Pellets manufacturing method

Abstract

To provide a manufacturing method of pellets of a resin composition containing a polycarbonate resin and titanium oxide particles, the method being capable of maintaining a high Charpy impact strength of the pellets when the pellets are made into resin molded products.SOLUTION: There is provided a manufacturing method of pellets of a resin composition containing 5.0 to 20.0 pts.mass of particles mainly composed of titanium oxide, based on 100 pts.mass of a polycarbonate resin by using a twin-screw extruder. A total length L of a kneading section in the twin-screw extruder is 3.0 D to 15.0 D when an average diameter of a screw in the kneading section is set as D, and a specific shear energy during melt-kneading is 0.145 kW or less per 1 kg of an extrusion amount of the resin composition per one hour.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for producing pellets. [Background technology]

[0002] BACKGROUND ART Titanium oxide has conventionally been blended into polycarbonate resin for the purpose of improving the shielding properties and coloring of resin molded products (Patent Document 1, Patent Document 2). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2019 / 172243 [Patent Document 2] Japanese Patent Application Publication No. 2019-123809 Summary of the Invention [Problem to be solved by the invention]

[0004] In order to improve the light-shielding properties of a resin molded article molded from a resin composition containing a polycarbonate resin, a large amount of titanium oxide particles may be blended into the resin composition. However, when a resin composition is blended with a large amount of titanium oxide, the impact strength of the resin molded article obtained from the resin composition tends to be poor. The present invention aims to solve the above problems and to provide a method for producing pellets of a resin composition containing a polycarbonate resin and titanium oxide particles, which pellets can maintain high impact strength when formed into a resin molded product. [Means for solving the problem]

[0005] In light of the above-mentioned problems, the present inventors have conducted research and found that the above-mentioned problems can be solved by setting the specific shear energy during melt-kneading in the production of pellets of the resin composition to 0.145 kW or less per hourly extrusion rate of 1 kg of the resin composition. Specifically, the above problems were solved by the following means. <1> A method for producing pellets of a resin composition containing 5.0 to 20.0 parts by mass of particles whose main component is titanium oxide per 100 parts by mass of polycarbonate resin using a twin-screw extruder, wherein the total length L of the kneading section of the twin-screw extruder is 3.0D to 15.0D, where D is the average diameter of the screws of the kneading section, and the specific shear energy during melt kneading is 0.145 kW or less per hourly extrusion rate of 1 kg of the resin composition. <2> The particles containing titanium oxide as a main component contain 90.0 to 98.0 mass% of TiO2, 0.5 to 3.5 mass% of Al2O3, and 0 to 6.0 mass% of SiO2. <1> The manufacturing method described in <3> When the pellets are molded into a thickness of 1 mm, the total light transmittance is 0.04% or less. <1> or <2> The manufacturing method described in <4> When the pellets are molded to a thickness of 1 mm, the total light transmittance is less than 0.02%. <1> or <2> The manufacturing method described in <5> The pellets were molded into a 3.0 mm thick ISO multipurpose test piece, and the notched Charpy impact strength measured according to ISO179-1 was 30 kJ / m 2 That's all. <1> ~ <4> 1. The manufacturing method according to any one of the preceding claims. <6> The total length L of the kneading section in the twin-screw extruder is 3.0D to 5.5D. <1> ~ <5> 1. The manufacturing method according to any one of the preceding claims. <7> The specific shear energy during the melt-kneading is 0.090 kW or more per 1 kg of extrusion rate of the resin composition per hour. <1> ~ <6> 1. The manufacturing method according to any one of the preceding claims. <8> The content of the particles containing titanium oxide as a main component is 8.0 to 20.0 parts by mass per 100 parts by mass of the polycarbonate resin. <1> ~ <7> 1. The manufacturing method according to any one of the preceding claims. [Effects of the Invention]

[0006] The present invention makes it possible to provide a method for producing pellets of a resin composition containing a polycarbonate resin and titanium oxide particles, which pellets can maintain high Charpy impact strength when formed into a resin molded article. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a schematic view showing an example of a screw used in the production method of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0008] Hereinafter, an embodiment for carrying out the present invention (hereinafter simply referred to as "the present embodiment") will be described in detail. Note that the present embodiment is an example for explaining the present invention, and the present invention is not limited to only this embodiment. In this specification, the symbol "to" is used to mean that the numerical values ​​before and after it are included as the lower limit and upper limit. In this specification, various physical properties and characteristic values ​​are those at 23°C unless otherwise specified. In this specification, the term "process" includes not only an independent process but also a process that cannot be clearly distinguished from other processes as long as the intended effect of the process is achieved. If the standards shown in this specification differ depending on the year and the measurement method, etc., they will be based on the standards as of January 1, 2021, unless otherwise stated.

