JP7707600B2 - Method for producing polyester resin composition - Google Patents

Description

The present invention relates to a method for producing a polyester resin composition. More specifically, the present invention relates to a method for producing a polyester resin composition that includes a step of adding a particle slurry to a polyester resin and kneading the mixture.

Biaxially oriented polyester resin films have excellent physical and chemical properties and are used as base films for magnetic recording media and as dielectrics for capacitors. In addition, 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 properties of polyester resin films, the surface of the film needs to be moderately roughened by adding particles such as calcium carbonate to the film, but it is desirable for the surface to be uniform and free of large protrusions.

When calcium carbonate particles are synthesized, they are obtained as a water slurry because the synthesis is carried out in a water solvent (Patent Document 1). However, this water slurry has a high pH and contains synthetic impurities. For commercially available particles, ethylene glycol ("EG") slurry is known. When EG slurry is added to the esterification process, which is a process for adding these particles to polyester resin, dispersibility is poor. In the polymerization process, dispersibility will be poor if the particle concentration is not adjusted to a low concentration, but if the concentration is low, there will be too much EG and the balance will be poor, so dispersion will also be poor. If it is added in another process, depolymerization will occur 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 is low, at 0.001 to 1.0% by weight of the composition, and the particle concentration in the aqueous dispersion is low, at 0.01 to 10% by weight.

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

Japanese Patent Application Publication No. 6-269615 JP 2019-112588 A JP 2020-146938 A

The object of the present invention is to provide a method for producing a polyester resin composition that has a high inorganic particle concentration and that is capable of producing a polyester resin composition that has good properties, i.e., particle dispersibility and particle aggregation properties, when made into a biaxially stretched film.

The inventors discovered that when polyester resin is mixed with a highly concentrated aqueous dispersion (aqueous slurry) of inorganic particles, the aqueous slurry is injected and sprayed into the first half of the mixing section of a mixer, and when the polyester resin composition is made into a biaxially stretched film, a film with good inorganic particle dispersibility and no particle aggregation is obtained, and the inventors have completed the invention based on this finding.

The gist of the present invention is as follows:

[1] A method for producing a polyester resin composition by supplying a polyester resin from a resin supply port side to a twin-screw extruder equipped with a plasticizing section, a kneading section, and a degassing section in this order, and adding a particle dispersion slurry from an addition section provided in the kneading section into the twin-screw extruder, the addition section being located in the middle of the kneading section in the longitudinal direction of the twin-screw extruder or closer to the plasticizing section than that.

[2] The method for producing a polyester resin composition according to [1], wherein the distance from the boundary between the plasticizing section and the kneading section to the adding section is within 40% of the length of the kneading section.

[3] The method for producing a polyester resin composition according to [1], wherein the distance from the boundary between the plasticizing section and the kneading section to the adding section is within 30% of the length of the kneading section.

The method for producing a polyester resin composition of the present invention makes it possible to produce a polyester resin composition having a high inorganic particle concentration and excellent properties, i.e., particle dispersibility and particle aggregation properties, when made into a biaxially stretched film.

FIG. 1 is a side view of a twin-screw extruder.

In the present invention, a polyester resin composition is produced by supplying a polyester resin from the resin supply port side to a twin-screw extruder equipped with a plasticizing section, a kneading section, and a degassing section in this order, and adding a particle dispersion slurry into the twin-screw extruder from an addition section provided in the kneading section.

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

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. In addition, as the glycol component, one or more of diethylene glycol, propylene glycol, butanediol, 1,4-cyclohexanedimethanol, and neopentyl glycol can be used. In the polyester resin of the present invention, 80 mol % or more of the repeating structural units have ethylene terephthalate units or ethylene-2,6-naphthalate units.

This polyester resin is fed into a twin-screw extruder, and the particle dispersion slurry is injected into the kneading section, where it is further kneaded and extruded to produce 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 which synthetic calcium carbonate, spherical silicon oxide, crosslinked organic particles, etc., which are produced by a synthetic method and have a narrow particle size distribution, are preferred. The average particle size (d50) of the particles is preferably 0.05 to 3 μm when used for film applications. In addition, when integrating from the large particle side, the value of the ratio [d25/d75] of the particle size (d25) at 25% of the particle cumulative weight to the particle size (d75) at 75% of the particle cumulative weight is preferably 2.2 or less, more preferably 2.0 or less, and even more preferably 1.8 or less.

