JPH02298512A - Production of polyester - Google Patents

Abstract

PURPOSE:To obtain a polyester with a low content of a cyclic compound and hardly any reduction or increase in viscosity by heat-treating a polyester in a specific inert gas atmosphere without flowing the inert gas. CONSTITUTION:A polyester, such as polyethylene terephthalate, is heat-treated at a temperature within the range of the melting point thereof to 80 deg.C lower than the melting point in an atmosphere of an inert gas (preferably nitrogen) with <=1000ppm, preferably <=400ppm moisture content in <=1000ppm, preferably <=50ppm oxygen concentration substantially without flowing the inert gas to afford the objective polyester. Furthermore, the pressure in the heat treatment is preferably 1.05-5.0kg/cm<2>.

Description

[Detailed description of the invention] [Industrial application field 1 The present invention relates to a method for producing polyester.

More specifically, the present invention relates to a method for producing a polyester that has a low content of cyclic compounds and a small decrease in viscosity or increase in viscosity.

``Prior Art'' Polyesters, represented by polyethylene terephthalate, have excellent physical and chemical properties, and therefore have high industrial value (and are widely used in fibers, films, molded products, etc.).

Such polyesters are usually so-called linear polymers produced by a polycondensation reaction from a dicarboxylic acid component and a diol component or an oxycarboxylic acid component.

However, for example, "Polymer Chemistry" by P.J. Flory (co-translated by Koten Oka and Kyo Kanemaru, published by Maruzen Publishing)
As described in et al., a cyclic compound is generated in a linear polymer based on an equilibrium relationship with a linear compound.

The lower the molecular weight of a cyclic compound, the greater the amount produced. Therefore, these low molecular weight cyclic compounds may precipitate from time to time during the molding process or in the form of a product. It is also known that when used, a large amount is extracted and causes troubles due to these low molecular weight cyclic compounds.

Various reports have been made regarding these cyclic compounds; for example, regarding polyethylene terephthalate,
The main component of the cyclic compound is a cyclic trimer, which is produced in an equilibrium reaction during the polycondensation reaction of polyethylene terephthalate, for example, Polymer 1384.
It was reported by Jay Guttman et al. (1960).

In addition, methods for reducing cyclic compounds have been proposed, for example, in the
Publication No. 1-4.8505, JP-A-49-101-462
JP-A No. 53-1-01092, etc., propose an in-phase polymerization method in which heat treatment is performed at a temperature of 180° C. to the melting point under reduced pressure or under inert gas flow. These contain 1-13 to 1.7% by weight of cyclic compounds, which are normally contained in polyethylene terephthalate.
．． It is disclosed that the amount can be reduced to 5% by weight or less.

However, with the technique of reducing cyclic compounds by such a known solid phase polymerization method, although the amount of cyclic compounds can certainly be reduced, the polycondensation reaction of polyester also proceeds at the same time, resulting in a large increase in the degree of polymerization. It was unsuitable as a raw material for manufacturing molded products due to its low content.

In other words, when the degree of polymerization of polyester increases, the viscosity of the polymer when melted during molding increases, and its slickness (
, the load during extrusion increases, and the polymer temperature rises due to shear heat generation, resulting in problems such as thermal decomposition.

In order to solve such problems, the degree of pressure reduction during solid phase polymerization is adjusted (Japanese Patent Application Laid-Open No. 55-89331), and the flow rate of inert gas is adjusted (Japanese Patent Application Laid-Open No. 55-89330). A method has been proposed. However, even with this method, the degree of polymerization of the polyester obtained fluctuates, making it difficult to industrially obtain polyester of constant quality.

Furthermore, in JP-A-56-118420, cyclic compounds are selectively hydrolyzed by heating in the presence of water in the range of 1-40°C to melting point in the same phase state, and the cyclic compounds are The following methods for reducing this are proposed. However, even with this method, there were still problems such as a decrease in the degree of polymerization due to hydrolysis of the linear polyester.

[Problem B to be Solved by the Invention] The present invention is to solve the above-mentioned problem. That is, an object of the present invention is to produce a polyester having a low content of cyclic compounds and suitable for molding with good reproducibility and productivity.

[Means for Solving the Problems] The object of the present invention described above is to provide an inert gas atmosphere with a water content of 11,000 pp or less and an oxygen concentration of 1,000 pp rr+ or less, and which is substantially free of inert gas. During distribution, polyester is heated to its melting point or below its melting point.
This can be achieved by a polyester manufacturing method characterized by heat treatment at a temperature in the range of 0°C or lower.

