, in the conventional method, when the effective heat penetration thickness exceeds the paper thickness, it is necessary to adjust the nip time to make the amount of heat supplied to the toner constant. That is, in the case of thick paper, it is necessary to supply a larger amount of heat to the paper in order to input the same amount of heat as that of the thin paper to the toner.

Japanese Patent No. 2875423

  The conventional fixing device described above has a problem that when the nip time is increased, the nip time needs to be changed depending on the paper thickness. As a result, there is a problem that reliability and usability are deteriorated.

  SUMMARY OF THE INVENTION An object of the present invention is to realize a fixing device that does not require changing the nip time at any paper thickness in a fixing device that requires a long nip time, and to provide high reliability and usability.

  The object is to provide an electrophotographic apparatus comprising an image forming device for forming at least a toner image on a recording medium, and a fixing device for fixing an unfixed toner image formed on the recording medium having at least a fixing member. In the recording apparatus, the temperature of the fixing member is changed when the thickness of the recording medium is switched, and the temperature of the fixing member is set to a non-visual offset region when the first recording medium after switching is fixed. Is achieved.

  According to the present invention, since the heat amount accompanying the change in the paper thickness can be adjusted by using the change in the fixing member temperature by starting the printing in the non-visual offset region, the printing speed or the fixing speed can be reduced even in the fixing device having a long nip time. This has the advantage of making it unnecessary to make changes.

  An embodiment of the present invention will be described below with reference to FIGS.

  FIG. 1 is a diagram showing the generation characteristics of offset toner. Reference numeral 19 denotes a low temperature region, 20 denotes a high temperature region, and 21 denotes a non-offset band. The horizontal axis shows the temperature of the fixing roller, and the vertical axis shows the amount of offset toner. The amount of offset toner is large in the low temperature region 19 and the high temperature region 20, and the offset generated in the low temperature region 19 is referred to as a low temperature offset, and the offset generated in the high temperature region 20 is referred to as a high temperature offset. The area narrowed by the low temperature area 19 and the high temperature area 20 is called a non-offset band 21 and the amount of offset toner is small. Further, the boundary region between the low-temperature region and the non-offset band 21 in the high-temperature region is referred to as a non-visual offset region 191, 201. In the non-visual offset areas 191, 201, the amount of offset toner is so small that the offset toner is not visible. When the offset occurs, the most serious problem is that the offset toner attached to the fixing roller is retransferred to the recording medium to cause erroneous printing. Therefore, this problem cannot occur unless the offset toner re-transferred to the recording medium is recognized as an image. Such a problem of erroneous printing does not occur in the non-visual offset areas 191 and 201. In the non-visual offset areas 191 and 201, no erroneous printing occurs, but a large amount of offset toner to be collected is generated. If printing continues in this temperature range, the cleaner must be replaced in a very short period of time. The problem of not becoming. Specifically, the number of printed sheets that affects the replacement of the cleaner is several thousand pages or more, and the replacement time of the cleaner is not substantially advanced by printing of several tens of pages in the non-visual offset areas 191 and 201.

  FIG. 5 is a diagram showing the relationship between the HR temperature and the occurrence of offset when fixing is performed using thin paper and when fixing is performed using thick paper in the recording apparatus of the present invention. In the figure, ○ indicates that no offset occurs, Δ indicates that a non-visual offset occurs, and × indicates that a visible offset occurs. In the recording apparatus of the present invention, since only the HR is heated and the nip time is as long as 100 ms, the amount of heat input to the toner at the same temperature differs between the thick paper and the thin paper. Therefore, non-offset bands also appear shifted. In the case of thin paper, the HR temperature is controlled to be constant at 170 ° C. In the case of thick paper, the amount of heat input to the toner decreases, but since the nip time is the same as that of thin paper, it is necessary to raise the HR temperature. Therefore, in the case of thick paper, the HR temperature is controlled to be constant at 190 ° C. Actually, the HR temperature cannot be set simply by matching the amount of heat input to the toner, and it is necessary to match the offset characteristics. It is desirable to set the HR temperature at the center of the offset band as much as possible with the same amount of heat input to the toner between the thick paper and the thin paper.

