Patent Description:
An electrophotographic system disclosed in Patent Literature <NUM> sets a printing speed used in a case where plural electrophotographic devices are connected to perform printing and a printing speed used in a case where plural electrophotographic devices are made independent of each other and printing is performed by separate electrophotographic devices, and includes a printing speed switching unit that switches between the printing speeds.

Patent Literature <NUM>: <CIT>
Reference may be made to <CIT>, which relates to an image forming apparatus provided with a fixing device for heat-fixing by allowing a transfer material to pass through a fixing nip part formed from a heat fixing rotating body with a heat source and a pressurizing rotating body which is rotated in a pressurized contact with the heat fixing rotating body, in such direction that a surface carrying an unfixed toner image of the transfer material is in contact with the heat fixing rotating body. The image fixing device is provided with a pre-heating means heating the transfer material on the upstream side of the transfer material transporting direction of the heat fixing rotating body than the fixing nip part, a pressurizing rotating body temperature detection means detecting the surface temperature of the pressurizing rotating body and a control means controlling the pre-heating means. The control means controls heat supplying amount by the pre-heating means to be variable according to the surface temperature detected result of the pressurizing rotating body detected by the pressurizing rotating body temperature detection means.

In the related art, when forming a toner image on both surfaces of a recording medium, the toner image is first transferred onto a first surface of the recording medium. Next, a preheating unit heats the recording medium having the toner image transferred onto the first surface thereof. Further, a main heating unit comes into contact with the recording medium to heat the recording medium, and fixes the toner image onto the first surface of the recording medium heated by the preheating unit. Next, the toner image is transferred onto a second surface of the recording medium having the toner image fixed onto the first surface thereof. Next, the preheating unit heats the recording medium having the toner image transferred onto the second surface thereof. Further, the main heating unit comes into contact with the recording medium to heat the recording medium, and fixes the toner image onto the second surface of the recording medium heated by the preheating unit.

Here, since the preheating unit heats the recording medium having the toner image transferred onto the second surface thereof, a temperature of the first surface of the recording medium becomes equal to or higher than a softening point of a toner. Thereafter, when the toner image on the first surface is heated a second time by the main heating unit, glossiness of the toner image on the first surface becomes higher than glossiness of the toner image on the second surface. That is, a glossiness difference (= gloss difference) occurs between the toner image on the first surface and the toner image on the second surface.

An object of the present invention is to reduce the difference between the glossiness of the toner image on the first surface and the glossiness of the toner image on the second surface, as compared with the case where, before the main heating unit heats the recording medium having the toner image transferred onto the second surface thereof, the temperature of the first surface of the recording medium is equal to or higher than the softening point of the toner since the recording medium having the toner image transferred onto the second surface thereof is heat by the preheating unit.

The present invention is defined by the independent claim, to which reference should now be made. Specific embodiments are defined in the dependent claims. The following first to fifth aspects are examples useful to understand the invention but not covered by appended independent claim. An image forming device according to a first aspect is characterized by including: a transfer unit that transfers a toner image onto a recording medium being conveyed; a main heating unit that is arranged downstream of the transfer unit in a conveyance direction of the recording medium, comes into contact with the recording medium to heat the recording medium, and fixes the toner image onto the recording medium; a reversing unit that reverses front and back of the recording medium having an image fixed onto a first surface of the recording medium by the main heating unit, and sends the recording medium to the transfer unit; and a preheating unit that is arranged between the transfer unit and the main heating unit in the conveyance direction of the recording medium and heats the recording medium having an image transferred onto a second surface of the recording medium, the preheating unit heating the recording medium so that a temperature of the first surface of the recording medium is lower than a softening point of a toner before the recording medium is heated by the main heating unit.

An image forming device according to a second aspect is characterized by that, in the image forming device according to the first aspect, the preheating unit heats the recording medium from a side of an unfixed toner image in a non-contact state.

An image forming device according to a third aspect is characterized by that, in the image forming device according to the second aspect, the recording medium is conveyed with a recording surface facing in a vertical direction when the preheating unit heats the recording medium having an image transferred onto the second surface, the preheating unit heats a recording member from above the recording member, and a blowing unit that blows air to the recording medium is provided on an opposite side of the recording medium being conveyed than the preheating unit.

An image forming device according to a fourth aspect is characterized by that, in the image forming device according to any one of the first to third aspects, a conveying unit that grips a leading end portion of the recording medium and conveys the recording medium is included, and, when the preheating unit heats the recording medium having an image transferred onto the second surface, the conveying unit conveys the recording medium with an image forming region on the first surface of the recording medium being in a non-contact state with another member.

An image forming device according to a fifth aspect is characterized by that, in the image forming device according to the fourth aspect, the conveying unit conveys the recording medium with a recording surface facing in a vertical direction when the preheating unit heats the recording medium having an image transferred onto the second surface, the preheating unit heats a recording member from above the recording member, and a stabilizing unit that stabilizes a conveyance posture of the recording member is arranged on a side opposite to the preheating unit on an opposite side of the recording medium being conveyed than the preheating unit in a non-contact state with the recording medium.

According to the image forming device of the first aspect, a difference between glossiness of the toner image on the first surface and glossiness of the toner image on the second surface may be reduced as compared with a case where, before the main heating unit heats the recording medium, the temperature of the first surface of the recording medium is equal to or higher than the softening point of the toner since the preheating unit heats the recording medium having the toner image transferred onto the second surface thereof.

According to the image forming device of the second aspect, when the preheating unit heats the recording medium having the image transferred onto the second surface thereof, a temperature of the second surface of the recording medium onto which an unfixed toner image is transferred may be made higher than the temperature of the first surface of the recording medium onto which a toner image is fixed.

According to the image forming device of the third aspect, when the preheating unit heats the recording medium having the image transferred onto the second surface thereof, the temperature of the first surface may be easily made lower than the softening point of the toner as compared with a case where air on the first surface side is stagnant.

According to the image forming device of the fourth aspect, when the preheating unit heats the recording medium having the image transferred onto the second surface thereof, it is possible to suppress deterioration in quality of the toner image formed on the first surface of the recording medium as compared with a case where the image forming region on the first surface of the recording medium comes into contact with another member.

According to the image forming device of the fifth aspect, as compared with a case where the recording medium is conveyed in a state of being bent by gravity, it is possible to suppress, in one recording medium, occurrence of a difference in glossiness in the recording medium heated by the preheating unit.

