Method for producing flame retardant polycarbonate resin composition pellets

Abstract

Provided is a method for producing polycarbonate resin composition pellets by a twin-screw extruder from 30-80 mass% of polycarbonate resin pellets (A), 5 to less than 25 mass% of a phosphate ester-based flame retardant (B) that is liquid at room temperature, 0-50 mass% of polycarbonate resin flakes (C), 0-30 mass% of a styrene-based resin (D) having an acrylonitrile unit, and 0-15 mass% of another additive (E), wherein the method is characterized by using a twin-screw extruder having three or more kneading parts and having two or more depressurizing vents, and by putting (A), (C), (D), and (E) into the twin-screw extruder, melt kneading by the first kneading part, then depressurizing and devolatilizing by the first depressurizing vent, allowing the molten resin to reside in the second kneading part, then adding the phosphate ester-based flame retardant (B) that is liquid at room temperature, also kneading the molten resin and the phosphate ester-based flame retardant (B) that is liquid at room temperature by the third kneading part, then depressurizing and devolatilizing by the second depressurizing vent, and extruding the product from a die.

Description

Method for producing flame-retardant polycarbonate resin composition pellets

[0001] The present invention relates to a method for producing flame-retardant polycarbonate resin composition pellets.

[0002] Polycarbonate resins are resins with excellent heat resistance and mechanical properties, and are therefore widely used in, for example, electrical appliances, electronic appliances, vehicles such as automobiles, office automation equipment such as printers and copiers, and materials for manufacturing parts in housing, construction, and other industrial fields. These products are required to be flame retardant from the viewpoint of safety in order to prevent fires caused by high temperatures, and flame-retardant polycarbonate resin compositions are particularly suitable for use as housings for office automation equipment such as printers and copiers, personal computers, various mobile terminals, batteries, and the like.

[0003] On the other hand, in recent years, with the rise in environmental awareness, there has been a strong social demand for the recycling of resins, and regulations are being strengthened under various legal systems. There is a particular demand for the use of recycled resins for the exteriors and housings of office automation equipment, electronic devices, etc., and there are an increasing number of cases in which polycarbonate resin compositions containing a predetermined amount of recycled resin are required.

[0004] To regenerate thermoplastics from used products, for example, as described in Patent Document 1, thermoplastic materials recovered from equipment parts are crushed, washed with a cleaning solution, and the crushed thermoplastic material is separated from the crushed mixture.

[0005] Examples of raw materials for recycled (regenerated) polycarbonate resin include optical disks such as CDs and DVDs, automobile headlamps, and containers such as water bottles, which are crushed, washed, separated, and recovered before being pelletized. Furthermore, by-products from molding, such as sprues and runners, are also repelletized and used.

[0006] High flame retardancy is required for such recycled materials to be used particularly in office equipment, etc. A widely known method for imparting flame retardancy to polycarbonate resins has been to blend halogen-based flame retardants such as organic bromine compounds into the polycarbonate resins, but in recent years, it has been proposed to blend phosphorus-based flame retardants into polycarbonate resins, and phosphorus-based flame retardants are now becoming the norm.

[0007] Japanese Patent Application Laid-Open No. 2000-198116

[0008] Phosphorus-based flame retardants, such as phosphate ester-based flame retardants, are available in solid and liquid forms at room temperature, and liquid forms require liquid addition to the extruder. However, when using an extruder to melt-mix a liquid phosphorus-based flame retardant with pelletized polycarbonate resin, such as the recycled material described above, the liquid phosphorus-based flame retardant is difficult to mix with the pelletized polycarbonate resin, resulting in unmelted polycarbonate resin, vent-up at the vent opening, a low output, and difficulty in collecting strands. Furthermore, pelletized polycarbonate resin is prone to moisture absorption, and the moisture evaporates into water vapor in the extruder, further expanding at high temperatures. This water vapor tends to result in insufficient mixing, further impeding mixing of the polycarbonate resin and the liquid phosphorus-based flame retardant. Furthermore, a large amount of water vapor evaporates from the vacuum vent. This generates a high-speed ascending air current, which carries the molten resin and easily rises to the vacuum vent, causing so-called vent-up. If vent-up occurs, the vacuum piping becomes clogged, the vacuum function is lost, and volatiles cannot be removed from the resin. An object (object) of the present invention is a production method for efficiently melt-kneading a liquid phosphorus-based flame retardant and pelletized polycarbonate resin. In particular, recycled polycarbonate resin pellets undergo processes of crushing, washing, separation, and pelletization, and are prone to moisture absorption, making insufficient kneading due to water vapor. The recycled polycarbonate resin and the liquid phosphorus-based flame retardant are difficult to mix, and large amounts of water vapor make vent-up more likely to occur. An object (object) of the present invention is a method for producing pellets of a flame-retardant polycarbonate resin composition containing a liquid phosphorus-based flame retardant, which solves the above problems.

[0009]

[0003] The present inventors have conducted extensive research to achieve the above-mentioned object, and as a result, have found that a flame-retardant polycarbonate resin composition can be efficiently produced by adding a phosphate ester flame retardant that is liquid at room temperature to polycarbonate resin pellets and producing the composition in a twin-screw extruder having three or more kneading sections and two or more pressure-reducing vents, feeding the polycarbonate resin pellets and other raw materials into the twin-screw extruder, melt-kneading the mixture in the first kneading section, removing water vapor and volatile components through the first pressure-reducing vent, melt-kneading the mixture in the second kneading section to retain the resin, adding a liquid phosphorus-based flame retardant, further kneading the molten resin and the liquid flame retardant in the third kneading section, reducing the pressure through the second pressure-reducing vent to remove the remaining volatile components, and extruding the mixture through a die, thereby completing the present invention.

[0004] The present invention relates to the following method for producing flame-retardant polycarbonate resin composition pellets.

