JP4882230B2 - Polyester resin and preform manufacturing method - Google Patents

Description

  The present invention relates to a polyester resin that can be molded at low temperature, and more particularly to a polyester resin that can provide a container having excellent flavor retention and transparency by low temperature molding and a method for producing a preform using the polyester resin.

  Biaxially stretched blow molded containers made of polyester resin, especially polyethylene terephthalate, are liquid products such as liquid detergents, shampoos, cosmetics, soy sauce, sauces, food, beer, cola, etc. due to their excellent transparency and moderate gas barrier properties. It is widely used as a container for carbonated beverages such as cider and other beverages such as fruit juice and mineral water.

  Generally, the melting point (Tm) of polyethylene terephthalate used for forming a container is in the range of 250 to 265 ° C. In order to form a biaxially stretched blow molded container having excellent transparency using such polyethylene terephthalate, the melting point (Tm It is necessary to mold the preform at a temperature 25 to 40 ° C. higher than However, when exposed to such high temperatures, polyethylene terephthalate is thermally decomposed and acetaldehyde, oligomers and the like are by-produced. Acetaldehyde remaining in such a polyethylene terephthalate container causes a decrease in the flavor retention of the bottle, and particularly when filling water such as mineral water as the contents, even a small amount of acetaldehyde affects the flavor retention. Therefore, it becomes a problem.

  As a conventional method for reducing the residual acetaldehyde concentration in a polyester container, for example, a method of melting and kneading a polyester resin while being degassed (for example, Patent Document 1) or a method of using the polyester resin after hydrothermal treatment is proposed. (For example, Patent Document 2).

JP 2000-117819 A JP 2001-31750 A

The method described in Patent Document 1 reduces the acetaldehyde concentration in a resin when molding using a polyester resin, but the amount of reduction is limited. Moreover, in the method described in the said patent document 2, it is necessary to post-process to a polyester resin, and it is inferior to productivity.
Moreover, as a method of reducing the acetaldehyde concentration of the polyester container, it is conceivable to perform molding at a low temperature, but in general polyethylene terephthalate currently used for molding a container, it is difficult to mold at a low temperature, Even if it was able to be molded, it had the problem that it was whitened and the transparency was significantly reduced.

Accordingly, an object of the present invention is to provide a polyester resin that can be molded by low-temperature molding and can provide a container having excellent transparency and flavor retention.
Another object of the present invention is to provide a method for producing a preform excellent in transparency and flavor retention, such as by injection molding at a low temperature.

According to the present invention, the total amount of metals contained in the resin is 240 ppm or less, the intrinsic viscosity is 0.56 dL / g or more and less than 0.70 dL / g, and the weight average molecular weight (Mw) is 30000-47000 g / mol. And a polyethylene terephthalate resin having a molecular weight distribution (Mz / Mn) of 3.4 or less within a range of Tm ≦ T ≦ Tm + 20 ° C. (where Tm is the melting point of the polyethylene terephthalate resin and T is the temperature of the molten polyethylene terephthalate resin). A preform characterized by being injection-molded at a resin temperature is provided.
In the preform of the present invention,
1. That the poly ethylene terephthalate is synthesized by melt polymerization,
2. The polyethylene terephthalate has a melt viscosity of Tm ≦ T ≦ Tm + 20 ° C. (Tm is the melting point of the polyethylene terephthalate resin, T is the temperature of the molten polyethylene terephthalate) and a shear rate of 2000 sec ^{−1 is} in the range of 100 to 240 Ns / m ² ;
Is preferred.

According to the polyester resin of the present invention, injection molding at a low temperature is possible, the acetaldehyde concentration in the molded product can be reduced, and a molded product excellent in flavor retention can be provided.
Further, according to the polyester resin of the present invention, it is possible to obtain a preform excellent in transparency and flavor retention without whitening even when the preform is molded by low temperature molding, particularly injection molding.
Furthermore, according to the polyester resin of the present invention, it is possible to omit the solidification of the polyester to the chip by the melting method, the solid-phase polymerization, the remelting for molding into the preform, etc., thereby simplifying the process and saving the energy cost. There are advantages such as.