An example of an image forming device according to an embodiment of the present invention will be described with reference to <FIG>. In the drawings, an arrow H indicates a device vertical direction (perpendicular direction), an arrow W indicates a device width direction (horizontal direction), and an arrow D indicates a device depth direction (horizontal direction).

An image forming device <NUM> according to the embodiment is an electrophotographic image forming device that forms a toner image on a sheet member P. As illustrated in <FIG>, the image forming device <NUM> includes a control unit <NUM>, an accommodating portion <NUM>, a discharge portion <NUM>, an image forming unit <NUM>, a conveying mechanism <NUM>, a reversing mechanism <NUM>, a fixing device <NUM>, and a cooling unit <NUM>.

The control unit <NUM> is configured with a central processing unit (CPU), a read only memory (ROM), a random access memory (RAM), and a hard disk drive (HDD) (none is shown). The CPU executes a processing program. The ROM stores various programs, various tables, parameters, and the like. The RAM is used as a work area or the like when the CPU executes various programs.

The accommodating portion <NUM> has a function of accommodating the sheet member P as a recording medium. The image forming device <NUM> may include plural (for example, two) accommodating portions <NUM>, and may selectively send out the sheet member P from the plural accommodating portions <NUM>.

The discharge portion <NUM> is a portion from which the sheet member P on which a toner image is formed is discharged. Specifically, after the toner image is fixed by the fixing device <NUM>, the sheet member P cooled by the cooling unit <NUM> is discharged to the discharge portion <NUM>.

The image forming unit <NUM> has a function of forming a toner image on the sheet member P by an electrophotographic method. Specifically, the image forming unit <NUM> includes a toner image forming unit <NUM> that forms a toner image, and a transfer device <NUM> that transfers the toner image formed by the toner image forming unit <NUM> to the sheet member P.

Plural toner image forming units <NUM> are provided so as to form a toner image for each color. The image forming device <NUM> includes toner image forming units <NUM> of a total of four colors of yellow (Y), magenta (M), cyan (C), and black (K). The (Y), (M), (C), and (K) shown in <FIG> show constituent portions corresponding to the respective colors.

The toner image forming units <NUM> of these colors have basically the same configuration except for toner to be used. Specifically, as illustrated in <FIG>, the toner image forming unit <NUM> of each color includes a photosensitive drum <NUM> (photoconductor) that rotates in a direction indicated by an arrow A in <FIG>, and a charger <NUM> that charges the photosensitive drum <NUM>. Further, the toner image forming unit <NUM> of each color includes an exposure device <NUM> that exposes the photosensitive drum <NUM> charged by the charger <NUM> to light to form an electrostatic latent image on the photosensitive drum <NUM>, and a developing device <NUM> that uses toner to develop the electrostatic latent image, which is formed on the photosensitive drum <NUM> by the exposure device <NUM>, so as to form a toner image.

The transfer device <NUM> has a function of primarily transferring toner images of the photosensitive drums <NUM> of the respective colors onto an intermediate transfer body in a superimposed manner, and secondarily transferring the superimposed toner images onto the sheet member P. Specifically, as illustrated in <FIG>, the transfer device <NUM> includes a transfer belt <NUM> as the intermediate transfer body, a primary transfer roll <NUM>, and a transfer unit <NUM>.

The primary transfer roll <NUM> has a function of transferring a toner image formed on the photosensitive drum <NUM> to the transfer belt <NUM> at a primary transfer position T (see <FIG>) between the photosensitive drum <NUM> and the primary transfer roll <NUM>.

The transfer belt <NUM> has an endless shape, and is wound around plural rolls <NUM> to determine a posture thereof. When at least one of the plural rolls <NUM> is driven to rotate, the transfer belt <NUM> rotates in a direction indicated by an arrow B, and conveys the primarily transferred toner image to a secondary transfer position NT to be described later.

The transfer unit <NUM> has a function of transferring the toner image, which is transferred onto the transfer belt <NUM>, to the sheet member P. Specifically, the transfer unit <NUM> includes a secondary transfer unit <NUM> and a facing roll <NUM>.

The facing roll <NUM> is disposed below the transfer belt <NUM> so as to face the transfer belt <NUM>. The secondary transfer unit <NUM> is disposed on an inner side of the transfer belt <NUM> such that the transfer belt <NUM> is disposed between the secondary transfer unit <NUM> and the facing roll <NUM>. Specifically, the secondary transfer unit <NUM> is configured with a corotron. In the transfer unit <NUM>, the toner image transferred onto the transfer belt <NUM> is transferred onto the sheet member P passing through the secondary transfer position NT by a electrostatic force generated due to electricity-discharge of the secondary transfer unit <NUM>. Here, the secondary transfer position NT is a position where the transfer belt <NUM> and the facing roll <NUM> are in contact with each other.

The conveying mechanism <NUM> has a function of conveying the sheet member P accommodated in the accommodating portion <NUM> to the secondary transfer position NT. Further, the conveying mechanism <NUM> has a function of conveying the sheet member P from the secondary transfer position NT to the main heating unit <NUM> to be described later. The conveying mechanism <NUM> will be described in detail later.

The reversing mechanism <NUM> has a function of reversing the front and back of the sheet member P. The reversing mechanism <NUM> will be described in detail later.

The fixing device <NUM> has a function of fixing the toner image, which is transferred onto the sheet member P by the transfer device <NUM>, onto the sheet member P. The fixing device <NUM> will be described in detail later.

The cooling unit <NUM> has a function of cooling the sheet member P heated by the fixing device <NUM>. As illustrated in <FIG>, the cooling unit <NUM> is disposed downstream of the main heating unit <NUM> of the fixing device <NUM> in a conveyance direction of the sheet member P. The cooling unit <NUM> includes two cooling rolls <NUM> arranged in the device width direction. Since the two cooling rolls <NUM> have the same configuration, one of the cooling rolls <NUM> will be described.

As illustrated in <FIG>, the cooling roll <NUM> includes a pair of rolls 92a and 92b that sandwich the sheet member P in a conveyance path thereof. The roll 92a is disposed above the conveyance path of the sheet member P. The roll 92b is disposed below the conveyance path of the sheet member P.

