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Title:
TONER FOR DEVELOPING ELECTROSTATIC IMAGE
Document Type and Number:
WIPO Patent Application WO/2021/150287
Kind Code:
A1
Abstract:
A toner for developing an electrostatic image includes a core including a binder resin, a colorant, and a release agent, and a shell disposed on at least a portion of the surface of the core. The binder resin includes a first styrene-acrylic resin and a second styrene-acrylic resin, and a crystalline polyester resin. A weight average molecular weight of the first styrene-acrylic resin (Mw1) is different from a weight average molecular weight of the second styrene-acrylic resin (Mw2). An amount of the crystalline polyester resin included in the binder resin is less than or equal to about 20 weight percent (wt.%) based on a total weight of the binder resin. A sum of the first and second styrene-acrylic resins is included in an amount of greater than or equal to about 80 wt.% based on the total weight of the binder resin. The first ratio (Mw/Mw1) of the weight average molecular weight of the crystalline polyester resin (Mw) to the weight average molecular weight of the first styrene-acrylic resin (Mw1) is in a range from 0.18 to 0.7, and the second ratio (Mw/Mw2) of the weight average molecular weight of the crystalline polyester resin (Mw) to the weight average molecular weight of the second styrene-acrylic resin (Mw2) is in a range from 0.01 to 0.05.

Inventors:
KIM DONGWON (KR)
KWON YOUNGJAE (KR)
KIM DONGWOO (KR)
KIM ILHYUK (KR)
KANG SUKJIN (KR)
Application Number:
PCT/US2020/058137
Publication Date:
July 29, 2021
Filing Date:
October 30, 2020
Export Citation:
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Assignee:
HEWLETT PACKARD DEVELOPMENT CO (US)
International Classes:
G03G9/087
Domestic Patent References:
WO2019209554A12019-10-31
Foreign References:
US20150079513A12015-03-19
US20090253065A12009-10-08
JP2009093083A2009-04-30
Attorney, Agent or Firm:
KO, Steve Sokbong et al. (US)
Download PDF:
Claims:
WHAT IS CLAIMED IS:

1. A toner for developing an electrostatic image, comprising: a core including a binder resin, a colorant, and a release agent; and a shell disposed on at least a portion of a surface of the core, wherein the binder resin comprises a first styrene-acrylic resin, a second styrene-acrylic resin, and a crystalline polyester resin, a weight average molecular weight of the first styrene-acrylic resin (Mwi) is different from a weight average molecular weight of the second styrene-acrylic resin (MW2), a weight average molecular weight of the crystalline polyester resin (Mw) is in a first ratio (Mw/Mwi) with respect to the weight average molecular weight of the first styrene-acrylic resin (Mwi) and in a second ratio (MW/MW2) with respect to the weight average molecular weight of the second styrene-acrylic resins (MW2), an amount of the crystalline polyester resin included in the binder resin is less than or equal to about 20 weight percent (wt.%) based on a total weight of the binder resin, a sum of the first styrene-acrylic resin and the second styrene- acrylic resin in the binder resin is greater than or equal to about 80 wt.% based on the total weight of the binder resin, the first ratio (Mw/Mwi) of the weight average molecular weight of the crystalline polyester resin (Mw) to the weight average molecular weight of the first styrene-acrylic resin (Mwi) is in a first range from 0.18 to 0.7, and the second ratio (Mw/Mw2) of the weight average molecular weight of the crystalline polyester resin (Mw) to the weight average molecular weight of the second styrene-acrylic resin (MW2) is in a second range from 0.01 to 0.05. 2. The toner of claim 1 , wherein the weight average molecular weight (Mw) of the crystalline polyester resin is about 1 ,000 g/mol to about 30,000 g/mol.

3. The toner of claim 1 , wherein the amount of the crystalline polyester resin included in the binder resin is about 5 wt.% to about 15 wt.%, in wt.% based on the total weight of the binder resin.

4. The toner of claim 1 , wherein the weight average molecular weight (Mwi) of the first styrene-acrylic resin is about 10,000 g/mol to about 50,000 g/mol, and the weight average molecular weight (MW2) of the second styrene-acrylic resin is about 100,000 g/mol to about 500,000 g/mol.

5. The toner of claim 1 , wherein an amount of the first styrene- acrylic resin included in the binder resin is about 70 wt.% to about 90 wt.% in wt.% based on the total weight of the binder resin, and an amount of the second styrene-acrylic resin included in the binder resin is in about 5 wt.% to about 15 wt.% in wt.% based on the total weight of the binder resin.

6. The toner of claim 1 , wherein the colorant comprises a black colorant, a yellow colorant, a magenta colorant, a cyan colorant, or a combination thereof.

7. The toner of claim 1 , wherein the release agent comprises polyethylene wax, polypropylene wax, silicone wax, paraffin wax, ester wax, carnauba wax, metallocene wax, or a mixture thereof.

8. The toner of claim 1 , wherein the shell has a higher glass transition temperature (Tg) than the binder resin of the core.

9. The toner of claim 1 , wherein a volume average particle diameter (D50) of the toner is greater than or equal to about 5 micrometers (pm) and less than or equal to about 8 pm. 10. The toner of claim 1 , wherein the toner has roundness of about

0.960 to about 0.990.

11 . The toner of claim 1 , wherein a glass transition temperature (Tg) of the toner is about 45 °C to about 60 °C.

12. The toner of claim 1 , wherein a fixation temperature of the toner is less than or equal to about 160 °C.

13. The toner of claim 1 , which further comprises an external additive disposed on at least a portion of the surface of the toner

14. A cartridge comprising the toner of claim 1 , wherein the cartridge is detachable from an image forming apparatus.

15. An image forming apparatus comprising the toner of claim 1.

Description:
TITLE

TONER FOR DEVELOPING ELECTROSTATIC IMAGE

BACKGROUND In order to cope with trends of color, high speed, and high quality of a printer, and to meet trends of miniaturization (light weight), low cost, and eco- friendliness, shapes and surface control technology of a toner become increasingly getting attentions to meet properties of toner for an electrophotographic process.

DETAILED DESCRIPTION

There is an increasing demand for a toner that is capable of simultaneously securing low temperature fixability and high-temperature storage stability. Due to the demands of an environmentally-friendly era, low- temperature fixation is becoming more demanded element in printing. Low- temperature fixation may reduce energy consumption per page and may also reduce volatile organic compounds (VOCs) generated during printing.

Hereinafter, an example of the disclosure will be described. The terminology used herein is for the purpose of describing specific examples and is not intended to be limiting of the disclosure. As used herein, the singular forms are intended to include plural forms as well, unless the context indicates otherwise. As used herein, the term "comprises" and/or "comprising" refers to the presence of specified features, integers, steps, acts, elements, and/or components, but it should also be understood that it does not exclude a presence or addition of another feature, integer, step, act, component, and/or group thereof. As used herein, the term “and/or” includes any one or all combinations of one or more related items. The term "coupled" denotes a physical relationship between two components in which components are directly connected to each other or indirectly connected through an intermediary component.

As used herein, when a specific definition is not otherwise provided, “substituted” means that at least one hydrogen atom of a functional group in a specific chemical formula is replaced by at least one substituent selected from a halogen atom (F, Br, Cl, or I), a hydroxy group, a nitro group, a cyano group, an amino group {NH2, NH(R 100 ), or N(R 101 )(R 102 ), wherein R 100 , R 101 , and R 102 are the same or different, and are independently a C1 to C10 alkyl group}, an amidino group, a hydrazine group, a hydrazone group, a carboxyl group, an oxo group, a C2 to C30 acyl group, a C1 to C30 alkyl group, a C1 to C30 alkyl group in which at least one hydrogen is replaced by a halogen atom, a C2 to C30 alkenyl group, a C2 to C30 alkynyl group, a C3 to C30 cycloalkyl group, a C3 to C30 cycloalkenyl group, a C6 to C30 aryl group, a C1 to C30 alkoxy group, and a C2 to C30 hetero cyclic group, and the foregoing substituents may be linked with each other to form a ring. As used herein, when a specific definition is not otherwise provided,

“alkyl group” refers to a C1 to C30 alkyl group, for example, a C1 to C15 alkyl group, “cycloalkyl group” refers to a C3 to C30 cycloalkyl group, for example, a C3 to C18 cycloalkyl group, “alkoxy group” refers to a C1 to C30 alkoxy group, for example, a C1 to C18 alkoxy group, “aryl group” refers to a C6 to C30 aryl group, for example, a C6 to C18 aryl group, “alkenyl group” refers to a C2 to C30 alkenyl group including at least one double bond, for example, a C2 to C18 alkenyl group including at least one double bond, “alkynyl group” refers to a C2 to C30 alkynyl group including at least one triple bond, for example, a C2 to C18 alkynyl group including at least one triple bond, “alkylene group” refers to a C1 to C30 alkylene group, for example, a C1 to C18 alkylene group, and “arylene group” refers to a C6 to C30 arylene group, for example, a C6 to C16 arylene group.

As used herein, when specific definition is not otherwise provided, "combination" may refer to "mixing" or "copolymerization".

Hereinafter, a toner for developing an electrostatic image according to an example of the disclosure will be described in detail.