  The polyester resin of the present invention has a total metal content of 240 ppm or less, an intrinsic viscosity of 0.55 dL / g or more and less than 0.70 dL / g, and a weight average molecular weight (Mw) of 47000 g / mol or less. It is an important feature that the molecular weight distribution (Mz / Mn) is 3.4 or less. In addition, the intrinsic viscosity in this invention is measured at 30 degreeC using the phenol / tetrachloroethane mixed solvent of 1: 1 weight ratio.

As described above, when molding a molded product such as a preform from a polyester resin, the temperature is generally 20 ° C. or more higher than the melting point (Tm) of the polyester resin, particularly 35 ° C. or more in the case of injection molding. In this case, the resin must be melt-kneaded. At this time, the resin is thermally decomposed, and mold contamination due to a by-product of acetaldehyde or oligomer causes a problem that the flavor retention and transparency of the container are lowered.
In the present invention, from this point of view, the polyester resin that can be molded at a low temperature in the temperature range of Tm ≦ T ≦ Tm + 20 ° C., based on the melting point (Tm) of the polyester resin and the temperature (T) of the molten polyester resin. According to the polyester resin of the present invention, since the amount of acetaldehyde remaining in the molded container is remarkably reduced, the flavor retention is excellent, and the container unique to low temperature molding Whitening is also prevented.

In the polyester resin of the present invention, when the total amount of metals contained in the resin is 240 ppm or less, particularly in the range of 110 to 230 ppm, the whitening of the molded product, which is a serious problem in low temperature molding, is effectively suppressed. It becomes possible to do.
The metal contained in the resin is a metal contained mainly in various additives such as metal catalyst residues and stabilizers blended in the production of the polyester resin. Such a metal is used when the polyester resin is melted. In addition to being involved in the promotion of thermal decomposition of the polyester resin, it acts as a crystal nucleating agent in the polyester resin, so that it particularly affects the crystallization speed of the polyester resin and causes whitening of the molded product.

This is also clear from the results of Examples described later. That is, the polyester resin of the present invention in which the total amount of metals contained in the resin is 240 ppm or less has excellent flavor retention and transparency (Examples 1 to 5), whereas in the resin When the total amount of the metals is larger than the above value, the transparency is inferior even when the weight average molecular weight (Mw) and molecular weight distribution (Mz / Mn) described below are within the scope of the present invention. (Comparative Example 2).
In addition, the metal in this invention refers to transition metal elements, such as Fe, Ti, and Mn, typical metal elements, such as Ca, Mg, and Al, and metalloid elements, such as Ge.

In the polyester resin of the present invention, the intrinsic viscosity is 0.55 dL / g or more and less than 0.70 dL / g, particularly 0.56 to 0.68 dL / g, and its weight average molecular weight (Mw) is 47000, particularly 30000. And a molecular weight distribution (Mz / Mn) of 3.4 or less, particularly 3.1 to 3.4, the melt viscosity necessary for molding at a low temperature (Tm ≦ T ≦ Tm + 20 ° C.) can be obtained. It becomes possible to present.
That is, as is clear from the examples described later, in the polyester resin of the present invention in which the intrinsic viscosity, the weight average molecular weight (Mw), and the molecular weight distribution (Mz / Mn) are in the above ranges, in the temperature range of Tm ≦ T ≦ Tm + 20 ° C. The melt viscosity under a shear rate of 2000 sec ⁻¹ is in the range of 100 to 240 Ns / m ² and can be molded with good moldability at a low temperature (Tm ≦ T ≦ Tm + 20 ° C.) (Examples 1 to 5), whereas the intrinsic viscosity , Any one of the weight average molecular weight (Mw) and the molecular weight distribution (Mz / Mn) is out of the range of the present invention, so that the melt viscosity becomes large, the flowability of the resin is poor, and molding is difficult. (Comparative Example 3), whitening along the flow of the resin (Comparative Examples 1 and 2), or a case where the resin is not sufficiently injected into the injection mold. It is apparent that moldability and sink marks (Comparative Examples 3 and 5), wrinkles and bubbles (Comparative Example 4) are observed, and the moldability is poor.