The rolls 92a and 92b have cylindrical base members 94a and 94b respectively that extend in the device depth direction. The base members 94a and 94b are, for example, aluminum tubes. An air blowing mechanism (not shown) is configured to generate an air flow inside the base members 94a and 94b. Due to the air flow, a temperature of surfaces of the rolls 92a and 92b is lower than a temperature thereof in a case where the air flow is not generated.

In this configuration, the roll 92b is rotated by a rotational force transmitted from a driving member (not shown). Further, the roll 92a is driven to rotate by the roll 92b. The rolls 92a and 92b convey the sheet member P while sandwiching the sheet member P therebetween, and cool the sheet member P.

In the image forming device <NUM> illustrated in <FIG>, a toner image is formed as follows.

First, the charger <NUM> (see <FIG>) of each color, to which a voltage is applied, uniformly charges a surface of the photosensitive drum <NUM> of each color at a predetermined negative potential. Subsequently, based on image data input from the outside, the exposure device <NUM> irradiates the charged surface of the photosensitive drum <NUM> of each color with exposure light to form an electrostatic latent image.

Accordingly, electrostatic latent images corresponding to the image data are formed on respective surfaces of the photosensitive drums <NUM>. Further, developing devices <NUM> of the respective colors develop the electrostatic latent images to form toner images on the respective surfaces of the photosensitive drums <NUM> of the respective colors. The transfer device <NUM> transfers the toner images formed on the surfaces of the photosensitive drums <NUM> of the respective colors onto the transfer belt <NUM>.

Meanwhile, the sheet member P is sent out from the accommodating portion <NUM> illustrated in <FIG> to the conveyance path of the sheet member P by the conveying mechanism <NUM> to be described later. The sheet member P being conveyed along the conveyance path is sent out to the secondary transfer position NT where the transfer belt <NUM> and the facing roll <NUM> are in contact with each other. At the secondary transfer position NT, the sheet member P is conveyed while being sandwiched between the transfer belt <NUM> and the facing roll <NUM>, and accordingly the toner images on a front surface of the transfer belt <NUM> are transferred onto a first surface (= front surface) of the sheet member P.

Further, the fixing device <NUM> fixes the toner images, which are transferred onto the first surface of the sheet member P, onto the sheet member P, and the sheet member P is conveyed to the cooling unit <NUM>. The cooling unit <NUM> cools the sheet member P onto which the toner images are fixed, and discharges the sheet member P to the discharge portion <NUM>.

On the other hand, in a case of forming a toner image on a second surface (= back surface) of the sheet member P, the sheet member P that passes through the fixing device <NUM> by being conveyed by the conveying mechanism <NUM> is conveyed to the reversing mechanism <NUM>. The sheet member P conveyed to the reversing mechanism <NUM> has the front and back thereof reversed by a reversing device <NUM>. Conveying rolls <NUM> convey the sheet member P, whose front and back are reversed, to the conveying mechanism <NUM>. In order to form a toner image on the second surface of the sheet member P, conveyance of the sheet member P to the secondary transfer position NT, transfer of the toner image onto the second surface of the sheet member, and fixing of the toner image onto the second surface are performed in the same manner as described above.

Next, the conveying mechanism <NUM>, the reversing mechanism <NUM>, and the fixing device <NUM> will be described.

As illustrated in <FIG>, the conveying mechanism <NUM> includes a sending-out roll <NUM>, plural conveying rolls <NUM>, and a chain gripper <NUM>. The conveying mechanism <NUM> is an example of a conveying unit.

The sending-out roll <NUM> is a roll that sends out the sheet member P accommodated in the accommodating portion <NUM>. The plural conveying rolls <NUM> include rolls that convey the sheet member P sent out by the sending-out roll <NUM> to the chain gripper <NUM>, and rolls that convey the sheet member P conveyed by the chain gripper <NUM> to the cooling unit <NUM>. The chain gripper <NUM> has a function of conveying the sheet member P while holding a leading end portion of the sheet member P. Specifically, as illustrated in <FIG>, the chain gripper <NUM> has a pair of chains <NUM>, and grippers <NUM> serving as holding portions (= gripping portions).

The pair of chains <NUM> is formed in an annular shape. The chains <NUM> in a pair are disposed at an interval in the device depth direction. The pair of chains <NUM> is wound around a pair of sprockets (not shown) disposed at both ends in an axial direction of the facing roll <NUM> (see <FIG>), a pair of sprockets <NUM> (see <FIG>) disposed at both ends in an axial direction of a pressing roll <NUM> to be described later, and a pair of sprockets <NUM> (see <FIG>). When one pair of the sprockets rotates, the chain <NUM> rotates in a direction indicated by an arrow C.

Plural attachment members <NUM> extend between the pair of chains <NUM> along the device depth direction, at predetermined intervals along a circumferential direction (rotational direction) of the chains <NUM>. The grippers <NUM> are attached.

Plural grippers <NUM> are attached to each attachment member <NUM> at predetermined intervals along the device depth direction. Each gripper <NUM> has a function of holding a leading end portion of the sheet member P. Specifically, each gripper <NUM> has a claw 76a. In addition, the attachment member <NUM> is formed with a contact portion 75a (see <FIG>) with which the claw 76a comes into contact.

When the leading end portion of the sheet member P is sandwiched between the claw 76a of the gripper <NUM> and the contact portion 75a of the attachment member <NUM>, the sheet member P gets held. For example, the claw 76a of the gripper <NUM> is pressed against the contact portion 75a of the attachment member <NUM> by a spring or the like, and the claw 76a is brought into contact with or separated from the contact portion 75a by an action of a cam or the like.

In the chain gripper <NUM>, the chain <NUM> rotates in the direction indicated by the arrow C in a state where the leading end portion of the sheet member P is held between the gripper <NUM> and the attachment member <NUM>, thereby conveying the sheet member P. The chain gripper <NUM> conveys the sheet member P conveyed by the plural conveying rolls <NUM> to the secondary transfer position NT, and further conveys the sheet member P to the main heating unit <NUM> described later after passing the sheet member P through a preheating unit <NUM> described later. A part of the conveyance path in the conveying mechanism <NUM> along which the sheet member P is conveyed is indicated by a one-dot chain line in <FIG>.

