JP7497606B2 - Electrostatic charge developing toner and method for producing same - Google Patents

Description

The present invention relates to a toner for electrostatic charge development and a manufacturing method thereof. More specifically, the present invention relates to a toner for electrostatic charge development that has excellent low-temperature fixing properties, as well as heat-resistant storage properties and fixing separation properties, and a manufacturing method thereof.

Conventionally, methods of fixing electrostatic image developing toner (hereinafter sometimes simply referred to as "toner") include the pressure fixing method using only a pressure roll at room temperature, the contact heating fixing method using a heated roll, and non-contact fixing methods such as the oven fixing method using oven heating, the flash fixing method using a xenon lamp, the electromagnetic wave fixing method using microwaves, and the solvent fixing method using solvent vapor. Of these, the oven fixing method and the contact heating fixing method using heat are primarily used from the standpoint of reliability and safety.

In particular, the contact heating fixing method using a heating roll or belt is usually composed of a heating roll or belt equipped with a heat source and a pressure roll or belt, and fixes the toner image surface of the transfer material by passing it through the heating roll or belt surface while making pressure contact with it. In this way, the contact heating fixing method has the characteristic that the heating roll or belt surface comes into direct contact with the toner image surface of the transfer material, so that the thermal efficiency is effective and fixing can be performed quickly, and it is widely adopted.

However, in these thermal fixing methods, it is desirable to be able to fix at lower temperatures in order to reduce energy consumption as well as shorten the so-called warm-up time, which is the time it takes for the temperature of the fixing device to rise quickly to the operating temperature after the power is turned on and become ready for fixing.

In recent years, in order to thoroughly conserve energy, it has become desirable to stop powering the fixing unit when it is not in use, and since the temperature of the fixing material in the fixing unit must reach a temperature at which fixing can be performed instantly when power is turned on, fixing at even lower temperatures is required. In addition, by lowering the fixing temperature, it is possible to increase the print speed even with the same power consumption, and in the case of contact heating fixing methods, it is possible to extend the life of fixing materials such as heating rolls, which is also preferable from the perspective of cost.

However, in conventional methods, lowering the fixing temperature of the toner also lowers the glass transition point of the toner, making it difficult to achieve both low-temperature fixing and toner storage stability. Therefore, in order to achieve both low-temperature fixing and toner storage stability, it is necessary for the toner to have so-called sharp melt properties, in which the viscosity of the toner drops rapidly in the high temperature range while maintaining the glass transition point of the toner at a higher temperature.

The resins normally used in toners, i.e. amorphous resins, have a certain degree of range in terms of glass transition point, molecular weight, etc., so in order to obtain sharp melting properties, it is necessary to extremely uniform the composition and molecular weight of the resin. However, in order to obtain such resins, it becomes necessary to use special manufacturing methods or to adjust the molecular weight of the resin by processing it with chromatography, etc., which inevitably increases the cost of resin production and also produces unnecessary resin, which is undesirable from the perspective of recent environmental protection.

In order to achieve such low-temperature fixability, a method of using a crystalline resin as a binder resin has been considered (see, for example, Patent Documents 1 and 2). By using a crystalline resin, the hardness of the toner is maintained below the melting point of the crystals, and when the melting point is exceeded, the viscosity drops rapidly as the crystals melt, achieving low-temperature fixation. However, the crystalline resins described in these patent documents have the problem that they do not provide sufficient fixing performance to transfer materials.

Crystalline polyester resins are an example of crystalline resins that are expected to improve fixability to transfer materials. As an example of using crystalline polyester resins in toner, a method has been proposed in which a non-crystalline polyester with a glass transition temperature of 40°C or higher is mixed with a crystalline polyester with a melting point of 130°C to 200°C (see, for example, Patent Document 3). However, although this method has excellent grindability and blocking resistance, the melting point of the crystalline polyester resin is high, so it is not possible to achieve lower-temperature fixability than before.

In some cases, a crystalline resin with a melting point of 110°C or less is used, mixed with a non-crystalline resin, and used as a toner (see, for example, Patent Document 4). However, when a crystalline resin is mixed with a non-crystalline resin, the melting point of the toner drops, resulting in problems such as toner blocking and deterioration of powder fluidity.

Furthermore, in these toners, a release agent is added to the toner in order to improve the separation property (fixing separation property) when the fixing heating roll or belt separates from the toner image on the transfer material after the toner image is fixed to the transfer material. However, these toners have not been designed with consideration given to the balance between the low-temperature fixing property and the heat-resistant storage property of the toner with respect to the fixing separation property.

In other words, with previous technology, it was difficult to obtain a toner that satisfied all of the following requirements: low-temperature fixability, heat-resistant storage stability, and fixation separation properties.

Japanese Patent Publication No. 56-13943 Japanese Patent Publication No. 63-25335 Japanese Patent Publication No. 62-39428 Japanese Patent Publication No. 4-30014

The present invention was made in consideration of the above problems and circumstances, and the problem to be solved is to provide a toner for developing electrostatic images that has excellent low-temperature fixing properties, as well as heat-resistant storage properties and fixing separation properties, and a method for producing the same.

In the process of investigating the causes of the above problems, the present inventors have focused on the endothermic peaks of the fusion characteristics of the crystalline resin and the release agent when the toner, whose toner base particles contain a crystalline resin and a release agent, is measured by differential scanning calorimetry.Then, by adjusting the melting start temperature (endothermic peak rising temperature), melting point (endothermic peak temperature), and temperature difference between the melting start temperature and the melting point of the crystalline resin, as well as the temperature difference between the melting point of the crystalline resin and the melting point (endothermic peak temperature) of the release agent within a specific range, it has been found that a toner for developing electrostatic images having excellent low-temperature fixing properties, heat-resistant storage properties, and fixing separation properties can be provided, and the present invention has been completed.
That is, the problems associated with the present invention are solved by the following means.

1. A toner for developing an electrostatic image, comprising toner base particles containing a binder resin and a release agent,
The binder resin contains an amorphous resin and a crystalline resin,
the content of the crystalline resin is within a range of 4 to 31 parts by mass relative to 100 parts by mass of the binder resin, and the content of the release agent is within a range of 6 to 20 parts by mass relative to 100 parts by mass of the binder resin;
the crystalline resin includes a crystalline polyester resin, and the weight average molecular weight of the crystalline polyester resin is within a range of 4,000 to 10,000;
The toner for developing electrostatic images is characterized in that, when the rise temperature of the endothermic peak derived from the crystalline resin is _T1 °C, the endothermic peak temperature is _T2 °C, and the endothermic peak temperature derived from the release agent is _T3 °C during the first heating process in differential scanning calorimetry measurement of the toner for developing electrostatic images, the toner satisfies the following conditions (6), (7), (8), and ( 9 ):
(6) _T1 is in the range of 60 to 61°C.
(7) _T2 is in the range of 62-66°C.
(8) _T1 and _T2 have the following relationship:
_T2 ≦ _T1 +5° C.
( 9 ) _T2 and _T3 have the following relationship.
_T2 < _T3 ≦ _T2 + 10 ° C.

2. The toner for developing electrostatic images according to paragraph 1, characterized in that the toner base particles have a core particle and a shell layer that covers the core particle, and the crystalline resin is contained in the core particle.

3. The toner for developing an electrostatic image according to item 1 or 2, further satisfying the following condition (5) when the flow starting temperature of the toner for developing an electrostatic image measured by a flow tester is T _fb ° C.
(5) _T2 and _Tfb have the following relationship:
_T2 ≦ _Tfb ≦ _T2 +10° C.

4. The toner for developing electrostatic images according to any one of claims 1 to 3 , characterized in that the content of the crystalline resin is within a range of 10 to 20 parts by mass with respect to 100 parts by mass of the binder resin.

5. A method for producing the toner for developing electrostatic images according to any one of claims 1 to 4 , comprising the steps of:
a first step of heating and stirring fine particles containing the binder resin and the release agent in an aqueous medium to aggregate and fuse the particles, thereby obtaining a dispersion liquid containing a toner base particle precursor;
a second step of cooling the dispersion heated in the first step to a temperature of 30° C. or less at a temperature decreasing rate of 6° C./min or more;
a third step of maintaining the dispersion cooled in the second step at a temperature in the range of 57 to 62° C. for 30 minutes or more;
2. A method for producing a toner for developing an electrostatic image, comprising the steps of: producing the toner base particles by a method comprising the steps of:

According to the above-mentioned means of the present invention, it is possible to provide a toner for developing electrostatic images, which has excellent low-temperature fixing property, heat-resistant storage property, and fixing separation property, and a method for producing the same.
Although the mechanism by which the effects of the present invention are expressed or the mechanism of action has not been clarified, it is speculated as follows.

In electrophotographic systems, in order to reduce the viscosity of the toner to a level that allows it to be fixed within the extremely short fixing nip time of several tens of milliseconds, the key is to incorporate a crystalline resin into the binder resin of the toner base particles and maximize its plasticizing effect. In other words, it is necessary to quickly start melting the crystalline resin within the time it takes for the toner placed on the transfer material, such as paper, to finish passing through the fixing nip, and to quickly diffuse the molten crystalline resin throughout the entire toner base particle. Reducing the molecular weight of the crystalline resin is an effective way to increase the diffusion speed.

However, crystalline resins have a wide molecular weight distribution, many crystal defects occur due to the influence of other materials in the toner, and they have a wide melting point distribution from the perspective of compatibility with amorphous resins, etc., so lowering the melting point of a crystalline resin also lowers the melting initiation temperature (the temperature at which the component with the lowest melting point begins to melt).

In addition, if the toner is exposed to high temperatures during transportation or inside an electrophotographic system, it will aggregate, resulting in poor images and reduced developer properties due to poor fluidity. In order to prevent this type of toner aggregation, unless special measures are taken, heat-resistant storage at around 60°C is required. Therefore, in order to prevent toner aggregation as much as possible, it is necessary to eliminate crystalline resins with melting points that are lower than necessary.

Therefore, in the present invention, in order to minimize the influence on quality due to the deterioration of heat-resistant storage properties, the melting start temperature (endothermic peak rising temperature T ₁ ) of the crystalline resin when the toner is subjected to differential scanning calorimetry (hereinafter also referred to as "DSC") is set to 57°C or higher. Hereinafter, the chart obtained by DSC is referred to as "DSC curve". Furthermore, since the crystalline resin needs to melt quickly during fixing and quickly wet and spread into the amorphous resin, it is desirable that the temperature difference between T ₁ and the melting point corresponding to the end of melting (endothermic peak temperature T ₂ in the DSC curve) is as small as possible. If T ₁ is too low, the heat-resistant storage properties deteriorate, and if it is too high, the timing of the start of melting is delayed, so the effect of low-temperature fixability is weakened. In addition, it is preferable that T ₂ is low, but as described above, it is difficult to manufacture a crystalline resin with a narrow melting point distribution. If the melting point T ₂ of the crystalline resin in the toner becomes too high, the timing of the completion of melting is delayed, so the effect of low-temperature fixability is weakened. In the toner of the present invention, taking all of these factors into consideration, the range of _T1 is set to 57 to 62° C., the range of _T2 is set to 60 to 70° C., and _T2 ≦ _T1 +12° C., thereby ensuring heat-resistant storage stability and low-temperature fixability.

Furthermore, in the toner of the present invention, in order to ensure heat-resistant storage stability and fixation separation property, a release agent is contained in the toner base particles, and the melting point of the release agent in the toner (endothermic peak temperature _T3 in the DSC curve) and the melting point _T2 of the crystalline resin have a relationship of _T2 < _T3 ≦ _T2 + 15° C. The mechanism of action is considered to be as follows.

When the temperature rises due to heating in the fixing nip, the crystalline resin melts while absorbing heat, and is fixed by being compatible with the amorphous resin. In the DSC curve of the toner, if there is a region where the endothermic peak derived from the release agent overlaps with the endothermic peak derived from the crystalline resin, the thermal energy transmitted from the fixing member is consumed not only for melting the crystalline resin but also for melting the release agent, and the melting of the crystalline resin is delayed, so that the speed at which the plasticizing effect of the crystalline resin is exerted decreases, and the effect of low-temperature fixing is reduced. If the melting point _T3 of the release agent is equal to or lower than the melting point _T2 of the crystalline resin, the amount of low-melting point components below the specified temperature ( _T1 in the present invention, 57°C or higher) increases, and the heat-resistant storage property deteriorates. Therefore, in the toner of the present invention, _T2 < _T3 .

The ability to separate the toner image on the transfer material from the fixing belt during fixing can be expressed in terms of the relationship between the internal cohesive force of the molten toner and the adhesive force between the molten toner and the fixing belt. If the internal cohesive force of the toner is smaller than the adhesive force between the molten toner and the fixing belt, the molten toner will have difficulty separating from the belt, causing separation failure. In the case of minor separation failure, the transfer material can be peeled off from the fixing belt, but the sparse presence of release agent on the fixed image may cause image failure.

