JP5415816B2 - Method for producing polyethylene terephthalate - Google Patents

Description

  The present invention relates to a production method capable of efficiently producing polyethylene terephthalate having good hydrolysis resistance.

  Polyethylene terephthalate is excellent in mechanical properties, thermal properties, chemical resistance, electrical properties, and moldability, and is used in various applications. However, since the mechanical properties of polyethylene terephthalate decrease due to hydrolysis, it is necessary to suppress hydrolysis when used over a long period of time or in a wet state, and various studies have been made.

  For example, Patent Document 1 discloses a technique for improving the hydrolysis resistance of polyester by using an epoxy compound. However, epoxy compounds gel when materials are recycled, causing molding defects and forming foreign objects during chemical recycling. Therefore, it is necessary to remove them separately in a later process. There was also a problem from this point. Patent Document 2 proposes that the hydrolysis resistance is improved by reducing the number of carboxylic acid end groups by containing an inorganic phosphate such as an alkali metal phosphate as a buffer. However, in addition to the phosphorus compound usually used as a catalyst deactivator (heat stabilizer), it is necessary to add an alkali metal phosphate, and there are other new problems such as precipitation of the alkali metal phosphate. .

  On the other hand, in order to reduce the number of carboxylic acid end groups, it is effective to carry out a polycondensation reaction at a low temperature so that the number of carboxylic acid end groups is not increased as much as possible. However, when the polycondensation reaction is carried out at a low temperature, the reaction rate of the polycondensation reaction is lowered to impair the productivity, which is not suitable for practical use.

JP-A-9-227767 JP 2007-277548 A

  An object of the present invention is to provide a production method capable of efficiently producing polyethylene terephthalate which has solved these conventional drawbacks and has excellent hydrolysis resistance.

  As a result of diligent research to solve the above-mentioned problems, the present inventors have added a phosphorus compound to be added to phenylphosphonic acid as a catalyst deactivator (hereinafter sometimes referred to as a heat-resistant stabilizer) before the polycondensation reaction. As a result, the polycondensation reaction can proceed efficiently even at low temperatures and the polymerization reaction can be carried out at low temperatures, so that carboxylic acid end groups that tend to cause hydrolysis without using a buffer material or an epoxy compound are used. The inventors have found that polyethylene terephthalate having a very small number can be produced, and have reached the present invention.

Thus, according to the present invention, a terephthalic acid or ester-forming derivative thereof and ethylene glycol are transesterified or esterified to produce a precursor, and the resulting precursor is polycondensed in a molten state. In the manufacturing method of
By the initial stage of the polycondensation reaction , 5 to 100 mmol% of phenylphosphonic acid and a polycondensation reaction catalyst are added in this order, based on the number of moles of all dicarboxylic acid components,
The melting point of the polyethylene terephthalate obtained by polycondensation reaction: There line to the intrinsic viscosity (Tm ° C.) or higher 280 ° C. below the temperature is higher than or equal to 0.45 dl / g, the carboxylic acid end groups is not more than 15 eq / t A method for producing polyethylene terephthalate is provided.

  Further, according to the present invention, as a preferred embodiment of the present invention, after completion of the polycondensation reaction in the molten state, the production of polyethylene terephthalate that undergoes solid phase polymerization until the intrinsic viscosity is in the range of 0.60 to 1.0. A method is also provided.

  According to the present invention, by using a specific phosphorus compound, sufficient polymerization reactivity can be maintained even when a polycondensation reaction is performed at a low temperature, and the polycondensation reaction can be efficiently performed at a low temperature. Polyethylene terephthalate having an extremely small number of carboxylic acid end groups and excellent hydrolysis resistance can be provided without impairing productivity.

