EP4592757A2

EP4592757A2 - Electrostatic latent image developing toner, image forming method, and image forming apparatus

Info

Publication number: EP4592757A2
Application number: EP25152209.0A
Authority: EP
Inventors: Yuka SUHARA; Kaori AKUTSU; Natsuko Kusaka
Original assignee: Konica Minolta Inc
Current assignee: Konica Minolta Inc
Priority date: 2024-01-26
Filing date: 2025-01-16
Publication date: 2025-07-30
Also published as: JP2025115440A; EP4592757A3

Abstract

An electrostatic latent image developing toner satisfies the following: in measurements 1 to 3, an amount of change in endothermic peak start temperature owing to a change in maintaining temperature is 2°C or less. Measurement 1: A toner sample is maintained at 40°C for three hours; the temperature is decreased to 0°C at a rate of -10°C/min; and differential scanning calorimetry is performed while increasing the temperature to 200°C at a rate of 10 °C/min. Measurement 2: After Measurement 1, the temperature is decreased to 0 °C at a rate of -10°C/min; and thereafter measurement is performed in the same manner as the measurement 1 except that the maintaining temperature is 50°C. Measurement 3: After Measurement 2, the temperature is decreased to 0°C at a rate of -10°C/min; and thereafter measurement is performed in the same manner as the measurement 1 except that the maintaining temperature is 60°C.

Description

TECHNICAL FIELD

The present invention relates to an electrostatic latent image developing toner, an image forming method, and an image forming apparatus. The present invention particularly relates to an electrostatic latent image developing toner that can reduce a difference in glossiness between front and back faces in double-sided printing and that has excellent varnish applicability and varnish adhesion.

BACKGROUND OF THE INVENTION

In electrophotographic double-sided printing, heat is applied differently to the front surface and the back surface of a sheet. A fixed image may be remelted and cause an image defect or a difference in glossiness between front and back surfaces.
Japanese Unexamined Patent Publication No. 2020-52211 discloses an apparatus configured to suppress an image defect caused by remelting of a fixed image in double-sided printing. However, depending on the type of base material, the fixing temperature, or other evaluation conditions, an image may have defect owing to remelting or have different levels of glossiness between front and back surfaces of the base material.
To improve image quality and durability, a varnish coat may be formed to part of or the whole surface of an image formed by electrophotography. However, varnish may be repelled on an image formed by an electrophotographic image forming apparatus, and an appropriate varnish coat may not be formed. Furthermore, although varnish is not repelled by an image, the varnish may not sufficiently adhere to the image and may easily peel off.
Such a problem is mainly caused by a release agent, which is precipitated on the surface of the image when the image is fixed by heating. A release agent is widely used in an electrophotographic image forming apparatus to improve offset resistance and toner separability. Owing to its nature, the release agent has a weak interaction with the varnish, so that the varnish is repelled by the image.
To deal with such a challenge, according to the techniques disclosed in Japanese Unexamined Patent Publications No. 2012-78565 and No. 2011-191536 , a polar wax is used as a release agent to improve affinity between varnish and the release agent, thereby improving coatability and adhesiveness of varnish to images. However, coatability and adhesiveness of varnish may be insufficient, and there is a trade-off between the offset resistance and the separability.
The present invention has been conceived in consideration of the above. An object of the present invention is to provide an electrostatic latent image developing toner, an image forming method, and an image forming apparatus that can reduce a difference in glossiness between the front and back surfaces of a sheet in double-sided printing and that can improve varnish coatability and adhesiveness.

SUMMARY OF THE INVENTION

To achieve the object, the inventors have studied the causes of the above problems. After the study, the present inventors devised a toner (i) that has a constant endothermic peak start temperature (fusion start temperature of crystalline components) on its DSC curve even when the maintaining temperature by the differential scanning calorimeter is changed and (ii) that contains a small amount of short-chain saturated hydrocarbon compounds. Thus, the inventors succeeded in providing an electrostatic latent image developing toner, an image forming method, and an image forming apparatus that can reduce a difference in glossiness between front and back faces in double-sided printing and that improve varnish coatability and varnish adhesiveness.
The object of the present invention described above is achieved by the following means.

1. An electrostatic latent image developing toner including toner base particles containing a binding resin and a release agent, wherein:
- the toner base particles contain a saturated hydrocarbon compound having 16 to 35 carbon atoms,
- an amount of the contained saturated hydrocarbon compound is in a range of 1 to 1000 ppm by mass with respect to a total mass of the electrostatic latent image developing toner, and
- the electrostatic latent image developing toner satisfies a following condition (i).
- Condition (i): In following measurements 1 to 3, an amount of change in endothermic peak start temperature owing to a change in maintaining temperature is 2 °C or less, the endothermic peak start temperature being observed at 20 °C or more on a differential scanning calorimetry (DSC) curve.
- (Measurement 1) A sample of the electrostatic latent image developing toner is maintained at a maintaining temperature of 40 °C for three hours; the temperature is decreased to 0 °C at a temperature decrease rate of -10 °C/min; and measurement by a differential scanning calorimeter is performed while increasing the temperature at a temperature increase rate of 10 °C/min in a range of 0 to 200 °C.
- (Measurement 2) For the sample after the measurement 1, the temperature is decreased at a temperature decrease rate of -10 °C/min in a range of 200 to 0 °C; and thereafter measurement is performed in a same manner as the measurement 1 except that the maintaining temperature is 50 °C.
- (Measurement 3) For the sample after the measurement 2, the temperature is decreased at a temperature decrease rate of -10 °C/min in a range of 200 to 0 °C; and thereafter measurement is performed in a same manner as the measurement 1 except that the maintaining temperature is 60 °C.
2. The electrostatic latent image developing toner according to the item 1, wherein the release agent contains hydrocarbon wax.
3. The electrostatic latent image developing toner according to the item 1, wherein the binding resin contains polyester.
4. The electrostatic latent image developing toner according to the item 1, wherein the binding resin contains styrene-acrylic resin.
5. The electrostatic latent image developing toner according to the item 1, wherein the toner base particles contain a crystalline substance other than the release agent.
6. The electrostatic latent image developing toner according to the item 1, wherein an external additive contains strontium titanate.
7. The electrostatic latent image developing toner according to the item 6, wherein a particle of the strontium titanate has a number-average primary particle size in a range of 20 to 200 nm.
8. The electrostatic latent image developing toner according to the item 7, wherein the particle of the strontium titanate has a number-average primary particle size in a range of 30 to 150 nm.
9. An image forming method including:
- attaching the electrostatic latent image developing toner according to any one of claims 1 to 8 to a recording medium; and
- fixing the attached electrostatic latent image developing toner onto the recording medium.
10. The image forming method according to the item 9, wherein in the fixing, the electrostatic latent image developing toner is fixed to the recording medium in two stages.
11. The image forming method according to the item 9, further including: applying varnish to a surface of a toner image formed by the fixed electrostatic latent image developing toner to form a varnish coat.
12. An image forming apparatus including at least a developing member, a transfer member, and a fixing member and configured to form a toner image on a recording medium using the electrostatic latent image developing toner according to any one of the items 1 to 8, wherein
- the fixing member has a fixing nip, and
- a fixing pad is used at the fixing nip.
13. The image forming apparatus according to the item 12, wherein the fixing member includes:
- an endless belt for heating the toner image on the recording medium at the fixing nip;
- a rotating member configured to form the fixing nip in cooperation with the endless belt;
- the fixing pad in contact with an inner circumferential surface of the endless belt and configured to form the fixing nip by sandwiching the endless belt between the fixing pad and the rotating body; and
- a heating roller in contact with the inner circumferential surface of the endless belt and configured to heat the endless belt.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the above-described means, the present invention can provide an electrostatic latent image developing toner, an image forming method, and an image forming apparatus that can reduce a difference in glossiness between front and back surfaces in double-sided printing and that improve varnish coatability and adhesiveness.
Although the mechanism of the effect of the present invention is not clear, the inventors infer the mechanism as follows.
According to the present invention, the amount of change in endothermic peak start temperature, which is observed at 20 °C or more on the DSC curve, owing to a change in maintaining temperature is 2 °C or less, and the melting start temperature does not greatly change. This is considered to contribute to equal glossiness between front and back surfaces in double-sided printing. Furthermore, since the maintaining temperature does not greatly affect the melting start temperature, the environmental temperature of images does not greatly affect the image quality (glossiness). Furthermore, the temperature at which toner is stored does not affect the quality of glossiness of fixed images. Furthermore, the temperature at which toner is transported does not affect the quality of toner.
In general, varnish is easily applied to an image when the compounds present on the image surface are evenly spread. Furthermore, adhesiveness of varnish on the image is improved when the compounds present on the image surface have a high level of affinity with the varnish.
However, a toner consists of various materials, and the image surface is a mixture of a release agent, a binding resin, and so forth. When varnish is applied on such a surface, varnish droplets remain on the surface of the binding resin and do not spread over the surface of the release agent, and the image is not sufficiently coated by varnish. For example, the image repels varnish.
In the present invention, a toner contains a small amount of saturated hydrocarbon compounds having a short chain length (having 16 to 35 carbon atoms) in addition to the release agent. Since the short-chain saturated hydrocarbon compounds easily move to the image surface when the images is fixed by pressing and heating, the short-chain saturated hydrocarbon compounds are scattered on the surface of the binding resin along with the release agent on the image surface. Accordingly, the image surface is smoothed, and varnish can be uniformly applied. Thus, high varnish coatability and adhesiveness is achieved. The above effect is presumably obtained by the short-chain saturated hydrocarbon compounds, which have a low viscosity and tend to be on the image surface.
If the amount of saturated hydrocarbon compounds having 16 to 35 carbon atoms is greater than 1,000 ppm by mass with respect to the total mass of toner, the saturated hydrocarbon compounds fully cover the image surface and completely cover compounds having a higher affinity with varnish than the saturated hydrocarbon compounds. As a result, the varnish is less adhesive to the image. On the other hand, when the amount of the saturated hydrocarbon compounds is less than 1 ppm by mass with respect to the total mass of toner, the varnish coatability is not improved. Furthermore, fixability and separability of toner is also improved when the saturated hydrocarbon compounds are scattered in an image area where no release agent is present.
Based on the above, the inventors determined that the amount of change in endothermic peak start temperature on the DSC curve owing to the change in maintaining temperature is 2 °C or less and that the amount of short-chain saturated hydrocarbon compounds with respect to the total mass of toner is in the range of 1 to 1,000 ppm by mass. Thus, differences in glossiness between front and back faces in double-sided printing can be reduced, and varnish coatability and adhesion is increased.

BRIEF DESCRIPTION OF THE DRAWINGS

The advantages and features provided by one or more embodiments of the invention will become more fully understood from the detailed description given hereinbelow and the appended drawings which are given by way of illustration only, and thus are not intended as a definition of the limits of the present invention, wherein:

FIG. 1 is a schematic view of an example of a surface treatment apparatus configured to perform surface treatment with hot air;
FIG. 2 is a schematic view of an example of another surface treatment apparatus configured to perform surface treatment with hot air;
FIG. 3 is a schematic configuration diagram illustrating an example of an image forming apparatus;
FIG. 4 is a schematic diagram illustrating a schematic configuration of a fixing device that forms a planar fixing nip by a non-rotating pressure pad; and
FIG. 5 is a diagram illustrating an example of DSC curves when toner is in temperatures of 40 °C, 50 °C, and 60 °C.

DETAILED DESCRIPTION

Hereinafter, one or more embodiments of the present invention will be described with reference to the drawings. However, the scope of the invention is not limited to the disclosed drawings.
An electrostatic latent image developing toner of the present invention includes toner base particles containing a binding resin and a release agent. The toner base particles contain saturated hydrocarbon compounds having 16 to 35 carbon atoms, and the amount of the saturated hydrocarbon compounds is in a range of 1 to 1,000 ppm by mass with respect to the total mass of the electrostatic latent image developing toner. Further, the electrostatic latent image developing toner of the present invention satisfies the following condition (i).
Condition (i): In following measurements 1 to 3, an amount of change in endothermic peak start temperature owing to a change in maintaining temperature is 2 °C or less, the endothermic peak start temperature being observed at 20 °C or more on a differential scanning calorimetry (DSC) curve. Measurement 1: A sample of the electrostatic latent image developing toner is maintained at a maintaining temperature of 40 °C for three hours; the temperature is decreased to 0 °C at a rate of -10 °C/min; and measurement by a differential scanning calorimeter is performed while increasing the temperature at a rate of 10 °C/min in a range of 0 to 200 °C. Measurement 2: For the sample after the measurement 1, the temperature is decreased at a rate of -10 °C/min in a range of 200 to 0 °C; and thereafter measurement is performed in a same manner as the measurement 1 except that the maintaining temperature is 50 °C. Measurement 3: For the sample after the measurement 2, the temperature is decreased at a rate of -10 °C/min in a range of 200 to 0 °C; and thereafter measurement is performed in a same manner as the measurement 1 except that the maintaining temperature is 60 °C. The above-described features are technical features common to or corresponding to the following embodiments.
As an embodiment of the present invention, the release agent preferably contains a hydrocarbon wax. Since the molecular structure of the hydrocarbon wax is similar to the molecular structure of the saturated hydrocarbon compounds having 16 to 35 carbon atoms, the saturated hydrocarbon compounds are easily compatible with the hydrocarbon wax. Accordingly, the saturated hydrocarbon compounds are finely and uniformly dispersed in the toner base particles and, in fixing, the saturated hydrocarbon compounds are easily precipitated from the toner base particles along with the release agent. As a result, vanish coatability is enhanced.
Preferably, the binding resin contains polyester, which has the polarity close to the polarity of varnish, to enhance varnish adhesion.
Preferably, the binding resin contains a styrene-acrylic resin, which has the polarity close to the polarity of varnish, to enhance varnish adhesion.
Preferably, the toner base particles contain a crystalline material other than the release agent because, with the crystalline material, the C16-35 saturated compounds are less compatible with the binding resin and precipitation of the C16-35 saturated compounds is facilitated in fixing.
It is preferable that the external additive contain strontium titanate to enhance varnish coatability and toner releasability.
Preferably, particles of the strontium titanate have an average primary particle size within the range of 20 to 200 nm, and more preferably within the range of 30 to 150 nm. According to the above, the strontium titanate particles exposed on the surfaces of the toner base particles do not deteriorate the uniformity of the image surface, and thus a decrease in the coatability is prevented.
The image forming method of the present invention includes a step of attaching the electrostatic latent image developing toner to a recording medium and a step of fixing the attached electrostatic latent image developing toner to the recording medium. Such an image forming method decreases the difference in glossiness between the front and back faces in double-sided printing and generates an image having improved varnish coatability and varnish adhesion.
In the fixing step, it is preferable that the electrostatic latent image developing toner is fixed to the recording medium in two stages. According to the two-stage fixing, the toner image is heated sufficiently for a long time, and the saturated hydrocarbon compounds are sufficiently precipitated from the toner base particles. As a result, varnish coatability and toner releasability from a fixing device in the second stage fixing are further enhanced.
It is preferable that the image forming method further includes a step of forming a varnish coat by applying varnish to the surface of the toner image, which is formed by the fixed electrostatic latent image developing toner. Thus, the quality and durability of the image are improved.
The image forming apparatus of the present invention includes at least a developing member, a transfer member, and a fixing member and forms a toner image on a recording medium by using the above-described electrostatic latent image developing toner. The fixing member includes a fixing pad for a fixing nip. Such an image forming method decreases the difference in glossiness between the front and back faces in double-sided printing and generates an image having improved varnish coatability and varnish adhesion.
Furthermore, it is preferable that the fixing member includes: an endless belt configured to heat the toner image on the recording medium at the fixing nip; a rotatable body configured to form the fixing nip in cooperation with the endless belt; the fixing pad configured to be in contact with an inner circumferential surface of the endless belt and to sandwich the endless belt between the fixing pad and the rotatable body to form the fixing nip; and a heating roller in contact with the inner circumferential surface of the endless belt and configured to heat the endless belt. Using the fixing pad widens the fixing area and increases the fixing time. Accordingly, the toner image is heated sufficiently for a long time, and the saturated hydrocarbon compounds are sufficiently precipitated from the toner base particles. As a result, varnish coatability and the toner releasability from the fixing device are enhanced.
Hereinafter, the present invention and constituent elements thereof, and modes and aspects for carrying out the present invention will be described. In the present description, when two figures are used to indicate a range of value before and after "to", these figures are included in the range as a lower limit value and an upper limit value.

