JP2002275258A - Modified polyethylene terephthalate and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a modified polyethylene terephthalate capable of being molded in high productivity to provide a hollow container suitable for the application for filling a liquid such as a drink, and further to provide a method for producing the modified polyethylene terephthalate. SOLUTION: This modified polyethylene terephthalate is obtained by introducing (A) a polyethylene terephthalate obtained by subjecting an esterified product of terephthalic acid with ethylene glycol to a polycondensation reaction, and (B) a polyethylene terephthalate containing a metal compound both in molten states into a mixing tool, stirring and mixing both of the polyesters to provide a metal compound-containing polyethylene terephthalate, granulating the metal compound-containing polyethylene terephthalate into chip shapes, optionally heating the chip-shaped and metal compound-containing polyethylene terephthalate to the temperature lower than the melting point of the polyethylene terephthalate forming the metal compound-containing polyethylene terephthalate to increase the intrinsic viscosity of the polyethylene terephthalate.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a modified polyethylene terephthalate and a method for producing the same.
The present invention relates to a modified polyethylene terephthalate which is suitable as a material for containers used for filling liquids such as beverages and which can be molded with high productivity, and a method for producing the same.

[0002]

BACKGROUND OF THE INVENTION In recent years, various plastic materials have been used as containers for filling liquids such as carbonated beverages, juices, mineral water, sake, various types of drinking tea, edible oils, and liquid seasonings. Among them, polyesters such as polyethylene terephthalate (PET) have transparency,
Because of its excellent gas barrier properties, heat resistance and mechanical strength, it is often used as a material for forming hollow molded containers for beverages.

In the production of such a hollow molded container, it is desired to produce at a high speed, and a material which can be produced with high productivity is required. In order to manufacture a hollow molded container at a high speed, it is preferable to use a material having a high heating crystallization rate as long as molding can be performed smoothly. However, if the crystallization rate is too high, the suitable range of molding conditions is narrowed, and the yield during the production of a molded article is reduced. For this reason, it is desirable that the material for producing a hollow molded container as described above has an appropriate crystallization rate in consideration of molding efficiency and molding conditions. From such a demand, a polyester composition in which various additives are added to a polyester such as polyethylene terephthalate to adjust a crystallization rate has been proposed.

For example, Japanese Patent Publication No. 11-824495 proposes a method for obtaining a polyester composition by statically mixing inorganic particles such as titanium oxide, silicon oxide and calcium carbonate. Japanese Patent No. 172082 proposes a method of obtaining a polyester composition by statically mixing inorganic particles or organic particles and then dynamically mixing the particles.

[0005] However, the above polyester compositions are all for polyethylene terephthalate for fiber use, and are not suitable for use in forming materials such as hollow molded containers.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned prior art, and is a modified polyethylene capable of forming a hollow molded container suitable for use in filling a liquid such as a beverage with high productivity. An object of the present invention is to provide terephthalate and a method for producing the same.

[0007]

The modified polyethylene terephthalate according to the present invention comprises (A) a polyethylene terephthalate obtained by subjecting an esterified product of terephthalic acid and ethylene glycol to a polycondensation reaction in a molten state, and (B) a metal compound. Polyethylene terephthalate is introduced into the mixer in a molten state, and then stirred and mixed to obtain a metal compound-containing polyethylene terephthalate, which is then obtained by granulating the metal compound-containing polyethylene terephthalate into chips. I have.

In the present invention, if necessary, the metal compound-containing polyethylene terephthalate granulated in a chip form is heated to a temperature lower than the melting point of polyethylene terephthalate forming the metal compound-containing polyethylene terephthalate, and the intrinsic viscosity of the polyethylene terephthalate is increased. May be raised to obtain a modified polyethylene terephthalate.

The metal compound includes, for example, at least one compound selected from metal oxides, metal acetates and metal carbonates. In the modified polyethylene terephthalate according to the present invention, the metal compound may be used in an amount of 1 ppb to 100 ppb based on the weight of the modified polyethylene terephthalate.
It is preferable to contain it at a ratio of 0 ppm.

