Toner and developer including the same

Abstract

 A toner having high productivity, heat resistance and improved fixability at a low temperature is provided by containing coloring particles having, as a binder resin, a crosslinking-type polyester resin made from an aliphatic alcohol and a carboxylic acid and a non-crosslinking-type polyester resin made from an aromatic alcohol and a carboxylic acid. A developer using the toner is also provided by mixing the toner with a carrier.

Description

[0001] The present invention relates to a toner having coloring particles containing polyester resins as a binder resin. More particularly, it relates to a toner having high productivity, improved fixability at a low temperature and heat resistance.

[0002] A styrene-acrylic resin has been widely used as a binder resin for coloring particles contained in a toner for electrophotograhy. However, with the recent development of high speed copying, in addition to a recent demand for a toner having good fixability to paper in a high speed copying machine, a demand for a toner which is capable of fixing at a low temperature has increased in view of energy-saving. To meet the demands, use of a polyester resin as a binder resin for coloring particles has been proposed.

[0003] The polyester resin used in coloring particles is generally obtained by condensation polymerization between alcohol components and dicarboxylic acid components such as terephthalic acid. Examples for the alcohol components are aromatic alcohol such as bisphenol, and aliphatic alcohol such as ethylene glycol and neopentyl glycol.

[0004] However, the polyester resin having an aromatic alcohol as alcohol components is liable to result in low production efficiency of coloring particles due to a low grindability of the resin. In addition, when the toner having such resin is used in a high speed copying machine, the toner do not have enough fixability to a paper at a low temperature in a fixation section of the machine. One of the solutions to solve these problems is liable to drop the softening point of the resin. But the dropped softening point of the resin may cause another problem for the toner to decrease heat resistance and shelf life.

[0005] On the other hand, the polyester resin having an aliphatic alcohol as alcohol component can improve the fixability of toners at a low temperature, but it may cause a problem of low heat resistance.

[0006] It is an object of the present invention to provide a toner and a developer which have overcome the problems residing in the prior art.

[0007] It is an object of the present invention to provide a toner and a developer which have a high productivity, improved fixability at a low temperature, and excellent heat resistance.

[0008] According to an aspect of the present invention, a toner containing coloring particles, each coloring particle including a binder resin. The binder resin has a crosslinking-type polyester resin made from an aliphatic alcohol and a carboxylic acid and a non-crosslinking-type polyester resin made from an aromatic alcohol and a carboxylic acid.

[0009] According to another aspect of the present invention, there is provided a developer containing carrying particles and coloring particles. Each coloring particle includes a binder resin having a crosslinking-type polyester resin made from an aliphatic alcohol and a carboxylic acid and a non-crosslinking-type polyester resin made from an aromatic alcohol and a carboxylic acid.

[0010] Resins made from an aromatic alcohol and a carboxylic acid generally have a higher softening temperature than that of resins made from an aliphatic alcohol and a carboxylic acid. On the other hand, resins having a crosslinking structure generally have a higher softening temperature than that of resins having no crosslinking structure. The inventors have attempted to produce toner having both high heat resistance and high fixability at a low temperature in combination of the above mentioned properties.

[0011] In the present invention, a mixture of a crosslinking-type polyester resin having an aliphatic alcohol as an alcohol component (hereinafter referred to as "POLYESTER RESIN I" ) and a non-crosslinking-type polyester resin having an aromatic alcohol as an alcohol component (hereinafter referred to as "POLYESTER RESIN II" ) is used as a binder resin contained in coloring particles.

[0012] POLYESTER RESIN I has relatively high softening point due to its crosslinking structure, it acts to provide viscoelasticity to the coloring particles for improving their fixability. Use of a toner including such coloring particles in a copying machine expands the allowable temperature range for a surface of a fixing roller of the machine that ensures the satisfactory fixation. Above the allowable temperature range, the cold offset is likely to occur. Below the allowable temperature range, the hot offset is likely to occur. However, a binder resin including only a crosslinking-type polyester, i.e., POLYESTER RESIN I, do not attribute to a good fixability at a low temperature such as below the softening point of POLYESTER RESIN I.

[0013] In this invention, in order to overcome the problem due to POLYESTER RESIN I, POLYESTER RESIN I is mixed with a non-crosslinking-type polyester resin, i.e., POLYESTER RESIN II,to use it as a binder resin. POLYESTER RESIN II has no crosslinking structure, and is thus able to soften at a temperature lower than POLYESTER RESIN I. Therefore, a mixture of POLYESTER RESIN I with POLYESTER RESIN II improves the fixability at low temperature.