<Concentration of particle dispersion 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.

<Addition amount of particle dispersion slurry>
The amount of the particle-dispersed slurry added to the twin-screw extruder is preferably an amount that results in a particle content in the produced polyester resin composition of 0.1 to 10.0% by weight, particularly 0.5 to 6.0% by weight, and especially 1.0 to 5.0% by weight. In order to suppress hydrolysis of the polyester resin, the amount of the particle-dispersed slurry added is preferably in the range of 0.5 to 10% by weight relative to the polyester resin.

<Particle Dispersion Slurry Medium>
The medium is mainly composed of water, and the proportion of water in the medium is preferably 40% by weight or more.

An example of a medium other than water is ethylene glycol, which is derived from the slurry raw material.

The ethylene glycol concentration in the water slurry is calculated by measuring the Brix value of the filtrate at the completion of the water slurry replacement using a saccharometer (manufactured by Atago Co., Ltd.) as described below. The ethylene glycol concentration in 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. The lower the ethylene glycol concentration in the slurry, the better, but to reduce it to 2% by weight or less, it takes a long time to replace the solvent. If it exceeds 5% by weight, the ethylene glycol tends to cause depolymerization of the polyester resin when added to the twin-screw extruder, and the intrinsic viscosity tends to decrease.

<Replacement of medium in slurry (raw material slurry) containing particles produced by synthetic method>
Particles produced by the synthesis 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 in particle synthesis. When the medium is water, the pH is high and undesirable impurities are mixed in. In addition, methanol and the like are often used as the organic solvent. These organic solvents are often not used in the polyester resin production process, and it is not desirable to add them to the polyester resin.

Therefore, in the case of a raw 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 slurry with ethylene glycol to obtain an ethylene glycol slurry is not particularly limited, and for example, there is a method of concentrating and drying the solvent liquid to obtain a powder, and then adding ethylene glycol, or a method of directly adding ethylene glycol and concentrating it under reduced pressure to remove the water or organic solvent, etc., but as described in JP-A-6-269615, it is preferable to use a filter material with a pore size (μm) of preferably d50×0.1 or more and d50×12 or less, and to repeat concentration by filtration and dilution with ethylene glycol to obtain an ethylene glycol slurry.

<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 by the following method. By converting it into a water slurry, the particle slurry can be added even during times other than polymerization.

The medium replacement for converting the ethylene glycol slurry into a water slurry is preferably carried out by repeatedly concentrating the mixture by filtration and diluting it with water using a filter medium whose pore size (μm) is preferably d50×0.1 or more and d50×12 or less.

<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 may be added as necessary. The material of the filter medium is preferably ceramic because of its corrosion resistance and solvent resistance.

There are two types of filtration methods: cross-flow filtration, in which the liquid to be filtered is passed over the surface of a membrane filter, and the accumulated cake layer is kept to a minimum by the shear force of parallel flow, and filtration is performed; direct filtration, in which the liquid to be filtered is directly filtered through a membrane filter. Either method may be used.

By filtering the slurry, it is separated into the medium as a filtrate and a concentrated slurry (particles + medium). Water is added to the concentrated slurry to dilute it and filter it 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, and it is diluted to a particle concentration of about 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 process, the ethylene glycol is gradually replaced with water, and a slurry whose medium is mainly water can be obtained. By concentrating the slurry obtained in this way, a slurry whose medium is mainly water and of the desired concentration can be obtained.

If the pore size of the filter medium used for the above concentration is less than d50 x 0.1 μm, the filtration speed is low, so concentration takes a long time, which is not preferable. If the pore size exceeds d50 x 12, particles will flow out together with the filtered dispersion medium during concentration by filtration, which is also not preferable.

The slurry concentration at the start of replacing the dispersion medium is preferably a concentration that can maintain good particle dispersibility, and varies depending on the type and particle size of the particles. In the case of synthetic calcium carbonate, spherical silicon oxide, and crosslinked organic polymer particles, the concentration at the start of replacement is usually in the range of 10 to 60% by weight, and preferably 15 to 50% by weight. If the concentrated slurry concentration is less than 10% by weight, efficiency tends to decrease, and if the slurry concentration exceeds 60% by weight, particles may aggregate in the concentrated slurry.

