Toner for electrostatic latent image development, image forming method, and image forming apparatus

Abstract

To provide a toner for electrostatic latent image development that can reduce the difference in glossiness between front and rear faces, and is excellent in varnish application properties and adhesion.SOLUTION: A toner includes toner base particles each containing a saturated hydrocarbon compound having 16-35 carbon atoms, and the content thereof is within a specific range and satisfies a condition (i). The condition (i): when the retention temperature of a toner measurement sample is retained at 40°C for three hours, and when the temperature is decreased to 0°C at a rate of -10°C / min, and measurement is carried out using a differential scanning calorimeter within a range of 0-200°C at a rate of 10°C / min (measurement 1); the temperature of the measurement sample after the measurement 1 is decreased within a range of 200-0°C at a ratio of -10°C / min, and subsequently measurement is carried out in the same manner as the measurement 1 except for setting the retention temperature to 50°C (measurement 2); and the temperature of the measurement sample after the measurement 2 is decreased within a range of 200-0°C at a ratio of -10°C / min, and subsequently measurement is carried out in the same manner as the measurement 1 except for setting the retention temperature to 60°C (measurement 3), the amount of change in an endothermic peak start temperature observed at 20°C or more in a DSC curve along with a change in the retention temperature is 2°C or less.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to a toner for developing electrostatic latent images, an image forming method, and an image forming apparatus.The present invention particularly relates to a toner for developing electrostatic latent images that can reduce the gloss difference between the front and back surfaces during double-sided printing and has excellent varnish applicability and adhesion. [Background technology]

[0002] In double-sided printing using electrophotography, the front and back sides are heated differently, and remelting of the fixed image is known to cause problems such as gloss differences and image defects. Patent Document 1 discloses a device that suppresses image defects caused by remelting of fixed images during double-sided printing. However, depending on the evaluation conditions such as the type of substrate and the fixing temperature, it is thought that image defects caused by remelting and gloss differences between the front and back surfaces of the substrate may occur.

[0003] Therefore, in order to improve image quality and durability, a varnish coating is sometimes applied to a part or the entire surface of an electrophotographic image. However, when a varnish coating is applied to an image formed by an electrophotographic image forming apparatus, the image repels the varnish, resulting in an inadequate coating film. Furthermore, even if the varnish coating does not repel the varnish, there are known problems such as insufficient adhesion between the image and the varnish, resulting in easy peeling. It is known that the main cause of this problem is release agents that are deposited on the image surface during thermal fixing. Release agents are widely used in electrophotographic image forming devices to improve offset resistance and separation properties, but due to their nature, they have low interaction with varnish, which causes the image to repel the varnish. To address these problems, the technologies disclosed in Patent Documents 2 and 3 use a polar wax as a release agent to improve the affinity between the varnish and the release agent, thereby improving the coatability and adhesion of the varnish. However, the coatability and adhesion of the varnish are insufficient, and there is a trade-off between the effects of the varnish and offset resistance and separation properties. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2020-52211 [Patent Document 2] Japanese Patent Application Laid-Open No. 2012-78565 [Patent Document 3] Japanese Patent Application Laid-Open No. 2011-191536 Summary of the Invention [Problem to be solved by the invention]

[0005] The present invention has been made in consideration of the above problems and circumstances. The problem to be solved by the present invention is to provide a toner for developing electrostatic latent images, which can reduce the difference in gloss between the front and back sides during double-sided printing and has excellent varnish applicability and adhesion, as well as an image forming method and image forming apparatus. [Means for solving the problem]

[0006] The present inventors have investigated the causes of the above problems in order to solve them. As a result, they have found that the endothermic peak onset temperature (the melting onset temperature of the crystalline component) of the DSC curve does not change even when the holding temperature in a differential scanning calorimeter is changed, and that a trace amount of a short-chain saturated hydrocarbon compound is added. They have found that this makes it possible to provide a toner for developing electrostatic latent images, an image forming method, and an image forming apparatus that can reduce the gloss difference between the front and back surfaces during double-sided printing and that have excellent varnish applicability and adhesion. That is, the above-mentioned problems of the present invention are solved by the following means.

[0007] 1. A toner for developing electrostatic latent images, comprising toner base particles containing a binder resin and a release agent, the toner base particles contain a saturated hydrocarbon compound having 16 to 35 carbon atoms, the content of the saturated hydrocarbon compound is within a range of 1 to 1000 ppm by mass relative to the total mass of the toner for developing an electrostatic latent image, and The following condition (i) is met: A toner for developing electrostatic latent images. Condition (i): A measurement sample of the electrostatic latent image developing toner is held at a holding temperature of 40°C for 3 hours, cooled to 0°C at a temperature decreasing rate of -10°C / min, and then measured with a differential scanning calorimeter at a temperature increasing rate of 10°C / min in the range of 0 to 200°C (Measurement 1). Next, using the measurement sample after Measurement 1, the temperature is decreased at a temperature decreasing rate of -10°C / min in the range of 200 to 0°C, and then a measurement is performed in the same manner as Measurement 1 except that the holding temperature is set to 50°C (Measurement 2). Next, using the measurement sample after Measurement 2, the temperature is decreased at a temperature decreasing rate of -10°C / min in the range of 200 to 0°C, and then a measurement is performed in the same manner as Measurement 1 except that the holding temperature is set to 60°C (Measurement 3). When this occurs, the amount of change in the onset temperature of the endothermic peak observed at 20°C or higher on the DSC curve due to a change in holding temperature is 2°C or less.

[0008] 2. The release agent contains a hydrocarbon wax. 2. The toner for developing electrostatic latent images according to claim 1,

[0009] 3. The binder resin contains polyester 2. The toner for developing electrostatic latent images according to claim 1,

[0010] 4. The binder resin contains a styrene-acrylic resin. 2. The toner for developing electrostatic latent images according to claim 1,

[0011] 5. The toner base particles contain a crystalline substance other than the release agent. 2. The toner for developing electrostatic latent images according to claim 1,

[0012] 6. The external additive contains strontium titanate 2. The toner for developing electrostatic latent images according to claim 1,

[0013] 7. The strontium titanate particles have a number average primary particle diameter in the range of 20 to 200 nm. 7. The toner for developing electrostatic latent images according to claim 6,

[0014] 8. The strontium titanate particles have a number average primary particle diameter in the range of 30 to 150 nm. 8. The toner for developing electrostatic latent images according to claim 7,

[0015] 9. A step of attaching the toner for developing an electrostatic latent image according to any one of items 1 to 8 to a recording medium; and a step of fixing the attached electrostatic latent image developing toner to the recording medium. An image forming method comprising:

[0016] 10. The fixing step is a step of fixing the electrostatic latent image developing toner to the recording medium in two stages. 10. The image forming method according to item 9, wherein

[0017] 11. A step of forming a varnish coat by applying varnish to the surface of the toner image formed by fixing the toner for developing an electrostatic latent image. 10. The image forming method according to item 9, wherein

[0018] 12. An image forming apparatus having at least a developing unit, a transferring unit, and a fixing unit, which forms a toner image on a recording medium using the toner for developing an electrostatic latent image according to any one of items 1 to 8, the fixing unit has a fixing nip portion, A fixing pad is used in the fixing nip portion. An image forming apparatus characterized by:

[0019] 13. The fixing means includes an endless belt that heats the toner image on the recording medium at the fixing nip portion; a rotating body that cooperates with the endless belt to form the fixing nip portion; a fixing pad that contacts an inner peripheral surface of the endless belt and sandwiches the endless belt between itself and the rotating body so as to form the fixing nip; a heating roller that contacts the inner circumferential surface of the endless belt and heats the endless belt; 13. The image forming apparatus according to claim 12, [Effects of the Invention]

[0020] The above-mentioned means of the present invention can reduce the difference in gloss between the front and back surfaces during double-sided printing, and can provide a toner for developing electrostatic latent images, an image forming method, and an image forming apparatus that have excellent varnish applicability and adhesion. The mechanism by which the effects of the present invention are manifested or the mechanism of action is not clear, but is speculated as follows. According to the present invention, the change in the endothermic peak onset temperature seen at 20°C or higher on the DSC curve with a change in holding temperature is 2°C or less, and the change in the melting onset temperature is small, so it is believed that there is no difference in gloss between the front and back sides during double-sided printing. Furthermore, since the melting onset temperature is unlikely to change with the holding temperature, image quality (gloss) is unlikely to deteriorate depending on the environmental temperature of the image. Furthermore, the gloss quality of the fixed image does not change depending on the toner storage temperature. Furthermore, the toner quality does not change depending on the toner transportation temperature, etc.

[0021] Generally, the varnish is easier to apply if the compounds present on the image surface are evenly distributed relative to the application of the varnish. Also, the higher the affinity between the compounds present on the image surface and the varnish, the better the adhesion. However, toner is made from a variety of materials, and the image surface is also a mixture of release agents, binder resins, etc. If varnishing is applied to such a surface, the varnish droplets will remain on the surface of the binder resin, preventing it from spreading to the release agent surface, resulting in poor varnish application. For example, the varnish will be repelled. Therefore, in the present invention, a small amount of a saturated hydrocarbon compound with a short chain length (carbon number of 16 to 35) is contained in addition to the release agent. This allows the saturated hydrocarbon compound with a short chain length to migrate to the image surface during heat fixation. Therefore, the saturated hydrocarbon compound, together with the release agent on the image surface, is scattered on the surface of the binder resin. As a result, the image surface is in a uniform state, allowing the varnish to be applied evenly, resulting in excellent varnish applicability and adhesion. It is believed that the short chain length of the saturated hydrocarbon compound results in low viscosity and allows the compound to be more easily oriented on the image surface, thereby achieving the above-mentioned effects. Furthermore, if the content of saturated hydrocarbon compounds having 16 to 35 carbon atoms exceeds 1,000 ppm by mass relative to the total mass of the toner, the image surface is sufficiently covered with short-chain components, completely hiding compounds with higher affinity than the saturated hydrocarbon compounds. This results in poor adhesion to varnish. On the other hand, if the content of the saturated hydrocarbon compounds is less than 1 ppm by mass relative to the total mass of the toner, the effect of varnish application is not achieved. Furthermore, the presence of the saturated hydrocarbon compounds in areas of the image where no release agent is present also has an effect on fixation separation. For these reasons, the change in the endothermic peak onset temperature of the DSC curve with changes in holding temperature is set to 2°C or less, and the content of short-chain saturated hydrocarbon compounds is set to the range of 1 to 1000 ppm by mass relative to the total mass of the toner. This reduces the difference in gloss between the front and back surfaces during double-sided printing, and also provides excellent varnish application and adhesion. [Brief explanation of the drawings]

[0022] [Figure 1] Schematic diagram showing an example of a surface treatment device that performs surface treatment using hot air [Figure 2] FIG. 1 is a schematic diagram showing an example of another surface treatment device for performing surface treatment using hot air. [Figure 3] 1 is a schematic diagram illustrating an example of an image forming apparatus; [Figure 4] FIG. 1 is a schematic diagram illustrating the general configuration of a fixing device that forms a planar fixing nip using a non-rotating pressure pad. [Figure 5]FIG. 1 shows an example of DSC curves of toner held at temperatures of 40° C., 50° C., and 60° C. DETAILED DESCRIPTION OF THE INVENTION

[0023] The electrostatic latent image developing toner of the present invention is a toner for developing electrostatic latent images, which has toner base particles containing a binder resin and a release agent, and is characterized in that the toner base particles contain a saturated hydrocarbon compound having 16 to 35 carbon atoms, the content of the saturated hydrocarbon compound being in the range of 1 to 1000 ppm by mass with respect to the total mass of the electrostatic latent image developing toner, and which satisfies the following condition (i): Condition (i): A measurement sample of the electrostatic latent image developing toner is held at a holding temperature of 40°C for 3 hours, cooled to 0°C at a temperature decreasing rate of -10°C / min, and then measured with a differential scanning calorimeter at a temperature increasing rate of 10°C / min in the range of 0 to 200°C (Measurement 1). Next, using the measurement sample after Measurement 1, the temperature is decreased at a temperature decreasing rate of -10°C / min in the range of 200 to 0°C, and then a measurement is performed in the same manner as Measurement 1 except that the holding temperature is set to 50°C (Measurement 2). Next, using the measurement sample after Measurement 2, the temperature is decreased at a temperature decreasing rate of -10°C / min in the range of 200 to 0°C, and then a measurement is performed in the same manner as Measurement 1 except that the holding temperature is set to 60°C (Measurement 3). When this occurs, the amount of change in the onset temperature of the endothermic peak observed at 20°C or higher on the DSC curve due to a change in holding temperature is 2°C or less. This feature is a technical feature common to or corresponding to each of the following embodiments.

[0024] In one embodiment of the present invention, the release agent preferably contains a hydrocarbon wax. The molecular structure of hydrocarbon wax is similar to that of saturated hydrocarbon compounds having 16 to 35 carbon atoms, making it easy to dissolve the saturated hydrocarbon compounds in the hydrocarbon wax. As a result, the saturated hydrocarbon compounds are more finely and uniformly dispersed in the toner base particles, and are more likely to precipitate from the toner base particles together with the release agent during fixing, improving the applicability of the varnish.

[0025] It is preferable that the binder resin contains polyester, since this has a polarity similar to that of the varnish and therefore the adhesion of the varnish can be easily improved. It is preferable that the binder resin contains a styrene-acrylic resin, since this has a polarity similar to that of the varnish and can easily improve the adhesion of the varnish.

[0026] It is preferable that the toner base particles contain a crystalline substance other than the release agent, in that this makes it difficult for the C16-35 saturated compound to be compatible with the binder resin and makes it easier for the C16-35 saturated compound to precipitate during fixing.

[0027] It is preferable that the external additive contains strontium titanate, since this enhances the effects of improving the coatability of the varnish and the releasability of the toner. The strontium titanate particles preferably have a number-average primary particle diameter in the range of 20 to 200 nm, more preferably 30 to 150 nm, which can prevent deterioration in the uniformity of the image surface due to strontium titanate exposed on the surface of the toner base particles, thereby preventing deterioration in coatability.

[0028] The image forming method of the present invention is characterized by comprising the steps of adhering the electrostatic latent image developing toner to a recording medium and fixing the adhered electrostatic latent image developing toner to the recording medium, thereby reducing the gloss difference between the front and back surfaces during double-sided printing and forming an image with excellent varnish applicability and adhesion.

[0029] The fixing step is preferably a step of fixing the electrostatic latent image developing toner to the recording medium in two stages, whereby the toner image is heated sufficiently and for a long period of time, the saturated hydrocarbon compound is sufficiently precipitated from the toner base particles, and the applicability of the varnish and the releasability from the second-stage fixing device are further improved. It is preferable to have a step of applying varnish to the surface of the toner image formed by fixing the electrostatic latent image developing toner to form a varnish coat, which improves the quality and durability of the image.