When the viscosity of the amorphous resin drops suddenly due to the plasticizing effect caused by the melting of the crystalline resin, and the internal cohesive force of the toner drops significantly, if the melting point _T3 of the release agent is significantly higher than the melting point _T2 of the crystalline resin, the timing for lowering the adhesive force between the toner and the fixing belt is significantly delayed, causing poor separation. Therefore, in the toner of the present invention, the melting point _T3 of the release agent is set to within the melting point _T2 of the crystalline resin + 15°C.

The toner for developing electrostatic images of the present invention is a toner for developing electrostatic images containing toner base particles which contain a binder resin and a release agent, and is characterized in that the binder resin contains an amorphous resin and a crystalline resin, and when the rise temperature of the endothermic peak derived from the crystalline resin is _T1 °C, the endothermic peak temperature is _T2 °C, and the endothermic peak temperature derived from the release agent is _T3 °C during the first heating process when the toner for developing electrostatic images is subjected to differential scanning calorimetry, the above conditions (1), (2), (3), and (4) are satisfied.
This feature is a technical feature common to each of the following embodiments.

In an embodiment of the present invention, from the viewpoint of more effectively achieving the effects of the present invention, particularly the effect of heat-resistant storage properties, it is preferable that the toner base particles have a core particle and a shell layer that covers the core particle, and that the crystalline resin is contained in the core particle.

As an embodiment of the toner of the present invention, from the viewpoint of more effectively exerting the effects of the present invention, particularly the effect of low-temperature fixability, it is preferable that the toner further satisfies the above condition (5) when the flow start temperature of the toner measured by a flow tester is T _fb °C.

The _Tfb of the toner is an index of how quickly the crystalline resin in the toner diffuses into and becomes compatible with the amorphous resin after melting, and how quickly the viscosity of the amorphous resin can be reduced at a low temperature. By satisfying the above condition (5), the low-temperature fixability of the toner can be improved.

In an embodiment of the toner of the present invention, it is preferable that the above conditions (6), (7), and (8) are further satisfied in order to more effectively exert the effects of the present invention.

In an embodiment of the toner of the present invention, from the viewpoint of achieving a higher effect of the present invention, the crystalline resin preferably contains a crystalline polyester resin, and the weight average molecular weight of the crystalline polyester resin is preferably within the range of 2,000 to 25,000, and more preferably within the range of 4,000 to 10,000. By having the weight average molecular weight of the crystalline polyester resin within the above range, the diffusion rate of the crystalline polyester resin into the amorphous resin can be kept within an appropriate range.

In an embodiment of the toner of the present invention, from the viewpoint of achieving a higher effect of the present invention, it is preferable that the content of the crystalline resin is within a range of 4 to 31 parts by mass per 100 parts by mass of the binder resin, and the content of the release agent is within a range of 6 to 20 parts by mass per 100 parts by mass of the binder resin. Furthermore, it is more preferable that the content of the crystalline resin is within a range of 10 to 20 parts by mass per 100 parts by mass of the binder resin.

The method for producing a toner for developing electrostatic images of the present invention is a method for producing a toner for developing electrostatic images of the present invention, characterized in that the toner base particles are produced by a method including the first to third steps described above.

The present invention, its components, and the forms and modes for implementing the present invention are described in detail below. Note that in this application, "~" is used to mean that the numerical values before and after it are included as the lower and upper limits.

[Toner for developing electrostatic images]
The toner of the present invention contains toner base particles containing a binder resin and a release agent. The toner may contain an external additive attached to the surface of the toner base particles in addition to the toner base particles. The binder resin contained in the toner base particles contains an amorphous resin and a crystalline resin. The toner base particles have a form in which, for example, a domain of a crystalline resin and a domain of a release agent are dispersed in a matrix composed of an amorphous resin.

The toner of the present invention is characterized in that, when the rise temperature of the endothermic peak derived from the crystalline resin is _T1 °C, the endothermic peak temperature is _T2 °C, and the endothermic peak temperature derived from the release agent is _T3 °C during the first heating process when the toner is subjected to differential scanning calorimetry, the toner satisfies the following conditions (1), (2), (3), and (4):

(1) _T1 is within the range of 57 to 62°C.
(2) _T2 is in the range of 60 to 70°C.
(3) _T1 and _T2 have the following relationship:
_T2 ≦ _T1 +12° C.
(4) _T2 and _T3 have the following relationship:
_T2 < _T3 ≦ _T2 + 15°C

In the present invention, the DSC of the toner can be performed in accordance with JIS K 7121-1987. A general DSC device can be used as the measuring device, for example, "Diamond DSC" (manufactured by PerkinElmer).

The measurement procedure involves sealing 3.0 mg of a measurement sample (toner) in an aluminum pan (KIT NO. B0143013) and setting it in a holder. An empty aluminum pan is used as a reference. The measurement conditions are a measurement temperature of 0° C. to 100° C. and a temperature rise rate of 10° C./min. T ₁ , T ₂ and T ₃ are temperatures (° C.) determined as follows during the first temperature rise process. In this specification, the endothermic peak derived from the crystalline resin and the endothermic peak derived from the release agent refer to the endothermic peaks observed during the first temperature rise process in the DSC of the toner.

_T1 and _T2 are temperatures associated with the endothermic peaks derived from the crystalline resin, and _T3 is a temperature associated with the endothermic peak derived from the release agent. The endothermic peaks can be identified based on elemental analysis of the toner, or the like. Alternatively, they can be identified based on the melting points of the raw material components used in the production of the toner. For example, when the melting point of the crystalline resin as a raw material component used in the production of the toner is lower than the melting point of the release agent, the endothermic peak derived from the crystalline resin is measured at a lower temperature side than the endothermic peak derived from the release agent in the DSC curve of the toner.

_T1 is the onset temperature of the endothermic peak (melting peak) derived from the crystalline resin. The onset temperature of the endothermic peak is generally defined as the extrapolated melting onset temperature, and is the temperature at the intersection of a straight line extending the low-temperature side baseline to the high-temperature side and a tangent drawn at the point where the slope of the curve on the low-temperature side of the melting peak is maximum.

_T2 and _T3 are the endothermic peak temperature derived from the crystalline resin and the endothermic peak temperature derived from the release agent, respectively. The endothermic peak temperature (melting peak temperature) is a temperature generally considered to be the melting point, and is the temperature at the apex of the endothermic peak.

The effects of satisfying the above conditions (1), (2), (3), and (4) are as described above. With respect to condition (1), it is preferable that _T1 satisfies the following condition (6). With respect to condition (2), it is preferable that _T2 satisfies the following condition (7). With respect to condition (3), it is preferable that the relationship between _T1 and _T2 satisfies the following condition (8). In the toner of the present invention, it is preferable that all of conditions (6) to (8) are satisfied.

(6) _T1 is in the range of 60 to 61°C.
(7) _T2 is within the range of 62 to 66°C.
(8) _T1 and _T2 have the following relationship:
_T2 ≦ _T1 +5° C.

Furthermore, with regard to condition (4), it is preferable that the relationship between _T2 and _T3 satisfies the relationship _T3 ≦ _T2 + 10° C. as condition (9).

In addition to satisfying the above conditions (1) to (4), the toner of the present invention preferably satisfies the following condition (5) when the toner flow start temperature measured by a flow tester is T _fb ° C.
(5) _T2 and _Tfb have the following relationship:
_T2 ≦ _Tfb ≦ _T2 +10° C.

In the present invention, the toner flow start temperature T _fb is measured by a flow tester, for example, as follows.

Specifically, first, in an environment of 20°C and 50% RH, 1.1 g of a measurement sample (toner) is placed in a petri dish and flattened, and left for 12 hours or more, and then a molding machine "SSP-10A" (manufactured by Shimadzu Corporation) is used to pressurize the sample with a force of 3820 kg/ ^cm2 for 30 seconds to produce a cylindrical molded sample with a diameter of 1 cm. Next, in an environment of 24°C and 50% RH, this molded sample is extruded from a hole (1 mm diameter x 1 mm) of a cylindrical die using a piston with a diameter of 1 cm from the end of preheating under conditions of a load of 196 N (20 kgf), a starting temperature of 45°C, a preheating time of 300 seconds, and a heating rate of 6°C/min using a flow tester "CFT-500D" (manufactured by Shimadzu Corporation), and the value measured with a melting temperature measurement method using a heating method with an offset value set to 5 mm is defined as the outflow start temperature T _fb .

When the relationship between _Tfb and _T2 measured in this manner satisfies the above condition (5), the low temperature fixability of the toner can be improved. With respect to the condition (5), it is more preferable that the relationship between _Tfb and _T2 satisfies the condition (10) of _Tfb ≦ _T2 + 5°C.

The components of the toner that have the above characteristics are described below.

<Toner Base Particles>
The toner base particles according to the toner of the present invention contain a binder resin and a release agent, and the binder resin contains an amorphous resin and a crystalline resin. In the toner of the present invention, the properties related to the above conditions (1) to (10) are properties determined by the toner base particles. In other words, the properties related to the above conditions (1) to (10) in the toner of the present invention are properties that are not influenced by external additives. Therefore, the properties related to the above conditions (1) to (10) in the toner of the present invention can be adjusted by appropriately selecting the types and compositions of the amorphous resin and crystalline resin as the binder resin and the release agent contained in the toner base particles, and appropriately adjusting the production method.

The form of the toner base particles is not particularly limited, and examples thereof include a single-layer structure, a core-shell structure, and a multi-layer structure. In particular, from the viewpoint of ensuring heat-resistant storage, a core-shell structure is preferable. Specifically, the core-shell structure refers to a structure having a core particle and a shell layer that covers the core particle. Hereinafter, the toner base particles having a core-shell structure are also referred to as "core-shell particles." Note that the shell layer is not limited to one that completely covers the core particle, and a part of the surface of the core particle may be exposed.

When the toner base particles are core-shell particles, it is preferable that the above-mentioned crystalline resin is contained in the core particles. More specifically, an embodiment is one in which the core particles contain a part of the amorphous resin, a crystalline resin, and a release agent, and the shell layer is composed of the remainder of the amorphous resin. The amorphous resin contained in the core particles and the amorphous resin constituting the shell layer may be the same or different.

The toner base particles may contain internal additives such as colorants and charge control agents in addition to the binder resin and release agent. When the toner base particles are core-shell particles, these are preferably added internally to the core particles.

[Binder Resin]
In the toner base particles according to the present invention, the binder resin contains an amorphous resin and a crystalline resin.

(Crystalline Resin)
As the crystalline resin according to the present invention, a crystalline resin conventionally known in the art can be used. As the crystalline resin, a crystalline polyester resin is preferable. When the toner base particles are core-shell particles, the crystalline resin is preferably contained in the core particles.

The crystalline resin according to the present invention is a resin that has a clear endothermic peak rather than a stepwise endothermic change in differential scanning calorimetry (DSC). A clear endothermic peak specifically means a peak whose half-width is within 15°C when measured in differential scanning calorimetry (DSC) at a heating rate of, for example, 10°C/min.

In the present invention, the melting point _Tmp of the crystalline resin used in the preparation of the toner base particles is preferably within a range of 63 to 75° C., and more preferably within a range of 63 to 70° C. When the melting point _Tmp of the crystalline resin is within the above range, it is easy to adjust _T2 of the obtained toner within the above range.

The melting point _Tmp of the crystalline resin can be determined, for example, as the temperature at the apex of the melting peak (endothermic peak) from the DSC curve of the crystalline resin in the same manner as determining _T2 from the DSC curve obtained by DSC of the toner.

The crystalline resin used in the production of the toner base particles is melted and recrystallized, for example, by heating and cooling during the production of the toner base particles. Therefore, the crystalline resin as a raw material and the crystalline resin in the toner base particles may have different DSC behaviors. In the above conditions (1) to (10) for the toner of the present invention, _T1 and _T2 used are values based on the DSC behavior of the crystalline resin in the toner base particles.

The content of the crystalline resin in the binder resin is preferably 4 to 31 parts by mass, and more preferably 10 to 20 parts by mass, per 100 parts by mass of the binder resin.

By keeping the content of the crystalline resin within the above range, it is possible to introduce an amount of crystalline resin into the toner base particles sufficient to achieve low-temperature fixability.

If the content of the crystalline resin is less than the lower limit of the above range, the low-temperature fixability may not be sufficient. If the content of the crystalline resin is less than the lower limit of the above range, the compatibility with the amorphous resin is improved, and the crystalline resin is less likely to crystallize, so that the glass transition point (Tg) of the toner base particles is lowered, and it may be difficult to ensure heat-resistant storage. The Tg of the toner base particles can be measured by the same method as the method for measuring the Tg of the amorphous resin (hereinafter referred to as "Tg _p ") described later.

On the other hand, if the content of the crystalline resin exceeds the upper limit of the above range, a large amount of latent heat is lost during melting, making it difficult for the temperature of the entire toner to increase, which may result in poor fixability.

(Crystalline polyester resin)
The crystalline polyester resin is a resin in the category of the above-mentioned crystalline resin among known polyester resins obtained by a polycondensation reaction between a divalent or higher carboxylic acid (polycarboxylic acid) and a divalent or higher alcohol (polyalcohol).

