JP2017178995A - Polyester resin composition and direct blow molded article made from the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyester resin composition capable of obtaining a direct blow molded article which enables blow molding with good productivity without causing draw down even when an end material of a resin generated in a molding step is used as a recycle pellet and is excellent in color tone and transparency.SOLUTION: A polyester resin composition contains a hindered phenol-based antioxidant of 0.01 to 1.0 mass% in a polyester resin containing a polyester resin, which has ethylene terephthalate as a main repeating unit and contains isophthalic acid of 2 to 20 mol% as a copolymer component, as a main component, has an intrinsic viscosity of 0.8-1.4 and a carboxyl end group concentration of 30 equivalent/ton or less, and has intrinsic viscosity retention after molding of 90% or more.SELECTED DRAWING: None

Description

  The present invention is a polyester resin composition suitable for blow molding applications, and once formed, then pellets obtained by pulverizing the molded product are used as a recycled material and mixed with an unmolded polyester resin composition. Even so, the present invention relates to a polyester resin composition that is low in intrinsic viscosity, can be blow-molded with good moldability, and can obtain a blow-molded product excellent in color tone and transparency.

  Polyethylene terephthalate (PET) is excellent in mechanical properties, chemical stability, transparency and the like, is inexpensive, and is widely used as various sheets, films, containers and the like. The growth in the use of hollow containers (bottles) for fruit juice drinks, liquid seasonings, edible oils, liquors, wines, etc. is remarkable. Moreover, since there is little concern about residual monomers and harmful additives in hollow molded articles made of vinyl chloride resin, and hygiene and safety are high, replacement from conventional bottles made of vinyl chloride resin and the like is also progressing.

  In general, when plastic bottles are manufactured, melt-plasticized resin is used as die orifices in terms of ease of molding, high productivity, and relatively low equipment costs such as molding machines and molds. A so-called direct blow molding method is employed in which a cylindrical parison is formed through extrusion, and air is blown into the mold by sandwiching the parison between the molds. In the case of this direct blow molding, it is necessary to avoid that the parison extruded in the molten state is drawn down during the blow molding in order to perform the molding smoothly. Therefore, a high melt viscosity is required for the resin used. Is done. Accordingly, vinyl chloride resins, polyolefin resins, and the like are widely used in direct blow molding as resins having a high melt viscosity.

  In direct blow molded products, replacement of vinyl chloride resin with polyester resin has been studied, but polyester resins generally do not have a high melt viscosity suitable for direct blow molding. For this reason, there is a problem that the extruded parison draws down during blow molding, and blow molding cannot be performed, and crystallization is likely to occur during blow, so whitening occurs even if molding is possible, and transparency is increased. There was a problem of becoming insufficient.

  In order to improve transparency, a polyester resin obtained by copolymerizing polyethylene terephthalate with other monomer components has been proposed. This can suppress crystallization, but it cannot increase the melt viscosity by itself. Therefore, a method has been proposed in which the viscosity is increased by means of crosslinking with a trifunctional or higher polyvalent carboxylic acid / polyhydric alcohol to solve the drawdown problem (see, for example, Patent Document 1). However, when the viscosity is increased by such a cross-linking means, the moldability is improved, but when the amount of polyvalent carboxylic acid or polyhydric alcohol is large, the gel is easily gelled, the heat stability is inferior, and the resulting molding is obtained. The product had a problem that it was inferior in color tone and transparency.

Also, in normal direct blow molding, a cylindrical parison extruded through a die from an extruder is clamped and clamped by a vertically split mold, and the bottom of the cavity of this split mold is inserted. Cut the lower part of the molten resin at the pinch-off part that is the arranged blade part and heat-weld and seal the upper part to form the parison of the bottomed cylindrical body by cutting the upper part of the cylindrical molten resin with a parison cutter, Next, blow molding is performed by blowing blow air into the parison through the air nozzle inserted from the top of the split mold. That is, the resin end material cut | disconnected in such a formation process generate | occur | produces. Then, the end material is recycled by cutting, dry blending the raw material resin chip as a recycled material, and using it again for direct blow molding.
However, when molding is performed using a resin composition that does not consider recyclability, the end material is often thermally decomposed by heat treatment during molding, and the intrinsic viscosity is often lowered. When such a milled material is dry blended and recycled, there is a problem that drawdown is likely to occur during molding and the moldability deteriorates.

