JPH0820765B2 - Polyester resin for toner and manufacturing method thereof - Google Patents

Description

The present invention relates to a polyester resin for a dry toner for developing an electrostatic image in electrophotography, electrostatic recording, electrostatic printing, and the like, and a method for producing the same. .. More specifically, it relates to a polyester resin for dry toner having excellent offset resistance and electrical characteristics, and a method for producing the same.

[Conventional technology]

In a method of obtaining a permanent visible image from an electrostatic charge image, the electrostatic charge image formed on a photoconductive photosensitive member or electrostatic recording material is developed and fixed using a toner charged in advance by friction. .. For fixing, the toner image obtained by development is directly fused on the photoconductive photoconductor or the electrostatic recording body, or the toner image is transferred onto paper or film and then fused onto the transfer sheet. Done by Toner image fusion is performed by contact with solvent vapor, pressurization and heating.There are contactless heating method using an electric oven and pressure heating method using a heating roller as heating methods, but it is required to speed up the fixing process. Recently, the latter is mainly used.

The toner used in the dry developing method includes a one-component toner and a two-component toner. The two-component toner is produced by first melt-kneading a resin, a colorant, a charge control agent and other necessary additives to sufficiently disperse them, and then coarsely pulverizing and finely pulverizing them and classifying them into a predetermined particle size range. It The one-component toner is manufactured in the same manner by adding magnetic iron powder in addition to the respective components of the above two-component toner.

Since the resin is the main component in the toner formulation, it controls most of the performance required for the toner. Therefore, the toner resin is required to have good dispersibility of the colorant in the melt-kneading step and good pulverizability in the pulverizing step in the production of the toner. Various performances such as good blocking property and good electrical property are required. Epoxy resins, polyester resins, polystyrene resins, methacrylic resins and the like are known as resins used in the production of toners, but for pressure-bonding heat fixing systems, copolymers of styrene and (meth)acrylic acid ester are mainly used. Has been used. However, polyester resins have recently been attracting attention because they can be fixed at lower temperatures and the fixed toner images have excellent PVC plasticizer resistance.

The polyester resin is produced by directly esterifying a divalent carboxylic acid and its lower alkyl ester and a diol or by a condensation reaction by transesterification.
In order to impart offset resistance in the fixing step, it has been proposed that the polyester resin for toner has a weak crosslinked structure by cocondensing a carboxylic acid or alcohol having a valence of 3 or more in addition to the above. However, a toner using a conventional polyester resin obtained by co-condensing a carboxylic acid or alcohol having a valency of 3 or more has a large electric characteristic, that is, a large negative chargeability, and a large temperature dependence of the charge, which varies depending on the image quality environment. There are drawbacks, and their improvement has been desired.

[Problems to be Solved by the Invention]

In the prior art, the inventors of the present invention can improve the offset resistance of the toner by co-condensing a trifunctional monomer, but on the other hand, examined the cause of the poor electrical characteristics of the toner as described above. However, they have found that this is due to the high acid value of the polyester resin. That is, in general, in order to achieve good offset resistance by co-condensing a trifunctional monomer, it is necessary to proceed with the condensation reaction until it has an appropriate cross-linking structure. At this time, the viscosity of the reaction system rapidly increases. However, it was difficult to obtain the desired resin because it was impossible to take it out of the reactor or the reaction could not be controlled. Therefore, it is necessary to take out without reacting until it has a necessary crosslinked structure, and as a result, the desired offset resistance cannot be improved or the condensation reaction cannot proceed sufficiently, resulting in a resin with a high acid value. However, as a result, there was a drawback in electrical characteristics. That is, it has been found that it is difficult in the prior art to satisfy both the provision of an appropriate cross-linking structure required for offset resistance and the low acid value for having excellent electrical characteristics.

[Means for Solving the Problem, Its Action and Effect of the Invention]

The present inventors have conducted extensive studies to solve these problems, and have found a polyester resin having both offset resistance and good electrical properties and a method for producing the same, and have completed the present invention.