[0030] The image forming apparatus of the present invention has at least a developing unit, a transfer unit, and a fixing unit, and forms a toner image on a recording medium using the toner for developing an electrostatic latent image, wherein the fixing unit has a fixing nip portion and a fixing pad is used in the fixing nip portion, thereby reducing the gloss difference between the front and back surfaces during double-sided printing and forming an image with excellent varnish applicability and adhesion. Furthermore, the fixing unit preferably includes an endless belt that heats the toner image on the recording medium at the fixing nip, a rotating body that cooperates with the endless belt to form the fixing nip, a fixing pad that contacts the inner circumferential surface of the endless belt and sandwiches the endless belt between the fixing pad and the rotating body to form the fixing nip, and a heating roller that contacts the inner circumferential surface of the endless belt and heats the endless belt. By using the fixing pad, the fixing area can be increased and the fixing time can be extended. As a result, the toner image can be heated sufficiently and for a longer period of time, the saturated hydrocarbon compound can be sufficiently precipitated from the toner base particles, and the varnish can be easily applied and the toner can be easily released from the fixing device.

[0031] The present invention, its components, and embodiments and modes for carrying out the present invention will be described below. In this application, the symbol "to" is used to mean that the numerical values before and after it are included as lower and upper limits.

[0032] [Outline of the toner for developing electrostatic latent images of the present invention] The electrostatic latent image developing toner of the present invention is a toner for developing electrostatic latent images, which has toner base particles containing a binder resin and a release agent, and is characterized in that the toner base particles contain a saturated hydrocarbon compound having 16 to 35 carbon atoms, the content of the saturated hydrocarbon compound being in the range of 1 to 1000 ppm by mass with respect to the total mass of the electrostatic latent image developing toner, and which satisfies the following condition (i): Condition (i): A measurement sample of the electrostatic latent image developing toner is held at a holding temperature of 40°C for 3 hours, cooled to 0°C at a temperature decreasing rate of -10°C / min, and then measured with a differential scanning calorimeter at a temperature increasing rate of 10°C / min in the range of 0 to 200°C (Measurement 1). Next, using the measurement sample after Measurement 1, the temperature is decreased at a temperature decreasing rate of -10°C / min in the range of 200 to 0°C, and then a measurement is performed in the same manner as Measurement 1 except that the holding temperature is set to 50°C (Measurement 2). Next, using the measurement sample after Measurement 2, the temperature is decreased at a temperature decreasing rate of -10°C / min in the range of 200 to 0°C, and then a measurement is performed in the same manner as Measurement 1 except that the holding temperature is set to 60°C (Measurement 3). When this occurs, the amount of change in the onset temperature of the endothermic peak observed at 20°C or higher on the DSC curve due to a change in holding temperature is 2°C or less.

[0033] In this specification, the term "toner" refers to a toner for developing an electrostatic latent image. The toner includes toner particles having toner base particles and an external additive disposed on the surface of the toner base particles. "Toner base particles" are particles that constitute the base of "toner particles." The "toner base particles" according to the present invention contain at least a binder resin, and may contain other components such as a colorant, a release agent (wax), and a charge control agent, as necessary. "Toner base particles" become "toner particles" when external additives are added. "Toner" refers to an aggregate of toner particles. The term "toner image" refers to a state in which toner is collected in an image form.

[0034] <Endothermic peak onset temperature> The toner of the present invention satisfies condition (i). Specifically, condition (i) means that a measurement sample of the toner is subjected to a differential scanning calorimeter measurement at a holding temperature of 40°C for 3 hours, cooled to 0°C at a temperature decreasing rate of -10°C / min, and then measured in a range of 0 to 200°C at a temperature increasing rate of 10°C / min (Measurement 1). Subsequently, using the measurement sample after Measurement 1, the temperature is decreased at a temperature decreasing rate of -10°C / min in a range of 200 to 0°C, and then a measurement is performed in the same manner as Measurement 1 except that the holding temperature is changed to 50°C (Measurement 2). Subsequently, using the measurement sample after Measurement 2, the temperature is decreased at a temperature decreasing rate of -10°C / min in a range of 200 to 0°C, and then a measurement is performed in the same manner as Measurement 1 except that the holding temperature is changed to 60°C (Measurement 3). In this case, the change in the onset temperature of the endothermic peak observed at 20°C or higher on the DSC curve with a change in the holding temperature is 2°C or less. If the change is 2°C or less, the difference in gloss between the front and back surfaces in double-sided printing is at a level that does not pose a problem, but it is preferably 1°C or less, more preferably 0.5°C or less, and particularly preferably 0°C.

[0035] The endothermic peak onset temperature is calculated as follows. The endothermic peak onset temperature can be measured using a "DSC-7 Differential Scanning Calorimeter" (manufactured by PerkinElmer) and a "TAC7 / DX Thermal Analysis Device Controller" (manufactured by PerkinElmer). The measurement procedure involves weighing 4.5 to 5.0 mg of toner accurately to two decimal places, sealing this as the sample in an aluminum pan (KIT NO. 0219-0041), and setting it in the DSC-7 sample holder. An empty aluminum pan is used as the reference.

[0036] (Method for measuring endothermic peak onset temperature) The specific measurement method is as follows. First, the temperature is decreased from room temperature (25°C) to 0°C at -10°C / min, then increased from 0°C to 200°C at 10°C / min, then decreased from 200°C to 0°C at -10°C / min, and then increased to 40°C at 10°C / min. After the temperature is held at 40°C for 3 hours, the temperature is decreased to 0°C at -10°C / min, and the calorific value is measured while increasing the temperature from 0°C to 200°C at 10°C / min (Measurement 1).

[0037] Next, the sample used in Measurement 1 is cooled from 200°C to 0°C at -10°C / min, and then heated to 50°C at 10°C / min. After holding at 50°C for 3 hours, the sample is cooled to 0°C at -10°C / min, and then heated at 10°C / min in the range from 0°C to 200°C while measuring the calorific value (Measurement 2).

[0038] Next, the sample used in Measurement 2 is cooled from 200°C to 0°C at -10°C / min, and then heated to 60°C at 10°C / min. After holding at 60°C for 3 hours, the sample is cooled to 0°C at -10°C / min, and then heated at 10°C / min in the range from 0°C to 200°C while measuring the calorific value (Measurement 3). In this manner, the calorific value is measured at 0 to 200° C. for three measurements using the same toner at different holding temperatures.

[0039] The endothermic peak onset temperature is indicated as the temperature at which the endothermic peak appears at 20°C or higher in the DSC curve when the temperature is increased after holding at each holding temperature (40°C, 50°C, 60°C). The "endothermic peak onset temperature" is the temperature at which the DSC curve deviates from the baseline, and the endothermic onset temperature can be confirmed at the inflection point of the baseline. The inflection point can also be confirmed by checking the differential curve (DDSC) of the DSC curve. Specifically, the derivative of the DSC curve is 0 before the peak rises, but if the endothermic peak is convex downward, the derivative becomes negative at the peak onset temperature. If the baseline is inclined, the temperature that deviates from the derivative before the peak rises is the peak rise temperature. For example, as shown in Fig. 5, the endothermic peak onset temperature at a holding temperature of 40°C is 51.6°C, the endothermic peak onset temperature at a holding temperature of 50°C is 56.8°C, and the endothermic peak onset temperature at a holding temperature of 60°C is 68.6°C. Note that Fig. 5 is an example in which the amount of change in the endothermic peak onset temperature with a change in holding temperature is 2°C or more. In a DSC-7 differential scanning calorimeter (manufactured by PerkinElmer), the point at which a change of at least 5 uW / min was observed in the differential curve DDSC can be determined as the peak onset temperature. From the endothermic peak onset temperatures at each holding temperature obtained as described above, the difference (amount of change) between the endothermic peak onset temperature at a holding temperature of 40°C and the endothermic peak onset temperature at a holding temperature of 50°C is calculated. Similarly, the difference (amount of change) between the endothermic peak onset temperature at a holding temperature of 40°C and the endothermic peak onset temperature at a holding temperature of 60°C, and the difference (amount of change) between the endothermic peak onset temperature at a holding temperature of 50°C and the endothermic peak onset temperature at a holding temperature of 60°C are calculated. In the present invention, all of these amounts of change are 2°C or less, that is, the maximum amount of change is 2°C or less.

[0040] The endothermic peak onset temperature is not clear, but is thought to be due to the state and structure of the crystalline components in the toner. The following can be mentioned as a means for keeping the change in endothermic peak onset temperature with a change in holding temperature to 2°C or less. (a) Type of crystalline component (e.g., structure or molecular weight of the crystalline component) or amount added (b) The drying temperature during the production of toner base particles, after aggregating and fusing binder resin particles, colorant particles, etc., the toner base particles are separated into solid and liquid from the dispersion of the toner base particles, and the toner cake obtained by the solid-liquid separation is washed to remove any attached surfactants, aggregating agents, etc., and then dried.

[0041] The crystalline component refers to a release agent or a crystalline component (binder resin) other than the release agent, but in the present invention, it is not necessary to include a crystalline component other than the release agent. When no crystalline component other than the release agent is contained, the change in the endothermic peak onset temperature can be kept at 2° C. or less. However, this method does not allow low-temperature fixability to be exhibited, and therefore, from the viewpoint of low-temperature fixability, it is preferable to contain a crystalline component other than the release agent. When the toner base particles contain a crystalline component (binder resin) other than the release agent, it is preferable to use a crystalline resin (for example, a crystalline polyester or a hybrid crystalline polyester) as the binder resin. The hybrid crystalline polyester is a resin formed by bonding an endothermic crystalline polyester polymer segment with a polymer segment of another type of resin. The drying temperature is preferably 45° C. or lower. If the drying temperature is higher than 45° C., the crystalline components in the toner will be in a molten state, making it difficult to control the structure. Therefore, the drying temperature is preferably within the range of 10 to 45° C., and more preferably within the range of 20 to 40° C.

[0042] The weight average molecular weight (Mw) of the crystalline polyester is preferably 5,000 or more and 50,000 or less. The number average molecular weight (Mn) of the crystalline polyester is preferably 2,000 or more and 10,000 or less. When the weight average molecular weight (Mw) and number average molecular weight (Mn) of the crystalline polyester are within the above ranges, the amount of change in endothermic peak onset temperature with change in the holding temperature can be kept within the above ranges, and low-temperature fixability is improved.

[0043] <Saturated hydrocarbon compounds with carbon numbers between 16 and 35> In the toner of the present invention, the toner base particles contain a saturated hydrocarbon compound having 16 to 35 carbon atoms. The content of the saturated hydrocarbon compound is in the range of 1 to 1000 ppm by mass relative to the total mass of the toner for developing electrostatic latent images. Hereinafter, the "saturated hydrocarbon compound having 16 to 35 carbon atoms" is also referred to as a "C16-35 saturated compound."

[0044] According to the findings of the present inventors, the surface of an image formed by fixing toner to a recording medium is sparsely dotted with binder resin, release agent precipitated during fixing, and other toner components. Due to differences in these components, the image surface is dotted with areas with different surface energies. This difference in surface energy between image areas makes it difficult for the varnish applied to the image surface to spread evenly, which is thought to result in varnish repellency.

[0045] The C16-35 saturated compound contained in the toner base particles is believed to be finely and uniformly dispersed within the toner base particles due to its relatively small molecular weight. Furthermore, it is believed that this finely and uniformly dispersed C16-35 saturated compound gradually precipitates on the surface of the toner base particles during toner fixation, uniformly coating the surface. Furthermore, because the C16-35 saturated compound has a low viscosity when melted, it is more likely to be oriented and precipitated toward the surface of the image than the release agent. As a result, the surface of the image formed by fixing the toner is uniformly coated with the C16-35 saturated compound, resulting in a uniform surface energy distribution. Therefore, when an image is formed using the toner, the varnish tends to wet and spread evenly across the image surface, reducing varnish repellency and improving varnish applicability.

[0046] On the other hand, C16-35 saturated compounds do not have a very high affinity with varnish, so if the amount of C16-35 saturated compounds in the toner is excessive and the image surface is densely coated with C16-35 saturated compounds, it is thought that the adhesion of the varnish will decrease. Thus, there is a trade-off between the improvement in varnish application properties due to the C16-35 saturated compound and the adhesion of the varnish, and to achieve both, the content of the C16-35 saturated compound is set to be within a range of 1 to 1000 ppm by mass relative to the total mass of the toner, and preferably within a range of 10 to 950 ppm by mass relative to the total mass of the toner. In addition, since the C16-35 saturated compound has a wax-like structure, it also has the effect of increasing the releasability of the toner from fixing members and the like to a certain extent.

[0047] [Composition of toner for developing electrostatic latent images] The constitution of the toner of the present invention will be described below. <Toner base particles> The toner base particles contain a binder resin, a release agent, and a C16-35 saturated compound.

[0048] (binder resin) The binder resin binds the toner to the recording medium, and may be a thermoplastic resin or a thermosetting resin, but is preferably a thermoplastic resin. Examples of thermoplastic resins include styrene resins, vinyl resins (such as acrylic resins and styrene-acrylic resins), polyesters, silicone resins, olefin resins, polyamide resins, and epoxy resins.

[0049] The binder resin may be an amorphous resin, a crystalline resin, or a composite resin in which a crystalline resin and an amorphous resin are hybridized. In this specification, a crystalline resin refers to a resin for which a melting point is observed in measurement by differential scanning calorimetry (DSC). An amorphous resin refers to a resin for which a melting point is not observed in measurement by DSC. In this specification, a resin having a melting point means that, when measured by DSC at a heating rate of 10°C / min, a peak with a half-width of an endothermic peak of 15°C or less is observed.

[0050] Examples of binder resins include styrene-based polymers (styrene homopolymers, homopolymers of styrene substitutes such as poly-p-chlorostyrene and polyvinyltoluene, and styrene-based copolymers such as styrene-p-chlorostyrene copolymer, styrene-vinyltoluene copolymer, styrene-vinylnaphthalene copolymer, styrene-butadiene copolymer, and styrene-isoprene copolymer), polyvinyl chloride, phenolic resins, vinyl resins such as (meth)acrylic resins (including styrene-(meth)acrylic acid ester copolymer, styrene-α-chloromethyl(meth)acrylate copolymer, styrene-(meth)acrylonitrile copolymer, styrene-vinyl methyl ether copolymer, styrene-vinyl ethyl ether copolymer, styrene-vinyl methyl ketone copolymer, and styrene-acrylonitrile-indene copolymer), 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 (naturally modified phenolic resins, natural resin-modified maleic acid resins, and other petroleum-based resins), and the like. Of these, vinyl resins such as styrene-acrylic resins and polyesters are preferred because they have a similar polarity to the varnish and are therefore likely to improve the adhesion of the varnish.

[0051] In this specification, (meth)acrylic means acrylic or methacrylic, (meth)acrylonitrile means acrylonitrile or methacrylonitrile, and (meth)acrylate means acrylate and methacrylate, respectively.

[0052] Furthermore, when the toner base particles contain a crystalline resin other than the release agent, it is preferable that the crystalline resin contains a crystalline polyester. By containing the crystalline polyester, it is possible to make the C16-35 saturated compound less compatible with the binder resin, and to facilitate precipitation of the C16-35 saturated compound during fixing. The crystalline resin other than the release agent may be a composite resin in which a crystalline resin and an amorphous resin are hybridized.

[0053] The content of the binder resin is preferably in the range of 20 to 99% by mass, more preferably in the range of 30 to 95% by mass, and even more preferably in the range of 40 to 90% by mass, based on the total mass of the toner base particles. When the content of the binder resin is 20% by mass or more, the strength of the formed image can be further increased.

