JP2008169328A - Method for producing polyester composition - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for efficiently producing a polyester composition scarcely having an oligomer content and suitable for production of a thick film. <P>SOLUTION: The invention relates to a method for producing a polyester composition (B) having intrinsic viscosity and a polymer powder content appropriate for producing a film and a reduced content of oligomers, by subjecting a polyester composition (A) comprising a dicarboxylic acid component mainly composed of terephthalic acid or its ester-forming derivatives and a diol component mainly composed of ethylene glycol, to a heat treatment in a temperature range between 205°C and 235°C, by circulating a heated inert gas in a fluidized type vertical heat treatment device provided with an agitator. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for producing a polyester composition. More specifically, the present invention relates to a method for producing a polyester composition having a low oligomer content and particularly having an intrinsic viscosity suitable for producing a polyester film.

  Conventionally, polyester compositions typified by polyethylene terephthalate are excellent in physical and chemical properties, and thus have high industrial value and are widely used as fibers, films, molded articles and the like.

  In particular, films using polyethylene terephthalate are widely used in IT-related applications such as liquid crystal display panel members, CRT surface protection, and magnetic recording medium members because of their transparency, strength, and availability of raw materials. is there.

  However, the oligomer is present in the polyester in an amount of about 1 to 2% by weight, mainly a cyclic trimer. In the film forming process, the oligomer may be deposited on the film surface, which may cause deterioration in product quality such as whitening or a decrease in transparency.

  As a method for reducing oligomers, a solid-phase polycondensation method in which heat treatment is performed at a temperature of 200 ° C. to the melting point of polyester under reduced pressure or in an inert gas flow has been proposed. Among these, it is disclosed that the amount of oligomer of 1.3 to 1.7% by weight usually contained in polyethylene terephthalate can be reduced to 0.5% by weight or less (see Patent Document 1 and Patent Document 2).

  However, in the technique for reducing oligomers by the known solid-phase polycondensation method, the amount of oligomers can surely be reduced, but at the same time, the polycondensation reaction of the polyester composition proceeds and the intrinsic viscosity increases. There was a problem that the polymer temperature was raised by shearing heat generation at the time of melting, resulting in oligomer regeneration and color deterioration.

  Moreover, in order to solve the problem of increasing the intrinsic viscosity, a method of adjusting the flow rate of the inert gas during solid phase polycondensation, a method of circulating an inert gas containing a glycol component in the presence of pressure, There has been proposed a method in which a solid-state polymerization treatment is performed and then a wet heat treatment is performed to make the intrinsic viscosity of the polymer equivalent to that before the treatment (see Patent Documents 3 and 4 and Patent Document 5).

  However, when the present inventors examined this method, in order to reduce to the target oligomer amount, a large amount of polymer powder was generated during a long-time treatment, but this polymer powder received a heat history from the product. Because of its ease, it has a high melting point selectively, cross-linking due to oxidation or thermal degradation, and it is mixed into the product in an unmelted state during molding, which may be a defect of the molded product, especially in the film production process There were problems in terms of quality and productivity, such as the starting point of fracture.

  Therefore, it is important to remove the polymer powder in the product, and it has been proposed to provide a removal step after the heat treatment (Patent Document 6).

  However, the amount of polymer powder generated during heat treatment has a distribution in the amount and heat history, so when polymer powder is removed after heat treatment, there is a lot of polymer powder that has stochastically received heat history on the product side. Therefore, it is difficult to effectively suppress an increase in product defects and a decrease in productivity in the next process due to variations among lots. Moreover, since it is necessary to add a removal process further, it becomes a problem also in an energy side and an installation cost side.

  On the other hand, a solid-phase polymerization method has been proposed that uses a fluidized vertical solid-phase polymerization apparatus having a stirrer to remove the polymer powder and prevent the pellets from fusing due to their own weight, which is a drawback of the apparatus. (Patent Document 7).

  Such a method is a method of effectively reducing the polymer powder that has been heated while removing the polymer powder generated during the heat treatment and has undergone a thermal history. However, since the intrinsic viscosity increases, The polymer temperature was increased by shearing heat generation at the time of melting, and the oligomer was regenerated and the color tone deteriorated.

In addition, a thick film using a polyester composition is usually produced by biaxial stretching in the vertical and horizontal directions after extrusion from a die. This longitudinal stretching is usually performed by a stretching method using a number of heated rolls. However, according to the study by the present inventors, if the amount of the carboxyl end group of the polyester composition is small, the adhesiveness between the film and the roll is lowered during longitudinal stretching, and a difference occurs between the roll peripheral speed and the passing speed of the film. As a result, it was found that scratches were generated on the polyester film of the product. The occurrence of this scratch was significant in the production of a thick film having a product thickness with a high stretching tension exceeding 30 μm. That is, in the methods of Patent Documents 1 and 6, the amount of carboxyl terminal groups of the polyester is reduced, and there is a problem that a scratch is generated when a thick film is formed.
JP 49-032973 A JP-A-53-101092 JP 55-89330 A JP-A-8-120062 JP 2006-265275 A JP 2003-160657 A Japanese Patent Laid-Open No. 11-158259

  An object of the present invention is to provide a method for efficiently producing a polyester composition having a low oligomer content, an intrinsic viscosity suitable for film molding, and further capable of suppressing unmelted foreign matters generated during molding.