As described above, in accordance with the demands of the recent environmentally friendly era, low-temperature fixation of toner has become a demanding element in printing. Low-temperature fixation may reduce energy consumption per page, and may also reduce volatile organic compounds (VOCs) from printing. On the other hand, high-temperature storage properties and durability against the environment should also be satisfied. High- temperature storage stability is valuable when a glass transition temperature (Tg) of the binder resin constituting the toner is high, while it is unfavorable in low-temperature fixability when the Tg of the binder resin is high. It may be a technical challenge to produce a toner that simultaneously satisfies high- temperature storage properties, durability, and low-temperature fixation characteristics. The toner for developing the electrostatic image according to an example of the disclosure satisfies the aforementioned demand by enabling low-temperature fixation while satisfying a certain level or more of high- temperature storage properties and durability against the environment. The toner for developing the electrostatic image according to an example includes a core and a shell disposed on at least a portion of the surface of the core, wherein the core includes a binder resin, a colorant, and a release agent, the binder resin includes first and second styrene-acrylic resins having different weight average molecular weights from each other, and a crystalline polyester resin having a weight average molecular weight in ratios with respect to the weight average molecular weights of the first and the second styrene-acrylic resins, the crystalline polyester resin is included in the binder resin in an amount of less than or equal to about 20 weight percent (wt.%), in wt.% based on a total weight of the binder resin, a sum of the first and second styrene-acrylic resins included in the binder resin is greater than or equal to about 80 wt.% based on a total weight of the binder resin, and each ratio Vi and V2 0f the weight average molecular weight of the crystalline polyester resin and the first and second styrene-acrylic resins satisfies the following ranges:

Vi in a range from 0.18 to 0.7, and V2 in a range from 0.01 to 0.05 Herein,

Vi=Mw (weight average molecular weight of crystalline polyester resin)/Mwi (weight average molecular weight of first styrene-acrylic resin), and

V2=MW (weight average molecular weight of crystalline polyester resin)/Mw2 (weight average molecular weight of second styrene-acrylic resin). That is, the binder resin included in the core of the toner according to an example includes two styrene-acrylic resins having different weight average molecular weights from each other, and a crystalline polyester resin having a weight average molecular weight where the ratios of the weight average molecular weight of the crystalline polyester resin relative to the weight average molecular weights of the two styrene-acrylic resins, which may be expressed as Vi and V2 as a content ratio. Therefore, due to the styrene-acrylic resin having a value of glass transition temperature (Tg) or more of a certain level, it is possible to suitably reflect the properties of the polyester resin, which is suitable for low-temperature fixation, without deteriorating high-temperature stability or heat storage properties.

The polyester resin may be suitable for low-temperature fixation due to an intermolecular interaction, but due to the above characteristics, the interaction between the toner particles may be strong, which may result in aggregation during toner production and demand strong crushing power. In addition, productivity may decrease due to a pipe adhesion phenomenon due to a decrease of fluidity during drying, and it may be to apply a physical impact to remove the toner adhered to the pipe. In addition, the water-absorbing property tends to be inferior in high-temperature/high-humidity conditions, and may cause toner solidification depending on distribution environments. In addition, poor flowability of the toner may cause a hindrance of toner supply from the cartridge.

On the other hand, the styrene-acrylic resin has a high glass transition temperature (Tg), which may be unsuitable for low-temperature fixation of the toner. In order to solve this, when the Tg is lowered, the styrene-acrylic resin becomes thermally vulnerable and thus heat storage properties in high- temperature/high-humidity conditions may be poor. In order to solve this, research has been conducted to secure high-temperature and high-humidity storage stability by changing the structure of the core-shell, but this method has a limitation in implementing low-temperature fixation performance.

According to an example, the toner includes a core made of a binder resin including two resins having the above characteristics in a range satisfying specific contents and ratios of specific molecular weights, thereby enabling low- temperature fixation without deteriorating heat storage properties. Thus, the toner according to an example may be fixed at a lower temperature, for example, a temperature of less than or equal to about 160 °C, about 150 °C to about 158 °C, or about 150 °C to about 155 °C, and may exhibit improved heat storage properties and fluidity. According to an example, Vi may be in a range from about 0.19 to about

0.69, for example, about 0.2 to about 0.68, or about 0.2 to about 0.67, and V2 may be in a range from about 0.012 to about 0.045, for example about 0.013 to about 0.04, or about 0.014 to about 0.04, but these ranges may not limited to thereto. As indicated by the ranges of Vi and V2, the crystalline polyester resin in the toner according to an example has a weight average molecular weight that is relatively low compared with the weight average molecular weight of the first styrene-acrylic resin and the second styrene-acrylic resin. Although the weight average molecular weight of the crystalline polyester resin is lower than the weight average molecular weight of the first and the second styrene-acrylic resins, a glass transition temperature of the toner according to an example including the crystalline polyester resin having such a low weight average molecular weight as the binder resin of the core is not sufficiently lowered, and thus heat storage properties of the toner are hardly lowered. As described above, the reason is that the content of the crystalline polyester resin is less than or equal to about 20 wt.% based on the total weight of the binder resin of the toner according to an example, while a sum of the first and the second styrene-acrylic resins is greater than or equal to about 80 wt.% based on the total weight of the binder resin, and thus a relatively small amount of crystalline polyester resin is included.

According to an example, the crystalline polyester resin may be included in an amount of about 5 wt.% to about 18 wt.%, for example, about 5 wt.% to about 15 wt.%, about 5 wt.% to about 13 wt.%, or about 5 wt.% to about 10 wt.%, based on the total weight of the binder resin, but may not be limited thereto. When the crystalline polyester resin is included in an amount of greater than or equal to about 20 wt.%, it may be leaked or exposed out of the toner and the glass transition temperature of the toner may be lowered. As a result, the heat storage properties of the toner may be reduced. When the crystalline polyester resin is included in an amount of less than or equal to about

5 wt.%, a low-temperature fixation effect due to the addition of the crystalline polyester resin may be insufficient.

According to an example, the sum of the first and the second styrene- acrylic resins may be included in an amount of about 80 wt.% to about 95 wt.%, for example, about 85 wt.% to about 95 wt.%, or about 90 wt.% to about 95 wt.%, based on the total weight of the binder resin, but may not be limited thereto. When the total sum of the first and the second styrene-acrylic resins is less than 80 wt.% based on the total weight of the binder resin, the glass transition temperature of the toner may be lowered, and thus, the heat storage properties may be lowered. If the sum of the first and the second styrene- acrylic resins exceeds 95 wt.% based on the total weight of the binder resin, the low-temperature fixation effect may be insufficient.

On the other hand, the first styrene-acrylic resin may be included in an amount of about 70 wt.% to about 90 wt.% based on the total weight of the binder resin and the second styrene-acrylic resin may be included in an amount of about 5 wt.% to about 15 wt.% based on the total weight of the binder resin. According to an example, the first styrene-acrylic resin may be included in an amount of about 75 wt.% to about 90 wt.%, for example, about 80 wt.% to about 90 wt.%, or about 85 wt.% to about 90 wt.%, based on the total weight of the binder resin, and the second styrene-acrylic resin may be included in an amount of about 5 wt.% to about 10 wt.% based on the total weight of the binder resin, but may not be limited thereto.

As described above, the content of the first styrene-acrylic resin is higher than that of the second styrene-acrylic resin, which means that the first styrene- acrylic resin having a smaller weight average molecular weight is included more than the second styrene-acrylic having a higher weight average molecular weight.

As seen from Vi and V2, among the components constituting the binder resin, the weight average molecular weight of the crystalline polyester resin is the lowest, the weight average molecular weight of the first styrene-acrylic resin is next lowest, and the weight average molecular weight of the second styrene- acrylic resin is the highest. According to an example, the weight average molecular weight of crystalline polyester resin may be about 1 ,000 gram/mole (g/mol) to about 30,000 g/mol, for example, about 1 ,000 g/mol to about 25,000 g/mol, about 1 ,000 g/mol to about 20,000 g/mol, about 1 ,000 g/mol to about 15,000 g/mol, about 1 ,000 g/mol to about 10,000 g/mol, about 2,000 g/mol to about 25,000 g/mol, about 2,000 g/mol to about 20,000 g/mol, about 2,000 g/mol to about 15,000 g/mol, about 2,000 g/mol to about 10,000 g/mol, about 2,500 g/mol to about 25,000 g/mol, about 2,500 g/mol to about 20,000 g/mol, about 2,500 g/mol to about 15,000 g/mol, about 2,500 g/mol to about 10,000 g/mol, about 3,000 g/mol to about 25,000 g/mol, about 3,000 g/mol to about 20,000 g/mol, about 3,000 g/mol to about 15,000 g/mol, about 3,000 g/mol to about 10,000 g/mol, about 4,000 g/mol to about 30,000 g/mol, about 4,000 g/mol to about 25,000 g/mol, about 4,000 g/mol to about 20,000 g/mol, about 4,000 g/mol to about 15,000 g/mol, about 4,000 g/mol to about 10,000 g/mol, about 5,000 g/mol to about 30,000 g/mol, about 5,000 g/mol to about 250,000 g/mol, about 5,000 g/mol to about 20,000 g/mol, about 5,000 g/mol to about 15,000 g/mol, or about 5,000 g/mol to about 10,000 g/mol, but may not be limited thereto.

As described above, the crystalline polyester resin has a relatively high glass transition temperature even at a low molecular weight. Accordingly, when it has a low weight average molecular weight as described above and is included in the binder resin of the toner according to an example in a small amount, the low-temperature fixation performance may be improved without substantially lowering the glass transition temperature of the toner. When the weight average molecular weight of the crystalline polyester resin exceeds about 30,000 g/mol, the weight average molecular weight of the first and the second styrene-acrylic resins must also be larger to satisfy the above- mentioned ratios of Vi and V2. In this case, the weight average molecular weight of the binder resin may become large as a whole, and as a result, the glass transition temperature may increase, which may deteriorate low temperature fixability of the toner. In addition, when the weight average molecular weight of the binder resin is too large, it may be difficult to produce a uniform core. According to an example, when the weight average molecular weight of the crystalline polyester resin is larger than the above range, there may be a possibility that the binder resin may leaked or exposed out of the toner. On the contrary, when the weight average molecular weight of the crystalline polyester resin is less than 1 ,000 g/mol, the molecular weight is too small to lower the glass transition temperature of the toner, which may lower the heat storage properties of the toner.

