JP2023134067A - Method for manufacturing polyester resin composition - Google Patents

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

The present invention relates to a method for producing a polyester resin composition. Specifically, it includes a kneading and extrusion step in which a slurry of particles is added to a polyester resin and kneaded to obtain a polyester resin composition through a filter section, and a cleaning step in which the kneading and extrusion step is stopped and the filter in the filter section is removed and washed. The present invention relates to a method for producing a polyester resin composition.

Biaxially oriented polyester resin films have excellent physical and chemical properties and are used as base films for magnetic recording media and dielectric materials for capacitors. Furthermore, due to its excellent transparency, it is widely used in fields such as graphic arts, displays, and packaging materials. In order to improve the running properties of polyester resin films, it is necessary to appropriately roughen the surface of the film by including particles such as calcium carbonate in the film, but it is desirable that the surface be uniform and free of rough protrusions. It is rare.

When calcium carbonate particles are synthesized, the synthesis is carried out in an aqueous solvent, so that they are obtained as an aqueous slurry (Patent Document 1). However, this water slurry has a high pH and contains synthetic impurities. For commercially available particles, ethylene glycol ("EG") slurries are known. When EG slurry is added to the esterification step in which the particles are added to the polyester resin, the dispersibility is poor. In the case of the polymerization process, if the particle concentration is not adjusted to a low concentration, dispersibility will deteriorate, but if the concentration is low, too much EG will be present and the balance will be poor, resulting in poor dispersion. When added in other steps, depolymerization occurs because EG cannot be discharged.

Patent Document 2 describes a method of adding an aqueous dispersion of particles to a twin-screw kneader when producing a composition of polyester resin and inorganic particles, but the amount of particles blended is The particle concentration in the aqueous dispersion is as low as 0.01 to 10% by weight.

Patent Document 3 describes that when producing a polyester resin/inorganic particle composition (amount of particles in the composition: 1 to 30% by weight), a slurry with a particle concentration of 5 to 80% by weight in an aqueous dispersion is used. A method is described in which the mixture is injected by spraying using the pressure difference between the inside of the kneader and the inside of the kneader. However, when a polyester resin composition is made into a biaxially stretched film, it is not sufficient to improve the dispersibility and cohesiveness of inorganic particles and to improve the film properties.

Patent Document 4 describes that a leaf disk type filter is provided at the tip of a polymer extruder to filter and extrude the polymer.

Japanese Patent Application Publication No. 6-269615 JP2019-112588A JP2020-146938A JP2012-213983A

Leaf disc filters become clogged over time, so they need to be removed and cleaned.

An object of the present invention is to provide a method for producing a polyester resin composition that can sufficiently clean a leaf disc type filter.

The gist of the invention is as follows.

[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 disk type filter in this order from the resin supply port side,
A polyester resin composition in which a polyester resin is supplied from a resin supply port, and a particle-dispersed slurry is added into a twin-screw extruder from an addition section provided in the kneading section to obtain a polyester resin composition filtered with a leaf disk type filter. The kneading and extrusion process,
A method for producing a polyester resin composition, comprising a washing step of stopping the kneading and extrusion step and removing and washing the filter from the leaf disc type filter,
A method for producing a polyester resin composition, wherein the washing step includes an acid washing step of washing the filter with an acid solution containing at least one of nitric acid, fluoronitric acid, and phosphoric acid.

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

[3] The method for producing a polyester resin composition according to [1] or [2], in which the acid washing step is performed by washing with an aqueous nitric acid solution.

[4] The method for producing a polyester resin composition according to [3], wherein the nitric acid concentration of the nitric acid aqueous solution is 30 to 400 g/L.

According to the present invention, the filter of a leaf disk type filter can be sufficiently cleaned.

It is a side view of a twin-screw extruder. FIG. 2 is a cross-sectional view of a leaf disc type filter. FIG. 3 is a plan view of the filter. 4 is a sectional view taken along the line IV-IV in FIG. 3. FIG.

