JP3068108B2 - Electrophotographic toner - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a toner used as a developer in an electrophotographic copying machine, a laser printer, a facsimile or the like.

[0002]

2. Description of the Related Art In general, an electrophotographic system is a photoconductive substance of an inorganic type such as selenium, amorphous silicon, zinc oxide or the like, or an organic type (often processed into a drum shape) such as a diazo compound or a dye. (: A photosensitive drum) is first charged uniformly, then an image-modulated light is applied to form an electrostatic latent image, and the electrostatic latent image is developed by applying powder to the electrostatic latent image by electrostatic force. If necessary, the powder is transferred onto a base material such as paper or film, and then fixed by a method such as pressure and heating. The electrophotographic system is currently widely used in copiers, laser printers, facsimile machines and the like.

In the electrophotographic system, a powder that develops an electrostatic latent image on a photosensitive drum and finally transfers the image onto a base material such as paper or film to form an image is called toner. These toners are usually mixed with carrier particles (carrier) such as glass beads, iron powder, and ferrite, and used as a so-called developer. As the toner used in the electrophotographic developer, a colorant, a charge control agent, a fluidity modifier, a grinding aid, etc. are added to the binder resin, kneaded, and then ground,
Particles produced by a so-called pulverization method for further classification are used. As the binder resin, a styrene / acrylic copolymer resin has been mainly used, but in recent years, a polyester resin having an excellent low-temperature fixing property has been tended to be used in accordance with an increase in speed of electrophotography and the like. Conventionally used polyester resins are mainly unsaturated polyester resins obtained by polycondensation of aliphatic unsaturated carboxylic acids such as fumaric acid and maleic acid with diols having a bisphenol structure.

[0004]

Toners using these unsaturated polyester resins exhibit good low-temperature fixability, but lack storage stability due to the low glass transition temperature of the resins themselves. -Low chemical stability due to unsaturated groups. -Low light fastness when colored with dye.・ Plasticizers used in vinyl chloride resin, eraser, etc. are easily transferred. And other drawbacks.

[0005]

In view of such circumstances, the present inventors have conducted intensive studies to obtain a toner capable of satisfying many of these required characteristics comprehensively and capable of industrial production. The next invention has been reached. That is, the present invention relates to a polyester resin mainly obtained from polyhydric carboxylic acids and polyhydric alcohols, wherein aromatic dicarboxylic acid containing terephthalic acid and / or a derivative thereof at 80 mol% or more and / or a derivative (A) of 90 mol% or more And a trivalent or higher polycarboxylic acid and / or a derivative thereof (B).
A polyvalent carboxylic acid containing 5 to 8 mol%;
A diol and / or its derivative (C) 4
0 to 98 mol% and a polyhydric alcohol containing 2 to 60 mol% of an alicyclic alcohol and / or a derivative (D) thereof, and substantially free of a gel component (a chloroform-insoluble component is 0.5% by weight). % Polyester resin)
An electrophotographic toner, which is a main component of a binder resin.

[0006]

Embedded image In Chemical Formula 2, R1 to R4 each independently represent hydrogen, methyl, or ethyl. As the polyester resin, either a saturated polyester resin or an unsaturated polyester resin can be used, but a saturated polyester resin is preferred from the viewpoint of stability. The polyester resin in the present invention comprises a polyvalent carboxylic acid component and a polyvalent alcohol component.

In the present invention, the polycarboxylic acid is required to contain at least 90 mol% of an aromatic dicarboxylic acid and / or a derivative thereof, and it is more preferable that all of the polycarboxylic acids are composed of aromatic polycarboxylic acids. Further, as the aromatic polycarboxylic acid component, 80 mol% or more of terephthalic acid is essential, 85 mol% or more is preferable, and 9 mol% or more is more preferable.
0 mol% or more is more preferable. If the content of the aromatic polycarboxylic acid or terephthalic acid is less than the above range, the quality of the copied image may be impaired especially by the plasticizer contained in the eraser, chlorite or the like. Other polyvalent carboxylic acids include trimellitic acid, trimesic acid,
0.5 or more trivalent or more polycarboxylic acid such as pyromellitic acid
8 mol% is essential.