  The method for producing the polyethylene terephthalate (hereinafter sometimes referred to as PET) of the present invention comprises producing a precursor by transesterifying or esterifying terephthalic acid or an ester-forming derivative thereof with ethylene glycol. This is a production method in which the obtained precursor is subjected to a polycondensation reaction in the presence of a catalyst, and a preferred embodiment of the present invention further includes a production method in which solid phase polymerization is performed. Examples of ester-forming derivatives of terephthalic acid include lower alkyl esters such as dimethyl ester, diethyl ester, and dipropyl ester of terephthalic acid.

  The production method of the present invention may pass through either a transesterification reaction using an ester-forming derivative of terephthalic acid as a raw material or an esterification reaction using terephthalic acid as a raw material. The conditions and catalyst for the transesterification reaction and esterification reaction are not particularly limited, and a method known per se can be suitably employed. Specific examples of the transesterification reaction catalyst include calcium compounds, magnesium compounds, manganese compounds, titanium compounds, and the like. On the other hand, in the case of passing through the esterification reaction, the conditions for the esterification reaction and the catalyst are not particularly limited, and a method known per se can be suitably employed. The esterification reaction catalyst may or may not be used, but when it is used, those exemplified for the above-mentioned transesterification reaction catalyst are preferable.

  In addition, in the production method of the present invention, a small amount of potassium hydroxide is used to further reduce the number of carboxylic acid end groups of the obtained PET between the early stage and the middle stage of the esterification reaction or before the beginning of the transesterification reaction and the early stage of the reaction. You may add alkali metal compounds, such as. In order to improve electrostatic application characteristics, a trace amount of a magnesium compound such as magnesium acetate may be added from the end of the esterification reaction to the beginning of the polycondensation reaction or before the start of the transesterification reaction.

  In this way, the precursor obtained via the transesterification or esterification reaction is subjected to a polycondensation reaction in a molten state. In this case, phenylphosphonic acid and the polycondensation reaction catalyst are prepared by the initial stage of the polycondensation reaction, preferably during the polycondensation reaction until the intrinsic viscosity becomes 0.3 dl / g after completion of the transesterification reaction or esterification reaction. It is preferable to add a catalyst such as an antimony compound, a germanium compound, or a titanium compound. As the order of addition, it is preferable from the viewpoint of polycondensation reactivity and hydrolysis resistance that the addition interval is 5 minutes or more in the order of phenylphosphonic acid and polycondensation reaction catalyst.

  By the way, the feature of the present invention is that phenylphosphonic acid is added as a heat-resistant stabilizer, and the polycondensation reaction is performed at a melting point (Tm: ° C.) or higher and 280 ° C. or lower, and further Tm or higher and 275 ° C. or lower of the obtained PET. It is in. Usually, polycondensation reaction is carried out at 280 to 300 ° C in PET, but by using phenylphosphonic acid as a phosphorus compound that is a heat stabilizer, the reaction rate of polycondensation reaction is usually insufficient and productivity is impaired. Even at such a low temperature, the number of carboxylic acid end groups could be reduced while maintaining a sufficient polycondensation reaction rate.

  The addition amount of phenylphosphonic acid is 5 to 100 mmol%, and further 10 to 80 mmol%, based on the number of moles of all acid components constituting PET. If the amount of phenylphosphonic acid added is less than the lower limit, sufficient hydrolysis resistance, that is, a reduction effect of carboxylic acid end groups cannot be obtained, and if the upper limit is exceeded, there is little effect of improving hydrolysis resistance with respect to the content, and heat resistance The productivity may be lowered, or the polycondensation reaction rate may be slowed to reduce the productivity. Of course, the manufacturing method of this invention should just use the phenylphosphonic acid as a phosphorus compound in the range of the said addition amount, and may use another phosphorus compound together in the range which does not impair the effect of this invention. However, from the viewpoint of reducing the number of carboxylic acid end groups without reducing the polycondensation reaction rate, most of the phosphorus compound added as a heat-resistant stabilizer, preferably 90% by weight or more, is preferably phenylphosphonic acid. .