[0009] In this specification, "particles containing titanium oxide as a main component" may be referred to as "titanium oxide particles."

[0010] The pellet manufacturing method of this embodiment is a method for manufacturing pellets of a resin composition containing 5.0 to 20.0 parts by mass of particles primarily composed of titanium oxide per 100 parts by mass of polycarbonate resin using a twin-screw extruder, characterized in that the total length L of the kneading section of the twin-screw extruder is 3.0D to 15.0D, where D is the average diameter of the screws of the kneading section, and the specific shear energy during melt kneading is 0.145 kW or less per hourly extrusion rate of 1 kg of the resin composition. By using this method, it is possible to obtain pellets of a resin composition containing a polycarbonate resin and titanium oxide particles, which can maintain high Charpy impact strength when formed into a resin molded article. In particular, even if the amount of titanium oxide particles is large, the decrease in Charpy impact strength of the resulting resin molded article can be effectively suppressed.

[0011] The reason why the resin molded article molded from the pellets obtained by the manufacturing method of this embodiment can maintain a high Charpy impact strength is believed to be as follows. In the production of pellets of a resin composition containing polycarbonate resin and titanium oxide, the components are commonly fed into an extruder, melt-kneaded, and pelletized. However, it has been found that using a high-mixing screw during melt-kneading results in poor impact resistance of the resin molded product formed from the resulting pellets. Further investigation by the present inventors has led to the conclusion that excessive shearing is the problem. Specifically, excessive shearing of titanium oxide particles in a secondary particle state is believed to result in their being pulverized into primary particles, making the active surfaces of the titanium oxide particles more likely to be exposed. These exposed titanium oxide particles then re-aggregate during the molding process from the pellets into a resin molded product, forming aggregates larger than the original titanium oxide particles, thereby reducing the impact resistance of the resulting resin molded product. It has been speculated that the aggregates, in particular, are likely to be the starting point for cracks and other defects in the resin molded product.

[0012] In this embodiment, the specific shear energy during melt-kneading of the polycarbonate resin and titanium oxide particles was adjusted to avoid excessive shear. As a result, it was presumed that reagglomeration of the titanium oxide particles could be effectively suppressed, and the impact strength of the resin molded product could be maintained at a high level. In particular, even when the blending ratio of titanium oxide particles relative to the polycarbonate resin was high, a decrease in the impact strength of the resulting resin molded product could be effectively suppressed. In particular, it was presumed that reagglomeration of titanium oxide particles is more likely to occur in large extruders, but this embodiment is advantageous in that it can effectively solve the above problem even when using a large extruder.

[0013] In this embodiment, a resin composition containing 5.0 to 20.0 parts by mass of particles mainly composed of titanium oxide per 100 parts by mass of polycarbonate resin is pelletized. Such a resin composition can improve the shielding properties of the resulting resin molded product. The resin composition used in this embodiment may contain other components within the scope of the present invention.

[0014] The polycarbonate resin is an optionally branched homopolymer or copolymer obtained by reacting a dihydroxy compound or a dihydroxy compound together with a small amount of a polyhydroxy compound with phosgene or a carbonic acid diester.

[0015] The dihydroxy compound used as the raw material is preferably an aromatic dihydroxy compound, more preferably 2,2-bis(4-hydroxyphenyl)propane (=bisphenol A), tetramethylbisphenol A, bis(4-hydroxyphenyl)-p-diisopropylbenzene, hydroquinone, resorcinol, 4,4-dihydroxydiphenyl, etc., and even more preferably bisphenol A. Furthermore, compounds in which one or more tetraalkylphosphonium sulfonates are bonded to the above aromatic dihydroxy compounds can also be used.

[0016] Among the polycarbonate resins mentioned above, aromatic polycarbonate resins derived from 2,2-bis(4-hydroxyphenyl)propane or aromatic polycarbonate copolymers derived from 2,2-bis(4-hydroxyphenyl)propane and other aromatic dihydroxy compounds are preferred. Also, copolymers mainly composed of aromatic polycarbonate resins, such as copolymers with polymers or oligomers having a siloxane structure, may be used. Furthermore, two or more of the above-mentioned polycarbonate resins may be mixed and used.

