JP2012032564A - Image forming method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve low temperature fixability as well as sufficient density, glossiness and color reproducibility as picture qualities in a comparable level to silver salt photographs and prints, by improving a concealing rate of toner on a recording sheet.SOLUTION: An image forming method is provided, including a fixing step of forming a toner image on a recording sheet, the toner image formed by using at least two kinds of toners having different types of temperature dependence of melt viscosity, and passing the recording sheet carrying the toner image through a fixing nip portion so as to fix the toner image. The fixing nip portion includes an effective pressure region where pressure of 0.05 MPa or more is applied. At least one kind in the toners having different types of temperature dependence of melt viscosity shows a minimum attained viscosity of 1.0×10Pa s or more and less than 5.0×10Pa s in the effective pressure region. The effective pressure region includes a fixing nip region where the melt viscosity Gof a toner having a low viscosity and the melt viscosity Gof a toner having a high viscosity used together with the low viscosity toner satisfy 0.5≤logG-logG≤2.5.

Description

  The present invention relates to a toner for developing an electrostatic latent image on a latent image carrier, and an image forming apparatus technique that transfers an image developed using the toner onto a recording sheet and then fixes it to obtain a printed image. Belonging to the field. In particular, the present invention relates to a toner for improving the density, glossiness, and color reproducibility of a printed image after fixing, and an image forming method.

  There are various demands on the image quality of printed images by electrophotographic printers and copiers depending on the intended use. In particular, in order to use it for posters, advertisements, art works, etc., silver salt photography and print-level image quality are required, and sufficient density, gloss, and full color reproducibility are required.

  In a fixing process of an electrophotographic printer or copying machine, the toner transferred onto the recording paper is fixed on the recording paper by heating and pressing. At this time, it is known that the toner sufficiently conceals the recording paper and forms a smooth toner image surface, thereby improving the density, glossiness, and color reproducibility of the image. This is a factor that affects the image quality.

  Parameters that have a large effect on this phenomenon include the heat and pressure applied to the toner by the fixing device, the application time, and the melt viscosity of the toner. Compatible printers and copiers have been developed.

  Low melt viscosity toner has excellent low-temperature fixability. It melts and spreads on the recording paper by the fixing process, conceals the recording paper, and is crushed by pressure to form a smooth toner image surface. This is effective for improving the degree of color and color reproducibility. However, at the same time, the toner permeates the recording paper excessively and cannot conceal the surface. Moreover, it becomes easy to generate | occur | produce hot offset, and it acts also to reduce preservability (blocking resistance).

  On the other hand, toner with high melt viscosity is disadvantageous for low-temperature fixability, and it is difficult to conceal the recording paper and form a smooth toner surface. However, excessive penetration into the recording paper, occurrence of hot offset, storage stability Works well. Proposals have been made using the melting characteristics of toner resulting from such differences in viscosity.

  For example, Japanese Patent Laid-Open No. 2004-228561 has been proposed to use a mixture of two or more types of toners having different softening points of toners in order to solve the problem that conventionally only one model can obtain a glossiness determined. Also, the glossiness of the printed image can be adjusted by adjusting the temperature.

  Japanese Patent Application Laid-Open No. 2005-228867 proposes an image forming apparatus in which toner developed on a latent image carrier is transferred to a recording sheet, and the toner remaining on the latent image carrier is collected and recycled as recycled toner. Among these, the glass transition point and toner melt viscosity of the binder resin of the replenishing toner used by mixing with the recycled toner are different from those of the initial toner. Recycled toners are less fixable than initial toners, so replenished toners maintain good image quality by using glass transition points and toner melt viscosities that are shifted in the direction of improving fixability. .

  However, with only the glossiness selecting function as in Patent Document 1 and the fixing property maintaining function as in Patent Document 2, it is not possible to obtain a sufficient image quality as a silver salt photograph or a printing level. In addition to glossiness and fixability, it is necessary to ensure sufficient density and color reproducibility at the same time. To that end, maintaining low temperature fixability of low-viscosity toner and reducing image quality due to excessive melting In particular, it is necessary to prevent a reduction in concealment rate due to penetration of toner into the recording paper.

Japanese Patent Laid-Open No. 2001-235892 JP-A-11-95553

  An object of the present invention is to improve the concealment rate of toner on recording paper, and to realize density, glossiness, and color reproducibility sufficient for image quality at silver salt photography and printing level as well as low-temperature fixability. .

  It is an object of the present invention to solve this problem.

In the image forming method of the present invention, a toner image formed using at least two types of toners having the same hue and different melt viscosity temperature dependence is formed on a recording paper, and the toner image is carried. An image forming method including a fixing step of fixing a toner image on a recording paper by passing the recording paper through a fixing nip formed by a fixing member having a heating member and a pressure member pressed against the fixing member. And
The fixing nip portion has an effective pressure region to which a pressure of 0.05 MPa or more is applied,
Among the toners having different melt viscosities, at least one of the toners has a minimum reached viscosity ( _GL-min ) in the effective pressure region of 1.0 × 10 ² Pa · s or more and 5.0 × 10 ³ Pa · s. less than s,
In the effective pressure area, and the melt viscosity G _H of high viscosity toner to be combined with the melt viscosity G _L and low viscosity toner of low viscosity toner satisfies the following formula 0.5 ≦ logG _H -logG _L ≦ 2.5
There is a region that satisfies the condition.

Further, the image forming method of the present invention forms on a recording paper a resin particle image formed using at least two types of resin particles having different temperature dependences of melt viscosity, and a recording paper carrying the resin particle image is formed. An image forming method including a fixing step of fixing a resin particle image on a recording paper by passing through a fixing nip formed by a fixing member having a heating member and a pressure member pressed against the fixing member,
The fixing nip portion has an effective pressure region to which a pressure of 0.05 MPa or more is applied,
Among the resin particles having different temperature dependences of the melt viscosity, at least one kind has a minimum ultimate viscosity ( _Gmin ) in the effective pressure region of 1.0 × 10 ² Pa · s or more and 5.0 × 10 ³ Pa · s. Is less than
In the effective pressure area, low viscosity and melt viscosity G _H melt viscosity G _L and low viscous resin particles used in combination with viscosity resin particles of the resin particles satisfies the following formula _{0.5 ≦ logG H -logG L ≦ 2} . 5
There is a fixing nip region that satisfies the above condition.

  According to the present invention, the density, glossiness, and color reproducibility can be improved by properly melting the toner on the recording paper to conceal the recording paper and forming a smooth toner image surface.

