JP2855572B2 - Polycarbonate pellet and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a polycarbonate pellet and a method for producing the same. More specifically, the present invention relates to polycarbonate pellets with less crazing and a method for producing the same. The less craze-producing polycarbonate pellets according to the present invention comprise the cooling and cutting of the melt extruded polycarbonate, wherein the cooling and the cutting are performed in this order or vice versa or simultaneously. In the manufacturing method, the electric conductivity measured at 25 ° C. is 1 mS.
/ Cm or less using cooling water. When molding is performed using the polycarbonate pellets of the present invention, it is possible to obtain a molded article with less crazing even when placed in a moist heat environment.

[0002]

2. Description of the Related Art Polycarbonate is widely used in many fields as engineering plastics having excellent heat resistance, impact resistance, transparency and the like.
However, when polycarbonate is used for medical applications or food applications where sterilization with hot water or steam is repeatedly performed, there is a problem that crazing occurs. Craze reduces the mechanical strength of the polycarbonate and impairs its appearance. Also, when polycarbonate is used for optical applications such as optical discs, when placed in a moist heat environment,
There is a problem that an optical defect occurs due to the occurrence of craze. Therefore, prevention of occurrence of craze of polycarbonate has been desired. It is known that foreign matter in polycarbonate contributes to the occurrence of craze in polycarbonate placed under moist heat conditions. That is, the mechanism of occurrence of craze is considered as follows. Once the polycarbonate placed under the moist heat condition is placed at room temperature, the moisture absorbed under the moist heat condition is released, but at this time, the released moisture cannot escape to the outside, and may be contaminated by foreign substances in the polycarbonate. get together. As a result, stress accumulates around the foreign matter in which moisture is collected, and craze occurs.

For this reason, several proposals have been made to prevent foreign substances (such as dust) from being mixed into polycarbonate. For example, for the polycarbonate obtained by the phosgene method, without passing through a drying step, which is a significant step of increasing foreign substances, the produced polycarbonate powder containing water and a solvent is directly supplied to an extruder with a vent to reduce dust. A method for obtaining polycarbonate pellets has been proposed (Japanese Patent Laid-Open No. 1-149827) (corresponding to US Pat. No. 4,845,193). For the polycarbonate obtained by the melt method (transesterification method), instead of pelletizing the manufactured molten polycarbonate once, in order to reduce the chance of contamination by foreign substances when adding additives to the manufactured polycarbonate, In addition, a method has been proposed in which additives are added and melt-kneaded while the polycarbonate is still in a molten state to suppress the incorporation of foreign substances (Japanese Patent Application Laid-Open No. 5-239334) (U.S. Pat. 926 and 5,502,153, corresponding to EP-A-615996A).

[0004] As for the method of pelletizing polycarbonate, polycarbonate is heated and melted by an extruder and extruded, and the polycarbonate is cut in a soft molten state by a knife rotating in close proximity to a die surface of the extruder. (Japanese Patent Laid-Open No. 7-9439) has been proposed to obtain polycarbonate pellets with less generation of metal foreign matters and polycarbonate chips derived from the above. Also, a method of suppressing the fluctuation of shear friction resistance in a molding machine by forming a specific curved cylindrical pellet and reducing the generation of foreign matter during molding by smoothing the rotation of a screw (Japanese Patent Publication No. -88251).

[0005]

However, the suppression of craze obtained by these conventional methods has not been satisfactory. The present invention provides polycarbonate pellets that generate less crazing even under wet heat conditions and a method for producing the same.

[0006]

Under these circumstances, the present inventors have conducted intensive studies in order to obtain polycarbonate pellets with reduced occurrence of craze. Including cooling and cutting, wherein the cooling and the cutting are performed in this order or vice versa or simultaneously, and the cooling is performed when the electrical conductivity measured at 25 ° C. is 1 mS / cm or less. It has been found that a polycarbonate pellet production method characterized in that the production is carried out by using a certain cooling water makes it possible to obtain a polycarbonate pellet with significantly reduced occurrence of craze. The present invention has been completed based on this finding.

