JPH072364B2 - Method for melt extrusion of polycarbonate - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for melt extrusion of polycarbonate, and more specifically, by injecting and adding a small amount of water to a polycarbonate in a molten state and removing the water from a vacuum vent port. Then, it relates to a method for obtaining an extruded product of polycarbonate having excellent properties.

<Prior Art> Polycarbonate has been used in many fields as engineering plastics due to its excellent mechanical properties and heat resistance. Recently, however, attention has been paid to its transparency as a glass substitute for windowing. It has come to be used in the fields of information recording disks, including glass, windshields, and spectacle lenses. In such optical applications, the hue of the molded product and the presence of foreign matter become a problem.

Many methods have been proposed in the past for preventing coloring and thermal decomposition of polycarbonate during thermoforming, but the addition of phosphite esters is the mainstream in industrial practice. However, a molded article containing a phosphite ester has a drawback that it is deteriorated by hydrolysis in the presence of water. Further, the aliphatic halogenated hydrocarbon causes a problem of mold corrosion in melt molding. In order to solve these problems, a small amount of water is added to the polycarbonate powder separated and recovered from the methylene chloride solution and extruded with a vented extruder to remove coloring impurities and methylene chloride insoluble matter. A method for suppressing the generation of coloring substances has been proposed (US Pat. No. 3,567,813,
(See JP-A-60-184814). However, in these methods, namely, a method of supplying a polycarbonate powder containing water to a hopper or a method of supplying water to a hopper, a part of the water is evaporated by the heat of the extruder and is discharged to the hopper side. Therefore, in a long-time operation, the water content in the hopper gradually accumulates and increases, and the charging of the polycarbonate powder into the extruder cannot be performed smoothly.
Between the hopper and the vent, the polycarbonate is kept in contact with water, resulting in hydrolysis, especially when a phosphite is added, which is a problem in industrial practice. Needed a solution to them.

<Object of the Invention> An object of the present invention is to provide a method for smoothly supplying raw materials to an extruder while adding water in a polycarbonate extrusion step, and to substantially eliminate hydrolysis by water. To provide.

<Structure of the Invention> The present invention relates to a method for melt-extruding a polycarbonate in which a polycarbonate is melt-extruded using an extruder having one or more pressure-reducing vents. 0.1 to 5 per part by weight
A method for melt-extruding a polycarbonate, characterized in that water in an amount of part by weight is added.

The polycarbonate used in the present invention has the general formula (1) A divalent phenol represented by, a carbonate precursor,
For example, a homopolymer or a copolymer obtained by reaction with phosgene, which is separated and recovered by a known method from a solution of a lower halogenated hydrocarbon such as methylene chloride, 1,2-dichloroethylene or chloroform. Powder,
It is in the form of fine particles or flakes.

Examples of the divalent phenol include 4,4'-dihydroxydiphenyl and 2,2-bis (4-hydroxyphenyl).
Propane (hereinafter referred to as bisphenol A), bis (4
-Hydroxyphenyl) methane, 1,1-bis (4-hydroxyphenyl) ethane, 1,1-bis (4-hydroxyphenyl) cyclohexane, bis (4-hydroxyphenyl) ether, bis (4-hydroxy) Phenyl) ketone, bis (4-hydroxyphenyl) sulfide, bis (4-hydroxyphenyl) sulfone, 2,2-bis (3,5
-Dibromo-4-hydroxyphenyl) propane, 2,2
-Bis (3,5-dimethyl-4-hydroxyphenyl) propane and the like can be mentioned.

The extruder used is a normally used extruder having one or more vent ports, but it has a water injection hole from the compression-melting part to the farthest vent port. It is necessary. The distance between the water injection hole and the nearest vent port on the discharge port side needs to be well mixed with resin and water between them, and it varies depending on the shape of the screw and the rotation speed. It is desirable to specify

The amount of water to inject is per 100 parts by weight of polycarbonate
It is 0.1 to 5 parts by weight, more preferably 0.3 to 2 parts by weight.
If the amount is less than 0.1 parts by weight, the effect of the present invention cannot be obtained, and if it exceeds 5 parts by weight, the decrease in the molecular weight of the polycarbonate becomes remarkable, which is not suitable.