FIG. 4 is a diagram showing a temperature and pressure profile in a fixing nip. FIG. 6 is a diagram illustrating an example of a change in melt viscosity in a fixing nip of two types of toner. FIG. 6 is a top view illustrating a toner melting process on recording paper. Sectional drawing explaining the melting process of the toner on a recording paper. FIG. 3 is a cross-sectional view of an example of a fixing device. 1 is a configuration model diagram of an example of an image forming apparatus. 1 is a configuration model diagram of an example of an image forming apparatus. 1 is a configuration model diagram of an example of an image forming apparatus. The figure which shows the melt viscosity of 4 types of toner used for image evaluation. The figure which made the image evaluation result of Table 1 into a graph. FIG. 4 is a diagram illustrating an example of a melt viscosity of a mixed toner. The figure which made the image evaluation result of Table 2 into a graph.

  Hereinafter, the best mode for carrying out the present invention will be described in detail by way of example.

[Example 1]
(1) Image Forming Apparatus FIG. 6 is a schematic sectional view of an example of an image forming apparatus according to the present invention. The image forming apparatus shown in this embodiment is a laser beam printer using a transfer method and an electrophotographic process.

  In FIG. 6, reference numeral 101 denotes a drum-shaped electrophotographic photosensitive member (hereinafter referred to as a photosensitive drum) as a latent image carrier that is rotatably supported. The photosensitive drum 101 is rotationally driven at a predetermined process speed in the direction of the arrow by a driving means (not shown).

  Around the photosensitive drum 101, along the rotation direction, a charging roller (charging means) 102, a laser exposure device (exposure means) 103, a developing device (developing means) 104, a transfer roller (transfer means) 106, and a cleaning device. (Cleaning means) 105 are arranged in that order.

  The outer peripheral surface (surface) of the photosensitive drum 101 is uniformly charged to a predetermined polarity and potential by the charging roller 102. Thereafter, the surface of the photosensitive drum 101 is irradiated with laser light L based on the target image information from the laser exposure device 103, the charge in the exposed portion is removed, and an electrostatic latent image is formed on the photosensitive drum.

  The electrostatic latent image formed on the photosensitive drum 101 is developed with a developer (toner) included in the developing device 104. The developing device 104 includes a toner container (not shown) containing toner and a developing roller. By applying a developing bias to the developing roller and attaching toner carried on the developing roller to the electrostatic latent image on the photosensitive drum 101, the electrostatic latent image is visualized (visualized) as a toner image. . The toner image is primarily transferred to the intermediate transfer belt 108 by applying a primary transfer bias to the primary transfer roller 106. This process is repeated in the image forming portion Py and thereafter also in Pm, Pc, and Pk, and toner images of four colors are superimposed on the intermediate transfer belt 108 to be formed.

  On the other hand, the recording paper P is fed from a feeding cassette (not shown) at a predetermined timing, and is conveyed to a transfer nip Tn formed by the intermediate transfer belt 108 and the secondary transfer roller 110 by a conveying roller 111 or the like. Is done. A transfer bias is applied to the secondary transfer roller 110, whereby the four-color toner images on the intermediate transfer belt 108 are secondarily transferred onto the recording paper P all at once.

  The recording paper P carrying an unfixed toner image exits the transfer nip Tn and is then fed into a heat fixing device (hereinafter abbreviated as a fixing device) 112. In the fixing device 112, the unfixed toner image is heated and pressurized to be fixed on the recording paper while the recording paper is nipped and conveyed at the fixing nip portion. The configuration of the fixing device 112 will be described in detail in section (3).

  The recording paper P on which the toner image is fixed is conveyed and discharged to a discharge tray (not shown) on the apparatus main body.

  On the other hand, the toner remaining without being transferred onto the photosensitive drum 101 and the intermediate transfer belt 108 after the toner image transfer is removed by the cleaning devices 105 and 109. As a result, the photosensitive drum 101 and the intermediate transfer belt 108 are cleaned to prepare for the next image formation.

  At least two types of toners having different melt viscosities used in the present invention may be mixed in a toner container included in the developing device 104. Alternatively, a developing device may be provided for each unmixed toner and developed separately (described in Example 4).

(2) Toner The toner used in the present invention can be produced by a conventionally known production method and is an electrostatic image developing toner containing at least a binder resin and a colorant. Or the resin particle for electrostatic charge image development which consists of binder resin and does not contain a coloring agent may be sufficient.

  The binder resin for the toner or resin particles used in the present invention is not particularly limited, and a thermoplastic resin made of a natural or synthetic polymer substance can be used. In addition to styrene acrylic resin synthesized using styrene, acrylic ester, methacrylic ester, etc., for example, epoxy resin, polyamide resin, polyester resin, polyvinyl resin, polyurethane resin, polybutadiene resin, etc. are used alone or in combination. Also good. Of these, styrene acrylic resin and polyester resin are preferable.

  One method for obtaining toners or resin particles having different melt viscosities includes changing the composition and blending ratio of the binder resin, the polymerization method, the polymerization conditions, and the like.

  As an example of a binder resin used as a low-viscosity toner or low-viscosity resin particles, a mixture of 95 parts of styrene monomer and 5 parts of butyl acrylate is used as a monomer composition, toluene is used as a solvent, and azobis is used as a polymerization initiator. Examples include relatively low molecular weight polymers obtained by solution polymerization using isobutyronitrile.

  As an example of a binder resin used as a high-viscosity toner or high-viscosity resin particles, a mixture of 80 parts of styrene monomer and 20 parts of butyl acrylate is used as a monomer composition, and 1,1-bis (t- Examples include relatively high molecular weight polymers obtained by suspension polymerization using (butylperoxy-isopropyl) cyclohexane.

  Then, for example, after sufficiently mixing the binder resin, colorant, and, if necessary, additives such as a crosslinking agent, charge control agent, and release agent with a ball mill or other kneader, heat kneading such as a heating roll It is cooled after being melt-kneaded using a machine, pulverized with an airflow pulverizer, and classified with an air classifier to adjust the particle size distribution to obtain a toner.

  The means for changing the melt viscosity is not limited to changing the binder resin, and the type and amount of the additive may be changed.

  In the present embodiment, a case where two types of toners having different temperature dependence of melt viscosity are used in combination (mixed) will be described. These toners have the same hue, but are not limited to the completely same hue. For example, in the case of a cyan toner, the hues are aligned to such an extent that they can be used as a cyan toner. It ’s fine.