[0017] To adjust the molecular weight of the polycarbonate resin, a monovalent aromatic hydroxy compound may be used, such as m- and p-methylphenol, m- and p-propylphenol, p-tert-butylphenol, and p-long-chain alkyl-substituted phenol.

[0018] The viscosity average molecular weight (Mv) of the polycarbonate resin is preferably 5,000 or more, more preferably 10,000 or more, and even more preferably 13,000 or more. By using a polycarbonate resin having a viscosity average molecular weight of 5,000 or more, the mechanical strength of the resulting resin composition tends to be further improved. Furthermore, the viscosity average molecular weight (Mv) of the polycarbonate resin is preferably 60,000 or less, more preferably 40,000 or less, and even more preferably 30,000 or less. By using a polycarbonate resin having a viscosity average molecular weight of 60,000 or less, the flowability of the resin composition tends to be improved, and moldability tends to be improved. When two or more types of polycarbonate resins are contained, it is preferable that the mixture satisfies the above range (hereinafter, the same applies to molecular weight).

[0019] In this embodiment, the viscosity average molecular weight (Mv) of the 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 20°C using an Ubbelohde viscometer, and then using the following Schnell viscosity formula: [η]=1.23×10 -4 Mv0.83

[0020] 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.

[0021] The proportion of polycarbonate resin in the resin composition used in this embodiment is preferably 83% by mass or more, more preferably 85% by mass or more, and even more preferably 87% by mass or more. By making the proportion equal to or greater than the lower limit, the light-blocking properties of the resulting resin molded article tend to be further improved. Furthermore, the proportion of polycarbonate resin in the resin composition used in this embodiment is preferably 95% by mass or less, more preferably 93% by mass or less. By making the proportion equal to or less than the upper limit, the impact resistance of the resulting resin molded article tends to be further improved. The resin composition used in the present embodiment may contain only one type of polycarbonate resin, or may contain two or more types. When two or more types are contained, the total amount is preferably in the above range.

[0022] The resin composition used in this embodiment contains particles containing titanium oxide as a main component (titanium oxide particles). By including titanium oxide particles, the light-blocking properties of the resulting resin molded article can be achieved. "Titanium oxide is the main component" means that titanium oxide is the most abundant component of the titanium oxide particles, and the proportion of titanium oxide in the titanium oxide particles is usually 85.0% by mass or more, and preferably 90.0% by mass or more. The titanium oxide particles preferably contain 90.0 to 98.0 mass% of TiO2, 0.5 to 3.5 mass% of Al2O3, and 0 to 6.0 mass% of SiO2. They may further contain 0 to 0.1 mass% of SO3, 0 to 0.15 mass% of Na2O, and 0 to 0.01 mass% of Cl. They may also contain other components, the total of which is 100 mass%.

[0023] In this embodiment, the titanium oxide particles are preferably rutile-type titanium oxide particles. The use of rutile-type titanium oxide can suppress decomposition of polycarbonate resin. Furthermore, the titanium oxide particles are preferably surface-treated with a surface treatment agent. That is, it is preferable that the surface of the titanium oxide particles has a layer (particularly an organic layer) formed from the surface treatment agent. This configuration makes it easier for the titanium oxide to disperse in the polycarbonate resin, resulting in a resin sheet with better appearance. Examples of the surface treatment agent include polymers, and siloxane compounds are preferred, with hydrogen methyl siloxane and dimethyl siloxane being particularly preferred. The surface treatment agent may be physically adsorbed or chemically bonded to the titanium oxide surface.

[0024] The average secondary particle diameter of the titanium oxide particles in the pellet state is preferably 50 nm or more and 2000 nm or less. By setting the average primary particle diameter of the titanium oxide in this range, the shielding performance tends to be further improved.

[0025] In this embodiment, the resin composition contains 5.0 to 20.0 parts by mass of titanium oxide particles per 100 parts by mass of polycarbonate resin. By setting the content at or above the lower limit, shielding properties tend to be improved. On the other hand, by setting the content at or below the upper limit, deterioration of impact resistance can be more effectively suppressed. In this embodiment, the content of titanium oxide particles is preferably 6.0 parts by mass or more, more preferably 8.0 parts by mass or more, and even more preferably 9.0 parts by mass or more, relative to 100 parts by mass of polycarbonate resin. In this embodiment, the content of titanium oxide particles is preferably 18.0 parts by mass or less, more preferably 16.0 parts by mass or less, even more preferably 14.0 parts by mass or less, and even more preferably 12.0 parts by mass or less, relative to 100 parts by mass of polycarbonate resin. The resin composition used in this embodiment may contain only one type of titanium oxide particles, or may contain two or more types. When two or more types are contained, the total amount is preferably in the above range.

