JPH09255856A - Crystallization accelerator and resin composition containing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a polyester crystallization accelerator which is composed of a polyester having a specific molecular weight, an acid value, a hydroxyl value, further a specific volatile loss and a specific form and gives polyester resins good moldability, excellent heat resistance and uniform appearance. SOLUTION: This crystallization accelerator is prepared from (A) an acid component and (B) an alcohol component, and is a polyester with a number- average molecular weight of 500-10,000 and has an acid value of <=0.7, a hydroxyl value of <=5.0, a volatile loss of <=2.5wt.% at 300 deg.C and is a liquid of low viscosity of <=3,000cps at 25 deg.C, or a solid melting at a high temperature of >=100 deg.C. The component A and the component B are preferably composed of (i) a 2-25C dihydric alcohol, (ii) a 4-14C aliphatic dibasic acid, (iii) a 4-18C monohydric alcohol and/or a 2-22C a monobasic acid. The objective accelerator is preferably formulated to a polyester resin in an amount of 0.1-30 pts.wt. per 100 pts.wt. of the polyester resin.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a crystallization accelerator, and more specifically, molding of a polyester resin mainly composed of polyester having a specific molecular weight, an acid value, a hydroxyl value, a specific volatilization loss and a specific form. The present invention relates to a crystallization accelerator which has good moldability in use and does not deteriorate in physical properties due to a decrease in molecular weight of the resin itself, and which has excellent heat resistance and a uniform appearance, and a resin composition containing the same.

[0002]

2. Description of the Related Art Polyester resins, especially polyethylene terephthalate, are excellent in mechanical properties, heat resistance, chemical resistance and electrical properties, and are usually stretched as fibers or films for use in many products. However, when it is intended to be used for plastics as an injection molded product, a satisfactory molded product cannot be obtained under normal injection conditions because of the low crystallization rate of polyethylene terephthalate.
Conventionally, various crystallization accelerators have been proposed to compensate for such drawbacks. For example, alkali metal salts of higher fatty acids such as sodium stearate (JP-A-54-1).
58452), neopentyl glycol dibenzoate (Japanese Patent Publication No. 55-47058), adipic acid dibenzyl ester (Japanese Patent Laid-Open No. 63-258948) and adipic acid dioctyl ester (Japanese Patent Laid-Open No. 53-6).
5354) and the like. However, the alkali metal salt of higher fatty acid is likely to cause molecular cleavage of the polyester resin under high temperature heat molding conditions. In addition, low molecular weight diesters also easily volatilize during molding, and the generated gas has a drawback that the mechanical properties of the molded product are significantly impaired.
In order to prevent gas generation during high temperature heat molding, a molecular weight of 400
Method using 0 or more polyester (Japanese Patent Laid-Open No. 58-2
No. 10957) has been proposed, and although the effect of preventing volatility is recognized, it has poor fluidity and is difficult to handle because of its high viscosity at room temperature.

Polyester resins generally have a high melt molding temperature of 250 ° C. to 300 ° C., and when they are kneaded into pellets by kneading additives such as plasticizers, colorants and fillers in an extruder, they undergo hydrolysis or transesterification reaction. It easily causes a decrease in molecular weight and discoloration. In order to prevent the deterioration of the polyester resin due to the additives in the extruder, a method of adding the liquid in the middle of the cylinder of the extruder has been adopted. However, high-viscosity polyester having a high molecular weight has poor fluidity, and production efficiency is extremely poor when added in liquid form.

[0004]

The object of the present invention is to improve the above-mentioned drawbacks of the polyester resin and to exhibit the excellent physical properties of the polyester resin, which are easily crystallizable, heat resistance, releasability, tensile properties and appearance. Is to provide a crystallization accelerator that gives

[0005]

DISCLOSURE OF THE INVENTION The inventors of the present invention have previously described a plasticizer for polyester resin (Japanese Patent Laid-Open No. 7-292223),
A melt viscosity reducing agent (JP-A-8-34904) has been submitted. In the study, as a means for solving the above-mentioned drawbacks of the conventional method, a specific molecular weight of polyester resin,
It has been found that the above objects can be achieved by adding a polyester compound having an acid value, a hydroxyl value, a specific volatilization loss, and a specific form as a crystallization accelerator, and the present invention has been completed.