Polyester in the present invention refers to terephthalic acid, 2,6
-naphthalenedicarboxylic acid, diphenyldicarboxylic acid,
Aromatic dicarboxylic acids such as inphthalic acid, adipic acid,
Dicarboxylic acid components such as aliphatic dicarboxylic acids such as sebacic acid, alicyclic dicarboxylic acids such as hexahydroterephthalic acid and hexahydroisophthalic acid, and glycol components such as ethylene glycol, butanediol, and cyclohexane dimetatool. It is a polyester obtained from, specifically, polyethylene terephthalate-1-,
Examples include polybutylene terephthalate and polyethylene naphthalate. Among these, polyethylene terephthalate is particularly preferable because it has a large influence as a cyclic compound.

Further, the polyester may be a homopolymer or a copolymer, and as the copolymer component, one or more of the above-mentioned dicarboxylic acids and diols can be used, and polyethylene glycol, polybutylene glycol, etc. Polyalkylene glycols, 5-sodium sulfoisophthalic acid, hydroxycarboxylic acids such as hydroxyethoxybenzoic acid, etc. can also be used.

Hereinafter, explanation will be given using polyethylene terephthalate, which is a typical polyester.

The starting material polyester used in the present invention is produced by conventionally known esterification reactions, transesterification reactions, and subsequent polycondensation reactions.

For example, polyethylene terephthalate is usually produced by esterifying or transesterifying terephthalic acid or dimethyl terephthalate and ethylene glycol, followed by polycondensation under reduced pressure. Here, Mn, Mg, Ca, Ti, Ge, which are conventionally known as catalysts, etc.
.

Sb, Co compounds and phosphorus compounds can be used. Further, stabilizers, pigments, dyes, nucleating agents, fillers, etc. may be used.

1. The polyester thus obtained is shaped into appropriate particles by sheet cutting, strand cutting, or the like. The shape of the particles may be arbitrary, but if the shape is too small and becomes a fine powder, it will cause trouble in the heat treatment process and subsequent molding process. If the shape is large, this is not a particular problem in terms of reducing the amount of cyclic compounds, but it is a problem in terms of operability. Therefore, the size of polyester particles is 1 mm to 50 mm in equivalent spherical diameter.
is preferable, and more preferably 2 mm to 20 mm.

Note that the equivalent spherical diameter here is the diameter of a sphere having the same volume as the particle.

The intrinsic viscosity of the polyester used in the present invention is preferably 0.4 or more. If the intrinsic viscosity is lower than 0.4, problems with poor moldability such as thread breakage during spinning, membrane tearing during film formation, and damage during molding are likely to occur, and if the intrinsic viscosity is too high, molding The temperature rises due to shear heat generation of the special melt resin, and it is necessary to set the molding resin temperature high to improve melt moldability, and as a result, cyclic compounds are likely to be generated in the product. In particular, it is preferable to use one having an intrinsic viscosity of 0.45 or more and 0.90 or less.

In the present invention, the heat treatment temperature is within the range of the melting point of the polyester used or 80° C. lower than the melting point. For ordinary polyethylene terephthalate, the temperature is preferably 190°C or higher and lower than 260°C, particularly preferably 200°C or higher and 250°C or lower. If the heat treatment temperature is lower than 190° C., the rate of reduction of the cyclic compound is unfavorable.

If the temperature exceeds 260°C, the polymer will dissolve and the cyclic compound will not be reduced even if heat treatment is performed. Therefore, the heat treatment must be performed at a temperature below the melting point of the polymer.

The heat treatment time is usually 2 hours or more and 60 hours, preferably 3 hours or more and 40 hours. When the time is shorter than 2 hours, the effect of reducing the cyclic compound is small, and when it is longer than 60 hours, the rate of reduction of the cyclic compound becomes slow, and problems such as thermal deterioration become serious.

The inert gas used in the present invention may be any gas inert to the polyester, and examples thereof include nitrogen, helium, carbon dioxide, etc. Nitrogen is preferably used from the viewpoint of economy.

In the method of the present invention, the atmosphere during heat treatment is important. Since polyester is susceptible to oxidative decomposition and hydrolysis due to oxygen and moisture, it is necessary to control oxygen and moisture in the atmosphere. The moisture content in the atmosphere is -000p
pm or less, more preferably 500 ppm or less, still more preferably 400 ppm or less. If the amount of water in the atmosphere exceeds 1-000 ppm, the amount of cyclic compounds will decrease, but at the same time the polyester will be hydrolyzed and the intrinsic viscosity of the resulting polymer will decrease, which is not preferable. However, it is more preferable that the water content is not lower than 1 ppm. This is because when the water content is less than lppm,
Increasing the purity of the inert gas not only complicates the process, but also tends to reduce the rate of reduction of cyclic compounds. In addition, the oxygen concentration is 11,000 pp or less, preferably 5
00 ppm or less, more preferably 1100 ppm or less, most preferably 50 ppm or less.
If it does not exceed 1000 pp, the polyester will deteriorate.