Therefore, one object of the present invention is to provide polycarbonate pellets with reduced occurrence of craze. Another object of the present invention is to provide a method for producing polycarbonate pellets having the above excellent properties. Hitherto, no study has been made on the relationship between the quality of cooling water used for pelletization and the occurrence of craze. Although slightly described in the above-mentioned Japanese Patent Application Laid-Open No. 5-239334, "preferably pelletized in circulating water from which foreign matter has been removed", the electric conductivity of the circulating water is described. No description is given on the amount of foreign matter. Also, there is no description about the relationship between the electrical conductivity of the cooling water and the occurrence of craze. In the examples of the above-mentioned patent publication, circulating water filtered with a 0.2 μm filter is used, but the electric conductivity of water cannot be reduced by filtration with a normal filter.

The present inventors have found that the electric conductivity of the cooling water, which has not been noticed so far, has a great influence on the quality of polycarbonate, especially on the occurrence of craze. The mechanism by which the electrical conductivity influences the occurrence of craze is not yet clear, but is presumed to be due to local water absorption by the ionic component and the interaction of the ionic component with polycarbonate, additives and impurities.

That is, according to the present invention, it includes the cooling and cutting of the melt extruded polycarbonate, wherein the cooling and the cutting are performed in this order or vice versa, or simultaneously, and The present invention provides polycarbonate pellets with low craze generation, characterized by being obtained by a method for producing polycarbonate pellets in which cooling is performed using cooling water having an electric conductivity of 1 mS / cm or less measured at 25 ° C.

Next, in order to facilitate understanding of the present invention,
First, the basic features and preferred embodiments of the present invention will be listed. 1. Including cooling and cutting of the melt extruded polycarbonate, wherein the cooling and the cutting are performed in this order or vice versa or simultaneously, and the cooling is conducted at 25 ° C. Polycarbonate pellets with little craze, which are obtained by a method for producing polycarbonate pellets using cooling water of 1 mS / cm or less. 2. The amount of foreign matter of 0.5 to 25 μm in cooling water is 25 ° C.
2. The polycarbonate pellet according to the above item 1, which has a particle size of 10 ⁵ particles / ml or less as measured by the method described in 1. above. 3. Including cooling and cutting of the melt extruded polycarbonate, wherein the cooling and the cutting are performed in this order or vice versa or simultaneously and the electrical conductivity measured at 25 ° C. A method for producing polycarbonate pellets, comprising using cooling water of 1 mS / cm or less. 4. When the amount of foreign matter of 0.5 to 25 μm in the cooling water is 25
4. The method for producing polycarbonate pellets according to the above item 3, which is measured at a temperature of 10 ° C. and equal to or less than 10 ⁵ pellets / ml. 5. Electric conductivity measured at 25 ° C of cooling water is 10 ² μS
/ Cm or less, and 0.5 to 2 in the cooling water.
^{4. The} method for producing polycarbonate pellets according to the above item 3, wherein the amount of foreign substances of 5 μm is 10 ⁴ particles / ml or less as measured at 25 ° C. 6. 6. The method for producing a polycarbonate pellet according to any one of the above items 3 to 5, wherein the temperature of the cooling water is 40 ° C. or more and less than 100 ° C. 7. The method for producing polycarbonate pellets according to any one of the above items 3 to 6, wherein after cooling the polycarbonate with the cooling water, the cooling water attached to the surface of the polycarbonate is removed. 8. 8. The method for producing polycarbonate pellets according to any one of items 3 to 7, wherein the polycarbonate is produced by a transesterification reaction between an aromatic dihydroxy compound and a carbonic acid diester.

Hereinafter, the present invention will be described in detail. The polycarbonate used in the present invention has a main chain composed of a repeating unit represented by the following formula 1.

[0012]

Embedded image (Wherein, Ar is a divalent C ₅ -C ₂₀₀ aromatic residues, e.g., phenylene, naphthylene, biphenylene and pyridylene, they may be unsubstituted or substituted, or also, Examples include those represented by the following chemical formula 2.)

[0013]

Embedded image (Wherein, Ar ¹ and Ar ² are each an arylene group, and represent, for example, a group such as phenylene, naphthylene, biphenylene, or pyridylene, which may be unsubstituted or substituted; An alkylene group or a substituted alkylene group represented by Chemical Formula 4.)

