JP4574042B2 - Fixing apparatus and image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
  The present inventionConstantMore particularly, the present invention relates to a method and apparatus for improving granularity.
[0002]
[Prior art]
In an image forming apparatus such as a copying machine, a facsimile machine, a printer, or a printing machine, when a latent image bearing member electrostatic latent image having a different diameter is subjected to visible image processing by a developing device, the visible image is displayed. The processed image is transferred to a recording medium such as a sheet.
The recording medium to which the image is transferred is discharged after the image in the unfixed state is fixed in the fixing device.
[0003]
Conventionally, as a method used for fixing an image, there are a method for fixing in a non-contact state with a sheet for flash fixing and oven fixing, and a contact fixing method using a heat roller method as a representative example.
Unlike the non-contact fixing method, the contact fixing method has good heat transfer efficiency and power saving by direct contact with the sheet. It is frequently used because of the low risk of fire.
[0004]
As a configuration of the heat roller system, which is a typical example of the contact fixing system, there is a configuration shown in FIG. 12 as an example.
In FIG. 12, a heat roller type fixing device A has a pair of rollers B and C opposed to each other across a sheet conveyance path P, and is supplied by an image surface of a sheet S, that is, a developing device. The roller B facing the surface carrying T is used as a fixing roller, and the roller C facing this is used as a pressure roller.
The fixing roller B is a heating roller including a heat source B1 such as a halogen rod lamp, and the pressure roller C has an elastic layer on the surface, and the surface is deformed by pressure at a position where it contacts the fixing roller B. By doing so, the nip region of the sheet S can be formed.
[0005]
In the heat roller type fixing device, the toner contained in the image is changed from a semi-fused state to a sheet penetrating state by applying heat and pressure to the sheet in the nip region, thereby supplying the toner to the sheet. Can be fixed.
[0006]
The fixing roller B has a configuration in which the surface of a core metal serving as a base material is exposed and a configuration in which an elastic layer is provided on the surface of the core metal.
The former configuration has the advantage that the amount of heat as a roller can be reduced by direct contact of a core metal with good thermal conductivity to the sheet, thereby shortening the rise time to the fixing temperature, thereby saving energy. Can be realized.
The latter configuration has the advantage of good adhesion to the sheet, and by applying heat and pressure to the toner, the action of heat and pressure can be applied uniformly and efficiently, and the color development of the toner can be improved. . For this reason, the latter configuration is frequently used when forming a color image.
[0007]
[Problems to be solved by the invention]
In the case of a fixing device using a heat roller system, the granularity, which is one of the evaluation items for image quality, may not be obtained properly.
In general, visual evaluation items for image quality include graininess in addition to sharpness, gradation reproducibility, and color reproducibility. The graininess means the roughness of the image due to the structure of the image itself having a granular structure using granular toner. For example, in the case of a digital image, the inside of the dot is set in units of one dot. The melting area ratio of the toner at an arbitrary position in FIG.
[0008]
FIG. 13 is a schematic diagram for explaining the degree of graininess. In FIGS. 13A to 13C, the first (A-1, B-1, C-1) diagrams show the transfer process. FIG. 5 is a side view showing the accumulation state of the toner transferred on the base sheet in FIG. 2, and the second (A-2, B-2, C-2) diagrams are plan views in the first state; The third (A-3, B-3, C-3) diagram is the second equivalent diagram after fixing.
The state shown in (A) is a state where the toner T is largely dispersed in the dot surface, the state shown in (B) is a state where a part T1 of the toner T overlaps, and (C) The state shown in FIG. 2 is a state in which the toners T are dispersed in a state of being substantially adjacent to each other.
[0009]
Regarding the state of the toner on the dot surface after fixing, in the dispersed state of the toner T shown in (A), as shown in (A-3), the toner T melts at a position where it is largely dispersed, and the sheet To penetrate.
In the accumulation state of the toner T shown in (B), the melting amount of the toner is increased, and the sheet penetrates into the sheet in a state where the spread is large.
In the dispersed state of the toner shown in (C), the respective toners are melted in a generally continuous state and penetrate into the sheet.
[0010]
In FIG. 13, the state shown in (B) is the largest amount of toner melted at an arbitrary position within the dot, and the state shown in (A) is the smallest. If dots having different melting area ratios according to the toner melting amount exist in the entire image, a uniform density cannot be obtained in the entire image.
[0011]
The reason why the granularity is not stable is considered to be influenced by heat propagation during heating and pressurization in the fixing device.