When having the weight average molecular weight described above, a melting point of the crystalline polyester resin may be between about 50 °C to about 70 °C. In addition, the glass transition temperature of the crystalline polyester resin may be less than or equal to about 45 °C, for example, about 40 °C to about 45 °C.

According to an example, the weight average molecular weight of the first styrene-acrylic resin may be about 10,000 g/mol to about 50,000 g/mol, for example, about 10,000 g/mol to about 45,000 g/mol, about 10,000 g/mol to about 40,000 g/mol, about 10,000 g/mol to about 35,000 g/mol, about 10,000 g/mol to about 30,000 g/mol, about 10,000 g/mol to about 25,000 g/mol, about 10,000 g/mol to about 20,000 g/mol, about 10,000 g/mol to about 15,000 g/mol, about 12,000 g/mol to about 50,000 g/mol, about 12,000 g/mol to about 45,000 g/mol, about 12,000 g/mol to about 40,000 g/mol, about 12,000 g/mol to about 35,000 g/mol, about 12,000 g/mol to about 30,000 g/mol, about 12,000 g/mol to about 25,000 g/mol, about 12,000 g/mol to about 15,000 g/mol, about 15,000 g/mol to about 50,000 g/mol, about 15,000 g/mol to about 45,000 g/mol, about 15,000 g/mol to about 40,000 g/mol, about 15,000 g/mol to about 35,000 g/mol, about 15,000 g/mol to about 30,000 g/mol, about 15,000 g/mol to about 25,000 g/mol, or about 15,000 g/mol to about 20,000 g/mol, but may not be limited thereto. When the weight average molecular weight of the first styrene-acrylic resin exceeds about 50,000 g/mol, the weight average molecular weights of the crystalline polyester resin and the second styrene-acrylic resin are further increased to satisfy the above-mentioned ratios of Vi and V2. In this case, the weight average molecular weight of the binder resin as a whole is too large, making it difficult to prepare a uniform core, and there is a possibility that low- temperature fixability of the toner may be deteriorated due to an increase of the glass transition temperature. On the contrary, when the weight average molecular weight of the first styrene-acrylic resin is less than about 10,000 g/mol, the molecular weight is too small to lower the glass transition temperature of the toner, which may lower heat storage properties of the toner. In particular, the first styrene-acrylic resin is included in the largest content range of the binder resin, and reduction of the weight average molecular weight of the first styrene- acrylic resin may greatly lower the glass transition temperature of the entire binder resin.

When having the aforementioned weight average molecular weight, the glass transition temperature of the first styrene-acrylic resin may be less than or equal to about 50 °C, for example, about 45 °C to about 50 °C.

According to an example, the weight average molecular weight of second styrene-acrylic resin may be about 100,000 g/mol to about 500,000 g/mol, for example, about 100,000 g/mol to about 450,000 g/mol, about 100,000 g/mol to about 400,000 g/mol, about 100,000 g/mol to about 350,000 g/mol, about 100,000 g/mol to about 300,000 g/mol, about 100,000 g/mol to about 250,000 g/mol, about 100,000 g/mol to about 200,000 g/mol, about 100,000 g/mol to about 150,000 g/mol, about 150,000 g/mol to about 500,000 g/mol, about 150,000 g/mol to about 450,000 g/mol, about 150,000 g/mol to about 400,000 g/mol, about 150,000 g/mol to about 350,000 g/mol, about 150,000 g/mol to about 300,000 g/mol, about 150,000 g/mol to about 250,000 g/mol, about 150,000 g/mol to about 200,000 g/mol, about 200,000 g/mol to about 500,000 g/mol, about 200,000 g/mol to about 450,000 g/mol, about 200,000 g/mol to about 400,000 g/mol, about 200,000 g/mol to about 350,000 g/mol, about 200,000 g/mol to about 300,000 g/mol, about 200,000 g/mol to about 250,000 g/mol, about 250,000 g/mol to about 500,000 g/mol, about 250,000 g/mol to about 450,000 g/mol, about 250,000 g/mol to about 400,000 g/mol, about 250,000 g/mol to about 350,000 g/mol, or about 250,000 g/mol to about 300,000 g/mol, but may not be limited thereto. When the weight average molecular weight of the second styrene-acrylic resin exceeds about 500,000 g/mol, the weight average molecular weights of the crystalline polyester resin and the first styrene-acrylic resin are further increased in order to satisfy the above-mentioned ratios of Vi and V2. In this case, the weight average molecular weight of the binder resin as a whole is too large, making it difficult to prepare a uniform core, and there is a concern that low-temperature fixability of the toner may be deteriorated due to an increase of the glass transition temperature. On the contrary, when the weight average molecular weight of the second styrene-acrylic resin is less than about 100,000 g/mol, the weight average molecular weight of all the resins forming the binder resin is too small to lower the glass transition temperature of the toner, which may lower heat storage properties of the toner. When having the aforementioned weight average molecular weight, the glass transition temperature of the second styrene-acrylic resin may be less than or equal to about 65 °C, for example, about 55 °C to about 65 °C, or about 58 °C to about 63 °C.

According to an example, the weight average molecular weight of first styrene-acrylic resin may be about 15,000 g/mol to about 25,000 g/mol, and the weight average molecular weight of second styrene-acrylic resin may be about 250,000 g/mol to about 350,000 g/mol. When the first styrene-acrylic resin and the second styrene-acrylic resin having weight average molecular weights in these ranges are selected and accordingly a crystalline polyester resin having a weight average molecular weight satisfying the Vi and V2 is selected, the binder resin for forming the core of the toner according to an example may be produced. According to an example, the weight average molecular weight of the crystalline polyester resin may be in a range of about 5,000 g/mol to about 15,000 g/mol.

Types of the crystalline polyester resin, the first styrene-acrylic resin, and the second styrene-acrylic resin for constituting the binder resin included in the core of the toner according to an example are not particularly limited. Any crystalline polyester resin, first styrene-acrylic resin, and second styrene-acrylic resin known in the art may be appropriately selected.

Generally, the polyester resin may be prepared by reacting aliphatic, cycloaliphatic, or aromatic polyhydric carboxylic acid or its alkyl esters with polyhydric alcohol, via direct esterification or transesterification reaction.

Examples of the polyhydric carboxylic acid that may be used for polyester production may include, but may not be limited to, phthalic acid, isophthalic acid, terephthalic acid, tetrachlorophthalic acid, chlorophthalic acid, nitrophthalic acid, p-carboxyphenylacetic acid, p-phenylene acetic acid, m- phenylenediglycolic acid, p-phenylenediglycolic acid, o-phenylenediglycolic acid, diphenylacetic acid, diphenyl-p,p'-dicarboxylic acid, naphthalene-1 ,4- dicarboxylic acid, naphthalene-1 , 5-dicarboxylic acid, naphthalene-2, 6- dicarboxylic acid, anthracenedicarboxylic acid, or cyclohexanedicarboxylic acid. Moreover, a polyhydric carboxylic acid other than dicarboxylic acid, for example, trimellitic acid, pyromellitic acid, naphthalene tricarboxylic acid, naphthalene tetracarboxylic acid, pyrene tricarboxylic acid, pyrene tetracarboxylic acid, and the like, may also be used. Moreover, the carboxy group of these carboxylic acids may be derived with an acid anhydride, an acid chloride, or an ester. Among these, terephthalic acid, its lower ester, diphenylacetic acid, cyclohexane dicarboxylic acid, and the like may be used. Lower ester refers to an ester of aliphatic alcohols having 1 to 8 carbon atoms.

In addition, examples of the polyhydric alcohol that may be used for polyester production may include, but may not be limited to, aliphatic diols such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, butanediol, hexanediol, neopentyl glycol, and glycerin; alicyclic diols such as cyclohexane diol, cyclohexane dimethanol, and hydrogenated bisphenol A; and aromatic diols such as an ethylene oxide addition product of bisphenol A and a propylene oxide addition product of bisphenol A. One or two or more types of these polyhydric alcohols may be used, among them, aromatic diols or alicyclic diols may be used, and for example, aromatic diols may be used. In order to secure good fixability, trivalent or higher polyhydric alcohols (glycerine, trimethylolpropane, or pentaerythritol) may be used together with the diols in order to obtain a cross-linked structure or a branched structure.

On the other hand, the polyester may be divided into amorphous polyester and crystalline polyester. The amorphous polyester may prepared by polymerizing an aromatic monomer, and the crystalline polyester may be polymerized using an aliphatic monomer alone.