In this specification, the term "polyester resin" refers to both resins consisting of polyester polymerized segments and modified resins to which other components are bonded at a ratio of 50% by mass or less. It is preferable to use vinyl polymerized segments as the other components to be bonded to the polyester polymerized segments.

A polycarboxylic acid is a compound containing two or more carboxy groups in one molecule. Examples of polycarboxylic acids for forming crystalline polyester resins include saturated aliphatic dicarboxylic acids such as succinic acid; alicyclic dicarboxylic acids such as cyclohexanedicarboxylic acid; aromatic dicarboxylic acids such as phthalic acid, isophthalic acid, and terephthalic acid; trivalent or higher polycarboxylic acids such as trimellitic acid and pyromellitic acid; and anhydrides of these carboxylic acid compounds, or alkyl esters having 1 to 3 carbon atoms. These may be used alone or in combination of two or more.

A polyhydric alcohol is a compound containing two or more hydroxyl groups in one molecule. Examples of polyhydric alcohols for forming a crystalline polyester resin include aliphatic diols such as 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, neopentyl glycol, and 1,4-butenediol; and trihydric or higher polyhydric alcohols such as glycerin, pentaerythritol, trimethylolpropane, and sorbitol. These may be used alone or in combination of two or more.

As for the crystalline polyester resin according to the present invention, from the viewpoint of keeping the diffusion rate of the crystalline polyester resin into the amorphous resin within an appropriate range as described above, it is preferable that the weight average molecular weight is within the range of 2,000 to 25,000, and more preferably within the range of 4,000 to 10,000.

If the weight average molecular weight of the crystalline polyester resin is less than the lower limit of the above range, the compatibility with the amorphous resin becomes too high in the manufacturing process of the toner base particles, making it difficult to promote crystallization and to increase the molecular weight to the specified T _2. If the weight average molecular weight of the crystalline polyester resin exceeds the upper limit of the above range, the diffusion speed into the amorphous resin decreases significantly, making it difficult to quickly reduce the viscosity of the amorphous resin beyond T ₂ , and the low-temperature fixability decreases.

In this specification, the weight average molecular weight of the crystalline polyester resin is a value measured by gel permeation chromatography (GPC). The weight average molecular weight of the crystalline polyester resin by GPC can be measured, for example, by the following method.

Specifically, the apparatus "HLC-8120GPC" (manufactured by Tosoh Corporation) and the column "TSKguard column + TSKgel Super HZ-M triple column" (manufactured by Tosoh Corporation) are used. While maintaining the column temperature at 40°C, tetrahydrofuran (THF) is passed as a carrier solvent at a flow rate of 0.2 mL/min. The measurement sample (crystalline resin) is dissolved in tetrahydrofuran to a concentration of 1 mg/mL under dissolution conditions of processing for 5 minutes using an ultrasonic disperser at room temperature, and then processed with a membrane filter with a pore size of 0.2 μm to obtain a sample solution. 10 μL of the above sample solution is injected into the apparatus together with the above carrier solvent, detected using a refractive index detector (RI detector), and the molecular weight distribution of the measurement sample is calculated using a calibration curve measured using monodisperse polystyrene standard particles. 10 points of polystyrene are used for the calibration curve measurement.

(Amorphous Resin)
The amorphous resin constituting the binder resin is constituted as a main component in the binder resin, specifically as a component that occupies 50 mass% or more. The amorphous resin according to the present invention refers to a resin that does not show a clear endothermic peak in differential scanning calorimetry (DSC). The "clear endothermic peak" is as explained for the crystalline resin. The content of the amorphous resin in the binder resin is preferably 70 to 96 parts by mass, more preferably 80 to 90 parts by mass, per 100 parts by mass of the binder resin.

By keeping the content of the amorphous resin within the above range, when it is used as a binder resin together with a crystalline resin, particularly a crystalline polyester resin, it is possible to ensure sufficient fixing properties, sufficient heat-resistant storage properties of the toner, and sufficient heat resistance of the fixed image.

There are no particular limitations on the amorphous resin. Specifically, vinyl resins such as styrene resin, acrylic resin, and styrene-acrylic copolymer resin (hereinafter also referred to as "styrene-acrylic resin"), and amorphous polyester resin are preferred from the viewpoints of fixability, heat-resistant storage of the toner, and heat resistance of the fixed image. Specifically, styrene-acrylic resin is a copolymer of monomers including a styrene-based monomer and a (meth)acrylic acid ester-based monomer. In this specification, "acrylic resin" includes methacrylic resin in its category. "(Meth)acrylic acid" means at least one of acrylic acid and methacrylic acid.

As the amorphous resin, vinyl resins other than those mentioned above, such as olefin-based resins, polyamide-based resins, polycarbonate resins, polyether resins, polyvinyl acetate resins, polysulfone resins, epoxy resins, polyurethane resins, urea resins, etc. can also be used. The amorphous resins can be used alone or in combination of two or more.

Examples of monomers for forming vinyl resins such as styrene resin, acrylic resin, and styrene-acrylic resin include vinyl monomers. Examples of vinyl monomers that can be used include the following. Vinyl monomers can be used alone or in combination of two or more types.

(1) Styrene-Based Monomers Styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, α-methylstyrene, p-phenylstyrene, p-ethylstyrene, 2,4-dimethylstyrene, p-tert-butylstyrene, p-n-hexylstyrene, p-n-octylstyrene, p-n-nonylstyrene, p-n-decylstyrene, p-n-dodecylstyrene, and derivatives thereof.

(2) (meth)acrylic acid ester monomers: methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, isopropyl (meth)acrylate, isobutyl (meth)acrylate, t-butyl (meth)acrylate, n-octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, stearyl (meth)acrylate, lauryl (meth)acrylate, phenyl (meth)acrylate, diethylaminoethyl (meth)acrylate, dimethylaminoethyl (meth)acrylate, and derivatives thereof.

(3) Vinyl esters: vinyl propionate, vinyl acetate, vinyl benzoate, etc.

(4) Vinyl ethers: vinyl methyl ether, vinyl ethyl ether, etc.

(5) Vinyl ketones Vinyl methyl ketone, vinyl ethyl ketone, vinyl hexyl ketone, etc.

(6) N-Vinyl Compounds N-vinylcarbazole, N-vinylindole, N-vinylpyrrolidone, and the like.

(7) Others Vinyl compounds such as vinylnaphthalene and vinylpyridine, acrylic acid or methacrylic acid derivatives such as acrylonitrile, methacrylonitrile, and acrylamide.

As the vinyl monomer, it is preferable to use a vinyl monomer having an ionic dissociation group such as a carboxy group, a sulfonic acid group, or a phosphate group. Specific examples include the following.

Examples of vinyl monomers having a carboxy group include acrylic acid, methacrylic acid, maleic acid, itaconic acid, cinnamic acid, fumaric acid, maleic acid monoalkyl esters, and itaconic acid monoalkyl esters. Examples of vinyl monomers having a sulfonic acid group include styrene sulfonic acid, allylsulfosuccinic acid, and 2-acrylamido-2-methylpropanesulfonic acid. Examples of vinyl monomers having a phosphoric acid group include acidophosphooxyethyl methacrylate.

Furthermore, polyfunctional vinyls can be used as the vinyl monomer to make the vinyl resin have a crosslinked structure. Examples of polyfunctional vinyls include divinylbenzene, ethylene glycol dimethacrylate, ethylene glycol diacrylate, diethylene glycol dimethacrylate, diethylene glycol diacrylate, triethylene glycol dimethacrylate, triethylene glycol diacrylate, neopentyl glycol dimethacrylate, and neopentyl glycol diacrylate.

Amorphous polyester resins are known polyester resins obtained by polycondensation of divalent or higher carboxylic acids (polycarboxylic acids) and divalent or higher alcohols (polyhydric alcohols), and are classified as amorphous resins.

Examples of polycarboxylic acids for forming the amorphous polyester resin include saturated fatty acids such as oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelic acid, sebacic acid, 1,9-nonanedicarboxylic acid, 1,10-decanedicarboxylic acid, 1,11-undecanedicarboxylic acid, 1,12-dodecanedicarboxylic acid, 1,13-tridecanedicarboxylic acid, 1,14-tetradecanedicarboxylic acid, 1,16-hexadecanedicarboxylic acid, and 1,18-octadecanedicarboxylic acid. aromatic dicarboxylic acids such as phthalic acid, isophthalic acid, terephthalic acid, and naphthalenedicarboxylic acid; unsaturated aliphatic dicarboxylic acids such as maleic acid, fumaric acid, itaconic acid, citraconic acid, glutaconic acid, isododecenylsuccinic acid, n-dodecenylsuccinic acid, and n-octenylsuccinic acid; and polyvalent carboxylic acids having three or more valences such as trimellitic acid, pyromellitic acid, naphthalenetricarboxylic acid, naphthalenetetracarboxylic acid, pyrenetricarboxylic acid, and pyrenetetracarboxylic acid. These may be used alone or in combination of two or more.

Examples of polyhydric alcohols for forming amorphous polyester resins include 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, and 1,18-octadecane. Examples of such polyols include aliphatic diols such as diols and 1,20-eicosanediol; bisphenols such as bisphenol A and bisphenol F, and alkylene oxide adducts of bisphenols such as their ethylene oxide adducts and propylene oxide adducts; and trivalent or higher polyols such as glycerin, pentaerythritol, hexamethylol melamine, hexaethylol melamine, tetramethylol benzoguanamine, and tetraethylol benzoguanamine. These may be used alone or in combination of two or more.

The glass transition point (Tg _p ) of the amorphous resin, as the Tg of the amorphous resin used as the raw material for the toner base particles, is preferably about 30 to 50° C. When Tg _p is in the above range, the low-temperature fixability of the obtained toner is ensured.

In the present invention, the glass transition point (Tg _p ) of the amorphous resin is a value measured using a "Diamond DSC" (manufactured by PerkinElmer). The measurement procedure is as follows: 3.0 mg of the measurement sample (amorphous resin) is sealed in an aluminum pan and set in a holder. An empty aluminum pan is used as a reference. The measurement conditions are a measurement temperature of 0°C to 100°C, a temperature increase rate of 10°C/min, a temperature decrease rate of 10°C/min, and a heat-cool-heat temperature control, and analysis is performed based on the data (DSC curve) in the 2nd heat. The first inflection point in the DSC curve is taken as the glass transition point (Tg).

The molecular weight of the amorphous resin measured by gel permeation chromatography (GPC) is preferably a weight average molecular weight (Mw) of 10,000 to 50,000, more preferably 25,000 to 35,000. Also, the number average molecular weight (Mn) is preferably 5,000 to 20,000, more preferably 6,500 to 12,000.

By having the molecular weight of the amorphous resin within the above range, low-temperature fixability and fixation separation properties can be reliably obtained. If the molecular weight of the amorphous resin exceeds the upper limit of the above range, there is a risk that sufficient low-temperature fixability will not be obtained. On the other hand, if the molecular weight of the amorphous resin is below the lower limit of the above range, there is a risk that sufficient fixation separation properties will not be obtained.

The molecular weight of the amorphous resin is measured by gel permeation chromatography (GPC) in the same manner as for the crystalline polyester resin, except that an amorphous resin is used as the measurement sample.

When the toner base particles are core-shell particles, the binder resin may be configured such that the core particles contain a portion of the amorphous resin and a crystalline resin, and the shell layer is configured with the remainder of the amorphous resin, as described above. The amorphous resin that constitutes the core particles and the amorphous resin that constitutes the shell layer may be the same or different.

As the amorphous resin constituting the core particles, among the above, vinyl resin is preferable, and styrene acrylic resin is preferable. Furthermore, as the resin constituting the shell layer, amorphous resin is preferable, and amorphous polyester resin and vinyl resin are more preferable, and amorphous polyester resin is particularly preferable.

When the toner base particles are core-shell particles, the content of the resin constituting the shell layer is preferably 5 to 30% by mass relative to the total amount of the binder resin contained in the toner base particles.

〔Release agent〕
The toner base particles according to the present invention contain a release agent in order to ensure the fixing and separating properties of the toner. When the toner base particles are core-shell particles, the release agent is preferably contained in the core particles.

The release agent used in the production of the toner base particles is, for example, composed of a wax, and has a melting point. The melting point _Tmw of the release agent used in the production of the toner base particles is preferably in the range of 70 to 95°C, and more preferably in the range of 75 to 85°C. When the melting point _Tmw of the release agent is in the above range, the relationship between _T3 and _T2 in the obtained toner is more likely to satisfy the above condition (4). Furthermore, in order to satisfy the above condition (4) in the obtained toner, the melting point _Tmw of the release agent is preferably higher than the melting point _Tmp of the crystalline resin.

The melting point _Tmw of the release agent can be determined, for example, as the temperature at the apex of the melting peak (endothermic peak) from the DSC curve of the release agent in the same manner as determining _T3 from the DSC curve obtained by DSC of the toner. Note that _T3 is a value based on the DSC behavior of the release agent in the toner base particles. Specifically, _T3 is the endothermic peak temperature derived from the release agent obtained from the DSC curve of the toner. Therefore, the melting point _Tmw of the release agent and _T3 may differ in some cases.