In general, in a fixing device, even when the toner layer height varies, the toner is infiltrated into the sheet in a melted state with a uniform pressure. However, the surface property of the sheet, particularly smoothness, is uneven. However, this unevenness in smoothness makes the contact state with the pressure roller non-uniform. For this reason, when the pressure is applied by the pressure roller in the thick toner layer, the heat propagation from the heating roller becomes good, the melting of the toner easily proceeds, and the melting area ratio also increases. On the other hand, when the toner layer is located in a depression or the like of the sheet, the pressure from the pressure roller becomes insufficient, and the heat propagation from the heating roller becomes insufficient, so that the melting area ratio becomes small. On the contrary, the brightness decreases at the portion where the melted area ratio increases, and on the contrary, the brightness increases at the portion where the melted area ratio is small. As a result, a portion having a large melting area ratio and a portion having a small melting area are mixed in the entire image, in other words, portions having different lightness are mixed, and this gives a rough visual effect to the image. FIG. 14 shows the difference in the melting area of the toner that affects the difference in brightness for each dot in the image.
According to an experiment by the present inventor, it has been found that this phenomenon is remarkable in a configuration in which the fixing roller does not have an elastic layer.
[0012]
As described above, the fixing roller has a configuration having no elastic layer and a configuration including the same, and a configuration in which a fluororesin serving as a release layer is coated on the surface and a tube configured by the fluororesin. There is a configuration in which is coated. Unlike the configuration in which the silicone elastic body layer is provided on the surface, it has been found by experiments of the present inventors that the granularity is poor.
[0013]
For the fixing roller having the above-described configuration, there is a case where silicone oil or the like as a release agent is applied to the surface and a case where it is not applied in order to prevent toner offset. When both cases were compared in terms of graininess, experiments revealed that the graininess was worse when no oil was applied.
[0014]
On the other hand, it has been experimentally found that there is a difference in graininess depending on the toner used in the fixing device having the fixing roller having the above-described configuration.
In some cases, the toner used in the image forming apparatus has a high coloring rate by increasing the content of the colorant contained in the toner in order to reduce the size of the toner bottle installed in the developing device. By using a high coloring rate, it is possible to reduce the amount of toner consumed and the amount of waste and to reduce the size of the structure. In general, the content of the colorant is set to 6 to 12% by weight in the case of monochrome, so that the density difference is small and no change in density occurs. In this case, it is about 3%. In the case of color, the above-mentioned content ratio eliminates the need to increase the thickness of the superimposed toner image, and can reduce the impression that the toner layer generated by increasing the thickness becomes thicker. It can be solved that the glossiness required for the image varies depending on the superimposed thickness.
It was found that when the color was increased, the graininess deteriorated.
[0015]
Among the requests regarding the use of toner, from the viewpoint of energy consumption in the fixing device, there is a case where the temperature of the glass transition point is lowered to reduce power consumption. In this way, it is confirmed that when the glass transition temperature, in other words, the softening point temperature is lowered, the stability of the toner is lowered, and the graininess is also deteriorated along with the problem that the spent adhering to the carrier surface is generated. Has been.
[0016]
There is also a difference in graininess in the types of images formed by the image forming apparatus. A monochrome image generally has many line images such as characters, while a color image has many solid images such as photographic images. For this reason, in the case of a color image, the graininess tends to be deteriorated due to an increased thermal burden on the fixing device as compared with a monochrome image.
[0017]
An object of the present invention is to provide a fixing method, a fixing device, and an image forming apparatus capable of improving the graininess and preventing the deterioration of image quality in view of the above-described problems relating to fixing.
[0018]
[Means for Solving the Problems]
  According to the first aspect of the present invention, the toner adhered on the sheet by electrostatic transfer is removed.By heat roller type heat fixing meansFixing fixingapparatusThe toner adhering to the sheet is removed before the fixing process in which the toner is permeated into the sheet by applying heat and pressure to the toner.A means for pressurizing and leveling the toner, and the toner leveling means is disposed upstream in the transport direction of the sheet transported toward the heat fixing unit, and is opposed to and abuts across the transport path of the sheet. The roller pair has a non-heated structure, and at least the roller on the side in contact with the toner has the surface hardness of the roller on the side facing the toner in the heat fixing unit. That it is smaller than the surface hardnessIt is a feature.
[0033]
  According to a second aspect of the present invention, the heat fixing unit is premised on a configuration in which the roller on the side in contact with the toner does not have a release structure.
[0034]
  Claim3The described invention is claimed.1 or 2The fixing device described above is used.
[0035]
  Claim4The described invention is a toner,Increased content of colorant in tonerIt is characterized by using toner.
