JP2024037558A - Heat fixing device and image forming device - Google Patents

Abstract

[Problem] To provide a fixing device capable of suppressing striped gloss unevenness that is likely to occur when printing on media with a large thermal expansion coefficient. [Solution] In the fixing device having a fixing member, a pressure member, a main heating section that presses the pressure member against the fixing member to form a nip, and a preheating device that preheats the media on which an unfixed toner image is placed, the media is primarily composed of a resin with a glass transition temperature Tg, and the toner is preheated until the temperature T of the media becomes Tg<T<Tm before entering the fixing nip, where Tm is the lowest temperature at which the toner can be fixed. [Selected Figure] Figure 5

Description

The present invention relates to an electrophotographic image forming apparatus capable of forming an image on a recording material, such as a multifunction machine, a copying machine, a printer, and a facsimile.

2. Description of the Related Art In image forming apparatuses such as copying machines and printers, when images are formed on media whose main component is resin such as PET, streak-like uneven gloss may occur.

The image forming apparatus disclosed in Patent Document 1 includes a lifting amount detection means for measuring the lifting amount of the sheet material upstream of the nip, and changes the contact pressure between the fixing member and the pressure member according to the lifting amount. This allows the configuration to suppress the occurrence of image defects.

Japanese Patent Application Publication No. 2020-16769

Media (for example, laser peach) whose main component is a resin such as PET has a coefficient of linear expansion that rapidly increases when the temperature exceeds the glass transition temperature, so it expands when heated in the fixing nip. However, since the media is restrained within the nip, a compressive force acts on the media in the thrust direction.

When this compressive force exceeds a threshold value, the media buckles and becomes wavy. When the wavy media comes into contact with the fixing member after leaving the nip, unevenness occurs in the contact pressure between the media and the fixing member, which causes a problem in that streak-like uneven gloss occurs.

SUMMARY OF THE INVENTION An object of the present invention is to provide a heat fixing device and an image forming apparatus that can suppress thermal expansion of resin media within a fixing nip and reduce streaky gloss unevenness.

In order to achieve the above object, the fixing device of the present invention includes a fixing member, a pressure member, a main heating section that forms a nip formed by pressing the pressure member against the fixing member, and a fixing device that removes unfixed toner. In a fixing device having a preheating device for preheating a medium on which an image is placed, the medium is mainly composed of a resin having a glass transition temperature Tg, and the toner has a minimum temperature at which it can be fixed, where Tm is the minimum temperature at which it can be fixed. When a media whose main component is resin is selected in the mode, the preheating means is a fixing device that preheats the media to a temperature T, and the temperature T of the media at this time is Tg<T<Tm. It is characterized by

By implementing the present invention, thermal expansion of the resin media within the fixing nip can be suppressed, and streaky gloss unevenness can be reduced.

FIG. 1 is a schematic diagram of an image forming apparatus in this embodiment. FIG. 2 is a functional block diagram of an image forming apparatus in this embodiment. 1 is a cross-sectional view of an image forming apparatus in this embodiment. FIG. 2 is a diagram showing the temperature dependence of the linear expansion coefficient of PET media. FIG. 3 is a cross-sectional view of the fixing device. FIG. 3 is a relationship diagram between preheating belt temperature and media temperature. FIG. 3 is a relationship diagram between fixing roller temperature and gloss value. 3 is a sectional view of a fixing device in Example 2. FIG.

Next, specific examples (examples) of embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited to the following examples.

<Image forming device>
Referring to FIG. 1, a multi-function peripheral (hereinafter referred to as MFP) 100, which is an example of an image forming apparatus according to the present embodiment, will be described. The MFP 100 includes an operation unit 300 that is operated by a user to change settings or execute a job, a scanner unit 310 that reads the current image, and a printer unit 320 that forms an image on paper.

The scanner unit 310 shines illumination light onto a document placed on a platen glass, scans the reflected light from the document with a CCD line sensor, and converts the image of the document into image data. The color and size of the original image are determined based on the converted image data, and an image is formed on the medium P by the printer section 320 based on the image data. An example of the media P is paper or label paper.

FIG. 2 is a schematic block diagram showing the configuration of functional blocks of the multifunction device 100. The multifunction device 100 includes a control section 200, an operation section 300, a printer section 320, an image reading section 330, a CPU 210, a ROM 220, and a DRAM 230. Each functional unit is connected to enable data communication. The control unit 200 controls each connected functional unit. The ROM 220 stores various control programs necessary for the operation of the control unit 200, such as programs for controlling image forming processing and image erasing processing. The CPU 210 performs various calculation processes based on control programs and information stored in the ROM 220. The DRAM 230 is used as a temporary data storage area when the control unit 200 executes a program. The operation unit 300 includes, for example, a liquid crystal display unit having a plurality of buttons. The operation unit 300 receives a user's operation and outputs a signal corresponding to the performed operation to the control unit of the multifunction device 100.