The object of the present invention can be achieved by the following method.
That is, a polyester obtained by esterifying or transesterifying a dicarboxylic acid component containing terephthalic acid or an ester-forming derivative thereof as a main component with a diol containing ethylene glycol as a main component, followed by a polycondensation reaction. By subjecting the composition (A) to pellets having an intrinsic viscosity (C) of 0.52 dl / g or more and 0.68 dl / g or less, and performing treatments that satisfy the following (a), (b), and (c) And a polyester composition (B) having an intrinsic viscosity (D) of 0.50 dl / g or more and 0.70 dl / g or less and an oligomer content of 0.4 wt% or less. Manufacturing method.
(A) In a flow type vertical heating apparatus having a stirrer, a circulating gas is circulated so that the pellet filling volume in the apparatus is 1.03 to 1.18 times that at the time of standing, and the polyester composition (A) A step of circulating solid inert gas while removing polymer powder of the same component from the circulating gas, and solid-phase polymerization in a range where the heat treatment temperature of the pellet is 205 ° C. or higher and 235 ° C. or lower.
(B) A step of subjecting the pellets obtained in (a) to the same filling volume as in (a) and circulating a heated mixed gas having a moisture content of 60% or more and less than 98% to wet-heat-treat the polymer.
(C) The relationship between the intrinsic viscosity (C) of the polyester composition (A) and the intrinsic viscosity (D) of the treated polyester composition (B) is −0.05 dl / g ≦ (D) − (C) ≦ 0.05 dl / g is satisfied.

  According to the present invention, the content of the oligomer is small, the amount of polymer powder that may be converted into a foreign substance during molding is suppressed, and the polyester composition having an intrinsic viscosity and an amount of carboxyl end groups particularly suitable for a medium-thick film is efficient. Can be produced. That is, a polyester that is generally produced and does not require any low oligomerization, and is a low-oligomerized polyester composition that is suitable for medium-thickness films. A composition can be produced.

  In the polyester composition of the present invention, a dicarboxylic acid component containing terephthalic acid or an ester-forming derivative thereof as a main component and a diol containing ethylene glycol as a main component are subjected to an esterification reaction or a transesterification reaction, followed by a polycondensation reaction. The polyester composition manufactured by this. Furthermore, you may contain a copolymerization component in 0-20 mol%. Examples of copolymer components include aromatic dicarboxylic acids such as 2,6-naphthalenedicarboxylic acid, diphenyldicarboxylic acid, and isophthalic acid, aliphatic dicarboxylic acids such as adipic acid and sebacic acid, hexahydroterephthalic acid, and hexahydroisophthalic acid. A dicarboxylic acid component represented by an alicyclic dicarboxylic acid or the like, an oxycarboxylic acid such as 5-sodium sulfoisophthalic acid or hydroxyethoxybenzoic acid, or the like can also be used. Further, as diols other than ethylene glycol, glycol components such as butanediol and cyclohexanedimethanol, and polyalkylene glycols such as polyethylene glycol and polybutylene glycol can also be used.

  Hereinafter, description will be made with polyethylene terephthalate, which is a typical polyester composition.

  The starting polyester composition (A) used in the present invention is terephthalic acid or dimethyl terephthalate and ethylene glycol, subjected to an esterification reaction or a transesterification reaction at 120 to 255 ° C. under normal pressure or slight pressure, After obtaining bishydroxyethyl terephthalate or its oligomer, it can be produced by a polycondensation method at 200 to 300 ° C. under reduced pressure.

  Here, conventionally known titanium compounds, germanium compounds, and antimony compounds can be used as the polycondensation catalyst, but antimony compounds are most suitable in terms of the influence on cost and color tone, and further oligomers reduced by heat treatment. In order to suppress regeneration during molding, the amount of the antimony element is preferably 0.005 wt% to 0.020 wt%, and more preferably 0.005 wt% to 0.012 wt%. By setting the content to 0.005% by weight or more, a sufficient polymerization rate in the solution polycondensation stage can be obtained, and a polymer having a good color tone can be obtained within an appropriate reaction time. Moreover, the reproduction | regeneration speed | rate of the oligomer in a film manufacture stage can be suppressed by making it 0.020 weight% or less, and the amount of oligomers in a film can be reduced.

  The polyester composition of the present invention contains, as additives, metal compounds such as manganese, magnesium, calcium and cobalt, or alkali metal salts and alkaline earth metal salts such as lithium acetate, sodium acetate, potassium acetate, magnesium acetate, water Magnesium oxide, magnesium alkoxide, magnesium carbonate, potassium hydroxide, calcium hydroxide, calcium acetate, calcium carbonate and the like can be added.