[0036]
  Claim5The described invention is characterized in that a material having a characteristic that the glass transition point is low is used as the toner.
[0037]
  Claim6The described invention is characterized in that the toner adhering to the sheet is used for forming a multicolor image by superimposing toners of respective colors having a complementary color relationship with respect to color separation.
[0038]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the illustrated examples.
FIG. 1 is a schematic view showing a main part of an image forming apparatus provided with an apparatus for executing a fixing method according to an embodiment of the present invention.
In FIG. 1, an image forming apparatus 1 is a printer having a configuration capable of forming a monochrome image, and a drum-shaped photoconductor 2 is provided therein as a latent image carrier.
[0039]
The photoreceptor 2 uses a conductor as a base, and a photosensitive layer is provided on the surface of the photoreceptor 2 so that the photoreceptor 2 can rotate in the direction of the arrow shown in the drawing. In this embodiment, the diameter of the photoreceptor 2 is 60 mm, and the peripheral speed is 230 mm / sec.
[0040]
Around the photosensitive member 2, a charging device 3, a writing device 4, a developing device 5, a transfer device 6 and a cleaning device 7 are arranged for executing an image forming process along the rotation direction.
The charging device 3 is a contact charging device provided with a roller that makes contact with the second position of the photoconductor, and is regenerated by forming an elastic layer (thickness 3 mm) having a medium resistance conductivity on the surface of the core metal serving as a base. The photosensitive member 2 is configured to be a roller and is charged to −600 V by applying a DC voltage (−1.35 KV) from a power source (not shown).
The writing means 4 is a laser beam scanning type writing device having a semiconductor laser as a light source, and scans the laser beam in the main scanning direction and the sub-scanning direction in accordance with image information, thereby converting the electrostatic latent image into a photosensitive member. 2 is formed.
[0041]
In the case of this embodiment, the developing device 5 has a configuration in which a two-component developer including a toner and a carrier is used. That is, the developing sleeve 5A that electrostatically transfers the toner in the developer carried on the peripheral surface facing the photoconductor 2 to the photoconductor 2, the toner and the carrier contained in the development tank 5B, A stirring member 5C that is stirred and mixed to be frictionally charged and then transferred to the developing sleeve 5A and a doctor blade 5D that defines the layer thickness of the developer in a picture matching the developing sleeve 5 are provided.
[0042]
In this embodiment, a developer is used in which the toner concentration is set to 5.0% by mixing a toner having a volume average particle diameter of 7.5 μm and a carrier having a particle diameter of 50 μm.
A gap where the developer can come into contact with the photosensitive member 2 is provided at a position where the photosensitive member 2 and the developing sleeve 5A are opposed to each other, and an electrostatic latent on the photosensitive member 2 is utilized using a developing bias applied to the developing sleeve 5A. Toner is supplied to the image.
[0043]
The transfer device 6 employs a configuration that also serves as a conveyance using a transfer belt wound around a pair of rollers, and a transfer bias voltage is applied to the transfer belt from a power supply (not shown) to supply paper (not shown). The toner image subjected to the visible image processing on the photosensitive member 2 is electrostatically transferred to the sheet fed from the apparatus.
[0044]
The cleaning device 7 is a device for removing toner remaining on the surface of the photoconductor 2 after transfer and residual charges, and includes a cleaning blade 7A that contacts the photoconductor 2, recovery means 5B for the removed toner, and A neutralizing means (not shown) is provided.
[0045]
The sheet S on which the toner image from the photoreceptor 2 has been transferred by the transfer device 6 is conveyed to the fixing device 8 where the toner is fixed.
The fixing device 8 in this embodiment employs a heat roller system including a fixing roller 8A and a pressure roller 8B, and the fixing roller 8A is on the side in contact with the toner image carried on the sheet S. This is a heating roller that is composed of a cored bar arranged and has no fluorine resin coating layer or silicone resin coating film on its surface and a halogen rod heater 8A1 inside. . In this embodiment, the surface temperature of the fixing roller 8A is set to 110 to 220 ° C.
In the pressure roller 8B, an elastic layer is laminated on the surface of the core metal, and a release layer made of a fluororesin layer is provided on the surface of the elastic layer. In this embodiment, the pressure roller 8B is pressed against the fixing roller 8A with a pressure of 20 to 100 N, and the nip width with the fixing roller 8A can be set to about 2 to 10 mm.
[0046]
A leveling means 9 is provided on the upstream side in the conveyance direction of the sheet S, that is, at a position corresponding to the position before reaching the fixing device 8.