[0026] The resin composition used in this embodiment may further contain other components in addition to those described above. Examples of other components include a release agent, a colorant other than titanium oxide, a stabilizer, a flame retardant, a flame retardant aid, an ultraviolet absorber, a fluorescent brightener, an antifogging agent, a flow improver, a plasticizer, a dispersant, an antibacterial agent, an antiviral agent, etc. The resin composition used in this embodiment may particularly contain at least one of a release agent, a colorant other than titanium oxide, and a stabilizer. When contained, the content of the above other components is, for example, 0.001 mass% or more and, for example, 5.0 mass% or less, preferably 3.0 mass% or less, and more preferably 1.0 mass% or less, based on the mass of the resin composition.

[0027] The release agent that may be used in this embodiment is not particularly limited, and a wide variety of release agents that are used for polycarbonate resins can be used. Examples of the release agent include aliphatic carboxylic acids, esters of aliphatic carboxylic acids and alcohols, aliphatic hydrocarbon compounds having a number average molecular weight of 200 to 15,000, and polysiloxane-based silicone oils.

[0028] Examples of aliphatic carboxylic acids include saturated or unsaturated aliphatic mono-, di-, or tri-carboxylic acids. Aliphatic carboxylic acids also include alicyclic carboxylic acids. Among these, preferred aliphatic carboxylic acids are mono- or di-carboxylic acids having 6 to 36 carbon atoms, with saturated aliphatic mono-carboxylic acids having 6 to 36 carbon atoms being more preferred. Specific examples of such aliphatic carboxylic acids include palmitic acid, stearic acid, caproic acid, capric acid, lauric acid, arachic acid, behenic acid, lignoceric acid, cerotic acid, melissic acid, tetralinic acid, montanic acid, adipic acid, and azelaic acid.

[0029] The aliphatic carboxylic acid in the ester of an aliphatic carboxylic acid and an alcohol can be, for example, the same as the aliphatic carboxylic acid described above. On the other hand, the alcohol can be, for example, a saturated or unsaturated monohydric or polyhydric alcohol. These alcohols may have a substituent such as a fluorine atom or an aryl group. Among these, a monohydric or polyhydric saturated alcohol having 30 or less carbon atoms is preferred, and an aliphatic saturated monohydric alcohol or an aliphatic saturated polyhydric alcohol having 30 or less carbon atoms is more preferred. Here, the term "aliphatic" is used to include alicyclic compounds.

[0030] Specific examples of such alcohols include octanol, decanol, dodecanol, stearyl alcohol, behenyl alcohol, ethylene glycol, diethylene glycol, glycerin, pentaerythritol, 2,2-dihydroxyperfluoropropanol, neopentylene glycol, ditrimethylolpropane, and dipentaerythritol.

[0031] The ester may contain an aliphatic carboxylic acid and / or alcohol as an impurity. The ester may be a pure substance or a mixture of multiple compounds. The aliphatic carboxylic acid and alcohol that combine to form an ester may each be used alone or in any combination and ratio of two or more.

[0032] Specific examples of esters of aliphatic carboxylic acids and alcohols include beeswax (a mixture containing myricyl palmitate as a main component), stearyl stearate, behenyl behenate, stearyl behenate, glycerin monopalmitate, glycerin monostearate, glycerin distearate, glycerin tristearate, pentaerythritol monopalmitate, pentaerythritol monostearate, pentaerythritol distearate, pentaerythritol tristearate, and pentaerythritol tetrastearate.

[0033] Examples of aliphatic hydrocarbons having a number average molecular weight of 200 to 15,000 include liquid paraffin, paraffin wax, microcrystalline wax, polyethylene wax, Fischer-Tropsch wax, and α-olefin oligomers having 3 to 12 carbon atoms. Aliphatic hydrocarbons also include alicyclic hydrocarbons. These hydrocarbons may also be partially oxidized. Among these, paraffin wax, polyethylene wax, or a partial oxide of polyethylene wax is preferred, and paraffin wax and polyethylene wax are more preferred. The number average molecular weight of the aliphatic hydrocarbon is preferably 5,000 or less. The aliphatic hydrocarbon may be a single substance, but even if it is a mixture of substances with various constituent components and molecular weights, it is preferable that the main component is within the above range.