[Outline of Electrostatic latent image developing toner of the present invention]

The electrostatic latent image developing toner of the present invention includes toner base particles containing a binding resin and a release agent. The electrostatic latent image developing toner is characteristic in that: the toner base particles contain saturated hydrocarbon compounds having 16 to 35 carbon atoms; the amount of the saturated hydrocarbon compounds is in the range of 1 to 1,000 ppm by mass with respect to the total mass of the electrostatic latent image developing toner; and the electrostatic latent image developing toner meets the following condition (i).
Condition (i): In following measurements 1 to 3, an amount of change in endothermic peak start temperature owing to a change in maintaining temperature is 2 °C or less, the endothermic peak start temperature being observed at 20 °C or more on a differential scanning calorimetry (DSC) curve. Measurement 1: A sample of the electrostatic latent image developing toner is maintained at a maintaining temperature of 40 °C for three hours; the temperature is decreased to 0 °C at a rate of -10 °C/min; and measurement by a differential scanning calorimeter is performed while increasing the temperature at a rate of 10 °C/min in the range of 0 to 200 °C. Measurement 2: For the sample after the measurement 1, the temperature is decreased at a rate of -10 °C/min in the range of 200 to 0 °C; and thereafter measurement is performed in a same manner as the measurement 1 except that the maintaining temperature is 50 °C. Measurement 3: For the sample after the measurement 2, the temperature is decreased at a rate of -10 °C/min in the range of 200 to 0 °C; and thereafter measurement is performed in a same manner as the measurement 1 except that the maintaining temperature is 60 °C.
In the present specification, "toner" refers to an electrostatic latent image developing toner. The toner includes toner particles each including a toner base particle and an external additive disposed on the surface of the toner base particle.
The "toner base particle" is a base particle of the "toner particle". The "toner base particle" of the present invention contains at least binding resin and may contain other constituent components, such as a colorant, a release agent (wax), and a charge control agent, if necessary. The toner base particles to which an external additive is added are referred to as "toner particles". The "toner" refers to an aggregate of toner particles.
The "toner image" refers to a state of toner aggregated in an image shape.

< Endothermic peak start temperature >

The toner of the present invention satisfies the condition (i). Specifically, the condition (i) is that an amount of change in endothermic peak start temperature owing to a change in maintaining temperature is 2 °C or less in following measurements 1 to 3, the endothermic peak start temperature being observed at 20 °C or more on a DSC curve. Measurement 1: A sample of the electrostatic latent image developing toner is maintained at a maintaining temperature of 40 °C for three hours; the temperature is decreased to 0 °C at a rate of -10 °C/min; and measurement by a differential scanning calorimeter is performed while increasing the temperature at a rate of 10 °C/min in the range of 0 to 200 °C. Measurement 2: For the sample after the measurement 1, the temperature is decreased at a rate of - 10 °C/min in the range of 200 to 0 °C; and thereafter measurement is performed in a same manner as the measurement 1 except that the maintaining temperature is 50 °C. Measurement 3: For the sample after the measurement 2, the temperature is decreased at a rate of -10 °C/min in the range of 200 to 0 °C; and thereafter measurement is performed in a same manner as the measurement 1 except that the maintaining temperature is 60 °C.
When the amount of change is 2 °C or less, the difference in glossiness between the front and back surfaces in double-sided printing is not problematic. The amount of change is preferably 1 °C or less, more preferably 0.5 °C or less, and further preferably 0 °C.
The method for calculating the endothermic peak start temperature is as follows.
The endothermic peak start temperature can be measured using "DSC-7 differential scanning calorimeter" (manufactured by PerkinElmer, Inc.) or "TAC7/DX thermal analyzer controller" (manufactured by PerkinElmer, Inc.).
In the measurement procedure, 4.5 to 5.0 mg of toner is precisely measured to the second decimal place; the measured toner is sealed in an aluminum pan (KIT NO. 0219-0041) as a sample; and the sample is set in a DSC-7 sample holder. A reference is an empty aluminum pan.

(Method for measuring endothermic peak start temperature)

The detailed measurement method is as follows.
First, the temperature is decreased from room temperature (25 °C) to 0 °C at the rate of -10 °C/min, then increased from 0 °C to 200 °C at the rate of 10 °C/min, then decreased from 200 °C to 0 °C at the rate of -10 °C/min, and then increased to 40 °C at the rate of 10 °C/min. The temperature is maintained at 40 °C as a maintaining temperature for three hours as a maintaining time, and the temperature is decreased to 0 °C at the rate of -10 °C/min. Then, the amount of heat is measured while increasing the temperature at the rate of 10 °C/min in the range of 0 °C to 200 °C (measurement 1).
Next, with the sample used in the measurement 1, the temperature is decreased from 200 °C to 0 °C at the rate of -10 °C/min, and the temperature is then increased to 50 °C at the rate of 10 °C/min. The temperature is maintained at 50 °C as the maintaining temperature for three hours as the maintaining time, and the temperature is decreased to 0 °C at the rate of -10 °C/min. Then, the amount of heat is measured while increasing the temperature at the rate of 10 °C/min in the range of 0 °C to 200 °C (measurement 2).
Next, with the sample used in the measurement 2, the temperature is decreased from 200 °C to 0 °C at the rate of -10 °C/min, and the temperature is then increased to 60 °C at the rate of 10 °C/min. The temperature is maintained at 60 °C as the maintaining temperature for three hours as the maintaining time, and the temperature is decreased to 0 °C at the rate of -10 °C/min. Then, the amount of heat is measured while increasing the temperature at the rate of 10 °C/min in the range of 0 °C to 200 °C (measurement 3).
As described above, the amount of heat of the same toner in the range of 0 to 200 °C is measured in the three measurements corresponding to different maintaining temperatures.
The endothermic peak start temperature is an endothermic peak rising temperature on a DSC curve. The endothermic peak is observed at 20 °C or more in the measurement while increasing the temperature after maintaining the temperature at each maintaining temperature (40 °C, 50 °C, 60 °C).
The "endothermic peak rising temperature" refers to a temperature at which the DSC curve deviates from a base line. The endothermic peak start temperature can be confirmed at the inflection point of the DSC line from the base line. The inflection point can also be confirmed by a differential curve (DDSC) of the DSC curve.
Specifically, the differential value of the DSC curve is zero (0) before the DSC curve rises to a peak, and the differential value turns negative at the peak start temperature if the endothermic peak is convex downward. If the baseline is inclined, the peak rising temperature is a temperature at which the differential value deviates from the differential value before the peak rising.
For example, as shown in FIG. 5, the endothermic peak start temperature when the maintaining temperature is 40 °C is 51.6 °C; the endothermic peak start temperature when the maintaining temperature is 50 °C is 56.8 °C; and the endothermic peak start temperature when the maintaining temperature is 60 °C is 68.6 °C. Note that Fig. 5 illustrates an example wherein the amount of change in the endothermic peak start temperature owing to a change in the maintaining temperature is 2 °C or more.
The DSC-7 differential scanning calorimeter (manufactured by PerkinElmer, Inc.) can identify the point at which the change of at least 5uW/min is observed in the differential curve DDSC as the peak start temperature.
Based on the endothermic peak start temperatures for the respective maintaining temperatures, which are obtained as described above, the difference (the amount of change) between the endothermic peak start temperature when the maintaining temperature is 40 °C and the endothermic peak start temperature when the maintaining temperature is 50 °C is calculated. Similarly, the difference (the amount of change) between the endothermic peak start temperature when the maintaining temperature is 40 °C and the endothermic peak start temperature when the maintaining temperature is 60 °C is calculated, and the difference (the amount of change) between the endothermic peak start temperature when the maintaining temperature is 50 °C and the endothermic peak start temperature when the maintaining temperature is 60 °C is calculated. In the present invention, these amounts of change are less than or equal to 2 °C. That is, the maximum amount of change in endothermic peak start temperature is less than or equal to 2 °C.
Although it is not clear, the endothermic peak start temperature is considered to depend on the state and structure of the crystalline components in the toner.
To achieve the amount of change in the endothermic peak start temperature less than or equal to 2 °C owing to a change in the maintaining temperature, the following are considered.

(a) The type of crystalline component (e.g., the structure or molecular weight of crystalline component) and/or the added amount of the crystalline component
(b) The drying temperature at which the toner base particles are dried in the preparation of the toner base particles, wherein binding resin fine particles, colorant fine particles, and so forth are aggregated and fused together; the toner base particles are separated from a dispersion of the toner base particles by a solid-liquid separation; from a toner cake obtained by the solid-liquid separation, attached substances, such as surfactants and aggregating agents, are removed; the toner cake is washed; and the toner base particles are dried.

The crystalline component refers to the release agent or a crystalline component (binding resin) other than the release agent. In the present invention, the toner may not contain a crystalline component other than the release agent.
When the toner does not contain a crystalline component other than the release agent, the amount of change in the endothermic peak start temperature can be 2 °C or less. However, when the toner does not contain a crystalline component other than the release agent, the toner cannot be fixed at a low temperature. It is therefore preferable that the toner contain a crystalline component other than the release agent in order to enable low-temperature fixing.
When the toner base particles contain a crystalline component (binding resin) other than the release agent, it is preferable that the binding resin be a crystalline component, such as crystalline polyester or hybrid crystalline polyester. The hybrid crystalline polyester is a resin formed by bonding an endothermic crystalline polyester polymerized segment and a polymerized segment of a different type of resin.
Furthermore, it is preferable that the drying temperature be equal to or lower than 45 °C. When the toner is dried at a temperature higher than 45 °C, crystalline components in the toner are brought into a molten state, and the toner structure is difficult to control. Therefore, the toner is preferably dried in the range of 10 to 45 °C, or more preferably, in the range of 20 to 40 °C.
Preferably, the average molecular weight (Mw) of the crystalline polyester is in the range of 5,000 to 50,000. Preferably, the number average molecular weight (Mn) of the crystalline polyester is in the range of 2,000 to 10,000. When the crystalline polyester has the weight-average molecular weight (Mw) and the number-average molecular weight (Mn) in the above ranges, the amount of change in the endothermic peak start temperature owing to a change in the maintaining temperature is within the above-described range, and the low-temperature fixability of toner is improved.

< Saturated hydrocarbon compounds having 16 to 35 carbon atoms >

In the present invention , the toner base particles of the toner contain saturated hydrocarbon compounds having 16 to 35 carbon atoms (C16-35 saturated compounds). The amount of the saturated hydrocarbon compounds is within the range of 1 to 1,000 ppm by mass with respect to the total mass of the electrostatic latent image developing toner. Hereinafter, "saturated hydrocarbon compounds having 16 to 35 carbon atoms" are also referred to as "C16-35 saturated compounds".
According to the findings of the present inventors, components such as the binding resin, the release agent precipitated during fixing, and other toner components are sparsely scattered on the surface of an image formed by the toner fixed on a recording medium. Owing to the difference in these components, portions having different surface energies are scattered on the surface of the image. It is considered that, owing to the difference in the surface energy between the image portions, the varnish applied to the image surface does not uniformly spread but is repelled by the image.
Since the C16-35 saturated compounds have a relatively small molecular weight, the C16-35 saturated compounds are considered to be finely and uniformly dispersed in each toner base particle. The C16-35 saturated compounds, which are finely and uniformly dispersed in each toner base particle, are considered to be precipitated on the surfaces of the toner base particles little by little when the toner is fixed and to uniformly cover the surfaces of the toner base particles. Further, since the C16-35 saturated compounds have a small molecular weight, the melted C16-35 saturated compounds have a low viscosity and tend to be precipitated on the front side of the image than the release agent. Accordingly, the surface of the image formed by the fixed toner is uniformly coated by the C16-35 saturated compounds, and the surface energy is uniformly distributed over the image. Thus, by using the above-described toner to form an image, the varnish is uniformly wet-spread on the surface of the image; the varnish is less likely to be repelled; and varnish coatability is improved.
On the other hand, the C16-35 saturated compounds do not have a high affinity for varnish. If the toner contains an excessive amount of C16-35 saturated compounds and the resulting image surface is densely covered by the C16-35 saturated compounds, the varnish adhesion may be decreased.
Thus, there is a trade-off between the varnish coatability effect by the C16-35 saturated compounds and the varnish adhesion effect. To achieve both of these effects, the amount of the C16-35 saturated compounds is in the range of 1 to 1,000 ppm by mass with respect to the total mass of the toner. The amount of the C16-35 saturated compounds is preferably in the range of 10 to 950 ppm by mass with respect to the total mass of the toner.
Since the C16-35 saturated compounds have a wax-like structure, the C16-35 saturated compounds also have an effect of enhancing the toner releasability from a fixing member to a certain extent.

[Structure of Electrostatic latent image developing toner]

Hereinafter, the structure of the toner of the present invention will be described.

< Toner base particles >

The toner base particles contain the binding resin, the release agent, and the C16-35 saturated compounds.

(Binding resin)

The binding resin binds the toner to a recording medium. The binding resin may be a thermoplastic resin or a thermosetting resin. Preferably, the binding resin is a thermoplastic resin.
Examples of the thermoplastic resin include styrene resins, vinyl resins (e.g., acrylic resins and styrene-acrylic resins), polyesters, silicone resins, olefin resins, polyamide resins, and epoxy resins.
The binding resin may be an amorphous resin or a crystalline resin. The binding resin may also be a composite resin in which a crystalline resin and an amorphous resin are hybridized.
In the present specification, the crystalline resin means a resin having a melting point that is observed in differential scanning calorimetry (DSC) measurement. Further, in the present specification, the amorphous resin means a resin having a melting point that is not observed in DSC measurement. In the present specification, observing a melting point of a resin means observing an endothermic peak having a half width equal to or less than 15 °C when the DSC measurement is performed at the temperature increase rate of 10 °C/min.
Examples of the binding resin include styrene-based polymers (e.g., styrene homopolymers, homopolymers of styrene substitutes such as poly-p-chlorostyrene and polyvinyltoluene, and styrene-based copolymers such as styrene-p-chlorostyrene copolymers, styrene-vinyltoluene copolymers, styrene-vinylnaphthalene copolymers, styrene-butadiene copolymers, and styrene-isoprene copolymers), polyvinyl chloride, phenol resins, vinyl resins such as (meth) acrylic resins (including styrene-(meth) acrylate ester copolymers, styrene-α-chloro (meth) acrylate copolymers, styrene-(meth) acrylonitrile copolymers, styrene-vinylmethyl ether copolymers, styrene-vinylethyl ether copolymers, styrene-vinylmethyl ketone copolymers, and styrene-acrylonitrile-indene copolymers), polyvinyl acetate, silicone resins, polyesters, polyurethane resins, polyamide resins, furan resins, epoxy resins, xylene resins, polyvinyl butyral, terpene resins, coumarone-indene resins, natural resins, modified natural resins (e.g., natural modified phenol resins and natural resin-modified maleic acid resins), and other petroleum-based resins.
Among these, vinyl resins such as styrene-acrylic resins and polyesters are preferred because they have a polarity close to the polarity of the varnish and contribute to improving the varnish adhesion.
In the present specification, (meth) acrylic means acrylic or methacrylic, (meth) acrylonitrile means acrylonitrile or methacrylonitrile, and (meth) acrylate means acrylate and methacrylate, respectively.
When the toner base particles further contain a crystalline resin other than the release agent, it is preferable that the toner base particles contain a crystalline polyester. When the crystalline polyester is contained, the C16-35 saturated compound is less compatible with the binding resin and can be easily precipitated in fixing.
Furthermore, the crystalline resin other than the release agent may be a composite resin that is a hybrid of a crystalline resin and an amorphous resin.
Preferably, the amount of the contained binding resin is in the range of 20 to 99% by mass with respect to the total mass of the toner base particles, more preferably in the range of 30 to 95% by mass, and further preferably in the range of 40 to 90% by mass. When the amount of the contained binding resin is equal to or greater than 20% by mass, the strength of a formed image can be further increased.
Following is the description on the crystalline polyester and the hybrid crystalline polyester that are used as the crystalline resin of the binding resin.