FIG. 2 shows the structure of the leveling means 9. In the figure, the leveling means 9 includes a pair of rollers that face each other across the sheet conveyance path, and is carried on the sheet after transfer. It is provided in order to make the deposited layer thickness of the toner uniform.
[0047]
In the leveling means 9, a pair of rollers 9 </ b> A and 9 </ b> B constituting the leveling means 9 are arranged in a non-heated state, and the rollers rotate at the same linear speed as the sheet S conveying speed in the fixing device 8, the so-called linear speed. It is like that.
[0048]
The roller pair used for the leveling means 9 is such that the roller 9A on the side in contact with the toner image carried on the sheet S has a surface hardness smaller than that of the fixing roller 8A in the fixing device 8, and A charged series material that does not electrostatically attract toner on the surface is used. In this embodiment, a material that does not induce static electricity having a polarity opposite to the electrostatic polarity of the toner is used as the base, and the base is directly exposed to the outside without a release layer or an elastic layer. is there.
[0049]
As a material constituting the roller 9A on the side in contact with the toner image, a metal is used when a charging series is a condition. Further, when the surface hardness of the fixing roller 8A is considered in the fixing device 8, when the elastic body layer or the release layer is provided on the surface of the fixing roller 8A, the roller 9A in the leveling means 9 also depends on the surface state. It is also possible to set the above relationship, that is, when an elastic body layer or a release layer is present on the surface of the fixing roller 8A, the elasticity of the elastic layer is also applied to the roller 9A on the leveling means 9 side. The above relationship is set by appropriately selecting coefficients and the like.
On the contrary, when the fixing roller 8A described above is a metal roller such as aluminum, the metal material may be selected so that the surface hardness between the metals has the above relationship.
[0050]
The contact pressure between the rollers 9A and 9B in the leveling means 9 is larger than the contact pressure between the fixing roller 8A and the pressure roller 8B in the fixing device 8, and the toner accumulated on the sheet is removed from the sheet. It can be pushed to the side.
[0051]
In this embodiment, fixing is performed by the following procedure using the fixing device having the above-described configuration.
The sheet S on which the toner image on the photoconductor 2 is transferred by the transfer device 6 passes through the leveling means 9 before the fixing process through the action of heat and pressure by the fixing device 8 is performed, whereby the toner is transferred. Leveled.
As shown in FIG. 13, the toner on the sheet S has different melting area ratios after being heat-fixed depending on the accumulated state and the dispersed state. For this reason, the toner deposit layer thickness is made uniform in the leveling means 9, and in particular, the toner shown in FIG. 13B is heated and fixed in the fixing device 8 by eliminating the overlapping state. In this case, the heat propagation efficiency for the toner is made uniform.
[0052]
In the leveling means 9, the pressure and surface hardness, which are the contact conditions between the toner image in the fixing device 8 and the fixing roller 8 A, are different from those of the fixing device 8, and in particular the difference in smoothness of the sheet S due to the high pressure. Regardless, the toner thickness can be made uniform by forcibly pushing in the toner, and the toner image is carelessly scraped because the surface hardness is weaker than that of the fixing device 8 and there is no difference in linear velocity. Therefore, the thickness of the deposited layer can be made uniform in a state where a partial defect of the image does not occur.
[0053]
When the toner having a uniform deposited layer thickness is subjected to the action of heat and pressure in the fixing device 8, the heat propagation efficiency between the toners is uniform, so that the melting area ratio on the dot surface is uniformized. As a result, the graininess becomes uniform and there is no occurrence of density unevenness in the image.
[0054]
The fixing roller 8A on the fixing device 8 side may have a material having a relatively high hardness on the surface thereof and a material that can obtain a large hardness in the surface hardness with the roller 9A on the leveling means 9 side. For example, fluorine such as a PTFE layer, a PTFE tube, a PFA layer or a tube using the same, an FEP layer or a tube using the same, an ETFE layer or a tube using the same, a PDVP layer or a tube using the same. Resin or fluororesin tubes can be used.
[0055]
With regard to graininess, the definition of “subjective evaluation value indicating how rough the image that should be uniform” is defined, and granularity is a representation of subjective graininess on an objective evaluation scale. It is said that.
RMS granularity is a standardized granularity, which is standardized by the following equation in “ANSI PH-2, 40-1985”.