[0054] The crystalline polyester and hybrid crystalline polyester used as the crystalline resin in the binder resin will be described below.

[0055] <Crystalline polyester> The crystalline polyester is usually obtained by subjecting a polycarboxylic acid and a polyhydric alcohol to a dehydration condensation reaction by a known method.

[0056] The polycarboxylic acid may be a divalent or higher carboxylic acid, such as trimellitic acid, pyromellitic acid, etc. Among these, dicarboxylic acids are preferred from the viewpoint of increasing 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, as well as 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 contain only structural units derived from one of these carboxylic acids, or may contain structural units derived from two or more of these carboxylic acids.

[0057] Among these, aliphatic carboxylic acids are preferred because they can easily increase the crystallinity of the crystalline polyester and also easily increase the affinity between the crystalline polyester and the diol di(meth)acrylate that may be contained in the varnish. The aliphatic carboxylic acid preferably has a linear hydrocarbon group having from 6 to 16 carbon atoms, and more preferably has a linear hydrocarbon group having from 10 to 14 carbon atoms. The hydrocarbon structure of the aliphatic carboxylic acid may be partially branched.

[0058] The polyhydric alcohol may be a dihydric or higher alcohol, such as glycerin, pentaerythritol, trimethylolpropane, sorbitol, etc. Among these, dihydric alcohols are preferred from the viewpoint of increasing the crystallinity of the crystalline polyester. Examples of the 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 an unsaturated double bond 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.

[0059] In order to fully achieve the above-mentioned effects, the content of the crystalline polyester is preferably within a range of 5 to 20 parts by mass, and more preferably within a range of 8 to 15 parts by mass, per 100 parts by mass of the total amount of the binder resin. From the viewpoint of sufficiently softening the toner base particles and enhancing the low-temperature fixability of the toner, the melting point of the crystalline polyester is preferably within a range of 50 to 85°C, and more preferably within a range of 60 to 80°C. The weight average molecular weight (Mw) of the crystalline polyester is preferably 5,000 or more and 50,000 or less. The number average molecular weight (Mn) of the crystalline polyester is preferably 2,000 or more and 10,000 or less. When the weight average molecular weight (Mw) and number average molecular weight (Mn) of the crystalline polyester are within the above ranges, the low temperature fixability is improved.

[0060] <Hybrid crystalline polyester> In the present invention, it is preferable that the crystalline resin contains a hybrid crystalline polyester formed by chemically bonding a crystalline polyester polymer segment and a vinyl resin polymer segment, as this is more easily finely dispersed in the toner and has excellent low-temperature fixing properties.

[0061] (a) Crystalline polyester polymer segment The crystalline polyester polymer segment is a portion derived from a crystalline polyester, and refers to a resin segment that exhibits a clear endothermic peak rather than a stepwise endothermic change in differential scanning calorimetry (DSC) of the toner. The crystalline polyester polymer segment is not particularly limited as long as it is as defined above. For example, with respect to a resin having a structure in which other components are copolymerized into a main chain of a crystalline polyester polymer segment, or a resin having a structure in which a crystalline polyester polymer segment is copolymerized into a main chain made of other components, if a toner containing this resin exhibits a clear endothermic peak as described above, then the resin falls under the category of hybrid crystalline polyester having a crystalline polyester polymer segment as defined in the present invention.

[0062] The crystalline polyester polymer segment is produced by polycondensing (esterifying) a polycarboxylic acid monomer and a polyhydric alcohol monomer. The polycarboxylic acid monomer and polyhydric alcohol monomer may be the same as the polycarboxylic acid monomer and polyhydric alcohol monomer that are the raw materials for the crystalline polyester. The method for forming the crystalline polyester polymer segment is not particularly limited, and the segment can be formed by polycondensing (esterifying) a polycarboxylic acid and a polyhydric alcohol using a known esterification catalyst.

[0063] (b) Preferred crystalline polyester polymer segment The crystalline polyester polymer segment used in the present invention is preferably one obtained by polymerizing a polyhydric alcohol monomer having 4 to 14 carbon atoms and a polycarboxylic acid monomer having 4 to 14 carbon atoms. If the number of carbon atoms is 4 or more, the number of hydrogen bonds derived from ester bonds will not be too large, and the melting point of the crystalline polyester will not be too high. As a result, low-temperature fixability can be more favorable. Furthermore, if the number of carbon atoms is 14 or less, the interaction between aliphatic groups will not be too strong, and the melting point of the crystalline polyester will not be too high. As a result, low-temperature fixability can be more favorable.

[0064] (c) Polymerized segment of vinyl resin The polymerized segment of the vinyl resin (also referred to as the vinyl polymerized segment) is synthesized from a vinyl monomer, which is a raw material of the vinyl resin. In the present invention, the crystalline resin preferably contains a vinyl-based polymerized segment in the range of 3 to 40% by mass, and most preferably in the range of 5 to 20% by mass. This allows for improved low-temperature fixability. In particular, if the vinyl-based polymerized segment is contained in an amount of 3% by mass or more, the stability of the interface between the crystalline resin and the vinyl-based resin serving as the main binder is not excessively reduced, and sufficient fine dispersion can be achieved. As a result, low-temperature fixability can be further improved.

[0065] The content of the vinyl polymerized segment in the crystalline resin is not particularly limited, but is preferably 40% by mass or less from the viewpoint of chargeability. Furthermore, particularly when hybridizing with a vinyl-based polymer segment having low heat resistance, if the content is 40% by mass or less, the compatibility of the crystalline resin with the vinyl-based resin, which is the main binder, will not become too high, and as a result, heat-resistant storage properties can be made favorable.

[0066] Examples of the synthesis method for the hybrid crystalline polyester include the following synthesis methods (a), (b) and (c).

[0067] (i) A method in which a bireactive monomer is reacted with a crystalline polyester polymer segment prepared in advance, and then a vinyl monomer, which is a raw material for vinyl resins, is reacted to chemically bond the vinyl polymer segment to the crystalline polyester polymer segment.

[0068] (b) A method in which a bireactive monomer is reacted with a vinyl resin prepared in advance, and then a polycarboxylic acid monomer and a polyhydric alcohol monomer, which are raw materials for crystalline polyester, are reacted to chemically bond the crystalline polyester polymer segment to the vinyl polymer segment.

[0069] (c) A method in which a crystalline polyester prepared in advance and a vinyl resin are reacted with a bireactive monomer to chemically bond the crystalline polyester polymer segment and the vinyl polymer segment, respectively.

[0070] The bireactive monomer is a monomer that bonds the crystalline polyester and the vinyl resin. The bireactive monomer is a monomer that has, in its molecule, a substituent such as a hydroxy group, a carboxy group, an epoxy group, a primary amino group, or a secondary amino group that can react with the crystalline polyester, and an ethylenically unsaturated group that can react with the amorphous resin. Among these, vinylcarboxylic acids having a hydroxy group or a carboxy group and an ethylenically unsaturated group are preferred.

[0071] As the bireactive monomer, for example, (meth)acrylic acid, fumaric acid, maleic acid, etc. can be used, and hydroxyalkyl (having 1 to 3 carbon atoms) esters of these acids may also be used. From the viewpoint of reactivity, acrylic acid, methacrylic acid, or fumaric acid is preferred.

[0072] The amount of the bireactive monomer used is preferably 1 to 10 parts by mass, more preferably 4 to 8 parts by mass, per 100 parts by mass of the total amount of the monomers used to form the vinyl-based polymerization segment. By using such an amount, the low-temperature fixability, hot offset resistance, and durability of the toner are improved.

[0073] (d) Crystal nucleating agent site In the present invention, a "crystal nucleating agent portion" refers to a portion having a faster crystallization rate than the portion having the crystalline structure, and upon cooling, the crystal nucleating agent portion having a faster crystallization rate quickly generates a crystal nucleus first, and by using this crystal nucleus as the starting point, crystallization of the portion having the crystalline structure is promoted. There are no particular limitations on the compound as long as it has a faster crystallization rate than the portion having the crystalline structure. From the viewpoint of a high crystallization rate, the main component is preferably a compound containing a hydrocarbon moiety and having one or more functional groups capable of reacting with the end of the polyester moiety. Furthermore, compounds in which the hydrocarbon moiety is linear and has one or more functional groups that react with the polyester moiety are preferred. A preferred embodiment of the crystal nucleating agent moiety is a moiety derived from at least one compound selected from the group consisting of aliphatic monocarboxylic acids having 10 to 30 carbon atoms and aliphatic monoalcohols having 10 to 30 carbon atoms.

[0074] Specific examples of the aliphatic monocarboxylic acid 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 monoalcohol include stearyl alcohol, lauryl alcohol, behenyl alcohol, arachidyl alcohol, 1-octadecanol, 1-icosanol, 1-docosanol, 1-tetracosanol, 1-hexacosanol, 1-octacosanol, and 1-triacontanol.

[0075] The proportion of the crystal nucleating agent moiety in the crystalline resin is preferably within a range of 1 to 15% by mass, more preferably within a range of 3 to 9% by mass, from the viewpoint of tacking suppression effect and folding fixability. The content of the above-mentioned crystalline resin in the binder resin is preferably within a range of 4 to 15% by mass, more preferably within a range of 7 to 12% by mass, from the viewpoint of achieving both low-temperature fixability and suppressing tacking.

[0076] (mold release agent) The release agent enhances the releasability of the toner from the fixing member, etc. The release agent is preferably a wax.

[0077] Examples of wax release agents include hydrocarbon waxes such as polyethylene wax, paraffin wax, microcrystalline wax, and Fischer-Tropsch wax; dialkyl ketone waxes such as distearyl ketone; carnauba wax; montan wax; ester waxes such as behenic acid behenate, trimethylolpropane tribehenate, pentaerythritol tetramyristate, pentaerythritol tetrastearate, pentaerythritol tetrabehenate, pentaerythritol diacetate dibehenate, glycerin tribehenate, 1,18-octadecanediol distearate, trimellitate tristearyl, and distearyl maleate; and amide waxes such as ethylenediamine dibehenylamide and trimellitate tristearylamide. Of these, hydrocarbon waxes are preferred because they have a similar molecular structure to C16-35 saturated compounds and are easy to dissolve in the release agent. When C16-35 saturated compounds are well dissolved, they tend to disperse more finely and uniformly in the toner base particles, and they also tend to precipitate from the toner base particles together with the wax during fixing, which tends to improve the coatability of the varnish.

[0078] The release agent, which is a wax, may be a C16-35 saturated compound, or a different hydrocarbon wax having from 36 to 76 carbon atoms. Since the amount of the C16-35 saturated compound in the toner base particles is extremely small, in order to achieve both the effect of the C16-35 saturated compound in improving the varnish coatability and the effect of the release agent in improving the releasability, it is preferable that the toner base particles contain a C16-35 saturated compound and another release agent, and it is preferable that the toner base particles contain both a C16-35 saturated compound and a hydrocarbon wax having from 36 to 76 carbon atoms.

[0079] The hydrocarbon wax preferably has a melting point of 50 to 95°C. When the melting point of the hydrocarbon wax is 50°C or higher, the hydrocarbon wax exuded from the toner particles is more likely to crystallize, which improves the release effect and the abrasion resistance of the formed image. When the melting point of the hydrocarbon wax is 95°C or lower, the hydrocarbon wax is more likely to exude from the toner base particles during fixing, which improves the release effect and the abrasion resistance of the formed image. Furthermore, when the melting point of the hydrocarbon wax is 95°C or lower, the toner base particles are more likely to melt during fixing, which improves the low-temperature fixability of the toner. From the above viewpoints, the melting point of the hydrocarbon wax (particularly a hydrocarbon wax having 36 to 76 carbon atoms) is more preferably 80 to 90°C.

[0080] The content of the release agent is preferably 3 to 20% by mass, more preferably 5 to 15% by mass, based on the total mass of the toner base particles. When the content of the release agent is 3% by mass or more, the releasability of the toner from the fixing member is sufficiently improved. When the content of the release agent is 20% by mass or less, a sufficient amount of binder resin can be contained in the toner base particles, thereby sufficiently improving the fixability of the image.

[0081] (C16-35 saturated compound) The C16-35 saturated compound improves the coatability of the varnish through the above-mentioned action. The content of the C16-35 saturated compound is in the range of 1 to 1000 ppm by mass, preferably 50 to 950 ppm by mass, and more preferably 100 to 900 ppm by mass, relative to the total mass of the toner. By keeping the content of the C16-35 saturated compound within this range, both the coatability and adhesion of the varnish can be achieved. The total mass of the toner refers to the sum of the mass of the toner base particles and the mass of the external additives.

[0082] The content of C16-35 saturated compounds is determined as follows. First, the C16-35 saturated compounds are separated from the toner using a solvent that dissolves them, and then the hydrocarbons with these carbon numbers are qualitatively analyzed by gas chromatography-mass spectrometry (GC-MC).Then, the amount of these hydrocarbons is quantified using a flame ionization detector (GC-FID) as the detector for gas chromatography. It should be noted that the extract extracted from the toner may also contain unsaturated hydrocarbons, so after extraction, polar groups may be added to the unsaturated bonds, and only saturated hydrocarbons may be separated by column separation utilizing the difference in polarity.

[0083] In this case, multiple internal standards may be added (dissolved) in the solvent to determine whether the quantification and pretreatment were performed properly. The concentrations of the internal standards to be added may be determined according to the amount of C16-35 saturated compounds (estimated amount obtained by provisional measurement, etc.).

[0084] The internal standard is preferably a saturated hydrocarbon compound not normally found in toner. For example, using n-undecane or n-tridecane can detect the loss of saturated hydrocarbon compounds due to volatilization during pretreatment, and can serve as a guide for the elution time of the target saturated hydrocarbon compound during solid-phase extraction or GC-FID analysis. Furthermore, bicyclohexyl is less likely to overlap with the elution time of C16-35 saturated compounds, making it easier to improve detection accuracy.

[0085] Extraction from the toner can be performed by a conventionally known method such as a solid-liquid extraction method, a method in which the toner is dissolved or swelled and then separated by centrifugation, a Soxhlet extraction method, a high-speed solvent extraction method, etc. A method can be selected from these methods depending on the expected carbon number of the C16-35 saturated compound and the type of compound that will become a contaminant component such as a binder resin.

[0086] The solvent used for extraction is not particularly limited, but n-hexane, which has high solubility for C16-35 saturated compounds, is preferred. Depending on the type of binder resin, polar solvents such as dichloromethane and ethanol may be used in combination to swell the binder resin.

[0087] The method for introducing polar groups into unsaturated hydrocarbons contained in the extract is not particularly limited. Examples of the introduction method include epoxidation using metachloroperbenzoic acid (mCPBA), addition of hydrogen halide, addition of water or alcohol using an acid catalyst, and derivatization into alcohol by oxidation after hydroboration. Among these, epoxidation using mCPBA is preferred due to its high reactivity and reaction selectivity. In this case, for example, 1 The progress of the reaction can be confirmed by confirming the disappearance of the double bond peak by H-NMR measurement. Note that the addition of polar groups may be omitted if sufficient detection accuracy can be ensured depending on the type of saturated hydrocarbon or unsaturated hydrocarbon.

