JP2013227511A - Method for producing polycarbonate resin - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a polycarbonate resin in which the generation of foreign matter is controlled and which little contains foreign matter and holds good quality.SOLUTION: A method for continuously producing a polycarbonate resin with a plurality of reaction devices is characterized in that at least one of the reaction devices set so that the viscosity-average molecular weight of the polycarbonate resin at the exits of the reaction devices is ≥10,000 has a stirring shaft and a scraper.

Description

  The present invention relates to a method for producing a polycarbonate resin, and more particularly to a method for producing a polycarbonate resin that reduces the amount of deposits on a stirring shaft of a polycondensation reaction apparatus and suppresses foreign matter from entering the product.

As a method for producing a polycarbonate resin, a melting method in which a dihydroxy compound and a carbonic acid diester are polycondensed is known.
In this method, as described in Patent Document 1, a method of producing a polycarbonate resin by continuously performing a polycondensation reaction using a plurality of reaction apparatuses is known.

JP 2005-146050 A

By the way, in the above-mentioned continuous polymerization, as the polymerization reaction proceeds, the molecular weight of the polycarbonate resin produced in the subsequent reaction apparatus increases. For this reason, when the polymerization reaction proceeds, a polycarbonate resin having a high viscosity is present in the latter reactor.
At this time, as the viscosity of the polycarbonate resin increases, the polycarbonate resin adheres to the stirring shaft or the like in the reaction apparatus. When the adhered polycarbonate resin has little contact with other polycarbonate resins, the polycondensation reaction proceeds gradually, the viscosity increases, and it may adhere to the stirring shaft or the like. Moreover, this fixed substance tends to be a highly branched mass having many branched structures.

The fixed substance of the polycarbonate resin is poorly compatible with the polycarbonate resin that is usually produced, and is often yellowed. For this reason, if it drops and removes from the stirring shaft or the like, it is mixed as a foreign substance in the polycarbonate resin, which causes a deterioration in color tone and an increase in foreign substances. Moreover, when this fallen object is large, the polymer filter etc. provided in the reaction apparatus may be damaged.
Therefore, an object of the present invention is to suppress the generation of foreign matters in the production of a polycarbonate resin and maintain the quality of the obtained polycarbonate resin.

That is, the present invention has the following gist.
(1) A method for continuously producing a polycarbonate resin using a plurality of reactors,
Production of polycarbonate resin, characterized in that at least one of the reaction devices set so that the viscosity average molecular weight of the polycarbonate resin at the reaction device outlet is 10,000 or more includes a stirring shaft and a scraper. Method.
(2) The method for producing a polycarbonate resin according to (1) above, wherein the polycarbonate resin is obtained by subjecting a carbonic acid diester and a dihydroxy compound to a polycondensation reaction in the presence of a transesterification catalyst.
(3) The method for producing a polycarbonate resin according to (2), wherein the carbonic acid diester is at least one selected from the group consisting of substituted or unsubstituted diphenyl carbonate and dialkyl carbonate.
(4) The polycarbonate according to (2) or (3) above, wherein the dihydroxy compound is an aromatic dihydroxy compound having one or more aromatic rings in the molecule and two hydroxyl groups bonded to the aromatic ring, respectively. Manufacturing method of resin.
(5) The transesterification catalyst is a long-period periodic table group 1 element (excluding hydrogen) compound, long-period periodic table group 2 element compound, basic boron compound, basic phosphorus compound, basic The method for producing a polycarbonate resin according to any one of the above (2) to (4), which is at least one basic compound selected from the group consisting of an ammonium compound and an amine compound. (6) The method for producing a polycarbonate resin according to any one of (1) to (5), wherein a distance between the scraping portion of the scraper and the stirring shaft is 30 mm or less.
(7) The method for producing a polycarbonate resin according to any one of (1) to (6), wherein a distance between the scraping part of the scraper and the stirring shaft is 1 mm or more.
(8) The method for producing a polycarbonate resin according to any one of (1) to (7), wherein the reaction apparatus including the stirring shaft and the scraper is a horizontal reactor.
(9) The method for producing a polycarbonate resin according to any one of (1) to (8), wherein a scraping portion of the scraper is located below an axis center of the stirring shaft.
(10) The method for producing a polycarbonate resin according to any one of (1) to (9), wherein a length of the scraping portion of the scraper is 30% or less and 3% or more with respect to a total length of the stirring shaft.
(11) The method for producing a polycarbonate resin according to any one of (1) to (10), wherein a peripheral speed of the stirring shaft is 5 cm / s or more and 15 cm / s or less.
(12) The method for producing a polycarbonate resin according to any one of (1) to (11), wherein a diameter of the stirring shaft is 200 mm or more and 600 mm or less.
(13) The method for producing a polycarbonate resin according to any one of (1) to (12), wherein the polycarbonate resin has a viscosity average molecular weight of 18,000 or more.
(14) The method for producing a polycarbonate resin according to any one of (1) to (13), wherein the polycarbonate resin has a melt viscosity of 50,000 poise or less.

