JP2002287545A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make use of toner releasability, energy conservation and recourse conservation and to prevent the degradation in the graininess of images in an image forming device equipped with a fixing device having a heating roller and a press roller. SOLUTION: The surface of the heating roller 12 is formed of a fluororesin and the toners of <=20 wt.% in the ratio of a binder resin having a molecular eight of >=100,000, >=9.0 μm in volume average grain size and <=5.0 wt.% in the rate of coloring agents.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a recording sheet carrying a toner image between a heated fixing member and a pressing member disposed opposite to the fixing member. The present invention relates to an image forming apparatus having a fixing device for fixing the toner image on a recording sheet by heating and pressing the toner of the toner image by passing the toner image in a direction in contact with a member.

[0002]

2. Description of the Related Art An image forming apparatus of the above-mentioned type constituted as an electronic copying machine, a printer, a facsimile or a multifunction machine having at least two of these functions has been conventionally known. As a fixing device used for an image forming apparatus of this type, for example, a fixing member configured as a heating roller or a fixing belt heated by a heating unit, and a pressing member configured as a pressing roller or a pressing belt are used. Is the mainstream. This type of fixing device heats and pressurizes the toner of the toner image on the recording sheet to fix the toner image on the recording sheet. Such a fixing device is referred to as a pressure heat fixing device and a fixing method thereof as necessary, and is distinguished from a non-pressing fixing method such as oven fixing, if necessary.

An example of a conventional pressure heat fixing device will be described in more detail. The cylindrical heating roller of the fixing device has a heat-resistant resin film (fluororesin) formed on the outer peripheral surface of a cored bar. The releasability of fixing the image on the recording sheet is ensured. Further, a halogen rod-shaped lamp is arranged inside the heating roller, and plays a role of heating the heating roller from the inside. Further, a pressure roller is pressed against the heating roller. The pressure roller has a configuration in which a tube is placed on the surface of the elastic layer. The coating tube on the surface of the elastic roller is also a material having excellent releasability, such as a fluororesin. In the pressure heat fixing method, a recording sheet such as paper carrying an unfixed toner image is passed between the two while a pressure roller is pressed against a heating roller.
At the same time as the toner is melted by the heat from the lamp inside the heating roller, the toner is fixed to the recording sheet by the pressure received from the heating roller and the pressure roller. This pressure fixing method is the most widely used fixing method at present because it has higher thermal efficiency and can save power as compared with an oven fixing method or the like, and is excellent in high speed. As described above, a fixing belt can be used instead of the heating roller, and a pressure belt can be used as the pressure member.

[0004] Although the pressure heat fixing device has many advantages as described above, according to experiments by the inventor, in the pressure heat fixing method, "granularity" which is a basic characteristic of image quality in an image after fixing is obtained. Worsened. On the other hand, in a non-pressurized fixing system such as oven fixing, the result that such deterioration of the graininess was not so large was obtained. The “granularity” is one item among sharpness, gradation, granularity, and color reproducibility, which are basic items of image quality, and is an index indicating image roughness. About this "granularity",
The definition will be described later in detail. Deterioration of graininess, by definition, directly leads to deterioration of image quality.

[0005] The configuration of the heating roller of the pressure fixing device is such that the surface of the heating roller is "type coated with fluororesin", "type coated with a tube formed of fluororesin", "silicone elasticity". Layer and the like having no surface layer ". Since the surfaces of the two types are made of a fluororesin, they are excellent in toner releasability and hot offset.
In an image forming apparatus that performs so-called oilless fixing without applying a release agent to the surface of the heating roller, the heating roller is one of the above two types.

On the other hand, with respect to toner used in an image forming apparatus, low fixing energy is required in recent years due to a demand for energy saving. In general, such a demand is met by lowering the softening temperature of the binder resin constituting the toner. Specifically, the softening temperature can be reduced by increasing the ratio of the low molecular weight component (molecular weight of 100,000 or less) of the binder resin.

From the viewpoint of resource saving in recent years, it is desirable that the toner has a large volume average particle diameter. Specifically, it is desirable that the volume average particle diameter of the toner is 9.0 μm or more. This is because the fine powder component (generally 3.0 μm or less) must be removed when the toner is pulverized and classified. If the toner still contains these fine powder components, problems such as spent on the carrier of the developer used in the developing device and sticking of the sleeve on the developing sleeve tend to occur. Since such fine powder must be removed in the toner crushing and classifying process, when the volume average particle diameter of the toner is reduced, the problem that the amount removed as fine powder increases is inevitable. Occurs (the so-called yield deteriorates). Since these removed fine powder components have to be discarded, they become a factor that hinders waste reduction. Specifically, when the volume average particle size is 9.0 μm or more, a good toner yield of about 95% can be ensured. Therefore, the volume average particle diameter of the toner is 9.0 from the viewpoint of reducing waste.
It is desirable that it is not less than μm.

However, the inventor has used a toner having a volume average particle diameter of not less than 9.0 μm, which is made of a binder resin having been subjected to the above-mentioned softening temperature reduction, and furthermore, has used this toner on the surface of the heating roller. It has been found that when combined with a fixing device of which is a fluororesin, the deterioration of the graininess in the above-mentioned fixing step becomes extremely large.

[0009]

SUMMARY OF THE INVENTION It is an object of the present invention to provide such a low softening temperature and to achieve a volume average particle size of 9.0 μm.
An object of the present invention is to provide an image forming apparatus which does not deteriorate in graininess even when the above toner is combined with a fixing device in which the surface of a fixing member is made of a fluororesin. With such an image forming apparatus, it is possible to simultaneously achieve excellent toner release properties and energy and resource savings.