The present invention comprises (a) at least one trihydric or higher alcohol, (b) at least one diol, (c) at least one divalent carboxylic acid and a lower alkyl ester thereof, and comprises at least one of all alcohol components. Of which (a) is 0.5
Mol% or more and 50 mol% or less, (b) of all alcohol components is 50 mol% or more and 99.5 mol% or less, and the softening temperature is 90 to 170° C. and the glass transition temperature is 30 to 70.
C., an acid value of 0.5 to 10 mgKOH/g, a gel fraction of 1.5 to 40% of the first invention, which is a polyester resin for toner, and (a) 0.5 mol% or more of all alcohol components, At least one trihydric or more alcohol monomer of 50 mol% or less, and (b) at least one of diol monomers of 50 mol% or more and 99.5 mol% or less of all alcohol components.
(C) a dicarboxylic acid component and at least one dicarboxylic acid component of a lower alkyl ester thereof are subjected to a condensation reaction in the presence of a catalyst, the dicarboxylic acid component (c) satisfies the following formula (1): The polyhydric alcohol (a), (b) and the carboxylic acid component (c) are esterified or transesterified with the diol component (b) under a vacuum of 150 mmHg or less. In the operation of forming a crosslinked state while distilling and removing
A method for producing a polyester resin for toner, characterized in that the pressure of the reaction system is increased according to the increase of the viscosity of the polymer to substantially control the crosslinking reaction rate. And the second invention.

Examples of the trihydric or higher alcohol (a) used in the present invention include, for example, sorbitol, 1,2,3,6-hexanetetrol, 1,4-sorbitan, pentaerythritol,
Dipentaerythritol, tripentaerythritol,
Sucrose, 1,2,4-butanetriol, 1,2,5-pentatriol, glycerol, 2-methylpropanetriol,
2-Methyl-1,2,4-butanetriol, trimethylolethane, trimethylolpropane, 1,3,5-trihydroxymethylbenzene and the like can be mentioned, and they can be used alone or in a mixture. In the present invention, a polyester resin having a neutral charging characteristic can be obtained by using such a trivalent or higher valent alcohol (a), and a conventional polyester resin using a trivalent or higher carboxylic acid is used. It has a large negative chargeability, and the problem that it was difficult to use as a polyester resin for positively chargeable toner can be solved, and a polyester resin that can be used for both positively chargeable toner and negatively chargeable toner can be obtained. .. Further, in the case of a polyester resin using a carboxylic acid having a valence of 3 or more, the resin exhibits a yellowish tint, and when it is used for a color toner, there is a problem in its color tone.
When a trihydric or higher alcohol is used as in the present invention, a transparent resin with almost no color is obtained, and the problem of color tone when used for a color toner can be solved.

The diol (b) used in the present invention is an aliphatic or aromatic diol. Specific examples of the aliphatic diol include, for example, ethylene glycol, neopentyl glycol, butanediol, polyethylene glycol and the like. Among them, ethylene glycol, neopentyl glycol and butanediol are preferable from the viewpoint of fixability.

Examples of aromatic diols include polyoxyethylene (2,0)-2,2-bis(4-hydroxyphenyl)propane and polyoxypropylene-(2,0)-.
Polyoxyethylene-(2,0)-2,2-bis(4-hydroxyphenyl)propane, polyoxypropylene(6)-2,2-bis(4-hydroxyphenyl)propane, polyoxypropylene(2 , 0)-2,2-bis(4
-Hydroxyphenyl)propane, polyoxypropylene (2,2)-2,2-bis(4-hydroxyphenyl)
Examples include propane, polyoxypropylene (2,4)-2,2-bis(4-hydroxyphenyl)propane and polyoxypropylene (3,3)-2,2-bis(4-hydroxyphenyl)propane. And used alone or as a mixture.

In the present invention, the trihydric or higher alcohol (a) is contained in an amount of 0.5 to 50 mol%, preferably 1 to 35%, based on all alcohol components.
The diol (b) is contained in an amount of 50 to 99.5 mol%, preferably 65 to 99 mol% in all alcohol components. 0.5 mol% of trihydric or higher alcohol (a)
If it is less than 50%, offset resistance is lowered, and if it exceeds 50 mol%, blocking resistance is lowered.

Examples of the divalent carboxylic acid or its lower alkyl ester (c) used in the present invention include terephthalic acid, isophthalic acid, sebacic acid, isodecyl succinic acid, maleic acid, fumaric acid and their monomethyl, monoethyl, dimethyl, Examples thereof include diethyl ester, and terephthalic acid, isophthalic acid and dimethyl esters thereof are particularly preferable in terms of blocking resistance and cost. These divalent carboxylic acid or its lower alkyl ester greatly affects the fixing property and blocking resistance of the toner. That is, although depending on the degree of condensation, if a large amount of aromatic terephthalic acid, isophthalic acid or the like is used, the blocking resistance is improved but the fixing property is lowered. On the contrary, aliphatic sebacic acid,
When a large amount of isodecyl succinic acid, maleic acid, fumaric acid or the like is used, the fixability is improved, but the blocking resistance is lowered. Therefore, these divalent carboxylic acids are used alone or in combination according to the composition and ratio of other monomers and the degree of condensation.