  As a method for adding phenylphosphonic acid, it may be added in any form such as an ethylene glycol solution or powder, but it is preferably added as an ethylene glycol solution. The concentration in the case of adding as an ethylene glycol solution is preferably 20% by weight or less from the viewpoint of less adhesion of phenylphosphonic acid in the vicinity of the addition port, reducing the error of the addition amount, and reactivity.

  Next, the polycondensation reaction in the production method of the present invention will be described. In the present invention, the polycondensation reaction is carried out in the presence of a catalyst in order to ensure a sufficient polycondensation reaction rate. Specific examples of the polycondensation catalyst include per se known antimony compounds, germanium compounds, titanium compounds, aluminum compounds, and the like.

  When an antimony compound, germanium compound or aluminum compound is used as a polycondensation reaction catalyst, the amount of addition is based on the number of moles of all acid components of the resulting PET as each metal (antimony, germanium, aluminum, etc.) element. 10 to 50 mmol% is preferable from the point of polycondensation reactivity and solid phase polymerization reactivity, and further from 15 to 40 mmol% from the viewpoint of heat resistance and hydrolysis resistance. If the amount of metal (antimony, germanium, aluminum, etc.) as a catalyst exceeds the upper limit, the polycondensation reactivity is improved, but the decomposition reaction at the time of remelting is also promoted, resulting in an increase in carboxylic acid end groups. The hydrolysis resistance and heat resistance of PET are likely to decrease. Specific examples of the antimony compound used as the catalyst include antimony pentoxide and antimony trioxide. Specific examples of the germanium compound include germanium dioxide, which can be used depending on the purpose. For example, the germanium compound has the best color tone, and the antimony compound has the best solid-phase polymerization reactivity.

  In addition, as described above, a titanium compound may be used as a polycondensation catalyst. In that case, the titanium element may be used in a range of 1 to 10 mmol% as a reference based on the number of moles of all acid components of the obtained PET. From the viewpoint of reactivity in polycondensation reaction and solid phase polymerization. When the amount of titanium element exceeds the upper limit, the reactivity of polycondensation reaction and solid phase polymerization is improved, but heat resistance, hydrolysis resistance and color tone tend to decrease. This reduces the reactivity of the product and tends to impair productivity. Examples of the titanium catalyst used as the polycondensation catalyst include alkoxides such as tetrabutoxy titanate and tetraisopropyl titanate, and titanium chelate compounds of titanium and lactic acid, citric acid, etc. Among them, titanium chelate compounds Is preferable from the viewpoint of heat resistance, hydrolysis resistance, and color tone.

  The PET production method of the present invention performs such a polycondensation reaction in a molten state (hereinafter sometimes referred to as melt polymerization) until the intrinsic viscosity of the resulting PET becomes 0.45 dl / g or more. It is necessary, and it is preferable to carry out in a range of 0.50 to 0.60 dl / g. If the intrinsic viscosity is less than 0.45, the molecular weight of the obtained PET may be too low to obtain sufficient mechanical properties. The upper limit of the intrinsic viscosity is not particularly limited, but is preferably 0.60 or less from the viewpoint of not excessively increasing the polymerization time of melt polymerization. In addition, the number of carboxylic acid terminal groups of PET obtained by the method for producing PET of the present invention is preferably 15 eq / t or less, more preferably 13 eq / t or less, from the viewpoint of hydrolysis resistance. Although a minimum in particular is not restrict | limited, From points, such as productivity, it is 5 eq / t or more.

  In addition, in the manufacturing method of this invention, you may copolymerize a copolymerization component known per se to PET obtained in the range which does not impair the effect of this invention. Preferably, 95 mol% or more is terephthalic acid component based on the number of moles of all dicarboxylic acid components of the obtained PET, and 95 mol% or more of ethylene glycol component is based on the number of moles of all glycol components. Decomposability and heat resistance are preferred. When the ratio of the copolymerization component is less than the lower limit, a decrease in heat resistance due to a melting point drop and a decrease in hydrolysis resistance due to a decrease in crystallinity can be suppressed.