  The molecular weight distribution (Mz / Mn) defined in the present invention directly represents the influence of the distribution of the high molecular weight component in the polyester resin, and the molecular weight distribution (Mz / Mn) is 3.4 or less, particularly 3 When the polyester resin of the present invention is in the range of 1 to 3.4, the polyester resin of the present invention contains more high molecular weight components than the general polyester resin having a melt viscosity in the above range, which is greater than the degree of entanglement. In addition, since it contains many low molecular weight components smaller than the degree of entanglement polymerization, the melt viscosity involved in the moldability is kept low, the molding at low temperature is easy, and the whitening of the molded product can be suppressed. It is.

(Synthesis of polyester resin)
The polyester resin of the present invention has a total metal content of 240 ppm or less, an intrinsic viscosity of 0.55 dL / g or more and less than 0.70 dL / g, and a weight average molecular weight (Mw) of 47000 g / mol or less. As long as the molecular weight distribution (Mz / Mn) is 3.4 or less, it can be prepared by a conventionally known polyester resin production method.
The polyester resin was produced by polycondensing a raw material mainly composed of terephthalic acid or an ester-forming derivative thereof and ethylene glycol or an ester-forming derivative thereof through an esterification reaction or an ester exchange reaction. It is preferable.

Hereinafter, the synthesis of polyethylene terephthalate will be described as an example.
The synthesis of polyethylene terephthalate is generally performed by a method of directly reacting high-purity terephthalic acid (TPA) and ethylene glycol (EG) to synthesize polyethylene terephthalate (PET), and is usually divided into two steps. A) reacting TPA and EG to synthesize bis-β-hydroxyethyl terephthalate (BHET) or a low polycondensate thereof; (B) removing ethylene glycol from BHET or a low polycondensate thereof; It consists of a process of polycondensation.

The synthesis of BHET or a low polycondensate thereof can be carried out under conditions known per se. For example, the amount of EG with respect to TPA is 1.1 to 1.5 mole times, and the boiling point of EG or higher, for example, 220 to 260 ° C. Esterification is performed while heating to temperature and distilling water out of the system under a pressure of 1 to 5 kg / cm ² .
In this case, it is known to use, for example, zinc acetate, zinc borate, metal magnesium, etc. as the esterification catalyst. However, TPA itself serves as a catalyst, and in the present invention, the total amount of metals in the resin is 240 ppm or less. It is desirable not to use a catalyst because it needs to be suppressed.

In the second stage polycondensation step, a known polycondensation catalyst is added to BHET obtained in the first stage or a low polycondensate thereof, and then the pressure is gradually increased while maintaining the reaction system at 260 to 290 ° C. The reaction is allowed to proceed, while stirring under reduced pressure of 1 to 3 mmHg and finally distilling the produced EG out of the system. When the molecular weight is detected by the viscosity of the reaction system and reaches a predetermined value, it can be discharged out of the system, pelletized after cooling, and made into resin pellets, or it can be put into an injection molding machine or compression molding machine in the molten state. It can also be fed and molded directly.
As the polycondensation catalyst, germanium compounds, titanium compounds, antimony compounds and the like are generally used. In the present invention, the catalyst concentration is preferably in the range of 0.01 to 0.03 mol / mol (BHET).

The intrinsic viscosity of the polyester resin of the present invention is preferably 0.55 dL / g or more and less than 0.7 dL / g, and particularly preferably in the range of 0.57 to 0.68 dL / g, because it has such an intrinsic viscosity. As described above, the polyester resin of the present invention can be synthesized only by melt polymerization, but the polyester resin by melt polymerization contains more acetaldehyde and low molecular weight components than the polyester resin that has undergone solid phase polymerization. Therefore, it is preferable to perform the processing described later.
That is, in general, the ease of removal of acetaldehyde contained in the polyester melt is closely related to the intrinsic viscosity (IV) of the polyester resin, and the higher the intrinsic viscosity (IV), the more difficult it is to remove. Since the intrinsic viscosity is as low as 0.55 dL / g or more and less than 0.70 dL / g, acetaldehyde can be efficiently removed without increasing the intrinsic viscosity by performing the treatment described later.