[0088] Separation utilizing the difference in polarity can be performed by known methods such as solid-phase extraction, online or offline GC, etc. When it is expected that a large amount of impurities will be contained, separation by solid-phase extraction is preferable.

[0089] The solvent used for solid-phase extraction is preferably n-hexane for both conditioning and extraction of saturated hydrocarbons. Depending on the type of contaminants expected, a polar solvent may also be used. After collecting the fraction containing the C16-35 saturated compounds, it is preferable to increase the polarity of the solvent and collect the fraction, and then perform qualitative analysis using GC / MS or other methods to confirm that the fraction does not contain saturated hydrocarbon components.

[0090] As the solid phase for solid-phase extraction, a highly polar solid phase used in normal-phase separation using polar interactions can be used. Examples of the solid phase include silica gel, silica gel activated with polar substances such as anhydrous sodium sulfate and silver nitrate, diol, cyanopropyl, magnesium silicate, etc. Among these, activated silica activated with silver nitrate is preferred. Note that alumina is preferably not used because it specifically retains long-chain n-alkanes.

[0091] The fraction containing saturated hydrocarbons extracted by solid-phase extraction is preferably concentrated or diluted to a concentration appropriate for qualitative and quantitative analysis by gas chromatography by a method such as vacuum concentration using an evaporator or concentration using a nitrogen stream, etc. The concentration conditions should be such that the internal standard does not disappear due to the concentration of low-boiling point components. The fractions after solid phase extraction can be subjected to GC-FID under the following conditions, for example, to quantify the C16-35 saturated compounds.

[0092] (GC conditions) Equipment used: Shimadzu GC-2010 Plus Injection volume: 1 μL, saturated hydrocarbon concentration: 500 to 1000 mg / L Guard column: Restek MXT Siltek (10 m x 0.53 mm id) Column: Restek MTX-1 (15 m x 0.25 mm id) x 0.1 μm df) Carrier gas: Helium

[0093] At this time, the elution times of n-alkanes (number of carbon atoms: 10, 16, 24, 35, and 50) measured under the same conditions are measured in advance. In addition, n-hexane alone is injected into the above-mentioned device to prepare a blank chromatogram.

[0094] A blank chromatogram obtained by measuring only the solvent is subtracted from the chromatogram obtained for the toner to determine the baseline. It is preferable that a horizontal baseline be created at the lowest point before and after the peak derived from the saturated hydrocarbon compound. However, if a horizontal baseline cannot be created even after subtracting the blank chromatogram due to column bleeding or other reasons, the baseline can be set by a horizontal line from the elution time of the C10 compound to the elution time of the C50 compound, whichever has the lower signal intensity.

[0095] Then, vertical lines are drawn on the chromatogram at positions corresponding to the elution times of the compounds with 16 and 35 carbon atoms, and the area of the chromatogram above the baseline enclosed by these vertical lines is calculated. Peaks that are confirmed not to be saturated hydrocarbon compounds are excluded from the calculation. The mass of the C16-35 saturated compound can be calculated from this area. When an internal standard is used, the mass of the C16-35 saturated compound can be calculated from the ratio of the above area to the area of the compound added as the internal standard. The amount of the C16-35 saturated compound in the toner can then be calculated by dividing the obtained mass of the C16-35 saturated compound by the mass of the toner.

[0096] (Other ingredients) The toner base particles may contain a colorant, a charge control agent, and the like.

[0097] The colorant may be a dye or a pigment. When the toner is a color toner that imparts a predetermined color tone to an image, the toner base particles may contain a colorant such as yellow, magenta, cyan, or black, depending on the color tone to be exhibited by the color toner. The toner base particles may contain only one type of colorant, or a combination of multiple types of colorants.

[0098] Examples of yellow colorants include yellow dyes, including CI Solvent Yellow 19, 44, 77, 79, 81, 82, 93, 98, 103, 104, 112, and 162, and yellow pigments, including CI Pigment Yellow 14, 17, 74, 93, 94, 138, 155, 180, and 185.

[0099] Examples of magenta colorants include magenta dyes, including CI Solvent Red 1, 49, 52, 58, 63, 111, and 122, and magenta pigments, such as CI Pigment Red 5, 48:1, 53:1, 57:1, 122, 139, 144, 149, 166, 177, 178, and 222.

[0100] Examples of cyan colorants include cyan dyes such as CI Solvent Blue 25, 36, 60, 70, 93, and 95, and cyan pigments such as CI Pigment Blue 1, 7, 15, 15:3, 60, 62, 66, and 76.

[0101] 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 magnetite, and iron-titanium composite oxides.

[0102] The content of the colorant is preferably 0.5 to 20% by mass, more preferably 2 to 10% by mass, relative to the total mass of the toner base particles. When the toner is a clear toner, the toner base particles preferably do not substantially contain a colorant, and the content of the colorant relative to the total mass of the toner base particles is preferably 0.1% by mass or less.

[0103] 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, metal salicylates or metal complexes thereof, and the like.

[0104] The content of the charge control agent is preferably 0.1 to 10% by mass, more preferably 0.5 to 5% by mass, based on the total mass of the binder resin. Attempting to control the chargeability of the toner by adding an excessive amount of charge control agent may significantly change other properties of the toner base particles. In contrast, in this embodiment, the chargeability of the toner is adjusted using strontium titanate as an external additive, so that the chargeability of the toner can be adjusted to a desired level while satisfying other required properties.

[0105] <External additives> The toner base particles may contain an external additive that is added to the surface of the toner base particles as a post-treatment agent in order to improve the fluidity, chargeability and cleaning properties of the toner.

[0106] (strontium titanate) The external additive preferably contains strontium titanate particles. Depending on the production method or composition, strontium titanate can have any of several particle shapes, including cubic or rectangular parallelepiped, irregular shape, and rounded cubic shape. Although strontium titanate may have any of these particle shapes, rectangular parallelepiped shape is preferred. The shape of the strontium titanate particles can be confirmed by observation with a scanning electron microscope (SEM).

[0107] Strontium titanate having these shapes forms planar exposed portions on the surface of the toner base particle. This reduces the proportion of resin that tends to inhibit the wetting and spreading of varnish on the surface of the toner base particle, thereby improving the applicability of the varnish. Similarly, reducing the proportion of resin on the surface of the toner base particle can also improve the releasability of the toner from the fixing member. In particular, when strontium titanate is rectangular, the area of the planar exposed portion on the surface of the toner base particle tends to be large, which tends to enhance the effects of improving the applicability of the varnish and the releasability of the toner due to the above-mentioned action.

[0108] In order to effectively exert the above-mentioned effects, the number average primary particle size of strontium titanate is preferably 20 to 200 nm, and more preferably 30 to 150 nm. In view of the above-mentioned effects, the larger the particle size of strontium titanate, the better. Furthermore, by setting the upper limit of the particle size within a predetermined range, deterioration in the uniformity of the image surface due to exposed strontium titanate can be suppressed, thereby suppressing deterioration in coatability. The number-average primary particle diameter of strontium titanate can be determined by binarizing image data of strontium titanate taken with a scanning electron microscope (SEM) using an image processing analyzer (LUZEX AP, manufactured by Nireco Corporation) and averaging the horizontal Feret diameters measured for 100 particles.

[0109] The content of strontium titanate is preferably 0.05 to 2.0% by mass, and more preferably 0.1 to 1.0% by mass, based on the total mass of the toner. When the strontium titanate content is 0.05% by mass or more, the strontium titanate is likely to improve the varnish coatability and toner releasability.When the strontium titanate content is 2.0 parts by mass or less, deterioration of coatability due to deterioration of the uniformity of the image surface is unlikely to occur.

[0110] 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 together, and then an alkaline aqueous solution is added while heating (warming) at normal pressure. As the titanium oxide source, a mineral acid peptized product of a hydrolyzed titanium compound can be used. The titanium oxide source is preferably metatitanic acid obtained by a sulfuric acid method and having an SO3 content of 1.0 mass % or less (preferably 0.5 mass % or less), which is peptized by adjusting the pH to 0.8 to 1.5 with hydrochloric acid.

[0111] As the strontium oxide source, metal nitrates, hydrochlorides, etc. For example, strontium nitrate and strontium chloride can be used as the strontium oxide source.

[0112] As the alkaline aqueous solution, a caustic alkali can be used, and as the alkaline aqueous solution, an aqueous sodium hydroxide solution is preferably used.

[0113] 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 at the beginning of the reaction, and the temperature and addition rate when adding the alkaline aqueous solution. In order to prevent the formation of carbonate during the reaction process, it is preferable to prevent the incorporation of carbon dioxide gas during the reaction by, for example, carrying out the reaction in a nitrogen gas atmosphere.

[0114] The mixing ratio of the titanium oxide source and the strontium oxide source during the reaction is preferably 0.90 to 1.40, more preferably 1.05 to 1.20, in terms of the molar ratio SrO / TiO2. Within this range, unreacted titanium oxide is less likely to remain. The concentration of the titanium oxide source at the initial stage of the reaction is preferably 0.05 to 1.3 mol / L, more preferably 0.08 to 1.0 mol / L, based on TiO2.

[0115] The temperature of the mixture when the aqueous alkaline solution is added is preferably 60 to 100°C. The slower the rate of addition of the alkaline aqueous solution, the larger the particle size of the strontium titanate particles that can be obtained, and the faster the rate of addition, the smaller the particle size of the strontium titanate particles that can be obtained. The rate of addition of the aqueous alkaline solution is preferably 0.001 to 1.2 equivalents / h, more preferably 0.002 to 1.1 equivalents / h, relative to the charged raw materials. The rate of addition of the aqueous alkaline solution can also be adjusted appropriately depending on the particle size of the strontium titanate to be obtained.

[0116] The strontium titanate particles thus obtained are preferably further treated with an acid. When the mixing ratio of the titanium oxide source to the strontium oxide source exceeds 1.0 in terms of the molar ratio of SrO / TiO2, the unreacted metal sources other than titanium remaining after the reaction may react with carbon dioxide in the air to produce impurities such as metal carbonates. To prevent performance degradation due to these impurities, it is preferable to add an alkaline aqueous solution and then perform an acid treatment to remove the unreacted metal sources.

[0117] The acid treatment is preferably carried out using hydrochloric acid, nitric acid, acetic acid, or the like at a pH of 2.5 to 7.0, more preferably 4.5 to 6.0.

[0118] (Other external additives) The external additive may contain particles mainly composed of an inorganic material other than the above-mentioned strontium titanate, such as 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. These particles containing inorganic materials as the main component may be hydrophobized with a surface treatment agent such as a silane coupling agent or silicone oil, if necessary. The particle size of these inorganic materials is preferably 20 to 200 nm, more preferably 30 to 150 nm, in terms of the number average primary particle size measured in the same manner as for strontium titanate.

[0119] The external additive may also contain particles whose main component is an organic material containing a homopolymer such as styrene or methyl methacrylate, or a copolymer thereof, etc. The particle size of these particles is preferably 10 to 1000 nm, as measured by the same method as for strontium titanate, at the peak top.

[0120] The external additive may also contain a lubricant such as a metal salt of a higher fatty acid. Examples of such higher fatty acids include stearic acid, oleic acid, palmitic acid, linoleic acid, and ricinoleic acid. Examples of metals that constitute the metal salt include zinc, manganese, aluminum, iron, copper, magnesium, and calcium.

[0121] The content of these external additives is preferably such that the total amount of the external additives together with strontium titanate is 0.05 to 5.0 parts by mass relative to the total mass of the toner base particles.

[0122] [Method for producing toner base particles and toner] The toner base particles can be produced in the same manner as known toners by a pulverization method, an emulsion polymerization aggregation method, an emulsion aggregation method, a suspension polymerization method, a solution suspension method, or the like.

[0123] Of these, the pulverization method, emulsion polymerization flocculation method, emulsion flocculation method or suspension polymerization method is preferred, and the pulverization method or emulsion polymerization flocculation method is more preferred. The toner base particles of pulverized toner produced by the pulverization method are irregular particles with a large surface area due to the existence of numerous randomly distributed minute irregularities throughout the particle. As a result, C16-35 saturated compounds tend to precipitate from the surface of the toner base particles produced by the pulverization method, which tends to improve the coatability of varnish and the releasability of the toner.

[0124] <Crushing method> According to the pulverization method, a binder resin, a release agent, a C16-35 saturated compound, and other materials are mixed and melted and kneaded to obtain a solid resin composition, which is then pulverized to a predetermined particle size to obtain toner base particles.

[0125] More specifically, in the pulverization method, first, predetermined amounts of materials constituting the toner base particles (binder resin, release agent, C16-35 saturated compound, and other materials that are optionally added) are weighed, blended, and mixed. Mixing can be carried out using a mixing device such as a double cone mixer, V-type mixer, drum mixer, super mixer, Henschel mixer, Nauta mixer, or Mechano Hybrid.

[0126] The mixed materials are then melt-kneaded. For the melt-kneading, a batch kneader such as a pressure kneader or a Banbury mixer, or a continuous kneader can be used. For continuous production, it is preferable to use a single-screw extruder or a twin-screw extruder. Examples of twin-screw extruders 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 KCK Corporation), a Co-kneader (manufactured by Buss Co., Ltd.), and a Kneedex (manufactured by Nippon Coke and Engineering Co., Ltd.). The melt-kneading temperature 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 rapidly cooled with water or the like to form a solid.

[0127] Next, the solid resin composition obtained by melt-kneading and cooling is pulverized to a desired particle size. The pulverization may be carried out by, for example, coarsely pulverizing the material using a pulverizer such as a crusher, hammer mill, or feather mill, followed by fine pulverization using a fine pulverizer such as a Cryptron System (manufactured by Kawasaki Heavy Industries, Ltd.), a Super Rotor (manufactured by Nisshin Engineering Inc.), or a Turbo Mill (manufactured by Freund Turbo Corporation), or an air jet type fine pulverizer.

[0128] Thereafter, the pulverized resin composition is classified into spheres as needed using a classifier or 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 a Faculty (manufactured by Hosokawa Micron Corporation). In this manner, toner base particles can be produced by the pulverization method.

[0129] (Hot air surface treatment) Toner particles obtained by these methods, particularly by the pulverization method, may be subjected to a surface treatment using hot air. The surface treatment using hot air can adjust the surface shape (sphericity) of the toner base particles and adjust the surface physical properties. The temperature of the hot air used in the surface treatment is preferably about 100°C to 450°C.

[0130] The method of surface treatment using hot air is not particularly limited, and can be carried out by methods such as those described in JP-A-59-125743 and JP-A-2022-96557. These publications describe a surface treatment method in which toner particles are caused to fall while being rotated by hot air in a heat treatment chamber, and then cooled by cold air supplied into the heat treatment chamber, and the toner particles are then collected.

[0131] FIG. 1 is a schematic diagram showing an example of a surface treatment apparatus 100 for performing surface treatment using hot air. Toner particles supplied from hopper 110 are mixed with compressed air supplied from nozzle 130 in mixing chamber 120, and are ejected as dispersed airflow 140 from diffuser 150 into heat treatment chamber 160. Hot air, which has been supplied to hot air swirling chamber 170 and made into a swirling flow, is blown into this ejected dispersed airflow 140, causing the toner particles in dispersed airflow 140 to swirl with the hot air. The toner particles that have been heat-treated by the swirling are cooled by cooling air introduced from cold air supply unit 180 along the side wall of heat treatment chamber 160, and are then discharged and collected from discharge unit 190.