[0014]

Embedded image

Embedded image (Wherein R ¹ , R ² , R ³ and R ⁴ are each a hydrogen atom, a C ₁ -C ₆ lower alkyl group, a C ₅ -C ₁₀ cycloalkyl group, a C ₆ -C ₃₀ aryl group, a C ₇ -C 4 _{31 is an} aralkyl group, which may be optionally substituted with a halogen atom or a C ₁ -C ₆ alkoxy group, k is an integer of 3 to 11, and at least one hydrogen atom of , A C ₁ -C ₆ lower alkyl group, a C ₆ -C ₃₀ aryl group, a halogen, or the like.) A divalent aromatic residue represented by the following formula (5) may be used as a copolymer component. May be contained.

[0015]

Embedded image (Wherein, Ar ¹ and Ar ² are the same as above. Z is a single bond or —O—, —CO—, —S—, —SO ₂ —, —CO
_2- , -CON (R ¹ )-, (R ¹ is as defined above) and the like. Specific examples of the divalent aromatic residue in the present invention include those represented by the following chemical formulas (6) and (7).

[0016]

Embedded image

Embedded image (Wherein R ⁵ and R ⁶ are each halogen, C _1-
C ₁₀ alkyl group, C ₁ -C ₁₀ alkoxy group, C ₅ -C ₁₀
An aryl group a cycloalkyl group or a C ₆ -C _30. m and n are integers of 1 to 4; when m is 2 to 4, each R ⁵ may be the same or different; and when n is 2 to 4, each R ⁶ is the same. However, they may be different. )

Among them, a divalent aromatic residue represented by the following formula 8 is a preferred example. Further, those containing 85 mol% or more (based on all monomer units in the polycarbonate) of a repeating unit represented by the following formula 8 as Ar are particularly preferable.

Embedded image Further, the polycarbonate used in the present invention may contain a trivalent or higher C ₆ -C ₃₀₀ aromatic residue as a copolymerization component. Although the molecular structure of the polymer terminal is not particularly limited, one or more terminal groups selected from a hydroxy group, an aryl carbonate group, and an alkyl carbonate group can be bonded. The aryl carbonate end group is
It is represented by the following formula 9.

Embedded image (Wherein, Ar ³ is a monovalent C ₆ -C ₃₀ aromatic residue;
The aromatic ring may be substituted. )

Specific examples of the aryl carbonate terminal group include those represented by the following formula (10).

Embedded image

The alkyl carbonate terminal group is represented by the following formula:
It is represented by 1.

Embedded image (Wherein R ⁷ is a linear or branched alkyl group having 1 to 20 carbon atoms) Specific examples of the alkyl carbonate terminal group include those represented by the following formula (12).

Embedded image

Among them, a phenyl carbonate group,
A pt-butylphenyl carbonate group, a p-cumylphenyl carbonate group and the like are preferably used. Also,
The molar ratio between the hydroxyl group terminal and the other terminal is not particularly limited, and is used in the range of 1: 1000 to 1000: 1 depending on the use.

The molecular weight of the polycarbonate used in the present invention is not particularly limited, but is generally in the range of 5,000 to 300,000, preferably in the range of 10,000 to 80,000. is there. As these polycarbonates, those produced by a known method can be used. Specifically, for example, an interfacial polymerization method (for example, a phosgene method) in which an aromatic dihydroxy compound and a carbonate precursor (for example, phosgene) are reacted in the presence of an aqueous sodium hydroxide solution and a methylene chloride solvent, and an aromatic dihydroxy compound and a carbonic acid diester (E.g., diphenyl carbonate), etc.
A method of solid-state polymerization of a crystallized carbonate prepolymer obtained by a phosgene method or a melt method (Japanese Patent Laid-Open No. 1-1580)
33, 1-271426, 3-68627, etc.).