In this configuration, at least from the secondary transfer position NT to the main heating unit <NUM>, the conveying mechanism <NUM> conveys the sheet member P with both sheet surfaces (= recording surfaces) thereof facing in the vertical direction. In other words, at least from the secondary transfer position NT to the main heating unit <NUM>, the conveying mechanism <NUM> conveys the sheet member P with a surface having an unfixed toner image being directed upward.

Further, there is case where toner images are formed on the first surface (= front surface) and the second surface (= back surface) of the sheet member P. Hereinafter, this is referred to as "the case of double-sided printing". In this case, when the sheet member P having an image transferred onto the second surface thereof is heated by the preheating unit <NUM> to be described later, the conveying mechanism <NUM> conveys the sheet member P with an image forming region of the first surface of the sheet member P in a state of not being in contact with other members. In other words, arrangement of other members is determined in consideration of a conveyance posture of the sheet member P being conveyed by the conveying mechanism <NUM>. The "image forming region" refers to a portion other than an outer peripheral portion of the sheet member P where an image cannot be formed, and is a region where an image is formed when a solid image is formed on the sheet member P.

As illustrated in <FIG>, the reversing mechanism <NUM> includes plural conveying rolls <NUM>, the reversing device <NUM>, and plural conveying rolls <NUM>. The reversing mechanism <NUM> is an example of a reversing unit.

The plural conveying rolls <NUM> convey the sheet member P sent from the fixing device <NUM> to the reversing device <NUM>. The reversing device <NUM> is, for example, a device that conveys the sheet member P while rotating the sheet member P plural times such that the conveyance direction of the sheet member P changes by, for example, <NUM> degrees each time, thereby twisting the sheet member P like a mevius band to reverse the front and back of the sheet member P. The plural conveying rolls <NUM> are rolls that convey the sheet member P whose front and back are reversed by the reversing device <NUM> to the chain gripper <NUM>.

In this configuration, in the case of double-sided printing, the reversing mechanism <NUM> reverses the front and back of the sheet member P having the toner image fixed onto the first surface thereof. Then, the reversing mechanism <NUM> sends the sheet member P again to the secondary transfer position NT through the conveying mechanism <NUM>.

As illustrated in <FIG>, the fixing device <NUM> includes the preheating unit <NUM> that heats the sheet member P being conveyed in a state of not being in contact with the sheet member P, the main heating unit <NUM> that comes into contact with the sheet member P to heat and press the sheet member P, and a blowing unit <NUM>.

As illustrated in <FIG>, the preheating unit <NUM> is disposed downstream of the secondary transfer position NT (see <FIG>) in the conveyance direction of the sheet member P and above the conveyance path of the sheet member P. In other words, the preheating unit <NUM> is disposed on a side of the unfixed toner image transferred onto the sheet member P. That is, the preheating unit <NUM> is provided on the same side as the transfer unit <NUM> with respect to the conveyance path of the sheet member P. The preheating unit <NUM> includes a reflecting plate <NUM>, plural infrared heaters <NUM> (hereinafter referred to as "heaters <NUM>"), and a wire mesh <NUM>.

The reflecting plate <NUM> is formed of an aluminum plate, and has a shallow bottomed box shape opened on a side of the sheet member P being conveyed. In the present embodiment, as viewed from above, the reflecting plate <NUM> covers, in the device depth direction, the sheet member P being conveyed.

The heater <NUM> has a cylindrical shape extending in the device depth direction, and plural the heaters <NUM> are accommodated inside the box-shaped the reflecting plate <NUM>. In the present embodiment, as viewed from above, the heaters <NUM> cover, in the device depth direction, the sheet member P being conveyed. Each heater <NUM> is separated from the conveyance path of the sheet member P by <NUM> in an upward direction.

The plural heaters <NUM> are arranged at intervals in the device width direction. In the present embodiment, as viewed from above, a region where the plural heaters <NUM> are arranged covers, in the device width direction, one sheet member P being conveyed. In other words, the plural heaters <NUM> heat at one time the entire sheet member P being conveyed.

In the above configuration, from the heater <NUM>, an infrared ray having a maximum spectral radiance at a wavelength of <NUM> or more and <NUM> or less is emitted. A surface temperature of the heater <NUM> is a predetermined temperature of <NUM> or higher and <NUM> or lower.

The wire mesh <NUM> is fixed to an edge portion of an opening of the box-shaped reflecting plate <NUM> by a fixing member (not shown), and partitions the inside of the box-shaped reflecting plate <NUM> from the outside of the reflecting plate <NUM>. Accordingly, the wire mesh <NUM> prevents the sheet member P being conveyed from coming into contact with the heater <NUM> inside the box-shaped reflecting plate <NUM>.

In this configuration, the preheating unit <NUM> heats the sheet member P in a non-contact state from the unfixed toner image side. In other words, the preheating unit <NUM> functions as a softening unit that softens an unfixed toner.

Further, in a case of single-sided printing, when heating the sheet member P having the toner image transferred onto the first surface thereof, the preheating unit <NUM> heats the sheet member P so that a temperature of the first surface of the sheet member P is equal to or higher than a softening point of the toner or close to the softening point before the sheet member P is heated by the main heating unit <NUM>.

In the case of double-sided printing, when heating the sheet member P having the toner image transferred onto the second surface thereof, the preheating unit <NUM> heats the sheet member P so that the temperature of the first surface of the sheet member P is lower than the softening point of the toner before the sheet member P is heated by the main heating unit <NUM>.

Here, the "temperature of the first surface of the sheet member P before the sheet member P being heated by the main heating unit <NUM>" is, as will be described later, the temperature of the first surface of the sheet member P at a position S01 separated from an upstream end of a nip portion N of the main heating unit <NUM> in the conveyance direction toward an upstream side in the conveyance direction by <NUM>. That is, when facing the second surface to heat the toner image transferred onto the second surface, the preheating unit <NUM> heats the sheet member P such that the temperature of the first surface at the position S01 is lower than the softening point of the toner. In other words, an output of the preheating unit <NUM> is adjusted such that the temperature of the first surface at the position S01 is lower than the softening point of the toner. Specifically, even when the toner image transferred onto the second surface is a black solid image, the output of the preheating unit <NUM> is adjusted such that the temperature of the first surface at the position S01 is lower than the softening point of the toner.