[0014] Next, POLYESTER RESIN I will be described. POLYESTER RESIN I, i.e., a crosslinking-type polyester resin having an aliphatic alcohol as an alcohol component, is primary obtained by condensation polymerization between aliphatic polyhydric alcohol and polybasic carboxylic acid. To ensure a crosslinking structure to the resin, it may be appreciated that: the alcohol have more than three hydroxyl groups; the carboxylic acid have more than three carboxyl groups; or the carboxylic acid and/or the alcohol have a crosslinkable functional group in the side chain.

[0015] As examples of the aliphatic polyhydric alcohol for the polyester resin, there may be diols such as ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,4-butanediol, 1,4-butenediol, neopentyl glycol, 1,5-pentane glycol, 1,6-hexane glycol, 1,4-cyclohexane dimethanol, dipropylene glycol, polyethylene glycol, polypropylene glycol and polytetramethylene glycol; trials such as 1,2,4-butanetriol, 1,2,5-pentanetriol, glycerol, 2-methylpropanetriol, 2-methyl-1,2,4-butanetriol, trimethylolethane, trimethyolpropanetrimethyolethane, trimethyolpropane, pentaerythritol; and tetraols.

[0016] As examples of the polybasic carboxylic acid for the polyester resin, there may be aromatic polybasic carboxylic acids such as phthalic acid, isophthalic acid, terephthalic acid, 1,2,4-benzene tricarboxylic acid, 2,5,7-naphthalene tricarboxylic acid, 1,2,4-naphthalene tricarboxylic acid and pyromellitic acid; aliphatic dicarboxylic acids such as maleic acid, fumaric acid, succinic acid, adipic acid, sebacic acid, malonic acid, azelaic acid, mesaconic acid, citraconic acid and glutaconic acid; alicyclic dicarboxylic acids such as cyclohexane dicarboxylic acid and methyl nadic acid; anhydrides of these carboxylic acids; and lower alkyl esters of these carboxylic acids.

[0017] Since degree of crosslinking of POLYESTER RESIN I depends upon the total amount of components of the alcohol having more than three hydroxyl groups and the carboxylic acid having more than three carboxyl groups, a desired degree of crosslinking is obtainable by adjusting the amounts of such components. It is usually preferable that the components are present in the amount of not more than 15 mol percent.

[0018] As examples of a crosslinkable functional group, there may be isocyanate group, vinyl sulfonic acid group, vinyl ketone group, aldehyde group, epoxy group, azide group or the like.

[0019] The mole ratio of the carboxylic acid component to the alcohol component ranges preferably from 9:10 to 10:9.

[0020] Preparation of POLYESTER RESIN I may be made by a known method, e.g., direct polymerization method. In a direct polymerization method, the alcohol component and the acid component are placed in a reactor at a time for esterification. In another direct polymerizaton method, one of the components is placed in a reactor and then the other component is put portion by portion into the reactor. The reaction generally occurs at a temperature between 150 and 300°C. preferably between 170 and 280°C, in the presence of a catalyst. The reaction may be conducted at an atmospheric pressure, a reduced pressure, or a high pressure. After the reaction rate reaches 50-90percent, however, the reaction preferably proceeds at a reduced pressure, e.g., 200mmHg or less.

[0021] As examples of the catalyst of the reaction, there may be metals such as tin, titanium, antimony, manganese, nickel, zinc, lead, iron, magnesium, calcium and germanium; and compounds containing these metals.

[0022] Next, POLYESTER RESIN II will be described. Aromatic polybasic alcohol usable as an alcohol component of POLYESTER RESIN II includes primary diols. As examples of the diol, there may be etherificated bisphenol such as polyoxypropylene(2.2)-2,2-bis(4-hydroxyphenyl)propane, polyoxypropylen(3.3)-2,2-bis(4-hydroxyphenyl)propane, polyoxyethylene(2.0)-2,2-bis(4-hydroxyphenyl)propane, polyoxypropylene(2.0)-polyoxyethylene(2.0)-2,2-bis(4-hydroxyphenyl)propane and polyoxypropylen(6)-2,2-bis(4-hydroxyphenyl)propane, bisphenol A, bisphenol Z or the like.

[0023] The polybasic carboxylic acid used as the acid component of POLYESTER RESIN II, and prepartion of POLYESTER RESIN II are similar with those for POLYESTER RESIN I.