The modified polyethylene terephthalate according to the present invention preferably has a crystallization temperature in the range of 132 to 160 ° C. when measured with a differential scanning calorimeter, and has a cyclic trimer content of 0. It is preferably at most 0.5% by weight. The method for producing a modified polyethylene terephthalate according to the present invention comprises: (A) polyethylene terephthalate obtained by subjecting an esterified product of terephthalic acid and ethylene glycol to a polycondensation reaction in a molten state; and (B) polyethylene containing a metal compound. Both terephthalate and terephthalate are introduced into the mixer in a molten state, and then stirred and mixed to obtain a metal compound-containing polyethylene terephthalate, and then the metal compound-containing polyethylene terephthalate is granulated into chips to obtain a modified polyethylene terephthalate. And

In the present invention, if necessary, the metal compound-containing polyethylene terephthalate granulated in the form of a chip is heated to a temperature lower than the melting point of polyethylene terephthalate forming the metal compound-containing polyethylene terephthalate. The modified polyethylene terephthalate may be formed by increasing the intrinsic viscosity.

[0012]

DETAILED DESCRIPTION OF THE INVENTION Hereinafter, the modified polyethylene terephthalate according to the present invention and a method for producing the same will be specifically described. The modified polyethylene terephthalate according to the present invention contains (A) polyethylene terephthalate and a metal compound. First, each of these components will be described.

(A) Polyethylene terephthalate Polyethylene terephthalate (A) used in the present invention
Is formed from a unit derived from terephthalic acid or its ester derivative (eg, lower alkyl ester, phenyl ester, etc.) and a unit derived from ethylene glycol or its ester derivative (eg, monocarboxylic acid ester, ethylene oxide, etc.) .

This polyethylene terephthalate (A)
May contain units derived from dicarboxylic acids other than terephthalic acid and units derived from diols other than ethylene glycol in an amount of 20 mol% or less, if necessary. Specific examples of such dicarboxylic acids other than terephthalic acid include phthalic acid, isophthalic acid, naphthalenedicarboxylic acid, diphenyldicarboxylic acid, diphenoxyethanedicarboxylic acid, and the like. These can be used alone or in combination of two or more.

[0015] Examples of the diols other than ethylene glycol include triethylene glycol, tetraethylene glycol, trimethylene glycol, propylene glycol, butanediol, pentanediol, and the like.
Neopentyl glycol, hexamethylene glycol,
Aliphatic diols such as dodecamethylene glycol and polyethylene glycol; alicyclic diols such as cyclohexanedimethanol; aromatic diols such as bisphenols and hydroquinone. These can be used alone or in combination of two or more.

The polyethylene terephthalate (A) used in the present invention is, if necessary, derived from a polyfunctional compound such as trimesic acid, pyromellitic acid, trimethylolethane, trimethylolpropane, trimethylolmethane, and pentaerythritol. The unit may be contained in a small amount, for example, 2 mol% or less per 100 mol% of dicarboxylic acid units.

The content of the diethylene glycol (DEG) unit in the polyethylene terephthalate (A) is usually 0.5 to 2.0% by weight, preferably 0.8 to 2.0% by weight.
~ 1.6% by weight. The content ratio of DEG unit is 0.5
When it is at least% by weight, the transparency of the bottle body after molding tends to be good. When the content is 2.0% by weight or less, the crystallization rate tends to be improved, and the heat resistance of the bottle tends to be improved.

As a method for adjusting the content of the DEG unit in polyethylene terephthalate to the above range, a method using diethylene glycol as a polymerization raw material,
A method of adjusting the by-product amount of diethylene glycol by-produced from ethylene glycol, which is a main raw material, by appropriately selecting reaction conditions and additives is mentioned. Examples of the additive that suppresses the formation of DEG include basic compounds such as tertiary amines such as triethylamine, quaternary ammonium salts such as tetraethylammonium hydroxide, and alkali metal compounds such as sodium carbonate.

Examples of the compound that promotes the formation of DEG include inorganic acids such as sulfuric acid and organic acids such as benzoic acid. The intrinsic viscosity (IV) (measured in a phenol / 1,1,2,2-tetrachloroethane mixed solvent at 25 ° C.) of the polyethylene terephthalate (A) used in the present invention as described above is usually 0.2 to 1 0.5 dl / g, preferably 0.3 to 1.0 dl / g. The melting point is usually 21
0 to 265 ° C, preferably 220 to 260 ° C, and the glass transition temperature is usually 50 to 120 ° C, preferably 60 to 260 ° C.
100 ° C.

In the above-mentioned polyethylene terephthalate (A), a cyclic trimer, that is, a cyclic trimer of oxyethyleneoxyterephthaloyl units, is usually contained in an amount of 0.5 to 2.
0% by weight. The polyethylene terephthalate (A) used in the present invention is produced from a dicarboxylic acid containing terephthalic acid as a main component and a diol containing ethylene glycol as a main component by a conventionally known method. Hereinafter, an example of the manufacturing method will be described.