[0010]

According to the present invention, in order to achieve the above object, in an image forming apparatus of the type described at the beginning, a surface of a fixing member in contact with the toner image is made of a fluororesin, In the binder resin, the ratio of the resin having a molecular weight of 100,000 or more is 20% by weight or less, the volume average particle diameter of the toner is 9.0 μm or more, and the ratio of the colorant in the toner is 5.0% by weight. % Is proposed (claim 1).

At this time, it is advantageous that the ratio of the colorant in the toner is 2.0% by weight or more.

In the image forming apparatus according to the first or second aspect, it is advantageous that the fixing member of the fixing device is configured as a fixing member having no elastic layer.

The image forming apparatus according to any one of claims 1 to 3, further comprising a developing device for forming the toner image, the developing device carrying a developer, and It is preferable that the image forming apparatus further includes a developer-carrying and conveying member that conveys the electrostatic latent image to a developing area where visualization of the electrostatic latent image is performed. (Claim 4).

Further, in the image forming apparatus according to any one of claims 1 to 4, it is advantageous that the fixing device is configured as an oilless fixing device that does not apply a release agent to the surface of the fixing member. (Claim 5).

Further, in the image forming apparatus according to any one of claims 1 to 5, it is advantageous that the binder resin of the toner is a polyester resin.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a cross-sectional view schematically showing a developing device configured as an electrostatic copying machine, a laser printer, a facsimile or a multifunction machine using an electrophotographic process.

Drum-shaped photosensitive member 1 as an example of an image carrier
Is formed by applying a photosensitive layer to the surface of the conductor, and rotates in the direction of the arrow. The image forming apparatus forms an image in the following procedure. 1. The charging device 2 charges the surface of the photoconductor 1 to a desired potential. 2. In the exposure device 3, the charged photoconductor 1 is exposed,
An electrostatic latent image corresponding to a desired image is formed on a photoconductor. 3. In the developing device 4, the electrostatic latent image created by the exposure device is developed with toner to form a toner image on the photoconductor. 4. The transfer device 5 transfers the toner image on the photoconductor onto a recording sheet 6 such as paper conveyed by a conveyance device (not shown). 5. The cleaning device 7 uses the transfer device 5 to record the recording sheet 6.
The toner remaining on the photoreceptor without being transferred onto the surface is cleaned. 6. The recording sheet 6 to which the toner image has been transferred by the transfer device is conveyed to the fixing device 8. In the fixing device 8, the toner is heated and fixed on the recording sheet. Since the photoreceptor 1 rotates in the direction of the arrow, a desired image is formed on the recording sheet by repeating the above steps 1 to 6.

(Embodiment 1) The more specific configuration of the image forming apparatus shown in FIG. 1 is as follows, but these are merely examples, and the present invention is not limited thereto.
An image forming apparatus having this configuration is referred to as a first embodiment.

The photosensitive member 1 is formed by applying a photosensitive layer to the surface of a conductor (such as aluminum). The diameter of the photosensitive member 1 is 60 mm, and the peripheral speed of the surface is 2 mm.
30 mm / sec. The charging device 2 shown in FIG.
This is a so-called contact roller charging device, and a direct current voltage (-1.35 k) is applied to a charging roller having a configuration in which an elastic layer (thickness: 3 mm) having medium resistance conductivity is formed on a cored bar.
V) to charge the photoconductor uniformly (-600 V).

The exposure device 3 forms an electrostatic latent image by irradiating the surface of the photoconductor 1 uniformly charged by the charging device 2 with light corresponding to a target image. The light source of the exposure device is a laser diode, which scans the photosensitive member while irradiating it with a laser beam by a polygon mirror. The beam diameter is 50 μm in the main scanning direction and 60 in the sub scanning direction.
μm.

The developing device 4 is a two-component developing device, in which a toner and a carrier (particle diameter: 50 μm) have a toner concentration of 5.0%.
Is stored in the developing container 9. In the developing device 4, the developer is transported by the developing sleeve 10 to a portion where the photoconductor 1 and the developing sleeve 10 are opposed to each other. The distance between the photoconductor and the developing sleeve (so-called developing gap) is 0.3 mm. Since a DC voltage (−400 V) is applied to the developing sleeve 10 from a power supply, toner adheres to the photoconductor in accordance with the electrostatic latent image on the photoconductor. So-called reversal development is performed. The peripheral speed of the developing sleeve 10 is 460 mm / sec here. The linear velocity ratio between the photosensitive member 1 and the developing sleeve 10 is 2.0
It is.

The transfer device 5 transfers the toner image developed by the developing device onto the recording sheet 6 conveyed from a paper feeding device (not shown). The transfer device according to the first embodiment includes a transfer belt and a power supply, and applies a voltage to the transfer belt from the power supply. The applied voltage is constant current control and is 30 μA.

The cleaning device 7 has a blade 11 made of an elastic material, and the blade 11 removes a residual toner image (transfer residual toner) on the photoreceptor to clean the surface of the photoreceptor.

The toner image transferred onto the recording sheet (paper or the like) by the transfer device is conveyed to a fixing device, and the toner image is fixed on the recording paper sheet by heating and pressurizing by a fixing unit. The image is discharged out of the machine and becomes an output image. The detailed configuration of the fixing device according to the first embodiment will be described later. By repeating the above steps, a desired image can be formed on the recording sheet.