[0034] Examples of polysiloxane-based silicone oils include dimethyl silicone oil, methylphenyl silicone oil, diphenyl silicone oil, and fluorinated alkyl silicone.

[0035] The above-mentioned release agents may be contained either alone or in any combination and ratio of two or more.

[0036] The content of the release agent in the resin composition is usually 0.001 part by mass or more, preferably 0.01 part by mass or more, and usually 2 parts by mass or less, preferably 1 part by mass or less, relative to 100 parts by mass of the polycarbonate resin. By setting the content of the release agent to be equal to or more than the lower limit of the above range, sufficient releasability effect is easily obtained, and by setting the content of the release agent to be equal to or less than the upper limit of the above range, sufficient hydrolysis resistance is obtained and mold contamination during injection molding is less likely to occur.

[0037] An example of a colorant other than titanium oxide that may be used in this embodiment is carbon black. By adding carbon black, the shielding properties of the resulting resin molded article can be further improved. As the carbon black, for example, at least one of furnace black, thermal black, channel black, lamp black, and acetylene black can be used alone or in combination of two or more. To facilitate dispersion, it is also preferable to use carbon black that has been previously masterbatched with a thermoplastic resin.

[0038] From the viewpoint of dispersibility, the primary particle size of the carbon black is preferably 10 nm to 30 nm, and more preferably 15 nm to 25 nm. Good dispersibility reduces uneven welding during laser welding. In addition, from the viewpoint of jet blackness, carbon black should have a nitrogen adsorption specific surface area of ​​30 to 400 m as measured according to JIS K6217. 2 / g is preferred, and 50m 2 / g or more, among which 80m 2 It is more preferable that the saturation coefficient is 1 / g or more.

[0039] Furthermore, from the viewpoint of dispersibility, the carbon black preferably has a DBP absorption of 20 to 200 cm3 / 100 g, more preferably 40 to 170 cm3 / 100 g, and even more preferably 50 to 150 cm3 / 100 g, as measured according to JIS K6221. Good dispersibility reduces uneven welding during laser welding.

[0040] The content of the colorant other than titanium oxide (preferably carbon black) in the resin composition used in this embodiment is preferably 1 ppm by mass or more, and more preferably 5 ppm by mass or more, per 100 parts by mass of the polycarbonate resin. By making the content equal to or greater than the lower limit, the shielding properties of the resulting resin molded article tend to be further improved. Furthermore, the content of the colorant other than titanium oxide (preferably carbon black) is preferably 100 ppm by mass or less, more preferably 50 ppm by mass or less, and even more preferably 30 ppm by mass or less, per 100 parts by mass of the polycarbonate resin. By making the content equal to or less than the upper limit, the decrease in reflectance tends to be suppressed and the shielding properties tend to be improved. The resin composition may contain only one colorant other than titanium oxide (preferably carbon black), or may contain two or more types. When two or more types are contained, the total amount is preferably in the above range.

[0041] The stabilizer that may be used in this embodiment is not particularly limited, and a wide variety of stabilizers that are used for polycarbonate resins can be used. As the stabilizer, phosphorus-based stabilizers and phenol-based stabilizers are preferred. Examples of stabilizers include hindered phenol compounds, hindered amine compounds, phosphorus compounds, and sulfur-based stabilizers. Among these, hindered phenol compounds are preferred. It is also preferred to use a hindered phenol compound and a phosphorus compound in combination. As the stabilizer, specifically, the descriptions in paragraphs 0046 to 0057 of JP 2018-070722 A, the descriptions in paragraphs 0030 to 0037 of JP 2019-056035 A, and the descriptions in paragraphs 0066 to 0078 of WO 2017 / 038949 A can be referred to, the contents of which are incorporated herein by reference.

[0042] The content of the stabilizer is usually 0.001 part by mass or more, preferably 0.01 part by mass or more, and usually 1.5 parts by mass or less, preferably 1 part by mass or less, relative to 100 parts by mass of the polycarbonate resin. If the content is less than 0.001 part by mass, the stabilizer effect is insufficient, and a decrease in molecular weight and deterioration in hue during molding are likely to occur. If the content exceeds 1.5 parts by mass, the amount becomes excessive, and silver streaking and deterioration in hue are more likely to occur.