  Further, phosphorus compounds as stabilizers, such as phosphoric acid, trimethyl phosphate, triethyl phosphate, tri-n-butyl phosphate, trioctyl phosphate, triphenyl phosphate, tricresyl phosphate, dibutyl phosphate, monobutyl phosphate, triethyl phosphonoacetate, Tris (triethylene glycol) phosphate, phosphorous acid, dioctyl phosphate, triphenyl phosphite, trisdodecyl phosphite, trisnonyl phenyl phosphite, methyl acid phosphate, ethyl acid phosphate, triethylene glycol acid phosphate, isopropyl acid phosphate Butyl acid phosphate may be used.

  Further, pigments, dyes, nucleating agents, fillers and the like may be used.

  The polyester composition thus obtained is formed into an appropriate pellet by a sheet cutting method, a strand cutting method, or the like.

  The polyester composition obtained by the above polycondensation, that is, the intrinsic viscosity (C) of the polyester composition (A) before the heat treatment is preferably 0.52 dl / g or more and 0.68 dl / g or less, and more preferably 0.54 dl / g. More preferably, it is at least 0.65 dl / g and below. When the intrinsic viscosity is 0.52 dl / g or more, it is advantageous in that a necessary strength can be obtained when the film is used for manufacturing a film, and it is possible to reduce film breakage and breakage of a molded product. Further, by setting the intrinsic viscosity to 0.68 dl / g or less, it is possible to suppress an increase in temperature due to shearing heat generation during melt molding, and it is advantageous in reducing the amount of oligomers in the product.

  In order to reduce the oligomer amount of the obtained polyester composition pellets, a wet heat treatment is performed following the solid phase polymerization. In the heat treatment, a good polyester composition free from product defects can be most efficiently produced by using a fluid type vertical drying apparatus having a batch type stirrer.

  A suitable apparatus will be specifically described with reference to FIG. This apparatus discharges the pellets to the heat treatment tower 2 consisting of a combination of a vertical cylinder and an inverted conical lower part, the raw material polyester pellet inlet 1, the circulating inert gas supply port 12, the exhaust port 13, and the heat treatment. A discharge port 5 is provided. The stirring unit inside the apparatus is composed of a stirring shaft 4 having a plurality of horizontal stirring blades 3.

  The flow of the inert gas is cooled by the heat exchanger 7 from the exhaust port 13 through the dust collector 6, circulated from the circulation blower 10 via the cooling tower 8 or the bypass 9, and finally is heated to a predetermined temperature by the heater 11. The temperature is raised to 2 and supplied to the heat treatment tower 2.

  The inert gas to be circulated is not particularly limited as long as it is inert to the polyester composition, and examples thereof include nitrogen, helium, carbon dioxide gas, etc. Nitrogen is preferably used from the viewpoint of economy.

  As a heat treatment method, first, an inert gas is continuously supplied, and the stirring shaft 4 is further rotated. In this state, pellets of the raw material polyester composition are quantitatively charged from the pellet inlet 1. After the completion of the charging, the temperature of the inert gas circulated from the inert gas supply port 12 through the cooling tower 8 is gradually raised to a predetermined temperature, and then raised to the solid-phase polymerization temperature while observing the dry state of the pellets. Solid state polymerization is carried out by keeping it warm. After reaching the target quality, the mixed gas is supplied through the mixed / inert gas supply line 15 and the wet heat treatment is started while maintaining a predetermined temperature and moisture content. In the meantime, the circulation uses the bypass 9 together and maintains the temperature and moisture content until the polyester pellets reach a predetermined quality. After reaching a predetermined quality, the inert gas that circulates immediately passes through the cooling tower 8 and is switched to cooling air, and the polyester pellets are cooled to 100 ° C. or lower. The polyester pellets after the heat treatment are discharged from the pellet discharge port 5.

  Moreover, the pellets in the tower of the heat treatment tower 2 of the present invention are kept in a floating state in order to prevent fusion of the pellets in the lower part of the heat treatment tower 2 due to their own weight. Specifically, in a state where circulating gas is circulated, a predetermined amount of polyester pellets is introduced from the pellet inlet 1 and then the inert gas circulation flow rate is controlled so as to float the pellets. At that time, the filling volume of the pellet is preferably 1.03 to 1.18 times that at the time of standing, preferably 1.05 to 1.15 times, and more preferably 1.07 to 1.14 times. If it is less than 1.03 times, there arises a problem that fusion due to the weight of the pellet occurs at the lower part of the heat treatment tower and the discharge becomes impossible. On the other hand, if it exceeds 1.18 times, the scattering of the pellets becomes severe and the production yield is lowered, and there is a problem that irregular shaped pellets are generated due to collision with the inner wall and the like, and the transportation pipe is blocked.

  In order to float the pellets uniformly, it is desirable to make the supply direction and the supply speed of the inert gas uniform. For example, the pellets may be supplied through a plate provided with many holes smaller than the pellet size.