The developing sleeve 10 of the developing device 4 is driven to rotate clockwise in FIG. 1 and cooperates with a magnet (not shown) provided therein to transfer the developer DA to the developing sleeve 10 and the photosensitive member. 1 to the developing area. The developing sleeve 10 forms an example of a developer-carrying / transporting member that carries the developer and transports the developer to a development area where the electrostatic latent image is visualized.

FIG. 2 is a schematic enlarged view of the fixing device 8 of the first embodiment shown in FIG. The fixing device 8 shown here adopts a pressure heat fixing method, and has a heating roller 12 as an example of a fixing member and a pressing roller 13 as an example of a pressing member. The pressure roller 13 is a heating roller 1
2, and the peripheral surface of the pressure roller 13 is pressed against the peripheral surface of the heating roller 12 to form a nip having a predetermined width. These rollers 12, 13 each rotate in the direction of the arrow. A heater 14 as a heating source is disposed inside the heating roller 12, and the heating roller 12 is heated by the heater 14, so that the surface of the heating roller 12 is maintained at a temperature suitable for fixing a toner image.

Unfixed toner image T transferred from photoreceptor 1
Is transported between the heating roller 12 and the pressure roller 13 as indicated by an arrow A in a direction in which the toner image T contacts the heating roller 12, and the recording sheet 6 passes through these nips. I do. At this time, the toner is melted by the heat from the heating roller 12 heated by the heater 14, and at the same time, receives the pressure from the heating roller 12 and the pressure roller 13. Thus, the toner image is fixed on the recording sheet 6. A fixing member including a fixing belt, a pressing member including a pressing belt, and the like can also be used. Further, the fixing member may be configured to be heated from the outside.

As described above, the fixing device transfers the recording sheet carrying the toner image between the heated fixing member and the pressing member disposed opposite to the fixing member. By passing the toner image in a direction in contact with the fixing member, the toner of the toner image is heated and pressed to fix the toner image on the recording sheet. This type of fixing device is a pressure heat fixing device.

In the fixing device according to the first embodiment shown in FIG. 2, the heating roller 12 has a cylindrical shape with a diameter of 30 mm and a length of 350 mm, and has a primer as an adhesive layer on an iron core (thickness 0.3 mm). Fluororesin layer (PTF)
E, 16 μm). As described above, the surface of the fixing member that is in contact with the toner image is made of fluororesin. Further, the fixing member including the heating roller 12 in this example is configured as a fixing member having no elastic layer. The heating source disposed in the heating roller is a halogen rod-shaped heater 14, which generates 800 W of heat. In the first embodiment, the surface of the heating roller is heated to 110 to 220 ° C. by the heat generated from the halogen rod heater 14. The pressure roller 13 has a diameter of 30 mm and a length of 35 m
The elastic layer (foamed silicone rubber, 5 mm) is formed on a metal core (diameter: 20 mm), and a fluororesin layer (PTFE, 50 μm) is formed on the surface of the elastic layer. The pressing force of the pressure roller 13 against the heating roller 12 is 20 N to 100 N, and the nip width is 2 to 10 mm. Each configuration shown here is merely an example, and other appropriate configurations may be adopted. In short, it is possible to fix the toner image on the recording sheet to the recording sheet by heating and pressing. The fixing member may be of any type as long as the surface is a fluororesin.

The fixing device of the image forming apparatus according to the first embodiment is a so-called oil-less type fixing device, which is configured so that the releasing agent is not applied to the surface of the fixing member including the heating roller 12. Alternatively, a configuration may be employed in which a release agent is applied to the peripheral surface of the heating roller 12.

The ratio of the resin having a molecular weight of 100,000 or more to the binder resin in the toner is 20% by weight or less. In Example 1, this ratio is set to 20% by weight. The molecular weight of the binder resin is GPC (gel permeation chromatography)
It is possible to measure with. According to this measuring method, the toner used in the image forming apparatus of Example 1 is limited so that the ratio of the high molecular weight component (molecular weight of 100,000 or more) in the binder resin is 20% by weight or less. When the binder resin of the toner has such a component configuration, the glass transition temperature and the softening temperature indicating the temperature characteristics of the toner can be lowered. As a result, the toner can be fixed on the recording sheet with a small fixing energy. Specifically, when the ratio of the component having a molecular weight of 100,000 or more in the binder resin is set to 20% by weight or less, the fixing energy becomes 0.2 ca.
1 / cm ² or less, and energy saving of the fixing device can be achieved.

On the other hand, if the ratio of the component having a molecular weight of 100,000 or more in the binder resin is made unnecessarily small, there is a problem that toner blocking and hot offset are likely to occur. For this reason, it is preferable that the ratio of the component having a molecular weight of 100,000 or more in the binder resin is at least about 5% because these problems are less likely to occur.

The binder resin constituting the toner of the first embodiment is a polyester resin. In addition to the resin constituting the toner, there is a styrene / acrylic copolymer, and a polyester resin is preferable in terms of pigment dispersibility and toughness. Monomers used in polyester resins include terephthalic acid, phthalic acid, fumaric acid, maleic acid,
Examples thereof include bifunctional acid monomers such as succinic acid or derivatives thereof, bisphenol A derivatives, and bifunctional alcohol monomers such as ethylene glycol and neopentyl glycol. A polyester resin can be produced by condensation polymerization of these acid monomers and alcohol monomers.