  According to the present invention, since the scraper is disposed near the stirring shaft in the reactor, the polycarbonate resin adhering to the stirring shaft can be scraped off. As a result, it is possible to prevent foreign substances that are high molecular weight substances or highly branched substances from being mixed in, and to efficiently produce a polymer with few foreign substances, and to stably produce a polycarbonate resin with stable quality. And the damage of the polymer filter provided in the reaction apparatus can also be prevented.

It is an example of the polycondensation reaction process figure which shows the example of a polycondensation reaction apparatus. (A) is a cross-sectional view of a polycondensation reaction apparatus provided with a scraper, and (b) is a bb cross-sectional view of the cross-sectional view of (a). (A), (b), (c), and (d) are figures which show the mode of the deposit | attachment adhering to the stirring shaft in an Example and a comparative example, respectively.

The present invention is a method for producing a polycarbonate resin, in which a polycarbonate resin is continuously produced using a plurality of polycondensation reaction apparatuses.
(Polycarbonate resin)
The polycarbonate resin that is the production object in the present invention is preferably a polymer compound produced by polycondensation reaction (ester exchange reaction) of a carbonic acid diester and a dihydroxy compound.

(Carbonated diester)
Examples of the carbonic acid diester include substituted diphenyl carbonates such as diphenyl carbonate (DPC) and ditolyl carbonate, and dialkyl carbonates such as dimethyl carbonate, diethyl carbonate, and di-t-butyl carbonate. These carbonic acid diesters can be used alone or in admixture of two or more.

In addition, the carbonic acid diester may preferably be substituted with dicarboxylic acid or dicarboxylic acid ester in an amount of 50 mol% or less, more preferably 30 mol% or less.
Representative dicarboxylic acids or dicarboxylic acid esters include terephthalic acid, isophthalic acid, diphenyl terephthalate, and diphenyl isophthalate. When substituted with such a dicarboxylic acid or dicarboxylic acid ester, a polyester carbonate is obtained.

  These carbonic acid diesters (including the substituted dicarboxylic acid or dicarboxylic acid ester, the same shall apply hereinafter) are used in excess with respect to the aromatic dihydroxy compound. That is, the carbonic acid diester is used in an amount of 1.01-1.30 times (molar ratio), preferably 1.02-1.20 times (molar ratio) with respect to the dihydroxy compound. When the molar ratio is too small, the amount of terminal hydroxyl groups of the obtained polycarbonate resin increases, and the thermal stability of the polycarbonate resin tends to deteriorate. In addition, if the molar ratio is too large, the reaction rate of the transesterification reaction decreases, and it becomes difficult to produce a polycarbonate resin having a desired molecular weight, or the residual amount of carbonic acid diester in the polycarbonate resin increases, and molding processing Occasionally, it may cause odor when used as a molded product.

(Dihydroxy compound)
The dihydroxy compound is a compound having two hydroxyl groups in the molecule. In the present invention, among the dihydroxy compounds, the molecule has one or more aromatic rings, and each of the two hydroxyl groups is bonded to the aromatic ring. Aromatic dihydroxy compounds are preferably used.
Specific examples of such aromatic dihydroxy compounds include, for example, bis (4-hydroxydiphenyl) methane, 2,2-bis (4-hydroxyphenyl) propane, and 2,2-bis (4-hydroxy-3-methyl). Phenyl) propane, 2,2-bis (4-hydroxy-3-tert-butylphenyl) propane, 2,2-bis (4-hydroxy-3,5-dimethylphenyl) propane, 2,2-bis (4- Bisphenols such as hydroxy-3,5-dibromophenyl) propane, 4,4-bis (4-hydroxyphenyl) heptane, 1,1-bis (4-hydroxyphenyl) cyclohexane; 4,4′-dihydroxybiphenyl, 3 , 3 ′, 5,5′-tetramethyl-4,4′-dihydroxybiphenyl and the like; bis (4-hydroxypheny And bis (4-hydroxyphenyl) sulfide, bis (4-hydroxyphenyl) ether, and bis (4-hydroxyphenyl) ketone. Among these, 2,2-bis (4-hydroxyphenyl) propane (that is, bisphenol A (BPA)) is preferable. These aromatic dihydroxy compounds can be used alone or in admixture of two or more.