The printer section 320 includes a transport section, an image forming section, a transfer section, and a fixing section. The printer section 320 will be explained with reference to FIG. FIG. 3 is a cross-sectional view of the printer section 320, and is a cross-sectional view taken along the conveyance direction of the media P. The printer section 320 includes an image forming section 10 for each color of non-erasable toner Y (yellow), M (magenta), C (cyan), Bk (black) and erasable toner Bl (blue). . Although it is a color electrophotographic method, if the media P is reused, a monochrome image will be obtained using only the color erasing toner Bl.

The printer of this embodiment executes image forming processing and image erasing processing. In the image forming process, the photosensitive drum 11 is charged in advance by a charger 12. Thereafter, a latent image is formed on the photosensitive drum 11 by a laser scanner 13. The latent image is turned into a toner image by the developing device 15. The toner images on the photosensitive drum 11 are sequentially transferred by a primary transfer blade 16 onto an image carrier, for example, an intermediate transfer belt 17 . After the transfer, the toner remaining on the photosensitive drum 11 is removed by the cleaner 14. As a result, the surface of the photosensitive drum 11 becomes clean and ready for the next image formation.

On the other hand, the media P is fed out one by one from the paper feed cassette 18 or the multi-sheet feed tray 19 and fed into the pair of registration rollers 20 . The registration roller pair 20 once receives the media P and straightens the media P if it is skewed. Then, the registration roller pair 20 feeds the medium P between the intermediate transfer belt 17 and the secondary transfer roller 21 in synchronization with the toner image on the intermediate transfer belt 17 .

The color toner image on the intermediate transfer belt is transferred to the medium P by a transfer body, for example, a secondary transfer roller 21. Thereafter, the toner image on the medium P is fixed in the fixing device 30 and is ejected.

<Waterproof paper>
In this example, a case will be described in which a waterproof paper (trade name: Laser Peach, model number: WEFY-120, thickness: 120 um) whose main component is PET is used as the media P.

Laser Peach has a PET base coated with a coating to improve printing performance. A characteristic of PET media is that it has a much higher expansion rate than pulp.

FIG. 4 shows the temperature dependence of the linear expansion coefficient of PET. The coefficient of linear expansion of PET increases significantly from around 60°C. The glass transition temperature (referred to as Tg) of PET is around 70°C, and the phase transition from a glass state to a rubber state significantly increases the linear expansion coefficient.

The coefficient of linear expansion of pulp is about 10 ppm/°C, whereas the coefficient of linear expansion of PET is 200 ppm/°C at around 90°C.

<Fixing device>
Next, the fixing device 30 will be explained.

FIG. 5 shows an outline of this fixing device. The fixing device 30 includes two heating sections: a preheating section 40 and a main heating section 50. First, the preheating section 40 will be explained.

The heat source 41 is a heating source that emits infrared light. As the type of heat source 41, a halogen heater, a carbon heater, a ceramic heater, or the like can be used.

The halogen heater is connected to a power source (not shown), and when 100V is applied, for example, it emits infrared rays with a power of 1000W.

The heating roller 42 is a hollow metal roller made of aluminum or the like, and is heated by radiation from the heat source 41. The two heating rollers are supported by a support member (not shown).

The temperature detection means 43 detects the temperature of the heating roller 42. The power supply duty to the heat source 41 is controlled so that the temperature of the temperature detection means 43 becomes the target temperature.

The temperature control temperature may be determined based on the target temperature for media preheating, and is set to, for example, 90°C.

The tension roller 44 is a metal roller that stretches the preheating belt 45. In this embodiment, two heating rollers and two tensioning rollers 44 apply tension to the preheating belt.

Further, torque is applied to the tension roller by a driving means (not shown), and the preheating belt rotates at a predetermined speed.

The preheating belt 45 is a belt made of resin such as polyimide, and is heated by the heating roller 42 . The preheating belt 45 is configured to come into contact with the media and warm it from the back side before the media enters the main heating section 50.

(Main heating section)
As shown in FIG. 5, the media P preheated in the preheating section 40 passes through the main heating section 50, and the toner is heated and pressurized and fixed on the media.

In this embodiment, the main heating section 50 employs a heat roller system. A heating nip N is formed by the fixing roller 51 and the pressure roller 52, and the heat of the fixing roller 51 heated by the heat source 53 is applied to the toner to perform fixing.

For example, a halogen heater can be used as the heat source 53. The halogen heater is capable of outputting 1000W at a rated voltage of 100V. The fixing roller 51 is warmed from the inside by the halogen heater, and the fixing roller surface temperature is maintained at a temperature that allows fixing according to the selected media type and preheating temperature.

(Print operation)
The operation of the fixing device will be described when an actual printing operation is performed.

The medium P carrying the toner image passes through a preheating section 40 and a main heating section 50, and a toner image is formed thereon.