  The hue may be the same as that for cyan, magenta, yellow and black for forming a full color image, and the colorant of each toner before mixing is changed so that the hue can be obtained by mixing, The hue may be adjusted. Further, the hue may be adjusted by changing the mixing ratio within a range in which the effect of the present invention can be obtained.

(3) Fixing Device FIG. 5 is a schematic sectional view of an example of the fixing device 112.

  A recording sheet having a heat source (heater) and a rotatable heating roller 10 and a rotatable pressure roller 20 that is in pressure contact with the heating roller 10 to form a fixing nip. While nipping and conveying P, the unfixed toner image is heated and pressurized to be fixed on the recording paper P.

  The heating roller 10 includes a hollow metal core 11 made of a metal having good thermal conductivity (aluminum, iron, etc.), an elastic layer 12 such as silicon rubber on the outside, and a mold release such as PFA that covers the surface of the elastic layer 12. Layer 13 is provided. A halogen heater 14 is disposed inside the hollow core 11 as a heat source. The operation of the halogen heater 14 is controlled by a temperature control device 15. The temperature control device 15 performs on / off control for the operation of the halogen heater 14 based on the surface temperature of the heating roller 10 detected by the thermistor 16.

  The pressure roller 20 includes a metal core 21 made of metal (aluminum or iron), an elastic layer 22 made of silicon rubber or the like on the outer side of the core metal 21, and a releasability such as PFA covering the surface of the elastic layer 22. It consists of layer 23.

  Note that the above description does not limit the configuration of the fixing device of the present invention. As a heating method of the fixing device, in addition to the above-described heat roller method, a film (belt) heating method, an induction heating method, a combination thereof, or a plurality of heating sources may be used. In the case of the film heating method, the fixing member is pressed by the pressing member through the film-like member, and the fixing nip portion is formed by the heating member and the film-like member.

(4) Image Evaluation with Mixed Toner Image obtained by fixing a toner image formed on recording paper using a mixture of at least two types of toners having different melt viscosities in the fixing nip. The evaluation results will be described.

First, four types of toners A, B, C, and D having different melt viscosities depending on temperature were used alone to form toner images on recording paper, fixed under various fixing conditions, and image evaluation was performed. Each toner has a weight average particle diameter of 6.0 μm and a specific gravity of 1.1 g / cm ³ , which is almost equal. The recording paper is plain paper with a basis weight of 80 g / m ² , and the toner image on the recording paper is a cyan solid image with an applied amount of 0.3 mg / cm ² .

  FIG. 9 is a graph showing the temperature dependence of the melt viscosity of toners A, B, C, and D.

  The melt viscosity is determined by the following method.

As an apparatus, for example, a flow tester CFT-500D (manufactured by Shimadzu Corporation) is used, and measurement is performed under the following conditions.
Sample: About 1.5 g of toner is weighed, and this is molded with a pressure molding machine at a load of 300 kg / cm ² for 1 minute to obtain a sample.
・ Die hole diameter: 1.0mm, 0.5mm
-Die length: 1.0mm
Cylinder pressure: 4.903 × 10 ⁵ (Pa) to 3.972 × 10 ⁷ (Pa)
Measurement mode: Temperature rising method Temperature rising rate: 4.0 ° C./min
Measurement temperature range: 50 ° C to 150 ° C

  FIG. 1 is a graph showing an example of a change in temperature and pressure on the surface of a recording sheet while a recording sheet carrying a toner image is passing through a fixing nip formed by a fixing member and a pressure member. It is. The temperature of the recording paper surface continues to rise while going from upstream to downstream of the fixing nip. The pressure has a peak at the center of the fixing nip portion, and has a region to which a pressure of 0.05 MPa or more is applied (hereinafter referred to as an effective pressure region). Here, although the pressure peaked at the center of the fixing nip, the peak does not necessarily have to be at the center. For example, the peak may be at the latter half of the fixing nip portion.

  Note that the temperature of the recording paper surface at the fixing nip was measured as follows. A thermocouple with a small heat capacity in the temperature detector (for example, K-type thermocouple wire diameter 50 μm manufactured by Anritsu Keiki Co., Ltd.) is attached to the recording paper, and the recording paper is sandwiched and transported to the fixing nip portion of the temperature-controlled fixing device. It was. And the electric potential difference signal was measured with Hioki Electric Co., Ltd. memory high coder (model number 8842) from the thermocouple at that time.

  The pressure at the fixing nip was measured using a pressure distribution measuring system PINCH manufactured by NITTA.

With the above method, the recording paper surface temperature in the fixing nip under each fixing condition was measured, and for example, the temperature profile of the recording paper surface in the fixing nip as shown in FIG. 1 was obtained. From the temperature profile and the temperature dependence of the toner melt viscosity shown in FIG. 9, for example, the change in the toner melt viscosity in the fixing nip as shown in FIG. 2 is converted (the melt viscosities of toner B and toner D in FIG. 2). Shows changes). Furthermore, the lowest reached viscosity _Gmin in the effective pressure region was extracted. The minimum attainable viscosity _Gmin means the minimum value of the viscosity that reaches the fixing nip. For example, in FIG. 2, the melt viscosity at the end of the effective pressure region at the nip downstream side corresponds to this, the lowest ultimate viscosity of toner B is point G _B-min , and the lowest ultimate viscosity of toner D is point G _D-min . is there.

  Table 1 summarizes the image evaluation results.

  As fixing conditions, image evaluation was performed by changing temperature, process speed, and pressure. Here, as an example, four levels of data (1) 140 ° C., (2) 160 ° C., (3) 200 ° C., and (4) 240 ° C. with different fixing member surface temperatures will be described. The fixing time is about 40 msec. In addition, regarding the process speed and pressure, the range in which the effect of the present invention is more preferably obtained will be described later.

  In the “Evaluation 1” column, ○ indicates that fixing is possible, Δ indicates that fiber is transparent, × indicates that fixing is not possible, and * indicates that hot offset is generated.

  ○ The method for determining whether fixing is possible or not fixing is as follows. The image after fixing is folded into a cross while applying a load of 1 kg, and further rubbed back and forth five times with sylbon paper applied with a load of 200 g. Was fixed, and 20% or more was determined not to be fixed.