[Twin-screw kneading extruder]
For the kneading, a twin-screw extruder (twin-screw kneading extruder) is used.

Figure 1 is a side view of a twin-screw kneading extruder. As is well known, this twin-screw kneading extruder performs kneading and extrusion by rotating the screws inside the barrel (cylinder) 1 using a drive device M.

The polyester resin supplied from the polymer inlet 2 is melted in the plasticization section A and transferred to the kneading section B. Then, the particle dispersion slurry is injected (preferably by pressure spraying) into the molten resin 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. The dispersion medium, water, is removed by suctioning the inside of the barrel 1 with a vacuum pump (not shown) connected to the vent port 4. The resin composition is extruded as strands from the extrusion port at the end of the barrel 1, and then, although not shown, is cut in water and pelletized.

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

The boundary positions between the plasticization section, kneading section, and degassing section are determined by the difference in the blades of the screws inside the barrel. Kneading disks are usually used as the screw pieces in the plasticization section and kneading section, and full-flight screws are usually used as the screw pieces in the degassing section. The boundary position between the plasticization section A and the kneading section B is determined by the blade switching 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 positioned on the side closer to the plasticization section A than the center of the barrel longitudinal direction of the kneading section B, i.e., within 50%, preferably within 40%, and more preferably within 30% of the upstream end of the kneading section B (the boundary between the plasticization section A and the kneading section B).

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

[Uses and intrinsic viscosity of polyester resin composition]
The polyester resin composition thus produced can be used to produce a film by various methods. As a molding method, a known film production method can be applied, for example, a polyester sheet can be obtained by melting at a temperature equal to or higher than the melting point of the polyester and then extruding the polyester. Furthermore, the obtained polyester sheet can be biaxially stretched to obtain a polyester film.

<Intrinsic Viscosity of Polyester Resin Composition>
The intrinsic viscosity of the polyester resin composition is preferably 0.50 dL/g or more, more preferably 0.52 dL/g or more. If this value is less than 0.50 dL/g, pelletization may not be possible. The upper limit is not particularly limited, but is preferably about 0.70 dL/g.

The intrinsic viscosity of the polyester resin composition was measured by dissolving about 0.25 g of a sample in about 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, cooling the solution to 30° C., and measuring the number of seconds it takes for the sample solution and the solvent alone to fall at 30° C. using a fully automatic solution viscometer (DT553, manufactured by Sentec Co., Ltd.), and calculating the intrinsic viscosity (IV) according to the following formula.
IV=((1+4KHηsp)0.5-1)/(2KHC)
Here, ηsp=η/η0-1, 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. KH is 0.33. The sample dissolution conditions are 110°C and 30 minutes.

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 as long as it does not deviate from the gist of the invention. The measurement methods and definitions for various physical properties and characteristics in the examples are as follows. In the examples and comparative examples, "parts" refers to "parts by weight."

[Measurement method]
<Average particle size of inorganic particles contained in slurry>
0.03 to 0.10 g of inorganic particle slurry was mixed with 200 ml of pure water and treated with a sample supplying device with an ultrasonic dispersion device (MICROTRAC SDC, manufactured by Microtrack Bell), and the average particle size was measured with a laser diffraction particle size distribution analyzer (MT-3000II, manufactured by Microtrack Bell). The average particle size in this case is the particle size at which the volume fraction reaches 50%.

<Particle concentration of inorganic particles contained in slurry>
3.0 to 5.0 g of inorganic particle slurry is weighed out onto an aluminum dish, placed on a 200°C hot plate, and left for 1 hour to evaporate only the dispersion solvent. Then, the dish is pre-cooled for 3 minutes in a desiccator, and re-weighed to obtain the particle concentration.

<Average particle size of inorganic particles (aggregated particles (secondary particles)) in produced polyester resin composition>
160 ml of a phenol-tetrachloroethane mixed solvent (weight ratio 2:3) is added to 3.2 g of the polyester resin composition, and the mixture is stirred for 30 minutes while heating at 130° C. to dissolve the polyester resin composition to obtain a slurry. The slurry is cooled to room temperature, and the average particle size is measured using a laser diffraction particle size distribution meter (manufactured by Microtrackbell, “MT-3000II”). The average particle size in this case is the particle size at which the volume fraction reaches 50%.