The degree to which the preheating section 40 is heated can be changed depending on the paper type selected at the time of printing.

If plain paper is selected, there is no need to preheat, so the printing operation is performed with the heat source 41 turned off.

When a resin media that tends to cause streaky uneven gloss, such as waterproof paper or an OHP sheet, is selected, preheating is performed. Electric power is applied to the heat source 41, and the preheating belt 45 is heated via the heating roller 42, and the temperature is controlled to a predetermined temperature.

In this embodiment, a case will be described in which a waterproof paper laser peach (thickness 120 um) is printed. As experimental conditions, printing was performed at a productivity of 30 ppm and a process speed of 130 mm/s, and the presence or absence of streak-like gloss unevenness was examined.

Comparative Example 1 is a case where preheating is not performed, Comparative Examples 2 and 3, and Example 1 are cases where preheating is performed, and the preheating temperature of the media is different. Table 1 summarizes the experimental conditions.

The preheat belt temperature can be varied depending on the target media temperature. The relationship between the preheating belt temperature and the media temperature before entering the fixing section 50 was measured in a preliminary experiment, and the relationship is shown in FIG.

In addition, in this experiment, the fixing roller temperature was changed according to the media temperature in order to compare the streaky gloss unevenness under conditions where the gloss was uniform. A preliminary experiment was conducted on the fixing roller temperature vs. gloss when the media temperature was different, and the relationship is shown in FIG. In this experiment, the comparison was made under conditions such that the 60° gloss was 20.

(Striped gloss unevenness experiment)
Under the experimental conditions shown in Table 1, an image was placed on the media and a paper feeding experiment was conducted to examine the occurrence of streaky gloss unevenness. Table 2 shows the results of ranking the samples for streaky gloss unevenness.

In Comparative Example 1, fixing was performed using a conventional method without preheating, and the rank was 1.

In Comparative Example 2, preheating was performed and main fixing 50 was started with the media temperature at 45° C., but the rank was 1. Since the coefficient of linear expansion is low at a temperature lower than the glass transition temperature, the media cannot be expanded in advance by preheating, and the effect of suppressing uneven gloss cannot be obtained.

In Comparative Example 3, when the media was preheated to 65° C. and entered into the main fixing step 50, the streaky gloss unevenness was ranked 2.

When the media is preheated to 65° C., it is possible to enter the main fixing 50 with the media already expanded, so that expansion of the media can be suppressed during the main fixing. However, the effect was insufficient and the streaky gloss unevenness rank was 2.

When the present invention is implemented (Example 1), if the media is preheated to 80°C, the media can be entered into the main fixing 50 in a more expanded state than in Comparative Example 3. can be suppressed.

At this time, the streaky gloss unevenness rank was 3, and almost no streaky gloss unevenness was observed.

In this way, by preheating the media to Tg or higher, streaky uneven gloss can be suppressed.

Note that if the media is preheated to a temperature higher than the minimum temperature at which toner can be fixed (referred to as Tm), the toner will begin to melt and spread on the media before entering the fixing nip, resulting in gloss that is not caused by media expansion. Unevenness occurs.

Therefore, by setting the preheating temperature T to Tg<T<Tm, uneven gloss can be suppressed.

<Example 2>
In Example 1, an example was described in which the media is heated from the back side via a heated preheating belt as the media preheating means.

The preheating means may be a non-contact heating means.

As shown in FIG. 8, a preheating means using radiation such as a halogen heater may be provided before entering the fixing section. The reflecting plate 45 is configured to reflect radiant heat from the heat source 41 and radiate infrared rays toward the medium P.

An advantage of non-contact heating is that there is no need to preheat the preheating belt 44 as in the first embodiment, and the waiting time is reduced.

10 Image forming section 11 Photosensitive drum 12 Charger 13 Laser scanner 14 Cleaner 15 Developing device 16 Primary transfer blade 17 Intermediate transfer belt 18 Paper feed cassette 19 Multi-sheet feed tray 20 Registration roller pair 21 Secondary transfer roller 30 Fixing device 40 Preheating Section 50 Main heating section P Media N Nip

Claims (3)

A fixing device that includes a fixing member, a pressure member, a main heating unit that forms a nip by pressing the pressure member against the fixing member, and a preheating device that preheats a medium on which an unfixed toner image is placed. In the device,
The media has a resin having a glass transition temperature Tg as a main component,
The fixing device is a fixing device in which the preheating means preheats the media to a temperature T when a medium containing resin as a main component is selected in the print mode, where the minimum temperature at which the toner can be fixed is Tm, A fixing device characterized in that the temperature T of the media at this time satisfies Tg<T<Tm. The fixing device according to claim 1, further comprising a heat source inside a conveyor belt for conveying the media before entering the main heating, and preheating the media via the conveyor belt heated by the heat source. . The fixing device according to claim 1, wherein the preheating means heats the toner surface of the medium in a non-contact manner.

Images