As the release agent, an ester wax or a hydrocarbon wax can be used. Such waxes may be synthesized or may be commercially available and purified. As a purification method, a method of dissolving the wax in n-hexane or heptane and recrystallizing the wax can be mentioned. Furthermore, these release agents may be used alone or in combination.

Examples of ester waxes include carnauba wax, montan wax, behenic acid behenate, trimethylolpropane tribehenate, pentaerythritol tetrabehenate, pentaerythritol diacetate dibehenate, glycerin tribehenate, 1,18-octadecanediol distearate, tristearyl trimellitate, and distearyl maleate.

Examples of hydrocarbon waxes include polyolefin waxes such as polyethylene wax and polypropylene wax, petroleum-derived paraffin wax, microcrystalline wax, and synthetic waxes such as Fischer-Tropsch wax and polyethylene wax.

The content of the release agent is preferably 1 to 20 parts by mass, and more preferably 5 to 12 parts by mass, per 100 parts by mass of the binder resin in the toner base particles. By ensuring that the content of the release agent in the toner base particles is within the above range, both separation and fixation properties can be reliably achieved.

[Coloring Agent]
The toner base particles may contain a colorant as an optional component. When the toner base particles are core-shell particles, the colorant is preferably contained in the core particles. When the toner base particles are configured to contain a colorant, various known colorants such as carbon black, black iron oxide, dyes, and pigments can be used as the colorant.

Examples of carbon black include channel black, furnace black, acetylene black, thermal black, and lamp black, and examples of black iron oxide include magnetite, hematite, and titanium iron trioxide.

Examples of dyes include C.I. Solvent Red 1, 49, 52, 58, 63, 111, and 122, C.I. Solvent Yellow 19, 44, 77, 79, 81, 82, 93, 98, 103, 104, 112, and 162, C.I. Solvent Blue 25, 36, 60, 70, 93, and 95.

Examples of pigments include C.I. Pigment Red 5, 48:1, 48:3, 53:1, 57:1, 81:4, 122, 139, 144, 149, 150, 166, 177, 178, 222, 238, 269, C.I. Pigment Orange 31, 43, C.I. Pigment Yellow 14, 17, 74, 93, 94, 138, 155, 156, 158, 180, 185, C.I. Pigment Green 7, C.I. Pigment Blue 15:3, 60, etc.

The colorants for each color may be used alone or in combination of two or more.

The colorant content is preferably 1 to 10 parts by mass, and more preferably 2 to 8 parts by mass, per 100 parts by mass of the binder resin in the toner base particles. If the colorant content is below the lower limit of the above range, the resulting toner may not have the desired coloring power, while if the colorant content exceeds the upper limit of the above range, the colorant may become detached or adhere to the carrier, affecting the charging properties.

[Charge control agent]
The toner base particles according to the present invention may contain a charge control agent, if necessary.

The charge control agent is not particularly limited as long as it is a substance that can provide a positive or negative charge through frictional charging, and various known positive charge control agents and negative charge control agents can be used.
The content of the charge control agent is preferably 0.01 to 30 parts by mass, and more preferably 0.1 to 10 parts by mass, based on 100 parts by mass of the binder resin.

<External Additives>
In the toner of the present invention, the toner base particles may be used as they are as a toner, or an external additive may be attached to the surface of the toner base particles. The external additive is used to improve flowability, chargeability, cleaning properties, etc. Examples of the external additive include fine particles such as known inorganic fine particles and organic fine particles, and lubricants. Various types of external additives may be used in combination.

Preferred examples of inorganic fine particles include inorganic fine particles made of silica, titania (titanium oxide), alumina, strontium titanate, zinc titanate, calcium titanate, etc. Two or more of these may be combined. The number average primary particle size of the inorganic fine particles is preferably about 10 to 100 nm. The number average primary particle size of the inorganic fine particles can be measured, for example, by calculating the horizontal Feret diameters of 100 particles using an image processing analyzer or the like for an image photographed using a scanning electron microscope (SEM) and calculating the average value.

These inorganic fine particles may be hydrophobized by surface modification as necessary. By using hydrophobized inorganic fine particles, for example, adhesion of white toner base particles (Am) to each other due to moisture adsorption caused by hydroxyl groups present on the surface of inorganic oxide particles can be suppressed.

Examples of surface modifiers used to modify the surface of inorganic fine particles include silane coupling agents and titanium coupling agents. Preferred silane coupling agents include dimethyldimethoxysilane, hexamethyldisilazane (HMDS), methyltrimethoxysilane, isobutyltrimethoxysilane, and decyltrimethoxysilane. In addition, higher fatty acids and silicone oils can also be used as surface modifiers. As silicone oils, organosiloxane oligomers, octamethylcyclotetrasiloxane, or cyclic compounds such as decamethylcyclopentasiloxane, tetramethylcyclotetrasiloxane, and tetravinyltetramethylcyclotetrasiloxane, and linear or branched organosiloxanes can be used.

The amount of external additive added is preferably 0.05 to 5 parts by weight, and more preferably 0.1 to 3 parts by weight, per 100 parts by weight of the toner base particles.

<Toner Form>
The toner of the present invention preferably has the following average particle size and average circularity. Usually, the average particle size and average circularity of the toner may be treated as being the same as the average particle size and average circularity of the toner base particles. In other words, even when the toner of the present invention contains an external additive, the effect of adding the external additive on the particle size and circularity of the toner base particles is as small as the range of measurement error.

[Average particle size of toner]
In the toner of the present invention, the average particle size is preferably, for example, 3 to 10 μm, more preferably 5 to 8 μm, in terms of the volume-based median diameter. The average particle size of the toner can be controlled by the production conditions. For example, when the toner base particles are produced by the emulsion polymerization aggregation method described below, the average particle size can be controlled by the concentration of the aggregating agent used during production, the amount of organic solvent added, the fusion time, the composition of the binder resin, and the like.

By having the volume-based median diameter fall within the above range, it is possible to faithfully reproduce extremely small dot images at the 1200 dpi level.

The volumetric median diameter of the toner is measured and calculated using a measuring device that is a "Multisizer 3" (manufactured by Beckman Coulter) connected to a computer system equipped with data processing software "Software V3.51."

Specifically, 0.02 g of the measurement sample (toner) is added to 20 mL of surfactant solution (a surfactant solution prepared by diluting, for example, a neutral detergent containing a surfactant component with pure water 10 times for the purpose of dispersing the toner) and allowed to mix, then ultrasonic dispersion is performed for 1 minute to prepare a toner dispersion, and this toner dispersion is pipetted into a beaker containing an "ISOTONII" (manufactured by Beckman Coulter) in a sample stand until the concentration indicated on the measuring device is 8%. By setting the concentration within this range, reproducible measurement values can be obtained. Then, in the measuring device, the measurement particle count is set to 25,000 particles, the aperture diameter is set to 100 μm, and the measurement range of 2 to 60 μm is divided into 256 parts to calculate the frequency value, and the particle diameter of the largest 50% of the volume cumulative fraction is taken as the volume-based median diameter.

[Average Circularity of Toner]
In the toner of the present invention, from the viewpoints of the stability of the charging characteristics and low-temperature fixability, the average circularity is preferably from 0.930 to 1.000, and more preferably from 0.950 to 0.995.

By having the average circularity within the above range, the individual toner particles are less likely to be crushed, contamination of the frictional charging member is suppressed, the chargeability of the toner is stabilized, and the image formed has high image quality.

The average circularity of the toner is a value measured using "FPIA-3000" (manufactured by Sysmex Corporation). Specifically, the measurement sample (toner) is mixed with an aqueous solution containing a surfactant, and dispersed by ultrasonic dispersion treatment for 1 minute. Then, using "FPIA-3000" (manufactured by Sysmex Corporation), images are taken at an appropriate concentration of 3,000 to 10,000 HPF detection numbers under measurement conditions of HPF (high magnification imaging) mode, and the circularity of each particle is calculated according to the following formula (y), and the circularity of each particle is added and divided by the total number of particles to obtain a calculated value. If the HPF detection number is within the above range, reproducibility is obtained.
Formula (y): Circularity = (perimeter of a circle having the same projected area as a particle image) / (perimeter of a projected particle image)

[Developer]
The toner of the present invention may be used alone as a magnetic or non-magnetic one-component developer, or may be used as a two-component developer containing the toner of the present invention and a carrier. The two-component developer can be obtained, for example, by mixing the toner of the present invention with a carrier. The mixing device used for mixing is not particularly limited, but examples thereof include a Nauta mixer, a W-cone, and a V-type mixer. The toner content (toner concentration) in the two-component developer is not particularly limited, but is preferably 4.0 to 8.0% by mass.

When the toner is used as a two-component developer, the carrier may be magnetic particles made of conventionally known materials such as metals such as iron, ferrite, and magnetite, and alloys of these metals with metals such as aluminum and lead, with ferrite particles being particularly preferred. In addition, the carrier may be a coated carrier in which the surface of magnetic particles is coated with a coating agent such as resin, or a dispersion-type carrier in which magnetic fine powder is dispersed in a binder resin.

The volume-based median diameter of the carrier is preferably 20 to 100 μm, and more preferably 25 to 80 μm. The volume-based median diameter of the carrier can be measured typically using a laser diffraction particle size distribution measuring device "HELOS" (manufactured by SYMPATEC) equipped with a wet disperser.

[Toner manufacturing method]
The method for producing the toner of the present invention is not particularly limited as long as the toner obtained satisfies the above conditions (1) to (4).

The toner base particles can be produced by, for example, a pulverization method, an emulsion dispersion method, a suspension polymerization method, a dispersion polymerization method, an emulsion polymerization method, an emulsion polymerization aggregation method, or other known methods. In particular, the emulsion polymerization aggregation method is preferred from the viewpoint of production cost and the ability to stably provide production conditions that satisfy conditions (1) to (4) in the resulting toner. When the toner contains an external additive, the toner is obtained by adhering the external additive to the surface of the toner base particles.

The emulsion aggregation method is a method in which an aqueous dispersion of binder resin particles (hereinafter also referred to as "binder resin particles") dispersed with a surfactant or dispersion stabilizer is mixed with a dispersion of various particles to be contained in the toner base particles, in this invention with an aqueous dispersion of release agent particles and an aqueous dispersion of various optional components, and an aggregating agent is added to aggregate the particles to the desired toner base particle size, and then, or simultaneously with the aggregation, the binder resin particles are fused together and the shape is controlled to form the toner base particles.

Here, "aqueous dispersion" refers to a dispersion (particles) dispersed in an aqueous medium, and an aqueous medium refers to a medium whose main component (50% by mass or more) is water. Examples of components other than water include organic solvents that dissolve in water, such as methanol, ethanol, isopropanol, butanol, acetone, methyl ethyl ketone, and tetrahydrofuran. Among these, alcohol-based organic solvents such as methanol, ethanol, isopropanol, and butanol, which do not dissolve resins, are particularly preferred.

The binder resin microparticles may have a multi-layer structure of two or more layers made of binder resins with different compositions. For example, binder resin microparticles having such a configuration and a two-layer structure can be obtained by preparing a dispersion of resin microparticles by a conventional polymerization process (first-stage polymerization), adding a polymerization initiator and a polymerizable monomer to this dispersion, and polymerizing this system (second-stage polymerization).

In the toner production method of the present invention, a specific example of producing toner base particles by an emulsion polymerization aggregation method includes a method of producing toner base particles by a method including the following first to third steps.
First step: A step of heating and stirring fine particles containing the binder resin and the release agent in an aqueous medium to aggregate and fuse them, thereby obtaining a dispersion liquid containing a toner base particle precursor. Second step: A step of cooling the dispersion liquid heated in the first step to a temperature of 30° C. or less at a temperature decreasing rate of 6° C./min or more. Third step: A step of maintaining the dispersion liquid cooled in the second step at a temperature within a range of 57 to 62° C. for 30 minutes or more.

In this way, toner base particles are formed through the first to third steps. Thereafter, the toner base particles are removed from the dispersion liquid, for example, through a filtering and washing step, and dried through a drying step. Furthermore, if necessary, an external additive is added to the surface of the toner base particles through an external additive addition step. Each step will be described below.

(First step)
The first step includes (a) a step of preparing an aqueous dispersion of fine particles of various components that constitute the toner base particles (hereinafter also referred to as an "aqueous dispersion preparation step"), and (b) a step of aggregating and fusing the fine particles of various components in an aqueous medium to form a toner base particle precursor (hereinafter also referred to as an "aggregation and fusing step").

The toner of the present invention contains a binder resin containing an amorphous resin and a crystalline resin, and a release agent. In the (a) step, an aqueous dispersion of amorphous resin particles (hereinafter also referred to as "amorphous resin particles"), an aqueous dispersion of crystalline resin particles (hereinafter also referred to as "crystalline resin particles"), and an aqueous dispersion of release agent particles (hereinafter also referred to as "release agent particles") are prepared, and can be subjected to the next aggregation and fusion step (b).