(Transesterification catalyst)
In the transesterification reaction, a transesterification catalyst is used. Examples of the transesterification catalyst include a catalyst usually used for producing a polycarbonate by a transesterification method, and are not particularly limited. In general, for example, a compound of a long-period periodic table group 1 element (excluding hydrogen) (hereinafter referred to as “group 1 element (excluding hydrogen)”), long-period group 2 At least one basic compound selected from the group consisting of elemental compounds (hereinafter sometimes referred to as “Group 2 elements”), basic boron compounds, basic phosphorus compounds, basic ammonium compounds, and amine compounds. Compounds.

Among these transesterification catalysts, practically, at least one compound selected from the group consisting of compounds of group 1 elements (excluding hydrogen) and compounds of group 2 elements is preferable. These transesterification catalysts may be used alone or in combination of two or more.
The amount of the transesterification catalyst used is usually preferably 1 × 10 ⁻⁹ to 1 × 10 ⁻¹ mol, more preferably 1 × 10 ⁻⁷ to 1 × 10 ⁻³ mol, even more preferably 1 mol of the dihydroxy compound. It is used at 1 × 10 ⁻⁷ to 1 × 10 ⁻⁵ mol.

  Examples of the compounds of Group 1 elements (excluding hydrogen) include inorganic compounds such as hydroxides, carbonates, hydrogen carbonate compounds of Group 1 elements (excluding hydrogen); Group 1 elements (excluding hydrogen) And organic compounds such as salts with alcohols, phenols and organic carboxylic acids. Here, as a group 1 element (except hydrogen), lithium, sodium, potassium, rubidium, and cesium are mentioned, for example. Among these Group 1 elements (excluding hydrogen), cesium compounds and potassium compounds are preferable, and cesium carbonate, cesium hydrogen carbonate, cesium hydroxide, potassium acetate, and potassium carbonate are particularly preferable.

  Examples of the Group 2 element compounds include hydroxides such as beryllium, magnesium, calcium, strontium and barium, inorganic compounds such as carbonates; alcohols such as beryllium, magnesium, calcium, strontium and barium. And salts with phenols and organic carboxylic acids. Of these Group 2 elements (excluding hydrogen), magnesium compounds are preferred.

  Examples of the basic boron compound include sodium salts, potassium salts, lithium salts, calcium salts, magnesium salts, barium salts, and strontium salts of boron compounds. Here, as the boron compound, for example, tetramethylboron, tetraethylboron, tetrapropylboron, tetrabutylboron, trimethylethylboron, trimethylbenzylboron, trimethylphenylboron, triethylmethylboron, triethylbenzylboron, triethylphenylboron, tributyl Examples include benzylboron, tributylphenylboron, tetraphenylboron, benzyltriphenylboron, methyltriphenylboron, and butyltriphenylboron.

  Examples of the basic phosphorus compound include triethylphosphine, tri-n-propylphosphine, triisopropylphosphine, tri-n-butylphosphine, triphenylphosphine, tris (pt-butylphenyl) phosphine, and tributyl. Examples thereof include trivalent phosphorus compounds such as phosphine, and quaternary phosphonium salts derived from these compounds. Of these, triphenylphosphine and tris (pt-butylphenyl) phosphine are preferable.

  Examples of the basic ammonium compound include tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, trimethylethylammonium hydroxide, trimethylbenzylammonium hydroxide, trimethylphenylammonium hydroxide. Side, triethylmethylammonium hydroxide, triethylbenzylammonium hydroxide, triethylphenylammonium hydroxide, tributylbenzylammonium hydroxide, tributylphenylammonium hydroxide, tetraphenylammonium hydroxide, benzyltriphenylammonium hydroxide, Le triphenyl ammonium hydroxide, butyltriphenyl ammonium hydroxide, and the like. Of these, tetramethylammonium hydroxide is preferable.

Examples of the amine compound include 4-aminopyridine, 2-aminopyridine, N, N-dimethyl-4-aminopyridine, 4-diethylaminopyridine, 2-hydroxypyridine, 2-methoxypyridine, 4- Examples include methoxypyridine, 2-dimethylaminoimidazole, 2-methoxyimidazole, imidazole, 2-mercaptoimidazole, 2-methylimidazole, and aminoquinoline.

(Manufacture of polycarbonate resin)
Next, the manufacturing method of polycarbonate resin is demonstrated.
The polycarbonate resin is prepared by preparing a mixture of the above-mentioned dihydroxy compound and carbonic acid diester using a raw material preparation device (raw material preparation step), and subjecting the raw material mixture to a polycondensation reaction using a reaction device in the presence of the transesterification catalyst. (Polycondensation step).

  As the reaction system, a batch system, a continuous system, a combination thereof, or the like can be used. In the present invention, the raw material preparation process and the polycondensation process are performed in a continuous system. Polycarbonate resin, after the polycondensation step, stop the reaction and devolatilize and remove unreacted raw materials and reaction by-products in the polymerization reaction solution, add a heat stabilizer, release agent, colorant, etc., necessary Depending on the process, it is manufactured through a process of forming pellets having a predetermined particle diameter.

