JP2001138321A - Method for producing thermoplastic resin pellet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing thermoplastic resin pellets of an extremely small amount of erroneously cut pellets stably and efficiently. SOLUTION: In a method for producing pellets in which a thermoplastic resin is extruded into strands with the use of an extruder, and the strands are cooled and cut by a cutter having a rotary blade and a fixed blade, gas is ejected to the rotary blade at a flow velocity of 10-75 m/s in a range of 0-270 deg. in the rotational direction of the rotary blade from the cutting position of the strands.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for stably and efficiently producing thermoplastic resin pellets having an extremely small amount of miscuts. Here, miscuts mean fine particles that are smaller than pellets of a desired size that are generated when the strand is cut.

[0002]

2. Description of the Related Art In recent years, various thermoplastic resins have been developed,
It is widely used in the fields of automobiles, electricity, machinery, optics, and construction by melt extrusion molding and melt injection molding. Most of these molding materials are melt-extruded into a strand shape or a plate shape by a melt extruder, and then cut by a cutter having a rotary blade to be supplied as pellets of a predetermined size. However, miscuts of hundreds to thousands of ppm are mixed in the pellets normally supplied, and if the mixed amount of the miscuts is large, molding defects occur frequently and the product yield is reduced. It has been desired to reduce the amount of mixed in. In particular, in a polycarbonate resin that is suitably used as a molding material for an optical disc substrate, if the amount of miscuts is large, carbides and silver are generated during molding and various defects are caused as a recording material, and At this time, the filling amount tends to fluctuate, and the birefringence of the obtained optical disc substrate is not stable. For these reasons, it is desired to reduce the mixing amount of miscuts.

Conventionally, a wet or dry classification method has been adopted as a method for reducing miscuts mixed in pellets. However, this method is a method of removing the generated miscuts later, and thus is not a preferable method because the yield of the obtained pellets is reduced and a processing facility for the miscuts is required. In JP-A-11-58373, the resin temperature to be cut and the rake angle of the rotary blade are set to specific ranges,
A method for producing a thermoplastic resin pellet having a uniform shape is shown. Although the amount of miscut is reduced to some extent by such a method, it is not sufficient, and a method capable of sufficiently preventing miscut from being mixed by a simpler method is desired.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for stably and efficiently producing thermoplastic resin pellets having an extremely small amount of miscuts.
The present inventor, in order to solve the above problems, as a result of intensive studies, pellets once cut by the rotary blade and the fixed blade remain on the rotary blade, this pellet is sent to the associated portion of the rotary blade and the fixed blade. Focusing on the fact that the amount of miscut increases due to cutting again, the thermoplastic resin is melt-extruded into a strand shape by a melt extruder, and after the strand is cooled, it is cut by a cutting machine having a rotary blade and a fixed blade. In a method of obtaining pellets by blowing a gas having a specific flow rate from a specific position to a rotary blade of a cutter, surprisingly, thermoplastic resin pellets with a very small amount of miscut are stably and efficiently produced. Finding what you can often get,
The present invention has been reached.

[0005]

That is, according to the present invention, a thermoplastic resin is melt-extruded into a strand shape using a melt extruder, and after the strand is cooled, a cutting machine having a rotary blade and a fixed blade is used. In the method of producing pellets by cutting, in the range of 0 to 270 ° along the rotation direction of the rotary blade from the cutting point of the strand, gas is supplied to the rotary blade at a flow rate of 10 to 10 °.
A method for producing thermoplastic resin pellets characterized by spraying at 75 m / sec is provided.

Hereinafter, the present invention will be described in more detail. Specific examples of the thermoplastic resin to be used in the present invention include a polycarbonate resin, a polyarylate resin, a polymethyl methacrylate resin, a polystyrene resin, and an amorphous cyclic polyolefin resin. Among them, the polycarbonate resin is most preferable. These resins have a common process of manufacturing pellets. Hereinafter, a polycarbonate resin will be described as an example.

A polycarbonate resin is obtained by reacting a dihydric phenol with a carbonate precursor by an interfacial polycondensation method or a melting method. Representative examples of the dihydric phenol used here include hydroquinone, resorcinol, 4,4'-dihydroxydiphenyl, bis (4-hydroxyphenyl) methane, bis {(4-hydroxy-3,5-dimethyl) Phenyl methane, 1,
1-bis (4-hydroxyphenyl) ethane, 1,1-
Bis (4-hydroxyphenyl) -1-phenylethane, 2,2-bis (4-hydroxyphenyl) propane (commonly known as bisphenol A), 2,2-bis {(4-hydroxy-3-methyl) phenyl} propane, 2,2-bis {(4-hydroxy-3,5-dimethyl) phenyl}
Propane, 2,2-bis {(3,5-dibromo-4-hydroxy) phenyl} propane, 2,2-bis} (3-
Isopropyl-4-hydroxy) phenyl} propane,
2,2-bis {(4-hydroxy-3-phenyl) phenyl} propane, 2,2-bis (4-hydroxyphenyl) butane, 2,2-bis (4-hydroxyphenyl)
-3-methylbutane, 2,2-bis (4-hydroxyphenyl) -3,3-dimethylbutane, 2,4-bis (4
-Hydroxyphenyl) -2-methylbutane, 2,2-
Bis (4-hydroxyphenyl) pentane, 2,2-bis (4-hydroxyphenyl) -4-methylpentane,
1,1-bis (4-hydroxyphenyl) cyclohexane, 1,1-bis (4-hydroxyphenyl) -4-isopropylcyclohexane, 1,1-bis (4-hydroxyphenyl) -3,3,5-trimethylcyclohexane , 9,9-bis (4-hydroxyphenyl) fluorene, 9,9-bis {(4-hydroxy-3-methyl) phenyl} fluorene, α, α'-bis (4-hydroxyphenyl) -o-diisopropylbenzene , Α, α'-
Bis (4-hydroxyphenyl) -m-diisopropylbenzene, α, α'-bis (4-hydroxyphenyl)
-P-diisopropylbenzene, 1,3-bis (4-hydroxyphenyl) -5,7-dimethyladamantane,
4,4'-dihydroxydiphenyl ketone, 4,4'-
Examples thereof include dihydroxydiphenyl ether and 4,4'-dihydroxydiphenyl ester, and these can be used alone or in combination of two or more.

Among them, bisphenol A, 2,2-bis {(4-hydroxy-3-methyl) phenyl} propane, 2,2-bis (4-hydroxyphenyl) butane,
2,2-bis (4-hydroxyphenyl) -3-methylbutane, 2,2-bis (4-hydroxyphenyl)-
3,3-dimethylbutane, 2,2-bis (4-hydroxyphenyl) -4-methylpentane, 1,1-bis (4
A homopolymer obtained from at least one bisphenol selected from the group consisting of -hydroxyphenyl) -3,3,5-trimethylcyclohexane and α, α'-bis (4-hydroxyphenyl) -m-diisopropylbenzene, or Copolymers are preferred. In particular, bisphenol A homopolymer and 1,1-bis (4-hydroxyphenyl) -3,3,5-trimethylcyclohexane and bisphenol A, 2,2-bis {(4-hydroxy- Copolymers with 3-methyl) phenyl} propane or α, α′-bis (4-hydroxyphenyl) -m-diisopropylbenzene are preferably used.

As the carbonate precursor, carbonyl halide, carbonate ester or haloformate is used, and specific examples include phosgene, diphenyl carbonate, dihaloformate of dihydric phenol and the like.

In producing the polycarbonate resin by reacting the dihydric phenol with the carbonate precursor by an interfacial polycondensation method or a melting method, if necessary, a catalyst, a terminal stopper and an antioxidant for the dihydric phenol may be used. Etc. may be used. Further, the polycarbonate resin may be a branched polycarbonate resin obtained by copolymerizing a trifunctional or higher polyfunctional aromatic compound, or a polyester carbonate resin obtained by copolymerizing an aromatic or aliphatic bifunctional carboxylic acid, In addition, 2 of the obtained polycarbonate resin
It may be a mixture of more than one species.