[0132] FIG. 2 is a schematic diagram showing an example of another surface treatment device 200 for performing surface treatment using hot air. The toner particles mixed with the compressed gas are introduced into an inlet pipe 220 installed on the central axis of the heat treatment chamber 210. The toner base particles introduced and passing through the inlet pipe 220 are uniformly dispersed by a conical protruding member 222 provided in the center of the inlet pipe 220, and pass through a supply pipe 230 that expands radially. The toner base particles are then introduced into a powder particle supply port 240, and are introduced into the heat treatment chamber 210 from the powder particle supply port 240. The hot air supplied from the hot air supply means 250 and introduced into the heat treatment chamber 210 from the hot air introduction section 260 is swirled by a swirling member 270 having multiple blades, and is introduced into the heat treatment chamber 210 while swirling in a spiral pattern. At this time, the approximately conical distribution member 280 distributes the swirling hot air evenly in all directions. The toner base particles supplied to the heat treatment chamber 210 are caused to fall while swirling inside the heat treatment chamber 210 by the spirally swirling hot air. Cold air is also introduced into the treatment chamber 6 from a plurality of cold air introduction sections 290, and the toner base particles falling while swirling are cooled by the cold air introduced from these cold air introduction sections 290.

[0133] <Emulsion polymerization aggregation method> The toner of the present invention can also be suitably produced by an emulsion polymerization aggregation method. An example in which a hybrid crystalline polyester is used as the crystalline resin will be described below. Specifically, the toner production method preferably includes the following steps (1) to (6).

[0134] Step (1): A step of mixing, in a reaction vessel, a monomer serving as a raw material for the crystalline polyester polymerization segment, a raw material monomer for an addition polymerization resin (styrene-acrylic resin) unit (a monomer serving as a raw material for a vinyl-based polymerization segment), and an esterification catalyst, and subjecting the raw material monomers to a polycondensation reaction. Step (2): After the raw material monomers are polycondensed in the step (1), a nucleating agent is added to the reaction vessel and reacted to form a nucleating agent moiety. Step (3): After step (2), a step of aggregating and fusing the amorphous resin (vinyl resin and amorphous polyester) particles, the crystalline resin (hybrid crystalline polyester) particles, the C16-35 saturated compound particles, and the colorant particles in at least an aqueous medium. Step (4): A step of separating the toner base particles from the dispersion liquid of the toner base particles into solid and liquid, and removing and washing the adhering substances such as surfactants and coagulants from the toner cake obtained by the solid-liquid separation. Step (5): Drying the washed toner cake Step (6): A step of subjecting the toner base particles obtained in step (5) to an external addition treatment.

[0135] (Process (1)) In step (1), the raw material monomers for the crystalline polyester polymer segment, the raw material monomers for the addition polymerization resin (styrene-acrylic resin) unit, and an esterification catalyst are mixed in a reaction vessel, and the raw material monomers are subjected to a polycondensation reaction. As the monomers serving as raw materials for the crystalline polyester polymer segment, known monomers such as the above-mentioned polyhydric alcohol monomers and polycarboxylic acid monomers can be suitably used.

[0136] (Polycondensation reaction) The polycondensation reaction of the raw material monomers, that is, the method for synthesizing the crystalline polyester polymer segment, is not limited, but the following methods (A) to (C) are preferred. (A) A method of polymerizing a trivalent or higher polycarboxylic acid or a trivalent or higher polyhydric alcohol (B) Addition polymerization of unsaturated dicarboxylic acids or unsaturated dialcohols (C) A method using a hybrid crystalline polyester in which a crystalline polyester and an amorphous resin unit are chemically bonded

[0137] In the polymerization in the above methods (A) and (B), known polymerization initiators and chain transfer agents can be used.

[0138] (esterification catalyst) Known esterification catalysts can be used. Examples of esterification catalysts include tin compounds such as tin dioctylate, dibutyltin oxide, and tin(II) 2-ethylhexanoate, and titanium compounds such as tetrabutyl orthotitanate and titanium diisopropylate bistriethanolamine. Among these, tetrabutyl orthotitanate (hereinafter also referred to as "Ti(OBu)4") is preferably used.

[0139] (Process (2)) In step (2), after the raw material monomers are subjected to a polycondensation reaction in step (1), a nucleating agent is added to the reaction vessel and reacted to form a nucleating agent moiety. That is, in step (1), after obtaining a crystalline polyester polymer segment by polycondensation reaction, a nucleating agent is added and reacted with the crystalline polyester polymer segment, thereby chemically bonding the nucleating agent to the crystalline polyester polymer segment and forming a nucleating agent moiety. The reaction at this time may be any reaction that can chemically bond the crystalline polyester polymer segment and the crystal nucleating agent, and may be carried out by heating, for example, at 200° C. under normal pressure, but is not limited to this.

[0140] After steps (1) and (2), the crystalline polyester polymerized segment to which the crystal nucleating agent is chemically bonded can be chemically bonded to a vinyl-based polymerized segment by the above-mentioned hybrid crystalline polyester synthesis method, thereby synthesizing a hybrid crystalline polyester having a crystal nucleating agent moiety in the crystalline polyester polymerized segment.

[0141] The nucleating agent may be any compound capable of forming a nucleating site as described above. The nucleating agent is preferably an aliphatic monocarboxylic acid having 10 to 30 carbon atoms or an aliphatic monoalcohol having 10 to 30 carbon atoms.

[0142] Specific examples include stearic acid, lauric acid, behenic acid, triacontanoic acid, arachidic acid, stearyl alcohol, lauryl alcohol, behenyl alcohol, and arachidyl alcohol.

[0143] (Step (3)) In step (3), after step (2), fine particles of the amorphous resin (vinyl resin and amorphous polyester), fine particles of the crystalline resin (hybrid crystalline polyester), fine particles of a C16-35 saturated compound, and fine particles of the colorant are mixed in at least an aqueous medium. and are aggregated and fused together.

[0144] According to these toner preparation methods, the polycarboxylic acid monomer and the polyhydric alcohol monomer are reacted first, and then the crystal nucleating agent moiety is introduced, so that the crystalline polyester can be suitably prepared. As a method for aggregating and fusing, for example, a known emulsion aggregation method can be suitably adopted.

[0145] In the emulsion aggregation method, a solution of an amorphous resin or crystalline resin (hereinafter collectively referred to as "binder resin") dissolved in a solvent and a C16-35 saturated compound is dropped into a poor solvent to form a binder resin particle dispersion. This binder resin particle dispersion is mixed with a colorant particle dispersion and a release agent dispersion such as wax, and the amorphous resin particles, crystalline resin particles, colorant particles, C16-35 saturated compound particles, and release agent are aggregated in an aqueous medium until the desired toner particle size is achieved. Furthermore, shape control is performed by fusing these particles together to produce toner particles. In addition to the above emulsion aggregation method, a preferred emulsion aggregation method is to add a release agent and a C16-35 saturated compound to a binder resin particle dispersion in which an emulsion-polymerized amorphous resin or crystalline resin is dispersed, and after aggregating them to a certain extent, add an additional binder resin particle dispersion that does not contain a C16-35 saturated compound. Then, shape control is performed by fusing the fine particles to produce toner particles.

[0146] In the present invention, the term "aqueous medium" refers to a medium containing at least 50% by mass of water, and examples of components other than water include organic solvents that are 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 such as methanol, ethanol, isopropanol, or butanol, which is an organic solvent that does not dissolve the resin. Preferably, only water such as ion-exchanged water is used as the aqueous medium.

[0147] (Step (4)) In step (4), the toner base particles are separated from the dispersion of the toner base particles (toner base particle dispersion liquid) by solid-liquid separation, and the toner cake obtained by solid-liquid separation is washed to remove any adhering substances such as surfactants and coagulants. The toner cake is an aggregate of wet toner particles that have aggregated into a cake-like mass. The solid-liquid separation is not particularly limited, and may be performed using a centrifugation method, a vacuum filtration method using a Nutsche or the like, a filtration method using a filter press or the like, etc. In addition, in the washing, it is preferable to wash with water until the electrical conductivity of the filtrate reaches 10 μS / cm.

[0148] (Step (5)) In step (5), the washed toner cake is dried. The drying step can be carried out in accordance with a drying step generally used in known methods for producing toner particles. Specifically, examples of the dryer used to dry the toner cake include a spray dryer, a vacuum freeze dryer, a reduced pressure dryer, etc. In particular, it is preferable to use a stationary shelf dryer, a mobile shelf dryer, a fluidized bed dryer, a rotary dryer, an agitator dryer, etc. as the dryer. The moisture content of the dried toner particles is preferably 5% by mass or less, and more preferably 2% by mass or less. In addition, when the dried toner particles are aggregated by weak inter-particle attractive forces, the aggregates may be subjected to a crushing treatment. As the crushing treatment device, a mechanical crushing device such as a jet mill, a Henschel mixer, a coffee mill, or a food processor can be used.

[0149] The drying temperature is preferably within a range of 10 to 45° C., and particularly preferably within a range of 20 to 40° C. If the drying temperature is higher than 45° C., the crystalline components in the toner will be in a molten state, which is thought to make it difficult to control the structure. By controlling the drying temperature, the amount of change in the endothermic peak onset temperature observed at 20°C or higher on the DSC curve due to a change in the holding temperature can be kept to 2°C or less in the present invention.

[0150] (Process (6)) In step (6), the toner base particles obtained through the steps up to step (5) are subjected to an external addition treatment with an external additive, if necessary. The toner base particles obtained through the steps up to step (5) may be used as they are. The external addition treatment using an external additive can be carried out by blending a predetermined amount of the toner base particles and the external additive, and stirring and mixing them in a mixer. Examples of the mixing device include a double cone mixer, a V-type mixer, a drum type mixer, a super mixer, a Henschel mixer, a Nauta mixer, a Mechano Hybrid (manufactured by Nippon Coke and Engineering Co., Ltd.), and a Nobilta (manufactured by Hosokawa Micron Corporation). The external additive may be the inorganic particles described above.

[0151] The carrier is mixed with the above-mentioned toner base particles to form a two-component magnetic toner. The carrier may be any known magnetic particle that can be contained in a toner.

[0152] Examples of the magnetic particles include particles containing magnetic materials such as iron, steel, nickel, cobalt, ferrite, and magnetite, as well as alloys of these with aluminum, lead, and the like. The carrier may be a coated carrier in which the surface of particles made of the magnetic material is coated with a resin or the like, or may be a resin-dispersed carrier in which the magnetic material is dispersed in a binder resin. Examples of the resin for the coating include olefin resin, styrene resin, styrene-acrylic resin, silicone resin, polyester, and fluororesin. Examples of the binder resin include acrylic resin, styrene-acrylic resin, polyester, fluororesin, and phenol resin.

[0153] The average particle size of the carrier is preferably 20 to 100 μm, more preferably 25 to 80 μm, on a volume basis, and can be measured using a laser diffraction particle size distribution analyzer, such as HELOS manufactured by SYMPATEC, which is equipped with a wet disperser. The content of the carrier is preferably 2 to 10% by mass based on the total mass of the toner base particles and the carrier.

[0154] [Image forming method and image forming apparatus] The image forming method will be described below together with the image forming apparatus. The image forming method according to the present invention is characterized by comprising the steps of: adhering the electrostatic latent image developing toner to a recording medium; and fixing the adhered electrostatic latent image developing toner to the recording medium. Furthermore, the fixing step is preferably a step of fixing the electrostatic latent image developing toner to the recording medium in two stages. By fixing in two stages, the toner image can be heated sufficiently and for a long period of time, and the C16-35 saturated compound can be sufficiently precipitated from the toner base particles. As a result, the varnish application property and the releasability from the second-stage fixing device can be further improved. Furthermore, it is preferable to have a step of applying varnish to the surface of the toner image formed by fixing the electrostatic latent image developing toner to form a varnish coat, in terms of improving image quality and durability.

[0155] The image forming apparatus of the present invention has at least a developing means, a transfer means, and a fixing means, and forms a toner image on a recording medium using the toner for developing an electrostatic latent image, and is characterized in that the fixing means has a fixing nip portion and uses a fixing pad in the fixing nip portion. Furthermore, the fixing unit preferably includes an endless belt that heats the toner image on the recording medium at the fixing nip, a rotating body that cooperates with the endless belt to form the fixing nip, a fixing pad that contacts the inner circumferential surface of the endless belt and sandwiches the endless belt between the fixing pad and the rotating body to form the fixing nip, and a heating roller that contacts the inner circumferential surface of the endless belt and heats the endless belt. Using a fixing pad increases the fixing area and extends the fixing time. As a result, the toner image can be heated sufficiently and for a longer period of time, allowing the C16-35 saturated compound to be fully precipitated from the toner base particles. This results in improved varnish applicability and release from the fixing device.

[0156] The image forming apparatus is preferably a four-cycle image forming apparatus configured with four color developing devices for yellow, magenta, cyan, and black and one electrophotographic photosensitive member, or may be a tandem image forming apparatus configured with four color developing devices for yellow, magenta, cyan, and black and four electrophotographic photosensitive members, one for each color.

[0157] 3 is a schematic diagram showing an example of an image forming apparatus 1 according to this embodiment. The image forming apparatus 1 shown in FIG. 3 includes an image processing unit 30, an image forming unit 40, a paper conveying unit 50, a fixing device 60, and an image reading unit 70.

[0158] Image forming section 40 has image forming units 41Y, 41M, 41C, and 41K that form images using toner of each color: Y (yellow), M (magenta), C (cyan), and K (black). These units all have the same configuration except for the toner they contain, so hereinafter, the symbols representing the colors may be omitted. Image forming section 40 also has an intermediate transfer unit 42 and a secondary transfer unit 43. These correspond to transfer devices.

[0159] The image forming unit 41 includes an exposure device 411, a developing device 412, an electrophotographic photosensitive member (image carrier) 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 photosensitive member 413 by bringing a contact charging member such as a charging roller, a charging brush, or a charging blade into contact with the electrophotographic photosensitive member 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 photosensitive member 413 with laser light corresponding to an image to be formed. The electrophotographic photoreceptor 413 is a negatively charged organic photoreceptor having photoconductivity. The electrophotographic photoreceptor 413 is charged by a charging device 414.

[0160] Developing device 412 is a two-component developing device. Developing device 412 has, for example, a developing container that stores a two-component developer, a developing roller (magnetic roller) that is rotatably arranged at the opening of the developing container, a partition that separates the inside of the developing container so that the two-component developer can communicate with each other, a transport roller that transports the two-component developer on the opening side of the developing container toward the developing roller, and a stirring roller that stirs the two-component developer in the developing container. The developer container contains, for example, a two-component developer.