  For example, the obtained polyester resin can be heated for a short time to reduce low molecular weight components such as acetaldehyde and cyclic trimer. That is, after the resin pellets after melt polymerization are treated with an inert gas such as air or nitrogen for about 0.5 hours in a pre-crystallized soot heated to 170 ° C. or outside, heating is performed from 200 ° C. to 230 ° C. Impurities contained in the pellets, mainly low molecular weight components, can be removed without increasing the intrinsic viscosity by heating to a trough and heating for a very short time while flowing a vacuum or an inert gas.

Furthermore, acetaldehyde in the resin can be reduced by providing a vent in the extruder when pelletizing the resin after melt polymerization to provide a reduced pressure atmosphere.
Furthermore, by performing water treatment on the resin pellets after melt polymerization, low molecular weight components such as acetaldehyde and cyclic trimers in the resin can be reduced. The water treatment can be carried out by bringing the resin pellets into contact with water, water vapor, water vapor-containing gas or water vapor-containing air, and the contact between the resin pellet and water is carried out at 40 to 100 ° C. for 3 minutes to 5 hours. Particularly preferably, it can be carried out by immersing in hot water at 50 to 100 ° C. for 5 minutes to 3 hours. Moreover, it can carry out by making 50-110 degreeC water vapor | steam or water vapor containing gas and a resin pellet contact normally for 5 minutes-14 days, Preferably it is 10 minutes-2 days, Most preferably, it is 20 minutes-10 hours.

  As the dicarboxylic acid component used for the synthesis of the polyester resin of the present invention, 50% or more, particularly 80% of the dicarboxylic acid component is preferably terephthalic acid from the viewpoint of mechanical properties and thermal properties. Of course, an acid component can be contained. Examples of carboxylic acid components other than terephthalic acid include isophthalic acid, naphthalenedicarboxylic acid, p-β-oxyethoxybenzoic acid, biphenyl-4,4′-dicarboxylic acid, diphenoxyethane-4,4′-dicarboxylic acid, 5- Sodium sulfoisophthalic acid, hexahydroterephthalic acid, adipic acid, sebacic acid, trimellitic acid, pyromellitic acid, hemimellitic acid, 1,1,2,2-ethanetetracarboxylic acid, 1,1,2-ethanetricarboxylic acid 1,3,5-pentanetricarboxylic acid, 1,2,3,4-cyclopentanetetracarboxylic acid, biphenyl-3,4,3 ′, 4′-tetracarboxylic acid and the like.

  As the diol component, 50% or more, particularly 80% or more of the diol component is preferably ethylene glycol in view of mechanical properties and thermal properties. As diol components other than ethylene glycol, 1,4-butanediol, Propylene glycol, neopentyl glycol, 1,6-hexylene glycol, diethylene glycol, triethylene glycol, cyclohexanedimethanol, ethylene oxide adduct of bisphenol A, glycerol, trimethylolpropane, pentaerythritol, glycerol, trimethylolpropane, 1, Examples include 2,6-hexanetriol, sorbitol, 1,1,4,4-tetrakis (hydroxymethyl) cyclohexane and the like.

  In the polyester resin of the present invention, a compounding agent known per se, for example, a colorant, an antioxidant, a stabilizer, various antistatic agents, a release agent, a lubricant, a nucleating agent, a thickener, and the like are blended. However, in the polyester resin of the present invention, since the amount of metal in the resin is 240 ppm or less, it can be blended according to a known formulation so as not to impair this range.

(Preform molding)
The preform using the polyester resin of the present invention can be molded by either injection molding or compression molding, but the polyester resin of the present invention can be used particularly advantageously for injection molding.
That is, in the injection molding, the polyester resin has a problem that the resin is easily decomposed because it is exposed to a high temperature for a long time as compared with the compression molding. Since Tm ≦ T ≦ Tm + 20 ° C. (Tm is the melting point of the polyester resin, T is the temperature of the molten polyester resin) and the melt viscosity at a shear rate of 2000 sec ^{−1 is} in the range of 100 to 240 Ns / m ² , Tm ≦ T ≦ Tm + 20 ° C. Injection molding is possible at resin temperatures in the range of (Tm is the melting point of the polyester resin and T is the temperature of the molten polyester resin), effectively suppressing the molecular weight reduction due to thermal decomposition of the resin and the by-production of acetaldehyde and oligomers. This makes it possible to form a preform having excellent transparency and flavor retention.