That is, the present invention provides (1) a number average molecular weight of 500 to 10,000 obtained from an acid component and an alcohol component.
Is a polyester compound having an acid value of 0.7 or less,
Hydroxyl value is 5.0 or less, volatilization loss (300 ° C) is 2.5
A crystallization accelerator characterized by being a liquid having a viscosity of 25% or less and having a low viscosity (25 ° C.) or a solid having a high melting point;
(2) Preferably, an ester compound obtained from an acid component and an alcohol component is (a) a dihydric alcohol having 2 to 25 carbon atoms, (b) an aliphatic dibasic acid having 4 to 14 carbon atoms,
(C) A monohydric alcohol having 4 to 18 carbon atoms or a monobasic acid having 2 to 22 carbon atoms, and (3) an ester compound obtained from an acid component and an alcohol component is preferably (a) carbon. 2 to 25 dihydric alcohols,
(B) An aromatic polybasic acid having 2 or more carboxylic acid groups having 8 to 18 carbon atoms, (c) a monohydric alcohol having 4 to 18 carbon atoms, or a monobasic acid having 2 to 22 carbon atoms. ,
(4) The viscosity is preferably 500 to 3000 cp at 25 ° C.
A polyester resin composition characterized by being a liquid of s, (5) a solid having a melting point of 100 to 250 ° C., (6) for a polyester resin, and (7) further containing a crystallization accelerator. (8) The present invention provides a polyester resin composition whose use is injection molding.

The present invention will be described in detail.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention comprises a polyester compound having a number average molecular weight of 500 to 10000, preferably 700 to 8000, obtained from an acid component and an alcohol component, and has an acid value of 0.7 or less, preferably 0. 5 or less, a hydroxyl value of 5.0 or less, preferably 3.5 or less, a volatilization loss (300 ° C.) of 2.5 wt% or less, and 3000 cps
It is in the form of a low-viscosity liquid (25 ° C.) or lower or a solid with a high melting point of 100 ° C. or higher. Outside this range, the crystallization rate cannot be increased without lowering the molecular weight of the resin. This is particularly noticeable for polyester resins.

The molecular weight of the crystallization accelerator composed of this polyester compound is 500 to 10,000 in terms of number average molecular weight. It is particularly preferably 700 to 8000. 500
If it is smaller, the volatilization loss is severe, and if it exceeds 10,000, the desired effect cannot be obtained without lowering the molecular weight of the polyester resin due to poor dispersibility in the polyester resin.

The polyester compound as the crystallization accelerator has a viscosity (25 ° C.) in the case of a low-viscosity liquid, which is 300.
0 or less, particularly preferably 500 to 3000 cps. 3
When it exceeds 000 cps, it is difficult to handle and it is difficult to sufficiently mix it with the polyester resin in a short time. 500
If it is less than cps, the molecular weight is substantially low and the volatilization loss is severely problematic. Therefore, if it deviates from this range, crystallization cannot be promoted without lowering the molecular weight of the polyester resin. Further, the melting point in the case of a solid having a high melting point is 100 ° C. or higher, particularly 100 to 2
50 ° C. is preferred. If the temperature exceeds 250 ° C, the crystallization accelerator will not be sufficiently melt-mixed during mixing with the polyester resin. If the temperature is lower than 100 ° C., the melt viscosity reducing agent melts and bridges on the hopper of the extruder, resulting in poor workability.

The alcohol component used for constituting the crystallization accelerator of the present invention preferably has 2 carbon atoms.
To 25 dihydric alcohols (a), more preferably dihydric alcohols having 2 to 23 carbon atoms, such as ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,2-butanediol. , 1,3-
Butanediol, 2-methyl 1,3-propanediol, 1,4-butanediol, neopentyl glycol, 1,5-pentanediol, 3-methyl 1,5-pentanediol, 1,6-hexanediol, 2, Two
4-trimethyl 1,3-pentanediol, 2-ethyl 1,3-hexanediol, 2-methyl 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, 1,12-octadecanediol Such as aliphatic glycol and diethylene glycol, polyalkylene glycol such as dipropylene glycol and hydrogenated bisphenol A, ethylene oxide adduct of bisphenol A or bisphenol S, 1,4-cyclohexanedimethanol, 1,4-cyclohexanediol, 1, Examples thereof include cyclic or aromatic ring-containing dihydric alcohols such as 2-cyclohexanediol and bishydroxyethoxybenzene. These alcohols are used alone or as a mixture of two or more.

