Method for manufacturing polyester resin composition

Abstract

To provide a method for manufacturing a polyester resin composition capable of satisfactorily cleaning filters of a leaf disk filter.SOLUTION: A method for manufacturing a polyester resin composition using a twin screw extruder provided with a plasticizing section, a kneading section, a degassing section, and a leaf disk filter from a resin supply port side in this order comprises: a kneading and extruding step of the polyester resin composition for supplying a polyester resin from a resin supply port, adding a particle dispersion slurry from an addition section installed on the kneading section into the twin screw extruder, and obtaining the polyester resin composition filtrated through the leaf disk filter; and a cleaning step of stopping the kneading and extruding step and removing filters from the leaf disk filter to clean them. In the cleaning step, the filters are cleaned by an acid solution containing at least one of nitric acid, fluoro-nitric acid, and phosphoric acid.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for producing a polyester resin composition. Specifically, it relates to a kneading and extrusion step of adding a slurry of particles to a polyester resin, kneading the mixture, and obtaining a polyester resin composition through a filter section, and a cleaning step of stopping the kneading and extrusion step, removing the filter in the filter section, and cleaning it, for the method of producing a polyester resin composition.

Background Art

[0002] Biaxially oriented films of polyester resin have excellent physical and chemical properties and are used as base films for magnetic recording media and dielectrics for capacitors. Also, due to their excellent transparency, they are widely used in fields such as graphic arts, displays, and packaging materials. In order to improve the running performance of the polyester resin film, it is necessary to moderately roughen the film surface by making particles such as calcium carbonate present in the film, but it is desired that there are no uniform and large protrusions.

[0003] When synthesizing calcium carbonate particles, it is carried out in an aqueous solvent, so it is obtained as an aqueous slurry (Patent Document 1). However, this aqueous slurry has a high pH and contains synthetic impurities. In the case of commercially available particles, an ethylene glycol (''EG'') slurry is known. As a step of adding these particles to a polyester resin, when adding an EG slurry to an esterification step, the dispersibility is poor. In the case of a polymerization step, if the particle concentration is not adjusted to a low concentration, the dispersibility becomes poor, but if it is made low, there is too much EG and the balance becomes poor, so the dispersion is still poor. When adding in other steps, since EG cannot be discharged, depolymerization occurs.

[0004] Patent Document 2 describes a method of adding an aqueous dispersion of particles to a biaxial kneader when producing a composition of a polyester resin and inorganic particles, but the blending amount of the particles is as low as 0.001 to 1.0% by weight with respect to the composition, and the particle concentration in the aqueous dispersion is 0.01 to 10% by weight.

[0005] Patent Document 3 describes a method for producing a polyester resin inorganic particle composition (particle content in the composition: 1 to 30% by weight) by spray-injecting a slurry with a particle concentration of 5 to 80% by weight in an aqueous dispersion using the pressure difference with the inside of a kneader. However, this is not sufficient to improve the dispersibility and cohesiveness of the inorganic particles and to improve the film properties when the polyester resin composition is made into a biaxially oriented film.

[0006] Patent Document 4 describes a method of filtration and extrusion of a polymer by providing a leaf-disc type filter at the tip of a polymer extruder. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 6-269615 [Patent Document 2] Japanese Patent Publication No. 2019-112588 [Patent Document 3] Japanese Patent Publication No. 2020-146938 [Patent Document 4] Japanese Patent Publication No. 2012-213983 [Overview of the project] [Problems that the invention aims to solve]

[0008] The filter in a leaf-disc type filter will become clogged over time, so it needs to be removed and cleaned.