In addition to the above-mentioned polycarboxylic acids, examples of the dicarboxylic acid component include aromatic dicarboxylic acids such as isophthalic acid, orthophthalic acid, 1,5-naphthalic acid, 2,6-naphthalic acid and diphenic acid; Oxybenzoic acid, p
-Aromatic oxycarboxylic acids such as (hydroxyethoxy) benzoic acid, aliphatic dicarboxylic acids such as succinic acid, adipic acid, azelaic acid, sebacic acid, dodecanedicarboxylic acid, fumaric acid, maleic acid, itaconic acid, hexahydroacid Unsaturated aliphatic and alicyclic dicarboxylic acids such as phthalic acid and tetrahydrophthalic acid can be used. However, use of an aliphatic polycarboxylic acid, in particular, requires a caution because it may lower the glass transition temperature of the resin and lead to a decrease in storage stability.

The polyhydric alcohols include diols represented by the general formula 1 and / or derivatives thereof 40 to 98.
mol% and 2 to 60 mol% of alicyclic polyhydric alcohol and / or a derivative thereof are essential. The diols represented by the general formula 1 include ethylene glycol, propylene glycol, 1,1 dimethyl ethane diol, 1,2 dimethyl ethane diol, and 1,1,2 trimethyl ethane diol.
, 1,1,2,2, tetramethylethanediol and / or derivatives thereof can be preferably used, and ethylene glycol and / or propylene glycol can be further used.
Can be more preferably used.

The alicyclic polyhydric alcohols and / or derivatives thereof include 1,4-cyclohexanediol and 1,4
-Cyclohexane dimethanol, spiroglycol, hydrogenated bisphenol A, an ethylene oxide adduct and a propylene oxide adduct of hydrogenated bisphenol A, tricyclodecanediol, tricyclodecanedimethanol, Dicyclohexyl 4,4'-diol and the like or a derivative thereof can be used, and 1,4-cyclohexanediol and / or tricyclodecane dimethanol can be preferably used.

Other glyco components include, for example,
1,3-propanediol, 1,4-butanediol,
1,5-pentanediole, 1,6-hexanediol-
, Neopentyl glycol, diethylene glycol,
Dipropylene glycol, 2,2,4-trimethyl-
1,3-pentaneddiol, para-xylene glycol,
Meta-xylene glycol, ortho-xylene glycol,
1,4-phenylene glycol, ethylene oxide adducts of 1,4-phenylene glycol, diols such as polyethylene glycol, polypropylene glycol and polytetramethylene glycol, bisphenol A, An ethylene oxide adduct and a propylene oxide adduct of bisphenol A can be used. In addition to these, small amounts of triol such as trimethylolethane, trimethylolpropane, glycerin, and pentaerthritol and tetraol may be contained as necessary.
Further, the polyester polyol may include a lactone-based polyester polyol obtained by ring-opening polymerization of a lactone such as ε-caprolactone. Attention must be paid to the combined use of aromatic polyhydric alcohols represented by bisphenol A and its derivatives, since this may reduce the resistance of the PVC plasticizer.

The glass transition point of the polyester resin in the present invention is 50 ° C. or higher, preferably 60 ° C. or higher, more preferably 65 ° C. or higher, and further preferably 70 ° C. or higher. If the glass transition point is lower than this, blocking tends to occur during handling or storage, which may cause a problem in storage stability. The softening point of the polyester resin in the present invention is in the range of 80 to 150 ° C. In a toner in which the softening temperature of the resin is kept lower than this, there is a tendency to agglomerate during handling or storage, and especially in long-term storage, the fluidity may be greatly deteriorated. If the softening point is higher than this, the fixability will be impaired. Further, since it is necessary to heat the fixing roll to a high temperature, the material of the fixing roll and the material of the base material to be copied are limited.

The polyester resin in the present invention essentially contains a trivalent or higher polyvalent carboxylic acid component and permits the use of a trivalent or higher polyvalent alcohol in combination, but the purpose is to broaden the molecular weight distribution of the polyester resin. This is not for the purpose of gelling the resin. The gelation of the resin makes it difficult to take out the resin from the polyester polymerization apparatus, and causes a significant decrease in productivity. In the present invention, there is substantially no gelation, and more specifically, the chloroform-insoluble content needs to be 0.5% by weight or less, preferably 0.25% by weight or less.