The acid component used in the crystallization accelerator of the present invention is preferably an aromatic dibasic acid having 4 to 14 carbon atoms and / or an aromatic compound having 2 or more carboxylic acid groups having 8 to 18 carbon atoms. It is a group polybasic acid (b).

Examples of the aliphatic dibasic acid having 4 to 14 carbon atoms include adipic acid, sebacic acid, azelaic acid,
Dodecane dicarboxylic acid and the like can be mentioned.

Examples of aromatic polybasic acids having 2 or more carboxylic acid groups having 8 to 18 carbon atoms include phthalic acid, isophthalic acid, terephthalic acid, 2,6-naphthalenedicarboxylic acid, α, β- Examples thereof include bis (4-carboxyphenoxy) ethane, 4,4′-biphenyldicarboxylic acid, trimellitic acid, trimesic acid, pyromellitic acid, and biphenyltetracarboxylic acid. Further, alicyclic polybasic acids such as 1,4-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, and hexahydrophthalic anhydride can also be used. Of course, these polybasic acids may be used alone or as a mixture of two or more.

The alcohol component used for constituting the crystallization accelerator of the present invention preferably has 4 carbon atoms.
~ 18 monohydric alcohol or, and C2-22
It is a monobasic acid (c).

Examples of the monohydric alcohol having 4 to 18 carbon atoms include butanol, hexanol, isohexanol, heptanol, octanol, isooctanol, 2-ethylhexanol, nonanol, isononanol, 2-methyloctanol, decanol, isodecanol and undecanol. , Aliphatic alcohols such as dodecanol, tridecanol, tetradecanol, hexadecanol, octadecanol, etc., alicyclic alcohols such as cyclohexanol, benzyl alcohol, 2-phenylethanol, 1-phenylethanol, 2-phenoxyethanol, 3- Phenyl-1-propanol, 2
-Aromatic alcohols such as hydroxyethyl benzyl ether may be mentioned, and they may be used alone or as a mixture of two or more.

As the monobasic acid having 2 to 22 carbon atoms, palm oil, palm oil, palm kernel oil, cacao butter, wax, olive oil, kapok oil, castor oil, dehydrated castor oil, rapeseed oil, rice bran 6 to 2 carbon atoms derived from animal and vegetable oils and fats such as oil, cottonseed oil, soybean oil, safflower oil, linseed oil, tung oil, beef tallow, lard and cod oil, or hydrogenated oil thereof.
2 aliphatic monobasic acids or synthetic monobasic acids having 2 to 18 carbon atoms such as acetic acid, butyric acid, isobutyric acid, heptanoic acid, isooctanoic acid, 2-ethylhexanoic acid, nonanoic acid and isostearic acid. It can be used as a mixture of two or more species.

The respective raw materials used as the components constituting the crystallization accelerator and the amount thereof used are selected according to the performance of the finally obtained product.

The crystallization accelerator can be produced by various known esterification methods. For example, it is possible to obtain the target ester by reacting the above-mentioned crystallization accelerator constituents all at once or by reacting two or three species, and then reacting the remaining ingredients.

A catalyst is used in the esterification reaction of the present invention. For example, an acid catalyst such as paratoluenesulfonic acid and phosphoric acid, a metal such as tetraisopropyl titanate, tetrabutyl titanate, dibutyltin oxide, dioctyltin oxide and zinc chloride. It is usually desirable to react in the presence of these catalysts as they are promoted by the catalysts.
The reaction is usually 100 to 250 ° C., preferably 1
It is obtained by heating to 30 to 250 ° C.

The polyester resin in the present invention is preferably an aromatic polyester resin having an aromatic ring as a chain unit, which is obtained by a condensation reaction containing an aromatic dicarboxylic acid or its ester derivative and a diol or its ester derivative as main components. The obtained polymer or copolymer.

Examples of the polyester resin in the present invention include polyethylene terephthalate, polybutylene terephthalate, polyhexamethylene terephthalate, polycyclohexyne dimethylene terephthalate, polyethylene-2,6-naphthalate and polybutylene-2,6-naphthalate. .