[0009] The object of the present invention is to provide a method for producing a polyester resin composition that can thoroughly clean the filter of a leaf-disc type filter. [Means for solving the problem]

[0010] The gist of this invention is as follows:

[0011] [1] A method for producing a polyester resin composition using a twin-screw extruder equipped with a plasticizing section, a kneading section, a degassing section, and a leaf-disc type filter in that order from the resin supply port side, A polyester resin composition kneading and extrusion process in which polyester resin is supplied from a resin supply port, a particle dispersion slurry is added to a twin-screw extruder from an additive section provided in the kneading section, and a polyester resin composition is obtained by filtering with a leaf disc type filter, The kneading and extrusion process is stopped, and the filter is removed from the leaf-disc type filter and washed in a washing process. In a method for producing a polyester resin composition having the following characteristics: A method for producing a polyester resin composition, characterized in that the cleaning step includes an acid cleaning step in which the filter is cleaned with an acid solution containing at least one of nitric acid, hydrofluoric acid, and phosphoric acid.

[0012] [2] A method for producing the polyester resin composition according to [1], wherein in the washing step, the filter is washed with a solvent, then roasted, and then acid washed.

[0013] [3] A method for producing the polyester resin composition according to [1] or [2], wherein the acid washing step is washed with an aqueous nitric acid solution.

[0014] [4] A method for producing the polyester resin composition of [3], wherein the nitric acid concentration of the aqueous nitric acid solution is 30 to 400 g / L. [Effects of the Invention]

[0015] According to the present invention, the filter of a leaf-disc type filter can be thoroughly cleaned. [Brief explanation of the drawing]

[0016] [Figure 1] This is a side view of a twin-screw extruder. [Figure 2] This is a cross-sectional view of a leaf-disk type filter. [Figure 3] This is a plan view of the filter. [Figure 4]It is a cross-sectional view taken along line IV-IV of FIG. 3.

Mode for Carrying Out the Invention

[0017] In the present invention, a polyester resin is supplied to a twin-screw extruder having a plasticizing section, a kneading section, a degassing section, and a leaf disk type filter in this order from the resin supply port side, and a particle dispersion slurry is added into the twin-screw extruder from an addition section provided in the kneading section, and filtered and extruded by the leaf disk type filter to produce a polyester resin composition.

[0018] [Polyester Resin] The polyester resin used in the present invention is not particularly limited, and refers to a polyester obtained from an aromatic dicarboxylic acid such as terephthalic acid or 2,6-naphthalenedicarboxylic acid or its ester and ethylene glycol as main starting materials, but may contain other third components.

[0019] As the dicarboxylic acid component, for example, one or more of isophthalic acid, terephthalic acid, 2,6-naphthalenedicarboxylic acid, adipic acid, and sebacic acid can be used. Further, as the glycol component, one or more of diethylene glycol, propylene glycol, butanediol, 1,4-cyclohexanedimethanol, and neopentyl glycol can be used. The polyester resin of the present invention has 80 mol% or more of the repeating structural units as ethylene terephthalate units or ethylene-2,6-naphthalate units.

[0020] This polyester resin is supplied to a twin-screw extruder, and a particle dispersion slurry is injected and further kneaded and extruded in the kneading section to obtain a polyester resin composition.

[0021] [Particle Dispersion Slurry] <Particles> The polyester-adding particles used in this invention are not particularly limited, but examples include calcium carbonate, silicon dioxide, crosslinked organic polymer particles, talc, clay, kaolin, etc. Among these, synthetic calcium carbonate, spherical silicon dioxide, and crosslinked organic particles, which are produced by synthesis and have a narrow particle size distribution, are preferred. The average particle diameter (d50) of the particles is preferably 0.05 to 3 μm when used in film applications. Furthermore, when the particles are accumulated from the largest particle side, the ratio [d25 / d75] of the particle size at 25% of the accumulated weight of the particles (d25) to the particle size at 75% of the accumulated weight of the particles (d75) is preferably 2.2 or less, more preferably 2.0 or less, and even more preferably 1.8 or less.

[0022] <Concentration of particle-dispersed slurry> The particle concentration in the particle dispersion slurry added to the twin-screw extruder is preferably 10-60% by weight, and particularly preferably 15-50% by weight.