The most important point of the present invention is that the resin obtained by condensation of the above monomers has a softening temperature of 90 to 170° C., a Tg of 30 to 70° C., an acid value of 0.5 to 10 mgKOH/g, and a gel fraction of 1.5 to 40. It is a polyester showing a characteristic value of %.

If the softening temperature is less than 90°C, the fixability will be good, but
Blocking resistance becomes poor, and if it exceeds 170°C, fixing property becomes poor. Therefore, the softening temperature needs to be 90 to 170°C, and particularly preferably 100 to 160°C.

Further, addition of an inorganic powder such as silica to the toner is effective in improving the blocking property, and the effect is particularly remarkable when the Tg of the binder is low. Further, when Tg is about 50 to 70° C., blocking resistance is good without adding inorganic powder. However, if the Tg is less than 30° C., the fixing property will be good, but the blocking property will be extremely poor, and it will be unusable even if an inorganic powder is added. On the other hand, if the temperature exceeds 70°C, the fixability will be poor. Therefore Tg should be 40-70°C,
Particularly, 50 to 70°C is preferable.

When the acid value is less than 0.5 mgKOH/g, the dispersibility of the colorant decreases, while when it exceeds 10 mgKOH/g, the negative chargeability increases, and the temperature dependence of the charge increases and the image quality changes depending on the environment. .. Therefore, the acid value must be 0.5 to 10 mgKOH/g, preferably 0.5 to 5 mmgKOH/g, and more preferably 1 to 3 mmgKOH/g.

If the gel fraction is less than 1.5%, the fixability will improve,
If the offset resistance required for the toner is not obtained, and conversely the gel fraction exceeds 40%, the offset resistance becomes good, but the fixability becomes extremely poor. Therefore, the gel fraction is 1.5-40
% Is necessary, and particularly preferably 5 to 30%.

Next, a method for producing the polyester resin of the present invention will be described.

In the present invention, the total amount of all alcohol components, that is, the total amount of the trihydric or higher alcohol (a) and the dihydric alcohol (b) is mixed with the dicarboxylic acid component (c) within the range satisfying the above formula (1), and the mixture is heated and heated. The esterification reaction or transesterification reaction is carried out by heating. At this time, if necessary, sulfuric acid,
Esterification catalysts or transesterification catalysts used in ordinary esterification reaction or transesterification reaction such as titanium butoxide, dibutyltin oxide, magnesium acetate, manganese acetate and the like can be used.

In the present invention, in order to prevent the gelation reaction from occurring during the esterification reaction or transesterification reaction, the addition amount of the dicarboxylic acid component (c) is the above formula (1).
It is necessary to satisfy.

Then, after the esterification reaction or transesterification reaction, water or alcohol generated in the reaction is removed according to a conventional method.

In the present invention, the polymerization reaction is subsequently carried out. At this time, the polymerization is carried out under a vacuum of 150 mmHg or less while distilling off the diol component (b).

In the polymerization, generally known polymerization catalysts such as titanium butoxide, dibutyltin oxide, tin acetate, zinc acetate, tin disulfide, antimony trioxide, germanium dioxide, germanium acetate and the like can be used.

In the reaction, the cross-linking polymerization reaction proceeds by distilling off the diol component (b), so that a polyester having an arbitrary degree of cross-linking can be obtained by controlling the amount of distilling out the diol component (b). .. Therefore, in the present invention, a resin having a desired degree of crosslinking can be obtained only by controlling the degree of vacuum during the polymerization reaction (optionally increasing the system pressure).

Further, the polymerization temperature and the amount of catalyst are not particularly limited, and may be arbitrarily set as needed.

Distillation and removal of the diol component (b) is determined by the degree of vacuum and temperature of the reaction system, but considering the pressurization conditions of the reaction system to stop the polymerization reaction, the degree of vacuum is preferably 150 mmHg or less, and 30 mmHg or less. Particularly preferred.