Among these methods, in a solid-phase polymerization method using a prepolymer obtained by a melting method or a transesterification method such as a melting method, no solvent or chlorine compound is used in any case. In the case of the method, the polycarbonate is further obtained in a molten state, so that there is little possibility that foreign substances are mixed.
Therefore, a transesterification method such as a solid-phase polymerization method or a melting method using a prepolymer obtained by a melting method is preferable because the content of chlorine, ionic impurities, and minute foreign substances (dust and the like) can be easily reduced. The melting method is preferred. Specifically, at a monomer stage that is easy to purify, by using an aromatic dihydroxy compound that has been subjected to distillation purification or filtration purification and a carbonate diester that has been subjected to distillation purification or filtration purification, it substantially does not contain a chlorine atom, It is possible to obtain a polycarbonate having a low content of ionic impurities and minute foreign substances.

At this time, it is preferable to implement a well-known measure for preventing foreign matter from entering, such as closing a clean room or a manufacturing process. 0.5 to 25 μm in polycarbonate
Is preferably 10 ⁵ particles / g or less, more preferably 5 × 10 ⁴ particles / g or less, and still more preferably 1 × 10 ⁴ particles / g or less.
It is 10 ⁴ pieces / g or less. In the present invention, “melt extrusion” means extruding a polycarbonate in a molten state through a die or a nozzle. The shape of the die or nozzle is not particularly limited. A known method can be used for the extrusion. For example, a method using a gear pump can be used in addition to a method using a screw type extruder or a piston type extruder.

In the present invention, when a melting method is used as a method for producing polycarbonate, the obtained molten polycarbonate can be extruded as it is or together with the following additives using an extruder or a gear pump. It is more preferable than the phosgene method or solid phase polymerization which requires remelting in an extruder, or repelletization of pellets.
Further, in the polycarbonate, as long as it does not prevent the achievement of the effects of the present invention, a heat stabilizer, an antioxidant, a weathering agent,
UV absorbers, release agents, lubricants, antistatic agents, plasticizers, polymers such as other resins and rubbers, pigments, dyes, fillers, reinforcing agents,
A flame retardant or the like may be added for use. These additives are
It can be used in amounts commonly used in the art.

The present invention involves the cooling and cutting of the melt extruded polycarbonate, wherein the cooling and the cutting are performed in this order or vice versa or simultaneously, and the cooling is performed at 25 ° C. The electric conductivity measured in 1
It is intended to provide polycarbonate pellets with low craze occurrence, characterized by being obtained by a method for producing polycarbonate pellets using cooling water of mS / cm or less, wherein the cooling water having the above specific low electrical conductivity is provided. The pelletizing method including the cooling and cutting is not particularly limited as long as the cooling is performed by using the pelletizing method. For example,
After extruding the molten polycarbonate from the die, a known cutting method such as strand cutting (strand) is used.
d cut) method, hot cut method,
A hot cut method using a small amount of cooling water [for example, hot cut in mist air st
method), underwater cut (unde)
Pellets can be formed by a method such as an r-water cut method. In the strand cutting method, a molten resin is extruded from a die into a strand shape, and the strand is cut after cooling with water, or the strand is cut while cooling with water. In the hot cutting method, a molten resin extruded from a die is cut with a knife installed on the die surface, and the obtained molten resin pellet is cooled with water. In the mist cutting method, the molten resin extruded from the die is cut with a knife placed on the die surface while cooling by spraying a mist of water. In the underwater cutting method, a molten resin extruded from a die placed in water is cut in water with a knife installed on the die surface.

The shape, particle size, and particle size distribution of the pellet of the present invention are not particularly limited. In the present invention, the method of cooling the molten polycarbonate with cooling water is not particularly limited as long as the molten polycarbonate and the cooling water come into contact and the molten polycarbonate becomes solid. Specific examples of the method of cooling with cooling water include a method of extruding molten resin directly into water from a die provided in water and cooling the same, and a method of temporarily cooling air or air from a die provided in air or an inert gas. After being extruded into an active gas, it can be cooled by throwing it into water or by spraying with water or mist. Incidentally, the cooling method of the molten polycarbonate is described in JP-A-5-239334 (U.S. Pat. Nos. 5,364,926 and 5,502,153;
European Patent Application Publication No. 615996A).