[0161] The intermediate transfer unit 42 includes an intermediate transfer belt (intermediate transfer member) 421, a primary transfer roller 422 that presses the intermediate transfer belt 421 against the electrophotographic photosensitive member 413, a plurality of support rollers 423 including a backup roller 423A, and a belt cleaning device 426. Intermediate transfer belt 421 is looped and stretched around a plurality of support rollers 423. When at least one drive roller among the plurality of support rollers 423 rotates, intermediate transfer belt 421 runs in the direction of arrow A at a constant speed.

[0162] The belt cleaning device 426 has an elastic member 426a. The elastic member 426a comes into contact with the intermediate transfer belt 421 after the secondary transfer, and removes any deposits on the surface of the intermediate transfer belt 421. The elastic member 426a is made of an elastic body, and includes a cleaning blade, a brush, and the like.

[0163] The secondary transfer unit 43 has an endless secondary transfer belt 432 and a plurality of support rollers 431 including a secondary transfer roller 431A. The secondary transfer belt 432 is stretched by the secondary transfer roller 431A and the support rollers 431 in a loop shape.

[0164] The fixing device 60 has, for example, a fixing roller 62, an endless heating belt 10 that covers the outer peripheral surface of the fixing roller 62 and heats and melts the toner that forms the toner image on the paper S, and a pressure roller 63 that presses the paper S against the fixing roller 62 and the heating belt 10. The paper S corresponds to a recording medium.

[0165] The image forming apparatus 1 further includes an image reading unit 70, an image processing unit 30, and a paper transport unit 50. The image reading unit 70 includes a paper feeder 71 and a scanner 72 . The paper transport section 50 includes a paper feed section 51 , a paper discharge section 52 , and a transport path section 53 . The three paper feed tray units 51a to 51c that make up the paper feed section 51 store paper sheets S (standard paper sheets, special paper sheets) that are identified based on basis weight, size, etc., according to preset types. The transport path section 53 has a plurality of transport roller pairs such as a registration roller pair 53a.

[0166] The formation of an image by the image forming apparatus 1 will be described. The scanner 72 optically scans and reads the document D on the contact glass. The light reflected from the document D is read by the CCD sensor 72a and becomes input image data. The input image data is subjected to predetermined image processing in the image processing unit 30 and sent to the exposure device 411.

[0167] The electrophotographic photosensitive member 413 rotates at a constant peripheral speed. The charging device 414 uniformly charges the surface of the electrophotographic photosensitive member 413 to a negative polarity. In the exposure device 411, a polygon mirror of a polygon motor rotates at high speed, and laser light corresponding to input image data of each color component is developed along the axial direction of the electrophotographic photosensitive member 413 and irradiated along the axial direction onto the outer circumferential surface of the electrophotographic photosensitive member 413. In this way, an electrostatic latent image is formed on the surface of the electrophotographic photosensitive member 413.

[0168] In the developing device 412, the toner base particles are charged by stirring and transporting the two-component developer in the developing container, and the two-component developer is transported to the developing roller, which forms a magnetic brush on the surface of the developing roller. The charged toner base particles electrostatically adhere from the magnetic brush to the electrostatic latent image on the electrophotographic photosensitive member 413. In this way, the electrostatic latent image on the surface of the electrophotographic photosensitive member 413 is visualized, and a toner image corresponding to the electrostatic latent image is formed on the surface of the electrophotographic photosensitive member 413.

[0169] The toner image on the surface of the electrophotographic photosensitive member 413 is transferred to an intermediate transfer belt 421 by an intermediate transfer unit 42. Residual toner remaining on the surface of the electrophotographic photosensitive member 413 after transfer is removed by a drum cleaning device 415 having a drum cleaning blade that comes into sliding contact with the surface of the electrophotographic photosensitive member 413.

[0170] The primary transfer roller 422 presses the intermediate transfer belt 421 against the electrophotographic photosensitive member 413, thereby forming a primary transfer nip for each electrophotographic photosensitive member between the electrophotographic photosensitive member 413 and the intermediate transfer belt 421. In the primary transfer nip, toner images of each color are transferred onto the intermediate transfer belt 421 in order, superimposed on one another.

[0171] Meanwhile, secondary transfer roller 431A is pressed against backup roller 423A via intermediate transfer belt 421 and secondary transfer belt 432. As a result, a secondary transfer nip is formed by intermediate transfer belt 421 and secondary transfer belt 432. Paper S passes through the secondary transfer nip. The sheet S is transported to the secondary transfer nip (adhesion portion) by the sheet transport section 50. Correction of the skew of the sheet S and adjustment of the transport timing are performed by a registration roller section in which a pair of registration rollers 53a is arranged.

[0172] When the paper S is transported to the secondary transfer nip, a transfer bias is applied to the secondary transfer roller 431A. By applying this transfer bias, the toner image carried on the intermediate transfer belt 421 is transferred to the paper S (a process of adhering the toner for developing an electrostatic latent image to the recording medium). The paper S onto which the toner image has been transferred is transported by the secondary transfer belt 432 toward the fixing device 60.

[0173] After the secondary transfer, deposits such as residual toner remaining on the surface of intermediate transfer belt 421 are removed by belt cleaning device 426, which has a cleaning blade that slides against the surface of intermediate transfer belt 421. In this case, since the intermediate transfer body described above is used as the intermediate transfer belt, dynamic friction can be reduced over time.

[0174] The fixing device 60 sandwiches the heating belt 10 between a rotating fixing roller 62 and a pressure roller 63 to form a fixing nip, and heats and presses the conveyed paper S in the fixing nip. In this way, the toner image is fixed to the paper S (a process of fixing the toner for developing an electrostatic latent image to the recording medium). The paper S with the fixed toner image is discharged outside the machine by a paper discharge unit 52 equipped with a paper discharge roller 52a.

[0175] In this embodiment, the fixing of the toner image on the paper S may be performed in two stages. That is, the image forming apparatus 1 may have two different fixing devices 60, and the fixing may be performed successively by these two fixing devices 60. Specifically, the toner image heated by the first-stage fixing device 60 may be heated and pressurized by the second-stage fixing device 60 before it is completely cooled. This allows the toner image to be heated sufficiently and for a longer period of time, allowing the C16-35 saturated compound to be sufficiently precipitated from the toner base particles, thereby further improving the applicability of the varnish and the releasability from the second-stage fixing device 60.

[0176] The second stage of fixing may be performed immediately after the first stage of fixing, or, for example, the paper S may be turned over and another image may be attached and fixed to the back side, and then the paper S may be turned over again and the second stage of fixing may be performed on the front side. In this case, it is preferable to turn the paper S over again and perform the second stage of fixing on the back side as well. Fixation may be carried out in stages from the third stage onwards.

[0177] The fixing device may also be configured to form the fixing nip with a non-rotating pressure pad. FIG. 4 is a schematic diagram showing the general configuration of a fixing device 600 that forms a planar fixing nip using a non-rotating pressure pad. The fixing device 600 includes a non-rotating pressure pad 610 , a pressure roller 620 , a heating roller 630 , a steering roller 640 and a heating belt 650 . Heating belt 650 is stretched over heating roller 630 and steering roller 640. A fixing nip is formed by sandwiching heating belt 650 between non-rotating pressure pad 610 and pressure roller 620. In the fixing nip, the conveyed paper S is heated and pressed. The pressure pad 610 is pressed against the heating belt by a stainless steel pressing member 660, thereby pressing the heating belt 650 against the pressure pad 610 to form a fixing nip.

[0178] The pressure pad 610 is a substantially rectangular parallelepiped pad member made of liquid crystal polymer (LCP) or the like. The pressure pad 610 presses the heating belt 650 with one surface of the rectangular parallelepiped to form a cotton-like fixing nip. A lubricating sheet (not shown) is interposed between the pressure pad 610 and the heating belt 650 to enable the heating belt 650 to rotate smoothly. The lubricating sheet can be, for example, a polyimide sheet coated with 100 μm thick polytetrafluoroethylene (PTFE). This polyimide sheet may have 100 μm protrusions formed at 1 mm intervals to reduce the contact area with the heating belt 650 and thereby reduce sliding resistance. A lubricant such as silicone oil may be applied to the surface of the heating belt 650 that comes into contact with the lubricating sheet to enable the heating belt 650 to rotate smoothly.

[0179] Forming a planar nip with this configuration allows for a longer fixing time, which allows the toner image to be heated sufficiently and for a longer time, resulting in sufficient precipitation of the C16-35 saturated compound from the toner base particles, and thus improving the applicability of the varnish and the releasability from the second-stage fixing device 600.

[0180] When fixing is performed in two stages as described above, both fixing devices may be fixing devices having pressure pads. Alternatively, either one of the fixing devices (the first-stage fixing device or the second-stage fixing device) may be a fixing device having a pressure pad. Of course, both fixing devices may be fixing devices having rotating fixing rollers.

[0181] The above-described apparatus configuration and image forming method are exemplary embodiments for carrying out the present invention, and the present invention is not limited to these.

[0182] [Formation of varnish coat] A varnish may be applied to the image formed by the above-described image forming method to form a varnish coat. When forming the varnish coat, for example, a photocurable varnish containing a photopolymerizable compound is applied to the image formed in the image forming process described above and cured to form a varnish layer. The photocurable varnish may be applied to cover the entire image or only a portion of the image.

[0183] The method for applying the photocurable varnish onto the image is not particularly limited as long as it allows the photocurable varnish to be applied uniformly. Examples of coating devices include liquid film coating devices including varnish coaters, roll coaters, foxo coaters, rod coaters, blades, wire bars, air knives, curtain coaters, slide coaters, doctor knives, screen coaters, gravure coaters (e.g., offset gravure coaters), slot coaters, and extrusion coaters, etc. These can be used in well-known types such as forward and reverse roll coating, offset gravure, curtain coating, lithographic coating, screen coating, and gravure coating.

[0184] Here, the photocurable varnish to be applied onto the image need only contain a photopolymerizable compound (polymerizable monomer for varnish), but typically contains a polymerization initiator (sensitizer) in addition to the photopolymerizable compound.

[0185] The photopolymerizable compound may be a monomer, an oligomer, or a polymer, provided that it contains at least a diol di(meth)acrylate having a linear hydrocarbon structure. When the photocurable varnish contains this diol di(meth)acrylate, the affinity with the crystalline polyester in the toner particles described above is increased, the wettability of the photocurable varnish to the image is improved, and the adhesion between the resulting varnish layer and the image is also improved.

[0186] Here, a 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, the hydrocarbon chain sandwiched between two oxygen atoms derived from the diol is specified as the linear hydrocarbon structure.

[0187] The number of carbon atoms in the linear hydrocarbon structure of the diol di(meth)acrylate is preferably 4 to 12, more preferably 6 to 10, and even more preferably 6 to 9. When the number of carbon atoms in the linear hydrocarbon structure of the diol di(meth)acrylate is within this range, the viscosity of the photocurable varnish falls within an appropriate range, which tends to improve coatability. Furthermore, the affinity with the crystalline polyester in the toner particles also tends to improve.

[0188] Specific examples of diol di(meth)acrylate include hexanediol diacrylate, nonanediol diacrylate, decanediol diacrylate, etc., and among these, hexanediol diacrylate is particularly preferred.

[0189] The amount of diol di(meth)acrylate having a linear hydrocarbon structure is preferably 10 to 80% by mass, more preferably 20 to 65% by mass, based on the total mass of the photopolymerizable compound. When the amount of diol di(meth)acrylate is within this range, good adhesion between the image and the varnish layer is achieved.

[0190] Examples of photopolymerizable compounds other than diol di(meth)acrylates include polymerizable oligomers and polymers such as acrylic resins, vinyl acrylic resins, acrylic esters of polyhydric alcohols, epoxy acrylates, urethane acrylates, polyester acrylates, polyether acrylates, acrylate alkyds, and melamine acrylates, as well as (meth)acrylate monomers such as trimethylolpropane (meth)acrylate and phenoxyethyl (meth)acrylate, and tri(meth)acrylate monomers. The amount and type of photopolymerizable compound other than diol di(meth)acrylate are selected appropriately depending on the curing properties, viscosity, surface tension, etc. of the photocurable varnish.

[0191] 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 relative to the total mass of the photocurable varnish. When the amount of the polymerization initiator is within this range, the photocurable varnish has good curability.

[0192] Furthermore, the light-curable varnish may contain a surfactant. Examples of surfactants include anionic surfactants, nonionic surfactants, silicone surfactants, and fluorosurfactants. Examples of anionic surfactants include sulfosuccinates, disulfonates, phosphates, sulfates, sulfonates, and the like. Examples of nonionic surfactants that can be used include polyvinyl alcohol, polyacrylic acid, isopropyl alcohol, acetylenic diol, ethoxylated octylphenol, ethoxylated branched secondary alcohol, perfluorobutane sulfonate, and alkoxylated alcohol. Examples of silicone surfactants include polyether-modified polydimethylsiloxanes and the like. Examples of fluorosurfactants include ethoxylated nonylphenol and the like. When the photocurable varnish contains a surfactant, it improves the adhesion between the image and the varnish layer, and also adjusts the surface tension of the photocurable varnish, thereby improving the wettability of the photocurable varnish.

[0193] The surface tension of the photocurable varnish at 25° C. is preferably 10 to 50 mN / m, more preferably 15 to 45 mN / m, and even more preferably 20 to 40 mN / m. When the surface tension of the photocurable varnish is within this range, the photocurable varnish easily wets and spreads over the image. The surface tension of the photocurable varnish is measured by the plate method using a KYOWA DY300 (manufactured by Kyowa Interface Science Co., Ltd.).

[0194] On the other hand, the viscosity of the photocurable varnish at 25°C, measured after 30 seconds by immersing the vibrator in the liquid using a vibration viscometer, is preferably 100 to 800 mPa·s. The viscosity is more preferably 150 to 700 mPa·s or less, and even more preferably 200 to 600 mPa·s. When the viscosity of the photocurable varnish falls within this range, it is easier to apply using the method described above.

[0195] After the photocurable varnish is applied, light energy is irradiated to cure the photocurable varnish. The type of light energy to be irradiated is appropriately selected depending on the type of the polymerization initiator, etc., but can usually be ultraviolet light, visible light, etc. Examples of light sources for light energy include low-pressure mercury lamps, medium-pressure mercury lamps, high-pressure mercury lamps, ultra-high-pressure mercury lamps, xenon lamps, carbon arc lamps, metal halide lamps, fluorescent lamps, tungsten lamps, and LEDs, and the light intensity, irradiation time, etc. are selected as appropriate.

[0196] The varnish coat may be formed by applying a solvent-based varnish and then drying the solvent, in addition to the photocurable varnish described above. [Example]

[0197] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. In the following examples, unless otherwise specified, operations were carried out at room temperature (25°C). Furthermore, unless otherwise specified, "%" and "parts" mean "% by mass" and "parts by mass," respectively.

[0198] 1. Prepare ingredients [Saturated hydrocarbon compounds (S)] Saturated hydrocarbons with carbon numbers of 20, 26, 30, and 34 (manufactured by GL Sciences Inc.) were separated in a mass ratio of 20:30:30:20. The mixture was then melted and mixed at 80°C, and then cooled and solidified to obtain a saturated hydrocarbon compound [S] with a carbon number of 16 to 35.

