JPS62174225A - Polyester for blow molding and its production - Google Patents

Abstract

PURPOSE:To make it possible to decrease acetaldehyde formation during melt molding and to lower the acetaldehyde content of a molding such as a food container, by specifying the conditions of esterification and polycondensation. CONSTITUTION:A polyester is produced from a terephthalic acid-based dicarboxylic acid and an ethylene glycol-based glycol. The esterification is performed so that the glycol to dicarboxylic acid molar ratio at the end of the esterification may be 1.02-1.10. The reaction mixture is subjected to a polycondensation reaction to obtain a polyester prepolymer of anintrinsic viscosity of 0.3-0.7. This polyester prepolymer is subjected to solid-state polymerization. The obtained polyester for blow molding has an intrinsic viscosity of 0.60-10, an acetaldehyde content <=100ppm and the ratio of the number of terminal carboxyl groups to the total of the terminal groups of 40-70%.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to polyester for blow molding. More specifically, the present invention relates to a blow-molding polyester suitable for food containers and the like, which reduces the generation of acetaldehyde during melt-molding, and a method for producing the same.

(Prior Art) Polyester, particularly polyethylene terephthalate, has excellent physical and chemical properties and is therefore widely used in the fields of fibers, films, bottles, and plastic molding. Particularly recently, polyester bottles have been attracting particular attention as containers for foods, cosmetics, and the like.

However, when using polyethylene terephthalate as a bottle, it has a negative impact on taste and odor.
Acetaldehyde (hereinafter referred to as AA) in the bottle, which is a molded product.
) must be reduced as much as possible. For this purpose, as a conventional method for reducing acetaldehyde in polyethylene terephthalate, chips or pulverized products of polyester prepolymer are heated under reduced pressure or under a stream of inert gas at a temperature 20 to 80°C higher than the melting point of polyester for several hours. A so-called solid phase polymerization method is known in which the treatment is carried out for several tens of hours. However, although the solid phase polymerization method can certainly reduce the λ people in polyethylene terephthalate, it has the disadvantage that when the polyester resin is melted and heated during bottle molding, the λ people are significantly generated again.

In addition, JP-A-58-286499 discloses that polyester containing ethylene glycol as the main glycol component is blended with a compound having a carboxylic acid anhydride group. The terminal hydroxyl group concentration of the polymer is 101 and 20.
It has been proposed to suppress the production of acetaldehyde during molding by reducing the amount of acetaldehyde to less than 10 ppm. However, the former proposal involves a complicated operation of adding the compound to the polyester, and it is also necessary to prove that the compound does not cause any hygienic problems. Furthermore, although the latter proposal can certainly suppress the generation of acetaldehyde during molding, since the terminal hydroxyl group is too low, the polymerization rate is too slow to achieve a viscosity suitable for bottle molding, making it difficult to put it to practical use. It has the disadvantage of not being able to

(Problems to be Solved by the Invention) In view of the current situation, the present inventors have conducted extensive research into polyester for use in hollow molded objects such as food containers, which reduces the generation of AA during melt molding, and a method for producing the same. As a result of stacking, it is possible to perform solid phase polymerization without using any compounding agents, without the hassle of compounding, and without the hygiene problems caused by using compounding agents, and furthermore, to achieve a limiting viscosity suitable for blow molding. This has led to the present invention.

(Means for Solving the Problem) That is, the non-invention is that the main structural unit is ethylene terephthalate, the limit YJ is 0.60 to 0, the content of acetaldehyde is 10 ppm or less, and the carboxyl This is a blow molding polyester characterized by having a group ratio of 40 to 70%.

Furthermore, in the method of the present invention, when producing a polyester from a dicarboxylic acid mainly consisting of terephthalic acid and a glycol mainly consisting of ethylene glycol, the molar ratio of glycol/dicarboxylic acid at the end of the Nisderization reaction is 1.02 to 1. ．．
10, followed by M condensation reaction to produce a polyester prepolymer with an intrinsic viscosity of 0.3 to 0.7, and solid phase polymerization to obtain a polyester prepolymer with an intrinsic viscosity of 0.60. The polyester resin for blow molding is characterized in that the content of 1.01 a7toaldehyde is 10 ppm or less and the ratio of carboxyl end groups to all end groups is 40 to 70%.