The volume average particle diameter of the toner is 9.0 μm or more. In Example 1, a ground toner having a volume average particle diameter of 9.5 μm is used. The toner of Example 1 is obtained by kneading the above-mentioned binder resin with a charge controlling agent, a colorant described below, etc., then cooling and coarsely pulverizing, and thereafter, has a predetermined particle size by a jet mill and an airflow classifier. This step is repeated as described above. The particle size of the toner was measured with a Coulter counter (manufactured by Coulter Corporation).

FIG. 3 is a graph showing the relationship between the occurrence rate of fine powder components of 3.0 μm or less and the volume average particle size of the pulverized toner. This fine powder component (particles having a volume average particle diameter of 3.0 μm or less) causes problems such as spent and sticking of the sleeve, as pointed out in the section of the prior art, and therefore must be removed. However, the fine powder component of the toner necessarily increases as the target value of the volume average particle diameter of the pulverized toner decreases. Fine powder components are practically difficult to reuse and must be discarded, thus causing a problem of increased waste. This is completely contrary to the recent demand for resource saving, and is not desirable from the viewpoint of global environmental conservation. Also, when the target value of the volume average particle size of the pulverized toner is reduced (9.0 μm or less), the number of repetitive pulverizations increases. It must be operated, which is not desirable from the viewpoint of energy saving.

As can be seen from FIG. 3, by setting the volume average particle size of the toner to 9.0 μm or more, the volume average particle size becomes 3 μm.
m or less can be reduced to 5.0% or less. As a guide for the incidence of fine powder components, 5.0%
It is. This 5.0% is removed in the process of pulverization and classification and discarded. Incidentally, in Example 1, since the volume average particle diameter of the toner is 9.5 μm, the ratio of the fine powder is 4.5%, which can contribute to resource saving in the toner manufacturing process.

The ratio of the colorant contained in the toner is 5.0.
% By weight or less. The colorant is dispersed in the binder resin together with the charge control agent and the like in the kneading step. In Example 1, the ratio of the coloring agent was set to 5.0% at this time. In Example 1, the colorant contained in the toner is carbon black.

In the first embodiment, the surface of the heating roller is made of a fluororesin as a fixing device, the binder resin in the toner has a ratio of a resin having a molecular weight of 100,000 or more to 20% by weight or less, and the volume average particle diameter of the toner. Is 9.0 μm or more, and the ratio of the colorant in the toner is 5.0% by weight or less. When an image forming apparatus is configured by a combination of the following, the combination of the prior art is excellent in hot offset,
Since the fixing energy can be suppressed, energy saving can be achieved, and an image forming apparatus that can achieve reduction of waste by reducing generation of fine powder in a toner manufacturing process can be realized. However, when the above-described combinations are combined, experiments by the inventors have revealed that the "granularity" which is a basic characteristic of an image is deteriorated.

This “granularity” is generally an index of high image quality.
Unlike “dot reproducibility,” which is considered to be
Is defined as In the image forming apparatus of the first embodiment,
The graininess does not deteriorate even after passing through the
Before we explain what is going to happen
A description of the graininess will be given first. Granularity is defined as "uniform
Subjective evaluation that shows how rough the power image should be
Value ". This subjective evaluation value, graininess,
The amount expressed objectively is an evaluation scale of granularity.
is there. RMS as standardized as granularity
Granularity, standardized in ANSI PH-2.40-1985
You. RMS granularity (σ_D) = [1 / NΣ (Di-D)²]
^1/2  Di is the density distribution, D is the average density (D = 1 / NΣDi)
is there. In addition, the power spectrum of image density fluctuation
Granularity using Winer Spectrum is defined.
You. Xerox Dooley and Shaw apply Winer Spectrum
And visual spatial frequency characteristics (Visual Transfer Function
 : VTF) and the integrated value is taken as the granularity (G
S) (For details, see Dooley, Rshaw Noise Perception in
 Electrophotography, J. Appl. Photogr. Eng., 5, 4 (1979),
pp190-196). GS = exp (−1.8D) ∫ (WS (f))^1/2V
TF (f) df D: average density f: spatial frequency (c / mm) WS (f): Winer Spctrum VTF (f): visual spatial frequency characteristics

Here, the granularity is further developed from the Dooley and Shaw granularity and is defined by the following equation. Granularity = exp (aL + b) ∫ (WS _L (f)) ^1/2
VTF (f) df L ^* : Average lightness f: Spatial frequency (c / mm) WS _L (f): Power spectrum of lightness fluctuation VTF (f): Visual spatial frequency characteristic a: Coefficient (= 0.1044) b: Coefficient (= 0.8944) In this case, the lightness L ^* is used instead of the image density D. The latter is characterized in that the linearity of the color space is excellent and the adaptability to a color image is also excellent. In the following, we will proceed with defining granularity by this equation.

The granularity represents the noise characteristics of an image by its definition. By measuring the granularity of the output image by the above-described method, the noise characteristics (roughness) of the image can be quantified. As can be seen from the definition, the numerical value of the granularity is small when the roughness is good, and increases as the roughness becomes poor. The inventor uses the output image as a scanner (FT-S5000:
After reading with Dainippon Screen), the granularity was calculated based on the above formula.