<Evaluation of particle dispersibility in polyester resin composition>
The percentage (volume basis, %) of particles with a particle diameter of 10 μm or more was calculated from the particle size cumulative distribution obtained by measuring the average particle diameter of the particles in the polyester resin composition. The smaller the percentage, the better the particle dispersibility. The percentage was judged as ◎ (excellent) when it was 5.0% or less, ○ (good) when it was 5.1% or more and 10.0% or less, △ (fair) when it was 10.1% or more and 15.0 or less, and × (bad) when it was 15.1% or more.

<Film characteristics (number of large protrusions)>
Measurements were made using Bruker AXS's "Contour GT-X" (registered trademark), and the maximum peak height Sp value was determined from the obtained surface profile curve. The number of Sp particles of 400 nm or more in 36 screens was counted and regarded as the number of coarse protrusions. The lower this value, the better. Five or fewer particles were regarded as good (◯), and six or more particles were regarded as unacceptable (×). (Foreign matter is counted as a coarse protrusion.)

[Method of preparing slurry]
<Preparation of calcium carbonate slurry (I)>
60 kg of ethylene glycol slurry of colloidal calcium carbonate particles having an average particle size d50 of 0.95 μm ("MG-10" manufactured by Maruo Calcium Co., Ltd.; particle concentration in the slurry is 40.0% by weight) was added with 60 kg of pure water, and diluted to a particle concentration of 20% by weight to obtain a slurry stock solution. Then, this slurry stock solution was concentrated by filtering with a filter (a ceramic concentration filter equipped with a ceramic membrane with a pore size of 0.2 μm (Cefilt filter manufactured by NGK Filtech Co., Ltd.)). Every time 10 kg of filtrate was discharged from the filter, 10 kg of pure water was added to the concentrated slurry to dilute it, and the particle concentration was returned to 20% by weight. This concentration and dilution operation was repeated 15 times. Next, 60 kg of filtrate was discharged from the filter, and concentrated to a slurry concentration of about 40% by weight. The particle concentration in the obtained slurry was 41.8% by weight, and the ethylene glycol concentration in the slurry was 3.9% by weight. The calcium carbonate in the obtained slurry had good dispersibility and was designated as calcium carbonate slurry (I).

<Preparation of calcium carbonate slurry (II)>
25 kg of pure water was added to 25 kg of ethylene glycol slurry of colloidal calcium carbonate particles having the same average particle size d50 of 0.95 μm as above, and the slurry was diluted to a particle concentration of 20% by weight to obtain a slurry stock solution. The slurry was then concentrated by filtering with the same ceramic concentration filter as above. Every time 10 kg of filtrate was discharged from the filter, the slurry stock solution was diluted by adding 10 kg of pure water to return the particle concentration to 20% by weight. This concentration and dilution operation was repeated six times. Next, 30 kg of filtrate was discharged from the filter, and the slurry was concentrated to a slurry concentration of about 50% by weight. The particle concentration in the obtained slurry was 52.8% by weight, and the ethylene glycol concentration in the slurry was 2.8% by weight. The dispersibility of calcium carbonate in the obtained slurry was good. This slurry was named calcium carbonate slurry (II).

<Preparation of calcium carbonate slurry (III)>
Calcium carbonate slurry (III) was prepared in the same manner as calcium carbonate (II) except that an ethylene glycol slurry of colloidal calcium carbonate particles having an average particle size d50 of 0.68 μm ("MG-7" manufactured by Maruo Calcium Co., Ltd.; particle concentration in the slurry was 40.0% by weight) was used. The particle concentration in the obtained slurry was 50.5% by weight, and the ethylene glycol concentration in the slurry was 3.5% by weight. The dispersibility of calcium carbonate in the obtained slurry was good.