In the present invention, polyester whose main constituent unit is ethylene terephthalate means polyethylene terephthalate and polyester whose main constituent is polyethylene terephthalate, but other third components may be copolymerized to the extent that the properties required for the molded product are not impaired. It may be contained as a component. Examples of the third component include aromatic dicarboxylic acids such as isophthalic acid, naphthalenedicarboxylic acid, diphenyldicarboxylic acid, and diphenylsulfonedicarboxylic acid, and aliphatic dicarboxylic acids such as adipic acid and sebacic acid. Among the third components, the glycol component includes diethylene glycol, trimethylene glycol, tetramethylene glycol, neopentyl glycol, and the like. Also, within the range that the polymer is substantially linear, for example, pentaerythritol,
A copolymer of polyfunctional compounds such as trimethylolpropane, trimellitic acid, and pyromellitic acid may also be used. When copolymerized polyethylene terephthalate is used, the copolymerization component is preferably 80 mol% or less.

Such polyester can also contain additives such as colorants, ultraviolet absorbers, antistatic agents, and lubricants in appropriate proportions, if necessary.

The polyester of the present invention needs to have an intrinsic viscosity of 0.60 to 1.0, preferably 0.70 to 0.90.
It is. If the intrinsic viscosity is less than 0.60, the mechanical strength of the resulting hollow molded product will be insufficient, and since the number of end groups is large, the occurrence of acetaldehyde spots during heating and melting will increase, making it impossible to achieve the object of the present invention. On the other hand, the intrinsic viscosity is 1
．． If it is 0 or more, the melt viscosity becomes too high, resulting in poor moldability, and the amount of acetaldehyde generated during molding also increases.

The acetaldehyde content in the polyester of the present invention is 1
It is necessary that the amount is 0 ppm or less, preferably 6 ppm or less, and more preferably a ppm or less. If the acetaldehyde content exceeds t o ppm, the acetaldehyde content of the hollow molded product will also increase, making it unsuitable for uses such as food containers.

Furthermore, the polyester of the present invention needs to have a ratio of carboxyl end groups to all end groups of 40 to 70%. If the carboxyl terminal ratio is less than 40%, the amount of acetaldehyde generated during heating will increase; on the other hand, if the carboxyl terminal ratio exceeds 70%, the reaction rate during melt thx synthesis or solid phase polymerization will decrease. This is extremely slow, making it difficult in practice to obtain a polyester having an intrinsic viscosity suitable for blow molding.

Next, the polyester prepolymer used in the method of the present invention is
It is produced by any esterification method from a dicarboxylic acid mainly having a terephthalic acid number and a glycol mainly having ethylene glycol. For example, the esterification reaction with terephthalic acid and ethylene glycol is carried out by adding a slurry of terephthalic acid and ethylene glycol to bis-β-hydroxyethyl terephthalate and/or its arbitrary polymer obtained in advance from terephthalic acid and ethylene glycol. be able to. At this time, it is necessary that the glycol/dicarboxylic acid molar ratio of the esterification reaction product obtained by the reaction is 1.02 to 1.10.

By setting the molar ratio within this range, the ratio of carboxy end groups to the total wood end groups of the polyester obtained by further solid-phase polymerization of the polyester prepolymer obtained by subsequent polycondensation can be set to 40 to 70%. I can do it. If the molar ratio of glycol/dicarboxylic acid at the end of esterification is less than 1.02, the ratio of carboxyl end groups to all end groups of the polyester obtained by solid phase polymerization will be 70% or more, resulting in a hairstyle condensation reaction and solid phase polymerization. Polymerization cannot be carried out within a reasonable time. On the other hand, when the molar ratio exceeds 1.10, the carboxyl end f'i+u u
If the ratio is less than 40%, the acetaldehyde-generating film during molding becomes extremely uniform, making it impossible to achieve the object of the present invention.