The acid value of the polyester resin in the present invention is preferably 3 mg KOH / g or less, and
/ G is still more preferred, and still more preferably 0.5 mg KOH / g
Is preferably adjusted so as not to exceed.

Further, it is preferable that the polyester resin of the present invention does not dissolve in methyl ethyl ketone and toluene at room temperature. When dissolved in these solvents, the PVC plasticizer resistance may decrease. The solubility of the resin depends on the aliphatic diol of the polyhydric alcohol component and the alicyclic polyhydric alcohol.
Can be adjusted by the ratio with the

In the present invention, a component having an ionic group can be contained in the polyester resin for the purpose of improving the charging stability of the toner. Examples of the ionic group contained in the resin include an anionic group such as a carboxyl group, a sulfonic acid group, a sulfate group, a phosphoric acid group, a phosphonic acid group, a phosphinic acid group or an ammonium salt or a metal salt thereof, or a primary to primary group. It is a cationic group such as a tertiary amine group, and preferably, a carboxyl group, an ammonium carboxylate group, a sulfonic acid group, an alkali metal sulfonic acid base and the like can be used. It is preferable that these ionic groups are contained in a form copolymerized with the polyester or a form introduced into the polymer terminal.

Examples of the sulfonic acid metal base-containing compound copolymerizable with polyester include sulfoterephthalic acid, 5-
Metal salts such as sulfoisophthalic acid, 4-sulfophthalic acid, 4-sulfonaphthalene-2,7-dicarboxylic acid, and 5 [4-sulfophenoxy] isophthalic acid can be given. Further, by using a metal salt of sulfobenzoic acid, a metal sulfonate group can be introduced into a polymer terminal. In addition, a carboxyl group can be introduced into a polymer terminal by introducing a polyvalent carboxylic acid such as trimellitic acid into the system at the end of polymerization. Li salt A N
Salts such as a, K, Mg, Ca, Cu, Fe and the like can be mentioned, and particularly preferred is a Na salt. Also, it is possible to use ammonium-based ions instead of metal ions. The content of these ionic groups is 10 to 1000 meq / 1000 g, preferably 20 to 500 meq / 1000 g, and more preferably 5 to 1000 meq / 1000 g with respect to the polyester resin.
0 to 200 meq / 1000 g. When the content of the ionic group is less than a predetermined amount, sufficient stability of the charged charge cannot be obtained. Further, when the ionic group content is more than necessary, it is particularly susceptible to humidity, and the long-term storage stability may be deteriorated.

In the present invention, particularly when the polyester resin contains an ionic group, the polyester resin exhibits water dispersibility. In this case, the ionic group-containing polyester resin that has been stably micro-dispersed in an aqueous medium is mixed with the micro-dispersed particles present in the surface of the micro-dispersed particles and in the vicinity of the surface in a state where the micro-dispersed particles are plasticized. By means of reducing the amount of ions having the function of stabilizing in a uniformly controlled state, the stable state of the micro-dispersed particles in the medium is broken, and the ionic Group-containing polyester particles can be obtained. As a means for reducing the amount of ions present on the surface of the microdispersed particles, and near the surface, the ionic groups contained in the polyester resin are cut off by photolysis, thermal decomposition, hydrolysis, or the like; Means such as control of the degree of dissociation by scanning pH or the like, blocking of the ionic group by a counter ion, and destruction of the electric double layer by an electrolyte can be used. In the present invention, a reactive monomer having a counterionic group is added into the system, and the ionic group is blocked using a polyion complex formed by polymerizing the monomer having a counterionic group. Method, or a method in which a monomer portion having an ionic group or an ionic group introduced as a part of the polymer chain through an ester bond or the like as a part thereof is cut off in combination with a perhydrolysis catalyst. be able to.

The method for producing an electrophotographic toner in the present invention is not particularly limited, and the above-mentioned particle forming method may be used. A so-called pulverization method in which a charge control agent, a fluidity modifier, a pulverization aid, and the like are added and kneaded, followed by pulverization and classification, may be used. The method for coloring the polyester resin in the present invention is not particularly limited, and a known coloring agent such as a pigment or dye or carbon black may be used. These dyes, pigments, carbon black and the like may be used alone or in combination as needed. It is particularly preferable to use a dye from the viewpoint of spectral transmission characteristics.