[0024] The mixing rate of POLYESTER RESIN I to POLYESTER RESIN II is preferably between 1:3 and 10:1 by weight, more preferably between 1:2 and 6:1, and further preferably between 1:1 and 4:1.

[0025] The mixing rate below the minimum rate is likely to cause problems such as fixation offset and paper winding due to a heated fixation roller. Also, the mixing rate above the maximum rate is likely to cause problems such as fixation failure.

[0026] In addition to POLYESTER RESIN I and POLYESTER RESIN II, other resins such as styrene-acrylic resin may be jointly used as a binder resin, without impairing the advantageous effect of the present invention.

[0027] POLYESTER RESIN I preferably has a gel portion ranging from 5 to 20 percent by weight, while POLYESTER RESIN II preferably has substantially no gel portion.

[0028] The "gel portion" means the portion of a polyester resin that remains insoluble in the solvent of tetrahydrofuran. Accordingly, the amount of gel portion indicates the degrees of crosslinking of the resin. If POLYESTER RESIN I has less than 5 percent by weight of the gel portion, i.e., the resin has too low degree of crosslinking, the allowable temperature range for the surface of a fixing roller for satisfactory fixation cannot be extended. On the other hand, if POLYESTER RESIN I has more than 20percent by weight of the gel portion, i.e., the resin has too high degree of crosslinking, the toner cannot have enough fixability at a low temperature.

[0029] The preferable softening point of POLYESTER RESIN I ranges from 130 to 155°C and that of POLYESTER RESIN II ranges from 90 to 120°C.

[0030] POLYESTER RESIN I having a softening point below 130°C is likely to decrease the heat resistance of the toner, whereas the resin having a softening point beyond 155°C is likely to decrease the fixability of the toner at a low temperature. Similarly, POLYESTER RESIN II having a softening point below 90°C is likely to decrease the heat resistance of the toner, whereas the resin having a softening point beyond 120° is likely to decrease the fixability of the toner at a low temperature.

[0031] The softening points of the resins are measured by using "flow tester CFT-500" (manufactured by Shimadzu Corp.). The method of measuring softening points includes the steps of: (1) forming a sample resin into a rod having a height of 1 cm; (2) placing the sample resin on a predetermined position in CFT-500; (3) heating the sample resin by the rate of 6°C/min at a pressure of 20 kg/cm² applied by a plunger, to extrude the sample resin from a die having a diameter of 1 mm and a length of 1 mm; and (4) recording a change in distance from the original position of the plunger relative to a change in temperature of the sample during the process of (3), to obtain a sigmoid curve. The temperature of h/2, wherein h denotes a height of the curve, is the softening point of the sample resin.

[0032] Next, preparation of an inventive toner will be described. The inventive toner may be prepared by a number of known methods, such as pulverization classification method, melt granulating method, spray granulating method, and polymerization method. In the pulverization classification method, for example, the binder resin is premixed together with other toner compositions such as coloring agent, charge controlling agent, and mold releasing agent, in a mixer such as Henschel's mixer. The mixture is kneaded with a kneading machine, e.g., a biaxial extruder. The obtained kneaded compositions are then cooled, pulverized and, if necessary, classified, to prepare main particles.

[0033] It may be preferable that the main particle has a median size from 5 to 15 µm, particularly from 7 to 12 µm, in terms of measurement of a Coulter counter.

[0034] To a surface of the main particle, a hydrophobic silica and magnetic powder may be added, to prepare coloring particles. Adding a hydrophobic silica to the surface enhances the flowability of the toner. The hydrophobic silica is preferably present in an amount of 0.1 to 2 percent by weight per main particle. Addition of magnetic powder to the surface improves the transfer efficiency of the toner. In addition, the magnetic powder added to the toner surface acts to effectively prevent toner from scattering.

[0035] In the case of adding the hydrophobic silica and magnetic powder to the toner, it is preferable to premix them closely, and add the mixture to main particles, and then mix all the components so sufficiently as to disperse the silica and magnetic powder in the toner uniformly.