[0010] 1. A method for producing polycarbonate resin composition pellets using a twin-screw extruder from 30 to 80% by mass of polycarbonate resin pellets (A), 5% by mass or more but less than 25% by mass of a phosphate ester-based flame retardant (B) that is liquid at room temperature, 0 to 50% by mass of polycarbonate resin flakes (C), 0 to 30% by mass of a styrene-based resin having acrylonitrile units (D), and 0 to 15% by mass of other additives (E) other than (B) [provided that the total of (A) to (E) is 100% by mass], the method comprising the steps of: a twin-screw extruder having a nozzle hole, wherein the components (A), (C), (D), and (E) are fed into the twin-screw extruder, melt-kneaded in a first kneading section, then reduced pressure in a first reduced pressure vent to devolatilize, the molten resin is retained in a second kneading section, after which a phosphate ester-based flame retardant (B) that is liquid at room temperature is added, and further the molten resin and the phosphate ester-based flame retardant (B) that is liquid at room temperature are kneaded in a third kneading section, after which reduced pressure in a second reduced pressure vent to devolatilize, and the resulting mixture is extruded through a die. A method for producing polycarbonate resin composition pellets using a twin-screw extruder, the method comprising: 30 to 80 mass% of polycarbonate resin pellets (A); 5 to less than 25 mass% of a phosphate ester-based flame retardant (B) that is liquid at room temperature; 0 to 50 mass% of polycarbonate resin flakes (C); 0 to 30 mass% of a styrene-based resin (D) having an acrylonitrile unit; and 0 to 15 mass% of an additive (E) other than (B) (provided that the total of (A) to (E) is 100 mass%), the method comprising the steps of: kneading the polycarbonate resin composition in a twin-screw extruder at three or more locations; 2. A method for producing flame-retardant polycarbonate resin composition pellets, comprising: feeding (A), (C), (D), and (E) into a twin-screw extruder having a die; melt-kneading the components in a first kneading section, reducing the pressure in a first vacuum vent to remove volatilization; retaining the molten resin in a second kneading section; adding a phosphate ester-based flame retardant (B) that is liquid at room temperature; further kneading the molten resin and the phosphate ester-based flame retardant (B) that is liquid at room temperature in a third kneading section; kneading the resulting mixture with the phosphate ester-based flame retardant (B) that is liquid at room temperature; then reducing the pressure in a second vacuum vent to remove volatilization; and extruding the resulting mixture through a die. 3. A method for producing flame-retardant polycarbonate resin composition pellets according to claim 1 or 2, wherein the moisture absorption of the polycarbonate resin pellets (A) is 2,000 ppm or more.4. The manufacturing method according to any one of the above 1 to 3, wherein the polycarbonate resin pellets (A) are recycled material. 5. The manufacturing method according to any one of the above 1 to 4, wherein the other additives (E) include a dispersion of polytetrafluoroethylene. 6. Pellets manufactured by the manufacturing method according to any one of the above 1 to 5.

[0011] According to the manufacturing method of the present invention, melt-kneading is promoted, the amount of water vapor volatilized in the second reduced pressure vent is reduced, vent-up does not occur, and strands can be stably drawn.

[0012] 1 is a cross-sectional view showing an example of the configuration of an extruder used in the method of the present invention. 2 is a view showing a die portion of the extruder used in the examples.

[0013] Hereinafter, the present invention will be described in detail with reference to embodiments and examples, but the present invention should not be construed as being limited to these embodiments and examples.

[0014] The raw materials used in the method for producing polycarbonate resin composition pellets of the present invention are 30 to 80 mass% polycarbonate resin pellets (A), 5 to 25 mass% or more of a phosphate ester-based flame retardant (B) that is liquid at room temperature, 0 to 50 mass% polycarbonate resin flakes (C), 0 to 30 mass% of a styrene-based resin having acrylonitrile units (D), and 0 to 15 mass% of additives other than (B) (E). The total of (A) to (E) is 100 mass%. The term "pellets" as used herein refers to a material obtained by melting a resin, resin composition, or the like and then molding it into granules approximately 2 to 5 mm long for ease of processing. Typically, after melting, the pellets are discharged from a die as strands, cooled, and cut.

[0015] [Polycarbonate Resin Pellets (A)] The polycarbonate resin pellets (A) may be unused, so-called virgin pellets, recycled (regenerated) pellets, or pellets containing recycled material pellets. Preferred raw materials for recycled material pellets include optical disks such as CDs and DVDs, light guide plates, automobile window glass, automobile headlamp lenses, transparent vehicle components such as windshields, containers such as water bottles, eyeglass lenses, soundproof walls, glass windows, and architectural components such as corrugated sheets. Furthermore, the polycarbonate resin pellets (A) may be crushed products obtained from non-conforming products, sprues, or runners during molding, or crushed, washed, separated, and recovered to form repellets. Hereinafter, these recycled materials, regenerated materials, repellets, etc. will collectively be referred to as recycled materials.

[0016] In the method for producing polycarbonate resin composition pellets of the present invention, it is particularly preferable to use pellets made from recycled materials. As mentioned above, recycled polycarbonate resin pellets, in particular, undergo the processes of crushing, washing, separating, and pelletizing the product, and are therefore prone to moisture absorption and insufficient mixing due to water vapor. The recycled polycarbonate resin and liquid phosphorus-based flame retardant are difficult to mix, and a large amount of water vapor makes venting more likely to occur. Recycled materials often contain other resins and various additives in addition to polycarbonate resin. Any polycarbonate resin can be used as long as it accounts for more than 40% by mass of the polycarbonate resin pellets (A). Preferably, it is more than 50% by mass, particularly more than 50%, 60%, 70%, 80%, and particularly more than 90% by mass. The upper limit is 100% by mass. Recycled polycarbonate resin pellets can also be purchased from recycled material manufacturers and used. The polycarbonate resin pellets (A) preferably have a moisture absorption rate (water content) of 2000 ppm or more. This moisture absorption rate means that the moisture absorption rate is 2000 ppm or more at the time of feeding the polycarbonate resin pellets (A) to the extruder. If the moisture absorption rate is low, the polycarbonate resin pellets are easily charged, which makes it easier for sparks to fly between the polycarbonate resin pellets and the production line. When used together with other powder raw materials, the possibility of a dust explosion also increases.

[0017] The moisture absorption rate of the polycarbonate resin pellets (A) is more preferably 2300 ppm or more, and even more preferably 2500 ppm or more. Furthermore, since polycarbonate resin pellets that have absorbed a large amount of moisture are difficult to knead, the moisture absorption rate is preferably 5000 ppm or less, more preferably 4500 ppm or less, and particularly preferably 4000 ppm or less. The moisture absorption rate is a value obtained by measurement using the method described in the examples.

[0018] [Polycarbonate Resin] Examples of polycarbonate resins include aromatic polycarbonate resins, aliphatic polycarbonate resins, and aromatic-aliphatic polycarbonate resins. Preferably, the polycarbonate resin is an aromatic polycarbonate resin. Specifically, an aromatic polycarbonate polymer or copolymer obtained by reacting an aromatic dihydroxy compound with phosgene or a diester of carbonic acid is used.

[0019] Examples of aromatic dihydroxy compounds include 2,2-bis(4-hydroxyphenyl)propane (i.e., bisphenol A), 2,2-bis(3-methyl-4-hydroxyphenyl)propane (i.e., bisphenol C), tetramethylbisphenol A, α,α'-bis(4-hydroxyphenyl)-p-diisopropylbenzene, hydroquinone, resorcinol, and 4,4'-dihydroxydiphenyl.

[0020] Preferred examples of polycarbonate resins include polycarbonate resins using bisphenol A as a dihydroxy compound or using bisphenol A in combination with other aromatic dihydroxy compounds, and polycarbonate resins using bisphenol C or using bisphenol C in combination with other aromatic dihydroxy compounds (particularly bisphenol A).

[0021] The polycarbonate resin may be a homopolymer consisting of one type of repeating unit, or a copolymer having two or more types of repeating units, and the copolymer may be a random copolymer, a block copolymer, or any of a variety of copolymer forms.