The reaction by the interfacial polycondensation method is usually a reaction between dihydric phenol and phosgene, and is carried out in the presence of an acid binder and an organic solvent. As the acid binder, for example, an alkali metal hydroxide such as sodium hydroxide or potassium hydroxide or an amine compound such as pyridine is used.
As the organic solvent, for example, halogenated hydrocarbons such as methylene chloride and chlorobenzene are used. Further, for promoting the reaction, for example, a catalyst such as a tertiary amine such as triethylamine, tetra-n-butylammonium bromide, or tetra-n-butylphosphonium bromide, a quaternary ammonium compound, or a quaternary phosphonium compound may be used. it can. At that time, the reaction temperature is usually 0 to 40 ° C., the reaction time is preferably about 10 minutes to 5 hours, and the pH during the reaction is preferably maintained at 9 or more.

In such a polymerization reaction, a terminal stopper is usually used. Monofunctional phenols can be used as such a terminal stopper. Monofunctional phenols are commonly used as molecular terminators for molecular weight control, and the resulting polycarbonate resins are capped by groups based on monofunctional phenols, so that Excellent heat stability. Such a monofunctional phenol is generally a phenol or a lower alkyl-substituted phenol, and may be a monofunctional phenol represented by the following general formula (1).

[0013]

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Wherein A is a hydrogen atom, a linear or branched alkyl or arylalkyl group having 1 to 9 carbon atoms, and r is an integer of 1 to 5, preferably 1 to 3. Specific examples of the above monofunctional phenols include, for example, phenol, p-tert-butylphenol, p-
Cumylphenol and isooctylphenol.

[0015] Other monofunctional phenols include:
Phenols or benzoic acid chlorides having a long-chain alkyl group or an aliphatic polyester group as a substituent, or long-chain alkyl carboxylic acid chlorides can be used. When blocked, they not only function as a terminal terminator or a molecular weight regulator, but also improve the melt flowability of the resin and facilitate not only the molding process, but also the physical properties particularly as an optical disk substrate, especially the resin. It has the effect of lowering the water absorption and the effect of reducing the birefringence of the substrate, and is preferably used. Among them, phenols having a long-chain alkyl group represented by the following general formulas (2) and (3) as a substituent are preferably used.

[0016]

Embedded image

[0017]

Embedded image

Wherein X is -RO-, -R-CO-O
— Or —RO—CO—, wherein R represents a single bond or a divalent aliphatic hydrocarbon group having 1 to 10, preferably 1 to 5 carbon atoms, and n represents an integer of 10 to 50. Show. ]

As the substituted phenols of the formula (2), those wherein n is 10 to 30, especially 10 to 26 are preferred.
Specific examples thereof include decylphenol, dodecylphenol, tetradecylphenol, hexadecylphenol, octadecylphenol, eicosylphenol, docosylphenol, and tricontylphenol.

Further, as the substituted phenols of the formula (3), a compound in which X is -R-CO-O- and R is a single bond is suitable, and n is 10 to 30, especially 10 to 26. Those are preferable, and specific examples thereof include decyl hydroxybenzoate, dodecyl hydroxybenzoate, tetradecyl hydroxybenzoate, hexadecyl hydroxybenzoate, eicosyl hydroxybenzoate, docosyl hydroxybenzoate and tricontyl hydroxybenzoate. .

It is desirable that these terminal stoppers are introduced at least at 5 mol%, preferably at least 10 mol%, based on all terminals of the obtained polycarbonate resin. Or a mixture of two or more.

The reaction by the melting method is usually a transesterification reaction between a dihydric phenol and a carbonate ester,
The method is carried out by a method in which a dihydric phenol and a carbonate ester are mixed while heating in the presence of an inert gas to distill off the produced alcohol or phenol. The reaction temperature varies depending on the boiling point of the produced alcohol or phenol, but is usually in the range of 120 to 350 ° C.
In the late stage of the reaction, the pressure of the system is reduced to about 1.3 to 0.013 kPa to facilitate the distillation of alcohol or phenol produced. The reaction time is usually about 1 to 4 hours.