In the present invention, polyester resin is supplied from the resin supply port side to a twin screw extruder equipped with a plasticizing section, a kneading section, a degassing section, and a leaf disk type filter in this order, and from an addition section provided in the kneading section. A polyester resin composition is produced by adding a particle-dispersed slurry into a twin-screw extruder, filtering it through a leaf disk type filter, and extruding it.

[Polyester resin]
The polyester resin used in the present invention is not particularly limited, and refers to a polyester obtained using aromatic dicarboxylic acids such as terephthalic acid and 2,6-naphthalene dicarboxylic acid or their esters, and ethylene glycol as the main starting materials, but other It may also contain a third component.

As the dicarboxylic acid component, one or more of, for example, isophthalic acid, terephthalic acid, 2,6-naphthalene dicarboxylic 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, neopentyl glycol, etc. can be used. In the polyester resin of the present invention, 80 mol% or more of repeating structural units have ethylene terephthalate units or ethylene-2,6-naphthalate units.

This polyester resin is supplied to a twin-screw extruder, and a particle-dispersed slurry is injected into the kneading section of the extruder, which is further kneaded and extruded to obtain a polyester resin composition.

[Particle dispersion slurry]
<Particle>
The polyester additive particles used in the present invention are not particularly limited, but include calcium carbonate, silicon oxide, crosslinked organic polymer particles, talc, clay, kaolin, etc. Among them, synthetic carbonic acid produced by a synthetic method and having a narrow particle size distribution Calcium, spherical silicon oxide, crosslinked organic particles, etc. are preferred. The average particle diameter (d50) of the particles is preferably 0.05 to 3 μm when used in film applications. In addition, when integrating from the large particle side, the ratio [d25/d75] of the particle diameter (d25) when the cumulative weight of the particles is 25% and the particle diameter (d75) when the cumulative weight of the particles is 75% is 2. .2 or less is preferable, 2.0 or less is more preferable, and 1.8 or less is even more preferable.

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

<Amount of particle dispersion slurry added>
The amount of the particle dispersion slurry added to the twin screw extruder is such that the particle content in the produced polyester resin composition is 0.1 to 10.0% by weight, particularly 0.5 to 6.0% by weight, In particular, the amount is preferably 1.0 to 5.0% by weight. In addition, in order to suppress hydrolysis of the polyester resin, the amount of the particle dispersion slurry added is preferably in the range of 0.5 to 10% by weight based on the polyester resin.

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

An example of the medium other than water is ethylene glycol derived from slurry raw materials.

The method for calculating the ethylene glycol concentration contained in the water slurry is to measure the filtrate at the time of completion of water slurry replacement, which will be described later, using a sugar content meter (manufactured by Atago Co., Ltd.), and calculate the Brix value. The ethylene glycol concentration (A) of the filtrate is calculated as A = 1.6153 * Brix value - 0.9458, and the ethylene glycol concentration (B) contained in the water slurry is calculated as B = (100 - particle concentration (C)) *Calculated by (A/100). The concentration of ethylene glycol contained in the water slurry is preferably 5% by weight or less. The lower the ethylene glycol concentration in the slurry, the better, but reducing the concentration to 2% by weight or less requires a long time for solvent replacement. If it exceeds 5% by weight, the polyester resin tends to depolymerize due to ethylene glycol when added to a twin-screw extruder, and the intrinsic viscosity tends to decrease.

<Replacement of medium of slurry (raw material slurry) containing particles produced by synthetic method>
Particles produced by a synthetic method are usually obtained as a particle-containing slurry (hereinafter sometimes referred to as raw material slurry) dispersed in the medium (water and/or organic solvent) used for particle synthesis. When the medium is water, it has a high pH and is contaminated with undesirable impurities. Furthermore, as the organic solvent, methanol or the like is often used. These organic solvents are often not used in the polyester resin manufacturing process, and it is not desirable to add them to the polyester resin.

