JP2015166441A - Polyester resin for blow molding, and blow-molded article obtained therefrom - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyester resin from which a blow-molded article excellent in thermal stability, a color tone and transparency and also in recyclability of a regeneration material thereof can be obtained with high productivity without causing a drawdown problem or a whitening problem due to crystallization, and to provide the blow-molded article obtained from the polyester resin.SOLUTION: The polyester resin for blow molding contains terephthalic acid mainly as an acid component and ethylene glycol and 1,4-butanediol mainly as a glycol component, has 80/20-30/70 mass ratio of the ethylene glycol to the 1,4-butanediol and satisfies the following conditions simultaneously. The condition (1) is that the crystalline melting point thereof is 160-205°C. The condition (2) is that the intrinsic viscosity thereof is 0.5-1.4. The condition (3) is that the carboxyl end group concentration thereof is 35 equivalent/ton or smaller.

Description

  The present invention relates to a polyester resin that can be molded at a low temperature and can obtain a blow molded product excellent in flexibility and transparency with high productivity.

  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. 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.

  Patent Document 1 describes a direct blow hollow molded article made of a copolymer polyether resin containing 90 to 40 mol% of ethylene-2,6-naphthalate units and 10 to 60 mol% of ethylene isophthalate units. It is shown that the gas barrier property and transparency are excellent. However, since such a copolyester resin has a high melting point, it cannot be molded at a low temperature, and the molded product obtained does not have a feature of excellent flexibility.

JP-A-5-008283

  The present invention is intended to solve the above problems and to provide a polyester resin that can be blow-molded at a low temperature and can obtain a blow-molded product excellent in transparency and flexibility with high productivity. . Furthermore, the present invention intends to provide a blow molded product made of the polyester resin for blow molding of the present invention and having excellent transparency and flexibility.

The inventor of the present invention has arrived at the present invention as a result of intensive studies to solve the above problems.
That is, the gist of the present invention is the following (a) to (d).
(I) The acid component is mainly composed of terephthalic acid, the glycol component is composed mainly of ethylene glycol and 1,4-butanediol, and the mass ratio of ethylene glycol and 1,4-butanediol is 80/20 to 30 A polyester resin for blow molding, wherein the polyester resin is / 70 and satisfies the following (1) to (3) simultaneously.
(1) Crystal melting point 160-205 ° C
(2) Intrinsic viscosity is 0.5 to 1.4
(3) The carboxyl end group concentration is 35 equivalent / t or less. (B) The polyester resin for blow molding according to (a), wherein the content of the cyclic trimer is 0.3% by mass or less.
(C) A blow molded product comprising the blow molding polyester resin according to any one of (a) and (b).

The polyester resin of the present invention is a copolymerized polyester resin having a specific composition, and has an intrinsic viscosity suitable for blow molding and a carboxyl end group concentration. Therefore, there is a problem of whitening due to drawdown or crystallization during blow molding. Thus, various blow-molded articles excellent in transparency and flexibility can be obtained with high productivity. Furthermore, since it has a low crystal melting point, it can be molded at a low temperature and has excellent productivity.
And since the blow molded product of this invention is obtained from the polyester resin of this invention, it is excellent in transparency and a softness | flexibility, and can be used for various uses.

Hereinafter, the present invention will be described in detail.
The polyester resin of the present invention is suitable for blow molding. Among them, a melt-plasticized resin is extruded through a die orifice to form a cylindrical parison, which is directly inserted into a mold to blow air inside. It is suitable for a stretch blow molding method in which a parison is formed by blow molding or injection molding, and this is stretch blow molded.

  In the polyester resin of the present invention, the acid component is mainly composed of terephthalic acid (hereinafter sometimes abbreviated as TPA), and terephthalic acid is preferably 90 mol% or more of the acid component. Furthermore, it is preferable that it is 95 mol% or more. As is known as the acid component of polyethylene terephthalate, terephthalic acid contributes to providing preferable physical properties common to polyesters in general. When the proportion of terephthalic acid is less than 90 mol%, a molded product obtained from such a resin is inferior in crystallinity.

  On the other hand, the glycol component in the polyester resin contains ethylene glycol (hereinafter sometimes abbreviated as EG) and 1,4-butanediol (hereinafter sometimes abbreviated as BD) as main components. In particular, the ratio of both components is preferably 80 mol% or more, and more preferably 85 mol% or more.

