JP4649221B2 - Method for producing polyethylene terephthalate with low acetaldehyde content in molded article - Google Patents

Description

  The present invention is a solid-phase-polymerized polyethylene that can obtain a molded article with a low content of acetaldehyde, which may cause bad odors and off-flavors or change the flavor of the contents, without causing deterioration of hue. The present invention relates to terephthalate and a manufacturing method thereof.

  Polyester, especially polyethylene terephthalate (PET), is widely used because it is molded into fibers, films, industrial resins, bottles, cups, trays, and the like because of its excellent mechanical and chemical properties. However, there is a possibility that the amount of acetaldehyde increases at the time of forming a hollow container for filling beverages, and malodor, odor, content flavor and aroma change.

In order to solve these problems, a method for reducing the acetaldehyde contained in the polyester has been studied, and the polyethylene terephthalate after solid-phase polymerization is treated with water in order to reduce the oligomers and acetaldehyde generated during molding. Has been proposed (see, for example, Patent Document 1), but since the treatment liquid is water, in order to obtain a sufficient effect, the treatment liquid must be made relatively hot or treated for a long time using cold water. In addition, when the polymerization catalyst is a titanium compound other than a germanium compound, there is no effect.
JP-A-3-72524 (Claims)

  The object of the present invention is to produce a poly (ethylene terephthalate) with a low content of acetaldehyde, which eliminates the problems of the prior art and may cause malodors and off-flavors or may alter the flavor of the contents. It is to provide a method.

As a result of intensive studies in view of the above prior art, the present inventors have completed the present invention.
That is, the object of the present invention can be achieved by a method for producing polyethylene terephthalate, characterized by bringing polyethylene terephthalate into contact with an aqueous solution of tetraethylphosphonium hydroxide having a concentration of 1 ppm to 10% by mass.

  A polyester having a low acetaldehyde content can be obtained by the production method of the present invention, and the polyester and a molded product made of the polyester have few bad odors and off-flavors. In addition, the molded product obtained by molding this polyester is suitable for foodstuffs such as beverages because it does not have a bad odor or a strange odor and does not cause a change in contents.

  Hereinafter, the present invention will be described in detail. The polyethylene terephthalate of the present invention is a polyester in which the main acid component is a terephthalic acid component and the main glycol component is an ethylene glycol component. Here, “main” means that the component occupies 85 mol% or more.

  Therefore, in the range of 15 mol% or less, other ester units other than the terephthalic acid component and the ethylene glycol component can be included. Examples of such copolymer components include dicarboxylic acid components other than terephthalic acid, and diol components or oxyacid components other than ethylene glycol. Specifically, examples of the aromatic dicarboxylic acid component include isophthalic acid, Naphthalenedicarboxylic acid, diphenyl dicarboxylic acid, diphenyl ether dicarboxylic acid, diphenyl sulfone dicarboxylic acid, diphenyl ketone dicarboxylic acid, sodium-sulfoisophthalic acid, dibromoterephthalic acid and the like can be mentioned. Examples of the aliphatic dicarboxylic acid component include decalin dicarboxylic acid and hexahydroterephthalic acid, and examples of the aliphatic dicarboxylic acid include malonic acid, succinic acid, and adipic acid.

  Examples of the glycol component include diethylene glycol, trimethylene glycol, tetramethylene glycol, hexamethylene glycol and the like as the aliphatic diol component. As aromatic diol components, for example, vitronone, catechol, naphthalenediol, resorcin, 4,4′-dihydroxy-diphenyl-sulfone, bisphenol A [2,2′-bis (4-hydroxyphenyl) propane], tetrabromobisphenol A, Examples thereof include bishydroxyethoxybisphenol A. Examples of the alicyclic diol component include cyclohexanediol. Examples of the aliphatic oxycarboxylic acid component include glycolic acid, hydroacrylic acid, and 3-oxypropionic acid. Examples of the alicyclic oxycarboxylic acid component include asiatic acid and quinobaic acid. Examples include salicylic acid, m-oxybenzoic acid, p-oxybenzoic acid, mandelic acid, and atrolactic acid.

  Further, a polyfunctional compound having three or more valences within the range in which the polymer chain constituting the polyester is substantially linear, such as glycerin, trimethylolpropane, pentaerythritol, trimellitic acid, trimesic acid, pyromellitic acid, tricarbaryl. An acid, gallic acid, or the like may be copolymerized, and a monofunctional compound such as o-benzoylbenzoic acid or naphthoic acid may be added as necessary.