< Crystalline polyester >

Commonly, the crystalline polyester is obtained by causing a dehydration condensation reaction between polyvalent carboxylic acid and polyhydric alcohol by a known method.
Preferably, the polyvalent carboxylic acid is a carboxylic acid having a valency of 2 or greater. The polyvalent carboxylic acid may be a carboxylic acid having a valency of 3 or greater, such as trimellitic acid or pyromellitic acid. Among these polyvalent carboxylic acids, dicarboxylic acid is preferable to increase the crystallinity of the crystalline polyester.
Examples of dicarboxylic acids include: aliphatic carboxylic acids such as oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, 1,9-nonanedicarboxylic acid, 1,10-decanedicarboxylic acid, 1,11-undecanedicarboxylic acid, 1,12-dodecanedicarboxylic acid (dodecanedioic acid), 1,13-tridecanedicarboxylic acid, 1,14-tetradecanedicarboxylic acid, 1,16-hexadecanedicarboxylic acid, and 1,18-octadecanedicarboxylic acid; and aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, orthophthalic acid, t-butylisophthalic acid, 2,6-naphthalenedicarboxylic acid, and 4,4'-biphenyldicarboxylic acid.
The crystalline polyester may include a structural unit derived from one kind of carboxylic acid among these carboxylic acids or may include structural units derived from two or more of these carboxylic acids.
Among the above, it is preferable to use an aliphatic carboxylic acid. The aliphatic carboxylic acid can increase the crystallinity of the crystalline polyester and increase the affinity between diol di (meth) acrylate, which may be contained in the varnish, and the crystalline polyester.
Preferably, the aliphatic carboxylic acid has a linear hydrocarbon group having 6 to 16 carbon atoms, and more preferably, has a linear hydrocarbon group having 10 to 14 carbon atoms. The hydrocarbon structure of the aliphatic carboxylic acid may be partially branched.
Preferably, the polyhydric alcohol is an alcohol having a valency of 2 or greater. The polyhydric alcohol may be an alcohol having a valency of 3 or greater, such as glycerol, pentaerythritol, trimethylolpropane, or sorbitol. Among the above, dihydric alcohols are preferable to increase the crystallinity of the crystalline polyester.
Examples of a dihydric alcohol include aliphatic diols such as ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, 1,11-undecanediol, 1,12-dodecanediol, 1,13-tridecanediol, 1,14-tetradecanediol, 1,18-octadecanediol, and 1,20-eicosanediol; diols having unsaturated double bonds such as 2-butene-1,4-diol, 3-hexene-1,6-diol, and 4-octene-1,8-diol; and diols having a sulfonic acid group.
To sufficiently obtain the above-described effect, the amount of contained crystalline polyester is preferably in the range of 5 to 20 parts by mass and more preferably in the range of 8 to 15 parts by mass with respect to 100 parts by mass of the total amount of the binding resin.
To sufficiently soften the toner base particles to enhance the low-temperature fixability of the toner, the melting point of the crystalline polyester is preferably in the range of 50 to 85 °C and more preferably in the range of 60 to 80 °C.
Preferably, the weight-average molecular weight (Mw) of the crystalline polyester is in the range of 5,000 to 50,000. Preferably, the number-average molecular weight (Mn) of the crystalline polyester is in the range of 2,000 to 10,000. The crystalline polyester having the weight-average molecular weight (Mw) and the number-average molecular weight (Mn) in the above ranges contributes to a high low-temperature fixability.

< Hybrid crystalline polyester >

In the present invention, it is preferable that the crystalline resin contain a hybrid crystalline polyester obtained by chemically bonding a crystalline polyester polymerized segment and a polymerized segment of a vinyl-based resin. This is because such a hybrid crystalline polyester is finely dispersed in the toner and contributes to a high low-temperature fixability.

(a) Crystalline polyester polymerized segment

The crystalline polyester polymerized segment is a portion derived from a crystalline polyester and is a resin segment having an evident endothermic peak in differential scanning calorimetry (DSC) of the toner instead o stepwise endothermic changes. The crystalline polyester polymerized segment is not limited to a specific kind as long as the above definition is met.
For example, if a toner contains (i) a resin having a structure in which the main chain of a crystalline polyester polymerization segment is copolymerized with a different component or (ii) a resin having a structure in which a crystalline polyester polymerization segment is copolymerized with the main chain of a different component, and if the toner shows a clear endothermic peak as described above, the resin corresponds to the hybrid crystalline polyester having a crystalline polyester polymerization segment in the present invention.
The crystalline polyester polymerization segment is generated by polycondensation (esterification) of a polyvalent carboxylic acid monomer and a polyhydric alcohol monomer.
The polyvalent carboxylic acid monomer and polyhydric alcohol monomer as the raw materials of the crystalline polyester described above can be used for generating the crystalline polyester polymerization segment.
Generation of the crystalline polyester polymerized segment is not limited to a specific method. The crystalline polyester polymerization segment can be formed by polycondensation (esterification) of a polyvalent carboxylic acid and a polyhydric alcohol using a known esterification catalyst.

(b) Preferable crystalline polyester polymerized segment

Preferably, the crystalline polyester polymerization segment used in the present invention is obtained by polymerizing a polyhydric alcohol monomer having 4 to 14 carbon atoms and a polycarboxylic acid monomer having 4 to 14 carbon atoms. When the carbon number is 4 or greater, the number of hydrogen bonds derived from ester bonds is not excessive, and the melting point of the crystalline polyester is not too high. Accordingly, the low-temperature fixability is further improved. Further, when the carbon number is 14 or less, the interaction between aliphatic groups is not excessive, and thus the melting point of the crystalline polyester is not too high. Accordingly, the low-temperature fixability is further improved.

(c) Polymerized segment of vinyl-based resin

The polymerized segment of the vinyl-based resin (also referred to as a vinyl-based polymerized segment) is synthesized from a vinyl monomer, which is a raw material of the vinyl-based resin.
In the present invention, it is preferable that the crystalline resin contain the vinyl-based polymerization segment in the range of 3 to 40% by mass, and most preferably in the range of 5 to 20% by mass. Thus, the low-temperature fixability can be improved. In particular, when the amount of the contained vinyl-based polymerization segment is equal to or greater than 3% by mass, the stability of the interface between the crystalline resin and the vinyl-based resin, which is a main binder, is not excessively decreased, and the hybrid crystalline polyester can be finely dispersed to a sufficient extent. Accordingly, the low-temperature fixability can be further improved.
The amount of the vinyl-based polymerization segment contained in the crystalline resin is not particularly limited but is preferably equal to or less than 40% by mass from the viewpoint of chargeability.
In particular, consider a case where a vinyl-based polymerization segment having a low heat resistance is used for hybridization. If the amount of the contained vinyl-based polymerization segment is equal to or less than 40% by mass, the compatibility with the vinyl-based resin as the main binder of the crystalline resin is not excessively high. As a result, a favorable heat-resistant storage property is obtained.
Following (a), (b), and (c) are examples of the method for synthesizing the hybrid crystalline polyester.

(a) A crystalline polyester polymerized segment prepared in advance is reacted with a bireactive monomer and then reacted with a vinyl monomer as a raw material of a vinyl-based resin, so that the crystalline polyester polymerized segment is chemically bonded with the vinyl-based polymerized segment.
(b) A vinyl-based resin prepared in advance is reacted with a bireactive monomer and then reacted with a polyvalent carboxylic acid monomer and a polyhydric alcohol monomer, which are raw materials of the crystalline polyester resin, so that the crystalline polyester polymerized segment is chemically bonded with the vinyl-based polymerized segment.
(c) A crystalline polyester and a vinyl-based resin prepared in advance are reacted with a bireactive monomer, and the crystalline polyester polymerization segment is chemically bonded with the vinyl-based polymerization segment.

The bireactive monomer bonds the crystalline polyester and the vinyl-based resin. The bireactive monomer is a monomer having, in a molecule, a substituent capable of reacting with crystalline polyester, such as a hydroxy group, a carboxy group, an epoxy group, a primary amino group, or a secondary amino group, and an ethylenically unsaturated group capable of reacting with the amorphous resin.
Among these, a vinylcarboxylic acid having a hydroxy group or a carboxy group and an ethylenically unsaturated group is preferable.
As the bireactive monomer, for example, (meth) acrylic acid, fumaric acid, or maleic acid can be used, and hydroxyalkyl (having 1 to 3 carbon atoms) esters thereof may also be used. In light of reactivity, acrylic acid, methacrylic acid, or fumaric acid is preferable.
The usage amount of the bireactive monomer is preferably in the range of 1 to 10 parts by mass, or more preferably in the range of 4 to 8 parts by mass with respect to 100 parts by mass of the total amount of the monomers to be used for forming the vinyl-based polymerization segment. With the above usage amount, the low-temperature fixability, hot offset resistance, and durability of the toner are increased.

(d) Crystal nucleating agent site

In the present invention, a "crystal nucleating agent site" refers to a site where the crystallization rate is higher than that of the site having the crystal structure. When cooled, the crystal nucleating agent site having a high crystallization rate quickly forms crystal nuclei first, and the formed crystal nuclei serves as the starting point to accelerate crystallization of sites having a crystal structure.
A compound that forms the crystal nucleating agent site is not particularly limited as long as the compound has a higher crystallization rate than sites having a crystal structure.
From the viewpoint of a high crystallization rate, it is preferable that the compound serving as the crystal nucleating agent site have one or more functional groups that have a main chain including a hydrocarbon-based moiety and that can react with the terminal of a polyester moiety.
Further, it is preferable that the compound serving as the crystal nucleating agent site have one or more functional groups that have a linear hydrocarbon-based moiety and that react with a polyester moiety.
A preferable crystal nucleating agent site is a site derived from at least one compound selected from the group consisting of aliphatic monocarboxylic acids having a carbon number in the range of 10 to 30 and aliphatic monoalcohols having a carbon number in the range of 10 to 30.
Specific examples of the aliphatic monocarboxylic acids include stearic acid, lauric acid, arachidic acid, N-behenic acid, N-tetradocosanoic acid, N-hexadocosanoic acid, N-octadocosanoic acid, and N-triacontanoic acid.
Examples of the aliphatic monoalcohols include stearyl alcohol, lauryl alcohol, behenyl alcohol, arachidyl alcohol, 1-octadecanol, 1-icosanol, 1-docosanol, 1-tetracosanol, 1-hexacosanol, 1-octacosanol, and 1-triacontanol.
The ratio of the crystal nucleating agent sites in the crystalline resin is preferably in the range of 1 to 15% by mass, and more preferably in the range of 3 to 9% by mass from the viewpoint of the tacking suppressing effect and the folding fixability.
The amount of the above-described crystalline resin contained in the binding resin is preferably in the range of 4 to 15% by mass, and more preferably in the range of 7 to 12% by mass from the viewpoint of achieving both low-temperature fixability and suppression of tacking.

(Release Agent)

The release agent enhances releasability of the toner from a fixing section and so forth. The release agent is preferably a wax.
Examples of the release agent, which is a wax, include hydrocarbon waxes such as polyethylene wax, paraffin wax, microcrystalline wax, and Fischer -Tropsch wax; dialkyl ketone waxes containing distearyl ketone; carnauba wax; montan wax; ester waxes containing behenic acid behenate, trimethylolpropane tribehenate, pentaerythritol tetramyristate, pentaerythritol tetrastearate, pentaerythritol tetrabehenate, pentaerythritol diacetate dibehenate, glycerin tribehenate, 1,18-octadecanediol distearate, tristearyl trimellitate, distearyl maleate, or the like; and amide waxes containing ethylenediamine dibehenylamide, and trimellitic acid tristearylamide.
Among these, hydrocarbon waxes are preferable because they have a molecular structure similar to that of the C16-35 saturated compounds and allow the release agent to be compatible with the C16-35 saturated compounds. When the C16-35 saturated compounds are satisfactorily compatible, the C16-35 saturated compounds are finely and uniformly dispersed in the toner base particles, and in fixing, the C16-35 saturated compounds are easily precipitated from the toner base particles along with the wax. Accordingly, the varnish applicability is enhanced.
The release agent as a wax may be a C16-35 saturated compound or may be a different hydrocarbon wax having 36 to 76 carbon atoms. The amount of the C16-35 saturated compounds in the toner base particles is extremely small. In order to balance the varnish applicability by the C16-35 saturated compounds and the toner releasability by the release agent, it is preferable that the toner base particles include both the C16-35 saturated compounds and a different release agent. It is further preferable that the toner base particles include both the C16-35 saturated compounds and a hydrocarbon wax having 36 to 76 carbon atoms.
The hydrocarbon wax preferably has a melting point of 50 to 95 °C. When the melting point of the hydrocarbon wax is equal to or higher than 50 °C, the hydrocarbon wax exuding from the toner particles is easily crystallized. Accordingly, the toner releasing effect and the abrasion resistance of formed images are enhanced. When the melting point of the hydrocarbon wax is equal to or lower than 95 °C, the hydrocarbon wax is more likely to exude from the toner base particles in fixing. Accordingly, the toner releasing effect and the abrasion resistance of formed images are enhanced. Further, when the melting point of the hydrocarbon wax is equal to or lower than 95 °C, the toner base particles are likely to melt during fixing, and the toner can be fixed at a low temperature. From the above viewpoints, it is preferable that the melting point of the hydrocarbon wax (in particular, the hydrocarbon wax having 36 to 76 carbon atoms) be 80 to 90 °C.
The amount of the contained release agent is preferably 3 to 20% by mass with respect to the total mass of the toner base particles and more preferably 5 to 15% by mass. When the amount of the contained release agent is equal to or greater than 3% by mass, the toner releasability from a fixing section is sufficiently enhanced. When the amount of the contained release agent is equal to or less than 20% by mass, the toner base particles can contain a sufficient amount of binding resin, and the image fixability is sufficiently enhanced.