As described below, when preparing the amorphous resin microparticles, it is possible and preferable to add a release agent to the amorphous resin microparticles. In that case, the preparation of an aqueous dispersion of the release agent microparticles can be omitted. Here, the "microparticles containing a binder resin and a release agent" in the first step includes both cases in which the microparticles contain both binder resin microparticles (in the present invention, amorphous resin microparticles and crystalline resin microparticles) and release agent microparticles as an aggregate, and cases in which the microparticles contain both a binder resin (e.g., amorphous resin) and a release agent (in the present invention, further crystalline resin microparticles).

When the toner base particles according to the present invention contain a colorant, it is preferable to prepare a separate aqueous dispersion of colorant particles in addition to the above aqueous dispersions in step (a) and subject this to the aggregation and fusion step (b).

(a) Preparation of an aqueous dispersion (preparation of an aqueous dispersion of amorphous resin fine particles)
In this step, an aqueous dispersion of amorphous resin particles is prepared using an amorphous resin. For example, when the amorphous resin is a vinyl resin such as a styrene-acrylic resin, the aqueous dispersion of amorphous resin particles can be prepared by mini-emulsion polymerization using a vinyl monomer for obtaining the amorphous resin. That is, for example, a vinyl monomer is added to an aqueous medium containing a surfactant, mechanical energy is applied to form droplets, and then a polymerization reaction is caused to proceed in the droplets by radicals from a water-soluble radical polymerization initiator. An oil-soluble polymerization initiator may be contained in the droplets.

(Surfactant)
As the surfactant used in this step, various conventionally known anionic surfactants, cationic surfactants, nonionic surfactants, etc. can be used.

(Polymerization initiator)
The polymerization initiator used in this step may be any of various known polymerization initiators. Specific examples of polymerization initiators that are preferably used include persulfates (potassium persulfate, ammonium persulfate, etc.). In addition, azo compounds (4,4'-azobis-4-cyanovaleric acid and its salts, 2,2'-azobis(2-amidinopropane) salts, etc.), peroxide compounds, azobisisobutyronitrile, etc. may also be used.

(Chain Transfer Agent)
In this step, a commonly used chain transfer agent can be used for the purpose of adjusting the molecular weight of the amorphous resin. The chain transfer agent is not particularly limited, and examples thereof include mercaptans such as 2-chloroethanol, octyl mercaptan, dodecyl mercaptan, and t-dodecyl mercaptan, and styrene dimer.

In addition, when the amorphous resin is an amorphous polyester resin, for example, the aqueous dispersion of amorphous resin particles can be prepared by synthesizing the amorphous polyester resin and dispersing the amorphous polyester resin in the form of fine particles in an aqueous medium. Specifically, the aqueous dispersion can be prepared by dissolving or dispersing the amorphous polyester resin in an organic solvent to prepare an oil phase liquid, dispersing the oil phase liquid in an aqueous medium by phase inversion emulsification or the like to form oil droplets in a state controlled to the desired particle size, and then removing the organic solvent.

The amount of the aqueous medium used is preferably 50 to 2000 parts by mass, and more preferably 100 to 1000 parts by mass, per 100 parts by mass of the oil phase liquid. A surfactant or the like may be added to the aqueous medium in order to improve the dispersion stability of the oil droplets. Examples of the surfactant include the same ones as those listed in the above process.

The organic solvent used to prepare the oil phase liquid is preferably one that has a low boiling point and low solubility in water, from the viewpoint of easy removal after the formation of the oil droplets. Specific examples include methyl acetate, ethyl acetate, methyl ethyl ketone, methyl isobutyl ketone, toluene, xylene, etc. These can be used alone or in combination of two or more. The amount of the organic solvent used is usually 1 to 300 parts by mass per 100 parts by mass of the amorphous polyester resin. The emulsification and dispersion of the oil phase liquid can be carried out using mechanical energy.

The toner base particles according to the present invention contain a release agent, which can be introduced into the toner base particles by, for example, dissolving or dispersing the release agent in advance in a solution of a vinyl monomer for forming a vinyl resin or in an oil phase liquid of an amorphous polyester resin in this process.

For example, when preparing amorphous resin microparticles having a three-layer structure made of vinyl resin through three stages of polymerization, namely, first, second, and third stages, a release agent is added to the polymerization liquid during the second stage polymerization together with the polymerizable monomer for obtaining the vinyl resin, and polymerization is carried out to obtain amorphous resin microparticles containing the release agent. Then, this aqueous dispersion of amorphous resin microparticles containing the release agent is used in the aggregation and fusion process (b).

The release agent can also be introduced into the toner base particles by separately preparing a dispersion of release agent particles consisting of only the release agent, and aggregating the release agent particles together with the amorphous resin particles and the crystalline resin particles in the aggregation and fusion step (b). However, it is preferable to adopt a method in which the release agent is introduced in advance in this step.

In addition, other internal additives, such as a charge control agent, which are optionally contained in the toner base particles according to the present invention, can be introduced into the toner base particles, for example, by dissolving or dispersing them in advance in the vinyl monomer solution (or the oil phase liquid of the amorphous polyester resin) for forming the amorphous resin in this process.

Although such internal additives can be introduced into the toner base particles by separately preparing a dispersion of internal additive fine particles consisting only of the internal additives, and aggregating the internal additive fine particles together with the amorphous resin fine particles, the crystalline polyester resin fine particles, and the colorant fine particles in the aggregation and fusion process, it is preferable to adopt a method in which the internal additives are introduced in advance in this process.

The average particle size of the amorphous resin microparticles is preferably in the range of 100 to 400 nm in terms of volume-based median diameter. In the present invention, the volume-based median diameter of the amorphous resin microparticles is a value measured using a "Microtrac UPA-150" (manufactured by Nikkiso Co., Ltd.).

[Preparation of aqueous dispersion of crystalline resin particles]
In this step, an aqueous dispersion of crystalline resin particles is prepared using a crystalline resin, preferably a crystalline polyester resin.

An aqueous dispersion of crystalline resin microparticles can be prepared by synthesizing a crystalline resin and dispersing the crystalline resin in the form of fine particles in an aqueous medium. Specifically, the crystalline resin is dissolved or dispersed in an organic solvent to prepare an oil phase liquid, and the oil phase liquid is dispersed in an aqueous medium by phase inversion emulsification or the like to form oil droplets controlled to the desired particle size, and then the organic solvent is removed.

The amount of the aqueous medium used is preferably 50 to 2000 parts by mass, and more preferably 100 to 1000 parts by mass, per 100 parts by mass of the oil phase liquid. A surfactant or the like may be added to the aqueous medium in order to improve the dispersion stability of the oil droplets. Examples of the surfactant include the same ones as those listed in the above process.

The organic solvent used to prepare the oil phase liquid is preferably one that has a low boiling point and low solubility in water, from the viewpoint of easy removal after the formation of the oil droplets. Specific examples include methyl acetate, ethyl acetate, methyl ethyl ketone, methyl isobutyl ketone, toluene, xylene, etc. These can be used alone or in combination of two or more. The amount of the organic solvent used is usually 1 to 300 parts by mass per 100 parts by mass of the crystalline resin. The emulsification and dispersion of the oil phase liquid can be carried out using mechanical energy.

The average particle size of the crystalline resin microparticles is preferably in the range of 100 to 400 nm in terms of volume-based median diameter. In the present invention, the volume-based median diameter of the crystalline resin microparticles is a value measured using a "Microtrac UPA-150" (manufactured by Nikkiso Co., Ltd.).

[Preparation of Water-Based Dispersion of Colorant Fine Particles]
This step is carried out as necessary when it is desired to have the toner base particles contain a colorant, and is a step in which the colorant is dispersed in the form of fine particles in an aqueous medium to prepare an aqueous dispersion of fine colorant particles.

An aqueous dispersion of colorant particles is obtained by dispersing the colorant in an aqueous medium to which a surfactant has been added at a critical micelle concentration (CMC) or higher. The colorant can be dispersed using mechanical energy. There are no particular limitations on the dispersing machine used, but preferred examples include ultrasonic dispersers, mechanical homogenizers, pressure dispersers such as Manton-Gaulin and pressure homogenizers, sand grinders, and media-type dispersers such as Getzmann mills and diamond fine mills.

The colorant particles preferably have a volume-based median diameter of 10 to 300 nm in a dispersed state, more preferably 100 to 200 nm, and particularly preferably 100 to 150 nm. In the present invention, the volume-based median diameter of the colorant particles is a value measured using an electrophoretic light scattering photometer "ELS-800" (manufactured by Otsuka Electronics Co., Ltd.).

(b) Aggregation and Fusion Step In this step, in an aqueous medium in which amorphous resin particles, crystalline resin particles, and release agent particles, as well as other toner constituents such as colorant particles as necessary, are dispersed, these particles are aggregated and then fused by heating. In the above, when the amorphous resin particles contain a release agent, the release agent particles may not be present in the aqueous medium.

Specifically, the aggregation and fusion step involves adding an aggregating agent at or above the critical aggregation concentration to an aqueous dispersion in which the fine particles are dispersed in an aqueous medium, and heating the mixture to a temperature equal to or above the glass transition point (Tg _p ) of the amorphous resin, thereby aggregating and fusing the fine particles to form a toner base particle precursor.

The heating temperature in the aggregation and fusion process may be equal to or higher than Tg _p , preferably from (Tg _p +10° C.) to (Tg _p +50° C.), and particularly preferably from (Tg _p +15° C.) to (Tg _p +40° C.). The heating temperature in the aggregation and fusion process is preferably equal to or higher than the melting point _Tmp of the crystalline resin. Furthermore, the heating temperature in the aggregation and fusion process is preferably equal to or higher than the melting point _Tmw of the release agent. By setting the heating temperature in the aggregation and fusion process as described above, it becomes easier to achieve the conditions (1) to (4) in the obtained toner.

[Flocculant]
The flocculant used in this step is not particularly limited, but is preferably selected from metal salts such as alkali metal salts and alkaline earth metal salts. Metal salts include monovalent metal salts such as sodium, potassium, and lithium; divalent metal salts such as calcium, magnesium, manganese, and copper; and trivalent metal salts such as iron and aluminum. Specific metal salts include sodium chloride, potassium chloride, lithium chloride, calcium chloride, magnesium chloride, zinc chloride, copper sulfate, magnesium sulfate, and manganese sulfate. Among these, it is particularly preferable to use divalent metal salts because they can be used in smaller amounts to promote flocculation. These can be used alone or in combination of two or more.

When the toner base particles have a core-shell structure, for example, in this process, amorphous resin particles, crystalline resin particles, release agent particles (however, if the amorphous resin particles contain a release agent, the release agent particles may not be necessary), and any colorant particles are aggregated and fused to form core particles, and then shell resin particles for forming the shell layer are aggregated and fused to the core particles to form the shell layer. The shell resin is preferably an amorphous resin.

The first step may further include an aging step, if necessary. In the aging step, the toner base particle precursor obtained in the aggregation and fusion step (b) is aged by thermal energy until it assumes the desired shape. Specifically, the aging step is performed by heating and stirring the system in which the toner base particle precursor is dispersed, and adjusting the heating temperature, stirring speed, heating time, etc., until the shape of the toner base particle precursor assumes the desired circularity.

The heating temperature is preferably, for example, about the glass transition point (Tg _p ) of the amorphous resin + 30 to 40° C. This can significantly reduce the viscosity of the binder resin, making it possible to shorten the time required to shape the toner base particles. It is also preferable to heat the toner base particles to a temperature equal to or higher than the melting points of the crystalline resin and release agent contained in the toner base particles. This allows the amorphous resin to be plasticized by the crystalline resin, and the viscosity of the binder resin is significantly reduced, making it possible to shorten the time required to shape the toner base particles.

(Second step)
The second step is a step of cooling the dispersion of the toner base particle precursor obtained in the first step. The cooling step is performed at a temperature drop rate of 6° C./min or more to a temperature of 30° C. or less. The temperature drop rate is preferably 10° C./min or more. From the viewpoint of operability, the upper limit of the temperature drop rate is about 20° C./min. The temperature after cooling is preferably 25° C. or less.

By cooling the dispersion of the toner base particle precursor at a temperature drop rate of 6°C/min or more, the supercooled state can be increased when the crystalline components such as the crystalline resin and release agent melted in the toner base particle precursor crystallize, thereby promoting the generation of crystal nuclei. By generating a large number of crystal nuclei, it becomes possible to generate many small crystals in the crystallization process, which has the effect of making it easier to control the melting point distribution. In addition, the above effect can be sufficiently obtained by setting the temperature after cooling to 30°C or less.

The specific method of cooling is not particularly limited, but examples include a method of cooling by introducing a refrigerant from outside the reaction vessel, or a method of cooling by directly pouring cold water into the reaction system.

(Third step)
The third step is a step of maintaining the dispersion liquid of the toner base particle precursor cooled in the second step at a temperature in the range of 57 to 62° C. for 30 minutes or more. Through the third step, crystallization of the crystalline resin in the toner base particle precursor is promoted, and the toner base particles in the toner of the present invention are obtained. That is, the _T1 and _T2 of the obtained toner base particles are determined by the heating temperature and heating time in the third step.