  Further, the flow rate of the circulating inert gas in the tower is preferably in the range of 0.4 to 1.0 m / s. At this time, in order to suppress the scattering of the pellet, a pellet scattering prevention plate may be attached. The shape is not particularly limited. For example, there is a method of installing a wire mesh smaller than the pellet size in the inert gas exhaust port.

  Controlling the heating rate for solid-phase polymerization of the polyester pellets is effective for preventing fusion. In the present invention, the object can be further achieved by heating and heating in the range of Tg-5 ° C to Tg + 15 ° C at a rate of 0.3 ° C / min or less. Preferably it is 0.2 degrees C / min or less. If it exceeds 0.3 ° C./minute or more, fusion is likely to occur particularly in the case of copolymerized polyester pellets.

  As the most important feature of the present invention, it is important to remove polymer powder generated with the progress of heat treatment.

  The polymer powder is defined by the measurement method of the embodiment, but when the pellets before heat treatment are supplied to the apparatus, the powder is subjected to heat treatment generated by contact with piping or contact between pellets during heat treatment or with apparatus members. Mainly refers to the same composition as the polyester composition.

  The method for discharging the polymer powder is not particularly limited, and can be achieved, for example, by installing a filtration dust collector, a cyclone dust collector or the like in an inert gas circulation device. That is, the polymer powder is separated from the pellets with the gas circulated to form a fluidized bed, introduced into the circulation device, and removed by the dust collector 6. As a result, the polymer powder having a large surface area that is easily affected by thermal deterioration during the treatment can be removed very efficiently, and the product quality can be improved. In particular, the amount of polymer powder is preferably 700 ppm or less, more preferably 500 ppm or less, based on the product pellets. By setting the pellet powder to 700 ppm or less, the probability of being a defect of the product as an unmelted foreign substance at the time of molding is suppressed to an extremely low level, and at the same time, the break starting from the defect is reduced at the time of film forming, thereby improving productivity. This is advantageous.

  In addition, when the polymer powder is removed by a vibration sieve or a cyclone classifier after heat treatment, a new device needs to be provided, and further energy load is required. In addition, when the polymer powder is removed after the treatment, the polymer powder that has received a thermal history that adversely affects the molded product remains probabilistically, which is not an effective means for the purpose. That is, by continuously removing the polymer powder generated during the heat treatment period, the heat history received by the remaining polymer powder can be made uniform among lots, and the influence on the molded product can be minimized. Can do. The inert gas from which the polymer powder has been removed is returned again into the heat treatment apparatus. At this time, the inert gas only needs to supplement the amount of heat lost by heat dissipation via the heater 11.

  In particular, in order to remove moisture and the like in the initial stage of heating at 150 ° C. or lower and in the solid phase polymerization circulating gas, the circulating gas is supplied via the cooling tower 8 or the molecular sieve, and a small amount of inert gas is supplied to maintain the dew point. Good. What is important here is that the chip can once reduce the target cyclic trimer by solid-phase polymerization, and then the intrinsic viscosity increased during the solid-phase polymerization can be reduced to a predetermined value by wet heat treatment. is there. By doing so, the time required for the entire treatment can be shortened and a polymer having a good color tone can be obtained. Further, during the wet heat treatment, in order to control the moisture content of the gas supplied to the heat treatment tower, it is possible to adjust the moisture content in the circulated gas by adjusting the amount by which the cooling tower 8 or the molecular sieve is bypassed. I can do it. Furthermore, for example, a tank filled with pure water is also provided for the inert gas to be supplied, and a gas having a predetermined moisture content is mixed at a ratio between the amount of inert gas passing through the tank and the amount of bypass. The moisture content can be controlled by supplying through 15. However, it is important to remove the polymer powder in the circulating gas even during the treatment. At this time, the heat exchanger 7 may be used to efficiently warm the temperature of the circulating gas.

  The processing temperature range of solid phase polycondensation is a temperature range of 205 ° C. or higher and 235 ° C. or lower, preferably 220 ° C. or higher and 235 ° C. or lower, more preferably 220 ° C. or higher and 230 ° C. or lower. When the solid phase polycondensation is lower than 205 ° C., it is not preferable because the decrease rate of the oligomer is small and the amount of the oligomer in the film is increased or the film color tone is deteriorated. When the temperature exceeds 235 ° C., the polymer pellets stick to each other, making it impossible to continue production.

  Further, a wet heat treatment is performed to adjust the polyester composition obtained by solid phase polycondensation to a predetermined oligomer amount, intrinsic viscosity, and carboxyl end group amount.

  The moist heat treatment is to make a mixed gas in which a predetermined concentration of moisture is contained in an inert gas and heated to a predetermined temperature, and is passed through the polyester composition or placed in an atmosphere.

  The wet heat treatment needs to be carried out after the solid phase polycondensation, and the color tone deteriorates when carried out before the solid phase polycondensation. The color of the polymer deteriorates with time to receive heat, but the color tone tends to deteriorate if there is a large amount of low molecular weight. For this reason, it is important to perform the wet heat treatment process accompanied by the cleavage of the molecular chain in the latter half and to heat without generating a lower molecular weight than necessary.

  The temperature of the wet heat treatment is in the temperature range of 205 ° C. or higher and 235 ° C. or lower. About usual polyethylene terephthalate, Preferably it is 210 degreeC or more and 235 degreeC or less, Most preferably, it is 220 degreeC or more and 230 degrees C or less. When the wet heat treatment temperature is lower than 205 ° C., the oligomer of the polyester composition does not decrease or the amount of carboxyl end groups decreases, which is not preferable. When the temperature exceeds 235 ° C., sticking occurs between polymer pellets, making it impossible to continue production.

  The wet heat treatment time is usually preferably 2 hours or longer and 60 hours or shorter, more preferably 3 hours or longer and 40 hours or shorter. By making it longer than 2 hours, oligomers can be reduced, and by making it 60 hours or less, deterioration of color tone can be suppressed and oligomers can be efficiently reduced.

  The moisture and oxygen in the gas used in the wet heat treatment of the present invention accelerate the hydrolysis and oxidative degradation of the polyester composition, so it is important to use a gas mixture with controlled moisture and oxygen concentrations.

  The moisture content of the mixed gas is 60% or more and less than 98%, more preferably 80% or more and less than 98%. When the moisture content is less than 60%, it takes time to increase the carboxyl end group amount decreased by solid-phase polycondensation to a suitable value, which causes deterioration in color tone. On the other hand, if it is 98% or more, latent heat due to water droplets generated in the process is lost, making it difficult to reduce oligomers and adjust the amount of carboxyl end groups.

  The oxygen concentration of the mixed gas needs to be 50 ppm or less, preferably 25 ppm or less. When the oxygen concentration exceeds 50 ppm, the color tone deteriorates due to deterioration of the polyester composition, which causes a problem in product quality.

  Furthermore, the wet heat treatment atmosphere is preferably wet heat treated from the normal pressure to the slightly pressurized state with the above-described mixed gas. The pressure of the wet heat treatment is preferably 0.1 to 0.5 MPa, more preferably 0.1 to 0.2 MPa. By setting the pressure in the tank to 0.1 MPa or more, it is advantageous for preventing deterioration of the color tone by preventing oxygen in the atmosphere from being mixed with the movement of the polyester composition / pellet in the tank. Moreover, an installation cost can be reduced by setting it as 0.5 Mpa or less.

  By these treatments, the intrinsic viscosity (D) of the polyester composition (B) after the heat treatment is preferably 0.50 dl / g or more and 0.70 dl / g or less, and further the polyester composition (A) before the heat treatment. It is preferable that −0.05 dl / g ≦ (D) − (C) ≦ 0.05 dl / g is satisfied with the intrinsic viscosity (C), and −0.02 dl / g ≦ (D) −. It is preferable that (C) ≦ 0.02 dl / g is satisfied. By setting the intrinsic viscosity (D) after the heat treatment to 0.50 dl / g or more, occurrence of film breakage during film formation is reduced, which is advantageous. Moreover, by setting it as 0.70 dl / g or less, it can reduce that a temperature rises by the shear heat_generation | fever at the time of melt molding, and it is advantageous in suppressing the amount of oligomers in a product.

  Further, by satisfying −0.05 dl / g ≦ (D) − (C) ≦ 0.05 dl / g, there is no unnecessary temperature increase during film forming, and the amount of polyester oligomer is small and the color tone is good. In addition to obtaining a film, the polyester composition (A) to be heat-treated does not require a special low-viscosity or high-viscosity brand, and the amount of oligomer using an existing polymer that can be used as another product This is economically advantageous.

  Moreover, it is necessary to make content of the oligomer of a polyester composition (B) into 0.4 weight% or less. More preferably, it is 0.35 weight%. When the content exceeds 0.4% by weight, the oligomer may be regenerated during film forming, and the oligomer may precipitate on the film surface during film production or film processing, causing problems such as film production defects and film product defects. .

  Furthermore, when a thick film is formed using the polyester composition (B), the oligomer amount of the thick film is preferably 0.7% by weight or less, preferably 0.6% by weight or less. By setting the oligomer amount of the obtained thick film to 0.7% by weight or less, precipitation on the film surface is suppressed during the film processing step or the storage period, which is advantageous in terms of transparency.

Also, the carboxyl terminal group content of the polyester composition (B) greater than 30 equivalents / 10 ⁶ g, preferably not more than 55 eq / 10 ⁶ g. When the carboxyl end group amount is 30 equivalents / 10 ⁶ g or less, scratches may occur when a thick film is formed using the polymer. Moreover, when it exceeds 55 equivalent / 10 < ⁶ > g, the heat-and-moisture resistance as a film product shape | molded using this polymer may fall.

That is, when a thick film is formed using the polyester composition (B), the amount of carboxyl end groups of the thick film is preferably more than 30 equivalents / 10 ⁶ g. More preferably, it is 35 equivalents / 10 ⁶ g or more. By making the carboxyl end group amount more than 30 equivalents / 10 ⁶ g, the adhesion to the stretching roll in the film forming stage is improved, so that scratching scratches generated between the rolls can be suppressed and the roll cleaning frequency This is advantageous in that it can be reduced. In particular, when manufacturing a thick film having a film thickness of 30 μm or more as referred to in the present invention, slippage is likely to occur between the rolls due to the large stretching tension, and it is affected by a decrease in adhesion due to a decrease in the amount of carboxyl end groups. easy. At this time, the upper limit of the amount of carboxyl end groups of the film is preferably 65 equivalents / 10 ⁶ g or less, and more preferably 60 equivalents / 10 ⁶ g or less. By making the carboxyl terminal group amount of the film 65 equivalents / 10 ⁶ g or less, it is possible to prevent the moisture and heat resistance of the product from being lowered and to improve the color tone of the product.

  In addition, the thick polyester film of this invention can be manufactured with the following method.

  That is, after drying the pellet under reduced pressure, it is supplied to an extruder, melted at 260 to 300 ° C., extruded into a sheet form from a T-shaped die, and a mirror surface having a surface temperature of 10 to 60 ° C. using an electrostatic application casting method. It is wound around a casting drum, cooled and solidified, and manufactured through an unstretched polyester film. This unstretched film is stretched 2.5 to 5 times in the machine direction (film traveling direction) between rolls heated to 70 to 100 ° C. At least one surface of the film may be subjected to a corona discharge treatment in air to apply a coating solution or the like. Subsequently, the polyester film was stretched 2.5 to 5 times in the width direction in a heating zone at 70 to 150 ° C., and subsequently subjected to a heat treatment in a heating zone at 200 to 240 ° C. for 5 to 40 seconds to complete the crystal orientation. Make it. During this heat treatment, a relaxation treatment of 3 to 12% may be performed as necessary. Moreover, although the thickness of a polyester film is not specifically limited, 30-300 micrometers is used preferably.

EXAMPLES Hereinafter, although an Example demonstrates this invention further more concretely, this invention is not limited to these Examples. In the examples, “parts” all represent parts by weight.

Each characteristic value used in the examples was determined by the following measurement method.
(1) Amount of oligomer of polyester composition: 100 mg of polymer or film was dissolved in 5 ml of orthochlorophenol, measured by liquid chromatography (model 8500, manufactured by Varian), and indicated as a ratio (% by weight) to the polymer.
(2) Intrinsic viscosity [η] of the polyester composition: After dissolving at 100 ° C. for 30 minutes using o-chlorophenol, the flow down seconds were measured at 25 ° C. using an Ostwald viscometer.
(3) Amount of carboxyl end group of polyester composition: 0.5 g of polymer or film was dissolved in o-cresol and titrated with potassium hydroxide. The unit was expressed in equivalent / 10 ⁶ g.
(4) Antimony element content of polyester composition: Measured by fluorescent X-ray method [TFK3064 type (manufactured by Geigerflex)].
(5) Color tone of polyester composition: Measured as Hunter value (L, a, b value) using a color difference meter (SM color computer model SM-3) manufactured by Suga Test Instruments Co., Ltd. In order to evaluate the difference between the b values before and after the treatment, the pellets before solid phase polycondensation and wet heat treatment were pre-depressurized to 133 Pa or less, crystallized by heating at 150 ° C. for 3 hours, and then cooled to room temperature. Measure b value. Subsequently, the pellets after solid phase polycondensation and wet heat treatment were measured with the same color difference meter, and the difference before and after the treatment was compared. Each sample was measured by adjusting the bulkiness of the glass cell to 9 mm.
(6) Measure the weight of pellets in which two or more pellets in 100 g of pellets taken out from the apparatus after the fusion heat treatment of the pellets were joined, and calculate the weight% by dividing by the total amount.
○ Decided as less than 1%, Δ 1% or more and less than 5%, × 5% or more.
(7) Amount of polymer powder: Take 100 g of pellets in a 200 ml beaker, add 100 ml of pure water, and stir for 10 minutes. A 10 mesh (mesh length 0.5 mm) wire mesh is placed on the upper stage, and a 400 mesh wire mesh is placed 10 mm or more apart on the lower stage. The whole pellet is poured, the pellet is placed on the upper stage, and the polymer powder is filtered on the lower stage. Further, the beaker and pellets are rinsed with 100 ml of pure water, and the polymer powder is collected on a 400 mesh wire net used in the lower stage. The collected filtrate was dried at 150 ° C. under reduced pressure for 3 hours, and the difference from the mass of the wire mesh before filtration was divided by 100 g of the pellet amount, and expressed as ppm as the amount of polymer powder.
(8) Oligomer precipitation characteristics: A film is cut into a size of 5 cm × 5 cm, and sandwiched with dust-free paper is treated in a hot air dryer at 150 ° C. for 30 minutes. The surface of both surfaces of each sample after heating is observed with a SEM (scanning electron microscope) at 1,000 times, and two positions on each surface are arbitrarily selected and photographed, and consists of a cyclic trimer in a 60 μm × 60 μm visual field. The number of crystals having a maximum major axis of 1 μm or more was counted, and the total value was judged according to the following criteria.