The cooling water used in the present invention must have an electric conductivity measured at 25 ° C. of 1 mS / cm or less. Tap water and industrial water commonly used are 25
The electric conductivity measured at ° C. is several tens mS / cm or more, and such water cannot be used in the present invention as it is. Electric conductivity measured at 25 ° C of cooling water is 1mS / c
If it is larger than m, a product molded using the obtained polycarbonate pellets is liable to cause craze, which is not preferable. The electric conductivity measured at 25 ° C. is preferably 10 ² μS / cm or less, more preferably 10 μS / cm or less.
The range is S / cm or less. Further, as for the cooling water used in the present invention, it is more preferable that the amount of foreign matter be small along with the electric conductivity. Preferably, the cooling water is 0.1 mm.
10 ⁵ particles / m when the amount of foreign matter of 5 to 25 μm is measured at 25 ° C.
1 or less, more preferably 10 ⁴ / ml or less, further preferably 10 ³ / ml or less. If the amount of foreign substances in the cooling water is more than 10 ⁵ / ml, products molded using the obtained polycarbonate pellets tend to cause craze. Particularly preferred is 2
When the electric conductivity measured at 5 ° C. is 10 ² μS / cm or less,
In addition, the cooling water has an amount of foreign substances of 10 ⁴ particles / ml or less.

Various methods can be applied to a method for obtaining water that can be used as cooling water in the present invention, and there is no particular limitation. For example, as a method of reducing electric conductivity,
Examples of the method for reducing the amount of foreign substances include a distillation method, a filtration method, and a filtration method using a microfiltration membrane or an ultrafiltration membrane. These methods can be combined or repeated. By these operations, chloride ion, nitrate ion,
Ions such as silicate ions, carbonate ions, alkali metal ions, alkaline earth metal ions, and iron ions, and foreign substances such as organic matter, dust, and sand can be removed. Among these ions, it is preferable to reduce alkali metal ions. Particularly, for sodium ions and iron ions, 1 wt.
pm or less.

In the present invention, "foreign matter" refers to a minute substance capable of scattering a laser beam, for example, sand particles, mineral particles, metal particles, organic particles, dust, and the like. In the present invention, the electric conductivity can be measured using an electric conductivity meter, the amount of foreign matter of 0.5 to 25 μm, for example,
It can be measured by a fine particle measuring device using a laser.

After cooling with the cooling water, the cooling water adhering to the polycarbonate is evaporated as it is,
Since ionic components and foreign substances in the cooling water remain on the surface of the polycarbonate, it is preferable to remove the cooling water attached to the surface of the polycarbonate. This removal can be performed, for example, by scattering the cooling water using a clean air blow or a centrifuge.

The temperature of the cooling water is 40 ° C. or more and 100 ° C.
It is preferred that the temperature be lower than 0 ° C. If the temperature is lower than 40 ° C., in particular, when using the strand cutting method, since vacuum bubbles are easily generated in the cooled polycarbonate, holes are formed in the obtained pellets, the amount of adhered water increases, or by the entrainment of air during molding, The hot water resistance of the obtained molded article is reduced, and particularly, the occurrence of craze is increased, which is not preferable. If the temperature of the cooling water is 100 ° C. or higher, the operability decreases, which is not preferable.

It is preferable that the content of the foreign matter of 0.5 to 25 μm in the polycarbonate pellet of the present invention is small. For example, the number is preferably 10 ⁵ / g or less, more preferably 5 × 10 ⁴ / g or less, and still more preferably 1 × 10 ⁴ / g.
It is 10 ⁴ pieces / g or less. The molding method for molding using the polycarbonate pellets of the present invention is not particularly limited, and any known molding method such as an injection molding method can be used. The polycarbonate pellet of the present invention,
Even when placed under moist heat conditions, it can be suitably used for medical applications and food applications where sterilization with hot water or steam is repeated, and for optical applications such as optical discs where optical defects are a problem, because craze is less generated.