The inventor uses the granularity obtained by the above-described definition as a measure of evaluation, and sets the ratio of the colorant of the toner to 9.0% by weight as compared with the image forming apparatus of Example 1 and Example 1. Then, the granularity of the image after fixing was compared with the image forming apparatus (Comparative Example 1) and the oven fixing method (Comparative Example 2) in which the image surface was not pressed during fixing. By the way,
The toner used in the oven fixing in Comparative Example 2 was the same as the toner in Example 1 (particle diameter: 9.5 μm, colorant ratio: 5.0%). Even with the toner used in Comparative Example 1 (particle size: 9.5 μm, colorant ratio: 9.0%), the granularity may be substantially the same as Comparative Example 2 when oven fixing is performed. Do you get it. (This result was very close to Comparative Example 2 and is not shown.) In the experiment, an unfixed toner image was formed on paper (Ricoh TYPE6200) using a modified Ricoh digital copying machine MF4570. The fixing method was changed.

FIG. 4 shows the result, in which the horizontal axis represents brightness and the vertical axis represents granularity. The granularity is given for each lightness, and the inventor takes 17 levels of lightness (prepared a 17-level patch that has been subjected to halftone processing with a screen ruling of 150 lines) to determine the granularity for each lightness. Calculated. Oven fixing method that does not press the image surface during fixing (Comparative Example 2)
Was the best, and was about 0.3 at the maximum (even near the brightness of 50). In contrast, Example 1
In the image forming apparatus of Example 1, the granularity is slightly deteriorated as compared with Comparative Example 2 described above.
It was about 5. On the other hand, when the ratio of the colorant in the toner was 9.0% by weight (Comparative Example 1), the deterioration of the granularity exceeded 1.0 at the maximum, and was extremely poor.

As a guide of the numerical value of the granularity of an image, it is desirable that the value be within 0.5 at the maximum. This is derived from the results of a panel test. When the maximum value of the granularity exceeds 0.5, the subject's attention concentrates on the granularity (roughness), whereas when the maximum value of the granularity exceeds 0.5, This is because items such as gradation and sharpness, which are other basic characteristics of the image quality, also have an influence, and an image with an excellent balance of these tends to be most preferred.

(Experiment 1) The inventor measured the granularity by varying the ratio of the colorant in the toner from 2.0 to 11.0% by weight with the above configuration. In the section of the first embodiment, the granularity is specified for each lightness.
Only the average value between 0 and 80 will be specified (since the graininess in the so-called medium lightness region having a lightness of 40 or more and 80 or less is most important from the viewpoint of high image quality). Table 1 shows the results.
It is. From Table 1, it can be seen that when the ratio of the colorant in the toner exceeds 5.0%, the granularity in the fixing step is significantly deteriorated. Further, the ratio of the toner colorant is 2.0% by weight.
When it was less than the above, a so-called low concentration occurred. Therefore, it is desirable that the ratio of the toner colorant is 2.0% by weight or more. The measurement was carried out using a spectrophotometric densitometer manufactured by X-Rite, and when the lightness value was not 21, the density was reduced.
The toner used in this experiment was prepared according to the specifications described in the first embodiment. Specifically, the binder resin of the toner is a polyester resin, and the ratio of components having a molecular weight of 100,000 or more is 20%. In addition, the volume average particle diameter of all the toners is adjusted to 9.5 μm. The configuration of the fixing device is exactly the same as that of the first embodiment, and the surface of the heating roller is a roller formed of fluororesin.

[0047]

[Table 1]

(Experiment 2) (Effect of Low-Molecular-Weight Component Ratio of Binder Resin)
In order to see the effect of the ratio of the components having a molecular weight of 100,000 or more on the granularity, the ratio of the components having a molecular weight of 100,000 or more was changed in the range of 5.0 to 30.0% by weight. A shaken toner was prototyped and the granularity was measured. At this time,
The ratio of the colorant of the toner is two levels of 5.0% by weight and 9.0% by weight. Table 2 shows the results of the granularity for each combination at this time. The numerical value of the granularity is still the lightness L ^* =
It is a value obtained by averaging the granularity in the range of 40 to 80. Table 2
As can be seen from the above, if the colorant ratio of the toner is 9.0%, sufficient image quality cannot be obtained from the viewpoint of granularity. Further, even if the colorant ratio of the toner is 5.0%, the molecular weight is 1%.
If the proportion of the components of 0000 or more is larger than 20% by weight, the fixing energy will be increased this time, making it difficult to save energy.

[0049]

[Table 2]

(Experiment 3) (Effect of Volume Average Particle Diameter of Toner) In order to see the effect of the volume average particle diameter of the toner on the granularity, the inventor of the present invention prepared a toner having a different volume average particle diameter (volume average particle diameter). Prototypes (diameter: 9.5, 7.5 μm) were measured, and the granularity was measured. At this time, the ratio of the colorant in the toner is two levels of 5.0% by weight and 9.0% by weight. The ratio of the high molecular weight component (the component having a molecular weight of 100,000 or more) in the binder resin was fixed at 20% by weight, and a trial production of the toner was performed. Table 3 shows that the toner having a particle diameter of 7.5 μm is more advantageous in terms of graininess. However, the 7.5 μm toner has a problem that the so-called yield decreases. If the toner particle size is 9.5 μm, the problem of the yield can be solved. However, as can be seen from Table 3, if the colorant ratio is not 5.0%, an image having poor graininess will result.

[0051]

[Table 3]

(Embodiment 2) Embodiment 2 is a high-speed image forming apparatus. Specifically, the peripheral speed of the photoconductor is 500 mm /
sec, the linear velocity of the peripheral surface of the developing sleeve is 900 mm / sec
c, The diameter of the photosensitive drum is 100 mm. Other configurations are the same as those of the first embodiment. With the image forming apparatus having such a configuration, printing can be performed at high speed.
The linear velocity on the peripheral surface of the developer carrying member is 900 mm / sec.
By setting as described above, a preferable high speed can be achieved. Further, since the above-described condition of the first embodiment is added,
A unique effect is obtained.

