JPH0820816B2 - Fixing method - Google Patents

Description

The present invention is used in the field of fixing technology, and particularly in an image forming apparatus using a toner, a support on which a toner image is formed is nip-conveyed and fixed. Regarding the fixing method to be performed.

(Prior Art) Conventionally, in an electrophotographic apparatus using a dry toner,
Thermal fixing devices and pressure fixing devices are used as fixing devices. Three types of oven fixing, heat roll fixing and flash fixing are mainly used for the heat fixing device, but all three types are sufficiently melted by heating the resin that constitutes the toner, and the toner is fixed to the support, that is, the transfer material. Adhesion is secured.

On the other hand, the pressure fixing device is based on a fixing method that does not use heat energy. In the case of this pressure fixing method, a toner made of a soft resin at room temperature is used.
The pressure is applied to the transfer material at a pressure of up to 200 Kg / Cm ^2, the toner is deformed by the pressure, and the toner is entangled in the transfer material, especially the fibers of the paper to obtain the adhesion.

(Problems to be solved) However, in the case of the fixing by the former thermal fixing device,
There is a problem that a large amount of heat energy is required to obtain good fixability.

That is, in the case of this heat fixing, since the toner is heated and melted to perform the fixing, when the heating amount is small and the toner is not melted uniformly, not only the adhesion of the toner to the transfer material is deteriorated but also the toner is There is a problem that the adhesive force between the rolls also decreases, resulting in unfixing. Further, when the heat roll fixing method is used, insufficient heating causes an offset phenomenon that unfixed toner adheres to the roll. Therefore, in the heat fixing method, it is usually necessary to use heat energy sufficient to make the temperature of the toner itself to be the melting point or softening point of all the resins constituting the toner or higher.
This is because even if the resin of the toner to be used is heated to a temperature near the softening point, the fluidity does not increase, and the fluidity is obtained only when heated above this temperature.

On the other hand, in the case of pressure fixing by the latter pressure fixing device,
There are problems in terms of fixability and writability after fixation.

That is, in this case, fixing is performed by pressure, and in this case, the fixed toner is in the form of flakes although it is deformed, whereas the toner at the time of heat fixing is not in the original shape but is melted. It's just Therefore, the adhesion of the toner to the transfer material and the adhesion between the toners are small, the fixability is poor as compared with the above-mentioned thermal fixing method, the toner is peeled off by bending the paper, and the high pressure as described above is used. When applied to a transfer material composed of paper fibers, the paper has gloss, and the writability after fixing deteriorates. Furthermore, since the toner itself is made of a soft resin (for example, polyethylene), it is difficult to use this toner for high-speed development, because the phenomenon that the toner adheres to the inside of the developing device when a high load is applied during development. It was From the above, up to now, a fixing method satisfying the fixing property and saving energy has not been developed.

(Means for Solving Problems) The present invention solves the problems as described above, and enables fixing property equivalent to that of heat fixing without using much heat energy as compared with the conventional heat fixing method. The recording paper carrying the unfixed toner is nipped and conveyed by a pair of rotating bodies that are in pressure contact with each other and set to a temperature below the softening point of the toner and fixed under pressure and heating. In the fixing method, the toner on the paper fibers among the toner on the recording paper is softened by the pressure and heat, and the toner between the paper fibers is softened by the pressure and the heat and is connected by the toner on the melted paper fiber. It is also characterized in that the toner is fixed on the recording paper.

(Example) Hereinafter, an example of the present invention will be described. The system for forming a toner image used in the present invention is used in a known electrophotographic apparatus and electrostatic recording apparatus. An electrostatic image formed by a known method is developed with a dry toner powder, and further, This is transferred electrostatically or with a light pressure to a sheet-shaped transfer material as a support mainly composed of a desired paper. This toner image is T shown in FIG. 1, and the transfer material is P. The transfer material P having the toner image T is nipped and conveyed by a roller (pressurizing roller) 13 and a roller (fixing roller) 14 which are in pressure contact with each other in the fixing device 11, and heat supplied by a heater 20 inside the roller 14. The toner image T is fixed on the transfer material P by the pressing force.

In FIG. 1, 15 is a separation claw, 16 is a pressure spring, and 18 is a temperature sensor.

For fixing to the transfer material P, a pair of rollers 13 and 14 are pressed against each other,
When a transfer material having a toner image on its surface is nipped and conveyed between the pair of rollers to fix the toner on the transfer material, a pressure exceeding the elastic limit of the transfer material is applied and at the same time, a slight amount of toner is applied to the toner. By applying heat, a part of the toner is made to have thermal fluidity, and thereby adhesion between the toners and between the toner and the transfer material is imparted.

Hereinafter, the toner and roller materials used in the present invention, and various conditions such as pressure and heat will be described in detail.

