JP7777934B2 - Pellets manufacturing method - Google Patents

Description

The present invention relates to a method for producing pellets.

Titanium oxide has traditionally been blended into polycarbonate resin to improve the shielding properties and color of resin molded products (Patent Document 1, Patent Document 2).

International Publication No. 2019/172243 Japanese Patent Application Laid-Open No. 2019-123809

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.

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 kg of extrusion rate of the resin composition per hour.
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 primarily composed of 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 method according to <1>, wherein the particles containing titanium oxide as a main component contain 90.0 to 98.0 mass % of TiO ₂ , 0.5 to 3.5 mass % of Al ₂ O ₃ , and 0 to 6.0 mass % of SiO ₂ .
<3> The method according to <1> or <2>, wherein the total light transmittance when the pellet is molded into a thickness of 1 mm is 0.04% or less.
<4> The method according to <1> or <2>, wherein the total light transmittance when the pellet is molded into a thickness of 1 mm is less than 0.02%.
<5> The manufacturing method according to any one of <1> to <4>, wherein 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/ ^m2 or more.
<6> The production method according to any one of <1> to <5>, wherein the total length L of the kneading section in the twin-screw extruder is 3.0D to 5.5D.
<7> The manufacturing method according to any one of <1> to <6>, 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.
<8> The manufacturing method according to any one of <1> to <7>, wherein 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.

The present invention makes it possible to provide a method for producing pellets of a resin composition containing polycarbonate resin and titanium oxide particles, which can maintain high Charpy impact strength when formed into a resin molded product.

FIG. 1 is a schematic view showing an example of a screw used in the production method of the present invention.

Hereinafter, an embodiment of 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 word "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.

In this specification, "particles primarily composed of titanium oxide" may be referred to as "titanium oxide particles."

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 mainly 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 in the twin-screw extruder is 3.0D to 15.0D, where D is the average diameter of the screws in 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.

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.

In this embodiment, the specific shear energy during melt-kneading of the polycarbonate resin and titanium oxide particles was adjusted to prevent excessive shear. As a result, it was believed 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 believed that reagglomeration of titanium oxide particles was 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.

In this embodiment, 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 is pelletized. Such a resin composition can enhance the shielding properties of the resulting resin molded product. The resin composition used in this embodiment may contain other components as long as they do not deviate from the spirit of the present invention.

Polycarbonate resins are optionally branched homopolymers or copolymers obtained by reacting a dihydroxy compound or a dihydroxy compound with a small amount of a polyhydroxy compound with phosgene or a carbonate diester.

The dihydroxy compound raw material is preferably an aromatic dihydroxy compound, with 2,2-bis(4-hydroxyphenyl)propane (bisphenol A), tetramethylbisphenol A, bis(4-hydroxyphenyl)-p-diisopropylbenzene, hydroquinone, resorcinol, 4,4-dihydroxydiphenyl, etc. being more preferred, and bisphenol A being even more preferred. It is also possible to use compounds in which one or more tetraalkylphosphonium sulfonates are bonded to the above aromatic dihydroxy compounds.

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. Copolymers primarily composed of aromatic polycarbonate resins, such as copolymers with polymers or oligomers having a siloxane structure, may also be used. Furthermore, two or more of the above-mentioned polycarbonate resins may be mixed and used.

To adjust the molecular weight of polycarbonate resin, monovalent aromatic hydroxy compounds can be used, such as m- and p-methylphenol, m- and p-propylphenol, p-tert-butylphenol, and p-long-chain alkyl-substituted phenols.

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 polycarbonate resins are contained, it is preferable that the mixture satisfies the above range (hereinafter, the same applies to molecular weight).

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 Mv ^0.83

There are no particular limitations on the method for producing polycarbonate resin, and polycarbonate resins produced by either the phosgene method (interfacial polymerization method) or the melt method (ester interchange method) can be used. Also preferred are polycarbonate resins produced by the melt method that have been post-treated to adjust the amount of terminal OH groups.

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.

The resin composition used in this embodiment contains particles containing titanium oxide as a main component (titanium oxide particles). By including the titanium oxide particles, the light-blocking properties of the resulting resin molded article can be achieved.
"Mainly composed of titanium oxide" means that titanium oxide is the most abundant component among the components contained in 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% _TiO2 , 0.5 to 3.5 mass% _Al2O3 , and 0 to 6.0 mass% _SiO2 . They may also contain 0 to 0.1 mass% _SO3 , 0 to 0.15 mass% _Na2O , and 0 to 0.01 mass% Cl. Other components may also be included, the total of which amounts to 100 mass%.

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 the polycarbonate resin. Furthermore, the titanium oxide particles preferably have their surfaces treated with a surface treatment agent. That is, the surface of the titanium oxide particles preferably has a layer (particularly an organic layer) formed from the surface treatment agent. This configuration facilitates dispersion of the titanium oxide in the polycarbonate resin, resulting in a resin sheet with superior appearance. Examples of surface treatment agents 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.

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

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. Meanwhile, by setting the content at or below the upper limit, deterioration in 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.

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 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.

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.

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 even 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.

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, monohydric or polyhydric saturated alcohols having 30 or fewer carbon atoms are preferred, and saturated aliphatic monohydric alcohols or saturated aliphatic polyhydric alcohols having 30 or fewer carbon atoms are even more preferred. The term "aliphatic" is used here to encompass alicyclic compounds as well.

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.

The above esters may contain aliphatic carboxylic acids and/or alcohols as impurities. Furthermore, the above esters may be pure substances or mixtures of multiple compounds. Furthermore, the aliphatic carboxylic acids and alcohols that combine to form an ester may each be used alone, or two or more may be used in any combination and ratio.