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. The method of replacing the water or organic solvent in the raw material slurry with ethylene glycol to obtain an ethylene glycol slurry is not particularly limited, and for example, the solvent solution is concentrated and dried to obtain a powder, and then ethylene glycol is added. There is also a method in which ethylene glycol is directly added and concentrated under reduced pressure to remove water or organic solvent, but as described in JP-A-6-269615, it is preferable that the pore diameter of the filter medium be d50×0. It is preferable to prepare an ethylene glycol slurry by repeating concentration by filtration and dilution with ethylene glycol using a filter medium having a size of .1 μm or more and d50×12 μm or less.

<Replacement of ethylene glycol with water in ethylene glycol slurry>
The ethylene glycol slurry obtained as described above or the ethylene glycol slurry of commercially available particles is converted into a water slurry in the following manner. This is because by forming a water slurry, the slurry of particles can be added even at times other than during polymerization.

The medium replacement for turning the ethylene glycol slurry into a water slurry is carried out by repeating concentration by filtration and dilution with water using a filter medium whose pore diameter is preferably d50 x 0.1 μm or more and d50 x 12 μm or less. It is preferable to do so.

<Filtration device used for medium replacement>
The filtration device used for medium replacement is composed of a slurry storage tank, a slurry circulation pump, a filter having a filter medium, a pressure gauge, a heat exchanger, etc., and a storage tank etc. may be added as necessary. The filter material is preferably made of ceramic from the viewpoint of corrosion resistance and solvent resistance.

The filtration method is a method called cross-flow filtration, in which the liquid to be filtered is filtered while flowing over the surface of the membrane filter, and the accumulated cake layer is kept to a minimum by the shear force caused by parallel flow. There is a method called direct filtration in which filtration is performed directly with a membrane filter, and either method may be used.

By filtering the slurry, it is separated into a medium as a filtrate 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 with water. For example, water is added to a concentrated ethylene glycol slurry with a particle concentration of 40% by weight, diluted to a particle concentration of about 20% by weight, filtered, and the same amount of water as the discharged filtrate is added to the concentrated slurry. By repeating this concentration and dilution operation, ethylene glycol is gradually replaced with water, and a slurry whose medium is mainly water can be obtained. By concentrating the slurry thus obtained, it is possible to obtain a slurry having a target concentration and whose medium is mainly water.

If the pore diameter of the filter medium used for the above concentration is less than d50×0.1 μm, the filtration rate will be low, which is undesirable because the concentration will take a long time. If the pore diameter exceeds d50×12 μm, it is not preferable because particles will flow out together with the filtered dispersion medium during concentration by filtration.

The slurry concentration when starting to replace the dispersion medium is preferably a concentration that can maintain good dispersibility of the particles, and varies depending on the type and diameter of the particles. In the case of synthetic calcium carbonate, spherical silicon oxide, and crosslinked 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 concentration of the concentrated slurry is less than 10% by weight, the efficiency tends to deteriorate, and if the concentration of the slurry exceeds 60% by weight, particles may aggregate in the concentrated slurry.

[Twin-screw kneading extruder]
A twin-screw extruder (twin-screw kneading extruder) is used for kneading.

FIG. 1 is a side view of a twin-screw kneading extruder. As is well known, this twin-screw kneading extruder rotates a screw in a barrel (cylinder) 1 using a drive device M to perform kneading and extrusion.

The polyester resin supplied from the polymer inlet 2 is melted in the plasticizing section A and transferred to the kneading section B. Then, the particle-dispersed slurry is injected into the molten resin (preferably by injection spraying) from the slurry addition nozzle 3, and the molten resin and the slurry are mixed and kneaded, and then transferred to the degassing section C. Water, which is a dispersion medium, is removed by suctioning the inside of the barrel 1 by a vacuum pump (not shown) connected to the vent port 4. Next, the resin composition is supplied to a leaf disk type filter 6 by a gear pump 5, and after being filtered, the resin composition is extruded as a strand from an extrusion port 7, and then, although not shown, it is cut underwater and pelletized.