As described above, the _T1 of the toner, i.e., the _T1 of the toner base particles, is closely related to the temperature of heat-resistant storage. Specifically, for example, in order to ensure heat-resistant storage at about 57°C, it is necessary to remove low-melting crystals having a melting point of less than 57°C from the toner. In this case, in the method of the present invention, the dispersion of the toner base particle precursor containing the crystalline resin that has not been completely crystallized after the second step is subjected to a heat treatment at a temperature of 57°C to melt the low-melting crystals having a melting point of less than 57°C and recrystallize the crystalline resin. The crystalline resin in the toner base particles obtained in this way is changed to a crystal having an endothermic peak rising temperature of about 57°C.

Thus, in the toner manufacturing method of the present invention, the heating temperature in the third step is set to the same temperature as the temperature range _T1 of 57 to 62° C., which is the above condition (1) for the toner of the present invention. The heating temperature in the third step is preferably set to the temperature range _T1 of 61 to 62° C., which is the above condition (6) for the toner of the present invention. By setting the temperature _T1 at 57° C. or higher, the heat-resistant storage stability of the toner can be sufficiently ensured, and by setting it at 62° C. or lower, the timing at which the crystalline resin starts to melt can be set to an appropriately low temperature, which ensures the low-temperature fixability of the toner.

In addition, with regard to the temperature _T2 , which is the endothermic peak temperature (melting point) of the crystalline resin in the toner base particles, by setting the heating temperature in the third step to a temperature range of _T1 of 57 to 62°C, it is possible to control the range of _T2 to 60 to 70°C. By setting the temperature of T2 to 60°C or higher, the heat-resistant storage stability of the toner can be sufficiently ensured, and by setting the temperature of _T2 to 70°C or lower, the low-temperature fixability of the toner can be ensured.

The heating time in the third step is 30 minutes or more from the viewpoint of sufficiently melting the low melting point crystals and promoting recrystallization, and is preferably in the range of 1 to 5 hours, and more preferably in the range of 1 to 3 hours.

When the dispersion of toner base particle precursor after the second step is heated to the heating temperature in the third step, it is preferable to carry out the heating at a rate of, for example, 6°C/min to 30°C/min in order to suppress aggregation of toner particles that occurs when heat is applied suddenly.

The third step may be carried out in two or more stages. In that case, the heating temperature is increased as the stages proceed, and the heating temperature in the final stage is set to the above-mentioned temperature of 57 to 62°C. The heating time in the final stage is also set to 30 minutes or more. For example, when carrying out a two-stage heating treatment, it is preferable to carry out the first heating at a temperature range of 40 to 55°C for 1 to 10 hours, and then the final heating at a temperature range of 57 to 62°C for 30 minutes or more. By carrying out two or more stages of heating treatment, it is preferable in terms of adjusting the degree of crystallization and the melting start temperature (the rise temperature of the endothermic peak) (T ₁ ) of the crystalline resin.

In this way, by controlling the time and temperature of the heat treatment in the third step, it is possible to control the melting point distribution of the crystalline resin in the toner base particles, thereby achieving both low-temperature fixability and heat-resistant storage stability.

There are no particular limitations on the method for cooling the dispersion of toner base particles after the third step. Although slow cooling is acceptable, it is preferable to cool the dispersion at a rate of, for example, 6°C/min or more from the standpoint of production efficiency.

(Filtering and washing process)
This step is a step in which the toner base particles are subjected to solid-liquid separation from the dispersion liquid of the toner base particles cooled after the third step, and then the toner cake (a mass of toner base particles in a wet state aggregated into a cake-like mass) obtained by the solid-liquid separation is washed to remove any attached substances such as surfactants and aggregating agents.

There are no particular limitations on the solid-liquid separation, and methods that can be used include centrifugation, reduced pressure filtration using a Nutsche filter, and filtration using a filter press. In addition, in the washing, it is preferable to wash with water until the electrical conductivity of the filtrate is 10 μS/cm or less.

(Drying process)
This step is a step of drying the washed toner cake, and can be carried out in accordance with a drying step generally performed in known methods for producing toner base particles.

Specific examples of dryers used to dry the toner cake include spray dryers, vacuum freeze dryers, and reduced pressure dryers, and it is preferable to use stationary shelf dryers, mobile shelf dryers, fluidized bed dryers, rotary dryers, and agitator dryers.

The moisture content of the dried toner base particles is preferably 5% by mass or less, and more preferably 2% by mass or less. If the dried toner base particles are aggregated by weak interparticle attractive forces, the aggregates may be subjected to a crushing process. The crushing process device may be a mechanical crushing device such as a jet mill, a Henschel mixer, a coffee mill, or a food processor.

(External additive addition process)
This step is carried out as necessary when an external additive is added to the toner base particles. The above toner base particles can be used as a toner as is, but in order to improve the flowability, chargeability, cleaning properties, etc., the toner base particles may be used in a state in which an external additive such as a so-called fluidizing agent or cleaning aid is added. The above-mentioned various external additives may be used in combination. The amount of these external additives added is as described above.

As a mixing device used to add external additives to the surface of the toner base particles, a mechanical mixing device such as a Henschel mixer or a coffee mill can be used.

The above describes the embodiment of the present invention in detail, but the embodiment of the present invention is not limited to the above example, and various modifications can be made.

The present invention will be described in detail below with reference to examples, but the present invention is not limited to these. In the examples, the terms "parts" and "%" are used, but unless otherwise specified, they represent "parts by mass" or "% by mass." Furthermore, the physical properties of each component are those measured by the above-mentioned method, unless otherwise specified.

Example 1: Production of Toner 1
Toner 1 having toner base particles, which are core-shell particles, and an external additive on the surface thereof was produced as follows. As for the binder resin, a styrene acrylic resin was used as the amorphous resin for the core particles, a crystalline polyester resin was used as the crystalline resin, and an amorphous polyester resin was used as the amorphous resin for the shell.

[Preparation of Microparticle Dispersion]
(1) Preparation of Aqueous Dispersion [1] of Styrene-Acrylic Resin Fine Particles (Containing Releasing Agent) (First-Stage Polymerization)
A 5 L reaction vessel equipped with a stirrer, a temperature sensor, a cooling tube, and a nitrogen introduction device was charged with a solution of 8 g of sodium dodecyl sulfate dissolved in 3 L of ion-exchanged water, and the inside temperature was raised to 80° C. while stirring at a stirring speed of 230 rpm under a nitrogen stream. Thereafter, a solution of 10 g of potassium persulfate dissolved in 200 g of ion-exchanged water was added, the liquid temperature was again raised to 80° C., and a vinyl monomer solution consisting of 480 g of styrene, 250 g of n-butyl acrylate, and 68 g of methacrylic acid was added dropwise over 1 hour, followed by heating and stirring at 80° C. for 2 hours to carry out polymerization, thereby obtaining a dispersion of resin fine particles [a1].

(Second stage polymerization)
A solution of 9.2 g of sodium dodecyl ether sulfate dissolved in 1,500 mL of ion-exchanged water was charged into a 5 L reaction vessel equipped with a stirrer, a temperature sensor, a cooling tube, and a nitrogen introducing device, and heated to 98°C. Then, 288.8 g (solid content mass) of the dispersion of the above resin microparticles [a1], a vinyl monomer solution consisting of 211.4 g of styrene, 26 g of 2-ethylhexyl acrylate, and 25 g of methacrylic acid, 3.3 g of n-octyl mercaptan, and a mixture of 240 g of N252 (product name, manufactured by Chukyo Yushi Co., Ltd., behenyl behenate, melting point T _mw 77°C) as a release agent, were added thereto, and the mixture was mixed and dispersed for 1 hour using a mechanical disperser "CLEARMIX" (manufactured by M Technique Co., Ltd.) having a circulation path to prepare a dispersion containing emulsified particles (oil droplets).

Next, an initiator solution in which 4.5 g of potassium persulfate was dissolved in 85 mL of ion-exchanged water was added to this dispersion, and the system was heated and stirred at 84°C for 1 hour to polymerize, thereby obtaining a dispersion of resin microparticles [a2].

(Third stage polymerization)
A solution of 6.7 g of potassium persulfate dissolved in 115 mL of ion-exchanged water was added to the dispersion of the resin fine particles [a2], and a mixed solution of a vinyl monomer solution consisting of 301.7 g of styrene, 145 g of n-butyl acrylate, 28.5 g of methacrylic acid, and 43 g of methyl methacrylate and 7.0 g of n-octyl mercaptan was added dropwise over 1 hour under a temperature condition of 82° C. After the dropwise addition, polymerization was carried out by heating and stirring for 2 hours, and then the mixture was cooled to 28° C., thereby preparing a styrene-acrylic resin fine particle dispersion [1] containing fine particles made of a styrene-acrylic resin containing a release agent (release agent: 12% by mass, styrene-acrylic resin: 88% by mass) at a solid content concentration of 30% by mass.

These amorphous resin microparticles (styrene acrylic resin microparticles) had a volume-based median diameter of 220 nm, a weight-average molecular weight (Mw) of 25,000, and a glass transition point of 40.0°C.

(2) Preparation of crystalline polyester resin particle dispersion (synthesis of crystalline polyester resin)
A 5 L reaction vessel equipped with a stirrer, a temperature sensor, a cooling pipe, and a nitrogen introducing device was charged with 300 parts by mass of dodecanedioic acid (1,10-decanedicarboxylic acid) as a polycarboxylic acid and 170 parts by mass of 1,4-butanediol as a polyhydric alcohol, and the internal temperature was raised to 190° C. over one hour while stirring the system. After confirming that the system was in a uniformly stirred state, Ti(OBu)4 was added as a catalyst in an amount of 0.003% by mass with respect to the amount of the polycarboxylic acid charged.

Thereafter, while distilling off the produced water, the internal temperature was raised from 190° C. to 240° C. over 6 hours, and the dehydration condensation reaction was continued for another 6 hours at 240° C. to carry out polymerization, thereby obtaining a crystalline polyester resin [1]. This crystalline polyester resin [1] had a melting point _Tmp of 68° C. and a weight average molecular weight (Mw) of 7,000.

(Preparation of Crystalline Polyester Resin Particle Dispersion)
200 parts by mass of crystalline polyester resin [1] was dissolved in 200 parts by mass of ethyl acetate, and while stirring the solution, an aqueous solution in which sodium polyoxyethylene lauryl ether sulfate was dissolved in 800 parts by mass of ion-exchanged water to a concentration of 1% by mass was slowly dropped. After removing ethyl acetate from this solution under reduced pressure, the pH was adjusted to 8.5 with ammonia. Then, the solid content concentration was adjusted to 20% by mass. This resulted in the preparation of a crystalline polyester resin microparticle dispersion [1] in which microparticles of crystalline polyester resin [1] were dispersed in an aqueous medium. The volume-based median diameter of the microparticles of crystalline polyester resin [1] was 200 nm.

(3) Preparation of amorphous polyester resin particle dispersion (synthesis of amorphous polyester resin)
In a reaction vessel equipped with a stirring device, a nitrogen inlet tube, a temperature sensor and a distillation column, 85 parts by mass of terephthalic acid, 6 parts by mass of trimellitic acid, 18 parts by mass of fumaric acid and 80 parts by mass of dodecenylsuccinic anhydride as polyvalent carboxylic acids, 381 parts by mass of bisphenol A propylene oxide adduct and 62 parts by mass of bisphenol A ethylene oxide adduct as polyhydric alcohols were charged, the temperature of the reaction system was raised to 190 ° C. over 1 hour, and it was confirmed that the reaction system was stirred uniformly. Then, Ti (OBu) ₄ was added as a catalyst in an amount of 0.006% by mass relative to the total amount of polyvalent carboxylic acids, and the temperature of the reaction system was raised from the same temperature to 240 ° C. over 6 hours while distilling off the water produced, and the dehydration condensation reaction was continued for 6 hours while maintaining the temperature at 240 ° C. to perform the polymerization reaction, thereby obtaining an amorphous polyester resin [1].

This amorphous polyester resin [1] had a weight average molecular weight (Mw) of 10,000 and a glass transition point of 60°C.

(Preparation of amorphous polyester resin particle dispersion)
200 parts by mass of amorphous polyester resin [1] was dissolved in 200 parts by mass of ethyl acetate, and while stirring the solution, an aqueous solution in which sodium polyoxyethylene lauryl ether sulfate was dissolved in 800 parts by mass of ion-exchanged water to a concentration of 1% by mass was slowly dropped. After removing ethyl acetate from this solution under reduced pressure, the pH was adjusted to 8.5 with ammonia. Then, the solid content concentration was adjusted to 20% by mass. This resulted in the preparation of an amorphous polyester resin microparticle dispersion [1] in which microparticles of amorphous polyester resin [1] were dispersed in an aqueous medium. The volume-based median diameter of the microparticles of amorphous polyester resin [1] was 130 nm.

(4) Preparation of water-based dispersion of colorant particles [Bk] 90 parts by mass of sodium dodecyl sulfate was added to 1600 parts by mass of ion-exchanged water. While stirring this solution, 420 parts by mass of carbon black (Regal 330R: manufactured by Cabot Corporation) was gradually added, and then the solution was dispersed using a stirring device "Clearmix" (manufactured by M Technique Co., Ltd.) to prepare water-based dispersion of colorant particles [Bk]. The average particle size (volume-based median diameter) of the colorant particles in the obtained water-based dispersion [Bk] was 110 nm.