[0022] The molecular weight of the polycarbonate resin is not limited, but the viscosity-average molecular weight (Mv) is typically about 10,000 to 100,000, preferably about 12,000 to 35,000. By adjusting the viscosity-average molecular weight to or above the lower limit of the above range, the mechanical strength of the polycarbonate resin composition can be further improved, making it more preferable for use in applications requiring high mechanical strength. On the other hand, by adjusting the viscosity-average molecular weight to or below the upper limit of the above range, the decrease in fluidity of the polycarbonate resin composition can be suppressed and improved, and molding processability can be improved, making it easier to mold thin walls. Two or more polycarbonate resins with different viscosity-average molecular weights may be mixed. In this case, polycarbonate resins with viscosity-average molecular weights outside the above-mentioned preferred range may be mixed, and it is preferable that the viscosity-average molecular weight of the polycarbonate resin obtained by mixing satisfies the above-mentioned range.

[0023] In the present invention, the viscosity average molecular weight (Mv) of a polycarbonate resin is a value calculated from the intrinsic viscosity ([η]) obtained by measuring the viscosity of a methylene chloride solution of the polycarbonate resin at 25°C using an Ubbelohde viscometer, and then using the following Schnell viscosity formula: [η] = 1.23 × 10 －４ Mv ０．８３

[0024] The method for producing the polycarbonate resin is not particularly limited, and polycarbonate resins produced by either the phosgene method (interfacial polymerization method) or the melt method (ester interchange method) can be used. Also preferred is a polycarbonate resin produced by the melt method and then subjected to post-treatment to adjust the amount of terminal OH groups.

[0025] [Phosphate ester-based flame retardant (B)] The phosphate ester-based flame retardant used in the present invention is a phosphate ester-based flame retardant that is liquid at room temperature. Here, "liquid at room temperature" means that it is liquid at 23° C. Examples of the phosphate ester-based flame retardant include phosphate compounds and condensed phosphate esters, with condensed phosphate esters being preferred.

[0026] As the condensed phosphate ester, a phosphate ester compound represented by the following general formula (1) which is liquid at room temperature is particularly preferred. (In the formula, R １ , R ２ , R ３ and R ４ represents an alkyl group having 1 to 6 carbon atoms or an aryl group having 6 to 20 carbon atoms which may be substituted with an alkyl group; p, q, r, and s are 0 or 1; k is an integer of 1 to 5; X １ represents an arylene group.)

[0027] The phosphate ester compound represented by the general formula (1) may be a mixture of compounds having different k values, and in the case of such a mixture of phosphate esters having different k values, k is the average value of the mixture. In the case of a mixture of compounds having different k values, the average k value is preferably in the range of 1 to 2, more preferably 1 to 1.5, even more preferably 1 to 1.2, and particularly preferably 1 to 1.15.

[0028] Also, X １ represents a divalent arylene group, for example, a divalent group derived from a dihydroxy compound such as resorcinol, hydroquinone, bisphenol A, 2,2'-dihydroxybiphenyl, 2,3'-dihydroxybiphenyl, 2,4'-dihydroxybiphenyl, 3,3'-dihydroxybiphenyl, 3,4'-dihydroxybiphenyl, 4,4'-dihydroxybiphenyl, 1,2-dihydroxynaphthalene, 1,3-dihydroxynaphthalene, 1,4-dihydroxynaphthalene, 1,5-dihydroxynaphthalene, 1,6-dihydroxynaphthalene, 1,7-dihydroxynaphthalene, 1,8-dihydroxynaphthalene, 2,3-dihydroxynaphthalene, 2,6-dihydroxynaphthalene, or 2,7-dihydroxynaphthalene. Of these, divalent groups derived from bisphenol A and 3,3'-dihydroxybiphenyl are particularly preferred.

[0029] In general formula (1), p, q, r, and s each represent 0 or 1, and preferably 1. １ , R ２ , R ３and R ４ and each represent an alkyl group having 1 to 6 carbon atoms or an aryl group having 6 to 20 carbon atoms which may be substituted with an alkyl group. Examples of such an aryl group include a phenyl group, a cresyl group, a xylyl group, an isopropylphenyl group, a butylphenyl group, a tert-butylphenyl group, a di-tert-butylphenyl group, and a p-cumylphenyl group, with a phenyl group, a cresyl group, and a xylyl group being more preferred.

[0030] Among the phosphate ester compounds represented by general formula (1), specific examples of those that are liquid at room temperature include bisphenol A bis-diphenyl phosphate, etc. Commercially available products include "ADEKA STAB FP-600" manufactured by ADEKA Corporation and "CR-741" manufactured by Daihachi Chemical Industry Co., Ltd.

[0031] [Production of Polycarbonate Resin Composition Pellets] The production method of the present invention includes a first step of placing the above-described polycarbonate resin pellets (A) and other components (C) to (E) in a twin-screw extruder, kneading them in a first kneading section, and then reducing the pressure in a first reduced-pressure vent to devolatilize the volatile components; a second step of retaining the resin in a second kneading section, adding a phosphate ester-based flame retardant (B) that is liquid at room temperature to the downstream portion thereof, and kneading the resulting mixture in a third kneading section; and a third step of reducing the pressure in a vent downstream of the third kneading section to devolatilize the remaining volatile components, and extruding the resin composition.

[0032] A twin-screw extruder is used in the production method of the present invention. Various types of twin-screw extruders can be used, and the screw rotation method may be either co-rotating or counter-rotating, but a co-intermeshing twin-screw extruder is preferred. The twin-screw extruder has three or more kneading sections and is equipped with two or more pressure-reducing vents.

[0033] Fig. 1 is a cross-sectional view showing an example of the configuration of a twin-screw extruder used in the method of the present invention, and shows an example of the cylinder configuration of the twin-screw extruder and the position of the kneading section, vent port, and liquid addition device for the phosphate ester-based flame retardant (B). Hereinafter, the production method of the present invention will be described with reference to Fig. 1.

[0034] The raw material polycarbonate resin pellets (A) and other components (C) to (E) are fed into the twin-screw extruder from a feed port 1 at the base of the extruder, and the polycarbonate resin pellets (A) are conveyed while being melt-kneaded toward a discharge port 12 on the right side in FIG. 1 by heating the extruder barrel and rotating the screw, and the strands discharged from the discharge port 12 are pelletized in a granulator to obtain pellets of a polycarbonate resin composition.

[0035] The polycarbonate resin pellets (A) and the like supplied from the supply port 1 are supplied, conveyed, and preheated in the conveying section 2. The conveying screw is preferably configured with a normal flight-like screw element. Next, the polycarbonate resin pellets (A) are melted in the first kneading section 3.

[0036] Preferred kneading discs and the like used in the kneading section include an R kneading disc, an N kneading disc, an L kneading disc, an L screw, a seal ring and the like.