The barrel inner diameter of the twin-screw kneading extruder is 60 to 90 mm, especially 65 to 85 mm, the length of plasticizing section A is 400 to 1000 mm, especially 500 to 900 mm, the length of kneading section B is 400 to 1000 mm, especially 500 to 900 mm, degassing The length of portion C is preferably about 400 to 1300 mm, particularly about 500 to 1200 mm.

The boundary position of the plasticizing section, kneading section, and degassing section is determined by the difference in the screw blades in the barrel. A kneading disk is usually used as the screw piece in the plasticizing section and the kneading section, and a full flight screw is usually used as the screw piece in the degassing section. The boundary position between the plasticizing section A and the kneading section B is defined by switching the blade from a kneading disk to a full-flight screw. The combination of screw pieces can be changed as appropriate.

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

[Leaf disc type filter 6]
FIG. 2 is a schematic vertical cross-sectional view showing an example of the leaf disk type filter 6. As shown in FIG.

The leaf disk type filter 6 has a configuration in which a filter set 20 is arranged within a housing 10.
<Housing 10>
The housing 10 has a lower block 11, an upper block 12, and a side block 13. The lower block 11 has a cylindrical recess 11a recessed from the upper surface, and the filter set 20 is disposed within this recess 11a.

A predetermined gap is provided between the inner peripheral surface of the recess 11a and the outer peripheral surface of the filter set 20.

The upper block 12 is mounted and fixed on the lower block 11 so as to cover the filter set 20. A resin inlet portion 14 is formed on the side surface of the housing 10. Further, a resin flow path space 15 is formed above the filter set 20 .

In the lower block 11, a flow passage hole 16 for the filtered resin extends laterally from the center of the bottom surface of the recess 11a. The recess 11a and a filter set 20, which will be described later, are arranged coaxially.

The side block 13 is attached to the side surface of the upper block 12 and lower block 11. The side block 13 is provided with a channel hole 17 that communicates the channel hole 16 and the resin outlet 18 .

Note that by removing the upper block 12, the filter set 20 can be taken out from the housing 10. Further, after the cleaned filter set 20 is placed in the recess 11a of the lower block 11, the upper block 12 is attached, so that the leaf disk type filter 6 can be reused.

<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 substantially disc-shaped filter bodies 23 fitted into the center column 22 , and a center column 22 that extends from the center of the bottom base 21 . It has a top base 24 which is attached and presses down the collection of filter bodies 23 from above. The center column 22 has a pipe shape with a closed upper end, and is provided with a large number of small holes 22a passing through in the radial direction.

As shown in FIGS. 3 and 4, the filter main body 23 includes two upper and lower filter media 24 and 25 each having a substantially disk shape with a circular hole in the center of the plate, and two filter media 24 and 25 on the lower side of the filter media 24 and the filter media 25. Disc-shaped punching plates 26 and 27 each having a large number of overlapping small holes on the upper surface side, a mesh 28 interposed between the punching plates 26 and 27, a spacer 29 on the upper surface side of the filter media 24, and the punching plate 26. , 27, and the like. The outer peripheral edges of the punching plates 26 and 27 overlap. The inner peripheral edges of the punching plates 26 and 27 are separated from each other, and a mesh 28 is interposed between them.

The filter media 24 and 25 are composed of at least two or more layers of metal fiber nonwoven fabric with a porosity of 40 to 80%, and are formed of a laminated sintered body or the like that is pressure sintered to a predetermined thickness.

As shown in FIG. 3, the spacers 29 are rod-shaped members extending in the radial direction, and a plurality of spacers (10 in this embodiment, but not limited to this) are provided. The spacer 29 is for forming a resin flow path between each filter main body 23.

In this leaf disk type filter 6, the resin flowing from the inlet portion 14 passes through the resin flow path space 15 and flows between the outer circumference of the filter set 20 and the inner circumferential surface of the recess 11a. It enters between the main bodies 23, passes through the filter media 24 and 25, and is filtered. The filtered resin flows between the punching plates 26 and 27 through the small holes of the punching plates 26 and 27. Then, it flows along the mesh 28 toward the center of the filter body 23, flows into the center column 22 through the hole 22a of the center column 22, and flows out from the outlet portion 18 through the flow passage holes 16 and 17.