[0023] <Amount of particle-dispersed slurry to add> The amount of particle-dispersed slurry added to the twin-screw extruder is preferably such that the particle content in the manufactured polyester resin composition is 0.1 to 10.0% by weight, particularly 0.5 to 6.0% by weight, and especially 1.0 to 5.0% by weight. Furthermore, in order to suppress hydrolysis of the polyester resin, the amount of particle-dispersed slurry added is preferably in the range of 0.5 to 10% by weight relative to the polyester resin.

[0024] <Medium for particle dispersion slurry> The medium is primarily water. The proportion of water in the medium is preferably 40% by weight or more.

[0025] Examples of media other than water include ethylene glycol derived from slurry raw materials.

[0026] The ethylene glycol concentration in the water slurry is calculated by measuring the filtrate after the water slurry replacement is complete using a refractometer (manufactured by Atago Co., Ltd.) and obtaining the Brix value. The ethylene glycol concentration of the filtrate (A) is calculated as A = 1.6153 * Brix value - 0.9458, and the ethylene glycol concentration in the water slurry (B) is calculated as B = (100 - particle concentration (C)) * (A / 100). The ethylene glycol concentration in the water slurry is preferably 5% by weight or less. A lower ethylene glycol concentration in the slurry is preferable, but achieving 2% by weight or less requires a longer solvent replacement time. If it exceeds 5% by weight, when added to a twin-screw extruder, the polyester resin tends to depolymerize due to the ethylene glycol, and the intrinsic viscosity tends to decrease.

[0027] <Substitution of the medium in a slurry (raw material slurry) containing particles manufactured by a synthesis method> Particles produced by synthesis methods are usually obtained as a particle-containing slurry (hereinafter sometimes referred to as the raw material slurry) dispersed in the medium (water and / or organic solvent) used in particle synthesis. When water is used as the medium, the pH is high and undesirable impurities are present. Furthermore, methanol and other organic solvents are often used. These organic solvents are often not used in the polyester resin manufacturing process and are therefore undesirable to add to polyester resins.

[0028] Therefore, in the case of a raw material slurry in which the medium of the particle-containing slurry is water or an organic solvent, it is preferable to replace the medium with ethylene glycol. There are no particular limitations on the method of replacing the water or organic solvent in the raw material slurry with ethylene glycol to make an ethylene glycol slurry. For example, there are methods such as concentrating and drying the solvent solution to obtain a powder and then adding ethylene glycol, or directly adding ethylene glycol and concentrating under reduced pressure to remove water or organic solvent. However, as described in Japanese Patent Application Publication No. 6-269615, it is preferable to make an ethylene glycol slurry by repeatedly concentrating by filtration and diluting with ethylene glycol using a filter material with a pore size preferably d50 × 0.1 μm or more and d50 × 12 μm or less.

[0029] <Replacement of ethylene glycol with water in ethylene glycol slurry> The ethylene glycol slurry obtained as described above, or commercially available ethylene glycol slurry in particle form, is converted to an aqueous slurry by the following method. This is because converting to an aqueous slurry allows for the addition of particle slurry even outside of polymerization.

[0030] The medium replacement for converting the ethylene glycol slurry to an aqueous slurry is preferably carried out by repeatedly concentrating by filtration and diluting with water using a filter medium with a pore size of preferably d50 × 0.1 μm or more and d50 × 12 μm or less.

[0031] <Filtration device used for media replacement> The filtration system used for media replacement consists of a slurry storage tank, a slurry circulation pump, a filter with filter media, a pressure gauge, a heat exchanger, etc., and additional storage tanks may be added as needed. The filter media is preferably made of ceramic due to its corrosion resistance and solvent resistance.

[0032] As for filtration methods, there is a method called cross-flow filtration, in which the liquid to be filtered is filtered while flowing it over the surface of a membrane filter, keeping the accumulated cake layer to a minimum by the shear force of the parallel flow, or a method called direct filtration, in which the liquid to be filtered is filtered directly by the membrane filter, and either method may be used.

[0033] By filtering the slurry, it is separated into a filtrate containing the medium and a concentrated slurry (particles + medium). The concentrated slurry is diluted with water and filtered again. By repeating this process, the medium is gradually replaced by water. For example, water is added to a concentrated ethylene glycol slurry with a particle concentration of 40% by weight to dilute it to a particle concentration of approximately 20% by weight, then filtered, and the same amount of water as the discharged filtrate is added to the concentrated slurry. By repeating this concentration and dilution operation, the ethylene glycol is gradually replaced by water, and a slurry in which the medium is mainly water can be obtained. By concentrating the slurry obtained in this way, a slurry of the desired concentration in which the medium is mainly water can be obtained.

[0034] If the pore size of the filter material used for the above concentration is less than d50 × 0.1 μm, the filtration rate will be low, which is undesirable because it will take a long time to concentrate. If the pore size exceeds d50 × 12 μm, the particles will also flow out along with the filtered dispersion medium during concentration by filtration, which is also undesirable.

[0035] The slurry concentration at the start of the dispersion medium substitution is preferably one that can maintain good particle dispersibility, and varies depending on the type and size of the particles. In the case of synthetic calcium carbonate, spherical silicon dioxide, and cross-linked organic polymer particles, the concentration at the start of substitution is usually in the range of 10 to 60% by weight, preferably 15 to 50% by weight. If the concentrated slurry concentration is less than 10% by weight, efficiency tends to be poor, and if the slurry concentration exceeds 60% by weight, particles may aggregate in the concentrated slurry.

[0036] [Twin-screw compounding extruder] A twin-screw extruder (twin-screw compounding extruder) is used for mixing.

[0037] Figure 1 is a side view of a twin-screw compounding extruder. As is well known, this twin-screw compounding extruder performs compounding and extrusion by rotating the screw inside the barrel (cylinder) 1 with a drive unit M.

[0038] The polyester resin supplied from the polymer inlet 2 is melted in the plasticizing section A and transferred to the kneading section B. Then, a particle-dispersed slurry is injected (preferably by pressure spraying) into the molten resin from the slurry addition nozzle 3, and after the molten resin and slurry are mixed and kneaded, the mixture is transferred to the degassing section C. The water, which is the dispersion medium, is removed by suction from inside the barrel 1 using a vacuum pump (not shown) connected to the vent port 4. Next, the mixture is supplied to the leaf disc type filter 6 by the gear pump 5, filtered, and then the resin composition is extruded as strands from the extrusion port 7. After that, although not shown, it is cut in water to form pellets.

[0039] For a twin-screw compounding extruder, the barrel inner diameter is preferably 60-90 mm, particularly 65-85 mm; the length of the plasticizing section A is preferably 400-1000 mm, particularly 500-900 mm; the length of the compounding section B is preferably 400-1000 mm, particularly 500-900 mm; and the length of the degassing section C is preferably 400-1300 mm, particularly 500-1200 mm.

[0040] The boundary positions of the plasticizing section, the kneading section, and the degassing section are defined by the differences in the screw blades within the barrel. Typically, a kneading disc is used as the screw piece in the plasticizing and kneading sections, while a full-flight screw is typically used as the screw piece in the degassing section. The boundary position between plasticizing section A and kneading section B is defined by the switch from a kneading disc to a full-flight screw blade. The combination of screw pieces can be changed as appropriate.

[0041] [Position of water slurry addition nozzle 3] The slurry addition nozzle 3 is positioned on the side of the kneading section B closer to the plasticizing section A than the center of the barrel longitudinal direction, that is, within 50%, preferably within 40%, and more preferably within 30%, of the upstream end of the kneading section B (the boundary between the plasticizing section A and the kneading section B).

[0042] [Leaf disc type filter 6] Figure 2 is a schematic longitudinal cross-sectional view showing an example of a leaf-disk type filter 6.

[0043] The leaf-disk type filter 6 has a configuration in which a filter set 20 is arranged inside a housing 10. <Housing 10> The housing 10 includes a lower block 11, an upper block 12, and a side block 13. The lower block 11 has a cylindrical recess 11a that is recessed from the top surface, and the filter set 20 is placed in this recess 11a.

[0044] A predetermined gap exists between the inner surface of the recess 11a and the outer surface of the filter set 20.

[0045] The upper block 12 is mounted and fixed on the lower block 11 so as to overlap the filter set 20. A resin inlet 14 is formed on the side of the housing 10. In addition, a resin flow path space 15 is formed above the filter set 20.

[0046] The lower block 11 has flow channels 16 for filtered resin extending laterally from the center of the bottom surface of the recess 11a. The recess 11a and the filter set 20, which will be described later, are arranged coaxially.

[0047] The side block 13 is attached to the sides of the upper block 12 and the lower block 11. The side block 13 is provided with a flow path hole 17 that connects the flow path hole 16 and the resin outlet 18.

[0048] Furthermore, by removing the upper block 12, the filter set 20 can be removed from the housing 10. After cleaning the filter set 20, placing it in the recess 11a of the lower block 11 and then attaching the upper block 12 makes the leaf disc type filter 6 reusable.

[0049] <Filter Set 20> The filter set 20 includes a bottom base 21, a center column 22 rising from the center of the bottom base 21, a plurality of roughly disc-shaped filter bodies 23 fitted into the center column 22, and a top base 24 attached to the top of the center column 22, which presses down on the aggregate of filter bodies 23 from above. The center column 22 is pipe-shaped with a closed upper end and has a number of small holes 22a that penetrate radially.

[0050] As shown in Figures 3 and 4, the filter body 23 includes two roughly disc-shaped filter media 24 and 25, one upper and one lower, each having a circular hole in the center; two disc-shaped perforated plates 26 and 27, each having numerous small holes that overlap the lower surface of the filter media 24 and the upper surface of the filter media 25, respectively; a mesh 28 interposed between the perforated plates 26 and 27; a spacer 29 on the upper surface of the filter media 24; and hubs 30 and 31 provided on the inner periphery of the perforated plates 26 and 27. The outer periphery of the perforated plates 26 and 27 overlaps. The inner periphery of the perforated plates 26 and 27 is separated, with the mesh 28 interposed between them.

[0051] The filter media 24 and 25 are formed from a laminated sintered body or the like, which is composed of at least two layers of nonwoven fabric made of metal fibers with a porosity of 40 to 80%, and the entire body is pressure-sintered to a predetermined thickness.

[0052] As shown in Figure 3, the spacers 29 are rod-shaped members extending radially, and multiple spacers (10 in this embodiment, but not limited to this number) are provided. The spacers 29 are for forming resin flow paths between each filter body 23.

[0053] In this leaf-disc type filter 6, the resin flowing in from the inlet 14 flows through the resin flow path space 15 between the outer circumference of the filter set 20 and the inner surface of the recess 11a, enters between the filter bodies 23, passes through the filter media 24 and 25 and is filtered. The filtered resin flows between the perforated plates 26 and 27 through the small holes in the perforated plates 26 and 27. Then it flows along the mesh 28 towards the center of the filter body 23, flows into the center column 22 through the holes 22a of the center column 22, and flows out from the outlet 18 through the flow path holes 16 and 17.

[0054] [Mixing conditions] The cylinder temperature during mixing is preferably 200-300°C, particularly 220-290°C; the screw rotation speed is preferably 80-270 rpm, particularly 100-200 rpm; and the discharge rate is preferably 80-180 kg / h, particularly 100-150 kg / h.

[0055] [Uses and intrinsic viscosity of polyester resin compositions] Films can be manufactured from the polyester resin composition produced in this manner by various methods. Known film manufacturing methods can be applied as molding methods; for example, a polyester sheet can be obtained by extrusion molding after melting at a temperature above the melting point of polyester. Furthermore, a polyester film can be obtained by biaxial stretching the obtained polyester sheet.