  The polyester may be produced using a conventionally known method for producing polyethylene terephthalate. For example, the polyester is esterified using terephthalic acid and ethylene glycol, or a lower alkyl ester of terephthalic acid (for example, dimethyl ester) and ethylene glycol. Can be produced by subjecting the resulting reaction product to a polycondensation reaction. An appropriate copolymer can be produced by adding the copolymer component before the transesterification reaction or before the polycondensation reaction.

  It is preferable to use a transesterification catalyst, a polymerization catalyst, a stabilizer and the like when producing these polyesters. As these catalysts and stabilizers, those known as polyesters, particularly polyethylene terephthalate catalysts, stabilizers and the like can be used. Of course, other additives such as colorants, antioxidants, ultraviolet absorbers, antistatic agents, flame retardants and the like may be used as necessary.

  The obtained polyethylene terephthalate may be pelletized and then further polycondensed in the solid phase polymerization step, and any conventionally known method may be adopted as the solid phase polymerization method.

  In the present invention, it is necessary to bring the solid phase polymerized polyester pellets into contact with an aqueous solution of a phosphonium compound. The phosphonium compound refers to a compound that generates phosphonium ions by ionization, and tetraalkylphosphonium salt, tetraalkylphosphonium hydroxide, tetraphenylphosphonium salt, tetraphenylphosphonium hydroxide, and monoalkyltriphenylphosphonium salt are particularly preferable. It is done. The alkyl group of the tetraalkylphosphonium salt, tetraalkylhydroxide, or monoalkyltriphenylphosphonium salt is preferably a linear or branched alkyl group having 1 to 6 carbon atoms. Specific examples of phosphonium salts include tetramethylphosphonium chloride, tetramethylphosphonium chloride, tetramethylphosphonium bromide, tetraethylphosphonium chloride, tetraethylphosphonium bromide, tetrabutylphosphonium fluoride, tetrabutylphosphonium chloride, tetrabutylphosphonium bromide, tetrahydroxy Methylphosphonium sulfate, tetraphenylphosphonium fluoride, tetraphenylphosphonium chloride, tetraphenylphosphonium bromide, tetraphenylphosphonium tetraphenylborate, ethyltriphenylphosphonium chloride, ethyltriphenylphosphonium bromide, ethyltriphenylphosphonium iodide, butyltri Phenyl Suho chloride, butyl triphenyl phosphonium bromide, benzyl triphenyl phosphonium chloride, can be exemplified benzyl triphenyl phosphonium bromide.

  On the other hand, as phosphonium hydroxide, tetramethylphosphonium hydroxide, tetraethylphosphonium hydroxide, tetrabutylphosphonium hydroxide, tetraphenylphosphonium hydroxide, ethyltriphenylphosphonium hydroxide, butyltriphenylphosphonium hydroxide, benzyltriphenylphosphonium hydroxide Can be illustrated. Among these phosphonium compounds, tetraethylphosphonium hydroxide is advantageous in terms of cost because it is commercially produced in large quantities and has a low molecular weight.

  The aqueous solution of the phosphonium compound needs to be in the range of 1 ppm to 10% by mass. If the concentration is less than 1 ppm, the effect of reducing acetaldehyde during molding is insufficient, and if it exceeds 10% by mass, the cost increases. A preferable range of the concentration is 10 ppm to 5% by mass, and more preferably 100 ppm to 2% by mass.

  As a method of bringing the phosphonium compound aqueous solution into contact with the polyester, either a batch method or a continuous method may be used. For example, in the case of a batch type, a method of putting a phosphonium compound aqueous solution and a polyethylene terephthalate chip into a processing apparatus and bringing them into contact can be exemplified. Moreover, in the case of a continuous type, the method etc. which supply a phosphonium compound aqueous solution continuously or in parallel flow, and make it contact with a pellet can be illustrated. Furthermore, when polyethylene terephthalate obtained by the polymerization reaction is chipped, a method in which an aqueous phosphonium compound solution is brought into contact with molten polyethylene terephthalate and solidified by cooling may be used. In addition, if there is an organic solvent that can dissolve the phosphonium compound at a sufficient concentration instead of the phosphonium compound aqueous solution, the organic solvent can be used.

  Moreover, the form of the polyethylene terephthalate to be contacted is not limited to the chip, and may be, for example, a sheet. In this case, for example, a method of continuously introducing a polyethylene terephthalate sheet into a continuous processing apparatus and bringing it into contact with an aqueous phosphonium compound can be exemplified. The temperature at which the phosphonium compound aqueous solution and polyethylene terephthalate are brought into contact with each other is not particularly limited, but it is usually preferred that the phosphonium compound aqueous solution is brought into contact in a heated state of about 10 ° C to 60 ° C. The contact time is usually about 5 minutes to 10 hours, preferably about 10 minutes to 8 hours, and more preferably about 30 minutes to 6 hours. Of these, the contact treatment with the phosphonium compound aqueous solution in the form of a chip is preferable because it can be easily performed.