  Also, a method for determining the occurrence of hot offset is as follows. A halftone horizontal band image of several gradations is formed on the leading edge of the recording paper and fixed, and the reflectance of the area around which the toner offset to the fixing member circulates and is re-fixed to the recording paper is measured. Find the difference in reflectance. The gradation halftone with the largest value was adopted, and the case where the difference was 0.5 or more was regarded as * hot offset occurrence.

  In addition, regarding the occurrence of Δ fiber see-through, the phenomenon and determination method will be described below.

  The toner is fixed on the recording paper and the recording paper is concealed to obtain a sufficient image density and color. By using a toner having a low viscosity characteristic or fixing at a high temperature for a long time, the toner can be further melted and the concealment rate of the toner to the recording paper can be improved. However, if the toner is excessively melted, the toner concealed on the recording paper penetrates between the fibers of the recording paper, and the fibers of the recording paper can be seen through (fiber transparency). As a result, the density decreases, and the coloring power inherently possessed by the toner cannot be fully exhibited.

  As a determination method, fixing is performed by increasing the temperature in increments of 10 ° C., and the transmission density of each sample that increases as the temperature increases is measured. Among them, the temperature at which the transmission density does not increase or the temperature at which the transmission density decreases is determined as the temperature at which the fiber shows through. At this time, the image is observed with a microscope, and it is determined comprehensively by simultaneously confirming that the white background portion has increased due to the see-through of the fiber and that no hot offset has occurred.

FIG. 10 shows the results of Table 1 in a bar graph. When the minimum attainable viscosity G _min is less than 1.0 × 10 ² Pa · s, the evaluation is *, and hot offset occurs. When the minimum attainable viscosity G _min is 1.0 × 10 ² Pa · s or more and less than 5.0 × 10 ³ Pa · s, the evaluation is Δ, and the fiber shows through. When the minimum attainable viscosity G _min is 5.0 × 10 ³ Pa · s or more and less than 1.0 × 10 ⁶ Pa · s, the evaluation is “good”, and fixing can be performed without any particular problem. When the minimum attainable viscosity G _min was 1.0 × 10 ⁶ Pa · s or more, the evaluation was ×, and fixing could not be performed.

  Next, any two of the above four types of toners are selected and mixed at a 1: 1 ratio (volume ratio) to form a toner image on the recording paper. Evaluation was performed. At this time, from the viewpoint of ease of image observation, the toner to be mixed is a combination of cyan and magenta. In order to evaluate the effect of the mixed toner, a single toner having a melt viscosity similar to the melt viscosity of the mixed toner was used as a reference toner, and the same image formation was performed.

  FIG. 11 shows the melt viscosity of toner B + D in which toner B and toner D are mixed at a volume ratio of 1: 1 as an example of the melt viscosity of the mixed toner. The melt viscosity of the mixed toner is measured as a single toner having an intermediate viscosity between high and low viscosity toners. This is a result of a flow tester using a macro quantity as a measurement sample. From the results of image observation to be described later, there is a difference in the melting method of the mixed high and low viscosity toner, which produces the effect of the present invention.

  The Ref toner is a single reference toner having substantially the same melt viscosity as that of the mixed toner B + D. The image evaluation was performed by calculating the image concealment rate when using Ref toner and mixed toner and estimating the increase in concealment rate due to the mixed toner. Although the image concealment ratio using Ref toner varies depending on the fixing conditions, it was about 80 to 90% under the fixing conditions used in this evaluation. A method for calculating the image concealment rate will be described below.

(Concealment rate calculation method)
When the image is observed with an optical microscope (manufactured by Keyence Corporation; digital microscope VHX-500), a microscope image can be obtained in which the recording paper is concealed and colored with toner. The microscope image acquisition conditions at this time are as follows.
Lens magnification: 450 times Real field area: 520 μm × 700 μm
Observation light: White transmitted light Output light quantity: MAX
Squeeze: Adjust as appropriate White balance adjustment: Perform on the white background of the recording paper

  The image acquired under the above conditions is saved in the Tiff format, and binarization processing is performed on the colored region and the background color (recording paper) region using image processing software (PhotoshopCS). Here, a threshold value is provided to extract a colored region, this portion is converted as black, and the other background color regions are converted as white. For the binarized image, the area ratio of the black region was calculated and used as the concealment ratio.

  Table 2 shows typical combinations of the mixed toner and the fixing conditions. In the “Evaluation 1 combination” column, combinations of evaluation results of fixed images with the single toner shown in Table 1 are shown. A circle in the “Evaluation 2” column indicates that the concealment rate has increased by 5% or more compared to the Ref toner. △ is an increase in the concealment rate of less than 5%, x is a state in which the increase in the concealment rate is not observed, □ is an increase in the concealment rate, but there is a large difference in melting of the high and low viscosity toners that are components of the mixed toner A state in which the melting is non-uniform and the smoothness of the image is deteriorated is shown.

  From this result, it is understood that “evaluation 2” is “x” when “x (fixing impossible)” or “* (hot offset occurrence)” is included in “evaluation 1 combination”. In other words, if the component of the mixed toner includes a component that cannot be fixed with the single toner or that causes a hot offset with the single toner, the effect of the mixed toner cannot be obtained.

  When "Evaluation 1 combination" is between Δ (fiber see-through), "Evaluation 2" is Δ. Among the single toners that cause fiber transparency, the degree of fiber transparency is somewhat suppressed by mixing high-viscosity toner, but the effect is slight.

  When “Evaluation 1 Combination” is ○ (fixable), mixing toners with different viscosities reduces the gap and improves the concealment rate, but “Evaluation 2” is Δ and the effect is slight. It is.

In “Evaluation 1 combination”, there was a case where “Evaluation 2” becomes “O” when ◯ (fixable) and Δ (fiber see-through) were combined. At this time, paying attention to the difference between the melt viscosity _{GH of the} toner exhibiting high viscosity and the melt viscosity _GL of the toner exhibiting low viscosity in the effective pressure region of the fixing nip portion, the difference in the lowest reached viscosity as a representative value: log _GH The value of _−min− log G _L-min is shown in the “lowest reached viscosity difference” column of Table 2. When this value is less than 0.5, a sufficient difference in viscosity cannot be obtained, and the effect of improving the concealment rate by the mixed toner becomes slight. On the other hand, when this value was larger than 2.5, the toner melted non-uniformly, resulting in an image with poor smoothness. Here, the difference in the minimum reached viscosity is shown as a representative value for the viscosity difference, but the effect was obtained when there was the appropriate viscosity difference within the effective pressure range of the fixing nip portion. That is, in order to obtain the effect of improving the concealment rate by the mixed toner, within the effective pressure range of the fixing nip portion,
0.5 ≦ log G _H −log G _L ≦ 2.5
It is sufficient if there is a fixing nip region that satisfies the above.