[0037] The R kneading disc is also called a progressive kneading disc (hereinafter sometimes referred to as R), and usually has two or more blades with a twist angle Θ of 10 to 75 degrees. By setting the blades at a predetermined angle in this way, it is possible to feed the resin and apply a strong shear force.

[0038] The N kneading disc is also called the orthogonal kneading disc (hereinafter sometimes referred to as N), and usually has two or more blades with a blade twist angle Θ of 75 to 105 degrees. Because the blades are installed offset by approximately 90 degrees, there is almost no force to feed the resin, but the kneading force is strong.

[0039] The L kneading disc is also called a reverse feed kneading disc (hereinafter sometimes referred to as L), and usually has two or more blades with a twist angle Θ of -10 to -75 degrees. The L kneading disc is an element with the ability to block incoming resin and increase pressure by acting in the direction of sending back the resin that has been fed. By installing it downstream of the element that promotes kneading, it blocks the resin and exerts a powerful kneading effect.

[0040] The L screw, also known as a reverse feed screw, is a screw that spirals in the opposite direction to a normal feed screw, and is an element that has the ability to block resin and increase pressure in the direction that returns the fed resin. Like the L kneading disc, by installing it downstream of an element that promotes kneading, it blocks resin and exerts a powerful kneading effect.

[0041] The blades are usually elliptical, with flat portions at the two vertices of the ellipse. These blades are also called disks, and each kneading disk is usually made up of 3 to 7 disks. These disks may also be roughly triangular with three vertices, and are also called three-row kneading disks. Similarly, there are R, N, and L types. These can also be used in the same way. Among kneading disks, there are also twist kneading disks, in which the vertices are twisted in the screw axial direction, and similar kneading effects can be obtained.

[0042] The seal ring is a ring-shaped device fitted to the screw, blocking approximately 70-90% of the flow path and causing the resin flow to stagnate, thereby increasing the resin pressure. As with the L kneading disk, by installing it downstream of the element that promotes kneading, it can block the resin and exert a powerful kneading effect.

[0043] The kneading section is usually composed of the above-mentioned kneading disks and seal rings, but in other cases, a mixing screw, a rotor screw, or a reverse full-flight screw may also be used.

[0044] Mixing screws are made by cutting off the crests of screw flights, and are single-, double-, or triple-start or reverse-start screws, and are elements with strong shear dispersion forces. There are forward-start notched mixing screws and reverse-start notched mixing screws.

[0045] The rotor screw has elliptical (two-blade structure) or triangular rotor blades, and the gap (tip clearance) between the rotor and the barrel inner wall surface allows for the generation of strong shearing force. The reverse feed full-flight screw is a screw that runs in the opposite direction to the feed screw, and has a strong resin blocking force.

[0046] In the present invention, there are three or more kneading sections, and each of the first to third kneading sections is composed of a combination of the above-mentioned components. However, any configuration may be used as long as the resin is retained and pressurized. Furthermore, the kneading sections in each of the first to third kneading sections may be combined into one location or divided into two or more sections. For example, a normal feed flight-like element may be inserted between multiple kneading discs. The length of such a feed flight-like element is not included in the length described below as the preferred length of each kneading section. The screw rotation speed of the twin-screw extruder is preferably about 300 to 900 rpm.

[0047] The first kneading section 3 is a combination of two or more of the above-mentioned components, but preferably a combination of an R kneading disc, an N kneading disc, and an L kneading disc. For example, a configuration in which multiple Ns are arranged between R and L, particularly RNNL, RNNNL, etc., is preferred.

[0048] The screw configuration of the first kneading section 3 preferably has a total length of 2.0D to 8.0D (D is the cylinder inner diameter), more preferably in the range of 3.0D to 7.0D.

[0049] The first kneading section configured as described above allows the polycarbonate resin pellets (A) and the components other than (B) to be sufficiently melted.

[0050] The resin is then transported by the transport unit 4 to the second kneading unit 6. The second kneading unit 6 can use the kneading disk or other screws as described above, but it is preferable to use a seal ring. In the second kneading unit 6, in order to reduce the pressure in the first vent 5 preceding it, it is preferable to use a seal ring suitable for retaining the resin. The length of the second kneading unit is preferably 0.3D to 2.0D.

[0051] The degree of pressure reduction at the first vent 5 is preferably a gauge pressure of greater than -0.05 MPa, more preferably greater than -0.06 MPa, and even more preferably greater than -0.07 MPa, assuming atmospheric pressure to be 0 MPa.

[0052] Next, the mixture is transported by the transport section 7 to the third kneading section 9. At this time, a liquid phosphate ester-based flame retardant (B) is added by a liquid adding device 8 (such as a liquid supply pump) provided downstream of the second kneading section 6.

[0053] The amount of the phosphate ester-based flame retardant (B) that is liquid at room temperature is, as described above, 5% by mass or more but less than 25% by mass relative to 100% by mass of the resulting polycarbonate resin composition. By using such an amount, high flame retardancy and heat resistance can be achieved. If the amount is 25% by mass or more, the heat resistance decreases. The amount is preferably 7% by mass or more, more preferably 10% by mass or more, and preferably 23% by mass or less, and particularly preferably 21% by mass or less.

[0054] In the third kneading section 9, the molten polycarbonate resin pellets (A) and the like are melt-kneaded with the phosphate ester-based flame retardant (B) which is liquid at room temperature.

[0055] The third kneading section 9 is a combination of the above-mentioned components, but a combination of an R kneading disc, an N kneading disc, and an L kneading disc is preferred, and for example, a configuration in which multiple Ns are arranged between R and L, particularly RNNL, RNNNL, etc. is preferred. The screw configuration of the third kneading section is preferably configured to have a total length of 1.0D to 6.0D, more preferably in the range of 1.5D to 5.0D.

[0056] Next, the polycarbonate resin pellets (A) and the like melt-kneaded in the third kneading section 9 and the phosphate ester-based flame retardant (B) that is liquid at room temperature are further conveyed, and at this time, the pressure is reduced to devolatilize the second vent 10 provided downstream of the third kneading section 9. The degree of reduction in pressure at the second vent 10 is preferably greater than -0.05 MPa, more preferably greater than -0.06 MPa, and even more preferably greater than -0.07 MPa, when atmospheric pressure is taken as 0 MPa.

[0057] Thereafter, the polycarbonate resin composition is extruded in the form of strands from an extrusion die at a discharge port 12 at the tip of the extruder by the extrusion section 11 .

[0058] The extruded strand-like melt of the polycarbonate resin composition is then cooled by water cooling or the like and cut into pellets. There are no particular limitations on the shape of the die, and known die shapes can be used. The diameter of the die holes varies depending on the extrusion pressure and the desired pellet size, but is usually about 2 to 5 mm. The temperature of the polycarbonate resin composition immediately after extrusion is preferably about 280 to 300°C, more preferably about 280 to 290°C.

[0059]

[0013] What is important about the production method of the present invention is that polycarbonate resin pellets or the like are melted in a first kneading section (first kneading section), then the pressure is reduced in a vacuum vent (first vent) to first devolatilize and remove moisture, then a pressure-increasing section is provided in the next kneading section (second kneading section), after which a liquid phosphorus-based flame retardant is added, and then the melted and devolatilized raw materials are kneaded with the liquid phosphorus-based flame retardant in the subsequent kneading section (third kneading section), and then the pressure is reduced in a next vacuum vent (second vent) to devolatilize, and the resulting mixture is extruded through a die. This configuration allows for sufficient melt-kneading of the moisture-absorbent pellet-like polycarbonate resin and the poorly miscible liquid phosphorus-based flame retardant, and prevents vent-up, enabling efficient and productive production of a flame-retardant polycarbonate resin composition.

[0060] In the method of the present invention, in addition to the polycarbonate resin pellets (A) and the phosphate ester-based flame retardant (B) that is liquid at room temperature, it is also preferable to blend polycarbonate resin flakes (C), a styrene-based resin having acrylonitrile units (D), and an additive (E) other than (B). The blending amounts of each component are 0 to 50 mass% of the polycarbonate resin flakes (C), 0 to 30 mass% of the styrene-based resin having acrylonitrile units (D), and 0 to 15 mass% of the additive (E) other than (B), based on 100 mass% of the total of (A) to (E). These components (C) to (E) are fed into the feed port 1 at the base of the twin-screw extruder together with the polycarbonate resin pellets (A) or as separate feeds, except when side feeding is particularly preferred.

[0061] The term "flake" in polycarbonate resin flakes (C) is commonly used in the art and refers to powder or granules, including, for example, powder, powder, granules, particles, and flakes. The average particle size (D50) of polycarbonate resin flakes (C) is preferably 2 mm or less, more preferably 1.5 mm or less. It is also preferably 0.3 mm or more, more preferably 0.5 mm or more. If the size is larger or smaller than this, segregation is likely to occur when mixed with other powder or granular raw materials. The average particle size (D50) refers to the particle size corresponding to 50% of the cumulative particle size distribution percentage of the sample, and can be measured using a laser light scattering device.

[0062] The polycarbonate resin flakes (C) can be obtained, for example, by producing polycarbonate resin by an interfacial polymerization method. The specific surface area of ​​the polycarbonate resin pellets is 0.001 to 0.01 m ２ / g and has difficulty in absorbing liquids, so that when a large amount of liquid material such as a liquid phosphate ester flame retardant is kneaded, the pellets tend to swim in the liquid, making it difficult to apply shear and making it difficult for melting to proceed. On the other hand, the specific surface area of ​​the polycarbonate resin flakes (C) is usually larger than that of the polycarbonate resin pellets, and is 0.1 to 10 m ２ / g, it has the property of readily absorbing liquid phosphate ester flame retardants and water. Therefore, when kneading liquid materials, melting proceeds easily and kneading proceeds easily. Therefore, by supplying polycarbonate resin flakes (C), the occurrence of unmelted materials and aggregation of additives are suppressed, and homogeneous polycarbonate resin composition pellets are easily obtained. When polycarbonate resin flakes (C) are used, the blending amount is 0 to 50 mass%, preferably 5 to 45 mass%, and more preferably 10 to 30 mass%. The specific surface area of ​​polycarbonate resin flakes (C) is 0.2 to 5 m ２ / g. ２ If the density is less than 5m / g, the liquid may not be absorbed sufficiently, and the effect of blending the polycarbonate resin flakes (C) is small. ２ If the specific surface area is larger than 0.4 to 3 m / g, the amount of oxygen molecules adsorbed on the surface increases, which may cause oxidation during kneading and deteriorate the color tone of the resulting pellets. ２ The specific surface area is a value obtained by measurement using the BET method in accordance with ISO 9277:202201.

[0063] The styrenic resin (D) having acrylonitrile units is a styrenic copolymer having acrylonitrile units as copolymerization units, and preferred examples include acrylonitrile-butadiene-styrene copolymer (ABS resin), acrylonitrile-styrene copolymer (AS resin), and acrylate-styrene-acrylonitrile copolymer (ASA resin). Because acrylonitrile has strong polarity and a high affinity for water, styrenic copolymers having acrylonitrile units have a high moisture absorption rate, and in some cases, they are prone to absorbing moisture twice as easily as polycarbonate resin. Therefore, when placed in an extruder, the amount of water vapor generated within the extruder further increases, causing weakening of the kneading, and further, the large amount of water vapor may make venting more likely. It is preferable to feed the styrenic resin (D) having acrylonitrile units in pellet form from the feed port 1 at the base of the twin-screw extruder together with the polycarbonate resin pellets (A). When the styrene-based resin (D) having acrylonitrile units is used, the blending amount is 0 to 30% by mass, preferably 5 to 25% by mass.

[0064] Preferred examples of the additive (E) other than the phosphate ester-based flame retardant (B) that is liquid at room temperature include flame retardant aids such as fluororesins (e.g., polytetrafluoroethylene (PTFE)), various elastomers (impact modifiers), release agents, stabilizers, fillers, reinforcing agents, other resin components, other flame retardants, colorants (dyes and pigments), ultraviolet absorbers, antistatic agents, antifogging agents, antiblocking agents, flow improvers, plasticizers, dispersants, and antibacterial agents. These may be used alone or in combination. When the additive (E) other than (B) is used, the total amount is 0 to 15% by mass, preferably 13% by mass or less, more preferably 12% by mass or less, 11% by mass or less, and particularly preferably 10% by mass or less.

[0065] Among these, PTFE is particularly preferred for its enhanced flame retardancy. The blending amount of PTFE is preferably 0.05 to 2% by mass, more preferably 0.1 to 1.5% by mass, and even more preferably 0.15 to 1% by mass. PTFE is available in emulsion-polymerized PTFE produced by emulsion polymerization and suspension-polymerized PTFE produced by suspension polymerization. Emulsion-polymerized PTFE is preferred due to its smaller particle size. PTFE is used as a flame retardant aid due to its drip resistance, which prevents dripping during combustion of molded articles made from polycarbonate resin compositions. However, emulsion-polymerized PTFE is preferred for achieving good drip resistance. Emulsion-polymerized PTFE includes fine powder PTFE and dispersion PTFE. Fine powder PTFE is obtained by emulsion polymerization of tetrafluoroethylene, followed by coagulation and drying. Fine powder PTFE exists as secondary particles formed by the coagulation of numerous primary particles, generally present as large particles of 100 μm or larger. An example of fine powder PTFE is "FA500H" manufactured by Daikin Industries, Ltd., and the average particle size (secondary particles) is about 500 μm.