[0199] <Release agent [W1] (microcrystalline wax)> A microcrystalline wax with a melting point of 82°C was prepared by solvent crystallization and filtration of the residual oil from vacuum distillation. Molecular distillation was repeated until the average carbon number was 41 and components with a carbon number of 16 to 35 could not be detected, thereby obtaining a microcrystalline wax (hydrocarbon wax) as a release agent [W1]. Molecular distillation was carried out at a temperature of 240°C and a pressure of 0.2 Pa to remove low molecular weight components, followed by removal of other components at a temperature of 400°C and a pressure of 0.2 Pa. The carbon number was qualitatively determined by GC-MS and quantitatively detected by GC-FID. The melting point of the obtained microcrystalline wax was 73° C. The melting point was determined as the temperature at which an endothermic peak with a half-width of 15° C. or less was observed when measured by DSC at a heating rate of 10° C. / min.

[0200] <Release Agent [W2] (Behenic Acid Behenate)> Commercially available behenic acid behenate was used as the behenic acid behenate (ester wax) as the release agent [W2].

[0201] <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 placed in a reactor equipped with a condenser, a stirrer, a nitrogen inlet tube, and a thermocouple. The atmosphere in the reactor was then replaced with nitrogen gas, and the temperature was gradually increased while stirring. The materials were reacted at 140°C for 3 hours while stirring.

[0202] Next, the pressure in the reaction vessel was reduced to 8.3 kPa, and the mixture was heated to 200°C with stirring and reacted for 4 hours. Thereafter, the pressure in the reaction vessel was reduced to 5 kPa or less again, and the mixture was reacted at 200°C for 3 hours to obtain amorphous polyester [c1].

[0203] <Hybrid crystalline polyester [c2]> The raw material monomers of the following addition polymerization resin (styrene acrylic resin: StAc) unit containing a bireactive monomer and a radical polymerization initiator were placed 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

[0204] Furthermore, the raw material monomers for the polycondensation resin (crystalline polyester: CPEs) unit shown below were placed in a four-neck flask equipped with a nitrogen inlet tube, a dehydration tube, a stirrer and a thermocouple, and heated to 170°C to dissolve. Acid: 280 parts by weight of tetradecanedioic acid Alcohol: 1,4-butanediol 105 parts by mass

[0205] Next, the above monomer was placed in a reaction vessel equipped with a stirrer, a thermometer, a condenser, and a nitrogen gas inlet tube, and the atmosphere in the reaction vessel was replaced with dry nitrogen gas. To the resulting mixture, 0.4 parts by mass of Ti(On-Bu)4 was added, and the mixture was heated to 235°C and reacted at normal pressure (101.3 kPa) for 5 hours and then under reduced pressure (8 kPa) for 1 hour. Next, the resulting reaction solution was cooled to 200°C, and then the reaction was carried out under reduced pressure (20 kPa) so that the acid value calculated by the above-mentioned measurement method would be 20.0 mgKOH / g after the introduction of the nucleating agent site. Next, the pressure in the reaction vessel was gradually released to return to normal pressure, and then 20.3 parts by mass of stearic acid was added as a crystal nucleating agent, followed by reaction at 200° C. for 1.5 hours under normal pressure. Thereafter, the pressure in the reaction vessel was reduced to 5 kPa or less at 200° C., and the reaction was carried out for 2.5 hours to obtain a hybrid crystalline polyester [c2]. The hybrid crystalline polyester [c2] had a weight average molecular weight (Mw) of 11,500 and an acid value of 20.0 mgKOH / g.

[0206] <Preparation of Hybrid Crystalline Resin Particle Dispersion [C2]> The following was added to 102 parts by mass of methyl ethyl ketone and stirred at 75°C for 30 minutes to dissolve. Hybrid crystalline polyester [c2] 174.3 parts by mass

[0207] Next, 3.1 parts by mass of a 25% by mass aqueous solution of sodium hydroxide was added to this solution. This solution was placed in a reaction vessel equipped with a stirrer, and 375 parts by mass of water heated to 70°C was added dropwise to the solution over a period of 70 minutes while stirring. The solution in the vessel became cloudy during the addition, and after the entire amount was added dropwise, a uniform emulsion was obtained. Next, while keeping this emulsion at 70°C, it was stirred for 3 hours under a reduced pressure of 15 kPa (150 mbar) using a diaphragm vacuum pump "V-700" (manufactured by BUCHI) to distill off the methyl ethyl ketone, and then cooled at a rate of 6°C / min to produce a hybrid crystalline resin microparticle dispersion [C2] in which microparticles of hybrid crystalline polyester [c2] were dispersed. As a result of measurement using the particle size distribution measuring instrument, the volume average particle size of the crystalline resin particles in the hybrid crystalline resin particle dispersion liquid [C2] was 202 nm.

[0208] <Preparation of Colorant Particle Dispersion [P]> 90.0 parts by mass of sodium n-dodecyl sulfate was added to 1600.0 parts by mass of ion-exchanged water, and 320.0 parts by mass of carbon black (Regal 330R, manufactured by Cabot Corporation) was gradually added to this aqueous solution while stirring. Next, a dispersion process was carried out using a stirring device (Clearmix W Motion CLM-0.8, manufactured by M-Technique Co., Ltd.) to prepare a colorant particle dispersion [P] with a volumetric median diameter of 110 nm. The median diameter was measured using a particle size distribution analyzer (MICROTRAC UPA-150, manufactured by HONEYWELL).

[0209] <Preparation of vinyl resin particle dispersion [A]> Styrene: 432.0 parts by mass n-Butyl acrylate: 225.0 parts by mass Methacrylic acid: 61.2 parts by mass A 5 L reaction vessel equipped with a stirrer, temperature sensor, condenser, and nitrogen inlet was charged with 8 parts by mass of sodium dodecyl sulfate and 3,000 parts by mass of ion-exchanged water. Under a nitrogen stream, the liquid temperature was raised to 80°C while stirring at a stirring speed of 230 rpm. After the temperature was raised, a solution of 10 parts by mass of potassium persulfate dissolved in 200 parts by mass of ion-exchanged water was added, and the liquid was heated again to 80°C, and the above-mentioned monomer mixture was added dropwise over 1 hour. After the dropwise addition, the liquid temperature was raised to 80°C, and polymerization was carried out by stirring for 2 hours, thereby preparing a vinyl resin microparticle dispersion [a1].

[0210] 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 [S] with carbon atoms of 16 to 35: 3.00 parts by mass A 5 L reaction vessel equipped with a stirrer, a temperature sensor, a cooling tube, and a nitrogen introducing device was charged with 7 parts by mass of sodium polyoxyethylene (2) dodecyl ether sulfate and 3,000 parts by mass of ion-exchanged water and heated to 80° C. After heating, 80 parts by mass (solid content equivalent) of vinyl resin microparticle dispersion liquid [a1] and a mixture prepared by dissolving the above-mentioned monomer, chain transfer agent, release agent [W1] (hydrocarbon wax), and saturated hydrocarbon compound [S] at 90° C. were added thereto.

[0211] Then, a mixing and dispersion process was carried out for 1 hour using a mechanical disperser with a circulation path (CLEARMIX, manufactured by M Technique Co., Ltd.) to prepare a dispersion containing emulsified particles (oil droplets). Next, an initiator aqueous 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, thereby polymerizing the monomers to prepare a vinyl resin particle dispersion [a2].

[0212] To the vinyl resin particle dispersion liquid [a2], 400 parts by mass of ion-exchanged water was added. Then, a solution of 11 parts by mass of potassium persulfate dissolved in 400 parts by mass of ion-exchanged water was added. Furthermore, at a temperature of 82°C, a mixed solution of the following monomers was added dropwise over one 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

[0213] After the dropwise addition was completed, the mixture was heated and stirred for 2 hours to polymerize the monomers, and then cooled to 28° C. to obtain a vinyl resin particle dispersion liquid [A].

[0214] <Preparation of amorphous polyester resin 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 polymerization initiator was placed in a dropping funnel.

[0215] Bisphenol A ethylene oxide 2 mole adduct: 50.2 parts by mass Bisphenol A propylene oxide 2 mole adduct: 249.8 parts by mass Terephthalic acid: 120.1 parts by mass Dodecenyl succinic acid: 46.0 parts by mass The above-mentioned amorphous polyester monomer was placed in a four-necked flask equipped with a nitrogen inlet tube, a dehydration tube, a stirrer and a thermocouple, and heated to 170° C. to dissolve.

[0216] With stirring, the mixed liquid placed in the dropping funnel was added dropwise to the four-necked flask over 90 minutes, and after aging for 60 minutes, the unreacted monomer was removed under reduced pressure (8 kPa). Then, 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 reaction was carried out under normal pressure (101.3 kPa) for 5 hours and under reduced pressure (8 kPa) for 1 hour. Next, the liquid temperature was cooled to 200° C., and the reaction was carried out under reduced pressure (20 kPa), after which the solvent was removed to obtain an amorphous polyester.

[0217] 100 parts by mass of the obtained amorphous polyester was dissolved in 400 parts by mass of ethyl acetate (manufactured by Kanto Chemical Co., Inc.) This solution was mixed with 638 parts by mass of a sodium lauryl sulfate solution (concentration: 0.26% by mass) that had been prepared in advance.

[0218] The resulting mixture was subjected to ultrasonic dispersion treatment at V-LEVEL 300 μA for 30 minutes using an ultrasonic homogenizer (US-150T, manufactured by Nippon Seiki Seisakusho Co., Ltd.) while stirring. After that, the liquid temperature was raised to 40°C, and the ethyl acetate was completely removed by stirring the mixture under reduced pressure for 3 hours using a diaphragm vacuum pump (V-700, manufactured by BUCHI). As a result, an amorphous polyester resin microparticle dispersion [D] with a solid content of 13.5% by mass was obtained.

[0219] 2. Preparation of toner base particles <Preparation of Toner Base Particles 1> 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 [S] with carbon atoms of 16 to 35: 0.07 parts by mass Carbon black (Regal 330R, manufactured by Cabot Corporation): 7.00 parts by mass The above materials were put into a Henschel mixer (Mitsui Mining Co., Ltd., FM-75 type) and rotated at a speed of 20 s -1 The mixture was mixed under the conditions of 100°C, ... and 5 minutes of rotation time. Thereafter, these were kneaded using a twin-screw kneader (manufactured by Ikegai Corporation, PCM-30 model) set at a temperature of 170°C. The obtained kneaded product was cooled and coarsely crushed to 1 mm or less using a hammer mill to obtain a coarsely crushed product. The obtained coarsely crushed product was finely crushed using a mechanical crusher (manufactured by Turbo Kogyo Co., Ltd., T-250). Furthermore, using a classifying device (manufactured by Hosokawa Micron Corporation, Faculty F-300), the classifying rotor rotation speed was set at 130 s -1 , distributed rotor rotation speed 120s -1 Classification was carried out as follows.

[0220] The particles after classification were heat-treated using the surface treatment device shown in Fig. 1. The temperature of the heat treatment chamber was set to 300°C, and the heat treatment time was set to 30 seconds. As a result, 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 using a measuring device (FPIA-3000, manufactured by Sysmex Corporation), and the volume average particle size was measured using a Coulter Multisizer 3 (manufactured by Beckman Coulter, Inc.).

[0221] <Preparation of Toner Base Particles 2> A reaction vessel equipped with a stirrer, a temperature sensor, and a cooling tube was charged with 180 parts by mass (solid content equivalent) of the vinyl resin microparticle dispersion liquid [A] and 2,000 parts by mass of ion-exchanged water. At room temperature (25°C), a 5 mol / L aqueous sodium hydroxide solution was added to adjust the pH of the dispersion liquid in the reaction vessel to 10. Further, 40 parts by mass (solid content equivalent) of a colorant particle dispersion was added, and an aqueous solution prepared by dissolving 30 parts by mass of magnesium chloride in 60 parts by mass of ion-exchanged water as an aggregating agent was added thereto over 10 minutes while stirring at 30° C. After leaving the system for 3 minutes, the temperature was raised to 80° C. over 60 minutes, and the stirring speed was adjusted so that the particle size growth rate was 0.01 μm / min when the temperature reached 80° C. The particles were then grown until the volumetric median diameter measured using a Coulter Multisizer 3 (Coulter-Beckman) reached 4.0 μm. When the median diameter reached 4.0 μm, 121 parts by mass (solids content equivalent) of vinyl resin microparticle dispersion [A] was added to the reaction vessel. The stirring speed was adjusted so that the particle size growth rate was 0.01 μm / min, and the particles were grown until the volumetric median diameter reached 6.0 μm. Next, 68 parts by mass (solid content equivalent) of amorphous polyester resin microparticle dispersion [D] was added over 30 minutes. When the supernatant of the reaction solution became transparent, an aqueous solution of 190 parts by mass of sodium chloride dissolved in 760 parts by mass of ion-exchanged water was added to stop the growth of particle size. Furthermore, as a maturation step, the mixture was heated and stirred at a liquid temperature of 80°C, and fusion between particles was promoted until the average circularity of the particles measured using a measuring device (FPIA-3000, manufactured by Sysmex) reached 0.970. Thereafter, the liquid temperature was cooled to 30°C. Next, solid-liquid separation was performed, and the dehydrated toner cake was washed by repeating the operation of redispersing the toner cake in ion-exchanged water and performing solid-liquid separation three times. Thereafter, the toner cake was dried at 40° C. for 24 hours to obtain toner base particles 2.

[0222] <Preparation of Toner Base Particles 3> Toner base particles 3 were prepared in the same manner as in the preparation of toner base particles 2, except that the amounts of the release agent [W1] (hydrocarbon wax) and the saturated hydrocarbon compound [S] having 16 to 35 carbon atoms added during the preparation of the vinyl-based resin fine particle dispersion [a2] were changed as follows: Release agent [W1]: 50 parts by mass Saturated hydrocarbon compounds [S] with carbon atoms of 16 to 35: 0.2 parts by mass

[0223] <Preparation of Toner Base Particles 4> Toner base particles 4 were prepared in the same manner as toner base particles 2, except that the amount of saturated hydrocarbon compound [S] having 16 to 35 carbon atoms added during the preparation of vinyl-based resin fine particle dispersion liquid [a2] was changed as follows: Saturated hydrocarbon compounds [S] with carbon atoms of 16 to 35: 6.0 parts by mass

[0224] <Preparation of Toner Base Particles 5> Toner base particles 5 were prepared in the same manner as toner base particles 2, except that the release agent [W1] (hydrocarbon wax) used in preparing the vinyl resin microparticle dispersion [a2] was changed to release agent [W2] (behenic acid behenate).

[0225] <Preparation of Toner Base Particles 6> Toner base particles 6 were prepared in the same manner as in the preparation of toner base particles 2, except that in the preparation method for toner base particles 2, 68 parts by mass of amorphous polyester resin microparticle dispersion liquid [D] was changed to 48 parts by mass of amorphous polyester resin microparticle dispersion liquid [D] and 20 parts by mass of hybrid crystalline polyester resin microparticle dispersion liquid [C2] was added at the same time.

[0226] <Preparation of Toner Base Particles 7> Toner base particles 7 were obtained in the same manner as in the preparation of toner base particles 6, except that the dehydrated toner cake was redispersed in ion-exchanged water and subjected to solid-liquid separation three times to wash, and then the drying temperature was changed to 30°C.