In order to set the glycol/dicarboxylic acid molar ratio at the end of the esterification reaction to 1.02 to 10, the slurry molar ratio with toethylene glycol terephthalate should be set to 1.02 to 1.
．． 10, or a predetermined amount of ethylene glycol may be extracted from the system while performing the esterification reaction at a molar ratio of 1.10 or more, or after performing the esterification reaction at a molar ratio of 1.10 or more, A predetermined amount of only terephthalic acid may be added.

The esterification reaction product obtained by the esterification reaction is subsequently subjected to a polycondensation reaction to obtain a polyester prepolymer. The intrinsic viscosity of the polyester prepolymer is preferably 0.3 to 0.7; if the intrinsic viscosity is less than 0.8, it is difficult to pelletize the polyester prepolymer and the subsequent solid phase heavy metal treatment time becomes too long.

On the other hand, if the intrinsic viscosity is 0.7 or more, it is difficult to reduce the acetaldehyde content to 10 ppm or less by solid phase polymerization.

The polyester prepolymer usually has a molecular weight of 50 to
Since it contains 0 ppm of acetaldehyde, it is necessary to subsequently perform solid phase polymerization to reduce the acetaldehyde content to 10 ppm or less. In solid phase polymerization, polyester prepolymer chips or pulverized products are heated under reduced pressure or in an inert gas stream at 20°C from the melting point of the polyester.
A conventional method of treating at a temperature as low as ~80°C for several hours to several tens of hours may be used.

(Example) Hereinafter, the present invention will be explained in more detail by giving examples. First, various measurement methods used in this example are shown below.

Intrinsic viscosity It was determined from the value measured at 20°C in a mixed solvent of phenol and tetrachloroethane (60/40 weight/2 ratio).

Acetaldehyde polyester was pulverized in liquid nitrogen, a certain amount was sealed in a glass insert, and the amount was quantified using a high-sensitivity gas chromatograph.1) It was expressed in pm (weight).

Terminal carboxyl! ! Concentration Add benzyl alcohol to the sample, dissolve by heating, and perform neutralization titration with KOH.

Example 1 Bis-β-hydroxyethyl terephthalate with an esterification reaction rate of 95% and its low polymer obtained from 500 parts of terephthalic acid and 225 parts of ethylene glycol were stored in a reactor at 260°C, and terephthalic acid was added to this. The esterification reaction is carried out at 260°C under normal pressure while continuously adding a slurry consisting of 1000 parts of ethylene glycol and 448 parts of ethylene glycol, and the ethylene glycol is completely removed before the esterification reaction is substantially completed. Quantitative distillation was performed to reduce the overall molar ratio of ethylene glycol component and terephthalic acid component to 1,
It was set as 06.

Next, 1,175 parts of the obtained esterification reaction product were transferred to an autoclave, 0.25 parts of trimethyl phosphoric acid and 0.12 parts of germanium dioxide were added, and the mixture was heated in a conventional manner at a final temperature of 285°C and a vacuum of 0.5 mm fl 17. A polycondensation reaction was carried out to obtain a polyester prepolymer having an intrinsic viscosity of 0.60. The terminal carboxyl group of the polyester prepolymer is 85 eQ/106. p, the ratio of terminal carboxyl groups to total terminal groups was 61%.

The resulting polyester prepolymer was converted to 225% by a conventional method.
Solid-state polymerization was carried out at 0.5 mrnHJ at 0.degree. C. for 8 hours to obtain a polyester having an intrinsic viscosity of 0.74. The acetaldehyde content of the polyester was 0.6 ppm, the terminal carboxyl group was 60 eq/10'#, and the ratio of the terminal carboxyl group to all terminal groups was 67%.

The obtained polyester chips are manufactured by Nissei Mu8B Machinery Co., Ltd.
Molding temperature: 280°C using B-50 stretch blow molding machine
A biaxially stretched bottle with an internal volume of t o o o m/ was molded. When the resulting bottle was crushed and the acetaldehyde content was measured, it was found to be 2.9 pPm.