[0066] Dispersion PTFE is obtained by emulsion polymerization of tetrafluoroethylene and concentrating the resulting solution. It is a milky white liquid in which fine particles of PTFE are dispersed in water. The dispersion PTFE thus obtained exists stably in the liquid as primary particles of PTFE (often in molecular form). The average particle size is 0.05 to 1 μm. The PTFE concentration of the dispersion PTFE is preferably 20 to 80% by mass. An example of dispersion PTFE is "D-210C" manufactured by Daikin Industries, Ltd., which has an average particle size of approximately 0.25 μm, with 60% by mass of the dispersion being PTFE primary particles and 40% by mass being water and surfactants.

[0067] PTFE fine powder has a tendency to form agglomerates during kneading, and these agglomerates can be large and exceed 1 mm.When the extruder for producing pellets of polycarbonate resin composition does not contain a reinforcing agent such as glass fiber, a breaker plate 25 (a perforated plate with many holes of several millimeters) as shown in Figure 2 is installed at the end of the cylinder, and a plurality of mesh screens (filtering wire mesh) are installed there for the purpose of filtering out foreign matter.However, the PTFE agglomerates are captured by the mesh screen, and the mesh screen gradually becomes clogged, resulting in the resin stagnation at the tip of the screw, and the resin pressure in that area increases, which may damage the mesh screen or the reducer of the extruder.Therefore, a resin pressure gauge is usually installed between the tip of the screw and the breaker plate, and when the resin pressure reaches about 10 MPa, the extruder is electrically controlled to automatically stop. When kneading a composition containing a large amount of polycarbonate resin pellets as in the present invention, the pellets are subjected to very large shear and compression forces in the first kneading section of the extruder, which in turn applies very large shear and compression forces to the PTFE fine powder nearby, easily agglomerating and forming large aggregates. As a result, the mesh screen is easily clogged, and the resin pressure easily increases in a short period of time. When the resin pressure approaches 10 MPa, the extruder must be stopped and the mesh screen replaced, significantly reducing productivity. On the other hand, dispersion PTFE is a primary particle, is extremely small, and is less likely to form aggregates. Therefore, even when a large amount of polycarbonate resin pellets is used as in the present invention, the mesh screen is less likely to clog and the resin pressure is less likely to increase. Therefore, when blending PTFE, it is preferable to use dispersion PTFE. When using this dispersion PTFE, it is preferable to use the following method 1 or method 2 as the method of addition to the supply port 1.

[0068] (Method 1) In this method, dispersion PTFE and polycarbonate resin flakes (preferably produced by interfacial polymerization) are premixed in a ratio of 1:3 to 1:30 (by mass), moisture is absorbed into the polycarbonate resin flakes, and the resulting mixture is introduced into the supply port 1, or the mixture is further mixed with other raw materials and then introduced into the supply port 1. If the polycarbonate resin flakes are in a ratio of less than 1:3, the content of dispersion PTFE increases, making the PTFE more likely to aggregate in the first kneading section. If the amount of polycarbonate resin flakes is greater than 1:30, uneven distribution of PTFE is likely to occur during mixing, making it more likely to aggregate in the first kneading section. When dispersion PTFE is used, the content of polycarbonate resin flakes (C) in the composition is preferably 5 to 45 mass%, more preferably 10 to 30 mass%. The content of the polycarbonate resin pellets (A) is preferably in the range of 45 to 75% by mass.

[0069] (Method 2) This method involves directly feeding the PTFE dispersion into the supply port 1. When feeding into the supply port 1, it is preferable to use a tube pump as the liquid pump. Although plunger pumps, gear pumps, and diaphragm pumps are also available, pumps other than tube pumps may generate local shear during the liquid transfer, which may cause the PTFE dispersion to be subjected to shear, leading to the PTFE aggregation and enlargement, which may clog the pump and prevent the liquid from being transferred for an extended period of time. In this way, even when feeding the PTFE dispersion directly into the supply port 1, it is possible to suppress PTFE aggregation during kneading, prevent mesh clogging, and enable long-term continuous production.

[0070] The polycarbonate resin composition pellets obtained by the production method of the present invention preferably consist of 30 to 80 mass% of polycarbonate resin derived from polycarbonate resin pellets (A), 5 mass% or more but less than 25 mass% of a phosphate ester-based flame retardant (B) that is liquid at room temperature, 0 to 50 mass% of polycarbonate resin derived from polycarbonate resin flakes (C), 0 to 30 mass% of a styrene-based resin (D) having an acrylonitrile unit, and 0 to 15 mass% of an additive (E) other than (B) [provided that the total of (A) to (E) is 100 mass%].

[0071] The method for producing a molded article from the obtained polycarbonate resin composition pellets is not particularly limited, and molding methods generally employed for polycarbonate resins, such as general injection molding, ultra-high speed injection molding, injection compression molding, multi-color injection molding, gas-assisted injection molding, molding using an insulated mold, molding using a rapid heating and cooling mold, foam molding (including supercritical fluid), insert molding, IMC (in-mold coating molding), extrusion molding, sheet molding, thermoforming, rotational molding, laminate molding, and press molding, can be used.

[0072] The obtained molded article can be suitably used as parts for office equipment such as printers and copiers, electrical equipment, electronic equipment, vehicles such as automobiles, office equipment such as printers and copiers, houses, buildings, and other applications, and can be particularly suitably used as housings for office equipment such as printers and copiers, computers, personal computers, various mobile terminals, batteries, and the like.

[0073] The present invention will be explained in more detail below by showing examples, but the present invention should not be construed as being limited to the following examples.

[0074] In the examples and comparative examples, a co-rotating twin-screw extruder ("TEX44αIII" manufactured by The Japan Steel Works, Ltd.) was used. The screw configuration of the extruder (Figure 1) is as follows. The cylinder inner diameter D (diameter) of the TEX44αIII is 47 mm. Screw configuration of the first kneading section: RNNL. Each kneading disc consists of five discs. The length of each kneading disc is 0.936D, and the length of the first kneading section is 3.744D. Second kneading section: A seal ring with a diameter of 42 mm and a length of 0.5D is used. The length of the second kneading section is 0.5D. Screw configuration of the third kneading section: RNNL. Each kneading disc consists of five discs. The length of each kneading disc is 0.468D, and the length of the third kneading section is 1.872D.