(Polycondensation process)
The raw material mixture is sent in a molten state to a plurality of reactors as shown in FIG. 1 and subjected to a polycondensation reaction. This polycondensation reaction is usually carried out continuously in a reactor of 2 or more, preferably 3 to 7 groups. Specific reaction conditions include temperature: 150 ° C. to 320 ° C., pressure: normal pressure to 0.01 Torr (1.3 Pa), average residence time: 5 minutes to 300 minutes, preferably temperature: 180 ° C. to 310 ° C. ° C, pressure: 20 Torr to 0.05 Torr (2.7 kPa to 6.7 Pa), average residence time: 60 minutes to 150 minutes In a plurality of reactors, monohydroxy compounds such as phenol that are by-produced as the polycondensation reaction proceeds In order to remove it outside the system more effectively, the temperature is set to a stepwise higher temperature and higher vacuum within the above reaction conditions. In order to prevent quality deterioration such as hue of the obtained polycarbonate resin, it is preferable to set a low temperature and a short residence time as much as possible.

In the present invention, usually, a plurality of reactors including a vertical reactor are provided to increase the average molecular weight of the polycarbonate resin. Usually, 3 to 6 groups, preferably 4 to 5 groups are installed.
As a specific example, in FIG. 1, three vertical reactors 11a, 11b, and 11c and one horizontal reactor 11d are used.
The melt of the raw material mixture A is supplied to the first vertical reactor 11a, and the polycondensation reaction is started in the presence of the transesterification catalyst. Next, the reaction mixture is sequentially sent to the vertical reactor 11b, vertical reactor 11c, and horizontal reactor 11d to advance the polycondensation reaction. At this time, phenol is produced as a by-product, which is liquefied by a heat exchanger and sent to the phenol tank 13. The phenol in the phenol tank 13 is appropriately treated and reused as a raw material for a dihydroxy compound or a carbonic acid diester compound.

A horizontal reactor 11d is used as the latter stage reactor of the group of reactors. This increases the viscosity as the polycondensation reaction proceeds, so that the latter stage has a high viscosity. This is to make the stirring in the easier.
The polycarbonate resin obtained in this polycondensation step is then devolatilized and cooled.
Examples of the vertical and horizontal reactors include, for example, a stirred tank reactor, a thin film reactor, a centrifugal thin film evaporation reactor, a surface renewal biaxial kneading reactor, a biaxial horizontal stirred reactor, and a wet wall type A reactor, a perforated plate type reactor that polymerizes while freely dropping, a perforated plate type reactor with wire that polymerizes while dropping along a wire, and the like are used. Especially, as a reactor, a stirring tank type reactor and a biaxial horizontal type stirring reactor are preferable.

  Examples of the type of agitator blades in the vertical reactor include turbine blades, paddle blades, fiddler blades, anchor blades, full zone blades (manufactured by Shinko Pantech Co., Ltd.), Sunmeler blades (manufactured by Mitsubishi Heavy Industries, Ltd.), Max Blend blades (Sumitomo) Heavy machinery industry), helical ribbon blades, twisted lattice blades (manufactured by Hitachi, Ltd.), and the like. Especially, as a stirring blade, a Max blend blade (made by Sumitomo Heavy Industries, Ltd.) and a helical ribbon blade are preferable.

In the present invention, the horizontal reactor refers to a reactor in which the rotation axis of the stirring blade is horizontal (horizontal direction).
As a stirring blade of a horizontal reactor, for example, a uniaxial stirring blade such as a disk type or a paddle type; HVR, SCR, N-SCR (manufactured by Mitsubishi Heavy Industries), Vivolac (manufactured by Sumitomo Heavy Industries, Ltd.), or And a biaxial stirring blade such as a spectacle blade or a lattice blade (manufactured by Hitachi, Ltd.).

  In addition, the transesterification catalyst used for the polycondensation reaction of a dihydroxy compound and a carbonic acid diester is usually used in advance as an aqueous solution. The concentration of the aqueous solution is not particularly limited, and is adjusted to an arbitrary concentration according to the solubility of the transesterification catalyst in water. Moreover, it can replace with water and other solvents, such as acetone, alcohol, toluene, and phenol, can also be selected.

The property of water used for dissolving the transesterification catalyst is not particularly limited as long as the kind and concentration of impurities contained are constant, but usually distilled water, deionized water, and the like are preferably used.
In the production method of the present invention, a polycarbonate resin is continuously produced using a plurality of reaction apparatuses. Among the reaction apparatuses in which the polycarbonate resin has a viscosity average molecular weight of 10,000 or more at the outlet of the constituting reaction apparatus. At least one has a stirring shaft and a scraper.