In the image forming apparatus of each embodiment described above, the surface of the heating roller of the fixing device is made of a fluororesin, and the ratio of the binder resin in the toner having a molecular weight of 100,000 or more is 20% by weight or less. , The volume average particle diameter of the toner is not less than 9.0 μm, and the ratio of the colorant of the toner is not more than 5.0% by weight. By adopting such a combination configuration, as described in the section of the prior art, excellent hot offset and fixing energy can be suppressed, so that energy saving can be achieved and fine powder generation in the toner manufacturing process can be reduced. It is possible to realize an image forming apparatus capable of reducing wastes, and to achieve an image in which the deterioration of granularity, which is a basic characteristic of image quality, in a fixed image is small.

In the image forming apparatus having the above-described structure, the mechanism that requires less deterioration in graininess even after passing through the fixing device can be considered as follows. When the thickness of the unfixed toner image on the paper was measured (using a laser microscope manufactured by KEYENCE CORPORATION), it was found to be about 15 μm (about three toner layers). It was also found that the height of the unfixed toner image had a variation of about 15 μm even in the same toner-attached portion. That is, the height of the toner image varies.
When a recording sheet (paper or the like) on which an unfixed toner image having such a varied toner layer height is passed, the toner is melted and pressed. At this time, the pressure applied to the toner by the heating roller and the recording sheet is extremely difficult to achieve a completely uniform pressure due to the effect of the paper fibers and the so-called "stiffness" of the paper itself. Even for OHP sheets with relatively good surface smoothness (about 2 μm),
Due to the “stiffness” of the sheet itself, the pressure applied to the toner layer varies from place to place. Thus, uneven pressure applied to the toner during the fixing process is inevitable. On the other hand, as described above, the thickness of the unfixed toner layer also varies in an amount of about 15 μm. Considering these facts, if the high-pressure portion of the unfixed toner layer happens to coincide with the high-pressure portion of the pressure unevenness caused by the stiffness of the recording sheet, the toner in this portion is melted by the heating roller. Besides being easy,
The pressure causes the recording sheet to spread greatly in the surface direction. On the other hand, when the low-pressure portion of the pressure unevenness coincides with the portion where the unfixed toner layer is low, it is considered that the spread in the toner surface direction hardly occurs, contrary to the above. At this time, the local lightness should be lower (darker) in the portion where the toner spreads more than in the portion where the toner does not spread much. Such non-uniformity of the spread of the toner in the direction of the recording sheet surface is considered to be the cause of the deterioration in graininess.

Although the surface of the heating roller in Examples 1 and 2 is made of fluororesin, the fluororesin is very hard. Normally, the fluororesin layer coated on the surface of the heating roller needs to be about 10 μm from the viewpoint of durability and the like, so that the very hard property of the fluororesin necessarily appears. For this reason, the adhesion between the heating roller and the toner tends to be insufficient (which is one of the factors that cause the above-mentioned uneven pressure to increase). It is considered that the condition of Example 1 is such that the graininess in the above-described fixing process is likely to be deteriorated for such a reason.

On the other hand, since the surface of the heating roller is formed of a fluororesin having excellent releasability, it is excellent in toner releasability and has a feature that so-called hot offset hardly occurs. The advantage in the case where the hot offset hardly occurs is that the fixing range (the range of the temperature at which the fixing can be performed) is widened, so that stable fixing performance can be exhibited without being affected by the outside air temperature, the paper temperature and the like. In addition, among the existing materials, materials capable of improving the releasability are:
In fact, there is no other material than fluororesin.

With respect to the binder resin constituting the toner, when the ratio of the component having a molecular weight of 100,000 or more is 20% by weight or less, the glass transition temperature and the softening temperature indicating the temperature characteristics of the binder resin become low. As a result, the so-called fixing energy can be reduced (according to the experiment of the inventor,
0.20 cal / cm ² ). This condition can achieve a heating roller temperature of 175 ° C. in the machine having the photosensitive member peripheral speed of 230 mm / sec described in the first embodiment. This means that energy saving of the fixing device is possible, and it responds to the recent demand for energy saving. This is approximately 70% of the total power consumption of the image forming apparatus.
In view of the current situation in which% is consumed in the fixing device, this is an urgent problem for the image forming device employing the pressure heating method, and the image forming device of the embodiment has a very excellent advantage because it can improve this point. .

On the other hand, when the ratio of the component having a molecular weight of 100,000 or more in the binder resin constituting the toner is set to 20% by weight or less, the temperature change of the viscoelasticity of the toner becomes sharp. It has the characteristic. Considering this by applying the toner layer sandwiched between the heating roller and the recording sheet, when the viscoelasticity is reduced to a temperature at which the toner on the recording sheet side can be fixed, the toner in contact with the heating roller Is considered to be too molten (too soft). As described in the paragraph describing the reason why the granularity is deteriorated in the fixing step, the spread of the toner in the portion in contact with the heating roller is increased, so that the granularity in the fixing step is increased. The condition is that the deterioration of the condition becomes larger.
In fact, the inventor conducted a molecular weight of 10 in the binder resin.
It has been confirmed in an experiment conducted by changing the ratio of ten thousand or more components that there is such a tendency as described above.