○ 0 to 2, △ 3 to 5, × 6 or more (9) Coarse foreign matter: The number of coarse protrusions found there by performing aluminum vapor deposition on the film surface and observing with a phase contrast microscope (250 times) Were judged according to the following criteria.

○ Coarse protrusion is less than 5 / 10cm ² ,
△ Coarse protrusion 5 pieces / 10 cm ² or more, less than 10 pieces / 10 cm ² ,
X 10 coarse protrusions / 10 cm ² or more As the coarse protrusions, in addition to surface defects such as oligomers and scratches having a maximum diameter (length) of 1 μm or more, gelled products and metal aggregates were also counted.
(10) Scratches on the film: When the film slides on the roll, the film surface is scratched. This is expressed as a scratch. Using a halogen light as a light source, the thick polyester film was observed with transmitted light, and the ease of conspicuous scratches on the raw film was evaluated according to the following criteria.

○: Scratches are not visible △: Scratches are hardly visible ×: Scratches are noticeable (11) Moisture content in the mixed gas: Fill the container with water, and distribute the inert gas from the bottom to the top The amount of water decreased per unit time M (mol) and the total amount of inert gas V (L) that passed through were determined using the following formula.

(M × 22.4) / (M × 22.4 + V) × 100 (%)
(12) Oxygen concentration in inert gas and mixed gas: measured using an oxygen concentration meter (OA-1 manufactured by Neutronics).

Example 1
100 parts of bishydroxyethyl terephthalate, which is a reaction product of terephthalic acid and ethylene glycol, is stored in a molten state at 255 ° C in advance, and a slurry composed of 100 parts of terephthalic acid and 45 parts of ethylene glycol is prepared in a separate mixing tank. Then, a constant amount is supplied while maintaining the temperature of the reaction vessel, water is distilled off, and an esterification reaction is carried out. When the esterification reaction is completed, it is transferred to another container capable of polycondensation reaction, 0.05 parts of magnesium acetate, 0.0065 parts of phosphoric acid and 0.0078 parts of antimony trioxide are added. The pressure was gradually reduced to 133 Pa or less in 60 minutes, and at the same time, the temperature was gradually raised to 290 ° C., and the polycondensation reaction was carried out until the target intrinsic viscosity was reached. Thereafter, the polyester composition (A) was obtained by forming a cylindrical pellet having a diameter of about 3 mm and a length of about 4 mm by an extrusion cutter from the discharge nozzle into water. The resulting polyester composition (A) has an intrinsic viscosity (C) of 0.64 dl / g, an antimony content of 0.0065 wt%, a carboxyl end group content of 32 equivalents / 10 ⁶ g, and an oligomer content of 1. It was 2% by weight.

  An outline of the heat treatment apparatus used in the practice of the present invention is shown in FIG.

  The heat treatment tower 2 composed of a combination of a vertical cylinder used for heat treatment and a lower conical shape is filled with nitrogen, gas is circulated through the gas supply port 12, and further, fusion of pellets in the tower is prevented, The raw material polyester composition was quantitatively charged from the pellet inlet 1 while rotating a stirrer composed of a stirring shaft 4 having a plurality of horizontal stirring blades 3 for uniform temperature increase. At this time, the flow rate in the tower was 0.6 m / s to float the pellets, and the packed volume was 1.10 times that at the time of standing. In this state, the gas that has passed through the polyester composition in the tower passes through the exhaust port 13 and is circulated by the gas circulation blower 10 while removing the polymer powder through the filter cloth type dust collector 6, and is heated from the heater 11. The temperature was raised at a rate of 0.2 ° C./min. During this time, it is carried out while removing moisture and reaction products through the cooling tower 8, and solid state polymerization is carried out at a pellet temperature of 225 ° C. for 10 hours. Further, the humidity is adjusted so that the moisture content in the gas becomes a predetermined concentration, and the temperature is maintained while the oligomer amount and the intrinsic viscosity are confirmed, and the wet heat treatment time is maintained for a predetermined time. After completion of the treatment, the gas is cooled again through the cooling tower 8 until the pellet temperature reaches 100 ° C., and further discharged from the discharge port 5.

The intrinsic viscosity (D) of the polyester composition (B) at this time was 0.63, the amount of carboxyl end groups was 40 equivalents / 10 ⁶ g, the amount of polymer powder was 380 ppm, and the amount of oligomer was 0.30% by weight. It was.

  Further, the heat-treated polyester composition was dried at 150 ° C. for 6 hours, extruded at 285 ° C. with an extruder, and cast on an electrostatically applied 20 ° C. cast drum to obtain an unstretched sheet. At the time of extrusion, extrusion was possible without increasing the pressure as in the case of the polymer without heat treatment. This unstretched sheet is roll-stretched 3.0 times in the longitudinal direction, then stretched 3.5 times in the transverse direction with a tenter, and then heat-set at 200 ° C. for 6 seconds to form a biaxially stretched film having a thickness of 188 μm Got.