Japanese Patent No. 3173755

  The present invention solves the above-mentioned problems, and even if the resin scraps generated in the molding process are used as recycled pellets, blow molding can be performed with high productivity without causing drawdown during direct blow molding. It is possible to provide a polyester resin composition capable of obtaining a direct blow molded product having excellent color tone and transparency, and a direct blow molded product comprising the resin composition of the present invention. It is something to be offered.

The inventors of the present invention have arrived at the present invention as a result of intensive studies in order to solve the above problems.
That is, the gist of the present invention is the following (1) to (2).
(1) A hindered phenolic antioxidant is added in an amount of 0.01 to 1 in a polyester resin mainly composed of a polyester resin containing ethylene terephthalate as a main repeating unit and 2 to 20 mol% of isophthalic acid as a copolymerization component. Polyester resin composition containing 0.0 mass%, intrinsic viscosity is 0.8 to 1.4, carboxyl end group concentration is 30 equivalent / t or less, and intrinsic viscosity retention after molding is 90% It is the above, The polyester resin composition characterized by the above-mentioned.
The intrinsic viscosity retention after molding is that the polyester resin composition is molded at a molding temperature of 280 ° C., and the intrinsic viscosity (IV _B ) of the obtained molded product and the intrinsic viscosity of the polyester resin composition before molding ( IV _A ) is measured and calculated by the following formula.
Intrinsic viscosity retention (%) = (IV _B / IV _A ) × 100
(2) A blow molded article formed by using the polyester resin composition according to (1).

Since the polyester resin composition of the present invention satisfies a specific composition and characteristic values, thermal decomposition due to heat treatment during blow molding is unlikely to occur, and the thermal stability is excellent. For this reason, even if the end material produced at the time of molding is reused as a recycled material, there is little reduction in the intrinsic viscosity, and it is possible to perform blow molding with high productivity without causing drawdown during direct blow molding. . And the direct blow molded product excellent in color tone and transparency can be obtained.
Moreover, since the direct blow molded product of this invention is obtained from the polyester resin composition of this invention, it is excellent in color tone and transparency and can be used for various uses.

Hereinafter, the present invention will be described in detail.
The polyester resin in the polyester resin composition of the present invention requires that 50 to 95 mol% of the acid component is terephthalic acid and 2 to 20 mol% is isophthalic acid. That is, terephthalic acid is the main component and isophthalic acid is the copolymer component. Among them, the copolymerization amount of isophthalic acid is preferably 3 to 18 mol%, and more preferably 4 to 15 mol%. By copolymerizing isophthalic acid, the crystallization speed of the polyester resin can be adjusted to those suitable for direct blow molding, and whitening due to crystallization during direct blow molding can be prevented.

  If the copolymerization amount of isophthalic acid is less than 2 mol%, the crystallization speed of the resin composition will be high, and when direct blow molding is performed, the molded product will crystallize and whiten, resulting in poor transparency. It becomes. On the other hand, if the copolymerization amount of isophthalic acid exceeds 20 mol%, the resin composition becomes amorphous, so that drying at a high temperature and solid-phase polymerization are likely to be difficult. Blocking easily occurs in the polymerization process.

  Examples of dicarboxylic acid components other than terephthalic acid and isophthalic acid include phthalic acid, 5-sodium sulfoisophthalic acid, phthalic anhydride, naphthalenedicarboxylic acid, adipic acid, sebacic acid, dimer acid, and the like. Alternatively, ester-forming derivatives of these acids may be used.