  And mass ratio (EG / BD) of both is 80 / 20-30 / 70, and it is preferable that it is 70 / 30-40 / 60 especially. Outside this range, the melting point of the polyester resin increases. Further, the crystallinity of the polyester resin is deteriorated, tetrahydrofuran is produced during the polycondensation reaction, and the thermal stability of the polyester is deteriorated. For this reason, blow molding cannot be performed at low temperatures, and even if blow molding is performed at high temperatures, resin drawdown occurs, making molding difficult, or molding with uneven thickness even if molding is possible. It becomes goods.

  Moreover, in order to improve the softness | flexibility of the blow molded product obtained, it is preferable that polytetramethylene glycol contains as a copolymerization component in the glycol component in a polyester resin. The content (copolymerization amount) of polytetramethylene glycol is preferably 0.1 to 20 mol%, and more preferably 0.1 to 15 mol%.

  Furthermore, as a component constituting the polyester, in addition to the above-described terephthalic acid, ethylene glycol, and 1,4-butanediol, the following components may be copolymerized as long as the object of the present invention is not impaired. Good. Examples include components such as isophthalic acid, 5-sodium sulfoisophthalic acid, 4-hydroxybenzoic acid, adipic acid, sebacic acid, naphthalenedicarboxylic acid, diethylene glycol, propylene glycol, pentaerythritol, neopentyl glycol, bisphenol A, and bisphenol S.

  The terephthalic acid, ethylene glycol, 1,4-butanediol, polytetramethylene glycol, and other components that constitute the above-described polyester include these ester-forming derivatives as a concept. Such an ester-forming derivative may be used in combination as a copolymerization component.

The polyester resin of the present invention satisfies the following conditions (1) to (3) at the same time.
(1) Crystal melting point 160-205 ° C
(2) Intrinsic viscosity is 0.5 to 1.4
(3) Carboxyl end group concentration is 35 equivalent / t or less

  First, the polyester resin of the present invention has a crystalline melting point as the condition (1), and the crystalline melting point is 160 to 205 ° C, preferably 180 to 200 ° C. When the crystal melting point is less than 160 ° C., the heat resistance of the obtained direct blow molded product is insufficient. On the other hand, if it exceeds 205 ° C., the heat treatment temperature during blow molding must be increased, which is disadvantageous in terms of cost.

  Next, as the condition of (2), the polyester resin of the present invention needs to have an intrinsic viscosity (IV) of 0.5 to 1.4, particularly 0.6 to 1.2. preferable. 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 0.5, since the viscosity of the resin is low, the drawdown of the parison becomes large at the time of blow molding, or the obtained molded product has uneven thickness. On the other hand, when the intrinsic viscosity exceeds 1.4, it is necessary to raise the temperature at the time of molding, which is disadvantageous in cost, and the obtained molded product is inferior in color tone and transparency.

  Further, as the condition (3), the polyester resin of the present invention needs to have a carboxyl end group concentration of 35 equivalent / t or less, preferably 30 equivalent / t or less, more preferably 28 equivalent / t. It is preferably t or less. By setting the carboxyl end group concentration of the polyester resin to 35 equivalent / t or less, the resin does not undergo thermal decomposition during blow molding, so that a decrease in viscosity can be suppressed and stable molding becomes possible. When the carboxyl end group concentration exceeds 35 equivalents / t, even if the intrinsic viscosity of the resin is in the above range, thermal decomposition of the resin occurs due to heat treatment during blow molding, Viscosity decreases. For this reason, the drawdown of the parison becomes large, making molding difficult, and even if it is obtained, the molded product has uneven thickness.

  The polyester resin of the present invention may contain an antioxidant. Among them, the hindered phenol-based antioxidant is preferably added so as to be 0.01 to 2.0% by mass in the polyester resin, and more preferably 0.1 to 1.0% by mass. . By adding an appropriate amount of a hindered phenol-based antioxidant, it has an effect of suppressing thermal decomposition of the phthalic acid component, and the color tone of the polyester resin is improved. Further, the antioxidant is decomposed to produce pentaerythritol (tetrafunctional component), which is incorporated into the molecular chain of the polyester, thereby increasing the viscosity of the polyester resin.

  If the hindered phenol-based antioxidant is less than 0.01% by mass, it is difficult to achieve the above effects. On the other hand, if it exceeds 2.0% by mass, the polycondensation reaction rate is lowered and the polyester resin is likely to be colored.