(5) Preparation of toner base particles (first step; (b) aggregation and fusion step)
In a Zebra flask (reaction vessel) equipped with a stirrer, a temperature sensor, a cooling tube and a nitrogen introduction device, 1600 parts by mass of styrene acrylic resin microparticle dispersion [1] (solid content equivalent, release agent: 12% by mass, styrene acrylic resin: 88% by mass), 300 parts by mass of crystalline polyester resin microparticle dispersion [1] (solid content equivalent), 1500 parts by mass of ion-exchanged water, and 500 parts by mass of water-based dispersion of colorant microparticles [Bk] (solid content equivalent) were charged, and the rotation speed of the stirrer was adjusted to 150 rpm. Next, after adjusting the liquid temperature to 25 ° C., a 25% by mass aqueous sodium hydroxide solution was added to adjust the pH to 10, and the rotation speed of the stirrer was adjusted to 245 rpm.

Next, an aqueous solution of 54.3 parts by mass of magnesium chloride hexahydrate dissolved in 54.3 parts by mass of ion-exchanged water was added, and the temperature of the system was then raised to 87°C. Once the temperature increase was complete, the rotation speed of the stirring device was reduced to 100 rpm, and the aggregation and fusion process of each resin microparticle and colorant microparticle was started.

After the aggregation and fusion process started, samples were taken periodically and the volume-based median diameter of the aggregated and fused particles was measured using a particle size distribution measuring device "Coulter Multisizer 3" (manufactured by Beckman Coulter, Inc.). The aggregation and fusion process was continued until the volume-based median diameter reached 6.3 μm. Once this particle size was reached, the rotation speed of the stirring device was increased to 245 rpm, and shear was applied to the extent that aggregation did not occur, preventing further aggregation and fusion, thereby obtaining a dispersion of core particles.

Next, the temperature of the reaction vessel containing the dispersion of the core particles was set to 75°C, and when the temperature was reached, 300 parts by mass (solid content equivalent) of the amorphous polyester resin microparticle dispersion [1] was added to form a shell layer on the surface of the core particles, forming core-shell particles.

After that, an aqueous solution of 23.0 parts by mass of sodium chloride dissolved in 96 parts by mass of ion-exchanged water was added to the reaction vessel, and stirring was continued for 2 hours until the average circularity of the core-shell particles reached 0.960 as measured by a flow particle image analyzer "FPIA-2100" (manufactured by Sysmex Corporation).

(Second step)
When the average circularity of the core-shell particles reached 0.960, the dispersion of the core-shell particles as the toner base particle precursor was cooled to 30° C. at a rate of 6° C./min to stop the reaction.

(Third step)
After cooling, the toner base particle precursor liquid was heated again to 60°C at a heating rate of 6°C/min and held at that temperature (60°C) for 3 hours to promote crystallization of the crystalline polyester resin. The reaction was then stopped by cooling at a heating rate of 6°C/min to obtain a dispersion of toner base particles. The toner base particles after cooling had an average particle size (volume-based median diameter) of 6.1 μm and an average circularity of 0.946.

(Filtering, washing and drying process)
The dispersion of the toner base particles thus obtained was subjected to solid-liquid separation using a basket-type centrifuge "MARK III Model No. 60x40" (manufactured by Matsumoto Kikai Co., Ltd.) to form a wet cake. The wet cake was repeatedly washed and separated using the basket-type centrifuge until the electrical conductivity of the filtrate reached 15 μS/cm. Thereafter, the wet cake was dried using a "Flash Jet Dryer" (manufactured by Seishin Enterprise Co., Ltd.) by blowing an airflow at a temperature of 40°C and a humidity of 20% RH until the moisture content was 0.5% by mass, and then cooled to 24°C to obtain toner base particles [1]. The toner base particles [1] had a volume-based median diameter of 6.1 μm and an average circularity of 0.966.

(6) Addition of external additives To 100 parts by mass of the obtained toner base particles [1], 1 part by mass of hydrophobic silica particles and 1.2 parts by mass of hydrophobic titanium oxide particles were added, and mixed for 20 minutes using a Henschel mixer under the condition of a rotor blade peripheral speed of 24 m/s, and further passed through a 400 mesh sieve to add the external additives, thereby obtaining toner [1]. Note that in toner [1], the addition of the external additives did not change the shape and particle size of the toner base particles [1].

<Example 2 to Comparative Example 3: Production of Toners 2 to 19>
In producing toners 2 to 19, crystalline polyester resin particle dispersions [2] to [7] and release agent-containing styrene acrylic resin particle dispersions [2] to [4] were prepared as follows. Hereinafter, Examples 2 to 5, 6 to 9 , and 14 to 16 will be read as Reference Examples 2 to 5, 6 to 9 , and 14 to 16 , respectively.

(Synthesis of crystalline polyester resin [2])
Crystalline polyester resin [2] was produced in the same manner as in the production process of crystalline polyester resin [1], except that the dehydration condensation reaction time in the production process of crystalline polyester resin [1] was changed from 6 hours to 3 hours. This crystalline polyester resin [2] had a melting point _Tmp of 67° C. and a weight average molecular weight (Mw) of 4,000.

(Synthesis of crystalline polyester resin [3])
Crystalline polyester resin [3] was produced in the same manner as in the production process of crystalline polyester resin [1], except that the dehydration condensation reaction time was changed from 6 hours to 12 hours. This crystalline polyester resin [3] had a melting point _Tmp of 64° C. and a weight average molecular weight (Mw) of 20,000.

(Synthesis of crystalline polyester resin [4])
Crystalline polyester resin [4] was produced in the same manner as in the production of crystalline polyester resin [1], except that 170 parts by mass of 1,4-butanediol was changed to 170 parts by mass of 1,6-hexanediol and the dehydration condensation reaction time was changed from 6 hours to 3 hours. This crystalline polyester resin [4] had a melting point _Tmp of 65° C. and a weight average molecular weight (Mw) of 5,000.

(Synthesis of crystalline polyester resin [5])
Crystalline polyester resin [5] was produced in the same manner as in the production of crystalline polyester resin [1], except that 170 parts by mass of 1,4-butanediol was changed to 170 parts by mass of 1,6-hexanediol and the dehydration condensation reaction time was changed from 6 hours to 12 hours. This crystalline polyester resin [5] had a melting point _Tmp of 63° C. and a weight average molecular weight (Mw) of 20,000.

(Synthesis of crystalline polyester resin [6])
Crystalline polyester resin [6] was produced in the same manner as in the production process of crystalline polyester resin [1], except that the dehydration condensation reaction time was changed from 6 hours to 16 hours. This crystalline polyester resin [6] had a melting point _Tmp of 64° C. and a weight average molecular weight (Mw) of 30,000.

(Synthesis of crystalline polyester resin [7])
Crystalline polyester resin [7] was produced in the same manner as in the production of crystalline polyester resin [1], except that 300 parts by mass of dodecanedioic acid (1,10-decanedicarboxylic acid) was replaced with 300 parts by mass of tetradecanedioic acid (1,12-dodecanedicarboxylic acid). This crystalline polyester resin [7] had a melting point _Tmp of 78° C. and a weight average molecular weight (Mw) of 7,000.

(Preparation of Crystalline Polyester Resin Particle Dispersion [2])
A crystalline polyester resin microparticle dispersion [2] was prepared in the same manner as in Example 1, except that 200 parts by mass of the crystalline polyester resin [1] in the preparation process of the crystalline polyester resin microparticle dispersion [1] was changed to a crystalline polyester resin [2]. The volume-based median diameter of the microparticles of the crystalline polyester resin [2] was 202 nm.

(Preparation of Crystalline Polyester Resin Particle Dispersion [3])
A crystalline polyester resin microparticle dispersion [3] was prepared in the same manner as in Example 1, except that 200 parts by mass of the crystalline polyester resin [1] in the preparation process of the crystalline polyester resin microparticle dispersion [1] was changed to a crystalline polyester resin [3]. The volume-based median diameter of the microparticles of the crystalline polyester resin [3] was 210 nm.

(Preparation of Crystalline Polyester Resin Particle Dispersion [4])
A crystalline polyester resin microparticle dispersion [4] was prepared in the same manner as in Example 1, except that 200 parts by mass of the crystalline polyester resin [1] in the preparation process of the crystalline polyester resin microparticle dispersion [1] was changed to a crystalline polyester resin [4]. The volume-based median diameter of the microparticles of the crystalline polyester resin [4] was 195 nm.

(Preparation of Crystalline Polyester Resin Particle Dispersion [5])
A crystalline polyester resin microparticle dispersion [5] was prepared in the same manner as in Example 1, except that 200 parts by mass of the crystalline polyester resin [1] in the preparation process of the crystalline polyester resin microparticle dispersion [1] was changed to a crystalline polyester resin [5]. The volume-based median diameter of the microparticles of the crystalline polyester resin [5] was 200 nm.

(Preparation of Crystalline Polyester Resin Particle Dispersion [6])
A crystalline polyester resin microparticle dispersion [6] was prepared in the same manner as in Example 1, except that 200 parts by mass of the crystalline polyester resin [1] in the preparation process of the crystalline polyester resin microparticle dispersion [1] was changed to a crystalline polyester resin [6]. The volume-based median diameter of the microparticles of the crystalline polyester resin [6] was 200 nm.

(Preparation of Crystalline Polyester Resin Particle Dispersion [7])
A crystalline polyester resin microparticle dispersion [7] was prepared in the same manner as in Example 1, except that 200 parts by mass of the crystalline polyester resin [1] in the preparation process of the crystalline polyester resin microparticle dispersion [1] was changed to a crystalline polyester resin [7]. The volume-based median diameter of the microparticles of the crystalline polyester resin [7] was 203 nm.

(Preparation of Styrene-Acrylic Resin Particle Dispersion (2))
An aqueous dispersion (2) of styrene-acrylic resin fine particles was prepared in the same manner as in Example 1, except that the 240 parts by mass of the release agent [N252] in the second polymerization step was changed to 240 parts by mass of a release agent "SELOSOL R-582 (product name, manufactured by Chukyo Yushi Co., Ltd., paraffin wax, melting point T _mw 70°C)". The amorphous resin fine particles had a volume-based median diameter of 230 nm, a weight average molecular weight (Mw) of 25,500, and a glass transition point of 40.5°C.

(Preparation of Aqueous Dispersion of Styrene-Acrylic Resin Fine Particles (3))
An aqueous dispersion (3) of styrene-acrylic resin fine particles was prepared in the same manner as in Example 1, except that the 240 parts by mass of the release agent [N252] in the second polymerization step was changed to 240 parts by mass of a release agent "HNP-0190 (product name, manufactured by Nippon Seiro Co., Ltd., microcrystalline wax (paraffin wax), melting point T _mw 83°C)". The amorphous resin fine particles had a volume-based median diameter of 230 nm, a weight average molecular weight (Mw) of 25,500, and a glass transition point of 40.5°C.

(Preparation of Aqueous Dispersion of Styrene-Acrylic Resin Fine Particles (4))
An aqueous dispersion (4) of styrene-acrylic resin fine particles was prepared in the same manner as in Example 1, except that the 240 parts by mass of the release agent [N252] in the second polymerization step was changed to 240 parts by mass of the release agent "FNP-0090 (product name, Nippon Seiro Co., Ltd., paraffin wax, melting point T _mw 90°C)". The amorphous resin fine particles had a volume-based median diameter of 230 nm, a weight average molecular weight (Mw) of 25,500, and a glass transition point of 41.0°C.

Example 2
Toner [2] was obtained in the same manner as in Example 1, except that the heating conditions in the third step of Example 1, which were 60° C. and 3 hours, were changed to 57° C. and 3 hours. Toner [2] had a volume-based median diameter of 6.2 μm and an average circularity of 0.966.

Example 3
Toner [3] was obtained in the same manner as in Example 1, except that the heating conditions in the third step of Example 1, which consisted of holding at 60° C. for 3 hours, were changed to holding at 53° C. for 5 hours, followed by holding at 62° C. for 1 hour. This toner [3] had a volume-based median diameter of 6.2 μm and an average circularity of 0.966.

Example 4
Toner [4] was obtained in the same manner as in Example 1, except that the heating conditions in the third step of Example 1, which consisted of holding at 60° C. for 3 hours, were changed to holding at 50° C. for 5 hours, followed by holding at 59° C. for 1 hour. This toner [4] had a volume-based median diameter of 6.2 μm and an average circularity of 0.966.

Example 5
Toner [5] was obtained in the same manner as in Example 1, except that the heating conditions in the third step of Example 1, which were 60° C. and 3 hours, were changed to 60° C. and 9 hours. This toner [5] had a volume-based median diameter of 6.1 μm and an average circularity of 0.966.