Examples of the carbonate ester include an optionally substituted ester such as an aryl group having 6 to 10 carbon atoms, an aralkyl group or an alkyl group having 1 to 4 carbon atoms. Specifically, diphenyl carbonate, bis (chlorophenyl) carbonate, dinaphthyl carbonate, bis (diphenyl) carbonate, dimethyl carbonate, diethyl carbonate, dibutyl carbonate and the like can be mentioned, with diphenyl carbonate being preferred.

A polymerization catalyst may be used to increase the polymerization rate. Examples of the polymerization catalyst include sodium hydroxide, potassium hydroxide, alkali metal compounds such as sodium and potassium salts of dihydric phenol, and water. Alkaline earth metal compounds such as calcium oxide, barium hydroxide and magnesium hydroxide; nitrogen-containing basic compounds such as tetramethylammonium hydroxide, tetraethylammonium hydroxide, trimethylamine and triethylamine; alkoxides of alkali metals and alkaline earth metals Manganese, organic acid salts of alkali metals and alkaline earth metals, zinc compounds, boron compounds, aluminum compounds, silicon compounds, germanium compounds, organic tin compounds, lead compounds, osmium compounds, antimony compounds Compounds, titanium compounds, usually the esterification reaction, such as zirconium compounds, there can be used a catalyst used in the transesterification reaction. The catalyst may be used alone or in combination of two or more. The amount of these polymerization catalysts to be used is preferably 1 × 10 ⁻⁹ to 1 × 10 ^{9 with} respect to 1 mol of the starting dihydric phenol.
^-3 equivalents, more preferably 1 × 10 ^{−8 to} 5 × 10 ⁻⁴ equivalents.

The molecular weight of the polycarbonate resin is determined based on the viscosity average.
10,000 to 100,000 is preferable in terms of the average molecular weight (M).
And 11,000-45,000 is more preferable.
2,000 to 30,000 are particularly preferred. Such viscosity
Polycarbonate resin with average molecular weight has sufficient strength
And the melt fluidity during molding is good.
This is preferable because shape distortion does not occur. Such a viscosity average molecular weight is a salt
0.7 g of polycarbonate resin in 100 ml of methylene chloride
Was determined from a solution in which was dissolved at 20 ° C. (η _sp) To
It is obtained by inserting it into the equation. η_sp/C=[η]+0.45×[η]^Twoc (however, [η]
Is the limiting viscosity) [η] = 1.23 × 10^-FourM^0.83 c = 0.7

The thermoplastic resin pellets obtained by the production method of the present invention include a heat stabilizer (phosphate ester, phosphite ester, etc.), a release agent (fatty acid ester, etc.), an antistatic agent, an ultraviolet absorber, Modification improvers such as antioxidants and antibacterial agents can be appropriately added and used.

The melt extruder used in the present invention includes:
A single-screw extruder, a twin-screw extruder or the like is used, and an extruder with a vent and a filter provided between a screw and a die is preferably used. As the filter provided between the screw and the die, a disk-shaped, candle-shaped, or leaf-disk-shaped metal filter is preferably used.

In the present invention, as a method of cooling the melt-extruded strand of the thermoplastic resin, a method of cooling by immersing the strand in water placed in a cooling bath is preferably adopted.
The water used at this time is desirably filtered with a filter having a filtration accuracy of 5 μm or less, preferably 0.2 to 3 μm. By using a filter having such a filtration accuracy, the amount of foreign substances in the pellets does not increase, and the filtration efficiency is good, which is preferable. The water used for cooling the strand is preferably ion-exchanged water or distilled water, and particularly preferably ion-exchanged water. The water temperature in the cooling bath is 25
-80 ° C is preferred, and 30-70 ° C is more preferred. Strands cooled at a water temperature in such a range are less likely to contain air bubbles in the strands, and the strands are sufficiently cooled, and when cut by a cutting machine, have a good cut surface and reduce the amount of miscuts, which is preferable. .

The number of strands supplied to the cutting machine is not limited to one, and several strands can be supplied to the cutting machine together to form pellets depending on the size and processing capacity of the cutting machine.