RMS granularity (σ_D) = [1 / N Σ (Di−D)²]^1/2
However, Di: concentration distribution, D: average concentration (D = 1 / NΣDi)
In addition, the granularity using Winer Spectrum, which is the power spectrum of image density fluctuation, is defined. Xerox Doo1ey and Shaw applied Winer Spectrum, cascaded with visual spatial frequency characteristics (Visua1 Transfer Function: VTF), and then integrated the value into granularity (GS) (for details, see RPDooley, Rshaw: Noise Perception in Electrophotography.eng, 5, 481979), pp 190-196).
[0056]
GS = exp (−1.8D) ∫ (WS (f))^1/2VTF (f) df
However, D: average density, f: spatial frequency (c / mm), WS (f): Winner Spectrum, VTF (f): visual spatial frequency characteristics
In order to analyze the granularity, the present inventor further developed the granularity of Doo1ey and Shaw and defined it by the following equation.
Granularity = exp (aL + b) ∫ (WS_L(F))^1/2VTF (f) df
Where L: average brightness, f: spatial frequency (c / mm), WS_L(F): Lightness fluctuation power spectrum, VTF (f): Visual spatial frequency characteristics, 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 superior in the linearity of the color space and has excellent adaptability to color images.
Hereinafter, the experimental results will be described assuming that the granularity is defined by this equation.
The granularity represents the noise characteristics of the image based on its definition.
By measuring the granularity of the output image by the above-described method, the noise characteristic (roughness) of the image can be quantified. As can be seen from the definition of the numerical value of the granularity, the value is small when the roughness is good, and the value becomes larger as the roughness becomes worse.
The present inventor calculated the granularity based on the above formula after reading the output image with a scanner (FT-S5000: manufactured by Dainippon Staren).
[0057]
The present inventor uses the granularity obtained by the above-described definition formula as a scale for evaluation, and the configuration equipped with the leveling means 9 shown in FIG. 2 and the leveling means 9 as shown in FIG. When the degree of granularity was compared using an unequipped configuration (Comparative Example 1) and a configuration using a non-contact system such as an oven fixing system (Comparative Example 2), the results shown in FIG. 3 were obtained. The experiment was performed in such a manner that an unfixed toner image was formed on paper (Ricoh TYPE 6000) by a laboratory machine that resolved the Ricoh digital copying machine MF4570, and only the fixing method was changed.
[0058]
FIG. 3 shows the lightness on the horizontal axis and the granularity on the vertical axis. The granularity is given for each lightness, and the inventor applied the lightness to 17 levels (halftone processing with 150 screen lines). A 17-level patch image was created) and the granularity at each brightness was calculated.
[0059]
As is clear from the experimental results, the granularity of the oven fixing method (Comparative Example 2) in which the image surface is not pressurized at the time of fixing is the best, and is about 0.2 at the maximum (even when the brightness is around 50). On the other hand, in the so-called conventional fixing device (Comparative Example 1 when there is no leveling process before fixing), the granularity of the image after passing through the fixing device is very deteriorated, and is 0.9 at the maximum. became.
[0060]
In the image forming apparatus (Example 1) provided with the leveling means 9 according to this example, the deterioration of the granularity was not as high as that of the above-mentioned Comparative Example 1, but about 0.4 at the maximum. As can be seen from this experiment, the granularity of the image after passing through the fixing device 8 is deteriorated only by providing a process of leveling the deposited layer by pressurizing the toner image on the sheet before passing through the fixing device 8. It becomes possible to improve.
[0061]
Next, another embodiment of the present invention will be described.
In this embodiment, the configuration of the fixing device 8 and the leveling means 9 is the same as that shown in FIG. In this embodiment, the contact pressure at the leveling means 9 is higher than the contact pressure between the fixing roller 9A and the pressure roller 9B of the fixing device 8, and 0.86 (N / cm on the fixing device 8 side). ) And 1.43 (N / cm) on the leveling means 9 side.
When the contact pressures on the fixing device 8 side and the leveling means 9 side are made different from each other, especially when the contact pressure on the leveling means 9 side is increased, the inventor reduces the contact pressure on the leveling means 9 side to 0. , 2 to 5.0 (N / cm), the granularity was measured and the results shown in FIG. 4 were obtained. In FIG. 4, only the average value between 40 and 80 is shown for the lightness in order to avoid complication. This is because the granularity in the middle lightness region of lightness 40 to 80 is extremely important from the viewpoint of high image quality.
In FIG. 4, the horizontal axis represents the contact pressure on the leveling means 9 side, and the vertical axis represents the average value of the granularity in the range of lightness L * = 40-80.