  The proportion of terephthalic acid in the acid component is 50 to 95 mol%, and the proportion of terephthalic acid is preferably 60 to 90 mol%. When the proportion of terephthalic acid is less than 50 mol%, the crystallinity of the resin composition is lowered and it tends to be amorphous. On the other hand, when the proportion of terephthalic acid exceeds 95 mol%, the amount of isophthalic acid copolymerization decreases, making it difficult to adjust the crystallization rate and poor effect of preventing whitening due to crystallization during blow molding. It becomes.

  On the other hand, 80 mol% or more of the glycol component in the polyester resin is ethylene glycol, and among them, 85 mol% or more of the glycol component is preferably ethylene glycol. Examples of glycol components other than ethylene glycol include neopentyl glycol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexamethylenediol, diethylene glycol, 1,4-cyclohexanedimethanol, dimer diol, An ethylene oxide adduct of bisphenol A or bisphenol S can be used.

  If the proportion of ethylene glycol in the glycol component is less than 80 mol%, the crystallinity of the resin composition is lowered and it tends to be amorphous, which is not preferable.

  And the resin composition of this invention contains 0.01-1.0 mass% of hindered phenolic antioxidants in the above polyester resins, Above all, 0.2-0.8 It is preferable to contain by mass. The hindered phenol-based antioxidant is preferably added during the polymerization reaction step of the polyester resin. By adding it during the polymerization reaction step, a part of the compound is copolymerized in the polyester resin. As a result, entanglement of molecular chains occurs in the polyester resin, and it is assumed that a state similar to cross-linking occurs, and the melt viscosity of the polyester resin becomes moderately high, so that drawdown is less likely to occur in direct blow molding, A container having a uniform thickness can be obtained.

  In addition, by including a hindered phenolic antioxidant in the resin composition of the present invention, the thermal stability of the resin composition is improved, and the resulting molded product is excellent in color tone and transparency. Become.

  If the content of the hindered phenolic antioxidant is less than 0.01% by mass, the resin composition with the entanglement of the molecular chain as described above cannot be obtained, so that the parison draw-down during direct blow molding can be prevented. Can not. It also becomes difficult to increase the melt viscosity of the resin composition. Furthermore, the thermal stability of the resin composition is not improved, and the resulting molded product is inferior in heat resistance, color tone and transparency.

  On the other hand, when the content exceeds 1.0% by mass, the entanglement of the molecular chains becomes too large, and the resin composition at the exit of the extrusion die is excessively expanded at the time of molding, and the surface of the resulting molded product becomes rough. The glossiness is impaired. Further, the melt viscosity of the resin composition becomes too high, and it is necessary to increase the molding temperature during molding, resulting in poor color tone of the molded product. Furthermore, the effect of improving the thermal stability is saturated and disadvantageous in terms of cost.

Examples of hindered phenol antioxidants include 2,6-di-t-butyl-4-methylphenol and n-octadecyl-3- (3 ′, 5′-di-t-butyl-4′-hydroxyphenyl). Propionate, tetrakis [methylene-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate] methane, tris (3,5-di-t-butyl-4-hydroxybenzyl) isocyanurate, 4, 4′-butylidenebis- (3-methyl-6-tert-butylphenol), triethylene glycol-bis [3- (3-tert-butyl-4-hydroxy-5-methylphenyl) propionate], 3,9-bis { 2- [3- (3-tert-butyl-4-hydroxy-5-methylphenyl) propionyloxy] -1,1′-dimethylethyl} -2,4,8 10-tetraoxaspiro [5,5] undecane and the like are used, but tetrakis [methylene-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate] methane is used in terms of effect and cost. preferable.

In the polyester resin composition of the present invention, the germanium compound is preferably contained in an amount of 5 × 10 ⁻⁵ mol to 3.0 × 10 ⁻⁴ mol with respect to 1 mol of the acid component of the polyester resin. It is preferable that 6 * 10 <-5> mol-2.0 * 10 < ^-4 > mol is contained.