Example 6
Toner [6] was obtained in the same manner as in Example 1, except that the crystalline polyester resin particle dispersion [1] used in Example 1 was replaced with crystalline polyester resin particle dispersion [2], and the heating conditions in the third step, which consisted of holding at 60° C. for 3 hours, were changed to holding at 48° C. for 5 hours and then holding at 60° C. for 1 hour. This toner [6] had a volume-based median diameter of 6.3 μm and an average circularity of 0.966.

Example 7
Toner [7] was obtained in the same manner as in Example 1, except that the crystalline polyester resin particle dispersion [1] used in Example 1 was replaced with crystalline polyester resin particle dispersion [3], and the heating conditions in the third step, which were 60° C. and 3 hours of holding, were changed to 50° C. and 5 hours of holding, followed by 1 hour of holding at 62° C. This toner [7] had a volume-based median diameter of 6.3 μm and an average circularity of 0.967.

Example 8
Toner [8] was obtained in the same manner as in Example 1, except that the crystalline polyester resin particle dispersion [1] used in Example 1 was replaced with the crystalline polyester resin particle dispersion [4], and the heating conditions in the third step were changed from 60° C. and 3 hours to 62° C. and 3 hours. This toner [8] had a volume-based median diameter of 6.3 μm and an average circularity of 0.967.

<Example 9>
Toner [9] was obtained in the same manner as in Example 1, except that the crystalline polyester resin particle dispersion [1] used in Example 1 was replaced with the crystalline polyester resin particle dispersion [5], and the heating conditions in the third step were changed from 60° C. and 3 hours to 58° C. and 3 hours. This toner [9] had a volume-based median diameter of 6.3 μm and an average circularity of 0.967.

Example 10
Toner [10] was obtained in the same manner as in Example 1, except that 1,600 parts by weight of styrene acrylic resin particle dispersion [1] and 300 parts by weight of crystalline polyester resin particle dispersion [1] were changed to 1,690 parts by weight of styrene acrylic resin particle dispersion [1] and 165 parts by weight of crystalline polyester resin particle dispersion [1], respectively. This toner [10] had a volume-based median diameter of 6.3 μm and an average circularity of 0.967.

Example 11
A toner [11] was obtained in the same manner as in Example 1, except that 1,600 parts by weight of the styrene-acrylic resin particle dispersion [1] and 300 parts by weight of the crystalline polyester resin particle dispersion [1] were changed to 1,240 parts by weight of the styrene-acrylic resin particle dispersion [1] and 840 parts by weight of the crystalline polyester resin particle dispersion [1], respectively. This toner [11] had a volume-based median diameter of 6.3 μm and an average circularity of 0.967.

Example 12
A toner [12] was obtained in the same manner as in Example 1, except that 1,600 parts by mass of the styrene-acrylic resin fine particle dispersion [1] used in the toner production process was changed to 1,600 parts by mass of the styrene-acrylic resin fine particle dispersion [2]. This toner [12] had a volume-based median diameter of 6.2 μm and an average circularity of 0.967.

Example 13
A toner [13] was obtained in the same manner as in Example 1, except that 1,600 parts by mass of the styrene-acrylic resin fine particle dispersion [1] used in the toner production process was changed to 1,600 parts by mass of the styrene-acrylic resin fine particle dispersion [3]. This toner [13] had a volume-based median diameter of 6.2 μm and an average circularity of 0.967.

<Example 14>
Toner [14] was obtained in the same manner as in Example 1, except that the crystalline polyester resin particle dispersion [1] used in Example 1 was changed to crystalline polyester dispersion [6], and the heating conditions in the third step, which were 60° C. and 3 hours of holding, were changed to 53° C. and 5 hours of holding, and then 62° C. and 1 hour of holding, respectively. This toner [14] had a volume-based median diameter of 6.1 μm and an average circularity of 0.967.

Example 15
A toner [15] was obtained in the same manner as in Example 1, except that 1,600 parts by weight of the styrene-acrylic resin particle dispersion [1] and 300 parts by weight of the crystalline polyester resin particle dispersion [1] were changed to 1,740 parts by weight of the styrene-acrylic resin particle dispersion [1] and 90 parts by weight of the crystalline polyester resin particle dispersion [1], respectively. This toner [15] had a volume-based median diameter of 6.3 μm and an average circularity of 0.967.

<Example 16>
A toner [16] was obtained in the same manner as in Example 1, except that 1,600 parts by mass of the styrene acrylic resin particle dispersion [1] and 300 parts by mass of the crystalline polyester resin particle dispersion [1] were changed to 1,100 parts by mass of the styrene acrylic resin particle dispersion [1] and 1,050 parts by mass of the crystalline polyester resin particle dispersion [1], respectively. This toner [16] had a volume-based median diameter of 6.3 μm and an average circularity of 0.968.

<Comparative Example 1>
Toner [17] was obtained in the same manner as in Example 1, except that the heating conditions in the third step of Example 1, which were 60° C. and 3 hours, were changed to 54° C. and 0.2 hours. This toner [17] had a volume-based median diameter of 6.2 μm and an average circularity of 0.966.

<Comparative Example 2>
Toner [18] was obtained in the same manner as in Example 1, except that the crystalline polyester resin particle dispersion [1] used in Example 1 was replaced with crystalline polyester resin particle dispersion [7], and the heating conditions in the third step, which consisted of holding at 60° C. for 3 hours, were changed to holding at 48° C. for 5 hours and then holding at 60° C. for 1 hour. This toner [18] had a volume-based median diameter of 6.3 μm and an average circularity of 0.966.

<Comparative Example 3>
A toner [19] was obtained in the same manner as in Example 1, except that 1,600 parts by mass of the styrene-acrylic resin fine particle dispersion [1] used in the toner production process was changed to 1,600 parts by mass of the styrene-acrylic resin fine particle dispersion [4]. This toner [19] had a volume-based median diameter of 6.2 μm and an average circularity of 0.967.

For the obtained toners [1] to [19], the endothermic peak rise temperature T ₁ °C derived from the crystalline polyester resin, the endothermic peak temperature T ₂ °C, the endothermic peak temperature T ₃ °C derived from the release agent, and the toner flow start temperature T _fb °C in a flow tester were measured during the first temperature rise process when the differential scanning calorimetry was measured for each toner. The results are shown in Table I together with the toner composition and the production conditions (heating conditions in the third step). The content of each resin constituting the binder resin is the mass parts per 100 mass parts of the binder resin. The content of the release agent is the mass parts relative to 100 mass parts of the binder resin. In the table, "StAc resin" refers to styrene acrylic resin. The release agent "R-582" refers to SELOSOL R-582.

[Developer Production Examples 1 to 19]
To each of the toners [1] to [19], a silicone resin-coated ferrite carrier having a volume-based median diameter of 60 μm was added so that the toner concentration was 6 mass %, and the toners were mixed in a V-type mixer to produce developers [1] to [19].

[Toner Evaluation]
The toners [1] to [19] and the developers [1] to [19] containing the toners [1] to [19] prepared as described above were evaluated as follows, and the results are shown in Table II.

(1) Evaluation of low-temperature fixing property For the low-temperature fixing property, a commercially available copying machine "bizhub PRO C6550" (manufactured by Konica Minolta) was used as an image evaluation device, which was modified so that the surface temperature of the heat fixing roller (measured at the center of the roller) could be changed to a range of 100 to 200°C. Developers [1] to [19] were installed as developers (black), and a fixing experiment was performed in which a solid image (black) with a toner adhesion amount of 8 mg/ ^cm2 was fixed on A4-sized fine paper under a normal temperature and normal humidity environment (temperature 20°C, humidity 50% RH). The fixing temperature setting was changed so that it was increased in 1°C increments from 120°C to 200°C. The lowest temperature among the fixing experiments at which image staining due to low-temperature offset was not visually observed was evaluated as the minimum fixing temperature. A minimum fixing temperature of less than 137°C was evaluated as passing.

(Evaluation criteria)
◎: Less than 130°C 〇: 130 to less than 134°C △: 134 to less than 137°C ×: 137°C or higher

(2) Evaluation of fixation separation property Using the same image evaluation device as that used for the evaluation of low-temperature fixation property, the surface temperature of the heat fixing roller was set to 160° C., and an A4 size paper having a 5 cm wide solid black belt image in the direction perpendicular to the conveying direction was conveyed in a vertical feed, and the separation property between the heat fixing roller on the image side and the paper was evaluated according to the following evaluation criteria. In the present invention, the evaluation criteria of "◯" or "△" are regarded as passing.

(Evaluation criteria)
◯: The paper is separated from the heat fixing roller without curling.
Δ: The paper is separated from the heat fixing roller, but the leading edge of the paper curls slightly (no problem in practical use).
x: The paper is separated from the heat fixing roller, but the gloss of the image surface is uneven, or the paper is wrapped around the heat fixing roller and cannot be separated from the heat fixing roller.

(3) Evaluation of heat-resistant storage stability 0.5 g of toner was placed in a 10 mL glass bottle with an inner diameter of 21 mm, the lid was closed, and the bottle was shaken 600 times at room temperature with a tap denser KYT-2000 (manufactured by Seishin Enterprise Co., Ltd.), and then the bottle was left for 2 hours in an environment with three levels of temperature, 57.5°C, 60.0°C, and 62.5°C, and 35% RH, with the lid removed. Next, the toner was placed on a 48 mesh (opening 350 μm) sieve while being careful not to break up the toner aggregates, and set in a powder tester (manufactured by Hosokawa Micron Corporation), fixed with a pressing bar and a knob nut, adjusted to a vibration intensity with a feed width of 1 mm, and vibration was applied for 10 seconds, after which the ratio (mass %) of the amount of toner remaining on the sieve was measured.
The toner cohesion rate is a value calculated by the following formula.
Toner cohesion rate (%)=mass of toner remaining on sieve (g)/0.5 (g)×100

The toner coagulation rate is measured at the above three temperature levels, and the temperature at which the coagulation rate is 50% is estimated and designated as the 50% coagulation temperature. The toner's heat-resistant storage stability (50% coagulation temperature) is evaluated according to the criteria described below, and in this invention, a toner that meets the evaluation criteria of "◎", "◯" or "△" is deemed to pass.

(Evaluation criteria)
◎: 50% coagulation temperature is 62°C or higher (the toner has excellent heat-resistant storage properties)
Good: 50% coagulation temperature is 60° C. or higher and less than 62° C. (the toner has good heat-resistant storage properties)
△: 50% coagulation temperature is 57.5° C. or more and less than 60° C. (heat resistance storage property of the toner is slightly poor, but at an acceptable level)
×: 50% coagulation temperature is less than 57.5° C. (the toner has poor heat resistance and cannot be used)

From Table II, it can be seen that the toner of the present invention has excellent low-temperature fixing properties, as well as heat-resistant storage properties and fixing separation properties.

Claims (5)

A toner for developing an electrostatic image, comprising toner base particles containing a binder resin and a release agent,
The binder resin contains an amorphous resin and a crystalline resin,
the content of the crystalline resin is within a range of 4 to 31 parts by mass relative to 100 parts by mass of the binder resin, and the content of the release agent is within a range of 6 to 20 parts by mass relative to 100 parts by mass of the binder resin;
the crystalline resin includes a crystalline polyester resin, and the weight average molecular weight of the crystalline polyester resin is within a range of 4,000 to 10,000;
The toner for developing electrostatic images is characterized in that, when the rise temperature of the endothermic peak derived from the crystalline resin is _T1 °C, the endothermic peak temperature is _T2 °C, and the endothermic peak temperature derived from the release agent is _T3 °C during the first heating process in differential scanning calorimetry measurement of the toner for developing electrostatic images, the toner satisfies the following conditions (6), (7), (8), and ( 9 ):
(6) _T1 is in the range of 60 to 61°C.
(7) _T2 is in the range of 62-66°C.
(8) _T1 and _T2 have the following relationship:
_T2 ≦ _T1 +5° C.
( 9 ) _T2 and _T3 have the following relationship.
_T2 < _T3 ≦ _T2 + 10 ° C. The toner for developing electrostatic images according to claim 1, characterized in that the toner base particles have a core particle and a shell layer that covers the core particle, and the crystalline resin is contained in the core particle. 3. The toner for developing an electrostatic image according to claim 1, further satisfying the following condition (5) when the flow start temperature of the toner for developing an electrostatic image measured by a flow tester is T _fb °C:
(5) _T2 and _Tfb have the following relationship:
_T2 ≦ _Tfb ≦ _T2 +10° C. 4. The toner for developing electrostatic images according to claim 1 , wherein the content of the crystalline resin is within a range of 10 to 20 parts by mass with respect to 100 parts by mass of the binder resin. A method for producing the toner for developing electrostatic images according to any one of claims 1 to 4 , comprising the steps of:
a first step of heating and stirring fine particles containing the binder resin and the release agent in an aqueous medium to aggregate and fuse the particles, thereby obtaining a dispersion liquid containing a toner base particle precursor;
a second step of cooling the dispersion heated in the first step to a temperature of 30° C. or less at a temperature decreasing rate of 6° C./min or more;
a third step of maintaining the dispersion cooled in the second step at a temperature in the range of 57 to 62° C. for 30 minutes or more;
2. A method for producing a toner for developing an electrostatic image, comprising the steps of: producing the toner base particles by a method comprising the steps of: