JPH09249744A - Method for treatment of polyester resin - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a process for producing a polyethylene terephthalate or a polyester resin mainly comprising the same, which is usable for bottles, films, sheets, fibers and foams and which is capable of decreasing a stain of a mold during the molding. SOLUTION: In the production of a polyethylene terephthalate having a limiting viscosity of 0.6 to 1.2 or a polyester resin mainly comprising the same through the liquid-phase polycondensation step and solid-phase polymerization step, a wet heat treatment is conducted at a temp. of 150 deg.C to the melting point of the polyester resin minus 10 deg.C for at least 1hr while flowing 1×10<-3> to 1×10<-1> l/hr, per gram of the polyester resin, of an inert gas having a water content of 5×10<2> to 1×10<4> ppm before, after or in the solid-phase polymerization step.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD [0001] The present invention is suitable for bottles, films, sheets, fibers, foams, etc., and is mainly composed of polyethylene terephthalate (PET), which can reduce mold contamination during molding. The present invention relates to a method for treating a polyester resin.

[0002]

2. Description of the Related Art PET resin is excellent in mechanical strength, chemical stability, heat resistance, transparency, gas barrier property, etc.
Since it is lightweight and inexpensive, it is widely used in bottles, films, sheets, fibers, foams, etc., especially for filling carbonated drinks, fruit juice drinks, liquid seasonings, edible oil, liquor, wine, etc. It is suitable as a material for containers.

Such a PET resin can be obtained by esterification of a terephthalic acid component and an ethylene glycol component, liquid phase polycondensation in the presence of a polycondensation catalyst, and then solid phase polymerization.

Then, the PET resin is supplied to a molding machine such as an injection molding machine to mold a bottle preform, and the preform is inserted into a mold having a predetermined shape to perform stretch blow molding or further heat treatment ( It is a general method to heat-set) and mold into a bottle.

However, the PET used in the above method
The resin includes ethylene terephthalate cyclic trimer (CTE
The oligomer such as T) is contained in a considerable amount, and this oligomer adheres to the gas exhaust port of the mold, the exhaust pipe, etc. during stretch blow molding, so that mold contamination is likely to occur. Further, since such mold contamination causes the surface roughness and whitening of the obtained bottle, it is necessary to wash the mold frequently, and there is a problem that productivity is significantly reduced.

Furthermore, when the above PET resin is used to form a film other than the bottle molding by the stretch blow molding method, whitening and dropout of the film are likely to occur. Therefore, it is difficult to produce oligomers such as CTET during molding, and a PET resin having a small content thereof has been desired.

Some proposals have hitherto been made on PET resins in which oligomers such as CTET are hardly generated even when remelted. For example, JP-A-56-118420 proposes a method in which a PET resin produced through a liquid phase polycondensation step is heated in the presence of water to hydrolyze an oligomer contained in the PET resin. Has been done. However, this method has a problem that a large amount of hydrolyzed linear oligomers and monomers adhere to the mold during molding.

Further, in producing a PET resin through a liquid phase polycondensation step and a solid phase polymerization step, hot water or steam treatment is carried out after the solid phase polymerization step to lose the polycondensation catalyst contained in the PET resin. CTE at the time of molding by activating
A method for suppressing the generation of oligomers such as T has been proposed (JP-A-3-174441 and JP-B-7-37515). However, these methods require a hydrothermal treatment device or a steam treatment device in addition to the solid-state polymerization device in order to deactivate the polycondensation catalyst, and have a problem that the cost is increased.

[0009]

DISCLOSURE OF THE INVENTION According to the present invention, C
An object of the present invention is to provide a method for treating PET or a polyester resin containing PET as a main component, which can reduce mold contamination by oligomers such as TET.

[0010]

Means for Solving the Problems As a result of intensive studies for solving the above problems, the present inventors have found that PET or a polyester resin mainly composed of PET is mixed with an inert gas having a specific water content at a specific flow rate. We have found that this object can be achieved by carrying out a moist heat treatment at a high temperature while flowing under the conditions described above, and have reached the present invention.