The polyethylene terephthalate treated by these methods is preferably dried, but a commonly used method for drying polyethylene terephthalate can be used, and it is not dried using a spinning machine with a vacuum suction device. May be spun into.
The various processing conditions described above may be appropriately selected depending on the production amount, intrinsic viscosity, form (chip or sheet, etc.), form size, etc. of the polyethylene terephthalate to be produced.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further more concretely, this invention does not receive any limitation by this.

[Example 1]
In a reactor in which 225 parts by mass of oligomers are retained in advance, 179 parts by mass of high-purity terephthalic acid and 95 parts by mass of ethylene glycol were stirred and maintained under a nitrogen atmosphere at 255 ° C. and normal pressure. The slurry prepared by mixing was supplied at a constant rate, and the esterification reaction was completed for 4 hours while water and ethylene glycol generated in the reaction were distilled out of the system to complete the reaction. The esterification rate at this time was 98% or more, and the polymerization degree of the produced oligomer was about 5 to 7.

  225 parts by mass of the oligomer obtained by this esterification reaction was transferred to a polycondensation reaction tank, and 0.018 parts by mass of tetrabutoxy titanate was added as a polycondensation catalyst. Subsequently, the reaction temperature in the polycondensation reaction tank is increased from 255 to 280 ° C., and the reaction pressure is gradually increased and reduced from normal pressure to 60 Pa, respectively, and water and ethylene glycol generated in the reaction are removed from the system while removing water. A condensation reaction was performed.

  The degree of progress of the polycondensation reaction was confirmed without monitoring the load on the stirring blade in the polycondensation reaction tank, and the polycondensation reaction was terminated when the desired degree of polymerization was reached. Thereafter, the reactant in the polycondensation reaction tank was continuously extruded in a strand form from the discharge part, cooled and cut to obtain a granular pellet of about 3 mm. The polycondensation reaction time at this time was 110 minutes, and the intrinsic viscosity of the obtained polyethylene terephthalate pellets was 0.52.

  Subsequently, the obtained polyethylene terephthalate pellets were subjected to solid phase polymerization at 220 ° C. for 15 hours under vacuum. 1 kg of the obtained pellets (intrinsic viscosity 0.75) was put into a 5 liter processing apparatus containing 2.5 kg of a 0.5 mass% aqueous solution of tetraethylphosphonium hydroxide at 25 ° C. and contact-treated for 4 hours. Subsequently, after removing the tetraethylphosphonium hydroxide aqueous solution and drying in a nitrogen stream at 160 ° C. for 5 hours, a preform molded body was molded by the following method.

5 kg of polyethylene terephthalate was dried for 3 hours under the conditions of 160 ° C., normal pressure and N ₂ inflow, and the dried polyethylene terephthalate was injected into an injection molding machine (FN-2000 manufactured by Nissei Plastic Industrial Co., Ltd., cylinder temperature 280 ° C., cycle 30 seconds). A cylindrical preform having an outer diameter of about 28 mm, an inner diameter of about 19 mm, a length of 136 mm, a barrel thickness of 4 mm, and a weight of about 56 g was injection-molded, and a sample piece was cut out from the mouth of the molded preform and freeze-ground. It prepared in the vial bottle, hold | maintained at 150 degreeC x 60 minutes, and measured and calculated | required the acetaldehyde (AA) content with the headspace gas chromatography by Hitachi, Ltd.

[Comparative Example 1]
In Example 1, the same operation was performed except that the contact treatment with the tetraethylphosphonium hydroxide aqueous solution was not performed. The results are shown in Table 1.

[Comparative Example 2]
In Example 1, the same operation was performed except that water was added into the treatment apparatus as a liquid to be contact-treated and subjected to high-temperature hot water treatment. The results are shown in Table 1.

  A polyester having a low acetaldehyde content can be obtained by the production method of the present invention, and the polyester and a molded product made of the polyester have few bad odors and off-flavors. In addition, the molded product obtained by molding this polyester is suitable for foodstuffs such as beverages because it does not have a bad odor or a strange odor and does not cause a change in contents. In this respect, the industrial significance is great.

Claims (1)

A method for producing polyethylene terephthalate, comprising bringing polyethylene terephthalate into contact with an aqueous solution of tetraethylphosphonium hydroxide having a concentration of 1 ppm to 10% by mass.