When a dye is used for coloring, azo, nitro, quinoline, quinophthalone and methine dyes are used for yellow coloring, and anthraquinone, azo and xanthene dyes are used for magenta coloring. An anthraquinone dye is preferably used for coloring. As the form of the dye, it is preferable to use a disperse dye or an oil-soluble dye. These may be directly used in the form of a commercially available dye as a disperse dye for dyeing textiles, and those which are not available in such a form include a dye base (kink cake), a dispersant, and an aqueous dye. The medium may be mixed with a ball mill, a sand mill, a shaker, or the like, and a condensed cake of the dye may be further finely pulverized and finely dispersed. As the dispersant, a condensate of naphthalene sulfonate, polystyrene sulfonate, a copolymer of styrene sulfonate and acrylic acid, or the like can be used.

When a pigment is used for coloring, benzidine and azo pigments are used for yellow coloring, azo lake, rhodamine lake, and quinacridone pigments are used for magenta coloring, and phthalocyanine is used for cyan coloring. A system pigment is preferably used. When black toner is obtained, carbon black or the like may be used. As carbon black, thermal black, acetylene black, channel black, furnace black, lamp black and the like can be used. Electrophotographic toner of the present invention
In the above, a charge control agent may be used in combination to give a predetermined charge amount. In the toner of the present invention, a fluidity modifier such as alumina fine particles and silica fine particles may be added. In the case of a magnetic one-component developer,
It may contain iron, cobalt, nickel, an alloy mainly containing them, or an oxide such as ferrite. As a method for adding these, a Henshall mixer
A known dry treatment method such as the above-mentioned method may be used, and in the case of passing through the above-mentioned aqueous dispersion, a wet method such as powder spray drying after mixing and stirring the water-dispersed additive with the aqueous dispersion of resin particles. May be used.

The electrophotographic toner of the present invention has good image characteristics, fixing characteristics, blocking resistance, storage stability and PVC plasticizer resistance. This achieves a low melt viscosity at high temperatures while the polyester resin used in the present invention maintains a relatively high glass transition temperature, and further has an affinity with a plasticizer contained in a vinyl chloride resin, an eraser, and the like. The reason for this is that the plasticizer does not migrate to the toner resin because it is low, and the bleeding of the coloring material in the toner is suppressed because the toner resin itself has a certain degree of crystallinity.

Therefore, even when the copy made by the toner using the polyester resin of the present invention is stored for a long time in a state in which the copy is in contact with a transparent PVC sheet or the like, the transfer of the coloring material and the transfer of the resin to the sheet are performed. Does not cause adhesion. The polyester resin of the present invention has excellent light-fastness due to excellent color development in dyeing and high stability to dyes.
Further, the toner in the present invention is excellent in transparency, so that not only color development in the case of a single color but also good color mixing in the case of overlapping with another color is excellent in reproducibility of an intermediate color. Further, when an image is formed on a transparent film used for an overhead projector or the like, an excellent color tone is exhibited in an image projected on a screen.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited thereto.

【Example】

(Synthesis of polyester resin) In an autoclave equipped with a thermometer and a stirrer, 165 parts by weight of dimethyl terephthalate, 21 parts by weight of dimethyl isophthalate, 8 parts by weight of trimellitic acid, ethylene glycol Then, 123 parts by weight of toluene, 20 parts by weight of tricyclodecane dimethanol and 0.1 part by weight of tetrabutoxy titanate were charged, and the mixture was heated at 180 to 230 ° C. for 120 minutes to carry out a transesterification reaction. Then, the temperature of the reaction system was raised to 250 ° C., and the reaction was continued at a system pressure of 1 to 10 mmHg for 60 minutes. As a result, a copolymerized polyester resin (A1) was obtained. The composition of the obtained copolymerized polyester resin (A1) was determined by NMR.
As a result of analysis, 85 mol% of terephthalic acid, 11 mol% of isophthalic acid, 4 mol% of trimellitic acid, 90 mol% of ethylene glycol and 10 mol% of tricyclodecane dimethanol as alcohol components. Hereinafter, polymerization was carried out in the same manner by changing the raw materials. The following polyester resins (A2) to (A6) were obtained.