[0033]

The present invention will be described in more detail with reference to the following examples and comparative examples, but the present invention is not limited to these examples. In the following Examples and Comparative Examples, each property was measured by the following methods. (1) Electric conductivity: Measured at 25 ° C. using a conductivity meter manufactured by Electrochemical Meter Co., Ltd. (2) Foreign substance amount of 0.5 to 25 μm: Pacific Scie, USA
ntific Company's particle analyzer HIAC / ROYCO
(Registered trademark) at 25 ° C. The amount of foreign matter of 0.5 to 25 μm in the polycarbonate was measured by dissolving the polycarbonate in a methylene chloride solvent at a concentration of 0.4% by weight (based on the weight of the methylene chloride solvent). (3) Anti-crazing property: Injection molding was performed in a clean room using the obtained pellets to obtain 20 × 200 × 3 mm.
Were immersed in hot water of 95 ° C., immersed in 70 hours, taken out, left in a room of 25 ° C. × 50 RH% for 24 hours, and arranged so that the polarization directions were orthogonal to each other. Each test piece was placed between two polarizing plates, the number of crazes generated was visually counted, and the number of crazes of the seven test pieces was totaled.

Example 1 A melt-produced bisphenol A and diphenyl carbonate having a viscosity average molecular weight of 24,500 and a foreign substance content of 0.5 to 25 μm containing 8,8
000 pieces / g of polycarbonate were withdrawn from the polymerization vessel with a gear pump, and a heat stabilizer [Tris (2,4-di-t-
Butylphenyl) phosphite] at a concentration of 100 ppm by weight, and then fed to a vented twin-screw extruder (extrusion temperature: 280 ° C.). The molten resin strand coming out of the die (orifice diameter: 5.5 mm) of the extruder was subjected to tap water using an ion-exchange resin (Organo pure water dispenser G-10) and an ultrafiltration membrane (Asahi Kasei SIP3013). The electric conductivity obtained by purification is 0.5 μm at 1 μS / cm.
After cooling by passing through a 1 m long strand bath filled with 60 ° C. water (cooling water) containing 1 particle / ml of foreign matter of １25 μm, take out into the air, and scatter attached water with clean air. 2.5m diameter cut with a pelletizer
m, polycarbonate pellets having a length of 3 mm were obtained. The amount of foreign matter of 0.5 to 25 μm in the pellet was as small as 8120 particles / g. When the anti-crazing property of the obtained pellets was evaluated, no crazing was observed.

(Example 2) As cooling water, the amount of foreign substances having an electric conductivity of 12 μS / cm and 0.5 to 25 μm was 83 particles /
The procedure was carried out in the same manner as in Example 1 except that ml of distilled water at 60 ° C. was used. When the anti-crazing property of the obtained pellets was evaluated, no crazing was observed.

(Example 3) As cooling water, the amount of foreign matter having an electric conductivity of 128 μS / cm and 0.5 to 25 μm was 213.
Example 1 except that 1 piece / ml of distilled water at 60 ° C. was used.
The same was done. When the anti-crazing property of the obtained pellet was evaluated, two crazes were found.

(Comparative Example 1) As cooling water, the amount of foreign substances having an electric conductivity of 50 mS / cm and 0.5 to 25 μm was 15.8
The procedure was performed in the same manner as in Example 1 except that tap water at 60 ° C. was used at 67 pieces / ml. When the anti-crazing property of the obtained pellet was evaluated, 37 crazes were found.

(Comparative Example 2) As cooling water, the amount of foreign matter having an electric conductivity of 72 mS / cm and 0.5 to 25 μm was 210,
The procedure was performed in the same manner as in Example 1 except that industrial water at 60 ° C. was used at 512 pieces / ml. When the anti-crazing property of the obtained pellet was evaluated, 49 crazes were found.

Comparative Example 3 Electric conductivity was 72 mS / cm
The amount of foreign matter of 0.5 to 25 μm is 210,512 particles / ml
Of industrial water was purified using an ultrafiltration membrane (SIP3013 manufactured by Asahi Kasei), and cooled to 60 ° C. water having an electric conductivity of 63 mS / cm and an amount of foreign matter of 0.5 to 25 μm having 3 particles / ml. The procedure was performed in the same manner as in Example 1 except that water was used.
When the anti-crazing property of the obtained pellet was evaluated,
27 crazes were seen.

Example 4 The same distilled water as used in Example 3 was purified using an ultrafiltration membrane (SIP3013 manufactured by Asahi Kasei) and the electrical conductivity obtained was 113 μS / cm.
The procedure was performed in the same manner as in Example 1 except that 60 ° C. water having a foreign substance amount of 1 particle / ml of 5 to 25 μm was used as cooling water. When the anti-crazing property of the obtained pellet was evaluated, two crazes were found.