FIG. 12 is a graph of the above results. The vertical axis represents the minimum attainable viscosity G _{min of} each of the high and low viscosity toners forming the mixed toner, and the horizontal axis represents the minimum attainable viscosity difference log G _H-min -log G _L-min of each of the high and low viscosity toners. The plot symbol is the same as the symbol of “Evaluation 1” shown in Table 1, and shows the result of image evaluation using toner alone (◯ indicates that fixing is possible, Δ indicates occurrence of fiber transparency, and × indicates that fixing is not possible) * Indicates hot offset). The plots connected by the lines represent the mixed toner. For example, the “◯ -Δ” plot has two types, “◯: fixable” and “Δ: occurrence of fiber see-through”, as evaluation 1 of the single toner, respectively. Indicates mixing. In FIG. 12, the conditions (O and Δ in “Evaluation 2”) at which the improvement of the concealment ratio, which is an effect of the present invention, is a mixed toner in which all of the toners to be mixed are in the halftone dot region. Among them, “◯ -Δ” shaded plot, that is, “Evaluation 1”, “◯: Fixable” and “Δ: Fiber translucency” toner are mixed, and “Evaluation 2” is “Evaluation 2”. ○: Concealment rate increased (5% or more). In addition, when compared with the same combination “◯ −Δ”, the experimental result shows that a sufficient effect is seen when the difference in the minimum reached viscosity is 0.5 ≦ log G _H-min −log G _L-min ≦ 2.5. Obtained.

  Next, how the two types of toners having different melt viscosities are melted on the recording paper based on the result of detailed observation of the fixed image by the above mixed toner will be described. The two types of toner are represented by toner B and toner D, representative of the toners used in the image evaluation described above.

  FIG. 2 shows the melt viscosity of each toner at each part of the fixing nip based on the temperature change of the recording paper surface in the fixing nip portion shown in FIG. 1, and shows the toner melt viscosity and the pressure at the fixing nip portion in an overlapping manner. It is a thing. The mixed toner on the recording paper continues to rise in temperature while passing through the fixing nip, and the high and low viscosity toners that are components of the mixed toner begin to decrease in melt viscosity when their respective outflow start temperatures are exceeded, and in the effective pressure region in the fixing nip. It changes while taking different melt viscosities and is fixed under pressure.

  FIGS. 3 and 4 are schematic diagrams showing how two types of toners having different melt viscosities in the effective pressure region in the fixing nip are simultaneously melted on the recording paper.

First, the characteristics of melting of the mixed toner in the recording paper in-plane direction will be described with reference to FIG. FIG. 3 is a schematic diagram viewed from the upper surface of the recording paper. The upper part shows the transition of the mixed toner B + D, the middle part shows only the toner B (high viscosity), and the lower part shows the transition of the melt state only of the toner D (low viscosity). Tf _B and Tf _D are outflow start temperatures which are indicators of the temperature at which toner B and toner D start to melt, respectively. 3 (a) is less than the temperature Tf _D of (room temperature) state, FIG. 3 (b) the temperature is less than or Tf _D Tf _B state, FIG. 3 (c) shows the above state Tf _B.

For mixed toner B + D, the fixing process begins, becomes more than the flow starting temperature Tf _D of the toner D, the toner D begins to melt. The toner D conceals the recording paper so as to fill the gap of the toner B, and at the same time, the toner and the toner and the paper are adhered to improve the fixing property. Moreover, it deform | transforms smoothly by pressurization and works so that a glossy surface may be formed. Subsequently, when the toner B starts to flow out at a temperature Tf _B or higher, the toner B starts to melt. The toner B is combined with the toner D, the toner B, and the recording paper to further improve the fixing property and further conceal the recording paper, so that a high image density can be obtained. At this time, the toner B also functions to prevent the toner D from penetrating excessively into the recording paper. This will be described later with reference to FIG.

On the other hand, in the case of toner B alone, the toner B transferred onto the recording paper does not start to melt until the temperature rises to the outflow start temperature Tf _B or higher. As a result, the recording paper cannot be concealed as compared with the toner mixture B + D, and a gap remains.

Further, when the toner D only, toner D that is transferred onto the recording starts melting the temperature from rising above the flow starting temperature Tf _D, continue to conceal the recording paper. However, since the viscosity is low, the toner that has been concealed on the recording paper penetrates between the fibers of the recording paper before it melts and spreads to obtain a sufficient concealment ratio, and the fibers of the recording paper can be seen through. (Fiber sheer). As a result, the density is lowered, and the coloring power inherently possessed by the toner cannot be fully exhibited.

  That is, when one kind of toner having a close melt viscosity is used, it is extremely difficult to achieve both the elimination of fiber transparency and the concealment of recording paper without gaps. By mixing and using different toners, it is possible to achieve both.

Next, the melting state of the toner in the thickness direction of the recording paper will be described with reference to FIG. FIG. 4 is a schematic diagram viewed from the cross section of the recording paper. The upper row shows the mixed toner B + D, and the lower row shows the transition of the melting of the Ref toner, which serves as a reference toner having the same temperature dependence of the melt viscosity as the mixed toner B + D for comparison. Is shown. Tf _Ref in the figure is the Ref toner outflow start temperature, which is equivalent to Tf _{B + D.} 4A is a state where the temperature is less than Tf _D (room temperature), FIG. 4B is a state where the temperature is Tf _D or more and less than Tf _B , and FIG. 4B ′ is a state where the temperature is Tf _Ref or more. FIG. 4C shows a state where the temperature is equal to or higher than Tf _B.

  In order to improve density, glossiness, and color reproducibility, it is necessary to cover the recording paper with toner and form a smooth toner image surface. However, since recording paper has irregularities, it is difficult to achieve both. If the heating and pressurization is insufficient, the toner does not melt sufficiently and does not spread, leaving gaps, resulting in insufficient concealment rate and insufficient crushing, so that a smooth toner image surface cannot be formed. When heating and pressurization are strengthened to solve this, the toner melts and spreads and the gaps are filled, but the viscosity decreases excessively, and the toner is excessively pressed between the fibers of the recording paper by being pressed and pressed. Will penetrate. As a result, the fibers that mainly form the convex portions of the recording paper can be seen through (fibre penetration), resulting in a decrease in the concealment ratio, and the uneven shape of the recording paper is exposed, thereby exposing the toner image surface. The smoothness of the is reduced.