  The polycarbonate resin has a viscosity average molecular weight of preferably 14,000 or more, more preferably 18,000 or more. If the viscosity average molecular weight is less than 10,000, adhesion to the stirring shaft 15 is unlikely to occur, so there is no need to provide a scraper. On the other hand, the upper limit of the viscosity average molecular weight is preferably 30,000, and more preferably 28,000. Although it may be larger than 30,000, it is sufficient if the viscosity average molecular weight of the target polycarbonate resin is 30,000.

  Generally, a substance in the middle of polymerization in the reactor (hereinafter sometimes referred to as “polymerization intermediate substance”) is likely to adhere to the stirring shaft. , Will come off immediately. However, there is a place on the agitation shaft where substances during polymerization are difficult to adhere, but once adhered, they are difficult to peel off. If the scraper is provided in such a place, it is effective to peel off a substance that is difficult to peel off during polymerization. As an example, FIG. 2A shows the case where the scraper 14 is attached to the horizontal reactor 11d.

  A horizontal reactor 11d shown in FIG. 2 (a) is a device in which a stirring blade 16 is attached to a horizontally arranged stirring shaft 15, and the polymerization melt inserted from the inlet 17 is stirred by the stirring blade 16. The polycondensation reaction proceeds while being discharged from the discharge port 18 to the outside. In order to facilitate external discharge near the discharge port 18, the stirring shaft 16 is often not provided with the stirring blade 16. In this case, a substance in the middle of polymerization adheres to the stirring shaft 15 in the vicinity of the discharge port 18 and is difficult to peel off. For this reason, by providing the scraper in the vicinity of the stirring shaft 15 where the stirring blade 16 on the discharge port 18 side is not provided, it is possible to scrape the deposits, and the polymerization proceeds in a state where the substances in the middle of the polymerization are adhered. In addition, it can be prevented from sticking to the stirring shaft 15.

Although not shown, in the case of a vertical reactor, a substance in the middle of polymerization tends to adhere to the vicinity of the interface of the polymerization solution. Therefore, if the scraper is provided in the vicinity of the stirring shaft 15 near this, The kimono can be scraped off, and it is possible to prevent the polymerization from proceeding in a state where the substance during the polymerization adheres and sticking to the stirring shaft.
The reactor equipped with the scraper needs to be provided with at least one of the reactors within the range of the viscosity average molecular weight at the outlet of the reactor. When there are a plurality of reactors corresponding to this condition, it is preferable to provide a scraper for all of them. However, by providing at least a reactor in which adhesion is particularly likely to occur, it is possible to efficiently prevent fixation. As this reactor, it is preferable to use a horizontal reactor arranged last, from the viewpoint of viscosity average molecular weight.

  The melt viscosity at the reactor outlet of the reactor equipped with the scraper is 500 poise or more, preferably 1000 poise or more, more preferably 5000 poise or more. If the melt viscosity is less than 500 poise, it is difficult for the agitation shaft 15 to adhere to the melt, so that it is not necessary to provide a scraper. On the other hand, the upper limit of melt viscosity is 50,000 poise, preferably 30,000 poise, more preferably 25,000 poise, and most preferably 15,000 poise. When the melt viscosity exceeds 50,000 poise, there is a possibility that deposits may also be generated on the scraper.

  The temperature of the polycarbonate resin at the reactor outlet of the reactor equipped with the scraper is 260 ° C or higher, preferably 265 ° C or higher, more preferably 270 ° C or higher. If the temperature of the polycarbonate resin is lower than 260 ° C., the melt viscosity of the polycarbonate resin becomes too high, and there is a possibility that deposits may also be generated on the scraper. On the other hand, the upper limit of the temperature of the polycarbonate resin is 320 ° C, preferably 310 ° C, and most preferably 300 ° C. When the temperature of the polycarbonate resin exceeds 320 ° C., the polycarbonate resin may be yellowed.

As shown in FIG. 2 (b), the scraper 14 is thinned to form a scraping portion, and is disposed in the vicinity of the stirring shaft 15. By making the tip portion as thin as a blade, it is possible to more easily remove the deposits on the stirring shaft 15.
The distance between the scraping portion 14a of the scraper 14 and the stirring shaft 15 is preferably 30 mm or less, and more preferably 20 mm or less. When it exceeds 30 mm, there is a possibility that the attached substance cannot be sufficiently peeled off. On the other hand, the distance between the scraping part and the stirring shaft 15 is preferably 1 mm or more, and more preferably 5 mm or more. If it is less than 1 mm, the scraping part and the stirring shaft 15 may come into contact with each other.