Among the polyester resins prepared by the method described above, the crystalline polyester resin that may be used as the binder resin of the toner according to an example may include, for example, poly(ethylene-adipate), poly(propylene-adipate), poly(butylene-adipate), poly(pentylene-adipate), poly(hexene-adipate), poly(octylene-adipate), poly(ethylene-succinate), poly(propylene-succinate), poly(butylene-succinate), poly(pentylene-succinate), poly(hexene-succinate), poly(octylene-succinate), poly(ethylene-sebacate), poly (propylene-sebacate), poly(butylene-sebacate), poly(pentylene-sebacate), poly(hexene-sebacate), poly(octylene-sebacate), poly(decylene-sebacate), poly(decylene-decanoate), poly(ethylene-decanoate), poly(ethylene- dodecanoate), poly(nonylene-sebacate), poly(nonylene-decanoate), copoly(ethylene-fumarate)-copoly(ethylene-sebacate), copoly(ethylene- fumarate)-copoly(ethylene-decanoate), copoly(ethylene-fumarate)- copoly(ethylene-dodecanoate), and the like. Among them, as a relatively inexpensive crystalline polyester, poly(1 ,9-nonylene-1 ,12-dodecanoate), poly(1 ,6-hexene-1 ,12-dodecanoate), poly(1 ,6-hexene-1 ,10-decanoate), and the like may be used. The first and second styrene-acrylic resins may each be a copolymer obtained by independently copolymerizing styrene with substituted or unsubstituted (meth)acrylic acid, substituted or unsubstituted (meth)acrylate, or a combination thereof. Examples of the substituted or unsubstituted (meth)acrylic acid or the substituted or unsubstituted (meth)acrylate may include methyl acrylate, ethyl acrylate, butyl acrylate, butyl isoacrylate, dodecyl acrylate, n-octyl acrylate, 2-chloroethyl acrylate, b-carboxyethyl acrylate (b-CEA), phenyl acrylate, methyl alpha chloroacrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, and the like, but may not be limited thereto. Examples of the copolymer in which styrene is copolymerized with substituted or unsubstituted (meth) acrylic acid, substituted or unsubstituted (meth) acrylate, or a combination thereof may independently be a styrene-acrylic acid ester copolymer, a styrene-methacrylic acid ester copolymer, a styrene-(alpha)-chloro methacrylate methyl copolymer, and the like, but may not be limited thereto. In the case where each resin is obtained by polymerization of monomers for preparing resins, a polymerization initiator may be potassium persulfate, ammonium persulfate, benzoyl peroxide, lauryl peroxide, sodium persulfate, hydrogen peroxide, t-butyl hydroperoxide, cumene hydroperoxide, para- methane peroxide, peroxy carbonate, or a mixture thereof, but may not be limited to these.

On the other hand, the binder resin included in the core of the toner according to an example includes the crystalline polyester resin and the first and second styrene-acrylic resins as a main component, but other additional resins may be further included, provided these are included in an amount of less than or equal to about 20 wt.% and greater than or equal to about 80 wt.%, respectively, based on the total weight of the binder resin. Examples of such other resins include vinyl resins, polyolefin resins, polyether polyol resins, phenol resins, silicone resins, epoxy resins, polyamide resins, polyurethane resins, polybutadiene resins, or mixtures thereof, but may not be limited thereto. A non-limiting example of the vinyl resin or polyolefin resin may include polyvinyl chloride, polyethylene, polypropylene, polyacrylonitrile, polyvinyl acetate, or a mixture thereof. The other resins may be included, for example, in an amount of less than or equal to about 5 wt.% based on the total weight of the binder resin. The colorant included in the core of the toner according to an example may include a black colorant, a yellow colorant, a magenta colorant, a cyan colorant, or a combination thereof, but may not be limited thereto.

The black colorant may be, but may not be limited to, carbon black, aniline black, or a mixture thereof, but may not be limited thereto.

The yellow colorant may be a condensed nitrogen compound, an isoindolinone compound, an anthrakin compound, an azo metal complex, an allyl imide compound, or a mixture thereof. It may be, for example, "Cl Pigment Yellow" 12, 13, 14, 17, 62, 74, 83, 93, 94, 95, 109, 110, 111 , 128, 129, 147, 168, or 180, but may not be limited thereto.

The magenta colorant may be a condensed nitrogen compound, an anthrakin compound, a quinacridone compound, a base dye rate compound, a naphthol compound, a benzo imidazole compound, a thioindigo compound, a perylene compound, or a mixture thereof. It may be for example "Cl Pigment Red" 2, 3, 5, 6, 7, 23, 48: 2, 48: 3, 48: 4, 57: 1 , 81 : 1 , 122, 144, 146, 166, 169, 177, 184 , 185, 202, 206, 220, 221 , or 254, but may not be limited thereto.

The cyan colorant may be a copper phthalocyanine compound or a derivative thereof, an anthrakin compound, a base dye rate compound, or a mixture thereof. It may be for example "Cl Pigment Blue" 1 , 7, 15, 15:1 , 15:2 , 15:3, 15:4, 60, 62, or 66, but may not be limited thereto.

The content of the colorant may not be limited thereto, but may be, for example, in a range of about 0.5 parts by weight to about 15 parts by weight, a range of about 1 part by weight to about 15 parts by weight, a range of about 1 part by weight to about 12 parts by weight, a range of about 2 parts by weight to about 15 parts by weight, a range of about 2 parts by weight to about 10 parts by weight, a range of about 3 parts by weight to about 15 parts by weight, a range of about 3 parts by weight to about 10 parts by weight, a range of about 5 parts by weight to about 15 parts by weight, or a range of about 5 parts by weight to about 10 parts by weight, based on 100 parts by weight of the binder resin. When the content of the colorant is greater than or equal to about 0.5 parts by weight based on 100 parts by weight of the toner, a coloring effect may be sufficiently realized. When it is less than or equal to about 15 parts by weight, a sufficient amount of triboelectric charge may be provided without substantially affecting the increase in the manufacturing cost of the toner.

A release agent may serve to impart glossiness to the toner and prevent the toner particles from adhering to a heating roller of the fixing unit or the like. Such a release agent may include, but may not be limited to, polyethylene wax, polypropylene wax, silicone wax, paraffin wax, ester wax, carnauba wax, metallocene wax, or a mixture thereof.

The release agent that may be used may be one having a melting point in the range of about 50 °C to about 150 °C, for example, about 60 °C to about 100 °C, or about 70 °C to about 90 °C, but may not be limited thereto. By having the melting point within the range, it is possible to aggregate well with the binder resin and the like in the preparation of the toner according to an example, thereby imparting proper glossiness and a proper release property to the toner during printing. The release agent is in physical contact with the toner particles but does not covalently bind with the toner particles.

Content of the release agent may be, for example, in a range of about 1 part by weight to about 20 parts by weight, about 1 part by weight to about 18 parts by weight, about 1 part by weight to about 15 parts by weight, about 1 part by weight to about 10 parts by weight, about 1 part by weight to about 8 parts by weight, about 2 parts by weight to about 20 parts by weight, about 2 parts by weight to about 15 parts by weight, about 2 parts by weight to about 10 parts by weight, about 2 parts by weight to about 8 parts by weight, or about 2 parts by weight to about 5 parts by weight based on 100 parts by weight of the binder resin, but may not be limited thereto.

The toner according to an example includes a shell disposed on at least a portion of the surface of the core. The shell may have a higher glass transition temperature (Tg) than the binder resin of the core.

The resin included in the shell may be any resin as long as it has a higher glass transition temperature than that of the binder resin included in the core and may be generally used in the field of toner production, and may not be limited to a particular resin. Examples of resins that may be used to form the shell may include, but may not be limited to, styrene resins, acrylic resins, polyolefin resins, polyamide resins, polyester resins, polyvinyl resins, polyurethane resins, epoxy resins, silicone resins, or mixtures or copolymers of two or more thereof, but may not be limited thereto. According to an example, the shell may be disposed on the entire surface of the core of the toner.

The toner according to an example may be prepared by a pulverization method, an emulsion polymerization method, a spray method, or the like.

The pulverization method may further include, for example, melting and mixing the binder resin, the colorant, and the release agent, and then pulverizing, selecting, and separating (or sieving) processes for selecting sizes of the pulverized toner particles having a predetermined range. The pulverization method may make it difficult to precisely control the sizes (particle sizes) of the toner particles, particle size distribution, and the toner structure. It may also be difficult to independently design each major characteristic required for a toner such as charging, fixation, fluidity, or storage properties.

The emulsion polymerization method may include, for example, mixing dispersion of the binder resin, dispersion of the colorant, and dispersion of the release agent; if necessary, by using a method such as stirring and/or heating or by adding a coagulant, aggregating the particles in the mixed dispersion to have a certain size; heating the obtained aggregates to aggregate them again to a larger particle size; and if necessary, with or without additional resin for shell formation, adding an inorganic salt to prevent further aggregation followed by further heating to fuse (or unify) the components in the toner particles. The heating of the aggregates to aggregate them to a larger particle size may be performed at a temperature below the glass transition temperature of the binder resin, for example, at a temperature of about 45 °C to about 55 °C. During the formation of the shell, a binder resin having a higher glass transition temperature than the binder resin of the core may be used, and the pH may be fixed to 6 to 7 in a fixing process to prevent further aggregation before shell formation. In addition, the fusion (unification) process of the components in the toner particles may be performed at about 90 °C to about 98 °C, which is about 30 °C to about 50 °C higher than the glass transition temperature of the toner. The toner particles obtained in the unification process may be further subjected to washing with water and drying. At this time, the reactor contents including toner particles are rapidly cooled to room temperature, then filtered, and the filtrate is removed, and then the toner particles are washed with water. Pure water having conductivity of less than or equal to about 5 uS/cm may be used for the washing, and the washing may be performed until the conductivity of the filtrate after washing the toner is less than or equal to about 5 uS/cm. The washing of the toner with pure water may be carried out in a batch or continuous manner. The washing of the toner using pure water may be performed to remove unnecessary components other than toner components such as impurities that may affect chargeability of the toner and an unnecessary coagulant that does not participate in aggregation. The toner obtained after the washing process may be dried using a flash jet dryer (FJD) or the like, and the moisture content percentage in the toner may be suppressed to less than or equal to about 1 wt.% during drying. The emulsion polymerization method may easily adjust sizes of the toner particles to have desired particle sizes and particle size distribution, and no additional process such as pulverizing or sieving is necessary. In addition, the toner produced by the emulsion polymerization method has a smaller particle size and a narrower particle size distribution than the toner produced by the pulverization method and thus has high charging and transferring efficiency, improved dot and line reproducibility, low toner consumption, high image quality, and the like. Therefore, the toner according to an example may be prepared by an emulsion polymerization method, but may not be limited thereto. The volume average particle diameter (D50) of the toner according to an example, which may be prepared by one of the above methods, may be, for example, in a range of greater than or equal to about 4 micrometers (pm) and less than or equal to about 9 pm, for example, greater than or equal to about 5 micrometers (pm) and less than or equal to about 8 pm, about 5 pm to about 7.5 pm, about 5 pm to about 7 pm, about 5.1 pm to about 8 pm, about 5.1 pm to about 7.5 pm, about 5.1 pm to about 7 pm, about 5.1 pm to about 6.5 pm, about

5.2 pm to about 8 pm, about 5.1 pm to about 7.5 pm, about 5.2 pm to about 7 pm, about 5.2 pm to about 6.5 pm, about 5.2 pm to about 6 pm, about 5.3 pm to about 8 pm, about 5.3 pm to about 7.5 pm, about 5.3 pm to about 7 pm, about

5.3 pm to about 6.5 pm, about 5.3 pm to about 6 pm, about 5.5 pm to about 8 pm, about 5.5 pm to about 7.5 pm, about 5.5 pm to about 7 pm, about 5.5 pm to about 6.5 pm, or about 5.5 pm to about 6 pm, but may not be limited thereto. Here, the volume average particle size (D50) represents a particle size of 50 % in the cumulative percentage in a cumulative distribution curve of the toner particles according to an example.