When the preform is molded using the polyester resin of the present invention, as described above, the melted polyester resin can be directly supplied to an injection molding machine or a compression molding machine without being pelletized after melt polymerization. The pellets can be melt-kneaded by an extruder and supplied to an injection molding machine or compression molding.
In the case of injection molding, a molten polyester resin is injected, and the preform having the shape including the mouth and neck corresponding to the final container is manufactured in an amorphous state. The injection conditions other than the resin temperature (injection temperature) are not particularly limited, but it is generally preferable to mold at an injection pressure of 30 to 60 kg / cm ² . If desired, the neck portion having a threaded portion, a fitting portion, a support ring and the like can be crystallized and whitened by heat treatment at the preform stage in order to impart heat resistance and rigidity to the obtained preform.

In the case of compression molding, the molten polyester resin supplied to the synthetic resin supply device is cut into a molten resin lump, held, supplied to a compression molding machine comprising a male mold and a female mold, compression molded, and injection molded. As in the case of, the preform is produced in an amorphous state.
Even in the case of compression molding, the melt extrusion temperature of the molten polyester resin is in the range of Tm ≦ T ≦ Tm + 20 ° C. (Tm is the melting point of the polyester resin) as in the case of injection molding. It is possible to prevent thermal degradation and drawdown of the resin.

The preform formed using the polyester resin of the present invention is formed into a stretch-molded container such as a bottle or a wide-mouthed cup by stretch blow molding.
In stretch blow molding, a preform molded using the polyester resin for compression molding of the present invention is heated to a stretching temperature, and the preform is stretched in the axial direction and biaxially stretched blow molded in the circumferential direction. An axial stretch container is manufactured.
The preform molding and the stretch blow molding can be applied to a hot parison system in which stretch blow molding is performed without completely cooling the preform, in addition to the cold parison system.
The obtained polyester container can be heat-set by a means known per se. The heat setting can be performed by a one-mold method performed in a blow molding die, or can be performed by a two-mold method performed in a heat fixing die separate from the blow molding die.

  The invention is further illustrated by the following examples, but the invention is not limited to these examples.

1. [Measurement of metal content]
A 1.0g polyester resin sample was incinerated with nitric acid in the presence of sulfuric acid in a conventional manner, completely decomposed, and then made up to 100ml with distilled water. A plasma emission spectroscopic analyzer (ICAP manufactured by Nippon Jarrell-Ash Co., Ltd.) -88) was used to quantify the content of each metal element.

2. [Measurement of intrinsic viscosity [η]]
A 0.20 g polyester resin sample was precisely weighed and completely dissolved in 20 ml of a 1,1,2,2-tetrachloroethane-phenol mixed solvent having a weight ratio of 1: 1 by stirring at 120 ° C. for 20 minutes. After dissolution, the solution was cooled to room temperature, and the intrinsic viscosity was determined with an Ubbelohde viscometer (manufactured by Kusano Science Opportunities Co., Ltd.) temperature-controlled at 30 ° C. using a solution passed through a glass filter.

3. [Measurement of weight average molecular weight and molecular weight distribution]
Using a solution prepared by accurately weighing 0.5 g of a polyester resin sample and dissolving in a 1: 1 solvent ratio of chloroform-hexafluoroisopropanol, gel permeation chromatography (System: Integrated System For GPC / SEC manufactured by Asahi Techneion Co., Ltd.) , Column: TSK G5000HHR + 4000HHR, detector: Triple Detector Module TriSEC Model 302 manufactured by VISCOTEC, solvent: chloroform, injection amount: 100 μL), and the weight average molecular weight Mw was determined. Moreover, molecular weight distribution (Mz / Mn) was calculated | required from the number average molecular weight Mn and z average molecular weight Mz obtained similarly.
Here, the z average molecular weight Mz is an average molecular weight given by ΣW _i M _i ² / W _i M _i , W _i represents the weight of the molecular species, and M _i represents the molecular weight.