It is preferable that the scraping portion 14a of the scraper 14 is below the shaft center of the stirring shaft. By doing in this way, the scraped deposits can be dropped downward without coming into contact with the stirring shaft again.
The length of the scraping portion 14a of the scraper 14 is preferably 30% or less, more preferably 20% or less, with respect to the total length of the stirring shaft 15. If it is longer than 30%, the resin adheres to the central portion of the scraper, and there is a possibility that a fixed matter is generated on the scraper. On the other hand, the lower limit of the length of the scraping portion 14a is preferably 3% and more preferably 5% with respect to the total length of the stirring shaft. If it is shorter than 3%, the scraping efficiency of the deposit may be reduced. Note that the length of the scraping portion 14a of the scraper 14 is premised on a length that does not contact the stirring blade 16.

When the scraper 14 is provided in a horizontal reactor, it is preferable that the installation position of the scraper is on the outlet side from the center. This is because the viscosity average molecular weight increases toward the downstream side, and deposits are easily generated.
The peripheral speed of the stirring shaft 15 is preferably 5 cm / s or more, more preferably 7 cm / s or more, and still more preferably 8 cm / s or more. When it is slower than 5 cm / s, the strength of the stirring shaft is lowered, and the stirring shaft may be broken when operated for a long time. On the other hand, the upper limit of the peripheral speed is preferably 15 cm / s, and more preferably 10 cm / s. When the speed is higher than 15 cm / s, the polymerizing substance adhering to the stirring shaft 15 may be lifted above the rotating shaft before falling below the stirring shaft 15, and the adhesion may proceed without being able to peel off.

  The diameter of the stirring shaft 15 is preferably 200 mm or more, more preferably 300 mm or more, and still more preferably 400 mm or more. If it is smaller than 200 mm, the strength of the stirring shaft is lowered, and the stirring shaft may be broken when it is operated for a long time. On the other hand, the upper limit of the diameter of the stirring shaft 15 is preferably 600 mm, and more preferably 500 mm. If it is larger than 600 mm, even if the peripheral speed of the stirring shaft 15 is in the above range, the linear speed on the surface of the stirring shaft 15 becomes too high, and the substance in the middle of polymerization adhering to the stirring shaft 15 cannot be peeled off and proceeds instead of adhering. There is a case.

The material of the scraper 14 is preferably made of stainless steel, more preferably SUS304, SUS304L, SUS310S, SUS316, SUS316L, and most preferably SUS316L, SUS310S. The surface of the scraper 14 is usually surface-treated, and preferred surface treatments are buffing, electrolytic polishing, acid treatment, heat treatment, various platings, and coating treatments. More preferred surface treatment buffing is followed by electrolytic polishing treatment. It is. Further, the surface roughness of the scraper 14 is such that the surface roughness Rmax is preferably 100 μm or less, more preferably 10 μm or less, and most preferably 1 μm or less. If this surface roughness Rmax is too large, the peeled deposits remain on the scraper, and foreign matter may increase. The surface roughness Rmax should be low, but it is difficult to construct, so it is preferably 0.01 μm or more, more preferably 0.1 μm or more. A surface roughness of the scraper 14 of 0.1 μm or more is sufficient.

Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention should not be construed as being limited thereto.
Each evaluation method of the polycarbonate resin will be described below.
(Number of fish eyes)
Polycarbonate resin pellets dried at 130 ° C. for 5 hours were extruded at 320 ° C. to obtain a film having a width of 140 mm and a thickness of 70 μm. A single screw extruder (manufactured by Isuzu Chemical Co., Ltd.) having a diameter of 30 mm was used for the extrusion molding. Next, the number of fish eyes (size: 50 μm to 500 μm) of a film having a width of 80 mm × a length of 1.7 m × a thickness of 70 μm selected from the center of the film using an optical foreign object inspection apparatus (manufactured by Dia Instruments, GX40K). Was measured. That is, using a light amount of 800 mV, the number of fish eyes in the absorbed light amount range of 100 mV to 300 mV is (A), and the number of light amount ranges of 300 mV or more is (B). The measurement was performed twice and the average value was shown.

Number of fish eyes = (A)-(B) (1)
(Evaluation of shaft adhesion thickness)
The average thickness of the polycarbonate resin adhering to the shaft was measured and evaluated using a polymer flow simulation (ANSYS Fluent manufactured by ANSYS).

(Viscosity average molecular weight)
The polycarbonate resin was dissolved in methylene chloride to prepare a methylene chloride solution (concentration (C) was 0.6 g / dl). The specific viscosity (η _sp ) of the methylene chloride solution at a temperature of 20 ° C. was measured using an Ubbelohde viscometer, and the viscosity average molecular weight (Mv) was calculated by the following equation.

η _sp /C=[η](1+0.28η _sp)
[Η] = 1.23 × 10 ⁻⁴ × (Mv) ^0.83
(Melt viscosity)
The polycarbonate resin dried at 120 ° C. for 5 hours is heated to 280 ° C. using a capillary rheometer (manufactured by Toyo Seiki Co., Ltd.) having a die diameter of 1 mmφ × 30 mm, and the melt viscosity is adjusted at a shear rate of 122 (sec ⁻¹ ). It was measured.