[0056] <Intrinsic viscosity of polyester resin composition> The intrinsic viscosity of the polyester resin composition is preferably 0.500 dL / g or higher, and more preferably 0.520 dL / g or higher. If this value falls below 0.500 dL / g, pelletization may not be possible. There is no particular upper limit, but it is preferably around 0.850 dL / g.

[0057] The intrinsic viscosity of the polyester resin composition is measured by dissolving approximately 0.25 g of the sample in approximately 25 mL of a mixed solvent of phenol / 1,1,2,2-tetrachloroethane (mass ratio 1 / 1) to a concentration of 1.00 g / dL. After cooling to 30°C, the sample solution and the solvent alone are measured using a fully automated solution viscometer (Sentec Co., Ltd., "DT553") at 30°C, and the intrinsic viscosity (IV) is calculated using the following formula.

[0058] IV = ((1 + 4KHηsp)0.5 - 1) / (2KHC) Here, ηsp = η / η0-1, where η is the number of seconds the sample solution falls, η0 is the number of seconds the solvent alone falls, C is the concentration of the sample solution (g / dL), and KH is Huggins' constant. A KH of 0.33 is used. The sample dissolution conditions are 110°C for 30 minutes.

[0059] [Filter cleaning process] To clean the leaf disc type filter 6, after stopping the kneading and extrusion process, the filter set 20 is removed from the housing 10 of the leaf disc type filter 6 and washed.

[0060] In a preferred embodiment of the present invention, after removing the filter set 20 from the housing 10, the attached resin is dissolved by immersing it in an organic solvent such as triethylene glycol at 240-250°C or ethylene glycol at 110-230°C and a pressure of 0-0.2 MPaG for 20-30 hours. Alternatively, the filter set is heated for 1-10 hours in an oxygen-containing atmosphere such as air at 350-480°C to roast (vaporize and burn) the resin components.

[0061] Subsequently, the filter set 20 is disassembled, the filter body 23 is removed from the center column 22, and preferably washed with water using a high-pressure washer to remove any attached residue, after which it is acid-washed.

[0062] At least one of nitric acid, hydrofluoric acid, and phosphoric acid is used as the acid for acid washing.

[0063] For nitric acid washing, a concentration of 1-10N, a water temperature of 50-60°C, and a washing time of 0.5-2 hours are preferable.

[0064] For hydrofluoric acid washing, a concentration of 1-10N, a water temperature of 50-60°C, and a washing time of 0.5-2 hours are preferable. The molar ratio of hydrofluoric acid to nitric acid in hydrofluoric acid is preferably around 1:1-1:2.

[0065] For phosphoric acid washing, a concentration of 1-10N, a water temperature of 50-70°C, and a washing time of 0.5-2 hours are preferable. Alternatively, washing may be performed using two or more acids, such as nitrate washing followed by nitrate washing.

[0066] After acid cleaning, rinse with water and dry. While it is preferable to use an ultrasonic cleaner for rinsing, the method is not limited to this.

[0067] Furthermore, when the polyester resin is PET and the added fine particles are calcium carbonate, it has been observed that the filter media is prone to clogging due to calcium carboxylates in addition to the calcium carbonate particles. If clogging progresses, the filter media and spacers may deform or be damaged. [Examples]

[0068] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist of the invention. The measurement methods and definitions of various physical properties and characteristics in the examples are as follows. In the examples and comparative examples, "parts" refers to "parts by weight".

[0069] [Method for preparing slurry] <Preparation of calcium carbonate slurry (I)> 60 kg of ethylene glycol slurry containing colloidal calcium carbonate particles with an average particle size d50 of 0.95 μm (Maruo Calcium Co., Ltd. "MG-10"; particle concentration in the slurry was 40.0 wt%) was diluted with 60 kg of pure water to obtain a slurry stock solution with a particle concentration of 20 wt%. This slurry stock solution was then concentrated by filtering it using a filtration device (ceramic concentration filtration device equipped with a 0.2 μm pore size ceramic membrane (NGK Filtec Sefilt filtration device)). Every 10 kg of filtrate discharged from the filtration device, 10 kg of pure water was added to the concentrated slurry to dilute it and return the particle concentration to 20 wt%. This concentration and dilution operation was repeated 15 times. Next, 60 kg of filtrate was discharged from the filtration device and concentrated to a slurry concentration of approximately 40 wt%. The resulting slurry had a particle concentration of 41.8 wt% and an ethylene glycol concentration of 3.9 wt%. The dispersibility of calcium carbonate in the obtained slurry was good. This slurry was designated as calcium carbonate slurry (I).