In general, the smaller the toner particles are, the more favorable it is to obtain a high resolution and high image quality, but at the same time, the toner particles are disadvantageous in view of transfer rates and washing powers. Accordingly, they may be adjusted to have an appropriate particle size. The volume average particle diameter of the toner may be measured by an electrical resistance method. When the volume average particle diameter of the toner particles is greater than or equal to about 4 pm, the photosensitive member is easy to wash, a yield of mass production may be improved, problems due to scattering may be prevented, and high resolution and high quality images may be obtained. When the volume average particle diameter of the toner particles is less than or equal to about 9 pm, charging may be made uniformly, the fixability of the toner may be improved, and a doctor blade may easily regulate the toner layer.

Shapes of the core particles are also not particularly limited. The closer the shapes of the core particles to the spherical shape, the more charge stability of the toner and dot reproducibility of the printed image may be further improved. For example, the core particle may have roundness within a range of about 0.940 to about 0.990, about 0.940 to about 0.985, about 0.960 to about 0.980, about 0.950 to about 0.990, about 0.950 to about 0.985, about 0.960 to about

0.980, about 0.960 to about 0.990, about 0.965 to about 0.990, about 0.965 to about 0.985, about 0.965 to about 0.980, about 0.970 to about 0.990, about 0.970 to about 0.985, about 0.970 to about 0.980, about 0.975 to about 0.990, about 0.975 to about 0.985, about 0.975 to about 0.980, about 0.980 to about

0.990, or about 0.985 to about 0.990. The average roundness of toner particles may be calculated by the method described below. The roundness value is a value between 0 and 1 . The closer the roundness value is to 1 , the closer to the spherical shape. When the average roundness of the toner particles is greater than or equal to about 0.940, the height of the image developed on the transfer material is appropriate to reduce toner consumption, and voids between the toners are not too large to obtain a sufficient coating ratio on the image developed on the transfer material. If the average roundness of the toner is less than or equal to 0.980, it is possible to prevent the toner from being excessively supplied onto the developing sleeve, thereby evening uneven coating of the sleeve with the toner, which causes contamination.

As an index of the toner particle size distribution, a volume average particle size distribution index GSDv or a number average particle size distribution index GSDp may be used. PSDv and PSDp values of the toner particles for developing an electrostatic image according to an example may be less than or equal to about 1.3 and less than or equal to about 1.25, respectively. The GSDv value may be less than or equal to about 1.30, for example, about 1.15 to about 1.30, and the GSDp value may be less than or equal to about 1.25, for example, about 1.20 to about 1.25. When the GSDv value and the GSDp value satisfy the above ranges, a uniform particle size of the toner may be obtained.

A glass transition temperature of the toner according to an example may be about 45 °C to about 60 °C, for example, about 45 °C to about 58 °C, about 45 °C to about 57 °C, about 45 °C to about 55 °C, about 45 °C to about 54 °C, or about 46 °C to about 53 °C, but may not be limited thereto. When the glass transition temperature of the toner is in the above range, a lower fixation temperature may be realized while maintaining appropriate high-temperature storage properties and durability against the environment. When the glass transition temperature exceeds 60 °C, it may be difficult to implement a low fixation temperature, while when the glass transition temperature is less than 45 °C, high-temperature storage properties or durability against the environment may be deteriorated. The toner according to an example includes a crystalline polyester resin together with the first and second styrene-acrylic resins to form the core, and thereby the core may have a low glass transition temperature within the above range compared with the toner including styrene-acrylic resin alone in the core. The fixation temperature of the toner according to an example may be less than or equal to about 160 °C. For example, the fixation temperature may be about 150 °C to about 160 °C, about 153 °C to about 157 °C, or about 155 °C. When in this temperature range, low-temperature fixation of the toner may be enabled. The toner according to an example may further include an external additive disposed on at least a portion of the surface of the toner. In order to impart improved charge uniformity, charge stability, transfer efficiency, and cleaning property to toner particles, surface properties of the toner particles may be improved. A method of improving the surface properties of the toner particles may include adding an external additive to the surface of the toner particles after toner production. The external additive may serve to help the toner powder maintain fluidity by making the surface of the toner particles more uniform and preventing the toner particles from sticking to each other. In addition, the external additive may also affect charging uniformity, charge stability, transfer efficiency, the cleaning property, and the like of the toner.

As the external additive, nanoparticles of various inorganic materials such as silica, titania, tin oxide, or composite nanoparticles of polymers and inorganic materials may be used, but may not be limited thereto. According to an example, the external additive may be silica particles. The silica may be, for example, fumed silica, sol gel silica, or a mixture thereof. In addition, the silica may be divided into small particle diameter silica and large particle diameter silica according to the size of primary particles.

If the primary particle size of the silica is too large, it may be relatively difficult for the externally added toner particles to pass through a developing blade, and thus a selection phenomenon of the toner may occur. That is, the particle size of the toner particles remaining in the toner cartridge may gradually be increased as a use time of the toner cartridge passes. As a result, the charge amount of the toner is lowered so that a thickness of the toner layer for developing the electrostatic latent image may be increased. In addition, if the primary particle size of the silica particles is too large, the possibility that the silica particles are detached from the core particles may be relatively increased by a stress applied to the toner particles from a member such as a feed roller. The detached silica particles may contaminate the charging member or the latent image carrier.

On the other hand, if the primary particle size of the silica is too small, there is a high possibility that the silica particles are buried inside the toner due to shearing stress of the developing blade applied to the toner. When the silica particles are buried inside the core, the silica loses its function as an external additive, and accordingly, the adhesion between the toner and the surface of the photosensitive member may increase unexpectedly. This may lead to deterioration of the cleaning property of the toner and deterioration of transfer efficiency of the toner.

Therefore, according to an example, the silica that may be used as the external additive may be a small particle diameter silica having a primary particle size, for example, a volume average particle diameter (D50), of a range of less than about 50 nm, for example, greater than or equal to about 1 nm and less than or equal to about 50 nm, greater than or equal to about 3 nm and less than or equal to about 50 nm, greater than or equal to about 5 nm and less than or equal to about 50 nm, greater than or equal to about 5 nm and less than or equal to about 40 nm, greater than or equal to about 5 nm and less than or equal to about 30 nm, greater than or equal to about 5 nm and less than or equal to about 20 nm, greater than or equal to about 10 nm and less than or equal to about 20 nm, greater than or equal to about 5 nm and less than or equal to about 10 nm, greater than or equal to about 10 nm and less than or equal to about 50 nm, greater than or equal to about 10 nm and less than or equal to about 40 nm, greater than or equal to about 10 nm and less than or equal to about 30 nm, or greater than or equal to about 10 nm and less than or equal to about 20 nm. Here, the volume average particle diameter (D50) represents a particle size of 50 % in the cumulative percentage in a cumulative distribution curve of the silica particles based on the volume distribution. Also in such small particle diameter silica, fumed silica particles may be used as an external additive. In addition, in order to compensate for using the small particle diameter silica alone, the external additive may further include a large particle diameter silica together with the small particle diameter silica. The large particle diameter silica may have a volume average particle size (D50) of greater than or equal to about 30 nm and less than or equal to about 300 nm, for example, greater than or equal to about 30 nm and less than or equal to about 200 nm, greater than or equal to about 30 nm and less than or equal to about 150 nm, greater than or equal to about 40 nm and less than or equal to about 300 nm, greater than or equal to about 40 nm and less than or equal to about 250 nm, greater than or equal to about 40 nm and less than or equal to about 200 nm, greater than or equal to about 40 nm and less than or equal to about 150 nm, greater than or equal to about 40 nm and less than or equal to about 100 nm, greater than or equal to about 50 nm and less than or equal to about 200 nm, greater than or equal to about 50 nm and less than or equal to about 150 nm, greater than or equal to about 50 nm and less than or equal to about 100 nm, greater than or equal to about 60 nm and less than or equal to about 100 nm, or greater than or equal to about 60 nm and less than or equal to about 80 nm. According to an example, as an example of large particle diameter silica, it may include large particle diameter sol-gel silica. For example, the large particle diameter silica may be mono-dispersed large particle diameter sol-gel silica. According to an example, the external additive may include a combination of large particle diameter silica and small particle diameter silica.