4). [Measurement of melt viscosity]
Using a capillograph (manufactured by Toyo Seiki Co., Ltd.), the melt viscosity of the polyester resin at a capillary L / D = 10/1 (mm) and a cylinder temperature of 265 ° C. was measured. The melt viscosity at a strain rate of 2000 sec ⁻¹ was read from the obtained melt viscosity curve.

5. [Measurement of Acetaldehyde (AA) Concentration]
1 g of the freeze-pulverized molded preform was precisely weighed into a vial, and 5 ml of ultrapure water was added to the lid. After ultrapure water and the sample were shaken well, the sample was heated in an electric oven set at 120 ° C. for 60 minutes. After heating, the mixture was cooled on ice and allowed to stand. 1 ml of the supernatant was taken out, 0.2 ml of 0.1% 2,4-dinitrophenylhydrazine / phosphoric acid solution was added, the cap was closed, and the mixture was allowed to stand at room temperature for 30 minutes or more. High performance liquid chromatography (Tosoh Corporation high performance liquid chromatography system: CCP & 8020 system, column: TSK-GEL ODS-80Ts 4.6 mm × 250 mm, detector: UV, 360 nm, solvent: distilled water: acetonitrile = 0.47: AA content was quantified from the obtained sample solution using 0.53 mixed solvent, injection amount: 50 μL).

[Example 1]
Intrinsic viscosity: 0.62 dL / g, weight average molecular weight Mw: 40400 g / mol, molecular weight distribution Mz / Mn: 3.2, metal content: 195 ppm, melt viscosity at a shear rate of 2000 sec ⁻¹ : 201 Ns / m ² (temperature: 265 ° C) polyester resin, a preform was molded at an injection speed of 30 mm / sec using an injection molding machine with a barrel temperature set to 270 ° C, and the preform acetaldehyde was confirmed and the acetaldehyde of the obtained preform was confirmed. The content of was measured.

[Example 2]
Intrinsic viscosity: 0.68 dL / g, weight average molecular weight Mw: 46990 g / mol, molecular weight distribution Mz / Mn: 3.2, metal content: 228 ppm, melt viscosity at a shear rate of 2000 sec ⁻¹ : 195 Ns / m ² (temperature: The preform was molded in the same manner as in Example 1 using a polyester resin at 265 ° C.), and the molding state of the preform was confirmed, and the acetaldehyde content of the obtained preform was measured.

[Example 3]
Intrinsic viscosity: 0.64 dL / g, weight average molecular weight Mw: 43920 g / mol, molecular weight distribution Mz / Mn: 3.2, metal content: 159 ppm, melt viscosity at a shear rate of 2000 sec ⁻¹ : 224 Ns / m ² (temperature: The preform was molded in the same manner as in Example 1 using a polyester resin at 265 ° C.), and the molding state of the preform was confirmed, and the acetaldehyde content of the obtained preform was measured.

[Example 4]
Intrinsic viscosity: 0.58 dL / g, weight average molecular weight Mw: 31,130 g / mol, molecular weight distribution Mz / Mn: 3.2, metal content: 157 ppm, melt viscosity at a shear rate of 2000 sec ⁻¹ : 157 Ns / m ² (temperature: The preform was molded in the same manner as in Example 1 using a polyester resin at 265 ° C.), and the molding state of the preform was confirmed, and the acetaldehyde content of the obtained preform was measured.

[Example 5]
Intrinsic viscosity: 0.61 dL / g, weight average molecular weight Mw: 39480 g / mol, molecular weight distribution Mz / Mn: 3.4, metal content: 218 ppm, melt viscosity at a shear rate of 2000 sec ⁻¹ : 191 Ns / m ² (temperature: The preform was molded in the same manner as in Example 1 using a polyester resin at 265 ° C.), and the molding state of the preform was confirmed, and the acetaldehyde content of the obtained preform was measured.