A germanium compound is used as a polymerization catalyst when a polyester resin is obtained. If the content of the germanium compound is less than 5 × 10 ⁻⁵ mol, it is difficult to obtain a polyester resin having a target degree of polymerization. . Or polymerization time becomes long in a polymerization reaction, As a result, the color tone of the obtained polyester resin worsens. On the other hand, even if it exceeds 3.0 × 10 ⁻⁴ mol, the effect as a polymerization catalyst is saturated and disadvantageous in cost.

  Examples of the germanium compound include germanium dioxide, germanium tetrachloride, germanium tetraethoxide, and the like, and germanium dioxide is preferred from the viewpoint of polymerization catalyst activity, physical properties of the resulting polyester resin, and cost.

  And the polyester resin composition of this invention needs that intrinsic viscosity (IV) is 0.8-1.4, and it is preferable that it is 1.0-1.3 especially. The intrinsic viscosity (IV) is measured at a temperature of 20 ° C. using a mixture of equal mass of phenol and ethane tetrachloride as a solvent.

  When the intrinsic viscosity is less than 0.8, since the viscosity of the resin composition is low, the drawdown of the parison becomes large during direct blow molding, and molding becomes difficult. On the other hand, when the intrinsic viscosity exceeds 1.4, it is necessary to raise the molding temperature, and the color tone and transparency of the obtained molded product are deteriorated. In addition, the melt viscosity becomes high, the resin composition expands too much at the exit of the extrusion die at the time of molding, and the resulting molded product has a rough surface and a loss of gloss.

  Furthermore, the polyester resin composition of the present invention needs to have a carboxyl end group concentration of 30 equivalent / t or less, preferably 28 equivalent / t or less, more preferably 24 equivalent / t or less. It is preferable. By setting the carboxyl end group concentration of the polyester resin composition to 30 equivalent / t or less, thermal decomposition of the resin due to heat treatment during blow molding can be suppressed, and stable molding can be achieved. It will be excellent.

The polyester resin composition of the present invention is required to have an intrinsic viscosity retention after molding of 90% or more. The intrinsic viscosity retention after molding is the intrinsic viscosity (IV _B ) of a molded product obtained by direct blow molding of a polyester resin composition at a molding temperature of 280 ° C. and the intrinsic viscosity of the polyester resin composition before molding. (IV _A ) is measured and calculated by the following formula.
Intrinsic viscosity retention (%) = (IV _B / IV _A ) × 100

  The polyester resin composition of the present invention contains an appropriate amount of a hindered phenol antioxidant, and the intrinsic viscosity value and the carboxyl end group concentration satisfy a specific range, so that thermal decomposition during molding hardly occurs. As a result, it becomes possible to achieve the above intrinsic viscosity retention. When the intrinsic viscosity is 90% or more, when the direct blow molding is performed using the polyester resin composition of the present invention, the end material generated when the molded product is obtained is converted into an unmolded polyester resin composition. Even if it is added to and further molded, the decrease in intrinsic viscosity becomes extremely low.

  In particular, the intrinsic viscosity retention is preferably 93% or more, and more preferably 95%. If the intrinsic viscosity retention rate is less than 90%, once the molding process is performed and then recovered and recycled, the intrinsic viscosity will be greatly reduced and added to the unmolded polyester resin composition as a recycled material. And difficult to use.

  When the polyester resin composition of the present invention is once molded and then added to an unmolded polyester resin composition as a recycled material, it is preferably added at 10 to 40% by mass.

  Moreover, the polyester resin composition of this invention may contain the phosphorus compound for the purpose of the further color tone improvement and the thermal stabilization of polyester. From the viewpoint of cost and the color tone of the resulting polyester resin composition, phosphoric acid or phosphoric acid ester is preferable as the phosphorus compound.