  Examples of the hindered phenol antioxidant include triethylene glycol-bis [3- (3-tert-butyl-5-methyl-4-hydroxyphenylpropionate], 1,6-hexanediol-bis [ 3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate, octadecyl-3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate, pentaerythrityl-tetrakis [3- (3,5-di-t-butyl-4-hydroxylphenyl) propionate] and the like.

  Furthermore, the polyester resin of the present invention preferably has a cyclic trimer content of 0.3% by mass or less, and more preferably 0.2% by mass or less. By using a polyester resin with a cyclic trimer content of 0.3% by mass or less for molding, improvement of contamination of molds and the like is recognized, and blow molding with excellent transparency without surface roughness or whitening. You can get a body. When the content of the cyclic trimer exceeds 0.3% by mass, it adheres to devices such as a mold and a nozzle during blow molding, resulting in contamination. These contaminations cause the surface roughness and whitening of the molded product, resulting in surface roughness and whitening, which tend to be a blow molded article having poor transparency.

  Further, the content of the cyclic trimer in polyethylene terephthalate containing terephthalic acid and ethylene glycol as main components is about 1% by mass, and it is 0.3 to 0.5% by mass even by performing solid phase polymerization treatment. It only decreases to the extent. On the other hand, the content of the cyclic trimer in the polyester resin of the present invention is as low as 0.3% by mass or less. This is achieved by comprising ethylene glycol and 1,4-butanediol in a specific ratio in the diol component.

And in the polyester resin of this invention, a titanium compound and a germanium compound are contained 5 * 10 < ^-5 > mol-3.0 * 10 < ^-4 > mol with respect to 1 mol of acid components of a polyester resin, Especially 6x It is preferable that 10 < ^-5 > mol-2.0 * 10 < ^-4 > mol is contained.
Titanium compounds and germanium compounds are used as a polymerization catalyst when obtaining a polyester resin, and when the content of these compounds is less than 5 × 10 ⁻⁵ mol, a polyester resin having a target degree of polymerization can be obtained. Otherwise, the polymerization time is increased in the polymerization reaction, and as a result, the color tone of the resulting polyester resin is deteriorated. 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.
As the titanium compound, tetra-n-butyl titanate, tetra-n-propyl titanate, tetraisopropyl titanate, potassium titanium oxalate and the like are preferably used, and tetra-n-butyl titanate is preferable from the viewpoint of cost and polycondensation catalytic activity. .

Furthermore, the polyester resin of the present invention preferably contains a cobalt compound. By containing a cobalt compound, it can be set as resin excellent in color tone, and it becomes possible to obtain the blow molded product excellent in color tone. Cobalt compound is preferably is 1 × ^{10 -5} mol to 2.0 × ^{10 -4} mol content based on the acid component to 1 mole of the polyester resin, among others 3 × ^{10 -5} mol to 1.0 × 10 ^- It is preferable that ⁴ mol is contained.

When the content of the cobalt compound is less than 1 × 10 ⁻⁵ mol, the effect of improving the color tone of the polyester resin is small. On the other hand, when the content exceeds 2.0 × 10 ⁻⁴ mol, the transparency of the polyester deteriorates and is stable over time. This is not preferable because the properties are also deteriorated. The cobalt compound is preferably used as a polymerization catalyst, and specific examples include cobalt acetate, cobalt formate, cobalt oxide, and cobalt chloride. Among these, cobalt acetate is preferable from the viewpoint of polymerization catalyst activity, physical properties of the resulting polyester resin, and cost.

  Further, in the polyester resin of the present invention, in addition to the above-described antioxidants, examples of coloring inhibitors include phosphorous acid, phosphoric acid, trimethyl phosphite, triphenyl phosphite, tridecyl phosphite, trimethyl. Phosphorus compounds such as phosphate, tridecyl phosphate and triphenyl phosphate can be used, and these phosphorus compounds may be used alone or in combination of two or more. Moreover, in order to suppress coloring by thermal decomposition of the polyester resin, additives such as manganese compounds such as manganese acetate, anthraquinone dye compounds, copper phthalocyanine compounds may be contained.

  Next, the manufacturing method of the polyester resin of this invention is demonstrated. The polyester resin in the present invention is preferably obtained through an esterification reaction and a melt polymerization reaction step. Further, a solid phase polymerization reaction step may be performed after the melt polymerization reaction step. By making these steps and conditions specific, the polyester resin of the present invention can be obtained.