The cutting machine having a rotary blade and a fixed blade used in the present invention is preferably a cutting machine having a structure provided with a rotary blade protection cover.

In the present invention, the amount of miscut is reduced by blowing gas to the rotary blade. However, the gas is blown at a position within a range of 0 to 270 ° along the rotation direction of the rotary blade from the cut portion of the strand. It is necessary to spray.

The angle from 0 to 270 ° along the direction of rotation of the rotary blade from the cutting position of the strand is the angle indicated by A in the cutting machine shown in FIG. Even if the gas is blown from a position exceeding 270 °, the ratio of the amount of the cut pellets cut again increases, and the object of the present invention of reducing the amount of miscuts is not achieved.

The preferred location for blowing the gas is in the range of 0 to 135 ° (the angle represented by B in the cutting machine shown in FIG. 1) along the rotation direction of the rotary blade from the strand cutting location. . The point where the gas is blown is set along the direction of rotation of the rotary blade from the cutting point of the strand to 13 points.
In the case of a range of 5 to 270 ° (an angle represented by C in the cutting machine shown in FIG. 1), the gas blowing direction is 0 to 90 ° with respect to the tangent from the direction opposite to the rotation direction.
It is preferable to spray at an angle.

As the gas blown to the rotary blade, air, nitrogen gas, carbon dioxide gas or the like is used, and air is particularly preferably used.

The flow rate of the gas blown to the rotary blade is 10 to 7
5 m / sec, preferably 20 to 60 m / sec, and 30 to
50 m / sec is more preferred. When the flow velocity is less than 10 m / sec, the ratio of the cut pellets being cut again is high,
If the amount of miscuts is large and the object of the present invention cannot be achieved, and if the flow velocity exceeds 75 m / sec, the cut pellets will be scattered due to the high wind speed, and some of the scattered pellets will be cut again to prevent mistakes. It is not preferable because the cut amount increases. The flow rate of the gas blown to the rotary blade may be any one that satisfies the flow rate range at the air outlet, and the interval between the air outlet and the rotary blade is an interval at which the outlet and the rotary blade do not contact each other, preferably. Is 1 cm or more, and preferably 50 cm or less, more preferably 30 cm or less.
The distance is more preferably 20 cm or less.

The temperature of the gas is preferably 40 ° C. or lower, more preferably -10 to 30 ° C., and particularly preferably -5 to 10 ° C. By setting the gas temperature within the above range, the occurrence of miscuts is further reduced, which is preferable.

As the gas used for the spraying of the present invention, it is preferable to use a gas filtered with a filter having a filtration accuracy of 5 μm or less without increasing foreign matter in the pellets.
As a method of spraying a gas to the rotary blade, it is desirable that after the gas is compressed by a compressor, the cooled gas is sprayed so as to uniformly hit the entire rotary blade. (In the width direction), preferably from two or more locations, and more preferably from three to ten locations.

As a method of blowing gas to the rotary blade, a slit method and a nozzle method are preferably used. In the case of the nozzle method, nozzles are preferably provided at intervals of 0.5 to 15 cm, more preferably at intervals of 3 to 10 cm, 4 ~
An interval of 8 cm is more preferable. An interval within such a range is preferable because the effect of reducing the amount of miscut increases.

In the present invention, by ionizing the gas and using the ionized gas as a gas for spraying, the amount of miscuts and the amount of foreign matter in the pellets are preferably reduced. As a method of ionizing a gas, there is a corona charging device, and a DC charging device, an AC charging device, and a pulse charging device are preferably used.

According to the method of the present invention, the amount of miscuts in the pellets is extremely small, and the amount of miscuts can be further reduced by combining the method of the present invention with a wet or dry classification method. is there.

The thermoplastic resin pellets obtained by the production method of the present invention and having a reduced miscut amount include, for example, magneto-optical disks, various write-once disks, digital audio disks (so-called compact disks), optical video disks ( So-called laser disk), digital
It can be suitably used as a material for an optical disk substrate such as a versatile disk (DVD) or as a material for a precision equipment storage container such as a silicon wafer. In particular, when the amount of miscuts is small, carbides and silver are less likely to be generated during molding, and various defects are reduced as a recording material. Since the birefringence of is stable, it is suitably adopted as a material for an optical disk substrate.