To produce a polyester having both a low acid value of 0.5 to 10 mg KOH/g for exhibiting excellent electrical properties in toner applications and a gel fraction of 1.5 to 40% required for offset resistance for the first time by this operation method. Can be done.

In the present invention, the softening temperature of the polyester resin is 1 mmφ×10 mm nozzle, load 30 kg, temperature rising rate 3° C./using a flow tester CF-500 manufactured by Shimadzu Corporation.
It is the temperature at which 1/2 of 1 g of a sample flows out when measured under a constant rate of temperature increase of 1 minute.

Tg is the temperature at the intersection of the tangent line of the endothermic curve near the chart base line and Tg when measured at a temperature rising rate of 10°C/min using a differential scanning calorimeter.

Acid value is KOH required for neutralization by neutralization titration with normal KOH solution
Of mg.

The gel fraction is 0.5 g of the sample placed in 50 ml of tetrahydrofuran, heated and dissolved at 70°C for 3 hours, filtered through a glass filter covered with Celite #545, and dried in a vacuum dryer at 80°C.
The value obtained by dividing the weight when fully dried by the initial weight.

Next, the present invention will be described with reference to examples, but the embodiments of the present invention are not limited thereto.

[Example 1] Isophthalic acid, terephthalic acid, pentaerythritol, trimethylolpropane, ethylene glycol,
According to the composition shown in Table 1, a reaction vessel having a distillation column was charged.

Furthermore, 0.03% by weight of dibutyltin oxide was added to the reaction vessel, the internal temperature was 220°C, and the stirring speed was 2
When the esterification reaction was carried out under atmospheric pressure while keeping the pressure at 00 rpm, the reaction system became transparent about 4.5 hours after the water started to distill, and the water distillation stopped. The torque meter of the stirrer at this time was 0.9 kg-cm. Next, keep the internal temperature at 235°C, the stirring speed at 200 rpm, and the pressure in the reaction system at 1.0 mmHg.
When the pressure was reduced to 1, ethylene glycol was distilled out from the reaction system, and the stirring torque gradually increased to about 1.
After 5 hours, when the stirring torque reached 1.2 kg-cm, gelation started and the stirring torque started to rise rapidly. At this time, when the pressure of the reaction system was changed to 15 mmHg, the rising speed of the stirring torque became slow, and after about 20 minutes, the stirring torque was 3.0 k
Reached g-cm. At this time, the pressure in the reaction system was set to normal pressure, and stirring was continued for about 1 hour in that state. As a result, the stirring torque remained at a substantially constant value at 3.05 kg-cm.

In this example, the degree of crosslinking of the polymer, that is, the stirring torque, or the viscosity can be easily controlled by controlling the pressure in the reaction system.
Moreover, it shows that the gelling reaction can be substantially stopped.

The obtained products R ₁ , R ₂ and R ₃ were all pale yellow and had the characteristic values shown in Table 1.

Next, 95 parts by weight of these resins and 5 parts by weight of carbon black are melt-kneaded using a twin-screw extruder, cooled, crushed by a jet mill, and then classified by a classifier to obtain T ₁ , I got T ₂ and T ₃ .

95 parts by weight of an iron powder carrier was added to 5 parts by weight of these toners, and copying was carried out using an electrophotographic copying machine for polyester toner which was modified so that the temperature of the fixing part could be freely changed. Performance was evaluated by continuously copying 5000 sheets at a speed of 30 sheets per minute under different atmospheres. The results are shown in Table 1-1.
It was shown to. No offset was observed in a wide temperature range and the fixability was good. Also, normal temperature (20°C) and normal humidity (relative humidity 60
%), the image quality was very good. Next, the image quality slightly deteriorated under high temperature and high humidity and low temperature and low humidity, but it was within a practically acceptable range.

When the toner was placed in a container and left in an atmosphere of 50° C. for 24 hours, the state was observed, and it was found that there was almost no blocking and there was no practical problem.

In the present invention, various toner performance evaluations were carried out by the following methods.

1. Offset resistance The temperature of the fixing roller was changed at intervals of 5°C, and the degree of offset when continuous copying was performed was evaluated in five levels.

A: Best to E: Worst (Practical up to C) 2. Fixing property A solid part when copying at a fixing temperature of 180° C. was rubbed with an eraser, and five grades were evaluated according to the degree of removal.