[0227] <Preparation of Toner Base Particles 12> In the preparation of toner base particles 6, the dehydrated toner cake was redispersed in ion-exchanged water and subjected to solid-liquid separation, which was repeated three times to wash the cake, and then the drying temperature was changed to 80°C, and toner base particles 12 were obtained in the same manner.

[0228] <Preparation of Toner Base Particles 13> Toner base particles 13 were prepared in the same manner as the toner base particles 2, except that the amounts of the release agent [W1] (hydrocarbon wax) and the saturated hydrocarbon compound [S] having 16 to 35 carbon atoms added during the preparation of the vinyl-based resin fine particle dispersion [a2] were changed as follows: Release agent [W1]: 50 parts by mass Saturated hydrocarbon compounds [S] with carbon atoms of 16 to 35: 0.12 parts by mass

[0229] <Preparation of Toner Base Particles 14> Toner base particles 14 were prepared in the same manner as the toner base particles 2, except that the amount of saturated hydrocarbon compound [S] having 16 to 35 carbon atoms added during the preparation of the vinyl-based resin fine particle dispersion [a2] was changed as follows: Saturated hydrocarbon compounds [S] with carbon atoms of 16 to 35: 6.3 parts by mass

[0230] 3. Toner Preparation <Preparation of Toner 1> The following materials were mixed in a Henschel mixer (FM-75, manufactured by Mitsui Miike Chemical Engineering Co., Ltd.) at a rotation speed of 30 s -1 The mixture was mixed for 10 minutes, and a toner 1 was obtained. Toner base particles 1: 100 parts by mass Hydrophobic silica particles (BET specific surface area: 200 m) hydrophobized with hexamethyldisilazane 2 / g): 1.0 parts by mass Titanium oxide particles (BET specific surface area: 80 m) surface-treated with isobutyltrimethoxysilane 2 / g): 1.0 parts by mass Strontium titanate 1 (number average primary particle diameter 50 nm): 0.5 parts by mass

[0231] <Preparation of Toners 2 to 14> Toners 2 to 14 were prepared in the same manner as Toner 1, except that the type of toner base particles and the strontium titanate were changed to strontium titanate having the number average primary particle diameter shown in Table I below. Note that no strontium titanate was added to Toner 7.

[0232] In Table I below, "drying temperature" refers to the temperature at which the dehydrated toner cake is dried after being washed by repeatedly dispersing the dehydrated toner cake in ion water and separating it into solid and liquid. Furthermore, the "content of C16-C35 saturated compounds" represents the content (ppm by mass) relative to the total mass of the toner base particles and external additives.

[0233] <Difference in endothermic peak onset temperature> 4.5 to 5.0 mg of the obtained toner was weighed accurately to two decimal places, and this was used as a sample, sealed in an aluminum pan (KIT NO. 0219-0041), and set in the DSC-7 sample holder. An empty aluminum pan was used as a reference. The endothermic peak onset temperature was measured using a "DSC-7 Differential Scanning Calorimeter" (manufactured by PerkinElmer) and a "TAC7 / DX Thermal Analysis Device Controller" (manufactured by PerkinElmer). Next, the toner measurement sample was first cooled from room temperature (25°C) to 0°C at -10°C / min, then heated from 0°C to 200°C at 10°C / min, then cooled from 200°C to 0°C at -10°C / min, and then heated at 10°C / min to 40°C. After maintaining the temperature at 40°C for 3 hours, the temperature was once cooled to 0°C at -10°C / min, and the calorific value was measured while heating from 0°C to 200°C at 10°C / min (Measurement 1).

[0234] Next, the sample used in Measurement 1 was cooled from 200°C to 0°C at -10°C / min, and then heated to 50°C at 10°C / min. After holding the sample at 50°C for 3 hours, the sample was cooled to 0°C at -10°C / min, and then heated at 10°C / min in the range from 0°C to 200°C, while measuring the calorific value (Measurement 2).

[0235] Next, the sample used in Measurement 2 was cooled from 200°C to 0°C at -10°C / min, and then heated to 60°C at 10°C / min. After holding at 60°C for 3 hours, the sample was cooled to 0°C at -10°C / min, and then heated at 10°C / min in the range from 0°C to 200°C, while measuring the calorific value (Measurement 3). In this manner, the calorific value was measured at 0 to 200° C. for three measurements using the same toner at different holding temperatures. Then, the difference (amount of change) between the endothermic peak onset temperature at a holding temperature of 40° C. and the endothermic peak onset temperature at a holding temperature of 50° C., the difference (amount of change) between the endothermic peak onset temperature at a holding temperature of 40° C. and the endothermic peak onset temperature at a holding temperature of 60° C., and the difference (amount of change) between the endothermic peak onset temperature at a holding temperature of 50° C. and the endothermic peak onset temperature at a holding temperature of 60° C. were calculated. Of these amounts of change, the largest amount of change is shown in Table II below as the difference in endothermic peak onset temperature. The above measurements were carried out for each of Toners 1 to 12.

[0236] <Preparation of developer> 100 parts by mass of ferrite particles (volume-based median diameter: 50 μm (manufactured by Powder Tech Co., Ltd.)) and 4 parts by mass of methyl methacrylate-cyclohexyl methacrylate copolymer resin (volume-based median diameter of primary particles: 85 nm) were placed in a high-speed mixer with horizontal mixing blades and mixed for 15 minutes at a mixing blade peripheral speed of 8 m / s and a temperature of 30°C. The mixture was then heated to 120°C and stirred for 4 hours. The mixture was then cooled, and fragments of the methyl methacrylate-cyclohexyl methacrylate copolymer resin were removed using a 200-mesh sieve to produce a resin-coated carrier. This resin-coated carrier was mixed with each of the above toners 1 to 14 so that the toner concentration was 7% by mass relative to the total mass of the toner and carrier, to produce two-component developers 1 to 14, respectively.

[0237] [evaluation] <Image formation> For Examples 1 to 11 and Comparative Examples 1 to 3, developers 1 to 14 were sequentially loaded into a multifunction printer (bizhub PRESS C1070, manufactured by Konica Minolta, Inc. ("bizhub PRESS" is a registered trademark of the company), which was modified to allow the amount of toner adhesion to be freely set). Under normal temperature and humidity conditions (temperature 20°C, humidity 50% RH), the test paper (POD-157 gloss coated paper, manufactured by Oji Paper Co., Ltd.) was coated with 8.0 g / m 2 A solid image was output. In Example 12, an image was output using a multifunction printer (manufactured by Konica Minolta, Inc., bizhub PRESS C8000) that fixes a toner image in two stages. In Example 12, an unfixed image was collected using a multifunction printer (bizhub PRESS C1070, manufactured by Konica Minolta, Inc.) modified to allow collection of an image before fixing, and the unfixed image was fixed using a multifunction printer (imagePRESS V1000, manufactured by Canon Inc.) with its fixing unit (a fixing unit in which a fixing nip is formed by a non-rotating pressure pad) removed and modified so that it could be driven independently. The image output conditions were the same as in Example 1.

[0238] <Difference in gloss between front and back surfaces> Using a gloss meter (Murakami Color Research Laboratory GMX-203), the gloss of the front and back of the solid image area was measured, and the difference in gloss between the front and back was calculated. According to the following criteria, "A" was considered to be acceptable. (standard) A: The difference in gloss between the front and back surfaces is less than 3° B: The difference in gloss between the front and back surfaces is 3° or more

[0239] <Varnish application> (Applying varnish) On the image prepared above, varnish (UV VECTA Coat Varnish PC-3KW2, manufactured by T&K Corporation) was applied to a thickness of 5 μm using a bar coater. After that, a high-pressure mercury lamp is used to illuminate the image, with an integrated light intensity of 120-130mJ / cm 2The varnish was cured by irradiating it with ultraviolet light so that the varnish layer was formed. The varnish used contained a polymerizable monomer for varnish having a polymerizable functional group containing an ethylenic double bond and a photopolymerization initiator (radical polymerization initiator). (Evaluation of Coatability) The surface of the varnish layer on the resulting image was visually inspected to see if the varnish was clearly repelled. If it was not repelled, the number of pinholes in a 10 cm x 10 cm area was counted. Based on these results, the varnish's applicability was evaluated according to the following criteria. In the following criteria, "A," "B," and "C" were deemed acceptable. (standard) A: No pinholes were found within a 10cm x 10cm area. B: There were one to two tiny pinholes in a 10cm x 10cm area. C: There were 3 to 10 tiny pinholes in a 10cm x 10cm area. D: 11 or more pinholes or cracks in a 10cm x 10cm area

[0240] <Varnish adhesion> (Evaluation of Adhesion) A photograph of the surface of the varnish layer of the solid image obtained by the varnish coating test was taken at a magnification of 100x using a microscope (Keyence Corporation, Digital Microscope VHX-6000). The captured image was then binarized using image processing software (Nireco Corporation, LUSEX-AP). Next, polyimide tape (Mending Tape No. 810-3-12, manufactured by Sumitomo 3M Co., Ltd.) was lightly attached to the surface of the varnish layer, and the tape was rubbed back and forth 3.5 times at a pressure of 1 kPa. The tape was then peeled off from the varnish layer at an angle of 180° with a force of 200 g. After the tape was removed, a photograph of the surface of the varnish layer was taken at 100x magnification using a microscope (Keyence Corporation, Digital Microscope VHX-6000). The captured image was binarized using image processing software (Nireco Corporation, LUSEX-AP). The varnish peeling rate was then calculated using the following formula: Varnish removal rate [%] = (1 - area of the concealed area relative to the image area of the varnish after tape removal) / area of the concealed area relative to the resin image area due to powder before tape removal) × 100 Based on the calculated varnish peeling rate, the adhesion of the varnish was evaluated according to the following evaluation criteria, where "A" and "B" were considered acceptable. (standard) A: No varnish peeling was observed B: The varnish peeling rate was over 0% and less than 5%. C: The varnish peeling rate was 5% or more but less than 10%. D: The varnish peeling rate was 10% or more.

[0241] [Table 1]

[0242] [Table 2]

[0243] As shown by the above results, the toner of the present invention can reduce the difference in gloss between the front and back surfaces, and is also superior in varnish application and adhesion, compared to the toner of the comparative example. [Explanation of symbols]

[0244] 1. Image forming device 10 Heating belt 30 Image processing section 40 Image forming unit 41Y, 41M, 41C, 41K Image forming units 42 Intermediate transfer unit 43 Secondary transfer unit 50 Paper transport section 51 Paper feed section 51a, 51b, 51c Paper feed tray units 52 Paper output section 52a Paper ejection roller 53 Conveying path section 53a Registration roller pair 60 Fixing device 62 Fixing roller 63 Pressure Roller 70 Image reading unit 71 Paper feeder 72 Scanner 72a CCD sensor 100 Surface Treatment Equipment 110 Hopper 120 Mixing room 130 nozzles 140 Dispersed Airflow 150 Diffuser 160 Heat Treatment Room 170 Hot air swirling room 180 Cold air supply section 190 Discharge section 200 Surface Treatment Equipment 210 Heat Treatment Room 220 Introductory pipe 222 Protruding members 230 Supply pipe 240 Powder particle supply port 250 Hot air supply means 260 Hot air inlet 270 Swivel member 280 Distribution member 290 Cold air introduction section 411 Exposure equipment 412 Developing device 413 Electrophotographic photoreceptor 414 Charging device 415 Drum cleaning device 421 Intermediate transfer belt 422 Primary transfer roller 423, 431 Support roller 423A Backup Roller 426 Belt cleaning device 426a Elastic member 431A Secondary transfer roller 432 Secondary transfer belt 600 Fixing device 610 Pressure Pad 620 Pressure Roller 630 heated roller 640 Stair Roller 650 Heating Belt 660 Pressing member D Manuscript S paper

Claims

1. A toner for developing an electrostatic latent image, comprising toner base particles containing a binder resin and a release agent, the toner base particles contain a saturated hydrocarbon compound having 16 to 35 carbon atoms, the content of the saturated hydrocarbon compound is in the range of 1 to 1000 ppm by mass relative to the total mass of the toner for developing an electrostatic latent image, and The following condition (i) is met: A toner for developing electrostatic latent images. Condition (i): A measurement sample of the electrostatic latent image developing toner is held at a holding temperature of 40°C for 3 hours, cooled to 0°C at a temperature-lowering rate of -10°C / min, and then measured with a differential scanning calorimeter in the range of 0 to 200°C at a temperature-raising rate of 10°C / min (Measurement 1). Subsequently, using the measurement sample after Measurement 1, the temperature is lowered in the range of 200 to 0°C at a temperature-lowering rate of -10°C / min, and then a measurement is performed in the same manner as Measurement 1 except that the holding temperature is set to 50°C (Measurement 2). Subsequently, using the measurement sample after Measurement 2, the temperature is lowered in the range of 200 to 0°C at a temperature-lowering rate of -10°C / min, and then a measurement is performed in the same manner as Measurement 1 except that the holding temperature is set to 60°C (Measurement 3). In this case, the amount of change in the onset temperature of the endothermic peak observed at 20°C or higher on the DSC curve due to a change in the holding temperature is 2°C or less.

2. The release agent contains a hydrocarbon wax.

2. The toner for developing electrostatic latent images according to claim 1.

3. The binder resin contains polyester.

2. The toner for developing electrostatic latent images according to claim 1.

4. The binder resin contains a styrene-acrylic resin.

2. The toner for developing electrostatic latent images according to claim 1.

5. The toner base particles contain a crystalline substance other than the release agent.

2. The toner for developing electrostatic latent images according to claim 1.

6. The external additive contains strontium titanate.

2. The toner for developing electrostatic latent images according to claim 1.

7. The strontium titanate is particles having a number average primary particle size in the range of 20 to 200 nm.

7. The toner for developing electrostatic latent images according to claim 6.

8. The strontium titanate is particles having a number average primary particle size in the range of 30 to 150 nm.

8. The toner for developing electrostatic latent images according to claim 7.

9. A step of adhering the toner for developing an electrostatic latent image according to any one of claims 1 to 8 to a recording medium; and a step of fixing the attached electrostatic latent image developing toner to the recording medium. An image forming method comprising:

10. The fixing step is a step of fixing the electrostatic latent image developing toner to the recording medium in two stages.

10. The image forming method according to claim 9.

11. a step of applying varnish to the surface of the toner image formed by fixing the toner for developing an electrostatic latent image to form a varnish coat.

10. The image forming method according to claim 9.

12. 9. An image forming apparatus comprising at least a developing unit, a transfer unit, and a fixing unit, and forming a toner image on a recording medium using the toner for developing an electrostatic latent image according to claim 1, the fixing unit has a fixing nip portion, A fixing pad is used in the fixing nip portion. An image forming apparatus characterized by:

13. the fixing unit includes an endless belt that heats the toner image on the recording medium at the fixing nip; a rotating body that cooperates with the endless belt to form the fixing nip portion; a fixing pad that contacts an inner peripheral surface of the endless belt and sandwiches the endless belt between itself and the rotating body so as to form the fixing nip; a heating roller that contacts the inner circumferential surface of the endless belt and heats the endless belt; 13. The image forming apparatus according to claim 12.

Images