That is, the gist of the present invention is as follows. After the liquid phase polycondensation process and the solid phase polymerization process, the intrinsic viscosity is
When producing PET of 0.6 to 1.2 or a polyester resin mainly composed of PET, the water content is 5 × 10 ² to before the solid phase polymerization step, after the solid phase polymerization step, or at the same time as the solid phase polymerization step.
While flowing 1 × 10 ⁴ ppm of inert gas at a flow rate of 1 × 10 ⁻³ to 1 × 10 ⁻¹ l / hr per 1 g of polyester resin, 1
A method for treating a polyester resin, which comprises performing a moist heat treatment at a temperature of 50 ° C to (melting point of polyester resin-10 ° C) for 1 hour or more.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below.

The PET or the polyester resin mainly composed of PET according to the present invention is produced mainly with a terephthalic acid component and an ethylene glycol component.

The intrinsic viscosity of polyester resin is 0.6 to 1.2.
And 0.7 to 1.1 is particularly preferable. When the intrinsic viscosity is less than 0.6, the mechanical properties of the molded article will be deteriorated, which is not preferable, and when the intrinsic viscosity exceeds 1.2, the molding temperature needs to be increased, which is not preferable.

In the polyester resin, in addition to the above components,
Aromatic dicarboxylic acid components such as phthalic acid, isophthalic acid, 5-sodium sulfoisophthalic acid, 2,6-naphthalenedicarboxylic acid, 4,4'-diphenyldicarboxylic acid, diphenylsulfonedicarboxylic acid, trimellitic acid, pyromellitic acid, etc. An aromatic polycarboxylic acid and its acid anhydride, oxalic acid, succinic acid, adipic acid, sebacic acid, azelaic acid, aliphatic dicarboxylic acid components such as decanedicarboxylic acid, propylene glycol, 1,2-propanediol,
1,3-propanediol, 1,2-butanediol, 1,3
-Butanediol, 1,4-butanediol, 2,3-butanediol, diethylene glycol, 1,5-pentanediol, neopentyl glycol, triethylene glycol, polyethylene glycol, and other aliphatic diol components, trimethylolpropane, pentaerythritol And other aliphatic polyhydric alcohol components, alicyclic diol components such as 1,4-cyclohexanedimethanol and 1,4-cyclohexanediethanol, aromatic diol components such as ethylene oxide adducts of bisphenol A and bisphenol S,
A copolymerization component such as a hydroxycarboxylic acid component such as 4-hydroxybenzoic acid or ε-caprolactone may be contained within a range that does not impair the characteristics of the PET resin.

Next, a method for producing a polyester resin by the liquid phase polycondensation step will be described.

For example, as a method for producing by a transesterification method, dimethyl terephthalate and ethylene glycol are used, and the transesterification reaction is carried out at a temperature of 160 to 280 ° C. under nitrogen gas to obtain the transesterification reaction product. There is a method of causing a polycondensation reaction. Further, as a method for producing by the direct esterification method, terephthalic acid and ethylene glycol are used, and the esterification reaction is performed at a temperature of 160 to 280 ° C. under nitrogen gas or under pressure, and the obtained esterification reaction product is obtained. There is a method of causing a polycondensation reaction. Furthermore, terephthalic acid and ethylene glycol were added to bis- (β-hydroxyethyl) terephthalate and its low polymer obtained by the esterification reaction of terephthalic acid and ethylene glycol, and the mixture was added at 160 to 280 ° C under nitrogen gas. There is a method in which the esterification reaction is carried out at the temperature of 1, and the obtained esterification reaction product is subjected to a polycondensation reaction.

The polycondensation reaction is usually conducted in the presence of a polycondensation catalyst.
It is carried out at a temperature of 260 to 310 ° C, preferably 275 to 290 ° C under a reduced pressure of about 0.01 to 13.3 hPa. Examples of the polycondensation catalyst include compounds of metals such as antimony, germanium, tin, titanium, zinc, aluminum, magnesium, calcium, manganese, and cobalt, and organic sulfonic acid compounds such as 5-sulfosalicylic acid and o-sulfobenzoic anhydride. It is preferably used. The addition amount of the catalyst is preferably 1 × 10 ⁻⁵ to 1 × 10 ⁻² mol, more preferably 5 × 10 ^{−5 to} 5 × 10 ⁻³ mol, and more preferably 1 ×, to 1 mol of the acid component constituting the polyester. 10 ^-4
It is particularly preferably about 3 × 10 ^-3 mol.

In the production of polyester resin, heat stabilizers such as trimethyl phosphate, triethyl phosphate, triphenyl phosphate, dibutyl phosphate, phosphoric acid and polyphosphoric acid, antioxidants such as hindered phenol compounds and cobalt compounds are used. In addition to such a color tone improving agent, additives such as an ultraviolet absorber and a light stabilizer may be contained.

The polyester resin obtained in the above liquid phase polycondensation step is discharged in a granular form (chip form) from the polycondensation reactor when the polycondensation reaction is completed. It is usually desirable that the chips have an average length of 2 to 5 mm and an average diameter of 1 to 4 mm.

In the present invention, the chips thus obtained are supplied to the next solid phase polymerization step.

The solid phase polymerization is preferably carried out for 10 hours or more at a temperature below the melting point under an inert gas flow or under reduced pressure.
At this time, the polymerization temperature is 10 ° C or more lower than the melting point, and
It is more preferable that the temperature is not lower than ° C. If the temperature is lower than 180 ° C., the rate of decrease of oligomers such as CTET is slow and a long solid phase polymerization time is required, which is not preferable. Further, at a temperature near the melting point, the chips are naturally fused, which is not preferable.

The inert gas means a gas which does not cause deterioration of resin performance in solid-state polymerization of polyester resin, and generally inexpensive nitrogen gas is used. The water content in the inert gas can be arbitrarily selected as long as the intrinsic viscosity of the polyester resin does not decrease during solid phase polymerization, but it is usually preferably less than 5 × 10 ² ppm. In the case of solid-state polymerization under reduced pressure, the degree of reduced pressure is preferably 67 hPa or less.

The polyester resin produced through the above liquid phase polycondensation step and solid phase polymerization step is usually CTET.
The content is 0.60% by weight or less, but since the polycondensation catalyst remains in the resin, if it is remelted during molding, C
TET increases, causing mold contamination.

Therefore, in the present invention, it is necessary to heat-treat the polyester resin before or after the solid phase polymerization step or at the same time as the solid phase polymerization step. In addition, performing wet heat treatment at the same time as the solid-state polymerization step means
The wet heat treatment and the solid-phase polymerization are simultaneously performed while an inert gas having a water content such that the intrinsic viscosity of the polyester resin does not decrease is caused to flow at a specific flow rate. By this treatment, oligomers such as CTET and residuals in the resin remain. It is possible to remove the polycondensation catalyst.

The moist heat treatment in the present invention needs to be carried out while flowing an inert gas. As the inert gas, it is preferable to use the same gas as that used in the solid phase polymerization, and nitrogen gas is usually used. To be The water content in the inert gas must be 5 × 10 ² to 1 × 10 ⁴ ppm, and 1 × 10 ³
〜1 × 10 ⁴ ppm is preferable, 3 × 10 ³ 〜8 × 10 ³ pp
More preferably m. If the water content is less than 5 × 10 ² ppm, the deactivation of the polycondensation catalyst is insufficient, which causes mold contamination during molding of bottles and films, which is not preferable. On the other hand, if the water content exceeds 1 × 10 ⁴ ppm, hydrolysis of the polyester resin occurs and the intrinsic viscosity decreases, which is not preferable.

The flow rate of the inert gas should be 1 × 10 ^-3 to 1 × 10 ^-1 l / hr for 1 g of the polyester resin. Even if the flow rate is less than 1 x 10 ^-3 l / hr, the flow rate is 1 x 10
Even if it exceeds ^-1 l / hr, a polyester resin having a small CTET content cannot be obtained, which is not preferable.

Further, the temperature and time of the wet heat treatment are 150 ° C.
It is necessary to set the temperature at 1 to 60 ° C (melting point of polyester resin -10 ° C) for 1 hour or more, and preferably at 2 hours or more at 160 ° C to 20 ° C (melting point of polyester resin). If the temperature of the moist heat treatment is lower than 150 ° C, it causes mold contamination during molding of bottles and films, which is not preferable. On the contrary, the temperature of the moist heat treatment is (melting point of polyester resin −10
If it exceeds (° C.), the polyester resin will be fused during heat treatment, which is not preferable. Further, if the time of the wet heat treatment is less than 1 hour, it causes mold contamination during molding of bottles and films, which is not preferable.

As the apparatus for performing the wet heat treatment, a rotary solid-state polymerization apparatus, a rotary dryer, a fluidized bed dryer, a dryer having various stirring blades, or the like can be used as long as the polyester resin chips can be uniformly heated. Although any one can be used, it is preferable to carry out the solid phase polymerization and the wet heat treatment using the same apparatus. That is, by using any of the above devices, by adjusting the amount of water in the inert gas and the flow rate, the solid phase polymerization and the wet heat treatment are simultaneously performed without recharging the polyester resin in a separate device. be able to.

The polyester resin obtained by the treatment method of the present invention usually has a CTET content of 0.60% by weight or less, and can be molded into a bottle or a film.

For example, to obtain a bottle, first,
The preform is molded by injection molding or extrusion molding using the same equipment used for blow molding of PET resin. Then, this preform is made into a bottle by applying a biaxial stretch blow molding method such as an injection blow method, a hot parison method or a cold parison method.

To obtain a film, a lubricant or the like is added to the polyester resin, and the film is formed by melt extrusion. Then, this film is biaxially stretched and heat set to obtain a biaxially stretched film.

In addition to bottles and films, the polyester resin obtained by the treatment method of the present invention can be used to make sheets, fibers, foams and the like.

[0034]

In general, the oligomer precipitated from PET or a polyester resin containing PET as a main component has CTET as a main component. The oligomer such as CTET is produced in the liquid phase polycondensation step and is contained in the polyester resin in an amount of about 2% by weight. In order to remove this oligomer, it is preferable to heat-treat the obtained polyester resin at a temperature of at least 150 ° C to (melting point of polyester resin-10 ° C). By exposing the polyester resin to a temperature in this range, the oligomer content in the polyester resin can be reduced regardless of the degree of pressure reduction, the amount of water in the inert gas, and the flow rate of the inert gas. This is because a cyclic oligomer such as CTET undergoes a ring chain equilibrium reaction even in a solid state, and even at a melting temperature or lower, the cyclic oligomer is opened to form a chain oligomer and is removed from the polyester resin.

However, even if the cyclic oligomer such as CTET in the polyester resin is reduced in the above heat treatment step, when the polyester resin is remelted, a considerable amount of cyclic oligomer such as CTET is again formed by the action of the OH end group. However, they are deposited in the mold during molding. However, as in the treatment method of the present invention, a polycondensation catalyst can be obtained by performing a wet heat treatment at a temperature of 150 ° C. to (melting point of polyester resin −10 ° C.) while flowing an inert gas containing an appropriate amount of water at a specific flow rate. Therefore, even if the polyester resin is re-melted, the cyclic oligomer generation rate such as CTET becomes slow, and the mold is not contaminated during molding.

[0036]

EXAMPLES Next, the present invention will be described in detail with reference to examples. In the examples, the characteristic values were measured as follows. (a) Intrinsic viscosity [η] Using an equal weight mixture of phenol and ethane tetrachloride as a solvent, it was measured at a temperature of 20 ° C and expressed in dl / g. (b) CTET content After dissolving a part of a polyester resin chip or bottle in a mixed solvent of hexafluoroisopropanol / chloroform (1/1, volume ratio), it is poured into acetonitrile to precipitate the polymer, and a membrane filter is used. The CTET in the filtrate filtered by 1. was determined by quantifying with a high performance liquid chromatograph (600E, manufactured by Waters).