[0025]

[Table 1]

In the composition (A7), the viscosity rapidly increased at the end of the polymerization, and the resin gelled in the autoclave. Although the polymerization was attempted several times with the same composition while adjusting the reaction pressure at the end of the polymerization, it was difficult to stop the reaction immediately before the complete gelation of the resin. It was extremely difficult to take out the gelled resin in the autoclave, and it became clear that the present composition did not withstand production on an industrial level. The molecular weight of the obtained resin varied greatly from one polymerization batch to another, highlighting the difficulty of stopping the polymerization with this composition immediately before gelation.

In an autoclave equipped with a thermometer and a stirrer, an ethylene oxide adduct of bisphenol A 70 was added.
Parts by weight, 19.6 parts by weight of maleic anhydride and 0.2 parts by weight of hydroquinone, nitrogen gas was introduced into the reaction system, and the reaction system was maintained in an inert atmosphere. To give a polyester resin (A8). Table 1 shows the composition of the polyester resin (A8). Shown in Table 1. Medium, TPA converts terephthalic acid, IP
A is isophthalic acid, TMA is trimellitic acid, PM
A is pyromellitic acid, SIP is 5-sodium sulfoisophthalic acid, MA is maleic acid, EG is ethylene glycol, PG is propylene glycol, TCD
Is tricyclodecane dimethanol, and CHD is 1,4-
Cyclohexanediol, CHDM indicates 1,4-cyclohexanedimethanol, and BPP indicates a propylene oxide adduct of bisphenol A.

(Preparation of Toner 1: Grinding and Classification Method) Carbon black (4 parts by weight) was added to 96 parts by weight of a polyester resin (A1), and the mixture was melt-kneaded in a hot roll mill. Next, after pulverizing with a fine pulverizer, the mixture is classified with a zigzag classifier, and 100 parts by weight of the obtained pulverized particles are mixed with 2 parts by weight of silica fine powder (trade name Aerosil) using a Henschel mixer to obtain an average particle diameter of 11 μm. A black toner (K11) was obtained. Hereinafter, the polyester resin and the coloring material were changed in the same manner as in Table 2. Toner shown in
I got Benzidine yellow-(CIPigmen
t Yellow 17) Quinacridone Red (CIPigment Red 1
22), Phthalocyanine-(CIPigment Blue15)
Was used.

[Table 2]

(Preparation of toner 2: wet granulation and dyeing) 34 parts by weight of copolymerized polyester resin (A2), dioxane 5
Parts by weight, 5 parts by weight of tetrahydrofuran, and 10 parts by weight of methyl ethyl ketone were dissolved at 80 ° C., and then water 56 at 80 ° C. was dissolved.
Was added to obtain an aqueous microdispersion of a copolymerized polyester resin having a particle diameter of about 0.1 μm. Further, the obtained aqueous microdispersion was placed in a distillation flask, and the fraction temperature was 100 ° C.
The solution was distilled until the temperature reached ° C. After cooling, water was added to adjust the solid content to 30%. In a four-necked 1-liter separable flask equipped with a thermometer, a condenser, and a stirring blade, 330 parts by weight of the aqueous dispersion of the copolymerized polyester and 7 parts by weight of dimethylaminoethyl methacrylate are heated and heated to 90 ° C. did. Stirring was continued for 240 minutes at 70 ° C. As a result, the copolymer having a particle size on the order of submicron which was present in the polyester aqueous microdispersion grew into coalesced particles, and when the average particle size was 6.8 μm and the diameter was D, 0.5% was obtained.
Occupancy (number) of particles having a particle size in the range of D to 2D 9
5% of polyester particles were obtained. The obtained polyester particles were filtered, washed with water, and water was added again to obtain a 25% by weight aqueous dispersion of polyester particles. 400 parts by weight of the obtained polyester particle aqueous dispersion, and as a yellow dye, Miketone polyester yellow-YL (CIDisperse Yello)
w42) 2 parts by weight (made by Mitsui Toatsu Dye) (converted to pure dye) were charged into a stainless steel pot of a dyeing tester minicolor [manufactured by Texam Giken] and dyed at 130 ° C for 60 minutes. Thereafter, the mixture was cooled to room temperature, dehydrated, washed with water, and again added with deionized water to obtain an aqueous dispersion of colored particles having a solid content of 20% by weight. To 500 parts by weight of the obtained water dispersion, 3% by weight of water-dispersible silica fine powder was added, and the mixture was stirred for 20 powders and then dried by atomization to obtain yellow toner (Y22). Similarly, Sumikaron Red S-BDF (CIDisperse Red 34) was used as a magenta dye in the same manner.
8) Sumikalon Brilliant Blue-S-BL (CIDisperse Blue 87) was used as a cyan dye. A toner was obtained.