A: The best to E: The worst (Practical up to C) 3. Blocking resistance The degree of blocking was evaluated in 5 levels.

A: No blocking at all.

B: It is a little blocking, but it easily returns to its original state by turning it upside down and slightly vibrating.

C: It is lightly blocked, but it can be used by turning it upside down and vibrating.

D: It's blocking, it collapses when rubbed by hand, but it doesn't return to the original state.

E: It's completely blocked, and it won't collapse even if you rub it with your hand.

4. Image quality The image quality of the copy on the test screen was evaluated by 5 grades by visual judgment.

A: Very good.

B: Excellent.

C: There is some rash, but it is practical.

D: A rash is seen, and it is inferior to the extent that is practically a problem.

E: The rash is severe and very inferior.

Comparative Example 1 Terephthalic acid, trimethylolpropane and ethylene glycol were used, and charged into a reaction vessel having a distillation column according to Table 1. The catalyst, the temperature conditions, and the agitation rotation speed were set in Example 1.
The esterification reaction was carried out under normal pressure under the same conditions as above. The viscosity of the reaction solution began to rise 4.1 hours after the start of the distillation of the water generated by the esterification reaction, so nitrogen was sucked into the reaction kettle and the inside of the kettle was pressurized to a pressure of 3 kg/cm ² , but gelation occurred. The reaction did not stop and finally stirring became impossible. This comparative example shows that the gelation reaction cannot be controlled in the esterification reaction stage.

Example 2 Resins R ₄ and R ₅ were obtained in the same manner as in Example 1 except that trimethylolpropane was used as the polyhydric alcohol and the composition of the monomers used was as shown in Table 2. The characteristic values of these resins are shown in Table 2. Using the same procedure as in Example 1, except that 1% by weight of Aerosil (registered trademark) R-972 (silica manufactured by Nippon Aerosil Co., Ltd.) was added to the toner in an amount of 100% by weight at the time of kneading, was used. Corresponding toners, T ₄ and T _5, were obtained. All toners showed good toner performance.

Comparative Example 2 Resins R ₆ and R ₇ were obtained in the same manner as in Example 1 except that trimethylolpropane was used as the polyhydric alcohol and the composition of the monomers used was as shown in Table 3. The characteristic values of these resins are shown in Table 3. Toners T ₆ and T ₇ corresponding to these resins were obtained by the same operation as in Example 1 using these resins. The toner performances are shown in Table 3-1.

0.3 mol% trimethylol propane only T ₆ was not used has no non-offset width was impossible replication.
Further, it was found that T ₇ using 55 mol% of trimethylolpropane had poor blocking resistance, and even if 1% of "Aerosil" R-972 was added, it was blocked and could not be used.

[Comparative Example 3] The composition of the monomers used was as shown in Table 4, and 0.03 mol% of tin oxide as a polymerization catalyst was added to the carboxylic acid in a monomer composition in which the molar ratio of the diol component to all the carboxylic acids was 1.00. The mixture was put into the same separable flask as in Example 1, heated to 220° C., and dehydrated and condensed. The viscosity of the system suddenly increased from the time when distilled water was taken out to some extent, and after about 5 minutes, the whole gelled state, and the condensation reaction could not be stopped at a viscosity that could be taken out from the reactor. In general, in industrial production, it takes 30 minutes to 1 hour to take out a product from a reactor, so that it is practically impossible to produce.

However, since this comparative example is a small-scale experiment,
In order to understand the resin properties and toner performance of the product, R _{8 to} R ₁₀ were obtained by forcibly taking out and cooling to stop the reaction while the viscosity was rapidly increasing. Table 4 shows the characteristic values of these resins.
Shown in. Also to obtain toner T ₈ through T ₁₀ corresponding respectively in the same manner as in Example 1 from these resins. The properties of these toners are shown in Table 4-1.

It was found that the toners obtained from these resins having a high acid value have high humidity dependence of image quality and are not suitable for practical use.

Was obtained Example 3 The molar ratio of total diol component composition of the monomer used and on the total carboxylic acid in the same manner as in Example 1 except that as shown in Table 5 Resin R ₁₁ to R _13. The characteristic values of these resins are shown in Table 5. To obtain toner T ₁₁ through T ₁₃ respectively corresponding in the same manner as in Example 1 using these resins. The performance of the toner is shown in Table 5-1.