  In the recording apparatus of the present invention, the HR temperature of thick paper that obtains a heat quantity equal to the HR temperature (170 ° C.) in the case of thin paper is 200 ° C. However, the HR temperature is set to 190 ° C. in the case of thick paper. This is because the paper type can be switched smoothly. That is, when switching from thick paper to thin paper, the HR temperature is controlled to 190 ° C. for thick paper, so the first sheet of thin paper has an HR temperature close to 190 ° C. At that time, since the HR temperature corresponds to the non-visual offset region 201 for thin paper, no visible offset occurs. Conversely, when switching from thin paper to thick paper, the HR temperature is controlled at 170 ° C. for thin paper, so the first sheet of thick paper has an HR temperature close to 170 ° C. At that time, since the HR temperature corresponds to the non-visual offset area 191 for the thick paper, no visible offset occurs. If the HR temperature is set to 200 ° C. for thick paper to completely match the amount of heat input to the toner, when switching from thick paper to thin paper, the first sheet of thin paper has an HR temperature close to 200 ° C. At this time, since the HR temperature corresponds to the outside of the non-visual offset area 201 of the offset area 20 in the case of thin paper, there arises a problem that a visible offset occurs. In the recording apparatus of the present invention, as soon as the paper thickness switching operation is performed, the control temperature is set to a value corresponding to the paper thickness, but when the temperature is switched from low temperature (170 ° C.) to high temperature (190 ° C.) (from thin paper) When switching to cardboard), continuous printing is 15 pages, and the HR temperature reaches a temperature equal to the set temperature of high temperature (190 ° C.). Further, when switching from high temperature (190 ° C.) to low temperature (170 ° C.) (when switching from thick paper to thin paper), continuous printing is 10 pages, and the HR temperature reaches a temperature equal to the set temperature of low temperature (170 ° C.). Since the HR temperature is as small as 15 pages or less in the non-visual offset areas 191 and 201, the cleaner replacement period is not shortened.

  According to the present embodiment described above, although the nip time is as long as 100 ms, it is not necessary to switch the nip time depending on the paper thickness, and there is no occurrence of erroneous printing due to offset. This eliminates the need to change the printing speed or fixing speed, so that it can be used for applications that do not allow a decrease in printing productivity when printing on thick paper. The sheet conveyance speed of the transfer process and the fixing process can be constantly made equal, and the distance from the final transfer process to the fixing process can be made shorter than the sheet length in the conveyance direction. As a result, the recording apparatus can be made compact, so that it can be installed even in a narrow space where the conventional recording apparatus cannot be installed.

  In this embodiment, the fixing device is composed of the fixing member HR and BR. However, the fixing member for forming the nip portion by pressing the belt so as to support one heating roller and the heating roller, and the roller for the heating belt. The same effect as described in the present embodiment can be obtained also in a fixing device that supports and forms a nip portion or a fixing device that forms a nip portion with a belt.

  Next, another embodiment of the present invention will be described with reference to FIGS.

  FIG. 6 is a diagram illustrating the relationship between the heat roller temperature and the occurrence of offset when fixing is performed using extremely thin paper, thin paper, and thick paper in the recording apparatus of the present embodiment. The recording apparatus of the present embodiment is the same as the recording apparatus described in the first embodiment, except that it supports ultrathin paper. The temperature switching between the thin paper and the thick paper is the same as in the first embodiment. The HR temperature in ultra-thin paper is controlled at a constant 160 ° C. The HR temperature for thin paper is 170 ° C. as in Example 1. Since the temperature switching between the ultrathin paper and the thin paper can be performed in any non-offset band 21 at the switching destination, there is no problem in the period until erroneous printing or cleaner replacement. However, when switching from very thin paper to thick paper or from thick paper to very thin paper, the situation is different from switching between thin paper and thick paper. In the recording apparatus of this embodiment, the HR temperature in ultrathin paper is controlled to 140 ° C. When the thick paper is passed with the temperature setting of ultrathin paper (140 ° C.), the HR temperature is outside the non-visual offset area 191 of the low temperature area 19 where the offset occurs in the thick paper, so that a visible offset occurs. Even if the set temperature is switched at the same time as the paper thickness is changed, the actual HR temperature does not rise immediately because the temperature change is delayed, and a visible offset occurs when the thick paper is passed simultaneously with the temperature setting change. . Therefore, in this embodiment, printing is set to be prohibited until the HR temperature rises to 170 ° C. which is the non-visual offset region 191. If printing is started at 170 ° C., a visible offset does not occur, and the HR temperature soon reaches the set temperature of 190 ° C. during printing, so that the non-visual offset does not affect the cleaner replacement. On the other hand, if ultrathin paper is passed with the thick paper temperature setting (190 ° C.), the HR temperature is outside the non-visual offset area 201 of the high temperature area 20 where the offset occurs in the ultrathin paper, so that the visible offset is appear. Even if the set temperature is switched at the same time as switching the paper thickness, if an ultrathin paper is passed at the same time, a visible offset occurs as in the case of switching from the ultrathin paper to the thick paper. Therefore, in this embodiment, printing is set to be prohibited until the HR temperature falls to 170 ° C. which is the non-visual offset region 201. If printing is started at 170 ° C., no visible offset occurs, and the HR temperature soon reaches the set temperature of 140 ° C. during printing, so that the non-visual offset does not affect the cleaner replacement.