First, a dicarboxylic acid containing terephthalic acid as a main component or an ester derivative thereof (for example, a lower alkyl ester or a phenyl ester) and a diol containing ethylene glycol as a main component or an ester derivative thereof (for example, a monocarboxylic acid ester such as ethylene) (E.g., oxides). The esterification reaction is
Preferably, the reaction is carried out by using a device in which two or more reactors are connected in series while removing water generated by the reaction under the condition where the diol is refluxed out of the system by a rectification column.

Subsequently, the esterified product obtained as described above is heated under a reduced pressure to a temperature equal to or higher than the melting point of polyethylene terephthalate in the presence of a catalyst to carry out a polycondensation reaction in a molten state (liquid phase polymerization). Produce polyethylene terephthalate (A). It is desirable to carry out the polycondensation reaction while removing unreacted diol out of the reaction system. Examples of the polycondensation catalyst used at this time include germanium compounds such as germanium dioxide and germanium alkoxide; antimony compounds such as antimony trioxide and antimony acetate; and titanium compounds such as titanium dioxide, titanium hydroxide and titanium alkoxide. . If necessary, alkali metal compounds such as lithium, sodium and potassium; magnesium, calcium,
Alkaline earth metal compounds such as strontium and barium; metal compounds such as aluminum, cobalt, zinc, manganese and nickel may be used. Further, a catalyst other than the above may be used.

These polycondensation catalysts may be added in a polycondensation reactor, or may be added before that, for example, in the course of a raw material monomer slurry or esterification step. Metal compound Examples of the metal compound used in the present invention include metal oxides such as magnesium oxide, aluminum oxide, barium oxide, zinc oxide, titanium oxide, and zirconium oxide;
Metal acetates such as magnesium acetate, zinc acetate, potassium acetate, calcium acetate and barium acetate; metal carbonates such as magnesium carbonate, zinc carbonate, calcium carbonate, barium carbonate and sodium carbonate; metal sulfates such as barium sulfate and calcium sulfate Inorganic salts such as phosphates such as calcium phosphate; metal powders such as aluminum and zinc.

The particle diameter of these metal compounds is preferably 1 μm or less, more preferably 0.5 μm or less. By using particles having a particle size of 1 μm or less, the crystallization temperature can be controlled in a suitable range without impairing the transparency. Since the required amount of these metal compounds is very small, if they are directly melt-mixed, they are not sufficiently dispersed in polyethylene terephthalate. Therefore, polyethylene terephthalate in which the metal compound is contained in advance in a concentration higher than that in the finally obtained modified polyethylene terephthalate is prepared. Polyethylene terephthalate (B) containing such a metal compound (hereinafter referred to as “masterbatch”) can be obtained, for example, by melt-kneading polyethylene terephthalate and a metal compound by a single-screw or twin-screw extruder. Melt kneading can be performed a plurality of times to gradually reduce the concentration of the metal compound in the master batch.

The ratio of the metal compound contained in the masterbatch (B) is not particularly limited, but is usually 10 ppb to 10%, preferably 1 ppb as the weight of the metal atom in the metal compound.
It is in the range of 0 ppm to 1%. Here, as the polyethylene terephthalate used when preparing the master batch, the same polyethylene terephthalate as the above-mentioned polyethylene terephthalate (A) is used. The polyethylene terephthalate used for preparing the masterbatch may be polyethylene terephthalate having the same constitutional unit and the same intrinsic viscosity as the polyethylene terephthalate (A), and polyethylene terephthalate in which at least one of the constitutional unit and the intrinsic viscosity is different. There may be.

Modified Polyethylene Terephthalate The modified polyethylene terephthalate according to the present invention increases the intrinsic viscosity of polyethylene terephthalate (A) by mixing the above-mentioned polyethylene terephthalate (A) and the above-mentioned master batch (B) and then heating. To be obtained. When mixing the polyethylene terephthalate (A) and the master batch (B) containing the metal compound, both the polyethylene terephthalate (A) and the master batch (B) are introduced into the mixer in a molten state. Is done.