  Next, the manufacturing method of the polyester resin composition of this invention is demonstrated. The polyester resin composition in the present invention is preferably obtained through an esterification reaction, a melt polymerization reaction, and a solid phase polymerization reaction step. It is difficult to obtain a polyester resin composition having a target intrinsic viscosity only by the esterification reaction and the melt polymerization reaction. Even if it is obtained, the reaction time of the melt polymerization reaction becomes long, and the resulting polyester resin composition has a poor color tone.

Specifically, for example, it can be produced by the following method.
Terephthalic acid or its ester-forming derivative as an acid component, ethylene glycol as a glycol component in a predetermined ratio are charged into an esterification reactor, and subjected to an esterification reaction at a temperature of 160 to 280 ° C. under pressure. Is transferred to a polymerization reactor, and a reaction solution of isophthalic acid and ethylene glycol, or a dispersion of isophthalic acid and ethylene glycol, a germanium compound as a polymerization catalyst, a cobalt compound and an alkali metal compound as necessary, and a hindered phenol antioxidant An agent is added, and a melt polymerization reaction is usually performed at a temperature of 240 to 290 ° C., preferably 250 to 280 ° C. under a reduced pressure of 1 hPa or less. The intrinsic viscosity of the copolymerized polyester (prepolymer) obtained here is preferably in the range of 0.5 to 0.8.

  Subsequently, a polyester resin composition having a target intrinsic viscosity is obtained by performing a solid phase polymerization reaction using the prepolymer obtained by the melt polymerization reaction. In the solid phase polymerization, after prepolymer is dried and crystallized in advance, usually under reduced pressure or under an inert gas such as nitrogen, the temperature is 20 to 30 ° C. lower than the melting point of the polyester resin for 3 hours to The reaction is carried out for 50 hours in the reactor.

  As described above, the polyester resin composition of the present invention is particularly suitable for direct blow molding, but even if an injection molding or stretching method is adopted, it is a molded product excellent in color tone and transparency (injection). Molded bodies, sheets, films, etc.) can be obtained.

Next, the direct blow molded article of the present invention is formed using the polyester resin composition of the present invention. That is, the molded article of the present invention may include not only the polyester resin composition of the present invention alone but also a part of the polyester resin composition of the present invention. Especially, it is preferable that content of the polyester resin composition of this invention is 50 mass% or more, and it is preferable that content of the polyester resin composition of this invention is 60 mass% or more especially.
The direct blow molded article of the present invention can be manufactured using a general-purpose direct blow molding machine, and the temperature of each part of the cylinder and the nozzle of the molding machine is preferably in the range of 240 to 290 ° C.

Next, the present invention will be specifically described using examples. The measurement and evaluation methods for various characteristic values in the examples are as follows.
(A) Intrinsic viscosity It was measured by the same method as described above.
(B) Copolymerization component copolymerization amount, hindered phenol antioxidant content The obtained polyester resin composition has a volume ratio of deuterated hexafluoroisopropanol and deuterated chloroform of 1/20. It was dissolved in a mixed solvent, and 1H-NMR was measured with a LA-400 type NMR apparatus manufactured by JEOL Ltd., and the copolymerization amount and content were determined from the integrated intensity of the proton peak of each component of the obtained chart. .
(C) Carboxyl end group concentration 0.1 g of the obtained polyester resin composition was dissolved in 10 ml of benzyl alcohol, 10 ml of chloroform was added to this solution, and then titrated with 1/10 N potassium hydroxide benzyl alcohol solution. Asked.