(Comparative Example 1)
Diphenyl carbonate (Mitsubishi Chemical Co., Ltd.) and bisphenol A (Mitsubishi Chemical Co., Ltd.) are mixed at a constant molar ratio (DPC / BPA = 1.050), and the raw material mixture is melted at a temperature of 155 ° C. Prepared. Subsequently, it was continuously fed into the first vertical stirring reactor having a capacity of 10 m ³ controlled at 220 ° C. and 13.3 × 10 ³ Pa at a flow rate of 4400 kg / hour, and the average residence time was The liquid level was kept constant while controlling the valve opening degree provided in the polymer discharge line at the bottom of the reactor so as to be 60 minutes. At the same time as starting the supply of the raw material melt, an aqueous cesium carbonate solution was used as a catalyst at a ratio of 0.5 μmol (1.0 μmol per 1 mol of bisphenol A as a metal amount) with respect to 1 mol of bisphenol A. Continuous supply.

The reaction liquid discharged from the bottom of the reactor is continuously continuously supplied to the second and third vertical stirring reactors (capacity 10 m ³ ) and the fourth horizontal reactor (capacity 15 m ³ ), and the fourth reaction. It was extracted from the polymer outlet at the bottom of the vessel. As the fourth polymerization tank, a biaxial horizontal reactor was used. The peripheral speed of the stirring shaft of this fourth polymerization tank was 8.8 cm / s, and the diameter of the stirring shaft was 560 mm.
Next, while the polymer extracted from the polymer outlet at the bottom of the fourth reactor is still in a molten state, a twin-screw extruder having a polymer filter installed at the die outlet (screw diameter 0.174 m, manufactured by Nippon Steel Co., Ltd., L / D = 39 (where L means the diameter of the screw and D means the full length of the screw)) and p-toluenesulfonate (5-fold molar amount relative to cesium carbonate used as the catalyst) ) Was continuously kneaded, extracted in a strand form from the die, and cut with a cutter to obtain polycarbonate resin pellets (viscosity average molecular weight (Mv) 21,000).

The reaction conditions in the second to fourth reactors were the second reactor (260 ° C., 4.00 × 10 ³ Pa, 75 rpm), the third reactor (270 ° C., 200 Pa, 75 rpm), and the fourth reaction, respectively. A vessel (280 ° C., 67 Pa, 4 rpm) was set to high temperature and high vacuum as the reaction progressed. During the reaction, the liquid level was controlled so that the average residence time of the second and third reactors was 60 minutes and the average residence time of the fourth reactor was 90 minutes. Distillation was also performed. At this time, the viscosity average molecular weight (Mv) of the reaction solution at the outlet of the fourth reactor was 21,000, and the melt viscosity at 280 ° C. was about 10,000 Poise.
Also, no scraper was installed in any reactor.

As the polymer filter in the reactor, a commercially available leaf disk polymer filter (manufactured by Nippon Pall Co., Ltd., metal nonwoven fabric type with an absolute filtration accuracy of 20 μm (material: SUS316L)) was used.
About one day after the start of operation, deposits were generated on the stirring shaft provided with no stirring blade near the outlet 18 of the horizontal reactor 11d disposed last. The number of fish eyes of the polycarbonate resin pellet at this time was 36.
Further, after about 7 days, a part of the deposit fell into the polymerization solution. Immediately thereafter, the number of fish eyes of the aromatic polycarbonate resin pellets was 1540.

Example 1
As shown in FIG. 1, the horizontal reactor 11d was operated in the same manner as in Comparative Example 1 except that a scraper was installed. Moreover, as shown in FIG.2 (b), the shape of a scraper is thin like a blade, and this front-end | tip part is used as a scraping part.
At the tip of the scraper, the distance between the scraper and the stirring shaft was set to 15 mm. The length of the tip of the scraper was 6% of the total length of the stirring shaft.

The number of fish eyes of the polycarbonate resin pellets about one day after the start of operation was 25.
Seven days after the start of operation, a slight amount of deposit was generated between the scraper and the stirring shaft, but no deposit was dropped. The number of fish eyes of the polycarbonate resin pellet at this time was 31. Moreover, the deposits did not drop even after 2 months of operation, and the number of fish eyes in the polycarbonate resin pellets at this time was 28.

(Comparative Examples 2 to 4)
Using the above polymer flow simulation, the state of shaft deposit generation was verified. That is, the simulation was performed on the polymer flow when the polymer was in contact with the stirring shaft at the viscosity average molecular weight (Mv 21,000) and the melt viscosity (10,000 Poise) at the outlet of the horizontal reactor 11d.
In Comparative Examples 2 to 4, no scraper was installed.
The diameter and peripheral speed of the stirring shaft were 280 mm and 5.1 cm / s in Comparative Example 2, 560 mm and 8.8 cm / s in Comparative Example 3, and 430 mm and 7.9 cm / s in Comparative Example 4, respectively.