(C16-35 saturated compounds)

The C16-35 saturated compounds, which function as described above, enhance the varnish coatability.
The amount of the contained C16-35 saturated compounds is in the range of 1 to 1,000 ppm by mass with respect to the total mass of the toner, preferably in the range of 50 to 950 ppm by mass, and more preferably in the range of 100 to 900 ppm by mass. When the amount of the C16-35 saturated compounds is within the above range, both the varnish coatability and the varnish adhesion can be achieved. The total mass of the toner refers to the total of the mass of the toner base particles and the mass of the external additives.
The amount of the C16-35 saturated compounds is determined as follows.
Firstly, separate the C16-35 saturated compounds from the toner by using solvents that dissolve the C16-35 saturated compounds, and perform qualitative analysis of hydrocarbons having 16 to 35 carbon atoms by gas chromatography-mass spectrometry (GC-MC). Then quantify these hydrocarbons using a flame ionization detector as a detector for gas chromatography (GC-FID).
Since the extracts from the toner may contain unsaturated hydrocarbons, polar groups are applied to the unsaturated bonds after the extraction, so that only the saturated hydrocarbons are separated by column separation utilizing the polarity difference.
At this time, some internal standard substances may be added to (dissolved in) the solvent to determine whether the quantification and the pretreatment thereof have been appropriately performed. The concentration of the internal standard substances to be added may be determined based on the amount of C16-35 saturated compounds (the estimated amount of C16-35 saturated compounds obtained by a provisional measurement, for example).
The internal standard substances are preferably saturated hydrocarbon compounds that are not usually contained in the toner. For example, use of N-undecane or N-tridecane allows detection of disappearance of saturated hydrocarbon compounds during the pretreatment due to volatilization and also allows estimation of an elution time of target saturated hydrocarbon compounds during solid-phase extraction or analysis by GC-FID. Furthermore, bicyclohexyl contributes to improving detection accuracy because the elution time of bicyclohexyl is less likely to overlap with that of the C16-35 saturated compounds.
The extraction from the toner can be performed by a known method, such as a solid-liquid extraction method, a centrifugation method after dissolving or swelling of the toner, a Soxhlet extraction method, or a high-speed solvent extraction method. The extraction method may be selected from these methods, based on the predicted number of carbon atoms of the C16-35 saturated compounds and the types of compounds as impurities, such as the binding resin.
Although the solvent used for extraction is not particularly limited, it is preferable to use N-hexane, in which C16-35 saturated compounds are highly soluble. To swell the binding resin, a polar solvent such as dichloromethane and ethanol may also be used depending on the type of the binding resin.
Also, the method for introducing polar groups into unsaturated hydrocarbons contained in the extracts is not particularly limited. The introduction can be performed by epoxidation using metachloroperbenzoic acid (mCPBA), addition of hydrogen halide, addition of water or alcohol using an acid catalyst, derivation to alcohol by oxidation after hydroboration, and so forth. Among these, the epoxidation reaction using mCPBA is preferable because of high reactivity and reaction selectivity. The sufficient reaction can be confirmed by confirming the disappearance of the peak of double bonds by the ¹H-NMR measurement. The application of polar groups may be omitted if asufficient detection accuracy is secured, depending on the type of saturated hydrocarbon or the type of unsaturated hydrocarbon.
The separation by a polarity difference can be done according to a known method, such as solid-phase extraction or online or offline GC. When a large amount of impurities is expected to be contained, separation by solid-phase extraction is preferable.
It is preferable that the solvent used for the separation by solid phase extraction be N-hexane for both the conditioning and the extraction of saturated hydrocarbons. A polar solvent may also be used depending on the kind of expected impurities. After collecting fractions containing C16-35 saturated compounds, it is preferable to collect fractions by further polarizing the solvent and to confirm, by qualitative analysis such as GC/MS, that saturated hydrocarbon components are not contained.
As the solid phase for solid-phase extraction, a highly polar solid phase used for separation of a normal phase system using a polar interaction can be used.
Examples of the solid phase include silica gel, silica gel activated with a polar substance such as anhydrous sodium sulfate and silver nitrate, diol, cyanopropyl, and magnesium silicate. Of these, silica activated with silver nitrate is preferable. To specifically retain a long-chain N-alkane, alumina is not preferable.
Preferably, the fractions containing saturated hydrocarbons extracted by the solid-phase extraction are concentrated or diluted to a concentration appropriate for qualitative and quantitative analysis by gas chromatography. The concentration can be done by vacuum concentration with an evaporator or concentration with nitrogen airflow. Conditions of concentration are determined such that under the conditions, the internal standard substances do not disappear owing to the concentration of low-boiling-point components.
The fractions after solid-phase extraction are subjected to GC-FID under the following conditions to quantify C16-35 saturated compounds, for example.

(GC conditions)

Instrument: GC-2010 Plus manufactured by Shimadzu Corporation
Injection amount: 1 µL, concentration of saturated hydrocarbon: 500 to 1,000 mg/L
Guard column: Restek MXT Siltek (10 m × 0.53 mm id)
Column: Restek MTX-1 (15 m × 0.25 mm id) × 0.1 µm df)
Carrier gas: helium

The elution time of N-alkanes (the number of carbon atoms: 10, 16, 24, 35, and 50) is measured beforehand under the same conditions. Further, only N-hexane is injected in the apparatus beforehand to prepare a blank chromatogram.
To determine a baseline, the blank chromatogram obtained beforehand by measurement with the solvent alone is subtracted from the chromatogram obtained for the toner. It is preferable that the base line be a horizontal line at the lowest point before or after a peak, which is derived from the saturated hydrocarbon compounds. If a horizontal baseline cannot be obtained by subtracting the blank chromatogram owing to column bleeding or the like, the baseline may be horizontally drawn on the lower signal intensity among the compounds having 10 carbon atoms to the compounds having 50 carbon atoms from the elution time of the compound having 10 carbon atoms to the elution time of the compound having 50 carbon atoms.
Next, in the chromatogram, perpendicular lines are drawn at positions corresponding to the elution time of the compound having 16 carbon atoms and the elusion time of the compound having 35 carbon atoms. Then, in the chromatogram above the baseline, the area surrounded by these perpendicular lines is calculated. Peaks not caused by saturated hydrocarbon compounds are excluded from the calculation. From the area, the mass of the C16-35 saturated compounds can be determined. When an internal standard substance is used, the mass of C16-35 saturated compounds can be determined based on the ratio of the area to the area of the compound added as the internal standard substance. The obtained mass of C16-35 saturated compounds is divided by the mass of toner to obtain the amount of C16-35 saturated compounds contained in the toner.

(Other components)

The toner base particles may contain a colorant agent and a charge control agent.
The coloring agent may be a dye or a pigment. When the toner has a color to impart a predetermined color tone to images, the toner base particles may contain a colorant agent, such as yellow, magenta, cyan, or black, corresponding to the color tone to be imparted by the color toner. The toner base particles may contain a single kind of colorant agent or a combination of multiple kinds of colorant agent.
Examples of yellow colorants include yellow dyes such as C. I. solvent yellow 19, 44, 77, 79, 81, 82, 93, 98, 103, 104, 112, and 162, and yellow pigments such as C. I. pigment yellow 14, 17, 74, 93, 94, 138, 155, 180, and 185.
Examples of magenta colorants include magenta dyes such as C. I. solvent red 1, 49, 52, 58, 63, 111, and 122, and magenta pigments such as C. I. pigment red 5, 48:1, 53:1, 57:1, 122, 139, 144, 149, 166, 177, 178, and 222.
Examples of cyan colorants include cyan dyes such as C. I. solvent blue 25, 36, 60, 70, 93, and 95, and cyan pigments such as C. I. pigment blue 1, 7, 15, 15:3, 60, 62, 66, and 76.
Examples of black colorants include carbon blacks such as channel black, furnace black, acetylene black, thermal black, and lamp black; magnetic materials such as ferrite and magnetic; and iron-titanium composite oxide.
The amount of contained colorant agent is preferably 0.5 to 20% by mass, or more preferably, 2 to 10% by mass with respect to the total mass of the toner base particles. When the toner is a clear toner, it is preferable that the toner base particles do not substantially contain a colorant agent and that the amount of the colorant be preferably equal to or less than 0.1% by mass with respect to the total mass of the toner base particles.
The charge control agent can adjust the chargeability of the toner base particles.
Examples of the charge control agent include nigrosine dyes, metal salts of naphthenic acid or higher fatty acids, alkoxylated amines, quaternary ammonium salt compounds, azo metal complexes, and metal salts of salicylic acid or metal complexes thereof.
The amount of the charge control agent is preferably 0.1 to 10% by mass and more preferably 0.5 to 5% by mass with respect to the total mass of the binding resin. Adding an excessive amount of the charge control agent to control the chargeability of the toner may significantly change other properties of the toner base particles. In the present embodiment, the chargeability of the toner is adjusted using strontium titanate as the external additive. Accordingly, the chargeability of the toner can be adjusted to a desired degree while the other required properties are satisfied.

The toner base particles may contain an external additive. The external additive is added as a post-treatment agent to the surfaces of the toner base particles to enhance fluidity, chargeability, and cleanability of the toner.

(Strontium titanate)

The external additive preferably contains particles of strontium titanate.
The particles of strontium titanate may have a cubic shape, a rectangular parallelepiped shape, an irregular shape, or a rounded cube shape, depending on the production method or the composition thereof. The particles of strontium titanate may have any of these shapes but preferably have a rectangular parallelepiped shape.
The shape of the strontium titanate particles can be observed with a scanning electron microscope (SEM).
The strontium titanate having such a particle shape forms planar exposed portions on the surface of the toner base particles. Accordingly, resin, which tends to inhibit the wetting and spreading of the varnish, covers a less proportion of the surface of the toner base particles, so that varnish coatability is enhanced. Similarly, by reducing the proportion of resin on the surface of the toner base particles, the releasability of toner from the fixing member is improved. In particular, the strontium titanate particles having a rectangular parallelepiped shape contribute to increasing the area of planar exposed portions on the surface of the toner base particle, thereby enhancing the varnish coatability and toner releasability as described above.
To effectively obtain the above-described effects, the number-average primary particle size of strontium titanate is preferably 20 to 200 nm, and more preferably 30 to 150 nm.
In the above-described action, it is preferable that strontium titanate have a greater particle size. When the particle size is limited in the above predetermined range, the exposed strontium titanate does not deteriorate uniformity of image surfaces and does not decrease coatability.
The number-average primary particle size of strontium titanate can be obtained as follows: obtaining image data of strontium titanate imaged by a scanning electron microscope (SEM); binarizing the image data using an image processing analyzer (LUZEX AP, manufactured by Nireco Corporation); and calculating the average value of Feret diameters in the horizontal direction of 100 particles, which can be used as the number-average primary particle size of strontium titanate.
The amount of the contained strontium titanate is preferably 0.05 to 2.0 % by mass and more preferably 0.1 to 1.0 % by mass with respect to the total mass of the toner.
When the amount of the contained strontium titanate is 0.05% by mass or greater, the varnish coatability and the toner releasability by strontium titanate can be effectively enhanced. When the amount of contained strontium titanate is 2.0 parts by mass or less, uniformity of an image surface is not deteriorated, and accordingly, a decrease in coatability is less likely to occur.
The strontium titanate can be produced by a normal-pressure heating reaction method in which a titanium oxide source and a strontium oxide source are mixed and then an alkaline aqueous solution is added while heating (warming) under normal pressure.
As the titanium oxide source, a mineral acid-peptized product of a hydrolysate of a titanium compound can be used.
The titanium oxide source is preferably metatitanic acid obtained by a sulfuric acid method and having a SO₃ content of 1.0% by mass or less, preferably 0.5% by mass or less, which is deflocculated by adjusting the pH in the range of 0.8 to 1.5 with hydrochloric acid.
As the strontium oxide source, metal nitrates or hydrochlorides can be used. For example, as the strontium oxide source, strontium nitrate or strontium chloride can be used.
As the aqueous alkali solution, a caustic alkali can be used. As the aqueous alkali solution, an aqueous sodium hydroxide solution is preferable.
The particle size of the strontium titanate particles can be adjusted by the mixing ratio of the titanium oxide source and the strontium oxide source, the concentration of the titanium oxide source in the initial reaction stage, the temperature and the addition rate when the alkaline aqueous solution is added, for example. To prevent generation of a carbonate in the reaction process, it is preferable to cause reaction under a nitrogen gas atmosphere or the like to prevent mixing of carbon dioxide gas during the reaction.
The mixing ratio of the titanium dioxide source and the strontium oxide source is preferably in the range of 0.90 to 1.40, more preferably in the range of 1.05 to 1.20, in terms of SrO/TiO₂ molar ratio. Within the above range, unreacted titanium oxide is less likely to remain.
The concentration of the titanium dioxide source in the initial reaction stage is preferably 0.05 to 1.3 mol/L, more preferably 0.08 to 1.0 mol/L, based on TiO₂.
The temperature of the mixture when the alkaline aqueous solution is added is preferably 60 to 100 °C.
The slower the addition rate of the alkaline aqueous solution is, the greater the particle size of the strontium titanate particles is. The faster the addition rate of the alkaline aqueous solution is, the smaller the particle size of the strontium titanate particles is.
The addition rate of the alkaline aqueous solution is preferably 0.001 to 12 equivalents/h, more preferably 0.002 to 1.1 equivalents/h, with respect to prepared raw materials. The addition rate of the alkaline aqueous solution can also be appropriately adjusted according to the target particle diameter of the strontium titanate.
Preferably, the strontium titanate particles obtained as described above are further subjected to acid treatment. When the mixing ratio of the titanium dioxide source and the strontium oxide source is greater than 1.0 in terms of SrO/TiO₂ molar ratio, unreacted metal sources other than titanium remaining after completion of the reactions may react with carbon dioxide in the air and produce impurities, such as a metallic carbonate. To prevent a decrease in performance caused by the impurities, it is preferable to perform acid treatment to remove unreacted metal sources after adding the alkaline aqueous solution.
The acid treatment is preferably performed at pH 2.5 to 7.0, more preferably at pH 4.5 to 6.0, using hydrochloric, nitric, acetic acids, or the like.

(Other external additives)

The external additive may contain particles the main component of which is an inorganic material other than strontium titanate. Specific examples thereof include silica particles, alumina particles, zirconia particles, zinc oxide particles, chromium oxide particles, cerium oxide particles, antimony oxide particles, tungsten oxide particles, tin oxide particles, tellurium oxide particles, manganese oxide particles, and boron oxide particles.
The particles containing these inorganic materials as a main component may be subjected to a hydrophobic treatment with a surface treatment agent such as a silane coupling agent or silicone oil, if necessary.
It is preferable that the number-average primary particle size of these inorganic materials, which is measured by the same method as the strontium titanate, be 20 to 200 nm, more preferably 30 to 150 nm.
The external additive may contain particles the main component of which is an organic material containing a homopolymer, such as styrene and methyl methacrylate, or a copolymer of these. It is preferable that the peak top particle size of these particles measured by the same method as strontium titanate be 10 to 1,000 nm.
The external additive may also include a lubricant, such as a metal salt of a higher fatty acid. Examples of the higher fatty acid include stearic acid, oleic acid, palmitic acid, linoleic acid, and ricinoleic acid. Examples of the metal constituting the metal salt include zinc, manganese, aluminum, iron, copper, magnesium, and calcium.
Preferably, the amount of these external additives is determined such that the total amount of the external additives including the strontium titanate is 0.05 to 5.0% by mass with respect to the total mass of the toner base particles.

[Methods for producing toner base particles and toner]

The toner base particles can be produced in the same manner as a known toner by a pulverization method, an emulsion polymerization aggregation method, an emulsion aggregation method, a suspension polymerization method, or a dissolution suspension method, for example.
Among these, the pulverization method, the emulsion polymerization aggregation method, the emulsion aggregation method, or the suspension polymerization method is preferable, and the pulverization method or the emulsion polymerization aggregation method is more preferable.
The toner base particles of the pulverized toner prepared by the pulverization method have irregular shapes and have a large number of minute and random recesses and projections over the entire particle, thereby having a large surface area. According to the toner base particles prepared by the pulverization method, the C16-35 saturated compounds can be easily precipitated from the surfaces of the toner base particles, and thus the varnish coatability and the toner releasability can be enhanced.

According to the pulverization method, the binding resin, the release agent, the C16-35 saturated compounds, and other materials are mixed, melted, and kneaded to obtain a solid resin composition, and the solid resin composition is pulverized to a predetermined particle size to obtain toner base particles.
More specifically, in the pulverization method, firstly predetermined amounts of materials constituting the toner base particles (binding resin, release agent, C16-35 saturated compounds, and other materials that are optionally added) are weighed, blended, and mixed.
The mixing can be performed by a mixing apparatus such as a double-cone mixer, a V-type mixer, a drum-type mixer, a super mixer, a Henschel mixer, a Nauta mixer, or a mechanohybrid.
Next, the mixed materials are melted and kneaded. The melting and kneading can be performed by a batch kneader, such as a pressure kneader or a Banbury mixer, or a continuous kneader.
In continuous production, a single-screw extruder or a twin-screw extruder is preferably used. Examples of the twin-screw extruder include a KTK type twin-screw extruder (manufactured by Kobe Steel, Ltd), a TEM type twin-screw extruder (manufactured by Toshiba Machine Co., Ltd), a PCM kneader (manufactured by Ikegai Corporation), a twin-screw extruder (manufactured by K.C. K. corporation), a Co-Kneader (manufactured by Buss Corporation), and a Kneadex (manufactured by Nippon Coke & Engineering Co., Ltd.).
The temperature of the melt-kneading is preferably about 100 to 200 °C. The resin composition obtained by melt kneading is rolled using a two-roll mill or the like, and then quenched by water or the like to form a solid.
Next, the solid resin composition obtained by melt-kneading and cooling is pulverized to a desired particle size.
The pulverization may be performed, for example, by coarsely pulverizing the solid resin composition with a pulverizer such as a crusher, a hammer mill, or a feather mill, and then finely pulverizing the composition with a pulverizer such as Kryptron System (manufactured by Kawasaki Heavy Industries, Ltd), Super Rotor (manufactured by Nisshin Engineering Inc), or Turbo Mill (manufactured by Freund-Turbo Corp.), or an air-jet pulverizer.
Thereafter, if necessary, particles of the pulverized resin composition are classified. The classification can be performed using a classifier or a sieving machine, such as an inertial classification type Elbow Jet (manufactured by Nittetsu Mining Co., Ltd), a centrifugal classification type Turboplex (manufactured by Hosokawa Micron Corporation), a TSP separator (manufactured by Hosokawa Micron Corporation), or Faculty (manufactured by Hosokawa Micron Corporation).
Thus, the toner base particles can be produced by the pulverization method.