Further, in the present invention, it is preferable to heat-treat the polyester by placing the inside of the heat-treating tank in a slightly pressurized state using the above-mentioned inert gas. The pressure of heat treatment is 1.05-5
．． 0kg,/Cm2, more preferably 1.10-2.0
kg/cm2. The pressure inside the tank is 1.05kg/'c
If it is less than m2, as the polyester particles move within the tank, oxygen and moisture in the atmosphere will be mixed in, causing a decrease in the intrinsic viscosity and easily causing oxidative decomposition and hydrolysis, which is not preferable. Moreover, if it exceeds 5.0 kg/cm2, the equipment becomes expensive and undesirable.

The heat treatment apparatus used in the present invention is preferably one that can uniformly heat polyester.

Specifically, a stationary dryer, a rotary dryer, a fluidized dryer, a dryer having various stirring blades, etc. can be used.

Further, in the present invention, it is preferable to appropriately remove moisture from the polyester before heat treatment. Furthermore, it is more preferable to partially crystallize the polymers in order to prevent fusion between the polymers during heat treatment.

"Examples" The present invention will be explained in more detail below with reference to Examples. In the Examples, all "parts" represent parts by weight.

(Quantification of cyclic compounds in polyester) Polyester 1
0 mg g to 1-ml 1. ．． Dissolve 1,2゜2-tel in chloroethane by heating at 200°C for 110 minutes in a glass ampoule, and after cooling, dilute the contents with chloroform to make 25ml. The analysis was carried out using a high performance liquid chromatograph (LC-802U R) using chloroporm as a developing solvent.

(intrinsic viscosity) It was measured at 25°C using orthochlorophenol.

Example 1 100 parts of dimethyl terephthalate, 7 parts of ethylene glycol
0 parts and 0.09 parts of calcium acetate into the reactor and 18
A transesterification reaction was performed at 0 to 210°C, and methanol was distilled off. When the transesterification reaction was completed, 0.02 parts of phosphoric acid and 0.03 parts of antimony trioxide were added, and the pressure in the system was gradually reduced to 1 mm in 60 minutes.
It was set to be below Hg. At the same time, the temperature was gradually raised to 290°C. The polycondensation reaction was carried out for 2 hours, and then extruded into water from a discharge nozzle and used with a cutter to form particles with a diameter of about 5 mm and a length of about 7 mm.
mm cylindrical chip. (The equivalent spherical diameter of the polymer is 6.4 mm.) The intrinsic viscosity of the obtained polymer is 0.650, the carboxy end group concentration is 25 equivalents/106 g polymer, and the amount of cyclic trimer in the polymer is 1 -13% by weight.

The obtained polymer was dried at 150° C. under reduced pressure, and then the system was slightly pressurized to 1.20 kg/crW with nitrogen gas.

The oxygen concentration in the reaction system was 50 ppm, and the water content was 10 ppm. The system is maintained at this pressure (no flow is maintained), temperature 2/IO'
Remove the polymer after carrying out the heat treatment for 9 hours at c. The i′L polymer obtained had an intrinsic viscosity of 0.645, a carboxy end group concentration of 28 units, and an it/106 g polymer. The amount of cyclic trimer in the polymer was 0.40% by weight.

The treated polymer was extruded at 285°C using an extrusion molding machine,
An unstretched sheet having a thickness of 150 μm was obtained.

During extrusion, it was possible to extrude without pressure increase, similar to the untreated polymer. 3 in the longitudinal direction to this unstretched sheet
．． Roll stretched 3 times, then 3°3 in the transverse direction with a dentist.
After double stretching, heat setting was performed at 200° C. for 6 seconds to obtain a biaxially stretched film with a thickness of 1 to 4 μm. The amount of cyclic trimer in the film was 0.60% by weight.

Example 2 Polyethylene terephthalate was synthesized by polycondensation reaction in the same manner as in Example 1, and a square with sides of about 6 mm and a thickness of about 2 m was prepared.
m rectangular parallelepiped polymer (the equivalent spherical diameter of the polymer is 5.
2mm). The intrinsic viscosity of the obtained polymer is 0.63
5, and the carboxy end group concentration is 28 equivalents/106g
It was a polymer, and the amount of cyclic 31 bodies in the polymer was 1.3% by weight.