In the present embodiment, as an example, an output condition of the preheating unit <NUM> under which the temperature of the first surface of the sheet member P is lower than the softening point of the toner is obtained in advance for each paper type or size by a test, and an output table of the preheating unit <NUM> is stored in the control unit <NUM>. Then, the control unit <NUM> adjusts the output of the preheating unit <NUM> based on information of the paper type or size input by a user. Accordingly, the preheating unit <NUM> heats the sheet member P such that the temperature of the first surface of the sheet member P is lower than the softening point of the toner. The temperature of the first surface at the position S01 may be measured by a temperature sensor, and the control unit <NUM> may adjust the output of the preheating unit <NUM> based on a measurement result, thereby heating the sheet member P such that the temperature of the first surface of the sheet member P is lower than the softening point of the toner.

Here, "the softening point of the toner (= glass transition temperature of the toner)" is a <NUM>/<NUM> descent rate measured under conditions of a die pore diameter of <NUM>, a pressure load of <NUM> MPa, and a temperature increase rate of <NUM>/min in a temperature increase test using a flow tester (CFT500, manufactured by Shimadzu Corporation). Note that the <NUM>/<NUM> descent rate is a temperature corresponding to <NUM>/<NUM> of a height obtained from an outflow start point to an end point when a toner sample is melted and flowed out.

As illustrated in <FIG>, the blowing unit <NUM> is disposed so as to face the preheating unit <NUM> in the vertical direction, and the sheet member P being conveyed passes between the blowing unit <NUM> and the preheating unit <NUM>. The blowing unit <NUM> includes plural fans <NUM> arranged in the device width direction and the device depth direction. The fan <NUM> is an example of a blowing unit.

In this configuration, when the plural fans <NUM> blow air toward the sheet member P passing between the blowing unit <NUM> and the preheating unit <NUM>, the conveyance posture of the sheet member P conveyed with the leading end portion thereof being held is stabilized. The fan <NUM> is an example of a stabilizing unit.

Here, "the conveyance posture of the sheet member P is stabilized" means that a distance from a rear end portion of the sheet member in a state of being bent by gravity to the preheating unit <NUM> is smaller than when the stabilizing unit is not provided. It is preferable that a distance from the sheet surface of the sheet member P to the preheating unit <NUM> is longer than a distance from the preheating unit <NUM> to the gripper <NUM>, and that variation in the distance to the preheating unit <NUM> depending on a position of the sheet surface is suppressed. In other words, the distance from the sheet surface of the sheet member P to the preheating unit <NUM> is preferably longer than the distance from the preheating unit <NUM> to the gripper <NUM>, and a difference between a longest distance from the sheet surface of the sheet member P to the preheating unit <NUM> and a shortest distance is preferably reduced. Here, an output of the fan <NUM> may be adjusted. In the present embodiment, as an example, an output condition of the fan <NUM> is obtained for each paper type or size, and an output table of the fan <NUM> is stored in the control unit <NUM>. Then, the control unit <NUM> adjusts the output of the fan <NUM> based on the information of the paper type or size input by the user. For example, when a paper thickness input by the user is larger than a predetermined value or a size is larger than a predetermined value, the output of the fan is increased. The distance from the sheet surface of the sheet member P to the preheating unit <NUM> may be measured by an optical sensor, and the control unit <NUM> may adjust the output of the fan <NUM> based on a measurement result thereof.

Further, when the plural fans <NUM> blow air toward the sheet member P, the temperature of the sheet surface of the sheet member P on a side to which the air is blown decreases. In this way, the fan <NUM> functions as a temperature reducing unit.

As illustrated in <FIG>, the main heating unit <NUM> is disposed downstream of the preheating unit <NUM> in the conveyance direction of the sheet member P. The main heating unit <NUM> includes a heating roll <NUM> that comes into contact with the sheet member P being conveyed to heat the sheet member P, a pressing roll <NUM> that presses the sheet member P toward the heating roll <NUM>, and a driven roll <NUM> that is driven to rotate by the rotating heating roll <NUM>.

As illustrated in <FIG>, the heating roll <NUM> is disposed so as to come into contact with a surface facing upward of the sheet member P being conveyed and extend in the device depth direction with an axial direction thereof serving as the device depth direction. The heating roll <NUM> includes a cylindrical base member <NUM>, a rubber layer <NUM> formed so as to cover an entire circumference of the base member <NUM>, a release layer <NUM> formed so as to cover an entire circumference of the rubber layer <NUM>, and a heater <NUM> accommodated in the base member <NUM>. An outer diameter of an outer circumferential surface of the release layer <NUM> of the heating roll <NUM> is, for example, <NUM>.

The base member <NUM> is an aluminum tube and has a thickness of <NUM>, for example. The rubber layer <NUM> is made of silicone rubber, and has a thickness of <NUM>, for example. Further, the release layer <NUM> is made of a copolymer of tetrafluoroethylene and perfluoroethylene (PFA resin), and has a thickness of <NUM>, for example.

As illustrated in <FIG>, shaft portions 139a extending in the device depth direction are formed at both end portions of the heating roll <NUM> respectively in the device depth direction. Each shaft portion 139a is supported by a support member 139b. The heating roll <NUM> is rotatably supported by support members 139b at both end portions of the heating roll <NUM>.

As illustrated in <FIG> and <FIG>, the driven roll <NUM> is disposed so as to extend in the device depth direction with an axial direction thereof serving as the device depth direction, on an opposite side of the heating roll <NUM> than the sheet member P being conveyed. The driven roll <NUM> includes a cylindrical base member <NUM> and a heater <NUM> accommodated in the base member <NUM>. An outer diameter of an outer circumferential surface of the base member <NUM> of the driven roll <NUM> is, for example, <NUM>.

The base member <NUM> is an aluminum tube and has a thickness of <NUM>, for example. The driven roll <NUM> is rotatably supported by a support member (not shown) at both end portions of the driven roll <NUM>.

In this configuration, the driven roll <NUM> is driven to rotate by the heating roll <NUM>. The driven roll <NUM> heats the heating roll <NUM>. As described above, since the heating roll <NUM> is heated by the driven roll <NUM> and the heating roll <NUM> itself has the heater <NUM>, a surface temperature of the heating roll <NUM> becomes a predetermined temperature of <NUM> or higher and <NUM> or lower.