(Surface Treatment with Hot Air)

The toner particles obtained by one of the above methods, particularly by the pulverization method, may be subjected to surface treatment with hot air. By the surface treatment with hot air, the surface shape of the toner base particles can be adjusted (made spherical), and the physical properties of the surfaces can be adjusted. It is preferable that the temperature of hot air during the surface treatment be about 100 °C to 450 °C.
The method of the surface treatment with hot air is not particularly limited. The surface treatment can be performed by methods described in Japanese Unexamined Patent Publication No. S59-125743 or No. 2022-96557 , for example. These publications describe a surface treatment method in which toner particles are dropped while being swirled by hot air in a heat treatment chamber, cooled by cold air flown inside the heat treatment chamber, and then collected.
Fig. 1 is a schematic view of an example of a surface treatment apparatus 100 configured to perform surface treatment with hot air.
The toner particles supplied from the hopper 110 are mixed with the compressed air supplied from the nozzle 130 in the mixing chamber 120. The toner particles are then ejected from the diffuser 150 into the heat treatment chamber 160 as the dispersed airflow 140. The ejected dispersed airflow 140 receives hot air that has been supplied to the hot-air swirling chamber 170 and turned into a swirling airflow. Thus, the toner particles in the dispersion airflow 140 are swirled by the hot air. After the heat treatment by swirling, the toner particles are cooled by cold wind, which is introduced along the side wall of the heat treatment chamber 160 from the cold wind supply section 180. The cooled toner particles are then ejected from the ejection section 190 and collected.
Fig. 2 is a schematic view of another example of the surface treatment apparatus 200 configured to perform surface treatment with hot air.
The toner particles mixed with the compressed gas are introduced into the introduction pipe 220 disposed on the central axis of the heat treatment chamber 210. The introduced toner base particles pass through the introduction pipe 220 and are uniformly dispersed by the conical projection member 222 provided at the central part of the introduction pipe 220, and then pass through the radially spread supply pipe 230. The toner base particles are guided to the powder particle supply port 240 and are guided from the powder particle supply port 240 to the heat treatment chamber 210.
Into the heat treatment chamber 210, hot air is supplied from the hot-air introducing section 260 by the hot-air supplying means 250. The hot air is swirled by the swirling member 270 having blades and introduced into the heat treatment chamber 210 while swirling spirally. At this time, the substantially conical distribution member 280 uniformly distributes the swirled hot air in each direction.
The toner base particles in the heat treatment chamber 210 falls inside the heat treatment chamber 210 while being swirled by the spirally swirling hot air. In the treatment chamber 6, cold air is introduced by cold air introduction portions 290. The toner base particles swirling and falling are cooled by the cold air introduced by the cold air introduction portions 290.

< Emulsion polymerization aggregation method >

The emulsion polymerization aggregation method is also suitably applicable for the toner of the present invention. Following is an example in which a hybrid crystalline polyester is used as the crystalline resin.
Specifically, the toner production method preferably includes the following steps (1) to (6).
Step (1): In a reaction tank, mix a monomer as a raw material of the crystalline polyester polymerization segment, a raw material monomer (as a raw material of a vinyl-based polymerization segment) of an addition polymerization-based resin unit (styrene-acrylic resin), and an esterification catalyst; and cause polycondensation reaction of the material monomers.
Step (2): After the polycondensation reaction of the material monomers in step (1), add a crystal nucleating agent into the reaction tank and cause reaction to form crystal nucleating agent sites.
Step (3): After Step (2), in an aqueous medium, aggregate and fuse at least fine particles of amorphous resin (vinyl resin and amorphous polyester), fine particles of crystalline resin (hybrid crystalline polyester), fine particles of the C16-35 saturated compounds, and fine particles of the colorant.
Step (4): Perform solid-liquid separation of the toner base particles from the dispersion of the toner base particles, remove deposits such as the surfactant and the aggregating agent from the toner cake obtained by the solid-liquid separation, and wash the toner cake.
Step (5): Dry the washed toner cake.
Step (6): Perform external additive treatment to the toner base particles obtained in Step (5).

(Step (1))

In Step (1), mix a monomer as a raw material of the crystalline polyester polymerization segment, a raw material monomer of an addition polymerization-based resin (styrene-acrylic resin) unit, and an esterification catalyst in a reaction tank; and cause polycondensation reaction of the raw material monomers.
As the monomer serving as a raw material of the crystalline polyester polymerized segment, known monomers can be suitably used, such as the above-described polyhydric alcohol monomers and polycarboxylic acid monomers.

(Polycondensation reaction)

The method of polycondensation reaction of the raw material monomers, namely the method of synthesizing the crystalline polyester polymerized segment is not limited to a specific method. However, it is preferable that any of the following methods (A) to (C) be used.

(A) Polymerize a polycarboxylic acid having a valency of three or more or a polyhydric alcohol having a valency of three or more
(B) Perform addition-polymerization of unsaturated dicarboxylic acid or unsaturated dialcohol
(C) Use hybrid crystalline polyester generated by chemically bonding crystalline polyester and amorphous

resin unit

In the polymerization of the above methods (A) and (B), a known polymerization initiator and a known chain transfer agent can be used.

(Esterification catalyst)

As the esterification catalyst, a known esterification catalyst can be used. Examples of the esterification catalyst include tin compounds such as tin dioctylate, dibutyltin oxide, and tin (II) 2-ethylhexanoate; and titanium compounds such as tetrabutyl orthotitanate and titanium diisopropylate bistriethanolaminate. Among these, tetrabutyl orthotitanate (also referred to as "Ti (OBu)₄) is preferably used.

(Step (2))

In Step (2), after causing the polycondensation reaction of the material monomers in step (1), add a crystal nucleating agent into the reaction tank and cause reaction to form crystal nucleating agent sites.
That is, after the crystalline polyester polymerized segment is obtained by the polycondensation reaction in step (1), the crystal nucleating agent is added to cause a reaction between the crystal nucleating agent and the crystalline polyester polymerized segment. Accordingly, the crystal nucleating agent can be chemically bonded to the crystalline polyester polymerization segment to form a crystal nucleating agent site.
The reaction in Step (2) may be any reaction that chemically bonds the crystalline polyester polymerized segment and the crystal nucleating agent. For example, the reaction is caused by heating to 200 °C under normal pressure but not limited thereto.
After steps (1) and (2), the crystalline polyester polymerized segment chemically bonded with the crystal nucleating agent is then chemically bonded to the vinyl-based polymerized segment by the method of synthesizing a hybrid crystalline polyester, as described above. Accordingly, a hybrid crystalline polyester having a crystal nucleating agent site in the crystalline polyester polymerized segment can be generated.
The crystal nucleating agent may be any compound that forms a crystal nucleating agent site as described above. The crystal nucleating agent is preferably an aliphatic monocarboxylic acid having a carbon number in the range of 10 to 30 or an aliphatic monoalcohol having a carbon number in the range of 10 to 30.
Specific examples thereof include stearic acid, lauric acid, behenic acid, triacontanoic acid, arachidic acid, stearyl alcohol, lauryl alcohol, behenyl alcohol, and arachidyl alcohol.

(Step (3))

In Step (3) after Step (2), in an aqueous medium, aggregate and fuse at least fine particles of amorphous resin (vinyl resin and amorphous polyester), fine particles of crystalline resin (hybrid crystalline polyester), fine particles of the C16-35 saturated compounds, and fine particles of the colorant.
According to these toner production methods, firstly the polycarboxylic acid monomer and the polyhydric alcohol monomer are reacted and then the crystal nucleating agent segment is introduced, so that the crystalline polyester can be suitably produced.
As a method of aggregating and fusing, a known emulsion aggregation method is applicable, for example.
In the emulsion aggregation method, a solution of amorphous resin and crystalline resin (hereinafter collectively referred to as "binding resin") dissolved in a solvent and the C16-35 saturated compounds are dripped to a poor solvent to obtain a fine particle dispersion of the binding resin. The dispersion of the binding resin fine particles is mixed with a dispersion of the colorant fine particles and a dispersion of the releasing agent (e.g., wax). The fine particles of the amorphous resin, the fine particles of the crystalline resin, the fine particles of the colorant, the fine particles of the C16-35 saturated compound, and the releasing agent are aggregated in the aqueous solvent until the toner particles have a desired size. These fine particles are fusion-bonded to control their shape. Thus, toner particles are produced.
As another preferable emulsion aggregation method other than the above-described method, the release agent and the C16-35 saturated compounds are added to a dispersion of binding resin particles in which emulsion-polymerized amorphous resin and crystalline resin are dispersed; these particles are aggregated to some extent; and a dispersion of binding resin particles that does not contain the C16-35 saturated compound is further added. These fine particles are fusion-bonded to control their shape. Thus, toner particles are produced.
In the present invention, the term "aqueous medium" refers to a medium containing at least 50% by mass of water. Examples of components other than water include organic solvents soluble in water, such as methanol, ethanol, isopropanol, butanol, acetone, methyl ethyl ketone, dimethylformamide, methyl cellosolve, and tetrahydrofuran.
Among these, it is preferable to use an alcohol-based organic solvent, which is an organic solvent that does not dissolve resins, such as methanol, ethanol, isopropanol, or butanol. Preferably, as the aqueous medium, only water such as ion-exchanged water is used.

(Step (4))

In Step (4), perform solid-liquid separation of the toner base particles from the dispersion of the toner base particles, remove deposits such as the surfactant and the aggregating agent from the toner cake obtained by the solid-liquid separation, and wash the toner cake.
The toner cake is an aggregate of wet toner particles aggregated into a cake shape.
The method of solid-liquid separation is not limited to a specific method. The solid-liquid separation can be performed by a centrifugation method, a vacuum filtration method with a nutsche, or a filtration method with a filter press, for example. Furthermore, it is preferable to wash the toner cake with water until the electrical conductivity of the filtrate becomes 10 µS/cm.

(Step (5))

In step (5), the washed toner cake is dried. The drying can be performed by a common drying step of a known toner particle production method.
Specific examples of a drier for the toner cake include a spray dryer, a vacuum freeze dryer, and a reduced pressure dryer. In particular, it is preferable to use a stationary shelf dryer, a movable shelf dryer, a fluidized bed dryer, a rotary dryer, or a stirring dryer be used as the drier.
The moisture content of the dried toner particles is preferably 5% by mass or less, and more preferably 2% by mass or less.
When the dried toner particles are aggregated by a weak inter-particle attractive force, the aggregate may be subjected to a crushing treatment. Examples of the crushing treatment apparatus include mechanical crushing apparatuses such as a jet mill, a Henschel mixer, a coffee mill, and a food processor.
The drying temperature is preferably in the range of 10 to 45 °C, more preferably in the range of 20 to 40 °C. If the drying temperature is higher than 45 °C, the crystalline component in the toner is brought into a molten state, which makes it difficult control the structure of the toner.
By controlling the drying temperature, the amount of change in the endothermic peak start temperature observed at 20 °C or more on the DSC curve owing to a change in the maintaining temperature is restrained to 2 °C or less in the present invention.

(Step (6))

In the step (6), the toner base particles obtained through steps (1) to (5) are subjected to an external additive treatment with an external additive, if necessary. The toner base particles obtained through steps (1) to (5) may be used as they are.
The external additive treatment with an external additive can be performed by stirring and mixing predetermined amounts of the toner base particles and the external additive with a mixing device.
Examples of the mixing apparatus include a double cone mixer, a V-type mixer, a drum-type mixer, a super mixer, a Henschel mixer, a Nauta mixer, Mechano Hybrid (manufactured by Nippon Coke & Engineering Co., Ltd.), and Nobilta (manufactured by Hosokawa Micron Corporation).
As the external additive, the above-described inorganic particles can be used.
Carrier is mixed with the toner base particles described above to form two-component magnetic toner.
The carrier may be any known magnetic particles that can be contained in the toner.
Examples of the magnetic particles include particles containing a magnetic material, such as iron, steel, nickel, cobalt, ferrite, and magnetic, and alloys thereof with aluminum or lead.
The carrier may be a coated carrier constituted of the above magnetic particles coated with resin, or a resin-dispersion-type carrier constituted of the above magnetic materials dispersed in a binding resin.
Examples of the coated resin include an olefin resin, a styrene resin, a styrene-acrylic resin, a silicone resin, polyester, and a fluororesin.
Examples of the binding resin include an acrylic resin, a styrene-acrylic resin, polyester, a fluororesin, and a phenol resin.
The average particle size of the carrier is preferably 20 to 100 µm, and more preferably 25 to 80 µm, in terms of the volume-based average particle size. The average particle diameter of the carrier can be measured with, for example, HELOS (manufactured by SYMPATEC GmbH) ,which is a laser diffraction particle size distribution analyzer equipped with a wet disperser.
The amount of the carrier is preferably 2% to 10% by mass with respect to the total mass of the toner base particles and the carrier.

[Image forming method and image forming apparatus]