[0043] In the manufacturing method of this embodiment, pellets of a resin composition containing a polycarbonate resin and titanium oxide particles are produced using a twin-screw extruder. Here, the total length L of the kneading sections of the twin-screw extruder, where D is the average screw diameter of the kneading sections, is 3.0D or more, preferably 3.5D or more, and more preferably 4.0D or more. By setting the total length L at or above the lower limit, the impact resistance of the resulting resin molded product tends to be further improved. Furthermore, the total length L of the kneading sections of the twin-screw extruder, where D is the average screw diameter of the kneading sections, is 15.0D or less, preferably 13.0D or less, more preferably 11.0D or less, even more preferably 9.0D or less, even more preferably 7.0D or less, and even more preferably 5.5D or less. By setting the total length L at or below the upper limit, the extrusion rate tends to be further improved while suppressing the specific shear energy.

[0044] Here, examples of the kneading section of the screw include an R kneading disc, an N kneading disc, an L kneading disc, an L screw, a sealing, a mixing screw, and a rotor screw, and usually, a combination of two or more of these is used. FIG. 1 shows an example of an extruder screw, where D is the screw diameter and L 1 and L 2 indicates each kneading section. When there are multiple kneading sections as shown in Figure 1, the total kneading time (L 1 +L 2) is the total length (L) of the kneading sections. The number of kneading sections in one screw is usually 1 to 5. In this embodiment, when the kneading section is made up of a combination of multiple screws, the average diameter D of the screws in the kneading section is the number average value of the diameters of the screws in each part. The average screw diameter (D) can be appropriately determined depending on the size of the extruder, etc., but may be, for example, 10 mm or more, 15 mm or more, 100 mm or more, or 120 mm or more. The upper limit of the screw diameter (D) may be, for example, 400 mm or less, 300 mm or less, 200 mm or less, 100 mm or less, or 90 mm or less.

[0045] In the manufacturing method of this embodiment, the specific shear energy during melt-kneading is 0.145 kW or less per hourly extrusion rate of 1 kg of the resin composition. By reducing the shear energy in this manner, it is possible to increase the impact resistance of a resin molded product molded using pellets obtained by the manufacturing method of this embodiment. Here, the specific shear energy during melt-kneading is a value calculated by the following formula. Specific shear energy (kW) = [rotation speed (rpm) x (maximum load (kW) / maximum rotation speed (rpm)) x (extrusion load (%) / 100)] / extrusion rate per hour (kg / h) Here, the rotation speed refers to the rotation speed of the screws of the twin-screw extruder, and the unit of rotation speed is rpm. The maximum load is the maximum load that can be applied to the twin-screw extruder being used, and can usually be determined from the description in the twin-screw extruder's catalog. Depending on the model of twin-screw extruder, it can also be determined from the motor capacity. The unit of maximum load is kW. The maximum rotation speed is the maximum rotation speed that the twin-screw extruder can handle, and is usually listed in the catalog of the twin-screw extruder. The maximum rotation speed is expressed in rpm. The extrusion load is the load applied during actual extrusion, and can usually be determined from the display on the control panel of the twin-screw extruder. Depending on the model of twin-screw extruder, it can also be determined from the motor torque during operation. The unit of extrusion load is kW. The extrusion amount per unit time is the mass of the resin composition extruded per hour when actually extruding, and is expressed in kg.

[0046] The specific shear energy during melt-kneading is preferably 0.143 kW or less, more preferably 0.136 kW or less, even more preferably 0.130 kW or less, even more preferably 0.125 kW or less, and even more preferably 0.119 kW or less per hourly extrusion rate of 1 kg of resin composition. The lower limit of the specific shear energy during melt-kneading is preferably 0.090 kW or more, more preferably 0.100 kW or more per hourly extrusion rate of 1 kg of resin composition. By setting the specific shear energy at or above the lower limit, TiO2 tends to be finely dispersed while reducing reagglomerates.

[0047] In this embodiment, the resin temperature is preferably 270°C or higher, more preferably 275°C or higher, even more preferably 280°C or higher, even more preferably 290°C or higher, and even more preferably 295°C or higher. By setting the temperature at or above the lower limit, the extrusion load tends to be reduced and productivity tends to be further improved. The resin temperature is also preferably 360°C or lower, more preferably 355°C or lower, even more preferably 350°C or lower, even more preferably 340°C or lower, and even more preferably 330°C or lower. By setting the temperature at or below the upper limit, decomposition of the polycarbonate base resin tends to be suppressed. Here, the resin temperature means the temperature of the resin when it is extruded from the die.