[0036] In preparing the hydrophobic silica, fine powder of silicon dioxide in which the silicon atom on the surface is silanol group is allowed to react with a compound, so that a hydrophobic group is bonded to the silicon dioxide of the silicon dioxide particles, via an oxygen atom. As examples of the above compound, there may be octyltrichlor silane, decyltrichlor silane, nonyltrichlor silane, 4-isopropylphenyl- trichlor silane, 4-tert-buthylphenyl trichlor silane, dimethylchlor silane, dipentyldichlor silane, dihexyldichlor silane, dioctyldichlor silane, dinonyldichlor silane, deciledichlor silane, didodecyldichlor silane, 4-tert-buthylphenyloctyldichlor silane, dioctyldichlor silane, didecenyldichlor silane, dinonenyldichlor silane, di-2-ethylhexyldichlor silane, di-3, 3-dimethyl pentyldichlor silane, trimethylchlor silane, trihexylchlor silane, trioctylchlor silane, tridecylchlor silane, dioctylchlor silane, octyldimethylchlor silane and 4-isopropylphenyl diethylchlor silane. It is preferable that the primary particle of the hydrophobic silica has a mean particle size of 30 µm or less.

[0037] As examples of the magnetic powder, there may be triiron tetroxide (Fe₃O₄), diiron trioxide (γ-Fe₂O₃), iron oxide zinc (ZnFe₃O₄), iron oxide yttrium (Y₃Fe₅O₁₂), iron oxide cadmium (CdFe₂O₄), iron oxide gadolinium (Gd₃Fe₅O₁₂), iron oxide copper (CuFe₂O₄), iron oxide lead (PbFe₁₂O₁₉), iron oxide nickel (NiFe₂O₄), iron oxide neodymium (NdFeO₃), iron oxide barium (BaFe₁₂O₁₉), iron oxide magnesium (MgFe₂O₄), iron oxide manganese (MnFe₂O₄), iron oxide lanthan (LaFeO₃), iron powder (Fe), cobalt powder (Co), and nickel powder (Ni). Preferable magnetic powder may be fine particles of triiron tetroxide (magnetite). Preferable magnetite may be of regular octahedron and its particle size is between 0.05 to 1.0 µm. The surface of the magnetite particles may be treated by silane coupling agent, titanium type coupling agent or the like.

[0038] The inventive toner may be used as a one-component developer. In this case, if necessary, the toner may be mixed with magnetic powder to prepare a magnetic toner.

[0039] Also, the inventive toner may be mixed with a carrier as a two-component developer. In this case, the toner density may be preferably from 2 to 20 percent by weight.

[0040] As examples of carrier for the two-component developer, there maybe iron powder carrier, ferrite carrier, magnetite carrier. Also, it may be appreciated to use these carriers coated with a suitable resin. Developer containing a resin-coated carrier can give excellent high quality and a prolonged life to a developed image.

Examples

[0041] First of all, Material Resins A to H were prepared as shown in Table-1. More specifically, Material Resin A was prepared as follows. Dibutyl tin oxide as a polymerization catalyst was added into a mixture of 20.1 mol percent of ethylene glycol and 27.5 mol percent of neopentyl glycol as fatty alcohol, 40.2 mol percent of terephthalic acid as a carboxylic acid, and 12.2 mol percent of absolute 1,2,4-benzene tricarboxylic acid. This mixture was then placed in a four-mouth flask. To the flask, a stirrer, a condenser, a thermometer, and a gas conduit pipe were attached and then placed in a mantle heater.

[0042] From the gas conduit pipe, nitrogen gas was flowed into the flask to hold it in an inert gas atmosphere. In this state, the flask was heated with stirring to 210 °C for dehydration condensation reaction. When the temperature of the reaction product in the flask reached a predetermined temperature Tm', the obtained resin was taken out of the flask and cooled to the room temperature to terminate the reaction, thereby obtaining polyester resin (i.e., Material Resign A). Its glass transition temperature (Tg) was 69 °C, its softening point (Tm) was 145°C, and its gel portion was 14.6 percent. The glass transition point and softening point were measured on a "flow tester" manufactured by Shimadzu Corp.

[0043] The predetermined temperature Tm' was the predicted softening point of a resin by a preliminary experiment performed during the above heating process. In the preliminary experiment, a part of the reaction product was taken out of the flask several times with an appropriate timing, in order to examine the relation between the softening point (Tm) of the reaction product and the reaction time. From the relation, the softening point of the resulting resin was predicted.

[0044] Material Resins B to H were prepared in the same manner as Material Resin A. Specific prescription and characteristic features of Material Resin A to H are given in Table 1.