An image forming method and an image forming apparatus are described below.
The image forming method of the present invention includes a step of attaching the electrostatic latent image developing toner to a recording medium and a step of fixing the attached electrostatic latent image developing toner to the recording medium.
In the fixing step, it is preferable that the electrostatic latent image developing toner is fixed to the recording medium in two stages. Fixing in two stages allows the toner image to be heated sufficiently for a long time, so that the C16-35 saturated compounds are sufficiently precipitated from the toner base particles. Accordingly, the varnish coatability and the releasability from the fixing device in the second stage are further enhanced.
To improve image quality and durability, it is preferable to include a step of forming a varnish coat by applying varnish to the surface of the toner image formed by fixing the electrostatic latent image developing toner.
The image forming apparatus of the present invention includes at least a developing member, a transfer member, and a fixing member and forms a toner image on a recording medium by using the above-described electrostatic latent image developing toner. The fixing member includes a fixing nip that is a fixing pad.
Furthermore, it is preferable that the fixing member includes: an endless belt configured to heat the toner image on the recording medium at the fixing nip; a rotatable body configured to form the fixing nip in cooperation with the endless belt; the fixing pad configured to be in contact with an inner circumferential surface of the endless belt and to sandwich the endless belt between the fixing pad and the rotatable body to form the fixing nip; and a heating roller in contact with the inner circumferential surface of the endless belt and configured to heat the endless belt. Use of the fixing pad widens the fixing area and lengthens the fixing time. Accordingly, the toner image can be heated sufficiently and for a longer time, so that the C16-35 saturated compounds are sufficiently precipitated from the toner base particles. As a result, the varnish coatability and the releasability from the fixing device are further enhanced.
Preferably, the image forming apparatus is a four-cycle-system image forming apparatus that includes one electrophotographic photoreceptor and four developing devices for colors of yellow, magenta, cyan, and black. The image forming apparatus may be a tandem-type image forming apparatus that includes four developing devices for colors of yellow, magenta, cyan, and black and four electrophotographic photoreceptors provided for the respective colors.
Fig. 3 is a schematic configuration of an example of the image forming apparatus 1 according to the present embodiment. The image forming apparatus 1 illustrated in FIG. 3 includes an image processing section 30, an image forming section 40, a sheet conveyance section 50, a fixing device 60, and an image reading section 70.
The image forming section 40 includes image forming units 41Y, 41M, 41C, and 41K that form images with toners of the respective colors of Y (yellow), M (magenta), C (cyan), and K (black). The image forming units have the same configuration except for the toner stored therein. Therefore, hereinafter, the symbol representing the color may be omitted. The image forming section 40 further includes an intermediate transfer unit 42 and a secondary transfer unit 43. The intermediate transfer unit 42 and the secondary transfer unit 43 correspond to a transfer device.
The image forming unit 41 includes an exposure device 411, a developing device 412, an electrophotographic photoreceptor (image bearing member) 413, a charging device 414, and a drum cleaning device 415. The charging device 414 is, for example, a corona charger.
The charging device 414 may be a contact charging device that charges the electrophotographic photoreceptor 413 by bringing a contact charging member, such as a charging roller, a charging brush, or a charging blade, into contact with the electrophotographic photoreceptor 413.
The exposure device 411 includes, for example, a semiconductor laser as a light source and a light deflection device (polygon motor) that irradiates the electrophotographic photoreceptor 413 with laser light, which corresponds to an image to be formed.
The electrophotographic photoreceptor 413 is a negatively chargeable organic photoreceptor having photoconductivity. The electrophotographic photoreceptor 413 is charged by the charging device 414.
The developing device 412 employs a two-component developing method. The developing device 412 includes, for example, a developer container that stores a two-component developer; a developing roller (magnetic roller) rotatably disposed at an opening of the developer container; a partition wall that partitions the inside of the developer container such that the two-component developer can pass through; a conveyance roller that conveys the two-component developer at the opening side in the developer container toward the developing roller; and a stirring roller that stirs the two-component developer in the developer container.
The developing container stores the two component developer, for example.
The intermediate transfer unit 42 includes an intermediate transfer belt (intermediate transfer member) 421; primary transfer rollers 422 that press the intermediate transfer belt 421 against the electrophotographic photoreceptors 413, support rollers 423 including a backup roller 423A and a belt cleaning device 426.
The intermediate transfer belt 421 has a loop shape and stretched around the support rollers 423. By the rotation of at least one drive roller among the support rollers 423, the intermediate transfer belt 421 is rotated to run at a constant speed in the direction of the arrow A.
The belt cleaning device 426 includes an elastic member 426a.
The elastic member 426a is brought into contact with the intermediate transfer belt 421 after the secondary transfer and removes substances on the surface of the intermediate transfer belt 421. The elastic member 426a is formed of an elastic body and includes a cleaning blade and a brush.
The secondary transfer unit 43 includes an endless secondary transfer belt 432 and support rollers 431 including a secondary transfer roller 431A. The secondary transfer belt 432 has a loop shape and is stretched by the support rollers 431 including the secondary transfer roller 431A.
The fixing device 60 includes, for example, a fixing roller 62; an endless heating belt 10 that covers an outer circumferential surface of the fixing roller 62 and that heats and melts toner constituting a toner image on a sheet S; and a pressure roller 63 that presses the sheet S against the fixing roller 62 and the heating belt 10. The sheet S corresponds to a recording medium.
The image forming apparatus 1 further includes the image reading section 70, the image processing section 30, and the sheet conveyance section 50.
The image reading section 70 includes a sheet feed device 71 and a scanner 72.
The sheet conveyance section 50 includes a sheet feed section 51, a sheet ejection section 52, and a conveyance path section 53.
The sheet feed section 51 includes three sheet feed trays 51a to 51c each of which houses a predetermined kind of sheets S (standard sheets, special sheets) identified based on the basis weight, the size, and so forth.
The conveyance path section 53 includes conveyance roller pairs, such as a registration roller pair 53a.
Formation of an image by the image forming apparatus 1 is described.
The scanner 72 optically scans and reads the document D on the contact glass. The light reflected on the document D is read by the CCD sensor 72a as input image data. The input image data is subjected to predetermined image processing in the image processing section 30 and sent to the exposure device 411.
The electrophotographic photoreceptor 413 rotates at a constant circumferential speed.
The charging device 414 uniformly and negatively charges the surface of the electrophotographic photoreceptor 413.
In the exposure device 411, the polygon mirror of the polygon motor rotates at a high speed; and laser light corresponding to the input image data of each color component spreads along the axial direction of the electrophotographic photoreceptor 413 and hits the outer circumferential surface of the electrophotographic photoreceptor 413 along the axial direction. Thus, an electrostatic latent image is formed on the surface of the electrophotographic photoreceptor 413.
In the developing device 412, the toner base particles are charged by stirring and conveying the two-component developer in the developing container. The two-component developer is conveyed to the developing roller and forms a magnetic brush on the surface of the developing roller. The charged toner base particles are electrostatically attached to the electrostatic latent image on the electrophotographic photoreceptor 413 from the magnetic brush. Thus, the electrostatic latent image on the surface of the electrophotographic photoreceptor 413 is visualized, and a toner image corresponding to the electrostatic latent image is formed on the surface of the electrophotographic photoreceptor 413.
The toner image on the surface of the electrophotographic photoreceptor 413 is transferred to the intermediate transfer belt 421 by the intermediate transfer unit 42. After the transfer, the transfer residual toner remaining on the surface of the electrophotographic photoreceptor 413 is removed by the drum cleaning device 415, which includes a drum cleaning blade that is brought into sliding contact with the surface of the electrophotographic photoreceptor 413.
The intermediate transfer belt 421 is pressed against the electrophotographic photoreceptor 413 by the primary transfer roller 422, so that a primary transfer nip is formed for each electrophotographic photoreceptor by the electrophotographic photoreceptor 413 and the intermediate transfer belt 421. At the primary transfer nips, the toner images of respective colors are sequentially transferred onto the intermediate transfer belt 421 and superposed on one another.
On the other hand, the secondary transfer roller 431A is pressed against the backup roller 423A with the intermediate transfer belt 421 and the secondary transfer belt 432 in-between. Thus, a secondary transfer nip is formed by the intermediate transfer belt 421 and the secondary transfer belt 432. The sheet S passes through the secondary transfer nip.
The sheet S is conveyed to the secondary transfer nip by the sheet conveyance section 50. The orientation of the sheet S and the timing of conveying the sheet S are adjusted by a registration roller section that includes the registration roller pair 53a.
When the sheet S is conveyed to the secondary transfer nip, a transfer bias is applied to the secondary transfer roller 431A. By the application of the transfer bias, the toner image carried on the intermediate transfer belt 421 is transferred onto the sheet S (a step of attaching the electrostatic latent image developing toner to the recording medium). The sheet S on which the toner image has been transferred is conveyed toward the fixing device 60 by the secondary transfer belt 432.
Adhered substances, such as transfer residual toner remaining on the surface of the intermediate transfer belt 421 after the secondary transfer, are removed by the belt cleaning device 426 with the cleaning blade that is brought into sliding contact with the surface of the intermediate transfer belt 421. Since the above-described intermediate transfer member is used as the intermediate transfer belt, the dynamic frictional force can be reduced with time.
The fixing device 60 forms a fixing nip by sandwiching the heating belt 10 between the rotating fixing roller 62 and the pressure roller 63, and heats and pressurizes the conveyed sheet S at the fixing nip. Thus, the toner image is fixed to the sheet S (a step of fixing the electrostatic latent image developing toner onto the recording medium). The sheet S on which the fixed toner image has been fixed is ejected outside the apparatus by the sheet ejection section 52 with the sheet ejection roller 52a.
In the present embodiment, fixing the toner image to the sheet S may be performed in two stages. That is, the image forming apparatus 1 may include two different fixing devices 60, and fixing may be continuously performed by the two fixing devices 60.
Specifically, the fixing device 60 of the first stage may heat the toner image, and the fixing device 60 of the second stage may heat and pressurize the toner image before the image heated in the first stage is completely cooled. According to the two-stage fixing, the toner image is heated sufficiently for a long time, and the C16-35 saturated compounds are sufficiently precipitated from the toner base particles. As a result, the varnish coatability and the toner releasability from the second-stage fixing device 60 can be further enhanced.
The second stage fixing may be performed immediately after the first stage fixing. For example, after the sheet S is reversed to form and fix another image on the back surface, the sheet S may be reversed again to perform the second stage fixing on the front surface. At this time, it is preferable that the sheet S be further reversed to perform the second stage fixing on the back surface.
The third and subsequent stages of fixing may be further performed.
Further, the fixing device may be configured to form a fixing nip by a non-rotatable pressure pad.
FIG. 4 illustrates a schematic configuration of the fixing device 600 configured to form a planar fixing nip by a non-rotatable pressure pad.
The fixing device 600 includes a non-rotatable pressure pad 610, a pressure roller 620, a heating roller 630, a steer roller 640, and a heating belt 650.
The heating belt 650 is stretched around the heating roller 630 and the steer roller 640. The heating belt 650 is sandwiched between the non-rotating pressure pad 610 and pressure roller 620 to form a fixing nip. At the fixing nip, the conveyed sheet S is heated and pressurized.
The pressure pad 610 is pressed against the heating belt by a pressing member 660 made of stainless steel, thereby pressing the heating belt 650 against the pressure pad 610 to form the fixing nip.
The pressure pad 610 is a substantially rectangular parallelepiped pad member formed of a liquid crystal polymer (LCP), for example. The pressure pad 610 presses the heating belt 650 with one face of the cuboid to form a cotton-like fixing nip. A lubricating sheet (not illustrated) is interposed between the pressure pad 610 and the heating belt 650 to allow smooth rotation of the heating belt 650.
The lubricating sheet may be, for example, a polyimide sheet coated with polytetrafluoroethylene (PTFE) having a thickness of 100 µm. The polyimide sheet may be formed with protrusions of 100 µm at 1 mm intervals to reduce the contact area with the heating belt 650 and thereby reduce sliding resistance. Furthermore, a lubricant such as silicone oil may be applied to a surface of the heating belt 650 that is brought into contact with the lubricating sheet to allow smooth rotation of the heating belt 650.
By forming the planar nip as described above, the fixing time can be further increased. According to the two-stage fixing, the toner image is heated sufficiently for a long time, and the C16-35 saturated compounds are sufficiently precipitated from the toner base particles. As a result, the varnish coatability and the toner releasability from the second-stage fixing device 600 can be further enhanced.
When the fixing is performed in two stages as described above, both of the two fixing devices may have a pressure pad. Alternatively, one of the fixing devices (the first stage fixing device or the second stage fixing device) may have a pressure pad. Both of the two fixing devices may have a rotating fixing roller.
The above-described apparatus configuration and image forming method are merely exemplary modes for carrying out the present invention, and the present invention is not limited thereto.

[Formation Of Varnish Coat]

Varnish may be applied to images formed by the above-described image forming method to form a varnish coat.
The varnish coat is formed by, for example, applying a photocurable varnish containing a photopolymerizable compound to the image formed by the above-described image forming process and curing the varnish to form a varnish layer. The photocurable varnish may be applied to cover the entire image or may be applied to cover only a part of the image.
The method for applying the photocurable varnish to the image is not limited to a specific method as long as the photocurable varnish is uniformly applied.
Examples of a coating device include liquid film coating devices, such as a varnish coater, a roll coater, a flexible coater, a rod coater, a blade, a wire bar, an air knife, a curtain coater, a slide coater, a doctor knife, a screen coater, a gravure coater (e.g., an offset gravure coater), a slot coater, and an extrusion coater. Further, coating may be done by well-known methods, such as forward and reverse roll coating, offset gravure, curtain coating, lithographic coating, screen coating, and gravure coating.
The photocurable varnish to be applied to the image may contain a photopolymerizable compound (polymerizable monomer for varnish). Usually, the photocurable varnish contains a polymerization initiator (sensitizer) along with the photopolymerizable compound.
The photopolymerizable compound may be a monomer, an oligomer, or a polymer. The photopolymerizable compound includes at least diol di (meth) acrylate having a linear hydrocarbon structure.
When the photocurable varnish contains the diol di (meth) acrylate, the varnish has an increased affinity with the crystalline polyester in the toner particles. Accordingly, the wettability of the photocurable varnish to an image is improved, and the adhesion between the varnish layer and the image is increased.
Here, the diol di (meth) acrylate having a linear hydrocarbon structure is a monomer obtained by dehydration assembly of an aliphatic diol and two (meth) acrylic acids. The hydrocarbon structure of the diol di (meth) acrylate may be partially branched. In this case, a hydrocarbon chain sandwiched between two oxygen atoms derived from the diol is specified as a linear hydrocarbon structure.
The number of carbon atoms of the linear hydrocarbon structure of the diol di (meth) acrylate is preferably 4 to 12, more preferably 6 to 10, and further preferably 6 to 9. When the number of carbon atoms of the linear hydrocarbon structure of the diol di (meth) acrylate is within the above range, the photocurable varnish has an appropriate level of viscosity, and a satisfactory level of coatability is achieved. Further, the varnish can have a satisfactory affinity with the crystalline polyester in the toner particles.
Specific examples of the diol di (meth) acrylate include hexanediol diacrylate, nonanediol diacrylate, and decanediol diacrylate. Among these, hexanediol diacrylate is preferable.
The amount of the diol di (meth) acrylate having a linear hydrocarbon structure is preferably 10 to 80% by mass, and more preferably 20 to 65% by mass, with respect to the total mass of the photopolymerizable compounds. When the amount of the diol di (meth) acrylate is within the above range, the adhesion between an image and the varnish layer becomes satisfactory.
Examples of the photopolymerizable compound other than diol di (meth) acrylate include an acrylic resin; a polymerizable oligomer or a polymerizable polymer, such as a vinyl-acrylic-based resin, an acrylic acid ester of a polyhydric alcohol, epoxy acrylate, urethane acrylate, polyester acrylate, polyether acrylate, acrylate alkyd, and melamine acrylate; a (meth) acrylate monomer, such as trimethylolpropane (meth) acrylate and phenoxy ethyl (meth) acrylate; and a tri (meth) acrylate monomer. The amount and type of the photopolymerizable compound other than the diol di (meth) acrylate are appropriately determined according to the curability, viscosity, and surface tension of the photocurable varnish.
Examples of the polymerization initiator (sensitizer) include known anthraquinone-based initiators, benzophenone-based initiators, 2-ethylanthraquinone-based initiators, acylphosphine oxide-based initiators, and alkylphenone-based photopolymerization initiators.
The amount of the polymerization initiator is preferably 5 to 25% by mass with respect to the total mass of the photocurable varnish. When the amount of the polymerization initiator is within the above range, the curability of the photocurable varnish becomes satisfactory.
Furthermore, the photocurable varnish may contain a surfactant.
Examples of the surfactant include an anionic surfactant, a nonionic surfactant, a silicone surfactant, and a fluorosurfactant.
Examples of the anionic surfactant include sulfosuccinates, disulfonates, phosphate esters, sulfates, and sulfonates.
Examples of nonionic surfactants include polyvinyl alcohol, polyacrylic acid, isopropyl alcohol, acetylenic diols, ethoxylated octylphenol, ethoxylated branched secondary alcohols, perfluorobutane sulfonate, and alkoxylated alcohols.
Examples of the silicone surfactant include polyether-modified polydimethylsiloxane.
Examples of fluorosurfactants include ethoxylated nonylphenol.
When the photocurable varnish contains a surfactant, the adhesion between the image and the varnish layer may be improved. Further, the surfactant contributes to adjusting the surface tension of the photocurable varnish to enhance the wettability of the photocurable varnish.
The surface tension of the photocurable varnish at 25 °C are preferably 10 to 50 mN/m, more preferably 15 to 45 mN/m, and further preferably 20 to 40 mN/m. When the surface tension of the photocurable varnish is within the above range, the photocurable varnish easily spreads on an image.
The surface tension of the photocurable varnish is measured by a plate method with KYOWA DY300 (manufactured by Kyowa Interface Science Co., Ltd).
On the other hand, the viscosity of the photocurable varnish at 25 °C measured 30 seconds after immersing a vibrator in the liquid is preferably 100 to 800 mPa s. The viscosity is more preferably 150 to 700 mPa·s, and further preferably 200 to 600 mPa s. When the viscosity of the photocurable varnish is within the above range, the varnish can be easily applied to images by the above-described method.
After applying the photocurable varnish, the photocurable varnish is cured by irradiation with light energy.
The type of light energy for irradiation is appropriately selected, based on the type of the polymerization initiator. Usually, ultraviolet light or visible light can be used, for example.
Examples of the light source of light energy include a low-pressure mercury lamp, a medium-pressure mercury lamp, a high-pressure mercury lamp, an ultrahigh-pressure mercury lamp, a xenon lamp, a carbon arc lamp, a metal halide lamp, a fluorescent lamp, a tungsten lamp, and an LED. The amount of light and the irradiation time are appropriately determined.
Other than the above-described photo-curable varnish, the varnish coat may be formed by applying a solvent-based varnish and drying the solvent.