Example 1 A slurry of terephthalic acid and ethylene glycol in a molar ratio of 1 / 1.6 was continuously fed to an esterification reaction vessel containing bis (β-hydroxyethyl) terephthalate and its low polymer, and the temperature was raised. The reaction was carried out under the conditions of 250 ° C. and a pressure of 50 hPaG, and the residence time was 8 hours to continuously obtain a reaction product having an esterification reaction rate of 95%. After transferring 60 kg of this reaction product to a polycondensation reactor and adding 3 × 10 ⁻⁴ mol of germanium dioxide to 1 mol of a terephthalic acid component, the pressure inside the polycondensation reactor was gradually reduced to finally Liquid phase polycondensation reaction was carried out at a pressure of 0.67 hPa and a temperature of 280 ° C. for 5 hours. When the polycondensation reaction was completed, the polyester resin was discharged from the polycondensation reactor to obtain polyester resin chips having an average length of 4 mm and an average diameter of 2 mm. The [η] of this polyester resin was 0.65. Next, this chip was placed in a rotary solid-state polymerization apparatus, and nitrogen gas with a water content of 10 ppm was added to 1 g of polyester resin.
Flow rate of 2 × 10 ^-2 l / hr against 70 ° C.
After predrying for an hour, it was heated at 130 ° C. for 4 hours for crystallization. Then, a wet heat treatment was carried out at 210 ° C. for 8 hours while flowing a nitrogen gas having a water content of 5 × 10 ³ ppm at a flow rate of 2 × 10 ⁻² l / hr with respect to 1 g of the polyester resin. Finally, wet the moisture-heat treated polyester resin chips with a water content of 4 x 10
² ppm of nitrogen gas is added to 4 x for 1 g of polyester resin.
Solid phase polymerization was carried out at 210 ° C. for 4 hours while flowing at a flow rate of 10 ² ppm l / hr. The [η] of the polyester resin after the solid phase polymerization was 0.70, and the CTET content was 0.40% by weight.
Using polyester resin chips obtained by the above method, each cylinder part and nozzle temperature 280 ℃, screw rotation speed 100 rpm, injection time 10 seconds, mold cooling water temperature 20 ℃
Injection molding machine set to (Abs-50 manufactured by Nissei ASB Co., Ltd.
HT type) was used to mold a preform. Then, this preform was stretch blow-molded in a preheating furnace at 90 ° C., a blow pressure of 2 MPa, and a molding cycle of 10 seconds, and an average wall thickness of the body was 300 μm.
A bottle having an internal volume of 1 liter was produced, compression-tensioned in a mold set at 160 ° C., and then heat set for 10 seconds. The CTET content in the obtained bottle was 0.51% by weight. Further, 2000 bottles were continuously molded under the above conditions, but no mold contamination was observed in any of injection molding, stretch blow molding and heat setting. Table 1 shows characteristic values of the obtained polyester resin and bottle.

Examples 2 to 5 The same as Example 1 except that [η], wet heat treatment conditions and solid phase polymerization conditions of the polyester resin after the liquid phase polycondensation step were changed as shown in Table 1. A polyester resin was produced and used to make a bottle. Table 1 shows characteristic values of the obtained polyester resin and bottle.

Example 6 First, a liquid-phase polycondensation reaction was carried out in the same manner as in Example 1, and when the polycondensation reaction was completed, the polyester resin was discharged from the polycondensation reactor, and the average length was 4 mm and the average length was 4 mm. A polyester resin chip having a diameter of 2 mm was obtained. Then, this chip was placed in a rotary solid-state polymerization apparatus, and nitrogen gas having a water content of 10 ppm was flown at a flow rate of 2 × 10 ^-2 l / hr with respect to 1 g of polyester resin, and pre-dried at 70 ° C. for 2 hours. After doing 130
Crystallization was carried out by heating at ℃ for 4 hours. Next, the water content 2 x
Nitrogen gas of 10 ² ppm is ² for 1 g of polyester resin.
Solid phase polymerization was carried out at 210 ° C. for 10 hours while flowing at a flow rate of × 10 ^-2 l / hr. Finally, the solid-phase polymerized polyester resin chips were heated at 210 ° C. for 8 hours while flowing nitrogen gas having a water content of 5 × 10 ³ ppm at a flow rate of 2 × 10 ⁻² l / hr per 1 g of the polyester resin. The wet heat treatment was performed for an hour. The polyester resin chips obtained by the above method were dried at 130 ° C. for 8 hours under a reduced pressure of 0.67 hPa, and then a bottle was prepared in the same manner as in Example 1. Table 1 shows characteristic values of the obtained polyester resin and bottle.