As illustrated in <FIG> and <FIG>, the pressing roll <NUM> is provided on an opposite side of the sheet member P being conveyed than the heating roll <NUM>, and is disposed so as to be in contact with a surface facing downward of the sheet member P being conveyed and extend in the device depth direction with an axial direction thereof serving as the device depth direction. The pressing roll <NUM> includes a cylindrical base member <NUM>, a rubber layer <NUM> formed so as to cover the base member <NUM>, a release layer <NUM> formed so as to cover the rubber layer <NUM>, and a pair of shaft portions <NUM> (see <FIG>) formed at both end portions in the device depth direction. An outer diameter of an outer circumferential surface of the release layer <NUM> of the pressing roll <NUM> is, for example, <NUM>. Thus, an outer diameter of the pressing roll <NUM> is larger than an outer diameter of the heating roll.

The base member <NUM> is an aluminum tube and has a thickness of <NUM>, for example. The rubber layer <NUM> is made of silicone rubber and has a thickness of <NUM>, for example. Further, the release layer <NUM> is made of a copolymer of tetrafluoroethylene and perfluoroethylene (PFA resin), and has a thickness of <NUM>, for example.

A recessed portion 140a extending in the device depth direction is formed in an outer circumferential surface of the pressing roll <NUM>. As illustrated in <FIG>, when the sheet member P passes between the pressing roll <NUM> and the heating roll <NUM>, the gripper <NUM> that grips the leading end portion of the sheet member P is accommodated in the recessed portion 140a.

As illustrated in <FIG>, the pair of shaft portions <NUM> are formed at both end portions of the pressing roll <NUM> in the device depth direction, have a diameter smaller than that of the outer circumferential surface of the release layer <NUM> of the pressing roll <NUM>, and extend in the axial direction.

In this configuration, the pressing roll <NUM> is rotated by a rotational force transmitted from a driving member (not shown). Further, the heating roll <NUM> is driven to rotate by the rotating pressing roll <NUM>, and the driven roll <NUM> is driven to rotate by the rotating heating roll <NUM>. When conveying the sheet member P while sandwiching the sheet member P onto which the toner image is transferred, the heating roll <NUM> and the pressing roll <NUM> fix the toner image onto the sheet member P.

As illustrated in <FIG>, the main heating unit <NUM> includes a support member <NUM> that supports the pressing roll <NUM>, and a biasing member <NUM> that biases the pressing roll <NUM> toward the heating roll <NUM> side via the support member <NUM>.

A pair of support members <NUM> is disposed so as to rotatably support the pair of shaft portions <NUM> of the pressing roll <NUM> from below.

Biasing members <NUM> in a pair are compression springs, and are disposed on an opposite side of the support members <NUM> than the shaft portions <NUM>.

In this configuration, the pair of biasing members <NUM> bias the pressing roll <NUM> toward the heating roll <NUM> side, so that the pressing roll <NUM> presses the sheet member P toward the heating roll <NUM>. Then, as illustrated in <FIG>, a portion of the heating roll <NUM> that is biased by the pressing roll <NUM> is deformed, and the nip portion N that is a region where the heating roll <NUM> and the pressing roll <NUM> are in contact with each other is formed.

Next, an operation of the image forming device <NUM> will be described in comparison with an image forming device <NUM> according to a comparative embodiment. First, with respect to a configuration of the image forming device <NUM> according to the comparative embodiment, portions different from those of the image forming device <NUM> will be described mainly. Note that with respect to an operation of the image forming device <NUM>, portions different from those of the image forming device <NUM> will also be described mainly.

The image forming device <NUM> includes the accommodating portion <NUM>, the discharge portion <NUM>, the image forming unit <NUM>, the conveying mechanism <NUM>, the reversing mechanism <NUM>, a fixing device <NUM>, and the cooling unit <NUM>. As illustrated in <FIG>, the fixing device <NUM> includes a preheating unit <NUM> that heats the sheet member P being conveyed in a state of not being in contact with the sheet member P, and the main heating unit <NUM>.

In this configuration, the preheating unit <NUM> heats the sheet member P in a non-contact state from an unfixed toner image side. In the case of double-sided printing, before the main heating unit <NUM> heats the sheet member P, the temperature of the first surface of the sheet member P is equal to or higher than the softening point of the toner since the preheating unit <NUM> heats the sheet member P having a toner image transferred onto the second surface thereof.

In the image forming device <NUM> illustrated in <FIG>, the conveying mechanism <NUM> conveys the sheet member P to the secondary transfer position NT, and at the secondary transfer position NT, the transfer belt <NUM> and the facing roll <NUM> convey the sheet member P while sandwiching the sheet member P. Accordingly, a toner image on a front surface of the transfer belt <NUM> is transferred onto the first surface (= front surface) of the sheet member P.

Thereafter, while the conveying mechanism <NUM> conveys the sheet member P with both sheet surfaces thereof facing in the vertical direction, the preheating units <NUM> and <NUM> illustrated in <FIG> and <FIG> heat the sheet member P in a non-contact state from the first surface side (= unfixed toner image side) of the sheet member P being conveyed by the conveying mechanism <NUM>. When the preheating unit <NUM> illustrated in <FIG> heats the sheet member P, the fan <NUM> blows air toward the second surface (= back surface) of the sheet member P. Accordingly, the conveyance posture of the sheet member P in a state of being heated by the preheating unit <NUM> is stabilized.

Further, the main heating units <NUM> illustrated in <FIG> and <FIG> fix the toner image onto the first surface of the sheet member P when the sheet member P is conveyed in a sandwiched manner by the heating roll <NUM> and the pressing roll <NUM>. In addition, the reversing mechanism <NUM> receives the sheet member P having the toner image fixed onto the first surface thereof from the main heating unit <NUM>, conveys the sheet member P, and reverses the front and back of the sheet member P. Further, the conveying mechanism <NUM> receives the sheet member P whose front and back are reversed from the reversing mechanism <NUM> and conveys the sheet member P.

The conveying mechanism <NUM> conveys the sheet member P again to the secondary transfer position NT, and at the secondary transfer position NT, the transfer belt <NUM> and the facing roll <NUM> convey the sheet member P while sandwiching the sheet member P. Accordingly, a toner image on the front surface of the transfer belt <NUM> is transferred onto the second surface (= back surface) of the sheet member P.