The aromatic dicarboxylic acid referred to here is
For example, terephthalic acid, isophthalic acid, phthalic acid, 2,
Examples thereof include 6-naphthalenedicarboxylic acid, α, β-bis (4-carboxyphenoxy) ethane, 4,4′-biphenyldicarboxylic acid, 5-sodium sulfoisophthalic acid and ester derivatives thereof. If the acid component is in the range of 10 mol% or less, aliphatic dicarboxylic acids such as adipic acid, sebacic acid, azelaic acid and dodecanedioic acid, 1,3-cyclohexanedicarboxylic acid,
It may be substituted with an alicyclic dicarboxylic acid such as 1,4-cyclohexanedicarboxylic acid and a dicarboxylic acid other than the aromatic dicarboxylic acid such as an ester derivative thereof.

The diol is preferably an aliphatic diol having 2 to 10 carbon atoms, such as ethylene glycol, propylene glycol, 1,4-butanediol, 3-methyl-1,3-propanediol, neopentyl. Glycol, 1,5-pentanediol, 1,6-
Hexane diol, decamethylene glycol, cyclohexane diol, cyclohexane dimethanol and the like can be mentioned, and a small amount of a long chain glycol having a number average molecular weight of 400 to 6000, that is, polyethylene glycol, poly-1,3-propylene glycol, polytetramethylene. It may be a copolymer of glycol and the like.

The crystallization accelerator of the present invention may be supplied to the extruder after being mixed with the polyester resin in advance using a Henschel mixer or the like, or may be added to the molten polyester resin in the extruder using a liquid feeder. May be supplied. Further, the polyester resin can be supplied by impregnating it with an oil-absorbing porous or finely divided inorganic filler such as zeolite, silica, or hydrotalcite.

When the crystallization accelerator of the present invention is blended with the polyester resin, the amount used is usually polyester resin 10
0.1 to 30 parts by weight, preferably 0.
5 to 10 parts by weight are suitable. If it is out of this range, the decrease in the molecular weight of the polyester resin can be prevented and the crystallization cannot be promoted.

The resin composition of the present invention includes fibrous reinforcing materials such as glass fiber and carbon fiber, talc, mica, clay,
Barium sulfate, ferrite, calcium carbonate, calcium silicate, zinc oxide, glass flakes, glass balloons,
An inorganic filler such as silica may be blended as necessary. In addition to these, release agents, lubricants, coloring agents,
You may mix a stabilizer etc.

Thus, the polyester compound having a specific molecular weight, acid value, hydroxyl value, volatilization weight loss and specific form provides a crystallization accelerator capable of increasing the crystallization rate without lowering the molecular weight. can do. In particular, since it is possible to suppress the decrease in the molecular weight at the time of high temperature melting due to hydrolysis or transesterification of the polyester resin, it is possible to provide a polyester resin composition having heat resistance and a uniform appearance for use in injection molding and the like. .

[0029]

EXAMPLES Next, the present invention will be described in detail with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples. In the following, all parts and% are based on weight unless otherwise specified.

(Example 1) <Synthesis of crystallization accelerator> Trimellitic anhydride 192 was placed in a 1-liter 4-necked flask.
g, 1,6-hexanediol 59 g, and 2-phenoxyethanol 317.4 g were charged, and the mixture was placed in a nitrogen gas stream 14
After the temperature was raised to 0 ° C., 0.05 g of octyl tin oxide was added, and then the temperature was raised to 230 ° C. in 6 hours to distill water. Further, excess alcohol was removed under reduced pressure of 5 mmHg to obtain 510 g of the ester compound of the present invention.

Example 2 <Synthesis of Crystallization Accelerator> In the same manner as in Example 1 except that 52 g of neopentyl glycol was used instead of 1,6-hexanediol in Example 1, 505 g of the ester compound of the present invention was used. Got

(Example 3) <Synthesis of crystallization accelerator> Example 3 except that 219 g of pyromellitic anhydride was used instead of trimellitic anhydride and 468 g of 2-ethylhexanol was used instead of 2-phenoxyethanol in Example 1. 660 g of the ester compound of the present invention was obtained in exactly the same manner as in 1.