When the external additive according to an example includes a combination of large particle diameter silica and small particle diameter silica, an addition amount of the large particle diameter silica may be greater than or equal to about 0.1 parts by weight and less than or equal to about 3 parts by weight, for example greater than or equal to about 0.5 parts by weight and less than or equal to about 2.5 parts by weight, greater than or equal to about 1 part by weight and less than or equal to about 2.5 parts by weight, or greater than or equal to or about 1 part by weight and less than or equal to about 2 parts by weight, based on 100 parts by weight of the toner according to an example. In addition, an additional amount of the small particle diameter silica may be greater than or equal to about 0.1 parts by weight and less than or equal to about 2 parts by weight, for example greater than or equal to about 0.3 parts by weight and less than or equal to about 1.5 parts by weight, greater than or equal to about 0.5 parts by weight and less than or equal to about 1.5 parts by weight, or greater than or equal to or about 0.5 parts by weight and less than or equal to about 1 part by weight, based on 100 parts by weight of the toner according to an example.

If the small particle diameter silica alone is used, charge stability is high, while a possibility of being buried inside the toner particles may be increased. If the large particle diameter silica alone is used, there are many voids on the surface of the toner particles, so that charge stability may be decreased, and silica particles are more likely to be detached from the surface of the toner. The above situations may be solved by using small particle diameter silica particle and large particle diameter silica particle having different particle diameters together. That is, the small particle diameter silica particles are disposed in the voids between the large particle diameter silica particles to fill the voids, thereby increasing charge stability of the toner and preventing the small particle diameter silica particles from being buried inside the toner, and thus fluidity of the toner may be maintained even in long-term printing and image retention may be improved.

The toner according to an example may further include tin oxide particles as the external additive in addition to the large particle diameter silica and small particle diameter silica described above. The tin oxide particles may help to improve a charge accumulation phenomenon, thereby improving developability, transferability, and charge stability in a high temperature/high humidity environment and in a low temperature and low humidity environment.

On the other hand, the small particle diameter fumed silica and tin oxide particles may be subjected to hydrophobization surface treatment. When one or more of the small particle diameter fumed silica and tin oxide particles are subjected to hydrophobization surface treatment, a degree of hydrophobicity of each of them may range from about 10 to about 90 %, for example about 30 % or more. The large particle diameter silica may or may not be treated with the hydrophobization surface treating agent described above. When at least one of the small particle diameter fumed silica particles and the tin oxide particles is subjected to hydrophobization surface treatment, more improved toner properties may be exhibited.

The hydrophobization surface treating agent that may be used for the hydrophobization surface treatment of the small particle diameter fumed silica particles and tin oxide particles may include, for example, silicone oils, silanes, siloxanes, or silazanes. Specific examples of these hydrophobization surface treating agents may include dimethyldiethoxy siloxane (DIVIDES), hexamethyl dimethyl siloxane (HMDS), polydimethyl siloxane (PDMS), diethyldimethyl siloxane (DDS), dimethyltrimethoxy silane (DTMS), and the like, and these may be used alone or in combination of two or more thereof.

A volume average particle diameter (D50) of the tin oxide particles may be greater than or equal to about 5 nm and less than or equal to about 200 nm, for example greater than or equal to about 10 nm and less than or equal to about 150 nm, or greater than or equal to or about 20 nm and less than or equal to about 100 nm. Herein, the volume average particle size (D50) represents a particle size of 50 % of the cumulative percentage in the cumulative distribution curve of the tin oxide particles based on the volume distribution. When the volume average particle diameter (D50) of the tin oxide particles is less than about 5 nm or greater than about 200 nm, the effect of the tin oxide particles may not be sufficient or the particle size may be excessively large and not suitable for use in the toner.

When the external additive includes tin oxide particles, the addition amount may be greater than or equal to about 0.1 parts by weight and less than or equal to about 3 parts by weight, for example greater than or equal to 0.3 parts by weight and less than or equal to about 2.5 parts by weight, greater than or equal to about 0.3 parts by weight and less than or equal to about 2 parts by weight, greater than or equal to about 0.3 parts by weight and less than or equal to about 1 .5 parts by weight, or greater than or equal to or about 0.3 parts by weight and less than or equal to about 1.5 parts by weight, based on 100 parts by weight of the toner according to an example, but may not be limited thereto. If the amount of tin oxide particles is out of the above range, one or more of the characteristics required for the toner, such as environmental chargeability, transferability, developability, background contamination of the photosensitive member, and development durability, may not exhibit desired effects.

In addition, a total weight of the external additive added to the toner is relative to the weight of the toner may be less than or equal to about 10 wt.%, for example, about 1 wt.% to about 10 wt.%, about 2 wt.% to about 10 wt.%, about 3 wt.% to about 10 wt.%, about 3 wt.% to about 9 wt.%, or about 3 wt.% to about 8 wt.%, but may not be limited thereto. The addition of the external additive particles to the surface of the toner may be performed by, for example, a powder mixing apparatus but may not be limited thereto. As a non-limiting powder mixing apparatus, a Henshell mixer, a V-shape mixer, a ball mill, or a Nauta mixer may be used.

The cartridge according to an example of the disclosure is a cartridge that includes the toner for developing the electrostatic image according to an example of the disclosure, and is detachable from the image forming apparatus.

An image forming apparatus according to an example of the disclosure is an image forming apparatus employing the toner for developing the electrostatic image according to an example of the disclosure described above. For example, the image forming apparatus may include: an image carrier; an image forming unit for forming an electrostatic latent image on the surface of the image carrier; a toner storage unit; a toner supply unit for supplying the toner to the surface of the image carrier to develop an electrostatic latent image on the surface of the image carrier as a visible image; and a toner transfer unit for transferring the visible image from the surface of the image carrier to the image receiving member, wherein the toner may be a toner according to an example of the disclosure described above.

According to an example of the disclosure, an image forming method includes adhering toner to a surface of an image carrier on which an electrostatic latent image is formed, for example, an electrophotographic photosensitive member, to form a visible image, and transferring the visible image to an image receiving member, for example, a transfer material, wherein the toner is the toner according to an example of the disclosure. The image forming method may be an electrophotographic method.

The electrophotographic method may generally include a charging process of uniformly charging a surface of an electrostatic latent image carrier, an exposure process of forming an electrostatic latent image using various photoconductive materials on the charged electrostatic latent image carrier, a developing process of developing a visible image (i.e. , a toner image) by adhering a developer such as toner to the latent image, a transferring process of transferring the visible image onto a transfer material such as paper, a cleaning process of removing the non-transferred and remaining toner from the electrostatic latent image carrier, an antistatic process of removing a residual charge of the electrostatic latent image carrier, and a fixing process of fixing a visible image by heat or pressure. The toner according to an example of the disclosure described above may be usefully used for such an electrophotographic method.

Hereinafter, the disclosure will be described in more detail with reference to examples and comparative examples, but the disclosure may not be limited to these examples and comparative examples.

Examples

Preparation Example 1 : Preparation of Crystalline Polyester Resin

Preparation Example 1 -1 A polymerizable monomer mixed solution (253 g of dodecanedioic acid and 197 g of 1 ,9-nonanediol) and 0.3 g of scandium triflate (respectively, Sigma Aldrich Co., Ltd.) as a catalyst were put in a 3 L beaker, and then polymerized for 9 hours by reducing pressure to 10 torr, while stirring at 90 °C, to prepare a crystalline polyester resin. The obtained crystalline polyester resin was cooled down to obtain a resin solid. A weight average molecular weight (Mw) of the obtained solid was about 8,000 g/mol, when measured using a gel permeation chromatography (GPC) method. A glass transition temperature measured at a temperature-increasing rate of 10 °C/min at the second scan using a DSC (TA Instruments Q-2000) method was about 40 °C.

100 g of the prepared resin was mixed with 80 g of butanone (Samchun Chemicals) and 20 g of isopropyl alcohol (Samchun Chemicals), and then stirred therewith at about 60 °C. Subsequently, 5 g of a 5 % ammonia aqueous solution (Samchun Chemicals) was mixed therewith, 200 g of distilled water was injected thereinto at 10 mL/min, and the resultant was stirred until the butanone and the isopropyl alcohol were removed, and then cooled down to prepare a crystalline polyester resin latex.

Sizes of the prepared latex particles were in a range of about 130 nm to about 200 nm, when measured by using a light scattering method (Microtrac Inc.). Solid content of the latex was about 30 %, when measured in a drying loss method.

Preparation Example 1 -2

A crystalline polyester resin was prepared according to the same method as Preparation Example 1-1 , except that the weight average molecular weight was about 10,000 g/mol and the glass transition temperature was about 43 °C, when measured at a temperature-increasing rate of 10 °C/min at the second scan using a DSC (TA Instruments Q-2000) method.

Preparation Example 1 -3 A crystalline polyester resin was prepared according to the same method as Preparation Example 1-1 , except that the weight average molecular weight was about 13,000 g/mol and the glass transition temperature was about 45 °C when measured at a temperature-increasing rate of 10 °C/min at the second scan using a DSC (TA Instruments Q-2000) method. Preparation Example 2: Preparation of First Styrene-acrylic Resin Preparation Example 2-1

A polymerizable monomer mixed solution (780 g of styrene and 180 g of n-butyl acrylate), 30 g of beta-carboxylethyl acrylate, and 17 g of 1- dodecanethiol as a chain-transfer agent (CTA) were put in a 3 L beaker, and 418 g of a sodium dodecyl sulfate (Sigma Aldrich Co., Ltd., 2% relative to a water amount) aqueous solution as an emulsifier was added thereto, and then stirred therewith to prepare a polymerizable monomer emulsion. 16 g of ammonium persulfate (APS) as an initiator and 696 g of a sodium dodecyl sulfate (Sigma Aldrich Co., Ltd., 0.4 % relative to a water amount) aqueous solution as an emulsifier was put in a 3 L double jacket reactor heated at about 75 °C, and the polymerizable monomer emulsion prepared above was added thereto in a dropwise fashion for greater than or equal to 2 hours. Subsequently, the obtained mixture was reacted at a temperature of about 75 °C for 8 hours. Sizes of the prepared resin particles were about 180 nm to about 250 nm when measured in a light scattering method (Microtrac Inc.). A solid content of the latex was about 42 %, when measured in a drying loss method. A weight average molecular weight (Mw) was about 15,000 g/mol in the molecular weight measurement of the tetrahydrofuran (THF) soluble content by the gel permeation chromatography (GPC) method. A glass transition temperature at a temperature-increasing rate of 10 °C/min at the second scan using a DSC (TA Instruments Q-2000) method was about 45 °C.