The obtained polymer was dried at 150° C. under reduced pressure, and then the inside of the system was slightly pressurized to 1.5 kg/− with nitrogen gas. The oxygen concentration in the system was 45 ppm, and the water content was 13 ppm. After heat treatment was carried out at a temperature of 230° C. for 9 hours, the polymer was taken out. The resulting polymer had an intrinsic viscosity of 0.625 and a carboxy end group concentration of 32 equivalents/106 g polymer.

The amount of cyclic trimer in the polymer was 0.45% by weight.

Comparative Example 1 Cyclic trimer synthesized in Example 1 concentration 1.3 times 1
Amount %0 melt polymerized boria ・Poly under normal pressure? Example 1 except that nitrogen gas was distributed at a rate of 60 parts per 1 kg.
Heat treatment was carried out in the same manner.

The amount of cyclic trimer in the obtained polymer was 0.40% by weight. The intrinsic viscosity of the polymer was 0.80, and the carboxy end group concentration was 20 equivalents/106 g of polymer.

When this polymer was extruded in the same manner as in Example 1, the load on the extruder was too large and normal extrusion was not possible.

Comparative Example 2 The polymer synthesized in Example 1 with a cyclic trimer concentration of 1.3% by weight was dried at 150°C under reduced pressure, and then the system was slightly charged with nitrogen gas at a rate of 1.5 kg/csR. I put pressure on it. The oxygen concentration in the reaction system was 1500 ppm, and the water content was 15 ppm. The system is maintained at this pressure (no flow is maintained in the system), and the temperature is 230
The polymer was taken out after heat treatment at .degree. C. for 9 hours. The cyclic trimer in the obtained polymer was 0.45% by weight, the intrinsic viscosity of the polymer was 0.510, and the carboxy end group concentration was 80 equivalents/1-06 g of polymer.
It was a polymer with a large decrease in viscosity and a high concentration of carboxy end groups.

Subsequently, film formation was carried out in the same manner as in Example 1, but the membrane was frequently broken during film formation and could not be formed into a film.

Comparative Example 3 In Comparative Example 2, the oxygen concentration in the system was 1500 ppm.
A heat treatment was performed for 9 hours in the same manner as in Comparative Example 2 except that the moisture content was 1500 ppm. The cyclic trimer content in the obtained polymer was 0.35% by weight, the intrinsic viscosity was 0.410,
The carboxy end group concentration was 90 equivalents/106 g polymer.

Example 3 Heat treatment was carried out in exactly the same manner as in Example 1, except that the moisture content in the system was changed to 0.5 ppm. The resulting polymer had an annular 3-terminus of 0.5% type nests.

Comparative Example 4 The vacuum-dried polymer obtained in Example 2 was dried at an oxygen concentration of 50 ppm,
After replacing the inside of the system with nitrogen gas containing 10 ppm of moisture, heat treatment was performed at 240°C for 9 hours under atmospheric pressure (L 01.3 kg/cm2), and then the polymer was taken out. The oxygen concentration in the system at this time was 4000 ppm. The resulting polymer had a cyclic trimer content of 0.4% by weight, an intrinsic viscosity of 0.490, and a carboxy terminal group concentration of 80 equivalents/106 g of polymer.

Comparative Example 5.6 In Example 1, the temperature in the system was set to 170°C and 265°C.
The heat treatment was carried out in the same manner as in Example 1, except that the temperature was changed to ℃. At 170°C, the cyclic 3x form was 1.3% by weight and did not decrease at all. On the other hand, in the case of 265° C., the polymer was fused to the inner wall of the device, and the cyclic trimer content was 1.2% by weight, so no reduction effect was observed.

[Effects of the Invention] According to the present invention, only cyclic compounds can be reduced with good productivity and at low cost without substantially changing the intrinsic viscosity of the raw material polymer. Polymers with a normal intrinsic viscosity and reduced cyclic compounds can be spun, drawn, film-formed, and molded without changing the conditions normally used, and are free from oil contamination and film-forming during spinning. This makes it possible to prevent contamination of casting and stretching equipment.

Further, defects caused by precipitation of cyclic compounds can be prevented when the molded product is used, and it can be effectively used for fibers, films, bottles, etc. It is particularly effective as food containers, packaging, magnetic tapes, and electrical insulation films.

Claims (2)

[Claims] (1) Moisture content is 1000 ppm or less, oxygen concentration is 100
A method for producing polyester, which is characterized by heat-treating the polyester at its melting point or at a temperature in the range of 80°C lower than its melting point in an inert gas atmosphere having a concentration of 0 ppm or less and without substantially inert gas flow. Production method. (2) Pressure during heat treatment is 1.05 to 5.0 kg/cm
^2. The method for producing polyester according to claim (1).