[0070] <Manufacturing of polyester resin> A continuous polymerization apparatus was used, consisting of one stock solution preparation tank, two esterification reaction tanks connected in series to it, and three melt polycondensation tanks connected in series to the second esterification reaction tank. Terephthalic acid and ethylene glycol were continuously supplied to the stock solution preparation tank in a weight ratio of 100:45, and an ethylene glycol solution of ethyl acid phosphate was continuously added in an amount that resulted in a phosphorus atom content of 7 ppm by weight relative to the resulting polyester resin. The mixture was then stirred and mixed to prepare a slurry-like stock solution. This slurry-like stock solution was continuously transferred to the first esterification reaction tank, and then to the second esterification reaction tank, to carry out the esterification reaction.

[0071] Next, an ethylene glycol solution of magnesium acetate tetrahydrate was added to the esterification reaction product in an amount that resulted in a magnesium atom content of 9 ppm by weight relative to the generated polyester resin. Furthermore, an ethylene glycol solution of tetra-n-butyl titanate was added in an amount that resulted in a titanium atom content of 4.5 ppm by weight relative to the generated polyester resin, and melt polycondensation was carried out in the first polycondensation reaction vessel, followed by the second polycondensation reaction layer.

[0072] Next, polycondensation reactions were carried out in a second-stage polycondensation reactor and then a third-stage polycondensation reactor at 277°C, an absolute pressure of 0.2 kPa, and an average residence time of 1 hour.

[0073] The molten polycondensation reaction product removed from the third-stage polycondensation reaction vessel was extruded from a die in a strand shape, cooled and solidified, and then cut with a cutter to obtain polyester resin pellets with an average weight of 24 mg each. The intrinsic viscosity of these pellets was 0.560 dL / g.

[0074] Next, these molten polycondensed polyester resin pellets were continuously supplied to a stirring crystallizer maintained at approximately 160°C under a nitrogen atmosphere for a residence time of approximately 60 minutes to crystallize them. After that, they were continuously supplied to a tower-type solid-phase polycondensation apparatus, where solid-phase polycondensation was carried out at 210°C for 18 hours under a nitrogen atmosphere.

[0075] The intrinsic viscosity of the obtained polyester resin was 0.700 dL / g.

[0076] [Polyester resin kneading and extrusion] A vented twin-screw extruder (AUTOMATIK "ZCM" with the configuration shown in Figure 1, co-rotating screws, barrel inner diameter D: 71 mm, length of plasticizer A: 800 mm, length of kneading section B: 600 mm, length of degassing section C: 1000 mm, position of slurry addition nozzle 3: 162 mm upstream of kneading section B (27% of the length of kneading section B) was used.

[0077] As the leaf-disk type filter 6, a filter set 10 having the structure shown in Figure 2 and comprising 10 filter bodies 23 was used. The configuration of the filter body 23 was as follows.

[0078] Outer diameter: 304.8mm Inner diameter: 63.5mm Spacer thickness: 2mm Filter media: 0.7mm thick stainless steel. Void ratio 40-80% Spacing between filter media (excluding the outer edge): 2.4 mm Mesh: Stainless steel wire mesh with a diameter of 1.2 mm. Mesh opening: 8 mm (8 mesh).