  In this way, PET having a predetermined melt viscosity by melt polymerization may end the polycondensation reaction, be ejected, and may be directly molded into fibers, films, etc., or may be converted into strands, cut, and chipped. May be.

  By the way, in the method for producing PET of the present invention, it is preferable to further carry out solid-phase polymerization since it can be a PET having better hydrolysis resistance. Hereinafter, the solid phase polymerization will be described in more detail.

  The solid phase polymerization in the present invention can be suitably performed by a method known per se, and is not particularly limited. For example, a desired intrinsic viscosity can be obtained at a temperature of 150 to 250 ° C. under a vacuum or a nitrogen stream. Until then, a solid state polyethylene terephthalate, for example, the above-mentioned chipped state may be retained to cause a polymerization reaction. Regarding the method of retaining the PET chip under the above-mentioned conditions, for example, the method of retaining in a rotating sealed reaction vessel, or the retention of an arbitrary time while moving the chip continuously in a reaction tank having a certain volume. Methods.

  Thus, it is preferable that PET obtained by solid phase polymerization has an intrinsic viscosity in the range of 0.60 to 1.0 dl / g. When the intrinsic viscosity is less than the lower limit, the increase in molecular weight due to solid phase polymerization is insufficient, and the effect of improving the PET resistance and hydrolysis resistance before solid phase polymerization becomes small. On the other hand, when the intrinsic viscosity exceeds the upper limit, the increase in molecular weight is sufficient, but since the viscosity is too high, the load during melt extrusion for forming a film or the like becomes large and normal extrusion becomes difficult. The intrinsic viscosity of PET after solid phase polymerization is preferably in the range of 0.65 to 0.95 dl / g, more preferably in the range of 0.70 to 0.90 dl / g.

  Further, the number of carboxylic acid end groups of PET after solid phase polymerization is preferably 12 eq / t or less, more preferably 10 eq / t or less, and particularly preferably 8 eq / t or less. If the number of carboxylic acid end groups in PET after solid-phase polymerization exceeds the upper limit, the effect of reducing the number of carboxylic acid end groups by solid-phase polymerization is insufficient, and the effect of improving hydrolysis resistance compared to PET before solid-phase polymerization Is scarce. Usually, even in solid phase polymerization, it is difficult to reduce the number of carboxylic acid end groups so far. However, in the production method of the present invention, the number of carboxylic acid end groups is already reduced at the stage of melt polymerization. The number of carboxylic acid end groups can be greatly reduced without taking the conditions for solid phase polymerization. The lower limit of the number of carboxylic acid end groups is not particularly limited, but is about 3 eq / t from the viewpoint of productivity.

  The PET obtained through the solid-phase polymerization in this way can be dried and then melt-extruded, for example, into fibers by spinning and stretching, or extruded into a sheet and biaxially stretched to obtain a biaxially oriented film. be able to. Of course, the time of the melt extrusion process at the time of forming into such a fiber or film is preferably as short as possible from the viewpoint of suppressing the increase in the number of carboxylic acid end groups, and is preferably 30 minutes or less, for example.

(1) Intrinsic viscosity The obtained PET was dissolved in a mixed solvent of P-chlorophenol / 1,1,2,2-tetrachloroethane (40/60 weight ratio) and measured at 25 ° C. When the obtained PET was solid-phase polymerized, it was measured after the PET was frozen with liquid nitrogen and finely pulverized.

(2) Carboxylic acid terminal group number After the obtained PET was dissolved in benzyl alcohol at 200 ° C. under a nitrogen atmosphere, the number of carboxylic acid terminal groups (eq / t) was determined as the number of equivalents per 1 ton of PET by titration. ) Was measured.