[Examples]

Hereinafter, the present invention will be specifically described with reference to Examples, but the present invention is not limited thereto. Note that in the following Examples, operations were performed at room temperature (25°C) unless otherwise specified. Further, unless otherwise specified, "%" and "part(s)" mean "% by mass" and "part(s) by mass", respectively.

1. Preparation of materials

[Saturated hydrocarbon compound [S]]

Saturated hydrocarbons having 20 carbon atoms, 26 carbon atoms, 30 carbon atoms, and 34 carbon atoms (manufactured by GL Science Co., Ltd) were fractionated at a mass ratio of 20:30:30:20. The saturated hydrocarbons were mixed and melted at 80 °C, and then cooled and solidified to obtain a saturated hydrocarbon compound [S] having 16 to 35 carbon atoms.

< Release agent [W1] (microcrystalline wax) >

A microcrystalline wax having a melting point of 82 °C was prepared by solvent crystallization and filtration of a vacuum distillation residual oil. The molecular distillation was repeated until the average number of carbon atoms became 41 and components having 16 to 35 carbon atoms were undetected. Thus, a microcrystalline wax (hydrocarbon wax) as the release agent [W1] was obtained.
In the molecular distillation, low-molecular-weight components were removed at 240 °C and at 0.2 Pa; and other components were removed at 400 °C and 0.2 Pa. The number of carbon atoms was qualitatively determined by GC-MS and quantitatively determined by GC-FID.
The obtained microcrystalline wax had the melting point of 73 °C. The melting point was defined as a temperature at which an endothermic peak having a half-value width of 15 °C or less was observed in DSC at a heating rate of 10 °C/min.
< Release agent [W2] (behenic acid behenate) >
Commercially available behenate was used as a release agent [W2] (ester wax).

< Amorphous polyester [c1] >

Terephthalic acid: 55.7 parts by mass
Propylene oxide adduct of bisphenol A (BPA-PO): 29.0 parts by mass
Propanediol: 15.3 parts by mass
Tin 2-ethylhexanoate (esterification catalyst): 0.50 parts by mass

The above materials were put in a reaction tank equipped with a cooling tube, a stirrer, a nitrogen introduction tube, and a thermocouple. Thereafter, the inside of the reaction tank was replaced with nitrogen gas, the temperature was gradually raised while stirring, and the above materials were reacted over three hours while stirring at a temperature of 140 °C.
Next, the pressure in the reaction tank was reduced to 8.3 kPa, the temperature was raised to 200 °C while stirring, and the mixture was reacted for four hours. Thereafter, the pressure in the reaction tank was reduced again to 5 kPa or less, and the mixture was reacted at 200 °C for three hours to obtain the amorphous polyester [c1].

< Hybrid Crystalline Polyester [c2] >

A radical polymerization initiator and the following raw material monomers of an addition polymerization-based resin (styrene acrylic resin: StAc) unit including a bireactive monomer were put in a dropping funnel.

Styrene 40.0 parts by mass
N-Butyl acrylate: 16 parts by mass
Acrylic acid: 3.5 parts by mass
Polymerization initiator (di-t-butyl peroxide): 8 parts by mass

Further, the following raw material monomers of a polycondensation resin (crystalline polyester: CPEs) unit were put in a four flask equipped with a nitrogen introduction tube, a dehydration tube, a stirrer, and a thermocouple, and were heated to 170 °C to be dissolved.

Acid: tetradecanedioic acid: 280 parts by mass
Alcohol: 1,4 -butanediol: 105 parts by mass

Next, the above monomers were placed in a reaction vessel equipped with a stirrer, a thermometer, a cooling tube, and a nitrogen gas introduction tube. The inside of the reaction vessel was replaced with dry nitrogen gas.
To the obtained mixed solution, 0.4 parts by mass of Ti (O-n-Bu)₄ was added; the temperature was raised to 235 °C; the reaction was performed under atmospheric pressure (101.3 kPa) for five hours; and the reaction was further performed under reduced pressure (8 kPa) for one hour.
Next, the obtained reaction liquid was cooled to 200 °C and reacted under reduced pressure (20 kPa) such that the acid number calculated by the above-described measurement method became 20.0 mgKOH/g after introducing the nucleating agent moiety.
Next, the reaction tank was gradually opened to return the pressure to normal pressure; thereafter, 20.3 parts by mass of stearic acid was added as a crystal nucleating agent; and the mixture was reacted under normal pressure at 200 °C for 1.5 hours.
Thereafter, the pressure in the reaction tank was reduced to 5 kPa or less at 200 °C, and the mixture was reacted for 2.5 hours to obtain hybrid crystalline polyester [c2].
The hybrid crystalline polyester [c2] had a weight-average molecular weight (Mw) of 11500 and an acid number of 20.0 mgKOH/g.

< Preparation of Hybrid crystalline resin fine particle dispersion [C2] >

The following materials were added to 102 parts by mass of methyl ethyl ketone and stirred at 75 °C for 30 minutes to be dissolved.

• Hybrid crystalline polyester [c2]: 174.3 parts by mass

Next, 3.1 parts by mass of a 25% by mass aqueous sodium hydroxide solution was added to the solution. The solution was put in a reaction vessel equipped with a stirrer, and while stirring, 375 parts by mass of water warmed to 70 °C was added dropwise over 70 minutes and mixed. The liquid in the container became cloudy during the dropwise addition, and a uniformly emulsified state was obtained after the dropwise addition of the entire amount.
Next, while the emulsion was kept at 70 °C, methylethyl ketone was removed by distillation by stirring for three hours under reduced pressure to 15 kPa (150mbar) using a diaphragm pump "V-700" (manufactured by Buchi Labortechnik GmbH). Then the emulsion was cooled at a cooling rate of 6 °C/min to prepare the hybrid crystalline resin microparticle dispersion liquid [C2] in which microparticles of the hybrid crystalline polyester [c2] were dispersed.
The volume-average particle size of the fine crystalline resin particles in the hybrid fine crystalline resin particle dispersion [C2] was 202 nm, which was measured by the particle size distribution analyzer.

< Preparation of Colorant fine particle dispersion [P] >

To 1600.0 parts by mass of ion-exchanged water, 90.0 parts by mass of sodium N-dodecyl sulfate was added. While the aqueous solution was stirred, 320.0 parts by mass of carbon black (REGAL 330R, manufactured by Cabot Corporation) was gradually added to the aqueous solution.
Next, a dispersion treatment was performed using a stirrer (CLEARMIX W Motion CLM-0. 8, manufactured by M Technique Co., Ltd.) to prepare a colorant fine particle dispersion [P] having a volume-based median particle size of 110 nm. The median diameter is a value measured with a particle size distribution analyzer (MICROTRAC UPA-150, manufactured by Honeywell International Inc.).

< Preparation of Vinyl resin fine particle dispersion [A] >

Styrene: 432.0 parts by mass
N-Butyl acrylate: 225.0 parts by mass
Methacrylic acid: 61.2 parts by mass

In a reaction vessel having a capacity of 5 liter and equipped with a stirrer, a temperature sensor, a cooling tube, and a nitrogen introduction device, 8 parts by mass of sodium dodecyl sulfate and 3000 parts by mass of ion exchanged water were prepared. Under a nitrogen gas stream, the liquid temperature was increased to 80 °C while being stirred at a stirring speed of 230 rpm. After the temperature was increased, a solution prepared by dissolving 10 parts by mass of potassium persulfate in 200 parts by mass of ion exchanged water was added; the liquid temperature was again heated to 80 °C; and the mixed liquid of the above monomers was added dropwise over 1 hour. After the dropwise addition, the liquid temperature was kept at 80 °C, and the liquid was stirred for 2 hours to cause polymerization. Thus, a vinyl resin fine particle dispersion [a1] was prepared.

Styrene: 256.5 parts by mass
2-ethylhexyl acrylate: 85.5 parts by mass
Methacrylic acid: 18.0 parts by mass
N-octyl-3-mercaptopropionate (chain transfer agent): 5.40 parts by mass
Release agent [W1]: 135.0 parts by mass
Saturated hydrocarbon compounds having 16 to 35 carbon atoms [S]: 3.00 parts by mass

In a 5-liter reaction vessel equipped with a stirrer, a temperature sensor, a cooling tube, and a nitrogen introduction device, 7 parts by mass of sodium polyoxyethylene (2) dodecyl ether sulfate and 3000 parts by mass of ion-exchanged water were put. The mixture was heated to 80 °C. After the heating, the following were added: 80 parts by mass of the vinyl polymer fine particle dispersion [a1] in terms of solid contents; and a mixed solution in which the above monomers, the chain transfer agent, the release agent [W1] (hydrocarbon wax), and the saturated hydrocarbon compounds [S] were dissolved at 90 °C.
Thereafter, a mixing and dispersing process was performed for 1 hour using a mechanical disperser having a circulation path (CLEARMIX, manufactured by M Technique Co., Ltd) to prepare a dispersion containing emulsified particles (oil droplets).
Next, an aqueous initiator solution prepared by dissolving 6 parts by mass of potassium persulfate in 200 parts by mass of ion-exchanged water was added to the dispersion, and the system was heated and stirred at 84 °C for 1 hour. Thus, the above monomers were polymerized to prepare a vinyl-based resin fine particle dispersion [a2].
To the vinyl resin fine particle dispersion [a2], 400 parts by mass of ion-exchanged H2O was further added. Thereafter, a solution prepared by dissolving 11 parts by mass of potassium persulfate in 400 parts by mass of ion-exchanged water was added to the vinyl resin fine particle dispersion [a2]. Under a temperature condition of 82 °C, a mixed liquid of the following monomers was added dropwise over 1 hour.

Styrene: 330.3 parts by mass
N-butyl acrylate: 148.5 parts by mass
Methacrylic acid: 49.5 parts by mass
N-octyl-3-mercaptopropionate: 7.2 parts by mass

After the dropwise addition, the mixture was heated and stirred for 2 hours to polymerize the above monomers, The mixture was then cooled to 28 °C to obtain a vinyl resin fine particle dispersion [A].

< Preparation of Amorphous polyester resin fine particle dispersion [D] >

Styrene: 80.0 parts by mass
N-butyl acrylate: 20.0 parts by mass
Acrylic acid: 10.0 parts by mass
Di-t-butyl peroxide (polymerization initiator): 16.0 parts by mass

The mixture of the above monomers and the polymerization initiator was put in a dropping funnel.

Bisphenol -A ethylene oxide-2 mol adduct: 50.2 parts by mass
Bisphenol A-propylene oxide 2 mol adduct: 249.8 parts by mass
Terephthalic acid: 120.1 parts by mass
Dodecenyl succinic acid: 46.0 parts by mass

The monomers of the amorphous polyester were placed in a four-neck flask equipped with a nitrogen introduction tube, a dewatering tube, a stirrer, and a thermocouple, and were heated to 170 °C to dissolve.
The mixed liquid in the dropping funnel was added dropwise to the four flask over 90 minutes while being stirred, and was ripened for 60 minutes. After the ripening, the unreacted monomer was removed under reduced pressure (8kPa).
Thereafter, 0.4 parts by mass of Ti(OBu)₄ was added as an esterification catalyst. After the addition, the liquid temperature was raised to 235 °C, and the mixed liquid was reacted for 5 hours under atmospheric pressure (101.3 kPa) and for 1 hour under reduced pressure (8 kPa).
Next, the liquid temperature was cooled to 200 °C; the mixed liquid was reacted under reduced pressure (20 kPa); and then the solvent was removed to obtain an amorphous polyester.
The obtained 100 parts by mass of amorphous polyester was dissolved in 400 parts by mass of ethyl acetate (manufactured by Kanto Chemical Co., Inc). The solution was mixed with 638 parts by mass of a sodium lauryl sulfate solution (concentration: 0.26% by mass), which was prepared beforehand.
On the obtained mixed solution, ultrasonic dispersion treatment was performed by an ultrasonic homogeniser (US-150T, manufactured by NIPPON SEIKI CO., LTD.) at V-LEVEL 300 µA for 30 minutes while stirring.
Thereafter, in a state where the liquid temperature was raised to 40 °C, ethyl acetate was completely removed from the mixed liquid using a diaphragm vacuum pump (V-700, manufactured by Buchi Labortechnik GmbH) while stirring the liquid under reduced pressure for 3 hours. Accordingly, an amorphous polyester resin fine particle dispersion [D] having a solid content of 13.5% by mass was obtained.

2. Preparation of toner base particles

Amorphous polyester [c1]: 90 parts by mass
Hybrid crystalline polyester [c2]: 10 parts by mass
Release agent [W1] (microcrystalline wax): 5.00 parts by mass
Saturated hydrocarbon compounds having 16 to 35 carbon atoms [S]: 0.07 parts by mass
Carbon black (Regal 330R, manufactured by Cabot Corp.): 7.00 parts by mass

The above materials were put in a Henschel mixer (FM-75 type, manufactured by Mitsui Mining Co., Ltd) and mixed at a rotational speed of 20 s^-1 for 5 minutes.
Thereafter, these materials were kneaded using a twin-screw kneader (PCM-30 type, manufactured by Ikegai Corporation) set to 170 °C. The obtained kneaded product was cooled and coarsely pulverized to 1 mm or less by a hammermill to obtain a coarsely pulverized product. The obtained coarsely pulverized product was finely pulverized with a mechanical pulverizer (T-250, manufactured by Turbo Kogyo Co., Ltd). Further, the coarsely pulverized product was classified using a classifier (Faculty F-300, manufactured by Hosokawa Micron Corporation) with the number of rotations of the classification rotor at 130 s^-1 and the number of rotations of the dispersion rotor at 120 s^-1.
The classified particles were heat-treated by the surface treatment apparatus illustrated in Fig. 1. The heat treatment was performed for 30 seconds with the temperature of the heat treatment chamber at 300 °C. Accordingly, toner base particles 1 having an average circularity of 0.96 and a volume-average particle size of 6.5 µm were obtained.
The average circularity was measured by a measuring apparatus (FPIA-3000, manufactured by SYSMEX CORPORATION). The volume-average particle size was measured using Coulter Multisizer 3 (manufactured by Beckman Coulter, Inc.).

In a reaction vessel equipped with a stirrer, a temperature sensor, and a cooling tube, 180 parts by mass (in terms of solid content) of the dispersion liquid of vinyl-based resin fine particles [A] and 2000 parts by mass of ion-exchanged water were put. At room temperature (25 °C), 5 mol/liter aqueous sodium hydroxide solution was added to adjust the pH of the dispersion in the reaction vessel to 10.
Further, 40 parts by mass (in terms of solid content) of the coloring agent fine particle dispersion was put, and an aqueous solution prepared by dissolving 30 parts by mass of magnesium chloride as an aggregating agent in 60 parts by mass of ion-exchanged water was added while being stirred at 30 °C over 10 minutes. After leaving the system for 3 minutes, the temperature of the system was raised to 80 °C over 60 minutes. When the temperature reached 80 °C, the stirring speed was adjusted such that the growth rate of the particle diameter was 0.01 µm/min.
Next, the particles were grown until the volume-based median diameter measured by Coulter Multisizer 3 (manufactured by Beckman Coulter, Inc) reached 4.0 µm. At the stage the median diameter reached 4.0 µm, 121 parts by mass (in terms of solid content) of the vinyl resin fine particle dispersion [A] was added to the reaction vessel. The stirring speed was adjusted such that the growth rate of the particle diameter was 0.01 µm/min, and the particles were grown until the volume-based median diameter reached 6.0 µm.
Next, 68 parts by mass (in terms of solid content) of the amorphous polyester resin fine particle dispersion [D] was added over 30 minutes. When the supernatant of the reaction liquid became transparent, an aqueous solution in which 190 parts by mass of sodium chloride was dissolved in 760 parts by mass of ion-exchanged water was added, so that the growth of the particle diameter stopped.
Further, as an ripening step, heating and stirring were performed at a liquid temperature of 80 °C, so that the particles were fusion-bonded until the average circularity of the particles, which was measured by a measuring device (FPIA 3000, manufactured by Sysmex Corporation), reached 0.970. Thereafter, the liquid temperature was decreased to 30 °C.
Next, solid-liquid separation was performed, and an operation of re-dispersing the dehydrated toner cake in ion-exchanged water and performing solid-liquid separation was repeated three times for washing. Thereafter, the resultant was dried at 40 °C for 24 hours to obtain toner base particles 2.