[0079] The above polyester resin was introduced through polymer inlet 2 and kneaded at a cylinder temperature of 280°C, a screw rotation speed of 150 rpm, and a discharge rate of 120 kg / h. Calcium carbonate slurry (I) was also injected through nozzle 3. The amount of slurry added was adjusted so that the particle concentration in the polyester resin composition was 1.5% by weight. The vent vacuum was set to -0.098 MPa for degassing. The extruded polyester resin composition was cut in water to form pellets.

[0080] After 53 hours of operation, the filter pressure reached 42 bar, so the filter set was removed and cleaned according to the following cleaning example 1 and cleaning comparative example 1.

[0081] [Cleaning Example 1] <Solvent cleaning treatment> The filter set was immersed in 100L of triethylene glycol (TEG) heated to 245°C for 24 hours to dissolve the resin. Then, the filter bodies were removed one by one from the filter set and washed with water using a high-pressure washer to remove the resin and TEG. After that, the leaf filters were immersed in an ultrasonic cleaner in a water bath and subjected to ultrasonic waves for 3 hours to further remove any deposits. The filters were then removed from the ultrasonic cleaner and allowed to air dry.

[0082] <Roasting process> After the solvent cleaning treatment described above, the leaf filters were roasted in an air atmosphere at 400°C for 2 hours, then immersed in an alkaline solution (NaOH, pH 13) for 2 hours, followed by ultrasonic cleaning in a water bath and natural drying.

[0083] <Acid cleaning> After the roasting process described above, the product was immersed in 100L of nitric acid solution for 2 hours, then ultrasonically cleaned in a water bath and air-dried.

[0084] Nitric acid solution is an aqueous solution containing 130 g / L of nitric acid.

[0085] [Cleaning Comparison Example 1] The same filter set used in Cleaning Example 1 was subjected to only the solvent cleaning treatment described in Cleaning Example 1.

[0086] [Manufacturing of polyester resin composition after reattachment] When leaf-disc type filters equipped with the filters cleaned in Cleaning Example 1 and Cleaning Comparative Example 1 were incorporated into a twin-screw extruder and a polyester resin composition was manufactured again under the same conditions, the time until the filter pressure reached 42 bar was 53 hours in Cleaning Example 1 and 33 hours in Cleaning Comparative Example 1. From these results, it was confirmed that the filter of a leaf-disc type filter can be sufficiently cleaned according to the method of the present invention. [Explanation of symbols]

[0087] 1 barrel 2 Polymer input port 3. Slurry Addition Nozzle 4 vent openings 5 Gear pump 6. Leaf-disk type filter 7 Extrusion port 10 Housing 20 filter sets 21 Bottom Base 22 Center Column 23 Filter body 24,25 Filter Media 26, 27 Perforated Plate 28 mesh 29 Spacers 30,31 Hub

Claims

1. A method for producing a polyester resin composition using a twin-screw extruder equipped with a plasticizing section, a kneading section, a degassing section, and a leaf-disc type filter in that order from the resin supply port side, A polyester resin composition kneading and extrusion process is performed by supplying polyester resin from a resin supply port, adding a calcium carbonate dispersion slurry to a twin-screw extruder from an additive section provided in the kneading section, and obtaining a polyester resin composition filtered by a leaf disc type filter. The kneading and extrusion process is stopped, and the filter is removed from the leaf-disc type filter and washed in a washing process. In a method for producing a polyester resin composition having the following characteristics: A method for producing a polyester resin composition, characterized in that the cleaning step includes a step of cleaning the filter with a solvent, then roasting it, and then cleaning it with an acid cleaning step in which the filter is cleaned with an acid solution containing at least one of nitric acid, hydrofluoric acid, and phosphoric acid.

2. The method for producing the polyester resin composition according to claim 1, wherein the acid washing step is performed by washing with an aqueous nitric acid solution.

3. A method for producing the polyester resin composition according to Claim 2, wherein the nitric acid concentration of the aqueous nitric acid solution is 30 to 400 g / L.

4. The method for producing a polyester resin composition according to any one of claims 1 to 3, wherein in the roasting process, the filter is heated in an oxygen-containing atmosphere at 350 to 480°C.

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