Example 7 First, a liquid phase polycondensation reaction was carried out in the same manner as in Example 1, and when the polycondensation reaction was completed, the polyester resin was discharged from the polycondensation reactor to obtain an average length of 4 mm and an average length. A polyester resin chip having a diameter of 2 mm was obtained. Then, this chip was placed in a rotary solid-state polymerization apparatus, and nitrogen gas having a water content of 10 ppm was flown at a flow rate of 2 × 10 ^-2 l / hr with respect to 1 g of polyester resin, and pre-dried at 70 ° C. for 2 hours. After doing 130
Crystallization was carried out by heating at ℃ for 4 hours. Then, the water content 1 ×
Nitrogen gas of 10 ³ ppm is 2 for 1 g of polyester resin.
The mixture was heated at 210 ° C. for 18 hours while flowing at a flow rate of × 10 ^-2 l / hr to perform wet heat treatment simultaneously with solid-phase polymerization. A polyester resin chip obtained by the above method was added to 0.67 hPa
After drying under reduced pressure at 130 ° C. for 8 hours, a bottle was prepared in the same manner as in Example 1. Table 1 shows characteristic values of the obtained polyester resin and bottle.

Comparative Examples 1 to 5 In the same manner as in Example 1 except that the [η] of the polyester resin after the liquid phase polycondensation step, the wet heat treatment conditions and the solid phase polymerization conditions were changed as shown in Table 1. A polyester resin was produced and used to make a bottle. Comparative Example 1
The [η] after wet heat treatment decreased to 0.50, and then solid phase polymerization was carried out, but [η] did not rise sufficiently and a bottle that could be put to practical use could not be obtained. Comparative Example 2
In, the polycondensation catalyst was not sufficiently deactivated due to the small amount of nitrogen gas used for the wet heat treatment, and the mold was contaminated during molding. In Comparative Example 3 and Comparative Example 4, the flow rate of nitrogen gas was not appropriate, a part of the polymer or oligomer was hydrolyzed by wet heat treatment, and then solid phase polymerization was carried out, but decomposition products could not be reduced, The mold was contaminated during molding. Comparative Example 5
Since the temperature of the wet heat treatment was low, the polycondensation catalyst was not sufficiently deactivated, and the mold was contaminated during molding. Table 1 shows characteristic values of the obtained polyester resin and bottle.

[0042]

[Table 1]

[0043]

INDUSTRIAL APPLICABILITY According to the present invention, PET or a polyester resin mainly composed of PET, which can be suitably used for bottles, films, sheets, fibers, foams and the like, and which can reduce mold contamination during molding. Obtainable.

Claims (1)

[Claims] 1. When producing a polyethylene terephthalate having an intrinsic viscosity of 0.6 to 1.2 or a polyester resin mainly containing the same through a liquid phase polycondensation step and a solid phase polymerization step,
Before the solid phase polymerization step or after the solid phase polymerization step or at the same time as the solid phase polymerization step, an inert gas having a water content of 5 × 10 ² to 1 × 10 ⁴ ppm is added to 1 g of the polyester resin at 1 × 10 ^-3 〜. 1 x 10
^A method for treating a polyester resin, which comprises subjecting a wet heat treatment to a temperature of 150 ° C to (melting point of polyester resin-10 ° C) for 1 hour or more while flowing at a flow rate of ^-1 l / hr.