Example 1

[0045] 75 weight parts of Material Resin A as POLYESTER RESIN I and 25 weight parts of Material Resin E as POLYESTER RESIN II were used as a binder resin. This 100 weight parts of the binder resin, 8 weight parts of carbon black "Raven 1255" (manufactured by Columbia Carbon Inc.) as coloring agent, and 5 weight parts of "carnauba wax" (manufactured by Kato Yoko Sha) as mold releasing agent were all placed in a Henschel's mixer and then mixed. This mixture was subjected to melt kneading by a biaxial extruder and then cooled by a drum flaker. Subsequently, this was roughly pulverized by a hammer mill, finely pulverized by a jet mill at a milling rate of 140g/min., and classified by a pneumatic classifier, to obtain main particles having a mean particle size of 9.0 micron.

[0046] As a surface treatment agent, 0.9 wt percent of magnetite "BL220W" (manufactured by Titan Kogyo K.K.) and 0.9 wt percent of hydrophobic silica "R812S" (manufactured by Nihon Aerosil Co., Ltd.) were added to the toner and mixed with high speed stirring, to obtain coloring particles.

[0047] 5 weight parts of the toner and 95 weight parts of ferrite carrier (being coated with acrylic resin) were mixed by a ball mill, to prepare a developer. This developer was set in a copying machine "DC5090" (manufactured by Mita Industrial Co., Ltd.), to measure the following characteristic performances. The results are given in Table 2.

(i) Occurrence of Jam:
It was examined whether paper jam occurred in a fixation section of the copying machine in copying of 30000 sheets.

(ii) Remain of Previous Toner Image on Fixing Roller:
It was examined whether a previous toner image remained on a periphery of a fixing roller of the machine.

(iii) Fixability
Paper sheets each bearing a toner-defined copy image were fed by an automatic paper feeder. Thereafter, it was examined how much toner defining the copy image on one sheet transferred onto another paper sheet. In Table 2, no transfer is represented at "○ " which means a high fixability; slight transfer is represented at "△"; and distinctive transfer is represented at "X" which means a low fixability.

(iv)Minimum Fixation Temperature
The minimum fixation temperature means the lowest surface temperature of a fixing roller for a satisfactory fixation. The minimum fixation temperature was obtained by copying an solid image (a square of 3 cm × 3 cm) having an image density of 1.2 at different temperatures, and calculating a fixation rate of the copied image. The minimum fixation temperature is a temperature at which a fixation rate of 95percent is obtainable. The minimum fixation temperature is usually required to be below 170°C.
The fixation rate was calculated as follows. The original solid image having an image density of 1.2 was copied to paper. The copied image was rubbed ten times by a 200g-weight wrapped with a gauze. Image densities before and after rubbed were put into the following Equation to obtain a fixation rate:

(v) Fogging Density
A fogging density was obtained by measuring the density of a blank portion of the paper sheet being a copy image by a reflection density meter (Model #TC-6D, Tokyo Denshoku Co., Ltd.). The fogging density is usually required to be below 0.005.

(vi) Chargeability
A chargeability of a toner was obtained by a blow-off charge measuring apparatus (manufactured by Toshiba chemical corp.) Specifically, a sample of 0.2g is placed into a faraday cage at a pressure of 1 kg/cm², and the chargeability of the sample was measured after nitrogen sprayed into the cage for 30 seconds.

(vii) Spent Amount
The spent amount means an weight percent of toner pieces which are broken out of the coloring particles and adhered to the surface of carrying particles after copying 30000 paper sheets. A spent amount was obtained as follows. First, an amount of carbon of resin coated on the surface of each carrying particles was measured by a "Carbon Analyzer". Thereafter, copying was performed for 30000 paper sheets using a sample developer including coloring particles and the above-measured carrying particles. After the 30000-copying, carrying particles were extracted from the sample developer. Similarly, a total of an amount of carbon of toner pieces adhered on the carrying particles and an amount of carbon of resin coated on each carrying particles was measured by a "Carbon Analyzer". Calculation was made for a difference between the carbon amount measured after the copying and the carbon amount measured before the copying. An amount of toner pieces adhered on the extracted carrying particles was calculated in the terms of weight based on the calculated difference. A ratio of an weight of the adhered toner pieces to a total weight of the coloring particles included in a sample developer was calculated as a spent amount.

Example 2

[0048] Toner was prepared in the same manner as in Example 1, except for the use of 75 weight parts of Material Resin B and 25 weight parts of Material Resin F as a binder resin. The same evaluations were made and the results are given in Table 2.

Example 3

[0049] Toner was prepared in the same manner as in Example 1, except for the use of 75 weight parts of Material Resin C and 25 weight parts of Material Resin G as a binder resin. The same evaluations were made and the results are given in Table 2.

Example 4

[0050] Toner was prepared in the same manner as in Example 1, except for the use of 25 weight parts of Material Resin A and 75 weight parts of Material Resin E as a binder resin. The same evaluations were made and the results are given in Table 2.