[0048] In this embodiment, the polycarbonate resin, titanium oxide particles, and other components to be blended as necessary may be premixed and fed all at once to the twin-screw extruder, or the components may be premixed or only a portion of the components may be premixed and fed to the extruder using a feeder. Also, some of the components may be melt-kneaded with a resin component (e.g., polycarbonate resin) to prepare a masterbatch, which may then be blended with the remaining components and melt-kneaded. When glass fibers are compounded, they are preferably fed from a side feeder midway through the cylinder of the extruder. The heating temperature during melt-kneading can usually be appropriately selected from the range of 170 to 350°C.

[0049] Next, the physical properties of the pellets used in this embodiment will be described. The pellets obtained by the manufacturing method of this embodiment can provide a resin molded product with high shielding properties. In particular, when the pellets are molded into a thickness of 1 mm, the total light transmittance is preferably 0.04% or less, more preferably less than 0.02%, and even more preferably 0.015% or less. The lower limit of the total light transmittance may be 0%, but even if it is 0.001% or more, the required performance is sufficiently met. The total light transmittance is measured according to the description in the Examples section below.

[0050] Furthermore, the pellets obtained by the manufacturing method of this embodiment can provide a resin molded product with excellent impact resistance. In particular, when the pellets are molded into an ISO multipurpose test piece with a thickness of 3.0 mm and the notched Charpy impact strength measured in accordance with ISO179-1 is 30 kJ / m 2 It is preferable that the concentration is 34 kJ / m or more. 2 More preferably, it is 40 kJ / m or more. 2 More preferably, it is 43 kJ / m or more. 2 More preferably, it is 46 kJ / m or more. 2 The upper limit of the notched Charpy impact strength is not particularly limited, but is preferably 60 kJ / m or more.2 The following is practical: The Charpy notched impact strength is measured as described in the Examples section below.

[0051] The pellets obtained by the manufacturing method of this embodiment are molded into various resin molded products. Although the molding method is not particularly limited, examples thereof include injection molding, ultra-high speed injection molding, injection compression molding, two-color molding, gas-assisted or other blow molding methods, molding using a heat-insulating mold, molding using a rapidly heated mold, foam molding (including supercritical fluid), insert molding, IMC (in-mold coating molding), extrusion molding, sheet molding, thermoforming, rotational molding, laminate molding, press molding, and blow molding, among which injection molding is preferred.

[0052] The shape of the resin molded article obtained from the pellets is not particularly limited and can be appropriately selected depending on the use and purpose of the molded article. Examples include various shapes such as a plate, plate, rod, sheet, film, cylinder, ring, circle, ellipse, polygon, irregular shape, hollow, frame, box, panel, and special shapes.

[0053] Resin molded products obtained by molding the pellets are preferably used as structural member components, portable electronic device components, vehicle and medical device components, other electronic components including electric circuits, food and pharmaceutical containers, and composite materials for forming these. In particular, the resin molded article is preferably used as an in-vehicle part, specifically a headlamp, and particularly a light guide base. That is, the pellets produced by the production method of this embodiment are preferably pellets used as an in-vehicle part, specifically a headlamp, and particularly a light guide base. [Example]

[0054] The present invention will be explained in more detail below with reference to examples. The materials, amounts used, ratios, processing details, processing procedures, etc. shown in the following examples can be appropriately changed without departing from the spirit of the present invention. Therefore, the scope of the present invention is not limited to the specific examples shown below. If the measuring instruments used in the examples are difficult to obtain due to discontinuation or the like, measurements can be performed using other instruments with equivalent performance.

[0055] Examples 1 to 11, Comparative Examples 1 to 9 <Raw materials> The following raw materials were used: [Table 1] Both of the titanium oxide particles A and B contain 90.0 to 98.0 mass % of TiO2, 0.5 to 3.5 mass % of Al2O3, and 0 to 6.0 mass % of SiO2. All samples examined in the examples and comparative examples were added with 0.1 mass % of S-100A manufactured by Riken Vitamin and 0.3 mass % of VPG861 manufactured by Emery Oleo as release agents, and 0.03 mass % of Adeka Stab 2112 manufactured by Adeka Kogyo as a stabilizer.