[0030]

[Table 3] Sumicaron Navy-S-GL is used as a dye.
(CIDisperse Blue 79) 3 parts by weight, Macrolex
Orange R [manufactured by Bayer] 3 parts by weight was used. Was obtained.

[0031]

[Table 4]

(Evaluation of storage stability)
The storage stability was evaluated based on the presence or absence of blocking after being left for 100 hours in a humidified atmosphere at 90 ° C. and 90% RH. Toner
Blocking was observed in (K81), but no blocking was observed in other toners.

(Evaluation of poppy rubber plasticizer resistance) 5 parts by weight of the obtained toner and 95 parts by weight of a ferrite carrier F-100 (manufactured by Powder-Tech Co., Ltd.) were stirred and mixed in a ball mill, followed by two-component development. Agent was obtained. Using the obtained two-component developer, a 7 cm square solid pattern was formed on paper by an electrophotographic copying machine using OPC as a photosensitive member. The average thickness of the toner layer on the paper was standardized to 8 μm. The obtained solid pattern was treated with 10 parts of dioctyl phthalate as a plasticizer.
Sandwiched between plastic poppy rubbers containing 50% by weight
The sample was left for 20 hours in a constant temperature bath at 50 ° C. under a load corresponding to cm ² . In the toners (K71) and (K81), the toner layer and the poppy rubber were completely adhered, and a part of the toner layer remained on the poppy rubber surface when peeled off. Other toners
Had no particular problems.

(Evaluation of Light Fastness) Of the above 7 cm square solid pattern, Table 3 (1) Carbon arc fade meter (63 ° C.)
For 40 hours. The value obtained by dividing the image density (optical density) after the test by the initial image density was defined as the residual color ratio. Shown in All have good light fastness.

(Resolution Evaluation) Table 2. Table 4. 5 parts by weight of black toner as shown in
300 [manufactured by Powder-Tech Co., Ltd.] was mixed with 100 parts by weight to obtain a developer, and a resolution test chart was copied using the above-described copying machine. Table 2 shows the results. Table 4. Shown in

(Evaluation of Image Characteristics) Table 3. Toner-5
Parts by weight and 95 parts by weight of a ferrite-based carrier F-100 [manufactured by Powder-Tech Co., Ltd.] were stirred and mixed by a ball mill,
Component developer, an electrophotographic copying machine using OPC as a photoreceptor, and a continuous tone image for color printing obtained in advance by color separation as a manuscript on paper;
YMC was superimposed on a transparent sheet for HP, copied, and observed visually. The obtained full-color image had high quality, and an image obtained by projecting a transparent sheet with OHP also showed a high color tone without turbidity.

[0037]

As described above, the toner for electrophotography according to the present invention has excellent storage stability that does not cause blocking even in a wet heat environment, exhibits high plasticizer resistance, and The resulting image was also shown to be of high quality.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-3-128924 (JP, A) JP-A-1-307767 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G03G 9/087

Claims (1)

(57) [Claims] 1. A polyester resin mainly obtained from a polycarboxylic acid and a polyhydric alcohol, wherein the aromatic dicarboxylic acid containing terephthalic acid and / or its derivative in an amount of 80 mol% or more and / or its derivative (A) 90 mol
l% or more and a trivalent or more polyvalent carboxylic acid and / or a derivative thereof (B) in an amount of 0.5 to 8 mol%, and a diol and / or a derivative thereof (C ) A polyhydric alcohol containing 40 to 98 mol% and an alicyclic alcohol and / or a derivative thereof (D) 2 to 60 mol%, and containing substantially no gel component (a chloroform-insoluble component is 0.5%). An electrophotographic toner comprising a polyester resin as a main component of a binder resin (by weight% or less). Embedded image In Chemical Formula 1, R1 to R4 each independently represent hydrogen, methyl, or ethyl.