(D) Formability The thickness of the body of the obtained hollow container 1 (100 samples) is measured, and the difference between the thickness of the thickest part and the thinnest part is up to 0.10 mm. In the case where the number of acceptable samples was 90 or more, it was marked as ◯, and in the case where the number of acceptable samples was 89 or less, it was marked as x. Even if the difference between the thickness of the thickest part and the thinnest part is 0.10 mm, crystallization occurs in the molded container, and the container is whitened or the container surface is rough. , Rejected.
And the intrinsic viscosity of the polyester resin composition obtained intrinsic viscosity retention after (e) forming (IV _A), measured the resulting intrinsic viscosity of the hollow container 1 (IV _B), was calculated by the following equation.
Intrinsic viscosity retention (%) = (IV _B / IV _A ) × 100

(F) Recyclable moldability Example 1 except that the obtained hollow container 1 was pulverized into a pellet and 30 parts by mass of the recycled pellets and 70 parts by mass of the obtained polyester resin composition were used. The hollow container 2 was produced in the same manner.
The thickness of the body part of the obtained molded product (100 samples) was measured, and the thickness difference between the thickest part and the thinnest part was up to 0.10 mm, and the number of accepted samples was 90. When it was more than one, it was marked as ◯, and when the number of accepted samples was 89 or less, it was marked as x. Even if the difference between the thickness of the thickest part and the thinnest part is 0.10 mm, crystallization occurs in the molded container, and the container is whitened or the container surface is rough. , Rejected.
(G) Color tone Cut out from each of the obtained hollow containers 1 and 2 to create sample pieces (100 pieces), and measure the color tone of the sample pieces using a color difference meter ND-Σ80 type manufactured by Nippon Denshoku Industries Co., Ltd. did. The color tone was determined with a Hunter Lab colorimeter, the b value was measured, and the average value of n number 20 was obtained. A b value of 2.0 or less was determined to be good color tone.
(H) Haze Cut out from each of the obtained hollow containers 1 and 2 to prepare sample pieces (100 pieces), and measure turbidity with a turbidimeter MODEL 1001DP manufactured by Nippon Denshoku Industries Co., Ltd. (air: haze 0 %) And the average value of n number 100. The smaller this value is, the better the transparency is, and if it is 5% or less, it is judged that the transparency is excellent.

Example 1
The esterification reactor is fed with a slurry of terephthalic acid (TPA) and ethylene glycol (EG) (TPA / EG molar ratio = 1 / 1.6) and reacted under the conditions of a temperature of 250 ° C. and a pressure of 50 hPa for esterification. A reaction product (number average degree of polymerization: 5) having a reaction rate of 95% was obtained. In another esterification reaction can, a slurry (IPA / EG molar ratio = 1 / 3.1) composed of isophthalic acid (IPA) and ethylene glycol is charged, and the esterification reaction is performed at a temperature of 200 ° C. for 3 hours. A reaction solution of ethylene glycol was obtained.
Charge 55.5 parts by mass of a reaction product of TPA and EG to a polymerization reactor, then 7.8 parts by mass of a reaction solution of isophthalic acid and ethylene glycol, 0.008 parts by mass of germanium dioxide as a polymerization catalyst, hindered phenol As an antioxidant, 0.12 parts by mass of tetrakis [methylene-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate] methane (Irganox-1010 manufactured by Ciba Specialty) In addition, the reactor was decompressed, and after 60 minutes, a melt polymerization reaction was performed for 4 hours at a final pressure of 0.9 hPa and a temperature of 280 ° C. to obtain a prepolymer of a copolyester.
This prepolymer had an intrinsic viscosity of 0.72. This prepolymer was pre-dried at 150 ° C. for 5 hours, and then solid-phase polymerized in a nitrogen stream at 210 ° C. for 15 hours to obtain a polyester resin composition.
After drying using this polyester resin composition, it was molded using a direct blow molding machine when the extrusion temperature was 280 ° C., the parison diameter was 3 cm, and the length was 25 cm to obtain a 500 cc hollow container 1.

Examples 2-8, Comparative Examples 1-7
The composition was changed so that the copolymerization amount of isophthalic acid and the content of the hindered phenol antioxidant were the values shown in Table 1, the solid phase polymerization reaction time was changed, and the intrinsic viscosity was the value shown in Table 1. A polyester resin composition was obtained in the same manner as in Example 1 except that.
In Comparative Example 2 and Comparative Example 6, solid phase polymerization was not performed.
And the direct blow molding was performed like Example 1 using the obtained resin composition, and the hollow container was obtained. In Comparative Example 7, direct blow molding was performed by changing the extrusion temperature of the direct blow molding machine when obtaining the hollow containers 1 and 2 to 290 ° C.