<Production of Polyester Resin>
A continuous polymerization apparatus was used, which consisted of one stock solution preparation tank, two esterification reaction tanks connected in series to the tank, and a three-stage melt polycondensation tank connected in series to the second esterification reaction tank. Terephthalic acid and ethylene glycol were continuously supplied to the stock solution preparation tank at a weight ratio of 100:45, and an ethylene glycol solution of ethyl acid phosphate was continuously added in an amount such that the phosphorus atom content in the produced polyester resin was 7 ppm by weight, and the mixture was stirred and mixed to prepare a slurry stock solution. This slurry 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.

Next, an ethylene glycol solution of magnesium acetate tetrahydrate was added to the esterification reaction product in an amount such that the magnesium atom content in the resulting polyester resin was 9 ppm by weight, and an ethylene glycol solution of tetra-n-butyl titanate was added in an amount such that the titanium atom content in the resulting polyester resin was 4.5 ppm by weight, and melt polycondensation was carried out in the first polycondensation reaction tank and then in the second polycondensation reaction tank.

Then, polycondensation reactions were carried out in the second-stage polycondensation reaction tank and then in the 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 of the third-stage polycondensation reaction tank was extruded from a die in the form of strands, cooled and solidified, and cut with a cutter into polyester resin pellets each weighing an average of 24 mg. The intrinsic viscosity of the pellets was 0.560 dL/g.

Next, the molten polycondensed polyester resin pellets were continuously fed into a stirring crystallizer maintained at approximately 160°C under a nitrogen atmosphere so that the residence time was approximately 60 minutes, and then continuously fed into a tower-type solid-phase polycondensation apparatus, where solid-phase polycondensation was carried out at 210°C for 18 hours under a nitrogen atmosphere.

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

[Example 1]
A vented twin-screw extruder having the configuration shown in FIG. 1 (AUTOMATIK's "ZCM", screws rotating in the same direction, barrel inner diameter D: 71 mm, length of plasticization section A: 800 mm, length of kneading section B: 600 mm, length of degassing section C: 1000 mm, position of nozzle 3 for adding slurry: 162 mm from the upstream of kneading section B (length of kneading section B: 27%)) was used.

The polyester resin produced as described above was fed 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. Calcium carbonate slurry (I) was also injected from nozzle 3. The amount of slurry added was set so that the particle concentration in the polyester resin composition was 1.5% by weight. The vent port vacuum degree was set to -0.098 MPa for degassing. The extruded polyester resin composition was cut in water to form pellets. The intrinsic viscosity of the pellets was 0.534 dL/g. The evaluation results of the calcium carbonate particle dispersibility and film properties of the obtained polyester resin composition are shown in Table 1.

[Example 2]
The polyester resin composition was melt-kneaded, pelletized, and evaluated in the same manner as in Example 1, except that the amount of calcium carbonate slurry (I) added was adjusted so that the particle concentration in the polyester resin composition was 2% by weight. The results are shown in Table 1.

[Example 3]
The polyester resin composition was melt-kneaded, pelletized, and evaluated in the same manner as in Example 1, except that the calcium carbonate slurry (II) was used and the amount added was adjusted so that the particle concentration in the polyester resin composition was 3.6% by weight. The results are shown in Table 1.

[Example 4]
The polyester resin composition was melt-kneaded, pelletized, and evaluated in the same manner as in Example 3, except that the calcium carbonate slurry (III) was used and the amount of the calcium carbonate slurry added was adjusted so that the particle concentration in the polyester resin composition was 2% by weight. The results are shown in Table 1.

[Example 5]
The polyester resin composition was melt-kneaded and pelletized in the same manner as in Example 1, except that calcium carbonate slurry (III) was used in such an amount that the particle concentration in the polyester resin composition was 4.7% by weight and the discharge rate during melt-kneading was 100 kg/h, and evaluation was performed. The results are shown in Table 1.

[Reference example 1]
<Preparation of Silica Slurry>
25 kg of ethylene glycol slurry of spherical silica particles having an average particle size d50 of 0.44 μm ("KE-E50" manufactured by Nippon Shokubai Co., Ltd.; particle concentration in the slurry is 20.0% by weight) was added with 25 kg of pure water, and diluted to a particle concentration of 10% by weight to obtain a slurry stock solution. The slurry was then concentrated by filtering with the same ceramic concentration filter as above, except that a ceramic membrane with a pore size of 0.1 μm was installed. Every time 10 kg of filtrate was discharged from the filter, 10 kg of pure water was added to dilute the filtrate and the particle concentration was returned to 10% by weight. This concentration and dilution operation was repeated six times. Next, 37.5 kg of filtrate was discharged from the filter, and the slurry was concentrated to a concentration of about 40% by weight. The particle concentration in the obtained slurry was 38.9% by weight, and the ethylene glycol concentration in the slurry was 3.7% by weight. The dispersibility of silica in the obtained water slurry was good.