[0062]
As apparent from FIG. 4, when the contact pressure on the leveling means 9 side is larger than that on the fixing device 8 side, the effect of preventing the deterioration of the graininess is increased, and the value of the granularity is good. (The broken line in FIG. 5 shows the case where the contact pressure on the leveling means 9 side is 0.86 (N / cm)). From this result, it can be said that when the contact pressure on the leveling means 9 side is equal to or greater than 0.86 (N / cm), the deterioration of the graininess in the fixing process is reduced.
[0063]
Next, another example according to the embodiment of the present invention will be described.
This embodiment is characterized in that the surface hardness of the roller 8A on the leveling means 9 side is made lower with respect to the fixing roller 8A on the fixing device 8 side by using the configuration shown in FIG.
[0064]
In accordance with the selection of the material used for the fixing roller 8A on the fixing device 8 side, the material of the roller 9A on the leveling means 9 side is selected so as to have the above-described surface hardness relationship.
In this embodiment, when the fixing roller 8A on the fixing device 8 side is provided with an elastic layer, the fixing roller 8A is formed of an elastic body having a surface hardness smaller than that of the elastic layer. As the material of the elastic body, SBR (styrene butadiene rubber), BR (butadiene rubber), U (urethane rubber), NBR (nitrile rubber), CR (chloro rubber), silicone rubber, fluorine rubber, and the like are used.
[0065]
The inventor made a trial manufacture of the roller 9A on the leveling means 9 side formed of the above-described rubber material (in this case, for the case where the rubber hardness varies, the trial production was carried out with several levels of hardness), and the output image When the granularity was measured, the results shown in FIG. 5 were obtained.
On the other hand, for the case where the fixing roller 8A is composed of a metal roller (iron, aluminum, stainless steel), a comparative experiment in which a material that reduces the surface height of the roller 9A on the leveling means 9 side is selected is also shown. went.
In FIG. 5, the horizontal axis indicates the measured value of the hardness of the roller 9A on the leveling means 9 side in the rubber hardness meter (the hardness measurement is a test piece made of the same material as the roller 9A on the leveling means 9 side). This was performed by the method described in JIS. The vertical axis represents the average value of the granularity between the lightness L * = 40 to 80, as in the case where the result shown in FIG. 4 is obtained.
[0066]
As is clear from the experimental results of FIG. 5, the roller surface hardness on the leveling means 9 side is smaller (softer) than that on the fixing device 8 side, and the deterioration of graininess on the fixing device 8 side is less. I understand that By the way, the average granularity of iron, aluminum and stainless steel metal rollers was about 0.7. From this, it can be seen that when the surface hardness of the roller 9A on the leveling means 9 side is smaller than the surface hardness of the roller on the fixing device 8 side, the deterioration of the graininess in the fixing device 8 becomes smaller. In this case, the roller material on the fixing device 8 side is iron.
[0067]
Next, another example according to the embodiment of the present invention will be described.
The present embodiment is characterized in that the leveling process is performed for a case where a toner with a high coloring rate is used as the toner.
The material constituting the toner is a binder resin, a colorant (pigment), and a wax. Specific material names are disclosed in, for example, Japanese Patent Application Laid-Open No. 9-265210.
The present inventor measured the granularity of the output image by selecting the colorant ratio of the toner for the monochrome image (the binder resin is polyester resin, the colorant is carbon black, and the wax amount is fixed at 5%). As a result, the results shown in FIG. 6 were obtained.
In FIG. 6, the horizontal axis represents the colorant ratio (% by weight) in the toner, and the vertical axis represents the average value of the granularity between lightness L * = 40-80.
[0068]
As apparent from FIG. 6, when the leveling process is not performed as compared with the case where the leveling process is performed by the leveling means 9 (the line indicated as the example in FIG. 6) (in FIG. 6, the comparative example and It can be seen that the displayed line) has poorer graininess.
It should be noted that the difference increases as the colorant ratio of the toner increases. That is, when the leveling process is performed using a toner having a high toner coloring power, the effect of improving the graininess is great. For this reason, it is desirable that the colorant ratio is 7% or more for the high coloring power type toner. Moreover, it can be said that a range image with a colorant ratio of 10% or more is desirable as a range in which the improvement in graininess is very large.
[0069]
As for the color toner, since the colorant ratio is fundamentally different from that in the case of monochrome, it is desirable that the colorant ratio is 3% or more as a high color strength type.
[0070]
Next, still another example according to the embodiment of the present invention will be described.
The present embodiment is characterized in that the leveling process is performed for a case where a toner having a relatively low glass transition temperature is used as the toner.
The material constituting the toner is a binder resin, a colorant (pigment) and a wax, as described in the right to obtain the result shown in FIG. -265210 and the like.