[0056] <Pellet production> Screws having a kneading section with a predetermined total screw length (L) were set in a twin-screw extruder (all manufactured by The Japan Steel Works, Ltd.) according to Tables 2 to 4. In the kneading section, R kneading discs, N kneading discs, L kneading discs, and twist kneading discs were arranged in predetermined numbers and positions. TEX54αII: Screw diameter 58mm TEX65αII: Screw diameter 69mm Each component was supplied from a feeder upstream of the twin-screw extruder and kneaded under the conditions of extrusion rate, rotation speed, extrusion load, and resin temperature shown in Tables 2 to 4. The molten resin extruded in the form of strands was quenched in a water tank and pelletized using a pelletizer to obtain pellets of the resin composition. The maximum rotation speed and maximum load of the extruder are determined depending on the twin-screw extruder.

[0057] <Calculation of specific shear energy> The specific shear energy was calculated by substituting the various values ​​shown in Tables 2 to 4 into the following calculation formula. Specific shear energy = [rotation speed (rpm) x (maximum load (kW) / maximum rotation speed (rpm)) x (extrusion load (%) / 100)] / extrusion rate per hour (kg / h)

[0058] <Impact strength> The pellets obtained by the above method were dried at 100°C for 5 hours and then injection molded in an injection molding machine (Shibaura Machine Co., Ltd., "EC75") under the following conditions: cylinder temperature 280°C, mold temperature 80°C, screw rotation speed 80 rpm, and injection speed 30 mm / s to produce ISO multipurpose test specimens (3.0 mmt). Using the obtained ISO multipurpose test piece (3.0 mm thick), the notched Charpy impact strength (unit: kJ / m) was measured at a temperature of 23°C in accordance with ISO standard 179-1. 2 ) was measured.

[0059] <Total light transmittance> The pellets obtained by the above method were dried at 100°C for 5 hours, and then 1 mm thick test pieces were produced using an injection molding machine (Shibaura Machine Co., Ltd., "EC75") under the following conditions: cylinder temperature 280°C, mold temperature 80°C, screw rotation speed 100 rpm, and injection speed 30 mm / s. The total light transmittance (unit: %) of the obtained test piece was measured using a haze meter. The haze meter used was a NDH-2000 type haze meter manufactured by Nippon Denshoku Industries Co., Ltd.

[0060] [Table 2]

[0061] [Table 3]

[0062] [Table 4]

[0063] As is clear from the above results, when pellets produced by the pellet production method of the present invention were used, the resulting resin molded articles had high Charpy impact strength. Furthermore, by blending a large amount of titanium oxide particles into the polycarbonate resin, resin molded articles with sufficiently low total light transmittance could be produced.

Claims

1. A method for producing pellets of a resin composition containing 5.0 to 16.0 parts by mass of particles containing titanium oxide as a main component per 100 parts by mass of polycarbonate resin using a twin-screw extruder, The total length L of the kneading section in the twin-screw extruder is 3.0D to 15.0D, where D is the average diameter of the screws in the kneading section; A method for producing pellets, wherein the specific shear energy during melt-kneading is 0.145 kW or less per kg of extrusion rate of the resin composition per hour.

2. A method for producing pellets of a resin composition containing 5.0 to 20.0 parts by mass of particles mainly composed of titanium oxide per 100 parts by mass of polycarbonate resin using a twin-screw extruder, The total length L of the kneading section in the twin-screw extruder is 3.0D to 15.0D, where D is the average diameter of the screws in the kneading section; the specific shear energy during melt-kneading is 0.145 kW or less per hourly extrusion rate of 1 kg of the resin composition; The pellets are molded into an ISO multipurpose test piece having a thickness of 3.0 mm, and the notched Charpy impact strength measured in accordance with ISO 179-1 is 30 kJ / m 2 or more.

3. 3. The method according to claim 1, wherein the total light transmittance of the pellets when molded into a thickness of 1 mm is 0.04% or less.

4. 3. The method according to claim 1, wherein the pellets have a total light transmittance of less than 0.02% when molded into a thickness of 1 mm.

5. The method according to any one of claims 1 to 4, wherein the total length L of the kneading section in the twin-screw extruder is 3.0D to 5.5D.

6. The method according to any one of claims 1 to 5, wherein the specific shear energy during the melt-kneading is 0.090 kW or more per kg of extrusion rate of the resin composition per hour.

7. The method according to any one of claims 1 to 6, wherein the content of the particles containing titanium oxide as a main component is 8.0 to 16.0 parts by mass per 100 parts by mass of the polycarbonate resin.

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