Preparation Example 2-2

A first styrene-acrylic resin was prepared according to the same method as Preparation Example 2-1 , except that the weight average molecular weight was about 20,000 g/mol and the glass transition temperature was about 47 °C, when measured at a temperature-increasing rate of 10 °C/min at the second scan using DSC (TA Instruments Q-2000).

Preparation Example 2-3 A first styrene-acrylic resin was prepared according to the same method as Preparation Example 2-1 , except that the weight average molecular weight was about 25,000 g/mol and the glass transition temperature was about 50 °C, when measured at a temperature-increasing rate of 10 °C/min at the second scan using DSC (TA Instruments Q-2000). Preparation Example 3: Preparation of Second Styrene-acrylic Resin Preparation Example 3-1

A polymerizable monomer mixed solution (700 g of styrene and 260 g of n-butyl acrylate), 30 g of beta-carboxylethyl acrylate, and 17 g of 1- dodecanethiol as a chain-transfer agent (CTA) were put in a 3 L beaker, and 418 g of a sodium dodecyl sulfate (Sigma Aldrich Co., Ltd., 2 % relative to a water amount) aqueous solution as an emulsifier was added thereto and stirred therewith to prepare a polymerizable monomer emulsion. 10 g of ammonium persulfate (APS) as an initiator and 696 g of a sodium dodecyl sulfate (Sigma Aldrich Co., Ltd., 0.4 % relative to a water amount) aqueous solution as an emulsifier was put in a 3 L double jacket reactor heated at about 75 °C, and the polymerizable monomer emulsion prepared above was slowly added thereto in a dropwise fashion for 2 hours and more, while stirring. The obtained mixture was reacted at a temperature of about 75 °C for 8 hours. Sizes of the prepared resin particles were about 180 nm to about 250 nm when measured by using a light scattering method (Microtrac Inc.). A solid content of the latex was about 42 %, when measured by a drying loss method. A weight average molecular weight (Mw) was about 250,000 g/mol in the molecular weight measurement of the tetrahydrofuran (THF) soluble content found by the gel permeation chromatography (GPC) method. A glass transition temperature at a temperature-increasing rate of 10 °C/min at the second scan using a DSC (TA Instruments Q-2000) method was about 58 °C.

Preparation Example 3-2

A second styrene-acrylic resin was prepared according to the same method as Preparation Example 3-1 , except that the weight average molecular weight was about 300,000 g/mol and the glass transition temperature was about 60 °C, when measured at a temperature-increasing rate of 10 °C/min at the second scan using a DSC (TA Instruments Q-2000) method.

Preparation Example 3-3 A second styrene-acrylic resin was prepared according to the same method as Preparation Example 3-1 , except that the weight average molecular weight was about 350,000 g/mol and the glass transition temperature was about 63 °C, when measured at a temperature-increasing rate of 10 °C/min at the second scan using a DSC (TA Instrument Q-2000) method.

Preparation Example 4: Preparation of Pigment Dispersion

10 g of the anionic reactive emulsifier (sodium dodecyl sulfate) was taken and put in a milling bath along with 60 g of a carbon black pigment (REGAR-330R, Cabot Corp.), and 400 g of glass beads having a diameter of 0.8 to 1 mm and about 300 g of distilled water were added thereto and milled therewith at room temperature to prepare a dispersion. The dispersion may be obtained by using an ultrasonic disperser or a microfluidizer. The pigment dispersion particle diameter was about 180 nm to about 200 nm when measured by a light scattering method (Horiba 910). The solid content of the pigment dispersion was about 20.0 %.

Preparation Example 5: Preparation of Wax Dispersion

10 g of the anionic reactive emulsifier (sodium dodecyl sulfate) was taken and mixed with 60 g of WAX (T-289, Chungyang Wax) and 200 g of distilled water, and then PandaPLUS (Niro Soavi) equipment was used at a high temperature under high pressure (90 C, 600 bar) to prepare a dispersion. When the wax dispersion was measured with respect to a particle diameter in a light scattering method (Horiba 910), the particle diameter was in a range of about 180 nm to about 200 nm. The solid content of the wax dispersion was about 30.0 %. Examples and Comparative Examples: Preparation of Toner Example 1

3000 g of deionized water, 700 g of a latex mixed solution for a core (a mixture of about 10 wt.% of the resin according to Preparation Example 1-1 , about 85 wt.% of the resin according to Preparation Example 2-2, and about 5 wt.% of the resin according to Preparation Example 3-3), 195 g of the pigment dispersion according to Preparation Example 4, and 237 g of the wax dispersion of Preparation Example 5 (solid content of about 30.0 %, T-289, Chungyang Wax) were put in a 7 L reactor. Subsequently, a mixed solution of 364 g of nitric acid (0.3 mol/L) and 182 g of polysilicate iron (Sudo Machinery) as a coagulant was added to the mixed solution, and then stirred therewith by using a homogenizer at about 11 ,000 rpm for 6 minutes, and 417 g of the latex mixed solution was additionally added thereto and stirred again for 6 minutes to obtain aggregates of about 1.5 pm to about 2.5 pm. The mixed solution was put in a 7 L double jacket reactor, and then heated from room temperature to about 55 °C (Tg-5 °C of the latex) at 0.5 °C/min. When a volume average particle diameter (D50) thereof reached about 4.5 pm, 442 g of the latex mixed solution for forming a shell (a mixture of 10 % of each of the latex of Preparation Example 2-2 and the latex of Preparation Example 3-2) was slowly added thereto for about 20 minutes, and when the volume average particle diameter (D50) became about 5.3 pm, NaOH (1 mol) was added thereto to adjust pH to about 7. When the volume average particle diameter (D50) was constantly maintained for 10 minutes, the temperature was increased up to about 96 °C. When the temperature reached 96 °C (about 30 °C to 50 °C higher than the Tg), the pH was set at about 6.0, and the mixture was unified for 3 hours to obtain a potato-shaped secondary aggregation toner having a volume average particle diameter (D50) of about 5.5 pm. Subsequently, the aggregation reaction solution was cooled down to lower than the Tg, filtered to separate toner particles, and dried.

Example 2

A toner was prepared according to the same method as Example 1 , except that 700 g of a mixture of about 15 wt.% of the resin according to Preparation Example 2-1 , about 80 wt.% of the resin according to Preparation Example 2-2, and about 5 wt.% of the resin according to Preparation Example 3-2 was used as a latex mixed solution for a core.

The toner was treated through aggregation and unification processes to obtain a potato-shaped secondary aggregation toner having a volume average particle diameter (D50) of about 6 pm. Subsequently, the aggregation reaction was cooled down to be lower than the Tg, filtered to separate toner particles, and dried.

Example 3

A toner was prepared according to the same method as Example 1 , except that 700 g of a mixture of about 10 wt.% of the resin of Preparation Example 1-1 , about 85 wt.% of the resin of Preparation Example 2-1 , and about 5 wt.% of the resin of Preparation Example 3-3 was used instead of the resin mixture of Preparation Examples 1-1 , 2-2, and 3-3 as a latex mixed solution for a core.

The toner was treated through aggregation and unification processes to obtain a potato-shaped secondary aggregation toner having a volume average particle diameter (D50) of about 5.5 pm. Subsequently, the aggregation reaction solution was cooled down to be lower than the Tg, filtered to separate toner particles, and dried. Example 4

A toner was prepared according to the same method as Example 1 , except that 700 g of a mixture of about 15 wt.% of the resin of Preparation Example 1-1 , about 80 wt.% of the resin of Preparation Example 2-1 , and about 5 wt.% of the resin of Preparation Example 3-2 was used instead of the resin mixture of Preparation Examples 1-1 , 2-2, and 3-3 as a latex mixed solution for a core.

The toner was treated through aggregation and unification processes to obtain a potato-shaped secondary aggregation toner having a volume average particle diameter (D50) of about 6 pm. Subsequently, the aggregation reaction solution was cooled down to be lower than the Tg, filtered to separate toner particles, and dried.

Comparative Example 1

A toner was prepared according to the same method as Example 1 , except that 700 g of a mixture of about 15 wt.% of the resin of Preparation Example 1-1 , about 80 wt.% of the resin of Preparation Example 2-3, and about 5 wt.% of the resin of Preparation Example 3-1 was used instead of the resin mixture of Preparation Examples 1-1 , 2-2, and 3-3 as a latex mixed solution for a core.

The toner was treated through aggregation and unification processes to obtain a potato-shaped secondary aggregation toner having a volume average particle diameter (D50) of about 5.5 pm. Subsequently, the aggregation reaction solution was cooled down to be lower than the Tg, filtered to separate toner particles, and dried. Comparative Example 2

A toner was prepared according to the same method as Example 3, except that 700 g of a mixture of about 90 wt.% of the resin of Preparation Example 2-2 and about 10 wt.% of the resin of Preparation Example 3-3 was used instead of the resin mixture of Preparation Examples 1-1 , 2-2, and 3-3 as a latex mixed solution for a core. In other words, the latex mixed solution for a core according to Comparative Example 2 included almost no crystalline polyester resin.

The toner was treated through aggregation and unification processes to obtain a potato-shaped secondary aggregation toner having a volume average particle diameter (D50) of about 5.5 pm.