(3) Hydrolysis resistance (production of film)
The obtained PET was made into chips, dried at 180 ° C. for 3 hours in a rotary vacuum dryer, supplied to an extruder, melt extruded at 280 ° C., and formed into a sheet from a slit die. Further, an unstretched film obtained by cooling and solidifying the sheet with a cooling drum having a surface temperature of 20 ° C. was stretched 3.5 times in the longitudinal direction (longitudinal direction) at 100 ° C. and cooled by a roll group at 25 ° C. Subsequently, in the atmosphere heated to 130 ° C. in an atmosphere guided to the tenter while holding both ends of the film stretched in the longitudinal direction in the width direction (direction orthogonal to the longitudinal direction and the thickness direction) with a clip, the width direction (lateral direction) The film was stretched 3.7 times. Thereafter, heat setting was performed in an atmosphere heated to 220 ° C. in a tenter, a width of 3% was placed in the transverse direction, and the mixture was cooled to room temperature to obtain a PET film having a thickness of 50 μm.

(Evaluation of hydrolysis resistance)
A strip-shaped sample piece obtained by cutting the obtained PET film into a length of 150 mm in the vertical direction and a width of 10 mm in the horizontal direction was prepared. Ten sample pieces were prepared, and five of them were longitudinally measured with an Instron type universal tensile tester under conditions of 100 mm between chucks, 10 mm / min tensile speed, and 500 mm / min chart speed. The elongation at break was measured, and the average value thereof was taken as the average breaking elongation before treatment.
On the other hand, the remaining five sample pieces were left in an environmental test machine set at a temperature of 85 ° C. and a humidity of 85% RH for 3000 hours, and then measured for the breaking elongation in the same manner as the initial breaking elongation. The average value of the five values was taken as the average breaking elongation after the treatment. And the value which divided the average breaking elongation after a process by the average breaking elongation before a process was made into the breaking elongation retention (%), and the following reference | standard evaluated. In addition, it is judged that a thing with a high breaking elongation retention rate has a favorable hydrolysis resistance.
A: Breaking elongation retention is 70% or more B: Breaking elongation retention is 50 or more and less than 70% B: Breaking elongation retention is 30 or more and less than 50% X: Breaking elongation retention is less than 30%

[Example 1]
A transesterification vessel was charged with 100 parts by weight of dimethyl terephthalate, 60 parts by weight of ethylene glycol, and 0.019 part of manganese acetate tetrahydrate, heated to 150 ° C., melted and stirred. The reaction was advanced while the temperature inside the reaction vessel was slowly raised to 235 ° C., and the methanol produced was distilled out of the reaction vessel. When the distillation of methanol was completed, 0.014 part of phenylphosphonic acid (17 mmol% based on the number of moles of dimethyl terephthalate) was added as a phosphorus compound to complete the transesterification reaction. Subsequently, 0.05 part of antimony trioxide and 0.005 part of tetrabutoxy titanate were added as a polycondensation catalyst after 5 minutes and heated to 240 ° C. to distill a part of ethylene glycol. It shifted to the polycondensation apparatus which has a stirring blade inside.

  Subsequently, the temperature in the polymerization apparatus was raised from 240 ° C. to 272 ° C. over 90 minutes, and at the same time, the pressure in the apparatus was reduced from atmospheric pressure to 60 Pa. When the stirring torque for rotating the stirring blade in the polymerization apparatus reached a predetermined value, the inside of the apparatus was returned to atmospheric pressure with nitrogen gas to complete the polymerization. The valve at the bottom of the polymerization apparatus was opened and the inside of the polymerization apparatus was pressurized with nitrogen gas, and the polymerized polyethylene terephthalate was made into a strand shape and discharged into water, and the discharged strand was cut by a cutter into chips. Thus, PET having an intrinsic viscosity of 0.54 dl / g and a carboxylic acid terminal group number of 13.8 eq / t was obtained. The properties and polymerization time of the obtained PET are shown in Table 1.

[Examples 2 to 5]
The same operation as in Example 1 was repeated except that the polymerization temperature and the addition amount of phenylphosphonic acid were changed as shown in Table 1. The properties and polymerization time of the obtained PET are shown in Table 1.