[Comparative Example 1]
Intrinsic viscosity: 0.71 dL / g, weight average molecular weight Mw: 61190 g / mol, molecular weight distribution Mz / Mn: 2.8, metal content: 360 ppm, melt viscosity at a shear rate of 2000 sec ⁻¹ : 239 Ns / m ² (temperature: When a preform was molded by an injection molding machine using a polyester resin of 265 ° C. and a barrel temperature set at 270 ° C., the molding had to be performed at an increased injection speed.
In the same manner as in Example 1, the molding state of this preform was confirmed, and the acetaldehyde content of the obtained preform was measured.

[Comparative Example 2]
Intrinsic viscosity: 0.68 dL / g, weight average molecular weight Mw: 46690 g / mol, molecular weight distribution Mz / Mn: 3.4, metal content: 266 ppm, melt viscosity at a shear rate of 2000 sec ⁻¹ : 206 Ns / m ² (temperature: When a preform was molded by an injection molding machine using a polyester resin of 265 ° C. and a barrel temperature set at 270 ° C., the molding had to be performed at an increased injection speed.
In the same manner as in Example 1, the molding state of this preform was confirmed, and the acetaldehyde content of the obtained preform was measured.

[Comparative Example 3]
Intrinsic viscosity: 0.75 dL / g, weight average molecular weight Mw: 48340 g / mol, molecular weight distribution Mz / Mn: 2.8, metal content: 238 ppm, melt viscosity at a shear rate of 2000 sec ⁻¹ : 250 Ns / m ² (temperature: 265 ° C) polyester resin and trying to mold a preform with an injection molding machine with a barrel temperature set at 270 ° C. Even if the injection speed was increased, the resin was not sufficiently injected into the mold and shorted. Occurred, and preform molding was difficult.

[Comparative Example 4]
Intrinsic viscosity: 0.50 dL / g, weight average molecular weight Mw: 35420 g / mol, molecular weight distribution Mz / Mn: 2.0, metal content: 226 ppm, melt viscosity at a shear rate of 2000 sec ⁻¹ : 90 Ns / m ² (temperature: 265 ° C) polyester resin and tried to form a preform with an injection molding machine with a barrel temperature set to 270 ° C. However, the resin at the nozzle tip was drastically drowned, causing bubbles and wrinkles in the preform. Molding was difficult.

[Comparative Example 5]
Intrinsic viscosity: 0.64 dL / g, weight average molecular weight Mw: 45740 g / mol, molecular weight distribution Mz / Mn: 3.5, metal content: 230 ppm, melt viscosity at a shear rate of 2000 sec ⁻¹ : 260 Ns / m ² (temperature: 265 ° C) polyester resin and attempted to form a preform with an injection molding machine with a barrel temperature set at 270 ° C. However, even if the injection speed was increased, the resin was not sufficiently injected into the mold and shorted. Occurred, and preform molding was difficult.

  The results of the above examples and comparative examples are shown in Table 1.

Claims (3)

The total amount of metals contained in the resin is 240 ppm or less, the intrinsic viscosity is 0.56 dL / g or more and less than 0.70 dL / g, the weight average molecular weight (Mw) is 30000-47000 g / mol, and the molecular weight distribution A polyethylene terephthalate resin having (Mz / Mn) of 3.4 or less is injection-molded at a resin temperature in the range of Tm ≦ T ≦ Tm + 20 ° C. (Tm is the melting point of the polyethylene terephthalate resin and T is the temperature of the molten polyethylene terephthalate resin). A preform characterized by The polyethylene terephthalate resin, preform according to claim 1, which is synthesized by the melting polymerization. The polyethylene terephthalate resin has Tm ≦ T ≦ Tm + 20 ° C. (Tm is the melting point of the polyethylene terephthalate resin, T is the temperature of the molten polyethylene terephthalate resin) and the melt viscosity at a shear rate of 2000 sec ^{−1 is} in the range of 100 to 240 Ns / m ^2. Purifo beam according to claim 1 or 2.