[0071]
The present inventor used many toners whose softening point temperature corresponding to the glass transition temperature was changed by a method of changing the molecular weight of the fixing resin in the toner, and measured the granularity when performing image output, The result shown in FIG. 7 was obtained.
[0072]
In FIG. 7, the horizontal axis is the softening point temperature of the toner, and the vertical axis is the average value of the granularity between lightness L * = 40-80.
As can be seen from FIG. 7, it can be seen that the graininess is worse when the leveling process is not performed than when the leveling process is performed (solid line in FIG. 8). It should be noted that the difference increases as the softening point temperature of the toner decreases. That is, when the leveling process by the leveling means 9 is performed using a toner having a low toner softening point temperature, the effect of improving the graininess is great. Therefore, in this embodiment, it is possible to select a toner softening point temperature of 100 ° C. or lower as the toner for the low-temperature fixing type. In addition, the graininess can be improved even when the toner softening point temperature is in the range of 80 ° C. or less as the range in which the graininess is greatly improved.
[0073]
The present invention is directed to an image forming apparatus capable of forming not only a monochrome image but also a multicolor image in which images formed using toners of a plurality of colors are superimposed and transferred onto a sheet in a fixing process. It is also possible to carry out a leveling process as a previous step.
FIG. 8 shows a configuration of a color image forming apparatus that is a typical example of a multicolor image. In FIG. 8, the same members as those used in the apparatus shown in FIG.
In FIG. 8, the color image forming apparatus 10 has a revolver structure including a developing unit for each color in which the developing device 11 can rotate among the devices provided around the photoreceptor 2. Further, a transfer device (indicated by reference numeral 6 'for convenience) facing the photosensitive member 2 is an intermediate transfer member configured in a drum shape, and an image for each color formed on the photosensitive member 2 is superimposed in the primary transfer process. After the transfer, the sheet S can be collectively transferred to the sheet S by the secondary transfer device 6A.
The sheet S on which the superimposed images are collectively transferred by the secondary transfer device 6A is subjected to a leveling process by the leveling means 9 before reaching the fixing device 8.
[0074]
When the smoothing process is carried out in such a configuration, the toner layer that is superposed and thick is averaged between the toners, and the melted area due to the action of heat and pressure in the fixing device 8. Is homogenized. For this reason, when obtaining the glossiness as a color image in the fixing device 8, there is no difference in the melting area due to the difference in the deposited layer thickness between the toners, so that the desired glossiness can be obtained.
[0075]
FIG. 9 is a view showing a modification of the color image forming apparatus. The color image forming apparatus shown in FIG. 9 does not have the intermediate transfer member in the configuration shown in FIG. That is, an image forming unit (for convenience, symbols Y, M, and CB representing color meanings) for executing image forming processing for each color are juxtaposed on the extended surface of the transfer / conveyance belt 12 and the sheet moves. Each color image is transferred to the sheet. Even in the image forming apparatus having this configuration, although not shown, the leveling process is performed before the sheet reaches the fixing device.
[0076]
Further, the present invention is not limited to the heat roller system shown in FIG. 2 as the fixing device, and as shown in FIG. 10, the fixing belt 12A is moved in accordance with the conveying speed of the sheet S, and is arranged on the extended surface thereof. 11 in which the toner is infiltrated into the sheet by applying heat and pressure to the toner subjected to the leveling process by the leveling means 9 by the heat source 13 and the pressure roller 14. As shown in FIG. 4, the sheet S is nipped and conveyed between a pair of opposed rollers, while the roller 15 on the side in contact with the toner on the sheet S is fixed to the other fixing roller 17 wound around the other roller 16. The present invention can also be applied to a configuration in which the other roller 16 and the pressure roller 18 are provided with a heat source. Incidentally, in the configuration of the fixing device shown in FIG. 11, since a belt having a small heat capacity can be used as the fixing belt as compared with the case where a heat source is built in the roller, the rise to the fixing temperature can be accelerated.
[0077]
【The invention's effect】
  According to the first aspect of the present invention, since the leveling means is smaller than the heat fixing means with respect to the surface hardness, the toner is crushed on the dot surface without applying inadvertent pressure to the toner. It is possible to prevent the melted area from changing by preventing.
[0085]
  Claims2According to the described invention, the roller used for the leveling means exposes the base material itself on the surface, and does not have a release layer or an elastic layer on the so-called surface., StaticIt is possible to prevent the reverse transfer of the toner by reliably avoiding the induction of the electric force.