Specific examples of esters of aliphatic carboxylic acids and alcohols include beeswax (a mixture mainly composed of myricyl palmitate), 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.

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 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.

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

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

The content of the release agent in the resin composition is typically 0.001 parts by mass or more, preferably 0.01 parts by mass or more, and typically 2 parts by mass or less, preferably 1 part by mass or less, per 100 parts by mass of polycarbonate resin. By setting the content of the release agent at or above the lower limit of the above range, sufficient release properties are easily achieved, while by setting the content of the release agent at or below the upper limit of the above range, sufficient hydrolysis resistance is achieved and mold contamination during injection molding is less likely to occur.

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 thereof.
To facilitate dispersion, it is also preferable to use carbon black that has been previously masterbatched with a thermoplastic resin.

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.
From the viewpoint of jet blackness, the carbon black preferably has a nitrogen adsorption specific surface area measured in accordance with JIS K6217 of 30 to 400 m ² /g, more preferably 50 m ² /g or more, and even more preferably 80 m ² /g or more.

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

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 colorants. When two or more colorants are contained, the total amount is preferably in the above range.

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.
Specific examples of stabilizers include the following: JP 2018-070722 A, paragraphs 0046 to 0057; JP 2019-056035 A, paragraphs 0030 to 0037; and WO 2017/038949 A, paragraphs 0066 to 0078. These contents are incorporated herein by reference.

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

In the manufacturing method of this embodiment, pellets of a resin composition containing polycarbonate resin and titanium oxide particles are produced using a twin-screw extruder. Here, the total length L of the kneading section of the twin-screw extruder, where D is the average screw diameter of the kneading section, 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 section of the twin-screw extruder, where D is the average screw diameter of the kneading section, 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.

Here, examples of the kneading portion 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, with D representing the screw diameter and ^L1 and ^L2 representing the kneading sections. When there are multiple kneading sections as shown in FIG. 1, the total length (L) of the kneading sections is the sum of the lengths of the kneading sections ( ^L1 + ^L2 ). 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 screw diameter D of the kneading section is the number average value of the screw diameters of each part.
The average screw diameter (D) can be appropriately determined depending on the size of the extruder, etc., and 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.

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 screw 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 used, and can usually be determined from the description in the twin-screw extruder 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 used can achieve, and is usually stated in the catalog of the twin-screw extruder, etc. The unit of the maximum rotation speed is rpm.
The extrusion load is the load applied during actual extrusion, and can usually be determined from the indicator 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 extrusion is actually carried out, and is expressed in kg.

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 re-agglomerates.

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.

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.

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.

Furthermore, the pellets obtained by the manufacturing method of this embodiment can provide a resin molded product with excellent impact resistance. In particular, the pellets are molded into a 3.0 mm thick ISO multipurpose test piece, and the notched Charpy impact strength measured in accordance with ISO 179-1 is preferably 30 kJ/ ^m² or more, more preferably 34 kJ/ ^m² or more, even more preferably 40 kJ/ ^m² or more, even more preferably 43 kJ/ ^m² or more, and even more preferably 46 kJ/ ^m² or more. There is no particular upper limit to the notched Charpy impact strength, but a practical upper limit is 60 kJ/ ^m² or less.
The Charpy notched impact strength is measured as described in the Examples section below.

The pellets obtained by the manufacturing method of this embodiment are molded into various resin molded products. While there are no particular restrictions on the molding method, examples include injection molding, ultra-high speed injection molding, injection compression molding, two-color molding, gas-assisted and other blow molding methods, molding using an insulated mold, molding using a rapidly heated mold, foam molding (including supercritical fluids), insert molding, IMC (in-mold coating molding), extrusion molding, sheet molding, thermoforming, rotational molding, laminate molding, press molding, and blow molding, with injection molding being preferred.

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

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.

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 made using other instruments with equivalent performance.

Examples 1 to 11, Comparative Examples 1 to 9
<Raw materials>
The following raw materials were used:
Both of the titanium oxide particles A and B contain 90.0 to 98.0% by mass of TiO ₂ , 0.5 to 3.5% by mass of Al ₂ O ₃ , and 0 to 6.0% by mass of SiO ₂ .
All samples investigated 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.

<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.

<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)

<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 ("EC75" manufactured by Shibaura Machine Co., Ltd.) under the conditions of a cylinder temperature of 280°C, a mold temperature of 80°C, a screw rotation speed of 80 rpm, and an injection speed of 30 mm/s to produce ISO multipurpose test specimens (3.0 mmt).
Using the obtained ISO multipurpose test piece (3.0 mmt), the notched Charpy impact strength (unit: kJ/m ² ) was measured at a temperature of 23° C. in accordance with ISO Standard 179-1.

<Total light transmittance>
The pellets obtained by the above method were dried at 100°C for 5 hours, and then test pieces with a thickness of 1 mm were produced using an injection molding machine ("EC75" manufactured by Shibaura Machine Co., Ltd.) under the conditions of a cylinder temperature of 280°C, a mold temperature of 80°C, a screw rotation speed of 100 rpm, and an injection speed of 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.

As is clear from the above results, when pellets produced using the pellet manufacturing method of the present invention were used, the resulting resin molded article had high Charpy impact strength. Furthermore, by blending a large amount of titanium oxide particles into the polycarbonate resin, it was possible to produce a resin molded article with a sufficiently low total light transmittance.

Claims (7)

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. A method for producing pellets of a resin composition containing 5.0 to 20.0 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;
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 were molded into a 3.0 mm thick ISO multipurpose test piece, and the notched Charpy impact strength measured in accordance with ISO 179-1 was 30 kJ/m ² This completes the method for producing pellets. 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. 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. The manufacturing method described in 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. The manufacturing method described in 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 resin composition extruded per hour. 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.