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EP-4737085-A1 - METHOD FOR PRODUCING POLYCARBONATE RESIN COMPOSITION PELLET

EP4737085A1EP 4737085 A1EP4737085 A1EP 4737085A1EP-4737085-A1

Abstract

A method for producing polycarbonate resin composition pellets with excellent transparency more stably while achieving high productivity, using an ultra-high torque twin screw extruder. The method uses a polycarbonate resin granular material having specific molecular weight and particle diameter as a raw material, and comprises kneading the polycarbonate resin granular material at condition of a screw shaft torque density of 9.0 to 17.0 Nm/cm 3 ; a screw rotation speed of 400 to 800 rpm; [output (kg/h) ÷ screw rotation speed (rpm) ÷ cube of center-to-center distance between two screw shafts (cm 3 )] of 0.015 to 0.026 kg/h/rpm/cm 3 , and an unmelted rate in a flange before a die holder of 2 to 30%; and extruding a strand from a die, and pelletizing the strand.

Inventors

  • TAJIRI, TOSHIYUKI
  • TOYOTA, AKINORI
  • MURAMATSU, Yuka

Assignees

  • Mitsubishi Engineering-Plastics Corporation

Dates

Publication Date
20260506
Application Date
20240611

Claims (4)

  1. A method for producing polycarbonate resin composition pellets from a polycarbonate resin granular material with a twin screw extruder, wherein the polycarbonate resin granular material has a viscosity-average molecular weight of 11000 to 27000 and a median diameter D 50 of 400 to 1500 µm as measured by a light-scattering wet method, and the method comprises: kneading the polycarbonate resin granular material under the following conditions: a screw shaft torque density at a base of each screw is in a range of from 9.0 to 17.0 Nm/cm 3 ; a screw rotation speed is in a range of from 400 to 800 rpm; and a value of [output (kg/h) ÷ screw rotation speed (rpm) ÷ cube of center-to-center distance between two screw shafts (cm 3 )] is 0.015 to 0.026 kg/h/rpm/cm 3 , so that an unmelted rate in a flange before a die holder is in a range of 2 to 30%; and extruding a strand from a die, and pelletizing the strand.
  2. The method of claim 1, wherein devolatilization is carried out under vacuum using a vent with an opening provided downstream of a kneading zone, the opening having a length of 2.0 to 6.0 D (D is a cylinder diameter) in a screw shaft direction and being provided such that a distance from a most downstream position of the vent opening to a tip of screw is 5.0 to 10.0 D.
  3. The method of claim 1 or 2, wherein the strand just extruded from the die has a temperature in a range of from 260°C to 330°C.
  4. The method of any one of claims 1 to 3, wherein the resultant polycarbonate resin composition pellets have a total light transmittance of 50% or more as measured using transmitted light in accordance with JIS K7361.

Description

[Technical Field] The present invention relates to a production method for polycarbonate resin composition pellets and, more specifically, to a highly productive and more stable method for producing polycarbonate resin composition pellets with excellent transparency using an ultra-high torque twin screw extruder. [Background Art] Polycarbonate resins are widely used in a variety of fields because they have excellent impact resistance, heat resistance, electrical insulation properties, dimensional stability, and the like, and because these properties are well balanced. In particular, polycarbonate resin produced from bisphenol compounds has the advantages of being excellent in transparency, impact resistance and heat resistance, being lightweight, and being difficult to break, and is therefore used as a substitute for glass in automobile parts, building materials, and optical parts such as lenses. Further, in recent years, this has been widely used as molded products such as panel components for display devices used in various mobile terminals such as smartphone, tablet computer, car navigation or car audio equipment, portable game console, digital camera, etc. For the production of such molded products, polycarbonate resin composition pellets (the term "pellet" refers to a product obtained by forming a once-molten material into a cylindrical, spherical or oval spherical shape) are used that are made of a polycarbonate resin raw material with various additives and the like added as needed. The polycarbonate resin composition pellets are usually produced using a twin screw extruder, which has long been required to provide improved plasticizing and kneading capabilities for productivity enhancement. Recently, ultra-high torque extruders (such as "TEXαIII" manufactured by The Japan Steel Works, Ltd. and "TEM-SX" manufactured by Shibaura Machine Co., Ltd.) with a maximum torque density as high as 18 Nm/cm3 have been developed, allowing for production in an unprecedentedly high torque region. Further, achieving higher torque has enabled increased screw rotation speed more than before. Thus, these extruders can operate in a high energy region (where both a higher torque density and a higher screw rotation speed are achieved), which has made it possible to achieve previously unimaginably high output. Regarding the torque density of extruder, PTL 1 describes an invention that uses a single reverse screw element having a flight portion with an arc-shaped notch, with the aim of increasing the productivity of glass fiber reinforced thermoplastic resin composition pellets compared to conventional methods and extremely reducing the probability that aggregates of monofilaments (un-defibrated glass fiber bundles) will remain in the produced pellets. The PTL 1 also specifies the conditions for this as follows: (i) a torque density, which is the value obtained by dividing the torque of the screw in the reverse transporting screw element by the cube of the center-to-center distance between the engaging screws, of 11 Nm/cm3 or more; and (ii) Q/Ns density, where Q is output and Ns is screw rotation speed, which is obtained by dividing Q/Ns by the cube of the center-to-center distance between the screws, is 0.013 kg/h/rpm/cm3 However, with regard to torque density, PDL 1 simply states in paragraph [0063] that "When the torque density is 11 (Nm/cm3) or more, the filling rate of the material in the extruder increases, the energy density decreases, and there are effects that even if the rotation speed is increased compared to conventional cases, the temperature rise is low. Furthermore, a preferable torque density range is 13 Nm/cm3 or more and 18 Nm/cm3 or less." However, there is no mention what the torque density was in the examples. In the examples of PDL 1, a twin-screw extruder "TEX44αII (manufactured by Japan Steel Works, Ltd.) with a screw element cylinder diameter D of 0.047 m" is used, but the allowable shaft torque density of the TEX44αII is 13.1 Nm/cm3, and since a torque density higher than this would damage the screw shaft or gearbox and cause the shaft to break, it is usually operated at a torque density of 80% or less. Therefore, the torque density of it can be said to be 10.5 Nm/cm3 at the highest. Since the ultra-high torque twin screw extruders as described above did not yet exist when PTL 1 was filed, the specific conditions disclosed in PTL 1 are those for conventional low torque extruders. There is no description or suggestion of the various problems that arise during ultra-high torque operation, which is the subject of the present invention, much less any solution to those problems. The torque density along the screw is highest at the base of the extruder, and this torque is used for melt-kneading, transporting, etc. of the resin, and it decreases toward the tip of the screw, reaching 0 at the tip. PTL 1 describes the torque density in the reverse feed screw element in the glass fiber mixing zone, PTL 1 menti