[0086]
  Claim3According to the described invention, since the toner to be heat-fixed has a uniform layer thickness, the molten state by heat and pressure is made uniform and the molten area becomes uniform. It is possible to prevent density unevenness in the image caused by the difference.
[0087]
  Claim4According to the described invention,Increased content of colorant in tonerWhen toner is used, even if the thermal burden on the heat fixing means increases, the toner deposition thickness is made uniform, so that the heat transfer efficiency can be made uniform between the toners and melted. It is possible to prevent the occurrence of density unevenness by making the area ratio uniform between the toners and making the granularity uniform.
[0088]
  Claim5According to the described invention, even when a toner having a low glass transition temperature is used, the thermal efficiency can be made uniform between the toners by the uniform thickness of the toner. It is possible to prevent the occurrence of density unevenness due to the difference in granularity by making the toner uniform.
[0089]
  Claim6According to the described invention, even when a multicolor image is formed by using toners in a superimposed relationship, the thickness of the deposited layer of toner of each color can be made uniform. It is possible to obtain a multicolor image having a desired glossiness by uniformizing the melting rate by preventing occurrence of a difference in granularity.
[Brief description of the drawings]
FIG. 1 is a schematic diagram illustrating a configuration of an image forming apparatus to which an apparatus for executing a fixing method according to an embodiment of the present invention is applied.
FIG. 2 is a schematic diagram showing a fixing device for executing a fixing method according to an embodiment of the present invention.
FIG. 3 is a diagram for explaining the relationship between toner brightness and graininess by the fixing method according to the embodiment of the present invention;
FIG. 4 is a diagram for explaining the difference in granularity due to the relationship between the contact pressure at the leveling means and the contact pressure at the fixing device according to the fixing method according to the embodiment of the present invention;
FIG. 5 is a diagram for explaining the difference in granularity due to the relationship between the surface hardness of the leveling means by the fixing method according to the embodiment of the present invention and the surface hardness of the fixing device.
FIG. 6 is a diagram for explaining a difference in granularity when the fixing method according to the embodiment of the present invention is performed on toners having different coloring ratios.
FIG. 7 is a diagram for explaining a difference in granularity when the fixing method according to the embodiment of the present invention is performed on toners having different softening point temperatures.
FIG. 8 is a schematic diagram illustrating another example of an image forming apparatus to which the fixing method according to the embodiment of the invention can be applied.
FIG. 9 is a schematic diagram illustrating another example of an image forming apparatus to which the fixing method according to the embodiment of the invention can be applied.
FIG. 10 is a schematic diagram showing another example of a fixing device capable of performing the fixing method according to the embodiment of the present invention.
FIG. 11 is a schematic diagram showing another example of a fixing device capable of performing the fixing method according to the embodiment of the present invention.
FIG. 12 is a schematic diagram for explaining a conventional example of a fixing device.
FIG. 13 is a diagram for explaining a toner accumulation state and a melting state when a conventional fixing device is used.
14 is a diagram for explaining a visual effect due to a difference in the melting state of the toner shown in FIG. 13; FIG.
[Explanation of symbols]
1 Image forming device
2 Photoconductor
6 Transfer device
8 Fixing device
8A fixing roller
8B Pressure roller
9 Leveling means
9A Roller in contact with toner
T Toner

Claims (6)

In a fixing device for fixing toner adhered on a sheet by electrostatic transfer by a heat roller type heat fixing means ,
Before the fixing process of applying heat and pressure to the toner to infiltrate the sheet, the toner has means for pressurizing and leveling the toner adhering to the sheet ,
The toner leveling means is arranged on the upstream side in the conveyance direction of the sheet conveyed toward the heating and fixing means, and is constituted by a rotatable roller pair that abuts against each other across the conveyance path of the sheet,
The roller pair has a non-heated structure, and at least the roller in contact with the toner has a surface hardness smaller than the surface hardness of the roller on the heating fixing unit facing the toner. a fixing device, characterized in that. The fixing device according to claim 1.
A fixing device which the heat fixing means, characterized in that it assumes a configuration having no releasing structure roller on the side in contact with the toner. An image forming apparatus using the fixing device according to claim 1. The image forming apparatus according to claim 3 .
An image forming apparatus comprising: a toner having an increased content of a colorant contained in a toner . The image forming apparatus according to claim 3 or 4, wherein:
An image forming apparatus characterized in that a material having a characteristic that a glass transition point is a low temperature is used as a toner . The image forming apparatus according to claim 3, wherein:
The image forming apparatus according to claim 1, wherein the toner adhering to the sheet is used for multicolor image formation by superimposing toner for each color having a complementary color relationship with respect to color separation .

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