[0042]

EXAMPLES The present invention will be described below in detail with reference to examples, but the present invention is not limited to these examples. The evaluation was performed by the following method. (1) Viscosity-average molecular weight of polycarbonate resin 0.7 g of polycarbonate resin was added to 100 m of methylene chloride.
1) and determined from the specific viscosity measured at 20 ° C. (2) Amount of Miscut in Pellet 1000 g of the obtained pellet was classified with a standard sieve having a mesh size of 2.0 mm, the amount passed through the sieve was weighed, and the amount passed through the sieve was regarded as the amount of miscut, and the weight ratio was calculated.

Example 1 A reactor equipped with a thermometer, a stirrer and a reflux condenser was charged with 219.4 parts of ion-exchanged water and 40.2 parts of a 48% aqueous sodium hydroxide solution.
-Bis (4-hydroxyphenyl) propane 57.5 parts (0.252 mol) and hydrosulfite 0.1
After dissolving 2 parts, 181 parts of methylene chloride were added, and 28.3 parts of the above phosgene was blown in with stirring at 15 to 25 ° C for 40 minutes. After the injection of phosgene was completed, 7.2 parts of a 48% aqueous sodium hydroxide solution and 2.42 parts of p-tert-butylphenol were added, stirring was started, and after emulsification, 0.06 part of triethylamine was added.
After stirring for an hour, the reaction was completed. After completion of the reaction, the product was diluted with methylene chloride, washed with water, acidified with hydrochloric acid, and washed with water.
When the conductivity of the aqueous phase became almost the same as that of the ion-exchanged water, the washed polycarbonate solution was dropped into warm water in a kneader provided with an isolation chamber having a foreign substance take-out port in the bearing, and methylene chloride was distilled off. While the polycarbonate resin was flaked. Next, the liquid-containing polycarbonate resin is pulverized and dried at 145 ° C. for 6 hours, and the viscosity-average molecular weight is 15,100 and the amount of foreign substances having a particle size of 0.5 μm or more is 1500
Pieces / g of polycarbonate resin powder was obtained. To this powder, 0.004% by weight of tris (2,4-di-tert-butylphenyl) phosphite and 0.06% by weight of monoglyceride stearate were added and mixed for 30 minutes to obtain a powder to be subjected to melt extrusion.

Next, the powder was placed between a screw and a die of a vent-type twin-screw extruder by SU SU with a filtration accuracy of 1 μm.
Using a vent type twin screw extruder [KTX-46 manufactured by Kobe Steel Co., Ltd.] equipped with a filter made of S304, cylinder temperature 260 ° C., vent gas vacuum degree 0.67 kPa
The extruded strand was melt-kneaded while being degassed at (5 mmHg), and the extruded strand was immersed in a cooling bath filled with ion-exchanged water whose water temperature was controlled at 50 ° C., filtered with a SUS304 filter having a filtration accuracy of 0.5 μm. Water cooled.
Next, at a position 90 ° (angle of range B in FIG. 1) along the rotation direction of the rotary blade from the cut portion of the strand, the surface of the rotary blade is rotated at an angle of 0 ° with respect to the tangent from the direction opposite to the rotation direction. Using a cutting machine having a rotary blade provided with five air-blowing nozzles equally spaced in the width direction of the rotary blade at a distance of 15 cm from the rotary blade so that air is applied,
The water-cooled strand was cut under the condition of blowing air at 5 ° C. at a flow rate of 40 m / sec to a diameter of 2.8 mm and a length of 3.
A 0 mm pellet was obtained. The miscut amount in the obtained pellet was 70 ppm.

Example 2 Example 2 was carried out in the same manner as in Example 1, except that the temperature of the blown air was changed to 25 ° C. The amount of miscut in the obtained pellet was 100 ppm.

Example 3 Example 3 was carried out in the same manner as in Example 1 except that the temperature of the blown air was changed to 50 ° C. The miscut amount in the obtained pellet was 1000 ppm.