  According to the present embodiment described above, it is not necessary to switch the nip time depending on the paper thickness from an extremely thin paper to a thick paper, and there is no occurrence of erroneous printing due to an offset, although the nip is a long time of 100 ms. This eliminates the need to change the printing speed or the fixing speed, so that it can be used for applications in which a decrease in printing productivity when printing on cardboard is not permitted, and from the final transfer process to the fixing process. Needless to say, since the distance can be shorter than the paper length in the transport direction, it can be installed even in a narrow space where the conventional recording apparatus cannot be installed.

  In this embodiment, the fixing device is composed of the fixing member HR and BR. However, the fixing member for forming the nip portion by pressing the belt so as to support one heating roller and the heating roller, and the roller for the heating belt. The same effect as described in the present embodiment can be obtained also in a fixing device that supports and forms a nip portion or a fixing device that forms a nip portion with a belt.

The figure which shows the generation | occurrence | production characteristic of offset toner. The figure which shows typically the heat penetration state in fixing when nip time is short. The figure which shows typically the heat penetration state in fixing when nip time is long. The figure which shows the state of the heat penetration at the time of extending | stretching nip time to the thick paper thickness. The figure which shows the relationship between heat roller temperature and offset generation | occurrence | production in the case of fixing using thin paper, and the case of fixing using thick paper. (Example 1) The figure which shows the relationship between heat roller temperature and offset generation | occurrence | production in the case of fixing using ultra-thin paper, thin paper, and thick paper. (Example 2)

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Heat roller, 2 ... Paper, 3 ... Range where temperature rose from paper temperature before entering fixing machine, 19 ... Low temperature region, 20 ... High temperature region, 21 ... Non-offset band, 31 ... Heat penetration of thin paper Profile showing the range of the part 3, 32... Profile showing the range of the heat penetration part 3 of the cardboard in FIG. 3, 191, 201.

Claims (4)

  An electrophotographic recording apparatus comprising: an image forming apparatus that forms at least a toner image on a recording body; and a fixing apparatus that includes at least a fixing member and fixes an unfixed toner image formed on the recording body. The temperature of the fixing member is changed when the thickness of the recording medium is switched, and the temperature of the fixing member is set to a non-visual offset region when fixing the first recording medium after switching. A fixing device for an electrophotographic recording apparatus.   2. The fixing device for an electrophotographic recording apparatus according to claim 1, wherein the nip time is set in a range where the square root of the product of the thermal diffusivity of the recording medium and the nip time is larger than the thickness of the recording medium.   3. The fixing device for an electrophotographic recording apparatus according to claim 1, wherein the nip time is constant when the thickness of the recording body is switched. An electrophotographic recording apparatus comprising: an image forming apparatus that forms at least a toner image on a recording body; and a fixing apparatus that includes at least a fixing member and fixes an unfixed toner image formed on the recording body. The temperature of the fixing member is changed when the thickness of the recording medium is switched, and the temperature of the fixing member is set in a non-visual offset region when the first recording medium after switching is fixed. An electrophotographic recording apparatus, wherein a distance from the fixing device to the fixing device is set to be shorter than a length in a conveyance direction of the recording medium.

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