First, the toner used in the present invention desirably has both heat fixing characteristics and pressure fixing characteristics.
A toner having a strong pressure fixing property is not preferable due to problems in development stability and toner preparation, as described in the description of the conventional example. Desirably, a soft material such as wax having a pressure fixing property is applied to a resin having a heat fixing property (see Experimental Examples 1 and 2 described later) to achieve the object. That is, it is achieved by a toner in which a high softening temperature resin is mixed with a low softening point wax. Further, the wax will be described in detail. It is desirable that the wax has a sharp melt property in which the fluidity rapidly increases when heated to a certain temperature. As a preparation method, this wax and the above-mentioned resin having heat fixing property are kneaded by a known method, or a monomer obtained by mixing the above-mentioned resin monomer and the wax and polymerizing the monomer is pulverized. Alternatively, a method of obtaining the toner by polarization may be used. Further, a magnetic powder may be mixed with the toner if necessary. The melting point of the wax used here is selected depending on the speed of the fixing device in the electrophotographic device to be used, the surface temperature of the roller 14 and the contact width with the roller 13.

Next, regarding the mixing ratio, this also changes depending on the resin that should be used. However, when the resin is 1, and the wax is mixed three times or more with respect to this, the above-mentioned pressure fixing property is strongly generated. This is not preferable because the toner itself becomes soft and the phenomenon characteristics deteriorate, and a blocking phenomenon occurs. Further, if the amount of wax is 30% or less, the adhesion between toner and toner fibers becomes weak, which is not preferable. Preferably, when the resin is 1, the wax content is 2 times or less to 0.4 or more. However, in the case of a resin such as Versamide 725 (manufactured by Nippon Henkel Co., Ltd., polyamide) that has sharp melt characteristics when pressure is applied to the above-mentioned mixed system, in the case of mixing the resin and wax as described above, etc. Alternatively, the resin such as Versamide 725 can be used alone (see Experimental Example 3 described later).

Next, the roller material will be described in detail. The roller 13 is made of a high-rigidity rod such as iron and a cylinder on which heat-resistant rubber such as silicon rubber and fluororubber is formed to a thickness of 0.5 to 2 mm. It is desirable that the transfer material has sufficient hardness in order to prevent unnecessary heat energy from being applied to the transfer material. For this reason, amorphous silica, crystalline silica, carbon powder or the like may be kneaded and used in the rubber. However, the rubber hardness and the wall thickness of the rubber depend on the fixing speed, the contact width of the roll pair, and the surface temperature of the roll 14, and when the sharp melt wax contained in the toner or the itself has a sharp melt property, the sharp melt wax is used. It may be set so that the toner temperature reaches the temperature.

In addition to the above rubber-based materials, ethylene / acrylic elastomers such as Baymac [made by DuPont] and heat-resistant resins such as polyamide, polyamideimide, epoxy, and polyethersulfone are used. Further, as the polyamide material, it is also possible to use a material obtained by processing an aromatic polyamide into a fibrous form and having a paper structure (Nomex [manufactured by DuPont]) in a roll form and compressing it.

The roll 14 is a cylinder made of aluminum or stainless steel with a fluororesin baked on it. Further, a heat source 20 such as a halogen lamp is installed inside the roll 14 to raise the surface of the roll 14 to the above-mentioned fixing temperature. The temperature of the surface of the roll 14 is adjusted by the temperature sensor 18.

At least one of the pair of rollers 13 and 14 (roller 14 in this case) may be heated.

Next, regarding the pressure to be applied, it is necessary that the toner particles are sufficiently brought into close contact with the paper and other toner particles at the time of fixing, and that the wax in the toner particles needs to be provided with sufficient heat so as to have sufficient fluidity. is there. Therefore, when the nip width (contact width of the roller pair) is as wide as 2 to 4 mm, the necessary pressure is applied until the elasticity of the transfer material used disappears.
The adhesion of the toner should be increased. For example, in the case of a paper having a thickness of about 80 μm, it is sufficient to apply a pressure of 25-40 Kg / Cm ² .
Further, when the nip width is narrow, for example, 1 to 1.5 mm, it is necessary to sufficiently deform the toner itself because heat is not sufficiently transferred due to the thickness of the toner layer at a low pressure as described above.
A pressure of 70 Kg / Cm ² is required. However, like pressure fixing,
When a pressure of 150 to 200 Kg / Cm ² is applied, the paper plastically deforms, the surface becomes glossy, and the writability of the paper after fixing is deteriorated.

By constructing the present invention as described above, the following fixing properties were tested and the effects thereof were confirmed.