Subsequently, the aggregation reaction solution was cooled down to be lower than the Tg, filtered to separate toner particles, and dried.

Comparative Example 3

A toner was prepared according to the same method as Example 3, except that 700 g of a mixture of about 30 wt.% of the resin of Preparation Example 1-1 , about 65 wt.% of the resin of Preparation Example 2-2, and about 5 wt.% of the resin of Preparation Example 3-3 was used instead of the resin mixture of Preparation Examples 1-1 , 2-2, and 3-3 as a latex mixed solution for a core. The toner was treated through aggregation and unification processes to obtain a potato-shaped secondary aggregation toner having a volume average particle diameter (D50) of about 5.5 pm. Subsequently, the aggregation reaction solution was cooled down to be lower than the Tg, filtered to separate toner particles, and dried.

Evaluation: Evaluation of Toner Characteristics

The latexes for cores of the toners according to Examples 1 to 4 and Comparative Examples 1 to 3 were respectively evaluated with respect to a ratio Vi of a weight average molecular weight of the crystalline polyester resin relative to a weight average molecular weight of the first styrene-acrylic resin and a ratio V2 of the weight average molecular weight of the crystalline polyester resin relative to a weight average molecular weight of the second styrene-acrylic resin, and the results are shown in Table 1. In addition, the toners of examples and comparative examples were measured with respect to a size (a volume average particle diameter (D50)), a glass transition temperature (Tg), a COT (Cold Offset Temperature), and an HOT (Hot Offset Temperature), and the results are also shown in Table 1.

Each method of measuring the sizes, the glass transition temperatures, COT, and HOT of the toners is as follows: (1) Toner size was measured as a volume average particle diameter

(D50) using a 100 pm Aperture tube with Beckman Coulter Multisizer-4

(2) Glass transition temperature (Tg) of toner was measured in a 2nd temperature curve of Tg measurement at a temperature rising rate of 10 °C/min by TA instruments Q-2000 (3) COT (Cold Offset Temperature) and HOT (Hot Offset Temperature): Evaluation method of fixation area of the toner

An NIF fixer (Samsung Digital Composite group SL-X7600, Samsung Electrons) was used to fix a test image under the following conditions to measure the fixed area:

- Unfixed image fortesting: 100 % pattern

-Test temperature: 100 °C to 200 °C (5 °C intervals)

-Test paper: 60 g paper (Boise X-9) and 90 g paper (Xerox Exclusive) -Fixation rate: 160 mm/s Herein, COT (Cold Offset Temperature) is the lowest temperature at which the image is normally printed from the image fixed using the 90 g paper, and

HOT (Hot Offset Temperature) is the highest temperature at which the image is normally printed from the image fixed using the 60 g paper. On the other hand, external toners were prepared on the surface of each toner prepared in examples and comparative examples as explained below, and their heat storage properties and fluidity were evaluated.

First, the method of preparing external toners is as below.

100 parts by weight of each prepared and dried toner according to examples and comparative examples was put in an external adding apparatus (KM-LS2K, Dae Wha Tech), and 2.0 parts by weight of sol-gel silica having a primary particle size of about 70 nm and apparent density of about 220 g/L (SG50, Sukkyung), 1.0 part by weight of small particle diameter fumed silica hydrophobization-treated with diethyldimethyl siloxane (DDS) and having a primary particle size of about 16 nm (Evonik, AEROSIL®R972), and a tin oxide (SG-SNO10, Sukkyung) were added thereto, and then mixed therewith at about 2,000 rpm for 30 seconds in a 2 L agitator and stirred at about 6,000 rpm for 3 minutes to obtain external toner particles. Volume average particle diameters (D50) of the external toner particles were about 5.5 to about 6.0 pm. An average roundness value of the obtained toner was about 0.971.

The external toner was evaluated with respect to heat storage properties and fluidity as follows. 100 g of each external toner was put in a developer (Samsung Digital

Composite Group SL-X7600, Samsung Electronics) and stored in a package state in a constant temperature and humidity oven as follows. r23 °C, 55 % RH (Relative Humidity) 2 hours => 40 °C, 90 % RH 48 hours => 50 °C, 80 % RH 48 hours => 40 °C, 90 % RH 48 hours => 23 °C, 55 % RH 6 hours j

After being stored in the above conditions, it was visually determined whether the toners in the developer were caked or not, and image defects were evaluated by printing 100 % images. The evaluation criteria are as follows.

®: Good image, excellent fluidity °; good image, no caking

D : inferior image, no caking c: caking occurrence Table 1 also shows the heat storage properties and fluidity evaluated above.

(Table 1)

5 equal to 20 wt.% of a crystalline polyester resin having the weight average molecular weight of the crystalline polyester resin (Mw) relative to the weight average molecular weight of the first styrene-acrylic resin (Mwi) in a range of 0.18 to 0.7, and the weight average molecular weight of the crystalline polyester resin (Mw) relative to the weight average molecular weight of the second styrene-acrylic resin (MW2) in a range of 0.01 to 0.05 based on the total weight of the binder resin for a core as latex for a core, and in addition, greater than or equal to 80 wt.% of first and second styrene-acrylic resins based on the total weight of the binder resin for a core had a glass transition temperature in a range of 46 °C to 53 °C, which was about 7 °C to 14 °C lower than that of the first styrene-acrylic resin included in the largest amount as the binder resin. Further, the toners according to Examples 1 to 4 maintained COT of about 155 °C, which is lower than or equal to 160 °C at which low-temperature fixation is enabled. The toners of Example 1 to 4 had a lower glass transition temperature and COT of less than or equal to 160 °C at which the low temperature fixation was enabled, but still exhibited satisfactory high- temperature storage properties and fluidity of the toners that were added with the external toners, and accordingly, the toner according to an example realized an excellent effect of securing low-temperature fixation without deteriorating high-temperature storage properties and fluidity.

On the contrary, in the toner of Comparative Example 1 showing Vi and V2 out of the ranges, the crystalline polyester as a binder resin for a core was used in the same amount as that of Example 2 or 4, but COT thereof sharply increased up to 170 °C and thus enabled the low-temperature fixation. The toner of Comparative Example 1 included the crystalline polyester in the same amount as that of Example 2 or 4, but also included the first styrene-acrylic resin having too large a weight average molecular weight and the second styrene-acrylic resin having too small a weight average molecular weight compared with that of the crystalline polyester. In other words, the crystalline polyester and the first and second styrene-acrylic resins included in the binder resin for a core satisfied each weight average molecular weight range and a particular ratio range therebetween.

On the other hand, as for Comparative Example 2, the binder resin for a core included no crystalline polyester but included the first and second styrene- acrylic resins alone, and a glass transition temperature of the toner was 46 °C, which was the same as that of the toner of Example 1 or 3, but COT thereof sharply increased up to 175 °C like Comparative Example 1. In other words, the toner including a core including a binder resin not including the crystalline polyester resin but including the styrene-acrylic resin alone did not enable low- temperature fixation. In addition, Comparative Example 3 exhibited Vi and V2 within the same ranges as Example 3, but the binder resin for a core included the crystalline polyester resin in an amount of 30 wt.%, which is greater than 20 wt.%, based on the total weight of the binder resin for a core. Herein, the toner had a glass transition temperature of 46 °C and COT of 155 °C, which were both same as those of the toner according to Example 3, and thus enabled low-temperature fixation, but as shown in Table 1 , the toner of Comparative Example 3 exhibited insufficient heat storage properties and fluidity. In other words, since the crystalline polyester resin having a low molecular weight was excessively included, the glass transition temperature and COT decreased and thus enabled low-temperature fixation, but heat storage properties and fluidity were deteriorated.

Comparative Example 4 exhibited V2 in the same or similar range as Example 3, but Vi thereof was greater than 0.7 of a maximum ratio of the weight average molecular weight of the crystalline polyester resin (Mw) relative to the weight average molecular weight of the first styrene-acrylic resin (Mwi) in the binder resin for a core of the toner according to an example, and accordingly, the weight average molecular weight of the first styrene-acrylic resin included in the largest amount in the binder resin relatively decreased. Herein, the glass transition temperature of the binder resin decreased, and accordingly, the glass transition temperature of the toner sharply decreased down to 44 °C, and accordingly, this toner had low-temperature fixability but deteriorated high temperature storage properties such as heat storage properties or fluidity.

Comparative Example 5, in contrast to Comparative Example 4, exhibited Vi within the same range as Example 1 or 2, but V2 of 0.008 which is lower than 0.01 of a minimum ratio of the weight average molecular weight of the crystalline polyester resin relative to the weight average molecular weight of the second styrene-acrylic resin in the binder resins for the core of the toner, indicating that the weight average molecular weight of the second styrene- acrylic resin, which has the highest weight average molecular weight among the binder resins for the core of the toner, of Comparative Example 5 is relatively higher than that of the second styrene-acrylic resin of Comparative Example 4. Herein, the glass transition temperature or COT of the binder resin may further increase. As shown in Table 1 , COT of the toner of Comparative Example 5 highly increased over 160 °C and reached 165 °C, and accordingly, the toner failed in implementing low-temperature fixability.

As disclosed above, the toner according to an example may be used as a toner for developing an electrostatic image because it is capable of realizing low-temperature fixation and improved properties that do not impair high temperature storage properties such as heat storage properties and fluidity.

As disclosed above, although examples have been disclosed by examples, those skilled in the art will recognize that various modifications and variations may be possible from the above descriptions. For example, the described techniques may be performed in a different order in addition to the described methods, and/or components of the described systems, structures, devices, circuits, materials, etc. may be connected or combined in a different form other than the described methods, or appropriate results may be achieved even if substituted with or replaced by another component or an equivalent. Therefore, the scope of the disclosure should not be limited to the described examples, but should be defined by the claims below and equivalents thereof.