Thereafter, while the conveying mechanism <NUM> conveys the sheet member P with both sheet surfaces thereof facing in the vertical direction, the preheating units <NUM> and <NUM> heat the sheet member P in a non-contact state from the second surface side (= unfixed toner image side) of the sheet member P being conveyed by the conveying mechanism <NUM>. When the preheating unit <NUM> illustrated in <FIG> heats the sheet member P, the fan <NUM> of the blowing unit <NUM> blows air toward the first surface (= front surface) of the sheet member P. Accordingly, a posture of the sheet member P in a state of being heated by the preheating units <NUM> and <NUM> is stabilized.

When the preheating units <NUM> and <NUM> heat the sheet member P having the image transferred onto the second surface thereof, the conveying mechanism <NUM> conveys the sheet member P with an image forming region on the first surface of the sheet member P in a state of not being in contact with other members.

Further, the main heating unit <NUM> fixes the toner image onto the second surface of the sheet member P when the sheet member P is conveyed in a sandwiched manner by the heating roll <NUM> and the pressing roll <NUM>. In this way, the toner image on the first surface is sandwiched twice by the heating roll <NUM> and the pressing roll <NUM>. In addition, the cooling unit <NUM> cools the sheet member P having the toner images fixed onto both surfaces thereof, and discharges the sheet member P to the discharge portion <NUM>.

Here, before the main heating unit <NUM> heats the sheet member P, the temperature of the first surface of the sheet member P becomes equal to or higher than the softening point of the toner since the sheet member P having the toner image transferred onto the second surface thereof is heated by the preheating unit <NUM> illustrated in <FIG>. In other words, since the preheating unit <NUM> heats the sheet member P having the toner image transferred onto the second surface thereof, the temperature of the first surface at the position S01 illustrated in <FIG> becomes equal to or higher than the softening point of the toner. As described above, when the temperature of the first surface at the position S01 is equal to or higher than the softening point of the toner, the sheet member P is heated by the main heating unit <NUM> in a state where the temperature of the first surface is equal to or higher than the softening point of the toner.

In contrast, when heating the sheet member P having the toner image transferred onto the second surface thereof, the preheating unit <NUM> illustrated in <FIG> heats the sheet member P so that the temperature of the first surface of the sheet member P is lower than the softening point of the toner before the sheet member P is heated by the main heating unit <NUM>. In other words, when heating the toner image transferred onto the second surface, the preheating unit <NUM> heats the sheet member P such that the temperature of the first surface at the position S01 illustrated in <FIG> is lower than the softening point of the toner. As described above, since the temperature of the first surface at the position S01 is lower than the softening point of the toner, the sheet member P is heated by the main heating unit <NUM> in a state where the temperature of the first surface is lower than the softening point of the toner.

Next, since the glossiness (= gloss) of the toner images output by the image forming devices <NUM> and <NUM> is evaluated, this evaluation will be described. Specifically, toner images were formed on both surfaces of the sheet member P, and a difference between the glossiness of the first surface and the glossiness of the second surface was evaluated. In this evaluation, a toner having a softening point temperature of <NUM> was used.

The details other than those described above were all similar to each other.

As the sheet member P, an OS coated paper of A4 size (manufactured by Fuji Xerox Co. , basis weight: <NUM>/m<NUM>) was used. Then, a black solid image (an image of <NUM>% black area coverage) was formed on both surfaces of the sheet member P.

The surface temperature of the heating roll <NUM> was set to <NUM>, and pressure at the nip portion N where the heating roll <NUM> and the pressing roll <NUM> were in contact with each other was set to <NUM> KPa.

The difference (= gloss difference) between the glossiness of the first surface and the glossiness of the second surface of the sheet member P, which was output, was evaluated. The glossiness was evaluated using a gloss meter (AG-<NUM> manufactured by BYK-Gardner). Specifically, this gloss meter was used to perform measurement at an incident angle of <NUM> degrees in a specular gloss measurement method (JIS Z <NUM>), and a measured value was defined as the glossiness.

When a difference between glossiness of a toner image on a first surface and glossiness of a toner image on a second surface is large even though the toner images are formed by the same image forming device, a user feels uncomfortable. In this evaluation, when the difference between the glossiness of the toner image on the first surface and the glossiness of the toner image on the second surface is <NUM> or less, it is considered that the user does not feel uncomfortable, and the evaluation is "good"; when the difference between the glossiness of the toner image on the first surface and the glossiness of the toner image on the second surface is larger than <NUM>, the evaluation is "poor".

The evaluation results are shown in a table of <FIG>. As shown in the table of <FIG>, in Examples <NUM> to <NUM> in which the temperature of the first surface was lower than the softening point of the toner, the evaluation result was "good". In contrast, in Comparative Examples <NUM> to <NUM> in which the temperature of the first surface was equal to or higher than the softening point of the toner, the evaluation result was "poor".

In the case of double-sided printing, the toner image on the first surface is sandwiched twice by the heating roll <NUM> and the pressing roll <NUM>, and the toner image on the second surface is sandwiched once by the heating roll <NUM> and the pressing roll <NUM>.

Here, in Comparative Examples <NUM> to <NUM>, the temperature of the first surface at the position S01 is equal to or higher than the softening point of the toner. Therefore, when the toner image formed on the first surface is sandwiched by the heating roll <NUM> and the pressing roll <NUM> for the second time, surface roughness of a surface of the toner image is reduced than that in a case where the toner image is sandwiched only once, and the glossiness is improved.

On the other hand, in Examples <NUM> to <NUM>, the temperature of the first surface at the position S01 is lower than the softening point of the toner. Therefore, when the toner image formed on the first surface is sandwiched by the heating roll <NUM> and the pressing roll <NUM> for the second time, the occurrence that the surface roughness of the surface of the toner image is reduced and the glossiness is improved is suppressed.

Therefore, as shown in the table of <FIG>, in Comparative Examples <NUM> to <NUM>, the difference between the glossiness of the first surface and the glossiness of the second surface was large, and the evaluation result was considered to be "poor". On the other hand, in Examples <NUM> to <NUM>, the difference between the glossiness of the first surface and the glossiness of the second surface was small and the evaluation result was considered to be "good".

As described above, when heating the sheet member P having the toner image transferred onto the second surface thereof, the preheating unit <NUM> heats the sheet member P so that the temperature of the first surface of the sheet member P is lower than the softening point of the toner before the sheet member P is heated by the main heating unit <NUM>. Therefore, as seen from the evaluation results described above, the difference between the glossiness of the toner image on the first surface and the glossiness of the toner image on the second surface is smaller than that in the case of using the image forming device <NUM> according to the comparative embodiment.