[Kneading conditions]
The cylinder temperature during kneading is preferably 200 to 300°C, particularly 220 to 290°C, the screw rotation speed is 80 to 270 rpm, particularly 100 to 200 rpm, and the discharge rate is preferably about 80 to 180 kg/h, particularly 100 to 150 kg/h.

[Applications and intrinsic viscosity of polyester resin composition]
Films can be produced from the polyester resin composition thus produced by various methods. As a molding method, a known film manufacturing method can be applied. For example, a polyester sheet can be obtained by extrusion molding after melting at a temperature equal to or higher than the melting point of polyester. Furthermore, a polyester film can be obtained by biaxially stretching the obtained polyester sheet.

<Intrinsic viscosity of polyester resin composition>
The intrinsic viscosity of the polyester resin composition is preferably 0.500 dL/g or more, more preferably 0.520 dL/g or more. If this value is less than 0.500 dL/g, pelletization may not be possible. The upper limit is not particularly limited, but is preferably about 0.850 dL/g.

To measure the intrinsic viscosity of a polyester resin composition, approximately 0.25 g of a sample was added to approximately 25 mL of a mixed solvent of phenol/1,1,2,2-tetrachloroethane (mass ratio 1/1) at a concentration of 1.00 g/1. dL, cooled to 30°C, measured the falling seconds of only the sample solution and solvent using a fully automatic solution viscometer (manufactured by Sentech, "DT553") at 30°C. Intrinsic viscosity (IV) is calculated using the formula.

IV=((1+4KHηsp)0.5-1)/(2KHC)
Here, ηsp=η/η0−1, η is the number of seconds for the sample solution to fall, η0 is the number of seconds for only the solvent to fall, C is the sample solution concentration (g/dL), and KH is Huggins' constant. KH adopts 0.33. Note that the conditions for dissolving the sample are 110° C. for 30 minutes.

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

In a preferred embodiment of the present invention, after the filter set 20 is taken out from the housing 10, it is immersed in an organic solvent such as triethylene glycol at 240 to 250°C, 110 to 230°C, and a pressure in the range of 0 to 0.2 MPaG. Soak for 20 to 30 hours to dissolve the adhering resin. Alternatively, the filter set is heated for 1 to 10 hours in an oxygen-containing atmosphere such as air at 350 to 480° C. to roast (vaporize and burn) the resin component.

Thereafter, the filter set 20 is disassembled and the filter body 23 is removed from the center column 22, preferably washed with water using a high-pressure washer to remove adhering residue, and then washed with acid.

At least one of nitric acid, fluoronitric acid, and phosphoric acid is used as the acid for acid cleaning.

In the case of nitric acid cleaning, the concentration is preferably 1 to 10 N, the water temperature is 50 to 60°C, and the cleaning time is preferably 0.5 to 2 hr.

In the case of hydrofluoric acid cleaning, the concentration is preferably 1 to 10 N, the water temperature is 50 to 60°C, and the cleaning time is preferably 0.5 to 2 hr. The molar ratio of hydrofluoric acid and nitric acid in the hydrofluoric nitric acid is preferably about 1:1 to 1:2.

In the case of phosphoric acid cleaning, the concentration is preferably 1 to 10 N, the water temperature is 50 to 70°C, and the cleaning time is preferably 0.5 to 2 hr. Note that cleaning may be performed using two or more types of acids, such as performing nitric acid cleaning after hydrofluoric nitric acid cleaning.

After acid cleaning, rinse with water and dry. It is preferable to use an ultrasonic cleaner for washing with water, but the method is not limited thereto.

In addition, when the polyester resin is PET and the added fine particles are calcium carbonate, it has been recognized that the filter media is likely to be clogged not only by the calcium carbonate particles but also by the calcium carboxylate. As clogging progresses, the filter media and spacers may become deformed or damaged.