(Example 4) <Synthesis of crystallization accelerator> Adipic acid 314 g, propylene glycol 152 g,
The ester compound 59 of the present invention was prepared in the same manner as in Example 1, except that 81 g of 1,3-butanediol and 181 g of lauric acid were used.
5 g were obtained.

(Example 5) <Synthesis of crystallization accelerator> Dimethyl terephthalate 1 was placed in a 1-liter 4-necked flask.
94 g, 1,4-butanediol 81 g, and 2-phenoxyethanol 97 g were charged, and the temperature was 130 ° C. in a nitrogen gas stream.
After the temperature was raised to 0.05, octyltin oxide (0.05 g) was added, and then the temperature was raised to 230 ° C. in 4 hours to distill off methanol. After holding for another 4 hours, excess alcohol is 5 mmH
330 g of the ester compound of the present invention removed under reduced pressure
I got

(Example 6) <Synthesis of crystallization accelerator> 1,6-butanediol instead of 1,4-butanediol of Example 5 was used.
355 g of the ester compound of the present invention was obtained in exactly the same manner as in Example 5 except that 106 g of hexanediol was used.

(Example 7) <Synthesis of crystallization accelerator> This example was prepared in the same manner as in Example 5 except that 135.8 g of dimethyl terephthalate and 58.2 g of dimethyl isophthalate were used instead of the dimethyl terephthalate of Example 5. 335 g of the invention ester compound was obtained.

(Example 8) <Synthesis of crystallization accelerator> Except for the case of Example 5 except that 135.8 g of dimethyl terephthalate and 51.6 g of 1,4-cyclohexanedicarboxylic acid were used instead of dimethyl terephthalate. Similarly, 325 g of the ester compound of the present invention was obtained by a dehydration reaction with methanol.

Comparative Example 1 Commercially available DOA (dioctyl adipate) was used as a comparative compound.

Comparative Example 2 Commercially available neopentyl glycol dibenzoate was used as a comparative compound.

Comparative Example 3 Adipic acid 146 g, 1,4
-Butanediol (85.5 g) and 2-ethylhexanol (44.2 g) were charged, the temperature was raised to 130 ° C in a nitrogen gas stream, 0.05 g of octyltin oxide was added, and then the temperature was raised to 230 ° C in 6 hours to remove water. Distilled. Further, a polyester compound obtained by removing excess alcohol under reduced pressure of 20 mmHg was used as a comparative compound.

Comparative Example 4 303 g of sebacic acid and 136.8 g of propylene glycol were charged, heated to 140 ° C. in a nitrogen gas stream, added with 0.05 g of octyltin oxide, and heated to 220 ° C. in 4 hours. To distill the water. After further holding for 4 hours, it was deglycolized under reduced pressure of 5 mmHg, and a polyester compound having a molecular weight of about 8000 was used as a comparative compound.

Tables 1 and 2 show the measurement results of acid value, hydroxyl value, volatilization loss rate and viscosity of the crystallization accelerator of the present invention compound and the comparative ester compound of the above Examples.

[0043]

[Table 1] * 1: 3500 cps with 75% nonvolatile xylene solution

[Measurement method and conditions] Volatilization loss: thermogravimetric analysis (TGA), heating rate 10 ° C.
/ Min (in air) Measures the weight loss at 300 ° C. Viscosity: 25 ° C, digital rotational viscometer Melting point: differential thermal analysis (DSC), heating speed 5 ° C / mi
n (in nitrogen)

<Production of Polyethylene Terephthalate Resin Containing Crystallization Accelerator> (Examples 1 to 13, Comparative Examples 1 to 8) A vent type extruder having a diameter of 40 mm was used at a barrel temperature of 280 ° C. (however, feeder part 2).
20 ° C.) and the die temperature was set to 230 ° C. Powdered polyethylene terephthalate (intrinsic viscosity, 30 ° C. phenol / ethane tetrachloride, 0.7 in 1: 1 weight ratio) dried at 150 ° C. for 15 hours was added to 100 parts by weight of chopped strand glass fiber 3 45 mm in length. Parts by weight and various samples described in Table 1 were blended in the proportions shown in Tables 2 and 3, and 150
The mixture was uniformly mixed in a Henschel mixer set at 0 ° C.
The obtained blend was supplied to an extruder, melt-kneaded, and passed through a pelletizer to obtain pellets.