  In the case of the mixed toner B + D, the low-viscosity toner D that is a component thereof melts and spreads sufficiently to conceal the recording paper. Moreover, it deform | transforms smoothly by pressurization and contributes to formation of a glossy surface. Since the toner B having a higher viscosity than the toner D remains on the recording paper fiber even when subjected to strong heating and pressurization, the fiber does not easily show through. By combining the toner B having such characteristics with the toner D, it functions to prevent the toner D from penetrating between the fibers and causing the fibers to see through. In other words, the toner B plays a role as a base of the toner D, and has an effect (base effect) of receiving a pressure and forming a smooth toner image surface while preventing excessive penetration into the recording paper.

  On the other hand, in the case of the Ref toner, the macro toner amount has the same melt viscosity temperature dependency as the mixed toner B + D. However, unlike the mixed toner B + D, the melt viscosity of each particle at a certain temperature is the same. The value is higher than that of the toner D in the mixed toner B + D and lower than that of the toner B. Therefore, it does not melt and spread more than the toner D, so that the gap is not filled, and it is more easily pushed away from the recording paper fiber than the toner B, and does not become the base of the surrounding toner. Therefore, a gap remains between the toners as compared with the mixed toner B + D, the fibers are seen through, and the smoothness is deteriorated due to the exposure of the fiber irregularities. As a result, the density, glossiness, and color reproducibility are reduced as compared with the mixed toner.

  As a means for preventing easiness of melting and see-through of the fiber, it may be possible to design a single toner resin by mixing a low molecular weight component and a high molecular weight component, but the present invention mixes toner as different particles. It has the characteristics. By separating the functions into a low-viscosity toner that fills the gap and ensures smoothness, and a high-viscosity toner that prevents the see-through of the fibers by the base effect, the effect can be obtained within the range of the melt viscosity specified in the present invention. .

  The effect of the present invention is obtained in a region where a pressure of 0.05 MPa or more is applied in the fixing nip. When the toner in a molten state is pressurized, it is spread and its shape changes greatly. A big difference is produced in the way of deformation by the melt viscosity at this time. Accordingly, in order to obtain the effect of the present invention in which toners having different melt viscosities are mixed and the difference in deformation is used, a pressure of a certain level or more is required, and the value is 0.05 MPa or more.

  Further, as the pressure increases, the toner on the recording paper is pressed more strongly, and as a result, image defects such as the see-through of the fibers and the exposure of the paper fiber irregularities are likely to occur. In this case, the above-mentioned image defect can be avoided by setting the toner melt viscosity in the fixing nip to a high (hard) state, that is, by lowering the temperature or shortening the fixing time. After adjusting the melt viscosity (temperature) and time, the pressure at which the effect of the present invention can be satisfactorily obtained is preferably 1.0 MPa or less.

  In order to obtain the effect of the present invention, it is necessary to provide a toner melt viscosity difference in the fixing nip under the above-described pressure, and let this state act for an effective time. By changing the nip width and fixing operation speed of the fixing device, the fixing time can be set to a length suitable for the pressure and melt viscosity used in the present invention. In the present invention, the fixing time is preferably in the range of 10 to 1000 msec, and if it is within this range, the effects of the present invention can be obtained satisfactorily.

If the pressure during fixing is the same, the melting behavior of the toner during fixing varies depending on the melt viscosity in the fixing nip. In the case of a single toner that is not mixed, the toner is divided into the following four molten states based on the above-described image evaluation results.
(I) If the minimum attainable viscosity G _min in the effective pressure region of the fixing nip is 1 × 10 ⁶ Pa · s or more, the fixing strength of the toner to the recording paper is lowered, and fixing failure tends to occur.
(II) If the minimum attainable viscosity _Gmin in the effective pressure region of the fixing nip is 5 × 10 ³ Pa · s or more and less than 1 × 10 ⁶ Pa · s, good fixing is possible.
(III) If the minimum attainable viscosity G _min in the effective pressure region of the fixing nip is 1 × 10 ² or more and less than 5 × 10 ³ Pa · s, fiber penetration and fiber unevenness are likely to occur, and the recording paper is sufficiently It becomes difficult to conceal and smooth the toner image surface.
(IV) Further, when the minimum attainable viscosity G _min in the effective pressure region of the fixing nip is reduced to less than 1 × 10 ² Pa · s, hot offset in which the toner adheres to the fixing member is likely to occur.

  Among the toners to be mixed in the present invention, at least one kind of toner is used in the state (III). A single toner is a toner that easily melts and spreads within a range where hot offset does not occur, and is smoothly deformed by filling a gap. By mixing this low-viscosity toner with a toner having a higher (harder) melt viscosity, it is possible to prevent the fibers from seeping through and exposing the fiber irregularities.

In the present invention, in the effective pressure region, the difference in viscosity between the melt viscosity _{GH of the} toner exhibiting high viscosity and the melt viscosity _{GL of the} toner exhibiting low viscosity is 0.5 to 2.5 in common logarithm. An effect can be obtained if there is a nip portion. That is, 0.5 ≦ log G _H −log G _L ≦ 2.5 may be satisfied.

Incidentally, the lower limit on the viscosity difference log G _H - log G _L, the viscosity difference log G _H - log G _L is too small, the viscosity difference is less than 0.5, disappears image much different that fixing toner alone. On the other hand, when the viscosity difference log G _H -log G _L exceeds 2.5, the viscosity difference is too large, so that the mixed toner is not uniformly melted and the smoothness of the image is lowered. In addition, when a toner having a melt viscosity that is too high to be fixed is mixed, the fixing strength is lowered. Therefore, it is preferable that the toner having a high melt viscosity can be fixed at least alone. If the melt viscosity _GH of the high-viscosity toner is about 2.5 higher than the melt viscosity _GL of the low-viscosity toner, it can be fixed after adjusting the fixing temperature, pressure, and time. Become. In view of the above, the upper limit of the viscosity difference log G _H - log G _L 2.5 is considered reasonable.

The present invention works more effectively when the amount of toner forming a toner image is small. The toner images formed on the recording paper are arranged with a gap between the toner particles. As the toner amount decreases, the gap generated between the toners increases and it becomes difficult to conceal the recording paper with toner. In particular, when the toner amount falls below the closest packing amount (mg / cm ² ) determined from the particle size, (μm) and specific gravity (g / m ³ ), the increase in the gap becomes significant. For example, in the toner (particle diameter 6.0 μm, specific gravity 1.1 g / m ³ ) used for the verification of the present invention, the condition is M / S≈0.4 mg / cm ² or less.