  Table 1 shows the characteristic values and evaluations of the polyester resin compositions and hollow containers obtained in Examples 1 to 8 and Comparative Examples 1 to 7.

As is clear from Table 1, the polyester resin compositions obtained in Examples 1 to 8 contain an appropriate amount of a hindered phenol antioxidant, and the intrinsic viscosity value and the carboxyl end group concentration satisfy a specific range. Since it was excellent in thermal stability, direct blow molding could be performed with good operability without causing the problem of whitening due to crystallization. And the intrinsic viscosity retention after shaping | molding was a high thing, and it was excellent also in the moldability at the time of recycling use.
Both of the obtained hollow containers 1 and 2 had no coloration, excellent color tone, and good transparency.

  On the other hand, since the polyester resin composition obtained in Comparative Example 1 had a low copolymerization amount of isophthalic acid, when direct blow molding was performed, the molded product crystallized and whitened, resulting in poor transparency. In Comparative Example 2, since the amount of isophthalic acid copolymerized was large, fusion occurred during solid phase polymerization, and a polyester resin composition having a desired IV could not be obtained. Since the polyester resin composition obtained in Comparative Example 3 did not contain a hindered phenol antioxidant, the thermal stability of the copolyester was poor, and the molded product was inferior in color tone. Moreover, since the drawdown of the parison at the time of molding was large, the molded product had a large difference between the thickest part and the thinnest part, resulting in poor moldability. Moreover, since the intrinsic viscosity retention after molding was low, the recycle moldability was poor. Since the polyester resin composition obtained in Comparative Example 4 had a high content of hindered phenolic antioxidants, the expansion of the resin composition at the exit of the extrusion die during molding was too large, and the resulting molded product was The surface became rough and the transparency was impaired.

Since the polyester resin composition obtained in Comparative Example 5 had a high carboxyl end group concentration, the thermal stability of the copolyester was poor, and the molded product was inferior in color tone. In addition, the drawdown of the parison during molding was large, the molded product had a large difference between the thickest part and the thinnest part, the moldability was inferior, and the intrinsic viscosity retention after molding was also low. . For this reason, it was inferior to recycle moldability. Since the intrinsic viscosity of the polyester resin composition obtained in Comparative Example 6 was low, the drawdown was large and could not be molded. Since the polyester resin composition obtained in Comparative Example 7 had a longer solid phase polymerization reaction time, the intrinsic viscosity was too high. For this reason, it is necessary to increase the molding temperature at the time of direct blow molding, and the expansion of the resin composition becomes too large at the time of molding, and the obtained molded product has a poor color tone, the surface is rough, and the transparency is inferior. became.

Claims (2)

In a polyester resin mainly composed of a polyester resin containing ethylene terephthalate as a main repeating unit and containing 2 to 20 mol% of isophthalic acid as a copolymerization component, 0.01 to 1.0 mass of a hindered phenol antioxidant is contained. % Polyester resin composition having an intrinsic viscosity of 0.8 to 1.4, a carboxyl end group concentration of 30 equivalent / t or less, and an intrinsic viscosity retention after molding of 90% or more. A polyester resin composition characterized by that.
It should be noted that the intrinsic viscosity retention after molding is a direct blow molding of the polyester resin composition at a molding temperature of 280 ° C., and the intrinsic viscosity (IV _B ) of the obtained molded product and the polyester resin composition before molding. The intrinsic viscosity (IV _A ) is measured and calculated by the following formula.
Intrinsic viscosity retention (%) = (IV _B / IV _A ) × 100 A direct blow molded article formed using the polyester resin composition according to claim 1.