As described above, for example, when a transfer material having a toner image made of a high softening point resin having sharp melt wax inside is applied to a fixing device by the fixing method according to the present invention, first,
When the paper is pressed to the elastic deformation limit or more by the pressure, the contact between the rollers 13 on the fiber of the paper, the adhesion between the toner and the toner and the transfer material is increased, and the toner is slightly deformed. Here, by applying sufficient heat to melt the wax of the toner, the wax is melted out, and the wax is also eluted into the toner other than the above-mentioned fiber, and the adhesive force is imparted to the toners without pressure. , Fixing of the entire image is completed.

In this way, under pressure heating, carrying by pinching,
Among the toners on the transfer material, those on the paper fibers are softened by pressure and heat, and those existing between the paper fibers are fixed by being connected by the toner on the paper fibers softened and melted by the pressure and heat.

Regarding pressurization and heating, the required thermal energy was reduced by more than 1/3 compared to the conventional one, and the pressure was low.

The following is a comparison between experimental examples using the present invention and comparative examples.

[Experimental Example 1] Toner: 100 parts of polystyrene and 100 parts of sharp melt wax (melted at 70 ° C) were kneaded with other pigments, pulverized and classified. Pressure: 30 Kg / Cm ² Roll temperature: 140 ℃ Nip width …… 3.5mm Fixing speed …… 600mm / sec When the above toner was mixed with an appropriate carrier, a sufficient image was obtained. When this was fixed under the above conditions, the fixing rate was 90% or more. The fixing ratio is represented by the ratio of the density before and after the image is fixed on the paper after fixing with a pressure of 50 g / Cm ² . The same applies to the following.

Further, when the fixed image was observed with a microscope, it was confirmed that the interfiber toner was not completely melted and was connected by the wax. Further, the toner on the fiber was partially melted and the other was also connected by wax.

[Experimental Example 2] Toner: 100 parts of styrene monomer and wax (melting point: 7)
Toner obtained by mixing 100 parts of the styrene monomer and then suspension-polymerizing the styrene monomer. Pressure 70 kg / Cm ² Roll temperature 140 ° C. Nip width 1.2 mm Fixing speed 600 mm / sec Above When toner was mixed with a carrier and developed, a good image was obtained. The fixing rate was almost 100%.

[Experimental Example 3] Toner ………… Versamide ^# 725 (melting point 125 ° C, softening point 80 ° C under pressure), magnetic material and pigment were added, kneaded, pulverized, and classified Pressure ………… 100Kg / Cm ² Roll temperature: 120 ° C Nip width: 0.8 mm Fixing speed: 470 mm / sec When the above toner was developed with a conventional one-component developing device, a good image was obtained. Further, when fixing was performed under the above conditions, the fixing rate was 95%.

[Comparative Example 1] Toner ......... 80 parts polystyrene were kneaded adding a magnetic substance and a pigment to 20 parts of acrylic, grinding, pressure those obtained by classifying ............ 30Kg / Cm ² roll temperature ... 140 ° C. nip Width: 4 mm Fixing speed: 600 mm / sec The conventional toner showed sufficient developability, but it did not fix at all under the above conditions. By the way, roll temperature 200
When the temperature and the nip width were changed to 10 mm, 90% fixing rate was shown for the first time. However, when observing the fixed image with a microscope,
The toner was completely melted.

Comparative Example 2 A fixing experiment was conducted with the toner used in Experimental Examples 1 to 3 under the following conditions.

Pressure ………… 10Kg / Cm ² Roll temperature… 195 ℃ Nip width …… 10mm Fixing speed …… 440mm / sec The above conditions are usually called thermal fixing. The fixing ratios were all less than 80%, and the fixing did not occur at all. Further, when the image after passing through the fixing roll was observed with a microscope, the toner was not deformed at all, and the wax did not spread between the toner and between the paper fibers.

(Effects of the Invention) As described above, according to the present invention, since fixing can be performed without completely melting the toner, the required thermal energy is reduced as compared with the conventional thermal fixing, and good fixing is impaired. Energy can be saved, and the applied pressure can be remarkably lower than in the prior art, so that the gloss after fixing can be eliminated and writability can be secured.

[Brief description of drawings]

FIG. 1 is a schematic vertical sectional view of a fixing device to which the present invention is applied. 11 …… Fixing device 13 …… Pressure roller 14 …… Fixing roller 16 …… Pressure spring 20 …… Heater T …… Toner P …… Support (transfer paper)

Claims (1)

[Claims] 1. A fixing method in which a recording paper carrying unfixed toner is nipped and conveyed by a pair of rotating bodies that are in pressure contact with each other and set at a temperature not higher than the softening point of the toner, and fixing is performed under pressure and heating. Toner on paper fibers is softened by pressure and heat, and toner between paper fibers is softened by pressure and heat, and the toner on fused paper fibers is connected to fix the toner on the recording paper. Fixing method characterized by.