  In order to conceal the recording paper with toner when the toner amount is small and form a smooth toner image surface, it is necessary to melt and spread the toner further than when the toner amount is large. As means for that purpose, it is conceivable to lower the viscosity of the toner, increase the fixing time, increase the fixing pressure, and the like. However, fiber transparency and fiber unevenness are likely to occur, and concealment rate and toner image surface smoothness are reduced.

  According to the present invention, it is possible to improve the concealment rate and the smoothness of the toner image surface while reducing the see-through of the fibers and the exposure of the fiber irregularities even with a small amount of toner. As a result, the image density, glossiness, and color reproducibility can be improved.

[Example 2]
Another example of the image forming method will be described. The same members / portions as those described in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted. The same applies to Examples 3 and 4.

  In the first embodiment, the usage ratio of the toner B and the toner D is 1: 1, but this ratio may be changed.

  Table 3 shows the results of image evaluation performed by changing the mixing ratio of the toner B in the mixed toner B + D from 5% to 80%, fixing under the fixing condition (2). Two types of image evaluation were performed. The “Evaluation 3” column in Table 3 evaluates the effect of improving the concealment ratio of the image by the mixed toner B + D for a single toner (Ref toner) having the same melt viscosity as the mixed toner prepared at each mixing ratio. It is the result. ○ indicates that the concealment rate has increased by 5% or more compared to Ref toner. Δ indicates that the increase in concealment rate was less than 5%. The column “Evaluation 4” in Table 3 is a result of evaluating the improvement effect of the glossiness of the image by the mixed toner B + D with respect to the Ref toner in order to check the smoothness of the image. ○ indicates that the glossiness has increased by 5 or more. Δ indicates that the increase in glossiness was less than 5. X indicates that the glossiness is equal or decreased.

  In addition, glossiness is the value of 60 degree gloss measured by Nippon Denshoku Co., Ltd. GlossMeter; VG2000.

  From this result, it was found that a sufficient effect of improving the concealment ratio can be obtained when the mixing ratio of the toner B of the mixed toner B + D is in the range of 10 volume% to 70 volume%. Further, it was found that when the mixing ratio of the toner B exceeds 50% by volume, the effect of improving the gloss of the image is reduced.

  Unfixed toner can have a gap of 30% by volume or more depending on the amount and arrangement. In the present invention, the concealment rate of the recording paper is improved by filling the gap formed by the high viscosity toner with the low viscosity toner. For this purpose, it is desirable to mix the low-viscosity toner at a ratio equal to or higher than the gap ratio of the high-viscosity toner. Then, it is appropriate that the low-viscosity toner is 30% by volume or more, and conversely, the high-viscosity toner is 70% by volume or less. If the high-viscosity toner is mixed in an amount of 10% by volume or more, the base effect can be obtained uniformly throughout the toner layer. Therefore, the mixing ratio of the high viscosity toner is preferably 10% by volume to 70% by volume.

  Further, in order to form a smooth toner image surface, it is preferable that the amount of low-viscosity toner that is easy to melt and spread is large. For this reason, it is effective to make the mixing ratio of the low-viscosity toner equal or larger than that of the high-viscosity toner. is there. Therefore, the mixing ratio of the high viscosity toner is more preferably 10% by volume to 50% by volume. Within this range, the fixing strength can be further increased.

[Example 3]
Another example of the image forming method will be described.

  A difference in particle diameter may be provided between the toners to be mixed, so that the particle diameter of the low viscosity toner may be larger than that of the high viscosity toner.

  Low-viscosity toner having a large particle size has a large amount of being crushed by pressurization, whereby a smooth toner image surface can be made wider. The high viscosity toner has a characteristic that it tends to remain on the fiber even if it has a small diameter, and a base effect that supports the low viscosity toner can also be obtained. Further, considering the difference in the amount of crushing between the high viscosity toner and the low viscosity toner, the height after the toner is crushed can be made uniform.

  Table 4-1 classifies toner B and toner D, adjusts the particle size distribution, produces a mixed toner B + D with a different ratio of weight average particle size, forms a toner image, and fixes it under fixing condition (2). This is a result of image evaluation.

  The image evaluation was performed for the concealment rate and the glossiness as described in Table 3. The meaning of the symbols in the table is the same.

From this result, the particle size ratio R _D / R _B of the mixed toner B + D has been found that sufficient effect of improving the contrast ratio in the range of 1 to 2 can be obtained. The particle diameter ratio R _D / R _B the effect of improving the gloss of the image was found to be reduced in the 0.75 or less.

Table 4-2 is a table showing the correspondence of the mixing ratio between (volume) particle size ratio R _D / R _B shown in Table 3. The value of “converted R _D / R _B ” is a value obtained by converting the value of the mixing ratio into a length by taking the cube root of the volume. "Experimental R _D / R _B" is the value of the particle size ratio R _D / R _B shown in Table 4 (a). Comparing both numerical values and the image evaluation result, it can be seen that the effective range of the particle size ratio corresponds to the effective range of the mixing ratio.

  Specifically, the weight average particle diameter (D4) of the low viscosity toner is preferably set to 1.0 to 2.0 times the weight average particle diameter (D4) of the toner having the highest melt viscosity.

  In the present invention, the weight average particle diameter of the toner is measured as follows.

  The weight average particle diameter (D4) of the toner is determined based on the precise particle size distribution measuring apparatus “Coulter Counter Multisizer 3” (registered trademark, manufactured by Beckman Coulter, Inc.) having a 100 μm aperture tube. Using the attached dedicated software “Beckman Coulter Multisizer 3 Version 3.51” (manufactured by Beckman Coulter, Inc.) for setting and analyzing the measurement data, the measurement data is measured with 25,000 effective channels. Analysis was performed and calculated.

  As the electrolytic aqueous solution used for the measurement, special grade sodium chloride is dissolved in ion-exchanged water so as to have a concentration of about 1% by mass, for example, “ISOTON II” (manufactured by Beckman Coulter, Inc.) can be used.

  Prior to measurement and analysis, the dedicated software was set as follows.