[Comparative Example 1]
PET having the intrinsic viscosity of 0.54 dl / g and the number of carboxylic acid end groups of 19.6 eq / t, except that the temperature in the polymerization apparatus is raised from 240 ° C. to 290 ° C. Got. The properties and polymerization time of the obtained PET are shown in Table 1.

[Comparative Example 2]
The same procedure as in Example 1 was performed, except that 0.020 part of triethylphosphonoacetate (17 mmol% based on the number of moles of dimethyl terephthalate) was added instead of phenylphosphonic acid as the phosphorus compound, and the intrinsic viscosity was PET having 0.54 dl / g and a carboxylic acid terminal group number of 14.6 eq / t was obtained. The properties and polymerization time of the obtained PET are shown in Table 1.
The polycondensation reaction time of this PET is about 1.5 times that of the PET of Example 1, and the productivity is remarkably inferior, making it difficult to adopt in production.

[Comparative Example 3]
PET having the intrinsic viscosity of 0.54 dl / g and the number of carboxylic acid end groups of 24.2 eq / t, except that the temperature in the polymerization apparatus was raised from 240 ° C. to 290 ° C. Got. The properties and polymerization time of the obtained PET are shown in Table 1.

[Example 6]
The PET obtained in Example 1 was pre-dried at 160 ° C. for 4 hours, then charged into a rotary tumbler type solid phase polymerization reactor, and subjected to solid phase polymerization at 225 ° C. and a vacuum of 67 Pa or less for 17 hours. A PET having an intrinsic viscosity of 0.78 dl / g and a carboxylic acid end group number of 9.3 eq / t was obtained. The properties of the obtained PET are shown in Table 2.

[Examples 7 to 10]
The same operation as in Example 6 was repeated except that the PET obtained in Examples 2 to 5 was used instead of the PET obtained in Example 1 and the solid phase polymerization time was changed. The properties of the obtained PET are shown in Table 2.

[Comparative Example 4]
The same operation as in Example 6 was carried out except that the PET obtained in Comparative Example 1 was used, and PET having an intrinsic viscosity of 0.79 dl / g and a carboxylic acid terminal group number of 14.1 eq / t was obtained. The properties of the obtained PET are shown in Table 2.

[Comparative Example 5]
The same operation as in Example 6 was performed except that the PET obtained in Comparative Example 3 was used, and PET having an intrinsic viscosity of 0.78 dl / g and a carboxylic acid terminal group number of 18.5 eq / t was obtained. The properties of the obtained PET are shown in Table 2.

  Since the PET production method of the present invention can efficiently produce PET having excellent hydrolysis resistance, it can be suitably used as a method for producing PET, which is a raw material for fibers and films, and particularly requires hydrolysis resistance. As a manufacturing method of the raw material of a molded object, it can use very suitably.

Claims (2)

In a method for producing polyethylene terephthalate in which terephthalic acid or an ester-forming derivative thereof and ethylene glycol are transesterified or esterified to produce a precursor, and the resulting precursor is polycondensed in a molten state,
By the initial stage of the polycondensation reaction, 5 to 100 mmol% of phenylphosphonic acid and a polycondensation reaction catalyst are added in this order, based on the number of moles of all dicarboxylic acid components,
And it is performed until the intrinsic viscosity becomes 0.45 dl / g or more at a temperature of the melting point (Tm: ° C.) or more and 280 ° C. or less of the polyethylene terephthalate capable of obtaining the polycondensation reaction, and the number of carboxylic acid end groups is 15 eq / t or less. A process for producing polyethylene terephthalate, characterized in that 2. The method for producing polyethylene terephthalate according to claim 1 , wherein after the polycondensation reaction in the molten state is completed, solid phase polymerization is further performed until the intrinsic viscosity is in the range of 0.60 to 1.0. 3.