Example 5

[0051] Toner was prepared in the same manner as in Example 1, except for the use of 90 weight parts of Material Resin A and 10 weight parts of Material Resin E as a binder resin. The same evaluations were made and the results are given in Table 2.

Comparative Example 1

[0052] Toner was prepared in the same manner as in Example 1, except for the use of 100 weight parts of Material Resin A as a binder resin. The same evaluations were made and the results are given in Table 2.

Comparative Example 2

[0053] Toner was prepared in the same manner as in Example 1, except for the use of 100 weight parts of Material Resin D as a binder resin. The same evaluations were made and the results are given in Table 2.

Comparative Example 3

[0054] Toner was prepared in the same manner as in Example 1, except for the use of 100 weight parts of Material Resin E as a binder resin. The same evaluations were made and the results are given in Table 2.

Comparative Example 4

[0055] Toner was prepared in the same manner as in Example 1, except for the use of 100 weight parts of Material Resin H as a binder resin. The same evaluations were made and the results are given in Table 2.

[0056] In Examples 1 to 5, no jam occurred in the continuous copying of 30000 sheets. These Examples also gave good results in fogging density, which was less than 0.0004, i.e., below the required value of 0.005. Also, these Examples had a spent amount of less than 14wtpercent, and are remarkably excellent in the aspect of the spent amount. Further, these Examples had the excellent fixability. Furthermore, these Examples had the minimum fixation temperature ranged between 150 °C and 165 °C, which is considerably lower than the required minimum fixation temperature, i.e., 190 °C.

[0057] On the other hand, Comparative Example 1 and 4 did not give good results in the fixability although no jam was found in Comparative Examples 1 and 4. Also, the minimum fixation temperatures in Comparative Example 1 and 4 were 185 °C and 190 °C, which were higher than in Examples 1 to 5.

[0058] Comparative Examples 2 and 3 show undesirable result in the previous image remain test in addition to the occurrence of jam. Further, the fixability of all Comparative Examples was smaller than in Examples 1 to 5.

Claims

1. A toner comprising coloring particles, each coloring particle including a binder resin having:

a crosslinking-type polyester resin made from an aliphatic alcohol and a carboxylic acid; and

a non-crosslinking-type polyester resin made from an aromatic alcohol and a carboxylic acid.

2. A toner according to claim 1, wherein the crosslinking-type polyester resin has a gel portion of 5-20 percent by weight and the non-crosslinking type polyester resin has substantially no gel portion.

3. A toner according to claim 1 or 2, wherein the crosslinking-type polyester resin has a softening point of 130°C-155°C and the non-crosslinking type polyester resin has a softening point of 90°C -120°C.

4. A toner according to claim 1, 2 or 3, wherein a mixing rate of the crosslinking-type polyester resin to the non-crosslinking-type polyester resin is from 1:3 to 10:1 by weight.

5. A toner according to one or more of claims 1 to 4, wherein the coloring particle further includes a hydrophobic silica on a surface thereof.

6. A toner according to one or more of claims 1 to 5, wherein the coloring particle further includes magnetic powder on a surface thereof.

7. A developer comprising:

carrying particles; and

coloring particles, each coloring particle including a binder resin having:

a crosslinking-type polyester resin made from an aliphatic alcohol and a carboxylic acid; and

a non-crosslinking-type polyester resin made from an aromatic alcohol and a carboxylic acid.

8. A developer according to claim 7, wherein the crosslinking-type polyester resin has a gel portion of 5-20 percent by weight and the non-crosslinking type polyester resin has substantially no gel portion.

9. A developer according to claim 7 or 8, wherein the crosslinking-type polyester resin has a softening point of 130°C-155°C and the non-crosslinking type polyester resin has a softening point of 90°C -120°C.

10. A developer according to claim 7 8 or 9, wherein a mixing rate of the crosslinking-type polyester resin to the non-crosslinking-type polyester resin is from 1:3 to 10:1 by weight.

11. A developer according to one or more of claims 7 to 10, wherein the coloring particle further includes a hydrophobic silica on a surface thereof.

12. A developer according to one or more of claims 7 to 11, wherein the coloring particle further includes magnetic powder on a surface thereof.

13. A developer according to one or more of claims 7 to 12, wherein the content of coloring particles is 2 to 20 percent by weight.

14. A developer according to one or more of claims 7 to 13, wherein each carrying particle is coated with a resin.