With respect to the average particle diameter of the toner, by setting the volume average particle diameter to 9.0 μm or more, the ratio of the fine powder component (3.0 μm or less) can be reduced to 5.0% or less. This greatly contributes to resource saving in the toner manufacturing process in view of the current situation where fine powder components must be discarded. On the other hand, the average particle size of the toner is 9.
When the thickness is set to 0 μm or more, the deterioration of the graininess caused by the uneven pressure applied to the toner in a state of being sandwiched between the heating roller and the recording sheet is worse due to the mechanism as the toner particle size is larger. I understand. That is,
When the same pressure is applied to the toner, the larger the toner particle size, the larger the spread in the paper surface direction (because the volume is large). This causes an increase in the image density of this portion, and thus has an adverse effect that the deterioration of the graininess in the fixing step becomes more remarkable.

As described above, the surface of the heating roller is made of fluororesin as a fixing device, and the binder resin in the toner is
The ratio of the resin having a molecular weight of 100,000 or more is 20% by weight or less,
The combination of toner having a volume average particle size of 9.0 μm or more has the above advantages. On the other hand, according to experiments by the inventor, it has been clarified that any of the above-mentioned (1) to (4) has an adverse effect on the granularity of an output image (this mechanism is as described above). On the other hand, in the image forming apparatus according to the embodiment, as a fourth condition, the ratio of the colorant of the toner is set to 5.0% by weight or less to suppress the deterioration of the graininess in the fixing process. . That is, this image forming apparatus
It is possible to realize an image forming apparatus in which the deterioration of the graininess in the fixing process does not occur without losing the above-mentioned advantages.

The mechanism by which the ratio of the colorant in the toner is 5.0% by weight or less can prevent the deterioration of the graininess in the fixing step can be considered as follows. When the toner layer on the recording sheet is pressed against the heating roller and the recording sheet (in this case, unevenness in pressure is necessarily generated due to "stiffness" of the recording sheet), the toner layer spreads in the surface direction of the recording sheet. When the coloring power of the toner is small (the colorant ratio is 5.0% by weight or less), even when the toner layer spreads in the surface direction of the recording sheet, the increase in density is suppressed in the portion where the toner layer is thinned. (The reflection component from the recording sheet below the toner layer increases due to the thinning of the toner layer.) Therefore, the effect of the density increase due to the spread of the toner layer and the effect of the density reduction due to the thinning of the toner layer are offset. As a result, there is no resulting increase in the concentration of that part. This means that the number of lines is relatively low (1 c / m
m) can be prevented from being a main cause of "granularity deterioration". In this way,
Non-uniformity in toner pressure in the fixing step can be prevented from being affected by low coloration.

In addition to the above-described configuration, the following effects can be obtained by using a heating roller having no elastic layer as the heating roller of the fixing device.

When the heating roller has no elastic layer,
It is possible to realize a fixing device that has a fast rise time and is excellent in energy saving. On the other hand, according to the inventors' experiments,
Graininess after passing through the fixing device is particularly poor. For this reason, there is a problem that the output image does not have a sense of uniformity in the middle density portion and the image has a rough impression. This problem,
This is because the “heating roller having no elastic layer” is in the worst state in view of the mechanism that the granularity deteriorates when passing through the fixing device described above.
That is, since the heating roller does not have an elastic layer having poor thermal conductivity, an excessive amount of heat is supplied to the toner that has contacted the heating roller. Further, since the heating roller has no elastic layer and is hard, the unevenness of the pressure applied to the toner layer due to the stiffness of the recording sheet increases. Obviously, these effects act in the direction of deteriorating the graininess after passing through the fixing device, in view of the above mechanism.

On the other hand, in the image forming apparatus of the embodiment, the surface of the heating roller is made of a fluororesin as a fixing device, and the binder resin in the toner has a ratio of a resin having a molecular weight of 100,000 or more to 20% by weight. Hereinafter, since the volume average particle diameter of the toner is 9.0 μm or more and the ratio of the colorant of the toner is 5.0% by weight or less, the heating roller has an elastic layer. At least, deterioration of the graininess in the fixing step does not occur.

As in the image forming apparatus according to the second embodiment, the peripheral speed of the developing sleeve is 900
By setting the speed to mm / sec or more, the following special effects can be obtained.

In an image forming apparatus in which the peripheral speed of the developing sleeve is high, that is, an image forming apparatus in which the process speed is high,
It is required that the developer moves at high speed. Further, the developer repeatedly rises and falls down on the surface of the developing sleeve by the magnetic pole of the magnet in the developing sleeve. When the magnetic brush rises, the toner in the developer scatters. The toner scattering tends to increase as the peripheral speed of the developing sleeve increases.
This is because the so-called centrifugal force when the magnetic brush rises and falls down increases as the peripheral speed of the sleeve increases. This greatly hinders the speeding up of the image forming apparatus.

On the other hand, the above-mentioned problem of toner scattering is more likely to occur as the volume average particle diameter of the toner becomes smaller. It is believed that this is because the so-called coverage decreases due to the reduction in the particle size of the toner, thereby lowering the chargeability of the toner and generating a toner having a low charge amount, but the mechanism has been clarified. Absent. When toner scatter occurs, the scattered toner accumulates inside the image forming apparatus, and a part of the scattered toner falls on the recording sheet, thereby contaminating the output image or contaminating the sensor. It causes problems such as being unable to perform.