The polyester resin composition was melt-kneaded and pelletized in the same manner as in Example 1, except that this silica slurry was used and the particle concentration in the polyester resin composition was 2% by weight. The evaluation was performed. The results are shown in Table 1.

[Comparative Example 1]
The same operations as in Example 1 were carried out except that the calcium carbonate slurry (I) was changed to the calcium carbonate ethylene glycol slurry prepared in Reference Example 2 below. However, the intrinsic viscosity was decreased, and strands could not be obtained.

[Reference example 2]
<Preparation of ethylene glycol slurry of calcium carbonate>
To 60 kg of an ethylene glycol slurry of colloidal calcium carbonate particles having an average particle size d50 of 0.95 μm ("MG-10" manufactured by Maruo Calcium Co., Ltd.; particle concentration in the slurry is 40.0% by weight), 60 kg of ethylene glycol was added to dilute the slurry to a particle concentration of 20% by weight.

100 parts by mass of dimethyl terephthalate and 65 parts by mass of ethylene glycol were charged into an ester exchange reaction tank equipped with a stirrer, a temperature raising device, and a distillate separation tower, and the dimethyl terephthalate was melted by heating to 150°C. Next, magnesium acetate was added to the resulting polyester resin in an ethylene glycol solution in an amount of 0.09 parts by mass, and the temperature was raised to 225°C over 3 hours under normal pressure, and the mixture was further stirred and held at 225°C for 1 hour and 15 minutes while distilling off the methanol to carry out the ester exchange reaction, essentially completing the ester exchange reaction and obtaining a polyester low polymer (oligomer).

Next, the polyester oligomer was transferred to a polycondensation reaction tank equipped with a stirring device, a heating device, and a pressure reducing device, and then an ethylene glycol slurry of colloidal calcium carbonate particles was added to the oligomer while stirring so that the particle concentration was 2.0% by weight relative to the polyester resin content.

Next, an ethylene glycol solution of phosphoric acid as a thermal stabilizer was added to the oligomer so that the phosphoric acid content was 0.03 parts by mass relative to the polyester resin content obtained, and an ethylene glycol solution of antimony trioxide as a polycondensation catalyst was added to the oligomer so that the antimony trioxide content was 0.04 parts by mass relative to the polyester resin content obtained. The pressure was then reduced from 101.3 kPa to 0.4 kPa over 85 minutes and held at 0.4 kPa, while the temperature was raised from 225°C to 280°C over 2 hours and held at 280°C for 1.5 hours to carry out a polycondensation reaction, yielding a polyester resin composition with an intrinsic viscosity of 0.62 dL/g. As a result of film formation, coarse foreign matter was generated.

1 Barrel 2 Polymer inlet 3 Slurry addition nozzle 4 Vent port

Claims (2)

A method for producing a polyester resin composition by feeding a polyester resin from a resin supply port side to a twin-screw extruder equipped with a plasticizing section, a kneading section, and a degassing section in this order, and adding a particle-dispersed slurry from an addition section provided in the kneading section into the twin-screw extruder,
The adding section is located on the plasticizing section side of the kneading section from the middle of the twin-screw extruder in the longitudinal direction, in the method for producing a polyester resin composition ,
The distance from the boundary between the plasticizing section and the kneading section to the adding section is within 40% (excluding 0%) of the length of the kneading section,
The ratio of water in the medium in the particle-dispersed slurry is 40% by weight or more, and the concentration of ethylene glycol in the particle-dispersed slurry is 5% by weight or less.
A method for producing a polyester resin composition. The method for producing a polyester resin composition according to claim 1, wherein the distance from the boundary between the plasticizing section and the kneading section to the adding section is within 30% of the length of the kneading section.