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to the following Examples unless the gist thereof is exceeded. Measurement methods and definitions of various physical properties and characteristics in Examples are as follows. In Examples and Comparative Examples, "parts" indicate "parts by weight."

[Slurry preparation method]
<Preparation of calcium carbonate slurry (I)>
Add 60 kg of pure water to 60 kg of ethylene glycol slurry of colloidal calcium carbonate particles with an average particle diameter d50 of 0.95 μm (“MG-10” manufactured by Maruo Calcium Co., Ltd., particle concentration in the slurry is 40.0% by weight) to make a slurry. The slurry was diluted to a particle concentration of 20% by weight to obtain a slurry stock solution. Thereafter, this slurry stock solution was concentrated by filtration using a filtration device (ceramic concentration filtration device equipped with a ceramic membrane having a pore size of 0.2 μm (Sefilt filtration device manufactured by NGK FILTECH)). Every time 10 kg of filtrate was discharged from the filtration device, 10 kg of pure water was added to the concentrated slurry to dilute it to return the particle concentration to 20% by weight. This concentration and dilution operation was repeated 15 times. Next, 60 kg of the filtrate was discharged from the filtration device and concentrated to a slurry concentration of about 40% by weight. The particle concentration in the resulting slurry was 41.8% by weight, and the ethylene glycol concentration in the slurry was 3.9% by weight. The dispersibility of calcium carbonate in the obtained slurry was good. This slurry was designated as calcium carbonate slurry (I).

<Production of polyester resin>
Continuous polymerization equipment 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. was used. Terephthalic acid and ethylene glycol are continuously supplied to the stock solution preparation tank at a weight ratio of 100:45, and an ethylene glycol solution of ethyl acid phosphate is added to the resulting polyester resin so that the content as phosphorus atoms is 7. A slurry-like stock solution was prepared by continuously adding, stirring and mixing in an amount of ppm by weight. This slurry-like stock solution was continuously transferred to a first-stage esterification reaction tank and then to a second-stage esterification reaction tank to perform an esterification reaction.

Next, to this esterification reaction product, an ethylene glycol solution of magnesium acetate tetrahydrate was added in an amount such that the content as magnesium atoms was 9 ppm by weight based on the produced polyester resin, and further tetra-n-butyl titanate was added. The ethylene glycol solution was added to the resulting polyester resin in an amount such that the titanium atom content was 4.5 ppm by weight, and melt polycondensation was carried out in the first stage polycondensation reaction tank and then in the second stage polycondensation reaction layer. I did it.

Next, a polycondensation reaction was carried out in a second-stage polycondensation reaction tank and further in a third-stage polycondensation reaction tank at 277° C., an absolute pressure of 0.2 kPa, and an average residence time of 1 hour.

The molten polycondensation reaction product taken out from the third-stage polycondensation reactor was extruded from a die into a strand, cooled and solidified, and cut with a cutter into polyester resin pellets each weighing an average of 24 mg. The intrinsic viscosity of this pellet was 0.560 dL/g.

Next, the molten polycondensed polyester resin pellets were continuously fed into a stirring crystallizer maintained at about 160°C under a nitrogen atmosphere for crystallization so that the residence time was about 60 minutes. The solid phase polycondensation was carried out at 210° C. for 18 hours under a nitrogen atmosphere.

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

[Kneading and extrusion of polyester resin]
A vented twin-screw extruder with the configuration shown in Figure 1 (“ZCM” manufactured by AUTOMATIK, screws rotating in the same direction, barrel inner diameter D: 71 mm, length of plasticizing section A: 800 mm, length of kneading section B: 600 mm, degassing The length of part C was 1000 mm, and the position of the nozzle 3 for adding slurry was 162 mm from the upstream of kneading part B (27% of the length of kneading part B).

As the leaf disk type filter 6, one having the structure shown in FIG. 2 and equipped with a filter set 10 having ten filter bodies 23 was used. The configuration of the filter body 23 was as follows.