The preheating unit <NUM> heats the sheet member P in a non-contact state from the unfixed toner image side. That is, when heating the sheet member P having the toner image transferred onto the second surface thereof, the preheating unit <NUM> heats the sheet member P from the second surface side. Therefore, the temperature of the second surface of the sheet member P onto which the unfixed toner image is transferred is higher than the temperature of the first surface of the sheet member P onto which the toner image is fixed.

In addition, since the temperature of the second surface of the sheet member P onto which the unfixed toner image is transferred is higher than the temperature of the first surface, the glossiness of the toner image on the second surface is improved as compared with a case where the temperature of the second surface is lower than the temperature of the first surface.

When the sheet member P is to be heated by the preheating unit <NUM>, the conveying mechanism <NUM> conveys the sheet member P with the sheet surface thereof facing in the vertical direction. Further, the preheating unit <NUM> heats the sheet member P from above the sheet member, and the fan <NUM> blows air to the sheet member P from below the sheet member P. As described above, when the sheet member P having the toner image transferred onto the second surface thereof is heated by the preheating unit <NUM>, the fan <NUM> blows air to the sheet member P from the first surface side of the sheet member P. Therefore, the temperature of the first surface is easily lower than the softening point of the toner, as compared with a case where air on the first surface side is stagnant.

When the sheet member P is to be heated by the preheating unit <NUM>, the conveying mechanism <NUM> conveys the sheet member P with the sheet surface thereof facing in the vertical direction. Further, the preheating unit <NUM> heats the sheet member P from above the sheet member, and the fan <NUM> blows air to the sheet member P from below the sheet member P. Therefore, the conveyance posture of the sheet member P being conveyed is stabilized as compared with a case where the sheet member P is conveyed in a state of being bent by gravity.

In addition, since the conveyance posture of the sheet member P is stabilized, a temperature of the rear end portion of the sheet member P is prevented from being lower than a temperature of the leading end portion of the sheet member P as compared with a case where the sheet member P is conveyed in a state of being bent by gravity.

When the preheating unit <NUM> heats the sheet member P having the image transferred onto the second surface thereof, the conveying mechanism <NUM> conveys the sheet member P with the image forming region on the first surface of the sheet member P in a state of not being in contact with other members. Therefore, as compared with a case where the image forming region on the first surface of the sheet member P is in contact with another member, occurrence of a difference in temperature in one sheet member P is suppressed, and thus a difference in glossiness of the toner image formed on the first surface of the sheet member P occurs.

When the sheet member P is to be heated by the preheating unit <NUM>, the conveying mechanism <NUM> conveys the sheet member P with the sheet surface thereof facing in the vertical direction. In addition, the preheating unit <NUM> heats the sheet member P from above the sheet member. Therefore, as compared with a case where the conveying mechanism conveys the sheet member P with the sheet surface thereof being directed in a horizontal direction and the preheating unit heats the sheet member P from the horizontal direction, hot air generated by the preheating unit is suppressed from rising and escaping from between the sheet member P and the preheating unit.

Although the present invention is described in detail with reference to specific embodiments, it is apparent to those skilled in the art that the present invention is not limited to the embodiments, and various other embodiments can be taken within the scope of the present invention. For example, in the above-described embodiment, the preheating unit <NUM> heats the sheet member P from the unfixed toner image side in a non-contact state, and alternatively, the preheating unit may heat the sheet member P in a state of being in contact with the sheet member P. However, in this case, an effect obtained when the preheating unit <NUM> heats the sheet member P in a non-contact state is not obtained.

Although not particularly described in the above-described embodiment, a temperature detection member may be provided at the position S01, and the output of the preheating unit <NUM> may be adjusted based on a detection result thereof.

Although not particularly described in the above-described embodiment, a cooling member may be provided that cools the first surface of the sheet member P before the toner image is fixed onto the second surface by the main heating unit <NUM>.

In the above-described embodiment, when the preheating unit <NUM> heats the sheet member P having the image transferred onto the second surface thereof, the conveying mechanism <NUM> conveys the sheet member P with the image forming region on the first surface of the sheet member P in a state of not being in contact with other members, and alternatively, the image forming region on the first surface may contact with other members. However, in this case, an effect produced by the non-contact state is not produced.

When the temperature of the first surface at the position S01 is lower than the softening point of the toner, the preheating unit <NUM> may cause the temperature of the second surface to be lower than the softening point of the toner, or to be equal to or higher than the softening point of the toner. However, in order to easily fix the toner onto the sheet member P with the main heating unit <NUM>, it is preferable that the temperature of the second surface is equal to or higher than the softening point of the toner.

Claim 1:
An image forming device (<NUM>) comprising:
a transfer unit (<NUM>) configured to transfer a toner image onto a recording medium being conveyed;
a first heating unit (<NUM>) that is arranged downstream of the transfer unit (<NUM>) in a conveyance direction of the recording medium, wherein the first heating unit (<NUM>) is configured to come into contact with the recording medium to heat the recording medium, and fix the toner image onto the recording medium, the first heating unit (<NUM>) comprising a heating roll (<NUM>), which is configured to come into contact with the recording medium being conveyed to heat the recording medium, and a pressing roll (<NUM>), which is provided on a side of the recording medium opposite from the heating roll (<NUM>) and is configured to press the recording medium toward the heating roll (<NUM>);
a reversing unit (<NUM>) configured to reverse front and back of the recording medium having a first toner image fixed onto a first surface of the recording medium by the first heating unit (<NUM>), and send the recording medium to the transfer unit (<NUM>); and
a second heating unit (<NUM>) that is arranged between the transfer unit (<NUM>) and the first heating unit (<NUM>) in the conveyance direction of the recording medium and is configured to heat the recording medium having a second toner image transferred onto a second surface of the recording medium,
wherein the second heating unit is configured to heat the recording medium so that a temperature of the first surface of the recording medium having the first toner image fixed onto it is lower than a softening point of a toner, before the recording medium is heated by the first heating unit (<NUM>), wherein the pressing roll (<NUM>) is configured to come into contact with the first surface of the recording medium when the recording medium having the second toner image transferred onto its second surface is heated by the first heating unit., characterized in that the pressing roll (<NUM>) does not comprise a heater.