The results of polymer flow simulations when a polycarbonate resin melt having a viscosity average molecular weight (Mv) of 21,000 is brought into contact with the stirring shaft are shown in FIG. 3 (a) in Comparative Example 2 and in FIG. 3 (b) in Comparative Example 3. In Comparative Example 4, it is shown in FIG. Moreover, the average thickness of the deposits in the polymer flow simulation was 33.3 mm in Comparative Example 2, 57.9 mm in Comparative Example 3, and 49.2 mm in Comparative Example 4.

(Example 2)
As shown in FIG. 2, a simulation was performed in the same manner as in Comparative Example 3 except that a scraper was installed in the horizontal reactor 11d. Moreover, as shown in FIG.2 (b), the shape of the scraper was thin like a blade, and this tip portion was used as a scraping portion.
The distance between the tip of the scraper and the stirring shaft was set to 10 mm. The length of the tip of the scraper was 6% of the total length of the stirring shaft.
The result of this polymer flow simulation is shown in FIG. Moreover, the average thickness of the deposit in the polymer flow simulation was 10.3 mm in Example 2.

  The method for producing a polycarbonate resin according to the present invention can prevent the introduction of foreign matter that is a high molecular weight product or a highly branched product, and can efficiently and stably produce a polycarbonate resin having a small amount of foreign matter and a stable quality. It is possible, and the industrial applicability is high, such as preventing damage to the polymer filter provided in the reaction apparatus.

11a, 11b, 11c Vertical reactor 11d Horizontal reactor 12 Heat exchanger 13 Phenol tank 14 Scraper 14a Scraper scraper 15 Stirring shaft 16 Stirring blade 17 Inlet 18 Outlet A Raw material mixture B Polycarbonate resin

Claims (14)

A method of continuously producing a polycarbonate resin using a plurality of reactors,
Production of polycarbonate resin, characterized in that at least one of the reaction devices set so that the viscosity average molecular weight of the polycarbonate resin at the reaction device outlet is 10,000 or more includes a stirring shaft and a scraper. Method.   The method for producing a polycarbonate resin according to claim 1, wherein the polycarbonate resin is obtained by subjecting a carbonic acid diester and a dihydroxy compound to a polycondensation reaction in the presence of a transesterification catalyst.   The method for producing a polycarbonate resin according to claim 2, wherein the carbonic acid diester is at least one selected from the group consisting of substituted or unsubstituted diphenyl carbonate and dialkyl carbonate.   4. The polycarbonate resin according to claim 2, wherein the dihydroxy compound is an aromatic dihydroxy compound having one or more aromatic rings in the molecule and two hydroxyl groups bonded to the aromatic rings. Manufacturing method.   The transesterification catalyst is a compound of a long-period periodic table group 1 element (excluding hydrogen), a long-period periodic table group 2 element compound, a basic boron compound, a basic phosphorus compound, a basic ammonium compound, The method for producing a polycarbonate resin according to any one of claims 2 to 4, wherein the polycarbonate resin is at least one basic compound selected from the group consisting of amine compounds.   The method for producing a polycarbonate resin according to any one of claims 1 to 5, wherein a distance between the scraping portion of the scraper and the stirring shaft is 30 mm or less.   The method for producing a polycarbonate resin according to any one of claims 1 to 6, wherein a distance between the scraping portion of the scraper and the stirring shaft is 1 mm or more.   The method for producing a polycarbonate resin according to any one of claims 1 to 7, wherein the reactor equipped with the stirring shaft and the scraper is a horizontal reactor.   The method for producing a polycarbonate resin according to any one of claims 1 to 8, wherein a scraping portion of the scraper is located below an axis center of the stirring shaft.   10. The method for producing a polycarbonate resin according to claim 1, wherein a length of the scraping portion of the scraper is 30% or less and 3% or more with respect to a total length of the stirring shaft. .   The method for producing a polycarbonate resin according to any one of claims 1 to 10, wherein a peripheral speed of the stirring shaft is 5 cm / s or more and 15 cm / s or less.   12. The method for producing a polycarbonate resin according to claim 1, wherein a diameter of the stirring shaft is 200 mm or more and 600 mm or less.   The method for producing a polycarbonate resin according to any one of claims 1 to 12, wherein the polycarbonate resin has a viscosity average molecular weight of 18,000 or more.   The method for producing a polycarbonate resin according to any one of claims 1 to 13, wherein the polycarbonate resin has a melt viscosity of 50,000 poise or less.