The inventor conducted a spinning experiment from the developing device, suctioned toner scattered from the developing device, and measured the mass. In the experiment, the toner particle size was 5.0.
μm, 7.5 μm, and 9.5 μm. In addition, the developing device was continuously rotated for one hour, and when the total weight of the scattered toner during this period was 0.01 g or less, it was determined that the amount of scattered toner was small and there was no problem. FIG. 5 shows the result.

As can be seen from FIG. 5, even if the peripheral speed of the developing sleeve is set to 900 mm / sec or more in order to realize high-speed printing, if the toner particle size is 9.5 μm, the toner scattering amount increases so much. do not do. On the other hand, when the toner particle diameter is 5.0 μm or 7.5 μm, if the peripheral speed of the developing sleeve is 900 mm / sec or more, toner scattering increases, and the above-described problem occurs.

Also in the image forming apparatus of the second embodiment, since the toner particle size is 9.0 μm or more, it can be seen that the above-mentioned effect is obtained. That is, even in an image forming apparatus in which the peripheral speed of the sleeve must be increased (900 mm / sec or more), there is a specific effect that toner scattering does not occur.

In each of the embodiments, the fixing device is an oilless fixing device.

When the fixing device is constructed without oil, as pointed out in the section of the prior art, the simplicity of the structure of the device such as the elimination of oil and its circulation mechanism, and the elimination of oil replenishment, etc. are eliminated. Easy maintenance is one of the advantages. On the other hand, in the case of fixing without oil, the granularity of the image after passing through the fixing device is deteriorated. This is thought to be because the oil applied to the surface of the heating roller plays a role of uniformly heating the toner layer (because the oil intervenes as if it wraps around the toner layer).

On the other hand, in the image forming apparatus of each embodiment, the surface of the heating roller is made of a fluororesin as a fixing device, and the binder resin in the toner contains 20% by weight of a resin having a molecular weight of 100,000 or more. % Or less, the volume average particle diameter of the toner is 9.0 μm or more, and the ratio of the colorant in the toner is 5.0% by weight or less. By the mechanism described above, the deterioration of the graininess in the fixing step does not occur.

Further, the image forming apparatus of each embodiment is characterized in that the binder resin constituting the toner is a polyester resin. When the binder resin constituting the toner is composed of a polyester resin, it is characterized by excellent pigment dispersibility and excellent toughness. In particular, the latter feature of excellent toughness is particularly effective in the case of a toner having a low softening temperature. In other words, when the binder resin has a low softening temperature, the toner is liable to be crushed when the toner is stirred in the developing device. On the other hand, such a problem can be solved by using a polyester resin having excellent toughness as a binder resin of the toner.

[0075]

According to the first aspect of the present invention, it is possible to prevent the deterioration of the graininess in the fixing step while taking advantage of the advantage that the toner has excellent releasability, energy saving and resource saving can be achieved. it can.

According to the second aspect of the present invention, it is possible to further prevent the image from having a low density.

According to the third aspect of the present invention, it is possible to achieve both energy saving, which is a feature of a fixing device in which a fixing member does not have an elastic layer, and prevention of deterioration in graininess in the fixing device. Can be.

According to the fourth aspect of the present invention, since the volume average particle diameter of the toner is 9.0 μm or more, it is possible to reduce the scattering of toner in a high-speed image forming apparatus. Can play.

According to the fifth aspect of the present invention, since the graininess of the fixing device does not deteriorate, an oilless fixing device can be adopted, and the structure of the fixing device can be simplified and maintenance can be simplified. realizable.

According to the sixth aspect of the present invention, a toner which is hardly crushed can be realized.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view illustrating an example of an image forming apparatus.

FIG. 2 is a cross-sectional view of a fixing device.

FIG. 3 is a graph showing a relationship between a volume average particle diameter of the toner and a fine powder generation rate.

FIG. 4 is a graph showing granularity.

FIG. 5 is a graph showing the relationship between the peripheral speed of a developing sleeve and the weight of scattered toner.

[Explanation of symbols]

 Reference Signs List 4 developing device 6 recording sheet 8 fixing device DA developer T toner image

Claims (6)

[Claims] 1. A recording sheet carrying a toner image between a heated fixing member and a pressing member disposed opposite to the fixing member, in such a direction that the toner image contacts the fixing member. In the image forming apparatus having a fixing device that fixes the toner image on the recording sheet by heating and pressing the toner of the toner image by passing the toner image, a surface of a fixing member that is in contact with the toner image is formed of a fluororesin, In the binder resin in the toner, the ratio of the resin having a molecular weight of 100,000 or more is 20% by weight or less, the volume average particle diameter of the toner is 9.0 μm or more, and the ratio of the colorant in the toner is 5%. 0.02% by weight or less. 2. The image forming apparatus according to claim 1, wherein the ratio of the colorant in the toner is 2.0% by weight or more. 3. The fixing member of the fixing device according to claim 1, wherein the fixing member has no elastic layer.
4. The image forming apparatus according to claim 1. 4. A developing device for forming the toner image, the developing device carrying a developer, and transporting the developer to a developing area where an electrostatic latent image is visualized. 2. The image forming apparatus according to claim 1, further comprising a developer carrying member, wherein a linear velocity of the peripheral surface of the developer carrying member is set to 900 mm / sec or more.
An image forming apparatus according to any one of claims 1 to 3. 5. The image forming apparatus according to claim 1, wherein the fixing device is configured as an oilless fixing device that does not apply a release agent to the surface of the fixing member. 6. The image forming apparatus according to claim 1, wherein the binder resin of the toner is a polyester resin.