In carrying out the method of the present invention, the starting polycarbonate is continuously fed from the hopper to the feed section of the extruder.
Polycarbonate is compressed according to the rotation of the screw, melted by heating from the cylinder and internal frictional heat, and advances to the discharge port side while being kneaded by the rotating screw filling the space between the cylinder and the screw. .
During this process, water is continuously or pulsatingly injected from the water injection hole. Since the resin is filled on both the supply side and the discharge side, all the injected water is mixed with the molten polycarbonate. 150T
Moisture reaches the vent portion which is maintained at orr or less and the water is rapidly evaporated and removed, and the advancing polycarbonate is continuously discharged from the discharge port.

In the present invention, since the contact time between the polycarbonate and water is short, the decrease in the molecular weight can be limited to a practical range even if a phosphorous acid ester of about 15 ppm or less as a phosphorus atom is added.

In the method of the present invention, various molded products can be obtained depending on the die attached to the discharge port. For example, a strand (a pellet when cut), a rod, a tube, a sheet, a film, a profile extruded product, or the like.

<Effects of the Invention> In the method of the present invention, the unstable supply of raw materials and the decrease in the molecular weight due to hydrolysis, which have been problems in the prior art, are almost eliminated, so that the method can be industrially carried out. The obtained molded product is excellent in terms of hue and foreign matters, and can be made into an excellent optical molded product by pelletizing it by injection molding or other molding methods.

<Examples> The present invention will be described in detail below with reference to Examples.

Example 1 A polycarbonate (hereinafter, referred to as polycarbonate A) powder obtained from bisphenol A having an average molecular weight of 14800 containing 600 ppm of methylene chloride as a chlorine atom was used as a raw material, and both vents of a two-vent type extruder having a screw diameter of 60 mm were used. Using an extruder with a water injection hole in the center,
Strands were extruded and cut at a temperature of 300 ° C. with a vent vacuum of 8 Torr on the supply side and 11 Torr on the discharge side, and the amount of water added was 0.8 PHR to obtain pellets. There were no troubles during continuous 5 hours of operation. The chlorine content of the obtained pellets is
It was 20 ppm, the b value by a color difference meter manufactured by Suga Test Instruments Co., Ltd. was 1.8, and the average molecular weight was 14700. The b value of a 2 mm thick molded plate obtained by injection molding this pellet at 380 ° C. was 4.7.

For comparison, the pellet obtained in the same manner as in Example 1 except that water was not added had a chlorine content of 62 ppm, ab value of 2.7 and an average molecular weight of 14700, and the molded plate had ab value of 5.3.

Example 2 Tris (nonylphenyl) phosphite was mixed with a polycarbonate A powder having a chlorine content of 370 ppm and an average molecular weight of 22100 so as to have a concentration of 200 ppm. Using the extruder used in Example 1, the resin temperature was 365 ° C., the degree of vacuum of the vent was 8 Torr on the supply side, 10 Torr on the discharge side, and the amount of water added was 1.0 PHR.

The obtained pellet had a chlorine content of 10 ppm, ab value of 2.2 and an average molecular weight of 22,000. The b value of a 2 mm thick molded plate obtained by injection molding this pellet at 380 ° C. was 5.2.

For comparison, the pellet obtained by the same operation as in Example 2 except that water was not added had a chlorine content of 21 ppm, ab value of 2.7 and an average molecular weight of 22,100, and the molded plate had ab value of 5.6.

Comparative Example Chlorine content used in Example 2 370ppm, average molecular weight 2210
Tris (nonylphenyl) phosphite was mixed with Polycarbonate A powder of 0 to a concentration of 200 ppm, and water was added through a pipe from the hopper so that the amount of water added was 1.0 PHR. Polycarbonate pellets were obtained in the same manner as in Example 2 except for the above.

The obtained pellets had a chlorine content of 15 ppm, ab value of 2.5 and an average molecular weight of 21,000. 380 ℃ using this pellet
The b value of a 2 mm-thick molded plate obtained by injection molding at 5.5 was 5.5.

Claims (1)

[Claims] 1. A method of melt extruding a polycarbonate by melt extruding a polycarbonate using an extruder having one or more vacuum vent ports, wherein 0.1 per 100 parts by weight of the polycarbonate is between the compression-melting part and the farthest vent port. ~
A method for melt extrusion of polycarbonate, characterized by adding 5 parts by weight of water.