[0075] The raw materials used in the examples and comparative examples are as follows: <Polycarbonate resin pellets (A)> Polycarbonate resin recycled pellets (A1): "PC2010ANC" manufactured by SHANGHAI AUSELL MATERIAL CO., LTD. MFR = 14 g / 10 min (300°C, 1.2 kg load) Length: 3 mm, diameter: 2.5 to 3 mm Specific surface area: 0.003 m, measured by the BET method in accordance with ISO 9277:202201 (adsorbate: nitrogen, volumetric method) ２ / g. <Phosphate ester-based flame retardant (B) liquid at room temperature> Bisphenol A bis-diphenyl phosphate (B1): "ADEKA STAB FP-600" manufactured by ADEKA Corporation <Polycarbonate resin flakes (C)> Polycarbonate resin flakes (C1): "S3000F" manufactured by Mitsubishi Engineering-Plastics Corporation, interfacially polymerized product, viscosity average molecular weight = 22,000. Measured by the BET method in accordance with ISO 9277:202201 (adsorbate: nitrogen, volumetric method), the specific surface area was 1.2 m ２ / g. Measurement was performed by a wet laser light scattering method using Malvern's "MS-3000" in the range of 0.01 μm to 3 mm, and the average particle diameter D50 was found to be 0.92 mm. <Styrene-based resin (D) having acrylonitrile units> ABS resin pellets (D1): Nippon A&L Co., Ltd., "SXH-330" <Additives (E) other than (B)> Fine powder PTFE (E1): Daikin Industries, Ltd., "FA500H" Dispersion PTFE (E2): Daikin Industries, Ltd., "D-210C"

[0076] The moisture absorption rate of the polycarbonate resin recycled pellets (A) used in the examples and comparative examples was measured by the following method immediately before feeding them into the extruder. A Mitsubishi Chemical Analytech Karl Fischer moisture meter "CA100 / VA100" was used, with a heating temperature of 280°C, a titration start delay time of 1 minute, a titration duration of 3 minutes, a titration forced termination time of 30 minutes, and an end-point detection level of 0.1 μg. The pellet weight was 1 g. As a result, it was found that 2800 ppm of moisture was absorbed. The moisture absorption rate of polycarbonate resin flakes (C) was also measured under similar conditions. As a result, it was found that 900 ppm of moisture was absorbed. This indicates that polycarbonate resin is about three times more likely to absorb moisture than resin flakes after pelletization. The moisture absorption rate of ABS resin pellets (D1) was also measured under similar conditions. As a result, it was found that 3700 ppm of moisture was absorbed.

[0077] Examples 1 to 4, Comparative Examples 1 to 4 Example 1 Polycarbonate resin recycled pellets (A1) 225 kg / h (75 mass%), polycarbonate resin flakes (C1) 28.5 kg / h (9.5 mass%), and fine powder PTFE (E1) 1.5 kg / h (0.5 mass%) were supplied to TEX44αIII from a supply port 1, kneaded in a first kneading section 3, reduced pressure at a first vent 5 for devolatilization, the molten resin was retained in a second kneading section 6, a phosphate ester-based flame retardant (B1) that was liquid at room temperature was added from a liquid addition device (liquid supply pump) 8 at a rate of 45 kg / h (15 mass%), kneaded in a third kneading section 9, reduced pressure at a second vent 10 for devolatilization, extruded through a die to form strands, cooled in a water tank, and cut with a pelletizer to obtain polycarbonate resin composition pellets. The screw rotation speed was 500 rpm, and the cylinder temperature was set to 260° C. The degree of reduced pressure at both the first and second vents was −0.09 MPa. Extrusion was carried out for 10 minutes under these conditions from the start of extrusion, and the extrusion proceeded smoothly without any vent-up or strand breakage.

[0078] Example 2 Extrusion was carried out in the same manner as in Example 1, except that polycarbonate resin recycled pellets (A1) were fed at 165 kg / h (55% by mass), polycarbonate resin flakes (C1) at 28.5 kg / h (9.5% by mass), ABS resin pellets (D1) at 60 kg / h (20% by mass), and fine powder PTFE (E1) at 1.5 kg / h (0.5% by mass) were fed from feed port 1. Extrusion was carried out for 10 minutes under these conditions from the start of extrusion, and extrusion proceeded smoothly, with no vent-up or strand breakage whatsoever.

[0079] Example 3 Extrusion was carried out in the same manner as in Example 1, except that polycarbonate resin recycled pellets (A1) were fed at 150 kg / h (50 mass%), polycarbonate resin flakes (C1) were fed at 90 kg / h (30 mass%) from feed port 1, and a phosphate ester-based flame retardant (B1) that was liquid at room temperature was added at an amount of 60 kg / h (20 mass%) from liquid addition device (liquid supply pump) 8. Extrusion was carried out for 10 minutes from the start of extrusion under these conditions, and extrusion proceeded smoothly, with no venting or strand breakage whatsoever.

[0080] Example 4 Extrusion was carried out in the same manner as in Example 1, except that polycarbonate resin recycled pellets (A1) were fed at 162.5 kg / h (65% by mass), no polycarbonate resin flakes (C1) were used, and ABS resin pellets (D1) were fed at 50 kg / h (20% by mass) from the feed port 1 and kneaded in the first kneading section 3, and a phosphate ester-based flame retardant (B1) in a liquid state at room temperature was fed at 37.5 kg / h (15% by mass) from the liquid feed pump 8. Extrusion was carried out under these conditions for 10 minutes from the start of extrusion, and the extrusion proceeded smoothly, with no venting or strand breakage whatsoever.

[0081] Comparative Example 1 Extrusion was performed in the same manner as in Example 1, except that the first vent was not depressurized and the vent port was opened to the atmosphere. Resin gradually began to rise from the second vent, and after a few minutes, the resin entered the depressurization piping and solidified, making it impossible to depressurize, resulting in the so-called vent-up phenomenon. The vent-up material appeared to be a mixture of resin and liquid particles that did not completely dissolve. Furthermore, strand breakage occurred multiple times. This was thought to be due to insufficient mixing of the molten resin and the phosphate ester-based flame retardant, which was liquid at room temperature. It was determined that extrusion was impossible, and extrusion was stopped 10 minutes after the start of extrusion.

[0082] Comparative Example 2 Extrusion was performed in the same manner as in Example 2, except that the first vent was not depressurized and the vent port was opened to the atmosphere. Resin gradually rose from the second vent, and after a few minutes, the resin entered the depressurization piping, solidified, and it became impossible to depressurize, resulting in vent-up. The vented-up material appeared to be a mixture of resin and liquid particles that did not completely dissolve. Furthermore, strand breakage occurred multiple times. This was thought to be due to insufficient mixing of the molten resin and the phosphate ester-based flame retardant, which was liquid at room temperature. It was determined that extrusion was impossible, and extrusion was stopped 10 minutes after the start of extrusion.

[0083] Comparative Example 3: Extrusion was performed in the same manner as in Example 3, except that the first vacuum vent was not depressurized and the vent port was opened to the atmosphere. Resin gradually rose from the second vent, and after a few minutes, the resin entered the vacuum piping, solidified, and it became impossible to depressurize, resulting in vent-up. The vent-up material appeared to be a mixture of resin and liquid particles that did not completely dissolve. Furthermore, strand breakage occurred multiple times. This was thought to be due to insufficient mixing of the molten resin and the phosphate ester-based flame retardant, which was liquid at room temperature. It was determined that extrusion was impossible, and extrusion was stopped 10 minutes after the start of extrusion.