As the polyethylene terephthalate (A), it is preferable to use polyethylene terephthalate in a molten state discharged from a polymerization vessel for performing liquid phase polymerization. Further, as the master batch (B), it is preferable to use one that is melted by, for example, an extruder. A known mixer and a known mixing method can be used for mixing the polyethylene terephthalate (A) in the molten state and the master batch (B) in the molten state. Since no power is required,
Equipment costs and operating costs can be reduced. The static mixing device is a device that repeatedly divides the polyethylene terephthalate flow in a molten state in the diameter direction and distributes and distributes the divided polyethylene terephthalate. In addition, the static mixer uses a rectangular plate for 18
This is a static mixer in which members (elements) having a shape twisted by 0 ° are arranged in series in a cylindrical body, and are commercially available, for example, from Noritake Company Limited. It is preferable to use a static mixer having 10 or more elements since the mixing is sufficiently performed.

When mixing the polyethylene terephthalate (A) and the master batch (B) in an amount of 0.1 to 10% by weight based on the polyethylene terephthalate (A), This is preferable because the equipment required for the above can be reduced in size and can be easily mixed. Next, the metal compound-containing polyethylene terephthalate obtained by the above method is formed into chips by a granulator.

Next, if necessary, the obtained chip-like metal compound-containing polyethylene terephthalate may be pre-crystallized by heating in an inert gas stream. Pre-crystallization is
The chip-shaped metal compound-containing polyethylene terephthalate is usually in a dry state at 120 to 200 ° C., preferably 13 to 200 ° C.
It can be performed by heating to a temperature of 0 to 180 ° C. for 1 minute to 5 hours.

Incidentally, the solid-state polycondensation reaction of polyethylene terephthalate does not proceed by this pre-crystallization, and the intrinsic viscosity of the pre-crystallized polyethylene terephthalate is almost equal to the intrinsic viscosity of the polyethylene terephthalate before the pre-crystallization. The same is true, and the difference between the intrinsic viscosity of the pre-crystallized polyester and the intrinsic viscosity of the polyester before pre-crystallization is usually 0.06 dl / g or less.

Subsequently, at a temperature higher than the pre-crystallization temperature and lower than the melting point of polyethylene terephthalate forming the metal compound-containing polyethylene terephthalate, if necessary, the chip-shaped metal compound-containing polyethylene terephthalate is added in a solid state. Polymerization (solid state polymerization) can be performed. Solid-state polymerization is carried out at a temperature of usually 190 to 230 ° C, preferably 195 to 225 ° C, 1 kg / cm ² G
10 Torr (0.1 MPaG to 0.001 MPa),
Preferably normal pressure to 100 Torr (0.01MP
The reaction is performed under an inert gas atmosphere such as nitrogen, argon, or carbon dioxide under the pressure condition of a). As the inert gas used, nitrogen gas is desirable.

Thereafter, post-treatment with hot water or steam is preferable because an increase in the cyclic trimer which causes a reduction in productivity during injection molding can be suppressed. The temperature for performing the post-treatment is usually 40 to 120 ° C, preferably 50 to 11 ° C.
0 ° C. and the time is usually 1 minute to 10 hours, preferably 5 minutes.
Minutes to 5 hours. The thus obtained modified polyethylene terephthalate according to the present invention has an amount of the metal compound of preferably 1 ppb to 10 as the weight of the metal atom.
00 ppm, more preferably in the range of 1 ppb to 100 ppm. In addition, the intrinsic viscosity is usually 0.3 to 2.0 d
l / g, preferably 0.5 to 1.5 dl / g, more preferably 0.6 to 1.2 dl / g. The melting point is usually 210 to 265 ° C, preferably 220 to 260 ° C, and the glass transition temperature is usually 50 to 120 ° C, preferably 60 to 100 ° C.

The content of the cyclic trimer of oxyethyleneoxyterephthaloyl units contained in the modified polyethylene terephthalate according to the present invention is 0.5% by weight or less, preferably 0.4% by weight or less. Desirably. When a modified polyethylene terephthalate having a cyclic trimer content of 0.5% by weight or less is used, a mold or the like is less likely to be contaminated when the resin composition is molded, and the body of the hollow molded body is less likely to whiten. It is preferred. The content of the content of the cyclic trimer in the modified polyethylene terephthalate can be reduced, for example, by increasing the solid-state polymerization temperature and further increasing the polymerization time.