Outer diameter: 304.8mm
Inner diameter: 63.5mm
Spacer thickness: 2mm
Filter media: Made of stainless steel with a thickness of 0.7 mm. Porosity 40-80%
Distance between filter media (excluding outer periphery): 2.4mm
Mesh: Stainless steel wire mesh with a wire diameter of 1.2 mm. Eye opening 8mm (8 mesh).

The above polyester resin was charged from the 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. Further, calcium carbonate slurry (I) was injected from nozzle 3. The amount of slurry added was such that the particle concentration in the polyester resin composition was 1.5% by weight. The degree of vacuum at the vent port was set to -0.098 MPa and degassed. The extruded polyester resin composition was cut into pellets in water.

After running for 53 hours, the filter pressure became 42 bar, so the filter set was taken out and washed as in Cleaning Example 1 and Cleaning Comparative Example 1 below.

[Cleaning Example 1]
<Solvent cleaning treatment>
The filter set was immersed in 100 L of triethylene glycol (TEG) heated to 245° C. for 24 hours to dissolve the resin. Thereafter, 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. Thereafter, the leaf filter was immersed in an ultrasonic cleaner in a water bath and subjected to ultrasonic waves for 3 hours to further remove deposits. Thereafter, the filter was removed from the ultrasonic cleaner and air-dried.

<Roasting process>
After the solvent cleaning treatment, the leaf filter was roasted at 400° C. for 2 hours in an air atmosphere, immersed in an alkaline solution (NaOH, pH 13) for 2 hours, and then ultrasonically cleaned in a water bath and air-dried.

<Acid cleaning>
After the above-mentioned roasting treatment, it was immersed in 100 L of nitric acid solution for 2 hours, and then subjected to ultrasonic cleaning in a water bath and air-dried.

The nitric acid solution is an aqueous solution containing 130 g/L of nitric acid.

[Cleaning Comparative Example 1]
The same filter set as that used for cleaning in Cleaning Example 1 was subjected to only the solvent cleaning treatment in Cleaning Example 1.

[Manufacture of polyester resin composition after reinstallation]
When the leaf disk type filter equipped with the filter cleaned in Cleaning Example 1 and Cleaning Comparative Example 1 was assembled into a twin-screw extruder and a polyester resin composition was produced again under the same conditions, the filter pressure reached 42 bar. The time was 53 hr in the case of Cleaning Example 1 and 33 hr in the case of Comparative Cleaning Example 1. From this result, it was confirmed that the filter of the leaf disk type filter could be sufficiently cleaned according to the method of the present invention.

1 Barrel 2 Polymer inlet 3 Slurry addition nozzle 4 Vent port 5 Gear pump 6 Leaf disc filter 7 Extrusion port 10 Housing 20 Filter set 21 Bottom base 22 Center column 23 Filter body 24, 25 Filter media 26, 27 Punching plate 28 Mesh 29 Spacer 30, 31 Hub

Claims (4)

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 disk type filter in this order from the resin supply port side, the method comprising:
A polyester resin composition in which a polyester resin is supplied from a resin supply port, and a particle-dispersed slurry is added into a twin-screw extruder from an addition section provided in the kneading section to obtain a polyester resin composition filtered with a leaf disk type filter. The kneading and extrusion process,
A method for producing a polyester resin composition, comprising a washing step of stopping the kneading and extrusion step and removing and washing the filter from the leaf disc type filter,
A method for producing a polyester resin composition, wherein the washing step includes an acid washing step of washing the filter with an acid solution containing at least one of nitric acid, fluoronitric acid, and phosphoric acid. 2. The method for producing a polyester resin composition according to claim 1, wherein in the washing step, the filter is washed with a solvent, then roasted, and then washed with an acid. 3. The method for producing a polyester resin composition according to claim 1, wherein in the acid washing step, washing is performed with an aqueous nitric acid solution. The method for producing a polyester resin composition according to claim 3, wherein the nitric acid concentration of the nitric acid aqueous solution is 30 to 400 g/L.

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