Example 4 Example 1 was repeated except that the air to be blown was changed to ionized air at 25 ° C. by using an AC corona discharge device ionizer [manufactured by Kasuga Electric Co., Ltd.]. This was performed in the same manner as in Example 1. The miscut amount in the obtained pellet was 50 ppm.

Example 5 The procedure of Example 1 was repeated, except that the amount of p-tert-butylphenol was changed to 1.55 parts to produce a polycarbonate resin. The miscut amount in the obtained pellet was 80 ppm.

Example 6 Example 5 was carried out in the same manner as in Example 5, except that the temperature of the blown air was changed to 50 ° C. The miscut amount in the obtained pellet was 1020 ppm.

[Comparative Example 1] The same procedure as in Example 1 was carried out except that the method was not changed to a method in which air was not blown to the rotary blade. The miscut amount in the obtained pellet was 6,500 ppm.

[Comparative Example 2] In Example 1, 300 ° from the cut portion of the strand along the rotation direction of the rotary blade.
At an angle of 90 ° to the tangent from the direction opposite to the rotation direction at the position (angle of range D in FIG. 1), air is evenly applied in the width direction of the rotary blade so that air is uniformly applied to the surface of the rotary blade at an angle of 90 ° to the tangent. A method of cutting water-cooled strands under the condition of blowing air at 50 ° C. at a flow rate of 40 m / sec using a cutting machine having a rotary blade provided with five spray nozzles at a distance of 15 cm from the rotary blade. Except having changed, it carried out by the method similar to Example 1. The amount of miscut in the obtained pellet was 6,200 ppm.

Comparative Example 3 The procedure of Comparative Example 1 was repeated, except that the amount of p-tert-butylphenol was changed to 1.55 parts to produce a polycarbonate resin. The miscut amount in the obtained pellet was 6,300 ppm.

[0053]

[Table 1]

[0054]

According to the present invention, thermoplastic resin pellets having an extremely small amount of miscut can be produced stably and efficiently, and such thermoplastic resin pellets are extremely easily affected by miscut. It is suitably used as a material for an optical disc substrate, and the industrial effects achieved are outstanding.

[Brief description of the drawings]

FIG. 1 is a schematic view of a strand cutter used in the present invention.

[Explanation of symbols]

1. Strand cutter 2. Strand 3. Feed roller 4. Guide 5. Fixed blade 6. Rotary blade 7. Cover 8. 8. Rotation direction of rotary blade Pellet 10. Pellet outlet 11. Gas blowing nozzle 12. 12. Angle range A (0 to 270 ° from the cutting point along the rotation direction of the rotary blade) 13. Angle range B (0 to 135 ° from the cutting point along the rotation direction of the rotary blade) 14. Angle range C (135 to 270 ° from the cutting point along the rotation direction of the rotary blade) Angle range D (270-360 ° from the cutting point along the rotation direction of the rotary blade)

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Akira Manabe 1-2-2 Uchisaiwaicho, Chiyoda-ku, Tokyo Inside Teijin Chemicals Co., Ltd. (72) Inventor Yutaka Kurata 1-2-2 Uchisaiwaicho, Chiyoda-ku, Tokyo N-Kasei Co., Ltd. F-term (reference) 4F201 AA28 AR06 AR08 BA02 BC01 BL12 BL37

Claims (4)

[Claims] 1. A method for producing a pellet by melt-extruding a thermoplastic resin into a strand using a melt extruder, cooling the strand, and cutting the pellet with a cutter having a rotary blade and a fixed blade. A method for producing thermoplastic resin pellets, wherein a gas is blown to the rotary blade at a flow rate of 10 to 75 m / sec within a range of 0 to 270 ° from a cutting position along a rotation direction of the rotary blade. 2. The temperature of the gas blown to the rotary blade is 40
The method for producing a thermoplastic resin pellet according to claim 1, wherein the temperature is not higher than 0C. 3. The method for producing thermoplastic resin pellets according to claim 1, wherein the gas blown to the rotary blade is an ionized gas. 4. The method for producing thermoplastic resin pellets according to claim 1, wherein the thermoplastic resin is a polycarbonate resin.