Specifically, for example, it can be produced by the following method.
First, in an esterification reaction vessel in which bis- (β-hydroxyethyl) terephthalate or its low polymer exists under nitrogen gas suppression at a temperature of 230 to 250 ° C., ethylene glycol and terephthalic acid are used. The slurry having a molar ratio of 1,1 to 2.0 is continuously added, and an ester oligomer having an average polymerization degree of 10 or less is continuously obtained with a residence time of 7 to 8 hours. Next, this ester oligomer consisting of terephthalic acid and ethylene glycol is transferred to a melt polycondensation reaction can, and 1,4-butanediol is added at a mass ratio of ethylene glycol / 1,4-butanediol of 80/20 to 30/70. The reaction is carried out at 200 to 230 ° C. In addition, when the temperature of reaction is less than 200 degreeC, reaction will only become slow, and there exists a possibility that ester oligomer may solidify. On the other hand, when it exceeds 230 ° C., 1,4-butanediol decomposes during the reaction to form tetrahydrofuran, and a polyester resin having a predetermined ratio of 1,4-butanediol cannot be obtained.

  Further, after adding a polycondensation catalyst, the temperature of the melt polycondensation reaction vessel is raised to 200 to 260 ° C., and the melt polycondensation reaction is performed under a reduced pressure of 0.01 to 13.3 hPa until a predetermined intrinsic viscosity is reached. I do. In this way, the polyester resin of the present invention produced by performing a melt polycondensation reaction under predetermined conditions is discharged into a number of rods by being extruded from a nozzle using gas pressure, cut into chips. Obtained as a form.

  The carboxyl end group concentration of the polyester resin of the present invention is 30 equivalents / t or less. This is because, as described above, the mass ratio of ethylene glycol / butanediol to butanediol is added to the ester oligomer composed of terephthalic acid and ethylene glycol. Is added in an amount that falls within the range of 80/20 to 30/70, and the depolymerization reaction is performed at a predetermined temperature.

  In the case of undergoing a solid-phase polymerization reaction step after the melt polymerization reaction step, the polyester resin is dried and crystallized in advance, and then usually from the melting point of the polyester under reduced pressure or under an inert gas flow such as nitrogen. Is preferably carried out by reacting the polyester in the reactor at a temperature lower by 20 to 30 ° C. for 3 to 50 hours. By carrying out the solid phase polymerization reaction, the intrinsic viscosity can be further increased or the amount of the oligomers contained can be further decreased.

  The polyester resin of the present invention is suitable for blow molding as described above. However, even if an injection molding, extrusion molding, or stretching method is adopted, a molded product excellent in color tone and transparency (injection molded body). Sheet, film, etc.).

  Next, the blow molded product of the present invention is made of the polyester resin of the present invention. The blow molded product of the present invention can be manufactured using a general-purpose direct blow molding machine or stretch blow molding machine, and the temperature of each part of the cylinder and the nozzle of the molding machine is in the range of 160 to 250 ° C. Is preferred.

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 ([η])
The measurement was carried out at a temperature of 20 ° C. using a mixture of equal mass of phenol and ethane tetrachloride as a solvent.
(B) Carboxyl end group concentration 0.1 g of the obtained polyester resin was dissolved in 10 ml of benzyl alcohol, 10 ml of chloroform was added to this solution, and then titrated with a 1/10 N potassium hydroxide benzyl alcohol solution. .

(C) Composition The obtained polyester resin was dissolved in a mixed solvent having a dose ratio of deuterated hexafluoroisopropanol and deuterated chloroform of 1/20, and the LA-400 NMR apparatus 1H-NMR manufactured by JEOL Ltd. was analyzed. The amount of copolymerization and the content were determined from the integrated intensity of the proton peak of each component of the obtained chart.
(D) Melting point (Tm)
A differential scanning calorimeter (DSC-7 manufactured by Perkin Elmer Co.) was used and the temperature was increased at a rate of 20 ° C./min.