Comparative Example 1 Esterification was carried out in the same manner as in Example 1, except that ethylene glycol was not distilled off during the esterification reaction, and the overall molar ratio of the ethylene glycol component and terephthalic acid component was set to 1.20. did. Thereafter, a polycondensation reaction was carried out in the same manner as in Example 1 to obtain a polyester prepolymer having an intrinsic viscosity of 0.50. The terminal carboxyl group of the polyester prepolymer is 81 eq/ill, 9.
The ratio of terminal carboxyl groups to all terminal groups was 22%.

The polyester prepolymer was subjected to solid phase polymerization in the same manner as in Example 1 to obtain a polyester having an intrinsic viscosity of 0.74. The acetaldehyde content of the polyester is 0.9 pp.
m, the terminal carboxyl group was 18.9 eq/1oay, and the ratio of the terminal carboxyl group to all terminal groups was 21%.

The obtained polyester chips were molded into a bottle in the same manner as in Example 1, and the acetaldehyde content in the bottle was measured and found to be 6.5 ppm. It can be seen that the generation of acetaldehyde during heating t'bFa molding is greater than in Example 1.

Example 2 500 parts of 11 terephthal and 22 parts of ethylene glycol
Bis-β- with an esterification reaction rate of 95% obtained from 5 parts
Hydroxyethyl terephthalate and its low polymer were stored in a reactor at 260°C, and 1000% of terephthalic acid was added to the reactor.
The esterification reaction is carried out at 260°C under normal pressure while continuously adding a slurry consisting of 448 parts of terephthalic acid and 448 parts of terephthalic acid at a constant rate. was added to reduce the overall molar ratio of ethylene glycol component and terephthalic acid component to 1.
．． It was set as 08. The obtained esterification reaction product was transferred to an autoclave, and the same procedure as in Example 1 was carried out to obtain a polyester prepolymer with an intrinsic viscosity of 0.55 (the terminal carboxyl group was 58 eq/10s, y, based on the total terminal group). The ratio of terminal carboxyl groups is 42%). The polyester prepolymer was subjected to solid phase polymerization in the same manner as in Example 1 to obtain a polyester having an intrinsic viscosity of 0.74. The acetaldehyde content of the polyester was 0.6 ppm, and the terminal carboxyl group was 88.1 eQ/106 #1. The ratio of terminal carboxyl groups to all terminal groups was 48%.

The obtained polyester chips were molded into a bottle in the same manner as in Example 1, and the acetaldehyde in the bottle was measured and found to be 8.5 ppm.

(Effects of the Invention) The polyester of the present invention generates a small amount of acetaldehyde during molding, and as a result, it is suitable as a material for hollow molded products such as foods and cosmetics. In addition, the method of the present invention does not use any compounds other than the raw materials for synthesizing polyester, so it is suitable for hygiene, and it is also possible to carry out solid phase polymerization advantageously by controlling the terminal carboxyl group. As a result, polyester with excellent bottle formability can be produced.

,'fI;nn・1、Ha Applicant: Kanebo Co., Ltd., W,,'q＞,・〃 Kanebo Gosen Co., Ltd.

Claims (3)

[Claims] (1) Ethylene terephthalate is the main structural unit,
A polyester for blow molding, which has an intrinsic viscosity of 0.60 to 1.0, an acetaldehyde content of 10 ppm or less, and a ratio of carboxyl end groups to all end groups of 40 to 70%. (2) The polyester according to claim 1, wherein the content of acetaldehyde is 3 ppm or less. (3) When producing polyester from dicarboxylic acid, mainly terephthalic acid, and glycol, mainly ethylene glycol, glycol/
An esterification reaction is carried out so that the molar ratio of dicarboxylic acid is 1.02 to 1.10, and then a polycondensation reaction is carried out to produce a polyester prepolymer with an intrinsic viscosity of 0.3 to 0.7. By phase polymerization, the intrinsic viscosity is 0.60 to 1.0 and the acetaldehyde content is 10.
A method for producing a blow molding polyester in which the ratio of carboxyl end groups to total end groups is 40 to 70%.