As is clear from Table 5-1, the softening temperature is 135°C,164
The toner exhibited good toner performance at ℃, but at the softening temperature of 98 ℃, the offset start temperature began to decrease to 170.

Comparative Example 4 Resins R ₁₄ and R ₁₅ were obtained in the same manner as in Example 1 except that the composition of the monomers used and the molar ratio of all diol components to all carboxylic acids were as shown in Table 5. The characteristic values of these resins are shown in Table 5. Using these resins, corresponding toners T ₁₄ and T ₁₅ were obtained in the same manner as in Example 1. The toner performance is shown in Table 5-1.

It was found from Table 5-1 that when the softening temperature exceeds 170° C., the fixability is extremely poor and the image quality begins to deteriorate, and when the softening temperature falls below 90° C., there is no non-offset width and it cannot be used.

Was obtained Example 4 the molar ratio of total diol component composition of the monomer used and on the total carboxylic acid in the same manner as in Example 1 except that as shown in Table 6 Resin R ₁₆ to R _18. The characteristic values of these resins are shown in Table 6. Using these resins, corresponding toners T _{16 to} T ₁₈ were obtained in the same manner as in Example 1. The toner performance is shown in Table 6-1. However, regarding the resin of R ₁₈ , "Aerosil" R-972 was used at 1% by weight with respect to 100% by weight of the toner at the time of toner production.

When the resin with Tg of 40, 60, 70 ℃ was used, the physical properties were well balanced and the image quality was good.

Comparative Example 5 Resins R ₁₉ and R ₂₀ were obtained in the same manner as in Example 1 except that the composition of the monomers used and the molar ratio of all diol components to all carboxylic acids were as shown in Table 6. The characteristic values of these resins are shown in Table 6. Using these resins, corresponding toners T ₁₉ and T ₂₀ were obtained in the same manner as in Example 1. The toner performances are shown in Table 6-1.

As is clear from Table 6-1, it was found that when Tg was 75° C., the fixability deteriorated, and when Tg was 27° C., the blocking resistance was poor and it was not used.

Comparative Example 6 Resins R ₂₁ and R ₂₂ were obtained in the same manner as in Example 1 except that the composition of the monomers used, the molar ratio of all diol components to all carboxylic acids, and the final stopping torque were as shown in Table 7. Using these resins, corresponding toners T ₂₁ and T ₂₂ were obtained in the same manner as in Example 1. The toner performance is shown in Table 7-1.

It was found from Table 7-1 that the resin having a gel fraction of 0.8 had an extremely low offset start temperature and was not put to practical use.
It was also found that when the gel fraction exceeds 40, not only the pulverizability during toner production becomes extremely bad, but also the fixability is bad and it is not put to practical use.

─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Koichi Ito 2-1, 4-Ushikawa-dori, Toyohashi-shi, Aichi Sanryo Rayon Co., Ltd. Examiner Yoshio Sugano (56) References JP-A-63-193155 (JP, 193155) A) JP 54-86342 (JP, A)

Claims (2)

[Claims] 1. An all-alcohol component comprising (a) at least one trihydric or higher alcohol, (b) at least one diol, (c) at least one dicarboxylic acid and its lower alkyl ester. Of which (a) is 0.5
Mol% or more and 50 mol% or less, (b) of all alcohol components is 50 mol% or more and 99.5 mol% or less, and the softening temperature is 90 to 170° C. and the glass transition temperature is 30 to 70.
A polyester resin for toner, which is characterized by having an acid value of 0.5 to 10 mgKOH/g and a gel fraction of 1.5 to 40% at ℃. 2. (a) 0.5 mol% of all alcohol components
As described above, 50 mol% or more of at least one trihydric or higher alcohol monomer, (b) 50 mol% of all alcohol components
And at least 1 of 99.5 mol% or less of the diol monomer
(C) a dicarboxylic acid component and at least one dicarboxylic acid component of a lower alkyl ester thereof are subjected to a condensation reaction in the presence of a catalyst, the dicarboxylic acid component (c) satisfies the following formula (1): The polyhydric alcohol (a), (b) and the carboxylic acid component (c) are esterified or transesterified with the diol component (b) under a vacuum of 150 mmHg or less. In the operation of forming a crosslinked state while distilling and removing
A method for producing a polyester resin for toner, which comprises substantially increasing the pressure of the reaction system according to the increase in the viscosity of the polymer to substantially control the crosslinking reaction rate.