Toner base particles 3 were prepared in the same manner as the preparation of the toner base particles 2 except that the amounts of the release agent [W1] (hydrocarbon wax) and the saturated hydrocarbon compounds having 16 to 35 carbon atoms [S] added in the preparation of the dispersion liquid of vinyl-based resin fine particles [a2] were changed as follows.

Release agent [W1]: 50 parts by mass
Saturated hydrocarbon compounds having 16 to 35 carbon atoms [S]: 0.2 parts by mass

Toner base particles 4 were prepared in the same manner as the preparation of the toner base particles 2 except that the amount of the saturated hydrocarbon compounds having 16 to 35 carbon atoms [S] added in the preparation of the dispersion liquid of vinyl-based resin fine particles [a2] was changed as follows.

• Saturated hydrocarbon compounds having 16 to 35 carbon atoms [S]: 6.0 parts by mass

Toner base particles 5 were prepared in the same manner as in the preparation of toner base particles 2 except that the release agent [W1] (hydrocarbon wax) used in the preparation of the vinyl-based resin fine particle dispersion [a2] was replaced by a release agent [W2] (behenic acid behenate).

Toner base particles 6 were prepared in the same manner as the preparation of the toner base particles 2 except that the 68 parts by mass of amorphous polyester fine resin particle dispersion [D] was replaced by 48 parts by mass of amorphous polyester fine resin particle dispersion [D] and that 20 parts by mass of the hybrid crystalline polyester fine resin particle dispersion [C2] was added at the same timing.

Toner base particles 7 were prepared in the same manner as in the production of the toner base particles 6 except that the dehydrated toner cake was washed by repeating the operation of re-dispersing the toner cake in ion exchanged water and performing solid-liquid separation three times and that the drying temperature was changed to 30 °C.

< Preparation of toner base particles 12 >

Toner base particles 12 were prepared in the same manner as in the production of the toner base particles 6 except that the dehydrated toner cake was washed by repeating the operation of re-dispersing the toner cake in ion exchanged water and performing solid-liquid separation three times and that the drying temperature was changed to 80 °C.

< Preparation of toner base particles 13 >

Toner base particles 13 were prepared in the same manner as the preparation of the toner base particles 2 except that the amounts of the release agent [W1] (hydrocarbon wax) and the saturated hydrocarbon compounds having 16 to 35 carbon atoms [S] added in the preparation of the dispersion liquid of vinyl-based resin fine particles [a2] were changed as follows.

Release agent [W1]: 50 parts by mass
Saturated hydrocarbon compounds having 16 to 35 carbon atoms [S]: 0.12 parts by mass

< Preparation of toner base particles 14 >

Toner base particles 14 were prepared in the same manner as the preparation of the toner base particles 2 except that the amount of the saturated hydrocarbon compounds having 16 to 35 carbon atoms [S] added in the preparation of the dispersion liquid of vinyl-based resin fine particles [a2] was changed as follows.

• Saturated hydrocarbon compounds having 16 to 35 carbon atoms [S]: 6.3 parts by mass

3. Preparation of Toner

The following materials were mixed using a Henschel mixer (FM-75, manufactured by Mitsuimiikekakouki, Inc.) for a rotation time of 10 minutes at a rotational speed of 30 s^-1 to obtain a toner 1.

Toner base particles 1: 100 parts by mass
Hydrophobic silica fine particles hydrophobized with hexamethyldisilazane (BET specific surface area: 200 m²/g): 1.0 parts by mass
Titanium dioxide fine particles surface-treated with isobutyltrimethoxysilane (BET specific surface area: 80 m²/g): 1.0 parts by mass
Strontium titanate 1 (number-average primary particle size 50 nm): 0.5 parts by mass

< Preparation of Toners 2 to 14 >

Toners 2 to 14 were prepared in the same manner as in the preparation of the toner 1 except that the kind of the toner base particles was changed and that strontium titanate of toner 1 was changed to strontium titanate having a number average primary particle diameter shown in Table I below. For Toner 7, strontium titanate was not added.
In the following Table I, "drying temperature" refers to a temperature at which the dehydrated toner cake is dried after being washed by repeating the operation of re-dispersing the toner cake in ion water and performing solid-liquid separation three times.
The "amount of the C16-C35 saturated compound" represents the amount (ppm by mass) with respect to the total mass of the toner base particles and the external additive.

< Difference in endothermic peak start temperature >

For the obtained toner, 4.5 to 5. 0 mg of toner was precisely measured to the second decimal place; the measured toner as a sample was sealed in an aluminum pan (KITNO. 0219-0041); and the sample was set in a DSC-7 sample holder. As a reference, an empty aluminum pan was used. The heat absorption peak start temperature was measured by "DSC-7 differential scanning calorimeter" and "TAC7/DX thermal analyzer controller" (both manufactured by PerkinElmer, Inc.).
Next, for the toner sample, the temperature was first decreased from room temperature (25 °C) to 0 °C by the rate of -10 °C/min; then increased from 0 °C to 200 °C at the rate of 10 °C/min; then decreased from 200 °C to 0 °C at the rate of -10 °C/min; and then increased to 40 °C at the rate of 10 °C/min. The maintaining temperature was kept at 40 °C for three hours. After the three hours, the temperature was decreased to 0 °C at the rate of -10 °C/min; and the amount of heat was measured while the temperature was increased at the rate of 10 °C/min in the range from 0 °C to 200 °C (measurement 1).
Next, for the sample used in the measurement 1, the temperature was decreased from 200 °C to 0 °C at the rate of -10 °C/min and then increased to 50 °C at the rate of 10 °C/min. The maintaining temperature was kept at 50 °C for three hours. after the three hours, the temperature was decreased to 0 °C at the rate of -10 °C/min; and the amount of heat was measured while the temperature was increased at the rate of 10 °C/min in the range of 0 °C to 200 °C (measurement 2).
Next, for the sample used in the measurement 2, the temperature was decreased from 200 °C to 0 °C at the rate of -10 °C/min and then increased to 60 °C at the rate of 10 °C/min. The maintaining temperature was kept at 60 °C for three hours. After the three hours, the temperature was decreased to 0 °C at the rate of -10 °C/min; and then the amount of heat was measured while the temperature was increased at the rate of 10 °C/min in the range from 0 °C to 200 °C (measurement 3).
Thus, the amount of heat of the same toner in the range of 0 to 200 °C was measured in the three measurements corresponding to different maintaining temperatures.
Next, following were calculated: the difference (amount of change) between the endothermic peak start temperature when the maintaining temperature was 40 °C and the endothermic peak start temperature when the maintaining temperature was 50 °C; the difference (amount of change) between the endothermic peak start temperature when the maintaining temperature was 40 °C and the endothermic peak start temperature when the maintaining temperature was 60 °C; and the difference (amount of change) between the endothermic peak start temperature when the maintaining temperature was 50 °C and the endothermic peak start temperature when the maintaining temperature was 60 °C. The following Table II shows the maximum amount of change among these amounts of changes as the difference in the endothermic peak start temperature.
The above measurement was performed for each of the toners 1 to 12.

First, 100 parts by mass of ferrite particles (volume-based median particle size: 50 µm, manufactured by Powdertech Co., Ltd.)) and 4 parts by mass of methyl methacrylate-cyclohexyl methacrylate (volume-based median particle size of primary particles: 85 nm) were put in a horizontal stirring blade type high-speed stirring apparatus and mixed for 15 minutes at 30 °C at a stirring blade peripheral speed of 8 m/s. Next, the temperature was increased to 120 °C and stirring was continued for 4 hours. Thereafter, the mixture was cooled, and broken pieces of the methyl methacrylate-cyclohexyl methacrylate copolymer resin were removed with a 200 mesh sieve to prepare a resin-coated carrier.
The resin-coated carrier was mixed with each of the toners 1 to 14 such that the concentration of the toner was 7% by mass with respect to the total mass of the toner and the carrier. Thus, two component developers 1 to 14 were prepared.

[Evaluation]

< Image formation >

For Examples 1 to 11 and comparative Examples 1 to 3, the developers 1 to 14 were sequentially loaded to a multifunction peripheral (bizhub PRESS C1070, manufactured by Konica Minolta, Inc.) modified so that the amount of toner adhesion can be freely adjusted ("bizhub PRESS" is a registered trademark of the company).
In a normal-temperature and normal-humidity environment (temperature: 20 °C, relative humidity: 50%), a solid image having an adhesion amount of 8.0 g/m² was formed on a sheet of evaluation paper (POD-157 gloss coated paper manufactured by Oji Paper Co., Ltd.).
In Example 12, an image was formed using a multifunction peripheral that fixes toner image in two stages (bizhub PRESS C8000 manufactured by Konica Minolta, Inc.).
In Example 12, an unfixed image was obtained using a multifunction peripheral (bizhub PRESS C1070 manufactured by Konica Minolta, Inc.) modified to obtain an unfixed image before fixing, and the unfixed image was fixed using a fixing device having a fixing nip formed by a non-rotating pressure pad. The fixing device was taken out from a multifunction peripheral (imagePRESS V1000 manufactured by CANON INC.) and modified to be driven independently. The image output conditions were the same as in Example 1.

< Difference in glossiness between front and back >

The glossiness of the solid image portion on the front surface and the back surface was measured by a glossmeter (GMX-203 manufactured by Murakami Color Research Laboratory), and the difference in glossiness between the front and back surfaces was calculated. In the following criteria, "A" corresponds to "acceptable".

(Criteria)

A: the difference in glossiness between the front and back surfaces is less than 3°
B: the difference in glossiness between the front and back surfaces is 3° or greater

< Varnish applicability >

(Application of varnish)

To the image prepared as described above, varnish (UV VECTA coat varnish PC-3KW2 manufactured by T&K Co., Ltd) was applied by a bar coater such that the varnish was 5µm thick.
Thereafter, the varnish was irradiated with ultraviolet rays from a high-pressure mercury lamp such that the integrated light amount on the image surface was 120 to 130 mJ/cm². Thus, the varnish was cured, and a varnish layer was formed. The used varnish contained a polymerizable monomer for varnish having a polymerizable functional group including an ethylenic double bond and a photopolymerization initiator (radical polymerization initiator).

(Evaluation of coatability)

The surface of the varnish layer of the obtained image was visually examined whether the varnish was clearly repelled or not. When the varnish was not repelled, the number of pinholes in a 10 cm × 10 cm area was counted. Based on the result of the above examination, the varnish coatability was evaluated according to the following evaluation criteria. In the following criteria, "A", "B", and "C" correspond to "acceptable".

(Criteria)

A: No pinholes were found in a 10cm × 10cm area.
B: One or two pinholes were found in a 10cm × 10cm area.
C: Three to ten pinholes were found in a 10cm × 10cm area.
D: 11 or more pinholes were found in a 10cm × 10cm area or the varnish was repelled.

< Varnish adhesion >

(Evaluation of adhesion)

The surface of the varnish layer of the varnish-coated solid image was photographed using a microscope (manufactured by Keyence Corporation, digital microscope VHX-6000) at the magnification of 100 times. The obtained image was binarized using image processing software (LUSEX-AP, manufactured by NIRECO CORPORATION).
Thereafter, a polyimide tape (Mending Tape No. 810-3-12 manufactured by Sumitomo 3M Limited) was lightly attached on the varnish layer, and the surface of the polyimide tape was rubbed back and forth by 3.5 times with the pressure of 1 kPa. Thereafter, the tape was peeled off from the varnish layer with the force of 200 g at the angle of 180°.
The surface of the varnish layer after the tape was peeled off was photographed at a magnification of 100 times using a microscope (digital microscope VHX-6000, manufactured by Keyence Corporation). The obtained image was binarized using image processing software (LUSEX-AP, manufactured by NIRECO CORPORATION). Then, the varnish peeling rate was calculated by the following formula.
Varnish peeling rate [%] = (1 - Covered area with respect to varnish-coated image region after tape is removed) / (Covered area with respect to powder resin image region before tape is removed) × 100
Based on the calculated varnish peeling rate, the adhesion of varnish was evaluated according to the following evaluation criteria. In the following criteria, "A" and "B" correspond to "acceptable".

(Criteria)

A: No varnish peeling was found.
B: Varnish peeling rate was greater than 0% and less than 5%.
C: Varnish peeling rate was 5% or greater and less than 10%.
D: Varnish peeling rate was 10% or greater.

As shown in the above results, the toner of the present invention reduces the difference in glossiness between the front and back surfaces and improves varnish coatability and varnish adhesion, as compared with the toners of the comparative examples.

Claims

An electrostatic latent image developing toner comprising toner base particles containing a binding resin and a release agent, wherein:
the toner base particles contain a saturated hydrocarbon compound having 16 to 35 carbon atoms,

an amount of the contained saturated hydrocarbon compound is in a range of 1 to 1000 ppm by mass with respect to a total mass of the electrostatic latent image developing toner, and

the electrostatic latent image developing toner satisfies a following condition (i).

Condition (i): In following measurements 1 to 3, an amount of change in endothermic peak start temperature owing to a change in maintaining temperature is 2 °C or less, the endothermic peak start temperature being observed at 20 °C or more on a differential scanning calorimetry (DSC) curve.

(Measurement 1) A sample of the electrostatic latent image developing toner is maintained at a maintaining temperature of 40 °C for three hours; the temperature is decreased to 0 °C at a temperature decrease rate of -10 °C/min; and measurement by a differential scanning calorimeter is performed while increasing the temperature at a temperature increase rate of 10 °C/min in a range of 0 to 200 °C.

(Measurement 2) For the sample after the measurement 1, the temperature is decreased at a temperature decrease rate of -10 °C/min in a range of 200 to 0 °C; and thereafter measurement is performed in a same manner as the measurement 1 except that the maintaining temperature is 50 °C.

(Measurement 3) For the sample after the measurement 2, the temperature is decreased at a temperature decrease rate of -10 °C/min in a range of 200 to 0 °C; and thereafter measurement is performed in a same manner as the measurement 1 except that the maintaining temperature is 60 °C.
The electrostatic latent image developing toner according to claim 1, wherein the release agent contains hydrocarbon wax.
The electrostatic latent image developing toner according to claim 1, wherein the binding resin contains polyester.
The electrostatic latent image developing toner according to claim 1, wherein the binding resin contains styrene-acrylic resin.
The electrostatic latent image developing toner according to claim 1, wherein the toner base particles contain a crystalline substance other than the release agent.
The electrostatic latent image developing toner according to claim 1, wherein an external additive contains strontium titanate.
The electrostatic latent image developing toner according to claim 6, wherein a particle of the strontium titanate has a number-average primary particle size in a range of 20 to 200 nm.
The electrostatic latent image developing toner according to claim 7, wherein the particle of the strontium titanate has a number-average primary particle size in a range of 30 to 150 nm.
An image forming method comprising:
attaching the electrostatic latent image developing toner according to any one of claims 1 to 8 to a recording medium; and

fixing the attached electrostatic latent image developing toner onto the recording medium.
The image forming method according to claim 9, wherein in the fixing, the electrostatic latent image developing toner is fixed to the recording medium in two stages.
The image forming method according to claim 9, further comprising: applying varnish to a surface of a toner image formed by the fixed electrostatic latent image developing toner to form a varnish coat.
An image forming apparatus (1) comprising at least a developing member (412), a transfer member (42, 43), and a fixing member (600) and configured to form a toner image on a recording medium using the electrostatic latent image developing toner according to any one of claims 1 to 8, wherein
the fixing member includes a fixing nip, and

a fixing pad (610) is used at the fixing nip.
The image forming apparatus according to claim 12, wherein the fixing member includes:
an endless belt (650) for heating the toner image on the recording medium at the fixing nip;

a rotating member (620) configured to form the fixing nip in cooperation with the endless belt;

the fixing pad (610) in contact with an inner circumferential surface of the endless belt and configured to form the fixing nip by sandwiching the endless belt between the fixing pad and the rotating member; and

a heating roller (630) in contact with the inner circumferential surface of the endless belt and configured to heat the endless belt.