The modified polyethylene terephthalate according to the present invention has an appropriate crystallization temperature so that a hollow molded container such as a bottle can be efficiently produced. Specifically, the crystallization temperature (Tcc) at the time of temperature rise when measured with a differential scanning calorimeter is usually 132 to 160 ° C, preferably 140 to 155 ° C. Further, the modified polyethylene terephthalate according to the present invention may contain other additives as necessary, for example, a coloring agent, an antioxidant, an ultraviolet absorber, an antistatic agent, a flame retardant, and a lubricant.

The modified polyethylene terephthalate obtained by the present invention can uniformly change the crystallization rate without variation between chips. Also, the amount of chips that have received the heat history for the modified polyethylene terephthalate is smaller than when melt kneading after mixing both polyethylene terephthalate and the masterbatch in chip form. Therefore, the crystallization rate can be changed without the adverse effect that the molded article becomes yellowish due to the heat history or the amount of acetaldehyde that adversely affects taste is increased.

In the case of modified polyethylene terephthalate in which a small amount of a metal compound is contained in polyethylene terephthalate, it is presumed that when the polyethylene terephthalate is heated and crystallized by heating during blow molding, the metal compound acts as a nucleus for crystallization. It is considered that the crystallization speed was increased. By the way, in general, when other components are added to polyethylene terephthalate for the purpose of providing an additional function, the transparency at the time of molding is inferior to that of the original polyethylene terephthalate, and the haze value at the time of molding increases.

However, by using the metal compound in a specific amount, in the modified polyethylene terephthalate of the present invention, the crystallization temperature of polyethylene terephthalate is controlled to a range suitable for molding, and the transparency of the molded product is improved. There is an unexpected effect that polyethylene terephthalate can be maintained at the same level as when polyethylene terephthalate is used alone.

[0038]

According to the modified polyethylene terephthalate of the present invention, a molded article having excellent transparency and heat resistance can be produced with high productivity.

[0039]

EXAMPLES Hereinafter, the present invention will be described more specifically based on examples, but the present invention is not limited to these examples. [Measurement Method] 1 g of a sample containing diethylene glycol was weighed and heated at 280 ° C. in 3 ml of monoethanolamine for hydrolysis. After cooling, the solution was neutralized with high-purity terephthalic acid. The mixture was filtered with 5C filter paper.
1 μl of the obtained filtrate was injected into a gas chromatograph (HP5890) manufactured by Hewlett-Packard Company, and the content of diethylene glycol was determined.

Cyclic trimer content A predetermined amount of polyethylene terephthalate was dissolved in o-chlorophenol, reprecipitated with tetrahydrofuran, filtered to remove linear polyethylene terephthalate, and then the obtained filtrate was subjected to liquid chromatography. (LC7A manufactured by Shimadzu Corporation) to determine the amount of cyclic trimer contained in polyethylene terephthalate, and divide this value by the amount of polyethylene terephthalate used in the measurement to obtain the cyclic trimer contained in polyethylene terephthalate. Content (% by weight).

Intrinsic viscosity (IV) Phenol / 1,1,2,2-tetrachloroethane mixed solvent (5
0/50 weight ratio), a sample solution of 0.5 g / dl was prepared, and the intrinsic viscosity (I
V) was calculated. Transparency (haze value) The dried sample was molded into a stepped square plate using an injection molding machine with a cylinder temperature of 275 ° C under the condition of a mold temperature of 10 ° C. (Diffuse reflectance).

Heating crystallization temperature (Tcc) was measured using a differential scanning calorimeter (DSC7, trade name) manufactured by PerkinElmer. Place sample in sample pan 10
mg, and the temperature was raised from room temperature at a rate of 10 ° C./min.
The peak temperature of the exothermic peak generated at that time was defined as Tcc.

[0043]

EXAMPLE 1 Magnesium oxide was added to polyethylene terephthalate (intrinsic viscosity (IV): 0.580 dl / g) at 1670 wt.
m (1000 ppm in terms of magnesium atom) and mixed and melt-kneaded by a twin-screw extruder to prepare a master batch.

Subsequently, the molten polyethylene terephthalate (intrinsic viscosity (I
V): 0.580 dl / g, diethylene glycol content: 1.3% by weight) and a master batch of 1% by weight based on the polyethylene terephthalate amount melted by a twin-screw extruder, both manufactured by Noritake Co., Ltd. The mixture was introduced into a static mixer and mixed to obtain a metal compound-containing polyethylene terephthalate containing 10 wt ppm of magnesium oxide as magnesium atoms. The metal compound-containing polyethylene terephthalate was formed into chips by a granulator.