  In the “Standard Measurement Method (SOM) Change Screen” of the dedicated software, set the total count in the control mode to 50000 particles, set the number of measurements once, and set the Kd value to “standard particles 10.0 μm” (Beckman Coulter, Inc.) Set the value obtained using The threshold and noise level are automatically set by pressing the threshold / noise level measurement button. Also, the current is set to 1600 μA, the gain is set to 2, the electrolyte is set to ISOTON II, and the aperture tube flash after measurement is checked.

  In the “pulse to particle size conversion setting screen” of the dedicated software, the bin interval is set to logarithmic particle size, the particle size bin is set to 256 particle size bin, and the particle size range is set to 2 μm to 60 μm.

The specific measurement method is as follows.
(1) About 200 ml of the electrolytic solution is placed in a glass 250 ml round bottom beaker exclusively for Multisizer 3, set on a sample stand, and the stirrer rod is stirred counterclockwise at 24 rpm. Then, dirt and bubbles in the aperture tube are removed by the “aperture flush” function of the analysis software.
(2) About 30 ml of the electrolytic aqueous solution is put in a glass 100 ml flat bottom beaker, and "Contaminone N" (nonionic surfactant, anionic surfactant, organic builder pH 7 precision measurement is used as a dispersant therein. About 0.3 ml of a diluted solution obtained by diluting a 10% by weight aqueous solution of a neutral detergent for washing a vessel (made by Wako Pure Chemical Industries, Ltd.) 3 times with ion-exchanged water is added.
(3) Two oscillators with an oscillation frequency of 50 kHz are incorporated in a state where the phase is shifted by 180 degrees, and placed in a water tank of an ultrasonic dispersion device “Ultrasonic Dissipation System Tetora 150” (manufactured by Nikki Bios Co., Ltd.) having an electrical output of 120 W. A fixed amount of ion-exchanged water is added, and about 2 ml of the above-mentioned Contaminone N is added to this water tank.
(4) The beaker of (2) is set in the beaker fixing hole of the ultrasonic disperser, and the ultrasonic disperser is operated. And the height position of a beaker is adjusted so that the resonance state of the liquid level of the electrolyte solution in a beaker may become the maximum.
(5) In a state where the electrolytic aqueous solution in the beaker of (4) is irradiated with ultrasonic waves, about 10 mg of toner is added to the electrolytic aqueous solution little by little and dispersed. Then, the ultrasonic dispersion process is continued for another 60 seconds. In the ultrasonic dispersion, the temperature of the water tank is appropriately adjusted so as to be 10 ° C. or higher and 40 ° C. or lower.
(6) To the round bottom beaker of (1) installed in the sample stand, the electrolyte solution of (5) in which the toner is dispersed is dropped using a pipette, and the measurement concentration is adjusted to about 5%. . Measurement is performed until the number of measured particles reaches 50,000.
(7) The measurement data is analyzed with the dedicated software attached to the apparatus, and the weight average particle diameter (D4) and the number average particle diameter (D1) are calculated. The “average diameter” on the analysis / volume statistics (arithmetic average) screen when the graph / volume% is set with the dedicated software is the weight average particle diameter (D4).

[Example 4]
Another example of the image forming method will be described.

  If at least two kinds of toners having different melt viscosities are finally mixed on the recording paper, the effects of the present invention can be obtained. The place where the toner is mixed is not limited to the toner container but may be on the photosensitive drum or the intermediate transfer belt, and the high-viscosity toner and the low-viscosity toner may be developed separately.

  FIG. 7 is a schematic sectional view of an example of the image forming apparatus according to the present invention. In this embodiment, a developing device 104a having a toner container (not shown) containing high viscosity toner for each color and a developing device 104b having a toner container (not shown) containing low viscosity toner are provided. The electrostatic latent image on the photosensitive drum 101 is developed by the developing devices 104 a and 104 b, and high and low viscosity toners are mixed on the photosensitive drum 101. At this time, the developing order of the high viscosity toner and the low viscosity toner may be changed.

  Further, as shown in FIG. 8, a photosensitive drum 101 and another set (B) similar to a set of apparatuses (A) configured to develop an electrostatic latent image thereon are provided for each color. The image may be formed as a high-viscosity toner developing unit or a low-viscosity toner developing unit. In this case, the high and low viscosity toners are mixed when primary transfer is performed on the intermediate transfer belt 108.

  7 and 8 are expressed as two types of toner, but more types of toner may be mixed. Further, a toner mixture may be used only for a specific color (for example, black).

  In the present invention, if at least two types of toners having different melt viscosities are finally mixed on the recording paper and then fixed on the conditions described above in the fixing device, the effect can be obtained.

  112: fixing device, N: nip, P: recording paper, A, B, C, D: toner

Claims (2)

A fixing member having a heating body for forming a toner image formed on at least two types of toner having the same hue and different temperature dependence of melt viscosity on the recording paper. An image forming method including a fixing step of fixing a toner image onto a recording paper by passing through a fixing nip portion formed by a pressure member pressed against the fixing member.
The fixing nip portion has an effective pressure region to which a pressure of 0.05 MPa or more is applied,
Among the toners having different melt viscosities, at least one of them has a minimum ultimate viscosity ( _Gmin ) in the effective pressure region of 1.0 × 10 ² Pa · s or more and less than 5.0 × 10 ³ Pa · s. And
In the effective pressure area, and the melt viscosity G _H of high viscosity toner to be combined with the melt viscosity G _L and low viscosity toner of low viscosity toner satisfies the following formula 0.5 ≦ logG _H -logG _L ≦ 2.5
An image forming method comprising a fixing nip region that satisfies A resin particle image formed using at least two types of resin particles having different temperature dependences of melt viscosity is formed on a recording paper, and the recording paper carrying the resin particle image is fixed to a fixing member having a heating member and the fixing An image forming method including a fixing step of fixing a resin particle image on a recording paper by passing through a fixing nip portion formed by a pressure member pressed against the member,
The fixing nip portion has an effective pressure region to which a pressure of 0.05 MPa or more is applied,
Among the resin particles having different temperature dependences of the melt viscosity, at least one kind has a minimum ultimate viscosity ( _Gmin ) in the effective pressure region of 1.0 × 10 ² Pa · s or more and 5.0 × 10 ³ Pa · s. Is less than
In the effective pressure area, low viscosity and melt viscosity G _H melt viscosity G _L and low viscous resin particles used in combination with viscosity resin particles of the resin particles satisfies the following formula _{0.5 ≦ logG H -logG L ≦ 2} . 5
An image forming method comprising a fixing nip region that satisfies

Images