[0084] Comparative Example 4 Extrusion was performed in the same manner as in Example 4, except that the first vacuum vent was not depressurized and the vent port was opened to the atmosphere. Resin gradually rose from the second vent, and after a few minutes, the resin entered the vacuum piping, solidified, and it became impossible to depressurize, resulting in vent-up. The vent-up material appeared to be a mixture of resin and liquid particles that did not completely dissolve. Furthermore, strand breakage occurred multiple times. This was thought to be due to insufficient mixing of the molten resin and the phosphate ester-based flame retardant, which was liquid at room temperature. It was determined that extrusion was impossible, and extrusion was stopped 10 minutes after the start of extrusion.

[0085] The following can be inferred from the above examples and comparative examples. Polycarbonate resin pellets enter the extruder and are heated in the conveying section 2 before the first kneading section 3. They then enter the first kneading section 3 and are melt-kneaded with strong kneading. The moisture in the polycarbonate resin pellets is released as water vapor after melt-kneading in the first kneading section 3. The moisture in the pellets evaporates, and their volume expands approximately 2000 times due to thermal expansion. The 2800 ppm (=0.28%) moisture in the pellets evaporates, expanding to a volume five to six times the pellet's volume, with most of this remaining as bubbles in the molten resin. The pellets then pass through the seal ring of the second kneading section 6, where they are mixed with a phosphate ester-based flame retardant that is liquid at room temperature and kneaded in the third kneading section 9. However, because many water vapor bubbles remain, the mixing in the third kneading section 9 weakens, resulting in insufficient mixing of the molten resin with the phosphate ester-based flame retardant that is liquid at room temperature. This results in a viscosity distribution, forming low-viscosity and high-viscosity regions, which makes venting more likely to occur. Furthermore, a large amount of water vapor volatilizes at the second vent 10, and the high-speed water vapor flow promotes venting. This viscosity distribution also makes strands more likely to break. On the other hand, if water is removed at the first vent 5 as in the example, the number of water vapor bubbles in the third kneading section 6 is drastically reduced, promoting mixing and kneading. Furthermore, the amount of water vapor volatilized at the second vent 10 is reduced, eliminating venting and allowing strands to be drawn stably.

[0086] Examples 5 and 6 Next, a breaker and a mesh screen were attached to the extruder, and extrusion was carried out using the dispersion PTFE (E2).

[0087] As shown in Figure 2, a twin-screw extruder has a die holder 24 attached to the tip 22 of a cylinder housing two screws 21, 21' via a flange 23. A breaker plate (or ring plate) 25 is located between the flange 23 and the die holder 24, and a mesh screen can be installed inside the breaker plate 25 to filter out foreign matter. If a mesh screen is not used, a ring-shaped plate is usually installed. The die holder 24 is also called the die plate, and the flange 23 is also called the hinge plate. A die 26 having a die hole 27 is incorporated into the die holder 24. A resin pressure gauge is attached at position 28.

[0088] Example 5: As shown in FIG. 2, a breaker plate 25 was attached to a co-rotating twin-screw extruder TEX44αIII. A 30-mesh screen, a 60-mesh screen, and a 30-mesh screen were stacked on top of each other and attached to the breaker plate 25 from downstream in the extrusion direction. Long-term extrusion was then carried out using the same raw materials, feed rates, and operating conditions as in Example 1. Dispersion PTFE (E2) was used as the PTFE at 2.5 kg / h (1.5 kg / h as PTFE). The resin pressure was 2.8 MPa at the start of extrusion, 3.5 MPa after 3 hours, and 5.8 MPa after 10 hours. It was found that the use of dispersion PTFE resulted in an extremely gradual increase in resin pressure, enabling long-term continuous operation. After 10 hours, the extruder was stopped, the mesh screen was removed, and the removed mesh screen was immersed in methylene chloride for one day to dissolve the polycarbonate resin. When the mesh screen was examined under an electron microscope, it was found that about half of the mesh holes were blocked by PTFE. Thus, when dispersion PTFE was used, continuous production for more than 10 hours was possible. Furthermore, there was no venting or strand breakage during these 10 hours.

[0089] Example 6: As shown in FIG. 2, a breaker plate 25 was attached to the TEX44αIII, and a 30-mesh screen, a 60-mesh screen, and a 30-mesh screen were stacked on top of each other and attached to the breaker plate 25 from downstream in the extrusion direction. Extrusion was then carried out using the same raw materials, feed rates, and operating conditions as in Example 2. Extrusion was carried out in the same manner as in Example 2, except that dispersion PTFE (E2) was used at 2.5 kg / h (1.5 kg / h as PTFE) as the PTFE. The resin pressure was 2.5 MPa at the start of extrusion, 3.8 MPa after 3 hours, and 7.9 MPa after 10 hours. It was found that the use of dispersion PTFE resulted in an extremely gradual increase in resin pressure, enabling long-term continuous operation. After 10 hours, the extruder was stopped, and the removed mesh screen was immersed in methylene chloride for one day to dissolve the polycarbonate resin. When the mesh screen was examined under an electron microscope, it was found that approximately 70% of the mesh holes were blocked by PTFE. Thus, when dispersion PTFE was used, continuous production for more than 10 hours was possible. Furthermore, there was absolutely no venting or strand breakage during these 10 hours.

[0090] According to the method of the present invention, a flame-retardant polycarbonate resin composition containing a pellet-like polycarbonate resin that easily absorbs moisture and a phosphate ester-based flame retardant that is liquid at room temperature is uniformly melt-kneaded in an extruder, and no vent-up occurs and strands can be stably drawn. This makes it possible to stably produce polycarbonate resin composition pellets, and the method has excellent industrial applicability.

[0091] 1: Supply port 2, 4, 7: Conveying section 3: First kneading section 5: First vent 6: Second kneading section 8: Liquid adding device 9: Third kneading section 10: Second vent 11: Extrusion section 12: Discharge port 21, 21': Screw 22: Tip of cylinder of extruder 23: Flange 24: Die holder 25: Breaker plate 26: Die 27: Die hole 28: Resin pressure gauge installation position

Claims

1. A method for producing polycarbonate resin composition pellets from 30-80% by mass of polycarbonate resin pellets (A), 5% by mass or more and less than 25% by mass of a phosphoric acid ester-based flame retardant (B) that is liquid at room temperature, 0-50% by mass of polycarbonate resin flakes (C), 0-30% by mass of a styrene-based resin having an acrylonitrile unit (D), and 0-15% by mass of other additives (E) other than (B) [however, the total of (A) to (E) is 100% by mass], using a twin-screw extruder, the method comprising the steps of: a twin-screw extruder having a first screw, said twin-screw extruder including ...

2. The method according to claim 1, wherein the moisture absorption rate of the polycarbonate resin pellets (A) is 2000 ppm or more.

3. The method according to claim 1 or 2, wherein the polycarbonate resin pellets (A) are recycled materials.

4. The process according to claim 1 or 2, wherein the other additive (E) comprises a dispersion of polytetrafluoroethylene.

5. Pellets produced by the method according to claim 1 or 2.

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