Next, after crystallizing the above chips in a fixed bed under a nitrogen stream, solid-state polymerization was performed in a fixed bed under a nitrogen stream at 220 ° C. to obtain an intrinsic viscosity (IV) of 0.76 dl / g. did. Subsequently, post-treatment was performed in 95 ° C. hot water for 4 hours. Thereafter, drying was performed under a nitrogen stream at 120 ° C. for 2 hours. This modified polyethylene terephthalate was melt-molded and injection molded.
A stepped square plate as shown in FIG.
cc), cyclic trimer content and haze value were measured. Table 1 shows the physical properties of the molded product.

[0046]

Example 2 In Example 1, the ratio of magnesium oxide in the masterbatch was 830 ppm by weight (500 ppm in terms of magnesium atoms), and the ratio of the masterbatch to polyethylene terephthalate discharged from the liquid phase polymerization vessel was 1% by weight. A modified polyethylene terephthalate was produced in the same manner as in Example 1 except for the above. Using this modified polyethylene terephthalate, the physical properties were measured in the same manner as in Example 1, and the results are shown in Table 1.

[0047]

Example 3 The procedure of Example 1 was repeated, except that magnesium acetate was used in place of magnesium oxide in Example 1 to obtain a modified polyethylene terephthalate containing 10 ppm by weight of magnesium acetate. A modified polyethylene terephthalate was produced. Using this modified polyethylene terephthalate, the physical properties were measured in the same manner as in Example 1, and the results are shown in Table 1.

[0048]

Comparative Example 1 Polyethylene terephthalate was produced in the same manner as in Example 1 except that no masterbatch was mixed with polyethylene terephthalate. Table 1 shows the results obtained by measuring the properties of this polyethylene terephthalate in the same manner as in Example 1.

[0049]

[Table 1]

[Brief description of the drawings]

FIG. 1 is a perspective view showing a stepped square plate, wherein a thickness of a portion A is approximately 6.5 mm, a thickness of a portion B is approximately 5 mm, and a thickness of a portion C is approximately 4 mm. .

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Claims (8)

[Claims] 1. Polyethylene terephthalate obtained by subjecting (A) an esterified product of terephthalic acid and ethylene glycol to a polycondensation reaction in a molten state, and (B) polyethylene terephthalate containing a metal compound are both in a molten state. A modified polyethylene terephthalate obtained by being introduced into a mixer, stirring and mixing to obtain a metal compound-containing polyethylene terephthalate, and then granulating the metal compound-containing polyethylene terephthalate into chips. 2. The polyethylene terephthalate containing the metal compound granulated in a chip form is heated to a temperature lower than the melting point of polyethylene terephthalate forming the metal compound-containing polyethylene terephthalate to increase the intrinsic viscosity of the polyethylene terephthalate. The modified polyethylene terephthalate according to claim 1, which is prepared. 3. The modified polyethylene terephthalate according to claim 1, wherein the metal compound is at least one compound selected from a metal oxide, a metal acetate, and a metal carbonate. 4. The modification according to claim 1, wherein the metal compound is contained in a proportion of 1 ppb to 1000 ppm by weight of the metal atom in the metal compound with respect to the weight of the modified polyethylene terephthalate. Polyethylene terephthalate. 5. The modified polyethylene terephthalate according to claim 1, wherein the crystallization temperature at the time of temperature rise measured by a differential scanning calorimeter is in the range of 132 to 160 ° C. 6. The modified polyethylene terephthalate according to claim 1, wherein the content of the cyclic trimer is 0.5% by weight or less. 7. Polyethylene terephthalate obtained by subjecting (A) an esterified product of terephthalic acid and ethylene glycol to a polycondensation reaction in a molten state, and (B) polyethylene terephthalate containing a metal compound, both in a molten state. A method for producing modified polyethylene terephthalate, characterized in that the mixture is stirred and mixed after being introduced into a mixer to obtain polyethylene terephthalate containing a metal compound, and then the polyethylene terephthalate containing the metal compound is granulated into chips to obtain modified polyethylene terephthalate. . 8. The method according to claim 1, wherein the metal compound-containing polyethylene terephthalate granulated in a chip shape is heated to a temperature lower than the melting point of polyethylene terephthalate forming the metal compound-containing polyethylene terephthalate to increase the intrinsic viscosity of the polyethylene terephthalate. The method for producing a modified polyethylene terephthalate according to claim 7, wherein the modified polyethylene terephthalate is obtained.