<Production of Polyethylene Terephthalate Resin Containing Crystallization Accelerator> (Example 14, Comparative Example 9) A vent type extruder having a diameter of 40 mm was used at a barrel temperature of 280 ° C. (however, feeder section 220).
), And the die temperature was set to 230 ° C. 15 at 150 ° C
100 parts by weight of powdery polyethylene terephthalate (intrinsic viscosity, 30 ° C. phenol / ethane tetrachloride, 0.7 in a weight ratio of 1) dried for 120 hours, polybutylene terephthalate (molecular weight 4 hours dried at 120 ° C. 250
(00) 2.5 parts by weight, 46 parts by weight of chopped strand glass fiber having a length of 3 mm, and various samples shown in Table 1 were mixed in the proportions shown in Table 3 and uniformly mixed in a Henschel mixer set at 150 ° C. The obtained blend was supplied to an extruder, melt-kneaded, and passed through a pelletizer to obtain pellets.

The pellets of the reinforced polyethylene terephthalate resin blended with the crystallization accelerator obtained above were used to prepare test pieces with an injection molding machine (mold temperature: 80 ° C.), and various physical properties were evaluated. The results are shown in Tables 2 and 3.

The measuring methods for evaluation of physical properties are as follows. Thermal characteristics: Using a sample obtained by performing a melting and quenching operation in advance with a differential calorimeter, a heating rate 1 in a nitrogen stream
The crystallization temperature T _ch at the time of temperature increase and the crystallization temperature T _cc at the time of temperature decrease were measured under the conditions of 0 ° C./min and the temperature decrease rate of 10 ° C./min.
The higher the value of _Tcc - _Tch, the higher the crystallization rate.

Tensile properties: Measured according to ASTM D638.

Heat resistance: Measured under a load of 1.82 MPa according to ASTM D648.

Releasability: Judgment was made by separating the molded product from the mold.

Appearance: The surface gloss and smoothness of the molded product were visually evaluated.

[Evaluation of releasability and appearance] Good: Good
△: Slightly bad ×: Bad

[0054]

[Table 2]

[0055]

[Table 3]

[0056]

INDUSTRIAL APPLICABILITY The present invention provides a specific molecular weight, an acid value, a hydroxyl value, and a specific volatilization loss, and easily crystallizable, heat resistance, releasability, tensile properties and appearance which are formed of a polyester having a specific form. Provided by the crystallization accelerator is a resin composition having good moldability without causing physical property deterioration due to a decrease in molecular weight of the resin itself, and also having excellent heat resistance and uniform appearance, mainly in molding applications of polyester resin. be able to.

Claims (8)

[Claims] 1. A polyester compound having a number average molecular weight of 500 to 10,000 obtained from an acid component and an alcohol component, and having an acid value of 0.7 or less, a hydroxyl value of 5.0 or less, and a volatilization loss (300 ° C.). A crystallization accelerator characterized by being a liquid having a low viscosity of 2.5% by weight or less and 3000 cps (25 ° C.) or less or a solid having a high melting point of 100 ° C. or more. 2. The acid component and the alcohol component are (a) a dihydric alcohol having 2 to 25 carbon atoms, (b) an aliphatic dibasic acid having 4 to 14 carbon atoms, and (c) a monohydric alcohol having 4 to 18 carbon atoms. Alternatively, and consisting of a monobasic acid having 2 to 22 carbon atoms, the crystallization accelerator according to claim 1. 3. The acid component and the alcohol component are (a) a dihydric alcohol having 2 to 25 carbon atoms (b) an aromatic polybasic acid having 2 or more carboxylic acid groups having 8 to 18 carbon atoms (c) The crystallization accelerator according to claim 1, comprising a monohydric alcohol having 4 to 18 carbon atoms or a monobasic acid having 2 to 22 carbon atoms. 4. A viscosity (25 ° C.) of 500 to 3000 c
The crystallization accelerator according to any one of claims 1 to 3, which is a liquid of ps. 5. The crystallization accelerator according to claim 1, which is a solid having a melting point of 100 to 250 ° C. 6. The crystallization accelerator according to claim 1, which is used for a polyester resin. 7. A polyester resin composition comprising the crystallization accelerator according to claim 1. 8. The polyester resin composition according to claim 7, which is used for injection molding.