(E) Cyclic trimer content 100 mg of the obtained polyester resin was dissolved in a mixed solvent having a volume ratio of hexafluoroisopropanol and chloroform of 1/20, and acetonitrile was added for extraction, followed by liquid chromatography. Measurement was performed under the following conditions, and the amount of cyclic trimer was calculated.
Column: Waters Micro Bonder Sphere
Filler: Si-C18 5μ 100A
Detector: Waters 2996 type PDA detector (light source wavelength 254 nm)
Measurement flow rate: 1 ml / min
Mobile phase solvent Acetonitrile / water = 7/3 and acetonitrile

(F) Formability Both the obtained molded product 1 and molded product 2 were measured for the thickness of the body of 100 samples, and the thickness difference between the thickest part and the thinnest part was up to 0.30 mm. The sample was accepted and the number of samples accepted was shown. The number of acceptable samples is preferably 90 or more.
(G) Haze Both the obtained molded product 1 and molded product 2 were cut out from the molded product to make 100 sample pieces (length 3 cm, width 3 cm), and the turbidity was made by Nippon Denshoku Industries Co., Ltd. The total was measured with MODEL 1001DP (air: haze 0%), and the average value of n number 100 was used. 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.
(H) Color tone Color tone of the obtained chip-like polyester resin was measured using a color difference meter ND-Σ80 type manufactured by Nippon Denshoku Industries Co., Ltd. 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.

(I) Flexibility 20 samples are arbitrarily selected from the samples that have passed the moldability of (f), the molded product is placed sideways, and a load is applied in order. At this time, the molded product was stopped when it was bent by about a quarter, and the number of cracked or cracked molded products was measured. Those having a number of cracked or cracked pieces up to 2 were regarded as acceptable. In addition, in the moldability of (f), what did not satisfy 20 acceptable samples was not measured.

Example 1
A slurry having a molar ratio of terephthalic acid and ethylene glycol of 1 / 1.6 is continuously fed to an esterification reaction vessel in which bis (β-hydroxyethyl) terephthalate and its low polymer are present, at a temperature of 250 ° C. and pressure The reaction was carried out under the condition of 0.2 MPa, the residence time was 8 hours, and an ester oligomer with an esterification reaction rate of 95% was continuously obtained. 60.3 kg of this ester oligomer was charged into a melt polycondensation reaction vessel, and 1,4-butanediol was added in an amount (16.2 kg) such that the molar ratio of ethylene glycol to 1,4-butanediol was 55/45, Further, tetra-n-butyl titanate was added as a polycondensation catalyst, and the pressure was gradually reduced. Finally, a polycondensation reaction was performed at a pressure of 0.9 hpa and a temperature of 250 ° C. for 4 hours, and the chips were discharged by a conventional method. A polyester resin was obtained. This polyester resin had the properties [η] = 0.67, carboxyl end group concentration = 28, and Tm = 181 ° C.
After drying using this polyester resin, a direct blow molding machine (MSE5043Y-A manufactured by Tahara Co., Ltd.) was used to extrude the resin at an extrusion temperature of 195 ° C. to form a cylindrical parison (a parison diameter of 3 cm and a length of 25 cm). Then, while the parison is in a softened state, it is sandwiched between molds, the bottom is formed, and this is blown, and the average thickness of the barrel is 1.0 mm, the inner diameter is 3.5 cm, and the height is 11. A 5 cm cylindrical bottle (hollow container with an internal capacity of 100 cc) was obtained. This is referred to as a molded product 1.
Further, after drying using this polyester resin, an injection molding machine (Nissei Co., Ltd.) in which each part of the cylinder and nozzle temperature were set to 230 ° C., screw rotation speed 100 rpm, injection time 10 seconds, cooling time 10 seconds, and mold temperature 15 ° C. A preform was molded using ASB-50TH manufactured by ASB Co., Ltd.). Next, this preform was stretch blow molded at a blow pressure of 2 MPa in an atmosphere of 100 ° C. to form a cylindrical bottle (hollow container with an internal volume of 150 cc) having an average body thickness of 300 μm, an inner diameter of 3.5 cm, and a height of 15 cm. Obtained. This is referred to as a molded product 2.

Examples 2-3 and Comparative Examples 1-2
A polyester resin was obtained in the same manner as in Example 1 except that the amount of butanediol added during production of the polyester resin was changed and the composition was changed to the values shown in Table 1.
And using the obtained polyester resin, it carried out similarly to Example 1, and performed direct blow molding and stretch blow molding, and obtained the molded products 1 and 2.