The amount of oligomer in the film was 0.57% by weight and the amount of carboxyl end groups was 44 equivalents / 10 ⁶ g. As a result of evaluation, the oligomer precipitation characteristics and scratches were good.

Examples 2-13
For the polyester composition (A), Example 1 was carried out under the conditions and methods described in Table 1. Regarding the heat treatment, Example 1 was carried out under the conditions and methods described in Table 1. The physical properties of each polyester composition (B) and film were good as shown in Table 1.

Comparative Example 1
For the polyester composition (A), Example 1 was carried out under the conditions and methods described in Table 1. As for the heat treatment, the conical rotary apparatus shown in FIG. 2 is used as the heat treatment apparatus, and the pellet temperature is 225 ° C. while reducing the pressure to 133 Pa or less, and the oligomer is 0.4 wt% or less. Heat treatment was performed for a predetermined time so that At this time, the intrinsic viscosity of the polyester composition (B) increased to 0.76 dl / g, and the oligomer content was 0.36 wt%. Moreover, the amount of polymer powder contained in the pellets was 800 ppm. As a result of evaluating this as a film in the same manner as in Example 1, fusion of the pellets was relatively good, but other physical properties were poor as shown in Table 1.

Comparative Example 2
The polyester composition (A) was carried out in the same manner as in Example 1 under the conditions and methods described in Table 1. As for the heat treatment, using the heat treatment apparatus described in Comparative Example 1, the temperature is raised under a reduced pressure of 133 Pa or less until the pellet temperature reaches 150 ° C., and then the atmospheric pressure is increased with nitrogen. It heated so that it might become 225 degreeC, and heat processing was implemented for predetermined time so that it might become 0.4 wt% or less of oligomers. However, the evaluation was poor as shown in Table 1.

Comparative Examples 3, 6, 7
For the polyester composition (A), Example 1 was carried out under the conditions and methods described in Table 1. Regarding the heat treatment, Example 1 was carried out under the conditions and methods described in Table 1. However, since fusion into the pellets and the apparatus occurred during the treatment, the treatment could not be continued and the polyester composition (B) to be evaluated could not be obtained.

Comparative Example 4
The polyester composition (A) was carried out in the same manner as in Example 1 under the conditions and methods described in Table 1. Moreover, regarding heat processing, it implemented according to the method of Example 1 except having made the filter cloth type dust collector 6 in circulation gas bypass. However, the evaluation was poor as shown in Table 1.

Comparative Examples 5, 8-11
The polyester composition (A) was carried out in the same manner as in Example 1 under the conditions and methods described in Table 1. However, the evaluation was poor as shown in Table 1.

Fluid type vertical heat treatment apparatus having a stirrer that can be preferably used in the present invention Typical conical rotation type heat treatment equipment

Explanation of symbols

1: Pellet inlet 2: Heat treatment tower 3: Stirring blade 4: Stirring shaft 5: Pellet outlet 6: Dust collector 7: Heat exchanger 8: Cooling tower 9: Bypass 10: Circulating blower 11: Heating heater 12: Circulating Inert gas supply port 13: Exhaust port 14: Gas monitoring monitor 15: Mixing / inert gas supply line

Claims (3)

A polyester composition obtained by subjecting a dicarboxylic acid component containing terephthalic acid or an ester-forming derivative thereof as a main component and a diol containing ethylene glycol as a main component to an esterification reaction or a transesterification reaction, followed by a polycondensation reaction By making (A) a pellet having an intrinsic viscosity (C) of 0.52 dl / g or more and 0.68 dl / g or less, and performing the treatment satisfying the following (a), (b), (c), A polyester composition characterized by obtaining a polyester composition (B) having a viscosity (D) of 0.50 dl / g or more and 0.70 dl / g or less and an oligomer content of 0.4 wt% or less. Production method.
(A) In a flow type vertical heating apparatus having a stirrer, a circulating gas is circulated so that the pellet filling volume in the apparatus is 1.03 to 1.18 times that at the time of standing, and the polyester composition (A) A step of circulating solid inert gas while removing polymer powder of the same component from the circulating gas, and solid-phase polymerization in a range where the heat treatment temperature of the pellet is 205 ° C. or higher and 235 ° C. or lower.
(B) A step of subjecting the pellets obtained in (a) to the same filling volume as in (a) and circulating a heated mixed gas having a moisture content of 60% or more and less than 98% to wet-heat-treat the polymer.
(C) The relationship between the intrinsic viscosity (C) of the polyester composition (A) and the intrinsic viscosity (D) of the treated polyester composition (B) is −0.05 dl / g ≦ (D) − (C) ≦ 0.05 dl / g is satisfied.   The method for producing a polyester composition according to claim 1, wherein the content of antimony in the polyester composition (A) before the heat treatment is 0.005 wt% or more and 0.020 wt% or less.   The method for producing a polyester composition according to claim 1 or 2, wherein the amount of polymer powder in the polyester composition (B) after treatment is 700 ppm or less.

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