Example 5 A viscosity average molecular weight of 23,700 obtained from bisphenol A and phosgene by the phosgene method.
Was added with a heat stabilizer [tris (2,4-di-t-butylphenyl) phosphite] at a concentration of 100 ppm by weight, and then vented 2
It was supplied to a screw extruder (extrusion temperature: 280 ° C.). The molten resin strand coming out of the die (orifice diameter: 5.5 mm) of the extruder was used at 60 ° C. as used in Example 3.
After cooling by passing through a 1m long strand bath filled with distilled water (cooling water), take out into the air, scatter attached water with clean air, cut with a pelletizer, cut 2.5mm in diameter, length 3 mm polycarbonate pellets were obtained. When the anti-crazing property of the obtained pellet was evaluated, eight crazes were found.

Example 6 The same operation as in Example 3 was carried out except that the temperature of the cooling water was set at 13 ° C. When the anti-crazing property of the obtained pellet was evaluated, eleven crazes were found.

Example 7 The same industrial water used in Comparative Example 2 was replaced with an ion-exchange resin (pure water purifier G-10 manufactured by Organo).
Has an electric conductivity of 304 μS / c.
34,200 particles / ml of foreign matter of 0.5 to 25 μm in m
The procedure was performed in the same manner as in Example 1 except that 60 ° C. water was used as cooling water. When the anti-crazing property of the obtained pellet was evaluated, 14 crazes were found.

[0044]

According to the present invention, it is possible to produce polycarbonate pellets with less crazing even under wet heat conditions. In addition, the polycarbonate pellets of the present invention are less susceptible to craze even when placed under moist heat conditions, and are used for medical and food applications where sterilization with hot water or steam is repeatedly performed, or for optical discs where optical defects are a problem. Can be suitably used for the production of polycarbonate molded products for optical applications.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ identification symbol FI // C08G64 / 40 C08G64 / 40 B29K 69:00 (58) Field surveyed (Int.Cl. ⁶ , DB name) B29B 9 / 06 B29B 9/10 B29B 13/04 C02F 1/42 C08G 64/20 C08G 64/40 B29K 69:00

Claims (8)

(57) [Claims] 1. Includes cooling and cutting of the melt extruded polycarbonate, wherein said cooling and said cutting are performed in this order or vice versa or simultaneously, and said cooling is measured at 25 ° C. Electric conductivity is 1mS / c
m. A polycarbonate pellet with less craze, which is obtained by a method for producing polycarbonate pellets using cooling water of m or less. 2. The polycarbonate pellets according to claim 1, wherein the amount of foreign substances having a size of 0.5 to 25 μm in the cooling water is 10 ⁵ particles / ml or less as measured at 25 ° C. 3. Includes cooling and cutting of the melt extruded polycarbonate, wherein the cooling and the cutting are performed in this order or vice versa or simultaneously, and the cooling is measured at 25 ° C. Electric conductivity is 1mS / c
m, using a cooling water of not more than m. 4. The method for producing polycarbonate pellets according to claim 3, wherein the amount of foreign substances having a size of 0.5 to 25 μm in the cooling water is 10 ⁵ particles / ml or less as measured at 25 ° C. 5. The electric conductivity measured at 25 ° C. of cooling water is 10 ² μS / cm or less, and the amount of foreign matter of 0.5 to 25 μm in said cooling water is 10 ⁴ particles measured at 25 ° C. The method for producing polycarbonate pellets according to claim 3, wherein the content is not more than / ml. 6. The method for producing polycarbonate pellets according to claim 3, wherein the temperature of the cooling water is 40 ° C. or more and less than 100 ° C. 7. The method for producing polycarbonate pellets according to claim 3, wherein after cooling the polycarbonate with the cooling water, the cooling water adhering to the surface of the polycarbonate is removed. 8. The method for producing polycarbonate pellets according to claim 3, wherein the polycarbonate is produced by a transesterification reaction between an aromatic dihydroxy compound and a carbonic acid diester.