Example 4
The kind and amount of the polymerization catalyst used in the production of the polyester resin are changed, and a hindered phenol antioxidant (manufactured by ADEKA: Adeka Stub AO-60) is used so that the content thereof becomes the value shown in Table 1. A polyester resin was obtained in the same manner as in Example 1 except that it was added. As the polymerization catalyst, germanium dioxide (shown as Ge-based in Table 1) and cobalt acetate (shown as Co-based in Table 1) were used.
And using the obtained polyester resin, it carried out similarly to Example 1, and performed direct blow molding and stretch blow molding, and obtained the molded products 1 and 2.

Examples 5-8, Comparative Example 3
The amount of butanediol added in the production of the polyester resin was changed, the composition was changed to the values shown in Table 1, and the type and amount of the polymerization catalyst, and a hindered phenol antioxidant (manufactured by ADEKA: A polyester resin was obtained in the same manner as in Example 4 except that the addition amount was changed so that the content of ADK STAB AO-60) was the value shown in Table 1.
And using the obtained polyester resin, it carried out similarly to Example 1, and performed direct blow molding and stretch blow molding, and obtained the molded products 1 and 2.

Comparative Example 4
A polyester resin was obtained in the same manner as in Example 1 except that the polycondensation reaction time was changed to 2.5 hours.
And using the obtained polyester resin, it carried out similarly to Example 1, and performed direct blow molding and stretch blow molding, and obtained the molded products 1 and 2.

Comparative Example 5
The esterification reactor was charged with terephthalic acid and ethylene glycol in a molar ratio of 1 / 1.6, and ethylene glycol and 1,4-butanediol were continuously added so that the molar ratio was 55/45. The mixture was supplied and reacted under the conditions of a temperature of 250 ° C. and a pressure of 0.2 MPa to obtain an ester oligomer with a residence time of 8 hours. Here, tetrabutyl titanate is added as a polymerization catalyst, the pressure is gradually reduced, and finally a polycondensation reaction is performed at a pressure of 0.9 hPa and a temperature of 280 ° C. for 4 hours. Obtained. This polyester resin had [η] = 0.69, carboxyl end group concentration = 38, and Tm = 179 ° C.
And using the obtained polyester resin, it carried out similarly to Example 1, and performed direct blow molding and stretch blow molding, and obtained the molded products 1 and 2.

  Table 1 shows the characteristic values and evaluation results of the polyester resins and molded articles obtained in Examples 1 to 8 and Comparative Examples 1 to 5.

  As is clear from Table 1, the polyester resins obtained in Examples 1 to 8 satisfied the characteristic values defined in the present invention, and therefore have good moldability, and excellent blow molding with excellent flexibility and transparency. I was able to get the goods.

On the other hand, the polyester resin obtained in Comparative Example 1 had a high melting point because the amount of 1,4-butanediol added was small. For this reason, molding was impossible at the molding temperature when obtaining the molded products 1 and 2.
The polyester resins obtained in Comparative Examples 2 and 3 had a high melting point because the amount of 1,4-butanediol added was large. For this reason, molding was impossible at the molding temperature when obtaining the molded products 1 and 2.
Therefore, in Comparative Examples 1 to 3, the molding processing temperature of the molded products 1 and 2 was changed to 270 ° C., but the viscosity decreased due to thermal decomposition, and none of the molded products could be obtained.

Since the polyester resin obtained in Comparative Example 4 had a low intrinsic viscosity, the drawdown at the time of molding increased, and the molded product 1 could not be obtained. Although the molded product 2 could be obtained, the obtained molded product had thickness unevenness.
Since the polyester resin obtained in Comparative Example 5 had a carboxyl end group amount exceeding 35, the resin was thermally decomposed by heat treatment during blow molding, and the drawdown during molding increased. For this reason, both of the molded products 1 and 2 were uneven in thickness and inferior in flexibility.

Claims (3)

The acid component is mainly composed of terephthalic acid, the glycol component is mainly composed of ethylene glycol and 1,4-butanediol, and the mass ratio of ethylene glycol and 1,4-butanediol is 80/20 to 30/70. A polyester resin for blow molding which is a certain polyester resin and satisfies the following (1) to (3) at the same time.
(1) Crystal melting point 160-205 ° C
(2) Intrinsic viscosity is 0.5 to 1.4
(3) Carboxyl end group concentration is 35 equivalent / t or less The polyester resin for blow molding according to claim 1, wherein the content of the cyclic trimer is 0.3% by mass or less. A blow molded product comprising the polyester resin for blow molding according to claim 1.